Coupling between 4f and itinerant electrons in SmFeAsO1-xFx (0.15 < x < 0.2) superconductors: an NMR study

$^{19}$F NMR measurements in SmFeAsO$_{1-x}$F$_x$, for $0.15\leq x\leq 0.2$, are presented. The nuclear spin-lattice relaxation rate $1/T_1$ increases upon cooling with a trend analogous to the one already observed in CeCu$_{5.2}$Au$_{0.8}$, a quasi two-dimensional heavy-fermion intermetallic compound with an antiferromagnetic ground-state. In particular, the behaviour of the relaxation rate either in SmFeAsO$_{1-x}$F$_x$ or in CeCu$_{5.2}$Au$_{0.8}$ 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 $^{19}$F $1/T_1$ is detected, a phenomenon which can hardly be explained within a single band model.Comment: 4 figure

Evaluating the effects of a deep excavation on monumental buildings: MarmorKirken station in Copenhagen

This paper describes the Building Risk Assessment (BRA) process implemented during the design and construction of MarmorKirken metro station in Copenhagen. Being the box station very near the monumental church, the evaluation of the effects induced by the excavation on the church was a key issue of the design. Surveys, structural and geotechnical investigations were carried out to setup reliable structural and geotechnical numerical models on which BRA, at the design stage, was based. During construction works, design predictions were systematically compared with monitoring measures, allowing to update the BRA. According to BRA results, no significant effects of construction works on the church was observed.Cet article décrit le processus d'Evaluation des Risques liés aux Bâtiments (BRA) mis en œuvre lors de la conception et de la construction de la station de métro MarmorKirken à Copenhague. Le box étant très proche de l'église monumentale, l'évaluation des effets induits par les fouilles sur l'église a été un enjeu clé de la conception. Des études, des investigations structurelles et géotechniques ont été réalisées pour établir des modèles numériques structurels et géotechniques fiables sur lesquels BRA, au stade de la conception, s'est basé. Lors des travaux de construction, les prévisions de conception ont été systématiquement comparées aux mesures de suivi, permettant ainsi de mettre à jour le BRA. Selon les résultats du BRA, aucun effet significatif des travaux de construction sur l'église n'a été observé

Superconducting phase fluctuations in SmFeAsO0.8_{0.8}F0.2_{0.2} from diamagnetism at low magnetic field above TcT_{c}

Superconducting fluctuations (SF) in SmFeAsO$_{0.8}$F$_{0.2}$ (characterized by superconducting transition temperature $T_{c} \simeq 52.3$ K) are investigated by means of isothermal high-resolution dc magnetization measurements. The diamagnetic response to magnetic fields up to 1 T above $T_{c}$ 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 ($H \gtrsim 1.5$ 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 $\lesssim H \ll H_{c2}$) 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