1,486 research outputs found
Effect of two gaps on the flux lattice internal field distribution: evidence of two length scales from muSR in Mg1-xAlxB2
We have measured the transverse field muon spin precession in the flux
lattice (FL) state of the two gap superconductor MgB2 and of the electron doped
compounds Mg1-xAlxB2 in magnetic fields up to 2.8T. We show the effect of the
two gaps on the internal field distribution in the FL, from which we determine
two coherence length parameters and the doping dependence of the London
penetration depth. This is an independent determination of the complex vortex
structure already suggested by the STM observation of large vortices in a MgB2
single crystal. Our data agrees quantitatively with STM and we thus validate a
new phenomenological model for the internal fields.Comment: now in press Phys. Rev. Lett., small modifications required by the
edito
Slow magnetic fluctuations and superconductivity in fluorine-doped NdFeAsO
Among the widely studied superconducting iron-pnictide compounds belonging to
the Ln1111 family (with Ln a lanthanide), a systematic investigation of the
crossover region between the superconducting and the antiferromagnetic phase
for the Ln = Nd case has been missing. We fill this gap by focusing on the
intermediate doping regime of NdFeAsO(1-x)F(x) by means of dc-magnetometry and
muon-spin spectroscopy measurements. The long-range order we detect at low
fluorine doping is replaced by short-range magnetic interactions at x = 0.08,
where also superconductivity appears. In this case, longitudinal-field
muon-spin spectroscopy experiments show clear evidence of slow magnetic
fluctuations that disappear at low temperatures. This fluctuating component is
ascribed to the glassy-like character of the magnetically ordered phase of
NdFeAsO at intermediate fluorine doping
Electron localization and possible phase separation in the absence of a charge density wave in single-phase 1T-VS
We report on a systematic study of the structural, magnetic and transport
properties of high-purity 1T-VS powder samples prepared under high
pressure. The results differ notably from those previously obtained by
de-intercalating Li from LiVS. First, no Charge Density Wave (CDW) is found
by transmission electron microscopy down to 94 K. Though, \textit{ab initio}
phonon calculations unveil a latent CDW instability driven by an acoustic
phonon softening at the wave vector (0.21,0.21,0)
previously reported in de-intercalated samples. A further indication of latent
lattice instability is given by an anomalous expansion of the V-S bond distance
at low temperature. Second, infrared optical absorption and electrical
resistivity measurements give evidence of non metallic properties, consistent
with the observation of no CDW phase. On the other hand, magnetic
susceptibility and NMR data suggest the coexistence of localized moments with
metallic carriers, in agreement with \textit{ab initio} band structure
calculations. This discrepancy is reconciled by a picture of electron
localization induced by disorder or electronic correlations leading to a phase
separation of metallic and non-metallic domains in the nm scale. We conclude
that 1T-VS is at the verge of a CDW transition and suggest that residual
electronic doping in Li de-intercalated samples stabilizes a uniform CDW phase
with metallic properties.Comment: 22 pages, 10 Figures. Full resolution pictures available at
http://journals.aps.org/prb/abstract/10.1103/PhysRevB.89.23512
P052: Molecular epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) strains at Geneva University Hospitals (HUG) over a 9 year period
Understanding the SR spectra of MnSi without magnetic polarons
Transverse-field muon-spin rotation (SR) experiments were performed on a
single crystal sample of the non-centrosymmetric system MnSi. The observed
angular dependence of the muon precession frequencies matches perfectly the one
of the Mn-dipolar fields acting on the muons stopping at a 4a position of the
crystallographic structure. The data provide a precise determination of the
magnetic dipolar tensor. In addition, we have calculated the shape of the field
distribution expected below the magnetic transition temperature at the 4a
muon-site when no external magnetic field is applied. We show that this field
distribution is consistent with the one reported by zero-field SR studies.
Finally, we present ab initio calculations based on the density-functional
theory which confirm the position of the muon stopping site inferred from
transverse-field SR. In view of the presented evidence we conclude that
the SR response of MnSi can be perfectly and fully understood without
invoking a hypothetical magnetic polaron state.Comment: 10 pages, 12 figure
Tuning of competing magnetic and superconducting phase volumes in LaFeAsO$_0.945F_0.055 by hydrostatic pressure
The interplay between magnetism and superconductivity in LaFeAsO_0.945F_0.055
was studied as a function of hydrostatic pressure up to p~2.4GPa by means of
muon-spin rotation (\muSR) and magnetization measurements. The application of
pressure leads to a substantial decrease of the magnetic ordering temperature
T_N and a reduction of the magnetic phase volume and, at the same time, to a
strong increase of the superconducting transition temperature T_c and the
diamagnetic susceptibility. From the volume sensitive \muSR measurements it can
be concluded that the superconducting and the magnetic areas which coexist in
the same sample are inclined towards spatial separation and compete for phase
volume as a function of pressure.Comment: 4 pages, 4 figure
Incidence of the temperature on the hydrophobic effect of alanine dissolved in water
El efecto hidrofóbico ocupa un lugar central en el estudio del plegamiento de las proteínas desde mediados del siglo pasado, cuando W. Kauzmann lo propuso como el principal responsable del colapso de éstas a su conformación nativa compacta, bajo condiciones fisiológicas normales. Experimentalmente se observa, que al variarle la temperatura al sistema se puede desplegar y replegar a una proteína, sin intervención de ningún otro elemento externo. Esto revela la importancia que presenta estudiar la influencia de la temperatura sobre ambos aspectos del efecto hidrofóbico: la hidratación hidrofóbica (estructura del agua alrededor de un aminoácido apolar) y la interacción hidrofóbica (el efecto neto que el medio acuoso ejerce sobre dos aminoácidos apolares disueltos en él).
En este trabajo consideramos un sistema formado por alanina disuelta en agua y calculamos las funciones de distribución radial alanina–agua y alanina–alanina, para cuatro temperaturas diferentes (4C, 25C, 50C y 75C). Para esto, utilizamos dos técnicas distintas y a la vez complementarias: (1) una teoría mecánico–estadística de líquidos clásicos, y (2) simulación numérica mediante dinámica molecular. De nuestros resultados se observa que al aumentar la temperatura, la hidratación disminuye y la interacción hidrofóbica alanina–alanina se hace más intensa.The hydrophobic effect has played a central role in the study of proteins folding since W. Kauzmann proposed it as the main responsible for their collapse to the compact native conformation under normal physiological conditions. By changing the medium temperature a protein can be unfolded and folded again to its native conformation, without any other external action. This reveals the importance of studying the influence of the temperature on both aspects of the hydrophobic effect: the hydrophobic hydration and the hydrophobic interaction. In this work we consider a system formed by alanine residues dissolved in water and calculate the alanine-water and alanine-alanine radial distribution functions, at four different temperatures (4C, 25C, 50C and 75C). We use two complementary theoretic techniques:
(1) a statistical mechanics theory of classical liquids, and (2) numerical simulations by molecular dynamics. From our results we conclude that when temperature is increased then the residue hydration diminishes and the alanine-alanine hydrophobic interaction becomes more intense.Instituto de Física de Líquidos y Sistemas BiológicosGrupo de Aplicaciones Matemáticas y Estadísticas de la Facultad de Ingenierí
Prevalence and acquisition rate of methicillin resistant Staphylococcus aureus (MRSA) in internal medicine wards at the University Hospital of Geneva (HUG)
Prevalence and acquisition rate of extended spectrum beta lactamase producing gram-negative organisms (ESBL-GNO) in general medical patients in Switzerland
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