200 research outputs found
Polyfluorene as a model system for space-charge-limited conduction
Ethyl-hexyl substituted polyfluorene (PF) with its high level of molecular
disorder can be described very well by one-carrier space-charge-limited
conduction for a discrete set of trap levels with energy 0.5 eV above
the valence band edge. Sweeping the bias above the trap-filling limit in the
as-is polymer generates a new set of exponential traps, which is clearly seen
in the density of states calculations. The trapped charges in the new set of
traps have very long lifetimes and can be detrapped by photoexcitation. Thermal
cycling the PF film to a crystalline phase prevents creation of additional
traps at higher voltages.Comment: 13 pages, 4 figures. Physical Review B (accepted, 2007
Effects of thermal treatments and germination on physico-chemical properties of corn flour
Certain physico-chemical properties including viscoelasticity, crystallinity and maltose content of corn depends on the gelatinization of starch under different treatments. Three different treatments were performed; boiling in water, steam heating, and germination. The effects of gelatinization onviscoelastic property of corn starch were measured and the morphological changes of corn after different treatments were determined by scanning electron microscope (SEM). Various grooves and fissures on the exterior surface of the granules were noticed in the treated sample compared tocontrol. The crystallinity of corn after different treatments was determined by X-ray diffraction studies (XRD). The control showed higher crystallinity than that of thermal treated samples
Harvesting triplet excitons for application in polymer solar cells
doi:10.1063/1.3082081Triplet enhanced ladder-type poly (para-phenylene) polymer (PhLPPP) with covalently bound trace amounts of palladium blended with a fullerene derivative [[6,6]-phenyl C61-butyric acid methyl ester (PCBM)] shows power conversion efficiencies (PCE) almost ten times greater than with pristine ladder-type polymer (with no palladium atom) blended with PCBM. The steady state optical properties of the triplet and nontriplet-enhanced polymers are comparable; the enhanced PCE and external quantum efficiency in PhLPPP photovoltaics are attributed to the presence of long-lived mobile triplet excitons. Furthermore, the luminescence from PhLPPP blends measured in a delayed setup correlates very well with the efficiency of the solar cells.This research was partially supported by grants from the U.S. National Science Foundation Grant No. ECCS-0823563 and the U.S. Army
Nickel silicide contact for silicon solar cells
Electroless nickel metallization on textured front surface is carried out to fabricate large area (13%) efficient silicon solar cells. It is established through XPS analysis that NiSi is formed at the front grid contact on the texturized surface at relatively low temperature leading to a low value of series resistance of the solar cells
Functional integral treatment of some quantum nondemolition systems
In the scheme of a quantum nondemolition (QND) measurement, an observable is
measured without perturbing its evolution. In the context of studies of
decoherence in quantum computing, we examine the `open' quantum system of a
two-level atom, or equivalently, a spin-1/2 system, in interaction with quantum
reservoirs of either oscillators or spins, under the QND condition of the
Hamiltonian of the system commuting with the system-reservoir interaction. For
completeness, we also examine the well-known non-QND spin-Bose problem. For all
these many-body systems, we use the methods of functional integration to work
out the propagators. The propagators for the QND Hamiltonians are shown to be
analogous to the squeezing and rotation operators, respectively, for the two
kinds of baths considered. Squeezing and rotation being both phase space
area-preserving canonical transformations, this brings out an interesting
connection between the energy-preserving QND Hamiltonians and the homogeneous
linear canonical transformations.Comment: 16 pages, no figure
Metastable Random Field Ising model with exchange enhancement: a simple model for Exchange Bias
We present a simple model that allows hysteresis loops with exchange bias to
be reproduced. The model is a modification of the T=0 random field Ising model
driven by an external field and with synchronous local relaxation dynamics. The
main novelty of the model is that a certain fraction f of the exchange
constants between neighbouring spins is enhanced to a very large value J_E. The
model allows the dependence of the exchange bias and other properties of the
hysteresis loops to be analyzed as a function of the parameters of the model:
the fraction f of enhanced bonds, the amount of the enhancement J_E and the
amount of disorder which is controlled by the width sigma of the Gaussian
distribution of the random fields.Comment: 8 pages, 11 figure
Realizations for Kepler and Oscillator Potentials and q-Canonical Transformations
The realizations of the Lie algebra corresponding to the dynamical symmetry
group SO(2,1) of the Kepler and oscillator potentials are q-deformed. The
q-canonical transformation connecting two realizations is given and a general
definition for q-canonical transformation is deduced. q-Schr\"{o}dinger
equation for a Kepler like potential is obtained from the q-oscillator
Schr\"{o}dinger equation. Energy spectrum and the ground state wave function
are calculated.Comment: 12 pages, Latex twice, (Comparison with the other approaches and some
refs. added. The version which will appear in J. Phys. A
Hawking Radiation of Black Holes in Infrared Modified Ho\v{r}ava-Lifshitz Gravity
We study the Hawking radiation of the spherically symmetric, asymptotically
flat black holes in the infrared modified Horava-Lifshitz gravity by applying
the methods of covariant anomaly cancellation and effective action, as well as
the approach of Damour-Ruffini-Sannan's. These black holes behave as the usual
Schwarzschild ones of the general relativity when the radial distance is very
large. We also extend the method of covariant anomaly cancellation to derive
the Hawking temperature of the spherically symmetric, asymptotically AdS black
holes that represent the analogues of the Schwarzschild AdS ones.Comment: no figures, 16 pages,accepted by EPJ
Back reaction, covariant anomaly and effective action
In the presence of back reaction, we first produce the one-loop corrections
for the event horizon and Hawking temperature of the Reissner-Nordstr\"om black
hole. Then, based on the covariant anomaly cancelation method and the effective
action technique, the modified expressions for the fluxes of gauge current and
energy momentum tensor, due to the effect of back reaction, are obtained. The
results are consistent with the Hawking fluxes of a (1+1)-dimensional blackbody
at the temperature with quantum corrections, thus confirming the robustness of
the covariant anomaly cancelation method and the effective action technique for
black holes with back reaction.Comment: 17 page
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