Thermodynamic Modeling of the Miscibility Gaps and the Metastable Liquidi in the MgO-SiO2, CaO-SiO2, and SrO-SiO2 Systems

A range of compositions and temperatures below the monotectic temperature exists where there are thermodynamic restrictions that prevent the equilibrium solid from forming directly from the undercooled homogeneous liquid. In this region, the solid can form only after liquid-liquid phase separation has occurred. As suggested by earlier research, the thermodynamic restrictions on the crystallization process may be useful to control the crystallized grain structure in glass-ceramic systems. Thus, understanding the thermodynamic limitations on the formation of the solid in monotectic systems could have commercial significance. In the present paper, the metastable liquidus boundaries, liquid miscibility gaps, and spinodal curves in binary MgO-SiO₂, CaO-SiO₂, and SrO-SiO₂ systems are calculated by using analytical expressions for the Gibbs free energies of the liquid phases. Calculating the metastable liquidus rather than using a simple extrapolation as originally proposed in the aforementioned previous research provides greater control of the heat-treatment processes and, thus, greater control over the resulting microstructure.     

Draft angle and surface roughness effects on stereolithography molds

Stereolithography (SL) is a rapid prototyping process, which allows one to build complex shapes quickly. Current research investigates the possibilities of using this process to make injection molds. This would allow designers to manufacture and test molds easily and rapidly. One of the main issues with this technique is the effects of its surface on the part. Molds built by SL have high roughness. This gives rise to a high friction force between the part and the mold, and increases the ejection force needed to eject the part from the mold. High ejection forces often lead to damage or breakage of the part and the mold. Research was undertaken on the effects of draft angle and roughness on ejection forces. It was found that increasing the draft angle does not necessary assist the ejection of the part. As the draft angle increases, the roughness and hence the friction force between the part and the mold also increase. There is a trade‐off between draft angle and roughness. A model based on Glanvill's equation was developed to predict ejection force and was consistent with experimental results.     

Lipoxygenase Products in the Urine Correlate with Renal Function and Body Temperature but not with Acute Transplant Rejection

Acute transplant rejection is the leading cause of graft loss in the first months after kidney transplantation. Lipoxygenase products mediate pro- and anti-inflammatory actions and thus we aimed to correlate the histological reports of renal transplant biopsies with urinary lipoxygenase products concentrations to evaluate their role as a diagnostic marker. This study included a total of 34 kidney transplant recipients: 17 with an acute transplant rejection and 17 controls. LTE4, LTB4, 12-HETE and 15-HETE concentrations were measured by enzyme immunoassay. Urinary lipoxygenase product concentrations were not significantly changed during an acute allograft rejection. Nevertheless, LTB4 concentrations correlated significantly with the body temperature (P ≤ 0.05) 3 months after transplantation, and 12- and 15-HETE concentrations correlated significantly with renal function (P ≤ 0.05) 2 weeks after transplantation. In conclusion, our data show a correlation for LTB4 with the body temperature 3 months after transplantation and urinary 12- and 15-HETE concentrations correlate positively with elevated serum creatinine concentrations but do not predict acute allograft rejection.     

采用分布式孔径的红外敏感器系统（上）

第三代焦平面列阵与能力越来越强的信号处理算法的结合,正在使电光技术不断走向成熟,同时也给军用和非军用电光敏感器系统的设计指出了新的方向,目前,美国国防部正在利用这些进展研制一种可安装在各种战术平台上的分布式孔径红外敏感器系统（DAIRS）,这种DAIRS是利用多个相同的固定敏感器来获得其功能度的,而在以前,这种功能度是通过对每一种功能都使用专用的敏感器来获得的,在战术飞机上,DAIRS的作用是利用一个包含六个按战略要求的敏感器列阵,向飞行人员提供4π立体弧度的敏感器覆盖范围,即全球面情况察觉（SA）,这种察觉提供：导弹威胁告警,红外搜索与跟踪,战斗损害估计,目标导向辅助以及领航。DAIRS还可以为水面舰艇,装甲登陆车以及无人驾驶空战飞行器提供扩展的全球面情况察觉。敏感器的重量,体积以及电功率需求,一般不到现有机载红外敏感器系统的25％,而且系统实际运行成本可以大为降低,如果与自动提示技术相结合,DAIRS就有可能在用于空中防撞的飞机防撞告警的系统技术发展方面起重要作用。DAIRS目前得到了海军研究局的部分资助,这将可以生产两台原型敏感器和实验室测试所需的支持软件,多功能红外分布式孔径系统（MIDAS）是作为一项海军先进技术演示（6．3计划）而获得资金的,根据此项计划,DAIRS将于2000年用四个敏感器进行飞行试验,MIDAS将配备一种装在头盔上的用于情况察觉成像的显示器。     

Calibration parameters for the integrated silver method for mercury in air. II

The analytical parameters for the measurement of mercury in air have been investigated for the integrated silver method. The ultimate sensitivity of the method and the reproducibility of the standard curve are discussed. The proper storage of the activated silver absorber is described, as well as the storage of a mercury-air sample on the silver element.The collection efficiency for mercury has been found to be quantitatively reversible, with respect to both capture and release. The collection process on silver is highly specific for mercury. Benzene, for example, is not retained on silver, though it can give a spurious response when sampled directly by a “continuous” ultraviolet photometer. Most commonly encountered organic vapors, which give a response at mercury absorption wavelengths, are not retained by the silver element and do not, therefore, interfere with subsequent ultraviolet measurement of the desorbed mercury vapor.For ambient air sampling, the optimum flow-rate was found to be 1.51/min. This also proved to be a suitable flow-rate for desorption and assay. Pure air, as carrier, has been found to be satisfactory, since no differences have been noticed when comparative measurements have been made using inert gases.Instrumental measurement by means of a digital integrator has been found to be superior to a recorder output using peak height. Peak area measurement, by integrator, is not affected by the rate of diffusion of the mercury vapor within the sampling system and optical train.     

Pyryliumverbindungen. 38. Zur Ringtransformation von 2,4,6-Triaryl-thiopyryliumsalzen mit Essigsäureanhydrid zu Arylbenzenen und Thiobenzophenonen

Pyrylium Compounds. 38. About the Ring Transformation of 2,4,6-Triarylthiopyrylium Salts by Acetic Acid Anhydride to Arylbenzenes and Thiobenzophenones 2,4,6-Triarylthiopyrylium salts 5 react in the presence of an appropriate condensing agent (sodium acetate, carbonate, methoxide, tert-butoxide or potassium acetate) with acetic acid anhydride to yield arylbenzenes 3 and thiobenzophenones 6 . This ring transformation represents the first example of the conversion of the moiety into the thiocarbonyl group Under the same conditions 3,5-dimethyl-2,4,6-triphenylthiopyrylium perchlorate ( 13 ) forms via [1,5]-sigmatropic rearrangement the thiobenzophenone 15 . The structure of the new compounds 6 was proved by spectroscopic methods as well as by degradation reactions. Thus, hydrogen peroxide converts 6a to the known benzophenone 4 . Alkaline saponification gives the 2-hydroxy-benzophenone 8 , whereas heating with hydrochloric acid causes a selective cleavage of the acetoxy group to the 2-hydroxy-thiobenzophenone 7 .     

Multicell converters: basic concepts and industry applications

Multicell power converters were introduced ten years ago. This paper summarizes the main results obtained through the research done on these converters over this period: topology and derivation of multicell choppers and voltage-source inverters; harmonics cancellation; open-loop modulation techniques; self-balancing understanding; and optimization. During this same period, industrial products using this technique have been developed and the corresponding know-how has contributed to the field in various ways, such as modular design, low inductance busbars, specific drivers, etc.     

基于ZigBee无线通信的汽车倾斜度测量的应用

引言ZigBee是一种新的无线局域网传输标准,它是基于IEEE802.15.4协议基础的一个通信标准。IEEE802.15.4定义了协议的物理层和媒体介质访问控制层(MAC),而ZigBee定义了网络层、安全层和应用层,见图1。这样,     

A field-portable thermal infrared grating spectrometer (THIRSPEC)

A thermal infrared grating spectrometer was developed for field studies in the Earth sciences. The design is based on a reflection grating and a 60-element HgCdTe detector array. The useful spectral range of the instrument covers 7.9-11.3 μm with a Nyquist limited resolution of 0.16 μm. The instrument averages over a 12° field of view and compares the exitance of the target to that of an internal black body at ambient temperature. The noise equivalent temperature is approximately 0.06°K over the useful spectral range. Background radiance reflected from the surface of the target can seriously impede the determination of emissivity. This effect is removed from the spectra of geological samples by the use of reference samples