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1.
Analysis of VLBI data obtained on the VLBA reveals an absence of BL Lac objects with high degrees of circular polarization (>0.4%) detected among quasars. This cannot be due to observational selection effects: such objects should have been detected if the distributions of the degree of circular polarization for BL Lac objects and quasars were the same. This observational result provides new evidence for the existence of fundamental differences in the “central engines“ of objects in these two optical classes, which lead to different physical properties of their relativistic jets, such as the composition of the jet plasma (e ??e + or e ??p); the energy spectra of the particles; the magnitude, geometry and degree of order of the jet magnetic field; the angular momentum of the black hole; etc. 相似文献
2.
Astronomy Reports - A comparative analysis of the observational characteristics of fast radio bursts at the frequencies 111 and 1400 MHz is carried out. The distributions of radio bursts... 相似文献
3.
R. T. Downs G. V. Gibbs M. B. Boisen Jr K. M. Rosso 《Physics and Chemistry of Minerals》2002,29(5):369-385
The procrystal calculation of the electron density is a very rapid procedure that offers a quick way to analyze various bonding
properties of a crystal. This study explores the extent to which the positions, number, and properties of bond-critical points
determined from the procrystal representations of the electron density for minerals are similar to those of first-principles
ab initio model distributions. The purpose of the study is to determine the limits imposed upon interpretation of the procrystal
electron density. Procrystal calculations of the electron density for more than 300 MO bonds in crystals were compared with those previously calculated using CRYSTAL98 and TOPOND software. For every bond-critical
point found in the ab initio calculations, an equivalent one was also found in the procrystal model, with similar magnitudes
of electron density, and at similar positions along the bonds. The curvatures of the electron densities obtained from the
ab initio and the procrystal distributions are highly correlated. It is concluded that the procrystal distributions are capable
of providing good estimates of the bonded radii of the atoms and the properties of the electron-density distributions at the
bond-critical points. Because the procrystal model is so fast to compute, it is especially useful in addressing the question
as to whether a pair of atoms is bonded or not. If the Bader criteria for bonding are accepted, then the successful generation
of the bond-critical points by the procrystal model demonstrates that bonding is an atomic feature. The main difference between
the critical-point properties of the procrystal and the ab initio model is that the curvature in the electron density perpendicular
to the bond path of the ab initio model is sharper than for the procrystal model. This is interpreted as indicating that the
electrons that migrate into a bond originate from its sides, and not from the regions closer to the nuclei. This observation
also suggests that ab initio optimization routines could see an improvement in speed if the parameters relating to the angular
components of atomic wave functions were to vary before the radial components.
Received: 6 August 2001 / Accepted: 21 November 2001 相似文献
4.
A. N. Baushev 《Astronomy Reports》2002,46(10):830-839
The spectrum of cyclotron radiation produced by electrons with a strongly anisotropic velocity distribution is calculated taking into account higher harmonics. The motion of the electrons is assumed to be ultrarelativistic along the magnetic field and nonrelativistic across the field. One characteristic feature of the resulting spectrum is that harmonics of various orders are not equally spaced. The physical properties and observed spectra of four X-ray pulsars displaying higher cyclotron harmonics are analyzed. It was shown that at least in one of them, the cyclotron feature can apparently be only an emission line. Moreover, the observed harmonics are not equidistant, and display certain other properties characteristic of emission by strongly anisotropic ultrarelativistic electrons. In addition, there are indirect theoretical arguments that the electrons giving rise to cyclotron features in the spectra of X-ray pulsars are ultrarelativistic and characterized by strongly anisotropic distributions. As a result, estimates of the magnetic fields of X-ray pulsars (which are usually derived from the energies of cyclotron lines) and certain other physical parameters require substantial revision. 相似文献
5.
Electric fields accelerate electrons and ions in the auroral zone at altitudes below 8000 km to produce several distinctive
particle distributions. The electric field of electrostatic shocks and double layers produces the inverted-V precipitating
electron and up-flowing ion beams. Electrostatic ion cyclotron waves heat ion beams. The electric field in low frequency plasma
waves and electrostatic shocks produces ion conics and field-aligned or counterstreaming electrons. Relationships between
electric fields and particle distributions are illustrated with data from the S3-3 satellite. 相似文献
6.
德兴斑岩铜矿成矿过程中地下热水运移的动力学模拟 总被引：4，自引：1，他引：4
按照质量，动量和能量守恒定律建立描述成矿流体运移过程的控制微分方程组，运用有限元方法求解，得到有关成矿流体运移的流函数和温度分布值，将上述理论应用于江西德兴斑岩铜矿区，取得了满意的效果。 相似文献
7.
《Quaternary Science Reviews》2003,22(18-19):1821-1834
Soil dust aerosol is an important factor of the climatic system. In order to evaluate the different aspects of the climatic effects of dust, estimates of its highly variable atmospheric distribution need to be computed by transport models. Such models also provide important means of evaluating the processes that govern changes in dustiness during different climatic periods. While models of the modern dust cycle are currently capable of simulating first-order patterns of its global distribution, the parameterization of dust emission in these models is still crude, since input information about soil properties and wind events cannot be resolved at a global scale. Regional models could be useful for evaluating emission parameterizations, as well as dust transport and depositional processes close to source regions. No single existing data set fully describes all aspects of the dust cycle. Validation of modeled dust distributions must therefore include comparisons with different types of observational data. While the compilation of such observational data sets is crucial for model development, model results can, in turn, provide guidance for new measurements of dust properties, which will be useful for future investigation of the dust cycle and its climatic effects. 相似文献
8.
The same model previously used to deduce an acceptable first order picture of the present zonally averaged macroclimate is now solved for the climatic response to the “glacial” surface boundary conditions that prevailed at 18,000 BP in the northern hemisphere. The equilibrium solution obtained gives the distributions with latitude of the mean temperature, wind, humidity, precipitation, evaporation, heat balance, transient baroclinic eddy statistics (i.e., kinetic energy of the meridional wind and meridional flux of heat, momentum, and water vapor), and the energy integrals. In general terms, the solution shows the glacial atmosphere to be colder and drier than at present, with an intensified polar front, stronger mean zonal and poloidal winds, more intense transient baroclinic eddies (storms) transporting heat, momentum and water vapor poleward at higher rates, and reduced precipitation and evaporation. Also evident is an equatorward shift of the climatic zones (as delineated by the mean surface zonal winds, the poloidal motion, and the difference between mean evaporation and precipitation), particularly in higher latitudes. Other properties of the solution, such as the effect of zonal wind changes on the length of the day, are discussed. 相似文献
9.
海洋飞沫及其对海—气相互作用影响的研究进展 总被引：4，自引：0，他引：4
按照海水滴生成机制和粒径大小,由海浪破碎生成的海洋飞沫分为膜滴、射滴和裂滴三大类,较小的海水滴在大气中滞留时间长,成为云的凝结核,对长期气候变化有重要影响,较大的海水滴参与海—气界面动量和热量交换过程,有利于热带气旋的形成和发展。海洋飞沫的生成与海上风速、海浪、海流和大气稳定度等因素有关,但由于缺乏观测数据,刻画海洋飞沫效应的关键物理量——海洋飞沫生成函数通常用海上风速进行参数化,忽略其他因素的影响,彼此间的差异非常大,给研究海洋飞沫对气候和海—气相互作用的影响造成困难,需要进一步开展海洋飞沫的观测,考虑风速之外的其他因素对海洋飞沫生成函数的作用,改进海洋飞沫热量和动量效应的参数化方案,进而阐明海洋飞沫对气候和海—气相互作用的影响。 相似文献
10.
The influence of various types of nonthermal electron and proton distributions and photoionization on the charge state of energetic heavy elements moving in a plasma is investigated. The mean charges of Mg, Si, and Fe are calculated for a bi-Maxwellian distribution of the background electrons and for electron and neutral beams with power-law energy distributions. An anomalously high density of the nonthermal component is required to obtain substantial deviations of the equilibrium mean charges of these elements (a few charge units) from the case when they interact with a purely Maxwellian plasma. In this context, the mean charges for O, Ne, Mg, Si, and Fe ions are also calculated for a model with charge-consistent acceleration. The results indicate that photoionization does not significantly influence the charge state of solar cosmic rays if the parameters of the plasma are those characteristic of impulsive solar events. 相似文献
11.
A model for the evolution of disk galaxies is used to investigate evolutionary variations in the star-formation rate (SFR)
and extinction in disk galaxies beginning from their formation. The results obtained are compared with observational estimates
of the SFRe and extinction at cosmological redshifts z ≤ 7. The formof themass-radius relation for disk galaxies is discussed. It is proposed that the mass-radius relation is a
consequence of a mass-angular momentum relation. Analysis of the influence of the form of the mass-radius relation on the
evolutionary variations in the SFR and extinction testify that this influence is very small. The SFRs and extinctions at various
redshifts z obtained in the models are in agreement with observations. 相似文献
12.
A one-dimensional method for reconstructing the structure of prestellar and protostellar clouds is presented. The method is
based on radiative-transfer computations and a comparison of theoretical and observed intensity distributions at both millimeter
and infrared wavelengths. The radiative transfer of dust emission is modeled for specified parameters of the density distribution,
central star, and external background, and the theoretical distribution of the dust temperature inside the cloud is determined.
The intensity distributions at millimeter and IR wavelengths are computed and quantitatively compared with observational data.
The best-fit model parameters are determined using a genetic minimization algorithm, which makes it possible to reveal the
ranges of parameter degeneracy as well. The method is illustrated by modeling the structure of two infrared dark clouds IRDC-320.27+029
(P2) and IRDC-321.73+005 (P2). The derived density and temperature distributions can be used to model the chemical structure
and spectral maps in molecular lines. 相似文献
13.
Determination of the cleat angle distribution of the RECOPOL coal seams, using CT-scans and image analysis on drilling cuttings and coal blocks 总被引：1，自引：1，他引：0
Karl-Heinz A.A. Wolf Frank van Bergen Rudy Ephraim Henk Pagnier 《International Journal of Coal Geology》2008,73(3-4):259-272
Cleat orientation, cleat frequency and cleat angle distribution of deep coal seams are only available by the use of drilling cores and from coal mine samples. Coal drilling cuttings are a cheap and fast alternative to measure cleat angle distributions with the use of image analysis techniques. In this study oriented coal samples and drilling cuttings of the RECOPOL field experiment are compared and used to explain and validate the proposed method. In other words, cleat angle distributions from drilling cuttings are measured by image analysis. The geological framework of the polish coals is described. The image analysis methodologies for the measurement of fracture faces of cuttings and from CT-scan images, derived from these coals, are explained. The results of the methods on the cuttings are compared with cleat orientation distributions from CT-scans and artificial fragments from coal blocks of the same seams. These evaluations show high agreements between the methods. The cleat angle distributions of drilling cuttings of four seams are compared with the cleat orientation distributions of a regional structural geological study. The high correlation in this study shows that cleat angle distributions of coal seams can be used as input parameters for reservoir modelling. 相似文献
14.
The present paper addresses statistical analysis and estimation of fracture-length distributions at scales influenced by the truncation and censoring effects. The computational method employed here uses fracture-length distributions of a given set of measurements and information about observational constraints (i.e., window of observation) to estimate the probability density of the truncated and censored parts of fracture data sets. The results are benchmarked against power-law based maximal likelihood estimations commonly used for the same purpose. The relationship between the accuracy of estimates and size of the window of observation is studied. The utility of employing statistical models with arbitrary probability distributions of fracture lengths in order to provide a valid statistical model approximation is also considered. A verification of the suggested approximation using the Kolmogorov–Smirnov test applied to truncated and censored data is proposed. Numerical computations show that the proposed method can represent an essential improvement compared to other commonly employed techniques. 相似文献
15.
A schematic but quantitative geochemical, petrological, model of the sub-marine lithosphere and its genesis is given. With this model we calculate numerically, a priori, the geophysical characteristics of the lithosphere, its acoustic properties, density, oceanic heat flow and ocean bottom topography. Comparison with observational data for these characteristics shows good agreement. Particular attention is given to anomalous upper mantle in the vicinity of spreading centres. Compressional and shear wave velocity distributions are given in tabular form for the submarine lithosphere as a function of age. Comparison between observations for Vp, Vs and the calculated acoustic properties suggests that the lower marine lithosphere is anisotropic. Possible thickening of layer 3 with age is discussed. Melt distribution in the ridge axial region has been evaluated. All calculations were done for a plate velocity of 1 cm y−1. 相似文献
16.
I. I. Fayrushin I. G. Dautov N. F. Kashapov 《International Journal of Environmental Science and Technology》2017,14(12):2555-2560
Using approximation of a uniform background (the jellium model) for a condensed dispersed phase, the analytical expressions describing a spatial distribution of the potential of the electric field and electron concentration in the low-temperature plasma at equilibrium which contains hollow spherical microparticles are obtained. The influence of heating temperature of plasma on the above distributions is studied, and the dependencies of the charge on microparticle radius, the size of the microparticle cavity and the absolute temperature of plasma are calculated. It is shown that electrons can be emitted not only into the surrounding plasma but also into the cavity of the particles. 相似文献
17.
18.
John Z. Shi Hong-Qiang Zhou Hua Liu Yong-Gang Zhang 《Environmental Earth Sciences》2010,61(8):1691-1702
Tidal flow and fine-sediment transport at the South Channel–North Passage of the partially-mixed Changjiang River estuary
were studied using a two-dimensional horizontal (2DH) numerical model. This 2DH model was achieved by depth-integrating the
momentum and convection–diffusion equations. The Alternating Direction Implicit scheme was used to solve the governing equations.
The iterative method was adopted for the calculation of convection and diffusion terms of momentum equation. Comparisons between
calculated and measured results (tidal elevations and depth-averaged velocities) have shown reasonable agreement. Horizontal
distributions of tidal current velocity and suspended sediment concentration were qualitatively consistent with observations.
Those modeled results were analyzed to elucidate the mechanisms for the formation of the turbidity maximum and intratidal
variations in fine-sediment transport processes. 相似文献
19.
A. P. Kropotkin 《Astronomy Reports》2011,55(12):1132-1143
The basis is laid out for a theory relating various phenomena in the solar atmosphere, including localized concentrations
of magnetic field at the bases of coronal magnetic arches, chromospheric spicules, twisted coronal magnetic flux tubes, and
flows of energy carried by Alfvén waves propagating upward into the corona. The structure of photospheric currents localized
in the vicinity of supergranule boundaries and excited by convective motions is studied. These currents exist primarily in
a “dynamo layer” of sharply enhanced transverse conductivity, which forms in the weakly ionized thermal photospheric plasma
located in the solar gravitational field. The motions of the electrons and ions in this layer have appreciably different characters:
the ions are collisionly driven by the flows of neutral atoms, while the electrons drift in the crossed electric and magnetic
fields. The electric field supporting the current arises due to the polarization of the electrons and ions. This field also
gives rise to Alfvén perturbations that propagate upward into the corona, together with their associated longitudinal currents.
The character of this “loading” makes the system of fields and currents uniquely defined. Moreover, the momentum flux carried
by these Alfvén waves should be transferred to the cool chromospheric gas, facilitating the vertical ejection of this gas
in the form of spicules, as was first proposed in 1992 by Haerendel. 相似文献
20.
A model for magnetic reconnection in high-conductivity plasma in the solar corona is analyzed in a strong-magnetic-field approximation. The model includes a Syrovatskii current layer and magnetohydrodynamic (MHD) discontinuities attached to the ends of the layer. A two-dimensional analytical solution for the magnetic field is used to compute the distributions of the plasma flow velocity and plasma density in the vicinity of the corresponding current configuration. The properties of jumps in the density and velocity along the attached discontinuities are studied. Based on the character of the variations of the magnetic field and plasma flows at the MHD discontinuities, it is shown that, with the parameter values considered, an MHDdiscontinuity can include regions of trans-Alfvénic, fast, and slowshocks. The results obtained could be useful to explain the presence of “super-hot” (with effective electron temperatures exceeding 10 keV) plasma in solar flares. Other possible applications of the theory of discontinuous flows near regions of magnetic reconnection to analogous non-stationary phenomena in astrophysical plasmas are noted. 相似文献