1,428 research outputs found
Compensating for Missing Data from Longitudinal Studies Using WinBUGS
Missing data is a common problem in survey based research. There are many packages that compensate for missing data but few can easily compensate for missing longitudinal data. WinBUGS compensates for missing data using multiple imputation, and is able to incorporate longitudinal structure using random effects. We demonstrate the superiority of longitudinal imputation over cross-sectional imputation using WinBUGS. We use example data from the Australian Longitudinal Study on Women's Health. We give a SAS macro that uses WinBUGS to analyze longitudinal models with missing covariate date, and demonstrate its use in a longitudinal study of terminal cancer patients and their carers.
Charting the TeV Milky Way: H.E.S.S. Galactic plane survey maps, catalog and source populations
Very-high-energy (VHE, E>100 GeV) gamma-rays provide a unique view of the
non-thermal universe, tracing the most violent and energetic phenomena at work
inside our Galaxy and beyond. The latest results of the H.E.S.S. Galactic Plane
Survey (HGPS) undertaken by the High Energy Stereoscopic System (H.E.S.S.), an
array of four imaging atmospheric Cherenkov telescopes located in Namibia, are
described here. The HGPS aims at the detection of cosmic accelerators with
environments suitable for the production of photons at the highest energies and
has led to the discovery of an unexpectedly large and diverse population of
over 60 sources of TeV gamma rays within its current range of l = 250 to 65
degrees in longitude and |b|<3.5 degrees in latitude. The data set of the HGPS
comprises 2800 hours of high-quality data, taken in the years 2004 to 2013. The
sensitivity for the detection of point-like sources, assuming a power-law
spectrum with a spectral index of 2.3 at a statistical significance of 5 sigma,
is now at the level of 2% Crab or better in the core HGPS region. The latest
maps of the inner Galaxy at TeV energies are shown alongside an introduction to
the first H.E.S.S. Galactic Plane Survey catalog. Finally, in addition to an
overview of the H.E.S.S. Galactic source population a few remarkable, recently
discovered sources will be highlighted.Comment: 8 pages, 6 figures, in Proceedings of the 48th Rencontres de Moriond
(2013), La Thuile (Italy
Supporting Intelligent and Trustworthy Maritime Path Planning Decisions
The risk of maritime collisions and groundings has dramatically increased in the past five years despite technological advancements such as GPS-based navigation tools and electronic charts which may add to, instead of reduce, workload. We propose that an automated path planning tool for littoral navigation can reduce workload and improve overall system efficiency,
particularly under time pressure. To this end, a Maritime Automated Path Planner (MAPP) was developed, incorporating information requirements developed from a cognitive task analysis, with special emphasis on designing for trust. Human-in-the-loop experimental results showed
that MAPP was successful in reducing the time required to generate an optimized path, as well as reducing path lengths. The results also showed that while users gave the tool high acceptance ratings, they rated the MAPP as average for trust, which we propose is the appropriate level of
trust for such a system.This work was sponsored by Rite Solutions Inc., Assett Inc., Mikel Inc., and the Office of Naval Research. We would also like to thank Northeast Maritime Institute, the MIT NROTC detachment, the crew of the USS New Hampshire, and the anonymous reviewers whose comments significantly improved the paper
No-vent fill pressurization tests using a cryogen simulant
The results are described of an experimental program which studied the performance of various no-vent fill techniques for tank-to-tank liquid transfer. The tests were performed using a cryogen simulant (Freon-114) and a test bed consisting of a multiple tank/plumbing network that enabled studies of a variety of different inlet flow and active mixing regimes. Several results and conclusions were drawn from the 26 transfer experiments comprising the program. Most notable was the significant improvement in fill performance (i.e., minimized fill time and maximized fill fraction) with increased agitation of the liquid surface. Another was the close correlation between measured condensation rates and those predicted by recent theories which express condensation as a function of turbulent eddy effects on the liquid surface. In most cases, test data exhibited strong agreement with an analytical model which accounts for tank heat transfer and thermodynamics in a 1 g environment
Possible observation of phase separation near a quantum phase transition in doubly connected ultrathin superconducting cylinders of aluminum
The kinetic energy of superconducting electrons in an ultrathin, doubly
connected superconducting cylinder, determined by the applied flux, increases
as the cylinder diameter decreases, leading to a destructive regime around
half-flux quanta and a superconductor to normal metal quantum phase transition
(QPT). Regular step-like features in resistance vs. temperature curves taken at
fixed flux values were observed near the QPT in ultrathin Al cylinders. It is
proposed that these features are most likely resulted from a phase separation
near the QPT in which normal regions nucleate in a homogeneous superconducting
cylinder.Comment: 4 pages, 4 figures, to appear in Phys. Rev. Let
Insular Celtic population structure and genomic footprints of migration
Previous studies of the genetic landscape of Ireland have suggested homogeneity, with population substructure undetectable using single-marker methods. Here we have harnessed the haplotype-based method fineSTRUCTURE in an Irish genome-wide SNP dataset, identifying 23 discrete genetic clusters which segregate with geographical provenance. Cluster diversity is pronounced in the west of Ireland but reduced in the east where older structure has been eroded by historical migrations. Accordingly, when populations from the neighbouring island of Britain are included, a west-east cline of Celtic-British ancestry is revealed along with a particularly striking correlation between haplotypes and geography across both islands. A strong relationship is revealed between subsets of Northern Irish and Scottish populations, where discordant genetic and geographic affinities reflect major migrations in recent centuries. Additionally, Irish genetic proximity of all Scottish samples likely reflects older strata of communication across the narrowest inter-island crossing. Using GLOBETROTTER we detected Irish admixture signals from Britain and Europe and estimated dates for events consistent with the historical migrations of the Norse-Vikings, the Anglo-Normans and the British Plantations. The influence of the former is greater than previously estimated from Y chromosome haplotypes. In all, we paint a new picture of the genetic landscape of Ireland, revealing structure which should be considered in the design of studies examining rare genetic variation and its association with traits
Metabolomic Evidence for a Field Effect in Histologically Normal and Metaplastic Tissues in Patients with Esophageal Adenocarcinoma
Patients with Barrett's esophagus (BO) are at increased risk of developing esophageal adenocarcinoma (EAC). Most Barrett's patients, however, do not develop EAC, and there is a need for markers that can identify those most at risk. This study aimed to see if a metabolic signature associated with the development of EAC existed. For this, tissue extracts from patients with EAC, BO, and normal esophagus were analyzed using 1H nuclear magnetic resonance. Where possible, adjacent histologically normal tissues were sampled in those with EAC and BO. The study included 46 patients with EAC, 7 patients with BO, and 68 controls who underwent endoscopy for dyspeptic symptoms with normal appearances. Within the cancer cohort, 9 patients had nonneoplastic Barrett's adjacent to the cancer suitable for biopsy. It was possible to distinguish between histologically normal, BO, and EAC tissue in EAC patients [area under the receiver operator curve (AUROC) 1.00, 0.86, and 0.91] and between histologically benign BO in the presence and absence of EAC (AUROC 0.79). In both these cases, sample numbers limited the power of the models. Comparison of histologically normal tissue proximal to EAC versus that from controls (AUROC 1.00) suggests a strong field effect which may develop prior to overt EAC and hence be useful for identifying patients at high risk of developing EAC. Excellent sensitivity and specificity were found for this model to distinguish histologically normal squamous esophageal mucosa in EAC patients and healthy controls, with 8 metabolites being very significantly altered. This may have potential diagnostic value if a molecular signature can detect tissue from which neoplasms subsequently arise
Factors associated with alcohol reduction in harmful and hazardous drinkers following alcohol brief intervention in Scotland: a qualitative enquiry
Background: Alcohol Brief Intervention (ABI) uses a motivational counselling approach to support individuals to
reduce excessive alcohol consumption. There is growing evidence on ABIâs use within various health care settings,
although how they work and which components enhance success is largely unknown. This paper reports on the
qualitative part of a mixed methods study. It explores enablers and barriers associated with alcohol reduction
following an ABI. It focuses on alcoholâs place within participantsâ lives and their personal perspectives on reducing
consumption. There are a number of randomised controlled trials in this field though few ABI studies have
addressed the experiences of hazardous/harmful drinkers. This study examines factors associated with alcohol
reduction in harmful/hazardous drinkers following ABI.
Methods: This qualitative study was underpinned by a realist evaluation approach and involved semistructured
interviews with ten harmful or hazardous alcohol drinkers. Participants (n = 10) were from the
intervention arm of a randomised controlled trial (n = 124). All had received ABI, a 20 min motivational
counselling interview, six months previously, and had reduced their alcohol consumption. Interviews were
recorded, transcribed verbatim and thematically analysed.
Results: Participants described their views on alcohol, itsâ place in their lives, their personal perspectives on
reducing their consumption and future aspirations.
Conclusions: The findings provide an insight into participantsâ views on alcohol, ABI, and the barriers and enablers
to change. Participants described a cost benefit analysis, with some conscious consideration of the advantages and
disadvantages of reducing intake or abstaining from alcohol. Findings suggest that, whilst hospital admission can act
as a catalyst, encouraging individuals to reflect on their alcohol consumption through ABI may consolidate this, turning
this reflective moment into action. Sustainability may be enhanced by the presence of a âsignificant otherâ who
encourages and experiences benefit. In addition having a purpose or structure with activities linked to employment
and/or social and leisure pursuits offers the potential to enhance and sustain reduced alcohol consumption.
Trial registration: Trial registration number TRN NCT00982306 September 22nd 200
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