5,627 research outputs found
Adverse events following influenza immunization reported by healthcare personnel using active surveillance based on text messages
Studies have demonstrated that healthcare personnel (HCP) have concerns about the potential side effects of trivalent inactivate influenza vaccine (IIV3).1-3 A recent metaanalysis of reasons HCP refuse IIV3 indicates the strongest predictors of vaccine acceptance are belief that the vaccine is safe and belief the vaccine does not cause the disease it is meant to prevent.
Human P450 CYP17A1: Control of Substrate Preference by Asparagine 202
CYP17A1 is a key steroidogenic enzyme known to conduct several distinct chemical transformations on multiple substrates. In its hydroxylase activity, this enzyme adds a hydroxyl group at the 17α position of both pregnenolone and progesterone at approximately equal rates. However, the subsequent 17,20 carbon–carbon scission reaction displays variable substrate specificity in the numerous CYP17A1 isozymes operating in vertebrates, manifesting as different Kd and kcat values when presented with 17α-hydroxypregnenlone (OHPREG) versus 17α-hydroxyprogesterone (OHPROG). Here we show that the identity of the residue at position 202 in human CYP17A1, thought to form a hydrogen bond with the A-ring alcohol substituent on the pregnene- nucleus, is a key driver of this enzyme’s native preference for OHPREG. Replacement of asparagine 202 with serine completely reverses the preference of CYP17A1, more than doubling the rate of turnover of the OHPROG to androstenedione reaction and substantially decreasing the rate of formation of dehydroepiandrosterone from OHPREG. In a series of resonance Raman experiments, it was observed that, in contrast with the case for the wild-type protein, in the mutant the 17α alcohol of OHPROG tends to form a H-bond with the proximal rather than terminal oxygen of the oxy–ferrous complex. When OHPREG was a substrate, the mutant enzyme was found to have a H-bonding interaction with the proximal oxygen that is substantially weaker than that of the wild type. These results demonstrate that a single-point mutation in the active site pocket of CYP17A1, even when far from the heme, has profound effects on steroidogenic selectivity in androgen biosynthesis
Viscous Bianchi type I universes in brane cosmology
We consider the dynamics of a viscous cosmological fluid in the generalized
Randall-Sundrum model for an anisotropic, Bianchi type I brane. To describe the
dissipative effects we use the Israel-Hiscock-Stewart full causal thermodynamic
theory. By assuming that the matter on the brane obeys a linear barotropic
equation of state, and the bulk viscous pressure has a power law dependence on
the energy density, the general solution of the field equations can be obtained
in an exact parametric form. The obtained solutions describe generally a
non-inflationary brane world. In the large time limit the brane Universe
isotropizes, ending in an isotropic and homogeneous state. The evolution of the
temperature and of the comoving entropy of the Universe is also considered, and
it is shown that due to the viscous dissipative processes a large amount of
entropy is created in the early stages of evolution of the brane world.Comment: 13 pages, 5 figures, to appear in Class. Quantum Gra
Dynamical simulation of transport in one-dimensional quantum wires
Transport of single-channel spinless interacting fermions (Luttinger liquid)
through a barrier has been studied by numerically exact quantum Monte Carlo
methods. A novel stochastic integration over the real-time paths allows for
direct computation of nonequilibrium conductance and noise properties. We have
examined the low-temperature scaling of the conductance in the crossover region
between a very weak and an almost insulating barrier.Comment: REVTex, 4 pages, 2 uuencoded figures (submitted to Phys. Rev. Lett.
Renormalization Group Approach to Causal Viscous Cosmological Models
The renormalization group method is applied to the study of homogeneous and
flat Friedmann-Robertson-Walker type Universes, filled with a causal bulk
viscous cosmological fluid. The starting point of the study is the
consideration of the scaling properties of the gravitational field equations,
of the causal evolution equation of the bulk viscous pressure and of the
equations of state. The requirement of scale invariance imposes strong
constraints on the temporal evolution of the bulk viscosity coefficient,
temperature and relaxation time, thus leading to the possibility of obtaining
the bulk viscosity coefficient-energy density dependence. For a cosmological
model with bulk viscosity coefficient proportional to the Hubble parameter, we
perform the analysis of the renormalization group flow around the scale
invariant fixed point, therefore obtaining the long time behavior of the scale
factor.Comment: 19 pages. RevTeX4. Revised version. Accepted in Classical and Quantum
Gravit
Multilevel blocking approach to the fermion sign problem in path-integral Monte Carlo simulations
A general algorithm toward the solution of the fermion sign problem in
finite-temperature quantum Monte Carlo simulations has been formulated for
discretized fermion path integrals with nearest-neighbor interactions in the
Trotter direction. This multilevel approach systematically implements a simple
blocking strategy in a recursive manner to synthesize the sign cancellations
among different fermionic paths throughout the whole configuration space. The
practical usefulness of the method is demonstrated for interacting electrons in
a quantum dot.Comment: 4 pages RevTeX, incl. two figure
Slow-light optical bullets in arrays of nonlinear Bragg-grating waveguides
We demonstrate how to control independently both spatial and temporal
dynamics of slow light. We reveal that specially designed nonlinear waveguide
arrays with phase-shifted Bragg gratings demonstrate the frequency-independent
spatial diffraction near the edge of the photonic bandgap, where the group
velocity of light can be strongly reduced. We show in numerical simulations
that such structures allow a great flexibility in designing and controlling
dispersion characteristics, and open a way for efficient spatiotemporal
self-trapping and the formation of slow-light optical bullets.Comment: 4 pages, 4 figures; available from
http://link.aps.org/abstract/PRL/v97/e23390
Quintessence and cosmic acceleration
A cosmological model with perfect fluid and self-interacting quintessence
field is considered in the framework of the spatially flat
Friedmann-Robertson-Walker (FRW) geometry. By assuming that all physical
quantities depend on the volume scale factor of the Universe, the general
solution of the gravitational field equations can be expressed in an exact
parametric form. The quintessence field is a free parameter. With an
appropriate choice of the scalar field a class of exact solutions is obtained,
with an exponential type scalar field potential fixed via the gravitational
field equations. The general physical behavior of the model is consistent with
the recent cosmological scenario favored by supernova Type Ia observations,
indicating an accelerated expansion of the Universe.Comment: 6 pages, 3 figures, to appear in Int. J. Mod. Phys.
Anisotropy of graphite optical conductivity
The graphite conductivity is evaluated for frequencies between
0.1 eV, the energy of the order of the electron-hole overlap, and 1.5 eV, the
electron nearest hopping energy. The in-plane conductivity per single atomic
sheet is close to the universal graphene conductivity and,
however, contains a singularity conditioned by peculiarities of the electron
dispersion. The conductivity is less in the direction by the factor of the
order of 0.01 governed by electron hopping in this direction.Comment: 3 pages, 3 figure
CVaR minimization by the SRA algorithm
Using the risk measure CV aR in �nancial analysis has become
more and more popular recently. In this paper we apply CV aR for portfolio optimization. The problem is formulated as a two-stage stochastic programming model, and the SRA algorithm, a recently developed heuristic algorithm, is applied for minimizing CV aR
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