46,649 research outputs found
Modeling Neutrino and Electron Scattering Cross Sections in the Few GeV Region with Effective
We use new scaling variables and , and add low
modifications to GRV94 and 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
energie.Comment: 8 pages, 3 figures, Invited talk given by Arie Bodek at the X Mexican
School of Particles and Fields, Playa del Carmen, Mexico, 200
Studies of Higher Twist and Higher Order Effects in NLO and NNLO QCD Analysis of Lepton-Nucleon Scattering Data on F_2 and R =sigma_L/sigma_T
We report on the extraction of the higher twist contributions to F_2 and R =
sigma_L/sigma_T from the global NLO and NNLO QCD fits to lepton nucleon
scattering data over a wide range of Q^2. The NLO fits require both target mass
and higher twist contributions at low Q^2. However, in the NNLO analysis, the
data are described by the NNLO QCD predictions (with target mass corrections)
without the need for any significant contributions from higher twist effects.
An estimate of the difference between NLO and NNLO parton distribution
functions is obtained.Comment: 5 pages, 6 figures, submitted to Eur. Phys.
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
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Investigation of Shallow Sedimentary Structure of the Anchorage Basin, Alaska, Using Simulated Annealing Inversion of Site Response
This study deals with shallow sedimentary structure of the Anchorage basin in Alaska. For this purpose, inversion of site response [SR(f)] data in the frequency range 0.5-11.0 Hz from various sites of the basin has been performed using the simulated annealing method to compute subsurface layer thickness, shear-wave velocity (beta), density, and shear-wave quality factor. The one-dimensional (1D) models for the aforementioned parameters were obtained with preset bounds on the basis of available geological information such that the L-2 norm error between the observed and computed site response attained a global minimum. Next, the spatial distribution of the important parameter beta was obtained by interpolating values yielded by the 1D models. The results indicate the presence of three distinct velocity zones as the source of spatial variation of SR(f) in the Anchorage basin. In the uppermost part of the basin, the beta values of fine-grain Quaternary sediments mainly lie in the range of 180-500 m/sec with thickness varying from 15 to 50 m. This formation overlies relatively thick (80-200 m) coarse-grain Quaternary sediments with beta values in the range of 600-900 m/sec. These two Quaternary units are, in turn, overlain on Tertiary sediments with beta > 1000 m/sec located at depths of 100 and 250 m, respectively, in the central and western side along the Knik Arm parts of the basin. The important implication of the result is that the sources of spatial variation of SR(f) in the Anchorage basin for the frequency band 0.5-11 Hz, besides in the uppermost 30 m, are found to be deeper than this depth. Thus, use of commonly considered geological formations in the depth intervals from 0 to 30 m for the ground-motion interpretation will likely yield erroneous results in the Anchorage basin.GIEnvironment and Natural Resources InstituteSchool of Engineering of the University of Alaska, AnchorageGeological Science
Renormalizability of the nuclear many-body problem with the Skyrme interaction beyond mean field
Phenomenological effective interactions like Skyrme forces are currently used
in mean--field calculations in nuclear physics. Mean--field models have strong
analogies with the first order of the perturbative many--body problem and the
currently used effective interactions are adjusted at the mean--field level. In
this work, we analyze the renormalizability of the nuclear many--body problem
in the case where the effective Skyrme interaction is employed in its standard
form and the perturbative problem is solved up to second order. We focus on
symmetric nuclear matter and its equation of state, which can be calculated
analytically at this order. It is shown that only by applying specific density
dependence and constraints to the interaction parameters could
renormalizability be guaranteed in principle. This indicates that the standard
Skyrme interaction does not in general lead to a renormalizable theory. For
achieving renormalizability, other terms should be added to the interaction and
employed perturbatively only at first order.Comment: Revised versio
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
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