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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.


Hu G.-D.,University of Science and Technology Beijing
Kybernetika | Year: 2014

In this paper, Runge-Kutta methods are discussed for numerical solutions of conservative systems. For the energy of conservative systems being as close to the initial energy as possible, a modified version of explicit Runge-Kutta methods is presented. The order of the modified Runge-Kutta method is the same as the standard Runge-Kutta method, but it is superior in energy-preserving to the standard one. Comparing the modified Runge-Kutta method with the standard Runge-Kutta method, numerical experiments are provided to illustrate the effectiveness of the modified Runge-Kutta method. Source


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. Source


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. Source


Xiao W.,University of Science and Technology Beijing | Xiao J.-L.,Inner Mongolia University
Superlattices and Microstructures | Year: 2012

We study the eigenenergies and the eigenfunctions of the ground and the first excited states of an electron, which is strongly coupled to LO-phonon in a quantum rod with a hydrogen-like impurity at the center by using the variational method of Pekar type. This quantum rod system may be used as a two-level quantum qubit. When the electron is in the superposition state of the ground and the first-excited states, the probability density of the electron oscillates in the quantum rod. It is found that the probability density and the oscillation period are individually increased and decreased due to the presence of the Coulomb interaction between the electron and the hydrogen-like impurity. The oscillation period is an increasing function of the ellipsoid aspect ratio and the effective confinement lengths of the quantum rod, whereas it is a decreasing one of the electron-phonon coupling strength. © 2012 Elsevier Ltd. All rights reserved. Source


Zhang Y.,Control Iron and Steel Research Institute, China | Hu B.,University of Science and Technology Beijing
Jinshu Xuebao/Acta Metallurgica Sinica | Year: 2015

Hafnium (Hf) is one of the most important microelements in powder metallurgy (P/M) superalloy. Hf modifies the microstructure and drastically improves mechanical properties in P/M superalloy. The effect of Hf in a nickel-based P/M superalloy was systematically studied by means of FEG-SEM, TEM, AES, EDS and physical and chemical phase analysis. Hf mainly distributes at interdendritic region of the solidification powder in form of solid solution, which is helpful to reduce prior particle boundary (PPB). Hf facilitates morphology of γ' phase to be unstable and enhances the large cubic γ' phase to split into smaller ones, so the γ' phase turns into a stable state with a lower energy faster. Hf is mainly distributed in γ' phase and MC carbides, which changes the distribution of element between the γ' phase, MC and g solid solution, which is beneficial to eliminate notch sensitivity and improves overall mechanical properties of the alloy. ©, 2015 All right reserved. Source


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. Source


Song B.,University of Science and Technology Beijing
Tumu Gongcheng Xuebao/China Civil Engineering Journal | Year: 2010

Based on the site investigations of the Wenchuan Earthquake in China and the Great Hanshin-Awaji Earthquake in southern part of Hyogo Prefecture in Japan, the characteristics or patterns of urban disasters in recent years were summarized and analyzed. These new characteristics included the complexity, the diversity, the extensiveness, the diffusion and the chain reaction of the disasters. Combining with the development and application status of disaster prevention planning in China, the status of urban facilities, the properties of urban disasters, and several aspects of urban disaster prevention were discussed, including countermeasures of urban disaster mitigation and the relationship between city planning and disaster prevention panning. The way of improving urban disaster prevention was also investigated. A series of new perspectives were proposed, such as rational disaster planning, building refuge parks, improving school-based prevention or community-based prevention strongholds, enhancing civic awareness of disaster prevention. Source


Tran H.T.,University of South Florida | Shirangi M.H.,Robert Bosch GmbH | Pang X.,University of Science and Technology Beijing | Volinsky A.A.,University of South Florida
International Journal of Fracture | Year: 2014

A systematic investigation and characterization of the interfacial fracture toughness of the bi-material copper leadframe/epoxy molding compound is presented. Experiments and finite element simulations were used to investigate delamination and interfacial fracture toughness of the bi-material. Two dimensional simulations using virtual crack closure technique, virtual crack extension and J-integral proved to be computationally cheap and accurate to investigate and characterize the interfacial fracture toughness of bi-material structures. The effects of temperature, moisture diffusion and mode-mixity on the interfacial fracture toughness of the bi-material were considered. Testing temperature and moisture exposure significantly reduce the interfacial fracture toughness, and should be avoided if possible. © 2013 Springer Science+Business Media Dordrecht. Source


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. Source


Geng K.,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
Dalton Transactions | Year: 2014

A novel blue-emitting double-phosphate phosphor Cs0.72Ca 0.72Gd1.28(PO4)2:Eu2+ was synthesized by the sol-gel method, and the structure and luminescence properties were investigated in detail. The crystal structure and chemical composition of Cs0.72Ca0.72Gd1.28(PO 4)2 matrix was analyzed and determined based on Rietveld refinements and phase and chemical composition analysis. The composition-optimized Cs0.72Ca0.72Gd 1.28(PO4)2:Eu2+ exhibited strong blue light, peaking at 462 nm upon excitation at 365 nm with the CIE coordinates of (0.139, 0.091). The quenching concentration of Eu2+ in the Cs0.72Ca0.72Gd1.28(PO4)2 phase was about 0.01 and attributed to the dipole-quadrupole interaction. The thermally stable luminescence properties, fluorescence decay curves and diffuse reflectance spectra of Cs0.72Ca0.72Gd 1.28(PO4)2:Eu2+ phosphors are also discussed, all of which indicate that the Cs0.72Ca 0.72Gd1.28(PO4)2:Eu2+ phosphor is a promising phosphor for application in white-light UV LEDs. © 2014 the Partner Organisations. Source


Wang W.,University of Salford | Wang W.,University of Science and Technology Beijing
Reliability Engineering and System Safety | Year: 2011

Inspection or condition monitoring is increasingly used in industry to identify the plant items state and to make maintenance decisions. This paper discusses an inspection model that is established under an assumption that the plant items state can be classified into four states corresponding to a three-stage failure process. The failed state is always observed immediately, but the other three states, namely normal, minor defective and severe defective, can only be identified by an inspection. The durations of the normal, minor defective and severe defective states constitute a three-stage failure process. This assumption is actually motivated by real world observations where the plant state is often classified by a three colour scheme, e.g., green, yellow and red corresponding to the three states before failure. The three-stage failure concept proposed is an extension to the delay time concept where the plant failure process is divided into a two-stage process. However such extension provides more modelling options than the two-stage model and is a step closer to reality since a binary description of the plat items state is restrictive. By formulating the probabilities of defective state identification and failure, we are able to establish a model to optimise the inspection interval with respect to a criterion function of interest. A real world example is presented to show the applicability of the model. © 2011 Elsevier Ltd. All rights reserved. Source


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. Source


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. Source


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. Source


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. Source


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. Source


Wu C.,University of Science and Technology Beijing
Journal of Coatings Technology Research | Year: 2010

The corrosion resistance characteristics of three coatings on magnesium alloy AZ31-conventional paint with phosphate film, cathodic electrodeposition coating (E-coating), and E-coating pretreated with silane (Mg/silane/E-coating)- have been studied by means of electrochemical impedance spectroscopy (EIS) in a 3.5 wt% NaCl neutral aqueous solution and salt spray test using ASTM B117. Silane film was obtained by dipping AZ31 specimens in diluted hydroalcoholic silanic solutions and successively curing. It was found that the corrosion resistance of the Mg alloy with E-coating was superior to conventional paint and could be further enhanced with silane pretreatment as an interfacial film. The results of water volume fraction (Φ saturation) and diffusion coefficient (D) also indicated that the Mg/silane/E-coating possessed excellent compactness and corrosion resistance. A model of the corrosion mechanism for Mg/silane/E-coating has been presented through EIS analysis. © 2010 ACA and OCCA. Source


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. Source


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. Source


Kelly F.J.,Kings 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. Source


Ping D.H.,Japan National Institute of Materials Science | Geng W.T.,University of Science and Technology Beijing
Materials Chemistry and Physics | Year: 2013

Steel remains to be one of the most common structural materials in the world as human civilization advances from the Iron Age to the ongoing Silicon Age. Our knowledge of its microstructure evolution and structure-performance relationship is nevertheless still incomplete. We report the observation and characterization of a long ignored metastable phase formed in steels with body-centered cubic (bcc) structure using both transmission electron microscopy and density functional theory calculations. This ω phase has a hexagonal structure and coherent interface with the matrix: aω = √2 × abcc and cω = √3/2 × a bcc. It is 3.6% smaller in volume and 0.18 eV higher in energy than bcc-Fe, with atoms in alternating close- and loose-packed layers couple anti-ferromagnetically. Carbon plays a crucial role in promoting bcc to ω transformation. At a concentration higher than 4 at.% they tend to segregate from the bcc matrix to the ω-phase; at about 14 at.%, they can induce bcc to ω transformation; and finally at 25 at.%, they stabilize the ω phase as ω-Fe3C. The ω phase in bcc Fe can serve as sinks for vacancies, H, and He atoms, leading to improved resistance of martensitic steels to irradiation damage. © 2013 Elsevier B.V. All rights reserved. Source


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

Planet passing effect or the rotation of sun gear and planet carrier produces extra amplitude modulation to gear meshing vibration, and thereby results in complex spectral structure of transverse vibration signals of planetary gearbox. Torsional vibration signals are theoretically free from extra amplitude modulation effects, and therefore their spectral structure is simpler than that of transverse vibration signals. Thus, it is a potentially effective approach to diagnose planetary gearbox faults via torsional vibration signal analysis. Explicit equations to model torsional vibration signals were given, and the Fourier spectrum and the demodulated spectra of amplitude envelope and instantaneous frequency were deduced in closed form. The torsional vibration signal characteristics of Fourier, envelope and instantaneous frequency spectra were summarized. The theoretical derivations were validated experimentally. Source


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. Source


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. Source


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. Source


Chu K.,Lanzhou University of Technology | Jia C.,University of Science and Technology Beijing | Guo H.,General Research Institute for Nonferrous Metals, China | Li W.,Lanzhou University of Technology
Materials and Design | Year: 2013

Interfaces and close proximity between the diamond and the metal matrix are very important for their thermal conductance performance. Matrix-alloying is a useful approach to greatly enhance the interfacial bonding and thermal conductivity. In this study, the copper-diamond (Cu/Dia) composites with addition of 0.8, 1.2 and 2.4. wt.% zirconium (Zr) are prepared to investigate the influence of minor addition of Zr on the microstructure and thermal conductivity of the composites. The thermal conductivity of the composites is analyzed both experimentally and theoretically. It is demonstrated that moderate interfacial modification due to the Zr added is beneficial to improve the thermal conductivity of the Cu/Dia composites. © 2012 Elsevier Ltd. Source


Shi C.,University of Quebec at Chicoutimi | Mao W.,University of Science and Technology Beijing | Chen X.-G.,University of Quebec at Chicoutimi
Materials Science and Engineering A | Year: 2013

The hot deformation behavior of a homogenized AA7150 aluminum alloy was studied in compression tests conducted at various temperatures (573-723K) and strain rates (0.001-10s-1). The flow stress behavior and microstructural evolution were observed during the hot deformation process. A revised Sellars' constitutive equation was proposed, which considered the effects of the deformation temperature and strain rate on the material variables and which provided an accurate estimate of the hot deformation behavior of the AA7150 aluminum alloy. The results revealed that the activation energy for the hot deformation of the AA7150 aluminum alloy is not a constant value but rather varies as a function of the deformation conditions. The activation energy for hot deformation decreased with increasing deformation temperature and strain rate. The peak flow stresses under various deformation conditions were predicted by a revised constitutive equation and correlated with the experimental data with excellent accuracy. © 2013 Elsevier B.V. Source


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. Source


Zhang W.,University of Science and Technology Beijing | Zhang W.,State Key Laboratory of Automotive Safety and Energy
International Journal of Control | Year: 2010

This article presents a unified understanding and judgement of the stability and convergence of a general self-tuning control (STC) system, which consists of arbitrary control strategy, arbitrary parameter estimation algorithm and a deterministic/stochastic linear time-invariant (LTI) plant. The necessary conditions required for the global stability and convergence of a general STC system are relaxed, i.e. the convergence of parameter estimates is removed for both deterministic and stochastic STC schemes. To reach this goal, 'virtual equivalent system (VES)' concept and methodology is adopted. With the help of VES, the original nonlinear dominant (nonlinear in structure) problem is converted to a linear dominant (linear in structure) problem. The results developed in this article show that STC systems are stable and convergent for the abundance of control strategies and parameter estimation algorithms, which will provide great flexibility in the applications of STC. © 2010 Taylor & Francis. Source


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. Source


Xiao W.,University of Science and Technology Beijing | Xiao J.-L.,Inner Mongolia University
Journal of Low Temperature Physics | Year: 2011

The Hamiltonian of a quantum rod with an ellipsoidal boundary is given after a coordinate transformation, which changes the ellipsoidal boundary into a spherical one. We then study the first excited state energy, the excitation energy and the transition frequency between the first excited and the ground states of the strong-coupling magnetopolaron in it. The effects of the magnetic field cyclotron frequency, the electron-phonon coupling strength, the transverse and longitudinal effective confinement lengths and the aspect ratio of the ellipsoid are taken into consideration by using linear combination operator and the unitary transformation methods. It is found that the first excited state energy, the excitation energy and the transition frequency will increase with increasing the cyclotron frequency. They will increase with decreasing the transverse and longitudinal effective confinement lengths and the aspect ratio of the ellipsoid. The first excited state energy is decreasing functions of the electron-phonon coupling strength, whereas the excitation energy and the transition frequency are increasing functions of the electron-phonon coupling strength. © 2011 Springer Science+Business Media, LLC. Source


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. Source


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. Source


Chellali M.R.,University of Munster | Balogh Z.,University of Munster | Zheng L.,University of Munster | Zheng L.,University of Science and Technology Beijing | Schmitz G.,University of Munster
Scripta Materialia | Year: 2011

Atomic transport along triple junctions (TJs) and grain boundaries (GBs) has been measured by atom probe tomography in nanocrystalline Ni/Cu bilayers. Heat treatment was chosen in the kinetic C-B regime according to generalized Harrison categories for the hierarchy of volume, GB and TJ transport. Diffusion coefficients at 623 K were found to be 4.65 × 10-20 and 1.65 × 10-17 m2 s-1 for the GB and TJ, respectively. Thus, TJs represent a significantly faster diffusion route than GBs. © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Source


Peng F.,University of Science and Technology Beijing
European Physical Journal B | Year: 2011

We study a quantum coherent effect of spins in magnetic nanodots. We quantize the Heisenberg Hamiltonian in a coherent representation so as to deal with the time evolution of spin components. We observe that the number of quantum states in a nanodot is dependent on the nanodot size. For a nanodot of small size, it has very rare quantum states with a discrete energy structures. The distribution patterns of spins in these quantum states rotate about a central axis normal to the nanodot plane, and the spin reversal occurs with time. These quantum states can be achieved by a resonant excitation of a time-varying magnetic field. As a suggestion, the reversal of coherent spins may serve as a mechanism of binary information storage. © 2011 EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg. Source


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. Source


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. Source


Jiao Z.B.,City University of Hong Kong | Luan J.H.,City University of Hong Kong | Zhang Z.W.,Oak Ridge National Laboratory | Miller M.K.,Oak Ridge National Laboratory | And 2 more authors.
Acta Materialia | Year: 2013

There is an increasing demand for ultrahigh-strength ferritic steels strengthened by nanoprecipitates. Improvement of the precipitation strengthening response requires an understanding of the nanoscale precipitation mechanisms. In this study, the synergistic effects of Cu and Ni on nanoscale precipitation and mechanical properties of ferritic steels were thoroughly investigated, and new steels with ultrahigh strength and high ductility have been developed. Our results indicate that Ni effectively increases the number density of Cu-rich nanoprecipitates by more than an order of magnitude, leading to a substantial increase in yield strength. It appears that Ni decreases both the strain energy for nucleation and the interfacial energy between the nucleus and the matrix, thereby decreasing the critical energy for nucleation of Cu-rich nanoprecipitates. Cu and Ni are also found to be beneficial to grain-size refinement, resulting from lowering the austenite-to-ferrite transformation temperature, as determined from thermodynamic calculations. In addition, the strengthening mechanisms of Cu and Ni were quantitatively evaluated in terms of precipitation strengthening, grain refinement strengthening and solid-solution strengthening. The current findings shed light on the composition- microstructure-property relationships in nanoprecipitate-strengthened ferritic steels. © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Source


Jiang Y.,University of Science and Technology Beijing | Tang G.,Tsinghua University | Shek C.,City University of Hong Kong | Liu W.,Tsinghua University
Journal of Alloys and Compounds | Year: 2011

The effect of electropulsing treatment (EPT) on the microstructure and texture evolution of the cold-rolled AZ91 magnesium alloy strip was investigated using X-ray diffraction (XRD) and electron backscattered diffraction patterns (EBSD). The results indicated that EPT accelerated tremendously the recrystallization behaviour of the cold-rolled AZ91 magnesium alloy strip at a relatively low temperature within a short time of 7 s. It also suppressed precipitation of β-Mg17Al12 phase, compared with conventional heat treatment. The recrystallized grains favourably weakened the intensity of the basal texture. A mechanism for rapid recrystallization process during EPT was proposed based on the enhancement of nucleation rate and atomic diffusion resulting from the coupling of the themal and athermal effects. © 2011 Elsevier B.V. Source


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. Source


Jia N.,Kyushu University | Mitani Y.,Kyushu University | Xie M.,University of Science and Technology Beijing | Djamaluddin I.,Kyushu University
Computers and Geotechnics | Year: 2012

Shallow landslides are common in mountainous areas after intense rainfall. Of all landslide hazard assessment methods, deterministic methods provide the best quantitative information on landslide hazard. However, they require a large amount of detailed in situ data, derived from laboratory tests and field measurements, and therefore it is difficult to apply them over large areas. One of the most important input parameters is soil depth. For large areas, it is impossible to obtain soil depth through field measurements. To overcome this difficulty, a statistics-based regression analysis is used to evaluate soil depths. All the terrain attributes that control soil depths are selected as influential factors. By using multi-linear regression, the soil depths at each location can be predicted. Slope stability analysis can then be performed using deterministic methods with the evaluated soil depths. The study area is divided into slope units. For each slope unit, Monte-Carlo simulation and a GIS-based 3D limit equilibrium model are used to locate the critical slip surface and calculate the corresponding safety factor. The effectiveness of the proposed method has been tested by applying it to a mountainous area in Japan. © 2012 Elsevier Ltd. Source


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. Source


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. Source


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. Source


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. Source


Yuan J.-K.,Ecole 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. Source


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. Source


Wang L.,University of Science and Technology Beijing
Advanced Materials Research | Year: 2011

In this paper, we investigated timeslot allocation scheme in medium access control protocol for cognitive satellite networks. The timeslots for satellite primary users were allocated according to the reserve channel with priority fit algorithm and the timeslots for cognitive users were allocated according to the prediction algorithm. Compared to random allocation scheme, the correction ratio of timeslot allocation using the prediction algorithm was improved. The proposed timeslot allocation scheme adopted the combined backoff algorithm to avoid collisions. And then the improved throughput and the reduced delay could be obtained. Simulation results verify the effectiveness of the proposed timeslot allocation scheme. © 2011 Trans Tech Publications, Switzerland. Source


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. Source


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. Source


Wang M.,CAS Institute of Process Engineering | Wang Z.,CAS Institute of Process Engineering | Gong X.,CAS Institute of Process Engineering | Guo Z.,CAS Institute of Process Engineering | Guo Z.,University of Science and Technology Beijing
Renewable and Sustainable Energy Reviews | Year: 2014

Water electrolysis derived by renewable energy such as solar energy and wind energy is a sustainable method for hydrogen production due to high purity, simple and green process. One of the challenges is to reduce energy consumption of water electrolysis for large-scale application in future. Cell voltage, an important criterion of energy consumption, consists of theoretical decomposition voltage (Uθ), ohmic voltage drop.© 2013 Elsevier Ltd. All rights reserved. Source


Gan M.,University of Science and Technology Beijing | Gan M.,University of California at Berkeley
Decision Support Systems | Year: 2016

Recently, such state-of-the-art methods as collaborative filtering, content-based, model-based and graph-based approaches have achieved remarkable success in recommendations. However, most of them make recommendations based on either information from users or objects, or bipartite relationships between them, without explicitly exploring object, user and object-user relationships simultaneously. Meanwhile, recent discoveries in sociology and behavior science have demonstrated that similar users tend to select similar objects, usually referred to the n-degree of influence. However, such understandings have not been systematically incorporated into recommendations yet. With these understandings, we propose a novel method named COUSIN (Correlating Object and User SImilarity profiles to personalized recommendatioN), adopting a regression model to incorporate object, user and object-user associations simultaneously in a global way for personalized recommendation. We also construct a power-law adjusted heterogeneous network for COUSIN to prevent adversely influence of popular nodes. We demonstrate the effectiveness of our method through comprehensive cross-validation experiments across two data sets (MovieLens and Netflix). Results show that our method outperforms the state-of-the-art methods in both accuracy and diversity performance, indicating its promising future for recommendation. © 2015 Elsevier B.V. All rights reserved. Source


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. Source


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. Source


Yu W.,Hunan University of Science and Technology | Gao Q.,University of Science and Technology Beijing | Zhu C.,Hunan University of Science and Technology
Yanshilixue Yu Gongcheng Xuebao/Chinese Journal of Rock Mechanics and Engineering | Year: 2010

At present, the combined support method of long anchor cable and bolt shotcrete mesh is widely used in deep soft surrounding rock, but it is very deficient in understanding on bearing behavior of the combined supporting structure; and it still lacks quantitative analytical formulae especially for bearing capacities of primary supporting and secondary supporting. In allusion to the united supporting characteristics of anchor, spray net and cable of deep wall rock, the mechanical model of overlap arch bearing body were put forward based on rock mechanics theory, which are composed with the main compression arch(bolt supporting) and the secondary compression arch(intensive cable supporting). By means of elastoplastic theory, neutral point theory of bolt and force transferring mechanism of cable, strength equations of the bearing body of primary supporting and second supporting were deduced. Community composed of wall rock and supporting structure is regarded as an equivalent coupling surrounding rock; and relation equations of rock mechanics parameters of surrounding rock with release displacements(yield displacements) were obtained from the method of elastoplastic mechanics. Computational results of engineering indicate that the peak intensity and bearing capability of rock mass were enhanced obviously for the breaking cavity of Jinchuan Mine III after the support of overlap arch; the limit bearing capacity of equivalent coupling surrounding rock can reach 513.34kN; the value of can reach 47.54o and the value of can reach 1.37 MPa. Monitoring data also show that deformations of surrounding rock supported by overlap arch bearing body trend to be stable, convergence rate of which is less than 0.1mm/d. Source


Qi Y.,University of Science and Technology Beijing
MATEC Web of Conferences | Year: 2015

An evaluation index system of regional economic development is established in this paper and STATA11.0 is used in the cluster analysis on samplings of 31 provincial regions. Results indicate that the economy of most regions is still in a backward stage except a few developed regions and the economic polarization of China is quite serious. This study provides a reference for the coordinated and rapid development of China's economy. © Owned by the authors, published by EDP Sciences, 2015. Source


Li W.,Ecole Centrale Paris | Dichiara A.,Ecole Centrale Paris | Zha J.,University of Science and Technology Beijing | Su Z.,Hong Kong Polytechnic University | Bai J.,Ecole 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. Source


Ling F.M.,University of Science and Technology Beijing
Advanced Materials Research | Year: 2011

The damping capacity of Fe-Ga rods and sheets has been studied using a computer-controlled automatic inverted torsion pendulum instruments in a wide temperature range in a series of frequency. The frequency and temperature has different influence on the damping capacity of solidified Fe 83Ga 17 rods and (Fe 83Ga 17) 97.25Cr 2B 0.75 sheets. The damping capacity of all specimens increased with frequencies. The solidified Fe-Ga rods showed an obvious low-temperature peak and a potential high-temperature peak with increasing temperature. However, the damping capacity of Fe-Ga sheets kept steady in a wide temperature range and then rapidly increased on further heating above 400°C. Damping capacity of about 0.02 was obtained in both Fe-Ga rods and sheets at temperatures from room temperature to 500°C. Thus, The Fe-Ga alloys are considered to be a class of promising high damping alloys. © (2011) Trans Tech Publications. Source


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. Source


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. Source


Shang S.L.,Pennsylvania State University | Wang Y.,Pennsylvania State University | Mei Z.G.,Pennsylvania State University | Hui X.D.,University of Science and Technology Beijing | Liu Z.K.,Pennsylvania State University
Journal of Materials Chemistry | Year: 2012

Gaps in our knowledge of phonon and thermodynamics still remain despite significant research efforts on cathode materials LiMPO 4 (M = Mn, Fe, Co, and Ni) for rechargeable Li-ion batteries. Here, we employ a mixed-space approach of first-principles phonon calculations to probe the lattice dynamics including LO-TO splitting (longitudinal and transverse optical phonon splitting), quantitative bonding strength between atoms, and finite-temperature thermodynamic properties of LiMPO 4. In order to take into account the strong on-site Coulomb interaction (U) presented in transition metals, the GGA + U calculations are used for LiMPO 4. It is found that the oxygen-phosphorus (O-P) bond with the minimal bond length is extremely strong, which is roughly five times larger than the second strongest O-O bond. The atom P-containing bonds are apparently stronger than the corresponding atom O-containing bonds, indicating the stability of LiMPO 4 is mainly due to atom P. It is observed that the equilibrium volume of LiMPO 4 decreases from Mn, Fe, Co, to Ni, and the bulk modulus, zero-point vibrational energy, and Debye temperature increase. Phonon results indicate that the largest vibrational contribution to Gibbs energy is for LiMnPO 4, followed by LiFePO 4, LiCoPO 4, and then LiNiPO 4, due to the decreasing trend of phonon densities of state at the low frequency region of LiMPO 4. Computed phonon and thermodynamic properties of LiMPO 4 are in close accord with available experiments, and provide knowledge to be validated experimentally. © The Royal Society of Chemistry 2011. Source


Xiao W.,University of Science and Technology Beijing | Xiao J.-L.,Inner Mongolia University
Pramana - Journal of Physics | Year: 2013

By employing a variational method of the Pekar-type, which has different variational parameters in the x-y plane and the z-direction, we study the ground and the first excited state energies and transition frequency between the ground and the first excited states of a strong-coupling polaron in an anisotropic quantum dot (AQD) under an applied magnetic field along the z-direction. The effects of the magnetic field and the electron-phonon coupling strength are taken into account. It is found that the ground and the first excited state energies and the transition frequency are increasing functions of the external applied magnetic field. The ground state and the first excited state energies are decreasing functions, whereas transition frequency is an increasing function of the electron-phonon coupling strength. We find two ways of tuning the state energies and the transition frequency: by adjusting (1) the magnetic field and (2) the electron-phonon coupling strength. © Indian Academy of Sciences. Source


Lu Q.,Hefei University of Technology | Yu H.,University of Science and Technology Beijing | Fu Y.,Hefei University of Technology
Journal of the American Chemical Society | Year: 2014

Itami et al. recently reported the C-O electrophile-controlled chemoselectivity of Ni-catalyzed coupling reactions between azoles and esters: the decarbonylative C-H coupling product was generated with the aryl ester substrates, while C-H/C-O coupling product was generated with the phenol derivative substrates (such as phenyl pivalate). With the aid of DFT calculations (M06L/6-311+G(2d,p)-SDD//B3LYP/6-31G(d)-LANL2DZ), the present study systematically investigated the mechanism of the aforementioned chemoselective reactions. The decarbonylative C-H coupling mechanism involves oxidative addition of C(acyl)-O bond, base-promoted C-H activation of azole, CO migration, and reductive elimination steps (C-H/Decar mechanism). This mechanism is partially different from Itami's previous proposal (Decar/C-H mechanism) because the C-H activation step is unlikely to occur after the CO migration step. Meanwhile, C-H/C-O coupling reaction proceeds through oxidative addition of C(phenyl)-O bond, base-promoted C-H activation, and reductive elimination steps. It was found that the C-O electrophile significantly influences the overall energy demand of the decarbonylative C-H coupling mechanism, because the rate-determining step (i.e., CO migration) is sensitive to the steric effect of the acyl substituent. In contrast, in the C-H/C-O coupling mechanism, the release of the carboxylates occurs before the rate-determining step (i.e., base-promoted C-H activation), and thus the overall energy demand is almost independent of the acyl substituent. Accordingly, the decarbonylative C-H coupling product is favored for less-bulky group substituted C-O electrophiles (such as aryl ester), while C-H/C-O coupling product is predominant for bulky group substituted C-O electrophiles (such as phenyl pivalate). © 2014 American Chemical Society. Source


Liu D.,University of Science and Technology Beijing
Microscopy and Microanalysis | Year: 2013

International standard ISO-25498 specifies the method of selected area electron diffraction (SAED) analysis in TEM. It is applicable to the acquisition of SAED patterns, indexing the patterns and calibration of diffraction constant. Several features of this standard are introduced. As an example of the applications, phosphide with nanometer scale in a low-carbon steel produced by compact strip production process was analyzed by SAED and EDX. The phosphide precipitates in the steel are identified as M xP, where x is 2-3 and M is Fe, Ti, Cr, or Ni. It possesses a hexagonal lattice with lattice parameter a = 0.609 nm and c = 0.351 nm. © 2013 Microscopy Society of America. Source


Peng F.,University of Science and Technology Beijing
European Physical Journal B | Year: 2011

We investigate the effect of the laser field on the polarization fluctuation of excitons in graphene ribbons. In order to calculate the fluctuation, we develop a bosonization method to deal with the electron-hole system. Our results show that the polarization fluctuation may be controlled by adjusting the strength and frequency of the laser field. The insulating armchair graphene ribbons may be divided into two types according to the width-dependences of the excitonic polarization fluctuation. © 2011 EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg. Source


Zhang W.,University of Science and Technology Beijing
IFAC Proceedings Volumes (IFAC-PapersOnline) | Year: 2012

The paper is concerned with the convergence rate of the weighting algorithm and the stability of weighted multiple model adaptive control (WMMAC). First a new weighting algorithms with convergence assurance is proposed. Second, the stability of the WMMAC system is proved based on virtual equivalent system (VES) concept and methodology, which is independent of specific 'local' control strategy. The obtained results indicate that the stability of a WMMAC system depends mainly on the 'stabilizing' property of each local controller and the convergence of weighting algorithm, i.e., the weight corresponding to the true (or the closest) model of the plant converges to 1, and others converge to 0. © 2012 IFAC. Source


Chen W.,University of Auckland | Gao W.,University of Auckland | He Y.,University of Science and Technology Beijing
Surface and Coatings Technology | Year: 2010

A new processing concept has been developed to produce nano-structured metal-matrix composite coatings. This method combines sol-gel and electroless plating techniques to prepare highly dispersive oxide nano-particle reinforced composite coatings. Transparent TiO2 sol was added into the standard electroless plated Ni-P solution at a controlled rate to produce Ni-P-TiO2 nano-composite coatings on Mg alloys. The coating was found to have a crystalline structure. The nano-sized TiO2 particles (∼ 15 nm) were well dispersed into the Ni-P coating matrix during the co-deposition process. This technique can effectively avoid the agglomeration of nano-particles in the coating matrix. As a result, the microhardness of the composite coatings were significantly increased to ∼ 1025 HV200 compared to ∼ 710 HV200 of the conventional composite coatings produced with solid particle mixing methods. Correspondingly, the wear resistance of the new composite coatings was also greatly improved. © 2010 Elsevier B.V. All rights reserved. Source


Zhang Y.,Beijing University of Civil Engineering and Architecture | Zheng L.,University of Science and Technology Beijing
Chemical Engineering Science | Year: 2012

The paper deals with thermosolutal Marangoni convection, which can be formed with an electrically conducting fluid along a vertical surface in the presence of a magnetic field, heat generation and a first-order chemical reaction. In conformity to actuality, it is assumed that the surface tension varies linearly with both the temperature and concentration and that both interface temperature and concentration are quadratic functions of the interface arc length x. The general governing partial differential equations are converted into nonlinear ordinary differential equations using unique similarity transformations. The analytical approximate solutions of similarity equations are firstly obtained by double-parameter transformation perturbation expansion method and Padé approximants technique. The effects of Hartmann number, heat generation coefficient and the chemical reaction coefficient on the velocity, temperature and concentration profiles as well as the wall velocity are presented and discussed. © 2011 Elsevier Ltd. Source


Ma C.,University of Science and Technology Beijing
Assembly Automation | Year: 2016

Purpose-The purpose of this paper is to investigate the neural-network-based containment control of multi-agent systems with unknown nonlinear dynamics. Moreover, communication constraints are taken into account to reflect more realistic communication networks. Design/methodology/approach-Based on the approximation property of the radial basis function neural networks, the control protocol for each agent is designed, where all the information is exchanged in the form of sampled data instead of ideal continuous-time communications. Findings-By utilizing the Lyapunov stability theory and the Lyapunov-Krasovskii functional approach, sufficient conditions are developed to guarantee that all the followers can converge to the convex hull spanned by the stationary leaders. Originality/value-As ideal continuous-time communications of the multi-agent systems are very difficult or even unavailable to achieve, the neural-network-based containment control of nonlinear multi-agent systems is solved under communication constraints. More precisely, sampled-data information is exchanged, which is more applicable and practical in the real-world applications. © Emerald Group Publishing Limited. Source


Su X.,North China Electrical Power University | Zheng L.,University of Science and Technology Beijing
Central European Journal of Physics | Year: 2013

This paper deals with the boundary layer flow and heat transfer of nanofluids over a stretching wedge with velocity-slip boundary conditions. In this analysis, Hall effect and Joule heating are taken into consideration. Four different types of water-base nanofluids containing copper (Cu), silver (Ag), alumina (Al2O3), and titania (TiO2) nanoparticles are analyzed. The partial differential equations governing the flow and temperature fields are converted into a system of nonlinear ordinary differential equations using a similarity transformation. The resulting similarity equations are then solved by using the shooting technique along with the fourth order Runge-Kutta method. The effects of types of nanoparticles, the volume fraction of nanoparticles, the magnetic parameter, the Hall parameter, the wedge angle parameter, and the velocityslip parameter on the velocity and temperature fields are discussed and presented graphically, respectively. © 2013 Versita Warsaw and Springer-Verlag Wien. Source


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. Source


Sun Z.,University of Science and Technology Beijing | Sun Z.,North China Electrical Power University
European Physical Journal D | Year: 2014

Based on Thomas-Fermi density functional theory, itinerant ferromagnetism of repulsive two-component Fermi gas trapped in a triple-well is studied. The density profiles of the two components are calculated in three types of triple-well trapping potential. The conclusion is drawn that phase separation relates closely not only to the interaction strength, but also to the shape of the trapping potential, which plays a critical role in determining the density profile of the gas. The separation in each type of trapping potential is a result of the competition between repulsive interaction energy and the kinetic energy. Numerical results show that phase separation occurs once the coupling constant reaches a critical value. With further increase in the coupling constant, the interplay between wells is enhanced, which may cause complex separation. Despite our crude treatment in the Thomas-Fermi approximation, the results may help to explore and understand the nature of itinerant ferromagnetism of trapped Fermi mixtures in both theoretical and experimental research in the future. © 2014 EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg. Source


Zhang W.,University of Science and Technology Beijing
International Journal of Adaptive Control and Signal Processing | Year: 2015

A new weighting algorithm is proposed to relax the convergence conditions and to improve the convergence rate for weighted multiple model adaptive control systems. The stability and convergence of the corresponding weighted multiple model adaptive control systems of two types of stochastic plants, one is linear time-invariant system (LTI) with unknown parameters, the other is linear time-varying system with jumping parameters, are proved. Finally, some simulation results are presented to verify the effectiveness of the proposed weighting algorithm and the performance of the closed-loop control system. © 2015John Wiley & Sons, Ltd. Source


Wang L.,KTH Royal Institute of Technology | Wang L.,University of Science and Technology Beijing | Seetharaman S.,KTH Royal Institute of Technology
Metallurgical and Materials Transactions B: Process Metallurgy and Materials Processing Science | Year: 2010

In view of the importance of the thermodynamic behavior of chromium in the slag phase as well as the serious discrepancies in the earlier reports on the valence state of chromium in slag melts, the oxidation state of chromium oxides in CaO-SiO 2-CrO x and CaO-MgO-(FeO-) Al 2O 3-SiO 2- CrO x were investigated experimentally in the present study using two different experimental techniques. The gas-slag equilibrium technique was adopted to study the CaO-SiO 2-CrO x system between 1823 K (1550 °C) and 1923 K (1650 °C) and equilibrated with mixtures of CO-CO 2-Ar gases corresponding to three different oxygen partial pressures (between 10 -4 and 10 -5 Pa). After equilibrating, the samples were quenched and subjected to analysis using the X-ray absorption near edge structure method to determine the distribution ratio of Cr 2+/Cr 3+ in the slags. The second technique examined the applicability of the high-temperature mass spectrometric method combined with the Knuden effusion cell for quantifying the valence states of Cr in the multicomponent system CaO-MgO-(FeO-) Al 2O 3-SiO 2-CrO x up to a maximum temperature of 2000 K (1727 °C). The results showed that the Knudsen cell-mass spectrometric method could be used successfully to estimate the valence ratio for Cr in silicate melts. According to the present study, the Cr 3+/Cr 2+ ratio increased with increasing temperature and a decreasing slag basicity as well as the oxygen partial pressure prevailing in the system. A mathematical correlation of X CrO/X CrO1.5 as a function of temperature, oxygen partial pressure, and basicity was developed in the present work based on the present results as well as on those assessed from earlier data. © The Minerals, Metals & Materials Society and ASM International 2010. Source


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. Source


Feng Z.,University of Science and Technology Beijing | Liang M.,University of Ottawa
Journal of Sound and Vibration | Year: 2014

The vibration signals from complex structures such as wind turbine (WT) planetary gearboxes are intricate. Reliable analysis of such signals is the key to success in fault detection and diagnosis for complex structures. The recently proposed iterative atomic decomposition thresholding (IADT) method has shown to be effective in extracting true constituent components of complicated signals and in suppressing background noise interferences. In this study, such properties of the IADT are exploited to analyze and extract the target signal components from complex signals with a focus on WT planetary gearboxes under constant running conditions. Fault diagnosis for WT planetary gearboxes has been a very important yet challenging issue due to their harsh working conditions and complex structures. Planetary gearbox fault diagnosis relies on detecting the presence of gear characteristic frequencies or monitoring their magnitude changes. However, a planetary gearbox vibration signal is a mixture of multiple complex components due to the unique structure, complex kinetics and background noise. As such, the IADT is applied to enhance the gear characteristic frequencies of interest, and thereby diagnose gear faults. Considering the spectral properties of planetary gearbox vibration signals, we propose to use Fourier dictionary in the IADT so as to match the harmonic waves in frequency domain and pinpoint the gear fault characteristic frequency. To reduce computing time and better target at more relevant signal components, we also suggest a criterion to estimate the number of sparse components to be used by the IADT. The performance of the proposed approach in planetary gearbox fault diagnosis has been evaluated through analyzing the numerically simulated, lab experimental and on-site collected signals. The results show that both localized and distributed gear faults, both the sun and planet gear faults, can be diagnosed successfully. © 2014 Elsevier Ltd. All rights reserved. Source


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. Source


Cao G.,University of Science and Technology Beijing
Polymers | Year: 2014

Recent progress of simulations/modeling at the atomic level has led to a better understanding of the mechanical behaviors of graphene, which include the linear elastic modulus E, the nonlinear elastic modulus D, the Poisson's ratio v, the intrinsic strength σint and the corresponding strain εint as well as the ultimate strain εmax (the fracture strain beyond which the graphene lattice will be unstable). Due to the two-dimensional geometric characteristic, the in-plane tensile response and the free-standing indentation response of graphene are the focal points in this review. The studies are based on multiscale levels: including quantum mechanical and classical molecular dynamics simulations, and parallel continuum models. The numerical studies offer useful links between scientific research with engineering application, which may help to fulfill graphene potential applications such as nano sensors, nanotransistors, and other nanodevices. © 2014 by the authors; licensee MDPI, Basel, Switzerland. Source


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. Source


Peng R.,University of Science and Technology Beijing | Mo H.,City University of Hong Kong | Xie M.,City University of Hong Kong | Levitin G.,Israel Electric
Reliability Engineering and System Safety | Year: 2013

Due to imperfect fault coverage, the reliability of redundant systems cannot be enhanced unlimitedly with the increase of redundancy. Thus it is essential to study the optimal structure of redundant systems. This paper considers a multi-state series-parallel system with two types of parallelization: redundancy and work sharing. Different from existing works which consider single-fault coverage, multi-fault coverage is considered in order to adapt to a wider range of fault tolerant mechanisms. For multi-fault coverage, the coverage factor of an element failure in a work sharing group depends on the status of other elements. It is assumed that the uncovered failures in the elements belonging to the group of elements sharing the same task can cause failure of the entire group. The optimal trade-off between the two kinds of parallelization has been studied based on various settings of fault coverage factor. Examples of data transmission systems and task processing systems are presented to illustrate the applications of results. © 2013 Elsevier Ltd. Source


Guo C.,National University of Defense Technology | Wang W.,University of Science and Technology Beijing | Guo B.,National University of Defense Technology | Si X.,HIGH-TECH
Reliability Engineering and System Safety | Year: 2013

Over the past few decades, condition-based maintenance (CBM) has attracted many researchers because of its effectiveness and practical significance. This paper deals with mission-oriented systems subject to gradual degradation modeled by a Wiener stochastic process within the context of CBM. For a mission-oriented system, the mission usually has constraints on availability/reliability, the opportunity for maintenance actions, and the monitoring type (continuous or discrete). Furthermore, in practice, a mission-oriented system may undertake some preventive maintenance (PM) and after such PM, the system may return to an intermediate state between an as-good-as new state and an as-bad-as old state, i.e., the PM is not perfect and only partially restores the system. However, very few CBM models integrated these mission constraints together with an imperfect nature of the PM into the course of optimizing the PM policy. This paper develops a model to optimize the PM policy in terms of the maintenance related cost jointly considering the mission constraints and the imperfect PM nature. A numerical example is presented to demonstrate the proposed model. The comparison with the simulated results and the sensitivity analysis show the usefulness of the optimization model for mission-oriented system maintenance presented in this paper. © 2012 Elsevier Ltd. All rights reserved. Source


Gao J.-T.,University of Science and Technology Beijing
Steel Research International | Year: 2014

The reactor of moving bed for counter-current gas-solid reduction test is researched and developed. By the reformed blast furnace gas, EAF dust is reduced continuously and quickly in a non-molten state with high reduction degree at 800-900°C. In the condition of moving speed of 0.06-0.10 m min-1 and reduction time of 10-16.7 min, the dust is highly transformed in form of FexOy (s) → MFe (s) and ZnO (s) → Zn (g) with the Fe and Zn separated. And Fe metallization rate averages 85%, and gas-dezincification rate averages 92%. When the temperature is <1000°C, the sintering would not occur in reduction process, moreover, P, S, and any other impurity elements are not reduced into Fe matrix. By some simple physical methods it can be achieved that Fe, Zn elements are enriched separately, obtaining high purity metal resources directly, including Fe rich material (TFe = 92%), Zn rich material (ZnO = 91%) and none Fe material (Fe < 2%). The reactor of moving bed for counter-current gas-solid reduction test is researched and developed. By the reformed blast furnace gas, EAF dust is highly transformed in form of FexOy (s) → MFe (s) and ZnO (s) → Zn (g) with the Fe and Zn separated continuously and quickly in a non-molten state with high reduction degree at 800-900°C. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source


Peng R.,University of Science and Technology Beijing | Xie M.,City University of Hong Kong | Ng S.H.,National University of Singapore | Levitin G.,Israel Electric | Levitin G.,University of Electronic Science and Technology of China
IIE Transactions (Institute of Industrial Engineers) | Year: 2012

This article considers optimal maintenance and allocation of elements in a Linear Multi-state Consecutively Connected System (LMCCS), which is important in signal transmission and other network systems. The system consists of N+1 linearly ordered positions (nodes) and fails if the first node (source) is not connected with the final node (sink). The reliability of an LMCCS has been studied in the past but has been restricted to the case when each system element has a constant reliability. In practice, system elements usually fail with increasing failure probability due to aging effects. Furthermore, in order to increase system availability, resources can be put into the maintenance of each element to increase the availability of the element. In this article, a framework is proposed to solve the cost optimal maintenance and allocation strategy of this type of system subject to an availability requirement. A universal generating function is used to estimate the availability of the system. A genetic algorithm is adopted for optimization. Illustrative examples are presented. © 2012 "IIE". Source


He B.B.,University of Hong Kong | Luo H.W.,University of Science and Technology Beijing | Huang M.X.,University of Hong Kong
International Journal of Plasticity | Year: 2016

The additional deep cryogenic treatment process prior to intercritical annealing was employed to tailor the mechanical stability of austenite grains in a new medium Mn steel. As a consequence, the medium Mn steel after intercritical annealing contains the austenite grains with different mechanical stability due to the different grain size and C content. The large austenite grains with low C content transform to martensite prior to the strain of 9.5% due to their low mechanical stability and provide the transformation-induced plasticity (TRIP) effect during tensile test. On the other hand, the small austenite grains with high C content have high mechanical stability and proper stacking fault energy, therefore do not transform to martensite but offer the twinning-induced plasticity (TWIP) effect from 9.5% strain up to fracture. Subsequently some of the twinned austenite grains provide the nucleation site for martensite formation from the strain of 26.2% up to fracture, providing the TRIP effect again in the large strain regime. In summary, the present novel medium Mn steel has TRIP effect firstly, followed by TWIP effect and then TWIP + TRIP effects during tensile test, therefore demonstrating enhanced work hardening behavior and excellent tensile properties. © 2015 Elsevier Ltd. All rights reserved. Source


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. Source


Li W.,Ecole Centrale Paris | He D.,Ecole Centrale Paris | Dang Z.,University of Science and Technology Beijing | Bai J.,Ecole 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. Source


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. Source


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. Source


Wang V.,Xian 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 Source


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. Source


Accurate estimates of the dependence of soil shear strength parameters (including cohesion and friction angle) play a crucial role in decision making by civil engineers in terms of geotechnical engineering safety. With increased site-specific information comes the need for joint soil strength models to account for the correlation characteristics between shear strength properties. In this study, using 16 sets of soil shear strength observations (consisting of 391 samples) as examples, the suitability of the dependence structure for these experimental observations is firstly identified by a goodness-of-fit test based on the Bayesian Information Criterion (BIC) with the normal, Student's t, Clayton, Frank, Gumbel, and Plackett copulas. The dependence structure between shear strength components is found to be asymmetric in most cases. Secondly, a set of paired samples of shear strength simulated from the different bivariate copulas, which contributed to various dependencies, is implemented as input for two typical geotechnical probabilistic analyses, e.g., infinite slope stability against a single sliding plane and the bearing capacity of a shallow foundation. The impact of the different choices for these dependence structures on the resulting reliability index is discussed. In both illustrative examples, the normal copula leads to an overestimation of the reliability index, whereas the Gumbel copula yields the lowest reliability index. Conservative reliability indices are obtained when the joint behaviour of the soil shear strength follows a bivariate normal distribution. © 2015 Japanese Geotechnical Society. Source


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. Source


Dong S.,University of Science and Technology Beijing | Medeiros D.J.,Pennsylvania State University
International Journal of Production Research | Year: 2012

We present a method to minimise the cost of batch schedules for a pipe manufacturing facility. The method determines the sequence of production and start date of the batch considering raw material and finished goods holding cost, late delivery cost, and changeover. Our approach is designed to interface to the company's manufacturing execution system, and uses a simplified model of the production line for speed of execution. We demonstrate that methodology results in significant cost savings when compared to existing schedules. © 2012 Taylor & Francis. Source


Zhang W.-C.,University of Science and Technology Beijing
Zidonghua Xuebao/Acta Automatica Sinica | Year: 2015

This paper is concerned with the weighted multiple model adaptive control (WMMAC) of discrete-time linear stochastic system with uncertain parameters. Firstly, an improved weighting algorithm is adopted with convergence guaranteed under smooth conditions. Then based on virtual equivalent system methodology, the stability of resulting WMMAC systems for both linear time-invariant (LTI) and parameter jump plants is presented. The analysis method is independent of specific local control strategy and specific weighting algorithm. Finally, the theoretical results have been verified by simulation results using Matlab. Copyright © 2015 Acta Automatica Sinica. All rights reserved. Source


Geng W.T.,Japan National Institute of Materials Science | Geng W.T.,University of Science and Technology Beijing | Ohno T.,Japan National Institute of Materials Science
Journal of Physical Chemistry C | Year: 2013

Carbon coating substantially promotes electron transport through LiFePO4 nanoparticles at the positive electrode in Li-ion batteries and approaches to forming thin, tightly attached, and uniform carbon layers are extremely desirable. On the basis of our recent first principles computational discovery that the graphite crystallites are more likely standing on the LiFePO4 (010) surface via C-O bonding rather than lying on van der Waals forces, we have in this work searched promising co-coating substances which can reinforce the perpendicular orientation of graphite crystallites by strengthening the C/LiFePO4 binding. Among the three supervalent elements we have studied, Sc (3+), Ti (4+), and V (5+), Sc and Ti are found to show good performance. The binding energy of perpendicular graphite on the LiFePO4 (010) surface increases noticeably from 0.52 to 0.58 (Sc) and 0.61 (Ti) eV/Å, whereas the binding of a parallel graphene sheet with the same surface is nearly unchanged. A strengthened perpendicular graphite orientation is very welcome for leaving diffusion channels of Li unblocked. © 2012 American Chemical Society. Source


Geng W.T.,Japan National Institute of Materials Science | Geng W.T.,University of Science and Technology Beijing | Ping D.H.,Japan National Institute of Materials Science | Nara J.,Japan National Institute of Materials Science | Ohno T.,Japan National Institute of Materials Science
Journal of Physical Chemistry C | Year: 2012

Coating carbon layers on LiFePO 4 nanoparticles used in Li-ion batteries greatly increase the electron transport in this cathode material. Using first-principles density functional theory calculations, we have theoretically investigated the interaction energies of graphene lying parallel and perpendicular to a LiFePO4 (010) surface and have found that the perpendicular orientation is energetically favorable. Our computations suggest that graphene nanosheets prefer standing vertically on LiFePO 4 (010) using C-O and C-Fe bonding rather than spreading on it, as has been widely assumed. The interfacial chemical bonding both fastens the coated carbon layer and facilitates electron conductivity across the interface. By contrast, encapsulating LiFePO 4 with parallel graphene sheets does not increase electron conductivity across the interface. © 2012 American Chemical Society. Source


Luo Y.,University of Science and Technology of China | Xia Z.,University of Science and Technology of China | Xia Z.,University of Science and Technology Beijing
Journal of Physical Chemistry C | Year: 2014

Garnet-type Y2.96Sc2Ga3-xAlxO12:0.04Ce3+ (x = 0-3) phosphors have been prepared by using the high temperature solid-state reaction. Al/Ga ratio dependent Y3Sc2(Ga,Al)3O12 phase structures, photoluminescence (PL) properties, and long-lasting phosphorescence (LLP) properties for the Ce3+-doped phosphors have been investigated in detail. The PL emission bands of Y2.96Sc2Ga3-xAlxO12:0.04Ce3+ showed a red-shift tendency gradually from 503 to 520 nm with increasing Al content (x value), and the emission intensities increased first, maximized at x = 1, and then decreased. Y3Sc2Ga3O12:Ce3+ can show the green LLP emission, and afterglow can be obviously enhanced when (1) Al ions replaced Ga ions for a small amount and (2) the reaction atmosphere was varied from reducing to oxidation one. The afterglow emission, decay curves, and thermoluminescence (TL) of Y2.96Sc2Ga3-xAlxO12:0.04Ce3+ (x = 0-0.7) phosphors have been investigated, and related luminescence mechanisms are systematically discussed as well. © 2014 American Chemical Society. Source


Luo C.,University of Science and Technology Beijing
International Journal of Electrochemical Science | Year: 2015

The corrosion of aluminium in concentrated LiNO3 solution at high temperature was studied with a weight loss method. The effects of concentration, temperature, pH and Li2CrO4 on corrosion rates were investigated. Results indicated that increasing concentration of LiNO3 had opponent effects on aluminium corrosion. Elevating temperature and pH could increase the corrosion rate. An incompact hydroxide film was observed on the surface of aluminium in LiNO3 solution. The corrosion was effectively depressed by adding inhibitor Li2CrO4, where a compact passive film comprising Al(OH)3 and Cr2O3 may be formed. The corrosion rate of aluminium in LiNO3 solution was much smaller than that in LiBr solution. © 2015 The Authors. Source


Wu X.Z.,University of Science and Technology Beijing
Geosynthetics International | Year: 2013

The sensitivity of landfill design to shear strength variability is controlled by the measured internal shear strength of the geosynthetic clay liner and the interface shear strength between the geosynthetic clay liner and the geomembrane. Based on the Mohr-Coulomb criterion, the measured shear strength values (including the internal and interface shear strength values) depend on the cohesion and friction angle. Here, a novel and efficient mathematical tool for analysing the properties of the bivariate and the correlated geosynthetic shear strength was constructed. The arbitrary marginal probability density distribution of the componential shear strength was organised as a bivariate joint distribution with a copula function to characterise the dependency between the different shear strengths. Generally, a copula-based method provides a simple and powerful framework for modelling interdependence among variables. Thus, the construction of copulas as an alternative to correlation coefficients is addressed. In addition, the shear strength marginal distributions were described by a non-normal distribution, which was identified by the Akaike information criterion. The dependency of these margins is implemented from several empirical copulas, which were chosen from the most frequently used Elliptical and Archimedean families. The simulated correlated material properties that were generated by the copula-based sampling method were used as input values to calculate the performance of a landfill lining problem. Moreover, the computed reliability indexes were compared with the reliability indexes that were obtained by the first-order second moment method. In addition, a sensitivity study with various correlation coefficients was conducted to determine the influence of the correlation measurements on the reliability index. © 2013 Thomas Telford Ltd. Source


Guo Z.C.,University of Science and Technology Beijing | Fu Z.X.,CAS Institute of Process Engineering
Energy | Year: 2010

A survey of the key issues associated with the development in the Chinese iron and steel industry and current situations of energy consumption are described in this paper. The apparent production of crude steel in China expanded to 418.78 million tonnes in 2006, which was about 34% share of the world steel production. The iron and steel industry in China is still one of the major high energy consumption and high pollution industries, which accounts for the consumption of about 15.2% of the national total energy, and generation of 14% of the national total wastewater and waste gas and 6% of the total solid waste materials. The average energy consumption per unit of steel is about 20% higher than that of other advanced countries due to its low energy utilization efficiency. However, the energy efficiency of the iron and steel industry in China has made significant improvement in the past few years and significant energy savings will be achieved in the future by optimizing end-use energy utilization. Finally, some measures for the industry in terms of the economic policy of China's 11th five-year plan are also presented. © 2009 Elsevier Ltd. Source


Lingfang G.,University of Science and Technology Beijing
Proceedings - 2015 6th International Conference on Intelligent Systems Design and Engineering Applications, ISDEA 2015 | Year: 2015

This paper puts forward a distributed coalition formation algorithm for the specific network structure of multi agent system. First, each agent puts forward an application to join their neighbors which "price ratio" is highest and forms a potential alliance. When the union resource is greater than the corresponding task resources demand, make corresponding agent to withdraw from the league, and choose "price ratio" second-highest task, thus improve the possibility of alliance formation. The simulation results show that compared with other methods, the proposed algorithm can greatly improve system efficiency and benefits. © 2015 IEEE. Source


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. Source


Ng C.,Hong Kong Polytechnic University | Guo S.,City University of Hong Kong | Luan J.,City University of Hong Kong | Luan J.,University of Science and Technology Beijing | And 2 more authors.
Intermetallics | Year: 2012

Previous work on the stability of the solid solution phases in the high entropy alloys is inconclusive. We used a series of thermo-mechanical treatments to study the stability of the solid solution phases in a high-entropy Al 0.5CoCrCuFeNi alloy. The solid solution phases were found to be stable, against the intermetallic compounds, at high temperatures >850 °C and at low temperatures <300 °C. At intermediate temperatures, however, the intermetallic σ-phase co-existed with the solid solution phases. The experimental observations were verified by the thermodynamic calculation results. The mechanisms for the phase stability, both at equilibrium and after quenching-equivalent annealing treatments, were discussed, and the roles of high entropy and slow diffusion kinetics were highlighted. © 2012 Elsevier Ltd. All rights reserved. Source


Pan D.,University of Science and Technology Beijing
Guti Lixue Xuebao/Acta Mechanica Solida Sinica | Year: 2015

When the Caughey damping matrix is constructed by traditional method, how to choose reasonable multi-reference frequencies and avoid negative modal damping ratios are challenges. Based on the seismic response spectral analysis, an optimal solution of Caughey damping coefficients is proposed by constrained quadratic programming. In the method, by minimizing the error of structural displacement peak and constraining all modal damping ratios to be greater than zero, the Caughey damping coefficients can be determined directly. Then, a dome structure with 90m-diameter and 15 m-height is analyzed to illustrate the necessity of Caughey damping when the significant modes for different responses are different and the associated frequencies can differ significantly. Meanwhile, the traditional method and the optimal method are compared in the effects on structural seismic response errors. Numerical results show that the traditional method ignores the difference in different modal contributions to choose reference frequencies and may cause inconsistent accuracies when a structure is subject to different excitations; the optimal method makes the damping ratios of significant contribution modes reasonable, and the errors of the optimal method are smaller than that of the traditional method for more than 4 Caughey series. ©, 2015, Huazhong University of Science and Technology. All right reserved. Source


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. Source


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. Source


Jiang Y.-Y.,Hefei University of Technology | Yu H.-Z.,University of Science and Technology Beijing | Fu Y.,Hefei University of Technology
Organometallics | Year: 2013

Recently the Chatani group reported the Rh(I)-catalyzed borylation of nitriles, which provided an efficient protocol for transformation of the C-CN bond to the C-B bond (J. Am. Chem. Soc.2012, 134, 115). Although an unconventional β-carbon elimination mechanism was proposed in their study, the other previously proposed mechanisms, i.e., oxidative addition, deinsertion, and initial C-H bond activation, cannot be excluded. To clarify the dominant mechanism of this reaction, a density functional theory study on borylation of PhCN and BnCN catalyzed by [Rh(XantPhos)(B(nep))] (nep = neopentylglycolate, XantPhos = 4,5-Bis(diphenylphosphino)-9,9-dimethylxanthene) was conducted. The computational results indicated that the deinsertion mechanism (2,1-insertion of the Rh-B bond into the C≡N bond occurs first, followed by the insertion of the metal center into C-CN bond) is favored over oxidative addition, β-carbon elimination, and the initial C-H bond activation mechanism within all the investigated reactions. The activation of the C-CN bond is a facile step in the deinsertion mechanism, and the oxidative addition of the diboron reagent is the rate-determining step. On this basis, the mechanism of borylation of PhCN catalyzed by a similar Ir-B complex ([Ir(XantPhos)(B(nep))]) was also examined. The deinsertion mechanism was found to be the most favorable. The overall energy barrier of the Ir-B complex-catalyzed borylation of benzonitriles was slightly higher than that of the same Rh-B complex-catalyzed reaction (by 1.1 kcal/mol), indicating that [Ir(XantPhos)(B(nep))] could act as an alternative catalyst for borylation of nitriles. © 2013 American Chemical Society. Source


Huang X.,University of Science and Technology Beijing
Expert Systems with Applications | Year: 2012

Since the security market is complex, sometimes the future security returns are available mainly based on experts judgements. This paper discusses a portfolio selection problem in which security returns are given subject to experts' estimations. The use of uncertain measure is justified, and two new mean-variance and mean-semivariance models are proposed. In addition, a hybrid intelligent algorithm for solving the optimization models is given. To illustrate the application of the new models, the method to obtain the uncertainty distributions of the security returns based on experts' evaluations is given, and two selection examples are provided. © 2011 Elsevier Ltd. All rights reserved. Source


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. Source


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. Source


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. Source


Ye Z.,Peking University | Zhao Q.,Peking University | Zhang M.,Peking University | Gao Y.,Peking University | Gao Y.,University of Science and Technology Beijing
Journal of Hazardous Materials | Year: 2011

The compositions of explosive wastewater generated from TNT (2,4,6-trinitrotoluene) purification stage were characterized by using UV-vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), high performance liquid chromatograph (HPLC) and gas chromatograph/mass spectroscopy (GC/MS). The acute toxicity was evaluated by bacterium bioluminescence assay using a freshwater luminescent bacterium (Vibrio qinghaiensis sp. Nov.) and a marine luminescent bacterium (Photobacterium phosphoreum). The results showed that the wastewater's biodegradability was poor due to the high amount of chemical oxygen demand (COD). The main organic components were dinitrotoluene sulfonates (DNTS) with small amount of TNT, dinitrotoluene (DNT), mononitrotoluene (MNT) and other derivatives of nitrobenzene. It was highly toxic to luminescent bacteria P. phosphoreum and V. qinghaiensis sp. Nov. After reaction time of 15min, the relative concentration of toxic pollutants (expressed as reciprocal of dilution ratio of wastewater) at 50% of luminescence inhibition ratio was 5.32×10-4 for P. phosphoreu, while that was 4.34×10-4 for V. qinghaiensis. V. qinghaiensis is more sensitive and suitable for evaluating the wastewater's acute toxicity than P. phosphoreum. After adsorption by resin, the acute toxicity can be greatly reduced, which is helpful for further treatment by biological methods. © 2010 Elsevier B.V. Source


Geng W.T.,Japan National Institute of Materials Science | He B.L.,University of Science and Technology Beijing | Ohno T.,Japan National Institute of Materials Science
Journal of Physical Chemistry C | Year: 2013

The dominant discharge product in Li-air batteries, lithium peroxide (Li2O2), is intrinsically a wide band gap insulator as a perfect crystal. Recent density functional theory studies have suggested both vacancy- and polaron-mediated electron transportation mechanisms. We here show computational evidence from both semilocal and hybrid density functional calculations that the Σ3(11 00)[112 0] tilt grain boundaries (GBs) in Li2O2 can produce spin-polarized gap states. For each type of Σ3 GBs, GB1, GB2, and GB2* which has different atomic layer as the mirror plane, we have examined stoichiometric and a number of O-rich chemistry and find that stable geometry can take both forms. We find stoichiometric GBs disturb negligibly the electronic structure of Li 2O2, yet the O-rich GBs produce spin-polarized gap states in a similar manner to free surface cases. Lithium deficiency leads to compression of interfacial O-O bonds, enlarges the πp- πp* split, and pushes up the antibonding πp* to (GB2) or beyond (GB2*) the Fermi energy. As a result, GB2 becomes half-metallic and GB2* becomes semiconducting with a small band gap of 1.0 eV. In both cases, spin polarization of O ions help to stabilize the GB by leaving the up spin of its gap states shifted down below the Fermi level and the down spin states open. Since Li2O2 is always polycrystalline as a discharge product, the presence of GBs may enhance conductivity. © 2013 American Chemical Society. Source


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. Source


Zhang Q.,Hefei University of Technology | Yu H.-Z.,University of Science and Technology Beijing | Fu Y.,Hefei University of Technology
Organometallics | Year: 2013

A theoretical study has been carried out on the palladium-catalyzed C(sp3)-H activation/amidation reaction of carbamoyl chloride precursors (Takemoto, Y. Angew. Chem. Int. Ed. 2012, 51, 2763). In Takemoto's reaction, although the C(sp2)-H bond of naphthalene was present in the substrate, the benzylic C(sp3)-H bond was activated exclusively. Mechanistic calculations have been performed on the two possible pathways: the C(sp3)-H activation/amidation pathway (Path-sp3) and the C(sp2)-H activation/amidation pathway (Path-sp2). Calculation results show that both paths include three steps: oxidative addition (via the mono-phosphine mechanism), C-H activation involving the PivNHO - anion (via the CMD mechanism), and final reductive elimination. The calculations indicate that the Path-sp3 mechanism is kinetically favored, and the C(sp3)-H amidated product is predicted to be the main product. This conclusion is consistent with Takemoto's experimental observations. The rate-determining step of Path-sp3 is the oxidative addition step, and the C(sp3)-H bond activation step determines the selectivity. Further examination on the origin of the selective C(sp 3)-H activation shows that the higher acidity of the benzylic C(sp3)-H (in comparison to the naphthalene C(sp2)-H in this system) is the main reason for the chemoselectivity. The additive might promote the reaction by forming a more soluble organic base (PivNHOCs) via reaction with Cs2CO3. © 2013 American Chemical Society. Source


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. Source


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. Source


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. Source


Li J.,University of Science and Technology Beijing
Advanced Materials Research | Year: 2012

Based on the generalized flexibility matrix, a method for detecting structural damage is presented in this paper. The generalized flexibility matrix is approximately constructed by using the first frequency and the corresponding mode shape only. Then the difference of generalized flexibility curvature between undamaged and damaged state is used to detect the possible damaged elements. Finally, a numerical example concerning a simple supported beam is used to illustrate the effectiveness of the proposed method. © (2012) Trans Tech Publications, Switzerland. Source


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. Source


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. Source


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. Source


Yang Y.,Georgia Institute of Technology | Pradel K.C.,Georgia Institute of Technology | Jing Q.,Georgia Institute of Technology | Wu J.M.,Georgia Institute of Technology | And 5 more authors.
ACS Nano | Year: 2012

We demonstrate a thermoelectric nanogenerator (NG) made from a single Sb-doped ZnO micro/nanobelt that generates an output power of about 1.94 nW under a temperature difference of 30 K between the two electrodes. A single Sb-doped ZnO microbelt was bonded at its ends on a glass substrate as a NG, which can give an output voltage of 10 mV and an output current of 194 nA. The single Sb-doped ZnO microbelt shows a Seebeck coefficient of about -350 μV/K and a high power factor of about 3.2 × 10 -4 W/mK 2. The fabricated NG demonstrated its potential to work as a self-powered temperature sensor with a reset time of about 9 s. © 2012 American Chemical Society. Source


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. Source


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. Source


Liu T.,University of Science and Technology Beijing
Journal of the Franklin Institute | Year: 2015

Asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) has become one of the most promising technologies for high speed optical wireless communications (OWCs). However, as a key challenge, improving the demodulation performance of ACO-OFDM in practical systems has not been well addressed. Most established demodulation schemes suffer from performance degradation either due to discarding of even sub-carriers or interference of direct current (DC) offset, which is one of the most common impairments in practical OWC systems. Up to our awareness, there was only one established scheme (Dissanayake and Armstrong, 2011 [1]) that addressed ACO-OFDM demodulation in the presence of DC offset, but it requires relatively high computation efforts. To deal with the challenge, we propose a novel demodulation scheme for ACO-OFDM in this paper. By making use of the virtual clean window (VCW), we develop methods to estimate and eliminate DC offset, so that the even sub-carriers of ACO-OFDM can be explored to improve demodulation performance even in the presence of DC offset. Compared with the scheme presented in (Dissanayake and Armstrong 2011 [1]), the proposed scheme significantly reduces processing complexity. Simulation results are given to demonstrate the performance of the proposed scheme. © 2014 The Franklin Institute. Source


Wu X.Z.,University of Science and Technology Beijing
Stochastic Environmental Research and Risk Assessment | Year: 2016

Uncertainty in bed roughness is a dominant factor in providing a sufficiently accurate simulation of floodplain flows. This study describes a method to compute the transition probability density distribution of time-varying water elevations where the evolutionary process is based on a conventional one-dimensional storage cell model with governing stochastic differential equation. By including the random inputs (or noise terms) of bed roughness and initial water depth, time-dependent and spatially varying probability density function of the water surface leads to a Fokker–Planck equation. The model’s performance is evaluated by applying it to shallow water flow with a horizontal bed. Sensitivity of model predictions to variations in the bed friction parameters is shown. By comparing the result of the proposed method with that of conventional Monte Carlo simulation, the advantage of the former as a method for density function prediction is confirmed. © 2015, Springer-Verlag Berlin Heidelberg. Source


Chen Z.,University of California at Los Angeles | Weng D.,University of California at Los Angeles | Wang X.,University of California at Los Angeles | Cheng Y.,University of California at Los Angeles | And 2 more authors.
Chemical Communications | Year: 2012

Thin-film pseudocapacitor electrodes with ultrafast lithium storage kinetics, high capacitance and excellent cycling stability were fabricated from monodispersed TiO 2 building nanocrystals, providing a novel approach towards next-generation micro-supercapacitor applications. This journal is © The Royal Society of Chemistry 2012. Source


Li J.,University of Science and Technology Beijing | Liu J.,North China Electrical Power University | Wang J.,North China Electrical Power University
Zhongguo Dianji Gongcheng Xuebao/Proceedings of the Chinese Society of Electrical Engineering | Year: 2011

Accurate mid-long term load forecasting can improve the economic and social benefits of power system. The model of support vector machine (SVM) was analyzed, and a new mid-long term load forecasting method based SVM method was proposed in order to overcome the shortcoming that some parameters have to be determined by experience. The simulated annealing algorithm was applied to optimize the parameters in the method. An example proved that the proposed method can efficiently select the parameters of the SVM method. It can reduce the support vector machine modeling training error and testing error. Compared to the method using the default parameters SVM method, the accuracy of load forecasting is effectively improved. © 2011 Chin. Soc. for Elec. Eng. Source


Hu L.,University of Science and Technology Beijing
Journal of Intelligent and Fuzzy Systems | Year: 2015

With respect to decision making problems by using probabilities and information that can be represented with linguistic labels, some new decision analysis is proposed. Firstly, we shall develop two new aggregation operators: generalized probabilistic uncertain linguistic weighted average (GP-ULWA) operator and generalized probabilistic uncertain linguistic ordered weighted average (GP-ULOWA) operator. These operators use the WA operator, the OWA operator, uncertain linguistic information and probabilistic information. They are quite useful because they can assess the uncertain information within the problem by using both linguistic labels and the probabilistic information that considers the attitudinal character of the decision maker. In these approaches, alternative appraisal values are calculated by the aggregation of uncertain linguistic information. Thus, the ranking of alternative or selection of the most desirable alternative(s) is obtained by the comparison of uncertain linguistic information. Finally, we give an illustrative example for evaluating the enterprise strategic crisis management with uncertain linguistic information to verify the developed approach and to demonstrate its feasibility and practicality. © 2015 - IOS Press and the authors. Source


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. Source


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. Source


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. Source


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. Source


Zhao J.,University of Science and Technology Beijing | Yang Q.,Nankai University
Inverse Problems in Science and Engineering | Year: 2013

In this article, we first introduce a simple but practical projection method for solving the multiple-sets split feasibility problem, which is to find a point in the intersection of a family of closed convex sets in one space, such that its image under a linear transformation is in the intersection of another family of closed convex sets in the image space. In each iteration of this method, the step-size is directly computed, and is shown to be the best for the current direction. Then we consider the corresponding relaxed projection scheme for the proposed method. The theoretical convergence results are established. Preliminary numerical experiments show that this simple method and its relaxed scheme are easy to implement and practical. © 2013 Copyright Taylor and Francis Group, LLC. Source


Tang H.,CAS Institute of Process Engineering | Tang H.,University of Chinese Academy of Sciences | Hessel C.M.,CAS Institute of Process Engineering | Wang J.,CAS Institute of Process Engineering | And 6 more authors.
Chemical Society Reviews | Year: 2014

Two-dimensional (2D) carbon allotropes, which are atomic thick layers made of network carbon atoms with hexagonal structured lattices, have been neglected until the direct investigation of mechanically exfoliated graphene by Novoselov et al. in 2004. Graphene is a 2D carbon allotrope with a unique structure of hexagonally arranged atoms that give it unparalleled electrical conductivity and carrier mobility, in addition to excellent mechanical flexibility and extremely high specific surface area. Graphene and its derivatives have been extensively studied for photovoltaic and photocatalytic applications due to their inherent nature to extract and transport charges from photon-absorbing semiconductors and conjugated polymers. Graphyne and graphdiyne, 2D carbon allotropes like graphene but containing not only doubly but also triply bonded carbon atoms, are predicted to possess intrinsic semiconductor bandgap and even more superior electrical properties than graphene. The current theoretical understanding and experimental status of graphyne and graphdiyne will be discussed in contrast of graphene, demonstrating those promising competitors to graphene in further lightening a new photoconversion. This review addresses the recent successes and current challenges of graphene, graphyne and graphdiyne, and provides insightful perspectives for the future applications of 2D carbon materials in photoelectric conversion and photocatalysis. © 2014 The Royal Society of Chemistry. Source


An important issue in the probabilistic prediction modelling of multivariate soil properties (usually including cohesion, friction angle, and unit weight) is the measurement of dependence structure among these properties. The use of Pearson's correlation as a dependence measure has several pitfalls; therefore, it may not be appropriate to use probabilistic prediction models in geotechnical engineering problems based on this correlation. As an alternative, a copula-based methodology for prediction modelling and an algorithm to simulate multivariate soil data are proposed. In this method, all different random variables are transformed to a rank/uniform domain in order to form a copula function by applying cumulative distribution function transformations. The technique of copulas, representing a promising alternative for solving multivariate problems to describe their dependence structure by a ranked correlation coefficient, is highlighted. Two existing observed soil data sets from river banks are used to fit a trivariate normal copula and a trivariate fully nested Frank copula. The ranking correlation coefficient Kendall's τ and the copula model parameters are estimated. The goodness-of-fit test to choose the best-fitting model is discussed. A series of triplet samples (i.e., cohesion, friction angle, and unit weight) simulated from the trivariate normal copula with flexible marginal distributions are used as input parameters to evaluate the uncertainties of soil properties and to define their correlations. The influence of the cross-correlation of these soil properties on reliability-based geotechnical design is demonstrated with two simple geotechnical problems: (a) the bearing capacity of a shallow foundation resting on a clayey soil and (b) the stability of a cohesive-frictional soil in a planar slope. The sensitivity analysis of their correlations of random variables on the influence of the reliability index provides a better insight into the role of the dependence structure in the reliability assessment of geotechnical engineering problems. © 2013 The Japanese Geotechnical Society. Production and hosting by Elsevier B.V. All rights reserved. Source


Shao D.,Rensselaer Polytechnic Institute | Yu M.,Rensselaer Polytechnic Institute | Yu M.,University of Science and Technology Beijing | Lian J.,Rensselaer Polytechnic Institute | Sawyer S.,Rensselaer Polytechnic Institute
Applied Physics Letters | Year: 2013

A heterojunction photodiode was fabricated from multiwalled carbon nanotubes (MWCNTs)/ZnO nanowires/p-Si (100) substrate composite structure. The heterojunction photodiode demonstrated a faster transient response and higher responsivity than the reference sample without deposition of MWCNTs, which is attributed to improved carrier collection and transport efficiency through the MWCNTs network. The high photoresponsivities of the devices are explained in terms of operation as a hybrid of photodiode and photoconductor modes. The spectral response of the devices showed dependence on voltage polarity and is attributed to the high valance band offset in the interfacial region of ZnO and p-Si substrate. © 2013 American Institute of Physics. Source


Li W.,CAS Research Center for Eco Environmental Sciences | Shi Y.,CAS Research Center for Eco Environmental Sciences | Gao L.,CAS Research Center for Eco Environmental Sciences | Liu J.,University of Science and Technology Beijing | Cai Y.,CAS Research Center for Eco Environmental Sciences
Chemosphere | Year: 2012

This study investigated the presence and distribution of 22 antibiotics, including eight quinolones, nine sulfonamides and five macrolides, in the water, sediments, and biota samples from Baiyangdian Lake, China. A total of 132 samples were collected in 2008 and 2010, and laboratory analyses revealed that antibiotics were widely distributed in the lake. Sulfonamides were the dominant antibiotics in the water (0.86-1563ngL-1), while quinolones were prominent in sediments (65.5-1166μgkg-1) and aquatic plants (8.37-6532μgkg-1). Quinolones (17.8-167μgkg-1) and macrolides [from below detection limit (BDL) to 182μgkg-1] were often found in aquatic animals and birds. Salvinia natans exhibited the highest bioaccumulation capability for quinolones among three species of aquatic plants. Geographical differences of antibiotic concentrations were greatly due to anthropogenic activities. Sewage discharged from Baoding City was likely the main source of antibiotics in the lake. Risk assessment of antibiotics on aquatic organisms suggested that algae and aquatic plants might be at risk in surface water, while animals were likely not at risk. © 2012 Elsevier Ltd. Source


Chen X.,University of Science and Technology Beijing | Fang Y.,Rensselaer Polytechnic Institute | Fang Y.,Illinois Institute of Technology
Enterprise Information Systems | Year: 2013

The use of enterprise systems has become increasingly popular in the financial service industry. This paper discusses the applications of enterprise systems in the financial sectors and presents an application in gold price forecasting. We carefully examine the impacts of a few most widely assumed factors that have significant impact on the long-term gold price using statistical regression techniques. The analysis on our proposed linear regression mode indicates that the United States ultra scale of M2 money supply has been the most important catalyst for the rising price of gold, and the CRB index upward trend has also been the weighty factor for pushing up the gold price. In addition, the gold price has a low negative correlation with the Dow Jones Industrial Average, and low positive correlations with the US dollar index and the gold ETFs holdings. © 2013 Copyright Taylor and Francis Group, LLC. Source


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. Source


Wang L.,CAS Institute of Physics | Hao Y.,University of Science and Technology Beijing | Chen S.,CAS Institute of Physics
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2010

We study how stable excited many-body states of the Bose-Hubbard model, including both the gaslike state for strongly attractive bosons and bound cluster state for repulsive bosons, can be produced with cold bosonic atoms in an one-dimensional optical lattice. Starting from the initial ground states of strongly interacting bosonic systems, we can achieve stable excited states of the systems with opposite interaction strength by suddenly switching the interaction to the opposite limit. By exactly solving dynamics of the Bose-Hubbard model, we demonstrate that the produced excited state can be a very stable dynamic state. This allows the experimental study of excited state properties of ultracold atoms system in optical lattices. © 2010 The American Physical Society. Source


Bai Y.,Hong Kong Polytechnic University | Bai Y.,University of Science and Technology Beijing | Zheng G.,Hong Kong Polytechnic University | Shi S.,Hong Kong Polytechnic University
Applied Physics Letters | Year: 2010

The electrocaloric (EC) effect of BaTiO3 multilayer thick film structure was investigated by direct measurement and theoretical calculation. The samples were prepared by the tape-casting method, which had 180 dielectric layers with an average thickness of 1.4 μm. The thermodynamic calculation based on the polarization-temperature curves predicted a peak heat adsorption of 0.32 J/g at 80 °C under 176 kV/cm electric field. The direct measurement via differential scanning calorimeter showed a much higher EC effect of 0.91 J/g at 80 °C under same electric field. The difference could result from the different trends of changes of electric polarization and lattice elastic energy under ultrahigh electric field. © 2010 American Institute of Physics. Source


Sun C.,University of Science and Technology Beijing
Journal of Software | Year: 2011

In regression testing, an important problem is how to select a smaller size of test set for execution. We present a novel constraint-oriented test suite reduction method for conservative regression testing by which we mean that all bugs discovered must be revealed by the reduced test suite. A test constraint for a bug is Boolean formulas defined over the input variables of program under test. The reduced test constraints for a pool of bugs are constructed using the sub sumption relationship between test constraint conditions. Test case selection is based on the reduced test constraint set. A test case is selected into the test suite when and only when it satisfies one or more test constraints. The selection process is completed when all test constraint conditions are satisfied by the selected test cases. An empirical study is conducted and the experimental results show that our method can significantly save efforts for the conservative regression testing. © 2011 Academy Publisher. Source


Zhang Q.,University of Science and Technology of China | Xia Z.,University of Science and Technology of China | Xia Z.,University of Science and Technology Beijing
RSC Advances | Year: 2014

CaMoO4:Eu3+, Li+ red phosphors have been successfully achieved by a microwave-assisted solid-state reaction, and their morphologies and luminescence properties have been studied in this paper. The as-prepared Ca0.9MoO4:0.05Eu3+, 0.05Li+ powders occur as uniform spherical particles with a size distribution of 1-2 μm via the optimized reaction temperature at 600 °C and reaction time of 1 h. The phosphors showed an intense red emission with maxima at 615 nm, which was ascribed to the Eu3+ electric dipole transition of 5D0 → 7F2. The comparison on the morphology and luminescence property between the as-prepared samples and the samples obtained by the conventional method was discussed in detail. A possible microwave-assisted solid-state reaction mechanism was proposed, and the effect of the microwave sintering temperature and time was also discussed. © the Partner Organisations 2014. Source


Pan D.-G.,University of Science and Technology Beijing
Gongcheng Lixue/Engineering Mechanics | Year: 2013

For the case of the multi-degree-of-freedom, viscous damping system subjected to seismic excitations, a formulation of optimizing Rayleigh damping coefficients is developed by using the objective function of the peak response error at certain degree of a structure. Then, based on the empirical equation of earthquake spectrum varying with damping ratio, the approximate solution on the derivation of response spectrum is obtained. Therefore, a formulation which includes the comprehensive effects of structural dynamic characteristics, direction and frequency content of seismic excitation is addressed. Finally, seismic responses of a high-rise building subjected to 10 earthquake waves are analyzed. Numerical examples demonstrate that the new method can reduce the numerical errors which are induced by the Rayleigh damping. Source


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. Source


Chen W.,University of Auckland | He Y.,University of Science and Technology Beijing | Gao W.,University of Auckland
Journal of the Electrochemical Society | Year: 2010

A Ni- TiO2 composite film was prepared by electrodeposition containing Ti precursor sol (sol-enhanced deposition). The electrochemical process, microstructures, and properties of the sol-enhanced and traditional composite coatings were studied and compared. The sol-enhanced Ni- TiO 2 composite coating possessed a smooth surface and a compact microstructure and showed higher mechanical properties (430 HV100) compared with the traditional coatings (360 HV100). It is believed that the strengthening effects resulted from the high dispersion of TiO2 nanoparticles. The sol added coatings also showed slower growth of Ni grains along the [220] direction but did not change the orientation. It is suggested that the sol addition reduced the thickness of the diffusion layer and increased the limited current density. Therefore, the polarization control in the sol-enhanced process changed from the traditional concentration polarization to electrochemical polarization, avoiding the formation of loose and dendritic structures at high current density. © 2010 The Electrochemical Society. Source


Hao Y.-J.,University of Science and Technology Beijing
Chinese Physics Letters | Year: 2011

By the density-functional calculation we investigate the ground-state properties of Bose-Fermi mixture confined in one-dimensional harmonic traps. The homogeneous mixture of bosons and polarized fermions with contact interaction can be exactly solved by the Bethe-ansatz method. After giving the exact formula of ground state energy density, we employ the local-density approximation to determine the density distribution of each component. It is shown that with the increase in interaction, the total density distribution evolves to Fermi-like distribution and the system exhibits phase separation between two components when the interaction is strong enough but finite. While in the infinite interaction limit both bosons and fermions display the completely same Fermi-like distributions and phase separation disappears. © 2011 Chinese Physical Society and IOP Publishing Ltd. Source


Wang C.,Qingdao University | Xu C.,Qingdao University | Cao Z.,University of Science and Technology Beijing | Di H.,Qingdao University
Energy Conversion and Management | Year: 2013

A set of experiments on biomass/coal co-combustion were performed to investigate the ashing behavior in a tube furnace and a Muffle furnace respectively. The eight blending samples in terms of coal contents were 0, 5, 15, 20, 40, 60, 90, and 100 wt.%. The blending ratios of coal/straw caused different ash quantity effects, ash quantity was inhibited when the coal ratio was from 5 wt.% to 15 wt.%, and promoted when higher coal ratios. Combined the morphology analysis, mineral analysis, and chlorine equilibrium analysis, the chlorine content in the drop-tube furnace ash rapidly decreased when the coal ratio was from 5 wt.% to 15 wt.%, and the Cl content of the fly ash from 40 wt.% coal blend was very low at 0.49%. In the ash from the 40 wt.% coal blend, the CaCO3 and CaSO4 contents were very low for coupling reaction between the biomass and coal minerals under high temperature, the new and stable CaAl2Si2O8, K2Fe 4Si12O30, and KAlSi3O8 minerals were produced, which accompanied the ash promotion effect. The ashing behavior of 40 wt.% coal-blending is largely significant in preventing slagging and corrosion during straw co-firing and coal plant operation. © 2013 Elsevier Ltd. All rights reserved. Source


Zheng J.,Kyushu University | Tashiro Y.,Kyushu University | Wang Q.,University of Science and Technology Beijing | Sakai K.,Kyushu University | Sonomoto K.,Kyushu University
Applied Energy | Year: 2015

The economic feasibility of acetone-butanol-ethanol (ABE) fermentation is greatly affected by the type of raw material used. The easy availability of eucalyptus from marginal environments is an alternative feedstock for use as raw material to reduce the production cost. In this study, hydrolyzed eucalyptus was used for ABE production without any nutrients supplementation. Increasing the solid concentration in the eucalyptus slurry from 6.7% (w-dry matter/. v) to 25% led to an increase in the initial glucose concentration from 33.7. g/L to 86.7. g/L after enzymatic hydrolysis. Dosed cellulases not only hydrolyzed cellulose but also supplied nitrogen source for ABE producing strain. However, ABE production from the obtained hydrolysate decreased when the solid concentration was increased to more than 10%. The maximum ABE of 12.3. g/L was obtained at 10% solid concentration, with an initial glucose concentration of approximately 40. g/L. In addition, the fermentation capability of eucalyptus hydrolysate was found to be improved by diluting the hydrolysate, which prevented inhibition by substrate and fermentation inhibitors. Finally, ABE concentration was improved to 13.1. g/L by diluting the hydrolysate from the initial solid concentration of 25% to an initial glucose concentration of 45. g/L, which resulted in ABE productivity of 0.109. g/L/h and ABE yield of 0.413. g/g. Thus, the high ABE production from eucalyptus makes it a potential feedstock for biofuel production. © 2014 Elsevier Ltd. Source


Pan D.-G.,University of Science and Technology Beijing
Gongcheng Lixue/Engineering Mechanics | Year: 2013

In order to avoid an arbitrary selection of two reference vibration modes which are used to evaluate the two coefficients of Rayleigh damping, an optimization method for direct determination of the two Rayleigh damping coefficients is proposed. In the method, by formulating and minimizing an objective function which is an error term of the peak response at certain degree of a structure, the two coefficients can be systematically evaluated following the deformation response spectrum of excitation and modal analysis. Then, based on the harmonic response analysis of a five-storey shear building, the effects of both spatial distribution and frequency content of excitations and the effects of structural dynamic characteristics on selection of natural frequencies in Rayleigh damping are investigated in detail, and the accuracy and effectiveness of the proposed method are demonstrated. Source


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

Fluid flow during steel casting is very important to steel quality because it affects other important phenomena during mixing, refining, and solidification processes. These phenomena include turbulent flow in the molten steel, the transport of bubbles and inclusions, multiphase flow phenomena, chemical and transport interactions between the steel and the slag, the effect of heat transfer, the transport of solute elements, and segregation. With the high cost of empirical investigation and the increasing power of computer hardware and software, computational fluid dynamics (CFD) is becoming an important tool to understand these fluid flow-related phenomena during steelmaking and casting processes. © 2012 TMS. Source


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. Source


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. Source


Yang Y.,Georgia Institute of Technology | Lin L.,Georgia Institute of Technology | Zhang Y.,University of Science and Technology Beijing | Jing Q.,Georgia Institute of Technology | And 3 more authors.
ACS Nano | Year: 2012

Magnetic sensors are usually based on the Hall effect or a magnetoresistive sensing mechanism. Here we demonstrate that a nanogenerator can serve as a sensor for detecting the variation of the time-dependent magnetic field. The output voltage of the sensor was found to exponentially increase with increasing magnetic field. The detection sensitivities for the change and the changing rate of magnetic field are about 0.0363 ± 0.0004 ln(mV)/G and 0.0497 ± 0.0006 ln(mV)/(G/s), respectively. The response time and reset time of the sensor are about 0.13 and 0.34 s, respectively. The fabricated sensor has a detection resolution of about 3 G and can work under low frequencies (<0.4 Hz). © 2012 American Chemical Society. Source


Li J.,University of Science and Technology Beijing | Yang Z.,Yunnan Normal University | Li H.,Beijing University of Technology
Journal of Physical Chemistry C | Year: 2010

Through a facile sublimation method, high-quality GaN nanowires with a length of several hundred micrometers were densely grown on amorphous substrates. The morphology and single-crystalline hexagonal structure of the GaN nanowires were characterized. Photoluminescence of the nanowires was studied, and a near-band-gap emission of wurtzite GaN was observed, indicating good optical quality of the GaN nanowires. Individual GaN nanowire devices were fabricated, and their photoconductivity and electrical transport properties were investigated. The results reveal that the sublimation-grown GaN nanowires possess outstanding UV sensitivity and an n-type gating effect. © 2010 American Chemical Society. Source


Chen S.,CAS Institute of Physics | Guan L.,CAS Institute of Physics | Yin X.,CAS Institute of Physics | Hao Y.,University of Science and Technology Beijing | Guan X.-W.,Australian National University
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2010

We investigate transition of a one-dimensional interacting Bose gas from a strongly repulsive regime to a strongly attractive regime, where a stable highly excited state known as the super Tonks-Girardeau gas was experimentally realized very recently. By solving exact dynamics of the integrable Lieb-Liniger Bose gas, we demonstrate that such an excited gas state can be a very stable dynamic state. Furthermore we calculate the breathing mode of the super Tonks-Girardeau gas which is found to be in good agreement with experimental observation. Our results show that the highly excited super Tonks-Girardeau gas phase can be well understood from the fundamental theory of the solvable Bose gas. © 2010 The American Physical Society. Source


Hao Y.,University of Science and Technology Beijing
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2016

Using an anyon-fermion mapping method, we investigate the ground-state properties of hard-core anyons confined in a one-dimensional harmonic trap. The concise analytical formula of the reduced one-body density matrix is obtained. Based on this formula, we evaluated the momentum distribution, the natural orbitals, and their occupation distributions for different statistical parameters. The occupation and occupation fraction of the lowest natural orbital versus anyon number are also displayed. It is shown that the ground-state properties of anyons interplay between bosons and fermions continuously. We can expect that the hard-core anyons of larger statistical parameters exhibit similar properties to the hard-core bosons although anyon systems satisfy specific fractional statistics. © 2016 American Physical Society. Source


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. Source


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. Source


Geng W.T.,Japan National Institute of Materials Science | Geng W.T.,University of Science and Technology Beijing | Ohno T.,Japan National Institute of Materials Science
Journal of Physical Chemistry C | Year: 2014

We report a first-principles study on the initial deposition of Li2O2 on three rutile oxide surfaces, RuO2(110)-(1×1)-O, TiO2(110), and SnO2(110). The intermediate discharge product in a Li-air battery, LiO2, is found to be less stable on all rutile surfaces and will be further reduced to Li2O2 through disproportionation reaction. For the first and second layers of deposited Li2O2, the adsorption energy is comparable to the cohesive energy of bulk Li2O2, suggesting Li2O2 will likely wet the oxide surfaces and grow into thin films rather than particles. Electronic structure analyses of interfaces demonstrate Li2O2/TiO2(110) is metallic and Li2O2/SnO2(110) is semiconducting with a bandgap of 0.2 eV, substantially smaller than in bulk Li2O2. The large lattice mismatch at these interfaces could create amorphousness of Li2O2 and grain boundaries might form abundantly thereafter, both of which can provide charge and ion transport channels needed for oxygen reduction and evolution reactions in Li-air batteries. Therefore, coating nanostructured carbon cathode with thin films of TiO2 or employing mesoporous TiO2 nanostructures as cathode could possibly lead to the formation of low-resistance Li2O2 thin films and thereby enhance the rate capacity of Li-air batteries. © 2014 American Chemical Society. Source


Yu C.Y.,City University of Hong Kong | Liu X.J.,University of Science and Technology Beijing | Liu C.T.,City University of Hong Kong
Intermetallics | Year: 2014

In the present study, the atomistic approach, developed previously by hybridizing both internal energies and atomic-scale defect structures, is extended to predict the trend of glass forming ability (GFA) from the Zr-Cu binary alloy system with good GFA to the Zr-Ni binary system with relatively poor GFA. The predicted composition dependence of the GFA in the Zr-Ni alloy system is consistent with those obtained from experimental results, indicating the validity of the proposed atomistic approach in both of the alloy systems. The different GFAs in the Zr-Cu and Zr-Ni systems have been puzzled by the metallic glass community for quite a long time, and our study provides the physical reasons for the different glass forming behaviors of the two alloy systems in terms of both atomic configurations and relative stability of their intermetallic phases. © 2014 Elsevier Ltd. All rights reserved. Source


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. Source


Huang X.,University of Science and Technology Beijing
Soft Computing | Year: 2011

This paper discusses fuzzy portfolio selection problem in the situation where each security return belongs to a certain class of fuzzy variables but the exact fuzzy variable cannot be given. Two credibility-based minimax mean-variance models are proposed. The crisp equivalents of the models to linear programming ones are given in three special cases. In addition, a general solution algorithm is also provided. To help understand the modeling idea and to illustrate the effectiveness of the proposed algorithm, one example is presented. © 2010 Springer-Verlag. Source


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). Source


Bi K.,Nanjing University of Aeronautics and Astronautics | Wang Y.G.,Nanjing University of Aeronautics and Astronautics | Pan D.A.,University of Science and Technology Beijing | Wu W.,Nanjing University of Aeronautics and Astronautics
Scripta Materialia | Year: 2010

A magnetoelectric (ME) Ni-PZT-TbFe2 trilayer with negative magnetostrictive/piezoelectric/positive magnetostrictive layers has been prepared. The influence of the bias magnetic field and the magnetic field frequency on ME coupling is discussed. The ME coefficient behavior of the Ni-PZT-TbFe2 trilayer is different from that of Ni-PZT-Ni and TbFe2-PZT-TbFe2 trilayers. Two remarkable resonance peaks have been observed in the dependence of the ME voltage coefficient on the magnetic field frequency, which makes these Ni-PZT-TbFe2 trilayers suitable for applications in multifunctional devices with multifrequency operation. © 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Source


Ding D.-W.,University of Science and Technology Beijing | Ding D.-W.,Northeastern University China | Yang G.-H.,Northeastern University China
IEEE Transactions on Fuzzy Systems | Year: 2010

This paper is concerned with the problem of fuzzy-filter design for discrete-time nonlinear systems in the TakagiSugeno (TS) form. Different from existing fuzzy filters, the proposed ones are designed in finite-frequency domain. First, a so-called finite-frequency l2 gain is defined that extends the standard l2 gain. Then, a sufficient condition for the filtering-error system with a finite-frequency l2 gain is derived. Based on the obtained condition, three fuzzy filters are designed to deal with noises in the low-, middle-, and high-frequency domain, respectively. The proposed fuzzy-filtering method can get a better noise-attenuation performance when frequency ranges of noises are known beforehand. An example about a tunnel-diode circuit is given to illustrate its effectiveness. © 2010 IEEE. Source


Jiang Y.-Y.,Hefei University of Technology | Zhang Q.,Hefei University of Technology | Yu H.-Z.,University of Science and Technology Beijing | Fu Y.,Hefei University of Technology
ACS Catalysis | Year: 2015

Traditional Wacker-type oxidations of unbiased alkenes produce ketones as major products. Recently, Grubbsgroup reported a Wacker-type oxidation system in which aldehydes (rather than ketones) have been generated predominantly in the presence of a nitrite co-catalyst. To elucidate the mechanistic origin of the aldehyde selectivity, density functional theory (DFT) studies have been conducted in this study. Two oxymetalation pathways, i.e., syn addition and anti addition pathways, were considered for various possible active species including monomeric Pd, bimetallic Pd-Pd, heterobimetallic Pd-Cu, and heterobimetallic Pd-Ag complexes. It is found that syn addition is kinetically more favored than anti addition in general. Meanwhile, the most feasible oxymetalation processes occur on the heterobimetallic Pd-Cu complexes. Investigations on the subsequent aldehyde formation process show that 1,2-H shift mechanism on tBuOH-ligated Pd-Cu complexes is superior to the betaH-elimination mechanism. Besides, the 1,2-H shift is the rate- and regioselectivity-determining step of the whole catalytic cycle. The analysis on spin density population indicates that the tBuOH-ligated Pd-Cu complex promotes a radical 1,2-H shift on the oxygenated alkene. The longer Pd-C(alkene) distance facilitates the aldehyde-selective pathway (relative to the ketone-selective pathway) due to the stronger stability of the secondary carbon radical and the smaller distortion energy therein. © 2015 American Chemical Society. Source


Rui L.,University of Science and Technology Beijing
AIP Advances | Year: 2014

The tribological behaviours of three kinds of multi-walled carbon nanotube (MWCNT) films, flattened pristine film, film with mixed acid treatment and vertically aligned film, were investigated in air at room temperature using a universal tribometer-II. The results indicated that the flattened pristine film with less defects and oxidation had the best tribological behaviour. The vertically aligned film obtained the highest friction coefficient, and vertical orientation is perhaps the most crucial factor when high friction is needed. © 2014 Author(s). Source


Tian J.J.,University of Science and Technology Beijing
Materials Science Forum | Year: 2015

Monodispersed magnetic SmCo nanoparticles have been prepared by polyol synthesis using non-toxic inorganic precursors (nitrates). The effect of the additives of NaOH, HNO3, CH3COOH and poly vinyl pyrrolidone (PVP) on the formation of SmCo nanoparticles is studied in this paper. The results indicate that base solution can boost the reduction of Co while acid solution is helpful for the formation of SmCo due to decreasing the reduction velocity of Co. CH3COOH is appropriate additive for the synthesis of SmCo nanoparticles, but more addition of CH3COOH will result in the emergence of CoC2 phase and decrease the coercivity of the resultants. The additive of PVP not only is a dispersing agent, but can prevent them from oxidating during preparation process. The SmCo nanoparticles with a size of 5-8 nm have the ferromagnetic properties of high coercivity (>1000 Oe). © (2015) Trans Tech Publications, Switzerland. Source


Yi F.,University of Science and Technology Beijing
RNA biology | Year: 2013

RNA transcripts are generally classified into polyA-plus and polyA-minus subgroups due to the presence or absence of a polyA tail at the 3' end. Even though a number of physiologically and pathologically important polyA-minus RNAs have been recently identified, a systematic analysis of the expression and function of these transcripts in adipogenesis is still elusive. To study the potential function of the polyA-minus RNAs in adipogenesis, a dynamic expressional profiling was performed in the induced differentiation of 3T3-L1 cells. In addition to identifying thousands of novel intergenic transcripts, differentiation-synchronized expression was characterized for many of them. Among these, several large intergenic transcripts were found to be upregulated by more than 19-fold during differentiation. Further study demonstrated a fat tissue-specific expression pattern for these regions and identified an adipogenesis-associated long non-coding RNA. Collectively, these lines of evidence contribute to the characterization of a super-long intergenic transcript functioning in adipogenesis. Source


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. Source


Zhang Y.,University of Science and Technology Beijing
Materials Science Forum | Year: 2010

Bulk metallic glasses (BMGs) and high entropy alloys (HEAs) have unique structures at the length scales of micro- and nano-metre, and exhibit unique properties, which make them potential materials for structural applications. The tensile ductility of dendrite/BMG composites can be greatly improved by Bridgman solidification. The BCC structured HEA with a composition of Ti 0.5AlCoCrFeNi exhibits ultrahigh fracture strength which is competitive to most of the BMGs, moreover, the strength can be sustained at high temperatures. The phase changes of HEAs are closely related to the atomic packing efficiency (APE). © (2010) Trans Tech Publications. Source


Li Y.F.,Ecole 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. Source


Shao D.,Rensselaer Polytechnic Institute | Sun H.,Rensselaer Polytechnic Institute | Yu M.,Rensselaer Polytechnic Institute | Yu M.,University of Science and Technology Beijing | And 2 more authors.
Nano Letters | Year: 2012

Enhanced near band gap edge (NBE) emissions of PVA-ZnO nanoparticles were achieved by employing SiO2-Au core/shell nanostructures whereas the defect-level emission (DLE) is greatly suppressed. A maximum enhancement of nearly 400% was observed using SiO2-Au for the emission with optical resonance at 554 nm. SiO2-Au core/shell nanostructures also show a superior tunability of resonance energy as compared to that of the pure metal nanoparticles. The enhancement of the NBE emission and suppressed DLE is ascribed to the transfer of the energetic electrons excited by surface plasmon from metal nanoparticles to the conduction band of ZnO nanoparticles. © 2012 American Chemical Society. Source


Guo J.,University of Science and Technology Beijing | Zhao Y.,Chinese Academy of Sciences
Automatica | Year: 2013

This paper studies the identification of finite impulse response (FIR) systems with binary-valued observations. Combining with the stochastic gradient algorithm and statistical property of the system noise, a recursive projection algorithm is proposed to estimate the unknown system parameters. Under some mild conditions on the a priori knowledge of the unknown parameters and inputs, the algorithm is proved to be convergent in the almost sure and mean square sense. Furthermore, the almost sure and mean square convergence rates of estimation errors are also obtained. A numerical example is given to demonstrate the effectiveness of the algorithm and the main results obtained. © 2013 Elsevier Ltd. All rights reserved. Source


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. Source


Liu W.,Communication University of China | Wang Y.-B.,Communication University of China | Wang X.-M.,University of Science and Technology Beijing
International Journal of Theoretical Physics | Year: 2014

We present a new multi-party quantum private comparison protocol based on d-dimensional basis states. Different from previous protocols, our protocol have some advantages. n parties can determine wether their private information are equal or not in one time execution of our protocol. Without using the entangled character of d-dimensional basis states, we only need to perform the local unitary operation on particles to encode the information and to get the comparison result. We also discuss that our protocol can withstand various kinds of outside attacks and participant attacks. © 2013 Springer Science+Business Media New York. Source


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. Source


Xiao H.,Southwestern University of Finance and Economics | Peng R.,University of Science and Technology Beijing
Computers and Industrial Engineering | Year: 2014

This article considers the optimal allocation and maintenance of multi-state elements in series-parallel systems with common bus performance sharing. The surplus performance from a sub-system can be transmitted to any other sub-system which is experiencing performance deficiency. The amount that can be transmitted is subjected to a random transmission capacity. In order to increase the system availability, maintenance actions can be performed during the system lifetime and the system elements can be optimally allocated into the sub-systems. In this paper, we consider the element allocation and maintenance simultaneously in order to minimize the total maintenance cost subject to the pre-specified system availability requirement. An algorithm based on universal generating function is suggested to evaluate the system availability and the genetic algorithm is explored to solve the optimization problem. Numerical experiments are presented to illustrate the applications. Source


Yu G.H.,University of Science and Technology Beijing | Peng X.,28151 E. Broadway Street and 2
Applied Surface Science | Year: 2010

In this paper, we investigated the elemental inter-diffusion in MgO TMR system, namely, between MgO barrier and free layer (CoFeB, NiFe or their combination) interface and the oxygen diffusion into the capping layers (Ta, Ru, TaN) at elevated temperatures using simple sheet film stack to simplify the results interpretation. Boron, cobalt, iron, and nickel show various diffusion tendencies into the MgO barrier after annealing the sheet film stack. Oxygen has different penetration depth into single CoFeB free layer upon annealing under N2 + Ar protective atmosphere for different capping layers. Ru and TaN capping layer provide much better O2 diffusion barrier, compared with Ta capping layer. This could potentially change the boron segregation tendency at free layer and capping layer interface and thus affect the interface crystallization process and lattice matching between the crystallized CoFeB free layer and the MgO(0 0 1) barrier layer. All these effects will impact the overall TMR performance. © 2010 Elsevier B.V. Source


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

Industrial plant maintenance is an area which has enormous potential to be improved. It is also an area attracted significant attention from mathematical modellers because of the random phenomenon of plant failures. This paper reviews the recent advances in delay-time-based maintenance modelling, which is one of the mathematical techniques for optimising inspection planning and related problems. The delay-time is a concept that divides a plant failure process into two stages: from new until the point of an identifiable defect, and then from this point to failure. The first stage is called the normal working stage and the second stage is called the failure delay-time stage. If the distributions of the two stages can be quantified, the relationship between the number of failures and the inspection interval can be readily established. This can then be used for optimizing the inspection interval and other related decision variables. In this review, we pay particular attention to new methodological developments and industrial applications of the delay-time-based models over the last few decades. The use of the delay-time concept and modeling techniques in other areas rather than in maintenance is also reviewed. Future research directions are also highlighted. © 2012 Elsevier Ltd. Source


Wang S.Z.,University of Science and Technology Beijing
Advances in Energy, Environment and Materials Science - Proceedings of the International Conference on Energy, Environment and Materials Science, EEMS 2015 | Year: 2016

We examined the cold region of the concrete inorganic protective agent through the experimental study of the concrete 30 flexural, the carbonization and the wear-resisting influence. The experimental results indicated that this inorganic protective agent produced on the concrete 30 can increase its flexural strength by about 10%, and the carbonization and the wear resistance can be, respectively, improved by 36 and 45%. This product was used in the Ningan Wolong River Reservoir in Heilongjiang Province for strengthening purposes, which produced an ideal effect. © 2016 Taylor & Francis Group, London. Source


Feng Z.,University of Science and Technology Beijing | Zuo M.J.,University of Alberta
Journal of Sound and Vibration | Year: 2012

A thorough understanding of the spectral structure of planetary gear system vibration signals is helpful to fault diagnosis of planetary gearboxes. Considering both the amplitude modulation and the frequency modulation effects due to gear damage and periodically time variant working condition, as well as the effect of vibration transfer path, signal models of gear damage for fault diagnosis of planetary gearboxes are given and the spectral characteristics are summarized in closed form. Meanwhile, explicit equations for calculating the characteristic frequency of local and distributed gear fault are deduced. The theoretical derivations are validated using both experimental and industrial signals. According to the theoretical basis derived, manually created local gear damage of different levels and naturally developed gear damage in a planetary gearbox can be detected and located. © 2012 Elsevier Ltd. All rights reserved. Source


Sun J.,Shandong University | Wu C.S.,Shandong University | Feng Y.,University of Science and Technology Beijing
International Journal of Thermal Sciences | Year: 2011

It is essential to model the transient heat transfer phenomena during the controlled pulse key-holing plasma arc welding (PAW) for practical application of this novel process. In this paper, a three-dimensional transient model is developed to analyze the periodic changes of the temperature field, weld pool and keyhole shape and dimensions during the controlled pulse key-holing process. An adaptive, combined, and volumetric heat source is proposed for the numerical analysis of the temperature fields in PAW process. The force action at the weld pool surface is considered to calculate the keyhole shape inside the weld pool. The dynamic variation features of weld pool and keyhole shape in a pulse cycle are numerically simulated. The phenomena of "one keyhole in each pulse" and periodic partial-open keyhole transformation are quantitatively simulated. Experiments are conducted to validate the numerical simulation results. The calculated weld cross-section is consistent with the measured ones. The predicted information on the dynamic evolution of the temperature profiles, weld pool and keyhole geometry is useful for optimizing the multi process parameters in the controlled pulse key-holing PAW process. © 2011 Elsevier Masson SAS. All rights reserved. Source


An experimental system for the thermal conductivity and diffusivity measurement by the step-wise transient method in high temperatures is established, the effective measurement range of thermal conductivity is from 0 to 2.5 W/(m.K), and the highest working temperature is 1250°C. Verification of apparatus was achieved by undertaking measurements on standard reference materials, the relative deviations for the thermal conductivity are within 5% at room temperature compared with the recommended values. The thermal conductivities and diffusivities for silica aerogel composite insulation material in temperature range 25-800°C, and for alumina aerogel composite material in temperature range 25-1200°C are measured in the pressure range 10-101300 Pa. The preliminary uncertainty analyses are performed for alumina aerogel composite material, the values of the overall uncertainties estimated are 3.57% for the thermal conductivity and 6.43% for thermal diffusivity at 25°C, and 5.15% for the thermal conductivity and 8.56% for thermal diffusivity at 1200°C, respectively. © 2015 Old City Publishing, Inc. Source


Wang G.,University of Science and Technology Beijing
Synthetic Metals | Year: 2010

A series of diaminonaphthalene derivatives with naphthalene as a core and butylamino and phenylamino as substituted groups were synthesized and their optical and electrochemical behavior were investigated. Phenylamino substituted naphthalene derivatives exhibit two absorption bands, which are assigned to n → π* electronic transitions that are due to electron transfer from nitrogen lone pairs to the π* orbital of the naphthalene group and the phenyl group, respectively. Comparing with butylamino substitutes, phenylated ones exhibit a red-shift in both absorption and emission for their electron-donating phenyl groups. The fluorescence quantum yields of the molecules were measured in THF. Cyclic voltammetric measurements demonstrated that the diaminonaphthalene derivatives possess two oxidation processes and the solid-state ionization potentials were estimated from the electrochemical potential. The phenylamino-naphthalenes possess higher ionization potentials than those of the alkylated ones. The relative HOMO and LUMO levels for these materials, important parameters for the design of efficient organic light-emitting or photovoltaic devices, were assessed through electrochemical and spectroscopic measurements. © 2009 Elsevier B.V. All rights reserved. Source


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. Source


Zhou X.-M.,University of Science and Technology Beijing
Yantu Lixue/Rock and Soil Mechanics | Year: 2015

This paper reports the design of an auxiliary shaft at a depth of more than 1000 m at Cixi colliery and its surrounding geological conditions, and addresses the scheme for monitoring the in-situ stress around the shaft and the principle of inverse calculation for the in-situ geostress using the "Baoshen" analytical solution. The average values and nonuniform distribution of horizontal stresses are actually obtained at the depth of 1208 m through inverse calculation and analysis of field monitoring data, which reveals that the ratio of horizontal stress to vertical stress conforms to the dead weight stress field. The lateral pressure coefficient ranges from 0.256 to 0.278. The in-situ stress distribution around the shaft is illustrated based on finite element simulations; and thus the reliability of inverse data based on field measurements is corroborated. Meanwhile, it is shown that the nonuniform distribution of horizontal stress is related to some factors such as the shear modulus of rock and geological tectonic, etc. With combining the information on tectonic evolution in this area and geomechanical principles, the consistence among the results of in-situ test, analytical solution and numerical simulations is comprehensively analyzed. In this context, the universality of the Hoek & Brown statistic principle about the distribution of horizontal in-situ stress is questioned, and the existing analytical methods for calculating the in-situ horizontal stress are also discussed, laying a foundation for using the "Baoshen" solution to the shaft lining design. ©, 2015, Academia Sinica. All right reserved. Source


Wang G.,University of Science and Technology Beijing
Jixie Gongcheng Xuebao/Journal of Mechanical Engineering | Year: 2010

A novel combined scroll compressor profile is proposed. It consists of some similar profile units and each unit includes a large arc, a small arc and a straight line. So the profile is named as arc-arc-line unit combined profile. The basic geometrical theory of the profile is established. The working chamber volume is derived and its change rule is studied. A prototype of scroll compressor with the arc-arc-line unit combined profile for automotive air conditioner is developed and its performance at variable speed is tested. The results show that the scroll compressor with arc-arc-line unit combined profile, in comparison with the one with the normal circle involute profile, has greater refrigeration quantity and higher coefficient of performance (COP) when they have the same overall dimensions of scroll plate. Source


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. Source


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. Source


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. Source


In this paper, we propose a lumped time delay compensation scheme for the all-optical analog-to-digital conversion (ADC) based on soliton self-frequency shift (SSFS) and optical interconnection techniques. By inserting a length of equiangular spiral photonic crystal fiber (PCF) between quantization and coding modules, the time delay of quantized pulses can be compensated. Simulation results show that the pulses can be synchronized utilizing a span of equiangular spiral PCF with flat negative dispersion of-258.92 ps/nm km in the wavelength range 1350 nm to 1675 nm. In addition, the amount of time delay and time error are analyzed, a maximum supportable sampling rate of 40 GSa/s is obtained. © 2016 Elsevier GmbH. All rights reserved. Source


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. Source