1,298 research outputs found
An Effective Lagrangian with Broken Scale and Chiral Symmetry IV: Nucleons and Mesons at Finite Temperature
We study the finite temperature properties of an effective chiral Lagrangian
which describes nuclear matter. Thermal fluctuations in both the nucleon and
the meson fields are considered. The logarithmic and square root terms in the
effective potential are evaluated by expansion and resummation with the result
written in terms of the exponential integral and the error function,
respectively. In the absence of explicit chiral symmetry breaking a phase
transition restores the symmetry, but when the pion has a mass the transition
is smooth. The nucleon and meson masses as a functions of density and
temperature are discussed.Comment: 21 pages LaTeX + 11 postscript figures, uses epsf.st
Involvement of the agmatinergic system in the depressive-like phenotype of the Crtc1 knockout mouse model of depression.
Recent studies implicate the arginine-decarboxylation product agmatine in mood regulation. Agmatine has antidepressant properties in rodent models of depression, and agmatinase (Agmat), the agmatine-degrading enzyme, is upregulated in the brains of mood disorder patients. We have previously shown that mice lacking CREB-regulated transcription coactivator 1 (CRTC1) associate behavioral and molecular depressive-like endophenotypes, as well as blunted responses to classical antidepressants. Here, the molecular basis of the behavioral phenotype of Crtc1(-/-) mice was further examined using microarray gene expression profiling that revealed an upregulation of Agmat in the cortex of Crtc1(-/-) mice. Quantitative polymerase chain reaction and western blot analyses confirmed Agmat upregulation in the Crtc1(-/-) prefrontal cortex (PFC) and hippocampus, which were further demonstrated by confocal immunofluorescence microscopy to comprise an increased number of Agmat-expressing cells, notably parvalbumin- and somatostatin-positive interneurons. Acute agmatine and ketamine treatments comparably improved the depressive-like behavior of male and female Crtc1(-/-) mice in the forced swim test, suggesting that exogenous agmatine has a rapid antidepressant effect through the compensation of agmatine deficit because of upregulated Agmat. Agmatine rapidly increased brain-derived neurotrophic factor (BDNF) levels only in the PFC of wild-type (WT) females, and decreased eukaryotic elongation factor 2 (eEF2) phosphorylation in the PFC of male and female WT mice, indicating that agmatine might be a fast-acting antidepressant with N-methyl-D-aspartate (NMDA) receptor antagonist properties. Collectively, these findings implicate Agmat in the depressive-like phenotype of Crtc1(-/-) mice, refine current understanding of the agmatinergic system in the brain and highlight its putative role in major depression
Dilatonic current-carrying cosmic strings
We investigate the nature of ordinary cosmic vortices in some scalar-tensor
extensions of gravity. We find solutions for which the dilaton field condenses
inside the vortex core. These solutions can be interpreted as raising the
degeneracy between the eigenvalues of the effective stress-energy tensor,
namely the energy per unit length U and the tension T, by picking a privileged
spacelike or timelike coordinate direction; in the latter case, a phase
frequency threshold occurs that is similar to what is found in ordinary neutral
current-carrying cosmic strings. We find that the dilaton contribution for the
equation of state, once averaged along the string worldsheet, vanishes, leading
to an effective Nambu-Goto behavior of such a string network in cosmology, i.e.
on very large scales. It is found also that on small scales, the energy per
unit length and tension depend on the string internal coordinates in such a way
as to permit the existence of centrifugally supported equilibrium
configuration, also known as vortons, whose stability, depending on the very
short distance (unknown) physics, can lead to catastrophic consequences on the
evolution of the Universe.Comment: 10 pages, ReVTeX, 2 figures, minor typos corrected. This version to
appear in Phys. Rev.
A hidden crisis: strengthening the evidence base on the sustainability of rural groundwater supplies: results from a pilot study in Uganda
Extending and sustaining access to rural water supplies remains central to improving the health and
livelihoods of poor people, particularly women, in Africa, where 400 million rural inhabitants have no
form of utility provided water, and universal access to water hinges on accelerated development of
groundwater (UN 2013). The âfuture proofingâ of groundwater investments is therefore vital,
especially in the context of global and local trends including demographic shifts, environmental
impacts of human activity and climate change (Taylor et al. 2013).
The emphasis, in recent years, on accelerating access to new infrastructure has obscured a hidden
crisis of failure. More than 30% of sources are nonâfunctional within a few years of construction
(Rietveld et al. 2009, RWSN 2009, Lockwood et al. 2011) and a greater number are seasonal (for
example 50% in Sierra Leone) (MoEWR 2012). The accumulated costs to governments, donors, and,
above all, rural people, are enormous. The original benefits generated by the new infrastructure â
improved health, nutrition, time savings, education, particularly for the poorest â are lost if
improved services cannot be sustained. The cumulative effect of rural water supply failure in Africa
over the past 20 years has been estimated by the World Bank to represent a lost investment in
excess of $1.2 billion.
Critically, there is limited data or analysis on why sources are nonâfunctional and therefore little
opportunity to learn from past mistakes.
This report provides a summary of the work undertaken by the UKâfunded UPGro research
programme ('Unlocking the Potential for Groundwater for the Poor') for subâSaharan Africa (SSA)
funded by the Natural Environment Research Council (NERC), the Economic and Social Research
Council (ESRC) and the Department for International Development (DfID). The Catalyst Grant project
âA Hidden Crisisâ was aimed at developing a methodology and toolbox to investigate the causes of
failure in groundwaterâbased water services in SSA, which could form the foundation for more
substantial and largerâscale research in the future to develop a statistically significant evidence base
to examine water point functionality and the underlying causes of failure across a range of physical,
social, institutional and governance environments in SSA. To test the toolbox and methodology
developed, a pilot study was conducted in northeast Uganda
Overall, the approach and methods developed in the catalyst project have been shown to make a
significant step towards developing a replicable and robust methodology which can be used to
generate a systematic evidence base for supply failure. The work has gone a significant way to
encapsulating the complexity of the interlinked aspects of the problem, balancing the natural science
and engineering (âtechnicalâ) aspects of the research with those concerning the ability of
communities to manage and maintain their water points (the âsocialâ aspects). The multiplicity of
interlinked causes of water point failure was explicitly acknowledged and taken into account through
the use of multiâdisciplinary field and analytical methods within the toolbox and in selection of the
research team. The multiâdisciplinary methods of investigation used were highly practical and
appropriate to the information sought, and based on detailed observational science
Impurity effects on s+g-wave superconductivity in borocarbides Y(Lu)Ni_2B_2C
Recently a hybrid s+g-wave pairing is proposed to describe the experimental
observation for a nodal structure of the superconducting gap in borocarbide
YNiBC and possibly LuNiBC. In this paper the impurity effects
on the s+g-wave superconductivity are studied in both Born and unitarity limit.
The quasiparticle density of states and thermodynamics are calculated. It is
found that the nodal excitations in the clean system are immediately prohibited
by impurity scattering and a finite energy gap increases quickly with the
impurity scattering rate. This leads to an activated behavior in the
temperature dependence of the specific heat. Qualitative agreement with the
experimental results is shown. Comparison with d-wave and some anisotropic
s-wave studied previously is also made.Comment: 6 pages, 6 eps figure
Counter-intuitive influence of Himalayan river morphodynamics on Indus Civilisation urban settlements
Urbanism in the Bronze-age Indus Civilisation (~4.6â3.9 thousand years before the present, ka) has been linked to water resources provided by large Himalayan river systems, although the largest concentrations of urban-scale Indus settlements are located far from extant Himalayan rivers. Here we analyse the sedimentary architecture, chronology and provenance of a major palaeochannel associated with many of these settlements. We show that the palaeochannel is a former course of the Sutlej River, the third largest of the present-day Himalayan rivers. Using optically stimulated luminescence dating of sand grains, we demonstrate that flow of the Sutlej in this course terminated considerably earlier than Indus occupation, with diversion to its present course complete shortly after ~8âka. Indus urban settlements thus developed along an abandoned river valley rather than an active Himalayan river. Confinement of the Sutlej to its present incised course after ~8âka likely reduced its propensity to re-route frequently thus enabling long-term stability for Indus settlements sited along the relict palaeochannel
Tight-binding g-Factor Calculations of CdSe Nanostructures
The Lande g-factors for CdSe quantum dots and rods are investigated within
the framework of the semiempirical tight-binding method. We describe methods
for treating both the n-doped and neutral nanostructures, and then apply these
to a selection of nanocrystals of variable size and shape, focusing on
approximately spherical dots and rods of differing aspect ratio. For the
negatively charged n-doped systems, we observe that the g-factors for
near-spherical CdSe dots are approximately independent of size, but show strong
shape dependence as one axis of the quantum dot is extended to form rod-like
structures. In particular, there is a discontinuity in the magnitude of
g-factor and a transition from anisotropic to isotropic g-factor tensor at
aspect ratio ~1.3. For the neutral systems, we analyze the electron g-factor of
both the conduction and valence band electrons. We find that the behavior of
the electron g-factor in the neutral nanocrystals is generally similar to that
in the n-doped case, showing the same strong shape dependence and discontinuity
in magnitude and anisotropy. In smaller systems the g-factor value is dependent
on the details of the surface model. Comparison with recent measurements of
g-factors for CdSe nanocrystals suggests that the shape dependent transition
may be responsible for the observations of anomalous numbers of g-factors at
certain nanocrystal sizes.Comment: 15 pages, 6 figures. Fixed typos to match published versio
A perspective on the landscape problem
I discuss the historical roots of the landscape problem and propose criteria
for its successful resolution. This provides a perspective to evaluate the
possibility to solve it in several of the speculative cosmological scenarios
under study including eternal inflation, cosmological natural selection and
cyclic cosmologies.Comment: Invited contribution for a special issue of Foundations of Physics
titled: Forty Years Of String Theory: Reflecting On the Foundations. 31
pages, no figure
A hidden crisis: strengthening the evidence base on the current failure of rural groundwater supplies
New ambitious international goals for universal access to safe drinking water depend critically on the ability of development partners to accelerate and sustain access to groundwater. However, available evidence (albeit fragmented and methodologically unclear) indicates >30% of new groundwater-based supplies are non-functional within a few years of construction. Critically, in the absence of a significant systematic evidence base or analysis on supply failures, there is little opportunity to learn from past mistakes, to ensure more sustainable services can be developed in the future. This work presents a new and robust methodology for investigating the causes of non-functionality, developed by an interdisciplinary team as part of a UK-funded development research project. The approach was successfully piloted within a test study in NE Uganda, and forms a basis for future research to develop a statistically significant systematic evidence base to unravel the underlying causes of failur
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