共查询到20条相似文献，搜索用时 889 毫秒
1.
G. A. Shul’man 《Astronomy Reports》2011,55(8):718-723
The quantum motion of non-relativistic and relativistic electrons in the presence of constant magnetic fields at the surfaces of magnetic stars, magnetic white dwarfs, and pulsars is considered. The quantizing magnetic-field strengths for charged particles with specified energies are determined. The quantum motion of these particles in a plane perpendicular to the magnetic field is accompanied by spontaneous radiation due to electron transitions from higher to lower discrete energy levels, right down to the ground state. In the non-relativistic case, this emission is monochromatic. In the non-relativistic case, various frequencies are emitted, but lie within an order of magnitude of each other. The electron kinetic energy along the magnetic field varies from zero to a maximum value, due to the one-dimensional character of the motion along the field, between each pair of potential barriers corresponding to the discrete energy levels. The results may be relevant to describing gamma-ray flares of pulsars. 相似文献
2.
2．5D磁法反演估算铁矿资源量,关键是在垂直磁异常走向上求拟合模型的截面积。该文利用一种常见模型拟合4种实测磁场,发现铁矿截面积与埋深和磁性大小有一定的规律：磁化强度一定时,截面积与埋深呈线性正相关;埋深一定时,截面积与磁化强度呈近似指数形式的反相关。固定深部或外围磁性体参数,单独考虑浅部或中问铁矿模型时也有这种规律。在无钻孔资料及磁性资料不清楚时,磁化强度100000×10^-3～150000×10^-3A／m为估算铁矿资源量的最佳磁参数。因磁法反演的多解性,此类方法适用于钻孔验证前的资源量估计。 相似文献
3.
The evolution of the angle between the magnetic moment and rotation axis of radio pulsars (inclination angle) is considered taking into account the presence of a non-dipolar magnetic field at the neutron-star surface and superfluid neutrons in the stellar interior. It is assumed that the total loss of angular momentum by the pulsar can be represented as a sum of magnetodipole and current losses. The neutron star is treated as a two-component system consisting of a charged component (including protons and electrons, as well as the crust, which is rigidly coupled with them, and normal neutrons) and a superfluid core. The components interact through scattering of degenerate electrons on magnetized Feynman-Onsager vortices. If a superfluid core is absent, then, in spite of the presence of stable equilibrium inclination angles, the rate with which these are reached is so slow that most pulsars do not have sufficient time to approach them during their lifetimes. The presence of superfluid neutrons results, first, in faster evolution of the inclination angle and, second, in the final stage of the evolution being either an orthogonal or a coaxial state. The proposed model fits the observations better in the case of small superfluid cores. 相似文献
4.
Yu. V. Balabin É. V. Vashenyuk O. V. Mingalev A. I. Podgorny I. M. Podgorny 《Astronomy Reports》2005,49(10):837-846
Analysis of the relativistic proton spectra of solar flares occurring in the 23rd solar activity cycle derived from data of a worldwide neutron monitor network and numerical modeling both provide evidence for the acceleration of charged particles by an electric field that arises in coronal current sheets during reconnection. The method used to obtain the spectra is based on simulating the response of a neutron monitor to an anisotropic flux of relativistic solar protons with specified parameters and determining the characteristics of the primary relativistic solar protons by fitting model responses to the observations. Studies of the dynamics of the energy spectra distinguish two populations of relativistic protons in solar cosmic-ray events: the so-called fast component, which arrives at the flux front of the solar cosmic rays, followed by the delayed slow component. The fast component is characterized by strong anisotropy and an exponential energy spectrum, in agreement with the spectrum yielded by mathematical modeling of particle acceleration by an electric field directed along the X line of the magnetic field. The slow component, whose propagation is probably diffusive, has a power-law spectrum. 相似文献
5.
We have calculated the degree and position angle of the polarization of radiation scattered in a magnetized, optically thin or optically thick envelope around a central source, taking into account Faraday rotation of the plane of polarization during the propagation of the scattered radiation and the finite size of the radiation source. The wavelength dependence of the degree of polarization can be used to estimate the magnetic field of the source (a star, the region around a neutron star, or a black hole), and we have used our calculations to estimate the magnetic fields in a number of individual objects: several hot O and Wolf-Rayet stars, compact objects in X-ray close binaries with black holes (SS 433, Cyg X-1), and supernovae. The spectrum of the linear polarization can be used to determine the magnetic field in the vicinity of a central supermassive black hole, where the polarized optical radiation is generated. In a real physical model, this value can be extrapolated to the region of the last stable orbit. In the future, the proposed technique will make it possible to directly estimate the magnetic field in the region of the last stable orbit of a supermassive black hole using X-ray polarimetry. 相似文献
6.
在某些浅水区域中, 常有大量工程障碍, 如磁性柱状体。依据磁性柱状体的特点, 从顺轴磁化无限延深柱状磁性体这一简化数学模型的磁场分析入手, 进而对更近实际的顺轴磁化有限延深柱状磁性体的磁场及其梯度场的分布规律进行讨论, 并据此提出了采用水平磁梯度测量法对磁性柱状体磁特性实施探测的可取途径。 相似文献
7.
常规磁性基底反演方法往往忽略基底磁性变化采用常磁化强度模型,这里分析了其中的局限性,提出了先构建相关搜索重磁三维定量反演技术的变磁化强度模型,然后通过Parker界面反演算法进行基底反演.其中,对反演磁化强度所需磁异常分离采用了小波变换方法,并分析了该方法的关键技术和措施.通过利用该方法对某工区进行了实际资料处理后,得到较好效果. 相似文献
8.
The drift loss cone instability, propagating nearly transverse to the ambient magnetic field, is studied in the ring current
plasma taking into account the relative driftU between electrons and protons due to density gradients. The growth rates attain maxima and then decrease as the wave number
parallel to the magnetic fieldk
II increases. The peak values of the growth rates, maximised with respect tok
II, are enhanced by the increase in number density, electron temperature and loss cone index, and by the decrease in βt, the ratio of the proton thermal pressure to magnetic field pressure. The unstable frequencies fall in the range of 5 to
30Ωp with the growth rate γ ≥Ωp. In the ring current region betweenL=4 and 5, the instability will generate a strong turbulence in the frequency range between 5–500 Hz which can produce fluctuating
electric fields 0. 5–5 mV/m and magnetic field 0.8–80mγ. This instability can also occur on the auroral field lines, which
connect to the region of intense earthward plasma flow in the distant magnetotail and produce a broad band electrostatic noise. 相似文献
9.
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
10.
A numerical solution of the full set of MHD equations shows the generation of a heliospheric current sheet during the thermal expansion of the corona. Calculations were performed for a compressible plasma taking into account dissipative terms and anisotropy of the thermal conductivity of the magnetized plasma. It is shown that the current sheet is not magnetically neutral. The sheet contains a normal component of the magnetic field, which plays a fundamental role during the formation of the sheet and in the stationary state. The sheet is stable against MHD perturbations, which are apparently carried away by the plasma flow. For the numerical scheme chosen, the minimum sheet thickness is determined by the length of the spatial integration step. The PERESVET code was used for the calculations. 相似文献
11.
We analyze observations of the compact GHZ-peaked-spectrum radio source in the nucleus of the weakly active galaxy NGC 1052,
assuming that the low-frequency turnover in its spectrum is due to synchrotron self-absorption. The analysis is based on a
model for an inhomogeneous source of synchrotron radiation. It is shown that the magnetic field is not uniform, but the change
in the field strength from the center to the edge of the compact radio source does not exceed an order of magnitude. The maximum
magnetic-field strength in the nucleus of NGC 1052 is 20 G < H
⊥ < 200 G, and the density of relativistic electrons is 0.018 cm−3 < n
e
< 0.18 cm−3 on scales of 0.1 pc; everywhere in the radio source, the energy density of the magnetic field exceeds the energy density
of the relativistic electrons. The physical conditions are similar to those in the nuclei of the nearby radio galaxies 3C
111 and 3C 465, and differ strongly from those in the nucleus of the radio galaxy 0108+388, which is a compact GHz-peaked-spectrum
source (these three galaxies were studied by the authors earlier using the same method). 相似文献
12.
Observations of the X-ray pulsar 4U 2206+54 obtrained over 15 years show that its period, which is now 5555 ± 9 s, is increasing dramatically. This behavior is difficult to explain using traditional scenarios for the spin evolution of compact stars. The observed spin-down rate of the neutron star in 4U 2206+54 is in good agreement with the value expected in a magnetic-accretion scenario, taking into account that, under certain conditions, the magnetic field of the accretion stream can affect the geometry and type of flow. The neutron star in this case accretes material from a dense gaseous slab with small angular momentum, which is kept in equilibrium by the magnetic field of the flow itself. A magnetic-accretion scenario can be realized in 4U 2206+54 if the magnetic-field strength at the surface of the optical counterpart to the neutron star is higher than 70 G. The magnetic field at the surface of the neutron star is 4 × 1012 G in this scenario, in agreement with estimates based on an analysis of X-ray spectra of the pulsar. 相似文献
13.
L. L. Kitchatinov 《Astronomy Reports》2008,52(3):247-255
The stability of a toroidal magnetic field in the rotating radiation zone of a star is analyzed to estimate the maximum possible magnitude of relic fields. Equations for small perturbations are obtained taking into account the finite diffusivity and the stabilizing effect of the subadiabatic stratification. The numerical solution of the eigenvalue problem indicates that the threshold field strength for the onset of instability in the radiation zone of the Sun is about 600 G. This figure sets an upper bound for the strength of the relic field. The assumption that magnetic instabilities are present in the solar radiation zone disagrees with the observed abundance of lithium. Our analysis of joint stability of toroidal field and nonuniform rotation shows that two-dimensional MHD solutions for the solar tachocline are stable against three-dimensional perturbations. 相似文献
14.
New data for the energy and location of the hard-emission centers of a solar flare agree with an electrodynamic model of a solar flare based on the idea of the accumulation of free magnetic energy in the field of a current sheet. Three-dimensional MHD simulations are used to show that the energy stored in the preflare magnetic field of the current sheet is sufficient for the development of a flare and a coronal mass ejection. The flare and coronal mass ejection result from the explosive decay of the current sheet. The position of the brightness-temperature maximum of the radio emission during the flare coincides with the maximum of the current in the current sheet. The exponential spectrum of relativistic protons generated during the flare is consistent with acceleration by the electric field during the current-sheet decay. 相似文献
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17.
Jeremy B. Fein Jean-François Boily Drew Gorman-Lewis 《Geochimica et cosmochimica acta》2005,69(5):1123-1132
To provide constraints on the speciation of bacterial surface functional groups, we have conducted potentiometric titrations using the gram-positive aerobic species Bacillus subtilis, covering the pH range 2.1 to 9.8. Titration experiments were conducted using an auto-titrator assembly, with the bacteria suspended in fixed ionic strength (0.01 to 0.3 M) NaClO4 solutions. We observed significant adsorption of protons over the entire pH range of this study, including to the lowest pH values examined, indicating that proton saturation of the cell wall did not occur under any of the conditions of the experiments. Ionic strength, over the range studied here, did not have a significant effect on the observed buffering behavior relative to experimental uncertainty. Electrophoretic mobility measurements indicate that the cell wall is negatively charged, even under the lowest pH conditions studied. These experimental results necessitate a definition of the zero proton condition such that the total proton concentration at the pH of suspension is offset to account for the negative bacterial surface charge that tends towards neutrality at pH <2.The buffering intensity of the bacterial suspensions reveals a wide spread of apparent pKa values. This spread was modeled using three significantly different approaches: a Non-Electrostatic Model, a Constant Capacitance Model, and a Langmuir-Freundlich Model. The approaches differ in the manner in which they treat the surface electric field effects, and in whether they treat the proton-active sites as discrete functional groups or as continuous distributions of related sites. Each type of model tested, however, provides an excellent fit to the experimental data, indicating that titration data alone are insufficient for characterizing the molecular-scale reactions that occur on the bacterial surface. Spectroscopic data on the molecular-scale properties of the bacterial surface are required to differentiate between the underlying mechanisms of proton adsorption inherent in these models. The applicability and underlying conceptual foundation of each model is discussed in the context of our current knowledge of the structure of bacterial cell walls. 相似文献
18.
The flare source of thermal X-rays above a magnetic arch in the corona arises from the dissipation of the magnetic energy
of the current sheet formed at the reconnection of magnetic-field lines. The sources of hard X-rays emitted from the footpoints
of the magnetic arch are beams of electrons accelerated in field-aligned currents induced by the Hall electric field generated
in the current sheet. Both the hard X-rays detected above the active region and the type III radio emission are radiated by
electrons accelerated in the field-aligned currents induced by Alfven waves. The solar cosmic rays are emitted promptly at
the instant of the flare. It is important that the Lorentz electric field accelerates protons along the singular magnetic
X line. The relativistic protons propagate along the interplanetary magnetic field. These protons have exponential spectra,
typical for acceleration occurring in current sheets. A mechanism that is relevant for the generation of delayed cosmic rays,
which demonstrate significant anisotropy and a power-law spectrum with γ ∼5, is also discussed. 相似文献
19.
An autosuspension criterion that has been developed directly from the fluid dynamical equations, by taking into account the vertical structure of turbidity currents, is compared to field observations of five turbidity currents. It is found that the criterion is consistent with the motion of all five currents, which suggests that the criterion may, at least under certain circumstances, be a reasonable guide in estimating the conditions necessary for a turbidity current to be self-sustaining. 相似文献
20.
We consider models of a wormhole (i) maintained by an electromagnetic field, taking into account quantum vacuum corrections to the equation of state, (ii) maintained by a combination of the magnetic field and phantom energy, with a spherically symmetrical equation of state, and (iii) with a magnetic field and phantom matter with an anisotropic equation of state. It is shown that the quantum corrections and the density and exoticity of phantom energy or matter can be as small as is desired. For an external observer, the entrance to the tunnel appears to be a magnetic monopole of macroscopic size. The accretion of ordinary matter onto the entrance to the tunnel may result in the formation of a black hole with a radial magnetic field. We consider the possibility that some active galactic nuclei and Galactic objects may be current or former entrances to magnetic wormholes. We consider the possible existence of a broad mass spectrum for wormholes, from several billion solar masses to masses of the order of 2 kg. The Hawking effect (evaporation) does not operate in such objects due to the absence of a horizon, making it possible for them to be retained over cosmological time intervals, even if their masses are smaller than 1015 g. We also discuss a model for a binary system formed by the entrances of tunnels with magnetic fields, which could be sources of nonthermal radiation and γ-ray bursts. 相似文献