10,513 research outputs found
A trajectory preprocessor for antenna pointing
A trajectory-preprocessing algorithm has been devised which matches antenna angular position, velocity, and acceleration to those of a target. This eliminates vibrations of the antenna structure caused by discontinuities in velocity and acceleration commands, and improves antenna-pointing performance by constraining antenna motion to a linear regime. The algorithm permits faster acquisition times and preserves antenna-tracking capability in situations where there would otherwise be an unacceptably sudden change in antenna velocity or acceleration. A simulation of DSS 13 shows that this preprocessor would reduce servo error to 1 mdeg during acquisition of a low-Earth-orbiting satellite
Three dimensional tracking with misalignment between display and control axes
Human operators confronted with misaligned display and control frames of reference performed three dimensional, pursuit tracking in virtual environment and virtual space simulations. Analysis of the components of the tracking errors in the perspective displays presenting virtual space showed that components of the error due to visual motor misalignment may be linearly separated from those associated with the mismatch between display and control coordinate systems. Tracking performance improved with several hours practice despite previous reports that such improvement did not take place
Nutritive Value of South-Central Kentucky Forbs
South Central Kentucky pastures serve as a host for a plethora of forbs found throughout the Upper South and Midwest United States. In this region, forbs can be numerous within pastures that are under- managed. Many producers view forbs as unwanted or weedy species and may not fully understand the value that some of these forbs provide to beef cattle. With little scientific information found on the subject for the specific geographic area, the purpose of this study was to determine what types of forbs will provide adequate nutrition for lactating beef cows. Three pastures from separate farms were used for this study. Botanical composition was assessed monthly starting in March and continuing through October 2022. Vegetative material from the five most numerous forbs was collected along with tall fescue, a predominate perennial forage, and submitted to a forage lab for quality testing using wet chemistry. Crude protein (CP), total digestible nutrients (TDN), sodium (Na), and copper (Cu) were reported for this presentation. The forbs were classified as palatable and non-palatable and compared to tall fescue. The results showed indicate the palatable forbs and tall fescue generally supported the nutritional requirement of a lactating beef cow. Overall, palatable forbs showed a higher TDN, CP, and Cu levels in comparison to tall fescue and the non-palatable forbs. In summary, it was found palatable forbs retained higher nutritive value than tall fescue and non-palatable forbs and met the nutritional requirements for a lactating beef cow apart from Na
Intervening in the Case (or Controversy): Article III Standing, Rule 24 Intervention, and the Conflict in the Federal Courts
Intervening in the Case (or Controversy): Article III Standing, Rule 24 Intervention, and the Conflict in the Federal Courts
Probing Light Atoms at Sub-nanometer Resolution: Realization of Scanning Transmission Electron Microscope Holography
Atomic resolution imaging in transmission electron microscopy (TEM) and
scanning TEM (STEM) of light elements in electron-transparent materials has
long been a challenge. Biomolecular materials, for example, are rapidly altered
when illuminated with electrons. These issues have driven the development of
TEM and STEM techniques that enable the structural analysis of electron
beam-sensitive and weakly scattering nano-materials. Here, we demonstrate such
a technique, STEM holography, capable of absolute phase and amplitude object
wave measurement with respect to a vacuum reference wave. We use an
amplitude-dividing nanofabricated grating to prepare multiple spatially
separated electron diffraction probe beams focused at the sample plane, such
that one beam transmits through the specimen while the others pass through
vacuum. We raster-scan the diffracted probes over the region of interest. We
configure the post specimen imaging system of the microscope to diffraction
mode, overlapping the probes to form an interference pattern at the detector.
Using a fast-readout, direct electron detector, we record and analyze the
interference fringes at each position in a 2D raster scan to reconstruct the
complex transfer function of the specimen, t(x). We apply this technique to
image a standard target specimen consisting of gold nanoparticles on a thin
amorphous carbon substrate, and demonstrate 2.4 angstrom resolution phase
images. We find that STEM holography offers higher phase-contrast of the
amorphous material while maintaining Au atomic lattice resolution when compared
with high angle annular dark field STEM.Comment: 9 pages, 5 figures in main text, 1 supplemental figure in the
appendi
Diffuse X-ray emission in spiral galaxies
We compare the soft diffuse X-ray emission from Chandra images of 12 nearby
intermediate inclination spiral galaxies to the morphology seen in Halpha,
molecular gas, and mid-infrared emission. We find that diffuse X-ray emission
is often located along spiral arms in the outer parts of spiral galaxies but
tends to be distributed in a rounder morphology in the center. The X-ray
morphology in the spiral arms matches that seen in the mid-infrared or Halpha
and so implies that the X-ray emission is associated with recent active star
formation. We see no strong evidence for X-ray emission trailing the location
of high mass star formation in spiral arms. However, population synthesis
models predict a high mechanical energy output rate from supernovae for a time
period that is about 10 times longer than the lifetime of massive ionizing
stars, conflicting with the narrow appearance of the arms in X-rays. The
fraction of supernova energy that goes into heating the ISM must depend on
environment and is probably higher near sites of active star formation. The
X-ray estimated emission measures suggest that the volume filling factors and
scale heights are high in the galaxy centers but low in the outer parts of
these galaxies. The differences between the X-ray properties and morphology in
the centers and outer parts of these galaxies suggest that galactic fountains
operate in outer galaxy disks but that winds are primarily driven from galaxy
centers.Comment: 28 pages, 4 figures, to be submitted to Ap
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