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21.
在中子星磁轴吸积柱的上部,少数高能电子通过磁镜点反射,可使部份电子的速度分布形成非热分布,由此激发激射(Maser)不稳定性。波被放大,发射出频率近似为电子迴旋频率及其倍频的相干辐射。用此模型计算了HerX-1的迴旋线发射。发现不稳定性增长率与吸积柱中电子数密度成正比,因而比非相干散射产生的连续辐射随电子数密度增长更快;而且发射线的强度和能量均与脉冲相位关联。这个理论可解释近期的HerX-1观测结果。 相似文献
22.
23.
FRICTIONAL SLIDING OF PLAGIOCLASE GOUGE UNDER LOWER-CRUST TEMPERATURE AND RELATIVELY LOW EFFECTIVE NORMAL STRESS 下载免费PDF全文
The discovery of tremors on the lower crust portion of the San Andreas Fault has attracted more attention on the mechanical properties of the lower crust in recent years, and some experimental studies have been carried out to understand the mechanical behavior. Previous experiments under effective normal stresses of 200MPa have shown that pyroxene and plagioclase mineral separated from the gabbro and their mixtures all show velocity weakening in the lower-crust temperature range, which results in unstable slip when frictional sliding is the dominant deformation mechanism. This work is to examine whether the velocity-weakening behavior of plagioclase gouge also applies to relatively lower effective normal stress. Our experiments were performed under effective normal stress of about 100MPa, with a constant confining pressure control, with pore pressure of 30MPa and temperature of 100℃ to 600℃. We found that the frictional sliding of plagioclase are basically the same with the previous results obtained under effective normal stress of 200MPa, both of which show velocity weakening over the entire temperature range. The only difference is the out-of-trend drop of constitutive parameter a at 600℃ for the lower effective normal stress of 100MPa. It is thus concluded that reducing the effective normal stress has little effect on the sliding stability of plagioclase, and the previous conclusion made for mechanical behavior of the lower crust that unstable slips are possible therein also applies to the lower effective normal stress of 100MPa. 相似文献
24.
Wave-induced instability of seabed may cause damage to coastal and offshore structures. This issue has been investigated mostly for mildly sloping () seabed considering uncoupled or one-way coupled response of wave and seabed interaction. However, some of the marine structures are founded on seabed with steeper slopes. In this study, the wave-induced response and instability of sloping seabed are evaluated using a coupled finite element model. The interaction between fluid and porous seabed accounting for the effect of fluid motion on the seabed response, and conversely the effect of seabed response on the fluid motion (but not on the surface wave profile) is considered. The results indicate that the system response (fluid pressure, stresses, etc.) and the extent of instantaneously liquefied zone within the sloping seabed with significant steepness are lesser than those for horizontal seabed. Moreover, for typical sediment and wave characteristics, for the flat seabed, the response obtained from fully coupled analysis is not significantly different from those obtained by uncoupled analysis. For the sloping bed, such difference is slightly greater as compared to that for the flat bed. 相似文献
25.
The coherent plasma process such as parametric decay instability (PDI) has been applied to a homogeneous and unmagnetized
plasma. These instabilities cause anomalous absorption of strong electromagnetic radiation under specific conditions of energy
and momentum conservation and thus cause anomalous heating of the plasma. The maximum plasma temperatures reached are functions
of luminosity of the radio radiation and plasma parameters. We believe that these processes may be taking place in many astrophysical
objects. Here, the conditions in the sources 3C 273, 3C 48 and Crab Nebula are shown to be conducive to the excitation of
PDI. These processes also contribute towards the absorption of 21cm radiation 相似文献
26.
The elements of dielectric tensor and dispersion relation for obliquely propagating whistler waves with finite in an infinite magnetoplasma are obtained for a kappa distribution in the presence of perpendicular a.c. electric field.
Integrals and modified plasma dispersion functions are reduced in power series form. Numerical calculations have been performed
to obtain temporal growth rate and real frequencies of the plasma waves for magnetospheric plasma, using linear theory of
dispersion relation. The effect and modification introduced by the perpendicular a.c. electric field on the temporal growth
rates, real frequencies and resonance condition are discussed for kappa and Maxwellian distributions. Our results and their
interpretation are compared with known whistler observations obtained by ground-based techniques and satellite observations. 相似文献
27.
D. D. Ryutov J. O. Kane A. Mizuta M. W. Pound B. A. Remington 《Astrophysics and Space Science》2007,307(1-3):173-177
The dynamics of photoevaporated molecular clouds is determined by the ablative pressure acting on the ionization front. An
important step in the understanding of the ensuing motion is to develop the linear stability theory for an initially flat
front. Despite the simplifications introduced by linearization, the problem remains quite complex and still draws a lot of
attention. The complexity is related to the large number of effects that have to be included in the analysis: acceleration
of the front, possible temporal variation of the intensity of the ionizing radiation, the tilt of the radiation flux with
respect to the normal to the surface, and partial absorption of the incident radiation in the ablated material. In this paper,
we describe a model where all these effects can be taken into account simultaneously, and a relatively simple and universal
dispersion relation can be obtained. The proposed phenomenological model may prove to be a helpful tool in assessing the feasibility
of the laboratory experiments directed towards scaled modeling of astrophysical phenomena.
PACS Numbers: 98.38.Dq, 98.38.Hv, 52.38.Mf, 5257.FG, 52.72.+v 相似文献
28.
Mikhail V. Medvedev 《Astrophysics and Space Science》2007,307(1-3):245-250
It has recently been realized that the Weibel instability plays a major role in the formation and dynamics of astrophysical
shocks of gamma-ray bursts and supernovae. Thanks to technological advances in the recent years, experimental studies of the
Weibel instability are now possible in laser-plasma interaction devices. We, thus, have a unique opportunity to model and
study astrophysical conditions in laboratory experiments – a key goal of the Laboratory Astrophysics program. Here we briefly
review the theory of strong non-magnetized collisionless GRB and SN shocks, emphasizing the crucial role of the Weibel instability
and discuss the properties of radiation emitted by (isotropic) electrons moving through the Weibel-generated magnetic fields,
which is referred to as the jitter radiation. We demonstrate that the jitter radiation field is anisotropic with respect to
the direction of the Weibel current filaments and that its spectral and polarization characteristics are determined by microphysical
plasma parameters. We stress that the spectral analysis can be used for accurate diagnostics of the plasma conditions in laboratory
experiments and in astrophysical GRB and SN shocks. 相似文献
29.
地电阻率仪器在工作中容易出现无电流、电流不稳等故障现象,不易排查维修.通过对仪器工作原理和供电回路过程进行研究,发现供电回路中间仪器的内部或外部各接头接触不良是造成上述现象的主要因素.根据存在的问题,洛阳地震台研制出供电回路故障检测板.该检测板可利用其继电器上LED灯的工作状态和动作时序,快速查找、排除相关供电回路故障... 相似文献
30.
本文提出了大气重力波触发Rayleigh-Taylor不稳定性并导致大尺度赤道扩展F的理论.重力波作为外部扰动派触发等离子体扰动,这种扰动在Rayleigh-Taylor不稳定性的作用下继续增长,经过400s扰动幅度就能增长到50%,经过700s后幅度趋近100%,即为完全的等离子体泡.由于E区的影响,赤道扩展F主要出现于晚上.本文的理论阐明了重力波与Rayleigh-Taylor不稳定性相互作用的性质,揭示了大尺度赤道扩展F的产生机制. 相似文献