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91.
在用人体模型计算内照射比吸收分数的Monte Carlo模拟中,对小尺寸、远距离器官的计算结果通常精度不够,可信度差,这就要求采用减方差技巧。该文采用一个简单模型比较了直接模拟和区域粒子分裂-轮盘赌、强迫碰撞与DXTRAN球、指向概率强迫碰撞3种减方差技巧的效果。结果表明指向概率强迫碰撞方法能更有效解决此类问题。利用中国人体数学模型,选择一组典型的源靶器官对,计算了一个实例,得到了可信度高的吸收分数值并体现了指向概率强迫碰撞方法的优越性。 相似文献
92.
93.
图书馆环境污染的危害及防治对策 总被引:3,自引:0,他引:3
分析了图书馆环境污染的主要来源及其危害,并提出了相应的防治对策。 相似文献
94.
The Canadian Light Source (CLS) is constructing two beamlines for Infrared Spectroscopy using synchrotron radiation (IRSR). One will supply mid-Infrared (2–25 μ) light to a Fourier Transform Infrared (FTIR) spectrometer and microscope for biological applications. The second will have a high resolution FTIR spectrometer for gas-phase and surface spectroscopy in the far-Infrared (beyond 25 μ). The Infrared beamlines will use dipole bending magnet radiation from a special bend magnet port design which provides a 50 mrad square acceptance. Issues with the first mirror and photon mask design, as well as the beamline layout and features are discussed. 相似文献
95.
We analyze the gauge ambiguity problem for the effective gravitational field from the standpoint of the measurement process. The motion of a test point particle playing the role of a measuring device is investigated in the field of a point gravitating mass in the one-loop approximation. We show that the gravitational field value determined from the effective equations of motion of the device explicitly depends on the Feynman gauge parameter. This dependence is essential in the sense that a gauge variation cannot be interpreted as a deformation of the reference frame, which leads to a gauge ambiguity in the values of observed quantities. In particular, this result disproves the hypothesis that gauge dependence is canceled in the effective equations of motion of a classical point particle. 相似文献
96.
Willem Potze 《Journal of Quantitative Spectroscopy & Radiative Transfer》2004,84(4):575-586
A mathematical model is proposed to describe the heat transfer in quartz glass axisymmetric tubes. Heat is transferred inside the glass by radiation and conduction. Scattering of thermal radiation inside the glass is ignored. At the boundaries of the tube the radiative intensity is specularly reflected. The spectral dependent radiative intensity and the temperature distribution inside the tube are determined. The model is applied to simulate the cooling process of a quartz glass tube. The calculated temperature is in agreement with that obtained from an experiment. Furthermore, steady-state temperature distributions in quartz glass tubes of different lengths have been determined. 相似文献
97.
SHI Bingren LI Jiquan DONG Jiaqi 《核工业西南物理研究院年报(英文版)》2004,(1):115-118
The geodesic acoustic mode (GAM), first predicted by Winsor, Johnson and Dawson in an attempt to explain some experimentally observed low frequency oscillations in stellarators, is a special electrostatic fluid mode with low mode number and coupled with the so-called geodesic curvature of a toroidally confined plasma. The recent on this mode are due to the close relevance of the stabi- lization of drift turbulence by both the zonal flow and the GAM. Previously, the GAM was illustrated in very simple geometries, 相似文献
98.
Using the multipoles method, we formulate the problems of radiation (both heave and sway) of water waves by a submerged sphere
in deep as well as in uniform finite depth water with an ice-cover, with the ice-cover being modelled as an elastic plate
of very small thickness. In each case this leads to an infinite system of linear equations which are solved numerically by
standard techniques. The added-mass and damping coefficients for a heaving and swaying sphere are obtained and depicted graphically
against the wave number for various values of the radius of the submerged sphere and flexural rigidity of the ice-cover to
show the effect of the presence of ice-cover on these quantities. When the flexural rigidity is taken to be zero, the numerical
results for the added-mass and damping coefficient for water with a free surface are recovered. 相似文献
99.
R. W. Home 《Physics in Perspective (PIP)》2005,7(4):473-490
I survey highlights of the practice of physics and allied sciences in Melbourne,Australia, from the 1850s, soon after Europeans
first settled in the area, to the present. I note recognizable sites of past and current physical-science activity that may
be visited, as well as exhibits of historic items of physics apparatus. I trace the role of physics, in the course of a century
and a half, in the evolution of a pioneering settlement into a large city embedded in a modern industrial economy. 相似文献
100.
A. S. Yasyukevich V. G. Shcherbitskii V. É. Kisel' A. V. Mandrik N. V. Kuleshov 《Journal of Applied Spectroscopy》2004,71(2):202-208
A new method of determining the stimulated emission cross-section spectra from the absorption cross-section spectra, which we call the integral method of reciprocity, is suggested it does not require knowledge of the structure of the impurity-center electron levels. Based on this method, formulas for calculating the radiation lifetime of impurity centers in crystals have been derived. The effectiveness of the integral method of reciprocity was demonstrated in determining the stimulated emission cross sections and radiation lifetime of an ytterbium ion in the laser crystals Yb3+:KYW and Yb3+:KGW. 相似文献