1,754 research outputs found
Lorentz-violating effects in the Bose-Einstein condensation of an ideal bosonic gas
We have studied the effects of Lorentz-violation in the Bose-Einstein
condensation (BEC) of an ideal boson gas, by assessing both the nonrelativistic
and ultrarelativistic limits. Our model describes a massive complex scalar
field coupled to a CPT-even and Lorentz-violating background. We irst analyze
the nonrelativistic case, at this level by using experimental data, we obtain
upper-bounds for some LIV parameters. In the sequel, we have constructed the
partition function for the relativistic ideal boson gas which to be able of a
consistent description requires the imposition of severe restrictions on some
LIV coefficients. In both cases, we have demonstrated that the LIV
contributions are contained in an overall factor, which multiplies almost all
thermodynamical properties. An exception is the fraction of the condensed
particles.Comment: 7 pages Latex2e. To be published in Modern Physics Letters
Qualitative Assessment of General Aviation Pilots’ Perceptions of Preflight Weather Briefings
Prior to departing on a flight, General Aviation pilots complete a pre-flight planning process to ensure the safety of their flight. One aspect of the pre-flight planning process is obtaining a briefing on the weather conditions that the pilot might encounter along their flight route. Traditionally pilots have utilized a phone-in service run by Flight Services to aid in their assessment of weather conditions. However, research indicates that pilots are increasingly reliant on conducting self- briefing using online resources. The purpose of this study is to determine pilot perceptions of obtaining a phone-in brief in comparison to self-briefing
Exposure to violence and PTSD symptoms among Somali women
Posttraumatic stress disorder (PTSD) symptoms, exposure to traumatic stressors, and health care utilization were examined in 84 women attending a primary health care clinic in Mogadishu, Somalia. The Somalia-Posttraumatic Diagnostic Scale was used in this active warzone to measure symptoms. Nearly all women reported high levels of confrontations with violence; half described being exposed to a potentially traumatizing event. Nearly one third had significant PTSD symptoms. Compared to those who did not, women who reported exposure to a traumatic stressor reported more confrontations with violence (7.1 vs. 3.3; p < . 001), health complaints (3.8 vs. 2.9; p = .03), and nearly 3 times as much (p = .03) health service utilization. A potentially traumatizing event was found to be a simplified proxy for assessing mental health distress in women attending a primary health care facility in highly insecure, unpredictable, resource-limited settings
Quasiblack holes with pressure: relativistic charged spheres as the frozen stars
In general relativity coupled to Maxwell's electromagnetism and charged
matter, when the gravitational potential and the electric potential field
obey a relation of the form , where , and are arbitrary constants, and (the
speed of light and Newton's constant are put to one), a class of very
interesting electrically charged systems with pressure arises. We call the
relation above between and , the Weyl-Guilfoyle relation, and it
generalizes the usual Weyl relation, for which . For both, Weyl and
Weyl-Guilfoyle relations, the electrically charged fluid, if present, may have
nonzero pressure. Fluids obeying the Weyl-Guilfoyle relation are called
Weyl-Guilfoyle fluids. These fluids, under the assumption of spherical
symmetry, exhibit solutions which can be matched to the electrovacuum
Reissner-Nordstr\"om spacetime to yield global asymptotically flat cold charged
stars. We show that a particular spherically symmetric class of stars found by
Guilfoyle has a well-behaved limit which corresponds to an extremal
Reissner-Nordstr\"om quasiblack hole with pressure, i.e., in which the fluid
inside the quasihorizon has electric charge and pressure, and the geometry
outside the quasihorizon is given by the extremal Reissner-Nordstr\"om metric.
The main physical properties of such charged stars and quasiblack holes with
pressure are analyzed. An important development provided by these stars and
quasiblack holes is that without pressure the solutions, Majumdar-Papapetrou
solutions, are unstable to kinetic perturbations. Solutions with pressure may
avoid this instability. If stable, these cold quasiblack holes with pressure,
i.e., these compact relativistic charged spheres, are really frozen stars.Comment: 16 pages, 8 figures; minor change
Intrusions related to indirectly experienced events in clinical offspring of World War Two survivors
Negative events may not only linger on in the form of intrusive memories in the minds of those directly exposed but also in those who are only indirectly confronted with these events. The aim of the present study was to investigate if intrusions referring to indirectly experienced traumatic events do indeed occur, and to compare their frequency and characteristics to intrusions about directly experienced negative events. Participants (N = 98) were adult postwar offspring of World War Two survivors currently in treatment in one of two clinics specialized in the treatment of war victims. We examined the frequency and characteristics of intrusions about indirectly experienced (i.e., parent war-related) events and two types of directly (self-) experienced events: Self-experienced traumatic events and negative events related to participants' upbringing. Intrusions referring to indirectly experienced traumatic events did indeed occur. The frequency as well as other characteristics of these intrusions did not differ from those of both types of intrusions about directly experienced events. The similarities between intrusions related to different types of events emphasize the (re)constructive nature of memory. Our findings indicate that traumatic events not only affect those directly involved but may also continue to plague the next generation
BLACK HOLES IN THREE-DIMENSIONAL DILATON GRAVITY THEORIES
Three dimensional black holes in a generalized dilaton gravity action theory
are analysed. The theory is specified by two fields, the dilaton and the
graviton, and two parameters, the cosmological constant and the Brans-Dicke
parameter. It contains seven different cases, of which one distinguishes as
special cases, string theory, general relativity and a theory equivalent to
four dimensional general relativity with one Killing vector. We study the
causal structure and geodesic motion of null and timelike particles in the
black hole geometries and find the ADM masses of the different solutions.Comment: 19 pages, latex, 4 figures as uuencoded postscript file
Quasi-black holes: definition and general properties
Objects that are on the verge of being extremal black holes but actually are
distinct in many ways are called quasi-black holes. Quasi-black holes are
defined here and treated in a unified way through the displaying of their
properties. The main ones are (i) there are infinite redshift whole regions,
(ii) the spacetimes exhibit degenerate, almost singular, features but their
curvature invariants remain perfectly regular everywhere, (iii) in the limit
under discussion, outer and inner regions become mutually impenetrable and
disjoint, although, in contrast to the usual black holes, this separation is of
a dynamical nature, rather than purely causal, (iv) for external far away
observers the spacetime is virtually indistinguishable from that of extremal
black holes. It is shown, in addition, that quasi-black holes must be extremal.
Connections with black hole and wormhole physics are also drawn.Comment: 29 pages, minor change
Exact boundary conditions at finite distance for the time-dependent Schrodinger equation
Exact boundary conditions at finite distance for the solutions of the
time-dependent Schrodinger equation are derived. A numerical scheme based on
Crank-Nicholson method is proposed to illustrate its applicability in several
examples.Comment: Latex.tar.gz file, 20 pages, 9 figure
Electron propagation in crossed magnetic and electric fields
Laser-atom interaction can be an efficient mechanism for the production of
coherent electrons. We analyze the dynamics of monoenergetic electrons in the
presence of uniform, perpendicular magnetic and electric fields. The Green
function technique is used to derive analytic results for the field--induced
quantum mechanical drift motion of i) single electrons and ii) a dilute Fermi
gas of electrons. The method yields the drift current and, at the same time it
allows us to quantitatively establish the broadening of the (magnetic) Landau
levels due to the electric field: Level number k is split into k+1 sublevels
that render the th oscillator eigenstate in energy space. Adjacent Landau
levels will overlap if the electric field exceeds a critical strength. Our
observations are relevant for quantum Hall configurations whenever electric
field effects should be taken into account.Comment: 11 pages, 2 figures, submitte
The number of transmission channels through a single-molecule junction
We calculate transmission eigenvalue distributions for Pt-benzene-Pt and
Pt-butadiene-Pt junctions using realistic state-of-the-art many-body
techniques. An effective field theory of interacting -electrons is used to
include screening and van der Waals interactions with the metal electrodes. We
find that the number of dominant transmission channels in a molecular junction
is equal to the degeneracy of the molecular orbital closest to the metal Fermi
level.Comment: 9 pages, 8 figure
- …