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Xiangtan, China

Xiangtan University, or XTU , is a university located in Xiangtan, Hunan. It was founded in 1958 and is organized into 22 Schools and Departments.Xiangtan University, located in Xiangtan City, the home town of Mao Zedong, is a comprehensive university operating under the joint support of the Hunan Provincial Government and the Ministry of Education. It is one of China’s first educational institutes authorized to award master’s degrees and is also among the earliest schools approved to enroll overseas students and students of national defense. In an evaluation conducted by the Ministry of Education, the university’s bachelor degree education was rated as excellent. Wikipedia.

Li C.,Xiangtan University | Li C.,Hong Kong Polytechnic University | Lo K.-T.,Hong Kong Polytechnic University
Signal Processing | Year: 2011

Recently, an image scrambling encryption algorithm of pixel bit based on chaos map was proposed. Considering the algorithm as a typical binary image scrambling/permutation algorithm exerting on plaintext of size M×(8N), this paper proposes a novel optimal method to break it with some known/chosen-plaintexts. The spatial complexity and computational complexity of the attack are only O(32·MN) and O(16·n0·MN) respectively, where n0 is the number of known/chosen-plaintexts used. The method can be easily extended to break any permutation-only encryption scheme exerting on plaintext of size M×N and with L different levels of values. The corresponding spatial complexity and computational complexity are only O(MN) and O(logL(MN)⌉·MN) respectively. In addition, some specific remarks on the performance of the image scrambling encryption algorithm are presented. © 2010 Elsevier B.V. All rights reserved.

Liu H.,Iowa State University | Yi N.,Xiangtan University
Journal of Computational Physics | Year: 2016

The invariant preserving property is one of the guiding principles for numerical algorithms in solving wave equations, in order to minimize phase and amplitude errors after long time simulation. In this paper, we design, analyze and numerically validate a Hamiltonian preserving discontinuous Galerkin method for solving the Korteweg-de Vries (KdV) equation. For the generalized KdV equation, the semi-discrete formulation is shown to preserve both the first and the third conserved integrals, and approximately preserve the second conserved integral; for the linearized KdV equation, all the first three conserved integrals are preserved, and optimal error estimates are obtained for polynomials of even degree. The preservation properties are also maintained by the fully discrete DG scheme. Our numerical experiments demonstrate both high accuracy of convergence and preservation of all three conserved integrals for the generalized KdV equation. We also show that the shape of the solution, after long time simulation, is well preserved due to the Hamiltonian preserving property. © 2016 Elsevier Inc.

Xie S.,Xiangtan University | Xie S.,University of Washington | Ma F.,University of Washington | Liu Y.,University of Washington | Li J.,University of Washington
Nanoscale | Year: 2011

Multiferroic CoFe2O4-Pb(Zr0.52Ti 0.48)O3 core-shell nanofibers have been synthesized by coaxial electrospinning in combination with a sol-gel process. The core-shell configuration of nanofibers has been verified by scanning electron microscopy and transmission electron microscopy, and the spinel structure of CoFe 2O4 and perovskite structure of Pb(Zr 0.52Ti0.48)O3 have been confirmed by X-ray diffraction and selected area electron diffraction. The multiferroic properties of core-shell nanofibers have been demonstrated by magnetic hysteresis and piezoresponse force microscopy, and their magnetoelectric coupling has been confirmed by evolution of piezoresponse under an external magnetic field, showing magnetically induced ferroelectric domain switching and changes in switching characteristics. The lateral magnetoelectric coefficient is estimated to be 2.95 × 104 mV/cmOe, two orders of magnitude higher than multiferroic thin films of similar composition. © 2011 The Royal Society of Chemistry.

Yi Z.,Hunan Normal University | Yi Z.,Xiangtan University | Lu W.,Hong Kong Polytechnic University | Liu H.,Hunan Normal University | Zeng S.,Hunan Normal University
Nanoscale | Year: 2015

Polyacrylic acid (PAA) modified NaYF4:Gd/Yb/Er upconversion nanorods (denoted as PAA-UCNRs) are demonstrated for tri-modal upconversion (UC) optical, computed X-ray tomography (CT), and magnetic resonance imaging (MRI). The hydrophilic PAA-UCNRs were obtained from hydrophobic oleic acid (OA) capped UCNRs (denoted as OA-UCNRs) using a ligand exchange method. The as-prepared UCNRs with a hexagonal phase structure present high monodispersity. These PAA-UCNRs are successfully used as ideal probes for in vivo UC luminescence bioimaging and synergistic X-ray and UC bioimaging. Moreover, X-ray CT imaging reveals that PAA-UCNRs can act as contrast agents for improved detection of the liver and spleen. In addition, a significant signal enhancement in the liver is observed in in vivo MRI, indicating that PAA-UCNRs are ideal T1-weighted MRI agents. More importantly, in vivo long-term tracking based on these PAA-UCNRs in the live mice and the corresponding ex vivo bioimaging of isolated organs also verify the translocation of PAA-UCNRs from the liver to the spleen, and the observed intense UC signals from the feces reveal the biliary excretion mechanism of these UCNRs. These findings contribute to understanding of the translocation and potential route for excretion of PAA-UCNRs, which can provide an important guide for the diagnosis and detection of diseases based on these UCNRs. This journal is © The Royal Society of Chemistry.

Hu J.,Peking University | Huang Y.,Xiangtan University
Advances in Applied Mathematics and Mechanics | Year: 2011

In this paper, we apply an a posteriori error control theory that we develop in a very recent paper to three families of the discontinuous Galerkin methods for the Reissner-Mindlin plate problem. We derive robust a posteriori error estimators for them and prove their reliability and efficiency. © 2011 Global Science Press.

Lu Z.,Chongqing Three Gorges University | Lu Z.,Xiangtan University
Mathematical Problems in Engineering | Year: 2011

We will investigate the adaptive mixed finite element methods for parabolic optimal control problems. The state and the costate are approximated by the lowest-order Raviart-Thomas mixed finite element spaces, and the control is approximated by piecewise constant elements. We derive a posteriori error estimates of the mixed finite element solutions for optimal control problems. Such a posteriori error estimates can be used to construct more efficient and reliable adaptive mixed finite element method for the optimal control problems. Next we introduce an adaptive algorithm to guide the mesh refinement. A numerical example is given to demonstrate our theoretical results. © 2011 Zuliang Lu.

Wang J.,Guizhou University | Zhou Y.,Xiangtan University
Nonlinear Analysis: Real World Applications | Year: 2011

In this paper, we prove the existence and controllability results for fractional semilinear differential inclusions involving the Caputo derivative in Banach spaces. The results are obtained by using fractional calculation, operator semigroups and BohnenblustKarlin's fixed point theorem. At last, an example is given to illustrate the theory. © 2011 Elsevier Ltd. All rights reserved.

Wang J.,Guizhou University | Wei W.,Guizhou University | Zhou Y.,Xiangtan University
Journal of Dynamical and Control Systems | Year: 2011

This paper concerns the fractional finite time delay evolution systems and optimal controls in infinite-dimensional spaces. A suitable mild solution of the fractional finite time delay evolution systems is introduced. Using the singular version of the Gronwall inequality with finite time delay, we obtain some sufficient conditions for the existence, uniqueness and continuous dependence of mild solutions of these control systems. A formulation for the fractional Lagrange problem is introduced. The existence of optimal pairs of fractional-time-delay evolution systems is also presented. Finally, an example is given for demonstration. © 2011 Springer Science+Business Media, LLC.

Wang J.,Guizhou University | Zhou Y.,Xiangtan University
International Journal of Dynamical Systems and Differential Equations | Year: 2011

In this paper, we consider a time optimal control problem of a system governed by a class of fractional semilinear evolution equations in the sense of the Caputo fractional derivative operator. The existence and uniqueness of mild solutions is proven. Then fractional time optimal control problem of the target varying with time is formulated. The existence of fractional time optimal controls is also presented. Finally, an example is given to illustrate the effectiveness of the results obtained. © 2011 Inderscience Enterprises Ltd.

Chen Q.N.,University of Washington | Ou Y.,Xiangtan University | Ma F.,University of Washington | Li J.,University of Washington
Applied Physics Letters | Year: 2014

Electromechanical coupling is ubiquitous in nature and underpins the functionality of materials and systems as diverse as ferroelectric and multiferroic materials, electrochemical devices, and biological systems, and strain-based scanning probe microscopy (s-SPM) techniques have emerged as a powerful tool in characterizing and manipulating electromechanical coupling at the nanoscale. Uncovering underlying mechanisms of electromechanical coupling in these diverse materials and systems, however, is a difficult outstanding problem, and questions and confusions arise from recent experiment observations of electromechanical coupling and its apparent polarity switching in some unexpected materials. We propose a series of s-SPM experiments to identify different microscopic mechanisms underpinning electromechanical coupling and demonstrate their feasibility using three representative materials. By employing a combination of spectroscopic studies and different modes of s-SPM, we show that it is possible to distinguish electromechanical coupling arising from spontaneous polarization, induced dipole moment, and ionic Vegard strain, and this offers a clear guidance on using s-SPM to study a wide variety of functional materials and systems. © 2014 AIP Publishing LLC.

Huang C.,Xiangtan University | Huang C.,Shaoguan University | Ding C.,Sun Yat Sen University
Analytica Chimica Acta | Year: 2011

A novel two-photon fluorescence probe for Pb2+ derived from 4-methyl-2,5-dicyano-4′-amino stilbene as a two-photon fluorophore and bis[2-(2-aminophenylsulfanyls)ethyl]amine as a novel Pb2+ ligand was developed. The probe possesses small molecule size, large two-photon absorption cross-section (1020GM), noncytotoxic effect, long-wavelength emission at 609nm, large Stokes shift (209nm), excellent photostability, moderate water-solubility, good cell-permeability, and pH-insensitivity in the biologically relevant pH range. The probe can selectively detect Pb2+ ions in live cells and living tissues without interference from other metal ions and the membrane-bound probes, and its quenching constant (KSVTP) is 7.58×105M-1. © 2011 Elsevier B.V.

Ye H.,Xiangtan University | Ye H.,CAS Shanghai Institute of Organic Chemistry | Li W.,Xiangtan University | Li W.,CAS Shanghai Institute of Organic Chemistry
Chinese Journal of Organic Chemistry | Year: 2012

Organic solar cells (OSCs) have attracted an extensive attention due to their light-weight, low cost and flexible features. Exploitation of novel polymeric donating materials is one of the mainstreams in the field. To date, a variety of conjugated polymers with excellent electron-donating properties have been developed. Based on these materials, power conversion efficiency of OSCs has reached to 9%. This review classifies these materials based on the chemical structures of the repeating units, and summarizes their progress accordingly. A number of representative materials, which have received much attention, are highlighted from the aspects of designing strategy, properties, device fabrication and performance. It is anticipated to penetrate more deeply the basic relationships among the chemical structure-packing structure-property, which could provide valuable information for the future materials exploitation. © 2012 Chinese Chemical Society & SIOC, CAS.

Pei Y.,Xiangtan University | Zeng X.C.,University of Nebraska - Lincoln
Nanoscale | Year: 2012

Unlike bulk materials, the physicochemical properties of nano-sized metal clusters can be strongly dependent on their atomic structure and size. Over the past two decades, major progress has been made in both the synthesis and characterization of a special class of ligated metal nanoclusters, namely, the thiolate-protected gold clusters with size less than 2 nm. Nevertheless, the determination of the precise atomic structure of thiolate-protected gold clusters is still a grand challenge to both experimentalists and theorists. The lack of atomic structures for many thiolate-protected gold clusters has hampered our in-depth understanding of their physicochemical properties and size-dependent structural evolution. Recent breakthroughs in the determination of the atomic structure of two clusters, [Au 25(SCH 2CH 2Ph) 18] q (q = -1, 0) and Au 102(p- MBA) 44, from X-ray crystallography have uncovered many new characteristics regarding the gold-sulfur bonding as well as the atomic packing structure in gold thiolate nanoclusters. Knowledge obtained from the atomic structures of both thiolate-protected gold clusters allows researchers to examine a more general "inherent structure rule" underlying this special class of ligated gold nanoclusters. That is, a highly stable thiolate-protected gold cluster can be viewed as a combination of a highly symmetric Au core and several protecting gold-thiolate "staple motifs", as illustrated by a general structural formula [Au] a+a′[Au(SR) 2] b[Au 2(SR) 3] c[Au 3(SR) 4] d[Au 4(SR) 5] e where a, a′, b, c, d and e are integers that satisfy certain constraints. In this review article, we highlight recent progress in the theoretical exploration and prediction of the atomic structures of various thiolate-protected gold clusters based on the "divide-and-protect" concept in general and the "inherent structure rule" in particular. As two demonstration examples, we show that the theoretically predicted lowest-energy structures of Au 25(SR) 8 - and Au 38(SR) 24 (-R is the alkylthiolate group) have been fully confirmed by later experiments, lending credence to the "inherent structure rule". This journal is © 2012 The Royal Society of Chemistry.

Qian S.-B.,CAS National Astronomical Observatories | Qian S.-B.,Chinese Academy of Sciences | Qian S.-B.,University of Chinese Academy of Sciences | Zhu L.-Y.,CAS National Astronomical Observatories | And 8 more authors.
Astrophysical Journal Letters | Year: 2012

We report here the tentative discovery of a Jovian planet in orbit around the rapidly pulsating subdwarf B-type (sdB-type) eclipsing binary NY Vir. By using newly determined eclipse times together with those collected from the literature, we detect that the observed-calculated (O - C) curve of NY Vir shows a small-amplitude cyclic variation with a period of 7.9yr and a semiamplitude of 6.1s, while it undergoes a downward parabolic change (revealing a period decrease at a rate of ). The periodic variation was analyzed for the light-travel-time effect via the presence of a third body. The mass of the tertiary companion was determined to be M 3sin i′ = 2.3( 0.3)M Jupiter when a total mass of 0.60 M ⊙ for NY Vir is adopted. This suggests that it is most probably a giant circumbinary planet orbiting NY Vir at a distance of about 3.3 astronomical units (AU). Since the rate of period decrease cannot be explained by true angular momentum loss caused by gravitational radiation or/and magnetic braking, the observed downward parabolic change in the O - C diagram may be only a part of a long-period (longer than 15years) cyclic variation, which may reveal the presence of another Jovian planet (2.5 M Jupiter) in the system. © 2012. The American Astronomical Society. All rights reserved..

Wu M.-M.,Guangxi University | Wen L.,Guangxi University | Tang B.-Y.,Guangxi University | Tang B.-Y.,Xiangtan University | And 2 more authors.
Journal of Alloys and Compounds | Year: 2010

The structural, electronic and elastic properties of typical hexagonal-close-packed MgZn2 and ScZn2 phases in Mg-Sc-Zn alloy were investigated by means of first-principles calculations within the framework of density functional theory (DFT). The calculated lattice constants were in good agreement with the experimental values. The obtained cohesive energy and formation enthalpy of both phases are negative, showing their structural stability from energetic point of view. The five independent elastic constants were calculated, and then the bulk modulus B, shear modulus G, Young's modulus E and Poisson's ratio ν of polycrystalline aggregates were derived. The ductility and plasticity of the MgZn2 and ScZn2 phases were further discussed. The elastic anisotropy of the two phases was also analyzed. Finally, the electronic density of states (DOS) and charge density distribution were also calculated to reveal the underlying mechanism of structural stability and mechanical properties. © 2010 Elsevier B.V. All rights reserved.

Tang H.,Xiangtan University | Tang H.,Louisiana State University | Zhang D.,Louisiana State University
Journal of Polymer Science, Part A: Polymer Chemistry | Year: 2013

A series of pyrenyl-terminated poly(γ-benzyl-l-glutamate)s (py-PBLGs) with controlled polymer molecular weight (MW = 2.3-14.8 kg mol -1) and molecular weight distribution (PDI = 1.17-1.55) have been prepared from 1-pyrenemethylamine hydrochloride-mediated ring-opening polymerization (ROP) of γ-benzyl-l-glutamic acid based N-carboxyanhydride (BLG-NCA). FTIR analysis revealed that the py-PBLG9 was conformationally heterogeneous with 35.0% α-helix, 55.6% β-sheet, and 9.4% random coil conformations in the solid state, whereas the py-PBLG 66 adopts 100% α-helix conformation. Py-PBLGs promote the dispersion of SWCNTs in organic solvents and in the PBLG solid through π-π interaction, as evidenced by the Raman spectroscopic studies. WAXD analysis revealed that the SWCNTs significantly affect the ordering of the py-PBLG self-assembly: the long range hexagonal packing of py-PBLG66 rods is notably enhanced by the addition of SWCNTs, whereas the lamellar packing of py-PGLG9 β-sheets is weakened. In the hexagonal lattice, the SWCNTs are intercalated parallel to the py-PBLG66 rods, in contrast to the normal orientation of the SWCNTs with respect to the extended py-PBLG9 chains in the β-sheets. The relative packing structure also affects the intermolecular interaction among the PBLGs: SWCNTs promote the interaction among the py-PBLG9 chains packed in a lamellar structure and weaken the intermolecular interaction among the py-PBLG66 columnar hexagonal array. © 2013 Wiley Periodicals, Inc.

Zeng Y.,Central South University | Xiong X.,Central South University | Wang D.,Central South University | Wu L.,Xiangtan University
Journal of Materials Processing Technology | Year: 2014

The effects of fibre architecture, reaction temperature and holding time on the infiltration performance of carbon/carbon (C/C)-Zr-Ti-C composites prepared by liquid metal infiltration were investigated. The results indicated that samples with a chopped-web needled preform and low initial density had a high final density. Increasing the reaction temperatures resulted in a decrease of the final density of samples. Additionally, increasing the initial holding time appeared to obviously result in a high final density, but its effectiveness was not obvious in later observations. An analysis of the infiltration kinetics and mechanisms indicated that the diffusivity of carbon in the carbide, the open-pore sizes and their distribution in C/C composites were the essential characteristics that controlled the height of infiltrating melts. © 2014 Elsevier B.V.

Chen Q.N.,University of Washington | Ma F.,University of Washington | Xie S.,Xiangtan University | Liu Y.,University of Washington | And 2 more authors.
Nanoscale | Year: 2013

Accurate scanning probing of magnetic materials at the nanoscale is essential for developing and characterizing magnetic nanostructures, yet quantitative analysis is difficult using the state of the art magnetic force microscopy, and has limited spatial resolution and sensitivity. In this communication, we develop a novel piezomagnetic force microscopy (PmFM) technique, with the imaging principle based on the detection of magnetostrictive response excited by an external magnetic field. In combination with the dual AC resonance tracking (DART) technique, the contact stiffness and energy dissipation of the samples can be simultaneously mapped along with the PmFM phase and amplitude, enabling quantitative probing of magnetic materials and structures at the nanoscale with high sensitivity and spatial resolution. PmFM has been applied to probe magnetic soft discs and cobalt ferrite thin films, demonstrating it as a powerful tool for a wide range of magnetic materials. © 2013 The Royal Society of Chemistry.

Wang J.,Guizhou University | Zhou Y.,Xiangtan University
Nonlinear Analysis: Real World Applications | Year: 2011

This paper concerns the existence of mild solutions for semilinear fractional evolution equations and optimal controls in the α-norm. A suitable α-mild solution of the semilinear fractional evolution equations is introduced. The existence and uniqueness of α-mild solutions are proved by means of fractional calculus, singular version Gronwall inequality and LeraySchauder fixed point theorem. The existence of optimal pairs of system governed by fractional evolution equations is also presented. Finally, an example is given for demonstration. © 2010 Published by Elsevier Ltd. All rights reserved.

Li M.,Brunel University | Yang S.,De Montfort University | Zheng J.,Xiangtan University | Liu X.,Brunel University
Evolutionary Computation | Year: 2014

The Euclideanminimum spanning tree (EMST), widely used in a variety of domains, is aminimum spanning tree of a set of points in spacewhere the edge weight between each pair of points is their Euclidean distance. Since the generation of an EMST is entirely determined by the Euclidean distance between solutions (points), the properties of EMSTs have a close relation with the distribution and position information of solutions. This paper explores the properties of EMSTs and proposes an EMST-based evolutionary algorithm (ETEA) to solve multi-objective optimization problems (MOPs). Unlike most EMO algorithms that focus on the Pareto dominance relation, the proposed algorithm mainly considers distance-based measures to evaluate and compare individuals during the evolutionary search. Specifically, in ETEA, four strategies are introduced: (1) An EMST-based crowding distance (ETCD) is presented to estimate the density of individuals in the population; (2)Adistance comparison approach incorporating ETCD is used to assign the fitness value for individuals; (3) A fitness adjustment technique is designed to avoid the partial overcrowding in environmental selection; (4) Three diversity indicators-the minimum edge, degree, and ETCD-with regard to EMSTs are applied to determine the survival of individuals in archive truncation. From a series of extensive experiments on 32 test instances with different characteristics, ETEA is found to be competitive against five state-of-the-art algorithms and its predecessor in providing a good balance among convergence, uniformity, and spread. © 2014 by the Massachusetts Institute of Technology.

Ma K.L.,Nanjing University of Aeronautics and Astronautics | Yan X.H.,Nanjing University of Aeronautics and Astronautics | Xiao Y.,Nanjing University of Aeronautics and Astronautics | Chen Y.P.,Xiangtan University
Solid State Communications | Year: 2010

We studied theoretically the electronic transport of metallic graphene nanoribbons (GNRs) with two vacancies using the tight-binding model and Green's function method. The results show that the conductance of zigzag GNR (ZGNR) varies with the relative position of two vacancies. However, when two vacancies reside on the edges, the conductance remain unchanged compared to that of perfect GNRs due to the interaction between vacancy state and edge state. Moreover, the conductance at the Fermi level for armchair GNR (AGNR) can be zero or finite depending on the position of vacancies on the GNRs. The demonstrated features of electronic transport open extremely attractive perspectives for designing well-defined GNR-based nanoelectronic devices. © 2010 Elsevier Ltd. All rights reserved.

Yang D.,CAS Dalian Institute of Chemical Physics | Yang D.,University of Chinese Academy of Sciences | Zhou L.,CAS Dalian Institute of Chemical Physics | Zhou L.,University of Chinese Academy of Sciences | And 4 more authors.
Chemical Communications | Year: 2012

We demonstrate O 2 plasma treated graphene oxides with a work function of 5.2 eV as a high performance hole transport layer in organic solar cells. The high transparency and high work function simultaneously increase short circuit current, threshold voltage and fill factor, resulting in a 30% increase in cell efficiency. © 2012 The Royal Society of Chemistry.

Liu W.,Xiangtan University | Liu W.,Hunan University of Science and Technology | Cao C.,Hunan University of Science and Technology
Huagong Xuebao/CIESC Journal | Year: 2012

The descriptors of polarizability effect index (PEI), the number of effective carbon(NC,eff), the differences in PEI and NC,eff between the branching chain and straight chain isomers, δPEI and δNC,eff, are derived from molecular structure. The quantitative structure-property relationships (QSPRs) between these descriptors and boiling points of 520 aliphatic alcohols, ethers, aldehydes, ketones, acids, and esters were obtained separately. The QSPRs between these descriptors and boiling points were developed for 520 aliphatic oxygen-containing organic compounds by best subsets regression method. For the training set, the correlation coefficient R2 is 0.9946 and the standard deviation (s) is 6.70 K. For the test set, R2 is 0.9857 and s is 6.10 K. The average relative error is 1.19%. According to the regression equation, the influences of the number of effective carbon of alkyl, the role of functional groups and their interaction on the boiling point were analyzed. These results showed a good correlation between the boiling points of organic compounds and these descriptors derived from PEI for aliphatic alcohols, ethers, aldehydes, ketones, acids, and esters. © All Rights Reserved.

Wang Y.-F.,Queensland University of Technology | Yu Z.-G.,Queensland University of Technology | Yu Z.-G.,Xiangtan University | Anh V.,Queensland University of Technology
International Journal of Data Mining and Bioinformatics | Year: 2013

Microarray techniques have revolutionised genomic research by making it possible to monitor the expression of thousands of genes in parallel. The Fuzzy C-Means (FCM) method is an efficient clustering approach devised for microarray data analysis. However, microarray data contains noise, which would affect clustering results. In this paper, we propose to combine the FCM method with the Empirical Mode Decomposition (EMD) for clustering microarray data to reduce the effect of the noise. The results suggest the clustering structures of denoised microarray data are more reasonable and genes have tighter association with their clusters than those using FCM only. Copyright © 2013 Inderscience Enterprises Ltd.

Yang S.,De Montfort University | Li M.,Brunel University | Liu X.,Brunel University | Zheng J.,Xiangtan University
IEEE Transactions on Evolutionary Computation | Year: 2013

Balancing convergence and diversity plays a key role in evolutionary multiobjective optimization (EMO). Most current EMO algorithms perform well on problems with two or three objectives, but encounter difficulties in their scalability to many-objective optimization. This paper proposes a grid-based evolutionary algorithm (GrEA) to solve many-objective optimization problems. Our aim is to exploit the potential of the grid-based approach to strengthen the selection pressure toward the optimal direction while maintaining an extensive and uniform distribution among solutions. To this end, two concepts - grid dominance and grid difference - are introduced to determine the mutual relationship of individuals in a grid environment. Three grid-based criteria, i.e., grid ranking, grid crowding distance, and grid coordinate point distance, are incorporated into the fitness of individuals to distinguish them in both the mating and environmental selection processes. Moreover, a fitness adjustment strategy is developed by adaptively punishing individuals based on the neighborhood and grid dominance relations in order to avoid partial overcrowding as well as guide the search toward different directions in the archive. Six state-of-the-art EMO algorithms are selected as the peer algorithms to validate GrEA. A series of extensive experiments is conducted on 52 instances of nine test problems taken from three test suites. The experimental results show the effectiveness and competitiveness of the proposed GrEA in balancing convergence and diversity. The solution set obtained by GrEA can achieve a better coverage of the Pareto front than that obtained by other algorithms on most of the tested problems. Additionally, a parametric study reveals interesting insights of the division parameter in a grid and also indicates useful values for problems with different characteristics. © 1997-2012 IEEE.

Yang S.,Xiangtan University | Ma F.,Wuhan University | Song Y.,Wuhan University | Qiu J.,Wuhan University
Scientometrics | Year: 2010

Over the past 30 years, the research behavior of Chinese scholars has continually evolved. This paper studied the citing behavior of Chinese scholars by employing three indicators of citation concentration from the perspective of citation breadth analysis. All the citations from 2,338,033 papers from the Chinese Citation Database (1979-2008) covering four disciplines-Chemistry; Clinical Medicine; Library, Information and Archival Science; and Chinese Literature and World Literature-were analyzed. Empirical results show a general weakening tendency towards citation concentration: (1) decreasing percentage of uncited published papers within a given year; (2) a higher percentage of papers required to account for the same proportion of citation than before; and (3) the steady decline in the Herfindahl-Hirschman index (HHI) of citation distribution. All three measures indicate a decline in citing concentration or an increase in citation breadth. This phenomenon may be the result of increased access to materials, perhaps because of the ease with which scholarly materials can be accessed through the Internet. © 2010 Akadémiai Kiadó, Budapest, Hungary.

Wang J.,Guizhou University | Zhou Y.,Xiangtan University | Wei W.,Guizhou University
Systems and Control Letters | Year: 2012

In this paper, we study optimal feedback controls of a system governed by semilinear fractional evolution equations via a compact semigroup in Banach spaces. By using the Cesari property, the Fillippove theorem and extending the earlier work on fractional evolution equations, we prove the existence of feasible pairs. An existence result of optimal control pairs for the Lagrange problem is presented. © 2012 Elsevier B.V. All rights reserved.

Li Y.-F.,Xiangtan University
Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy | Year: 2010

The design and synthesis of meso-tetra(p-methoxylpheny1)porphyrin (T(p-OCH3)PPH2) and its application in fluorescent detections of Ag(I) in aqueous solution are reported. The fluorescence quenching of T(p-OCH3)PPH2 is attributed to the formation of a complex between T(p-OCH3)PPH2 and Ag(I) by 1:1 complex ratio (K = 3.7 × 105), which has been utilized as the basis of the fabrication of the Ag(I)-sensitive fluorescent chemosensor. The analytical performance characteristics of the proposed Ag(I)-sensitive chemosensor were investigated. The chemosensor can be applied to the quantification of Ag(I) with a linear range covering from 1.0 × 10-7 to 5.0 × 10-5 M with a detection limit of 2.5 × 10-8 M. The experiment results show that the response behavior of T(p-OCH3)PPH2 towards Ag(I) is pH independent in medium condition(pH 4.0-8.0). Most importantly, the fluorescence changes of the chemosensor are remarkably specific for Ag(I) in the presence of other heavy and transition metal ions (even those that exist in high concentration), which meet the selective requirements for practical application. The proposed chemosensor has been used for direct measurement of Ag(I) content in river water samples with satisfying results, which further demonstrates its value of practical applications in environmental systems. © 2010 Elsevier B.V. All rights reserved.

Liu Y.Y.,Xiangtan University | Li J.Y.,University of Washington
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

We report new insights on morphotropic phase boundary (MPB) learnt from the nonlinear thermodynamics analysis of epitaxial ferroelectric films, including (1) MPB can be induced in an otherwise tetragonal ferroelectric system under a wide range of misfit shears; (2) the coexistence of tetragonal and rhombohedral phases at MPB does not necessarily lead to superior electromechanical coupling; and (3) the discontinuity in polarization across MPB is essential for the enhanced piezoelectricity. These insights point to alternative pathways to strain engineered MPB and superior electromechanical coupling that are not readily realized otherwise. © 2011 American Physical Society.

Deng J.,Xiangtan University | Deng Z.,Port Machinery BU of Sany Group Co. Changsha
Neurocomputing | Year: 2016

In this paper, applying the fixed point theorem and a new method, we study the existence, uniqueness, and global exponential stability of solutions of NNs with continuously distributed delays and obtain some new results in terms of system parameters. In our results, the exponentially convergent rate is given and the conditions are less restrictive than previously known criteria. Therefore they can be applied to NNs with a broad range of activation functions though these functions are neither differentiability nor strict monotonicity. © 2015 Elsevier B.V.

Tang K.,Hunan Institute of Science and Technology | Fu T.,Xiangtan University | Zhang P.,Hunan Institute of Science and Technology
Process Biochemistry | Year: 2012

Enantioselective liquid-liquid extraction of homophenylalanine (Hph) enantiomers was investigated with metal-BINAP complexes as enantioselective extractants. The metal complexes were synthesized by the complexation of (s)-2,2′-Bis(diphenylphosphino)-1,1′-binaphthalene (BINAP) with different central ions, among which, copper(I) complex allowed the separation of the Hph enantiomers with the highest operational selectivity. Efficiency of the extraction depends, often strongly, on a number of process variables, including types of organic solvents, pH of the aqueous phase, concentration of host and substrate, and temperature. In order to better understand the extraction process, equilibrium of the system were modeled by a homogeneous reaction model and an interfacial reaction model, respectively. Important parameters required by the modeling, such as complexation equilibrium constant and physical distribution coefficients were determined experimentally. When coupled with the parameters, extraction performance can be predicted by the models. Comparison between the experimental values and the model predictions indicates that the homogeneous reaction model can predict more accurately. By modeling and experiment, an optimal extraction condition concerning pH of 8 and host concentration of 2 mmol/L was obtained with high enantioselective (α) of 1.837 and performance factor (pf) of 0.086. © 2012 Elsevier Ltd.

Zheng W.-T.,Jilin University | Sun C.Q.,Nanyang Technological University | Sun C.Q.,Xiangtan University
Energy and Environmental Science | Year: 2011

As a new class of materials, carbon nanotubes (CNTs) and graphene nanoribbons (GNRs) have been continuing fascinating the community with properties that can be seen from neither bulk graphite nor diamond. Although the physics and chemistry of these carbon allotropes have been intensively investigated from various perspectives, the laws governing the fascinations and their interdependence remain as yet undetermined. From the perspectives of bond and nonbond formation, dissociation, relaxation, vibration, and the associated energetics and dynamics of charge repopulation, polarization, densification, and localization, this article aims to show that the broken-bond-induced local bond contraction and bond strength gain, quantum entrapment and densification of charge and energy, polarization of the unpaired edge dangling σ-bond electrons, and the formation of the pseudo-π-bond between the dangling σ-bond electrons along the edges are responsible for the anomalies. Theoretical reproduction of the experimentally observed elastic modulus enhancement, melting point depression, layer-number, strain, pressure and temperature induced Raman shift, C 1s core-level positive shift, work function reduction, band gap expansion, edge and defect selective generation of the Dirac-Fermi polarons and the associated magnetism consistently confirmed that the shorter and stronger bonds between undercoordinated carbon atoms modulate locally the atomic cohesive energy, the Hamiltonian, and hence the detectable bulk properties. The polarization of the unpaired dangling σ-bond electrons by the densely, deeply, and locally entrapped core and bonding electrons generates the massless, magnetic and mobile Dirac-Fermi polarons at sites surrounding vacancies and zigzag-GNR edges. The pseudo-π-bond formation between the nearest dangling σ-bond electrons along the armchair-GNR and the reconstructed zigzag-GNR edges discriminates them from the zigzag-GNR edges or vacancies in the electronic and magnetic properties. Consistency between predictions and observations confirmed that the C-C bond contracts by up to 30% with a 152% bond strength gain at the edges with respect to those in the bulk diamond. © 2011 The Royal Society of Chemistry.

Sun Z.,Sun Yat Sen University | Zhang C.,Sun Yat Sen University | Wang B.,Guangdong University of Technology | Li Q.,Xiangtan University | Long D.,Sun Yat Sen University
Quantum Information Processing | Year: 2013

Recently, Liu et al. (Quantum Inf Process 12: 1797-1805, 2013) proposed a secure multiparty quantum key agreement (MQKA) protocol with single particles. Their protocol allows N parties to negotiate a secret session key in such away that (1) outside eavesdroppers cannot gain the session key without introducing any errors; (2) the session key cannot be determined by any non-trivial subset of the participants. However, the particle efficiency of their protocol is only 1/k+1)N(N-1). In this paper, we show that the efficiency of the MQKA protocol can be improved to 1/N(k+1) by introducing two additional unitary operations. Since, in some scenarios, the secret keys are confidential, neither party is willing to divulge any of the contents to the other. Therefore, in our protocol, no participant can learn anything more than its prescribed output, i.e., the secret keys of the participants can be kept secret during the protocol instead of being exposed to others, thus, the privacy of the protocol is also improved. Furthermore, we explicitly show the scheme is secure. © 2013 Springer Science+Business Media New York.

Zhao W.,U.S. Food and Drug Administration | Zhao W.,Xiangtan University | Zou W.,U.S. Food and Drug Administration | Chen J.J.,U.S. Food and Drug Administration
BMC Bioinformatics | Year: 2014

Background: The big data moniker is nowhere better deserved than to describe the ever-increasing prodigiousness and complexity of biological and medical datasets. New methods are needed to generate and test hypotheses, foster biological interpretation, and build validated predictors. Although multivariate techniques such as cluster analysis may allow researchers to identify groups, or clusters, of related variables, the accuracies and effectiveness of traditional clustering methods diminish for large and hyper dimensional datasets. Topic modeling is an active research field in machine learning and has been mainly used as an analytical tool to structure large textual corpora for data mining. Its ability to reduce high dimensionality to a small number of latent variables makes it suitable as a means for clustering or overcoming clustering difficulties in large biological and medical datasets. Results: In this study, three topic model-derived clustering methods, highest probable topic assignment, feature selection and feature extraction, are proposed and tested on the cluster analysis of three large datasets: Salmonella pulsed-field gel electrophoresis (PFGE) dataset, lung cancer dataset, and breast cancer dataset, which represent various types of large biological or medical datasets. All three various methods are shown to improve the efficacy/effectiveness of clustering results on the three datasets in comparison to traditional methods. A preferable cluster analysis method emerged for each of the three datasets on the basis of replicating known biological truths. Conclusion: Topic modeling could be advantageously applied to the large datasets of biological or medical research. The three proposed topic model-derived clustering methods, highest probable topic assignment, feature selection and feature extraction, yield clustering improvements for the three different data types. Clusters more efficaciously represent truthful groupings and subgroupings in the data than traditional methods, suggesting that topic model-based methods could provide an analytic advancement in the analysis of large biological or medical datasets. © 2014 Zhao et al.; licensee BioMed Central Ltd.

Chen Y.,South China Normal University | Lu Z.,Xiangtan University
Computer Methods in Applied Mechanics and Engineering | Year: 2010

In this paper we study the fully discrete mixed finite element methods for quadratic convex optimal control problem governed by semilinear parabolic equations. The space discretization of the state variable is done using usual mixed finite elements, whereas the time discretization is based on difference methods. The state and the co-state are approximated by the lowest order Raviart-Thomas mixed finite element spaces and the control is approximated by piecewise constant elements. By applying some error estimates techniques of mixed finite element methods, we derive a priori error estimates both for the coupled state and the control approximation. Finally, we present a numerical example which confirms our theoretical results. © 2009.

Yu Z.-G.,Queensland University of Technology | Yu Z.-G.,Xiangtan University | Anh V.,Queensland University of Technology | Anh V.,University of Central Florida | And 3 more authors.
Journal of Geophysical Research: Space Physics | Year: 2010

In this paper, we investigate the characteristics and develop a stochastic model for the horizontal component Bx of the magnetic field at 22 stations of the global near-real-time magnetic observatory network INTERMAGNET. The model is in the form of a fractional stochastic differential equation. A method to estimate the parameters on the basis of observed data and to simulate the data using the model is given. The degree of fractional differentiation and the alpha-stability exponent of the process are employed to cluster the stations. The Bx time series possess pronounced local trends, which must be removed before modeling and simulation can be performed. This trend removal is carried out by an empirical mode decomposition. An outcome is an efficient method to simulate the Bx time series by empirical mode decomposition and fractional stochastic differential equation. The numerical results indicate the existence of two distinct clusters of the INTERMAGNET: one in the mid- and low latitudes consistent with the Dst index, and the other above geomagnetic latitude 60°N consistent with the AE index. This clustering corresponds to the inner magnetosphere and the outer magnetosphere, respectively. Copyright 2010 by the American Geophysical Union.

Wang D.,Northwest University, China | Xiao A.,Xiangtan University
Nonlinear Dynamics | Year: 2015

This paper concerns the dissipativity and contractivity of the Caputo fractional initial value problems. We prove that the systems have an absorbing set under the same assumptions as the classic integer-order systems. This directly extends the dissipativity from integer-order systems to the Caputo fractional-order ones. The fractional dissipativity conditions can be satisfied by many fractional chaotic systems and the systems from the spatial discretization of some time-fractional partial differential equations. The fractional-order systems satisfying the so-called one-sided Lipschitz condition are also considered in a similar way, and the contractivity property of their solutions is proved. Two numerical examples are provided to illustrate the theoretical results. © 2014, Springer Science+Business Media Dordrecht.

Yu X.,Hunan Institute of Engineering | Yi B.,Hunan Institute of Engineering | Wang X.,Xiangtan University | Chen J.,Hunan Institute of Engineering
Atmospheric Environment | Year: 2012

The reaction rate constants of ozone with organic compounds in the atmosphere were predicted by a quantitative structure-activity relationship (QSAR) model. Density functional theory (DFT) calculations, for the first time, were carried out on the radicals from organic compounds, at the UB3LYP level of theory with 6-31G(d) basis set. A set of quantum chemical descriptors calculated from the radicals, the energy of the highest occupied molecular orbital of beta spin states (E βHOMO), the molecular average polarizability (α), and the total energy (E T), were used to build the general QSAR model for aliphatic compounds, applying the genetic algorithm (GA) technique and support vector machine (SVM) regression. The root mean square errors (RMSE) are 0.680 for the training set (68 compounds), 0.777 for the validation set (36 compounds) and 0.709 for the test set (35 compounds). Investigated results indicate that the SVM model given here has good predictivity for aliphatic compounds. © 2012 Elsevier Ltd.

Pollmann J.,University of Munster | Peng X.,University of Munster | Peng X.,Xiangtan University | Wieferink J.,University of Munster | Kruger P.,University of Munster
Surface Science Reports | Year: 2014

Adsorption of hydrogen and hydrocarbon molecules on semiconductor surfaces plays a key role in surface science and technology. Most studies have employed silicon (Si) as a substrate because of its paramount technological importance and scientific interest. However, other semiconductor substrates are gaining an increasing interest as well. Silicon carbide (SiC), which is a material with very special properties allowing developments of novel devices and applications, offers particularly fascinating new degrees of freedom for exceptional adsorption behaviour. For example, a very unusual hydrogen-induced metallization of a SiC(001) surface has been reported and hydrogen molecules show very different adsorption behaviour on different SiC(001) reconstructions although the latter exhibit very similar surface dimers. In marked contrast to the Si(001) surface, the adsorption of hydrocarbon molecules on SiC(001) can yield structurally well-defined adlayers in favourable cases which may have large potential for organic functionalization. We review and discuss theoretical ab initio results on conceivable adsorption scenarios of atomic and molecular hydrogen as well as acetylene, ethylene, butadiene, benzene and cyclohexadiene on various reconstructions of the SiC(001) surface. The main emphasize is on a detailed understanding of these adsorption systems and on identifying the physical origin of the particular adsorption behaviour. The results will be discussed in the light of related adsorption events on the Si(001) surface and in comparison with available experimental data. © 2014 Elsevier B.V.

Zhou N.,Central South University | Wang X.,Central South University | Chen Z.,Central South University | Wang Z.,Central South University | Wang Z.,Xiangtan University
Energy | Year: 2013

An experimental system for heat recovery from low-temperature flue gas based on Organic Rankine Cycle (ORC) was constructed. In the system, R123 was selected as working fluid, a scroll expander was used to produce work, and fin tubes heat exchanger was designed as evaporator. Low-temperature flue gas produced by an liquefied petroleum gas (LPG) stove was used as the heat source to simulate industrial flue gas, and its temperature can be controlled in the range of 90-220°C. Relationships between output performance of the system and the evaporating pressure, temperature of the heat source as well as the superheat degree of the working fluid were investigated. The results show that the cycle efficiency, the output power of the expander and its exergetic efficiency increase whilst the heat recovery efficiency decreases with the increment of the evaporating pressure at a certain temperature of the heat source. The influence of the superheat degree of the working fluid on the system output parameters is slight. Under the present experimental conditions, the maximum output power of the expander is 645W, and the cycle efficiency and the heat recovery efficiency are 8.5% and 22%, respectively. © 2013 Elsevier Ltd.

Chen Y.,Guangxi University of Technology | Huang S.,Xiangtan University | Tang Z.,Guangxi University of Technology | Tang Z.,CAS Shanghai Institute of Applied Physics | And 3 more authors.
Carbohydrate Polymers | Year: 2011

The structural changes of cassava starch granules were studied by scanning electron microscope (SEM), X-ray diffraction (XRD), and differential scanning calorimeter after starch granules were hydrolyzed by a mixture of α-amylase and glucoamylase. The surface of starch granules was porous after hydrolysis treatment. Enzymatic erosion occurred mainly at the surface for cassava starch. The BET-specific surface area of hydrolyzed cassava starch improved 10.7 times compared with that of native starch. The powder XRD intensity of hydrolyzed starch was higher than that of native starch. The crystallinity in the hydrolyzed cassava starch increased due to hydrolysis. Compound enzymes could hydrolyze cassava starch granules at sub-gelatinization temperature, and could produce porous starch. © 2011 Published by Elsevier Ltd. All rights reserved.

Xue D.,CAS Changchun Institute of Applied Chemistry | Xue D.,Dalian University of Technology | Li K.,Dalian University of Technology | Liu J.,Xiangtan University | And 4 more authors.
Materials Research Bulletin | Year: 2012

In this article, we briefly summarized our recent work on the studies of crystallization and functionality of inorganic materials. On the basis of the chemical bonding theory of single crystal growth, we can quantitatively simulate Cu 2O crystallization processes in solution system. We also kinetically controlled Cu 2O crystallization process in the reduction solution route. Lithium ion battery and supercapacitor performances of some oxides such as Co 3O 4 and MnO 2 were shown to elucidate the important effect of crystallization on functionality of inorganic materials. This work encourages us to create novel functionalities through the study of crystallization of inorganic materials, which warrants more chances in the field of functional materials. © 2012 Elsevier Ltd. All rights reserved.

Li Y.,Sun Yat Sen University | Zhang Q.,Sun Yat Sen University | Zhu J.,Sun Yat Sen University | Wei X.-L.,Xiangtan University | Shen P.K.,Sun Yat Sen University
Journal of Materials Chemistry A | Year: 2014

A rational design of MnO2/3D porous graphene-like (PG) (denoted as 3D PG-Mn) composites and their fabrication via a simple and cost-effective redox process have been achieved for the first time. The 3D PG can provide a highly conductive structure in conjunction with a large surface area to support good contact between the MnO2 nanoparticles and effectively enhance the mechanical strength of the composite during volume changes as well as suppress the aggregation of MnO2 nanoparticles during Li ion insertion/extraction. As a result, the 3D PG-Mn composite with a content of 62.7 wt% MnO2 shows a highly stable capacity of up to 836 mA h g -1 after 200 cycles at a current density of 100 mA g-1 and reversible high rate charge-discharge performance. Such a highly stable 3D PG-Mn composite can be produced on a large-scale and might have even wider applications as an anode material in lithium-ion batteries. © 2014 The Royal Society of Chemistry.

Yuquan X.,Xiangtan University
Mathematical Methods in the Applied Sciences | Year: 2012

In this paper, we consider a relation between two-parameter and one-parameter transition functions for Markov processes and obtain a very useful result to be regarded as relation theorem. Copyright © 2012 John Wiley & Sons, Ltd.

Mu B.,Georgia Institute of Technology | Li F.,Xiangtan University | Huang Y.,Georgia Institute of Technology | Walton K.S.,Georgia Institute of Technology
Journal of Materials Chemistry | Year: 2012

This work reports a new three-dimensional flexible lanthanide metal-organic framework [La(BTB)(H2O)·3DMF]n (BTB = 1,3,5-tris(4-carboxyphenyl) benzene) that possesses a rare chiral space group (P6522), very high thermal stability (560 °C), and high surface area (1014 m2 g-1). This new MOF demonstrates a large adsorption hysteresis loop on the N2 isotherm at 77 K after activation at 300 °C. Powder X-ray thermodiffraction experiments reveal that structural transformation occurs upon removal of guest molecules. The as-synthesized material is the "open" form, while the activated sample is "closed". Adsorption isotherms of CO2 exhibit a dramatic step near a relative pressure of 0.3, which is similar to the location of the step in the N2 isotherm at 77 K. Upon desorption, the material transforms to the closed form near a reduced pressure of 0.15, where it collapses back to the adsorption isotherm. Adsorption kinetic studies show that equilibrium is reached more slowly during the opening/closing steps compared to adsorption loadings measured on the static portion of the isotherm. © 2012 The Royal Society of Chemistry.

Jiao F.,Guangzhou University | Zhou Y.,Xiangtan University
International Journal of Bifurcation and Chaos | Year: 2012

In this paper, by the critical point theory, the boundary value problem is discussed for a fractional differential equation containing the left and right fractional derivative operators, and various criteria on the existence of solutions are obtained. To the authors' knowledge, this is the first time, the existence of solutions to the fractional boundary value problem is dealt with by using critical point theory. © 2012 World Scientific Publishing Company.

Fan Y.,Nanyang Technological University | Huang K.,Xiangtan University | Zhang Q.,Nanyang Technological University | Xiao Q.,Nanyang Technological University | And 2 more authors.
Journal of Materials Chemistry | Year: 2012

We report on a high performance silicon anode based on silicon-nickel cone arrays. The composite electrode exhibits good capacity retention and remarkable rate performance. A de-lithiation capacity of 2639, 2341, 2042, 1806, 1693, 1523 and 1308 mA h g-1 is retained at 0.2, 0.5, 1, 2, 3, 4 and 5 C, respectively. This journal is © 2012 The Royal Society of Chemistry.

Wu M.,University of Nebraska - Lincoln | Pei Y.,Xiangtan University | Zeng X.C.,University of Nebraska - Lincoln
Chemical Physics Letters | Year: 2013

We present ab initio calculation evidence of a hitherto unreported one-dimensional nanostructure, where both planar tetracoordinate carbon (ptC) strips and planar tetracoordinate silicon (ptSi) strips can coexist. The host nanostructure for ptC and ptSi strips is the SiC zigzag nanoribbons (SCNRs) whose edges are decorated by transition metal atoms. © 2013 Published by Elsevier B.V.

Lu S.B.,University of Science and Technology of China | Miao L.L.,Hunan University | Guo Z.N.,University of Science and Technology of China | Qi X.,Xiangtan University | And 6 more authors.
Optics Express | Year: 2015

Black phosphorous (BP), the most thermodynamically stable allotrope of phosphorus, is a high-mobility layered semiconductor with direct band-gap determined by the number of layers from 0.3 eV (bulk) to 2.0 eV (single layer). Therefore, BP is considered as a natural candidate for broadband optical applications, particularly in the infrared (IR) and mid-IR part of the spectrum. The strong light-matter interaction, narrow direct band-gap, and wide range of tunable optical response make BP as a promising nonlinear optical material, particularly with great potentials for infrared and mid-infrared opto-electronics. Herein, we experimentally verified its broadband and enhanced saturable absorption of multi-layer BP (with a thickness of ∼10 nm) by wide-band Z-scan measurement technique, and anticipated that multi-layer BPs could be developed as another new type of two-dimensional saturable absorber with operation bandwidth ranging from the visible (400 nm) towards mid-IR (at least 1930 nm). Our results might suggest that ultra-thin multi-layer BP films could be potentially developed as broadband ultra-fast photonics devices, such as passive Q-switcher, mode-locker, optical switcher etc. © 2015 Optical Society of America.

Li Q.,University of Southampton | Luo K.H.,University of Southampton | Luo K.H.,Tsinghua University | Li X.J.,Xiangtan University
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2012

In this paper, we aim to address several important issues about the recently developed lattice Boltzmann (LB) model for relativistic hydrodynamics. First, we study the conservation law of the particle number in the relativistic LB model. Through the Chapman-Enskog analysis, it is shown that in the relativistic LB model the conservation equation of the particle number is a convection-diffusion equation rather than a continuity equation, which makes the evolution of the particle number dependent on the relaxation time. Furthermore, we investigate the origin of the discontinuities that appeared in the relativistic problems with high viscosities, which were reported in a recent study. A multiple-relaxation-time relativistic LB model is presented to examine the influences of different relaxation times on the discontinuities. Numerical experiments show the discontinuities can be eliminated by setting the relaxation time τ e (related to the bulk viscosity) to be sufficiently smaller than the relaxation time τ ν (related to the shear viscosity). Meanwhile, it is found that the relaxation time τ ε, which has no effect on the conservation equations at the Navier-Stokes level, will affect the numerical accuracy of the relativistic LB model. Moreover, the accuracy of the relativistic LB model for simulating moderately relativistic problems is also investigated. © 2012 American Physical Society.

Chen Y.,South China Normal University | Huang Y.,Xiangtan University | Liu W.,University of Kent | Yan N.,CAS Academy of Mathematics and Systems Science
Journal of Scientific Computing | Year: 2010

In this paper, we investigate the discretization of general convex optimal control problem using the mixed finite element method. The state and co-state are discretized by the lowest order Raviart-Thomas element and the control is approximated by piecewise constant functions. We derive error estimates for both the control and the state approximation. Moreover, we present the superconvergence analysis for mixed finite element approximation of the optimal control problem. Finally, some numerical examples are given to demonstrate the practical side of the theoretical results about superconvergence. © 2009 Springer Science+Business Media, LLC.

Li Z.,Xiangtan University | Chen W.,Brookhaven National Laboratory
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment | Year: 2014

A novel on-chip, customer-design spiral biasing adaptor (SBA) has been developed. A single SBA is used for biasing a Si drift detector (SDD) and SDD array. The use of an SBA reduces the biasing current. This paper shows the calculation of the geometry of an SBA and an SDD to get the best drift field in the SDD and SDD array. Prototype SBAs have been fabricated to verify the concept. Electrical measurements on these SBAs are in agreement with the expectations. The new SDD array with an SBA can be used for X-ray detection and in nuclear physics experiments. © 2014 Elsevier B.V.

Liu S.,SUNY College of Environmental Science and Forestry | Liu S.,South China University of Technology | Lu H.,University of Sichuan | Hu R.,SUNY College of Environmental Science and Forestry | And 4 more authors.
Biotechnology Advances | Year: 2012

Woody biomass is renewable only if sustainable production is imposed. An optimum and sustainable biomass stand production rate is found to be one with the incremental growth rate at harvest equal to the average overall growth rate. Utilization of woody biomass leads to a sustainable economy. Woody biomass is comprised of at least four components: extractives, hemicellulose, lignin and cellulose. While extractives and hemicellulose are least resistant to chemical and thermal degradation, cellulose is most resistant to chemical, thermal, and biological attack. The difference or heterogeneity in reactivity leads to the recalcitrance of woody biomass at conversion. A selection of processes is presented together as a biorefinery based on incremental sequential deconstruction, fractionation/conversion of woody biomass to achieve efficient separation of major components. A preference is given to a biorefinery absent of pretreatment and detoxification process that produce waste byproducts. While numerous biorefinery approaches are known, a focused review on the integrated studies of water-based biorefinery processes is presented. Hot-water extraction is the first process step to extract value from woody biomass while improving the quality of the remaining solid material. This first step removes extractives and hemicellulose fractions from woody biomass. While extractives and hemicellulose are largely removed in the extraction liquor, cellulose and lignin largely remain in the residual woody structure. Xylo-oligomers, aromatics and acetic acid in the hardwood extract are the major components having the greatest potential value for development. Higher temperature and longer residence time lead to higher mass removal. While high temperature (> 200 °C) can lead to nearly total dissolution, the amount of sugars present in the extraction liquor decreases rapidly with temperature. Dilute acid hydrolysis of concentrated wood extracts renders the wood extract with monomeric sugars. At higher acid concentration and higher temperature the hydrolysis produced more xylose monomers in a comparatively shorter period of reaction time. Xylose is the most abundant monomeric sugar in the hydrolysate. The other comparatively small amounts of monomeric sugars include arabinose, glucose, rhamnose, mannose and galactose. Acetic acid, formic acid, furfural, HMF and other byproducts are inevitably generated during the acid hydrolysis process. Short reaction time is preferred for the hydrolysis of hot-water wood extracts. Acid hydrolysis presents a perfect opportunity for the removal or separation of aromatic materials from the wood extract/hydrolysate. The hot-water wood extract hydrolysate, after solid-removal, can be purified by Nano-membrane filtration to yield a fermentable sugar stream. Fermentation products such as ethanol can be produced from the sugar stream without a detoxification step. © 2012 Elsevier Inc.

An T.,Chinese Academy of Sciences | Baan W.A.,Chinese Academy of Sciences | Wang J.-Y.,Guilin University of Electronic Technology | Wang J.-Y.,Xiangtan University | And 2 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

Time series analysis techniques, Lomb-Scargle periodogram and weighted wavelet Z-transform, have been employed to search for year-time-scale periodicities fromthe radio light curves of a typical blazar NRAO 530. The periodicity analysis using the two methods show consistent results: two strong and persistent periods of ̃10 and ̃6 yr are prominent at all three wavelengths; three other weaker periodicities with shorter time-scales (̃5, ̃3.5 and ̃3 yr) were also seen; in addition, the14.5-GHz WWZ power spectrum revealed a ̃2-yr periodiccomponent during the time interval 1983-1990. Statistical significance analysis suggests that these periodicities might result from physically periodic process. Thecharacteristic frequencies of these periodicities seem to have a harmonic relationship, and the fundamental frequency, i.e. the first-order harmonic, is about 0.05 yr-1 (P0 = 20 yr). But the fundamental frequency was not pronounced. The multiplicity and apparent harmonic relationship of the periodicities could be interpreted by the global p-mode oscillation of the accretion disc, if the jet and disc are coupled. In this scenario, theperiodic fluctuations in the accretion rate consequently lead to the observed periodic variabilities of the radio luminosity. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Deng W.,Dalian Jiaotong University | Deng W.,Dalian University | Deng W.,Xiangtan University | Li W.,Dalian Jiaotong University | Yang X.-H.,Dalian Jiaotong University
Expert Systems with Applications | Year: 2011

A novel hybrid optimization algorithm combining computational intelligence techniques is presented to solve the multifactor highway passenger volume prediction problem. In this paper, we can get and discretize a reduced decision table, which implies that the number of evaluation criteria such as travel quantity, fixed-asset investment, railway mileage, and waterway passenger volume are reduced with no information loss through rough set theory (RST) method. Particle swarm optimization (PSO) algorithm based on the random global optimization is inducted into the network training. The PSO algorithm is used for glancing study in order to confirm the initial values, and then the back propagation neural network (BPNN) is used for given accuracy to found the PSO-BPNN model. And this reduced information is used to form a classification rule set, which is regarded as an appropriate input parameter to training PSO-BPNN model. The RST-PSO-BPNN model is obtained to forecast highway passenger volume. The rules developed by RST analysis show the best prediction accuracy if a case matches any one of the rules. The keystone of this hybrid optimization algorithm is using rules developed by RST for an object that matches any one of the rules and the PSO-BPNN model for one that does not match any of them. The effectiveness of our optimization algorithm was verified by experiments comparing the traditional gray model method. For the experiment, highway passenger volumes of China during the period 1995-2009 were selected, and for the validation, the novel hybrid optimization algorithm is reliable. © 2010 Elsevier Ltd. All rights reserved.

Jing Yu.,Nankai University | Tan X.,Xiangtan University | Zhou Z.,Nankai University | Shen P.,Nankai University
Journal of Materials Chemistry A | Year: 2014

Density functional theory computations were performed to investigate the adsorption of four organic molecules, including tetracyanoquinodimethane (TCNQ), tetracyanoethylene (TCNE), tetrathiafulvalene (TTF) and benzyl viologen (BV) on the basal plane of MoS2 monolayer (MoS2ML). There mainly exist non-covalent weak interactions between these organic molecules and MoS2ML with considerable charge transfer. Due to the adsorption of organic molecules, the band gap of MoS2ML can be efficiently reduced as the flat molecular levels lie in the band gap region of MoS2ML. Moreover, the adsorption of TCNQ can significantly enhance the optical absorption of MoS2ML in the infrared region of solar spectrum, whereas the adsorption of other molecules has negligible effect on the optical properties of MoS2ML. Our computations provide a flexible approach towards tuning the electronic and optical properties of MoS2ML. This journal is © the Partner Organisations 2014.

Pang C.-Y.,Sichuan Normal University | Zhou R.-G.,East China Jiaotong University | Zhou R.-G.,Xiangtan University | Ding C.-B.,Sichuan Normal University | Hu B.-Q.,Chengdu University of Technology
Quantum Information Processing | Year: 2013

The operations of data set, such as intersection, union and complement, are the fundamental calculation in mathematics. It's very significant that designing fast algorithm for set operation. In this paper, the quantum algorithm for calculating intersection set C=A∩B is presented. Its runtime is O (√|A|×|B|×|C|)for case |C|≠ φ and O(√|A|× |B|) for case |C|= φ (i.e. C is empty set), while classical computation needs O (|A| × |B|) steps of computation in general, where |.| denotes the size of set. The presented algorithm is the combination of Grover's algorithm, classical memory and classical iterative computation, and the combination method decrease the complexity of designing quantum algorithm. The method can be used to design other set operations as well. © 2012 Springer Science+Business Media, LLC.

Liu J.,CAS Institute of Process Engineering | Liu J.,University of Chinese Academy of Sciences | Shen W.,Xiangtan University | Cui D.,CAS Institute of Process Engineering | And 4 more authors.
Catalysis Communications | Year: 2013

A comparative study was conducted for laboratory syngas methanation over a self-made Ni-Mg/Al2O3 catalyst to demonstrate the technical advantages of fluidized bed over fixed bed reactor. At different reaction temperatures, gas velocities and pressures, the CO conversion and selectivity to CH4 in fluidized bed were shown to be higher than in fixed bed, and much closer to the thermodynamic equilibriums. The spent catalysts from fluidized bed methanation had distinctively low and easy-oxidizing deposited carbon in comparison with that from fixed bed. The results were attributed to the bigger effective catalytic surface, better heat and mass transfer in fluidized bed reactor. © 2013 Elsevier B.V. All rights reserved.

Chen J.,Hunan University of Science and Technology | Chen J.,Xiangtan University | Zhang P.,Hunan University of Science and Technology | Fang G.,South China University of Technology | And 3 more authors.
Journal of Physical Chemistry B | Year: 2012

Novel multicolor and photoswitchcable fluorescent polymer nanoparticles were prepared by one-step miniemulsion via methyl methacrylate (MMA) copolymerization with 4-ethoxy-9-allyl-1,8-naphthalimide (EANI), allyl-(7-nitro-benzo[1,2,5]oxadiazol-4-yl)-amine (NBDAA) and spiropyran-linked methacrylate (SPMA). Under visible-light conditions, SPMA moieties in polymer nanoparticles are colorless and nonfluorescent, by varying the incorporating ratio of two dyes (EANI and NBDAA), fluorescence resonance energy transfer (FRET)-mediated emission signatures can be tuned so that the nanoparticles exhibit multiple colors under a single wavelength excitation. Moreover, the fluorescence emission of EANI and NBDAA dyes in nanoparticles can be reversibly switched "on" and "off" through the FRET process by the alternating irradiation of UV and visible light. This class of novel photoswitchable multicolor fluorescent polymer nanoparticles may find potential applications in multiplexed bioanalysis. © 2012 American Chemical Society.

Deng P.,Hengyang Normal University | Fei J.,Xiangtan University | Feng Y.,Hengyang Normal University
Analyst | Year: 2011

Chitosan was modified by salicylaldehyde via Schiff's base reaction and the resulting product was modified on the surface of an acetylene black paste electrode (ABPE) by the drop-coating method. In 0.5 mol L -1 acetate buffer (pH 4.2), a substantial increase in the anodic stripping peak current of tryptophan (Trp) (compared to conventional bare carbon paste electrode (CPE) and bare ABPE) is observed at the Schiff's base chitosan-modified electrode. The parameters influencing voltammetric determination of Trp have been optimized. Under the selected conditions, the linearity between the anodic peak currents and concentrations of Trp demonstrated a wide range of 6.0 × 10 -8 mol L -1 to 2.0 × 10 -6 mol L -1, 2.0 × 10 -6 mol L -1 to 4.0 × 10 -5 mol L -1 and 4.0 × 10 -5 mol L -1 to 1.0 × 10 -4 mol L -1, a low detection limit of 2.0 × 10 -9 mol L -1 was obtained after a 60 s accumulation. In addition, the developed electrochemical sensor has been successfully applied for the determination of Trp in pharmaceutical and biological samples with satisfactory assay results. This journal is © The Royal Society of Chemistry.

Zhou C.,Fudan University | Gao Y.,Fudan University | Gao Y.,Xiangtan University | Chen D.,Fudan University
Journal of Physical Chemistry B | Year: 2012

Poly(propargyl pyridinium bromide), a kind of conjugated polyelectrolyte with polyacetylene as the backbone and pyridinium as side groups, was synthesized simply via reaction between pyridine and propargyl bromide under mild conditions. The resultant polymer was characterized by 1H NMR, elemental analysis, FT-IR, and GPC-MALLS. An alkyne group was confirmed as the end group of the polymer chains by the alkyne/azide click chemistry, which reveals that the polymerization is terminated by the reaction between propargyl bromide and carbon anions. It is known that monosubstituted polyacetylenes reported have very weak fluorescence intensities, which limit their applications. As a monosubstituted polyacetylene, the freshly prepared poly(propargyl pyridinium bromide) also has a very weak fluorescence. However, we confirmed that addition of some anions to the polymer solution in DMF or DMSO leads to the fluorescence enhancements up to 25 times. Besides, heating the polymer solution at a temperature between 70 and 130 °C for longer than 0.5 h greatly enhanced the fluorescence intensity. The interaction with the anions or the heating enhances the effective exciton confinement within the conjugated backbone and thus results in the fluorescence enhancements. After the fluorescence enhancements, poly(propargyl pyridinium bromide) has relatively strong fluorescence emissions, which will make it promising in fluorescence-based applications. © 2012 American Chemical Society.

Yang Y.,University of Washington | Ma F.Y.,University of Washington | Lei C.H.,University of Washington | Liu Y.Y.,Xiangtan University | Li J.Y.,University of Washington
Journal of the Mechanics and Physics of Solids | Year: 2013

Thermoelectric materials are promising in converting heat directly into electricity, and composite materials are often used to enhance thermoelectric figure of merit. In this work, we develop a nonlinear asymptotic homogenization theory to analyze the effective behavior of layered thermoelectric composite with coupled transport of electricity and heat. The nonlinearly coupled thermoelectric transport equations are homogenized using asymptotic analysis, from which the macroscopic field distributions are derived with local fluctuation averaged out, and overall thermoelectric conversion efficiency is established using an idealized thermoelectric module. It is discovered that the thermoelectric field distributions in the composite are different from those in a homogeneous material, and they are difficult to be fitted by homogeneous solution. Furthermore, it is noted that while the effective thermoelectric properties of the composite can be defined through a set of equivalency principle, these effective properties depend on specific boundary conditions, resulting in effective figure of merit that is not correlated with thermoelectric conversion efficiency directly. The analysis thus sheds considerable insight into the effective behavior of thermoelectric composites for their design and optimization. © 2013 Elsevier Ltd.

Yu D.,University of Washington | Yu D.,Chongqing University | Chen C.,Chongqing University | Xie S.,University of Washington | And 8 more authors.
Energy and Environmental Science | Year: 2011

Mesoporous V2O5 nanofibers were fabricated by a method combining sol-gel processing with electrospinning followed by annealing in air. The resultant nanofibers were 350 nm in diameter and consisted of porous polycrystalline vanadium oxide with a specific surface area of ∼97 m 2 g-1. The mesoporous V2O5 nanofibers demonstrated a significantly enhanced Li ion storage capacity of above 370 mA h g-1 and a high charge/discharge rate of up to 800 mA g-1 with little cyclic degradation. © 2011 The Royal Society of Chemistry.

Tang K.,Hunan Institute of Science and Technology | Luo J.,Xiangtan University | Zhang P.,Hunan Institute of Science and Technology | Zhou C.,Hunan Institute of Science and Technology | Yi J.,Hunan Institute of Science and Technology
Chemical Engineering Research and Design | Year: 2013

Kinetics data is important for the reliable scale-up of a lab-scale process and for selection, design and operation of related equipment. This paper reports on the kinetics study for reactive extraction of hydroxy-(2-methyl-phenyl)-acetic acid (HA) enantiomers by hydroxypropyl-β-cyclodextrin (HP-β-CD) from the organic phase to the aqueous phase. The theory of extraction with chemical reaction was used. The effects of agitation speed, interfacial area, pH value of aqueous phase, initial concentration of HA enantiomers and initial concentration of extractant on the specific rate of extraction were investigated. The reactions have been found to be first order in HA and second order in HP-β-CD with the forward rate constants of 4.873×10-4m6/(mol2s) for R-HA and 4.343×10-4m6/(mol2s) for S-HA, respectively. © 2012 The Institution of Chemical Engineers.

Tang H.,Xiangtan University | Tang H.,CAS Beijing National Laboratory for Molecular | Fan X.,CAS Beijing National Laboratory for Molecular | Shen Z.,CAS Beijing National Laboratory for Molecular | Zhou Q.,CAS Beijing National Laboratory for Molecular
Polymer Engineering and Science | Year: 2014

Hyperbranched poly(aryl ether ketone)s with hydroxyl end groups (HBP-OH) and high degree of branching value (83%) were synthesized via an A2 + B3 approach. The polymerization conditions (e.g., polymerization temperature and time, monomer concentration, stoichiometric ratio of functional groups) were explored to avoid the gelation. Allyl-terminated hyperbranched PAEKs (HBP-AL) with low molecular weight (Mn = 3.4 × 10 3) and narrow polydispersity (PDI = 1.65) were obtained via the etherification of HBP-OH and it has been used for the modification of bismaleimide (BMI) resins. The prepolymers showed good processibilities with a viscosity below 0.6 Pa s at 110C, though the viscosities slightly increased as the increase of HBP-AL contents. The cured BMI resins showed high glass transition temperatures (Tg > 320C) and good thermal stabilities (Td > 400C, both in nitrogen and air). It is inspiring to note that the incorporation of HBP-AL into BMI matrix results in a significant enhancement of toughness without any noticeable loss in modulus, processibility, and Tg. POLYM. ENG. SCI., 54:1675-1685, 2014. © 2013 Society of Plastics Engineers © 2013 Society of Plastics Engineers.

Huang Y.,Xiangtan University | Li J.,University of Nevada, Las Vegas | Lin Y.,Hong Kong Polytechnic University | Lin Y.,University of Alberta
Advances in Applied Mathematics and Mechanics | Year: 2013

In this paper, the time-dependent Maxwell's equations used to modeling wave propagation in dispersive lossy bi-isotropic media are investigated. Existence and uniqueness of the modeling equations are proved. Two fully discrete finite element schemes are proposed, and their practical implementation and stability are discussed. © 2013 Global Science Press.

Wang J.,Guizhou University | Zhou Y.,Xiangtan University | Feckan M.,Comenius University | Feckan M.,Slovak Academy of Sciences
Nonlinear Dynamics | Year: 2013

In this paper, a generalized Darbo's fixedpoint theorem associated with Hausdorff measure of noncompactness is established. Then we apply this new variant fixed-point theorem to study some fractional differential equations in Banach spaces via the technique of measure of noncompactness. Many novel existence and uniqueness results for solutions are obtained under the more general conditions. © Springer Science+Business Media B.V. 2012.

Yu J.,CAS Institute of Process Engineering | Guo F.,Shenyang Institute of Chemical Technology | Wang Y.,CAS Institute of Process Engineering | Zhu J.,Xiangtan University | And 4 more authors.
Applied Catalysis B: Environmental | Year: 2010

Mesoporous MnO2-Fe2O3-CeO2-TiO2 was prepared with sol-gel method and demonstrated to have good low-temperature activity and sulfur-poisoning resistance for selective catalytic reduction (SCR) of NO with NH3 in SO2-containing gases. In comparison with this, the catalyst with the same composition but made according to the conventional impregnation method exhibited obviously lower SO2-poisoning resistance and selectivity to the formation of N2 in the SCR reactions. FTIR analysis of the spent catalysts after SCR reactions for 16 h and 60 h in a SO2-contaning gas demonstrated that there was little difference in the amount of deposited ammonium sulfate over the mesoporous catalyst between the two cases. The mesopore channels existing in the mesoporous catalyst enabled probably a dynamic balance between the formation and decomposition of ammonium sulfate in SCR reactions. This concern was justified through comparing the N2 adsorptions and XPS spectra for the catalysts made with the impregnation and sol-gel methods. The article clarified as well the facilitation effects of introducing Ce and Fe into the mesoporous catalyst on activity, selectivity and SO2-poisoning resistance. Crown Copyright © 2009.

Tang K.,Hunan Institute of Science and Technology | Cai J.,Xiangtan University | Zhang P.,Hunan Institute of Science and Technology
Industrial and Engineering Chemistry Research | Year: 2012

This paper reports on the equilibrium and kinetics of the reactive extraction of hydrophobic ibuprofen (IBU) enantiomers from the organic phase to the aqueous phase by hydroxypropyl-β-cyclodextrin (HP-β-CD). The modeling and experimental data of extraction performance factors were investigated to obtain the optimal extraction conditions. The best conditions identified involve the use of an HP-β-CD concentration of 0.03 mol/L and pH value of 2.5 at 10°C. The theory of extraction accompanied by chemical reactions was used to obtain the intrinsic kinetics of the extraction of IBU enantiomers by HP- β-CD. The effects of process parameters, including the agitation speed, interfacial area, initial concentration of IBU enantiomers, initial concentration of extractant, and pH value of aqueous phase, on the initial extraction rate were separately studied. The reactions are first order in IBU and second order in HP-β-CD with forward rate constants of 7.21 × 10 -4 m 6/(mol 2 ·s) for S-IBU and 4.58 × 10 -4 m 6/(mol 2 · s) for R-IBU, respectively. © 2011 American Chemical Society.

Chen C.,Xiangtan University | Zhang J.,Central South University
International Journal of Geomechanics | Year: 2013

Developing reliable and versatile constitutive models for geomaterials has been a challenging task for nonlinear finite-element analysis of geotechnical engineering systems.This paper is mainly concerned with the elastoplastic constitutive relationship of unbound granular materials under various stress paths. The fuzzy set plasticity theory has been developed to account for the nonlinear soil stress-strain behavior. The theory in many ways resembles the bounding surface plasticity, where the plastic modulus is a function of the distance between the current and image stress states in the stress space. Based on the concept of fuzzy set theory in mathematics, a membership function whose value ranges from 1 and 0 is introduced to specify the plastic modulus at a given stress state. Hollow cylinder and cubical test results on Hostun sand from the CASE database were selected to assess the fuzzy set plasticity model. The numerical results showed that the fuzzy set model is capable of mimicking and simulating the nonlinear behavior of loose sands under various loading paths. © 2012 American Society of Civil Engineers.

Deng P.-H.,Hengyang Normal University | Fei J.-J.,Xiangtan University | Feng Y.-L.,Hengyang Normal University
Journal of Electroanalytical Chemistry | Year: 2010

A sensitive and simplified voltammetric method is developed for the determination of trace amounts of vanadium(V) by adsorptive anodic stripping voltammetry using an acetylene black (AB) paste electrode. The method is based on the preconcentration of the V(V)-alizarin violet (AV) complex at open circuit while stirring the solution for 90 s in 0.15 mol dm-3 hexamethylenetetraamine-hydrochloric acid buffer (pH 4.4), the adsorbed complex is then oxidized, producing a response with a peak potential of 564 mV when scanning linearly from 0 to 1000 mV. For voltammetric determination of V(V), the parameters influencing the peak current have been optimized. Under the selected conditions, the peak current and concentration of V(V) accorded with linear relationship in the range of 8.0 × 10-10 mol dm -3-1.0 × 10-7 mol dm-3 (cAV = 2.0 × 10-6 mol dm-3) and 1.0 × 10-7 mol dm-3-8.0 × 10-6 mol dm-3 (c AV = 2.0 × 10-5 mol dm-3), the detection limit (three times signal to noise) was estimated to be 6.0 × 10 -10 mol dm-3 for 90 s accumulation. The relative standard deviation (RSD) is 1.9% and 2.3% for V(V) concentrations of 1.0 × 10 -7 mol dm-3 and 1.0 × 10-8 mol dm -3 respectively. Finally, this proposed method was successfully applied to the determination of V(V) in natural water samples. © 2010 Elsevier B.V. All rights reserved.

Yu X.,Hunan Institute of Engineering | Wang X.,Xiangtan University | Li B.,Hunan Institute of Engineering
Colloid and Polymer Science | Year: 2010

To construct reliable quantitative structureproperty relationship models of Q and e parameters, density functional theory (DFT) calculations were carried out for 56 radicals with structure C 1 H 3-C 2 HR 3 • (formed from the monomer + H•) at the B3LYP level of theory with 6-31G(d) basis set. The multiple linear regression technique was used to select the descriptors as inputs for the artificial neural network (ANN). A three-descriptor ANN for the parameter lnQ was developed that produced training set root mean square (rms) error=0.317 and rms error=0.313 for an external prediction set. A two-descriptor ANN for the parameter e was built with rms errors of 0.264 for the training set and 0.271 for the prediction set. Comparing to existing models, our ANN models show better or comparable statistical characteristics, which shows that calculating quantum chemical descriptors from radicals to develop ANN models and predict lnQ and e values is feasible. © Springer-Verlag 2010.

Tang K.,Hunan Institute of Science and Technology | Fu T.,Xiangtan University | Zhang P.,Hunan Institute of Science and Technology
Journal of Chemical and Engineering Data | Year: 2012

The deparation of phenylalanine (Phe) enantiomers by reactive liquid-liquid extraction with (s)-BINAP-metal complexes as enantioselective extractants was investigated. Metal complexes formed by different central ions with (s)-BINAP as a ligand were used as chiral extractants, among which the CuPF 6-(s)-BINAP complex (BINAP-Cu) allowed the separation of the Phe enantiomers with the highest operational selectivity. The efficiency of the extraction depends, often strongly, on a number of process variables, including the types of metal precursors and organic solvents, pH of the aqueous phase, concentration of extractant and substrate, and temperature. To better understand the extraction process, an interfacial reaction model was established. The best conditions involving a pH value of 7, feed concentration of 2.0·10 -3 mol·kg-1, BINAP-Cu concentration of 1.59·10-3 mol·kg-1, and temperature of 5 °C are obtained by modeling and optimization with a high enantioselectivity of 5.2038. The model quantitatively predicts the extraction performance and provides a simple computational approach to process optimization. © 2012 American Chemical Society.

Huang Y.-C.,National Cheng Kung University | Liu Y.,Xiangtan University | Lin Y.-T.,National Cheng Kung University | Liu H.-J.,National Chiao Tung University | And 5 more authors.
Advanced Materials | Year: 2014

A large enhancement of nanodomain retention is shown in the mixed-phase region of a strained BiFeO3 epitaxial fi lm. The superior ferroelectric retention is attributed to a lower elastic-energy density at the phase boundaries, which act as periodic pinning centers for the domain wall motion. This study delivers a new pathway of incorporating an elastic-energy term to assist ferroelectric retention. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Jin X.,Xiangtan University | Yang J.,University of Western Ontario
IEEE Sensors Journal | Year: 2013

This paper presents a high-performance complementary metal-oxide- semiconductor (CMOS) imager with a new analog-to-digital-converter (ADC) scheme. The new ADC scheme, adopting the visual perception of human eyes, has realized a maximal 13 bit variable resolution and reduced clipped noise for imaging. The response probability of human eyes to a flashlight falls in the region of [-1+σ, 1-σ]$ of a normal distribution, where σ is the standard deviation. In the region effective to human eyes [-1+σ, 1-σ], there exists a point corresponding to a maximum 13 bit variable resolution to improve the image quality and to save the power consumption and the chip size of sensors. The new ADC architecture uses an adjustable reference at both the top and bottom of the series of nonuniform resistors to reduce the clipped noise and to provide a wide dynamic range to image sensors. Based on reports of similar device design in the literature, this paper is particularly related to achieving a higher performance without increasing the chip size and power consumption. UXGA CMOS sensors with the newly developed ADC scheme are fabricated by the 0.18-μm CMOS process. The test results show improved image quality compared to typical CMOS products with a linear ADC. Test results also show 79-dB signal-to-noise ratio (at rm gain=0 dB) with a power consumption of 90 mW at 54 MHz. © 2001-2012 IEEE.

Pei Y.,University of Nebraska - Lincoln | Pei Y.,Xiangtan University | Shao N.,Oak Ridge National Laboratory | Li H.,University of Nebraska - Lincoln | And 2 more authors.
ACS Nano | Year: 2011

Using ab initio methods, we investigate the structural evolution of a family of gold-sulfide cluster anions (AumSn -). We show that this family of clusters exhibits simple size-evolution rules and novel hollow polyhedron structures. The highly stable AumS n - species such as Au6S4 -, Au9S5 -, Au9S 6 -, Au10S6 -, Au 11S6 -, Au12S8 -, and Au13S8 - detected in the recent ion mobility mass spectrometry experiment of Au25(SCH 2CH2Ph)18 (Angel et al. ACS Nano2010, 4, 4691) are found to possess either quasi-tetrahedron, pyramidal, quasi-triangular prism, or quasi-cuboctahedron structures. The formation of these polyhedron structures are attributed to the high stability of the S-Au-S structural unit. A unique "edge-to-face" growth mechanism is proposed to understand the structural evolution of the small AumSn - cluster. A 3:2 ratio rule of Au/S is suggested for the formation of a hollow polyhedron structure among small-sized AumSn clusters. © 2011 American Chemical Society.

Chen J.,Hunan University of Science and Technology | Chen J.,Xiangtan University | Zhang P.,Hunan University of Science and Technology | Fang G.,South China University of Technology | And 5 more authors.
Journal of Physical Chemistry B | Year: 2011

In the present study, novel polymeric nanoparticles of ca. 55 nm in diameter with reversibly photoswitchable fluorescence properties were synthesized using a facile one-step miniemulsion polymerization, in which the donor of fluorescence resonance energy transfer (FRET), 4-methamino-9-allyl-1,8- naphthalimide (MANI), and the acceptor, spiropyran-linked methacrylate (SPMA), were covalently incorporated into a polymeric matrix during the polymerization process. The fluorescence emission of MANI dye in nanoparticles can be reversibly switched using the alternating irradiation of UV and visible light, which can induce the structural interconversion between the SP form and MC form of spiropyran moieties inside nanoparticles and thus reversibly switch on and switch off the FRET process. The prepared photoswitchable fluorescent polymer nanoparticles not only show a high load capacity of dyes, controllable amount and ratio of the two dyes, and tunable FRET efficiency but also exhibit higher spectral stability because of covalent linkage between dye molecules and the particle, relatively fast photoresponsibility, and better photoreversibility compared to some previously reported systems. © 2011 American Chemical Society.

Gong W.,Hunan University | Gao P.,Hunan University | Gao P.,Xiangtan University | Wang W.,Hunan University
Ceramics International | Year: 2011

A biomorphic porous carbon coated with SiC (SiC/BPC) was prepared by controlled carbonizing native pine under Ar atmosphere and then processed with precursor infiltration-pyrolysis (PIP) of organosilane. Microstructure and component of SiC/BPC were analyzed by FT-IR, XRD, SEM and EDS (attached with line scanning program). The non-isothermal oxidation properties and mechanism of SiC/BPC were studied by TGA. The kinetic parameters were calculated through model-free kinetics methods. Experimental results showed that SiC/BPC had a topologically uniform interconnected porous network microstructure; the obtained gradient SiC coating on BPC surface was amorphous and combined well with the carbon surface, which can improve the oxidation resistance of BPC clearly. The non-isothermal oxidation reaction of SiC/BPC exhibited a partial self-accelerating characteristic. The oxidation process was complicated, firstly it was controlled by gas diffusion in coating, then controlled by chemical reaction, and at last it was controlled by gas diffusion and chemical reaction together, the corresponding effective activation energy was calculated also. © 2011 Elsevier Ltd and Techna Group S.r.l.

Fan Y.,Nanyang Technological University | Zhang Q.,Nanyang Technological University | Xiao Q.,Nanyang Technological University | Wang X.,Nanyang Technological University | Huang K.,Xiangtan University
Carbon | Year: 2013

We report a carbon nanotube (CNT)-silicon core-shell nanowire for lithium ion battery anodes. In this material, the core consists of vertically aligned CNTs synthesized through plasma enhanced chemical vapor deposition. The CNTs exhibit quite large diameters and large inter-wire spacing and are advantageous in strain accommodation and electrolyte access. The silicon shell is tailored with a thickness gradient along its length to eliminate excessive strain accumulation at the nanowire roots and cater for free space distribution in the CNT core array. In addition, the silicon shell exhibits a unique vertically opened pore structure, which is expected to have further improved strain accommodation and Li+ transport. As a result, the CNT-silicon anode demonstrates excellent cyclability with a capacity retention of more than 90% over 100 cycles. It also shows remarkable rate performance that is to our knowledge, the best among all core-shell nanowires reported. © 2013 Elsevier Ltd.

Tang Y.,Xiangtan University | Chen Y.,South China Normal University
Journal of Systems Science and Complexity | Year: 2012

This paper studies variational discretization for the optimal control problem governed by parabolic equations with control constraints. First of all, the authors derive a priori error estimates where {double pipe}{pipe}u - U h{double pipe}{pipe} L∞(J;L2(Ω)) = O(h 2 + k). It is much better than a priori error estimates of standard finite element and backward Euler method where {double pipe}{pipe}u - U h{double pipe}{pipe} L∞(J;L2(Ω)) = O(h + k). Secondly, the authors obtain a posteriori error estimates of residual type. Finally, the authors present some numerical algorithms for the optimal control problem and do some numerical experiments to illustrate their theoretical results. © 2012 Institute of Systems Science, Academy of Mathematics and Systems Science, CAS and Springer-Verlag Berlin Heidelberg.

Su N.,Xiangtan University | Su N.,James Cook University
Journal of Hydrology | Year: 2010

The majority of infiltration equations in use today were developed for infiltration into rigid porous media based either on the classic diffusion equation or empirical formulation. In this paper, we present new equations of infiltration into swelling soils derived from the fractional Fokker-Planck equation (fFPE) of flow in swelling porous media formulated in a material coordinate. The cumulative infiltration we derived is I(t)=At+Stβ/2, where S is the fractional sorptivity, A the final infiltration rate, and β the order of fractional derivative in the fFPE. Using the data published in the literature on cumulative infiltration against time, β, S and A are determined. The determined value of β=0.2385 for this reported soil is much less than 1.0 which implies that infiltration into this specific swelling soil belongs to the category of sub-diffusion. We show that the new cumulative infiltration equation not only fits the reported data exceptionally better than Philip's two-term infiltration equation, more importantly, it provides fresh explanation and understanding of infiltration into swelling media. The new infiltration equation deviates from the majority of infiltration equations which were developed for rigid soils and ignore the realistic swelling and shrinking properties of the soils. © 2010 Elsevier B.V.

Shafiefarhood A.,North Carolina State University | Galinsky N.,North Carolina State University | Huang Y.,North Carolina State University | Huang Y.,Xiangtan University | And 3 more authors.
ChemCatChem | Year: 2014

Efficient and environmentally friendly conversion of methane into syngas is a topic of practical relevance for the production of hydrogen, chemicals, and synthetic fuels. At present, methane-derived syngas is produced primarily through the steam methane reforming processes. The efficiencies of such processes are limited owing to the endothermic steam methane reforming reaction and the high steam to methane ratio required by the reforming catalysts. Chemical looping reforming represents an alternative approach for methane conversion. In the chemical looping reforming scheme, a solid oxygen carrier or "redox catalyst" is used to partially oxidize methane to syngas. The reduced redox catalyst is then regenerated with air. The cyclic redox operation reduces the steam usage while simplifying the heat integration scheme. Herein, a new Fe2O3@LaxSr1-xFeO3 (LSF) core-shell redox catalyst is synthesized and investigated. Compared with several other commonly investigated iron-based redox catalysts, the newly developed core-shell redox catalyst is significantly more active and selective for syngas production from methane. It is also more resistant toward carbon formation and maintains high activity over cyclic redox operations. Loop-the-loop: A FeOx@LaxSr1-xFeO 3-δ core-shell redox catalyst was designed and synthesized. The redox catalyst, capable of converting methane into syngas in the absence of gaseous oxidants, was found to be active, selective, and carbon formation resistant under cyclic redox conditions at elevated temperature. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Han H.,Xiangtan University
2011 IEEE 3rd International Conference on Communication Software and Networks, ICCSN 2011 | Year: 2011

Improving the performance of the transmission control protocol (TCP) in wireless environment has been an active research area. In wireless environment, TCP erroneously responds to all losses by invoking congestion control algorithm resulting in degraded end-to-end performance. In this paper, we proposes a new modification of TCP-Reno based on monitoring the wireless packet loss rate in real time. When the modified Reno cooperates with the router configured with explicit congestion notification(ECN), it is capable of distinguishing the wireless packet losses from the congestion packet losses, and reacting accordingly. At the same time, the sender takes advantage of the monitor result to adjustment the TCP segment size. The simulations in this paper show that the modification of TCP is feasible, and the performance of TCP is improved actually. © 2011 IEEE.

Jin X.,Xiangtan University | Liu Y.,University of Western Ontario | Yang J.,University of Western Ontario
Optics Communications | Year: 2011

Utilization of the zero space microlens technology can significantly improve the image quality of CMOS sensors. In this study, we present systematical data of design, simulation, characterization and silicon level testing during the initial stage of development of the zero space microlens based CMOS imaging technology. The optimal structure of zero space microlens was obtained based on the simulation results. Sample CMOS image sensors with a 2.8 μm pitch zero space microlens above each pixel have been successfully fabricated based on 0.18 μm CMOS technology. Using AFM (atomic force microscopy) and sensor test platform, the structural and optical properties of both space microlens and zero space microlens have been characterized, and their performances have been evaluated respectively. Both AFM results and silicon tests have demonstrated that the 2.8 μm pitch zero space microlens can remarkably improve the pixel sensitivity and pixel array non-uniformity, and reduce the optical crosstalk. Compared to the space 2.8 μm square microlens, the zero space microlens shows 78.83% (68.42% and 75.93%) enhancement of photosensitivity and increment of pixel non-uniformity up to 20% (45.6% and 30.77%) for R (G and B), and reduction of the optical crosstalk up to 44.49%, under 45 lux light and 30 ms exposure time. In addition, the zero space microlens has also shown a great potential in further reducing pixel size down to less than 2.8 μm and meanwhile improving imaging performance of CMOS image sensors. © 2010 Elsevier B.V. All rights reserved.

Tian W.W.,CAS National Astronomical Observatories | Tian W.W.,University of Calgary | Li Z.,Harvard - Smithsonian Center for Astrophysics | Leahy D.A.,University of Calgary | And 4 more authors.
Astrophysical Journal | Year: 2010

We present new results of the HESS J1731-347/SNR G353.6-0.7 system from XMM-Newton and Suzaku X-ray observations and Delinha CO observations. We discover extended hard X-rays coincident with the bright, extended TeV source HESS J1731-347 and the shell of the radio supernova remnant (SNR). We find that spatially resolved X-ray spectra can generally be characterized by an absorbed power-law model, with a photon index of ∼2, typical of non-thermal emission. A bright X-ray compact source, XMMS J173203-344518, is also detected near the center of the SNR. We find no evidence of a radio counterpart or an extended X-ray morphology for this source, making it unlikely to be a pulsar wind nebular (PWN). The spectrum of the source can be well fitted by an absorbed blackbody with a temperature of ∼0.5keV plus a power-law tail with a photon index of ∼5, reminiscent of the X-ray emission of a magnetar. CO observations toward the inner part of the High Energy Stereoscopic System (HESS) source reveal a bright cloud component at -20 ± 4 km s-1, which is likely located at the same distance of ∼3.2kpc as the SNR. Based on the probable association between the X-ray and γ-ray emissions and likely association between the CO cloud and the SNR, we argue that the extended TeV emission originates from the interaction between the SNR shock and the adjacent CO clouds rather than from a PWN. © 2010. The American Astronomical Society. All rights reserved.

Ye W.-B.,Xiangtan University
Applied Thermal Engineering | Year: 2016

Thermal non-destructive detection is inherently related to some methods and technical means of thermal stimulation. Electrode non-uniformity can result in quality control defectively. The infrared thermograph or thermal imaging technique is explored as a thermal non-destructive detection to detect the electrode non-uniformity during the manufacturing processes quantitatively. In order to assess the feasibility of this technique, the numerical simulation is used based on finite volume method (FVM). A heat conduction model has been developed to provide the numerical study. The results of numerical model are in good agreement with the published experimental data. The effects of convection heat transfer coefficients (2, 5, and 10 W/m2 K) at electrode surface, electrode surface areas (100 and 1000 cm2), and bubbles on detecting validation are examined in detail. It is found that temperature changes are independent of convection heat transfer coefficients and electrode surface areas. The bubbles are observed inside the electrode through the temperature signals. Therefore, thermal imaging is a further prospected method to detect non-uniformity. The values, evaluated here for the practical conditions, indicate that thermal imaging technique is promising for investigating the non-uniformity behavior of electrode. Analogically, the method can also be used in other thermal related equipment or products as a valuable and robust reference. © 2015 Elsevier Ltd. All rights reserved.

Sun C.Q.,Nanyang Technological University | Sun C.Q.,Jilin University | Sun C.Q.,Xiangtan University | Zhang X.,Nanyang Technological University | Zheng W.,Jilin University
Chemical Science | Year: 2012

Coulomb repulsion between the unevenly-bound bonding "-" and nonbonding ":" electron pairs in the "O 2-:H +/p-O 2-" hydrogen bond is shown to originate the anomalies of ice under compression. Consistency between experimental observations, density functional theory and molecular dynamics calculations confirmed that the resultant force of the compression, the repulsion, and the recovery of electron-pair dislocations differentiates ice from other materials in response to pressure. The compression shortens and strengthens the longer-and-softer intermolecular "O 2-:H +/p" lone-pair virtual bond; the repulsion pushes the bonding electron pair away from the H +/p and hence elongates and weakens the intramolecular "H +/p-O 2-" real bond. The virtual-bond compression and the real-bond elongation symmetrize the "O 2--H +/p:O 2-" as observed at ∼60 GPa and result in the abnormally low compressibility of ice. The virtual-bond stretching phonons (<400 cm -1) are thus stiffened and the real-bond stretching phonons (>3000 cm -1) softened upon compression. The cohesive energy loss of the real bond dominates and lowers the critical temperature for the VIII-VII phase transition. The polarization of the lone electron pairs and the entrapment of the bonding electron pairs by compression expand the band gap consequently. Findings should form striking impact to understanding the physical anomalies of H 2O. © 2012 The Royal Society of Chemistry.

Long Y.,A+ Network | Ouyang J.,Xiangtan University | Sun X.,A+ Network
Journal of Networks | Year: 2013

Network intrusion detection is of great importance in the research field of information security in computer networks. In this paper, we concentrate on how to automatically detect the network intrusion behavior utilizing fuzzy support vector machine. After analyzing the related works of the proposed paper, we introduce the main characterics of fuzzy support vector machine, and demonstrate its formal description in detail. Next, the proposed intrusion detection system is organized as five modules, which are Data source, AAA protocol, FSVM module located in local computer, Guest computer and Terminals. Particularly, the intrusion detection module is constructed by four sections, which are data gathering section, data pre-processing section, intrusion detecting section and decision response section. Then, the intrusion detection algorithm based on fuzzy support vector machine is implemented by training process and testing process. Utilizing this algorithm, a sample in testing data can be judged whether it is belonged to network intrusion behavior. Finally, experimental results verify the effectiveness of our method comparing with other methods under different metric. © 2013 ACADEMY PUBLISHER.

Chen Y.,South China Normal University | Liu L.,Xiangtan University | Lu Z.,Chongqing Three Gorges University
Numerical Functional Analysis and Optimization | Year: 2010

In this article, we shall give a brief review on the fully discrete mixed finite element method for general optimal control problems governed by parabolic equations. The state and the co-state are approximated by the lowest order Raviart-Thomas mixed finite element spaces and the control is approximated by piecewise constant elements. Furthermore, we derive a posteriori error estimates for the finite element approximation solutions of optimal control problems. Some numerical examples are given to demonstrate our theoretical results. Copyright © Taylor & Francis Group, LLC.

Zhang X.,Nanyang Technological University | Nie Y.,Nanyang Technological University | Zheng W.,Jilin University | Kuo J.-L.,Academia Sinica, Taiwan | And 2 more authors.
Carbon | Year: 2011

Using a combination of the bond order-length-strength correlation theory, the spin-polarized tight binding method, the first-principles calculations, and the atomistic photoelectron distillation experiments, we investigated the mechanisms of edge-selective generation and hydrogenated modulation of Dirac-Fermi polarons (DFPs) surrounding the atomic vacancies at a graphite surface and at the edges of graphene nanoribbons (GNR). We found that: (i) the DFPs with a high-spin density at a zigzag-GNR edge and at an atomic vacancy result from the isolation and polarization of the dangling σ-bond electrons of √3d (d is the C-C bond length) distance along the edge by the locally and densely entrapped bonding electrons; (ii) along an armchair-GNR edge and a reconstructed-zigzag-GNR edge, however, the formation of quasi-triple-bond between the nearest edge atoms of d distance prevents the DFPs from generation; and (iii) hydrogenation reduces the spin density substantially and turns the asymmetric dumb-bell-like density into the spherical-like p z density. A further C 1s photoelectron spectroscopic purification has confirmed that the generation of the DFPs is associated with two extra peaks of energy states located at the bottom and the top edge of the C 1s band. © 2011 Elsevier Ltd. All rights reserved.

Jin X.,Xiangtan University | Jin X.,University of Western Ontario | Yang J.,University of Western Ontario
IEEE Photonics Technology Letters | Year: 2010

A low-dark-current, high-sensitivity, low-optical-crosstalk, and small-pixel-size pinned photodiode with no-gap microlens is designed, fabricated, and measured. Compared with nonpinned photodiodes of the same size, the dark current of a 2 μm × 2 μm pinned photodiode is reduced about 41.2%, while the photocurrent is reduced less than only 1% at the low reverse biased voltage Vpd = 2 V under illumination of the same light source (470 nm, 450 μw/cm2). Due to the use of the pinning layer, the equivalent capacitance of the 2-μm pinned photodiode is increased about 1.1 fF. In addition, the no-gap microlens technology has been developed here to improve the photodiode performance. Prototype complementary metaloxidesemiconductor (CMOS) imagers consisting of a 640 (row) by 480 (column) array of pinned photodiodes with no-gap or conventional microlens have been designed and fabricated based on 0.18-μm CMOS process. The test results show that, compared with the photodiode with a conventional microlens, the sensitivity is increased about 74% and the optical crosstalk is reduced up to 7.2% for the photodiode with a no-gap microlens. Thus, the small-pixel-size pinned photodiode with no-gap microlens shows advantages in applications of high-resolution optical detectors and high-quality CMOS image sensors. © 2010 IEEE.

Fen Y.,Wuhan University of Science and Technology | Dandan Z.,Xiangtan University
Acta Mathematica Scientia | Year: 2011

The asymptotic behavior at infinity and an estimate of positive radial solutions of the equation (0.1)Δu+∑i=1kcirliuPi=0, x∈Rn,are obtained and the structure of separation property of positive radial solutions of Eq. (0.1) with different initial data α is discussed. © 2011 Wuhan Institute of Physics and Mathematics.

Li X.,Ningbo University | Zhao X.,Ningbo University | Zhang J.,Xiangtan University | Zhao Y.,Ningbo University
Chemical Communications | Year: 2013

A multilayer film (Pd2+/1)n was prepared with Pd(ii) ions and platinum compound trans-[Pt(PPh3)2(CCPy) 2] (1) using the layer-by-layer self-assembly method. The film loaded on the quartz slide could be capable of discharging high catalytic active Pd species to promote the C-C coupling reaction, with extraordinarily low Pd-loading (6.6 × 10-6 mol%) and high catalytic efficiency in H2O-EtOH solution. © 2013 The Royal Society of Chemistry.

Zhou R.,East China Jiaotong University | Zhou R.,Xiangtan University | Cao J.,East China Jiaotong University
Artificial Intelligence Review | Year: 2014

A quantum novel genetic algorithm based on subpopulation parallel computing is presented, where quantum coding and rotation angle are improved to inspire more efficient genetic computing methods. In the algorithm, each axis of the solution space is divided into k parts, the individual (or chromosome) from each different subspace being coded differently, and the probability amplitude of each quantum bit or Q-bit is regarded as two paratactic genes. The basic quantum computing theory and classical quantum genetic algorithm are briefly introduced before a novel algorithm is presented for the function optimum and PID problem. Through a comparison between the novel algorithm and the classical counterpart, it is shown that the quantum inspired genetic algorithm performs better on running speed and optimization capability. © 2012 Springer Science+Business Media B.V.

Cheng H.,Xiangtan University
Acta Crystallographica Section E: Structure Reports Online | Year: 2011

In the title molecule, C 9H 4I 2OS 2, the two five-membered rings form a dihedral angle of 64.2 (2)°. In the crystal, weak intermolecular C - H⋯O hydrogen bonds link the molecules into layers parallel to the ab plane. The crystal packing exhibits short C⋯I contacts of 3.442 (5) Å between the molecules of adjacent layers.

Wang W.-Q.,Xiangtan University
Acta Crystallographica Section E: Structure Reports Online | Year: 2011

In the title adduct, C6H4Cl3N· C6H3N3O7, the two benzene rings are almost coplanar, with a dihedral angle of 1.19 (1)° and an inter-ring centroid-centroid separation of 4.816 (2) Å. The crystal structure is stabilized by intermolecular N - H⋯Onitro hydrogen bonds, giving a chain structure. In addition, there are phenol-nitro O - H⋯O inter-actions.

Wang J.,Guizhou University | Zhou Y.,Xiangtan University | Wei W.,Guizhou University
Nonlinear Analysis: Real World Applications | Year: 2012

In this paper, we study fractional Schrödinger equations with potential and optimal controls. The first novelty is a suitable concept on a mild solution for our problems. Existence, uniqueness, local stability and attractivity, and data continuous dependence of mild solutions are also presented respectively. The second novelty is an initial study on the optimal control problems for the controlled fractional Schrödinger equations with potential. Existence and uniqueness of optimal pairs for the standard Lagrange problem are obtained. © 2012 Elsevier Ltd. All rights reserved.

Lin Z.-J.,CAS Fujian Institute of Research on the Structure of Matter | Liu T.-F.,CAS Fujian Institute of Research on the Structure of Matter | Zhao X.-L.,Xiangtan University | Lu J.,CAS Fujian Institute of Research on the Structure of Matter | Cao R.,CAS Fujian Institute of Research on the Structure of Matter
Crystal Growth and Design | Year: 2011

A flexible tetrapodal octacarboxylate ligand with four 1,3- benzenedicarboxylate units has been used to construct three polyhedral metal-organic frameworks, which show a (4,8)-connected structure of a rare scu topology comprising octahedral and cuboctahedral cages. © 2011 American Chemical Society.

Gui G.,University of Wisconsin - Madison | Morgan D.,University of Wisconsin - Madison | Booske J.,University of Wisconsin - Madison | Zhong J.,Xiangtan University | Ma Z.,University of Wisconsin - Madison
Applied Physics Letters | Year: 2015

We have systematically investigated the effect of local strain on electronic properties of graphene by first-principles calculations. Two major types of local strain, oriented along the zigzag and the armchair directions, have been studied. We find that local strain with a proper range and strength along the zigzag direction results in opening of significant band gaps in graphene, on the order of 10-1eV; whereas, local strain along the armchair direction cannot open a significant band gap in graphene. Our results show that appropriate local strain can effectively open and tune the band gap in graphene; therefore, the electronic and transport properties of graphene can also be modified. © 2015 AIP Publishing LLC.

Tan J.,Xiangtan University | Yang X.,Hunan Normal University | Yang X.,HPCSIP Key Laboratory
Journal of Systems Science and Complexity | Year: 2012

Consider the compound binomial risk model with interest on the surplus under a constant dividend barrier and periodically paying dividends. A system of integral equations for the arbitrary moments of the sum of the discounted dividend payments until ruin is derived. Moreover, under a very relaxed condition, the solutions for arbitrary moments are obtained by setting up iteration processes because of a special property of the system of integral equations. © 2012 Institute of Systems Science, Academy of Mathematics and Systems Science, CAS and Springer-Verlag Berlin Heidelberg.

Liao N.H.,Chinese Academy of Sciences | Liao N.H.,University of Chinese Academy of Sciences | Bai J.M.,Chinese Academy of Sciences | Liu H.T.,Chinese Academy of Sciences | And 3 more authors.
Astrophysical Journal | Year: 2014

S5 0716+714 is a typical BL Lacertae object. In this paper we present the analysis and results of long-term simultaneous observations in the radio, near-infrared, optical, X-ray, and γ-ray bands, together with our own photometric observations for this source. The light curves show that the variability amplitudes in γ-ray and optical bands are larger than those in the hard X-ray and radio bands and that the spectral energy distribution (SED) peaks move to shorter wavelengths when the source becomes brighter, which is similar to other blazars, i.e., more variable at wavelengths shorter than the SED peak frequencies. Analysis shows that the characteristic variability timescales in the 14.5 GHz, the optical, the X-ray, and the γ-ray bands are comparable to each other. The variations of the hard X-ray and 14.5 GHz emissions are correlated with zero lag, and so are the V band and γ-ray variations, which are consistent with the leptonic models. Coincidences of γ-ray and optical flares with a dramatic change of the optical polarization are detected. Hadronic models do not have the same natural explanation for these observations as the leptonic models. A strong optical flare correlating a γ-ray flare whose peak flux is lower than the average flux is detected. The leptonic model can explain this variability phenomenon through simultaneous SED modeling. Different leptonic models are distinguished by average SED modeling. The synchrotron plus synchrotron self-Compton (SSC) model is ruled out because of the extreme input parameters. Scattering of external seed photons, such as the hot-dust or broad-line region emission, and the SSC process are probably both needed to explain the γ-ray emission of S5 0716+714. © 2014. The American Astronomical Society. All rights reserved.

Chen A.,Xiangtan University | Chen A.,Xiangnan University | Chen F.,Xiangnan University | Deng S.,Xiangnan University
Computers and Mathematics with Applications | Year: 2010

This paper investigates almost automorphic mild solutions of the fractional semilinear equation Dα x (t) = A x (t) + f (t, x (t)), 0 < α < 1, considered in a Banach space X, where A is a linear operator of sectorial type ω < 0. Some sufficient conditions are given for the existence, uniqueness and uniform stability of almost automorphic mild solutions to this semilinear equation. © 2009 Elsevier Ltd. All rights reserved.

Liu Y.Y.,Xiangtan University | Liu Y.Y.,University of Washington | Zhu Z.X.,Tsinghua University | Li J.-F.,Tsinghua University | Li J.Y.,University of Washington
Mechanics of Materials | Year: 2010

It is well known that the structures and properties of ferroelectric films can be remarkably different from their bulk counterpart, and a nonlinear phenomenological theory of ferroelectrics is applied to study phase structures and electromechanical properties of epitaxial Pb(Zr1-xTi x)O3 (PZT) thin films, focusing on the effects of substrate and film thickness. The effective misfit strain induced by lattice mismatch between film and substrate has been calculated, and the misfit strain-composition, temperature-composition, and thickness-composition phase diagrams of PZT films have been constructed. The temperature-composition phase diagram differs substantially from that of bulk PZT ceramics, and the calculated phase structures in thin films allow us to explain numerous previous experimental observations. In particular, it is confirmed that the morphotropic phase boundary (MPB) of PZT films is shifted from that of bulk PZT, resulting in substantially different electromechanical response in PZT thin films. Good agreement with experimental data is observed in general. © 2010 Elsevier Ltd.

Liu Y.Y.,Xiangtan University | Li J.Y.,University of Washington
Applied Physics Letters | Year: 2010

A continuum theory is developed to investigate the effects of space charges and size on ferroelectric superlattices, treating the ferroelectric perovskites as wide band-gap semiconductors instead of insulators, making it possible to couple the distribution of polarization and space charges through Maxwell's equation. It is found that the space charges tend to accumulate near the superlattice interface, resulting in large electric field near the interface, and thus enhanced polarization and asymmetric hysteresis loop. It also eliminates the uniform polarization that would exist in the superlattice in the absence of space charges. The effect of superlattice thickness is also investigated, and good agreements with experiments are observed. © 2010 American Institute of Physics.

Gong H.,McGill University | Gong H.,Xiangtan University | Zeng H.,McGill University | Zhou F.,McGill University | Li C.-J.,McGill University
Angewandte Chemie - International Edition | Year: 2015

2,2'-Diaryl acids are key building blocks for some of the most important and high-performance polymers such as polyesters and polyamides (imides), as well as structural motifs of MOFs (metal-organic frameworks) and biological compounds. In this study, a direct, regiospecific and practical dimerization of simple aromatic acids to generate 2,2'-diaryl acids has been discovered, which proceeds through two rhodium-catalyzed C-H activations in water. This reaction can be easily scaled up to gram level by using only 0.4-0.6 mol% of the rhodium catalyst. As a proof-of-concept, the natural product ellagic acid was synthesized in two steps by this method. On the double: An efficient, regiospecific, and general oxidative dimerization of simple aryl acids to generate diaryl acids was developed. The reaction involves two direct aryl C-H activations catalyzed by rhodium, uses water as the solvent, and can be easily scaled up. The natural product ellagic acid was obtained in only two steps by using this method. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Yu P.,CAS Institute of Chemistry | Zhou H.,CAS Institute of Chemistry | Zhou H.,Xiangtan University | Cheng H.,CAS Institute of Chemistry | And 4 more authors.
Analytical Chemistry | Year: 2011

This study demonstrates a new strategy to simplify the biosensor fabrication and thus minimize the biosensor-to-biosensor deviation through rational design and one-step formation of a multifunctional gel electronic transducer integrating all elements necessitated for efficiently transducing the biorecognition events to signal readout, by using glucose dehydrogenase (GDH) based electrochemical biosensor as an example. To meet the requirements for preparing integrated biosensors and retaining electronic and ionic conductivities for electronically transducing process, ionic liquids (ILs) with enzyme cofactor (i.e., oxidized form of nicotinamide adenine dinucleotide) as the anion were synthesized and used to form a bucky gel with single-walled carbon nanotubes, in which methylene green electrocatalyst was stably encapsulated for the oxidation of nicotinamide adenine dinucleotide. With such kind of rationally designed and one-step-formed multifunctional gel as the electronic transducer, the GDH-based electrochemical biosensors were simply fabricated by polishing the electrodes onto the gel followed by enzyme immobilization. This capability greatly simplifies the biosensor fabrication, prolongs the stability of the biosensors, and, more remarkably, minimizes the biosensor-to-biosensor deviation. The relative standard deviations obtained both with one electrode for the repeated measurements of glucose and with the different electrodes prepared with the same method for the concurrent measurements of glucose with the same concentration were 3.30% (n = 7) and 4.70% (n = 6), respectively. These excellent properties of the multifunctional gel-based biosensors substantially enable them to well-satisfy the pressing need of rapid measurements, for example, environmental monitoring, food analysis, and clinical diagnoses. © 2011 American Chemical Society.

Yang H.-M.,University of Science and Technology of China | Wang D.-Y.,Xiangtan University
Guangdianzi Jiguang/Journal of Optoelectronics Laser | Year: 2012

To achieve higher coding efficiency and less coding time for scalable vedio coding (SVC), this paper presents a fast inter-frame encoding algorithm suitable for the enhancement layer, in which the weights of the various models are calculated and ordered with the combination of the residual prediction and rate distortion as the early termination criteria. The Experiment results show that the proposed algorithm can significantly improve the encoding speed with negligible influence on encoding quality.

Liu X.,Xiangtan University
2010 International Conference on Intelligent Computation Technology and Automation, ICICTA 2010 | Year: 2010

According to the image characteristics in weld seam tracking with laser vision, Radon transform is first used to find the location of the laser stripe; then, the transformed image is processed by using the way the information from laser stripe is reserved and the other information from noises is removed, after that inverse Radon transform is applied for image recovery. Finally, improved fast FCM clustering is used for image segmentation so that the groove area can be recognized. These methods can bring good effects with little time cost, and the anti-disturbance performance is well, therefore they are suitable for weld seam tracking with laser vision. © 2010 IEEE.

Hu Y.,Beijing Jiaotong University | Li D.,Beijing Jiaotong University | Shu S.,Xiangtan University | Niu X.,Shantou University
International Journal of Heat and Mass Transfer | Year: 2015

A novel thermal immersed boundary-lattice Boltzmann method is developed to simulate the 2D natural convection in a concentric horizontal annulus with a constant flux wall. In the present work, we focus on the multiple steady solutions of this problem. And the case with a fixed aspect ratio Ar=2 is considered. In addition to the dual steady solutions which was reported by the previous work (Yoo, 2003), a new steady solution consisting more of eddies is found in this paper when the Rayleigh number exceeds a certain critical value. © 2014 Elsevier Ltd. All rights reserved.

Yan X.-M.,Yangtze University | Mei P.,Yangtze University | Xiong L.,Yangtze University | Gao L.,Yangtze University | And 2 more authors.
Catalysis Science and Technology | Year: 2013

A series of mesoporous titania-silica-polyoxometalate (HPW-TiO 2-SiO2) nanocomposite materials with different silica-titania ratios were prepared in the presence of non-ionic surfactant by evaporation induced self-assembly method. XRD, TEM, nitrogen adsorption-desorption isotherm and FTIR measurements indicated these materials possess mesoporous structure with relatively uniform channel-like pores and large internal BET surface areas. The incorporated polyoxometalate clusters preserve intact their Keggin structure into the mesoporous frameworks. The nanocomposites were used as catalysts for oxidative desulfurization of model fuel, which was composed of dibenzothiophene (DBT) and hydrocarbon, while H 2O2 is used as oxidant. The catalytic oxidation results show that the catalysts are very active in refractory bulky molecule organosulfur compounds in fuel oil. The mesoporous HPW-TiO2-SiO 2 also shows high selectivity for DBT oxidation in the presence of benzene and achieved the goal of desulfurization. The surface acid strength and acidic sites were characterized by NH3-TPD and Py-FT-IR. It revealed that Lewis acidic sites play an important role in the removal of organic sulfur compounds from the DBT-petroleum ether-benzene system. After regeneration of used catalysts three times, the activity of catalysts has not obviously decreased. This journal is © 2013 The Royal Society of Chemistry.

Zhang S.,CAS Institute of High Energy Physics | Weng S.-S.,CAS Institute of High Energy Physics | Weng S.-S.,Xiangtan University | Zhang S.-N.,CAS Institute of High Energy Physics | And 2 more authors.
Astrophysical Journal | Year: 2013

We analyze all of the available RXTE observations of Cyg X-3 in order to investigate the connection between the central X-ray source and its surrounding environment. The hardness-intensity diagram of Cyg X-3 displays a "shoe" shape rather than the Q-type shape commonly seen in other black hole X-ray binary, and exhibits no apparent hysteresis effect. During the γ-ray outbursts, no existing data are located in the hard and intermediate states, which suggest the absence of a significant population of non-thermal electrons when the source is in these states. For the first time, we present the orbital modulation of the X-ray light curve (LC) of all five states. The different energy band LCs are in phase with each other in all five states, and the modulation amplitude of both soft and hard X-ray LCs monotonously increases with decreasing hardness from hard to soft non-thermal states. We confirm that the modulation depth decreases with increasing energy in the hard, intermediate, and very high states, as originally reported by Zdziarski et al. However, in the soft non-thermal state, the hard X-ray modulation strength significantly increases and is even larger than the soft X-ray one. Our results rule out both wind absorption and jet origins of the hard X-ray LC modulation in the soft non-thermal state, and challenge our understanding of the states of Cyg X-3. © 2013. The American Astronomical Society. All rights reserved.

Ge S.,Central China Normal University | Zhao K.,Xiangtan University | Zhang L.,Central China Normal University
Journal of Nanoparticle Research | Year: 2012

In this study, we demonstrate that the photoelectrochemical and photocatalytic properties of BiOI strongly depend on their microstructures. Compared to BiOI nanoplates with thickness <100 nm, BiOI nanoplate microspheres of 2-5 μm in size exhibited a superior photocatalytic methyl orange degradation performance, but their photocurrent was only 1/11 of that of BiOI nanoplates. The insights into the microstructure-dependent difference are discussed in detail. We think that the higher photocurrent of BiOI nanoplates film lies in more photogenerated electrons because of narrower band gap and less surface defects and better electron transport between nanoplates owing to good connectivity, while the superior photocatalytic degradation activity of BiOI nanoplate microspheres is attributed to their better methyl orange adsorption ability and abundant surface reaction sites as well as more powerful oxidative ability because of larger band gap. This study provides some clues to enhance photoelectrochemical property and photocatalytic activity of semiconductor materials. © 2012 Springer Science+Business Media B.V.

Purpose - The purpose of this paper is to present an upscale theory of the thermal-mechanical coupling particle simulation for non-isothermal problems in two-dimensional quasi-static system, under which a small length-scale particle model can exactly reproduce the same mechanical and thermal results with that of a large length-scale one. Design/methodology/approach - The objective is achieved by extending the upscale theory of particle simulation for two-dimensional quasi-static problems from an isothermal system to a non-isothermal one. Findings - Five similarity criteria, namely geometric, material (mechanical and thermal) properties, gravity acceleration, (mechanical and thermal) time steps, thermal initial and boundary conditions (Dirichlet/Neumann boundary conditions), under which a small-length-scale particle model can exactly reproduce both the mechanical and thermal behavior with that of a large length-scale model for non-isothermal problems in a two-dimensional quasi-static system are proposed. Furthermore, to test the proposed upscale theory, two typical examples subjected to different thermal boundary conditions are simulated using two particle models of different length scale. Originality/value - The paper provides some important theoretical guidances to modeling thermal-mechanical coupled problems at both the engineering length scale (i.e. the meter scale) and the geological length scale (i.e. the kilometer scale) using the particle simulation method directly. The related simulation results from two typical examples of significantly different length scales (i.e. a meter scale and a kilometer scale) have demonstrated the usefulness and correctness of the proposed upscale theory for simulating non-isothermal problems in two-dimensional quasi-static system. © Emerald Group Publishing Limited.

Yang Y.,University of Washington | Ma F.Y.,University of Washington | Lei C.H.,University of Washington | Liu Y.Y.,Xiangtan University | Li J.Y.,University of Washington
Applied Physics Letters | Year: 2013

We analyze the conversion efficiency of a bilayered thermoelectric composite, and conclude that thermoelectric conversion efficiency of a composite is not bounded by its constituents, and can be higher than all its constituents in the absence of size and interface effects. Conditions on constituent phases for enhanced conversion efficiency are also identified, and the upper bound on their conversion efficiency is established. This points to a new route for high efficiency thermoelectric materials. © 2013 American Institute of Physics.

Mao W.G.,City University of Hong Kong | Mao W.G.,Xiangtan University | Shen Y.G.,City University of Hong Kong | Lu C.,Curtin University Australia
Journal of the European Ceramic Society | Year: 2011

The nanoscale elastic-plastic characteristics of the C plane of sapphire single crystal were studied by ultra-low nanoindentation loads with a Berkovich indenter within the indentation depth less than 60. nm. The smaller the loading rate is, the greater the corresponding critical pop-in loads and the width of pop-in extension become. It is shown that hardness obviously exhibits the indentation size effect (ISE), which is 46.7 ± 15. GPa at the ISE region and is equal to 27.5 ± 2. GPa at the non-ISE region. The indentation modulus of the C plane decreases with increasing the indentation depth and equals 420.6 ± 20. GPa at the steady-state when the indentation depth exceeds 60. nm. Based on the Schmidt law, Hertzian contact theory and crystallography, the possibilities of activation of primary slip systems indented on the C surface and the distributions of critical resolved shear stresses on the slip plane were analyzed. © 2011 Elsevier Ltd.

Mao W.G.,City University of Hong Kong | Mao W.G.,Xiangtan University | Shen Y.G.,City University of Hong Kong | Lu C.,Curtin University Australia
Scripta Materialia | Year: 2011

The nanoscale pop-in phenomena in polycrystalline α-Al 2O3 and single crystal α-Al2O 3(0 0 0 1) were comparatively investigated by nanoindentation with Berkovich indenters. It was found that different radii and loading rates have significant effects on the pop-ins formation, stress distributions and dislocation nucleations. Using the Hertzian contact theory and energetic model approach, the pop-in observations and resolved shear stress analysis are consistent with the explanation that the first pop-in corresponds to the nucleation of homogeneous dislocations when the theoretical shear strength is exceeded. © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Cao H.-Y.,Fudan University | Guo Z.-X.,Xiangtan University | Xiang H.,Fudan University | Gong X.-G.,Fudan University
Physics Letters, Section A: General, Atomic and Solid State Physics | Year: 2012

Using nonequilibrium molecular dynamics method (NEMD), we have found that the thermal conductivity of multilayer graphene nanoribbons monotonously decreases with the increase of the number of layers which can be attributed to the phonon resonance effect of out-of-plane phonon modes. The reduction of thermal conductivity is proportional to the layer size, which is caused by the increase of phonon resonance. The results clearly show the dimensional evolution of thermal conductivity from quasi-one dimension to higher dimensions in graphene nanoribbons. © 2011 Elsevier B.V. All rights reserved.

Cao Z.,Nanjing University | She Q.,Nanjing University | Huang Y.,Xiangtan University | Meng X.,Nanjing University
Nanoscale Research Letters | Year: 2011

Nanoindentation creep and loading rate change tests were employed to examine the rate sensitivity (m) and hardness of nanocrystalline tetragonal Ta films. Experimental results suggested that the m increased with the decrease of feature scale, such as grain size and indent depth. The magnitude of m is much less than the corresponding grain boundary (GB) sliding deformation with m of 0.5. Hardness softening behavior was observed for smaller grain size, which supports the GB sliding mechanism. The rate-controlling deformation was interpreted by the GB-mediated processes involving atomic diffusion and the generation of dislocation at GB. © 2011 Cao et al.

Liu J.,CAS Beijing National Laboratory for Molecular | Feng Y.,CAS Beijing National Laboratory for Molecular | He Y.,CAS Beijing National Laboratory for Molecular | Yang N.,Xiangtan University | Fan Q.-H.,CAS Beijing National Laboratory for Molecular
New Journal of Chemistry | Year: 2012

A new kind of codendrimer consisting of a Fréchet-type dendron and a Tomalia-type PAMAM dendron has been synthesized via a liquid-phase approach, which could easily be purified using a simple precipitation method without the need for chromatographic separation. Functionalization at the periphery of a PAMAM dendron with bis(diphenylphosphinomethyl)amino groups led to a novel class of Janus dendritic phosphines. Their use as a recyclable homogeneous catalyst has been demonstrated with the Pd-catalyzed Suzuki coupling reaction. © 2012 The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.

Pal R.,University of Nebraska - Lincoln | Wang L.-M.,University of Pittsburgh | Pei Y.,Xiangtan University | Wang L.-S.,Brown University | Zeng X.C.,University of Nebraska - Lincoln
Journal of the American Chemical Society | Year: 2012

The activation of dioxygen is a key step in CO oxidation catalyzed by gold nanoparticles. It is known that small gold cluster anions with even-numbered atoms can molecularly chemisorb O 2 via one-electron transfer from Au n - to O 2, whereas clusters with odd-numbered atoms are inert toward O 2. Here we report spectroscopic evidence of two modes of O 2 activation by the small even-sized Au n - clusters: superoxo and peroxo chemisorption. Photoelectron spectroscopy of O 2Au 8 - revealed two distinct isomers, which can be converted from one to the other depending on the reaction time. Ab initio calculations show that there are two close-lying molecular O 2-chemisorbed isomers for O 2Au 8 -: the lower energy isomer involves a peroxo-type binding of O 2 onto Au 8 -, while the superoxo chemisorption is a slightly higher energy isomer. The computed detachment transitions of the superoxo and peroxo species are in good agreement with the experimental observation. The current work shows that there is a superoxo to peroxo chemisorption transition of O 2 on gold clusters at Au 8 -: O 2Au n - (n = 2, 4, 6) involves superoxo binding and n = 10, 12, 14, 18 involves peroxo binding, whereas the superoxo binding re-emerges at n = 20 due to the high symmetry tetrahedral structure of Au 20, which has a very low electron affinity. Hence, the two-dimensional (2D) Au 8 - is the smallest anionic gold nanoparticle that prefers peroxo binding with O 2. At Au 12 -, although both 2D and 3D isomers coexist in the cluster beam, the 3D isomer prefers the peroxo binding with O 2. © 2012 American Chemical Society.

Li S.-T.,National University of Defense Technology | Li J.-C.,National University of Defense Technology | Gu X.-C.,National University of Defense Technology | Wang H.-Y.,National University of Defense Technology | And 2 more authors.
IEEE Journal of Solid-State Circuits | Year: 2013

This paper presents a direct-conversion, multi-standard TV receiver implemented in a 0.13 m CMOS technology occupying less than 4 mm. The receiver is compliant with several direct broadcasting satellite (DBS) standards, including DVB-S, DVB-S2, and ABS-S. A novel automatic frequency tuning (AFT) technique is adopted based on a searching algorithm to ensure less than 6% bandwidth deviation of the different bandwidths (over 40 bandwidth channels) for multi-standard applications. Moreover, digitally-assisted DC offset calibration is used to improve second-order distortion and calibration time of the receiver and the residual output offset achieved is less than 3 mV. An integrated fractional-N synthesizer utilizing an optimized automatic frequency calibration (AFC) scheme enables a fast and high-precision calibration process for dual-VCO phase-locked loop (PLL) operation. The measured linearity exceeds the desired target with the minimum margin in excess of 7 dBm, and the maximum carrier-to-noise ratio (CNR) values are better than 30 dB over wide input power levels, ensuring robust reception in variable environments. All circuit blocks are operated at 2.8 V stabilized by an LDO and consuming a total current of about 56 mA. © 2013 IEEE.

Xie Y.,Xiangtan University
Advances in Intelligent and Soft Computing | Year: 2011

We find that a generalized transition function P s,t (x, y, z,A) with two parameters s, t> 0 on a measurable space has a very interesting and important property: its total transition probability P s,t (x, y, z, E) is only related to the product st of the two parameters s, t> 0 and is unrelated to the states x, y, z ∈ E. To be more exact, there is a constant 0 ≤ λ ≤ + ∞ such that P s,t (x, y, z, E) ≡ exp(-λst), ∀s, t > 0, x, y, z E. © 2011 Springer-Verlag Berlin Heidelberg.

Zhao Y.,Hunan University | Luo W.,Hunan University | Kanda P.,McMaster University | Cheng H.,Hunan University | And 4 more authors.
Talanta | Year: 2013

Silver nanoparticles coated amino modified polystyrene microspheres (PS-NH2/Ag NPs) with extremely high surface enhanced Raman scattering (SERS) activity and uniform surface morphology were created by precise controlling of deposition time. Nanojets that were formed underneath the individual microspheres could be used for nondestructive analysis of species adsorbed on the smooth gold or glass surface. A 10 fold enhancement of SERS was observed between PS-NH2/Ag NPs and gold surface compared to glass surface due to more effective coupling of surface plasmonic resonance. These microsphere SERS substrates could detect 2-Mercaptopyridine down to 10 -9M. Four different thiol compounds have been successfully utilized as tags to prepare SERS encoded PS-NH2/Ag NPs microspheres. Furthermore, the potential application of these SERS substrate for rapid detection of melamine in milk powder was explored. A linear relationship was observed between SERS intensity and logarithm of melamine concentrations with the limit of detection (LOD) of 1.9×10-8 mol/L. The promising advantages of easy sample pretreatment, low protein background interference, short detection time and low cost makes the PS-NH2/Ag NPs substrate a potential detection tool in the field of food safety. © 2013 Elsevier B.V. All rights reserved.

Li Q.,Xiangtan University | Li Q.,University of Missouri | Liang S.L.,University of Missouri | Li A.,University of Missouri
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2014

While it is well recognized that interstellar grains are made of amorphous silicates and some form of carbonaceous materials, it remains debated regarding what exact chemical and physical form the carbonaceous component takes. Contemporary grain models assume that the silicate and carbon components are either physically separated or they form a core-mantle structure, or they agglomerate to form porous composites. The core-mantle model posits that the mantle is made of some sort of aliphatic hydrocarbon materials and is responsible for the 3.4 μm absorption feature ubiquitously seen in the diffuse interstellar medium (ISM) of the Milky Way and external galaxies. This model is challenged by the non-detection of polarization in the 3.4 μm absorption feature as the 9.7 μm silicate feature is observed to be polarized. To alleviate this challenge, we calculate the degree of polarization of the 3.4 μm feature for spheroidal silicate dust coated by a layer of spherical aliphatic hydrocarbon. It is found that the 3.4 μm feature polarization still exceeds the observational upper limit, even though spherical aliphatic hydrocarbon mantles are expected to causemuch less polarization than non-spherical (e.g. spheroidal) mantles. We have also shown that the composite grain model which consists of amorphous silicate, aliphatic hydrocarbon and vacuum also predicts the 3.4 μm feature polarization to well exceed what is observed. These results support the earlier arguments that the aliphatic hydrocarbon component is physically separated from the silicate component unless the 3.4 μm absorption feature is just a minor carbon sink in the ISM. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Lu S.,Guilin University of Technology | Ban J.,Guilin University of Technology | Yu C.,Guilin University of Technology | Deng W.,Xiangtan University
Iranian Polymer Journal (English Edition) | Year: 2010

A new kind of reactive toughening agent, defined as liquid crystalline polyurethane (LCPB), having both flexible chain and rigid biphenyl mesogenic groups was synthesized by polyaddition of 2,4-toluenediisocyanate (TDI) with diethylene glycol and 4,4'-dihydroxybiphenyl in DMF. The structure and morphology of the LCPB were investigated systematically by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), wide angle X-ray diffractometry (WAXD) and polarizing optical microscopy (POM), respectively. The POM observation confirmed that the LCPB exhibited nematic texture and good mesophase stability. The LCPB was used to modify the epoxy resin as toughening agents. The mechanical properties, dynamic mechanical behaviour, fracture surface morphology and apparent activation energy (Ea) of the modified systems were systematically investigated. The experimental results revealed that the impact strength of the epoxy resin modified with LCPB reached the highest value of 47.21 kJ/m 2, and it is 1.8 times higher than that of the unmodified system when the content of LCPB loading reached 5 wt%. In addition, the tensile strength and the fracture strength also enhanced with increasing concentration of LCPB. The DMA results showed that the storage modulus in rubbery state and glass transition temperature (T g) of the modified systems were higher than those of the unmodified system, indicating that the motion of epoxy matrix chains was strongly restricted by the rigidity of mesogenic units, while the E a at glassy relaxation process of modified system was about 100-120 kJ/mol higher than that of the unmodified system. The effects of reinforcement on mechanisms of the damaging process of the modified systems were investigated by scanning electron microscopy.

Li D.-J.,JiShou University | Tang Y.,Xiangtan University
Modern Physics Letters B | Year: 2012

Starting with the Heisenberg Hamiltonian of the one-dimensional ferromagnetic chain in external fields, we have studied quantum characteristics of solitary waves and interactions between solitary waves and the time-varying electromagnetic field. It is shown that the energy and magnetic moments of the solitary wave are quantized. Utilizing these novel results, we have obtained the Bloch's equation of the two-level quantum solitary wave in a simple harmonic magnetic field. © 2012 World Scientific Publishing Company.

Hu Y.,Beijing Jiaotong University | Li D.,Beijing Jiaotong University | Shu S.,Xiangtan University | Niu X.,Shantou University
International Journal of Heat and Mass Transfer | Year: 2016

Numerical simulations are performed for natural convection in a square enclosure with a cylinder covered by a porous layer. The Darcy-Brinkmann-Forchheimer equation is adopted to describe the flow in both fluid and porous regions. To avoid the treatment of complicated interface conditions, the single domain approach based on lattice Boltzmann method (LBM) is used to solve the unified governing equation. The curved velocity and thermal boundary conditions are treated by immersed boundary method (IBM). The effects of several physical parameters, including thermal conductivity ratio, Rayleigh number and Darcy number on flow and heat transfer characteristics are investigated. The numerical results indicate the addition of a porous layer can change the flow pattern and enhance the heat transfer. © 2015 Elsevier Ltd. All rights reserved.

Deng C.-S.,Xiangtan University | Xu H.,University of South China
Physica E: Low-Dimensional Systems and Nanostructures | Year: 2012

The localization behaviors of electronic states and the role of long-range correlation (LRC) in a one-dimensional tight-binding Anderson model with long-range correlated diagonal disorder were numerically studied at the band center by using the transfer matrix method. Two different kinds of localized states with anomalous properties were found in two special localized regimes: regime I with both weak correlation and weak disorder and regime II with both strong correlation and strong disorder. Further calculations show that the LRC plays inverse role in these two regimes: by increasing the degree of LRC, the localization is suppressed in regime I while the localization is enhanced in regime II. © 2011 Elsevier B.V.

Tang P.-Y.,Guangxi University | Tang B.-Y.,Guangxi University | Tang B.-Y.,Xiangtan University | Peng L.-M.,Shanghai JiaoTong University | Ding W.-J.,Shanghai JiaoTong University
Materials Chemistry and Physics | Year: 2012

Theoretical investigations of the effect of Y and Zn atom substitution on elastic properties of 6H-type ABCBCB LPSO structure in Mg 97Zn 1Y 2 alloy have been performed from density function theory. Elastic properties, including elastic constants and elastic modulus were investigated, and the influence of Y and Zn substitution were discussed in detail. Elastic anisotropies were analyzed by several methods, and the results show that the anisotropy in compression is almost negligible, whereas the anisotropy in shear is relatively large. Furthermore, the shear anisotropy becomes larger with Zn substitution than Y substitution. The electronic characteristics indicate that the Mg-Y and Mg-Zn bonds exhibit covalent feature due to hybridization, so the interactions of Mg with Y and Zn are enhanced. © 2011 Elsevier B.V. All rights reserved.

Zhang J.,Huazhong University of Science and Technology | Zhang J.,Xiangtan University | Shi D.,Huazhong University of Science and Technology
Diangong Jishu Xuebao/Transactions of China Electrotechnical Society | Year: 2013

Four-leg converters are used to supply three-phase balanced voltages under an unbalanced or nonlinear load condition. But if the neutral point of the fourth leg is controlled incorrect, which will make output voltage contain DC component, and cause the output voltage of the four-leg converter asymmetry or the output voltage amplitude change. In order to resolve the problems of DC component caused by the neutral point voltage shift, the new topology structure of the fourth leg which contains the split DC link capacitance and series inductance of neutral line is proposed in this paper, and the mathematical model of the fourth bridge leg is established. Also the voltage and current double closed-loop control strategy is forwarded according to the mathematical model of the fourth bridge leg. At the same time, the controller of the fourth bridge leg is designed, and the steady-state error of the scheme is analyzed too. The control method of the fourth leg proposed in this paper is decoupled from the control of the other three-phase converter, and resolves the problem of DC component caused by the neutral point voltage shift. The feasibility and effectiveness of this control method is verified by PSIM simulation and experimental results.

Hu Y.,Beijing Jiaotong University | Li D.,Beijing Jiaotong University | Shu S.,Xiangtan University | Niu X.,Shantou University
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2016

Based on the Darcy-Brinkman-Forchheimer equation, a finite-volume computational model with lattice Boltzmann flux scheme is proposed for incompressible porous media flow in this paper. The fluxes across the cell interface are calculated by reconstructing the local solution of the generalized lattice Boltzmann equation for porous media flow. The time-scaled midpoint integration rule is adopted to discretize the governing equation, which makes the time step become limited by the Courant-Friedricks-Lewy condition. The force term which evaluates the effect of the porous medium is added to the discretized governing equation directly. The numerical simulations of the steady Poiseuille flow, the unsteady Womersley flow, the circular Couette flow, and the lid-driven flow are carried out to verify the present computational model. The obtained results show good agreement with the analytical, finite-difference, and/or previously published solutions. © 2016 American Physical Society.

Deng C.-S.,Xiangtan University | Xu H.,University of South China
Physica E: Low-Dimensional Systems and Nanostructures | Year: 2012

The combined effects of long-range correlations and disorder strength on critical properties of electronic states in one-dimensional systems with long-range correlated off-diagonal disorder are investigated for the whole energy band. Numerical studies on the localization length demonstrate the existence of disorder-induced delocalization-to-localization transition (DLT) and energy-induced DLT in such systems when the correlations of hopping terms are strong enough to generate extended states. Further calculations confirm that the critical disorder strength and critical energy related to these DLTs are Wc=2 t0-|E| and ± Ec=±|2 t0-W|, respectively. Based on these critical points, the detailed phase diagrams in different parameter spaces are obtained. © 2012 Elsevier B.V.

Zhang Y.,CAS Institute of Process Engineering | Zhang Y.,University of Chinese Academy of Sciences | Yu D.,Xiangtan University | Li W.,CAS Institute of Process Engineering | And 4 more authors.
Applied Energy | Year: 2013

The article is devoted to investigating some fundamentals about a residue cracking gasification (RCG) process for petroleum residues which integrates the catalytic cracking of the residue and the gasification of the cracking-generated coke. Three heat carrier particles were tested to show their different activities in cracking a vacuum residue (VR), finding that the synthesized kaolin catalyst allowed the higher liquid yield and higher conversion in comparison with silica sand and a commercial FCC catalyst. The parametric influences on the product distribution for VR cracking were thus studied over the kaolin catalyst for the major parameters including reaction temperature, catalyst-to-oil ratio, steam-to-oil ratio and different VRs. The conversion over 90% and the liquid yield above 80wt.% were achieved at 500°C under the optimized operating conditions. The VR with higher content of residual carbon was proven to generate more coke in the cracking. The coke deposited on the catalyst was well gasified via its interaction with steam and oxygen at 800°C, and the CO and H2 together was up to 80vol.% in the produced syngas. The gasification-regenerated kaolin catalyst enabled the similar product distribution of VR cracking, thus justifying the technology feasibility for the tested RCG process. © 2013 Elsevier Ltd.

Gong H.,Xiangtan University | Zeng H.,McGill University | Zhou F.,McGill University | Li C.-J.,McGill University
Angewandte Chemie - International Edition | Year: 2015

2,2'-Diaryl acids are key building blocks for some of the most important and high-performance polymers such as polyesters and polyamides (imides), as well as structural motifs of MOFs (metal-organic frameworks) and biological compounds. In this study, a direct, regiospecific and practical dimerization of simple aromatic acids to generate 2,2'-diaryl acids has been discovered, which proceeds through two rhodium-catalyzed C-H activations in water. This reaction can be easily scaled up to gram level by using only 0.4-0.6 mol% of the rhodium catalyst. As a proof-of-concept, the natural product ellagic acid was synthesized in two steps by this method. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Ye W.-B.,Xiangtan University
Journal of Thermal Analysis and Calorimetry | Year: 2015

Thermal energy storage is critical for reducing the mismatch between energy supply and demand as well as plays an important role in energy conservation. The melting process in a rectangular thermal storage cavity is investigated numerically. The numerical model is developed and verified by the experimental results. The cavity aspect ratios are varied from 0.1 to 10. The vertical walls of the cavity are heated uniformly, while the horizontal walls are considered insulated. The computational results show how the transient phase-change process depends on the aspect ratio. It is found that the aspect ratios affect dramatically not only the time of full thermal energy storage but also convection currents inside the cavity. The optimized thermal storage performance is obtained for the aspect ratios ≥1. © 2015 Akadémiai Kiadó, Budapest, Hungary

Fang Z.,Central South University | Fang Z.,Hunan Institute of Engineering | Cao C.,Hunan University of Science and Technology | Cao C.,Xiangtan University
Journal of Molecular Structure | Year: 2013

The relationship between the molecular conformation and spectroscopic properties of symmetrical bis-Schiff bases was explored experimentally. Seven samples of compounds p-X-C6H4CHNC6H 4NCHC6H4-p-X (X = OMe, Me, Et, Cl, F, CF 3, or CN) were prepared for this study, and their crystal structures were measured by X-ray diffraction. Their λmax values in ethanol, acetonitrile, chloroform and cyclohexane solvents were measured, and their δC(CN) values in chloroform-d were determined. The results show that the νmax is dependent on the substituents at the benzylidene ring and the dihedral angle τ of the titled molecules, and the term sin(τ) is suitable to modify the substituent effects on the νmax. However, experimental investigations indicate that the dihedral angle τ has a limited effect on the values of δ C(CN). This study provides a new understanding for the molecular conformation on spectroscopic properties of symmetrical Schiff bases. © 2012 Elsevier B.V. All rights reserved.

Liu Y.,Central South University | Liu Y.,Xiangtan University | Li H.,Central South University | Li Z.,Central South University
International Journal of Electrochemical Science | Year: 2013

Corrosion behavior of hot-dipped zinc-based coatings (pure zinc, Zn-0.25%Al and Zn-5%Al) was studied through potentiodynamic polarization test and electrochemical impedance spectroscopy in 3.5% NaCl solution. Corrosion products were analysed by means of SEM, EDS and XRD. The results reveal that Zn-5%Al coating exhibited the highest corrosion resistance. The corrosion product layer formed on Zn-5%Al coating is more compact than the other two coatings. The β phase has two different influences on the corrosion behavior: the β phase can act as a galvanic cathode to accelerate corrosion and act as a corrosion barrier to hinder corrosion. © 2013 by ESG.

Liu B.,Xiangtan University
Advanced Materials Research | Year: 2012

In the paper, an approach, based on bounded-error estimation via interval analysis, is presented to identify viscous damping coefficient and Coulomb friction coefficient of such-rod pumping system of directional well. The approach assumes the error of colleted output data of suck-rod pumping system is bounded. Hence, the problem of parameter estimation can be viewed as that of set inversion, which will be effectively solved via interval analysis. The main advantage of the proposed method in comparison with the traditional estimation methods is that, as it is global, it bypasses the problem of initialization. Moreover, the method avoids amount error due to transformation of measurement output data. An identification example is given to show the correctness and efficiency of the proposed method. © (2012) Trans Tech Publications, Switzerland.

Ma Y.,Xiangtan University
Wuli Xuebao/Acta Physica Sinica | Year: 2011

Variable charge molecular dynamics simulations of vitreous silica have been performed based on the iterative fluctuation charge model. The vitreous silica was formed using the standard melt-quench process. The pair distribution function, angle distribution and frequency spectrum were then obtained. The results are in good agreement with experimental data. More importantly, our results show that the atomic charge in vitreous silica is significantly different from those in the crystalline silica, and larger fluctuations are observed. © 2011 Chinese Physical Society.

Tan C.,Hunan University of Science and Technology | Liu Y.,Hunan University of Science and Technology | Liu Y.,Xiangtan University | Han Y.,Hunan University of Science and Technology | Li W.,Hunan University of Science and Technology
Journal of Luminescence | Year: 2011

Uniform Yb3 and Er3-codoped Y2O 3 hollow microspheres were synthesized via urea co-precipitation using carbon spheres as templates. Intense red emission (4F 9/2→4I15/2) and weak green emission ( 2H11/2, 4S3/2→ 4I15/2) of Er3 were observed for the Yb 3 and Er3-codoped Y2O3 hollow microspheres under 980 nm infrared excitation. The integrated intensity of visible emission and the ratio of red to green were found to be strongly dependent on the amount of carbon sphere templates and the concentration of Yb3 ions. The amount of carbon sphere templates also plays an important role in adjusting the size of crystallite. Multi-phonon relaxation resulted from the absorbents (OH- and CO3 2-) on the surface of the crystallite, and efficient occur of energy transfer processes and cross-relaxation between Er3 and Yb3 are responsible for the enhancement of intensity ratio of red to green emission. Interestingly, for higher concentration of Yb3 ions, the green emission is assigned to a three-phonon process in Y2O 3:Yb/Er hollow microspheres, which also could result in the increase of the red to green emission ratio. An explanation to account for these behaviors was presented. © 2011 Elsevier B.V. All rights reserved.

Liu Y.,Central South University | Li Y.,Xiangtan University | Li W.,Central South University | Han S.,Central South University | Liu C.,Central South University
Applied Surface Science | Year: 2012

In the present work, nitrogen-doped tungsten oxide (WO 3) nanoporous photoelectrode was studied by photoelectrochemical and photocatalytic methods in order to evaluate the photoactivity and the possibility of its application in solar photocatalysis. WO 3 nanoporous photoelectrodes were prepared by anodization of tungsten foil in NH 4F/(NH 4) 2SO 4 electrolytes, followed by annealing in NH 3/N 2 to incorporate N as a dopant. The crystal structure, composition and morphology of pure and nitrogen doped WO 3 were compared using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM). The results indicate that nitrogen can be doped successfully into WO 3 nanoporous photoelectrodes by controlling annealing temperature. Incident photon to current efficiency measurements carried out on PEC cell with N-doped WO 3 nanoporous photoelectrodes as anodes demonstrate a significant increase of photoresponse in the visible region compared to undoped WO 3 nanoporous photoelectrodes prepared at similar conditions. In particular, the photocatalytic and photoelectrocatalytic activity under visible light irradiation for newly synthesized N-doped WO 3 nanoporous photoelectrodes were investigated by degradation of methyl orange. The photoelectrocatalytic activity of N-doped WO 3 nanoporous photoelectrodes was 1.8-fold enhancement compared with pure WO 3 nanoporous photoelectrodes. © 2011 Elsevier B.V. All rights reserved.

Hang B.,Xiangtan University | Hang B.,Wuhan University
CCTAE 2010 - 2010 International Conference on Computer and Communication Technologies in Agriculture Engineering | Year: 2010

The traditional biding system does not meet the social development now. Along with the quick development of the Internet, the online biding system should be developed. This thesis focuses on analyzing how to design a secure online biding system. This system is designed for users who can release biding information, upload or download mark book and query medium mark information. © 2010 IEEE.

Cao Z.H.,Nanjing University | Huang Y.L.,Xiangtan University | Meng X.K.,Nanjing University
Scripta Materialia | Year: 2010

The rate sensitivity of hexagonal close-packed nanocrystalline Ru films was investigated by nanoindentation, which is found to be a function not only of grain size but also of indentation depth. The enhanced magnitude of the sensitivity is comparable to that of face-centered cubic nanocrystalline metals. Experimental results suggest that the interaction of dislocations with grain boundaries (GBs) and the diffusion along the tip-sample interface are the dominant mechanisms, whereas both GB sliding and Coble creep are ruled out as the rate-controlling deformations. © 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Zeng Z.-H.,Xiangtan University
Xitong Fangzhen Xuebao / Journal of System Simulation | Year: 2010

A new method of constructing symmetric orthogonal multiwavelets was designed by way of parameterization and genetic algorithm. Through this method, multifilter banks having all properties of arbitrary order vanishing moment, optimum time-frequency resolution, symmetry and orthogonality were constructed for the first time. Thus the shortcoming of the present orthogonal optimum time-frequency resolution multifilter banks was overcome that had only 2-order vanishing moment. In the same time, varies of multiwavelets were attained which appeared better in optimum time-frequency resolution and regularity. Result of image compressing shows that the multiwavelets constructed which are used in texture image compression perform better than most of the other multiwavelets which are used by other researchers. More over, these multiwavelets are better than the best wavelets up to now in a certain compression rate.

Zhu S.S.,Xiangtan University
Advanced Materials Research | Year: 2012

The current flow and pressure drop of ER valve which is a new type power control valve could be adjusted by the electric field signal directly. In this paper, the fluid power control performance of concentric cylindrical ER valve and parallel plate-type ER valve based on ER principal is comparative studied. First power control equation has been analysed, and then flow simulation of internal flow field of ER valve has been taken based on FLUENT software. The results show that with the increasing of the strength of excitation field, the flow through the two different type of ER valve decreases, the pressure drop between import and export is even greater; and the fluid power control performance of parallel plate-type ER valve is superior to concentric cylindrical ER valve under the same control volume. © (2012) Trans Tech Publications.

Ouyang T.,RWTH Aachen | Ouyang T.,Xiangtan University | Zhang X.,RWTH Aachen | Hu M.,RWTH Aachen
Nanotechnology | Year: 2015

Thermoelectric devices, which can generate electricity from waste heat, offer an attractive pathway for addressing an important niche in the globally growing landscape of energy demand. In the past few decades, the search for high-efficiency thermoelectrics has been guided by the concept of 'phonon-glass electron-crystal ' (PGEC), i.e. an ideal thermoelectric material should have high carrier mobility and low thermal conductivity. Although remarkable progress has already been made along this line, the efficiency of thermoelectrics is still too poor to compete with other electricity producing methods. Ordered-disordered material, an emerging trend of high performance thermoelectrics under the concept of PGEC, is a new hot topic in the current thermoelectric research community. Taking superionic phase silver telluride (α-Ag2Te) as an example, we performed a comprehensive study of the thermal transport properties and of its physical mechanism by means of equilibrium molecular dynamic simulations. The results show that the thermal conductivity of α-Ag2Te is intrinsically very low. By analyzing the different contributions to the overall thermal conductivity, we revealed for the first time from atomistic simulations that the vibration of the Te2- sublattice dominates the thermal transport of α-Ag2Te, while the collision between the randomly diffusing Ag+ ions and the Te2- sublattice yields a significant negative contribution to the thermal transport. We also studied the effect of isotropic compressive stain and carrier concentration on the thermal conductivity of α-Ag2Te. It has been found that the thermal conductivity can be largely reduced by applying compressive strain or with stoichiometric quantity modulation. Our studies shed light on the governing mechanism of thermal transport in ordered-disordered materials and could offer useful guidance for engineering the thermal transport properties of superionic conductors in terms of enhancing their thermoelectric performance. © 2015 IOP Publishing Ltd.

Fu X.,South China University of Technology | Fu X.,Xiangtan University | He X.,South China University of Technology | Hu X.,South China University of Technology
Colloids and Surfaces A: Physicochemical and Engineering Aspects | Year: 2012

Silica hollow microspheres with a single hole in the shell have been prepared by the precipitation-phase separation method. The synthesis was performed by mixing a tetrahydrofuran (THF)-ethanol solution of poly(styrene- co-methyl methacrylate) (P(St- co-MMA)) and tetraethyl orthosilicate (TEOS) with water, adding ammonia to catalyze the hydrolysis of TEOS and finally removing P(St- co-MMA) by calcination. The effects of the THF-to-ethanol volume ratio, the P(St- co-MMA)-to-TEOS mass ratio, the organic solvent-to-water volume ratio, and the amount of ammonia on the final morphology, size and hole size of the microspheres have been investigated. Generally, the morphology of the microspheres ranged from single-hole to bowl-like, depending on the P(St- co-MMA)-to-TEOS mass ratio; the size of the microspheres decreased with increasing THF-to-ethanol volume ratio; and the size of the holes increased with decreasing THF-to-ethanol volume ratio and decreasing organic solvent-to-water volume ratio. The formation process of single-hole silica/P(St- co-MMA) composite microspheres was monitored with transmission electron microscopy (TEM). The TEOS and P(St- co-MMA) microphases separated from each other to form a hemispherical structure, which transformed to a single-hole structure after ammonia was added. A plausible mechanism for the formation of the single-hole hollow microspheres is proposed. © 2012 Elsevier B.V.

Li D.-J.,JiShou University | Tang B.,Xiangtan University
Communications in Theoretical Physics | Year: 2014

The existence and properties of intrinsic localized spin-wave modes in a ferromagnetic XXZ spin chain with Dzyaloshinsky - Moriya interaction are investigated analytically in the semiclassical limit. The model Hamiltonian is quantized by introducing the Dyson - Maleev transformation and the coherent state representation is chosen as the basic representation of the system. By making use of the method of multiple scales combined with a quasidiscreteness approximation, the equation of motion for the coherent-state amplitude is reduced to the nonlinear Schrödinger equation. It is shown that a bright intrinsic localized spin-wave mode whose eigenfrequency lies below the bottom of the magnon frequency band can exist in the ferromagnetic system. We also show that the system can produce a dark intrinsic localized spin-wave mode, i.e., nonpropagating kink, whose eigenfrequency is below the upper of the magnon frequency band. In addition, we find that the introduction of the Dzyaloshinsky - Moriya interaction changes wave numbers in the Brillouin-zone corresponding to the appearance of intrinsic localized spin-wave modes. © 2014 Chinese Physical Society and IOP Publishing Ltd.

Li L.,University of Nebraska - Lincoln | Gao Y.,CAS Shanghai Institute of Applied Physics | Li H.,University of Nebraska - Lincoln | Zhao Y.,University of Nebraska - Lincoln | And 3 more authors.
Journal of the American Chemical Society | Year: 2013

We performed a comprehensive study of catalytic activities of subnanometer Au clusters supported on TiO2(110) surface (Aun/TiO 2, n = 1-4, 7, 16-20) by means of density functional theory (DFT) calculations and microkinetics analysis. The creditability of the chosen DFT/microkienetics methodologies was demonstrated by the very good agreement between predicted catalytic activities with experimental measurement (J. Am. Chem. Soc, 2004, 126, 5682-5483) for the Au1-4/TiO2 and Au7/TiO2 benchmark systems. For the first time, the size- and shape-dependent catalytic activities of the subnanometer Au clusters (Au16-Au20) on TiO2 supports were systematically investigated. We found that catalytic activities of the Au n/TiO2 systems increase with the size n up to Au 18, for which the hollow-cage Au18 isomer exhibits highest activity for the CO oxidation, with a reaction rate ∼30 times higher than that of Au7/TiO2 system. In stark contrast, the pyramidal isomer of Au18 exhibits much lower activity comparable to the Au 3-4/TiO2 systems. Moreover, we found that the hollow-cage Au18 is robust upon the soft-landing with an impact velocity of 200 m/s to the TiO2 substrate, and also exhibits thermal stability upon CO and O2 co-adsorption. The larger pyramidal Au19 and Au20 clusters (on the TiO2 support) display much lower reaction rates than the pyramidal Au18. Results of rate of reactions for unsupported (gas-phase) and supported Au clusters can be correlated by a contour plot that illustrates the dependence of the reaction rates on the CO and O2 adsorption energies. With the TiO2 support, however, the catalytic activities can be greatly enhanced due to the weaker adsorption of CO on the TiO2 support than on the Au clusters, thereby not only the ratio of O2/CO adsorption energy and the probability for the O 2 to occupy the Ti sites are increased but also the requirement for meeting the critical line becomes weaker. The obtained contour plot not only can provide guidance for the theoretical investigation of catalytic activity on other metal cluster/support systems, but also assist experimental design of optimal metal cluster/support systems to achieve higher catalytic efficiency. © 2013 American Chemical Society.

Hu Y.,Beijing Jiaotong University | Li D.,Beijing Jiaotong University | Shu S.,Xiangtan University | Niu X.,Shantou University
International Communications in Heat and Mass Transfer | Year: 2015

In the present study, a numerical method based on the lattice Boltzmann method and smoothed profile method is proposed to simulate the forced and natural convection flows in complex geometries. The solid-fluid boundaries are replaced by a smoothed continuous interface with a finite thickness. A concentration function is used to identify the fluid and solid regions. The flow and temperature fields in different regions are solved on fixed grids. The force term and heat source/sink are added in evolution equations to impose the velocity and temperature boundary conditions. The present approach is validated by some thermal flows examples: flow around a heated circular cylinder, natural convection in a square cavity with a heated circular cylinder, natural convection in a concentric annulus. The computed results show good agreement with the previous data. The high efficiency of the present method is also verified. © 2015 Elsevier Ltd.

Gao S.,Jiangsu University of Science and Technology | Gao S.,Xiangtan University | Cao C.,CAS Institute of Computing Technology
Advances in Information Sciences and Service Sciences | Year: 2012

Using Particle Swarm Optimization to handle complex functions with high-dimension it has the problems of low convergence speed and sensitivity to local convergence. The convergence of particle swarm algorithm is studied from the dynamic system theory, and the condition for the convergence of particle swarm algorithm is given. The analysis provided qualitative guidelines for the general algorithm parameter selection. Results of numerical tests show the efficiency of the results.

Jiang K.,Xiangtan University | Tong J.,Peking University | Zhang P.,Peking University
Communications in Computational Physics | Year: 2016

In this article, we discuss the stability of soft quasicrystalline phases in a coupled-mode Swift-Hohenberg model for three-component systems, where the characteristic length scales are governed by the positive-definite gradient terms. Classic two-mode approximation method and direct numerical minimization are applied to the model. In the latter approach, we apply the projection method to deal with the potentially quasiperiodic ground states. A variable cell method of optimizing the shape and size of higher-dimensional periodic cell is developed to minimize the free energy with respect to the order parameters. Based on the developed numerical methods, we rediscover decagonal and dodecagonal quasicrystalline phases, and find diverse periodic phases and complex modulated phases. Furthermore, phase diagrams are obtained in various phase spaces by comparing the free energies of different candidate structures. It does show not only the important roles of system parameters, but also the effect of optimizing computational domain. In particular, the optimization of computational cell allows us to capture the ground states and phase behavior with higher fidelity. We also make some discussions on our results and show the potential of applying our numerical methods to a larger class of mean-field free energy functionals. © Global-Science Press 2016.

Li Y.,Central South University of forestry and Technology | Luo H.,Xiangtan University | Luo J.,Hunan Judicial Police Vocational College
Advances in Information Sciences and Service Sciences | Year: 2012

The association rules of data mining technology have been applied into various fields. With the gradual rise of Chinese football, the connection of data mining technology and the football tactics have been imminent. This paper introduces the basic concept of data association rules, makes use of the association rules to give the characteristics of the data mining into full play, and extracts the useful information from the coaches, key players and the club information in the football match as the research object, so as to research how to apply the data mining technology into the football tactics. Through using data mining technology, the paper makes research on the football tactics, discovers and knows about the important information that is unable to be obtained from the conventional experience and intuition, and provides the effective information for the football match, so as to ensure the initiative in the football match.

Zhao C.,Ningbo Institute of Materials Technology and Engineering | Zhao C.,Xiangtan University | Shen C.,Ningbo Institute of Materials Technology and Engineering | Han W.,Ningbo Institute of Materials Technology and Engineering
RSC Advances | Year: 2015

Metal organic nanofibers (MONFs) synthesized from precursors of amino acid and copper nitrate were applied as anode materials for Li-ion batteries. Excellent cyclic stability as well as a moderate reversible capacity within the voltage range of 0.01-3.0 V were obtained (ca. 233 mA h g-1 at a current density of 50 mA g-1 following 200 cycles). This journal is © The Royal Society of Chemistry 2015.

Ma H.,Northwest Normal University | Zhao W.,Xiangtan University | Shi Z.,CAS Institute of Computing Technology
Knowledge and Information Systems | Year: 2013

In this paper, we propose a new semi-supervised co-clustering algorithm Orthogonal Semi-Supervised Nonnegative Matrix Factorization (OSS-NMF) for document clustering. In this new approach, the clustering process is carried out by incorporating both prior domain knowledge of data points (documents) in the form of pair-wise constraints and category knowledge of features (words) into the NMF co-clustering framework. Under this framework, the clustering problem is formulated as the problem of finding the local minimizer of objective function, taking into account the dual prior knowledge. The update rules are derived, and an iterative algorithm is designed for the co-clustering process. Theoretically, we prove the correctness and convergence of our algorithm and demonstrate its mathematical rigorous. Our experimental evaluations show that the proposed document clustering model presents remarkable performance improvements with those constraints. © 2012 Springer-Verlag London.

Wu M.,University of Nebraska - Lincoln | Wu X.,Anhui University of Science and Technology | Pei Y.,Xiangtan University | Wang Y.,University of Nebraska - Lincoln | Zeng X.C.,University of Nebraska - Lincoln
Chemical Communications | Year: 2011

We design two network models of carbon and boron nitride crystalline networks, namely, the honeycomb and triangular foams. The triangular carbon foam is a unique 3D network model of carbon which contains only sp 2-carbon bonds. Also, it has large internal surface area per unit volume and bulk modulus. © 2011 The Royal Society of Chemistry.

Guo Y.,Nanjing University | Lan X.,Nanjing University | Cao J.,Xiangtan University | Xu B.,Nanjing University | And 3 more authors.
International Journal of Hydrogen Energy | Year: 2013

In virtue of the first-principle calculations, the hydrogen storage behavior in several metal decorated graphyne was investigated. It is found that the hydrogen storage capacity can be as large as 18.6, 10.5, 9.9 and 9.5 wt% with average adsorption energy of about -0.27, -0.36, -0.76 and -0.70 eV/H 2 for Li, Ca, Sc, Ti decorated graphyne, respectively. The results suggest potential candidates for hydrogen storage at ambient condition. The adsorption mechanism for H2 on metal coated graphyne was mainly attributed to the polarization induced by electrostatic field of metal atoms on graphyne and the hybridization between the metal atoms and hydrogen molecules. Furthermore, the formation of super-molecules of hydrogen can enhance the adsorption energy. © 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Zeng Y.,Central South University | Xiong X.,Central South University | Wang D.,Central South University | Wu L.,Xiangtan University
Carbon | Year: 2015

Carbon/carbon(C/C)-Zr-Ti-C composites were fabricated using chemical vapor infiltration and liquid metal infiltration processes. The residual thermal stress (RTS) distribution in the C/C-Zr-Ti-C composites was analyzed by Raman spectroscopy and finite element (FE) calculation. The mechanical behaviors of C/C-Zr-Ti-C composites with three types of carbon fiber preforms were tested. The results showed that there was very high compressive RTS in the fibers and high tensile RTS in the pyrocarbon (PyC) in the marginal region near the carbide. However, in the central region away from the carbide, relatively low compressive stress and tensile RTS were found in the fibers and PyC, respectively. The FE analysis showed that the introduction of carbide into the C/C composites caused a significant increase of the RTS in the PyC near the carbide, indicating that the carbide could change the RTS distribution in C/C composites. Moreover, the distribution of the RTS and its release combined with the carbide distribution and fiber architecture led to variations in the mechanical performance of composites with different preforms. © 2014 Elsevier Ltd. All rights reserved.

Li Z.-S.,Xiangtan University | Li Z.-S.,Beijing University of Technology
Astronomische Nachrichten | Year: 2015

The Rossi X-ray Timing Explorer observed three photospheric radius expansion bursts in 4U 1746-37, all with low touchdown fluxes. We discuss the possibiity of a low-mass neutron star in 4U 1746-37 if the touchdown flux corresponds to its Eddington limit. 4U 1746-37 is a dipping binary system which has a high inclination angle. Two geometric effects, the reflection of the far side accretion disc and the obscuration of the near side accretion disc have also been included. We apply a Monte-Carlo simulation, with typical values of hydrogen mass fraction and color correction factor, to constrain the mass and radius of the neutron star in 4U 1746-37. We found that the mass of 4U 1746-37 is 0.41+0.70 –0.30 M® at 99.7 % confidence which is an ultra-low-mass compact star candidate. It could be reproduced by a self-bound compact star, i.e., quark star or quark-cluster star, from an ccretion-induced collapse process. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim). Copyright © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Guo X.,Tianjin University of Science and Technology | Wang Z.,Tianjin University of Technology and Education | Zheng Q.,Guizhou Normal University | Peng J.,Xiangtan University
International Journal of Modern Physics B | Year: 2015

We investigate the topological phases of a three-dimensional (3D) topological insulator (TI) without the top-bottom inversion symmetry. We calculate the momentum depended spin Chern number to extract the phase diagram. Various phases are found and we address the dependence of phase boundaries on the strength of inversion asymmetry. Opposite to the quasi-two-dimensional thin film TI, in our 3D system the TI state is stabilized by the structure inversion asymmetry (SIA). With a strong SIA the 3D TI phase can exist even under a large Zeeman field. In a tight-binding form, the surface modes are discussed to confirm with the phase diagram. Particularly we find that the SIA cannot destroy the surface states but open a gap on its spectrum. © 2015 World Scientific Publishing Company.

Jiang K.,Xiangtan University | Jiang K.,Peking University | Xu W.,Peking University | Zhang P.,Peking University
Communications in Computational Physics | Year: 2015

This paper concerns the analytic structure of the self-consistent field theory (SCFT) energy functional of multicomponent block copolymer systems which contain more than two chemically distinct blocks. The SCFT has enjoyed considered success and wide usage in investigation of the complex phase behavior of block copolymers. It is well-known that the physical solutions of the SCFT equations are saddle points, however, the analytic structure of the SCFT energy functional has received little attention over the years. A recent work by Fredrickson and collaborators [see the monograph by Fredrickson, The Equilibrium Theory of Inhomogeneous Polymers, (2006), pp. 203-209] has analysed the mathematical structure of the field energy functional for polymeric systems, and clarified the index-1 saddle point nature of the problem caused by the incompressible constraint. In this paper, our goals are to draw further attention to multicomponent block copolymers utilizing the Hubbard-Stratonovich transformation used by Fredrickson and co-workers. We firstly show that the saddle point character of the SCFT energy functional of multicomponent block copolymer systems may be high index, not only produced by the incompressible constraint, but also by the Flory-Huggins interaction parameters. Our analysis will be beneficial to many theoretical studies, such as the nucleation theory of ordered phases, the mesoscopic dynamics. As an application, we utilize the discovery to develop the gradient-based iterative schemes to solve the SCFT equations, and illustrate its performance through several numerical experiments taking ABC star triblock copolymers as an example. © Global-Science Press 2015.

Sun C.Q.,Nanyang Technological University | Sun C.Q.,Xiangtan University | Sun C.Q.,Jilin University
Nanoscale | Year: 2010

Although they exist ubiquitously in human bodies and our surroundings, the impact of nonbonding lone electrons and lone electron pairs has long been underestimated. Recent progress demonstrates that: (i) in addition to the shorter and stronger bonds between under-coordinated atoms that initiate the size trends of the otherwise constant bulk properties when a substance turns into the nanoscale, the presence of lone electrons near to broken bonds generates fascinating phenomena that bulk materials do not demonstrate; (ii) the lone electron pairs and the lone pair-induced dipoles associated with C, N, O, and F tetrahedral coordination bonding form functional groups in biological, organic, and inorganic specimens. By taking examples of surface vacancy, atomic chain end and terrace edge states, catalytic enhancement, conducting-insulating transitions of metal clusters, defect magnetism, Coulomb repulsion at nanoscale contacts, Cu3C2H2 and Cu3O 2 surface dipole formation, lone pair neutralized interface stress, etc, this article will focus on the development and applications of theory regarding the energetics and dynamics of nonbonding electrons, aiming to raise the awareness of their revolutionary impact to the society. Discussion will also extend to the prospective impacts of nonbonding electrons on mysteries such as catalytic enhancement and catalysts design, the density anomalies of ice and negative thermal expansion, high critical temperature superconductivity induced by B, C, N, O, and F, the molecular structures and functionalities of CF 4 in anti-coagulation of synthetic blood, NO signaling, and enzyme telomeres, etc. Meanwhile, an emphasis is placed on the necessity and effectiveness of understanding the properties of substances from the perspective of bond and nonbond formation, dissociation, relaxation and vibration, and the associated energetics and dynamics of charge repopulation, polarization, densification, and localization. Finding and grasping the factors controlling the nonbonding states and making them of use in functional materials design and identifying their limitations will form, in the near future, a subject area of "nonbonding electronics and energetics", which could be even more challenging, fascinating, promising, and rewarding than dealing with core or valence electrons alone. © The Royal Society of Chemistry 2010.

Wang Y.,Max Planck Institute for Polymer Research | Wang Y.,Xiangtan University | Chen L.,Max Planck Institute for Polymer Research | Chen L.,Tianjin University | And 3 more authors.
Chemical Communications | Year: 2014

A series of benzodipyrrolidone-based dimeric aza-BODIPY dyes with a push-pull structure are synthesized. Single crystal X-ray diffraction demonstrates these extended aza-BODIPY dyes are planar. The resulting aza-BODIPY chromophores exhibit intense absorption in the 450-800 nm regions and possess lower-lying LUMO energy levels. Furthermore, the push-pull substituents on aza-BODIPYs core have a positive effect on their optophysical properties. This journal is © The Royal Society of Chemistry 2014

Liu C.,Nanjing University | Pei Y.,Xiangtan University | Sun H.,Nanjing University | Ma J.,Nanjing University
Journal of the American Chemical Society | Year: 2015

The understanding of the evolution mechanism of thiolate-protected Au nanoclusters from the homoleptic Au(I)-SR clusters to core-stacked ones is crucial for the synthesis of novel thiolated Au clusters. In this work, the global search for a series of "intermediate" Aum(SR)n clusters with m and n ranging from 5 to 12 was implemented by combining basin hopping algorithm, genetic algorithm, and density functional theory (DFT) calculations. Most of Aum(SR)n clusters possess the core-shell structure. Specifically, some typical topologies, such as tetrahedral Au4, triangular bipyramid Au5, octahedral Au6, and vertex-shared Au7, are found to be dominant within the inner core of various clusters. Along with the increase in the number of gold atoms and thiolates, the preliminary nucleation and growth processes of both inner-core and staple-motif protecting units are grouped into three kinds of size evolution routes, i.e., core growth, core dissolution, and staple-motif growth, respectively. Some metastable isomers may also play an important role in the evolution of clusters. The core structures in the lowest-lying isomers and some metastable isomers are similar to the intact or part of the cores found in experimentally detected species. Both the lowest-lying and metastable intermediate clusters may serve as the building block for the further growth. These results rationalize the preliminary nucleation in the "reduction growth" stage, shedding light on the size-evolution mechanism of RS-AuNPs. © 2015 American Chemical Society.

Liu B.,Central South University | Zou Y.,Central South University | Peng B.,Central South University | Zhao B.,Xiangtan University | And 3 more authors.
Polymer Chemistry | Year: 2011

Three new low bandgap isoindigo-based conjugated polymers were synthesized, namely poly {(N-octyl)-carbazole-2,7-diyl-alt-[N,N'-(2-ethylhexyl)-isoindigo]- 6',6"-diyl} (PCzID), poly{(9, 9-dioctylfluorene)-2,7-diyl-alt-[N,N-(2- ethylhexyl)-isoindigo]-6',6-diyl} (PFID), and poly{4, 8-bis(2-ethylhexoxy)- benzo[1,2-b,3,4-b]-dithiophene-2,6-diyl-alt-[N,N'-(2-ethylhexyl)-isoindigo]-6', 6''-diyl} (PBDTID), by Stille or Suzuki coupling polymerization reaction. All of the polymers were soluble in common organic solvents, such as chloroform, tetrahydrofuran, and chlorobenzene with good film forming properties. The polymer films exhibit broad absorption bands in the wavelength region from 300 nm to 810 nm. Especially, PBDTID possesses the smallest bandgap of 1.54 eV calculated from its absorption cut-off at 806 nm. Preliminary photovoltaic cells based on the device structure of ITO/ PEDOT:PSS/PBDTID:PC60BM (1 : 1 w/w)/Ca/Al showed an open-circuit voltage of 0.56 V, a power conversion efficiency of 0.9% and a short circuit current of 3.81 mA cmr2. © The Royal Society of Chemistry 2011.

Huang Y.,Xiangtan University | Li J.,University of Nevada, Las Vegas
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2010

In this paper, we present three second-order finite element methods solving Maxwell's equations when metamaterials are involved. The first method is based on integral-differential equations transformed from the governing equations; the other two methods solve the original governing differential equations. Numerical results are presented for the last two methods. © 2010 Springer-Verlag.

Nyamoradi N.,Razi University | Zhou Y.,Xiangtan University
JVC/Journal of Vibration and Control | Year: 2016

In this paper, by using variational methods, we prove the existence for a class of fractional Hamiltonian systems with Liouville-Weyl fractional derivatives { t D α (-∞ Dt α u (t)) + b (t) u (t) - λ u (t) = μf (t, u (t)), t εℝ u ε H α (ℝ) where α ε (1 / 2, 1 ], t D ∞ α and -∞ D t α are the right and left inverse operators of the corresponding Liouville-Weyl fractional integrals of order α respectively, u ε ℝ, b: ℝ → ℝ, b ε L ∞ (ℝ), inf t εℝ b (t) > 0, λ, μ are real parameters and f: ℝ × ℝ → ℝ is a function that satisfies some suitable conditions. © SAGE Publications.

Hu G.,University of Macau | Hu G.,UM Zhuhai Research Institute | Yi N.,Xiangtan University
Journal of Computational Physics | Year: 2016

In this paper, we present an adaptive finite volume method for steady Euler equations with a non-oscillatory k-exact reconstruction on unstructured mesh. The numerical framework includes a Newton method as an outer iteration to linearize the Euler equations, and a geometrical multigrid method as an inner iteration to solve the derived linear system. A non-oscillatory k-exact reconstruction of the conservative solution in each element is proposed for the high order and non-oscillatory behavior of the numerical solutions. The importance on handling the curved boundary in an appropriate way is also studied with the numerical experiments. The h-adaptive method is introduced to enhance the efficiency of the algorithm. The numerical tests show successfully that the quality solutions can be obtained smoothly with the proposed algorithm, i.e., the expected convergence order of the numerical solution with the mesh refinement can be reached, while the non-oscillation shock structure can be obtained. Furthermore, the mesh adaptive method with the appropriate error indicators can effectively enhance the implementation efficiency of numerical method, while the steady state convergence and numerical accuracy are kept in the meantime. © 2016 Elsevier Inc.

Cao Z.H.,University College of Applied Sciences | Wang L.,University College of Applied Sciences | Hu K.,University College of Applied Sciences | Huang Y.L.,Xiangtan University | Meng X.K.,University College of Applied Sciences
Acta Materialia | Year: 2012

Indentation creep and stress relaxation tests were performed on rolled and annealed nanocrystalline (NC) Ni to study the influence of microstructure evolution on plastic deformation behavior. Dislocation density (ρ) increases with increasing rolling strain, reaching a maximum at 20% strain, followed by a decrease at larger strain. The ρ of Ni decreases significantly with increasing annealing temperature. Softening behavior is observed in NC Ni with grain size <40 nm, i.e., an inverse-like Hall-Petch effect. For rolling NC Ni, both creep strain rate and rate sensitivity first increase and then decrease, while those of annealed Ni continuously decrease. With increasing grain size, creep activation volume unusually decreases first, then starts to rise, which is different from that of coarse-grained metal. A model involving dislocation annihilation and emission at grain boundaries under indenters is used to explain the anomalous behavior of rolled and annealed Ni, respectively. © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Li C.-Y.,Key Laboratory of Environmentally Friendly Chemistry and Applications | Zou C.-X.,Key Laboratory of Environmentally Friendly Chemistry and Applications | Li Y.-F.,Xiangtan University | Tang J.-L.,Key Laboratory of Environmentally Friendly Chemistry and Applications | Weng C.,Key Laboratory of Environmentally Friendly Chemistry and Applications
Dyes and Pigments | Year: 2014

A new rhodamine-based compound (1) has been synthesized and applied as an "off-on" chemosensor for Fe3+. The comparison of this method with some other fluorescence methods for Fe3+ indicates that the method can detect Fe3+ in living cells by fluorescence enhancement and color changes with high sensitivity and selectivity. The fluorescence intensity of 1 is significantly increased about 60-fold with 20 equiv of Fe3+ added. Most importantly, the fluorescence changes of the chemosensor are remarkably specific for Fe3+ in the presence of other metal ions, which meet the selective requirements for practical application. Moreover, the experiment results show that the response behavior of 1 towards Fe3+ is pH independent in neutral condition (pH 6.0-8.0) and the response of the chemosensor is fast (response time less than 2 min). In addition, the proposed chemosensor has been used for imaging of Fe3+ in living cells with satisfying results. © 2014 Elsevier Ltd. All rights reserved.

Mao W.,City University of Hong Kong | Mao W.,Xiangtan University | Shen Y.,City University of Hong Kong
Journal of the American Ceramic Society | Year: 2012

The pop-in behavior and mechanical properties of sapphire crystal vertically indented to its rhombohedral R (101̄2) plane were investigated by nanoindentation using a Berkovich indenter. Effect of loading rate on pop-in load and pop-in extension width was observed within the indentation depth of h < 120 nm. The indentation size effect (ISE) of hardness within an indentation depth of 60 nm was systematically analyzed using Nix-Gao and Al-Rub models. Our experiments provided the consistent evaluations of hardness (H = 27.5 GPa), true hardness (H true = 68.9 GPa) at the non-ISE region and effective indentation modulus (M = 423 GPa) for the contact depth of h c > 20 nm. Using the Hertzian contact theory, Schmid's law, and energy principle of indentation, the possible dominant slip system, which mainly contributed to the first pop-in event when indented normal to the (101̄2) plane, was estimated as {101̄1} <1̄21̄0>. The distributions of corresponding resolved shear stress and principal stresses at the slip plane were also estimated. © 2012 The American Ceramic Society.

Yang J.,Hunan Institute of Engineering | Yang J.,Xiangtan University
International Journal of Computer Mathematics | Year: 2015

Discontinuous Galerkin (DG) approximations for non-linear parabolic problems are investigated. To linearize the discretized equations, we use a two-grid method involving a small non-linear system on a coarse gird of size H and a linear system on a fine grid of size h. Error estimates in H1-norm are obtained, O(hr+Hr+1) where r is the order of the DG space. The analysis shows that our two-grid DG algorithm will achieve asymptotically optimal approximation as long as the mesh sizes satisfy h=O(H(r+1)/r). The numerical experiments verify the efficiency of our algorithm. © 2014 Taylor & Francis.

Hu Y.,Beijing Jiaotong University | Li D.,Beijing Jiaotong University | Shu S.,Xiangtan University | Niu X.,Shantou University
Computers and Mathematics with Applications | Year: 2015

In this paper, we extend the lattice Boltzmann method (LBM) in combination with the immersed boundary method (IBM) to simulate the steady-state fluid-solid conjugate heat transfer problems in complex geometries. The no-slip boundary condition is handled by the immersed boundary method. The "pseudo-solid-specific-heat" technique is used to ensure the continuity of heat flux at the fluid-solid interface. The present LB thermal field solver retains the simple structure of standards thermal LB model. The performance of the present method is validated by several heat conduction/convection problems. The numerical results agree well with exact solutions or published results. © 2015 Elsevier Ltd. All rights reserved.

Zeng S.,Hong Kong Polytechnic University | Zeng S.,Xiangtan University | Tsang M.-K.,Hong Kong Polytechnic University | Chan C.-F.,Hong Kong Polytechnic University | And 3 more authors.
Biomaterials | Year: 2012

Herein, a multi-functional nanoprobe of polyethylene glycol (PEG) modified BaGdF5:Yb/Er upconversion nanoparticles (UCNPs) for tri-modal bioimaging of fluorescence, computed X-ray tomography (CT), and magnetic application is demonstrated for the first time. The PEG-modified BaGdF5:Yb/Er UCNPs with optimal small size were synthesized by a facile one-pot hydrothermal method. The as-designed single-phase nanoprobe presents near-infrared to visible upconversion emissions in UC fluorescent bioimaging of HeLa cell. Importantly, we have demonstrated in vivo CT images with enhanced signals of spleen of a mouse for 2 h, indicating the UCNPs can be successfully used as CT contrast agent for improving the detection of splenic diseases. In addition, these UCNPs also exhibit excellent intrinsic paramagnetic property which can be also for magnetic imaging. Therefore, our results indicate that a tri-modal nanoprobe served as fluorescent/CT/magnetic bioimaging can be realized using the PEG-modified BaGdF5:Yb/Er UCNPs with very low cytotoxicity and long circulation time, which would be very useful in a variety of biomedical application fields. © 2012 Elsevier Ltd.

Pei Y.,University of Nebraska - Lincoln | Pei Y.,Xiangtan University | Zeng X.C.,University of Nebraska - Lincoln
Journal of Applied Physics | Year: 2011

We computed structural and elastic properties of totally nine phases of poly(vinyldene fluoride) (PVDF) crystals using the density-functional theory (DFT) method with and without inclusion of the dispersion corrections. In addition to the four known crystalline forms, mechanic properties of five theoretically predicted crystalline forms of PVDF are also investigated. The all-trans form Ip exhibits the largest cohesive energy, bulk, and Young's modulus among the nine crystalline forms. The DFT calculations suggest that the λ crystalline forms (IIIau, IIIpu, IIIpd, and IIIad) possess poor chain rigidity among the nine PVDF crystalline forms. In contrast, a change of relative orientation of PVDF chains does not lead to significant change in cohesive energy and mechanic properties. A comparison of the cohesive energies of nine crystalline forms of PVDF suggests that the theoretically proposed crystalline forms of PVDF are quite stable. © 2011 American Institute of Physics.

Jianxin D.,Xiangtan University | Jianxin D.,Shandong University | Hui Z.,Shandong University | Ze W.,Shandong University | Aihua L.,Shandong University
International Journal of Refractory Metals and Hard Materials | Year: 2011

The friction and wear behavior of the polycrystalline diamond (PCD) were evaluated in ambient air at temperatures up to 700 °C using a ball-on-disk high temperature tribometer. The wear surface features of the PCD were examined by scanning electron microscopy. Energy dispersive X-ray analysis was used to investigate the chemical composition. XRD experiments were performed to study the crystal structure of the PCD specimens at different temperatures. Results showed that the friction coefficient of the PCD is different depending on the temperature, and decreases with the increase of temperature. The PCD exhibited the lowest friction coefficient of approximately 0.16 in the case of 700 °C sliding operation. The difference of the worn surface features of the PCD after sliding at different temperatures is related to the chemical transformation during sliding wear tests. The surface damage of the PCD appears to happen around 600 °C accompanied by extensive Co phase extrusion out of PCD. Numerous micro-cracks both at the grain boundaries and in the grains are observed with the increase of temperature to 700 °C. At this temperature, surface graphitization of diamond is to be expected, and the formation of graphite on the wear track is beneficial to the reduction of friction coefficient. © 2011 Elsevier Ltd.

Tan S.,Xiangtan University
Solar Energy Materials and Solar Cells | Year: 2010

A new type of stainless steel mesh-based flexible quasi-solid dye-sensitized solar cell (DSSC) was designed and fabricated by using electrospun TiO2 nanofibers web as a light scattering layer and stainless steel foil coated with polypyrrole (PPy) nanoparticles as counter electrode. The photovoltaic performance measurements showed that electrospun TiO2 nanofibers web was propitious to light harvesting ability and energy conversion efficiency. Cyclic voltammogram measurement revealed that PPy electrode possessed smaller charge-transfer resistance and higher electrocatalytic activity for the I2/I- redox reaction than that of Pt electrode. A overall energy conversion efficiency (η) of 2.36% was obtained based on a DSSC with N719 dye as sensitizer and PPy nanoparticles coated on the stainless steel foil as counter electrode, which attained 84% of the η value (2.80%) of the quasi-solid DSSC with Pt foil as counter electrode. © 2010 Elsevier B.V. All rights reserved.

Jiang K.,Peking University | Jiang K.,Xiangtan University | Zhang P.,Peking University
Journal of Computational Physics | Year: 2014

Quasicrystals are one kind of space-filling structures. The traditional crystalline approximant method utilizes periodic structures to approximate quasicrystals. The errors of this approach come from two parts: the numerical discretization, and the approximate error of Simultaneous Diophantine Approximation which also determines the size of the domain necessary for accurate solution. As the approximate error decreases, the computational complexity grows rapidly, and moreover, the approximate error always exits unless the computational region is the full space. In this work we focus on the development of numerical method to compute quasicrystals with high accuracy. With the help of higher-dimensional reciprocal space, a new projection method is developed to compute quasicrystals. The approach enables us to calculate quasicrystals rather than crystalline approximants. Compared with the crystalline approximant method, the projection method overcomes the restrictions of the Simultaneous Diophantine Approximation, and can also use periodic boundary conditions conveniently. Meanwhile, the proposed method efficiently reduces the computational complexity through implementing in a unit cell and using pseudospectral method. For illustrative purpose we work with the Lifshitz-Petrich model, though our present algorithm will apply to more general systems including quasicrystals. We find that the projection method can maintain the rotational symmetry accurately. More significantly, the algorithm can calculate the free energy density to high precision. © 2013 Elsevier Inc.

Leung Y.,Chinese University of Hong Kong | Ge E.,Chinese University of Hong Kong | Yu Z.,Xiangtan University
Annals of the Association of American Geographers | Year: 2011

The highly pathogenic avian influenza A H5N1 has become a serious public health problem, fatal to poultry and humans all over the world. Since its detection in 2003, H5N1 viruses have exhibited considerable capability of transmission from wild birds to humans, spreading from southeastern Asia across Europe and into Africa. Avian influenza has been recognized as a potential pandemic by practitioners and scientists and has become an important research issue in virology, molecular biology, phylogeography, and spatial epidemiology. Although avian influenza has explicit spatial and temporal dimensions, rigorous geographical analysis, particular its temporal process, of the outbreaks is at its initial stage. The purpose of this article is to provide an approach to study the temporal behaviors of avian influenza A (H5N1) over multiple time scales by analyzing the global and continental outbreak time series from December 2003 to March 2009. The detection of long-range correlation and multifractality in the outbreak series provide answers to the following questions: (1) whether previous H5N1 outbreaks are responsible for and have long-term effects on current infections; (2) whether H5N1 outbreaks have special temporal patterns manifested by multiscaling behaviors; and (3) whether H5N1 outbreaks over time are heterogeneous in different parts of the world. Multifractal detrended fluctuation analysis is employed in this study to detect long-range correlation and multifractal scaling behaviors of the H5N1 outbreaks. Experimental results show that H5N1 outbreaks are long-range correlated and multifractal. The temporal patterns are heterogeneous over space. This implies that H5N1 outbreaks behave differently under different ecosystems, poultry farm practices, and public health measures. © 2011 by Association of American Geographers.

Hu J.,Peking University | Huang Y.,Xiangtan University | Lin Q.,CAS Academy of Mathematics and Systems Science
Journal of Scientific Computing | Year: 2014

The paper is to introduce a new systematic method that can produce lower bounds for eigenvalues. The main idea is to use nonconforming finite element methods. The conclusion is that if local approximation properties of nonconforming finite element spaces are better than total errors (sums of global approximation errors and consistency errors) of nonconforming finite element methods, corresponding methods will produce lower bounds for eigenvalues. More precisely, under three conditions on continuity and approximation properties of nonconforming finite element spaces we analyze abstract error estimates of approximate eigenvalues and eigenfunctions. Subsequently, we propose one more condition and prove that it is sufficient to guarantee nonconforming finite element methods to produce lower bounds for eigenvalues of symmetric elliptic operators. We show that this condition hold for most low-order nonconforming finite elements in literature. In addition, this condition provides a guidance to modify known nonconforming elements in literature and to propose new nonconforming elements. In fact, we enrich locally the Crouzeix-Raviart element such that the new element satisfies the condition; we also propose a new nonconforming element for second order elliptic operators and prove that it will yield lower bounds for eigenvalues. Finally, we prove the saturation condition for most nonconforming elements. © 2014 Springer Science+Business Media New York.

He L.,South China University of Technology | He L.,Xiangtan University | Ling Z.,South China University of Technology
Applied Physics Letters | Year: 2011

Mn1.85Co0.3Ni0.85O4 thin films with single cubic spinel phase and compact surface were prepared by chemical solution deposition method on Al2 O3 substrates. Temperature dependent ac impedance spectroscopy was employed to analyze the contributions of grain boundary (GB) and grain to the conduction mechanism. The major characteristics (hopping type, resistance versus temperature behavior, and characteristic temperature T0) of the GB and grain were obtained. The hopping type of GB is nearest-neighbor-hopping (NNH), and that of grain might be a transition from variable-range-hopping to NNH. The GB shows dominating resistance while the grain shows stronger temperature dependence. © 2011 American Institute of Physics.

Yanxiang F.,Xiangtan University
International Journal of Digital Content Technology and its Applications | Year: 2012

Human-computer interaction, also called user interface or man-machine interface, refers to the method and action of transmitting and exchanging messages between man and computer. In its narrow sense, it indicates the interaction between the man and the computer system, namely the user utilizes the computer program me and the program me responding to the man's operation. This paper discusses the human-computer interaction design of the software based on unified interactive mode.

Zhou J.,South China University of Technology | Luo G.,Xiangtan University | Fang X.,South China University of Technology
Jianzhu Jiegou Xuebao/Journal of Building Structures | Year: 2011

This paper addressed the seismic vulnerability of vertically irregular reinforced concrete structure subjected to velocity pulse-like ground motions. Employing a 5-story and a 10-story frame structure with vertical irregularities at the first story and considering the randomness of input ground motions, the maximum inter-story displacement demands of the first story were obtained by nonlinear dynamic time history analysis and were related to spectrum acceleration of the fundamental vibration period by curve fitting method. Logarithm normal distribution was assumed for the maximum inter-story displacement demands and limit performance target displacement, the seismic fragility curves for evaluating the irregular limit parameters were produced. The results show that strength and stiffness irregularities have important influence on the structural inter-story drift under different strong velocity pulse-like ground motions. The maximum inter-story drift at the first story increases with the increase of the degree of irregularity, whereas the maximum inter-story drift at the middle story decreases. The dispersion of the maximum inter-story drift increases with the increase of ground motion intensity. In addition, strength and stiffness irregularities also have significant influence on the seismic fragility curve. The shape of the fragility curve varies due to the different number of story.

Zhang J.,University of Liverpool | Zhang J.,Xiangtan University | Chen K.,University of Liverpool
Journal of Computational Physics | Year: 2015

In this paper, a new framework of nonlocal deformation in non-rigid image registration is presented. It is well known that many non-rigid image registration techniques may lead to unsteady deformation (e.g. not one to one) if the dissimilarity between the reference and template images is too large. We present a novel variational framework of the total fractional-order variation to derive the underlying fractional Euler-Lagrange equations and a numerical implementation combining the semi-implicit update and conjugate gradients (CG) solution to solve the nonlinear systems. Numerical experiments show that the new registration not only produces accurate and smooth solutions but also allows for a large rigid alignment, the evaluations of the new model demonstrate substantial improvements in accuracy and robustness over the conventional image registration approaches. © 2015 Elsevier Inc.

Zhong L.,South China Normal University | Liu C.,Hunan University | Shu S.,Xiangtan University
Computers and Mathematics with Applications | Year: 2013

Two-level additive preconditioners are presented for edge element discretizations of time-harmonic Maxwell equations. The key is to construct a special "coarse mesh" space, which adds the kernel of the curl-operator in a fine space to a coarse mesh space, to solve the original problem, and then uses the fine mesh space to solve the H(curl)-elliptic problem. It is shown that the generalized minimal residual (GMRES) method applied to the preconditioned system converges uniformly provided that the coarsest mesh size is reasonably small (but independent of the fine mesh size) and the parameter for the "coarse mesh" space solver is sufficiently large. Numerical experiments show the efficiency of the proposed approach. © 2013 Elsevier Ltd. All rights reserved.

Hang B.,Xiangtan University
Proceedings - 2011 International Symposium on Computer Science and Society, ISCCS 2011 | Year: 2011

On-line online examination system development's overall goal is in realizes in Internet and local area network's online test. On-line online test system is the typical B/S construction system, its development mainly includes the development of the application, the database establishment and maintains. In the application procedure's development aspect, IBM Corporation's My Eclipse is used in design to carry on the programming design. It has introduced the object-oriented programming thought that causes the system interface to be friendly, the function is perfect, and the operation is flexible, easy to operate. At the same time, in the database establishment and the maintenance aspect, My SQL is used as the development kit of the database system. It is suitable for the Unix/Windowes service platform, is the database development platform, which is used widely in the large and middle scale system. © 2011 IEEE.

Jia Z.,Xiangtan University
ICMREE2011 - Proceedings 2011 International Conference on Materials for Renewable Energy and Environment | Year: 2011

In this paper, single-crystalline Ni(SO 4) 0.3(OH) 1.4 nanocrystals could be synthesized on a large scale by a facile hydrothermal treatment without using templates or organic additives. Ammonia concentration played an important role for the composition, phase structure and shape control of the the Ni(SO 4) 0.3(OH) 1.4 nanobelts. Electrochemical measurement revealed that the asprepared Ni(SO 4) 0.3(OH) 1.4 nanobelts exhibited high specific capacity close to the theoretical capacity performance of -Ni(OH)2. On the other hand, the single-crystalline porous nickel oxide nanobeltsnanobelts can be obtained through calcination of the Ni(SO 4) 0.3(OH) 1.4. nanobelts. © 2011 IEEE.

Zhang Y.-M.,CAS Beijing National Laboratory for Molecular | Zhang Y.-M.,Xiangtan University | Shao J.-Y.,CAS Beijing National Laboratory for Molecular | Yao C.-J.,CAS Beijing National Laboratory for Molecular | And 2 more authors.
Dalton Transactions | Year: 2012

The first series of cyclometalated ruthenium complexes with a CCC-pincer bis-carbene ligand have been obtained as bench-stable compounds. Single-crystal X-ray analysis of one of these complexes with 4′-di-p-anisylamino-2, 2′:6′,2′′-terpyridine is presented. The Ru II/III redox potentials and MLCT absorptions of these complexes can be varied by attaching an electron-donating or -withdrawing group on the noncyclometalating ligand. © 2012 The Royal Society of Chemistry.

Huang R.,Xiangtan University
BIT Numerical Mathematics | Year: 2013

In this paper, we consider how to factor symmetric totally nonpositive matrices and their inverses by taking advantage of the symmetric property. It is well-known that the Bunch-Kaufman algorithm is the most commonly used pivoting strategy which can, however, produce arbitrarily large entries in the lower triangular factor for such matrices as illustrated by our example. Therefore, it is interesting to show that when the Bunch-Parlett algorithm is simplified for these matrices, it only requires O(n 2) comparisons with the growth factor being nicely bounded by 4. These facts, together with a nicely bounded lower triangular factor and a pleasantly small relative backward error, show that the Bunch-Parlett algorithm is more preferable than the Bunch-Kaufman algorithm when dealing with these matrices. © 2012 Springer Science+Business Media Dordrecht.

Deng P.-H.,Hengyang Normal University | Feng Y.-L.,Hengyang Normal University | Fei J.-J.,Xiangtan University
Journal of Electroanalytical Chemistry | Year: 2011

A sensitive procedure was developed for the determination of trace molybdenum(VI) by adsorptive anodic stripping voltammetry based on the oxidation of molybdenum(VI)-2′,3,4′,5,7-pentahydroxyflavone (morin) complex at a sodium dodecyl sulfate modified carbon paste electrode (denoted as SDS/CPE). Compared with the poor response at a conventional paste electrode, the electrooxidation of molybdenum(VI)-morin complex at the SDS/CPE was greatly improved, as confirmed from the significant enhancement of peak current and the negative shift of peak potentials. The optimum conditions for the analysis of molybdenum(VI) include 0.1 M sulfuric acid, 3.0 × 10 -5 M or 3.0 × 10 -6 M morin, an accumulation potential of -0.1 V (versus SCE), an accumulation period of 60 s or 120 s and a scan rate of 0.1 V s -1. Under the selected conditions, the linearity between peak currents and concentrations of molybdenum(VI) existed for a wide range of 8.0 × 10 -10-6.0 × 10 -8 M (c morin = 3 × 10 -6 M) for 120 s accumulation and 6.0 × 10 -8-6.0 × 10 -6 M (c morin = 3 × 10 -5 M) for 60 s accumulation, a low detection limit (three times signal to noise) of 4.0 × 10 -10 M was obtained after a 120 s preconcentration. The proposed method was successfully applied to the determination of molybdenum(VI) in real samples with enhanced selectivity. © 2011 Elsevier B.V. All rights reserved.

Jia Z.,Xiangtan University
Advanced Materials Research | Year: 2011

Single crystalline Cd(OH)2 low-dimensional nanostructures, such as nanowires, nanobelts, and nanorolls have been controlled synthesized through a convenient, low-temperature hydrothermal method. Moreover, the shape and diameter of 1D Cd(OH)2 nanostructures can be facilely controlled through adjusting the experiment factors. The influences of the ammonia concentration, temperature on the morphology of Cd(OH)2 are investigated, and a possible mechanism involved adjustable growth properties from kinetic growth stage to thermodynamic growth stage has been discussed. This work has also provided a general, simple, and effective method to control the shape of other transition-metal carbonate. © (2011) Trans Tech Publications.

Long Y.,A+ Network | Ouyang J.,Xiangtan University
Journal of Networks | Year: 2013

This paper proposes a novel multicast reliability algorithm in distributed virtual environment. Firstly, architecture of the distributed virtual environment system is made up of three layers, which are 1) Layer 1 is made up of distributed virtual environment server, which can transmit information from internet to clients, 2) Layer 2 is constructed by clients, which are connected to a specific server and can only solve a specific task, and 3) Layer 3 are tasks which should be solved by the distributed virtual environment system. Afterwards, the multicast problem of distributed virtual environment can be converted into a tree network with several nodes, of which the key issue is how to obtain a multicast strategy with the maximum reliability satisfying several constraints. Then, a multicast reliability algorithm for the distributed virtual environment system is present by finding key nodes and key paths in the tree network. Finally, experiments are conducted by both the performance evaluation metric "average cost" and "blocking probability" to demonstrate the effectiveness of the proposed algorithm. © 2013 ACADEMY PUBLISHER.

Peng X.,Xiangtan University | Peng X.,Uppsala University | Ahuja R.,Uppsala University
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

We studied very large graphene/Ru systems by ab initio calculations. It is shown that the graphene monolayer on Ru is nearly flat rather than strongly corrugated. The large corrugation is found to be unfavorable and disagrees with the observed bias dependence of scanning tunnel microscope images. The C-Ru bonds are metallic instead of covalent. A new moiré structure arises between graphene bilayers and the generally supposed Bernal stacking is broken. The second layer has higher density of C atoms and is slightly corrugated. While the electronic states of the first graphene layer are shifted down by about 1 eV, the electronic structure of the second one resembles that of the free graphene, in good agreement with the experiments. © 2010 The American Physical Society.