1,683 research outputs found
Many-body position operator in lattice fermionic systems with periodic boundary conditions
A total position operator in the position representation is derived for
lattice fermionic systems with periodic boundary conditions. The operator is
shown to be Hermitian, the generator of translations in momentum space, and its
time derivative is shown to correspond to the total current operator in a
periodic system. The operator is such that its moments can be calculated up to
any order. To demonstrate its utility finite size scaling is applied to the
Brinkman-Rice transition as well as metallic and insulating Gutzwiller
wavefunctions.Comment: to appear in Journal of Physics A: Mathematical and General
(reference will be added later
Transport and the Order Parameter of Superconducting UPt3
We calculate the ultrasonic absorption and the thermal conductivity in the
superconducting state of UPt as functions of temperature and direction of
propagation and polarization. Two leading candidates for the superconducting
order parameter are considered: the and representations. Both
can fit the data except for the ultrasonic absorption in the phase. To do
that, it is necessary to suppose that the system has only a single domain, and
that must be chosen as the most favorable one. However, the theory
requires fine-tuning of parameters to fit the low temperature thermal
conductivity. Thus, transport data favor the theory. Measurements of
the thermal conductivity as a function of pressure at low temperature could
help to further distinguish the two theories.Comment: 7 pages, 4 figure
Tilting instability and other anomalies in the flux-lattice in some magnetic superconductors
The flux-line lattice in the compound , which has a tendency to
ferromagnetic order in the a-b plane is studied with external magnetic field
direction close to the c-axis. We show the existence of an instability where
the direction of flux-lines spontaneously tilts away from that of the applied
field near the onset of ferromagnetic order. The enhanced fluctuations in the
flux lattice and the square flux lattice recently observed are explained and
further experiments suggested.Comment: 12 pages, Latex file, no figur
Theory of Ferromagnetic Superconductivity
It is argued that the pairing symmetry realized in a ferromagnetic
superconductor UGe must be a non-unitary triplet pairing. This particular
state is free from the Pauli limitation and can survive under a huge internal
molecular filed. To check our identification we examine its basic properties
and several experiments are proposed. In particular, the external field is used
to raise by controlling the internal spontaneous dipole field.Comment: 4 pages, no figure
Association of prenatal perchlorate, thiocyanate, and nitrate exposure with neonatal size and gestational age
BACKGROUND: Perchlorate and similar anions compete with iodine for uptake into the thyroid by the sodium iodide symporter (NIS). This may restrict fetal growth via impaired thyroid hormone production. METHODS: We collected urine samples from 107 pregnant women and used linear regression to estimate differences in newborn size and gestational age associated with increases in perchlorate, thiocyanate, nitrate, and perchlorate equivalence concentrations (PEC; measure of total NIS inhibitor exposure). RESULTS: NIS inhibitor concentrations were not associated with newborn weight, length, or gestational age. Each 2.62ng/mug creatinine increase in perchlorate was associated with smaller head circumference (0.32cm; 95% CI: -0.66, 0.01), but each 3.38ng/mug increase in PEC was associated with larger head circumference (0.48cm; -0.01, 0.97). CONCLUSIONS: These anions may have effects on fetal development (e.g. neurocognitive) that are not reflected in gross measures. Future research should focus on other abnormalities in neonates exposed to NIS inhibitors
Quantum kinetic theory of shift current electron pumping in semiconductors
We develop a theory of laser beam generation of shift currents in
non-centrosymmetric semiconductors. The currents originate when the excited
electrons transfer between different bands or scatter inside these bands, and
asymmetrically shift their centers of mass in elementary cells. Quantum kinetic
equations for hot-carrier distributions and expressions for the induced
currents are derived by nonequilibrium Green functions. In applications, we
simplify the approach to the Boltzmann limit and use it to model laser-excited
GaAs in the presence of LO phonon scattering. The shift currents are calculated
in a steady-state regime.Comment: 23 pages, 5 figures (Latex
Traffic-Related Air Pollution and All-Cause Mortality during Tuberculosis Treatment in California.
BackgroundAmbient air pollution and tuberculosis (TB) have an impact on public health worldwide, yet associations between the two remain uncertain.ObjectiveWe determined the impact of residential traffic on mortality during treatment of active TB.MethodsFrom 2000-2012, we enrolled 32,875 patients in California with active TB and followed them throughout treatment. We obtained patient data from the California Tuberculosis Registry and calculated traffic volumes and traffic densities in 100- to 400-m radius buffers around residential addresses. We used Cox models to determine mortality hazard ratios, controlling for demographic, socioeconomic, and clinical potential confounders. We categorized traffic exposures as quintiles and determined trends using Wald tests.ResultsParticipants contributed 22,576 person-years at risk. There were 2,305 deaths during treatment for a crude mortality rate of 1,021 deaths per 10,000 person-years. Traffic volumes and traffic densities in all buffers around patient residences were associated with increased mortality during TB treatment, although the findings were not statistically significant in all buffers. As the buffer size decreased, fifth-quintile mortality hazards increased, and trends across quintiles of traffic exposure became more statistically significant. Increasing quintiles of nearest-road traffic volumes in the 100-m buffer were associated with 3%, 14%, 19%, and 28% increased risk of death during TB treatment [first quintile, referent; second quintile hazard ratio (HR)=1.03 [95% confidence interval (CI): 0.86, 1.25]; third quintile HR=1.14 (95% CI: 0.95, 1.37); fourth quintile HR=1.19 (95% CI: 0.99, 1.43); fifth quintile HR=1.28 (95% CI: 1.07, 1.53), respectively; p-trend=0.002].ConclusionsResidential proximity to road traffic volumes and traffic density were associated with increased all-cause mortality in patients undergoing treatment for active tuberculosis even after adjusting for multiple demographic, socioeconomic, and clinical factors, suggesting that TB patients are susceptible to the adverse health effects of traffic-related air pollution. https://doi.org/10.1289/EHP1699
Superconductivity in ferromagnetic metals and in compounds without inversion centre
The symmetry properties and the general overview of the superconductivity
theory in the itinerant ferromagnets and in materials without space parity are
presented. The basic notions of unconventional superconductivity are introduced
in broad context of multiband superconductivity which is inherent property of
ferromagnetic metals or metals without centre of inversion.Comment: 38 pages, no figure
model of superconducting UPt
The phase diagram of superconducting UPt is explained in a
Ginzburg-Landau theory starting from the hypothesis that the order parameter is
a pseudo-spin singlet which transforms according to the representation
of the point group. We show how to compute the positions of the phase
boundaries both when the applied field is in the basal plane and when it is
along the c-axis. The experimental phase diagrams as determined by longitudinal
sound velocity data can be fit using a single set of parameters. In particular
the crossing of the upper critical field curves for the two field directions
and the apparent isotropy of the phase diagram are reproduced. The former is a
result of the magnetic properties of UPt and their contribution to the free
energy in the superconducting state. The latter is a consequence of an
approximate particle-hole symmetry. Finally we extend the theory to finite
pressure and show that, in contrast to other models, the model
explains the observed pressure dependence of the phase boundaries.Comment: RevTex, 29 pages, 18 PostScript figures in a uuencoded, gzipped tar
file. PostScript version of paper, tar file of PostScript figures and
individual PostScript figures are also available via anonymous ftp at
ftp://nym.physics.wisc.edu/anonymou/papers/upt3
Electron-Phonon Interaction and Ultrasonic Attenuation in the Ruthenate and Cuprate superconductors
This article derives an electron-phonon interaction suitable for interpreting
ultrasonic attenuation measurements in the ruthenate and cuprate
superconductors. The huge anisotropy found experimentally (Lupien et al., 2001)
in Sr2RuO4 in the normal state is accounted for in terms of the layered
square-lattice structure of Sr2RuO4, and the dominant contribution to the
attenuation in Sr2RuO4 is found to be due to electrons in the gamma band. The
experimental data in the superconducting state is found to be inconsistent with
vertical lines nodes in the gap in either (100) or (110) planes. Also, a
general method, based on the use of symmetry, is developed to allow for the
analysis of ultrasonic attenuation experiments in superconductors in which the
electronic band structure is complicated or not known. Our results, both for
the normal-state anisotropy, and relating to the positions of the gap nodes in
the superconducting state, are different from those obtained from analyses
using a more traditional model for the electron-phonon interaction in terms of
an isotropic electron stress tensor. Also, a brief discussion of the ultrasonic
attenuation in UPt3 is given.Comment: 12 pages. Comments have been added to the original version of this
article showing how, for the ultrasonic attenuation for a hexagonal crystal
(which must be isotropic with respect to rotations about the c axis) our
approach reproduces the results of the traditional isotropic electron stress
tensor mode
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