2,620 research outputs found
Large collection of astrophysical S-factors and its compact representation
Numerous nuclear reactions in the crust of accreting neutron stars are
strongly affected by dense plasma environment. Simulations of superbursts, deep
crustal heating and other nuclear burning phenomena in neutron stars require
astrophysical S-factors for these reactions (as a function of center-of-mass
energy E of colliding nuclei). A large database of S-factors is created for
about 5000 non-resonant fusion reactions involving stable and unstable isotopes
of Be, B, C, N, O, F, Ne, Na, Mg, and Si. It extends the previous database of
about 1000 reactions involving isotopes of C, O, Ne, and Mg. The calculations
are performed using the Sao Paulo potential and the barrier penetration
formalism. All calculated S-data are parameterized by an analytic model for
S(E) proposed before [Phys. Rev. C 82, 044609 (2010)] and further elaborated
here. For a given reaction, the present S(E)-model contains three parameters.
These parameters are easily interpolated along reactions involving isotopes of
the same elements with only seven input parameters, giving an ultracompact,
accurate, simple, and uniform database. The S(E) approximation can also be used
to estimate theoretical uncertainties of S(E) and nuclear reaction rates in
dense matter, as illustrated for the case of the 34Ne+34Ne reaction in the
inner crust of an accreting neutron star.Comment: 13 pages, 2 figures, Phys. Rev. C, accepte
Special Section Guest Editorial: Celebrating the Exponential Growth of Optoacoustic/Photoacoustic Imaging
Guest editors introduce contributors to the Special Section Celebrating the Exponential Growth of Optoacoustic/Photoacoustic Imaging.
We are pleased to introduce the contributions to this JBO Special Section entitled “Celebrating the Exponential Growth of Biomedical Optoacoustic/Photoacoustic Imaging.” This title was chosen to reflect the strong growth of the field over the last two and a half decades. The diversity of papers in this special section bears witness to this, with contributions that encompass numerical modelling, advanced instrumentation, functional imaging, clinical translation, and novel biomedical applications
The Two-Dimensional S=1 Quantum Heisenberg Antiferromagnet at Finite Temperatures
The temperature dependence of the correlation length, susceptibilities and
the magnetic structure factor of the two-dimensional spin-1 square lattice
quantum Heisenberg antiferromagnet are computed by the quantum Monte Carlo loop
algorithm (QMC). In the experimentally relevant temperature regime the
theoretically predicted asymptotic low temperature behavior is found to be not
valid. The QMC results however, agree reasonably well with the experimental
measurements of La2NiO4 even without considering anisotropies in the exchange
interactions.Comment: 4 Pages, 1 table, 4 figure
Ultrafast supercontinuum spectroscopy of carrier multiplication and biexcitonic effects in excited states of PbS quantum dots
We examine the multiple exciton population dynamics in PbS quantum dots by
ultrafast spectrally-resolved supercontinuum transient absorption (SC-TA). We
simultaneously probe the first three excitonic transitions over a broad
spectral range. Transient spectra show the presence of first order bleach of
absorption for the 1S_h-1S_e transition and second order bleach along with
photoinduced absorption band for 1P_h-1P_e transition. We also report evidence
of the one-photon forbidden 1S_{h,e}-1P_{h,e} transition. We examine signatures
of carrier multiplication (multiexcitons for the single absorbed photon) from
analysis of the first and second order bleaches, in the limit of low absorbed
photon numbers (~ 10^-2), at pump energies from two to four times the
semiconductor band gap. The multiexciton generation efficiency is discussed
both in terms of a broadband global fit and the ratio between early- to
long-time transient absorption signals.. Analysis of population dynamics shows
that the bleach peak due to the biexciton population is red-shifted respect the
single exciton one, indicating a positive binding energy.Comment: 16 pages, 5 figure
Bayesian Geostatistical Analysis and Ecoclimatic Determinants of Corynebacterium pseudotuberculosis Infection among Horses
Citation: Boysen, C., Davis, E. G., Beard, L. A., Lubbers, B. V., & Raghavan, R. K. (2015). Bayesian Geostatistical Analysis and Ecoclimatic Determinants of Corynebacterium pseudotuberculosis Infection among Horses. Plos One, 10(10), 15. doi:10.1371/journal.pone.0140666Kansas witnessed an unprecedented outbreak in Corynebacterium pseudotuberculosis infection among horses, a disease commonly referred to as pigeon fever during fall 2012. Bayesian geostatistical models were developed to identify key environmental and climatic risk factors associated with C. pseudotuberculosis infection in horses. Positive infection status among horses (cases) was determined by positive test results for characteristic abscess formation, positive bacterial culture on purulent material obtained from a lanced abscess (n = 82), or positive serologic evidence of exposure to organism (>= 1:512)(n = 11). Horses negative for these tests (n = 172)(controls) were considered free of infection. Information pertaining to horse demographics and stabled location were obtained through review of medical records and/or contact with horse owners via telephone. Covariate information for environmental and climatic determinants were obtained from USDA (soil attributes), USGS (land use/land cover), and NASA MODIS and NASA Prediction of Worldwide Renewable Resources (climate). Candidate covariates were screened using univariate regression models followed by Bayesian geostatistical models with and without covariates. The best performing model indicated a protective effect for higher soil moisture content (OR = 0.53, 95% CrI = 0.25, 0.71), and detrimental effects for higher land surface temperature (>= 35 degrees C) (OR = 2.81, 95% CrI = 2.21, 3.85) and habitat fragmentation (OR = 1.31, 95% CrI = 1.27, 2.22) for C. pseudotuberculosis infection status in horses, while age, gender and breed had no effect. Preventative and ecoclimatic significance of these findings are discussed
Continuous-Time Quantum Monte Carlo Algorithm for the Lattice Polaron
An efficient continuous-time path-integral Quantum Monte Carlo algorithm for
the lattice polaron is presented. It is based on Feynman's integration of
phonons and subsequent simulation of the resulting single-particle
self-interacting system. The method is free from the finite-size and
finite-time-step errors and works in any dimensionality and for any range of
electron-phonon interaction. The ground-state energy and effective mass of the
polaron are calculated for several models. The polaron spectrum can be measured
directly by Monte Carlo, which is of general interest.Comment: 5 pages, 4 figures, published versio
QCD as a Quantum Link Model
QCD is constructed as a lattice gauge theory in which the elements of the
link matrices are represented by non-commuting operators acting in a Hilbert
space. The resulting quantum link model for QCD is formulated with a fifth
Euclidean dimension, whose extent resembles the inverse gauge coupling of the
resulting four-dimensional theory after dimensional reduction. The inclusion of
quarks is natural in Shamir's variant of Kaplan's fermion method, which does
not require fine-tuning to approach the chiral limit. A rishon representation
in terms of fermionic constituents of the gluons is derived and the quantum
link Hamiltonian for QCD with a U(N) gauge symmetry is expressed in terms of
glueball, meson and constituent quark operators. The new formulation of QCD is
promising both from an analytic and from a computational point of view.Comment: 27 pages, including three figures. ordinary LaTeX; Submitted to Nucl.
Phys.
Exact, Complete, and Universal Continuous-Time Worldline Monte Carlo Approach to the Statistics of Discrete Quantum Systems
We show how the worldline quantum Monte Carlo procedure, which usually relies
on an artificial time discretization, can be formulated directly in continuous
time, rendering the scheme exact. For an arbitrary system with discrete Hilbert
space, none of the configuration update procedures contain small parameters. We
find that the most effective update strategy involves the motion of worldline
discontinuities (both in space and time), i.e., the evaluation of the Green's
function. Being based on local updates only, our method nevertheless allows one
to work with the grand canonical ensemble and non-zero winding numbers, and to
calculate any dynamic correlation function as easily as expectation values of,
e.g., total energy. The principles found for the update in continuous time
generalize to any continuous variables in the space of discrete virtual
transitions, and in principle also make it possible to simulate continuous
systems exactly.Comment: revtex, 14 pages, 6 figures, published version (modified and
extended
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