3,057 research outputs found
Photoelectric effect on dust grains across the L1721 cloud in the rho Ophiuchi molecular complex
We present ISO-LWS measurements of the main gas cooling lines, C+ 158 mum and
O 63 mum towards a moderate opacity molecular cloud (Av=3), L1721, illuminated
by the B2 star nu Sco (X = 5-10). These data are combined with an extinction
map and IRAS dust emission images to test our understanding of gas heating and
cooling in photo-dissociation regions (PDRs). This nearby PDR is spatially
resolved in the IRAS images; variations in the IRAS colors across the cloud
indicate an enhanced abundance of small dust grains within the PDR. A spatial
correlation between the gas cooling lines and the infrared emission from small
dust grains illustrates the dominant role of small dust grains in the gas
heating through the photoelectric effect. The photoelectric efficiency,
determined from the observations by ratioing the power radiated by gas and
small dust grains, is in the range 2 to 3% in close agreement with recent
theoretical estimates. The brightness profiles across the PDR in the C+ 158 mum
and O 63 mum lines are compared with model calculations where the density
profile is constrained by the extinction data and where the gas chemical and
thermal balances are solved at each position. We show that abundance variations
of small dust grains across the PDR must be considered to account for the LWS
observations.Comment: 10 pages, 15 figure
Alien Registration- Boulanger, Marie L. (Westbrook, Cumberland County)
https://digitalmaine.com/alien_docs/20566/thumbnail.jp
Diffuse infrared emission of the galaxy: Large scale properties
The Infrared Astronomy Satellite (IRAS) survey is used to study large scale properties and the origin of the diffuse emission of the Galaxy. A careful subtraction of the zodiacal light enables longitude profiles of the galactic emission at 12, 25, 60, and 100 microns to be presented
Small scale variations of abundances of transiently heated grains in molecular clouds
IRAS images of a variety of fragments in nearby molecular clouds show that the energy distribution of their IR emission varies widely from cloud to cloud and from place to place within a given cloud. These variations at small scale are all the more unexpected since the colors of the IR emission of cold material differ very little at large scale: the colors of the cirrus emission above the 3kpc molecular ring are the same as those of the cirrus emission in the solar neighborhood. To quantitatively study these variations, 12, 60, and 100 microns brightnesses were obtained of small areas centered at different positions within the set of clouds and complexes. The range of observed 12/100 micron colors is given for each cloud. Variations by an order of magnitude are found in most clouds. Variations by a factor of 2 to 3 are observed within a cloud on scales as small as 0.5pc, the resolution of this study. It is concluded that large variations of the abundances of small particles with respect to those of the large grains responsible for the 100 micron emission are required to explain the observed color variations and that these abundances have to vary by large factors; an order of magnitude from cloud to cloud
Costs of Inaction on Maternal Mortality: Qualitative Evidence of the Impacts of Maternal Deaths on Living Children in Tanzania.
Little is known about the interconnectedness of maternal deaths and impacts on children, beyond infants, or the mechanisms through which this interconnectedness is established. A study was conducted in rural Tanzania to provide qualitative insight regarding how maternal mortality affects index as well as other living children and to identify shared structural and social factors that foster high levels of maternal mortality and child vulnerabilities. Adult family members of women who died due to maternal causes (N = 45) and key stakeholders (N = 35) participated in in-depth interviews. Twelve focus group discussions were also conducted (N = 83) among community leaders in three rural regions of Tanzania. Findings highlight the widespread impact of a woman's death on her children's health, education, and economic status, and, by inference, the roles that women play within their families in rural Tanzanian communities. The full costs of failing to address preventable maternal mortality include intergenerational impacts on the nutritional status, health, and education of children, as well as the economic capacity of families. When setting priorities in a resource-poor, high maternal mortality country, such as Tanzania, the far-reaching effects that reducing maternal deaths can have on families and communities, as well as women's own lives, should be considered
Calibrated Dynamic Response Analysis of Stafford Dam
Stafford Dam, an approximately 79-ft high compacted earthfill founded on stream alluvium approximately 40 feet thick, was shaken by the 1989 Lorna Prieta Earthquake. Records of the earthquake motions were obtained from seismographs located at the dam crest and at the right abutment on rock. Two-dimensional dynamic finite element analyses were performed to calibrate a model of the dam using the recorded motions. Excellent agreement between the recorded and calculated response was obtained by appropriate adjustments to material parameters based on shear wave velocity measurements. Various deconvolution methods for obtaining input bedrock motions to calculate the dam response are discussed
Statistical properties of dust far-infrared emission
The description of the statistical properties of dust emission gives
important constraints on the physics of the interstellar medium but it is also
a useful way to estimate the contamination of diffuse interstellar emission in
the cases where it is considered a nuisance. The main goals of this analysis of
the power spectrum and non-Gaussian properties of 100 micron dust emission are
1) to estimate the power spectrum of interstellar matter density in three
dimensions, 2) to review and extend previous estimates of the cirrus noise due
to dust emission and 3) to produce simulated dust emission maps that reproduce
the observed statistical properties. The main results are the following. 1) The
cirrus noise level as a function of brightness has been previously
overestimated. It is found to be proportional to instead of ^1.5, where
is the local average brightness at 100 micron. This scaling is in
accordance with the fact that the brightness fluctuation level observed at a
given angular scale on the sky is the sum of fluctuations of increasing
amplitude with distance on the line of sight. 2) The spectral index of dust
emission at scales between 5 arcmin and 12.5 degrees is =-2.9 on average
but shows significant variations over the sky. Bright regions have
systematically steeper power spectra than diffuse regions. 3) The skewness and
kurtosis of brightness fluctuations is high, indicative of strong
non-Gaussianity. 4) Based on our characterization of the 100 micron power
spectrum we provide a prescription of the cirrus confusion noise as a function
of wavelength and scale. 5) Finally we present a method based on a modification
of Gaussian random fields to produce simulations of dust maps which reproduce
the power spectrum and non-Gaussian properties of interstellar dust emission.Comment: 13 pages, 13 figures. Accepted for publication in A&
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