Development and Microstructural Characterization of High-Thermal-Conductivity Aluminum Nitride Ceramics

The effect of several additives, such as CaC₂, CaO, Y₂O₃, and C, on thermal conductivity of hot-pressed AlN ceramics was investigated. The addition of CaC₂ reductant was found to be useful for achieving high thermal conductivity of 180 W/(m·K) at room temperature. The characterization of AlN ceramics with CaC₂ additive was performed by chemical analysis of Ca, C, and O and microstructural analysis using transmission electron microscopes equipped with an energy-dispersive X-ray analyzer and an electron energy loss spectrometer. The major influence on high thermal conductivity is the disappearance of a thermal barrier caused by oxygen impurities at the grain boundary.     

Photosensitive Mechanism of Dopant-Free, Ultraviolet-Sensitive Calcium Aluminate Glasses

Calcium aluminate glasses show high sensitivity to ultraviolet radiation without the doping of optically active components. A mechanism is proposed to account for their photosensitivity on the basis of the result that the cause of UV-induced coloring is the emergence of two kinds of paramagnetic centers, an aluminum-oxygen hole center (Al-OHC) and an ozonide (O^-₃). In this model, a peroxy linkage connecting tetrahedrally coordinated Al³⁺s and a physically dissolved O₂ molecule are assumed to be present in the glasses as structural defects. On exposure to UV rays, the peroxy linkage homolvtically dissociates into a pair of A1-OHC's by absorbing UV quanta and one of the two resulting A1-OHC's combines with a nearby O₂ to form an ozonide. Experimental evidences substantiating the mechanism are also reported.     

High-Temperature Creep of Polycrystalline Magnesia: II,Effects of Additives *

The creep of magnesia doped with 0.035 to 2.26 cation % of nine other oxides and three binary mixtures thereof and of three seawater products (about 96, 98, and 99.5y0 MgO) was evaluated in transverse bending at 1200° to 1500°C, with strain rates of about 10−²%/hr, and average grain sizes of 5 to 50p. The results obtained were compared with those for pure magnesia. Most additives accentuated the plastic (diffusion-controlled) nature of the creep process presumably by pinning dislocations and/or slowing grain growth. In most cases the rate-determining diffusing species seemed to be the cation, Mg, but in two cases it was suspected that oxygen boundary diffusion was controlling. Porosities above ˜10% appear to increase the temperature dependence of creep, probably by introducing boundary sliding. The agreement of the creep data with those of other diffusion-controlled processes (electrical conductivity, sintering, and grain growth) is demonstrated.     

Photosensitive Characteristics of Dopant-Free, Ultraviolet-Sensitive Calcium Aluminate Glasses

Calcium aluminate glasses show high sensitivity to ultraviolet radiation without the doping of optically active components. In this paper, photosensitive characteristics and the cause of UV-induced coloring were investigated for these glasses. Ultraviolet rays below 270 nm were effective for inducing the coloring. The most effective wavelength agreed with that of the apparent absorption edge. In the ternary system with SiO₂ or GeO₂, the sensitivity was monotonically reduced with the amount of the third component and almost vanished for the compositions containing 40 mol%. On the basis of the establishment of a close correlation between two optical absorption bands and two electron spin resonance signals induced by UV illumination, the UV-induced coloring was concluded to be due to the emergence of an aluminum-oxygen hole center (Al-OHC) and an ozonide (O₃^-).     

Light-Focusing Glass Fibers and Rods

Glass fibers and rods with radially parabolic refractive-index distributions were produced by exchanging potassium ions from a salt bath or a lower-index cladding glass for thallium ions in the glass composition. A fiber 1 m long and 0.25 mm in diameter could be bent around a curve of radius 10 cm without deforming the Gaussian mode pattern; the depolarization of a laser beam was < −20 dB. The resolution of a rod 3.14 mm long and 1.0 mm in diameter with a focal length of 1.64 mm was of the order of 450 lines/mm. Attenuation (caused primarily by absorption induced by trace impurities) was 100 to 250 dB/km at 6328 Å; since further improvement with respect to loss is expected, these fiber guides are promising materials for use in long-distance optical communications.     

A Fast Display Method of Sky Colour Using Basis Functions

Computer graphics are being used for visual environmental assessment or architectural designs. Displaying the sky as a background is indispensable in generating photorealistic images for such applications. In this paper, we propose a fast display method of the sky colour by expressing the intensity distribution of the sky using basis functions, even if the sun position and/or the camera position are altered. In the proposed method, cosine functions are used as basis functions. The sun altitude is altered at certain intervals and the distributions of the sky colour for each sun altitude are precalculated and stored efficiently using basis functions. The colour of the sky in the view direction of an arbitrary sun position can be obtained from the stored distributions and displayed quickly. © 1997 by John Wiley & Sons, Ltd.     

Synthesis of robust tracking systems with specified transfer matrices

In this paper we study linear time-invariant multivariable systems in which the compensators consist of both feedforward and feedback parts. Firstly, a necessary and sufficient condition for the system to be an internally stable robust tracking system is obtained. Secondly, the class of attainable transfer matrices from reference signal to plant output of internally stable robust tracking systems is clarified. Thirdly, a simple method is proposed for specifying two feedback properties, i.e., sensitivity and stability margin. Finally, based on these results, we propose a synthesis procedure of robust tracking systems with desirable transient responses, sensitivity and stability margin     

Curdlan Properties for Application in Fat Mimetics for Meat Products

Gelling characteristics and viscoelastic properties of aqueous suspensions of curdlan were investigated by dynamic viscoelasticity measurements. The mechanical spectrum of the suspension was similar to that of weak gels, suggesting the suspension has a well-regulated particle-alignment with yield stress. Curdlan reached the highest moisture absorption rate within the temperature range in which the most significant moisture loss of meat occurs. These results suggest that curdlan could be an effective main ingredient in fat mimetics for meat products. Nonfat sausages using the curd lan-based fat mimetics were prepared and evaluated by a creep test and indicated curdlan was effective as a fat re-placer in such systems.     

基于FastDTW的道岔故障智能诊断方法

道岔控制列车的行驶方向,是轨道交通系统的关键设备.文中采用ZD7型号道岔转辙机动作电流数据,提出基于快速动态时间规整算法(FastDTW)的道岔故障智能诊断方法.根据原始电流曲线特性将曲线分段处理,通过FastDTW计算待诊断电流曲线与模板电流曲线的扭曲路径距离,根据动态确定的最优阈值诊断故障.实验表明,该方法可适用于单动、双动型号道岔故障诊断问题,仅需200条道岔动作电流历史数据.该方法诊断准确率较高,时间较短,也适用于准确性、实时性要求较高的新型列控系统.