2,793 research outputs found
DC-assisted microwave quenching of YBa2Cu3O7-{\delta} coplanar waveguide to a highly dissipative state
The paper reports on finding the effect of a strong change in the microwave
losses in an HTS-based coplanar waveguide (CPW) at certain values of the input
power Pin and direct current Idc. CPW on the basis of 150 nm thick
YBa2Cu3O7-{\delta} epitaxial film on a single crystal MgO substrate was studied
experimentally. A sharp and reversible transition of the CPW into a strongly
dissipative state at the certain meanings of Pin and Idc depending on
temperature was observed. Apparently the effect can be explained by
self-heating of HTS structure caused by magnetic flux flow under the joint
influence of MW and DC.Comment: 9 pages, 5 figures, 17 reference
CO ro-vibrational lines in HD100546: A search for disc asymmetries and the role of fluorescence
We have studied the emission of CO ro-vibrational lines in the disc around
the Herbig Be star HD100546 with the final goal of using these lines as a
diagnostic to understand inner disc structure in the context of planet
formation. High-resolution IR spectra of CO ro-vibrational emission at eight
different position angles were taken with CRIRES at the VLT. From these spectra
flux tables, CO ro-vibrational line profiles, and population diagrams were
produced. We have investigated variations in the line profile shapes and line
strengths as a function of slit position angle. We used the thermochemical disc
modelling code ProDiMo based on the chemistry, radiation field, and temperature
structure of a previously published model for HD100546. Comparing observations
and the model, we investigated the possibility of disc asymmetries, the
excitation mechanism (UV fluorescence), the geometry, and physical conditions
of the inner disc. The observed CO ro-vibrational lines are largely emitted
from the inner rim of the outer disc at 10-13 AU. The line shapes are similar
for all v levels and line fluxes from all vibrational levels vary only within
one order of magnitude. All line profile asymmetries and variations can be
explained with a symmetric disc model to which a slit correction and pointing
offset is applied. Because the angular size of the CO emitting region (10-13
AU) and the slit width are comparable the line profiles are very sensitive to
the placing of the slit. The model reproduces the line shapes and the fluxes of
the v=1-0 lines as well as the spatial extent of the CO ro-vibrational
emission. It does not reproduce the observed band ratios of 0.5-0.2 with higher
vibrational bands. We find that lower gas volume densities at the surface of
the inner rim of the outer disc can make the fluorescence pumping more effcient
and reproduce the observed band ratios.Comment: 20 pages, 21 figure
Coherent control of trapped ions using off-resonant lasers
In this paper we develop a unified framework to study the coherent control of
trapped ions subject to state-dependent forces. Taking different limits in our
theory, we can reproduce two different designs of a two-qubit quantum gate
--the pushing gate [1] and the fast gates based on laser pulses from Ref.
[2]--, and propose a new design based on continuous laser beams. We demonstrate
how to simulate Ising Hamiltonians in a many ions setup, and how to create
highly entangled states and induce squeezing. Finally, in a detailed analysis
we identify the physical limits of this technique and study the dependence of
errors on the temperature. [1] J.I. Cirac, P. Zoller, Nature, 404, 579, 2000.
[2] J.J. Garcia-Ripoll, P. Zoller, J.I. Cirac, PRL 67, 062318, 200
State-dependent, addressable subwavelength lattices with cold atoms
We discuss how adiabatic potentials can be used to create addressable
lattices on a subwavelength scale, which can be used as a tool for local
operations and readout within a lattice substructure, while taking advantage of
the faster timescales and higher energy and temperature scales determined by
the shorter lattice spacing. For alkaline-earth-like atoms with non-zero
nuclear spin, these potentials can be made state dependent, for which we give
specific examples with Yb atoms. We discuss in detail the limitations
in generating the lattice potentials, in particular non-adiabatic losses, and
show that the loss rates can always be made exponentially small by increasing
the laser power.Comment: replaced with the published version. 23 pages, 11 figure
A web server for inferring the human N-acetyltransferase-2 (NAT2) enzymatic phenotype from NAT2 genotype
Summary:N-acetyltransferase-2 (NAT2) is an important enzyme that catalyzes the acetylation of aromatic and heterocyclic amine carcinogens. Individuals in human populations are divided into three NAT2 acetylator phenotypes: slow, rapid and intermediate. NAT2PRED is a web server that implements a supervised pattern recognition method to infer NAT2 phenotype from SNPs found in NAT2 gene positions 282, 341, 481, 590, 803 and 857. The web server can be used for a fast determination of NAT2 phenotypes in genetic screens
A cohort study on the effect of parental mind-mindedness in parentâchild interaction therapy
Comparative Methods for Gene Structure Prediction in Homologous Sequences
The increasing number of sequenced genomes motivates the use of evolutionary patterns to detect genes. We present a series of comparative methods for gene finding in homologous prokaryotic or eukaryotic sequences. Based on a model of legal genes and a similarity measure between genes, we find the pair of legal genes of maximum similarity. We develop methods based on genes models and alignment based similarity measures of increasing complexity, which take into account many details of real gene structures, e.g. the similarity of the proteins encoded by the exons. When using a similarity measure based on an exiting alignment, the methods run in linear time. When integrating the alignment and prediction process which allows for more fine grained similarity measures, the methods run in quadratic time. We evaluate the methods in a series of experiments on synthetic and real sequence data, which show that all methods are competitive but that taking the similarity of the encoded proteins into account really boost the performance
Graph states in phase space
The phase space for a system of qubits is a discrete grid of points, whose axes are labeled in terms of the elements of the
finite field \Gal{2^n} to endow it with proper geometrical properties. We
analyze the representation of graph states in that phase space, showing that
these states can be identified with a class of non-singular curves. We provide
an algebraic representation of the most relevant quantum operations acting on
these states and discuss the advantages of this approach.Comment: 14 pages. 2 figures. Published in Journal of Physics
Dynamics of vortex penetration, jumpwise instabilities and nonlinear surface resistance of type-II superconductors in strong rf fields
We consider nonlinear dynamics of a single vortex in a superconductor in a
strong rf magnetic field . Using the London theory, we
calculate the dissipated power , and the transient time scales
of vortex motion for the linear Bardeen-Stephen viscous drag force, which
results in unphysically high vortex velocities during vortex penetration
through the oscillating surface barrier. It is shown that penetration of a
single vortex through the ac surface barrier always involves penetration of an
antivortex and the subsequent annihilation of the vortex antivortex pairs.
Using the nonlinear Larkin-Ovchinnikov (LO) viscous drag force at higher vortex
velocities results in a jump-wise vortex penetration through the surface
barrier and a significant increase of the dissipated power. We calculate the
effect of dissipation on nonlinear vortex viscosity and the rf vortex
dynamics and show that it can also result in the LO-type behavior,
instabilities, and thermal localization of penetrating vortex channels. We
propose a thermal feedback model of , which not only results in the LO
dependence of for a steady-state motion, but also takes into account
retardation of temperature field around rapidly accelerating vortex, and a
long-range interaction with the surface. We also address the effect of pinning
on the nonlinear rf vortex dynamics and the effect of trapped magnetic flux on
the surface resistance calculated as a function or rf frequency and
field. It is shown that trapped flux can result in a temperature-independent
residual resistance at low , and a hysteretic low-field dependence of
, which can {\it decrease} as is increased, reaching a minimum
at much smaller than the thermodynamic critical field .Comment: 18 figure
Tunable coaxial cavity resonator for linear and nonlinear microwave characterization of superconducting wires
We discuss experimental results obtained using a tunable cylindrical coaxial
cavity constituted by an outer Cu cylinder and an inner Pb-BSCCO wire. We have
used this device for investigating the microwave response of the
superconducting wire, both in the linear and nonlinear regimes. In particular,
by tuning the different modes of the cavity to make them resonant at exactly
harmonic frequencies, we have detected the power emitted by the superconducting
inner wire at the second- and third-harmonic frequency of the driving field.
The results obtained in the nonlinear regime, whether for the microwave surface
impedance or the harmonic emission, are qualitatively accounted for considering
intergrain fluxon dynamics. The use of this kind of device can be of strong
interest to investigate and characterise wires of large dimensions to be used
for implementing superconducting-based microwave devices.Comment: 14 pages, 6 embedded figures, accepted for publication in Supercond.
Sci. Techno
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