7,856 research outputs found
Neutron matter under strong magnetic fields: a comparison of models
The equation of state of neutron matter is affected by the presence of a
magnetic field due to the intrinsic magnetic moment of the neutron. Here we
study the equilibrium configuration of this system for a wide range of
densities, temperatures and magnetic fields. Special attention is paid to the
behavior of the isothermal compressibility and the magnetic susceptibility. Our
calculation is performed using both microscopic and phenomenological approaches
of the neutron matter equation of state, namely the Brueckner--Hartree--Fock
(BHF) approach using the Argonne V18 nucleon-nucleon potential supplemented
with the Urbana IX three-nucleon force, the effective Skyrme model in a
Hartree--Fock description, and the Quantum Hadrodynamic formulation with a mean
field approximation. All these approaches predict a change from completely spin
polarized to partially polarized matter that leads to a continuous equation of
state. The compressibility and the magnetic susceptibility show characteristic
behaviors, which reflect that fact. Thermal effects tend to smear out the
sharpness found for these quantities at T=0. In most cases a thermal increase
of 10 MeV is enough to hide the signals of the change of polarization. The set
of densities and magnetic field intensities for which the system changes it
spin polarization is different for each model. However, there is an overall
agreement between the three theoretical descriptions.Comment: updated to correspond with the published versio
On the Conformal Geometry of Transverse Riemann-Lorentz Manifolds
Physical reasons suggested in \cite{Ha-Ha} for the \emph{Quantum Gravity
Problem} lead us to study \emph{type-changing metrics} on a manifold. The most
interesting cases are \emph{Transverse Riemann-Lorentz Manifolds}. Here we
study the conformal geometry of such manifolds
An 80 pc Long Massive Molecular Filament in the Galactic Mid-Plane
The ubiquity of filaments in star forming regions on a range of scales is
clear, yet their role in the star formation process remains in question. We
suggest that there are distinct classes of filaments which are responsible for
their observed diversity in star-forming regions. An example of a massive
molecular filament in the Galactic mid-plane formed at the intersection of
UV-driven bubbles which displays a coherent velocity structure (< 4 km/s) over
80 pc is presented. We classify such sources as Massive Molecular Filaments
(MMFs; M > 10^4 Msun, length > 10 pc, velocity gradient < 5 km/s) and suggest
that MMFs are just one of the many different classes of filaments discussed in
the literature today. Many MMFs are aligned with the Galactic Plane and may be
akin to the dark dust lanes seen in Grand Design Spirals.Comment: To appear in proceedings of the 'Labyrinth of Star Formation' meeting
(18-22 June 2012, Chania, Greece), published by Springe
Ion Beams in Multi-Species Plasma
Argon and xenon ion velocity distribution functions are measured in Ar-He, Ar-Xe, and Xe-He expanding helicon plasmas to determine if ion beam velocity is enhanced by the presence of lighter ions. Contrary to observations in mixed gas sheath experiments, we find that adding a lighter ion does not increase the ion beam speed. The predominant effect is a reduction of ion beam velocity consistent with increased drag arising from increased gas pressure under all conditions: constant total gas pressure, equal plasma densities of different ions, and very different plasma densities of different ions. These results suggest that the physics responsible for the acceleration of multiple ion species in simple sheaths is not responsible for the ion acceleration observed in expanding helicon plasmas
Measuring the properties of extragalactic dust and implications for the Hubble diagram
Scattering and absorption of light by a homogeneous distribution of
intergalactic large dust grains has been proposed as an alternative,
non-cosmological explanation for the faintness of Type Ia supernovae at z\s im
0.5. We investigate the differential extinction for high-redshift sources
caused by extragalactic dust along the line of sight.
Future observations of Type Ia supernovae up to , e.g. by the
proposed SNAP satellite, will allow the measurement of the properties of dust
over cosmological distances. We show that 1% {\em relative} spectrophotometric
accuracy (or broadband photometry) in the wavelength interval 0.7--1.5 m
is required to measure the extinction caused by ``grey'' dust down to magnitudes.
We also argue that the presence of grey dust is not necessarily inconsistent
with the recent measurement of the brightness of a supernova at (SN
1997ff), in the absence of accurate spectrophotometric information of the
supernova.Comment: Accepted by A&
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