23,692 research outputs found
Modeling Three and Four Coupled Phase Qubits
The Josephson junction phase qubit has been shown to be a viable candidate
for quantum computation. In recent years, the two coupled phase system has been
extensively studied theoretically and experimentally. We have analyzed the
quantum behavior of three and four capacitively-coupled phase qubits with
different possible configurations, using a two-level system model. Energy
levels and eigenstates have been calculated as a function of bias current and
detuning. The properties of these simple networks are discussed
Nuclear binding energies: Global collective structure and local shell-model correlations
Nuclear binding energies and two-neutron separation energies are analyzed
starting from the liquid-drop model and the nuclear shell model in order to
describe the global trends of the above observables. We subsequently
concentrate on the Interacting Boson Model (IBM) and discuss a new method in
order to provide a consistent description of both, ground-state and
excited-state properties. We address the artefacts that appear when crossing
mid-shell using the IBM formulation and perform detailed numerical calculations
for nuclei situated in the 50-82 shell. We also concentrate on local deviations
from the above global trends in binding energy and two-neutron separation
energies that appear in the neutron-deficient Pb region. We address possible
effects on the binding energy, caused by mixing of low-lying intruder
states into the ground state, using configuration mixing in the IBM framework.
We also study ground-state properties using a deformed mean-field approach.
Detailed comparisons with recent experimental data in the Pb region are amply
discussed.Comment: 69 pages, TeX (ReVTeX). 23 eps figures. 1 table. Modified version.
Accepted in Nucl. Phys.
Dynamical transitions and sliding friction of the phase-field-crystal model with pinning
We study the nonlinear driven response and sliding friction behavior of the
phase-field-crystal (PFC) model with pinning including both thermal
fluctuations and inertial effects. The model provides a continuous description
of adsorbed layers on a substrate under the action of an external driving force
at finite temperatures, allowing for both elastic and plastic deformations. We
derive general stochastic dynamical equations for the particle and momentum
densities including both thermal fluctuations and inertial effects. The
resulting coupled equations for the PFC model are studied numerically. At
sufficiently low temperatures we find that the velocity response of an
initially pinned commensurate layer shows hysteresis with dynamical melting and
freezing transitions for increasing and decreasing applied forces at different
critical values. The main features of the nonlinear response in the PFC model
are similar to the results obtained previously with molecular dynamics
simulations of particle models for adsorbed layers.Comment: 7 pages, 8 figures, to appear in Physcial Review
Local tetragonal distortion in La_{0.7}Sr_{0.3}MnO_3 strained thin films probed by x-ray absorption spectroscopy
We report on an angular resolved X-ray Absorption Spectroscopy study of
thin films epitaxially grown by pulsed laser
deposition on slightly mismatched substrates which induce tensile or
compressive strains. XANES spectra give evidence of tetragonal distortion
within the octahedra, with opposite directions for tensile and
compressive strains. Quantitative analysis has been done and a model of
tetragonal distortion reflecting the strain has been established. EXAFS data
collected in plane for tensile substrate confirm the change in the
average bond distance and the increase of length matching with the
enlargement of the cell parameter. From these results we conclude that there is
no significant change in the angle. Our observations conflict with
the scenarios which this angle is the main driving parameter in the sensitivity
of manganite films properties to external strains and suggest that the
distortion within the octahedra plays a key role in the modification of the
transport and magnetic properties.Comment: 8 pages, 6 figure
Comparison of coherence times in three dc SQUID phase qubits
We report measurements of spectroscopic linewidth and Rabi oscillations in
three thin-film dc SQUID phase qubits. One device had a single-turn Al loop,
the second had a 6-turn Nb loop, and the third was a first order gradiometer
formed from 6-turn wound and counter-wound Nb coils to provide isolation from
spatially uniform flux noise. In the 6 - 7.2 GHz range, the spectroscopic
coherence times for the gradiometer varied from 4 ns to 8 ns, about the same as
for the other devices (4 to 10 ns). The time constant for decay of Rabi
oscillations was significantly longer in the single-turn Al device (20 to 30
ns) than either of the Nb devices (10 to 15 ns). These results imply that
spatially uniform flux noise is not the main source of decoherence or
inhomogenous broadening in these devices.Comment: 4 pages, 5 figures, accepted for publication in IEEE Trans. Appl.
Supercon
A CF3I-based SDD Prototype for Spin-independent Dark Matter Searches
The application of Superheated Droplet Detectors (SDDs) to dark matter
searches has so far been confined to the light nuclei refrigerants C2ClF5 and
C4F10 (SIMPLE and PICASSO, respectively), with a principle sensitivity to
spin-dependent interactions. Given the competitive results of these devices, as
a result of their intrinsic insensitivity to backgrounds, we have developed a
prototype trifluoroiodomethane (CF3I)-loaded SDD with increased sensitivity to
spin-independent interactions as well. A low (0.102 kgd) exposure test
operation of two high concentration, 1 liter devices is described, and the
results compared with leading experiments in both spin-dependent and
-independent sectors. Although competitive in both sectors when the difference
in exposures is accounted for, a problem with fracturing of the detector gel
must be addressed before significantly larger exposures can be envisioned.Comment: revised and updated; accepted Astrop. Phy
O uso de unidades de referência como ferramenta para a construção de sistemas agrícolas biodiversos para a agricultura familiar.
Resumo: Os sistemas de produção biodiversos são formas inovadoras de agricultura e pecuária que buscam aliar benefícios econômicos e ambientais, apoiados no incremento da biodiversidade. O Programa ?Sistemas agrícolas familiares biodiversos?, desenvolvido pela Equipe de Agroecologia da Embrapa Meio Ambiente, se caracteriza pela gradual formação de redes sócio-técnicas, articuladas em torno de Unidades de Referência (URs). As URs são parcelas ou unidades produtivas onde se desenvolvem todas as atividades técnicas sobre sistemas biodiversos (experimentação, capacitação e irradiação do conhecimento). O objetivo principal das URs é o de se tornarem inspiração para os demais agricultores na forma de exemplos práticos que possam ser adaptados à situação dos agricultores beneficiários finais, servindo como base para a criação de pequenas redes interligando URs em nível de microrregiões. Por meio destas estratégias de gestão reforça-se a replicabilidade dos conhecimentos gerados e o impacto sobre um número maior de beneficiários, podendo servir de base para a formulação de políticas públicas para a diversificação produtiva da agricultura familiar. Abstract: Biodiverse production systems are innovative forms of agriculture and livestock willing to align economic and environmental benefits, supported in increasing biodiversity. The 'family biodiverse agricultural systems' program, developed by Embrapa Environment Team Agroecology, is characterized by the gradual formation of socio-technical networks, articulated around the Reference Units (RUs ). The RUs are plots or production units where they develop all technical activities on biodiverse systems (experimentation, training and knowledge irradiation). The main objective of RUs is to become inspiration for other farmers in the form of practical examples that can be adapted to the situation of the beneficiaries end farmers, serving as a basis for creating small networks interconnecting RUs. Through these management strategies reinforces the replicability of knowledge generated and the impact on a larger number of beneficiaries, could be a basis for the formulation of public policies for productive diversification of family farming
Glassy phases and driven response of the phase-field-crystal model with random pinning
We study the structural correlations and the nonlinear response to a driving
force of a two-dimensional phase-field-crystal model with random pinning. The
model provides an effective continuous description of lattice systems in the
presence of disordered external pinning centers, allowing for both elastic and
plastic deformations. We find that the phase-field crystal with disorder
assumes an amorphous glassy ground state, with only short-ranged positional and
orientational correlations even in the limit of weak disorder. Under increasing
driving force, the pinned amorphous-glass phase evolves into a moving
plastic-flow phase and then finally a moving smectic phase. The transverse
response of the moving smectic phase shows a vanishing transverse critical
force for increasing system sizes
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