The effect of heat and IR radiation on the fluorescence of cellulose

The emission spectra of pure cellulose samples of various origins were monitored during several heating/cooling cycles. During heating the emission intensity decreased due to the greater probability for internal conversion at higher temperatures. Cooling resulted in an emission recovery that was nearly reversible over several heating/cooling cycles, provided that the final 0temperature was sufficiently low. The change in the relative emission yield with temperature showed two regimes, both with linear decreases but different slopes, suggesting different mechanisms for the internal conversion in these regions. Heating to temperatures higher than 160°C for filter papers and higher than 145°C for microcrystalline cellulose initiated reactions that caused changes in the emission spectra typical of thermal degradation. If the samples were heated beyond these threshold temperatures the emission recovery on cooling after the first heat treatment occurred to a much higher intensity level than that observed initially, indicating the formation of a multitude of new chromophores due to thermal reactions. Exposure of the samples to IR radiation caused a slow increase in the emission intensity for almost 600h.     

手持热像仪的设计

从手持热像仪的性能要求出发,讨论了手持热像仪设计中应考虑的几个问题,并给出了一个设计实例。     

硅基稀土热扩散法初探

稀土元素在我国有丰富的贮量．近年来,稀土元素在各种新科技领域中得到不断的开发和利用．各类稀土功能材料在发光和光通信领域中正展现巨大的应用潜力［１］．稀土磁光薄膜材料是优良的记录介质;稀土Ｅｒ由于其特殊的电子结构,已用来制造掺铒光纤激光器和光纤放大器［２］;掺铒硅还可制造发光谱线单一的发光器件［３］,这为实现人们所期待的硅基光电集成提供了有益途径．此外,基于对掺铒硅荧光发射衰减时间的分析,可用于制造温度传感器［４］．因此,稀土在共价半导体材料如Ｓｉ、ＧａＡｓ中的行为研究日益受到重视．但这些工作主要…     

The use of thermal analysis in the approximate determination of the cement content in concrete

Thermal analysis was first used to investigate the pattern of dissociation of hydrated ordinary Portland cement. Portlandite (Ca(OH)₂) decomposes at about 500°C. This was confirmed by kinetic calculations. Thermal analysis was then performed to establish the effect of varying the cement content on the percent mass loss associated with the decomposition of Ca(OH)₂ in cement mortar cured for 28 days. An increasing relation was obtained. Standard concrete cubes were then prepared with cement contents ranging from 200 to 450 kg m^-3. The loss in mass on heating, up to 750°C, of concrete samples cured for 28 days was then related to the cement content in concrete. The relation obtained was tested for concrete cubes of known cement content and found to be in better agreement than the results obtained by conventional chemical analysis. This method can be used for an approximate determination of the cement content in concrete. This revised version was published online in July 2006 with corrections to the Cover Date.     

Studies on the thermal decomposition of N,N'-ethylenebis(salicylideneiminato) diaquochromium(III) nitrate

A complex of N,N'-ethylenebis(salicylideneiminato)diaquochromium(III) nitrate, [Cr(salen)(H₂O)₂]NO₃ was characterized and its decomposition mechanism was studied by TG. The IR spectrum and X-ray analysis were examined for the complex. The non-isothermal kinetic data were analyzed by means of the Achar method and the Coats—Redfern method. The most probable kinetic model function was suggested by comparison of the kinetic parameters.This revised version was published online in November 2005 with corrections to the Cover Date.     

单晶硅纳米薄膜面向导热MD研究的探讨

本文分析了经典分子动力学(Molecular Dynamics)技术在模拟厚度在纳米量级的单晶硅薄膜平行于薄膜平面方向的热导率时出现的用难,指出精确计算薄膜表面附近处的原子运动状态对于单晶硅纳米薄膜面向热导率的分子动力学模拟具有重要意义,并在此基础上提出采用基于分子动力学和预处理共轭梯度法(Preconditioned conjugate Gradients)的Ab Initio方案模拟面向热导率。     

Thermal behavior of n-alcohols, benzene, and toluene in water urea and water ethyleneglycol systems

Relations are suggested for calculating the heat characteristics of alcohols, benzene, and toluene in aqueous solutions of urea and ethylene glycol. The solution heat of an alcohol shows greater dependence on the glycol concentration, while the heat capacity of solution, on the urea concentration. For n-butanol in aqueous glycol, the characteristic temperature at which the solution heat of the alcohol is zero decreases as the glycol concentration increases. The dependence of the characteristic temperature of 1-butanol on the urea concentration has a maximum.     

DEEP LEVEL DEFECTS IN SI-IMPLANTED LEC UNDOPED Si-GaAs

The residual electrically active defects in(4×10~(12)cm~(-2)(30KeV)+5×10~(12)cm~(-2)(130KeV))si-implanted LEC undoped si-GaAs activated by two-step rapid thermal annealing(RTA)LABELED AS 970℃(9S)+750℃(12S)have been investigated with deep level transient spec-troscopy(DLTS).Two electron traps ET_1(E_c-0.53eV,σ_n=2.3×10~(-16)cm~2)and ET_2(E_c-0.81eV,σ_n=9.7×10(-13)cm~2)are detected.Furthermore,the noticeable variations of trap's con-centration and energy level in the forbidden gap with the depth profile of defects induced by ion im-plantation and RTA process have also been observed.The[As_i·V_(As)·As_(Ga)]and[V_(As)·As_i·V_(Ga)·As_(Ga)]are proposed to be the possible atomic configurations of ET_1 and ET_2,respectively to explaintheir RTA behaviors.     

切向气流对激光加热材料的影响

 在重复频率YAG激光加载下，研究了30CrMnSiA钢片分别处于空气自然对流和切向强迫气流环境中不同的温度响应。实验用红外热像仪对靶前表面的温度进行了实时诊断，结果表明，在激光作用下，靶材的温升与靶前表面的对流换热状况有较大的关系，当靶面存在马赫数为0.1左右的切向气流时，材料的温升曲线明显低于靶处于空气自然对流环境下的温升曲线，气流与靶面的对流换热使得材料的激光加工所需能量或功率增加。这与应用热边界层换热动力学理论得到的结论一致。     

Characterizing domain mixing effects in hydrogen bond-compatibilized polymer blends

The nature and extent of phase mixing in blends of hydroxyl-functionalized polystyrene and poly(ethyl acrylate) (PS/PEA), where the driving force for mixing is hydrogen bonding, are characterized by several techniques. Small-angle x-ray scattering (SAXS) shows a reduction in average domain size with increasing functionalization level, a result also evident from scanning electron microscopy (SEM). Together, the two techniques reveal a very broad distribution of domain sizes. At high functionalization levels, both SAXS and SEM indicate a high degree of “in-domain” mixing, with little or no pure PS or PEA remaining in the blends. Mathematical modeling of dynamic mechanical thermal analysis (DMTA) data is employed to quantify this progression. Initially, mixing is primarily interfacial, but as the functionalization level increases, the mixed interphase rapidly grows to occupy the entire material. In agreement with the SAXS and SEM results, DMTA modeling shows that further increases in the functionalization level suppress the amplitude of composition variations in the sample. The onset of extensive in-domain mixing coincides with the marked changes in stress-strain behavior observed previously in these materials. © 1994 John Wiley & Sons, Inc.