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Search Results: 1 - 10 of 104219 matches for " ZHANG Shiliang "
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Hybrid Orthogonal Projection and Estimation (HOPE): A New Framework to Probe and Learn Neural Networks
Shiliang Zhang,Hui Jiang
Computer Science , 2015,
Abstract: In this paper, we propose a novel model for high-dimensional data, called the Hybrid Orthogonal Projection and Estimation (HOPE) model, which combines a linear orthogonal projection and a finite mixture model under a unified generative modeling framework. The HOPE model itself can be learned unsupervised from unlabelled data based on the maximum likelihood estimation as well as discriminatively from labelled data. More interestingly, we have shown the proposed HOPE models are closely related to neural networks (NNs) in a sense that each hidden layer can be reformulated as a HOPE model. As a result, the HOPE framework can be used as a novel tool to probe why and how NNs work, more importantly, to learn NNs in either supervised or unsupervised ways. In this work, we have investigated the HOPE framework to learn NNs for several standard tasks, including image recognition on MNIST and speech recognition on TIMIT. Experimental results have shown that the HOPE framework yields significant performance gains over the current state-of-the-art methods in various types of NN learning problems, including unsupervised feature learning, supervised or semi-supervised learning.
Characterizing Spatiotemporal Dynamics of Methane Emissions from Rice Paddies in Northeast China from 1990 to 2010
Yuan Zhang, Shiliang Su, Feng Zhang, Runhe Shi, Wei Gao
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0029156
Abstract: Background Rice paddies have been identified as major methane (CH4) source induced by human activities. As a major rice production region in Northern China, the rice paddies in the Three-Rivers Plain (TRP) have experienced large changes in spatial distribution over the recent 20 years (from 1990 to 2010). Consequently, accurate estimation and characterization of spatiotemporal patterns of CH4 emissions from rice paddies has become an pressing issue for assessing the environmental impacts of agroecosystems, and further making GHG mitigation strategies at regional or global levels. Methodology/Principal Findings Integrating remote sensing mapping with a process-based biogeochemistry model, Denitrification and Decomposition (DNDC), was utilized to quantify the regional CH4 emissions from the entire rice paddies in study region. Based on site validation and sensitivity tests, geographic information system (GIS) databases with the spatially differentiated input information were constructed to drive DNDC upscaling for its regional simulations. Results showed that (1) The large change in total methane emission that occurred in 2000 and 2010 compared to 1990 is distributed to the explosive growth in amounts of rice planted; (2) the spatial variations in CH4 fluxes in this study are mainly attributed to the most sensitive factor soil properties, i.e., soil clay fraction and soil organic carbon (SOC) content, and (3) the warming climate could enhance CH4 emission in the cool paddies. Conclusions/Significance The study concluded that the introduction of remote sensing analysis into the DNDC upscaling has a great capability in timely quantifying the methane emissions from cool paddies with fast land use and cover changes. And also, it confirmed that the northern wetland agroecosystems made great contributions to global greenhouse gas inventory.
Atomic packing and short-to-medium range order evolution of Zr-Pd metallic glass
Li Qi,Mei Liu,ShiLiang Zhang,XinYu Zhang,ChunLin Tan
Chinese Science Bulletin , 2011, DOI: 10.1007/s11434-011-4841-0
Abstract: A larger-scale Zr70Pd30 alloy system has been simulated using molecular dynamics (MD) to investigate structure evolution in Zr70Pd30 metallic glass. The simulated pair distribution function of Zr70Pd30 metallic glass agrees well with the experimental results. Voronoi polyhedron analysis indicates that the icosahedra are not randomly distributed in space, but form characteristic intercrossed icosahedral clusters with medium-range order. Intercrossed icosahedral clusters are the dominant local configurations in Zr70Pd30 metallic glass and probably cause the quasicrystalline phase discovered in Zr70Pd30 metallic glass.
Improving AOR Method for a Class of Two-by-Two Linear System  [PDF]
Cuixia Li, Shiliang Wu
Applied Mathematics (AM) , 2011, DOI: 10.4236/am.2011.22026
Abstract: In this paper, the preconditioned accelerated overrelaxation (AOR) method for solving a class of two-by-two linear systems is presented. A new preconditioner is proposed according to the idea of [1] by Wu and Huang. The spectral radii of the iteration matrix of the preconditioned and the original methods are compared. The comparison results show that the convergence rate of the preconditioned AOR methods is indeed better than that of the original AOR methods, whenever the original AOR methods are convergent under certain conditions. Finally, a numerical example is presented to confirm our results.
Pressure influence on bound polarons in a strained wurtzite GaN/AlxGa1-xN heterojunction under an electric field
电场下应变纤锌矿GaN/AlxGa1-xN异质结中束缚极化子的压力效应

Zhang Min,Ban Shiliang,
张敏
,班士良

半导体学报 , 2010,
Abstract: The binding energies of bound polarons near the interface of a strained wurtzite GaN/Al_xGa_(1-x)N het-erojunction are studied by using a modified LLP variational method and a simplified coherent potential approximation under hydrostatic pressure and an external electric field.Considering the biaxial strain due to lattice mismatch or epitaxial growth,the uniaxial strain effects and the influences of the electron-phonon interaction as well as impurity-phonon interaction including the effects of interface-opt...
DNA barcoding: species delimitation in tree peonies
JinMei Zhang,JianXiu Wang,Tao Xia,ShiLiang Zhou
Science China Life Sciences , 2009, DOI: 10.1007/s11427-009-0069-5
Abstract: Delimitations of species are crucial for correct and precise identification of taxa. Unfortunately “species” is more a subjective than an objective concept in taxonomic practice due to difficulties in revealing patterns of infra- or inter-specific variations. Molecular phylogenetic studies at the population level solve this problem and lay a sound foundation for DNA barcoding. In this paper we exemplify the necessity of adopting a phylogenetic concept of species in DNA barcoding for tree peonies (Paeonia sect. Moutan). We used 40 samples representing all known populations of rare and endangered species and several populations of widely distributed tree peonies. All currently recognized species and major variants have been included in this study. Four chloroplast gene fragments, i.e. ndhF, rps16-trnQ, trnL-F and trnS-G (a total of 5040 characters, 96 variable and 69 parsimony-informative characters) and one variable and single-copy nuclear GPAT gene fragment (2093–2197 bp, 279 variable and 148 parsimony-informative characters) were used to construct phylogenetic relationships among the taxa. The evolutionary lineages revealed by the nuclear gene and the chloroplast genes are inconsistent with the current circumscriptions of P. decomposita, P. jishanensis, P. qiui, and P. rockii based on morphology. The inconsistencies come from (1) significant chloroplast gene divergence but little nuclear GPAT gene divergence among population systems of P. decomposita + P. rockii, and (2) well-diverged nuclear GPAT gene but little chloroplast gene divergence between P. jishanensis and P. qiui. The incongruence of the phylogenies based on the chloroplast genes and the nuclear GPAT gene is probably due to the chloroplast capture event in evolutionary history, as no reproductive barriers exist to prevent inter-specific hybridization. We also evaluated the suitability of these genes for use as DNA barcodes for tree peonies. The variability of chloroplast genes among well-defined species or population systems of a species complex is 4.82 times the figure within the groups, and the GPAT gene is twice as variable between the groups as within the groups. The number of completely divergent sites is sufficient to mark the two subsections, the two species in subsection Delavayanae, and the well-divergent species in subsection Vaginatae. But the genes currently used either from the chloroplast genome or from the nuclear genome alone cannot correctly assign samples of P. decomposita, P. jishanensis, P. qiui, or P. rockii to the species as currently defined. We conclude that (1) DNA barcoding should be based on prior phylogenetic studies to understand the evolutionary lineages and how well the taxonomic species correspond to the lineages; (2) it is unlikely to find a single short fragment as a barcode for every plant and such a fragment could result in misidentification when a chloroplast capture event happened in the evolutionary history of plants like tree peonies; and (3) w
Influence of Magnetic Field on Bound Polarons in Semiconductor GaAs/AlxGa1-xAs Heterojunctions
磁场对GaAs/Al_xGa_(1-x)As异质结系统中束缚极化子的影响

Zhang Min,Ban Shiliang,
张敏
,班士良

半导体学报 , 2004,
Abstract: A modified LLP variational method is adopted to investigate the binding energies of bound polarons near the interface of single heterojunction system of semiconductor in the presence of static uniform magnetic field by using a triangular potential approximate to the interface potential.The influences of the electron-phonon and impurity-phonon interaction including the effect of half-space bulk longitudinal and interface-optical phonon modes are considered.The computation is performed for GaAs/Al xGa 1-xAs structure.The relations among the impurity binding energies and the impurity position,magnetic field strength,the electron areal density are calculated,respectively.It is found that binding energy of the bound polaron shows a monotonic increase tendency with increasing the magnetic field strength B.The contribution from bulk longitudinal optical phonons to the binding energy obviously increases with increasing B,but the interface optical phonons are insensitive to magnetic field except for the impurity being near the interface.It also shows that the conductive band bending can not be neglected.Furthermore,the influence of the electron image potential is negligibly small so that it can be neglected in the further discussion.
Temperature effects on interface polarons in a strained (111)-oriented zinc-blende GaN/AlGaN heterojunction under pressure
压力下应变闪锌矿(111)取向GaN/AlGaN异质结中界面极化子的温度效应

Zhang Min,Ban Shiliang,
张敏
,班士良

半导体学报 , 2009,
Abstract: The properties of interface polarons in a strained (111)-oriented zinc-blende GaN/AlxGa1-xN heterojunc-tion at finite temperature under hydrostatic pressure are investigated by adopting a modified LLP variational method and a simplified coherent potential approximation. Considering the effect of hydrostatic pressure on the bulk longitu-dinal optical phonon mode, two branches interface-optical phonon modes and strain, respectively, we calculated the polaronic self-trapping energy and effective mass as functions of temperature, pressure and areal electron density. The numerical result shows that both of them near linearly increase with pressure but the self-trapping energies are nonlinear monotone increasing with increasing of the areal electron density. They are near constants below a range of temperature whereas decrease dramatically with increasing temperature beyond the range. The contributions from the bulk longitudinal optical phonon mode and one branch of interface optical phonon mode with higher frequency are important whereas the contribution from another branch of interface optical phonon mode with lower frequency is extremely small so that it can be neglected in the further discussion.
DNA barcoding: species delimitation in tree peonies

ZHANG JinMei,WANG JianXiu,XIA Tao &,ZHOU ShiLiang,

中国科学C辑(英文版) , 2009,
Abstract:
Vulnerability of Worldwide Pastoralism to Global Changes and Interdisciplinary Strategies for Sustainable Pastoralism
Shikui Dong,Lu Wen,Shiliang Liu,Xiangfeng Zhang
Ecology and Society , 2011,
Abstract: Ten case studies from seven major pastoral regions across six continents were studied in this paper by conceptualizing three factors (agro-ecosystem resilience, livelihood options, and institution capacity) as the axes of a three-dimensional vulnerability framework. This analysis highlights the vulnerability of agriculture-based livelihood systems to global changes and helps identify what institutions have the potential to mobilize effective relief in different pastoral regions. In terms of results, this vulnerability assessment shows that the vulnerability of pastoralism was very different in all the cases across the globe. As such, a further analysis, based on the pressure-state-response (PSR) model was undertaken to enhance our understanding of the ways that global changes put pressures on pastoral livelihoods worldwide. From this we conclude that climate change and climate variability are driving fragile pastoral ecosystems into more vulnerable conditions. Socioeconomic factors, such as changes in land tenure, agriculture, sedentarization, and institutions are fracturing large-scale pastoral ecosystems into spatially isolated systems. The implications of this analysis are that professionals, practitioners, and policy makers should jointly develop a coupled human and natural systems approach that focuses on enhancing the resilience of pastoral communities and their practices. This requires institutional developments to support asset building and good governance to enhance adaptive capability. In addition, pastoralists' adaptation strategies to global change need to be supported by public awareness and improved by institutional decisions at different scales and dimensions.
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