279 research outputs found
Characterization of sediment dynamics in an estuary environment using acoustic techniques
In recent years, acoustic-based methods have been developed to characterize the dynamical behavior of loose sediments and bed deposits in very shallow water environments. In this paper, we present preliminary results on the estimation of the dynamic changes in an estuarine environment using data from dual-frequency echosounding at high resolution and contemporaneous hydrological measurements including suspended matter concentration, density subbottom profiling, and data assimilation based on a sediment transport model. Those measurements are being conducted in the lower estuary of the Scheldt (Belgium) at the Sint Anna site where strong tide and season-dependent phenomena can be observed. This allows us to construct a ground-truthed, time-dependent geoacoustic model of the environment, i.e., a characterization of sound speed, density, and attenuation in function of time and depth. Synthetic acoustic data generated by that model will then be used to test inversion methods for monitoring sediment dynamics in real time
Depairing currents in the superconductor/ferromagnet proximity system Nb/Fe
We have investigated the behaviour of the depairing current J_{dp} in
ferromagnet/superconductor/ferromagnet (F/S/F) trilayers as function of the
thickness d_s of the superconducting layers. Theoretically, J_{dp} depends on
the superconducting order parameter or the pair density function, which is not
homogeneous across the film due to the proximity effect. We use a proximity
effect model with two parameters (proximity strength and interface
transparency), which can also describe the dependence of the superconducting
transition temperature T_c on d_s. We compare the computations with the
experimentally determined zero-field critical current J_{c0} of small strips
(typically 5~ \mu m wide) of Fe/Nb/Fe trilayers with varying thickness d_{Nb}
of the Nb layer. Near T_c the temperature dependence J_{c0}(T) is in good
agreement with the expected behaviour, which allows extrapolation to T = 0.
Both the absolute values of J_{c0}(0) and the dependence on d_{Nb} agree with
the expectations for the depairing current. We conclude that J_{dp} is
correctly determined, notwithstanding the fact that the strip width is larger
than both the superconducting penetration depth and the superconducting
coherence length, and that J_{dp}(d_s) is correctly described by the model.Comment: 10 pages, 5 figures, submitted to PR
Ferromagnetic/superconducting proximity effect in La0.7Ca0.3MnO3 / YBa2Cu3O7 superlattices
We study the interplay between magnetism and superconductivity in high
quality YBa2Cu3O7 (YBCO) / La0.7Ca0.3MnO3(LCMO)superlattices. We find evidence
for the YBCO superconductivity depression in presence of the LCMO layers. We
show that due to its short coherence length superconductivity survives in the
YBCO down to much smaller thickness in presence of the magnetic layer than in
low Tc superconductors. We also find that for a fixed thickness of the
superconducting layer, superconductivity is depressed over a thickness interval
of the magnetic layer in the 100 nm range. This is a much longer length scale
than that predicted by the theory of ferromagnetic/superconducting proximity
effect.Comment: 10 pages + 5 figures, submitted to Phys. Rev.
Proximity effect, quasiparticle transport, and local magnetic moment in ferromagnet-d-wave superconductor junctions
The proximity effect, quasiparticle transport, and local magnetic moment in
ferromagnet--d-wave superconductor junctions with {110}-oriented interface are
studied by solving self-consistently the Bogoliubov-de Gennes equations within
an extended Hubbard model. It is found that the proximity induced order
parameter oscillates in the ferromagnetic region. The modulation period is
shortened with the increased exchange field while the oscillation amplitude is
depressed by the interfacial scattering. With the determined superconducting
energy gap, a transfer matrix method is proposed to compute the subgap
conductance within a scattering approach. Many novel features including the
zero-bias conductance dip and splitting are exhibited with appropriate values
of the exchange field and interfacial scattering strength. The conductance
spectrum can be influenced seriously by the spin-flip interfacial scattering.
In addition, a sizable local magnetic moment near the {110}-oriented surface of
the d-wave superconductor is discussed.Comment: 10 pages, 16 ps-figures, to appear in Phys. Rev.
A Systematic Approach to Multiple Breath Nitrogen Washout Test Quality
Background: Accurate estimates of multiple breath washout (MBW) outcomes require correct operation of the device, appropriate distraction of the subject to ensure they breathe in a manner representative of their relaxed tidal breathing pattern, and appropriate interpretation of the acquired data. Based on available recommendations for an acceptable MBW test, we aimed to develop a protocol to systematically evaluate MBW measurements based on these criteria. Methods: 50MBWtest occasions were systematically reviewed for technical elements and whether the breathing pattern was representative of relaxed tidal breathing by an experienced MBW operator. The impact of qualitative and quantitative criteria on inter-observer agreement was assessed across eight MBW operators (n = 20 test occasions, compared using a Kappa statistic). Results: Using qualitative criteria, 46/168 trials were rejected: 16.6%were technically unacceptable and 10.7% were excluded due to inappropriate breathing pattern. Reviewer agreement was good using qualitative criteria and further improved with quantitative criteria from (Îș = 0.53â 0.83%) to (Îș 0.73â0.97%), but at the cost of exclusion of further test occasions in this retrospective data analysis. Conclusions: The application of the systematic review improved inter-observer agreement but did not affect reported MBW outcomes
Supine posture changes lung volumes and increases ventilation heterogeneity in cystic fibrosis
INTRODUCTION: Lung Clearance Index (LCI) is recognised as an early marker of cystic fibrosis (CF) lung disease. The effect of posture on LCI however is important when considering longitudinal measurements from infancy and when comparing LCI to imaging studies. METHODS: 35 children with CF and 28 healthy controls (HC) were assessed. Multiple breath washout (MBW) was performed both sitting and supine in triplicate and analysed for LCI, Scond, Sacin, and lung volumes. These values were also corrected for the Fowler dead-space to create 'alveolar' indices. RESULTS: From sitting to supine there was a significant increase in LCI and a significant decrease in FRC for both CF and HC (p<0.01). LCI, when adjusted to estimate 'alveolar' LCI (LCIalv), increased the magnitude of change with posture for both LCIalv and FRCalv in both groups, with a greater effect of change in lung volume in HC compared with children with CF. The % change in LCIalv for all subjects correlated significantly with lung volume % changes, most notably tidal volume/functional residual capacity (Vtalv/FRCalv (r = 0.54,p<0.001)). CONCLUSION: There is a significant increase in LCI from sitting to supine, which we believe to be in part due to changes in lung volume and also increasing ventilation heterogeneity related to posture. This may have implications in longitudinal measurements from infancy to older childhood and for studies comparing supine imaging methods to LCI
Tidal Volume Single Breath Washout of Two Tracer Gases - A Practical and Promising Lung Function Test
Small airway disease frequently occurs in chronic lung diseases and may cause ventilation inhomogeneity (VI), which can be assessed by washout tests of inert tracer gas. Using two tracer gases with unequal molar mass (MM) and diffusivity increases specificity for VI in different lung zones. Currently washout tests are underutilised due to the time and effort required for measurements. The aim of this study was to develop and validate a simple technique for a new tidal single breath washout test (SBW) of sulfur hexafluoride (SF(6)) and helium (He) using an ultrasonic flowmeter (USFM)
Bronchial Responsiveness Is Related to Increased Exhaled NO (FENO) in Non-Smokers and Decreased FENO in Smokers
Rationale Both atopy and smoking are known to be associated with increased bronchial responsiveness. Fraction of nitric oxide (NO) in the exhaled air (FENO), a marker of airways inflammation, is decreased by smoking and increased by atopy. NO has also a physiological bronchodilating and bronchoprotective role. Objectives To investigate how the relation between FENO and bronchial responsiveness is modulated by atopy and smoking habits. Methods Exhaled NO measurements and methacholine challenge were performed in 468 subjects from the random sample of three European Community Respiratory Health Survey II centers: Turin (Italy), Gothenburg and Uppsala (both Sweden). Atopy status was defined by using specific IgE measurements while smoking status was questionnaire-assessed. Main Results Increased bronchial responsiveness was associated with increased FENO levels in non-smokers (p = 0.02) and decreased FENO levels in current smokers (p = 0.03). The negative association between bronchial responsiveness and FENO was seen only in the group smoking less <10 cigarettes/day (p = 0.008). Increased bronchial responsiveness was associated with increased FENO in atopic subjects (p = 0.04) while no significant association was found in non-atopic participants. The reported interaction between FENO and smoking and atopy, respectively were maintained after adjusting for possible confounders (p-values<0.05). Conclusions The present study highlights the interactions of the relationship between FENO and bronchial responsiveness with smoking and atopy, suggesting different mechanisms behind atopy- and smoking-related increases of bronchial responsiveness
Alcohol-Related Context Modulates Performance of Social Drinkers in a Visual Go/No-Go Task: A Preliminary Assessment of Event-Related Potentials
Background Increased alcohol cue-reactivity and altered inhibitory processing have been reported in heavy social drinkers and alcohol-dependent patients, and are associated with relapse. In social drinkers, these two processes have been usually studied separately by recording event-related potentials (ERPs) during rapid picture presentation. The aim of our study was to confront social drinkers to a task triggering high alcohol cue-reactivity, to verify whether it specifically altered inhibitory performance, by using long-lasting background picture presentation. Methods ERP were recorded during visual Go/No-Go tasks performed by social drinkers, in which a frequent Go signal (letter âMâ), and a rare No-Go signal (letter âWâ) were superimposed on three different types of background pictures: neutral (black background), alcohol-related and non alcohol-related. Results Our data suggested that heavy social drinkers made more commission errors than light drinkers, but only in the alcohol-related context. Neurophysiologically, this was reflected by a delayed No-Go P3 component. Conclusions Elevated alcohol cue-reactivity may lead to poorer inhibitory performance in heavy social drinkers, and may be considered as an important vulnerability factor in developing alcohol misuse. Prevention programs should be designed to decrease the high arousal of alcohol stimuli and strengthen cognitive control in young, at-risk individuals.This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.SCOPUS: ar.jinfo:eu-repo/semantics/publishe
Genome-wide meta-analysis of 158,000 individuals of European ancestry identifies three loci associated with chronic back pain
Back pain is the #1 cause of years lived with disability worldwide, yet surprisingly little is known regarding the biology underlying this symptom. We conducted a genome-wide association study (GWAS) meta-analysis of ch
- âŠ