The properties of phenyl cyclohexyl ferroelectric liquid crystals

To continue the search for novel series of ferroelectric liquid crystals, an additional two series of compounds, C S(+)-4-[(2-methylbutyl)phenyl]4'-trans-n-alkylcyclohexyl) benzoates and D S(+)-4-[(4-methylhexanoyl)phenyl]4'(4'-trans-n-alkylcyclohexyl) benzoates, where alkyl = C₅-C₆ are reported in this paper. Their mesomorphic properties have been characterized by optical textural observations and DSC. Some of these compounds show a C-S*_C-S_A-N*-I phase transition sequence. The effects of the alkyl chains on transition temperatures and optically active terminal groups on phase behaviour are discussed.     

An isomorphism theorem for Teichmüller curves

It is proved that for any Fuchsian group Γ such that ℍ/Γ is a hyperbolic Riemann surface, the Teichmüller curve V(Γ) has a unique complex manifold structure so that the natural projection of the Bers fiber space F(Γ) onto V(Γ) is holomorphic with local holomorphic sections. An isomorphism theorem for Teichmüller curves is deduced, which generalizes a classical result that the Teichmüller curve V(Γ) depends only on the type of Γ and not on the orders of the elliptic elements of Γ when ℍ/Γ is a compact hyperbolic Riemann surface.     

A multilayer recognition model for twitter user geolocation

Wireless Networks - Geolocation is important for many emerging applications such as disaster management and recommendation system. In this paper, we propose a multilayer recognition model (MRM) to...     

A survey on TCP Incast in data center networks

In high bandwidth, low latency data center networks, when multiple data senders simultaneously communicate with a single receiver, namely in many‐to‐one communication pattern, the burst data overload the receiver's switch buffers, which leads to Transmission Control Protocol (TCP) throughput collapse. This is the so‐called TCP Incast problem. It has become a new hot research topic in recent years. Also, many proposals have been put forward from the aspects of multiple layers including link layer, transport layer, and application layer, etc., to mitigate TCP Incast. In this paper, an in‐depth survey on these proposals is given, and the principles, merits, and drawbacks of the main proposals for solving the TCP Incast issue are analyzed and summarized. Copyright © 2012 John Wiley & Sons, Ltd.     

分散聚合法制备窄分布聚苯乙烯微球

窄分布聚合物微球有相当广泛的用途，如用于色谱柱填料，过滤器效能和孔径的测定标准，生化反应的载体等［１］．制备聚合物微球的方法有多种：如悬浮聚合物法可以制得微米级球体，但粒径分布较宽［２］；超微乳液聚合法，却仅能制得小于１μｍ的超微球［３］；唯有分散聚...     

Preliminary study on ductile fracture of imperfect lattice materials

The ductile fracture behavior of two-dimensional imperfect lattice material under dynamic stretching is studied by finite element method using ABAQUS/Explicit code. The simulations are performed with three isotopic lattice materials: the regular hexagonal honeycomb, the Kagome lattice and the regular triangular lattice. All the three lattices are made of an elastic/visco-plastic metal material. Two typical imperfections: vacancy defect and rigid inclusion are introduced separately. The numerical results reveal novel deformation modes and crack growth patterns in the ductile fracture of lattice material. Various crack growth patterns as defined according to their profiles, “X”-type, “Butterfly”-type, “Petal”-type, are observed in different combinations of imperfection type and lattice topology. Crack propagation could induce severe material softening and deduce the plastic dissipation of the lattices. Subsequently, the effects of the strain rate, relative density, microstructure topology, and defect type on the crack growth pattern, the associated macroscopic material softening and the knock-down of total plastic dissipation are investigated.     

茁壮成长 后继有人

本期发表的“茁壮成长后继有人”等三篇文章,从不同侧面评述、介绍了上海市开展化学科中青年教师教学评选活动的情况,向我们展示了辛勤工作在教学第一线的一大批中青年教师刻苦钻研、勇于改革、矢志创新的可喜局面。本栏今后在发表青年教师著文的同时,还将刊出关于中青年教师教学评选活动的评介文章。欢迎供稿。     

Flexoelectricity induced increase of critical thickness in epitaxial ferroelectric thin films

Flexoelectricity describes the coupling between polarization and strain/stress gradients in insulating crystals. In this paper, using the Landau–Ginsburg–Devonshire phenomenological approach, we found that flexoelectricity could increase the theoretical critical thickness in epitaxial BaTiO₃ thin films, below which the switchable spontaneous polarization vanishes. This increase is remarkable in tensile films while trivial in compressive films due to the electrostriction caused decrease of potential barrier, which can be easily destroyed by the flexoelectricity, between the ferroelectric state and the paraelectric state in tensile films. In addition, the films are still in a uni-polar state even below the critical thickness due to the flexoelectric effect.     

纤维支气管镜激光治疗气道疤痕狭窄11例

我院使用Nd~3+:YAG激光治疗气道疤痕狭窄11例,取得了满意的疗效,现报道如下。临床资料男5例,女6例。年龄25～43岁。狭窄口位于左主支气管中间段6例,右主支气管开口处1例,右中间支气管中间段4例。全部病例均为内膜结核治疗后结缔组织增生疤痕所形成,狭窄口纤维支气管镜均无法通过。狭窄口最小约0.3 cm~2。病程在1～2年者8例,2～4年者3例.患者均有反复出现病侧肺部感染及气急。其中3例曾诊断为“支气管哮     

常利率因素下的双险种风险模型

本文引入了一类常利率因素下的双险种风险模型,就不带干扰和带干扰两个方面进行讨论,给出了破产概率Ψ（u）的显式表达式和Lundberg上界。