The Bernstein-Von Mises Theorem in Semiparametric Competing Risks Models

Semiparametric Bayesian models are nowadays a popular tool in survival analysis. An important area of research concerns the investigation of frequentist properties of these models. In this paper, a Bernstein-von Mises theorem is derived for semiparametric Bayesian models of competing risks data. The cause-specific hazard is taken as the product of the conditional probability of a failure type and the overall hazard rate. We model the conditional probability as a smooth function of time and leave the cumulative overall hazard unspecified. A prior distribution is defined on the joint parameter space, which includes a beta process prior for the cumulative overall hazard. We show that the posterior distribution for any differentiable functional of interest is asymptotically equivalent to the sampling distribution derived from maximum likelihood estimation. A simulation study is provided to illustrate the coverage properties of credible intervals on cumulative incidence functions.Bayesian nonparametrics, Bernstein-von Mises theorem, beta process, competing risks, conditional probability of a failure type, semiparametric inference.

The Passing of Sovereign Immunity in Montana: The King Is Dead!

The Passing Of Sovereign Immunity In Montana: The King Is Dead

The Passing of Sovereign Immunity in Montana: The King Is Dead!

The Passing Of Sovereign Immunity In Montana: The King Is Dead

Theoretical model of structure-dependent conductance crossover in disordered carbon

We analyze the effects of sp^2/sp^3 bond-aspect ratio on the transport properties of amorphous carbon quasi-1D structures where structural disorder varies in a very non-linear manner with the effective bandgap. Using a tight-binding approach the calculated electron transmission showed a high probability over a wide region around the Fermi-level for sp^2-rich carbon and also distinct peaks close to the band edges for sp^3-rich carbon structures. This model shows a sharp rise of the structure resistance with the increase of sp^3C % followed by saturation in the wide bandgap regime for carbon superlattice-like structures and suggests the tuneable characteristic time of carbon-based devices.Comment: 6 pages, 6 figure

Molecular evolution of the vesicle coat component βCOP in Toxoplasma gondii

Author Posting. © The Author(s), 2007. This is the author's version of the work. It is posted here by permission of Elsevier for personal use, not for redistribution. The definitive version was published in Molecular Phylogenetics and Evolution 44 (2007): 1284-1294, doi:10.1016/j.ympev.2007.02.031.Coatomer coated (COPI) vesicles play a pivotal role for multiple membrane trafficking steps throughout the eukaryotic cell. Our focus is on βCOP, one of the most well known components of the COPI multi-protein complex. Amino acid differences in βCOP may dictate functional divergence across species during the course of evolution, especially with regards to the evolutionary pressures on obligate intracellular parasites. A bioinformatic analysis of βCOP amino acid sequences was conducted for 49 eukaryotic species. Cloning and sequence analysis of the Toxoplasma gondii βCOP homologue revealed several amino acid insertions unique to T. gondii and one C-terminal insertion that is unique to apicomplexan parasites. These findings led us to investigate the possibility that βCOP experienced functional divergence during the course of its evolution. Bayesian phylogenetic analysis revealed a tree consistent with pan eukaryote distribution and long-branch lengths were observed among the apicomplexans. Further analysis revealed that kinetoplast βCOP underwent the most amount of change, leading to perhaps an overall change of function. In comparison, T. gondii exhibited subtle yet specific amino acid changes. The amino acid substitutions did not occur in the same places as other lineages, suggesting that TgβCOP has a role specific to the apicomplexans. Our work identifies forty-eight residues that are likely to be functionally important when comparing apicomplexan, kinetoplastid, and fungal βCOP.KMH is an Ellison Medical Foundation New Scholar in Infectious Disease; SLP was supported by an NIH training grant (NIH/NIAID/TMP T 32 7030); AGM was supported by the Marine Biological Laboratory’s Program in Global Infectious Diseases, also funded by the Ellison Medical Foundation

Environmental Controls of InSAR-Based Periglacial Ground Dynamics in a Sub-Arctic Landscape

Periglacial environments are characterized by highly dynamic landscapes. Freezing and thawing lead to ground movement, associated with cryoturbation and solifluction. These processes are sensitive to climate change and variably distributed depending on multiple environmental factors. In this study, we used multi-geometry Sentinel-1 Synthetic Aperture Radar Interferometry (InSAR) to investigate the spatial distribution of the mean annual ground velocity in a mountainous landscape in Northern Norway. Statistical modeling was employed to examine how periglacial ground velocity is related to environmental variables characterizing the diverse climatic, geomorphic, hydrological and biological conditions within a 148 km(2) study area. Two-dimensional (2D) InSAR results document mean annual ground velocity up to 15 mm/yr. Vertical and horizontal velocity components in the East-West plane show variable spatial distribution, which can be explained by the characteristics of cryoturbation and solifluction operating differently over flat and sloping terrain. Statistical modeling shows that slope angle and mean annual air temperature variables are the most important environmental factors explaining the distribution of the horizontal and vertical components, respectively. Vegetation and snow cover also have a local influence, interpreted as indicators of the ground material and moisture conditions. The results show contrasted model performance depending on the velocity component used as a response variable. In general, our study highlights the potential of integrating radar remote sensing and statistical modeling to investigate mountainous regions and better understand the relations between environmental factors, periglacial processes and ground dynamics.Peer reviewe

Compound Markov counting processes and their applications to modeling infinitesimally over-dispersed systems

We propose an infinitesimal dispersion index for Markov counting processes. We show that, under standard moment existence conditions, a process is infinitesimally (over-) equi-dispersed if, and only if, it is simple (compound), i.e. it increases in jumps of one (or more) unit(s), even though infinitesimally equi-dispersed processes might be under-, equi- or over-dispersed using previously studied indices. Compound processes arise, for example, when introducing continuous-time white noise to the rates of simple processes resulting in Levy-driven SDEs. We construct multivariate infinitesimally over-dispersed compartment models and queuing networks, suitable for applications where moment constraints inherent to simple processes do not hold.Comment: 26 page

Leukocyte telomere length is associated with elevated plasma glucose and HbA1c in young healthy men independent of birth weight.

Telomeres are protein-bound regions of repetitive nucleotide sequences (TTAGGG) at the end of human chromosomes, and their length is a marker of cellular aging. Intrauterine growth restriction is associated with shorter blood cell telomeres at birth and individuals with type 2 diabetes have shorter telomeres. Individuals with a low birth weight (LBW) have an increased risk of metabolic disease and type 2 diabetes. Therefore, we aimed to investigate the relationship between birth weight and telomere length and the association between birth weight, telomere length and cardiometabolic phenotype in adulthood. Young, healthy men with LBW (n = 55) and normal birth weight (NBW) (n = 65) were examined including blood pressure, blood samples and body composition. Leukocyte telomere length was determined using a high-throughput qPCR method. The LBW men were more insulin resistant as determined by the HOMA-IR index. There was no difference in telomere length between LBW and NBW subjects. When adjusting for birth weight and cohort effect, significant negative associations between telomere length and fasting glucose (P = 0.003) and HbA1c (P = 0.0008) were found. In conclusion, no significant difference in telomere length was found between LBW and NBW men. The telomere length was negatively associated with glucose concentrations and HbA1c levels within the normal non-diabetic range independent of birth weight