Synthesis and mesophase behaviour of rigid rod‐like phenylthiophene‐based amphiphilic diol derivatives

Novel amphiphilic block molecules consisting of a rigid 2‐phenylthiophene or 5‐phenylbithienyl core, with a polar glycerol group attached to the phenyl ring and one or two alkyl chains attached to the thiophene ring on the other side, have been synthesised by using Ni(0) and Pd(0) catalyzed coupling reactions as key steps. The thermotropic and solvent‐induced liquid crystalline behaviour of these compounds was investigated by polarising optical microscopy and X‐ray diffraction. The influence of the length, number and position of the alkyl chains, and the length of the rigid core, on their mesophase behaviour was investigated. Compounds with one alkyl chain in the terminal 5‐position on the thiophene ring form only smectic A phases, compounds with two adjacent alkyl chains attached in the 4‐ and 5‐positions of the thiophene ring exhibit thermotropic columnar mesophases, and those with two long alkyl chains attached to the 3‐ and 5‐positions form columnar LC phases only in the presence of water. Another compound containing the longer 5‐phenylbithienyl core unit and two alkyl chains attached in lateral positions to each of the thiophene rings is not mesogenic.     

Eu3+在M3La2(BO3)4(M=Ca,Sr,Ba)中的发光性质

本文报导了M3La2(BO3)4:Eu3+(M=Ca,Sr,Ba)磷光体的制备方法及晶体结构。三种磷光体均属正交晶系。研究了Eu3+离子的光谱特征与基质化合物的关系。发现在三种磷光体中,被Eu3+所取代的La3+离子均只有一种格位,且在此格位上不具备反演操作的对称性;Eu3+在Ca3La2(BO3)4:Eu3+中所处格位的局部对称性最低,属C1,C2和Cs中之一种,在M3La2(BO3)4:Eu3+(M=Sr,Ba)中Eu3+所处格位的局部对称性可能为C2v。     

Nonlinear stability and instability of relativistic Vlasov‐Maxwell systems

We prove the nonlinear stability or instability of certain periodic equilibria of the 1½D relativistic Vlasov‐Maxwell system. In particular, for a purely magnetic equilibrium with vanishing electric field, we prove its nonlinear stability under a sharp criterion by extending the usual Casimir‐energy method in several new ways. For a general electromagnetic equilibrium we prove that nonlinear instability follows from linear instability. The nonlinear instability is macroscopic, involving only the L¹‐norms of the electromagnetic fields. © 2006 Wiley Periodicals, Inc.     

STRENGTH CRITERION FOR PLAIN CONCRETE UNDER MULTIAXIAL STRESS BASED ON DAMAGE POISSON''S RATIO

A new unified strength criterion in the principal stress space has been proposed for use with normal strength concrete (NC) and high strength concrete (HSC) in compressioncompression-tension, compression-tension-tension, triaxial tension, and biaxial stress states. The study covers concrete with strengths ranging from 20 to 130 Mpa. The conception of damage Poisson's ratio is defined and the expression for damage Poisson's ratio is determined basically.The failure mechanism of concrete is illustrated, which points out that damage Poisson's ratio is the key to determining the failure of concrete. Furthermore, for the concrete under biaxial stress conditions, the unified strength criterion is simplified and a simplified strength criterion in the form of curves is also proposed. The strength criterion is physically meaningful and easy to calculate, which can be applied to analytic solution and numerical solution of concrete structures.     

A sharp stability criterion for the Vlasov–Maxwell system

We consider the linear stability problem for a 3D cylindrically symmetric equilibrium of the relativistic Vlasov–Maxwell system that describes a collisionless plasma. For an equilibrium whose distribution function decreases monotonically with the particle energy, we obtained a linear stability criterion in our previous paper [24]. Here we prove that this criterion is sharp; that is, there would otherwise be an exponentially growing solution to the linearized system. We also treat the considerably simpler periodic D case. The new formulation introduced here is applicable as well to the non-relativistic case, to other symmetries, and to general equilibria.     

Mechanism analysis on synergistic leaching of uranium from pyrite oxidized by Acidithiobacillus ferrivorans

Journal of Radioanalytical and Nuclear Chemistry - Low-grade uranium ore, which was challenging to be treated economically by conventional methods, can be treated by uranium leaching by bacteria....     

Removal of high concentrations of NO3− from nuclear industrial wastewater by using a fixed-bed bioreactor

In this work, a down-flow fixed bed anaerobic biofilm reactor filled by biological ceramsites were prepared to remove the high concentration of NO₃^? (>?20 g/L) from nuclear industry wastewaters. The effects of hydraulic retention time, the concentration of NO₃^?, the molar ratio of C/N and temperature on the removal efficiencies of NO₃^? were investigated. The results showed that the removal rate of NO₃^? with the initial concentration of 6 g/L can reach 99% or more by controlling the hydraulic retention time at 0.75 h, the molar ratio of C/N at 1.5 and the temperature over 18 °C. In the process, the NO₂^? was not accumulated, and the autotrophic denitrifying bacteria grow well in anaerobic biofilm reactors, proving a usable method for removing the high concentration NO₃^? from nuclear industrial wastewaters.

     

Interaction behaviors at the interface between liquid Al–Si and solid Ti–6Al–4V in ultrasonic-assisted brazing in air

Power ultrasonic vibration (20 kHz, 6 μm) was applied to assist the interaction between a liquid Al–Si alloy and solid Ti–6Al–4V substrate in air. The interaction behaviors, including breakage of the oxide film on the Ti–6Al–4V surface, chemical dissolution of solid Ti–6Al–4V, and interfacial chemical reactions, were investigated. Experimental results showed that numerous 2–20 μm diameter-sized pits formed on the Ti–6Al–4V surface. Propagation of ultrasonic waves in the liquid Al–Si alloy resulted in ultrasonic cavitation. When this cavitation occurred at or near the liquid/solid interface, many complex effects were generated at the small zones during the bubble implosion, including micro-jets, hot spots, and acoustic streaming. The breakage behavior of oxide films on the solid Ti–6Al–4V substrate, excessive chemical dissolution of solid Ti–6Al–4V into liquid Al–Si, abnormal interfacial chemical reactions at the interface, and phase transformation between the intermetallic compounds could be wholly ascribed to these ultrasonic effects. An effective bond between Al–Si and Ti–6Al–4V can be produced by ultrasonic-assisted brazing in air.     

Stability of peakons for the Degasperis‐Procesi equation

The Degasperis‐Procesi equation can be derived as a member of a one‐parameter family of asymptotic shallow‐water approximations to the Euler equations with the same asymptotic accuracy as that of the Camassa‐Holm equation. In this paper, we study the orbital stability problem of the peaked solitons to the Degasperis‐Procesi equation on the line. By constructing a Lyapunov function, we prove that the shapes of these peakon solitons are stable under small perturbations. © 2007 Wiley Periodicals, Inc.     

圆柱空腔上裂纹的爬波检测方法

通过牛顿迭代法求解了固体内部圆柱空腔上爬波的频散方程,分析了爬波的频散和衰减特性。利用动态光弹法显示了爬波的直观图像和圆柱空腔附近各散射波的空间关系。根据爬波具有的频散、衰减以及辐射横波特征,设计了斜入射脉冲回波实验装置,测量了特定位置处裂纹反射爬波辐射出的横波信号,其与柱面反射波的时差和理论预测一致。进一步实验研究发现,爬波回波幅度与特定位置的裂纹长度具有近似单调的对应关系,在裂纹长度较大时,回波幅度趋于稳定。以上工作为圆柱空腔上裂纹的爬波定量检测提供了物理基础和实现方法。