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Behavior of the Lyapunov Exponent and Phase Transition in Nuclei
WANG Nan, WU Xi-Zhen, LI Zhu-Xia, , WANG Ning, ZHUO Yi- Zhong, , SUN Xiu-Quan
Chin. Phys. Lett. 2000, 17 (10):
711-713
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Based on the quantum molecular dynamics model, we investigate the dynamical behaviors of the excited nuclear system to simulate the latter stage of heavy ion reactions, which associate with a liquid-gas phase transition. We try to search a microscopic way to describe the phase transition in real nuclei. The Lyapunov exponent is employed and examined for our purpose. We find out that the Lyapunov exponent is one of good microscopic quantities to describe the phase transition in hot nuclei. Coulomb potential and the finite size effect may give a strong influence on the critical temperature. However, the collision term plays a minor role in the process of the liquid-gas phase transition in finite systems.
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Deformed Relativistic Hartree Theory in Coordinate Space and in Harmonic Oscillator Basis
ZHOU Shan-Gui, , MENG Jie, , Shuhei YAMAJI, YANG Si-Chun,
Chin. Phys. Lett. 2000, 17 (10):
717-719
.
The deformed relativistic Hartree theory (DRH) is solved both in coordinate space (DRH-c) and in harmonic oscillator basis (DRH-o). Results obtained from these two methods are compared in details. The DRH-c and DRH-o calculations give similar total binding energies, deformation, level structures and radii for nitrogen iso-topes, while their descriptions on the density distributions for drip-line nuclei are very different. The large spatial distributions of nucleon densities, which is crucial to understand a weakly bound system, can only be obtained by DRH-c calculations. This implies that the DRH theory should be solved in coordinate space in order to describe nuclei close to the drip line.
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A Schrödinger Formulation for Paraxial Light Beam Propagation and Its Application to Propagation through Nonlinear Parabolic-Index Media
LIU Cheng-Yi, GUO Hong, HU Wei, DENG Xi-Ming
Chin. Phys. Lett. 2000, 17 (10):
734-736
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The Helmholtz equation is reduced to the Schrödinger-like equation and then the quantities representing the gross features for a paraxial optical beam, such as the width, divergence, radius of curvature of the wave front, complex beam parameter, beam quality factor, and the potential function representing beam propagation stability, are studied by using the quantum mechanical methods. The results derived in other ways previously are rederived by our formulation in a more systematical and explicit fashion analytically, and some new results are demonstrated. The general equations for the evolution of these quantities, i.e., the first- and second-order differential equations with respect to the propagation distance, such as the universal formula for the width and curvature radius, the general formula for the first derivative of the complex beam parameter with respect to the axial coordinate, the general formula for the second derivative of the width with respect to the axial coordinate, and some general criteria for the conservation of the beam quality factor and the existence of a potential well of the potential function, are derived. We also discuss the application of our formulation to nonlinear parabolic-index media.
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Magnetocrystalline Anisotropy and Exchange Interaction in YCo12-xTix Compounds
WANG Jian-Li, TANG Ning, YANG Dong, YANG Chang-Ping, BAO Fu-Quan, SHEN Yu-Ping, WU Guang-Heng, YANG Fu-Ming, E. Brück, F.R. de Boer
Chin. Phys. Lett. 2000, 17 (10):
765-767
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Magnetic and structural properties of YCo12-xTixcompounds have been investigated by x-ray diffraction and magnetic measurements. X-ray diffraction patterns of aligned powder samples indicate that the easy magnetization direction at room temperature is along the c-axis for all the compounds. The lattice parameters increase monotonously while Curie temperature TC decreases with increasing Ti content. It was found that all the compounds investigated are strong ferromagnets by analysis of magnetic moments using a magnetic valence model. The values of anisotropy fields Ba at room temperature and 1.5K decrease with increasing x. The easy-axis anisotropy of the YCo12-xTixcompounds is mainly contributed by the Co atoms at 8i sites according to the individual-site-anisotropy model.
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Carrier-Transporting and Blue Electroluminescence Properties of a Novel Pyrazoline Derivative
LU Zhi-Yun, YUAN Tong-Suo, ZHU Wei-Guo, LIU Yu, WEI Xiao-Qiang, XIE Ming-Gui, QIU Yong, GAO Yu-Di
Chin. Phys. Lett. 2000, 17 (10):
773-774
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A novel compound of pyrazoline derivative, 3-(4-methoxyphenyl)-5-[4-(1,1-dimethylethylpheny1)]-4,5-dihydro-1-Phenyl 1H-Pyrazole (PYZ) has been synthesized. It has a good photoluminescence property and could give blue A uorescence. Four devices have been fabricated to study the carrier-transporting and electroluminescence properties of PYZ. The results indicate that PYZ is a good blue electroluminescent material. The emission peak is observed at 449nm and the half bandwidth is about 80nm, showing that it could emit pure blue light. As to carrier-transporting property, PYZ is found to have electron-transporting ability besides its excellent hole-transporting ability.
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28 articles
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