Beijing, China
Beijing, China

Beijing Institute of Technology , is a co-educational public university, located in Beijing, China. Established in 1940 in Yan'an, the university is now under the direct administration of the Ministry of Industry and Information Technology.As a member university of National Key Universities, “Project 211” and “Project 985”, it has been given priority for development from the Chinese government, the Commission of Science, Technology and Industry for National Defense, the Ministry of Education and the Beijing Government. Wikipedia.

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Beijing Institute of Technology | Date: 2017-01-18

The present disclosure is to provide a divided-aperture laser differential confocal Brillouin-Raman spectrum measuring method and the device thereof, which belongs to microscopic spectrum imaging field. By using the abandoned Rayleigh scattering light in the traditional confocal Raman spectrum detection, a divided-aperture laser differential confocal microscopy is constructed to realize high resolution imaging of three-dimensional geometrical structure of the measured sample. In addition, the characteristic that the zero-crossing point of the divided-aperture laser differential confocal imaging device accurately corresponds to the focus of objective is used to control the spectrum detector to accurately capture the excited Raman spectrum information excited at the focus of the objective, thereby achieving the detection of micro-area geometrical structure and spectrum information of the measured sample with high-spatial resolution, that is achieving mapping-spectrum with high-spatial resolution, and balancing resolution and measuring range. By complementing the advantages of confocal Raman spectrum detecting technology and confocal Brillouin spectrum detecting technology, the confocal spectrum detecting solution which detects the Raman spectrum and Brillouin spectrum at the same time is designed, the multi-property parameters of materials are measured and decoupled in composite.

Cui L.,Beijing Institute of Technology | Du S.,Beijing Institute of Technology | Hawkes A.G.,University of Swansea
IIE Transactions (Institute of Industrial Engineers) | Year: 2012

This article analyzes a single-unit repairable system consisting of an operating subsystem and a maintenance subsystem that is solely used to repair the operating subsystem in the event of it breaking down. Formulae for reliability indexes such as availability and distributions concerned with visits to certain subsets of states are presented in terms of state aggregations in which two partitions are used. The situation with exponentially distributed operational times is discussed not only as a special case of the approach used in this article but also using a Markov model. A numerical example is given to illustrate the results obtained in this article. © 2012 "IIE".

Chen Z.,Beijing Institute of Technology | Wang C.-C.,Peregrine Semiconductor | Yao H.-C.,HTC Corp | Heydari P.,University of California at Irvine
IEEE Journal of Solid-State Circuits | Year: 2012

This paper presents a W-band 2$\,\times\,$ 2 focal-plane array (FPA) for passive millimeter-wave imaging in a standard 0.18 $\mu{\hbox{m}}$ SiGe BiCMOS process ($f -{\rm T} /f -{\max} =200/180 ~{\hbox{GHz}}$). The FPA incorporates four Dicke-type receivers representing four imaging pixels. Each receiver employs the direct-conversion architecture consisting of an on-chip slot folded dipole antenna, an SPDT switch, a low noise amplifier, a single-balanced mixer, an injection-locked frequency tripler (ILFT), an IF variable gain amplifier, a power detector, an active bandpass filter and a synchronous demodulator. The LO signal is generated by a shared Ka-band PLL and distributed symmetrically to four local ILFTs. The measured LO phase noise is $-93~{\rm dBc}/{\rm Hz}$ at 1 MHz offset from the 96 GHz carrier. This imaging receiver (without antenna) achieves a measured average responsivity and noise equivalent power of 285 MV/W and 8.1 {\rm fW}/{\rm Hz} 1/2 respectively, across the 86-106 GHz bandwidth, which results a calculated NETD of 0.48 K with a 30 ms integration time. The system NETD increases to 3 K with on-chip antenna due to its low efficiency at W-band. MMW images have been generated in transmission mode. This work demonstrates the highest integration level of any silicon-based systems in the 94 GHz imaging band. © 1966-2012 IEEE. Pu K.-Y.,National University of Singapore | Shi J.,Beijing Institute of Technology | Cai L.,National University of Singapore | Li K.,National University of Singapore | Liu B.,National University of Singapore Biomacromolecules | Year: 2011 A hyperbranched conjugated polyelectrolyte (HCPE) with a core-shell structure is designed and synthesized via alkyne polycyclotrimerization and click chemistry. The HCPE has an emission maximum at 565 nm with a quantum yield of 12% and a large Stokes shift of 143 nm in water. By virtue of its poly(ethylene glycol) shell, this polymer naturally forms spherical nanoparticles that minimize nonspecific interaction with biomolecules in aqueous solution, consequently allowing for efficient bioconjugation with anti-HER2 affibody via carbodiimide-activated coupling reaction. The resulting affibody-attached HCPE can be utilized as a reliable fluorescent probe for targeted cellular imaging of HER2-overexpressed cancer cells such as SKBR-3. Considering its low cytotoxicity and good photostability, the HCPE nanoprobe holds great promise in practical imaging tasks. This study also provides a molecular engineering strategy to overcome the intrinsic limitations of traditional fluorescent polymers (e.g., chromophore-tethered polymers and linear conjugated polyelectrolytes) for bioconjugation and applications. © 2011 American Chemical Society. Zhao Y.,Beijing Institute of Technology | Liu J.,Beijing Institute of Technology | Hu Y.,Beijing Institute of Technology | Cheng H.,Beijing Institute of Technology | And 5 more authors. Advanced Materials | Year: 2013 Deformation-tolerant devices are vital for the development of high-tech electronics of unconventional forms. In this study, a highly compressible supercapacitor has been fabricated by using newly developed polypyrrole-mediated graphene foam as electrode. The assembled supercapacitor performs based on the unique and robust foam electrodes achieves superb compression tolerance without significant variation of capacitances under long-term compressive loading and unloading processes. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Li Z.,Beijing Institute of Technology | Duan Z.,Peking University | Chen G.,Peking University IET Control Theory and Applications | Year: 2011 This study concerns the consensus of a network of agents with general linear or linearised dynamics, whose communication topology contains a directed spanning tree. An observer-type consensus protocol based on the relative outputs of the neighbouring agents is adopted. The notion of consensus region is introduced, as a measure for the robustness of the protocol and as a basis for the protocol design. For neutrally stable agents, it is shown that there exists a protocol achieving consensus together with a consensus region that is the entire open right-half plane if and only if each agent is stabilisable and detectable. An algorithm is further presented for constructing such a protocol. For consensus with a prescribed convergence speed, a multi-step protocol design procedure is given, which yields an unbounded consensus region and at the same time maintains a favourable decoupling property. Finally, the consensus algorithms are extended to solve the formation control problems. © 2011 The Institution of Engineering and Technology. Chen H.,Peking University | Long H.,Peking University | Long H.,Beijing Institute of Technology | Cui X.,Peking University | And 3 more authors. Journal of the American Chemical Society | Year: 2014 Four putative G-quadruplex sequences (PGSs) in the HIF1α promoter and the 5′UTR were evaluated for their G-quadruplex-forming potential using ESI-MS, CD, FRET, DMS footprinting, and a polymerase stop assay. An important G-quadruplex (S1) has been proven to inhibit HIF1α transcription by blocking AP2 binding. A benzo[c]phenanthridine derivative was found to target the S1 G-quadruplex and induce its conformational conversion from antiparallel to parallel orientation. The transcriptional suppression of HIF1α by this compound was demonstrated using western blotting, Q-RT-PCR, luciferase assay, and ChIP. Our new findings provided a novel strategy for HIF1α regulation and potential insight for cancer therapy. © 2014 American Chemical Society. Ren W.,University of California at Riverside | Liu X.,Beijing Institute of Technology | Fu M.,Beijing Institute of Technology IEEE Transactions on Automatic Control | Year: 2013 This technical brief considers the distributed consensus problems for multi-agent systems with general linear and Lipschitz nonlinear dynamics. Distributed relative-state consensus protocols with an adaptive law for adjusting the coupling weights between neighboring agents are designed for both the linear and nonlinear cases, under which consensus is reached for all undirected connected communication graphs. Extensions to the case with a leader-follower communication graph are further studied. In contrast to the existing results in the literature, the adaptive consensus protocols here can be implemented by each agent in a fully distributed fashion without using any global information. © 1963-2012 IEEE. Zuo C.,Nanjing University of Science and Technology | Zuo C.,Nanyang Technological University | Zuo C.,Beijing Institute of Technology | Chen Q.,Nanjing University of Science and Technology | And 3 more authors. Optics Express | Year: 2013 Several existing strategies for estimating the axial intensity derivative in the transport-of-intensity equation (TIE) from multiple intensity measurements have been unified by the Savitzky-Golay differentiation filter - an equivalent convolution solution for differentiation estimation by least-squares polynomial fitting. The different viewpoint from the digital filter in signal processing not only provides great insight into the behaviors, the shortcomings, and the performance of these existing intensity derivative estimation algorithms, but more important, it also suggests a new way of improving solution strategies by extending the applications of Savitzky-Golay differentiation filter in TIE. Two novel methods for phase retrieval based on TIE are presented - the first by introducing adaptivedegree strategy in spatial domain and the second by selecting optimal spatial frequencies in Fourier domain. Numerical simulations and experiments verify that the second method outperforms the existing methods significantly, showing reliable retrieved phase with both overall contrast and fine phase variations well preserved. © 2013 Optical Society of America. Liu Y.,Beijing Institute of Technology | Liu Y.,Beijing Normal University | Wang R.,Beijing Institute of Technology | Zhang X.,Beijing Institute of Technology Optics Express | Year: 2014 Recently, there are great interest in studying the interaction between chiral molecules and plasmonic particles, because a weak circular dichroism (CD) signal in the ultraviolet (UV) region from chiral molecules can be both enhanced and transferred to the visible wavelength range by using plasmonic particles. Thus, ultrasensitive probe of tiny amounts of chiral substance by CD are worth waiting for. Here we present another way to strongly enhance CD of chiral molecules by using plasmonic particle cluster, which need not transfer to the visible wavelength. The method to calculate CD of chiral molecules in nanosphere clusters has been developed by means of multiple scattering of electromagnetic multipole fields. Our calculated results show that 2 orders of magnitude CD enhancement in the UV region for chiral molecules can be realized. Such a CD enhancement is very sensitive to the cluster structure. The cluster structure can cause chiroptical illusion in which a mirror symmetry in the CD spectra ofopposite enantiomeric molecules is broken. The correction of quantum size effect on the phenomenon has also been considered. Our findings open up an alternative avenue for the ultrasensitive detection and illusion of chiral information. © 2014 Optical Society of America. Zhu L.,Beijing Institute of Technology | Nie Y.,Beijing Institute of Technology | Chang C.,University of Hong Kong | Gao J.-H.,Peking University | Niu Z.,Beijing Institute of Technology Human Brain Mapping | Year: 2014 The neural systems for phonological processing of written language have been well identified now, while models based on these neural systems are different for different language systems or age groups. Although each of such models is mostly concordant across different experiments, the results are sensitive to the experiment design and intersubject variability. Activation likelihood estimation (ALE) meta-analysis can quantitatively synthesize the data from multiple studies and minimize the interstudy or intersubject differences. In this study, we performed two ALE meta-analysis experiments: one was to examine the neural activation patterns of the phonological processing of two different types of written languages and the other was to examine the development characteristics of such neural activation patterns based on both alphabetic language and logographic language data. The results of our first meta-analysis experiment were consistent with the meta-analysis which was based on the studies published before 2005. And there were new findings in our second meta-analysis experiment, where both adults and children groups showed great activation in the left frontal lobe, the left superior/middle temporal gyrus, and the bilateral middle/superior occipital gyrus. However, the activation of the left middle/inferior frontal gyrus was found increase with the development, and the activation was found decrease in the following areas: the right claustrum and inferior frontal gyrus, the left inferior/medial frontal gyrus, the left middle/superior temporal gyrus, the right cerebellum, and the bilateral fusiform gyrus. It seems that adults involve more phonological areas, whereas children involve more orthographic areas and semantic areas. © 2013 Wiley Periodicals, Inc. Li R.,Beijing Institute of Technology | Ren X.,Beijing Institute of Technology | Feng X.,Beijing Institute of Technology | Li X.,Peking University | And 2 more authors. Chemical Communications | Year: 2014 A facile strategy has been developed to synthesize a highly stable and in situ metal- and nitrogen-doped porous composite capable of CO2 capture and separation. Remarkably, this novel composite can survive extensive heating and can be fully reactivated after recycling, which makes it a promising candidate for carbon capture in an industrial temperature-swing adsorption process. © the Partner Organisations 2014. Zhang J.,Beijing University of Chemical Technology | Xia Y.,Beijing Institute of Technology | Shi P.,University of South Wales | Shi P.,Victoria University of Melbourne | Shi P.,University of Adelaide IEEE Transactions on Control Systems Technology | Year: 2013 This brief is concerned with the networked predictive control and stability analysis for networked control systems (NCSs) with time-varying network communication delay. By taking the full advantage of the packet-based transmission in NCSs, a state-based networked predictive control approach is proposed to actively compensate the network communication delay. Based on switched system approach, stability analysis result is also established via the average dwell time technique. Finally, the effectiveness of the proposed method is illustrated by a practical experiment. © 1993-2012 IEEE. Xiao F.,Beijing Institute of Technology | Xiao F.,University of Alberta | Wang L.,Peking University | Chen T.,University of Alberta Automatica | Year: 2012 This paper proposes a new connectivity-preserving protocol in terms of rectangle-like regions. The protocol consists of a set of distributed control rules; their working together guarantees the network connectivity as well as rendezvous of a discrete-time multi-agent system. It is assumed that all agents share a common minimum sensing radius, but the information exchange may suffer from link failure and recovery. Consequently, the interaction topology is in fact directed and time-varying. By rigorous mathematical arguments, we show the effectiveness and robustness of the protocol in the presence of alignment errors in local coordinate orientations of agents and measurement errors in relative positions of neighbors. We also present simulations to demonstrate the effectiveness of the theoretical results. © 2011 Elsevier Ltd. All rights reserved. Li Z.,Peking University | Ren W.,University of California at Riverside | Liu X.,Beijing Institute of Technology | Xie L.,Nanyang Technological University Automatica | Year: 2013 This paper considers the distributed consensus problem of multi-agent systems with general continuous-time linear dynamics for both the cases without and with a leader whose control input might be nonzero and time varying. For the case without a leader, based on the relative output information of neighboring agents, two types of distributed adaptive dynamic consensus protocols are proposed, namely, the edge-based adaptive protocol which assigns a time-varying coupling weight to each edge in the communication graph and the node-based adaptive protocol which uses a time-varying coupling weight for each node. These two adaptive protocols are designed to ensure that consensus is reached in a fully distributed fashion for all undirected connected communication graphs. It is shown that the edge-based adaptive consensus protocol is applicable to arbitrary switching connected graphs. For the case where there exists a leader whose control input is possibly nonzero and bounded, a distributed continuous adaptive protocol is designed to guarantee the ultimate boundedness of the consensus error with respect to any communication graph which contains a directed spanning tree with the leader as the root and whose subgraph associated with the followers is undirected, requiring neither global information of the communication graph nor the upper bound of the leader's control input. A distributed discontinuous protocol is also discussed as a special case. Simulation examples are finally given to illustrate the theoretical results. © 2013 Published by Elsevier Ltd. Yang F.,Beijing Institute of Technology | Wang F.,Peking University | Lee D.-H.,University of California at Berkeley | Lee D.-H.,Lawrence Berkeley National Laboratory Physical Review B - Condensed Matter and Materials Physics | Year: 2013 We address two important issues that arise in recent studies of iron-based superconductivity. (1) Why are the Tc of AxFe 2-ySe2 (A=K, Rb, Cs) and the single unit cell FeSe on SrTiO3 so high despite both only having electron pockets? (2) What (if any) are the effects of orbital order and orbital fluctuation on the Cooper pairing. Our main conclusions are the following: (1) removing hole pockets releases frustration of Cooper pairing from their band vorticity, therefore can enhance Tc, and (2) orbital fluctuation has negligible effect on Cooper pairing. © 2013 American Physical Society. Wang L.,Peking University | Xiao F.,Beijing Institute of Technology IEEE Transactions on Automatic Control | Year: 2010 In this note, we discuss finite-time state consensus problems for multi-agent systems and present one framework for constructing effective distributed protocols, which are continuous state feedbacks. By employing the theory of finite-time stability, we investigate both the bidirectional interaction case and the unidirectional interaction case, and prove that if the sum of time intervals, in which the interaction topology is connected, is sufficiently large, the proposed protocols will solve the finite-time consensus problems. © 2006 IEEE. Gao Y.,Tsinghua National Laboratory for Information Sciences and Technology | Ji R.,Xiamen University | Zhang L.,Beijing Institute of Technology | Hauptmann A.,Carnegie Mellon University IEEE Transactions on Circuits and Systems for Video Technology | Year: 2014 Tracking people and objects is a fundamental stage toward many video surveillance systems, for which various trackers have been specifically designed in the past decade. However, it comes to a consensus that there is not any specific tracker that works sufficiently well under all circumstances. Therefore, one potential solution is to deploy multiple trackers, with a tracker output fusion step to boost the overall performance. Subsequently, an intelligent fusion design, yet general and orthogonal to any specific tracker, plays a key role in successful tracking. In this paper, we propose a symbiotic tracker ensemble toward a unified tracking framework, which is based on only the output of each individual tracker, without knowing its specific mechanism. In our approach, all trackers run in parallel, without requiring any details for tracker running, which means that all trackers are treated as black boxes. The proposed symbiotic tracker ensemble framework aims at learning an optimal combination of these tracking results. Our method captures the relation among individual trackers robustly from two aspects. First, the consistency between two successive frames is calculated for each tracker. Then, the pair-wise correlation among different trackers is estimated in the new coming frame by a graph-propagation process. Experimental results on the Caremedia dataset and the Caviar dataset demonstrate the effectiveness of the proposed method, with comparisons to several state-of-the-art methods. © 1991-2012 IEEE. Xing C.,Beijing Institute of Technology | Xia M.,King Abdullah University of Science and Technology | Gao F.,Tsinghua National Laboratory for Information Sciences and Technology | Wu Y.-C.,University of Hong Kong IEEE Journal on Selected Areas in Communications | Year: 2012 In this paper, robust transceiver design with Tomlinson-Harashima precoding (THP) for multi-hop amplify-and-forward (AF) multiple-input multiple-output (MIMO) relaying systems is investigated. At source node, THP is adopted to mitigate the spatial intersymbol interference. However, due to its nonlinear nature, THP is very sensitive to channel estimation errors. In order to reduce the effects of channel estimation errors, a joint Bayesian robust design of THP at source, linear forwarding matrices at relays and linear equalizer at destination is proposed. With novel applications of elegant characteristics of multiplicative convexity and matrix-monotone functions, the optimal structure of the nonlinear transceiver is first derived. Based on the derived structure, the transceiver design problem reduces to a much simpler one with only scalar variables which can be efficiently solved. Finally, the performance advantage of the proposed robust design over non-robust design is demonstrated by simulation results. © 2012 IEEE. Wen G.,Peking University | Duan Z.,Peking University | Li Z.,Beijing Institute of Technology | Chen G.,City University of Hong Kong IET Control Theory and Applications | Year: 2012 In this study, the problem of stochastic consensus in multi-agent systems of non-linear dynamical agents with state-dependent noise perturbations and repairable actuator failures is investigated. By appropriately constructing a Lyapunov function and using tools from the stochastic differential equations theory, it is proved that mean-square consensus in the closed-loop multi-agent systems with a fixed strongly connected topology can be achieved exponentially if the coupling strength of relative states among neighbouring agents is larger than a threshold value depending on the actuator failure rate. The convergence rate is also analytically given. The results are then extended to the more general case where the communication topology only contains a directed spanning tree. Numerical simulations are finally provided to illustrate the effectiveness of the theoretical analysis. © 2012 The Institution of Engineering and Technology. Zhang Y.,Beijing Normal University | Wan W.-H.,Beijing Institute of Technology Frontiers of Physics | Year: 2014 A network is named as mixed network if it is composed of N nodes, the dynamics of some nodes are periodic, while the others are chaotic. The mixed network with all-to-all coupling and its corresponding networks after the nonlinearity gap-condition pruning are investigated. Several synchronization states are demonstrated in both systems, and a first-order phase transition is proposed. The mixture of dynamics implies any kind of synchronous dynamics for the whole network, and the mixed networks may be controlled by the nonlinearity gap-condition pruning. © 2014, Higher Education Press and Springer-Verlag Berlin Heidelberg. Liu X.,Beijing Institute of Technology | Ju Y.,Beijing Institute of Technology | Wang A.,Peking University Journal of Convergence Information Technology | Year: 2012 Due to the different educational background, experience, career and social status etc., decision makers have different acquaintance degrees of each attribute. Therefore, in this paper, a novel multiple attribute group decision making (MAGDM) method is proposed, in which the weights of decision makers on each attribute are evaluated separately by using similarity. Then, intuitionistic fuzzy weighted averaging (IFWA) operator is used to aggregate individual preference information a collective opinion. Secondly, modified grey relational analysis (GRA) method is used to obtain the relative relational degree of each alternative from positive ideal solution (PIS). Finally, according to the descending order of the relative relational degree, all feasible alternatives are ranked. A numerical example of emergency alternative assessment is used to illustrate the application of the proposed MAGDM method and to demonstrate its feasibility and effectiveness. Shen J.,Swinburne University of Technology | Lu G.,Nanyang Technological University | Zhao L.,Taiyuan University of Technology | Zhang Q.,Beijing Institute of Technology Engineering Structures | Year: 2013 The response of sandwich tubes under internal explosive loading was investigated experimentally, numerically and analytically in this paper. Experiments were conducted first to capture the fundamental deformation and failure patterns and they served as a basis of validation for both the FE and analytical models. Further detailed deformation and blast loading history were revealed by the FE model. An explicit analytical solution for the deformation of sandwich tubes under blast loading has been worked out and used to obtain the optimum sandwich configurations, which would outperform their corresponding monolithic tubes. © 2011 Elsevier Ltd. Wan X.,Beijing Institute of Technology | Wan X.,Peking University | Xiao J.,Beijing Institute of Technology ACM Transactions on Information Systems | Year: 2010 Document summarization and keyphrase extraction are two related tasks in the IR and NLP fields, and both of them aim at extracting condensed representations from a single text document. Existing methods for single document summarization and keyphrase extraction usually make use of only the information contained in the specified document. This article proposes using a small number of nearest neighbor documents to improve document summarization and keyphrase extraction for the specified document, under the assumption that the neighbor documents could provide additional knowledge and more clues. The specified document is expanded to a small document set by adding a few neighbor documents close to the document, and the graph-based ranking algorithm is then applied on the expanded document set to make use of both the local information in the specified document and the global information in the neighbor documents. Experimental results on the Document Understanding Conference (DUC) benchmark datasets demonstrate the effectiveness and robustness of our proposed approaches. The cross-document sentence relationships in the expanded document set are validated to be beneficial to single document summarization, and the word cooccurrence relationships in the neighbor documents are validated to be very helpful to single document keyphrase extraction. © 2010 ACM. Liu C.-C.,CAS Institute of Physics | Jiang H.,Peking University | Yao Y.,CAS Institute of Physics | Yao Y.,Beijing Institute of Technology Physical Review B - Condensed Matter and Materials Physics | Year: 2011 Starting from symmetry considerations and the tight-binding method in combination with first-principles calculation, we systematically derive the low-energy effective Hamiltonian involving spin-orbit coupling (SOC) for silicene. This Hamiltonian is very general because it applies not only to silicene itself but also to the low-buckled counterparts of graphene for the other group-IVA elements Ge and Sn, as well as to graphene when the structure returns to the planar geometry. The effective Hamitonian is the analog to the graphene quantum spin Hall effect (QSHE) Hamiltonian. As in the graphene model, the effective SOC in low-buckled geometry opens a gap at the Dirac points and establishes the QSHE. The effective SOC actually contains the first order in the atomic intrinsic SOC strength ξ0, while this leading-order contribution of SOC vanishes in the planar structure. Therefore, silicene, as well as the low-buckled counterparts of graphene for the other group-IVA elements Ge and Sn, has a much larger gap opened by the effective SOC at the Dirac points than graphene, due to the low-buckled geometry and larger atomic intrinsic SOC strength. Further, the more buckled is the structure, the greater is the gap. Therefore, the QSHE can be observed in low-buckled Si, Ge, and Sn systems in an experimentally accessible temperature regime. In addition, the Rashba SOC in silicene is intrinsic due to its own low-buckled geometry, which vanishes at the Dirac point K, while it has a nonzero value with deviation of k from the K point. Therefore, the QSHE in silicene is robust against the intrinsic Rashba SOC. © 2011 American Physical Society. Xing C.,Beijing Institute of Technology | Ma S.,University of Macau | Fei Z.,Beijing Institute of Technology | Wu Y.-C.,University of Hong Kong | Poor H.V.,Princeton University IEEE Transactions on Signal Processing | Year: 2013 In this paper, linear transceiver design for multi-hop amplify-and-forward (AF) multi-input multi-output (MIMO) relaying systems with Gaussian distributed channel estimation errors is investigated. Commonly used transceiver design criteria including weighted mean-square-error (MSE) minimization, capacity maximization, worst-MSE/MAX-MSE minimization and weighted sum-rate maximization, are considered and unified into a single matrix-variate optimization problem. A general robust design algorithm is proposed to solve the unified problem. Specifically, by exploiting majorization theory and properties of matrix-variate functions, the optimal structure of the robust transceiver is derived when either the covariance matrix of channel estimation errors seen from the transmitter side or the corresponding covariance matrix seen from the receiver side is proportional to an identity matrix. Based on the optimal structure, the original transceiver design problems are reduced to much simpler problems with only scalar variables whose solutions are readily obtained by an iterative water-filling algorithm. A number of existing transceiver design algorithms are found to be special cases of the proposed solution. The differences between our work and the existing related work are also discussed in detail. The performance advantages of the proposed robust designs are demonstrated by simulation results. © 1991-2012 IEEE. Ju Y.,Beijing Institute of Technology | Wang A.,Peking University | Liu X.,Beijing Institute of Technology Expert Systems with Applications | Year: 2012 Emergency management (EM) is a very important issue with various kinds of emergency events frequently taking place. One of the most important components of EM is to evaluate the emergency response capacity (ERC) of emergency department or emergency alternative. Because of time pressure, lack of experience and data, experts often evaluate the importance and the ratings of qualitative criteria in the form of linguistic variable. This paper presents a hybrid fuzzy method consisting fuzzy AHP and 2-tuple fuzzy linguistic approach to evaluate emergency response capacity. This study has been done in three stages. In the first stage we present a hierarchy of the evaluation index system for emergency response capacity. In the second stage we use fuzzy AHP to analyze the structure of the emergency response capacity evaluation problem. Using linguistic variables, pairwise comparisons for the evaluation criteria and sub-criteria are made to determine the weights of the criteria and sub-criteria. In the third stage, the ratings of sub-criteria are assessed in linguistic values represented by triangular fuzzy numbers to express the qualitative evaluation of experts' subjective opinions, and the linguistic values are transformed into 2-tuples. Use the 2-tuple linguistic weighted average operator (LWAO) to compute the aggregated ratings of criteria and the overall emergency response capacity (OERC) of the emergency alternative. Finally, we demonstrate the validity and feasibility of the proposed hybrid fuzzy approach by means of comparing the emergency response capacity of three emergency alternatives. © 2011 Elsevier Ltd. All rights reserved. Zhao X.,Beijing University of Technology | Xia Z.,Beijing Institute of Technology | Xia D.,Peking University Electrochimica Acta | Year: 2010 Sn/Cu nanowire composite film was electrodeposited on copper foil substrates and used as an anode material for lithium-ion batteries. The structure of the obtained composite film anode was characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The electrochemical performance was evaluated by cyclic voltammetry, galvanostatic cycling and impedance spectroscopy. It was found that the Sn/Cu nanowire composite film anode showed a better cycle stability than Sn film anode, whereas the Sn/CNT composite film anode indicated poor capacity retention. It could be deduced that copper nanowire reinforced the Sn film anode due to the better wetting property of Sn on the surface of copper and reduced the loss of electric contact among tin particles in the Sn/Cu nanowire composite film anode. © 2010 Elsevier Ltd. All rights reserved. Ju Y.,Beijing Institute of Technology | Wang A.,Peking University Expert Systems with Applications | Year: 2012 How to select suitable emergency alternative is critical to emergency management and has attracted much attention for both researchers and practitioners. In the process of evaluating emergency alternative problems, there usually exists incomplete and uncertain information, and the decision makers can not easily express their judgments on the candiates with exact and crisp values. The Dempster-Shafer theory (DST) is well suited for dealing with such problems and can generate comprehensive assessments for different alternatives. In this paper, the DS/AHP method and extended TOPSIS method are incorporated to solve group multi-criteria decision making (GMCDM) problems with incomplete information. The proposed method involves three steps: (1) Identify the focal elements of each decision maker according to the group decision matrix. (2) Construct the group weighted normalized belief interval decision matrix using Dempster's rule of combination. (3) Propose the Extended TOPSIS approach for group interval data to rank the emergency alternatives. In this method, the positive ideal solution vector is defined as the maximum plausibility of all emergency alternatives with respect to each criterion, and the negative ideal solution vector is defined as the minimum belief of all emergency alternatives with respect to each criterion. An emergency alternative evaluation selection problem is taken as an illustrative example to demonstrate the feasibility and practicability of the proposed methods for group decision making in emergency management. © 2011 Elsevier Ltd. All rights reserved. Qu S.-W.,University of Electronic Science and Technology of China | Chen Q.-Y.,Beijing Institute of Technology | Xia M.-Y.,Peking University | Zhang X.Y.,South China University of Technology IEEE Transactions on Antennas and Propagation | Year: 2014 This paper presents two kinds of novel elements to design single-layer dual-band reflectarray, with identical polarization in two closely separated bands. Several degrees of freedom of the proposed elements are tuned to match the desired phase compensations at two center frequencies simultaneously. It is noted that the dual-band characteristics are realized by a single integrated element rather than conventional dual-band elements with independent tunable components corresponding to two center frequencies. A 10× 10-element offset-fed reflectarray operating at 9 and 13.5 GHz, with a ratio of the center frequencies 1.5, is designed and fabricated to validate the performance of the element, and the measured results show reasonable agreements with simulations. Due to the incompleteness of reflection phase distribution at the two center frequencies of the presented element, a complementary element with four resonances is introduced. Then, a 20× 20-element reflectarray composed of both kinds of elements is also designed, and the measured results demonstrate a good availability of the proposed elements. © 2013 IEEE. You Y.-Z.,Tsinghua University | Yang F.,Beijing Institute of Technology | Kou S.-P.,Beijing Normal University | Weng Z.-Y.,Tsinghua University Physical Review Letters | Year: 2011 We propose a theoretical description of the phase diagram and physical properties in A2Fe4Se5-type (A=K, Tl) compounds based on a coexistent local moment and itinerant electron picture. Using neutron scattering and angle-resolved photoemission spectroscopy measurements to fix the general structure of the local moment and itinerant Fermi pockets, we find a superconducting phase with s-wave pairing at the M pockets and an incipient sign-change s wave near the Γ point, which is adjacent to the insulating phases. The uniform susceptibility and resistivity are found to be consistent with the experiment. The main distinction with iron pnictide superconductors is also discussed. © 2011 American Physical Society. Sun G.,Beijing Normal University | Dong B.,Beijing Normal University | Cao M.,Beijing Institute of Technology | Wei B.,University of Delaware | Hu C.,Beijing Institute of Technology Chemistry of Materials | Year: 2011 Iron-based microstructured or nanostructured materials, including Fe, γ-Fe2O3, and Fe3O4, are highly desirable for magnetic applications because of their high magnetization and a wide range of magnetic anisotropy. An important application of these materials is use as an electromagnetic wave absorber to absorb radar waves in the centimeter wave (2-18 GHz). Dendrite-like microstructures were achieved with the phase transformation from dendritic α-Fe2O3 to Fe3O4, Fe by partial and full reduction, and γ-Fe2O3 by a reduction-oxidation process, while still preserving the dendritic morphology. The investigation of the magnetic properties and microwave absorbability reveals that the three hierarchical microstructures are typical ferromagnets and exhibit excellent microwave absorbability. In addition, this also confirms that the microwave absorption properties are ascribed to the dielectric loss for Fe and the combination of dielectric loss and magnetic loss for Fe3O4 and γ-Fe2O3. © 2011 American Chemical Society. Li Z.,Beijing Institute of Technology | Ren W.,Utah State University | Ren W.,University of California at Riverside | Liu X.,Beijing Institute of Technology | Fu M.,Beijing Institute of Technology International Journal of Robust and Nonlinear Control | Year: 2013 This paper considers the containment control problems for both continuous-time and discrete-time multi-agent systems with general linear dynamics under directed communication topologies. Distributed dynamic containment controllers based on the relative outputs of neighboring agents are constructed for both continuous-time and discrete-time cases, under which the states of the followers will asymptotically converge to the convex hull formed by those of the leaders if, for each follower, there exists at least one leader that has a directed path to that follower. Sufficient conditions on the existence of these dynamic controllers are given. Static containment controllers relying on the relative states of neighboring agents are also discussed as special cases. Copyright © 2011 John Wiley & Sons, Ltd. Wen G.,Peking University | Duan Z.,Peking University | Li Z.,Beijing Institute of Technology | Chen G.,City University of Hong Kong International Journal of Robust and Nonlinear Control | Year: 2012 In this paper, the problem of flocking control in networks of multiple dynamical agents with intermittent nonlinear velocity measurements is studied. A new flocking algorithm is proposed to guarantee the states of the velocity variables of all the dynamical agents to converge to consensus while ensuring collision avoidance of the whole group, where each agent is assumed to obtain some nonlinear measurements of the relative velocity between itself and its neighbors only on a sequence of non-overlapping time intervals. The results are then extended to the scenario of flocking with a nonlinearly dynamical virtual leader, where only a small fraction of agents are informed and each informed agent can obtain intermittent nonlinear measurements of the relative velocity between itself and the virtual leader. Theoretical analysis shows that the achieved flocking in systems with or without a virtual leader is robust against the time spans of the agent speed-sensors. Finally, some numerical simulations are provided to illustrate the effectiveness of the new design. Copyright © 2011 John Wiley & Sons, Ltd. Copyright © 2011 John Wiley & Sons, Ltd. Ren J.,Beijing Institute of Technology | Yuan J.,Beijing Normal University | Zhang X.,Beijing Institute of Technology Journal of the Optical Society of America B: Optical Physics | Year: 2014 The Dicke subradiance and superradiance resulting from the interaction between surface plasmons of a nanosphere and an ensemble of quantum emitters have been investigated using a Green's function approach. Based on such an investigation, we propose a scheme for a deterministic multi-qubit quantum phase gate. As an example, two-qubit, three-qubit, and four-qubit quantum phase gates have been designed and analyzed in detail. Phenomena due to the losses in the metal are discussed. Potential applications of these phenomena to quantum-information processing are anticipated. © 2014 Optical Society of America. Liu H.,Beijing Institute of Technology | Guo X.,Beijing Institute of Technology | Shao W.,Peking University IEEE Transactions on Software Engineering | Year: 2013 Software refactoring is an effective method for improvement of software quality while software external behavior remains unchanged. To facilitate software refactoring, a number of tools have been proposed for code smell detection and/or for automatic or semi-automatic refactoring. However, these tools are passive and human driven, thus making software refactoring dependent on developers' spontaneity. As a result, software engineers with little experience in software refactoring might miss a number of potential refactorings or may conduct refactorings later than expected. Few refactorings might result in poor software quality, and delayed refactorings may incur higher refactoring cost. To this end, we propose a monitor-based instant refactoring framework to drive inexperienced software engineers to conduct more refactorings promptly. Changes in the source code are instantly analyzed by a monitor running in the background. If these changes have the potential to introduce code smells, i.e., signs of potential problems in the code that might require refactorings, the monitor invokes corresponding smell detection tools and warns developers to resolve detected smells promptly. Feedback from developers, i.e., whether detected smells have been acknowledged and resolved, is consequently used to optimize smell detection algorithms. The proposed framework has been implemented, evaluated, and compared with the traditional human-driven refactoring tools. Evaluation results suggest that the proposed framework could drive inexperienced engineers to resolve more code smells (by an increase of 140 percent) promptly. The average lifespan of resolved smells was reduced by 92 percent. Results also suggest that the proposed framework could help developers to avoid similar code smells through timely warnings at the early stages of software development, thus reducing the total number of code smells by 51 percent. © 1976-2012 IEEE. Zhang M.,Beijing Normal University | Zhang X.,Beijing Institute of Technology Physics Letters, Section A: General, Atomic and Solid State Physics | Year: 2014 The Mie theory for electromagnetic scattering is extended to the case of coated metal sphere with liquid crystals. A new set of vector basis functions for the electric displacement vector inside the liquid crystal layer has been constructed. The expansion coefficients of transmitted and scattered fields are obtained analytically by applying the continuous boundary conditions. The dependence of the scattering property on the geometrical parameters has been investigated in detail. The appearance of photonic Hall effect for such a Mie scatterer is confirmed. It is interesting that such a photonic Hall effect not only depends on the ratio of the inner to outer radius of coated sphere, it is also tunable by the application of an external voltage. © 2014 Elsevier B.V. Yang F.,Beijing Institute of Technology | Kou S.-P.,Beijing Normal University | Weng Z.-Y.,Tsinghua University Physical Review B - Condensed Matter and Materials Physics | Year: 2010 We study collective spin excitations of a magnetically ordered state in a multicomponent system composed of both itinerant electrons and local moments. Here the induced spin-density-wave (SDW) ordering of itinerant electrons and the collinear antiferromagnetic ordering of local moments are locked together via a Hund's rule coupling. We show that the Goldstone theorem still holds at the random-phase approximation level with the gapless spin wave protected inside the small SDW gap of itinerant electrons, which, however, is fragile in the presence of ion anisotropy. A gapped "out-of-phase" spin mode extending over a much wider energy scale above the SDW gap is found to be more robust against the ion anisotropy, which is mainly contributed by the local moment fluctuations. While the scattering between the Goldstone mode and itinerant electrons diminishes within the SDW gap, the out-of-phase mode will strongly interact with itinerant electrons and thus dominate the spin and charge dynamics in such an ordered phase. Possible relevance of such a model to the iron pnictides will be also discussed. © 2010 The American Physical Society. Su Y.,Beijing Institute of Technology | Zhao Q.,Beijing Institute of Technology | Zhao L.,Beijing Institute of Technology | Gu D.,University of Essex Pattern Recognition | Year: 2014 Abrupt motion is a significant challenge that commonly causes traditional tracking methods to fail. This paper presents an improved visual saliency model and integrates it to a particle filter tracker to solve this problem. Once the target is lost, our algorithm recovers tracking by detecting the target region from salient regions, which are obtained in the saliency map of current frame. In addition, to strengthen the saliency of target region, the target model is used as a prior knowledge to calculate a weight set which is utilized to construct our improved saliency map adaptively. Furthermore, we adopt the covariance descriptor as the appearance model to describe the object more accurately. Compared with several other tracking algorithms, the experimental results demonstrate that our method is more robust in dealing with various types of abrupt motion scenarios. © 2013 Elsevier Ltd. All rights reserved. Xing C.,Beijing Institute of Technology | Ma S.,University of Macau | Zhou Y.,CAS Institute of Computing Technology IEEE Transactions on Signal Processing | Year: 2015 For MIMO systems, due to the deployment of multiple antennas at both the transmitter and the receiver, the design variables, e.g., precoders, equalizers, and training sequences, are usually matrices. It is well known that matrix operations are usually more complicated compared with their vector counterparts. In order to overcome the high complexity resulting from matrix variables, in this paper, we investigate a class of elegant multi-objective optimization problems, namely matrix-monotonic optimization problems (MMOPs). In our work, various representative MIMO optimization problems are unified into a framework of matrix-monotonic optimization, which includes linear transceiver design, nonlinear transceiver design, training sequence design, radar waveform optimization, the corresponding robust design and so on as its special cases. Then, exploiting the framework of matrix-monotonic optimization the optimal structures of the considered matrix variables can be derived first. Based on the optimal structure, the matrix-variate optimization problems can be greatly simplified into the ones with only vector variables. In particular, the dimension of the new vector variable is equal to the minimum number of columns and rows of the original matrix variable. Finally, we also extend our work to some more general cases with multiple matrix variables. © 2014 IEEE. Jiang H.,Beijing Institute of Technology | Lu T.,Peking University | Cai W.,University of North Carolina at Charlotte Journal of Computational Physics | Year: 2014 In this paper, an improved inflow boundary condition is proposed for Wigner equations in simulating a resonant tunneling diode (RTD), which takes into consideration the band structure of the device. The original Frensley inflow boundary condition prescribes the Wigner distribution function at the device boundary to be the semi-classical Fermi-Dirac distribution for free electrons in the device contacts without considering the effect of the quantum interaction inside the quantum device. The proposed device adaptive inflow boundary condition includes this effect by assigning the Wigner distribution to the value obtained from the Wigner transform of wave functions inside the device at zero external bias voltage, thus including the dominant effect on the electron distribution in the contacts due to the device internal band energy profile. Numerical results on computing the electron density inside the RTD under various incident waves and non-zero bias conditions show much improvement by the new boundary condition over the traditional Frensley inflow boundary condition. © 2013 Elsevier Inc. Wang Z.,University of California at Irvine | Chiang P.-Y.,University of California at Irvine | Nazari P.,University of California at Irvine | Wang C.-C.,Peregrine Semiconductor | And 2 more authors. Digest of Technical Papers - IEEE International Solid-State Circuits Conference | Year: 2013 The vastly under-utilized spectrum in the sub-THz frequency range enables disruptive applications including 10Gb/s chip-to-chip wireless communications and imaging/spectroscopy. Owing to aggressive scaling in feature size and device fT/fmax, nanoscale CMOS technology potentially enables integration of sophisticated systems at this frequency range. For example, CMOS sub-THz signal sources and TRXs have been reported [1-4], employing techniques such as distributed active radiator (DAR) and super-harmonic signal generator. The lack of RF amplification in CMOS sub-THz TRXs reported in prior work, however, results in low efficiency (and thus higher power dissipation), and high noise-figure (NF). This paper addresses these issues by demonstrating a 210GHz TRX with on-off-keying (OOK) modulation incorporating a 2×2 TX antenna array, a 2×2 spatial combining power amplifier (PA), a fundamental frequency VCO, and a low noise amplifier (LNA) in a 32nm SOI CMOS process (fT/fmax=250/350GHz). © 2013 IEEE. Zhou X.,Capital Normal University | Lu Y.,Beijing Institute of Technology | Lu J.,Advanced Digital science Center | Zhou J.,Tsinghua University IEEE Transactions on Image Processing | Year: 2012 The robust tracking of abrupt motion is a challenging task in computer vision due to its large motion uncertainty. While various particle filters and conventional Markov-chain Monte Carlo (MCMC) methods have been proposed for visual tracking, these methods often suffer from the well-known local-trap problem or from poor convergence rate. In this paper, we propose a novel sampling-based tracking scheme for the abrupt motion problem in the Bayesian filtering framework. To effectively handle the local-trap problem, we first introduce the stochastic approximation Monte Carlo (SAMC) sampling method into the Bayesian filter tracking framework, in which the filtering distribution is adaptively estimated as the sampling proceeds, and thus, a good approximation to the target distribution is achieved. In addition, we propose a new MCMC sampler with intensive adaptation to further improve the sampling efficiency, which combines a density-grid-based predictive model with the SAMC sampling, to give a proposal adaptation scheme. The proposed method is effective and computationally efficient in addressing the abrupt motion problem. We compare our approach with several alternative tracking algorithms, and extensive experimental results are presented to demonstrate the effectiveness and the efficiency of the proposed method in dealing with various types of abrupt motions. © 2011 IEEE. Mahmood N.,Peking University | Tahir M.,Beijing Institute of Technology | Mahmood A.,Peking University | Zhu J.,Peking University | And 2 more authors. Nano Energy | Year: 2015 Development of supercapacitors which exhibit high energy density without much compromise on power density is a great challenge. Although the pseudocapacitors are very promising in this regard but only surface redox reactions are not sufficient to solve future energy demands. Thus the involvement of the entire electrode materials in Faradaic redox reaction is necessary for excellent results. Here, we have synthesized well-defined and self-stabilized chlorine-doped carbonated cobalt hydroxide (Co(CO3)0.35Cl0.20(OH)1.10) nanowires (NWs) composed of discrete particles (which allow the involvment of entire NW) via a facile hydothermal method for supercapacitors to introduce the concept of deep Faradaic redox reaction. The engineered structure and unique composition along with define porosity, existence of structure stabilizer counter anions and hydrophilic nature of NWs allow deep diffusion of electrolyte ions. The NWs have shown extraordinary capacitance (9893.75F/g at 0.5A/g) and excellent energy density (220Wh/kg) along with high rate capability and stability for 10,000 cycles. We believe that higher energy density devices can be developed using our concept of deep Faradaic redox reactions which will help the practical realization of supercapacitors. © 2014 Elsevier Ltd. Li Z.,Beijing Institute of Technology | Duan Z.,Peking University Science China Technological Sciences | Year: 2011 This paper addresses the distributed attitude synchronization problem of multiple spacecraft with unknown inertia matrices. Two distributed adaptive controllers are proposed for the cases with and without a virtual leader to which a time-varying reference attitude is assigned. The first controller achieves attitude synchronization for a group of spacecraft with a leaderless communication topology having a directed spanning tree. The second controller guarantees that all spacecraft track the reference attitude if the virtual leader has a directed path to all other spacecraft. Simulation examples are presented to illustrate the effectiveness of the results. © 2011 Science China Press and Springer-Verlag Berlin Heidelberg. Zhao H.,Huaiyin Institute of Technology | Ren W.,University of California at Riverside | Yuan D.,Nanjing University of Science and Technology | Chen J.,Beijing Institute of Technology Systems and Control Letters | Year: 2012 This paper deals with the distributed discrete-time coordinated tracking problem for multi-agent systems with Markovian switching topologies. In the multi-agent team, only some of the agents can obtain the leader's state directly. The leader's state considered is time varying. We present necessary and sufficient conditions for boundedness of the tracking error system and show the ultimate bound of the tracking errors. A linear matrix inequality approach is developed to determine the allowable sampling period and the feasible control gain. A simulation example is given to illustrate the effectiveness of the results. © 2012 Elsevier Ltd. All rights reserved. Li Z.,Beijing Institute of Technology | Duan Z.,Peking University | Chen G.,City University of Hong Kong Automatica | Year: 2011 This paper addresses the distributed H2 and H∞ control problems for multi-agent systems with linear or linearized dynamics. An undirected multigraph with loops is used to represent the communication topology of a multi-agent network. A distributed controller is designed, based on the relative states of neighboring agents and a subset of absolute states of the networked agents. The notions of H∞ and H2 performance regions are introduced and analyzed, respectively. A necessary and sufficient condition for the existence of a controller yielding an unbounded H∞ performance region is derived. A multi-step procedure for suboptimal H∞ controller synthesis is presented. It is also shown that the H∞ performance limit of the network under the distributed controller is equal to the minimal H∞ norm of a single agent achieved by using the state feedback controller. It is finally shown that, contrarily to the H∞ case, the H2 performance limit scales with the number of agents in the network. © 2011 Elsevier Ltd. All rights reserved. Hawkes A.G.,University of Swansea | Cui L.,Beijing Institute of Technology | Zheng Z.,Beijing Institute of Technology IIE Transactions (Institute of Industrial Engineers) | Year: 2011 The dynamics of a system represented by a finite-state Markov process operating under two alternating regimes, for example, day/night, machine working/machine idling, etc., are modeled in this article. The transition rate matrices under the two regimes will usually be different. Also, the set of states of the system that are regarded as satisfactory may depend on the regime in operation: for example, a particular state of the system that may be regarded as satisfactory by day might not be tolerated at night (e.g., the headlights on a car not working). It is assumed that the regime durations are random variables and results are obtained for the availability of such a system and probability distributions for uptimes. Results and numerical examples are also given for two special cases: (i) when the regimes are of fixed duration; and (ii) when the regime durations have negative exponential distributions. Copyright © "IIE". Grant Agency: Cordis | Branch: FP7 | Program: CSA-SA | Phase: ENV.2008.1.1.6.3. | Award Amount: 1.09M | Year: 2009 Developing countries are reluctant to make any binding commitment as their per capita emissions are low and climate abatement measures conflict with their main priorities on socio-economic development. The question is if there is a way to simultaneously provide sufficient energy (which is also the main source of GHG emissions), to support poverty alleviation and economic growth and achieve sufficient emission reductions. Finding an answer is the main aim of this project. It may be possible with a combination of policies and measures encompassing from international level to national level supported by committed international cooperation to achieve both the goals together. The main focus of the study is on India and China. The primary objective is to develop a portfolio of policy options including both international and national policies as well as institutional frameworks for international cooperation for these two emerging economies to engage them in climate protection measures under a post-2012 regime. By applying an integrated modeling framework, the study will explore possible multiple pathways which may exist for these countries to contribute into international climate initiatives without compromising their national development priorities. Specific objectives are, 1) developing country-specific integrated modeling framework to analyse policies and identify multiple pathways to achieve socio-economic and climate targets; 2) identifying/designing international climate polices in post-Kyoto regime for future commitments and participations of emerging economies (India and China); 3) designing national polices (in socio-economic sectors, energy and environment) compatible with the global climate targets; 4) designing and quantifying as much as possible the international co-operations needed to make the participation in a post-2012 regime acceptable at least in economic terms; 5) disseminating the results to potential users for use in future negotiations. News Article | November 15, 2016 Site: phys.org These rising environmental concerns are driving the development of new energy vehicles (NEVs)—aka plug-in electric vehicles—as a way to help mitigate the environmental problems associated with automobile usage. But sales of NEVs are still relatively low. In 2014, the 74,763 NEVs sold accounted for only 0.3 percent of total automobile sales in China that year. So, a group of researchers from the Center for Energy and Environmental Policy Research at Beijing Institute of Technology, the Collaborative Innovation Center of Electric Vehicles in Beijing, and the Sustainable Development Research Institute for Economy and Society of Beijing set out to find out what motivates or influences consumer to purchase electric vehicles within seven cities in China. They report their findings this week in the Journal of Renewable and Sustainable Energy. "China has a responsibility to make efforts to reduce the pollution for fossil consumption," said Yu Hao, an associate professor in the School of Management and Economics at Beijing Institute of Technology. The group's work is based on "a carefully designed questionnaire and an empirical analysis of its data to determine the main factors influencing NEV purchases," explained Hao. To aid and speed the development of China's NEV industry, "it's essential to understand both the motives behind consumers' purchases and any existing barriers to the popularization of NEVs," Hao continued. "Our studies revealed that monthly income, the number of cars a family owns, sustainability, and vehicle comfort are the factors that most strongly influence customers' purchasing behavior." They also found that factors such as age, marital status and city of residence are playing a role in consumers' decision-making process. Based on the group's findings, "several suggestions are now being provided to help develop the Chinese NEV market," Hao said. Their primary recommendation is that the Chinese government should consider scaling up "effective targeting of financial support and subsidies, while improving the financial incentive system for NEVs." Beyond that, "companies within the NEV industry should also be encouraged to increase their research and development investments," Hao added. "Ultimately, the government ought to encourage citizens to raise their awareness of the environment and sustainable development." As far as the next step for their work, "low carbon economy and NEVs are both hot topics around the world, so governments are competing to regulate subsidy policies for NEVs," Hao said. "We're interested in further exploring how these differentiated policies may affect consumers' purchase intentions so we can make corresponding policy recommendations." Explore further: China's Panda orders electric cars for12 bn from Nevs, ex-Saab More information: "What influences personal purchases of new energy vehicles in China? An empirical study based on a survey of Chinese citizens," Journal of Renewable and Sustainable Energy, DOI: 10.1063/1.4966908

News Article | November 15, 2016

A group of researchers in China explored the factors behind buyers' decisions to purchase electric vehicles and ways to increase their popularity WASHINGTON, D.C., November, 15, 2016 -- Many Chinese cities are suffering from deteriorating environmental quality -- particularly due to air pollution that contributes to fog and haze. Air pollutant levels now far exceed "safe" limits established by the European Union, and one of the main culprits behind it is the rapid increase in automobile ownership and usage. These rising environmental concerns are driving the development of new energy vehicles (NEVs) -- aka plug-in electric vehicles -- as a way to help mitigate the environmental problems associated with automobile usage. But sales of NEVs are still relatively low. In 2014, the 74,763 NEVs sold accounted for only 0.3 percent of total automobile sales in China that year. So, a group of researchers from the Center for Energy and Environmental Policy Research at Beijing Institute of Technology, the Collaborative Innovation Center of Electric Vehicles in Beijing, and the Sustainable Development Research Institute for Economy and Society of Beijing set out to find out what motivates or influences consumer to purchase electric vehicles within seven cities in China. They report their findings this week in the Journal of Renewable and Sustainable Energy, from AIP Publishing. "China has a responsibility to make efforts to reduce the pollution for fossil consumption," said Yu Hao, an associate professor in the School of Management and Economics at Beijing Institute of Technology. The group's work is based on "a carefully designed questionnaire and an empirical analysis of its data to determine the main factors influencing NEV purchases," explained Hao. To aid and speed the development of China's NEV industry, "it's essential to understand both the motives behind consumers' purchases and any existing barriers to the popularization of NEVs," Hao continued. "Our studies revealed that monthly income, the number of cars a family owns, sustainability, and vehicle comfort are the factors that most strongly influence customers' purchasing behavior." They also found that factors such as age, marital status and city of residence are playing a role in consumers' decision-making process. Based on the group's findings, "several suggestions are now being provided to help develop the Chinese NEV market," Hao said. Their primary recommendation is that the Chinese government should consider scaling up "effective targeting of financial support and subsidies, while improving the financial incentive system for NEVs." Beyond that, "companies within the NEV industry should also be encouraged to increase their research and development investments," Hao added. "Ultimately, the government ought to encourage citizens to raise their awareness of the environment and sustainable development." As far as the next step for their work, "low carbon economy and NEVs are both hot topics around the world, so governments are competing to regulate subsidy policies for NEVs," Hao said. "We're interested in further exploring how these differentiated policies may affect consumers' purchase intentions so we can make corresponding policy recommendations." The article, "What influences personal purchases of new energy vehicles in China? An empirical study based on a survey of Chinese citizens," is authored by Yu Hao, Xiao-Ying Dong, Yu-Xin Deng, Ling-Xi Li and Ye Ma. The article will appear in the journal of Renewable and Sustainable Energy on November 15, 2016 (DOI: 10.1063/1.4966908). After that date, it can be accessed at: http://scitation. . Journal of Renewable and Sustainable Energy is an interdisciplinary, peer-reviewed journal covering all areas of renewable and sustainable energy that apply to the physical science and engineering communities. See http://jrse. .

News Article | November 20, 2016
Site: www.sciencedaily.com

Many Chinese cities are suffering from deteriorating environmental quality -- particularly due to air pollution that contributes to fog and haze. Air pollutant levels now far exceed "safe" limits established by the European Union, and one of the main culprits behind it is the rapid increase in automobile ownership and usage. These rising environmental concerns are driving the development of new energy vehicles (NEVs) -- aka plug-in electric vehicles -- as a way to help mitigate the environmental problems associated with automobile usage. But sales of NEVs are still relatively low. In 2014, the 74,763 NEVs sold accounted for only 0.3 percent of total automobile sales in China that year. So, a group of researchers from the Center for Energy and Environmental Policy Research at Beijing Institute of Technology, the Collaborative Innovation Center of Electric Vehicles in Beijing, and the Sustainable Development Research Institute for Economy and Society of Beijing set out to find out what motivates or influences consumer to purchase electric vehicles within seven cities in China. They report their findings this week in the Journal of Renewable and Sustainable Energy, from AIP Publishing. "China has a responsibility to make efforts to reduce the pollution for fossil consumption," said Yu Hao, an associate professor in the School of Management and Economics at Beijing Institute of Technology. The group's work is based on "a carefully designed questionnaire and an empirical analysis of its data to determine the main factors influencing NEV purchases," explained Hao. To aid and speed the development of China's NEV industry, "it's essential to understand both the motives behind consumers' purchases and any existing barriers to the popularization of NEVs," Hao continued. "Our studies revealed that monthly income, the number of cars a family owns, sustainability, and vehicle comfort are the factors that most strongly influence customers' purchasing behavior." They also found that factors such as age, marital status and city of residence are playing a role in consumers' decision-making process. Based on the group's findings, "several suggestions are now being provided to help develop the Chinese NEV market," Hao said. Their primary recommendation is that the Chinese government should consider scaling up "effective targeting of financial support and subsidies, while improving the financial incentive system for NEVs." Beyond that, "companies within the NEV industry should also be encouraged to increase their research and development investments," Hao added. "Ultimately, the government ought to encourage citizens to raise their awareness of the environment and sustainable development." As far as the next step for their work, "low carbon economy and NEVs are both hot topics around the world, so governments are competing to regulate subsidy policies for NEVs," Hao said. "We're interested in further exploring how these differentiated policies may affect consumers' purchase intentions so we can make corresponding policy recommendations."

News Article | January 4, 2016
Site: phys.org

Wang Z.,Shanghai JiaoTong University | Wei P.,Shanghai JiaoTong University | Qian Y.,Shanghai JiaoTong University | Liu J.,Beijing Institute of Technology
Composites Part B: Engineering | Year: 2014

In this paper, a novel graphene-based inorganic-organic hybrid flame retardant (GFR) was prepared via sol-gel reaction of FGO and phenyl-bis-(triethoxysilylpropyl) phosphamide (PBTP) and characterized by FT-IR, XPS, XRD, TGA and AFM. The influence of the GFR on the thermal stability and flame retardance of epoxy resin composites were characterized by TGA, LOI as well as micro-cone, which indicated that GFR brought a good effect in enhancing the residual char and flame retardance of epoxy composites. The dynamic mechanical properties and electrical properties of EP composites were also analyzed. © 2013 Elsevier Ltd. All rights reserved.

Liu F.,Beijing Institute of Technology | Liu F.,CAS Institute of Mechanics | Liu C.-C.,Beijing Institute of Technology | Liu C.-C.,CAS Institute of Physics | And 4 more authors.
Physical Review Letters | Year: 2013

We investigate the structure and physical properties of the undoped bilayer silicene through first-principles calculations and find the system is intrinsically metallic with sizable pocket Fermi surfaces. When realistic electron-electron interaction turns on, the system is identified as a chiral d+id′ topological superconductor mediated by the strong spin fluctuation on the border of the antiferromagnetic spin density wave order. Moreover, the tunable Fermi pocket area via strain makes it possible to adjust the spin density wave critical interaction strength near the real one and enables a high superconducting critical temperature. © 2013 American Physical Society.

Yang W.,CAS Institute of Physics | Chen G.,Fudan University | Shi Z.,CAS Institute of Physics | Liu C.-C.,CAS Institute of Physics | And 13 more authors.
Nature Materials | Year: 2013

Hexagonal boron nitride (h-BN) has recently emerged as an excellent substrate for graphene nanodevices, owing to its atomically flat surface and its potential to engineer graphene's electronic structure. Thus far, graphene/h-BN heterostructures have been obtained only through a transfer process, which introduces structural uncertainties due to the random stacking between graphene and h-BN substrate. Here we report the epitaxial growth of single-domain graphene on h-BN by a plasma-assisted deposition method. Large-area graphene single crystals were successfully grown for the first time on h-BN with a fixed stacking orientation. A two-dimensional (2D) superlattice of trigonal moiré pattern was observed on graphene by atomic force microscopy. Extra sets of Dirac points are produced as a result of the trigonal superlattice potential and the quantum Hall effect is observed with the 2D-superlattice- related feature developed in the fan diagram of longitudinal and Hall resistance, and the Dirac fermion physics near the original Dirac point is unperturbed. The macroscopic epitaxial graphene is in principle limited only by the size of the h-BN substrate and our synthesis method is potentially applicable on other flat surfaces. Our growth approach could thus open new ways of graphene band engineering through epitaxy on different substrates. © 2013 Macmillan Publishers Limited. All rights reserved.

Li J.,Nanjing University of Information Science and Technology | Li X.,Beijing Institute of Technology | Yang B.,Beijing Institute of Technology | Sun X.,Nanjing University of Information Science and Technology
IEEE Transactions on Information Forensics and Security | Year: 2015

In this paper, we propose a scheme to detect the copy-move forgery in an image, mainly by extracting the keypoints for comparison. The main difference to the traditional methods is that the proposed scheme first segments the test image into semantically independent patches prior to keypoint extraction. As a result, the copy-move regions can be detected by matching between these patches. The matching process consists of two stages. In the first stage, we find the suspicious pairs of patches that may contain copy-move forgery regions, and we roughly estimate an affine transform matrix. In the second stage, an Expectation-Maximization-based algorithm is designed to refine the estimated matrix and to confirm the existence of copy-move forgery. Experimental results prove the good performance of the proposed scheme via comparing it with the state-of-the-art schemes on the public databases. © 2014 IEEE.

Chen L.,CAS Institute of Physics | Liu C.-C.,CAS Institute of Physics | Feng B.,CAS Institute of Physics | He X.,CAS Institute of Physics | And 6 more authors.
Physical Review Letters | Year: 2012

Silicene, a sheet of silicon atoms in a honeycomb lattice, was proposed to be a new Dirac-type electron system similar to graphene. We performed scanning tunneling microscopy and spectroscopy studies on the atomic and electronic properties of silicene on Ag(111). An unexpected √3×√3 reconstruction was found, which is explained by an extra-buckling model. Pronounced quasiparticle interferences (QPI) patterns, originating from both the intervalley and intravalley scatter, were observed. From the QPI patterns we derived a linear energy-momentum dispersion and a large Fermi velocity, which prove the existence of Dirac fermions in silicene. © 2012 American Physical Society.

Ma Q.,Key Laboratory of Dynamics and Control of Flight Vehicles | Ma Q.,Beijing Institute of Technology | Ma S.,Key Laboratory of Dynamics and Control of Flight Vehicles | Ma S.,Beijing Institute of Technology
Optics Express | Year: 2013

The systematic error for photomechanic methods caused by selfheating induced image expansion when using a digital camera was systematically studied, and a new physical model to explain the mechanism has been proposed and verified. The experimental results showed that the thermal expansion of the camera outer case and lens mount, instead of mechanical components within the camera, were the main reason for image expansion. The corresponding systematic error for both image analysis and fringe analysis based photomechanic methods were analyzed and measured, then error compensation techniques were proposed and verified. © 2013 Optical Society of America.

Zhou J.-J.,Beijing Institute of Technology | Zhou J.-J.,CAS Institute of Physics | Feng W.,Beijing Institute of Technology | Liu C.-C.,Beijing Institute of Technology | And 2 more authors.
Nano Letters | Year: 2014

Quantum spin Hall (QSH) insulators have gapless topological edge states inside the bulk band gap, which can serve as dissipationless spin current channels. The major challenge currently is to find suitable materials for this topological state. Here, we predict a new large-gap QSH insulator with bulk direct band gap of ∼0.18 eV, in single-layer Bi4Br4, which could be exfoliated from its three-dimensional bulk material due to the weakly bonded layered structure. The band gap of single-layer Bi 4Br4 is tunable via strain engineering, and the QSH phase is robust against external strain. Moreover, because this material consists of special one-dimensional molecular chain as its basic building block, the single layer Bi4Br4 could be torn to ribbons with clean and atomically sharp edges. These nanoribbons, which have single-Dirac-cone edge states crossing the bulk band gap, are ideal wires for dissipationless transport. Our work thus provides a new promising material for experimental studies and practical applications of the QSH effect. © 2014 American Chemical Society.

Qin W.,Beijing Institute of Technology | Wang C.,Beijing University of Posts and Telecommunications | Zhang X.,Beijing Institute of Technology
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2015

We propose and analyze a robust quantum-state transfer protocol by the use of a combination of coherent quantum coupling and decoherence-free subspaces in a coupled quantum spin chain. Under decoherence, an arbitrary unknown quantum state embedded in a decoherence-free subspace can be perfectly transferred through a noisy channel being weakly coupled to two end registers. The method protects quantum information from both the channel noise and the environmental decoherence. A special case of utilizing two physical qubits to encode one logical qubit is considered as an example and the robustness is confirmed by numerical performances. © 2015 American Physical Society.

Zhou J.-J.,CAS Institute of Physics | Feng W.,Beijing Institute of Technology | Liu G.-B.,Beijing Institute of Technology | Yao Y.,CAS Institute of Physics | Yao Y.,Beijing Institute of Technology
New Journal of Physics | Year: 2015

Topological edge states at the boundary of quantum spin Hall (QSH) insulators hold great promise for dissipationless electron transport. The device application of topological edge states has several critical requirements for QSH insulator materials, e.g. a large band gap, appropriate insulating substrates, and multiple conducting channels. In this paper, based on first-principles calculations, we show that Bi4Br4 is a suitable candidate. Single-layer Bi4Br4 was recently demonstrated to be a QSH insulator with sizable gap. Here we find that, in multilayer systems, both the band gaps and low-energy electronic structures are only slightly affected by the interlayer coupling. On the intrinsic insulating substrate of bulk Bi4Br4, the single-layer Bi4Br4 preserves its topological edge states well. Moreover, at the boundary of multilayer Bi4Br4, the topological edge states stemming from different single-layers are weakly coupled, and can be fully decoupled by constructing a stair-stepped edge. The decoupled topological edge states are very suitable for multi-channel dissipationless transport. Our work indicates that an ideal QSH insulator can be prepared by nano-fabricaton on the cleaved surface of layered Bi4Br4 single crystal. © 2015 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.

Feng B.,CAS Institute of Physics | Ding Z.,CAS Institute of Physics | Meng S.,CAS Institute of Physics | Yao Y.,CAS Institute of Physics | And 5 more authors.
Nano Letters | Year: 2012

In the search for evidence of silicene, a two-dimensional honeycomb lattice of silicon, it is important to obtain a complete picture for the evolution of Si structures on Ag(111), which is believed to be the most suitable substrate for growth of silicene so far. In this work we report the finding and evolution of several monolayer superstructures of silicon on Ag(111), depending on the coverage and temperature. Combined with first-principles calculations, the detailed structures of these phases have been illuminated. These structures were found to share common building blocks of silicon rings, and they evolve from a fragment of silicene to a complete monolayer silicene and multilayer silicene. Our results elucidate how silicene forms on Ag(111) surface and provides methods to synthesize high-quality and large-scale silicene. © 2012 American Chemical Society.

Tian Q.,Beijing Institute of Technology | Liu C.,Beijing Institute of Technology | MacHado M.,University of Minho | Flores P.,University of Minho
Nonlinear Dynamics | Year: 2011

A new approach to model and analyze flexible spatial multibody systems with clearance of cylindrical joints is presented in this work. The flexible parts are modeled by using absolute nodal coordinate formulation (ANCF)-based elements, while the rigid parts are described by employing the natural coordinate formulation (NCF), which can lead to a constant system mass matrix for the derived system equations of motion. In a simple way, a cylindrical joint with clearance is composed of two main elements, that is, a journal inside a bearing. Additionally, a lubricant fluid can exist between these two mechanical elements to reduce the friction and wear and increase the system's life. For the case in which the joint is modeled as a dry contact pair, a technique using a continuous approach for the evaluation of the contact force is applied, where the energy dissipation in the form of hysteresis damping is considered. Furthermore, the frictional forces developed in those contacts are evaluated by using a modified Coulomb's friction law. For the lubricated case, the hydrodynamic theory for dynamically loaded journal bearings is used to compute the forces generated by lubrication actions. The lubricated model is based on the Reynolds equation developed for the case of journal bearings with length-to-diameter ratios up to 1. Using this approach, the misalignment of the journal inside the bearing can be studied. Finally, two demonstrative examples of application are used to provide results that support the discussion and show the validity of the proposed methodologies. © 2010 Springer Science+Business Media B.V.

Li T.-L.,Shanghai Dianji University | Sun Z.-Y.,Beijing Institute of Technology
Advanced Materials Research | Year: 2012

The sharp rise in the development of vehicle industry in China not only promotes both the national economy development and the people living quality, but also aggravates both the national energy security and the environmental issues. Adopting alternative fuels instead of petroleum is commonly regarded as the utmost promising solution, however, which alternative fuel(s) is more suitable for China is still in the argument. The present paper compared the characteristics and performance of hydrogen gas and fossil-based fuels, and pointed that hydrogen gas is more suitable for China than fossil-based fuels. © (2012) Trans Tech Publications, Switzerland.

Horke D.A.,Durham University | Horke D.A.,German Electron Synchrotron | Li Q.,University of Girona | Li Q.,Beijing Institute of Technology | And 2 more authors.
Nature Chemistry | Year: 2013

Quinones feature prominently as electron acceptors in nature. Their electron-transfer reactions are often highly exergonic, for which Marcus theory predicts reduced electron-transfer rates because of a free-energy barrier that occurs in the inverted region. However, the electron-transfer kinetics that involve quinones can appear barrierless. Here, we consider the intrinsic properties of the para-benzoquinone radical anion, which serves as the prototypical electron-transfer reaction product involving a quinone-based acceptor. Using time-resolved photoelectron spectroscopy and ab initio calculations, we show that excitation at 400 and 480 nm yields excited states that are unbound with respect to electron loss. These excited states are shown to decay on a sub-40 fs timescale through a series of conical intersections with lower-lying excited states, ultimately to form the ground anionic state and avoid autodetachment. From an isolated electron-acceptor perspective, this ultrafast stabilization mechanism accounts for the ability of para-benzoquinone to capture and retain electrons. © 2013 Macmillan Publishers Limited. All rights reserved.

Wang Y.,RF Micro Devices | Liu Q.,Beijing Institute of Technology | Fathy A.E.,University of Tennessee at Knoxville
IEEE Transactions on Geoscience and Remote Sensing | Year: 2013

Chen T.,State University of New York at Buffalo | Zhu L.,Beijing Institute of Technology | Wu F.,Shanghai JiaoTong University | Zhong S.,State University of New York at Buffalo
IEEE Transactions on Vehicular Technology | Year: 2011

In vehicular ad hoc networks (VANETs), because of the nonexistence of end-to-end connections, it is essential that nodes take advantage of connection opportunities to forward messages to make end-to-end messaging possible. Thus, it is crucial to make sure that nodes have incentives to forward messages for others, despite the fact that the routing protocols in VANETs are different from traditional end-to-end routing protocols. In this paper, we study how to stimulate message forwarding in VANETs. Our approach is based on coalitional game theory. In particular, we propose an incentive scheme for VANETs and rigorously show that with our scheme, faithfully following the routing protocol is in the best interest of each node. In addition, we extend our scheme to taking the limited storage space of each node into consideration. Experiments on testbed trace data verify that our scheme is effective in stimulating cooperation of message forwarding in VANETs. © 2006 IEEE.

News Article | October 26, 2016
Site: www.rdmag.com

Researchers have developed a prototype of a next-generation lithium-sulphur battery which takes its inspiration in part from the cells lining the human intestine. The batteries, if commercially developed, would have five times the energy density of the lithium-ion batteries used in smartphones and other electronics. The new design, by researchers from the University of Cambridge, overcomes one of the key technical problems hindering the commercial development of lithium-sulphur batteries, by preventing the degradation of the battery caused by the loss of material within it. The results are reported in the journal Advanced Functional Materials. Working with collaborators at the Beijing Institute of Technology, the Cambridge researchers based in Dr Vasant Kumar's team in the Department of Materials Science and Metallurgy developed and tested a lightweight nanostructured material which resembles villi, the finger-like protrusions which line the small intestine. In the human body, villi are used to absorb the products of digestion and increase the surface area over which this process can take place. In the new lithium-sulphur battery, a layer of material with a villi-like structure, made from tiny zinc oxide wires, is placed on the surface of one of the battery's electrodes. This can trap fragments of the active material when they break off, keeping them electrochemically accessible and allowing the material to be reused. "It's a tiny thing, this layer, but it's important," said study co-author Dr Paul Coxon from Cambridge's Department of Materials Science and Metallurgy. "This gets us a long way through the bottleneck which is preventing the development of better batteries." A typical lithium-ion battery is made of three separate components: an anode (negative electrode), a cathode (positive electrode) and an electrolyte in the middle. The most common materials for the anode and cathode are graphite and lithium cobalt oxide respectively, which both have layered structures. Positively-charged lithium ions move back and forth from the cathode, through the electrolyte and into the anode. The crystal structure of the electrode materials determines how much energy can be squeezed into the battery. For example, due to the atomic structure of carbon, each carbon atom can take on six lithium ions, limiting the maximum capacity of the battery. Sulphur and lithium react differently, via a multi-electron transfer mechanism meaning that elemental sulphur can offer a much higher theoretical capacity, resulting in a lithium-sulphur battery with much higher energy density. However, when the battery discharges, the lithium and sulphur interact and the ring-like sulphur molecules transform into chain-like structures, known as a poly-sulphides. As the battery undergoes several charge-discharge cycles, bits of the poly-sulphide can go into the electrolyte, so that over time the battery gradually loses active material. The Cambridge researchers have created a functional layer which lies on top of the cathode and fixes the active material to a conductive framework so the active material can be reused. The layer is made up of tiny, one-dimensional zinc oxide nanowires grown on a scaffold. The concept was trialled using commercially-available nickel foam for support. After successful results, the foam was replaced by a lightweight carbon fibre mat to reduce the battery's overall weight. "Changing from stiff nickel foam to flexible carbon fibre mat makes the layer mimic the way small intestine works even further," said study co-author Dr Yingjun Liu. This functional layer, like the intestinal villi it resembles, has a very high surface area. The material has a very strong chemical bond with the poly-sulphides, allowing the active material to be used for longer, greatly increasing the lifespan of the battery. "This is the first time a chemically functional layer with a well-organised nano-architecture has been proposed to trap and reuse the dissolved active materials during battery charging and discharging," said the study's lead author Teng Zhao, a PhD student from the Department of Materials Science & Metallurgy. "By taking our inspiration from the natural world, we were able to come up with a solution that we hope will accelerate the development of next-generation batteries." For the time being, the device is a proof of principle, so commercially-available lithium-sulphur batteries are still some years away. Additionally, while the number of times the battery can be charged and discharged has been improved, it is still not able to go through as many charge cycles as a lithium-ion battery. However, since a lithium-sulphur battery does not need to be charged as often as a lithium-ion battery, it may be the case that the increase in energy density cancels out the lower total number of charge-discharge cycles. "This is a way of getting around one of those awkward little problems that affects all of us," said Coxon. "We're all tied in to our electronic devices - ultimately, we're just trying to make those devices work better, hopefully making our lives a little bit nicer."

News Article | October 26, 2016

Researchers have developed a prototype of a next-generation lithium-sulphur battery which takes its inspiration in part from the cells lining the human intestine. The batteries, if commercially developed, would have five times the energy density of the lithium-ion batteries used in smartphones and other electronics. The new design, by researchers from the University of Cambridge, overcomes one of the key technical problems hindering the commercial development of lithium-sulphur batteries, by preventing the degradation of the battery caused by the loss of material within it. The results are reported in the journal Advanced Functional Materials. Working with collaborators at the Beijing Institute of Technology, the Cambridge researchers based in Dr Vasant Kumar's team in the Department of Materials Science and Metallurgy developed and tested a lightweight nanostructured material which resembles villi, the finger-like protrusions which line the small intestine. In the human body, villi are used to absorb the products of digestion and increase the surface area over which this process can take place. In the new lithium-sulphur battery, a layer of material with a villi-like structure, made from tiny zinc oxide wires, is placed on the surface of one of the battery's electrodes. This can trap fragments of the active material when they break off, keeping them electrochemically accessible and allowing the material to be reused. "It's a tiny thing, this layer, but it's important," said study co-author Dr Paul Coxon from Cambridge's Department of Materials Science and Metallurgy. "This gets us a long way through the bottleneck which is preventing the development of better batteries." A typical lithium-ion battery is made of three separate components: an anode (negative electrode), a cathode (positive electrode) and an electrolyte in the middle. The most common materials for the anode and cathode are graphite and lithium cobalt oxide respectively, which both have layered structures. Positively-charged lithium ions move back and forth from the cathode, through the electrolyte and into the anode. The crystal structure of the electrode materials determines how much energy can be squeezed into the battery. For example, due to the atomic structure of carbon, each carbon atom can take on six lithium ions, limiting the maximum capacity of the battery. Sulphur and lithium react differently, via a multi-electron transfer mechanism meaning that elemental sulphur can offer a much higher theoretical capacity, resulting in a lithium-sulphur battery with much higher energy density. However, when the battery discharges, the lithium and sulphur interact and the ring-like sulphur molecules transform into chain-like structures, known as a poly-sulphides. As the battery undergoes several charge-discharge cycles, bits of the poly-sulphide can go into the electrolyte, so that over time the battery gradually loses active material. The Cambridge researchers have created a functional layer which lies on top of the cathode and fixes the active material to a conductive framework so the active material can be reused. The layer is made up of tiny, one-dimensional zinc oxide nanowires grown on a scaffold. The concept was trialled using commercially-available nickel foam for support. After successful results, the foam was replaced by a lightweight carbon fibre mat to reduce the battery's overall weight. "Changing from stiff nickel foam to flexible carbon fibre mat makes the layer mimic the way small intestine works even further," said study co-author Dr Yingjun Liu. This functional layer, like the intestinal villi it resembles, has a very high surface area. The material has a very strong chemical bond with the poly-sulphides, allowing the active material to be used for longer, greatly increasing the lifespan of the battery. "This is the first time a chemically functional layer with a well-organised nano-architecture has been proposed to trap and reuse the dissolved active materials during battery charging and discharging," said the study's lead author Teng Zhao, a PhD student from the Department of Materials Science & Metallurgy. "By taking our inspiration from the natural world, we were able to come up with a solution that we hope will accelerate the development of next-generation batteries." For the time being, the device is a proof of principle, so commercially-available lithium-sulphur batteries are still some years away. Additionally, while the number of times the battery can be charged and discharged has been improved, it is still not able to go through as many charge cycles as a lithium-ion battery. However, since a lithium-sulphur battery does not need to be charged as often as a lithium-ion battery, it may be the case that the increase in energy density cancels out the lower total number of charge-discharge cycles. "This is a way of getting around one of those awkward little problems that affects all of us," said Coxon. "We're all tied in to our electronic devices - ultimately, we're just trying to make those devices work better, hopefully making our lives a little bit nicer."

News Article | October 26, 2016
Site: www.cemag.us

A new prototype of a lithium-sulphur battery — which could have five times the energy density of a typical lithium-ion battery — overcomes one of the key hurdles preventing their commercial development by mimicking the structure of the cells which allow us to absorb nutrients. Researchers have developed a prototype of a next-generation lithium-sulphur battery which takes its inspiration in part from the cells lining the human intestine. The batteries, if commercially developed, would have five times the energy density of the lithium-ion batteries used in smartphones and other electronics. The new design, by researchers from the University of Cambridge, overcomes one of the key technical problems hindering the commercial development of lithium-sulphur batteries, by preventing the degradation of the battery caused by the loss of material within it. The results are reported in the journal Advanced Functional Materials. Working with collaborators at the Beijing Institute of Technology, the Cambridge researchers based in Dr. Vasant Kumar’s team in the Department of Materials Science and Metallurgy developed and tested a lightweight nanostructured material which resembles villi, the finger-like protrusions which line the small intestine. In the human body, villi are used to absorb the products of digestion and increase the surface area over which this process can take place. In the new lithium-sulphur battery, a layer of material with a villi-like structure, made from tiny zinc oxide wires, is placed on the surface of one of the battery’s electrodes. This can trap fragments of the active material when they break off, keeping them electrochemically accessible and allowing the material to be reused. “It’s a tiny thing, this layer, but it’s important,” says study co-author Dr. Paul Coxon from Cambridge’s Department of Materials Science and Metallurgy. “This gets us a long way through the bottleneck which is preventing the development of better batteries.” A typical lithium-ion battery is made of three separate components: an anode (negative electrode), a cathode (positive electrode) and an electrolyte in the middle. The most common materials for the anode and cathode are graphite and lithium cobalt oxide respectively, which both have layered structures. Positively-charged lithium ions move back and forth from the cathode, through the electrolyte and into the anode. The crystal structure of the electrode materials determines how much energy can be squeezed into the battery. For example, due to the atomic structure of carbon, each carbon atom can take on six lithium ions, limiting the maximum capacity of the battery. Sulphur and lithium react differently, via a multi-electron transfer mechanism meaning that elemental sulphur can offer a much higher theoretical capacity, resulting in a lithium-sulphur battery with much higher energy density. However, when the battery discharges, the lithium and sulphur interact and the ring-like sulphur molecules transform into chain-like structures, known as a poly-sulphides. As the battery undergoes several charge-discharge cycles, bits of the poly-sulphide can go into the electrolyte, so that over time the battery gradually loses active material. The Cambridge researchers have created a functional layer which lies on top of the cathode and fixes the active material to a conductive framework so the active material can be reused. The layer is made up of tiny, one-dimensional zinc oxide nanowires grown on a scaffold. The concept was trialed using commercially-available nickel foam for support. After successful results, the foam was replaced by a lightweight carbon fiber mat to reduce the battery’s overall weight. “Changing from stiff nickel foam to flexible carbon fiber mat makes the layer mimic the way small intestine works even further,” said study co-author Dr. Yingjun Liu. This functional layer, like the intestinal villi it resembles, has a very high surface area. The material has a very strong chemical bond with the poly-sulphides, allowing the active material to be used for longer, greatly increasing the lifespan of the battery. “This is the first time a chemically functional layer with a well-organized nano-architecture has been proposed to trap and reuse the dissolved active materials during battery charging and discharging,” said the study’s lead author Teng Zhao, a PhD student from the Department of Materials Science & Metallurgy. “By taking our inspiration from the natural world, we were able to come up with a solution that we hope will accelerate the development of next-generation batteries.” For the time being, the device is a proof of principle, so commercially-available lithium-sulphur batteries are still some years away. Additionally, while the number of times the battery can be charged and discharged has been improved, it is still not able to go through as many charge cycles as a lithium-ion battery. However, since a lithium-sulphur battery does not need to be charged as often as a lithium-ion battery, it may be the case that the increase in energy density cancels out the lower total number of charge-discharge cycles. “This is a way of getting around one of those awkward little problems that affects all of us,” says Coxon. “We’re all tied in to our electronic devices — ultimately, we’re just trying to make those devices work better, hopefully making our lives a little bit nicer.”

Si L.-M.,Beijing Institute of Technology | Zhu W.,Monash University | Sun H.-J.,Beijing Institute of Technology
IEEE Antennas and Wireless Propagation Letters | Year: 2013

A novel compact, planar, and coplanar waveguide (CPW)-fed dual-band antenna is designed and proposed using composite metamaterial. Such composite metamaterial consists of an inner split-ring resonator (SRR) and an outer closed-ring resonator (CRR). The composite metamaterial can provide dual-band operation at 2.595-2.654 and 3.185-4.245 GHz with reflection coefficient better than-10 dB by the two resonant modes of SRR and CRR, respectively. A CPW-fed line with trapeziform ground plane and tapered impedance transformer line is employed to improve the impedance matching of the antenna. The uniqueness of this design is that the inner SRR with size much smaller than the resonant wavelength is used for obtaining the lower narrow frequency band, which makes the dual-band antenna very compact. Antenna parameters, including reflection coefficient, radiation pattern, radiation efficiency, and gain, are analyzed with numerical simulation and experimental measurement. Good agreement between the simulation and measurement is observed. © 2002-2011 IEEE.

Zhang X.-J.,Beihang University | Wang G.-S.,Beihang University | Cao W.-Q.,Beijing Institute of Technology | Wei Y.-Z.,Beihang University | And 3 more authors.
ACS Applied Materials and Interfaces | Year: 2014

MnFe2O4 nanoparticles have been synthesized on a large scale by a simple hydrothermal process in a wild condition, and the RGO/MnFe2O4 nanocomposites were also prepared under ultrasonic treatment based on the synthesized nanoparticles. The absorption properties of MnFe2O4/wax, RGO/MnFe2O 4/wax and the RGO/MnFe2O4/PVDF (polyvinylidene fluoride) composites were studied; the results indicated that the RGO/MnFe 2O4/PVDF composites show the most excellent wave absorption properties. The minimum reflection loss of RGO/MnFe2O 4/PVDF composites with filler content of 5 wt % can reach -29.0 dB at 9.2 GHz, and the bandwidth of frequency less than -10 dB is from 8.00 to 12.88 GHz. The wave absorbing mechanism can be attributed to the dielectric loss, magnetic loss and the synergetic effect between RGO+MnFe2O 4, RGO+PVDF and MnFe2O4+PVDF. © 2014 American Chemical Society.

Zhang X.-J.,Beihang University | Wang G.-S.,Beihang University | Wei Y.-Z.,Beihang University | Guo L.,Beihang University | Cao M.-S.,Beijing Institute of Technology
Journal of Materials Chemistry A | Year: 2013

Novel reduced graphene oxide (RGO)/CuS nanocomposites, featuring CuS microspheres embedded in reduced graphene oxide (RGO) layers, are successfully fabricated by using an in situ growth approach in the presence of cexadecyl trimethyl ammonium bromide (CTAB) under mild wet-chemical conditions (140 °C). Characterization of the nanocomposites indicates that the CuS complex microspheres with relatively uniform size are embedded in the RGO layers to form unique core-shell nanostructures. A simple hot-press process is employed to synthesize the RGO/CuS/PVDF composites. With a filler loading of 15 wt%, the dielectric constant of the composites can reach 36 at 2 GHz, which is 10 times higher than that of pure PVDF. The composites with a filler loading of 5 wt% exhibit high values of reflection loss and the maximum loss is 32.7 dB at 10.7 GHz when the thickness is just 2.5 mm, and it can be adjusted by the thickness. The enhanced mechanism is also explained based on the Debye dipolar relaxation of the composites. The composite with a high dielectric constant is a promising material in high capacitance, while the composite with enhanced absorption can decrease the environmental pollution caused by microwave irradiation. © 2013 The Royal Society of Chemistry.

Huang Y.,University of Electronic Science and Technology of China | Wen G.,University of Electronic Science and Technology of China | Zhu W.,Monash University | Li J.,University of Electronic Science and Technology of China | And 2 more authors.
Optics Express | Year: 2014

We synthesize and systematically characterize a novel type of magnetically tunable metamaterial absorber (MA) by integrating ferrite as a substrate or superstrate into a conventional passive MA. The nearly perfect absorption and tunability of this device is studied both numerically and experimentally within X-band (8-12 GHz) in a rectangular waveguide setup. Our measurements clearly show that the resonant frequency of the MA can be shifted across a wide frequency band by continuous adjustment of a magnetic field acting on the ferrite. Moreover, the effects of substrate/superstrate's thickness on the MA's tunability are discussed. The insight gained from the generic analysis enabled us to design an optimized tunable MA with relative frequency tuning range as larger as 11.5% while keeping the absorptivity higher than 98.5%. Our results pave a path towards applications with tunable devices, such as selective thermal emitters, sensors, and bolometers. © 2014 Optical Society of America.

Dai L.,Case Western Reserve University | Xue Y.,Case Western Reserve University | Qu L.,Beijing Institute of Technology | Choi H.-J.,Ulsan National Institute of Science and Technology | Baek J.-B.,Ulsan National Institute of Science and Technology
Chemical Reviews | Year: 2015

The rising global energy demand and environmental impact of traditional energy resources pose serious challenges to human health, energy security, and environmental protection. One promising solution is fuel cell technology, which provides clean and sustainable power. Besides, the catalytic performance of many non-precious metal catalysts still needs to be further improved to meet the requirement for practical applications. These special physicochemical properties, in turn, allow for controlled structural modifications of fullerenes, leading to the formation of various advanced fullerene derivatives with appropriate properties for many potential applications.

Zeng R.,Guizhou Normal University | Zhang T.,Hunan Agricultural University | Dai G.,Beijing Institute of Technology | Zou B.,Beijing Institute of Technology
Journal of Physical Chemistry C | Year: 2011

High-quality Mn:ZnSe/ZnS core/shell and Mn:ZnSeS shell-alloyed doped nanocrystals (d-dots) with up to 50% photoluminescence (PL) quantum yield (QY) have been synthesized based on nucleation-doping strategy through a phosphine-free approach. The formation of MnSe nanoclusters was achieved by adjusting the ratio of stearic acid to manganese stearate and using a highly reactive Se precursor. Mn: ZnSe/ZnS core/shell d-dots were prepared by an epitaxial ZnS growth on the Mn:ZnSe core. The PL QY of Mn:ZnSe/ZnS core/shell d-dots decreased dramatically after injections of S precursor but was completely recovered through an UV irradiation. After annealing at 240 °C for 30 min, the core/shell Mn:ZnSe/ZnS d-dots evolved to the Mn:ZnSeS shell-alloyed d-dots with high PL QY. The PL peak position of the d-dots could be tuned within a relatively large optical window, from 584 to 605 nm. © 2011 American Chemical Society.

Xu M.,Shandong University of Science and Technology | Hu H.,Beijing Institute of Technology
Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences | Year: 2011

A ballistic-diffusive heat conduction model is derived from the Boltzmann transport equation by a coarse-graining approach developed in the present study. By taking into account of the lagging effect, this model avoids the infinite heat propagation speed implied by the classical Fourier law. By expressing the heat conductivity as a function of the Knudsen number, it accounts for the size effect of the nanoscale heat conduction. The variation of the obtained effective heat conductivity with respect to the characteristic length shows an agreement with the experimental results for thin silicon films and nanowires in the nanoscale regime.© 2011 The Royal Society.

Zhu W.,Monash University | Rukhlenko I.D.,Monash University | Si L.-M.,Beijing Institute of Technology | Premaratne M.,Monash University
Applied Physics Letters | Year: 2013

We present an effective method for actively controlling intrinsic resonances of optical metamaterials using graphene. Exploiting the Fermi level shift and associated variations in optical transitions of graphene due to voltage biasing, we attain the ability to significantly modulate the intrinsic resonance of the fishnet structure. Despite being atomically thin and having a weak optical response, graphene can be strongly coupled with the left-handed resonance of the fishnet metamaterial. We unambiguously demonstrate that the resonant transmission, absorption, and effective constitutive parameters of the graphene-coupled fishnet metamaterial can be precisely controlled by varying the bias voltage. © 2013 American Institute of Physics.

Wang S.,Beijing Institute of Technology | Zong Q.,Beijing Institute of Technology | Zong Q.,University of Massachusetts Lowell | Zhang H.,University of Alaska Fairbanks
Journal of Geophysical Research: Space Physics | Year: 2013

Case and statistical studies of the bow shock geometry at hot flow anomaly (HFA) edges have been performed based on 87 HFAs with large flow deflections observed by the Cluster C1 spacecraft from 2003 to 2009. The results suggest that HFAs can be formed at both quasi-parallel and quasi-perpendicular shocks. In an accompanying paper, we show that the ions might be near-specularly reflected at the bow shock and interact with the solar wind to form HFAs. The guiding center of specularly reflected ions will typically be swept downstream to the bow shock at quasi-perpendicular shocks. However, this study shows that in at least 13 of these 87 (15%) HFAs, both the leading and trailing edges are at quasi-perpendicular shocks. These HFAs show a high gyration velocity and a high fast magneto-sonic Mach number, increasing the gyro-radius and the possibility of pitch angle scattering, which might help the ions escape from the bow shock and move upstream. In addition, HFAs with both edges at quasi-perpendicular shocks are closer to the bow shock than those with both edges at quasi-parallel shocks. This might help the reflected ions at a quasi-perpendicular shock interact with the incident solar wind immediately after the reflection and increase the possibility of HFA formation. © 2012. American Geophysical Union. All Rights Reserved.

Zou L.,Beijing Institute of Technology | Chen L.,Hong Kong University of Science and Technology
IEEE Transactions on Knowledge and Data Engineering | Year: 2011

Given a record set D and a query score function F, a top-k query returns k records from D, whose values of function F on their attributes are the highest. In this paper, we investigate the intrinsic connection between top-k queries and dominant relationships between records, and based on which, we propose an efficient layer-based indexing structure, Pareto-Based Dominant Graph (DG), to improve the query efficiency. Specifically, DG is built offline to express the dominant relationship between records and top-k query is implemented as a graph traversal problem, i.e., Traveler algorithm. We prove theoretically that the size of search space (that is the number of retrieved records from the record set to answer top-k query) in our algorithm is directly related to the cardinality of skyline points in the record set (see Theorem 3). Considering I/O cost, we propose cluster-based storage schema to reduce I/O cost in Traveler algorithm. We also propose the cost estimation methods in this paper. Based on cost analysis, we propose an optimization technique, pseudorecord, to further improve the search efficiency. In order to handle the top-k query in the high-dimension record set, we also propose N-Way Traveler algorithm. In order to handle DG maintenance efficiently, we propose Insertion and Deletion algorithms for DG. Finally, extensive experiments demonstrate that our proposed methods have significant improvement over its counterparts, including both classical and state art of top-k algorithms. © 2006 IEEE.

Tan E.-Z.,Beihang University | Tan E.-Z.,Beijing Institute of Technology | Yin P.-G.,Beihang University | You T.-T.,Beihang University | And 2 more authors.
ACS Applied Materials and Interfaces | Year: 2012

We have designed a large-scale three-dimensional (3D) hybrid nanostructure as surface-enhanced Raman scattering (SERS) sensor by decorating silver nanoparticles on TiO 2 nanorods scaffold (Ag/TiO 2). Taking p-mercaptobenzoic acid (PMBA) as the probe molecule, the SERS signals collected by point-to-point and time mapping modes show that the relative standard deviation (RSD) in the intensity of the main Raman vibration modes (1079, 1586 cm -1) is less than 10%, demonstrating good spatial uniformity and time stability. This hybrid substrate also exhibits excellent SERS enhancement effect due to the formation of high-density hot spots among the AgNPs, which was proved by finite-difference time-domain (FDTD) simulations. The application of the new nanostructures as SERS sensors was demonstrated with the detection of malachite green (MG). The quantification of MG can be accomplished with the detection limit of 1 × 10 -12 M based on the Raman intensity. The results show that the Ag/TiO 2 nanostructure can be a promising candidate for SERS sensor. © 2012 American Chemical Society.

Chen D.,Beihang University | Chen D.,Nanchang Hangkong University | Wang G.-S.,Beihang University | He S.,Beihang University | And 3 more authors.
Journal of Materials Chemistry A | Year: 2013

Novel RGO-hematite nanocomposites have been successfully fabricated using a surfactant-governed approach in the presence of polyvinylpyrrolidone (PVP) under mild wet chemical conditions (105 °C). A series of characterization methods including X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) indicated that the as-prepared single-crystal hematite particles with relatively uniform size are embedded in RGO layers to form unique quasi shell-core nanostructures. The microwave absorption properties of the RGO-hematite composites were studied in detail; as an absorber, the RGO-hematite nanocomposites possess excellent microwave absorbing properties. The enhanced microwave absorbing properties were also explained based on the structures of the nanocomposites. © The Royal Society of Chemistry 2013.

Qu L.,Beijing Institute of Technology | Liu Y.,Wenzhou Medical College | Baek J.-B.,Ulsan National Institute of Science and Technology | Dai L.,Case Western Reserve University
ACS Nano | Year: 2010

Nitrogen-doped graphene (N-graphene) was synthesized by chemical vapor deposition of methane in the presence of ammonia. The resultant N-graphene was demonstrated to act as a metal-free electrode with a much better electrocatalytic activity, long-term operation stability, and tolerance to crossover effect than platinum for oxygen reduction via a four-electron pathway in alkaline fuel cells. To the best of our knowledge, this is the first report on the use of graphene and its derivatives as metal-free catalysts for oxygen reduction. The important role of N-doping to oxygen reduction reaction (ORR) can be applied to various carbon materials for the development of other metal-free efficient ORR catalysts for fuel cell applications, even new catalytic materials for applications beyond fuel cells. © 2010 American Chemical Society.

Ba J.,Petrochina | Carcione J.M.,National Institute of Oceanography and Applied Geophysics - OGS | Nie J.X.,Beijing Institute of Technology
Journal of Geophysical Research: Solid Earth | Year: 2011

We derive the equations of motion of a double-porosity medium based on Biot's theory of poroelasticity and on a generalization of Rayleigh's theory of fluid collapse to the porous case. Spherical inclusions are imbedded in an unbounded host medium having different porosity, permeability, and compressibility. Wave propagation induces local fluid flow between the inclusions and the host medium because of their dissimilar compressibilities. Following Biot's approach, Lagrange's equations are obtained on the basis of the strain and kinetic energies. In particular, the kinetic energy and the dissipation function associated with the local fluid flow motion are described by a generalization of Rayleigh's theory of liquid collapse of a spherical cavity. We obtain explicit expressions of the six stiffnesses and five density coefficients involved in the equations of motion by performing "gedanken" experiments. A plane wave analysis yields four wave modes, namely, the fast P and S waves and two slow P waves. As an example, we consider a sandstone and compute the phase velocity and quality factor as a function of frequency, which illustrate the effects of the mesoscopic loss mechanism due to wave-induced fluid flow. Copyright 2011 by the American Geophysical Union.

Na J.,Kunming University of Science and Technology | Ren X.,Beijing Institute of Technology | Shang C.,Beijing Institute of Technology | Guo Y.,Kunming University of Science and Technology
Journal of Process Control | Year: 2012

This paper presents an adaptive neural control design for nonlinear pure-feedback systems with an input time-delay. Novel state variables and the corresponding transform are introduced, such that the state-feedback control of a pure-feedback system can be viewed as the output-feedback control of a canonical system. An adaptive predictor incorporated with a high-order neural network (HONN) observer is proposed to obtain the future system states predictions, which are used in the control design to circumvent the input delay and nonlinearities. The proposed predictor, observer and controller are all online implemented without iterative predictive calculations, and the closed-loop system stability is guaranteed. The conventional backstepping design and analysis for pure-feedback systems are avoided, which renders the developed scheme simpler in its synthesis and application. Practical guidelines on the control implementation and the parameter design are provided. Simulation on a continuous stirred tank reactor (CSTR) and practical experiments on a three-tank liquid level process control system are included to verify the reliability and effectiveness. © 2011 Elsevier Ltd. All Rights Reserved.

Xu W.,Pohang University of Science and Technology | Wang F.,Beijing Institute of Technology | Rhee S.-W.,Pohang University of Science and Technology
Journal of Materials Chemistry | Year: 2012

In this study, we report the observation of quasi-ordering in spontaneously associated highly polar surface functional groups (CN) in the high-k polymer dielectric, cyanoethyl pullulan, and its impact on the organic field-effect transistor (OFET) characteristics. We find that the association originates from CN⋯H-C-CN hydrogen bonding as confirmed by XPS, NEXAFS experiments and molecular simulations. The quasi-ordered surface dipoles preferentially induce vertically well-stacked local semiconductor molecular clusters during the initial deposition process, which then promote large-area layer-by-layer growth. By maintaining sufficient quasi-ordering, high transistor performance (μ ≈ 6.5 cm 2 V -1 s -1, SS ≈ 0.062 V dec -1) is obtained under low driving voltages (-3 to -5 V), while breakup of the association at higher baking temperatures leads to a dramatic drop in μ by a factor of ∼10. Our results demonstrate that local quasi-ordering of polymeric surface dipoles, which has a significant effect on the initial semiconductor molecular growth, represents a novel and sensitive factor affecting OFET characteristics. © The Royal Society of Chemistry 2012.

Na J.,Kunming University of Science and Technology | Ren X.,Beijing Institute of Technology | Zheng D.,Beijing Institute of Technology
IEEE Transactions on Neural Networks and Learning Systems | Year: 2013

Most of the available control schemes for pure-feedback systems are derived based on the backstepping technique. On the contrary, this paper presents a novel adaptive control design for nonlinear pure-feedback systems without using backstepping. By introducing a set of alternative state variables and the corresponding transform, state-feedback control of the pure-feedback system can be viewed as output-feedback control of a canonical system. Consequently, backstepping is not necessary and the previously encountered explosion of complexity and circular issue are also circumvented. To estimate unknown states of the newly derived canonical system, a high-order sliding mode observer is adopted, for which finite-time observer error convergence is guaranteed. Two adaptive neural controllers are then proposed to achieve tracking control. In the first scheme, a robust term is introduced to account for the neural approximation error. In the second scheme, a novel neural network with only a scalar weight updated online is constructed to further reduce the computational costs. The closed-loop stability and the convergence of the tracking error to a small compact set around zero are all proved. Comparative simulation and practical experiments on a servo motor system are included to verify the reliability and effectiveness. © 2013 IEEE.

Wu G.,CAS Institute of Policy and Management | Liu L.-C.,Chinese Ministry of Environmental Protection | Han Z.-Y.,National Science Foundation | Wei Y.-M.,Beijing Institute of Technology
Applied Energy | Year: 2012

Since 1996 China became a net importer of crude oil, energy security has faced lots of supply risks and the issues of security on energy using have become more and more acute. The Chinese government has taken a series of policies and measures and enacted relevant laws to guarantee energy security and mitigate global climate change. What changes has energy security in China experienced in these years? What impacts has the implementation of energy security and climate protection policies brought to China's energy security? This paper has established the evaluation indicators and model of the energy security index. The model evaluation results show that: (1) in 1996-2009, the index of China's energy supply security presented an uptrend and then downtrend. For example, it presented a rapid uptrend in 1996-2001, a quick downtrend in 2002-2005, and a slow downtrend in 2006-2009. The energy supply security index in 2009 was kept basically the same as that in 1996. (2) In 1996-2009, the index of China's energy using security presented a fluctuated uptrend. For example, it presented a fluctuating uptrend in 1996-2002, and dropped to a relative low level in 2003-2005, and then quickly rose in 2006-2009. (3) The policy of "China's energy-saving and emission reduction" has slowed down the decreasing speed of the index of energy supply security and also conspicuously improved the index of energy using security, so that the composite index of China's energy security presented an uptrend, then downtrend and finally uptrend. The policy of "China's energy-saving and emission reduction" has been successfully conducted, proving that a win-win result can be achieved between climate change protection and China's energy security. © 2011.

Li Y.,Beijing Institute of Technology | Li Y.,Tsinghua University | Song J.,Tsinghua University | Yang J.,Beihang University
Renewable and Sustainable Energy Reviews | Year: 2014

Structure properties of lithium-ion battery determine the specific energy and specific power of renewable energy vehicle and have attracted extensive concerns. Fundamental innovations in battery system depend on the structure properties, of which graphene and concentration gradient structures become increasingly prospective. As the performance of structure closely relates to the battery performance and the advancement of battery technologies, the paper, based on the research work at our laboratory, discusses about the structure model and energy system design and analyzes the evolution of lithium batteries to provide scientific insights and technical advices for the development of renewable energy vehicle. The review shows that nano and graphene models, with their corresponding energy systems, significantly improve the performance of lithium batteries, thus supporting longer mileage and service life, while providing new ideas for the design of renewable energy vehicles. Compared with other power batteries, lithium-ion batteries are advantageous in addressing the requirements raised by battery electric vehicles, such as, long mileage, high-current charging, and safety. Therefore, lithium batteries are reliable and feasible for the deployment in battery electric vehicles. © 2014 Elsevier Ltd.

Pan H.,Beihang University | Li Z.,Beihang University | Liu C.-C.,Beijing Institute of Technology | Zhu G.,Heze University | And 3 more authors.
Physical Review Letters | Year: 2014

We find theoretically a new quantum state of matter - the valley-polarized quantum anomalous Hall state in silicene. In the presence of Rashba spin-orbit coupling and an exchange field, silicene hosts a quantum anomalous Hall state with Chern number C=2. We show that through tuning the Rashba spin-orbit coupling, a topological phase transition results in a valley-polarized quantum anomalous Hall state, i.e., a quantum state that exhibits the electronic properties of both the quantum valley Hall state (valley Chern number Cv=3) and quantum anomalous Hall state with C=-1. This finding provides a platform for designing dissipationless valleytronics in a more robust manner. © 2014 American Physical Society.

Xu J.,Beijing Institute of Technology | Xu J.,Beijing Computational Science Research Center | Zhang X.,Beijing Institute of Technology
Optics Express | Year: 2012

The theory of second harmonic generation (SHG) in three-dimensional structures consisting of arbitrary distributions of metallic spheres made of centrosymmetric materials is developed by means of multiple scattering of electromagnetic multipole fields. The electromagnetic field at both the fundamental frequency and second harmonic, as well as the scattering cross section, are calculated in a series of particular cases such as a single metallic sphere, two metallic spheres, chains of metallic spheres, and other distributions of the metallic spheres. It is shown that the linear and nonlinear optical response of all ensembles of metallic spheres is strongly influenced by the excitation of localized surface plasmon-polariton resonances. The physical origin for such a phenomenon has also been analyzed. © 2012 Optical Society of America.

Na J.,Kunming University of Science and Technology | Ren X.,Beijing Institute of Technology | Xia Y.,Beijing Institute of Technology
Systems and Control Letters | Year: 2014

An adaptive online parameter identification is proposed for linear single-input-single-output (SISO) time-delay systems to simultaneously estimate the unknown time-delay and other parameters. After representing the system as a parameterized form, a novel adaptive law is developed, which is driven by appropriate parameter estimation error information. Consequently, the identification error convergence can be proved under the conventional persistent excitation (PE) condition, which can be online tested in this paper. A finite-time (FT) identification scheme is further studied by incorporating the sliding mode scheme into the adaptation to achieve FT error convergence. The previously imposed constraint on the system relative degree is removed and the derivatives of the input and output are not required. Comparative simulation examples are provided to demonstrate the validity and efficacy of the proposed algorithms. © 2014 Elsevier B.V. All rights reserved.

Na J.,Kunming University of Science and Technology | Chen Q.,Zhejiang University of Technology | Ren X.,Beijing Institute of Technology | Guo Y.,Kunming University of Science and Technology
IEEE Transactions on Industrial Electronics | Year: 2014

This paper proposes an adaptive control for a class of nonlinear mechanisms with guaranteed transient and steady-state performance. A performance function characterizing the convergence rate, maximum overshoot, and steady-state error is used for the output error transformation, such that stabilizing the transformed system is sufficient to achieve the tracking control of the original system with a priori prescribed performance. A continuously differentiable friction model is adopted to account for the friction nonlinearities, for which primary model parameters are online updated. A novel high-order neural network with only a scalar weight is developed to approximate unknown nonlinearities and to dramatically diminish the computational costs. Comparative experiments on a turntable servo system are included to verify the reliability and effectiveness. © 1982-2012 IEEE.

Zhu Z.,Beijing Institute of Machinery | Xu D.,Beihang University | Liu J.,Beihang University | Xia Y.,Beijing Institute of Technology
IEEE Transactions on Industrial Electronics | Year: 2013

The problem of missile interception is investigated in this paper. Sliding-mode controllers with finite-time convergence are proposed for the design of guidance laws. In particular, the control design consists of the estimation of the target acceleration by the extended state observer (ESO), and thus, it achieves the decrease of undesired chattering effectively. Also, simulation results are presented to illustrate the effectiveness of the control strategies. © 1982-2012 IEEE.

Patent
Beijing Institute of Technology, Nanjing Southeast University and Jiangsu University | Date: 2013-05-21

A method and an apparatus for injecting a water restraint layer of a laser shock processing blade, including a laser device distance measuring instrument platform bracket distance measuring instrument controller I, and water tap transition joint, signal wires, hose, and water tank. A standard curved section corresponding to two probe points I, and a point to be processed, on a vertical section along a laser beam direction on the blade is used for approximately replacing an actual curved section on the blade, so that a water flow flows into the blade from a middle point of the standard curved section approximately as a middle point of the actual curved section, and the long side of a flat nozzle is parallel to the tangent plane of the point to be processed of the blade through the controller according to feedback information of the distance measuring instrument.

Zhang G.-F.,Beihang University | Zhang G.-F.,Oklahoma State University | Jiang Z.-T.,Beijing Institute of Technology | Abliz A.,Xinjiang Normal University
Annals of Physics | Year: 2011

Quantum correlation in two-qubit spin models is investigated by use of measurement-induced disturbance [S. Luo, Phys. Rev. A, 77 (2008) 022301]. Its dependences on external magnetic field, spin-spin coupling, and Dzyaloshinski-Moriya (DM) interactions are presented in detail. We also compare measurement-induced disturbance and thermal entanglement in spin models and illustrate their different characteristics. © 2010.

News Article | December 9, 2015
Site: www.materialstoday.com

News Article | November 7, 2016
Site: www.materialstoday.com

Fashion is changing in the avant-garde world of next-generation computer component materials. Traditional semiconductors like silicon are releasing their last new lines. Exotic materials called topological insulators (TIs) are on their way in. And when it comes to cool, nitrogen is the new helium. This was clearly on display in a novel experiment at the US National Institute of Standards and Technology (NIST). This experiment was performed by a multi-institutional collaboration involving researchers from NIST, the University of California, Los Angeles (UCLA) and the Beijing Institute of Technology in China, and is reported in a paper in Nature Materials. TIs are a new class of materials that were discovered less than a decade ago after earlier theoretical work, recently recognized with the 2016 Nobel Prize in physics, predicted they could exist. These materials are electrical insulators on the inside, but conduct electricity on their outer surface. They are of great interest to computer designers because electric current travels along them without shedding heat, meaning components made from them could reduce the high heat production that plagues modern computers. They also might be harnessed one day in quantum computers, which would exploit less familiar properties of electrons, such as their spin, to make calculations in entirely new ways. When TIs conduct electricity, all of the electrons flowing in one direction have the same spin, a useful property that could be harnessed by quantum computer designers. One major problem, however, is the special properties that make TIs so exciting for technologists are usually observed only at very low temperatures, typically requiring liquid helium to cool the materials. Not only does this demand for extreme cold make TIs unlikely to find use in electronics until this problem is overcome, but it also makes it difficult to study them in the first place. Furthermore, making TIs magnetic is key to developing exciting new computing devices with them. But even getting them to the point where they can be magnetized is a laborious process. Two ways to do this have been to infuse, or ‘dope’, the TI with a small amount of magnetic metal and/or to stack thin layers of TI between alternating layers of a magnetic material known as a ferromagnet. However, increasing the doping to push the operating temperature higher disrupts the TI properties, while the alternate layers' more powerful magnetism can overwhelm the TIs, making them hard to study. To get around these problems, UCLA scientists tried using a different substance for the alternating layers: an antiferromagnet. Unlike conventional permanent magnets, whose atoms all have north poles that point in the same direction, the multilayered antiferromagnetic (AFM) materials have north poles pointing one way in one layer and the opposite way in the next layer. Because the magnetism of these layers cancels each other out, the overall AFM doesn't possess a net magnetism, although a single layer of its molecules does. It was the outermost layer of the AFM that the UCLA team hoped to exploit. In their experiments, they found that the outermost layer's influence magnetizes the TI, but without the overwhelming force that the previously-used magnetic materials would bring. And they found that the new approach allowed the TIs to become magnetic and demonstrate all of the TI's appealing properties at temperatures far above 77K (-196°C). Although this is still too cold for TIs to be used as consumer electronics components, it’s warm enough that scientists can use liquid nitrogen to cool them rather than liquid helium. "It makes them far easier to study," explains Alex Grutter of the NIST Center for Neutron Research, which partnered with the UCLA scientists to clarify the interactions between the overall material's layers as well as its spin structure. "Not only can we explore TIs' properties more easily, but we're excited because to a physicist, finding one way to increase the operational temperature this dramatically suggests there might be other accessible ways to increase it again. Suddenly, room temperature TIs don't look as far out of reach." This story is adapted from material from NIST, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.

News Article | October 28, 2016
Site: en.prnasia.com

Ma J.,Beijing Institute of Technology | Porter A.L.,Georgia Institute of Technology | Porter A.L.,Search Technology Inc
Scientometrics | Year: 2015

As a basic knowledge resource, patents play an important role in identifying technology development trends and opportunities, especially for emerging technologies. However patent mining is restricted and even incomplete, because of the obscure descriptions provided in patent text. In this paper, we conduct an empirical study to try out alternative methods with Derwent Innovation Index data. Our case study focuses on nanoenabled drug delivery (NEDD) which is a very active emerging biomedical technology, encompassing several distinct technology spaces. We explore different ways to enhance topical intelligence from patent compilations. We further analyze extracted topical terms to identify potential innovation pathways and technology opportunities in NEDD. © Akadémiai Kiadó, Budapest, Hungary 2014

Huang S.,Tsinghua University | Xiong J.,Beijing Institute of Technology | Zhang Y.,Tsinghua University
Journal of Hazardous Materials | Year: 2013

The indoor pollution caused by formaldehyde and volatile organic compounds (VOCs) emitted from building materials poses an adverse effect on people's health. It is necessary to understand and control the behaviors of the emission sources. Based on detailed mass transfer analysis on the emission process in a ventilated chamber, this paper proposes a novel method of measuring the three emission characteristic parameters, i.e., the initial emittable concentration, the diffusion coefficient and the partition coefficient. A linear correlation between the logarithm of dimensionless concentration and time is derived. The three parameters can then be calculated from the intercept and slope of the correlation. Compared with the closed chamber C-history method, the test is performed under ventilated condition thus some commonly-used measurement instruments (e.g., GC/MS, HPLC) can be applied. While compared with other methods, the present method can rapidly and accurately measure the three parameters, with experimental time less than 12h and R2 ranging from 0.96 to 0.99 for the cases studied. Independent experiment was carried out to validate the developed method, and good agreement was observed between the simulations based on the determined parameters and experiments. The present method should prove useful for quick characterization of formaldehyde/VOC emissions from indoor materials. © 2013 Elsevier B.V.

Xu H.,Jilin University | Yu B.,Beijing Institute of Technology
Expert Systems with Applications | Year: 2010

Email has become one of the fastest and most economical forms of communication. Email is also one of the most ubiquitous and pervasive applications used on a daily basis by millions of people worldwide. However, the increase in email users has resulted in a dramatic increase in spam emails during the past few years. This paper proposes a new spam filtering system using revised back propagation (RBP) neural network and automatic thesaurus construction. The conventional back propagation (BP) neural network has slow learning speed and is prone to trap into a local minimum, so it will lead to poor performance and efficiency. The authors present in this paper the RBP neural network to overcome the limitations of the conventional BP neural network. A well constructed thesaurus has been recognized as a valuable tool in the effective operation of text classification, it can also overcome the problems in keyword-based spam filters which ignore the relationship between words. The authors conduct the experiments on Ling-Spam corpus. Experimental results show that the proposed spam filtering system is able to achieve higher performance, especially for the combination of RBP neural network and automatic thesaurus construction. © 2009 Elsevier Ltd. All rights reserved.

Yang H.,Beijing Institute of Technology | Xia Y.,Beijing Institute of Technology | Shi P.,University of South Wales | Shi P.,Victoria University of Melbourne
International Journal of Robust and Nonlinear Control | Year: 2011

In this paper, a new linear delayed delta operator switched system model is proposed to describe networked control systems with packets dropout and network-induced delays. The plant is a continuous-time system, which is sampled by time-varying random sampling periods. A general delta domain Lyapunov stability criterion is given for delta operator switched systems with time delays. Sufficient conditions for asymptotic stability of closed-loop networked control systems with both packets dropout and network-induced delays are presented in terms of linear matrix inequalities (LMIs). A verification theorem is given to show the solvability of the stabilization conditions by solving a class of finite LMIs. Both the case of data packets arrive instantly and the case of invariant sampling periods in delta operator systems are given, respectively. Three numerical examples are given to illustrate the effectiveness and potential of the developed techniques. © 2010 John Wiley & Sons, Ltd.

You Y.-Z.,Tsinghua University | Yang F.,Beijing Institute of Technology | Kou S.-P.,Tsinghua University | Weng Z.-Y.,Tsinghua University
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

We study a unified mechanism for spin-density-wave (SDW) and superconductivity in a minimal model in which itinerant electrons and local moments coexist as previously proposed for the iron pnictides. The phase diagram obtained at the mean-field level is in qualitative agreement with the experiment, which shows how the magnetic and superconducting (SC) instabilities are driven by the critical coupling between the itinerant/localized electrons. The spin and charge response functions at the random-phase-approximation level further characterize the dynamical evolution of the system. In particular, the dynamic spin susceptibility displays a Goldstone mode in the SDW phase, which evolves into a gapped resonance-like mode in the SC phase. The latter persists all the way into the normal state above Tc where a strong scattering between the itinerant electrons and local moments is restored, as an essential feature of the model. © 2011 American Physical Society.

Lu Y.,Beijing Institute of Technology | Zhang X.,Tsinghua University | Chen M.,Tsinghua University
Journal of Physical Chemistry B | Year: 2013

The nucleation rate from classical nucleation theory is independent of sample size. In the past decades, several experimental and theoretical studies argued that the homogeneous nucleation rate of ice in supercooled droplets increases when the drop size is decreased. In this paper, we investigate the nucleation of ice in nanoscale water films using molecular dynamics simulations. We found that the nucleation rate of ice actually decreases when the film thickness decreases in the nanoscale regime. A theoretical model is presented to interpret the mechanism of nucleation rate decrease, which agrees well with the simulation results. The model divides films into the near-surface and the middle regions that are characterized by relatively low and high nucleation rates, respectively. The middle region dominates the nucleation process of films, whereas its effect is continuously weakened when increasing volume fraction of the near-surface region by decreasing the film size, leading to a decrease of the total nucleation rate. The structural and thermodynamic analyses indicate that the high stress induced by the surface layering slows down the diffusion and increases the nucleation barrier in the near-surface region, which is responsible for the low nucleation rate and eventually the decrease of the total nucleation rate. © 2013 American Chemical Society.

He Z.,University of Science and Arts of Iran | Yao C.,University of Science and Arts of Iran | Zou J.,Beijing Institute of Technology
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2013

Using the weak measurement (WM) and quantum measurement reversal (QMR) approach, robust state transfer and entanglement distribution can be realized in the spin-12 Heisenberg chain. We find that the ultrahigh fidelity and long distance of quantum state transfer with certain success probability can be obtained using proper WM and QMR, i.e., the average fidelity of a general pure state from 80% to almost 100%, which is almost size independent. We also find that the distance and quality of entanglement distribution for the Bell state and the general Werner mixed state can be obviously improved by the WM and QMR approach. © 2013 American Physical Society.

Li C.,Tsinghua University | Liu Z.,Beijing Institute of Technology | Xie H.,Tsinghua University | Wu D.,Tsinghua University
Optics Express | Year: 2013

A 3D SEM Moiré Method (SMM) is proposed in this investigation for the first time for 3D shape measurement with nano-scale sensitivity. The geometric model of the 3D SMM has been theoretically established, combining the stereovision technology in an SEM with the existing principles of in-plane SMM. The Virtual Projection Fringe (VPF) generated under different conditions has been analyzed for 3D reconstructions. Two typical applications have been used to experimentally validate the theoretical model. Experimental results, with the height measurement sensitivity less than 10nm, agree well with the theoretical model we proposed. The uncertainty analysis for the method has also been performed by other auxiliary measurements. © 2013 Optical Society of America.

Sun J.,Beijing Institute of Technology | Sun J.,University of South Wales | Liu G.P.,University of South Wales | Liu G.P.,Harbin Institute of Technology | And 2 more authors.
Automatica | Year: 2010

This paper is concerned with the stability analysis of linear systems with time-varying delays in a given range. A new type of augmented Lyapunov functional is proposed which contains some triple-integral terms. In the proposed Lyapunov functional, the information on the lower bound of the delay is fully exploited. Some new stability criteria are derived in terms of linear matrix inequalities without introducing any free-weighting matrices. Numerical examples are given to illustrate the effectiveness of the proposed method. © 2009 Elsevier Ltd. All rights reserved.

Zhao Y.,Beijing Institute of Technology | Hu C.,Beijing Institute of Technology | Song L.,Beijing Institute of Technology | Wang L.,Beijing Institute of Technology | And 3 more authors.
Energy and Environmental Science | Year: 2014

Rationally designed graphene nanomesh assembled foam (GMF) with hierarchical pore arrangement has been successfully fabricated for the first time by a site-localized nanoparticle-induced etching strategy on the basis of hydrothermally self-assembled graphene architecture. The newly developed GMF provides a new material platform for developing high-performance functional devices. Specially, the N- and S-codoped GMF electrode exhibits excellent electrocatalytic activities for oxygen reduction reaction (ORR), better than most of the graphene-based ORR catalysts reported previously. This journal is © the Partner Organisations 2014.

Miao C.,Changchun University | Ge W.,Beijing Institute of Technology
Mathematical Methods in the Applied Sciences | Year: 2015

In this paper, we study the existence of positive solutions for singular impulsive differential equations with integral boundary conditions u′′(t) + q(t)f(t,u(t),u′(t)) = 0,t ∈ J′, Δu(tk) = Ik(u(tk),u′(tk)),k = 1,2,p, Δu′(tk) = -Lk(u(tk),u′(tk)),k = 1,2,p, u(0) =∫01g(t)u(t)dt,u′(1) = 0, where the nonlinearity f(t,u,v) may be singular at u-=-0 and v-=-0. The proof is based on the theory of Leray-Schauder degree, together with a truncation technique. Some recent results in the literature are generalized and improved. Copyright © 2014 John Wiley & Sons, Ltd.

Xiong J.,Beijing Institute of Technology | Liu C.,Tsinghua University | Zhang Y.,Tsinghua University
Atmospheric Environment | Year: 2012

A general analytical model for characterizing emission and sorption of formaldehyde and volatile organic compounds (VOCs) in single-layer building materials is developed. Compared with traditional models, the present model can be applicable for four kinds of typical physical processes, i.e., emission in ventilated and airtight chambers, and sorption in these two types of chambers. Based on the general analytical model, a novel method is proposed to determine the characteristic parameters (the diffusion coefficient, D m, and the material/air partition coefficient, K) of formaldehyde and VOC sorption in ventilated and airtight chambers. It establishes a linear relationship between the logarithm of dimensionless excess concentration and sorption time, and the D m and K can be conveniently obtained from the slope and intercept of the regression line. The results of applying the present model are compared with the experimental data in the literature. The good agreement between them not only validates the model but also demonstrates that the measured characteristic parameters are accurate and reliable. The general analytical model should prove useful for unified characterization and prediction of emission/sorption in building materials as well as for parameter measurement. © 2011 Elsevier Ltd.

Wei W.,Tsinghua University | Zhang Y.,Tsinghua University | Xiong J.,Beijing Institute of Technology | Li M.,Tsinghua University
Atmospheric Environment | Year: 2012

Environmental chambers are widely used to test formaldehyde and other volatile organic compound (VOC) emissions from indoor materials and furniture. However, there is a lack of a proven method to assess the precision of the test results of the chamber system. In this paper, we describe a new standard reference, LIFE (liquid-inner tube diffusion-film-emission), to address this problem. This reference has the following salient features: (1) Constant emission rate, with less than 3.0% change with an ambient airflow speed (>0.014-m/s) at furniture emission range (0.1-1.0-mg/m 3 in a 30-m 3 chamber with air change rate of 1/h) under standard chamber test conditions as specified by ISO 16000-9 (23-°C, 50% RH); (2) Long duration of emissions, on the order of 1000-h; (3) Easy to store, apply and maintain. The design principle and criteria of the LIFE reference are presented. An analytical model and dimensionless analysis were applied to optimize the factors influencing the emission rate, and experiments were conducted to validate the analytical results. In addition, the equivalent emission parameters of the reference, i.e., the initial emittable concentration, the diffusion coefficient and the partition coefficient, were determined through a three-parameter optimizing regression. This can then be used to check the reliability of a chamber method for testing these three parameters. The developed standard reference should prove useful for calibrating chamber systems for indoor material/furniture VOC emissions tests. © 2011 Elsevier Ltd.

Song Y.,Beijing Institute of Technology | Zhang K.,Beijing Institute of Technology | Hao Q.,Beijing Institute of Technology | Rolland J.P.,University of Rochester
Optics Express | Year: 2012

The method of Mach-Zehnder electro-optical modulation is applied to Intra-Body Communication (IBC), where the modeling and characterization of this type of IBC are discussed. The mathematical model of the electrostatic coupling IBC based on Mach-Zehnder electro-optical modulation is developed. The main characteristics of this IBC form have been simulated within the frequency range of 200 kHz-40MHz and compared to in-vivo measurements, with close agreements. Results show that the proposed method will help achieving good temperature characteristics, small size, and lower power consumption IBC system. ©2012 Optical Society of America.

Zhang X.,Beijing Institute of Technology | Chang D.,Tsinghua University | Liu J.,Beijing Institute of Technology | Luo Y.,Beijing Institute of Technology
Journal of Materials Chemistry | Year: 2010

The organic conducting PEDOT-PSS aerogels can be prepared by supercritical CO2 drying of metal ion crosslinked PEDOT-PSS supermolecular hydrogels. The PEDOT-PSS hydrogel precursors were synthesized by polymerizing 3,4-ethylenedioxythiophene with excess ferric nitrate as oxidizing agent as well as crosslinking agent in the presence of poly(sodium 4-styrenesulfonate). The supermolecular crosslinking mechanism of the hydrogel precursors and the chemical composition of the resulting aerogels were revealed by X-ray photoelectron spectroscopy (XPS). The molecular structure of the resulting PEDOT-PSS aerogels was further confirmed by Raman and infra-red spectroscopy. The morphology and textural properties of the resultant aerogels were investigated by scanning electron microscopy (SEM), nitrogen adsorption/desorption, and X-ray powder diffraction (XRD) tests, respectively. The resulting aerogels show light weight (0.138-0.232 g cm-3), large BET surface area (170-370 m2 g-1) and hierarchically porous structure with wide pore size distribution. The large surface area and wide pore size distribution, together with their electro-optical properties, would allow these organic conducting aerogels to be applied in many fields with unexpected performance. © 2010 The Royal Society of Chemistry.

Zhao Y.,Beijing Institute of Technology | Hu C.,Beijing Institute of Technology | Hu Y.,Beijing Institute of Technology | Cheng H.,Beijing Institute of Technology | And 2 more authors.
Angewandte Chemie - International Edition | Year: 2012

Graphene lite: A density of (2.1±0.3) mg cm -3, the lowest to date for a graphene framework architecture, is achieved by preparing an ultralight, N-doped, 3D graphene framework (see photo of a block of the material balancing on a dandelion). Its adsorption capacity for oils and organic solvents is much higher than that of the best carbonaceous sorbents, and it is a promising electrode material for supercapacitors (484 F g -1) and as a metal-free catalyst for the oxygen reduction reaction. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Xu Z.,Massachusetts Institute of Technology | Xue K.,Tsinghua University | Xue K.,Beijing Institute of Technology
Nanotechnology | Year: 2010

Graphene epoxide, with oxygen atoms lining up on pristine graphene sheets, is investigated theoretically here using first-principles calculations. Two distinct phases - metastable clamped and stable unzipped structures - are observed consistent with experimental observations. In the clamped structure, oxygen atoms form a regular lattice on the graphene sheet. In the unzipped phase, an epoxy group breaks the lower sp2 bond and modifies the mechanical and electronic properties of graphene remarkably. The foldable epoxy ring structure reduces its Young's modulus by 42.4%, while leaving the tensile strength almost unchanged. The perturbation of epoxidation on the band structures depends on the density and symmetry of oxidation. These results pave the way for oxidation-based engineering of graphene-related materials. © 2010 IOP Publishing Ltd.

Dong Z.,Key Laboratory of Cluster Science | Jiang C.,Key Laboratory of Cluster Science | Cheng H.,Key Laboratory of Cluster Science | Zhao Y.,Key Laboratory of Cluster Science | And 3 more authors.

Macroscopic graphene fibers with strength comparable to carbon nanotube yarns have been fabricated with a facile dimensionally-confined hydrothermal strategy from low-cost, aqueous graphite oxide suspensions, which is shapable, weavable, and has a density of less than 1/7 conventional carbon fibers. In combination with the easy in situ and post-synthesis functionalization, the highly flexible graphene fibers can be woven into smart textiles. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Chen Y.,Beijing Institute of Technology | He L.,Tsinghua University
Archive for Rational Mechanics and Analysis | Year: 2011

In this work, we are concerned with the regularities of the solutions to the Boltzmann equation with physical collision kernels for the full range of intermolecular repulsive potentials, r-(p-1) with p < 2. We give new and constructive upper and lower bounds for the collision operator in terms of standard weighted fractional Sobolev norms. As an application, we get the global entropy dissipation estimate which is a little stronger than that described by Alexandre et al. (Arch Rational Mech Anal 152(4):327-355, 2000). As another application, we prove the smoothing effects for the strong solutions constructed by Desvillettes and Mouhot (Arch Rational Mech Anal 193(2):227-253, 2009) of the spatially homogeneous Boltzmann equation with "true" hard potential and "true" moderately soft potential. © 2010 Springer-Verlag.

Tan L.-L.,Jilin University | Li H.,Beijing Institute of Technology | Tao Y.,Jilin University | Zhang S.X.-A.,Jilin University | And 3 more authors.

A study was conducted to create pillar[5]arene-based supramolecular organic frameworks for highly selective CO2-capture at ambient conditions. Pillar[5]arene (P5) supramolecular organic framework (SOF) was obtained by the slow addition of H2O into a CH2 Cl2 solution of P5 with stirring. The corresponding scanning electron microscopy (SEM) image showed that the P5-SOF materials were bar-shaped, providing direct insight into the formation of SOFs. Thermogravimetric analysis (TGA) of activated P5-SOF showed a rapid weight loss of solvent molecules up to 270 °C, which corresponded to the liberation of approximately 0.5 acetone molecules trapped inside the P5 cavity followed by a plateau region up to 370 °C where the material began decomposing.

Song X.,Beijing Institute of Technology | Wu T.,Beijing Institute of Technology | Wu T.,University of California at Los Angeles | Jia Y.,Beijing Institute of Technology | Zhu S.-C.,University of California at Los Angeles
Proceedings of the IEEE Computer Society Conference on Computer Vision and Pattern Recognition | Year: 2013

This paper presents a method of learning reconfigurable And-Or Tree (AOT) models discriminatively from weakly annotated data for object detection. To explore the appearance and geometry space of latent structures effectively, we first quantize the image lattice using an over complete set of shape primitives, and then organize them into a directed a cyclic And-Or Graph (AOG) by exploiting their compositional relations. We allow overlaps between child nodes when combining them into a parent node, which is equivalent to introducing an appearance Or-node implicitly for the overlapped portion. The learning of an AOT model consists of three components: (i) Unsupervised sub-category learning (i.e., branches of an object Or-node) with the latent structures in AOG being integrated out. (ii) Weakly supervised part configuration learning (i.e., seeking the globally optimal parse trees in AOG for each sub-category). To search the globally optimal parse tree in AOG efficiently, we propose a dynamic programming (DP) algorithm. (iii) Joint appearance and structural parameters training under latent structural SVM framework. In experiments, our method is tested on PASCAL VOC 2007 and 2010 detection benchmarks of 20 object classes and outperforms comparable state-of-the-art methods. © 2013 IEEE.

Xiong J.,Beijing Institute of Technology | Cao J.,Tsinghua University | Zhang Y.,Tsinghua University
Building and Environment | Year: 2016

The accurate and rapid determination of the emission parameters of semi-volatile organic compounds (SVOCs) from indoor materials is of great importance for estimating and controlling indoor exposure. By virtue of a simplified mass transfer model we derived, a new method called the early stage C-history method, has been developed to measure the key emission parameters: the gas phase SVOC concentration adjacent to the material surface (y0) and the convective mass transfer coefficient (hm). We validate this model using experimental data found in the literature. When compared with established methods, the new method has the following salient features: (1) rapid (the experimental time is reduced from several months to several days); (2) accurate (R2 in the range of 0.92-0.97). Further analysis shows that both features can be further improved if the test system has a smaller chamber wall/air partition coefficient. The new method is also extended to measure the key parameters of SVOCs from sorption materials. This method should prove useful for screening SVOC emission characteristics and for assessing exposure, as well as for chamber and test design. © 2015 Elsevier Ltd.

Yang F.,Beijing Institute of Technology | Yao H.,Tsinghua University | Yao H.,Stanford University
Physical Review Letters | Year: 2012

Resonating valence bond (RVB) states are of crucial importance in our intuitive understanding of quantum spin liquids in 2D. We systematically classify short-range bosonic RVB states into symmetric or nematic spin liquids by examining their flux patterns. We further map short-range bosonic RVB states into projected BCS wave functions, on which we perform large-scale MonteCarlo simulations without the minus sign problem. Our results clearly show that both spin and dimer correlations decay exponentially in all the short-range frustrated (nonbipartite or Z 2) bosonic RVB states we studied, indicating that they are gapped Z 2 quantum spin liquids. Generically, we conjecture that all short-range frustrated bosonic RVB states in 2D have only short-range correlations. © 2012 American Physical Society.

Pei M.,Beijing Institute of Technology | Pei M.,University of California at Los Angeles | Jia Y.,Beijing Institute of Technology | Zhu S.-C.,University of California at Los Angeles
Proceedings of the IEEE International Conference on Computer Vision | Year: 2011

In this paper, we present an event parsing algorithm based on Stochastic Context Sensitive Grammar (SCSG) for understanding events, inferring the goal of agents, and predicting their plausible intended actions. The SCSG represents the hierarchical compositions of events and the temporal relations between the sub-events. The alphabets of the SCSG are atomic actions which are defined by the poses of agents and their interactions with objects in the scene. The temporal relations are used to distinguish events with similar structures, interpolate missing portions of events, and are learned from the training data. In comparison with existing methods, our paper makes the following contributions. i) We define atomic actions by a set of relations based on the fluents of agents and their interactions with objects in the scene. ii) Our algorithm handles events insertion and multi-agent events, keeps all possible interpretations of the video to preserve the ambiguities, and achieves the globally optimal parsing solution in a Bayesian framework; iii) The algorithm infers the goal of the agents and predicts their intents by a top-down process; iv) The algorithm improves the detection of atomic actions by event contexts. We show satisfactory results of event recognition and atomic action detection on the data set we captured which contains 12 event categories in both indoor and outdoor videos. © 2011 IEEE.

Si Z.,University of California at Los Angeles | Pei M.,Beijing Institute of Technology | Yao B.,University of California at Los Angeles | Zhu S.-C.,University of California at Los Angeles
Proceedings of the IEEE International Conference on Computer Vision | Year: 2011

We study the problem of automatically learning event AND-OR grammar from videos of a certain environment, e.g. an office where students conduct daily activities. We propose to learn the event grammar under the information projection and minimum description length principles in a coherent probabilistic framework, without manual supervision about what events happen and when they happen. Firstly a predefined set of unary and binary relations are detected for each video frame: e.g. agent's position, pose and interaction with environment. Then their co-occurrences are clustered into a dictionary of simple and transient atomic actions. Recursively these actions are grouped into longer and complexer events, resulting in a stochastic event grammar. By modeling time constraints of successive events, the learned grammar becomes context-sensitive. We introduce a new dataset of surveillance-style video in office, and present a prototype system for video analysis integrating bottom-up detection, grammatical learning and parsing. On this dataset, the learning algorithm is able to automatically discover important events and construct a stochastic grammar, which can be used to accurately parse newly observed video. The learned grammar can be used as a prior to improve the noisy bottom-up detection of atomic actions. It can also be used to infer semantics of the scene. In general, the event grammar is an efficient way for common knowledge acquisition from video. © 2011 IEEE.

Li Z.,South China University of Technology | Xia Y.,Beijing Institute of Technology | Sun F.,Tsinghua University
IEEE Transactions on Fuzzy Systems | Year: 2014

In this paper, an adaptive fuzzy control is investigated for multilateral teleoperation of two cooperating robotic manipulators that manipulate an object with constrained trajectory/force in the presence of dynamics uncertainties and random network-induced delays. First, the interconnected dynamics that consist of two master robots and cooperating slave robots are formulated. To consider multiple stochastic delays in communication channels, Markov processes are used to model these random network-induced delays. The interconnected dynamics of the teleoperation are divided into a local master/slave position/force subsystem and a stochastic-delayed motion synchronization subsystem. Then, an adaptive fuzzy control strategy, which is based on linear matrix inequalities (LMIs) that combine adaptive update techniques, is proposed to suppress the dynamics uncertainties, the external disturbances, and the multiple stochastic delays in communication channels. The control approach ensures that the defined synchronization errors converge to zero. The stochastic stability in mean square of the closed-loop system is proved using LMIs based on Lyapunov-Krasovskii functional synthesis. The proposed controls are validated using extensive simulation studies. © 1993-2012 IEEE.

Sheng X.,Inner Mongolia Agricultural University | Zhang J.,Beijing Institute of Technology
Colloids and Surfaces A: Physicochemical and Engineering Aspects | Year: 2011

Sustaining an air layer on superhydrophobic surface is known necessary for the applications of the "air layer effect" underwater on basis of previous literatures. However, the air layer becomes unstable when put underwater and even disappears when the hydraulic pressure increases. Thus much attention has been focused on the sustainability of an air layer on a superhydrophobic surface. This article studies the sustainability of the air layer on the surface of a lotus leaf by applying external pressure on the surface, which is a direct method to measure the sustainability of the air layer. It is displayed that the hydraulic pressure is a key factor to sustain an air layer on a superhydrophobic surface. Maintaining a certain amount of hydraulic pressure is necessary to sustain an air layer on a superhydrophobic surface, which may be important for the low drag or friction reduction of a superhydrophobic surface underwater. Therefore, we believe that the micro-designs of superhydrophobic surface which is capable of the "air layer effect" underwater should be connected with hydraulic pressure applied on it. © 2011 Elsevier B.V.

Shen Y.,Beijing Institute of Technology | Shen Y.,Tianshui Normal University
Information Sciences | Year: 2014

In this paper, some useful properties associated with the probabilistic Hausdorff distance are further derived. Especially, we provide a direct proof for an existing important result. Afterwards, the t-norm-based probabilistic decomposable measure is presented, in which the value of measure is characterized by a probability distribution function. Meantime, several examples are constructed to illustrate different notions, and then further properties are examined. Moreover, for a given Menger PM-space, a probabilistic decomposable measure can be induced by means of the resulting probabilistic Hausdorff distance. We prove that this type of measure is (σ)- probabilistic subdecomposable measure for the strongest t-norm. Furthermore, we also prove that the class of all measurable sets forms an algebra. Finally, an outer probabilistic measure is induced by a class of probabilistic decomposable measures and the t-norm. Based on this kind of measure, a Menger probabilistic pseudometric space can be obtained for a non-strict continuous Archimedean t-norm. © 2014 Published by Elsevier Inc.

Lu Y.,Beijing Institute of Technology | Chen M.,Tsinghua University
Acta Materialia | Year: 2012

The crystallization of Ni 90Si 10 drops has been studied using molecular dynamics simulations. The atoms in the surface monolayer of the drop prematurely pack into a long-range ordered structure prior to volume crystallization, whereas diffusion dynamics maintains characteristic liquid-like features until the onset of volume crystallization. This surface crystallization process arises from strong density layering in the direction perpendicular to the drop surface. Due to density oscillations induced by the surface layering a high density state is produced in the drop surface, which is analogous to the effect of high pressure and locally increases the crystallization temperature of the surface layer, ultimately initiating crystallization from the surface. Such a layered structure causes pressure oscillation near the surface that produce a decrease in surface tension with decreasing temperature. The high density crystalline nature of the surface does not thermodynamically favor volume crystallization, which occurs separately via homogeneous nucleation in the interior with further decreasing temperature. © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Tian H.,Beijing Institute of Technology | Tian H.,Tsinghua University | Zhu C.,Tsinghua University | Yang H.,Beijing Institute of Technology | And 2 more authors.
Chemical Communications | Year: 2014

A simple, efficient and environmentally friendly method for iron or boron-catalyzed C-H arylthiation of substituted phenols at room temperature has been developed, and the corresponding diaryl sulfides were prepared in good to excellent yields. The protocol uses readily available 1-(substituted phenylthio)pyrrolidine-2,5-diones as the arylthiation reagents and inexpensive and environmentally friendly FeCl3 or BF3·OEt 2 as the catalyst, moreover no ligands, additives or extrusion of air are required, and the reactions can be performed successfully at room temperature. This journal is © the Partner Organisations 2014.

Zhang J.,Beijing Institute of Technology | Shi P.,University of South Wales | Shi P.,Victoria University of Melbourne | Shi P.,University of South Australia | Xia Y.,Beijing Institute of Technology
IEEE Transactions on Fuzzy Systems | Year: 2010

This paper is devoted to design adaptive sliding-mode controllers for the Takagi-Sugeno (T-S) fuzzy system with mismatched uncertainties and exogenous disturbances. The uncertainties in state matrices are mismatched and norm-bounded, while the exogenous disturbances are assumed to be bounded with an unknown bound, which is estimated by a simple and effective adaptive approach. Both state- and static-output-feedback sliding-mode-control problems are considered. In terms of linear-matrix inequalities (LMIs), both sliding surfaces and sliding-mode controllers can be easily obtained via a convex optimization technique. Finally, two simulation examples and a real experiment are utilized to illustrate the applicability and effectiveness of the design procedures proposed in this paper. © 2006 IEEE.

Zhao Y.,Beijing Institute of Technology | Zhao F.,Beijing Institute of Technology | Wang X.,Beijing Institute of Technology | Xu C.,Beijing Institute of Technology | And 3 more authors.
Angewandte Chemie - International Edition | Year: 2014

The development of new promising metal-free catalysts is of great significance for the electrocatalytic hydrogen evolution reaction (HER). Herein, a rationally assembled three-dimensional (3D) architecture of 1D graphitic carbon nitride (g-C3N4) nanoribbons with 2D graphene sheets has been developed by a one-step hydrothermal method. Because of the multipathway of charge and mass transport, the hierarchically structured g-C3N4 nanoribbon-graphene hybrids lead to a high electrocatalytic ability for HER with a Tafel slope of 54 mV decade-1, a low onset overpotential of 80 mV and overpotential of 207 mV to approach a current of 10mAcm-2, superior to those non-metal materials and well-developed metallic catalysts reported previously. This work presents a great advance for designing and developing highly efficient metal-free catalyst for hydrogen evolution. © 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Xiong J.,Beijing Institute of Technology | Huang S.,Tsinghua University | Zhang Y.,Tsinghua University
PLoS ONE | Year: 2012

The diffusion coefficient (Dm) and material/air partition coefficient (K) are two key parameters characterizing the formaldehyde and volatile organic compounds (VOC) sorption behavior in building materials. By virtue of the sorption process in airtight chamber, this paper proposes a novel method to measure the two key parameters, as well as the convective mass transfer coefficient (hm). Compared to traditional methods, it has the following merits: (1) the K, Dm and hm can be simultaneously obtained, thus is convenient to use; (2) it is time-saving, just one sorption process in airtight chamber is required; (3) the determination of hm is based on the formaldehyde and VOC concentration data in the test chamber rather than the generally used empirical correlations obtained from the heat and mass transfer analogy, thus is more accurate and can be regarded as a significant improvement. The present method is applied to measure the three parameters by treating the experimental data in the literature, and good results are obtained, which validates the effectiveness of the method. Our new method also provides a potential pathway for measuring hm of semi-volatile organic compounds (SVOC) by using that of VOC. © 2012 Xiong et al.

Shen Y.,Tianshui Normal University | Shen Y.,Beijing Institute of Technology
Fuzzy Sets and Systems | Year: 2015

In this paper we investigate, under some suitable conditions and generalized differentiability, the Ulam stability problems of three variants of first order linear fuzzy differential equations, respectively. © 2015 Elsevier B.V.

Guo B.-Z.,CAS Academy of Mathematics and Systems Science | Guo B.-Z.,University of Witwatersrand | Liu J.-J.,Beijing Institute of Technology
International Journal of Robust and Nonlinear Control | Year: 2014

In this paper, we are concerned with the boundary stabilization of a one-dimensional anti-stable Schrödinger equation subject to boundary control matched disturbance. We apply both the sliding mode control (SMC) and the active disturbance rejection control (ADRC) to deal with the disturbance. By the SMC approach, the disturbance is supposed to be bounded only. The existence and uniqueness of the solution for the closed-loop system is proved and the 'reaching condition' is obtained. Considering the SMC usually requires the large control gain and may exhibit chattering behavior, we develop the ADRC to attenuate the disturbance for which the derivative is also supposed to be bounded. Compared with the SMC, the advantage of the ADRC is not only using the continuous control but also giving an online estimation of the disturbance. It is shown that the resulting closed-loop system can reach any arbitrary given vicinity of zero as time goes to infinity and high gain tuning parameter goes to zero. Copyright © 2013 John Wiley & Sons, Ltd.

Ma J.,Beijing Institute of Technology | Ma J.,University of Tokyo | Hashimoto K.,University of Tokyo | Koganezawa T.,Japan Synchrotron Radiation Research Institute | And 2 more authors.
Journal of the American Chemical Society | Year: 2013

Controlling the orientation of highly anisotropic structures of polymers is important because the majority of their mechanical, electronic, and optical properties depend on the orientation of the polymer backbone. In thin films, the polymer chains tend to adopt an orientation parallel to the substrate; therefore, forcing the chains to stand perpendicular to the substrate is challenging. We have developed a simple way to achieve this end-on orientation. We functionalized one end of a poly(3-butylthiophene) (P3BT) chain with a 1H,1H,2H,2H,3H,3H-perfluoroundecyl group, which caused spontaneous self-segregation of the polymer (P3BT-F17) to the surface of the polymer film. In P3BT-F17/polystyrene (PS) blend films, a highly ordered end-on orientation of the conjugated backbone was observed in the surface-segregated layer of the crystalline P3BT-F17. Furthermore, when the film was spin-coated from a mixture of P3BT-F17 and P3BT, the chain orientation of P3BT-F17 at the surface forced the P3BT in the bulk of the film to adopt the end-on orientation because of the high crystallinity of P3BT. The electronic conductivity measured perpendicular to the film surface also reflected the end-on orientation in the bulk, resulting in a more than 30-fold enhancement of the hole mobility. © 2013 American Chemical Society.

Xie X.,Beijing Institute of Technology | Bai H.,Tsinghua University | Shi G.,Tsinghua University | Qu L.,Beijing Institute of Technology
Journal of Materials Chemistry | Year: 2011

Superior strain-responsive graphene sheets with load tolerance have been demonstrated, which have the maximum available strain response of up to 0.85%, four times higher than that for carbon nanotube based actuators. The high strain response plus the capability for loading makes the graphene promising as building blocks for fabricating advanced actuator systems. © The Royal Society of Chemistry.

Wang K.,Beijing Institute of Technology | Wang K.,Energy and Environmental Research Center | Yu S.,Energy and Environmental Research Center | Yu S.,University of Management and Economics | Zhang W.,University of Jinan
Mathematical and Computer Modelling | Year: 2013

Data envelopment analysis (DEA) has recently become a popular approach in measuring the energy and environmental performance at the macro-economy level. A common limitation of several previous studies is that they ignored the undesirable outputs and did not consider the separation of inputs into energy resources and non-energy resources under the DEA framework. Thus, within a joint production framework of considering both desirable and undesirable outputs, as well as energy and non-energy inputs, this study analyzes China's regional total-factor energy and environmental efficiency. This paper utilizes improved DEA models to measure the energy and environmental efficiency of 29 administrative regions of China during the period of 2000-2008. In addition, the DEA window analysis technique is applied to measure the efficiency in cross-sectional and time-varying data. The empirical results show that the east area of China has the highest energy and environmental efficiency, while the efficiency of the west area is worst. All three areas of China have similar trends in the variation of efficiency and in general the energy and environmental efficiency of China slightly increased from 2000 to 2008. The regions of the east area have a more balanced development than the regions of the central area and west area according to energy and environmental efficiency. © 2011 Elsevier Ltd.

Chen Y.,Beijing Institute of Technology | He L.,Tsinghua University
Archive for Rational Mechanics and Analysis | Year: 2012

In this paper, we study the regularity of the solution to the Boltzmann equation with full-range interactions but for the spatially inhomogeneous case. Under the initial regularity assumption on the solution itself, we show that the solution will become immediately smooth for all the variables as long as the time is far way from zero. Our strategy relies upon the new upper and lower bounds for the collision operator established in Chen and He (Arch Ration Mech Anal 201(2):501-548, 2011), a hypo-elliptic estimate for the transport equation and the element energy method. © 2012 Springer-Verlag.

Sheng X.,Inner Mongolia Agricultural University | Zhang J.,Beijing Institute of Technology
Applied Surface Science | Year: 2011

In this article, directional movements of drops on the ratchet-like superhydrophobic surfaces were observed. High-speed CCD images showed the caterpillar-like crawl of a drop on the inclined superhydrophobic surfaces as it rolled along the ridge of ratchet. In contrast, along the opposite direction, the movement of the drop only depended on the end of triple phase contact line while the front of contact line was pinned. The sliding angle (SA) measurements indicated that the ratchet-like superhydrophobic surfaces had directional drop retention traits. Moreover, the reduction of the rise angle ω1, the height d of the ratchet's ridge and the volume V of the drop can greatly enhance the directional difference of drop retention on the ratchet-like superhydrophobic surfaces. Therefore, it was concluded that the superhydrophobicity and the periodic ratchet-like microstructures were the keys to the directional drop sliding at one-dimensional level. We believe that these findings would be helpful to better understand the ratchet-like effect on the superhydrophobic surfaces and guide some novel engineering applications. © 2011 Published by Elsevier B.V. All rights reserved.

Zou Y.,Beijing Institute of Technology | Hu X.,University of California at Berkeley | Ma H.,Beijing Institute of Technology | Li S.E.,Tsinghua University
Journal of Power Sources | Year: 2014

A combined SOC (State Of Charge) and SOH (State Of Health) estimation method over the lifespan of a lithium-ion battery is proposed. First, the SOC dependency of the nominal parameters of a first-order RC (resistor-capacitor) model is determined, and the performance degradation of the nominal model over the battery lifetime is quantified. Second, two Extended Kalman Filters with different time scales are used for combined SOC/SOH monitoring: the SOC is estimated in real-time, and the SOH (the capacity and internal ohmic resistance) is updated offline. The time scale of the SOH estimator is determined based on model accuracy deterioration. The SOC and SOH estimation results are demonstrated by using large amounts of testing data over the battery lifetime. © 2014 The Authors.

Yang H.,Beijing Institute of Technology | Yang H.,Yanshan University | Xia Y.,Beijing Institute of Technology | Shi P.,Beijing Institute of Technology | And 2 more authors.
IEEE Transactions on Automatic Control | Year: 2012

This note generalizes the stability analysis for a high frequency networked control system. The high-frequency networked control system is described by a delta operator system with a high frequency constraint. Stability conditions are given for the high frequency delta operator system. Furthermore, by developing the generalized Kalman-Yakubovic-Popov lemma, improved stability conditions are also presented in terms of linear matrix inequalities. Some experiment results are presented to illustrate the effectiveness of the developed techniques. © 2012 IEEE.

Li H.,Tsinghua University | Yang H.,Yanshan University | Sun F.,Tsinghua University | Xia Y.,Beijing Institute of Technology
Automatica | Year: 2013

This paper presents a new stabilization method for networked control systems (NCSs). An improved stability criterion dependent on both time delay bound and packet loss bound is derived and the corresponding stabilizing controller design technique is also provided. The merit of the proposed method lies in its much less conservatism, which is achieved by explicitly considering NCSs physical properties and by guaranteeing the deceasement of Lyapunov functional at each control signal updating step rather than at each sampling step, which is largely ignored in the existing literature. Illustrative examples are provided to show the advantage and effectiveness of the developed results. © 2013 Elsevier Ltd. All rights reserved.

Li Y.,Beijing Institute of Technology | Hu Y.,Beijing Institute of Technology | Zhao Y.,Beijing Institute of Technology | Shi G.,Tsinghua University | And 3 more authors.

Green-luminescent functional graphene quantum dots (GQDs) are prepared by a facile electrochemical approach. The GQDs are rich in oxygen-containing functional groups and soluble in aqueous or organic media, facilitating further functionalization and various applications. Polymer photovoltaic devices using GQDs as a new type of electron-acceptor material are also demonstrated. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Patent
Tsinghua University and Beijing Institute of Technology | Date: 2014-07-31

An inter-domain virtual network mapping method, an inter-domain virtual network and an inter-domain virtual network mapping system are provided. The method comprises: receiving an inter-domain virtual network request; obtaining a latest physical network architecture information of each of N network domains; calculating an optimized mapping solution according to the latest physical network architecture information of the N network domains to divide an inter-domain virtual network into N virtual sub-networks, each virtual sub-network corresponding to one of the N network domains; sending each virtual sub-network to a corresponding network domain thereof and performing a mapping in each network domain; initializing SUM=0, and updating SUM according to a result of the mapping in each network domain; determining whether SUM is equal to N; if yes, instructing each network domain to distribute a physical network source for the inter-domain virtual network request; and if no, instructing each network domain to undo any procedure.

Patent
Beijing Institute of Technology, Beijing Information Science and Technical University | Date: 2013-09-02

The present invention provides an angular rate gyro in which a bell-shaped vibrator having nonuniform thickness, axially symmetric and multi curved surface combined structural features is used as a sensitive element. The angular rate gyro is composed of the bell-shaped vibrator, a vibrator fixing shaft, a vibrator base, an airtight hood, a housing and a circuit system. The bell-shaped vibrator includes a bell shoulder having a hemispheric shell structure, a bell waist having a cylindrical shell structure and a bell lip having a hyperboloidal shell structure. The bell-shaped vibrator, the base and a central shaft are mechanically and fixedly connected together to be formed into an integral core having sensitive gyratory effect. A circuit system is used to control vibration forms of the bell-shaped vibrator, perform signal processing and solve the applied angular rate.

Wang J.,Tsinghua University | Zhang L.,Tsinghua University | Zhang L.,Beijing Institute of Technology | Zhang D.,Tsinghua University | Li K.,Tsinghua University
IEEE Transactions on Intelligent Transportation Systems | Year: 2013

A prototype of a longitudinal driving-assistance system, which is adaptive to driver behavior, is developed. Its functions include adaptive cruise control and forward collision warning/avoidance. The research data came from driver car-following tests in real traffic environments. Based on the data analysis, a driver model imitating the driver's operation is established to generate the desired throttle depression and braking pressure. Algorithms for collision warning and automatic braking activation are designed based on the driver's pedal deflection timing during approach (gap closing). A self-learning algorithm for driver characteristics is proposed based on the recursive least-square method with a forgetting factor. Using this algorithm, the parameters of the driver model can be identified from the data in the manual operation phase, and the identification result is applied during the automatic control phase in real time. A test bed with an electronic throttle and an electrohydraulic brake actuator is developed for system validation. The experimental results show that the self-learning algorithm is effective and that the system can, to some extent, adapt to individual characteristics. © 2000-2011 IEEE.

Kong Y.,Northeastern University | Jia Y.,Beijing Institute of Technology | Fu Y.,Northeastern University
IEEE Transactions on Pattern Analysis and Machine Intelligence | Year: 2014

This paper addresses the problem of recognizing human interactions from videos. We propose a novel approach that recognizes human interactions by the learned high-level descriptions, interactive phrases. Interactive phrases describe motion relationships between interacting people. These phrases naturally exploit human knowledge and allow us to construct a more descriptive model for recognizing human interactions. We propose a discriminative model to encode interactive phrases based on the latent SVM formulation. Interactive phrases are treated as latent variables and are used as mid-level features. To complement manually specified interactive phrases, we also discover data-driven phrases from data in order to find potentially useful and discriminative phrases for differentiating human interactions. An information-theoretic approach is employed to learn the data-driven phrases. The interdependencies between interactive phrases are explicitly captured in the model to deal with motion ambiguity and partial occlusion in the interactions. We evaluate our method on the BIT-Interaction data set, UT-Interaction data set, and Collective Activity data set. Experimental results show that our approach achieves superior performance over previous approaches. © 1979-2012 IEEE.

Nan G.,Harbin Institute of Technology | Li Z.,Harbin Institute of Technology | Li Z.,Beijing Institute of Technology
Physical Chemistry Chemical Physics | Year: 2012

The influence of lattice dynamics on carrier mobility has received much attention in organic crystalline semiconductors, because the molecular components are held together by weak interactions and the transfer integrals between neighboring molecular orbitals are extremely sensitive to small nuclear displacements. Recently, it has been shown that the dynamic disorder has little effect on hole mobility in the ab plane of pentacene, but a reasonable explanation is absent for such a puzzle. To better understand the effect of lattice vibrations on carrier transport, a further study is required for other organic materials. In this work, a mixed molecular dynamic and quantum-chemical methodology is used to assess the effect of nuclear dynamics on hole mobility in the dianthra[2,3-b:2′,3′-f]-thieno[3,2-b]thiophene (DATT) crystals which exhibit high air stability with the hole mobility as large as that in rubrene-based devices. It is found that the lattice vibrations lead to an increasing encumbrance for hole transport in the ab plane of the DATT crystals as the temperature increases. By comparing the crystal structures of DATT and pentacene, the reduced hole mobility in DATT is attributed to the unsymmetric arrays of nearest-neighboring molecular dimers in the ab plane, because the electronic coupling exhibits unbalanced thermal fluctuations for the nearest-neighboring dimers which then induces a stronger oscillation for carriers along the directions with asymmetric packing. To further relate the dynamic disorder with hole transport, the variations of anisotropic mobilities are also analyzed. As a result, the negligible effect of lattice dynamics on the hole mobility in pentacene is explained by the centrosymmetric molecular packing of the nearest-neighboring molecular pairs in the ab plane. © 2012 the Owner Societies.

Lu Y.J.,University of Duisburg - Essen | Lu Y.J.,Beijing Institute of Technology | Entel P.,University of Duisburg - Essen
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

We study the thermophysical properties and structure of liquid Ni-Si alloys using molecular dynamics simulations. The liquid Ni-5% and 10%Si alloys crystallize to form the face-centered cubic (Ni) at 900 and 850 K, respectively, and the glass transitions take place in Ni-20% and 25%Si alloys at about 700 K. The temperature-dependent self-diffusion coefficients and viscosities exhibit more pronounced non-Arrhenius behavior with the increase of Si content before phase transitions, indicating the enhanced glass-forming ability. These appearances of thermodynamic properties and phase transitions are found to closely relate to the medium-range order clusters with the defective face-centered cubic structure characterized by both local translational and orientational order. This locally ordered structure tends to be destroyed by the addition of more Si atoms, resulting in a delay of nucleation and even glass transition instead. © 2011 American Physical Society.

Yang J.,Hebei Medical University | Liang S.,Beijing Institute of Technology | Zhang Y.,Hebei Medical University
PLoS ONE | Year: 2011

This paper is concerned with the existence of travlelling waves to a SIR epidemic model with nonlinear incidence rate, spatial diffusion and time delay. By analyzing the corresponding characteristic equations, the local stability of a disease-free steady state and an endemic steady state to this system under homogeneous Neumann boundary conditions is discussed. By using the cross iteration method and the Schauder's fixed point theorem, we reduce the existence of travelling waves to the existence of a pair of upper-lower solutions. By constructing a pair of upper-lower solutions, we derive the existence of a travelling wave connecting the disease-free steady state and the endemic steady state. Numerical simulations are carried out to illustrate the main results. © 2011 Yang et al.

Xin B.,Beijing Institute of Technology | Chen B.,Beijing Institute of Technology | Duan N.,Chinese Research Academy of Environmental Sciences | Zhou C.,Chinese Research Academy of Environmental Sciences
Bioresource Technology | Year: 2011

Extraction of manganese from electrolytic manganese residues using bioleaching was investigated in this paper. The maximum extraction efficiency of Mn was 93% by sulfur-oxidizing bacteria at 4.0g/l sulfur after bioleaching of 9days, while the maximum extraction efficiency of Mn was 81% by pyrite-leaching bacteria at 4.0g/l pyrite. The series bioleaching first by sulfur-oxidizing bacteria and followed by pyrite-leaching bacteria evidently promoted the extraction of manganese, witnessing the maximum extraction efficiency of 98.1%. In the case of sulfur-oxidizing bacteria, the strong dissolution of bio-generated sulfuric acid resulted in extraction of soluble Mn2+, while both the Fe2+ catalyzed reduction of Mn4+ and weak acidic dissolution of Mn2+ accounted for the extraction of manganese with pyrite-leaching bacteria. The chemical simulation of bioleaching process further confirmed that the acid dissolution of Mn2+ and Fe2+ catalyzed reduction of Mn4+ were the bioleaching mechanisms involved for Mn extraction from electrolytic manganese residues. © 2010 Elsevier Ltd.

Nan G.,Harbin Institute of Technology | Li Z.,Harbin Institute of Technology | Li Z.,Beijing Institute of Technology
Organic Electronics: physics, materials, applications | Year: 2012

The organic semiconductor dibenzo-tetrathiafulvalene (DBTTF) has presented different polymorphs in solid packing, but the structure-property relationship is little clarified in the literature which is important for the design of high-performance organic semiconductors. In this study, the charge transport in DBTTF crystals for the α phase and β phase is investigated from the first-principles calculations and the Marcus charge transfer theory. The one-, two- and three-dimensional mobilities are obtained simultaneously from a set of identical trajectories with an improved random walk technique. It is found that the α-phase crystal presents a smaller three-dimensional mobility than that in the β-phase crystal although the mobility is much large along the c axis in the α-phase crystal. This is attributed to that the electronic couplings are mainly confined within the c axis for the α-DBTTF while the electronic couplings are more uniform in the three-dimensional space for the β-DBTTF which thus provides more transport pathways for the charge transport. As a result, the β-DBTTF may have a larger potential for practical applications in organic electronics. © 2012 Elsevier B.V. All rights reserved.

Liu X.N.,University of Arkansas at Little Rock | Liu X.N.,Beijing Institute of Technology | Hu G.K.,Beijing Institute of Technology | Huang G.L.,University of Arkansas at Little Rock | Sun C.T.,Purdue University
Applied Physics Letters | Year: 2011

In this letter, an elastic metamaterial which exhibits simultaneously negative effective mass density and bulk modulus is presented with a single unit structure made of solid materials. The double-negative properties are achieved through a chiral microstructure that is capable of producing simultaneous translational and rotational resonances. The negative effective mass density and effective bulk modulus are numerically determined and confirmed by the analysis of wave propagation. The left-handed wave propagation property of this metamaterial is demonstrated by the negative refraction of acoustic waves. © 2011 American Institute of Physics.

Su Y.,Beijing Institute of Technology | Liu N.,Beijing Institute of Technology | Weng G.J.,Rutgers University
Acta Materialia | Year: 2015

In this study we take the view that frequency dependence of ferroelectric hysteresis is a result of direct competition between the speed of polarization evolution and the speed of external loading. We used the Ginzburg-Landau kinetic equation to evaluate the evolution of polarization vectors. We also devised a polycrystal model with a core-shell grain configuration to reflect the effect of the grain-boundary (GB) affected zone. The phase-field results showed that the coercive field tended to increase with frequency, but remnant polarization increased only slightly while the dielectric constant and piezoelectric constant d33, tended to decrease. We also found that, while both hysteresis and butterfly loops exhibited the familiar sharp tails at low frequencies, the tails disappeared and the loops became elliptic- and kidney-shaped, respectively, at high frequencies. The calculated low-frequency phenomena are widely supported by experiments, but the high-frequency ones are not commonly found in the literature. We substantiated both types of findings with details of the underlying domain dynamics. They clearly showed a complete 180° polarization reversal at low frequencies, but stopped mostly at 90° at high frequencies. We also examined the influence of the kinetic coefficient and the loading amplitude, and found that, as either increases, the elliptic and kidney shapes of the loops would occur at a higher frequency. The calculated grain-size effects indicated that the remnant polarization, dielectric constant, and d33 all decreased with decreasing grain size. This is again widely supported by experiments. But we also found that the grain-size effect of coercive field is more complicated. It may increase or decrease, and it is the magnitude of spontaneous polarization of the GB affected zone that determines its outcome. © 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Xia Y.,Beijing Institute of Technology | Zhu Z.,Beijing Institute of Technology | Fu M.,Beijing Institute of Technology | Wang S.,CAS Institute of Automation
IEEE Transactions on Industrial Electronics | Year: 2011

The problem of attitude control for a spacecraft model that is nonlinear in dynamics with inertia uncertainty and external disturbance has been investigated. Adaptive law and extended state observer are applied to estimate the disturbance, by which sliding-mode controllers are designed to combine the two approaches in order to force the state variables of the closed-loop system to converge to the reference attitude states. Also, simulation results are presented to illustrate the effectiveness of the control strategies. © 2011 IEEE.

Yue F.,Beijing Institute of Technology | Zuo W.,Harbin Institute of Technology
Information Sciences | Year: 2014

A typical palmprint identification system identifies a query palmprint by matching it with the templates in the database and comparing the similarity score with a pre-defined threshold. However, continual database expansion would make conventional brute force search method inefficient for large-scale palmprint identification. In this paper, we propose a consistent orientation pattern (COP) hashing method to enforce fast search. Using the orientation and response features extracted by steerable filter, we first give an analysis on the consistency of orientation features, and then introduce a method to construct COP using the consistent features. Because the COP is very stable across the samples of the same subject, the COP hashing method can find the target template quickly and thus can lead to early termination of the searching process. Experiments have been carried out on several real and synthetic databases, and the results show that the COP hashing method can accelerate the identification process by more than an order of magnitude, and can achieve comparable identification accuracy while compared with the state-of-the-art approaches. © 2013 Elsevier Inc. All rights reserved.

Liu F.,Beijing Institute of Technology | Antoniou M.,University of Birmingham | Zeng Z.,University of Birmingham | Cherniakov M.,University of Birmingham
IEEE Transactions on Geoscience and Remote Sensing | Year: 2013

This paper presents proof-of-concept methods and results on a passive synthetic aperture radar for surface change monitoring. The bistatic topology comprises navigation satellites (such as Global Positioning System, GLObal Navigation Satellite System (GLONASS), Galileo, or Beidou) as transmitters of opportunity and a fixed receiver on the ground. Surface monitoring is to be provided through coherent change detection. An experimental test bed built to confirm the concept of the system is described, and the appropriate experimental program is presented. Preliminary signal processing algorithms for change detection are derived. Experimentally measured changes are compared to the theoretical predictions, and the obtained results are discussed. © 1980-2012 IEEE.

Chen B.,Beijing Institute of Technology | Zhong H.,Beijing Institute of Technology | Zhang W.,North China Electrical Power University | Tan Z.,North China Electrical Power University | And 6 more authors.
Advanced Functional Materials | Year: 2012

The off-stoichiometry effects and gram-scale production of luminescent CuInS 2-based semiconductor nanocrystals, as well as their application in electroluminescence devices are reported. The crystal structures and optical properties of CuInS 2 nanocrystals can be significantly influenced by controlling their [Cu]/[In] molar ratio. A simple model adapted from the bulk materials is proposed to explain their off-stoichiometry effects. Highly emissive and color-tunable CuInS 2-based NCs are prepared by a combination of [Cu]/[In] molar ratio optimization, ZnS shell coating, and CuInS 2-ZnS alloying. The method is simple, hassle-free, and easily scalable to fabricate tens of grams of nanocrystal powders with photoluminescence quantum yields up to around 65%. Furthermore, the performance of high-quality CuInS 2-based NCs in electroluminescence devices is examined. These devices have lower turn-on voltages of around 5 V, brighter luminance up to approximately 2100 cd m -2 and improved injection efficiency of around 0.3 lm W -1 (at 100 cd m -2) in comparison to recent reports. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Antoniou M.,University of Birmingham | Zeng Z.,University of Birmingham | Feifeng L.,Beijing Institute of Technology | Cherniakov M.,University of Birmingham
IEEE Geoscience and Remote Sensing Letters | Year: 2012

This letter demonstrates the feasibility of space-surface bistatic synthetic aperture radar using navigation satellites as transmitters of opportunity and a fixed ground-based receiver. Experiments with real satellite signals are described, and the obtained imagery is presented and discussed. © 2012 IEEE.

Nan G.,Harbin Institute of Technology | Li Z.,Beijing Institute of Technology
Journal of Materials Chemistry C | Year: 2014

[1]Benzothieno[3,2-b][1]benzothiophene derivatives with high air stability have recently displayed excellent charge transport properties in field-effect devices. In particular, the average charge mobilities can reach as high as 16.4 ± 6.1 cm2 V-1 s-1 in devices with a high quality semiconductor/insulator interface, which is comparable to the performance for a rubrene single-crystal device. To better understand these excellent charge transport properties, a multiscale approach combining molecular dynamics and quantum-chemical calculations was used in this work to assess the structure-property relationship for three of the [1]benzothieno[3,2-b][1] benzothiophene derivatives with different alkyl side chains. It is indicated that the extremely large electronic couplings along the a-axis direction are responsible for the excellent charge transport properties in these systems. While the molecular packings are centrosymmetrical in the ab plane, the lattice vibrations were found to hamper the charge transport in optimized crystal structures at the COMPASS molecular mechanics level which is opposite to the recent findings that the lattice dynamics should have a negligible effect on the charge mobility in the centrosymmetrical plane. The reason for such behavior was analyzed and the predicted order of the overall charge mobilities for the studied systems was consistent with the experiments. Meanwhile, how well the force field reproduces the observed crystal structures and dimer intermolecular separations and orientations is discussed in this work. In addition, it is shown that the present charge transport model can not only predict the magnitude of the charge mobility but also the measured "band-like" charge transport in experiments, so the nuclear tunneling effect is very important for charge transport in organic semiconductors as was demonstrated in recent theoretical work. © 2014 The Royal Society of Chemistry.

News Article | October 31, 2016
Site: phys.org

This was clearly on display in a novel experiment at the National Institute of Standards and Technology (NIST) that was performed by a multi-institutional collaboration including UCLA, NIST and the Beijing Institute of Technology in China. Topological insulators are a new class of materials that were discovered less than a decade ago after earlier theoretical work, recognized in the 2016 Nobel Prize in physics, predicted they could exist. The materials are electrical insulators on the inside and they conduct electricity on the outer surface. They are exciting to computer designers because electric current travels along them without shedding heat, meaning components made from them could reduce the high heat production that plagues modern computers. They also might be harnessed one day in quantum computers, which would exploit less familiar properties of electrons, such as their spin, to make calculations in entirely new ways. When TIs conduct electricity, all of the electrons flowing in one direction have the same spin, a useful property that quantum computer designers could harness. The special properties that make TIs so exciting for technologists are usually observed only at very low temperature, typically requiring liquid helium to cool the materials. Not only does this demand for extreme cold make TIs unlikely to find use in electronics until this problem is overcome, but it also makes it difficult to study them in the first place. Furthermore, making TIs magnetic is key to developing exciting new computing devices with them. But even getting them to the point where they can be magnetized is a laborious process. Two ways to do this have been to infuse, or "dope," the TI with a small amount of magnetic metal and/or to stack thin layers of TI between alternating layers of a magnetic material known as a ferromagnet. However, increasing the doping to push the temperature higher disrupts the TI properties, while the alternate layers' more powerful magnetism can overwhelm the TIs, making them hard to study. To get around these problems, UCLA scientists tried a different substance for the alternating layers: an antiferromagnet. Unlike the permanent magnets on your fridge, whose atoms all have north poles that point in the same direction, the multilayered antiferromagnetic (AFM) materials had north poles pointing one way in one layer, and the opposite way in the next layer. Because these layers' magnetism cancels each other out, the overall AFM doesn't have net magnetism—but a single layer of its molecules does. It was the outermost layer of the AFM that the UCLA team hoped to exploit. Fortunately, they found that the outermost layer's influence magnetizes the TI, but without the overwhelming force that the previously used magnetic materials would bring. And they found that the new approach allowed the TIs to become magnetic and demonstrate all of the TI's appealing hallmarks at temperatures far above 77 Kelvin—still too cold for use as consumer electronics components, but warm enough that scientists can use nitrogen to cool them instead. "It makes them far easier to study," says Alex Grutter of the NIST Center for Neutron Research, which partnered with the UCLA scientists to clarify the interactions between the overall material's layers as well as its spin structure. "Not only can we explore TIs' properties more easily, but we're excited because to a physicist, finding one way to increase the operational temperature this dramatically suggests there might be other accessible ways to increase it again. Suddenly, room temperature TIs don't look as far out of reach." Explore further: A new class of materials could realize quantum computers More information: Q.L. He, X. Kou, A.J. Grutter, G. Yin, L. Pan, X. Che, Y. Liu, T. Nie, B. Zhang, S.M. Disseler, B.J. Kirby, W. Ratcliff II, Q. Shao, K. Murata, X. Zhu, G. Yu, Y. Fan, M. Montazeri, X. Han, J.A. Borchers and K.L. Wang. Tailoring Exchange Couplings in Magnetic Topological Insulator/Antiferromagnet Heterostructures. Nature Materials, October 31, 2016. DOI: 10.1038/nmat4783

News Article | October 31, 2016

Fashion is changing in the avant-garde world of next-generation computer component materials. Traditional semiconductors like silicon are releasing their last new lines. Exotic materials called topological insulators (TIs) are on their way in. And when it comes to cool, nitrogen is the new helium. This was clearly on display in a novel experiment at the National Institute of Standards and Technology (NIST) that was performed by a multi-institutional collaboration including UCLA, NIST and the Beijing Institute of Technology in China. Topological insulators are a new class of materials that were discovered less than a decade ago after earlier theoretical work, recognized in the 2016 Nobel Prize in physics, predicted they could exist. The materials are electrical insulators on the inside and they conduct electricity on the outer surface. They are exciting to computer designers because electric current travels along them without shedding heat, meaning components made from them could reduce the high heat production that plagues modern computers. They also might be harnessed one day in quantum computers, which would exploit less familiar properties of electrons, such as their spin, to make calculations in entirely new ways. When TIs conduct electricity, all of the electrons flowing in one direction have the same spin, a useful property that quantum computer designers could harness. The special properties that make TIs so exciting for technologists are usually observed only at very low temperature, typically requiring liquid helium to cool the materials. Not only does this demand for extreme cold make TIs unlikely to find use in electronics until this problem is overcome, but it also makes it difficult to study them in the first place. Furthermore, making TIs magnetic is key to developing exciting new computing devices with them. But even getting them to the point where they can be magnetized is a laborious process. Two ways to do this have been to infuse, or "dope," the TI with a small amount of magnetic metal and/or to stack thin layers of TI between alternating layers of a magnetic material known as a ferromagnet. However, increasing the doping to push the temperature higher disrupts the TI properties, while the alternate layers' more powerful magnetism can overwhelm the TIs, making them hard to study. To get around these problems, UCLA scientists tried a different substance for the alternating layers: an antiferromagnet. Unlike the permanent magnets on your fridge, whose atoms all have north poles that point in the same direction, the multilayered antiferromagnetic (AFM) materials had north poles pointing one way in one layer, and the opposite way in the next layer. Because these layers' magnetism cancels each other out, the overall AFM doesn't have net magnetism--but a single layer of its molecules does. It was the outermost layer of the AFM that the UCLA team hoped to exploit. Fortunately, they found that the outermost layer's influence magnetizes the TI, but without the overwhelming force that the previously used magnetic materials would bring. And they found that the new approach allowed the TIs to become magnetic and demonstrate all of the TI's appealing hallmarks at temperatures far above 77 Kelvin--still too cold for use as consumer electronics components, but warm enough that scientists can use nitrogen to cool them instead. "It makes them far easier to study," says Alex Grutter of the NIST Center for Neutron Research, which partnered with the UCLA scientists to clarify the interactions between the overall material's layers as well as its spin structure. "Not only can we explore TIs' properties more easily, but we're excited because to a physicist, finding one way to increase the operational temperature this dramatically suggests there might be other accessible ways to increase it again. Suddenly, room temperature TIs don't look as far out of reach." Paper: Q.L. He, X. Kou, A.J. Grutter, G. Yin, L. Pan, X. Che, Y. Liu, T. Nie, B. Zhang, S.M. Disseler, B.J. Kirby, W. Ratcliff II, Q. Shao, K. Murata, X. Zhu, G. Yu, Y. Fan, M. Montazeri, X. Han, J.A. Borchers and K.L. Wang. Tailoring Exchange Couplings in Magnetic Topological Insulator/Antiferromagnet Heterostructures. Nature Materials, October 31, 2016. DOI: 10.1038/nmat4783

News Article | November 1, 2016
Site: www.sciencedaily.com

Fashion is changing in the avant-garde world of next-generation computer component materials. Traditional semiconductors like silicon are releasing their last new lines. Exotic materials called topological insulators (TIs) are on their way in. And when it comes to cool, nitrogen is the new helium. This was clearly on display in a novel experiment at the National Institute of Standards and Technology (NIST) that was performed by a multi-institutional collaboration including UCLA, NIST and the Beijing Institute of Technology in China. Topological insulators are a new class of materials that were discovered less than a decade ago after earlier theoretical work, recognized in the 2016 Nobel Prize in physics, predicted they could exist. The materials are electrical insulators on the inside and they conduct electricity on the outer surface. They are exciting to computer designers because electric current travels along them without shedding heat, meaning components made from them could reduce the high heat production that plagues modern computers. They also might be harnessed one day in quantum computers, which would exploit less familiar properties of electrons, such as their spin, to make calculations in entirely new ways. When TIs conduct electricity, all of the electrons flowing in one direction have the same spin, a useful property that quantum computer designers could harness. The special properties that make TIs so exciting for technologists are usually observed only at very low temperature, typically requiring liquid helium to cool the materials. Not only does this demand for extreme cold make TIs unlikely to find use in electronics until this problem is overcome, but it also makes it difficult to study them in the first place. Furthermore, making TIs magnetic is key to developing exciting new computing devices with them. But even getting them to the point where they can be magnetized is a laborious process. Two ways to do this have been to infuse, or "dope," the TI with a small amount of magnetic metal and/or to stack thin layers of TI between alternating layers of a magnetic material known as a ferromagnet. However, increasing the doping to push the temperature higher disrupts the TI properties, while the alternate layers' more powerful magnetism can overwhelm the TIs, making them hard to study. To get around these problems, UCLA scientists tried a different substance for the alternating layers: an antiferromagnet. Unlike the permanent magnets on your fridge, whose atoms all have north poles that point in the same direction, the multilayered antiferromagnetic (AFM) materials had north poles pointing one way in one layer, and the opposite way in the next layer. Because these layers' magnetism cancels each other out, the overall AFM doesn't have net magnetism -- but a single layer of its molecules does. It was the outermost layer of the AFM that the UCLA team hoped to exploit. Fortunately, they found that the outermost layer's influence magnetizes the TI, but without the overwhelming force that the previously used magnetic materials would bring. And they found that the new approach allowed the TIs to become magnetic and demonstrate all of the TI's appealing hallmarks at temperatures far above 77 Kelvin -- still too cold for use as consumer electronics components, but warm enough that scientists can use nitrogen to cool them instead. "It makes them far easier to study," says Alex Grutter of the NIST Center for Neutron Research, which partnered with the UCLA scientists to clarify the interactions between the overall material's layers as well as its spin structure. "Not only can we explore TIs' properties more easily, but we're excited because to a physicist, finding one way to increase the operational temperature this dramatically suggests there might be other accessible ways to increase it again. Suddenly, room temperature TIs don't look as far out of reach."

News Article | August 26, 2014
Site: www.techtimes.com

Chinese researchers say it's possible they may one day have high-tech submarines capable of a journey across the width of the Pacific Ocean in just under two hours. Scientists from Harbin Institute of Technology say they've made great steps in updating a Cold War-era Soviet military technology that uses a phenomenon known as supercavitation that can allow submersible craft to travel at high speeds. In supercavitation, and entire submerged vessel would be enveloped in a surrounding air bubble of gases emitted from the sub's nose, removing friction with the water and allowing it to reach speeds of thousands of miles an hour. At those speeds a trip from Shanghai across the Pacific to San Francisco might take less that two hours, the researchers said. The Russians reportedly used supercavitation to create torpedoes that, once launched, reached speeds of around 230 mph. "We are very excited by [the technology's] potential," lead researcher Li Fengchen, a professor of fluid machinery and engineering, told the South China Morning Post. One hurdle, the researchers acknowledge, is the difficulty of steering a vessel once it is surround by its air bubble and traveling at high speed. The Chinese researchers say one solution would be for the vessel to coat itself in a liquid while inside the bubble, forming a membrane that, if manipulated, would control the amount of friction and drag on certain parts of the vessel, allowing it to be steered. "By combining liquid-membrane technology with supercavitation, we can significantly reduce the launch challenges and make cruising easier," Li says. Supercavitation has attracted research by the U.S. military, with reports the Defense Advanced Research Projects Agency, or DARPA, was once working on the technology. Some experts, however, have expressed doubts as to the feasibility of creating such supecavitation vessels. "The size of the bubble is difficult to control, and the vessel is almost impossible to steer," says Wang Guoyu, who heads the Fluid Mechanics Laboratory at the Beijing Institute of Technology. If any portion of the sub were to breach its bubble, the whole bubble would collapse from the density difference of the surrounding water, he says. How that could be avoided is just the kind of question that the Harbin researchers have been keeping mum on, which Wang says is no surprise given the technology's obvious military applications. "The primary drive [behind the research] still comes from the military, so most research projects are shrouded in secrecy," he said.

Zhu Y.,Beijing Institute of Technology | Li C.,Zhengzhou University of Light Industry | Cao C.,Beijing Institute of Technology

A strongly coupled mesoporous SnO2-graphene hybrid has been prepared via direct nucleation, growth, and anchoring of a SnO2 nanocrystal on graphene substrate under microwave irradiation followed by heat-treatment. Investigations reveal that the well-dispersed SnO2 nanocrystals with a uniform particle size of 3-5 nm are homogeneously distributed on the surface of graphene through strong chemical attachment and electrical interaction. The formed structure exhibits a high specific surface area (280.7 m2 g-1) and an ideal synergistic effect, which can provide improved activity and durability for the electrochemical and photocatalytic reaction. Lithium-ion battery performance and photocatalytic activity of the resultant mesoporous SnO2-graphene hybrid are thoroughly investigated. In comparison to bare SnO2 nanoparticles, the hybrid shows substantial enhancement in electrochemical lithium storage properties and photocatalytic hydrogen evolution. More strikingly, the as-synthesized SnO2-graphene hybrid anode could deliver initial discharge and charge capacities of 2445.7 and 1329.4 mAh g-1 with a high initial Coulombic efficiency (54.4%), as well as an excellent cycling stability. © The Royal Society of Chemistry 2013.

Mahmoud M.S.,King Fahd University of Petroleum and Minerals | Xia Y.,Beijing Institute of Technology
Asian Journal of Control | Year: 2012

The objective of this paper is to propose a generalized approach to stabilization of systems which are composed of linear time-delay subsystems coupled by linear time-varying interconnections. The proposed algorithms, which are formulated within the convex optimization framework, provide decentralized solutions to the problem of delay-dependent asymptotic stability with strict dissipativity. It is established that the new methodology can reproduce earlier results on passivity, positive realness and disturbance attenuation. Then a decentralized structure of dissipative state-feedback controllers is designed to render the closed-loop interconnected system delay-dependent asymptotically stable with strict dissipativity. Numerical examples are presented to illustrate the applicability of the design method. © 2011 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society.

Chen S.-L.,Chung Yuan Christian University | Wang J.-G.,Beijing Institute of Technology
Electronics Letters | Year: 2013

An efficient VLSI architecture of a lossless ECG encoding circuit is proposed for wireless healthcare monitoring applications. To reduce the transmission and storage data, a novel lossless compression algorithm is proposed for ECG signal compression. It consists of a novel adaptive rending predictor and a novel two-stage entropy encoder based on two Huffman coding tables. The proposed lossless ECG encoder design was implemented using only simple arithmetic units. To improve the performance, the proposed ECG encoder was designed by pipeline technology and implemented the two-stage entropy encoder by the architecture of a look-up table. The VLSI architecture of this work contains 3.55 K gate counts and its core area is 45987 μm2 synthesised by a 0.18 μm CMOS process. It can operate at 100 MHz processing rate with only 36.4 μW. The data compression rate reaches an average value 2.43 for the MIT-BIH Arrhythmia Database. Compared with the previous low-complexity and high performance techniques, this work achieves lower hardware cost, lower power consumption, and a better compression rate than other lossless ECG encoder designs. © The Institution of Engineering and Technology 2013.

Kim S.,Kyung Hee University | Yoon P.H.,Kyung Hee University | Yoon P.H.,University of Maryland University College | Choe G.S.,Kyung Hee University | Wang L.,Beijing Institute of Technology
Astrophysical Journal | Year: 2015

This paper presents a theory for the asymptotically steady-state solar wind electron velocity distribution function (VDF) in a local equilibrium with plasma wave turbulence. By treating the local solar wind electron VDF as superposition of three populationsthe low-energy Maxwellian core electrons with an energy range of tens of eV, the intermediate ∼103105 eV energy-range halo electrons, and the high ∼103105 eV energy-range superhalo electronsthe present paper puts forth a model in which the halo electrons are in dynamical steady state with the pervasive whistler fluctuations, while the superhalo electrons maintain dynamical steady-state equilibrium with the Langmuir fluctuations, known as the quasi-thermal noise. Customary models of the solar wind electrons include only the Maxwellian core and the halo (plus highly field-aligned strahl). While the present paper does not consider the strahl population in the discussion, the highly energetic superhalo component, which is observed to be present in all solar conditions, is explicitly taken into account as part of the total solar wind electron model. Comparisons with STEREO and WIND spacecraft observations are also made. © 2015. The American Astronomical Society. All rights.

Zhao Q.,Beijing Institute of Technology | Ji M.,Beijing Institute of Technology | Qian H.,Beijing Institute of Technology | Dai B.,Beijing Institute of Technology | And 5 more authors.

The existence of lattice strain between two different materials can be used to control the fine structural configuration in a hybrid colloidal nanostructure. Enabled by such, the relative position change of Au and CdX in Au-CdX from a symmetric to an asymmetric configuration is demonstrated, which can further lead to fine tuning of plasmon-exciton coupling and different hydrogen photocatalytic performance. These results provide new insight into plasmon enhanced photocatalytic mechanisms and provide potential catalysts for photoreduction reactions. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Mahmoud M.S.,King Fahd University of Petroleum and Minerals | Xia Y.,Beijing Institute of Technology
IET Control Theory and Applications | Year: 2010

In this study, the problem of designing regular robust ℓ2- ℓ∞ filter for a class of linear singular discrete-time systems with norm-bounded uncertainties is investigated. A class of regular linear filters is fully analysed, then necessary and sufficient conditions of robust admissibility are established. Guaranteed ℓ2- ℓ∞ performance of the filtered system is provided and expressed in terms of the solution of strict linear matrix inequalities (LMIs). The cases of full- and zeroth-order realisable filter are derived as limiting cases of design. Numerical examples are worked out to illustrate the theoretical development. © 2010 The Institution of Engineering and Technology.

Wang W.,University of Waterloo | Wang W.,Beijing Institute of Technology | Gumfekar S.P.,University of Waterloo | Jiao Q.,Beijing Institute of Technology | Zhao B.,University of Waterloo
Journal of Materials Chemistry C | Year: 2013

A functional structure of Mn0.5Zn0.5Fe 2O4-on-polyaniline nanocomposites with high dielectric absorbing properties and electromagnetic shielding effectiveness at low frequencies was successfully fabricated through a facile in situ emulsion polymerization. Polyaniline (PANI) was doped with hydrochloric acid to improve its electrical properties and interactions with ferrite nanoparticles. The electrostatic force, paramagnetic force and hydrogen bonding strongly bonded or assembled ferrite nanoparticles on the polyaniline surface and improved the thermal stability of the polyaniline nanostructure. Polyaniline nanofibers were found to have an average diameter of 100 nm and length of 500 nm, consisting of a bundle of smaller individual units, whereas ferrite nanoparticles were of spherical shape with an average diameter 30 nm. The research findings show that ferrite particles overcome the common problem of aggregation and evenly dispersed on the surface of polyaniline. The ferrite-grafted polyaniline nanostructures were demonstrated as a promising functional material for the absorbing of electromagnetic microwaves because of a large amount of dipole polarizations in the polymer backbone and at the interfaces of the ferrite nanoparticles and polyaniline nanofibers. Both the complex permittivity and shielding effectiveness of the ferrite-grafted polyaniline nanocomposites increased with the increasing weight percentage of PANI. There is also a good match of real and imaginary parts of the complex permittivity, giving rise to almost an equal dielectric loss angle tangent in the measured frequency (30 MHz to 1 GHz). This superior property allows the nanocomposites to function within an extended absorbing band. © 2013 The Royal Society of Chemistry.

Li X.,Beijing Institute of Technology | Yang B.,Beijing Institute of Technology | Zeng T.,Hong Kong Baptist University
IEEE Transactions on Image Processing | Year: 2011

Prediction-error expansion (PEE) is an important technique of reversible watermarking which can embed large payloads into digital images with low distortion. In this paper, the PEE technique is further investigated and an efficient reversible watermarking scheme is proposed, by incorporating in PEE two new strategies, namely, adaptive embedding and pixel selection. Unlike conventional PEE which embeds data uniformly, we propose to adaptively embed 1 or 2 bits into expandable pixel according to the local complexity. This avoids expanding pixels with large prediction-errors, and thus, it reduces embedding impact by decreasing the maximum modification to pixel values. Meanwhile, adaptive PEE allows very large payload in a single embedding pass, and it improves the capacity limit of conventional PEE. We also propose to select pixels of smooth area for data embedding and leave rough pixels unchanged. In this way, compared with conventional PEE, a more sharply distributed prediction-error histogram is obtained and a better visual quality of watermarked image is observed. With these improvements, our method outperforms conventional PEE. Its superiority over other state-of-the-art methods is also demonstrated experimentally. © 2006 IEEE.

Mahmoud M.S.,King Fahd University of Petroleum and Minerals | Xia Y.,Beijing Institute of Technology
International Journal of Robust and Nonlinear Control | Year: 2011

The objective of this paper is to design a switched robust control for a class of continuous-time systems subject to linear fractional uncertainty and interval time delays. The controller is based on state feedback and the LMI-based stability conditions are derived using an improved Lyapunov-Krasovskii functional. Moreover, the switching rule as well as the state feedback gains are determined from the minimization of a guaranteed cost function. The theoretical results are illustrated with a numerical example. Copyright © 2010 John Wiley & Sons, Ltd.

Mahmoud M.S.,King Fahd University of Petroleum and Minerals | Xia Y.,Beijing Institute of Technology
Neurocomputing | Year: 2010

In this paper, we investigate the problem of global exponential stability analysis for a class of bidirectional associative memory (BAM) neural networks with interval time-delays. Improved exponential stability condition is derived by employing new Lyapunov-Krasovskii functional and the integral inequality. Several special cases of interest are derived. The developed stability criteria are delay dependent and characterized by linear matrix inequalities (LMIs). The developed results are shown to be less conservative than previous published ones in the literature. Finally, simulations of two numerical examples are provided to demonstrate the efficacy of our approach. © 2010 Elsevier B.V.

Fu Y.,Beijing Institute of Technology | Song J.,Beijing Composite Materials Co. | Song J.,Beijing University of Chemical Technology | Zhu Y.,Beijing Institute of Technology | Cao C.,Beijing Institute of Technology
Journal of Power Sources | Year: 2014

Amorphous mesoporous Ni(OH)2 nanoboxes are synthesized by template-engaged routes. The nanoboxes are characterized by SEM, TEM, XRD, XPS and BET methods. The nanoboxes have uniform morphology of 450-500 nm, high surface area of 214.6 m2 g-1 and mesoporous structure of 4-20 nm. Electrochemical characterization are tested using cyclic voltammetry, chronopotentiometry and impedance spectroscopy, respectively. These amorphous mesoporous Ni(OH)2 hollow nanoboxes shows high specific capacitance of 2495, 2378, 2197, 1993 F g-1 at discharge current of 1, 2, 5 and 10 A g-1 respectively. The property tests demonstrate the high specific capacitance and excellent cycling of the amorphous Ni(OH)2 nanoboxes material for high-performance electrochemical pseudocapacitors. © 2014 Elsevier Ltd. All rights reserved.

Mahmoud M.S.,King Fahd University of Petroleum and Minerals | Xia Y.,Beijing Institute of Technology
International Journal of Robust and Nonlinear Control | Year: 2010

A novel delay-dependent filtering design approach is developed for a class of linear piecewise discrete-time systems with convex-bounded parametric uncertainties and time-varying delays. The time-delays appear in the state as well as the output and measurement channels. The filter has a linear full-order structure and guarantees the desired estimation accuracy over the entire uncertainty polytope. The desired accuracy is assessed in terms of either ℋ∞-performance or ℒ2- ℒ∞ criteria. A new parametrization procedure based on a combined Finsler's Lemma and piecewise Lyapunov-Krasovskii functional is established to yield sufficient conditions for delay-dependent filter feasibility. The filter gains are determined by solving a convex optimization problem over linear matrix inequalities. In comparison to the existing design methods, the developed methodology yields the least conservative measures since all previous overdesign limitations are almost eliminated. By means of simulation examples, the advantages of the developed technique are readily demonstrated. © 2009 John Wiley & Sons, Ltd.

Li X.,Beijing Institute of Technology | Li B.,Shenzhen University | Yang B.,Beijing Institute of Technology | Zeng T.,Hong Kong Baptist University
IEEE Transactions on Image Processing | Year: 2013

Histogram shifting (HS) is a useful technique of reversible data hiding (RDH). With HS-based RDH, high capacity and low distortion can be achieved efficiently. In this paper, we revisit the HS technique and present a general framework to construct HS-based RDH. By the proposed framework, one can get a RDH algorithm by simply designing the so-called shifting and embedding functions. Moreover, by taking specific shifting and embedding functions, we show that several RDH algorithms reported in the literature are special cases of this general construction. In addition, two novel and efficient RDH algorithms are also introduced to further demonstrate the universality and applicability of our framework. It is expected that more efficient RDH algorithms can be devised according to the proposed framework by carefully designing the shifting and embedding functions. © 1992-2012 IEEE.

Tong H.-J.,University of Bristol | Tong H.-J.,Beijing Institute of Technology | Reid J.P.,University of Bristol | Bones D.L.,University of Bristol | And 2 more authors.
Atmospheric Chemistry and Physics | Year: 2011

The influence of glassy states and highly viscous solution phases on the timescale of aerosol particle equilibration with water vapour is examined. In particular, the kinetics of mass transfer of water between the condensed and gas phases has been studied for sucrose solution droplets under conditions above and below the glass transition relative humidity (RH). Above the glass transition, sucrose droplets are shown to equilibrate on a timescale comparable to the change in RH. Below the glass transition, the timescale for mass transfer is shown to be extremely slow, with particles remaining in a state of disequilibrium even after timescales of more than 10 000 s. A phenomenological approach for quantifying the time response of particle size is used to illustrate the influence of the glassy aerosol state on the kinetics of mass transfer of water: the time is estimated for the droplet to reach the halfway point from an initial state towards a disequilibrium state at which the rate of size change decreases below 1 nm every 10 000 s. This half-time increases above 1000 s once the particle can be assumed to have formed a glass. The measurements are shown to be consistent with kinetic simulations of the slow diffusion of water within the particle bulk. When increasing the RH from below to above the glass transition, a particle can return to equilibrium with the gas phase on a timescale of 10's to 100's of seconds, once again forming a solution droplet. This is considerably shorter than the timescale for the size change of the particle when glassy and suggests that the dissolution of the glassy core can proceed rapidly, at least at room temperature. Similar behaviour in the slowing of the mass transfer rate below the glass transition RH is observed for binary aqueous raffinose solution droplets. Mixed component droplets of sucrose/sodium chloride/water also show slow equilibration at low RH, illustrating the importance of understanding the role of the bulk solution viscosity on the rate of mass transfer with the gas phase, even under conditions that may not lead to the formation of a glass. © Author(s) 2011.

Jiao Q.,Beijing Institute of Technology | Fu M.,Beijing Institute of Technology | You C.,Patent Examination Cooperation Center | Zhao Y.,Beijing Institute of Technology | Li H.,Beijing Institute of Technology
Inorganic Chemistry | Year: 2012

The hollow Co 3O 4 microspheres were prepared by a gas-liquid diffusion reaction in the presence of ionic liquid [Bmim][BF 4] in combination with calcination at 300 °C. Their structures and morphologies were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Raman spectrometry, and X-ray photoelectron spectroscopy. The growth mechanism of hollow Co 3O 4 microspheres was proposed. The ethanol sensing properties were measured using a WS-30A gas sensor measurement system. The influence of working temperatures, ethanol concentrations, and specific surface areas of Co 3O 4 microspheres on the ethanol sensing properties was investigated. The hollow Co 3O 4 microspheres showed excellent sensitivity to ethanol vapor at a lower operating temperature. © 2012 American Chemical Society.

Grant
Agency: GTR | Branch: ESRC | Program: | Phase: Research Grant | Award Amount: 260.54K | Year: 2012

This project probes the growth strategies of innovative small and medium-size enterprises (SMEs). Our research focuses on emerging green goods industries that manufacture outputs which benefit the environment or conserve natural resources, with an international comparative element involving the UK, the US, and China.

The project investigates the contributions of strategy, resources and relationships to how innovative British, American, and Chinese SMEs achieve significant growth. The targeted technology-oriented green goods sectors are strategically important to environmental rebalancing and have significant potential (in the UK) for export growth. The research examines the diverse pathways to innovation and growth across different regions. We use a mix of methodologies, including analyses of structured and unstructured data on SME business and technology performance and strategies, case studies, and modelling. Novel approaches using web mining are pioneered to gain timely information about enterprise developmental pathways. Findings from the project will be used to inform management and policy development at enterprise, regional and national levels.

The project is led by the Manchester Institute of Innovation Research at the University of Manchester, in collaboration with Georgia Institute of Technology, US; Beijing Institute of Technology, China, and Experian, UK.

Mahmoud M.S.,King Fahd University of Petroleum and Minerals | Xia Y.,Beijing Institute of Technology
Journal of the Franklin Institute | Year: 2011

In this paper, we investigate the problem of global exponential stability analysis for a class of delayed recurrent neural networks. This class includes Hopfield neural networks and cellular neural networks with interval time-delays. Improved exponential stability condition is derived by employing new LyapunovKrasovskii functional and the integral inequality. The developed stability criteria are delay dependent and characterized by linear matrix inequalities (LMIs). The developed results are less conservative than previous published ones in the literature, which are illustrated by representative numerical examples. © 2010 The Franklin Institute.

Qu L.,Beijing Institute of Technology | Vaia R.A.,Air Force Research Lab | Dai L.,Case Western Reserve University
ACS Nano | Year: 2011

A simple multiple contact transfer technique has been developed for controllable fabrication of multilevel, multicomponent microarchitectures of vertically aligned carbon nanotubes (VA-CNTs). Three dimensional (3-D) multicomponent micropatterns of aligned single-walled carbon nanotubes (SWNTs) and multiwalled carbon nanotubes (MWNTs) have been fabricated, which can be used to develop a newly designed touch sensor with reversible electrical responses for potential applications in electronic devices, as demonstrated in this study. The demonstrated dependence of light diffraction on structural transfiguration of the resultant CNT micropattern also indicates their potential for optical devices. Further introduction of various components with specific properties (e.g., ZnO nanorods) into the CNT micropatterns enabled us to tailor such surface characteristics as wettability and light response. Owing to the highly generic nature of the multiple contact transfer strategy, the methodology developed here could provide a general approach for interposing a large variety of multicomponent elements (e.g., nanotubes, nanorods/wires, photonic crystals, etc.) onto a single chip for multifunctional device applications. © 2011 American Chemical Society.

Xu B.,Beijing Research Institute of Chemical Defense | Hou S.,China University of Mining and Technology | Cao G.,Beijing Research Institute of Chemical Defense | Wu F.,Beijing Institute of Technology | Yang Y.,Beijing Research Institute of Chemical Defense
Journal of Materials Chemistry | Year: 2012

Gelatin, a renewable animal derivative composed of various proteins, was used as a precursor for nitrogen-doped porous carbon with high surface areas for supercapacitors for the first time. The preparation procedure is very simple, including the carbonization of gelatin under inert atmosphere, followed by NaOH activation of the carbonized char at 600 °C for 1 h. The porosity and surface chemistry of the carbon depend strongly on the weight ratio of NaOH/char, with the specific surface area and nitrogen content varying between 323 and 3012 m 2 g -1 and between 0.88 and 9.26 at%, respectively. The unique microstructure and nitrogen functionalities enable the carbon to exhibit a high capacitance of up to 385 F g -1 in 6 mol L -1 KOH aqueous electrolytes, attributed to the co-contribution of double layer capacitance and pseudo-capacitance. It also shows excellent rate capability (235 F g -1 remained at 50 A g -1) and cycle durability, making it a promising electrode material for supercapacitors. This journal is © The Royal Society of Chemistry.

Xu B.,Beijing Research Institute of Chemical Defense | Yue S.,China University of Mining and Technology | Sui Z.,Beijing Institute of Technology | Zhang X.,Beijing Institute of Technology | And 3 more authors.
Energy and Environmental Science | Year: 2011

Graphene oxide, an intermediate during graphene synthesis by a modified Hummers's method, exhibits higher capacitance, up to 189 F g -1, than graphene due to an additional pseudo-capacitance effect of attached oxygen-containing functional groups on its basal planes. Taking its higher capacitance, lower cost and shorter processing time into consideration, graphene oxide may be a better choice than graphene as an electrode material for supercapacitors. © 2011 The Royal Society of Chemistry.

Miao L.-X.,Beijing Institute of Technology | Miao L.-X.,Beijing Research Institute of Chemical Defense | Wang W.-K.,Beijing Research Institute of Chemical Defense | Wang A.-B.,Beijing Research Institute of Chemical Defense | And 2 more authors.
Journal of Materials Chemistry A | Year: 2013

Lithium-sulfur (Li-S) batteries have received significant attention in recent years because of their high theoretical specific capacity (1675 mA h g-1) and energy density (2600 W h kg-1). Many papers focus on cells that exhibit very high capacity per gram of sulfur, which contain sulfur contents well below 50% which greatly reduces their overall energy density per gram of cathode. Moreover, they do not address the issues of practical sulfur loading and large-scale technology for commercial applications. In general, the lower the sulfur content, the higher the sulfur capacity. In this paper, a high sulfur content (80% S) carbon-sulfur (P-AB@S) material with core-shell structure has been successfully synthesized by grafting of polymer electrolyte (polyethylene glycol, PEG) chains and depositing sulfur onto the surface of electronically conductive acetylene black (AB). The PEG chains are inserted into the sulfur layer to reinforce the material's structural stability. More importantly, with a cathode containing 66% sulfur and approximately 3 mg cm-2 sulfur loading on the electrode, P-AB@S as a cathode material for lithium sulfur batteries shows a specific capacity of 577 mA h g -1 after 500 cycles at 100 mA g-1 between 1.5 V and 2.8 V. Moreover, the preparation method of the P-AB@S composite is a facile, cost-effective and template-free method and easy to implement large-scale technology for commercial applications. © 2013 The Royal Society of Chemistry.

Hu J.,Beijing Institute of Technology | Xu B.,Jiangxi Normal University | Ouyang C.,Jiangxi Normal University | Yang S.A.,Singapore University of Technology and Design | Yao Y.,Beijing Institute of Technology
Journal of Physical Chemistry C | Year: 2014

First-principles calculations are performed to study the electronic properties and Li storage capability of V2C and its corresponding fluoride and hydroxide. We find that the V2C monolayer is metallic with antiferromagnetic configuration, while its derived V2CF2 and V2C(OH)2 in their the most stable configurations are small-gap antiferromagnetic semiconductors. Li adsorption could enhance the electric conductivity of V2C fluoride and hydroxide. The bare V2C monolayer shows fast Li diffusion with low diffusion barrier height and very high Li storage capacity (with theoretical value ∼940 mAh/g), while the passivated F or OH atoms on its surface tend to impede Li diffusion and largely reduce the Li storage capacity. Moreover, the average intercalation potentials for V2C-based materials are calculated to be relatively low. Our results suggest that V2C monolayer could be a promising anode material for Li-ion batteries. © 2014 American Chemical Society.

Mukhtar A.,Petronas University of Technology | Xia L.,Beijing Institute of Technology | Tang T.B.,Petronas University of Technology
IEEE Transactions on Intelligent Transportation Systems | Year: 2015

Over the past decade, vision-based vehicle detection techniques for road safety improvement have gained an increasing amount of attention. Unfortunately, the techniques suffer from robustness due to huge variability in vehicle shape (particularly for motorcycles), cluttered environment, various illumination conditions, and driving behavior. In this paper, we provide a comprehensive survey in a systematic approach about the state-of-the-art on-road vision-based vehicle detection and tracking systems for collision avoidance systems (CASs). This paper is structured based on a vehicle detection processes starting from sensor selection to vehicle detection and tracking. Techniques in each process/step are reviewed and analyzed individually. Two main contributions in this paper are the following: survey on motorcycle detection techniques and the sensor comparison in terms of cost and range parameters. Finally, the survey provides an optimal choice with a low cost and reliable CAS design in vehicle industries. © 2000-2011 IEEE.

Xu Y.,Beijing Institute of Technology | Sui Z.,Beijing Institute of Technology | Xu B.,Beijing Research Institute of Chemical Defense | Duan H.,Beijing Research Institute of Chemical Defense | Zhang X.,Beijing Institute of Technology
Journal of Materials Chemistry | Year: 2012

4-(2,3-Dihydrothieno[3,4-b][1,4]dioxin-2-yl)-methoxybutane-1-sulfonate (EDOT-S) as a reactive surfactant was used to disperse 3,4- ethylenedioxythiophene (EDOT) to make a PEDOT-S/PEDOT hydrogel by emulsion polymerization. The corresponding all conducting polymer aerogels have been obtained by supercritical drying or freeze drying of the as-synthesized PEDOT-S/PEDOT hydrogels. The stability of the EDOT-S stabilized EDOT emulsion has been investigated by zeta potential and size tests. The mechanical property and gelation mechanism of the resulting PEDOT-S/PEDOT hydrogels have been studied by rheological experiments, X-ray powder diffraction and X-ray photoelectron spectroscopy. The molecular structure of the resulting PEDOT-S/PEDOT aerogels has been revealed by infra-red and Raman spectroscopy, and the porous attribute of the as-synthesized PEDOT-S/PEDOT aerogels has been investigated by scanning electron microscopy, transmission electron microscopy and nitrogen sorption tests. It has been found that molar ratios of EDOT-S to EDOT have played a significant role in determining the stability of the resulting emulsion, the mechanical properties of the resulting hydrogel, and the porous properties of the resulting aerogels. The electrical, electrochemical and adsorption properties have also been disclosed in this manuscript. The results show that the as-prepared all conducting polymer aerogels have high conductivity with the level of 10 1 S m -1, enhanced electrochemical capacitance with good rate capability and excellent cycling stability, and superb adsorption capacity to dyestuff and heavy metals ions. © The Royal Society of Chemistry 2012.

Zhang X.,Beijing Institute of Technology | Sui Z.,Beijing Institute of Technology | Xu B.,Beijing Research Institute of Chemical Defense | Yue S.,Beijing Research Institute of Chemical Defense | And 3 more authors.
Journal of Materials Chemistry | Year: 2011

Mechanically strong and electrically conductive graphene aerogels can be prepared by either supercritical drying or freeze drying of hydrogel precursors synthesized from reduction of graphene oxide with l-ascorbic acid, and the resulting graphene aerogels possess the specific capacitance of 128 F g -1 with superior rate performance. © 2011 The Royal Society of Chemistry.

Sutton J.E.,University of Delaware | Guo W.,University of Delaware | Guo W.,Beijing Institute of Technology | Katsoulakis M.A.,University of Massachusetts Amherst | Vlachos D.G.,University of Delaware
Nature Chemistry | Year: 2016

Kinetic models based on first principles are becoming common place in heterogeneous catalysis because of their ability to interpret experimental data, identify the rate-controlling step, guide experiments and predict novel materials. To overcome the tremendous computational cost of estimating parameters of complex networks on metal catalysts, approximate quantum mechanical calculations are employed that render models potentially inaccurate. Here, by introducing correlative global sensitivity analysis and uncertainty quantification, we show that neglecting correlations in the energies of species and reactions can lead to an incorrect identification of influential parameters and key reaction intermediates and reactions. We rationalize why models often underpredict reaction rates and show that, despite the uncertainty being large, the method can, in conjunction with experimental data, identify influential missing reaction pathways and provide insights into the catalyst active site and the kinetic reliability of a model. The method is demonstrated in ethanol steam reforming for hydrogen production for fuel cells. © 2016 Macmillan Publishers Limited. All rights reserved.

Liu Z.,Beijing Institute of Technology | Zeng X.,Hubei University
European Journal of Combinatorics | Year: 2012

A special type of two-weight code is defined by using subcodes. The generalized Hamming weight and the chain property of this kind of two-weight code are determined. The higher-weight enumerators and an application of this kind of two-weight code are given. © 2012 Elsevier Ltd.

Xue P.,Samsung | Gong P.,Beijing Institute of Technology | Park J.H.,Inha University | Park D.,Inha University | Kim D.K.,Inha University
IEEE Transactions on Wireless Communications | Year: 2012

We study the radio resource management (RRM) in orthogonal frequency division multiple access (OFDMA) involved heterogeneous networks, to maximize the system sum-rate under the proportional user rate constraint. An analytical model which reflects the network access features is presented. Allowing multi-homing access and resource element sharing, the RRM problem can be formulated as a linear programming (LP) problem, and the optimal solution provides upper-bound performance. In order to analyze the network selection criterion, we consider an approximated RRM problem with average resource allocations. Two different multi-homing formulations are used, and both are proven to have the same solution, where the network selection is related to the users' rate ratios between different networks. Then, we propose a low complexity suboptimal RRM algorithm, which is composed of a basic part without multi-homing access and a supplementary part with multi-homing support. The basic part makes single network selection and resource allocations. The network selection algorithm is designed based on the criterion found in the approximated problem. After network selection, an efficient resource allocation algorithm is utilized in the OFDMA network, which can employ the multi-user time and frequency diversity well. If multi-homing is allowed, the supplementary part selects the multi-homing users and reallocates partial resources to further improve the performance. Our simulation results show that the proposed suboptimal algorithm can achieve considerable gains over the previous schemes with minor performance degradation compared with the optimal solution. © 2011 IEEE.

Zhang W.,Beijing Institute of Technology | Li X.,Beijing Institute of Technology | Li L.,Beijing Institute of Technology | Yang R.,Beijing Institute of Technology
Polymer Degradation and Stability | Year: 2012

A series of flame retarded epoxy resins (EP) was prepared loaded with OPS (octaphenyl polyhedral oligomeric silsesquioxane) and DOPO (9,10-dihydro-9-oxa- 10-phosphaphenanthrene-10-oxide). The flame retarding properties of these EP composites were tested using the LOI and UL-94 procedures. The results indicate that the mixture of OPS and DOPO has a remarkable influence on the blowing-out effect of these flame retarded EP composites. The pyrolytic gases produced and the thermal stability of the EP composites with different flame retardant were detected by TGA-FTIR in an air atmosphere. The gaseous species produced by the flame retarded EP composites are the same as those from pure EP. The synergistic effect of the OPS and DOPO was detected from the HRR, p-HRR, TSR, and SEA results after the cone calorimeter test. The char produced by the EP composites after the cone calorimeter test were investigated by FTIR and XPS. It is proposed that the interaction between OPS and DOPO takes place through a chemical reaction in the condensed phase. Further investigation is required to fully reveal the reason behind the remarkable blowing-out effect. © 2012 Elsevier Ltd. All rights reserved.

Jiang W.,Beijing Institute of Technology | Hao J.,Beijing Institute of Technology | Han Z.,Harbin University of Science and Technology
Polymer Degradation and Stability | Year: 2012

Feng J.,Beijing Institute of Technology | Hao J.,Beijing Institute of Technology | Du J.,Beijing Institute of Technology | Yang R.,Beijing Institute of Technology
Polymer Degradation and Stability | Year: 2012

Investigation of thermal degradation is essential for understanding flame retardancy mechanism and further tailoring of materials. In this work, polycarbonate was compounded with solid bisphenol A bis(diphenyl phosphate) (S-BDP) and organo-montmorillonite (OMMT) to form a nanocomposite with mainly intercalated and partially exfoliated morphology, and the main flame retardancy activity of the nanocomposite was shown to be in the condensed phase as revealed by cone calorimetry, thermogravimetric analysis coupled with Fourier transform infrared spectrometry (TGA/FTIR) and thermogravimetric analysis coupled with mass spectrometry (TGA/MS). Although the main gaseous pyrolysis products of polycarbonate can't be greatly altered by S-BDP and OMMT, carbonate linkage would be stabilized and vigorous decomposition at higher temperature would be delayed, thereby char residue formation could be promoted. S-BDP also shows slight gaseous phase effect as proved by the detection of phosphorus-oxygen species in TGA/MS. Moreover, the relatively enhanced evolution of PO radicals in the sample filled with only S-BDP suggests that S-BDP alone exhibits a slightly stronger gaseous phase effect than the combination of S-BDP and OMMT. This enhanced condensed phase effect of S-BDP in the presence of OMMT could be associated with the delayed vigorous decomposition at higher temperature due to the barrier effect of OMMT. The peak heat release rate of polycarbonate could not be significantly reduced by substituting S-BDP with OMMT, yet it would prolong the time to peak heat release rate and reduce the smoke toxicity with a smaller release of carbon monoxide. The reduced carbon monoxide release was probably caused by further oxidation of carbon monoxide in the hotter char surface due to the barrier effect of OMMT. © 2012 Elsevier Ltd. All rights reserved.

Tao J.,Nanyang Technological University | Yu X.,Nanyang Technological University | Hu B.,Nanyang Technological University | Hu B.,Beijing Institute of Technology | And 2 more authors.
Optics Letters | Year: 2014

We propose and numerically analyze a plasmonic Bragg reflector formed in a graphene waveguide. The results show that the graphene plasmonic Bragg reflector can produce a broadband stopband that can be tuned over a wide wavelength range by a small change in the Fermi energy level of graphene. By introducing a defect into the Bragg reflector, we can achieve a Fabry-Perot-like microcavity with a quality factor of 50 for the defect resonance mode formed in the stopband. The proposed Bragg reflector could be used as a broadband ultrafast tunable integrated filter and a broadband modulator. In addition, the defect microcavity may find applications in graphene-based resonators. © 2013 Optical Society of America.

Liu G.-B.,Beijing Institute of Technology | Liu G.-B.,University of Hong Kong | Shan W.-Y.,Carnegie Mellon University | Yao Y.,Beijing Institute of Technology | And 2 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2013

We present a three-band tight-binding (TB) model for describing the low-energy physics in monolayers of group-VIB transition metal dichalcogenides MX2 (M=Mo, W; X=S, Se, Te). As the conduction- and valence-band edges are predominantly contributed by the dz2, dxy, and d x2-y2 orbitals of M atoms, the TB model is constructed using these three orbitals based on the symmetries of the monolayers. Parameters of the TB model are fitted from the first-principles energy bands for all MX2 monolayers. The TB model involving only the nearest-neighbor M-M hoppings is sufficient to capture the band-edge properties in the ±K valleys, including the energy dispersions as well as the Berry curvatures. The TB model involving up to the third-nearest-neighbor M-M hoppings can well reproduce the energy bands in the entire Brillouin zone. Spin-orbit coupling in valence bands is well accounted for by including the on-site spin-orbit interactions of M atoms. The conduction band also exhibits a small valley-dependent spin splitting which has an overall sign difference between MoX2 and WX 2. We discuss the origins of these corrections to the three-band model. The three-band TB model developed here is efficient to account for low-energy physics in MX2 monolayers, and its simplicity can be particularly useful in the study of many-body physics and physics of edge states. © 2013 American Physical Society.

He S.,Beijing Institute of Technology | Su Y.,Beijing Institute of Technology | Su Y.,Northwestern University | Ji B.,Beijing Institute of Technology | Gao H.,Brown University
Journal of the Mechanics and Physics of Solids | Year: 2014

Cells constantly probe their surrounding microenvironment by pushing and pulling on the extracellular matrix (ECM). While it is widely accepted that cell induced traction forces at the cell-matrix interface play essential roles in cell signaling, cell migration and tissue morphogenesis, a number of puzzling questions remain with respect to mechanosensing in cell-substrate interactions. Here we show that these open questions can be addressed by modeling the cell-substrate system as a pre-strained elastic disk attached to an elastic substrate via molecular bonds at the interface. Based on this model, we establish analytical and numerical solutions for the displacement and stress fields in both cell and substrate, as well as traction forces at the cell-substrate interface. We show that the cell traction generally increases with distance away from the cell center and that the traction-distance relationship changes from linear on soft substrates to exponential on stiff substrates. These results indicate that cell adhesion and migration behaviors can be regulated by cell shape and substrate stiffness. Our analysis also reveals that the cell traction increases linearly with substrate stiffness on soft substrates but then levels off to a constant value on stiff substrates. This biphasic behavior in the dependence of cell traction on substrate stiffness immediately sheds light on an existing debate on whether cells sense mechanical force or deformation when interacting with their surroundings. Finally, it is shown that the cell induced deformation field decays exponentially with distance away from the cell. The characteristic length of this decay is comparable to the cell size and provides a quantitative measure of how far cells feel into the ECM. © 2014 Elsevier Ltd. All rights reserved.

Zhu J.,Beijing Institute of Technology | Qin Y.,Nanjing University | Zhang Y.,Beijing Institute of Technology
Analytical Chemistry | Year: 2010

A novel magnesium-selective ion-channel mimetic sensor based on a well-known calcium ionophore, ETH 5234, was demonstrated. Due to different stoichiometry of the ionophore with Mg2+ and Ca2+, the sensor exhibits high selectivity to Mg2+ by controlling ionophore concentration on the electrode surface, which allows the measurement Of Mg 2+ in a 1 mM Ca2+ background solution. © 2010 American Chemical Society.

Liu B.,Beijing Institute of Technology | Xia Y.,Beijing Institute of Technology
IEEE Transactions on Industrial Electronics | Year: 2011

This paper proposes a fault detection and compensation scheme based on likelihood ratios (LRs) for networked predictive control systems with random network-induced time delays and clock asynchronism. The compensator is applied to compensate for the network-induced time delays. The measured outputs are sent back to the local node with random delays and the observer updates based on the time schedule of a remote node clock to avoid the deficiency of asynchronism. Two schemes are proposed in this paper to update the LRs of fault. One of them is to set up a buffer in the local node to save the measured outputs out of sequence, and the observer processes the measured outputs one by one in their original sequence. The other scheme is to discard the measured outputs that are out of sequence; thus, the observer has to estimate the state and update the LRs with intermittent observations. The convergence analysis of a generalized LR test with intermittent observations is proposed as well. A numerical simulation is also given to validate the proposed method. © 2010 IEEE.

Sun S.,Beijing Institute of Technology | Li Z.-S.,Beijing Institute of Technology | Chen S.-L.,Beijing Institute of Technology
Dalton Transactions | Year: 2014

Chlorite dismutase (Cld) is a heme-dependent enzyme that catalyzes the decomposition of toxic chlorite (ClO2 -) into innocuous chloride and O2. In this paper, using the hybrid B3LYP density functional theory (DFT) method including dispersion interactions, the Cld reaction mechanism has been studied with a chemical model constructed on the X-ray crystal structure. The calculations indicate that the reaction proceeds along a stepwise pathway in the doublet state, i.e. a homolytic O-Cl bond cleavage of the substrate leading to an O-Fe(heme) species and a ClO radical, followed by a rebinding O-O bond formation between them. The O-Fe(heme) species is demonstrated to be a low-spin triplet-state Fe(iv)=O diradicaloid. A low-spin singlet-state Fe(iv)=O is much less stable than the former, with an energy difference of 9.2 kcal mol-1. The O-Cl bond cleavage is rate-limiting with a barrier of 10.6 kcal mol-1, in good agreement with the experimental reaction rate of 2.0 × 105 s-1. Furthermore, a heterolytic O-Cl bond dissociation in the initial step is shown to be unreachable, which ensures the high efficiency of the Cld enzyme by avoiding the generation of chlorate byproduct observed in the reactions of synthetic Fe porphyrins. Also, the pathways in the quartet and sextet states are unfavorable for the Cld reaction. The present results reveal a detailed mechanism III (defined in the text) including an interesting di-radical intermediate composed of a low-spin triplet-state Fe(iv)=O and a ClO radical. Compared to a competitive heterolytic Cl-O cleavage in synthetic Fe porphyrins, the revelation of the domination of homolysis in Cld indicates not only the high efficiency of enzyme, but also the sensitivity of a heme and the significance of the enzymatic active-site surroundings (the His170 and Arg183 residues in the present case), which gives more insights into heme chemistry. © The Royal Society of Chemistry 2014.

Huang L.,Beijing Institute of Technology | Zhang Q.T.,City University of Hong Kong | Cheng L.L.,City University of Hong Kong
IEEE Transactions on Signal Processing | Year: 2011

Most existing stopping criteria for turbo decoding have their root in hypothesis test, requiring a subjective threshold for decision making. A consequence is that the turbo decoding receiver so-constructed can converge at high signal-to-noise ratios (SNRs) but fails at low SNRs, thereby calling for a new design philosophy for stopping criteria. In this correspondence, the problem is tackled in the framework of information theoretic criterion, which enables the turbo decoding to properly work in a changing SNR environment. Numerical results are presented for illustrating the good performance of the proposed method. © 2006 IEEE.

Wan Y.,Beijing Institute of Technology
Optik | Year: 2016

We report theoretical studies of the coherent random lasing behavior in active weakly scattering random fiber lasers by using finite-difference time-domain (FDTD) method. We design and simulate a model of active weakly scattering random fiber lasers. Results show that the scattering mean free path reduces significantly with reducing the dimension of systems. For same situation, the scattering mean free path in our model is at least two orders of magnitude lower than that in high dimensional systems. We calculate the length of lasing oscillation cavity by using power Fourier transform, and we found Lc<

Feng W.,Beijing Institute of Technology | Yao Y.,Beijing Institute of Technology
Science China: Physics, Mechanics and Astronomy | Year: 2012

In recent years, three-dimensional topological insulators (3DTI) as a novel state of quantum matter have become a hot topic in the fields of condensed matter physics and materials sciences. To fulfill many spectacularly novel quantum phenomena predicted in 3DTI, real host materials are of crucial importance. In this review paper, we first introduce general methods of searching for new 3DTI based on the density-functional theory. Then, we review the recent progress on materials realization of 3DTI including simple elements, binary compounds, ternary compounds, and quaternary compounds. In these potential host materials, some of them have already been confirmed by experiments while the others are not yet. The 3DTI discussed here does not contain the materials with strong electron-electron correlation. Lastly, we give a brief summary and some outlooks in further studies. © 2012 Science China Press and Springer-Verlag Berlin Heidelberg.

Zeng T.,Beijing Institute of Technology | Wang R.,Beijing Institute of Technology | Li F.,Beijing Institute of Technology | Long T.,Beijing Institute of Technology
IEEE Transactions on Geoscience and Remote Sensing | Year: 2013

This paper proposes a method of focusing the bistatic synthetic aperture radar (SAR) (BiSAR) data in spaceborne/stationary configuration. The key problem for imaging is the space variance of Doppler phase. The stationary platform induces additional and different range offsets to the range migration of targets. It causes targets with the same Doppler history, which are determined only by the moving platform, to shift into different bistatic range cells in the echo data. Therefore, the processing is not the same as monostatic SAR imaging which can be fast performed by the uniform matched-filter function in the frequency domain. In this paper, a modified nonlinear chirp scaling (NLCS) algorithm based on series reversion is formulated, which could achieve different range cell migration correction and the equalization of effective range and azimuth frequency modulation rates. The proposed algorithm is validated by simulated and real BiSAR data. In the spaceborne/stationary BiSAR experiment, the YaoGan-1 (an L-band spaceborne SAR system launched by China) is selected as the transmitter, and the stationary receiver is mounted on top of a tall building. The results show that modified NLCS algorithm can effectively focus BiSAR data with serious space variance in spaceborne/stationary configuration. © 2012 IEEE.

Yang H.,Beijing Institute of Technology | Xia Y.,Beijing Institute of Technology | Liu B.,Beijing Institute of Technology
IEEE Transactions on Systems, Man, and Cybernetics, Part B: Cybernetics | Year: 2011

This paper investigates the problem of fault detection for Takagi-Sugeno (T-S) fuzzy discrete systems in finite-frequency domain. By means of the T-S fuzzy model, both a fuzzy fault detection filter system and the dynamics of filtering error generator are constructed. Two finite-frequency performance indices are introduced to measure fault sensitivity and disturbance robustness. Faults are considered in a middle frequency domain, while disturbances are considered in another certain finite-frequency domain interval. By using the generalized Kalman-Yakubovič-Popov Lemma in a local linear system model, the design methods are presented in terms of solutions to a set of linear matrix inequalities, which can be readily solved via standard numerical software. The design problem is formulated as a two-objective optimization algorithm. A numerical example is given to illustrate the effectiveness and potential of the developed techniques. © 2011 IEEE.

Xia Y.,Beijing Institute of Technology
IEEE/CAA Journal of Automatica Sinica | Year: 2015

The concept of cloud control systems is discussed in this paper, which is an extension of networked control systems (NCSs). With the development of internet of things (IOT), the technology of NCSs has played a key role in IOT. At the same time, cloud computing is developed rapidly, which provides a perfect platform for big data processing, controller design and performance assessment. The research on cloud control systems will give new contribution to the control theory and applications in the near future. © 2014 Chinese Association of Automation.

Li D.,Beijing Institute of Technology | Ji B.,Beijing Institute of Technology
Physical Review Letters | Year: 2014

We present for the first time a theoretical model of studying the saturation of the rupture force of a single molecular bond that causes the rupture force to be rate independent under an ultralow loading rate. This saturation will obviously bring challenges to understanding the rupture behavior of the molecular bond using conventional methods. This intriguing feature implies that the molecular bond has a nonzero strength at a vanishing loading rate. We find that the saturation behavior is caused by bond rebinding when the loading rate is lower than a limiting value depending on the loading stiffness. © 2014 American Physical Society.

Pang B.,Beijing Institute of Technology
Journal of Intelligent and Fuzzy Systems | Year: 2014

In this paper, we introduce L-continuity degree, L-openness degree, L-closedness degree of mappings between L-fuzzifying topological spaces. Moreover, we show that most of elementary results related to continuous mappings, open mappings, and closed mappings in general topology can be extended to L-fuzzifying topological spaces by means of the graded concepts. © 2014-IOS Press and the authors. All rights reserved.

Yang C.,University of Plymouth | Ma H.,Beijing Institute of Technology | Fu M.,Beijing Institute of Technology
IET Control Theory and Applications | Year: 2013

Many practical non-linear systems can be described by non-linear auto-regressive moving average (NARMA) system models, whose stabilisation problem is challenging in the presence of large parametric uncertainties and non-parametric uncertainties. In this work, to address this challenging problem for a wide class of discrete-time NARMA systems, in which there are uncertain periodic parameters as well as uncertain non-linear part with unknown periodic time delays, we develop adaptive predictive control laws using the key ideas of 'future outputs prediction' and 'nearest-neighbour compensation', among which the former is carried out to overcome the non-causalness problem and the latter novel idea is proposed to completely compensate for the effect of non-linear uncertainties as well as unknown time delays. To achieve the desired asymptotic tracking performance in the presence of semi-parametric uncertainties with time delays, an 'n-step parameter update law' is first designed, based on which an 'one-step update law' is then elaborately constructed to obtain smoother closed-loop signals. This study in general develops a systematic adaptive control framework for periodic NARMA systems with guaranteed boundedness stability and asymptotic tracking performance, which are established by rigorous theoretic proof and verified by simulation studies. © 2013 The Institution of Engineering and Technology.

Zhou G.,University of Chinese Academy of Sciences | Chung W.,University of Hong Kong | Zhang Y.,Beijing Institute of Technology
Expert Systems with Applications | Year: 2014

This study presents an application of data envelopment analysis (DEA) approach with considering undesirable outputs, and not only examines the energy efficiency performance of China's transport sector from 2003 to 2009, but also maximizes energy-saving potential of transport sector of China's 30 administrative regions. Environmental DEA technology is adopted, which treats undesirable measures by distinguishing between weak and strong disposability. The output directional distance function is used, which explicitly expands desirable outputs and simultaneously reduces undesirable outputs. From the empirical results, the lowest number of efficient regions was recorded in 2007 or 2008, which eventually slightly recovered. Similarly, the overall average energy efficiency reached the lowest record in 2007 or 2008. These results are consistent with the policy guidance in the 11th Five-Year Plan (2006-2010) period that a series of new policies in the transport sector are implemented to reverse the trend of energy intensity increase. The Eastern area generally performed better than the Central area and Western area. The Central area was better than the Western area, except in some critical years such as in 2008, the financial crisis significantly affected port turnover. The total potential energy saving from 2003 to 2009 was 35.72 Mtce, the total potential energy saving was approximately 2.75% of the total transport energy use. © 2013 Elsevier Ltd. All rights reserved.

Jiang Y.,Beijing Institute of Technology | Ding W.,Beijing Institute of Technology
Photonic Sensors | Year: 2011

Recent developments in spectral white-light interferometry (WLI) are reviewed. Firstly, the techniques for obtaining optical spectrum are introduced. Secondly, some novel measurement techniques are reviewed, including the improved peak-to-peak WLI, improved wavelength-tracking WLI, Fourier transform WLI, and 3 × 3 coupler based WLI. Furthermore, a hybrid measurement for the intensity-type sensors, interferometric sensors, and fiber Bragg grating sensors is achieved. It is shown that these developments have assisted in the progress of WLI. © The Authors(s) 2010.

Xiong R.,Beijing Institute of Technology | Xiong R.,University of Michigan | Sun F.,Beijing Institute of Technology | Chen Z.,University of Michigan | He H.,Beijing Institute of Technology
Applied Energy | Year: 2014

Accurate estimations of battery parameter and state play an important role in promoting the commercialization of electric vehicles. This paper tries to make three contributions to the existing literatures through advanced time scale separation algorithm. (1) A lumped parameter battery model was improved for achieving accurate voltage estimate against different battery aging levels through an electrochemical equation, which has enhanced the relationship of battery voltage to its State-of-Charge (SoC) and capacity. (2) A multi-scale extended Kalman filtering was proposed and employed to execute the online measured data driven-based battery parameter and SoC estimation with dual time scales in regarding that the slow-varying characteristic on battery parameter and fast-varying characteristic on battery SoC, thus the battery parameter was estimated with macro scale and battery SoC was estimated with micro scale. (3) The accurate estimate of battery capacity and SoC were obtained in real-time through a data-driven multi-scale extended Kalman filtering algorithm. Experimental results on various degradation states of lithium-ion polymer battery cells further verified the feasibility of the proposed approach. © 2013 Elsevier Ltd.

Li B.-Z.,Beijing Institute of Technology | Xu T.-Z.,Beijing Institute of Technology
Mathematical Problems in Engineering | Year: 2012

This paper investigates the interpolation formulae and the sampling theorem for bandpass signals in the linear canonical transform (LCT) domain. Firstly, one of the important relationships between the bandpass signals in the Fourier domain and the bandpass signals in the LCT domain is derived. Secondly, two interpolation formulae from uniformly sampled points at half of the sampling rate associated with the bandpass signals and their generalized Hilbert transform or the derivatives in the LCT domain are obtained. Thirdly, the interpolation formulae from nonuniform samples are investigated. The simulation results are also proposed to verify the correctness of the derived results. © 2012 Bing-Zhao Li and Tian-Zhou Xu.

Lu K.,Beijing Institute of Technology | Xia Y.,Beijing Institute of Technology | Fu M.,Beijing Institute of Technology
Information Sciences | Year: 2013

This paper investigates the attitude tracking control problem for rigid spacecraft with actuator saturations, inertia uncertainties and external disturbances. First, based on adaptive algorithm, a sliding mode control (SMC) law is designed to achieve accurate attitude tracking, and asymptotic convergence is guaranteed by means of the Barbalat lemma. Then, the spacecraft dynamic equation is optimized, and a novel method plays a crucial role toward ensuring stability robustness to actuator saturations in the control design. Using backstepping technique (BT) associated with extended state observer (ESO) or modified differentiator (MD), the corresponding SMC approaches are appropriately designed, which not only achieve a faster and more accurate response, better transient performance, but also afford stronger capability of resistance to inertia uncertainties, external disturbances and control input saturations. Finally, simulation results are presented to illustrate effectiveness of the control strategies. © 2012 Elsevier Inc. All rights reserved.

Xiong R.,Beijing Institute of Technology | Xiong R.,University of Michigan | Sun F.,Beijing Institute of Technology | Gong X.,University of Michigan | Gao C.,University of Michigan
Applied Energy | Year: 2014

An accurate State of Charge (SoC) estimation method is one of the most significant and difficult techniques to promote the commercialization of electric vehicles. The paper attempts to make three contributions. (1) Through the recursive least square algorithm based identification method, the parameter of the lumped parameter battery model can be updated at each sampling interval with the real-time measurement of battery current and voltage, which is called the data-driven method. Note that the battery model has been improved with a simple electrochemical equation for describing the open circuit voltage against different aging levels and SoC. (2) Through the real-time updating technique of model parameter, a data-driven based adaptive SoC estimator is established with an adaptive extended Kalman filter. It has the potential to overcome the estimation error against battery degradation and varied operating environments. (3) The approach has been verified by different loading profiles of various health states of Lithium-ion polymer battery (LiPB) cells. The results indicate that the maximum estimation errors of voltage and SoC are less than 1% and 1.5% respectively. © 2013 Elsevier Ltd.

Ma X.,Beijing Institute of Technology | Li Y.,Beijing Institute of Technology
Journal of Micro/Nanolithography, MEMS, and MOEMS | Year: 2011

Li B.-Z.,Beijing Institute of Technology | Xu T.-Z.,Beijing Institute of Technology
Mathematical Problems in Engineering | Year: 2012

The spectral analysis of uniform or nonuniform sampling signal is one of the hot topics in digital signal processing community. Theories and applications of uniformly and nonuniformly sampled one-dimensional or two-dimensional signals in the traditional Fourier domain have been well studied. But so far, none of the research papers focusing on the spectral analysis of sampled signals in the linear canonical transform domain have been published. In this paper, we investigate the spectrum of sampled signals in the linear canonical transform domain. Firstly, based on the properties of the spectrum of uniformly sampled signals, the uniform sampling theorem of two dimensional signals has been derived. Secondly, the general spectral representation of periodic nonuniformly sampled one and two dimensional signals has been obtained. Thirdly, detailed analysis of periodic nonuniformly sampled chirp signals in the linear canonical transform domain has been performed. Copyright © 2012 Bing-Zhao Li and Tian-Zhou Xu.

Zhang X.,China Institute of Policy and Management | De Pablos P.O.,University of Oviedo | Zhang Y.,Beijing Institute of Technology
International Journal of Engineering Education | Year: 2012

Knowledge contribution is a very important issue in online engineering education. This study investigates how to encourage knowledge contribution in a large Asia online engineering education project. Based on long-term empirical research, we found economic incentive is more critical to facilitate explicit knowledge contribution, while social incentive is more important in encouraging tacit knowledge contribution. Moreover, we also found incentives may have different effects due to students' individual difference, e.g., personal value. That is, economic incentive may have positive effect on some students, but none or negative to others. These findings provides some theoretical contributions on e-learning and knowledge management, and also provides some implications for choosing technology in online engineering education system, and designing incentive mechanism. © 2012 TEMPUS Publications.

Ren B.,Texas Tech University | Wang J.-M.,Beijing Institute of Technology | Krstic M.,University of California at San Diego
Systems and Control Letters | Year: 2013

We consider the problem of stabilization of a linear ODE with input dynamics governed by the linearized Schrödinger equation. The interconnection between the ODE and Schrödinger equation is bi-directional at a single point. We construct an explicit feedback law that compensates the Schrödinger dynamics at the inputs of the ODE and stabilizes the overall system. Our design is based on a two-step backstepping transformation by introducing an intermediate system and an intermediate control. By adopting the Riesz basis approach, the exponential stability of the closed-loop system is built with the pre-designed decay rate and the spectrum-determined growth condition is obtained. A numerical simulation is provided to illustrate the effectiveness of the proposed design. © 2013 Elsevier B.V. All rights reserved.

Jia S.-J.,Beijing Institute of Technology | Du D.-M.,Beijing Institute of Technology
Tetrahedron Asymmetry | Year: 2014

Enantioselective Friedel-Crafts alkylation reactions of indoles with β,γ-unsaturated α-ketoesters catalyzed by novel chiral C 2-symmetric squaramide-linked bisoxazoline-Zn(OTf)2 complexes were investigated. The corresponding indole ketoesters were obtained in good to excellent yields (up to 98%) and with high enantioselectivities (up to 94% ee). This is the first report on the use of chiral squaramide-linked bisoxazoline SQBOX in a catalytic enanitioselective Friedel-Crafts alkylation reaction. © 2014 Elsevier Ltd. All rights reserved.

Fu M.,Beijing Institute of Technology | Jiao Q.,Beijing Institute of Technology | Zhao Y.,Beijing Institute of Technology | Li H.,Beijing Institute of Technology
Journal of Materials Chemistry A | Year: 2014

Novel CoFe2O4 hollow sphere/graphene composites were synthesized by a facile vapor diffusion method in combination with calcination at 550 °C. The structure and morphology of as-prepared hybrid materials were characterized by electron microscopy, X-ray diffractometry, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and Raman spectroscopy. Uniform CoFe2O4 hollow spheres with a diameter of about 500 nm and a shell thickness of approximately 50 nm were homogeneously distributed on graphene sheets. The electromagnetic parameters were measured using a vector network analyzer. A minimum reflection loss of -18.5 dB was observed at 12.9 GHz for the CoFe2O4 hollow sphere/graphene composites with a thickness of 2 mm, and the effective absorption frequency ranged from 11.3 to 15.0 GHz. The CoFe2O 4 hollow sphere/graphene composites exhibited better microwave absorbing performance than the CoFe2O4 hollow spheres. A possible formation mechanism for CoFe2O4 hollow sphere/graphene composites was proposed. © 2014 The Royal Society of Chemistry.

Zhu Y.,Beijing Institute of Technology | Guo H.,Beijing Institute of Technology | Wu Y.,Beijing Institute of Technology | Cao C.,Beijing Institute of Technology | And 2 more authors.
Journal of Materials Chemistry A | Year: 2014

Two-dimensional nanomaterials hold great potential for next-generation energy storage and conversion devices. Here, we report a large-scale synthesis of high-quality ultrathin NiO nanosheets. The well-defined nanosheets show a graphene-like morphology with large planar area, ultrathin thickness (<2 nm), and high percentage of surface atoms. In comparison with the bulk material, the NiO nanosheets exhibit unique surface and electronic structure with considerable under-coordinated surface nickel atoms and crystal lattice volume expansion. The detected local coordination geometry and the electronic states endow the ultrathin NiO nanosheets with great potential in surface-dependent electrochemical reactions and catalytic processes. When used as anode materials for lithium-ion batteries, the ultrathin NiO nanosheets exhibit a high reversible lithium storage capacity of 715.2 mA h g-1 at 200 mA g-1 current density in 130 cycles with an excellent cycling stability and rate capability. In particular, the large-area ultrathin 2D nanostructure can shorten lithium ion diffusion paths and provide a large exposed surface for more lithium-insertion channels. The large-scale and cost-efficient synthesis and the excellent electrochemical performance highlight the high-quality ultrathin 2D NiO nanosheets as a competitive anode material for lithium-ion batteries. This journal is © the Partner Organisations 2014.

Feng Z.-H.,Hefei University of Technology | Feng Z.-H.,Beijing Institute of Technology | Zou L.-L.,CAS Institute of Policy and Management | Wei Y.-M.,Beijing Institute of Technology
Energy | Year: 2011

In this paper, the consumer lifestyle approach is applied to analyze the impact of consumption by urban and rural households on energy use and CO2 emissions for different regions and income levels in China. Grey Model is used to compare the relationship between energy consumption, consumption expenditure and CO2 emissions for different lifestyles. The results show that direct energy consumption is diverse for urban households and simple for rural households in China. Direct energy consumption and CO2 emissions are increasing faster for urban than for rural households. Indirect energy consumption and CO2 emissions for urban households are much greater than the direct consumption values. The total indirect energy consumption and CO2 emissions differ by regions and the structures are different, but the latter differences are not obvious. The impact of household income is enormous. Indirect energy consumption and CO2 emissions are higher for high-income than for low-income households. The structural difference for indirect energy consumption and CO2 emissions for households with different income levels is significant. The higher the income, the more diverse is the energy consumption and CO2 emission structure. The structures for indirect energy use and CO2 emissions are diverse for urban households, but simple for rural households. © 2010.

Yu Z.,Beijing Institute of Technology
Lecture Notes in Electrical Engineering | Year: 2016

By applying finite element method and static analysis, the front transmission gearbox model of a tracked vehicle is simplified and the boundary conditions treatment and finite element mesh generation techniques were used to ensure the correctness of the analysis. Then, based on the analysis and computation, the displacement and stress distribution of the gearbox are calculated. Then, dynamic modal analysis is conducted for the gearbox to obtain the natural frequencies of various orders and the corresponding vibration modes in constraint mode, which provided basis for subsequent structure optimization. According to the results of finite element computation, the strength and the stiffness of each part of the gearbox are analyzed and the weak link is obtained. After extending the design space, the structure is redesigned through topology optimization to improve the strength and stiffness. © Springer-Verlag Berlin Heidelberg 2016.

Zhu W.,Nanjing University of Science and Technology | Zhu W.,Beijing Institute of Technology | Xiao H.,Nanjing University of Science and Technology
Journal of Physical Chemistry C | Year: 2011

Ab initio molecular dynamics simulations have been performed to study the effects of different temperatures on the structure and stability of energetic solid silver azide. The results indicate that the N-N bond fission takes place at 523 K. The azide sublattice structure broke down prior to the silver sublattice. The initiation decomposition of silver azide is triggered by the N-N bond breaking. This will initiate many decomposition reactions and produce many nitrogen radicals, N2, and silver clusters. Silver azide has metallic properties at 573 K. As the temperature increases, its sensitivity becomes more and more sensitive. The calculated power spectra of the velocity autocorrelation function show that the low-frequency vibrational modes become more prominent than the high-frequency ones with increasing temperature. This would allow low-frequency vibrations and rotations to occur more freely than in the solid. © 2011 American Chemical Society.

Zhao Y.H.,Beijing Institute of Technology
Applied Mechanics and Materials | Year: 2013

The new environmentally friendly materials have broad application prospects in environmental protection and the environmental governance. This paper reviewed the recent progress of the new-style environmentally friendly materials in environmental protection and the aspects of research and applications are discussed in this paper one by one of several kinds of new-style environmentally friendly materials in environmental protection and governance, and introduces the application of new environmentally friendly technology in air pollution, sewage treatment and other aspects of environmental protection. The noise pollution control, solid waste disposal, environmental monitoring and other applications are also introduced. With the development of science and technology, new environmentally friendly materials are used more and more in the field of environmental protection, with the nano materials and nano carbon materials the typical representatives. Nano materials are a kind of ultrafine materials with the grain size of nanometer (10-9m). Broadly speaking, nanometer materials are the materials with the nanometer scale in at least one dimension or a basic element. Nanotechnology is considered to be the most promising research field in twenty-first century, and the research on nanometer materials is a hot topic in material science. It should be said that nanometer materials have different influence and infiltration on various fields. Especially the application of nanometer materials in environmental protection and environmental governance brings new opportunities to our country and even the whole world in the treatment of environmental pollution. Activated carbon is a typical representative of carbon materials, which is an excellent adsorbent, with unique pore structure and surface functional groups. There are enough chemical stability and certain mechanical strength, acid and alkali resistance, high temperature resistance, insoluble in water and organic solvents and the regeneration cycle. Activated carbon was first used in sugar industry refining. After rapid development for more than a century, its application scope has been expanded to various departments of industrial production. At present, with the deterioration of ecological environment, people' voice of protecting the earth and the green technology and green products is higher and higher. The application of new environmentally friendly materials with nano materials and active carbon as the representatives in the field of environmental protection will be developed further. The following are the introduction to the research and application of the environmental protection and governance of several kinds of current nanometer materials and carbon materials. © (2013) Trans Tech Publications, Switzerland.

Chen Z.,Northeast Normal University | Cao M.,Northeast Normal University | Cao M.,Beijing Institute of Technology | Hu C.,Beijing Institute of Technology
Journal of Physical Chemistry C | Year: 2011

In this work, highly ordered Zn2SnO4 three-dimensional flowerlike superstructures assembled with nanorods have been synthesized by a facile one-step hydrothermal route at 180 °C. The products were characterized by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, and selected-area electron diffraction. The morphology of the final products was found to depend strongly on the concentrations of EDA and CTAB used. A possible mechanism for the formation of self-assembled Zn2SnO4 flowerlike superstructures is proposed. In addition, the novel Zn2SnO 4 three-dimensional superstructures exhibited good gas-sensing properties that are even better than those of the competing binary metal oxide ±-Fe2O3 and In2O3 sensors. The excellent gas-sensing properties make this material interesting not only for use in sensor devices, but also for a number of related electrochemical applications. © 2011 American Chemical Society.

Sun F.,Beijing Institute of Technology | Hu X.,Beijing Institute of Technology | Zou Y.,Beijing Institute of Technology | Li S.,Beijing Institute of Technology
Energy | Year: 2011

An accurate battery State of Charge estimation is of great significance for battery electric vehicles and hybrid electric vehicles. This paper presents an adaptive unscented Kalman filtering method to estimate State of Charge of a lithium-ion battery for battery electric vehicles. The adaptive adjustment of the noise covariances in the State of Charge estimation process is implemented by an idea of covariance matching in the unscented Kalman filter context. Experimental results indicate that the adaptive unscented Kalman filter-based algorithm has a good performance in estimating the battery State of Charge. A comparison with the adaptive extended Kalman filter, extended Kalman filter, and unscented Kalman filter-based algorithms shows that the proposed State of Charge estimation method has a better accuracy. © 2011 Elsevier Ltd.

Zhang X.,CAS Institute of Mechanics | Yu Y.,Beijing Institute of Technology
Combustion and Flame | Year: 2011

The three-dimensional effects of flame spread over thin solid materials were experimentally studied using a natural-convection-suppressing horizontal narrow-channel. In a sufficiently wide narrow-channel, the variation of flame spread against the width of the material sample showed different trends for different gas flow speeds and oxygen concentrations. The extent of three-dimensional effects was inversely proportional to the gas flow speed or its square. Near quenching extinction limits, the effects were significant because weak combustion is sensitive to a slight variation of heat loss and oxygen concentration. The effects may be due to different factors such as side heat loss, side oxygen diffusion, or both. Far away from quenching extinction limits, the effects were weak because vigorous combustion is insensitive to a small variation of oxygen concentration and heat loss. In all tests, the effects were limited to the samples of width less than 10 times of the diffusion length. Moreover, a higher oxygen concentration suppressed the effects at a lower gas flow speed. For sufficiently wide samples, in the most range of gas flow speeds, the channel width had almost no effect on flame spread. However, near extinction limits, the flame spread rate decreased with the increasing channel width. © 2010 The Combustion Institute.

Su J.,Beijing Institute of Technology | Cao M.,Beijing Institute of Technology | Ren L.,Beijing Institute of Technology | Hu C.,Beijing Institute of Technology
Journal of Physical Chemistry C | Year: 2011

In this paper, we proposed a facile one-step strategy to prepare graphene-Fe3O4 (GN-Fe3O4) nanocomposites under hydrothermal conditions, where the reduction process of graphite oxide (GO) sheets into GN was accompanied by the generation of Fe 3O4 nanoparticles. The reduction extent of GO by this process could be comparable to that by conventional methods. A transmission electron microscopy image has shown that the as-formed Fe3O 4 nanoparticles with a diameter as small as 7 nm were densely and uniformly deposited on GN sheets, and, as a result, the aggregating of the Fe3O4 nanoparticles was effectively prevented. The GN-Fe3O4 nanocomposites exhibit improved cycling stability and rate performances as a potential anode material for high-performance lithium ion batteries. In addition, the GN-Fe3O4 nanocomposites exhibit a superparamagnetic behavior, making them promising candidates for practical applications in the fields of bionanotechnology/ controlled targeted drug delivery. © 2011 American Chemical Society.

Shen J.,Beijing Institute of Technology | Du Y.,Beijing Institute of Technology | Wang W.,Beijing Institute of Technology | Li X.,CAS Xi'an Institute of Optics and Precision Mechanic
IEEE Transactions on Image Processing | Year: 2014

We present a novel image superpixel segmentation approach using the proposed lazy random walk (LRW) algorithm in this paper. Our method begins with initializing the seed positions and runs the LRW algorithm on the input image to obtain the probabilities of each pixel. Then, the boundaries of initial superpixels are obtained according to the probabilities and the commute time. The initial superpixels are iteratively optimized by the new energy function, which is defined on the commute time and the texture measurement. Our LRW algorithm with self-loops has the merits of segmenting the weak boundaries and complicated texture regions very well by the new global probability maps and the commute time strategy. The performance of superpixel is improved by relocating the center positions of superpixels and dividing the large superpixels into small ones with the proposed optimization algorithm. The experimental results have demonstrated that our method achieves better performance than previous superpixel approaches. © 2013 IEEE.

Zheng G.,Beijing Institute of Technology
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2010

A new-conceptual fiber-optic gyroscope is introduced. The gyroscope employs the two newly-emerged novel technologies: the optical frequency-modulated continuous-wave (FMCW) interference, and the differential fiber-optic gyroscope, and therefore, it can overcome the problems in the traditional fiber-optic gyroscopes, such as temperature drift and poor long-term stability. The FMCW interference, which was originally investigated in radar technology, has been successfully used to construct various fiber-optic interferometers and sensors. The advantages of this technology include accurate calibration of the phase, simple count of fringes, and easy signal processing. The interest in the application of the FMCW technique to rotation sensing has been growing for a long period. The problem in the FMCW fiber-optic gyroscope is that the gyroscope must be an unbalanced, and the initial optical path difference in the gyroscope will cause an unexpected non-reciprocal phase drift if the environmental conditions are unstable. This paper reports a differential FMCW fiber-optic gyroscope. The advantages of this fiber-optic gyroscope include: (1) Due to the nature of the differential interferometer structure, the unexpected non-reciprocal phase drift is automatically removed, and the calibration fact of the gyroscope is automatically doubled. (2) Benefited from the FMCW technology, this gyroscope has no zero-sensitivity point problem, and it has a higher resolution and a larger dynamic range. © 2010 SPIE.

Xu B.,Northwestern Polytechnical University | Yang C.,University of Plymouth | Yang C.,Beijing Institute of Technology | Shi Z.,Northwestern Polytechnical University
IEEE Transactions on Neural Networks and Learning Systems | Year: 2014

In this brief, a novel adaptive-critic-based neural network (NN) controller is investigated for nonlinear pure-feedback systems. The controller design is based on the transformed predictor form, and the actor-critic NN control architecture includes two NNs, whereas the critic NN is used to approximate the strategic utility function, and the action NN is employed to minimize both the strategic utility function and the tracking error. A deterministic learning technique has been employed to guarantee that the partial persistent excitation condition of internal states is satisfied during tracking control to a periodic reference orbit. The uniformly ultimate boundedness of closed-loop signals is shown via Lyapunov stability analysis. Simulation results are presented to demonstrate the effectiveness of the proposed control. © 2012 IEEE.

Gao Z.,Beijing Institute of Technology | Liao X.,Beijing Institute of Technology
Nonlinear Dynamics | Year: 2012

In this paper, a rational approximation me-thod is proposed for the fractional-order system using the particle swarm optimization (PSO). Firstly, the approximation method for the fractional-order operator is studied, because a fractional-order system consists of many fractional-order operators. The coefficients of the transfer function are calculated using PSO with a fitness function under the continued fraction expansion (CFE) framework in the frequency domain. The average velocity of the particle swarm is defined to reflect the real state of particle swarm. To improve the global optimization and achieve a more satisfactory fitting result, comparing with the linear PSO, the chaotic optimization is combined with PSO. The numerical examples of fractional-order systems demonstrate the effectiveness of this method. © 2011 Springer Science+Business Media B.V.

Gong P.,Beijing Institute of Technology | Li P.,Beijing Institute of Technology | Shi W.,Northeastern University China
Nonlinear Dynamics | Year: 2012

To guarantee secure communication, many maps-based key agreement protocols have been proposed. Due to inherent tamper-resistance, most of them are based on smart cards. Unfortunately, the cost of cards and readers makes these protocols costly. In the real world, common storage devices, such as universal serial bus (USB) thumb drives, portable HDDs, mobile phones, and laptop or desktop PCs, are widely used, and they are much cheaper or more convenient for storing user authentication information. These devices do not provide tamper-resistance; it is a challenge to design a secure authentication protocol using these kinds of memory devices. In this paper, we will propose a maps-based key agreement protocol without using smart cards. According to our analysis, the proposed protocol guarantees mutual authentication, and also resists different attacks. Therefore, our protocol is suitable even for practical applications. © Springer Science+Business Media Dordrecht 2012.

He H.-X.,Beijing Institute of Technology | Du D.-M.,Beijing Institute of Technology
Tetrahedron Asymmetry | Year: 2014

Highly enantioselective Mannich reactions of imines bearing a benzothiazole moiety with tert-butyl acetoacetate, catalyzed by a cinchona-based squaramide organocatalyst have been developed. The corresponding benzothiazole β-keto ester derivatives were obtained in high yields (up to 99%) and with excellent enantioselectivities (up to 98% ee). © 2014 Elsevier Ltd. All rights reserved.

Liu G.,Beijing Institute of Technology | Tang K.,Beijing Institute of Technology
Journal of Composite Materials | Year: 2016

This article presents a detailed analysis on stress concentration in notched unidirectional fiber-reinforced composites. Due to the formation of longitudinal splitting at notch tips along the fiber direction, the extremely high stress concentrations ahead of the notch tips could be drastically reduced for composites under remote tension. The inability of the widely used material property degradation method to accurately redistribute the local stresses at the notch tips is examined. The notch blunting effect is investigated by modeling the longitudinal splitting as a thin plastic cohesive layer or debonding, and results for the stress redistribution in the unnotched section directly ahead of the notch tips are presented. By introducing the intra- and inter-ply damage modes, the failure of a double-notched cross-ply laminate is predicted and compared with the experimental results from open literature. © The Author(s) 2015.

Wang H.,Beijing Institute of Technology
Journal of Intelligent and Fuzzy Systems | Year: 2016

This paper provides some existence results about first-order fuzzy differential equations with two-point boundary value conditions. We firstly study a class of linear fuzzy differential equation, the results are applied to discuss some nonlinear fuzzy boundary value problems. By using contraction mapping principle in complete metric space, we obtain some existence results about first-order nonlinear fuzzy differential equation with boundary value condition x (0) = αx (T), where α ∈ R. © 2016 - IOS Press and the authors. All rights reserved.

Han W.,Beijing Institute of Technology | Jiang L.,Beijing Institute of Technology | Li X.,Beijing Institute of Technology | Liu P.,Beijing Institute of Technology | And 2 more authors.
Optics Express | Year: 2013

Large-area, uniform laser-induced periodic surface structures (LIPSS) are of wide potential industry applications. The continuity and processing precision of LIPSS are mainly determined by the scanning intervals of adjacent scanning lines. Therefore, continuous modulations of LIPSS and scanned line-widths within one laser scanning pass are of great significance. This study proposes that by varying the laser (800 nm, 50 fs, 1 kHz) polarization direction, LIPSS and the scanned line-widths on a silicon (111) surface can be continuously modulated with high precision. It shows that the scanned line-width reaches the maximum when the polarization direction is perpendicular to the scanning direction. As an application example, the experiments show large-area, uniform LIPSS can be fabricated by controlling the scanning intervals based on the one-pass scanned linewidths. The simulation shows that the initially formed LIPSS structures induce directional surface plasmon polaritons (SPP) scattering along the laser polarization direction, which strengthens the subsequently anisotropic LIPSS fabrication. The simulation results are in good agreement with the experiments, which both support the conclusions of continuous modulations of the LIPSS and scanned line-widths. © 2013 Optical Society of America.

Yu S.,University of Management and Economics | Yu S.,Beijing Institute of Technology | Wei Y.-M.,Beijing Institute of Technology | Guo H.,University of Management and Economics | Ding L.,University of Management and Economics
Applied Energy | Year: 2014

Coal-fired electricity generation has become the largest source of carbon emission in China. This study utilizes life-cycle assessment to assess the effect of carbon emissions and to calculate the coefficient of carbon emissions in coal-to-energy chains. Results show that the carbon emission coefficient of the coal-to-energy chain in China is 875g/kWh-1, which is a relatively low level compared with that of other countries. CO2 is the main type of greenhouse gas emission and is the most abundant type of direct emission. China has to reduce electrical consumption in the coal-mining process to reduce carbon emissions in coal-to-energy chains. Moreover, China has to facilitate railway-line construction to improve the proportion of railway transportation to coal transportation. © 2013 Elsevier Ltd.

Wang K.,Beijing Institute of Technology | Wei Y.-M.,Beijing Institute of Technology
Applied Energy | Year: 2014

Evaluating the energy and emissions efficiency, measuring the energy saving and emissions reduction potential, and estimating the carbon price in China at the regional level are considered a crucial way to identify the regional efficiency levels and efficiency promotion potentials, as well as to explore the marginal abatement costs of carbon emissions in China. This study applies a newly developed Data Envelopment Analysis (DEA) based method to evaluate the regional energy and emissions efficiencies and the energy saving and emissions reduction potentials of the industrial sector of 30 Chinese major cities during 2006-2010. In addition, the CO2 shadow prices, i.e., the marginal abatement costs of CO2 emissions from industrial sector of these cities are estimated during the same period. The main findings are: (i) The coast area cities have the highest total factor industrial energy and emissions efficiency, but efficiency of the west area cities are lowest, and there is statistically significant efficiency difference between these cities. (ii) Economically well-developed cities evidence higher efficiency, and there is still obviously unbalanced and inequitable growth in the nationwide industrial development of China. (iii) Fortunately, the energy utilization and CO2 emissions efficiency gaps among different Chinese cities were decreasing since 2006, and the problem of inequitable nationwide development has started to mitigate. (iv) The Chinese major cities could have, on average, an approximately 19% or 17% efficiency increase on energy utilization or CO2 emissions during 2006-2010. (v) Promoting the industrial energy utilization efficiency is comparatively more crucial for Chinese cities at the current stage, and the efficiency promotion burdens on the west area cities are the heaviest among all Chinese cities. (vi) An N-shaped Environmental Kuznets Curve (EKC) exists between the level of industrial CO2 emissions efficiency and income, and the inflection point the EKC is located between 12,052 and 12,341 US$of GDP per capita, indicating that an accelerated CO2 emissions efficiency increase will accrue when this income level is reached. (vii) In 2010, the industrial total energy saving and CO2 emissions reduction potentials for Chinese major cities were 41 million tce and 143 million tCO2, respectively. (viii) The average industrial CO2 emissions abatement cost for Chinese major cities is 45 US$ during 2006-2010, and the existence of large gap on CO2 shadow prices between different Chinese regions provide a necessity and possibility for establishing a regional carbon emissions trading system in China. © 2014 Elsevier Ltd.

Ma X.,Beijing Institute of Technology | Li Y.,Beijing Institute of Technology | Cao M.,Beijing Institute of Technology | Hu C.,Beijing Institute of Technology
Journal of Materials Chemistry A | Year: 2014

Highly porous N-doped carbon monoliths have been successfully prepared by using binary H3PO4-HNO3 mixed acid as a co-activating agent for the first time and sodium alginate (SA), a natural biopolymer, as a carbon precursor. The resultant N-doped carbon monoliths have a narrow size distribution and high content of pyrrolic N. Particularly, the sample SA-2N-P with the highest surface area (1740 m2 g-1) exhibits the highest CO2 adsorption capacity of 8.99 mmol g -1 at 273 K and 4.57 mmol g-1 at 298 K, along with an initial CO2 adsorption energy of 43 kJ mol-1 at lower CO2 coverage and 32 kJ mol-1 at higher CO2 coverage. Remarkably, this sample also shows the highest CO2 capacity [66.44 mg (CO2) g-1 (adsorbent) at 25 °C and 0.15 atm] under low CO2 pressures, which is of more relevance for flue gas applications. Furthermore, the selectivity of CO2 over N2 is also calculated for the binary gas mixture [V (N2) : V (CO 2) = 85 : 15] according to the ideal adsorbed solution theory (IAST). Combined with its simple preparation, high adsorption capacity, and high selectivity for CO2, the sample SA-2N-P is one of the promising solid-state absorbents reported so far for CO2 capture and storage. © 2014 The Royal Society of Chemistry.

Yu S.,University of Management and Economics | Yu S.,Beijing Institute of Technology | Wei Y.-M.,Beijing Institute of Technology | Wang K.,Beijing Institute of Technology
Energy Policy | Year: 2014

An approach to determine carbon emission reduction target allocation based on the particle swarm optimization (PSO) algorithm, fuzzy c-means (FCM) clustering algorithm, and Shapley decomposition (PSO-FCM-Shapley) is proposed in this study. The method decomposes total carbon emissions into an interaction result of four components (i.e., emissions from primary, secondary, and tertiary industries, and from residential areas) which composed totally by 13 macro influential factors according to the KAYA identity. Then, 30 provinces in China are clustered into four classes according to the influential factors via the PSO-FCM clustering method. The key factors that determine emission growth in the provinces representing each cluster are investigated by applying Shapley value decomposition. Finally, based on guaranteed survival emissions, the reduction burden is allocated by controlling the key factors that decelerate CO2 emission growth rate according to the present economic development level, energy endowments, living standards, and the emission intensity of each province. A case study of the allocation of CO2 intensity reduction targets in China by 2020 is then conducted via the proposed method. The per capita added value of the secondary industry is the primary factor for the increasing carbon emissions in provinces. Therefore, China should limit the growth rate of its secondary industry to mitigate emission growth. Provinces with high cardinality of emissions have to shoulder the largest reduction, whereas provinces with low emission intensity met the minimum requirements for emission in 2010. Fifteen provinces are expected to exceed the national average decrease rates from 2011 to 2020. © 2013 Elsevier Ltd.

Zhang B.,Beijing Institute of Technology | Wang Z.,Beijing Institute of Technology
Energy Economics | Year: 2014

The purpose of this paper is to explore the determinants that influence the industrial firms to cooperate on carbon emission reduction (CER) within their industrial chains. And whether the CER collaborations could improve the performance of participants is another focus of our study. This paper provides a questionnaire survey about CER inter-firm collaborations on energy intensive industries in China. Three regression models including Multiple Linear Regression, Binary Choice Model, and Ordinal Choice Regression are employed to identify the determinants that drive or impede the implementation of CER collaborations. The results show that inter-firm CER collaborations are generally at an infancy stage in China. The main driver for CER collaborations derives from the CER demands of other stakeholders in the industrial chains. And the lack of infrastructure and mechanism is the main barrier that impedes the inter-firm collaborations. Moreover, CER collaborations through industrial symbiosis play a positive role in improving economic performance. However, the effects are to a large extent related to the improved environmental performance through the CER collaborations. Our results also indicate that there is much room for industrial firms to conduct CER collaborations in China, and market tools are somewhat more effective than compulsive regulations for promoting CER collaborations. © 2013 Elsevier B.V.

Zhang W.,Beijing Institute of Technology | Li X.,Beijing Institute of Technology | Yang R.,Beijing Institute of Technology
Polymer Degradation and Stability | Year: 2011

The pyrolysis and fire behaviour of epoxy resin (EP) composites based on a novel polyhedral oligomeric silsesquioxane containing 9,10-dihydro-9-oxa-10- phosphaphenanthrene-10-oxide (DOPO-POSS) and diglycidyl ether of bisphenol A (DGEBA) have been investigated. The pre-reaction between the hydroxyl groups of DOPO-POSS and the epoxy groups of DGEBA at 140 °C is confirmed by FTIR, which means that DOPO-POSS molecules of hydroxyl group could easily disperse into the epoxy resin at the molecular level. The EP composites with the DOPO-POSS were prepared through a curing agent, m-phenylenediamine (m-PDA). The morphologies of the EP composites observed by SEM indicate that DOPO-POSS disperses with nano-scale particles in the EP networks, which implies good compatibility between them. The thermal properties and pyrolysis of the EP composites were analyzed by DSC and TGA, TGA-FTIR, and TGA-MS. The analysis indicates that the DOPO-POSS change the decomposition pathways of the epoxy resin and increase its residue at high temperature; moreover, the release of phosphorous products in the gas phase and the existence of Si-O and P-O structures in the residue Is noted. The fire behaviour of the EP composites was evaluated by cone calorimeter (CONE). The CONE tests show that incorporation of DOPO-POSS into epoxy resin can significantly improve the flame retardancy of EP composites. SEM and XPS were used to explore micro-structures and chemical components of the char from CONE tests of the EP composites, they support the view that DOPO-POSS makes the char strong with the involvement of Si-O and P-O structures. © 2011 Elsevier Ltd. All rights reserved.

Li S.G.,Shaanxi Automobile Group Co. | Sharkh S.M.,University of Southampton | Sharkh S.M.,HiT Systems Ltd. | Walsh F.C.,University of Southampton | Zhang C.N.,Beijing Institute of Technology
IEEE Transactions on Vehicular Technology | Year: 2011

Fuzzy logic is used to define a new quantity called the battery working state (BWS), which is based on both battery terminal voltage and state of charge (SOC), to overcome the problem of battery over-discharge and associated damage resulting from inaccurate estimates of the SOC. The BWS is used by a fuzzy logic energy-management system of a plug-in series hybrid electric vehicle (HEV) to make a decision on the power split between the battery and the engine, based on the BWS and vehicle power demand, while controlling the engine to work in its fuel economic region. The fuzzy logic management system was tested in real time using an HEV simulation test bench with a real battery in the loop. Simulation results are presented to demonstrate the performance of the proposed fuzzy logic energy-management system under different driving conditions and battery SOCs. The results indicate that the fuzzy logic energy-management system using the BWS was effective in ensuring that the engine operates in the vicinity of its maximum fuel efficiency region while preventing the battery from over-discharging. © 2011 IEEE.

Li J.-H.,Beijing Institute of Technology | Du D.-M.,Beijing Institute of Technology

An efficient chiral squaramide-catalysed enantioselective Michael addition of pyrazolin-5-ones to β,γ-unsaturated α-ketoesters has been developed. The chiral pyrazolone derivatives were obtained in moderate to high yields (up to 99% yield) with high enantioselectivities (up to 96% ee) for most substrates. This catalytic asymmetric reaction provides valuable and easy access to chiral pyrazolone ketoester derivatives. This journal is © the Partner Organisations 2014.

Zhao B.-L.,Beijing Institute of Technology | Du D.-M.,Beijing Institute of Technology

A bifunctional squaramide catalysed enantioselective conjugate Michael addition reaction of various α-mercaptoketones to α,β- unsaturated N-acylated oxazolidinones under mild reaction conditions has been developed. This catalytic reaction afforded the corresponding adducts in good yields with high enantioselectivities (up to 92% ee). This is the first example of organocatalysed sulfa-Michael addition using various α-mercaptoketones as the Michael donors. © 2014 the Partner Organisations.

Jiang Y.,Beijing Institute of Technology
Zhongguo Jiguang/Chinese Journal of Lasers | Year: 2010

Fiber optic white-light interferometry (WLI) possesses a considerable advantage with regard to the ability to provide absolute and unambiguous measurement, comparing to laser interferometry. The research on fiber optic white-light interferometry in recent years is reviewed in this paper, and fiber optic WLI based on phase measurement method is focused, including interference-order method, Fourier-transform WLI, Fourier-transform relative WLI, wavelength-scanning WLI, and phase-shifted WLI. The main problems, such as spectrum acquirement, measurement resolution and automatic measurement, are solved in the work in order to accelerate the technique in instrumentation and engineering application.

Zhang R.,Taiyuan University of Technology | Song L.,Taiyuan University of Technology | Wang Y.,Beijing Institute of Technology
Applied Surface Science | Year: 2012

A density functional theory slab calculations of CH 4 dissociation on Pt(h k l) surfaces have been systematically presented. On the basis of the energetic analysis, the favorable adsorption sites and stable configurations of CH x(x = 0-4) and H species on Pt(1 1 1), Pt(1 1 0) and Pt(1 0 0) surfaces are first obtained, respectively. Afterwards, the most stable configurations of coadsorbed CH x/H(x = 0-3) are located. Further, the kinetic and thermodynamical results of CH 4 dissociation on Pt(h k l) surface suggest that CH is the most abundant CH x species. Our results mean that Pt catalyst can resist the carbon deposition in the CH 4 dissociation, which can give a microscopic reason that why Pt catalyst can lead to lower carbon deposition and show a high activity in the reaction related to CH 4. © 2012 Elsevier B.V.

Peng J.,Beijing Institute of Technology | Du D.-M.,Beijing Institute of Technology

An efficient highly enantioselective fluorination of β-keto esters/amides catalysed by diphenylamine-linked bis(thiazoline)-Cu(OTf) 2 complexes has been developed. The corresponding products could be obtained with good to excellent enantioselectivities (up to > 99% ee) in excellent yields by utilizing N-fluorobisbenzenesulphonimide (NFSI) as fluorination reagent. © 2014 The Royal Society of Chemistry.

Zhong J.,Beijing Institute of Technology | Cao C.,Beijing Institute of Technology | Liu Y.,Beijing Institute of Technology | Li Y.,Beijing Institute of Technology | Khan W.S.,Beijing Institute of Technology
Chemical Communications | Year: 2010

Hollow core-shell η-Fe2O3 microspheres exhibit not only superior electrochemical performance as lithium storage electrodes but also excellent sensitivities to trace levels of gases. © 2010 The Royal Society of Chemistry.

Zhao H.-K.,Beijing Institute of Technology | Zhao L.-L.,Beijing Institute of Technology
European Physical Journal B | Year: 2011

We have investigated the shot noise spectral density in the parallel double-quantum-dot (DQD) interferometer threaded with an Aharonov-Bohm (AB) flux under the perturbation of ac fields. The derivations are based on the nonequilibrium Green's function (NGF) technique in the Coulomb blockade regime. The AB flux and the perturbation of ac fields together provide a photon-assisted AB interferometer for controlling the shot noise efficiently. The signature of the shot noise reflects the intrinsic microstructure of the DQD system, which plays important roles for the enhancement and suppression of shot noise. The versatile resonant structures of shot noise, Fano factor have been revealed to exhibit the sub-Poissonian and super-Poissonian types of shot noise by adjusting the gate voltages sequentially. © 2011 EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg.

Wang Z.-L.,CAS Fujian Institute of Research on the Structure of Matter | Fang W.-H.,CAS Fujian Institute of Research on the Structure of Matter | Yang G.-Y.,CAS Fujian Institute of Research on the Structure of Matter | Yang G.-Y.,Beijing Institute of Technology
Chemical Communications | Year: 2010

Two three-fold interpenetrated frameworks, [LnCuL4][Ln 0.25Cu0.25L] (Ln = Dy 1, Er 2; HL = 4-(pyridin-4-yl) benzoic acid), have been made. Their structures contain two kinds of four-connected uniform nets: dia and mdf nets. The mdf net is a new chiral 86 net with the long vertex symbol (81.8 3.84.84.84.84). © 2010 The Royal Society of Chemistry.

Chen R.,Beijing Institute of Technology | Zhao T.,Beijing Institute of Technology | Wu F.,Beijing Institute of Technology
Chemical Communications | Year: 2015

In terms of sustainable development and environmental issues, the design and fabrication of efficient energy storage devices will be more critical in the future than at any time in the past. Li-S batteries are promising candidates for such a purpose due to their high specific capacity and low environmental impact. This review has systematically retraced the advances in the field of Li-S batteries over the past half century and highlighted the main breakthroughs in a number of areas, covering the mechanism determination, cathode engineering, theoretical simulation, and electrolyte tailoring and anode protection. Furthermore, we discuss the remaining challenges towards their practical application. It is expected that Li-S batteries with 3D inter-connected or conformal assemblies will surpass new horizons in the coming years. © 2015 The Royal Society of Chemistry.

Han T.,Beijing Institute of Technology | Feng X.,Beijing Institute of Technology | Feng X.,Japan Institute for Molecular Science | Tong B.,Beijing Institute of Technology | And 4 more authors.
Chemical Communications | Year: 2012

A water-soluble, 'turn-on' fluorescent chemosensor based on aggregation-induced emission (AIE) has been developed. It exhibits rapid response, excellent selectivity, and sensitivity to Al 3+.

Wang S.-S.,CAS Fujian Institute of Research on the Structure of Matter | Yang G.-Y.,CAS Fujian Institute of Research on the Structure of Matter | Yang G.-Y.,Beijing Institute of Technology
Chemical Reviews | Year: 2015

The latest advancements in polyoxometalate (POM)-catalyzed reactions are discussed. POMs have also been modified into surfactant-type catalysts by several research groups. Some of these surfactant-type catalysts feature automatic behavior. They are sensitive to temperature, chemicals, or light. Temperature-controlled catalysts are homogeneous during the reaction with elevated temperature and precipitate from the reaction solution when the temperature drops.

Liu C.,Beijing Institute of Technology | Tian Q.,Beijing Institute of Technology | Yan D.,Beijing Institute of Technology | Hu H.,Beijing Institute of Technology
Computer Methods in Applied Mechanics and Engineering | Year: 2013

A computational approach is proposed for the dynamic analysis of complicated membrane systems, such as parachutes and solar sails, which undergo overall motions, large deformations, as well as wrinkles owing to the small membrane resistance to the compressive stress therein. Based on previous studies, a thin shell element of gradient deficient Absolute Nodal Coordinate Formulation (ANCF) is proposed first. Then, the strain energy of the above shell element is derived by using the definition of the Green-Lagrange strain tensor in continuum mechanics. The computationally efficient formulations of elastic forces and their Jacobian for the above shell element are also derived via the skills of tensor analysis. Afterwards, a membrane element of ANCF is proposed by integrating the criterion of wrinkle/slack into the above shell element. To deal with the small compressive stiffness for the membrane element, the Stiffness Reduction Model (SRM) is introduced to the membrane elements. Finally, four case studies including both statics and dynamics of different membrane systems are given to validate the proposed approach. The final example of the spinning deployment of a solar sail shows the efficacy of the proposed approach in the dynamic analysis of complicated membrane system undergoing an overall motion, large deformations and wrinkles. © 2013 Elsevier B.V.

Liang M.,Beijing Institute of Technology
Quantum Information Processing | Year: 2013

Suppose some data have been encrypted, can you compute with the data without decrypting them? This problem has been studied as homomorphic encryption and blind computing. We consider this problem in the context of quantum information processing, and present the definitions of quantum homomorphic encryption (QHE) and quantum fully homomorphic encryption (QFHE). Then, based on quantum one-time pad (QOTP), we construct a symmetric QFHE scheme, where the evaluate algorithm depends on the secret key. This scheme permits any unitary transformation on any $$n$$ n -qubit state that has been encrypted. Compared with classical homomorphic encryption, the QFHE scheme has perfect security. Finally, we also construct a QOTP-based symmetric QHE scheme, where the evaluate algorithm is independent of the secret key. © 2013 Springer Science+Business Media New York.

Weijermars R.,Technical University of Delft | Taylor P.,University of Leeds | Bahn O.,HEC Montréal | Das S.R.,University of Petroleum and Energy Studies | Wei Y.-M.,Beijing Institute of Technology
Energy Strategy Reviews | Year: 2012

Organizational behavior and stakeholder processes continually influence energy strategy choices and decisions. Although theoretical optimizations can provide guidance for energy mix decisions from a pure physical systems engineering point of view, these solutions might not be optimal from a political or social perspective. Improving the transparency of our vision sharing and strategy making processes in a systematic way is therefore as important as the actual systems engineering solutions proposed by the modeling tools. Energy trend forecasting and back-casting, scenarios and system analysis have matured into powerful modeling tools for providing advice on optimizing our future energy solutions. The integrated use and iterative improvement of all these approaches can result in energy systems that become better optimized. Such an integrated approach is particularly important to those who have decision-making power over our future energy direction. Some of the challenges and opportunities for energy strategists that strive to promote optimal decisions on our future energy solutions are highlighted in this state-of-the-art review. © 2011 Elsevier Ltd.

Liu H.,CAS Beijing National Laboratory for Molecular | Du D.-M.,Beijing Institute of Technology | Du D.-M.,CAS Beijing National Laboratory for Molecular
Advanced Synthesis and Catalysis | Year: 2010

The new diphenylamine-linked bis(imidazoline) ligands were prepared through Kelly-You's imidazoline formation procedure mediated by Hendrickson 's reagent in good yields. The novel ligands were tested in the asymmetric Friedel-Crafts alkylation of indole derivatives with nitroalkenes. In most cases, good yields (up to 97%) and excellent enantioselectivities (up to 98%) can be achieved. The optimized bis(imidazoline) ligand with trans-diphenyl substitution on the imidazoline ring gave better enantioselectivity than the corresponding bis(oxazoline) ligand. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA,.

Liu Q.,Beijing Institute of Technology | Peng G.-Z.,Beijing Institute of Technology
CAR 2010 - 2010 2nd International Asia Conference on Informatics in Control, Automation and Robotics | Year: 2010

For sophisticated background, a fast and self-adaptive face detection algorithm based on skin color is introduced. In this algorithm, histogram skin color model was built with great amount of skin color pixels in HS color space first, and then skin color segmentation was made to images by using histogram backprojection, in which a binary image of skin color area was obtained after thresholding. Morphological and Blob analysis were used to make further optimization to the segmentation result. Experimental results show that the proposed algorithm can detect faces with different sizes, rotations and expressions under different illumination conditions fast and accurately. ©2010 IEEE.

Luo Q.,South China Normal University | Luo Q.,Beijing Institute of Technology
Physical Chemistry Chemical Physics | Year: 2012

The neutral carbon aluminium cluster Al 3C and its anion Al 3C - have been investigated at the B3LYP/6-311+G(d) and BP86/6-311+G(d) levels of theory. It is suggested that the C 2v neutral cluster Al 3C could be considered as a pseudohalogen superatom with a smaller electron affinity than the iodine atom. The DFT calculation results confirm that, similar to the halogen atoms, the pseudohalogen superatom Al 3C cluster could form the compounds corresponding to the dimer, salts, interhalogen compounds, oxides, acid radicals, and coordination complexes as well as superatom compounds of halogen, showing that Al 3C has similar chemical properties to halogens and maintains its integrity in the related reactions. Based on the maintenance of integrity in the chemical assemblies [(Al 3C)(KCAl 3) n] - (n = 1-5), it could be anticipated that the neutral cluster Al 3C holds great potential as a building block for the development of future nanostructured materials. Further, corresponding experimental verifications are invited. This journal is © 2012 the Owner Societies.

Liu P.,Beijing Institute of Technology | Jiang L.,Beijing Institute of Technology | Hu J.,Beijing Institute of Technology | Han W.,Beijing Institute of Technology | Lu Y.,University of Nebraska - Lincoln
Optics Letters | Year: 2013

An interesting anisotropy phenomenon in femtosecond laser processing of crystalline silicon is revealed by changing the angle between the writing direction and the laser polarization. The experimental results indicate the surface patterning is dependent on the laser polarization direction, showing that it is beneficial to forming continuous, ordered, and better-controlled ripples when the writing direction is parallel to the laser polarization. The anisotropy is attributed mainly to the elliptical shape of the induced ripples. The formation mechanisms of the elliptical ripples are also discussed. This observation promotes the fabrication of self-assembled subwavelength structures, which is important for electro-optic devices. © 2013 Optical Society of America.

Yang W.,Beijing Institute of Technology | He H.-X.,Beijing Institute of Technology | Gao Y.,Beijing Institute of Technology | Du D.-M.,Beijing Institute of Technology
Advanced Synthesis and Catalysis | Year: 2013

An efficient organocatalytic highly asymmetric cascade aza-Michael/Michael addition reaction for the synthesis of tetrahydroquinolines and tetrahydrochromanoquinolines has been developed. This cascade reaction proceeds well at low catalyst loading with a broad substrate scope, furnishing the desired products in excellent yields with excellent diastereoselectivities and enantioselectivities (up to >99:1 dr, 99% ee) under mild conditions. Importantly, it is the first catalytic asymmetric method for tetrahydrochromanoquinolines. This protocol provides a straightforward entry to highly functionalized chiral tetrahydroquinoline and tetrahydrochromanoquinoline derivatives from simple starting materials. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Pang B.,Beijing Institute of Technology
Fuzzy Sets and Systems | Year: 2014

In this paper, the concepts of stratified L-filter space, complete stratified L-filter space and symmetric stratified L-Kent convergence space are introduced. It is shown that (1) the category of stratified L-filter spaces with Cauchy continuous maps is a strong topological universe; (2) the category of complete stratified L-filter spaces, as a bicoreflective subcategory of the category of stratified L-filter spaces, is isomorphic to the category of symmetric stratified L-Kent convergence spaces; (3) the category of complete stratified L-filter spaces, as an isomorphism-closed full subcategory of the category of stratified L-filter spaces, is strongly Cartesian closed. © 2013 Elsevier B.V. All rights reserved.

Gao R.,Beijing Institute of Technology | Jiang Y.,Beijing Institute of Technology
Optics Letters | Year: 2013

A method for measurement of a magnetic field by filling a microhole with magnetic fluid (MF) in a photonic crystal fiber (PCF) is presented and experimentally demonstrated. A microhole is created in the collapsed region between the PCF and the single-mode fiber by using femtosecond laser micromachining, and a PCF-based Mach-Zehnder interferometer is formed. The MF is filled into the microhole. Due to the tunable refractive index property of the MF the mode field diameter of the propagation light is changed with the external magnetic field, and the magnetic field can be detected by measuring the visibility contrast of the white light interferogram. The experimental results show that sensitivity of up to 0.042 dB/Oe is achieved. © 2013 Optical Society of America.

Yang M.,Beijing Institute of Technology | Yang M.,INSA Rouen | Ren K.F.,INSA Rouen | Gou M.,Beijing Institute of Technology | Sheng X.,Beijing Institute of Technology
Optics Letters | Year: 2013

A full-wave numerical method based on the surface integral equation for computing radiation pressure force (RPF) exerted by a shaped light beam on arbitrary shaped homogenous particles is presented. The multilevel fast multipole algorithm is employed to reduce memory requirement and to improve its capability. The resultant matrix equation is solved by using an iterative solver to obtain equivalent electric and magnetic currents. Then RPF is computed by vector flux of the Maxwell's stress tensor over a spherical surface tightly enclosing the particle. So the analytical expressions for electromagnetic fields of incident beam in near region are used. Some numerical results are performed to illustrate the validity and capability of the developed method. Good agreements between our method and the Lorenz-Mie theory for spherical and small spheroidal particle are found while our method has powerful capability for computing RPF of any shaped beam on a relatively large particle of complex shape. Tests for ellipsoidal and red blood cell-like particles illuminated by Gaussian beam have shown that the size of the particle can be as large as 50-100 wavelengths, respectively, for the relative refractive of 1.33 and 1.1. © 2013 Optical Society of America.

Pang B.,Beijing Institute of Technology
Fuzzy Sets and Systems | Year: 2014

This paper presents a definition of (L,M)-fuzzy convergence spaces. It is shown that the category (L,M)-FC of (L,M)-fuzzy convergence spaces, which embeds the category (L,M)-FTop of (L,M)-fuzzy topological spaces as a reflective subcategory, is a Cartesian closed topological category. Further, it is proved that the category of (topological) pretopological (L,M)-fuzzy convergence spaces is isomorphic to the category of (topological) (L,M)-fuzzy quasi-coincident neighborhood spaces. Moreover, the relations among (L,M)-fuzzy convergence spaces, pretopological (L,M)-fuzzy convergence spaces and topological (L,M)-fuzzy convergence spaces are investigated in the categorical sense. © 2013 Elsevier B.V.

Gao R.,Beijing Institute of Technology | Jiang Y.,Beijing Institute of Technology | Abdelaziz S.,Beijing Institute of Technology
Optics Letters | Year: 2013

A method for measurement of a magnetic field by combining photonic crystal fibers (PCFs) and magnetic fluid is presented and experimentally demonstrated. The magnetic fluid is filled into the air holes of the cladding layer in the PCF. Due to the tunable refractive index property of the magnetic fluid, the refractive index difference between the fiber core and cladding layer is changed with the external magnetic field. The magnetic field can be directly detected by measuring the intensity of the transmission light. A series of magnetic fields with different strengths have been measured with the sensor. The experimental results show that a resolution of up to 0.09 Oe is achieved, and a good repetition is demonstrated experimentally. Compared with other expensive methods, the proposed method possesses high sensitivity and low cost. © 2013 Optical Society of America.

Li X.,Beijing Institute of Technology | Liu J.,Beijing Institute of Technology | Jia J.,Beijing Institute of Technology | Pan Y.,Beijing Institute of Technology | Wang Y.,Beijing Institute of Technology
Optics Express | Year: 2013

Complex amplitude modulation method is presented theoretically and performed experimentally for three-dimensional (3D) dynamic holographic display with reduced speckle using a single phase-only spatial light modulator. The determination of essential factors is discussed based on the basic principle and theory. The numerical simulations and optical experiments are performed, where the static and animated objects without refinement on the surfaces and without random initial phases are reconstructed successfully. The results indicate that this method can reduce the speckle in reconstructed images effectively; furthermore, it will not cause the internal structure in the reconstructed pixels. Since the complex amplitude modulation is based on the principle of phase-only hologram, it does not need the stringent alignment of pixels. This method can be used for high resolution imaging or measurement in various optical areas. ©2013 Optical Society of America.

Wang F.,Beijing Institute of Technology | Zhang K.,Hanseo University
Journal of Molecular Catalysis A: Chemical | Year: 2011

Reduced graphene oxide-TiO 2 (RGO-TiO 2) nanocomposites have been successfully synthesized through a facile hydrothermal reaction with minor modification using graphene oxide (GO) and commercial P25 as starting materials in an ethanol-water solvent, followed by calcining temperature at 400 °C for 2 h in Ar. These nanocomposites prepared with different ratios of graphene oxide (GO) were characterized by BET surface area, X-ray diffraction (XRD), Raman spectroscopy, UV-vis diffuse reflectance spectroscopy (UV-vis DRS), Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), Transmission Electron Microscopy (TEM) and ultraviolet-visible (UV-vis) absorption spectroscopy. The RGO-TiO 2 nanocomposites exhibited much higher photocatalytic activity than bare P25 for the degradation of rhodamine B (Rh.B) in an aqueous solution. The improved photocatalytic activities may be attributed to increased adsorbability for Rh.B molecular, light absorption levels in visible region and charge transfer rate in the presence of a two-dimensional graphene network.

Mao J.,Beijing Institute of Technology | Zuo Z.,Beijing Institute of Technology | Li W.,Beijing Institute of Technology | Feng H.,Beijing Institute of Technology
Applied Energy | Year: 2011

A free-piston linear alternator (FPLA) is being developed by the Beijing Institute of Technology to improve the thermal efficiency relative to conventional crank-driven engines. A two-stroke scavenging process recharges the engine and is crucial to realizing the continuous operation of a free-piston engine. In order to study the FPLA scavenging process, the scavenging system was configured using computational fluid dynamics. As the piston dynamics of the FPLA are different to conventional crank-driven two-stroke engines, a time-based numerical simulation program was built using Matlab to define the piston's motion profiles. A wide range of design and operating options were investigated including effective stroke length, valve overlapping distance, operating frequency and charging pressure to find out their effects on the scavenging performance. The results indicate that a combination of high effective stroke length to bore ratio and long valve overlapping distance with a low supercharging pressure has the potential to achieve high scavenging and trapping efficiencies with low short-circuiting losses. © 2010 Elsevier Ltd.

Gao R.,Beijing Institute of Technology | Jiang Y.,Beijing Institute of Technology | Jiang L.,Beijing Institute of Technology
Optics Express | Year: 2014

A compact temperature-insensitive optical fiber twist sensor based on multi-phase-shifted helical long period fiber grating has been proposed and experimentally demonstrated in this paper. A multi-phaseshifted helical long period fiber grating is fabricated with a multi-period rotation technology. A, π"/2 and a 3π/2 phase shift is introduced in the helical long period fiber grating by changing the period. The helical pitch can be effectively changed with a different twist rate, which is measured by calculating the wavelength difference between two phase shift peaks. Although the wavelength of the phase shift peak also shifts with a change of the temperature, the wavelength difference between two phase shift peaks is constant due to two fixed phase shifts in the helical long period fiber grating, which is extremely insensitive to temperature change for the multiphase-shifted helical long period fiber grating. The experimental results show that a sensitivity of up to 1.959 nm/(rad/m) is achieved. © 2014 Optical Society of America.

Pan X.-M.,Beijing Institute of Technology | Gou M.-J.,Beijing Institute of Technology | Sheng X.-Q.,Beijing Institute of Technology
Optics Express | Year: 2014

A fast full-wave method for computing radiation pressure force (RPF) exerted by shaped light beams on moving particles is presented. The problem of evaluating RPF exerted on a moving particle by a single excitation beam is converted into that of computing RPF's exerted on a static particle by multiple beams. The discretization of different beams leads to distinct right hand sides (RHS's) for the matrix system. To avoid solving each RHS by the brute-force manner, the algorithm conducts low-rank decomposition on the excitation matrix consisting of all RHS's to figure out the so-called skeleton light beams by interpolative decomposition (ID). The peak memory requirement of the skeletonization is a bottle-neck if the particle is large. A two-level skeletonization scheme is proposed to solve this problem. Some numerical experiments on arbitrarily shaped homogeneous particles are performed to illustrate the performance and capability of the developed method. © 2014 Optical Society of America.

Wang L.,Beijing Institute of Technology | Gao C.,Beijing Institute of Technology | Gao M.,Beijing Institute of Technology | Li Y.,Beijing Institute of Technology | And 3 more authors.
Optics Express | Year: 2014

We demonstrated a Q-switched Ho:YAG ceramic laser operating at 2097 nm. The Ho:YAG ceramic laser was resonantly pumped by a Tm:YLF laser at 1908 nm. The laser performance with two Ho-doping concentrations of Ho:YAG ceramics in a U-shaped resonator was studied. Different pump spots were investigated to obtain high extract efficiency. The wavelength of Ho:YAG ceramic laser was tuned from 2090.70 nm to 2098.10 nm. The Q-switched pulse energy were 9.6 mJ at a pulse repetition frequency (PRF) of 200 Hz and 10.2 mJ at a PRF of 100 Hz, respectively. The beam quality M2 factors were measured to be less than 1.1 in both directions. © 2014 Optical Society of America.

Shi W.,Beijing Institute of Technology | Huang X.,CAS Institute of Mechanics | Liu Z.,Beijing Institute of Technology
Optics Express | Year: 2014

Quantitatively measuring a dynamic liquid surface often presents a challenge due to high transparency, fluidity and specular reflection. Here, a novel Transmission-Lattice based Geometric Phase Analysis (TLGPA) method is introduced. In this method, a special lattice is placed underneath a liquid to be tested and, when viewed from above, the phase of the transmission-lattice image is modulated by the deformation of the liquid surface. Combining this with multi-directional Newton iteration algorithms, the dynamic deformation field of the liquid surface can be calculated from the phase variation of a series of transmission-lattice images captured at different moments. The developed method has the advantage of strong selfadaption ability to initial lattice rotational errors and this is discussed in detail. Dynamic 3D ripples formation and propagation was investigated and the results obtained demonstrated the feasibility of the method. © 2014 Optical Society of America.

He H.-X.,Beijing Institute of Technology | Yang W.,Beijing Institute of Technology | Du D.-M.,Beijing Institute of Technology
Advanced Synthesis and Catalysis | Year: 2013

An efficient enantioselective aza-Henry reaction of nitroalkanes to imines bearing a benzothiazole moiety catalyzed by a Cinchona-based squaramide has been developed. In the reaction of imines, the corresponding products were obtained in good to excellent yields (up to 99%) with excellent enantioselectivities (up to >99% ee) for most of the aromatic substituted imines. The imines with electron-withdrawing groups gave better yields than those bearing electron-donating groups in the aza-Henry reaction. Moreover, a one-pot three-component enantioselective aza-Henry reaction using 2-aminobenzothiazoles, aldehydes, and nitromethane was also developed. Moderate to good yields and high enantioselectivities were obtained in the one-pot cases (up to 98% ee). Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Mao J.,Beijing Institute of Technology | Zuo Z.,Beijing Institute of Technology | Feng H.,Beijing Institute of Technology
Applied Energy | Year: 2011

This research presents a novel parameters coupling designation method of diesel free-piston linear alternator. The relationship between the main parameters of linear alternator and free-piston engine is built up based on the energy conservation relationship between these two devices. An iterative procedure is carried out among the zero-dimensional numerical simulation of the free-piston linear alternator, CFD calculation of the gas exchanging process and combustion process of the free-piston engine to define the main geometric dimensions of the free-piston engine. A starting method of using the resonance characteristics of free-piston engine is simulated with different relatively small constant thrust forces and the designed free-piston engine could be started by the linear alternator. The results indicate that the load of the linear alternator is primarily associated with the bore of the engine, and the maximum electromagnetic force is approximately proportional to the square of the bore; the effective stroke length is associated with the optimum working point of free-piston linear alternator which could be defined using the numerical simulation program. © 2011 Elsevier Ltd.

Yang S.-J.,Beijing Institute of Technology
Fuzzy Sets and Systems | Year: 2014

In this paper, we study the optimal solution of minimizing a linear objective function subject to the fuzzy relation inequalities with addition-min composition. We first discuss some properties about the minimal solutions of fuzzy relation inequalities with addition-min composition, and define the pseudo-minimal indexes of this system. Next we give an algorithm to get the set of the pseudo-minimal indexes, which is called PMI algorithm. Finally, we obtain an algorithm for this optimization system by utilizing these concepts and results. The example is provided to show that our algorithm is simple and convenient. © 2014 Elsevier B.V.

Ma X.,Beijing Institute of Technology | Arce G.R.,University of Delaware
Optics Express | Year: 2011

Optical proximity correction (OPC) methods are resolution enhancement techniques (RET) used extensively in the semiconductor industry to improve the resolution and pattern fidelity of optical lithography. In pixel-based OPC (PBOPC), the mask is divided into small pixels, each of which is modified during the optimization process. Two critical issues in PBOPC are the required computational complexity of the optimization process, and the manufacturability of the optimized mask. Most current OPC optimization methods apply the steepest descent (SD) algorithm to improve image fidelity augmented by regularization penalties to reduce the complexity of the mask. Although simple to implement, the SD algorithm converges slowly. The existing regularization penalties, however, fall short in meeting the mask rule check (MRC) requirements often used in semiconductor manufacturing. This paper focuses on developing OPC optimization algorithms based on the conjugate gradient (CG) method which exhibits much faster convergence than the SD algorithm. The imaging formation process is represented by the Fourier series expansion model which approximates the partially coherent system as a sum of coherent systems. In order to obtain more desirable manufacturability properties of the mask pattern, a MRC penalty is proposed to enlarge the linear size of the sub-resolution assistant features (SRAFs), as well as the distances between the SRAFs and the main body of the mask. Finally, a projection method is developed to further reduce the complexity of the optimized mask pattern. © 2011 Optical Society of America.

Zhao W.,Beijing Institute of Technology | Cao G.,Beijing Institute of Technology
Optics Express | Year: 2011

An active segmented cophasing imaging testbed with a high accurate optical adjustment and control in nanoscale is set up. A two-dimensional dispersed fringe analysis method is used to calculate the piston error between the adjacent segments. Segments alignment of tip-tilt is fulfilled by overlapping diffraction pattern centroids of the individual segment on the focal plane. The cophasing errors are corrected by sensitive micro-displacement actuators under a computer closed-loop control. A FISBA interferometer is introduced to evaluate that a final total residual surface error of about 0.08λ RMS and the residual piston error of 0.026λ RMS are achieved (λ = 633nm). © 2011 Optical Society of America.

Ju Y.,Beijing Institute of Technology | Zhang Q.,Beijing Institute of Technology
Physics of Plasmas | Year: 2015

Molecular dynamics method is used to study the threshold for plasma phase transition of aluminum single crystal induced by hypervelocity impact. Two effective simulation methods, piston-driven method and multi-scale shock technique, are used to simulate the shock wave. The simulation results from the two methods agree well with the experimental data, indicating that the shock wave velocity is linearly dependent on the particle velocity. The atom is considered to be ionized if the increase of its internal energy is larger than the first ionization energy. The critical impact velocity for plasma phase transition is about 13.0 km/s, corresponding to the threshold of pressure and temperature which is about 220 GPa and 11.0 × 103K on the shock Hugoniot, respectively. © 2015 AIP Publishing LLC.

Chang H.-R.,Sichuan Normal University | Zhou J.,Carnegie Mellon University | Zhang H.,Ohio University | Yao Y.,Beijing Institute of Technology
Physical Review B - Condensed Matter and Materials Physics | Year: 2014

We theoretically investigated two kinds of density oscillations, the Friedel oscillation and collective excitation in the silicene and germanene within the random phase approximation, and found that the tunable spin-valley coupled band structure could lead to some exotic properties in these two phenomena. Based on an exact analytical and numerical analysis, we demonstrated that the beating of the screened potential as well as the undamped plasmon mode can be taken as fingerprints of a topological phase transition in doped silicene and doped germanene. Thus our proposal here establishes the connection between the topological phase transition and the density oscillations that can be accessed by a variety of experimental techniques. © 2014 American Physical Society.

Liu G.,Beijing Institute of Technology
Acta Mechanica | Year: 2015

Experimental results have shown that composite cantilever beams with ultra high molecular-weight polyethylene fibres are collapsed by a new mode of microbuckling, which involves elastic bending and shearing of the plies, and plastic shear of the interfaces. Different finite element modelling strategies were employed in this study. Simulation results reveal that an enough number of interfacial cohesive layers, accurate partition of the shear stiffness between plies and interfaces, and accurate partition of the flexural stiffness between plies are important in predicting the collapse responses. The sensitivity of the predicted microbuckling responses to the overall effective shear modulus and interlaminar shear strength of long composite beams are also investigated. © 2014, Springer-Verlag Wien.

Zhang L.,Beijing Institute of Technology | Chen L.,Beijing Institute of Technology
Wuli Xuebao/Acta Physica Sinica | Year: 2013

The thermal decomposition of solid nitromethane (NM) is studied by ReaxFF molecular dynamics simulations to obtain the time evolution of the mechanism of NM under high temperature and pressure. It is determined that the initial decomposition mechanism of NM is dependent on pressure effect. In the 0-3 GPa pressure regime, the initial reactions is the C-N bond dissociation and the unimolecular rearrangement connecting between NM and methyl nitrite isomers; in the 4-7 GPa, the initial pathways of NM are the intermolecular proton transfer and C-N, C-O bond rupture. In the secondary reactions step, several fragments, like H2O, NO, NO2, HONO, play a role of catalysis. The product decomposition of NM contains many different structures of carbon clusters, and the configuration of cluster is dependent on pressure. © 2013 Chinese Physical Society.

Wang L.,Beijing Institute of Technology | Wang X.,Beijing Institute of Technology | Qi M.,Beijing Institute of Technology | Fu R.,Beijing Institute of Technology
Journal of Chromatography A | Year: 2014

Cucurbit[. n]urils (CBs) possess unique structures and selective interactions with analytes of different variety and high thermal stability and show a great potential as stationary phases for capillary gas chromatography (GC). This work presents the first description of CB6 in combination with a new guanidinium-based ionic liquid (GBIL) as the GC stationary phase by using sol-gel coating method for the preparation of the CB6-GBIL and GBIL columns. Introduction of GBIL greatly improved the solubility of CB6 in the sol solution and successfully made the use of CBs for the intended purpose feasible. The CB6-GBIL and GBIL columns had average polarity of 179 and 280, respectively, suggesting their medium polar nature. The CB6-GBIL column achieves good resolution for a wide range of analytes and exhibits different retention behaviors and resolution for some of the analytes from the GBIL column and the commercial column. Moreover, it also shows good thermal stability up to 250. °C. The proposed method integrates the full advantages of CBs, ionic liquids and sol-gel coating method and provides an efficient and feasible way for the wider application of CBs in separation science. © 2014 Elsevier B.V.

Zhang P.,Beijing Institute of Technology | Qin S.,Beijing Institute of Technology | Qi M.,Beijing Institute of Technology | Fu R.,Beijing Institute of Technology
Journal of Chromatography A | Year: 2014

These characteristics concur to make them good candidates for stationary phases in capillary gas chromatographic (GC) separations. Herein, CB7 and CB8 in neat (CB7, CB8) and binary (CB7-CB8) forms were investigated for this purpose. After they were statically coated onto fused silica capillary columns, the CB columns were evaluated in terms of chromatographic parameters, separation performance, thermal stability and column repeatability. The columns had efficiencies ranging from 1060 to 2200 plates per meter determined by n-dodecane at 100. °C and exhibited nonpolar to weakly polar nature. These CBs columns showed good separation performance for a wide range of analytes such as n-alkanes, aromatic hydrocarbons, esters, aldehydes, ketones, alcohols and the Grob mixture, and exhibited nice peak shapes for analytes that are liable to peak-tailing in GC analysis. The results also proved the good column repeatability and thermal stability of the CB columns. No noticeable decreases in both retention times and resolution or appreciable baseline drift were observed after the columns were conditioned up to 250. °C (CB8 and CB7-CB8 columns) or 280. °C (CB7 column). This work demonstrates the promising future of CBs as a new class of GC stationary phase. To the best of our knowledge, this is the first report on using CB stationary phases in capillary GC separations. © 2014 Elsevier B.V.

Zhao X.,Beijing Institute of Technology | Cui L.,Beijing Institute of Technology
International Journal of Systems Science | Year: 2010

Most studies on k-out-of-n systems are in the binary context. The k-out-of-n system has failed if and only if at least k components have failed. The generalised multi-state k-out-of-n: G and F system models are defined by Huang etal. [Huang, J., Zuo, M.J., and Wu, Y.H. (2000), 'Generalized Multi-state k-out-of-n: G Systems', IEEE Transactions on reliability, 49, 105-111] and Zuo and Tian [Zuo, M.J., and Tian, Z.G. (2006), 'Performance Evaluation of Generalized Multi-state k-out-of-n Systems', IEEE Transactions on Reliability, 55, 319-327], respectively. In this article, by using the finite Markov chain imbedding (FMCI) approach, we present a unified formula with the product of matrices for evaluating the system state distribution for generalised multi-state k-out-of-n: F systems which include the decreasing multi-state F system, the increasing multi-state F system and the non-monotonic multi-state F system. Our results can be extended to the generalised multi-state k-out-of-n: G system. Three numerical examples are presented to illustrate the results. © 2010 Taylor & Francis.

Wen Y.,Beijing Institute of Technology | Ren X.,Beijing Institute of Technology
IET Control Theory and Applications | Year: 2010

A novel fuzzy state observer-based adaptive control is proposed for a class of strict-feedback non-linear time-varying delay systems with unknown control direction. A state observer with fuzzy approximators is established to estimate the system states. Based on the Nussbaum-type function in detecting the control direction and backstepping method, adaptive output feedback controller is constructed without requiring a priori knowledge of the signs of the unknown control directions, which can achieve the output tracking. It is rigourously proven that the proposed Lyapunov-Krasovskii functionals and the adaptive backstepping method are able to guarantee semi-globally uniform ultimate boundedness of all the signals in the closed-loop systems, whereas the tracking error converges to a small neighbourhood of the origin. A main advantage of the proposed controller is that it contains only one novel adaptive parameter that needs to be updated online, which can improve the transient and steady-state performances, and the other one is that the proposed scheme can be applied to the systems that do not satisfy the matching conditions. Finally, the simulations had been provided to verify the effectiveness of the proposed scheme. © 2010 The Institution of Engineering and Technology.

Zhan J.,Beijing Institute of Technology
Lecture Notes in Electrical Engineering | Year: 2016

Cement production is one major anthropogenic carbon dioxide (CO2) emission source. In China, domestic demand saturated situation caused the rapid increase of the cement exports. Western developed countries, in order to prevent leakage of carbon, will apply carbon tariffs to carbon intensive imports from developing countries such as China. Under the pressure of reducing carbon emissions, it is of important significance to study CO2 emissions in cement production process. We adopt the plant level micro data in 2500 t and 5000 t new suspension preheater dry-process (NSP) cement production line, and through data analysis, calculated CO2 emissions in each stage of cement production process, conducted environmental appraisal, measured the amount of carbon emissions in domestic cement production and implied carbon emissions in cement for export. As a result, we found a big deviation between CO2 emissions factors based on the direct data and in the previous literatures, and believe that the CO2 emission factor in Chinese cement production may be overstated in previous studies. © Springer Science+Business Media Singapore 2016.

Li Z.,Beijing Institute of Technology | Qu H.,Beijing Institute of Technology | Li C.,Beijing Institute of Technology | Zhou X.,Beijing Institute of Technology
Bioresource Technology | Year: 2013

In this study, four engineered Saccharomyces cerevisiae carrying xylanase, β-xylosidase and xylose reductase genes by different transcriptional