5,960 research outputs found
Reference priors for high energy physics
Bayesian inferences in high energy physics often use uniform prior
distributions for parameters about which little or no information is available
before data are collected. The resulting posterior distributions are therefore
sensitive to the choice of parametrization for the problem and may even be
improper if this choice is not carefully considered. Here we describe an
extensively tested methodology, known as reference analysis, which allows one
to construct parametrization-invariant priors that embody the notion of minimal
informativeness in a mathematically well-defined sense. We apply this
methodology to general cross section measurements and show that it yields
sensible results. A recent measurement of the single top quark cross section
illustrates the relevant techniques in a realistic situation
Counting States: A Combinatorial Analysis of SQM Fragmentation
The Strange Quark matter (SQM) hypothesis states that at extreme pressure and
density conditions a new ground state of matter would arise, in which half of
the \textit{down} quarks become strange quarks. If true, it would mean that at
least the core of neutron stars is made of SQM. In this hypothesis, SQM would
be released in the inter-stellar medium when two of these objects merge. It is
estimated that of SQM would be released this way. This matter
will undergo a sequence of processes that should result in a fraction of the
released SQM becoming heavy nuclei through \textit{r-process}. In this work we
are interested in characterizing the fragmentation of SQM, with the novelty of
keeping track of the \textit{quark configuration} of the fragmented matter.
This is accomplished by developing a methodology to estimate the energy of each
fragment as the sum of its \textit{constituent quarks}, the Coulomb interaction
among the quarks and fragments' momenta. The determination of the fragmentation
output is crucial to fully characterize the subsequent nucleosynthesis.Comment: 4 pages, 2 figures, 2 table
Geometry of the energy landscape of the self-gravitating ring
We study the global geometry of the energy landscape of a simple model of a
self-gravitating system, the self-gravitating ring (SGR). This is done by
endowing the configuration space with a metric such that the dynamical
trajectories are identified with geodesics. The average curvature and curvature
fluctuations of the energy landscape are computed by means of Monte Carlo
simulations and, when possible, of a mean-field method, showing that these
global geometric quantities provide a clear geometric characterization of the
collapse phase transition occurring in the SGR as the transition from a flat
landscape at high energies to a landscape with mainly positive but fluctuating
curvature in the collapsed phase. Moreover, curvature fluctuations show a
maximum in correspondence with the energy of a possible further transition,
occurring at lower energies than the collapse one, whose existence had been
previously conjectured on the basis of a local analysis of the energy landscape
and whose effect on the usual thermodynamic quantities, if any, is extremely
weak. We also estimate the largest Lyapunov exponent of the SGR using
the geometric observables. The geometric estimate always gives the correct
order of magnitude of and is also quantitatively correct at small
energy densities and, in the limit , in the whole homogeneous
phase.Comment: 20 pages, 12 figure
Using a glass-fibre reinforced polymer composite in the production of sustainable water storage vessels
The quest for sustainability by rethinking materials, products and production strategies is an enormous challenge currently laid upon the economic sector. Materials selection plays a critical role in this challenge. The present work describes a technological, environmental and economic study of the production of a water storage glass-fibre reinforced composite vessel. The vessel was evaluated via a Life Cycle Assessment/Life Cycle Costing (LCA/LCC) integrated model. The most significant life cycle phase was found to be the raw materials production, in which the Fossil fuels, Respiratory inorganics and Climate change were the relevant impact categories. The vessel environmental and economic performances could be improved if an end of life (EoL) option different from landfill had been chosen. The present work describes a new integrated way of analysing the environmental and economic performances of a structural product full life cycle. It also highlights the role and importance of fibre reinforced polymer composites in the quest for sustainable products.FCT projeto SFRH/BD/60852/2009 e IPC projeto UID/CTM/50025/201
Myxomycete communities occurring in fragmented forest patches in two municipalities of Laguna, Philippines
In spite of the increasing number of myxomycete studies in the tropical Southeast Asia over the last decades, many forest patches are still left unexplored for the region, in particular in the Philippine archipelago. Thus, an assessment of myxomycete diversity, occurrence, and composition was carried out in forest fragments from two municipalities of the province of Laguna, Philippines. From the 12 established 5 m × 5 m plots, a total of 240 moist chamber cultures were prepared for this study and yielded 42 myxomycete species belonging to 14 genera. Rarefaction curves and several heterogeneity indices revealed higher species diversity in Los Baños than in Calauan. Moreover, the taxonomic diversity index also showed that the taxonomic diversity of myxomycete in Los Baños is more intuitively diverse than in Calauan. In terms of community analysis between the two municipalities, it showed that myxomycete communities clustered between different microhabitats. High values of coefficient of community and percentage similarity indices possibly implicates that spore dispersal in forest fragments in closer proximities may cause high number of shared species (60%). With an addition of Cribraria lepida as a new record for the country, this study now updates the myxomycete profile for Laguna, Philippines
Piecewise smooth systems near a co-dimension 2 discontinuity manifold: can one say what should happen?
We consider a piecewise smooth system in the neighborhood of a co-dimension 2
discontinuity manifold . Within the class of Filippov solutions, if
is attractive, one should expect solution trajectories to slide on
. It is well known, however, that the classical Filippov
convexification methodology is ambiguous on . The situation is further
complicated by the possibility that, regardless of how sliding on is
taking place, during sliding motion a trajectory encounters so-called generic
first order exit points, where ceases to be attractive.
In this work, we attempt to understand what behavior one should expect of a
solution trajectory near when is attractive, what to expect
when ceases to be attractive (at least, at generic exit points), and
finally we also contrast and compare the behavior of some regularizations
proposed in the literature.
Through analysis and experiments we will confirm some known facts, and
provide some important insight: (i) when is attractive, a solution
trajectory indeed does remain near , viz. sliding on is an
appropriate idealization (of course, in general, one cannot predict which
sliding vector field should be selected); (ii) when loses attractivity
(at first order exit conditions), a typical solution trajectory leaves a
neighborhood of ; (iii) there is no obvious way to regularize the
system so that the regularized trajectory will remain near as long as
is attractive, and so that it will be leaving (a neighborhood of)
when looses attractivity.
We reach the above conclusions by considering exclusively the given piecewise
smooth system, without superimposing any assumption on what kind of dynamics
near (or sliding motion on ) should have been taking place.Comment: 19 figure
Hydrogen bonding and coordination in normal and supercritical water from X-ray inelastic scattering
A direct measure of hydrogen bonding in water under conditions ranging from
the normal state to the supercritical regime is derived from the Compton
scattering of inelastically-scattered X-rays. First, we show that a measure of
the number of electrons involved in hydrogen bonding at varying
thermodynamic conditions can be directly obtained from Compton profile
differences. Then, we use first-principles simulations to provide a connection
between and the number of hydrogen bonds . Our study shows that
over the broad range studied the relationship between and is
linear, allowing for a direct experimental measure of bonding and coordination
in water. In particular, the transition to supercritical state is characterized
by a sharp increase in the number of water monomers, but also displays a
significant number of residual dimers and trimers.Comment: 14 pages, 5 figures, 1 tabl
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