175 research outputs found
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Thermally induced evolution of morphology on ceramic surfaces in a thermionic converter
The morphology of alumina and scandia ceramics exposed to controlled vacuum and diffusion modes in a thermionic converter has been studied. Evidence for vaporization at a temperature of 1,770 K is manifest in the resulting surface morphologies of both ceramics, consistent with reported sample mass loss. Alumina shows intergranular relief with the formation of terrace--step structure on the grain surfaces. Terrace formation is not directly observed on scandia, however the development of vertical structure and maintenance of voids indicates that vaporization is initiated by structure at the grain edges. Extensive Sc{sub 2}O{sub 3} re-deposition occurs on the scandia surface, possibly mediated by the presence of molybdenum and tungsten. Evidence exists for refractory metal secondary phase formation in this deposit in the form of Sc{sub 6}MO{sub 12} (M = W or Mo). Alumina also shows evidence for materials` interactions in the form of tantalum assisted vaporization which significantly alters the terrace structure
Effects of Zilpaterol Hydrochloride Supplementation on Growth Performance,Carcass Characteristics and Production Economics of SteersDiffering in Breed Composition
The β–adrenergic agonist zilpaterol hydrochloride (ZH) affects skeletal muscle growth, but little is known if this response is influenced by differences in genetic background of cattle. The objective of this study was to determine the effects of ZH on growth, carcass characteristics and production economic responses of Angus-sired (ANG) and SimAngus-sired (SIMANG) steers. Pens within each block × breed composition were randomly assigned to either ZH (8.3 ppm of DM; fed for the final 20 d before slaughter) or control (CON; 0 ppm ZH). Steers were ultrasounded before ZH inclusion and following withdrawal to determine the influence of ZH on change in ribeye area (REA), fat thickness and percent intramuscular fat (IMF). Carcass and feedlot performance data were collected and used to determine breed composition and ZH effects on economic responses. The interaction of breed composition × ZH had no influence on measured responses. Breed composition did not influence change in ultrasound measurements during the ZH feeding period or feedlot performance. Carcasses from SIMANG steers had larger REA and improved YG, while ANG steers had increased marbling scores. SimAngus-sired steers produced a greater percentage of YG 2 and a lower percentage of YG 3 carcasses than ANG steers. A greater proportion of ANG carcasses were classified as upper 2/3 Choice while a greater proportion of SIMANG carcasses were included in the lower 1/3 Choice designation. Carcass value per cwt was greater for ANG compared to SIMANG carcasses while other economic responses were similar. Feeding ZH improved ADG, YG, and REA and resulted in increased YG 2 carcasses. Total carcass value was greater for ZH compared to CON. While CON had increased IMF during ZH feeding, this did not manifest into differences in QG. Breed composition influenced carcass grid premiums, but not overall carcass value. Feeding ZH improved carcass value by increasing HCW. Responses among breed composition were as expected for ANG vs SIMANG cattle types. The resultant economic effect was that grid premiums for higher-grading ANG cattle were offset by larger HCW for SIMANG, leading to similar overall carcass values. Finally, the influence of ZH on growth and carcass traits was as expected with increased carcass value being realized through heavier HCW
Similar hibernation physiology in bats across broad geographic ranges
This is a post-peer-review, pre-copyedit version of an article published in Journal of Comparative Physiology B. The final authenticated version is available online at: http://dx.doi.org/10.1007/s00360-021-01400-xSpecies with broad geographic ranges may experience varied environmental conditions throughout their range leading to local adaptation. Variation among populations reflects potential adaptability or plasticity, with implications for populations impacted by disease, climate change, and other anthropogenic influences. However, behavior may counteract divergent selection among populations. We studied intraspecific variation in hibernation physiology of Myotis lucifugus (little brown myotis) and Corynorhinus townsendii (Townsend's big-eared bat), two species of bats with large geographic ranges. We studied M. lucifugus at three hibernacula which spanned a latitudinal gradient of 1500 km, and C. townsendii from 6 hibernacula spread across 1200 km latitude and 1200 km longitude. We found no difference in torpid metabolic rate among populations of either species, nor was there a difference in the effect of ambient temperature among sites. Evaporative water loss was similar among populations of both species, with the exception of one C. townsendii pairwise site difference and one M. lucifugus site that differed from the others. We suggest the general lack of geographic variation is a consequence of behavioral microhabitat selection. As volant animals, bats can travel relatively long distances in search of preferred microclimates for hibernation. Despite dramatic macroclimate differences among populations, hibernating bats are able to find preferred microclimate conditions within their range, resulting in similar selection pressures among populations spread across wide geographic ranges.Department of Defense Strategic Environmental Research and Development Program || United States Fish and Wildlife Service, Grant F17AP00593 || Texas Tech University || Alberta Conservation Association
Deficiencies in the soil quality concept and its application
Soil quality is a concept that has deeply divided the soil science community. It has
been institutionalized and advocated without full consideration of concept weaknesses and
contradictions. Our paper highlights its disfunctional definition, flawed approach to
quantification, and failure to integrate simultaneous functions, which often require contradictory
soil properties and/or management. While the concept arose from a call to protect the
environment and sustain the soil resource, soil quality indexing as implemented may actually
impair some soil functions, environmental quality, or other societal priorities. We offer the
alternative view that emphasis on known principles of soil management is a better expenditure of
limited resources for soil stewardship than developing and deploying subjective indices which fail
to integrate across the necessary spectrum of management outcomes. If the soil quality concept
is retained, we suggest precisely specifying soil use, not function or capacity, as the criteria for
attribute evaluation. Emphasis should be directed toward using available technical information to
motivate and educate farmers on management practices that optimize the combined goals of high
crop production, low environmental degradation, and a sustained resource
The Ekpyrotic Universe: Colliding Branes and the Origin of the Hot Big Bang
We propose a cosmological scenario in which the hot big bang universe is
produced by the collision of a brane in the bulk space with a bounding orbifold
plane, beginning from an otherwise cold, vacuous, static universe. The model
addresses the cosmological horizon, flatness and monopole problems and
generates a nearly scale-invariant spectrum of density perturbations without
invoking superluminal expansion (inflation). The scenario relies, instead, on
physical phenomena that arise naturally in theories based on extra dimensions
and branes. As an example, we present our scenario predominantly within the
context of heterotic M-theory. A prediction that distinguishes this scenario
from standard inflationary cosmology is a strongly blue gravitational wave
spectrum, which has consequences for microwave background polarization
experiments and gravitational wave detectors.Comment: 67 pages, 4 figures. v2,v3: minor corrections, references adde
Ichthyophonus-induced cardiac damage: a mechanism for reduced swimming stamina in salmonids
Simulação da expectativa de perdas de solo em microbacia sob diferentes manejos florestais
Kinetics of the fcc → hcp Phase Transformation in Cu-Ge Solid Solutions Upon Isothermal Aging
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Energetic particle influence on the Earth's atmosphere
This manuscript gives an up-to-date and comprehensive overview of the effects of energetic particle precipitation (EPP) onto the whole atmosphere, from the lower thermosphere/mesosphere through the stratosphere and troposphere, to the surface. The paper summarizes the different sources and energies of particles, principally
galactic cosmic rays (GCRs), solar energetic particles (SEPs) and energetic electron precipitation (EEP). All the proposed mechanisms by which EPP can affect the atmosphere
are discussed, including chemical changes in the upper atmosphere and lower thermosphere, chemistry-dynamics feedbacks, the global electric circuit and cloud formation. The role of energetic particles in Earth’s atmosphere is a multi-disciplinary problem that requires expertise from a range of scientific backgrounds. To assist with this synergy, summary tables are provided, which are intended to evaluate the level of current knowledge of the effects of energetic particles on processes in the entire atmosphere
Tides in colliding galaxies
Long tails and streams of stars are the most noticeable upshots of galaxy
collisions. Their origin as gravitational, tidal, disturbances has however been
recognized only less than fifty years ago and more than ten years after their
first observations. This Review describes how the idea of galactic tides
emerged, in particular thanks to the advances in numerical simulations, from
the first ones that included tens of particles to the most sophisticated ones
with tens of millions of them and state-of-the-art hydrodynamical
prescriptions. Theoretical aspects pertaining to the formation of tidal tails
are then presented. The third part of the review turns to observations and
underlines the need for collecting deep multi-wavelength data to tackle the
variety of physical processes exhibited by collisional debris. Tidal tails are
not just stellar structures, but turn out to contain all the components usually
found in galactic disks, in particular atomic / molecular gas and dust. They
host star-forming complexes and are able to form star-clusters or even
second-generation dwarf galaxies. The final part of the review discusses what
tidal tails can tell us (or not) about the structure and content of present-day
galaxies, including their dark components, and explains how tidal tails may be
used to probe the past evolution of galaxies and their mass assembly history.
On-going deep wide-field surveys disclose many new low-surface brightness
structures in the nearby Universe, offering great opportunities for attempting
galactic archeology with tidal tails.Comment: 46 pages, 13 figures, Review to be published in "Tidal effects in
Astronomy and Astrophysics", Lecture Notes in Physics. Comments are most
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