650 research outputs found
Variational Bayes with Intractable Likelihood
Variational Bayes (VB) is rapidly becoming a popular tool for Bayesian
inference in statistical modeling. However, the existing VB algorithms are
restricted to cases where the likelihood is tractable, which precludes the use
of VB in many interesting situations such as in state space models and in
approximate Bayesian computation (ABC), where application of VB methods was
previously impossible. This paper extends the scope of application of VB to
cases where the likelihood is intractable, but can be estimated unbiasedly. The
proposed VB method therefore makes it possible to carry out Bayesian inference
in many statistical applications, including state space models and ABC. The
method is generic in the sense that it can be applied to almost all statistical
models without requiring too much model-based derivation, which is a drawback
of many existing VB algorithms. We also show how the proposed method can be
used to obtain highly accurate VB approximations of marginal posterior
distributions.Comment: 40 pages, 6 figure
Variable Selection and Model Averaging in Semiparametric Overdispersed Generalized Linear Models
We express the mean and variance terms in a double exponential regression
model as additive functions of the predictors and use Bayesian variable
selection to determine which predictors enter the model, and whether they enter
linearly or flexibly. When the variance term is null we obtain a generalized
additive model, which becomes a generalized linear model if the predictors
enter the mean linearly. The model is estimated using Markov chain Monte Carlo
simulation and the methodology is illustrated using real and simulated data
sets.Comment: 8 graphs 35 page
The Kohn mode for trapped Bose gases within the dielectric formalism
The presence of undamped harmonic center of mass oscillations of a weakly
interacting Bose gas in a harmonic trap is demonstrated within the dielectric
formalism for a previously introduced finite temperature approximation
including exchange. The consistency of the approximation with the Kohn theorem
is thereby demonstrated. The Kohn modes are found explicitly, generalizing an
earlier zero-temperature result found in the literature. It is shown how the
Kohn mode disappears from the single-particle spectrum, while remaining in the
density oscillation spectrum, when the temperature increases from below to
above the condensation temperature.Comment: 6 pages revte
Recent Assembly of an Imprinted Domain from Non-Imprinted Components
Genomic imprinting, representing parent-specific expression of alleles at a locus, raises many questions about how—and especially why—epigenetic silencing of mammalian genes evolved. We present the first in-depth study of how a human imprinted domain evolved, analyzing a domain containing several imprinted genes that are involved in human disease. Using comparisons of orthologous genes in humans, marsupials, and the platypus, we discovered that the Prader-Willi/Angelman syndrome region on human Chromosome 15q was assembled only recently (105–180 million years ago). This imprinted domain arose after a region bearing UBE3A (Angelman syndrome) fused with an unlinked region bearing SNRPN (Prader-Willi syndrome), which had duplicated from the non-imprinted SNRPB/B′. This region independently acquired several retroposed gene copies and arrays of small nucleolar RNAs from different parts of the genome. In their original configurations, SNRPN and UBE3A are expressed from both alleles, implying that acquisition of imprinting occurred after their rearrangement and required the evolution of a control locus. Thus, the evolution of imprinting in viviparous mammals is ongoing
Isotopic ordering in eggshells reflects body temperatures and suggests differing thermophysiology in two Cretaceous dinosaurs
Our understanding of the evolutionary transitions leading to the modern endothermic state of birds and mammals is incomplete, partly because tools available to study the thermophysiology of extinct vertebrates are limited. Here we show that clumped isotope analysis of eggshells can be used to determine body temperatures of females during periods of ovulation. Late Cretaceous titanosaurid eggshells yield temperatures similar to large modern endotherms. In contrast, oviraptorid eggshells yield temperatures lower than most modern endotherms but ~6 °C higher than co-occurring abiogenic carbonates, implying that this taxon did not have thermoregulation comparable to modern birds, but was able to elevate its body temperature above environmental temperatures. Therefore, we observe no strong evidence for end-member ectothermy or endothermy in the species examined. Body temperatures for these two species indicate that variable thermoregulation likely existed among the non-avian dinosaurs and that not all dinosaurs had body temperatures in the range of that seen in modern birds
Decoherence of Bose-Einstein condensates in traps at finite temperature
The phase diffusion of the order parameter of trapped Bose-Einstein
condensates at temperatures large compared to the mean trap frequency is
determined, which gives the fundamental limit of the line-width of an atom
laser. In addition a prediction of the correlation time of the number
fluctuations in the condensate is made and related to the phase diffusion via
the fluctuation-dissipation relation.Comment: 4 pages Revtex, revised version, to appear in Phys. Rev. Letter
External Bone Size Is a Key Determinant of Strength‐Decline Trajectories of Aging Male Radii
Given prior work showing associations between remodeling and external bone size, we tested the hypothesis that wide bones would show a greater negative correlation between whole‐bone strength and age compared with narrow bones. Cadaveric male radii (n = 37 pairs, 18 to 89 years old) were evaluated biomechanically, and samples were sorted into narrow and wide subgroups using height‐adjusted robustness (total area/bone length). Strength was 54% greater (p < 0.0001) in wide compared with narrow radii for young adults (<40 years old). However, the greater strength of young‐adult wide radii was not observed for older wide radii, as the wide (R2 = 0.565, p = 0.001), but not narrow (R2 = 0.0004, p = 0.944) subgroup showed a significant negative correlation between strength and age. Significant positive correlations between age and robustness (R2 = 0.269, p = 0.048), cortical area (Ct.Ar; R2 = 0.356, p = 0.019), and the mineral/matrix ratio (MMR; R2 = 0.293, p = 0.037) were observed for narrow, but not wide radii (robustness: R2 = 0.015, p = 0.217; Ct.Ar: R2 = 0.095, p = 0.245; MMR: R2 = 0.086, p = 0.271). Porosity increased with age for the narrow (R2 = 0.556, p = 0.001) and wide (R2 = 0.321, p = 0.022) subgroups. The wide subgroup (p < 0.0001) showed a significantly greater elevation of a new measure called the Cortical Pore Score, which quantifies the cumulative effect of pore size and location, indicating that porosity had a more deleterious effect on strength for wide compared with narrow radii. Thus, the divergent strength–age regressions implied that narrow radii maintained a low strength with aging by increasing external size and mineral content to mechanically offset increases in porosity. In contrast, the significant negative strength–age correlation for wide radii implied that the deleterious effect of greater porosity further from the centroid was not offset by changes in outer bone size or mineral content. Thus, the low strength of elderly male radii arose through different biomechanical mechanisms. Consideration of different strength–age regressions (trajectories) may inform clinical decisions on how best to treat individuals to reduce fracture risk. © 2019 American Society for Bone and Mineral Research.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/149566/1/jbmr3661_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/149566/2/jbmr3661.pd
Adipocyte-specific protein tyrosine phosphatase 1B deletion increases lipogenesis, adipocyte cell size and is a minor regulator of glucose homeostasis
Peer reviewedPublisher PD
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