10,829 research outputs found
On some key research issues in Enterprise Risk Management related to economic capital and diversification effect at group level
The goal of this short communication is to give an overview of the key research issues in Enterprise Risk Management that arose during the talks and the brainstorming session of the first ERMII research workshop, which was held at ISFA, University of Lyon in June 2007. To define and compute economic capital at group level, fundamental problems related for example to value creation, correlation and capital allocation are stated. The ideas gathered in this paper are not directly ours, we just collected and summarized the ones that arose during the workshop.
Models of f(R) Cosmic Acceleration that Evade Solar-System Tests
We study a class of metric-variation f(R) models that accelerates the
expansion without a cosmological constant and satisfies both cosmological and
solar-system tests in the small-field limit of the parameter space.
Solar-system tests alone place only weak bounds on these models, since the
additional scalar degree of freedom is locked to the high-curvature
general-relativistic prediction across more than 25 orders of magnitude in
density, out through the solar corona. This agreement requires that the
galactic halo be of sufficient extent to maintain the galaxy at high curvature
in the presence of the low-curvature cosmological background. If the galactic
halo and local environment in f(R) models do not have substantially deeper
potentials than expected in LCDM, then cosmological field amplitudes |f_R| >
10^{-6} will cause the galactic interior to evolve to low curvature during the
acceleration epoch. Viability of large-deviation models therefore rests on the
structure and evolution of the galactic halo, requiring cosmological
simulations of f(R) models, and not directly on solar-system tests. Even small
deviations that conservatively satisfy both galactic and solar-system
constraints can still be tested by future, percent-level measurements of the
linear power spectrum, while they remain undetectable to cosmological-distance
measures. Although we illustrate these effects in a specific class of models,
the requirements on f(R) are phrased in a nearly model-independent manner.Comment: 13 pages, 10 figures. Submitted to Phys. Rev.
Challenges to the DGP Model from Horizon-Scale Growth and Geometry
We conduct a Markov Chain Monte Carlo study of the Dvali-Gabadadze-Porrati
(DGP) self-accelerating braneworld scenario given the cosmic microwave
background (CMB) anisotropy, supernovae and Hubble constant data by
implementing an effective dark energy prescription for modified gravity into a
standard Einstein-Boltzmann code. We find no way to alleviate the tension
between distance measures and horizon scale growth in this model. Growth
alterations due to perturbations propagating into the bulk appear as excess CMB
anisotropy at the lowest multipoles. In a flat cosmology, the maximum
likelihood DGP model is nominally a 5.3 sigma poorer fit than Lambda CDM.
Curvature can reduce the tension between distance measures but only at the
expense of exacerbating the problem with growth leading to a 4.8 sigma result
that is dominated by the low multipole CMB temperature spectrum. While changing
the initial conditions to reduce large scale power can flatten the temperature
spectrum, this also suppresses the large angle polarization spectrum in
violation of recent results from WMAP5. The failure of this model highlights
the power of combining growth and distance measures in cosmology as a test of
gravity on the largest scales.Comment: 12 pages, 7 figures, 4 tables, minor revisions reflect PRD published
versio
T-cadherin deficiency increases vascular vulnerability in T2DM through impaired NO bioactivity.
BACKGROUND: Endothelial dysfunction plays a critical role in the development of type 2 diabetes (T2DM). T-cadherin (T-cad) has gained recognition as a regulator of endothelial cell (EC) function. The present study examined whether T-cad deficiency increases vascular vulnerability in T2DM.
METHODS: Vascular segments were isolated from WT or T-cad knockout mice. Endothelial function, total NO accumulation, and the expression of T-cad related proteins were determined.
RESULTS: Ach and acidified NaNO2 induced similar vasorelaxation in WT groups. T-cad KO mice exhibited normal response to acidified NaNO2, but manifested markedly reduced response to Ach. NO accumulation was also decreased in T-cad KO group. T-cad expression was reduced in WT mice fed 8 weeks of high fat diet (HFD). Furthermore, exacerbated reduction of vasorelaxation was observed in T-cad KO mice fed 8 weeks of HFD.
CONCLUSIONS: In the current study, we provide the first in vivo evidence that T-cadherin deficiency causes endothelial dysfunction in T2DM vascular segments, suggesting the involvement of T-cad deficiency in T2DM pathogenesis
On the origin of critical temperature enhancement in atomically-thin superconductors
Recent experiments showed that thinning gallium, iron selenide and 2H
tantalum disulfide to single/several monoatomic layer(s) enhances their
superconducting critical temperatures. Here, we characterize these
superconductors by extracting the absolute values of the London penetration
depth, the superconducting energy gap, and the relative jump in specific heat
at the transition temperature from their self-field critical currents. Our
central finding is that the enhancement in transition temperature for these
materials arises from the opening of an additional superconducting gap, while
retaining a largely unchanged bulk superconducting gap. Literature data reveals
that ultrathin niobium films similarly develop a second superconducting gap.
Based on the available data, it seems that, for type-II superconductors, a new
superconducting band appears when the film thickness becomes smaller than the
out-of-plane coherence length. The same mechanism may also be the cause of
enhanced interface superconductivity.Comment: 43 pages, 12 figure
IV Regressions without Exclusion Restrictions
We study identification and estimation of endogenous linear and nonlinear
regression models without excluded instrumental variables, based on the
standard mean independence condition and a nonlinear relevance condition. Based
on the identification results, we propose two semiparametric estimators as well
as a discretization-based estimator that does not require any nonparametric
regressions. We establish their asymptotic normality and demonstrate via
simulations their robust finite-sample performances with respect to exclusion
restrictions violations and endogeneity. Our approach is applied to study the
returns to education, and to test the direct effects of college proximity
indicators as well as family background variables on the outcome
Weighing Neutrinos with Galaxy Cluster Surveys
Large future galaxy cluster surveys, combined with cosmic microwave
background observations, can achieve a high sensitivity to the masses of
cosmologically important neutrinos. We show that a weak lensing selected sample
of ~100,000 clusters could tighten the current upper bound on the sum of masses
of neutrino species by an order of magnitude, to a level of 0.03 eV. Since this
statistical sensitivity is below the best existing lower limit on the mass of
at least one neutrino species, a future detection is likely, provided that
systematic errors can be controlled to a similar level.Comment: 4 pages, 1 figure, version accepted for publication in PR
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