3,779 research outputs found
Electromagnetic properties of ice coated surfaces
The electromagnetic scattering from ice coated structures is examined. The influence of ice is shown from a measurement standpoint and related to a simple analytical model. A hardware system for the realistic measurement of ice coated structures is also being developed to use in an existing NASA Lewis icing tunnel. Presently, initial measurements have been performed with a simulated tunnel to aid in the development
Electromagnetic properties of material coated surfaces
The electromagnetic properties of material coated conducting surfaces were investigated. The coating geometries consist of uniform layers over a planar surface, irregularly shaped formations near edges and randomly positioned, electrically small, irregularly shaped formations over a surface. Techniques to measure the scattered field and constitutive parameters from these geometries were studied. The significance of the scattered field from these geometries warrants further study
The Two-Dimensional S=1 Quantum Heisenberg Antiferromagnet at Finite Temperatures
The temperature dependence of the correlation length, susceptibilities and
the magnetic structure factor of the two-dimensional spin-1 square lattice
quantum Heisenberg antiferromagnet are computed by the quantum Monte Carlo loop
algorithm (QMC). In the experimentally relevant temperature regime the
theoretically predicted asymptotic low temperature behavior is found to be not
valid. The QMC results however, agree reasonably well with the experimental
measurements of La2NiO4 even without considering anisotropies in the exchange
interactions.Comment: 4 Pages, 1 table, 4 figure
Muon spin rotation studies of niobium for superconducting RF applications
In this work we investigate superconducting properties of niobium samples via
application of the muon spin rotation/relaxation (muSR) technique. We employ
for the first time the muSR technique to study samples that are cutout from
large and small grain 1.5 GHz radio frequency (RF) single cell niobium
cavities. The RF test of these cavities was accompanied by full temperature
mapping to characterize the RF losses in each of the samples. Results of the
muSR measurements show that standard cavity surface treatments like mild baking
and buffered chemical polishing (BCP) performed on the studied samples affect
their surface pinning strength. We find an interesting correlation between high
field RF losses and field dependence of the sample magnetic volume fraction
measured via muSR. The muSR line width observed in ZF-muSR measurements matches
the behavior of Nb samples doped with minute amounts of Ta or N impurities. An
upper bound for the upper critical field Hc2 of these cutouts is found.Comment: 20 pages, 14 figure
Limitations of the Pilot in Applying Forces to Airplane Controls
Measurements were made to determine the relative maximum forces a pilot can exert on the controls of an airplane with the view of obtaining systematic data upon which to base the location of controls within the cockpit and the design of the control surfaces. A cockpit model of generous proportions, capable of being rotated to any attitude, was built with the location of the control stick and rudder pedals adjustable over a wide range of positions with respect to the seat. Besides measurements of maximum forces obtainable with various control locations and with the pilot in several attitudes, estimates of forces within the range normally encountered in flight were made to gain an indication of the accuracy of estimating control forces. The maximum aileron forces measured were of the order of 90 pounds, maximum elevator 200 pounds, and maximum rudder 450 pounds. The average forces applied with the controls in the neutral position for the various cockpit attitudes were of the order of 35, 95, and 400 pounds, respectively, for the ailerons, elevators, and rudder
A pH-Dependent Kinetic Model of Dihydrolipoamide Dehydrogenase from Multiple Organisms
AbstractDihydrolipoamide dehydrogenase is a flavoenzyme that reversibly catalyzes the oxidation of reduced lipoyl substrates with the reduction of NAD+ to NADH. In vivo, the dihydrolipoamide dehydrogenase component (E3) is associated with the pyruvate, α-ketoglutarate, and glycine dehydrogenase complexes. The pyruvate dehydrogenase (PDH) complex connects the glycolytic flux to the tricarboxylic acid cycle and is central to the regulation of primary metabolism. Regulation of PDH via regulation of the E3 component by the NAD+/NADH ratio represents one of the important physiological control mechanisms of PDH activity. Furthermore, previous experiments with the isolated E3 component have demonstrated the importance of pH in dictating NAD+/NADH ratio effects on enzymatic activity. Here, we show that a three-state mechanism that represents the major redox states of the enzyme and includes a detailed representation of the active-site chemistry constrained by both equilibrium and thermodynamic loop constraints can be used to model regulatory NAD+/NADH ratio and pH effects demonstrated in progress-curve and initial-velocity data sets from rat, human, Escherichia coli, and spinach enzymes. Global fitting of the model provides stable predictions to the steady-state distributions of enzyme redox states as a function of lipoamide/dihydrolipoamide, NAD+/NADH, and pH. These distributions were calculated using physiological NAD+/NADH ratios representative of the diverse organismal sources of E3 analyzed in this study. This mechanistically detailed, thermodynamically constrained, pH-dependent model of E3 provides a stable platform on which to accurately model multicomponent enzyme complexes that implement E3 from a variety of organisms
Maternal inflammation at 0.7 gestation in ewes leads to intrauterine growth restriction and impaired glucose metabolism in offspring at 30 d of age
Fetal programming associated with intrauterine growth restriction (IUGR) leads to lifelong deficits in growth and metabolic function (Hales and Barker, 2013). IUGR arises when fetuses respond to poor in utero conditions by developing adaptations that repartition nutrients to critical tissues and away from skeletal muscle (Yates et al., 2012, 2018). This fetal programming is beneficial in utero but leads to persistent reductions in muscle mass and glucose homeostasis in offspring (DeFronzo et al., 1981). Recent studies by our laboratory in sheep and rats demonstrate that maternal inflammation during gestation induces fetal inflammatory adaptations that impair growth and disrupt muscle glucose metabolism (Cadaret et al., 2017, 2018). IUGR fetal skeletal muscle exhibits indicators of enhanced inflammatory sensitivity, which could disrupt glucose uptake and oxidation (Yates et al., 2016; Cadaret et al., 2018). Enhanced inflammatory responsiveness would help explain growth and metabolic deficits observed in IUGR offspring. We hypothesize that fetal programming induced by maternal inflammation persists in offspring and contributes to impaired growth and glucose metabolism at 30 d. Therefore, the objective of this study was to determine whether sustained maternal inflammation induced by bacterial endotoxin at 0.7 gestation leads to fetal programming that contributes to deficits in growth and glucose metabolism in offspring
A Quantitative Evaluation of the Galaxy Component of COSMOS and APM Catalogs
We have carried out an independent quantitative evaluation of the galaxy
component of the "COSMOS/UKST Southern Sky Object Catalogue" (SSC) and the
"APM/UKST J Catalogue" (APM). Using CCD observations our results corroborate
the accuracy of the photometry of both catalogs, which have an overall
dispersion of about 0.2 mag in the range 17 <= b_J <= 21.5. The SSC presents
externally calibrated galaxy magnitudes that follow a linear relation, while
the APM instrumental magnitudes of galaxies, only internally calibrated by the
use of stellar profiles, require second-order corrections. The completeness of
both catalogs in a general field falls rapidly fainter than b_J = 20.0, being
slightly better for APM. The 90% completeness level of the SSC is reached
between b_J = 19.5 and 20.0, while for APM this happens between b_J = 20.5 and
21.0. Both SSC and APM are found to be less complete in a galaxy cluster field.
Galaxies misclassified as stars in the SSC receive an incorrect magnitude
because the stellar ones take saturation into account besides using a different
calibration curve. In both cases, the misclassified galaxies show a large
diversity of colors that range from typical colors of early-types to those of
blue star-forming galaxies. A possible explanation for this effect is that it
results from the combination of low sampling resolutions with properties of the
image classifier for objects with characteristic sizes close to the
instrumental resolution. We find that the overall contamination by stars
misclassified as galaxies is < 5% to b_J = 20.5, as originally estimated for
both catalogs. Although our results come from small areas of the sky, they are
extracted from two different plates and are based on the comparison with two
independent datasets.Comment: 14 pages of text and tables, 8 figures; to be published in the
Astronomical Journal; for a single postscript version file see
ftp://danw.on.br/outgoing/caretta/caretta.p
Heisenberg antiferromagnet on the square lattice for S>=1
Theoretical predictions of a semiclassical method - the pure-quantum
self-consistent harmonic approximation - for the correlation length and
staggered susceptibility of the Heisenberg antiferromagnet on the square
lattice (2DQHAF) agree very well with recent quantum Monte Carlo data for S=1,
as well as with experimental data for the S=5/2 compounds Rb2MnF4 and KFeF4.
The theory is parameter-free and can be used to estimate the exchange coupling:
for KFeF4 we find J=2.33 +- 0.33 meV, matching with previous determinations. On
this basis, the adequacy of the quantum nonlinear sigma model approach in
describing the 2DQHAF when S>=1 is discussed.Comment: 4 pages RevTeX file with 5 figures included by psfi
The Effect of Cow Udder Score on Subsequent Calf Performance in the Nebraska Sandhills
Cow records were evaluated over a 5-yr period to investigate how cow udder score affected calf growth and carcass performance. Cows from 2 calving herds, March and May, were classified as bad or good based on udder scores recorded at calving. Calves suckling dams with bad udders performed similarly during the pre-weaning period to good udder counterparts, with no differences in overall steer feedlot performance between udder groups. However, steers suckling good udder cows had heavier carcass weights and greater back fat thickness
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