Showing papers by "Xi'an Jiaotong University published in 2011"

FSIM: A Feature Similarity Index for Image Quality Assessment

Abstract: Image quality assessment (IQA) aims to use computational models to measure the image quality consistently with subjective evaluations. The well-known structural similarity index brings IQA from pixel- to structure-based stage. In this paper, a novel feature similarity (FSIM) index for full reference IQA is proposed based on the fact that human visual system (HVS) understands an image mainly according to its low-level features. Specifically, the phase congruency (PC), which is a dimensionless measure of the significance of a local structure, is used as the primary feature in FSIM. Considering that PC is contrast invariant while the contrast information does affect HVS' perception of image quality, the image gradient magnitude (GM) is employed as the secondary feature in FSIM. PC and GM play complementary roles in characterizing the image local quality. After obtaining the local quality map, we use PC again as a weighting function to derive a single quality score. Extensive experiments performed on six benchmark IQA databases demonstrate that FSIM can achieve much higher consistency with the subjective evaluations than state-of-the-art IQA metrics.

Learning to Detect a Salient Object

Abstract: In this paper, we study the salient object detection problem for images. We formulate this problem as a binary labeling task where we separate the salient object from the background. We propose a set of novel features, including multiscale contrast, center-surround histogram, and color spatial distribution, to describe a salient object locally, regionally, and globally. A conditional random field is learned to effectively combine these features for salient object detection. Further, we extend the proposed approach to detect a salient object from sequential images by introducing the dynamic salient features. We collected a large image database containing tens of thousands of carefully labeled images by multiple users and a video segment database, and conducted a set of experiments over them to demonstrate the effectiveness of the proposed approach.

Nanostructured WO3/BiVO4 Heterojunction Films for Efficient Photoelectrochemical Water Splitting

Abstract: We report on a novel heterojunction WO3/BiVO4 photoanode for photoelectrochemical water splitting. The heterojunction films are prepared by solvothermal deposition of a WO3 nanorod-array film onto fluorine-doped tin oxide (FTO) coated glass, with subsequent deposition of a low bandgap, 2.4 eV, visible light responding BiVO4 layer by spin-coating. The heterojunction structure offers enhanced photoconversion efficiency and increased photocorrosion stability. Compared to planar WO3/BiVO4 heterojunction films, the nanorod-array films show significantly improved photoelectrochemical properties due, we believe, to the high surface area and improved separation of the photogenerated charge at the WO3/BiVO4 interface. Synthesis details are discussed, with film morphologies and structures characterized by field emission scanning electron microscopy and X-ray diffraction.

Anisotropic Swelling and Fracture of Silicon Nanowires during Lithiation

Abstract: We report direct observation of an unexpected anisotropic swelling of Si nanowires during lithiation against either a solid electrolyte with a lithium counter-electrode or a liquid electrolyte with a LiCoO2 counter-electrode. Such anisotropic expansion is attributed to the interfacial processes of accommodating large volumetric strains at the lithiation reaction front that depend sensitively on the crystallographic orientation. This anisotropic swelling results in lithiated Si nanowires with a remarkable dumbbell-shaped cross section, which develops due to plastic flow and an ensuing necking instability that is induced by the tensile hoop stress buildup in the lithiated shell. The plasticity-driven morphological instabilities often lead to fracture in lithiated nanowires, now captured in video. These results provide important insight into the battery degradation mechanisms.

Toward ubiquitous massive accesses in 3GPP machine-to-machine communications

Abstract: To enable full mechanical automation where each smart device can play multiple roles among sensor, decision maker, and action executor, it is essential to construct scrupulous connections among all devices. Machine-to-machine communications thus emerge to achieve ubiquitous communications among all devices. With the merit of providing higher-layer connections, scenarios of 3GPP have been regarded as the promising solution facilitating M2M communications, which is being standardized as an emphatic application to be supported by LTE-Advanced. However, distinct features in M2M communications create diverse challenges from those in human-to-human communications. To deeply understand M2M communications in 3GPP, in this article, we provide an overview of the network architecture and features of M2M communications in 3GPP, and identify potential issues on the air interface, including physical layer transmissions, the random access procedure, and radio resources allocation supporting the most critical QoS provisioning. An effective solution is further proposed to provide QoS guarantees to facilitate M2M applications with inviolable hard timing constraints.

Vertically Aligned WO3 Nanowire Arrays Grown Directly on Transparent Conducting Oxide Coated Glass: Synthesis and Photoelectrochemical Properties

Abstract: Photocorrosion stable WO3 nanowire arrays are synthesized by a solvothermal technique on fluorine-doped tin oxide coated glass. WO3 morphologies of hexagonal and monoclinic structure, ranging from nanowire to nanoflake arrays, are tailored by adjusting solution composition with growth along the (001) direction. Photoelectrochemical measurements of illustrative films show incident photon-to-current conversion efficiencies higher than 60% at 400 nm with a photocurrent of 1.43 mA/cm2 under AM 1.5G illumination. Our solvothermal film growth technique offers an exciting opportunity for growth of one-dimensional metal oxide nanostructures with practical application in photoelectrochemical energy conversion.

Recombination centres and the orchestration of V(D)J recombination.

Abstract: The initiation of V(D)J recombination by the recombination activating gene 1 (RAG1) and RAG2 proteins is carefully orchestrated to ensure that antigen receptor gene assembly occurs in the appropriate cell lineage and in the proper developmental order. Here we review recent advances in our understanding of how DNA binding and cleavage by the RAG proteins are regulated by the chromatin structure and architecture of antigen receptor genes. These advances suggest novel mechanisms for both the targeting and the mistargeting of V(D)J recombination, and have implications for how these events contribute to genome instability and lymphoid malignancy.

Automatic Salient Object Segmentation Based on Context and Shape Prior

Abstract: We propose a novel automatic salient object segmentation algorithm which integrates both bottom-up salient stimuli and object-level shape prior, i.e., a salient object has a well-defined closed boundary. Our approach is formalized as an iterative energy minimization framework, leading to binary segmentation of the salient object. Such energy minimization is initialized with a saliency map which is computed through context analysis based on multi-scale superpixels. Object-level shape prior is then extracted combining saliency with object boundary information. Both saliency map and shape prior update after each iteration. Experimental results on two public benchmark datasets show that our proposed approach outperforms state-of-the-art methods.

What Is New for an Old Molecule? Systematic Review and Recommendations on the Use of Resveratrol

Abstract: Background: Resveratrol is a natural compound suggested to have beneficial health effects. However, people are consuming resveratrol for this reason without having the adequate scientific evidence for its effects in humans. Therefore, scientific valid recommendations concerning the human intake of resveratrol based on available published scientific data are necessary. Such recommendations were formulated after the Resveratrol 2010 conference, held in September 2010 in Helsingor, Denmark. Methodology: Literature search in databases as PubMed and ISI Web of Science in combination with manual search was used to answer the following five questions: 1 Can resveratrol be recommended in the prevention or treatment of human diseases?; 2 Are there observed ‘‘side effects’’ caused by the intake of resveratrol in humans?; 3 What is the relevant dose of resveratrol?; 4 What valid data are available regarding an effect in various species of experimental animals?; 5 Which relevant (overall) mechanisms of action of resveratrol have been documented? Conclusions/Significance: The overall conclusion is that the published evidence is not sufficiently strong to justify a recommendation for the administration of resveratrol to humans, beyond the dose which can be obtained from dietary sources. On the other hand, animal data are promising in prevention of various cancer types, coronary heart diseases and diabetes which strongly indicate the need for human clinical trials. Finally, we suggest directions for future research in resveratrol regarding its mechanism of action and its safety and toxicology in human subjects.

Glacial-Interglacial Indian Summer Monsoon Dynamics

Abstract: The modern Indian summer monsoon (ISM) is characterized by exceptionally strong interhemispheric transport, indicating the importance of both Northern and Southern Hemisphere processes driving monsoon variability. Here, we present a high-resolution continental record from southwestern China that demonstrates the importance of interhemispheric forcing in driving ISM variability at the glacial-interglacial time scale as well. Interglacial ISM maxima are dominated by an enhanced Indian low associated with global ice volume minima. In contrast, the glacial ISM reaches a minimum, and actually begins to increase, before global ice volume reaches a maximum. We attribute this early strengthening to an increased cross-equatorial pressure gradient derived from Southern Hemisphere high-latitude cooling. This mechanism explains much of the nonorbital scale variance in the Pleistocene ISM record.

New Design Tactics in OLEDs Using Functionalized 2‐Phenylpyridine‐Type Cyclometalates of Iridium(III) and Platinum(II)

Abstract: As a result of their outstanding attributes, organic light-emitting diodes (OLEDs) and white organic light-emitting diodes (WOLEDs) have been recognized in recent years as the most promising candidates for future flat-panel display technologies and next generation solid-state energy-saving lighting sources New advancements in the area of high performance triplet emitters become vital for realizing more practical applications In this regard, several critical issues must be carefully identified and addressed, and these include the ways to enhance device efficiency and suppress efficiency roll-off, to achieve versatile color tuning and simple device manufacture, as well as to obtain high-quality white light from WOLEDs It has been shown that some functionalized phosphorescent Ir(III) and Pt(II) ppy-type cyclometalated complexes (ppy = 2-phenylpyridine) possess unique features that are suitable for solving these difficult and challenging tasks In this Focus Review, we will highlight the recent design tactics adopted for these functional metallophosphors and the critical roles they may play in developing more realistic devices

Large dielectric constant and high thermal conductivity in poly(vinylidene fluoride)/barium titanate/silicon carbide three-phase nanocomposites.

Abstract: Dielectric polymer composites with high dielectric constants and high thermal conductivity have many potential applications in modern electronic and electrical industry. In this study, three-phase composites comprising poly(vinylidene fluoride) (PVDF), barium titanate (BT) nanoparticles, and β-silicon carbide (β-SiC) whiskers were prepared. The superiority of this method is that, when compared with the two-phase PVDF/BT composites, three-phase composites not only show significantly increased dielectric constants but also have higher thermal conductivity. Our results show that the addition of 17.5 vol % β-SiC whiskers increases the dielectric constants of PVDF/BT nanocomposites from 39 to 325 at 1000 Hz, while the addition of 20.0 vol % β-SiC whiskers increases the thermal conductivity of PVDF/BT nanocomposites from 1.05 to 1.68 W m–1 K–1 at 25 °C. PVDF/β-SiC composites were also prepared for comparative research. It was found that PVDF/BT/β-SiC composites show much higher dielectric constants in compariso...

Glucose-assisted growth of MoS2 nanosheets on CNT backbone for improved lithium storage properties.

Abstract: As a typical layered inorganic material, molybdenum disulfide (MoS2) has a similar structure to graphite. In the crystal structure of MoS2, each Mo(IV) sits in the center of a triangular prism, and is bound to six S atoms. Each S atom is connected to three Mo centers. In this way, the triangular prisms are interconnected to give a layered structure, wherein the Mo atoms are sandwiched between two layers of S atoms. Because of the weak van der Waals interactions between the sheets, MoS2 has a low friction coefficient; this gives rise to its superior lubricating properties. It has also been found attractive in many other application, including catalysts and transistors. Additionally, the layered structure of MoS2 enables easy intercalation of metal ions, such as Li or Mg . Many different MoS2 nanostructures, such as nanoflakes, nanotubes and nanoflowers, have been reported so far as anode materials for lithium ion batteries (LIBs). Although some of them show relatively high capacities of up to 1000 mAhg , the unsatisfactory cycling stability hinders their practical application as anode materials of LIBs. Some methods have been proposed to improve the cycling performance of MoS2, for example, construction of composite materials of MoS2 and conductive carbonaceous materials, like amorphous carbon, carbon nanotubes (CNTs), or graphene. For example, Li et al. reported a hybrid material of CNTs coated with several layers of MoS2. [15] When tested for lithium storage capabilities, the CNT@MoS2 hybrid structure shows a relatively good cyclic capacity retention with a reversible capacity of only up to 400 mAhg , probably due to the low mass fraction of MoS2 in the composite. Thus, obtaining a high content of MoS2 in the CNT@MoS2 is important for a better lithium storage capability. Many CNT-based hybrid structures have been prepared for different applications. 17] Herein, we report a simple glucose-assisted hydrothermal method to directly grow MoS2 nanosheets (NSs) on the CNT backbone (CNT@MoS2 NSs). The content of MoS2 in the hybrid structure is greatly increased because the shell is composed of sheet-like subunits. At the same time, the large surface area provided by this unique hierarchical structure can perhaps help to store more lithium, and the void space between these sheet-like subunits can buffer the volume change during the charge/ discharge processes, and lead to improved cyclic capacity retention. Furthermore, the carbon derived from glucose could ensure an excellent contact between the CNT backbone and the shell of MoS2 NSs, and give rise to a good conducting network. As expected, in comparison with pure MoS2 flakes, these CNT@MoS2 NS nanocomposites show enhanced lithium storage properties with better cyclic capacity retention and a higher reversible capacity. Figure 1 shows the morphology of the as-prepared CNT@MoS2 NSs. From the scanning electron microscopy

Twins in Cd1−xZnxS solid solution: Highly efficient photocatalyst for hydrogen generation from water

Abstract: Cd1−xZnxS solid solution with nano-twin structures are synthesized and exhibit superior photocatalytic activities for H2 evolution from water under visible light irradiation (λ ≥ 430 nm) without noble metal co-catalysts. Such Cd0.5Zn0.5S nanocrystals show the highest activity for hydrogen evolution with an extremely high apparent quantum yield (AQY = 43%) at 425 nm, achieving a hydrogen evolution rate of 1.79 mmol h−1 without noble metals. The hydrogen evolution rate of 1.70 mmol h−1 was achieved under simulated sunlight conditions (without infrared light). The “back to back” potential formed by parallel nano-twins in the Cd1−xZnxS crystals can significantly improve the separation of the photo-generated electrons/holes (preventing their recombination) thus enhancing the photocatalytic activity. Photodeposition experiments of noble metals strongly support such a mechanism. It is found that noble metals were selectively photo-deposited at central regions between the twin boundaries. The concentration of free electrons at the central region of twins was markedly higher and the twins can effectively separate the H2 evolution sites (electrons) from oxidation reaction sites (holes).

Numerics of the lattice Boltzmann method: Effects of collision models on the lattice Boltzmann simulations

Abstract: We conduct a comparative study to evaluate several lattice Boltzmann (LB) models for solving the near incompressible Navier-Stokes equations, including the lattice Boltzmann equation with the multiple-relaxation-time (MRT), the two-relaxation-time (TRT), the single-relaxation-time (SRT) collision models, and the entropic lattice Boltzmann equation (ELBE). The lid-driven square cavity flow in two dimensions is used as a benchmark test. Our results demonstrate that the ELBE does not improve the numerical stability of the SRT or the lattice Bhatnagar-Gross-Krook (LBGK) model. Our results also show that the MRT and TRT LB models are superior to the ELBE and LBGK models in terms of accuracy, stability, and computational efficiency and that the ELBE scheme is the most inferior among the LB models tested in this study, thus is unfit for carrying out numerical simulations in practice. Our study suggests that, to optimize the accuracy, stability, and efficiency in the MRT model, it requires at least three independently adjustable relaxation rates: one for the shear viscosity ν (or the Reynolds number Re), one for the bulk viscosity ζ, and one to satisfy the criterion imposed by the Dirichlet boundary conditions which are realized by the bounce-back-type boundary conditions.

A General Software Defect-Proneness Prediction Framework

Abstract: BACKGROUND - Predicting defect-prone software components is an economically important activity and so has received a good deal of attention. However, making sense of the many, and sometimes seemingly inconsistent, results is difficult. OBJECTIVE - We propose and evaluate a general framework for software defect prediction that supports 1) unbiased and 2) comprehensive comparison between competing prediction systems. METHOD - The framework is comprised of 1) scheme evaluation and 2) defect prediction components. The scheme evaluation analyzes the prediction performance of competing learning schemes for given historical data sets. The defect predictor builds models according to the evaluated learning scheme and predicts software defects with new data according to the constructed model. In order to demonstrate the performance of the proposed framework, we use both simulation and publicly available software defect data sets. RESULTS - The results show that we should choose different learning schemes for different data sets (i.e., no scheme dominates), that small details in conducting how evaluations are conducted can completely reverse findings, and last, that our proposed framework is more effective and less prone to bias than previous approaches. CONCLUSIONS - Failure to properly or fully evaluate a learning scheme can be misleading; however, these problems may be overcome by our proposed framework.

Organometallic acetylides of PtII, AuI and HgII as new generation optical power limiting materials

Abstract: Within the scope of nonlinear optics, optical power limiting (OPL) materials are commonly regarded as an important class of compounds which can protect the delicate optical sensors or human eyes from sudden exposure to damaging intense laser beams. Recent efforts have been devoted to developing organometallic acetylide complexes, dendrimers and polymers as high performance OPL materials of the next generation which can favorably optimize the optical limiting/transparency trade-off issue. These metallated materials offer a new avenue towards a new family of highly transparent homo- and heterometallic optical limiters with good solution processability which outperform those of current state-of-the-art visible-light-absorbing competitors such as fullerenes, metalloporphyrins and metallophthalocyanines. This critical review aims to provide a detailed account on the recent advances of these novel OPL chromophores. Their OPL activity was shown to depend strongly on the electronic characters of the aryleneethynylene ligand and transition metal moieties as well as the conjugation chain length of the compounds. Strategies including copolymerization with other transition metals, change of structural geometry, use of a dendritic platform and variation of the type and content of transition metal ions would strongly govern their photophysical behavior and improve the resulting OPL responses. Special emphasis is placed on the structure–OPL response relationships of these organometallic acetylide materials. The research endeavors for realizing practical OPL devices based on these materials have also been presented. This article concludes with perspectives on the current status of the field, as well as opportunities that lie just beyond its frontier (106 references).

Microwave assisted extraction of secondary metabolites from plants: Current status and future directions

Abstract: Plant secondary metabolites are known to be an important source of foods, fragrances, pigment, drugs and so on. Extraction is one of the crucial steps for research and development of plant secondary metabolites. Over the past 25 years, a large number of manuscripts of microwave assisted extraction have been published and lots of remarkable results have been achieved. However, there are still many theoretical and technical barriers in the area of microwave assisted extraction of plant secondary metabolites, which need to be overcome. This paper reviews recent advances in microwave assisted extraction of plant secondary metabolites, such as flavonoids, quinones, phenylpropanoids, terpenoids and alkaloids. Principles and mechanisms, apparatuses and equipment, advantages and disadvantages of microwave assisted extraction are also summarized. The last part of the paper introduces new and emerging technologies of microwave technique, and then suggests strategies for further research into microwave assisted extraction of plant secondary metabolites.

Gradient Profile Prior and Its Applications in Image Super-Resolution and Enhancement

Abstract: In this paper, we propose a novel generic image prior-gradient profile prior, which implies the prior knowledge of natural image gradients. In this prior, the image gradients are represented by gradient profiles, which are 1-D profiles of gradient magnitudes perpendicular to image structures. We model the gradient profiles by a parametric gradient profile model. Using this model, the prior knowledge of the gradient profiles are learned from a large collection of natural images, which are called gradient profile prior. Based on this prior, we propose a gradient field transformation to constrain the gradient fields of the high resolution image and the enhanced image when performing single image super-resolution and sharpness enhancement. With this simple but very effective approach, we are able to produce state-of-the-art results. The reconstructed high resolution images or the enhanced images are sharp while have rare ringing or jaggy artifacts.

EEMD method and WNN for fault diagnosis of locomotive roller bearings

Abstract: Research highlights? EEMD and WNN are combined to propose an automated fault diagnosis method. ? Features are extracted from the sensitive IMF of EEMD in this method. ? The features are fed into WNN to identify the bearing health conditions. ? The method can identify the fault severities and the compound faults. The ensemble empirical mode decomposition (EEMD) can overcome the mode mixing problem of the empirical mode decomposition (EMD) and therefore provide more precise decomposition results. Wavelet neural network (WNN) possesses the advantages of both wavelet transform and artificial neural networks. This paper combines the merits of EEMD and WNN to propose an automated and effective fault diagnosis method of locomotive roller bearings. First, the vibration signals captured from the locomotive roller bearings are preprocessed by EEMD method and intrinsic mode functions (IMFs) are produced. Second, a kurtosis based method is presented and used to select the sensitive IMF. Third, time- and frequency-domain features are extracted from the sensitive IMF, its frequency spectrum and its envelope spectrum. Finally, these features are fed into WNN to identify the bearing health conditions. The diagnosis results show that the proposed method enables the identification of the single faults in the bearings and at the same time the recognition of the fault severities and the compound faults.

Entrepreneurial Orientation, Organizational Learning, and Performance: Evidence From China

Abstract: This study examined the relationships among entrepreneurial orientation (EO), experimental learning (EL) and acquisitive learning (AL), and firm performance (FP). We tested our model in China as EO...

Mechanisms of Large Actuation Strain in Dielectric Elastomers

Abstract: Subject to a voltage, a dielectric elastomer (DE) deforms. Voltage-induced strains of above 100% have been observed when DEs are prestretched, and for DEs of certain net- work structures. Understanding mechanisms of large actuation strains is an active area of research. We propose that the volt- age-stretch response of DEs may be modified by prestretch, or by using polymers with ''short'' chains. This modification results in suppression or elimination of electromechanical instability, leading to large actuation strains. We propose a method to select and design a DE, such that the actuation strain is maxi- mized. The theoretical predictions agree well with existing exper- imental data. The theory may contribute to the development of DEs with exceptional performance. V C 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 504-515, 2011