Short-Circuit Diffusion in Ceramics

This article discusses grain boundary diffusion in ceramics. It gives a brief review of the experimental data available for ionic oxides and the problems of interpretation associated with it. The fundamental differences between grain boundary diffusion in metals and ceramics are noted. Calculations of the segregation of defects and impurities to grain boundaries are discussed together with methods of calculating diffusion coefficients in these boundaries. New results for alumina and chromia are presented. The problem of defining a grain boundary width is discussed with respect to new calculations on nickel oxide.     

Generation of Electrical Currents and Magnetic Fields by Grain Boundary Motion

The effect of an induced magnetic moment due to grain boundary motion in a magnetic field was studied theoretically in a microscopic and a mesoscopic approximation. It was found that the induced moment generates a drag force on the boundary, which depends on the orientation of the magnetic field with regard to the crystal axis, as observed experimentally. However, the magnitude of the theoretically predicted dependency is much smaller than experimentally observed and even opposite with regard to the orientation dependence. Therefore, the electromagnetic drag can be neglected in comparison with other driving forces for grain boundary motion, but the effect may play a role for fast moving dislocations in a magnetic field.     

钩刺山羊草Aegilops triuncialis籽粒硬度主效基因的克隆与表达

根据小皮Pin a，Pin b，GSP基㈥的保守序列，设计合成了3对特异性引物，对四倍体钩刺山羊草Aegilopstriumialis的基因组DNA和胚乳RNA进行Pin a，Pin b，CSP基因扩增、克降、序列测定和表达分析，发现了两个新型Pin a等位堆因、一个新刑Pin b等化基因和一个新型GSP等位基因，基因序列均与六倍体小麦的同源基因存在较大的差异，Southern Blot分析结果表明，该材料巾含有2个拷贝Pin a。基因，5个拷贝Pin b基因，2个拷贝GSP基因．RT-PCR和Western Blot都证实了Pin a，Pin b，GSP基因在籽粒胚乳中的表达．研究结果显示由羊草可以为小麦分子育种提供有用的遗传资源。     

Shielding against noise interfering with quantitation of insect infestations by acoustic detection systems in grain elevators

Acoustic devices used to detect hidden insect infestations must be shielded from noise in most practical applications. One device developed specifically for use in a noisy environment, the Acoustic Location ‘Fingerprinting’ Insect Detector (ALFID), counts the numbers of insects present in grain samples from shipments being graded for export at commercial grain elevators. This report considers the performance of ALFID's noise-shielding components, which include an enclosure for passive reduction of ambient noise, and an electronic system for active detection and masking of sounds originating outside the grain sample container. Sound pressure levels (SPLs) of ambient noise are reduced inside the enclosure by 60–90 dB at frequencies between 1 and 10 kHz, with a reduction of ~6.5 dB per octave (frequency doubling). The active noise-masking system protects ALFID from loud ambient sounds not sufficiently attenuated by the enclosure. If the output from one of four sensors mounted on the outside of the grain sample container rises above a preset amplitude threshold, a signal is triggered that inhibits acquisition of insect sound data from sensors inside the container. In tests of the complete ALFID system at a grain elevator with ambient noise of 73 ± W dB re 20 μPa SPL, the mean rate of noise-mask triggering was 5.5 s⁻¹, inhibiting acquisition of insect sounds for only 3.9% of the total testing period. This level of performance is sufficient to enable successful operation of ALFID under such noise conditions.     

应变对纳米铜晶界迁移的影响

用分子动力学方法模拟了金属铜纳米双晶中晶界在应变作用下的迁移过程，晶界类型为〈11l〉倾侧∑19晶界。原子问相互作用力采用Finnis-Sinclair型EAM势计算。结果表明：平行于晶界方向的压应变可以促进晶界在相邻品界交互作用下发生迁移；垂直于晶界方向的压应变则不能对晶界迁移产生明显的效果。晶界迁移大致可分为两个阶段，前阶段晶界迁移缓慢，随晶界间距减小，晶界间交互作用加强，使晶界迁移显著加速。     

Interaction of Point Defects with Grain Boundaries in fcc Metals

Structures of several symmetrical tilt grain boundaries (GBs) with different tilt axes in Cu and Al and their interaction with vacancies and interstitials are studied using atomistic computer simulations with embedded-atom potentials. The lowest defect formation energy in a GB is found to correlate with the GB energy in both Cu and Al. Importantly, vacancies and self-interstitials in GBs have comparable formation energies, suggesting that both defects are equally important for GB diffusion and other properties. Vacancies in GBs can be either localized at certain sites or be delocalized over several sites. Some GB sites do not support a stable vacancy at all. Self-interstitial atoms can occupy relatively open interatomic positions, form split dumbbell configurations, or give rise to highly delocalized displacement zones. These structural forms of point defects have been observed across the whole set of twelve GBs in Cu and six GBs in Al studied in this paper as well as in our previous work [Interface Science 11, 131–148 (2003)]. It is suggested that these structural forms are general to all GBs in fcc metals. They can be explained by the existence of internal stresses and alternating tension and compression regions in the GB core.     

A new type of periodie boundary condition useful for high-temperature atomistic simulations of grain boundaries: Applications in semiconductors

A new type of boundary condition, named Möbius or antiperiodic boundary conditions, is proposed and tested, both analytically and within the context of numerical simulations. It is shown that these boundary conditions are very useful for twist grain boundary atomistic simulations. By contrast to the use of the ordinary Born von Kármán periodic boundary conditions, they allow only one grain boundary per box instead of two. The risk of migration and overinteraction of two grain boundaries at high temperature is thus avoided while more complex grain boundaries can also be tackled at the same computer price. Such examples are presented and discussed.     

Detection of impurity segregation in zone-confined, polycrystalline tin-doped indium oxide thin films by STM and AFM

This paper discusses the possibility of using STM and AFM to image the dopant material in a segregated state. Samples of tin-doped indium oxide were prepared using a zone-confining process. The resultant material has dopant species segregated over certain grain boundaries at desired positions while the others remain dopant free. Samples were then imaged using STM, AFM and STEM. Enhanced contrast from the dopant rich grain boundaries and a larger grain size are observed at the surface making an interface with the substrate as compared to the free surface of the sample, while secondary electron STEM images show these grains to be smaller in size and the boundaries to be almost physically flat. This is interpreted to be a consequence of the zone-confining effect.     

The Shape of the Moving Grain Boundary in the Reversed-Capillary Technique Under Consideration of the Drag Effect

The shape of the curved part of the migrating grain boundary driven by capillary forces was studied for the reversed-capillary bicrystal technique. A comparison of experimentally observed and theoretically calculated shapes showed good agreement when the drag effect by mobile obstacles was taken into account. So far previous studies dealing with the reversed-capillary technique have not considered the drag effect. Consequently, they assume a scaling behavior of the shape of the moving grain boundary. In this study it is shown that this assumption generally is not possible for the reversed-capillary technique. Furthermore, it is shown that the geometry factor used for determination of the driving force is dependent on the displacement. Problems specific to the reversed-capillary technique due to the drag effect are discussed. The analysis of the boundary shape is presented as a tool to distinguish free and dragged motion.     

因瓦合金纳米微粉的恒磁导率及其压力、频率特性和压力相变

 以Fe-30wt%Ni合金片为母合金，用蒸发冷凝法制备了三种粗细不同的纳米微粒。经透射电镜和X光衍射物相分析，微粒成分与母合金一致。5T、5H和3K粉的平均粒度分别为13.6、27和40 mm。在室温和43~28个不同的流体静压力（0.000 1~2.205 GPa）下测量了它们的磁化曲线、磁导率曲线和起始磁化曲线。结果表明：（1）在H＝(20－132)(1000/4π)A/m范围内Fe-30Ni合金三种纳米粉均具有恒磁导率。（2）三种纳米粉恒磁导率随静水压的变化规律如下：μ_r＝3.83+0.253p-0.022 1p²-0.007 22p³（5T粉）；μ_r＝3.93+1.20p-1.97p²+1.52p³-0.510p⁴+0.059 9p⁵（5H粉）；μ_r＝5.96-0.276p+0.107p²-0.045 9p³（3K粉）。前两者随压力增加而升高。后者随压力增加而下降。（3）γ-α马氏体相变明显存在于5T、5H粉中，而3K粉中未见到。（4）Fe-30Ni合金片的μ_i从200kHz至2 MHz已下降一个数量级，而其纳米粉μ_i的频率范围高于300 MHz，增大两个数量级以上。