611 research outputs found
Vortex Washboard Voltage Noise in Type-II Superconductors
In order to characterize flux flow through disordered type-II
superconductors, we investigate the effects of columnar and point defects on
the vortex velocity / voltage power spectrum in the driven non-equilibrium
steady state. We employ three-dimensional Metropolis Monte Carlo simulations to
measure relevant physical observables including the force-velocity /
current-voltage (I-V) characteristics, vortex spatial arrangement and structure
factor, and mean flux line radius of gyration. Our simulation results compare
well to earlier findings and physical intuition. We focus specifically on the
voltage noise power spectra in conjunction with the vortex structure factor in
the presence of weak columnar and point pinning centers. We investigate the
vortex washboard noise peak and associated higher harmonics, and show that the
intensity ratios of the washboard harmonics are determined by the strength of
the material defects rather than the type of pins present. Through varying
columnar defect lengths and pinning strengths as well as magnetic flux density
we further explore the effect of the material defects on vortex transport. It
is demonstrated that the radius of gyration displays quantitatively unique
features that depend characteristically on the type of material defects present
in the sample.Comment: Latex, 17 pages, 14 figure
Correlations, fluctuations and stability of a finite-size network of coupled oscillators
The incoherent state of the Kuramoto model of coupled oscillators exhibits
marginal modes in mean field theory. We demonstrate that corrections due to
finite size effects render these modes stable in the subcritical case, i.e.
when the population is not synchronous. This demonstration is facilitated by
the construction of a non-equilibrium statistical field theoretic formulation
of a generic model of coupled oscillators. This theory is consistent with
previous results. In the all-to-all case, the fluctuations in this theory are
due completely to finite size corrections, which can be calculated in an
expansion in 1/N, where N is the number of oscillators. The N -> infinity limit
of this theory is what is traditionally called mean field theory for the
Kuramoto model.Comment: 25 pages (2 column), 12 figures, modifications for resubmissio
Mol Cell Proteomics
Protein biochips have a great potential in future parallel processing of complex samples as a research tool and in diagnostics. For the generation of protein biochips, highly automated technologies have been developed for cDNA expression library production, high throughput protein expression, large scale analysis of proteins, and protein microarray generation. Using this technology, we present here a strategy to identify potential autoantigens involved in the pathogenesis of alopecia areata, an often chronic disease leading to the rapid loss of scalp hair. Only little is known about the putative autoantigen(s) involved in this process. By combining protein microarray technology with the use of large cDNA expression libraries, we profiled the autoantibody repertoire of sera from alopecia areata patients against a human protein array consisting of 37,200 redundant, recombinant human proteins. The data sets obtained from incubations with patient sera were compared with control sera from clinically healthy persons and to background incubations with anti-human IgG antibodies. From these results, a smaller protein subset was generated and subjected to qualitative and quantitative validation on highly sensitive protein microarrays to identify novel alopecia areata-associated autoantigens. Eight autoantigens were identified by protein chip technology and were successfully confirmed by Western blot analysis. These autoantigens were arrayed on protein microarrays to generate a disease-associated protein chip. To confirm the specificity of the results obtained, sera from patients with psoriasis or hand and foot eczema as well as skin allergy were additionally examined on the disease-associated protein chip. By using alopecia areata as a model for an autoimmune disease, our investigations show that the protein microarray technology has potential for the identification and evaluation of autoantigens as well as in diagnosis such as to differentiate alopecia areata from other skin diseases
Simulated ecology-driven sympatric speciation
We introduce a multi-locus genetically acquired phenotype, submitted to
mutations and with selective value, in an age-structured model for biological
aging. This phenotype describes a single-trait effect of the environment on an
individual, and we study the resulting distribution of this trait among the
population. In particular, our simulations show that the appearance of a double
phenotypic attractor in the ecology induces the emergence of a stable
polymorphism, as observed in the Galapagos finches. In the presence of this
polymorphism, the simulations generate short-term speciation, when mating
preferences are also allowed to suffer mutations and acquire selective value.Comment: 11 pages, 5 figures, 1 table, uses package RevTe
The COBRAS/SAMBA space mission
COBRAS/SAMBA is an ESA mission designed for extensive, accurate mapping of the anisotropies of the Cosmic Background Radiation, with angular sensitivity from
sub-degree scales up to and overlapping with the COBE-DMR resolution. This will allow a full identification of the primordial density perturbations which grew to form the large-scale structures observed in the present universe. The COBRAS/SAMBA maps will provide powerful tests for the inflationary model and decisive answers on the origin of cosmic structure. A combination of bolometric and radiometric instrumentation will ensure the sensitivity and wide spectral coverage required for accurate foreground discrimination. A far-Earth orbit has been selected to minimize the unwanted emission from the Earth. The project is currently in the Phase A study within the European Space Agency M3 programme
Benefit of early commencement of growth hormone therapy in children with Prader-Willi syndrome
Prader-Willi syndrome (PWS) is a chromosomal disorder and growth failure is a common presentation. Growth hormone (GH) treatment is beneficial in PWS although the optimal age for starting GH is unknown. We investigated whether GH response in PWS was associated with the age of GH commencement by comparing 16 children who commenced GH before 3 years of age (early group) with 40 children who commenced GH after 3 years of age (late group) from the Ozgrow database. Height SDS, body mass index (BMI) SDS, bone age (BA)-chronological age (CA) ratio, change in height (Delta Ht) SDS and change in BMI during 4 years of GH treatment were compared between the groups. The early group had better height SDS and Delta Ht SIDS. BA delay was more pronounced in the early group but BA did not mature beyond CA with GH therapy in either group. Although the initial GH dose for the early group was lower than that of the late group, the former had better height outcome. The starting GH dose seen in the database is lower than the dose used by international centres
In vivo study of experimental pneumococcal meningitis using magnetic resonance imaging
<p>Abstract</p> <p>Background</p> <p>Magnetic Resonance Imaging (MRI) methods were evaluated as a tool for the study of experimental meningitis. The identification and characterisation of pathophysiological parameters that vary during the course of the disease could be used as markers for future studies of new treatment strategies.</p> <p>Methods</p> <p>Rats infected intracisternally with <it>S. pneumoniae </it>(n = 29) or saline (n = 13) were randomized for imaging at 6, 12, 24, 30, 36, 42 or 48 hours after infection. T1W, T2W, quantitative diffusion, and post contrast T1W images were acquired at 4.7 T. Dynamic MRI (dMRI) was used to evaluate blood-brain-barrier (BBB) permeability and to obtain a measure of cerebral and muscle perfusion. Clinical- and motor scores, bacterial counts in CSF and blood, and WBC counts in CSF were measured.</p> <p>Results</p> <p>MR images and dMRI revealed the development of a highly significant increase in BBB permeability (P < 0.002) and ventricle size (P < 0.0001) among infected rats. Clinical disease severity was closely related to ventricle expansion (P = 0.024).</p> <p>Changes in brain water distribution, assessed by ADC, and categorization of brain 'perfusion' by cortex ΔSI<sub>(bolus) </sub>were subject to increased inter-rat variation as the disease progressed, but without overall differences compared to uninfected rats (P > 0.05). Areas of well-'perfused' muscle decreased with the progression of infection indicative of septicaemia (P = 0.05).</p> <p>Conclusion</p> <p>The evolution of bacterial meningitis was successfully followed <it>in-vivo </it>with MRI. Increasing BBB-breakdown and ventricle size was observed in rats with meningitis whereas changes in brain water distribution were heterogeneous. MRI will be a valuable technique for future studies aiming at evaluating or optimizing adjunctive treatments</p
Canny Algorithm, Cosmic Strings and the Cosmic Microwave Background
We describe a new code to search for signatures of cosmic strings in cosmic
microwave anisotropy maps. The code implements the Canny Algorithm, an edge
detection algorithm designed to search for the lines of large gradients in
maps. Such a gradient signature which is coherent in position space is produced
by cosmic strings via the Kaiser-Stebbins effect. We test the power of our new
code to set limits on the tension of the cosmic strings by analyzing simulated
data with and without cosmic strings. We compare maps with a pure Gaussian
scale-invariant power spectrum with maps which have a contribution of a
distribution of cosmic strings obeying a scaling solution. The maps have
angular scale and angular resolution comparable to what current and future
ground-based small-scale cosmic microwave anisotropy experiments will achieve.
We present tests of the codes, indicate the limits on the string tension which
could be set with the current code, and describe various ways to refine the
analysis. Our results indicate that when applied to the data of ongoing cosmic
microwave experiments such as the South Pole Telescope project, the sensitivity
of our method to the presence of cosmic strings will be more than an order of
magnitude better than the limits from existing analyses.Comment: 19 pp, 14 figures; v4. minor corrections, as appears in journa
Rare region effects at classical, quantum, and non-equilibrium phase transitions
Rare regions, i.e., rare large spatial disorder fluctuations, can
dramatically change the properties of a phase transition in a quenched
disordered system. In generic classical equilibrium systems, they lead to an
essential singularity, the so-called Griffiths singularity, of the free energy
in the vicinity of the phase transition. Stronger effects can be observed at
zero-temperature quantum phase transitions, at nonequilibrium phase
transitions, and in systems with correlated disorder. In some cases, rare
regions can actually completely destroy the sharp phase transition by smearing.
This topical review presents a unifying framework for rare region effects at
weakly disordered classical, quantum, and nonequilibrium phase transitions
based on the effective dimensionality of the rare regions. Explicit examples
include disordered classical Ising and Heisenberg models, insulating and
metallic random quantum magnets, and the disordered contact process.Comment: Topical review, 68 pages, 14 figures, final version as publishe
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