22,021 research outputs found
Formed platelet combustor liner construction feasibility, phase A
Environments generated in high pressure liquid rocket engines impose severe requirements on regeneratively cooled combustor liners. Liners fabricated for use in high chamber pressures using conventional processes suffer from limitations that can impair operational cycle life and can adversely affect wall compatibility. Chamber liners fabricated using formed platelet technology provide an alternative to conventional regeneratively cooled liners (an alternative that has many attractive benefits). A formed platelet liner is made from a stacked assembly of platelets with channel features. The assembly is diffusion bonded into a flat panel and then three-dimensionally formed into a section of a chamber. Platelet technology permits the liner to have very precisely controlled and thin hot gas walls and therefore increased heat transfer efficiency. Further cooling efficiencies can be obtained through enhanced design flexibility. These advantages translate into increased cycle life and enhanced wall compatibility. The increased heat transfer efficiency can alternately be used to increase engine performance or turbopump life as a result of pressure drop reductions within the regeneratively cooled liner. Other benefits can be obtained by varying the materials of construction within the platelet liner to enhance material compatibility with operating environment or with adjoining components. Manufacturing cost savings are an additional benefit of a formed platelet liner. This is because of reduced touch labor and reduced schedule when compared to conventional methods of manufacture. The formed platelet technology is not only compatible with current state-of-the art combustion chamber structural support and manifolding schemes, it is also an enabling technology that allows the use of other high performance and potentially low cost methods of construction for the entire combustion chamber assembly. The contract under which this report is submitted contains three phases: (1) phase A - feasibility study and technology development; (2) phase B - sub-scale fabrication feasibility; and (3) phase C - large scale fabrication validation. This report covers the Phase A activities, which began in December of 1988
Gypsy moths and American dog ticks: Space partners
An experiment intended for the space shuttle and designed to investigate the effects of weightlessness and total darkness on gypsy moth eggs and engorged American dog ticks is described. The objectives are: (1) to reevaluate the effects of zero gravity on the termination of diapause/hibernation of embryonated gypsy moth eggs, (2) to determine the effect of zero gravity on the ovipositions and subsequent hatch from engorged female American dog ticks that have been induced to diapause in the laboratory, and (3) to determine whether morphological or biochemical changes occur in the insects under examination. Results will be compared with those from a similar experiment conducted on Skylab 4
Economic Impacts of Aquatic Vegetation to Angling in Two South Carolina Reservoirs
Angler creel surveys and economic impact models were
used to evaluate potential expansion of aquatic vegetation in
Lakes Murray and Moultrie, South Carolina. (PDF contains 4 pages.
Predation rate by wolves on the Porcupine caribou herd
Large migratory catibou {Rangifer tarandus) herds in the Arctic tend to be cyclic, and population trends are mainly driven by changes in forage or weather events, not by predation. We estimated daily kill rate by wolves on adult caribou in winter, then constructed a time and space dependent model to estimate annual wolf (Canis lupus) predation rate (P annual) on adult Porcupine caribou. Our model adjusts predation seasonally depending on caribou distribution: Pannual = SIGMAdaily* W *Ap(2)*Dp. In our model we assumed that wolves killed adult caribou at a constant rate (Kdaily, 0.08 caribou wolf1 day1) based on our studies and elsewhere; that wolf density (W) doubled to 6 wolves 1000 km2-1 on all seasonal ranges; and that the average area occupied by the Porcupine caribou herd (PCH) in eight seasonal life cycle periods (Dp ) was two times gteater than the area described by the outer boundaries of telemetry data (Ap /1000 km2). Results from our model projected that wolves kill about 7600 adult caribou each year, regardless of herd size. The model estimated that wolves removed 5.8 to 7.4% of adult caribou as the herd declined in the 1990s. Our predation rate model supports the hypothesis of Bergerud that spacing away by caribou is an effective anti-predatory strategy that greatly reduces wolf predation on adult caribou in the spring and summer
Fully three dimensional breather solitons can be created using Feshbach resonance
We investigate the stability properties of breather solitons in a
three-dimensional Bose-Einstein Condensate with Feshbach Resonance Management
of the scattering length and con ned only by a one dimensional optical lattice.
We compare regions of stability in parameter space obtained from a fully 3D
analysis with those from a quasi two-dimensional treatment. For moderate con
nement we discover a new island of stability in the 3D case, not present in the
quasi 2D treatment. Stable solutions from this region have nontrivial dynamics
in the lattice direction, hence they describe fully 3D breather solitons. We
demonstrate these solutions in direct numerical simulations and outline a
possible way of creating robust 3D solitons in experiments in a Bose Einstein
Condensate in a one-dimensional lattice. We point other possible applications.Comment: 4 pages, 4 figures; accepted to Physical Review Letter
Multiwavelength analysis of the Lyman alpha emitting galaxy Haro 2: relation between the diffuse Lyman alpha and soft X-ray emissions
In order to use Lyman alpha (Lya) emission as star formation tracer in
cosmological studies, we must understand how the resonant scattering affects
the escape fraction of the Lya photons. Thus, high spatial resolution
multiwavelength studies of nearby Lya emitters, like Haro 2, are highly needed.
For that purpose, we have used Chandra X-ray and HST (UV, optical and NIR)
images of Haro 2, and STIS and ground-based spectral images along its major and
minor axes, to characterize the Lya emission and the properties of the stellar
population. The UV, Ha (Halpha) and FIR luminosities of the Haro 2 nuclear
starburst are reproduced using evolutionary synthesis models assuming a young
stellar population with ages ~3.5-5.0 Myr, affected by differential
interstellar extinctions. The observed X-ray emission is attributed to gas
heated by the mechanical energy released by the starburst (soft component) and
a Ultra-Luminous X-ray source candidate (hard). Both compact and diffuse Lya
components are observed. Whereas Lya is spatially decoupled from Balmer lines
emission, Balmer decrement and UV continuum, the diffuse Lya component is
spatially correlated with the diffuse soft X-ray emission. Moreover, unlike the
compact one, diffuse Lya shows luminosities larger than predicted from Ha,
assuming case B recombination and dust extinction as derived from Ha/Hbeta. We
propose that, whereas the compact Lya emission is associated to the massive
stellar clusters and is affected by outflows and dust extinction, the diffuse
Lya originates in gas ionized by the hot plasma responsible for the soft X-ray
radiation, as suggested by their spatial correlation and by the measured
L(Ha)/LsoftX ratios. Calibration of Lya as star formation rate tracer should
therefore include both effects (destruction vs. enhancement) to avoid biases in
the study of galaxies at cosmological distances.Comment: Accepted for publication in A&A, 18 pages, 8 figures, 9 tables. If
problems with quality of images, see
http://www.cab.inta-csic.es/users/otih/haro2-v63.clean.pd
Physical properties and evolutionary state of the Lyman alpha emitting starburst galaxy IRAS 08339+6517
Though Lyman alpha emission (Lya) is one of the most used tracers of massive
star formation at high redshift, a correct understanding of radiation transfer
effects by neutral gas is required to properly quantify the star formation rate
along the history of the Universe. We are embarked in a program to study the
properties of the Lya emission (spectral profile, spatial distribution,
relation to Balmer lines intensity,...) in several local starburst galaxies. We
present here the results obtained for IRAS 08339+6517.
Using evolutionary population synthesis models, we have characterized the
properties of the starburst (UV continuum, Halpha, total infrared and X-ray
emissions, etc.), which transformed 1.4e+8 Mo of gas into stars around 5-6 Myr
ago. In addition to the central compact emission blob, we have identified a
diffuse Lya emission component smoothly distributed over the whole central area
of IRAS 08339+6517. This diffuse emission is spatially decoupled from the UV
continuum, the Halpha emission or the Halpha/Hbeta ratio. Both locally and
globally, the Lya/Halpha ratio is lower than the Case B predictions, even after
reddening correction, with an overall Lya escape fraction of only 4%.
We conclude that in IRAS 08339+6517 the resonant scattering of Lya photons by
an outflowing shell of neutral gas causes their highly-efficient destruction by
dust, which explains the low Lya escape fraction measured. These results stress
again the importance of a proper correction of scattering and transfer effects
when using Lya to derive the star formation rate in high-redshift galaxies.Comment: Accepted for publication in A&A, 17 pages, 13 figures, 8 tables. If
problems with quality of images, see
https://cloud.cab.inta-csic.es/public.php?service=files&file=%2Fotih%2Ffiles%2Foti_mas%2Firas%2Firas-v53.ack_referee.pd
Effect of coronavirus-19 restrictions in male handball players:physical activity, sedentary behavior, and satisfaction with life
This experiment examined physical activity (PA), sitting time, and satisfaction with life (SL) in European (45%) and Middle Eastern and North African (MENA; 55%) handball players (n = 418; age: 25.6 ± 6.8 years; body mass: 88.1 ± 11.7 kg; height: 1.83 ± 0.08 m) during the coronavirus (COVID)-19 pandemic. The International Physical Activity (IPAQ) and Satisfaction of Life (LS) Questionnaires were administered. All PA variables (vigorous, moderate, walking, total PA) were negatively influenced, but no interaction effects (IE; region x time) were observed. Sitting time increased from 2.5 to 4.9 h∙weekday−1 (ηp2 = 0.80) and walking time decreased from 66.8 to 33.5 min∙day−1 (ηp2 = 0.83). Based on effect sizes (d), pre- to during-confinement reductions were similar between regions (MENA: d = 3.29; Europe: d = 3.41; IE: ηp2 = 0.01). The largest regional difference was in moderate PA (MENA: d = 1.88; Europe: d = 2.99; IE: ηp2 = 0.09). SL in the total sample reduced from 30.6 ± 2.02 to 13.9 ± 2.20 arbitrary units (AU). SL reduction was similar in both regions (dMENA = 8.44; dEUROPE = 8.06; IE: ηp2 = 0.01). To conclude, PA decreased during COVID-19 confinement, sitting time increased, and SL decreased irrespective of geographical region. These preliminary findings highlight risk of SL and physical inactivity during COVID-19 restrictions in 2021
Exoplanetary atmosphere target selection in the era of comparative planetology
The large number of new planets expected from wide-area transit surveys means
that follow-up transmission spectroscopy studies of their atmospheres will be
limited by the availability of telescope assets. We argue that telescopes
covering a broad range of apertures will be required, with even 1m-class
instruments providing a potentially important contribution. Survey strategies
that employ automated target selection will enable robust population studies.
As part of such a strategy, we propose a decision metric to pair the best
target to the most suitable telescope, and demonstrate its effectiveness even
when only primary transit observables are available. Transmission spectroscopy
target selection need not therefore be impeded by the bottle-neck of requiring
prior follow-up observations to determine the planet mass. The decision metric
can be easily deployed within a distributed heterogeneous network of telescopes
equipped to undertake either broadband photometry or spectroscopy. We show how
the metric can be used either to optimise the observing strategy for a given
telescope (e.g. choice of filter) or to enable the selection of the best
telescope to optimise the overall sample size. Our decision metric can also
provide the basis for a selection function to help evaluate the statistical
completeness of follow-up transmission spectroscopy datasets. Finally, we
validate our metric by comparing its ranked set of targets against lists of
planets that have had their atmospheres successfully probed, and against some
existing prioritised exoplanet lists.Comment: 20 pages, 16 figures, 3 tables. Revision 3, accepted by MNRAS.
Improvements include always using planetary masses where available and
reliable, treatment for sky backgrounds and out-of-transit noise and a use
case for defocused photometr
- âŠ