4,875 research outputs found
Polygonization and plastic bending of whiskers induced by pulsed power electron beam
Dynamics of bending of NaCl whisker is studied with use of high speed camera
VFU-1 synchronized with high power electron accelerator GIN-600. The dynamics
of bending turns to be non-monotonous and quite complicated. The figures of
etching of whisker after bombardment by electron beam are analysed, thin
polygonization in samples is found. The time of bending in experiment and time
of forming of dislocation walls computed on the base of theory of plastical
bending are compared.Comment: LaTeX, 6 page
Global structure of the pulsar force-free magnetosphere revisited
A new model of the pulsar force-free magnetosphere is suggested, which
includes the presence of the polar, outer and slot gaps. It is based on a new
exact solution of the pulsar equation in the form of an offset monopole and the
resultant split-offset monopole scheme.Comment: 3 pages, 2 figures; to appear in Proceedings of IAUS 291 "Neutron
Stars and Pulsars: Challenges and Opportunities after 80 years", J. van
Leeuwen (ed.
Mechanisms of the physical connection between the radio- and high-energy emissions of pulsars
The high-energy emission mechanisms based on the radio photon reprocessing by
the ultrarelativistic plasma particles in the open field line tube of a pulsar
are considered. The particles are believed to acquire relativistic gyration
energies as a result of resonant absorption of pulsar radio emission. The
spontaneous synchrotron re-emission of these particles falls into the optical
and soft X-ray ranges and can at least partially account for the pulsar
non-thermal high-energy emission. Besides that, the radio photons, which are
still below the resonance, can be deposited into the high-energy range by means
of the scattering off the gyrating particles. This process can also markedly
contribute to the pulsar high-energy emission and underlie the potentially
observable features of the radio -- high-energy connection. Based on the theory
developed, we interpret the manifestations of the radio -- high-energy
connection already observed in the Crab and Vela pulsars. Furthermore, it is
shown that generally the most prominent connection is expected at the lowest
radio frequencies, beyond the low-frequency turnover of a pulsar.Comment: 5 pages, 2 figures. To appear in the Proceedings of The Low-Frequency
Radio Universe Conference held at NCRA-TIFR, Pune, 8-12 December 2008, eds.
D.J. Saikia, D. Green, Y. Gupta, and T. Ventur
On the Global Structure of Pulsar Force-free Magnetosphere
The dipolar magnetic field structure of the neutron star is modified by the
plasma originating in the pulsar magnetopshere. In the simplest case of a
stationary axisymmetric force-free magnetosphere, a self-consistent description
of the fields and currents is given by the well-known pulsar equation. Here we
revise the commonly used boundary conditions of the problem in order to
incorporate the plasma-producing gaps and to provide a framework for a truly
self-consistent treatment of the pulsar magnetosphere. The generalized
multipolar solution of the pulsar equation is found, which, as compared to the
customary split monopole solution, is suggested to better represent the
character of the dipolar force-free field at large distances. In particular,
the outer gap location entirely inside the light cylinder implies that beyond
the light cylinder the null and critical lines should be aligned and go
parallel to the equator at a certain altitude. Our scheme of the pulsar
force-free magnetosphere, which will hopefully be followed by extensive
analytic and numerical studies, may have numerous implications for different
fields of pulsar research.Comment: 5 pages, 2 figures; accepted for publication in Ap
Physics of radio emission in gamma-ray pulsars
Propagation of radio emission in pulsar magnetosphere is reviewed. The
effects of polarization transfer, induced scattering and reprocessing to high
energies are analysed with an especial emphasis on the implications for the
gamma-ray pulsars. The possibilities of the pulsar plasma diagnostics based on
the observed radio pulse characteristics are outlined as well. As an example,
the plasma number density profiles obtained from the polarization data for the
Vela and the gamma-ray millisecond pulsars J1446-4701, J1939+2134 and
J1744-1134 are presented. The number densities derived tend to be the
highest/lowest when the radio pulse leads/lags the gamma-ray peak. In the PSR
J1939+2134, the plasma density profiles for the main pulse and interpulse
appear to fit exactly the same curve, testifying to the origin of both radio
components above the same magnetic pole and their propagation through the same
plasma flow in opposite directions. The millisecond radio pulse components
exhibiting flat position angle curves are suggested to result from the induced
scattering of the main pulse by the same particles that generate gamma-rays.
This is believed to underlie the wide-sense radio/gamma-ray correlation in the
millisecond pulsars. The radio quietness of young gamma-ray pulsars is
attributed to resonant absorption, whereas the radio loudness to the radio beam
escape through the periphery of the open field line tube.Comment: 25 pages, 5 figures. Invited contribution to a Special Collection
'Plasma Physics of Gamma Ray Emission from Pulsars and their Nebulae' ed. by
J. Arons and D. Uzdensk
Elastic Properties of KH2PO4 at the ferroelectric phase transition
We report results of ultrasonic studies of a single crystal of KDP in the
temperature range 2-300 K. The longitudinal and transverse sound velocities
along [001] and [100] directions were obtained as functions of temperature. The
analysis of the temperature evolution of pseudomoduli and in
the ferroelectric phase shows that these quantities can be approximated by the
expression in the temperature range
0.001K0.2K
Resonant inverse Compton scattering by secondary pulsar plasma
We consider resonant inverse Compton scattering of thermal photons by
secondary particles above the pulsar polar gap. The process appears to be an
essential energy loss mechanism for the particles. The distribution function of
the secondary plasma particles is found to be strongly affected by the
scattering. It becomes two-humped implying the development of two-stream
instability. The resonantly upscattered Compton photons are found to gain
energy of 1 - 10 MeV forming an additional component in the pulsar gamma-ray
spectrum. The corresponding gamma-ray flux is estimated as well.Comment: 17 pages, LaTe
Notes on the Vollhardt "invariant" and phase transition in the helical itinerant magnet MnSi
In this paper we argue that rounded "hills" or "valleys" demonstrated by the
heat capacity, thermal expansion coefficient, and elastic module are
indications of a smeared second order phase transition, which is flattened and
spread out by the application of a magnetic field. As a result, some of the
curves which display a temperature dependence of the corresponding quantities
cross almost at a single point. Thus, the Vollhardt crossing point should not
be identified with any specific energy scale. The smeared phase transition in
MnSi preceding the helical first order transition most probably corresponds to
the planar ferromagnetic ordering, with a small or negligible correlation
between planes. At lower temperatures, the system of ferromagnetic planes
becomes correlated, acquiring a helical twist
Inexhaustible physics of the helical magnet MnSi: field evolution of the magnetic phase transition inferred from ultrasound studies
The longitudinal and transverse ultrasound speeds and attenuation were
measured in a MnSi single crystal in the temperature range of 2 - 40 K and
magnetic fields to 7 Tesla. The magnetic phase diagram of MnSi in applied
magnetic field appears to depend on the experimental setups, which is related
to a difference in demagnetization factors arising due to the disc shape of the
sample. The magnetic phase transition in MnSi in zero magnetic field is
signified by a quasi discontinuity in the c11 elastic constant, which varies
significantly with magnetic field. It is notable that the region where the c11
discontinuity almost vanishes closely corresponds to the extent of skyrmion
phase along the magnetic to paramagnetic transition. This implies that the c11
elastic constant is almost continuous through the transition from the skyrmion
to paramagnetic phases. A recovery of the discontinuity of c11 and enhanced
sound absorption occur at the crossing of the phase transition line and the
line of minima in c11. The powerful fluctuations at the minima of c11 make the
mentioned crossing point similar to a critical end point, where a second order
phase transition meets a first order one. The skyrmion domain in the case of a
perpendicular setup with a smaller demagnetization factor has a reduced
temperature range, which suggests that the magnetic field inhomogeneity plays
an important role in the skyrmion occurrence and, hence, opens a way of
skyrmion manipulation. The small anisotropy of the shear moduli in the (001)
plane found in the parallel setup is most probably also caused by the magnetic
field inhomogeneity, which distorts the hexagonal symmetry of the skyrmion
crystal.Comment: 7 pages, 9 figure
On the circular polarization of pulsar radiation
We consider the polarization behaviour of radio waves propagating through an
ultrarelativistic highly magnetized electron-positron plasma in a pulsar
magnetosphere. The rotation of magnetosphere gives rise to the wave mode
coupling in the polarization-limiting region. The process is shown to cause
considerable circular polarization in the linearly polarized normal waves.
Thus, the circular polarization observed for a number of pulsars, despite the
linear polarization of the emitted normal waves, can be attributed to the
limiting-polarization effect.Comment: 11 pages, LaTe
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