810 research outputs found
Angular dependence of magnetoresistivity in c-oriented MgB2 thin film
The anisotropy of MgB2 is still under debate: its value, strongly dependent
on the sample and on the measuring method, ranges between 1.2 and 13. In this
work we present our results on a MgB2 c-oriented superconducting thin film. To
evaluate the anisotropy, we followed two different approaches. Firstly,
magnetoresistivity was measured as a function of temperature at selected
magnetic fields applied both parallel and perpendicular to the c-axis;
secondly, we measured magnetoresistivity at selected temperatures and magnetic
fields, varying the angle q between the magnetic field and the c-axis. The
anisotropy estimated from the ratio between the upper critical fields parallel
and perpendicular to the c-axis and the one obtained in the framework of the
scaling approach within the anisotropic Ginzburg-Landau theory are different
but show a similar trend in the temperature dependence. The obtained results
are compared and discussed in the light of the two-band nature of MgB2. A
comparison between critical fields in thin films and single crystal is also
performed.Comment: 13 pages, 4 figures, European Physical Journal B in pres
Tc=21K in epitaxial FeSe0.5Te0.5 thin films with biaxial compressive strain
High purity epitaxial FeSe0.5Te0.5 thin films with different thickness were
grown by Pulsed Laser Ablation on different substrates. By varying the film
thickness, Tc up to 21K were observed, significantly larger than the bulk
value. Structural analyses indicated that the a axis changes significantly with
the film thickness and is linearly related to the Tc. The latter result
indicates the important role of the compressive strain in enhancing Tc. Tc is
also related to both the Fe-(Se,Te) bond length and angle, suggesting the
possibility of further enhancement
Thermoelectric behavior of Ruddlesden-Popper series iridates
The goal of this work is studying the evolution of thermoelectric transport
across the members of the Ruddlesden-Popper series iridates Srn+1IrnO3n+1,
where a metal-insulator transition driven by bandwidth change occurs, from the
strongly insulating Sr2IrO4 to the metallic non Fermi liquid behavior of
SrIrO3. Sr2IrO4 (n=1), Sr3Ir2O7 (n=2) and SrIrO3 (n=inf.) polycrystals are
synthesized at high pressure and characterized by structural, magnetic,
electric and thermoelectric transport analyses. We find a complex
thermoelectric phenomenology in the three compounds. Thermal diffusion of
charge carriers accounts for the Seebeck behavior of Sr2IrO4, whereas
additional drag mechanisms come into play in determining the Seebeck
temperature dependence of Sr3Ir2O7 and SrIrO3. These findings reveal close
relationship between magnetic, electronic and thermoelectric properties, strong
coupling of charge carriers with phonons and spin fluctuations as well as
relevance of multiband description in these compounds.Comment: main paper + supplementary informatio
Prognostic Value of the Insertion/Deletion Polymorphism of the ACE Gene in Type 2 Diabetic Subjects: Results from the Non-Insulin-Dependent Diabetes, Hypertension, Microalbuminuria or Proteinuria, Cardiovascular Events, and Ramipril (DIABHYCAR), Diabete de type 2, Nephropathie et Genetique (DIAB2NEPHROGENE), and Survie, Diabete de type 2 et Genetique (SURDIAGENE) studies
OBJECTIVE—We tested whether determination of the ACE insertion/deletion polymorphism is useful for renal and cardiovascular prognoses of type 2 diabetic subjects
High quality epitaxial FeSe0.5Te0.5 thin films grown on SrTiO3 substrates by pulsed laser deposition
Superconducting epitaxial FeSe0.5Te0.5 thin films were prepared on SrTiO3
(001) substrates by pulsed laser deposition. The high purity of the phase, the
quality of the growth and the epitaxy were studied with different experimental
techniques: X-rays diffraction, reflection high energy electron diffraction,
scanning tunnelling microscopy and atomic force microscopy. The substrate
temperature during the deposition was found to be the main parameter governing
sample morphology and superconducting critical temperature. Films obtained in
the optimal conditions show an epitaxial growth with c axis perpendicular to
the film surface and the a and b axis parallel to the substrates one, without
the evidence of any other orientation. Moreover, such films show a metallic
behavior over the whole measured temperature range and critical temperature
above 17K, which is higher than the target one.Comment: 10 pages including 4 figure
Follow-up of blood-pressure lowering and glucose control in type 2 diabetes.
BACKGROUND
In the Action in Diabetes and Vascular Disease: Preterax and Diamicron Modified Release Controlled Evaluation (ADVANCE) factorial trial, the combination of perindopril and indapamide reduced mortality among patients with type 2 diabetes, but intensive glucose control, targeting a glycated hemoglobin level of less than 6.5%, did not. We now report results of the 6-year post-trial follow-up.
METHODS
We invited surviving participants, who had previously been assigned to perindopril–indapamide or placebo and to intensive or standard glucose control (with the glucose-control comparison extending for an additional 6 months), to participate in a post-trial follow-up evaluation. The primary end points were death from any cause and major macrovascular events.
RESULTS
The baseline characteristics were similar among the 11,140 patients who originally underwent randomization and the 8494 patients who participated in the post-trial follow-up for a median of 5.9 years (blood-pressure–lowering comparison) or 5.4 years (glucose-control comparison). Between-group differences in blood pressure and glycated hemoglobin levels during the trial were no longer evident by the first post-trial visit. The reductions in the risk of death from any cause and of death from cardiovascular causes that had been observed in the group receiving active blood-pressure–lowering treatment during the trial were attenuated but significant at the end of the post-trial follow-up; the hazard ratios were 0.91 (95% confidence interval [CI], 0.84 to 0.99; P=0.03) and 0.88 (95% CI, 0.77 to 0.99; P=0.04), respectively. No differences were observed during follow-up in the risk of death from any cause or major macrovascular events between the intensive-glucose-control group and the standard-glucose-control group; the hazard ratios were 1.00 (95% CI, 0.92 to 1.08) and 1.00 (95% CI, 0.92 to 1.08), respectively.
CONCLUSIONS
The benefits with respect to mortality that had been observed among patients originally assigned to blood-pressure–lowering therapy were attenuated but still evident at the end of follow-up. There was no evidence that intensive glucose control during the trial led to long-term benefits with respect to mortality or macrovascular events
Adaptive cluster expansion for the inverse Ising problem: convergence, algorithm and tests
We present a procedure to solve the inverse Ising problem, that is to find
the interactions between a set of binary variables from the measure of their
equilibrium correlations. The method consists in constructing and selecting
specific clusters of variables, based on their contributions to the
cross-entropy of the Ising model. Small contributions are discarded to avoid
overfitting and to make the computation tractable. The properties of the
cluster expansion and its performances on synthetic data are studied. To make
the implementation easier we give the pseudo-code of the algorithm.Comment: Paper submitted to Journal of Statistical Physic
Testing data types implementations from algebraic specifications
Algebraic specifications of data types provide a natural basis for testing
data types implementations. In this framework, the conformance relation is
based on the satisfaction of axioms. This makes it possible to formally state
the fundamental concepts of testing: exhaustive test set, testability
hypotheses, oracle. Various criteria for selecting finite test sets have been
proposed. They depend on the form of the axioms, and on the possibilities of
observation of the implementation under test. This last point is related to the
well-known oracle problem. As the main interest of algebraic specifications is
data type abstraction, testing a concrete implementation raises the issue of
the gap between the abstract description and the concrete representation. The
observational semantics of algebraic specifications bring solutions on the
basis of the so-called observable contexts. After a description of testing
methods based on algebraic specifications, the chapter gives a brief
presentation of some tools and case studies, and presents some applications to
other formal methods involving datatypes
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