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Optimization of the imaginary time step evolution for the Dirac equation

Science china(physics,Mechanics & Astronomy) 2011年第2期54卷 231-235页

作者： LI FangQiong1,ZHANG Ying2,LIANG HaoZhao2,3 & MENG Jie4,2,5 1Guizhou university for Nationalities,Guiyang 550025,china 2state key lab nuclear physics & technology,school of physics,peking university,beijing 100871,china 3Institut de Physique Nucle’aire,IN2P3-CNRS and Universite’ Paris-Sud,F-91406 Orsay Cedex,France 4school of physics and nuclear Energy Engineering,Beihang university,beijing 100191,china 5Department of physics,university of Stellenbosch,Stellenbosch,South Africa Guizhou university for Nationalities Guiyang China (GRID:grid.443382.a) (ISNI:***) peking university State Key Lab Nuclear Physics &amp technology School of Physics Beijing China (GRID:grid.11135.37) (ISNI:***) peking university State Key Lab Nuclear Physics &amp technology School of Physics Beijing China (GRID:grid.11135.37) (ISNI:***) IN2P3-CNRS and Université Paris-Sud Institut de Physique Nucléaire Orsay Cedex France (GRID:grid.4444.0) (ISNI:***) Beihang university School of Physics and Nuclear Energy Engineering Beijing China (GRID:grid.64939.31) (ISNI:***) peking university State Key Lab Nuclear Physics &amp technology School of Physics Beijing China (GRID:grid.11135.37) (ISNI:***) university of Stellenbosch Department of Physics Stellenbosch South Africa (GRID:grid.11956.3a) (ISNI:***)

Taking the single neutron levels of 12C in the Fermi sea as examples,the optimization of the imaginary time step(ITS) evolution with the box size and mesh size for the Dirac equation is *** the weakly bound states,in order to reproduce the exact single-particle energies and wave functions,a relatively large box size is *** long as the exact results can be reproduced,the ITS evolution with a smaller box size converges faster,while for both the weakly and deeply bound states,the ITS evolutions are less sensitive to the mesh ***,one can find a parabola relationship between the mesh size and the corresponding critical time step,i.e.,the largest time step to guarantee the convergence,which suggests that the ITS evolution with a larger mesh size allows larger critical time step,and thus can converge faster to the exact *** conclusions are very helpful for optimizing the evolution procedure in the future self-consistent calculations.

关键词： Dirac equation Schrdinger-like equation imaginary time step method convergence

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Study of the structure of unstable nuclei through the reaction experiments

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Science china(physics,Mechanics & Astronomy) 2011年第S1期54卷 1-5页

作者： CAO ZhongXin & YE YanLin state key laboratory of nuclear physics and technology, school of physics, peking university, beijing 100871, china peking university State Key Laboratory of Nuclear Physics and Technology School of Physics Beijing China (GRID:grid.11135.37) (ISNI:***)

Along with the development of the radioactive nuclear beam facility, the study of the structure of unstable nuclei has progressed rapidly over the last few decades. Due to the weakly binding property, the structure information of the unstable nuclei comes primarily from the scattering or reaction experiments. Therefore it would be very important to understand clearly the reaction mechanism involved in the experiment. We outlined here the major reaction mechanisms which are adequate to the study of unstable nuclei, with the focus on the new phenomena and methods in comparison with those with traditional stable nucleus beam. Especially emphasized are the breakup and knockout reactions, developed as accurate tools for spectroscopy investigation into the nuclear structure with low intensity secondary beam. Couplings of the breakup channel to the elastic scattering and the fusion and transfer reactions are also reviewed.

关键词： binaries: unstable nuclei nuclear structure breakup reaction knockout reaction fusion reaction transfer reaction

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X-ray flares of γ-ray bursts: Quakes of solid quark stars?

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Science china(physics,Mechanics & Astronomy) 2009年第2期52卷 315-320页

作者： XU RenXin1 & LIANG EnWei2 1 school of physics and state key laboratory of nuclear physics and technology, peking university, beijing 100871, china 2 Department of physics, Guangxi university, Nanning 530004, china school of physics and state key laboratory of nuclear physics and technology Peking University Beijing China Department of physics Guangxi University Nanning China

A star-quake model is proposed to understand X-ray flares of both long and short γ-ray bursts (GRBs) in a solid quark star regime. Two kinds of central engines for GRBs are available if pulsar-like stars are actually (solid) quark stars, i.e., the SNE-type GRBs and the SGR-type GRBs. It is found that a quark star could be solidified about 103 to 106 s later after its birth if the critical temperature of phase transi- tion is a few Metga-electron-volts, and then a new source of free energy (i.e., elastic and gravitational ones, rather than rotational or magnetic energy) could be possible to power GRB X-ray flares.

关键词： γ-rays bursts: X-rays neutron stars elementary particles

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Magnetic moments of ^(33)Mg in the time-odd relativistic mean field approach

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Science china(physics,Mechanics & Astronomy) 2009年第10期52卷 1586-1592页

作者： LI Jian1,ZHANG Ying1,YAO JiangMing1 & MENG Jie1,2 1 school of physics,state key laboratory of nuclear physics and technology,peking university,beijing 100871,china 2 school of physics and nuclear Energy Engineering,Beihang university,beijing 100191,china school of physics State Key Laboratory of Nuclear Physics and Technology Peking University Beijing China school of physics and nuclear Energy Engineering Beihang University Beijing China

The configuration-fixed deformation constrained relativistic mean field approach with time-odd component has been applied to investigate the ground state properties of 33Mg with effective interaction *** ground state of 33Mg has been found to be prolate deformed,β2=0.23,with the odd neutron in 1/2[330] orbital and the energy -251.85 MeV which is close to the data -252.06 *** magnetic moment -0.9134 μN is obtained with the effective electromagnetic current which well reproduces the data -0.7456 μN self-consistently without introducing any *** energy splittings of time reversal conjugate states,the neutron current,the energy contribution from the nuclear magnetic potential,and the effect of core polarization are discussed in detail.

关键词： magnetic moment binding energy time-odd component configuration-fixed deformation constrained calculation relativistic mean field theory

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Recent HERMES Results on DVCS from Proton and nuclear Targets

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原子核物理评论 2009年第S1期26卷 124-128页

作者： YE Hong-xue,MAO Ya-jun (school of physics and state key laboratory of nuclear physics and technology,peking university,beijing 100871,china) school of physics and state key laboratory of nuclear physics and technology Peking UniversityBeijing 100871China

Spin structure is one of the fundamental subjects in the study of nucleon structure. Recently it is found that Generalized Parton Distributions(GPDs) are related to the total angular momentum carried by partons,which offers a possible solution to the spin puzzle in the first time. We get access to certain GPDs by looking at the azimuthal angle asymmetries attributed to the interference between Deeply Virtual Compton Scattering(DVCS) and Bethe-Heilter processes in HERMES experiment. By measuring the asymmetry with respect to transverse target polarization from proton target,a model-dependent constraint on Ju vs Jd is obtained. Another worldwide unique channel is nuclear DVCS. The preliminary results on asymmetries with respect to beam spin and beam charge are reported.

关键词： GPDs DVCS TTSA nuclear DVCS

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β-decay studies of the neutron-rich ^(18,21)N isotopes

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Science china(physics,Mechanics & Astronomy) 2011年第S1期54卷 53-60页

作者： HUA Hui, LI ZhiHuan, YE YanLin, JIANG DongXing, LOU JianLing, LI XiangQing & XU FuRong school of physics and state key laboratory of nuclear physics and technology, peking university, beijing 100871, china peking university School of Physics and State Key Laboratory of Nuclear Physics and Technology Beijing China (GRID:grid.11135.37) (ISNI:***)

The β-decay studies of neutron-rich 18,21N isotopes have been performed using β-n, β-γ, and β-n-γ coincidence methods. The 18,21N ions were produced by the fragmentation of the 22Ne and 26Mg beams, respectively, on a thick beryllium target. The time of flight of the emitted neutrons following the β-decay of 18,21N was measured by a neutron detector system with wide energy detection range and low-energy detection threshold. In addition, several clover germanium detectors were used to detect the β-delayed γ-rays. The half-lives of the β-decays of 18N and 21N were determined to be (619±2) ms and (82.9±7.5) ms, respec tively. Several new β-delayed neutron groups were observed with a total branching ratio of (6.98±1.46)% and (90.5±4.2)% for 18N and 21N, respectively. The level schemes of 18O and 21O were deduced. The experimental Gamow-Teller β-decay strengths of 18N and 21N to these levels were compared with the shell model calculations.

关键词： β-delayed neutron decay 18 21N neutron detector system branching ratio Gamow-Teller strength

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Convergence for Imaginary Time Step evolution in the Fermi and Dirac seas

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Science china(physics,Mechanics & Astronomy) 2010年第2期53卷 327-330页

作者： LI FangQiong1,ZHANG Ying2 & MENG Jie2,3,4 1Guizhou university for Nationalities,Guiyang 550025,china 2state key lab Nucl. Phys. & Tech.,school of physics,peking university,beijing 100871,china 3school of physics and nuclear Energy Engineering,Beihang university,beijing 100191,china 4Department of physics,university of Stellenbosch,Stellenbosch,South Africa Guizhou university for Nationalities Guiyang China (GRID:grid.443382.a) (ISNI:***) peking university State Key Lab Nucl. Phys. &amp Tech. School of Physics Beijing China (GRID:grid.11135.37) (ISNI:***) peking university State Key Lab Nucl. Phys. &amp Tech. School of Physics Beijing China (GRID:grid.11135.37) (ISNI:***) Beihang university School of Physics and Nuclear Energy Engineering Beijing China (GRID:grid.64939.31) (ISNI:***) university of Stellenbosch Department of Physics Stellenbosch South Africa (GRID:grid.11956.3a) (ISNI:***)

The convergence for the Imaginary Time Step (ITS) evolution with time step is investigated by performing the ITS evolution for the Schrdinger-like equation and the charge-conjugate Schrdinger-like equation deduced from Dirac equation for the single proton levels of 12C in both the Fermi and Dirac seas. For the guaranteed convergence of the ITS evolution to the "exact" results,the time step should be smaller than a "critical" time step Δtc for a given single-particle level. The "critical" time step Δtc is more sensitive to the quantum numbers |κ| than to the energy of the single-particle level. For the single-particle levels with the same κ,their "critical" time steps are in the same order. For the single-particle levels with similar energy,a relatively small (large) "critical" time step for larger (smaller) |κ| is needed. These conclusions can be used in the future self-consistent calculation to optimize the evolution procedure.

关键词： Dirac equation Schrdinger-like equation Imaginary Time Step method convergence

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Near-field properties of a shell nanocylinder pair with gain materials

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Chinese physics B 2012年第11期21卷 388-392页

作者：王乔吴世法王晓钢 MOE key laboratory of Materials Modification by Beams School of Physics&Optoelectronic EngineeringDalian University of Technology state key laboratory of nuclear physics and technology School of PhysicsPeking University

We study the near-field response of a shell nanocylinder pair, with its core filled by gain materials, using a two- dimensional finite-difference time-domain method. It is shown that the gain materials in the core of the cylinder can compensate for the intrinsic absorption of the metal shell, leading to local-field enhancement in the gap of the active pair. A linear dependence is found between the field enhancement and the gain coefficient at resonance. The detailed physics is studied by calculating the electrical-field distribution of the shell pair filled with different gain materials. The influence of the gap width and the shell thickness on the interaction of two adjacent active shell cylinders is also investigated.

关键词： shell nanocylinder pair gain material local-field enhancement

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Shape phase transitions in nuclei:Effective order parameters and trajectories

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Science china(physics,Mechanics & Astronomy) 2011年第S1期54卷 88-97页

作者： ZHANG Yu1,2, HOU ZhanFeng2 & LIU YuXin2,3 1Department of physics, Liaoning Normal university, Dalian 116029, china 2Department of physics and the state key laboratory of nuclear physics and technology, peking university, beijing 100871, china 3Center of Theoretical nuclear physics, National laboratory of Heavy Ion Accelerator, Lanzhou 720000, china Liaoning Normal university Department of Physics Dalian China (GRID:grid.440818.1) peking university Department of Physics and the State Key Laboratory of Nuclear Physics and Technology Beijing China (GRID:grid.11135.37) (ISNI:***) peking university Department of Physics and the State Key Laboratory of Nuclear Physics and Technology Beijing China (GRID:grid.11135.37) (ISNI:***) peking university Department of Physics and the State Key Laboratory of Nuclear Physics and Technology Beijing China (GRID:grid.11135.37) (ISNI:***) National laboratory of Heavy Ion Accelerator Center of Theoretical Nuclear Physics Lanzhou China (GRID:grid.450259.f) (ISNI:0000 0004 1804 2516)

We analyze systematically the effective order parameters in nuclear shape phase transition both in experiments and in the interacting boson model. We find that energy ratios and B(E2) ratios can distinguish the first from the second-order phase transition in theory above a certain boson number N (about 50), but in experiments, only those quantities, such as E(L1+)/E(02+) and B(E2; (L+2)1 → L1)/B(E2; 21 → 01), etc., of which the monotonous transitional behavior in the second-order phase transition is broken in the first order phase transition independent of N, are qualified as the effective order parameters. By implementing the originally proposed effective order parameters and the new ones, we find that the isotones with neutron number Nn = 62 are a trajectory of the second order phase transition. In addition, we predict that the transitional behavior of isomer shifts of Xe, Ba isotopes and Nn = 62 isotones is approximately monotonous due to the finiteness of nuclear system.

关键词： nuclear shape phase transition interacting boson model effective order parameter finite particle number effect transition trajectory

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On Hoava-Lifshitz cosmology

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Chinese physics C 2011年第5期35卷 429-435页

作者： CHEN Bin1) Department of physics, and state key laboratory of nuclear physics and technology, peking university, beijing 100871, china Department of physics and State Key Laboratory of Nuclear Physics and Technology Peking University

We give a brief overview of the Horava-Lifshitz-gravity theory, its modifications and its implications in cosmology. In particular, we discuss the various issues on the gravitational scalar mode, including its decoupling, its role as inflaton and its stability. Our analysis shows that the scalar mode could decouple naturally at λ = 1 due to the extra gauge symmetry. On the other hand, the fact that the scalar mode becomes ghost when 1/3 〈 λ 〈 1 is a real challenge to the theory. We try to overcome this problem by modifying the action such that the RG flow lies outside the problematic region. We discuss the cosmological implications of the theory.

关键词： Horava-Lifshitz-gravity cosmology ghost

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