Correlation between deformation bleaching and mechanoluminescence in coloured alkali halide crystals

The present paper reports the correlation between deformation bleaching of coloration and mechanoluminescence (ML) in coloured alkali halide crystals. When the F-centre electrons captured by moving dislocations are picked up by holes, deep traps and other compatible traps, then deformation bleaching occurs. At the same time, radiative recombination of dislocation captured electrons with the holes gives rise to the mechanoluminescence. Expressions are derived for the strain dependence of the density of colour centres in deformed crystals and also for the number of colour centres bleached. So far as strain, temperature, density of colour centres, E _a and volume dependence are concerned, there exists a correlation between the deformation bleaching and ML in coloured alkali halide crystals. From the strain dependence of the density of colour centres in deformed crystals, the value of coefficient of deformation bleaching D is determined and it is found to be 1.93 and 2.00 for KCl and KBr crystals, respectively. The value of (D+χ) is determined from the strain dependence of the ML intensity and it is found to be 2.6 and 3.7 for KCl and KBr crystals, respectively. This gives the value of coefficient of deformation generated compatible traps χ to be 0.67 and 1.7 for KCl and KBr crystals, respectively.     

Peristaltic transport of a Newtonian fluid in a vertical asymmetric channel with heat transfer and porous medium

The problem of peristaltic flow of a Newtonian fluid with heat transfer in a vertical asymmetric channel through porous medium is studied under long-wavelength and low-Reynolds number assumptions. The flow is examined in a wave frame of reference moving with the velocity of the wave. The channel asymmetry is produced by choosing the peristaltic wave train on the walls to have different amplitudes and phase. The analytical solution has been obtained in the form of temperature from which an axial velocity, stream function and pressure gradient have been derived. The effects of permeability parameter, Grashof number, heat source/sink parameter, phase difference, varying channel width and wave amplitudes on the pressure gradient, velocity, pressure drop, the phenomenon of trapping and shear stress are discussed numerically and explained graphically.     

光纤探针型近场光镊光阱力特性研究

基于动量守恒原理,结合麦克斯韦应力张量和三维时域有限差分方法,建立了近场空间内激光光镊对纳米微粒的光阱力计算模型.分析了光纤探针型近场光镊的近场分布以及操作纳米微粒时各轴向光阱力的分布情况,并探讨了光纤探针尖端的捕获尺寸、捕获位置和操作稳定性.结果表明:微粒应处于光纤探针针尖的近场空间内才可实现稳定可靠的纳米操作,不同尺寸的微粒具有不同的捕获效果,且随初始位置的不同微粒的捕获位置亦不同.计算结果为激光近场光镊纳米操作装置的设计和制造提供了理论基础.     

Comparative study on the photocatalytic mineralization of homologous aliphatic acids and alcohols

The photocatalytic mineralization of methanol, ethanol and 1-propanol is compared with those of their homologous carboxylic acids (formic, acetic and propanoic). The presence of S₂O₈²⁻ ions almost does not affect the alcohols mineralization. But, those of the acids are slowed down. In addition to this, adding H₂O₂ inhibits the alcohols mineralization and those of the acids, but to a lesser extent.FT-IR studies have shown that carboxylates generated from the oxidation of the corresponding alcohols adsorb at different centres from those where carboxylates directly generated from formic, acetic and propanoic acids do.From the obtained results, mineralizations of these compounds have been correlated with their proximity and accessibility to photoactive centres.     

Oscillator strength of F2 − colour centres in LiF crystal

The absorption cross-section integral and the oscillator strength of the 960 nm absorption band due to F₂ ^– colour centres in LiF crystal is determined at room temperature from the absorption cross-section spectrum of the F₂ ^– centres obtained from saturable absorption studies. A comparison with previous results is made.     

电子陷获型红外上转换材料的光谱测试

本文通过对电子陷获型红外上转换材料的激发光谱和发光光谱特性曲线的测试,论证该材料与一般红外器件相比,具有响应光谱范围广(0.8～1.6μm)等优点,为该材料的推广应用提供了可靠的依据。     

Quantum and stochastic aspects of low-temperature trapping and reaction dynamics

We discuss theoretical work on motion-limited trapping kinetics at very low temperatures where theories based upon strictly diffusive models break down due to quantum mechanical effects. In addition, we present numerical results which confirm earlier asymptotic predictions regarding the survival probability for one-dimensional chains, and discuss the important role fluctuations and selfaveraging (or the lack thereof) play in the analysis of finite systems.     

Silica surface controversies,strong adsorption sites,their blockage and removal. Part I

Summary The review describes many different controversies concerning the surface chemistry of silica. The first part concerns the variable nature of alkyl bonded phases for HPLC, the physical requirements for silica and the role of silanols as adsorption centres. The existence of a small population of strong adsorption sites is pointed out and the reasons for the strong and undesirable adsorption discussed; the part played by trace metals in the silica matrix is emphasised.     

Optimised hydrothermal synthesis of multi-dimensional hybrid coordination polymers containing flexible organic ligands

In this paper, we summarise our recent research interest in the hydrothermal synthesis and structural characterisation of multi-dimensional coordination polymers. The use of N-(phosphonomethyl)iminodiacetic acid (also referred to as H₄pmida) in the literature as a versatile chelating organic ligand is briefly reviewed. This molecule plays an important role in the formation of centrosymmetric dimeric [V₂O₂(pmida)₂]⁴⁻ anionic units, which were first used by us as building blocks to construct novel coordination polymers. Starting with [V₂O₂(pmida)₂]⁴⁻ in solution, we have isolated [M₂V₂O₂(pmida)₂(H₂O)₁₀] species (where M²⁺ = Mn²⁺, Co²⁺ or Cd²⁺) via the hydrothermal synthetic approach, which were then employed for the construction of [CdVO(pmida)(4,4′-bpy)(H₂O)₂]·(4,4′-bpy)_0.5·(H₂O), [CoVO(pmida)(4,4′-bpy)(H₂O)₂]·(4,4′-bpy)_0.5, [Co(H₂O)₆][CoV₂O₂(pmida)₂(pyr)(H₂O)₂]·2(H₂O) and [Cd₂V₂O₂(pmida)₂(pyr)₂(H₂O)₄]·4(H₂O) by the inclusion of bridging organic ligands in the reactive mixtures, such as pyrazine (pyr) and 4,4′-bipyridine (4,4′-bpy). These materials can contain channel systems, and exhibit magnetic behaviour, not only due to the V⁴⁺ centres but also to the transition metal centres which establish the links between neighbouring dimeric [V₂O₂(pmida)₂]⁴⁻ anionic units. A closely related anionic moiety, [Ge₂(pmida)₂(OH)₂]²⁻, was engineered to allow the study of such crystalline hybrid materials using one- and two-dimensional high-resolution solid-state NMR.