液氮制冷低气压试验箱的仿真设计

在采用液氮制冷的低气压试验箱的设计中,用常规工程设计方法计算的降温过程冷负荷过大,从而导致真空系统设计容量过大。本文采用分布参数模型对试验箱低气压条件下降温过程的冷负荷进行了精确仿真模拟,以此作为真空系统容量设计的基础,减小了设计规模,取得了良好的效果。     

RF-MBE生长的AlGaN/GaN高电子迁移率晶体管特性

用射频分子束外延技术研制出了室温迁移率为10 35 cm2 /(V·s) ,二维电子气浓度为1.0×10 1 3cm- 2 ,77K迁移率为2 6 5 3cm2 /(V·s) ,二维电子气浓度为9.6×10 1 2 cm- 2 的Al Ga N/Ga N高电子迁移率晶体管材料.用此材料研制的器件(栅长为1μm,栅宽为80μm,源-漏间距为4μm )的室温非本征跨导为186 m S/m m,最大漏极饱和电流密度为92 5 m A/m m,特征频率为18.8GHz.     

碲酸盐系统玻璃组成和结构对非线性光学性能的影响

碲酸盐系统重金属氧化物玻璃是一种优秀的非线性光学玻璃材料，具有较大的三阶非线性光学效应、超快光学响应、较宽红外透过范围、较好稳定性以及广泛应用前景。碲酸盐系统玻璃中的中间离子和网络外离子的加入会改变组成网络的配位多面体组成、键性和能带结构，进而影响玻璃的非线性光学性能。探讨了碲酸盐系统玻璃的网络结构，阐述了玻璃组成、结构以及纳米簇和非线性光学性能之间的相互关系。     

A practical SPICE model based on the physics and characteristics of realistic single-electron transistors

A practical model for a single-electron transistor (SET) was developed based on the physical phenomena in realistic Si SETs, and implemented into a conventional circuit simulator. In the proposed model, the SET current calculated by the analytic model is combined with the parasitic MOSFET characteristics, which have been observed in many recently reported SETs formed on Si nanostructures. The SPICE simulation results were compared with the measured characteristics of the Si SETs. In terms of the bias, temperature, and size dependence of the realistic SET characteristics, an extensive comparison leads to good agreement within a reasonable level of accuracy. This result is noticeable in that a single set of model parameters was used, while considering divergent physical phenomena such as the parasitic MOSFET, the Coulomb oscillation phase shift, and the tunneling resistance modulated by the gate bias. When compared to the measured data, the accuracy of the voltage transfer characteristics of a single-electron inverter obtained from the SPICE simulation was within 15%. This new SPICE model can be applied to estimating the realistic performance of a CMOS/SET hybrid circuit or various SET logic architectures.     

Current distribution, resistance, and inductance forsuperconducting strip transmission lines

A method for the calculation of the current distribution, resistance, and inductance matrices for a system of coupled superconducting transmission lines having finite rectangular cross-section is presented. These calculations allow accurate characterization of both high-T_c and low-T _c superconducting strip transmission lines. For a single stripline geometry with finite ground planes, the current distribution, resistance, inductance, and kinetic inductance are calculated as functions of the penetration depth for various film thicknesses. These calculations are then used to determine the penetration depth for Nb, NbN, and YBa₂Cu₃O_7-x superconducting thin films from the measured temperature dependence of the resonant frequency of a stripline resonator. The calculations are also used to convert measured temperature dependence of the quality factor to the intrinsic surface resistance as a function of temperature for an Nb stripline resonator     

TiAl＋Sb合金的热稳定性的研究

研究了退火处理对Ｔｉ－３４ｗｔ．％Ａｌ－０．５ｗｔ．％Ｓｂ合金的室温抗弯性能，显微组织，相组成和断口形貌的影响。发现，低于１０００℃退火处理，ＴｉＡｌ＋Ｓｂ合金的显微组织没有变化，其力学性能仍然保持较高的值。此合金成分适应高温使用条件。     

溶胶－凝胶法制备Pb（Zr，Ti）O_3玻璃陶瓷过程中的结构变化

本文介绍溶胶－凝胶法制备均匀ＰｂＺｒ－Ｔｉ－Ｂ－Ｓｉ凝胶玻璃，并通过适当热处理在凝胶玻璃中原位生长Ｐｂ（Ｚｒ；Ｔｉ）Ｏ３微晶的新工艺·利用ＩＲ谱考察了凝胶玻璃中的元素键合结构随温度的变化．结合热分析和ＸＲＤ；ＳＥＭ技术，研究了Ｐｂ（Ｚｒ，Ｔｉ）Ｏ３微晶在凝胶玻璃中的生长过程及该材料的结构特点．发现Ｐｂ２（Ｚｒ，Ｔｉ）２Ｏ６＋ｘ立方焦绿石介稳过渡相的纳米微晶首先出现于该体系中，并在更高的温度下先后完全转变成三方和四方Ｐｂ（Ｚｒ，Ｔｉ）Ｏ３钙钛矿相．电子显微观察结果表明，该工艺制备的Ｐｈ（Ｚｒ；Ｔｉ）Ｏ３玻璃陶瓷具有均匀的细晶结构．     

Differential competitive learning for centroid estimation and phoneme recognition.

A comparison is made of a differential-competitive-learning (DCL) system with two supervised competitive-learning (SCL) systems for centroid estimation and for phoneme recognition. DCL provides a form of unsupervised adaptive vector quantization. Standard stochastic competitive-learning systems learn only if neurons win a competition for activation induced by randomly sampled patterns. DCL systems learn only if the competing neurons change their competitive signal. Signal-velocity information provides unsupervised local reinforcement during learning. The sign of the neuronal signal derivative rewards winners and punishes losers. Standard competitive learning ignores instantaneous win-rate information. Synaptic fan-in vectors adaptively quantize the randomly sampled pattern space into nearest-neighbor decision classes. More generally, the synaptic-vector distribution estimates the unknown sampled probability density function p( x). Simulations showed that unsupervised DCL-trained synaptic vectors converged to class centroids at least as fast as, and wandered less about these centroids than, SCL-trained synaptic vectors did. Simulations on a small set of English phonemes favored DCL over SCL for classification accuracy.     

Chemistry and Physics of Alkali Metals on MoS2 Surfaces

The interaction of alkali metal with surfaces has been of great interest to the community of catalysis since alkali metal can play an important role as a promoter. On alkali-doped MoS₂, such a promotion effect of alkali metal has been exemplified in the direct synthesis of linear alcohols from CO and H₂, where the alkali-doping switches the catalyst selectivity from methanation to alcohol synthesis. This paper reviews recent high-resolution X-ray photoelectron spectroscopy experiments that have provided direct observation of electron transfer from alkali metals to a model single crystal MoS₂ and the capture of the supra-valence electrons in the subsequent oxidation reactions.