Four-Dimensional Newton’s Constant in Brane World with a Sloping Extra Dimension

We show the four-dimensional Newton’s constant obtained naturally from five-dimensional brane world with a tinily sloping extra dimension, which is independent of the bulk Weyl tensor. The corresponding universe is stiff fluid dominated when the slope of extra dimension is very small. Otherwise, the universe may be undergoing a self-acceleration at present epoch and have a decelerated phase in very recent past.     

Nematicidal coumarins from Heracleum candicans Wall

The root extract of Heracleum candicans Wall. exhibited antagonistic activities against nematodes Bursaphelenchus xylophilus (Steiner et Buhrer) Nickle and Panagrellus redivivus (Linn.) Goodey. Through bioassay-guided fractionations, three coumarins were obtained from the extract of H. candicans and determined to be 8-geranyloxypsoralen (1), imperatorin (2), and heraclenin (3) based on spectra data. All three compounds possessed nematicidal activities against the two tested nematodes. The median lethal concentrations (LC(50)) of compounds 1-3 at 72 h were 188.3, 161.7, and 114.7 mg L(-1) respectively against B. xylophilus and were 117.5, 179.0, and 148.7 mg L(-1) respectively against P. redivivus. This is the first report about species in the Umbelliferae family that possesses nematicidal activity.     

Haldane's instanton in 2D Heisenberg model revisited: Along the avenue of topology

Deconfined quantum phase transition from Néel phase to valence bond crystal state in 2D Heisenberg model is under debate nowadays. One crucial issue is the suppression of Haldane's instanton on quantum critical point which drives the spinon deconfined. In this Letter, by making use of the ?-mapping topological current theory, we reexamine the Haldane's instanton in an alternative way along the direction of topology. We find that the monopole events are space-time singularities of Néel field , the corresponding topological charges are the wrapping number of around the singularities which can be expressed in terms of the Hopf indices and Brouwer degrees of ?-mapping. The suppression of the monopole events can only be guaranteed when the ?-field possesses no zero points. Moreover, the quadrapolarity of monopole events in the Heisenberg model due to the Berry phase is also reproduced in this topological argument.     

基于布拉格反射镜的X射线多色单能成像谱仪

报道了一种基于布拉格反射镜的多色单能成像谱仪研制工作,谱仪由针孔阵列、布拉格反射镜和CCD相机组成.大约有300个微孔的针孔阵列板置于布拉格镜前用于空间成像,通过布拉格反射镜的单色化,投射到CCD上的数百个小孔成像沿色散方向获得了能量分辨.经过图像处理,可以还原得到目标的多色单能二维成像.根据采用的布拉格分光元件和图像还原方法,谱仪的能量分辨达到了50—200（λ/Δλ）;针孔成像的空间分辨优于10 μm.同时还为该谱仪开发了专门的单能图像重建软件及图像数据后处理软件,可以在任意选择的窄能带内还原准单能图像.并重点介绍了该谱仪的优化设计、获得的技术指标以及专门研制的超短周期（2.5 nm）X射线W/B₄C多层镜. 关键词： X射线光学 诊断技术 布拉格反射镜 X射线多层镜     

Rank-based deactivation model for networks with age

We study the impact of age on network evolution which couples addition of new nodes and deactivation of old ones. During evolution, each node experiences two stages: active and inactive. The transition from the active state to the inactive one is based on the rank of the node. In this paper, we adopt age as a criterion of ranking, and propose two deactivation models that generalize previous research. In model A, the older active node possesses the higher rank, whereas in model B, the younger active node takes the higher rank. We make a comparative study between the two models through the node-degree distribution.     

Stability of Disclinations in Nematic Liquid Crystals

In the light of φ-mapping method and topological current theory, the stability of disclinations around a spherical particle in nematic liquid crystals is studied. We consider two different defect structures around a spherical particle: disclination ring and point defect at the north or south pole of the particle. We calculate the free energy of these different defects in the elastic theory. It is pointed out that the total Frank free energy density can be divided into two parts. One is the distorted energy density of director field around the disclinations. The other is the free energy density of disclinations themselves, which is shown to be concentrated at the defect and to be topologically quantized in the unit of (k-k₂₄)π/2. It is shown that in the presence of saddle-splay elasticity a dipole (radial and hyperbolic hedgehog) configuration that accompanies a particle with strong homeotropic anchoring takes the structure of a small disclination ring, not a point defect.     

Effect of Disclination Lines on Free Energy of Nematic Liquid Crystals

In the light of φ-mapping method-and topological current theory, the effect of disclination lines on the free energy density of nematic liquid crystals is studied. It is pointed out that the total Frank free energy density can be divided into two parts. One is the distorted energy density of director field around the disclination lines. The other is the saddle-splay energy density, which is shown to be centralized at the disclination lines and to he topologically quantized in the unit of kπ/2 when the Jacobian determinant of the director field does not vanish at the singularities of the director field. The topological quantum numbers are determined by the Hopf indices and Brouwer degrees of the director field at the disclination lines, i.e., the disclination strengthes. When the Jacobian determinant vanishes, the generation, annihilation, intersection, splitting and merging processes of the saddle-splay energy density are detailed in the neighborhoods of the limit points and bifurcation points, respectively. It is shown that the disclination line with high topological quantum number is unstable and will evolve to the low topological quantum number states through the splitting process.     

Contribution of Disclination Lines to Free Energy of Liquid Crystals in Single-Elastic Constant Approximation

In the light of C-mapping method and topological current theory, the contribution of disclination lines to free energy density of liquid crystals is studied in the single-elastic constant approximation. It is pointed out that the total free energy density can be divided into two parts. One is the usual distorted energy density of director field around the disclination lines. The other is the free energy density of disclination lines themselves, which is shown to be centralized at the disclination lines and to be topologically quantized in the unit of kn/2. The topological quantum numbers are determined by the Hopf indices and Brouwer degrees of the director l~eld at the disclination lines, i.e. the disclination strengths. From the Lagrange‘s method of multipliers, the equilibrium equation and the molecular field ofliquid crystals are also obtained. The physical meaning of the Lagrangian multiplier is just the distorted energy density.     

铁磁/反铁磁双层薄膜自旋波共振谱

本文在一维海森堡模型的基础上,采用界面参数化方法,研究了铁磁/反铁磁双层薄膜中自旋波低温激发问题．重点讨论了表面各向异性对薄膜中自旋波共振谱的影响．结果表明：体系中的自旋波本征模存在共振行为,表面各向异性场对体模、完全禁闭模的共振谱影响较大,对界面模没有影响．     

肥皂草素和膜脂相互作用的研究

利用外源荧光探针研究了肥皂草素和膜脂相互作用后膜物理状态变化的特征。ＳＯ－６与磷脂双分子层作用后，可以引起双分子层内含物的释放，使磷脂双分子层发生搅动；ＳＯ－６可以降低磷双分子层膜的流动性。根据上结果，提出了肥皂草素与模拟膜作用的初步机制。