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Theoretical observation of hexaatomic molecules containing pentacoordinate planar carbon

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science china Chemistry 2008年第11期51卷 1030-1035页

作者： LUO Qiong State Key laboratory of Explosion science and technology, beijing Institute of technology, beijing 100081, china State Key laboratory of Explosion science and technology Beijing Institute of Technology Beijing China

The smallest molecules up to date containing a D5h pentacoordinate planar carbon (PPC) atom, CBe5 and CBe54-, are presented by means of ab initio calculations. To gain a better understanding about which electronic factors contribute to their stabilization, natural bond orbital (NBO) analysis and the nucleus independent chemical shifts (NICS) were calculated. The data reported here suggest that D5h CBe5 is σ aromaticity in nature, while in D5h CBe54- π aromaticity is dominating. The classical octet rule is well satisfied in both molecules, and is one of the fundamental reasons to understand the stability of the pentagon structures. The Be5 ring serves as σ donor in D5h CBe5, and π-acceptor in D5h CBe54-. The D5h CBe54- possessing 18 valence electrons with a closed-shell electron configuration is the most plau-sible candidate for experimental detection.

关键词： pentacoordinate planar carbon Be5 ring ab initio

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

Threshold quantum secure direct communication without entanglement

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science china(Physics,Mechanics & Astronomy) 2008年第2期51卷 176-183页

作者： YANG YuGuang1,3 & WEN QiaoYan2 1 College of Computer science and technology, beijing University of technology, beijing 100022, china 2 School of science, beijing University of Posts and Telecommunications, beijing 100876, china 3 State Key laboratory of information Security (Graduate School of Chinese Academy of sciences), beijing 100049, china College of Computer science and technology Beijing University of Technology Beijing China State Key laboratory of information Security (Graduate School of Chinese Academy of sciences) Beijing China School of science Beijing University of Posts and Telecommunications Beijing China

For the first time, a threshold quantum secure direct communication (TQSDC) scheme is presented. Similar to the classical Shamir's secret sharing scheme, the sender makes n shares, S1, …, Sn of secret key K and each receiver keeps a share secretly. If the sender wants to send a secret message M to the receivers, he en-codes the information of K and M on a single photon sequence and sends it to one of the receivers. According to the secret shares, the t receivers sequentially per-form the corresponding unitary operations on the single photon sequence and ob-tain the secret message M. The shared shares may be reusable if it can be judged that there is no eavesdropper in line. We discuss that our protocol is feasible with current technology.

关键词： quantum secure direct communication threshold secure direct communication quantum secret sharing

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

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

Analysis of a kind of quantum cryptographic schemes based on secret sharing

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science china(Physics,Mechanics & Astronomy) 2009年第9期52卷 1313-1316页

作者： ZHANG XingLan1 & JI DongYao2 1 College of Computer science and technology, beijing University of technology, beijing 100124, china 2 State Key laboratory of information Security, Graduate University of Chinese Academy of sciences, beijing 100049, china College of Computer science and technology Beijing University of Technology Beijing China State Key laboratory of information Security Graduate University of Chinese Academy of Sciences Beijing China

Recently, Yang et al. proposed a kind of quantum cryptographic schemes based on secret sharing. The main idea is drawn from the case, where any n participants who share a secret K can co-operate as K does. This process can be applied to encryption, authentication, signature and so on. Unfortunately, since there is no identity authentication of the share's holder, these schemes inherit the limitation of secret sharing in practice. If some participants do not follow the protocol, the protocol would be a failure at last. Moreover, these schemes encounter another serious attack. Any two participants can co-operate to defeat the schemes by sending different shares to the parties unknown to the distributor of the secret K, such that these parties can execute the protocol as well. The attack proves that it is not enough for quantum cryptographic schemes that only the secret key is secure.

关键词： quantum identity authentication quantum secure direct communication quantum signature secret sharing

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

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

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