检索结果-南通市图书馆

Effects of Na/K ratio on the phase structure and electrical properties of Na_xK_(1-x)NbO_3 lead-free piezoelectric ceramics

在线全文

学校读者我要写书评

暂无评论

Rare Metals 2010年第2期29卷 220-225页

作者： ZHANG Qian, ZHANG Boping, Li Haitao, and SHANG Pengpeng school of Materials science and engineering, university of science and technology Beijing, Beijing 100083, china school of Materials science and engineering University of Science and Technology Beijing

Lead-free piezoelectric NaxK1-xNbO3（x = 0.3-0.8）（NKN） ceramics were fabricated by normal sintering at 1060°C for 2 *** and electrical properties of the ceramics were investigated with a special emphasis on the influence of Na *** grain size of the produced dense ceramic was decreased by increasing Na content.A discontinuous change in the space distance was found at the composition close to Na0.7K0.3NbO3 ceramic, which indicates the presence of a transitional composition between two different orthorhombic phases, which is similar to the behavior of morphotropic phase boundary（MPB） in NaxK1-xNbO3 *** MPB-like behavior contributes to the enhanced piezoelectric coefficient d33 of 122 pC/N, planar-mode electromechanical coupling coefficient kP of 28.6%, and dielectric constant εr of 703, respectively for the Na0.7K0.3NbO3 *** temperature TC and the transitional temperature TO-T from orthorhombic to tetragonal phase are observed at around 420°C and 200°C, respectively.

关键词： lead-free piezoelectric ceramics NKN sintering morphotropic phase boundary(MPB)

A phenomenological constitutive equation for Rene 95 PM alloy and its application to isothermal forging process of turbine disk

在线全文

学校读者我要写书评

暂无评论

Journal of university of science and technology Beijing 2002年第4期9卷 282-286页

作者： Maicang Zhang, Jianxin Dong, Yanping Zeng, Xishan XieMaterials science and engineering school, university of science and technology Beijing, Beijing 100083, china Mat. Sci. and Eng. Sch. Univ. of Sci. and Technol. Beijing Beijing 100083 China

The flow behavior of Rene 95 PM alloy was studied from 1050 to 1150 deg Cwith strain rate of 1 X 10^(-3), 1 X 10^(-2), 1 X 10^(-1) and 1 s^(-1). At a given temperature andstrain rate, flow curves exhibit a peak followed by flow softening up to a steady state. Moreover,at constant strain, flow stress increases with increasing strain rate and decreasing temperature. Anequation relating hyperbolic sine of flow stress to hot working parameters, such as strain, strainrate and temperature, was established by using multiple nonlinear regression method. A very goodagreement was found between predicted and experimental flow stress in all the strain rangeinvestigated. Application of the constitutive equation in predicting forming loads and flow behaviorand temperature distribution in both upper and lower dies in an isothermal forging process ofturbine disk of large dimension (about 630 mm) by means of a finite element code was systematicallyanalyzed.

关键词： constitutive equation finite element method isothermal forging Rene 95PM alloy

Dissolving of Nb and Ti carbonitride precipitates in microalloyed steels

在线全文

学校读者我要写书评

暂无评论

Journal of university of science and technology Beijing 2003年第5期10卷 78-80页

作者： Wenjin Nie, Shanwu Yang, Shaoqiang Yuan, and Xinlai HeMaterials science and engineering school, university of science and technology Beijing, Beijing 100083, china Materials science and engineering school University of Science and Technology Beijing Beijing 100083 China

The dissolving behaviour of Nb and Ti carbonitride precipitates inmicroalloyed steels during isothermal holding at 1300℃ was investigated by Transmission electronmicroscopy (TEM) and energy dispersion x-ray spectrum (EDX). It was found that all precipitates inNb-Ti microalloyed steel are (Nb, Ti)(C, N). With holding time increasing, the atomic ratio of Nb/Tiin precipitates decrease gradually. These precipitates still existe even after holding for 48 h at1300℃ while Nb(C, N) precipitates dissolve away in Nb microalloyed steel only after 4 h at the sametemperature. These results show that formation and thermostability of precipitates are considerablyinfluenced by interaction between Nb and Ti.

关键词： dissolving (Nb, Ti)(C, N) TEM EDX

Special Orientation Relationships Observed at the Early Stages of Recrystallization in Pure AlMn Alloy

在线全文

学校读者我要写书评

暂无评论

International Journal of Minerals,Metallurgy and Materials 1998年第3期12卷 140-146页

作者： Ping Yang(Material science and engineering school, university of science and technology Beijing, Beijing 100083, china)(Institute for Metal science and Metal Physics, Aachen university of technology, D-52056, Aachen, Germany) Material science and engineering school University of Science and Technology Beijing Beijing 100083 China Institute for Metal science and Metal Physics Aachen University of Technology D-52056 Aachen Germany

Electron Back Scattering Diffraction (EBSD) technique in a SEM was used to obtain local orientationalinformation on new grains and their surrounding deformed matrices at the early stages of recrystallization in pureA1-1 .3%Mn alloy. Results show that special orientation relationships including twin-relationship often exist betweennew grains, between new grains and deformed grains or between deformed grains. The occurrence of such specialorientation relationships is attributed to the special deformation behavior in the samples with large initial grain *** formation of recrystallization twins is discussed in a different way to those of traditional ones.

关键词： Orientation relationship recrystallization AlMn, EBSD

Clustering and Synchronization in an Array of Repulsively Coupled Phase Oscillators

在线全文

学校读者我要写书评

暂无评论

Communications in Theoretical Physics 2007年第7期48卷 159-162页

作者： LI Juan WU Liang ZHU Shi-Qun school of physical science and technology,Suzhou university,Suzhou 215006,china school of physical science and technology Suzhou University

Clustering and synchronization in an array of repulsively coupled phase oscillators are numerically *** is found that oscillators are divided into several clusters according to the symmetry in the *** occurs between oscillators in each cluster,while those oscillators belonging to different clusters *** synchronization may collapse for all clusters when the dynamics of only one oscillator is *** synchronous state may return back after a short period of transient *** is determined by thestrength of the oscillator *** application in the communication of one-to-several is suggested.

关键词： phase oscillators clustering synchronization

High Performance Speech Compression System

在线全文

学校读者我要写书评

暂无评论

Journal of university of science and technology Beijing 2001年第3期8卷 229-233页

作者： Ke Liu, Zhichun Mu, Zhong Wang Information engineering school, university of science & technology Beijing, Beijing 100083, china Univ Sci & Technol Beijing Informat Engn Sch Beijing 100083 Peoples R China

Since Pulse Code Modulation emerged in 1937, digitized speech has experienced rapid development due to its outstanding voice quality, reliability, robustness and security in communication. But how to reduce channel width without loss of speech quality remains a crucial problem in speech coding theory. A new full-duplex digital speech communication system based on the Vocoder of AMBE-1000(TM) and microcontroller ATMEL 89C51 is introduced. It shows higher voice quality than current mobile phone system with only a quarter of channel width needed for the latter. The prospective areas in which the system can be applied include satellite communication, IP Phone, virtual meeting and the most important, defence industry.

关键词： digital signal processing digital speech compression digital communication full-duplex coding rate

Nonequilibrium Thermodynamic and Dissipative Structure Mechanism of Fluidized Beds

在线全文

学校读者我要写书评

暂无评论

International Journal of Minerals,Metallurgy and Materials 1999年第2期13卷 90-93页

作者： Maozhan Qi Li Wang Xuezi Ni (Mechanical engineering school, university of science and technology Beijing, Beijing 100083, china) Mechanical engineering school University of Science and Technology Beijing Beijing 100083 China

Fluidized beds are nonlinear dynamic systems that exchange mass and energy with outside. They are governed not only byfluid dynamics, but by thermodynamics, especially the second law of thermodynamics as well. According to Prigogine's dissipative structure theory, the following have been concluded: (l) a fixed bed is on thermodynamic blanch, and bubbling, turbulent and fast beds areon the dissipatve structure branches. (2) Entropy in fluidized beds is divided into tWo parts: entropy production and entropy flux. The latter increases with gas velocity and decreases with pressure of the systems. That means the entropy of a system may reduce and the systemwith higher gas velocity behaves as dissipative structure characteristics. (3) For a giVen velocity, a fluidized bed operates stably on thewhole, but it is unstable to local gas-solid phases. The unstable phases are described by fluid dynamic equations, While the minimum ofsystem energy function assures whole stability of the system. (4) A transition criterion of a bubbling bed is derived from Prigogine's stability theory.

关键词： fluidized bed nonequilibrium thermodynamics dissipative structure energy extremum

H~∞ Theory and its Application to the Position of Rolling Mill Control System

在线全文

学校读者我要写书评

暂无评论

International Journal of Minerals,Metallurgy and Materials 1999年第3期13卷 230-233页

作者： Jie Dong Chaonan Tong Kaixiang Peng(Information engineering school, university of science and technology Beijing, Beijing 100083, china) Information engineering school University of Science and Technology Beijing Beijing 100083 China

The controller designed according to classical or modern control theory will not satisfy the performance requirements when the controlled object in industrial field can not be described by exact mathematical model or the disturbance of the controlled system. In order to make the controlled system stable and having good performance, H∞ control theory was put forward to solve this practical problem. Taking the position of a rolling mill as the controlled object, it was rectified by optimal engineering way. Then, three different plans were put forward according to Bang-Bang control, LQ control and H∞ control, respectively. The result of the simulation shows that the controller designed according to H∞ method whose robust performance and ability to restrain colors disturbance is satisfactory.

关键词： position control H~∞ control LQ control Bang-Bang controll

Synthetical Control of AGC/LPC System Based on Neural Networks Internal Model Control

在线全文

学校读者我要写书评

暂无评论

Journal of university of science and technology Beijing 2001年第1期8卷 75-77页

作者： Hu He, Xiaodong Luan, Yikang Sun Information engineering school, university of science and technology Beijing, Beijing 100083, china Univ Sci & Technol Beijing Informat Engn Sch Beijing 100083 Peoples R China

One synthetical control method of AGC/LPC system based on intelligence control theory-neural networks internal model control method is presented. Genetic algorithm (GA) is applied to optimize the parameters of the neu... 详细信息

关键词： hot strip rolling AGC looper neural networks internal model control GA