44,685 research outputs found
Atmospheres and Spectra of Strongly Magnetized Neutron Stars II: Effect of Vacuum Polarization
We study the effect of vacuum polarization on the atmosphere structure and
radiation spectra of neutron stars with surface magnetic fields B=10^14-10^15
G, as appropriate for magnetars. Vacuum polarization modifies the dielectric
property of the medium and gives rise to a resonance feature in the opacity;
this feature is narrow and occurs at a photon energy that depends on the plasma
density. Vacuum polarization can also induce resonant conversion of photon
modes via a mechanism analogous to the MSW mechanism for neutrino oscillation.
We construct atmosphere models in radiative equilibrium with an effective
temperature of a few \times 10^6 K by solving the full radiative transfer
equations for both polarization modes in a fully ionized hydrogen plasma. We
discuss the subtleties in treating the vacuum polarization effects in the
atmosphere models and present approximate solutions to the radiative transfer
problem which bracket the true answer. We show from both analytic
considerations and numerical calculations that vacuum polarization produces a
broad depression in the X-ray flux at high energies (a few keV \la E \la a few
tens of keV) as compared to models without vacuum polarization; this arises
from the density dependence of the vacuum resonance feature and the large
density gradient present in the atmosphere. Thus the vacuum polarization effect
softens the high energy tail of the thermal spectrum, although the atmospheric
emission is still harder than the blackbody spectrum because of the non-grey
opacities. We also show that the depression of continuum flux strongly
suppresses the equivalent width of the ion cyclotron line and therefore makes
the line more difficult to observe.Comment: 21 pages, 21 figures; MNRAS; corrected minor typo
Atmospheres and Spectra of Strongly Magnetized Neutron Stars
We construct atmosphere models for strongly magnetized neutron stars with
surface fields G and effective temperatures K. The atmospheres directly determine the characteristics
of thermal emission from isolated neutron stars, including radio pulsars, soft
gamma-ray repeaters, and anomalous X-ray pulsars. In our models, the atmosphere
is composed of pure hydrogen or helium and is assumed to be fully ionized. The
radiative opacities include free-free absorption and scattering by both
electrons and ions computed for the two photon polarization modes in the
magnetized electron-ion plasma. Since the radiation emerges from deep layers in
the atmosphere with \rho\ga 10^2 g/cm, plasma effects can significantly
modify the photon opacities by changing the properties of the polarization
modes. In the case where the magnetic field and the surface normal are
parallel, we solve the full, angle-dependent, coupled radiative transfer
equations for both polarization modes. We also construct atmosphere models for
general field orientations based on the diffusion approximation of the
transport equations and compare the results with models based on full radiative
transport. In general, the emergent thermal radiation exhibits significant
deviation from blackbody, with harder spectra at high energies. The spectra
also show a broad feature (\Delta E/\Ebi\sim 1) around the ion cyclotron
resonance \Ebi=0.63 (Z/A)(B/10^{14}{G}) keV, where and are the atomic
charge and atomic mass of the ion, respectively; this feature is particularly
pronounced when \Ebi\ga 3k\Teff. Detection of the resonance feature would
provide a direct measurement of the surface magnetic fields on magnetars.Comment: 29 pages, 11 figures; corrected factor of 2 in He models: minor
changes to figs 4 and 9 as a result; other very minor change
Old chinese and friends: new approaches to historical linguistics of the Sino-Tibetan area
List J-M, Starostin G, Yunfan L. âOld Chinese and Friendsâ: new approaches to historical linguistics of the Sino-Tibetan area. Journal of Language Relationship. 2019;17(1-2):1-6
The final measurement of by NA48
The direct CP violation parameter Re() has been measured
from the decay rates of neutral kaons into two pions using the NA48 detector at
the CERN SPS. The 2001 running period was devoted to collecting additional data
under varied conditions compared to earlier years (1997-99). The 2001 data
yield the result: Re()=.
Combining this result with that published from the 1997,98 and 99 data, an
overall value of Re()= is
obtained from the NA48 experiment.Comment: 5 pages, 3 figures. Proceedings for the ICHEP02 conferenc
Partially ionized atmospheres of neutron stars with strong magnetic fields
We construct hydrogen atmosphere models for strongly magnetized neutron stars
in thermodynamic equilibrium, taking into account partial ionization. The
presence of bound states affects the equation of state, absorption
coefficients, and polarizability tensor of a strongly magnetized plasma.
Therefore the partial ionization influences the polarization vectors and
opacities of normal electromagnetic waves, and thus the spectra of outgoing
radiation. Here we review a model suitable for the most typical neutron-star
atmospheres and focus on the problems that remain to be solved for its
extension to other atmospheric parameters.Comment: 7 pages, 1 figure, Adv. Sp. Res., in pres
Orbital Decay of the PSR J0045-7319/B Star Binary System: Age of Radio Pulsar and Initial Spin of Neutron Star
Recent timing observations of PSR J0045-7319 reveal that the neutron star/B
star binary orbit is decaying on a time scale of |\Porb/\dot\Porb|=0.5 Myr,
shorter than the characteristic age ( Myr) of the pulsar (Kaspi et
al.~1996a). We study mechanisms for the orbital decay. The standard weak
friction theory based on static tide requires far too short a viscous time to
explain the observed \dot\Porb. We show that dynamical tidal excitation of
g-modes in the B star can be responsible for the orbital decay. However, to
explain the observed short decay timescale, the B star must have some
significant retrograde rotation with respect to the orbit --- The retrograde
rotation brings lower-order g-modes, which couple much more strongly to the
tidal potential, into closer ``resonances'' with the orbital motion, thus
significantly enhancing the dynamical tide. A much less likely possibility is
that the g-mode damping time is much shorter than the ordinary radiative
damping time. The observed orbital decay timescale combined with a generic
orbital evolution model based on dynamical tide can be used as a ``timer'',
giving an upper limit of Myr for the age of the binary system since the
neutron star formation. Thus the characteristic age of the pulsar is not a good
age indicator. Assuming standard magnetic dipole braking for the pulsar and no
significant magnetic field decay on a timescale \lo 1 Myr, the upper limit
for the age implies that the initial spin of the neutron star at birth was
close to its current value.Comment: AASTeX, 9 pages, 3 ps figures. ApJ Letters, in pres
Experimental investigation of the effects of polarization on the measured radiation efficiency of a dielectric resonator antenna
©2008 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE. This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.The radiation efficiencies of two rectangular dielectric resonant antennas (DRAs) were investigated using the directivity/ gain (D/G) method and the Wheeler cap method. Both antennas are linearly polarized but have different linear polarization purities. Through comparison of their radiation efficiencies, itpsilas shown that the polarization purity strongly affects the D/G measurement of the DRAspsila radiation efficiency.Qinghua Lai, Georgios Almpanis, Christophe Fumeaux, Hansruedi Benedickter, and RĂŒdiger Vahldiec
Depression and anxiety in prostate cancer: a systematic review and meta-analysis of prevalence rates
ObjectivesTo systematically review the literature pertaining to the prevalence of depression and anxiety in patients with prostate cancer as a function of treatment stage.DesignSystematic review and meta-analysis.Participants4494 patients with prostate cancer from primary research investigations.Primary outcome measureThe prevalence of clinical depression and anxiety in patients with prostate cancer as a function of treatment stage.ResultsWe identified 27 full journal articles that met the inclusion criteria for entry into the meta-analysis resulting in a pooled sample size of 4494 patients. The meta-analysis of prevalence rates identified pretreatment, on-treatment and post-treatment depression prevalences of 17.27% (95% CI 15.06% to 19.72%), 14.70% (95% CI 11.92% to 17.99%) and 18.44% (95% CI 15.18% to 22.22%), respectively. Pretreatment, on-treatment and post-treatment anxiety prevalences were 27.04% (95% CI 24.26% to 30.01%), 15.09% (95% CI 12.15% to 18.60%) and 18.49% (95% CI 13.81% to 24.31%), respectively.ConclusionsOur findings suggest that the prevalence of depression and anxiety in men with prostate cancer, across the treatment spectrum, is relatively high. In light of the growing emphasis placed on cancer survivorship, we consider that further research within this area is warranted to ensure that psychological distress in patients with prostate cancer is not underdiagnosed and undertreated
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