Diffusion properties of Cu(0 0 1)-c(2 × 2)-Pd surface alloys

Structural and diffusion properties of a Cu(0 0 1)-c(2 × 2)-Pd surface and sub-surface ordered alloys are studied by using interaction potentials obtained from the embedded-atom method. The calculated diffusion energies are in agreement with observed kinetics of the surface alloy formation and confirm stability of the underlayer alloy. Activation energy of planar diffusion of palladium at the initial stage of the alloy formation as well as the activation energy of the overlayer-underlayer diffusion of the Pd atoms are in good agreement with those obtained by the scanning tunneling microscopy and low energy electron diffraction measurements, respectively.     

Surface texturing of Si, porous Si and TiO2 by laser ablation

Excimer laser ablation at 308 nm has been used to texture the surfaces of a variety of materials of interest for optoelectronic and biotechnological applications. Using a range of pre- and post-processing methods, we are able to produce nano-, micro- and meso-scale features over large areas rapidly in materials such as crystalline Si, porous silicon and TiO₂. Texturing of porous silicon leads to the growth of crystalline dendritic structures, which distinguishes them dramatically from the conical pillars formed from crystalline silicon. Regular arrays of Si microdots are formed by irradiating a Si surface pre-covered with a Cr thin film grating. Nano-crystalline porous TiO₂ films are easily ablated or compacted with laser irradiation. However, at low enough laser fluence, surface roughening without complete loss of porosity is possible.     

基于叠栅技术的二维亚波长周期结构成像设计

用光子学方法研究了叠栅技术中,当试件光栅被拉压和旋转后,叠栅条纹的空间周期和相对于基准光栅的取向,试件光栅被拉压后的节距等相关问题。根据衍射光波的空间周期可能大于试件光栅空间周期的特点,对二维亚波长周期结构衍射成像进行了设计研究。首先,对二维亚波长周期结构衍射物进行编码,以获得包含编码光栅空间信息的均匀波;其次,使编码得到的均匀波通过光学系统,并被放大到CCD相机所能辨识的大小;再次,经解码光栅解码,滤掉编码波,最终获得二维亚波长周期结构物的空间结构信息,达到超分辨的目的。同时,对成像过程进行了较为详尽的分析,对编码器、解码器的位置以及它们相对衍射物的取向进行了设计研究,对滤波器的选择给予了必要的说明,指出了取得超分辨成像的关键。     

类椭球氧化锌纳米结构的制备与表征

"用普通氧化锌晶须作为原材料, 采用高压釜腐蚀法和高温(600 ℃)裂解结合的方法合成纳米棒构成的氧化锌类椭球结构．XRD、SEM和TEM结果表明这种类椭球结构是单晶的,纳米棒取向一致,自组装生长而成．"     

Energy and number of collision fluctuations in inelastic gases

The two-dimensional Inelastic Maxwell Model (IMM) is studied by numerical simulations. It is shown how the inelasticity of collisions together with the fluctuations of the number of collisions undergone by a particle lead to energy fluctuations. These fluctuations are associated to a shrinking of the available phase space. We find the asymptotic scaling of these energy fluctuations and show how they affect the tail of the velocity distribution during long time intervals. We stress that these fluctuations relax like power laws on much slower time scales than the usual exponential relaxations taking place in kinetic theory.     

济南地区表层土壤及沉积物中饱和烃分布特征及源解析

研究了济南地区不同功能区的表层土壤及沉积物中饱和烃的组成和分布特征,在此基础上初步分析了其来源.结果表明,饱和烃主要有正构烷烃、类异戊二烯、环烷烃等组成,正构烷烃碳数分布范围为n-C10-n-C34,类异戊二烯类主要是姥姣烷、植烷及甲基C13-C17烷等,同时还检出烷基环己烷,甾烷、三萜烷及藿烷等环烷烃.饱和烃总体含量分布为北高南低,北部化工区、高速入口处等饱和烃主要来源于原油或成品油等化石燃料及其燃烧产物;南部山区、水库沉积物及农田土壤等饱和烃主要来源于化石燃料的燃烧及高等植物.     

用于校准能见度仪的标准散射体定标系统中光学系统的误差分析

为了实现用于校准能见度仪的标准散射体的快速高精度定标,依据标准散射体校准前向散射式能见度仪的校准原理,建立定标系统中光学系统的误差分析方法.分析标准散射体定标系统的工作原理,结合其光学系统、机械结构的加工及装调偏差,建立了标准散射体定标系统的光学系统模型并设计实验证明其正确性.分析影响定标系统中光学系统精度的主要误差,得到标准散射体定标系统中光学系统的误差传递模型.通过对畸变偏差、像面位置偏差、主点位置偏差、像面倾斜偏差和焦距偏差的分析,提出了一种系统综合误差分析的方法并建立了综合偏差模型,对每个偏差单独分析,得出畸变偏差、像面位置偏差、主点位置偏差、像面倾斜偏差和焦距偏差的偏差范围依次为0.024 mm,0.399 mm,0.02 mm,0.28 rad和0.392 mm.该研究为提高用于校准能见度仪的标准散射体定标系统的精度以及校准时误差的来源分析与补偿提供理论依据.     

Theoretical research on the spin-Hamiltonian parameters of the square-planar CuS46− clusters in Cu(II)–dithiophosphonate complexes

The spin-Hamiltonian parameters (g-factors g_//, g_⊥ and hyperfine structure constants A_//, A_⊥) of the square-planar CuS^{6 ?}₄ clusters in Cu(II)–bis [4-ethoxphenyl-O-alkyl]-dithiophosphonate complexes are computed with the high-order perturbation formulas based on the two-mechanism model. The model includes the contributions to spin-Hamiltonian parameters from the vastly-utilised crystal-field (CF) mechanism concerning the CF excited states and the generally-omitted charge-transfer (CT) mechanism due to CT excited states. The energy levels of CF and CT excited states needed in the calculation are obtained from the observed optical spectra. The calculated results are in rational accordance with the experimental values. The signs of constants A_// and A_⊥ are suggested and the reasons of the very small g-shifts |?g_i| (= | g_i ? g_e |, where g_e ≈ 2.0023 and i = // or ⊥) are discussed.     

Experimental study of heat transfer characteristics in oscillating fluid flow in tube

In the present work, an experimental investigation of heat transfer enhancement parameters of the oscillating flow heat exchanger under different frequencies, tidal displacement, and heat fluxes is carried out. The effect of different parameters on experimental effective thermal conductivity and convective heat transfer coefficient in cooling region is studied using correlations given by different researchers. A correlation for experimental effective thermal conductivity in terms of S²√ω is derived based on experimental data. This correlation is useful for predicting the optimum value of S²√ω before onset of turbulence.     

Track revelation and optical properties of pentaerythritol tetrakis (allyl carbonate) plastic for application as nuclear track detector: effects of gamma radiations

The etching conditions of an indigenously prepared thin film of pentaerythritol tetrakis(allyl carbonate) (PETAC) were standardised for the use as a nuclear track detector. The optimum etching times in 6?N NaOH at 70°C for the appearance of fission and alpha tracks recorded in this detector from a ²⁵²Cf solid source were found to be 30 min and 1.50?h, respectively. The experimentally determined values for the bulk and track-etch rates for this detector in 6?N NaOH at 70°C were found to be 1.7?±?0.1 and 88.4?±?10.7?µm/h, respectively. From these results, the important track etching properties such as the critical angle of etching, the sensitivity and the fission track registration efficiency were calculated and compared with the commercially available detectors. The activation energy value for bulk etching calculated by applying Arrhenius equation to the bulk etch rates of the detector determined at different etching temperatures was found to be 0.86?±?0.02?eV. This compares very well with the value of about 1.0?eV reported for most commonly used track detectors. The effects of gamma irradiation on this new detector in the dose range of 200–1000?kGy have also been studied using bulk etch rate technique. The activation energy values for bulk etching calculated from bulk etch rates measurements at different temperatures were found to decrease with the increase in gamma dose indicating scission of the detector due to gamma irradiation. The optical band gap of this detector was also determined using UV–visible spectrometry and the value was found to be 4.37?±?0.05?eV.