Gamma ray irradiation induced point defects in BaF2

There are some original nonmagnetic point defects in the BaF2 crystallite powder,such as interstitial and vacant F^- which can become paramagnetic centers by γ-ray-irradiation at room temperature,Afterγ-ray irradiation the paramagnetic point defects Vk,H,F and M centers,have been observed in the sample with experiment of electron spin resonance(ESR).Frenkel exciton,a nonmagnetic point defect,can also be induced by the γ-ray irradiation in the sample at room temperature,the existence of the Frenkel exciton is affirmed by an anomalous change of the ESR signal of Vk center with temperature,The signals of the ESR of the H,F and M centers weaken and vanish with the temperature increasing monotonously,But the ESR signal of the Vk enhances when the temperature goes up about 127℃,then weakens and vanishes.An increase in the Vk center follows an annihilation of the Frenkel exciton with heating.     

砷化镓材料中EPR“As_(Ga)”的退火行为

本文比较了中子辐照。压缩变形和原生LEC砷化镓等三种不同来源样品的EPR“As_(Ga)”的Hamiltonian参数。并系统地研究了EPR“As_(Ga)”的浓度和低温光猝灭行为随退火温度的变化,从而进一步验证了EPR“As_(Ga)”的本性,即除孤立As_(Ga)反位原子外,还可能包括As_(Ga)的一些空位络合物。这些不同本性的EPR“As_(Ga)”缺陷及其它有关的缺陷在样品热处理过程中可能相互转化。按照物理化学中Le Chatlier原理,缺陷的原始浓度和晶体内部应变能似应是引起这些转化反应的重要因素。     

The “Paramagnetic” Meissner Effect in Superconductors

There are a number of publications concerning the observation of a paramagnetic signal in HTSC ceramic samples during field-cooling procedures. Some authors assume that this signal is connected with spontaneous currents and discuss the possibility of the existence of -junctions in Josephson media. In this work, it is shown that the paramagnetic signal could appear in the case of capture and compression of the magnetic flux in a sample during field-cooling procedures. The results of numerical calculation of the magnetic moment for different configurations of the sample and flux compression are presented. The unusual behavior of longtime relaxation of the magnetic moment in experiments on capture of magnetic flux is discussed.     

我国气体氧分析仪的研究现状

本文介绍了我国气体氧分析仪的应用领域、分类,详细描述了电化学原理氧分析器（电化学氧测定仪、原电池氧测定仪、氧化锆氧分析仪）和顺磁式原理氧分析仪的组成、原理、技术参数（测量范围、响应时间、示值误差、零点漂移、量程漂移、重复性等）,并且结合当前市场上普遍使用的仪器分别对百分含量氧分析仪和微量氧分析仪的国内外发展现状进行了比较。     

Enhancing natural convection in a cube using a strong magnetic field — Experimental heat transfer rate measurements and flow visualization

The effect of a strong magnetic field on the average heat transfer rate and flow profiles of joint gravitational and thermo-magnetic convection of a paramagnetic fluid in a cubic enclosure heated from below and cooled from above was experimentally investigated. The working fluid consisted of 80% mass glycerol aqueous solution with a concentration of 0.8 mol/kg gadolinium nitrate hexahydrate making it paramagnetic. The cubic enclosure of 32-mm sides was located in the 10-cm bore of a horizontally oriented 5-Tesla super-conducting magnet at a position where the magnetic force distribution was relatively uniform. Under this configuration, the magnetic field imposed in the horizontal direction acted perpendicularly to gravity. It was found that the heat transfer rate through the cube increased with the increase of the magnetic induction. Furthermore, steady and transient state flow visualizations were carried out with a 10-Tesla super-conducting magnet to show a change in the temperature field when magnet-thermo convection dominated. Visualization was made using thermo-chromic liquid crystal slurry added to the working fluid and illuminated in a vertical cross-section of the cube.     

六氟苯(C_6F_6)体系中氧对正子素(Ps)寿命的影响

本工作研究了溶解在六氟苯(C_6F_6)中的氧对正子素(Ps)寿命的影响。分别得到了在C_6F_6中三重态正电子素(O-Ps)的原始摘除寿命τ_3~0=4.15 ns;氧猝灭O-Ps的速率常数k_(O_2)=1.8×10~(10)(1mol~(-1)s~(-1));三重态激发分子~3(C_6F_6)猝灭O-Ps的速率常数k~3(C_6F_6)=1.7×10~(10)(1mol~(-1)s~(-1)),以及六氟苯体系中三重态激发分子~3(C_6F_6)猝灭O-Ps的贡献。结果表明:~3(C_6F_6)对O-Ps寿命的影响并不很大。     

施主掺杂BaTiO_3陶瓷的正电子湮没和顺磁共振研究

本文用正电子湮没和电子顺磁共振相结合的方法对施主掺杂BaTiO_3陶瓷的缺陷进行了研究。正电子湮没寿命测量说明与Ba/Ti=1的样品相比Ba过量或Ti过量都会引起材料中的空位增加。顺磁共振图谱表明,g=1.997峰的强度在铁电相变为顺电相后,强度有很大的增长(约20倍)。该峰强度随Ba/Ti的变化与正电子捕获率随Ba/Ti的变化相同。因此该峰是由阳离子空位(V_(Ba)和V_(Ti))引起的。它实质上是由O~-产生的,随施主掺量的增加g=1.997峰急剧增强,这很可能是由于施主增加引起V_(Ti)大量生成的缘故。     

KINETICS OF HETEROGENEOUS MAGNETIC FLOCCULATION USING A BIVARIATE POPULATION-BALANCE EQUATION

The discrete bivariate population-balance equation is formulated and solved to describe the kinetics of heterogeneous magnetic flocculation of colloidal paramagnetic particles in a uniform magnetic field. The particles are allowed to have various sizes and values of magnetic susceptibility. Computations show the importance of particle size and magnetic susceptibility on the flocculation rate and the transient bivariate (size/magnetic susceptibility) density function. The particle size distribution of certain magnetic-susceptibility particles and the magnetic-susceptibility distribution of certain size particles are calculated as functions of time and initial and operatingconditions. The composition of a floe at any time depends on magnetic, van der Waals, double layer, and hydrodynamic forces among pairs of particles. The magnetic force is a function of the particle size, magnetic susceptibility, and strength of the magnetic field. Results are presented for various initial conditions of particles after ten minutes of flocculation. The results are of significance in understanding the forces among the particles and designing efficient magnetic separation processes.