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Numerical study of point spread function of a fast neutron radiography system based on scintillating-fiber array

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Science China(Physics,Mechanics & Astronomy) 2007年第6期50卷 698-706页

作者： ZHANG FaQiang1,LI ZhengHong1,YANG JianLun1,YE Fan1,2,WANG Zhen1,2,XIA GuangXin1,YING ChunTong2 & LIU GuangJun2 1 Institute of Nuclear Physics and Chemistry,Mianyang 621900,China 2 Department of Engineering Physics,Tsinghua University,Beijing 100084,China Institute of Nuclear Physics and Chemistry Mianyang China Department of Engineering Physics Tsinghua University Beijing China

For a scintillating-fiber array fast-neutron radiography system,a point-spread-function computing model was introduced,and the simulation code was developed. The results of calculation show that fast-neutron radiographs vary with the size of fast neutron sources,the size of fiber cross-section and the imaging geometry. The results suggest that the following qualifications are helpful for a good point spread function: The cross-section of scintillating fibers not greater than 200 μm×200 μm,the size of neutron source as small as a few millimeters,the distance between the source and the scintillating fiber array greater than 1 m,and inspected samples placed as close as possible to the array. The results give suggestions not only to experiment considerations but also to the estimation of spatial resolution for a specific system.

关键词： fast neutron radiography, scintillating-fiber array, point spread function, Monte Carlo simulation For a scintillating-fiber array fast-neutron radiography system, a point-spread- function computing model was introduced, and the simulation code was developed. The results of calculation show that fast-neutron radiographs vary with the size of fast neutron sources, the size of fiber cross-section and the imaging geometry. The results suggest that the following qualifications are helpful for a good point spread function: The cross-section of scintillating fibers not greater than 200μm×200μm, the size of neutron source as small as a few millimeters, the distance between the source and the scintillating fiber array greater than 1 m, and inspected samples placed as close as possible to the array. The results give suggestions not only to experiment considerations but also to the estimation of spatial resolution for a specific system.……

The impulse influence function for de-centralized control

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Science China Mathematics 2004年第Z1期47卷 200-221页

作者： ZHONG WanxieState Key Laboratory of Structure Analysis for Industrial Equipment, Dalian University of Technology, Dalian 116023, China Key Laboratory of Complex Systems & Intelligence Science, Chinese Academy of Sciences, Beijing 100080, China (email: wxzhong@***) State Key Laboratory of Structure Analysis for Industrial Equipment Dalian University of Technology Dalian China Key Laboratory of Complex Systems & Intelligence Science Chinese Academy of Sciences Beijing China

Impulse influence matrix function is introduced based on that the de-centralized control analysis is analogous to the sub-structural analysis in structural mechanics. The static sub-structural analysis is analogous to the usual de-centralized control, whereas the dynamic sub-structural analysis corresponds to the de-centralized control theory. The reciprocal symmetry for the impulse influence matrix function is proved, and is solved by the precise integration method for time invariant system, giving the results up to computer precision. Based on the impulse influence functions of subsystems, the combination of subsystems can lead to a set of integral equations and be solved numerically. Numerical example demonstrates the effectiveness of the method.

关键词： de-centralized control, subsystem, impulse influence function, precise integration.

A transient energy function for power systems including the induction motor model

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Science China(Technological Sciences) 2007年第5期50卷 575-584页

作者： MIN Yong CHEN Lei State Key Lab of Power Systems Department of Electrical Engineering Tsinghua University Beijing 100084 China State Key Lab of Power Systems Department of Electrical Engineering Tsinghua University Beijing 100084 China

A construction method for power system transient energy function is studied in the paper, which is simple and universal, and can unify the forms of some current en- ergy functions. A transient energy function including the induction motor model is derived using the method. The unintegrable term is dealt with to get an approxi- mate energy function. Simulations in a 3-bus system and in the WSCC 4-generator system verify the validity of the proposed energy function. The function can be applied to direct transient stability analysis of multi-machine large power systems and provides a tool for analysis of the interaction between the generator angle stability and the load voltage stability.

关键词： power system stability, transient stability, energy function, direct method, induction motor

Standard tri-point transition function

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Science China Mathematics 2005年第7期48卷 904-914页

作者： XIE Yuquan School of Mathematics and Computational Science Xiangtan University Xiangtan 411105 China

It is usually difficult to express a family of tri-point transition function (TTF)by a transition matrix as Markov processes with one parameter. In this paper, we define three kinds of connection matrixes on the states of standard tri-point transition function (STTF) and study their essential character, give a constructive method on the constantvalue standard tri-point transition function and a general expression of the state-symmetric standard tri-point transition function by a sequence of the transition matrixes of special and simple Markov processes with one parameter.

关键词： tri-point transition function, standard, constant-value, state-symmetry, connection matrix, Markov processes.

Wigner function:from Ensemble Average of Density Operator to Its One Matrix Element in Entangled Pure States

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Communications in Theoretical Physics 2002年第5期38卷 533-536页

作者： FAN Hong-Yi Department of Physics Shanghai Jiao Tong UniversityShanghai 200030China Department of Material Science and Engineering University of Science and Technology of China Hefei 230026 China

We show that the Wigner function W = Tr(△ρ) (an ensemble average of the density operator ρ, △ is theWigner operator) can be expressed as a matrix element of ρ in the entangled pure states. In doing so, converting fromquantum master equations to time-evolution equation of the Wigner functions seems direct and concise. The entangledstates are defined in the enlarged Fock space with a fictitious freedom.

关键词： Wigner function, ensemble average of density operator, matrix element in entangled pure states

New Jacobian Elliptic function Solutions to Modified KdV Equation: Ⅰ

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Communications in Theoretical Physics 2002年第8期38卷 143-146页

作者： YAN Zhen-Ya Department of Applied Mathematics Dalian University of Technology Dalian 116024 China

An extended Jacobian elliptic function expansion method presented recently by us is applied to the mKdVequation such that thirteen families of Jacobian elliptic function solutions including both new solutions and Fu's allresults are obtained. When the modulus m → 1 or 0, we can find the corresponding six solitary wave solutions and sixtrigonometric function solutions. This shows that our method is more powerful to construct more exact Jacobian ellipticfunction solutions and can be applied to other nonlinear differential equations.

关键词： modified KdV equation, Jacobian elliptic function, solitary wave solution, trigonometric functionsolution

Alternative Derivation of the Propagator in Polar Coordinates by Feynman's Physical Interpretation of the Characteristic function

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Communications in Theoretical Physics 2002年第11期38卷 529-532页

作者： QIAN Shang-Wu CHAN King-Man GU Zhi-Yu Physics Department Peking University Beijing 100871 China Physics Department Peking University Beijing 100871 China Physics Department Capital Normal University Beijing 100037 China

This article revisits Feynman's characteristic function, and points out the insight and usefulness of hisphysical interpretation. As an example, the tedious and rather long derivation of the propagator in polar coordinatescan be easily and clearly obtained by merely using Feynman's physical intepretation of the characteristic function andsome well-known results of central force problem.

关键词： Feynman's characteristic function, propagator in polar coordinates

New Jacobian Elliptic function Solutions of Modified KdV Equation: Ⅱ

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Communications in Theoretical Physics 2002年第10期38卷 400-402页

作者： YAN Zhen-Ya Department of Mathematics University of British Columbia Vancouver BC Canada V6T 1Z2

Recently, we obtained thirteen families of Jacobian elliptic function solutions of mKdV equation by usingour extended Jacobian elliptic function expansion method. In this note, the mKdV equation is investigated and anotherthree families of new doubly periodic solutions (Jacobian elliptic function solutions) are fbund again by using a newtransformation, which and our extended Jacobian elliptic function expansion method form a new method still called theextended Jacobian elliptic function expansion method. The new method can be more powertul to be applied to othernonlinear differential equations.

关键词： modified KdV equation, Jacobian elliptic function, doubly periodic solution

Source time-function as discriminant using empirical Green's function

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Science China Earth Sciences 2005年第12期48卷 2118-2122页

作者： HE Yongfeng1,2 & CHEN Xiaofei1 1. Department of Geophysics, School of Earth & Space Sciences, Peking University, Beijing 100871, China 2. North-West Institute of Nuclear Technology, Xi’an 710024, China Department of Geophysics School of Earth & Space Sciences Peking University Beijing China North-West Institute of Nuclear Technology Xi’an China

The source mechanism of underground nuclear explosions is remarkably different from that of earthquakes in both spatial radiation pattern and source time-function (STF). Small underground nuclear explosions can be used as empirical Green’s functions (EGF) to isolate the source-time spectrum of a large suspected earthquake occurred in a Nuclear Test Site (target area) by the spectral division method. As this study shows, with high-quality data, the quotient spectrum can be transformed to the time domain, yielding the apparent far-field source-time function of the large suspected event. The relative source time-function (RSTF) of a nuclear ex-plosion is usually a simple pulse with a duration of about 1 s., while an earthquake’s is more complicated with a series of pulses and a longer duration. The RSTF can be used as a nice dis-criminant to distinguish the nature earthquakes from underground nuclear explosions in target areas.

关键词： target-area, empirical Green's function, RSTF.