1,232 research outputs found
Space shuttle nonmetallic materials age life prediction
The chemiluminescence from samples of polybutadiene, Viton, Teflon, Silicone, PL 731 Adhesive, and SP 296 Boron-Epoxy composite was measured at temperatures from 25 to 150 C. Excellent correlations were obtained between chemiluminescence and temperature. These correlations serve to validate accelerated aging tests (at elevated temperatures) designed to predict service life at lower temperatures. In most cases, smooth or linear correlations were obtained between chemiluminescence and physical properties of purified polymer gums, including the tensile strength, viscosity, and loss tangent. The latter is a complex function of certain polymer properties. Data were obtained with far greater ease by the chemiluminescence technique than by the conventional methods of study. The chemiluminescence from the Teflon (Halon) samples was discovered to arise from trace amounts of impurities, which were undetectable by conventional, destructive analysis of the sample
Prediction of service life of polymeric sealant compositions for fuel tanks in aerospace structures from measurements of viscoelastic properties Annual report
Prediction of service life of polymeric sealers for fuel tanks from viscoelastic measurement
Full-scale wind tunnel-investigation of the Advanced Technology Light Twin-Engine airplane (ATLIT)
An investigation was conducted to evaluate the aerodynamic performance, stability, and control characteristics of the Advanced Technology Light Twin Engine airplane (ATLIT). Data were measured over an angle of attack range from -4 deg to 20 deg for various angles of sideslip between -5 deg and 15 deg at Reynolds numbers of 0.0000023 and 0.0000035 for various settings of power and flap deflection. Measurements were also made by means of special thrust torque balances to determine the installed propeller characteristics. Part of the investigation was devoted to drag cleanup of the basic airplane and to the evaluation of the effect of winglets on drag and stability
Analysis of the linearity characteristics, tape recorders and compensation effects in the FM/FM telemetry system
Linearity characteristics, tape recorder effects, and tape speed compensation effects in FM/FM TELEMETRY syste
The fundamental solution and Strichartz estimates for the Schr\"odinger equation on flat euclidean cones
We study the Schr\"odinger equation on a flat euclidean cone of cross-sectional radius , developing
asymptotics for the fundamental solution both in the regime near the cone point
and at radial infinity. These asymptotic expansions remain uniform while
approaching the intersection of the "geometric front", the part of the solution
coming from formal application of the method of images, and the "diffractive
front" emerging from the cone tip. As an application, we prove Strichartz
estimates for the Schr\"odinger propagator on this class of cones.Comment: 21 pages, 4 figures. Minor typos corrected. To be published in Comm.
Math. Phy
Poincar\'e Husimi representation of eigenstates in quantum billiards
For the representation of eigenstates on a Poincar\'e section at the boundary
of a billiard different variants have been proposed. We compare these
Poincar\'e Husimi functions, discuss their properties and based on this select
one particularly suited definition. For the mean behaviour of these Poincar\'e
Husimi functions an asymptotic expression is derived, including a uniform
approximation. We establish the relation between the Poincar\'e Husimi
functions and the Husimi function in phase space from which a direct physical
interpretation follows. Using this, a quantum ergodicity theorem for the
Poincar\'e Husimi functions in the case of ergodic systems is shown.Comment: 17 pages, 5 figures. Figs. 1,2,5 are included in low resolution only.
For a version with better resolution see
http://www.physik.tu-dresden.de/~baecker
Amplitude dependent frequency, desynchronization, and stabilization in noisy metapopulation dynamics
The enigmatic stability of population oscillations within ecological systems
is analyzed. The underlying mechanism is presented in the framework of two
interacting species free to migrate between two spatial patches. It is shown
that that the combined effects of migration and noise cannot account for the
stabilization. The missing ingredient is the dependence of the oscillations'
frequency upon their amplitude; with that, noise-induced differences between
patches are amplified due to the frequency gradient. Migration among
desynchronized regions then stabilizes a "soft" limit cycle in the vicinity of
the homogenous manifold. A simple model of diffusively coupled oscillators
allows the derivation of quantitative results, like the functional dependence
of the desynchronization upon diffusion strength and frequency differences. The
oscillations' amplitude is shown to be (almost) noise independent. The results
are compared with a numerical integration of the marginally stable
Lotka-Volterra equations. An unstable system is extinction-prone for small
noise, but stabilizes at larger noise intensity
Fuelling and moult in Red Knots before northward departure:A visual evaluation of differences between ages, sexes and subspecies
The departure of migratory birds from their non-breeding grounds is thought to be driven by the phenology of their breeding destination. In north-west Australia, two plumage morphs of Red Knot (Calidris canutus) prepare for a 5500-km journey to Yellow Sea staging areas. These morphs are recognised as the subspecies C. c. piersmai and C. c. rogersi, which breed at different latitudes and have different seasonalities. From February to May 2011, we observed the migratory preparation of individually marked birds of known age, sex and type. This enabled a comparison of fuelling rates and pre-alternate moult among these classes. First-year birds did not prepare for migration. Second-year birds accumulated smaller fuel stores and reached lower plumage scores than adults. Adults of both types reached their highest abdominal profile scores by the end of April when they were last observed in Roebuck Bay. This lack of difference between types in the timing of fuelling and departure is surprising. Based on the differences in staging and breeding phenology, C. c. rogersi is expected to leave north-west Australia 2–4 weeks before C. c. piersmai. Assuming that types and subspecies are equivalent, our findings in combination with other research on Red Knots in the East Asian–Australasian Flyway suggest that it takes more than breeding origin alone to explain annual cycles in migratory birds. Concurrent migratory schedules imply that, during northward staging in the Yellow Sea, there is strong variation in fuelling rates between and within subspecies depending on non-breeding origin. The ongoing loss of staging habitat may therefore have differential effects on Red Knots in the East Asian–Australasian Flyway
Internationally trained pharmacists in Great Britain: what do registration data tell us about their recruitment?
This is an Open Access article distributed under the terms of the Creative Commons Attribution Licens
A statistical investigation of the effects contributed by tape recorders and by wow and flutter of magnetic tape on the accuracy of a telemetry system Technical report no. 15
Effects contributed by tape recorders and by wow and flutter of magnetic tape on accuracy of telemetry syste
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