3,437 research outputs found
Thermoelasticity of Fe2+-bearing bridgmanite
We present LDA+U calculations of high temperature elastic properties of
bridgmanite with composition (MgFe)SiO for
. Results of elastic moduli and acoustic velocities for the
Mg-end member (x=0) agree very well with the latest high pressure and high
temperature experimental measurements. In the iron-bearing system, we focus
particularly on the change in thermoelastic parameters across the state change
that occurs in ferrous iron above 30 GPa, often attributed to a high-spin
(HS) to intermediate spin (IS) crossover but explained by first principles
calculations as a lateral displacement of substitutional iron in the perovskite
cage. We show that the measured effect of this change on the equation of state
of this system can be explained by the lateral displacement of substitutional
iron, not by the HS to IS crossover. The calculated elastic properties of
(MgFe)SiO along an adiabatic mantle geotherm,
somewhat overestimate longitudinal velocities but produce densities and shear
velocities quite consistent with Preliminary Reference Earth Model data
throughout most of the lower mantle.Comment: Accepted for Geophysical Research Letters (DOI: 10.1002/2014GL062888
Probabilistic Fragmentation and Effective Power Law
A simple fragmentation model is introduced and analysed. We show that, under
very general conditions, an effective power law for the mass distribution
arises with realistic exponent. This exponent has a universal limit, but in
practice the effective exponent depends on the detailed breaking mechanism and
the initial conditions. This dependence is in good agreement with experimental
results of fragmentation.Comment: 4 pages Revtex, 2 figures, zipped and uuencode
Quantum criticality as a resource for quantum estimation
We address quantum critical systems as a resource in quantum estimation and
derive the ultimate quantum limits to the precision of any estimator of the
coupling parameters. In particular, if L denotes the size of a system and
\lambda is the relevant coupling parameters driving a quantum phase transition,
we show that a precision improvement of order 1/L may be achieved in the
estimation of \lambda at the critical point compared to the non-critical case.
We show that analogue results hold for temperature estimation in classical
phase transitions. Results are illustrated by means of a specific example
involving a fermion tight-binding model with pair creation (BCS model).Comment: 7 pages. Revised and extended version. Gained one author and a
specific exampl
17,β-estradiol inhibits hepatitis C virus mainly by interference with the release phase of its life cycle
Rationale & Aim:
Estrogen and estrogen-mediated signalling protect from hepatitis C virus through incompletely understood mechanisms. We aimed to ascertain which phase(s) of HCV life cycle is/are affected by estrogens.
Methods:
Huh7 cells infected with the JFH1 virus (genotype 2a) were exposed to dehydroepiandrosterone, testosterone, progesterone and 17β-estradiol (tested with/without its receptor antagonist fulvestrant). Dose-response curves were established to calculate IC50 values. To dissect how 17β-estradiol interferes with phases of HCV life cycle, its effects were measured on the HCV pseudo-particle system (viral entry), the sub-genomic replicon N17/JFH1 and the replicon cell line Huh7-J17 (viral replication). Finally, in a dual-step infection model, infectious supernatants, collected from infected cells exposed to hormones, were used to infect naïve cells.
Results:
Progesterone and testosterone showed no inhibitory effect on HCV; dehydroepiandrosterone was only mildly inhibitory. In contrast, 17β-estradiol inhibited infection by 64-67% (IC50 values 140 to 160 nM). Fulvestrant reverted the inhibition by 17β-estradiol in a dose-dependent manner. 17β-estradiol exerted only a slight inhibition (<20%) on HCV pseudo-particles, and had no effect on cells either transiently or stably (Huh7-J17 cells) expressing the N17/JFH1 replicon. In the dual-step infection model, a significant IC50 decline occurred between primary (134 nM) and secondary (100 nM) infections (p=0.02), with extracellular HCV RNA and infectivity being reduced to a higher degree in comparison to its intracellular counterpart.
Conclusions:
17β-estradiol inhibits HCV acting through its intracellular receptors, mainly interfering with late phases (assembly/release) of the HCV life cycle
Exploring complex networks via topological embedding on surfaces
We demonstrate that graphs embedded on surfaces are a powerful and practical
tool to generate, characterize and simulate networks with a broad range of
properties. Remarkably, the study of topologically embedded graphs is
non-restrictive because any network can be embedded on a surface with
sufficiently high genus. The local properties of the network are affected by
the surface genus which, for example, produces significant changes in the
degree distribution and in the clustering coefficient. The global properties of
the graph are also strongly affected by the surface genus which is constraining
the degree of interwoveness, changing the scaling properties from
large-world-kind (small genus) to small- and ultra-small-world-kind (large
genus). Two elementary moves allow the exploration of all networks embeddable
on a given surface and naturally introduce a tool to develop a statistical
mechanics description. Within such a framework, we study the properties of
topologically-embedded graphs at high and low `temperatures' observing the
formation of increasingly regular structures by cooling the system. We show
that the cooling dynamics is strongly affected by the surface genus with the
manifestation of a glassy-like freezing transitions occurring when the amount
of topological disorder is low.Comment: 18 pages, 7 figure
Angular momentum effects in Michelson-Morley type experiments
The effect of the angular momentum density of a gravitational source on the
times of flight of light rays in an interferometer is analyzed. The calculation
is made imagining that the interferometer is at the equator of the gravity
source and, as long as possible, the metric, provided it is stationary and
axisymmetric, is not approximated. Finally, in order to evaluate the size of
the effect in the case of the Earth a weak field approximation is introduced.
For laboratory scales and non-geodesic paths the correction turns out to be
comparable with the sensitivity expected in gravitational waves interferometric
detectors, whereas it drops under the threshold of detectability when using
free (geodesic) light rays.Comment: 12 pages, LaTeX; more about the detection technique, references
added; accepted for publication in GR
Extended DFT+U+V method with on-site and inter-site electronic interactions
In this article we introduce a generalization of the popular DFT+U method
based on the extended Hubbard model that includes on-site and inter-site
electronic interactions. The novel corrective Hamiltonian is designed to study
systems for which electrons are not completely localized on atomic states
(according to the general scheme of Mott localization) and hybridization
between orbitals from different sites plays an important role. The application
of the extended functional to archetypal Mott - charge-transfer (NiO) and
covalently bonded insulators (Si and GaAs) demonstrates its accuracy and
versatility and the possibility to obtain a unifying and equally accurate
description for a broad range of very diverse systems
Quantum estimation via minimum Kullback entropy principle
We address quantum estimation in situations where one has at disposal data
from the measurement of an incomplete set of observables and some a priori
information on the state itself. By expressing the a priori information in
terms of a bias toward a given state the problem may be faced by minimizing the
quantum relative entropy (Kullback entropy) with the constraint of reproducing
the data. We exploit the resulting minimum Kullback entropy principle for the
estimation of a quantum state from the measurement of a single observable,
either from the sole mean value or from the complete probability distribution,
and apply it as a tool for the estimation of weak Hamiltonian processes. Qubit
and harmonic oscillator systems are analyzed in some details.Comment: 7 pages, slightly revised version, no figure
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