382 research outputs found
Faint, moving objects in the Hubble Deep Field: components of the dark halo?
The deepest optical image of the sky, the Hubble Deep Field (HDF), obtained
with the Hubble Space Telescope (HST) in December 1995, has been compared to a
similar image taken in December 1997. Two very faint, blue, isolated and
unresolved objects are found to display a substantial apparent proper motion,
23+/-5 mas/yr and 26+/-5 mas/yr; a further three objects at the detection limit
of the second epoch observations may also be moving. Galactic structure models
predict a general absence of stars in the color-magnitude range in which these
objects are found. However, these observations are consistent with
recently-developed models of old white dwarfs with hydrogen atmospheres, whose
color, contrary to previous expectations, has been shown to be blue. If these
apparently moving objects are indeed old white dwarfs with hydrogen atmospheres
and masses near 0.5 M_Sun, they have ages of approximately 12 Gyr, and a local
mass density that is sufficient, within the large uncertainties arising from
the small size of the sample, to account for the entire missing Galactic
dynamical mass.Comment: 6 pages, using emulateapj, including 2 colour figures, accepted for
publication in ApJ Letter
An epidemiologic proïŹle of pediatric concussions: Identifying urban and rural differences
BACKGROUND: The objective of this study was to describe the epidemiology of concussions presenting to the emergency department (ED).
METHODS: A retrospective cohort of concussions for pediatric (age G 18 years) patients treated in the ED of a regional pediatric Level 1 trauma center from 2006 to 2011 was examined. Descriptive and geographic analyses were completed, with comparisons by age groups and residence (urban/rural).
RESULTS: There were a total of 2,112 treated pediatric concussions. Two thirds of the concussions occurred in males (67%), with a median age of 13 years (interquartile range [IQR], 6). Nearly half of the pediatric concussions were sports related (48%); 36% of these concussions were from hockey. Significant differences were found in the distribution of the mechanism of injury across age groups (p G 0.001). Falls were most prevalent among young children, and sports concussions, for children 10 years and older. Two fifths of concussions occurred during winter months. Discharge disposition significantly differed by age ( p G 0.001), with home discharge increasing with age up to 14 years. There were a total of 387 rural (19%) and 1,687 urban (81%) concussed patients, for a mean ED concussion visit rate of 2.2 per 1,000 and 3.5 per 1,000, respectively. Rural patients were older (14 [IQR, 6] vs. 13 [IQR, 6], p = 0.019] and sustained 2.5 times more concussions from a motor vehicle crash compared with urban youth patients ( p G 0.001).
CONCLUSION: Males in early adolescence are at highest risk for concussion, particularly from sport-related activities. Urban and rural children have differences in their etiology and severity of concussions. Concussions are predictable, and their prevention should be targeted based on epidemiologic and environmental data
Solid-phase microextraction/gas chromatographyâmass spectrometry method optimization for characterization of surface adsorption forces of nanoparticles
A complete characterization of the different physical chemical properties of nanoparticles (NPs) is necessary for the evaluation of their impact on health and environment. Among these properties, the surface characterization of the nanomaterial is the least developed and in many cases limited to the measurement of surface composition and Zeta potential. The biological surface adsorption index approach (BSAI) for characterization of surface adsorption properties of nanoparticles (NPs) has been recently introduced [1,2]. BSAI approach offers in principle the possibility to characterize the different interaction forces exerted between a nanomaterial surface and an organic âand by extension biological- entity. The present work develops further the BSAI approach of and optimizes a solid-phase microextraction â gas chromatography mass spectrometry (SPME/GC-MS) method, which is applied to measure the adsorption properties of different nanomaterials taking into account their specific surface area. This approach gives thus a better defined quantification of the adsorption properties on NPs.
To optimize the SPME/GC-MS method, we investigated the various aspects of the process including: kinetics of adsorption of probe compounds on SPME fiber, kinetic of adsorption of probe compounds on NPs surface, and optimization of NPs concentration. The optimized conditions were then tested on 33 probe compounds and on Au NPs (15 nm) and SiO2 NPs (50 nm).
The results demonstrated that this detailed optimization of the SPME/GC-MS method under various conditions is a critical factor and pre-requisite to the application of BSAI approach as a tool to characterize surface adsorption properties of NPs and therefore to any further conclusions on their potential impact on health.JRC.I.4-Nanobioscience
An evidence-based method for targeting an abusive head trauma prevention media campaign and its evaluation
BACKGROUND: A triple-dose abusive head trauma (AHT) prevention program (Period of PURPLE Crying) was implemented. The third dose consisted of an education media campaign. The study objectives were to describe the qualitative and spatial methods developed to target AHT prevention and to evaluate this campaign.
METHODS: A questionnaire on the level of importance of factors, rated on a 7-point Likert scale, was distributed to a panel of experts to determine the best advertising locations. Ranked factors were used to create weights for statistical modeling and mapping within a Geographic Information Systems to determine optimal ad locations. The media campaign was evaluated via a telephone survey of randomly selected households.
RESULTS: The survey found locations of new families, high population density, and high percentage of lone parents to be the most important factors for selecting billboard sites. Spatial analysis revealed six areas that ranked highest in our factors. Five billboards, four media posters, and six transit shelters were selected for our advertisements. A population-based telephone survey revealed that 23% of respondents knew the campaign. Nearly half (42%) heard the radio public service announcements, and 9% saw billboards.
CONCLUSION: Extending primary prevention efforts to the public helps to create a cultural change in the way inconsolable crying, the trigger for AHT, is viewed. With the use of ranked factors and Geographic Information Systems, geographic locations with high visibility and specific risk factors for AHTwere identified for targeting the campaign, facilitating the likelihood that our message was reaching the population in greatest need
Multimethod approach for the detection and characterisation of food-grade synthetic amorphous silica nanoparticles
AbstractSynthetic amorphous silica (SAS) has been used as food additive under the code E551 for decades and the agrifood sector is considered a main exposure vector for humans and environment. However, there is still a lack of detailed methodologies for the determination of SASâ particle size and concentration. This work presents the detection and characterization of NPs in eleven different food-grade SAS samples, following a reasoned and detailed sequential methodology. Dynamic Light Scattering (DLS), Multiangle Light Scattering (MALS), Asymmetric Flow-Field Flow Fractionation (AF4), Inductively Coupled Plasma Mass Spectrometry (ICPMS) and Transmission Electron Microscopy (TEM) were used. The suitability and limitations, information derived from each type of analytical technique and implications related to current EC Regulation 1169/2011 on the provision of food information to consumers are deeply discussed. In general the z-average, AF4 hydrodynamic diameters and root mean square (rms) radii measured were in good agreement. AF4-ICPMS coupling and pre channel calibration with silica NPs standards allowed the reliable detection of NPs below 100nm for ten of eleven samples (AF4 diameters between 20.6 and 39.8nm) and to quantify the mass concentration in seven different samples (at mgLâ1 concentration level). TEM characterisation included the determination of the minimum detectable size and subsequent measurement of the equivalent circle diameter (ECD) of primary particles and small aggregates, which were between 10.3 and 20.3nm. Because of the dynamic size application range is limited by the minimum detectable size, all the techniques in this work can be used only as positive tests
Kepler Mission Stellar and Instrument Noise Properties
Kepler Mission results are rapidly contributing to fundamentally new
discoveries in both the exoplanet and asteroseismology fields. The data
returned from Kepler are unique in terms of the number of stars observed,
precision of photometry for time series observations, and the temporal extent
of high duty cycle observations. As the first mission to provide extensive time
series measurements on thousands of stars over months to years at a level
hitherto possible only for the Sun, the results from Kepler will vastly
increase our knowledge of stellar variability for quiet solar-type stars. Here
we report on the stellar noise inferred on the timescale of a few hours of most
interest for detection of exoplanets via transits. By design the data from
moderately bright Kepler stars are expected to have roughly comparable levels
of noise intrinsic to the stars and arising from a combination of fundamental
limitations such as Poisson statistics and any instrument noise. The noise
levels attained by Kepler on-orbit exceed by some 50% the target levels for
solar-type, quiet stars. We provide a decomposition of observed noise for an
ensemble of 12th magnitude stars arising from fundamental terms (Poisson and
readout noise), added noise due to the instrument and that intrinsic to the
stars. The largest factor in the modestly higher than anticipated noise follows
from intrinsic stellar noise. We show that using stellar parameters from
galactic stellar synthesis models, and projections to stellar rotation,
activity and hence noise levels reproduces the primary intrinsic stellar noise
features.Comment: Accepted by ApJ; 26 pages, 20 figure
NICMOS Observations of the Transiting Hot Jupiter XO-1b
We refine the physical parameters of the transiting hot Jupiter planet XO-1b
and its stellar host XO-1 using HST NICMOS observations. XO-1b has a radius
Rp=1.21+/-0.03 RJup, and XO-1 has a radius Rs=0.94+/-0.02 RSun, where the
uncertainty in the mass of XO-1 dominates the uncertainty of Rp and Rs. There
are no significant differences in the XO-1 system properties between these
broad-band NIR observations and previous determinations based upon ground-based
optical observations. We measure two transit timings from these observations
with 9 s and 15 s precision. As a residual to a linear ephemeris model, there
is a 2.0 sigma timing difference between the two HST visits that are separated
by 3 transit events (11.8 days). These two transit timings and additional
timings from the literature are sufficient to rule out the presence of an Earth
mass planet orbiting in 2:1 mean motion resonance coplanar with XO-1b. We
identify and correct for poorly understood gain-like variations present in
NICMOS time series data. This correction reduces the effective noise in time
series photometry by a factor of two, for the case of XO-1.Comment: 13 pages, 8 figures, submitted to Ap
- âŠ