6,081 research outputs found
Bayesian Inference under Cluster Sampling with Probability Proportional to Size
Cluster sampling is common in survey practice, and the corresponding
inference has been predominantly design-based. We develop a Bayesian framework
for cluster sampling and account for the design effect in the outcome modeling.
We consider a two-stage cluster sampling design where the clusters are first
selected with probability proportional to cluster size, and then units are
randomly sampled inside selected clusters. Challenges arise when the sizes of
nonsampled cluster are unknown. We propose nonparametric and parametric
Bayesian approaches for predicting the unknown cluster sizes, with this
inference performed simultaneously with the model for survey outcome.
Simulation studies show that the integrated Bayesian approach outperforms
classical methods with efficiency gains. We use Stan for computing and apply
the proposal to the Fragile Families and Child Wellbeing study as an
illustration of complex survey inference in health surveys
Effects of the liquid-gas phase transition and cluster formation on the symmetry energy
Various definitions of the symmetry energy are introduced for nuclei, dilute
nuclear matter below saturation density and stellar matter, which is found in
compact stars or core-collapse supernovae. The resulting differences are
exemplified by calculations in a theoretical approach based on a generalized
relativistic density functional for dense matter. It contains nucleonic
clusters as explicit degrees of freedom with medium dependent properties that
are derived for light clusters from a quantum statistical approach. With such a
model the dissolution of clusters at high densities can be described. The
effects of the liquid-gas phase transition in nuclear matter and of cluster
formation in stellar matter on the density dependence of the symmetry energy
are studied for different temperatures. It is observed that correlations and
the formation of inhomogeneous matter at low densities and temperatures causes
an increase of the symmetry energy as compared to calculations assuming a
uniform uncorrelated spatial distribution of constituent baryons and leptons.Comment: 20 pages, 19 figures, version accepted for publication in EPJA
special volume on Nuclear Symmetry Energ
X-ray tracing using Geant4
We describe an extension to the Geant4 software package that allows it to be
used as a general purpose X-ray tracing package. We demonstrate its use by
building a model of the X-ray optics of the XMM-Newton, calculating its
effective area, and comparing the results with the published calibration
curves.Comment: 9 pages, 5 figures, accepted for publication by NIMA, DOI know
Composition and thermodynamics of nuclear matter with light clusters
We investigate nuclear matter at finite temperature and density, including
the formation of light clusters up to the alpha particle The novel feature of
this work is to include the formation of clusters as well as their dissolution
due to medium effects in a systematic way using two many-body theories: a
microscopic quantum statistical (QS) approach and a generalized relativistic
mean field (RMF) model. Nucleons and clusters are modified by medium effects.
Both approaches reproduce the limiting cases of nuclear statistical equilibrium
(NSE) at low densities and cluster-free nuclear matter at high densities. The
treatment of the cluster dissociation is based on the Mott effect due to Pauli
blocking, implemented in slightly different ways in the QS and the generalized
RMF approaches. We compare the numerical results of these models for cluster
abundances and thermodynamics in the region of medium excitation energies with
temperatures T <= 20 MeV and baryon number densities from zero to a few times
saturation density. The effect of cluster formation on the liquid-gas phase
transition and on the density dependence of the symmetry energy is studied.
Comparison is made with other theoretical approaches, in particular those,
which are commonly used in astrophysical calculations. The results are relevant
for heavy-ion collisions and astrophysical applications.Comment: 32 pages, 15 figures, minor corrections, accepted for publication in
Physical Review
Mechanisms for Direct Breakup Reactions
We review some simple mechanisms of breakup in nuclear reactions. We mention
the spectator breakup, which is described in the post-form DWBA. The relation
to other formulations is also indicated. An especially important mechanism is
Coulomb dissociation. It is a distinct advantage that the perturbation due to
the electric field of the nucleus is exactly known. Therefore firm conclusions
can be drawn from such measurements. Some new applications of Coulomb
dissociation for nuclear astrophysics are discussed.Comment: 17 pages, 5 figures, to appear in the proceedings of the RCNP-TMU
Symposium on Spins in Nuclear and Hadronic Reactions, October 16-18 199
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