Studies of the Temperature and Frequency Dependent Impedance of an Electroceramic Functional Oxide NTC Thermistor

The charge transport mechanism and the macroscopic dielectric constant in polycrystalline device materials commonly exhibit several components such as electrode‐sample interface, grain boundary and bulk contributions. In order to gain precise understanding of the functionality of polycrystalline electroceramic device materials it is essential to deconvolute these contributions. The paradigm of functional NTC thermistor ceramics based on thick film spinel manganates has been studied by temperature dependent alternating current impedance spectroscopy. Three typical relaxation phenomena were detected, which all showed a separated temperature dependence of resistivity consistent with thermally activated charge transport. The dominating grain boundary and the interface contributions exhibited distinctively different capacitance allowing clear identification. The composite nature of the dielectric properties in polycrystalline functional ceramics was emphasized, and impedance spectroscopy was shown to be a powerful tool to account for and model such behavior.     

32APSK调制在多径信道中的星座优化

为了提升APSK调制在多径信道中的使用性能,提出基于误码率分析的新星座构造方法,该方法通过星座点的旋转,能很好的对抗多径失真对信号的影响.本文以32APSK为例进行星座优化,通过计算机仿真搜索,得到32MAPSK调制星座的最优旋转角度.仿真表明,该方法不需要增加任何硬件设备,具有简便、性能提升明显的特点.     

I-V characteristics of carbon black-loaded crystalline polyethylene

The I-V characteristics of carbon black-loaded crystalline polyethylene were investigated at room temperature and at few degrees above the melting temperature, T _m. The material was chemically cross-linked using silane. It had a large carbon black content of 28 parts per hundred by weight and displayed a strong positive temperature coefficient of resistance (PTCR) effect with a resistivity jump of four orders of magnitude. Logarithmic current-voltage plots were found to be linear with unity slopes at temperatures above and below T _m, indicating good ohmic behaviour. This is in contrast with previous theories which explain the PTCR effect on the basis of electron tunnelling as the current conduction mechanism. A new model capable of explaining both the PTCR effect and the steep reduction in resistance above T _m is presented, according to which the PTCR effect is the result of the co-operative effect of changes in crystallinity and volume expansion.     

A molecular redox switch on p21(ras). Structural basis for the nitric oxide-p21(ras) interaction

We have identified the site of molecular interaction between nitric oxide (NO) and p21(ras) responsible for initiation of signal transduction. We found that p21(ras) was singly S-nitrosylated and localized this modification to a fragment of p21(ras) containing Cys118. A mutant form of p21(ras), in which Cys118 was changed to a serine residue and termed p21(ras)C118S, was not S-nitrosylated. NO-related species stimulated guanine nucleotide exchange on wild-type p21(ras), resulting in an active form, but not on p21(ras)C118S. Furthermore, in contrast to parental Jurkat T cells, NO-related species did not stimulate mitogen-activated protein kinase activity in cells transfected with p21(ras)C118S. These data indicate that Cys118 is a critical site of redox regulation of p21(ras), and S-nitrosylation of this residue triggers guanine nucleotide exchange and downstream signaling.     

Determination of roquefortine C in blue cheese using on-line column-switching liquid chromatography

A method is described for the determination of roquefortine C in (blue) cheese. After liquid liquid extraction with a mixture of hydrochloric acid and methanol, and filtration, an aliquot is analysed using column-switching reversed-phase liquid chromatography. The recovery of roquefortine C in Fetta cheese is about 85%, the calibration curve is linear from 10 to 2500 ng g(-1) (r2 = 0.998), and the detection limit is about 10 ng g(-1). In different batches of Danish Blue concentrations of 1000-2000 ng g(-1) of roquefortine C are found. As regards the stability of roquelfortine C its half-life in diffuse daylight is ca. 50 min, while after irradiation with ultraviolet light, it is about 10 min.     

Helicobacter pylori infection decreases gastric alcohol dehydrogenase activity and first-pass metabolism of ethanol in man

Current world stockpiles of nuclear weapons and the status of treaties for nuclear disarmament and the ultimate elimination of nuclear weapons are summarised. The need for including stockpiles of civil plutonium in a programme for ending production and disposing of fissile materials is emphasized, and the ultimate difficulty of disposing of the last few nuclear weapons discussed.     

A study of the effect of optimization function on calculated parameters of wilson equation

Estimated values of Wilson parameters depend upon the objective function which is used in the optimization procedure. The relationships between these estimated parameters seem to be more important than the values themselves, and the desirable paired parameters are confined to a region near ridge lines. This region represents a high level of joint confidence. In this study four different objective functions were used in the investigation of binary and ternary systems. Also, comparisons were made on calculated V/L equilibrium values predicted for ternary systems by using parameters estimated from binary and from the sole use of ternary data. Using the parameters estimated from binary data with a chosen objective function did not produce the best sum of squares of errors in a ternary system for the same objective function. Based on the overall performance, the best objective function to fit parameters in three ternaries is the one to fit the pressure.     

Mechanical property characterization in support of elevated temperature reactor design

The mechanical properties data used for the design of nuclear reactors and reactor components for operation at elevated temperatures often show considerable variation. In types 304 and 316 stainless steels, much of the heat-to-heat variation is due to variation in chemical composition and grain size. For a heat-treatable ferritic steel such as 2 1/4 Cr-1 Mo steel, chemical composition is again important, but the heat treatment is more important. An understanding of the metallurgical processes that lead to data variation and property changes in these steels can be used to optimize reactor design.