16,815 research outputs found
Effect of Varying Dietary Selenium Levels on Tissue Composition, Blood Composition and Performance of Growing Swine Fed Seleniferous Grains
It is established that selenium is an essential micronutrient as well as a natural toxicant for domestic livestock. However, reports of selenium toxicosis in swine are limited and not well documented. The level at which selenium becomes toxic to swine is thought to be about 8 ppm. This value was derived from the initial selenium research of the 1930\u27s, with considerable extrapolation from other species used in this determination. Since that time, diet composition has become much more complex, nutrient level of diets has increased and feed additives are commonly used. It is not known what effect these factors or other nutritional interrelationships may have on the level at which selenium becomes toxic. Due to the variability of selenium content in feedstuffs and because selenium is now approved as a feed additive, it is important to better define the level at which selenium becomes toxic to swine. This research was conducted to determine the effect of varying dietary selenium levels on tissue and blood composition and performance of growing swine fed seleniferous grains
Developmental design, fabrication, and test of acoustic suppressors for fans of high bypass turbofan engines
An analysis procedure was developed for design of acoustically treated nacelles for high bypass turbofan engines. The plan was applied to the conceptual design of a nacelle for the quiet engine typical of a 707/DC-8 airplane installation. The resultant design was modified to a test nacelle design for the NASA Lewis quiet fan. The acoustic design goal was a 10 db reduction in effective perceived fan noise levels during takoff and approach. Detailed nacelle designs were subsequently developed for both the quiet engine and the quiet fan. The acoustic design goal for each nacelle was 15 db reductions in perceived fan noise levels from the inlet and fan duct. Acoustically treated nacelles were fabricated for the quiet engine and quiet fan for testing. Performance of selected inlet and fan duct lining configurations was experimentally evaluated in a flow duct. Results of the tests show that the linings perform as designed
Which processes drive observed variations of HCHO columns over India?
We interpret HCHO column variations observed by the Ozone
Monitoring Instrument (OMI), aboard the NASA Aura satellite, over India
during 2014 using the GEOS-Chem atmospheric chemistry and transport model. We
use a nested version of the model with a horizontal resolution of
approximately 25 km. HCHO columns are related to local emissions of volatile
organic compounds (VOCs) with a spatial smearing that increases with the VOC
lifetime. Over India, HCHO has biogenic, pyrogenic, and anthropogenic VOC
sources. Using a 0-D photochemistry model, we find that isoprene has the
largest molar yield of HCHO which is typically realized within a few hours. We also
find that forested regions that neighbour major urban conurbations are
exposed to high levels of nitrogen oxides. This results in depleted hydroxyl
radical concentrations and a delay in the production of HCHO from isoprene
oxidation. We find that propene is the only anthropogenic VOC emitted in
major Indian cities that produces HCHO at a comparable (but slower) rate to
isoprene. The GEOS-Chem model reproduces the broad-scale annual mean HCHO
column distribution observed by OMI (<i>r</i> = 0.6), which is dominated by a
distinctive meridional gradient in the northern half of the country, and by
localized regions of high columns that coincide with forests. Major
discrepancies are noted over the Indo-Gangetic Plain (IGP) and Delhi. We find that the
model has more skill at reproducing observations during winter (JF) and
pre-monsoon (MAM) months with Pearson correlations <i>r</i> > 0.5 but with a
positive model bias of <mo form="infix">≃</mo> 1×10<sup>15</sup> molec cm<sup>−2</sup>. During the
monsoon season (JJAS) we reproduce only a diffuse version of the observed
meridional gradient (<i>r</i> = 0.4). We find that on a continental scale most of
the HCHO column seasonal cycle is explained by monthly variations in surface
temperature (<i>r</i> = 0.9), suggesting a role for biogenic VOCs, in agreement with
the 0-D and GEOS-Chem model calculations. We also find that the seasonal
cycle during 2014 is not significantly different from the 2008 to 2015 mean
seasonal variation. There are two main loci for biomass burning (the states of
Punjab and Haryana, and northeastern India), which we find makes a significant contribution
(up to 1×10<sup>15</sup> molec cm<sup>−2</sup>) to
observed HCHO columns only during March and April over northeastern India.
The slow production of HCHO from propene oxidation results in a smeared
hotspot over Delhi that we resolve only on an annual mean timescale by using
a temporal oversampling method. Using a linear regression model to relate
GEOS-Chem isoprene emissions to HCHO columns we infer seasonal isoprene
emissions over two key forest regions from the OMI HCHO column data. We find
that the a posteriori emissions are typically lower than the a priori
emissions, with a much stronger reduction of emissions during the monsoon
season. We find that this reduction in emissions during monsoon months
coincides with a large drop in satellite observations of leaf phenology that
recovers in post monsoon months. This may signal a forest-scale response to
monsoon conditions
Research Notes : Canada : Linkage tests
Results reported by Buzzell (1974) were not conclusive as to whether or not E3 (daylength response) and Ep (seedcoat peroxidase) are independent or loosely linked. Palmer et al. (1984) has shown that Ep is linked with Frl in linkage group 12. Using F2 plants of \u27Minsoy\u27 x \u27Hark\u27 previously reported (Palmer et al., 1984) for seedcoat peroxidase and root fluorescence, we tested for linkage of E3 with Ep and Frl by testing F3 material for response under a daylength extended to 20 h with cool white fluorescent light
Cosmic Ray Propagation: Nonlinear Diffusion Parallel and Perpendicular to Mean Magnetic Field
We consider the propagation of cosmic rays in turbulent magnetic fields. We
use the models of magnetohydrodynamic turbulence that were tested in numerical
simulations, in which the turbulence is injected on large scale and cascades to
small scales. Our attention is focused on the models of the strong turbulence,
but we also briefly discuss the effects that the weak turbulence and the slab
Alfv\'enic perturbations can have. The latter are likely to emerge as a result
of instabilities with in the cosmic ray fluid itself, e.g., beaming and
gyroresonance instabilities of cosmic rays. To describe the interaction of
cosmic rays with magnetic perturbations we develop a non-linear formalism that
extends the ordinary Quasi-Linear Theory (QLT) that is routinely used for the
purpose. This allows us to avoid the usual problem of 90 degree scattering and
enable our computation of the mean free path of cosmic rays. We apply the
formalism to the cosmic ray propagation in the galactic halo and in the Warm
Ionized medium (WIM). In addition, we address the issue of the transport of
cosmic rays perpendicular to the mean magnetic field and show that the issue of
cosmic ray subdiffusion (i.e., propagation with retracing the trajectories
backwards, which slows down the diffusion) is only important for restricted
cases when the ambient turbulence is far from what numerical simulations
suggest to us. As a result, this work provides formalism that can be applied
for calculating cosmic ray propagation in a wide variety of circumstances.Comment: minor changes, accepted to Ap
Leading the evaluation of institutional online learning environments for quality enhancement in times of change
This paper reports on findings from a nationally funded project which aims to design and implement a quality management framework for online learning environments (OLEs). Evaluation is a key component of any quality management system and it is this aspect of the framework that is the focus of this paper. In developing the framework initial focus groups were conducted at the five participating institutions. These revealed that, although regarded as important, there did not appear to be a shared understanding of the nature and purpose of evaluation. A second series of focus groups revealed there were multiple perspectives arising from those with a vested interest in online learning. These perspectives will be outlined. Overall, how evaluation was undertaken was highly variable within and across the five institutions reflecting where they were at in relation to the development of their OLE
Relativistic Particle-In-Cell Simulation Studies of Prompt and Early Afterglows from GRBs
Nonthermal radiation observed from astrophysical systems containing
relativistic jets and shocks e.g. gamma-ray bursts (GRBs) active galactic
nuclei (AGNs) and microquasars commonly exhibit power-law emission spectra.
Recent PIC simulations of relativistic electron-ion (or electron-positron) jets
injected into a stationary medium show that particle acceleration occurs within
the downstream jet. In collisionless relativistic shocks particle (electron,
positron and ion) acceleration is due to plasma waves and their associated
instabilities (e.g. the Weibel (filamentation) instability) created in the
shock region. The simulations show that the Weibel instability is responsible
for generating and amplifying highly non-uniform small-scale magnetic fields.
These fields contribute to the electron's transverse deflection behind the jet
head. The resulting ``jitter'' radiation from deflected electrons has different
properties compared to synchrotron radiation which assumes a uniform magnetic
field. Jitter radiation may be important for understanding the complex time
evolution and/or spectra in gamma-ray bursts, relativistic jets in general and
supernova remnants.Comment: 19 pages,7 figures, contributed talk at Seventh European Workshop on
Collisionless Shocks, Paris, 7- 9 November 2007. High resolution version can
be obtained at http://gammaray.nsstc.nasa.gov/~nishikawa/shockws07.pd
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