475 research outputs found
Early phases of different types of isolated neutron star
Two Galactic isolated strong X-ray pulsars seem to be in the densest
environments compared to other types of Galactic pulsar. X-ray pulsar
J1846-0258 can be in an early phase of anomalous X-ray pulsars and soft gamma
repeaters if its average braking index is ~1.8-2.0. X-ray pulsar J1811-1925
must have a very large average braking index (n~11) if this pulsar was formed
by SN 386AD. This X-ray pulsar can be in an early phase of evolution of the
radio pulsars located in the region P~50-150 ms and \.{P}~10
s/s of the P-\.{P} diagram. X-ray/radio pulsar J0540-69 seems to be evolving in
the direction to the dim isolated thermal neutron star region on the P-\.{P}
diagram. Possible progenitors of different types of neutron star are also
discussed.Comment: to appear in the International Journal of Modern Physics
Possible evolution of dim radio quiet neutron star 1E 1207.4-5209 based on a B-decay model
Dim radio-quiet neutron star (DRQNS) 1E 1207.4-5209 is one of the most
heavily examined isolated neutron stars. Wide absorption lines were observed in
its spectrum obtained by both XMM-Newton and Chandra X-ray satellites. These
absorption lines can be interpreted as a principal frequency centered at 0.7
keV and its harmonics at 1.4, 2.1 and possibly 2.8 keV. The principal line can
be formed by resonant proton cyclotron scattering leading to a magnetic field
which is two orders of magnitude larger than the perpendicular component of the
surface dipole magnetic field (B) found from the rotation period (P) and the
time rate of change in the rotation period (\.{P}) of 1E 1207.4-5209. Besides,
age of the supernova remnant (SNR) G296.5+10.0 which is physically connected to
1E 1207.4-5209 is two orders of magnitude smaller than the characteristic age
(=P/2\.{P}) of the neutron star. These huge differences between the
magnetic field values and the ages can be explained based on a B-decay model.
If the decay is assumed to be exponential, the characteristic decay time turns
out to be several thousand years which is three orders of magnitude smaller
than the characteristic decay time of radio pulsars represented in an earlier
work. The lack of detection of radio emission from DRQNSs and the lack of point
sources and pulsar wind nebulae in most of the observed SNRs can also be partly
explained by such a very rapid exponential decay. The large difference between
the characteristic decay times of DRQNSs and radio pulsars must be related to
the differences in the magnetic fields, equation of states and masses of these
isolated neutron stars.Comment: 13 pages, 1 figur
Effects of the background radiation on radio pulsar and supernova remnant searches and the birth rates of these objects
In different directions of the Galaxy the Galactic background radio radiation
and radiation of complex star formation regions which include large number of
OB associations have different influences on radio pulsar (PSR) and supernova
remnant (SNR) searches. In this work we analyse the effects of these background
radiations on the observations of PSRs at 1400 MHz and SNRs at 1000 MHz. In the
interval l=0 the PSRs with flux F0.2 mJy and the SNRs
with surface brightness WmHzsr are
observable for all values of l and b. All the SNRs with
WmHzsr can be observed in the
interval 60l. We have examined samples of PSRs and SNRs to
estimate the birth rates of these objects in the region up to 3.2 kpc from the
Sun and also in the Galaxy. The birth rate of PSRs is about one in 200 years
and the birth rate of SNRs is about one in 65 years in our galaxy.Comment: revised versio
Sturm-Liouville operators on time scales
We establish the connection between Sturm-Liouville equations on time scales
and Sturm--Liouville equations with measure-valued coefficients. Based on this
connection we generalize several results for Sturm-Liouville equations on time
scales which have been obtained by various authors in the past.Comment: 12 page
Nanotransformation and current fluctuations in exciton condensate junctions
We analyze the nonlinear transport properties of a bilayer exciton condensate
that is contacted by four metallic leads by calculating the full counting
statistics of electron transport for arbitrary system parameters. Despite its
formal similarity to a superconductor the transport properties of the exciton
condensate turn out to be completely different. We recover the generic features
of exciton condensates such as counterpropagating currents driven by excitonic
Andreev reflections and make predictions for nonlinear transconductance between
the layers as well as for the current (cross)correlations and generalized
Johnson-Nyquist relationships. Finally, we explore the possibility of
connecting another mesoscopic system (in our case a quantum point contact) to
the bottom layer of the exciton condensate and show how the excitonic Andreev
reflections can be used for transforming voltage at the nanoscale.Comment: 5 pages, 4 figures, accepted by PR
An integrable discretization of KdV at large times
An "exact discretization" of the Schroedinger operator is considered and its
direct and inverse scattering problems are solved. It is shown that a
differential-difference nonlinear evolution equation depending on two arbitrary
constants can be solved by using this spectral transform and that for a special
choice of the constants it can be considered an integrable discretization of
the KdV equation at large times. An integrable difference-difference equation
is also obtained.Comment: 12 page
Density imbalance effect on the Coulomb drag upturn in an electron-hole bialyer
A low-temperature upturn of the Coulomb drag resistivity measured in an
undoped electron-hole bilayer (uEHBL) device, possibly manifesting from exciton
formation or condensation, was recently observed. The effects of density
imbalance on this upturn are examined. Measurements of drag as a function of
temperature in a uEHBL with a 20 nm wide AlGaAs barrier layer
at various density imbalances are presented. The results show drag increasing
as the density of either two dimensional system was reduced, both within and
above the upturn temperature regime. A comparison of the data with numerical
calculations of drag in the presence of electron-hole pairing fluctuations,
which qualitatively reproduce the drag upturn behavior, is also presented. The
calculations, however, predict a peak in drag at matched densities, which is
not reflected by the measurements.Comment: 4 pages, 4 figures, submitted to PRB Rapi
An Alternative Interpretation of Recent ARPES Measurements on TiSe2
Recently there has been a renewed interest in the charge density wave
transition of TiSe2, fuelled by the possibility that this transition may be
driven by the formation of an excitonic insulator or even an excitonic
condensate. We show here that the recent ARPES measurements on TiSe2 can also
be interpreted in terms of an alternative scenario, in which the transition is
due to a combination of Jahn-Teller effects and exciton formation. The hybrid
exciton-phonons which cause the CDW formation interpolate between a purely
structural and a purely electronic type of transition. Above the transition
temperature, the electron-phonon coupling becomes ineffective but a finite
mean-field density of excitons remains and gives rise to the observed diffuse
ARPES signals.Comment: 4 pages, 2 figure
A discrete Schrodinger spectral problem and associated evolution equations
A recently proposed discrete version of the Schrodinger spectral problem is
considered. The whole hierarchy of differential-difference nonlinear evolution
equations associated to this spectral problem is derived. It is shown that a
discrete version of the KdV, sine-Gordon and Liouville equations are included
and that the so called `inverse' class in the hierarchy is local. The whole
class of related Darboux and Backlund transformations is also exhibited.Comment: 14 pages, LaTeX2
Resonance Phenomenon Related to Spectral Singularities, Complex Barrier Potential, and Resonating Waveguides
A peculiar property of complex scattering potentials is the appearance of
spectral singularities. These are energy eigenvalues for certain scattering
states that similarly to resonance states have infinite reflection and
transmission coefficients. This property reveals an interesting resonance
effect with possible applications in waveguide physics. We study the spectral
singularities of a complex barrier potential and explore their application in
designing a waveguide that functions as a resonator. We show that for the
easily accessible sizes of the waveguide and its gain region, we can realize
the spectral singularity-related resonance phenomenon at almost every
wavelength within the visible spectrum or outside it.Comment: Published version, 20 pages, 2 tables, 7 figure
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