22,413 research outputs found
Central Compact Objects in Supernova Remnants
Central Compact Objects (CCOs) are a handful of sources located close to the
geometrical center of young supernova remnants. They only show thermal-like,
soft X-ray emission and have no counterparts at any other wavelength. While the
first observed CCO turned out to be a very peculiar magnetar, discovery that
three members of the family are weakly magnetised Isolated Neutron Stars (INSs)
set the basis for an interpretation of the class. However, the phenomeology of
CCOs and their relationship with other classes of INSs, possibly ruled by
supernova fall-back accretion, are still far from being well understood.Comment: 7 pages, to appear in the proceedings of "Physics of Neutron Stars -
2017" Conference (July 10-14, Saint Petersburg), JPCS, eds. G.G. Pavlov, J.A.
Pons, P.S. Shternin & D.G. Yakovle
First Order Phase Transition and Phase Coexistence in a Spin-Glass Model
We study the mean-field static solution of the Blume-Emery-Griffiths-Capel
model with quenched disorder, an Ising-spin lattice gas with quenched random
magnetic interaction. The thermodynamics is worked out in the Full Replica
Symmetry Breaking scheme. The model exhibits a high temperature/low density
paramagnetic phase. When the temperature is decreased or the density increased,
the system undergoes a phase transition to a Full Replica Symmetry Breaking
spin-glass phase. The nature of the transition can be either of the second
order
(like in the Sherrington-Kirkpatrick model) or, at temperature below a given
critical value (tricritical point), of the first order in the Ehrenfest sense,
with a discontinuous jump of the order parameter and a latent heat. In this
last case coexistence of phases occurs.Comment: 4 pages, 8 figure
Momentum coupling in non-Markovian Quantum Brownian motion
We consider a model of non-Markovian Quantum Brownian motion that consists of
an harmonic oscillator bilinearly coupled to a thermal bath, both via its
position and momentum operators. We derive the master equation for such a model
and we solve the equations of motion for a generic Gaussian system state. We
then investigate the resulting evolution of the first and second moments for
both an Ohmic and a super-Ohmic spectral density. In particular, we show that,
irrespective of the specific form of the spectral density, the coupling with
the momentum enhances the dissipation experienced by the system, accelerating
its relaxation to the equilibrium, as well as modifying the asymptotic state of
the dynamics. Eventually, we characterize explicitly the non-Markovianity of
the evolution, using a general criterion which relies on the positivity of the
master equation coefficients
Existence and non-existence results for the SU(3) singular Toda system on compact surfaces
We consider the SU(3) Toda system on a compact surface. We give both
existence and non-existence results under some conditions on the parameters.
Existence results are obtained using variational methods, which involve a
geometric inequality of new type; non-existence results are obtained using
blow-up analysis and localized Pohozaev identities.Comment: 41 pages, 9 figures, accepted on Journal of Functional Analysi
A Moser-Trudinger inequality for the singular Toda system
In this paper we prove a sharp version of the Moser-Trudinger inequality for
the Euler-Lagrange functional of a singular Toda system, motivated by the study
of models in Chern-Simons theory. Our result extends those for the scalar case,
as well as for the regular Toda system. We expect this inequality to be a basic
tool to attack variationally the existence problem under general assumptions.Comment: 13 pages, accepted on Bulletin of the Institute of Mathematica
Academia Sinic
Statistical characterization of spatio-temporal sediment dynamics in the Venice lagoon
Characterizing the dynamics of suspended sediment is crucial when investigating the long-term evolution of tidal landscapes. Here we apply a widely tested mathematical model which describes the dynamics of cohesive and noncohesive sediments, driven by the combined effect of tidal currents and wind waves, using 1 year long time series of observed water levels and wind data from the Venice lagoon. The spatiotemporal evolution of the computed suspended sediment concentration (SSC) is analyzed on the basis of the \u201cpeak over threshold\u201d theory. Our analysis suggests that events characterized by high SSC can be modeled as a marked Poisson process over most of the lagoon. The interarrival time between two consecutive over threshold events, the intensity of peak excesses, and the duration are found to be exponentially distributed random variables over most of tidal flats. Our study suggests that intensity and duration of over threshold events are temporally correlated, while almost no correlation exists between interarrival times and both durations and intensities. The benthic vegetation colonizing the central
southern part of the Venice lagoon is found to exert a crucial role on sediment dynamics: vegetation locally decreases the frequency of significant resuspension events by affecting patiotemporal patterns of SSCs also in adjacent areas. Spatial patterns of the mean interarrival of over threshold SSC events are found to be less heterogeneous than the corresponding patterns of mean interarrivals of over threshold bottom shear stress events because of the role of advection/dispersion processes in mixing suspended sediments within the lagoon. Implications for long-term morphodynamic modeling of tidal environments are discussed
Vlasov simulation of laser-driven shock acceleration and ion turbulence
We present a Vlasov, i.e. a kinetic Eulerian simulation study of nonlinear
collisionless ion-acoustic shocks and solitons excited by an intense laser
interacting with an overdense plasma. The use of the Vlasov code avoids
problems with low particle statistics and allows a validation of
particle-in-cell results. A simple original correction to the splitting method
for the numerical integration of the Vlasov equation has been implemented in
order to ensure the charge conservation in the relativistic regime. We show
that the ion distribution is affected by the development of a turbulence driven
by the relativistic "fast" electron bunches generated at the laser-plasma
interaction surface. This leads to the onset of ion reflection at the shock
front in an initially cold plasma where only soliton solutions without ion
reflection are expected to propagate. We give a simple analytic model to
describe the onset of the turbulence as a nonlinear coupling of the ion density
with the fast electron currents, taking the pulsed nature of the relativistic
electron bunches into account
Thermal signatures of human pheromones in sexual and reproductive behaviour
Chemically mediated sexual communication in humans has been largely neglected due to its non-conscious and relatively concealed nature. However, menstrual cycle synchronisation, puberty onset in young pre-pubertal girls exposed to their stepfather, and consanguinity avoidance suggest a function in the physiological regulation of sexual and reproductive behaviour in humans. These phenomena are related to activation of the limbic system by pheromones. On the basis of sexually dimorphic activation of brain hypothalamic areas and the control of body temperature via the hypothalamus, our hypothesis is that human sexual pheromones can induce thermal effects that can be revealed by high-resolution thermal infrared imaging. Here we show that in women, male sexual pheromones induce thermal effects that are linked to the ovarian cycle. These findings suggest a dramatic influence of pheromones on human sexual and reproductive behaviour through neuroendocrine brain control, established on the plesiomorphic nature of chemical communication across species
- …