570 research outputs found
Absorption Line Studies in the Halo
Significant progress has been made over the last few years to explore the
gaseous halo of the Milky Way by way of absorption spectroscopy. I review
recent results on absorption line studies in the halo using various
instruments, such as the Far Ultraviolet Spectroscopic Explorer, the Space
Telescope Imaging Spectrograph, and others. The new studies imply that the
infall of low-metallicity gas, the interaction with the Magellanic Clouds, and
the Galactic Fountain are responsible for the phenomenon of the intermediate-
and high-velocity clouds in the halo. New measurements of highly-ionized gas in
the vicinity of the Milky Way indicate that these clouds are embedded in a
corona of hot gas that extends deep into the intergalactic space.Comment: 7 pages, 1 figure; Invited review at the conference "How does the
Galaxy work ?", Granada/Spain, June 200
The directed flow maximum near c_s=0
We investigate the excitation function of quark-gluon plasma formation and of
directed in-plane flow of nucleons in the energy range of the BNL-AGS and for
the E(Lab)=40AGeV Pb+Pb collisions performed recently at the CERN-SPS. We
employ the three-fluid model with dynamical unification of kinetically
equilibrated fluid elements. Within our model with first-order phase transition
at high density, droplets of QGP coexisting with hadronic matter are produced
already at BNL-AGS energies, E(Lab)=10AGeV. A substantial decrease of the
isentropic velocity of sound, however, requires higher energies, E(Lab)=40AGeV.
We show the effect on the flow of nucleons in the reaction plane. According to
our model calculations, kinematic requirements and EoS effects work
hand-in-hand at E(Lab)=40AGeV to allow the observation of the dropping velocity
of sound via an increase of the directed flow around midrapidity as compared to
top BNL-AGS energy.Comment: 10 pages, 4 figures; plot of p(e) at various specific entropies shows
why mixed phase is not soft at AGS energ
The temporal dynamics of Arc expression regulate cognitive flexibility
YesNeuronal activity regulates the transcription and
translation of the immediate-early gene Arc/Arg3.1,
a key mediator of synaptic plasticity. Proteasomedependent
degradation of Arc tightly limits its
temporal expression, yet the significance of this
regulation remains unknown. We disrupted the temporal
control of Arc degradation by creating an Arc
knockin mouse (ArcKR) where the predominant Arc
ubiquitination sites were mutated. ArcKR mice had
intact spatial learning but showed specific deficits
in selecting an optimal strategy during reversal
learning. This cognitive inflexibility was coupled to
changes in Arc mRNA and protein expression resulting
in a reduced threshold to induce mGluR-LTD and
enhanced mGluR-LTD amplitude. These findings
show that the abnormal persistence of Arc protein
limits the dynamic range of Arc signaling pathways
specifically during reversal learning. Our work
illuminates how the precise temporal control of activity-dependent
molecules, such as Arc, regulates synaptic
plasticity and is crucial for cognition.Open access funded by Biotechnology and Biological Sciences Research Counci
One-Loop Matching of the Heavy-Light A_0 and V_0 Currents with NRQCD Heavy and Improved Naive Light Quarks
One-loop matching of heavy-light currents is carried out for a highly
improved lattice action, including the effects of dimension 4 O(1/M) and O(a)
operators. We use the NRQCD action for heavy quarks, the Asqtad improved naive
action for light quarks, and the Symanzik improved glue action. As part of the
matching procedure we also present results for the NRQCD self energy and for
massless Asqtad quark wavefunction renormalization with improved glue.Comment: 25 pages, 3 eps-figure
Excluded Volume Effects in the Quark Meson Coupling Model
Excluded volume effects are incorporated in the quark meson coupling model to
take into account in a phenomenological way the hard core repulsion of the
nuclear force. The formalism employed is thermodynamically consistent and does
not violate causality. The effects of the excluded volume on in-medium nucleon
properties and the nuclear matter equation of state are investigated as a
function of the size of the hard core. It is found that in-medium nucleon
properties are not altered significantly by the excluded volume, even for large
hard core radii, and the equation of state becomes stiffer as the size of the
hard core increases.Comment: 14 pages, revtex, 6 figure
Talk the talk, walk the walk: Defining Critical Race Theory in research
Over the last decade there has been a noticeable growth in published works citing Critical Race Theory (CRT). This has led to a growth in interest in the UK of practical research projects utilising CRT as their framework. It is clear that research on 'race' is an emerging topic of study. What is less visible is a debate on how CRT is positioned in relation to methodic practice, substantive theory and epistemological underpinnings. The efficacy of categories of data gathering tools, both traditional and non-traditional is a discussion point here to explore the complexities underpinning decisions to advocate a CRT framework. Notwithstanding intersectional issues, a CRT methodology is recognisable by how philosophical, political and ethical questions are established and maintained in relation to racialised problematics. This paper examines these tensions in establishing CRT methodologies and explores some of the essential criteria for researchers to consider in utilising a CRT framework. © 2012 Copyright Taylor and Francis Group, LLC
Scaling critical behavior of superconductors at zero magnetic field
We consider the scaling behavior in the critical domain of superconductors at
zero external magnetic field. The first part of the paper is concerned with the
Ginzburg-Landau model in the zero magnetic field Meissner phase. We discuss the
scaling behavior of the superfluid density and we give an alternative proof of
Josephson's relation for a charged superfluid. This proof is obtained as a
consequence of an exact renormalization group equation for the photon mass. We
obtain Josephson's relation directly in the form , that
is, we do not need to assume that the hyperscaling relation holds. Next, we
give an interpretation of a recent experiment performed in thin films of
. We argue that the measured mean field like
behavior of the penetration depth exponent is possibly associated with a
non-trivial critical behavior and we predict the exponents and
for the correlation lenght and specific heat, respectively. In the
second part of the paper we discuss the scaling behavior in the continuum dual
Ginzburg-Landau model. After reviewing lattice duality in the Ginzburg-Landau
model, we discuss the continuum dual version by considering a family of
scalings characterized by a parameter introduced such that
, where is the bare mass of the magnetic
induction field. We discuss the difficulties in identifying the renormalized
magnetic induction mass with the photon mass. We show that the only way to have
a critical regime with is having , that
is, with having the scaling behavior of the renormalized photon mass.Comment: RevTex, 15 pages, no figures; the subsection III-C has been removed
due to a mistak
Absolute Proper Motions to B~22.5: IV. Faint, Low Velocity White Dwarfs and the White Dwarf Population Density Law
The reduced proper motion diagram (RPMD) for a complete sample of faint stars
with high accuracy proper motions in the North Galactic Pole field SA57 is
investigated. Eight stars with very large reduced proper motions are identified
as faint white dwarf candidates. We discriminate these white dwarf candidates
from the several times more numerous QSOs based on proper motion and
variability.
We discuss the implausibility that these stars could be any kind of survey
contaminant. If {\it bona fide} white dwarfs, the eight candidates found here
represent a portion of the white dwarf population hitherto uninvestigated by
previous surveys by virtue of the faint magnitudes and low proper motions. The
newly discovered stars suggest a disk white dwarf scaleheight larger than the
values of 250-350 pc typically assumed in assessments of the local white dwarf
density. Both a <V/V_{max}> and a more complex maximum likelihood analysis of
the spatial distribution of our likely thin disk white dwarfs yield
scaleheights of 400-600 pc while at the same time give a reasonable match to
the local white dwarf volume density found in other surveys.
Our results could have interesting implications for white dwarfs as potential
MACHO objects. We can place some direct constraints (albeit weak ones) on the
contribution of halo white dwarfs to the dark matter of the Galaxy. Moreover,
the elevated scale height that we measure for the thin disk could alter the
interpretation of microlensing results to the extent of making white dwarfs
untenable as the dominant MACHO contributor. (Abridged)Comment: 38 pages, 5 figures, to appear in April Ap
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