12,835 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
Linear response formula for open systems
An exact expression for the finite frequency response of open classical
systems coupled to reservoirs is obtained. The result is valid for any
conserved current. No assumption is made about the reservoirs apart from
thermodynamic equilibrium. At non-zero frequencies, the expression involves
correlation functions of boundary currents and cannot be put in the standard
Green-Kubo form involving currents inside the system
LensMEM: A Gravitational Lens Inversion Algorithm Using the Maximum Entropy Method
We present a new algorithm for inverting poorly resolved gravitational lens
systems using the maximum entropy method (MEM). We test the method with
simulations and then apply it to an 8 GHz VLA map of the radio ring lens
MG1654+134. We model the lens as a singular isothermal sphere embedded in an
external shear field and find the critical radius of the lens is
b=0\parcs9820, the dimensionless shear is , and the position
angle of the shear is \theta=100\pdeg8. These results are consistent with the
results obtained by Kochanek (1995) using a complementary inversion algorithm
based on Clean.Comment: 27 pages, uuencoded, gzip compressed postscrip
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
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