Particle Gibbs with Ancestor Sampling

Particle Markov chain Monte Carlo (PMCMC) is a systematic way of combining the two main tools used for Monte Carlo statistical inference: sequential Monte Carlo (SMC) and Markov chain Monte Carlo (MCMC). We present a novel PMCMC algorithm that we refer to as particle Gibbs with ancestor sampling (PGAS). PGAS provides the data analyst with an off-the-shelf class of Markov kernels that can be used to simulate the typically high-dimensional and highly autocorrelated state trajectory in a state-space model. The ancestor sampling procedure enables fast mixing of the PGAS kernel even when using seemingly few particles in the underlying SMC sampler. This is important as it can significantly reduce the computational burden that is typically associated with using SMC. PGAS is conceptually similar to the existing PG with backward simulation (PGBS) procedure. Instead of using separate forward and backward sweeps as in PGBS, however, we achieve the same effect in a single forward sweep. This makes PGAS well suited for addressing inference problems not only in state-space models, but also in models with more complex dependencies, such as non-Markovian, Bayesian nonparametric, and general probabilistic graphical models

Baryon Resonance Phenomenology

The Japan Hadron Facility will provide an unprecedented opportunity for the study of baryon resonance properties. This talk will focus on the chiral nonanalytic behaviour of magnetic moments exclusive to baryons with open decay channels. To illustrate the novel features associated with an open decay channel, we consider the ``Access'' quark model, where an analytic continuation of chiral perturbation theory is employed to connect results obtained using the constituent quark model in the limit of SU(3)-flavour symmetry to empirical determinations.Comment: 10 pages, 4 figures, ws-procs9x6.cls(included), Proceedings from the Joint CSSM/JHF Workshop, Adelaide, March 14-21, 200

A Compact Apparatus for Muon Lifetime Measurement and Time Dilation Demonstration in the Undergraduate Laboratory

We describe a compact apparatus that automatically measures the charge averaged lifetime of atmospheric muons in plastic scintillator using low-cost, low-power electronics and that measures the stopping rate of atmospheric muons as a function of altitude to demonstrate relativistic time dilation. The apparatus is designed for the advanced undergraduate physics laboratory and is suitable for field measurements.Comment: 5 pages, 2 figure

Loop-Less Electric Dipole Moment of the Nucleon in the Standard Model

We point out that the electric dipole moment of the neutron in the Standard Model is generated already at tree level to the second order in the weak interactions due to bound-state effects, without short-distance Penguin loops. The related contribution has a regular nonvanishing chiral limit and does not depend on the mass splitting between s and d quarks. We estimate it to be roughly 10^(-31)e*cm and expect a more accurate evaluation in the future. We comment on the connection between d_n and the direct CP-violation in D decays.Comment: 10 pages, 2 figure

Infinite-randomness critical point in the two-dimensional disordered contact process

We study the nonequilibrium phase transition in the two-dimensional contact process on a randomly diluted lattice by means of large-scale Monte-Carlo simulations for times up to $10^{10}$ and system sizes up to $8000 \times 8000$ sites. Our data provide strong evidence for the transition being controlled by an exotic infinite-randomness critical point with activated (exponential) dynamical scaling. We calculate the critical exponents of the transition and find them to be universal, i.e., independent of disorder strength. The Griffiths region between the clean and the dirty critical points exhibits power-law dynamical scaling with continuously varying exponents. We discuss the generality of our findings and relate them to a broader theory of rare region effects at phase transitions with quenched disorder. Our results are of importance beyond absorbing state transitions because according to a strong-disorder renormalization group analysis, our transition belongs to the universality class of the two-dimensional random transverse-field Ising model.Comment: 13 pages, 12 eps figures, final version as publishe

Using body mapping as part of the risk assessment process - a case study

This paper reports on a study undertaken to identify levels of MSD in relation to methods of waste collection. The need to quantify and eliminate ill health arising out of work is vital to reduce workplace absence leading to debate on associated relationships between the methods of waste collection and musculoskeletal disorders (MSDs). Body mapping is a participatory research tool that has been successfully used to investigate workplace ill health problems. Participatory body mapping exercises were carried out using staff at a UK District Council 2 years before and after the move from boxes and baskets to a wheeled bin recycling service. The study introduces the concept of Average Pain Count (APC). The data, supports previous studies showing wheeled bin based services (APC 2.07 & 2.80) are associated with less MSD outcomes than services including boxes, baskets and sacks (APC 4.02).The surveys provided compelling evidence to suggest that there are associations between age and self-reported pain although there appeared to be no patterns with regards length of service. These findings should help Local Authorities better understand critical factors regarding waste collection strategies and self-reported pain. There are recommendations regarding the use of body mapping and for industry practice

Does ursodeoxycholic acid change the proliferation of the colorectal mucosa? A randomized, placebo-controlled study

Background: In animal models ursodeoxycholic acid (UDCA) showed a chemoprotective effect against colon cancer. To explain this, a reduced proliferation of the colorectal mucosal proliferation was suggested. We, therefore, examined the influence of UDCA on the proliferation of normal colorectal mucosa in humans. Methods: Following endoscopic polypectomy, 20 patients with colorectal adenomas were randomized to receive either UDCA (750 mg/day, n = 10, group A) or placebo (n = 10, group B) for 6 months in a double-blinded way. Colorectal biopsies were sampled before and at the end of the medication by total colonoscopy. Colorectal mucosal proliferation was measured by FACScan analysis of propidium iodine labeling. Serum was sampled, and serum bile acids were analyzed by gas chromatography. Results: The proliferation rates at the end of the study were similar in both groups (median 15.4%; range 12.0-20.9 in group A; median 16.0%, 14.0-20.2 in group B, p = 0.41). Serum lithocholic acid levels at the end of the study were significantly higher in group A (1.3 mumol/l, 0.9-1.8) than in group B (0.7 mumol/l, 0-1.7, p < 0.02), whereas serum deoxycholic acid levels were similar in both groups. Conclusions: In this study, UDCA treatment for 6 months does not seem to induce changes in the proliferative behavior of the colorectal mucosa in patients with adenomas. It seems likely that a putative chemopreventive effect of UDCA in humans is not exerted by a reduction of the colorectal proliferation. Copyright (C) 2003 S. Karger AG, Basel

Ac hopping conduction at extreme disorder takes place on the percolating cluster

Simulations of the random barrier model show that ac currents at extreme disorder are carried almost entirely by the percolating cluster slightly above threshold; thus contradicting traditional theories contributions from isolated low-activation-energy clusters are negligible. The effective medium approximation in conjunction with the Alexander-Orbach conjecture leads to an excellent analytical fit to the universal ac conductivity with no nontrivial fitting parameters