4,247 research outputs found
Frequency dependence of the photonic noise spectrum in an absorbing or amplifying diffusive medium
A theory is presented for the frequency dependence of the power spectrum of
photon current fluctuations originating from a disordered medium. Both the
cases of an absorbing medium (``grey body'') and of an amplifying medium
(``random laser'') are considered in a waveguide geometry. The semiclassical
approach (based on a Boltzmann-Langevin equation) is shown to be in complete
agreement with a fully quantum mechanical theory, provided that the effects of
wave localization can be neglected. The width of the peak in the power spectrum
around zero frequency is much smaller than the inverse coherence time,
characteristic for black-body radiation. Simple expressions for the shape of
this peak are obtained, in the absorbing case, for waveguide lengths large
compared to the absorption length, and, in the amplifying case, close to the
laser threshold.Comment: 17 pages, 6 figure
Properties of real metallic surfaces: Effects of density functional semilocality and van der Waals nonlocality
We have computed the surface energies, work functions, and interlayer surface
relaxations of clean (111), (110), and (100) surfaces of Al, Cu, Ru, Rh, Pd,
Ag, Pt, and Au. Many of these metallic surfaces have technological or catalytic
applications. We compare experimental reference values to those of the local
density approximation (LDA), the Perdew-Burke-Ernzerhof (PBE) generalized
gradient approximation (GGA), the PBEsol (PBE for solids) GGA, the SCAN
meta-GGA, and SCAN+rVV10 (SCAN with a long-range van der Waals or vdW
correction). The closest agreement with uncertain experimental values is
achieved by the simplest density functional (LDA) and by the most sophisticated
general-purpose one (SCAN+rVV10). The long-range vdW interaction increases the
surface energies by about 10%, and the work functions by about 1%. LDA works
for metal surfaces through a stronger-than-usual error cancellation. PBE yields
the most-underestimated and presumably least accurate surface energies and work
functions. Surface energies within the random phase approximation (RPA) are
also reported. Interlayer relaxations from different functionals are in
reasonable agreement with one another, and usually with experiment
Coarse-Grained Model for Phospholipid/Cholesterol Bilayer
We construct a coarse-grained (CG) model for dipalmitoylphosphatidylcholine
(DPPC)/cholesterol bilayers and apply it to large-scale simulation studies of
lipid membranes. Our CG model is a two-dimensional representation of the
membrane, where the individual lipid and sterol molecules are described by
point-like particles. The effective intermolecular interactions used in the
model are systematically derived from detailed atomic-scale molecular dynamics
simulations using the Inverse Monte Carlo technique, which guarantees that the
radial distribution properties of the CG model are consistent with those given
by the corresponding atomistic system. We find that the coarse-grained model
for the DPPC/cholesterol bilayer is substantially more efficient than atomistic
models, providing a speed-up of approximately eight orders of magnitude. The
results are in favor of formation of cholesterol-rich and cholesterol-poor
domains at intermediate cholesterol concentrations, in agreement with the
experimental phase diagram of the system. We also explore the limits of the
novel coarse-grained model, and discuss the general validity and applicability
of the present approach
Double Beta Decay, Lepton Flavour Violation and Collider Signatures of Left-Right Symmetric Models with Spontaneous D Parity Breaking
We propose a class of left-right symmetric models (LRSMs) with spontaneous D
parity breaking, where SU(2)_R breaks at the TeV scale while discrete
left-right symmetry breaks around 10^9 GeV. By embedding this framework in a
non-supersymmetric SO(10) Grand Unified Theory (GUT) with Pati-Salam symmetry
as the highest intermediate breaking step, we obtain g_R / g_L ~ 0.6 between
the right- and left-handed gauge couplings at the TeV scale. This leads to a
suppression of beyond the Standard Model phenomena induced by the right-handed
gauge coupling. Here we focus specifically on the consequences for neutrinoless
double beta decay, low energy lepton flavour violation and LHC signatures due
to the suppressed right handed currents. Interestingly, the reduced g_R allows
us to interpret an excess of events observed recently in the range of 1.9 TeV
to 2.4 TeV by the CMS group at the LHC as the signature of a right handed gauge
boson in LRSMs with spontaneous D parity breaking. Moreover, the reduced
right-handed gauge coupling also strongly suppresses the non-standard
contribution of heavy states to the neutrinoless double beta decay rate as well
as the amplitude of low energy lepton flavour violating processes. In a
dominant type-II Seesaw mechanism of neutrino mass generation, we find that
both sets of observables provide stringent and complimentary bounds which make
it challenging to observe the scenario at the LHC.Comment: 20 pages, 11 figure
Signal of Right-Handed Charged Gauge Bosons at the LHC?
We point out that the recent excess observed in searches for a right-handed
gauge boson W_R at CMS can be explained in a left-right symmetric model with D
parity violation. In a class of SO(10) models, in which D parity is broken at a
high scale, the left-right gauge symmetry breaking scale is naturally small,
and at a few TeV the gauge coupling constants satisfy g_R ~ 0.6 g_L. Such
models therefore predict a right-handed charged gauge boson W_R in the TeV
range with a suppressed gauge coupling as compared to the usually assumed
manifest left-right symmetry case g_R = g_L. The recent CMS data show excess
events which are consistent with the cross section predicted in the D parity
breaking model for 1.9 TeV < M_{W_R} < 2.4 TeV. If the excess is confirmed, it
would in general be a direct signal of new physics beyond the Standard Model at
the LHC. A TeV scale W_R would for example not only rule out SU(5) grand
unified theory models. It would also imply B-L violation at the TeV scale,
which would be the first evidence for baryon or lepton number violation in
nature and it has strong implications on the generation of neutrino masses and
the baryon asymmetry in the Universe.Comment: 4 pages, 2 figures, matches published versio
Chronic ethanol feeding alters miRNA expression dynamics during liver regeneration.
BACKGROUND: Adaptation to chronic ethanol (EtOH) treatment of rats results in a changed functional state of the liver and greatly inhibits its regenerative ability, which may contribute to the progression of alcoholic liver disease.
METHODS: In this study, we investigated the effect of chronic EtOH intake on hepatic microRNA (miRNA) expression in male Sprague-Dawley rats during the initial 24 hours of liver regeneration following 70% partial hepatectomy (PHx) using miRNA microarrays. miRNA expression during adaptation to EtOH was investigated using RT-qPCR. Nuclear factor kappa B (NFκB) binding at target miRNA promoters was investigated with chromatin immunoprecipitation.
RESULTS: Unsupervised clustering of miRNA expression profiles suggested that miRNA expression was more affected by chronic EtOH feeding than by the acute challenge of liver regeneration after PHx. Several miRNAs that were significantly altered by chronic EtOH feeding, including miR-34a, miR-103, miR-107, and miR-122 have been reported to play a role in regulating hepatic metabolism and the onset of these miRNA changes occurred gradually during the time course of EtOH feeding. Chronic EtOH feeding also altered the dynamic miRNA profile during liver regeneration. Promoter analysis predicted a role for NFκB in the immediate-early miRNA response to PHx. NFκB binding at target miRNA promoters in the chronic EtOH-fed group was significantly altered and these changes directly correlated with the observed expression dynamics of the target miRNA.
CONCLUSIONS: Chronic EtOH consumption alters the hepatic miRNA expression profile such that the response of the metabolism-associated miRNAs occurs during long-term adaptation to EtOH rather than as an acute transient response to EtOH metabolism. Additionally, the dynamic miRNA program during liver regeneration in response to PHx is altered in the chronically EtOH-fed liver and these differences reflect, in part, differences in miRNA expression between the EtOH-adapted and control livers at the baseline state prior to PHx
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