The critical pressure and impeding pressure of Al evaporation during induction skull melting processing of TiAl

In this article, two key pressures, the critical pressure P _crit and the impeding pressure P _impe of elemental evaporation, are defined and studied based on the calculation relationship between the evaporation loss rate N _m and the chamber pressure P during melting of titanium-aluminum alloys. When the chamber pressure is below P _crit or above P _impe, N _m tends to the maximum or the minimum value and remains almost unchanged. However, if P _crit<P<P _impe, with the increase of the chamber pressure, N _m declines sharply. A method has been put forward to calculate P _crit and P _impe of Al evaporation in a Ti-XAl (at pct) (X=25 to 50) melt. The calculation result shows that P _crit or P _impe is a second-order function of the molar percentage of Al and the melt temperature.     

Preparation and characterization of organic-inorganic poly(ethylene glycol)/WS2 nanocomposite

Layered nanocomposite PEG/WS₂, intercalating oligomeric poly(ethylene glycol) (PEG6000) into the tungsten disulfide host galleries, was synthesized using the exfoliation-adsorption technique. X-ray diffraction revealed that the intercalated oligomer within the host galleries is in a double-layer arrangement with an interlayer expansion of about 8.8 Å. The optimum conditions were explored to prepare the single-phase product with a composition of Li_0.12(PEG)_1.51WS₂. Thermal analyses suggested that the resulting material shows good thermal stability, with the decomposition of the interacted oligomeric chains within the disulfide galleries occurring at around 258 °C. Despite high conductivity of the host material, those of the PEG/WS₂ nanocomposite were found to be high in the order of 1 × 10⁻² S cm⁻¹ at ambient temperature, resulted from the host guest-host charge transfers.     

我国职业教育法规中受教育者的权利主张

人本理念,是在对当代社会发展过程中人的主体地位和作用日益突出的反思中,提出的一种发展理念,是一种对人在社会发展中的主体作用与地位的肯定.教育科学中的人本理念,关键是要以学生为本,坚持"一切为了学生、为了一切学生、为了学生一切".     

暖通空调计算机辅助广义设计模式探讨

本文在研究人类设计技能模型的基础上，建立暖通空调广义设计过程模式，提出暖通空调广义设计过程及其CAD系统的信息模型，并以此为基础建立了暖通空调广义CAD系统的框架。     

环氧基的PCB对无铅组装的兼容性

综述了环氧树脂基的PCB与无铅化组装的兼容性问题。经过大量试验表明,常规的FR-4基材和双氰胺固化的高Tg基材是不能满足无铅化组装要求的,而采用酚醛固化的中等-Tg的环氧树脂基材是可能成为无铅化组装用基材的。同时,PCB制造过程也起着重要的作用。PCB设计和再(回)流焊的加热梯度也影响着无铅化的性能。     

基于通信信道的视频传输系统的设计

提出了一种利用PCM基群信道进行视频信号传输的方法,介绍了传输系统的工作原理,对视频编码器进行了较为详细的分析,并采用数字信号处理器作控制器,实现了视频信号的实时传输。     

Fisher最优分割法在星星哨水库汛期分期划分中的应用

Fisher最优分割法是对有序样本进行最优化分段的一种数学方法。本文利用该方法对星星哨水库汛期进行相应的划分,结果表明该方法是可行的。因此,可利用该结果对分期实施不同的汛限水位,使水库的防洪和兴利效益达到最大。     

On the relationship between parity space and approaches to fault detection

Parity space approach and H₂ approach are two important fault detection approaches. This paper studies the relationship between these two approaches, which reveals frequency domain characteristics of the optimal solution of the parity space approach on the one side and provides a numerical solution of the H₂-optimal design of residual generators on the other side.     

Phase regression approach for estimating the parameters of a noisy multifrequency signal

A novel approach for estimating the parameters of a multifrequency signal from discrete samples corrupted by additive noise is presented. An established mathematical model indicates that noise influence on the discrete phase and amplitude spectra is equivalent to additive phase and amplitude noise, respectively. On this basis, a simple algorithm is proposed to estimate the frequency and phase of each sinusoid component by linear regression on the phase spectra of segmented signal blocks, while an amplitude estimator is directly derived from the spectrum of the window function. The circular nature of the phase spectrum is thoroughly explored. Also, an algorithmic scheme is presented. The derived variances of the estimators show that for a noisy signal this approach provides superior accuracy over the traditional approaches. Simulations and engineering application confirm the validity of the presented method.