3,652 research outputs found
Inelastic cotunneling in quantum dots and molecules with weakly broken degeneracies
We calculate the nonlinear cotunneling conductance through interacting
quantum dot systems in the deep Coulomb blockade regime using a rate equation
approach based on the T-matrix formalism, which shows in the concerned regions
very good agreement with a generalized master equation approach. Our focus is
on inelastic cotunneling in systems with weakly broken degeneracies, such as
complex quantum dots or molecules. We find for these systems a characteristic
gate dependence of the non-equilibrium cotunneling conductance. While on one
side of a Coulomb diamond the conductance decreases after the inelastic
cotunneling threshold towards its saturation value, on the other side it
increases monotonously even after the threshold. We show that this behavior
originates from an asymmetric gate voltage dependence of the effective
cotunneling amplitudes.Comment: 12 pages, 12 figures; revised published versio
Strong magnetic coupling of an ultracold gas to a superconducting waveguide cavity
Placing an ensemble of ultracold atoms in the near field of a
superconducting coplanar waveguide resonator (CPWR) with one can
achieve strong coupling between a single microwave photon in the CPWR and a
collective hyperfine qubit state in the ensemble with kHz larger than the cavity line width of
kHz. Integrated on an atomchip such a system constitutes a hybrid quantum
device, which also can be used to interconnect solid-state and atomic qubits,
to study and control atomic motion via the microwave field, observe microwave
super-radiance, build an integrated micro maser or even cool the resonator
field via the atoms
The Anomalous Infrared Emission of Abell 58
We present a new model to explain the excess in mid and near infrared
emission of the central, hydrogen poor dust knot in the planetary nebula (PN)
Abell 58. Current models disagree with ISO measurement because they apply an
average grain size and equilibrium conditions only. We investigate grain size
distributions and temperature fluctuations affecting infrared emission using a
new radiative transfer code and discuss in detail the conditions requiring an
extension of the classical description. The peculiar infrared emission of V605
Aql, the central dust knot in Abell 58, has been modeled with our code. V605
Aql is of special interest as it is one of only three stars ever observed to
move from the evolutionary track of a central PN star back to the post-AGB
state.Comment: 17 pages, 4 figures; accepted and to be published in Ap
Type I Planet Migration in Nearly Laminar Disks
We describe 2D hydrodynamic simulations of the migration of low-mass planets
() in nearly laminar disks (viscosity parameter ) over timescales of several thousand orbit periods. We consider disk
masses of 1, 2, and 5 times the minimum mass solar nebula, disk thickness
parameters of and 0.05, and a variety of values and
planet masses. Disk self-gravity is fully included. Previous analytic work has
suggested that Type I planet migration can be halted in disks of sufficiently
low turbulent viscosity, for . The halting is due to a
feedback effect of breaking density waves that results in a slight mass
redistribution and consequently an increased outward torque contribution. The
simulations confirm the existence of a critical mass () beyond which migration halts in nearly laminar disks. For \alpha
\ga 10^{-3}, density feedback effects are washed out and Type I migration
persists. The critical masses are in good agreement with the analytic model of
Rafikov (2002). In addition, for \alpha \la 10^{-4} steep density gradients
produce a vortex instability, resulting in a small time-varying eccentricity in
the planet's orbit and a slight outward migration. Migration in nearly laminar
disks may be sufficiently slow to reconcile the timescales of migration theory
with those of giant planet formation in the core accretion model.Comment: 3 figures, accepted to ApJ
A randomised controlled trial of ion-exchange water softeners for the treatment of eczema in children
Epidemiological studies and anecdotal reports suggest a possible link between household use of hard water and atopic eczema. We sought to test whether installation of an ion-exchange water softener in the home can improve eczema in children
Diagnóstico de morte de pastagens de Brachiaria brizantha nas regiões de AraguaÃna, TO e Redenção, PA.
Ocorrência de morte de pastagens de Brachiaria brizantha nas regiões de AraguaÃna, em Tocantins e Redenção, no sul do Pará, motivou pesquisadores da Embrapa Gado de Corte a realizarem uma viagem de diagnóstico, durante o perÃodo de 4 a 9 de março de 1999. Constatou-se que a morte das pastagens ocorria em áreas localizadas (reboleiras) das pastagens. Apesar de terem sido verificadas altas infestações de cigarrinhas-das-pastagens, bem como de cupins subterrâneos, em alguns locais, o excesso de água em áreas de depressão do terreno (condição favorável ao ataque de fungos nas raÃzes - principalmente do gênero Rhizoctonia), associado a um estado geral de degradação de pastagens por excesso de uso (manejo inadequado), foram consideradas as principais causas da morte de braquiária nas regiões visitadas.bitstream/item/136448/1/DOC-96.pd
Patterning of ultrathin YBCO nanowires using a new focused-ion-beam process
Manufacturing superconducting circuits out of ultrathin films is a
challenging task when it comes to patterning complex compounds, which are
likely to be deteriorated by the patterning process. With the purpose of
developing high-T superconducting photon detectors, we designed a novel
route to pattern ultrathin YBCO films down to the nanometric scale. We believe
that our method, based on a specific use of a focused-ion beam, consists in
locally implanting Ga^{3+} ions and/or defects instead of etching the film.
This protocol could be of interest to engineer high-T superconducting
devices (SQUIDS, SIS/SIN junctions and Josephson junctions), as well as to
treat other sensitive compounds.Comment: 13 pages, 7 figure
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