12,540 research outputs found
On Nilcompactifications of Prime Spectra of Commutative Rings
Given a ring R and S one of its ideals, we obtain a compactification of the
prime spectrum of S through a mainly algebraic process. We name it the
R-nilcompactification of SpecS. We study some categorical properties of this
construction.Comment: 12 pages, 8 Tikz figure
A numerical study of planar arrays of correlated spin islands
We present our analysis of a system of interacting islands of XY spins on a
triangular lattice that has been introduced a few years ago by Eley et al. to
account for the phenomenology in experiments on tunable arrays of proximity
coupled long superconductor-normal metal-superconductor junctions. The main
features of the model are the separation of a local and a global interaction
energy scale and the mesoscopic character of the spin islands. Upon lowering
the temperature the model undergoes two crossovers corresponding to an
increasing phase coherence on a single island and to the onset of global
coherence across the array; the latter is a thermodynamical phase transition in
the Ising universality class. The dependence of the second transition on the
island edge-to-edge spacing is related to the proximity-effect of the coupling
constant.Comment: 6 pages, 5 figures, accepted for publication in EPJ
The impact of the new Earth gravity model EIGEN-CG03C on the measurement of the Lense-Thirring effect with some existing Earth satellites
The impact of the latest combined CHAMP/GRACE/terrestrial measurements Earth
gravity model EIGEN-CG03C on the measurement of the Lense-Thirring effect with
some linear combinations of the nodes of some of the existing Earth's
artificial satellites is presented. The 1-sigma upper bound of the systematic
error in the node-node LAGEOS-LAGEOS II combination is 3.9% (4% with
EIGEN-GRACE02S, \sim 6% with EIGEN-CG01C and \sim 9% with GGM02S), while it is
1$% for the node-only LAGEOS-LAGEOS II-Ajisai-Jason-1 combination (2% with
EIGEN-GRACE02S, 1.6% with EIGEN-CG01C and 2.7% with GGM02S).Comment: LaTex2e, 7 pages, 16 references, 1 table. It is an update of the
impact of the even zonal harmonics of the geopotential on the Lense-Thirring
effect with the EIGEN-GGM03C Earth gravity model publicly released on May 11
2005. Typos corrected. Reference added. To appear in General Relativity and
Gravitation, March 200
Numerical study of barriers and valleys in the free-energy landscape of spin glasses
We study the problem of glassy relaxations in the presence of an external
field in the highly controlled context of a spin-glass simulation. We consider
a small spin glass in three dimensions (specifically, a lattice of size L=8,
small enough to be equilibrated through a Parallel Tempering simulations at low
temperatures, deep in the spin glass phase). After equilibrating the sample, an
external field is switched on, and the subsequent dynamics is studied. The
field turns out to reduce the relaxation time, but huge statistical
fluctuations are found when different samples are compared. After taking care
of these fluctuations we find that the expected linear regime is very narrow.
Nevertheless, when regarded as a purely numerical method, we find that the
external field is extremely effective in reducing the relaxation times.Comment: 22 pages, 10 figures; Published versio
Astrophysical parameters and orbital solution of the peculiar X-ray transient IGR J00370+6122
BD+6073 is the optical counterpart of the X-ray source IGR J00370+6122, a
probable accretion-powered X-ray pulsar. The X-ray light curve of this binary
system shows clear periodicity at 15.7 d, which has been interpreted as
repeated outbursts around the periastron of an eccentric orbit. We obtained
high-resolution spectra of BD+6073 at different epochs. We used the FASTWind
code to generate a stellar atmosphere model to fit the observed spectrum and
obtain physical magnitudes. The synthetic spectrum was used as a template for
cross-correlation with the observed spectra to measure radial velocities. The
radial velocity curve provided an orbital solution for the system. We have also
analysed the RXTE/ASM and Swift/BAT light curves to confirm the stability of
the periodicity. BD +6073 is a BN0.7 Ib low-luminosity supergiant located at an
approximate distance of 3.1 kpc, in the CasOB4 association. We derive
Teff=24000 K and log gc=3.0, and chemical abundances consistent with a
moderately high level of evolution. The spectroscopic and evolutionary masses
are consistent at the 1 sigma level with a mass of 15 solar masses. The
recurrence time of the X-ray flares is the orbital period of the system. The NS
is in a high eccentricity (e=0.56) orbit, and the X-ray emission is strongly
peaked around orbital phase 0.2, though the observations are consistent with
some level of X-ray activity happening at all orbital phases. The X-ray
behaviour of IGR J00370+6122 is reminiscent of intermediate SFXTs, though its
peak luminosity is rather low. The orbit is somewhat wider than those of
classical persistent supergiant X-ray binaries, which, combined with the low
luminosity of the mass donor, explains the low X-ray luminosity. IGR
J00370+6122 will likely evolve towards a persistent supergiant system,
highlighting the evolutionary connection between different classes of
wind-accreting X-ray sources.Comment: Accepted for publication in A&
An alternative derivation of the gravitomagnetic clock effect
The possibility of detecting the gravitomagnetic clock effect using
artificial Earth satellites provides the incentive to develop a more intuitive
approach to its derivation. We first consider two test electric charges moving
on the same circular orbit but in opposite directions in orthogonal electric
and magnetic fields and show that the particles take different times in
describing a full orbit. The expression for the time difference is completely
analogous to that of the general relativistic gravitomagnetic clock effect in
the weak-field and slow-motion approximation. The latter is obtained by
considering the gravitomagnetic force as a small classical non-central
perturbation of the main central Newtonian monopole force. A general expression
for the clock effect is given for a spherical orbit with an arbitrary
inclination angle. This formula differs from the result of the general
relativistic calculations by terms of order c^{-4}.Comment: LaTex2e, 11 pages, 1 figure, IOP macros. Submitted to Classical and
Quantum Gravit
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