A first-principles investigation on mechanical and metallic properties of titanium carbides under pressure

The titanium carbides are potential candidates to achieve both high hardness and refractory property. We carried out a structural search for titanium carbides at three pressures of 0 GPa, 30 GPa and 50 GPa. A phase diagram of the Ti-C system at 0 K was obtained by elucidating formation enthalpies as a function of compositions, and their mechanical and metallic properties of titanium carbides were investigated systematically. We also discussed the relation of titanium concentration to the both mechanical and metallic properties of titanium carbides. It has been found that the average valence electron density and tractility improved at higher concentrations of titanium, while the degree of covalent bonding directionality decreased. To this effect, the hardness of titanium carbide decreases as the content of titanium increases. Our results indicated that the titanium content significantly affected the metallic properties of the Ti-C system.     

PTT直接酯化反应动力学研究

研究了不同温度下PTT(聚对苯二甲酸丙二醇酯)直接酯化反应动力学。建立了零级和一级反应动力学模型。用实验数据进行的检验表明,一级动力学模型更为接近该反应过程。     

一种适用于有限长度混合相位未知脉冲的最小平方反褶积新方法

普通的最小平方反褶积只有在子波为最小相位脉冲和反射序列为白噪声的假设下才是成立的,而对于混合相位未知脉冲来说,这种最小平方反褶积就不再适用了。本文提出一种适合于有限长度混合相位未知脉冲的最小平方反褶积方法。运用此法只需预先估计一个混合相位子波的长度。合成数据的试验结果表明,该方法有较好的效果,且对预先估计出的子波长度不敏感。文中还证明混合相位未知脉冲最小平方反褶积等效于一种有间隙的平滑误差滤波器的作用,而这种有间隙的平滑误差滤波又可分解为一个前向多步预测误差滤波与一个后向多步预测误差滤波之和。可以预计这种新的反滤积方法将在地震数据处理中得到有效的应用。     

Ti-45Al-10Nb合金的高温氧化行为

研究了Ti—45A1—10Nb(原子分数，％)合金在800-960℃在氧气和空气中的氧化行为．结果表明，该合金具有较好的高温抗氧化性能，其氧化增重速率与铁基耐热不锈钢相似或略优．与Ti—50A1合金相反，Ti-45A1-10Nb合金在空气中的氧化增重速率明显低于在纯氧中的氧化增重速率．X射线衍射与能谱分析表明，Ti-45Al一10Nb合金在氧气中的氧化产物主要有TiO2和Al2O3，但在空气中的氧化产物中有TiN相．这是降低氧化速率的主要原因，同时，合金元素Nb稳定了氧化层中的TiN相，因而提高了合金在空气中的抗氧化性能．     

MMSE-optimal approximation of continuous-phase modulated signal as superposition of linearly modulated pulses

The optimal linear modulation approximation of any M-ary continuous-phase modulated (CPM) signal under the minimum mean-square error (MMSE) criterion is presented in this paper. With the introduction of the MMSE signal component, an M-ary CPM signal is exactly represented as the superposition of a finite number of MMSE incremental pulses, resulting in the novel switched linear modulation CPM signal models. Then, the MMSE incremental pulse is further decomposed into a finite number of MMSE pulse-amplitude modulated (PAM) pulses, so that an M-ary CPM signal is alternatively expressed as the superposition of a finite number of MMSE PAM components, similar to the Laurent representation. Advantageously, these MMSE PAM components are mutually independent for any modulation index. The optimal CPM signal approximation using lower order MMSE incremental pulses, or alternatively, using a small number of MMSE PAM pulses, is also made possible, since the approximation error is minimized in the MMSE sense. Finally, examples of the MMSE-optimal CPM signal approximation and its comparison with the Laurent approximation approach are given using raised-cosine frequency-pulse CPM schemes.     

Study of Desorption Agent for LADS Process

This article refers to the procedure for selection, evaluation and development of the LADS-D desorption agent associated with the LADS-A adsorbent used in the non-hydroprocessing adsorptive desulfurization (LADS) process for FCC naphtha developed by LPEC Refining Research Institute. The LADS-D desorption agent can effectively remove the sulfides adsorbed on the LADS-A adsorbent. The saturated LADS-A adsorbent can be instantly regenerated by the LADS-D desorption agent to recover its adsorption activity. The LADS-D desorption agent can not only effectively remove all impurities adsorbed on the adsorbent, but also has strong ability to dissolve the impurities to keep a stable desorption efficiency of adsorbent to be basically commensurate with fresh adsorbent after extended use.     

多陀螺自动化测试系统研究

针对动力调谐挠性陀螺大批量生产中存在的性能调试和参数标定工作量大的问题，我们专门研制了一套多陀螺自动化测试系统，该系统主要包括多陀螺真空恒温安装基准体、测控台、计算机程控自动化数据采集和仪器等部分，本文着重介绍该系统的组成原理，设计特点和研制成果。     

白河、潮河底栖动物分布与特征研究

在对潮河和白河北京境内段底栖动物调查基础上,采用群落分析法并运用BI指数和Shannon-Wiener多样性指数进行水质评价.结果表明:本次共采集底栖动物44种,水生昆虫及幼虫占比最大.底栖动物种类丰富度白河优于潮河.河流评价结果显示,潮河和白河水质整体为优.BI指数法评价中,潮河和白河以清洁为主.Shannon-Wiener多样性指数评价结果中,白河以轻污染为主,潮河以中污染为主.BI指数法适用性较好,而且评价结果较为准确,评价结果对潮河、白河水质判别具有借鉴作用.     

单片机教学改革初探

本文针对目前单片机课程的教学现状,提出了一些关于单片机教学改革的措施和方法。     

A Polynomial Algorithm for Computing Elementary Siphons in a Class of Petri Nets

A set of elementary siphons plays a key role in the development of deadlock prevention policies for automated manufacturing systems. This paper addresses the computation problem for elementary siphons in a subclass of Petri nets which are basic systems of simple sequential processes with resources (BS³PR) and can model many automated manufacturing systems. An algorithm for enumerating elementary siphons is established by the one‐to‐one relationship between maximal perfect resource‐transition circuits (MPCs) and strict minimal siphons. A set of MPCs is first computed, followed by a set of elementary siphons in a BS³PR. The presented algorithm is proved to have polynomial‐time complexity. An example is used to illustrate the algorithm.