2,433 research outputs found
What limits supercurrents in high temperature superconductors? A microscopic model of cuprate grain boundaries
The interface properties of high-temperature cuprate superconductors have
been of interest for many years, and play an essential role in Josephson
junctions, superconducting cables, and microwave electronics. In particular,
the maximum critical current achievable in high-Tc wires and tapes is well
known to be limited by the presence of grain boundaries, regions of mismatch
between crystallites with misoriented crystalline axes. In studies of single,
artificially fabricated grain boundaries the striking observation has been made
that the critical current Jc of a grain boundary junction depends exponentially
on the misorientation angle. Until now microscopic understanding of this
apparently universal behavior has been lacking. We present here the results of
a microscopic evaluation based on a construction of fully 3D YBCO grain
boundaries by molecular dynamics. With these structures, we calculate an
effective tight-binding Hamiltonian for the d-wave superconductor with a grain
boundary. The critical current is then shown to follow an exponential
suppression with grain boundary angle. We identify the buildup of charge
inhomogeneities as the dominant mechanism for the suppression of the
supercurrent.Comment: 28 pages, 12 figure
Frame dragging with optical vortices
General Relativistic calculations in the linear regime have been made for
electromagnetic beams of radiation known as optical vortices. These exotic
beams of light carry a physical quantity known as optical orbital angular
momentum (OAM). It is found that when a massive spinning neutral particle is
placed along the optical axis, a phenomenon known as inertial frame dragging
occurs. Our results are compared with those found previously for a ring laser
and an order of magnitude estimate of the laser intensity needed for a
precession frequency of 1 Hz is given for these "steady" beams of light.Comment: 13 pages, 2 figure
Chiral perturbation theory in a magnetic background - finite-temperature effects
We consider chiral perturbation theory for SU(2) at finite temperature in
a constant magnetic background . We compute the thermal mass of the pions
and the pion decay constant to leading order in chiral perturbation theory in
the presence of the magnetic field. The magnetic field gives rise to a
splitting between and as well as between
and . We also calculate the free energy and the
quark condensate to next-to-leading order in chiral perturbation theory. Both
the pion decay constants and the quark condensate are decreasing slower as a
function of temperature as compared to the case with vanishing magnetic field.
The latter result suggests that the critical temperature for the chiral
transition is larger in the presence of a constant magnetic field. The increase
of as a function of is in agreement with most model calculations but
in disagreement with recent lattice calculations.Comment: 24 pages and 9 fig
Substellar and low-mass dwarf identification with near-infrared imaging space observatories
AIMS: We aim to evaluate the near-infrared colors of brown dwarfs as observed
with four major infrared imaging space observatories: the Hubble Space
Telescope (HST), the James Webb Space Telescope (JWST), the Euclid mission, and
the WFIRST telescope.
METHODS: We used the SPLAT SPEX/ISPEX spectroscopic library to map out the
colors of the M-, L-, and T-type dwarfs. We have identified which color-color
combination is optimal for identifying broad type and which single color is
optimal to then identify the subtype (e.g., T0-9). We evaluated each
observatory separately as well as the narrow-field (HST and JWST) and
wide-field (Euclid and WFIRST) combinations.
RESULTS: The Euclid filters perform poorly typing brown dwarfs and WFIRST
performs only marginally better, despite a wider selection of filters. WFIRST's
W146 and F062 combined with Euclid's Y-band discriminates somewhat better
between broad brown dwarf categories. However, subtyping with any combination
of Euclid and WFIRST observations remains uncertain due to the lack of medium
or narrow-band filters. We argue that a medium band added to the WFIRST filter
selection would greatly improve its ability to preselect brown dwarfs its
imaging surveys.
CONCLUSIONS: The HST filters used in high-redshift searches are close to
optimal to identify broad stellar type. However, the addition of F127M to the
commonly used broad filter sets would allow for unambiguous subtyping. An
improvement over HST is one of two broad and medium filter combinations on
JWST: pairing F140M with either F150W or F162M discriminates very well between
subtypes
The course of untreated anxiety and depression, and determinants of poor one-year outcome: a one-year cohort study
<p>Abstract</p> <p>Background</p> <p>Little is known about the course and outcome of untreated anxiety and depression in patients with and without a self-perceived need for care. The aim of the present study was to examine the one-year course of untreated anxiety and depression, and to determine predictors of a poor outcome.</p> <p>Method</p> <p>Baseline and one-year follow-up data were used of 594 primary care patients with current anxiety or depressive disorders at baseline (established by the Composite Interview Diagnostic Instrument (CIDI)), from the Netherlands Study of Depression and Anxiety (NESDA). Receipt of and need for care were assessed by the Perceived Need for Care Questionnaire (PNCQ).</p> <p>Results</p> <p>In depression, treated and untreated patients with a perceived treatment need showed more rapid symptom decline but greater symptom severity at follow-up than untreated patients without a self-perceived mental problem or treatment need. A lower education level, lower income, unemployment, loneliness, less social support, perceived need for care, number of somatic disorders, a comorbid anxiety and depressive disorder and symptom severity at baseline predicted a poorer outcome in both anxiety and depression. When all variables were considered at the same time, only baseline symptom severity appeared to predict a poorer outcome in anxiety. In depression, a poorer outcome was also predicted by more loneliness and a comorbid anxiety and depressive disorder.</p> <p>Conclusion</p> <p>In clinical practice, special attention should be paid to exploring the need for care among possible risk groups (e.g. low social economic status, low social support), and support them in making an informed decision on whether or not to seek treatment.</p
Integrated method for quantitative morphometry and oxygen transport modelling in striated muscle
Identifying structural limitations in O2 transport is primarily restricted by current methods employed to characterise the nature of physiological remodelling. Inadequate resolution or breadth of available data has impaired development of routine diagnostic protocols and effective therapeutic strategies. Understanding O2 transport within striated muscle faces major challenges, most notably in quantifying how well individual fibres are supplied by the microcirculation, which has necessitated exploring tissue O2 supply using theoretical modelling of diffusive exchange. Having identified capillary domains as a suitable model for the description of local O2 supply, and requiring less computation than numerically calculating the trapping regions that are supplied by each capillary via biophysical transport models, we sought to design a high throughput method for histological analysis. We present an integrated package that identifies optimal protocols for identification of important input elements, processing of digitised images with semi-automated routines, and incorporation of these data into a mathematical modelling framework with computed output visualised as the tissue partial pressure of O2 (PO2) distribution across a biopsy sample. Worked examples are provided using muscle samples from experiments involving rats and humans
Excess Mortality Rate During Adulthood Among Danish Adoptees
BACKGROUND AND OBJECTIVE: Adoption studies have been used to disentangle the influence of genes from shared familial environment on various traits and disease risks. However, both the factors leading to adoption and living as an adoptee may bias the studies with regard to the relative influence of genes and environment compared to the general population. The aim was to investigate whether the cohort of domestic adoptees used for these studies in Denmark is similar to the general population with respect to all-cause mortality and cause-specific mortality rates. METHODS: 13,111 adoptees born in Denmark in 1917, or later, and adopted in 1924 to 1947 were compared to all Danes from the same birth cohorts using standardized mortality ratios (SMR). The 12,729 adoptees alive in 1970 were similarly compared to all Danes using SMR as well as cause-specific SMR. RESULTS: The excess in all-cause mortality before age 65 years in adoptees was estimated to be 1.30 (95% CI 1.26-1.35). Significant excess mortality before age 65 years was also observed for infections, vascular deaths, cancer, alcohol-related deaths and suicide. Analyses including deaths after age 65 generally showed slightly less excess in mortality, but the excess was significant for all-cause mortality, cancer, alcohol-related deaths and suicides. CONCLUSION: Adoptees have an increased all-cause mortality compared to the general population. All major specific causes of death contributed, and the highest excess is seen for alcohol-related deaths
Holographic rho mesons in an external magnetic field
We study the rho meson in a uniform magnetic field eB using a holographic
QCD-model, more specifically a D4/D8/Dbar8 brane setup in the confinement phase
at zero temperature with two quenched flavours. The parameters of the model are
fixed by matching to corresponding dual field theory parameters at zero
magnetic field. We show that the up- and down-flavour branes respond
differently to the presence of the magnetic field in the dual QCD-like theory,
as expected because of the different electromagnetic charge carried by up- and
down-quark. We discuss how to recover the Landau levels, indicating an
instability of the QCD vacuum at eB = m_rho^2 towards a phase where charged rho
mesons are condensed, as predicted by Chernodub using effective QCD-models. We
improve on these existing effective QCD-model analyses by also taking into
account the chiral magnetic catalysis effect, which tells us that the
constituent quark masses rise with eB. This turns out to increase the value of
the critical magnetic field for the onset of rho meson condensation to eB = 1.1
m_rho^2 = 0.67 GeV^2. We briefly discuss the influence of pions, which turn out
to be irrelevant for the condensation in the approximation made.Comment: 26 pages, 10 .pdf figures, v2: version accepted for publication in
JHE
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