34 research outputs found
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
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
Optima Nutrition: an allocative efficiency tool to reduce childhood stunting by better targeting of nutrition-related interventions
Published online: 20 March 2018Background: Child stunting due to chronic malnutrition is a major problem in low- and middle-income countries due, in part, to inadequate nutrition-related practices and insufficient access to services. Limited budgets for nutritional interventions mean that available resources must be targeted in the most cost-effective manner to have the greatest impact. Quantitative tools can help guide budget allocation decisions. Methods: The Optima approach is an established framework to conduct resource allocation optimization analyses. We applied this approach to develop a new tool, βOptima Nutritionβ, for conducting allocative efficiency analyses that address childhood stunting. At the core of the Optima approach is an epidemiological model for assessing the burden of disease; we use an adapted version of the Lives Saved Tool (LiST). Six nutritional interventions have been included in the first release of the tool: antenatal micronutrient supplementation, balanced energy-protein supplementation, exclusive breastfeeding promotion, promotion of improved infant and young child feeding (IYCF) practices, public provision of complementary foods, and vitamin A supplementation. To demonstrate the use of this tool, we applied it to evaluate the optimal allocation of resources in 7 districts in Bangladesh, using both publicly available data (such as through DHS) and data from a complementary costing study. Results: Optima Nutrition can be used to estimate how to target resources to improve nutrition outcomes. Specifically, for the Bangladesh example, despite only limited nutrition-related funding available (an estimated $0.75 per person in need per year), even without any extra resources, better targeting of investments in nutrition programming could increase the cumulative number of children living without stunting by 1.3 million (an extra 5%) by 2030 compared to the current resource allocation. To minimize stunting, priority interventions should include promotion of improved IYCF practices as well as vitamin A supplementation. Once these programs are adequately funded, the public provision of complementary foods should be funded as the next priority. Programmatic efforts should give greatest emphasis to the regions of Dhaka and Chittagong, which have the greatest number of stunted children. Conclusions: A resource optimization tool can provide important guidance for targeting nutrition investments to achieve greater impact.Ruth Pearson, Madhura Killedar, Janka Petravic, Jakub J. Kakietek, Nick Scott, Kelsey L. Grantham, Robyn M. Stuart, David J. Kedziora, Cliff C. Kerr, Jolene Skordis-Worrall, Meera Shekar and David P. Wilso
Chameleonic Generalized Brans--Dicke model and late-time acceleration
In this paper we consider Chameleonic Generalized Brans--Dicke Cosmology in
the framework of FRW universes. The bouncing solution and phantom crossing is
investigated for the model. Two independent cosmological tests: Cosmological
Redshift Drift (CRD) and distance modulus are applied to test the model with
the observation.Comment: 20 pages, 15 figures, to be published in Astrophys. Space Sci. (2011
Enhanced x-ray detection sensitivity in semiconducting polymer diodes containing metallic nanoparticles
Gravitational Lensing with Three-Dimensional Ray Tracing
High redshift sources suffer from magnification or demagnification due to
weak gravitational lensing by large scale structure. One consequence of this is
that the distance-redshift relation, in wide use for cosmological tests,
suffers lensing-induced scatter which can be quantified by the magnification
probability distribution. Predicting this distribution generally requires a
method for ray-tracing through cosmological N-body simulations. However,
standard methods tend to apply the multiple thin-lens approximation. In an
effort to quantify the accuracy of these methods, we develop an innovative code
that performs ray-tracing without the use of this approximation. The efficiency
and accuracy of this computationally challenging approach can be improved by
careful choices of numerical parameters; therefore, the results are analysed
for the behaviour of the ray-tracing code in the vicinity of Schwarzschild and
Navarro-Frenk-White lenses. Preliminary comparisons are drawn with the multiple
lens-plane ray-bundle method in the context of cosmological mass distributions
for a source redshift of .Comment: 17 pages, 10 figures, 0 tables; Accepted for publication in MNRA
Dysregulation of Gene Expression in a Lysosomal Storage Disease Varies between Brain Regions Implicating Unexpected Mechanisms of Neuropathology
The characteristic neurological feature of many neurogenetic diseases is intellectual disability. Although specific neuropathological features have been described, the mechanisms by which specific gene defects lead to cognitive impairment remain obscure. To gain insight into abnormal functions occurring secondary to a single gene defect, whole transcriptome analysis was used to identify molecular and cellular pathways that are dysregulated in the brain in a mouse model of a lysosomal storage disorder (LSD) (mucopolysaccharidosis [MPS] VII). We assayed multiple anatomical regions separately, in a large cohort of normal and diseased mice, which greatly increased the number of significant changes that could be detected compared to past studies in LSD models. We found that patterns of aberrant gene expression and involvement of multiple molecular and cellular systems varied significantly between brain regions. A number of changes revealed unexpected system and process alterations, such as up-regulation of the immune system with few inflammatory changes (a significant difference from the closely related MPS IIIb model), down-regulation of major oligodendrocyte genes even though white matter changes are not a feature histopathologically, and a plethora of developmental gene changes. The involvement of multiple neural systems indicates that the mechanisms of neuropathology in this type of disease are much broader than previously appreciated. In addition, the variation in gene dysregulation between brain regions indicates that different neuropathologic mechanisms may predominate within different regions of a diseased brain caused by a single gene mutation
Genome-wide association studies of cancer: current insights and future perspectives.
Genome-wide association studies (GWAS) provide an agnostic approach for investigating the genetic basis of complex diseases. In oncology, GWAS of nearly all common malignancies have been performed, and over 450 genetic variants associated with increased risks have been identified. As well as revealing novel pathways important in carcinogenesis, these studies have shown that common genetic variation contributes substantially to the heritable risk of many common cancers. The clinical application of GWAS is starting to provide opportunities for drug discovery and repositioning as well as for cancer prevention. However, deciphering the functional and biological basis of associations is challenging and is in part a barrier to fully unlocking the potential of GWAS
Relationship in fluoride adsorption on fish-bone charcoal
157-162<span style="font-size:11.0pt;line-height:115%;
font-family:" calibri","sans-serif";mso-ascii-theme-font:minor-latin;mso-fareast-font-family:="" "times="" new="" roman";mso-fareast-theme-font:minor-fareast;mso-hansi-theme-font:="" minor-latin;mso-bidi-font-family:arial;mso-ansi-language:en-us;mso-fareast-language:="" en-us;mso-bidi-language:ar-sa"="">Batch adsorption studies have been conducted to
determine the effects of some parameters such as contact time, initial solute
concentration and dose of adsorbent on the adsorption of fluoride on the
fish-bone charcoal. To simulate field conditions, the test fluoride solutions
of different concentrations are prepared by using the tap water. The percentage
fluoride removal is found to be function of the dose of adsorbent and time at a
given initial concentration. Empirical relationship has been attempted to
predict the percentage fluoride removal at any time for known values of dose of
adsorbent and initial solute concentration under observed test conditions.</span
Defluoridation and empirical models in column studies using fishbone charcoal
237-244<span style="font-size:11.0pt;mso-bidi-font-size:10.0pt;
line-height:115%;font-family:" calibri","sans-serif";mso-ascii-theme-font:minor-latin;="" mso-fareast-font-family:"times="" new="" roman";mso-fareast-theme-font:minor-fareast;="" mso-hansi-theme-font:minor-latin;mso-bidi-font-family:"times="" roman";="" mso-ansi-language:en-us;mso-fareast-language:en-us;mso-bidi-language:ar-sa"="">Column
bed adsorption studies have been carried out to study the fluoride removal on
fishbone charcoal, and to determine the effects of the various operating
variables. The useful (or effective) treated effluent volume (corresponding to
the desired breakthrough concentration of 1.0 mg/L of fluoride) is found to be
a function of the effluent flow rate, initial solute concentration and column
bed depth. The useful treated effluent volume decreased with an increase in the
flow rate and initial fluoride concentration, but it increased with the column
bed depth. Empirical relationships have been developed to predict the stated useful
treated effluent volume for the known values of flow rate, column bed depth and
initial fluoride concentration for the observed test conditions. The
relationships evolved manifest high correlation coefficients. The studies are
useful in small installations.</span