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Tsinghua University is a research university located in Beijing, People's Republic of China , and is one of the nine members in the C9 League. The institution was originally established in 1911 under the name "Tsinghua College" and had been renamed several times since then: from "Tsinghua School" which was used one year after its establishment, to "National Tsinghua University" which was adopted three years after the foundation of its university section in 1925. With its motto of Self-Discipline and Social Commitment, Tsinghua University describes itself as being dedicated to academic excellence, the well-being of Chinese society and to global development. It has consistently received top rankings in both domestic and international university rankings, alongside Peking University, which is the top elite higher learning institution in the mainland People's Republic of China .Tsinghua University in the People's Republic of China is a separate institution from the Taiwanese National Tsing Hua University located in Hsinchu city in the high-tech democratic industrialized developed country of the Republic of China . After the Chinese Civil War and the subsequent split of China into the two present-day separate sovereign independent countries of the Republic of China and the People's Republic of China , some academics and staff from the original Tsinghua University in the mainland People's Republic of China left and created the National Tsing Hua Institute of Nuclear Technology in 1955 in Hsinchu, Republic of China , which later became the National Tsing Hua University of island nation of Taiwan.The two Tsinghua universities are not affiliated with each other, but both claim to be successors of the original Tsinghua University. As a result of this dispute, the universities claimed to be the rightful recipient of the funds from the Boxer Rebellion indemnity that was used to start Tsinghua University. This indemnity was transferred to the university in Taiwan after the democratic Republic of China retreated to the island of Taiwan following the invasions and take over of mainland China by the communist People's Republic of China . Wikipedia.

Wang J.-T.,Tsinghua University
Soil Dynamics and Earthquake Engineering | Year: 2011

The overall damping of linear arch dam-water-foundation rock systems depends on the material damping of dam concrete, the material and radiation damping of semi-unbounded foundation rock, and the dam-water interaction. In this paper, the effective damping ratio of these factors is separately evaluated for Mauvoisin arch dam in Switzerland to quantitatively discuss their contributions, and to guide the damping selection in the numerical analysis. This paper also aims to investigate if the material and radiation damping of the foundation rock can be replaced by increasing the material damping of the dam to simplify numerical analysis models. The seismic responses of Mauvoisin arch dam are analyzed using the semi-unbounded and massless foundation models, respectively. The results show that the overall effective damping ratio of the system can be approximately expressed as the summation of the individual effective damping and thus the increased material damping of the dam can approximate the material and radiation damping of the semi-unbounded foundation rock. © 2010 Elsevier Ltd.

Xia L.,Tsinghua University | Shihada B.,King Abdullah University of Science and Technology
IEEE Transactions on Automatic Control | Year: 2013

In this technical note, we discuss the optimality properties of service rate control in closed Jackson networks. We prove that when the cost function is linear to a particular service rate, the system performance is monotonic w.r.t. (with respect to) that service rate and the optimal value of that service rate can be either maximum or minimum (we call it Max-Min optimality); When the second-order derivative of the cost function w.r.t. a particular service rate is always positive (negative), which makes the cost function strictly convex (concave), the optimal value of such service rate for the performance maximization (minimization) problem can be either maximum or minimum. To the best of our knowledge, this is the most general result for the optimality of service rates in closed Jackson networks and all the previous works only involve the first conclusion. Moreover, our result is also valid for both the state-dependent and load-dependent service rates, under both the time-average and customer-average performance criteria. © 1963-2012 IEEE.

Wang J.,Atkins | Shi Q.,Tsinghua University
Transportation Research Part C: Emerging Technologies | Year: 2013

Based on the previous literature review, this paper builds a short-term traffic speed forecasting model using Support Vector Machine (SVM) regression theory (referred as SVM model in this paper). Besides the advantages of the SVM model, it also has some limitations. Perhaps the biggest one lies in choice of the appropriate kernel function for the practical problem; how to optimize the parameters efficiently and effectively presents another one. Unfortunately, these limitations are still research topics in current literature. This paper puts an effort to investigate these limitations. In order to find the effective way to choose the appropriate and suitable kernel function, this paper constructs a new kernel function using a wavelet function to capture the non-stationary characteristics of the short-term traffic speed data. In order to find the efficient way to identify the model structure parameters, this paper uses the Phase Space Reconstruction theory to identify the input space dimension. To take the advantage of these components, the paper proposes a short-term traffic speed forecasting hybrid model (Chaos-Wavelet Analysis-Support Vector Machine model, referred to as C-WSVM model in this paper). The real traffic speed data is applied to evaluate the performance and practicality of the model and the results are encouraging. The theoretical advantage and better performance from the study indicate that the C-WSVM model has good potential to be developed and is feasible for short-term traffic speed forecasting study. © 2012 Elsevier Ltd.

Wang X.,Donghua University | Ding B.,Donghua University | Sun G.,Donghua University | Wang M.,Tsinghua University | Yu J.,Donghua University
Progress in Materials Science | Year: 2013

Since 2006, a rapid development has been achieved in a subject area, so called electro-spinning/netting (ESN), which comprises the conventional electrospinning process and a unique electro-netting process. Electro-netting overcomes the bottleneck problem of electrospinning technique and provides a versatile method for generating spider-web-like nano-nets with ultrafine fiber diameter less than 20 nm. Nano-nets, supported by the conventional electrospun nanofibers in the nano-fiber/nets (NFN) membranes, exhibit numerious attractive characteristics such as extremely small diameter, high porosity, and Steiner tree network geometry, which make NFN membranes optimal candidates for many significant applications. The progress made during the last few years in the field of ESN is highlighted in this review, with particular emphasis on results obtained in the author's research units. After a brief description of the development of the electrospinning and ESN techniques, several fundamental properties of NFN nanomaterials are addressed. Subsequently, the used polymers and the state-of-the-art strategies for the controllable fabrication of NFN membranes are highlighted in terms of the ESN process. Additionally, we highlight some potential applications associated with the remarkable features of NFN nanostructure. Our discussion is concluded with some personal perspectives on the future development in which this wonderful technique could be pursued. © 2013 Elsevier Ltd. All rights reserved.

Wang H.-Y.,Tsinghua University
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

The magnetic properties of the two-dimensional J 1-J 2 model with both exchanges J 1 and J 2 being antiferromagnetic and a single-ion anisotropy at nonzero temperature are investigated. As J 2/J 1<1/2 (>1/2), only the Néel (collinear) state exists. When J 2/J 1=1/2, both the Néel and collinear states can exist and have the same Néel temperature. The calculated free energies show that there can occur a phase transition between the two states below the Néel point when the single-ion anisotropy is strong enough. It is a first-order transition at nonzero temperature. It is possible that the doping in real materials can modify the ratio of J 2/J 1 to reach 1/2 so as to implement the phase transition. © 2012 American Physical Society.

Wang Z.,Tsinghua University | Yan B.,Johannes Gutenberg University Mainz
Journal of Physics Condensed Matter | Year: 2013

We propose the concept of 'topological Hamiltonian' for topological insulators and superconductors in interacting systems. The eigenvalues of the topological Hamiltonian are significantly different from the physical energy spectra, but we show that the topological Hamiltonian contains the information of gapless surface states, therefore it is an exact tool for topological invariants. © 2013 IOP Publishing Ltd.

Huang L.,Tsinghua University | Neely M.J.,University of Southern California
IEEE/ACM Transactions on Networking | Year: 2013

In this paper, we show how to achieve close-to-optimal utility performance in energy-harvesting networks with only finite capacity energy storage devices. In these networks, nodes are capable of harvesting energy from the environment. The amount of energy that can be harvested is time-varying and evolves according to some probability law. We develop an online algorithm, called the Energy-limited Scheduling Algorithm (ESA), which jointly manages the energy and makes power allocation decisions for packet transmissions. ESA only has to keep track of the amount of energy left at the network nodes and does not require any knowledge of the harvestable energy process. We show that ESA achieves a utility that is within O(ε) of the optimal, for any ε>0, while ensuring that the network congestion and the required capacity of the energy storage devices are deterministically upper-bounded by bounds of size O(1/ε). We then also develop the Modified-ESA (MESA) algorithm to achieve the same O(ε) close-to-utility performance, with the average network congestion and the required capacity of the energy storage devices being only O(log (1/ε)]2) , which is close to the theoretical lower bound O(log (1/ε)). © 1993-2012 IEEE.

Luo M.J.,Tsinghua University
Nuclear Physics B | Year: 2014

We abandon the interpretation that time is a global parameter in quantum mechanics, replace it by a quantum dynamical variable playing the role of time. This operational re-interpretation of time provides a solution to the cosmological constant problem. The expectation value of the zero-point energy under the new time variable vanishes. The fluctuation of the vacuum energy as the leading contribution to the gravitational effect gives a correct order to the observed "dark energy". The "dark energy" as a mirage is always seen comparable with the matter energy density by an observer using the internal clock time. Conceptual consequences of the re-interpretation of time are also discussed. © 2014 The Authors.

Zhang Q.,Tsinghua University
IEEE Transactions on Systems, Man, and Cybernetics: Systems | Year: 2015

A new approach for uncertain causality representation and probabilistic reasoning named as dynamic uncertain causality graph (DUCG) was presented previously, in which only the discrete variables and certain evidence were addressed. In this paper, the free mixtures of discrete and continuous variables as well as uncertain evidence are addressed. The general idea to deal with continuous variables is to transform them into fuzzy discrete variables along with their corresponding uncertain causalities, and then treat them as ordinary discrete variables, which involves how to deal with fuzzy evidence. It is pointed out that uncertain evidence is either: 1) fuzzy evidence that is an observed certain value of a continuous variable falling into a fuzzy area across two or more fuzzy discrete states of a variable or 2) soft evidence that can only be understood as a probability distribution over the states of a variable. The algorithm for utilizing uncertain evidence in inference is presented, in which uncertain evidence is treated as a virtual child variable of the observed variable without changing the knowledge and inference algorithm encoded in DUCG. It is proved that the two types of uncertain evidence are the same in nature and can be treated indiscriminatingly. Moreover, this method dealing with fuzzy evidence in DUCG can be used for failure forecasting of systems. Examples are provided to illustrate the methodology. © 2015 IEEE.

A family of layered lanthanide (Pr, Nd, Sm, Eu, and Gd) hydroxide nanowires (NWs) has been synthesized via a hydrothermal route. These NWs are ∼8 nm in diameter and a few micrometres in length. The obtained Eu- and Gd-based layered hydroxide NWs consist of layered structure with two interlayer spacings. The effects of hydrothermal temperature and time on the transition of the layered structure were investigated. Photoluminescence of the Eu-based layered hydroxide NWs was also studied. These layered lanthanide hydroxide NWs combine the advantages of lanthanide and layered hydroxides, which will expand the inorganic layered materials and can be expected to be used as building blocks for further fabrication of functional nanostructures.

Yu L.,University of Hong Kong | Xi J.,Tsinghua University
Electrochimica Acta | Year: 2012

A simple and efficient method to enhance the activity of Pt/C catalysts for direct ethanol fuel cells (DEFCs) by ultrasonically mixing commercial Pt/C catalyst and TiO 2 nanoparticles is reported. In this novel composite anode catalyst, the as-prepared TiO 2 nanoparticles are dispersed homogeneously in the interspaces of Pt based C nanoparticles, resulting in a great deal of TiO 2-Pt-C interfaces, which greatly accelerate the ethanol electro-oxidation reaction. Cyclic voltammetry (CV), CO stripping, chronoamperometry and electrochemical impedance spectroscopy (EIS) measurements confirm that this composite catalyst structure has excellent activity and stability toward ethanol and CO electro-oxidation compared to the pure Pt/C catalyst. Particle size and content of TiO 2 are also discussed with respect to effect on catalyst performance. © 2012 Elsevier Ltd. All rights reserved.

Liu T.,Tsinghua University
Bulletin of the Seismological Society of America | Year: 2010

This paper presents an efficient and effective scheme for reforming the original Thomson-Haskell transfer matrix method for the stable modeling of surface waves in a layered half-space. The proposed scheme splits the layer propagator matrix and then determines the interface stiffness instead of directly building the propagator matrix as the original Thomson-Haskell method does. For the Love wave, an explicit solution for the interface stiffness is obtained. The reformulation of the Thomson-Haskell method keeps the simplicity of the original method but naturally excludes its exponential growth terms. Hence, the modified Thomson-Haskell method is computationally stable for high frequency and increasing layer thickness. Moreover, both analytical and numerical results indicate the modified Thomson-Haskell method is the most efficient of all the complex arithmetic algorithms available, including the original Thomson-Haskell method and generated reflection and transmission matrix method. The computational speed of the modified Thomson-Haskell method rises by more than 15% for the Love and Rayleigh waves. Furthermore, a discussion of the effect of frequency and layer thickness on the phase velocity of Gutenberg Earth model indicates the modified Thomson-Haskell method is a powerful candidate for efficiently and effectively simulating surface waves in a layered half-space.

Osteogenic differentiation of mesenchymal stem cells (MSCs) is a complex process, which is regulated by various factors including microRNAs. Our preliminary data showed that the expression of endogenous miR-20a was increased during the course of osteogenic differentiation. Simultaneously, the expression of osteoblast markers and regulators BMP2, BMP4, Runx2, Osx, OCN and OPN was also elevated whereas adipocyte markers PPARγ and osteoblast antagonist, Bambi and Crim1, were downregulated, thereby suggesting that miR-20a plays an important role in regulating osteoblast differentiation. To validate this hypothesis, we tested its effects on osteogenic differentiation by introducing miR-20a mimics and lentiviral-miR20a-expression vectors into hMSCs. We showed that miR-20a promoted osteogenic differentiation by the upregulation of BMP/Runx2 signaling. We performed bioinformatics analysis and predicted that PPARγ, Bambi and Crim1 would be potential targets of miR-20a. PPARγ is a negative regulator of BMP/Runx2 signaling whereas Bambi or Crim1 are antagonists of the BMP pathway. Furthermore, we confirmed that all these molecules were indeed the targets of miR-20a by luciferase reporter, quantitative RT-PCR and western blot assays. Similarly to miR-20a overexpression, the osteogenesis was enhanced by the silence of PPARγ, Bambi or Crim1 by specific siRNAs. Taken together, for the first time, we demonstrated that miR-20a promoted the osteogenesis of hMSCs in a co-regulatory pattern by targeting PPARγ, Bambi and Crim1, the negative regulators of BMP signaling.

Zhou T.,Tsinghua University
Automatica | Year: 2015

Some necessary and sufficient conditions are obtained for the controllability and observability of a networked system with linear time invariant (LTI) dynamics. The topology of this system is fixed but arbitrary, and every subsystem is permitted to have different dynamics. These conditions essentially depend only on transmission zeros of every subsystem and the subsystem connection matrix, which makes them attractive in the analysis and synthesis of a large-scale networked system. As an application, these conditions are utilized to characterize systems whose steady estimation accuracy with the distributed predictor of Zhou (2013) is equal to that of the lumped Kalman filter. It has been made clear that to guarantee this equivalence, the steady update gain matrix of the Kalman filter must be block diagonal. © 2014 Elsevier. Ltd All rights reserved.

Wright J.S.,Tsinghua University | Fueglistaler S.,Princeton University
Atmospheric Chemistry and Physics | Year: 2013

We present the time mean heat budgets of the tropical upper troposphere (UT) and lower stratosphere (LS) as simulated by five reanalysis models: the Modern-Era Retrospective Analysis for Research and Applications (MERRA), European Reanalysis (ERA-Interim), Climate Forecast System Reanalysis (CFSR), Japanese 25-yr Reanalysis and Japan Meteorological Agency Climate Data Assimilation System (JRA-25/JCDAS), and National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) Reanalysis 1. The simulated diabatic heat budget in the tropical UTLS differs significantly from model to model, with substantial implications for representations of transport and mixing. Large differences are apparent both in the net heat budget and in all comparable individual components, including latent heating, heating due to radiative transfer, and heating due to parameterised vertical mixing. We describe and discuss the most pronounced differences. Discrepancies in latent heating reflect continuing difficulties in representing moist convection in models. Although these discrepancies may be expected, their magnitude is still disturbing. We pay particular attention to discrepancies in radiative heating (which may be surprising given the strength of observational constraints on temperature and tropospheric water vapour) and discrepancies in heating due to turbulent mixing (which have received comparatively little attention). The largest differences in radiative heating in the tropical UTLS are attributable to differences in cloud radiative heating, but important systematic differences are present even in the absence of clouds. Local maxima in heating and cooling due to parameterised turbulent mixing occur in the vicinity of the tropical tropopause. © Author(s) 2013.

Jiang W.,Tsinghua University
Qiangjiguang Yu Lizishu/High Power Laser and Particle Beams | Year: 2014

This review article summarizes the applications of repetitive pulsed power in many fields, such as material development, environment protection, bio-and medical-science, light sources, and high-energy accelerators. The plasma immersion ion implantation and pulsed electron-beam surface treatment have been used in industrial production. Flue-gas and wastewater treatment by pulsed atmospheric discharge are being developed toward practical application. Sterilization and cancer-cell treatment using pulsed electric field have attracted great attention from academic and industrial communities. Plasma generated extreme ultraviolet(EUV) radiation is hopefully going to be used in photo-lithography for mass production in the near future. The thyratrons used on high-energy accelerators will eventually be replaced by power semiconductor devices.

Jia Q.-S.,Tsinghua University
IEEE Transactions on Automatic Control | Year: 2013

The dynamics of many systems nowadays follow not only physical laws but also man-made rules. These systems are known as discrete event dynamic systems and their performances can be accurately evaluated only through simulations. Existing studies on simulation-based optimization (SBO) usually assume deterministic simulation time for each replication. However, in many applications such as evacuation, smoke detection, and territory exploration, the simulation time is stochastic due to the randomness in the system behavior. We consider the computing budget allocation for SBOs with stochastic simulation time in this technical note, which has not been addressed in existing literatures to the author's best knowledge. We make the following major contribution. The relationship between simulation time and performance estimation accuracy is quantified. It is shown that when the asymptotic performance is of interest only the mean value of individual simulation time matters. Then based on the existing optimal computing budget allocation (OCBA) method for deterministic simulation time we develop OCBA for stochastic simulation time (OCBAS), and show that OCBAS is asymptotically optimal. Numerical experiments are used to discuss the impact of the variance of simulation time, the impact of correlated simulation time and performance estimation, and to demonstrate the performance of OCBAS on a smoke detection problem in wireless sensor network. The numerical results also show that OCBA for deterministic simulation time is robust even when the simulation time is stochastic. © 2012 IEEE.

Jiang W.,Tsinghua University
Qiangjiguang Yu Lizishu/High Power Laser and Particle Beams | Year: 2012

This is the first of a series of review papers on repetitive pulsed power technology. It gives general description about the technological characteristics such as high number of working-cycles, short time interval, and high average power. Typical applications in excimer laser, atmospheric gas discharge, and high-energy accelerator are introduced in order to highlight the significance of the technology. Repetitive pulsed power technology will be further developed mainly in the direction of short pulse and waveform control, while operation parameters of practical generators for specific applications will be pushed to the component limit. Future development of repetitive pulsed power and related technologies will bring more benefits into industrial and civil areas.

Zhou T.,Tsinghua University
IEEE Transactions on Automatic Control | Year: 2010

Convergence and stability of the robust state estimator obtained in is reinvestigated in this technical note. Some new relations have been established for matrix updates in the recursive state estimation. It is proved that under certain stabilizability and detectability conditions, this robust estimator converges to a stable time invariant system, provided that plant nominal parameters are time invariant and the filter design parameter is fixed. These results are consistent with existent ones, but different from them at the point that there are no orthogonality constraints on uncertainty related system matrices, and therefore widen theoretical guarantees for the effectiveness of the estimation procedure. © 2010 IEEE.

Yang Z.,Tsinghua University
Nuclear Physics A | Year: 2014

The production of J/ψ and ϒ-mesons decaying into the dimuon final state is studied at the LHCb experiment, covering the rapidity intervals 1.5

Zhu X.,Tsinghua University
Nuclear Physics A | Year: 2014

We report STAR's high precision measurements on Ω production at mid-rapidity from s=200GeV p+p, central sNN=200GeV Au+Au, and central sNN=193GeV U+U collisions. With the significantly reduced uncertainty in p+p reference, we observe that the Ω enhancement factors at RHIC are in between SPS and LHC, while enhancement factors are systematically larger in central U+U collisions than in central Au+Au collisions. The Ω RAA is much larger than protons and pions for pT up to 4 GeV/c in central Au+Au collisions. The ratio of Ω RAA in central U+U to that in central Au+Au collisions is above unity for pT up to 6 GeV/c, which indicates coalescence/recombination to be the dominant production mechanism for Ω in these collisions for the measured pT range. © 2014 Elsevier B.V.

Kong L.,Tsinghua University | Kong L.,University of New Hampshire
Nuclear Physics B | Year: 2014

Instead of studying anyon condensation in various concrete models, we take a bootstrap approach by considering an abstract situation, in which an anyon condensation happens in a 2-d topological phase with anyonic excitations given by a modular tensor category C; and the anyons in the condensed phase are given by another modular tensor category D. By a bootstrap analysis, we derive a relation between anyons in D-phase and anyons in C-phase from natural physical requirements. It turns out that the vacuum (or the tensor unit) A in D-phase is necessary to be a connected commutative separable algebra in C, and the category D is equivalent to the category of local A-modules as modular tensor categories. This condensation also produces a gapped domain wall with wall excitations given by the category of A-modules in C. A more general situation is also studied in this paper. We will also show how to determine such algebra A from the initial and final data. Multi-condensations and 1-d condensations will also be briefly discussed. Examples will be given in the toric code model, Kitaev quantum double models, Levin-Wen types of lattice models and some chiral topological phases. © 2014 The Author.

Liu H.,Hunan Normal University | Cheng L.,Tsinghua University
Science | Year: 2015

Double-stranded RNA (dsRNA) viruses possess a segmented dsRNA genome and a number of RNA-dependent RNA polymerases (RdRps) enclosed in a capsid. Until now, the precise structures of genomes and RdRps within the capsids have been unknown. Here we report the structures of RdRps and associated RNAs within nontranscribing and transcribing cypoviruses (NCPV and TCPV, respectively), using a combination of cryo-electron microscopy (cryo-EM) and a symmetry-mismatch reconstruction method. The RdRps and associated RNAs appear to exhibit a pseudo-D3 symmetric organization in both NCPV and TCPV. However, the molecular interactions between RdRps and the genomic RNA were found to differ in these states. Our work provides insight into the mechanisms of the replication and transcription in dsRNA viruses and paves a way for structural determination of lower-symmetry complexes enclosed in higher-symmetry structures.

Jia Q.-S.,Tsinghua University
IEEE Transactions on Automatic Control | Year: 2011

Many small electronic devices such as cell phones and wireless sensors have restrictive memory space, computing power, and battery. The pervasive applications of these devices in industry, military, and our daily lives require simple policies that are easy to implement, and can be executed in a reasonably short time. The Markov decision process (MDP) provides a general framework for these policy optimization problems with complexity constraint. In many cases, we can use a powerful computer to find the optimal (or a good) policy and the value function first, and then approximate by a simple one. The approximation usually depends on heuristics or experiences because the relationship between the complexity of a function and the approximation error is not clear in general. In this paper we assume the optimal value function is known (or a reasonably good estimate is available) and consider how to approximate a complex value function. Due to the broad application of state aggregation in the large-scale MDP, we focus on piecewise constant approximate value functions and use the number of aggregated states to measure the complexity of a value function. We quantify how the complexity of a value function affects the approximation error. When the optimal value function is known for sure we develop an algorithm that finds the best simple state aggregation within polynomial time. When we have estimates of the optimal value function, we apply ordinal optimization to find good simple state aggregations with high probability. The algorithms are demonstrated on a node activation policy optimization problem in wireless sensor network. We hope this work can shed some insight on how to find simple policies with good performances. © 2006 IEEE.

Wu B.,Tsinghua University
Journal of Spinal Disorders and Techniques | Year: 2014

STUDY DESIGN:: Retrospective study.OBJECTIVE:: To analyze the reasons, clinical manifestation, risk factors, prevention and treatment of dysphagia after operation of anterior cervical decompression and fusion.SUMMARYOF BACKGROUND DATA:: Dysphagia is one of severe complications after anterior cervical decompression and fusion. There were a few studies about reasons and prevention of dysphagia.METHODS:: We retrospectively reviewed medical charts of patients underwent anterior cervical decompression and fusion in our hospital from January 2012 to December 2012. Clinical symptom of dysphagia was recorded at the perioperative period, third and sixth month of the follow-up after surgery and assign according to the Bazaz dysphagia score. We analyzed the reasons and risk factors leading to dysphagia and tried to find effective programs of prevention and treatment.RESULTS:: There were 358 patients underwent anterior cervical decompression and fusion. Of 358 patients, 39 patients including 14 males and 25 females complained dysphagia. The mean aged was 46.8 years with the age from 38 to 67 years old. Clinical manifestation of dysphagia included difficulty to swallow, swallowing pain, sticky throat feeling and choking. All the patients were followed up over six months. The incidences of dysphagia were 10.9%, 6.4%, 2.7% respectively at 1-5 days, three months and six months after surgery. There was no severe dysphagia at three months after surgery. Mild or moderate dysphagia slightly affected the quality of life. Logistic regression showed multilevel cervical spine and high-level cervical spine surgeries are high risk factors for postoperative dysphagia.CONCLUSIONS:: Dysphagia is common complication of anterior cervical decompression and fusion. Causes of leading to dysphagia are multilevel cervical spine and upper cervical spine surgeries. Using methylprednisolone and careful operating can reduce the incidence and receive a good prognosis. © 2014 by Lippincott Williams & Wilkins, Inc.

Han Y.,Tsinghua University | Davidson R.A.,University of Delaware
Earthquake Engineering and Structural Dynamics | Year: 2012

Two key issues distinguish probabilistic seismic risk analysis of a lifeline or portfolio of structures from that of a single structure. Regional analysis must consider the correlation among lifeline components or structures in the portfolio, and the larger scope makes it much more computationally demanding. In this paper, we systematically identify and compare alternative methods for regional hazard analysis that can be used as the first part of a computationally efficient regional probabilistic seismic risk analysis that properly considers spatial correlation. Specifically, each method results in a set of probabilistic ground motion maps with associated hazard-consistent annual occurrence probabilities that together represent the regional hazard. The methods are compared according to how replicable and computationally tractable they are and the extent to which the resulting maps are physically realistic, consistent with the regional hazard and regional spatial correlation, and few in number. On the basis of a conceptual comparison and an empirical comparison for Los Angeles, we recommend a combination of simulation and optimization approaches: (i) Monte Carlo simulation with importance sampling of the earthquake magnitudes to generate a set of probabilistic earthquake scenarios (defined by source and magnitude); (ii) the optimization-based probabilistic scenario method, a mixed-integer linear program, to reduce the size of that set; (iii) Monte Carlo simulation to generate a set of probabilistic ground motion maps, varying the number of maps sampled from each earthquake scenario so as to minimize the sampling variance; and (iv) the optimization-based probabilistic scenario again to reduce the set of probabilistic ground motion maps. © 2012 John Wiley & Sons, Ltd.

Ge J.,Tsinghua University | Ge J.,CAS Institute of Process Engineering | Lei J.,Stanford University | Lei J.,CAS Institute of Process Engineering | Zare R.N.,CAS Institute of Process Engineering
Nature Nanotechnology | Year: 2012

Flower-shaped inorganic nanocrystals have been used for applications in catalysis and analytical science, but so far there have been no reports of ĝ€ nanoflowersĝ€™ made of organic components. Here, we report a method for creating hybrid organic-inorganic nanoflowers using copper (II) ions as the inorganic component and various proteins as the organic component. The protein molecules form complexes with the copper ions, and these complexes become nucleation sites for primary crystals of copper phosphate. Interaction between the protein and copper ions then leads to the growth of micrometre-sized particles that have nanoscale features and that are shaped like flower petals. When an enzyme is used as the protein component of the hybrid nanoflower, it exhibits enhanced enzymatic activity and stability compared with the free enzyme. This is attributed to the high surface area and confinement of the enzymes in the nanoflowers. © 2012 Macmillan Publishers Limited.

Feng H.,Tsinghua University | Soria R.,Curtin University Australia
New Astronomy Reviews | Year: 2011

Ultraluminous X-ray sources (ULXs) are accreting black holes that may contain the missing population of intermediate mass black holes or reflect super-Eddington accretion physics. Ten years of Chandra and XMM-Newton observations of ULXs, integrated by multiband studies of their counterparts, have produced a wealth of observational data and phenomenological classifications. We review the properties of their host galaxies, list popular spectral models and implications for standard and supercritical accretion physics, demonstrate how X-ray timing of these objects places constraints on their masses. We also review multiwavelength studies of ULXs, including the optical emission of the binary system and nebulosity around them. We summarize that three classes of black holes could power ULXs: normal stellar mass black holes (~10M⊙), massive stellar black holes (≲100M⊙), and intermediate mass black holes (102-104M⊙). We collect evidence for the presence of these three types of compact objects, including caveat of each interpretation, and briefly review their formation processes. © 2011 Elsevier B.V.

Ma X.,Tsinghua University | Fung C.-H.F.,University of Hong Kong | Razavi M.,University of Leeds
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2012

Measurement-device-independent quantum key distribution with a finite number of decoy states is analyzed under finite-data-size assumption. By accounting for statistical fluctuations in parameter estimation, we investigate vacuum+weak- and vacuum+two-weak-decoy-state protocols. In each case, we find proper operation regimes, where the performance of our system is comparable to the asymptotic case for which the key size and the number of decoy states approach infinity. Our results show that practical implementations of this scheme can be both secure and efficient. © 2012 American Physical Society.

Cui X.,Tsinghua University | Cui X.,Ohio State University
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2012

We present exact solutions of a two-body problem for spin-1/2 fermions with isotropic spin-orbit (SO) coupling and interacting with an arbitrary short-range potential. We find that in each partial-wave scattering channel, the parametrization of a two-body wave function at short interparticle distance depends on the scattering amplitudes of all channels. This reveals the mixed-partial-wave scattering induced by SO couplings. By comparing with results from a square-well potential, we investigate the validity of original pseudopotential models in the presence of SO coupling. We find the s-wave pseudopotential provides a good approximation for low-energy solutions near s-wave resonances, given the length scale of SO coupling much longer than the potential range. However, near p-wave resonance the p-wave pseudopotential gives low-energy solutions that are qualitatively different from exact ones, based on which we conclude that the p-wave model can not be applied to the fermion system if the SO coupling strength is larger or comparable to the Fermi momentum. © 2012 American Physical Society.

Yu Z.,Tsinghua University
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2012

We study the short-range correlation strength of three-dimensional spin-half dilute atomic Fermi gases with spin-orbit coupling. The interatomic interaction is modeled by the contact pseudopotential. In the high-temperature limit, we derive the expression for the second-order virial expansion of the thermodynamic potential via the ladder diagrams. We further evaluate the second-order virial expansion in the limit that the spin-orbit coupling constants are small and find that the correlation strength between the fermions increases as the fourth power of the spin-orbit coupling constants. At zero temperature, we consider the cases in which there are symmetric spin-orbit couplings in two or three directions. In such cases, there is always a two-body bound state of zero net momentum. In the limit that the average interparticle distance is much larger than the dimension of the two-body bound state, the system primarily consists of condensed bosonic molecules that fermions pair to form; we find that the correlation strength also becomes bigger compared to that in the absence of spin-orbit coupling. Our results indicate that generic spin-orbit coupling enhances the short-range correlations of the Fermi gases. Measurement of such enhancement by photoassociation experiment is also discussed. © 2012 American Physical Society.

Wu Y.,Tsinghua University | Zhao R.C.H.,Peking Union Medical College | Tredget E.E.,University of Alberta
Stem Cells | Year: 2010

Our understanding of the role of bone marrow (BM)-derived cells in cutaneous homeostasis and wound healing had long been limited to the contribution of inflammatory cells. Recent studies, however, suggest that the BM contributes a significant proportion of noninflammatory cells to the skin, which are present primarily in the dermis in fibroblast-like morphology and in the epidermis in a keratinocyte phenotype; and the number of these BM-derived cells increases markedly after wounding. More recently, several studies indicate that mesenchymal stem cells derived from the BM could significantly impact wound healing in diabetic and nondiabetic animals, through cell differentiation and the release of paracrine factors, implying a profound therapeutic potential. This review discusses the most recent understanding of the contribution of BM-derived noninflammatory cells to cutaneous homeostasis and wound healing. © AlphaMed Press.

You K.,Tsinghua University
Automatica | Year: 2015

This paper studies a parameter estimation problem of networked linear systems with fixed-rate quantization. Under the minimum mean square error criterion, we propose a recursive estimator of stochastic approximation type, and derive a necessary and sufficient condition for its asymptotic unbiasedness. This motivates to design an adaptive quantizer for the estimator whose strong consistency, asymptotic unbiasedness, and asymptotic normality are rigorously proved. Using the Newton-based and averaging techniques, we obtain two accelerated recursive estimators with the fastest convergence speed of O(1/k), and exactly evaluate the quantization effect on the estimation accuracy. If the observation noise is Gaussian, an optimal quantizer and the accelerated estimators are co-designed to asymptotically approach the minimum Cramer-Rao lower bound. All the estimators share almost the same computational complexity as the gradient algorithms with un-quantized observations, and can be easily implemented. Finally, the theoretical results are validated by simulations. © 2014 Elsevier. Ltd All rights reserved.

Liu B.,Tsinghua University
Fuzzy Optimization and Decision Making | Year: 2014

Uncertain process is a sequence of uncertain variables indexed by time. This paper presents a concept of uncertainty distribution for describing uncertain process. Some sufficient and necessary conditions are also proved for uncertainty distribution and inverse uncertainty distribution of uncertain process. Finally, this paper proposes an independence definition of uncertain processes and shows some mathematical properties of it. © 2014 Springer Science+Business Media New York.

Shao J.-J.,Tianjin University | Lv W.,Tsinghua University | Yang Q.-H.,Tianjin University
Advanced Materials | Year: 2014

Due to its amphiphilic property, graphene oxide (GO) can achieve a variety of nanostructures with different morphologies (for example membranes, hydrogel, crumpled particles, hollow spheres, sack-cargo particles, Pickering emulsions, and so on) by self-assembly. The self-assembly is mostly derived from the self-concentration of GO sheets at various interfaces, including liquid-air, liquid-liquid and liquid-solid interfaces. This paper gives a comprehensive review of these assembly phenomena of GO at the three types of interfaces, the derived interfacial self-assembly techniques, and the as-obtained assembled materials and their properties. The interfacial self-assembly of GO, enabled by its fantastic features including the amphiphilicity, the negatively charged nature, abundant oxygen-containing groups and two-dimensional flexibility, is highlighted as an easy and well-controlled strategy for the design and preparation of functionalized carbon materials, and the use of self-assembly for uniform hybridization is addressed for preparing hybrid carbon materials with various functions. A number of new exciting and potential applications are also presented for the assembled GO-based materials. This contribution concludes with some personal perspectives on future challenges before interfacial self-assembly may become a major strategy for the application-targeted design and preparation of functionalized carbon materials. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Zhang C.,Tsinghua University
IEEE Journal on Selected Areas in Communications | Year: 2011

In order to provide autonomous broadband communications among mobile vehicles, especially in an environment without fixed terrestrial vehicular base stations, a Cognitive Non-Continuous Carrier Interferometry Orthogonal Signal Division Multiplexing (Cognitive NCI-OSDM) transmission system is proposed in this paper. Specifically, Orthogonal Signal Division Multiplexing (OSDM) provides the system with high transmission capacity and good adaptability to variable mobile speeds. Carrier Interferometry (CI) codes make a system with limited Peak to Average Power Ratio (PAPR) of the transmitted signal. The incorporation of adaptive OSDM scheme provides an efficient approach to control Inter-Carrier Interference (ICI). Moreover, the non-continuous scheme is quite suitable in cognitive radio applications. Compared with traditional broadband OFDM-based transmission, such as Non-Continuous OFDM (NC-OFDM) in IEEE802.22, Cognitive NCI-OSDM has advantages of higher transmission capacity and spectrum efficiency, lower ICI, limited PAPR, adaptability to its cognitive environment and variable mobile speed. In this paper, the application system and the structure of Cognitive NCI-OSDM transmission is proposed for autonomous vehicular communications. Furthermore, the performance is evaluated, including the Bit Error Rate (BER), throughput, PAPR and Power of Inter-Carrier Interference (PICI). Finally, the system complexity, which is considered as the potential drawback when compared with an OFDM-based system, is investigated and confirmed to be controllable. The results reported in this paper show the promise of the proposed cognitive NCI-OSDM system and identify some possibilities for its future application in autonomous vehicular communications. © 2006 IEEE.

Wang X.,Tsinghua University
Operations Research | Year: 2016

Discontinuities are common in the pricing and hedging of complex financial derivatives. Quasi-Monte Carlo (QMC) methods for high-dimensional finance problems with discontinuities can be inefficient because of the lack of good smoothness and high dimensionality. Interestingly, path simulation method (PSM) may affect both factors, implying its significance in QMC methods. What defines a "good" PSM for problems with discontinuities? The ability to align the discontinuities with the coordinate axes is a desirable property for a PSM. We show that for an arbitrary PSM, there exists a class of options with discontinuous payoff functions such that the transformed functions have only axis-parallel discontinuities, for which good QMC performance can be expected. In this sense, any PSM can be "good" in QMC methods for a specific class of problems. We analyze the structure of discontinuities for digital options using the new approach and show the superiority and the uniqueness (up to a permutation) of the standard construction. We develop a two-step procedure for pricing and hedging derivatives with discontinuous payoff functions. The first step is to design a good PSM that has the ability to align the discontinuities with the coordinate axes and the second step is to further exploit this nice property to remove the discontinuities completely. We prove that the new estimate is unbiased and has smaller variance. Numerical experiments demonstrate that the two-step procedure is very effective in QMC methods for pricing options and estimating Greeks, leading to a dramatic variance reduction. Both the path simulation step and the smoothing step are crucial and beneficial for QMC methods, with the contribution from each step varying depending on the severity of discontinuity. © 2016 INFORMS.

Dong Z.,Tsinghua University
IEEE Transactions on Nuclear Science | Year: 2011

Power-level regulation is a significant technique for guaranteeing both operation stability and efficiency of nuclear reactors. With the wide application of the digital instrument and control platforms, the implementation of modern state-feedback power control strategies, which have the ability of strengthening both the operation stability and efficiency for nuclear reactors, becomes much easier than before. Due to the advanced property of state-feedback power-level control and nonlinearity of reactor dynamics, it is so meaningful to develop nonlinear state-feedback power-level control laws. In this paper, a novel nonlinear state-feedback dissipation power-level control strategy is presented, which guarantees both the asymptotic closed-loop stability and convergent state-observation. Numerical simulation results show the feasibility and relationship between the observer-gain and control performance, and theoretic analysis corresponding to the simulation results is also given. © 2011 IEEE.

Pan J.,Tsinghua University | Seeger-Nukpezah T.,Fox Chase Cancer Center | Golemis E.A.,Fox Chase Cancer Center
Cellular and Molecular Life Sciences | Year: 2013

The primary cilium protrudes from the cell surface and acts as a sensor for chemical and mechanical growth cues, with receptors for a number of growth factors (PDGFα, Hedgehog, Wnt, Notch) concentrated within the ciliary membrane. In normal tissues, the cilium assembles after cells exit mitosis and is resorbed as part of cell cycle re-entry. Although regulation of the cilium by cell cycle transitions has been appreciated for over 100 years, only recently have data emerged to indicate the cilium also exerts influence on the cell cycle. The resorption/protrusion cycle, regulated by proteins including Aurora-A, VHL, and GSK-3β, influences cell responsiveness to growth cues involving cilia-linked receptors; further, resorption liberates the ciliary basal body to differentiate into the centrosome, which performs discrete functions in S-, G2-, and M-phase. Besides these roles, the cilium provides a positional cue that regulates polarity of cell division, and thus directs cells towards fates of differentiation versus proliferation. In this review, we summarize the specific mechanisms mediating the cilia-cell cycle dialog. We then emphasize the examples of polycystic kidney disease (PKD), nephronopthisis (NPHP), and VHL-linked renal cysts as cases in which defects of ciliary function influence disease pathology, and may also condition response to treatment. © 2012 Springer Basel AG.

Tao Z.,Tsinghua University
RSC Advances | Year: 2014

This review highlights and addresses issues related to research on the development of mesoporous silica nanomaterials (MSNs) based nanodevices for biological applications. Through the review, a variety of synthetic routes and surface functionalization is first introduced with regard to the preparation of MSNs with different chemical and physical features. Then, the effects of their various structural and compositional features on the induced biological activities are described, as recent biological applications of MSNs are summarized, typified by drug/biomolecule delivery, bioimaging, biocatalysis and biosensing. Conclusions are reached and prospects in the field are also envisioned. © 2014 the Partner Organisations.

Tang X.,Tsinghua University
Advances in Mechanical Engineering | Year: 2014

In the last two decades, cable-driven parallel robots have attracted a lot of attention in robot community as a hot topic of robot research. In this paper, the development of the cable-driven parallel manipulator is first introduced in general. Second, the latest advance in theory and applications of cable-driven parallel manipulator is presented in detail, especially some notable implementations. Finally, an other probable application foresight with this cable manipulator is proposed and discussed. © 2014 Xiaoqiang Tang.

Gao H.,Tsinghua University | Xu W.,Jiangnan University
IEEE Transactions on Systems, Man, and Cybernetics, Part B: Cybernetics | Year: 2011

Particle swarm optimization (PSO) is a population-based optimization technique that can be applied to a wide range of problems. Here, we first investigate the behavior of particles in the PSO using a Monte Carlo method. The results reveal the essence of the trajectory of particles during iterations and the reasons why the PSO lacks a global search ability in the last stage of iterations. Then, we report a novel PSO with a moderate-random-search strategy (MRPSO), which enhances the ability of particles to explore the solution spaces more effectively and increases their convergence rates. Furthermore, a new mutation strategy is used, which makes it easier for particles in hybrid MRPSO (HMRPSO) to find the global optimum and which also seeks a balance between the exploration of new regions and the exploitation of the already sampled regions in the solution spaces. Thirteen benchmark functions are employed to test the performance of the HMRPSO. The results show that the new PSO algorithm performs much better than other PSO algorithms for each multimodal and unimodal function. Furthermore, compared with recent evolutionary algorithms, experimental results empirically demonstrate that the proposed framework yields promising search performance. © 2011 IEEE.

With the indirect thrust measurement of electric thrusters working at a low vacuum chamber pressure as the research background, this paper analyses the impact force acting on a flat plate exposed normally to a rarefied plasma plume issuing from a thruster with an annular or circular exit section for the free-molecule flow regime (at large Knudsen numbers). The constraint relation proposed by Cai and Boyd (2007 J. Spacecr. Rockets 44 619, 1326) about the velocity components of gas particles leaving a location on the nozzle exit section and arriving at a given spatial point outside the nozzle has been employed here to derive the analytical expressions for calculating the impact force. Sample calculation results show that if the flat plate is sufficiently large, the impact force acting on the flat plate calculated for the case without accounting for gas particle reflection at the plate surface agrees well with the axial momentum flux calculated at the thruster exit or the theoretical thrust force of the studied thruster, while accounting for the contribution of gas particles reflected from the plate surface to the impact force production may significantly increase the calculated impact force acting on the flat plate. For a Hall-effect thruster in which the thrust force is dominantly produced by the ions with high directional kinetic energy and the ions are not directly reflected from the plate surface, the contribution to the impact force production of atom species and of gas particles reflected from the plate surface is negligibly small and thus the measured axial impact force acting on a sufficiently large plate can well represent the thrust force of the thruster. On the other hand, if the contribution of the gas particles reflected from the plate surface to the impact force production cannot be neglected (e.g. for the electric thrusters with comparatively low thruster exit temperatures), appreciable error would appear in the indirect thrust measurement. © 2010 IOP Publishing Ltd Printed in the UK & the USA.

Wang W.,Tsinghua University
Fuel | Year: 2011

Dry reforming of butanol for hydrogen production has been studied by Gibbs free energy minimization method. The calculation results showed that the formation of hydrogen and carbon monoxide was through a multi-step pathway via the dehydrogenation, dehydration, decomposition and carbon dioxide reforming of butanol. The optimum conditions for hydrogen production are identified: reaction temperatures between 1150 and 1200 K and carbon dioxide-to-butanol molar ratios between 3.5 and 4.0 at 1 atm. Under the above conditions, 100% conversion of butanol, 34.91-37.98% concentration of hydrogen and 57.34-57.87% concentration of carbon monoxide could be achieved in the absence of coke formation. The butanol dry reforming with carbon dioxide is suitable for providing fuels for Solid Oxide Fuel Cell (SOFC). The coke-formed and coke-free regions are found, which are useful in guiding the search for suitable catalysts for the reaction. © 2011 Elsevier Ltd All rights reserved.

9,10-Anthraquinone (AQ) and its derivatives, i.e., benzofuro[5,6-b]furan-4, 8-dione (BFFD), benzo[1,2-b:4,5-b′]dithiophene-4,8-dione (BDTD) and pyrido[3,4-g]isoquinoline-5,10-dione (PID), are environmentally friendly and cheap electrode materials. However, their significant solubility in electrolyte solutions limits the cycle performance of lithium-ion batteries. In this work a comparative investigation of these four organic molecules adsorbed on monolayer graphene and hexagonal boron nitride (h-BN) has been carried out using van der Waals (vdW) dispersion-corrected density-functional theory (DFT). The calculated results indicate that the vdW dispersion contributes to more than 80% of the total attractive interaction for all the complexes studied. The binding energies range from 1.06 to 1.31 eV, showing strong physisorption. The calculated binding energies of the four organic molecules are in the order: BFFD < BDTD < AQ < PID on monolayer graphene and BFFD < BDTD < PID < AQ on monolayer h-BN. The physisorption causes a work function shift relative to the isolated graphene or h-BN nanosheet in the order: AQ < BDTD < BFFD < PID on both the graphene and h-BN nanosheets. This sequence is dominated by the work functions of the four organic molecules. The strong physisorption suggests that the solubility of the four organic compounds in the electrolyte solutions can be reduced by binding them to a graphene or h-BN nanosheet, making the organic compound-graphene or organic compound-h-BN composite a promising electrode material for lithium-ion batteries. This journal is © the Partner Organisations 2014.

Zhou Q.,Chinese University of Hong Kong | Cui X.,Tsinghua University
Physical Review Letters | Year: 2013

Intensive theoretical studies have recently predicted that a Bose-Einstein condensate will exhibit a variety of novel properties if spin-orbit coupling is present. However, an unambiguous fact has also been pointed out: Rashba coupling destroys a condensate of noninteracting bosons even in high dimensions. Therefore, a conceptually important question arises as to whether or not a condensate exists in the presence of interaction and a general type of spin-orbit coupling. Here we show that interaction qualitatively changes the ground state of bosons under Rashba spin-orbit coupling. Any infinitesimal repulsion forces bosons either to condense at one or two momentum states or to form a superfragmented state that is a superposition of infinite numbers of fragmented condensates. The superfragmented state is unstable against the anisotropy of spin-orbit coupling in systems with large numbers of particles, leading to the revival of a condensate in current experiments. © 2013 American Physical Society.

Wang X.-B.,Tsinghua University | Wang X.-B.,China Institute of Technology
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2013

We study the measurement-device-independent quantum key distribution (MDIQKD) in practice with limited resources when there are only three different states in implementing the decoy-state method and when there are basis-dependent coding errors. We present general formulas for the decoy-state method for two-pulse sources with three different states, which can be applied to the recently proposed MDIQKD with imperfect single-photon sources such as the coherent states or the heralded states from the parametric down-conversion. We point out that the existing result for secure MDIQKD with source coding errors does not always hold. We find that very accurate source coding is not necessary. In particular, we loosen the precision of the existing result by several orders of magnitude. © 2013 American Physical Society.

The All Sky Monitor (ASM) on board the Rossi X-ray Timing Explorer has continuously monitored a number of active galactic nuclei (AGNs) with similar sampling rates for 14 years, from 1996 January to 2009 December. Utilizing the archival ASM data of 27 AGNs, we calculate the normalized excess variances of the 300-day binned X-ray light curves on the longest timescale (between 300 days and 14 years) explored so far. The observed variance appears to be independent of AGN black-hole mass and bolometric luminosity. According to the scaling relation of black-hole mass (and bolometric luminosity) from galactic black hole X-ray binaries (GBHs) to AGNs, the break timescales that correspond to the break frequencies detected in the power spectral density (PSD) of our AGNs are larger than the binsize (300 days) of the ASM light curves. As a result, the singly broken power-law (soft-state) PSD predicts the variance to be independent of mass and luminosity. Nevertheless, the doubly broken power-law (hardstate) PSD predicts, with the widely accepted ratio of the two break frequencies, that the variance increases with increasing mass and decreases with increasing luminosity. Therefore, the independence of the observed variance on mass and luminosity suggests that AGNs should have soft-state PSDs. Taking into account the scaling of the break timescale with mass and luminosity synchronously, the observed variances are also more consistent with the softstate than the hard-state PSD predictions. With the averaged variance of AGNs and the soft-state PSD assumption, we obtain a universal PSD amplitude of 0.030± 0.022. By analogy with the GBH PSDs in the high/soft state, the longest timescale variability supports the standpoint that AGNs are scaled-up GBHs in the high accretion state, as already implied by the direct PSD analysis. © 2011. The American Astronomical Society. All rights reserved. Printedin the U.S.A.

Ng H.T.,Tsinghua University
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2013

We propose a method to detect the amplitude gradient of a microwave field by using a pair of entangled two-component Bose-Einstein condensates. We consider the two spatially separated condensates to be coupled to the two different magnetic fields. The magnetic-field gradient can be determined by measuring the variances of population differences and relative phases between the two-component condensates in two wells. The precision of measurement can reach the Heisenberg limit. We study the effects of one-body and two-body atom losses on the detection. We find that the entangled atoms can outperform the uncorrelated atoms in probing the magnetic fields in the presence of atom losses. The effect of atom-atom interactions is also discussed. © 2013 American Physical Society.

Dong Z.,Tsinghua University
Annals of Nuclear Energy | Year: 2014

After the Fukushima accident, safe, stable and efficient operation of reactors is very necessary for the development of nuclear power industry. Since pressurized water reactor (PWR) is the mostly widely used fission reactor, the improvement of its operation performance is quite meaningful. Self-stability is the most important dynamic feature of any reactors, and analyzing the self-stability can give the approach of improving the operation performance. With this in mind, the self-stability analysis of the PWR is presented through the shifted-ectropy based approach, and sufficient conditions for the globally asymptotic self-stability in cases of negative, zero and positive coolant temperature feedback coefficient are all established. The correctness of the theoretical results are finally verified through numerical simulation. The results of this paper give the way to not only guaranteeing self-stability through physical and thermal-hydraulic reactor design but also strengthening closed-loop stability and robustness by the means of feedback control. © 2013 Elsevier Ltd. All rights reserved.

Liu B.,Tsinghua University
Journal of Uncertain Systems | Year: 2014

This paper proposes a concept of uncertain random graph in which some edges exist with some degrees in probability measure and others exist with some degrees in uncertain measure, and discusses the connectivity index of an uncertain random graph. In addition, this paper presents a concept uncertain random network in which some weights are random variables and others are uncertain variables, and obtains the shortest path distribution of an uncertain random network. © 2014 World Academic Press, UK. All rights reserved.

Lau R.Y.K.,University of Hong Kong | Xia Y.,Tsinghua University | Ye Y.,Harbin Institute of Technology
IEEE Computational Intelligence Magazine | Year: 2014

Abstract-There has been a rapid growth in the number of cybercr imes that cause tremendous financial loss to organizations. Recent studies reveal that cybercriminals tend to collaborate or even transact cyber-attack tools via the dark markets established in online social media. Accordingly, it presents unprecedented opportunities for researchers to tap into these underground cybercriminal communities to develop better insights about collaborative cybercrime activities so as to combat the ever increasing number of cybercrimes. The main contribution of this paper is the development of a novel weakly supervised cybercriminal network mining method to facilitate cybercrime forensics. In particular, the proposed method is underpinned by a probabilistic generative model enhanced by a novel context-sensitive Gibbs sampling algorithm. Evaluated based on two social media corpora, our experimental results reveal that the proposed method significantly outperforms the Latent Dirichlet Allocation (LDA) based method and the Support Vector Machine (SVM) based method by 5.23% and 16.62% in terms of Area Under the ROC Curve (AUC), respectively. It also achieves comparable performance as the state-of-the-art Partially Labeled Dirichlet Allocation (PLDA) method. To the best of our knowledge, this is the first successful research of applying a probabilistic generative model to mine cybercriminal networks from online social media. © 2014 IEEE.

Zhou W.,Tsinghua University
Yanshilixue Yu Gongcheng Xuebao/Chinese Journal of Rock Mechanics and Engineering | Year: 2010

Firstly, the significances of rock structure and stability are introduced. Then, the methods to calculate limit bearing capacity for structure stability are presented. Finally, the basic problems on geotechnical stability, the constitutive relations and their positive-definition relations are studied. So far, the finite element method(FEM) for geotechnical structure stability could not obtain its exact solutions. However, by means of energy criteria, surplus-force reinforcement method and potential energy criteria, the solutions for engineering stability can be reasonably achieved. The following items could be preceded by FEM: limit load analysis in terms of structure failure and material failure, limit analysis of upper bound load and lower bound load of structures, nonlinear analysis of structure behaviors. The FEM is emphasized on how to solve structure stability problems for engineering projects, and on how to use energy criteria to problems of stability study for large-scale dam projects, and they could be optimized, through the context, from theory to practice. The real engineering problems are illustrated that are encountered in dam constructions during the last 40 years, and factors of safety gained from geomechanical rupture tests and rupture processes are submitted. With the corresponding achieved numerical analytical results, their factors of safety are reasonably cited in related codes or specifications. The results from these studies show that the large-scale dams in China have undergone the above-mentioned simulations, and their results are primarily verified with practical cases. Almost all of the dams are now under control and they are safe and stable.

You K.-Y.,Tsinghua University | Xie L.-H.,Nanyang Technological University
Zidonghua Xuebao/Acta Automatica Sinica | Year: 2013

With the rapid development of sensing, information processing, and communication technologies, the research in the emerging area of networked control systems (NCS) has attracted considerable attention in the research community. The purpose of this survey is to provide a review of state-of-the-art of such research. We particularly discuss various network conditions required for different control purposes, such as the minimum rate coding for stabilizability of linear systems in the presence of time-varying channel capacity, the critical packet loss rate for the stability of the Kalman filter with intermittent observations, network topology for coordination of networked multi-agent systems, as well as event-driven sampling for energy and communication efficiency. The common goal of discussion on these topics is to reveal the effect of the communication network on the operation of the networked systems. Copyright © 2013 Acta Automatica Sinica. All rights reserved.

Liu Q.,Tsinghua University | Liu Q.,CAS Beijing National Laboratory for Molecular
Electrochimica Acta | Year: 2014

Mg salts [Mg(NO3)2·6H2O]-doped TiO2 electrodes prepared well-optimized by the hydrothermal method. To prepare the working electrode, the TiO2 or Mg-doped TiO 2 slurry was coated onto the fluorine-doped tin oxide glass substrate by the doctor blade method and was then sintered at 450 °C. X-ray photoelectron spectroscopy (XPS) data indicated that the doped Mg ions exist in form of Mg2+, which can play a role as e- or h+ traps and reduce e-/h+ pair recombination rate, The Mott-Schottky plot indicates that the Mg-doped TiO2 photoanode shifts the flat band potential positively. The positive shift of the flat band potential improves the driving force of injected electrons from the LUMO of the dye to the conduction band of TiO2. This study show a photovoltaic efficiency of 7.12%, which is higher than that of the undoped TiO2 thin film (5.62%) and increase short-current by 26.7% from 14.9 mA to 19.1 mA. © 2014 Elsevier Ltd.

We show that some results presented in the aforementioned article are rather limited. One of the major restrictions on applicability of the obtained results is the ergodic requirement on the received plant output measurements, which is generally not satisfied by a time-varying system. Another major restriction is that the comparisons are not appropriate for its numerical simulations, that is, using the state estimation results of an estimator that utilizing current and past observations to compare with those of a one-step state predictor is not appropriate. To evaluate the filter performances objectively, we do a numerical simulation with the robust state estimator and the well-known Kalman filter that does not take either parametric errors or random measurement loss into account; and the simulation results show that there is no significant difference in filtering performance between these two estimators. © 2014 Elsevier Ltd. All rights reserved.

Chang C.,SLAC | Tang C.,Tsinghua University | Wu J.,SLAC
Physical Review Letters | Year: 2013

A novel approach to generating coherent x rays with 109-1010 photons and femtoseconds duration per laser pulse is proposed. This high intensity x-ray source is realized first by the pulse front tilt of a lateral fed laser to extend the electron-laser synchronic interaction time by several orders, which accomplishes the high-gain free-electron-laser-type exponential growth process and coherent emission with highly microbunched electron beam. Second, two methods are presented to enhance the effective optical undulator strength parameter. One is to invoke lenses to focus two counterpropagating lasers that are at normal incidence to the electron beam as a transverse standing wave; the other is to invent a periodic microstructure that can significantly enhance the center electromagnetic field realized by a resonant standing wave and the quadrupole waveguides. The energy coupling efficiency between the electron beam and laser is therefore greatly improved to generate the high brightness x rays, which is demonstrated by analytical and simulation results. © 2013 American Physical Society.

Special rings with iridescent color were found around erosion pits on mild carbon steel surface in rotate disk cavitation erosion experiments. The EDS and XPS examinations proved that the ring was an oxidation film mainly composed of Fe2O3. The mean diameter of iridescent rings was 200-300μm, and the thickness was 200-500nm. The rings have four main kinds of the shapes, named as O-shaped, U-shaped, pies and comet rings. Their special shapes and chemical compositions indicate that the iridescent rings are products of a kind of local oxidizations related to the collapsing bubbles above them. Based on numerical and experimental results, it is explained that the hot gas in a collapsing bubble is possible to contact the metal surface to cause the high temperature oxidization, and the shape of the bubble at its final stage of collapsing is responsible for the special shape of the ring. © 2010 Elsevier B.V.

Wang Y.,Beijing Normal University | Liang S.,Tsinghua University
Energy Policy | Year: 2013

China proposed a CO2 mitigation target in 2020 to deal with anthropogenic global climate change. Chinese policy makers mainly focus on three factors comprising consumption structure changes, energy technology development, and new energy increments. In addition, sectoral CO2 reduction is increasingly concerned in the world. Thus, it is significant to investigate integrated impacts of three factors to China's CO2 mitigation target as well as to identify key economic sectors for achieving this target. In this study, energy demand and CO2 emission in 2020 are predicted. Five scenarios are generated to illustrate the contributions of three factors. In addition, twelve key economic sectors for reducing energy demand and CO2 emission are identified from both production and final demand perspectives. Under integrated impacts of three factors, China's CO2 intensity per unit gross domestic product in 2020 will decrease by about 43.9% in 2020 than 2005 level. In the short term, China's CO2 mitigation will be highly dependent on energy technology development. In the long term, it will mainly rely on reshaped consumption structure changes and new energy development. In addition, China's future policies should focus on 12 identified key economic sectors. © 2013 Elsevier Ltd.

In this paper, the concept of entropy resistance is proposed based on the entropy generation analyses of heat transfer processes. It is shown that smaller entropy resistance leads to larger heat transfer rate with fixed thermodynamic force difference and smaller thermodynamic force difference with fixed heat transfer rate, respectively. For the discussed two-stream heat exchangers in which the heat transfer rates are not given and the three-stream heat exchanger with prescribed heat capacity flow rates and inlet temperatures of the streams, smaller entropy resistance leads to larger heat transfer rate. For the two-stream heat exchangers with fixed heat transfer rate, smaller entropy resistance leads to larger effectiveness. Furthermore, it is shown that smaller values of the concepts of entropy generation numbers and modified entropy generation number do not always correspond to better performance of the discussed heat exchangers. © 2013 Elsevier Ltd.

Liu Z.-X.,Tsinghua University | Liu Z.-X.,Massachusetts Institute of Technology | Wen X.-G.,Massachusetts Institute of Technology | Wen X.-G.,Perimeter Institute for Theoretical Physics
Physical Review Letters | Year: 2013

Symmetry-protected topological (SPT) states are short-range entangled states with symmetry. Nontrivial SPT states have symmetry-protected gapless edge excitations. In 2 dimension (2D), there are an infinite number of nontrivial SPT phases with SU(2) or SO(3) symmetry. These phases can be described by SU(2) or SO(3) nonlinear-sigma models with a quantized topological θ term. At an open boundary, the θ term becomes the Wess-Zumino-Witten term and consequently the boundary excitations are decoupled gapless left movers and right movers. Only the left movers (if θ>0) carry the SU(2) or SO(3) quantum numbers. As a result, the SU(2) SPT phases have a half-integer quantized spin Hall conductance and the SO(3) SPT phases have an even-integer quantized spin Hall conductance. Both the SU(2) and SO(3) SPT phases are symmetric under their U(1) subgroup and can be viewed as U(1) SPT phases with even-integer quantized Hall conductance. © 2013 American Physical Society.

Fu Z.,Sichuan University | Fu K.,Tsinghua University
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2012

We deliver an exploratory lattice QCD examination of the K *(892) meson decay width via the p-wave scattering phase shift of a pion-kaon (πK) system in the isospin I=1/2 channel. The modified Rummukainen-Gottlieb formula for a two-particle system with arbitrary mass is employed to extract phase shifts, which clearly reveal the existence of a resonance at a mass around the K *(892) meson mass. The effective range formula is applied to describe the energy dependence of the phase shift and we extract the effective K *→πK coupling constant as g K*πK=6.38(78). The decay width estimated from the phase shift is about 64.9±8.0MeV, which is in reasonable accordance with the experiment. Our lattice investigations are conducted on a 203×48 MILC gauge configuration with the N f=2+1 flavors of the asqtad-improved staggered dynamical sea quarks at (m π+m K)/m K *0.739 and lattice spacing a0.15fm. © 2012 American Physical Society.

Gao Z.,Tsinghua University
Physics of Plasmas | Year: 2013

The frequency and damping rate of the geodesic acoustic mode (GAM) is revisited by using a gyrokinetic model with a number-conserving Krook collision operator. It is found that the damping rate of the GAM is non-monotonic as the collision rate increases. At low ion collision rate, the damping rate increases linearly with the collision rate; while as the ion collision rate is higher than v t i / R, where v t i and R are the ion thermal velocity and major radius, the damping rate decays with an increasing collision rate. At the same time, as the collision rate increases, the GAM frequency decreases from the (7 / 4 τ) v t i / R to (1 τ) v t i / R, where τ is the ratio of electron temperature to ion temperature. © 2013 American Institute of Physics.

This paper presents a detailed analysis of the temporal and spectral variability of the low-energy peaked BL Lac object S5 0716+714 with a long (∼74 ks) X-ray observation performed by XMM-Newton on 2007 September 24-25. The source experiences recurrent flares on timescales of hours. The soft X-ray variations, up to a factor of ∼4, are much stronger than the hard X-ray variations. With higher energy, the variability amplitude increases in the soft X-rays but decreases in the hard X-rays. The hard X-ray variability amplitude, however, is effectively large. For the first time, we detect a soft lag of ∼1000 s between the soft and hard X-ray variations. The soft lags might become larger with larger energy differences. The overall X-ray spectra exhibit a softer-when-brighter trend, whereas the soft X-ray spectra appear to show a harder-when-brighter trend. The concave X-ray spectra of the source can be interpreted as the sum of the high-energy tail of the synchrotron emission, dominating in the soft X-rays, and the low-energy end of the inverse Compton (IC) emission, contributing more in the hard X-rays. The synchrotron spectra are steep (Γ ∼ 2.6), while the IC spectra are flat (Γ ∼ 1.2). The synchrotron spectra appear to harden with larger synchrotron fluxes, while the IC spectra seem to soften with larger IC fluxes. When the source brightens, the synchrotron fluxes increase but the IC fluxes decrease. The synchrotron tail exhibits larger flux variations but smaller spectral changes than the IC component does. The crossing energies between the two components and the trough energies of spectral energy distributions (SEDs) increase when the source brightens. The X-ray spectral variability demonstrates that the synchrotron and IC SED peaks of S5 0716+714 shift to higher energies when it brightens. The temporal variability also elucidates that the hard X-ray variations of the source might be dominated by the synchrotron tail. The simultaneous optical and UV data obtained with XMM-Newton are compared with the X-ray observations. © 2010. The American Astronomical Society. All rights reserved.

Pastor-Pareja J.C.,Tsinghua University | Pastor-Pareja J.C.,Howard Hughes Medical Institute | Xu T.,Howard Hughes Medical Institute | Xu T.,Fudan University
Annual Review of Genetics | Year: 2013

Cancer was seen for a long time as a strictly cell-autonomous process in which oncogenes and tumor-suppressor mutations drive clonal cell expansions. Research in the past decade, however, paints a more integrative picture of communication and interplay between neighboring cells in tissues. It is increasingly clear as well that tumors, far from being homogenous lumps of cells, consist of different cell types that function together as complex tissue-level communities. The repertoire of interactive cell behaviors and the quantity of cellular players involved call for a social cell biology that investigates these interactions. Research into this social cell biology is critical for understanding development of normal and tumoral tissues. Such complex social cell biology interactions can be parsed in Drosophila. Techniques in Drosophila for analysis of gene function and clonal behavior allow us to generate tumors and dissect their complex interactive biology with cellular resolution. Here, we review recent Drosophila research aimed at understanding tissue-level biology and social cell interactions in tumors, highlighting the principles these studies reveal. © 2013 by Annual Reviews. All rights reserved.

Guo Z.,Tsinghua University | Zhang L.,Hong Kong Polytechnic University | Zhang D.,Hong Kong Polytechnic University
IEEE Transactions on Image Processing | Year: 2010

In this correspondence, a completed modeling of the local binary pattern (LBP) operator is proposed and an associated completed LBP (CLBP) scheme is developed for texture classification. A local region is represented by its center pixel and a local difference sign-magnitude transform (LDSMT). The center pixels represent the image gray level and they are converted into a binary code, namely CLBP-Center (CLBP-C), by global thresholding. LDSMT decomposes the image local differences into two complementary components: The signs and the magnitudes, and two operators, namely CLBP-Sign (CLBP-S) and CLBP-Magnitude (CLBP-M), are proposed to code them. The traditional LBP is equivalent to the CLBP-S part of CLBP, and we show that CLBP-S preserves more information of the local structure than CLBP-M, which explains why the simple LBP operator can extract the texture features reasonably well. By combining CLBP-S, CLBP-M, and CLBP-C features into joint or hybrid distributions, significant improvement can be made for rotation invariant texture classification. © 2010 IEEE.

Liu Y.,Xian Jiaotong University | Xu Z.,Tsinghua University
Journal of the Mechanics and Physics of Solids | Year: 2014

Recent studies have shown that graphene-derived materials not only feature outstanding multifunctional properties, but also act as model materials to implant nanoscale structural engineering insights into their macroscopic performance optimization. In this work, we explore strengthening and toughening strategies of this class of materials by introducing multimodal crosslinks, including long, strong and short, self-healable ones. We identify two failure modes by fracturing functionalized graphene sheets or their crosslinks, and the role of brick-and-mortar hierarchy in mechanical enhancement. Theoretical analysis and atomistic simulation results show that multimodal crosslinks synergistically transfer tensile load to enhance the strength, whereas reversible rupture and formation of healable crosslinks improve the toughness. These findings lay the ground for future development of high-performance paper-, fiber- or film-like macroscopic materials from low-dimensional structures with engineerable interfaces. © 2014 Elsevier Ltd.

Shi Y.,Tsinghua University
Protein and Cell | Year: 2012

Phagocytosis and innate immune responses to solid structures are topics of interest and debate. Alum, monosodium urate, calcium pyrophosphate dehydrate, silica and by extension all solid entities draw varying degrees of attention from phagocytes, such as antigen presenting cells. For some, innocuous soluble metabolites turn into fierce irritants upon crystallization, pointing to divergent signaling mechanisms of a given substance in its soluble and solid states. Over the years, many mechanisms have been proposed, including phagocytic receptors, toll like receptors, and NACHT-LRRs (NLRs), as well as several other protein structure mediated recognition of the solids. Is there a more general mechanism for sensing solids? In this perspective, I present an alternative view on the topic that membrane lipids can engage solid surfaces, and the binding intensity leads to cellular activation. I argue from the stands of evolution and biological necessity, as well as the progression of our understanding of cellular membranes and phagocytosis. The effort is to invite debate of the topic from a less familiar yet equally thrilling viewing angle. © 2012 Higher Education Press and Springer-Verlag Berlin Heidelberg.

Zhao Q.,Tsinghua University
Trends in Plant Science | Year: 2016

Lignin is a complex phenolic polymer that is deposited in the secondary cell wall of all vascular plants. The evolution of lignin is considered to be a critical event during vascular plant development, because lignin provides mechanical strength, rigidity, and hydrophobicity to secondary cell walls to allow plants to grow tall and transport water and nutrients over a long distance. In recent years, great research efforts have been made to genetically alter lignin biosynthesis to improve biomass degradability for the production of second-generation biofuels. This global focus on lignin research has significantly advanced our understanding of the lignification process. Based on these advances, here I provide an overview of lignin composition, the biosynthesis pathway and its regulation. The eukaryotic Mediator complex is a conserved central component of the transcriptional machinery.Recently, plant Mediator subunits have been reported to participate in numerous biological processes, such as plant defense, noncoding RNA production, and cold tolerance.Originally reported as REDUCED EPIDERMAL FLURESCENCE 4 (REF4) and REF4-RELATED 1 (RFR1), now renamed as MED5a and MED5b, these two genes are suggested to be critical for phenylpropanoid homeostasis.It is possible that MED5a and MED5b regulate lignin biosynthetic genes translationally or repress the gene transcription in the step of lignin monomer transport or polymerization. © 2016 Elsevier Ltd.

Teng M.-J.,CAS Beijing National Laboratory for Molecular | Jia X.-R.,CAS Beijing National Laboratory for Molecular | Chen X.-F.,CAS Beijing National Laboratory for Molecular | Wei Y.,Tsinghua University
Angewandte Chemie - International Edition | Year: 2012

Color schemes: A mechanochromic material composed of two types of peptides bearing a pyrene group and rhodamine B moieties, respectively, displays multiluminescent colors, such as blue, green, and reddish in one sample (see picture). The mechanochromic behavior is based on a combined switching of molecular assemblies and chemical structure. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Chen G.-Q.,Tsinghua University | Patel M.K.,University Utrecht
Chemical Reviews | Year: 2012

A technical and environmental review dealt with the derivation of plastics from biological sources in the past and to be done so in the future. Bio-based sustainable plastics needed to be developed to avoid problems caused by the petrochemical plastics. Materials derived from biological sources including starch, cellulose, fatty acids, sugars, proteins, and other sources were consumed by microorganisms that converted these raw materials into various monomers. These monomers were suitable for polymer production including, hydroxyalkanoic acids, D- and L-lactic acid, succinic acid, bio-1,4-butanediol, (R)-3-hydroxypropionic acid, bio-ethylene, and 1,3-propanediol. These monomers were used to produce various bio-based plastics including polyhydroxyalkanoates (PHA), polylactic acid (PLA), and poly(butylene succinate) (PBS).

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.

Yong W.-A.,Tsinghua University
Archive for Rational Mechanics and Analysis | Year: 2014

In this paper, we revise Maxwell’s constitutive relation and formulate a system of first-order partial differential equations with two parameters for compressible viscoelastic fluid flows. The system is shown to possess a nice conservation–dissipation (relaxation) structure and therefore is symmetrizable hyperbolic. Moreover, for smooth flows we rigorously verify that the revised Maxwell’s constitutive relations are compatible with Newton’s law of viscosity. © 2014, Springer-Verlag Berlin Heidelberg.

Zhang Z.,Tsinghua University
Nature Nanotechnology | Year: 2016

The development of new, high-quality functional materials has been at the forefront of condensed-matter research. The recent advent of two-dimensional black phosphorus has greatly enriched the materials base of two-dimensional electron systems (2DESs). Here, we report the observation of the integer quantum Hall effect in a high-quality black phosphorus 2DES. The high quality is achieved by embedding the black phosphorus 2DES in a van der Waals heterostructure close to a graphite back gate; the graphite gate screens the impurity potential in the 2DES and brings the carrier Hall mobility up to 6,000 cm2 V-1 s-1. The exceptional mobility enabled us to observe the quantum Hall effect and to gain important information on the energetics of the spin-split Landau levels in black phosphorus. Our results set the stage for further study on quantum transport and device application in the ultrahigh mobility regime. © 2016 Nature Publishing Group

You K.,Tsinghua University | Xie L.,Nanyang Technological University
IEEE Transactions on Signal Processing | Year: 2013

This paper is concerned with the design of transmission scheduler and estimator for linear discrete-time stochastic systems to reduce the number of measurements to be transmitted from sensor to estimator. To this purpose, both controllable and uncontrollable scheduling schemes are considered, respectively. A controllable scheduler is designed as a deterministic function of system measurements, and sequentially decides the transmission of each element of a measurement vector to the estimator. We derive an approximate minimum mean square error (MMSE) estimator. On the other hand, an uncontrollable scheduler means that the transmission of the measurement vector is driven by a random process which is independent of system evolution. The MMSE estimator under this scheduler is cast as the Kalman filtering with intermittent observations. Some stability conditions are established for both the estimators. Finally, illustrative examples are included to validate the theoretical results. © 1991-2012 IEEE.

Shuai Z.,Tsinghua University | Peng Q.,CAS Beijing National Laboratory for Molecular
Physics Reports | Year: 2014

Photo- or electro-excited states in polyatomic molecules, aggregates, and conjugated polymers are at the center of organic light-emitting diodes (OLEDs). These can decay radiatively or non-radiatively, determining the luminescence quantum efficiency of molecular materials. According to Kasha's rule, light-emission is dictated by the lowest-lying excited state. For conjugated polymers, the electron correlation effect can lead the lowest-lying excited state to the even-parity 2Ag state which is non-emissive. To understand the nature of the low-lying excited state structure, we developed the density matrix renormalization group (DMRG) theory and its symmetrization scheme for quantum chemistry applied to calculate the excited states structure. We found there are three types of 1Bu/2Ag crossover behaviors: with electron correlation strength U, with bond length alternation, and with conjugation length. These directly influence the light-emitting property.For the electro-excitation, carriers (electron and hole) are injected independently, forming both singlet and triplet excited bound states with statistically 25% and 75% portions, respectively. We found that the exciton formation rate can depend on spin manifold, and for conjugated polymers, the singlet exciton can have larger formation rate leading to the internal electroluminescence quantum efficiency larger than the 25% spin statistical limit. It is originated from the interchain electron correlation as well as intrachain lattice relaxation.For the dipole allowed emissive state, the radiative decay process via either spontaneous emission or stimulated emission can be computed from electronic structure plus vibronic couplings. The challenging issue lies in the non-radiative decay via non-adiabatic coupling and/or spin-orbit coupling. We developed a unified correlation function formalism for the excited state radiative and non-radiative decay rates. We emphasized the low-frequency mode mixing (Duschinsky rotation) effect on the non-radiative decay. We further combined the non-adiabatic coupling and spin-orbit coupling for the triplet state decay (phosphorescence) quantum efficiency. All the formalisms have been developed analytically, which have been applied to optical spectroscopy, aggregation-induced emission phenomena, and polymer photovoltaic property. © 2013 Elsevier B.V.

Wang Z.,Tsinghua University
IEEE Microwave Magazine | Year: 2011

Recently, terahertz (THz) technology has attracted a great deal of interest from academia and industry. This is due to a number of interesting features of THz waves, including the tens and hundreds of gigahertz bandwidths available, and the fact that this frequency band poses only a minor health threat. Also, as millimeter-wave communication systems mature [1], [2], the focus of research is, naturally, moving to the THz range. © 2011 IEEE.

Rao Y.,Tsinghua University
Synlett | Year: 2013

An efficient sp2 C-H hydroxylation has been developed for the synthesis of a wide range of functionalized phenols with aryl ketones, benzoates, benzamides, acetanilides and sulfonamides through palladium(II) catalysis. A trifluoroacetic acid (TFA)/trifluoroacetic anhydride (TFAA) co-solvent system serves as the oxygen source and is the critical factor for weak coordination promoted C-H activation. © Georg Thieme Verlag Stuttgart New York.

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.

Background: Patient's satisfaction with medical service delivery/assessment of medical service/trust in health delivery system may have significant influence on patient's life satisfaction in China's health delivery system/in various kinds of hospitals.The aim of this study was to test whether and to what extent patient's satisfaction with medical service delivery/patient's assessments of various major aspects of medical service/various major aspects of patient's trust in health delivery system influenced patient's life satisfaction in China's health delivery system/in various kinds of hospitals.Methods: This study collaborated with National Bureau of Statistics of China to carry out a 2008 national urban resident household survey in 17 provinces, autonomous regions, and municipalities directly under the central government (N = 3,386), and specified ordered probit models were established to analyze dataset from this household survey.Results: The key considerations in generating patient's life satisfaction involved patient's overall satisfaction with medical service delivery, assessment of doctor-patient communication, assessment of medical cost, assessment of medical treatment process, assessment of medical facility and hospital environment, assessment of waiting time for medical service, trust in prescription, trust in doctor, and trust in recommended medical examination. But the major considerations in generating patient's life satisfaction were different among low level public hospital, high level public hospital, and private hospital.Conclusion: The promotion of patient's overall satisfaction with medical service delivery, the improvement of doctor-patient communication, the reduction of medical cost, the improvement of medical treatment process, the promotion of medical facility and hospital environment, the reduction of waiting time for medical service, the promotion of patient's trust in prescription, the promotion of patient's trust in doctor, and the promotion of patient's trust in recommended medical examination could all help promote patient's life satisfaction. But their promotion effects were different among low level public hospital, high level public hospital, and private hospital. © 2012 Tang; licensee BioMed Central Ltd.

Yao H.,Stanford University | Yao H.,Tsinghua University | Kivelson S.A.,Stanford University
Physical Review Letters | Year: 2012

We study a generalized quantum hard-core dimer model on the square and honeycomb lattices, allowing for first and second neighbor dimers. At generalized Rokhsar-Kivelson points, the exact ground states can be constructed, and ground-state correlation functions can be equated to those of interacting (1+1)-dimensional Grassmann fields. When the concentration of second neighbor dimers is small, the ground-state correlations are shown to be short ranged corresponding to a (gaped) spin liquid phase. On a 2-torus, the ground states exhibit fourfold topological degeneracy. On a finite cylinder we have found a dramatic even-odd effect depending on the circumference and propose that this can be used as a numerical diagnostic of gapped spin-liquid phases, more generally. © 2012 American Physical Society.

Lim W.A.,University of California at San Francisco | Lim W.A.,Howard Hughes Medical Institute | Lee C.M.,University of California at San Francisco | Tang C.,Tsinghua University
Molecular Cell | Year: 2013

A challenge in biology is to understand how complex molecular networks in the cell execute sophisticated regulatory functions. Here we explore the idea that there are common and general principles that link network structures to biological functions, principles that constrain the design solutions that evolution can converge upon for accomplishing a given cellular task. We describe approaches for classifying networks based on abstract architectures and functions, rather than on the specific molecular components of the networks. For any common regulatory task, can we define the space of all possible molecular solutions? Such inverse approaches might ultimately allow the assembly of a design table of core molecular algorithms that could serve as a guide for building synthetic networks and modulating disease networks. © 2013 Elsevier Inc.

Jia Q.-S.,Tsinghua University
IEEE Transactions on Automation Science and Engineering | Year: 2011

Many systems nowadays follow not only physical laws but also manmade rules. These systems are known as discrete-event dynamic systems (DEDSs), where simulation is the only faithful way for performance evaluation. Due to various advantages in practice, designs (or solution candidates) with low descriptive complexity (called simple designs) are usually preferred over complex ones when their performances are close. However, the descriptive complexity (DC) is usually nonlinear and takes discrete value, which makes traditional methods such as linear programming and gradient-based local search not applicable. Existing methods for simulation-based optimization (SBO) do not explore the preference on descriptive complexity and thus cannot solve the problem efficiently. The major contributions of this paper are to point out the importance of considering SBO problems with DC preference, and to develop an adaptive sampling algorithm (ASA) to find the simplest good design. It is shown that ASA terminates within finite iterations and with controllable probability of making mistake. The computational complexity of ASA and its dependence on various parameters are discussed. ASA is then applied to three parameter optimization problems and a node activation policy optimization problem in a wireless sensor network. Numerical results show that ASA is more efficient than blind picking and Levin search in most cases. We hope this work can shed some insight to how to find simple and good designs in general. © 2011 IEEE.

Chen G.-Q.,Tsinghua University
Advances in Biochemical Engineering/Biotechnology | Year: 2011

Polyhydroxyalkanoates (PHAs) are a family of biopolyesters synthesized by many types of bacteria as carbon and energy reserve materials. PHAs combine properties of thermal processibility, biodegradability, biocompatibility and sustainability. They have attracted attention from fermentation, materials and biomedical industries. Recent environmental concerns such as CO2 emissions and plastic pollution as well as rapid exhaustion of petroleum resources have increased public and industrial interests in these unique materials.purification, chiral chemicals and drug development. This chapter will discuss microbial PHA production and its applications in various fields. © Springer-Verlag Berlin Heidelberg 2010.

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

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

Teng M.-J.,CAS Beijing National Laboratory for Molecular | Jia X.-R.,CAS Beijing National Laboratory for Molecular | Yang S.,CAS Beijing National Laboratory for Molecular | Chen X.-F.,CAS Beijing National Laboratory for Molecular | Wei Y.,Tsinghua University
Advanced Materials | Year: 2012

A smart luminescent material whose emission color and emission intensity can be separately modulated by external force is demonstrated. The rational manipulation of rich noncovalent interactions and fluorophore packing style promotes an in-depth understanding between supramolecular structure and photophysical property and offers an effective strategy to modulate the light-emitting property in a predicative way. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Zhang R.,Nanchang University | Wu C.,Tsinghua University
Information Sciences | Year: 2012

Practical production scheduling problems usually involve some "bottleneck" machines, the scheduling policies for which could significantly affect the final solution quality. Therefore, it is beneficial to identify the bottleneck machines beforehand, so that we can intensify the optimization for these machines in the subsequent solving stage. To this end, a bottleneck machine identification algorithm is proposed in this paper for the job shop scheduling problem with the objective of minimizing total tardiness. In order to obtain the instance-specific information about bottleneck machine distribution, we first propose a new optimization model which relaxes some conventional constraints of the standard job shop problem. Then, a simulated annealing algorithm is applied to solve this newly defined problem. Based on the optimization result, the bottleneck characteristic value (which is a measure of bottleneck level) is calculated for each machine. To utilize the obtained bottleneck information for job shop scheduling, we design a genetic algorithm which allocates more computational resources to the identified bottleneck machines by using a hybrid encoding scheme. Computational results verify the effectiveness and the robustness of the proposed bottleneck identification procedure. It is shown that intensifying the local search effort for the bottleneck machines will generally result in higher solution quality within reasonably short computational time. © 2011 Elsevier Inc. All rights reserved.

Fang S.,Tsinghua University
Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine | Year: 2010

The sensitivity encoding (SENSE) reconstruction reconstruction of parallel imaging can suffer from amplified noise at high reduction factors due to the ill-conditioned system matrix. Regularization alleviates this problem by imposing priors on the reconstructed image. These priors typically introduce both intrastructure smoothness and interstructure smoothness. The former mainly reduces noise, while the latter can also decrease intensity changes between different structures and cause structure loss. In this study, coherence regularization was proposed to impose only intrastructure smoothness in order to enhance the preservation of the image structure. Its energy functional was formed by examining the connection between regularization and the diffusion equation of adaptive image filtering. The coherence regularization extracts image structure information directly from the noisy data by adapting diffusion equation-related image-filtering methods. In this study, a nonlocal operator derived from the nonlocal mean filter was used for structure detection. Based on this structure information, only intrastructure intensity changes are penalized while the interstructure intensity changes are preserved. Both phantom simulation and in vivo experiments demonstrate that the coherence regularization would be able to effectively suppress noise in SENSE reconstruction at high reduction factors while suffering from much less image degradation, compared to Tikhonov and total variation methods. Copyright © 2010 Wiley-Liss, Inc.

Zhang J.,University of California at San Diego | Wang C.,Tsinghua University
Journal of Environmental Economics and Management | Year: 2011

The Clean Development Mechanism (CDM) allows industrialized countries to comply with the Kyoto Protocol by using carbon offsets from developing countries. There are two puzzles within this carbon market: additionality (the proposed activity would not have occurred in its absence) and co-benefits (the project has other environmental benefits besides climate mitigation). This paper proposes an econometric approach to evaluate the CDM effect on sulfur dioxide emission reductions and assess its additionality indirectly. Our empirical model is applied to China's emissions at the prefecture level. We found that the CDM does not have a statistically significant effect in lowering sulfur dioxide emissions. This result casts doubt on additionality of these CDM activities, that is, they would have happened anyway. © 2011 Elsevier Inc.

Yu D.,Nanyang Technological University | Goh K.,Nanyang Technological University | Wang H.,Nanyang Technological University | Wei L.,Nanyang Technological University | And 4 more authors.
Nature Nanotechnology | Year: 2014

Micro-supercapacitors are promising energy storage devices that can complement or even replace batteries in miniaturized portable electronics and microelectromechanical systems. Their main limitation, however, is the low volumetric energy density when compared with batteries. Here, we describe a hierarchically structured carbon microfibre made of an interconnected network of aligned single-walled carbon nanotubes with interposed nitrogen-doped reduced graphene oxide sheets. The nanomaterials form mesoporous structures of large specific surface area (396 m 2 g-1) and high electrical conductivity (102 S cm-1). We develop a scalable method to continuously produce the fibres using a silica capillary column functioning as a hydrothermal microreactor. The resultant fibres show a specific volumetric capacity as high as 305 F cm-3 in sulphuric acid (measured at 73.5 mA cm-3 in a three-electrode cell) or 300 F cm-3 in polyvinyl alcohol (PVA)/H 3 PO 4 electrolyte (measured at 26.7 mA cm-3 in a two-electrode cell). A full micro-supercapacitor with PVA/H 3 PO 4 gel electrolyte, free from binder, current collector and separator, has a volumetric energy density of ∼6.3 mWh cm-3 (a value comparable to that of 4 V-500 μAh thin-film lithium batteries) while maintaining a power density more than two orders of magnitude higher than that of batteries, as well as a long cycle life. To demonstrate that our fibre-based, all-solid-state micro-supercapacitors can be easily integrated into miniaturized flexible devices, we use them to power an ultraviolet photodetector and a light-emitting diode. © 2014 Macmillan Publishers Limited.

Yu Y.-X.,Tsinghua University
Physical Chemistry Chemical Physics | Year: 2013

The electronic and adsorption properties of graphene can be changed significantly through substitutional doping with nitrogen and nitrogen decoration of vacancies. Here ab initio density functional theory with a dispersion correction was used to investigate the stability, magnetic and adsorption properties of nine defects in graphene, including both nitrogen substitutional doping and nitrogen decoration of vacancies. The results indicate that only pyridinic N2V2 defect in graphene shows a ferromagnetic spin structure with high magnetic moment and magnetic stabilization energy. Not all nitrogen-doped defects can improve the capacity of the lithium-ion batteries. The adsorption energies of a lithium atom on nitrogen-substituted graphenes are more positive, indicating that they are meta-stable and no better than the pristine graphene as anode materials of lithium-ion batteries. Nitrogen-decorated single and double vacancy defects, especially for the pyridinic N2V2 defect in graphene, can greatly improve the reversible capacity of the battery in comparison with the pristine graphene. The theoretical prediction of the reversible capacity of the battery is 1039 mA h g-1 for the nitrogen-doped graphene material synthesized by Wu et al., which is in good agreement with the experimental data (1043 mA h g-1). The theoretical computations suggest that nitrogen-decorated single and double vacancy defects in graphene are the promising candidate for anode materials of lithium-ion batteries. Each nitrogen atom in the decoration can improve the reversible capacity of the battery by 63.3-124.5 mA h g-1 in a 4 × 4 supercell of graphene. The present work provides crucial information for the development of N-doped graphene-based anode materials of lithium-ion batteries. © 2013 The Owner Societies.

Yu Y.-X.,Tsinghua University
Journal of Materials Chemistry A | Year: 2013

It is known that low-dimensional carbon allotropes can be used as a new class of anode materials for lithium-ion batteries. However, the existing carbon allotropes cannot meet the increasing energy and power demand, and thus there is still a need for further development of new materials for lithium-ion batteries. In the present work, a new graphene allotrope, known as graphenylene, is found to be capable of storing lithium with greater density of energy. Ab initio density functional theory calculations indicate that the unique dodecagonal holes in graphenylene enable lithium ions to diffuse both on and through graphenylene layers with energy barriers no higher than 0.99 eV. Adsorption of a lithium atom on graphenylene is stronger than that on pristine graphene. The highest lithium storage capacities for monolayer and bilayer graphenylene compounds are Li3C6 and Li 2.5C6, respectively, which correspond to specific capacities of 1116 and 930 mA h g-1. Both specific and volumetric capacities of lithium-intercalated graphenylene compounds are significantly larger than those for graphene. The high lithium mobility and large lithium storage capacity demonstrate that graphenylene is a promising anode material for modern lithium-ion batteries. This journal is © The Royal Society of Chemistry 2013.

Pei Z.,Zhejiang University of Technology | Zheng L.,Tsinghua University
Expert Systems with Applications | Year: 2012

In this paper we present a new approach to solve multi-attribute decision making problems in intuitionistic fuzzy environment. This approach is based on a new ranking method of intuitionistic fuzzy sets, in which the evaluated values (in the form of intervals) of the same alternative with different attributes are considered as one unified entity. According to people's intuition, the ranking method proposed in this paper is mainly grounded on a revised score function and a revised accuracy function of intuitionistic fuzzy sets. Different from the traditional methods, in this new approach, the degree of membership, the degree of nonmembership and the degree of hesitation are considered with various importance in reflecting the true image of the respective alternative. Furthermore, an optimization model is established to estimate the relative degree of importance of each quantity. Finally, two practical examples are provided to illustrate our approach. © 2011 Elsevier Ltd. All rights reserved.

Li S.,Tsinghua University
Zhongguo Zhongyao Zazhi | Year: 2011

Understanding the interactions between numerous chemical compounds of herbs or herbal formulae and complex biological systems related with diseases or traditional Chinese medicine (TCM) syndromes is one of great dilemmas in current studies on TCM. To address such a difficult issue, we propose a novel concept and methodology of "Network Target" based on our previous works and from the perspective of network pharmacology as well as systems biology. The network target treats a disease-specific biomolecular network as a target to help design and predict the best possible treatments. Focused on mapping disease phenotypes and herbal compounds into biomolecular networks and then calculating, analyzing and predicting the mechanism of their mutual interactions, the network target approaches will facilitate discovery of effective compounds and their combinations, elucidation of mechanistic relationships between herbal formulae and diseases or TCM syndromes, and development of rational drug designs for TCM. In this paper, our recent progresses on the methodology of Network Target and its applications in herbal medicine are reviewed to provide reference for the coming TCM network pharmacology.

Zhang A.,Capital Normal University | Feng K.,Tsinghua University
IEEE Transactions on Information Theory | Year: 2012

In this paper, the value of I max(C) for codebooks C = C(D) constructed by certain almost difference sets D in double-struck F sign q x is determined and expressed in terms of Jacobi sums from which it shows that such codebooks nearly meet the Welch bound. This result is an answer of a question raised by C.Ding and T.Feng in [2]. We also present another series of codebooks which nearly meet the Welch bound, where the codebook is constructed by a subset D ε in additive group R = double-struck F sign q1 ⊕ double-struck F sign q2. When q 1 = q 2, D ε is an almost difference set of R. © 2006 IEEE.

Xu S.X.,Tsinghua University | Zhang X.M.,Hong Kong University of Science and Technology
MIS Quarterly: Management Information Systems | Year: 2013

In this paper, we seek to determine whether a typical social media platform, Wikipedia, improves the information environment for investors in the financial market. Our theoretical lens leads us to expect that information aggregation about public companies on Wikipedia may influence how management's voluntary information disclosure reacts to market uncertainty with respect to investors' information about these companies. Our empirical analysis is based on a unique data set collected from financial records, management disclosure records, news article coverage, and a Wikipedia modification history of public companies. On the supply side of information, we find that information aggregation on Wikipedia can moderate the timing of managers' voluntary disclosure of companies' earnings disappointments, or bad news. On the demand side of information, we find that Wikipedia's information aggregation moderates investors' negative reaction to bad news. Taken together, these findings support the view that Wikipedia improves the information environment in the financial market and underscore the value of information aggregation through the use of information technology.

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.

Cui X.,CAS Institute of Physics | Zhai H.,Tsinghua University
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2010

We construct a variational wave function to study whether a fully polarized Fermi sea of ultracold atoms is energetically stable against a single spin flip. Our variational wave function contains short-range correlations at least to the same level as Gutzwiller's projected wave function. For the Hubbard lattice model and the continuum model with pure repulsive interaction, we show that a fully polarized Fermi sea is generally unstable even for infinite repulsive strength. By contrast, for a resonance model, the ferromagnetic state is possible if the s-wave scattering length is positive and sufficiently large and the system is prepared to be orthogonal to the molecular bound state. However, we cannot rule out the possibility that more exotic correlations can destabilize the ferromagnetic state. © 2010 The American Physical Society.

Huang Y.,Tsinghua University
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2010

A general theorem as a necessary condition for the separability of quantum states in both finite and infinite dimensional systems, based on concave-function uncertainty relations, is derived. Two special cases of the general theorem are stronger than two known entanglement criteria based on the Shannon entropic uncertainty relation and the Landau-Pollak uncertainty relation, respectively; other special cases are able to detect entanglement where some famous entanglement criteria fail. © 2010 The American Physical Society.

Niu C.-Y.,Tsinghua University
Cell Research | Year: 2016

The eukaryotic multi-subunit RNA exosome complex plays crucial roles in 3′-to-5′ RNA processing and decay. Rrp6 and Ski7 are the major cofactors for the nuclear and cytoplasmic exosomes, respectively. In the cytoplasm, Ski7 helps the exosome to target mRNAs for degradation and turnover via a through-core pathway. However, the interaction between Ski7 and the exosome complex has remained unclear. The transaction of RNA substrates within the exosome is also elusive. In this work, we used single-particle cryo-electron microscopy to solve the structures of the Ski7-exosome complex in RNA-free and RNA-bound forms at resolutions of 4.2 Å and 5.8 Å, respectively. These structures reveal that the N-terminal domain of Ski7 adopts a structural arrangement and interacts with the exosome in a similar fashion to the C-terminal domain of nuclear Rrp6. Further structural analysis of exosomes with RNA substrates harboring 3′ overhangs of different length suggests a switch mechanism of RNA-induced exosome activation in the through-core pathway of RNA processing.Cell Research advance online publication 13 May 2016; doi:10.1038/cr.2016.56. © 2016 Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences

Xiang D.,Tsinghua University
IEEE Transactions on Dependable and Secure Computing | Year: 2011

A new deadlock-free routing scheme for meshes is proposed based on a new virtual network partitioning scheme, called channel overlapping. Two virtual networks can share some common virtual channels based on the new virtual network partitioning scheme. The deadlock-free adaptive routing method is then extended to deadlock-free adaptive fault-tolerant routing in 3D meshes still with two virtual channels. A few faulty nodes can make a higher dimensional mesh unsafe for fault-tolerant routing methods based on the block fault model, where the whole system (n-dimensional space) forms a fault block. Planar safety information in meshes is proposed to guide fault-tolerant routing and classifies fault-free nodes inside 2D planes. Many nodes globally marked as unsafe in the whole system become locally enabled inside 2D planes. This fault-tolerant deadlock-free adaptive routing algorithm is also extended to the one in an n-dimensional meshes with two virtual channels. Extensive simulation results are presented and compared to previous methods. © 2006 IEEE.

Li X.,University of California at Irvine | Li D.,Tsinghua University | Li D.,Tsinghua National Laboratory for Information Sciences and Technology
Physical Review Letters | Year: 2012

We solve the entanglement classification under stochastic local operations and classical communication (SLOCC) for general n-qubit states. For two arbitrary pure n-qubit states connected via local operations, we establish an equation between the two coefficient matrices associated with the states. The rank of the coefficient matrix is preserved under SLOCC and gives rise to a simple way of partitioning all the pure states of n qubits into different families of entanglement classes, as exemplified here. When applied to the symmetric states, this approach reveals that all the Dicke states |n with =1,[n/2] are inequivalent under SLOCC. © 2012 American Physical Society.

Wang J.,Tsinghua University
Nature Materials | Year: 2015

Ferroelectrics are widespread in technology, being used in electronics and communications, medical diagnostics and industrial automation. However, extension of their operational temperature range and useful properties is desired. Recent developments have exploited ultrathin epitaxial films on lattice-mismatched substrates, imposing tensile or compressive biaxial strain, to enhance ferroelectric properties. Much larger hydrostatic compression can be achieved by diamond anvil cells, but hydrostatic tensile stress is regarded as unachievable. Theory and ab initio treatments predict enhanced properties for perovskite ferroelectrics under hydrostatic tensile stress. Here we report negative-pressure-driven enhancement of the tetragonality, Curie temperature and spontaneous polarization in freestanding PbTiO3 nanowires, driven by stress that develops during transformation of the material from a lower-density crystal structure to the perovskite phase. This study suggests a simple route to obtain negative pressure in other materials, potentially extending their exploitable properties beyond their present levels. © 2015 Nature Publishing Group

Zhou K.,University of Chinese Academy of Sciences | Li Y.,Tsinghua University
Angewandte Chemie - International Edition | Year: 2012

Using bottom-up chemistry techniques, the composition, size, and shape in particular can now be controlled uniformly for each and every nanocrystal (NC). Research into shape-controlled NCs have shown that the catalytic properties of a material are sensitive not only to the size but also to the shape of the NCs as a consequence of well-defined facets. These findings are of great importance for modern heterogeneous catalysis research. First, a rational synthesis of catalysts might be achieved, since desired activity and selectivity would be acquired by simply tuning the shape, that is, the exposed crystal facets, of a NC catalyst. Second, shape-controlled NCs are relatively simple systems, in contrast to traditional complex solids, suggesting that they may serve as novel model catalysts to bridge the gap between model surfaces and real catalysts. Shape-controlled nanocrystals (NCs) are a new frontier in heterogeneous catalysis. Research into these NCs has shown that the catalytic properties of a material are sensitive not only to the size but also to the shape of the NCs owing to well-defined facets. Shape-controlled NCs may serve to bridge the gap between model surfaces and real catalysts. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Liu Z.,Beijing University of Chemical Technology | Li J.,Tsinghua University | Woo S.I.,Korea Advanced Institute of Science and Technology
Energy and Environmental Science | Year: 2012

Selective catalytic reduction of NOx by hydrogen (H 2-SCR) in the presence of oxygen has received much attention as a potential technology for reducing NOx emissions. A lot of research has been done in order to understand the reaction mechanism of H2-SCR and some possible mechanisms have been proposed. These mechanisms can be classified into two categories: NO adsorption/dissociation mechanisms and oxidation-reduction mechanisms. Based on the discussion of the reaction mechanism, the influence of the nature of the noble metal, catalyst support, catalyst preparation method, promoters and reaction conditions (including the presence of H2 and O2, water, sulfur, CO and CO 2) on the catalytic performance of some H2-SCR catalysts has been discussed. Finally, future research directions in the area of H 2-SCR have been proposed. © 2012 The Royal Society of Chemistry.

Shi Y.,Tsinghua University
Annual Review of Biophysics | Year: 2013

Secondary active transporters exploit the electrochemical potential of solutes to shuttle specific substrate molecules across biological membranes, usually against their concentration gradient. Transporters of different functional families with little sequence similarity have repeatedly been found to exhibit similar folds, exemplified by the MFS, LeuT, and NhaA folds. Observations of multiple conformational states of the same transporter, represented by the LeuT erfamily members Mhp1, AdiC, vSGLT, and LeuT, led to proposals that structural changes are associated with substrate binding and transport. Despite recent biochemical and structural advances, our understanding of substrate recognition and energy coupling is rather preliminary. This review focuses on the common folds and shared transport mechanisms of secondary active transporters. Available structural ormation generally ports the alternating access model for substrate transport, with variations and extensions made by emerging structural, biochemical, and computational evidence. Copyright © 2013 by Annual Reviews.

Feng J.,Tsinghua University | Jain A.K.,Michigan State University | Jain A.K.,Korea University
IEEE Transactions on Pattern Analysis and Machine Intelligence | Year: 2011

Fingerprint matching systems generally use four types of representation schemes: grayscale image, phase image, skeleton image, and minutiae, among which minutiae-based representation is the most widely adopted one. The compactness of minutiae representation has created an impression that the minutiae template does not contain sufficient information to allow the reconstruction of the original grayscale fingerprint image. This belief has now been shown to be false; several algorithms have been proposed that can reconstruct fingerprint images from minutiae templates. These techniques try to either reconstruct the skeleton image, which is then converted into the grayscale image, or reconstruct the grayscale image directly from the minutiae template. However, they have a common drawback: Many spurious minutiae not included in the original minutiae template are generated in the reconstructed image. Moreover, some of these reconstruction techniques can only generate a partial fingerprint. In this paper, a novel fingerprint reconstruction algorithm is proposed to reconstruct the phase image, which is then converted into the grayscale image. The proposed reconstruction algorithm not only gives the whole fingerprint, but the reconstructed fingerprint contains very few spurious minutiae. Specifically, a fingerprint image is represented as a phase image which consists of the continuous phase and the spiral phase (which corresponds to minutiae). An algorithm is proposed to reconstruct the continuous phase from minutiae. The proposed reconstruction algorithm has been evaluated with respect to the success rates of type-I attack (match the reconstructed fingerprint against the original fingerprint) and type-II attack (match the reconstructed fingerprint against different impressions of the original fingerprint) using a commercial fingerprint recognition system. Given the reconstructed image from our algorithm, we show that both types of attacks can be successfully launched against a fingerprint recognition system. © 2011 IEEE.

Jain A.K.,Michigan State University | Feng J.,Tsinghua University
IEEE Transactions on Pattern Analysis and Machine Intelligence | Year: 2011

Latent fingerprint identification is of critical importance to law enforcement agencies in identifying suspects: Latent fingerprints are inadvertent impressions left by fingers on surfaces of objects. While tremendous progress has been made in plain and rolled fingerprint matching, latent fingerprint matching continues to be a difficult problem. Poor quality of ridge impressions, small finger area, and large nonlinear distortion are the main difficulties in latent fingerprint matching compared to plain or rolled fingerprint matching. We propose a system for matching latent fingerprints found at crime scenes to rolled fingerprints enrolled in law enforcement databases. In addition to minutiae, we also use extended features, including singularity, ridge quality map, ridge flow map, ridge wavelength map, and skeleton. We tested our system by matching 258 latents in the NIST SD27 database against a background database of 29,257 rolled fingerprints obtained by combining the NIST SD4, SD14, and SD27 databases. The minutiae-based baseline rank-1 identification rate of 34.9 percent was improved to 74 percent when extended features were used. In order to evaluate the relative importance of each extended feature, these features were incrementally used in the order of their cost in marking by latent experts. The experimental results indicate that singularity, ridge quality map, and ridge flow map are the most effective features in improving the matching accuracy. © 2006 IEEE.

Gao Y.,Tsinghua University
Computers and Mathematics with Applications | Year: 2011

Uncertainty theory provides a new tool to deal with the shortest path problem with nondeterministic arc lengths. With help from the operational law of uncertainty theory, this paper gives the uncertainty distribution of the shortest path length. Also, it investigates solutions to the α-shortest path and the most shortest path in an uncertain network. It points out that there exists an equivalence relation between the α-shortest path in an uncertain network and the shortest path in a corresponding deterministic network, which leads to an effective algorithm to find the α-shortest path and the most shortest path. Roughly speaking, this algorithm can be broken down into two parts: constructing a deterministic network and then invoking the Dijkstra algorithm. © 2011 Elsevier Ltd. All rights reserved.

Geng H.,Ryerson University | Yang G.,Tsinghua University
IEEE Transactions on Energy Conversion | Year: 2010

A robust pitch control strategy for the output power control of wind generator systems in wide-wind-speed range is presented in this paper. The corresponding controller is designed, which consists of a nominal inverse-system controller and a robust compensator. The advantages of the proposed strategy include the simple implementation, tolerance of turbine parameter or some nonparametric uncertainties, and robust control of the generator output power with wind-speed variations. Theoretical analyses, simulation, and experimental results show that the proposed controller can work better in a wide-wind-speed range compared with the traditional proportional-integral-derivative controller. It has similar performance with the neural network controller, but less complexity. Additionally, it can be easily adapted to other wind generator systems. © 2010 IEEE.

Niu Z.,Tsinghua University
IEEE Wireless Communications | Year: 2011

This article addresses the potential paradigm shift of the next-generation cellular networks from the viewpoint of energy efficiency. In particular, it reveals that networks planning and operation should be more energy efficiency oriented; and in the meantime, the radio resources distributed over different cellular networks, and base stations should be optimized in a global way to be globally resource-optimized and energy-efficient networks (GREEN). A new framework, called traffic-aware network planning and green operation (TANGO), is proposed toward GREEN. Some key technologies for the migration to TANGO are then presented and evaluated. Theoretical modeling and simulation studies show that TANGO schemes can greatly improve the energy efficiency of cellular networks, while keeping QoS at a satisfactory level. © 2011 IEEE.

Yan Y.-B.,Tsinghua University
Wiley Interdisciplinary Reviews: RNA | Year: 2014

Lengths of the eukaryotic messenger RNA (mRNA) poly(A) tails are dynamically changed by the opposing effects of poly(A) polymerases and deadenylases. Modulating poly(A) tail length provides a highly regulated means to control almost every stage of mRNA lifecycle including transcription, processing, quality control, transport, translation, silence, and decay. The existence of diverse deadenylases with distinct properties highlights the importance of regulating poly(A) tail length in cellular functions. The deadenylation activity can be modulated by subcellular locations of the deadenylases, cis-acting elements in the target mRNAs, trans-acting RNA-binding proteins, posttranslational modifications of deadenylase and associated factors, as well as transcriptional and posttranscriptional regulation of the deadenylase genes. Among these regulators, the physiological functions of deadenylases are largely dependent on the interactions with the trans-acting RNA-binding proteins, which recruit deadenylases to the target mRNAs. The task of these RNA-binding proteins is to find and mark the target mRNAs based on their sequence features. Regulation of the regulators can switch on or switch off deadenylation and thereby destabilize or stabilize the targeted mRNAs, respectively. The distinct domain compositions and cofactors provide various deadenylases the structural basis for the recruitments by distinct RNA-binding protein subsets to meet dissimilar cellular demands. The diverse deadenylases, the numerous types of regulators, and the reversible posttranslational modifications together make up a complicated network to precisely regulate intracellular mRNA homeostasis. This review will focus on the diverse regulators of various deadenylases and will discuss their functional implications, remaining problems, and future challenges. For further resources related to this article, please visit the WIREs website. Conflict of interest: The author has declared no conflicts of interest for this article. © 2014 John Wiley & Sons, Ltd.

Wang D.-X.,CAS Beijing National Laboratory for Molecular | Wang M.-X.,Tsinghua University
Journal of the American Chemical Society | Year: 2013

Anion-π interactions have been systematically studied using tetraoxacalix[2]arene[2]triazine 1, an electron-deficient and cavity self-tunable macrocyclic host, as an electron-neutral molecular probe. As revealed by electrospray ionization mass spectrometry (ESI-MS), fluorescence titration and X-ray crystallography, tetraoxacalix[2]arene[2]triazine has been found to form 1:1 complexes with four typical polyatomic anions of different geometries and shapes in the gaseous phase, in solution, and in the solid state. The association constants for the formation of anion-π complexes in acetonitrile are in the range of 239 to 16950 M-1, following the order of 1·NO3 - > 1·BF4 - > 1·PF6 - > 1·SCN -. X-ray molecular structures of the complexes showed that two opposing triazine rings of tetraoxacalix[2]arene[2]triazine act as a pair of tweezers to interact with the included anions through cooperative anion-π and lone-pair electron-π interactions. The generality of anion-π interactions and diverse anion-π interaction motifs can provide a new dimension in the study of molecular recognition and self-assembly. Moreover, this study potentiates the effect of anion-π interactions in chemical and biological systems, especially those involving anion and electron-deficient aromatic species. © 2012 American Chemical Society.

Yan N.,Tsinghua University
Trends in Biochemical Sciences | Year: 2013

The major facilitator superfamily (MFS) is one of the largest groups of secondary active transporters conserved from bacteria to humans. MFS proteins selectively transport a wide spectrum of substrates across biomembranes and play a pivotal role in multiple physiological processes. Despite intense investigation, only seven MFS proteins from six subfamilies have been structurally elucidated. These structures were captured in distinct states during a transport cycle involving alternating access to binding sites from either side of the membrane. This review discusses recent progress in MFS structure analysis and focuses on the molecular basis for substrate binding, co-transport coupling, and alternating access. © 2013 Elsevier Ltd.

Xia L.-G.,Tsinghua University
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2016

To study the decays of ψ(3770) going to baryon anti-baryon pairs (BB-), all available experiments of measuring the cross sections of e+e-→BB at center-of-mass energy ranging from 3.0 GeV to 3.9 GeV are combined. To relate the baryon octets, a model based on the SU(3) flavor symmetry is used and the SU(3) breaking effects are also considered. Assuming the electric and magnetic form factors are equal (|GE|=|GM|), a global fit including the interference between the QED process and the resonant process is performed. The branching fraction of ψ(3770)→BB- is determined to be (2.4 ± 0.8 ± 0.3) × 10-5, (1.7 ± 0.6 ± 0.1) × 10-5, (4.5 ± 0.9 ± 0.1) × 10-5, (4.5 ± 0.9 ± 0.1) × 10-5, (2.0 ± 0.7 ± 0.1) × 10-5, and (2.0 ± 0.7 ± 0.1) × 10-5 for B=p, Λ, σ+, σ0, Ξ- and Ξ0, respectively, where the first uncertainty is from the global fit and the second uncertainty is the systematic uncertainty due to the assumption |GE|=|GM|. They are at least one order of magnitude larger than a simple scaling of the branching fraction of J/ψ/ψ(3686)→BB- © 2016 The Author.

Li X.,Shandong Normal University | Song S.,Tsinghua University
IEEE Transactions on Neural Networks and Learning Systems | Year: 2013

In this paper, a class of recurrent neural networks with discrete and continuously distributed delays is considered. Sufficient conditions for the existence, uniqueness, and global exponential stability of a periodic solution are obtained by using contraction mapping theorem and stability theory on impulsive functional differential equations. The proposed method, which differs from the existing results in the literature, shows that network models may admit a periodic solution which is globally exponentially stable via proper impulsive control strategies even if it is originally unstable or divergent. Two numerical examples and their computer simulations are offered to show the effectiveness of our new results. © 2012 IEEE.

Ng H.T.,Tsinghua University
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2015

We study the nonequilibrium dynamics of two-component bosonic atoms in a one-dimensional optical lattice in the presence of spin-orbit coupling. In the Mott-insulating regime, the two-component bosonic system at unity filling can be described by the quantum spin XXZ model. The atoms are initially prepared in their lower spin states. The system becomes out of equilibrium by suddenly introducing spin-orbit coupling to the atoms. The system shows the relaxation and nonstationary dynamics, respectively, in the different interaction regimes. We find that the time average of magnetization is useful to characterize the many-body dynamics. The effects of even and odd numbers of sites are discussed. Our result sheds light on nonequilibrium dynamics due to the interplay between spin-orbit coupling and atomic interactions. © 2015 American Physical Society.

Shi Y.,Tsinghua University
Cell | Year: 2014

Since determination of the myoglobin structure in 1957, X-ray crystallography, as the anchoring tool of structural biology, has played an instrumental role in deciphering the secrets of life. Knowledge gained through X-ray crystallography has fundamentally advanced our views on cellular processes and greatly facilitated development of modern medicine. In this brief narrative, I describe my personal understanding of the evolution of structural biology through X-ray crystallography - using as examples mechanistic understanding of protein kinases and integral membrane proteins - and comment on the impact of technological development and outlook of X-ray crystallography. © 2014 Elsevier Inc.

Miao J.,Tsinghua University
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2015

We study an extended Bose-Hubbard model with next-nearest-neighbor (NNN) hopping in a shaken optical lattice. We show how mean-field phase diagram evolves with the change of NNN hopping amplitude t2, which can be easily tuned via shaking amplitude. As t2 increases, a Z2-symmetry-breaking superfluid (Z2SF) phase emerges at the bottom of the Mott lobs. The tricritical points between normal superfluid, Z2SF, and Mott insulator (MI) phases are identified. We further demonstrate the tricritical point can be tuned to the tip of the Mott lobe, in which case a new critical behavior has been predicted. Within random-phase approximation, excitation spectra in the three phases are obtained, which indicate how the phase transitions occur. ©2015 American Physical Society.

Chiribella G.,Tsinghua University | Adesso G.,University of Nottingham
Physical Review Letters | Year: 2014

Teleportation and storage of continuous variable states of light and atoms are essential building blocks for the realization of large-scale quantum networks. Rigorous validation of these implementations require identifying, and surpassing, benchmarks set by the most effective strategies attainable without the use of quantum resources. Such benchmarks have been established for special families of input states, like coherent states and particular subclasses of squeezed states. Here we solve the longstanding problem of defining quantum benchmarks for general pure Gaussian single-mode states with arbitrary phase, displacement, and squeezing, randomly sampled according to a realistic prior distribution. As a special case, we show that the fidelity benchmark for teleporting squeezed states with totally random phase and squeezing degree is 1/2, equal to the corresponding one for coherent states. We discuss the use of entangled resources to beat the benchmarks in experiments. © 2014 American Physical Society.

Because of its strong inherent safety features and high outlet temperature, the modular high temperature gas-cooled nuclear reactor (MHTGR) is already seen as the central part of the next generation of nuclear plants. Such power plants are being considered for industrial applications with a wide range of power levels, and thus power-level control is an important technique for their efficient and stable operation. Stimulated by the high regulation performance provided by nonlinear controllers, a novel dynamic output-feedback nonlinear power-level regulator is developed in this paper based on the technique of iterative damping assignment (IDA). This control strategy can provide the L2 disturbance attenuation performance under modeling uncertainty or exterior disturbance, and can also guarantee the globally asymptotic closed-loop stability without uncertainty and disturbance. This newly built control strategy is then applied to the power-level regulation of the HTR-PM plant, and numerical simulation results show both the feasibility and high performance of this newly-built control strategy. Furthermore, the relationship between the values of the parameters and the performance of this controller is not only illustrated numerically but also analyzed theoretically. © 2012 by the authors.

Li W.,University of California at Riverside | Jiang T.,University of California at Riverside | Jiang T.,Tsinghua University
Bioinformatics | Year: 2012

Motivation: RNA-Seq uses the high-throughput sequencing technology to identify and quantify transcriptome at an unprecedented high resolution and low cost. However, RNA-Seq reads are usually not uniformly distributed and biases in RNA-Seq data post great challenges in many applications including transcriptome assembly and the expression level estimation of genes or isoforms. Much effort has been made in the literature to calibrate the expression level estimation from biased RNA-Seq data, but the effect of biases on transcriptome assembly remains largely unexplored.Results: Here, we propose a statistical framework for both transcriptome assembly and isoform expression level estimation from biased RNA-Seq data. Using a quasi-multinomial distribution model, our method is able to capture various types of RNA-Seq biases, including positional, sequencing and mappability biases. Our experimental results on simulated and real RNA-Seq datasets exhibit interesting effects of RNA-Seq biases on both transcriptome assembly and isoform expression level estimation. The advantage of our method is clearly shown in the experimental analysis by its high sensitivity and precision in transcriptome assembly and the high concordance of its estimated expression levels with quantitative reverse transcription-polymerase chain reaction data. © 2012 The Author.

Background: It is widely accepted that patient generates overall satisfaction with medical service and sub satisfaction on the basis of response to patient's trust in medical service and response to patient's attitude towards health policy in China. This study aimed to investigate the correlations between patient's trust in medical service/patient's attitude towards health policy and patient's overall satisfaction with medical service/sub satisfaction in current medical experience and find inspiration for future reform of China's health delivery system on improving patient's overall satisfaction with medical service and sub satisfaction in considering patient's trust in medical service and patient's attitude towards health policy. Methods. This study collaborated with the National Bureau of Statistics to collect a sample of 3,424 residents from 17 provinces and municipalities in a 2008 China household survey on patient's trust in medical service, patient's attitude towards health policy, patient's overall satisfaction and sub satisfaction in current medical experience. Results: Patient's overall satisfaction with medical service and most kinds of sub satisfaction in current medical experience were significantly influenced by both patient's trust in medical service and patient's attitude towards health policy; among all kinds of sub satisfaction in current medical experience, patient's trust in medical service/patient's attitude towards health policy had the largest influence on patient's satisfaction with medical costs, the influences of patient's trust in medical service/patient's attitude towards health policy on patient's satisfaction with doctor-patient interaction and satisfaction with treatment process were at medium-level, patient's trust in medical service/patient's attitude towards health policy had the smallest influence on patient's satisfaction with medical facilities and hospital environment, while patient's satisfaction with waiting time in hospital was not influenced by patient's trust in medical service/patient's attitude towards health policy. Conclusion: In order to improve patient's overall satisfaction with medical service and sub satisfaction in considering patient's trust in medical service and patient's attitude towards health policy, both improving patient's interpersonal trust in medical service from individual's own medical experience/public trust in medical service and improving patient's attitude towards health policy were indirect but effective ways. © 2011 Tang; licensee BioMed Central Ltd.

He L.,Tsinghua University
Journal of Statistical Physics | Year: 2014

In the present work, we consider the asymptotic problem of the spatially homogeneous Boltzmann equation when almost all collisions are grazing, that is, the deviation angle θ of the collision is limited near zero (i.e., θ ≤ ε{lunate}). We show that by taking the proper scaling to the cross-section which was used in [37], that is, assuming (Formula presented.) the solutionε{lunate} of the Boltzmann equation with initial data f0 can be globally or locally expanded in some weighted Sobolev space as (Formula presented.) where the function f is the solution of Landau equation, which is associated with the grazing collisions limit of Boltzmann equation, with the same initial data f0. This gives the rigorous justification of the Landau approximation in the spatially homogeneous case. In particular, if taking γ=-3 and s = 1-ε{lunate} in the cross-section Bε{lunate}, we show that the above asymptotic formula still holds and in this case f is the solution of Landau equation with the Coulomb potential. Going further, we revisit the well-posedness problem of the Boltzmann equation in the limiting process. We show there exists a common lifespan such that the uniform estimates of high regularities hold for each solution fε{lunate}. Thanks to the weak convergence results on the grazing collisions limit in [37], in other words, we establish a unified framework to establish the well-posedness results for both Boltzmann and Landau equations. © 2014 Springer Science+Business Media New York.

Lu X.,Tsinghua University
Journal of Statistical Physics | Year: 2014

We study regularity and finite time condensation of distributional solutions of the space-homogeneous and velocity-isotropic Boltzmann equation for Bose-Einstein particles for the hard sphere model. Global in time existence of distributional solutions had been proven before. Here we prove that the equation is locally and can be globally (in time) well-posed for the class of distributional solutions having finite moment of the negative order -1/2, and solutions in this class with regular initial data are mild solutions in their regularity time-intervals. By observing a necessary condition on the initial data for the absence of condensation at some finite time, we also propose a sufficient condition on the initial data for the occurrence of condensation at all large time, and then using a positivity of a partial collision integral we prove further that the critical time of condensation can be strictly positive. © 2014 The Author(s).

Yan N.,Tsinghua University
Current Opinion in Structural Biology | Year: 2013

Transmembrane proton gradients, known as Proton Motive Force (PMF), serve important physiological functions. In addition to driving ATP synthesis, PMF is harnessed by a large variety of secondary transporters to achieve 'uphill' translocation of specific substrates across the membrane. Proton-coupled secondary transporters, including both symporters and antiporters, are widely involved in nutrient uptake and metabolite expulsion, multidrug resistance, and the maintenance of electrolyte homeostasis. Structural studies have led to the identification of several new folds for proton co-transporters, and establish an important framework for the mechanistic understanding of proton-dependent substrate transport. This review focuses on recent advances in the structural elucidation of proton-coupled secondary transporters. © 2013 Elsevier Ltd.

Li L.,Tsinghua University
Journal of the Optical Society of America A: Optics and Image Science, and Vision | Year: 2012

I extend a previous work [J. Opt. Soc. Am. A 28, 738 (2011)] on field singularities at lossless metal-dielectric rightangle edges and their ramifications to the numerical modeling of gratings to the case of arbitrary metallic wedge angles. Simple criteria are given that allow one knowing the lossless permittivities and the arbitrary wedge angles to determine if the electric field at the edges is nonsingular, can be regularly singular, or can be irregularly singular without calculating the singularity exponent. Furthermore, the knowledge of the singularity type enables one to predict immediately if a numerical method that uses Fourier expansions of the transverse electric field components at the edges will converge or not without making any numerical tests. All conclusions of the previous work about the general relationships between field singularities, Fourier representation of singular fields, and convergence of numerical methods for modeling lossless metal-dielectric gratings have been reconfirmed. © 2012 Optical Society of America.

Sun Q.-C.,Tsinghua University
Wuli Xuebao/Acta Physica Sinica | Year: 2015

Granular materials posses disorder structures which are the origin of dynamical heterogeneity. On the basis of non-equilibrium thermodynamics, the structure characteristics, complex deformations, and energy dissipations are analysed. Based on the photoelastic tests, the granular elasticity is discussed. The strain increments are classified into three categories. By means of the non-equilibrium thermodynamics, two granular temperatures, Tk; Tc, are introduced as the state variables, which denote the fluctuations of the kinetic energy and the elastic energy, respectively. Further, a two-granular-temperature thermodynamics (i.e. TGT theory) are developed for granular materials. The thermodynamic forces and fluxes are particularly analyzed. TGT theory is also compared with the previous internal variable thermodynamics for sands (IVT theory) developed a few decades ago. It is found that from TGT the Gibbs free energy in the IVT theory can be deduced, and the energy dissipation function can be apparently expressed from TGT theory. ©, 2015 Chinese Physical Society.

Chiribella G.,Tsinghua University
New Journal of Physics | Year: 2012

We investigate the optimal estimation of a quantum process that can possibly consist of multiple time steps. The estimation is implemented by a quantum network that interacts with the process by sending an input and processing the output at each time step. We formulate the search for the optimal network as a semidefinite program and use duality theory to give an alternative expression for the maximum payoff achieved by estimation. Combining this formulation with a technique devised by Mittal and Szegedy we prove a general product rule for the joint estimation of independent processes, stating that the optimal joint estimation can be achieved by estimating each process independently, whenever the figure of merit is of a product form. We illustrate the result in several examples and exhibit counterexamples showing that the optimal joint network may not be the product of the optimal individual networks if the processes are not independent or if the figure of merit is not of the product form. In particular, we show that entanglement can reduce by a factor K the variance in the estimation of the sum of K independent phase shifts. © IOP Publishing and Deutsche Physikalische Gesellschaft.

Wang Z.,Tsinghua University | Zhang S.-C.,Stanford University
Physical Review X | Year: 2012

We propose general topological order parameters for interacting insulators in terms of the Green's function at zero frequency. They provide a unified description of various interacting topological insulators including the quantum anomalous Hall insulators and the time-reversal-invariant insulators in four, three, and two dimensions. Since only the Green's function at zero frequency is used, these topological order parameters can be evaluated efficiently by most numerical and analytical algorithms for strongly interacting systems.

We propose a systematic T-matrix approach to solve few-body problems with s-wave contact interactions in ultracold atomic gases. The problem is generally reduced to a matrix equation expanded by a set of orthogonal molecular states, describing external center-of-mass motions of pairs of interacting particles; while each matrix element is guaranteed to be finite by a proper renormalization for internal relative motions. This approach is able to incorporate various scattering problems and the calculations of related physical quantities in a single framework, and also provides a physically transparent way to understand the mechanism of resonance scattering. For applications, we study two-body effective scattering in 2D-3D mixed dimensions, where the resonance position and width are determined with high precision from only a few number of matrix elements. We also study three fermions in a (rotating) harmonic trap, where exotic scattering properties in terms of mass ratios and angular momenta are uniquely identified in the framework of T-matrix. © 2011 Springer-Verlag.

Li X.,Tsinghua University
Research Policy | Year: 2012

This paper examines a number of forces that have possibly contributed to the explosive growth of Chinese patenting over the past decade. After a review of previous hypotheses and conventional wisdom, this study proposes an additional explanation and argues that patent subsidy programs implemented by each provincial region have played an important role in the growth of Chinese patenting. This institutional change, taking place at the province-level, has induced an increase in patent propensity among not only firms, universities, and research institutes, but also individuals. Empirical evidence based on publicly available data provides solid support for this argument. It was also found that a larger fraction of applications are granted patent rights since the implementation of such programs, suggesting that reduction in patent application quality may not be a serious concern, unless the criteria used for patent examination have been lowered. © 2011 Elsevier B.V. All rights reserved.

Li C.,Tsinghua University | Kitani K.M.,Carnegie Mellon University
Proceedings of the IEEE International Conference on Computer Vision | Year: 2013

Egocentric cameras can be used to benefit such tasks as analyzing fine motor skills, recognizing gestures and learning about hand-object manipulation. To enable such technology, we believe that the hands must detected on the pixel-level to gain important information about the shape of the hands and fingers. We show that the problem of pixel-wise hand detection can be effectively solved, by posing the problem as a model recommendation task. As such, the goal of a recommendation system is to recommend the n-best hand detectors based on the probe set-a small amount of labeled data from the test distribution. This requirement of a probe set is a serious limitation in many applications, such as ego-centric hand detection, where the test distribution may be continually changing. To address this limitation, we propose the use of virtual probes which can be automatically extracted from the test distribution. The key idea is that many features, such as the color distribution or relative performance between two detectors, can be used as a proxy to the probe set. In our experiments we show that the recommendation paradigm is well-equipped to handle complex changes in the appearance of the hands in first-person vision. In particular, we show how our system is able to generalize to new scenarios by testing our model across multiple users. © 2013 IEEE.

Li C.,Tsinghua University | Kitani K.M.,Carnegie Mellon University
Proceedings of the IEEE Computer Society Conference on Computer Vision and Pattern Recognition | Year: 2013

We address the task of pixel-level hand detection in the context of ego-centric cameras. Extracting hand regions in ego-centric videos is a critical step for understanding hand-object manipulation and analyzing hand-eye coordination. However, in contrast to traditional applications of hand detection, such as gesture interfaces or sign-language recognition, ego-centric videos present new challenges such as rapid changes in illuminations, significant camera motion and complex hand-object manipulations. To quantify the challenges and performance in this new domain, we present a fully labeled indoor/outdoor ego-centric hand detection benchmark dataset containing over 200 million labeled pixels, which contains hand images taken under various illumination conditions. Using both our dataset and a publicly available ego-centric indoors dataset, we give extensive analysis of detection performance using a wide range of local appearance features. Our analysis highlights the effectiveness of sparse features and the importance of modeling global illumination. We propose a modeling strategy based on our findings and show that our model outperforms several baseline approaches. © 2013 IEEE.

Eltawil M.A.,King Faisal University | Eltawil M.A.,Kafr El Sheikh University | Zhao Z.,Tsinghua University
Renewable and Sustainable Energy Reviews | Year: 2013

The photovoltaic (PV) system is one of the renewable energies that attract the attention of researchers in the recent decades. The PV generators exhibit nonlinear I-V and P-V characteristics. The maximum power produced varies with both irradiance and temperature. Since the conversion efficiency of PV arrays is very low, it requires maximum power point tracking (MPPT) control techniques. The maximum power point tracking (MPPT) is the automatic control algorithm to adjust the power interfaces and achieve the greatest possible power harvest, during moment to moment variations of light level, shading, temperature, and photovoltaic module characteristics. The purpose of the MPPT is to adjust the solar operating voltage close to the MPP under changing atmospheric conditions. It has become an essential component to evaluate the design performance of PV power systems. This investigation aims to assess different MPPT techniques, provide background knowledge, implementation topology, grid interconnection of PV and solar microinverter requirements presented in the literature, doing depth comparisons between them with a brief discussion. The MPPT merits, demerits and classification, which can be used as a reference for future research related to optimizing the solar power generation, are also discussed. Conventional methods are easy to implement but they suffer from oscillations at MPP and tracking speed is less due to fixed perturb step. Intelligent methods are efficient; oscillations are lesser at MPP in steady state and tracked quickly in comparison to conventional methods. © 2013 Elsevier Ltd.

Wang X.,Tsinghua University
Tissue engineering. Part B, Reviews | Year: 2010

Presently, there is a recognized and imperative need for bioartificial organs. The technological advances in transgenosis, tissue engineering, and rapid prototyping have led to the development of spatially complex tissues. An ideal artificial organ should provide nutrient transport system, mechanical stable architecture, and synergetic multicellular organization in one construct. The multinozzle rapid prototyping technique simultaneously assembles vascular systems including hierarchical multicellular structures in an automated and reproducible manner and offers an effective way for treating organ failures. In this article, a brief overview of the recent trends and outstanding challenges in organ manufacturing is provided. From the viewpoint of disciplinary crossing, integration, and development, future directions in the coming years were pointed out.

Zhou T.,Tsinghua University
IEEE Transactions on Automatic Control | Year: 2013

A new recursive one-step state prediction procedure is derived for a networked dynamic system. Under the coordination of a collaboration unit that provides optimal update gains for each individual subsystem utilizing merely system parameters, this predictor estimates plant's local states based only on local system output measurements. This estimator can be easily realized in a distributed way, and can also be simply scaled to systems with a large amount of subsystems, provided it has enough communication and storage capacities. It is proved that when prediction error variances are adopted in performance comparisons, the optimal gain matrix is usually unique. Recursive and explicit expressions are derived for both this optimal gain matrix and the covariance matrix of the corresponding prediction errors. The optimal gain matrix for every subsystem in this distributed recursive predictor has been shown to be equal to that of the well known Kalman filter utilizing only local system output measurements, which makes it possible to robustify this state predictor using a sensitivity penalization approach. Numerical simulation results illustrate that prediction accuracy of the suggested procedure may sometimes be as good as that of the lumped Kalman filter. © 2013 IEEE.

Tian C.,Tsinghua University
Physica E: Low-Dimensional Systems and Nanostructures | Year: 2013

Many complex systems exhibit hydrodynamic (or macroscopic) behavior at large scales characterized by few variables such as the particle number density, temperature and pressure obeying a set of hydrodynamic (or macroscopic) equations. Does the hydrodynamic description exist also for waves in complex open media? This is a long-standing fundamental problem in studies on wave localization. Practically, if it does exist, owing to its simplicity macroscopic equations can be mastered far more easily than sophisticated microscopic theories of wave localization especially for experimentalists. The purposes of the present paper are two-fold. On the one hand, it is devoted to a review of substantial recent progress in this subject. We show that in random open media the wave energy density obeys a highly unconventional macroscopic diffusion equation at scales much larger than the elastic mean free path. The diffusion coefficient is inhomogeneous in space; most strikingly, as a function of the distance to the interface, it displays novel single parameter scaling which captures the impact of rare high-transmission states that dominate long-time transport of localized waves. We review aspects of this novel macroscopic diffusive phenomenon. On the other hand, it is devoted to a review of the recently developed supersymmetric field theory of light localization in open media. In particular, we review its application in establishing a microscopic theory of the aforementioned unconventional diffusive phenomenon. © 2013 Elsevier B.V.

Duan L.-M.,University of Michigan | Duan L.-M.,Tsinghua University
Physical Review Letters | Year: 2011

Dicke states represent a class of multipartite entangled states that can be generated experimentally with many applications in quantum information. We propose a method to experimentally detect genuine multipartite entanglement in the vicinity of arbitrary Dicke states. The detection scheme can be used to experimentally quantify the entanglement depth of many-body systems and is easy to implement as it requires measurement of only three collective spin operators. The detection criterion is strong as it heralds multipartite entanglement even in cases where the state fidelity goes down exponentially with the number of qubits. © 2011 American Physical Society.

Xia L.,Tsinghua University
Discrete Event Dynamic Systems: Theory and Applications | Year: 2014

In this paper, we use the event-based optimization framework to study the admission control problem in an open Jackson network. The external arriving customers are controlled by an admission controller. The controller makes decision only at the epoch when an event of customer arrival happens. Every customer in the network obtains a fixed reward for each service completion and pays a cost with a fixed rate during its sojourn time (including waiting time and service time). The complete information of the system state is not available for the controller. The controller can observe only the number of total customers in the network. Based on the property of closed form solution of Jackson networks, we prove that the system performance is monotonic with respect to the admission probabilities and the optimal control policy has a threshold form. That is, when the number of total customers is smaller than a threshold, all of the arriving customers are admitted; otherwise, all are rejected. The sufficient condition and necessary condition of optimal policy are also derived. Furthermore, we develop an iterative algorithm to find the optimal policy. The algorithm can be executed based on a single sample path, which makes the algorithm online implementable. Simulation experiments are conducted to demonstrate the effectiveness of our approach. © 2013 Springer Science+Business Media New York.

Ge S.-F.,Tsinghua University | Dicus D.A.,University of Texas at Austin | Repko W.W.,Michigan State University
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2011

Model-independent consequences of applying a generalized hidden horizontal Z2 symmetry to the neutrino mass matrix are explored. The Dirac CP phase δD can be expressed in terms of the three mixing angles as 4casacssssxcosδD=(ss2-cs2sx2)(ca2-sa2) where the si, ci are sines and cosines of the atmospheric, solar, and reactor angles. This relation is independent of neutrino masses and whether neutrinos are Dirac- or Majorana-type. Given the present constraints on the angles, δD is constrained to be almost maximal, a result which can be explored in experiments such as NO νA and T2K. The Majorana CP phases do not receive any constraint and are thus model-dependent. Also a distribution of Θx with a lower limit is obtained without specifying δD. © 2011 Elsevier B.V.

Tang E.,Massachusetts Institute of Technology | Mei J.-W.,Massachusetts Institute of Technology | Mei J.-W.,Tsinghua University | Wen X.-G.,Massachusetts Institute of Technology
Physical Review Letters | Year: 2011

We show that a suitable combination of geometric frustration, ferromagnetism, and spin-orbit interactions can give rise to nearly flatbands with a large band gap and nonzero Chern number. Partial filling of the flatband can give rise to fractional quantum Hall states at high temperatures (maybe even room temperature). While the identification of material candidates with suitable parameters remains open, our work indicates intriguing directions for exploration and synthesis. © 2011 American Physical Society.

Cao Y.,Tsinghua University | Hutchinson J.W.,Harvard University
Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences | Year: 2012

The stability of the wrinkling mode experienced by a compressed half-space of neo-Hookean material is investigated using analytical and numerical methods to study the post-bifurcation behaviour of periodic solutions. It is shown that wrinkling is highly unstable owing to the nonlinear interaction among the multiple modes associated with the critical compressive state. Concomitantly, wrinkling is sensitive to exceedingly small initial imperfections that significantly reduce the compressive strain at which the instability occurs. The study provides insight into the connection between wrinkling and an alternative surface mode, the finite amplitude crease or sulcus. The shape of the critical combination of wrinkling modes has the form of an incipient crease, and a tiny initial imperfection can trigger a wrinkling instability that collapses into a crease. © 2011 The Royal Society.

Pomianowski M.,University of Aalborg | Heiselberg P.,University of Aalborg | Zhang Y.,Tsinghua University
Energy and Buildings | Year: 2013

Thermal energy storage systems (TES), using phase change material (PCM) in buildings, are widely investigated technologies and a fast developing research area. Therefore, there is a need for regular and consistent reviews of the published studies. This review is focused on PCM technologies developed to serve the building industry. Various PCM technologies tailored for building applications are studied with respect to technological potential to improve indoor environment, increase thermal inertia and decrease energy use for building operation. What is more, in this review special attention is paid to discussion and identification of proper methods to correctly determine the thermal properties of PCM materials and their composites and as well procedures to determine their energy storage and saving potential. The purpose of the paper is to highlight promising technologies for PCM application in buildings with focus on room application and to indicate in which applications the potential is less significant. © 2013 Elsevier B.V. All rights reserved.

Li P.,Tsinghua University
IEEE Transactions on Fuzzy Systems | Year: 2013

The fuzzy relational equations with min-implication composition are considered, where the implication operation involved is the residuum with respect to the minimum operation. The solution set of such a system of equations, whenever nonempty, can be characterized by a minimum solution and finitely many maximal solutions. It is shown that a system of fuzzy relational equations with min-implication composition can be reformulated in polynomial time into a system of 0-1 mixed integer linear inequalities, and consequently, the structure of its solution set can be revealed in a succinct manner. Besides, it is shown that the determination of all maximal solutions is polynomially reducible to the transversal hypergraph generation problem, of which some practically well-performed algorithms are available. © 1993-2012 IEEE.

Xia M.,Tsinghua University | Xu Z.,PLA University of Science and Technology | Liao H.,Shanghai JiaoTong University
IEEE Transactions on Fuzzy Systems | Year: 2013

Preference relations are powerful techniques to express the preferences over alternatives (or criteria) and mainly fall into two categories: fuzzy preference relations (also called reciprocal preference relations) and multiplicative preference relations. For a pair of alternatives, a fuzzy preference relation only gives the degree that an alternative is prior to another; thus, the intuitionistic fuzzy preference relation is introduced by adding the degree that an alternative is not prior to another, which can describe the preferences over two alternatives more comprehensively. However, the intuitionistic fuzzy preference uses the symmetrical scale to express the decision makers' preference relations, which are inconsistent with our intuition in some situations. If we use the unsymmetrical scale to express the preferences about two alternatives instead of the symmetrical scale in intuitionistic fuzzy preference relation, then a new concept is introduced, which we call the intuitionistic multiplicative preference relation reflecting our intuition more objectively. In this paper, we study the aggregation of intuitionistic multiplicative preference information, propose some aggregation techniques, investigate their properties, and apply them to decision making based on intuitionistic multiplicative preference relations. © 2012 IEEE.

Liu Z.,Tsinghua University
Nanotechnology | Year: 2014

For relative sliding between two rigid graphene sheets that are interacted on by a van der Waals force, we show that the friction behavior is significantly dependent on the interlayer separation distance h. Around the equilibrium interlayer distance he, the friction behavior exactly obeys a linear law. When h is far smaller than he, the linear friction behavior transforms to over-linear behavior. On the other hand, when h is larger than he, there is another critical value of the interlayer distance, hc; when h is larger than he and smaller than hc, the friction behavior transforms from linear to sub-linear behavior; however, when h is larger than hc, the coefficient of friction becomes negative. Further, the different friction behaviors are found to be well described by a universal power law, τ = μ(σ + σ0)n. © 2014 IOP Publishing Ltd.

Ge S.-F.,Tsinghua University | Dicus D.A.,University of Texas at Austin | Repko W.W.,Michigan State University
Physical Review Letters | Year: 2012

The residual Z2s(k) and Z̄2s(k) symmetries induce a direct and unique phenomenological relation with θ x(θ 13) expressed in terms of the other two mixing angles θ s(θ 12) and θ a(θ 23) and the Dirac CP phase δ D. Z2s(k) predicts a θ x probability distribution centered around 3°-6° with an uncertainty of 2°-4°, while those from Z̄2s(k) are approximately a factor of 2 larger. Either result fits the T2K, MINOS, and Double Chooz measurements. Alternately, a prediction for the Dirac CP phase δ D results in a peak at ±74°(±106°) for Z2s(k) or ±123°(±57° ) for Z̄2s(k) which is consistent with the latest global fit. We also give a distribution for the leptonic Jarlskog invariant J ν which can provide further tests from measurements at T2K and NOνA. © 2012 American Physical Society.

Li T.,Tsinghua University
Nature Structural and Molecular Biology | Year: 2016

SWI2/SNF2 family proteins regulate a myriad of nucleic acid transactions by sliding, removing and reconstructing nucleosomes in eukaryotic cells. They contain two RecA-like core domains, which couple ATP hydrolysis and DNA translocation to chromatin remodeling. Here we report the crystal structure of Snf2 from the yeast Myceliophthora thermophila. The data show the two RecA-like core domains of Snf2 stacking together and twisting their ATP-binding motifs away from each other, thus explaining the inactivity of the protein in the ground state. We identified several DNA-binding elements, which are fully exposed to solvent, thus suggesting that the protein is poised for its incoming substrate. The catalytic core of Snf2 showed a high chromatin-remodeling activity, which was suppressed by the N-terminal HSA domain. Our findings reveal that the catalytic core of Snf2 is a competent remodeling machine, which rests in an inactive conformation and requires a large conformational change upon activation. © 2016 Nature Publishing Group, a division of Macmillan Publishers Limited. All Rights Reserved.

Wu C.,Tsinghua University | Mohsenian-Rad H.,Texas Tech University | Huang J.,Chinese University of Hong Kong
IEEE Transactions on Smart Grid | Year: 2012

Electric vehicles (EVs) are likely to become very popular worldwide within the next few years. With possibly millions of such vehicles operating across the country, one can establish a distributed electricity storage system that comprises of the EVs' batteries with a huge total storage capacity. This can help the power grid by providing various ancillary services, once an effective vehicle-to-grid (V2G) market is established. In this paper, we propose a new game-theoretic model to understand the interactions among EVs and aggregators in a V2G market, where EVs participate in providing frequency regulation service to the grid. We develop a smart pricing policy and design a mechanism to achieve optimal frequency regulation performance in a distributed fashion. Simulation results show that our proposed pricing model and designed mechanism work well and can benefit both EVs (in terms of obtaining additional income) and the grid (in terms of achieving the frequency regulation command signal). © 2011 IEEE.

This paper studied the key strategies used by Datang, a local Chinese firm, to promote TD-SCDMA in order to explore an under-researched topic: how could a latecomer promote a technology standard? The findings suggest that Datang faced formidable challenges because of latecomer disadvantage and transitional institutions. The development of innovation capabilities and new technologies is needed but far from sufficient. It is necessary to develop special capabilities to get support from the government and public stakeholders such as scholars. The experience of Datang offers new insights into the development and adoption of technology standards sponsored by latecomers in developing countries. © 2013 Elsevier B.V. All rights reserved.

We investigated the interaction between two phases by numerical simulation of a turbulent channel flow laden with heavy particles. We calculated the fluid phase turbulence by a large eddy simulation with a point-force two-way coupling model and tracked particles by the Lagrangian trajectory method. Six cases with different particle volume concentrations for three kinds of particles were simulated. The particle dispersion properties on the inter-phase interaction were presented in this first part. The simulations provided comprehensive instantaneous two-phase turbulent flow fields. The particle streaky and cloudy preferential distributions, which weaken with increased particle inertia, are suppressed by particle modulation of turbulence. Modulation of turbulence is stronger near the wall than in other regions, because particle volume concentration is higher close to the wall and modulation increases with local particle concentration. The streaky particle distribution structures near the wall disappear earlier than the outer layer cloudy structures as the particle mass loading increases. Particle-phase instantaneous velocity scatter distributions, characterized by a Y-shape changing to a Λ-shape from the viscous sub-layer to the central plane, are altered by particle modulation of turbulence. © 2010 Elsevier Ltd. All rights reserved.

Li S.-J.,Tsinghua University
Cell Research | Year: 2016

The Ca2+/calmodulin-dependent protein phosphatase calcineurin (CN), a heterodimer composed of a catalytic subunit A and an essential regulatory subunit B, plays critical functions in various cellular processes such as cardiac hypertrophy and T cell activation. It is the target of the most widely used immunosuppressants for transplantation, tacrolimus (FK506) and cyclosporin A. However, the structure of a large part of the CNA regulatory region remains to be determined, and there has been considerable debate concerning the regulation of CN activity. Here, we report the crystal structure of full-length CN (β isoform), which revealed a novel autoinhibitory segment (AIS) in addition to the well-known autoinhibitory domain (AID). The AIS nestles in a hydrophobic intersubunit groove, which overlaps the recognition site for substrates and immunosuppressant-immunophilin complexes. Indeed, disruption of this AIS interaction results in partial stimulation of CN activity. More importantly, our biochemical studies demonstrate that calmodulin does not remove AID from the active site, but only regulates the orientation of AID with respect to the catalytic core, causing incomplete activation of CN. Our findings challenge the current model for CN activation, and provide a better understanding of molecular mechanisms of CN activity regulation.Cell Research advance online publication 22 January 2016; doi:10.1038/cr.2016.14. © 2016 Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences

Tang L.,Tsinghua University
International Journal for Equity in Health | Year: 2012

Background: The promotion of patient safety and drug safety through promotion of pharmacist's drug safety practice was among the most important aims of China's health delivery system reform, but regional inequity in pharmacist's drug safety practice was still serious in China. Methods. The 2011 national patient safety and medication error baseline survey was carried out for the first time in China, and through analyzing dataset from the survey, this study was set up to test both China's regional inequity in pharmacist's drug safety practice and major influencing factors for pharmacist's drug safety practice among different districts of China. Results: Pharmacist's drug safety practice in regions with higher per capita GDP and more abundant medical resources was still better than that in regions with lower per capita GDP and less abundant medical resources. In all districts of China, pharmacist's drug safety knowledge, drug safety attitude, self-perceived pressure and fatigue, hospital management quality, and hospital regulation were major influencing factors for pharmacist's drug safety practice, while only in regions with higher per capita GDP and more abundant medical resources, hospital drug safety culture, supervisor's work team management, cooperation atmosphere of work team, and drug safety culture of work team were major influencing factors for pharmacist's drug safety practice. Conclusion: Regional inequity in pharmacist's drug safety practice still existed in China. In all districts of China, promoting pharmacist's drug safety knowledge, drug safety attitude, self-perceived pressure and fatigue, hospital management quality, and hospital regulation could help promote pharmacist's drug safety practice, while only in regions with higher per capita GDP and more abundant medical resources, promoting hospital drug safety culture, supervisor's work team management, cooperation atmosphere of work team, and drug safety culture of work team could help promote pharmacist's drug safety practice. And in regions with lower per capita GDP and less abundant medical resources, the link between pharmacist's drug safety practice and hospital drug safety culture/supervisor's work team management/cooperation atmosphere of work team/drug safety culture of work team should also be gradually established. © 2012 Tang; licensee BioMed Central Ltd.

An Y.,Tsinghua University
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2012

For cavitation clouds generated in a standing sound wave driven by an ultrasonic horn, the nonlinear acoustic wave equation governing cavitation dynamics is numerically solved together with the bubble motion equation under an approximation. This conceptual calculation can qualitatively reproduce the observed characteristics of cavitation. © 2012 American Physical Society.

Bose S.K.,University of Wurzburg | Fucke K.,University of Wurzburg | Liu L.,Tsinghua University | Steel P.G.,Durham University | Marder T.B.,University of Wurzburg
Angewandte Chemie - International Edition | Year: 2014

A new catalytic system based on a ZnII NHC precursor has been developed for the cross-coupling reaction of alkyl halides with diboron reagents, which represents a novel use of a Group XII catalyst for C=X borylation. This approach gives borylations of unactivated primary, secondary, and tertiary alkyl halides at room temperature to furnish alkyl boronates, with good functional-group compatibility, under mild conditions. Preliminary mechanistic investigations demonstrated that this borylation reaction seems to involve one-electron processes. Coupling a la carte: A catalytic system based on a ZnII N-heterocyclic carbene precursor has been developed for the cross-coupling reaction of alkyl halides with diboron reagents (see scheme). This is a novel use of a Group 12 catalyst for C=X borylation. IMes=1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Dong Y.,Tsinghua University
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2012

The fluxes in transport processes expressed as a time derivative of state variables is a crucial requirement in Onsager's proof of his reciprocal relations, which is a much debated question existing in nonequilibrium thermodynamics. Thermomass theory is used to show that the linear decay of the fluctuation is a balance between the inertial forces and resistant force. Therefore, products of the drift velocities and relaxation times, namely, the displacements from equilibrium, can be used as the state variables, whose time derivatives give the transport fluxes. The Onsager reciprocal relations can be macroscopically derived from the principle that every action has an equal and opposite reaction, applicable in steady nonequilibrium systems and nonlinear couplings. © 2012 American Physical Society.

Yong W.-A.,Tsinghua University
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2012

In this Brief Report, we show that balanced chemical reaction systems governed by the law of mass action have an elegant conservation-dissipation structure. From this structure a number of important conclusions can be easily deduced. In particular, with the help of this structure we can rigorously justify the classical partial equilibrium approximation in chemical kinetics. © 2012 American Physical Society.

Tian F.,Tsinghua University
Annual Review of Earth and Planetary Sciences | Year: 2015

It has been known for decades that atmospheric escape is important for the evolution of terrestrial planets in the Solar System, although exactly how atmospheric escape changes the atmospheres of these bodies is still hotly debated. Rapidly increasing numbers of exoplanet observations provide new targets against which atmospheric escape models are tested. In this review we summarize recent studies related to atmospheric escape from exoplanets. The most important conclusions are that (a) escape can significantly influence the volatile contents of low-mass exoplanets (with mass lower than those of Uranus and Neptune) and the atmosphere and climate evolution histories of Solar System terrestrial planets; (b) models including detailed physics and chemistry in planetary upper atmospheres will be important for the interpretation of existing and future observations of exoplanets; and (c) fluid models considering 2D or 3D planetary upper atmospheres and particle models for planetary exospheres will be important not only for comparisons with observations but also for order of magnitude estimates of atmospheric escape rates. Our understanding of how escape shapes planetary atmospheres and influences the climate of low-mass planets can be expected to advance substantially in the coming decade. Copyright © 2015 by Annual Reviews. All rights reserved.

Bouaziz S.,Ecole Polytechnique Federale de Lausanne | Wang Y.,Tsinghua University | Pauly M.,Ecole Polytechnique Federale de Lausanne
ACM Transactions on Graphics | Year: 2013

We present a new algorithm for realtime face tracking on commodity RGB-D sensing devices. Our method requires no user-specific training or calibration, or any other form of manual assistance, thus enabling a range of new applications in performance-based facial animation and virtual interaction at the consumer level. The key novelty of our approach is an optimization algorithm that jointly solves for a detailed 3D expression model of the user and the corresponding dynamic tracking parameters. Realtime performance and robust computations are facilitated by a novel subspace parameterization of the dynamic facial expression space. We provide a detailed evaluation that shows that our approach significantly simplifies the performance capture workflow, while achieving accurate facial tracking for realtime applications. Copyright © ACM 2013.

The emission parameters and expose-response functions of some pollutants, such as sulphur dioxide (SO2) and Inhalable Particulate Matter (PM10), were introduced to calculate the emission caused by energy consumption in various sectors and regions in China under different scenarios. The impacts of economic growth, population, and technology progress on energy consumption and on the environment were also analyzed. Finally, the economic value of public health damage caused by the changes of pollutants' concentration related to energy consumption under various scenarios, different regions and sectors in China was analyzed. The results show that the PM-10 and SO2 emissions and consequent health damage will increase significantly in the next 12 years. Thus, energy efficiency, population, economy, and urbanization are the main factors to be considered in this system. © 2009 Elsevier Ltd.

Yanjia W.,Tsinghua University
Energy Policy | Year: 2010

China is the largest nonferrous metals producer in the world and largest consumer for six kinds of common nonferrous metals including copper, aluminum, zinc, lead, nickel and tin. This paper provides an overview of the nonferrous metals industry in China, from a CO2 emissions reduction perspective. It addresses energy use disaggregated by energy carrier and by province. It focuses on an analysis of energy efficiency in the production of aluminum, copper and nickel. A few large-scale enterprises produce most of the aluminum, copper and nickel in China, and use manufacturing facilities that were built within the last 20 years or have recently upgraded their main production equipment and processes. The energy efficiency of these operations is not particularly low compared to international practice. A large number of small and medium-sized enterprises (SME) operate nonferrous metals production facilities which rank low in energy efficiency and therefore are highly energy intensive per unit of physical output. Backward production capacity would be phased out continuously by enforcing the energy intensity norms. © 2009 Elsevier Ltd.

Uphoff J.,Goethe University Frankfurt | Fochler O.,Goethe University Frankfurt | Xu Z.,Tsinghua University | Greiner C.,Goethe University Frankfurt
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2012

The space-time evolution of open heavy flavor is studied in Pb + Pb collisions at s=2.76TeV using the partonic transport model Boltzmann Approach to MultiParton Scatterings (BAMPS). An updated version of BAMPS is presented which allows interactions among all partons: gluons, light quarks and heavy quarks. Heavy quarks, in particular, interact with the rest of the medium via binary scatterings with a running coupling and a Debye screening which is matched by comparing to hard thermal loop calculations. The lack of radiative processes in the heavy flavor sector is accounted for by scaling the binary cross section with a phenomenological factor K=3.5, which describes well the elliptic flow v2 and nuclear modification factor R AA at RHIC. Within this framework we calculate in a comprehensive study the v2 and R AA of all interesting open heavy flavor particles at the LHC: electrons, muons, D mesons, and non-prompt J/ψ from B mesons. We compare to experimental data, where it is already available, or make predictions. To do this accurately next-to-leading order initial heavy quark distributions are employed which agree well with proton-proton data of heavy flavor at s=7TeV. © 2012 Elsevier B.V.

Ma Y.,Tsinghua University
International journal of nanomedicine | Year: 2011

The formulation of docetaxel available for clinical use (Taxotere) contains a high concentration of polysorbate 80 (Tween 80). After incorporation of Tween 80 into poly-e-caprolactone (PCL)-Tween 80 copolymer, the relative amount of Tween 80 should be decreased and the advantages of PCL and Tween 80 should be combined. A novel PCL-Tween 80 copolymer was synthesized from e-caprolactone and Tween 80 in the presence of stannous octoate as a catalyst via ring opening polymerization. Two types of nanoparticle formulation were made from commercial PCL and a self-synthesized PCL-Tween 80 copolymer using a modified solvent extraction/evaporation method. The nanoparticles were found by field emission scanning electron microscopy to have a spherical shape and be 200 nm in diameter. The copolymers could encapsulate 10% of the drug in the nanoparticles and release 34.9% of the encapsulated drug over 28 days. PCL-Tween 80 nanoparticles could be internalized into the cells and had higher cellular uptake than the PCL nanoparticles. The drug-loaded PCL-Tween 80 nanoparticles showed better in vitro cytotoxicity towards C6 cancer cells than commercial Taxotere at the same drug concentration. Nanoparticles using PCL-Tween 80 copolymer as drug delivery vehicles may have a promising outcome for cancer patients.

The molecular mechanism controlling the dismantling of naive pluripotency is poorly understood. Here we show that microRNAs (miRNAs) have important roles during naive to primed pluripotency transition. Dgcr8-/- embryonic stem cells (ESCs) failed to completely silence the naive pluripotency program, as well as to establish the primed pluripotency program during differentiation. miRNA profiling revealed that expression levels of a large number of miRNAs changed dynamically and rapidly during naive to primed pluripotency transition. Furthermore, a miRNA screen identified numerous miRNAs promoting naive to primed pluripotency transition. Unexpectedly, multiple miRNAs from miR-290 and miR-302 clusters, previously shown as pluripotency-promoting miRNAs, demonstrated the strongest effects in silencing naive pluripotency. Knockout of both miR-290 and miR-302 clusters but not either alone blocked the silencing of naive pluripotency program. Mechanistically, the miR-290/302 family of miRNAs may facilitate the exit of naive pluripotency in part by promoting the activity of MEK pathway and through directly repressing Akt1. Our study reveals miRNAs as an important class of regulators potentiating ESCs to transition from naive to primed pluripotency, and uncovers context-dependent functions of the miR-290/302 family of miRNAs at different developmental stages.Cell Research advance online publication 8 January 2016; doi:10.1038/cr2016.2. © 2016 Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences

Morel A.,Tsinghua University
Bioresource technology | Year: 2012

A novel configuration of microbial desalination cell (MDC) packed with ion-exchange resin (R-MDC) was proposed to enhance water desalination rate. Compared with classic MDC (C-MDC), an obvious increase in desalination rate (DR) was obtained by R-MDC. With relatively low concentration (10-2 g/L NaCl) influents, the DR values of R-MDC were about 1.5-8 times those of C-MDC. Ion-exchange resins packed in the desalination chamber worked as conductor and thus counteracted the increase in ohmic resistance during treatment of low concentration salt water. Ohmic resistances of R-MDC stabilized at 3.0-4.7 Ω. By contrast, the ohmic resistances of C-MDC ranged from 5.5 to 12.7 Ω, which were 55-272% higher than those of R-MDC. Remarkable improvement in desalination rate helped improve charge efficiency for desalination in R-MDC. The results first showed the potential of R-MDC in the desalination of water with low salinity. Copyright © 2012 Elsevier Ltd. All rights reserved.

Lu J.,Tsinghua University
Regional Studies | Year: 2010

Lu J. Agglomeration of economic activities in China: evidence from establishment censuses, Regional Studies. This paper documents the whole picture of economic activities spatial distribution in China based on two recent nationwide censuses of establishments. The robust increasing trend of agglomeration supports the argument that interregional trade barriers in China decreased during 1996-2001. The agglomeration literature was extended by studying agglomeration patterns of establishments with various ownership types. It is found that non-public-owned establishments are more spatially concentrated compared with public owned ones. Determinants of agglomeration economies were also examined with multivariate regressions. Results show that micro-foundations of agglomeration work well in explaining agglomeration of non-public-owned establishments, but not for public owned ones. © 2010 Regional Studies Association.

Han Z.Y.,Tsinghua University
Journal of the Royal Society, Interface / the Royal Society | Year: 2013

This work focuses on the size distribution of sneeze droplets exhaled immediately at mouth. Twenty healthy subjects participated in the experiment and 44 sneezes were measured by using a laser particle size analyser. Two types of distributions are observed: unimodal and bimodal. For each sneeze, the droplets exhaled at different time in the sneeze duration have the same distribution characteristics with good time stability. The volume-based size distributions of sneeze droplets can be represented by a lognormal distribution function, and the relationship between the distribution parameters and the physiological characteristics of the subjects are studied by using linear regression analysis. The geometric mean of the droplet size of all the subjects is 360.1 μm for unimodal distribution and 74.4 μm for bimodal distribution with geometric standard deviations of 1.5 and 1.7, respectively. For the two peaks of the bimodal distribution, the geometric mean (the geometric standard deviation) is 386.2 μm (1.8) for peak 1 and 72.0 μm (1.5) for peak 2. The influences of the measurement method, the limitations of the instrument, the evaporation effects of the droplets, the differences of biological dynamic mechanism and characteristics between sneeze and other respiratory activities are also discussed.

This paper was the second of a two-part study concerning inter-phase interaction in a turbulent vertical channel flow laden with heavy particle. The simulations considering two-way coupling model provided two phases' velocity statistics. Through the particle backward modulations, statistical fluctuations in the streamwise direction are transferred to the other two directions for both phases, which decrease the turbulence fluctuation anisotropy. The behavior of particle drift depends on the particle dispersion modes; consequently low-inertia particles travel toward the wall with negative velocities, even if they encounter fluid environments with adverse velocities directed toward the outer layer at the macroscopic statistical level. The particle drifts are altered by particle modulation of turbulence. © 2010 Elsevier Ltd. All rights reserved.

Jiang W.,Tsinghua University
IEEE Transactions on Plasma Science | Year: 2010

It is proposed that linear transformer driver (LTD) concept can be applied to compact repetitive pulsed-power generation. For experimental demonstration, a table-top LTD module has been constructed by using power metaloxidesemiconductor field-effect transistors (MOSFETs) and film capacitors. It consists of 24 basic circuits and a magnetic core, contained in a cavity case having a diameter of 32 cm and a height of 1.1 cm. All MOSFETs can be turned on and off synchronously, controlled by a single optic fiber. This LTD module has been tested with operation voltage of 900 V for single shot and 700 V for repetitive operation at 500 Hz. Near-rectangle waveforms were obtained on a resistive load of ∼ 3.2 Ω , with pulsewidth of ∼200 ns, rise time of∼20 ns, and fall time of∼40 ns. The overall system efficiency was obtained to be ∼76%. © 2010 IEEE.

Wan X.,Tsinghua University
Journal of vision | Year: 2010

Path integration refers to the ability to integrate self-motion information to estimate one's current position and orientation relative to the origin. To investigate the effect of active selection in path integration, we used a virtual homing task in which participants traveled along hallways and attempted to directly return to the origin. Two groups of participants differed in the voluntary selection of the path structure, but received the same perceptual and motor information. Information about distance traveled was purely visual via optic flow, whereas turnings were specified both visually and through body senses. The active group made free (Experiment 1) or forced (Experiment 2) selections to determine the structure of the outbound path, whereas the passive group followed these outbound paths. We found no facilitation effects of the active selection on homing performance, suggesting that humans' limited path integration abilities cannot be attributed to the nature of the task.

Liu B.,Tsinghua University
Fuzzy Optimization and Decision Making | Year: 2013

Uncertain sets are an effective tool to describe unsharp concepts like "young", "tall" and "most". As a key concept in uncertain set theory, the independence was first defined in the paper (Liu in Fuzzy Optim Decis Mak 11(4):387-410, 2012b). However, the definition is somewhat weak to deal with uncertain sets completely. In order to overcome this disadvantage, this paper presents a stronger definition of independence of uncertain sets and discusses its mathematical properties. © 2013 Springer Science+Business Media New York.

Zhou T.,Tsinghua University
IEEE Transactions on Automatic Control | Year: 2010

This technical note deals with robust state estimation when parametric uncertainties nonlinearly affect a plant state-space model, based on a simultaneous minimization of nominal estimation errors and their sensitivities. An analytic solution is derived for the optimal estimator which can be recursively realized. This estimator has a form similar to the robust estimator of , and its computational complexity is comparable to the Kalman filter. Under certain conditions, this robust estimator is proved to converge to a stable system, its estimation errors have a bounded covariance matrix, and the estimate is asymptotically unbiased. Numerical simulations show that the obtained estimator has nice estimation performances. © 2006 IEEE.

Gao Y.,Tsinghua University
Journal of Uncertain Systems | Year: 2012

It has been proved that uncertain differential equation (UDE) has a unique solution, under the conditions that the coefficients are global Lipschitz continuous. This paper extends this existence and uniqueness theorem from the following aspect: UDE has a unique solution, under the conditions that the coefficients are local Lipschitz continuous. Besides, it is also proved that UDE has at least one solution, under the conditions that the coefficients are continuous and linear growth. © 2012 World Academic Press, UK. All rights reserved.

Liu B.,Tsinghua University
Journal of Uncertain Systems | Year: 2012

Uncertainty theory is a branch of mathematics for modeling human uncertainty. This paper will answer the following questions: What is uncertainty? In what situations does uncertainty arise? What is the difference between uncertain variable and uncertain set? This paper will also discuss the relations and differences among uncertainty, fuzziness and probability. © 2012 World Academic Press, UK. All rights reserved.

Yoon S.,Michigan State University | Feng J.,Tsinghua University | Jain A.K.,Michigan State University
IEEE Transactions on Pattern Analysis and Machine Intelligence | Year: 2012

The widespread deployment of Automated Fingerprint Identification Systems (AFIS) in law enforcement and border control applications has heightened the need for ensuring that these systems are not compromised. While several issues related to fingerprint system security have been investigated, including the use of fake fingerprints for masquerading identity, the problem of fingerprint alteration or obfuscation has received very little attention. Fingerprint obfuscation refers to the deliberate alteration of the fingerprint pattern by an individual for the purpose of masking his identity. Several cases of fingerprint obfuscation have been reported in the press. Fingerprint image quality assessment software (e.g., NFIQ) cannot always detect altered fingerprints since the implicit image quality due to alteration may not change significantly. The main contributions of this paper are: 1) compiling case studies of incidents where individuals were found to have altered their fingerprints for circumventing AFIS, 2) investigating the impact of fingerprint alteration on the accuracy of a commercial fingerprint matcher, 3) classifying the alterations into three major categories and suggesting possible countermeasures, 4) developing a technique to automatically detect altered fingerprints based on analyzing orientation field and minutiae distribution, and 5) evaluating the proposed technique and the NFIQ algorithm on a large database of altered fingerprints provided by a law enforcement agency. Experimental results show the feasibility of the proposed approach in detecting altered fingerprints and highlight the need to further pursue this problem. © 2012 IEEE.

Wei Y.,Tsinghua University
Gongcheng Lixue/Engineering Mechanics | Year: 2012

The upward lift due to moisture gradient, which couples with joint loading, can cause early-age transverse cracking in jointed concrete pavements. Though the importance of moisture effect on concrete pavement has been widely recognized, usually moisture deformations and stresses were ignored in pavement analysis because of a lack of comprehensive understanding on moisture transport properties and the difficulties in characterizing their magnitudes. This paper discusses three moisture transport processes and their effects on internal relative humidity distributions which are thought to be the major factors affecting concrete pavement deformations and stresses. In this study, the mechanism of moisture warping in concrete pavement is revealed and a new methodology is proposed for characterizing moisture-related deformations in slab on ground based on a relationship of shrinkage versus relative pore humidity for concrete. The proposed methodology provides for a simple post-processing of moisture-related deformations and stresses in concrete pavement.

Hao X.,University of Southern California | Jiang R.,Tsinghua University | Chen T.,University of Southern California
Bioinformatics | Year: 2011

Motivation: With the advancements of next-generation sequencing technology, it is now possible to study samples directly obtained from the environment. Particularly, 16S rRNA gene sequences have been frequently used to profile the diversity of organisms in a sample. However, such studies are still taxed to determine both the number of operational taxonomic units (OTUs) and their relative abundance in a sample. Results: To address these challenges, we propose an unsupervised Bayesian clustering method termed Clustering 16S rRNA for OTU Prediction (CROP). CROP can find clusters based on the natural organization of data without setting a hard cut-off threshold (3%/5%) as required by hierarchical clustering methods. By applying our method to several datasets, we demonstrate that CROP is robust against sequencing errors and that it produces more accurate results than conventional hierarchical clustering methods. © The Author(s) 2011. Published by Oxford University Press.

Liu Y.,Tsinghua University
Journal of Uncertain Systems | Year: 2012

Uncertain differential equations are a type of differential equations driven by canonical process, and are quite different from stochastic differential equations that are driven by Brownian motion. A solution of an uncertain differential equation is an uncertain process. This paper presents an analytic method to solve a particular class of nonlinear uncertain differential equations and gives some examples to illustrate the proposed analytic method. © 2012 World Academic Press, UK. All rights reserved.

An Y.,Tsinghua University
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2011

With the appropriate approximation, we have formulated the equation of multibubble motion for two cases: a filament of bubbles and a small spherical cluster of bubbles. Our results have yielded a collective mode of bubble motion in which individual bubbles of similar size expand and compress almost simultaneously. Each vibrating bubble radiates sound waves and originates the radiation sound pressure, which affects the motion of the other bubbles. The numerical simulation has revealed that this interaction suppresses single-bubble motion and tends to homogeneously spread the energy of the acoustic standing wave to each individual bubble. © 2011 American Physical Society.

Chen Q.,Tsinghua University
International Journal of Heat and Mass Transfer | Year: 2013

Optimal design of heat exchanger performance is of the key issue in energy conservation. Based on the entransy theory, this study deduced the formula of entransy dissipation-based thermal resistance (EDTR) for different types of heat exchangers, analyzed the factors influencing heat exchanger performance and, more importantly, developed an alternative EDTR method for the design and optimization of heat exchanger performance. The results indicate that the EDTR of parallelflow, counterflow and TEMA E-type shell-and-tube heat exchangers have a general formula, which directly connects heat exchanger performance to heat capacity rates of fluids, thermal conductance and flow arrangement of heat exchanger without introducing any phenomenological non-dimensional parameter. From this formula, it is clear that there are three factors influencing heat exchanger performance, including finite thermal conductance, different heat capacity rates of hot and cold fluids, and non-counterflow arrangement of heat exchangers. Furthermore, based on the relation among heat transfer rate, arithmetical mean temperature difference and EDTR, the total heat transfer rate in a heat exchanger can be easily calculated by the thermal conductance of heat exchanger and the heat capacity rates of fluids. Therefore, the EDTR method can analyze, compare and optimize heat exchanger performance conveniently. © 2013 Elsevier B.V. All rights reserved.

Liu B.,Tsinghua University
Soft Computing | Year: 2013

Uncertain process is a sequence of uncertain variables indexed by time. This paper presents a series of extreme value theorem of uncertain independent increment process and provides uncertainty distribution of first hitting time. This paper also proposes an insurance risk model with uncertain claims. Finally, a concept of ruin index is defined and a ruin index formula is given. © 2012 Springer-Verlag.

Liu Y.,Tsinghua University
Soft Computing | Year: 2013

In many cases, human uncertainty and objective randomness simultaneously appear in a system. In order to describe this phenomena, this paper presents a new concept of uncertain random variable. To measure uncertain random events, this paper also combines probability measure and uncertain measure into a chance measure. Based on the tool of chance measure, the concepts of chance distribution, expected value and variance of uncertain random variable are proposed. © 2012 Springer-Verlag.

Liu Y.,Tsinghua University
Fuzzy Optimization and Decision Making | Year: 2013

Uncertain random variable is a tool to deal with a mixture of uncertainty and randomness. This paper presents an operational law of uncertain random variables, and shows an expected value formula by using probability and uncertainty distributions. This paper also provides a framework of uncertain random programming that is a type of mathematical programming involving uncertain random variables. Finally, some applications of uncertain random programming are discussed. © 2012 Springer Science+Business Media New York.

Dong Z.,Tsinghua University
IEEE Transactions on Nuclear Science | Year: 2013

Pressurized water reactor (PWR) is the most widely used nuclear fission reactor, and the renaissance of fission energy industry needs the safe, stable and efficient operation of PWRs. Power-level control technique which strengthens the closed-loop stability and dynamic performance is meaningful to build a strong operation strategy for PWRs. In this paper, after extending the shifted-ectropy of thermodynamic systems to that of transport systems, a proportional-differential (PD) power-level controller is proposed for PWRs based on the physically-based approach. A sufficient condition for this PD controller to provide the globally asymptotic stability of those reactor state variables is established. Numerical simulation results not only verify the correctness of the theoretic results but also illustrate the relationship between the control performance and controller parameters. The meaning of this result is giving a theoretic explanation to why the simple PD control is effective for PWR power-level regulation practically. © 1963-2012 IEEE.

Lv R.,Tsinghua University | Cruz-Silva E.,Pennsylvania State University | Terrones M.,Pennsylvania State University | Terrones M.,Shinshu University
ACS Nano | Year: 2014

Graphene is theoretically a robust two-dimensional (2D) sp 2-hybridized carbon material with high electrical conductivity and optical transparency. However, due to the existence of grain boundaries and defects, experimentally synthesized large-Area polycrystalline graphene sheets are easily broken and can exhibit high sheet resistances; thus, they are not suitable as flexible transparent conductors. As described in this issue of ACS Nano, Tour et al. circumvented this problem by proposing and synthesizing a novel hybrid structure that they have named "rebar graphene", which is composed of covalently interconnected carbon nanotubes (CNTs) with graphene sheets. In this particular configuration, CNTs act as "reinforcing bars" that not only improve the mechanical strength of polycrystalline graphene sheets but also bridge different crystalline domains so as to enhance the electrical conductivity. This report seems to be only the tip of the iceberg since it is also possible to construct novel and unprecedented hybrid carbon architectures by establishing covalent interconnections between CNTs with graphene, thus yielding graphene-CNT hybrids, three-dimensional (3D) covalent CNT networks, 3D graphene networks, etc. In this Perspective, we review the progress of these carbon hybrid systems and describe the challenges that need to be overcome in the near future. © 2014 American Chemical Society.

Dong Z.,Tsinghua University
IEEE Transactions on Nuclear Science | Year: 2013

After the Fukushima nuclear accident, much more attention has to be drawn on the safety issues. The improvement of safety has already become the focus of the developing trend of the nuclear energy systems. Due to the inherent safety feature and the potential economic competitiveness, the modular high temperature gas-cooled reactor (MHTGR) has been seen as the central part of the next generation of nuclear plant (NGNP). Power-level control is one of the key techniques that guarantee the safe, stable and efficient operation for nuclear reactors. Since the MHTGR dynamics has the features of strong nonlinearity and uncertainty, in order to improve the operation performance, it is meaningful to develop the nonlinear adaptive power-level control law for the MHTGR. Based on using the natural dynamic features beneficial to system stabilization, a novel nonlinear adaptive power-level control is given for the MHTGR in this paper. It is theoretically proved that this newly-built controller does not only provide globally asymptotic closed-loop stability but is also adaptive to the system uncertainty. This control law is then applied to the power-level regulation of the pebble-bed MHTGR of the HTR-PM power plant. Numerical simulation results show the feasibility of this control law and the relationship between the performance and controller parameters. © 1963-2012 IEEE.

Plants can achieve amazing lifespans because of their continuous and repetitive formation of new organs by stem cells present within meristems. The balance between proliferation and differentiation of meristem cells is largely regulated by the CLAVATA3/ENDOSPERM SURROUNDING REGION (CLE) peptide hormones. One of the well-characterized CLE peptides, CLE41/TDIF (tracheary elements differentiation inhibitory factor), functions to suppress tracheary element differentiation and promote procambial cell proliferation, playing important roles in vascular development and wood formation. The recognition mechanisms of TDIF or other CLE peptides by their respective receptors, however, remain largely elusive. Here we report the crystal structure of TDIF in complex with its receptor PXY, a leucine-rich repeat receptor kinase (LRR-RK). Our structure reveals that TDIF mainly adopts an “Ω”-like conformation binding to the inner surface of the LRR domain of PXY. Interaction between TDIF and PXY is predominately mediated by the relatively conserved amino acids of TDIF. Structure-based sequence alignment showed that the TDIF-interacting motifs are also conserved among other known CLE receptors. Our data provide a structural template for understanding the recognition mechanism of CLE peptides by their receptors, offering an opportunity for the identification of receptors of other uncharacterized CLE peptides.Cell Research advance online publication 8 April 2016; doi:10.1038/cr.2016.45. © 2016 Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences

Liu B.,Tsinghua University
Journal of Uncertain Systems | Year: 2011

This paper discusses uncertain set theory and proposes the concepts of membership function, variance, entropy and distance of uncertain sets. In order to determine membership functions, uncertain statistics is also suggested. Based on uncertain set theory, uncertain logic is presented for dealing with human language by using uncertain quanti_er, uncertain subject and uncertain predicate. As an application, uncertain logic provides a means for extracting linguistic summary from a collection of raw data. Finally, fuzzy logic will be discussed at the end of this paper. © 2011 World Academic Press, UK. All rights reserved.

Zhang R.,Nanchang University | Wu C.,Tsinghua University
Computers and Operations Research | Year: 2011

In modern manufacturing systems, due date related performance is becoming increasingly important in maintaining a high service reputation. However, compared with the extensive research on makespan minimization, research on the total weighted tardiness objective is comparatively scarce, partly because this objective function is more difficult and complex to optimize. In this paper, we focus on the job shop scheduling problem with the objective of minimizing total weighted tardiness. First, we discuss the mathematical programming model and its duality when the processing orders for each machine are fixed. Then, a block-based neighborhood structure is defined and its important properties are shown. Finally, a simulated annealing algorithm is designed which directly utilizes the features of this neighborhood. According to the computational results, the new neighborhood considerably promotes the searching capability of simulated annealing and helps it converge to high-quality solutions. © 2010 Elsevier Ltd.

Van Zuylen A.,Tsinghua University
Theoretical Computer Science | Year: 2011

We consider the feedback vertex set and feedback arc set problems on bipartite tournaments. We improve on recent results by giving a 2-approximation algorithm for the feedback vertex set problem. We show that this result is the best that we can attain when using optimal solutions to a certain linear program as a lower bound on the optimal value. For the feedback arc set problem on bipartite tournaments, we show that a recent 4-approximation algorithm proposed by Gupta (2008) [8] is incorrect. We give an alternative 4-approximation algorithm based on an algorithm for the feedback arc set on (non-bipartite) tournaments given by van Zuylen and Williamson (2009) [14]. © 2010 Elsevier B.V. All rights reserved.

Xu Z.-F.,University of Tokyo | You L.,Tsinghua University | Ueda M.,University of Tokyo
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2013

We discuss a general scheme for creating atomic spin-orbit coupling (SOC) such as the Rashba or Dresselhaus types using magnetic-field-gradient pulses. In contrast to conventional schemes based on adiabatic center-of-mass motion with atomic internal states restricted to a dressed-state subspace, our scheme works for the complete subspace of a hyperfine-spin manifold by utilizing the coupling between the atomic magnetic moment and external magnetic fields. A space-dependent pulsed magnetic field acts as an internal-state-dependent impulse, thereby coupling the atomic internal spin with its orbital center-of-mass motion, as in the Einstein-de Haas effect. This effective coupling can be dynamically manipulated to synthesize SOC of any type (Rashba, Dresselhaus, or any linear combination thereof). Our scheme can be realized with most experimental setups of ultracold atoms and is especially suited for atoms with zero nuclear spins. © 2013 American Physical Society.

Yan N.,Tsinghua University
Annual Review of Biophysics | Year: 2015

The ancient and ubiquitous major facilitator superfamily (MFS) represents the largest secondary transporter family and plays a crucial role in a multitude of physiological processes. MFS proteins transport a broad spectrum of ions and solutes across membranes via facilitated diffusion, symport, or antiport. In recent years, remarkable advances in understanding the structural biology of the MFS transporters have been made. This article reviews the history, classification, and general features of the MFS proteins; summarizes recent structural progress with a focus on the sugar porter family transporters exemplified by GLUT1; and discusses the molecular mechanisms of substrate binding, alternating access, and cotransport coupling. © Copyright ©2015 by Annual Reviews. All rights reserved.

Lu X.,Tsinghua University
Journal of Statistical Physics | Year: 2013

The paper considers the problem of the Bose-Einstein condensation in finite time for isotropic distributional solutions of the spatially homogeneous Boltzmann equation for Bose-Einstein particles with the hard sphere model. We prove that if the initial datum of a solution is a function which is singular enough near the origin (the zero-point of particle energy) but still Lebesgue integrable (so that there is no condensation at the initial time), then the condensation continuously starts to occur from the initial time to every later time. The proof is based on a convex positivity of the cubic collision integral and some properties of a certain Lebesgue derivatives of distributional solutions at the origin. As applications we also study a special type of solutions and present a relation between the conservation of mass and the condensation. © 2013 Springer Science+Business Media New York.

Zhang J.,Beijing Jiaotong University | Chen J.,Tsinghua University
International Journal of Production Economics | Year: 2013

In this paper, we study information sharing in a supply chain consisting of one supplier and one retailer, in which both the supplier and the retailer possess partial information on the demand. Under the single price contract, we show that whether a firm reveals its private information depends on the quality (variance) and the correlation of the two firms' information and the other firm's information revelation behavior. For the case that one firm (the retailer or the supplier) has complete information on the demand, the equilibrium is that the firm with complete information conceals its information and another reveals its information. Finally, we show that revenue sharing contract is coordinative, which ensures that both firms share their information completely and the retailer chooses the sale quantity which maximizes the total profit of the supply chain. This study shows that the members in a supply chain must sign coordinative contract in order to ensure that they share their information. © 2013 Elsevier B.V. All rights reserved.

We construct exact dimensional measures whose support is the whole interval $$[0,1]$$[0,1] and whose Olsen’s multifractal functions b and B are real analytic and agree at two points only. These measures $$\nu $$ν satisfy an extended multifractal formalism in the sense that, for α in some interval, the Hausdorff dimension of the level sets X(α) of the local Hölder exponent of ν is the Legendre transform of b whereas their packing dimension is the Legendre transform of B. We first construct such measures μ on a symbolic space. Then we obtain the measures ν by projecting μ on [0,1] after composition with a Gray code. © 2015, Springer Science+Business Media New York.

Wang C.,Beijing Jiaotong University | Li Y.,Tsinghua University
IEEE Transactions on Industrial Electronics | Year: 2010

The neutral-point (NP) potential of the three-level neutral-point-clamped converters is needed to maintain balancing. Zero-sequence voltage is the only freedom degree when carrier-based pulsewidth modulation is utilized. Appropriate zero-sequence voltage should be identified to control the NP potential. The relationship between the neutral current and injected zero-sequence voltage is studied comprehensively, and two balancing algorithms of NP potential, respectively adopting searching-optimization and interpolation methods, are presented. The theoretical optimum zero-sequence voltage for controlling NP potential can be obtained by the latter proposed algorithm. Simulation and experimental results are shown to verify the validity and practicability of the proposed algorithms. © 2010 IEEE.

Levine A.G.,Sloan Kettering Cancer Center | Arvey A.,Sloan Kettering Cancer Center | Arvey A.,Gilead Sciences | Jin W.,Sloan Kettering Cancer Center | And 3 more authors.
Nature Immunology | Year: 2014

Foxp3+ regulatory T cells (Treg cells) maintain immunological tolerance, and their deficiency results in fatal multiorgan autoimmunity. Although heightened signaling via the T cell antigen receptor (TCR) is critical for the differentiation of Treg cells, the role of TCR signaling in Treg cell function remains largely unknown. Here we demonstrated that inducible ablation of the TCR resulted in Treg cell dysfunction that could not be attributed to impaired expression of the transcription factor Foxp3, decreased expression of Treg cell signature genes or altered ability to sense and consume interleukin 2 (IL-2). Instead, TCR signaling was required for maintaining the expression of a limited subset of genes comprising 25% of the activated Treg cell transcriptional signature. Our results reveal a critical role for the TCR in the suppressor capacity of Treg cells. © 2014 Nature America, Inc. All rights reserved.

In this paper we establish the global existence of smooth solutions to vacuum free boundary problems of the one-dimensional compressible isentropic Navier-Stokes equations for which the smoothness extends all the way to the boundaries. The results obtained in this work include the physical vacuum for which the sound speed is C1/2-Holder continuous near the vacuum boundaries when 1<γ < 3. The novelty of this result is its global-in-time regularity which is in contrast to the previous main results of global weak solutions in the literature. Moreover, in previous studies of the one-dimensional free boundary problems of compressible Navier-Stokes equations, the Lagrangian mass coordinates method has often been used, but in the present work the particle path (flow trajectory) method is adopted, which has the advantage that the particle paths and, in particular, the free boundaries can be traced. © 2015 IOP Publishing Ltd & London Mathematical Society.

Yao K.,Tsinghua University
Knowledge-Based Systems | Year: 2012

Stock model is used to describe the evolution of stock price in financial markets. Mean-reverting stock model in uncertain environment has been proposed to describe the stock price in long run. Arbitrage means that an investor can obtain profit without any risk, which does not exist in a complete market. This paper aims at proposing a sufficient condition as well as a necessary condition for an uncertain mean-reverting stock model being no-arbitrage. Besides, some examples are given to illustrate the usefulness of the no-arbitrage determinant theorem. © 2012 Elsevier B.V. All rights reserved.

White A.,Tsinghua University
International Journal of Industrial Organization | Year: 2013

Search engines face an interesting tradeoff in choosing the way to display their results. While providing high quality unpaid, or "left side" results attracts users, doing so can also cannibalize the revenue that comes from paid ads on the "right side". This paper examines this tradeoff, focusing, in particular, on the role of users' post-search interaction with the websites whose links are displayed. In the model, high quality left side results boost demand from users, causing them to tolerate a search engine on which advertisers do not offer the lowest possible prices for the goods that they sell. However, because websites appearing on the left side still have an incentive to compete in the same market as advertisers, an increase in quality on the left side may reduce advertisers' equilibrium prices. I analyze the circumstances under which this will occur and discuss the model's potential implications for antitrust policy. © 2013 Elsevier B.V.

Li R.,Stanford University | Wang J.,Stanford University | Wang J.,Tsinghua University | Qi X.-L.,Stanford University | Zhang S.-C.,Stanford University
Nature Physics | Year: 2010

Axions are weakly interacting particles of low mass, and were postulated more than 30 years ago in the framework of the Standard Model of particle physics. Their existence could explain the missing dark matter of the Universe. However, despite intensive searches, axions have yet to be observed. Here we show that magnetic fluctuations of topological insulators couple to the electromagnetic fields exactly like the axions, and propose several experiments to detect this dynamical axion field. In particular, we show that the axion coupling enables a nonlinear modulation of the electromagnetic field, leading to attenuated total reflection. We propose a new optical-modulator device based on this principle. © 2010 Macmillan Publishers Limited. All rights reserved.

Schechter M.,University of California at Irvine | Zou W.,Tsinghua University
Archive for Rational Mechanics and Analysis | Year: 2010

We study the following Brézis-Nirenberg problem (Comm Pure Appl Math 36:437-477, 1983): where Ω is a bounded smooth domain of RN (N ≧ 7) and 2* is the critical Sobolev exponent. We show that, for each fixed λ > 0, this problem has infinitely many sign-changing solutions. In particular, if λ ≧ λ1, the Brézis-Nirenberg problem has and only has infinitely many sign-changing solutions except zero. The main tool is the estimates of Morse indices of nodal solutions. © 2010 The Author(s).

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

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

Gao Z.,Tsinghua University
Physics of Plasmas | Year: 2010

Plasma shaping effects on the geodesic acoustic mode (GAM) are revisited analytically in the large orbit drift width limit. Comparing with results from the small orbit drift width expansion method [Z. Gao, Phys. Plasmas 15, 074502 (2008)] the behavior of the real frequency is almost the same but the effect on the damping rate is different due to the change of dominant resonant mechanism, from low order harmonic transit resonance to high order harmonic resonance, or equivalently, to the magnetic drift resonance. As a result, although the GAM frequency decreases with an increasing elongation κ by dependence of [2/ (κ2 +1)]1/2, the damping is weakened mildly in the large orbit drift width limit, which is quite different from the result in the low small orbit drift limit, where the damping is enhanced exponentially with the decrease in frequency. Also, in the large orbit drift width limit, the dependence of the GAM damping rate on inverse aspect ratio ε is analytically obtained for the first time. As ε increases, the frequency behaves as a weakly decreasing parabola function of ε, and the damping rate increases parabolically, but more rapidly than the frequency decreases. The GAM with longer radial wavelength is more easily damped by the finite aspect ratio effect. It is also found that the Shafranov shift gradient has the similar effect as the inverse aspect ratio. © 2010 American Institute of Physics.

Chen M.,Tsinghua University
IEEE Transactions on Circuits and Systems II: Express Briefs | Year: 2010

This brief proposes a new complex dynamical network model, in which nodes are connected by measured outputs experiencing the random sensor delay. This model is totally different from some existing network models. Then, synchronization in the proposed network model is analyzed by the stochastic stability theory. A sufficient synchronization condition is given to ensure that the proposed network model is exponentially mean-square stable. Theoretical analysis and numerical simulation fully verify the main results. © 2006 IEEE.

Zhu Y.,University of North Carolina at Charlotte | Xu B.,Tsinghua University | Shi X.,Harvard University | Wang Y.,University of North Carolina at Charlotte
IEEE Communications Surveys and Tutorials | Year: 2013

Delay tolerant networks (DTNs) may lack continuous network connectivity. Routing in DTNs is thus challenging since it must handle network partitioning, long delays, and dynamic topology in such networks. In recent years, social-based approaches, which attempt to exploit social behaviors of DTN nodes to make better routing decision, have drawn tremendous interests in DTN routing design. In this article, we summarize the social properties in DTNs, and provide a survey of recent social-based DTN routing approaches. To improve routing performance, these methods either take advantages of positive social characteristics such as community and friendship to assist packet forwarding or consider negative social characteristics such as selfishness. We conclude by discussing some open issues and challenges in social-based approaches regarding the design of DTN routing protocols. © 1998-2012 IEEE.

Yao K.,Tsinghua University | Li X.,Beijing Jiaotong University
IEEE Transactions on Fuzzy Systems | Year: 2012

Uncertain process is a sequence of uncertain variables indexed by time and space. First, this paper presents a kind of uncertain process, known as the uncertain alternating renewal process, whose alternating interarrival times are uncertain variables. Then, it proves an uncertain alternating renewal theorem on the limit value of average working rate. Finally, an application of the alternating renewal theorem is discussed. © 2012 IEEE.

Calculation of actual crop evapotranspiration under soil water stress conditions is crucial for hydrological modeling and irrigation water management. Results of actual evapotranspiration depend on the estimation of water stress coefficient from soil water storage in the root zone, which varies with numerical methods and time step used. During soil water depletion periods without irrigation or precipitation, the actual crop evapotranspiration can be calculated by an analytical method and various numerical methods. We compared the results from several commonly used numerical methods, including the explicit, implicit and modified Euler methods, the midpoint method, and the Heun's third-order method, with results of the analytical method as the bench mark. Results indicate that relative errors of actual crop evapotranspiration calculated with numerical methods in one time step are independent of the initial soil water storage in the range of soil water stress. Absolute values of relative error decrease with the order of numerical methods. They also decrease with the number of time step, which can ensure the numerical stability of successive simulation of soil water balance. Considering the calculation complexity and calculation errors caused by numerical approximation for different time step and maximum crop evapotranspiration, the explicit Euler method is recommended for the time step of 1day (d) or 2d for maximum crop evapotranspiration less than 5mm/d, the midpoint method or the modified Euler method for the time step of up to one week or 10d for maximum crop evapotranspiration less than 5mm/d, and the Heun's third-order method for the time step of up to 15d. © 2011 John Wiley & Sons, Ltd.

Yao K.,Tsinghua University
Fuzzy Optimization and Decision Making | Year: 2012

Uncertain calculus is a branch of mathematics that deals with differentiation and integration of function of uncertain processes. As a fundamental concept, uncertain integral has been defined with respect to canonical process. However, emergencies such as economic crisis and war occur occasionally, which may cause the uncertain process a sudden change. So far, uncertain renewal process has been employed to model these jumps. This paper will present a new uncertain integral with respect to renewal process. Besides, this paper will propose a type of uncertain differential equation driven by both canonical process and renewal process. © 2012 Springer Science+Business Media, LLC.

Xu Z.,PLA University of Science and Technology | Xia M.,Tsinghua University
International Journal of Intelligent Systems | Year: 2012

We introduce the concepts of entropy and cross-entropy for hesitant fuzzy information, and discuss their desirable properties. Several measure formulas are further developed, and the relationships among the proposed entropy, cross-entropy, and similarity measures are analyzed, from which we can find that three measures are interchangeable under certain conditions. Then we develop two multiattribute decision-making methods in which the attribute values are given in the form of hesitant fuzzy sets reflecting humans' hesitant thinking comprehensively. In one method, the weight vector is determined by the hesitant fuzzy entropy measure, and the optimal alternative is obtained by comparing the hesitant fuzzy cross-entropies between the alternatives and the ideal solutions; in another method, the weight vector is derived from the maximizing deviation method and the optimal alternative is obtained by using the TOPSIS method. An actual example is provided to compare our methods with the existing ones. Copyright © 2012 Wiley Periodicals, Inc.

Liu B.,Tsinghua University
Fuzzy Optimization and Decision Making | Year: 2012

Uncertain set is a set-valued function on an uncertainty space, and attempts to model "unsharp concepts" that are essentially sets but their boundaries are not sharply described. This paper will propose a concept of membership function and define the independence of uncertain sets. This paper will also present an operational law of uncertain sets via membership functions or inverse membership functions. Finally, the linearity of expected value operator is verified. © Springer Science+Business Media, LLC 2012.

Gao Y.,Tsinghua University
Fuzzy Optimization and Decision Making | Year: 2012

Fuzzy inference control uses fuzzy sets to describe the antecedents and consequents of If-Then rules. However, most surveys show the antecedents and consequents are uncertain sets rather than fuzzy sets. This fact provides a motivation to invent an uncertain inference control method. This paper gives an introduction to the design procedures of uncertain inference controller. As an example, an uncertain inference controller for balancing an inverted pendulum system is successfully designed. The computer simulation shows the developed uncertain inference controller is of good robustness. © Springer Science+Business Media, LLC 2012.

Dong C.,Tsinghua University
Cell Research | Year: 2014

Last decade has seen quick developments in the understanding of a new type of T lymphocytes, Th17 cells. This information is benefiting the understanding and treatment of a variety of inflammatory diseases, as suggested by a recent paper in Immunity. © 2014 IBCB, SIBS, CAS.

Dong Z.,Tsinghua University
IEEE Transactions on Nuclear Science | Year: 2012

Because of its strong inherent safety, the modular high temperature gas-cooled nuclear reactor (MHTGR) has been regarded as the central part of the next generation nuclear plants (NGNPs). Power-level control is one of the key techniques which provide safe, stable and efficient operation for the MHTGRs. The physically-based regulation theory is definitely a promising trend of modern control theory and provides a control design method that can suppress the unstable part of the system dynamics and remain the stable part. Usually, the control law designed by the physically-based control theory has a simple form and high performance. Stimulated by this, a novel nonlinear dynamic output feedback power-level control is established in this paper for the MHTGR based upon its own dynamic features. This newly-built control strategy guarantees the globally asymptotic stability and provides a satisfactory transient performance through properly adjusting the feedback gains. Simulation results not only verify the correctness of the theoretical results but also illustrate the high control performance. © 2012 IEEE.

In this paper, we examine the effects of correlated Gaussian noise on a two-dimensional neuronal network that is locally modeled by the Rulkov map. More precisely, we study the effects of the noise correlation on the variations of the mean firing rate and the correlations among neurons versus the noise intensity. Via numerical simulations, we show that the mean firing rate can always be optimized at an intermediate noise intensity, irrespective of the noise correlation. On the other hand, variations of the population coherence with respect to the noise intensity are strongly influenced by the ratio between local and global Gaussian noisy inputs. Biological implications of our findings are also discussed.

Zhang J.-L.,Beijing Jiaotong University | Chen J.,Tsinghua University
Computers and Operations Research | Year: 2013

In this paper, we study the supplier selection and procurement decision problem with uncertain demand, quantity discounts and fixed selection costs. In addition, a holding cost is incurred for the excess inventory if the buyer orders more than the realized demand and the shortage must be satisfied by an emergent purchase at a higher price otherwise. The objective is to select the suppliers and to allocate the ordering quantity among them to minimize the total cost (including selecting, procurement, holding and shortage costs, etc.). The problem is modeled as a Mixed Integer Programming (MIP) and is shown to be NP-hard. Some properties of the optimal policy are provided and an optimal algorithm is proposed based on the generalized Bender's decomposition. Numerical experiments are conducted to show the efficiency of the algorithm and to obtain some managerial insights. © 2013 Elsevier Ltd.

Li G.-X.,Tsinghua University
Yantu Gongcheng Xuebao/Chinese Journal of Geotechnical Engineering | Year: 2011

Some mistakes and wrong concepts about the principle of effective stress in saturated soil are pointed out and analyzed. Some problems in the field are discussed, for example, the reduction of pore water pressure in clay, the diffusion of bound water in clay, the accuracy of the principle of effective stress in rock, concrete and clay, the measurement of pore water pressure in clay and uplift pressure on basement. Through the long processs of practice and experiments, a conclusion is drawn that the principle of effective stress is applicable and effective in both saturated sand and clay.

Li D.,Tsinghua University
Quantum Information Processing | Year: 2012

Coffman et al. presented the 3-tangle of three qubits in Phys Rev A 61, 052306 (2000). Wong and Christensen (Phys Rev A 63, 044301, 2001) extended the standard form of the 3-tangle to even number of qubits, known as n-tangle. In this paper, we propose a generalization of the standard form of the 3-tangle to any odd n-qubit pure states and call it the n-tangle of odd n qubits. We show that the n-tangle of odd n qubits is invariant under permutations of the qubits, and is an entanglement monotone. The n-tangle of odd n qubits can be considered as a natural entanglement measure of any odd n-qubit pure states, and used for stochastic local operations and classical communication classification. © 2011 Springer Science+Business Media, LLC.

Hu Z.,Tsinghua University | Li F.,University of Bath
IEEE Transactions on Smart Grid | Year: 2012

With more and more renewable energy generation (REG) connections, busbar voltage violation and line overloading problems may occur for some parts of a distribution network. However, building new circuits to accommodate REG may have high monetary and environmental costs. This paper considers distribution automation as a supplementary scheme to traditional primary asset investments and analyzes the operational benefits from introducing an autonomous regional active network management system (AuRA-NMS) to a practical distribution system with rich renewable sources. The benefits are quantified in terms of optimal power flow control and investment deferral, and the resulting quantification will inform distribution network operators of the trade-offs between investment in the automation system and in the primary assets, thus helping them to make cost-effective investment decisions. Time-series-based simulation for over an entire year is implemented to calculate the benefits of active power loss and curtailment reductions for AuRA-NMS over the current practice. Part I of this paper illustrates the current schemes for voltage control and constraint management, advanced voltage control and constraint management enabled by the distribution automation, and the annual benefit by introducing the AuRA-NMS to the system with different considerable new DG integrations. Part II analyzes the investment deferral benefit by deploying AuRA-NMS. © 2010-2012 IEEE.

Hu Z.,Tsinghua University | Li F.,University of Bath
IEEE Transactions on Smart Grid | Year: 2012

Based on the traditional network expansion planning formulation, a new formulation is built by taking into consideration the curtailment of renewable energy generation (REG), e.g., wind farm generation. The objective is to minimize the total cost of building new circuits and to curtail the output of REG generation. Loss in REG generation curtailment is computed according to its annual output duration curve. In the proposed formulation, operational conditions under peak and trough load levels, the different outputs of REG, and the N-1 security criterion are altogether considered. The whole formulation is solved by Benders' decomposition method. The proposed method is tested on a practical network. Network expansion schemes obtained from the classical and the proposed methods are compared and analyzed. Test results show that network investment can be reduced or deferred by deploying the autonomous regional active network management system (AuRA-NMS). Although some of the wind farm generation is curtailed, the loss is smaller than the reduction of network investment cost. The present work shows the potential of installing an active control system as an alternative of network reinforcement to accommodate increasing REG connections. © 2010-2012 IEEE.

Mollusks shell formation is mediated by matrix proteins and many of these proteins have been identified and characterized. However, the mechanisms of protein control remain unknown. Here, we report the ubiquitylation of matrix proteins in the prismatic layer of the pearl oyster, Pinctada fucata. The presence of ubiquitylated proteins in the prismatic layer of the shell was detected with a combination of western blot and immunogold assays. The coupled ubiquitins were separated and identified by Edman degradation and liquid chromatography/mass spectrometry (LC/MS). Antibody injection in vivo resulted in large amounts of calcium carbonate randomly accumulating on the surface of the nacreous layer. These ubiquitylated proteins could bind to specific faces of calcite and aragonite, which are the two main mineral components of the shell. In the in vitro calcium carbonate crystallization assay, they could reduce the rate of calcium carbonate precipitation and induce the calcite formation. Furthermore, when the attached ubiquitins were removed, the functions of the EDTA-soluble matrix of the prismatic layer were changed. Their potency to inhibit precipitation of calcium carbonate was decreased and their influence on the morphology of calcium carbonate crystals was changed. Taken together, ubiquitylation is involved in shell formation. Although the ubiquitylation is supposed to be involved in every aspect of biophysical processes, our work connected the biomineralization-related proteins and the ubiquitylation mechanism in the extracellular matrix for the first time. This would promote our understanding of the shell biomineralization and the ubiquitylation processes.

Ng H.T.,Tsinghua University
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2014

We study the topological phases in spin-orbit-coupled dipolar bosons in a one-dimensional optical lattice. The magnetic dipolar interactions between atoms give rise to intersite interactions. In the Mott-insulating regime, this system can be described by the quantum XYZ spin model with Dzyaloshinskii-Moriya interactions in a transverse field. We focus on investigating the effect of dipolar interactions on the topological phase. The topological phase can be shown when spin-orbit coupling combines with the repulsive dipolar interaction. We find that the dipolar interaction can broaden the range of parameters of spin-orbit coupling and transverse field for exhibiting the topological phase. The sum of spin correlations between the two nearest-neighboring atoms can be used to indicate the topological phase. This may be useful for detecting topological phases in experiments. © 2014 American Physical Society.

Zhai H.,Tsinghua University
Reports on Progress in Physics | Year: 2015

This review focuses on recent developments in synthetic spin-orbit (SO) coupling in ultracold atomic gases. Two types of SO coupling are discussed. One is Raman process induced coupling between spin and motion along one of the spatial directions and the other is Rashba SO coupling. We emphasize their common features in both single-particle and two-body physics and the consequences of both in many-body physics. For instance, single particle ground state degeneracy leads to novel features of superfluidity and a richer phase diagram; increased low-energy density-of-state enhances interaction effects; the absence of Galilean invariance and spin-momentum locking gives rise to intriguing behaviours of superfluid critical velocity and novel quantum dynamics; and the mixing of two-body singlet and triplet states yields a novel fermion pairing structure and topological superfluids. With these examples, we show that investigating SO coupling in cold atom systems can, enrich our understanding of basic phenomena such as superfluidity, provide a good platform for simulating condensed matter states such as topological superfluids and more importantly, result in novel quantum systems such as SO coupled unitary Fermi gas and high spin quantum gases. Finally we also point out major challenges and some possible future directions. © 2015 IOP Publishing Ltd.

Xie W.,University of California at San Diego | Xie W.,Tsinghua University | Ren B.,University of California at San Diego
Science | Year: 2013

The identification of large numbers of human embryonic stem cell enhancers provides a useful tool to study cell fate and disease.

Zhang X.-L.,Tsinghua University
IEEE Transactions on Pattern Analysis and Machine Intelligence | Year: 2015

Multitask clustering tries to improve the clustering performance of multiple tasks simultaneously by taking their relationship into account. Most existing multitask clustering algorithms fall into the type of generative clustering, and none are formulated as convex optimization problems. In this paper, we propose two convex Discriminative Multitask Clustering (DMTC) objectives to address the problems. The first one aims to learn a shared feature representation, which can be seen as a technical combination of the convex multitask feature learning and the convex Multiclass Maximum Margin Clustering (M3C). The second one aims to learn the task relationship, which can be seen as a combination of the convex multitask relationship learning and M3C. The objectives of the two algorithms are solved in a uniform procedure by the efficient cutting-plane algorithm and further unified in the Bayesian framework. Experimental results on a toy problem and two benchmark data sets demonstrate the effectiveness of the proposed algorithms. © 2014 IEEE.

Weng Z.-Y.,Tsinghua University
New Journal of Physics | Year: 2011

A d-wave superconducting ground state for a doped Mott insulator is obtained. It is distinguished from a Gutzwiller-projected Bardeen-Cooper- Schrieffer (BCS) superconductor by an explicit separation of Cooper pairing and resonating valence bond (RVB) pairing. Such a state satisfies the precise sign structure of the t-J model, just as a BCS state satisfies the Fermi-Dirac statistics. This new class of wavefunctions can be intrinsically characterized and effectively manipulated by electron fractionalization with neutral spinons and 'backflow' spinons forming a twocomponent RVB structure. While the former spinon is bosonic, originating from the superexchange correlation, the latter spinon is found to be fermionic, accompanying the hopping of bosonic holons. The low-lying emergent gauge fields associated with such a specific fractionalization are of mutual Chern-Simons type. Corresponding to this superconducting ground state, three types of elementary excitations are identified. Among them a Bogoliubov nodal quasiparticle is conventional, while the other two are neutral excitations of non-BCS type that play crucial roles in higher-energy/temperature regimes. Their unique experimental implications for the cuprates are briefly discussed. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.

Li Z.,Georgia Institute of Technology | Li Z.,Tsinghua University | Wang Z.L.,Georgia Institute of Technology
Advanced Materials | Year: 2011

We present a new approach for fabricating flexible fiber nanogenerators (FNGs) that can be used for smart shirts, flexible electronics, and medical applications. These FNGs are based on carbon fibers that are covered cylindrically by textured zinc oxide (ZnO) thin films. Once subjected to uni-compression by applying a pressure, the cylindrical ZnO thin film is under a compressive strain, resulting in a macroscopic piezopotential across its inner and exterior surfaces owing to the textured structure of the film, which is the driving force for generating an electric current in the external load. Using such a structure, an output peak voltage of 3.2 V and average current density of 0.15 μA cm-2 are demonstrated. The FNGs rely on air pressure, so that it can work in a non-contact mode in cases of rotating tires, flowing air/liquid, and even in blood vessels. Pressure-driven FNGs added to a syringe show potential to harvest energy in blood vessels, gas pipes, and oil pipes, as long as there is a fluctuation in pressure (or turbulence). Heart-pulse driven FNGs can serve as ultrasensitive sensors for monitoring the behavior of the human heart, which may possibly be applied to medical diagnostics as sensors and measurement tools. A pressure-driven flexible fiber nanogenerator (FNG) is demonstrated that can be used for smart shirts, flexible electronics, and medical applications. An output peak voltage of 3.2 V and average current density of 0.15 μA cm-2 are demonstrated. The pressure-driven FNG added to a syringe shows potential to harvest energy in a blood vessel, as well as in gas pipes and oil pipes. The heart-pulse driven FNG can serve as an ultrasensitive sensor for monitoring the behavior of a human heart for medical diagnostics. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

This work primarily focused on the influence of ultrasonic cavitation on the transport property of the point defect in the passive film on formed Nb in 0.5 M HCl solution via electrochemical techniques based on the point defect model (PDM). The influence of ultrasonic cavitation on the composition and structure of the passive film was detected by X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). The transport property of a point defect in the passive film was characterized by the diffusivity of the point defect (D0). The influences of the ultrasonic cavitation power, passivated time and the distance between horn bottom and sample surface on D0 were analyzed. The results demonstrated that the passive film formed on Nb was an n-type semiconductor with a donor density (ND) ranging from 1019 cm-3to 1020 cm-3 in the case of static state, while the order of ND increased one to two times by applying ultrasonic cavitation during film formation. The diffusivity of the point defect (D0) in the passive film formed on Nb at 0.5 V for 1 h in a 0.5 M HCl solution in the static state was calculated to be 9.704 ×10-18cm2 s-1, and it increased to 1.255 × 10-16cm2 s-1, 7.259 ×10-16cm2 s-1and 7.296 ×10-15cm2 s-1when applying the 180 W, 270W and 450W ultrasonic cavitation powers during film formation. D0 increased with the increment of the ultrasonic cavitation power, and decreased with the increased in formation time and distance between the horn bottom and sample surface. AES results showed the film structure and composition were changed by applying the ultrasonic cavitation. XPS results revealed that the passive film was mainly composed of Nb2O5 in the static state, and the low valence Nb-oxide (NbO) appeared in the passive film except Nb2O5 in the case of applying a 270Wultrasonic cavitation power. © 2015 Elsevier B.V. All rights reserved.

Tian F.,Tsinghua University | Ida S.,Tokyo Institute of Technology
Nature Geoscience | Year: 2015

Efforts to identify habitable extrasolar planets have focused on systems around M dwarfs, faint stars with less than half the solar mass. Habitable planets around M dwarfs are thought to be more plentiful and easier to detect than those orbiting Sun-like G dwarfs. However, unlike G dwarfs, M dwarfs experience a prolonged decline in luminosity early in their history, leading to an inward migration of the habitable zone to where planets may have lost their water through dissociation and hydrodynamic escape. Water-poor planets, such as Venus, are considered uninhabitable. In contrast, planets with too much water (>1 wt%) would lack continents, leading to climate instability and nutrient limitation problems. Here we combine a numerical planet population synthesis model with a model for water loss to show that the evolution of stellar luminosity leads to two types of planets of Earth-like mass (0.1 to 10 Earth masses) in the habitable zones around M dwarfs: ocean planets without continents, and desert planets, on which there are orders of magnitude less surface water than on Earth. According to our simulations, Earth-mass planets with Earth-like water contents are rare around M dwarfs and occur 10-100 times less frequently than around G dwarfs. We suggest that stars close to the size of the Sun should be the primary targets for detecting Earth-like planets. © 2015 Macmillan Publishers Limited.

An analytic method for predicting the performance of track-to-track association (TTTA) with biased data in multi-sensor multi-target tracking scenarios is proposed in this paper. The proposed method extends the existing results of the bias-free situation by accounting for the impact of sensor biases. Since little insight of the intrinsic relationship between scenario parameters and the performance of TTTA can be obtained by numerical simulations, the proposed analytic approach is a potential substitute for the costly Monte Carlo simulation method. Analytic expressions are developed for the global nearest neighbor (GNN) association algorithm in terms of correct association probability. The translational biases of sensors are incorporated in the expressions, which provide good insight into how the TTTA performance is affected by sensor biases, as well as other scenario parameters, including the target spatial density, the extraneous track density and the average association uncertainty error. To show the validity of the analytic predictions, we compare them with the simulation results, and the analytic predictions agree reasonably well with the simulations in a large range of normally anticipated scenario parameters.

Kitaev A.,California Institute of Technology | Kong L.,Tsinghua University
Communications in Mathematical Physics | Year: 2012

We define a class of lattice models for two-dimensional topological phases with boundary such that both the bulk and the boundary excitations are gapped. The bulk part is constructed using a unitary tensor category C as in the Levin-Wen model, whereas the boundary is associated with a module category over C. We also consider domain walls (or defect lines) between different bulk phases. A domain wall is transparent to bulk excitations if the corresponding unitary tensor categories are Morita equivalent. Defects of higher codimension will also be studied. In summary, we give a dictionary between physical ingredients of lattice models and tensor-categorical notions. © 2012 Springer-Verlag.

Li G.,Tsinghua University
Yanshilixue Yu Gongcheng Xuebao/Chinese Journal of Rock Mechanics and Engineering | Year: 2012

Foundation pit excavation is constructed in intact soil strata. So, the stress path of soil is different from that in conventional retaining wall and in conventional triaxial compression test. In foundation pit engineering, in the soil in front of and behind retaining wall, the mean principal stress p or some principal stresses decrease in excavation, generally. As a result, the negative excess hydrostatic pressure in consolidated undrained(CU) triaxial test of saturated soil will conduct, that has effects on strength parameters of soil. It is pointed out that, for the excavation in clay soil, earth pressure calculation and stability analysis using strength parameters of CU triaxial test or consolidated quick shear test are unsafe under conditions of under-consolidation soil foundation and overcharge q which is applied recently. Meanwhile, in checkings of anti-sliding stability, anti-overturning stability and global stability by Swedish circle method for gravity cement-soil wall, if the strength parameters of saturated clay soil in CU triaxial test are adopted, the gravity of soil and wall in the calculation of resistant force has to be calculated by buoyant unit. According to the discussion on Technical specification for retaining and protection of building foundation excavations(JGJ120-201×), the action of water pressure in calculation of excavation support structure is discussed;and it is proposed that for the silt soil foundation, whether the water pressure and earth pressure are estimated together or separately lies on the properties of the under soils.

Zhu W.,Tsinghua University | Liang S.,Tongji University | Wei Y.,Microsoft | Sun J.,Microsoft
Proceedings of the IEEE Computer Society Conference on Computer Vision and Pattern Recognition | Year: 2014

Recent progresses in salient object detection have exploited the boundary prior, or background information, to assist other saliency cues such as contrast, achieving state-of-the-art results. However, their usage of boundary prior is very simple, fragile, and the integration with other cues is mostly heuristic. In this work, we present new methods to address these issues. First, we propose a robust background measure, called boundary connectivity. It characterizes the spatial layout of image regions with respect to image boundaries and is much more robust. It has an intuitive geometrical interpretation and presents unique benefits that are absent in previous saliency measures. Second, we propose a principled optimization framework to integrate multiple low level cues, including our background measure, to obtain clean and uniform saliency maps. Our formulation is intuitive, efficient and achieves state-of-the-art results on several benchmark datasets. © 2014 IEEE.

Zhu X.,Tsinghua University
Acta Physica Polonica B, Proceedings Supplement | Year: 2012

We report on the measurements of K 0 S, Λ and Ξ spectra at mid-rapidity (|y| < 0.5) in the most central (0-5%) Au + Au collisions at √s NN = 7.7, 11.5 and 39 GeV from the STAR experiment. The extracted yields are consistent with the corresponding data from Pb + Pb collisions measured by the NA49 and CERES experiments at SPS. The Λ, Λ̄, Ξ - and Ξ̄ + to π ratios agree well with the predictions of the statistical hadronization model at all three energies.

Zhang X.,Tsinghua University
Acta Physica Polonica B, Proceedings Supplement | Year: 2012

We present φ-meson transverse momentum distribution as well as its elliptic flow (υ 2) measurements in Au + Au collisions at center-of-mass energy per nucleon pair √s NN= 7.7, 11.5 and 39 GeV with the data taken from STAR experiment at RHIC in the year 2010. We discuss the energy dependence of φ-meson elliptic flow (υ 2) and central-to-peripheral nuclear modification factors (R CP). The υ 2 of φ-mesons are compared to those from other hadron species. The implications on partonic-hadronic phase transition are discussed.

Xu Z.,Tsinghua University
Scientific Reports | Year: 2013

There have been growing evidences for the critical roles of metal-coordination complexes in defining structural and mechanical properties of unmineralized biological materials, including hardness, toughness, and abrasion resistance. Their dynamic (e.g. pH-responsive, self-healable, reversible) properties inspire promising applications of synthetic materials following this concept. However, mechanics of these coordination crosslinks, which lays the ground for predictive and rational material design, has not yet been well addressed. Here we present a first-principles study of representative coordination complexes between metals and catechols. The results show that these crosslinks offer stiffness and strength near a covalent bond, which strongly depend on the coordination state and type of metals. This dependence is discussed by analyzing the nature of bonding between metals and catechols. The responsive mechanics of metal-coordination is further mapped from the single-molecule level to a networked material. The results presented here provide fundamental understanding and principles for material selection in metal-coordination-based applications.

Wang M.-X.,Tsinghua University
Accounts of Chemical Research | Year: 2015

The hydration and hydrolysis of nitriles are valuable synthetic methods used to prepare carboxamides and carboxylic acids. However, chemical hydration and hydrolysis of nitriles involve harsh reaction conditions, have low selectivity, and generate large amounts of waste. Therefore, researchers have confined the scope of these reactions to simple nitrile substrates.However, biological transformations of nitriles are highly efficient, chemoselective, and environmentally benign, which has led synthetic organic chemists and biotechologists to study these reactions in detail over the last two decades. In nature, biological systems degrade nitriles via two distinct pathways: nitrilases catalyze the direct hydrolysis of nitriles to afford carboxylic acids with release of ammonia, and nitrile hydratases catalyze the conversion of nitriles into carboxamides, which then furnish carboxylic acids via hydrolysis in the presence of amidases. Researchers have subsequently developed biocatalytic methods into useful industrial processes for the manufacture of commodity chemicals, including acrylamide.Since the late 1990s, research by my group and others has led to enormous progress in the understanding and application of enantioselective biotransformations of nitriles in organic synthesis. In this Account, I summarize the important advances in enantioselective biotransformations of nitriles and amides, with a primary focus on research from my laboratory. I describe microbial whole-cell-catalyzed kinetic resolution of various functionalized nitriles, amino- and hydroxynitriles, and nitriles that contain small rings and the desymmetrization of prochiral and meso dinitriles and diamides. I also demonstrate how we can apply the biocatalytic protocol to synthesize natural products and bioactive compounds.These nitrile biotransformations offer an attractive and unique protocol for the enantioselective synthesis of polyfunctionalized organic compounds that are not readily obtainable by other methods. Nitrile substrates are readily available, and the mild reaction conditions are specific toward cyano and amido functional groups without interfering with other reactive functional groups. I anticipate that further advances in this field will lead to new and engineered nitrile-hydrolyzing enzymes or catalytic systems with improved activity and altered selectivity. These advances will broaden the scope of these transformations and their applications in organic synthesis. (Chemical Equation Presented). © 2015 American Chemical Society.

Zhou L.X.,Tsinghua University
International Journal of Multiphase Flow | Year: 2010

Particle/droplet/bubble fluctuation and dispersion are important to mixing, heat and mass transfer, combustion and pollutant formation in dispersed multiphase flows, but are insufficiently studied before the 90 years of the last century. In this paper, the present author reports his systematic studies within nearly 20 years on two-phase turbulence in dispersed multiphase flows, including particle fluctuation in dilute gas-particle and bubble-liquid flows, particle-wall collision effect, coexistence of particle turbulence and inter-particle collisions, fluid turbulence modulation due to the particle wake effect and validation of the two-fluid RANS modeling using large-eddy simulation. © 2009 Elsevier Ltd. All rights reserved.

Ying L.,Tsinghua University | Liang Z.-P.,University of Illinois at Urbana - Champaign
IEEE Signal Processing Magazine | Year: 2010

Magnetic resonance imaging (MRI) is a relatively slow imaging technique that has limited its application to imaging of time-varying objects. Developing fast MRI methods has been an active research area for the last three decades. Recently, parallel imaging using phased array coils has provided another avenue to significantly speed up the MRI process. In this article, we describe parallel MRI from a signal processing perspective, invoking the multichannel sampling theory (and filter bank theory). We review several basic reconstruction algorithms and discuss some practical issues and outstanding signal processing problems. © 2006 IEEE.

Chen M.,Huazhong University of Science and Technology | Mao S.,Auburn University | Liu Y.,Tsinghua University
Mobile Networks and Applications | Year: 2014

In this paper, we review the background and state-of-the-art of big data. We first introduce the general background of big data and review related technologies, such as could computing, Internet of Things, data centers, and Hadoop. We then focus on the four phases of the value chain of big data, i.e., data generation, data acquisition, data storage, and data analysis. For each phase, we introduce the general background, discuss the technical challenges, and review the latest advances. We finally examine the several representative applications of big data, including enterprise management, Internet of Things, online social networks, medial applications, collective intelligence, and smart grid. These discussions aim to provide a comprehensive overview and big-picture to readers of this exciting area. This survey is concluded with a discussion of open problems and future directions. © 2014 Springer Science+Business Media New York.

A method for making graphene-based highly dense but porous carbon material with a high degree of hardness includes forming a sol by dispersing a graphene-based component in a solvent; preparing a graphene-based gel by reacting the sol in a reacting container at a temperature of about 20 C. to about 500 C. for about 0.1 hours to about 100 hours; and drying the gel at a temperature of about 0 C. to about 200 C. to obtain a material. A graphene-based porous carbon material and applications thereof are also disclosed.

Tsinghua University and Hon Hai Precision Industry Co. | Date: 2014-06-06

An electric heater includes a base, a bracket, a working head and a protecting structure. The bracket is disposed on the base. The working head is disposed on the bracket. The working head includes a supporter and a heating module. The heating module is disposed on the supporter. The heating module includes a heating element and at least two electrodes. The at least two electrodes are electrically connected with the heating element. The heating element includes a carbon nanotube layer structure. The protecting structure covers the heating module.

Hon Hai Precision Industry Co. and Tsinghua University | Date: 2013-12-16

An incandescent light source display includes a container and a number of incandescent light sources. The incandescent light sources are located in the container. Each of the incandescent light sources includes a first electrode, a second electrode and an incandescent element. The second electrode is spaced from the first electrode. The incandescent element is electrically connected to the first electrode and the second electrode. The incandescent element includes a carbon nanotube structure.