Mechanisms for extra conductance plateaus in quantum wires

Spin-density-functional theory is employed to calculate the conductance G through a quasi-one-dimensional quantum wire. In addition to the usual subband quantization plateaus at G=n(2e(2)/h), we find additional structures at (n+1/2)(2e(2)/h). The extra structures appear whether or not the electrons in the wire spin polarize. However, only the spin-polarized case reproduces the experimental temperature and magnetic field dependences.

Forced extension of P-selectin construct using steered molecular dynamics

P-selectin, a 70-nm-long cellular adhesive molecule, possesses elastic and extensible properties when neutrophils roll over the activated endotheliam of blood vessel in inflammatory reaction. Transient formation and dissociation of P-selectin/ligand bond on applied force of blood flow induces the extension of P-selectin and relevant ligands. Steered molecular dynamics simulations were performed to stretch a single P-selectin construct consisting of a lectin (Lec) domain and an epithelial growth factor (EGF)-like domain, where P-selectin construct was forced to extend in water with pulling velocities of 0.005-0.05 nm/ps and with constant forces of 1000-2500 pN respectively. Resulting force-extension profiles exhibited a dual-peak pattern on various velocities, while both plateaus and shoulders appeared in the extension-time profiles on various forces. The force or extension profiles along stretching pathways were correlated to the conformational changes, suggesting that the structural collapses of P-selectin Lec/EGF domains were mainly attributed to the burst of hydrogen bonds within the major beta sheet of EGF domain and the disruptions of two hydrophobic cores of Lee domain. This work furthers the understanding of forced dissociation of P-selectin/ligand bond.

Space-resolved spectral diagnosis of line-shaped laser-produced magnesium plasmas

Space-resolved spectra of line-shaped laser-produced magnesium plasmas in the normal direction of the target have been obtained using a pinhole crystal spectrograph. These spectra are treated by a spectrum analyzing code for obtaining the true spectra and fine structures of overlapped lines. The spatial distributions of electron temperature and density along the normal direction of the target surface have been obtained with different spectral diagnostic techniques. Especially, the electron density plateaus beyond the critical surface in line-shaped magnesium plasmas have been obtained with a fitting technique applied to the Stark-broadened Ly-alpha wings of hydrogenic ions. The difference of plasma parameters between those obtained by different diagnostic techniques is discussed. Other phenomena, such as plasma satellites, population inversion, etc., which are observed in magnesium plasmas, are also presented.

Spin-Hall effect in the generalized honeycomb lattice with Rashba spin-orbit interaction

We study the spin-Hall effect in a generalized honeycomb lattice, which is described by a tight-binding Hamiltonian including the Rashba spin-orbit coupling and inversion-symmetry breaking terms brought about by a uniaxial pressure. The calculated spin-Hall conductance displays a series of exact or approximate plateaus for isotropic or anisotropic hopping integral parameters, respectively. We show that these plateaus are a consequence of the various Fermi-surface topologies when tuning epsilon(F). For the isotropic case, a consistent two-band analysis, as well as a Berry-phase interpretation. are also given. (C) 2009 Elsevier B.V. All rights reserved.

Spin Hall effect on the kagome lattice with Rashba spin-orbit interaction

We study the spin Hall effect in the kagome lattice with Rashba spin-orbit coupling. The conserved spin Hall conductance sigma(s)(xy) (see text) and its two components, i.e., the conventional term sigma(s0)(xy) and the spin-torque-dipole term sigma(s tau)(xy), are numerically calculated, which show a series of plateaus as a function of the electron Fermi energy epsilon(F). A consistent two-band analysis, as well as a Berry-phase interpretation, is also given. We show that these plateaus are a consequence of various Fermi-surface topologies when tuning epsilon(F). In particular, we predict that compared to the case with the Fermi surface encircling the Gamma point in the Brillouin zone, the amplitude of the spin Hall conductance with the Fermi surface encircling the K points is twice enhanced, which makes it highly meaningful in the future to systematically carry out studies of the K-valley spintronics.

Study of persistent photoconductivity and subband electronic properties of the two-dimensional electron gas in modulation doped GaAs/AlGaAs structure

We obtained the high mobility Of mu(2K) = 1.78 x 10(6) cm(2)/V . s in Si-doped GaAs/AlGaAs two-dimensional electron gas (2DEG) structures. After the sample was illuminated by a light-emitting diode in magnetic fields up to 6 T at T = 2K, we did observe the persistent photoconductivity effect and the electron density increased obviously. The electronic properties of 2DEG have been studied by Quantum-Hall-effect and Shubnikov-de Haas (SdH) oscillation measurements. We found that the electron concentrations of two subbands increase simultaneity with the increasing total electron concentration, and the electron mobility also increases obviously after being illuminated. At the same time, we also found that the electronic quantum lifetime becomes shorter, and a theoretical explunation is given through the widths of integral quantum Hall plateaus.

Effect of small-angle scattering on the integer quantum Hall plateau

A GaAs/AlGaAs two-dimensional electron gas (2 DEG) structure with the high mobility of mu(2K) = 1.78 x 10(6) cm(2)/Vs has been studied by low-temperature Hall and Shubnikov de Hass (SdH) measurements. Quantum lifetimes related to all-angle scattering events reduced from 0.64 ps to 0.52 ps after illuminating by Dingle plots, and transport lifetimes related to large-angle scattering events increasing from 42.3 ps to 67.8 ps. These results show that small-angle scattering events become stronger. It is clear that small-angle scattering events can cause the variation of the widths of the quantum Hall plateaus.

Structures of energy spectrum and persistent currents in mesoscopic rings with radial potential barrier in magnetic field

The energy spectrum and the persistent currents are calculated for finite-width mesoscopic annular structures with radial potential barrier in the presence of a magnetic field. The introduction of the tunneling barrier leads to the creation of extra edge states around the barrier and the occurrence of oscillatory structures superimposed on the bulk Landau level plateaus in the energy spectrum. We found that the Fermi energy E-F increases with the number of electrons N emerging many kinks. The single eigenstate persistent current exhibits complicated structures with vortex-like texture, ''bifurcation'', and multiple ''furcation'' patterns as N is increased. The total currents versus N display wild fluctuations.

A STUDY OF THE COMPOSITION DISTRIBUTION AT THE TI/AL2O3 INTERFACE USING THE MCS(+)-SIMS TECHNIQUE

In this article, the MCs(+)-SIMS technique has been used to characterize Ti/Al2O3 metal/insulator interfaces. Our experiment shows that by detecting MCs(+) secondary ions, the matrix and interface effects are reduced, and good depth profiles have been obtained. The experimental result also shows that with the increase of the annealing temperature (RT, 300 degrees C, 600 degrees C, 850 degrees C), the interface gets broadened gradually, indicating diffusion and reaction take place at the interface, and the interface reaction is enhanced with the increase in annealing temperature. When the temperature increases, the AlCs+ signal forms two plateaus in the Ti layer, indicating Al from the decomposition of Al2O3 diffuses into the Ti layer and exists as two new forms (phases). Also, with the increase of the annealing temperature, oxygen diffuses into the Ti layer gradually, and makes the O signal in the Ti layer increase significantly in the 850 degrees C annealed sample.

High-order harmonic generation and multi-photon ionization of Na-2 in laser fields

In this paper high-order harmonic generation (HHG) spectra and the ionization probabilities of various charge states of small cluster Na-2 in the multiphoton regimes are calculated by using time-dependent local density approximation (TDLDA) for one-colour (1064 nm) and two-colour (1064 nm and 532 nm) ultrashort (25 fs) laser pulses. HHG spectra of Na2 have not the large extent of plateaus due to pronounced collective effects of electron dynamics. In addition, the two-colour laser field can result in the breaking of the symmetry and generation of the even order harmonic such as the second order harmonic. The results of ionization probabilities show that a two-colour laser field can increase the ionization probability of higher charge state.

Dependence of superconducting temperature on chemical bond parameters in YBa2Cu3O6+delta (delta=0-1)

The chemical bond parameters, that is ionicities and average energy gaps, for all types of chemical bonds in YBa2Cu3O6+delta have been investigated with variation of oxygen content delta (delta = 0.0, 0.35, 0.45, 0.58, 0.64, 0.73, 0.78, 0.81, 0.95, 1.00). The theory used is the complex crystal chemical bond theory, which is the development of P-V-L theory. The two plateaus near 90 K and 60 K in superconducting transition temperatures, and the disappearance of superconductivity with the change of oxygen content, were reasonably explained by chemical bond parameters. The results also showed that the Cu-O chains play a vital role in the transition from non-superconductors to superconductors, and the highest transition temperature occurred when the plane-chain reached a coupling state. (C) 1998 Elsevier Science Ltd. All rights reserved.

Propagators and ridge jumps in a back-arc basin, the West Philippine Basin

We explore the tectono-magmatic processes in the western West Philippine Basin, Philippine Sea Plate, using bathymetric data acquired in 2003 and 2004. The northwestern part of the basin formed through a series of northwestward propagating rifts. We identify at least five sequences of propagating rifts, probably triggered by mantle flow away from the mantle thermal anomaly that is responsible for the origin of the Benham and Urdenata plateaus. Gravitational forces caused by along-axis topographic gradient and a similar to 30 degrees ridge reorientation appear to also be driving the rift propagations. The along-axis mantle flow appears to be reduced and deflected along the Luzon-Okinawa fracture zone, because the spreading system remained stable west of this major fault zone. North-east of the Benham plateau, a left-lateral fracture zone has turned into a NE-SW-trending spreading axis. As a result, a microplate developed at the triple junction.

地幔柱与岩浆成矿-峨嵋山大火成岩省地震波速层物相解释及典型PGE矿床成岩成矿机制研究

地幔柱概念在19世纪60至70年代就被提出，但是由于板块构造理论在解释地球上岩浆活动的分布规律时取得了空前的成功，在当时这一理论是被排斥的。板块边界概念可以解释地球上绝大部分的岩浆产出，但在解释板内岩浆的成因时往往显得力不从心，尽管这些岩浆的体积只占地球岩浆总量的2％。地幔柱理论模型发展到现在得到不同学科的支持。地质学、地球化学、地球物理学、古生物学、比较行星学、实验岩石学等等都提供了直接或间接的证据，证明地幔柱几乎存在整个地：质历史时期。当前地幔柱理论中在地球化学领域有两大研究热点：高钦低钦玄武岩的起源以及地幔柱中是否存在循环俯冲洋壳物质。完全解决这些问题才可能深入系统地建立地慢柱成矿作用模型。现在已经建立了一些矿床类型与地慢柱作用的联系：如现在认为赋存在金伯利岩中的金刚石矿床的形成与地慢柱作用密不可分，一些岩浆硫化物矿床和岩浆氧化物矿床很显然是地慢柱岩浆作用形成的，如西伯利亚火成岩省的Noril'sk-Talnakh铜镍铂族元素矿床以及KeweenawaJI大陆裂谷体系的Dultlth杂岩体的Cu-Ni矿床。另外还有赋存在大型基性一超基性层状岩体中的PGE、Ni和cu矿床，如Great Dyke和布什维尔德杂岩体。一些超大型热液矿床也与地慢柱有可能的联系（Pirajno，2000）：如270oMa形成的超大型Kidd Creek火山成因块状硫化物矿床（Bleeker et al.，1 999；Wynan et al.，1999）和南澳大利亚1600Ma形成的超大型olymPicD翻矿床。本文的研究工作包含两方面内容：通过热力学计算峨眉山玄武岩在深部的结晶分异，对峨眉山大火成岩省的岩浆量分布和岩浆氧化物矿床（华Ti磁铁矿矿床）的分布以及下地壳高波速层的物相进行理论解释；对峨眉山大火成岩省金宝山PGE典型矿床进行成岩成矿的地球化学研究，预测整个大火成岩省的岩浆硫化物矿床产出位置。大多数峨眉山玄武岩的 MgO＜7％，Ni为4-232ppm，它们是原始岩浆结晶分异后的产物。峨眉山玄武岩省下地壳和上地幔之间存在厚度为：8-25km1，P彼速为7.1-7.8km／s的附加层（高地震波速层）。滇西地区出露的洲套第三纪富碱斑岩，地球化学和同位素研究表明斑岩的岩浆源是来自“壳一慢混合层”，源区的形成时代为220-25Ma，与峨眉山玄武岩的形成时代一致。所以有理由认为该附加层是由峨眉山玄武岩在此结晶分异形成的。与地慢柱有关的洋岛Hawaii、Marquesas Islands；海底高原Oniong Java、大陆火山岩省ColumbiaRiver Plateaus地震彼研究都表明在上地慢顶部有一高速附加层，Farnetani etal.（1996）的研歼表明高速附加层是由来自地幔柱的岩浆在此结晶分异形成的。玄武岩是一种混合的部分熔融产物，是不同成分的地幔橄榄岩在不同的压力下熔出的。这种降压熔融高温高压实验是做不到的。熔出的熔体成分是温度、压力及橄榄岩成分（源区）的函数，形成的岩浆是一个多压熔融的集合体。热力学计算能够较为精确地计算出生成的岩浆成分和约束岩浆产生的过程。岩浆的结晶分异也是同样的情形，尤其是分离结晶过程，实验岩石学是很精确难模拟其过程的。热力学计算使用的MELTS程序，MELTS适用范围很广，适用于模拟岩石熔融生成岩浆和岩浆的冷却结晶。现今峨眉山大火成岩省的地壳厚度为40恤，这被认为是后期褶皱加厚的缘故。根据峨眉山玄武岩中辉石斑晶成分和玄武岩本身成分计算出分异结晶的压力为6kb，那么当时的地壳厚度约为20km：选择氧逸度为QFM，这一氧逸度范围认为是大多数大陆溢流玄武岩结晶分异时的氧化还原环境。热力学计算结果通过峨眉山玄武岩成分进行约束和验证。Al2O3、NaZO＋K 20、CaO与MgO计算的演化趋势线与实际观察的演化符合较好，橄榄石和斜方辉石的结晶使得CaO随着MgO的降低而增高；当单斜辉石成为液相线矿物时，cao也随着Mgo的降低而降低了。单斜辉石在岩浆演化到MgO＝10．3％时成为液相线矿物。整个计算过程中斜长石未成为液相线矿物，这与大多数玄武岩不具有Eu异常是一致的，并月＿Al2O3随着MgO的减小单调增加也说明了这点。不过大多数峨眉山玄武岩常含有斜长石斑晶，这是低压下结晶分异的结果。由于斜长石密度小，所有很难与高铁玄武岩分离。整个计算的难点也是创新点是波速计算。通过分离的堆晶矿物组合中各种矿物的成分和质量分数计算的附加层波速比观察值高，不过堆积岩体常常会有残留岩浆存在矿物晶粒间，这样会降低岩石的压缩波速。大型基性一超基性岩体常常会残留有或者捕获5-30％的岩浆。假定两个高波速附加层分别捕获7叭，和巧％的残留岩浆，计算的结果就大体等于观察值。热力学和质量平衡计算研究表明：高地震波速层为橄榄辉石岩一辉石岩的巨型侵入岩体；峨眉山中岩区的岩浆量最大也符合含V-Ti磁铁矿矿床只产在中岩区，如太和、白马、攀枝花、红格等岩体；西岩区的岩浆量最小表明几乎没有可能在西岩区形成有规模的V-Ti磁铁矿矿床，实际观察仅仅只见到数量少而小的岩体；东岩区下地壳厚达20灿1的高波速层暗示东岩区上地壳的侵入岩体积也应该具有相当规模，应该是V－Ti磁铁矿矿床成矿区。目前在东岩区很少发现与峨眉山玄武岩有关的岩浆矿床的主要原因是：东岩区的剥蚀深度不够，没有可观的侵入岩体出露，而中岩区侵入岩都侵入在元古代地层中。按照质量平衡的计算方法，最保守的估算整个峨眉地慢柱岩浆事件产生的岩浆量为8.9*106km3，上地壳峨眉山玄武岩和侵入岩体积为3.9*106km3。如果按照初始覆盖面积5x106km2计算（与西伯利亚暗色岩初始覆盖面积相当），喷发高峰期为2Ma，计算的喷发速率为3.9km3／year。这并不亚于西伯利亚暗色岩的喷发速率4km3／year。这对于研究峨眉山大火成岩浆事件与二叠·三叠交界或end-QuadaluPian生物灭绝之间的可能联系具有重要意义。本文另一方面的研究工作是：首先系统地介绍了岩浆硫化物矿床的基本原理，然后通过金宝山PGE矿床实例研究，提出金宝山岩体成岩模式，并且对整个峨眉山大火成岩省的岩浆硫化物矿床产出位置进行理论预测。详细地球化学研究表明金宝山镁铁一超镁铁岩是峨眉山大火成岩省古老火山岩浆房的残留物。岩体主要由底部超镁铁岩和上部镁铁岩组成，两种岩石的质量大致相同。根据超镁铁岩的矿物组合计算的成岩时的氧逸度较高，热力学方法计算的成岩压力为2kb左右。超镁铁岩的包嵌结构和铁铁岩的微晶一细晶结构说明超镁铁岩为镁铁岩结晶的矿物堆积形成的。镁铁一超镁铁岩的蚀变程度不同以及Sc、Sr、Eu等元素在两类岩石中的不同特征指示了整个成岩过程。金宝山岩体的原始岩浆 MgO=8％说明高镁玄武岩并不是形成PGE矿床的必要条件。金宝山的成岩模式是：在火山喷发前，岩浆侵位时橄榄石和少量铬尖晶石先结晶，沉淀在岩浆房底部；随后结晶的是斜方辉石和斜长石，斜方辉石也沉淀在岩浆房底部，斜长石由于密度较小集中中岩浆房上部，岩浆房的中部是：少量的斜长石小斑晶。由于斜方辉石和斜长石的结晶，这样岩浆中的Sc、Sr和Eu就会亏损，也是岩浆房底部堆积岩的原始捕获岩浆。火山喷发后，由于压力的突然降低，岩浆房底部的堆晶会发生再熔融，几乎消耗掉所有的斜方辉石，橄榄石也呈熔蚀状浑圆形态，重新熔融的斜方辉石导致超镁铁岩中残留岩浆比原始捕获岩浆更加富Sc，这种岩浆由于富MgO和在快速冷却的环境下同时结晶，最终形成光性方位一致的单刹辉石。喷发后岩浆房空间的剩余导致围岩-灰岩进入，造成岩浆房中剩余岩浆强烈的碳酸盐化。峨眉山玄武岩Cr-Mg#的相关关系定义一条正常玄武岩演化线。大多数这些玄武岩的Ni也保持了这种演化关系，其中低钦玄武岩和过渡型高钦玄武岩Ni-Mg＃相关关系远离了正常演化线，这些玄武岩的Cu-Mg#相关关系也有类似的情形。峨眉山低钦和过渡类型高钦玄武岩Ni和 Cu的非正常亏损，表明它们在地表下经历了硫饱和事件。金宝山岩浆硫化物矿床成岩模型的建立，为在整个大火成岩省寻找岩浆硫化物矿床提供了一种新认识。低钦和过渡型高钦玄武岩的古老火山口下部是岩浆硫化物矿床的所在地。