中国物理B

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THEORETICAL CALCULATION ON THE PAIR POTENTIALS BETWEEN LIGHT RARE-EARTH METALLIC ATOMS

杨仕清, 张文旭, 龚捷, 张万里, 王豪才

1999 (11): 801-807. doi: 10.1088/1004-423X/8/11/001

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In order to calculate the pair potentials between light rare-earth metallic atoms with double hexagonal close-packed (dhcp) crystal structure, a M?bius inversion transform formula for the dhcp structure is proposed. The pair potentials for the light rare-earth atoms are calculated by this formula. These pair potentials are fitted to the analytic Morse-type potential expressions.

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THE TRANSITION RATE OF A DOUBLE WELL SYSTEM DRIVEN BY CROSS-CORRELATED NOISES

梅冬成, 陈洛恩, 谢光中, 曹力, 吴大进

1999 (11): 808-812. doi: 10.1088/1004-423X/8/11/002

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The transition rate of a double well system driven by cross-correlated noises has been investigated, in when the correlation times between the noises are nonzero. From numerical computation, we find followings: (1) The transition rate decreases as the ,λ(λ is the strength of the correlations between noises) increases. (2) The transition rate increases as the τ(τ is the correlation time between noises) increases. It imglies that τ and λ play opposite roles in the transition rate of the system (3). For the case of perfectly correlated noises (λ= 1), there is no the suppressed phenomenon in the double well system with cross-correlated noise sources.

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LUMINESCENCE OF Bi³⁺ and Eu²⁺ DOUBLE CENTERS DOPED IN CaS HOST

贾冬冬, 吴伯群, 朱静

1999 (11): 813-819. doi: 10.1088/1004-423X/8/11/003

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In this work, double-center.doped luminescent material CaS:Bi³⁺, Eu²⁺ was made via flux NH₄Cl by sintering in excess sulfur environment. The sample had a purplish red net luminescent color. Excitation spectra at both red, 650 nm and blue, 487 nrn were taken. The red emission from Eu²⁺ center was mainly come from the 4f⁶5d¹ absorption in the CaS host. The blue emission from the Bi³⁺ center on the other hand showed no big difference from the singly doped CaS:Bi³⁺ materials in excitation spectrum. Emission spectra were obtained at excitaton of 270nm and 300nm. Stokes shift was moved about 20-30nm, under different point excitation. Emission peaks of both Bi³⁺ and Eu²⁺ centers appeared at 463nm, 642.5nm by 270nm excitation and 487 nm, 620 nm by 300 nm excitation respectively. After-glow decay cures were also obtained and the shapes of decay curves are similar and it is due to the single hole-trap system by lattice defects.

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A NEW APPROACH TO STRUCTURES OF NICKEL CLUSTERS

罗成林, 周延怀

1999 (11): 820-825. doi: 10.1088/1004-423X/8/11/004

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A transferable tight-binding potential for nickel was used with molecular-dynamics methods and simulated-annealing techniques to study the structure properties of nickel clusters Ni_n (n≤55), The mean coordination number and structure of some clusters and their relative stability have been obtained.

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GENERATION OF ARBITRARY QUANTUM STATE VIA ATOMIC FEEDBACK

冯勋立, 张庆华, 龚尚庆, 徐至展

1999 (11): 826-830. doi: 10.1088/1004-423X/8/11/005

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We present a scheme to realize the arbitrary control of the time evolution of an atom-cavity system via atomic feedback for the generation of an arbitrary quantum state. The scheme does not need to detect the atomic state, thus the uncontrollable measurement can be avoided.

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MODELING AND SCALING OF CHIELECTRIC RELAXATION OF NONLINEAR OPTICAL POLYMERS IN FREQUENCY DOMAIN

史伟, 房昌水, 潘奇伟, 孙洵, 顾庆天, 许东

1999 (11): 831-837. doi: 10.1088/1004-423X/8/11/006

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chielectric relaxation theory was demonstrated, chielectric relaxation that selectively probes chromophore reorientation in the frequency domain was described by the Havriliak Negami(HN) function, chielectric spectra of several nonlinear optical (NLO) polymers were fitted well by the HN function. To describe the scaling of chromophore reorientation relaxation in frequency domain, two-shape parameters m and n describing the low- and high- frequency wings of the chielectric spectra need to be specified, besides the chielectric characteristic relaxation time τ and the chielectric strength Δχ⁽²⁾. From the temperature dependences of m and n of NLO polymers, the relations between the chromophore relaxation and the a relaxation of the polymer host have been revealed.

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NOVEL ANALYTIC THEORY FOR ACTIVELY MODE-LOCKED FIBER LASER

常国庆, 娄采云, 李玉华, 高以智

1999 (11): 838-844. doi: 10.1088/1004-423X/8/11/007

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The time-domain ABCD matrix formalism is based on the propagation of a Gaussian pulse which is characterized by the pulsewidth and chirp. In this paper, the time-domain ABCD matrix of th SPM (self phase modulation) is perfected so as to acquire more information. With the time-domain ABCD matrices of amplitude modulation, filtration from the optical bandpass, group velocity dispersion and SPM, the detailed characteristics of actively mode-locked fiber laser are described and the steady-state solutions are derived for two simple cases. The application of the formalism is also helpful to understand the mechanism of mode-locking in an actively mode-locked fiber laser.

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SIZE AND SHAPE DEPENDENCE OF THE LOWEST CONDUCTION BAND STATES IN GaAs QUANTUM DOTS

赵国念, 鲜于海清, 宋健, 李效白, 任尚元

1999 (11): 845-852. doi: 10.1088/1004-423X/8/11/008

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Using a recently developed new scheme, we investigated the electronic structure of the lowest conduction band states of cuboid GaAs quantum dots with different shapes and sizes in a wide range from 4 to 120a (a is the lattice constant). The critical edge length of the direct/indirect crossover in GaAs cuboid quantum dots depends on the size and shape of the quantum dots. As a deduction we also discussed the critical size of dlrect/indirect transition in GaAs quantum wires and thin films.

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A NEW METHOD TO ENHANCE THE MAGNETISM OF Fe OVERLAYER ON GaAs(100): SULFUR PASSIVATION USING CH₃CSNH₂

徐彭寿, 郭红志, 张发培, 陆尔东, 徐法强, 潘海斌, 张新夷

1999 (11): 853-859. doi: 10.1088/1004-423X/8/11/009

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Ferromagnetic resonance (FMR) has been used to investigat the magnetism of Fe overlayer on S-passivated GaAs(lO0) pretreated by CH₃CSNH₂. Comparing with the magnetism of Fe overlayer on clean GaAs(100), we find that sulfur passivation can prevent Aa diffusion into Fe overlayer and weaken the interaction of As and Fe. It results in enhancing the magnetism of Fe overlayer on GaAs(100). We also investigate the effects of the pre-annealing of S- pasaivated GaAs(100) substrate on the magnetism of Fe overlayers. The results show that the maximum effective magnetization can be obtained at annealing temperature of 400℃. According to the experimental results of synchrotron radiation photoemission, it can be explained by the change of chemical composition and surface structure of the passivation layer on GaAs(100) surface after the annealing.

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NON-EQUILIBRIUM MICROWAVE RESPONSE OF Yba₂Cu₃O_7-δ GRANULAR THIN FILMS UNDER MAGNETIC FIELDS

ABBAS A.ESSA, 徐克西, 周世平, 鲍家善

1999 (11): 860-868. doi: 10.1088/1004-423X/8/11/010

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Microwave responses of YBa₂Cu₃O_7-δ(YBCO) granular film have been studied at the microwave frequency of 30.5 GHz. In the absence of a magnetic field the dependence of a normal microwave response on the bias current is observed at a temperature close to T_c. When a magnetic field ranged from 5.0 mT to 33.0 mT is applied, the responses broaden and shift toward a lower temperature. In the superconducting state, the responses were found to be highly dependent on the magnetic field. For the current equal to 5.0mA and a magnetic field above 17.0mT the response increases and did not vanish even at a very low temperature, the fact is believed to be correlated to the anisotropic character of the structure.

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