153 research outputs found
Il ruolo degli effetti di sito sulla risposta strutturale degli edifici nella conca aquilana
Il terremoto de LâAquila del 6 aprile 2009 Ăš stato significativamente caratterizzato dagli effetti di sito, evidenziati sia dalla variabilitĂ delle registrazioni accelerometriche in zona near fault che dalla disuniforme distribuzione del danno rilevato. In particolare, nel quartiere aquilano di Pettino, in corrispondenza di un complesso residenziale composto da sette edifici della stessa tipologia strutturale, Ăš stato osservato un danneggiamento molto diversificato.
La nota riporta i risultati di una serie di analisi di risposta sismica locale 1D, condotte in corrispondenza di alcuni degli edifici del quartiere, per i quali si disponeva di indagini geotecniche di dettaglio, finalizzate a valutare lâinfluenza degli effetti di sito sulla risposta delle strutture. I risultati delle analisi condotte in condizioni di campo libero hanno mostrato significative amplificazioni del moto proprio in corrispondenza delle frequenze fondamentali del moto di input. Le analisi del sistema sottosuolo-edificio, condotte mediante lâutilizzo di un codice con formulazione a masse concentrate hanno inoltre consentito di verificare lâincidenza dellâinterazione inerziale sul moto in superficie, nonchĂ© di riprodurre in forma semplificata il meccanismo di piano soffice osservato
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
Specific-heat study of superconducting and normal states in FeSe1-xTex (0.6<=x<=1) single crystals: Strong-coupling superconductivity, strong electron-correlation, and inhomogeneity
The electronic specific heat of as-grown and annealed single-crystals of
FeSe1-xTex (0.6<=x<=1) has been investigated. It has been found that annealed
single-crystals with x=0.6-0.9 exhibit bulk superconductivity with a clear
specific-heat jump at the superconducting (SC) transition temperature, Tc. Both
2Delta_0/kBTc [Delta_0: the SC gap at 0 K estimated using the single-band BCS
s-wave model] and Delta C/(gamma_n-gamma_0)Tc [Delta C$: the specific-heat jump
at Tc, gamma_n: the electronic specific-heat coefficient in the normal state,
gamma_0: the residual electronic specific-heat coefficient at 0 K in the SC
state] are largest in the well-annealed single-crystal with x=0.7, i.e., 4.29
and 2.76, respectively, indicating that the superconductivity is of the strong
coupling. The thermodynamic critical field has also been estimated. gamma_n has
been found to be one order of magnitude larger than those estimated from the
band calculations and increases with increasing x at x=0.6-0.9, which is
surmised to be due to the increase in the electronic effective mass, namely,
the enhancement of the electron correlation. It has been found that there
remains a finite value of gamma_0 in the SC state even in the well-annealed
single-crystals with x=0.8-0.9, suggesting an inhomogeneous electronic state in
real space and/or momentum space.Comment: 22 pages, 1 table, 6 figures, Version 2 has been accepted for
publication in J. Phys. Soc. Jp
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
Isoelectronic Ru substitution at Fe-site in Sm(Fe1-xRux)As(O0.85F0.15) compound and its effects on structural, superconducting and normal state properties
In this work we present a systematic experimental and theoretical study of
the structural, transport and superconducting properties of
Sm(Fe1-xRux)As(O0.85F0.15) polycrystalline samples as a function of Ru content
(x) ranging from 0 to 1. The choice of Ru as isoelectronic substitution at Fe
site of F-doped compounds allows to better clarify the role of structural
disorder in modifying the normal and superconducting properties of these newly
discovered multiband superconductors. Two different regions are identified: the
Fe-rich phase (x<0.5) where superconducting and normal state properties are
strongly affected by disorder induced by Ru substitution; the Ru-rich phase
(x>0.5) where the system is metallic and strongly compensated and the presence
of Ru frustrates the magnetic moment on Fe ions. Here the lack of magnetic
features and related spin fluctuations may be the cause for the suppression of
superconductivity.Comment: Accepted on Physical Review
An extended infrared study of the (p,T) phase diagram of the p-doped Cu-O plane
The ab-plane optical conductivity of eleven single crystals, belonging to the
families Sr2-xCuO2Cl2, Y1-xCaxBa2Cu3O6, Bi2Sr2-xLaxCuO6, and Bi2Sr2CaCu2O8 has
been measured with hole concentrations p between 0 and 0.18, and for 6 K < T <
500 K to obtain an infrared picture of the p,T phase diagram of the Cu-O plane.
At extreme dilution (p = 0.005), a narrow peak is observed at 1570 cm-1 (195
meV), that we assign to a single-hole bound state. For increasing doping, that
peak broadens into a far-infrared (FIR) band whose low-energy edge sets the
insulating gap. The insulator-to-metal transition (IMT) occurs when the
softening of the FIR band closes the gap thus evolving into a Drude term. In
the metallic phase, a multi-band analysis identifies a mid-infrared band which
weakly depends on temperature and softens for increasing p, while the
extended-Drude analysis leads to an optical scattering rate larger than the
frequency, as found in other cuprates. The infrared spectral weight W(T) is
consistent with a Fermi liquid renormalized by strong correlations, provided
that the T^4 term of the Sommerfeld expansion is included above 300 K. In the
superconducting phase, the optical response of single-layer Bi2Sr2-xLaxCuO6 at
optimum doping is similar to that of the corresponding optimally-doped bilayer
Bi2Sr2CaCu2O8.Comment: 28 pages, 14 figure
Interplay between magnetism and superconductivity and appearance of a second superconducting transition in alpha-FeSe at high pressure
We synthesized tetragonal alpha-FeSe by melting a powder mixture of iron and
selenium at high pressure. Subsequent annealing at normal pressure results in
removing traces of hexagonal beta- FeSe, formation of a rather sharp transition
to superconducting state at Tc ~ 7 K, and the appearance of a magnetic
transition near Tm = 120 K. Resistivity and ac-susceptibility were measured on
the annealed sample at hydrostatic pressure up to 4.5 GPa. A magnetic
transition visible in ac-susceptibility shifts down under pressure and the
resistive anomaly typical for a spin density wave (SDW) antiferromagnetic
transition develops near the susceptibility anomaly. Tc determined by the
appearance of a diamagnetic response in susceptibility, increases linearly
under pressure at a rate dTc/dP = 3.5 K/GPa. Below 1.5 GPa, the resistive
superconducting transition is sharp; the width of transition does not change
with pressure; and, Tc determined by a peak in drho/dT increases at a rate ~
3.5 K/GPa. At higher pressure, a giant broadening of the resistive transition
develops. This effect cannot be explained by possible pressure gradients in the
sample and is inherent to alpha-FeSe. The dependences drho(T)/dT show a
signature for a second peak above 3 GPa which is indicative of the appearance
of another superconducting state in alpha-FeSe at high pressure. We argue that
this second superconducting phase coexists with SDW antiferromagnetism in a
partial volume fraction and originates from pairing of charge carriers from
other sheets of the Fermi surface
GEANT4 : a simulation toolkit
Abstract Geant4 is a toolkit for simulating the passage of particles through matter. It includes a complete range of functionality including tracking, geometry, physics models and hits. The physics processes offered cover a comprehensive range, including electromagnetic, hadronic and optical processes, a large set of long-lived particles, materials and elements, over a wide energy range starting, in some cases, from 250 eV and extending in others to the TeV energy range. It has been designed and constructed to expose the physics models utilised, to handle complex geometries, and to enable its easy adaptation for optimal use in different sets of applications. The toolkit is the result of a worldwide collaboration of physicists and software engineers. It has been created exploiting software engineering and object-oriented technology and implemented in the C++ programming language. It has been used in applications in particle physics, nuclear physics, accelerator design, space engineering and medical physics. PACS: 07.05.Tp; 13; 2
Engineering reconnaissance following the August 24, 2016 M6.0 Central Italy earthquake
An earthquake with a moment magnitude reported as 6.0 from INGV (Istituto Nazionale di Geofisica e Vulcanologia);
occurred at 03:36 AM (local time) on 24 August 2016 in the central part of Italy. The epicenter was located at the borders of
the Lazio, Abruzzi, Marche and Umbria regions, about 2.5 km north-east of the village of Accumoli and about 100 km from
Rome. The hypocentral depth was about 8 km (INGV). We summarize preliminary findings of the Italy-US GEER
(Geotechnical Extreme Events Reconnaissance) team, on damage distribution, causative faults, earthquake-induced landslides
and rockfalls, building and bridge performance, and ground motion characterization. Our reconnaissance team used multidisciplinary approaches, combining expertise in geology, seismology, geomatics, geotechnical engineering, and structural
engineering. Our approach was to combine traditional reconnaissance activities of on-ground recording and mapping of field
conditions, with advanced imaging and damage detection routines enabled by state-of-the-art geomatics technology. We
anticipate that results from this study, will be useful for future post-earthquake reconnaissance efforts, and improved
emergency respons
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