8,633 research outputs found
Universality in Intensity Modulated Photocurrent in Bulk-Heterojunction Polymer Solar Cells
We observe a universal feature in the frequency dependence of intensity
modulated photocurrent Iph based on studies of a variety of efficient
bulk-heterojunction polymer solar cells (BHJ-PSCs). This feature of Iph appears
in the form of a local maximum in the 5 kHz < frequency < 10 kHz range and is
observed to be largely independent of the external parameters such as modulated
light intensity (Lac), wavelength, temperature (T), and external field (EF)
over a wide range. Simplistic kinetic models involving carrier generation,
recombination and extraction processes are used to interpret the overall
essential features of Iph and correlate it to the device parameters
On holography from redux, renormalization group flows and -functions
Extremal black branes upon compactification in the near horizon throat region
are known to give rise to dilaton-gravity-matter theories. Away from
the throat region, the background has nontrivial profile. We interpret this as
holographic renormalization group flow in the 2-dim dilaton-gravity-matter
theories arising from dimensional reduction of the higher dimensional theories
here. The null energy conditions allow us to formulate a holographic c-function
in terms of the 2-dim dilaton for which we argue a c-theorem subject to
appropriate boundary conditions which amount to restrictions on the ultraviolet
theories containing these extremal branes. At the infrared fixed point,
the c-function becomes the extremal black brane entropy. We discuss the
behaviour of this inherited c-function in various explicit examples, in
particular compactified nonconformal branes, and compare it with other
discussions of holographic c-functions. We also adapt the holographic
renormalization group formulated in terms of radial Hamiltonian flow to 2-dim
dilaton-gravity-scalar theories, which while not Wilsonian, gives qualitative
insight into the flow equations and -functions.Comment: Latex, 40pgs incl appendices; v2: minor tweaks, figure added; v3:
minor clarifications added, matches version to be publishe
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
Hyperscaling violation and the shear diffusion constant
We consider holographic theories in bulk -dimensions with Lifshitz and
hyperscaling violating exponents at finite temperature. By studying
shear gravitational modes in the near-horizon region given certain
self-consistent approximations, we obtain the corresponding shear diffusion
constant on an appropriately defined stretched horizon, adapting the analysis
of Kovtun, Son and Starinets. For generic exponents with , we
find that the diffusion constant has power law scaling with the temperature,
motivating us to guess a universal relation for the viscosity bound. When the
exponents satisfy , we find logarithmic behaviour. This relation
is equivalent to where is the effective
boundary spatial dimension (and the actual spatial dimension). It is
satisfied by the exponents in hyperscaling violating theories arising from null
reductions of highly boosted black branes, and we comment on the corresponding
analysis in that context.Comment: Latex, 17pgs, v3: clarifications added on z<2+d_{eff} and standard
quantization, to be publishe
One pion events by atmospheric neutrinos: A three flavor analysis
We study the one-pion events produced via neutral current (NC) and charged
current (CC) interactions by the atmospheric neutrinos. We analyze the ratios
of these events in the framework of oscillations between three neutrino
flavors. The ratios of the CC events induced by to that of the NC
events and a similar ratio defined with help us in distinguishing the
different regions of the neutrino parameter space.Comment: 14 pages, 4 figures (separate postscript files
Determining the sign of at long baseline neutrino experiments
Recently it is advocated that high intensity and low energy neutrino beams should be built to probe the mixing angle to
a level of a few parts in . Experiments using such beams will have better
signal to background ratio in searches for oscillations. We
propose that such experiments can also determine the sign of even
if the beam consists of {\it neutrinos} only. By measuring the transitions in two different energy ranges, the effects due to
propagation of neutrinos through earth's crust can be isolated and the sign of
can be determined. If the sensitivity of an experiment to
is , then the same experiment is automatically sensitive to matter
effects and the sign of for values of .Comment: Title changed and paper rewritten. 4 pages, 1 figure, revte
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