2,814 research outputs found
Low-energy electronic properties of clean CaRuO: elusive Landau quasiparticles
We have prepared high-quality epitaxial thin films of CaRuO with residual
resistivity ratios up to 55. Shubnikov-de Haas oscillations in the
magnetoresistance and a temperature dependence in the electrical
resistivity only below 1.5 K, whose coefficient is substantially suppressed in
large magnetic fields, establish CaRuO as a Fermi liquid (FL) with
anomalously low coherence scale. Non-Fermi liquid (NFL) dependence is
found between 2 and 25 K. The high sample quality allows access to the
intrinsic electronic properties via THz spectroscopy. For frequencies below 0.6
THz, the conductivity is Drude-like and can be modeled by FL concepts, while
for higher frequencies non-Drude behavior, inconsistent with FL predictions, is
found. This establishes CaRuO as a prime example of optical NFL behavior in
the THz range.Comment: 12 pages, 21 figures including supplemental materia
Alfven Wave Reflection and Turbulent Heating in the Solar Wind from 1 Solar Radius to 1 AU: an Analytical Treatment
We study the propagation, reflection, and turbulent dissipation of Alfven
waves in coronal holes and the solar wind. We start with the Heinemann-Olbert
equations, which describe non-compressive magnetohydrodynamic fluctuations in
an inhomogeneous medium with a background flow parallel to the background
magnetic field. Following the approach of Dmitruk et al, we model the nonlinear
terms in these equations using a simple phenomenology for the cascade and
dissipation of wave energy, and assume that there is much more energy in waves
propagating away from the Sun than waves propagating towards the Sun. We then
solve the equations analytically for waves with periods of hours and longer to
obtain expressions for the wave amplitudes and turbulent heating rate as a
function of heliocentric distance. We also develop a second approximate model
that includes waves with periods of roughly one minute to one hour, which
undergo less reflection than the longer-period waves, and compare our models to
observations. Our models generalize the phenomenological model of Dmitruk et al
by accounting for the solar wind velocity, so that the turbulent heating rate
can be evaluated from the coronal base out past the Alfven critical point -
that is, throughout the region in which most of the heating and acceleration
occurs. The simple analytical expressions that we obtain can be used to
incorporate Alfven-wave reflection and turbulent heating into fluid models of
the solar wind.Comment: 9 pages, 9 figures, accepted for publication in Ap
Electrical conductivity of plasmas of DB white dwarf atmospheres
The static electrical conductivity of non-ideal, dense, partially ionized
helium plasma was calculated over a wide range of plasma parameters:
temperatures and mass density . Calculations of
electrical conductivity of plasma for the considered range of plasma parameters
are of interest for DB white dwarf atmospheres with effective temperatures
.
Electrical conductivity of plasma was calculated by using the modified random
phase approximation and semiclassical method, adapted for the case of dense,
partially ionized plasma. The results were compared with the unique existing
experimental data, including the results related to the region of dense
plasmas. In spite of low accuracy of the experimental data, the existing
agreement with them indicates that results obtained in this paper are correct
Dimensional crossover in dipolar magnetic layers
We investigate the static critical behaviour of a uniaxial magnetic layer,
with finite thickness L in one direction, yet infinitely extended in the
remaining d dimensions. The magnetic dipole-dipole interaction is taken into
account. We apply a variant of Wilson's momentum shell renormalisation group
approach to describe the crossover between the critical behaviour of the 3-D
Ising, 2-d Ising, 3-D uniaxial dipolar, and the 2-d uniaxial dipolar
universality classes. The corresponding renormalisation group fixed points are
in addition to different effective dimensionalities characterised by distinct
analytic structures of the propagator, and are consequently associated with
varying upper critical dimensions. While the limiting cases can be discussed by
means of dimensional epsilon expansions with respect to the appropriate upper
critical dimensions, respectively, the crossover features must be addressed in
terms of the renormalisation group flow trajectories at fixed dimensionality d.Comment: 25 pages, Latex, 12 figures (.eps files) and IOP style files include
Do high fetal catecholamine levels affect heart rate variability and tneconiutn passage during labour?
Objectives. To deternrine the relationship between Umbilical arterial catecholamine levels and fetal heart rate variability and meconium passage.Study design. A prospective descriptive study was perfonned. Umbilical artery catecholamine levels were measured in 55 newborns and correlated with fetal heart rate before delivery, Umbilical arterial pH, base excess and the presence of meconum-stained liquor.Results and conclusion. The range of catecholanrine levels was enonnous, with very high epinephrine or norepinephrine levels in several fetuses. We were unable to demonstrate an association between high catecholamine levels and the presence of nonnal fetal heart rate variability despite acidaemia. We postulate that high catecholamine levels may inhibit fetal meconiUITl passage
Intercomparison of tritium and noble gases analyses, 3H/3He ages and derived parameters excess air and recharge temperature
International audienceGroundwater age dating with the tritium-helium (3H/3He) method has become a powerful tool for hydrogeologists. The uncertainty of the apparent 3H/3He age depends on the analytical precision of the 3H measurement and the uncertainty of the tritiogenic 3He component. The goal of this study, as part of the groundwater age-dating interlaboratory comparison exercise, was to quantify the analytical uncertainty of the 3H and noble gas measurements and to assess whether they meet the requirements for 3H/3He dating and noble gas paleotemperature reconstruction. Samples for the groundwater dating intercomparison exercise were collected on 1 February, 2012, from three previously studied wells in the Paris Basin (France). Fourteen laboratories participated in the intercomparison for tritium analyses and ten laboratories participated in the noble gas intercomparison. Not all laboratories analyzed samples from every borehole. The reproducibility of the tritium measurements was 13.5%. The reproducibility of the 3He/4He ratio and 4He, Ne, Ar, Kr and Xe concentrations was 1.4%, 1.8%, 1.5%, 2.2%, 2.9%, and 2.4% respectively. The uncertainty of the tritium and noble gas measurements results in a typical 3H/3He age precision of better than 2.5 years in this case. However, the measurement uncertainties for the noble gas concentrations are insufficient to distinguish the appropriate excess air model if the measured helium concentration is not included. While the analytical uncertainty introduces an unavoidable source of uncertainty in the 3H/3He apparent age estimate, other sources of uncertainty are often much greater and less well defined than the analytical uncertainty
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