152 research outputs found
Generalized Species Sampling Priors with Latent Beta reinforcements
Many popular Bayesian nonparametric priors can be characterized in terms of
exchangeable species sampling sequences. However, in some applications,
exchangeability may not be appropriate. We introduce a {novel and
probabilistically coherent family of non-exchangeable species sampling
sequences characterized by a tractable predictive probability function with
weights driven by a sequence of independent Beta random variables. We compare
their theoretical clustering properties with those of the Dirichlet Process and
the two parameters Poisson-Dirichlet process. The proposed construction
provides a complete characterization of the joint process, differently from
existing work. We then propose the use of such process as prior distribution in
a hierarchical Bayes modeling framework, and we describe a Markov Chain Monte
Carlo sampler for posterior inference. We evaluate the performance of the prior
and the robustness of the resulting inference in a simulation study, providing
a comparison with popular Dirichlet Processes mixtures and Hidden Markov
Models. Finally, we develop an application to the detection of chromosomal
aberrations in breast cancer by leveraging array CGH data.Comment: For correspondence purposes, Edoardo M. Airoldi's email is
[email protected]; Federico Bassetti's email is
[email protected]; Michele Guindani's email is
[email protected] ; Fabrizo Leisen's email is
[email protected]. To appear in the Journal of the American
Statistical Associatio
Interacting Multiple Try Algorithms with Different Proposal Distributions
We propose a new class of interacting Markov chain Monte Carlo (MCMC)
algorithms designed for increasing the efficiency of a modified multiple-try
Metropolis (MTM) algorithm. The extension with respect to the existing MCMC
literature is twofold. The sampler proposed extends the basic MTM algorithm by
allowing different proposal distributions in the multiple-try generation step.
We exploit the structure of the MTM algorithm with different proposal
distributions to naturally introduce an interacting MTM mechanism (IMTM) that
expands the class of population Monte Carlo methods. We show the validity of
the algorithm and discuss the choice of the selection weights and of the
different proposals. We provide numerical studies which show that the new
algorithm can perform better than the basic MTM algorithm and that the
interaction mechanism allows the IMTM to efficiently explore the state space
String-like Clusters and Cooperative Motion in a Model Glass-Forming Liquid
A large-scale molecular dynamics simulation is performed on a glass-forming
Lennard-Jones mixture to determine the nature of dynamical heterogeneities
which arise in this model fragile liquid. We observe that the most mobile
particles exhibit a cooperative motion in the form of string-like paths
(``strings'') whose mean length and radius of gyration increase as the liquid
is cooled. The length distribution of the strings is found to be similar to
that expected for the equilibrium polymerization of linear polymer chains.Comment: 6 pages of RevTex, 6 postscript figures, uses epsf.st
Gesundheit und LeistungsfĂ€higkeit von MilchkĂŒhen im ökologischen Landbau interdisziplinĂ€r betrachtet â eine (Interventions-) Studie zu Stoffwechselstörungen und Eutererkrankungen unter BerĂŒcksichtigung von Grundfuttererzeugung, FĂŒtterungsmanagement und Tierhaltung
Im Mittelpunkt des Projektes stand die Stoffwechsel- und Eutergesundheit von ökologisch gehaltenen MilchkĂŒhen im prĂ€- und peripartalen Zeitraum sowie in den ersten 100 Laktationstagen und deren Beeinflussung durch die Futter- und NĂ€hrstoffversorgung und die Haltungsumwelt im umfassenden Sinn. In einer bundesweiten Feldstudie auf 106 ökologisch wirtschaftenden Milchviehbetrieben erfolgten Erhebungen mit dem Ziel einer Risikomodellierung zu Stoffwechsel- und Eutererkrankungen. Vor diesem Hintergrund wurden die Produktionssysteme von der Pflanzenzusammensetzung im GrĂŒnland und im Ackerfutter ĂŒber die Grobfutterproduktion, FutterqualitĂ€t und Rationsgestaltung, Haltungsumwelt bis hin zur Tiergesundheit und MilchqualitĂ€t analysiert, um hier einzelbetriebliche RisikoeinschĂ€tzungen vorzunehmen, Optimierungspotenziale aufzuzeigen und Handlungsempfehlungen abzuleiten, die anschlieĂend betriebsindividuell implementiert wurden. Die EffektivitĂ€t des so geschaffenen prĂ€ventiv orientierten Tiergesundheitsmanagements wurde anhand der Entwicklung ausgewĂ€hlter Kennzahlen der Euter- und Stoffwechselgesundheit geprĂŒft. Es konnte gezeigt werden, dass sich mit dieser Vorgehensweise auch unter Praxisbedingungen die Tiergesundheitssituation signifikant verbes-sern lĂ€sst. Die Feldstudie wurde mit experimentellen Untersuchungen ergĂ€nzt, die sich speziellen Fragen der Analyse von nXP in Grasprodukten, des Kraftfuttereinsatzes, der Wahl der geeigneten Rasse, dem Infektionsgeschehen, der Nutzung von Haltungstechniken im FĂŒtterungsmanagement und der Verbesserung der Grasnarbe widmeten. Die im Projekt generierten, aufgrund ihrer Ableitung aus der Praxis widerspruchsarmen Erkenntnisse wurden ĂŒber vielfĂ€ltige Formen des Wissenstransfers an die Akteure in der Ăkologischen Milchviehhaltung vermittelt. Ein Merkblatt zur Euter- und Stoffwechselgesundheit bei BiomilchkĂŒhen und ein modular aufgebautes Wissenstransferkonzept wurden erarbeitet, um die Projektergebnisse nachhaltig nutzen zu können
Spatially controlled cell adhesion on three-dimensional substrates
The microenvironment of cells in vivo is defined by spatiotemporal patterns of chemical and biophysical cues. Therefore, one important goal of tissue engineering is the generation of scaffolds with defined biofunctionalization in order to control processes like cell adhesion and differentiation. Mimicking extrinsic factors like integrin ligands presented by the extracellular matrix is one of the key elements to study cellular adhesion on biocompatible scaffolds. By using special thermoformable polymer films with anchored biomolecules micro structured scaffolds, e.g. curved and ”-patterned substrates, can be fabricated. Here, we present a novel strategy for the fabrication of ”-patterned scaffolds based on the âSubstrate Modification and Replication by Thermoformingâ (SMART) technology: The surface of a poly lactic acid membrane, having a low forming temperature of 60°C and being initially very cell attractive, was coated with a photopatterned layer of poly(L-lysine) (PLL) and hyaluronic acid (VAHyal) to gain spatial control over cell adhesion. Subsequently, this modified polymer membrane was thermoformed to create an array of spherical microcavities with diameters of 300 ”m for 3D cell culture. Human hepatoma cells (HepG2) and mouse fibroblasts (L929) were used to demonstrate guided cell adhesion. HepG2 cells adhered and aggregated exclusively within these cavities without attaching to the passivated surfaces between the cavities. Also L929 cells adhering very strongly on the pristine substrate polymer were effectively patterned by the cell repellent properties of the hyaluronic acid based hydrogel. This is the first time cell adhesion was controlled by patterned functionalization of a polymeric substrate with UV curable PLL-VAHyal in thermoformed 3D microstructures
Continuum-Scale Modeling of Liquid Redistribution in a Stack of Thin Hydrophilic Fibrous Layers
Comparison of Two Smallâgroup Learning Methods in 12thâgrade Physics Classes Focusing on Intrinsic Motivation and Academic Performance
Fostering German-language learnersâ constructions of meanings for fractionsâdesign and effects of a language- and mathematics-integrated intervention
An analysis of written lesson plans to examine pedagogical adaptivity in the planning competences of trainee teachers
PTSD among women survivors of domestic violence in Hawaii.
Empirical evidence suggests that between 33% and 83% of Hawaii women receiving services from programs that serve battered women meet diagnostic criteria for posttraumatic stress disorder (PTSD). In addition, PTSD symptom severity is associated with depression severity, lowered self-esteem, and diminished quality of life. Combined with evidence that domestic violence often goes on for years, these findings provide additional compelling reasons why domestic violence screening should be conducted routinely in medical settings
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