13,249 research outputs found
Spin-dependent pump current and noise in an adiabatic quantum pump based on domain walls in a magnetic nanowire
We study the pump current and noise properties in an adiabatically modulated
magnetic nanowire with double domain walls (DW). The modulation is brought
about by applying a slowly oscillating magnetic and electric fields with a
controllable phase difference. The pumping mechanism resembles the case of the
quantum dot pump with two-oscillating gates. The pump current, shot noise, and
heat flow show peaks when the Fermi energy matches with the spin-split resonant
levels localized between the DWs. The peak height of the pump current is an
indicator for the lifetime of the spin-split quasistationary states between the
DWs. For sharp DWs, the energy absorption from the oscillating fields results
in side-band formations observable in the pump current. The pump noise carries
information on the correlation properties between the nonequilibrium electrons
and the quasi-holes created by the oscillating scatterer. The ratio between the
pump shot noise and the heat flow serves as an indicator for quasi-particle
correlation.Comment: 18 pages, 5 figure
Second Quantization and the Spectral Action
We consider both the bosonic and fermionic second quantization of spectral
triples in the presence of a chemical potential. We show that the von Neumann
entropy and the average energy of the Gibbs state defined by the bosonic and
fermionic grand partition function can be expressed as spectral actions. It
turns out that all spectral action coefficients can be given in terms of the
modified Bessel functions. In the fermionic case, we show that the spectral
coefficients for the von Neumann entropy, in the limit when the chemical
potential approaches can be expressed in terms of the Riemann zeta
function. This recovers a result of Chamseddine-Connes-van Suijlekom.Comment: Author list is expanded. The calculations in the new version are
extended to two more Hamiltonians. New references adde
Interface Fluctuations, Burgers Equations, and Coarsening under Shear
We consider the interplay of thermal fluctuations and shear on the surface of
the domains in various systems coarsening under an imposed shear flow. These
include systems with nonconserved and conserved dynamics, and a conserved order
parameter advected by a fluid whose velocity field satisfies the Navier-Stokes
equation. In each case the equation of motion for the interface height reduces
to an anisotropic Burgers equation. The scaling exponents that describe the
growth and coarsening of the interface are calculated exactly in any dimension
in the case of conserved and nonconserved dynamics. For a fluid-advected
conserved order parameter we determine the exponents, but we are unable to
build a consistent perturbative expansion to support their validity.Comment: 10 RevTeX pages, 2 eps figure
Age and growth of Zapteryx brevirostris (Elasmobranchii: Rhinobatidae) in southern Brazil
Age and growth studies are fundamental to successful fisheries management. Zapteryx brevirostris (Muller & Henle, 1841) is distributed off the Brazilian continental shelf and this species is assessed as "Vulnerable" in the Red List of the International Union for the Conservation of Nature (IUCN). Thus, the objective of this study was to present previously unknown information about the age and growth of Z. brevirostris that can be used for its management, conservation, and fisheries. A total of 162 specimens were sampled, with total lengths (TL) varying between 35.7 cm and 56 cm. The vertebrae were embedded in resin, sectioned in cuts with 0.5 mm thickness and the growth bands of the vertebrae were read under a light microscope. In the studied area, Z. brevirostris ages were estimated from 4 to 10 years according to vertebrae patterns. The species reaches its maximum asymptotic size (Linf) around 56 cm (56 cm for females and 50.37 cm for males). This is the first estimate of age and growth for a species of the Zapteryx genus, and the results support the hypothesis that this ray requires future management conservation, particularly due to its slow growth rate and consequent susceptibility to overexploitation.Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES); Portuguese Foundation for Science and Technology (FCT, Fundacao para a Ciencia e Tecnologia) [IF/00253/2014
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