89 research outputs found
Anomalous density of states in a metallic film in proximity with a superconductor
We investigated the local electronic density of states in
superconductor-normal metal (Nb-Au) bilayers using a very low temperature (60
mK) STM. High resolution tunneling spectra measured on the normal metal (Au)
surface show a clear proximity effect with an energy gap of reduced amplitude
compared to the bulk superconductor (Nb) gap. Within this mini-gap, the density
of states does not reach zero and shows clear sub-gap features. We show that
the experimental spectra cannot be described with the well-established Usadel
equations from the quasi-classical theory.Comment: 4 pages, 5 figure
Inverse proximity effect in superconductors near ferromagnetic material
We study the electronic density of states in a mesoscopic superconductor near
a transparent interface with a ferromagnetic metal. In our tunnel spectroscopy
experiment, a substantial density of states is observed at sub-gap energies
close to a ferromagnet. We compare our data with detailed calculations based on
the Usadel equation, where the effect of the ferromagnet is treated as an
effective boundary condition. We achieve an excellent agreement with theory
when non-ideal quality of the interface is taken into account.Comment: revised, 7 pages, 3 figure
Density of states in SF bilayers with arbitrary strength of magnetic scattering
We developed the self-consistent method for the calculation of the density of
states in the SF bilayers. It based on the quasi-classical Usadel
equations and takes into account the suppression of superconductivity in the S
layer due to the proximity effect with the F metal, as well as existing
mechanisms of the spin dependent electron scattering. We demonstrate that the
increase of the spin orbit or spin flip electron scattering rates results in
completely different transformations of at the free F layer
interface. The developed formalism has been applied for the interpretation of
the available experimental data.Comment: 5 pages, 8 figure
Absolute spin-valve effect with superconducting proximity structures
We investigate spin dependent transport in hybrid
superconductor(S)--normal-metal(N)--ferromagnet(F) structures under conditions
of proximity effect. We demonstrate the feasibility of the absolute spin-valve
effect for a certain interval of voltages in a system consisting of two coupled
tri-layer structures. Our results are also valid for non-collinear magnetic
configurations of the ferromagnets.Comment: 1 TEX file, 2 Postscript files. Accepted for publication in Physical
Review Letter
Superconducting proximity effect in clean ferromagnetic layers
We investigate superconducting proximity effect in clean ferromagnetic layers
with rough boundaries. The subgap density of states is formed by Andreev bound
states at energies which depend on trajectory length and the ferromagnetic
exchange field. At energies above the gap, the spectrum is governed by resonant
scattering states. The resulting density of states, measurable by tunneling
spectroscopy, exhibits a rich structure, which allows to connect the
theoretical parameters from experiments.Comment: 11 pages, 5 figures (included
Proximity effects at ferromagnet-superconductor interfaces
We study proximity effects at ferromagnet superconductor interfaces by
self-consistent numerical solution of the Bogoliubov-de Gennes equations for
the continuum, without any approximations. Our procedures allow us to study
systems with long superconducting coherence lengths. We obtain results for the
pair potential, the pair amplitude, and the local density of states. We use
these results to extract the relevant proximity lengths. We find that the
superconducting correlations in the ferromagnet exhibit a damped oscillatory
behavior that is reflected in both the pair amplitude and the local density of
states. The characteristic length scale of these oscillations is approximately
inversely proportional to the exchange field, and is independent of the
superconducting coherence length in the range studied. We find the
superconducting coherence length to be nearly independent of the ferromagnetic
polarization.Comment: 13 Pages total. Compressed .eps figs might display poorly, but will
print fin
Josephson effect in double-barrier superconductor-ferromagnet junctions
We study the Josephson effect in ballistic double-barrier SIFIS planar
junctions, consisting of bulk superconductors (S), a clean metallic ferromagnet
(F), and insulating interfaces (I). We solve the scattering problem based on
the Bogoliubov--de Gennes equations and derive a general expression for the dc
Josephson current, valid for arbitrary interfacial transparency and Fermi wave
vectors mismatch (FWVM). We consider the coherent regime in which quasiparticle
transmission resonances contribute significantly to the Andreev process. The
Josephson current is calculated for various parameters of the junction, and the
influence of both interfacial transparency and FWVM is analyzed. For thin
layers of strong ferromagnet and finite interfacial transparency, we find that
coherent (geometrical) oscillations of the maximum Josephson current are
superimposed on the oscillations related to the crossover between 0 and
states. For the same case we find that the temperature-induced
transition occurs if the junction is very close to the crossovers at zero
temperature.Comment: 13 pages, 6 figure
Three-dimensional Numerical Modeling and Computational Fluid Dynamics Simulations to Analyze and Improve Oxygen Availability in the AMC Bioartificial Liver
A numerical model to investigate fluid flow and oxygen (O(2)) transport and consumption in the AMC-Bioartificial Liver (AMC-BAL) was developed and applied to two representative micro models of the AMC-BAL with two different gas capillary patterns, each combined with two proposed hepatocyte distributions. Parameter studies were performed on each configuration to gain insight in fluid flow, shear stress distribution and oxygen availability in the AMC-BAL. We assessed the function of the internal oxygenator, the effect of changes in hepatocyte oxygen consumption parameters in time and the effect of the change from an experimental to a clinical setting. In addition, different methodologies were studied to improve cellular oxygen availability, i.e. external oxygenation of culture medium, culture medium flow rate, culture gas oxygen content (pO(2)) and the number of oxygenation capillaries. Standard operating conditions did not adequately provide all hepatocytes in the AMC-BAL with sufficient oxygen to maintain O(2) consumption at minimally 90% of maximal uptake rate. Cellular oxygen availability was optimized by increasing the number of gas capillaries and pO(2) of the oxygenation gas by a factor two. Pressure drop over the AMC-BAL and maximal shear stresses were low and not considered to be harmful. This information can be used to increase cellular efficiency and may ultimately lead to a more productive AMC-BAL
Case-Control Cohort Study of Patients' Perceptions of Disability in Mastocytosis
BACKGROUND: Indolent forms of mastocytosis account for more than 90% of all cases, but the types and type and severity of symptoms and their impact on the quality of life have not been well studied. We therefore performed a case-control cohort study to examine self-reported disability and impact of symptoms on the quality of life in patients with mastocytosis. METHODOLOGY/PRINCIPAL FINDINGS: In 2004, 363 mastocytosis patients and 90 controls in France were asked to rate to their overall disability (OPA score) and the severity of 38 individual symptoms. The latter was used to calculate a composite score (AFIRMM score). Of the 363 respondents, 262 were part of an ongoing pathophysiological study so that the following data were available: World Health Organization classification, standard measures of physical and psychological disability, existence of the D816V KIT mutation, and serum tryptase level. The mean OPA and AFIRMM scores and the standard measures of disability indicated that most mastocytosis patients suffer from disabilities due to the disease. Surprisingly, the patient's measurable and perceived disabilities did not differ according to disease classification or presence or absence of the D816V KIT mutation or an elevated (> or = 20 ng/mL) serum tryptase level. Also, 32 of the 38 AFIRMM symptoms were more common in patients than controls, but there were not substantial differences according to disease classification, presence of the D816V mutation, or the serum tryptase level. CONCLUSIONS: On the basis of these results and for the purposes of treatment, we propose that mastocytosis be first classified as aggressive or indolent and that indolent mastocytosis then be categorized according to the severity of patients' perceived symptoms and their impact on the quality of life. In addition, it appears that mastocytosis patients suffer from more symptoms and greater disability than previously thought, that mastocytosis may therefore be under-diagnosed, and that the symptoms of the indolent forms of mastocytosis might be due more to systemic release of mediators than mast cell burden
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