9,665 research outputs found
Control Surface Actuator
A device which actuates aircraft control surfaces is disclosed. The actuator is disposed entirely within the control surface structure. This allows the gap between the wing structural box and the control surface to be reduced. Reducing the size of the gap is especially desirable for wings with high aspect ratio, wherein the volume of the structural box is at a premium
Tight bounds for break minimization
We consider round-robin sports tournaments with n teams and n − 1 rounds. We construct an infinite family of opponent schedules for which every home-away assignment induces at least 1/4 n(n−2) breaks. This construction establishes a matching lower bound for a corresponding upper bound from the literature
Triaxial Black-Hole Nuclei
We demonstrate that the nuclei of galaxies containing supermassive black
holes can be triaxial in shape. Schwarzschild's method was first used to
construct self-consistent orbital superpositions representing nuclei with axis
ratios of 1:0.79:0.5 and containing a central point mass representing a black
hole. Two different density laws were considered, with power-law slopes of -1
and -2. We constructed two solutions for each power law: one containing only
regular orbits and the other containing both regular and chaotic orbits.
Monte-Carlo realizations of the models were then advanced in time using an
N-body code to verify their stability. All four models were found to retain
their triaxial shapes for many crossing times. The possibility that galactic
nuclei may be triaxial complicates the interpretation of stellar-kinematical
data from the centers of galaxies and may alter the inferred interaction rates
between stars and supermassive black holes.Comment: 4 pages, 4 postscript figures, uses emulateapj.st
Chromosome Centromeres: Structural and Analytical Investigations with High Resolution Scanning Electron Microscopy in Combination with Focused Ion Beam Milling
Whole mount mitotic metaphase chromosomes of different plants and animals were investigated with high resolution field emission scanning electron microscopy (FESEM) to study the ultrastructural organization of centromeres, including metacentric, acrocentric, telocentric, and holocentric chromosome variants. It could be shown that, in general, primary constrictions have distinctive ultrastructural features characterized by parallel matrix fibrils and fewer smaller chromomeres. Exposure of these structures depends on cell cycle synchronization prior to chromosome isolation, chromosome size, and chromosome isolation technique. Chromosomes without primary constrictions, small chromosomes, and holocentric chromosomes do not exhibit distinct ultrastructural elements that could be directly correlated to centromere function. Putative spindle structures, although rarely observed, spread over the primary constriction to the bordering pericentric regions. Analytical FESEM techniques, including specific DNA staining with Pt blue, staining of protein as a substance class with silver-colloid, and artificial loosening of fixed chromosomes with proteinase K, were applied, showing that centromere variants and ultrastructural elements in the centromere differ in DNA and protein distribution. Immunogold localization allowed high-resolution comparison between chromosomes with different centromere orientations of the distribution of centromere-related histone variants, phosphorylated histone H3 (ser10), and CENH3. A novel application of FESEM combined with focused ion beam milling (FIB) provided new insights into the spatial distribution of these histone variants in barley chromosomes. Copyright (C) 2009 S. Karger AG, Base
Design space for low sensitivity to size variations in [110] PMOS nanowire devices: The implications of anisotropy in the quantization mass
A 20-band sp3d5s* spin-orbit-coupled, semi-empirical, atomistic tight-binding
model is used with a semi-classical, ballistic, field-effect-transistor (FET)
model, to examine the ON-current variations to size variations of [110]
oriented PMOS nanowire devices. Infinitely long, uniform, rectangular nanowires
of side dimensions from 3nm to 12nm are examined and significantly different
behavior in width vs. height variations are identified and explained. Design
regions are identified, which show minor ON-current variations to significant
width variations that might occur due to lack of line width control. Regions
which show large ON-current variations to small height variations are also
identified. The considerations of the full band model here show that ON-current
doubling can be observed in the ON-state at the onset of volume inversion to
surface inversion transport caused by structural side size variations. Strain
engineering can smooth out or tune such sensitivities to size variations. The
cause of variations described is the structural quantization behavior of the
nanowires, which provide an additional variation mechanism to any other
ON-current variations such as surface roughness, phonon scattering etc.Comment: 24 pages, 5 figure
Long-term evolution of 1991 DA: A dynamically evolved extinct Halley-type comet
The long-term dynamical evolution of 21 variational orbits for the intermediate-period asteroid 1991 DA was followed for up to +/-10(exp 5) years from the present. 1991 DA is close to the 2:7 resonance with Jupiter; it has avoided close encounters, within 1 AU, with this planet for at least the past 30,000 years, even at the node crossing. The future evolution typically shows no close encounters with Jupiter within at least 50,000 years. This corresponds to the mean time between node crossings with either Jupiter or Saturn. Close encounters with Saturn and Jupiter lead to a chaotic evolution for the whole ensemble, while secular perturbations cause large-amplitude swings in eccentricity and inclination (the latter covering the range 15 deg approximately less than i approximately less than 85 deg) which correlate with deep excursions of the perihelion distance to values much less than 1 AU. These variations are similar to those found in P/Machholz and a variety of other high-inclination orbits, e.g., P/Hartley-IRAS. We emphasize the connection between the orbital evolution of 1991 DA and that of Halley-type comets. If 1991 DA was once a comet, it is not surprising that it is now extinct
- …