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THERMALLY STIMULATED SHAPE MEMORY BEHAVIOR OF POLYMERS WITH PHYSICAL CROSSLINKS

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Chinese Journal of Polymer Science 1999年第3期17卷 203-213页

作者： Mao Xu Feng-kui Li Polymer physics laboratory, institute of Chemistry, Chinese academy of sciences, beijing 100080, china Chinese Acad Sci Inst Chem Polymer Phys Lab Beijing 100080 Peoples R China

The shape memory effect of polymers was investigated for the purpose of improving the processing conditions of their preparation and broadening the list of polymers for shape memory applications. Emphasis was put on the possibility of using polymers with physical crosslinks as shape memory materials and their structure-function relationships. Segmented block polyurethanes and polyethylene/nylon 6 graft copolymers were used as examples of polymers with physical crosslinks. It was found that these copolymers can really be used as thermally stimulated shape memory materials with large recoverable strain and high final recovery rate. The main advantage of using copolymers is their improved processing conditions as compared with polymers with chemical crosslinks. As only physical crosslinks are introduced, all conventional processing techniques for thermal plastics can be used, and the materials become easily reusable. The results indicate that the high crystallinity of these copolymers at room temperature and the formation of stable physical crosslinks are the two prerequisites for these polymers to exhibit shape memory effect. The successful use of block and graft copolymers imply the possibility of using polymers of various structure and properties as shape memory materials.

关键词： shape memory effect segmented polyurethanes polyethylene nylon graft copolymers

CHEMICAL STRUCTURE DEPENDENCE OF THE INTERNAL ENERGY CONTRIBUTION IN RUBBER ELASTICITY

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Chinese Journal of Polymer Science 2001年第5期19卷 447-449页

作者： Juan Sun Xiao-zhen Yang Polymer physics laboratory Center for Molecular sciences, institute of Chemistry Chinese academy of sciences beijing 100080 china Chinese Acad Sci Polymer Phys Lab Ctr Mol Sci Inst Chem Beijing 100080 Peoples R China

Conformational elasticity theory recently developed has been used to explore the internal energy contribution to the elastic force f(e)/f as a function of strain for poly(cis-1,4-isoprene) and poly(trans-1,4-isoprene). Calculated f(e)/f values are in good agreement with those obtained experimentally. Results show that behavior of f(e)/f is mainly contributed by chemical structure, or intramolecular interaction, supporting the experimental observations, and that the internal energy contribution is strain dependent.

关键词： conformational elasticity theory internal energy contribution poly(cis-1,4-isoprene) poly(trans-1,4-isoprene)

Single-molecule studies of DNA by molecular combing

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Progress in Natural Science:Materials International 2007年第5期17卷 493-499页

作者： Liu Yuying, Wang Pengye and Dou Shuoxing (College of Science, china Agricultural University, beijing 100083, china laboratory of Soft Matter physics, beijing National laboratory for Condensed Matter physics, institute of physics, Chinese academy of sciences, beijing 100080, china) [a]College of Science China Agricultural University Beijing China [b]laboratory of Soft Matter physics Beijing National Laboratory for Condensed Matter PhysicsInstitute of Physics Chinese Academy of Sciences Beijing China

Molecular combing is a powerful method for aligning a large array of DMA molecules onto a surface. It is a process whereby DNA molecules are stretched and aligned on a glass surface by the force via fluid flow. The ability to comb up to several hundred DNAs on a single cover slip allows for a statistically significant number of measurements to be made. These features make molecular combing an attractive tool for genomic studies, such as DNA replication, DNA transcription, DNA-protein interaction and so on. In this review article, we discuss the molecular combing principle, method and its applications.

关键词： DNA molecule molecular combing DNA-protein interaction.

An Explicit Function Expression for dc Bias and Temperature Dependence of Magnetoresistances in Magnetic Tunnel Junctions

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Journal of Materials Science & Technology 2002年第6期18卷 497-501页

作者： Xiufeng HANState Key laboratory of Magnetism, institute of physics and Center of Condensed Matter physics, Chinese academy of sciences, beijing 100080, china Chinese Acad Sci Inst Phys State Key Lab Magnetism Beijing 100080 Peoples R China Chinese Acad Sci Ctr Condensed Matter Phys Beijing 100080 Peoples R China

An explicit function expression for the bias voltage or/and temperature dependences of tunnel magnetoresistance ratio and resistances were obtained with a unique set of intrinsic parameters. Two of these intrinsic parameters are the Curie temperature TC and the density of state (DOS) for itinerant majority and minority electrons ξ(ρM/ρm), which are the eigen parameters of ferromagnetic electrodes. Others are the spin-dependent matrix-element ratio (i.e., |Td|2/|TJ|2 ) and the anisotropic-wavelength-cutoff energy ECγ of spin-wave spectrum in magnetic tunnel junction (MTJ), which are the structure parameters of an MTJ. These intrinsic parameters can be predetermined using the experimental measurement or, in principle, using the first-principle calculation method for an MTJ with the three key layers of FM/I/FM. Furthermore, a series of experimental data for an MTJ, for example, a spin-valve-type MTJ of Ta (5 nm)/Ni79Fe21(25 nm)/lr22Mn78(12.nm)/Co75Fe25(4 nm)/AI(0.8 nm)-oxide/Co75Fe25(4 nm)/Ni79Fe21(20 nm)/Ta (5 nm) in this work, can be self-consistently evaluated and explained using such concise explicit function formulations.

关键词： Magnetic tunnel junction TMR Spin-electron transport Magnon excitation Spin-polarization Magnetotransport

Pairwise entanglement and local polarization of Heisenberg model

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Science china(physics,Mechanics & Astronomy) 2008年第10期51卷 1515-1522页

作者： XI XiaoQiang1,2, ZHANG Tao3, YUE RuiHong3,4 & LIU WuMing2 1 Department of Applied Mathematics and physics, Xi’an institute of Post and Telecommunications, Xi’an 710061, china 2 beijing National laboratory for Condensed Matter physics, institute of physics, Chinese academy of sciences, beijing 100080, china 3 institute of Modern physics, Northwest University, Xi’an 710069, china 4 Department of physics, Ningbo University, Ningbo 315211, china Department of Applied Mathematics and physics Xi’an Institute of Post and Telecommunications Xi’an 710061 China beijing National laboratory for Condensed Matter physics Institute of Physics Chinese Academy of Sciences Beijing 100080 China institute of Modern physics Northwest University Xi’an 710069 China Department of physics Ningbo University Ningbo 315211 China

The characteristics of pairwise entanglement and local polarization (LP) are dis-cussed by studying the ground state (states) of the Heisenberg XX model. The re-sults show that: the ground state (states) is (are) composed of the micro states with the minimal polarization (0 for even qubit and 1/2 for odd qubit); LP and the prob-ability of the micro state have an intimate relation, i.e. the stronger the LP, the smaller the probability, and the same LP corresponds to the same probability; the pairwise entanglement of the ground state is the biggest in all eigenvectors. It is found that the pairwise entanglement is decreased by the state degeneracy and the system size. The concurrence approaches a fixed value of about 0.3412.(for odd-qubit chain) or 0.3491 (for even-qubit chain) if the qubit number is large enough.

关键词： Heisenberg XX model local polarization pairwise entanglement

The gravity wave instability induced by photochemistry in summer polar mesopause region

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Chinese Science Bulletin 2000年第3期45卷 267-272页

作者： Center for Space Science and Applied Research, Chinese academy of sciences, beijing 100080, china laboratory of Numeric Study of Heliospheric physics, Chinese academy of sciences, beijing 100080, china Center for Space Science and Applied Research Chinese Academy of Sciences Beijing China laboratory of Numeric Study of Heliospheric physics Chinese Academy of Sciences Beijing China

The effect of diabatic process due to the photochemical heating and cooling on the gravity wave propagation in middle atmosphere is studied. A linear gravity wave model which considers the diabatic process is established. The unstable region and the growth rate of the gravity wave caused by photochemistry are calculated. And the comparison between the model and the adiabatic gravity wave theory of pure dynamics is made. The results indicate that the photochemical heating process can induce the instability of gravity wave at mesopause. The intensity of the instability becomes stronger as the temperature decreases. The temperature feature and the altitude characteristics of the instability are consistent with the observation. Therefore, the instability of the gravity wave induced by photochemistry may be an important mechanism in polar mesopause region in summer.

关键词： photochemistry instability gravity wave growth rate.

Ab-initio molecular dynamics simulation on nano-system under external pressure

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Science china Mathematics 2004年第z1期47卷 92-100页

作者： Jl Min, SUN Deyan & GONG XingaoSurface physics laboratory and Department of physics, Fudan University, Shanghai 200433, china institute of Solid State physics, Chinese academy of sciences, Hefei 230031, china Interdisciplary Center for Theoretical studies, Chinese academy of sciences, beijing 100080, china Fudan Univ Surface Phys Lab Shanghai 200433 Peoples R China Fudan Univ Dept Phys Shanghai 200433 Peoples R China Chinese Acad Sci Inst Solid State Phys Hefei 230031 Peoples R China Chinese Acad Sci Interdisciplinary Ctr Theoret Studies Beijing 100080 Peoples R China

A new constant-pressure molecular dynamics (MD) method is developed to simulate the dynamic behavior and structure transition of finite system under external pressure. In this method, no artificial parameter is introduced and the computation overheads are very small. As an application, a hard-soft transition of single wall carbon nanotube (SWCNT) under external pressure is found, which is in agreement with the experiments.

关键词： phase transition, simulation, nano-particles

Compression behavior of Zr_(41)Ti_(14)Cu_(12.5)Ni_(10)Be_(22.5) bulk metallic glass up to 24 GPa

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Science china(physics,Mechanics & Astronomy) 2005年第3期48卷 319-324页

作者： LI Gong 1, 2 , ZHAN Zaiji 2 , LIU Jing 3 , YUN Jinku 1 , SUN Liling 2 , LIU Riping 1 , ZHANG Jun 2 & WANG Wenkui 1, 2 1. Key laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004, china 2. Center for Condensed Matter physics, institute of physics, Chinese academy of sciences, beijing 100080, china 3. BSRF, institute of High Energy physics, Chinese academy of sciences, {12. 100039, china 1. Key laboratory of Metastable Materials Science and Technology Yanshan University 066004 Qinhuangdao China 2. Center for Condensed Matter physics Institute of Physics Chinese Academy of Sciences 100080 Beijing China 3. BSRF Institute of High Energy Physics Chinese Academy of Sciences 100039 Beijing China

The compression of a Zr41Ti14Cu12.5Ni10Be22.5 bulk metallic glass (BMG) is investigated at room temperature up to 24 GPa using in-situ high pressure energy dispersive X-ray diffraction with a synchrotron radiation source. The pressure-induced structural relaxation is exhibited. It is found that below about 8 GPa, the existence of excess free volume contributes to the rapid structural relaxation, which gives rise to the rapid volumetric change, and the structural relaxation results in the structural stiffness under higher pressure.

关键词： bulk metallic glass, high pressure, structural relaxation, synchrotron radiation.

Atomic and field dynamics in the time-dependent Jaynes-Cummings model with arbitrary detuning

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原子与分子物理学报 2000年第3期17卷 385-389页

作者： WANG Xiao guang (laboratory of optical physics, institute of physics, Chinese academy of sciences, beijing 100080, People’s Republic of china) 中科院物理所光学物理开放实验室北京 100080

We propose a general numerical method for solving the time dependent Jaynes Cummings model with arbitrary detuning by integrating related groups of coupled equations using Runge Kutta numerical technique. The atomic and field dynamics such as evolution of atomic population inversion and second order correlation function of photons are studied in case of different detuning. The results show that the field tends to exhibit bunching effect due to the increasing of detuning.

关键词： Time dependent Jaynes Cumminge model population inversion correlation function Runge Kutta method