9,797 research outputs found
The risk of Cerebral Palsy in survivors of multiple pregnancies with co-fetal loss or death
Objective. This study investigated the risks for cerebral palsy in survivors of multiple pregnancies with cofetal loss (< 20 weeks gestation) or cofetal death. Study Design. The total Western Australian population-based case-control study included 741 cases of cerebral palsy. Results. Antenatal cofetal loss or death occurred in 3% of all cases of cerebral palsy, which is a small but significant contribution. The odds ratio for cerebral palsy in survivors of cofetal loss that included iatrogenic pregnancy reduction was 2.65 (95% confidence interval [CI], 0.78-8.98), which gave a population-attributable proportion of 7.28% (95% CI, 0-27.5), compared with 4.25 (95% CI, 1.12-16.10) and 10.6% (95% CI, 1.0-35.6) for survivors of cofetal death. Conclusion. This study quantifies the contribution of cofetal death to cerebral palsy and suggests that cofetal loss makes a similar, although somewhat smaller, contribution to the risk for cerebral palsy in survivors of multiple pregnancies
Inelastic X-ray Scattering by Electronic Excitations in Solids at High Pressure
Investigating electronic structure and excitations under extreme conditions
gives access to a rich variety of phenomena. High pressure typically induces
behavior such as magnetic collapse and the insulator-metal transition in 3d
transition metals compounds, valence fluctuations or Kondo-like characteristics
in -electron systems, and coordination and bonding changes in molecular
solids and glasses. This article reviews research concerning electronic
excitations in materials under extreme conditions using inelastic x-ray
scattering (IXS). IXS is a spectroscopic probe of choice for this study because
of its chemical and orbital selectivity and the richness of information it
provides. Being an all-photon technique, IXS has a penetration depth compatible
with high pressure requirements. Electronic transitions under pressure in 3d
transition metals compounds and -electron systems, most of them strongly
correlated, are reviewed. Implications for geophysics are mentioned. Since the
incident X-ray energy can easily be tuned to absorption edges, resonant IXS,
often employed, is discussed at length. Finally studies involving local
structure changes and electronic transitions under pressure in materials
containing light elements are briefly reviewed.Comment: submitted to Rev. Mod. Phy
Low-crosstalk bifurcation detectors for coupled flux qubits
We present experimental results on the crosstalk between two AC-operated
dispersive bifurcation detectors, implemented in a circuit for high-fidelity
readout of two strongly coupled flux qubits. Both phase-dependent and
phase-independent contributions to the crosstalk are analyzed. For proper
tuning of the phase the measured crosstalk is 0.1 % and the correlation between
the measurement outcomes is less than 0.05 %. These results show that
bifurcative readout provides a reliable and generic approach for multi-partite
correlation experiments.Comment: Copyright 2010 American Institute of Physics. This article may be
downloaded for personal use only. Any other use requires prior permission of
the author and the American Institute of Physics. The following article
appeared in Applied Physics Letters and may be found at
http://link.aip.org/link/?apl/96/12350
Spin-orbit induced mixed-spin ground state in NiO perovskites probed by XAS: new insight into the metal to insulator transition
We report on a Ni L edges x-ray absorption spectroscopy (XAS) study
in NiO perovskites. These compounds exhibit a metal to insulator ()
transition as temperature decreases. The L edge presents a clear
splitting in the insulating state, associated to a less hybridized ground
state. Using charge transfer multiplet calculations, we establish the
importance of the crystal field and 3d spin-orbit coupling to create a
mixed-spin ground state. We explain the transition in NiO
perovskites in terms of modifications in the Ni crystal field splitting
that induces a spin transition from an essentially low-spin (LS) to a
mixed-spin state.Comment: 4 pages, 4 figures, accepted as PRB - Rapid Comm. Dez. 200
Violation of particle number conservation in the it GW approximation
We present a nontrivial model system of interacting electrons that can be solved analytically in the GW approximation. We obtain the particle number from the GW Green's function strictly analytically, and prove that there is a genuine violation of particle number conservation if the self-energy is calculated non-self-consistently from a zeroth order Green's function, as done in virtually all practical implementations. We also show that a simple shift of the self-energy that partially restores self-consistency reduces the numerical deviation significantly
Quasi-Particle Theory of Shear and Bulk Viscosities of Hadronic Matter
A theoretical framework for the calculation of shear and bulk viscosities of
hadronic matter at finite temperature is presented. The framework is based on
the quasi-particle picture. It allows for an arbitrary number of hadron species
with point-like interactions, and allows for both elastic and inelastic
collisions. Detailed balance is ensured. The particles have temperature
dependent masses arising from mean field or potential effects, which maintains
self-consistency between the equation of state and the transport coefficients.
As an example, we calculate the shear and bulk viscosity in the linear
model. The ratio of shear viscosity to entropy density shows a minimum in the
vicinity of a rapid crossover transition, while the ratio of bulk viscosity to
entropy density shows a maximum.Comment: 45 page
The thermodynamic dual structure of linear-dissipative driven systems
The spontaneous emergence of dynamical order, such as persistent currents, is
sometimes argued to require principles beyond the entropy maximization of the
second law of thermodynamics. I show that, for linear dissipation in the
Onsager regime, current formation can be driven by exactly the Jaynesian
principle of entropy maximization, suitably formulated for extended systems and
nonequilibrium boundary conditions. The Legendre dual structure of equilibrium
thermodynamics is also preserved, though it requires the admission of
current-valued state variables, and their correct incorporation in the entropy
Fluctuation-Dissipation theorems and entropy production in relaxational systems
We show that for stochastic dynamical systems out of equilibrium the
violation of the fluctuation-dissipation equality is bounded by a function of
the entropy production. The result applies to a much wider situation than `near
equilibrium', comprising diffusion as well as glasses and other macroscopic
systems far from equilibrium. For aging systems this bounds the age-frequency
regimes in which the susceptibilities satisfy FDT in terms of the rate of decay
of the H-function, a question intimately related to the reading of a
thermometer placed in contact with the system.Comment: 4 pages, RevTex; formula and reference added plus various minor
changes in the tex
Liouville equations for neutrino distribution matrices
The classical notion of a single-particle scalar distribution function or
phase space density can be generalized to a matrix in order to accommodate
superpositions of states of discrete quantum numbers, such as neutrino
mass/flavor. Such a `neutrino distribution matrix' is thus an appropriate
construct to describe a neutrino gas that may vary in space as well as time and
in which flavor mixing competes with collisions. The Liouville equations obeyed
by relativistic neutrino distribution matrices, including the spatial
derivative and vacuum flavor mixing terms, can be explicitly but elegantly
derived in two new ways: from a covariant version of the familiar simple model
of flavor mixing, and from the Klein-Gordon equations satisfied by a quantum
`density function' (mean value of paired quantum field operators). Associated
with the latter derivation is a case study in how the joint position/momentum
dependence of a classical gas (albeit with Fermi statistics) emerges from a
formalism built on quantum fields.Comment: 17 pages. Version accepted for publication in Phys. Rev. D. Section
II shortened; some changes in notation that mostly affect Section III through
Subsubsec. IIIC2; revised argument and swapping of Subsubsections IIIC1 and
IIIC
Spin-transfer in an open ferromagnetic layer: from negative damping to effective temperature
Spin-transfer is a typical spintronics effect that allows a ferromagnetic
layer to be switched by spin-injection. Most of the experimental results about
spin transfer are described on the basis of the Landau-Lifshitz-Gilbert
equation of the magnetization, in which additional current-dependent damping
factors are added, and can be positive or negative. The origin of the damping
can be investigated further by performing stochastic experiments, like one shot
relaxation experiments under spin-injection in the activation regime of the
magnetization. In this regime, the N\'eel-Brown activation law is observed
which leads to the introduction of a current-dependent effective temperature.
In order to justify the introduction of these counterintuitive parameters
(effective temperature and negative damping), a detailed thermokinetic analysis
of the different sub-systems involved is performed. We propose a thermokinetic
description of the different forms of energy exchanged between the electric and
the ferromagnetic sub-systems at a Normal/Ferromagnetic junction. The
corresponding Fokker Planck equations, including relaxations, are derived. The
damping coefficients are studied in terms of Onsager-Casimir transport
coefficients, with the help of the reciprocity relations. The effective
temperature is deduced in the activation regime.Comment: 65 pages, 10 figure
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