812 research outputs found
Dim Isolated Neutron Stars, Cooling and Energy Dissipation
The cooling and reheating histories of dim isolated neutron stars(DINs) are
discussed. Energy dissipation due to dipole spindown with ordinary and magnetar
fields, and due to torques from a fallback disk are considered as alternative
sources of reheating which would set the temperature of the neutron star after
the initial cooling era. Cooling or thermal ages are related to the numbers and
formation rates of the DINs and therefore to their relations with other
isolated neutron star populations. Interaction with a fallback disk, higher
multipole fields and activity of the neutron star are briefly discussed.Comment: To appear in Astrophysics and Space Science, in the proceedings of
the conference "Isolated Neutron Stars: from the Interior to the Surface",
London, April 2006; eds. D. Page, R. Turolla and S. Zane. Revised version:
with minor change and typos correcte
Persistent and Transient Blank Field Sources
Blank field sources (BFS) are good candidates for hosting dim isolated
neutron stars (DINS). The results of a search of BFS in the ROSAT HRI images
are revised. We then focus on transient BFS, arguing that they belong to a
rather large population. The perspectives of future research on DINS are then
discussed.Comment: 3 pages, 0 figures. Paper presented at the Conference "Isolated
Neutron Stars: from the interior to the surface", London, April 2006.
Astrophysics and Space Science, in pres
Tkachenko waves, glitches and precession in neutron star
Here I discuss possible relations between free precession of neutron stars,
Tkachenko waves inside them and glitches. I note that the proposed precession
period of the isolated neutron star RX J0720.4-3125 (Haberl et al. 2006) is
consistent with the period of Tkachenko waves for the spin period 8.4s. Based
on a possible observation of a glitch in RX J0720.4-3125 (van Kerkwijk et al.
2007), I propose a simple model, in which long period precession is powered by
Tkachenko waves generated by a glitch. The period of free precession,
determined by a NS oblateness, should be equal to the standing Tkachenko wave
period for effective energy transfer from the standing wave to the precession
motion. A similar scenario can be applicable also in the case of the PSR
B1828-11.Comment: 6 pages, no figures, accepted to Ap&S
The beta function of N=1 SYM in Differential Renormalization
Using differential renormalization, we calculate the complete two-point
function of the background gauge superfield in pure N=1 Supersymmetric
Yang-Mills theory to two loops. Ultraviolet and (off-shell) infrared
divergences are renormalized in position and momentum space respectively. This
allows us to reobtain the beta function from the dependence on the ultraviolet
renormalization scale in an infrared-safe way. The two-loop coefficient of the
beta function is generated by the one-loop ultraviolet renormalization of the
quantum gauge field via nonlocal terms which are infrared divergent on shell.
We also discuss the connection of the beta function to the flow of the
Wilsonian coupling.Comment: 20 pages, 2 figures. Reference added, minor correction
Hysteretic damper based on Bouc-Wen model
In the presented work we consider the dynamics of the mechanical system under internal force with a damper taking into account the hysteretic nature of the damper. As a mathematical model of this hysteretic damper we consider the Bouc-Wen model. The obtained numerical results in the form of the force transfer function demonstrates the efficiency of the hysteretic damper in comparison with the nonlinear viscous damper.This work is supported by the RFBR grant No 16-08-00312, 17-01-00251
Boundary element formulations for the numerical solution of two-dimensional diffusion problems with variable coefficients
This is the post-print version of the final paper published in Computers & Mathematics with Applications. The published article is available from the link below. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. Copyright @ 2012 Elsevier B.V.This paper presents new formulations of the radial integration boundary integral equation (RIBIE) and the radial integration boundary integro-differential equation (RIBIDE) methods for the numerical solution of two-dimensional diffusion problems with variable coefficients. The methods use either a specially constructed parametrix (Levi function) or the standard fundamental solution for the Laplace equation to reduce the boundary-value problem (BVP) to a boundary–domain integral equation (BDIE) or boundary–domain integro-differential equation (BDIDE). The radial integration method (RIM) is then employed to convert the domain integrals arising in both BDIE and BDIDE methods into equivalent boundary integrals. The resulting formulations lead to pure boundary integral and integro-differential equations with no domain integrals. Furthermore, a subdomain decomposition technique (SDBDIE) is proposed, which leads to a sparse system of linear equations, thus avoiding the need to calculate a large number of domain integrals. Numerical examples are presented for several simple problems, for which exact solutions are available, to demonstrate the efficiency of the proposed approaches
Chandra Smells a RRAT: X-ray Detection of a Rotating Radio Transient
"Rotating RAdio Transients" (RRATs) are a newly discovered astronomical
phenomenon, characterised by occasional brief radio bursts, with average
intervals between bursts ranging from minutes to hours. The burst spacings
allow identification of periodicities, which fall in the range 0.4 to 7
seconds. The RRATs thus seem to be rotating neutron stars, albeit with
properties very different from the rest of the population. We here present the
serendipitous detection with the Chandra X-ray Observatory of a bright
point-like X-ray source coincident with one of the RRATs. We discuss the
temporal and spectral properties of this X-ray emission, consider counterparts
in other wavebands, and interpret these results in the context of possible
explanations for the RRAT population.Comment: 5 pages, 2 b/w figures, 1 color figure. To appear in the proceedings
of "Isolated Neutron Stars", Astrophysics & Space Science, in pres
Variational self-consistent theory for trapped Bose gases at finite temperature
We apply the time-dependent variational principle of Balian-V\'en\'eroni to a
system of self-interacting trapped bosons at finite temperature. The method
leads to a set of coupled non-linear time dependent equations for the
condensate density, the thermal cloud and the anomalous density. We solve
numerically these equations in the static case for a harmonic trap. We analyze
the various densities as functions of the radial distance and the temperature.
We find an overall good qualitative agreement with recent experiments as well
as with the results of many theoretical groups. We also discuss the behavior of
the anomalous density at low temperatures owing to its importance to account
for many-body effects.Comment: 8 pages, 8 figure
Microstructure evolution during warm working of Ti–5Al–5Mo–5V–1Cr–1Fe at 600 and 800 °C
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