3,605 research outputs found
Worsening of cerebral hyperemia by the administration of terlipressin in acute liver failure with severe hepatic encephalopathy
There is increasing evidence that terlipressin is useful in patients with cirrhosis and
hepatorenal syndrome, but there are no data of its use in patients with acute liver
failure (ALF) in whom hepatorenal syndrome is common. Although terlipressin
produces systemic vasoconstriction, it produces cerebral vasodilatation and may
increase cerebral blood flow (CBF). Increased CBF contributes to intracranial
hypertension in patients with ALF. The aim of this study was to evaluate the safety of
terlipressin in patients with ALF with respect to cerebral haemodynamics. Six
successive patients with ALF were electively ventilated for grade IV hepatic
encephalopathy. Patients were monitored invasively and CBF was measured (Kety-
Schmidt technique). Measurements were made before, at 1, 3 hour and 5 hours after
intravenous (single bolus) administration of terlipressin (0.005 mg/kg) )intravenously
(single bolus), median 0.25mg (range 0.2-0.3). There was no significant change in
heart rate, mean arterial pressure or cardiac output. CBF and jugular venous oxygen
saturation both increased significantly at 1 hour (p<0.0=0.016) respectively.
Intracranial pressure increased significantly at 21 hours (p<0=.0.031), returning back
to baseline values at 42 hours. This study shows that administration of terlipressin, at
a dose that did not alter systemic haemodynamicshemodynamics, resulted in
worsening of cerebral hyperemia and intracranial hypertension in patients with ALF
and severe hepatic encephalopathy. These data suggest the need to exercise extreme
caution in the use of terlipressin in these patients in view of its potentially deleterious
consequences on cerebral haemodynamics
Effects of stoichiometry, purity, etching and distilling on resistance of MgB2 pellets and wire segments
We present a study of the effects of non-stoichiometry, boron purity, wire
diameter and post-synthesis treatment (etching and Mg distilling) on the
temperature dependent resistance and resistivity of sintered MgB2 pellets and
wire segments. Whereas the residual resistivity ratio (RRR) varies between RRR
\~ 4 to RRR > 20 for different boron purity, it is only moderately affected by
non-stoichiometry (from 20% Mg deficiency to 20% Mg excess) and is apparently
independent of wire diameter and presence of Mg metal traces on the wire
surface. The obtained set of data indicates that RRR values in excess of 20 and
residual resistivities as low as rho{0} ~ 0.4 mu Ohm cm are intrinsic material
properties of high purity MgB2
Non-topological solitons in brane world models
We examine some general properties of a certain class of scalar filed theory
models containing non-topological soliton solutions in the context of brane
world models with compact large extra dimensions. If a scalar field is allowed
to propagate in extra space, then, beside standard Kaluza-Klein type
excitations, a whole new class of very massive soliton-type states can exist.
Depending on their abundance, they can be important dark matter candidates or
give significant contribution to entropy and energy density in our universe. .Comment: version accepted for publication in Physical Review
Temperature-dependent Raman spectroscopy in BaRuO systems
We investigated the temperature-dependence of the Raman spectra of a
nine-layer BaRuO single crystal and a four-layer BaRuO epitaxial film,
which show pseudogap formations in their metallic states. From the polarized
and depolarized spectra, the observed phonon modes are assigned properly
according to the predictions of group theory analysis. In both compounds, with
decreasing temperature, while modes show a strong hardening, (or
) modes experience a softening or no significant shift. Their different
temperature-dependent behaviors could be related to a direct Ru metal-bonding
through the face-sharing of RuO. It is also observed that another
mode of the oxygen participating in the face-sharing becomes split at low
temperatures in the four layer BaRuO. And, the temperature-dependence of
the Raman continua between 250 600 cm is strongly correlated to
the square of the plasma frequency. Our observations imply that there should be
a structural instability in the face-shared structure, which could be closely
related to the pseudogap formation of BaRuO systems.Comment: 8 pages, 6 figures. to be published in Phys. Rev.
Functional Methods in Stochastic Systems
Field-theoretic construction of functional representations of solutions of
stochastic differential equations and master equations is reviewed. A generic
expression for the generating function of Green functions of stochastic systems
is put forward. Relation of ambiguities in stochastic differential equations
and in the functional representations is discussed. Ordinary differential
equations for expectation values and correlation functions are inferred with
the aid of a variational approach.Comment: Plenary talk presented at Mathematical Modeling and Computational
Science. International Conference, MMCP 2011, Star\'a Lesn\'a, Slovakia, July
4-8, 201
Robust optimization in simulation: Taguchi and response surface methodology
Optimization of simulated systems is tackled by many methods, but most methods assume known environments. This article, however, develops a `robust' methodology for uncertain environments. This methodology uses Taguchi's view of the uncertain world, but replaces his statistical techniques by Response Surface Methodology (RSM). George Box originated RSM, and Douglas Montgomery recently extended RSM to robust optimization of real (non-simulated) systems. We combine Taguchi's view with RSM for simulated systems. We illustrate the resulting methodology through classic Economic Order Quantity (EOQ) inventory models, which demonstrate that robust optimization may require order quantities that differ from the classic EOQ
Effects of Boron Purity, Mg Stoichiometry and Carbon Substitution on Properties of Polycrystalline MgB
By synthesizing MgB using boron of different nominal purity we found
values of the residual resistivity ratio () from 4 to
20, which covers almost all values found in literature. To obtain high values
of , high purity reagents are necessary. With the isotopically pure boron
we obtained the highest 20 for the stoichiometric compound. We also
investigated MgB samples with 0.8 1.2. For the range
MgB up to MgB we found average values
of between 14 and 24. For smaller variations in stoichiometry () . All of our data point to the conclusion that high
() and low () are intrinsic
material properties associated with high purity MgB. In addition we have
performed initial work on optimizing the formation of carbon doped MgB
via the use of BC. Nearly single phase material can be formed by reaction
of nominal Mg(BC) for 24 hours at . The
for this composition is between and (depending on
criterion).Comment: accepted to Physica C, special MgB2 issu
Observational constraints on the neutron star mass distribution
Radio observations of neutron star binary pulsar systems have constrained
strongly the masses of eight neutron stars. Assuming neutron star masses are
uniformly distributed between lower and upper bounds and , the
observations determine with 95\% confidence that and . These limits give observational
support to neutron star formation scenarios that suggest that masses should
fall predominantly in the range , and will also be
important in the interpretation of binary inspiral observations by the Laser
Interferometer Gravitational-wave Observatory.Comment: Postscript, 4 pages, NU-GR-
Parallelization, Special Hardware and Post-Newtonian Dynamics in Direct N - Body Simulations
The formation and evolution of supermassive black hole (SMBH) binaries during and after galaxy mergers is an important ingredient for our understanding of galaxy formation and evolution in a cosmological context, e.g. for predictions of cosmic star formation histories or of SMBH demographics (to predict events that emit gravitational waves). If galaxies merge in the course of their evolution, there should be either many binary or even multiple black holes, or we have to find out what happens to black hole multiples in galactic nuclei, e.g. whether they come sufficiently close to merge resulting from emission of gravitational waves, or whether they eject each other in gravitational slingshot interactions
Determination of superconducting anisotropy from magnetization data on random powders as applied to LuNiBC, YNiBC and MgB
The recently discovered intermetallic superconductor MgB2 appears to have a
highly anisotopic upper critical field with Hc2(max)/Hc2(min} = \gamma > 5. In
order to determine the temperature dependence of both Hc2(max) and Hc2(min) we
propose a method of extracting the superconducting anisotropy from the
magnetization M(H,T) of randomly oriented powder samples. The method is based
on two features in dM/dT the onset of diamagnetism at Tc(max), that is commonly
associated with Hc2, and a kink in dM/dT at a lower temperature Tc(min).
Results for LuNi2B2C and YNi2B2C powders are in agreement with anisotropic Hc2
obtained from magneto-transport measurements on single crystals. Using this
method on four different types of MgB2 powder samples we are able to determine
Hc2(max)(T) and Hc2(min)(T) with \gamma \approx 6
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