Financial Fragility in the Current European crisis

The paper argues that the European financial system in the years following the great financial crisis started in 2007 has become increasingly fragile. Minsky’s notion of fragility, on which it is based, is related to history, policy and institutions. In the current European environment, fragility depends on the rise of shadow banks’ assets, the expansion of derivatives and the changes in financial regulation. All these elements have jointly triggered several feedback loops. In Minsky’s opinion, policies should have the scope of thwarting self-enforcing feedback loops. Yet the policies that have been implemented so far seem to have produced the opposite effects. They have created new feedback loops that nurture fragility again. This outcome, however, is not surprising for policies may change initial conditions and have unintended consequences, as Minsky has taught us since a long time

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

Parametri di intensità sismica per la stima degli spostamenti permanenti di pendii omogenei

Gli attuali criteri di progettazione in condizioni sismiche si avvalgono di procedure legate alla valutazione della prestazione del sistema espressa in termini di perdite quantificabili (costi di riparazione), di funzionalità o di beni inestimabili (vite umane, beni storico-culturali). In tale ottica il parametro rappresentativo della risposta è correlato attraverso procedure più o meno sofisticate a uno o più parametri che descrivano le caratteristiche del moto sismico. La scelta di tali parametri deve essere effettuata attraverso criteri di efficienza e sufficienza (cfr. p.es. Tothong & Luco, 2007; Luco & Cornell, 2007) inoltre devono poter essere prevedibili attraverso opportune leggi di ricorrenza. In tale ambito, la presente nota propone una applicazione dei criteri citati per la stima della curva di pericolosità degli spostamenti cosismici dei pendii e per la valutazione critica dell’efficienza dei parametri di intensità del moto considerati significativi. In particolare vengono confrontate alcune relazioni indicate nella letteratura nazionale ed internazionale, e viene presentata una relazione che tiene conto dell’intensità di Housner, IH, quale parametro efficace per la stima degli spostamenti. Per la previsione del parametro IH viene proposta, inoltre, una legge di attenuazione in funzione di magnitudo e distanza

Effect of grain refinement on enhancing critical current density and upper critical field in undoped MgB2 ex-situ tapes

Ex-situ Powder-In-Tube MgB2 tapes prepared with ball-milled, undoped powders showed a strong enhancement of the irreversibility field H*, the upper critical field Hc2 and the critical current density Jc(H) together with the suppression of the anisotropy of all of these quantities. Jc reached 104 A/cm2 at 4.2 K and 10 T, with an irreversibility field of about 14 T at 4.2 K, and Hc2 of 9 T at 25 K, high values for not-doped MgB2. The enhanced Jc and H* values are associated with significant grain refinement produced by milling of the MgB2 powder, which enhances grain boundary pinning, although at the same time also reducing the connectivity from about 12% to 8%. Although enhanced pinning and diminished connectivity are in opposition, the overall influence of ball milling on Jc is positive because the increased density of grains with a size comparable with the mean free path produces strong electron scattering that substantially increases Hc2, especially Hc2 perpendicular to the Mg and B planes.Comment: 26 pages, 9 figures, submitted to J. Appl. Phy

Prevalence of heavy smokers in the year 2000 in the province of Varese, Italy.

ABSTRACT: Prevalence of heavy smokers in the year 2000 in the Province of Varese, Italy. A. Imperatori, N. Rotolo, V. Conti, D. Di Natale, V. Tropeano, W. Mantovani. Background. Knowing the prevalence of heavy smokers (HS) by gender and age is a pre-requisite for bringing into effect public health measures against smoking-related diseases. Smoking prevalence data is available for the Italian Regions, however it is generally unknown for the Italian Provinces. Methods. In the year 2000 a survey of smoking prevalence was conducted by 47 general practitioners (GPs), by personal interview, in a large sample of the Varese Province population 45-74 years of age (28,034 subjects; 13,528 men, 14,506 women). Each surveyed subject was categorised either as ever HS (current/former smoker of at least 10 pack-years) or as non HS. The information on smoking habit collected by the GPs was anonymously pooled for analysis. Prevalence figures of smoking were tabulated by gender and by 5-year age-strata. Results. In the population 45-74 years of age the percentage of ever HS overall was 22.3% (34.4% of men; 11.0% of women). The prevalence of ever HS in both sexes combined progressively decreased with advancing age, from 23.6% (45-49 year stratum) to 19.5% (70-74 year stratum). Current HS were 24.5% of men and 9.5% of women. Conclusions. The year 2000 survey on smoking habit, showing 22.3% prevalence of ever HS in age range 45-74 years, is the first conducted in the Varese Province using a large population sample. The data on heavy cigarette smoking presented in this paper, stratified by gender and age, may be used to monitor changes in the smoking habit and in the incidence of smoking-related illnesses at the provincial level

Generation of non-synchronous accelerograms for evaluate the seismic bridge response, including local site amplification.

Non-synchronous seismic actions particularly affect the behaviour of infrastructures with significant longitudinal extension, as bridges, interacting with the soil at surface or below ground level. Some authors state that non synchronism may increase by a large amount the structural response. Several acceleration records relative to different points of the ground with different soil profiles at distances meaningful for bridge analyses, are not available in data banks. The objective of this work is the generation of arrays of asynchronous signals at different points in space, starting from natural accelerograms related to a given seismic event, to increase the number of the available data. The computer code GAS has been modified to use natural accelerograms. The procedure has been applied to a real case, L’Aquila main-shock, for which records in different points of the free field are known

Transport and superconducting properties of Fe-based superconductors: SmFeAs(O1-x Fx) versus Fe1+y (Te1-x, Sex)

We present transport and superconducting properties - namely resistivity, magnetoresistivity, Hall effect, Seebeck effect, thermal conductivity, upper critical field - of two different families of Fe-based superconductors, which can be viewed in many respects as end members: SmFeAs(O1-xFx) with the largest Tc and the largest anisotropy and Fe1+y(Te1-x,Sex), with the largest Hc2, the lowest Tc and the lowest anisotropy. In the case of the SmFeAs(O1-xFx) series, we find that a single band description allows to extract an approximated estimation of band parameters such as carrier density and mobility from experimental data, although the behaviour of Seebeck effect as a function of doping demonstrates that a multiband description would be more appropriate. On the contrary, experimental data of the Fe1+y(Te1-x,Sex) series exhibit a strongly compensated behaviour, which can be described only within a multiband model. In the Fe1+y(Te1-x,Sex) series, the role of the excess Fe, tuned by Se stoichiometry, is found to be twofold: it dopes electrons in the system and it introduces localized magnetic moments, responsible for Kondo like scattering and likely pair-breaking of Cooper pairs. Hence, excess Fe plays a crucial role also in determining superconducting properties such as the Tc and the upper critical field Bc2. The huge Bc2 values of the Fe1+y(Te1-x,Sex) samples are described by a dirty limit law, opposed to the clean limit behaviour of the SmFeAs(O1-xFx) samples. Hence, magnetic scattering by excess Fe seems to drive the system in the dirty regime, but its detrimental pairbreaking role seems not to be as severe as predicted by theory. This issue has yet to be clarified, addressing the more fundamental issue of the interplay between magnetism and superconductivity

From antiferromagnetism to superconductivity in Fe 1+y(Te1-x,Sex) (0 < x < 0.20): a neutron powder diffraction analysis

The nuclear and magnetic structure of Fe1+y(Te1-x,Sex) (0 < x < 0.20) compounds was analyzed between 2 K and 300 K by means of Rietveld refinement of neutron powder diffraction data. Samples with x < 0.075 undergo a tetragonal to monoclinic phase transition at low temperature, whose critical temperature decreases with increasing Se content; this structural transition is strictly coupled to a long range antiferromagnetic ordering at the Fe site. Both the transition to a monoclinic phase and the long range antiferromagnetism are suppressed for 0.10 < x < 0.20. The onset of the structural and of the magnetic transition remains coincident with the increase of Se substitution. The low temperature monoclinic crystal structure has been revised. Superconductivity arises for x > 0.05, therefore a significant region where superconductivity and long range antiferromagnetism coexist is present in the pseudo-binary FeTe - FeSe phase diagram.Comment: 33 pages, 4 tables, 13 figure

New Fe-based superconductors: properties relevant for applications

Less than two years after the discovery of high temperature superconductivity in oxypnictide LaFeAs(O,F) several families of superconductors based on Fe layers (1111, 122, 11, 111) are available. They share several characteristics with cuprate superconductors that compromise easy applications, such as the layered structure, the small coherence length, and unconventional pairing, On the other hand the Fe-based superconductors have metallic parent compounds, and their electronic anisotropy is generally smaller and does not strongly depend on the level of doping, the supposed order parameter symmetry is s wave, thus in principle not so detrimental to current transmission across grain boundaries. From the application point of view, the main efforts are still devoted to investigate the superconducting properties, to distinguish intrinsic from extrinsic behaviours and to compare the different families in order to identify which one is the fittest for the quest for better and more practical superconductors. The 1111 family shows the highest Tc, huge but also the most anisotropic upper critical field and in-field, fan-shaped resistive transitions reminiscent of those of cuprates, while the 122 family is much less anisotropic with sharper resistive transitions as in low temperature superconductors, but with about half the Tc of the 1111 compounds. An overview of the main superconducting properties relevant to applications will be presented. Upper critical field, electronic anisotropy parameter, intragranular and intergranular critical current density will be discussed and compared, where possible, across the Fe-based superconductor families

Growth conditions, structure, and superconductivity of pure and metal-doped FeTe1-xSex single crystals

Superconducting single crystals of pure FeTe1 xSex and FeTe0.65Se0.35 doped with Co, Ni, Cu, Mn, Zn, Mo, Cd, In, Pb, Hg, V, Ga, Mg, Al, Ti, Cr, Sr or Nd into Fe ions site have been grown applying Bridgman's method. It has been found that the sharpness of transition to the superconducting state in FeTe1 xSex is evidently inversely correlated with crystallographic quality of the crystals. Among all of the studied dopants only Co, Ni and Cu substitute Fe ions in FeTe0.65Se0.35 crystals. The remaining examined ions do not incorporate into the crystal structure. Nevertheless, they form inclusions together with selenium, tellurium and/or iron, what changes the chemical composition of host matrix and therefore influences Tc value. Small disorder introduced into magnetic sublattice, by partial replacement of Fe ions by slight amount of nonmagnetic ions of Cu (~ 1.5 at%) or by magnetic ions of Ni (~ 2 at%) and Co (~5 at%) with spin value different than that of Fe ion, completely suppresses superconductivity in FeTe1 xSex system. This indicates that even if superconductivity is observed in the system containing magnetic ions it can not survive when the disorder in magnetic ions sublattice is introduced, most likely because of magnetic scattering of Cooper pairs.Comment: 18 pages, 12 figures, 3 table