Influence of lattice self-heating and hot-carrier transport ondevice performance

As device technologies improve, the traditional drift-diffusion transport model becomes inadequate to predict the performance of state-of-the-art semiconductor devices. The reasons are believed to be the larger field and field gradient inside advanced devices which cause lattice heating and hot carrier nonlocal transport phenomena. For more accurate prediction on device performance, a new device simulator capable of full thermodynamic simulation was developed. The carrier and carrier energy transport equations are directly derived from the Boltzmann transport equation, and the energy transfer among electrons, holes and crystal lattice takes into account most of the possible mechanisms. This simulator was used to simulate the DC behavior of a BJT and a half-micron NMOS. The simulation results show that for advanced devices, not only the drift-diffusion model becomes inadequate, but including only one of the two thermal effects results in error in simulated device characteristics     

二维地震过障碍观测系统模式及其参数设计

在二维地震勘探中,为了避免因地表障碍物使地震反射剖面出现间断现象,需要改变观测系统设计,跨越障碍物(江河、城镇等),以保证反射同相轴能连续追踪对比。在以往地震勘探中,有时因过障碍观测系统设计不合理,不但增加勘探费用,而且影响采集质量。因此只有科学合理地设计过障碍观测系统模式和参数,才能保证地震测线顺利通过障碍物,得到较好的障碍物下方的地震资料并降低勘探成本。为此本文在调查和研究大量野外实际的过障碍观测系统的基础上,总结归纳成三大类过障碍观测系统模式,并分析其特点和应用范围。采用图解法,推导出主要模式的跨越宽度、最小炮检距及最大炮检距等参数公式。采用这套过障碍观测模式不仅可以得到和障碍区两侧等质量的地震资料,而且可以有效地降低勘探成本。     

添加CaF2-YF3的AlN陶瓷的热导率

用CaF2和YF3做添加剂，在1750℃制备了热导率高于170W/m.K的的AlN陶瓷，并用XRD和SEM研究了AlN陶瓷在烧结过程中的相组成，微结构以及晶格参数的变化，并讨论了其对热导率的影响，研究发现，当使用CaF2-YF3做添加剂时，微结构差异对AlN陶瓷热导率的影响很小，AlN陶瓷的热导率主要由AlN晶格氧缺陷浓度决定，由于CaF2-YF3能有效降低AlN颗粒表面的氧含量，从而有利于获得高的热导率。     

Synthesis of Nearly Monodisperse Iron Oxide and Oxyhydroxide Nanocrystals

Uniform magnetite, hematite, and goethite nanocrystals were prepared through an attractive method based on an oleic acid/alcohol/water system. By adjusting the synthetic parameters (base concentration, alcohol content, categories of alcohols, etc.), the controlled synthesis of uniform magnetite, hematite, and goethite nanocrystals can be easily achieved. Detailed investigations on the effect of the experimental parameters on the morphology of the final products and the phase transitions among the magnetite, hematite, and goethite phases were carried out. Finally, a method of doping other metal ions into magnetite was developed and the magnetic properties of magnetite doped with different metal elements were studied.     

Electromagnetics of superconductors

It is shown that a superconductor cannot be simply treated as a low-loss conductor; rather, it should be treated as a negative dielectric material (with a negative dielectric constant). This approach is good only for vanishingly small field application with frequency significantly smaller than gap frequency and temperature not too close to the critical temperature of the superconductor. The electromagnetics of negative dielectric materials are discussed in terms of causality, perturbation technique, surface impedance, time-domain interpretation of current components, and computational electrodynamics     

Radiation of millimeter waves from NRD leaky wave antennas withtapered transition and tuning aperture

The radiation of millimeter waves from the nonradiative dielectric (NRD) leaky wave antennas with the tapered transition and the tuning aperture is investigated. An accurate theory for the leakage constant and the phase constant of the antennas is presented, which is based on the generalized scattering parameters considering the higher-order mode interactions at the discontinuities. The associated transverse equivalent network involves the characterization of the mode couplings at two air-to-dielectric interfaces, the coupled mode analysis of the tapered transition, and the calculation of the radiation fields at the tuning aperture via the extended spectral domain approach. The interesting behavior of the present modified configuration of NRD leaky wave antennas is illustrated by typical examples. The validity of the theory is confirmed by the comparison of the theoretical results with experimental data for the limiting cases     

一种用于强振环境的转速传感器

该文介绍一种简单、可靠、小巧的转速传感器。它的特点是在强振环境下仍具有很高的可靠,可用于坦克底盘、重型工程机械,燃气轮机组等机械作为转速监测。     

Process conditions for separating fatty acid esters by supercritical CO2

The solubilities of ethyl palmitate, ethyl oleate, ethyl eicosapentaenoate (EPA) and ethyl docosahexaenoate (DHA) in supercritical carbon dioxide were determined by a continuous flow method. The solubilities of fatty acid ethyl esters increased with pressure and decreased as the temperature was increased. An empirical equation, similar to Chrastil's equation, was used to describe the relationship between solute solubility and the density of carbon dioxide. The empirical equation was further used to qualitatively estimate the separation efficiency of isolating EPA and DHA ethyl esters from fatty acid esters. The operating conditions yielding high solubility gave fast extraction rate but resulted in low separation efficiency. Experiments were conducted to separate ethyl EPA and ethyl DHA from a model mixture containing four fatty acid ethyl esters and from esterified squid visceral oil. The experimental data compared closely with the calculated values.     

Characterization of the ntrBC genes of Azospirillum brasilense Sp7: their involvement in the regulation of nitrogenase synthesis and activity

The in vitro effect of citric acid application on periodontally involved root surfaces was investigated using scanning electron microscopy. Teeth were selected following specific criteria. The specimens were prepared for observation, and the features of the root surface were studied. The results demonstrated that a 3-minute application of citric acid (pH = 1.0) to the root surface after scaling and root planing demineralized the outer root surface, opened the dentinal tubules, and exposed collagen fibers. Scaling and root planing alone left the surface with a smear layer, scattered islands of cementum, and no collagen fibers or exposed dentinal tubules.