130 research outputs found
Space Telescopes
Space telescopes have been a dominant force in astrophysics and astronomy over the last two decades. As Lyman Spitzer predicted in 1946, space telescopes have opened up much of the electromagnetic spectrum to astronomers, and provided the opportunity to exploit the optical performance of telescopes uncompromised by the turbulent atmosphere. This special section of Optical Engineering is devoted to space telescopes. It focuses on the design and implementation of major space observatories from the gamma-ray to far-infrared, and highlights the scientific and technical breakthroughs enabled by these telescopes. The papers accepted for publication include reviews of major space telescopes spanning the last two decades, in-depth discussions of the design considerations for visible and x-ray telescopes, and papers discussing concepts and technical challenges for future space telescopes
Chandra X-ray Observation of a Mature Cloud-Shock Interaction in the Bright Eastern Knot of Puppis A
We present Chandra X-ray images and spectra of the most prominent cloud-shock interaction region in the Puppis A supernova remnant. The Bright Eastern Knot (BEK) has two main morphological components: (1) a bright compact knot that lies directly behind the apex of an indentation in the eastern X-ray boundary and (2) lying 1 westward behind the shock, a curved vertical structure (bar) that is separated from a smaller bright cloud (cap) by faint diffuse emission. Based on hardness images and spectra, we identify the bar and cap as a single shocked interstellar cloud. Its morphology strongly resembles the "voided sphere" structures seen at late times in Klein et al. experimental simulat.ions of cloud-shock interactions, when the crushing of the cloud by shear instabilities is well underway. We infer an intera.ction time of roughly cloud-crushing timescales, which translates to 2000-4000 years, based on the X-ray temperature, physical size, and estimated expansion of the shocked cloud. This is the first X-ray identified example of a cloud-shock interaction in this advanced phase. Closer t o the shock front, the X-ray emission of the compact knot in the eastern part of the BEK region implies a recent interaction with relatively denser gas, some of which lies in front of the remnant. The complex spatial relationship of the X-ray emission of the compact knot to optical [O III] emission suggests that there are multiple cloud interactions occurring along the line of sight
Chandra X-ray Observation of a Mature Cloud-Shock Interaction in the Bright Eastern Knot Region of Puppis A
We present Chandra X-ray images and spectra of the most prominent cloud-shock
interaction region in the Puppis A supernova remnant. The Bright Eastern Knot
(BEK) has two main morphological components: (1) a bright compact knot that
lies directly behind the apex of an indentation in the eastern X-ray boundary
and (2) lying 1' westward behind the shock, a curved vertical structure (bar)
that is separated from a smaller bright cloud (cap) by faint diffuse emission.
Based on hardness images and spectra, we identify the bar and cap as a single
shocked interstellar cloud. Its morphology strongly resembles the ``voided
sphere'' structures seen at late times in Klein et al.'s experimental
simulations of cloud-shock interactions, when the crushing of the cloud by
shear instabilities is well underway. We infer an interaction time of roughly 3
cloud-crushing timescales, which translates to 2000-4000 years, based on the
X-ray temperature, physical size, and estimated expansion of the shocked cloud.
This is the first X-ray identified example of a cloud-shock interaction in this
advanced phase. Closer to the shock front, the X-ray emission of the compact
knot in the eastern part of the BEK region implies a recent interaction with
relatively denser gas, some of which lies in front of the remnant. The complex
spatial relationship of the X-ray emission of the compact knot to optical [O
III] emission suggests that there are multiple cloud interactions occurring
along the line of sight.Comment: 22 pages LaTeX with multiple figures, to appear in Ap
X-ray Emitting Ejecta in Puppis A Observed with Suzaku
We report the detection and localization of X-ray emitting ejecta in the
middle-aged Galactic supernova remnant Puppis A using five observations with
the Suzaku X-ray Imaging Spectrometer to survey the eastern and middle portions
of the remnant. A roughly 3' by 5', double-peaked region in the north center is
found to be highly enriched in Si and other elements relative to the rest of
the remnant. The X-ray fitted abundances are otherwise well below the solar
values. While the ejecta-enhanced regions show some variation of relative
element abundances, there is little evidence for a very strong enhancement of
one element over the others in the imaged portion of the remnant, except
possibly for a region of O and Ne enhancement in the remnant's south center.
There is no spatial correlation between the compact [O III] emitting ejecta
knots seen optically and the abundance enhancements seen in X-rays, although
they are located in the same vicinity. The map of fitted column density shows
strong variations across the remnant that echo earlier X-ray spectral hardness
maps. The ionization age (as fitted for single temperature models) is sharply
higher in a ridge behind the northeast-east boundary of the remnant, and is
probably related to the strong molecular cloud interaction along that boundary.
The temperature map, by comparison, shows relatively weak variations.Comment: 25 pages latex, 6 postscript figures; ApJ, in pres
Development of the iCook 4-H Curriculum for Youth and Adults: Cooking, Eating, and Playing Together for Childhood Obesity Prevention
The objective was to describe the development process of a curriculum (iCook 4-H) targeted to low-income, rural, and/or diverse youths and their adult primary meal preparer to promote cooking, eating, and playing together. Lessons learned highlighted the importance of grounding the curriculum in Social Cognitive Theory and applying the experiential 4-H learning model using a multiphased, community-based participatory approach with cyclical development and evaluation, and key modifications made for dissemination and distribution. Findings across 4 testing phases over 6 years and 5 states demonstrated the time-intensive, cyclical process that required flexibility with fidelity to form a hands-on, interactive curriculum
Distinct ECM mechanosensing pathways regulate microtubule dynamics to control endothelial cell branching morphogenesis
The compliance and dimensionality of the ECM regulate distinct changes in microtubule growth speed and growth persistence
The Chandra High Energy Transmission Grating: Design, Fabrication, Ground Calibration and Five Years in Flight
Details of the design, fabrication, ground and flight calibration of the High
Energy Transmission Grating, HETG, on the Chandra X-ray Observatory are
presented after five years of flight experience. Specifics include the theory
of phased transmission gratings as applied to the HETG, the Rowland design of
the spectrometer, details of the grating fabrication techniques, and the
results of ground testing and calibration of the HETG. For nearly six years the
HETG has operated essentially as designed, although it has presented some
subtle flight calibration effects.Comment: 34 pages (including 30 figures), accepted for publication in PAS
Diet and the human gut microbiome : an international review
CITATION: Wilson, A. S. et al. 2020. Diet and the Human Gut Microbiome: An International Review. Digestive diseases and sciences, 65(3):723–740. doi:10.1007/s10620-020-06112-wThe original publication is available at https://www.springer.com/journal/10620This review summarizes the key results of recently published studies on the effects of dietary change and nutritional intervention on the human microbiome from around the world, focusing on the USA, Canada, Europe, Asia, and Africa. It first explores mechanisms that might explain the ability of fiber-rich foods to suppress the incidence and mortality from westernized diseases, notably cancers of the colon, breast, liver, cardiovascular, infectious, and respiratory diseases, diabetes, and obesity (O'Keefe in Lancet Gastroenterol Hepatol 4(12):984-996, 2019; Am J Clin Nutr 110:265-266, 2019). It summarizes studies from Africa which suggest that disturbance of the colonic microbiome may exacerbate chronic malnutrition and growth failure in impoverished communities and highlights the importance of breast feeding. The American section discusses the role of the microbiome in the swelling population of patients with obesity and type 2 diabetes and examines the effects of race, ethnicity, geography, and climate on microbial diversity and metabolism. The studies from Europe and Asia extoll the benefits of whole foods and plant-based diets. The Asian studies examine the worrying changes from low-fat, high-carbohydrate diets to high-fat, low-carbohydrate ones and the increasing appearance of westernized diseases as in Africa and documents the ability of high-fiber traditional Chinese diets to reverse type 2 diabetes and control weight loss. In conclusion, most of the studies reviewed demonstrate clear changes in microbe abundances and in the production of fermentation products, such as short-chain fatty acids and phytochemicals following dietary change, but the significance of the microbiota changes to human health, with the possible exception of the stimulation of butyrogenic taxa by fiber-rich foods, is generally implied and not measured. Further studies are needed to determine how these changes in microbiota composition and metabolism can improve our health and be used to prevent and treat disease.https://pubmed.ncbi.nlm.nih.gov/32060812/Publishers versio
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