991 research outputs found
Electronic, magnetic properties and correlation effects in the layered quaternary iron oxyselenide Na2Fe2Se2O from first principles
By means of the first-principle calculations, we have investigated
electronic, magnetic properties and correlation effects for the newly
discovered layered oxyselenide Na2Fe2Se2O. Our results reveal that the electron
correlations in the Fe 3d bands promote a transition of Na2Fe2Se2O from
magnetic metallic or half-metallic states to the antiferromagnetic
Mott-insulating state. In addition, the bonding picture in Na2Fe2Se2O is
described as an anisotropic mixture of ionic and covalent contributions.Comment: 12 pages, 3 figure
Gate-controlled spin polarized current in ferromagnetic single electron transistors
We theoretically investigate spin dependent transport in ferromagnetic/normal
metal/ferromagnetic single electron transistors by applying master equation
calculations using a two dimensional space of states involving spin and charge
degrees of freedom. When the magnetizations of ferromagnetic leads are in
anti-parallel alignment, the spins accumulate in the island and a difference of
chemical potentials of the two spins is built up. This shift in chemical
potential acts as charge offset in the island and alternates the gate
dependence of spin current. Taking advantage of this effect, one can control
the polarization of current up to the polarization of lead by tuning gate
voltages.Comment: 5 pages, 4 figure
A Bargmann-Wightman-Wigner Type Quantum Field Theory
This version corrects an inportant typographical error in Eq. 17. COMMENTS,
FOR THE RECORD: A referees reoprt from Phys. Rev. Lett. read in part ``The
first named author has appreciated my exceptionally long report. He has read
and well assimilated the literature I suggested. Congratulations! This very new
version of the manuscript has now three authors and carries a very well chosen
title. Indeed Bargmann, Wightman and Wigner had studied, this subject forty
years ago, in an unpublished book (several chapters were distributed as
preprints). The authors explain well the scope of their paper. They have made a
thorough construction of a field theory of a non usual Wigner type; that is
completely new and all references are relevant. {\it This paper should be
published.}" Despite the fact that no other report was received, the editors of
Phys. Rev. Lett. rejected this paper.
D.V.A.Comment: 13 pages, RevTex, LA-UR-92-3726-RE
Maternal health, pregnancy and birth outcomes for women involved in care proceedings in Wales: a linked data study
Background: Under the Children Act 1989, local authorities in Wales, UK, can issue care proceedings if they are concerned about the welfare of a child, which can lead to removal of a child from parents. For mothers at risk of child removal, timely intervention during pregnancy may avert the need for this and improve maternal/fetal health; however, little is known about this specific population during the antenatal period. The study examined maternity characteristics of mothers whose infants were subject to care proceedings, with the aim of informing preventative interventions targeted at high risk mothers. Methods: Anonymised administrative data from Cafcass Cymru, who provide child-focused advice and support for family court proceedings in Wales, were linked to population-based maternity and health records held within the Secure Anonymised Information Linkage Databank. Linked data were available for 1111 birth mothers of infants involved in care proceedings between 2015 and 2018. Findings were benchmarked with reference to an age-deprivation-matched comparison group (n = 23,414), not subject to care proceedings but accessing maternity services during this period. Demographic characteristics, maternal health, reproductive history, interaction with midwifery services, and pregnancy and birth outcomes were examined. Descriptive and statistical tests of independence were used. Results: Half of the women in the cohort (49.4%) resided in the most deprived areas. They were more likely to be younger at entry to motherhood (63.5% <21 years-of-age compared to 42.7% in the comparison group), to have mental health (28.6% compared to 8.2%) and substance use issues (10.4% compared to 0.6%) and to smoke (62.7% compared to 24.8%) during pregnancy. The majority first engaged with maternity services within their first trimester of pregnancy (63.5% compared to 84.4%). Babies were more likely to be born preterm (14.2% compared to 6.7%) and, for full-term babies, to have low birthweights (8.0% compared to 2.8%). Conclusion: This novel linkage study highlights multiple vulnerabilities experienced by pregnant mothers who have experienced care proceedings concerning an infant. Policy and practice colleagues require a clearer picture of women’s needs if child protection and health services are to offer effective services which prevent the need for family court proceedings and infant removal
Dynamical structure factor of the anisotropic Heisenberg chain in a transverse field
We consider the anisotropic Heisenberg spin-1/2 chain in a transverse
magnetic field at zero temperature. We first determine all components of the
dynamical structure factor by combining exact results with a mean-field
approximation recently proposed by Dmitriev {\it et al}., JETP 95, 538 (2002).
We then turn to the small anisotropy limit, in which we use field theory
methods to obtain exact results. We discuss the relevance of our results to
Neutron scattering experiments on the 1D Heisenberg chain compound .Comment: 13 pages, 14 figure
Summing up the perturbation series in the Schwinger Model
Perturbation series for the electron propagator in the Schwinger Model is
summed up in a direct way by adding contributions coming from individual
Feynman diagrams. The calculation shows the complete agreement between
nonperturbative and perturbative approaches.Comment: 10 pages (in REVTEX
Exclusion Statistics of Quasiparticles in Condensed States of Composite Fermion Excitations
The exclusion statistics of quasiparticles is found at any level of the
hierarchy of condensed states of composite fermion excitations (for which
experimental indications have recently been found). The hierarchy of condensed
states of excitations in boson Jain states is introduced and the statistics of
quasiparticles is found. The quantum Hall states of charged -anyons
( -- the exclusion statistics parameter) can be described as
incompressible states of -anyons ( -- an even number).Comment: 4 page
Comprehensive calculations of three--body breakup cross sections
We present in detail a theoretical model for fragmentation reactions of
three--body halo nuclei. The different reaction mechanisms corresponding to the
different processes are described and discussed. Coulomb and nuclear
interactions are simultaneously included and the method is therefore applicable
for any target, light, intermediate and heavy. Absolute values of many
differential cross sections are then available as function of beam energy and
target. We apply the method to fragmentation of He and Li on C, Cu
and Pb. A large variety of observables, cross sections and momentum
distributions, are computed. In almost all cases we obtain good agreement with
the available experimental data.Comment: 41 pages, 10 figures, to be published in Nucl. Phys.
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Complete Muon Cooling Channel Design and Simulations
Considerable progress has been made in developing promising subsystems for muon beam cooling channels to provide the extraordinary reduction of emittances required for an energy-frontier muon collider. However, it has not yet been demonstrated that the various proposed cooling subsystems can be consolidated into an integrated end-to-end design. Presented here are concepts to address the matching of transverse emittances between subsystems through an extension of the theoretical framework of the Helical Cooling Channel (HCC), which allows a general analytical approach to guide the transition from one set of cooling channel parameters to another
Quantum information processing with superconducting qubits in a microwave field
We investigate the quantum dynamics of a Cooper-pair box with a
superconducting loop in the presence of a nonclassical microwave field. We
demonstrate the existence of Rabi oscillations for both single- and
multi-photon processes and, moreover, we propose a new quantum computing scheme
(including one-bit and conditional two-bit gates) based on Josephson qubits
coupled through microwaves.Comment: 7 pages, 1 figur
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