5,198 research outputs found
Radiative neutron capture on a proton at BBN energies
The total cross section for radiative neutron capture on a proton, , is evaluated at big bang nucleosynthesis (BBN) energies. The
electromagnetic transition amplitudes are calculated up to next-to leading
order within the framework of pionless effective field theory with dibaryon
fields. We also calculate the cross section and the photon
analyzing power for the process from the amplitudes. The
values of low energy constants that appear in the amplitudes are estimated by a
Markov Chain Monte Carlo analysis using the relevant low energy experimental
data. Our result agrees well with those of other theoretical calculations
except for the cross section at some energies estimated by an
R-matrix analysis. We also study the uncertainties in our estimation of the
cross section at relevant BBN energies and find that the
estimated cross section is reliable to within 1% error.Comment: 21 pages and 12 eps figures; 6 eps figures and 2 references added,
and accepted for publication in Phys. Rev.
Strongly Coupled Quark Gluon Plasma (SCQGP)
We propose that the reason for the non-ideal behavior seen in lattice
simulation of quark gluon plasma (QGP) and relativistic heavy ion collisions
(URHICs) experiments is that the QGP near T_c and above is strongly coupled
plasma (SCP), i.e., strongly coupled quark gluon plasma (SCQGP). It is
remarkable that the widely used equation of state (EoS) of SCP in QED (quantum
electrodynamics) very nicely fits lattice results on all QGP systems, with
proper modifications to include color degrees of freedom and running coupling
constant. Results on pressure in pure gauge, 2-flavors and 3-flavors QGP, are
all can be explained by treating QGP as SCQGP as demonstated here.Energy
density and speed of sound are also presented for all three systems. We further
extend the model to systems with finite quark mass and a reasonably good fit to
lattice results are obtained for (2+1)-flavors and 4-flavors QGP. Hence it is
the first unified model, namely SCQGP, to explain the non-ideal QGP seen in
lattice simulations with just two system dependent parameters.Comment: Revised with corrections and new results, Latex file (11 pages),
postscript file of 7 figure
Gyrations: The Missing Link Between Classical Mechanics with its Underlying Euclidean Geometry and Relativistic Mechanics with its Underlying Hyperbolic Geometry
Being neither commutative nor associative, Einstein velocity addition of
relativistically admissible velocities gives rise to gyrations. Gyrations, in
turn, measure the extent to which Einstein addition deviates from commutativity
and from associativity. Gyrations are geometric automorphisms abstracted from
the relativistic mechanical effect known as Thomas precession
Harold Jeffreys's Theory of Probability Revisited
Published exactly seventy years ago, Jeffreys's Theory of Probability (1939)
has had a unique impact on the Bayesian community and is now considered to be
one of the main classics in Bayesian Statistics as well as the initiator of the
objective Bayes school. In particular, its advances on the derivation of
noninformative priors as well as on the scaling of Bayes factors have had a
lasting impact on the field. However, the book reflects the characteristics of
the time, especially in terms of mathematical rigor. In this paper we point out
the fundamental aspects of this reference work, especially the thorough
coverage of testing problems and the construction of both estimation and
testing noninformative priors based on functional divergences. Our major aim
here is to help modern readers in navigating in this difficult text and in
concentrating on passages that are still relevant today.Comment: This paper commented in: [arXiv:1001.2967], [arXiv:1001.2968],
[arXiv:1001.2970], [arXiv:1001.2975], [arXiv:1001.2985], [arXiv:1001.3073].
Rejoinder in [arXiv:0909.1008]. Published in at
http://dx.doi.org/10.1214/09-STS284 the Statistical Science
(http://www.imstat.org/sts/) by the Institute of Mathematical Statistics
(http://www.imstat.org
Bayesian parameter estimation in the second LISA Pathfinder Mock Data Challenge
A main scientific output of the LISA Pathfinder mission is to provide a noise
model that can be extended to the future gravitational wave observatory, LISA.
The success of the mission depends thus upon a deep understanding of the
instrument, especially the ability to correctly determine the parameters of the
underlying noise model. In this work we estimate the parameters of a simplified
model of the LISA Technology Package (LTP) instrument. We describe the LTP by
means of a closed-loop model that is used to generate the data, both injected
signals and noise. Then, parameters are estimated using a Bayesian framework
and it is shown that this method reaches the optimal attainable error, the
Cramer-Rao bound. We also address an important issue for the mission: how to
efficiently combine the results of different experiments to obtain a unique set
of parameters describing the instrument.Comment: 14 pages, 4 figures, submitted to PR
Internationalisation, cultural distance and country characteristics: a Bayesian analysis of SME's financial performance
Relying on the accounting data of a panel of 403 Italian manufacturing SMEs collected over a period of 5 years, we find results suggesting that multinationality per se does not impact on the economic performance of international small and medium sized firms. It is the characteristics of the country selected i.e. the political hazard, the financial stability and the economic performance that significantly influence SMEs financial performance. The management implication for small and medium sized firms selecting and entering new geographic markets is significant, since our results show that for SMEs it is the market selection process that really matters and not the degree of multinationality
Children Seek Historical Traces of Owned Objects
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141553/1/cdev12453.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/141553/2/cdev12453_am.pd
Environment-sensitive mass changes influence breeding frequency in a capital breeding marine top predator
UK Natural Environment Research Council funding to the Sea Mammal Research Unit enabled this work. NERC grant no. NE/G008930/1 and EsmĂ©e Fairbairn Foundation (PP). SCS was supported as a EPSRC postdoctoral fellow (RK, PP).1. The tradeâoff between survival and reproduction in resourceâlimited iteroparous animals can result in some individuals missing some breeding opportunities. In practice, even with the best observation regimes, deciding whether âmissedâ years represent real pauses in breeding or failures to detect breeding can be difficult, posing problems for the estimation of individual reproductive output and overall population fecundity. 2. We corrected fecundity estimates by determining whether breeding had occurred in skipped years, using longâterm captureârecapture observation datasets with parallel longitudinal mass measurements, based on informative underlying relationships between individualsâ mass, breeding status and environmental drivers in a capital breeding phocid, the grey seal. 3. Bayesian modelling considered interacting processes jointly: temporal changes in a phenotypic covariate (mass); relationship of mass to breeding probability; effects of maternal breeding state and mark type on resighting. Full reproductive histories were imputed, with the status of unobserved animals estimated as breeding or nonâbreeding, accounting for local environmental variation. Overall fecundity was then derived for Scottish breeding colonies with contrasting pup production trends. 4. Maternal mass affected breeding likelihood. Mothers with low body mass at the end of breeding were less likely to bear a pup the following year. Successive breeding episodes incurred a cost in reduced body mass which was more pronounced for North Rona, Outer Hebrides (NR) mothers. Skipping breeding increased subsequent pupping probability substantially for low mass females. Poor environmental conditions were associated with declines in breeding probability at both colonies. Seal mass gain between breeding seasons was (a) negatively associated with lagged North Atlantic Oscillation for seals at NR and (b) positively associated with an index of seal prey (Ammodytes spp) abundance at Isle of May, Firth of Forth (IM). Overall fecundity was marginally greater at IM (increasing/stable pup production) than at NR (decreasing). No effects of mass were detected on maternal survival. 5. Skipping breeding in female grey seals appears to be an individual massâdependent constraint moderated by previous reproductive output and local environmental conditions. Different demographic trends at breeding colonies were consistent with the fecundities estimated using this method, which is general and adaptable to other situations.PostprintPeer reviewe
A TV-Gaussian prior for infinite-dimensional Bayesian inverse problems and its numerical implementations
Many scientific and engineering problems require to perform Bayesian
inferences in function spaces, in which the unknowns are of infinite dimension.
In such problems, choosing an appropriate prior distribution is an important
task. In particular we consider problems where the function to infer is subject
to sharp jumps which render the commonly used Gaussian measures unsuitable. On
the other hand, the so-called total variation (TV) prior can only be defined in
a finite dimensional setting, and does not lead to a well-defined posterior
measure in function spaces. In this work we present a TV-Gaussian (TG) prior to
address such problems, where the TV term is used to detect sharp jumps of the
function, and the Gaussian distribution is used as a reference measure so that
it results in a well-defined posterior measure in the function space. We also
present an efficient Markov Chain Monte Carlo (MCMC) algorithm to draw samples
from the posterior distribution of the TG prior. With numerical examples we
demonstrate the performance of the TG prior and the efficiency of the proposed
MCMC algorithm
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