Molecular Beams

Contains research objectives, summary of research and reports on three research projects.Joint Services Electronics Programs (U. S. Army, U.S. Navy, and U. S. Air Force) under Contract DA 28-043-AMC-02536(E)Sloan Fund for Basic Research (M. I. T. Grant 249

SAM: A Tool for Measurement of Moderate to Vigorous Physical Activity (MVPA) in School Physical Education

Int J Exerc Sci 5(2) : 127-135, 2012. Observational methods have been a primary methodology used by physical educators for assessing teacher and student behaviors in school physical education (PE) classes for over 30 years. Observational instruments traditionally used in PE are economical, but are time intensive and complicated. Recently national PE recommendations have been promoted to encourage practitioners to achieve ≥ 50% of PE class in moderate to vigorous physical activity (MVPA). The purpose of this preliminary study was to develop, validate, and test the reliability of the Simple Activity Measurement (SAM) instrument for assessing MVPA during school PE classes. Students (N=36, representing grades 3-10) from a convenient sample of schools in San Antonio, TX were randomly selected to wear SUUNTOTM heart rate (HR) monitors during PE classes as an MVPA intensity measure, and the SAM instrument was used to observe 6 classes (N=281 students) for MVPA each minute using the SAM 0-10 scale. The SAM instrument was found to be a significant predictor for HR (r=0.555, r2=0.308, p\u3c0.05) using linear regression, and the intra class correlation coefficient to test reliability was found to be R=0.803, p\u3c0.05. Students averaged 88.5 % of class time spent in MVPA at the elementary level and only 36.5 % of class time spent in MVPA at the high school level. The results of this preliminary study indicate that the SAM has promise to provide school PE evaluators with an effective economical observation tool to document minutes of student MVPA in PE classes, and to promote accountability with national MVPA recommendations

The Ellipticity and Orientation of Clusters of Galaxies from N-Body Experiments

In this study we use simulations of 128$^3$ particles to study the ellipticity and orientation of clusters of galaxies in N-body simulations of differing power-law initial spectra (P(k) \propto k^n ,n = +1, 0, -1, -2$), and density parameters ($\Omega_0 = 0.2$to 1.0). Furthermore, unlike most theoretical studies we mimic most observers by removing all particles which lie at distances greater than 2 1/h Mpc from the cluster center of mass. We computed the axial ratio and the principal axes using the inertia tensor of each cluster. The mean ellipticity of clusters increases strongly with increasing$n$. We also find that clusters tend to become more spherical at smaller radii. We compared the orientation of a cluster to the orientation of neighboring clusters as a function of distance (correlation). In addition, we considered whether a cluster's major axis tends to lie along the line connecting it to a neighboring cluster, as a function of distance (alignment). Both alignments and correlations were computed in three dimensions and in projection to mimic observational surveys. Our results show that significant alignments exist for all spectra at small separations ($D < 15 h^{-1}$Mpc) but drops off at larger distance in a strongly$n-$dependent way.Comment: 22 pages, requires aaspp4.sty, flushrt.sty, and epsf.sty Revised manuscript, accepted for publication in Ap

Molecular Beams

Contains research objectives and reports on two research projects.Joint Services Electronics Programs (U. S. Army, U. S. Navy, and U. S. Air Force) under Contract DA 28-043-AMC-02536(E)Sloan Fund for Basic Research (M. I. T. Grant 249

Molecular Beams

Contains research objectives and reports on one research project.Joint Services Electronics Programs (U. S. Army, U.S. Navy, and U.S. Air Force) under Contract DA 28-043-AMC-02536(E)Sloan Fund for Basic Research (M.I.T. Grant 99

An examination of the relationship between hotspots and recombination associated with chromosome 21 nondisjunction

Trisomy 21, resulting in Down Syndrome (DS), is the most common autosomal trisomy among live-born infants and is caused mainly by nondisjunction of chromosome 21 within oocytes. Risk factors for nondisjunction depend on the parental origin and type of meiotic error. For errors in the oocyte, increased maternal age and altered patterns of recombination are highly associated with nondisjunction. Studies of normal meiotic events in humans have shown that recombination clusters in regions referred to as hotspots. In addition, GC content, CpG fraction, Poly(A)/Poly(T) fraction and gene density have been found to be significant predictors of the placement of sex-averaged recombination in the human genome. These observations led us to ask whether the altered patterns of recombination associated with maternal nondisjunction of chromosome 21 could be explained by differences in the relationship between recombination placement and recombination-related genomic features (i.e., GC content, CpG fraction, Poly(A)/Poly(T) fraction or gene density) on 21q or differential hot-spot usage along the nondisjoined chromosome 21. We found several significant associations between our genomic features of interest and recombination, interestingly, these results were not consistent among recombination types (single and double proximal or distal events). We also found statistically significant relationships between the frequency of hotspots and the distribution of recombination along nondisjoined chromosomes. Collectively, these findings suggest that factors that affect the accessibility of a specific chromosome region to recombination may be altered in at least a proportion of oocytes with MI and MII errors

The Race Between Stars and Quasars in Reionizing Cosmic Hydrogen

The cosmological background of ionizing radiation has been dominated by quasars once the Universe aged by ~2 billion years. At earlier times (redshifts z>3), the observed abundance of bright quasars declined sharply, implying that cosmic hydrogen was reionized by stars instead. Here, we explain the physical origin of the transition between the dominance of stars and quasars as a generic feature of structure formation in the concordance LCDM cosmology. At early times, the fraction of baryons in galaxies grows faster than the maximum (Eddington-limited) growth rate possible for quasars. As a result, quasars were not able to catch up with the rapid early growth of stellar mass in their host galaxies.Comment: 5 pages, 1 figure, Accepted for publication in JCA