171 research outputs found
The angiotensin II type I receptor contributes to impaired cerebral blood flow autoregulation caused by placental ischemia in pregnant rats
BACKGROUND: Placental ischemia and hypertension, characteristic features of preeclampsia, are associated with impaired cerebral blood flow (CBF) autoregulation and cerebral edema. However, the factors that contribute to these cerebral abnormalities are not clear. Several lines of evidence suggest that angiotensin II can impact cerebrovascular function; however, the role of the renin angiotensin system in cerebrovascular function during placental ischemia has not been examined. We tested whether the angiotensin type 1 (AT1) receptor contributes to impaired CBF autoregulation in pregnant rats with placental ischemia caused by surgically reducing uterine perfusion pressure. METHODS: Placental ischemic or sham operated rats were treated with vehicle or losartan from gestational day (GD) 14 to 19 in the drinking water. On GD 19, we assessed CBF autoregulation in anesthetized rats using laser Doppler flowmetry. RESULTS: Placental ischemic rats had impaired CBF autoregulation that was attenuated by treatment with losartan. In addition, we examined whether an agonistic autoantibody to the AT1 receptor (AT1-AA), reported to be present in preeclamptic women, contributes to impaired CBF autoregulation. Purified rat AT1-AA or vehicle was infused into pregnant rats from GD 12 to 19 via mini-osmotic pumps after which CBF autoregulation was assessed. AT1-AA infusion impaired CBF autoregulation but did not affect brain water content. CONCLUSIONS: These results suggest that the impaired CBF autoregulation associated with placental ischemia is due, at least in part, to activation of the AT1 receptor and that the RAS may interact with other placental factors to promote cerebrovascular changes common to preeclampsia
quasiharmonic equations of state for dynamically-stabilized soft-mode materials
We introduce a method for treating soft modes within the analytical framework
of the quasiharmonic equation of state. The corresponding double-well
energy-displacement relation is fitted to a functional form that is harmonic in
both the low- and high-energy limits. Using density-functional calculations and
statistical physics, we apply the quasiharmonic methodology to solid periclase.
We predict the existence of a B1--B2 phase transition at high pressures and
temperatures
Systematic review of economic evaluations and cost analyses of guideline implementation strategies
Objectives To appraise the quality of economic studies undertaken as part of evaluations of guideline implementation strategies; determine their resources use; and recommend methods to improve future studies. Methods Systematic review of economic studies undertaken alongside robust study designs of clinical guideline implementation strategies published (1966-1998). Studies assessed against the BMJ economic evaluations guidelines for each stage of the guideline process (guideline development, implementation and treatment). Results 235 studies were identified, 63 reported some information on cost. Only 3 studies provided evidence that their guideline was effective and efficient. 38 reported the treatment costs only, 12 implementation and treatment costs, 11 implementation costs alone, and two guideline development, implementation and treatment costs. No study gave reasonably complete information on costs. Conclusions Very few satisfactory economic evaluations of guideline implementation strategies have been performed. Current evaluations have numerous methodological defects and rarely consider all relevant costs and benefits. Future evaluations should focus on evaluating the implementation of evidence based guidelines. Keywords: Cost-effectiveness analysis, physician (or health care professional) behaviour, practice guidelines, quality improvement, systematic review.Peer reviewedAuthor versio
Resummations of free energy at high temperature
We discuss resummation strategies for free energy in quantum field theories
at nonzero temperatures T. We point out that resummations should be performed
for the short- and long-distance parts separately in order to avoid spurious
interference effects and double-counting. We then discuss and perform Pade
resummations of these two parts for QCD at high T. The resummed results are
almost invariant under variation of the renormalization and factorization
scales. We perform the analysis also in the case of the massless scalar
theory.Comment: 16 pages, revtex4, 15 eps-figures; minor typographic errors
corrected; the version as it appears in Phys.Rev.
Soliton back-action evading measurement using spectral filtering
We report on a back-action evading (BAE) measurement of the photon number of
fiber optical solitons operating in the quantum regime. We employ a novel
detection scheme based on spectral filtering of colliding optical solitons. The
measurements of the BAE criteria demonstrate significant quantum state
preparation and transfer of the input signal to the signal and probe outputs
exiting the apparatus, displaying the quantum-nondemolition (QND) behavior of
the experiment.Comment: 5 pages, 5 figure
Thermodynamics of Large-N_f QCD at Finite Chemical Potential
We extend the previously obtained results for the thermodynamic potential of
hot QCD in the limit of large number of fermions to non-vanishing chemical
potential. We give exact results for the thermal pressure in the entire range
of temperature and chemical potential for which the presence of a Landau pole
is negligible numerically. In addition we compute linear and non-linear quark
susceptibilities at zero chemical potential, and the entropy at small
temperatures. We compare with the available perturbative results and determine
their range of applicability. Our numerical accuracy is sufficiently high to
check and verify existing results, including the recent perturbative results by
Vuorinen on quark number susceptibilities and the older results by Freedman and
McLerran on the pressure at zero temperature and high chemical potential. We
also obtain a number of perturbative coefficients at sixth order in the
coupling that have not yet been calculated analytically. In the case of both
non-zero temperature and non-zero chemical potential, we investigate the range
of validity of a scaling behaviour noticed recently in lattice calculations by
Fodor, Katz, and Szabo at moderately large chemical potential and find that it
breaks down rather abruptly at , which points to a
presumably generic obstruction for extrapolating data from small to large
chemical potential. At sufficiently small temperatures , we find
dominating non-Fermi-liquid contributions to the interaction part of the
entropy, which exhibits strong nonlinearity in the temperature and an excess
over the free-theory value.Comment: 18 pages, 7 figures, JHEP style; v2: several updates, rewritten and
extended sect. 3.4 covering now "Entropy at small temperatures and
non-Fermi-liquid behaviour"; v3: additional remarks at the end of sect. 3.4;
v4: minor corrections and additions (version to appear in JHEP
Diffusion quantum Monte Carlo study of three-dimensional Wigner crystals
We report diffusion quantum Monte Carlo calculations of three-dimensional
Wigner crystals in the density range r_s=100-150. We have tested different
types of orbital for use in the approximate wave functions but none improve
upon the simple Gaussian form. The Gaussian exponents are optimized by directly
minimizing the diffusion quantum Monte Carlo energy. We have carefully
investigated and sought to minimize the potential biases in our Monte Carlo
results. We conclude that the uniform electron gas undergoes a transition from
a ferromagnetic fluid to a body-centered-cubic Wigner crystal at r_s=106+/-1.
The diffusion quantum Monte Carlo results are compared with those from
Hartree-Fock and Hartree theory in order to understand the role played by
exchange and correlation in Wigner crystals. We also study "floating" Wigner
crystals and give results for their pair-correlation functions
Statistical Survey of Type III Radio Bursts at Long Wavelengths Observed by the Solar TErrestrial RElations Observatory (STEREO)/Waves Instruments: Radio Flux Density Variations with Frequency
We have performed a statistical study of Type III radio bursts observed
by Solar TErrestrial RElations Observatory (STEREO)/Waves between May 2007 and
February 2013. We have investigated the flux density between kHz and
MHz. Both high- and low-frequency cutoffs have been observed in of
events suggesting an important role of propagation. As already reported by
previous authors, we observed that the maximum flux density occurs at MHz on
both spacecraft. We have developed a simplified analytical model of the flux
density as a function of radial distance and compared it to the STEREO/Waves
data.Comment: published in Solar Physic
The effect of memory on relaxation in a scalar field theory
We derive a kinetic equation with a non-Markovian collision term which
includes a memory effect, from Kadanoff-Baym equations in theory
within the three-loop level for the two-particle irreducible (2PI) effective
action. The memory effect is incorporated into the kinetic equation by a
generalized Kadanoff-Baym ansatz.Based on the kinetic equations with and
without the memory effect, we investigate an influence of this effect on decay
of a single particle excitation with zero momentum in 3+1 dimensions and the
spatially homogeneous case. Numerical results show that, while the time
evolution of the zero mode is completely unaffected by the memory effect due to
a separation of scales in the weak coupling regime, this effect leads first to
faster relaxation than the case without it and then to slower relaxation as the
coupling constant increases.Comment: 12 pages, 6 eps figure
Neutrino Propagation in a Strongly Magnetized Medium
We derive general expressions at the one-loop level for the coefficients of
the covariant structure of the neutrino self-energy in the presence of a
constant magnetic field. The neutrino energy spectrum and index of refraction
are obtained for neutral and charged media in the strong-field limit () using the lowest Landau level
approximation. The results found within the lowest Landau level approximation
are numerically validated, summing in all Landau levels, for strong and weakly-strong fields. The neutrino energy in
leading order of the Fermi coupling constant is expressed as the sum of three
terms: a kinetic-energy term, a term of interaction between the magnetic field
and an induced neutrino magnetic moment, and a rest-energy term. The leading
radiative correction to the kinetic-energy term depends linearly on the
magnetic field strength and is independent of the chemical potential. The other
two terms are only present in a charged medium. For strong and weakly-strong
fields, it is found that the field-dependent correction to the neutrino energy
in a neutral medium is much larger than the thermal one. Possible applications
to cosmology and astrophysics are considered.Comment: 23 pages, 4 figures. Corrected misprints in reference
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