643 research outputs found
Coupling between 4f and itinerant electrons in SmFeAsO1-xFx (0.15 < x < 0.2) superconductors: an NMR study
F NMR measurements in SmFeAsOF, for ,
are presented. The nuclear spin-lattice relaxation rate increases upon
cooling with a trend analogous to the one already observed in
CeCuAu, a quasi two-dimensional heavy-fermion intermetallic
compound with an antiferromagnetic ground-state. In particular, the behaviour
of the relaxation rate either in SmFeAsOF or in
CeCuAu can be described in the framework of the self-consistent
renormalization theory for weakly itinerant electron systems. Remarkably, no
effect of the superconducting transition on F is detected, a
phenomenon which can hardly be explained within a single band model.Comment: 4 figure
Superconducting phase fluctuations in SmFeAsOF from diamagnetism at low magnetic field above
Superconducting fluctuations (SF) in SmFeAsOF (characterized
by superconducting transition temperature K) are
investigated by means of isothermal high-resolution dc magnetization
measurements. The diamagnetic response to magnetic fields up to 1 T above
is similar to what previously reported for underdoped cuprate
superconductors and it can be justified in terms of metastable superconducting
islands at non-zero order parameter lacking of long-range coherence because of
strong phase fluctuations. In the high-field regime ( T) scaling
arguments predicted on the basis of the Ginzburg-Landau theory of conventional
SF are found to be applicable, at variance with what observed in the low-field
regime. This fact enlightens that two different phenomena are simultaneously
present in the fluctuating diamagnetism, namely the phase SF of novel character
and the conventional SF. High magnetic fields (1.5 T )
are found to suppress the former while leaving unaltered the latter one.Comment: 7 pages, 5 figure
Experimental confirmation of the low B isotope coefficient in MgB2
Recent investigations have shown that the first proposed explanations of the
disagreement between experimental and theoretical value of isotope coefficient
in MgB2 need to be reconsidered. Considering that in samples with residual
resistivity of few mu-Ohm cm critical temperature variations produced by
disorder effects can be comparable with variations due to the isotopic effect,
we adopt a procedure in evaluating the B isotope coefficient which take account
of these effects, obtaining a value which is in agreement with previous results
and then confirming that there is something still unclear in the physics of
MgB2.Comment: 8 pages, 3 figures Title has been changed A statement has been added
in page 7 of the pdf file "Finally we would..." Reference 21 has been added
Figure 1 anf Figure 2 have been change
Some Remarks on the Seismic Design of Multipropped Retaining Walls
The behavior under seismic condition of embedded retaining structures is quite complex. When the geometry (prop levels) prevents the formation of kinematic mechanisms and the structural elements do not achieve yield strength conditions, permanent displacements are expected to be relatively low and, therefore, seismic actions may cause significant increases of the forces acting on the structures: these forces are dependent on a number of factors such as the characteristics of the ground motion, the problem geometry, the mechanical behavior of the soil and the soil-structure relative stiffness. In the present study, the results of several dynamic numerical analyses of a multi-propped retaining wall in a dry coarse soil are presented and discussed. The results of the analyses indicate that large structural stresses (bending moments in walls and axial loads on props) develop as consequence of seismic actions. Post seismic stresses remain significantly large as compared to the static condition. The maximum ground acceleration in the free-field seems not to be an effective parameter in order to evaluate the seismic performance of this kind of retaining structures
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
2D equivalent linear analysis for the seismic vulnerability evaluation of multi-propped retaining structures
The evaluation of the seismic behaviour of underground structures represents one of the most actual seismic geotechnical and structural engineering research topics about the study of the complex phenomena of soil-structural interaction. In the last decades, different types of simplified and numerical approaches have been developed for the correct analysis of the seismic vulnerability of these important infrastructures and a series of laboratory tests for the seismic behaviour characterization of the soils (resonant column test, etc.) and of the coupled soil-structure system (centrifuge test, etc.) have been conducted, especially after the recent strong earthquakes where the underground structures have been subjected to significant damages. In the same way, in the last few years, the International Codes are beginning to pay attention to the concepts of the seismic design of these structures. Despite the significant development of knowledge, described above, still remain open several uncertainties of the correct reproduction of the underground structures behaviour under seismic load. In this paper, the evaluation of the seismic behaviour of a multi-propped retaining structure was conducted, considering the soil-structure interaction effects. The results of the 2D equivalent linear analysis are analysed in terms of bending moment acting on the concrete retaining walls.L‘évaluation du comportement sismique des structures souterraines représentent un des sujets de
recherche les plus courants sismique, géotechnique et de construction, qui concerne l‘étude du phénomène
complexe de l‘interaction sol-structure. Pendant les dernières décennies, différents types d‘approches simples et
numeriques ont été développés pour une analyse exacte de la vulnérabilité sismique de ces infrastructures
importantes et encore une série de tests de laboratoire pour la caractérisation du comportement sismique du sols
(test de colonne résonnante etc.) et du système couplé du sol-structure (test de centrifugation etc.) ont été menées,
après le fort tremblement de terre où les structures souterraines ont subi des dommages importants. De la même
manière, pendant les dèrnieres années, les Codes Internationales ont commencé a prêter plus d‘attention aux
concepts de désign sismique de ces structures. Malgré la considèrable connaissance, décrit ci-dessus, il y a quand
même de l‘incertitude sur la correcte reproduction du comportement des structures sous charge sismique. Dans
cet article, il a été mené l‘evaluation du comportement sismique des structures de soutenement multi-etayé,
considérant que les effets de l‘interaction sol-structure. Les resultats de l‘analyse linéaire 2D equivalente sont
analysées en termes de moment de flexion agissant sur les murs de soutènement en béton
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