4,142 research outputs found
Preliminary QCGAT program test results
NASA Lewis Research Center is conducting a program to demonstrate that large commercial engine technology can be applied to general aviation engines to reduce noise, emissions and fuel consumption and to develop new technology where required. The overall engine program, design, and technology incorporated into the QCGAT engines are described. In addition, preliminary engine test results are presented and compared to the technical requirements the engines were designed to meet
Reintroduction Biology of Head-Started Ornate Box Turtles
The ornate box turtle (Terrapene ornata) is a prairie-dwelling species that has experienced population declines, especially near the northern edge of its range. In order to provide supporting research for a reintroduction program at the Upper Mississippi River National Wildlife and Fish Refuge in northwestern Illinois, I compared the relative success of different approaches to reintroduction. Specifically, I tested the null hypothesis that reintroduced turtles exhibited equal reintroduction success when, 1) released at a site that is known to support a viable ornate box turtle population, 2) ‘soft-released\u27 in a fenced enclosure at a site where very few ornate box turtles persist, or 3) ‘hard-released\u27 at the same site without the protection of a fence. I also characterized important habitat components that are likely to maximize the quality of a reintroduction site. By many measures, the three treatments returned comparable results. Home ranges were not smaller when turtles were confined to a soft release enclosure, growth rates were not significantly influenced by either the enclosure or by whether or not the release location already supported an ornate box turtle population, diet was similarly varied among all three treatments, and mortality rates during the activity season were similarly low across the three treatments
Quantum dynamics of localized excitations in a symmetric trimer molecule
We study the time evolution of localized (local bond) excitations in a
symmetric quantum trimer molecule. We relate the dynamical properties of
localized excitations such as their spectral intensity and their temporal
evolution (survival probability and tunneling of bosons) to their degree of
overlap with quantum tunneling pair states. We report on the existence of
degeneracy points in the trimer eigenvalue spectrum for specific values of
parameters due to avoided crossings between tunneling pair states and
additional states. The tunneling of localized excitations which overlap with
these degenerate states is suppressed on all times. As a result local bond
excitations may be strongly localized forever, similar to their classical
counterparts.Comment: 9 pages, 12 figures. Improved version with more discussions. Some
figures were replaced for better understanding. Accepted in Phys. Rev.
Insect (Arthropoda: Insecta) Composition in the Diet of Ornate Box Turtles (Terrapene ornata ornata) in Two Western Illinois Sand Prairies, with a New State Record for Cyclocephala (Coleoptera: Scarabaeidae)
A study of fecal samples collected over a two-year period from juvenile ornate box turtles (Terrapene ornata ornata Agassiz) revealed diets consisting of six orders of insects representing 19 families. Turtles were reared in captivity from eggs harvested from local, wild populations, and released at two remnant prairies. Identifiable insect fragments were found in 94% of samples in 2013 (n=33) and 96% in 2014 (n=25). Frequency of occurrence of insects in turtle feces is similar to results reported in previous studies of midwestern Terrapene species. A comparison of insect composition presented no significant difference between release sites. There is no significant difference in consumed insect species between turtles released into or outside of a fenced enclosure at the same site. Specimens of Cyclocephala longula LeConte collected during this study represent a new state record for Illinois
Driven Intrinsic Localized Modes in a Coupled Pendulum Array
Intrinsic localized modes (ILMs), also called discrete breathers, are
directly generated via modulational instability in an array of coupled
pendulums. These ILMs can be stabilized over a range of driver frequencies and
amplitudes. They are characterized by a pi-phase difference between their
center and wings. At higher driver frequencies, these ILMs are observed to
disintegrate via a pulsating instability, and the mechanism of this breather
instability is investigated.Comment: 5 pages, 6 figure
Hsp90 globally targets paused RNA polymerase to regulate gene expression in response to environmental stimuli
The molecular chaperone Heat shock protein 90 (Hsp90) promotes the maturation of several important proteins and plays a key role in development, cancer progression, and evolutionary diversification. By mapping chromatin-binding sites of Hsp90 at high resolution across the Drosophila genome, we uncover an unexpected mechanism by which Hsp90 orchestrates cellular physiology. It localizes near promoters of many coding and noncoding genes including microRNAs. Using computational and biochemical analyses, we find that Hsp90 maintains and optimizes RNA polymerase II pausing via stabilization of the negative elongation factor complex (NELF). Inhibition of Hsp90 leads to upregulation of target genes, and Hsp90 is required for maximal activation of paused genes in Drosophila and mammalian cells in response to environmental stimuli. Our findings add a molecular dimension to the chaperone's functionality with wide ramifications into its roles in health, disease, and evolution
Acoustic breathers in two-dimensional lattices
The existence of breathers (time-periodic and spatially localized lattice
vibrations) is well established for i) systems without acoustic phonon branches
and ii) systems with acoustic phonons, but also with additional symmetries
preventing the occurence of strains (dc terms) in the breather solution. The
case of coexistence of strains and acoustic phonon branches is solved (for
simple models) only for one-dimensional lattices.
We calculate breather solutions for a two-dimensional lattice with one
acoustic phonon branch. We start from the easy-to-handle case of a system with
homogeneous (anharmonic) interaction potentials. We then easily continue the
zero-strain breather solution into the model sector with additional quadratic
and cubic potential terms with the help of a generalized Newton method. The
lattice size is . The breather continues to exist, but is dressed
with a strain field. In contrast to the ac breather components, which decay
exponentially in space, the strain field (which has dipole symmetry) should
decay like . On our rather small lattice we find an exponent
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