1,468 research outputs found
Design and Fabrication of the NASA Decoupler Pylon for the F-16 Aircraft
The NASA Decoupler Pylon is a passive means of suppressing wing-store flutter. The feasibility of demonstrating this concept on the F-16 aircraft was established through model wind tunnel tests and analyses. As a result of these tests and studies a ship set of Decoupler Pylons was designed and fabricated for a flight test demonstration on the F-16 aircraft. Basic design criteria were developed during the analysis study pertaining to pylon pitch stiffness, alignment system requirements, and damping requirements. A design was developed which utilized an electrical motor for the pylon alignment system. The design uses a four pin, two link pivot design which results in a remote pivot located at the center of gravity of the store when the store is in the aligned position. The pitch spring was fabricated from a tapered constant stress cantilevered beam. The pylon has the same external lines as the existing production pylon and is designed to use a MAU-12 ejection rack which is the same as the one used with the production pylon. The detailed design and fabrication was supported with a complete ground test of the pylon prior to shipment to NASA
Full counting statistics for noninteracting fermions: Exact finite temperature results and generalized long time approximation
Exact numerical results for the full counting statistics (FCS) of a
one-dimensional tight-binding model of noninteracting electrons are presented
at finite temperatures using an identity recently presented by Abanov and
Ivanov. A similar idea is used to derive a new expression for the cumulant
generating function for a system consisting of two quasi-one-dimensional leads
connected by a quantum dot in the long time limit. This provides a
generalization of the Levitov-Lesovik formula for such systems.Comment: 17 pages, 6 figures, extended introduction, additional comment
Using Qubits to Measure Fidelity in Mesoscopic Systems
We point out the similarities in the definition of the `fidelity' of a
quantum system and the generating function determining the full counting
statistics of charge transport through a quantum wire and suggest to use flux-
or charge qubits for their measurement. As an application we use the notion of
fidelity within a first-quantized formalism in order to derive new results and
insights on the generating function of the full counting statistics.Comment: 5 pages, 1 figur
Full counting statistics for noninteracting fermions: Joint probability distributions
The joint probability distribution in the full counting statistics (FCS) for
noninteracting electrons is discussed for an arbitrary number of initially
separate subsystems which are connected at t=0 and separated at a later time. A
simple method to obtain the leading order long time contribution to the
logarithm of the characteristic function is presented which simplifies earlier
approaches. New explicit results for the determinant involving the scattering
matrices are found. The joint probability distribution for two leads is
discussed for Y-junctions and dots connected to four leads.Comment: 17 pages, 3 figure
Suppression of 2\pi\ phase-slip due to hidden zero modes in one dimensional topological superconductors
We study phase slips in one-dimensional topological superconducting wires.
These wires have been proposed as building blocks for topologically protected
qubits in which the quantum information is distributed over the length of the
device and thus is immune to local sources of decoherence. However, phase-slips
are non-local events that can result in decoherence. Phase slips in topological
superconductors are peculiar for the reason that they occur in multiples of
4\pi\ (instead of 2\pi\ in conventional superconductors). We re-establish this
fact via a beautiful analogy to the particle physics concept of dynamic
symmetry breaking by explicitly finding a "hidden" zero mode in the fermion
spectrum computed in the background of a 2\pi\ phase-slip. Armed with the
understanding of phase-slips in topological superconductors, we propose a
simple experimental setup with which the predictions can be tested by
monitoring tunneling rate of a superconducting flux quantum through a
topological superconducting wire.Comment: 18 pages,14 figures, Updated referenc
Grand zigzag knight's paths
We study the enumeration of different classes of grand knight's paths in the
plane. In particular, we focus on the subsets of zigzag knight's paths subject
to constraints. These constraints include ending at ordinate 0, bounded by a
horizontal line, confined within a tube, among other considerations. We present
our results using generating functions or direct closed-form expressions. We
derive asymptotic results, finding approximations for quantities such as the
probability that a zigzag knight's path stays in some area of the plane, or for
the average of the final height of such a path. Additionally, we exhibit some
bijections between grand zigzag knight's paths and some pairs of compositions.Comment: 21 pages, 9 figure
What is known about the health and living conditions of the indigenous people of northern Scandinavia, the Sami?
The Sami are the indigenous ethnic population of northern Scandinavia. Their health condition is poorly known, although the knowledge has improved over the last decade.The aim was to review the current information on mortality, diseases, and risk factor exposure in the Swedish Sami population.Health-related research on Sami cohorts published in scientific journals and anthologies was used to compare the health condition among the Sami and the majority non-Sami population. When relevant, data from the Sami populations in Swedish were compared with corresponding data from Norwegian and Finnish Sami populations.Life expectancy and mortality patterns of the Sami are similar to those of the majority population. Small differences in incidences of cancer and cardiovascular diseases have been reported. The traditional Sami lifestyle seems to contain elements that reduce the risk to develop cancer and cardiovascular diseases, e.g. physical activity, diet rich in antioxidants and unsaturated fatty acids, and a strong cultural identity. Reindeer herding is an important cultural activity among the Sami and is associated with high risks for accidents. Pain in the lower back, neck, shoulders, elbows, and hands are frequent among both men and women in reindeer-herding families. For men, these symptoms are related to high exposure to terrain vehicles, particularly snowmobile, whereas for women psychosocial risk factors seem to more important, e.g. poor social support, high effort, low reward, and high economical responsibilities.Although the health condition of the Sami population appears to be rather similar to that of the general Swedish population, a number of specific health problems have been identified, especially among the reindeer-herding Sami. Most of these problems have their origin in marginalization and poor knowledge of the reindeer husbandry and the Sami culture in the majority population. It is suggested that the most sustainable measure to improve the health among the reindeer-herding Sami would be to improve the conditions of the reindeer husbandry and the Sami culture
Wave-packet Formalism of Full Counting Statistics
We make use of the first-quantized wave-packet formulation of the full
counting statistics to describe charge transport of noninteracting electrons in
a mesoscopic device. We derive various expressions for the characteristic
function generating the full counting statistics, accounting for both energy
and time dependence in the scattering process and including exchange effects
due to finite overlap of the incoming wave packets. We apply our results to
describe the generic statistical properties of a two-fermion scattering event
and find, among other features, sub-binomial statistics for nonentangled
incoming states (Slater rank 1), while entangled states (Slater rank 2) may
generate super-binomial (and even super-Poissonian) noise, a feature that can
be used as a spin singlet-triplet detector. Another application is concerned
with the constant-voltage case, where we generalize the original result of
Levitov-Lesovik to account for energy-dependent scattering and finite
measurement time, including short time measurements, where Pauli blocking
becomes important.Comment: 20 pages, 5 figures; major update, new figures and explanations
included as well as a discussion about finite temperatures and subleading
logarithmic term
Design and Fabrication of the NASA Decoupler Pylon for the F-16 Aircraft, Addendum 2
The decoupler pylons which were originally designed and assembled with bushings in the pivot joints were retrofitted with roller bearings. This retrofit, the supporting analyses and the fixture tests of the modified pylons are reported in this document. The loads and stress analysis was directed toward the redesigned parts which were the pylon links and pins. The loads and stress analysis indicates that the pylons with the bearing installation have reduced capacity with respect to the bushing design. Fixture tests of the redesigned pylons were conducted in the GD/FW facility. Breakout friction tests and vibration tests were conducted. The tests show that the joint friction is approximately one-half the level with bearings as compared with the bushing installation. The vibration test data was used to tune the pylon mathematical simulation and this revised pylon simulation was used to recompute airplane modes of vibration. These computed modes of vibration were used in complete airplane symmetric and antisymmetric flutter and aeroservoelastic analyses
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