653 research outputs found
The Bean model of the critical state in a magnetically shielded superconductor filament
We study the magnetization of a cylindrical type-II superconductor filament
covered by a coaxial soft-magnet sheath and exposed to an applied transverse
magnetic field. Examining penetration of magnetic flux into the superconductor
core of the filament on the basis of the Bean model of the critical state, we
find that the presence of a non-hysteretic magnetic sheath can strongly enhance
the field of full penetration of magnetic flux. The average magnetization of
the superconductor/magnet heterostructure under consideration and hysteresis AC
losses in the core of the filament are calculated as well.Comment: 4 pages, 3 figures; Proceedings of the 7th European Conference on
Applied Superconductivity, Vienna, Austria, September 11-15, 200
The Bean-Livingston barrier at a superconductor/magnet interface
The Bean-Livingston barrier at the interface of type-II
superconductor/soft-magnet heterostructures is studied on the basis of the
classical London approach. This shows a characteristic dependence on the
geometry of the particular structure and its interface as well as on the
relative permeability of the involved magnetic constituent. The modification of
the barrier by the presence of the magnet can be significant, as demonstrated
for a cylindrical superconducting filament covered with a coaxial magnetic
sheath. Using typical values of the relative permeability, the critical field
of first penetration of magnetic flux is predicted to be strongly enhanced,
whereas the variation of the average critical current density with the external
field is strongly depressed, in accord with the observations of recent
experiments.Comment: RevTeX 4; revised version; accepted in Journal of Physics: Condensed
Matte
Direct detection and characterization of foot-and-mouth disease virus in East Africa using a field-ready real-time PCR platform
Effective control and monitoring of foot-and-mouth disease (FMD) relies upon rapid and accurate disease confirmation. Currently, clinical samples are usually tested in reference laboratories using standardized assays recommended by The World Organisation for Animal Health (OIE). However, the requirements for prompt and serotype-specific diagnosis during FMD outbreaks, and the need to establish robust laboratory testing capacity in FMD-endemic countries have motivated the development of simple diagnostic platforms to support local decision-making. Using a portable thermocycler, the T-COR™ 8, this study describes the laboratory and field evaluation of a commercially available, lyophilized pan-serotype-specific real-time RT-PCR (rRT-PCR) assay and a newly available FMD virus (FMDV) typing assay (East Africa-specific for serotypes: O, A, Southern African Territories [SAT] 1 and 2). Analytical sensitivity, diagnostic sensitivity and specificity of the pan-serotype-specific lyophilized assay were comparable to that of an OIE-recommended laboratory-based rRT-PCR (determined using a panel of 57 FMDV-positive samples and six non-FMDV vesicular disease samples for differential diagnosis). The FMDV-typing assay was able to correctly identify the serotype of 33/36 FMDV-positive samples (no cross-reactivity between serotypes was evident). Furthermore, the assays were able to accurately detect and type FMDV RNA in multiple sample types, including epithelial tissue suspensions, serum, oesophageal–pharyngeal (OP) fluid and oral swabs, both with and without the use of nucleic acid extraction. When deployed in laboratory and field settings in Tanzania, Kenya and Ethiopia, both assays reliably detected and serotyped FMDV RNA in samples (n = 144) collected from pre-clinical, clinical and clinically recovered cattle. These data support the use of field-ready rRT-PCR platforms in endemic settings for simple, highly sensitive and rapid detection and/or characterization of FMDV
Fractal Stability Border in Plane Couette Flow
We study the dynamics of localised perturbations in plane Couette flow with
periodic lateral boundary conditions. For small Reynolds number and small
amplitude of the initial state the perturbation decays on a viscous time scale
. For Reynolds number larger than about 200, chaotic transients
appear with life times longer than the viscous one. Depending on the type of
the perturbation isolated initial conditions with infinite life time appear for
Reynolds numbers larger than about 270--320. In this third regime, the life
time as a function of Reynolds number and amplitude is fractal. These results
suggest that in the transition region the turbulent dynamics is characterised
by a chaotic repeller rather than an attractor.Comment: 4 pages, Latex, 4 eps-figures, submitted to Phys. Rev. Le
Hall conductance of Bloch electrons in a magnetic field
We study the energy spectrum and the quantized Hall conductance of electrons
in a two-dimensional periodic potential with perpendicular magnetic field
WITHOUT neglecting the coupling of the Landau bands. Remarkably, even for weak
Landau band coupling significant changes in the Hall conductance compared to
the one-band approximation of Hofstadter's butterfly are found. The principal
deviations are the rearrangement of subbands and unexpected subband
contributions to the Hall conductance.Comment: to appear in PRB; Revtex, 9 pages, 5 postscript figures; figures with
better resolution may be obtained from http://www.chaos.gwdg.d
Hyperon weak radiative decays in chiral perturbation theory
We investigate the leading-order amplitudes for weak radiative decays of
hyperons in chiral perturbation theory. We consistently include contributions
from the next-to-leading order weak-interaction Lagrangian. It is shown that
due to these terms Hara's theorem is violated. The data for the decays of
charged hyperons can be easily accounted for. However, at this order in the
chiral expansion, the four amplitudes for the decays of neutral hyperons
satisfy relations which are in disagreement with the data. The asymmetry
parameters for all the decays can not be accounted for without higher-order
terms. We shortly comment on the effect of the 27-plet part of the weak
interaction.Comment: 8 pages of REVTeX and using macro-package "feynman.tex" (available at
http://xxx.lanl.gov/ftp/hep-ph/papers/macros) for the 2 figure
Detailed study of N,N'-(diisopropylphenyl)- terrylene-3,4:11,12-bis(dicarboximide) as electron acceptor for solar cells application
We report on terrylene-3,4:11,12-bis(dicarboximide) (TDI) as electron
acceptor for bulk-heterojunction solar cells using poly(3-hexyl thiophene)
(P3HT) as complementary donor component. Enhanced absorption was observed in
the blend compared to pure P3HT. As shown by the very efficient
photoluminescence (PL) quenching, the generated excitons are collected at the
interface between the donor and acceptor, where they separate into charges
which we detect by photoinduced absorption and electron-spin resonance (ESR).
Time-of-flight (TOF) photoconductivity measurements reveal a good electron
mobility of 10-3 cm2 V-1 s-1 in the blend. Nevertheless, the photocurrent in
solar cells was found to be surprisingly low. Supported by the external quantum
efficiency (EQE) spectrum as well as morphological studies by way of X-ray
diffraction and atomic force microscopy, we explain our observation by the
formation of a TDI hole blocking layer at the anode interface which prevents
the efficiently generated charges to be extracted.Comment: Original research article, 9 pages, 10 figures, 1 tabl
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