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Geology of Ore Deposits - The paper discusses the concepts of pegmatitic rocks, pegmatite and pegmatoid bodies, and classification of granitic pegmatites and their relationships with various types... 相似文献
23.
We explore the possibilities for detecting pulsars that have ceased to radiate in the radio band. We consider two models: the model with hindered particle escape from the pulsar surface [first suggested by Ruderman and Sutherland (1975)] and the model with free particle escape (Arons 1981; Mestel 1999). In the model with hindered particle escape, the number of particles that leave the pulsar magnetosphere is small and their radiation cannot be detected with currently available instruments. At the same time, for Arons' model, both the number of particles and the radiation intensity are high enough for such “extinct” pulsars to be detectable with the GLAST and INTEGRAL satellites. 相似文献
24.
We analyze the statistical distribution of neutron stars at the stage of a supersonic propeller. An important point of our analysis is allowance for the evolution of the angle of inclination of the magnetic axis to the spin axis of the neutron star for the boundary of the transition to the supersonic propeller stage. We have determined the spin period distributions of pulsars at the propeller stage for two models: the model with hindered particle escape from the stellar surface and the model with free particle escape. As a result, we have shown that consistent allowance for the evolution of the inclination angle in the region of extinct radio pulsars for the two models leads to an increase in the total number of neutron stars at the supersonic propeller stage. This increase stems from the fact that when allowing for the evolution of the inclination angle χ for neutron stars in the region of extinct radio pulsars and, hence, for the boundary of the transition to the propeller stage, this transition is possible at shorter spin periods (P ~ 5–10 s) than assumed in the standard model. 相似文献
25.
We have studied the two-dimensional structure of an accretion disk without angular momentum near a black hole using the Grad-Shafranov
equation. When the two-dimensional structure of the flow is systematically taken into account, the singularity of the hydrodynamic
equations is located at the sonic surface, rather than at a displaced surface, as occurs when the disk thickness is estimated
using the standard technique. A transonic flow can also exist for negative energies, which is not possible when the accretion
is strictly radial. 相似文献
26.
Our paper is dedicated to the problem of anomalous values of braking indices n
obs and spin frequency second derivatives [(n)\ddot]\ddot \nu of isolated radio pulsars. Observations of these objects for over 40 years have shown that in addition to the complex short-term
irregular component in the evolution of the pulsars’ frequency, secular values of its second derivative are orders of magnitude
greater than the predicted theoretical ones, and in a good half of cases—they are even negative. We earlier attributed this
behavior of secular values of the second derivative to the presence of a cyclic component in the secular evolution of ν(t), with a characteristic recurrence time of thousands to tens of thousand years. We continue to develop this hypothesis based
on a more detailed statistical analysis of the characteristics of 297 isolated radio pulsars: we analyze the model of these
objects spin-down, consisting of two components, monotonic and cyclic, and determine their parameters. We demonstrate that
the monotonic spin-down component is described by the classical magnetodipolar power law with an braking index of about 3,
while the large amplitude of the cyclic component causes a significant variation of the observed spin-down rate ([(n)\dot] )(\dot \nu ) (with respect to magnetodipolar one), and fully determines the anomalous values of [(n)\ddot]\ddot \nu and n
obs. An important consequence of the existence of a cyclic component of the pulsar rotational variations is the difference between
their characteristic ages and respective secular values (by about 0.5–5 times). This allows to explainthe observed discrepancy
of the characteristic and physical ages of some objects, as well as very large, up to 108 years, characteristic ages of some old pulsars. The paper argues that the cyclic component of the observed spin-down is due
to the long-term precession of neutron stars around their magnetic axes, which, in particular, may be driven by the anomalous
braking torque. In the model of purely magnetodipolar braking this torque is a consequence of emission in the near field zone. 相似文献
27.
A cylindrical magneto-hydrodynamical model for the transverse structures of the nonrelativisitic jets observed from young
stars is proposed. The importance of the temperature terms in the equations describing one-dimensional cylindrical flows is
discussed. It is shown that taking into account heating at an oblique shock at the base of the jet makes it possible to obtain
physical parameters of the jet that are in good agreement with observations. In particular, the jet can be confined by an
external magnetic field of the order of 10−6 G at a distance of 100 AU from the rotational axis. 相似文献
28.
The problem of the efficiency of particle acceleration for a paraboloidal poloidal magnetic field is considered within the approach of steady axisymmetric magnetohydrodynamic (MHD) flow. For the large Michel magnetization parameter σ it is possible to linearize the stream equation near the force-free solution and to solve the problem self-consistently as was done by Beskin, Kuznetsova & Rafikov for a monopole magnetic field. It is shown that, on the fast magnetosonic surface (FMS), the particle Lorentz factor γ does not exceed the standard value σ1/3 . On the other hand, in the supersonic region, the Lorentz factor grows with the distance z from the equatorial plane as γ≈ ( z / R L )1/2 up to the distance z ≈σ2 R L , where R L = c /ΩF is the radius of the light cylinder. Thus, the maximal Lorentz factor is γmax ≈σ , which corresponds to almost the full conversion of the Poynting energy flux into the particle kinetic one. 相似文献
29.
S. Karpov G. Beskin A. Biryukov V. Debur V. Plokhotnichenko M. Redfern A. Shearer 《Astrophysics and Space Science》2007,308(1-4):595-599
The fine structure and the variations of the optical pulse shape and phase of the Crab pulsar are studied on various time
scales. The observations have been carried out on 4-m William Hershel and 6-m BTA telescopes with APD photon counter, photomultiplier
based 4-channel photometer and PSD based panoramic spectrophotopolarimeter with 1 μs time resolution in 1994, 1999, 2003 and
2005–2006 years. The upper limit on the pulsar precession on Dec 2, 1999 is placed in the 10 s–2 hr time range. The evidence
of a varying from set to set fine structure of the main pulse is found in the 1999 and 2003 years data. No such fine structure
is detected in the integral pulse shape of 1994, 1999 and 2003 years.
The drastic change of the pulse shape in the 2005–2006 years set is detected along with the pulse shape variability and quasi-periodic
phase shifts.
This work has been supported by the Russian Foundation for Basic Research (grant No 04-02-17555), Russian Academy of Sciences
(program “Evolution of Stars and Galaxies”), by the Russian Science Support Foundation, and by INTAS (grant No 04-78-7366). 相似文献
30.
The problem of effective transform of Poynting flux energy into the kinetic energy of relativistic plasma outflow in a magnetosphere
is considered. In this article we present an example of such acceleration. In order to perform it, we use the approach of
ideal axisymmetric magnetohydrodynamics (MHD). For highly magnetized plasma outflow we show that a linear growth of Lorentz
factor with a cylindrical distance from the rotational axis is a general result for any field configuration in the sub-magnetosonic
flow. In the far region the full magnetohydrodynamics problem for one-dimensional flow is considered. It turns out that the
effective plasma outflow acceleration is possible in the paraboloidal magnetic field. It is shown that such an acceleration
is due to the drift of charged particles in the crossed electric and magnetic field. The clear explanation of the absence
of acceleration in the monopole magnetic field if given.
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