Beijing, China

The University of Science and Technology Beijing , formerly known as Beijing Steel and Iron Institute before 1988, is a national key university in Beijing, China. USTB's metallurgy and materials science programmes are highly regarded in China. Wikipedia.


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University of Science and Technology Beijing | Date: 2016-03-15

This present invention provides a method for preparing a stainless reinforcing steel bar resistant to corrosion of chloride ions, and belongs to the technical field of corrosion-resistant materials. This method particularly comprises the steps of: selecting a reinforcing steel bar blank, and performing oil removing, rust removing, water washing, and drying treatments on the surface of the reinforcing steel bar blank to be treated, or directly performing sand blasting or shot blasting on a reinforcing steel bar blank whose surface is only slightly rusted; placing the reinforcing steel bar blank in a chromium-containing environment, and keeping at a certain temperature for a certain time such that chromium in the environment is capable of diffusing into the surface of the reinforcing steel bar blank to form a chromium-containing diffusion layer, wherein an area in the diffusion layer where the weight content of Cr exceeds 12% meets the basic component requirements for a stainless steel, and this area is the effective diffusion layer described in this invention; and performing cooling treatment on the heat diffusion treated reinforcing steel bar. In this invention, a reinforcing steel bar blank is pre-formed, a heat diffusion technique is optimized, and the corrosion resistance to chloride ions of the stainless reinforcing steel bar of this invention is superior to that of the 316L stainless reinforcing steel bar.


Li H.-Y.,Huafan University | Weng W.-C.,Huafan University | Yan W.-M.,National University of Tainan | Wang X.-D.,University of Science and Technology Beijing
Journal of Power Sources | Year: 2011

This work establishes three-dimensional transient numerical models of proton exchange membrane fuel cells (PEMFCs) with different cathode flow field designs. Exactly how flow field design and voltage loading affect the transient characteristics of the PEMFCs are examined. When the operating voltage instantaneously drops from 0.7 V to 0.5 V, the electrochemical reactions increase. To ensure sufficient oxygen supply for the fuel cell, the oxygen mass fractions are high in the cathode gas diffusion and cathode catalyst layers, causing overshoot of the local current density distribution. When the operating voltage suddenly increases from 0.5 V to 0.7 V, the electrochemical reactions become mild, and furthermore the oxygen mass fraction distribution becomes low, leading to undershoot of the local current density distribution. The transient response time required to reach the steady state for the parallel flow field with baffle design is longest in the event of overshoot or undershoot among the different cathode flow field designs. The overshoot or undershoot phenomena become more obvious with larger voltage loading variations. Moreover, the transient response time for the Z-type flow field with baffle design is longer than for the Z-type flow field design. © 2010 Elsevier B.V. All rights reserved.


Pan G.,Beijing Normal University | Zhu J.,Beijing Normal University | Ma S.,Beijing Normal University | Sun G.,Beijing Normal University | And 2 more authors.
ACS Applied Materials and Interfaces | Year: 2013

Cobalt is a promising soft metallic magnetic material used for important applications in the field of absorbing stealth technology, especially for absorbing centimeter waves. However, it frequently presents a weak dielectric property because of its instability, aggregation, and crystallographic form. A method for enhancing the electromagnetic property of metal Co via phase-controlled synthesis of Co nanostructures grown on graphene (GN) networks has been developed. Hexagonal close-packed cobalt (α-Co) nanocrystals and face-centered cubic cobalt (β-Co) nanospheres with uniform size and high dispersion have been successfully assembled on GN nanosheets via a facile one-step solution-phase strategy under different reaction conditions in which the exfoliated graphite oxide (graphene oxide, GO) nanosheets were reduced along with the formation of Co nanocrystals. The as-synthesized Co/GN nanocomposites showed excellent microwave absorbability in comparison with the corresponding Co nanocrystals or GN, especially for the nanocomposites of GN and α-Co nanocrystals (the reflection loss is -47.5 dB at 11.9 GHz), which was probably because of the special electrical properties of the cross-linked GN nanosheets and the perfect electromagnetic match in their microstructure as well as the small particle size of Co nanocrystals. The approach is convenient and effective. Some magnetic metal or alloy materials can also be prepared via this route because of its versatility. © 2013 American Chemical Society.


Wang H.,University of Science and Technology Beijing | Qian K.,Peking University | Wang K.,University of Science and Technology Beijing | Bian Y.,University of Science and Technology Beijing | And 2 more authors.
Chemical Communications | Year: 2011

Homoleptic tetrakis[2,3,9,10,16,17,23,24-octa(butyloxy)phthalocyaninato] dysprosium-cadmium quadruple-decker complex 1 was isolated in relatively good yield of 43% from a simple one-pot reaction. This compound represents the first sandwich-type tetrakis(phthalocyaninato) rare earth-cadmium quadruple-decker SMM that has been structurally characterized. © The Royal Society of Chemistry 2011.


Chen Y.,University of Science and Technology Beijing | Yu H.,Peking University | Zhang L.,Peking University | Yang H.,University of Science and Technology Beijing | And 2 more authors.
Chemical Communications | Year: 2014

A series of photoresponsive halogen-bonded liquid crystals (LCs) were successfully constructed using molecular halogen and azopyridine compounds, which show interesting properties of photoinduced phase transition upon UV irradiation. In addition, bromine-bonded LCs were first obtained with high mesophase stability. This journal is © the Partner Organisations 2014.


Yin X.-C.,University of Science and Technology Beijing | Yin X.,University of Science and Technology Beijing | Huang K.,Xi'an Jiaotong - Liverpool University | Hao H.-W.,CAS Institute of Automation
IEEE Transactions on Pattern Analysis and Machine Intelligence | Year: 2014

Text detection in natural scene images is an important prerequisite for many content-based image analysis tasks. In this paper, we propose an accurate and robust method for detecting texts in natural scene images. A fast and effective pruning algorithm is designed to extract Maximally Stable Extremal Regions (MSERs) as character candidates using the strategy of minimizing regularized variations. Character candidates are grouped into text candidates by the single-link clustering algorithm, where distance weights and clustering threshold are learned automatically by a novel self-training distance metric learning algorithm. The posterior probabilities of text candidates corresponding to non-text are estimated with a character classifier; text candidates with high non-text probabilities are eliminated and texts are identified with a text classifier. The proposed system is evaluated on the ICDAR 2011 Robust Reading Competition database; the f -measure is over 76%, much better than the state-of-the-art performance of 71%. Experiments on multilingual, street view, multi-orientation and even born-digital databases also demonstrate the effectiveness of the proposed method. Finally, an online demo of our proposed scene text detection system has been set up at http://prir.ustb.edu.cn/TexStar/ scene-text-detection/. © 2013 IEEE.


Chen W.,University of Science and Technology Beijing | Chen W.,Xidian University | Li X.,Baoji University of Arts And Sciences | Ren W.,University of California at Riverside | Wen C.,Nanyang Technological University
IEEE Transactions on Automatic Control | Year: 2014

This note addresses the adaptive consensus problem of first-order and second-order linearly parameterized multi-agent systems with unknown identical control directions. First, we propose a new Nussbaum-type function based on which a key lemma is established. The lemma plays an important role in analyzing the consensus of the closed-loop multi-agent systems. Second, the Nussbaum-type function is used to design adaptive control laws for first-order and second-order linearly parameterized multi-agent systems so that each agent seeks for the unknown control direction adaptively and cooperatively. Then, under the assumption that the interconnection topology is undirected and connected, it is proved that the first-order and second-order multi-agent systems can achieve consensus by choosing proper design parameters. Two simulation examples are given to illustrate the effectiveness of the proposed control laws. © 1963-2012 IEEE.


Yang H.,University of Science and Technology Beijing | Jing L.,University of Science and Technology Beijing | Zhang B.,Peking University
Journal of Hazardous Materials | Year: 2011

A technique with coal-based direct reduction followed by magnetic separation is presented in this study for recovering and reusing iron otherwise wasted in vanadium tailings. Process parameters such as usage of additives, tailings/reductant/additives ratio, reduction temperature and time, as well as particle size were experimentally determined. The optimum process parameters were proposed as follows: using lime as the additive, lignite as the reductant, weight ratios of vanadium tailings/lignite/lime at 100:30:10, reduction roasting at 1200. °C for 60. min, and particle size of 98% less than 30. μm in the final roasted product feeding to magnetic separation. Under these conditions, a magnetic concentrate containing 90.31% total iron and 89.76% metallization iron with a total iron recovery rate of 83.88% was obtained. In addition, mineralography of vanadium tailings, coal-based reduction product and magnetic concentrate were studied by X-ray powder diffraction technique (XRD). The microstructures of above products were analyzed by scanning electron microscope (SEM) to help understand the mechanism. © 2010 Elsevier B.V.


Yang W.,CAS Beijing National Laboratory for Molecular | Yang W.,Shanghai University | Li J.,CAS Beijing National Laboratory for Molecular | Wang Y.,Shanghai University | And 4 more authors.
Chemical Communications | Year: 2011

Anatase TiO2 nanosheets-based hierarchical spheres with over 90% {001} facets synthesized via a diethylene glycol-solvothermal route were used as photoanodes of dye-sensitized solar cells, which generated an energy conversion efficiency of 7.51%. © 2011 The Royal Society of Chemistry.


Zhou E.P.,University of Science and Technology Beijing | Lu J.G.,University of Science and Technology Beijing | Tong H.,Chinese Academy of Sciences | Xu R.X.,University of Science and Technology Beijing | Xu R.X.,Peking University
Monthly Notices of the Royal Astronomical Society | Year: 2014

Glitch (sudden spin-up) is a common phenomenon in pulsar observations. However, the physical mechanism of glitch is still a matter of debate because it depends on the puzzle of pulsar's inner structure, i.e. the equation of state of dense matter. Some pulsars (e.g. Vela like) show large glitches (Δν/ν ~ 10-6) but release negligible energy, whereas the large glitches of AXPs/SGRs (anomalous X-ray pulsars/soft gamma repeaters) are usually (but not always) accompanied with detectable energy releases manifesting as X-ray bursts or outbursts.We try to understand this aspect of glitches in a starquake model of solid quark stars. There are two kinds of glitches in this scenario: bulk-invariable (type I) and bulk-variable (type II) ones. The total stellar volume changes (and then energy releases) significantly for the latter but not for the former. Therefore, glitches accompanied with X-ray bursts (e.g. that of AXP/SGRs) could originate from type II starquakes induced probably by accretion, while the others without evident energy release (e.g. that of Vela pulsar) would be the result of type I starquakes due to, simply, a change of stellar ellipticity. © 2014 The Authors.Published by Oxford University Press on behalf of the Royal Astronomical Society.


Feng Y.,Peking University | Zhang M.,University of Science and Technology Beijing | Guo M.,University of Science and Technology Beijing | Wang X.,Peking University
Crystal Growth and Design | Year: 2010

With the introduction of poly ethylene glycol (PEG) (10000), relatively well dispersed and oriented ZnO microrod arrays and ZnO microsphere arrays were successfully synthesized on unmodified indium tin oxide (ITO) substrate by a hydrothermal method. The growth behaviors of the two different kinds of ZnO arrays were experimentally investigated with variations of PEG addition and the precursor solution's concentration. The PEG-assisted growth mechanism of ZnO microrod arrays and ZnO microsphere arrays has also been carefully discussed. Both the dissolved state of PEG and the interaction between PEG and ZnO crystalline grains were found to play important roles in the fabrication of the two different ZnO structure arrays. The research on PEG-assisted growth mechanism for these two kinds of ZnO structure arrays will provide more theoretical references for preparations of ZnO one-dimensional rod arrays and other kinds of assembled structures on the substrate. © 2010 American Chemical Society.


Xu T.,Control Iron and Steel Research Institute, China | Zheng L.,University of Science and Technology Beijing | Wang K.,Control Iron and Steel Research Institute, China | Misra R.D.K.,University of Louisiana at Lafayette
International Materials Reviews | Year: 2013

The review is aimed at presenting a unified approach in understanding the mechanism of nonequilibrium grain boundary segregation, which can satisfactorily describe the three types of intergranular embrittlement, namely, reverse temper embrittlement of steels, intergranular corrosion embrittlement of stainless steels and intermediate temperature embrittlement of metals and alloys. The review starts with a broad perspective of non-equilibrium grain boundary segregation, including thermally induced non-equilibrium grain boundary segregation and stress induced non-equilibrium grain-boundary segregation. Next, it focuses on the recent progress made in the non-equilibrium grain boundary segregation, including (1) critical time, (2) segregation peak temperature, (3) segregation peak temperature movement for thermally induced and stress induced non-equilibrium grain boundary segregation, and (4) the effect of temperature difference on thermally-induced non-equilibrium grain boundary segregation. Next, the attention is focused on the grain boundary coverage of elements and intergranular embrittlement phenomena. Three types of intergranular embrittlement is analysed in terms of (1) the ductility healing effect induced by the critical time, (2) embrittlement peak or ductility trough induced by the segregation peak temperature, (3) embrittlement peak or ductility trough movement induced by the segregation peak temperature movement and (4) widening and deepening of ductility trough induced by differences in temperature. These experimental phenomena concerning the three types of intergranular embrittlement are consistent with the models of thermally induced and stress induced non-equilibrium grain boundary segregations of impurities, instead of precipitation or equilibrium grain boundary segregation. Towards the end, we visit the subject of grain boundary segregation and associated embrittlement process from the viewpoint of fracture resistance and briefly discuss different perspectives that are of practical significance. © 2013 Institute of Materials, Minerals and Mining and ASM International.


Zhang Z.,University of Science and Technology Beijing | Long K.,University of Science and Technology Beijing | Wang J.,City University of Hong Kong | Dressler F.,University of Innsbruck
IEEE Communications Surveys and Tutorials | Year: 2014

Inspired by swarm intelligence observed in social species, the artificial self-organized networking (SON) systems are expected to exhibit some intelligent features (e.g., flexibility, robustness, decentralized control, and self-evolution, etc.) that may have made social species so successful in the biosphere. Self-organized networks with swarm intelligence as one possible solution have attracted a lot of attention from both academia and industry. In this paper, we survey different aspects of bio-inspired mechanisms and examine various algorithms that have been applied to artificial SON systems. The existing well-known bio-inspired algorithms such as pulse-coupled oscillators (PCO)-based synchronization, ant-and/or bee-inspired cooperation and division of labor, immune systems inspired network security and Ant Colony Optimization (ACO)-based multipath routing have been surveyed and compared. The main contributions of this survey include 1) providing principles and optimization approaches of variant bio-inspired algorithms, 2) surveying and comparing critical SON issues from the perspective of physical-layer, Media Access Control (MAC)-layer and network-layer operations, and 3) discussing advantages, drawbacks, and further design challenges of variant algorithms, and then identifying their new directions and applications. In consideration of the development trends of communications networks (e.g., large-scale, heterogeneity, spectrum scarcity, etc.), some open research issues, including SON designing tradeoffs, Self-X capabilities in the 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE)/LTE-Advanced systems, cognitive machine-to-machine (M2M) self-optimization, cross-layer design, resource scheduling, and power control, etc., are also discussed in this survey. © 2014 IEEE.


Xie H.,University of Science and Technology Beijing | Zhang C.,University of Science and Technology Beijing | Zou K.,University of Science and Technology Beijing
Renewable and Sustainable Energy Reviews | Year: 2012

Solar energy utilization can not only decrease conventional energy consumption but also reduce environmental pollution. China has abundant solar energy resources and has the biggest solar water heater market in the world, so it is necessary for Chinese government to enact incentive policies and measures to enlarge the utilization scale of solar water heaters. According to international experience, solar obligation is probably the most powerful instrument for promoting the use of solar thermal in buildings and expanding the solar water heater market. Currently, there are many provinces and cities in China having adopted the solar obligation, leading to the discussion of solar obligation at national level. This paper firstly analyzed basic conditions to implement the solar obligations in China. Then, 34 provinces and cities' local regulations were reviewed and main problems of them were analyzed. According to domestic and international practices, some recommendations for the design and implementation of solar obligations at national level were induced at the end. © 2011 Elsevier Ltd. All rights reserved.


Qin L.,Beijing Normal University | Qin J.,University of Science and Technology Beijing | Feng S.,Beijing Normal University
Philosophical Magazine Letters | Year: 2014

One of the most essential aspects of cuprate superconductors is a large pseudogap coexisting with a superconducting gap, then some anomalous properties can be understood in terms of the formation of the pseudogap. Within the kinetic energy-driven superconducting mechanism, the effect of the pseudogap on the infrared response of cuprate superconductors in the superconducting state is studied. By considering the interplay between the superconducting gap and pseudogap, the electron current-current correlation function is evaluated based on the linear response approach and it then is employed to calculate finite-frequency conductivity. It is shown that in the underdoped and optimally doped regimes, the transfer of the part of the low-energy spectral weight of the conductivity spectrum to the higher energy region to form a midinfrared band is intrinsically associated with the presence of the pseudogap. © 2014 © 2014 Taylor & Francis.


Qiu J.,Peking University | Guo M.,University of Science and Technology Beijing | Feng Y.,Peking University | Wang X.,Peking University
Electrochimica Acta | Year: 2011

Branched hierarchical ZnO nanowire arrays are synthesized on fluorine-doped tin oxide (FTO) substrate via a two-step electrochemical deposition process, which involves the electrodeposition of ZnO nanowire arrays on conductive glass substrate, followed by the electrochemical growth of ZnO nanorod branches on the backbones of the primary ZnO nanowires. The formation mechanism of the branched hierarchical nanostructure is discussed. It is demonstrated that coating the primary nanowire arrays with ZnO nanoparticles seed layer plays a key role in synthesising the branched hierarchical ZnO nanostructure. By adjusting the concentration of Zn(CH3COO)2 colloid in coating process and the reaction time of the second-step deposition, the density and the length of the secondary nanorod branches in the hierarchical nanostructures can be both varied. Moreover, the photoelectrochemical properties of the dye-sensitized solar cell (DSSC) based on branched hierarchical ZnO nanowire arrays are investigated. Due to the enlargement of the internal surface area within the branched nanostructure photoelectrode, the DSSC consisting of branched hierarchical ZnO nanowire arrays yields a power conversion efficiency of 0.88%, which is almost twice higher than that of the DSSC fabricated using bare ZnO nanowire arrays. © 2011 Elsevier Ltd. All rights reserved.


Zhang L.X.,Beijing Normal University | Song B.,University of Science and Technology Beijing | Chen B.,Beijing Normal University
Journal of Cleaner Production | Year: 2012

The Chinese government has increasingly turned to agricultural industry policy as a means of promoting rural development, which have not necessarily led to an improvement in rural incomes nor to the achievement of other social and environmental goals. Emergy synthesis methods were applied to four agricultural production systems, i.e.; two local traditional production systems as maize plantation and pond fish farming, one scaled Shaoxing duck (Anas Platyrhyncha var. domestica) rearing system, and one newly introduced specialty production system of common mushroom (Agaricus Bisporus) cultivation, in Weishan county of Shandong province of China in the year 2007, to assess and compare their environmental performances. Additionally, aiming at understanding the benefits and driving forces of agricultural diversification, environmental performance results were contrasted with traditional economic indicators. As indicated by EYR, ELR and ESI, it can be clearly shown that the scaled duck rearing and newly introduced common mushroom cultivation alternatives are not in a sustainable pattern, although having better economic performance than maize cropping and pond fish farming. Nevertheless, the development of rural agricultural diversification is also affected by land accessibility, investment ability and even labor availability. Therefore, achieving a profitable and environmental sustainable diversified farming system is not an easy task in Weishan area as well as in whole China. It is unwise to encourage development of agricultural diversification in current manners without too much consideration on environmental degradation. © 2011 Elsevier Ltd. All rights reserved.


Fang Y.,Peking University | Wang C.,Peking University | Su S.,University of Science and Technology Beijing | Yu H.,University of Science and Technology Beijing | Huang Y.,Peking University
Organic and Biomolecular Chemistry | Year: 2014

We described two orthogonal heterocycle syntheses, where an arene bearing both an alkyne and a triazene functionality underwent two distinct cyclization pathways mediated by different transition metals. Starting from the same substrates, a synthesis of 2H-indazole was accomplished by a Cu(ii) salt promoted oxidative cyclization, while 2-substituted indoles could be accessed via a Ag(i) salt mediated N-N bond cleavage. This method represents the first synthesis of indoles from alkynyl triazenes. Computational analysis was performed for both reaction pathways, supporting a Lewis acid role for Cu and a π-acid catalysis for Ag. This journal is © The Royal Society of Chemistry.


Wang V.,Xi'an University of Technology | Kawazoe Y.,Tohoku University | Kawazoe Y.,RAS Kutateladze Institute of Thermophysics | Geng W.T.,University of Science and Technology Beijing | Geng W.T.,Psi Quantum Materials LLC
Physical Review B - Condensed Matter and Materials Physics | Year: 2015

Using hybrid density functional theory combined with a semiempirical van der Waals dispersion correction, we have investigated the structural and electronic properties of vacancies and self-interstitials in defective few-layer phosphorene. We find that both a vacancy and a self-interstitial defect are more stable in the outer layer than in the inner layer. The formation energy and transition energy of both a vacancy and a self-interstitial P defect decrease with increasing film thickness, mainly due to the upward shift of the host valence band maximum in reference to the vacuum level. Consequently, both vacancies and self-interstitials could act as shallow acceptors, and this well explains the experimentally observed p-type conductivity in few-layer phosphorene. On the other hand, since these native point defects have moderate formation energies and are stable in negatively charged states, they could also serve as electron compensating centers in n-type few-layer phosphorene. © 2015 American Physical Society


Chen L.,Peking University | Zhang X.-R.,Peking University | Zhang X.-R.,Doshisha University | Cao S.,University of Science and Technology Beijing | Bai H.,University of Science and Technology Beijing
International Journal of Heat and Mass Transfer | Year: 2012

Natural convective flow of supercritical fluid has become hot topic both in scientific research and engineering applications. Natural circulation thermosyphon using supercritical/trans-critical CO 2 can be a potential substitute for effective transportation of heat and mass without valves/pumping devices. This paper presents numerical investigations into the effect of unsteady heat input on the trans-critical CO 2 thermosyphon, including sudden/quick increase of heat input, gradual/slow increase of heat input and sudden decrease of heat input. Those unsteady input situations are often seen in real applications and have become the core problem of efficiency and safety improvement. In the present study, two-dimensional rectangular natural circulation loop model is set up and numerically investigated. New heat transport model aiming at trans-critical thermosyphon heat input and system stability laws is proposed with supercritical/trans-critical turbulence model incorporated. It is found that when compared with supercritical CO 2 condition, trans-critical CO 2 thermosyphon has quite different behaviors. Natural convective thermosyphon stability is found to be of routinely dependent for different heat input change mode. Stability factors of natural convective trans-critical CO 2 flow and its implications on real system control are also discussed in this paper. © 2012 Elsevier Ltd. All rights reserved.


Hsieh Y.-H.,National Chiao Tung University | Liou J.-M.,National Cheng Kung University | Huang B.-C.,National Sun Yat - sen University | Liang C.-W.,National Chiao Tung University | And 5 more authors.
Advanced Materials | Year: 2012

In strongly correlated oxides, heterointerfaces, manipulating the interaction, frustration, and discontinuity of lattice, charge, orbital, and spin degrees of freedom, generate new possibilities for next generation devices. In this study, existing oxide heterostructures are examined and local conduction at the BiFeO3-CoFe2O4 vertical interface is found. In such hetero-nanostructures the interface cannot only be the medium for the coupling between phases, but also a new state of the matter. This study demonstrates a novel concept on for oxide interface design and opens an alternative pathway for the exploration of diverse functionalities in complex oxide interfaces. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Wang Z.-Q.,China Institute of Technology | Wang Z.-Q.,University of Science and Technology Beijing | Hu C.-H.,China Institute of Technology | Wang W.,University of Science and Technology Beijing | And 2 more authors.
IEEE Transactions on Reliability | Year: 2014

Hybrid deteriorating systems, which are made up of both linear and nonlinear degradation parts, are often encountered in engineering practice, such as gyroscopes which are frequently utilized in ships, aircraft, and weapon systems. However, little reported literature can be found addressing the degradation modeling for a system of this type. This paper proposes a general degradation modeling framework for hybrid deteriorating systems by employing an additive Wiener process model that consists of a linear degradation part and a nonlinear part. Furthermore, we derive the analytical solution of the remaining useful life distribution approximately for the presented model. For a specific system in service, the posterior estimates of the stochastic parameters in the model are updated recursively by using the condition monitoring observations based on a Bayesian framework with the consideration that the stochastic parameters in the linear and nonlinear deteriorating parts are correlated. Thereafter, the posterior distribution of stochastic parameters is used to update in real-time the distribution of the remaining useful life where the uncertainties in the estimated stochastic parameters are incorporated. Finally, a numerical example and a practical case study are provided to verify the effectiveness of the proposed method. Compared with two existing methods in literature, our proposed degradation modeling method increases the one-step prediction accuracy slightly in terms of mean squared error, but gains significant improvements in the estimated remaining useful life. © 2014 IEEE.


Zhang G.-H.,University of Science and Technology Beijing | Chou K.-C.,University of Science and Technology Beijing | Chou K.-C.,Shanghai University
Metallurgical and Materials Transactions B: Process Metallurgy and Materials Processing Science | Year: 2010

The electrical conductivity of oxide melts is an important physicochemical property for designing the electric smelting furnaces. Although the data of many slag systems have been measured, the quantitative relationships of electrical conductivity to slag composition and temperature are still limited. In this article, a model is proposed based on the optical basicity corrected for the cations required for the charge balance of AlO4 -5, in which Arrhenius Law is used to describe the relationship between electrical conductivity and temperature. In this model, the activation energy is expressed as a linear function of the corrected optical basicity. Successful applications to CaO-MgO-Al2O3-SiO2 and CaO-Al 2O3-SiO2 systems indicate that this model can work well in the electrical conductivity estimation. © The Minerals, Metals & Materials Society and ASM International 2009.


Zhang L.X.,Beijing Normal University | Wang C.B.,Beijing Normal University | Song B.,University of Science and Technology Beijing
Journal of Cleaner Production | Year: 2013

Given the rising expectations for the substitution of fossil energy with renewable energy as one of the solutions to cope with climate change, the carbon emission reduction potential of possible solutions should be evaluated in a holistic and systematic way. In this paper, a systematic account of carbon emission reduction potential was conducted for a typical household biogas system with a digester volume of 8 m3, using a hybrid life-cycle assessment method. Using a 20 year operation scenario, the total life cycle CO2 emission of this family-size biogas utilization system is 2.60 tons, i.e., 0.02 kg CO2/MJ, of which 98.46% is attributed to indirect emissions from building materials and labor inputs. Considering the carbon emission savings due to energy and fertilizer substitution, the annual CO2 emission reduction potential is 1.25 tons for the biogas system that is under consideration. Consequently, such rural household biogas systems should be operated for at least 1.78 years to achieve a positive reduction benefit, i.e., cumulative CO2 emission savings could offset the life-cycle-related CO2 emissions. The results also indicate that long-term, stable running and maintenance are key points to maximize the benefits of household biogas as an effective approach for carbon emission abatement in the rural areas of China. © 2012 Elsevier Ltd. All rights reserved.


Ren H.,University of Science and Technology Beijing | Yu R.,University of Science and Technology Beijing | Wang J.,CAS Institute of Process Engineering | Jin Q.,CAS Institute of Process Engineering | And 6 more authors.
Nano Letters | Year: 2014

Herein, uniform multishelled TiO2 hollow microspheres were synthesized, especially 3- and 4-shelled TiO2 hollow microspheres were synthesized for the first time by a simple sacrificial method capable of controlling the shell thickness, intershell spacing, and number of internal multishells, which are achieved by controlling the size, charge, and diffusion rate of the titanium coordination ions as well as the calcination process. Used as anodes for lithium ion batteries, the multishelled TiO2 hollow microspheres show excellent rate capacity, good cycling performance, and high specific capacity. A superior capacity, up to 237 mAh/g with minimal irreversible capacity after 100 cycles is achieved at a current rate of 1 C (167.5 mA/g), and a capacity of 119 mAh/g is achieved at a current rate of 10 C even after 1200 cycles. © 2014 American Chemical Society.


Dong J.,University of Science and Technology Beijing | Wang Y.,University of Science and Technology Beijing | Zhang J.,University of Science and Technology Beijing | Zhan X.,Peking University | And 3 more authors.
Soft Matter | Year: 2013

Multiple stimuli-responsive polymeric micelles that can respond to light, temperature and pH have been prepared by a novel polymer, pyrene-functionalized poly (dimethylaminoethyl methacrylate), where the pyrene-quaternized segments form a light-responsive shell and the unquaternized segments form a temperature/pH-responsive core. Under UV irradiation, the micelles could be dissociated; when the temperature increased above the lower critical solution temperature, the micelles shrunk. At pH 3, the micelles could be swelled/dissociated and at pH 10, the micelles could be collapsed to complex micelles. The controlled release of Nile Red from the micelle under stimuli was demonstrated. This novel multiple stimuli-responsive micelle shows potential as a new nanocarrier and delivery system. © The Royal Society of Chemistry 2013.


Xie X.,Henan Polytechnic University | Ma H.,Northeastern University China | Zhao Y.,Shenyang Institute of Engineering | Ding D.-W.,University of Science and Technology Beijing | Wang Y.,Northeastern University China
IEEE Transactions on Fuzzy Systems | Year: 2013

This paper proposes relaxed stabilization conditions of discrete-time nonlinear systems in the Takagi-Sugeno (T-S) fuzzy form. By using the algebraic property of fuzzy membership functions, a novel nonparallel distributed compensation (non-PDC) control scheme is proposed based on a new class of fuzzy Lyapunov functions. Thus, relaxed stabilization conditions for the underlying closed-loop fuzzy system are developed by applying a new slack variable technique. In particular, some existing fuzzy Lyapunov functions and non-PDC control schemes are special cases of the new Lyapunov function and fuzzy control scheme, respectively. Finally, two numerical examples are provided to illustrate the effectiveness of the proposed method. © 2012 IEEE.


Ma H.,Cisco Systems | Bastani F.,Massachusetts Institute of Technology | Yen I.-L.,University of Texas at Dallas | Mei H.,University of Science and Technology Beijing
IEEE Transactions on Services Computing | Year: 2013

Service-oriented architecture provides a framework for achieving rapid system composition and deployment. To satisfy different system QoS requirements, it is possible to select an appropriate set of concrete services and compose them to achieve the QoS goals. In addition, some of the services may be reconfigurable and provide various QoS tradeoffs. To make use of these reconfigurable services, the composition process should consider not only service selection, but also configuration parameter settings. However, existing QoS-driven service composition research does not consider reconfigurable services. Moreover, the decision space may be enormous when reconfigurable services are considered. In this paper, we deal with the issues of reconfigurable service modeling and efficient service composition decision making. We introduce a novel compositional decision making process, CDP, which explores optimal solutions of individual component services and uses the knowledge to derive optimal QoS-driven composition solutions. Experimental studies show that the CDP approach can significantly reduce the search space and achieve great performance gains. We also develop a case study system to validate the proposed approach and the results confirm the feasibility and effectiveness of reconfigurable services. © 2013 IEEE.


Sun C.-A.,University of Science and Technology Beijing | El Khoury E.,University of Groningen | Aiello M.,University of Groningen
IEEE Transactions on Services Computing | Year: 2011

Service-Oriented Computing (SOC) is becoming the mainstream development paradigm of applications over the Internet, taking advantage of remote independent functionalities. The cornerstone of SOC's success lies in the potential advantage of composing services on the fly. When the control over the communication and the elements of the information system is low, developing solid systems is challenging. In particular, developing reliable web service compositions usually requires the integration of both composition languages, such as the Business Process Execution Language (BPEL), and of coordination protocols, such as WS-AtomicTransaction and WS-BusinessActivity. Unfortunately, the composition and coordination of web services currently have separate languages and specifications. The goal of this paper is twofold. First, we identify the major requirements of transaction management in Service-oriented systems and survey the relevant standards. Second, we propose a semiautomatic approach to integrate BPEL specifications and web service coordination protocols, that is, implementing transaction management within service composition processes, and thus overcoming the limitations of current technologies. © 2011 IEEE.


Zhong A.,Peking University | Bian Y.,University of Science and Technology Beijing | Zhang Y.,University of Science and Technology Beijing
Journal of Physical Chemistry C | Year: 2010

Density functional theory (DFT) calculations were carried out to investigate the semiconductor performance for the organic field effect transistor (OFET) of PbPc, PbPc(α-OC2H5) 4, and PbPc(α-OC5H11)4 {Pc2- = dianion of phthalocyanine; [Pc(α-OC2H 5)4]2- = dianion of 1, 8, 15, 22-tetraethoxyphthalocyanine; [Pc(α-OC5H11) 4]2- = dianion of 1, 8, 15, 22-tetrakis(3-pentyloxy) phthalocyanine} in terms of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy, ionization energy (IE), electron affinity (EA), and their reorganization energy (λ) during the charge-transport process. On the basis of Marcus electron transfer theory, transfer integral (t) and field effect transistor (FET) properties for the three compounds with known crystal structure have been calculated. In line with the experimental result that PbPc can also work as an n-type semiconductor in addition to a p-type one, theoretical calculations reveal that PbPc has relatively large electron affinity to ensure effective electron injection from Au electrode. Introducing four ethoxy groups on the nonperipheral positions of PbPc decreases both the hole and electron injection barrier relative to Au electrode, and the hole and electron reorganization energy becomes very balanced, making PbPc(α-OC2H5)4 a better ambipolar semiconductor material than PbPc. However, nonperipheral pentyloxy substitution lifts the energy level of both HOMO and LUMO and thus decreases both the IP and EA value of PbPc, resulting in improved hole injection ability but worsened electron injection process. The transfer mobility for electron is revealed to be as large as 0.39 cm2 V-1 s-1 for PbPc and 0.16 cm2 V-1 s-1 for PbPc(α-OC5H11)4. The present work will be helpful to understand the electronic nature for PbPc to work as ambipolar semiconductor and to rationally design novel semiconductor materials for OFET usage. © 2010 American Chemical Society.


Xiang X.,University of Science and Technology Beijing | Lin C.,Tsinghua National Laboratory for Information Sciences and Technology | Chen X.,Beijing Information Science and Technology University
IEEE Wireless Communications Letters | Year: 2014

Mobile cloud computing (MCC) converges mobile computing and Cloud computing for augmenting resource-poor mobile devices to run ¿¿ heavier¿¿ applications. With the increasing ubiquity of mobile devices, MCC exhibits vast application potential in various areas. Energy-efficient data transmission is a key issue in MCC due to energy-poverty of mobile devices. In this letter, we address the issue of energy-efficient link selection and data transmission scheduling for delay-tolerant and data-intensive applications in MCC. We first formulate the problem as a discrete-time stochastic dynamic program (SDP) that aims to optimize both system throughput and energy consumption. To solve the formulated SDP, we then propose a scalable approximate dynamic programming (ADP) algorithm that does not require the statistics of exogenous stochastic information (e.g., data arrival). Simulation studies show that the proposed ADP algorithm can reduce the average energy consumed for delivering a packet by a maximum of over 40 percent compared to alternative minimum-delay and SALSA policies. © 2012 IEEE.


Guo S.F.,Huazhong University of Science and Technology | Guo S.F.,University of Science and Technology Beijing | Liu L.,Huazhong University of Science and Technology | Li N.,Huazhong University of Science and Technology | Li Y.,National University of Singapore
Scripta Materialia | Year: 2010

Using alloy design, an Fe77Mo5P9C7.5B1.5 bulk metallic glass matrix composite reinforced by in situ formed ductile α-Fe dendrites has been developed. In contrast to the monolithic Fe-based bulk metallic glasses that usually fail in brittle fracture, the resulting composite shows a significant plastic strain of more than 30% as well as a high fracture strength of over 3.0 GPa. The in situ formation of the ductile α-Fe dendrites accounts for the significant enhancement of the plasticity. © 2009 Acta Materialia Inc.


Wang L.J.,University of Science and Technology Beijing | Sheng L.Y.,Peking University | Sheng L.Y.,PKU HKUST ShenZhen Hong Kong Institution | Hong C.M.,China Banknote Printing and Minting Corporation
Materials and Design | Year: 2012

Precipitation behavior of grain boundary carbides and its influence on mechanical properties and fracture mechanism of the high nitrogen austenitic stainless steel produced by different processing methods were studied. The simulation software Thermo-calc was applied to analyze the effects of element content on precipitation of carbides. The results show that hot-rolled plate has higher strength, but solution-treated one followed by water quenching has excellent combination of strength and ductility (toughness). M23C6 is the main precipitate and deteriorates the toughness of the steel obviously when it precipitates along grain boundaries. In this case, intergranular fracture is the predominant failure mechanism and the fracture surface is characterized by the shape of rock candy. The toughness at -40°C is decreased by 53% when small amount of carbides precipitates during sand cooling process after solution treatment. The simulation results exhibit that with the decrease of C content, both the precipitation quantity and precipitation temperature of M23C6 decrease. Cr and N have no influence on precipitation quantity of M23C6, but the precipitation temperature will increase with the increase of Cr and the decrease of N. © 2012 Elsevier Ltd.


Hou X.-m.,University of Science and Technology Beijing | Chou K.-C.,University of Science and Technology Beijing | Chou K.-C.,Shanghai University
Corrosion Science | Year: 2010

The isothermal oxidation mechanism of the carbon-containing composites has been investigated based on the experimental data reported in the literature. The results showed that the oxidation kinetics was affected not only by temperature and time but also by carbon content and the sample shape. For the oxidation kinetics, a series of quantitative kinetic models have been developed based on the controlling step. In this model, the effects of carbon content, sample size and temperature on the reaction fraction have been especially discussed. Incorporation of the experimental data into the new model indicates that a good agreement has been reached. © 2009 Elsevier Ltd. All rights reserved.


Li X.,University of Science and Technology Beijing | Zhang T.-Y.,Shanghai University | Su Y.J.,University of Science and Technology Beijing
Nano Letters | Year: 2015

First-principles calculations were conducted on armchair graphene nanoribbons (AGNRs) to simulate the elastic behavior of AGNRs with hydrogen-terminated and bare edges. The results show width-dependent elastic properties with a periodicity of three, which depends on the nature of edge. The edge eigenstress and eigendisplacement models are able to predict the width-dependent nominal Youngs modulus and Poissons ratio, while the Clar structure explains the crucial role of edges in the periodically modulated size-dependent elastic properties. © 2015 American Chemical Society.


Guo S.,University of Science and Technology Beijing | Xu L.,University of Science and Technology Beijing | Zhang L.,University of Science and Technology Beijing | Chang W.,China National Offshore Oil Corporation | Lu M.,University of Science and Technology Beijing
Corrosion Science | Year: 2012

Scanning electron microscopy (SEM), X-ray Diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) were employed to analyze the corrosion scale formed on API X65, 1Cr, 2Cr and 3Cr steels in CO 2 containing environment. The evolution of scale on 2Cr steel was characterized with electrochemical impedance spectroscopy (EIS) and in situ pH monitoring. The results show that Cr content can alter the crystalline state of corrosion scale via changing pH value. Localized corrosion occurs on 2Cr steel when FeCO 3 crystal stripes form on the amorphous scale. The critical Cr content for general corrosion is 3wt.%. © 2012 Elsevier Ltd.


Gan M.,University of Science and Technology Beijing | Jiang R.,Tsinghua National Laboratory for Information Sciences and Technology
Expert Systems with Applications | Year: 2013

Nowadays, personalized recommender systems have become more and more indispensable in a wide variety of commercial applications due to the vast amount of overloaded information accompanying the explosive growth of the internet. Based on the assumption that users sharing similar preferences in history would also have similar interests in the future, user-based collaborative filtering algorithms have demonstrated remarkable successes and become one of the most dominant branches in the study of personalized recommendation. However, the presence of popular objects that meet the general interest of a broad spectrum of audience may introduce weak relationships between users and adversely influence the correct ranking of candidate objects. Besides, recent studies have also shown that gains of the accuracy in a recommendation may be frequently accompanied by losses of the diversity, making the selection of a reasonable tradeoff between the accuracy and the diversity not obvious. With these understandings, we propose in this paper a network-based collaborative filtering approach to overcome the adverse influence of popular objects while achieving a reasonable balance between the accuracy and the diversity. Our method starts with the construction of a user similarity network from historical data by using a nearest neighbor approach. Based on this network, we calculate discriminant scores for candidate objects and further sort the objects in non-ascending order to obtain the final ranking list. We validate the proposed approach by performing large-scale random sub-sampling experiments on two widely used data sets (MovieLens and Netflix), and we evaluate our method using two accuracy criteria and two diversity measures. Results show that our approach significantly outperforms the ordinary user-based collaborative filtering method by not only enhancing the recommendation accuracy but also improving the recommendation diversity. © 2012 Elsevier Ltd. All rights reserved.


Zhao D.,Beihang University | Zhou W.,Beihang University | Cui X.,University of Science and Technology Beijing | Tian Y.,Beihang University | And 2 more authors.
Advanced Materials | Year: 2011

Uniform homeotropic and homogeneous alignment of liquid crystals (LCs) is facilely achieved by dispersing Ni nanoparticles (Ni NPs) into the LCs. The alignment mode depends on the morphology of the Ni NPs. The mechanism of NP-induced LC alignment is elucidated clearly, indicating that the perfect orientation arises from the adsorption of Ni NPs on the substrate. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Faccenda A.,University of Windsor | Bonham C.A.,University of Windsor | Vacratsis P.O.,University of Windsor | Zhang X.,World Precision Instruments | And 2 more authors.
Journal of the American Chemical Society | Year: 2010

We present a simple method by which gold nanoparticles (AuNPs) are used to simultaneously isolate and enrich for free or modified thiol-containing peptides, thus facilitating the identification of protein S-modification sites. Here, protein disulfide isomerase (PDI) and dual specificity phosphatase 12 (DUSP12 or hYVH1) were S-nitrosylated or S-glutathionylated, their free thiols differentially alkylated, and subjected to proteolysis. AuNPs were added to the digests, and the AuNP-bound peptides were isolated by centrifugation and released by thiol exchange. These AuNP-bound peptides were analyzed by MALDI-TOF mass spectrometry revealing that AuNPs result in a significant enrichment of free thiol-containing as well as S-nitrosylated, S-glutathionylated, and S-alkylated peptides, leading to the unequivocal assignment of thiols susceptible to modification. © 2010 American Chemical Society.


Grant
Agency: GTR | Branch: NERC | Program: | Phase: Research Grant | Award Amount: 203.66K | Year: 2016

Our overall aim is to build earthquake resilience in China by improving (a) the assessment of seismic hazard and risk from earthquakes and consequent events and (b) the communication and use of probabilistic information in the development of more proportionate and risk-based strategies for disaster risk reduction. We will build on and extend a recently-developed historical catalogue for earthquakes, extend it for the first time to include consequent events (landslides, debris/mud-flows, outburst floods), unify this new database with modern instrumental data, use state-of the art statistical techniques to quantify the associated uncertainties, and incorporate social science-based understanding of risk communication and governance to improve policy development and implementation. The work programme will be carried out in Si-chuan (including the 2008 Wenchuan earthquake) and Yun-nan provinces. While they are both tectonically active, and mountainous, and thus vulnerable not only to earthquakes but also to consequent hazards of earthquake-triggered landslides and flooding, Si-chuan is one of the wealthiest provinces in China, while Yun-nan is one of poorest. These differences in wealth, combined with the recency of the devastating 2008 Wenchuan in Si-chuan compared to the more attenuated memory of the 1996 Lijiang earthquake in Yun-nan, make for a natural experiment in which to test the efficacy of improved probabilistic assessment of risk and associated uncertainty to people and property by earthquakes, and consequent event hazards, in supporting more risk-based approaches to disaster reduction. This project will promote long-term sustainable growth in earthquake prone regions of China by improving both the assessment of earthquake hazard and consequent event risk and the communication, understanding, and use of the resulting probabilistic forecasts for disaster risk reduction by policymakers and local publics. It addresses several specific capacity gaps identified in successive Chinese national disaster risk reduction strategies. As well as engaging with policymakers at both the national and local levels to improve the effectiveness of emergency planning and building code regulation, we will also engage directly with local publics to enhance public understanding of risk and capacity to deal with it. In so doing, the project will also fulfil the UKs Official Development Assistance (ODA) commitment to promoting the economic development and welfare of developing countries by drawing on UKs science base to address a key vulnerability differentially affecting the very poorest in China.


Qiao J.W.,University of Science and Technology Beijing | Qiao J.W.,Taiyuan University of Technology | Sun A.C.,Yuan Ze University | Huang E.W.,National Central University | And 3 more authors.
Acta Materialia | Year: 2011

A Ti-based bulk metallic glass matrix composite (BMGMC) with a homogeneous distribution of dendrites and the composition of Ti46Zr 20V12Cu5Be17 is characterized by a high tensile strength of ∼1640 MPa and a large tensile strain of ∼15.5% at room temperature. The present BMGMC exhibits the largest tensile ductility and highest fracture absorption energy under the stress-strain curve of all dendrite-reinforced BMGMCs developed to date. Tensile deformation micromechanisms are explored through experimental visualization and theoretical analyses. After tension, fragmentation of the dendrites, rather than crystallization within the glass matrix and/or atom debonding near the interface of dual-phase composites, is responsible for the high tensile ductility. The subdivisions within the interior of dendrites are separated by shear bands and dense dislocation walls, and local separation of dendrites under modes I and II prevails. The multiplication of dislocations, severe lattice distortions, and even local amorphization dominate within the dendrites. Good structural coherency of the interface is demonstrated, despite being subjected to significant plastic deformation. Theoretical analyses reveal that the constitutive relations elastic-elastic, elastic-plastic, and plastic-plastic of dual-phase BMGMC generally correspond to the (1) elastic, (2) work-hardening, and (3) softening deformation stages, respectively. The capacity for work-hardening is highly dependent on the large plastic deformation of the dendrites and the high yield strength of the glass matrix. The present study provides a fundamental basis for designing work-hardening dual-phase BMGMCs exhibiting remarkably homogeneous deformation. © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.


Song L.,Peking University | Han Z.,University of Houston | Han Z.,Kyung Hee University | Zhang Z.,University of Science and Technology Beijing | Jiao B.,Peking University
IEEE Journal on Selected Areas in Communications | Year: 2012

It has been well recognized that channel state information (CSI) feedback is of great importance for dowlink transmissions of closed-loop wireless networks. However, the existing work typically researched the CSI feedback problem for each individual mobile station (MS), and thus, cannot efficiently model the interactions among self-interested mobile users in the network level. To this end, in this paper, we propose an alternative approach to investigate the CSI feedback-rate control problem in the analytical setting of a game theoretic framework, in which a multiple-antenna base station (BS) communicates with a number of co-channel MSs through linear precoder. Specifically, we first present a non-cooperative feedback-rate control game (NFC), in which each MS selects the feedback-rate to maximize its performance in a distributed way. To improve efficiency from a social optimum point of view, we then introduce pricing, called the non-cooperative feedback-rate control game with price (NFCP). The game utility is defined as the performance gain by CSI feedback minus the price as a linear function of the CSI feedback-rate. The existence of the Nash equilibrium of such games is investigated, and two types of feedback protocols (FDMA and CSMA) are studied. Simulation results show that by adjusting the pricing factor, the distributed NFCP game results in close optimal performance compared with that of the centralized scheme. © 2012 IEEE.


Qiu J.,Peking University | Guo M.,University of Science and Technology Beijing | Wang X.,Peking University
ACS Applied Materials and Interfaces | Year: 2011

We present a two-step electrochemical deposition process to synthesize hierarchical zinc oxide (ZnO) nanorod-nanosheet structures on indium tin oxide (ITO) substrate, which involves electrodeposition of ZnO nanosheet arrays on the conductive glass substrate, followed by electrochemical growth of secondary ZnO nanorods on the backbone of the primary ZnO nanosheets. The formation mechanism of the hierarchical nanostructure is discussed. It is demonstrated that annealing treatment of the primary nanosheets synthesized by the first-step deposition process plays a key role in synthesizing the hierarchical nanostructure. Photovoltaic properties of dye-sensitized solar cells (DSSCs) based on hierarchical ZnO nanostructures are investigated. The hierarchical ZnO nanorod-nanosheet DSSC exhibits improved device performance compared to the DSSC constructed using photoelectrode of bare ZnO nanosheet arrays. The improvement can be attributed to the enhanced dye loading, which is caused by the enlargement of internal surface area within the nanostructure photoelectrode. Furthermore, we perform a parametric study to determine the optimum geometric dimensions of the hierarchical ZnO nanorod-nanosheet photoelectrode through adjusting the preparation conditions of the first- and second-step deposition process. By utilizing a hierarchical nanostructure photoelectrode with film thickness of about 7 μm, the DSSC with an open-circuit voltage of 0.74 V and an overall power conversion efficiency of 3.12% is successfully obtained. © 2011 American Chemical Society.


Wei Y.,CAS Institute of Mechanics | Li Y.,CAS Institute of Mechanics | Zhu L.,CAS Institute of Mechanics | Liu Y.,CAS Institute of Mechanics | And 7 more authors.
Nature Communications | Year: 2014

The strength-ductility trade-off has been a long-standing dilemma in materials science. This has limited the potential of many structural materials, steels in particular. Here we report a way of enhancing the strength of twinning-induced plasticity steel at no ductility trade-off. After applying torsion to cylindrical twinning-induced plasticity steel samples to generate a gradient nanotwinned structure along the radial direction, we find that the yielding strength of the material can be doubled at no reduction in ductility. It is shown that this evasion of strength-ductility trade-off is due to the formation of a gradient hierarchical nanotwinned structure during pre-torsion and subsequent tensile deformation. A series of finite element simulations based on crystal plasticity are performed to understand why the gradient twin structure can cause strengthening and ductility retention, and how sequential torsion and tension lead to the observed hierarchical nanotwinned structure through activation of different twinning systems. © 2014 Macmillan Publishers Limited.


I’ve apparently been collected extra stories to share for a few weeks. Scroll on down if you want some more EV and clean transport reading. To kick things off, here’s one looking forward to the new year: 11–13 Electric Cars To Light Up The Market In 2016 Between the electric car models that are just arriving on the US market and the ones that will likely hit the market by the end of 2016, we have an exciting year ahead. Below are 11 electric cars that I think will light up 2016 (or 13 if you count cars in a particular way). The Tesla Model X SUV will begin hitting the company’s showrooms throughout the US towards the beginning of January, according to some recent reports. Mark Templeton Shares His Thoughts On The Model X (After Owning It For A Few Months) The CEO of Citrix Systems, Mark Templeton, was one of the lucky ones to have taken delivery of his Tesla Model X SUV at the Model X launch event at the end of September — more than 2 months ago, as of the time of writing this. Tesla Model S (and Model X, I suppose) owners throughout Europe, Australia, and Hong Kong, will be given access to Spotify Premium following a new firmware update, according to recent reports. Tesla HQ Running Out of Room for Employee Parking Success brings its own set of new problems to be solved. There are so many people working at Tesla headquarters these days that the company has set up a valet parking service, according to Business Insider. Tesla currently has 14,000 total employees with 1,600 open positions to fill, and over the next 4 years, Tesla plans to add another 4,500 new employees just in California alone. As indicated, it’s a wiki for FAQ regarding the Tesla Model X. This excellent resource deserves it’s own thread. Although it obviously suffers from the same selection bias as any other nonrandom voluntary data set, the numbers are substantial enough to provide real information. Anyone who has reserved a MX is encouraged to register, then update their information through the order and delivery process. Although the Tesla Model X all-electric SUV was first unveiled in prototype form way back in February 2012, and limited customer deliveries began in September of this year, the car is still shrouded in mystery. With somewhere between 20,000 and 30,000 pre-orders for the vehicle, the Model X is arguably the most highly anticipated SUV of the decade. And yet you still can’t go to the Tesla web site to find out pricing details or a comprehensive description of the various options and configurations that are available. I’m new to the forum (but long time lurker). Doing a random search on Google I find this document that I think was never mentioned: https://www.teslamotors.com/sites/de…onse_Guide.pdf It contains lot’s of new informations (to me at least ) In Light of Model X Options, Did the Shareholder “Vegan Uprising” Succeed? While browsing YouTube for elusive new Model X videos, I got this “recommended” video, hilariously titled: “Elon Musk faces the Vegan Uprising at Tesla shareholder meeting (6.9.15).” Is There Really a Difference? 2015 vs 2013 Took delivery of my 2015 P90D last week. Love the car, but also loved my 2013. Aside from the performance, is there really a difference worth the upgrade? It’s a decision I struggled with for 8 months before finally pulling the trigger. The auto pilot software was what finally put me over the edge. Beyond that and Next Gen seats, can’t say there’s really much of a difference. I got the same joy out of my 2013 as I do the 2015. The 2015 allows me to show off its muscle to friends. Is that worth another $33,000?? That’s for each individual to decide. The next gen seats are certainly nicer, but not quite as big of a difference as I expected. The Auto Pilot feature so far has done more of scaring the crap out of me than it has been a useful tool. Jury is still out on that one. Assuming it will get better with time. Overall, absolutely love my new car, but at the same time, I loved my 2013 too. We’ve had our S85 for about 2.5 years and have loved every minute of it. My wife is not a car person at all, but with the Tesla it’s a different story. We live in New England and the while the rear wheel drive isn’t bad in the snow, we shy away from taking it to the mountains and on occasion we find ourselves having to dig a path through the snow to get up our driveway. So, this weekend we decided to take a look at the 70D and take it for a spin. I had not driven any AWD version yet, nor had I experienced AP. AWD is a different experience… less of a push feel and more of a launch feel… if that makes sense. And, the AP and additional safety features were very cool and helped with selling the idea of trading to the wife. I’ve owned Porsches, plenty of BMWs and my new Tesla replaced my Merc SLK… I cannot get rid of the Tesla grin… I am incapable of putting words to describe my feeling, just incredible. SpaceX’s immaculate reception last night gives Tesla Motors (and Tesla Energy) a brand boost that Big Auto would love to have, but never will. They’ve tried for decades to associate their cars with rockets and aircraft, especially during the space-happy 1950s and 60s. Space-age design, space-age materials, jet-inspired fins, turbine taillights, cockpit ergonomics. Well, now we have a car company that actually does share engineering DNA with flying things, since the CEO is a real-life rocketeer who is taking us where no man has gone before. The 500k number comes from Tesla’s ability to produce cars given the restraints of the NUMMI factory and Gigafactory 1 at fully operational. But what if after the March reveal, preorders exceed expectations? What if preorders hit 500k in a few months? Or even higher? Once the Model 3 goes into production, it would take years to clear the backlog. Would Tesla really stand idly by? 30 Reasons Why Tesla Model S is Such a Great Car My friend asked me yesterday “Why have your ordered Tesla?”. Well, I didn’t have much time, so I said “Because it’s best car in the world.” And since he knew nothing on how true my statement was, I did this short list of major reasons why it is so and emailed it to him. Let me know if you think I’ve missed some that should be in top 30. On New Year’s Day, a Tesla Model S in Norway caught fire while charging and was totally destroyed. There is no known cause for the incident but Tesla is investigating and promises a full report soon. I Upgraded to Ludicrous and got Launch Mode!!! Is it worth it? Here is my review. This last thursday I picked up my newly retrofitted P85DL which also came with the new software upgrade offering “Launch Mode.” First off to help put some context to my opinion towards the “is it worth it” debate, I was looking at this decision from a mostly impractical view. A.) the performance it gets you is way cheaper than what you’d have to pay to make any ice to improve it that much, B.) it gets my P85D back up to the king of the hill status and C.) I have always wanted a sub 3 second 0-60 car and a sub 11 second quarter mile car and I am done with ICE so here we are. Cruising down the Florida Turnpike on cruise control is probably what the “beta” version of our software was programed for? I drove 3+ hours and the software made almost no mistakes with the exception of wanting to “exit out” a few times driving in the right lane. The car steered to follow the right lane indicator and wanted to exit out to the right. I have now learned to “guide the car” through exit areas and the autopilot is getting more adaptive. Nevertheless, the car basically drove itself for 220 miles, and in my book, this is very impressive. Why I Think Tesla is Unlikely to Fail Speculation and predictions of Tesla’s demise are rampant. Some people here as well as a number of “experts” in the auto media believe that the mainstream car makers are on the verge of killing Tesla with their own BEV. Tesla may still fail, their success is not guaranteed, but I don’t believe any failure will be for the reasons the experts believe. What Will The TSLA Share Price Be At Closing December 30th 2016? I think we have a very exciting year ahead of us, due to many reasons: And I think TSLA will do very well this year as a result. I would be surprised if we don’t see the share price go over 300 this year, so I’m betting on 318.27 USD per share at closing on Friday the 30th of December. Happy New Year everyone! A 2016 Chevrolet Volt driven by Wayne Gerdes in Southern California returned 111.9 miles on a single charge and he said under ideal circumstances 125 miles is possible. Saab, the former Swedish car maker, is now NEVS and has been awarded a $12 billion contract to build 225.000 electric cars. It plans to launch 5 new models. The city of Leipzig in Germany recently took delivery of a new 50-strong fleet of BMW i3s, to be used by city council and municipal waterworks employees, amongst others, according to a recent press release. On a recent trip to Vermont I stopped at Prestige BMW in New Jersey on both legs of the journey. They recently installed two 24 kW DC Fast Charge stations that are accessible 24/7 and free to use. A robust DC Fast charge infrastructure is crucial for mass EV adoption. The Mercedes-Benz S550e Plug-In Hybrid is packed with some of the best safety technology and creature comforts you can get in any new car today, regardless of price. It also moves smartly, with an advanced plug-in hybrid system that lets you plug in overnight—or even for a few hours—and then drive for a dozen or so miles before transitioning into an especially smooth gasoline-electric hybrid. Mercedes says its GLE 500 e plug-in hybrid SUV is 42% more energy efficient than its conventional cousin over its lifetime, even though it requires more energy to build. XALT Energy to Supply Li-ion Packs to Efficient Drivetrains for PHEVs XALT Energy and Efficient Drivetrains (EDI) announced a tentative agreement through which XALT will supply EDI with its NMC graphite Lithium-ion battery energy storage packs for use in EDI’s PHEV PowerDrive and electric power export solutions. Chevrolet has trademarked the names Corvette E-Ray and E-Ray. Does that mean an electric Corvette is planned? Maybe, if only to compete with Porsche. Researchers at Tsinghua University, with colleagues from the University of Science and Technology Beijing, have discovered that the multi-reversible magnetization of ferromagnetic material can be controlled via the lithiation/delithiation reaction in a Li-ion battery by varying the discharge–charge potential at room temperature. This phenomenon couples magnetism and electrochemistry, and enables precise quantitative magnetization manipulation using an electrochemical method. An open-access paper on their discovery is published in the ACS journal Nano Letters. Navigant Forecasts Global Light Duty Electrified Vehicle Sales to Exceed 6.0M in 2024; PEVs to Account for Roughly Half In a new report, Electric Vehicle Market Forecasts, Navigant research projects that under its base scenario, global sales of light duty electrified vehicles (i.e., vehicles that use electricity for traction, including hybrids, plug-in hybrids, and battery-electrics) will grow from 2.6 million vehicle sales in 2015 to more than 6.0 million in 2024. As discussed in this article by Ambrose Evans-Pritchard in the Telegraph, the “OPEC Oil Outlook” recently published assumes that neither global warming regulation nor electric vehicles will influence oil demand much until 2040. The California DMV announced that the maximum of 85,000 Green Clean Air Vehicle Decals had been issued to plug-in hybrid electric vehicles, denying new Volt and plug-in Prius owners the coveted sticker allowing them free access to HOV and HOT lanes. I don’t know which channel my daughter in law was streaming onto their projector, but just before they dropped the ball in Times Square, Bill Nye the Science Guy told the world that he hopes in 2031 that we can reach 80% electric cars on the road. He said once you drive an electric vehicle you will never go back… How true, how true. The fifth race of the second Formula E season will be held March 12 in Mexico City at the historic Autodromo Hermano Rodriguez before moving to Long Beach. Bain: Germany’s Goal of 1M Electric Cars by 2020 is Unattainable; Fewer than 50,000 Units on Road by End of This Year The German Federal Government plan to have one million electric cars on its roads by 2020 has failed, according to the analysis of international management consulting firm Bain & Company. By the end of 2015, there will be a total of about 50,000 electric cars and plug-in hybrids on the roads in Germany (about 75% below plan); nevertheless, structural transformation towards electromobility is continuing, according to the firm. Environmental groups have sent a letter to CARB urging the Volkswagen be punished to the full extent of the law for selling diesel powered cars it knew did not conform to state emissions regulations. If every other passenger car in Norway is plugged into the electric network by 2020, Europe will have to produce more electricity – mainly from coal-fired power plants – to meet the demand. But it will be a plus for the climate nonetheless. Aside from my own presentation, which I’ll share soon, there are a couple more EV Transportation & Technology Summit presentations that I recorded and wanted to share. I don’t have much to say about them, so I’ll just drop the videos below. COP21 was arguably one of the most epic meetings in the history of humanity. In a spirit of mutual cooperation, the international community agreed to finally begin to turn away from a fossil fuel-powered economy toward a clean, sustainable future. While it may be important to make general commitments to cut CO2 and methane emissions, and to keep under a certain temperature increase, what it comes down to in the end is making practical changes in how we live our lives and run our societies. Analysis of EV Charging in Ireland Suggests Public Fast-Charging Infrastructure May Become Commercially Viable in Short- to Medium Term A study of EV charging behavior by a team at Trinity College Dublin has found that, from the household data available, EV users prefer to carry out the majority of their charging at home in the evening—the period of highest demand on the electrical grid indicating that incentivization may be required to shift charging away from this peak grid demand period. The Dutch electric vehicle charging solutions company EV-Box will now be entering the markets of the nearby countries of Belgium and Luxembourg, according to a recent email sent to EV Obsession. A new solar powered EV charging station in the city of Vestby, Norway will produce 16,000 kWh of electricity annually, enough to go 47,000 miles in a Tesla. Aside from my own presentation, which I’ll share soon, there are a couple more EV Transportation & Technology Summit presentations that I recorded and wanted to share. I don’t have much to say about them, so I’ll just drop the videos below. Tesla faces headwinds from rivals. You’ve read it ad nauseum. But it you’re American, then Tesla could face headwinds from you. American motorists fall into two categories: current plaintiffs and future plaintiffs. We like to sue. In fact, we sue better than we drive. And we’re about to give ourselves more excuses to sue. Autonomous driving could start a litigation beat-down for any company that dares pioneer it. Autonomous technology will be the hot topic in the world of automobiles in 2016, as all carmakers rush to bring self-driving cars to market. Oil giant Exxon was studying climate change impacts in the 1970s and 80s, and their projections from 35 years ago accurately portray what is happening now. Knowing what they knew, they chose to continue business as usual. Now this astounding article in the LA Times. Car-Free Movement Gaining Steam in Europe and Elsewhere Athlyn Cathcart-Keays of The Guardian-Cities chronicles the advancement of the international urban car-free movement as well as auto regulations that focus on air pollution. The most recent city to join the growing list is Oslo, Norway. On December 18, Congress passed a bill to fund the government for fiscal year 2016. This particular bill includes $500 million in funding for the tremendously popular TIGER discretionary grant program, the same funding level as fiscal year 2015. The TIGER program helps communities build a broad range of innovative transportation projects, including improvements for people on bikes. Chicago, with funding from the four major wireless carriers, has achieved a major amenity for transit users: 4G internet service along 22 miles of subway tracks in the CTA system. The Los Angeles County Metropolitan Transportation Authority (Metro) is implementing a new vision for “transit-oriented communities.” As a result of the “defeat device” software it installed in diesel cars, Volkswagen faces multiple criminal investigations in Europe. And it will likely face criminal penalties in the U.S., along with hundreds of civil suits from angered owners. Now, it seems the company may also be in legal trouble in China over potential diesel-emissions cheating. COP21: Shows the End of Fossil Fuels is Near, We Must Speed Its Coming The wheel of climate action turns slowly, but in Paris it has turned. There’s much in this deal that frustrates and disappoints me, but it still puts the fossil fuel industry squarely on the wrong side of history.    Get CleanTechnica’s 1st (completely free) electric car report → “Electric Cars: What Early Adopters & First Followers Want.”   Come attend CleanTechnica’s 1st “Cleantech Revolution Tour” event → in Berlin, Germany, April 9–10.   Keep up to date with all the hottest cleantech news by subscribing to our (free) cleantech newsletter, or keep an eye on sector-specific news by getting our (also free) solar energy newsletter, electric vehicle newsletter, or wind energy newsletter.  


Cheng F.,Beijing Jiaotong University | Yu J.,University of Science and Technology Beijing | Xiong H.,Shanghai JiaoTong University
IEEE Transactions on Neural Networks | Year: 2010

The Gaussian process (GP) approaches to classification synthesize Bayesian methods and kernel techniques, which are developed for the purpose of small sample analysis. Here we propose a GP model and investigate it for the facial expression recognition in the Japanese female facial expression dataset. By the strategy of leave-one-out cross validation, the accuracy of the GP classifiers reaches 93.43% without any feature selection/extraction. Even when tested on all expressions of any particular expressor, the GP classifier trained by the other samples outperforms some frequently used classifiers significantly. In order to survey the robustness of this novel method, the random trial of 10-fold cross validations is repeated many times to provide an overview of recognition rates. The experimental results demonstrate a promising performance of this application. © 2010 IEEE.


Song L.,University of Science and Technology Beijing | Xu X.J.,Zhongyuan University of Technology | Sun J.,Shanghai JiaoTong University | Lin J.P.,University of Science and Technology Beijing
Materials Characterization | Year: 2014

The cooling rate effects on the βo → ωo phase transformation in Ti-45Al-8.5Nb-(W, B, Y) (at.%) alloy were investigated by annealing the alloy at 950 °C followed by different cooling methods. The morphology and the distribution of the ω-related phases were analyzed by TEM. The amount and morphology of the ω-related phases are very sensitive to the cooling rate. The ω-related phases could not be resolved in the water-quenched sample whereas it grew into nano-particles in the air-cooled sample. In the furnace-cooled sample, the ωo phase with B82 structure grew into micron-sized particles and occupied the whole βo area. The nucleation of the ordered ω embryos can be explained by the well accepted displacive mechanism because of the instability of the βo(B2) structure, accompanied by a short-range diffusion process between neighboring {111}βo planes. However, the growth of the ω-related phases is controlled by a long-range diffusion process. Due to ready nucleation and growth, the ordered ω formation is bound to occur in as-cast and heat-treated high Nb-TiAl alloys. © 2014 Elsevier Inc. All rights reserved.


Kelly F.J.,King's College London | Zhu T.,University of Science and Technology Beijing
Science | Year: 2016

In cities across the globe, road transport remains an important source of air pollutants that are linked with acute and chronic health effects. Decreasing vehicle emissions-while maintaining or increasing commuter journeys-remains a major challenge for city administrators. In London, congestion-charging and a citywide low-emission zone failed to bring nitrogen dioxide concentrations under control. n Beijing, controls on the purchase and use of cars have not decreased transport emissions to a sufficient extent. As cities continue to grow, not even zero-emission vehicles are the solution. Moving increasingly large numbers of people efficiently around a city can only be achieved by expanding mass transit systems.


Hao Y.,University of Science and Technology Beijing | Chen S.,CAS Institute of Physics
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2012

We investigate the dynamical properties of anyons confined in one-dimensional optical lattices combined with a weak harmonic trap using the exact numerical method based on a generalized Jordan-Wigner transformation. The evolving density profiles, momentum distributions, occupation distributions, and occupations of the lowest natural orbital after quench of the harmonic trap are obtained for different statistical parameters. The density profiles of anyons display the same behaviors irrespective of statistical parameter in the full evolving period, while the behaviors dependent on statistical property are shown in the momentum distributions and occupations of natural orbitals. © 2012 American Physical Society.


Zhang X.,University of Science and Technology Beijing | Zhang X.,Pacific Northwest National Laboratory | Zhang Y.,University of Science and Technology Beijing | Liao Q.,University of Science and Technology Beijing | And 2 more authors.
Small | Year: 2013

We designed and constructed reduced graphene oxide (rGO) functionalized high electron mobility transistor (HEMT) for rapid and ultra-sensitive detection of label-free DNA in real time. The micrometer sized rGO sheets with structural defects helped absorb DNA molecules providing a facile and robust approach to functionalization. DNA was immobilized onto the surface of HEMT gate through rGO functionalization, and changed the conductivity of HEMT. The real time monitor and detection of DNA hybridization by rGO functionalized HEMT presented interesting current responses: a "two steps" signal enhancement in the presence of target DNA; and a "one step" signaling with random DNA. These two different recognition patterns made the HEMT capable of specifically detecting target DNA sequence. The working principle of the rGO functionalized HEMT can be demonstrated as the variation of the ambience charge distribution. Furthermore, the as constructed DNA sensors showed excellent sensitivity of detect limit at 0.07 fM with linear detect range from 0.1 fM to 0.1 pM. The results indicated that the HEMT functionalized with rGO paves a new avenue to design novel electronic devices for high sensitive and specific genetic material assays in biomedical applications. A rapid and ultra-sensitive DNA sensor with a novel recognition pattern is constructed by a reduced graphene oxide (rGO)-functionalized high electron mobility transistor (HEMT). The rGO-HEMT DNA sensor presents interesting "two step" current responses toward target DNA, which paves a new avenue to design novel electronic devices for highly sensitive and specific genetic material assays in biomedical applications. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Zhang Y.,University of Science and Technology Beijing | Zuo T.T.,University of Science and Technology Beijing | Tang Z.,University of Tennessee at Knoxville | Gao M.C.,U.S. National Energy Technology Laboratory | And 4 more authors.
Progress in Materials Science | Year: 2014

This paper reviews the recent research and development of high-entropy alloys (HEAs). HEAs are loosely defined as solid solution alloys that contain more than five principal elements in equal or near equal atomic percent (at.%). The concept of high entropy introduces a new path of developing advanced materials with unique properties, which cannot be achieved by the conventional micro-alloying approach based on only one dominant element. Up to date, many HEAs with promising properties have been reported, e.g., high wear-resistant HEAs, Co1.5CrFeNi1.5Ti and Al0.2Co 1.5CrFeNi1.5Ti alloys; high-strength body-centered-cubic (BCC) AlCoCrFeNi HEAs at room temperature, and NbMoTaV HEA at elevated temperatures. Furthermore, the general corrosion resistance of the Cu 0.5NiAlCoCrFeSi HEA is much better than that of the conventional 304-stainless steel. This paper first reviews HEA formation in relation to thermodynamics, kinetics, and processing. Physical, magnetic, chemical, and mechanical properties are then discussed. Great details are provided on the plastic deformation, fracture, and magnetization from the perspectives of crackling noise and Barkhausen noise measurements, and the analysis of serrations on stress-strain curves at specific strain rates or testing temperatures, as well as the serrations of the magnetization hysteresis loops. The comparison between conventional and high-entropy bulk metallic glasses is analyzed from the viewpoints of eutectic composition, dense atomic packing, and entropy of mixing. Glass forming ability and plastic properties of high-entropy bulk metallic glasses are also discussed. Modeling techniques applicable to HEAs are introduced and discussed, such as ab initio molecular dynamics simulations and CALPHAD modeling. Finally, future developments and potential new research directions for HEAs are proposed.


Song L.,University of Science and Technology Beijing | Zhang L.Q.,University of Science and Technology Beijing | Xu X.J.,Zhongyuan University of Technology | Sun J.,Shanghai JiaoTong University | Lin J.P.,University of Science and Technology Beijing
Scripta Materialia | Year: 2013

The omega phase in as-cast high-Nb-containing TiAl alloy exhibits particles with sizes on the nano- or microscale within the B2 matrix. Omega particles are transformed from the B2 phase by heterogeneous nucleation on the B2/γ boundaries or homogeneous nucleation within the B2 phase. After annealing at 900 °C, the omega particles disappear and transform into B2 phase. The transformation is rapidly initiated, but is difficult to complete. © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.


Peng R.,University of Science and Technology Beijing | Li Y.F.,École Centrale Paris | Zhang W.J.,University of Warwick | Hu Q.P.,CAS Academy of Mathematics and Systems Science
Reliability Engineering and System Safety | Year: 2014

This paper studies the fault detection process (FDP) and fault correction process (FCP) with the incorporation of testing effort function and imperfect debugging. In order to ensure high reliability, it is essential for software to undergo a testing phase, during which faults can be detected and corrected by debuggers. The testing resource allocation during this phase, which is usually depicted by the testing effort function, considerably influences not only the fault detection rate but also the time to correct a detected fault. In addition, testing is usually far from perfect such that new faults may be introduced. In this paper, we first show how to incorporate testing effort function and fault introduction into FDP and then develop FCP as delayed FDP with a correction effort. Various specific paired FDP and FCP models are obtained based on different assumptions of fault introduction and correction effort. An illustrative example is presented. The optimal release policy under different criteria is also discussed. © 2014 The Authors. Published by Elsevier Ltd. All rights reserved.


Zhang H.,University of Science and Technology Beijing | Shen B.G.,CAS Institute of Physics | Xu Z.Y.,CAS Institute of Physics | Shen J.,CAS Technical Institute of Physics and Chemistry | And 3 more authors.
Applied Physics Letters | Year: 2013

Magnetic properties and magnetocaloric effects (MCEs) of ternary intermetallic ErFeSi compound have been investigated in detail. It is found that ErFeSi exhibits a second-order magnetic transition from ferromagnetic to paramagnetic states at the Curie temperature TC=22 K, which is quite close to the liquid hydrogen temperature (20.3 K). A thermomagnetic irreversibility between zero-field-cooling and field-cooling curves is observed below TC in low magnetic field, and it is attributed to the narrow domain wall pinning effect. For a magnetic field change of 5 T, the maximum values of magnetic entropy change (-ΔSM) and adiabatic temperature change (ΔTad) are 23.1 J/kg K and 5.7 K, respectively. Particularly, the values of -ΔSM and refrigerant capacity reach as high as 14.2 J/kg K and 130 J/kg under a magnetic field change of 2 T, respectively. The large MCE without hysteresis loss for relatively low magnetic field change suggests that ErFeSi compound could be a promising material for magnetic refrigeration of hydrogen liquefaction. © 2013 American Institute of Physics.


Zhu Z.,Beijing Materials University | Zhang D.,Taiyuan University of Technology | Yan H.,Beijing Materials University | Li W.,University of Science and Technology Beijing | Qilu,Beijing Materials University
Journal of Materials Chemistry A | Year: 2013

This work developed a novel ammonium oxalate-carbonate composite co-precipitation method to prepare spinel LiNi0.5Mn 1.5O4. By this method combined with a facile hydrothermal treatment and particular cooling process, an ideal spinel with precise stoichiometric Ni/Mn and classic Fd3m structure is obtained, and furthermore, the Mn3+ content can be strictly limited. Additionally, the prepared LiNi0.5Mn1.5O4 has a spherical hierarchical morphology, composed of nano or submicron primary particles. This LiNi 0.5Mn1.5O4 shows superlative electrochemical performance. It delivers a discharge capacity of 141.2 mA h g-1, and importantly 98.2% of which discharges at 4.7 V. After 200 cycles at 0.3 C, 1 C and 3 C, the capacity retentions are 96.3%, 94.4% and 91.1%, respectively. Chemical and electrochemical measurements indicate that the elimination of the majority of Mn3+ in the obtained LiNi0.5Mn 1.5O4 results in the high capacity proportion at 4.7 V. Additionally, the retained Fd3m structure and spherical hierarchical morphology also effectively favour the cycling and rate performances. This journal is © 2013 The Royal Society of Chemistry.


Li P.,University of Science and Technology Beijing | Liao Q.,University of Science and Technology Beijing | Yang S.,CAS Institute of Physics | Bai X.,CAS Institute of Physics | And 7 more authors.
Nano Letters | Year: 2014

The fatigue behavior of ZnO nanowires (NWs) and microwires was systematically investigated with in situ transmission electron microscopy electromechanical resonance method. The elastic modulus and mechanical quality factors of ZnO wires were obtained. No damage or failure was found in the intact ZnO wires after resonance for about 108-109 cycles, while the damaged ZnO NW under electron beam (e-beam) irradiation fractured after resonance for seconds. The research results will provide a useful guide for designing, fabricating, and optimizing electromechanical nanodevices based on ZnO nanomaterials, as well as future applications. © 2014 American Chemical Society.


Li J.,Beijing University of Posts and Telecommunications | Li X.,University of Science and Technology Beijing | Zhang X.,Beijing University of Posts and Telecommunications | Tian F.,Beijing University of Posts and Telecommunications | Xi L.,Beijing University of Posts and Telecommunications
Optics Express | Year: 2010

The stability of single-sideband (SSB) modulator based recirculating frequency shifter (RFS) is analyzed theoretically. The optimum radio frequency (RF) drive peak-to-peak voltage used to drive the modulator is studied with considering the amplified spontaneous emission (ASE) noise of optical amplifier and crosstalk so as to obtain a maximum overall effective optical signal to noise ratio (OSNR) which is defined to quantify the quality of generated tones. Small desired tones number and lower RF peak-to-peak voltage can reduce the crosstalk effectively. While the trade-off should be considered since the larger desired tones number it is, the higher optimum drive voltage should be used when the SSB-based RFS reached the maximum OSNR. The theoretical results show that the optimum operation condition is helpful to improve the performance of RFS which can be a good application for the T-bit/s optical transmission in practice. © 2010 Optical Society of America.


Li S.,University of Science and Technology Beijing | Li S.,University of Illinois at Urbana - Champaign | Hoefler T.,ETH Zurich | Snir M.,University of Illinois at Urbana - Champaign
HPDC 2013 - Proceedings of the 22nd ACM International Symposium on High-Performance Parallel and Distributed Computing | Year: 2013

As the number of cores per node keeps increasing, it becomes increasingly important for MPI to leverage shared memory for intranode communication. This paper investigates the design and optimizations of MPI collectives for clusters of NUMA nodes. We develop performance models for collective communication using shared memory, and we develop several algorithms for various collectives. Experiments are conducted on both Xeon X5650 and Opteron 6100 InfiniBand clusters. The measurements agree with the model and indicate that different algorithms dominate for short vectors and long vectors. We compare our shared-memory allreduce with several traditional MPI implementations - Open MPI, MPICH2, and MVAPICH2 - that utilize system shared memory to facilitate interprocess communication. On a 16-node Xeon cluster and 8-node Opteron cluster, our implementation achieves on average 2.5X and 2.3X speedup over MVAPICH2, respectively. Our techniques enable an efficient implementation of collective operations on future multi- and manycore systems. © 2013 ACM.


Xiao W.,University of Science and Technology Beijing | Xiao J.-L.,Inner Mongolian University for Nationalities
International Journal of Modern Physics B | Year: 2011

We study the vibrational frequency, the ground-state energy and the ground-state binding energy of the strong-coupling impurity bound magnetopolaron in an anisotropic quantum dot. The effects of the transverse and longitudinal effective confinement lengths, the electronphonon coupling strength, the cyclotron frequency of a magnetic field and the Coulomb bound potential are taken into consideration by using an linear combination operator and unitary transformation methods. It is found that the vibrational frequency, the ground-state energy and the ground-state binding energy will increase rapidly with decreasing confinement lengths. The vibrational frequency is an increasing function of the Coulomb bound potential, the electronphonon coupling strength and cyclotron frequency, whereas the ground-state energy is a decreasing function of the potential and coupling strength, and the ground-state binding energy is an increasing function of the potential and coupling strength. The ground-state energy and the ground-state binding energy increases with increasing cyclotron frequency. © 2011 World Scientific Publishing Company.


Wei D.,University of Wollongong | Jiang Z.,University of Wollongong | Han J.,University of Science and Technology Beijing
Computational Materials Science | Year: 2013

Metal owns the ability of self-healing to some extent, and the ability of the internal crack healing is most desirable for improving the reliability of metal. A molecular dynamics simulation has been further developed to investigate the evolution of a nanoscale crack in body centred cubic Fe crystal under the conditions of heating or compressive pressure. When system temperature drops, the evolution of the crack that was at elevated temperature has been studied for the first time. N-body potential according to the embedded atom method has been adopted. The original nanoscale crack is expressed by removing some atoms in the centre of the cell, and the minimum vertical distance between the atoms on the top and bottom crack surfaces has been defined as Dm for assessing the process of crack evolution. The results show that a crack healing process can be accelerated significantly with an increase of temperature. When the system temperature decreases, Dm of the crack that was in healing process does not change significantly but fluctuates in a narrow range. This means that the crack healing is the result of Fe atoms diffusing into the crack area but not the thermal stress incurred in the simulation cell at elevated temperature. The pre-compressive pressure under the condition of both biaxial and uniaxial loadings can help promote the crack healing significantly and results in more uniform distribution of defects after healing. © 2012 Elsevier B.V. All rights reserved.


Zhou X.,University of Science and Technology Beijing | Chen X.,Beijing University of Posts and Telecommunications | Long K.,University of Science and Technology Beijing
IEEE Photonics Technology Letters | Year: 2012

A wide-range frequency offset estimation algorithm is proposed for optical coherent systems, which removes the modulated phase information from the received signal accurately using training sequence instead of traditional Mth power operation. A large frequency offset approximating to ±0.5 times the symbol rate can be traced in arbitrary M-ary phase-shift-keying (MPSK) M-ary quadrature amplitude modulation (MQAM) systems by the proposed algorithm with the low computational complexity and the negligible training overhead. © 2011 IEEE.


Zhu Z.,Beijing Materials University | Yan H.,Beijing Materials University | Zhang D.,Taiyuan University of Technology | Li W.,University of Science and Technology Beijing | Lu Q.,Beijing Materials University
Journal of Power Sources | Year: 2013

LiNi0.5Mn1.5O4 as a 4.7 V cathode material is prepared through an oxalic acid-pretreated solid-state method. Oxalic acid is added to react with the mixture of LiOH•H2O, MnO2 and Ni(OH)2. This chemical pretreatment results in a sufficient mixing of Li, Ni and Mn ions in the precursor, and therefore promotes the generation of pure LiNi0.5Mn1.5O4 in the following calcination even at a temperature as low as 500 °C. The material prepared at 750 °C has a highest crystallinity and a regular crystal shape with smoothly surface. Compared to traditional method, the LiNi 0.5Mn1.5O4 synthesized by this novel method shows much better electrochemical performances with an initial discharging capacity of 136.9 mAh g-1 and capacity retention of 93.4% after 300 cycles under 0.3C. And most importantly 97.2% of the total capacity displays at 4.7 V, which significantly favors the cell energy density. The novel preparation technique is also available to get high rate performance for LiNi 0.5Mn1.5O4. The material synthesized at 900 °C has a capacity of 121.2 mAh g-1 and stable cycling performance under 3C due to its lower polarization resistance. © 2012 Elsevier B.V. All rights reserved.


Yu M.,University of Science and Technology Beijing | Qiu H.,University of Science and Technology Beijing | Chen X.,Beijing Technology and Business University
Thin Solid Films | Year: 2010

About 300 nm-thick Zn0.87Al0.06Ni0.07O, Zn0.83Al0.06Ni0.11O and Zn 0.81Al0.04Ni0.15O films were deposited on glass substrates at 300 K by co-sputtering ZnO:Al and Ni targets. The films were annealed in vacuum at 673 K for 2 h under a magnetic field of 4.8 × 104 A/m applied along the film plane and then were cooled down to room temperature without magnetic field. All the films have a wurtzite structure and consist of thin columnar grains perpendicular to the substrate. The annealing promotes the (002) orientation growth in the film growing direction for the Zn0.87Al0.06Ni0.07O and Zn 0.83Al0.06Ni0.11O films as well as the (100) orientation growth for the Zn0.81Al0.04Ni0.15O film. The annealing results in a slight increase in the grain size. A weak Ni diffraction peak was detected for the annealed films with high Ni content. The annealing enhances the room temperature ferromagnetism of the films. A temperature dependence of magnetization confirms that the Curie temperature is above 400 K for the annealed films. The films magnetically annealed exhibit an anisotropic magnetization behavior. The annealed Zn0.87Al 0.06Ni0.07O film has the lowest resistivity AR (8.73 × 10-3 Ω cm), the highest free electron concentration (1.73 × 1020 cm- 3) and Hall mobility AR (4.16 cm2V- 1 s- 1). A temperature dependence of the resistivity AR from 50 K to 300 K reveals that the carrier transport mechanism is Mott's variable range hopping in the low temperature range and thermally activated band conduction in the high temperature range. © 2010 Elsevier B.V.


Wu Z.,University of Western Australia | Liu Z.,University of Science and Technology Beijing | Yang H.,University of Western Australia | Liu Y.,University of Western Australia | Wu G.,CAS Institute of Physics
Applied Physics Letters | Year: 2011

This letter reports on an alloy design of Mn50 Ni37 In10 Co3 based on the principle of Mn-Mn ferromagnetic coupling via Co doping. The alloy is shown to exhibit a metamagnetic martensitic transformation and a high saturation magnetization of 118 emu/g in its austenitic state. The transformation generates a large magnetization difference of 89 emu/g, more than 200% of what is reported in the literature for similar alloys. A complete magnetic field induced martensitic transformation was achieved at 170 K. Such a high magnetization difference provides a strong driving force for magnetic-field-induced transformation, making this material a promising candidate for magnetic actuation applications. © 2011 American Institute of Physics.


Xia Z.,University of Science and Technology Beijing | Xia Z.,Northwestern University | Ma C.,Chongqing University of Posts and Telecommunications | Molokeev M.S.,RAS Kirensky Institute of Physics | And 3 more authors.
Journal of the American Chemical Society | Year: 2015

The union of structural and spectroscopic modeling can accelerate the discovery and improvement of phosphor materials if guided by an appropriate principle. Herein, we describe the concept of chemical unit cosubstitution as one such potential design scheme. We corroborate this strategy experimentally and computationally by applying it to the Ca2(Al1-xMgx)(Al1-xSi1+x)O7:Eu2+ solid solution phosphor. The cosubstitution is shown to be restricted to tetrahedral sites, which enables the tuning of luminescent properties. The emission peaks shift from 513 to 538 nm with a decreasing Stokes shift, which has been simulated by a crystal-field model. The correlation between the 5d crystal-field splitting of Eu2+ ions and the local geometry structure of the substituted sites is also revealed. Moreover, an energy decrease of the electron-phonon coupling effect is explained on the basis of the configurational coordinate model. © 2015 American Chemical Society.


Cheng S.,University of Science and Technology Beijing | Li Z.,University of Science and Technology Beijing | Mang H.-P.,University of Science and Technology Beijing | Neupane K.,Civil Engineer | And 2 more authors.
Applied Energy | Year: 2014

Biogas technology is becoming increasingly popular throughout the world, particularly in countries where governments promote domestic biogas systems. Despite its popularity, problems exist in biogas technology, such as low-quality construction, leakage of pipelines, low biogas production, and lack of maintenance. These problems should be identified and analyzed for effective implementation and efficient operation of small-sized biogas systems (SBS). This research applies the fault tree approach (FTA) to identify failures, and evaluate their effects on the operation of SBS from a technical point of view, based on a nationwide field study in Nepal. Ninety-four sets of SBS were selected and sampled in targeted areas. Five subsystems of SBS were defined, including structural components, biogas utilization equipment, piping system, biogas production, and effluent disposal system. Based on the statistical analysis of the 94 targeted cases, the fault probabilities of the five subsystems are 0.67, 0.48, 0.73, 0.26, and 0.64, respectively. The weights of five subsystems are determined by Delphi method and fault probability of SBS is calculated. The results show that faults on piping systems happen most frequently, and that proper disposal and reuse of bio-slurry are often neglected. Regardless of the social and economic benefits of SBS, implementation scenarios of SBS throughout Nepal are evaluated under a technical perspective, as follows: (1) the operational status of SBS is not optimal. (2) Based on criteria for failures, well-operation ratio is about 53% in practice. (3) Skilled masons are prerequisites for efficient functioning of SBS. (4) Maintenance plays a key role for efficient functioning. The study results prove that FTA is mostly suitable for SBS evaluation and is an effective analysis tool for technical evaluation in the field of biogas technology. © 2013 Elsevier Ltd.


Xiao X.,University of Science and Technology Beijing | Zhang Y.,University of Science and Technology Beijing | Wang J.,University of Science and Technology Beijing | Du H.,University of Wollongong
IEEE Transactions on Industrial Electronics | Year: 2016

The dc-link voltage fluctuation caused by the change of working state of the load motor has been one of the key issues in the pulse width modulation rectifier-inverter system. In this study, an improved model predictive control (MPC) scheme is proposed to address this problem. The MPC is applied to both the rectifier stage and the inverter stage in the system. Direct power control is used in the rectifier stage and the direct torque control is employed in the inverter stage, with the key novelty of the active power reference values being defined by both real-time and periodic compensation power based on the system-level power-balance model. Meanwhile, an MPC algorithm based on a two-step prediction is introduced to compensate for the delay of a digital controller. Comparison has been conducted between the proposed scheme and three other methods. Simulation and experimental results show that the proposed control scheme exhibits good performance in both the rectifier stage and the inverter stage with improved dynamic response and suppressed voltage fluctuation of the dc-link voltage. © 2016 IEEE.


Gao R.-Q.,North China University of Water Conservancy and Electric Power | Hou X.-M.,University of Science and Technology Beijing
International Journal of Minerals, Metallurgy and Materials | Year: 2013

Medical stone-based porous ceramics as a carrier were prepared by ultra-fine grinding and low-temperature sintering method. Nano-TiO2 thin films were loaded on the carrier by chemical liquid deposition method using titanium tetrachloride as a precursor. The micro-morphology and microstructure of the synthesized samples were characterized using X-ray diffraction, scanning electron microscopy with energy dispersive spectrometry, and mercury injection method. The photo-catalytic activity of the TiO2 thin films was investigated by degrading formaldehyde. The main crystalline phase in the TiO2 thin films calcined at 550 C is anatase with the average particle size about 10 nm. The specific surface area of the carrier-coated nano-TiO2 increases from 3.68 to 5.32 m2/g. The formaldehyde removal rate of the TiO2/medical stone-based porous ceramics irradiated under an ultraviolet lamp for 120 min reaches 85.6%. © 2013 University of Science and Technology Beijing and Springer-Verlag Berlin Heidelberg.


Wang H.,University of Science and Technology Beijing | Liu G.,University of Science and Technology Beijing | Ullah A.,University of Science and Technology Beijing | Ullah A.,Karakoram International University | Luan J.,University of Science and Technology Beijing
Applied Physics Letters | Year: 2012

Topological correlations of three-dimensional grains were investigated by Monte Carlo-Potts model simulation. The result shows that, unlike first nearest neighbors (the Aboav-Weaire law [D. Aboav, Metallography 3, 383 (1970) and D. Weaire, Metallography 7, 157 (1974)] holds), there appears to be very little correlation between grains and their second and third nearest neighbors (on average), i.e., the average number of faces of second nearest neighbors, m 2, and third nearest neighbors, m 3, are independent of faces f of the center grain (nearly m 2 14.984 and m 3 14.489). This result indicates that long range correlations beyond first nearest neighbors may have negligible effect on the growth of center grains and thus provides support to a topologically averaged growth law that only considered the non-random first nearest-neighbor interactions. © 2012 American Institute of Physics.


Li B.,Tsinghua University | Cao H.,Tsinghua University | Zhang J.,CAS Chengdu Institute of Organic Chemistry | Qu M.,CAS Chengdu Institute of Organic Chemistry | And 2 more authors.
Journal of Materials Chemistry | Year: 2012

Anchoring SnO 2 NPs encapsulated in carbon shells onto RGO exhibits superior anode performances in lithium ion batteries with specific capacities of 622 mA h g -1 after 100 cycles. © 2012 The Royal Society of Chemistry.


Yan R.,University of Science and Technology Beijing | Lapata M.,University of Edinburgh | Li X.,University of Edinburgh | Li X.,Beihang University
50th Annual Meeting of the Association for Computational Linguistics, ACL 2012 - Proceedings of the Conference | Year: 2012

As one of the most popular micro-blogging services, Twitter attracts millions of users, producing millions of tweets daily. Shared information through this service spreads faster than would have been possible with traditional sources, however the proliferation of user-generation content poses challenges to browsing and finding valuable information. In this paper we propose a graph-theoretic model for tweet recommendation that presents users with items they may have an interest in. Our model ranks tweets and their authors simultaneously using several networks: The social network connecting the users, the network connecting the tweets, and a third network that ties the two together. Tweet and author entities are ranked following a co-ranking algorithm based on the intuition that that there is a mutually reinforcing relationship between tweets and their authors that could be reflected in the rankings. We show that this framework can be parametrized to take into account user preferences, the popularity of tweets and their authors, and diversity. Experimental evaluation on a large dataset shows that our model outperforms competitive approaches by a large margin. © 2012 Association for computational Linguistics.


Wu H.-N.,Beihang University | Wang J.-W.,University of Science and Technology Beijing | Wang J.-W.,Beihang University | Li H.-X.,City University of Hong Kong | Li H.-X.,Central South University
IEEE Transactions on Fuzzy Systems | Year: 2014

This paper deals with the problem of fuzzy boundary control design for a class of nonlinear distributed parameter systems which are described by semilinear parabolic partial differential equations (PDEs). Both distributed measurement form and collocated boundary measurement form are considered. A Takagi-Sugeno (T-S) fuzzy PDE model is first applied to accurately represent the semilinear parabolic PDE system. Based on the T-S fuzzy PDE model, two types of fuzzy boundary controllers, which are easily implemented since only boundary actuators are used, are proposed to ensure the exponential stability of the resulting closed-loop system. Sufficient conditions of exponential stabilization are established by employing the Lyapunov direct method and the vector-valued Wirtinger's inequality and presented in terms of standard linear matrix inequalities. Finally, the advantages and effectiveness of the proposed control methodology are demonstrated by the simulation results of two examples. © 2014 IEEE.


Xing Y.,University of Science and Technology Beijing | Chen W.-H.,Beijing Institute of Technology | Jia W.,China Agricultural University | Zhang J.,Chinese University of Hong Kong
Journal of Experimental Botany | Year: 2015

Superoxide dismutases (SODs) are involved in plant adaptive responses to biotic and abiotic stresses but the upstream signalling process that modulates their expression is not clear. Expression of two iron SODs, FSD2 and FSD3, was significantly increased in Arabidopsis in response to NaCl treatment but blocked in transgenic MKK5-RNAi plant, mkk5. Using an assay system for transient expression in protoplasts, it was found that mitogen-activated protein kinase kinase 5 (MKK5) was also activated in response to salt stress. Overexpression of MKK5 in wild-type plants enhanced their tolerance to salt treatments, while mkk5 mutant exhibited hypersensitivity to salt stress in germination on salt-containing media. Moreover, another kinase, MPK6, was also involved in the MKK5-mediated iron superoxide dismutase (FSD) signalling pathway in salt stress. The kinase activity of MPK6 was totally turned off in mkk5, whereas the activity of MPK3 was only partially blocked. MKK5 interacted with the MEKK1 protein that was also involved in the salt-induced FSD signalling pathway. These data suggest that salt-induced FSD2 and FSD3 expressions are influenced by MEKK1 via MKK5-MPK6-coupled signalling. This MAP kinase cascade (MEKK1, MKK5, and MPK6) mediates the salt-induced expression of iron superoxide dismutases. © 2015 The Author.


Peng R.,University of Science and Technology Beijing | Zhai Q.,Beihang University | Xing L.,University of Massachusetts Dartmouth | Yang J.,Beihang University
Reliability Engineering and System Safety | Year: 2014

In many real-world applications, a mission may consist of several different tasks or phases that have to be accomplished in sequence. Such systems are referred to as phased-mission systems (PMS). In this paper we consider the demand-based PMS with parallel structure, where the system components function in parallel with different capacities in each phase of the mission and the mission is successful if and only if the total system capacity meets the predetermined mission demand in each phase. The reliability of the demand-based PMS (DB-PMS) with parallel structure subject to fault-level coverage (FLC) is first studied using a multi-valued decision diagram (MDD) based technique. The traditional MDD is modified to accommodate the FLC mechanism and new MDD construction and evaluation procedures are proposed for DB-PMS. To reduce the size of the MDD, an alternative construction procedure applying the branching truncation method and new reduction rules are further proposed. An upwards algorithm is put forward to evaluate the reliability of DB-PMS subject to FLC. The proposed approaches are illustrated through examples. © 2013 Elsevier Ltd.


Wang S.,CAS Research Center for Eco Environmental Sciences | Wang S.,University of Science and Technology Beijing | Wang Y.,CAS Research Center for Eco Environmental Sciences | Feng X.,CAS Research Center for Eco Environmental Sciences | And 2 more authors.
Applied Microbiology and Biotechnology | Year: 2011

With the rapid development of ammonia-synthesizing industry, the ammonia-nitrogen pollution in wetlands acting as the sink of point and diffuse pollution has been increased dramatically. Most of ammonia-nitrogen is oxidized at least once by ammonia-oxidizing prokaryotes to complete the nitrogen cycle. Current research findings have expanded the known ammonia-oxidizing prokaryotes from the domain Bacteria to Archaea. However, in the complex wetlands environment, it remains unclear whether ammonia oxidation is exclusively or predominantly linked to Archaea or Bacteria as implied by specific high abundance. In this research, the abundance and composition of Archaea and Bacteria in sediments of four kinds of wetlands with different nitrogen concentration were investigated by using quantitative real-time polymerase chain reaction, cloning, and sequencing approaches based on amoA genes. The results indicated that AOA distributed widely in wetland sediments, and the phylogenetic tree revealed that archaeal amoA functional gene sequences from wetlands sediments cluster as two major evolutionary branches: soil/sediment and sediment/water. The bacteria functionally dominated microbial ammonia oxidation in different wetlands sediments on the basis of molecule analysis, potential nitrification rate, and soil chemistry. Moreover, the factors influencing AOA and AOB abundances with environmental indicator were also analyzed, and the results addressed the copy numbers of archaeal and bacterial amoA functional gene having the higher correlation with pH and ammonia concentration. The pH had relatively great negative impact on the abundance of AOA and AOB, while ammonia concentration showed positive impact on AOB abundance only. These findings could be fundamental to improve understanding of the importance of AOB and AOA in nitrogen and other nutrients cycle in wetland ecosystems. © 2011 Springer-Verlag.


Gao H.,Beihang University | Zhang J.,Beihang University | Wang R.,University of Science and Technology Beijing | Wang M.,Beihang University
Applied Catalysis B: Environmental | Year: 2015

Herein, Cu2O microcrystals are found to perform efficiently in hydrogen generation and formaldehyde degradation at room temperature, with MgO as a sacrificial agent, while other photocatalytic semiconductors such as TiO2, ZnO, Bi2O3, Fe2O3 and CuO exhibit poor capability under the same condition. This peculiarity of Cu2O microcrystals is comprehensively analyzed, focusing on exploring the formation of [Cu+]· paramagnetic during the reaction, which is first proposed as a principal factor for the hydrogen generation and formaldehyde degradation. Even more exciting, abundant hydroxyl radicals produced during this reaction process are detected via electron paramagnetic resonance spectrometry, which are particularly efficient in oxidizing formaldehyde and producing hydrogen. © 2015 Elsevier B.V.


Aleksandrov A.Y.,Saint Petersburg State University | Hu G.-D.,University of Science and Technology Beijing | Zhabko A.P.,Saint Petersburg State University
IEEE Transactions on Automatic Control | Year: 2014

Some classes of nonlinear time-delay systems are studied. It is assumed that the zero solution of a system is asymptotically stable when delay is equal to zero. By the Lyapunov direct method, and the Razumikhin approach, it is shown that in the case when the system is essentially nonlinear, i.e., the right-hand side of the system does not contain linear terms, the asymptotic stability of the trivial solution is preserved for an arbitrary positive value of the delay. Based on homogeneous approximation of a time-delay system some stability conditions are found. We treat large-scale systems with nonlinear subsystems. New stability conditions in certain cases, critical in the Lyapunov sense, are obtained. Three examples are given to demonstrate effectiveness of the presented results. © 2014 IEEE.


Pei Y.-L.,Beihang University | Liu Y.,University of Science and Technology Beijing
Journal of Alloys and Compounds | Year: 2012

Electrical and thermal transport properties of lead-based chalcogenides (PbTe, PbSe, and PbS) were studied with special emphasis on the lattice and the bipolar thermal conductivity. Both electrical resistivity and Seebeck coefficient show the transport behaviors related to the intrinsic excitation that determined by the band gap, power factors at room temperature reach 12 μW cm -1 K -2, 14 μW cm -1 K -2, and 16 μW cm -1 K -2 for PbS, PbSe and PbTe, respectively. PbTe shows the lowest total thermal conductivity, and PbS shows the highest total thermal conductivity, in which the bipolar thermal conductivity is proportional to the width of band gap, these contributions at 723 K were estimated to be 2.2%, 3.1%, and 1.1% for the PbTe, PbSe and PbS, respectively. This study demonstrates the possibility to enhance ZT value by the suppression of bipolar thermal conductivity by tuning the width of band gap, also indicates that inexpensive and earth-abundant PbSe and PbS would be promising alternative for PbTe in the thermoelectric applications. © 2011 Elsevier B.V. All rights reserved.


Xu Y.,University of Science and Technology Beijing | Wen X.,University of Science and Technology Beijing | Wen L.-S.,Liaoning University | Wu L.-Y.,CAS Academy of Mathematics and Systems Science | And 3 more authors.
PLoS ONE | Year: 2014

Nitrotyrosine is one of the post-translational modifications (PTMs) in proteins that occurs when their tyrosine residue is nitrated. Compared with healthy people, a remarkably increased level of nitrotyrosine is detected in those suffering from rheumatoid arthritis, septic shock, and coeliac disease. Given an uncharacterized protein sequence that contains many tyrosine residues, which one of them can be nitrated and which one cannot? This is a challenging problem, not only directly related to in-depth understanding the PTM's mechanism but also to the nitrotyrosine-based drug development. Particularly, with the avalanche of protein sequences generated in the postgenomic age, it is highly desired to develop a high throughput tool in this regard. Here, a new predictor called "iNitro-Tyr" was developed by incorporating the position-specific dipeptide propensity into the general pseudo amino acid composition for discriminating the nitrotyrosine sites from non-nitrotyrosine sites in proteins. It was demonstrated via the rigorous jackknife tests that the new predictor not only can yield higher success rate but also is much more stable and less noisy. A web-server for iNitro-Tyr is accessible to the public at http://app.aporc.org/iNitro-Tyr/. For the convenience of most experimental scientists, we have further provided a protocol of step-by-step guide, by which users can easily get their desired results without the need to follow the complicated mathematics that were presented in this paper just for the integrity of its development process. It has not escaped our notice that the approach presented here can be also used to deal with the other PTM sites in proteins. © 2014 Xu et al.


Bao C.,University of Science and Technology Beijing | Bao C.,German Aerospace Center | Bessler W.G.,German Aerospace Center
Journal of Power Sources | Year: 2012

Computational efficiency is highly important for upscaling detailed electrode-level and cell-level models to the system level required for the design and control of fuel cells. We present a computationally efficient 1D + 1D fuel cell model based on a combination of analytical and numerical approaches. On the electrode level, we develop approximate analytical solutions for the 1D current/potential distribution via a hybrid algorithm of power-law approach and perturbation method. Compared to the conventional perturbation method, this work keeps the intrinsic nonlinearity of electrochemical kinetics, while providing clearer physical meaning than some purely mathematical methods like the Adomian decomposition method. By integrating the resulting overpotential profile into mass transfer models, concentration overpotentials are obtained and the thermodynamic framework is then used for analyzing the H 2/CO electrochemical co-oxidation kinetics. A novel expression is also presented to interconvert volume- and area-specific exchange current densities. On the cell level, a linear relationship between local current density and solid temperature is further developed for efficient 1D + 1D thermal along-the-channel numerical simulations without requiring computational iterations. Both the electrode-level and cell-level macroscopic fuel cell models are validated against full numerical solutions available in the open literatures over a wide range of operating conditions. With the hybrid analytical/numerical approximation in two dimensions, the computational framework is predicted to be sufficiently efficient for real-time simulations. © 2012 Elsevier B.V. All rights reserved.


Du Y.,Beihang University | Fang J.,Beihang University | Miao C.,University of Science and Technology Beijing
IEEE Transactions on Industrial Electronics | Year: 2014

This paper presents a frequency-domain identification method for an unmanned helicopter (UH) based on an adaptive genetic algorithm (AGA). By using a homemade microguidance, navigation, and control system (MGNCS), data regarding the inputs (control signals of servos) and outputs (states of the UH) are recorded. After data preprocessing, the attitude model of the UH is identified by employing the AGA. The identified model is then analyzed in the time domain and the frequency domain in comparison with the least squares (LS) method. Control compensators are designed based on the identified model. Automatic hovering is successfully achieved based on the compensators. Simulation and experimental results demonstrate the effectiveness and superiority of this identification method. © 1982-2012 IEEE.


Cao H.,Tsinghua University | Li B.,Tsinghua University | Zhang J.,CAS Chengdu Institute of Organic Chemistry | Lian F.,University of Science and Technology Beijing | And 2 more authors.
Journal of Materials Chemistry | Year: 2012

Herein, we report the synthesis of TiO 2-reduced graphene oxide composite (termed as TGC) nanostructures using tetrabutyl titanate as the titanium source via a solvothermal route. The TGC nanostructures were characterized by transmission electron microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and adsorption-desorption isotherms for nitrogen measurements. The TGC was used as the anode of lithium ion batteries for investigation. The hybrid nanocomposite exhibited remarkable improvement in lithium ion insertion/extraction behaviour compared with TiO 2, which showed an initial irreversible capacity and a reversible capacity of 386.4 and 152.6 mAh g -1 for TGC after 100 cycles at a high charge rate of 5 C (1000 mA g -1), compared to 69.5 and 9.7 mAh g -1 for TiO 2, respectively. The enhanced electrochemical performance of TGC is attributed to the increased conductivity in the presence of reduced graphene oxide in TGC, the small size of the TiO 2 particles in TGC, which can shorten the transport paths for both Li + ions and electrons, and the enlarged electrode-electrolyte contact area, leading to more electroactive sites in TGC. © 2012 The Royal Society of Chemistry.


Duan S.,Beihang University | Wang R.,Beihang University | Wang R.,University of Science and Technology Beijing
NPG Asia Materials | Year: 2014

A synthetic route to achieve core/shell nanostructures consisting of noble metal cores and single crystal semiconductor shells with different crystal systems is proposed, which involves a simple phosphorization process from corresponding bimetallic heterostructures. The triphenylphosphine is designed to serve as both a capping agent and a phosphorous source during the formation of Au/Ni12P5 core/shell nanoparticles (NPs) from Au-Ni bimetallic heterodimers. The semiconductor shells of the obtained Au/Ni12P5 nanostructures are controlled to form single crystals with a thickness of B5 nm. The structure-dependent supercapacitor properties of Au-modified Ni12P5 nanostructures were further investigated. The synergistic effect of the metal/semiconductor nanostructure is observed to be superior to its oligomer-like counterpart when serving as a supercapacitor electrode. The specific capacitance of an electrode fabricated from core/shell NPs is 806.1 F g-1 with a retention of 91.1% after 500 charge-discharge cycles. © 2014 Nature Publishing Group All rights reserved.


Li S.,University of Science and Technology Beijing | Yu J.,Beihang University
Chinese Journal of Mechanical Engineering (English Edition) | Year: 2014

In design of flexure mechanism, diminishing the parasitic-motion is a key point to improve the accuracy. However, most of existing topics concentrate on improving the accuracy of linear-motion flexure mechanisms via compensating the parasitic error, but few research the multi-dimensional flexure mechanisms. A general design principle and method for high-precision flexure mechanisms based on the parasitic-motion compensation is presented, and the proposed method can compensate the parasitic rotation in company with translation, or the parasitic translation in company with rotation, or both. The crucial step for the method is that the parasitic motion of a flexure mechanism is formulated and evaluated in terms of its compliance. The overall compliance matrix of a general flexure mechanism is formulated by using screw theory firstly, then the criteria for the parasitic motions is introduced by analyzing the characteristics of the resultant compliance matrix as well as with aid of the concept of instantaneous rotation center. Subsequently, a compliance-based compensation approach for reducing parasitic-motion is addressed as the most important part. The design principles and procedure are further discussed to help with improving the accuracy of flexure mechanisms, and case studies are provided to illustrate this method. Finally, an analytical verification is provided to demonstrate that the symmetry design philosophy widely used in flexure design can effectively improve accuracy in terms of the proposed method. The proposed compensation method can be well used to diminish the parasitic-motion of multi-dimensional flexure mechanisms. © Chinese Mechanical Engineering Society and Springer-Verlag Berlin Heidelberg 2014.


Sun L.,Sichuan University | Yang T.,Sichuan University | Jia C.,University of Science and Technology Beijing | Xiong J.,Sichuan University
International Journal of Refractory Metals and Hard Materials | Year: 2011

The influence of the addition of 0.3, 0.5 and 0.7 wt.% VC on the density, microstructure and mechanical properties of WC-Cr3C2-11 wt.% Co with 0, 0.2, 0.4 and 0.6 wt.% Cr3C2 hard metals prepared by spark plasma sintering (SPS) at a temperature of 1200 °C (5 min, 40 MPa) was investigated. Microstructure analysis revealed that the WC grain size in the sintered hard metals was strongly influenced by the VC and Cr 3C2 content. With the addition of inhibitors and the increased amount of Cr3C2, the density is reduced, and on the contrary, the addition of VC as an inhibitor contributes to promoting the densification. The combined addition of Cr3C2 and VC could strongly reduce the WC grain growth to about 350 nm. Observation suggests that the fracture of WC-Co cemented carbide is brittle and intergranular. The amount of added VC/Cr3C2 should be controlled in a certain range. Samples with an appropriate proportion of VC/Cr3C2 added exhibit higher hardness which can be up to 1938 HV30. Toughness, too, can reach 16.34 MPa m1/2. © 2010 Elsevier Ltd. All rights reserved.


Wang J.-A.,University of Science and Technology Beijing | Wei X.-H.,Beijing Municipal Engineering Design Institute | Chen S.-J.,Shandong University of Science and Technology
Zhongguo Kuangye Daxue Xuebao/Journal of China University of Mining and Technology | Year: 2012

A quantitative relationship for the fractured rock permeability coefficient was obtained by conducting stress-strain permeability tests on intact and fractured rock samples. The stress seepage coupling mechanism is elucidated from these results. Mining a lower coal seam located above a confined aquifer in Shanxi province motivated this research. A discrete element numerical model was used to simulate fluid-solid coupling and determine stress and seepage in the floor strata. Four typical zones appear in the floor strata that are closely related to the horizontal stress. The damage state and the permeability are used to define these zones. If the direct floor stratum is seriously affected by mining induced pressure the horizontal stress is disordered and the damaged zone is about 13 m thick. The confining pressure in the strata above the Ordovician aquifer is low and hydraulic splitting fractures it easily. The thickness of the zone where water rises is about 17 m. The middle of the floor strata are less affected by mining and the confined aquifer. The horizontal stresses increase with increasing depth and the thickness of the water resisting layer is about 38 m. This is the zone that provides the key water resistant layer in the floor.


Liu X.,Tsinghua University | Wang W.,Tsinghua University | Gao X.,Tsinghua University | Gao X.,Chinese Research Academy of Environmental Sciences | And 2 more authors.
Waste Management | Year: 2012

The effects of thermal pretreatment on the physical and chemical properties of three typical municipal biomass wastes (MBWs), kitchen waste (KW), vegetable/fruit residue (VFR), and waste activated sludge (WAS) were investigated. The results show that thermal pretreatment at 175°C/60. min significantly decreases viscosity, improves the MBW dewatering performance, as well as increases soluble chemical oxygen demand, soluble sugar, soluble protein, and especially organic compounds with molecular weights >10. kDa. For KW, VFR and WAS, 59.7%, 58.5% and 25.2% of the organic compounds can be separated in the liquid phase after thermal treatment. WAS achieves a 34.8% methane potential increase and a doubled methane production rate after thermal pretreatment. In contrast, KW and VFR show 7.9% and 11.7% methane decrease because of melanoidin production. © 2011 Elsevier Ltd.


Tao H.-C.,University of Science and Technology Beijing | Huang M.,Tsinghua University | Fan L.-Z.,University of Science and Technology Beijing | Qu X.,University of Science and Technology Beijing
Solid State Ionics | Year: 2012

Si@SiO x/C nanoporous spheres as anode materials for high-performance lithium ion batteries were fabricated through a facile magnesiothermic reduction of well-ordered mesoporous silica and subsequent impregnating of carbon precursor into the Si@SiO x nanoporous spheres followed by carbonization at 800 °C. The obtained nanoporous spheres present an interweaved porous structure composed of high-capacity Si, inactive SiO x and conductive carbon, which can effectively enhance the electrochemical performance of the composite materials. The resulting Si@SiO x/C nanoporous spheres display a reversible specific capacity of 913 mA h g - 1 at the first cycle and the capacity retention ratio is 97% after 60 cycles at a current density of 100 mA g - 1. The nanoporous structure of Si, SiO x and C can effectively accommodate the volume change for Si-based materials' expansion, release the mechanical stress and improve the electronic conductivity. The Si@SiO x/C nanoporous spheres exhibit a great potential as anode materials for lithium ion batteries. © 2012 Elsevier B.V.


Zhu C.,University of Tennessee at Knoxville | Lu Z.P.,University of Science and Technology Beijing | Nieh T.G.,University of Tennessee at Knoxville
Acta Materialia | Year: 2013

Instrumented nanoindentation was conducted on a FeCoCrMnNi high-entropy alloy with a single face-centered cubic structure to characterize the nature of incipient plasticity. Experiments were carried out over loading rates of 25-2500 μN s-1 and at temperatures ranging from 22 to 150 °C. The maximum shear stress required to initiate plasticity was found to be within 1/15 to 1/10 of the shear modulus and relatively insensitive to grain orientation. However, it was strongly dependent upon the temperature, indicating a thermally activated process. Using a statistical model developed previously, both the activation volume and activation energy were evaluated and further compared with existing dislocation nucleation models. A mechanism consisting of a heterogeneous dislocation nucleation process with vacancy-like defects (∼3 atoms) as the rate-limiting nuclei appeared to be dominant. © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.


He J.Y.,University of Science and Technology Beijing | Liu W.H.,University of Science and Technology Beijing | Wang H.,University of Science and Technology Beijing | Wu Y.,University of Science and Technology Beijing | And 3 more authors.
Acta Materialia | Year: 2014

A series of six-component (FeCoNiCrMn)100-xAlx (x = 0-20 at.%) high-entropy alloys (HEAs) was synthesized to investigate the alloying effect of Al on the structure and tensile properties. The microstructures of these alloys were examined using transmission electron microscopy, and crystalline phase evolution was characterized and compared with existing models. It was found that the crystalline structure changed from the initial single face-centered cubic (fcc) structure to a duplex fcc plus body-centered cubic (bcc) structure and then a single bcc structure as the Al concentration was increased. Resulting from the structural changes there were also corresponding variations in tensile properties. In the single fcc region, alloys behaved like a solid solution with relatively low strength but extended ductility. In the mixed structure region, alloys behaved like a composite with a sharp increase in strength but reduced ductility. In the single bcc region, alloys became extremely brittle. In this study, close correlation between the microstructure and mechanical properties was also discussed and presented. © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.


Feng Z.,University of Science and Technology Beijing | Feng Z.,University of Alberta | Zuo M.J.,University of Alberta | Chu F.,Tsinghua University
Mechanical Systems and Signal Processing | Year: 2010

Fractal dimension provides a measure of the complexity of a dynamic system, and contains the health information of a machine. The basics of regularization dimension and the effects of Gaussian kernel parameters on the regularization of a signal are introduced. Regularization dimension has advantages over other fractal dimensions because the scale-independent range can be selected according to the signal frequency components of interest. Experimental gearbox vibration signals are analyzed by means of spectral analysis firstly, and then according to the spectral structure, the scale-independent range is selected for computing the regularization dimension, which increases monotonically with increasing gear damage degree. Comparison with correlation dimension and kurtosis shows the advantages of regularization dimension in assessing the localized gear damage. © 2009 Elsevier Ltd. All rights reserved.


Wang J.J.,University of Science and Technology Beijing | Ma X.Q.,University of Science and Technology Beijing | Li Q.,Xi'an Jiaotong University | Britson J.,Pennsylvania State University | And 2 more authors.
Acta Materialia | Year: 2013

An efficient numerical algorithm based on a Fourier spectral iterative perturbation method is proposed to accurately compute the electrostatic fields in three-dimensional (3D) microstructures with arbitrary dielectric inhomogeneity and anisotropy. The method can be conveniently implemented in phase field modeling of microstructure evolution in systems with inhomogeneous dielectric constants as well as inhomogeneous polarization and charge distributions. It is employed to determine the temperature-shape (aspect ratio) phase diagram, domain structures, and domain switching of PbTiO3 nanoparticles using phase field simulations. It is shown that the Curie temperature is enhanced for nanowires and nanorods and reduced for nanodots. The critical sizes below which the ferroelectricity disappears for the nanowire and thin film are estimated to be around 1.4 nm. Vortex domain structures are found in nanorods, nanodots, and nanodisks. Results are in general agreement with existing experimental observations and first principle calculations. © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.


Feng Z.,University of Science and Technology Beijing | Chu F.,Tsinghua University
Zhongguo Dianji Gongcheng Xuebao/Proceedings of the Chinese Society of Electrical Engineering | Year: 2013

A thorough understanding of the vibration signal spectral structure is helpful for fault diagnosis of planetary gearboxes via common yet effective spectral analysis. Considering both the amplitude modulation and the frequency modulation effects due to gear manufacturing errors or distributed faults, as well as the amplitude modulation caused by the passing effect of planets, signal models of normal and distributed fault cases and their Fourier transforms were given, and the spectral characteristics were summarized in closed form. Meanwhile, explicit equations for calculating the characteristic frequency of distributed gear fault were deduced. The theoretical derivations were validated using experimental datasets. According to the theoretical derivations, the naturally developed gear fault in a planetary gearbox was detected and located. © 2013 Chinese Society for Electrical Engineering.


Wang H.,University of Science and Technology Beijing | Wang K.,University of Science and Technology Beijing | Tao J.,Xiamen University | Jiang J.,University of Science and Technology Beijing
Chemical Communications | Year: 2012

Correlation between molecular structures and slow relaxation of magnetization of three mixed (phthalocyaninato)(porphyrinato) dysprosium(iii) double-deckers clearly reveals the effect of the sandwich-type molecular structure, in particular the twist angle, on the quantum tunneling (QT) at zero dc field of these complexes, providing the first direct evidence to the theoretical inference. © 2012 The Royal Society of Chemistry.


Zhang Y.,University of Science and Technology Beijing | Yang X.,University of Science and Technology Beijing | Liaw P.K.,University of Tennessee at Knoxville
JOM | Year: 2012

This article reviews the recent work on the high-entropy alloys (HEAs) in our group and others. HEAs usually contain five or more elements, and thus, the phase diagram of HEAs is often not available to be used to design the alloys. We have proposed that the parameters of δ and Ω can be used to predict the phase formation of HEAs, namely Ω ≥ 1.1 and δ ≤ 6.6%, which are required to form solid-solution phases. To test this criterion, alloys of TiZrNbMoV x and CoCr FeNiAlNb x were prepared. Their microstructures mainly consist of simple bodycentered cubic solid solutions at low Nb contents. TiZrNbMoV x alloys possess excellent mechanical properties. Bridgman solidification was also used to control the microstructure of the CoCrFeNiAl alloy, and its plasticity was improved tobe about 30%. Toour surprise, the CoCrFeNiAl HEAs exhibit no apparent ductile-to-brittle transition even when the temperatures are lowered from 298 K to 77 K. © 2012 TMS.


Feng Z.,University of Science and Technology Beijing | Chu F.,Tsinghua University
Zhongguo Dianji Gongcheng Xuebao/Proceedings of the Chinese Society of Electrical Engineering | Year: 2013

The frequency modulation part contains the gear fault information, and is free from the effect of time varying vibration transfer paths. This feature is helpful to avoid the complex sidebands in Fourier spectra and additional amplitude modulation caused by the planet passing effect or the time variant vibration propagation paths. According to the frequency modulation characteristics of planetary gearbox vibration signals, a frequency demodulation analysis method based on empirical mode decomposition was proposed to simplify the signal analysis in fault diagnosis. The criterion for selecting sensitive intrinsic mode function was proposed, the explicit equations for the Fourier spectra of instantaneous frequency were deduced, and the instantaneous frequency spectral characteristics of sun, planet and ring gear faults were summarized. The proposed method was validated using simulated signal and lab experimental datasets, and the localized damage of sun, planet and ring gears was diagnosed via frequency demodulation analysis. © 2013 Chin. Soc. for Elec. Eng.


Feng Z.,University of Science and Technology Beijing | Zhao L.,University of Science and Technology Beijing | Chu F.,Tsinghua University
Zhongguo Dianji Gongcheng Xuebao/Proceedings of the Chinese Society of Electrical Engineering | Year: 2013

Gear faults are usually originated from localized damage. The vibration spectral characteristics of sun, planet and ring gears with localized damage are different from those of distributed gear faults, thus it is important to investigate them for fault diagnosis of planetary gearboxes via vibration signal spectral analysis. Considering both the amplitude modulation and the frequency modulation effects due to localized gear damage, as well as the time variation of vibration transfer paths, signal models of sun, planet and ring gear localized damage cases and their Fourier spectra were given in closed form, and the spectral characteristics were summarized. Meanwhile, explicit equations for calculating the characteristic frequency of localized gear faults were deduced. The theoretical derivations were validated using experimental datasets. According to the theoretical derivations, the localized damage of sun, planet and ring gears in a planetary gearbox was detected and located via spectral analysis. © 2013 Chinese Society for Electrical Engineering.


Zhu L.-F.,University of Science and Technology Beijing | Zhang B.-P.,University of Science and Technology Beijing | Zhao L.,University of Science and Technology Beijing | Li J.-F.,Tsinghua University
Journal of Materials Chemistry C | Year: 2014

A series of solid solutions of BaTiO3-x(0.4CaTiO 3-0.6BaSnO3) (abbreviated as BT-x(CT-BS), x = 0.00-0.20 mol) were prepared to search for high performance lead-free piezoelectric ceramics. Through content tailoring, a complex phase transition was confirmed by X-ray diffraction and Raman spectra as well as temperature dependence of the dielectric constant, which occurs from tetragonal(T)-orthorhombic(O) coexistence at 0 ≤ x ≤ 0.12 to rhombohedral(R)-O-T and R-O/T-cubic(C) multiphase coexistence at x = 0.16 and 0.20, respectively. The lower EC = 1.31 kV cm-1 and higher Pr = 9.48 μm cm-2 as well as high piezoelectric response d33 = 570 pC N-1 were achieved in BT-x(CT-BS) ceramics at an optimal composition of x = 0.16. The ultrahigh converse piezoelectric coefficient d*33 = 1444 pm V-1 and strain = 0.070% which are the highest values reported so far in lead-free ceramics also were achieved at x = 0.16, suggesting that a BT-x(CT-BS) system is a promising lead-free alternative material for electromechanical actuator applications. This journal is © the Partner Organisations 2014.


Xu K.,Tsinghua University | Wang C.,Tsinghua University | Liu H.,University of Science and Technology Beijing | Qian Y.,Tsinghua University
Chemosphere | Year: 2011

This study investigated the simultaneous removal of P and K from synthetic urine through the precipitation of magnesium potassium phosphate hexahydrate (MPP, MgKPO4·6H2O) in bench-scale experiments. Results show that the removal efficiencies of P and K are mainly determined by the solution pH and the molar ratio of Mg:K:P. Co-precipitation of struvite-type compounds, i.e., magnesium ammonium phosphate hexahydrate (MAP, MgNH4PO4·6H2O), magnesium sodium phosphate heptahydrate (MSP, MgNaPO4·7H2O), and MPP, was confirmed by analysis of the solid precipitates using a Scanning Electron Microscope/Energy Dispersive X-ray Apparatus and an X-ray Diffractometer. The co-precipitation significantly influenced the removal of K. As much ammonium as possible should be removed prior to MPP precipitation because MAP had higher tendency to form than MPP. The inevitable co-precipitation of MPP and MSP resulted in the addition of more MgCl2·6H2O and Na2HPO4·12H2O to obtain the high removal of K. In total, the removal efficiencies of P and K were 77% and 98%, respectively, in the absence of ammonium when pH was 10 and the molar ratio of Mg:K:P was 2:1:2. The results indicate that the MPP precipitation is an efficient method for the simultaneous removal of P and K to yield multi-nutrient products. © 2011.


Ahmad M.,Tsinghua University | Rafi-Ud-din,University of Science and Technology Beijing | Pan C.,Tsinghua University | Zhu J.,Tsinghua University
Journal of Physical Chemistry C | Year: 2010

Hydrogen storage capabilities of controlled synthesized ZnO-based nanostructures have been investigated. The microscopic results reveal that the products consist of hollow ZnO microspheres composed of nanowires, hollow Sb-doped nanospheres, and Al-doped nanobelts. Energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) give evidence that Sb and Al dopants are successfully substituted into nanospheres and nanobelts, respectively. The photoluminescence (PL) spectra exhibit a strong green emission band due to defects in nanostructures which lead to a significant role in the hydrogen storage applications. The hydrogen storage characteristics prove that the defects in nanostructures are responsible for higher hydrogen absorption. Among the nanostructures the maximum hydrogen storage capacity of about 2.94 wt % is achieved under the pressure of 5 MPa for Al-doped ZnO nanobelts, and about 81.6% of the stored hydrogen can be released under ambient pressure at 373 K. The highly reversible absorption/desorption reactions exhibit that Al-doped nanobelts are promising material for hydrogen storage. © 2010 American Chemical Society.


Gao X.,University of Science and Technology Beijing | Xu L.-P.,University of Science and Technology Beijing | Xue Z.,CAS Beijing National Laboratory for Molecular | Feng L.,Tsinghua University | And 4 more authors.
Advanced Materials | Year: 2014

Large-area dual-scaled porous nitrocellulose (p-NC) membranes are fabricated by a facile, inexpensive and scalable perforating approach. These p-NC membranes show stable superhydrophilicity in air and underwater superoleophobicity. The p-NC membranes with intrinsic nanopores and array of microscale perforated pores could selectively and efficiently separate water from various oil/water mixtures with high efficiency (> 99%) rapidly. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


He J.Y.,University of Science and Technology Beijing | Zhu C.,University of Tennessee at Knoxville | Zhou D.Q.,University of Science and Technology Beijing | Liu W.H.,University of Science and Technology Beijing | And 2 more authors.
Intermetallics | Year: 2014

Steady state flow behavior of the FeCoNiCrMn high-entropy alloy at temperatures ranging from 1023 to 1123 K was systematically characterized. It was found that the stress exponent (i.e., the reciprocal of strain-rate sensitivity) was dependent on the applied strain rate, and specifically the stress exponent is high (∼5) in the high strain rate regime, but decreases with decreasing strain rate. Microstructural examinations of the samples before and after deformation were performed to understand the interplay of the microstructures with the corresponding properties. Based on the observations, it was proposed that, at high strain rates, the deformation of the current high-entropy alloy was controlled by dislocation climb and the rate limiting process was the diffusion of Ni. At low strain rates, however, the deformation appeared to be controlled by the viscous glide of dislocations. Moreover, at the slowest strain rate (i.e., the longest thermal exposure time), new phases evolved, which caused elemental redistribution and weakening of the material. © 2014 Elsevier Ltd. All rights reserved.


Wang H.,University of Science and Technology Beijing | Wang K.,University of Science and Technology Beijing | Bian Y.,University of Science and Technology Beijing | Jiang J.,University of Science and Technology Beijing | Kobayashi N.,Tohoku University
Chemical Communications | Year: 2011

Two novel mixed (phthalocyaninato)(porphyrinato) rare-earth and cadmium heterometal complexes have been fabricated in one-pot reaction and their sandwich quadruple-decker nature is unambiguously revealed by X-ray single crystal analysis. © 2011 The Royal Society of Chemistry.


Wang L.,University of Science and Technology Beijing | Wang L.,University of Tennessee at Knoxville | Lu Z.P.,University of Science and Technology Beijing | Nieh T.G.,University of Tennessee at Knoxville
Scripta Materialia | Year: 2011

Nanoindentation tests were performed on an Au49Ag 5.5Pd2.3Cu26.9Si16.3 metallic glass. The critical shear stress for the first pop-in, i.e. the onset of yielding, was measured at different temperatures. The volume and the activation free energy for the shear transformation zones were determined from the stress-temperature relationship. The strain-rate dependence of serrated flow in nanoindentation was also characterized. The sizes of shear band nucleus at different temperatures were found to be practically constant. The implication of a constant nucleus size is discussed. © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.


Xiao L.-L.,University of Science and Technology Beijing | Xiao L.-L.,Chinese Academy of Geological Sciences | Liu F.-L.,Chinese Academy of Geological Sciences | Chen Y.,CAS Institute of Geology and Geophysics
Precambrian Research | Year: 2014

Garnet-bearing metapelites are cropped out in the Zanhuang metamorphic complex located in the central section of the N-S trending Trans-North China Orogen. Petrological studies indicate that these garnet-bearing metapelites preserve three distinct metamorphic assemblages (M1-M3). The cores of garnet porphyroblasts and fine-grained inclusions of plagioclase+quartz±biotite±apatite±magnetite±rutile±ilmenite define the prograde metamorphic stage (M1). The assemblage of the peak metamorphic stage (M2) consists of biotite+plagioclase+quartz±kyanite±hornblende±magnetite±ilmenite in equilibrium with the lowest-XMn garnet rims. The peak metamorphism was followed by a near-isothermal decompressional stage (M3) and the development of symplectitic coronas of biotite+plagioclase+quartz±hornblende±magnetite surrounding garnet porphyroblasts. Quantitative phase equilibria modeling and traditional thermobarometric estimations were applied to yield P-T conditions of 4.5-5.9kbar and 551-596°C for stage M1, 9.6-12.3kbar and 770-830°C for stage M2, and ~4.7kbar and ~635°C for stage M3. The combination of the mineral inclusions, mineral compositions, and metamorphic reactions in the Zanhuang metapelites defines a clockwise P-T path with nearly isothermal decompression, which is considered to have been related to the amalgamation of the Eastern and Western Blocks to form the North China Craton. Abundant U-Pb spot analyses of metamorphic zircons from the gneiss and amphibolite reveal two discrete, meaningful ages of metamorphism within the Zanhuang complex: the first age dates to ~2507Ma, and the second age dates to ~1839Ma. The first age group (~2507Ma) was most likely associated with a regional Neoarchean granulite-facies metamorphic event within the North China Craton, whereas the second age group (~1839Ma) is interpreted as the result of a Paleoproterozoic orogenic event that occurred in the Trans-North China Orogen (TNCO). © 2014 Elsevier B.V.


Zhang D.,Shandong University of Technology | Zhang D.,University of Science and Technology Beijing | Wang P.,Shandong University of Technology
Inorganic Chemistry Communications | Year: 2012

With a new pentacyanidecobalt(III) precursor K 2[Co(CN) 5(CH 3CN)] and a bicompartimental Schiff base manganese(III) compound, a new two-dimensional cyanide-bridged Co(III)-Mn(III) coordination polymer constructed by hydrogen-bond interactions has been successfully synthesized and characterized by elemental analysis, IR spectroscopy and X-ray structure determination. Single X-ray diffraction analysis reveals this cationic cyanide-bridged tetranuclear complex is self-complementary through coordinated aqua ligands from one complex and the free O 4 compartments from the neighboring complex, giving interesting 2D supramolecular structure. Investigation over magnetic susceptibility reveals the overall weak antiferromagnetic coupling between the adjacent Mn(III) ions. © 2012 Elsevier B.V.


Liu L.,Tsinghua University | Fu L.,Tsinghua University | Jiang Y.,Tsinghua University | Guo S.,University of Science and Technology Beijing
Renewable and Sustainable Energy Reviews | Year: 2011

Charging heating fees based on floor space in China leaves building developers no economic returns on the investment to weatherize the buildings and install regulation devices with terminal equipment. Therefore, they lack incentives to improve the thermal insulation properties of the buildings. Tenants also lack incentives to efficiently use heat, opening windows to cool down rooms when they are overheated, without concern for the amount of heat wasted. In response, over the past decade, the Chinese government has invested large amounts of resources in an effort to promote energy conservation with heating systems by trying to change the fee method based on floor space to amount of heat used, but with little effect. The major issues related to reform with the heat-metering system are elaborated in this paper by comparing the pros and cons of several metering methods. Firstly, room temperatures are unable to be effectively adjusted using the current methods, meaning that the original intention to save energy cannot be achieved. Secondly, current heat-metering methods are not acceptable to users, which creates its own problems. Heat metering based on households in apartment buildings, the primary living space for Chinese people, causes two problems: the energy consumed by households located at the top or at the corner of buildings is two to three times higher than households located elsewhere within the building; heating fees may increase by 20-30% if surrounding households are not heated. Current metering methods are unable to effectively resolve these two problems, therefore, they are not accepted. To overcome these difficulties, a proper metering and charging method must be developed which is both acceptable to users and able to guarantee good room temperature control at the same time. To achieve this goal, this paper presents a new method: the total heating fee of a building is allocated according to the accumulated on-time as well as the floor space of each household. Not only can this new method control the user behavior of opening windows or setting the starting point too high, but also resolve problems caused by location and heat transfer between households. It is also effective in promoting energy saving by users and appears to be acceptable to users. Survey results show that it is acceptable to a large number of users. It seems that this is the most practical way to reform the current methods for heat metering based on household use. © 2010 Elsevier Ltd.


Ge Z.-H.,University of Science and Technology Beijing | Zhang B.-P.,University of Science and Technology Beijing | Liu Y.,University of Science and Technology Beijing | Li J.-F.,Tsinghua University
Physical Chemistry Chemical Physics | Year: 2012

Nanostructured Bi 2-xCu xS 3 (x = 0, 0.002, 0.005, 0.007, 0.01, 0.03) thermoelectric polycrystals were fabricated by combining mechanical alloying (MA) and spark plasma sintering (SPS) methods. The effect of Cu content on the microstructure and thermoelectric property of Bi 2-xCu xS 3 bulk samples was investigated. It was found that the subtle tailoring of Cu content could reduce both the electrical resistivity and the thermal conductivity at the same time, and consequently enhancing the thermoelectric property. A low electrical resistivity of 1.34 × 10 -4 Ω m -1 and a low thermal conductivity of 0.52 W m -1 K -1 were obtained for the Bi 1.995Cu 0.005S 3 sample at 573 K. The low thermal conductivity is supposed to be due to the nanoscopic Cu-rich regions embedded in the host matrix. A peak ZT value of 0.34 at 573 K was achieved for the Bi 1.995Cu 0.005S 3 composition, which is the highest value in the Bi 2S 3 system reported so far. © 2012 the Owner Societies.


Du Y.,University of Science and Technology Beijing | Xiong P.,Georgia Institute of Technology | Fan Y.,Tsinghua University | Li X.,Massachusetts Institute of Technology
IEEE Transactions on Systems, Man, and Cybernetics Part A:Systems and Humans | Year: 2011

Current methods that deal with concurrent workflow temporal violations only focus on checking whether there are any temporal violations. They are not able to point out the path where the temporal violation happens and thus cannot provide specific solutions. This paper presents an approach based on a sprouting graph to find out the temporal violation paths in concurrent workflow processes as well as possible solutions to resolve the temporal violations. First, we model concurrent workflow processes with time workflow net and a sprouting graph. Second, we update the sprouting graph at the checking point. Finally, we find out the temporal violation paths and provide solutions. We apply the approach in a real business scenario to illustrate its advantages: 1) It can dynamically check temporal constraints of multiple concurrent workflow processes with resource constraints; 2) it can give the path information in the workflow processes where the temporal violation happens; and 3) it can provide solution to the temporal violation based on the analysis. © 2011 IEEE.


Ge Z.-H.,University of Science and Technology Beijing | Zhang B.-P.,University of Science and Technology Beijing | Li J.-F.,Tsinghua University
Journal of Materials Chemistry | Year: 2012

We have designed a composite-like microstructure to improve the thermoelectric (TE) properties of Bi 2S 3 polycrystals. The nanosized Bi 2S 3 powders derived from mechanical alloying (MA) were mixed with [001] oriented single crystalline Bi 2S 3 nanorods prepared by hydrothermal synthesis (HS), which were densified by spark plasma sintering (SPS) to form a composite-like microstructure bulk with road-like structures consisting of nanorods. Because the nanorods provide good electron transport paths, the carrier mobility of the composite-like Bi 2S 3 bulk materials was improved by more than two orders of magnitude by mixing 10 wt% nanorods into the MA-derived powders. The electrical resistivity was also reduced from 2.5 × 10 -2 to 8.5 × 10 -4 Ωm at 323 K, but the thermal conductivity was just slightly increased, resulting in a significantly enhanced ZT value, which was almost two times higher than that of the nanorod-free sample. This study demonstrated the possibility to significantly enhance the ZT value of TE bulks by combining the advantages of single crystals and polycrystals via controlling the microstructure without any chemical doping. © 2012 The Royal Society of Chemistry.


Zhang D.-P.,China University of Mining and Technology | Zhang D.-P.,Shandong University of Technology | Zhang D.-P.,University of Science and Technology Beijing | Zhang L.-F.,China University of Mining and Technology | And 2 more authors.
Chemical Communications | Year: 2013

One cyanide-bridged W(iv)-Ni(ii) wheel-like complex and two three-dimensional (3D) networks can be directly synthesized based on K 4[W(CN)8] and [Ni(L)](ClO4)2 precursors by controlling the quantity of water in organic solvent. The water-controlled single-crystal structural transformations among these complexes are described. © The Royal Society of Chemistry 2013.


Wang Q.,Shandong University | Chen Y.,University of Jinan | Ma P.,Shandong University | Lu J.,Shandong University | And 2 more authors.
Journal of Materials Chemistry | Year: 2011

An optically active porphyrin-pentapeptide conjugate 1, actually a porphyrinato zinc complex covalently linked with a glycinyl-alanyl-glycinyl- alanyl-glycine (GAGAG) peptide chain, was designed and synthesized. The self-assembly properties of this novel porphyrin-pentapeptide conjugate in THF/n-hexane and THF/water were comparatively investigated by electronic absorption, circular dichroism (CD), IR spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray diffraction (XRD) technique. Associated with the different secondary conformation of the pentapeptide chain covalently linked to the porphyrin ring in different solvent systems, self-assembly of conjugate 1 leads to the formation of nanofibers with right-handed helical arrangement and nanotubes with left-handed helical arrangement in a stack of porphyrin chromophores according to the CD spectroscopic result in apolar THF/n-hexane (1:3) and polar THF/water (1:3) system depending on the cooperation between intramolecular or intermolecular hydrogen bonding interaction with chiral discrimination between pentapeptide chains and porphyrin-porphyrin interactions in the direction parallel to the tetrapyrrole ring of neighboring conjugate molecules. IR spectroscopic result clearly reveals the α-helix and β-sheet secondary conformation, respectively, employed by the pentapeptide chain attached at the porphyrin core in the nanostructures formed in THF/n-hexane (1:3) and THF/water (1:3). The X-ray diffraction (XRD) result confirms that in the nanotubes, a dimeric supramolecular bilayer structure was formed through an intermolecular hydrogen bonding interaction between two conjugate molecules which, as the building block, self-assembles into the target nanostructures. These results clearly reveal the effect of a secondary conformation of pentapeptide chain in the conjugate molecule on the packing mode of porphyrin chromophore, supramolecular chirality, and morphology of the self-assembled nanostructure. The present result represents not only the first example of organic nanostructures self-assembled from a covalently linked porphyrin-pentapeptide conjugate, but more importantly the first effort towards controlling and tuning the morphology and in particular the supramolecular chirality of porphyrin nanostructures via tuning the secondary conformation of peptides in different solvent systems, which is helpful towards understanding, designing, preparing, and mimicking the structure and role of naturally occurring porphyrin-peptide conjugates. In addition, both nanofibers and nanotubes were revealed to show good semiconducting properties. © 2011 The Royal Society of Chemistry.


Wang L.,University of Science and Technology Beijing | Chen Y.,University of Jinan | Bian Y.,University of Science and Technology Beijing | Jiang J.,University of Science and Technology Beijing
Journal of Physical Chemistry C | Year: 2013

Crystalline nanostructures with octahedral morphology have been prepared by self-assembling of cationic porphyrin (H6TPyP)4+· 4Cl- produced through chemical reaction route in aqueous solution depending on the synergistic interactions among hydrogen-bonding, π-π stacking, and ion pairing. Unexpectedly, the gradual decrease in pH by the slow evaporation of solvent in the nano-octahedron aqueous suspension obtained in situ led to the selective etching of the original nanocrystal and the isolation of (H6TPyP)4+·4Cl- bulk single crystals in the last stage. More interestingly, the increase in pH by adding water again into this bulk single-crystal-containing system led to the regeneration of nano-octahedrons, indicating the reversible transformation between porphyrin nano-octahedrons and bulk single crystals triggered by pH. Mechanistic investigations through powder and single-crystal X-ray diffraction analyses together with the electron microscopic, in particular, HRTEM, clearly reveal that the unique surface effect and anisotropic character of the nanomaterials differing from the bulk organic materials are responsible for such pH-sensitive reversible transformation of the two crystalline materials by controlling the dissolution or aggregation of (H6TPyP)4+·4Cl -, which actually induces the reversible formation and breaking of the (pyridine)N+-H···Cl -···H-O(H2O) ···H-N+(pyridine) hydrogen bonds among cationic porphyrin building blocks at different pH. This result, to control the crystallinity and the unprecedented reversible transformation between nanocrystal and bulk single crystals just by tuning the pH of the synthesis process, as well as the use of the peculiar nanoeffect such as surface effect to adjust the self-assembling process, provides useful a tool for the controllable synthesis of crystalline materials and is expected to be helpful for further research and application of organic nanomaterials. © 2013 American Chemical Society.


Li Z.,Tsinghua University | Feng Z.,University of Science and Technology Beijing | Chu F.,Tsinghua University
Journal of Sound and Vibration | Year: 2014

Load identification, as a kind of indirect identification method, uses system characteristic and responses to calculate loads. A method based on wavelet multi-resolution analysis is proposed in this paper. By wavelet decomposition and transform at certain resolutions, the proposed method transforms the convolution relation between responses and loads in time domain into the linear multiplicative relation between system responses and wavelet responses in the wavelet domain. Loads can be identified as long as the linear multiplicative relation is solved. Qualitative and quantitative rules are proposed for selecting parameters that affect the accuracy of the proposed method, and are illustrated via numerical investigations. The method is illustrated by a multi-input-multi-output numerical simulation. A multi-input-multi-output laboratory experiment is performed to compare the proposed method with the frequency method on the identification ability. © 2013 Elsevier Ltd.


Si X.-S.,HIGH-TECH | Si X.-S.,Tsinghua University | Wang W.,University of Science and Technology Beijing | Hu C.-H.,HIGH-TECH | Zhou D.-H.,Tsinghua University
IEEE Transactions on Reliability | Year: 2014

The use of the observed degradation data of a system can help to estimate its remaining useful life (RUL). However, the degradation progression of the system is typically stochastic, and thus the RUL is also a random variable, resulting in the difficulty to estimate the RUL with certainty. In general, there are three sources of variability contributing to the uncertainty of the estimated RUL: 1) temporal variability, 2) unit-to-unit variability, and 3) measurement variability. In this paper, we present a relatively general degradation model based on a Wiener process. In the presented model, the above three-source variability is simultaneously characterized to incorporate the effect of three-source variability into RUL estimation. By constructing a state-space model, the posterior distributions of the underlying degradation state and random effect parameter, which are correlated, are estimated by employing the Kalman filtering technique. Further, the analytical forms of not only the probability distribution but also the mean and variance of the estimated RUL are derived, and can be real-time updated in line with the arrivals of new degradation observations. We also investigate the issues regarding the identifiability problem in parameter estimation of the presented model, and establish the according results. For verifying the presented approach, a case study for gyros in an inertial platform is provided, and the results indicate that considering three-source variability can improve the modeling fitting and the accuracy of the estimated RUL. © 2014 IEEE.


Lin C.,Tsinghua University | Li Y.,Tsinghua University | Wan J.-X.,University of Science and Technology Beijing
Jisuanji Xuebao/Chinese Journal of Computers | Year: 2011

Optimization approaches provide powerful theoretical support for designing mechanisms to guarantee quality of services (QoS) in computer networks. In contrast to heuristic methods for network design, optimization approaches can find out the optimal solutions theoretically, so that overcome the drawbacks of heuristic methods which cannot be proven to be optimal. It becomes the leading edge of the QoS-aware networking research field. Many researches begin to use optimization theory to reanalyze network models, and design protocols according to the solutions of optimization problems. Optimization approaches in networks can be categorized into several different subjects: resource allocation, task scheduling, resource deployment, and parameter configuration. The modeling, solving, implementing, and evaluating techniques for optimization of QoS in networks have become a hot research topic nowadays. According to the latest research progress, this paper delves into the optimization techniques for improving QoS in networks. It includes four parts: formulating the generic expressions for optimization of networks and classifying the optimization problems according to different perspectives; discussing solving methods to the models with different structures; comparing diverse ways of implementations by considering the connection and difference between them; presenting methods for performance and cost evaluation of optimization schemes. Finally, we summarize the points of this paper and discuss the possible research challenges.


Li J.,University of Science and Technology Beijing | Wang Y.,University of Science and Technology Beijing | Dong E.,University of Science and Technology Beijing | Chen H.,University of Science and Technology Beijing | Chen H.,Tsinghua University
Lab on a Chip - Miniaturisation for Chemistry and Biology | Year: 2014

A technology is presented to fabricate a microfluidic chip in which the microchannels and the microelectrodes of sensors are integrated directly into the copper sheet on a printed circuit board. Then, we demonstrate an application of the generation of oil-in-water and water-in-oil emulsion droplets on this microfluidic chip driven by a USB interface, and the droplet size is detected by the microelectrodes on the downstream microchannel. The integration of the microfluidic chip is improved by the direct connection of the channels to the microelectrodes of the driving unit and of the sensors on the same substrate, and it is a promising way to integrate microfluidics into a more complex micro electrical-mechanical system (MEMS). This journal is © The Royal Society of Chemistry 2014.


Fukuma Y.,RIKEN | Wang L.,RIKEN | Wang L.,University of Science and Technology Beijing | Idzuchi H.,University of Tokyo | And 7 more authors.
Nature Materials | Year: 2011

The non-local spin injection in lateral spin valves is strongly expected to be an effective method to generate a pure spin current for potential spintronic application. However, the spin-valve voltage, which determines the magnitude of the spin current flowing into an additional ferromagnetic wire, is typically of the order of 1μV. Here we show that lateral spin valves with low-resistivity NiFe/MgO/Ag junctions enable efficient spin injection with high applied current density, which leads to the spin-valve voltage increasing 100-fold. Hanle effect measurements demonstrate a long-distance collective 2π spin precession along a 6-μm-long Ag wire. These results suggest a route to faster and manipulable spin transport for the development of pure spin-current-based memory, logic and sensing devices. © 2011 Macmillan Publishers Limited. All rights reserved.


Wang D.,University of Science and Technology Beijing | Zhou T.,Beijing University of Chemical Technology | Zha J.-W.,University of Science and Technology Beijing | Zhao J.,University of Science and Technology Beijing | And 3 more authors.
Journal of Materials Chemistry A | Year: 2013

The fabrication and dielectric properties of a novel multi-component high-k composite system consisting of poly(vinylidene fluoride), surface- functionalized graphene nanosheets and BT nanoparticles (fRGO-BT/PVDF) were investigated. The fRGO nanosheets were prepared through the π-π stacking of polyaniline and GO following in situ hydrazine reduction. The fRGO-BT/PVDF nanocomposites were fabricated by a solution casting and hot-pressing approach. SEM results confirm that fRGO and BT are well dispersed within the PVDF matrix. The dielectric properties of the binary fRGO/PVDF nanocomposites exhibit a typical percolation transition with the percolation threshold of 1.49 vol%. This type of nanocomposite, co-filled with conductive graphene nanosheets and high-k ceramics, shows a high kr (65) and a relatively low dielectric loss (tan δ = 0.35) at a high frequency of 1 MHz. Meanwhile, the dielectric properties of the fRGO-BT/PVDF nanocomposites show temperature independent behavior over a wide temperature range. These flexible, high-k fRGO-BT/PVDF nanocomposites are potential flexible dielectric materials for use in high-frequency capacitors and electronic devices. © 2013 The Royal Society of Chemistry.


Tao H.-C.,University of Science and Technology Beijing | Huang M.,Tsinghua University | Fan L.-Z.,University of Science and Technology Beijing | Qu X.,University of Science and Technology Beijing
Electrochimica Acta | Year: 2013

Core-shell structured Si/C nanocomposites with different nitrogen contents are prepared by in situ polymerization of aniline in the suspension of silicon nanoparticles followed by carbonization of Si/polyaniline (PANI) nanocomposites at different temperatures. The nitrogen contents of Si/C nanocomposites decrease gradually with increasing carbonization temperatures. The effect of nitrogen contents on the electrochemical performance of Si/C nanocomposites as anode materials for lithium ion batteries is investigated. It is found that the Si/C nanocomposites with 4.75 wt.% nitrogen exhibit the high specific capacity of 795 mAh g-1 after 50 cycles at a current density of 100 mA g -1 and excellent cycling stability. The appropriate nitrogen in Si/C nanocomposites plays a beneficial role in the improvement of electrochemical performance. The nitrogen in Si/C nanocomposites increases the reversible capacity, which may be due to the formation of vacancies and dangling bonds around the nitrogen sites. © 2012 Elsevier Ltd. All Rights Reserved.


Chen Y.,University of Science and Technology Beijing | Xu G.,University of Science and Technology Beijing | Li J.,University of Science and Technology Beijing | Zhang Y.,University of Science and Technology Beijing | And 2 more authors.
Electrochimica Acta | Year: 2013

Solid solution material of 0.5Li2MnO3·0. 5LiNi0.33Co0.33Mn0.33O2 (alternatively Li[Li0.2Mn0.54Ni0.13Co 0.13]O2) was synthesized by a fast co-precipitation method which takes sulfates with high solubility as the transition metal sources of mixed hydroxide precursor. The optimal synthetic conditions were determined through the design of orthogonal experiments. The properties of samples synthesized under the best conditions were investigated in detail. The XRD pattern of 0.5Li2MnO3·0.5LiNi0.33Co 0.33Mn0.33O2 revealed a well ordered hexagonal layered structure with the evident feature of super lattice caused by Li 2MnO3. FESEM images showed that the powders possess small and unagglomerated particles with size range of 100-300 nm. XPS analysis results demonstrated that the valence states of Ni, Co, Mn are +2, +3, and +3.52 respectively. The electrochemical measurements showed that the optimal material delivers initial discharge capacity of 315.3 mAh g-1 at 1/20 C between 2.0 and 4.8 V with good cycle stability after firstly several cycles. CV test proved that the high capacity performance is ascribed to the redox of oxygen or its species at the electrode surface. Rate test showed that 179.5 mAh g-1 was obtained at 2 C which is considerably high, as far as we concerned. © 2012 Elsevier Ltd.


Hou J.,University of Science and Technology Beijing | Cheng H.,University of Science and Technology Beijing | Takeda O.,Tohoku University | Zhu H.,University of Science and Technology Beijing
Angewandte Chemie - International Edition | Year: 2015

The photochemical conversion of carbon dioxide provides a straightforward and effective strategy for the highly efficient production of solar fuels with high solar-light utilization efficiency. However, the high recombination rate of photoexcited electron-hole (e-h) pairs and the poor photostability have greatly limited their practical applications. Herein, a practical strategy is proposed to facilitate the separation of e-h pairs and enhance the photostability in a semiconductor by the use of a Schottky junction in a bimetal-graphene-semiconductor stack array. Importantly, Au-Cu nanoalloys (ca. 3nm) supported on a 3D ultrathin graphene shell encapsulating a p-type Cu2O coaxial nanowire array promotes the stable photochemical reduction of CO2 to methanol by the synergetic catalytic effect of interfacial modulation and charge-transfer channel design. This work provides a promising lead for the development of practical catalysts for sustainable fuel synthesis. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


He F.,University of Science and Technology Beijing | Zhang Q.,Tsinghua University | Zhang Q.,University of Science and Technology Beijing | Lei J.,Tsinghua University | And 2 more authors.
Energy Policy | Year: 2013

This paper used data from 50 enterprises in China's iron and steel industry to evaluate their energy efficiency and productivity change. The study first used a conventional data envelopment analysis model and the Malmquist Productivity Index (MPI) to measure the energy efficiency and productivity change over the period 2001-2008. The results indicated inefficiency in many of the plants: The average energy efficiency was only 61.1%. The annual growth rate of productivity was 7.96$ over this period and technical change was the main contributor to this growth. The research then took undesirable outputs into consideration by using the Malmquist-Luenberger Productivity Index (MLPI) to explore the productivity change from 2006 to 2008. Omitting undesirable outputs would result in biased efficiency change and technical change. This paper also claimed that environmental regulation has a potentially positive impact on technical change. © 2012 Elsevier Ltd.


Ren H.,Tsinghua University | Wu Y.,Tsinghua University | Ma N.,University of Science and Technology Beijing | Xu H.,Tsinghua University | Zhang X.,Tsinghua University
Soft Matter | Year: 2012

In this paper we report the synthesis and study of a series of side-chain selenium-containing amphiphilic poly(ethylene oxide-b-acrylic acid) block copolymers PEO-b-PAA-Se. These block copolymers can self-assemble in aqueous solution and form spherical micellar aggregates. The selenide group of PEO-b-PAA-Se can change into hydrophilic selenoxide under mild oxidation of 0.1% hydrogen peroxide, leading to the disassembly of the spherical micellar aggregates. Small compounds like Nile Red can be encapsulated into the micellar aggregates and show fast release upon the addition of 0.1% hydrogen peroxide. More interestingly, the oxidation state of selenoxide can be reversed to selenide under reduction of Vitamin C, thus recovering the spherical aggregates. The reversible oxidation and reduction process shows good reversibility and can be repeated at least 7 times. It is hoped that this reversible redox controlled system may function as nanocontainers for potential application in the areas such as responsive drug delivery and anti-oxidation studies. © 2012 The Royal Society of Chemistry.


Xie S.,Tsinghua University | Liang P.,Tsinghua University | Chen Y.,University of Science and Technology Beijing | Xia X.,Tsinghua University | Huang X.,Tsinghua University
Bioresource Technology | Year: 2011

A coupled microbial fuel cell (MFC) system comprising of an oxic-biocathode MFC (O-MFC) and an anoxic-biocathode MFC (A-MFC) was implemented for simultaneous removal of carbon and nitrogen from a synthetic wastewater. The chemical oxygen demand (COD) of the influent was mainly reduced at the anodes of the two MFCs; ammonium was oxidized to nitrate in the O-MFC's cathode, and nitrate was electrochemically denitrified in the A-MFC's cathode. The coupled MFC system reached power densities of 14W/m3 net cathodic compartment (NCC) and 7.2W/m3 NCC for the O-MFC and the A-MFC, respectively. In addition, the MFC system obtained a maximum COD, NH4 +-N and TN removal rate of 98.8%, 97.4% and 97.3%, respectively, at an A-MFC external resistance of 5 Ω, a recirculation ratio (recirculated flow to total influent flow) of 2:1, and an influent flow ratio (O-MFC anode flow to A-MFC anode flow) of 1:1. © 2010 Elsevier Ltd.


Jia X.,Tsinghua University | Chen Z.,University of California at Los Angeles | Cui X.,University of California at Los Angeles | Peng Y.,University of California at Los Angeles | And 4 more authors.
ACS Nano | Year: 2012

Design and fabrication of effective electrode structure is essential but is still a challenge for current lithium-ion battery technology. Herein we report the design and fabrication of a class of high-performance robust nanocomposites based on iron oxide spheres and carbon nanotubes (CNTs). An efficient aerosol spray process combined with vacuum filtration was used to synthesize such composite architecture, where oxide nanocrystals were assembled into a continuous carbon skeleton and entangled in porous CNT networks. This material architecture offers many critical features that are required for high-performance anodes, including efficient ion transport, high conductivity, and structure durability, therefore enabling an electrode with outstanding lithium storage performance. For example, such an electrode with a thickness of ∼35 μm could deliver a specific capacity of 994 mA h g-1 (based on total electrode weight) and high recharging rates. This effective strategy can be extended to construct many other composite electrodes for high-performance lithium-ion batteries. © 2012 American Chemical Society.


Wang L.,University of Science and Technology Beijing | Chen Y.,University of Jinan | Jiang J.,University of Science and Technology Beijing
Nanoscale | Year: 2014

A series of porphyrin nanospindles with controlled long axis length distributions of 330, 550, 800 nm, and 4 μm have been successfully fabricated via hierarchical self-assembly of cationic porphyrin (H6TPyP) 4+ with the help of anionic surfactant sodium dodecyl sulfonate (SDS) due to the effective electrostatic interaction. These newly fabricated nanostructures are characterized by TEM and SEM techniques, powder X-ray diffraction analysis, electronic absorption spectroscopy, and confocal laser scanning microscopy (CLSM). The Z-scan technique with a laser duration of 5 ns at the wavelength of 532 nm reveals unreported size-dependent third-order NLO switching properties: the nonlinear absorption changes from saturation absorption to reversed saturation absorption and the nonlinear refraction from self-defocus to self-focus due to the change of the dominant scattering effect, from Rayleigh scattering for nanostructures with a smaller size than the wavelength of laser light, to Mie scattering for nanostructures with a larger size than the laser wavelength. This result is useful for the development of organic nanostructures with desired NLO properties, in particular the optical limiting properties. © 2013 The Royal Society of Chemistry.


Li S.,Tsinghua University | Li S.,University of Science and Technology Beijing | Lin Y.-H.,Tsinghua University | Zhang B.-P.,University of Science and Technology Beijing | And 2 more authors.
Journal of Physical Chemistry C | Year: 2010

Bismuth ferrite (BiFeO3) uniform microcrystals with various morphologies (microspheres and micro/submirocubes) were successfully synthesized by a controlled hydrothermal method. The resulting microstructures were characterized using X-ray diffraction, scanning/transmission electron microscopies and Raman spectroscopy. Possible formation mechanism for BiFeO 3 microcrystals was proposed. UV-vis spectra showed that the optical properties of the microsized BiFeO3 crystals were strongly related to their shape and size. We further demonstrated the useful photocatalytic activity of these regular-shaped structures as determined by degradation of Congo red under visible-light irradiation (λ > 400 nm). Additionally, magnetic responses were observed to be influenced by the morphology of as-synthesized BiFeO3 products, and the ferroelectric performance of BiFeO3 submicrocube was also studied by piezoelectric force microscopy (PFM). Being a multiferroic semiconductor with suitable narrow band gap (∼2.2 eV) and uniform morphologies, these BiFeO3 microcrystals might be useful for the design of devices combining magnetic, electronic, and optical functionalities. © 2010 American Chemical Society.


Yang X.,University of Science and Technology Beijing | Zhang Y.,University of Science and Technology Beijing | Zhang Y.,University of Tennessee at Knoxville | Liaw P.K.,University of Tennessee at Knoxville
Procedia Engineering | Year: 2012

The novel refractory high entropy alloys with the compositions of NbTiVTaAlx were prepared under a high-purity argon atmosphere and their microstructure and compressive properties at room temperature were investigated. Despite containing many constituents, all alloys had a single solid solution phase with body-centered cubic (BCC) structure, and possessed high compressive yield strength and ductility, which should be attributed to solid solution strengthening. © 2012 Published by Elsevier Ltd.


Kong X.,University of Jinan | Zhang X.,University of Jinan | Gao D.,University of Jinan | Qi D.,University of Science and Technology Beijing | And 2 more authors.
Chemical Science | Year: 2015

Simple solvent vapor annealing over QLS film-based OFET devices fabricated from (Pc)Eu[Pc(ONh)8]Eu[Pc(ONh)8] led to a high and balanced ambipolar performance that has never been observed for small molecule single-component-based solution processed devices, with mobilities of 1.71 and 1.25 cm2 V-1 s-1 for holes and electrons, respectively, under ambient conditions. © The Royal Society of Chemistry 2015.


Wang X.-D.,North China Electrical Power University | An B.,North China Electrical Power University | Lin L.,University of Science and Technology Beijing | Lee D.-J.,National Taiwan University of Science and Technology | Lee D.-J.,National Taiwan University
Applied Thermal Engineering | Year: 2013

An inverse geometric optimization for nanofluid-cooled microchannel heat sink (MCHS) considering effects of temperature-dependent thermophyiscal properties for the water-based Al2O3 nanofluid with 1% particle volume fraction was performed under a constant pumping power constraint. A three-dimensional fluid-solid conjugated MCHS model combining the simplified-conjugate-gradient-method was used as the optimization tool. The channel number, N, the channel aspect ratio, α, and the width ratio of channel to pitch, β, affect the cooling performance of MCHS, and were all incorporated in the present, three-parameter optimization study. Increase in viscosity of the nanofluid did not always lead to enhanced MCHS performance under fixed pumping power constraint, contradicting to the results for pure water. The optimal MCHS design is closely related to the assigned pumping power: increase in the pumping power enhances cooling performance; however, in high pumping power regime the performance enhancement is not as effective as in low pumping power regime. At pumping power of 0.05 W and a uniform heat flux of qw = 100 W cm-2, the optimal design for the nanofluid-cooled MCHS presented N = 51, α = 5.69 and β = 0.62, yielding the optimal thermal resistance of RT = 0.1059 K W -1. © 2013 Elsevier Ltd. All rights reserved.


Peng K.,University of Science and Technology Beijing | Zhang K.,University of Science and Technology Beijing | Li G.,Tsinghua University | Zhou D.,Tsinghua University
Control Engineering Practice | Year: 2013

In this paper, a nonlinear fault diagnosis scheme is established for the hot strip mill process (HSMP). In HSMP, the faults affecting quality index are denoted as quality-related faults, which should be taken care as soon as possible. Projection to latent structures (PLS) is a basic model for quality-related fault detection in linear processes. In the presented work, a total kernel PLS (T-KPLS) model is utilized for modeling and monitoring HSMP, which is a typical nonlinear process. However, diagnosis tools have not been developed aiming at the nonlinear case based on T-KPLS model. Motivated by the successful use of contribution plot for the linear case, a contribution rate plot is proposed to extend contribution plots to the nonlinear case. In the end of this paper, the proposed method is applied to the hot strip mill process effectively. © 2012 Elsevier Ltd.


Li Q.,University of Science and Technology Beijing | Zhang Z.,University of Tennessee at Knoxville
Journal of Physical Chemistry C | Year: 2016

In order to explore the fundamental features of plasmon evolutions in the plasmonic nanostructures along variable geometrical parameters, TiO2-Ag core-shell nanospheroids, which have the distinguishable antibonding and bonding modes, are first used to illustrate the phenomena of plasmon evolutions by simulations. The usual peak-shift behaviors and appearance of the new modes are observed in the far-field extinction spectra. Beneath those phenomena, the unusual mode transformations occur in some modes. In the variable core configuration, when the inner surface of the silver shell is in a close proximity to the outer surface, the dipole antibonding mode evolves to be mixed with the quadrupole mode on the outer surface, while the new emerging mode evolves to the octupole antibonding modes. In the variable shell configuration, when the outer surface approaches the inner surface, the dipole bonding mode tends to evolve to the octupole bonding mode and the new modes emerge and tend to be the triakontadipole-like and octupole-like mode on the outer and inner surfaces. When the polar radius is so large that the outer surface is far away from the inner surface, the dipole antibonding mode evolves to the octupole antibonding mode and the new mode emerges which belongs to the octupole bonding mode. In mode transformation phenomena, one feature is that the evolution is associated with the odd l number (l = 1 for dipole, l = 3 for octupole, and l = 5 for triakontadipole) except for the mixed modes. Another feature is that the antibonding modes can evolve from the octupole to dipole and then octupole modes, in which process the charge distributions for the octupole modes are totally inverse. The retardation effects and the dielectric core effects are also discussed based on the phenomena of the higher order modes. The peak-shift behaviors, the appearance of the new modes, and the mode transformation along variable geometrical parameters have great importance in plasmonic applications due to the tunable resonance wavelength and the local field control. © 2016 American Chemical Society.


Wang D.,Tsinghua University | Wang D.,University of Science and Technology Beijing | Wang X.,Tsinghua University
Progress in Polymer Science | Year: 2013

Amphiphilic polymers are well known for their characteristics to form various self-assembling structures under proper conditions. Amphiphilic azo polymers, which are amphiphilic polymers functionalized with aromatic azo moieties, can combine wealthy photoresponsive properties with the self-assembling feature. In recent years, a wide variety of amphiphilic azo polymers have been developed through different molecular design strategies and synthetic routes. This article reviews the background, recent development, current approaches, and outlook of this rapidly developing research area. The emphasis is placed on the synthesis, self-assembly, and photoresponsive properties of amphiphilic azo polymers. According to the molecular architecture, the amphiphilic azo polymers are classified as homopolymers, random copolymers, block copolymers, star-like and dendritic polymers. The polymers show strong tendency to form well-organized structures at surfaces or interfaces, in solutions or dispersion mediums, and through phase-separation in solid thin-films. Colloidal arrays and porous thin films of amphiphilic azo polymers can be obtained through the vertical deposition method and solvent-induced structure inversion. The amphiphilic azo polymers and their self-assembled structures exhibit a variety of photoresponsive properties triggered by the trans-cis photoisomerization of azo chromophores. Some interesting variations caused by the light irradiation, such as the surface wettability change, surface-relief-grating formation, domain orientation, colloid deformation, micelle dissociation, vesicle bursting and fusion, are described in this review in detail. Such properties are promising for applications in areas such as optical devices, sensors, and drug delivery. © 2012 Elsevier Ltd.


Gan M.,University of Science and Technology Beijing | Dou X.,University of Science and Technology Beijing | Jiang R.,Tsinghua University
The Scientific World Journal | Year: 2013

Advances in high-throughput experimental techniques in the past decade have enabled the explosive increase of omics data, while effective organization, interpretation, and exchange of these data require standard and controlled vocabularies in the domain of biological and biomedical studies. Ontologies, as abstract description systems for domain-specific knowledge composition, hence receive more and more attention in computational biology and bioinformatics. Particularly, many applications relying on domain ontologies require quantitative measures of relationships between terms in the ontologies, making it indispensable to develop computational methods for the derivation of ontology-based semantic similarity between terms. Nevertheless, with a variety of methods available, how to choose a suitable method for a specific application becomes a problem. With this understanding, we review a majority of existing methods that rely on ontologies to calculate semantic similarity between terms. We classify existing methods into five categories: methods based on semantic distance, methods based on information content, methods based on properties of terms, methods based on ontology hierarchy, and hybrid methods. We summarize characteristics of each category, with emphasis on basic notions, advantages and disadvantages of these methods. Further, we extend our review to software tools implementing these methods and applications using these methods. © 2013 Mingxin Gan et al.


Feng Z.,University of Science and Technology Beijing | Chu F.,Tsinghua University | Zuo M.J.,University of Alberta
Journal of Sound and Vibration | Year: 2011

Energy separation algorithm is good at tracking instantaneous changes in frequency and amplitude of modulated signals, but it is subject to the constraints of mono-component and narrow band. In most cases, time-varying modulated vibration signals of machinery consist of multiple components, and have so complicated instantaneous frequency trajectories on time-frequency plane that they overlap in frequency domain. For such signals, conventional filters fail to obtain mono-components of narrow band, and their rectangular decomposition of time-frequency plane may split instantaneous frequency trajectories thus resulting in information loss. Regarding the advantage of generalized demodulation method in decomposing multi-component signals into mono-components, an iterative generalized demodulation method is used as a preprocessing tool to separate signals into mono-components, so as to satisfy the requirements by energy separation algorithm. By this improvement, energy separation algorithm can be generalized to a broad range of signals, as long as the instantaneous frequency trajectories of signal components do not intersect on time-frequency plane. Due to the good adaptability of energy separation algorithm to instantaneous changes in signals and the mono-component decomposition nature of generalized demodulation, the derived time-frequency energy distribution has fine resolution and is free from cross term interferences. The good performance of the proposed time-frequency analysis is illustrated by analyses of a simulated signal and the on-site recorded nonstationary vibration signal of a hydroturbine rotor during a shut-down transient process, showing that it has potential to analyze time-varying modulated signals of multi-components. © 2010 Elsevier Ltd. All rights reserved.


Wang L.,University of Science and Technology Beijing | Wang L.,University of Tennessee at Knoxville | Bei H.,Oak Ridge National Laboratory | Gao Y.F.,University of Tennessee at Knoxville | And 3 more authors.
Acta Materialia | Year: 2011

Nanoindentation experiments were conducted on Zr-based metallic glass samples, which were elastically and plastically bent in order to investigate the effect of residual stresses on hardness. It was found that tensile residual stress reduced the hardness significantly, while compressive residual stress produced only a small effect on the hardness. These observations are consistent with three-dimensional continuum-plasticity-based finite-element simulations. The hardness was also found to vary more significantly with residual stresses, in particular in tension, than that caused by shear-banding-induced softening, suggesting hardness measurement is a practical method for the evaluation of tensile residual stresses in a metallic glass. Hardness variation in the bent sample was correlated with the residual-stress-induced volume dilatation through a free-volume-based model. In this paper, we also present a detailed stress analysis based on yield asymmetry under tension and compression to describe the distribution of residual stresses in bent metallic glass specimens. The calculations agree well with the hardness variations measured experimentally. © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.


Liu H.,University of Queensland | Du X.,Tianjin University | Xing X.,University of Science and Technology Beijing | Wang G.,University of Technology, Sydney | Qiao S.Z.,University of Queensland
Chemical Communications | Year: 2012

Highly ordered mesoporous Cr 2O 3 materials with high specific surface area and narrow pore size distribution were successfully prepared by a vacuum assisted impregnation method. Both 2-dimensional hexagonal and 3-dimensional cubic Cr 2O 3 mesoporous replicas from SBA-15 and KIT-6 templates exhibit enhanced performance for gas sensors and lithium ion batteries, compared to the bulk Cr 2O 3 counterpart.


Feng Z.,University of Science and Technology Beijing | Liang M.,University of Ottawa | Chu F.,Tsinghua University
Mechanical Systems and Signal Processing | Year: 2013

Nonstationary signal analysis is one of the main topics in the field of machinery fault diagnosis. Time-frequency analysis can identify the signal frequency components, reveals their time variant features, and is an effective tool to extract machinery health information contained in nonstationary signals. Various time-frequency analysis methods have been proposed and applied to machinery fault diagnosis. These include linear and bilinear time-frequency representations (e.g., wavelet transform, Cohen and affine class distributions), adaptive parametric time-frequency analysis (based on atomic decomposition and time-frequency auto-regressive moving average models), adaptive non-parametric time-frequency analysis (e.g., Hilbert-Huang transform, local mean decomposition, and energy separation), and time varying higher order spectra. This paper presents a systematic review of over 20 major such methods reported in more than 100 representative articles published since 1990. Their fundamental principles, advantages and disadvantages, and applications to fault diagnosis of machinery have been examined. Some examples have also been provided to illustrate their performance. © 2013 Elsevier Ltd.


Kan J.,University of Science and Technology Beijing | Chen Y.,University of Jinan | Qi D.,University of Science and Technology Beijing | Liu Y.,CAS Institute of Chemistry | Jiang J.,University of Science and Technology Beijing
Advanced Materials | Year: 2012

A novel sandwich-type tris(phthalocyaninato) europium triple-decker complex bearing peripheral electron-withdrawing groups (see center of figure) is used to fabricate a field-effect transistor by the quasi-Langmuir-Schaefer method. The air-stable, single-component ambipolar OFET device displays the best carrier properties of a device fabricated by solution processing of a single phthalocyanine derivative so far, which makes the complex very promising for applications in nanoelectronics. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Li J.,University of Science and Technology Beijing | Wang Y.,University of Science and Technology Beijing | Chen H.,Tsinghua University | Wan J.,Rochester Institute of Technology
Lab on a Chip - Miniaturisation for Chemistry and Biology | Year: 2014

We present the manipulation of oil, organic and gaseous chemicals by electrowetting-on-dielectric (EWOD) technology using aqueous-shell compound drops. We demonstrate that the transport and coalescence of viscous oil drops, the reaction of bromine with styrene in benzene solution, and the reaction of red blood cells with carbon monoxide bubbles can be accomplished using this method. © the Partner Organisations 2014.


Li M.,University of Science and Technology Beijing | Li D.,Chongqing Three Gorges University | Wang J.,University of Science and Technology Beijing | Zhao C.,Tsinghua University | Zhao C.,Chongqing Three Gorges University
ISA Transactions | Year: 2013

Fractional-order proportional-integral (PI) and proportional-integral- derivative (PID) controllers are the most commonly used controllers in fractional-order systems. However, this paper proposes a simple integer-order control scheme for fractional-order system based on active disturbance rejection method. By treating the fractional-order dynamics as a common disturbance and actively rejecting it, active disturbance rejection control (ADRC) can achieve the desired response. External disturbance, sensor noise, and parameter disturbance are also estimated using extended state observer. The ADRC stability of rational-order model is analyzed. Simulation results on three typical fractional-order systems are provided to demonstrate the effectiveness of the proposed method. © 2013 ISA.


Tu R.,University of Science and Technology Beijing | Liu X.-H.,Tsinghua University | Jiang Y.,Tsinghua University
Energy Conversion and Management | Year: 2014

Rotary wheel dehumidification is an effective air drying method. This paper analyzes the factors influencing the regeneration temperature from the perspective of exergy. When the dehumidification capacity is fixed, there are two main ways to reduce the regeneration temperature. One is to decrease the exergy destruction during heat and mass transfer in the desiccant wheel, and the other is to decrease the thermal exergy obtained by the processed air after dehumidification. For the first way, the exergy destruction is influenced by the uniformity of the heat and mass transfer driving forces in the desiccant wheel, which can be described by the unmatched coefficient ς. The wheel should be evenly divided, and the two streams of air should have the same flow rate to reduce the exergy destruction. The regeneration temperature can be reduced from above 130 °C to below 70 °C when the air is dehumidified from 20 g/kg to 11 g/kg. For the second way, the thermal exergy obtained by the processed air is influenced by the temperature variation range during dehumidification. Multi-stage dehumidification and pre-cooling are effective mode, with required regeneration temperature lower than 40 °C. © 2014 Elsevier Ltd. All rights reserved. 2014 Elsevier Ltd. All rights reserved.


Kan J.,University of Science and Technology Beijing | Wang H.,University of Science and Technology Beijing | Sun W.,University of Science and Technology Beijing | Cao W.,University of Science and Technology Beijing | And 2 more authors.
Inorganic Chemistry | Year: 2013

Employment of the raise-by-one step method starting from M(TClPP)(acac) (acac = monoanion of acetylacetone) and [Pc(OPh)8]M′[Pc(OPh) 8] led to the isolation and free modulation of the two rare-earth ions in the series of four mixed tetrapyrrole dysprosium sandwich complexes {(TClPP)M[Pc(OPh)8]M′[Pc(OPh)8]} [1-4; TClPP = dianion of meso-tetrakis(4-chlorophenyl)porphyrin; Pc(OPh)8 = dianion of 2,3,9,10,16,17,23,24-octa(phenoxyl)phthalocyanine; M-M′ = Dy-Dy, Y-Dy, Dy-Y, and Y-Y]. Single-crystal X-ray diffraction analysis reveals different octacoordination geometries for the two metal ions in terms of the twist angle (defined as the rotation angle of one coordination square away from the eclipsed conformation with the other) between the two neighboring tetrapyrrole rings for the three dysprosium-containing isostructural triple-decker compounds, with the metal ion locating between an inner phthalocyanine ligand and an outer porphyrin ligand with a twist angle of 9.64-9.90 and the one between two phthalocyanine ligands of 25.12-25.30. Systematic and comparative studies over the magnetic properties reveal magnetic-field-induced single-molecule magnet (SMM), SMM, and non-SMM nature for 1-3, respectively, indicating the dominant effect of the coordination geometry of the spin carrier, instead of the f-f interaction, on the magnetic properties. The present result will be helpful for the future design and synthesis of tetrapyrrole lanthanide SMMs with sandwich molecular structures. © 2013 American Chemical Society.


Zhu L.-F.,University of Science and Technology Beijing | Zhang B.-P.,University of Science and Technology Beijing | Zhao X.-K.,University of Science and Technology Beijing | Zhao L.,University of Science and Technology Beijing | And 2 more authors.
Journal of the American Ceramic Society | Year: 2013

(Ba1-xCax)(Ti0.92Sn0.08)O 3 (x = 0.00-0.06 mol) ceramics with a high relative density over 96% were prepared by a conventional sintering method at 1480°C. At room temperature, a polymorphic phase transition from orthorhombic phase to tetragonal phase was confirmed by the XRD patterns in the composition range of 0.04 ≤ x ≤ 0.06. A high piezoelectric coefficient d33 up to 568 pC/N was obtained at x = 0.05 mol, which is higher than the other component of (Ba,Ca)(Ti,Sn)O3 system. At the same time, the corresponding planar electromechanical coupling factor kp, converse piezoelectric coefficient dS/dE, and dielectric constant εr reach 47.7%, 1013 pm/V, and 23000, respectively. These results indicate that the (Ba,Ca)(Ti,Sn)O3 ceramics are a promising candidate to replace for the lead-based piezoelectric materials. © 2012 The American Ceramic Society.


Lan J.-L.,Tsinghua University | Liu Y.-C.,Tsinghua University | Zhan B.,Tsinghua University | Lin Y.-H.,Tsinghua University | And 5 more authors.
Advanced Materials | Year: 2013

A high-performance thermoelectric oxyselenide BiCuSeO ceramic with ZT > 1.1 at 823 K and higher average ZT value (ZTave ≈0.8) is obtained. The heavy doping element and nanostructures can effectively tune its electronic structure, hole concentration, and thermal conductivity, resulting in substantially enhanced mobility, power factor, and thus ZT value. This work provides a path to high-performance thermoelectric ceramics. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Ge Z.-H.,University of Science and Technology Beijing | Zhang B.-P.,University of Science and Technology Beijing | Chen Y.-X.,University of Science and Technology Beijing | Yu Z.-X.,University of Science and Technology Beijing | And 2 more authors.
Chemical Communications | Year: 2011

Polycrystalline Cu1.8S compounds were fabricated by using a combined process of mechanical alloying and spark plasma sintering. The Cu 1.8S sample with a second Cu1.96S phase and a lot of micro pores shows its maximum ZT value 0.5 at 673 K which is the highest value for p-type sulfide thermoelectric materials so far. © The Royal Society of Chemistry 2011.


Zhang Y.,University of Science and Technology Beijing | Li J.,University of Science and Technology Beijing | Kang F.,Tsinghua University | Gao F.,University of Science and Technology Beijing | Wang X.,University of Science and Technology Beijing
International Journal of Hydrogen Energy | Year: 2012

A nanoporous manganese oxide (MnO 2) film was fabricated via a polystyrene templated electrodeposition in the solution containing MnSO 4. The nanoporous MnO 2 film obtained has been characterized by field emission scanning electron microscopy, cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge/discharge methods. The specific capacitance of 1018 F g -1 was observed at a low current density of 500 mA g -1. When the current density increased to 30.0 A g -1, the specific capacitance of 277 F g -1 remained. The high capacitance retention at high rates makes the prepared MnO 2 a promising candidate for supercapacitor applications. © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.


Hou J.,University of Science and Technology Beijing | Hou J.,Tohoku University | Yang C.,University of Science and Technology Beijing | Cheng H.,University of Science and Technology Beijing | And 4 more authors.
Energy and Environmental Science | Year: 2014

Considerable efforts have been made to design and discover photoactive nanostructured (oxy)nitride materials that can be used as photoanodes for photoelectrochemical (PEC) water splitting. However, the high recombination rate of photoexcited electron-hole pairs and the poor photostability have greatly limited their practical applications. Herein, a p-type Cu2O/n-type TaON heterojunction nanorod array passivated with an ultrathin carbon sheath (carbon-Cu2O/TaON) as a surface protection layer was produced via a solution-based process. Due to the shape anisotropy and p-n heterojunction structure, the photocurrent density of carbon-Cu2O/TaON heterojunction nanorod arrays as the integrated photoanode, with a maximum IPCE of 59% at a wavelength of 400 nm, reached 3.06 mA cm-2 under AM 1.5G simulated sunlight at 1.0 V vs. RHE and remained at about 87.3% of the initial activity after 60 min irradiation. Not only is the onset potential negatively shifted but the photocurrent density and photostability are also significantly improved for this photoanode compared to those of TaON and Cu2O/TaON. These improvements are due to a high built-in potential in the p-n heterojunction device that is protected from the electrolyte by being encapsulated in an ultrathin graphitic carbon sheath. Our design introduces material components to provide a dedicated charge-transport pathway, alleviating the reliance on the materials' intrinsic properties, and therefore has the potential to greatly broaden where and how various existing materials can be used in energy-related applications. © 2014 the Partner Organisations.


Ge Z.-H.,University of Science and Technology Beijing | Zhang B.-P.,University of Science and Technology Beijing | Shang P.-P.,University of Science and Technology Beijing | Li J.-F.,Tsinghua University
Journal of Materials Chemistry | Year: 2011

After fabricating Bi2S3 nanorods with preferential (001) orientation by hydrothermal synthesis (HS) using Bi(NO3) 3 and Na2S2O3 as raw materials and ethylenediamine (EDA) as a pH modifier, Bi2S3 bulk materials were consolidated by spark plasma sintering (SPS). A single-phase, rod-like Bi2S3 crystal with a length in range of 2-10 μm and a diameter in range of 100-400 nm was formed by optimizing the hydrothermal process parameters. The rod-like structures were maintained in the Bi2S3 bulk, and as a result the orientation degree of the bulk sample prepared from Bi2S3 nanorods powders reached 0.69, being higher than 0.18 found for mechanical alloying (MA)-derived powder. The measurement of electric transport properties also confirmed that the Bi 2S3 bulk has obvious anisotropy. The electric resistivity normal to the pressing direction is one order higher than that in parallel to the pressing direction due to their anisotropic orientation. The power factor of the bulk sample along the direction perpendicular to the pressing direction is twice higher than that in parallel to the pressing direction, and also higher than the sample using the MA-processed powders. © 2011 The Royal Society of Chemistry.


Liu X.,University of Science and Technology Beijing | Zhang N.,Tsinghua University
Waste Management and Research | Year: 2011

Red mud is a solid waste residue of the digestion of bauxite ores with caustic soda for alumina production. Its disposal remains a worldwide issue in terms of environmental concerns. During the past decades, extensive work has been done by a lot of researchers to develop various economic ways for the utilization of red mud. One of the economic ways is using red mud in cement production, which is also an efficient method for large-scale recycling of red mud. This paper provides a review on the utilization of red mud in cement production, and it clearly points out three directions for the use of red mud in cement production, namely the preparation of cement clinkers, production of composite cements as well as alkali-activated cements. In the present paper, the chemical and mineralogical characteristics of red mud are summarized, and the current progresses on these three directions are reviewed in detail. © The Author(s) 2011.


Li F.,Tsinghua University | Li J.-F.,Tsinghua University | Zhao L.-D.,Northwestern University | Xiang K.,Tsinghua University | And 6 more authors.
Energy and Environmental Science | Year: 2012

This work revealed that BiCuSeO oxyselenide is a potential oxide-based thermoelectric material, whose dimensionless figure of merit (ZT) reaches ∼0.70 at 773 K. High phase-purity BiCuSeO polycrystalline materials with fine grains were synthesized by a facile method combining a solid-state reaction and spark plasma sintering. Purifying the constitutive phase and reducing the grain sizes by introducing a high-energy ball milling process before spark plasma sintering were found to be effective in property enhancement. The resultant single-phased BiCuSeO sample derived from ball-milled powders shows good electrical conductivity above 4.0 × 103 S m-1 and a large Seebeck coefficient above 200 μV K-1. This compound has a low thermal conductivity (∼0.5 W m-1 K-1), which is associated with its low phonon transport speed and Young's modulus. Results indicated that BiCuSeO-based materials are promising for energy conversion applications in the moderate temperature range. © 2012 The Royal Society of Chemistry.


Wang M.-S.,University of Science and Technology Beijing | Fan L.-Z.,University of Science and Technology Beijing | Huang M.,Tsinghua University | Li J.,University of Science and Technology of China | Qu X.,University of Science and Technology Beijing
Journal of Power Sources | Year: 2012

Diatomite, a natural clay mineral, is mainly composed of silica and contains a large number of fine microscopic pores. In the present work, a series of porous Si/C composites are successfully synthesized by employing diatomite as a raw material, followed by low temperature magnesiothermic reduction, impregnation and carbonization of phenolic resin. The obtained Si/C composites are consisted of porous Si coated with a 15 nm thick amorphous layer of carbon. Porous Si/C composites with different ratios of Si and C are investigated as anode materials for Li-ion batteries. The porous Si/C composite containing 33% carbon exhibits the highest reversible capacity of about 1628 mAh g -1 at the first cycle with excellent capacity retention in the following cycles. Moreover, the porous Si/C composites display the excellent rate performance at high current densities such as 1 and 2 A g -1. The optimum electrochemical performance could also be tuned by varying the proportions of porous Si and carbon precursors during the preparation process. The results indicate that the natural pore structures of Si and C are conducive to the electrochemical performance and clay mineral diatomite could be considered as a promising raw material for Si/C composites for lithium-ion batteries. © 2012 Elsevier B.V. All rights reserved.


Liu L.,University of Science and Technology Beijing | Fu L.,Tsinghua University | Jiang Y.,Tsinghua University
Applied Thermal Engineering | Year: 2012

Field test results show that 20%-30% of thermal energy is wasted because of poor heating system regulation in China. In order to solve these problems, a new "wireless on-off control" system for adjusting and metering household heat is proposed. The technology works in the following way: 1) a calorimeter is installed in each building to measure the total heat consumption of the building; 2) on-off valves are installed in each household with an individual indoor temperature control provided. The room temperature can be maintained by controlling the valves according to the on-time ratio which is predicted by the thermal strategies; and 3) the heating cost of each household can be allocated according to the heating area and the accumulative open time of the valve. The proposed technique has been applied in twenty-five residential communities with a total area of 2,500,000 m 2. The test results show that: 1) indoor temperatures were accurately controlled within ±0.5 °C of the set point; 2) the temperature difference in different rooms is less than 1 °C; 3) energy consumption in the households using a controlled system was approximately 30% lower than a similar within a similar building type with an uncontrolled system. © 2011 Published by Elsevier Ltd. All rights reserved.


Xia L.C.,University of Southern California | Ai D.,University of Southern California | Ai D.,University of Science and Technology Beijing | Cram J.,University of Southern California | And 3 more authors.
Bioinformatics | Year: 2013

Motivation: Local similarity analysis of biological time series data helps elucidate the varying dynamics of biological systems. However, its applications to large scale high-throughput data are limited by slow permutation procedures for statistical significance evaluation.Results: We developed a theoretical approach to approximate the statistical significance of local similarity analysis based on the approximate tail distribution of the maximum partial sum of independent identically distributed (i.i.d.) random variables. Simulations show that the derived formula approximates the tail distribution reasonably well (starting at time points > 10 with no delay and > 20 with delay) and provides P-values comparable with those from permutations. The new approach enables efficient calculation of statistical significance for pairwise local similarity analysis, making possible all-to-all local association studies otherwise prohibitive. As a demonstration, local similarity analysis of human microbiome time series shows that core operational taxonomic units (OTUs) are highly synergetic and some of the associations are body-site specific across samples. © 2012 The Author. Published by Oxford University Press. All rights reserved.


Qiao J.W.,University of Science and Technology Beijing | Qiao J.W.,University of Tennessee at Knoxville | Zhang Y.,University of Science and Technology Beijing | Liaw P.K.,University of Tennessee at Knoxville
Intermetallics | Year: 2010

At different strain rates, the stress-flow serrations in the compressive stress-time curves of a Zr-based bulk metallic glass (BMG) exhibit different magnitudes and time scales. A critical strain rate can be identified, at which the serrated flow kinetics is characterized to be homogeneous in both time and magnitude. Below the critical strain rate, the serrations are lack of homogeneous magnitudes and time scales because the excessive elastic energy results in distinct softening within the viscous fluid-like shearing layer due to the adiabatic heating. As a consequence, the tiny disturbances, such as the vibration of test machines, affect the shear banding behavior. A periodic function is established for the critical instability, and two pertinent parameters, the mean stress drop magnitude and the mean waiting time (MWT), can be determined, which may be associated with the deformation micromechanism, the mechanical property, and the glass-forming ability of BMGs. The present approach may provide a new way to study the serration-deformation behavior of BMGs. Crown Copyright © 2010 Published by Elsevier Ltd. All rights reserved.


Xiao X.,University of Science and Technology Beijing | Sun J.,University of Science and Technology Beijing | Sun J.,Guizhou University | Jiang J.,University of Science and Technology Beijing
Chemistry - A European Journal | Year: 2013

A host-guest supramolecular polymer was constructed from cucurbit[6]uril host molecules (orange) and porphyrin guest molecules (red and blue) and its formation depends on host-enhanced hydrogen-bonding interactions in combination with ion-dipole interactions. The polymer is the first structurally characterized cucurbit[n]uril-porphyrin supramolecular polymer. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Zhang D.,Shandong University of Technology | Zhang D.,University of Science and Technology Beijing | Si W.,Shandong University of Technology | Wang P.,Shandong University of Technology | And 2 more authors.
Inorganic Chemistry | Year: 2014

Five new heterobimetallic complexes, namely, {[Ni(L)][Fe(bpb)(CN) 2]}ClO4 (L = 2,12-dimethyl-3,7,11,17-tetraazabicyclo[11.3. 1]heptadeca-1(17),13,15-triene, bpb2- = 1,2-bis(pyridine-2- carboxamido)benzenate) (1), {[Ni(L)]3[M(CN)6] 2}·7H2O (M = Fe (2), Cr (3)), {[Ni(L)] 2[Mo(CN)8]}·CH3CN·13H 2O (4), and {[Ni(L)]2[W(CN)8]}·16H 2O (5), were assembled from the polyaza macrocycle nickel(II) compound and five cyanidometalate precursors containing different numbers of cyanide groups. Single-crystal X-ray diffraction analysis reveals their different structure ranging from a cyanide-bridged cationic polymeric single chain for 1, a two-dimensional network for 2 and 3, and a three-dimensional network for 4 and 5. In addition, a systematic investigation over the magnetic properties of 1-3 indicates the ferromagnetic magnetic coupling between neighboring Fe(III)/Cr(III) and Ni(II) ions through the bridging cyanide group. For complex 1, the magnetic susceptibility has been simulated by the Seiden model using the Hamiltonian H = -J∑i=0 NS iSi+1, leading to the magnetic coupling constant of J = 3.67 cm-1. The two-dimensional magnetic complexes exhibit three-dimensional magnetic ordering behavior with a magnetic phase transition temperature of TC = 4.0 K for 2 and TN = 6.0 K for 3, respectively. © 2014 American Chemical Society.


Si X.-S.,HIGH-TECH | Si X.-S.,Tsinghua University | Wang W.,University of Science and Technology Beijing | Hu C.-H.,HIGH-TECH | And 3 more authors.
IEEE Transactions on Reliability | Year: 2012

Remaining useful life estimation is central to the prognostics and health management of systems, particularly for safety-critical systems, and systems that are very expensive. We present a non-linear model to estimate the remaining useful life of a system based on monitored degradation signals. A diffusion process with a nonlinear drift coefficient with a constant threshold was transformed to a linear model with a variable threshold to characterize the dynamics and nonlinearity of the degradation process. This new diffusion process contrasts sharply with existing models that use a linear drift, and also with models that use a linear drift based on transformed data that were originally nonlinear. Both existing models are based on a constant threshold. To estimate the remaining useful life, an analytical approximation to the distribution of the first hitting time of the diffusion process crossing a threshold level is obtained in a closed form by a time-space transformation under a mild assumption. The unknown parameters in the established model are estimated using the maximum likelihood estimation approach, and goodness of fit measures are applied. The usefulness of the proposed model is demonstrated by several real-world examples. The results reveal that considering nonlinearity in the degradation process can significantly improve the accuracy of remaining useful life estimation. © 2006 IEEE.


Chen J.,University of Science and Technology Beijing | Yin Y.,University of Science and Technology Beijing | Sun F.,Tsinghua University
Asian Journal of Control | Year: 2012

This paper presents the novel results for stabilizing uncertain standard discrete-time fuzzy singularly perturbed systems (SPSs) via a state feedback control law. Two standard discrete-time fuzzy SPSs are constructed firstly by using the Takagi-Sugeno (T-S) fuzzy model. Based on a matrix spectral norm approach, two new ε-dependent stability conditions are derived, which guarantee the resulting closed-loop systems are asymptotically stable. The gains of controllers are obtained by solving a set of ε-dependent linear matrix inequalities (LMIs). In contrast to the existing results, the proposed methods have two advantages: (i) the designed controllers can overcome the external disturbances and parameter uncertainty; and (ii) the upper bound of ε is improved, especially it is not required to be smaller than one. Examples are provided to illustrate the reduced conservatism of our results. Copyright © 2011 John Wiley and Sons Asia Pte Ltd.


Jiang R.,Tsinghua University | Gan M.,University of Science and Technology Beijing | He P.,Tsinghua University
BMC Systems Biology | Year: 2011

Motivation: The inference of genes that are truly associated with inherited human diseases from a set of candidates resulting from genetic linkage studies has been one of the most challenging tasks in human genetics. Although several computational approaches have been proposed to prioritize candidate genes relying on protein-protein interaction (PPI) networks, these methods can usually cover less than half of known human genes.Results: We propose to rely on the biological process domain of the gene ontology to construct a gene semantic similarity network and then use the network to infer disease genes. We show that the constructed network covers about 50% more genes than a typical PPI network. By analyzing the gene semantic similarity network with the PPI network, we show that gene pairs tend to have higher semantic similarity scores if the corresponding proteins are closer to each other in the PPI network. By analyzing the gene semantic similarity network with a phenotype similarity network, we show that semantic similarity scores of genes associated with similar diseases are significantly different from those of genes selected at random, and that genes with higher semantic similarity scores tend to be associated with diseases with higher phenotype similarity scores. We further use the gene semantic similarity network with a random walk with restart model to infer disease genes. Through a series of large-scale leave-one-out cross-validation experiments, we show that the gene semantic similarity network can achieve not only higher coverage but also higher accuracy than the PPI network in the inference of disease genes.Contact: ruijiang@tsinghua.edu.cn . © 2011 Jiang et al; licensee BioMed Central Ltd.


Zhao J.-J.,Tsinghua University | Duan Y.-Y.,Tsinghua University | Wang X.-D.,University of Science and Technology Beijing | Wang B.-X.,Tsinghua University
International Journal of Heat and Mass Transfer | Year: 2011

A model based on the augmented Young-Laplace equation and the Clausius-Clapeyron equation was developed to describe the extended evaporating meniscus in a microchannel. The effects of the adsorbed film thickness, channel height and temperature-dependent thermophysical properties of the fluid are included in the model at wall superheats up to 50 K. The liquid flow is coupled with the vapor flow to obtain the mass transport across the liquid-vapor interface. The results show that the constant thermophysical property model greatly overestimates the liquid pressure difference and the total thin film heat transfer rate at higher superheats compared with the variable thermophysical property model. The adsorbed film thickness, which is controlled by the disjoining pressure limit, reaches a minimum near about 20 K superheat for water. The maximum film curvature and liquid pressure difference then decrease at superheats larger than 20 K. The effects of the capillary pressure limit produced by the channel height can be reduced by increasing the superheat. © 2010 Elsevier Ltd. All rights reserved.


Gan M.,University of Science and Technology Beijing | Jiang R.,Tsinghua University
Decision Support Systems | Year: 2013

Recommender systems have become more and more indispensable in both commercial and research communities, due to the increasingly serious problem of information overload accompanying the rapid development of the internet technology in the recent years. As one of the dominant branches, collaborative filtering approaches base on similarities of user preferences in historical data have achieved remarkable successes in producing personalized recommendations. Nevertheless, the existence of popular objects may adversely influence the correct scoring of candidate objects and further yield unreasonable recommendation results. Meanwhile, it has been increasingly recognized that the gains of the recommendation accuracy are often accompanied by the losses of the diversity, yielding the accuracy-diversity dilemma for a personalized recommender system. In order to overcome these limitations while keeping a reasonable tradeoff between the accuracy and the diversity, we propose in this paper a method called PLUS (Power Law adjustments of User Similarities) to achieve personalized recommendations via the introduction of a power function to adjust user similarity scores, for the purpose of reducing adverse effects of popular objects in the user-based collaborative filtering framework. We perform a series of large scale validation experiments on two real data sets (MovieLens and Netflix) and compare the performance of our approach against that of an ordinary collaborative filtering method. Results show that our method outperforms the existing method not only in recommendation accuracy measured by the mean rank ratio and the recall enhancement, but also in recommendation diversity quantified by the mean personality and the mean novelty. © 2013 Elsevier B.V.


Jiang Y.,University of Science and Technology Beijing | Guan L.,Aerospace Research Institute of Materials And Processing Technology | Tang G.,Tsinghua University
Journal of Alloys and Compounds | Year: 2016

The recrystallized microstructure and texture of AZ31 Mg alloy after rapid thermal annealing (RTA) was investigated. A mathematical model of RTA temperature of AZ31 Mg alloy was established based on the thermal equilibrium theory. The two double-peak textures with basal poles tilted 5-10° away from the normal direction towards the rolling direction or towards the transverse direction were formed in the AZ31 alloy during RTA. The tilted basal texture was originated from recrystallized grains formed along grain boundaries for the low rolling reduction or recrystallized grains formed within the shear bands and twins for the high rolling reduction. During RTA, the recrystallization mechanism was sensitive to the previous rolling reduction and the annealing temperature, and the mechanisms of the microstructure and texture evolution of the AZ31 alloy during RTA were discussed. © 2015 Elsevier B.V.


Si X.-S.,HIGH-TECH | Si X.-S.,Tsinghua University | Wang W.,University of Science and Technology Beijing | Hu C.-H.,HIGH-TECH | And 2 more authors.
Mechanical Systems and Signal Processing | Year: 2013

Remaining useful life estimation (RUL) is an essential part in prognostics and health management. This paper addresses the problem of estimating the RUL from the observed degradation data. A Wiener-process-based degradation model with a recursive filter algorithm is developed to achieve the aim. A novel contribution made in this paper is the use of both a recursive filter to update the drift coefficient in the Wiener process and the expectation maximization (EM) algorithm to update all other parameters. Both updating are done at the time that a new piece of degradation data becomes available. This makes the model depend on the observed degradation data history, which the conventional Wiener-process-based models did not consider. Another contribution is to take into account the distribution in the drift coefficient when updating, rather than using a point estimate as an approximation. An exact RUL distribution considering the distribution of the drift coefficient is obtained based on the concept of the first hitting time. A practical case study for gyros in an inertial navigation system is provided to substantiate the superiority of the proposed model compared with competing models reported in the literature. The results show that our developed model can provide better RUL estimation accuracy. © 2012 Elsevier Ltd. All rights reserved.


Wang H.,University of Science and Technology Beijing | Kobayashi N.,Tohoku University | Jiang J.,University of Science and Technology Beijing
Chemistry - A European Journal | Year: 2012

Quintuple-decker sandwich: Homoleptic pentakis(2,3,9,10,16,17,23,24- octa(butyloxy)phthalocyaninato) lanthanide-cadmium quintuple-decker complexes were isolated and structurally characterized. They represent the first example of sandwich-type stacked tetrapyrrole-metal complexes with five decks (see figure; the tetrapyrrole molecules are represented by the blue/pink discs, TCB=1,2,4-trichlorobenzene). Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Li J.-F.,Tsinghua University | Liu W.-S.,Tsinghua University | Liu W.-S.,University of Science and Technology Beijing | Zhao L.-D.,Tsinghua University | And 3 more authors.
NPG Asia Materials | Year: 2010

Thermoelectric effects enable direct conversion between thermal and electrical energy and provide an alternative route for power generation and refrigeration. Over the past ten years, the exploration of high-performance thermoelectric materials has attracted great attention from both an academic research perspective and with a view to industrial applications. This review summarizes the progress that has been made in recent years in developing thermoelectric materials with a high dimensionless figure of merits (ZT) and the related fabrication processes for producing nanostuctured materials. The challenge to develop thermoelectric materials with superior performance is to tailor the interconnected thermoelectric physical parameters - electrical conductivity, Seebeck coefficient and thermal conductivity - for a crystalline system. Nanostructures provide a chance to disconnect the linkage between thermal and electrical transport by introducing some new scattering mechanisms. Recent improvements in thermoelectric efficiency appear to be dominated by efforts to reduce the lattice thermal conductivity through nanostructural design. The materials focused in this review include Bi-Te alloys, skutterudite compounds, Ag-Pb-Sb-Te quaternary systems, half-Heusler compounds and some high-ZT oxides. Possible future strategies for developing thermoelectric materials are also discussed. © 2011 Tokyo Institute of Technology.


Qiao J.W.,University of Science and Technology Beijing | Liaw P.K.,University of Tennessee at Knoxville | Zhang Y.,University of Science and Technology Beijing
Scripta Materialia | Year: 2011

The maximum strength of monolithic bulk metallic glasses (BMGs) at 77 K is predicted according to the proposed equation, σmax.77= 55ρ0MΔTg+Δσ. For the dendrite-reinforced BMG-matrix composites, a distinctly increased maximum strength is seen; however, a ductile-to-brittle transition seems to be present when lowering the temperature to 77 K, which is caused by the ductile-to-brittle transition of the dendrites. The crack, initiated within the dendrites, may extend to the glass matrix at low temperatures. As a result, early failure of the composites occurs. © 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.


Patent
Princeton University, Tsinghua University, University of Science and Technology Beijing | Date: 2015-08-18

Emulsion breaking and phase separation is achieved by droplet adhesion. An emulsion breaking device includes a channel having distinct adjacent zones with distinctly different surface wettability characteristics, namely, solvophilic and solvophobic surfaces. The device is positioned such that the upstream portion of the device is configured to be wetted by the continuous phase of the emulsion, and the downstream portion of the device is configured to be wetted by the dispersed phase of the emulsion. As the emulsion flows from the upstream zone to the downstream zone, the change in surface wettability characteristics promotes adhesion of the dispersed phase as the dispersed phase wets the surface of the downstream portion of the channel, which results in breaking of the emulsion. Subsequent collection of the broken emulsion in a collection vessel results in separation of the disparate phases to facilitate their recapture and recycling.


Fan L.-Z.,University of Science and Technology Beijing | Liu J.-L.,University of Science and Technology Beijing | Ud-Din R.,University of Science and Technology Beijing | Ud-Din R.,Pakistan Institute of Nuclear Science and Technology | And 2 more authors.
Carbon | Year: 2012

Graphene nanosheets were prepared by reducing graphite oxide with hydrazine hydrate. The effects of reduction time on the structure and morphology of graphene nanosheets have been investigated. Their electrochemical performance in aqueous and organic electrolytes was also analyzed. With an increase of reduction time, the C and N contents of graphene nanosheets increased, while the specific surface areas and the specific capacitances decreased. Changes in reduction time produced a significant effect on the numbers as well as the types of oxygen and nitrogen functionalities. The graphene nanosheets, prepared by using a reduction time of 30 min have the highest specific capacitance of 192 F g -1 in a 6 mol L -1 KOH electrolyte. All prepared graphene nanosheets have a good rate performance and cycle stability. © 2012 Elsevier Ltd. All rights reserved.


News Article | January 2, 2016
Site: www.greencarcongress.com

« Visteon showcasing advanced gesture recognition and HUD technologies at CES | Main | Fulcrum BioEnergy files LCFS application for municipal solid waste to FT diesel pathway with low CI of 37.47 g/MJ » Researchers at Tsinghua University, with colleagues from the University of Science and Technology Beijing, have discovered that the multi-reversible magnetization of ferromagnetic material can be controlled via the lithiation/delithiation reaction in a Li-ion battery by varying the discharge–charge potential at room temperature. This phenomenon couples magnetism and electrochemistry, and enables precise quantitative magnetization manipulation using an electrochemical method. An open-access paper on their discovery is published in the ACS journal Nano Letters. In their paper, they reported achieving reversible manipulation of magnetism over 3 orders of magnitude by controlling the lithiation/delithiation of a nanoscale α-Fe O -based electrode. The process was completed rapidly under room-temperature conditions. Our work reveals that magnetic properties are linked to the voltage control of LIBs. The concept of tuning physical properties using battery cycling clearly has strong potential because hundreds of active materials have already been developed as LIB electrodes. Our results indicate that in addition to energy storage LIBs, which have been under continuous development for several decades, provide exciting opportunities for the multireversible magnetization of magnetic fields.


Yan P.,CAS Institute of Automation | Liu D.,University of Science and Technology Beijing | Wang D.,CAS Institute of Automation | Ma H.,CAS Institute of Automation
Neurocomputing | Year: 2016

In this paper, we develop a novel data-driven multivariate nonlinear controller design method for multi-input-multi-output (MIMO) nonlinear systems via virtual reference feedback tuning (VRFT) and neural networks. To the best of authors' knowledge, it is the first time to introduce VRFT to MIMO nonlinear systems in theory. Unlike the standard VRFT for linear systems, we restate the model reference control problem with time-domain model in the absence of transfer functions and simplify the objective function of VRFT without a linear filter. Then, we prove that the objective function of VRFT reaches the minimum at the same point as the optimization problem of model reference control and give the relationship between the bounds of the two optimization problems of model reference control and VRFT. A three-layer neural network is used to implement the developed method. Finally, two simulations are conducted to verify the validity of our method. © 2015 Elsevier B.V.


Song R.,University of Science and Technology Beijing | Wei Q.,CAS Institute of Automation | Sun Q.,Northeastern University China
Neurocomputing | Year: 2015

In this paper, a novel adaptive dynamic programming (ADP) algorithm is developed to solve the nearly optimal finite-horizon control problem for a class of deterministic nonaffine nonlinear time-delay systems. The idea is to use ADP technique to obtain the nearly optimal control which makes the optimal performance index function close to the greatest lower bound of all performance index functions within finite time. The proposed algorithm contains two cases with respective different initial iterations. In the first case, there exists control policy which makes arbitrary state of the system reach to zero in one time step. In the second case, there exists a control sequence which makes the system reach to zero in multiple time steps. The state updating is used to determine the optimal state. Convergence analysis of the performance index function is given. Furthermore, the relationship between the iteration steps and the length of the control sequence is presented. Two neural networks are used to approximate the performance index function and compute the optimal control policy for facilitating the implementation of ADP iteration algorithm. At last, two examples are used to demonstrate the effectiveness of the proposed ADP iteration algorithm. © 2014 Elsevier B.V.


Zhang Y.,University of Science and Technology Beijing | Pang X.,University of Science and Technology Beijing | Qu S.,University of Science and Technology Beijing | Li X.,China Petroleum Pipeline Engineering Corporation | And 2 more authors.
Corrosion Science | Year: 2012

The corrosion behaviour of X65 pipeline steel at various temperatures for different immersion time under low CO 2 partial pressure and supercritical CO 2 condition were investigated by weight loss measurements and surface analysis techniques. By comparing the characteristics of CO 2 corrosion product scale formed under experimental conditions and the variation rule of corrosion rate with temperature, the CO 2 corrosion mechanism under low partial pressure and supercritical condition was studied. To explain the big difference of corrosion rate between low CO 2 partial pressure and supercritical CO 2 condition, thermodynamic calculation of the solubility of CO 2 in H 2O were discussed. © 2012 Elsevier Ltd.


Tutuncu G.,University of Florida | Damjanovic D.,Ecole Polytechnique Federale de Lausanne | Chen J.,University of Science and Technology Beijing | Jones J.L.,University of Florida
Physical Review Letters | Year: 2012

In ferroic materials, the dielectric, piezoelectric, magnetic, and elastic coefficients are significantly affected by the motion of domain walls. This motion can be described as the propagation of a wall across various types and strengths of pinning centers that collectively constitute a force profile or energetic landscape. Biased domain structures and asymmetric energy landscapes can be created through application of high fields (such as during electrical poling), and the material behavior in such states is often highly asymmetric. In some cases, this behavior can be considered as the electric analogue to the Bauschinger effect. The present Letter uses time-resolved, high-energy x-ray Bragg scattering to probe this asymmetry and the associated deaging effect in the ferroelectric morphotropic phase boundary composition 0.36BiScO 3-0.64PbTiO 3. © 2012 American Physical Society.


Ding X.F.,University of Science and Technology Beijing | Lin J.P.,University of Science and Technology Beijing | Zhang L.Q.,University of Science and Technology Beijing | Su Y.Q.,Harbin Institute of Technology | Chen G.L.,University of Science and Technology Beijing
Acta Materialia | Year: 2012

The lamellar microstructure of TiAl-Nb alloys with and without low boron additions is controlled using double directional solidification (DS). In alloys without the addition of boron, the β phase is seeded during double DS. Complete peritectic transformation occurs in both the dendritic and interdendritic regions, which can lead to the successful alignment of both the high-temperature α phase and the lamellar microstructures. Well-aligned lamellar microstructures can be easily achieved if the alloy composition is close to the peritectic point on the hypo-peritectic side. In alloys with low boron additions, however, the competitive growth of the α phase breaks the continuity of the lamellar microstructure in the region ahead of stable growth, which finally results in columnar grain coarsening and unsuccessful alignment of the lamellar microstructures. © 2011 Published by Elsevier Ltd. on behalf of Acta Materialia Inc. All rights reserved.


Niu H.Z.,Harbin Institute of Technology | Chen Y.Y.,Harbin Institute of Technology | Kong F.T.,Harbin Institute of Technology | Lin J.P.,University of Science and Technology Beijing
Intermetallics | Year: 2012

A novel high Nb, low Al contained TiAl alloy Ti-43Al-6Nb-1B (at %) was fabricated by induction skull melting (ISM) technique. The as-cast alloy exhibits fully lamellar (FL) microstructure with mean colony size of 90 μm. By means of thermophysical simulation, the hot deformation mechanism at 1250 °C is concluded as dislocation slip and twinning in γ phase; bending, rotating and elongation of lamellar colonies are the primary deformation modes. A large-size TiAl pancake was successfully produced by triple-step canned forging at 1250 °C. The forged alloy displays duplex (DP) microstructure consisting of elongated lamellar colonies and γ grains. Typical DP and FL microstructures were further obtained by different heat treatments. The tensile strength increases rapidly from 670 MPa in as-cast state to 975 MPa in as-forged condition at room temperature, with elongation increasing from 0.4% to 1.5%. The as-forged alloy maintains strength higher than 950 MPa until 750 °C; also the DP and FL materials hold excellent strength more than 830 MPa and 770 MPa respectively. The superior tensile properties after forging are mainly ascribed to the microstructure refinement and homogenization, the lamellar spacing reducing, as well as the low Al and relatively low Nb additions in this novel high Nb containing TiAl alloy. Crown Copyright © 2012 Published by Elsevier Ltd. All rights reserved.


Wang X.,University of Science and Technology Beijing | Wang Q.,University of Science and Technology Beijing | Wang S.,Chinese Research Academy of Environmental Sciences | Li F.,Chinese Research Academy of Environmental Sciences | Guo G.,Chinese Research Academy of Environmental Sciences
Bioresource Technology | Year: 2012

Four biopiles were constructed for the bioremediation of total petroleum hydrocarbons (TPHs) in aged oily sludge by indigenous microorganisms. Three biopiles were treated with bulking agent, nutrients or their combination with the fourth pile serving as the control. Responses of microbial community level physiological profiles (CLPPs) to these biostimulation strategies were estimated, and variances among three layers within each biopile were evaluated. Microbial metabolic activity and diversity and the numbers of two species of bacteria were significantly enhanced by the addition of bulking agent, which also made the layers more homogeneous. In contrast, the application of large amounts of nutrients had a suppressing effect on the microbes. After 220. days, 49.62% of TPHs were removed from the middle layer of the bulking agent pile, whereas only 20.44% were removed from the inner layer of the control. This study aims to provide experience to improve the remediation efficiency of future investigations. © 2012.


Ding S.X.,University of Duisburg - Essen | Yin S.,Harbin Institute of Technology | Peng K.,University of Science and Technology Beijing | Hao H.,University of Duisburg - Essen | Shen B.,University of Duisburg - Essen
IEEE Transactions on Industrial Informatics | Year: 2013

In this paper, a data-driven scheme of key performance indicator (KPI) prediction and diagnosis is developed for complex industrial processes. For static processes, a KPI prediction and diagnosis approach is proposed in order to improve the prediction performance. In comparison with the standard partial least squares (PLS) method, the alternative approach significantly simplifies the computation procedure. By means of a data-driven realization of the so-called left coprime factorization (LCF) of a process, efficient KPI prediction, and diagnosis algorithms are developed for dynamic processes, respectively, with and without measurable KPIs. The proposed KPI prediction and diagnosis scheme is finally applied to an industrial hot strip mill, and the results demonstrate the effectiveness of the proposed scheme. © 2013 IEEE.


Chen J.,University of Science and Technology Beijing | Nittala K.,University of Florida | Forrester J.S.,University of Florida | Jones J.L.,University of Science and Technology Beijing | And 3 more authors.
Journal of the American Chemical Society | Year: 2011

PbTiO3-based compounds are well-known ferroelectrics that exhibit a negative thermal expansion more or less in the tetragonal phase. The mechanism of negative thermal expansion has been studied by high-temperature neutron powder diffraction performed on two representative compounds, 0.7PbTiO3 - 0.3BiFeO3 and 0.7PbTiO3 - 0.3Bi(Zn1/2Ti1/2)O3, whose negative thermal expansion is contrarily enhanced and weakened, respectively. With increasing temperature up to the Curie temperature, the spontaneous polarization displacement of Pb/Bi (|zPb/Bi) is weakened in 0.7PbTiO3 - 0.3BiFeO3 but well-maintained in 0.7PbTiO3 - 0.3Bi(Zn1/2Ti1/2)O3. There is an apparent correlation between tetragonality (c/a) and spontaneous polarization. Direct experimental evidence indicates that the spontaneous polarization originating from Pb/Bi - O hybridization is strongly associated with the negative thermal expansion. This mechanism can be used as a guide for the future design of negative thermal expansion of phase-transforming oxides. © 2011 American Chemical Society.


Wang Y.,University of Science and Technology Beijing | Wang X.,University of Science and Technology Beijing | Jiang X.,Harbin Institute of Technology
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2015

A theory for nonlinear excitations in quantum plasmas is presented for narrow-gap semiconductors by considering the combined effects of quantum and pseudorelativity. The system is governed by a coupled Klein-Gordon equation for the collective wave functions of the conduction electrons and Poisson's equation for the electrostatic potential. This gives a closed system, including the effects of charge separation, quantum tunneling, and pseudorelativity. By choosing the typical parameters of semiconductor InSb, the quasistationary soliton solution, which is a multipeaked dark soliton, is obtained numerically and shows depleted electron densities correlated with a localized potential. The dynamical simulation result shows that the dark soliton is stable and has a multipeaked profile, which is consistent with the quasistationary solution. The present model and results may be useful in understanding the nonlinear properties of semiconductor plasma on an ultrafast time scale. © 2015 American Physical Society.


Zhang Z.-H.,Beijing Institute of Technology | Zhang Z.-H.,Impact Lab | Liu Z.-F.,Beijing Institute of Technology | Lu J.-F.,Beijing Institute of Technology | And 4 more authors.
Scripta Materialia | Year: 2014

Typical sintering experiments were conducted to understand the spark plasma sintering (SPS) mechanisms. Based on the results of the direct visual observations and characteristic microstructure analysis, we believe that spark discharge does indeed occur during the SPS process. The high-temperature spark plasma could be generated in the microgaps due to the discharge effect. Fast and efficient sintering can be achieved under the combined action of spark discharge, Joule heating, electrical diffusion and plastic deformation effect in the SPS process. © 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.


Li H.,Harbin Institute of Technology | Lan C.M.,University of Science and Technology Beijing | Ju Y.,China University of Mining and Technology | Li D.S.,Dalian University of Technology
Journal of Bridge Engineering | Year: 2012

Corroded cables from a cable-stayed bridge in China that had been in service for 18years were employed to investigate the basic mechanical properties and residual fatigue life of wires and cables. First, the wires were randomly selected from the cables near the bottom anchorages and cut into segments as test specimens. The extent of corrosion of the wires was experimentally investigated. A tensile loading test was conducted on the wires to obtain the mechanical properties of the corroded single wires. The fatigue life of the corroded single wires was experimentally studied, and a dramatic degradation in fatigue life was observed. This phenomenon was interpreted using SEM images. Fatigue tests on two corroded cables were also conducted, and the test results indicated that the fatigue life of the cables had also decreased dramatically. A MonteCarlo simulation was conducted to obtain the fatigue life of cables. The simulation results indicated that the fatigue life of a cable was controlled by the small fraction of wires in the cable with the shortest fatigue lives. The fatigue life of a cable at a certain failure probability was dependent on the number of wires in the cable, but the mean fatigue life of a cable was not affected by the number of wires in the cable. © 2012 American Society of Civil Engineers.


Yin X.,University of Science and Technology Beijing | Yin X.-C.,University of Science and Technology Beijing | Hao H.-W.,CAS Institute of Automation | Iqbal K.,University of Science and Technology Beijing
Proceedings - International Conference on Pattern Recognition | Year: 2012

Text localization in natural scene images is an important prerequisite for many content-based image analysis tasks. In this paper, we proposed a novel and effective approach to accurately localize scene texts. Firstly, Maximally stable extremal regions(MSER) are extracted as letter candidates. Secondly, after elimination of non-letter candidates by using geometric information, candidate regions are constructed by grouping similar letter candidates using disjoint set. Candidate region features based on horizontal and vertical variances, stroke width, color and geometry are extracted. An AdaBoost classifier is built from these features and text regions are identified. The overall system is evaluated on the ICDAR 2011 competition dataset and the experimental results show that the proposed algorithm yields high precision and recall compared with the latest published algorithms. © 2012 ICPR Org Committee.


Ding H.,University of Science and Technology Beijing | Long Y.,Qingdao University | Shen J.,Suzhou University of Science and Technology | Wan M.,CAS Institute of Chemistry
Journal of Physical Chemistry B | Year: 2010

This article exposes a facial approach to self-assemble polyaniline (PANI) nanowires with thin diameter (∼10 nm) and high room-temperature conductivity (∼10° S/cm) by using Fe2(SO4)3 as a binary oxidant and dopant. The new method not only saves hard templates and postprocess of template removal but also simplifies the reagent. Formation yield, diameter, and room-temperature conductivity of the nanowires are affected by the molar ratios of Fe2(SO4)3 to aniline. The low redox potential of Fe2(SO4)3 not only results in a thinner diameter and higher room-temperature conductivity (10° S/cm) of the nanowires but also shows a much weaker temperature dependence of resistivity and smaller characteristic Mott temperature (T0 = 2.5 x 103 K). © 2010 American Chemical Society.


Chen S.,University of Science and Technology Beijing | Chen S.,Harbin Institute of Technology | Li L.,Harbin Institute of Technology | Chen Y.,Harbin Institute of Technology | Huang J.,University of Science and Technology Beijing
Journal of Alloys and Compounds | Year: 2011

Joining mechanism of Ti/Al dissimilar alloys was investigated during laser welding-brazing process with automated wire feed. The microstructures of fusion welding and brazing zones were analysed in details by transmission electron microscope (TEM). It was found that microstructures of fusion welding zone consist of α-Al grains and ternary near-eutectic structure with α-Al, Si and Mg2Si. Interfacial reaction layers of brazing joint were composed of α-Ti, nanosize granular Ti7Al 5Si12 and serration-shaped TiAl3. For the first time, apparent stacking fault structure in intermetallic phase TiAl3 was found when the thickness of the reaction layer was very thin (approximately less than 1 μm). Furthermore, crystallization behavior of fusion zone and mechanism of interfacial reaction were discussed in details. © 2010 Elsevier B.V. All rights reserved.


Li W.,École Centrale Paris | He D.,École Centrale Paris | Dang Z.,University of Science and Technology Beijing | Bai J.,École Centrale Paris
Composites Science and Technology | Year: 2014

Damage sensing of the fiber-reinforced structural composites have attracted a lot of attention. In this work, a small amount of carbon nanotubes (CNT)-Al2O3 hybrids are introduced into the woven glass fabric reinforced epoxy composites and serve as in situ sensor to monitor the damage initiation and propagation under mechanical loading. The hybrids with CNTs grown on the Al2O3 micro-spheres are synthesized by chemical vapor deposition. The addition of 0.5wt.% CNT-Al2O3 increased ac electrical conductivity of the glass fabric/epoxy composites at 103Hz 4-5 orders of magnitude in both in-plane and through-thickness directions. The electrical resistance of the composites was in situ measured under quasi-static tensile testing. With the increase of strain, the resistance response could be classified into three distinguished stages, corresponding to various damage modes (microcracks, fiber/matrix interfacial debonding, transverse cracks, delamination, fiber breakage, etc.). © 2014.


Liu Z.Y.,University of Science and Technology Beijing | Liu Z.Y.,Nanchang Hangkong University | Li X.G.,University of Science and Technology Beijing | Cheng Y.F.,University of Calgary
Corrosion Science | Year: 2012

This paper investigates mechanistically stress corrosion cracking (SCC) of an X70 pipeline steel that is under cathodic protection (CP) in a near-neutral pH solution. It was found that there is a critical potential range, i.e., -730 and -920mV SCE, where the steel is in a non-equilibrium electrochemical state, and anodic dissolution (AD) reaction may occur when the steel is polarized cathodically. When the applied potential is more positive than this range, SCC is AD-based; while the applied potential is more negative, SCC of pipelines is under hydrogen embrittlement (HE) mechanism. When the polarization potential is within the range, SCC of the steel is under the combined effect of AD and HE. Therefore, AD may still occur on pipeline steel that is under CP with the potential within this critical range, contributing to the cracking process. © 2011 Elsevier Ltd.


Li W.,École Centrale Paris | Dichiara A.,École Centrale Paris | Zha J.,University of Science and Technology Beijing | Su Z.,Hong Kong Polytechnic University | Bai J.,École Centrale Paris
Composites Science and Technology | Year: 2014

The multi-scale hybridization of carbon nanotubes (CNTs) with micro-particles in polymers offers new opportunity to develop high performance multifunctional composites. In this study, hybrid fillers comprised of CNTs directly grown on alumina micro-spheres by chemical vapor deposition were incorporated into epoxy matrix that was then reinforced with woven glass fibers. The hierarchical composites with 0.5. wt.% hybrid loading was observed to exhibit an improvement of 19% and 11% in flexural modulus and interlaminar shear strength, respectively. Moreover, the glass transition temperature was increased by 15. °C and the storage modulus at 50. °C was enhanced by 20%. These reinforcements are mainly attributed to the improvements of matrix properties resulted from the good dispersion of hybrids and their hindering effect on the formation and development of matrix cracks. This study reveals the potential in improving mechanical and thermo-mechanical properties of the fiber-reinforced composite by using multi-scale carbon hybrids. © 2014 Elsevier Ltd.


Zha J.-W.,University of Science and Technology Beijing | Li W.-K.,École Centrale Paris | Liao R.-J.,Chongqing University | Bai J.,École Centrale Paris | And 3 more authors.
Journal of Materials Chemistry A | Year: 2013

Aiming to enhance the positive temperature coefficient (PTC) effect of resistance, immiscible polymer blends [ultra-high molecular weight polyethylene (UHMWPE)/polyvinylidene fluoride (PVDF) = 4 : 1] based composites containing hybrid fillers [carbon nanotubes (CNTs) and carbon black (CB)] were explored. The conductive fillers were premixed with UHMWPE by melt-mixing and then PVDF was introduced into the blends. The preferential distribution of conductive fillers in the UHMWPE phase was desirably observed. Besides decreasing the electrical resistivity of the single UHMWPE based PTC materials, the addition of PVDF with much higher melting point could improve the temperature range of the PTC materials, which is important for their potential applications. A remarkable synergetic effect arising from the combination of CB and CNTs with different geometric structures and aspect ratios on improving the PTC behavior was demonstrated. By introducing 0.5 vol% CNTs into the 4 vol% CB filled UHMWPE 0.8-PVDF0.2 composites, the initial resistivity decreased by about two orders of magnitude and the PTC intensity (PTCI) increased by about 30%. Owing to the 3-dimensional conductive networks provided by tube-shaped CNTs and spherical CB and the high viscosity of the UHMWPE matrix, favorable PTC repeatability was also achieved. This journal is © 2013 The Royal Society of Chemistry.


Yuan J.-K.,École Centrale Paris | Yao S.-H.,Joseph Fourier University | Dang Z.-M.,University of Science and Technology Beijing | Sylvestre A.,Joseph Fourier University | And 2 more authors.
Journal of Physical Chemistry C | Year: 2011

Carbon nanotubes have unprecedented electronic properties and large specific areas as nanoscale fillers, but their potential has not been fully realized in polymer composites due to the poor dispersion and weak interfacial interaction. Here, we present a robust and simple procedure to prepare polymer-based composites with a remarkable molecular level interaction at interfaces through melt-mixing pristine multiwalled carbon nanotubes (MWNTs) within poly(vinylidene fluoride) (PVDF) matrix. The interfacial interaction is confirmed by Raman spectroscopy as well as the formation of much thin PVDF layer on individual MWNT. The resultant nanocomposite with a huge interfacial area possesses a giant dielectric permittivity (3800) of 3 orders of magnitude higher than the PVDF matrix, while retaining a low conductivity level (6.3 A - 10 a-5 S.ma-1) and an excellent thermal stability. These results could be explained by a reinforced Maxwell-Wagner-Sillars (MWS) effect based on the remarkable molecular level interaction. © 2011 American Chemical Society.


Wang W.,University of Science and Technology Beijing | Hussin B.,University of Technology Malaysia | Jefferis T.,UK Defence Science and Technology Laboratory
International Journal of Production Economics | Year: 2012

This paper presents a case study of condition based maintenance modelling based on measured metal concentrations observed in oil samples of a fleet of marine diesel engines. The decision model for optimising the replacement time of the diesel engines conditional on observed measurements is derived and applied to the case discussed. We described the datasets, which were cleaned and re-organised according to the need of the research. The residual time distribution required in the decision model was formulated using a technique called stochastic filtering. Procedures for model parameter estimation are constructed and discussed in detail. The residual life model presented has been fitted to the case data, and the modelling outputs are discussed. © 2011 Elsevier B.V.


Sun J.,Nanjing University of Aeronautics and Astronautics | Sun J.,University of Maryland University College | Zuo H.,Nanjing University of Aeronautics and Astronautics | Wang W.,University of Science and Technology Beijing | And 2 more authors.
Mechanical Systems and Signal Processing | Year: 2012

This paper presents the application of a state space model (SSM) for prognostics of an engineering system subject to degradation. A health index (HI) is inferred from a set of sensor signals to characterize the hidden health state of the system. Bayesian state estimation and prediction formulas, on the basis of the health indices modeled by the linear regression of observed signals, are carried out to sequentially update the current health state and then predict the future health state of the system. A Sequential Monte Carlo (SMC) method is used for computation. If a failure is defined in terms of a specified level of degradation, a time-to-failure distribution can be obtained based on the predicted degradation. The method is applied to a gas turbine that is simulated via a gas turbine software package and is subject to both gradual performance deterioration and abrupt faults in service. The analysis of the case study shows that the method can provide an estimate of Remaining Useful Life (RUL) with uncertainty as well as other reliability indices of interest for operators to plan effective condition-based maintenance. © 2011 Elsevier Ltd. All rights reserved.


Cao J.-P.,University of Science and Technology Beijing | Zhao X.,University of Science and Technology Beijing | Zhao J.,University of Science and Technology Beijing | Zha J.-W.,University of Science and Technology Beijing | And 2 more authors.
ACS Applied Materials and Interfaces | Year: 2013

The effect of selective localization of silicon carbide (SiC) and polystyrene (PS)-coated SiC (p-SiC) nanoparticles on the thermal conductivity and flame retardancy of immiscible PS/poly(vinylidene fluoride) (PVDF) blends has been systematically studied. The scanning electron microscopy (SEM) images reveal that SiC and p-SiC nanoparticles have different selective localizations in the PS/PVDF blends. The melting and crystallization behaviors of the PVDF component investigated by using differential scanning calorimetry are consistent with the SEM results. To reduce the volume fraction of fillers in the composites, a cocontinuous structure of PS/PVDF has also been built up. The cocontinuity window for PS/PVDF blends is ∼30-70 vol % according to the selective solvent dissolution technique. The selective localization of SiC in the PVDF phase of the PS/PVDF 70/30 blends produces a slightly higher thermal conductivity than that of p-SiC in the PS phase of the PS/PVDF 30/70 blends. However, the composites with selective localization of p-SiC exhibit the best combined properties of thermal conductivity and flame retardancy. © 2013 American Chemical Society.


Sun J.,Datang Research and Development Center on Circular Utilization of High aluminum Coal Resources | Chen P.,University of Science and Technology Beijing
Advanced Materials Research | Year: 2013

High-alumina fly ash in central and western regions of Inner Mongolia is a very valuable renewable mineral resource resulting from the content of Al2O3 up to 50% and some available elements, such as gallium, titanium and light rare earth. According to the resource characteristics of high-alumina fly ash and the market demand of the non-ferrous metals and chemical products in national economic development, a technique route was researched and developed, which included high-alumina fly ash as the main raw material, extraction of alumina co-generated with active calcium silicate (chemical packing) and calcium silicon slag cement clinker. It is the process characteristics that according to the development concept about circular economy, making full use of fly ash and recycling water as sewage disposal from thermal power plants, calcium carbide slag from chemical plants and other disused resources, and achieving the separation of alumina and silica and their respective resource utilization. © (2013) Trans Tech Publications, Switzerland.


Li Y.F.,École Centrale Paris | Peng R.,University of Science and Technology Beijing
Reliability Engineering and System Safety | Year: 2014

Most studies on multi-state series-parallel systems focus on the static type of system architecture. However, it is insufficient to model many complex industrial systems having several operation phases and each requires a subset of the subsystems combined together to perform certain tasks. To bridge this gap, this study takes into account this type of dynamic behavior in the multi-state series-parallel system and proposes an analytical approach to calculate the system availability and the operation cost. In this approach, Markov process is used to model the dynamics of system phase changing and component state changing, Markov reward model is used to calculate the operation cost associated with the dynamics, and universal generating function (UGF) is used to build system availability function from the system phase model and the component models. Based upon these models, an optimization problem is formulated to minimize the total system cost with the constraint that system availability is greater than a desired level. The genetic algorithm is then applied to solve the optimization problem. The proposed modeling and solution procedures are illustrated on a system design problem modified from a real-world maritime oil transportation system. © 2014 Elsevier Ltd.


Heinecke G.,ETH Zurich | Heinecke G.,Siemens AG | Syntetos A.A.,University of Salford | Wang W.,University of Science and Technology Beijing
International Journal of Production Economics | Year: 2013

Different spare parts are associated with different underlying demand patterns, which in turn require different forecasting methods. Consequently, there is a need to categorise stock keeping units (SKUs) and apply the most appropriate methods in each category. For intermittent demands, Croston's method (CRO) is currently regarded as the standard method used in industry to forecast the relevant inventory requirements; this is despite the bias associated with Croston's estimates. A bias adjusted modification to CRO (Syntetos-Boylan Approximation, SBA) has been shown in a number of empirical studies to perform very well and be associated with a very 'robust' behaviour. In a 2005 article, entitled 'On the categorisation of demand patterns' published by the Journal of the Operational Research Society, Syntetos et al. (2005) suggested a categorisation scheme, which establishes regions of superior forecasting performance between CRO and SBA. The results led to the development of an approximate rule that is expressed in terms of fixed cut-off values for the following two classification criteria: the squared coefficient of variation of the demand sizes and the average inter-demand interval. Kostenko and Hyndman (2006) revisited this issue and suggested an alternative scheme to distinguish between CRO and SBA in order to improve overall forecasting accuracy. Claims were made in terms of the superiority of the proposed approach to the original solution but this issue has never been assessed empirically. This constitutes the main objective of our work. In this paper the above discussed classification solutions are compared by means of experimentation on more than 10,000 SKUs from three different industries. The results enable insights to be gained into the comparative benefits of these approaches. The trade-offs between forecast accuracy and other implementation related considerations are also addressed. © 2012 Elsevier B.V. All rights reserved.


He A.,University of Science and Technology Beijing | He A.,Inner Mongolia University of Science and Technology | Chen L.,Inner Mongolia University of Science and Technology | Hu S.,Inner Mongolia University of Science and Technology | And 2 more authors.
Materials and Design | Year: 2013

The experimental true strain-true stress data from isothermal hot compression tests on a Gleeble-1500D thermal simulation machine, across a wide range of temperatures (1173-1373K) and strain rates (1.5×10-3-1.5×10-2s-1), were employed to study the deformation behavior and develop constitutive equations of 20CrMo alloy continuous casting billet steel. The objective was to obtain the relational expression for deformation activation energy and material constants as a function of true strain and the constitutive equation for high temperature deformation of 20CrMo based on the hyperbolic sine form model. A correlation coefficient of 0.988 and an average absolute relative error between the experimental and the calculated flow stress of 8.40% have been obtained. This indicates that the constitutive equations can be used to accurately predict the flow behavior of 20CrMo alloy steel continuous casting billet during high temperature deformation. © 2012 Elsevier Ltd.


Sun D.,Henan Polytechnic University | Wang M.,University of Science and Technology Beijing | Li Z.,Henan Polytechnic University | Fan G.,Henan Polytechnic University | And 2 more authors.
Electrochemistry Communications | Year: 2014

Two-dimensional (2D) Ti3C2 was synthesized by the exfoliation of Ti3AlC2 with HF solution and subsequently intercalation with dimethyl sulfoxide. As anode for lithium ion batteries, Ti3C2 after intercalation had an obvious higher capacity than that before intercalation. The capacity can be 123.6 mAh g- 1 at 1C rate with a coulombic efficiency of 47%. It is higher than that of 2D Ti2C and close to the theoretical capacity of Ti3C 2 with F termination. It was suggested that MXene with pure F groups may be a way to further improve its Li storage performance. © 2014 Elsevier B.V.


Wei S.,Beijing University of Chemical Technology | Zhang H.,Beijing Research Institute of Chemical Defense | Zhang H.,University of Science and Technology Beijing | Huang Y.,Beijing University of Chemical Technology | And 3 more authors.
Energy and Environmental Science | Year: 2011

Pig bone derived carbon with a unique hierarchical porous structure was prepared by potassium hydroxide (KOH) activation. The effects of activation temperature on the textural properties of the pig bone based carbons were investigated. The hierarchical porous carbons exhibit the largest BET specific surface areas and pore volume when the activation temperature reaches 850 °C, and the carbon still maintains a highly hierarchical structure even when the temperature is up to 950 °C. The pig bone derived hierarchical porous carbon/sulfur composites have been tested as a novel cathode for lithium-sulfur batteries. The result shows that the cycle stability and the utilization of sulfur in the lithium-sulfur batteries have been largely improved. The hierarchical porous carbon/sulfur cathode has a high initial capacity of 1265 mAh g-1 and 643 mAh g-1 after 50 cycles, which is higher than that of the normal cathodes with compact structures. © 2011 The Royal Society of Chemistry.


Zhou D.,University of Minnesota | Wang H.,University of Minnesota | Wang H.,University of Science and Technology Beijing
Sensors and Actuators, A: Physical | Year: 2013

This paper presents the development of a new type of skin-like tactile pressure sensor array. The sensor array is scalable, flexible and stretchable and can measure pressure up to 250 kPa within 30% stretching rate without damaging its mechanical structure. It can also conform to irregular three-dimensional surfaces. The sensor array consists of three layers. The top and bottom layers are formed by the array of parallel conductive strips made of silver nanowires (AgNWs) embedded in polydimethylsiloxane (PDMS) thin films. The AgNWs/PDMS conductor strips are used as stretchable interconnections to transmit electrical signals. The middle layer is made of PDMS. This film is pre-molded with holes filling with cylinder-shaped conductive elastomer for pressure measurement. In this paper, the characteristic of the AgNWs/PDMS conductor strips as stretchable interconnections is studied. The piezoresistive properties of the sensels (one sensing element is called a sensel) were measured and discussed. The performance of the tactile sensor array under stretching was also tested. With the associated scanning power-supply circuit and data acquisition system, it is demonstrated that the system can successfully capture the tactile images induced by objects of different shapes. Such sensor system could be applied on curved or non-planar surfaces in robots or medical devices for force detection and feedback. © 2013 Elsevier B.V. All rights reserved.


Wang H.,University of Science and Technology Beijing | Wang H.,University of Minnesota | Zhou D.,University of Minnesota | Cao J.,University of Science and Technology Beijing
IEEE Sensors Journal | Year: 2014

In this paper, we develop a skin-like tactile sensor array to measure the contact pressure of curved surfaces. The sensor array is laminated into a thin film 3 mm in thickness and can easily be wrapped around a pencil without damaging its skin-like structure. So far, we have achieved the array containing 8 × 16 sensor elements. Its spatial resolution is 1 element per 9 mm 2 area and it can measure the pressure up to 360 kPa. The sensor-array patch contains three layers. The upper and lower layers are polydimethylsiloxane (PDMS) thin films embedded with the conductor strips formed by PDMS-based silver nanowires (AgNWs) networks. The middle layer is formed by the mixing of nickel powder with liquid PDMS for contact force measurement. Experimental tests have demonstrated that conductor strips on the upper layer can maintain their resistances ~23 Ω with <4 Ω increase when the tensile strain is up to 50%. Noted is the conductor made with carbon nanotubes can keep its conductivity unchanged for up to only 40% tensile strain. Through fatigue tests, it is observed that the measured AgNWs/PDMS conductor strip exhibits low and stable resistances. This is one of the most desired behaviors of the stretchable interconnects for signal transmission. The integrated sensor system can successfully measure the contact pressure induced by objects of different shapes. It can be applied on curved or non-planar surfaces in robots or medical devices for force detection and feedback. © 2001-2012 IEEE.


Liu Z.-Q.,University of Science and Technology Beijing | Liu Z.-Q.,Tiandi Science And Technology
Meitan Xuebao/Journal of the China Coal Society | Year: 2013

Firstly, the paper reviews the status quo of mechanical shaft boring technology overseas. Secondly, describes generation and development of shaft drilling technology used in domestic alluvium. Then drilling technology development is divided into four stages: Basic technical preparations; field application test of drilling process; mature technology and equipment stage and breakthrough stage. List the drilling method used in western soft rock, small diameter vertical channels in mines, municipal engineering and other mines, as well as technical problems need to be solved. Thirdly, the development of Raise Boring Machine and the difficult in drilling in coal mine was analyzed, and technical issues need to be addressed in the Raise Boring Machine construction is described. Fourthy, the development of full face shaft boring machine is prospected and performances of rock-cutter, slagging, supporting and auxiliary systems are discussed. Through analysis, conclusions are that using suitable mechanical drilling method to construct shaft under different geological and project conditions can reduce the workers in the underground construction, then complete the construction safety and efficiency.


Wang F.,University of Science and Technology Beijing | Yao J.,University of Science and Technology Beijing | Chen H.,University of Science and Technology Beijing | Yi Z.,University of Science and Technology Beijing | Xing B.,University of Massachusetts Amherst
Environmental Pollution | Year: 2013

The environmental behavior of carbon nanotubes (CNTs) and humic acid (HA) is a prominent concern, but effect of functionalities on their sorption is not clear yet. Functionalized multi-walled CNTs (MCNT15) and HA were used to study their sorption behavior. Sorption rate of HA to MCNTs was dominantly controlled by its diffusion from liquid-MCNT boundary to MCNT surfaces. The sorption is in the sequence of MCNT15 > MCNT15-NH2 > MCNT15-OH > MCNT15-COOH > MCNT15-Ni, which was dependent on their surface area and meso- and macro-pore volume. The functionalities of MCNTs regulated the sorption by affecting their interaction mechanisms (i.e., H-bonding, π-π, and hydrophobic interaction). Additionally, the amount of these functionalities on the MCNT surface reduced indirectly the sorption sites due to the steric hindrance. Electrostatic repulsion deceased the sorption of HA by MCNTs with increasing pH. This study demonstrated the importance of functionalities on the MCNTs for the sorption of HA. © 2013 Elsevier Ltd. All rights reserved.


Huang G.,University of Shizuoka | Takeuchi Y.,University of Shizuoka | Ma W.,University of Science and Technology Beijing | Wei D.,Hubei University for Nationalities
Bulletin of Mathematical Biology | Year: 2010

In this paper, based on SIR and SEIR epidemic models with a general nonlinear incidence rate, we incorporate time delays into the ordinary differential equation models. In particular, we consider two delay differential equation models in which delays are caused (i) by the latency of the infection in a vector, and (ii) by the latent period in an infected host. By constructing suitable Lyapunov functionals and using the Lyapunov-LaSalle invariance principle, we prove the global stability of the endemic equilibrium and the disease-free equilibrium for time delays of any length in each model. Our results show that the global properties of equilibria also only depend on the basic reproductive number and that the latent period in a vector does not affect the stability, but the latent period in an infected host plays a positive role to control disease development. © 2009 Society for Mathematical Biology.


Song X.,Shandong Institute of Business and Technology | Song X.,University of Science and Technology Beijing | Mu X.,University of Dundee
Energy Policy | Year: 2013

Small scale coal mines (SCMs) have played an important role in China's energy supply. At the same time, they also suffer from many social, economic, environmental, and safety problems. The Chinese government has made considerable efforts to strengthen the safety regulation of the coal mining industry. Yet, few of these efforts have proven to be very effective. This paper analyzes the interests and influences of key stakeholders in the safety regulation of SCMs, which includes the safety regulator, the local government, the mine owner, and mineworkers. We argue that the effective regulation of coal mine safety must both engage and empower mineworkers. © 2012 Elsevier Ltd.


Lin Y.,Huaqiao University | Zheng L.,University of Science and Technology Beijing
AIP Advances | Year: 2015

In this paper we present a study of the Marangoni boundary layer flow and heat transfer of copper-water nanofluid over a porous medium disk. It is assumed that the base fluid water and the nanoparticles copper are in thermal equilibrium and that no slippage occurs between them. The governing partial differential equations are transformed into a set of ordinary differential equations by generalized Kármán transformation. The corresponding nonlinear two-point boundary value problem is solved by the Homotopy analysis method and the shooting method. The effects of the solid volume fraction, the permeability parameter and the Marangoni parameter on the velocity and temperature fields are presented graphically and analyzed in detail. © 2015 Author(s).


Chen W.,Beijing University of Chemical Technology | Zhang H.,Beijing Research Institute of Chemical Defense | Zhang H.,University of Science and Technology Beijing | Huang Y.,Beijing University of Chemical Technology | Wang W.,Beijing Research Institute of Chemical Defense
Journal of Materials Chemistry | Year: 2010

A hierarchical lamellar porous carbon material was prepared with fish scale using a natural template. Electric double layer capacitors electrodes prepared from this kind of porous carbon exhibited exceptional ration ability which demonstrated that fish scale is a promising candidate precursor to prepare low cost but high performance porous carbon material. © The Royal Society of Chemistry 2010.


Sun K.,University of California at San Diego | Pang X.,University of Science and Technology Beijing | Shen S.,Xi'an Jiaotong University | Qian X.,University of Science and Technology Beijing | And 2 more authors.
Nano Letters | Year: 2013

We present a study of a transition metal oxide composite modified n-Si photoanode for efficient and stable water oxidation. This sputter-coated composite functions as a protective coating to prevent Si from photodecomposition, a Schottky heterojunction, a hole conducting layer for efficient charge separation and transportation, and an electrocatalyst to reduce the reaction overpotential. The formation of mixed-valence oxides composed of Ni and Ru effectively modifies the optical, electrical, and catalytic properties of the coating material, as well as the interfaces with Si. The successful application of this oxide composite on nanotextured Si demonstrates improved conversion efficiency due to enhanced catalytic activity, minimized reflection, and increased surface reaction sites. Although the coated nanotextured Si shows a noticeable degradation from 500 cycles of operation, the oxide composite provides a simple method to enable unstable photoanode materials for solar fuel conversion. © 2013 American Chemical Society.


Huang W.,Beijing University of Chemical Technology | Zhang H.,Beijing Research Institute of Chemical Defense | Zhang H.,University of Science and Technology Beijing | Huang Y.,Beijing University of Chemical Technology | And 2 more authors.
Carbon | Year: 2011

Animal bone, an abundant biomass source and high volume food waste, had been converted into a hierarchical porous carbon in a simple two-step sustainable manner to yield a highly textured material. The structures were characterized by nitrogen sorption at 77 K, scanning electron microscopy and X-ray diffraction. The electrochemical measurement in 7 M KOH electrolyte showed that the porous carbon had excellent capacitive performances, which can be attributed to the unique hierarchical porous structure (abundant micropores with the size of 0.5-0.8 and 1-2 nm, mesopores and macropores with the size of 2-10 and 10-100 nm), high surface area (SBET = 2157 m2/g) and high total pore volume (Vt = 2.26 cm3/g). Its specific capacitance was 185 F/g at a current density of 0.05 A/g. Of special interest was the fact that the porous carbon still maintained 130 F/g even at a high current density of 100 A/g. © 2010 Published by Elsevier Ltd. All rights reserved.


Dong H.,University of Science and Technology Beijing | Hao K.,University of Science and Technology Beijing | Tian Y.,Chinese PLA General Hospital | Jin S.,University of Science and Technology Beijing | And 3 more authors.
Biosensors and Bioelectronics | Year: 2014

A label-free and high-sensitive microRNA (miRNA) detection approach by coupling a metal ion-meditated conformational molecular beacon (MB), using novel fluorescent Ag nanocluster (AgNCs) as fluorophore, with endonuclease-assisted target recycling amplification was developed. The assay comprised an Hg2+ ion-meditated conformational MB probe and an assistant probe that do not hybridize with each other at a specific temperature and can be annealed to each other in the presence of the target to form a Y-shape junction structure and released Hg2+. The target-MB hybridization event with the help of assistant probe can readily be read out based on the efficient fluorescence quenching of AgNCs by released Hg2+, while the Y-shape junction structure consisting of the probe MB, assistant probe and target miRNA could be recognized by the endonuclease Nt.BbvCI. The MB probe was then effectively cleaved by the endonuclease, and the regenerated assistant probe and the target further attended another cleavage cycle to implement the signal amplification. The competition displacing interaction between the target and the Hg2+ endows the biosensor with high sequence discrimination capability, while the high signal-to-noise ratio and target recycling amplification allows the biosensor to detect the target with high sensitivity. Under the optimal conditions, the concentration of target miRNA could be conveniently read out with a linear range from 10pM to 1fM. The proposed approach, avoiding any laborious label, possessing high sensitivity and selectivity, provided significant potential applications in future clinical analysis. © 2013 Elsevier B.V.


Huang L.,University of Science and Technology Beijing | Huang L.,Beijing Institute of Technology | Cong D.Y.,University of Science and Technology Beijing | Suo H.L.,Beijing University of Technology | Wang Y.D.,University of Science and Technology Beijing
Applied Physics Letters | Year: 2014

We report a giant effective magnetic refrigeration capacity in a Ni 40Co10Mn40Sn10 multifunctional alloy. With a large magnetization difference between austenite and martensite, this alloy shows a strong magnetic field dependence of transformation temperatures. Complete magnetic-field-induced structural transformation and a considerable magnetic entropy change are observed in a broad operating temperature window of 33K near room temperature. Consequently, an effective magnetic refrigeration capacity of 251J/kg for 5T is achieved, which is the largest value for Ni-Mn-based Heusler alloys and comparable to that of the high-performance Gd-Si-Ge and La-Fe-Si magnetocaloric materials. Incorporating the advantages of low cost and non-toxicity, this alloy shows very promising prospects for room-temperature magnetic refrigeration. © 2014 AIP Publishing LLC.


Jakupi P.,University of Western Ontario | Wang F.,University of Science and Technology Beijing | Noel J.J.,University of Western Ontario | Shoesmith D.W.,University of Western Ontario
Corrosion Science | Year: 2011

Surface analytical techniques were applied to characterize corrosion products formed during the crevice corrosion of the Ni-Cr-Mo(W) Alloy-22 in 5. mol/L NaCl at 120 °C. Micro-Raman spectroscopy demonstrated the formation of polymeric molybdates within the crevice corroded region where intergranular corrosion dominated. The location and chemical speciation of the Mo and W species formed was investigated by Raman mapping. Crevice corrosion was found to propagate preferentially across the alloy surface rather than to penetrate deeply at localized sites, a feature which appears to be linked to the formation and build-up of polymeric molybdates. © 2011 Elsevier Ltd.


Khan M.,University of Science and Technology Beijing | Khan M.,Sudan University of Science and Technology | Cao W.,University of Science and Technology Beijing
Materials Research Bulletin | Year: 2014

Titanium dioxide co-doped with yttrium and nitrogen with different yttrium doping concentration has been synthesized by mild one pot hydrothermal method without any post calcination for crystallization. Irrespective of the yttrium doping concentration, all the synthesized samples were composed of pure anatase phase with good crystallinity. And the synthesized co-doped samples have spherical morphology with uniform particle size distribution. The absorption edge of the co-doped TiO2 was shifted toward visible light region depicting that the intrinsic band gap of TiO2 was affected by the co-doping. Among the different samples, the co-doped sample with 0.05% yttrium doping concentration exhibits enhanced visible light photocatalytic activity by degradation of methylene blue in aqueous solution. Compensated and non-compensated yttrium-nitrogen co-doped TiO2 models were simulated using density functional theory to explain the experimental findings. The calculation results show that the compensated yttrium-nitrogen co-doped TiO2 model may reasonably explain the experimental observations due to its stable configuration, narrowed band gap and enhanced separation of photoexcited carriers. © 2013 Elsevier Ltd. All rights reserved.


Zhao H.,Beijing Institute of Technology | Qian X.-M.,Beijing Institute of Technology | Li J.,University of Science and Technology Beijing
Safety Science | Year: 2012

In order to check structural strength of coal mine mobiles refuge chamber, and do security evaluation of the mobile refuge chamber, a refuge chamber model was established, then a finite element method was instituted for it to ensure the refuge chamber would not be severely damaged when gas or coal dust explosion suddenly happened. A triangle shock wave with 1.2. MPa over-pressure, 300. ms lasting time was settled. Explicit nonlinear dynamic analysis program was used to simulate response of the refuge chamber. The maximum stress was 244. MPa, located in central part of sides and tail end of the last capsule. The maximum displacement was 29.32. mm, located in central part of sides and tail end of the last capsule. The calculation indicated that the refuge chamber was not obviously damaged. It could reliable work to meet safety requirements. Compared with the reported experimental results, the simulation method was verified. Based on analysis, suggestions were put forward for further improving. © 2011 Elsevier Ltd.


Cui Q.,University of Science and Technology Beijing | Cui Q.,Max Planck Institute of Colloids and Interfaces | He F.,University of Science and Technology Beijing | Li L.,University of Science and Technology Beijing | Mohwald H.,Max Planck Institute of Colloids and Interfaces
Advances in Colloid and Interface Science | Year: 2014

In recent years, considerable efforts have been devoted to better understand the unique emission properties of fluorophores enhanced by the localized surface plasmon resonance of metal nanoparticles (NPs), due to the widespread applications of fluorescence techniques. It is demonstrated by experiment and theoretical calculation that the enhancement efficiency strongly depends on the morphology of the metal NPs, the spectral overlap between metal and fluorophores, the separation distance between them, and other factors. Among these aspects to be considered are suitable spacer material and assembling methods to control the spatial arrangement of plasmonic NPs and fluorophore with proper optical properties and interactions. In this contribution, we provide a brief overview on recent progress of metal-enhanced fluorescence in organized films and colloidal systems. © 2013 Elsevier B.V.


Lv P.,University of Science and Technology Beijing | Zhao H.,University of Science and Technology Beijing | Zhao H.,New Energy Technologies | Zeng Z.,University of Science and Technology Beijing | And 3 more authors.
Journal of Power Sources | Year: 2014

Carbon coated Fe3O4 nanocomposite (Fe 3O4/C) is synthesized via a simple sol-gel route and a subsequent carbon CVD process, with Fe2O3 xerogel as intermediate product. The nanoporous Fe2O3 xerogel is reduced to Fe3O4 during the CVD process. The prepared Fe3O4/C composite presents a well-distributed nanostructure composing of Fe3O4 nanoparticles coated with carbon layer. The electrode exhibits a stable reversible capacity of over 850 mAh g-1 at 0.1 A g-1, excellent cycling performance and good rate capability. Both of the nano-scale particle size of Fe 3O4 and the carbon layer contribute to the excellent electrochemical performance of Fe3O4/C. An increase in electrode capacity with cycling is observed for the prepared Fe 3O4/C composite when cycled at 50 C, which is similar to other reported transition metal oxides. The preparation process of Fe 3O4/C composite is facile, mild and productive. © 2014 Elsevier B.V. All rights reserved.


Khan M.,University of Science and Technology Beijing | Khan M.,Sudan University of Science and Technology | Cao W.,University of Science and Technology Beijing
Journal of Applied Physics | Year: 2013

To employ TiO2 as an efficient photocatalyst, high reactivity under visible light and improved separation of photoexcited carriers are required. An effective co-doping approach is applied to modify the photocatalytic properties of TiO2 by doping vanadium (transition metal) and yttrium (rare earth element). V and/or Y codoped TiO2 was prepared using hydrothermal method without any post calcination for crystallization. Based on density functional theory, compensated and noncompensated V, Y codoped TiO2 models were constructed and their structural, electronic, and optical properties were calculated. Through combined experimental characterization and theoretical modeling, V, Y codoped TiO 2 exhibited high absorption coefficient with enhanced visible light absorption. All the prepared samples showed pure anatase phase and spherical morphology with uniform particle distribution. Electronic band structure demonstrates that V, Y codoping drastically reduced the band gap of TiO 2. It is found that both the doped V and Y exist in the form of substitutional point defects replacing Ti atom in the lattice. The photocatalytic activity, evaluated by the degradation of methyl orange, displays that the codoped TiO2 sample exhibits enhanced visible light photocatalytic activity. The synergistic effects of V and Y drastically improved the Brunauer-Emmett-Teller specific surface area, visible light absorption, and electron-hole pair's separation leading to the enhanced visible light catalytic activity. © 2013 AIP Publishing LLC.


Khan M.,University of Science and Technology Beijing | Khan M.,Sudan University of Science and Technology | Cao W.,University of Science and Technology Beijing
Journal of Molecular Catalysis A: Chemical | Year: 2013

Nano-sized yttrium (Y)-doped TiO2 with different Y doping concentrations has been synthesized by hydrothermal method. With pure anatase phase, the as-synthesized samples possess good crystallinity and spherical morphology with uniform particle size distribution. Y doping shifted the absorption edge of TiO2 towards visible light region, as observed from the UV-vis. absorption spectra. XPS (X-ray photoelectron spectroscopy) analysis indicates that Y3+ replaces lattice Ti4+ leading to substitutional point defects. The photocatalytic activity of the synthesized sample was evaluated by the degradation of methylene blue in aqueous solution under visible light irradiations. Y-doped TiO2 shows enhanced photocatalytic activity compared with that of bare TiO2. Compensated and non-compensated density functional theory based calculations were performed for reasonable explanation of the experimental findings. Compensated model with Y3+ replacing Ti4+ along with concomitant presence of an oxygen vacancy might explain the improved photocatalytic activity of Y-doped TiO2. The enhanced photoactivity of Y-doped TiO2 is assigned to the reduced band gap, enhanced visible light absorption and improved separation of electron-hole pairs.© 2013 Elsevier B.V. All rights reserved.


Zhao L.,Max Planck Institute of Colloids and Interfaces | Zhao L.,Shanxi Institute of Coal CAS Chemistry | Fan L.-Z.,University of Science and Technology Beijing | Zhou M.-Q.,University of Science and Technology Beijing | And 4 more authors.
Advanced Materials | Year: 2010

Microporous nitrogen-doped carbons produced by hydrothermal carbonization of biomass derivative followed by chemical activation showed excellent supercapacitive capacitance performance both in acid and base electrolytes. Copyright © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Wang J.,University of Science and Technology Beijing | Zhao H.,University of Science and Technology Beijing | Zhao H.,New Energy Technologies | Yang Q.,University of Science and Technology Beijing | And 3 more authors.
Journal of Power Sources | Year: 2013

In an effort to improve the rate-capability of Li4Ti5O12 anode material, a dual-phase composite Li4Ti5O12-TiO2 is in situ prepared via a solvothermal route. The Li4Ti5O12-TiO2 composite shows higher reversible capacity and better rate-capability compared to single phase Li4Ti5O12. The TiO2 can decrease significantly the particle size of Li4Ti5O12-TiO2 powders due to a steric hindrance effect, which thereby shortens the lithium ion diffusion distance and enhances the electrode reaction. Meanwhile, anatase TiO2 can contribute some capacity to the Li4Ti5O12-TiO2 electrode. Coating the Li4Ti5O12-TiO2 composite with carbon (∼2.5 wt.%) can further improve the rate-capability of Li4Ti5O12-TiO2 electrode, a reversible capacity of ∼140 mA h g-1 is maintained after 100 cycles at 5 C. © 2012 Elsevier B.V. All rights reserved.


Ji H.-X.,Leibniz Institute for Solid State and Materials Research | Wu X.-L.,CAS Institute of Chemistry | Fan L.-Z.,University of Science and Technology Beijing | Krien C.,Leibniz Institute for Solid State and Materials Research | And 4 more authors.
Advanced Materials | Year: 2010

Self-wound nanomembranes out of functional multilayered structures were designed to improve lithium storage performance. The intrinsic strain is relaxed by rolling; the composite components are uniformly dispersed; the micro/nanohierarchical structure assumes a mixed ion/electron conduction network; and conventional nanomembrane deposition techniques allow for various materials combinations, suitable to meet different demands of lithium ion batteries. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Lin J.,Beijing Institute of Technology | Mu D.,Beijing Institute of Technology | Jin Y.,University of Science and Technology Beijing | Wu B.,Beijing Institute of Technology | And 2 more authors.
Journal of Power Sources | Year: 2013

Li-rich layered composite Li[Li0.2Ni0.2Mn 0.6]O2 is prepared by a novel approach in which carbon felt acts as a carrier for synthesis reaction. The as-prepared material is characterized by SEM, ICP and XRD, its electrochemical performance is also examined with galvanostatic charge/discharge and CV measurements. It is showed that the facile process controls effectively the particle growth (in size around 100-200 nm) of the composite and its chemical composition. The as-prepared material shows a high initial discharge capacity about 288 mAh g-1 when charged to 4.8 V, and a retained value of 246.8 mAh g-1 in the 40th cycle. The crystalline structure of the composite is simulated further by Material Studio. It is revealed that the composite has a compatible layer structure merged by Li2MnO3 and LiNi0.5Mn 0.5O2, which makes substantial contribution to the cycleability of the electrode. In addition, the lithiation/delithiaion properties including charge transfer resistance and lithium ion diffusion coefficient are studied with electrochemical impedance spectra. © 2012 Elsevier B.V. All rights reserved.


Gong K.,University of Science and Technology Beijing | Gong K.,McGill University | Zhang L.,McGill University | Ji W.,Renmin University of China | Guo H.,McGill University
Physical Review B - Condensed Matter and Materials Physics | Year: 2014

We report first-principles theoretical investigations of possible metal contacts to monolayer black phosphorus (BP). By analyzing lattice geometry, five metal surfaces are found to have minimal lattice mismatch with BP: Cu(111), Zn(0001), In(110), Ta(110), and Nb(110). Further studies indicate Ta and Nb bond strongly with monolayer BP causing substantial bond distortions, but the combined Ta-BP and Nb-BP form good metal surfaces to contact a second layer BP. By analyzing the geometry, bonding, electronic structure, charge transfer, potential, and band bending, it is concluded that Cu(111) is the best candidate to form excellent Ohmic contact to monolayer BP. The other four metal surfaces or combined surfaces also provide viable structures to form metal/BP contacts, but they have Schottky character. Finally, the band bending property in the current-in-plane (CIP) structure where metal/BP is connected to a freestanding monolayer BP, is investigated. By both work function estimates and direct calculations of the two-probe CIP structure, we find that the freestanding BP channel is n type. © 2014 American Physical Society.


Bai H.,Henan Normal University | Zhou Q.,Henan Normal University | Xie G.,Henan Institute of Science and Technology | Xiao J.,University of Science and Technology Beijing
Talanta | Year: 2010

Hydrophobic ionic liquid could be dispersed into infinite droplets under driving of high temperature, and then they can aggregate as big droplets at low temperature. Based on this phenomenon a new liquid-phase microextraction for the pre-concentration of lead was developed. In this experiment, lead was transferred into its complex using dithizone as chelating agent, and then entered into the infinite ionic liquid drops at high temperature. After cooled with ice-water bath and centrifuged, lead complex was enriched in the ionic liquid droplets. Important parameters affected the extraction efficiency had been investigated including the pH of working solution, amount of chelating agent, volume of ionic liquid, extraction time, centrifugation time, and temperature, etc. The results showed that the usually coexisting ions containing in water samples had no obvious negative effect on the recovery of lead. The experimental results indicated that the proposed method had a good linearity (R = 0.9951) from 10 ng mL-1 to 200 ng mL-1. The precision was 4.4% (RSD, n = 6) and the detection limit was 9.5 ng mL-1. This novel method was validated by determination of lead in four real environmental samples for the applicability and the results showed that the proposed method was excellent for the future use and the recoveries were in the range of 94.8-104.1%. © 2009 Elsevier B.V. All rights reserved.


Song W.-L.,University of Science and Technology Beijing | Cao M.-S.,Beijing Institute of Technology | Fan L.-Z.,University of Science and Technology Beijing | Lu M.-M.,Beijing Institute of Technology | And 3 more authors.
Carbon | Year: 2014

We have demonstrated a highly ordered porous carbon (HOPC) as an effective electromagnetic absorber. The unique porous structures allow HOPC to possess high surface area and establish effective three-dimensional (3D) conductive interconnections at very low filler loading, which is responsible for effective electrical loss in terms of dissipating the induced current in the corresponding wax composites. Owing to the 3D porous frame, the wax composites with 1 and 5 wt% HOPC have shown effective bandwidth ∼2 and ∼4.5 GHz, respectively, which is considerably competitive to the performance found in the carbon nanotube- (CNT) and graphene-based composites of much higher filler loadings. This concept based on porous absorbers demonstrates more advantages in the fabrication of lightweight microwave-absorbing materials. Furthermore, the composite with 20 wt% HOPC has exhibited highly effective electromagnetic shielding performance up to 50 dB, which competes well with what has already been achieved in the composites embedded with CNTs and graphene. The fundamental mechanism based on electrical conductivity and complex impedance suggests specific strategies in the achievement of high-performance composites for electromagnetic attenuation and shielding. © 2014 Elsevier Ltd. All rights reserved.


Zhou T.,Beijing University of Chemical Technology | Zha J.-W.,University of Science and Technology Beijing | Cui R.-Y.,Shandong Polytechnic University | Fan B.-H.,Beijing University of Chemical Technology | And 3 more authors.
ACS Applied Materials and Interfaces | Year: 2011

Dielectric properties of poly(vinylidene fluoride) (PVDF) based nanocomposites filled with surface hydroxylated BaTiO3 (h-BT) nanoparticles were reported. The h-BT fillers were prepared from crude BaTiO3 (c-BT) in aqueous solution of H2O2. Results showed that the dielectric properties of the h-BT/PVDF nanocomposites had weaker temperature and frequency dependences than that of c-BT/PVDF nanocomposites. Meanwhile, the h-BT/PVDF composites showed lower loss tangent and higher dielectric strength. It is suggested that the strong interaction between h-BT fillers and PVDF matrix is the main reason for the improved dielectric properties. © 2011 American Chemical Society.


XU C.(C.),Lakehead University | CANG D.-q.,University of Science and Technology Beijing
Journal of Iron and Steel Research International | Year: 2010

The global steel production has been growing for the last 50 years, from 200 Mt in 1950s to 1 240 Mt in 2006. Iron and steel making industry is one of the most energy-intensive industries, with an annual energy consumption of about 24 EJ, 5% of the world's total energy consumption. The steel industry accounts for 3%-4% of total world greenhouse gas emissions. Enhancing energy efficiency and employing energy saving/recovering technologies such as coke dry quechning (CDQ) and top pressure recovery turbine (TRT) can be short-term approaches to the steel industry to reduce greenhouse gas emission. The long-term approaches to achieving a significant reduction in CO2 emissions from the steel industry would be through developing and applying CO2 breakthrough technologies for iron and steel making, and through increasing use of renewable energy for iron and steel making. Thus, an overview of new CO2 breakthrough technologies for iron and steel making was made. © 2010 Central Iron and Steel Research Institute.


Zhou Q.,China University of Petroleum - Beijing | Zhou Q.,Henan Normal University | Pang L.,Henan Normal University | Xiao J.,University of Science and Technology Beijing
Microchimica Acta | Year: 2011

A simple and sensitive method was developed for the determination of three carbamate pesticides in water samples. It is based on temperature controlled ionic liquid dispersive liquid phase microextraction combined with high-performance liquid chromatography. The ionic liquid 1-hexyl-3-methylimidazolium hexafluorophosphate was used as the extractant, and the factors affecting the extraction were investigated in detail. The detection limits obtained for isoprocarb, diethofencarb and fenothiocarb are 0. 91, 0. 45, and 1. 40 μgL-1, respectively, and the precisions are in the range between 1. 0 and 1. 8% (n = 6). The method was validated with environmental water samples and the results indicate that it represents a viable alternative to existing methods. © 2011 Springer-Verlag.


Zhang Z.,Shandong Polytechnic University | Wen Y.,University of Science and Technology Beijing
Applied Physics Letters | Year: 2012

In this work, a series of highly sensitive surface-enhanced Raman scattering substrates have been achieved based on the controllable aggregation of silver nanoparticles. In such system, hexadecylamine-capped silver nanoparticles were ink-jet printed on glass substrates and subsequently dipped into methanol solution. An aggregation was induced due to preferential dissolution of hexadecylamine into methanol and partial removal of the protective layers on silver nanoparticle surfaces, which exhibited stable and controllable Raman enhancement effect. This strategy could be further extended to construct various chemical and biological functional sensors. © 2012 American Institute of Physics.


Wang H.,Shanxi University | Wang H.,Taiyuan Normal University | Hao Y.,University of Science and Technology Beijing | Zhang Y.,Shanxi University
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2012

We present a density-functional theory for the one-dimensional harmonically trapped Bose-Fermi mixture with repulsive contact interactions. The ground-state density distribution of each component is obtained by solving the Kohn-Sham equations numerically based on the local density approximation and the exact solution for the homogeneous system given by Bethe ansatz method. It is shown that for sufficiently strong interaction, a considerable amount of fermions are repelled out of the central region of the trap, exhibiting partial phase separation of Bose and Fermi components. Oscillations emerge in the Bose density curves, reflecting the strong correlation with fermions. For infinitely strong interaction, the ground-state energy of the mixture and the total density are consistent with the scenario that all atoms in the mixture are fully fermionized. © 2012 American Physical Society.


Ling X.,University of Science and Technology Beijing | Xie L.,University of Science and Technology Beijing | Fang Y.,University of Science and Technology Beijing | Xu H.,CAS Beijing National Laboratory for Molecular | And 6 more authors.
Nano Letters | Year: 2010

Graphene is a monolayer of carbon atoms packed into a two-dimensional (2D) honeycomb crystal structure, which is a special material with many excellent properties. In the present study, we will discuss the possibility that graphene can be used as a substrate for enhancing Raman signals of adsorbed molecules. Here, phthalocyanine (Pc), rhodamine 6G (R6G), protoporphyin IX (PPP), and crystal violet (CV), which are popular molecules widely used as a Raman probe, are deposited equally on graphene and a SiO2/Si substrate using vacuum evaporation or solution soaking. By comparing the Raman signals of molecules on monolayer graphene and on a SiO2Si substrate, we observed that the intensities of the Raman signals on monolayer graphene are much stronger than on a SiO2/Si substrate, indicating a clear Raman enhancement effect on the surface of monolayer graphene. For solution soaking, the Raman signals of the molecules are visible even though the concentration is low to 10-8 mol/L or less. What's more interesting, the enhanced efficiencies are quite different on monolayer, few-layer, multilayer graphene, graphite, and highly ordered pyrolytic graphite (HOPG). The Raman signals of molecules on multilayer graphene are even weaker than on a SiO2/Si substrate, and the signals are even invisible on graphite and HOPG. Taking the Raman signals on the SiO2/Si substrate as a reference. Raman enhancement factors on the surface of monolayer graphene can be obtained using Raman Intensity ratios. The Raman enhancement factors are quite different for different peaks, changing from 2 to 17. Furthermore, we found that the Raman enhancement factors can be distinguished through three classes that correspond to the symmetry of vibrations of the molecule. We attribute this enhancement to the charge transfer between graphene and the molecules, which result in a chemical enhancement. This is a new phenomenon for graphene that will expand the application of graphene to microanalysis and is good for studying the basic properties of both graphene and SERS. © 2010 American Chemical Society.


Du Y.,University of Science and Technology Beijing | Li X.,Massachusetts Institute of Technology | Xiong P.,Georgia Institute of Technology
IEEE Transactions on Automation Science and Engineering | Year: 2012

Recently, mediation-aided composition has been widely adopted when dealing with incompatibilities of services. However, existing approaches suffer from state space explosion in compatibility verification and cannot automatically generate the BPEL code. This paper presents a Petri net approach to mediation-aided composition of Web services. First, services are modeled as open WorkFlow Nets (oWFNs) and are composed using mediation transitions (MTs). Second, the modular reachability graph (MRG) of composition is automatically constructed and the compatibility is analyzed, so that the problem of state space explosion is significantly alleviated. Furthermore, an Event-Condition-Action (ECA) rule-based technique is developed to automatically generate the BPEL code of the composition, which can significantly save the time and labor of designers. Finally, the prototype system has been developed. © 2012 IEEE.


Shi F.,Shandong Normal University | Song X.,University of Science and Technology Beijing
International Journal of Hydrogen Energy | Year: 2010

The influence of niobium (Nb) on the microstructure, hydrogen embrittlement, and hydrogen permeability of the NbxHf (1-x)/2Ni(1-x)/2 ternary alloys has been studied in particular. The results show that the quantity of the primary (Nb, Hf) phase decreases with the increase of Nb content from 14 mol% to 16 mol%, and then increases with the increase of the Nb content from 16 mol% to 40 mol%. The Nb14Hf43Ni43 alloy is brittle at all temperatures from 523 K to 673 K, as it possesses the largest amount of the Bf-HfNi compound; however, the Nb40Hf30Ni 30 alloy has high resistance to hydrogen embrittlement at all temperatures from 523 K to 673 K, as it possesses the largest amount of the primary (Nb, Hf) phase. The hydrogen permeability (Φ) increases with the increase in Nb content, as the quantity of the primary (Nb, Hf) phase in the NbxHf(1-x)/2Ni(1-x)/2 ternary alloys also increases with the increase in Nb content. © 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.


Hao Z.,University of Science and Technology Beijing | Chen W.,University of Science and Technology Beijing | Lippold C.,Qingdao Stollberg and Samil Co.
Metallurgical and Materials Transactions B: Process Metallurgy and Materials Processing Science | Year: 2010

The heat transfer behavior between mold and slab changes when titania is absorbed into the mold flux during the continuous casting of titanium-stabilized stainless steel. The trend and the extent of this effect were investigated in the laboratory. Furthermore, to investigate the effect of titania on heat transfer, the effect of titania on the crystallization properties of the mold flux was studied. The results showed that with an increasing titania content of mold fluxes, the heat transfer coefficient and the heat flux of the slag film increases, whereas the heat transfer resistance decreases; the effect is that the growth and crystallization temperature of the cuspidine crystallites in the slag are suppressed by the absorption of titania. © 2010 The Minerals, Metals & Materials Society and ASM International.


Zhang Y.,University of Science and Technology Beijing | Ma S.G.,University of Science and Technology Beijing | Qiao J.W.,Taiyuan University of Technology
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science | Year: 2012

The AlCoCrFeNi high-entropy alloys (HEAs) were prepared by the copper mold casting and Bridgman solidification. X-ray diffraction (XRD) results verify that the main phase was bodycentered- cubic (bcc) solid solution by these two solidification processes, indicating its good phase stability. Interestingly, the metallographic photos show a morphology transition from dendrites to equiaxed grains after Bridgman solidification, which was considered to have a strong dependence on the parameter of the G/V (the temperature gradient to the growth rate ratio). Compared to the as-cast sample, the plasticity of alloys synthesized by Bridgman solidification was improved by a maximum of 35 pct. © The Minerals, Metals & Materials Society and ASM International 2011.


Dang Z.-M.,Beijing University of Chemical Technology | Yao S.-H.,University of Science and Technology Beijing | Yao S.-H.,PRES UniverSud | Yuan J.-K.,PRES UniverSud | Bai J.,PRES UniverSud
Journal of Physical Chemistry C | Year: 2010

The carbon nanotube (CNT) has been chosen as an excellent candidate for acquiring high dielectric constant polymer matrix composites according to percolation theory. However, its nanometer-scale dimension makes it naturally form bundles, which makes it difficult to use. Compared with chemical modification of multiwalled carbon nanotube (MWNT), the incorporation of the third component (nanosized BaTiO3 (NBT)) particles into MWNT/polymer composites would realize the uniform dispersion of MWNT without sacrificing the inherent properties of MWNT. We reported a three-phase (NBT-MWNT)/polyvinylidene fluoride nanocomposite with a significantly enhanced dielectric constant (643 at 103 Hz) and a gradually decreased loss, which was extremely hard to be realized at the same time for composites only filled by conductive MWNT filler. Adjustable dielectric properties were discovered by employing the three-phase system due to the nanocomposites microstructure change. Furthermore, impedance analysis and simulated circuit confirmed the existence of microcapacitors comprised of MWNT- and NBT-rich composites. © 2010 American Chemical Society.


Zhao K.,Heilongjiang Bayi Agricultural University | Zhao K.,Petrochina | Yu X.,University of Science and Technology Beijing
Expert Systems with Applications | Year: 2011

Petroleum is an important strategic material which is connected with the vitals and safety of the national economy, and the supplier selections are related to the safety of petroleum production and supply. However, the traditional approaches for supplier selections are limited in subjective evaluation of weights, inaccurate assessing rules, and inefficient decision-making. Although most of the current methods are widely applied in corporation management, a more efficient approach needs to be proposed for supplier selection of oil enterprise. This paper summarizes the particular characteristics of the supply chain of Chinese petroleum enterprises, analyzes the limitations of the traditional methods of supplier selection, and brought forward the method based on case reasoning system (CBR) for petroleum enterprises. The method based on data mining techniques which solves three key problems of CBR, includes calculating the weights of the attributes with information entropy in case warehouse organizing process objectively, evaluating the similarities with k-prototype clustering between the original and target cases in case retrieving process exactly, and extracting the potential rules with back propagation neural networks from conclusions in maintenance and revising process efficiently. It demonstrates the advantages, practicability and validity of this method via case study finally. © 2010 Elsevier Ltd. All rights reserved.


Zhao H.,University of Science and Technology Beijing | Zhao H.,Beijing University of Chemical Technology | Wang D.-R.,University of Science and Technology Beijing | Zha J.-W.,University of Science and Technology Beijing | And 3 more authors.
Journal of Materials Chemistry A | Year: 2013

Flexible polymer materials with obvious electrostriction characteristics display a significant potential for application as novel potential actuators in the future. We report advanced TiO2-polydimethylsilicone (TiO 2-PDMS) nanocomposites with electroaction that is effectively increased through a molecular flexibility tuning process. The increase in the electromechanical sensitivity (by 550%) and actuation strain (by 230%) under a low electric field in low elastic modulus TiO2-PDMS composites originates from the flexibility tuning process by the introduction of dimethylsilicone oil (DMSO). The DMSO is miscible with PDMS resulting in a uniform composition at the molecular level, which can significantly decrease the elastic modulus of the dielectric elastomer composites from 820 kPa to 95 kPa. The experimental results are interpreted using the swelling elastomers theory. It suggests that reducing the elastic modulus could be a good strategy to improve the actuation performance with a low electric field. © 2013 The Royal Society of Chemistry.


Dang Z.-M.,University of Science and Technology Beijing | Dang Z.-M.,Beijing University of Chemical Technology | Dang Z.-M.,Chongqing University | Yuan J.-K.,Beijing University of Chemical Technology | And 2 more authors.
Advanced Materials | Year: 2013

Study of flexible nanodielectric materials (FNDMs) with high permittivity is one of the most active academic research areas in advanced functional materials. FNDMs with excellent dielectric properties are demonstrated to show great promise as energy-storage dielectric layers in high-performance capacitors. These materials, in common, consist of nanoscale particles dispersed into a flexible polymer matrix so that both the physical/chemical characteristics of the nanoparticles and the interaction between the nanoparticles and the polymers have crucial effects on the microstructures and final properties. This review first outlines the crucial issues in the nanodielectric field and then focuses on recent remarkable research developments in the fabrication of FNDMs with special constitutents, molecular structures, and microstructures. Possible reasons for several persistent issues are analyzed and the general strategies to realize FNDMs with excellent integral properties are summarized. The review further highlights some exciting examples of these FNDMs for power-energy-storage applications. Recent progress in the development of flexible nanodielectric materials (FNDMs) with high dielectric permittivity is highlighted. Particular focus is given to increasing the energy density of various FNDMs. Key issuses in the synthesis, structure, and dielectric properties of nanodielectrics are reviewed. Some long-standing problems and topics that warrant further investigation are also addressed. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Feng Z.,University of Science and Technology Beijing | Zuo M.J.,University of Electronic Science and Technology of China | Zuo M.J.,University of Alberta
Mechanical Systems and Signal Processing | Year: 2013

Torsional vibration signals are theoretically free from the amplitude modulation effect caused by time variant vibration transfer paths due to the rotation of planet carrier and sun gear, and therefore their spectral structure are simpler than transverse vibration signals. Thus, it is potentially easy and effective to diagnose planetary gearbox faults via torsional vibration signal analysis. We give explicit equations to model torsional vibration signals, considering both distributed gear faults (like manufacturing or assembly errors) and local gear faults (like pitting, crack or breakage of one tooth), and derive the characteristics of both the traditional Fourier spectrum and the proposed demodulated spectra of amplitude envelope and instantaneous frequency. These derivations are not only effective to diagnose single gear fault of planetary gearboxes, but can also be generalized to detect and locate multiple gear faults. We validate experimentally the signal models, as well as the Fourier spectral analysis and demodulation analysis methods. © 2012 Elsevier Ltd.


Miao X.,China University of Mining and Technology | Cui X.,China University of Mining and Technology | Wang J.,University of Science and Technology Beijing | Xu J.,China University of Mining and Technology
Engineering Geology | Year: 2011

The height of fractured water conducting zone is of significant importance for the safety of underground mining. Because of the conspicuous discrepancy of the height of fractured water conducting zone in Bulianta Coal Mine as predicted by the traditional method with those observed in practice, a systematic research has been carried out. The study indicates that two aspects should be taken into account. Firstly, the traditionally proposed empirical formula in prediction of the height of fractured zone was based on the conditions of single-slice mining where the mining height was less than 3. m and the total slice mining height was limited within 15. m. In such a case, it would not be suitable to predict the maximum fractured zone height for the conditions where a single mining height is larger than 3. m. Secondly, the stratum structure such as the thick and strong rock layer termed as key stratum plays an important role in controlling of the height of movement in the overburden. Physical model tests by making use of a similar material illustrate that if the vertical distance from the primary key stratum to the coal seam is shorter than a certain value, then the developing fracture zone will extend above the key stratum into the top of bedrock, resulting in a larger height of water conducting zone than is calculated by the empirical method. The outcome of the work presented will be helpful in practice to prevent the overburden aquifer inrush and to avoid mine water hazard. © 2011 Elsevier B.V.


Xue Q.,Tianjin University | Liu Y.,University of Science and Technology Beijing
Separation Science and Technology | Year: 2011

A novel adsorbent of CO2 from biogas was prepared by synthesizing and modifying the mesoporous molecular silica of SBA-15 with methyl-diethyl-amine (MDEA) and piperazine (PZ). The adsorbent showed good performance in separating CO2 from biogas. The loaded amines did not change the ordered structure of SBA-15, but enhanced its adsorption of CO2. The adsorbents were characterized by X-ray powder diffraction (XRD) and N2 adsorption/desorption. With the increase in MDEA loading, the surface area, pore size, and pore volume of the MDEA-loaded SBA-15 decreased. The modification of amines enlarged the difference between the equilibrium adsorption of CO2 and CH4. Quantitatively evaluated on the basis of the breakthrough curves, the separation factors between CO2 and CH4, was increased more than seven fold due to the MDEA modification. With mixed-amine (MDEA{thorn}PZ) modification, the separation factors between CO2 and CH4 was further improved. In addition, not only the adsorbent was regenerable by purging with the purified gas, but also the adsorption performance is stable in adsorption cycles. Effect of moisture on adsorption of CO2 is investigated and the results show the increase in the adsorption performance. © Taylor & Francis Group, LLC.


Yan H.,CAS Institute of Chemistry | Zhu Z.,CAS Institute of Chemistry | Zhang D.,Taiyuan University of Technology | Li W.,University of Science and Technology Beijing | Qilu,CAS Institute of Chemistry
Journal of Power Sources | Year: 2012

As-prepared anatase TiO 2 with different particle sizes are heated in a lithium hydroxide solution to form Li-Ti-O precursors by using hydrothermal method. Spherical Li 4Ti 5O 12 powders with different particle sizes are obtained by calcining the precursors at 800 °C. The X-ray diffraction (XRD) indicates that elevated hydrothermal reaction temperature and higher concentration of lithium hydroxide solution eliminate the content of impurity in the final product. Scanning electron microscopy (SEM) shows the obtained powders have regular spherical morphology. The obtained Li 4Ti 5O 12 with particle size of about 0.5 μm exhibits excellent electrochemical performance, and the initial discharge capacity reaches 165 mAh g -1 at 35 mA g -1 (0.2 C) and more than 97% of the initial capacity is retained after 70 cycles. © 2012 Elsevier B.V. All rights reserved.


Shi F.,Shandong Normal University | Song X.,University of Science and Technology Beijing
Journal of Alloys and Compounds | Year: 2011

The effect of the Hf/Ni ratio on the microstructures and hydrogen permeabilities of the Nb-Hf-Ni ternary alloys is studied in particular. The results demonstrate that with the increase in the Hf/Ni ratio, (i) the quantity of the primary (Nb, Hf) phase increases; (ii) a new HfNi phase with more Hf content appears; (iii) the Φ value decreases except that of the alloys with the same Hf and Ni contents. © 2010 Elsevier B.V. All rights reserved.


Wang H.,University of Science and Technology Beijing | Cao W.,University of Science and Technology Beijing | Liu T.,Dalian University of Technology | Duan C.,Dalian University of Technology | Jiang J.,University of Science and Technology Beijing
Chemistry - A European Journal | Year: 2013

Double- and quadruple-decker complexes of rare-earth metals with mixed phthalocyanine and Schiff base ligands have been synthesized and structurally and magnetically characterized. These complexes (see picture: Dy pink, Ca green, N blue, C black) extend the scope of sandwich-type tetrapyrrole-based rare-earth molecular materials. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Wang Q.,Dalian University of Technology | Yang Z.,University of Science and Technology Beijing
Environmental Pollution | Year: 2016

The negative health effects of water pollution remain a major source of morbidity and mortality in China. The Chinese government is making great efforts to strengthen water environment treatment; however, no studies have evaluated the effects of water treatment on human health by water pollution in China. This study evaluated the association between water pollution and health outcomes, and determined the extent to which environmental regulations on water pollution may lead to health benefits. Data were extracted from the 2011 and 2013 China Health and Retirement Longitudinal Study (CHARLS). Random effects model and random effects Logit model were applied to study the relationship between health and water pollution, while a Mediator model was used to estimate the effects of environmental water treatment on health outcomes by the intensity of water pollution. Unsurprisingly, water pollution was negatively associated with health outcomes, and the common pollutants in industrial wastewater had differential impacts on health outcomes. The effects were stronger for low-income respondents. Water environment treatment led to improved health outcomes among Chinese people. Reduced water pollution mediated the associations between water environment treatment and health outcomes. The results of this study offer compelling evidence to support treatment of water pollution in China. © 2016 Elsevier Ltd


Wang H.,University of Science and Technology Beijing | Liu T.,Dalian University of Technology | Wang K.,University of Science and Technology Beijing | Duan C.,Dalian University of Technology | Jiang J.,University of Science and Technology Beijing
Chemistry - A European Journal | Year: 2012

Long-distance f-f interactions: Systematic and comparative studies of the magnetic properties of a series of isostructural sandwich-type tetrakis-ACHTUNGTRENUNG(phthalocyaninato) diterbium and monoterbium quadruple-decker complexes clearly reveal the suppression of the quantum tunneling of magnetization by the long-distance intramolecular f-f interactions (see figure). © 2012 Wiley-VCH Verlag GmbH&Co. KGaA, Weinheim.


Sun E.,China Academy of Safety Science and Technology | Sun E.,University of Science and Technology Beijing | Zhang X.,China Academy of Safety Science and Technology | Li Z.,University of Science and Technology Beijing
Safety Science | Year: 2012

Tailings disposal is a significant consideration for the mining industry, with the majority of the ore processed in most mining operations ending up as tailings. Several tailings dam failure accidents have occurred during the past few years and mine tailings dam failures, which are disastrous with the serious damage and the loss of lives, are occurring at relatively high rates. To improve the tailings dam safety, a tailings dam monitoring and pre-alarm system (TDMPAS) based on the internet of things (IOT) and cloud computing (CC) is accomplished with the abilities of real-time monitoring of the saturated line, impounded water level and the dam deformation. TDMPAS has helped the mine engineers monitor the dam safety 24/7 and acquire pre-alarm information automatically and remotely in any kind of weather conditions. TDMPAS has been applied in several mines and has demonstrated the feasibility of monitoring the tailings dam physical condition. © 2011 Elsevier Ltd.


Luo X.,University of Science and Technology Beijing | Luo X.,National Laboratory of Space Intelligent Control | Li J.,University of Science and Technology Beijing
Science China Information Sciences | Year: 2011

The intelligent autonomous control of hypersonic vehicles has aroused great interest from the field of spacecraft. To solve the problem of longitudinal attitude control of hypersonic vehicle in gliding phase, a new intelligent controller is proposed in this paper. This new controller is based on the fuzzy dynamic characteristic modeling method. The fuzzy logic is introduced into the characteristic modeling by dividing the whole restriction range into several subspaces. Simulations show that this modification greatly improves the performance of the original method. With the same whole restriction range the fuzzy dynamic characteristic modeling decreases the time of convergence, and at the same time makes the attitude angle tracing more precise and robust. Since the sub-model is a characteristic model that has stronger adaptiveness than a fixed local model, the number of fuzzy rules is greatly reduced. Our model sharply reduces the complexity in constructing a fuzzy dynamic model. Finally, simulation results are given to show the effectiveness of the proposed approach in dealing with the attitude control problem of hypersonic vehicle in gliding phase. © 2011 Science China Press and Springer-Verlag Berlin Heidelberg.


Wang Y.-M.,China Academy of Safety Science and Technology | Wang Y.-M.,University of Science and Technology Beijing
Xitong Fangzhen Xuebao / Journal of System Simulation | Year: 2010

Traffic incidents will reduce the traffic capacity, and even cause the traffic congestion. So building an effective simulation model is necessary to study the rules of congestion's propagating. The behavioral characteristics of individual vehicles in the traffic jam are different from others, but the current traffic CA (cellular automaton) models neglect those differences. The differences were taken into account by introducing some new rules into the old CA model. With the new CA model, the process of traffic congestion's propagating could be simulated correctly. Lastly, the relationships between congestion's propagating and some traffic parameters were explored by this model.


Chen Y.,Dezhou University | Chen Y.,University of Science and Technology Beijing | Chen Y.,Shandong University | Jiang J.,University of Science and Technology Beijing | Jiang J.,Shandong University
Organic and Biomolecular Chemistry | Year: 2012

Two metal-free tetra(aryl)porphyrin derivatives modified by one and four N,N-bis(2-pyridylmethyl)amino group(s), namely porphyrin-1-DPA (1) and porphyrin-4-DPA (2) respectively, have been designed, synthesized, and characterized. Binding with Pb2+ induces a significant change in their solution color and in the ratio of two absorption/fluorescence signal peaks, rendering them the first example of porphyrin-based triple-signal optical sensors for Pb2+. Their dual-mode Cu2+-selective sensing properties via either the porphyrin fluorescence ON-OFF mechanism or metal displacement from the 1-Pb2+ complex that results in a triple-signal change clearly reveals their potential application as excellent and versatile sensors. © 2012 The Royal Society of Chemistry.


Jiang C.S.,China Academy of Safety Science and Technology | Yuan F.,University of Science and Technology Beijing | Chow W.K.,Hong Kong Polytechnic University
Safety Science | Year: 2010

With the rapid development in economics, subway systems have been constructed in many big cities of China. Computer evacuation models developed overseas are commonly applied in working out safety management scheme. However, input evacuation parameters are not compiled from surveying passenger behavior in China. In fact, very few studies were conducted on justifying such parameters. Staircases in subway stations, particularly those connecting the platform and the ticket hall, are identified as the 'bottleneck' during evacuation in the subway stations. The maximum upstairs speed and the average minimum width of staircase utilized per person are the two key parameters affecting the evacuation through the staircase. Effect of varying these two parameters will be studied in this paper by taking two subway stations in China as examples. Evacuation performance is predicted with the software buildingEXODUS. The default values in the software are used and adjusted through field survey. Effect of varying either or both of the two parameters is discussed. The possible causes on the differences and the factors to affect such effect are explored. It is found that changing both parameters simultaneously would reduce the overall evacuation time by 50%. The effect of varying the two parameters on the overall evacuation performance of the whole station depends also on the occupancy density in the station; and the travel distance from the outlet of the staircase between the platform and the ticket hall to the inlet of the staircase between the ticket hall and the ground surface. © 2009 Elsevier Ltd. All rights reserved.


Wang N.,Brunel University | Burugapalli K.,Brunel University | Song W.,Brunel University | Halls J.,Brunel University | And 3 more authors.
Biomaterials | Year: 2013

This study reports methods for coating miniature implantable glucose biosensors with electrospun polyurethane (PU) membranes, their effects on sensor function and efficacy as mass-transport limiting membranes. For electrospinning fibres directly on sensor surface, both static and dynamic collector systems, were designed and tested. Optimum collector configurations were first ascertained by FEA modelling. Both static and dynamic collectors allowed complete covering of sensors, but it was the dynamic collector that produced uniform fibro-porous PU coatings around miniature ellipsoid biosensors. The coatings had random fibre orientation and their uniform thickness increased linearly with increasing electrospinning time. The effects of coatings having an even spread of submicron fibre diameters and sub-100 μm thicknesses on glucose biosensor function were investigated. Increasing thickness and fibre diameters caused a statistically insignificant decrease in sensor sensitivity for the tested electrospun coatings. The sensors' linearity for the glucose detection range of 2-30 m. m remained unaffected. The electrospun coatings also functioned as mass-transport limiting membranes by significantly increasing the linearity, replacing traditional epoxy-PU outer coating. To conclude, electrospun coatings, having controllable fibro-porous structure and thicknesses, on miniature ellipsoid glucose biosensors were demonstrated to have minimal effect on pre-implantation sensitivity and also to have mass-transport limiting ability. © 2012 Elsevier Ltd.


Wang W.,University of Science and Technology Beijing | Banjevic D.,University of Toronto
Reliability Engineering and System Safety | Year: 2012

The delay time concept and the techniques developed for modelling and optimising plant inspection practice have been reported in many papers and case studies. For a system subject to a few major failure modes, component based delay time models have been developed under the assumptions of an age-based inspection policy. An age-based inspection assumes that an inspection is scheduled according to the age of the component, and if there is a failure renewal, the next inspection is always, say τ times, from the time of the failure renewal. This applies to certain cases, particularly important plant items where the time since the last renewal or inspection is a key to schedule the next inspection service. However, in most cases, the inspection service is not scheduled according to the need of a particular component, rather it is scheduled according to a fixed calendar time regardless whether the component being inspected was just renewed or not. This policy is called a block-based inspection which has the advantage of easy planning and is particularly useful for plant items which are part of a larger system to be inspected. If a block-based inspection policy is used, the time to failure since the last inspection prior to the failure for a particular item is a random variable. This time is called the forward time in this paper. To optimise the inspection interval for block-based inspections, the usual criterion functions such as expected cost or down time per unit time depend on the distribution of this forward time. We report in this paper the development of a theoretical proof that a limiting distribution for such a forward time exists if certain conditions are met. We also propose a recursive algorithm for determining such a limiting distribution. A numerical example is presented to demonstrate the existence of the limiting distribution. © 2011 Elsevier Ltd. All rights reserved.


Yao X.,University of Science and Technology Beijing | Han X.,University of Science and Technology Beijing | Du X.,Temple University
Proceedings - IEEE INFOCOM | Year: 2014

In order to meet the security requirement, most data are stored in cloud as cipher-texts. Hence, a cipher-text based access control mechanism is needed for data sharing in cloud. A popular solution is to use the attribute-based encryption. However, it is not suitable for mobile cloud due to the heavy computation overhead caused by bilinear pairing, which also makes it difficult to change the access control policy. In addition, attribute-based encryption can't achieve fine-grained access control yet. In this paper, we present a lightweight cipher-text access control mechanism for mobile cloud computing, which is based on authorization certificates and secret sharing. Only the certificate owner can reconstruct decryption keys for his/her files. Our analyses show that the mechanism can achieve efficient and fine-grained access control on cipher-text at a much lower cost than the attribute-based encryption solution. © 2014 IEEE.


Wang L.,University of Science and Technology Beijing | May V.,Humboldt University of Berlin
Journal of Physical Chemistry C | Year: 2014

Plasmon enhancement of photoinduced charge injection from a perylene dye into a large TiO2 cluster is studied theoretically. A system is investigated where a spherical metal nanoparticle (MNP) is placed near the dye at the cluster surface. The simulations account for optical excitation of the dye coupled to the MNP and subsequent electron injection into the rutile TiO2 cluster with (110) surface. The electron motion in the cluster is described in a tight-binding model and focuses on excess electron localization at the Ti atoms and inter Ti charge transfer. Clusters with about 105 atoms can be treated. Charge injection dynamics is described in the framework of the density matrix theory which, however, ignores in this first attempt molecular vibrations. Considering short optical excitations, the overall probability to have the electron injected into the cluster reaches an intermediate steady state. This probability is used to introduce an enhancement factor which rates the influence of the MNP. Values larger than 1000 are obtained mainly caused by MNP induced photoabsorption enhancement. The also considered Coulomb coupling of the injected electron with the molecular cation and with the image charge induced at the MNP is of minor importance. © 2014 American Chemical Society.


Wang L.,University of Science and Technology Beijing | May V.,Humboldt University of Berlin
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

Charge transmission through a single oligomer placed perpendicular to a junction formed by a left and a right nanoelectrode is discussed theoretically. Photoinduced Frenkel-exciton formation in the oligomer is shown to essentially affect the current through that particular monomer, which has been sandwiched by the two electrodes. In order to demonstrate this, systems are considered with different charging energies of the contacted monomer. In the case of a small charging energy relative to the leads chemical potential, the photoinduced current switch is based on transitions from exciton states that belong to the uncharged oligomer to exciton states of the singly charged one. If the charging energy relative to the leads chemical potential is comparable to the energy of Frenkel-exciton formation, charging of the oligomer proceeds via exciton states that belong to the neutral system. This scheme offers an efficient photoinduced current switch. © 2011 American Physical Society.


He Y.,Chongqing University | Liu B.,Chongqing University | Zhang X.,University of Science and Technology Beijing | Gao H.,Chongqing Machine Tools Group Co. | Liu X.,IBM
Journal of Cleaner Production | Year: 2012

Machining tasks are performed on machine tools with enormous amount of energy consumption in manufacturing system. Understanding and characterizing task-oriented energy consumption is significantly essential to explore the potential on energy-saving in production management. To achieve it, this paper proposes a modeling method of task-oriented energy consumption for machining manufacturing system. The energy consumption characteristics driven by task flow in machining manufacturing system are analyzed, which describes that energy consumption dynamically depends on the flexibility and variability of task flow in production processes. Based on the task-oriented energy consumption characteristics, an event graph methodology has been exploited to model the energy consumption driven by tasks in production processes of machining manufacturing system. The proposed modeling method is solved in Simulink simulation environment, and applied to select the flexible processes of tasks for optimizing energy consumption. The results show a valuable insight of energy consumption in machining manufacturing system so as to make robust decisions on the potential for improving energy efficiency. © 2011 Elsevier Ltd. All rights reserved.


Wang L.,University of Science and Technology Beijing | May V.,Humboldt University of Berlin
Journal of Physical Chemistry C | Year: 2010

Photoinduced changes of the current voltage (IV) characteristics of a single molecule attached to a left and a right electrode are revisited including the inevitable photon absorption by the leads due to electron-hole pair generation. To determine the related nonequilibrium electron distribution, a method is utilized based on the introduction of an effective electron temperature Tel in the Fermi distribution. By varying Tel, possible excitation conditions in the experiments are modeled. Heating of the molecule as well as the effect of intramolecular vibrational energy redistribution (IVR) is also accounted for. An intermediate excitation regime can be identified where the optical current switch is dominated by molecular excitations and less by an electron-hole pair generation in the leads. Vibrational distributions in the molecule induced due to either current formation or optical excitation are found to strongly deviate from thermal equilibrium. To observe the current switch, it is essential that these distributions are only slightly affected by IVR. © 2010 American Chemical Society.


Wang D.,University of Science and Technology Beijing | Bao Y.,University of Science and Technology Beijing | Zha J.-W.,University of Science and Technology Beijing | Zhao J.,University of Science and Technology Beijing | And 2 more authors.
ACS Applied Materials and Interfaces | Year: 2012

In this work, two series of nanocomposites of poly(vinylidene fluoride) (PVDF) incorporated with reduced graphene oxide (rGO) and poly(vinyl alcohol)-modified rGO (rGO-PVA) were fabricated using solution-cast method and their dielectric properties were carefully characterized. Infrared spectroscopy and atom force microscope analysis indicated that PVA chains were successfully grafted onto graphene through ester linkage. The PVA functionalization of graphene surface can not only prevent the agglomeration of original rGO but also enhance the interaction between PVDF and rGO-PVA. Strong hydrogen bonds and charge transfer effect between rGO-PVA and PVDF were determined by infrared and Raman spectroscopies. The dielectric properties of rGO-PVA/PVDF and rGO/PVDF nanocomposites were investigated in a frequency range from 102 Hz to 107 Hz. Both composite systems exhibited an insulator-to-conductor percolating transition as the increase of the filler content. The percolation thresholds were estimated to be 2.24 vol % for rGO-PVA/PVDF composites and 0.61 vol % for rGO/PVDF composites, respectively. Near the percolation threshold, the dielectric permittivity of the nanocomposites was significantly promoted, which can be well explained by interfacial polarization effect and microcapacitor model. Compared to rGO/PVDF composites, higher dielectric constant and lower loss factor were simultaneously achieved in rGO-PVA/PVDF nanocomposites at a frequency range lower than 1 × 103 Hz. This work provides a potential design strategy based on graphene interface engineering, which would lead to higher-performance flexible dielectric materials. © 2012 American Chemical Society.


Zhang L.,University of Science and Technology Beijing | Wang Y.,SSAB
JOM | Year: 2012

Understanding the entrapment of inclusions in the solidifying shell within a steel continuous-casting strand is important to predict and improve the internal quality of the steel product. The current work presents two approaches to predict the particle entrapment in the full length of a billet caster. First, the sink term approach assumed a cone-shaped solidification shell and ignored the heat transfer and solidification, and sink terms were added to the equations to represent the mass loss and momentum loss during solidification. The inclusions were entrapped once they touched the shell. Second, full solidification considered the effect of turbulent flow, heat transfer, solidification, and the motion of inclusions. Inclusions were entrapped once they moved to the location with a liquid fraction of 0.6. The calculated inclusion distribution in the billet by the full solidification approach agreed with the industrial measurement better than the sink term approach. For future study, the effects of the inclusion size and the first arm spacing on the entrapment of inclusions will be included in the full solidification approach. © 2012 TMS.


Liu T.,University of Science and Technology Beijing | Li H.,China Mobile
Journal of the Franklin Institute | Year: 2014

Orthogonal frequency division multiplexing (OFDM) has been widely adopted in radar and communication systems. High sensitivity to carrier frequency offset (CFO) is one of the major drawbacks of OFDM. CFO estimation for OFDM systems had been extensively studied and various algorithms had been proposed. However, the established algorithms may be compromised by the adoption of direct-conversion architecture and multi-mode low noise amplifier in the OFDM receiver, which introduces time-varying direct current offset (TV-DCO) into the system. In our previous study, we developed an eigen-decomposition based estimation algorithm, which is robust to TV-DCO but suffers from performance degradation under low to medium signal-to-noise ratio and requires high computation efforts. To address those issues, we in this paper propose a novel blind CFO estimation algorithm. By making use of the second order differential filtering and subspace method, the proposed algorithm achieves great performance improvement with reduced complexity. The performance of the proposed algorithm is demonstrated by simulations. © 2013 The Franklin Institute. Published by Elsevier Ltd. All rights reserved.


Liu T.,University of Science and Technology Beijing | Li H.,China Mobile
Signal Processing | Year: 2011

Orthogonal frequency division multiplexing (OFDM) systems with direct-conversion receiver (DCR) are vulnerable to carrier frequency offset (CFO), dc offset (DCO) and in-phase/quadrature (I/Q) imbalance. In this paper, we propose blind estimator for joint estimation of CFO, DCO and I/Q imbalance in OFDM systems with DCR. Simulation results show that performance of proposed estimator approaches CramrRao lower bound (CRLB) asymptotically, which demonstrates its effectiveness. © 2010 Elsevier B.V. All rights reserved.


Wang L.,University of Science and Technology Beijing | May V.,Humboldt University of Berlin
Chemical Physics | Year: 2010

A density matrix based description of charge transmission through a single molecule attached to two nano-electrodes is presented. By concentrating on a steady state situation the net current, electronic state populations and nonequilibrium vibrational distributions are computed. The dependence of these quantities on the applied voltage and on a cw-infrared as well as optical excitation is discussed. Effects are included of intra-molecular vibrational energy redistribution (IVR), of different charging states, and of an electron-hole pair generation in the leads. The considerations are valid for a sequential mechanism of charge transmission through the molecule. A possible current switch due to an infrared as well as an optical excitation is demonstrated and the crucial dependence of the switching mechanism on the strength of IVR is underlined. If the molecule attached to nano-electrodes is a part of an oligomer or supramolecular chromophore complex the current can be controlled by an external field induced Frenkel-exciton formation. © 2010 Elsevier B.V. All rights reserved.


Wang L.,University of Science and Technology Beijing | May V.,Humboldt University of Berlin
Journal of Electroanalytical Chemistry | Year: 2011

Net electron transfer through a single molecule attached to nano electrodes can undergo a pronounced change by resonant optical excitation. Caused by the population of excited electronic states of the molecule new transmission channels are opened which alter the current-voltage characteristics of the junction. This recent suggestion is further investigated here by studying the transient behavior of the current if the external laser pulse excitation is switched-on and -off within a certain time-interval. The computations concentrate on the case of weak and intermediate molecule-lead coupling. They are carried out in using rate equations which govern the populations of the different electron-vibrational states of the molecule being in its neutral or charged state. The interrelation of the switching-time and the time of charging and discharge of the molecule as well as of the time of vibrational relaxation is demonstrated by working in a switching-time range of some hundreds fs up to about 50 ps. © 2010 Elsevier B.V. All rights reserved.


Wang L.,University of Science and Technology Beijing | May V.,Humboldt University of Berlin
Physical Chemistry Chemical Physics | Year: 2011

Laser pulse control of electron transfer through a single molecule attached to nano electrodes is demonstrated theoretically by concentrating on the case of weak and intermediate molecule-lead coupling. A rate equation description is used to determine the populations of the different electron-vibrational states of the molecule in its neutral or charged state. Caused by the photoinduced population of excited electronic states new transmission channels are opened which change the current through the molecular junction. The transient behavior of the current is studied if the external laser pulse excitation is switched on and off or if a pulsed excitation is applied. Pulse durations of some hundreds of fs up to 50 ps are considered. Within this computational scheme the interrelation of characteristic times of charging, discharge, vibrational relaxation, and the turn on and off of the photoexciation is demonstrated. Possible self-stabilization of an excited junction state is found. Some estimates of potential effects of plasmon excitations in the leads are also given. To have a quantity available which offers direct experimental access to the transient state of the junction the time and frequency resolved photo emission spectrum of the molecule is calculated. © 2011 the Owner Societies.


Tao H.-C.,University of Science and Technology Beijing | Fan L.-Z.,University of Science and Technology Beijing | Mei Y.,Fudan University | Qu X.,University of Science and Technology Beijing
Electrochemistry Communications | Year: 2011

Self-supporting Si/Reduced Graphene Oxide (RGO) nanocomposite films have been prepared by thermal reduction of Si/graphene oxide nanocomposite, which is fabricated by dispersing silicon nanoparticles into an aqueous suspension of graphene oxide nanosheets. The Si nanoparticles are well encapsulated in a RGO matrix and the Si/RGO composite has much higher reversible discharge capacity and a better cycle stability than pure nanosized Si particles as well as the RGO. Such enhancement can be attributed to the RGO matrix, which offers an efficient electrically conductive channel and a flexible mechanical support for strain release. © 2011 Elsevier B.V. All rights reserved.


Shi P.,University of Science and Technology of China | Xia Z.,University of Science and Technology of China | Xia Z.,University of Science and Technology Beijing | Molokeev M.S.,RAS Kirensky Institute of Physics | Atuchin V.V.,Tomsk State University
Dalton Transactions | Year: 2014

Scheelite related alkali-metal rare-earth double molybdate compounds with a general formula of ALn(MoO4)2 can find wide application as red phosphors. The crystal chemistry and luminescence properties of red-emitting CsGd1-xEux(MoO4)2 solid-solution phosphors have been evaluated in the present paper. A detailed analysis of the structural properties indicates the formation of isostructural scheelite-type CsGd1-xEux(MoO4)2 solid-solutions over the composition range of 0 ≤ x ≤ 1. The photoluminescence emission (PL) and excitation (PLE) spectra, and the decay curves were measured for this series of compounds. The critical doping concentration of Eu3+ is determined to be x = 0.6 in order to realize the maximum emission intensity. The emission spectra of the as-obtained CsGd(1-x)Eux(MoO4)2 phosphors show narrow high intensity red lines at 592 and 615 nm upon excitation at 394 or 465 nm, revealing great potential for applications in white light-emitting diode devices. © 2014 the Partner Organisations.


Xu X.,University of Science and Technology Beijing | Liu B.,Central South University | Zou Y.,Central South University | Guo Y.,CAS Beijing National Laboratory for Molecular | And 2 more authors.
Advanced Functional Materials | Year: 2012

The interface between the organic semiconductor and dielectric plays an important role in determining the device performance of organic field-effect transistors (OFETs). Although self-assembled monolayers (SAMs) made from organosilanes have been widely used for dielectric modification to improve the device performance of OFETs, they suffer from incontinuous and lack uniform coverage of the dielectric layer. Here, it is reported that by introduction of a solution-processed organozinc compound as a dielectric modification layer between the dielectric and the silane SAM, improved surface morphology and reduced surface polarity can be achieved. The organozinc compound originates from the reaction between diethylzinc and the cyclohexanone solvent, which leads to formation of zinc carboxylates. Being annealed at different temperatures, organozinc compound exists in various forms in the solid films. With organozinc modification, p-type polymer FETs show a high charge carrier mobility that is about two-fold larger than a control device that does not contain the organozinc compound, both for devices with a positive threshold voltage and for those with a negative one. After organozinc compound modification, the threshold voltage of polymer FETs can either be altered to approach zero or remain unchanged depending on positive or negative threshold voltage they have. A solution-processed organozinc compound is utilized as a dielectric modification layer in polymer field-effect transistors to improve the surface morphology and to reduce the surface polarity. Enhanced charge carrier mobility is achieved. The organozinc compound originates from the reaction between diethylzinc and the cyclohexanone solvent, which leads to formation of zinc carboxylates. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Tian J.,University of Science and Technology Beijing | Tian J.,University of Washington | Zhang Q.,University of Washington | Zhang L.,University of Washington | And 5 more authors.
Nanoscale | Year: 2013

Photoelectrode made of nanocable structure of ZnO nanorods (NR) coated with TiO2 nanosheets (NSs) was investigated for CdS/CdSe quantum dot co-sensitized solar cells. ZnO NRs prepared solution reaction at 60 °C served as the backbone for direct electron transport in view of the single crystallinity of the ZnO NRs and the high electron mobility of ZnO semiconductor. Anatase TiO2 NSs with the thickness of ∼10 nm and the length of ∼100 nm were assembled onto the surface of ZnO NRs via a solvothermal method. It was found that the thin shell of TiO2 might have remarkable influence on the quantum dot sensitized solar cells (QDSCs) through (a) increasing the surface area of ZnO NRs to allow for adsorbing more quantum dots (QDs), which led to high short current density, (b) forming an energy barrier that hindered the electrons in the ZnO from being back to the electrolyte and QDs, and thus, reduced the charge recombination rate, resulting in prolonged electron lifetime and enhanced open voltage. In comparison with the case of ZnO NRs, the short-circuit current density, open-circuit voltage, fill factor and charge recombination resistance of ZnO/TiO2 nanocable photoelectrode increase by 3%, 44%, 48% and 220%, respectively. As a result, a power conversion efficiency of 2.7% of QDSCs with core-shell structural nanocable photoelectrode has been obtained, which is as much as 230% of that of 1.2% obtained for ZnO NR photoelectrode. © 2013 The Royal Society of Chemistry.


Tian J.,University of Science and Technology Beijing | Uchaker E.,University of Washington | Zhang Q.,University of Washington | Cao G.,University of Washington | Cao G.,CAS Beijing Institute of Nanoenergy and Nanosystems
ACS Applied Materials and Interfaces | Year: 2014

ZnO nanorods (NRs) and nanosheets (NSs) were fabricated by adjusting the growth orientation of ZnO crystals in the reaction solution, respectively. The thin ZnO NSs were slowly assembled on the surface of NRs to form a hierarchically structured NR-NS photoelectrode for constructing CdS/CdSe quantum-dot-sensitized solar cells (QDSCs). This hierarchical structure had two advantages in improving the power conversion efficiency (PCE) of the solar cells: (a) it increased the surface area and modified the surface profile of the ZnO NRs to aid in harvesting more quantum dots, which leads to a high short-current density (Jsc); (b) it facilitated transportation of the electrons in this compact structure to reduce the charge recombination, which led to enhancement of the open-circuit voltage (Voc) and fill factor (FF). As a result, the QDSC assembled with the hierarchical NR-NS photoelectrode exhibited a high PCE of 3.28%, which is twice as much as that of the NR photoelectrode (1.37%). © 2014 American Chemical Society.


Ning H.S.,University of Science and Technology Beijing | Liu H.,RUN Technologies Co.
Science China Information Sciences | Year: 2015

The Internet of Things (IoT) as an emerging network paradigm is bringing the next scientific and technological revolution for ubiquitous things’ interactions in cyber-physical-social spaces. The IoT influences the current science and technology system by enabling its relatively stable interrelations for an inevitable architecture reconfiguration. In this paper, we aim to explore an updated science and technology framework for the IoT. Particularly, a novel cyber-physical-social-thinking (CPST) space is established by involving an attractive concept of the Internet of Thinking (IoTk), and a science and technology framework is accordingly proposed referring to both scientific aspect (i.e., cyber-physical, social, and noetic sciences) and technological aspect (i.e., fundamental, physical, cyber, and social technologies). According to the perspective of the traditional Chinese culture, we explain the established science and technology framework, in which the “Five Elements” (i.e., wood, fire, earth, metal, and water) have common properties with the restructured cyber-physical science in the IoT. Moreover, we introduce a scenario of smart city to identify the technological aspect in the IoT, and discuss the key enabling technologies, including resource management, energy management, data management, session management, security and privacy, loop control, space-time consistency, nanotechnology, and quantum technology. It turns out that the established science and technology framework will launch an innovation for academia and industry communities. © 2015, Science China Press and Springer-Verlag Berlin Heidelberg.


Wu Y.,CAS Institute of Chemistry | Li Z.,CAS Institute of Chemistry | Li Z.,University of Science and Technology Beijing | Guo X.,CAS Institute of Chemistry | And 3 more authors.
Journal of Materials Chemistry | Year: 2012

A feasible synthetic route to alkoxy-substituted DTBDT was designed and the first DTBDT-based polymer was prepared and applied in organic solar cells. The preliminary results indicate that the DTBDT unit can be used as a potential building block in organic semiconductor materials. © 2012 The Royal Society of Chemistry.


Zhang S.,University of Science and Technology Beijing | Zhang S.,CAS Institute of Chemistry | Ye L.,CAS Institute of Chemistry | Zhao W.,CAS Institute of Chemistry | And 4 more authors.
Macromolecules | Year: 2014

Recently, the benzodithiophene- (BDT-) based polymers with conjugated side groups attracted considerable attention due to their superior properties in polymer solar cells (PSCs), so the investigation of the side chain effects on the photovoltaic properties of this type of polymers is an interesting and important topic for molecular design. Herein, three conjugated polymers based on BDT and thieno[3,4-b]thiophene units with furan, thiophene and selenophene as side groups, named as PBDTTT-EFF, PBDTTT-EFT, and PBDTTT-EFS, were synthesized and applied in polymer solar cells. The polymers were characterized in parallel by absorption spectroscopy, thermogravimetric analysis (TGA), density functional theory (DFT), ultraviolet photoemission spectroscopy (UPS), X-ray diffraction (XRD), and photovoltaic measurements. The results show that the dihedral angles between the BDT and conjugated side groups play important roles in affecting the absorption bands, HOMO levels, crystallinities, and aggregation sizes of the polymers. The photovoltaic results indicate that PBDTTT-EFT and PBDTTT-EFS show similar photovoltaic characteristics in device, and PCEs of 9.0% and 8.78% were obtained, respectively. The device of PBDTTT-EFF shows a Voc of 0.69 V and a Jsc of 11.77 mA/cm2, which are lower than those in the devices based on the other two polymers. Overall, this work suggests that the photovoltaic properties of the BDT-based polymers can be effectively tuned by introducing conjugated side groups with varied steric hindrance. © 2014 American Chemical Society.


Xu L.-P.,University of Science and Technology Beijing | Zhao J.,University of Science and Technology Beijing | Su B.,CAS Beijing National Laboratory for Molecular | Liu X.,CAS Beijing National Laboratory for Molecular | And 8 more authors.
Advanced Materials | Year: 2013

Superoleophobicity under seawater: An ion-induced low-oil-adhesion film with underwater superoleophobicity is prepared by a typical layer-by-layer (LBL) method. Under an artificial marine environment with high ion-strength, the prepared polyelectrolytes/AuNPs hybrid film becomes rougher and possesses a higher water ratio, which in turn endows the film with superoleophobicity and low underwater oil adhesion. The as-prepared film shows excellent environmental stability in artificial seawater. This study provides a new strategy for controlling the self-cleaning property and accelerating the development of stable underwater superoleophobic films. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Du Y.,University of Science and Technology Beijing | Tan W.,IBM | Zhou M.,Tongji University | Zhou M.,New Jersey Institute of Technology
IEEE Transactions on Automation Science and Engineering | Year: 2014

Recently, the temporal constraint satisfiability is regarded as an important criterion in Web service composition to guarantee its timely completion. This leads to a new challenge in analyzing the compatibility of Web services under temporal constraints. The existing methods either do not consider message mismatches between services in a composition or suffer from state-space explosion by verifying a service composition model as a whole; or lack the ability to generate execution paths of each participating service. In this paper, we present a Petri net-based method to address these three issues in a holistic manner, and also in a modular way. Compared with the existing work, the proposed approach not only composes Web services by adding a mediation net to deal with message mismatches, but also checks the compatibility w.r.t. temporal constraints by generating modular timed state graphs. Furthermore, the reliable and usable execution paths that satisfy the timed compatibility can be derived to guide service execution and avoid any temporal exception. © 2004-2012 IEEE.


Cheng F.,University of Science and Technology of China | Xia Z.,University of Science and Technology of China | Xia Z.,University of Science and Technology Beijing | Jing X.,CAS Beijing National Laboratory for Molecular | Wang Z.,University of Science and Technology of China
Physical Chemistry Chemical Physics | Year: 2015

A series of double molybdate scheelite-type phosphors LixAg1-xYb0.99(MoO4)2:0.01Er3+ (x = 0, 0.1, 0.3, 0.5, 0.7, 0.9, 1.0) were synthesized by the solid state reaction method, and their crystal structures and upconversion (UC) luminescence properties were investigated in detail. The phase structure evolution of this series samples was discussed and the selected Li0.5Ag0.5Yb0.99(MoO4)2:0.01Er3+ was analyzed based on the Rietveld refinement. The UC emission properties and the related UC mechanism were also studied. With an increasing Li/Ag ratio in this host, the UC emission intensities of LixAg1-xYb0.99(MoO4)2:0.01Er3+ increased obviously, and the enhancement could be attributed to the coupling effect and the nonradiative transition between two energy levels of LixAg1-xYb(MoO4)2 matrices and the activator Er3+, which have also been analyzed based on the results of the ultraviolet-visible diffuse reflection spectroscopy (UV-vis DRS) and Raman spectroscopy. © the Owner Societies 2015.


Ji H.,University of Science and Technology of China | Huang Z.,University of Science and Technology of China | Xia Z.,University of Science and Technology Beijing | Molokeev M.S.,RAS Kirensky Institute of Physics | And 3 more authors.
Journal of Physical Chemistry C | Year: 2015

The cation substitution-dependent phase transition was used as a strategy to discover new solid solution phosphors and to efficiently tune the luminescence property of divalent europium (Eu2+) in the M3(PO4)2:Eu2+ (M = Ca/Sr/Ba) quasi-binary sets. Several new phosphors including the greenish-white SrCa2(PO4)2:Eu2+, the yellow Sr2Ca-(PO4)2:Eu2+, and the cyan Ba2Ca(PO4)2:Eu2+ were reported, and the drastic red shift of the emission toward the phase transition point was discussed. Different behavior of luminescence evolution in response to structural variation was verified among the three M3(PO4)2:Eu2+ joins. Sr3(PO4)2 and Ba3(PO4)2 form a continuous isostructural solid solution set in which Eu2+ exhibits a similar symmetric narrow-band blue emission centered at 416 nm, whereas Sr2+ substituting Ca2+ in Ca3(PO4)2 induces a composition-dependent phase transition and the peaking emission gets red shifted to 527 nm approaching the phase transition point. In the Ca3-xBax(PO4)2:Eu2+ set, the validity of crystallochemical design of phosphor between the phase transition boundary was further verified. This cation substitution strategy may assist in developing new phosphors with controllably tuned optical properties based on the phase transition. (Figure Presented). © 2015 American Chemical Society.


Wang C.,CAS Beijing National Laboratory for Molecular | Wang C.,University of Science and Technology Beijing | Feng L.,CAS Beijing National Laboratory for Molecular | Li W.,CAS Beijing National Laboratory for Molecular | And 3 more authors.
Solar Energy Materials and Solar Cells | Year: 2012

The phase change behaviors of polyethylene glycol (PEG)/porous carbon composites are extensively studied. Three types of shape-stabilized PCMs were prepared using expanded graphite (EG), active carbon (AC) and ordered mesoporous carbon (CMK-5) as supporting materials with various pore structures. They have distinct influences on the phase change behaviors of PEG/porous carbon composites. The highest stabilized PEG content is 70 wt% for AC and 90% for both EG and CMK-5. The phase change enthalpy and the PEG crystallinity increases in the order AC


Dou R.,University of Science and Technology Beijing | Wen Z.,Beijing Key Laboratory for Energy Saving and Emission Reduction of Metallurgical Industry | Zhou G.,China ENFI Engineering Corporation
Applied Thermal Engineering | Year: 2016

A 2D axisymmetric inverse heat-conduction model based on the Levenber-Marquardt method was built. The equivalent Nusselt number Nuequ of air jet impinging on a stainless steel plate with finite thickness were obtained. Radiant heat transfer is significant when the temperature of the target plate is high, which induces the nonlinear feature of the inverse heat-conduction problem. The results of the experiments and the inverse analysis provide the following findings. First, the inverse heat-conduction model is accurate. Second, Nuequ maintains a relatively small value before the onset of the air jet. After the air jet starts, however, the values of Nuequ within the stagnation zone (dimensionless radius R/Dn≤&1.0) increase dramatically, reach the peak points in the next 20s, and then remain nearly constant until the end of the experiments. Third, the radial distribution of Nu;bsubesub shows that it decreases rapidly within the region of R/D;bsubesub≤;8.0. When R/Dn exceeds 10, Nuequ appears unaffected by the Reynolds number and R/Dn. Lastly, Nuequ decreases slowly with the increase in time, which indicates that radiant heat-transfer flux decreases with target plate temperature. © 2015 Elsevier Ltd. All rights reserved.


Xu L.-P.,University of Science and Technology Beijing | Wu X.,University of Science and Technology Beijing | Meng J.,CAS Beijing National Laboratory for Molecular | Peng J.,University of Science and Technology Beijing | And 3 more authors.
Chemical Communications | Year: 2013

Inspired by selective wettability and hierarchical structure of papillae on lotus seeds, papilla-like magnetic particles were fabricated by thermal treatment of Fe microparticles. The papilla-like magnetic particles modified by lauric acid exhibited superhydrophobicity, superoleophilicity and great oil removing capability from water. © The Royal Society of Chemistry 2013.


Wang H.,University of Science and Technology Beijing | Qian K.,CAS Beijing National Laboratory for Molecular | Qi D.,University of Science and Technology Beijing | Cao W.,University of Science and Technology Beijing | And 3 more authors.
Chemical Science | Year: 2014

Effective and different inter-molecular interactions between fullerene C60 and tetrapyrrole-based double-decker single molecule magnets (SMMs) of three cocrystallates with different molar ratios rationalize the slight structural changes and different magnetic properties. The presented results indicate that different integration modes between the SMM and conjugated sp2-carbon substrate are able to affect the magnetic properties of the spintronic devices to different degrees, representing the effort towards understanding the effect of the conjugated sp2-carbon substrate on the magnetic properties of SMM spintronic devices at a molecular level. © the Partner Organisations 2014.


Tian J.,University of Science and Technology Beijing | Tian J.,CAS Beijing Institute of Nanoenergy and Nanosystems | Zhang Q.,University of Washington | Uchaker E.,University of Washington | And 5 more authors.
Energy and Enviro