137 research outputs found
Minimal Standard Heterotic String Models
Three generation heterotic-string vacua in the free fermionic formulation
gave rise to models with solely the MSSM states in the observable Standard
Model charged sector. The relation of these models to Z_2 x Z_2 orbifold
compactifications dictates that they produce three pairs of untwisted Higgs
multiplets. The reduction to one pair relies on the analysis of supersymmetric
flat directions, that give superheavy mass to the dispensable Higgs states. We
explore the removal of the extra Higgs representations by using the free
fermion boundary conditions and hence directly at the string level, rather than
in the effective low energy field theory. We present a general mechanism that
achieves this reduction by using asymmetric boundary conditions between the
left- and right-moving internal fermions. We incorporate this mechanism in
explicit string models containing three twisted generations and a single
untwisted Higgs doublet pair. We further demonstrate that an additional effect
of the asymmetric boundary conditions is to substantially reduce the
supersymmetric moduli space.Comment: 20 pages, LaTeX; added reference
Switching model with two habitats and a predator involving group defence
Switching model with one predator and two prey species is considered. The
prey species have the ability of group defence. Therefore, the predator will be
attracted towards that habitat where prey are less in number. The stability
analysis is carried out for two equilibrium values. The theoretical results are
compared with the numerical results for a set of values. The Hopf bifuracation
analysis is done to support the stability results
Acoustic Power Absorption and its Relation with Vector Magnetic Field of a Sunspot
The distribution of acoustic power over sunspots shows an enhanced absorption
near the umbra--penumbra boundary. Earlier studies revealed that the region of
enhanced absorption coincides with the region of strongest transverse potential
field. The aim of this paper is to (i) utilize the high-resolution vector
magnetograms derived using Hinode SOT/SP observations and study the
relationship between the vector magnetic field and power absorption and (ii)
study the variation of power absorption in sunspot penumbrae due to the
presence of spine-like radial structures. It is found that (i) both potential
and observed transverse fields peak at a similar radial distance from the
center of the sunspot, and (ii) the magnitude of the transverse field, derived
from Hinode observations, is much larger than the potential transverse field
derived from SOHO/MDI longitudinal field observations. In the penumbra, the
radial structures called spines (intra-spines) have stronger (weaker) field
strength and are more vertical (horizontal). The absorption of acoustic power
in the spine and intra-spine shows different behaviour with the absorption
being larger in the spine as compared to the intra-spine.Comment: 18 pages, 7 figures, In Press Solar Physics, Topical Issue on
Helio-and-Astroseismolog
Can Europe recover without credit?
Data from 135 countries covering five decades suggests that creditless recoveries, in which
the stock of real credit does not return to the pre-crisis level for three years after the GDP
trough, are not rare and are characterised by remarkable real GDP growth rates: 4.7 percent
per year in middle-income countries and 3.2 percent per year in high-income countries.
However, the implications of these historical episodes for the current European situation are
limited, for two main reasons. First, creditless recoveries are much less common in highincome
countries, than in low-income countries which are financially undeveloped. European
economies heavily depend on bank loans and research suggests that loan supply played a
major role in the recent weak credit performance of Europe. There are reasons to believe that,
despite various efforts, normal lending has not yet been restored. Limited loan supply could
be disruptive for the European economic recovery and there has been only a minor
substitution of bank loans with debt securities. Second, creditless recoveries were associated
with significant real exchange rate depreciation, which has hardly occurred so far in most of
Europe. This stylised fact suggests that it might be difficult to re-establish economic growth
in the absence of sizeable real exchange rate depreciation, if credit growth does not return
Generalized Parton Distributions at x->1
Generalized parton distributions at large are studied in perturbative QCD
approach. As and at finite , there is no dependence for the
GPDs which means that the active quark is at the center of the transverse
space. We also obtain the power behavior: for pion; and
for nucleon, where
represents the additional dependence on .Comment: 7 pages, 2 figure
Modeling the Subsurface Structure of Sunspots
While sunspots are easily observed at the solar surface, determining their
subsurface structure is not trivial. There are two main hypotheses for the
subsurface structure of sunspots: the monolithic model and the cluster model.
Local helioseismology is the only means by which we can investigate
subphotospheric structure. However, as current linear inversion techniques do
not yet allow helioseismology to probe the internal structure with sufficient
confidence to distinguish between the monolith and cluster models, the
development of physically realistic sunspot models are a priority for
helioseismologists. This is because they are not only important indicators of
the variety of physical effects that may influence helioseismic inferences in
active regions, but they also enable detailed assessments of the validity of
helioseismic interpretations through numerical forward modeling. In this paper,
we provide a critical review of the existing sunspot models and an overview of
numerical methods employed to model wave propagation through model sunspots. We
then carry out an helioseismic analysis of the sunspot in Active Region 9787
and address the serious inconsistencies uncovered by
\citeauthor{gizonetal2009}~(\citeyear{gizonetal2009,gizonetal2009a}). We find
that this sunspot is most probably associated with a shallow, positive
wave-speed perturbation (unlike the traditional two-layer model) and that
travel-time measurements are consistent with a horizontal outflow in the
surrounding moat.Comment: 73 pages, 19 figures, accepted by Solar Physic
Neutron structure function and inclusive DIS from H-3 and He-3 at large Bjorken-x
A detailed study of inclusive deep inelastic scattering (DIS) from mirror A =
3 nuclei at large values of the Bjorken variable x is presented. The main
purpose is to estimate the theoretical uncertainties on the extraction of the
neutron DIS structure function from such nuclear measurements. On one hand,
within models in which no modification of the bound nucleon structure functions
is taken into account, we have investigated the possible uncertainties arising
from: i) charge symmetry breaking terms in the nucleon-nucleon interaction, ii)
finite Q**2 effects neglected in the Bjorken limit, iii) the role of different
prescriptions for the nucleon Spectral Function normalization providing baryon
number conservation, and iv) the differences between the virtual nucleon and
light cone formalisms. Although these effects have been not yet considered in
existing analyses, our conclusion is that all these effects cancel at the level
of ~ 1% for x < 0.75 in overall agreement with previous findings. On the other
hand we have considered several models in which the modification of the bound
nucleon structure functions is accounted for to describe the EMC effect in DIS
scattering from nuclei. It turns out that within these models the cancellation
of nuclear effects is expected to occur only at a level of ~ 3%, leading to an
accuracy of ~ 12 % in the extraction of the neutron to proton structure
function ratio at x ~ 0.7 -0.8$. Another consequence of considering a broad
range of models of the EMC effect is that the previously suggested iteration
procedure does not improve the accuracy of the extraction of the neutron to
proton structure function ratio.Comment: revised version to appear in Phys. Rev. C; main modifications in
Section 4; no change in the conclusion
Meta-analysis identifies seven susceptibility loci involved in the atopic March
Eczema often precedes the development of asthma in a disease course called the a 'atopic march'. To unravel the genes underlying this characteristic pattern of allergic disease, we conduct a multi-stage genome-wide association study on infantile eczema followed by childhood asthma in 12 populations including 2,428 cases and 17,034 controls. Here we report two novel loci specific for the combined eczema plus asthma phenotype, which are associated with allergic disease for the first time; rs9357733 located in EFHC1 on chromosome 6p12.3 (OR 1.27; P=2.1 Ă 10 a'8) and rs993226 between TMTC2 and SLC6A15 on chromosome 12q21.3 (OR 1.58; P=5.3 Ă 10 a'9). Additional susceptibility loci identified
Genotoxic effect induced by hydrogen peroxide in human hepatoma cells using comet assay
Background: Hydrogen peroxide is a common reactive oxygen intermediate generated by variousforms of oxidative stress. Aims: The aim of this study was to investigate the DNA damage capacity ofH2O2 in HepG2 cells. Methods: Cells were treated with H2O2 at concentrations of 25 ÎŒM or 50 ÎŒM for5 min, 30 min, 40 min, 1 h or 24 h in parallel. The extent of DNA damage was assessed by the cometassay. Results: Compared to the control, DNA damage by 25 ÎŒM and 50 ÎŒM H2O2 increasedsignificantly with increasing incubation time up to 1 h, but it was not increased at 24 h. Conclusions:Our Findings confirm that H2O2 is a typical DNA damage inducing agent and thus is a good modelsystem to study the effects of oxidative stress. DNA damage in HepG2 cells increased significantlywith H2O2 concentration and time of incubation but later decreased likely due to DNA repairmechanisms and antioxidant enzyme
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