80,719 research outputs found
Polarization-dependent discharge in fibers of semiconducting ladder-type polymer
We report results on polarization-dependent photoinduced discharge in
oriented fibers and films of ladder-type, electron-transporting polymer poly
(benzimidazobenzophenanthroline), BBL. The photocarrier generation efficiency
in the fiber which is indicated by the rate of discharge, is found to be
distinctly higher for light polarized parallel to the fiber axis as compared to
the radially perpendicular direction . Similar results, with photocarrier
generation efficiency anisotropy ~ 10 are obtained for oriented films. These
observations are different from previously obtained results on
polyparaphenylenevinylene (PPV). The results are compared with the
polarization-dependent steady- state photoconductivity measurements. We
interpret these results on the basis of molecular and macroscopic features of
the material.Comment: This article has been accepted for publication in applied physics
letters and tentatively to be published in March 12, 2001 issu
Distribution of the delay time and the dwell time for wave reflection from a long random potential
We re-examine and correct an earlier derivation of the distribution of the
Wigner phase delay time for wave reflection from a long one-dimensional
disordered conductor treated in the continuum limit. We then numerically
compare the distributions of the Wigner phase delay time and the dwell time,
the latter being obtained by the use of an infinitesimal imaginary potential as
a clock, and investigate the effects of strong disorder and a periodic
(discrete) lattice background. We find that the two distributions coincide even
for strong disorder, but only for energies well away from the band-edges.Comment: Final version with minor corrections in text, 4 pages, 2 PS figure
Element test experiments and simulations: from dry towards cohesive powders
Findings from experiments and particle simulations for dry and cohesive granular materials are presented with the goal to reach quantitative agreement between simulations and experiments. Results for the compressibility, tested with the FT4 Powder Rheometer are presented. The first simulation results involve the strain controlled uniaxial compression of frictionless polydisperse spheres in a biaxial box using a linear visco-elastic contact model.\ud
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As main result, the evolution of pressure as a function of volume fraction is reported. Our anisotropic, uniaxial findings compare astonishingly well with results for purely isotropic compression. Concerning the second stress response, namely anisotropy, we present the evolution of the deviatoric stress as a function of the volume fraction, which cannot be measured with the FT4 experiment, but requires a bi-axial experiment
Bed blockers: A study on the elderly patients in a teaching hospital in India
A cross-sectional study of in-patients over the age of 60 years was conducted at district McGann Hospital, Shimoga on patients who were classified as bed blockers. Level of dependency and cognitive function of these patients were assessed using Barthel scale and Abbreviated mental test (AMT) respectively. Median age of the study population was 67 years; majority of them were men. Most of them were admitted in the medical ward and the median time to be labeled as bed blocker was 32 days. These bed blockers were a weak group of patients with an average 3.1 pathology per case. Majority of them suffered from neurological disorders and cardiovascular disease. High level of dependence was noted with a mean Barthel score of 29.68 (Range 0 -100). Low levels of cognitive function was also noted among these patients with a mean AMT of 4.76 (Range 0 -10).These findings demonstrate that the bed blockers in McGann hospital suffer not only from genuine health problems but also have a high dependency level in activities of daily living which hamper their discharge to the community. Community based rehabilitation using an intersectoral approach may help at least the less dependent to return home
Flow-induced voltage and current generation in carbon nanotubes
New experimental results, and a plausible theoretical understanding thereof,
are presented for the flow-induced currents and voltages observed in
single-walled carbon nanotube samples. In our experiments, the electrical
response was found to be strongly sublinear -- nearly logarithmic -- in the
flow speed over a wide range, and its direction could be controlled by an
electrochemical biasing of the nanotubes. These experimental findings are
inconsistent with the conventional idea of a streaming potential as the
efficient cause. Here we present a new, physically appealing, Langevin-equation
based treatment of the nanotube charge carriers, assumed to be moving under
coulombic forcing by the correlated ionic fluctuations, advected by the liquid
in flow. The resulting 'Doppler-shifted' force-force correlation, as seen by
the charge carriers drifting in the nanotube, is shown to give a strongly
sublinear response, broadly in agreement with experiments.Comment: 11 pages including 3 figures. To appear in Phys. Rev B (2004
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