4,419 research outputs found
The Overlooked Potential of Generalized Linear Models in Astronomy-III: Bayesian Negative Binomial Regression and Globular Cluster Populations
In this paper, the third in a series illustrating the power of generalized
linear models (GLMs) for the astronomical community, we elucidate the potential
of the class of GLMs which handles count data. The size of a galaxy's globular
cluster population is a prolonged puzzle in the astronomical
literature. It falls in the category of count data analysis, yet it is usually
modelled as if it were a continuous response variable. We have developed a
Bayesian negative binomial regression model to study the connection between
and the following galaxy properties: central black hole mass,
dynamical bulge mass, bulge velocity dispersion, and absolute visual magnitude.
The methodology introduced herein naturally accounts for heteroscedasticity,
intrinsic scatter, errors in measurements in both axes (either discrete or
continuous), and allows modelling the population of globular clusters on their
natural scale as a non-negative integer variable. Prediction intervals of 99%
around the trend for expected comfortably envelope the data,
notably including the Milky Way, which has hitherto been considered a
problematic outlier. Finally, we demonstrate how random intercept models can
incorporate information of each particular galaxy morphological type. Bayesian
variable selection methodology allows for automatically identifying galaxy
types with different productions of GCs, suggesting that on average S0 galaxies
have a GC population 35% smaller than other types with similar brightness.Comment: 14 pages, 12 figures. Accepted for publication in MNRA
The Overlooked Potential of Generalized Linear Models in Astronomy - I: Binomial Regression
Revealing hidden patterns in astronomical data is often the path to
fundamental scientific breakthroughs; meanwhile the complexity of scientific
inquiry increases as more subtle relationships are sought. Contemporary data
analysis problems often elude the capabilities of classical statistical
techniques, suggesting the use of cutting edge statistical methods. In this
light, astronomers have overlooked a whole family of statistical techniques for
exploratory data analysis and robust regression, the so-called Generalized
Linear Models (GLMs). In this paper -- the first in a series aimed at
illustrating the power of these methods in astronomical applications -- we
elucidate the potential of a particular class of GLMs for handling
binary/binomial data, the so-called logit and probit regression techniques,
from both a maximum likelihood and a Bayesian perspective. As a case in point,
we present the use of these GLMs to explore the conditions of star formation
activity and metal enrichment in primordial minihaloes from cosmological
hydro-simulations including detailed chemistry, gas physics, and stellar
feedback. We predict that for a dark mini-halo with metallicity , an increase of in the gas
molecular fraction, increases the probability of star formation occurrence by a
factor of 75%. Finally, we highlight the use of receiver operating
characteristic curves as a diagnostic for binary classifiers, and ultimately we
use these to demonstrate the competitive predictive performance of GLMs against
the popular technique of artificial neural networks.Comment: 20 pages, 10 figures, 3 tables, accepted for publication in Astronomy
and Computin
Genetic and biochemical analysis of the adenylyl cyclase-associated protein, cap, in Schizosaccharomyces pombe
We have identified, cloned, and studied a gene, cap, encoding a protein that is associated with adenylyl cyclase in the fission yeast Schizosaccharomyces pombe. This protein shares significant sequence homology with the adenylyl cyclase-associated CAP protein in the yeast Saccharomyces cerevisiae. CAP is a bifunctional protein; the N-terminal domain appears to be involved in cellular responsiveness to RAS, whereas loss of the C-terminal portion is associated with morphological and nutritional defects. S. pombe cap can suppress phenotypes associated with deletion of the C-terminal CAP domain in S. cerevisiae but does not suppress phenotypes associated with deletion of the N-terminal domain. Analysis of cap disruptants also mapped the function of cap to two domains. The functional loss of the C-terminal region of S. pombe cap results in abnormal cellular morphology, slow growth, and failure to grow at 37-degrees-C. Increases in mating and sporulation were observed when the entire gene was disrupted. Overproduction of both cap and adenylyl cyclase results in highly elongated large cells that are sterile and have measurably higher levels of adenylyl cyclase activity. Our results indicate that cap is required for the proper function of S. pombe adenylyl cyclase but that the C-terminal domain of cap has other functions that are shared with the C-terminal domain of S. cerevisiae CAP
Short small-polaron lifetime in the mixed-valence perovskite CsAuI from high-pressure pump-probe experiments
We study the ultrafast phonon response of mixed-valence perovskite
CsAuI using pump-probe spectroscopy under high-pressure in a
diamond anvil cell. We observed a remarkable softening and broadening of the Au
- I stretching phonon mode with both applied pressure and photoexcitation.
Using a double-pump scheme we measured a lifetime of the charge transfer
excitation into single valence Au of less than 4 ps, which is an
indication of the local character of the Au excitation. Furthermore, the
strong similarity between the pressure and fluence dependence of the phonon
softening shows that the inter-valence charge transfer plays an important role
in the structural transition.Comment: 4 pages, 4 figure
Factors related to adolescent drinking in Appalachia
Objectives: To examine the relationships among parental monitoring, perceptions of peer drinking, and adolescent alcohol consumption.
Methods: Tenth- and 12thgrade students (N=648) in a rural,
Appalachian county were surveyed.
Results: A binomial logistic regression revealed a composite of those who had perceptions that many
peers drank, low parental monitoring, and no biological male guardian in the home were 8.496 times more likely to have ever been drunk.
Other characteristics resulted in lower odds. Conclusions: Parental monitoring and perceptions of peer drinking were important predictors of drinking in this rural sample.
Prevention efforts in school and at home should address both variables
The String Calculation of QCD Wilson Loops on Arbitrary Surfaces
Compact string expressions are found for non-intersecting Wilson loops in
SU(N) Yang-Mills theory on any surface (orientable or nonorientable) as a
weighted sum over covers of the surface. All terms from the coupled chiral
sectors of the 1/N expansion of the Wilson loop expectation values are
included.Comment: 10 pages, LaTeX, no figure
Transfer of spectral weight across the gap of Sr2IrO4 induced by La doping
We study with Angle Resolved PhotoElectron Spectroscopy (ARPES) the evolution
of the electronic structure of Sr2IrO4, when holes or electrons are introduced,
through Rh or La substitutions. At low dopings, the added carriers occupy the
first available states, at bottom or top of the gap, revealing an anisotropic
gap of 0.7eV in good agreement with STM measurements. At further doping, we
observe a reduction of the gap and a transfer of spectral weight across the
gap, although the quasiparticle weight remains very small. We discuss the
origin of the in-gap spectral weight as a local distribution of gap values
Application of dissociation curve analysis to radiation hybrid panel marker scoring: generation of a map of river buffalo (B. bubalis) chromosome 20
<p>Abstract</p> <p>Background</p> <p>Fluorescence of dyes bound to double-stranded PCR products has been utilized extensively in various real-time quantitative PCR applications, including post-amplification dissociation curve analysis, or differentiation of amplicon length or sequence composition. Despite the current era of whole-genome sequencing, mapping tools such as radiation hybrid DNA panels remain useful aids for sequence assembly, focused resequencing efforts, and for building physical maps of species that have not yet been sequenced. For placement of specific, individual genes or markers on a map, low-throughput methods remain commonplace. Typically, PCR amplification of DNA from each panel cell line is followed by gel electrophoresis and scoring of each clone for the presence or absence of PCR product. To improve sensitivity and efficiency of radiation hybrid panel analysis in comparison to gel-based methods, we adapted fluorescence-based real-time PCR and dissociation curve analysis for use as a novel scoring method.</p> <p>Results</p> <p>As proof of principle for this dissociation curve method, we generated new maps of river buffalo (<it>Bubalus bubalis</it>) chromosome 20 by both dissociation curve analysis and conventional marker scoring. We also obtained sequence data to augment dissociation curve results. Few genes have been previously mapped to buffalo chromosome 20, and sequence detail is limited, so 65 markers were screened from the orthologous chromosome of domestic cattle. Thirty bovine markers (46%) were suitable as cross-species markers for dissociation curve analysis in the buffalo radiation hybrid panel under a standard protocol, compared to 25 markers suitable for conventional typing. Computational analysis placed 27 markers on a chromosome map generated by the new method, while the gel-based approach produced only 20 mapped markers. Among 19 markers common to both maps, the marker order on the map was maintained perfectly.</p> <p>Conclusion</p> <p>Dissociation curve analysis is reliable and efficient for radiation hybrid panel scoring, and is more sensitive and robust than conventional gel-based typing methods. Several markers could be scored only by the new method, and ambiguous scores were reduced. PCR-based dissociation curve analysis decreases both time and resources needed for construction of radiation hybrid panel marker maps and represents a significant improvement over gel-based methods in any species.</p
Possible scale invariant linear magnetoresistance in pyrochlore iridates Bi2Ir2O7
We report the observation of a linear magnetoresistance in single crystals and epitaxial thin films of the pyrochlore iridate Bi2Ir2O7. The linear magnetoresistance is positive and isotropic at low temperatures, without any sign of saturation up to 35 T. As temperature increases, the linear field dependence gradually evolves to a quadratic field dependence. The temperature and field dependence of magnetoresistance of Bi2Ir2O7 bears strikingly resemblance to the scale invariant magnetoresistance observed in the strange metal phase in high Tc cuprates. However, the residual resistivity of Bi2Ir2O7 is more than two orders of magnitude higher than the curpates. Our results suggest that the correlation between linear magnetoresistance and quantum fluctuations may exist beyond high temperature superconductors
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