529 research outputs found
Specific heat of single crystal MgB_2: a two-band superconductor with two different anisotropies
Heat-capacity measurements of a 39 microgramm MgB_2 single crystal in fields
up to 14 T and below 3 K allow the determination of the low-temperature linear
term of the specific heat, its field dependence and its anisotropy. Our results
are compatible with two-band superconductivity, the band carrying the small gap
being isotropic, that carrying the large gap having an anisotropy of ~ 5. Three
different upper critical fields are thus needed to describe the superconducting
state of MgB2.Comment: 4 pages, 4 figures - V2: Bibliography updated and some typo
corrected. One reference added - V3: version accepted for publication in PRL,
changes made in the tex
Specific heat of MgB_2 after irradiation
We studied the effect of disorder on the superconducting properties of
polycrystalline MgB_2 by specific-heat measurements. In the pristine state,
these measurements give a bulk confirmation of the presence of two
superconducting gaps with 2 Delta 0 / k_B T_c = 1.3 and 3.9 with nearly equal
weights. The scattering introduced by irradiation suppresses T_c and tends to
average the two gaps although less than predicted by theory. We also found that
by a suitable irradiation process by fast neutrons, a substantial bulk increase
of dH_{c2}/dT at T_c can be obtained without sacrificing more than a few
degrees in T_c. The upper critical field of the sample after irradiation
exceeds 28 T at T goes to 0 K.Comment: 11 pages text, 6 figures, accepted by Journal of Physics: Condensed
Matte
La santé des aînés : portrait de la santé et de ses déterminants sociaux en ville de Lausanne
L'influence du vieillissement démographique se ressent dans divers secteurs de la société. Le financement des assurances sociales, l'organisation des soins et l'accueil destiné aux aînés doivent être repensés. Une récente analyse de l'Office fédéral de la statistique suggère que l'on vieillit en meilleure santé, avec une meilleure qualité de vie que par le passé. La mise en place de programmes pour un vieillissement en bonne santé s'impose en même temps qu'évolue notre système de santé. Les données actuelles décrivant la population des Lausannois de 65 ans et plus (la cohorte Lc65+) nous invitent à réfléchir à la question. Le présent document est le premier de trois rapports qui présenteront les données de la cohorte Lc65+. Il se fonde principalement sur les informations recueillies durant les années 2010 et 2011, et présentera avant tout les problèmes de santé d'une population âgée entre 68 et 77 ans. Les aspects de la santé seront mis en perspective avec des facteurs sociaux structurels, les déterminants sociaux de la santé. Le rapport se divise en deux parties. La première donne un aperçu de l'état de santé dans la population des seniors domiciliés à Lausanne; les fréquences relatives à chaque indicateur ont été calculées et les résultats présentés sous forme de graphiques ou tableaux. La seconde partie s'attache à évaluer le lien entre les variables de santé et les facteurs socio-économiques. La significativité statistique de l'association (brute, puis ajustée sur le sexe et le groupe d'âge) entre les facteurs socio-économiques et les variables de santé a été testée par des tests du" chi" d'indépendance
Critical dynamics, duality, and the exact dynamic exponent in extreme type II superconductors
The critical dynamics of superconductors is studied using renormalization
group and duality arguments. We show that in extreme type II superconductors
the dynamic critical exponent is given exactly by . This result does not
rely on the widely used models of critical dynamics. Instead, it is shown that
follows from the duality between the extreme type II superconductor and
a model with a critically fluctuating gauge field. Our result is in agreement
with Monte Carlo simulations.Comment: 7 pages, no figures; version accepted for publication in PR
Superconductivity mediated by a soft phonon mode: specific heat, resistivity, thermal expansion and magnetization of YB6
The superconductor YB6 has the second highest critical temperature Tc among
the boride family MBn. We report measurements of the specific heat,
resistivity, magnetic susceptibility and thermal expansion from 2 to 300 K,
using a single crystal with Tc = 7.2 K. The superconducting gap is
characteristic of medium-strong coupling. The specific heat, resistivity and
expansivity curves are deconvolved to yield approximations of the phonon
density of states, the spectral electron-phonon scattering function and the
phonon density of states weighted by the frequency-dependent Grueneisen
parameter respectively. Lattice vibrations extend to high frequencies >100 meV,
but a dominant Einstein-like mode at ~8 meV, associated with the vibrations of
yttrium ions in oversized boron cages, appears to provide most of the
superconducting coupling and gives rise to an unusual temperature behavior of
several observable quantities. A surface critical field Hc3 is also observed.Comment: 29 pages, 5 tables, 17 figures. Accepted for publication in Phys.
Rev.
Specific heat of heavy fermion CePd2Si2 in high magnetic fields
We report specific heat measurements on the heavy fermion compound CePd2Si2
in magnetic fields up to 16 T and in the temperature range 1.4-16 K. A sharp
peak in the specific heat signals the antiferromagnetic transition at T_N ~ 9.3
K in zero field. The transition is found to shift to lower temperatures when a
magnetic field is applied along the crystallographic a-axis, while a field
applied parallel to the tetragonal c-axis does not affect the transition. The
magnetic contribution to the specific heat below T_N is well described by a sum
of a linear electronic term and an antiferromagnetic spin wave contribution.
Just below T_N, an additional positive curvature, especially at high fields,
arises most probably due to thermal fluctuations. The field dependence of the
coefficient of the low temperature linear term, gamma_0, extracted from the
fits shows a maximum at about 6 T, at the point where an anomaly was detected
in susceptibility measurements. The relative field dependence of both T_N and
the magnetic entropy at T_N scales as [1-(B/B_0)^2] for B // a, suggesting the
disappearance of antiferromagnetism at B_0 ~ 42 T. The expected suppression of
the antiferromagnetic transition temperature to zero makes the existence of a
magnetic quantum critical point possible.Comment: to be published in Journal of Physics: Condensed Matte
Unusual effects of anisotropy on the specific heat of ceramic and single crystal MgB2
The two-gap structure in the superconducting state of MgB_2 gives rise to
unusual thermodynamic properties which depart markedly from the isotropic
single-band BCS model, both in their temperature- and field dependence. We
report and discuss measurements of the specific heat up to 16 T on ceramic, and
up to 14 T on single crystal samples, which demonstrate these effects in the
bulk. The behavior in zero field is described in terms of two characteristic
temperatures, a crossover temperature Tc_pi ~ 13 K, and a critical temperature
Tc = Tc_sigma ~ 38 K, whereas the mixed-state specific heat requires three
characteristic fields, an isotropic crossover field Hc2_pi ~ 0.35 T, and an
anisotropic upper critical field with extreme values Hc2_sigma_c ~ 3.5 T and
Hc2_sigma_ab ~ 19 T, where the indexes \pi and \sigma refer to the 3D and 2D
sheets of the Fermi surface. Irradiation-induced interband scattering tends to
move the gaps toward a common value, and increases the upper critical field up
to ~ 28 T when Tc = 30 K.Comment: 31 pages, 9 figures. Accepted in the Physica C special issue on MgB
SO(5) superconductor in a Zeeman magnetic field: Phase diagram and thermodynamic properties
In this paper we present calculations of the SO(5) quantum rotor theory of
high-T superconductivity in Zeeman magnetic field. We use the spherical
approach for five-component quantum rotors in three-dimensional lattice to
obtain formulas for critical lines, free energy, entropy and specific heat and
present temperature dependences of these quantities for different values of
magnetic field. Our results are in qualitative agreement with relevant
experiments on high-T cuprates.Comment: 4 pages, 2 figures, to appear in Phys. Rev. B, see http://prb.aps.or
Dense breast on screening mammography: utility and futility of additional ultrasound.
High breast density decreases the sensitivity of mammography. Regardless of masking effect, it is also a stronger predictor for breast cancer than most other risk factors, including family history. Up to 50% of women have dense breast (categories C+D).
The relative risk is 2.1 to 2.3 in women with extremely dense breast (category d). There is little consensus on the potential need of additional measures. Breast Ultrasound (US) may be proposed as an adjunctive test, as it is non-invasive and non-irradiating. Since 2012, our program for breast cancer screening propose to realise an additional US to the women with category d breasts. An evaluation of the data of the first year showed that less 50% of the women act upon the recommendation. In spite of the low compliance supplementary cancers were found. Since, no more evaluation was performed.
The aim of this study was: To evaluate the effect of the recommendation in term of additional cancer's identification, additional biopsies and additional investigations. To identify the reasons of non compliance
Thermodynamic transitions in inhomogeneous d-wave superconductors
We study the spectral and thermodynamic properties of inhomogeneous d-wave
superconductors within a model where the inhomogeneity originates from atomic
scale pair disorder. This assumption has been shown to be consistent with the
small charge and large gap modulations observed by scanning tunnelling
spectroscopy (STS) on BSCCO. Here we calculate the specific heat within the
same model, and show that it gives a semi-quantitative description of the
transition width in this material. This model therefore provides a consistent
picture of both surface sensitive spectroscopy and bulk thermodynamic
properties.Comment: 4 pages, 4 figure
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