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Study on internal quantum efficiency of blue InGaN multiple-quantum-well with an InGaN underneath layer

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science china(Technological sciences) 2010年第2期53卷 306-308页

作者： WANG JiaXing, WANG Lai, ZHAO Wei, ZOU Xiang & LUO Yi national laboratory for information science and technology/State Key laboratory on Integrated Optoelectronics, Department of Electronic Engineering, tsinghua University, beijing 100084, china 1. national laboratory for information science and technology/State Key laboratory on Integrated Optoelectronics Department of Electronic Engineering Tsinghua University Beijing 100084 China

Blue InGaN multiple-quantum-well (MQW) samples with different InxGa1-xN (x=0.01–0.04) underneath layers (ULs) were grown by metal organic vapor phase epitaxy (MOVPE). Temperature dependent photoluminescence showed that the InGaN UL can improve the internal quantum efficiency (IQE) of MQW effectively due to strain release. And a maximum IQE of 50% was obtained when the thickness and In content of the InGaN UL were 60 nm and 0.01, respectively. Furthermore, the larger In content or thickness of the InGaN UL makes the IQE lower. Arrhenius fit to the experiment data showed that the IQE fall was mainly caused by the quantity increase of the nonradiative recombination centers, which was believed related to the accumulated stress in InGaN ULs.

关键词： InGaN underneath layer (UL) multiple-quantum-well (MQW) internal quantum efficiency (IQE) Arrhenius formula

Anomalous magnetotransport in LaMn_(1-x)Te_xO_3

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science china(Physics,Mechanics & Astronomy) 2009年第7期52卷 987-992页

作者： TAN GuoTai1,2, CHEN ZhengHao3 & ZHANG XiaoZhong4,5 1 Key laboratory of Beam technology & Materials Modification of the Ministry of Education, Institute of Low Energy Nuclear Physics, beijing Normal University, beijing 100875, china 2 beijing Radiation Center, beijing 100875, china 3 laboratory of Optical Physics, Institute of Physics, Chinese Academy of sciences, beijing 100080, china 4 Key laboratory of Advanced Materials of the Ministry of Education, Department of Materials science and Engineering, tsinghua University, beijing 100084, china 5 beijing national Center for Electron Microscopy, tsinghua University, beijing 100084, china 1. Key laboratory of Beam technology & Materials Modification of the Ministry of Education Institute of Low Energy Nuclear Physics Beijing Normal University Beijing 100875 China 2. beijing Radiation Center Beijing 100875 China 3. laboratory of Optical Physics Institute of Physics Chinese Academy of Sciences Beijing 100080 China 4. Key laboratory of Advanced Materials of the Ministry of Education Department of Materials Science and Engineering Tsinghua University Beijing 100084 China 5. beijing national Center for Electron Microscopy Tsinghua University Beijing 100084 China

The LaMn1-xTexO3+δ (x=0.1, 0.2, 0.3) were synthesized using solid-state reaction method for the first time. X-ray photoemission spectrum (XPS) shows that in the samples the Te ions have a valence of Te4+, and Mn3+ ions are partly converted into Mn2+ and Mn4+ due to the excess oxygen and Te doping. The magnetotransport associated with Mn2+, Mn3+ and Mn4+ was investigated. The experimental results show that the samples are insulator at 0 T when the amount of Mn3+ is much larger or less than the sum of Mn2+ and Mn4+; by contrast, the samples display metal to insulator transition with increasing temperature when the amount of Mn3+ is close to the sum of Mn2+ and Mn4+. These anomalous magnetotransport behaviors were analyzed in the frame of the double-exchange (DE) mechanism.

关键词： colossal magnetoresistance La-Te-Mn-O magnetotransport

A new method of fabricating strained Silicon materials

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Rare Metals 2006年第z2期25卷 41-44页

作者： YANG Zongren LIANG Renrong XU Jun Institute of Microelectronics Tsinghua University Beijing 100084 China Institute of Microelectronics Tsinghua University Beijing 100084 China Microelectronics and Nanoelectronics Division of the Tsinghua National Lab for Information Science and Technology Beijing 100084 China Institute of Microelectronics Tsinghua University Beijing 100084 China

Strain-relaxed SiGe virtual substrates are of great importance for fabricating strained Si materials. Instead of using graded buffer method to obtain fully relaxed SiGe film, in this study a new method to obtain relaxed SiGe film and strained Si film with much thinner SiGe film was proposed. Almost fully relaxed thin SiGe buffer layer was obtained by Si/SiGe/Si multi-structure oxidation and the SiO2 layer removing before SiGe regrowth. Raman spectroscopy analysis indicates that the regrown SiGe film has a strain relaxation ratio of about 93% while the Si cap layer has a strain of 0.63%. AFM shows good surface roughness. This new method is proved to be a useful approach to fabricate thin relaxed epilayers and strain Si films.

关键词： strained Si SiGe oxidation strain relaxation

Dense coding scheme using superpositions of Bell-states and its NMR implementation

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science china(Physics,Mechanics & Astronomy) 2005年第1期48卷 57-67页

作者： ZHANG Jingfu, XIE Jingyi, DENG Zhiwei & LU Zhiheng Key laboratory for Quantum information and Measurements, Department of Physics, tsinghua University, beijing 100084, china Center for Quantum information, tsinghua University, beijing 100084, china Department of Materials science and Engineering, beijing Normal University, beijing 100875, china Testing and Analytical Center, beijing Normal University, beijing 100875, china Department of Physics, beijing Normal University, beijing 100875, china 1. Key laboratory for Quantum information and Measurements Department of Physics Tsinghua University 100084 Beijing China 2. Center for Quantum information Tsinghua University 100084 Beijing China 3. Department of Materials science and Engineering Beijing Normal University 100875 Beijing China 4. Testing and Analytical Center Beijing Normal University 100875 Beijing China 5. Department of Physics Beijing Normal University 100875 Beijing China

Dense coding using superpositions of Bell-states is proposed. The generalized Grover's algorithm is used to prepare the initial entangled states, and the reverse process of the quantum algorithm is used to determine the entangled state in the decoding measurement. Compared with the previous schemes, the superpositions of two Bell-states are exploited. Our scheme is demonstrated using a nuclear magnetic resonance (NMR)quantum computer. The corresponding manipulations are obtained. Experimental results show a good agreement between theory and experiment. We also generalize the scheme to transmit eight messages by introducing an additional two-state system.

关键词： dense coding, superpositions of Bell-states, generalized Grover's algorithm, nuclear magnetic res-onance, quantum computer.

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) [a]Department of Physics Tsinghua University Key Laboratory for Quantum Information and Measurements Beijing China [b]tsinghua University Key Laboratory for Atomic and Molecular NanoSciences Beijing 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.

Multi-dimensional project management models for mega-construction companies and their applications

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science china(Technological sciences) 2011年第S1期54卷 118-124页

作者： LIN ZhengHang 1,2,QIANG MaoShan 1,2,TANG WenZhe 1,2,FAN QiXiang 3 &LIU Qiang 4 1 Institute of Project Management and Construction technology,tsinghua University,beijing 100084,china 2 State Key laboratory of Hydraulic and Engineering,tsinghua University,beijing 100084,china 3 china Three Gorges Corporation,Yichang 443002,china 4 School of Software,tsinghua University,beijing 100084,china 1. Institute of Project Management and Construction technology Tsinghua University Beijing 100084 China2. State Key Laboratory of Hydraulic and Engineering Tsinghua University Beijing 100084 China3. China Three Gorges Corporation Yichang 443002 China4. School of Software Tsinghua University Beijing 100084 China

china is undertaking an increasing number of mega-infrastructure projects along with its rapid economic *** participants in these projects,understand how to adapt the proper and efficient management strategies is *** this paper,we propose three distinct models for companies under various background and management requirements,based on sophisticated data analysis and model ***,we successfully committed these models with hydropower development projects and achieved a great progress in enhancing management efficiency.

关键词： project management models mega-construction companies applications hydropower development companies

A verifiable low-level concurrent programming model based on colored Petri nets

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science china(information sciences) 2011年第10期54卷 2013-2027页

作者： WANG ShengYuan & DONG Yuan Department of Computer science and technology,tsinghua University,beijing 100084,china 1. Department of Computer science and technology Tsinghua University Beijing 100084 China

Concurrent programs written in a machine-level language are being used in many areas,but the verification of such programs brings various new challenges to the programming language *** of existing contributions on verifying the safety properties of concurrent programs are for high-level languages,specifications,or calculi in the *** to the lack of abstraction at a low level,additional work is needed to extend these methods to machine-level *** paper describes an approach to integrate Petri nets into low-level concurrent programs to form a new programming model (abstract machine).A program in the programming model is a restricted version of colored Petri net,with transitions colored by assembly codes for machine-level threads,and places colored by shared data consisting of memory locations or *** analysis and verification approaches for usual Petri nets can be applied indirectly for such a low-level concurrent program.

关键词： low-level concurrent programs colored Petri nets abstract machine verification

Cavitation-erosion resistance of arc ion-plated (Ti, Cr) N coatings

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science china Mathematics 2001年第S1期44卷 369-374页

作者： PAN Guoshun YANG Wenyan national Tribology laboratory, tsinghua University, beijing 100084, china tsinghua Univ Natl Tribol Lab Beijing 100084 Peoples R China

The cavitation-erosion behavior of (Ti,Cr)N multi-component coatings produced by arcion-plating on grey cast iron was studied by using an ultrasonic cavitation -erosion testing appara-tus and scanning electron microscopy. The test results indicated that surface roughness of thesubstrate, surface morphology of the coating, substrate bias voltage and the thickness of the coat-ing had certain influence on the erosion rate. Arc ion-plated (Ti,Cr)N multi-component coatingsshowed better cavitation -erosion resistance than single component coatings because of highermicrohardness and good adhesion.

关键词： cavitation-erosion ion plating (Ti, Cr) N coatings grey cast iron

Degradation of 4-chlorophenol in aqueous solution by γ-radiation and ozone oxidation

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science china Chemistry 2006年第2期49卷 186-192页

作者： HU Jun1, WANG Jianlong1,2 & CHEN Rong1 1. laboratory of Environmental technology, Institute of Nuclear Energy technology, tsinghua University, beijing 100084, china 2. State Key Joint laboratory of Environmental Simulation and Pollution Control, tsinghua University, beijing 100084, china Correspondence should be addressed to Wang Jianlong 1. laboratory of Environmental technology Institute of Nuclear Energy Technology Tsinghua University Beijing 100084 China 2. State Key Joint laboratory of Environmental Simulation and Pollution Control Tsinghua University Beijing 100084 China

The degradation of 4-chlorophenol (4-CP) by using gamma rays generated by a 60Co source in the presence of O3 was investigated. The radiolysis of 4-CP and the kinetics of 4-CP min-eralization were analyzed based on the determination of total organic carbon (TOC). The influence of initial 4-CP concentration and the free radicals scavengers (such as NaHCO3 and t-butanol) on the 4-CP degradation was also studied. The results showed that when the radiation rate was 336 Gy·min?1, 4-chlorophenol at concentration of 10 mg·L?1 could be completely degraded at the radiation dose of 2 kGy. The degradation of 4-chlorophenol could be described by a first-order reaction model, the rate constant of 4-CP degradation by combined ozonation and radiation was 0.1016 min?1, which was 2.4 times higher than the sum of radiation (0.0294 min?1) and ozonation (0.0137 min?1). It re-vealed that the combination of radiation and ozonation resulted in synergistic effect, which can re-markably increase the degradation efficiency of 4-CP.

关键词： radiolysis, 4-chlorophenol, priority pollutant, degradation, O3, synergistic effect, kinetics.