4,690 research outputs found
Terrestrial Planet Formation I. The Transition from Oligarchic Growth to Chaotic Growth
We use a hybrid, multiannulus, n-body-coagulation code to investigate the
growth of km-sized planetesimals at 0.4-2 AU around a solar-type star. After a
short runaway growth phase, protoplanets with masses of roughly 10^26 g and
larger form throughout the grid. When (i) the mass in these `oligarchs' is
roughly comparable to the mass in planetesimals and (ii) the surface density in
oligarchs exceeds 2-3 g/sq cm at 1 AU, strong dynamical interactions among
oligarchs produce a high merger rate which leads to the formation of several
terrestrial planets. In disks with lower surface density, milder interactions
produce several lower mass planets. In all disks, the planet formation
timescale is roughly 10-100 Myr, similar to estimates derived from the
cratering record and radiometric data.Comment: Astronomical Journal, accepted; 22 pages + 15 figures in ps format;
eps figures at http://cfa-www.harvard.edu/~kenyon/dl/ revised version
clarifies evolution and justifies choice of promotion masse
Risk factors for sporadic human infection with shiga toxin-producing Escherichia coli in South Australia
This paper reports the findings from a preliminary study seeking to identify risk factors for sporadic human infection with shiga toxin-producing Escherichia coli (STEC) in South Australia. This phase of the study, conducted between February and September 2002, aimed to make recommendations regarding study methodology, and provided an opportunity to identify any potential risk factors for STEC infections in South Australia. The study design was a prospective age-matched case control study. A case was defined as a person with macroscopic or microscopic evidence of blood in a faecal specimen, and in which a gene associated with the production of shiga toxin (stx 1 or 2) was identified. Two community controls per case were randomly selected from the Social Environmental Risk Context Information System database. Eleven cases and 22 controls were enrolled in the pilot phase of the case control study. Cases were more likely than controls to have eaten berries, including strawberries, blueberries, and blackberries, in the 10 days preceding illness (Mantel Haenszel matched OR 11; 95 per cent CI 1.26-96.12). No other exposures were significantly associated with illness. Due to the small number of study participants, the power of the study was insufficient to expect any significant results. National participation will be vital to obtain sufficient cases in a realistic time, however this would necessitate more consistent ascertainment and reporting of STEC disease between the states and territories
Dates of birth and seasonal changes in well-being among 4904 subjects completing the seasonal pattern assessment questionnaire
Background: Abnormal distributions of birthdates, suggesting intrauterine aetiological factors, have been found in several psychiatric disorders, including one study of out-patients with Seasonal Affective Disorder (S.A.D.). We investigated birthdate distribution in relation to seasonal changes in well-being among a cohort who had completed the Seasonal Pattern Assessment Questionnaire (SPAQ). Method: A sample of 4904 subjects, aged 16 to 64, completed the SPAQ. 476 were cases of S.A.D. on the SPAQ and 580 were cases of sub-syndromal S.A.D. (S-S.A.D.). 92 were interview confirmed cases of S.A.D. Months and dates of birth were compared between S.A.D. cases and all others, between S.A.D. and S-S.A.D. cases combined and all others, and between interview confirmed cases and all others. Seasonality, as measured through seasonal fluctuations in well-being on the Global Seasonality Scores (GSS) of the SPAQ, was compared for all subjects by month and season of birth. Results: There was no evidence of an atypical pattern of birthdates for subjects fulfilling criteria for S.A.D., for the combined S.A.D. / S-S.A.D. group or for interview confirmed cases. There was also no relationship between seasonality on the GSS and month or season of birth. Limitations: Diagnoses of S.A.D. made by SPAQ criteria are likely to be overinclusive. Conclusion: Our findings differ from studies of patients with more severe mood disorders, including psychiatric out-patients with S.A.D. The lack of association between seasonality and birthdates in our study adds credence to the view that the aetiology of S.A.D. relates to separable factors predisposing to affective disorders and to seasonality
Stochastic Gradient Annealed Importance Sampling for Efficient Online Marginal Likelihood Estimation
We consider estimating the marginal likelihood in settings with independent
and identically distributed (i.i.d.) data. We propose estimating the predictive
distributions in a sequential factorization of the marginal likelihood in such
settings by using stochastic gradient Markov Chain Monte Carlo techniques. This
approach is far more efficient than traditional marginal likelihood estimation
techniques such as nested sampling and annealed importance sampling due to its
use of mini-batches to approximate the likelihood. Stability of the estimates
is provided by an adaptive annealing schedule. The resulting stochastic
gradient annealed importance sampling (SGAIS) technique, which is the key
contribution of our paper, enables us to estimate the marginal likelihood of a
number of models considerably faster than traditional approaches, with no
noticeable loss of accuracy. An important benefit of our approach is that the
marginal likelihood is calculated in an online fashion as data becomes
available, allowing the estimates to be used for applications such as online
weighted model combination
Evaluating the climate effects of mid-1800s deforestation in New England, USA, using a Weather, Research, and Forecasting (WRF) Model Multi-Physics Ensemble
The New England region of the northeastern United States has a land use history characterized by forest clearing for agriculture and other uses during European colonization and subsequent reforestation following widespread farm abandonment. Despite these broad changes, the potential influence on local and regional climate has received relatively little attention. This study investigated wintertime (December through March) climate impacts of reforestation in New England using a high-resolution (4 km) multiphysics ensemble of the Weather Research and Forecasting Model. In general, the conversion from mid-1800s cropland/grassland to forest led to warming, but results were sensitive to physics parameterizations. The 2-m maximum temperature (T2max) was most sensitive to choice of land surface model, 2-m minimum temperature (T2min) was sensitive to radiation scheme, and all ensemble members simulated precipitation poorly. Reforestation experiments suggest that conversion of mid-1800s cropland/grassland to present-day forest warmed T2max +0.5 to +3 K, with weaker warming during a warm, dry winter compared to a cold, snowy winter. Warmer T2max over forests was primarily the result of increased absorbed shortwave radiation and increased sensible heat flux compared to cropland/grassland. At night, T2min warmed +0.2 to +1.5 K where deciduous broadleaf forest replaced cropland/grassland, a result of decreased ground heat flux. By contrast, T2min of evergreen needleleaf forest cooled â0.5 to â2.1 K, primarily owing to increased ground heat flux and decreased sensible heat flux
FIT-MART: Quantum Magnetism with a Gentle Learning Curve
We present a new open-source software package, FIT-MART, that allows
non-experts to quickly get started simulating quantum magnetism. FIT-MART can
be downloaded as a platform-idependent executable Java (JAR) file. It allows
the user to define (Heisenberg) Hamiltonians by electronically drawing pictures
that represent quantum spins and operators. Sliders are automatically generated
to control the values of the parameters in the model, and when the values
change, several plots are updated in real time to display both the resulting
energy spectra and the equilibruim magnetic properties. Several experimental
data sets for real magnetic molecules are included in FIT-MART to allow easy
comparison between simulated and experimental data, and FIT-MART users can also
import their own data for analysis and compare the goodness of fit for
different models
The Development of a Detailed Abundance Analysis Method Intended for the Integrated Light Spectra of Extragalactic Globular Clusters.
Globularâ© clustersâ© areâ© stellarâ© systemsâ© thatâ© possessâ© anâ© astrophysicallyâ© rareâ© combinationâ© ofâ© theoreticalâ© andâ© observationalâ© simplicity,â© whichâ© makeâ© themâ© idealâ© diagnosticâ© tracers â©ofâ© astrophysicalâ© processes â©in â©bothâ© spaceâ© andâ© time.â©â© Capitalizing â©onâ© thisâ© simplicity,â© thisâ© dissertationâ© developsâ© andâ© demonstratesâ© aâ© detailedâ© abundanceâ© analysis â©methodâ© that â©isâ© capable â©ofâ© computing â©allâ© observableâ© lineâ© abundancesâ© (i.e. â©Feâ
peakâ© elements,â© alphaâelements,â© neutronâcaptureâ© elements,â© andâ© lightâelements) â©fromâ© theâ© integratedâ© lightâ© spectraâ© ofâ© extragalacticâ© globularâ© clustersâ© (GCs).â© â© Theâ© premiseâ© behindâ© theâ© methodâ© isâ© thatâ© theâ© preciseâ© andâ© accurateâ© techniquesâ© usedâ© forâ© singleâ© starâ© abundanceâ© analysisâ© canâ© beâ© combinedâ© withâ© theoreticalâ© simpleâ© stellarâ© populationâ© (SSP)â© modelsâ© toâ© synthesizeâ© lightâweightedâ© absorptionâ© lineâ© equivalentâ© widthsâ© (EWs).â© Byâ© iterating â©onâ© theâ© assumedâ© abundanceâ© forâ© aâ© line â©until â©its â©synthesized â©EWâ© equalsâ© itsâ© observedâ© EWâ© allowsâ© itsâ© lineâ© abundanceâ© toâ© beâ© determined.â© â© Theâ©
developmentâ©â© and demonstration ofâ© thisâ© methodâ© isâ© carriedâ© outâ© usingâ© aâ© trainingâ© setâ© ofâ© sevenâ© Milkyâ© Wayâ© GCsâ© (NGCâ©104,â© NGCâ©362,â© NGCâ©2808,â© NGCâ©6093,â© NGCâ©6388,â© NGCâ©6397,â© NGCâ©6752),â© whichâ© wereâ© observedâ© usingâ© aâ© spectrographâ© scanningâ© techniqueâ©
thatâ© producesâ© integratedâ© lightâ© spectraâ© thatâ© mimicâ© extragalacticâ© GCâ© spectra.â© â© Theâ© roleâ© ofâ© theâ© trainingâ© setâ© isâ© twoâ© fold.â© â© First,â© becauseâ© theâ© trainingâ© setâ© clustersâ© areâ© spatiallyâ© resolved,â© theirâ© stellar â©populationsâ© areâ© knownâ© aâ© priori â©inâ© theâ© formâ© of â©colorâmagnitudeâ© diagrams.â© â© Theâ© useâ© ofâ© theseâ© knownâ© stellarâ© populationsâ© inâ© theâ© analysisâ© methodâ© serveâ© toâ© initiallyâ© testâ© theâ© feasibilityâ© ofâ© theâ© methodâ© withoutâ© encounteringâ© anyâ© ofâ© theâ©
potential â©complicationsâ© that â©mayâ© stemâ© fromâ© usingâ© theoreticalâ© SSPs.â©â© Second,â© becauseâ© theâ© clustersâ© areâ© spatiallyâ© resolved,â© theirâ© stellarâ© abundancesâ© areâ© knownâ© aâ© priori fromâ© singleâ© starâ© abundanceâ© analysis.â© Theseâ© stellarâ© abundancesâ© criticallyâ© serveâ© asâ© fiducialâ© abundancesâ© againstâ© whichâ© theâ© dissertation'sâ© abundanceâ© resultsâ© areâ© tested.â© â© Theâ©
majorâ© conclusionâ© fromâ© thisâ© dissertationâ© isâ© thatâ© itsâ© abundanceâ© analysisâ© methodâ© usingâ© theoreticalâ© SSPsâ© isâ© capableâ© ofâ© derivingâ© theâ© detailedâ© abundancesâ© ofâ© extragalacticâ© GCsâ© withâ© anâ© accuracyâ© andâ© precisionâ© thatâ© areâ© competitiveâ© withâ© standardâ© stellarâ© abundance â©analysis. â©â©â©The â©method â©producesâ© abundances â©thatâ© areâ© onâ© averageâ© onlyâ©â© <â© 0.1â© dex largerâ© thanâ© theâ© abundancesâ© fromâ© stellarâ© analysis,â© andâ© theirâ© statisticalâ© uncertaintiesâ© are â©onâ© averageâ© ~â©0.2â© dex.â©Ph.D.Astronomy and AstrophysicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/64633/1/sacamero_1.pd
Winter Harbor Dredge Channel Data Report
Winter Harbor is a tidal creek that flows between a sandy barrier system and an eroding marsh shoreline. It is an important waterway that provides access to the Chesapeake Bay from the Winter Harbor watershed. In the past, Winter Harbor Inlet was the only hydraulic connection from the Winter Harbor watershed and Chesapeake Bay. The two open water areas of Winter Harbor were separated by marsh channels that hydraulically connected to the mouth at the present-day Winter Harbor Inlet. The federally-defined channel at Winter Harbor was authorized by Congress in 1950. It was authorized as a 12 feet (ft) deep, 100 ft wide channel extending to the 12-ft contour in Chesapeake Bay into Winter Harbor to a point just east of the public landing, a distance of about 7,600 ft. A mooring and turning basin were constructed 12 ft deep and 400 feet2 with a flared entranced 300 ft long. A traffic survey in 1982 found that the 12 ft depth was not justified and a 6 ft deep channel was maintained. (...
Cedarbush Creek Dredge Channel Data Report
Cedarbush Creek is located in Gloucester County, Virginia. It is a long, but narrow creek that empties into the York River. The mouth is a wide embayment, but farther north, the creek narrows to about 400 feet wide and extends for about 1.5 miles to its marshy headwaters. Cedarbush Creek has never been dredged, but due to shoaling within the creek, it needs dredging to accommodate vessel traffic. Oliverâs Landing, located near the mouth of Cedarbush Creek, is a working waterfront that supports commercial and recreational boaters in Gloucester. (...
Differential effects of food availability and nest predation risk on avian reproductive strategies
Spatial and temporal variation in resource abundance and predation risk can favor the evolution of phenotypic plasticity as a means of tracking changing environments. However, because food abundance and predation risk often covary in nature, few studies have separated their effects or tested whether different phenotypic traits respond to the same sources of environmental variation. We investigated patterns of parental investment and behavior over a 7-year period in 2 island populations of orange-crowned warblers (Oreothlypis celata) that showed little genetic divergence but experienced dramatic temporal variation in rainfall and spatial variation in nest predation risk. The amount of rainfall in each year was correlated with food abundance, and birds on both islands initiated breeding earlier and laid larger clutches in wetter years. In contrast, the rate at which parents visited their nests was not affected by rainfall but was negatively correlated with nest predation risk both within and between islands. Our results suggest that although the effects of food availability and nest predation have been viewed as mutually exclusive drivers of entire suites of life-history and behavioral traits, these traits can differ in their sensitivity to resource abundance or mortality risk, and traits that are often correlated can be decoupled under appropriate environmental conditions.Fil: Sofaer, Helen R.. State University Of Colorado-fort Collins. Dept.of Biology; Estados UnidosFil: Sillett, T. Scott. No especifĂca;Fil: Peluc, Susana Ines. Universidad Nacional de CĂłrdoba. Facultad de Ciencias Exactas, FĂsicas y Naturales. Centro de ZoologĂa Aplicada; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - CĂłrdoba; ArgentinaFil: Morrison, Scott A.. No especifĂca;Fil: Ghalambor, Cameron K.. State University Of Colorado-fort Collins. Dept.of Biology; Estados Unido
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