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Simulation of polarization effects in AlGaN/GaN heterojunction

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Science China(Physics,Mechanics & Astronomy) 2004年第6期47卷 694-701页

作者： LI Na ZHAO Degang YANG Hui State Key Laboratory on Integrated Optoelectronics Institute of Semiconductors Chinese Academy of Sciences Beijing 100083 China State Key Laboratory on Integrated Optoelectronics Institute of Semiconductors Chinese Academy of Sciences Beijing 100083 China State Key Laboratory on Integrated Optoelectronics Institute of Semiconductors Chinese Academy of Sciences Beijing 100083 China

A method for introducing polarization effects in the simulation of GaN-based heterojunction devices is proposed. A δ doping layer is inserted at the interface of heterojunction and the ionized donors or acceptors act as polarization induced fixed charges. Thus polarization effects can be taken into account in a traditional device simulator. Ga-face and N-face single AlGaN/GaN heterostructures are simulated, and the simulation results show that carrier confinement takes place only in the former structure while not in the latter one. The sheet density of free electrons at the interface of Ga-face AlGaN/GaN increases with the Al composition and the thickness of AlGaN. The consistence of simulation results with the experiments and calculations reported elsewhere shows that this method can effectively introduce polarization effects in the simulation of GaN-based heterojunction devices.

关键词： AlGaN/GaN, heterojunction, polarization, simulation.

An Informational Approach to the Sinusoidal Law of Photon polarization

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Communications in Theoretical Physics 2002年第3期38卷 281-284页

作者： LUO Shun-Long Institute of Applied Mathematics Acadcmy of Mathematics and System Sciences the Chinese Academy of SciencesBeijing 100080 China

The photon polarization law po ＝ sin2θ is derived from a simple informational consideration by twomethods: The first is via an intuitive principle of mininum Fisher information, the second is via a symmetry andinvariance argument. The results demonstrate that in photon polarization, Nature has a tendency to hide herselfas deepas possible while obeying some regular conditions.

关键词： photon polarization, Fisher information, Cramér-Rao bound, two-person game, binomial distri-bution

Concentration polarization of atherogenic lipids in the arterial system

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Science China(Life Sciences) 2003年第2期46卷 153-164页

作者：邓小燕王贵学 Key Lab for Biomechanics & Tissue Engineering of Ministry of Education Chongqing University Chongqing 400044 ChinaState Key Laboratory of Structural Analysis for Industrial Equipment Dalian University of Technology Dalian 116023 China Key Lab for Biomechanics & Tissue Engineering of Ministry of Education Chongqing University Chongqing 400044 China

The transport of atherogenic lipids (LDL) in a straight segment of an artery with a semi-permeable wall was simulated numerically. The numerical analysis predicted that a mass transport phenomenon called 慶oncentration polarization?of LDL might occur in the arterial system. Under normal physiological flow conditions, the luminal surface LDL concentration was 5%—14% greater than the bulk concentration in a straight segment of an artery. The luminal surface LDL concentration at the arterial wall was flow-dependent, varying linearly with the filtration rate across the arterial wall and inversely with wall shear rate. At low wall shear rate, the luminal surface LDL concentration was very sensitive to changes in flow conditions, decreasing sharply as wall shear rate increased. In order to verify the numerical analysis, the luminal surface concentration of bo-vine serum albumin (as a tracer macromolecule) in the canine carotid artery was measured in vitro by directly taking liquid samples from the luminal surface of the artery. The experimental result was in very good agreement with the numerical analysis. The authors believe that the mass transport phenomenon of 慶oncentration polarization?may indeed exist in the human circulation and play an important role in the localization of atherosclerosis.

关键词： mass transport, concentration polarization, wall shear rate, atherosclerosis.

Reflection and transmission coefficients of multiple chiral layers

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Science China(Technological Sciences) 2006年第4期49卷 457-467页

作者： SABAH Cumali UCKUN Savas Electrical and Electronics Engineering Department Engineering Faculty University of Gaziantep Gaziantep 27310 Turkey

This paper presents a general analysis of reflection and transmission coeffi- cients of multiple chiral layers in detail. Reflection and transmission coefficients through multiple chiral layers are computed and presented particularly for the incident wave of parallel polarization for a number of cases―a wide range of incidence angle, neigh- boring center frequency and different chirality parameters. Transfer matrix method is used in the analysis. From the numerical results, it can be seen that multiple chiral layers may be used as a polarization-conversion transmission filter and antireflection filter at the fre- quency band around the central frequency.

关键词： multiple chiral, reflection, transmission, polarization, filters.

Electronic structure and magnetic properties of metastable SmCo_(7) compound

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Science China(Physics,Mechanics & Astronomy) 2005年第3期48卷 325-335页

作者： ZHANG Changwen 1 , LI Hua 1 , DONG Jianmin 1 , WANG Yongjuan 1 , PAN Fengchun 1 , ZHANG Jian 1 , GUO Yongquan 2 & LI Wei 2 1. School of Physics and Microelectronics, Shandong University, Jinan 250100, China 2. Institute of Functional Materials, Central Iron and Steel Research Institute, Beijing 100081, China School of Physics and Microelectronics Shandong University Jinan China Institute of Functional Materials Central Iron and Steel Research Institutes Beijing China

The electronic density of states, spin-splittings and atomic magnetic moments of SmCo 7 compound have been studied using spin-polarized MS-Xα method. The results show that a few of electrons are transferred to Sm(5d 0 ) orbital because of orbital hybridization between Sm and Co atoms in the compound. The exchange interactions between 3d and 5d electrons lead to the magnetic coupling between Sm and Co, and therefore, result in the long-range ferromagnetic order inside the SmCo 7 compound. There are negative exchange couplings occurring at some levels, which weakens the strength of average coupling around Co lattice. So, the Curie temperature and Co-moment of SmCo 7 decrease distinctly compared with pure Co. Compared with SmCo 5 compound, the disordered substitution of Co-Co “dumbbell-atom” pairs for Sm changes the local environment of Co lattice, which makes the 2e site bear negative magnetic moment. The strength of hybridization near Fermi level weakens and the free energy of the compound increases obviously. Thus, SmCo 7 is a metastable compound at room temperature. Considering the localization of 4f electrons and a few of 5d electrons arising from the orbital hybridization, the magnetic moment of Sm atom will be 1.61μ B in SmCo 7 compound, which is in agreement with the experimental values of Sm 3+ ion- moment and Sm atom-moment in metals.

关键词： electronic structure, spin polarization, atomic magnetic moment, exchange coupling, Curie temperature.

Spectral Representation Theory for Dielectric Behavior of Nonspherical Cell Suspensions

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Communications in Theoretical Physics 2002年第7期38卷 113-120页

作者： HUANG Ji-Ping YU Kin-Wah LEI Jun SUN Hong Department of Physics the Chinese University of Hong Kong Shatin NT Hong Kong China Department of Physics the Chinese University of Hong Kong Shatin NT Hong Kong China Department of Applied Physics Shanghai Jiao Tong University Shanghai 200030 China Department of Applied Physics Shanghai Jiao Tong University Shanghai 200030 China Department of Physics University of California Berkeley California 94720-7300 U.S.A.

Recent experiments revealed that the dielectric dispersion spectrum of fission yeast cells in a suspension was mainly composed of two sub-dispersions. The low-frequency sub-dispersion depended on the cell length, while the high-frequency one was independent of it. The cell shape effect was simulated by an ellipsoidal cell model but the comparison between theory and experiment was far from being satisfactory. Prompted by the discrepancy, we proposed the use of spectral representation to analyze more realistic cell models. We adopted a shell-spheroidal model to analyze the effects of the cell membrane. It is found that the dielectric property of the cell membrane has only a minor effect on the dispersion magnitude ratio and the characteristic frequency ratio. We further included the effect of rotation of dipole induced by an external electric field, and solved the dipole-rotation spheroidal model in the spectral *** agreement between theory and experiment has been obtained.

关键词： dielectric relaxation, interfacial polarization, cell model

Electronic structure and magnetic properties of SmCo7-xTix

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Science China(Physics,Mechanics & Astronomy) 2006年第1期49卷 38-45页

作者： ZHANG Changwen1, LI Hua1, DONG Jianmin1, GUO Yongquan2 & LI Wei2 1. School of Physics and Microelectronics, Shandong University, Jinan 250100, China 2. Institute of Functional Materials, Central Iron and Steel Research Institute, Beijing 100081, China School of Physics and Microelectronics Shandong University Jinan China Institute of Functional Materials Central Iron and Steel Research Institute Beijing China

Electronic structure of SmCo7-xTix alloy has been studied by means of the spin-polarized MS-Xα method. It is shown that a few of electrons are transferred to Sm(5d) orbital due to orbital hybridization between Sm and Co atoms. The exchange interaction between 5d-3d electrons is stronger, which is the main reason resulting in the long-range ferromagnetic order between Co and Sm atoms. The Curie temperature of SmCo7-xTix is generally lower than that of pure Co metal, which may be explained by the weaker aver- age of coupling strength between Co sites due to some negative exchange couplings occurring mainly at 2e site. The calculated results for the Sm5Co28Ti6 cluster may lead to a better understanding of why SmCo7-xTix is stable phase. Since the negative interaction of 2e sites weakens and the bonding at EF strengthens with increasing Ti concentration, which result in the decrease in the free energy of the alloy, the stable ferromagnetic order forms inside SmCo7-xTix. Considering the localization of 4f states and 5d moment arising from the orbital hybridization, the calculated moment is 9.47μB per formula unit that is in agreement with experiments.

关键词： electronic structure, spin polarization, atomic magnetic moment, exchange coupling, Curie temperature.

Confirming Ground Geophysical Survey for Mineralization in Al Bayda Area,Yemen

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Global Geology 2003年第2期8卷 191-202页

作者： Faisal S. Al-Huzaim Geo-exploration College of Science and Technology Jilin University Changchun 130026 China

The Jabal Mabal-prospect of Al Bayda area is covered by meta-volcano sedimentary rocks. The importance of the study area comes from previous studies, which proved that the area has mineralization zones at the periphery of Jabal Al-Mabal. These mineralized zones lie along northwest-southeast shear zones, which occur inside the meta-volcanic rocks. The previous studies concluded that the mineralization was mostly associated with sulphides, especially at the reduction zones. These sulphides give a good response to electrical or electromagnetic techniques. The present study uses electrically induced polarization and Genie electromagnetic surveys to explore the extension of the mineralization zones at the *** self-potential (SP) technique shows numerous of mineralized zones. Most of these zones are distributed in the southern area along the contact between the quartz and gabbro. The induced polarization (IP) method has been applied on the selected profiles to delineate the subsurface contact between calcite, gabbro and quartz in Al-Jarra Valley and to calculate the shape and depth of the mineralization zones in the subsurface along these profiles. The Genie electromagnetic survey, which has been applied on selected profiles, delineated some weak mineralization occurrences corresponding to the shear zones. The integration of the results obtained using these three techniques, in addition to the different ground geophysical methods previously used, makes it possible to determine the most appropriate zones for development of exploration at the area of investigation.

关键词： geophysical methods, induced polarization, self-potential, EM Genie, Yemen