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1.
In anisotropic plasmas, the radiative power emitted and the power observed per unit solid angle should be calculated along the direction of the group velocityv
g
. The two power functions referred differ by a product of two factors: one is the group Doppler factor and the other is the squeezing effect of the radiative energy due to the dependence ofv
g
on direction. In this paper, the group Doppler factor is derived using two different methods, and the relevant physical concepts are analyzed in details. A number of numerical examples pertaining to astrophysical situations are presented, to illustrate the significance of the group Doppler effect with respect to the wave Doppler effect which is valid in isotropic media. 相似文献
2.
We analyze the propagation features of synchrotron radiation of a charge moving with a gyrating helix trajectory (3-dimensional) in a magnetoplasma. We found that a new factor (1+ cot ) should be included into the relevant spectrum radiation formulae and the usual relativistic factor has to be modified as
, ifv <v
g
, the radiative energy are more concentrated along the velocity of the moving charge; but ifv>v
g, the direction of maximum energy cone deviates from the direction of the moving charge. 相似文献
3.
外资:发展中国家城市化的新动力:珠江三角洲个案研究 总被引:106,自引:9,他引:106
城市化的研究历来都偏重于内力的营造,例如区域经济的不同发展步伐,乡村-市的人口流动,政府的地区性经济政策以及新城市的建设等。在资本、人力、技术和市场走向“全球化”的情况下,新的国际分工自1980年以来已成为一些发展中国家和地区的人口及经济活动急剧增长与集中的主要动力。本文对这一类型城市化的特点和空间形态作出了概括性的描述。 相似文献
4.
An update on the IEM surface backscattering model 总被引:1,自引:0,他引:1
The integral equation approach to modeling scattering from rough surfaces was introduced in 1992. At that time, it was noted that there was a need to find a transition reflection coefficient that could change its argument from the incident angle to the specular angle as frequency or roughness scale got large. One such reflection coefficient was published in 2001. In this letter, we would like to include this reflection coefficient in the integral equation model to interpret several multifrequency backscattering measurements from surfaces with surface parameters defined by the investigators who acquired the data. 相似文献
5.
6.
地震标准化进展综述(之一) 总被引:1,自引:0,他引:1
在地震标准化10周年之际,回顾了地震标准化取得的进展,提出了十五期间地震标准化的重点工作及其发展中应注意的问题。 相似文献
7.
We report the results of 1966, 1968, and 1969 polarization measurements of solar type III radio noise bursts made by recording the output of two orthogonally polarized receiving channels and subsequent digital processing of selected data. The processed data yield total intensity, degree of polarization, ellipticity, and polarization ellipse orientation at 1 second intervals. The measurements are made in a 100 Hz bandwith to minimize the influence of the propagating medium on the measurements. The mean degree of polarization was found to be about 65% in contrast to previous studies which indicated that type III events were more weakly polarized. By assuming that type III bursts are flare related we study the polarization characteristics of type III bursts as a function of the solar longitude of the related flares. The relation between type III event polarization characteristics and flare importance is also investigated. The significance of polarization measurements in studies of solar radio events is pointed out and suggestions for further theoretical research are given. 相似文献
8.
We analyze the special features of cyclotron radiation in four different modes radiated by a mildly relativistic electron current in an anisotropic plasma, taking into consideration that the radiation is transmitted along the group velocity, rather than the wave normal direction. A systematic series of numerical analysis is carried out, to demonstrate the characteristics of the focussing effect and Doppler effect of the radiation, arising from anisotropy. The parameters used pertain to plasmas and radiators of the types encountered in the terrestrial upper atmosphere and the solar corona. 相似文献
9.
P. C. W. Fung 《Astrophysics and Space Science》1972,16(2):249-273
In this investigation, we attempt to analyze the quasi-linear cyclotron instability (under the weak turbulence regime) for whistler-mode waves due to pitch angle anisotropy of nonthermal electrons. The motivation of this study is to explain the triggered discrete VLF emissions occurring in the terrestrial magnetosphere. The time evolution of the growth rate and the induced waves spectrum for a loss cone type of nonthermal electrons is analyzed numerically. The diffusion of particles in pitch angles due to quasilinear cyclotron instability is illustrated. It is shown that several major features of triggered VLF emissions can be explained by the stated instability. Some predictions of the theory is given and suggestions for further research are presented.On special leave during the summer of 1971 from the Physics Department, Faculty of Science, University of Hong Kong. 相似文献
10.
So MK Zhang X Giesy JP Fung CN Fong HW Zheng J Kramer MJ Yoo H Lam PK 《Marine pollution bulletin》2005,51(8-12):677-687
Concentrations of persistent organic pollutants including polychlorinated biphenyls (PCBs), organochlorine (OC) pesticides and dioxin-like compounds were measured in green-lipped mussels, Perna viridis, collected from seven mariculture zones in Hong Kong between September and October in 2002 in order to evaluate the status, spatial distribution and potential sources of pollution in these areas. Concentrations ranged from 300 to 4400 ng/g lipid weight for total OCs and 170–1000 ng/g lipid weight for total PCBs (based on 28 congeners). Relatively smaller DDT concentrations in mussels compared with previous studies suggest reduced discharges of DDTs from nearby regions into Hong Kong waters. Detection of a mixture of HCH isomers in the mussels indicated that Hong Kong waters were predominantly contaminated by technical HCHs rather than lindane. Mussel samples from all sampling locations elicited significant dioxin-like activity in the H4IIE-luc bioassay. The greatest magnitude of dioxin-like response (39 pg TEQ/g wet wt.) was detected in mussels from Ma Wan in the western waters of Hong Kong, which is strongly influenced by the Pearl River discharge. Human health risk assessment was undertaken to evaluate potential risks associated with the consumption of the green-lipped mussels. Risk quotient (RQ) for dioxin-like compounds was greater than unity suggesting that adverse health effects may be associated with high mussel consumption. 相似文献