865 research outputs found
Longwave radiation parameterization for UCLA/GLAS GCM
This document describes the parameterization of longwave radiation in the UCLA/GLAS general circulation model. Transmittances have been computed from the work of Arking and Chou for water vapor and carbon dioxide and ozone absorptances are computed using a formula due to Rodgers. Cloudiness has been introduced into the code in a manner in which fractional cover and random or maximal overlap can be accommodated. The entire code has been written in a form that is amenable to vectorization on CYBER and CRAY computers. Sample clear sky computations for five standard profiles using the 15- and 9-level versions of the model have been included
Exposure to antibiotics and neurodevelopmental disorders: could probiotics modulate the gut–brain axis?
In order to develop properly, the brain requires the intricate interconnection of genetic factors and pre-and postnatal environmental events. The gut–brain axis has recently raised considerable interest for its involvement in regulating the development and functioning of the brain. Consequently, alterations in the gut microbiota composition, due to antibiotic administration, could favor the onset of neurodevelopmental disorders. Literature data suggest that the modulation of gut microbiota is often altered in individuals affected by neurodevelopmental disorders. It has been shown in animal studies that metabolites released by an imbalanced gut–brain axis, leads to alterations in brain function and deficits in social behavior. Here, we report the potential effects of antibiotic administration, before and after birth, in relation to the risk of developing neurodevelopmental disorders. We also review the potential role of probiotics in treating gastrointestinal disorders associated with gut dysbiosis after antibiotic administration, and their possible effect in ameliorating neurodevelopmental disorder symptoms
Debt Sustainability and the Terms of Official Support
We study theoretically and quantitatively how official lending regimes affect a government's decision to raise saving as opposed to defaulting, and its implication for sovereign bond pricing by investors. We reconsider debt sustainability in the face of both output and rollover risk under two types of institutional bailouts: one based on long-maturity, low-spread loans similar to the ones offered by the euro area official lenders; the other, on shorter maturity and high-spread loans, close to the International Monetary Fund standards. We show that official lending regimes raise the stock of safe debt and facilitate consumption smoothing through debt reduction. However, to the extent that bailouts translates into higher future debt stocks and countercyclical deficits in persistent recessions, they also have countervailing effects on sustainability. Quantitatively, the model is able to replicate Portuguese debt and spread dynamics in the years of the bailout after 2011. We show that, depending on the composition of debt by maturity and official lending, sustainable debt levels can vary between 50% of GDP and 180% of GDP depending on the state of the economy and the conditions for market access. Longer maturities have a stronger effect on sustainability than lower spreads
Official Sector Lending Strategies During the Euro Area Crisis
In response to the euro area crisis, European policymakers took a gradual, incremental approach to official lending, at first relying on the approach followed by the International Monetary Fund, then developing their own crisis resolution framework. We review this development, marked by a substantial divergence in the terms of official loans offered to the crisis countries by the IMF and the euro area official lenders. Based on a unique dataset, we use event analysis to assess the impact of changing maturity and spreads of official loans on bond yields, liquidity and market access. In light of the euro area experience, we discuss arguments for rebalancing Debt Sustainability Analysis and programme design towards cash-flow management. While the official assistance granted to crisis countries in the euro area may not be replicable elsewhere, key lessons from it that could foster a reconsideration of the modalities by which official lending institutions handle crises
Higgsino Dark Matter in a SUGRA Model with Nonuniversal Gaugino Masses
We study a specific SUGRA model with nonuniversal gaugino masses as an
alternative to the minimal SUGRA model in the context of supersymmetric dark
matter. The lightest supersymmetric particle in this model comes out to be a
Higgsino dominated instead of a bino dominated lightest neutralino. The thermal
relic density of this Higgsino dark matter is somewhat lower than the
cosmologically favoured range, which means it may be only a subdominant
component of the cold dark matter. Nonetheless, it predicts favourable rates of
indirect detection, which can be seen in square-km size neutrino telescopes.Comment: Version to appear in Phys. Rev. D. A few references added in the
bibliography and a comment added in Section 2. LaTex, 16 pages, 4 figure
QuantumATK: An integrated platform of electronic and atomic-scale modelling tools
QuantumATK is an integrated set of atomic-scale modelling tools developed
since 2003 by professional software engineers in collaboration with academic
researchers. While different aspects and individual modules of the platform
have been previously presented, the purpose of this paper is to give a general
overview of the platform. The QuantumATK simulation engines enable
electronic-structure calculations using density functional theory or
tight-binding model Hamiltonians, and also offers bonded or reactive empirical
force fields in many different parametrizations. Density functional theory is
implemented using either a plane-wave basis or expansion of electronic states
in a linear combination of atomic orbitals. The platform includes a long list
of advanced modules, including Green's-function methods for electron transport
simulations and surface calculations, first-principles electron-phonon and
electron-photon couplings, simulation of atomic-scale heat transport, ion
dynamics, spintronics, optical properties of materials, static polarization,
and more. Seamless integration of the different simulation engines into a
common platform allows for easy combination of different simulation methods
into complex workflows. Besides giving a general overview and presenting a
number of implementation details not previously published, we also present four
different application examples. These are calculations of the phonon-limited
mobility of Cu, Ag and Au, electron transport in a gated 2D device, multi-model
simulation of lithium ion drift through a battery cathode in an external
electric field, and electronic-structure calculations of the
composition-dependent band gap of SiGe alloys.Comment: Submitted to Journal of Physics: Condensed Matte
International Emission Policy with Lobbying and Technological Change
I examine the implementation of emission policy in a union of countries. Production in any country incurs emissions that pollute all over the union, but efficiency in production can be improved by research and development (R&D). I compare four cases: laissez-faire, Pareto optimal policy, lobbying with centrally-determined emission quotas and lobbying with emission trade. The main findings are as follows. With emission quotas, the growth rate is socially optimal, but welfare sub-optimal. Emission trade speeds up growth from the initial position of laissez-faire, but slows down from the initial position of centrally-determined emission quotas
WMAP Data and Recent Developments in Supersymmetric Dark Matter
A brief review is given of the recent developments in the analyses of
supersymmetric dark matter. Chief among these is the very accurate
determination of the amount of cold dark matter in the universe from analyses
using WMAP data. The implications of this data for the mSUGRA parameter space
are analyzed. It is shown that the data admits solutions on the hyperbolic
branch (HB) of the radiative breaking of the electroweak symmetry. A part of
the hyperbolic branch lies in the so called inversion region where the LSP
neutralino becomes essentially a pure Higgsino and degenerate with
the next to the lightest neutralino and the light chargino
. Thus some of the conventional signals for the observation of
supersymmetry at colliders (e.g., the missing energy signals) do not operate in
this region. On the other hand the inversion region contains a high degree of
degeneracy of , , leading to coannihilations
which allow for the satisfaction of the WMAP relic density constraints deep on
the hyperbolic branch. Further, an analysis of the neutralino-proton cross
sections in this region reveals that this region can still be accessible to
dark matter experiments in the future. Constraints from and from
are discussed. Future prospects are also discussed.Comment: 15 pages Latex. Invited talk at the IV International Conference on
Non-accelerator New Physics (NANP'03), Dubna, Russia, June 23-28, 200
Gaugino Mass Nonuniversality and Dark Matter in SUGRA, Strings and D Brane Models
The effects of nonuniversality of gaugino masses on dark matter are examined
within supersymmetric grand unification, and in string and D brane models with
R parity invariance. In SU(5) unified models nonuniversality in the gaugino
sector can be generated via the gauge kinetic energy function which may depend
on the 24, 75 and 200 dimensional Higgs representations. We also consider
string models which allow for nonuniversality of gaugino masses and D brane
models where nonuniversality arises from embeddings of the Standard Model gauge
group on five branes and nine branes. It is found that with gaugino mass
nonuniversality the range of the LSP mass can be extended much beyond the range
allowed in the universal SUGRA case, up to about 600 GeV even without
coannihilation effects in some regions of the parameter space. The effects of
coannihilation are not considered and inclusion of these effects may further
increase the allowed neutralino mass range. Similarly with the inclusion of
gaugino mass nonuniversality, the neutralino-proton () cross-section
can increase by as much as a factor of 10 in some of regions of the parameter
space. An analysis of the uncertainties in the quark density content of the
nucleon is given and their effects on cross-section are discussed.
The predictions of our analysis including nonuniversality is compared with the
current limits from dark matter detectors and implications for future dark
matter searches are discussed.Comment: Revised version, 23 pages, Latex, and 7 figure
Supersymmetric Dark Matter and Yukawa Unification
An analysis of supersymmetric dark matter under the Yukawa unification
constraint is given. The analysis utilizes the recently discovered region of
the parameter space of models with gaugino mass nonuniversalities where large
negative supersymmetric corrections to the b quark mass appear to allow
unification for a positive sign consistent with the and constraints. In the present analysis we use the
revised theoretical determination of ()
in computing the difference which takes account of
a reevaluation of the light by light contribution which has a positive sign.
The analysis shows that the region of the parameter space with
nonuniversalities of the gaugino masses which allows for unification of Yukawa
couplings also contains regions which allow satisfaction of the relic density
constraint. Specifically we find that the lightest neutralino mass consistent
with the relic density constraint, unification for SU(5) and
unification for SO(10) in addition to other constraints lies in the region
below 80 GeV. An analysis of the maximum and the minimum neutralino-proton
scalar cross section for the allowed parameter space including the effect of a
new determination of the pion-nucleon sigma term is also given. It is found
that the full parameter space for this class of models can be explored in the
next generation of proposed dark matter detectors.Comment: 28 pages,nLatex including 5 fig
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