Effects of thermal conduction in sonoluminescence

We show by numerical hydrodynamic calculations that there are two important effects of thermal conduction in sonoluminescence: (i) the bubble remains close to being isothermal during the expansion phase; and (ii) a cold, dense layer of air is formed at the bubble wall during the contraction phase. These conclusions are not sensitive to the particular equation of state used, although details of the dynamical evolution of the bubble are

Spurious regressions of stationary AR(p) processes with structural breaks

When a pair of independent series is highly persistent, there is a spurious regression bias in a regression between these series, closely related to the classic studies of Granger and Newbold (1974). Although this is well known to occur with independent I(1) processes, this paper provides theoretical and numerical evidence that the phenomenon of spurious regression also arises in regressions between stationary AR(p) processes with structural breaks, which occur at different points in time, in the means and the trends. The intuition behind this is that structural breaks can increase the persistence levels in the processes (e.g., Granger and Hyung (2004)), which then leads to spurious regressions. These phenomena occur for general distributions and serial dependence of the innovation terms

Operative mortality in resource-limited settings: the experience of Medecins Sans Frontieres in 13 countries.

OBJECTIVE: To determine operative mortality in surgical programs from resource-limited settings. DESIGN, SETTING, AND PARTICIPANTS: A retrospective cohort study of 17 surgical programs in 13 developing countries by 1 humanitarian organization, Médecins Sans Frontières, was performed between January 1, 2001, and December 31, 2008. Participants included patients undergoing surgical procedures. MAIN OUTCOME MEASURE: Operative mortality. Determinants of mortality were modeled using logistic regression. RESULTS: Between 2001 and 2008, 19,643 procedures were performed on 18,653 patients. Among these, 8329 procedures (42%) were emergent; 7933 (40%) were for obstetric-related pathology procedures and 2767 (14%) were trauma related. Operative mortality was 0.2% (31 deaths) and was associated with programs in conflict settings (adjusted odds ratio [AOR] = 4.6; P = .001), procedures performed under emergency conditions (AOR = 20.1; P = .004), abdominal surgical procedures (AOR = 3.4; P = .003), hysterectomy (AOR = 12.3; P = .001), and American Society of Anesthesiologists classifications of 3 to 5 (AOR = 20.2; P < .001). CONCLUSIONS: Surgical care can be provided safely in resource-limited settings with appropriate minimum standards and protocols. Studies on the burden of surgical disease in these populations are needed to improve service planning and delivery. Quality improvement programs are needed for the various stakeholders involved in surgical delivery in these settings

A Computational Approach to Estimating Nondisjunction Frequency in Saccharomyces cerevisiae.

Errors segregating homologous chromosomes during meiosis result in aneuploid gametes and are the largest contributing factor to birth defects and spontaneous abortions in humans. Saccharomyces cerevisiae has long served as a model organism for studying the gene network supporting normal chromosome segregation. Measuring homolog nondisjunction frequencies is laborious, and involves dissecting thousands of tetrads to detect missegregation of individually marked chromosomes. Here we describe a computational method (TetFit) to estimate the relative contributions of meiosis I nondisjunction and random-spore death to spore inviability in wild type and mutant strains. These values are based on finding the best-fit distribution of 4, 3, 2, 1, and 0 viable-spore tetrads to an observed distribution. Using TetFit, we found that meiosis I nondisjunction is an intrinsic component of spore inviability in wild-type strains. We show proof-of-principle that the calculated average meiosis I nondisjunction frequency determined by TetFit closely matches empirically determined values in mutant strains. Using these published data sets, TetFit uncovered two classes of mutants: Class A mutants skew toward increased nondisjunction death, and include those with known defects in establishing pairing, recombination, and/or synapsis of homologous chromosomes. Class B mutants skew toward random spore death, and include those with defects in sister-chromatid cohesion and centromere function. Epistasis analysis using TetFit is facilitated by the low numbers of tetrads (as few as 200) required to compare the contributions to spore death in different mutant backgrounds. TetFit analysis does not require any special strain construction, and can be applied to previously observed tetrad distributions

Test of the Skyrme Effective Field Theory Using Quenched Lattice QCD

The Skyrme effective field theory is tested by evaluating nucleon ground state matrix elements of the correlation functions for two flavor density operators and two pseudoscalar density operators in the Skyrme model and comparing them with results in quenched lattice QCD. The possiblility of using quenched lattice QCD to study higher-order terms in effective field theory is also discussed.Comment: 20 pages in TeX, 6 figures added using "figures", MIT-CTP-200