434 research outputs found
Supercurrent flow through an effective double barrier structure
Supercurrent flow is studied in a structure that in the Ginzburg-Landau
regime can be described in terms of an effective double barrier potential. In
the limit of strongly reflecting barriers, the passage of Cooper pairs through
such a structure may be viewed as a realization of resonant tunneling with a
rigid wave function. For interbarrier distances smaller than no
current-carrying solutions exist. For distances between and , four
solutions exist. The two symmetric solutions obey a current-phase relation of
, while the two asymmetric solutions satisfy
for all allowed values of the current. As the distance
exceeds , a new group of four solutions appears, each contaning
soliton-type oscillations between the barriers. We prove the inexistence of a
continuous crossover between the physical solutions of the nonlinear
Ginzburg-Landau equation and those of the corresponding linearized
Schr\"odinger equation. We also show that under certain conditions a repulsive
delta function barrier may quantitatively describe a SNS structure. We are thus
able to predict that the critical current of a SNSNS structure vanishes as
, where is lower than the bulk critical temperature.Comment: 20 pages, RevTex, to appear in Phys. Rev. B, 6 figures on request at
[email protected]
Sensitivity to perturbations in a quantum chaotic billiard
The Loschmidt echo (LE) measures the ability of a system to return to the
initial state after a forward quantum evolution followed by a backward
perturbed one. It has been conjectured that the echo of a classically chaotic
system decays exponentially, with a decay rate given by the minimum between the
width of the local density of states and the Lyapunov exponent. As the
perturbation strength is increased one obtains a cross-over between both
regimes. These predictions are based on situations where the Fermi Golden Rule
(FGR) is valid. By considering a paradigmatic fully chaotic system, the
Bunimovich stadium billiard, with a perturbation in a regime for which the FGR
manifestly does not work, we find a cross over from to Lyapunov decay.
We find that, challenging the analytic interpretation, these conjetures are
valid even beyond the expected range.Comment: Significantly revised version. To appear in Physical Review E Rapid
Communication
The Saffman-Taylor problem on a sphere
The Saffman-Taylor problem addresses the morphological instability of an
interface separating two immiscible, viscous fluids when they move in a narrow
gap between two flat parallel plates (Hele-Shaw cell). In this work, we extend
the classic Saffman-Taylor situation, by considering the flow between two
curved, closely spaced, concentric spheres (spherical Hele-Shaw cell). We
derive the mode-coupling differential equation for the interface perturbation
amplitudes and study both linear and nonlinear flow regimes. The effect of the
spherical cell (positive) spatial curvature on the shape of the interfacial
patterns is investigated. We show that stability properties of the fluid-fluid
interface are sensitive to the curvature of the surface. In particular, it is
found that positive spatial curvature inhibits finger tip-splitting. Hele-Shaw
flow on weakly negative, curved surfaces is briefly discussed.Comment: 26 pages, 4 figures, RevTex, accepted for publication in Phys. Rev.
Compaction of Rods: Relaxation and Ordering in Vibrated, Anisotropic Granular Material
We report on experiments to measure the temporal and spatial evolution of
packing arrangements of anisotropic, cylindrical granular material, using
high-resolution capacitive monitoring. In these experiments, the particle
configurations start from an initially disordered, low-packing-fraction state
and under vertical vibrations evolve to a dense, highly ordered, nematic state
in which the long particle axes align with the vertical tube walls. We find
that the orientational ordering process is reflected in a characteristic, steep
rise in the local packing fraction. At any given height inside the packing, the
ordering is initiated at the container walls and proceeds inward. We explore
the evolution of the local as well as the height-averaged packing fraction as a
function of vibration parameters and compare our results to relaxation
experiments conducted on spherically shaped granular materials.Comment: 9 pages incl. 7 figure
Universality of the Lyapunov regime for the Loschmidt echo
The Loschmidt echo (LE) is a magnitude that measures the sensitivity of
quantum dynamics to perturbations in the Hamiltonian. For a certain regime of
the parameters, the LE decays exponentially with a rate given by the Lyapunov
exponent of the underlying classically chaotic system. We develop a
semiclassical theory, supported by numerical results in a Lorentz gas model,
which allows us to establish and characterize the universality of this Lyapunov
regime. In particular, the universality is evidenced by the semiclassical limit
of the Fermi wavelength going to zero, the behavior for times longer than
Ehrenfest time, the insensitivity with respect to the form of the perturbation
and the behavior of individual (non-averaged) initial conditions. Finally, by
elaborating a semiclassical approximation to the Wigner function, we are able
to distinguish between classical and quantum origin for the different terms of
the LE. This approach renders an understanding for the persistence of the
Lyapunov regime after the Ehrenfest time, as well as a reinterpretation of our
results in terms of the quantum--classical transition.Comment: 33 pages, 17 figures, uses Revtex
Drake-Scotia Sea gateways: onset and evolution of the Drake Passage and Scotia Sea, implications for global ocean circulation and climate
Australasian IODP Regional Planing Workshop (2017. Sidney)Instituto Geológico y Minero de España, EspañaInstituto Andaluz de Ciencias de la Tierra, Consejo Superior de Investigaciones Científicas, EspañaIstituto Nazionale di Oceanografia e Geofisica Sperimentale, ItaliaSan Diego State University, Estados UnidosPeer reviewe
Field-testing solutions for drinking water quality monitoring in low- and middle-income regions and case studies from Latin American, African and Asian countries
Identifying potential causal effects of age at menarche: A Mendelian randomization phenome-wide association study
Background: Age at menarche has been associated with various health outcomes. We aimed to identify potential causal effects of age at menarche on health-related traits in a hypothesis-free manner. Methods: We conducted a Mendelian randomization phenome-wide association study (MR-pheWAS) of age at menarche with 17,893 health-related traits in UK Biobank (n = 181,318) using PHESANT. The exposure of interest was the genetic risk score for age at menarche. We conducted a second MR-pheWAS after excluding SNPs associated with BMI from the genetic risk score, to examine whether results might be due to the genetic overlap between age at menarche and BMI. We followed up a subset of health-related traits to investigate MR assumptions and seek replication in independent study populations. Results: Of the 17,893 tests performed in our MR-pheWAS, we identified 619 associations with the genetic risk score for age at menarche at a 5% false discovery rate threshold, of which 295 were below a Bonferroni-corrected P value threshold. These included potential effects of younger age at menarche on lower lung function, higher heel bone-mineral density, greater burden of psychosocial/mental health problems, younger age at first birth, higher risk of childhood sexual abuse, poorer cardiometabolic health, and lower physical activity. After exclusion of variants associated with BMI, the genetic risk score for age at menarche was related to 37 traits at a 5% false discovery rate, of which 29 were below a Bonferroni-corrected P value threshold. We attempted to replicate findings for bone-mineral density, lung function, neuroticism, and childhood sexual abuse using 5 independent cohorts/consortia. While estimates for lung function, higher bone-mineral density, neuroticism, and childhood sexual abuse in replication cohorts were consistent with UK Biobank estimates, confidence intervals were wide and often included the null. Conclusions: The genetic risk score for age at menarche was related to a broad range of health-related traits. Follow-up analyses indicated imprecise evidence of an effect of younger age at menarche on greater bone-mineral density, lower lung function, higher neuroticism score, and greater risk of childhood sexual abuse in the smaller replication samples available; hence, these findings need further exploration when larger independent samples become available
A oferta e a procura de saúde através do medicamento: proposta de um campo de pesquisa
Manual de referência FPN para o ensino e aperfeiçoamento em natação: um modelo multidisciplinar
ligadas à prática da natação e pretende, com a sua experiência na missão de melhorar as
condições de prática das disciplinas competitivas, estender a todas as entidades e praticantes
de atividades aquáticas os benefícios duma organização de âmbito nacional, com abrangência
insular, regional e local.
No âmbito do PEFPN_2014-2024, e da análise dos fatores de competitividade, da missão e visão
institucionais da FPN, decorreram quatro vetores estratégicos: (i) massificar a prática da natação;
(ii) desenvolver a prática desportiva; (iii) render e competir ao alto nível; (iv) sustentar a atividade:
estrutural e funcional (transversal a todos os restantes).info:eu-repo/semantics/publishedVersio
- …