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Distribution of Nb atom in the TiAl+Nb system

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Rare Metals 2001年第1期20卷 5-12页

作者： Xiaodong Ni, Xidong Hui, Guoliang Chen (Applied science School, University of science and technology beijing, beijing 100083, china State Key laboratory for Advanced Metals and Materials, University of science and technology beijing, china) Appl. Sci. Sch. Univ. of Sci. and Technol. Beijing Beijing 100083 China

Based on MEAM (the modified embedded atom method) potential and an average atom model similar to B-W (Bragg-Williams) method, the distribution of Nb atoms in TiAl+Nb compounds with various composition was calculated. The calculation results showed that Nb atoms prefer to occupy the Ti sublattice of L10 structure for all compounds in question. With increasing atomic fraction of Nb and Al, Nb atoms exhibited a trend of ordered distribution on the Ti sublattice and result in a new L10 derivative superlattice structure.

关键词： Computer simulation Intermetallics Superlattices Ternary systems

COMPUTER SIMULATION OF RAYLEIGH FADING CHANNELS IN MC-CDMA SYSTEMS

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Journal of Electronics(china) 2007年第5期24卷 577-582页

作者： Han Fangming Zhang Xianda national laboratory of Radar Signal Processing Xidian University Xi＇an 710071 China national laboratory of tsinghua information science and technology Department of AutomationTsinghua University Beijing 100084 China

For Multi-Carrier-Code Division Multiple Access （MC-CDMA） systems, it is usually assumed that the fading of the subcarriers is frequency non-selective and independent of each other. This paper shows that the two assumptions are incompatible. In fact, the MC-CDMA signals at each subcarrier undergo fading that are highly correlated. Based on this observation, this paper develops a simulation algorithm for Rayleigh fading channels via frequency-domain correlation functionl which incorporates the Doppler effect simultaneously. Numerical examples are presented to demonstrate the effectiveness of the new algorithm, with the conclusion that the independence assumption of subcarrier fading overrates the system performance.

关键词： Multi-Carrier-Code Division Multiple Access (MC-CDMA) Rayleigh fading Channelsimulation Frequency-domain correlation

Effect of carbon source on the denitrification in constructed wetlands

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Journal of Environmental sciences 2009年第8期21卷 1036-1043页

作者： LU Songliu, HU Hongying, SUN Yingxue, YANG Jia ESPC State Key Joint laboratory, Department of Environmental science and Engineering, tsinghua University, beijing 100084, china. ESPC State Key Joint laboratory Department of Environmental Science and Engineering Tsinghua University Beijing 100084 China

The ability of constructed wetlands with different plants in nitrate removal were investigated. The factors promoting the rates of denitrification including organic carbon, nitrate load, plants in wetlands, pH and water temperature in field were systematically investigated. The results showed that the additional carbon source （glucose） can remarkably improve the nitrate removal ability of the constructed wetland. It demonstrated that the nitrate removal rate can increase from 20% to more than 50% in summer and from 10% to 30% in winter, when the nitrate concentration was 30-40 rag/L, the retention time was 24 h and 25 mg/L dissolved organic carbon （DOC） was ploughed into the constructed wetland. However, the nitrite in the constructed wetland accumulated a little with the supply of the additional carbon source in summer and winter, and it increased from 0.15 to 2 mg/L in the effluent. It was also found that the abilities of plant in adjusting pH and temperature can result in an increase of denitrification in wetlands. The seasonal change may also impact the denitrification.

关键词： constructed wetland carbon source denitrification nitrate nitrite

Human knowledge acquisition from 3D interaction in virtual environments

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science china(information sciences) 2012年第7期55卷 1528-1540页

作者： CHENG Cheng,JIANG Ru & DONG XueMei beijing laboratory of Intelligent information technology,School of Computer science,beijing Institute of technology,beijing 100081,china beijing laboratory of Intelligent information technology School of Computer Science Beijing Institute of Technology Beijing China

Recently,virtual environment (VE) based design and planning,which is a kind of interaction intensive computing,has shown great *** users of such systems are specialists or technicians and their 3D interactions with the system embed a great deal of knowledge and ***,how to integrate human knowledge and skills into VE is a great challenge to researchers in the human computer interaction *** paper proposes a method for acquiring user knowledge from *** main ideas and work include,abstracting the interactive process and formalizing the interactive semantics,as well as providing a semantic model of an interactive information repository,from which user interactive processes can be retrieved and all kinds of application logics can be established.A virtual assembly planning system is introduced as an example of a practical application of this *** show that the related models can well capture user knowledge and retrieve the interaction process.

关键词： human computer interaction interactive semantics virtual environment temporal logic virtual manufacturing virtual assembly

A variational method for contour tracking via covariance matching

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science china(information sciences) 2012年第11期55卷 2635-2645页

作者： WU YuWei,MA Bo & LI Pei beijing laboratory of Intelligent information technology,School of Computer science,beijing Institute of technology,beijing 100081,china beijing laboratory of Intelligent information technology School of Computer Science Beijing Institute of Technology Beijing China

This paper presents a novel formulation for contour *** model the second-order statistics of image regions and perform covariance matching under the variational level set ***,covariance matrix is adopted as a visual object representation for partial differential equation(PDE) based contour ***-Euclidean calculus is used as a covariance distance metric instead of Euclidean distance which is unsuitable for measuring the similarities between covariance matrices,because the matrices typically lie on a non-Euclidean manifold.A novel image energy functional is formulated by minimizing the distance metric between the candidate object region and a given template,and maximizing the one between the background region and the *** corresponding gradient flow is then derived according to a variational approach,enabling partial differential equations(PDEs) based contour *** on several challenging sequences prove the validity of the proposed method.

关键词： contour tracking covariance region descriptor level set Log-Euclidean Riemannian metric

Fuzzy dynamic characteristic modeling and adaptive control of nonlinear systems and its application to hypersonic vehicles

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science china(information sciences) 2011年第3期54卷 460-468页

作者： LI HongBo , SUN ZengQi, MIN HaiBo & DENG JianQiu Department of Computer science and technology, tsinghua University, beijing 100084, china Department of Computer science and technology Tsinghua University Beijing China

In this paper, a fuzzy dynamic characteristic modeling and adaptive control method is proposed for a class of nonlinear systems. By employing fuzzy dynamic characteristic model, the controlled plant is described as a slowly time-varying fuzzy system, wherein the parameters are estimated online by using recursive Least-Squares algorithm. Under this framework, a fuzzy adaptive controller is constructed, and the stability condition of the closed-loop system is also derived. The main advantage of the proposed method lies in no requirement for the prior knowledge of system model and less parameters to tune, which allows engineers to operate it in a simple, straightforward manner. The proposed method is applied to the control of hypersonic vehicle, and simulation results are given to demonstrate the effectiveness of the obtained results.

关键词： fuzzy control dynamic characteristic model adaptive control hypersonic vehicle

Measuring-basis-encrypted six-state quantum key distribution scheme

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Progress in Natural science:Materials International 2006年第1期16卷 84-89页

作者： CHEN Pan1, DENG Fuguo1, WANG Pingxiao1 and LONG Guilu1,2 (Key laboratory for Quantum information and Measurements and Department of Physics, tsinghua University, beijing 100084, china 2. Key laboratory for Atomic and Molecular Nanosciences, tsinghua University, beijing 100084, china) Key laboratory for Quantum information and Measurements Department of Physics Tsinghua University Beijing 100084 China Key laboratory for Atomic and Molecular Nanosciences Tsinghua University Beijing 100084 China

A six-state quantum key distribution scheme with measuring-basis encryption technique, which is based on the six-state protocol and the MBE protocol, is proposed. In this modified six-state quantum key distribution protocol, Alice and Bob use a control key to synchronize the use of their measuring-basis so that they always use the same measuring-basis. This modified six-state quantum key distribution protocol retains the advantage of higher security and at the same time has a higher efficiency.

关键词： quantum key distribution measuring-basis encrypted six-state security.

Influence of Ru addition on microstructure and stress-rupture property of Ni-based single crystal superalloys

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Progress in Natural science:Materials International 2010年第1期20卷 61-69页

作者： Jing-yang CHEN~1,Qiang FENG~(1,2),La-mei CAO~3,Zu-qing SUN~1 1.State Key laboratory for Advanced Metals and Materials,University of science and technology beijing, beijing 100083,china 2.national Center for Materials Service Safety,University of science and technology beijing,beijing 100083,china 3.national Key laboratory of science and technology on Advanced High Temperature Structural Materials, beijing Institute of Aeronautical Materials,beijing 100095,china State Key laboratory for Advanced Metals and Materials University of Science and Technology Beijing Beijing 100083 China national Center for Materials Service Safety University of Science and Technology Beijing Beijing 100083 China national Key laboratory of science and technology on Advanced High Temperature Structural Materials Beijing Institute of Aeronautical Materials Beijing 100095 China

The effects of Ru on the microstructure and stress-rupture property were investigated in two experimental Ni-based single crystal superalloys with and without Ru addition(5.1%,mass fraction).The results indicate that the morphology ofγ' precipitates in the dendrite core and interdendritic region are intermediate and nearly spherical,respectively,in the Ru-free alloy after being aged at 1100℃for 8 *** Re partitioning ratio increases due to Ru addition and Ru partitioned preferentially to theγphase in both dendrite core and interdendritic region of the Ru-containing alloy,which results in more negative lattice misfit and more cuboidalγ' ***,theγ' volume fraction increases while the precipitate size and y channel width decreases due to Ru addition in both dendrite core and interdendritic *** addition improves the stress-rupture life at 1100℃/140 MPa significantly due to higherγ' volume fraction,more negative lattice misfit and a well rafting structure as well as lessγchannel width.

关键词： Ni-based superalloys ruthenium elemental partitioning ratio lattice misfit γ’ morphology stress-rupture property

An efficient quantum secret sharing protocol with orthogonal product states

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science china(Physics,Mechanics & Astronomy) 2007年第3期50卷 331-338页

作者： YANG YuGuang1,2, WEN QiaoYan3 & ZHU FuChen4 1 School of Computer, beijing University of technology, beijing 100022, china 2 State Key laboratory of information Security, Graduate University of Chinese Academy of sciences, beijing 100022, china 3 School of science, beijing University of Posts and Telecommunications, beijing 100876, china 4 national Key laboratory for Modern Communications, Chengdu 610041, china School of Computer Beijing University of Technology Beijing China State Key laboratory of information Security Graduate University of Chinese Academy of Sciences Beijing China School of science Beijing University of Posts and Telecommunications Beijing China national Key laboratory for Modern Communications Chengdu China

An efficient quantum secret sharing protocol with orthogonal product states in the 33 Hilbert space is presented. The particles in the orthogonal product states form two particle sequences. One sequence is sent to Bob and the other is sent to Charlie after rearranging the particle orders. With the help of Alice, Bob and Charlie make the corresponding local measurement to obtain the information of the or- thogonal product states prepared. This protocol has many distinct features such as great capacity and high efficiency.

关键词： quantum secret sharing orthogonal product state orthogonal measurement