Modern Statistical Methods for GLAST Event Analysis

We describe a statistical reconstruction methodology for the GLAST LAT. The methodology incorporates in detail the statistics of the interactions of photons and charged particles with the tungsten layers in the LAT, and uses the scattering distributions to compute the full probability distribution over the energy and direction of the incident photons. It uses model selection methods to estimate the probabilities of the possible geometrical configurations of the particles produced in the detector, and numerical marginalization over the energy loss and scattering angles at each layer. Preliminary results show that it can improve on the tracker-only energy estimates for muons and electrons incident on the LAT.Comment: To appear in the proceedings of the First GLAST Symposium (held at Stanford University, 5-8 February 2007

Bayesian Research at the NASA Ames Research Center,Computational Sciences Division

NASA Ames Research Center is one of NASA s oldest centers, having started out as part of the National Advisory Committee on Aeronautics, (NACA). The site, about 40 miles south of San Francisco, still houses many wind tunnels and other aviation related departments. In recent years, with the growing realization that space exploration is heavily dependent on computing and data analysis, its focus has turned more towards Information Technology. The Computational Sciences Division has expanded rapidly as a result. In this article, I will give a brief overview of some of the past and present projects with a Bayesian content. Much more than is described here goes on with the Division. The web pages at http://ic.arc. nasa.gov give more information on these, and the other Division projects

Parameter and Structure Inference for Nonlinear Dynamical Systems

A great many systems can be modeled in the non-linear dynamical systems framework, as x = f(x) + xi(t), where f() is the potential function for the system, and xi is the excitation noise. Modeling the potential using a set of basis functions, we derive the posterior for the basis coefficients. A more challenging problem is to determine the set of basis functions that are required to model a particular system. We show that using the Bayesian Information Criteria (BIC) to rank models, and the beam search technique, that we can accurately determine the structure of simple non-linear dynamical system models, and the structure of the coupling between non-linear dynamical systems where the individual systems are known. This last case has important ecological applications

A Parameterization Invariant Approach to the Statistical Estimation of the CKM Phase α\alpha

In contrast to previous analyses, we demonstrate a Bayesian approach to the estimation of the CKM phase $\alpha$ that is invariant to parameterization. We also show that in addition to {\em computing} the marginal posterior in a Bayesian manner, the distribution must also be {\em interpreted} from a subjective Bayesian viewpoint. Doing so gives a very natural interpretation to the distribution. We also comment on the effect of removing information about $\mathcal{B}^{00}$.Comment: 14 pages, 3 figures, 1 table, minor revision; to appear in JHE

ISOGAL-DENIS detection of red giants with weak mass loss in the Galactic Bulge

The ISOGAL project is a survey of the stellar populations, structure, and recent star formation history of the inner disk and bulge of the Galaxy. ISOGAL combines 15 and 7micron ISOCAM observations with DENIS IJKs data to determine the nature of a source and the interstellar extinction. In this paper we report an ISOGAL study of a small field in the inner Galactic Bulge (l=0deg, b=1.0deg, area=0.035 sq. deg) as a prototype of the larger area ISOGAL survey of the inner Galaxy. The five wavelengths of ISOGAL+DENIS, together with the relatively low and constant extinction in front of this specific field, allow reliable determination of the nature of the sources. The primary scientific result of this paper is evidence that the most numerous class of ISOGAL 15micron sources are Red Giants in the Galactic bulge and central disk, with luminosities just above or close to the RGB tip and weak mass-loss rates. They form loose sequences in the magnitude-colour diagrams [15]/Ks-[15] and [15]/[7]-[15]. Their large excesses at 15micron with respect to 2micron and 7micron is due to circumstellar dust produced by mass-loss at low rates. These ISOGAL results are the first systematic evidence and study of dust emission at this early stage (''Intermediate'' AGB), before the onset of the large mass-loss phase. It is thus well established that efficient dust formation is already associated with such low mass-loss rates during this early phase.Comment: 15 pages, 9 figures, accepted for publication in Astronomy and Astrophysics Journa

Investigating and learning lessons from early experiences of implementing ePrescribing systems into NHS hospitals:a questionnaire study

Background: ePrescribing systems have significant potential to improve the safety and efficiency of healthcare, but they need to be carefully selected and implemented to maximise benefits. Implementations in English hospitals are in the early stages and there is a lack of standards guiding the procurement, functional specifications, and expected benefits. We sought to provide an updated overview of the current picture in relation to implementation of ePrescribing systems, explore existing strategies, and identify early lessons learned.Methods: a descriptive questionnaire-based study, which included closed and free text questions and involved both quantitative and qualitative analysis of the data generated.Results: we obtained responses from 85 of 108 NHS staff (78.7% response rate). At least 6% (n = 10) of the 168 English NHS Trusts have already implemented ePrescribing systems, 2% (n = 4) have no plans of implementing, and 34% (n = 55) are planning to implement with intended rapid implementation timelines driven by high expectations surrounding improved safety and efficiency of care. The majority are unclear as to which system to choose, but integration with existing systems and sophisticated decision support functionality are important decisive factors. Participants highlighted the need for increased guidance in relation to implementation strategy, system choice and standards, as well as the need for top-level management support to adequately resource the project. Although some early benefits were reported by hospitals that had already implemented, the hoped for benefits relating to improved efficiency and cost-savings remain elusive due to a lack of system maturity.Conclusions: whilst few have begun implementation, there is considerable interest in ePrescribing systems with ambitious timelines amongst those hospitals that are planning implementations. In order to ensure maximum chances of realising benefits, there is a need for increased guidance in relation to implementation strategy, system choice and standards, as well as increased financial resources to fund local activitie

Modeling Child-Based Theoretical Reading Constructs with Struggling Adult Readers

This study examined whether measurement constructs behind reading-related tests for struggling adult readers are similar to what is known about measurement constructs for children. The sample included 371 adults reading between the third- and fifth-grade levels, including 127 men and 153 English speakers of other languages. Using measures of skills and subskills, confirmatory factor analyses were conducted to test child-based theoretical measurement models of reading: an achievement model of reading skills, a core deficit model of reading subskills, and an integrated model containing achievement and deficit variables. Although the findings present the best measurement models, the contribution of this article is the description of the difficulties encountered when applying child-based assumptions to developing measurement models for struggling adult readers

Change in multimodal MRI markers predicts dementia risk in cerebral small vessel disease.

OBJECTIVE: To determine whether MRI markers, including diffusion tensor imaging (DTI), can predict cognitive decline and dementia in patients with cerebral small vessel disease (SVD). METHODS: In the prospective St George's Cognition and Neuroimaging in Stroke study, multimodal MRI was performed annually for 3 years and cognitive assessments annually for 5 years in a cohort of 99 patients with SVD, defined as symptomatic lacunar stroke and confluent white matter hyperintensities (WMH). Progression to dementia was determined in all patients. Progression of WMH, brain volume, lacunes, cerebral microbleeds, and a DTI measure (the normalized peak height of the mean diffusivity histogram distribution) as a marker of white matter microstructural damage were determined. RESULTS: Over 5 years of follow-up, 18 patients (18.2%) progressed to dementia. A significant change in all MRI markers, representing deterioration, was observed. The presence of new lacunes, and rate of increase in white matter microstructural damage on DTI, correlated with both decline in executive function and global functioning. Growth of WMH and deterioration of white matter microstructure on DTI predicted progression to dementia. A model including change in MRI variables together with their baseline values correctly classified progression to dementia with a C statistic of 0.85. CONCLUSIONS: This longitudinal prospective study provides evidence that change in MRI measures including DTI, over time durations during which cognitive change is not detectable, predicts cognitive decline and progression to dementia. It supports the use of MRI measures, including DTI, as useful surrogate biomarkers to monitor disease and assess therapeutic interventions

ISOGAL: A deep survey of the obscured inner Milky Way with ISO at 7 and 15 micron and with DENIS in the near-infrared

The ISOGAL project is an infrared survey of specific regions sampling the Galactic Plane selected to provide information on Galactic structure,stellar populations,stellar mass-loss and the recent star formation history of the inner disk and Bulge of the Galaxy. ISOGAL combines 7 and 15 micron ISOCAM observations - with a resolution of 6'' at worst - with DENIS IJKs data to determine the nature of the sources and theinterstellar extinction. We have observed about 16 square degrees with a sensitivity approaching 10-20mJy, detecting ~10^5 sources,mostly AGB stars,red giants and young stars. The main features of the ISOGAL survey and the observations are summarized in this paper,together with a brief discussion of data processing and quality. The primary ISOGAL products are described briefly (a full description is given in Schuller et al. 2003, astro-ph/0304309): viz. the images and theISOGAL-DENIS five-wavelength point source catalogue. The main scientific results already derived or in progress are summarized. These include astrometrically calibrated 7 and 15um images,determining structures of resolved sources; identification and properties of interstellar dark clouds; quantification of the infrared extinction law and source dereddening; analysis of red giant and (especially) AGB stellar populations in the central Bulge,determining luminosity,presence of circumstellar dust and mass--loss rate,and source classification,supplemented in some cases by ISO/CVF spectroscopy; detection of young stellar objects of diverse types,especially in the inner Bulge with information about the present and recent star formation rate; identification of foreground sources with mid-IR excess. These results are the subject of about 25 refereed papers published or in preparation.Comment: A&A in press. 19 pages,10 Ps figures; problems with figures fixe