25,827 research outputs found
Anomalous spin-dependent behaviour of one-dimensional subbands
We report a new electron interaction effect in GaAs/AlGaAs quantum wires.
Using DC-bias spectroscopy, we show that large and abrupt changes occur to the
energies of spin-down (lower energy) states as they populate. The effect is not
observed for spin-up energy states. At B=0, interactions have a pronounced
effect, in the form of the well-known 0.7 Structure. However, our new results
show that interactions strongly affect the energy spectrum at all magnetic
fields, from 0 to 16T, not just in the vicinity of the 0.7 Structure.Comment: 4 pages, 2 figure
Energy-level pinning and the 0.7 spin state in one dimension: GaAs quantum wires studied using finite-bias spectroscopy
We study the effects of electron-electron interactions on the energy levels
of GaAs quantum wires (QWs) using finite-bias spectroscopy. We probe the energy
spectrum at zero magnetic field, and at crossings of opposite-spin-levels in
high in-plane magnetic field B. Our results constitute direct evidence that
spin-up (higher energy) levels pin to the chemical potential as they populate.
We also show that spin-up and spin-down levels abruptly rearrange at the
crossing in a manner resembling the magnetic phase transitions predicted to
occur at crossings of Landau levels. This rearranging and pinning of subbands
provides a phenomenological explanation for the 0.7 structure, a
one-dimensional (1D) nanomagnetic state, and its high-B variants.Comment: 6 pages, 4 figure
Systematic derivation of a rotationally covariant extension of the 2-dimensional Newell-Whitehead-Segel equation
An extension of the Newell-Whitehead-Segel amplitude equation covariant under
abritrary rotations is derived systematically by the renormalization group
method.Comment: 8 pages, to appear in Phys. Rev. Letters, March 18, 199
A multispecies model for the transmission and control of mastitis in dairy cows
Mastitis in dairy cows is a significant economic and animal welfare issue in the dairy industry. The bacterial pathogens responsible for infection of the mammary gland may be split into two main categories: major and minor pathogens. Infection with major pathogens generally results in clinical illness or strong inflammatory responses and reduced milk yields, whereas minor pathogen infection is usually subclinical. Previous investigations have considered the transmission of these pathogens independently. Experimental evidence has shown cross-protection between species of pathogens. In this study a mathematical model for the coupled transmission of major and minor pathogens along with their interaction via the host was developed in order to consider various methods for controlling the incidence of major pathogen infection. A stability analysis of the model equilibria provides explanations for observed phenomena and previous decoupled modelling results. This multispecies model structure has provided a basis for quantifying the extent of cross-protection between species and assessing possible control strategies against the disease
Virtual Data in CMS Analysis
The use of virtual data for enhancing the collaboration between large groups
of scientists is explored in several ways:
- by defining ``virtual'' parameter spaces which can be searched and shared
in an organized way by a collaboration of scientists in the course of their
analysis;
- by providing a mechanism to log the provenance of results and the ability
to trace them back to the various stages in the analysis of real or simulated
data;
- by creating ``check points'' in the course of an analysis to permit
collaborators to explore their own analysis branches by refining selections,
improving the signal to background ratio, varying the estimation of parameters,
etc.;
- by facilitating the audit of an analysis and the reproduction of its
results by a different group, or in a peer review context.
We describe a prototype for the analysis of data from the CMS experiment
based on the virtual data system Chimera and the object-oriented data analysis
framework ROOT. The Chimera system is used to chain together several steps in
the analysis process including the Monte Carlo generation of data, the
simulation of detector response, the reconstruction of physics objects and
their subsequent analysis, histogramming and visualization using the ROOT
framework.Comment: Talk from the 2003 Computing in High Energy and Nuclear Physics
(CHEP03), La Jolla, Ca, USA, March 2003, 9 pages, LaTeX, 7 eps figures. PSN
TUAT010. V2 - references adde
Cloud service localisation
The essence of cloud computing is the provision of software
and hardware services to a range of users in dierent locations. The aim of cloud service localisation is to facilitate the internationalisation and localisation of cloud services by allowing their adaption to dierent locales.
We address the lingual localisation by providing service-level language translation techniques to adopt services to dierent languages and regulatory localisation by providing standards-based mappings to achieve regulatory compliance with regionally varying laws, standards and regulations. The aim is to support and enforce the explicit modelling of
aspects particularly relevant to localisation and runtime support consisting of tools and middleware services to automating the deployment based on models of locales, driven by the two localisation dimensions.
We focus here on an ontology-based conceptual information model that integrates locale specication in a coherent way
Dynamical preparation of EPR entanglement in two-well Bose-Einstein condensates
We propose to generate Einstein-Podolsky-Rosen (EPR) entanglement between
groups of atoms in a two-well Bose-Einstein condensate using a dynamical
process similar to that employed in quantum optics. The local nonlinear S-wave
scattering interaction has the effect of creating a spin squeezing at each
well, while the tunneling, analogous to a beam splitter in optics, introduces
an interference between these fields that results in an inter-well
entanglement. We consider two internal modes at each well, so that the
entanglement can be detected by measuring a reduction in the variances of the
sums of local Schwinger spin observables. As is typical of continuous variable
(CV) entanglement, the entanglement is predicted to increase with atom number,
and becomes sufficiently strong at higher numbers of atoms that the EPR paradox
and steering non-locality can be realized. The entanglement is predicted using
an analytical approach and, for larger atom numbers, stochastic simulations
based on truncated Wigner function. We find generally that strong tunnelling is
favourable, and that entanglement persists and is even enhanced in the presence
of realistic nonlinear losses.Comment: 15 pages, 19 figure
Effects of accidental microconstriction on the quantized conductance in long wires
We have investigated the conductance of long quantum wires formed in
GaAs/AlGaAs heterostructures. Using realistic fluctuation potentials from donor
layers we have simulated numerically the conductance of four different kinds of
wires. While ideal wires show perfect quantization, potential fluctuations from
random donors may give rise to strong conductance oscillations and degradation
of the quantization plateaux. Statistically there is always the possibility of
having large fluctuations in a sample that may effectively act as a
microconstriction. We therefore introduce microconstrictions in the wires by
occasional clustering of donors. These microconstrictions are found to restore
the quantized plateaux. A similar effect is found for accidental lithographic
inaccuracies.Comment: 4 pages, 2 figures, paper for NANO2002 symposium, will appear in SPIE
proceeding
Quantum Energies of Interfaces
We present a method for computing the one-loop, renormalized quantum energies
of symmetrical interfaces of arbitrary dimension and codimension using
elementary scattering data. Internal consistency requires finite-energy sum
rules relating phase shifts to bound state energies.Comment: 8 pages, 1 figure, minor changes, Phys. Rev. Lett., in prin
Modelling the dynamics of intramammary E. coli infections in dairy cows: understanding mechanisms that distinguish transient from persistent infections
The majority of intramammary infections with Escherichia coli in dairy cows result in transient infections with duration of about 10 days or less, although more persistent infections (2 months or longer) have been identified. We apply a mathematical model to explore the role of an intracellular mammary epithelial cell reservoir in the dynamics of infection. We included biological knowledge of the bovine immune response and known characteristics of the bacterial population in both transient and persistent infections. The results indicate that varying the survival duration of the intracellular reservoir reproduces the data for both transient and persistent infections. Survival in an intracellular reservoir is the most likely mechanism that ensures persistence of E. coli infections in mammary glands. Knowledge of the pathogenesis of persistent infections is essential to develop preventive and treatment programmes for these important infections in dairy cows
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