52,114 research outputs found
The role of triplet excitons in enhancing polymer solar cell efficiency: a photo-induced absorption study
Inclusion of heavy metal atoms in a polymer backbone allows transitions
between the singlet and triplet manifolds. Interfacial dissociation of triplet
excitons constitutes a viable mechanism for enhancing photovoltaic (PV)
efficiencies in polymer heterojunction-based solar cells. The PV efficiency
from polymer solar cells utilizing a ladder-type poly (para-phenylene) polymer
(PhLPPP) with trace quantity of Pd atoms and a fullerene derivative (PCBM) is
much higher than its counterpart (MeLPPP) with no Pd atom. Evidence is
presented for the formation of a weak ground-state charge-transfer complex
(CTC) in the blended films of the polymer and PCBM, using photo-induced
absorption (PIA) spectroscopy. The CTC state in MeLPPP:PCBM has a singlet
character to it, resulting in a radiative recombination. In contrast, the CTC
states in PhLPPP:PCBM are more localized with a triplet character. An
absorption peak at 1.65 eV is observed in PhLPPP:PCBM blend in the PIA, which
may be converted to weakly-bound polaron-pairs, contributing to the enhancement
of PV efficiency.Comment: 19 pages, 11 figure
Spatial Distribution of Metal Emissions in SNR 3C 397 Viewed with Chandra and XMM
We present X-ray equivalent width imaging of the supernova remnant (SNR) 3C
397 for Mg He\alpha, Si He\alpha, S He\alpha, and Fe K\alpha complex lines with
the Chandra and XMM-Newton observations. The images reveal that the heavier the
element is, the smaller the extent of the element distribution is. The Mg
emission is evidently enhanced in the southeastern blow-out region, well along
the radio boundary there, and appears to partially envelope the eastern Fe
knot. Two bilateral hat-like Si line-emitting structures are along the northern
and southern borders, roughly symmetric with respect to the southeast-northwest
elongation axis. An S line-emitting shell is located just inner to the northern
radio and IR shell, indicating of a layer of reversely shocked sulphur in the
ejecta. A few enhanced Fe features are basically aligned along the diagonal of
the rectangular shape of the SNR, which implicates an early asymmetric SN
explosion.Comment: 4 pages, 4 figures, appears in Science China Physics, Mechanics &
Astronomy, 2010, 53 (Suppl.1), 267-27
Quantum Phase Transition, O(3) Universality Class and Phase Diagram of Spin-1/2 Heisenberg Antiferromagnet on Distorted Honeycomb Lattice: A Tensor Renormalization Group Study
The spin-1/2 Heisenberg antiferromagnet on the distorted honeycomb (DHC)
lattice is studied by means of the tensor renormalization group method. It is
unveiled that the system has a quantum phase transition of second-order between
the gapped quantum dimer phase and a collinear Neel phase at the critical point
of coupling ratio \alpha_{c} = 0.54, where the quantum critical exponents \nu =
0.69(2) and \gamma = 1.363(8) are obtained. The quantum criticality is found to
fall into the O(3) universality class. A ground-state phase diagram in the
field-coupling ratio plane is proposed, where the phases such as the dimer,
semi-classical Neel, and polarized phases are identified. A link between the
present spin system to the boson Hubbard model on the DHC lattice is also
discussed.Comment: 6 pages, 5 figures, published in Phys. Rev.
Higher Twist, Scaling, and Effective for Lepton Scattering in the Few GeV Region
We use a new scaling variable , and add low modifications to
GRV98 leading order parton distribution functions such that they can be used to
model electron, muon and neutrino inelastic scattering cross sections (and also
photoproduction) at both very low and high energies.Comment: 6 pages, 3 figures. To be published in J. Phys. G (Conf. Proceedings)
based on two talks by Arie Bodek at the NuFact conference, Imperial
College, London, England, July 200
s-Process Xe and Kr and Ne-E in a ^(13)C Rich Murchison Sample; Noble Gas Analysis by Stepped Combustion
Some of the more interesting isotopic anomalies in meteorites are located in minor phases that are extremely resistant to chemical treatments. Among these are Ne-E (Black and Pepin, 1969; Eberhardt, 1978; Alaerts et al., 1980) and s-process Kr and Xe (Srinivasan and Anders, 1978; Alaerts et al., 1980), which have been detected in samples that at the same time contain a carbon component enriched in ^(13)C by about a factor of two (Swart et al., 1983). Swart et al. (1983) have concluded that s-Xe and Ne-E (L)- that subcomponent of Ne-E that is released at low temperature in pyrolysis (Eberhardt, 1978)- are related to isotopically heavy carbon. Their argument involved a comparison of stability in pyrolysis (for noble gas retention) and combustion (carbon). Since it is preferrable to compare stability under identical conditions, we have analyzed for its noble gases by stepped combustion Murchison sample CFP. This sample had been prepared using HF/HC1 and HC10_4 and analyzed for carbon by Yang and Epstein (1984), who found a δ^(13)C of + 977‰ in the highest temperature step. We followed their schedule except for an intermediate combustion step at 1000°C
An exact equilibrium reduced density matrix formulation I: The influence of noise, disorder, and temperature on localization in excitonic systems
An exact method to compute the entire equilibrium reduced density matrix for
systems characterized by a system-bath Hamiltonian is presented. The approach
is based upon a stochastic unraveling of the influence functional that appears
in the imaginary time path integral formalism of quantum statistical mechanics.
This method is then applied to study the effects of thermal noise, static
disorder, and temperature on the coherence length in excitonic systems. As
representative examples of biased and unbiased systems, attention is focused on
the well-characterized light harvesting complexes of FMO and LH2, respectively.
Due to the bias, FMO is completely localized in the site basis at low
temperatures, whereas LH2 is completely delocalized. In the latter, the
presence of static disorder leads to a plateau in the coherence length at low
temperature that becomes increasingly pronounced with increasing strength of
the disorder. The introduction of noise, however, precludes this effect. In
biased systems, it is shown that the environment may increase the coherence
length, but only decrease that of unbiased systems. Finally it is emphasized
that for typical values of the environmental parameters in light harvesting
systems, the system and bath are entangled at equilibrium in the single
excitation manifold. That is, the density matrix cannot be described as a
product state as is often assumed, even at room temperature. The reduced
density matrix of LH2 is shown to be in precise agreement with the steady state
limit of previous exact quantum dynamics calculations.Comment: 37 pages, 12 figures. To appear in Phys. Rev.
Kinetic stabilization of Fe film on (4 by 2)-GaAs(100)
We grow Fe film on (4 by 2)-GaAs(100) at low temperature, (~ 130 K) and study
their chemical structure by photoelectron spectroscopy using synchrotron
radiation. We observe the effective suppression of As segregation and
remarkable reduction of alloy formation near the interface between Fe and
substrate. Hence, this should be a way to grow virtually pristine Fe film on
GaAs(100). Further, the Fe film is found stable against As segregation even
after warmed up to room temperature. There only forms very thin, ~ 8 angstrom
thick interface alloy. It is speculated that the interface alloy forms via
surface diffusion mediated by interface defects formed during the low
temperature growth of the Fe film. Further out-diffusion of both Ga and As are
suppressed because it should then proceed via inefficient bulk diffusion.Comment: 4 figure
Narrow Band Chandra X-ray Analysis of Supernova Remnant 3C391
We present the narrow-band and the equivalent width (EW) images of the
thermal composite supernova remnant (SNR) 3C391 for the X-ray emission lines of
elements Mg, Si, & S using the Chandra ACIS Observational data. These EW images
reveal the spatial distribution of the emission of the metal species Mg, Si, &
S in the remnant. They have clumpy structure similar to that seen from the
broadband diffuse emission, suggesting that they are largely of interstellar
origin. We find an interesting finger-like feature protruding outside the
southwestern radio border of the remnant, which is somewhat similar to the
jet-like Si structure found in the famous SNR Cas A. This feature may possibly
be the debris of the jet of ejecta which implies an asymmetrical supernova
explosion of a massive progenitor star.Comment: 9 pages, 4 embedded figures, Chinese Journal of Astronomy and
Astrophysics (ChJAA), in pres
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