1,293 research outputs found
Superconductors as ideal spin sources for spintronics
Spin-polarized transport is investigated in normal metal-superconductor (NS)
junctions as a function of interface transmissivity as well as temperature when
the density of states of a superconductor is Zeeman-split in response to an
exchange field (h_exc). Similarly to the "absolute spin-valve effect" predicted
by D. Huertas-Hernando et al. [Phys. Rev. Lett. 88, 047003 (2002)] in
superconducting proximity structures, we show that NS junctions can be used to
generate highly spin-polarized currents, in alternative to half-metallic
ferromagnets. In particular, the spin-polarized current obtained is largely
tunable in magnitude and sign by acting on bias voltage and h_exc. While for
tunnel contacts the current polarization can be as high as 100%, for
transparent junctions it is dominated by the minority spin species. The effect
can be enhanced by electron "cooling" provided by the superconducting gap.Comment: 4 pages, 4 color figures, published versio
Gauge fields and interferometry in folded graphene
Folded graphene flakes are a natural byproduct of the micromechanical
exfoliation process. In this Letter we show by a combination of analytical and
numerical methods that such systems behave as intriguing interferometers due to
the interplay between an externally applied magnetic field and the gauge field
induced by the deformations in the region of the fold.Comment: 4 pages, 3 figure
Crossed Andreev reflection-induced magnetoresistance
We show that very large negative magnetoresistance can be obtained in
magnetic trilayers in a current-in-plane geometry owing to the existence of
crossed Andreev reflection. This spin-valve consists of a thin superconducting
film sandwiched between two ferromagnetic layers whose magnetization is allowed
to be either parallelly or antiparallelly aligned. For a suitable choice of
structure parameters and nearly fully spin-polarized ferromagnets the
magnetoresistance can exceed -80%. Our results are relevant for the design and
implementation of spintronic devices exploiting ferromagnet-superconductor
structures.Comment: 5 pages, 4 figures, final published versio
Andreev interference in adiabatic pumping
Within the scattering approach, we develop a model for adiabatic quantum
pumping in hybrid normal/superconductor systems where several superconducting
leads are present. This is exploited to study Andreev-interference effects on
adiabatically pumped charge in a 3-arm beam splitter attached to one normal and
two superconducting leads with different phases of the order parameters. We
derive expressions for the pumped charge through the normal lead for different
parameters for the scattering region, and elucidate the effects due to Andreev
interference. In contrast to what happens for voltage-driven transport, Andreev
interference does not yield in general a pumped current which is a symmetric
function of the superconducting-phase difference.Comment: 4 pages, 1 figur
Interactions between sympathetic nervous system and endogenous endothelin in patients with essential hypertension
Experimental evidence indicates that endothelin 1 stimulates the sympathetic nervous system by activation of the subtype A receptor. The aim of the present study was to assess whether this mechanism is active in humans and to investigate its potential role in the pathogenesis of essential hypertension. In 15 hypertensive patients and 12 normotensive subjects, blood pressure, heart rate, and muscle sympathetic nerve activity were evaluated during intravenous 20-minute infusion of BQ123 (0.1 mg/kg per hour), an endothelin A receptor antagonist, and sodium nitroprusside (SNP; 0.4 μg/kg per minute). In hypertensive patients, blood pressure was reduced similarly by BQ123 and SNP. In contrast, the increase in muscle sympathetic nerve activity induced by BQ123 (from 52.0±4.9 to 56.8±5.5 bursts per 100 heartbeats; P<0.05 versus baseline) was significantly lower (P<0.05) than that induced by SNP (from 50.6±4.9 to 61.1±5.1 bursts per 100 heartbeats; P<0.05 versus baseline). In normotensive subjects, SNP reduced blood pressure and increased muscle sympathetic activity, whereas BQ123 was ineffective. Thus, in a subgroup (n=9) of normotensive subjects, we administered BQ123 at a higher dose (0.2 mg/kg per hour), representing an equidepressor dose of SNP, inducing a blunted increase in sympathetic activity (from 44.1±2.4 to 50.1±6.4 bursts per 100 heartbeats; P<0.05 versus baseline). Finally, administration of a different vasodilator (papaverine, 0.5 mg/kg per hour) exerted results superimposable to SNP. Endogenous endothelin 1 appears to have a sympathoexcitatory effect both in normotensive and hypertensive subjects through endothelin A receptors, contributing to basal sympathetic vasomotor tone. Moreover, essential hypertension shows an increased susceptibility to the sympathoexcitatory effect of endogenous endothelin 1
Inferior vena cava resection and reconstruction with a peritoneal patch for a leiomyosarcoma: A case report
Congenital/infantile fibrosarcoma of the colon: morphologic, immunohistochemical, molecular, and ultrastructural features of a relatively rare tumor in an extraordinary localization.
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