510 research outputs found
The in-plane electrodynamics of the superconductivity in Bi2Sr2CaCu2O8+d: energy scales and spectral weight distribution
The in-plane infrared and visible (3 meV-3 eV) reflectivity of
Bi2Sr2CaCu2O8+d (Bi-2212) thin films is measured between 300 K and 10 K for
different doping levels with unprecedented accuracy. The optical conductivity
is derived through an accurate fitting procedure. We study the transfer of
spectral weight from finite energy into the superfluid as the system becomes
superconducting. In the over-doped regime, the superfluid develops at the
expense of states lying below 60 meV, a conventional energy of the order of a
few times the superconducting gap. In the underdoped regime, spectral weight is
removed from up to 2 eV, far beyond any conventional scale. The intraband
spectral weight change between the normal and superconducting state, if
analyzed in terms of a change of kinetic energy is ~1 meV. Compared to the
condensation energy, this figure addresses the issue of a kinetic energy driven
mechanism.Comment: 13 pages with 9 figures include
Radioactive decays at limits of nuclear stability
The last decades brought an impressive progress in synthesizing and studying
properties of nuclides located very far from the beta stability line. Among the
most fundamental properties of such exotic nuclides, usually established first,
is the half-life, possible radioactive decay modes, and their relative
probabilities. When approaching limits of nuclear stability, new decay modes
set in. First, beta decays become accompanied by emission of nucleons from
highly excited states of daughter nuclei. Second, when the nucleon separation
energy becomes negative, nucleons start to be emitted from the ground state.
Here, we present a review of the decay modes occurring close to the limits of
stability. The experimental methods used to produce, identify and detect new
species and their radiation are discussed. The current theoretical
understanding of these decay processes is overviewed. The theoretical
description of the most recently discovered and most complex radioactive
process - the two-proton radioactivity - is discussed in more detail.Comment: Review, 68 pages, 39 figure
Integer Quantum Hall Effect in Graphite
We present Hall effect measurements on highly oriented pyrolytic graphite
that indicate the occurrence of the integer quantum-Hall-effect. The evidence
is given by the observation of regular plateau-like structures in the field
dependence of the transverse conductivity obtained in van der Pauw
configuration. Measurements with the Corbino-disk configuration support this
result and indicate that the quasi-linear and non-saturating longitudinal
magnetoresistance in graphite is governed by the Hall effect in agreement with
a recent theoretical model for disordered semiconductors.Comment: 3 figures, to be published in Solid State Communication (2006
Virtual reality, ultrasound-guided liver biopsy simulator: Development and performance discrimination
Objectives: The aim of this article was to identify and prospectively investigate simulated ultrasound-guided targeted liver biopsy performance metrics as differentiators between levels of expertise in interventional radiology.
Methods: Task analysis produced detailed procedural step documentation allowing identification of critical procedure steps and performance metrics for use in a virtual reality ultrasound-guided targeted liver biopsy procedure. Consultant (n=14; male=11, female=3) and trainee (n=26; male=19, female=7) scores on the performance metrics
were compared. Ethical approval was granted by the Liverpool Research Ethics Committee (UK). Independent t-tests and analysis of variance (ANOVA) investigated differences between groups.
Results: Independent t-tests revealed significant differences between trainees and consultants on three performance metrics: targeting, p=0.018, t=22.487 (22.040 to
20.207); probe usage time, p=0.040, t=2.132 (11.064 to 427.983); mean needle length in beam, p=0.029, t=22.272 (20.028 to 20.002). ANOVA reported significant differences across years of experience (0–1, 1–2, 3+ years) on seven performance metrics: no-go area touched, p=0.012; targeting, p=0.025; length of session, p=0.024; probe usage time, p=0.025; total needle distance moved, p=0.038; number of skin contacts, p<0.001; total time in no-go area, p=0.008. More experienced participants consistently received better performance scores on all 19 performance metrics.
Conclusion: It is possible to measure and monitor performance using simulation, with performance metrics providing feedback on skill level and differentiating levels of expertise. However, a transfer of training study is required
Combined potential and spin impurity scattering in cuprates
We present a theory of combined nonmagnetic and magnetic impurity scattering
in anisotropic superconductors accounting for the momentum-dependent impurity
potential. Applying the model to the d-wave superconducting state, we obtain a
quantitative agreement with the initial suppression of the critical temperature
due to Zn and Ni substitutions as well as electron irradiation defects in the
cuprates. We suggest, that the unequal pair-breaking effect of Zn and Ni may be
related to a different nature of the magnetic moments induced by these
impurities.Comment: 5 pages, 3 tables, RevTex, to be published in Phys. Rev.
Ventricle Surface Reconstruction from Cardiac MR Slices Using Deep Learning
Reconstructing 3D ventricular surfaces from 2D cardiac MR data is challenging due to the sparsity of the input data and the presence of interslice misalignment. It is usually formulated as a 3D mesh fitting problem often incorporating shape priors and smoothness regularization, which might affect accuracy when handling pathological cases. We propose to formulate the 3D reconstruction as a volumetric mapping problem followed by isosurfacing from dense volumetric data. Taking advantage of deep learning algorithms, which learn to predict each voxel label without explicitly defining the shapes, our method is capable of generating anatomically meaningful surfaces with great flexibility. The sparse 3D volumetric input can process contours with any orientations and thus can utilize information from multiple short- and long-axis views. In addition, our method can provide correction of motion artifacts. We have validated our method using a statistical shape model on reconstructing 3D shapes from both spatially consistent and misaligned input data
Expression of UDP-glucuronosyltransferase 1A4 in human placenta at term
The placenta contains a large variety of metabolizing enzymes, among them UDP-glucuronosyltransferase (UGT). Several UGT2B isozymes have so far been detected in human placenta, but little is known on placental expression of UGT1A isozymes. The antiepileptic drug lamotrigine (LTG) is a UGT1A4-substrate, and its serum concentration falls by over 50% during pregnancy, leading to impaired seizure control. The placenta may be involved in this. Microsomes from term placentas of 4 LTG-users and 10 healthy control subjects were prepared. Western blot analysis detected UGT1A proteins in all placentas. The presence of UGT1A4 in placenta from LTG users was confirmed with UGT1A4 commercial standard and a specific UGT1A4 primary antibody. Since LTG is primarily metabolized by UGT1A4 and this isozyme is shown to be present in placenta at term, it may be hypothesized that the placenta is involved in the fall of LTG serum concentrations during pregnancy
The ALMA Frontier Fields Survey
CONTEXT: Dusty star-forming galaxies are among the most prodigious systems at high redshift (z > 1), characterized by high star-formation rates and huge dust reservoirs. The bright end of this population has been well characterized in recent years, but considerable uncertainties remain for fainter dusty star-forming galaxies, which are responsible for the bulk of star formation at high redshift and thus play a key role in galaxy growth and evolution.
AIMS: In this first paper of our series, we describe our methods for finding high redshift faint dusty galaxies using millimeter observations with ALMA.
METHODS: We obtained ALMA 1.1 mm mosaic images for three strong-lensing galaxy clusters from the Frontier Fields Survey, which constitute some of the best studied gravitational lenses to date. The ≈2′ × 2′ mosaics overlap with the deep HST WFC3/IR footprints and encompass the high magnification regions of each cluster for maximum intrinsic source sensitivity. The combination of extremely high ALMA sensitivity and the magnification power of these clusters allows us to systematically probe the sub-mJy population of dusty star-forming galaxies over a large surveyed area.
RESULTS: We present a description of the reduction and analysis of the ALMA continuum observations for the galaxy clusters Abell 2744 (z = 0.308), MACS J0416.1-2403 (z = 0.396) and MACS J1149.5+2223 (z = 0.543), for which we reach observed rms sensitivities of 55, 59 and 71 μJy beam-1 respectively. We detect 12 dusty star-forming galaxies at S/N ≥ 5.0 across the three clusters, all of them presenting coincidence with near-infrared detected counterparts in the HST images. None of the sources fall close to the lensing caustics, thus they are not strongly lensed. The observed 1.1 mm flux densities for the total sample of galaxies range from 0.41 to 2.82 mJy, with observed effective radii spanning ≲0.̋05 to 0.̋37 ± 0.̋21 . The lensing-corrected sizes of the detected sources appear to be in the same range as those measured in brighter samples, albeit with possibly larger dispersion
EUROfusion-theory and advanced simulation coordination (E-TASC) : programme and the role of high performance computing
This paper is a written summary of an overview oral presentation given at the 1st Spanish Fusion High Performance Computer (HPC) Workshop that took place on the 27 November 2020 as an online event. Given that over the next few years ITER24 will move to its operation phase and the European-DEMO design will be significantly advanced, the EUROfusion consortium has initiated a coordination effort in theory and advanced simulation to address some of the challenges of the fusion research in Horizon EUROPE (2021-2027), i.e. the next EU Framework Programme for Research and Technological Development. This initiative has been called E-TASC, which stands for EUROfusion-Theory and Advanced Simulation Coordination. The general and guiding principles of E-TASC are summarized in this paper. In addition, an overview of the scientific results obtained in the pilot phase (2019-2020) of E-TASC are provided while highlighting the importance of the required progress in computational methods and HPC techniques. In the initial phase, five pilot theory and simulation tasks were initiated: towards a validated predictive capability of the low to high transition and pedestal physics; runaway electrons in tokamak disruptions in the presence of massive material injection; fast code for the calculation of neoclassical toroidal viscosity in stellarators and tokamaks; development of a neutral gas kinetics modular code; European edge and boundary code for reactor-relevant devices. In this paper, we report on recent progress made by each of these projects.Peer reviewe
First Results from High Angular Resolution ALMA Observations Toward the HL Tau Region
We present Atacama Large Millimeter/submillimeter Array (ALMA) observations
from the 2014 Long Baseline Campaign in dust continuum and spectral line
emission from the HL Tau region. The continuum images at wavelengths of 2.9,
1.3, and 0.87 mm have unprecedented angular resolutions of 0.075 arcseconds (10
AU) to 0.025 arcseconds (3.5 AU), revealing an astonishing level of detail in
the circumstellar disk surrounding the young solar analogue HL Tau, with a
pattern of bright and dark rings observed at all wavelengths. By fitting
ellipses to the most distinct rings, we measure precise values for the disk
inclination (46.72pm0.05 degrees) and position angle (+138.02pm0.07 degrees).
We obtain a high-fidelity image of the 1.0 mm spectral index (), which
ranges from in the optically-thick central peak and two
brightest rings, increasing to 2.3-3.0 in the dark rings. The dark rings are
not devoid of emission, we estimate a grain emissivity index of 0.8 for the
innermost dark ring and lower for subsequent dark rings, consistent with some
degree of grain growth and evolution. Additional clues that the rings arise
from planet formation include an increase in their central offsets with radius
and the presence of numerous orbital resonances. At a resolution of 35 AU, we
resolve the molecular component of the disk in HCO+ (1-0) which exhibits a
pattern over LSR velocities from 2-12 km/s consistent with Keplerian motion
around a ~1.3 solar mass star, although complicated by absorption at low
blue-shifted velocities. We also serendipitously detect and resolve the nearby
protostars XZ Tau (A/B) and LkHa358 at 2.9 mm.Comment: 11 pages, 5 figures, 2 tables, accepted for publication in the
Astrophysical Journal Letter
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