1,445 research outputs found
Specific heat evidence for two-gap superconductivity in ternary-iron silicide LuFeSi
We report low-temperature specific heat studies on single-crystalline
ternary-iron silicide superconductor LuFeSi with = 6.1 K
down to . We confirm a reduced normalized jump in specific heat at
, and find that the specific heat divided by temperature shows
sudden drop at and goes to zero with further decreasing
temperature. These results indicate the presence of two distinct
superconducting gaps in LuFeSi, similar to a typical two-gap
superconductor MgB. We also report Hall coefficients, band structure
calculation, and the anisotropy of upper critical fields for
LuFeSi, which support the anisotropic multiband nature and
reinforce the existence of two superconducting gaps in
LuFeSi.Comment: 5 pages, 5 figure
Photoinduced Changes of Reflectivity in Single Crystals of YBa2Cu3O6.5 (Ortho II)
We report measurements of the photoinduced change in reflectivity of an
untwinned single crystal of YBa2Cu3O6.5 in the ortho II structure. The decay
rate of the transient change in reflectivity is found to decrease rapidly with
decreasing temperature and, below Tc, with decreasing laser intensity. We
interpret the decay as a process of thermalization of antinodal quasiparticles,
whose rate is determined by an inelastic scattering rate of quasiparticle
pairs.Comment: 4 pages, 4 figure
Long Range Correlations in the Disordered Phase of a Simple Three State Lattice Gas
We investigate the dynamics of a three-state stochastic lattice gas,
consisting of holes and two oppositely "charged" species of particles, under
the influence of an "electric" field, at zero total charge. Interacting only
through an excluded volume constraint, particles can hop to nearest neighbour
empty sites. With increasing density and drive, the system orders into a
charge-segregated state. Using a combination of Langevin equations and Monte
Carlo simulations, we study the steady-state structure factors in the
disordered phase where homogeneous configurations are stable against small
harmonic perturbations. They show a discontinuity singularity at the origin
which in real space leads to an intricate crossover between power laws of
different kinds.Comment: 7 RevTeX pages, 1 postscript figure include
Lyapunov spectra and nonequilibrium ensembles equivalence in 2D fluid mechanics
We perform numerical experiments to study the Lyapunov spectra of dynamical
systems associated with the Navier–Stokes (NS) equation in two spatial dimensions truncated over the Fourier basis. Recently new equations, called GNS equations, have been introduced and conjectured to be equivalent to the NS equations at large Reynolds numbers. The Lyapunov spectra of the NS and of the corresponding GNS systems overlap, adding evidence in favor of the conjectured equivalence already studied and partially extended in previous papers. We make use of the Lyapunov spectra to study a fluctuation relation which had been proposed to extend the “fluctuation theorem” to strongly dissipative systems. Preliminary results towards the formulation of a local version of the fluctuation formula are also presented
Italian and Argentine olive oils: a NMR and gas chromatographic study
High-field Nuclear Magnetic Resonance (NMR) spectroscopy and Gas Chromatography (GC) were used to analyze 16 monovarietal olive oils obtained from few matched Mediterranean cultivars grown in experimental fields located in Italy and in the Catamarca region of Argentina. The Catamarca region is characterized by extreme pedoclimatic conditions and by a wild spontaneous vegetation. The proposed sampling allows to study the effect of different pedoclimatic conditions on olive oil composition. GC gives the fatty acid profile of olive oil samples. 1H and 13C NMR techniques provide different information: the 1H NMR spectrum allows the measurement of minor components of olive oils such as b-sytosterol, hexanal, trans-2-hexenal, formaldehyde, squalene, cycloartenol and linolenic acid; the 1C NMR spectrum allows to obtain information about glycerol tri-esters of olive oils, i.e., about their acyl composition and positional distribution on glycerol moiety. All the NMR and GC results have been submitted to Linear Discriminant Analysis (LDA) and Tree Cluster Analysis (TCA). A careful analysis of the statistical results allows to select the Mediterranean cultivars less affected by the climatic conditions present in the Catamarca region. The selected cultivars produce olive oils which keep their Mediterranean characteristics and which can be proposed as colonizing plants in this wild Argentine region.La espectroscopía de Resonancia Magnética Nuclear de alta resolución (RMN) y Cromatografía Gaseosa (CG) fueron utilizadas para analizar 16 monovariedades de aceites de oliva, obtenidas de algunos olivares Mediterráneos cultivados contemporáneamente en campos experimentales localizados en Italia y en la región de Catamarca en Argentina. Estas muestras permiten estudiar diferentes condiciones pedoclimáticas en la composición de los aceite de oliva. La CG proporciona el perfil en ácidos grasos de los aceites de oliva y las técnicas RMN 1H y RMN 13C suministran diferentes informaciones: el espectro RMN 1H permite medir los componentes menores del aceite de oliva tales como b-sitoesterol, hexanol, trans - 2 hexanol, formaldehido, escualeno, cicloartenol y ácido linolénico y el espectro RMN 13C da información referente a los triésteres de glicerol de los aceites de oliva, por ejemplo, la composición y distribución de la posición acílica en el glicerol. Los datos de CG y RMN han sido sometidos a un análisis discriminante lineal (LDA) y a un análisis cluster en árbol (TCA). Un minucioso análisis de estos resultados ha permitido seleccionar olivares que han sido menos afectados por las condiciones climáticas presentes en la región de Catamarca. Los olivares seleccionados producen aceites de oliva que pueden mantener sus características Mediterráneas y pueden ser propuestos como plantas colonizantes en esta región silvestre de Argentina
Mixing by polymers: experimental test of decay regime of mixing
By using high molecular weight fluorescent passive tracers with different
diffusion coefficients and by changing the fluid velocity we study dependence
of a characteristic mixing length on the Peclet number, , which controls
the mixing efficiency. The mixing length is found to be related to by a
power law, , and increases faster than
expected for an unbounded chaotic flow. Role of the boundaries in the mixing
length abnormal growth is clarified. The experimental findings are in a good
quantitative agreement with the recent theoretical predictions.Comment: 4 pages,5 figures. accepted for publication in PR
- …