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Search Results: 1 - 10 of 38012 matches for " Xian-Lei Sheng "
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Topological Insulator to Dirac Semimetal Transition Driven by Sign Change of Spin-Orbit Coupling in Thallium Nitride
Xian-Lei Sheng,Zhijun Wang,Rui Yu,Hongming Weng,Zhong Fang,Xi Dai
Physics , 2014, DOI: 10.1103/PhysRevB.90.245308
Abstract: Based on the first-principles calculations, we reveal that TlN, a simple binary compound with Wurtzite structure, is a three-dimensional (3D) topological insulator (TI) with effectively negative spin-orbit coupling $\lambda_{eff} < 0$, which makes it distinguished from other TIs by showing opposite spin-momentum locking effect in its surface states. The sign of $\lambda_{eff}$ depends on the hybridization between N-$2p$ and Tl-$5d$ states, and can be tuned from negative to postive by lattice strain or chemical substitution, which drive the system into a Dirac semimetal with 3D Dirac cones in its bulk states. Such topological phase transition can be realized by electronic mechanism without breaking any crystal symmetry.
T-Carbon: A Novel Carbon Allotrope
Xian-Lei Sheng,Qing-Bo Yan,Fei Ye,Qing-Rong Zheng,Gang Su
Physics , 2011, DOI: 10.1103/PhysRevLett.106.155703
Abstract: A structurally stable crystalline carbon allotrope is predicted by means of the first-principles calculations. This allotrope can be derived by substituting each atom in diamond with a carbon tetrahedron, and possesses the same space group Fd^1 3m as diamond, which is thus coined as T- carbon. The calculations on geometrical, vibrational and electronic properties reveal that T-carbon, with a considerable structural stability and a much lower density 1.50 g/cm3, is a semiconductor with a direct band gap about 3.0 eV, and has a Vickers hardness 61.1 GPa lower than diamond but comparable with cubic boron nitride. Such a form of carbon, once obtained, would have wide applications in photocatalysis, adsoption, hydrogen storage and aerospace materials.
Family of boron fullerenes: general constructing schemes, electron counting rule and ab initio calculations
Qing-Bo Yan,Xian-Lei Sheng,Qing-Rong Zheng,Li-Zhi Zhang,Gang Su
Physics , 2008, DOI: 10.1103/PhysRevB.78.201401
Abstract: A set of general constructing schemes is unveiled to predict a large family of stable boron monoelemental, hollow fullerenes with magic numbers 32+8k (k>=0). The remarkable stabilities of these new boron fullerenes are then studied by intense ab initio calculations. An electron counting rule as well as an isolated hollow rule are proposed to readily show the high stability and the electronic bonding property, which are also revealed applicable to a number of newly predicted boron sheets and nanotubes.
Superstructures of Cubic and Hexagonal Diamonds Comprising a Family of Novel $sp^3$ Superhard Carbon Allotropes
Hui-Juan Cui,Xian-Lei Sheng,Qing-Bo Yan,Qing-Rong Zheng,Gang Su
Physics , 2013,
Abstract: Superstructures of cubic and hexagonal diamonds (h- and c-diamond) comprising a family of stable diamond-like $sp^3$ hybridized novel carbon allotropes are proposed, which are referred to as U$_n$-carbon where $n \geq 2$ denotes the number of structural layers in a unit cell. The conventional h- and c-diamond are included in this family as members with $n=2$ and 3, respectively. U$_n$-carbon ($n=4-6$), which are unveiled energetically and thermodynamically more stable than h-diamond and possess remarkable kinetic stabilities, are shown to be insulators with indirect gaps of $5.6 \sim 5.8$ eV, densities of $ 3.5 \sim 3.6$ g/cm$^3$, bulk modulus of $4.3 \sim 4.4 \times 10^{2}$ GPa, and Vickers hardness of $92.9 \sim 97.5$ GPa even harder than h- and c-diamond. The simulated x-ray diffraction and Raman spectra are presented for experimental characterization. These new structures of carbon would have a compelling impact in physics, chemistry, materials science and geophysics.
Strain-induced Dirac cone-like electronic structures and semiconductor-semimetal transition in graphdiyne
Hui-Juan Cui,Xian-Lei Sheng,Qing-Bo Yan,Qing-Rong Zheng,Gang Su
Physics , 2012, DOI: 10.1039/c3cp44457k
Abstract: By means of the first-principles calculations combined with the tight-binding approximation, the strain-induced semiconductor-semimetal transition in graphdiyne is discovered. It is shown that the band gap of graphdiyne increases from 0.47 eV to 1.39 eV with increasing the biaxial tensile strain, while the band gap decreases from 0.47 eV to nearly zero with increasing the uniaxial tensile strain, and Dirac cone-like electronic structures are observed. The uniaxial strain-induced changes of the electronic structures of graphdiyne come from the breaking of geometrical symmetry that lifts the degeneracy of energy bands. The properties of graphdiyne under strains are disclosed different remarkably from that of graphene.
Octagraphene as a Versatile Carbon Atomic Sheet for Novel Nanotubes, Unconventional Fullerenes and Hydrogen Storage
Xian-Lei Sheng,Hui-Juan Cui,Fei Ye,Qing-Bo Yan,Qing-Rong Zheng,Gang Su
Physics , 2012, DOI: 10.1063/1.4757410
Abstract: We study a versatile structurally favorable periodic $sp^2$-bonded carbon atomic planar sheet with $C_{4v}$ symmetry by means of the first-principles calculations. This carbon allotrope is composed of carbon octagons and squares with two bond lengths and is thus dubbed as octagraphene. It is a semimetal with the Fermi surface consisting of one hole and one electron pocket, whose low-energy physics can be well described by a tight-binding model of $\pi$-electrons. Its Young's modulus, breaking strength and Poisson's ratio are obtained to be 306 $N/m$, 34.4 $N/m$ and 0.13, respectively, which are close to those of graphene. The novel sawtooth and armchair carbon nanotubes as well as unconventional fullerenes can also be constructed from octagraphene. It is found that the Ti-absorbed octagraphene can be allowed for hydrogen storage with capacity around 7.76 wt%.
Global Active Bandwidth Adjustment (GABA) Algorithm

FENG Xian-lei,YU Neng-hai,

计算机应用 , 2007,
Abstract: In recent years, there has been a more and more serious phenomenon that the unresponsive flows such as UDP have occupied the bandwidth of responsive flows such as TCP. An algorithm called GABA (Global Active Bandwidth Adjustment) algorithm was proposed with the cooperation of edge routers and core routers. Core router got the information of unresponsive flows and edge router blocked invalid unresponsive flows. The NS2 experiment proves that GABA can improve the network utilization and the bandwidth fairness.
A Cluster Based Solution to BGP on Mobile Ad hoc Network

Liu Yang,Yu Neng-hai,Feng Xian-lei,
刘 洋

电子与信息学报 , 2006,
Abstract: In this paper, a novel scheme to detect Byzantine fault on mobile Ad hoc network is presented. A fault-tolerant algorithm is introduced combined with CBRP, which improves the security and reliability of manet(mobile Ad hoc network). Algorithm analysis shows the scheme can reduce the messages complexity effectively.
An overview of researches on environmental contamination by perchlorate and its remediation

CAI Xian-Lei,XIE Yin-Feng,LIU Wei-Long,DENG Wei,

生态学报 , 2008,
Abstract: Perchlorate is a new emerging persistent pollutant that can alter endocrine function in animals by blocking iodide uptake into thyroid tissue. Perchlorate contamination has attracted a great attention from scientists, because perchlorate is very stable and quite soluble, extremely mobile in aqueous systems, and diffuse rapidly in environment. Based on the analyses on the harmfulness of perchlorate, this paper firstly introduced the current pollution status of perchlorate in China, and the analytical techniques and pretreatment methods of perchlorate in different mediums. Futhermore, the researches on toxicological effects, migration and transformation of perchlorate in different mediums, accumulation in plants, and the environmental remediation methods in two categories i.e. bioremediation and non-bioremediation were reviewed. Finally, the significance and direction of researches on perchlorate contamination in the future were suggested.
Effects of Perchlorate on Growth and Chlorophyll Fluorescence Parameters of Alternanthera philoxeroides

XIE Yin-feng,CAI Xian-lei,LIU Wei-long,DENG Wei,

环境科学 , 2009,
Abstract: 高氯酸盐是一种新型的持久性污染物,其对植物影响作用的研究国内外鲜见报道.以空心莲子草为实验材料,在水培及可控条件下,探讨不同浓度(1、5、20、100、500 mg/L)ClO4-对空心莲子草生长及生理的影响.结果表明,①不同浓度的ClO4-处理均不同程度地抑制根、茎、叶生物量及单株相对生长量,其中根生物量对照与各浓度处理之间均存在显著差异.处理40d后,各浓度(由低到高)处理的相对生长量分别为对照的61.6%、60.8%、53.1%、20.4%和3.3%;ClO4-处理下根、茎、叶生物量的变异系数大小依次为:叶>根>茎;ClO4-处理使根茎叶三者之间的生物量分配关系发生变化,使茎的生物量分配系数增大,而叶降低,其中100、500 mg/L ClO4-处理组与对照相比差异显著;②不同浓度的ClO4-处理均使空心莲子草幼叶出现明显的伤害症状,顶叶反卷、叶缘变黑、焦枯,受害程度随处理浓度及时间的增加而加重;③ClO4-处理使叶片SPAD值、Fv/Fm、F′v/F′m、ΦPSⅡ、ETR、ETRmax等荧光参数均出现不同程度的下降趋势,SPAD、ΦPSⅡ等荧光参数可以作为反映受ClO4-胁迫影响的内在敏感生理指标.以...
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