24,483 research outputs found
The radiation resistance of cylindrical shells
Radiation resistance of cylindrical shells in ideal compressible acoustic mediu
Development and evaluation of a device to simulate a sonic boom
A device to simulate the vibrational and acoustical properties of a sonic boom was developed and evaluated. The design employed a moving circular diaphragm which produced pressure variations by altering the volume of an air-tight enclosure that was located adjacent to an acoustical test chamber. A review of construction oriented problems, along with their solutions, is presented. The simulator is shown to produce the effects of sonic booms having pressure signatures with rise times as low as 5 milliseconds, durations as short as 80 milliseconds, and overpressures as high as 2.5 pounds per square foot. Variations in the signatures are possible by independent adjustments of the simulator. The energy spectral density is also shown to be in agreement with theory and with actual measurements for aircraft
Psychological distress and chronic obstructive pulmonary disease in the Renfrew and Paisley (MIDSPAN) study
Background: This study examined whether psychological distress might be a predictor of chronic obstructive pulmonary disease (COPD).
Method: The relation between psychological distress at baseline, measured by the general health questionnaire (GHQ), and chronic bronchitis three years later, as measured by the Medical Research Council (MRC) bronchitis questionnaire and forced expiratory flow in one second (FEV1), was examined in 1682 men and 2203 women from the Renfrew and Paisley (MIDSPAN) study. The analyses were run on men and women separately and adjustments were made for age, socioeconomic position, and lung function at baseline (FEV1). People with chronic diseases at baseline were then excluded to give a "healthy" baseline cohort. The effect of psychological distress on individual components of the MRC bronchitis questionnaire and FEV1 was also assessed.
Results: In multivariate analyses of the whole cohort baseline psychological distress in women was associated with reduced FEV1 at follow up (OR 1.31 95% CI 1.0 to 1.73) after adjustment. In women, in the healthy cohort, psychological distress was associated with chronic bronchitis (OR 2.00, 95% CI 1.16 to 3.46), symptoms of bronchial infection (OR 2.14, 95% CI 1.44 to 3.19), symptoms of breathlessness (OR 3.02, 95% CI 1.99 to 4.59), and reduced FEV1 (OR 1.62, 95% CI 1.13 to 2.32). In men psychological distress predicted symptoms of bronchial infection (OR 2.09, 95% CI 1.28 to 3.42).
Conclusion: This study supports research suggesting that psychological distress is associated with COPD and shows that psychological distress predicts COPD in women. The robustness of the association and the exact mechanism requires further investigation
Analysis of control concepts for gas and shaft-coupled V/STOL aircraft lift fan systems
For lift-fan powered V/STOL aircraft, two unconventional propulsion system types were proposed. The first type uses fans connected by hot gas ducting, and the second type uses fans connected by cross shafting. An analytical study identified the basic steady-state and dynamic characteristics for each type of system. For the gas-coupled system, the control concepts analyzed were variable-area fan turbines and throttling valves in the ducting. For the shaft-coupled system, the control concepts analyzed were variable-pitch fans and variable fan inlet guide vanes. All of these concepts are capable of meeting V/STOL aircraft control moment and transient response requirements when appropriate propulsion controls are used
Observation of a possible superflare on Proxima Centauri
We report the observation on UT 2017 July 1 of an unusually powerful flare detected in near-infrared continuum photometry of Proxima Centauri. During a campaign monitoring the star for possible exoplanet transits, we identified an increase in Sloan i' flux leading to an observed peak at BJD 2457935.996 that was at least 10 per cent over pre-flare flux in this band. It was followed by a two-component rapid decline in the first 100 s that became a slower exponential decay with time constant of 1350 s. A smaller flare event 1300 s after the first added an incremental peak flux increase of 1 per cent of pre-flare flux. Since the onset of the flare was not fully time resolved at a cadence of 62 s, its actual peak value is unknown but greater than the time average over a single exposure of 20 s. The i' band is representative of broad optical and near-IR continuum flux over which the integrated energy of the flare is 100 times the stellar luminosity. This meets the criteria that established the concept of superflares on similar stars. The resulting implied ultraviolet flux and space weather could have had an extreme effect on the atmospheres of planets within the star's otherwise habitable zone
Loss of redundant gene expression after polyploidization in plants
Based on chromosomal location data of genes encoding 28 biochemical systems in allohexaploid wheat,Triticum aestivum L. (genomes AABBDD), it is concluded that the proportions of systems controlled by triplicate, duplicate, and single loci are 57%, 25%, and 18% respectively
The effect of short ray trajectories on the scattering statistics of wave chaotic systems
In many situations, the statistical properties of wave systems with chaotic
classical limits are well-described by random matrix theory. However,
applications of random matrix theory to scattering problems require
introduction of system specific information into the statistical model, such as
the introduction of the average scattering matrix in the Poisson kernel. Here
it is shown that the average impedance matrix, which also characterizes the
system-specific properties, can be expressed in terms of classical trajectories
that travel between ports and thus can be calculated semiclassically.
Theoretical results are compared with numerical solutions for a model
wave-chaotic system
Query Complexity of Approximate Equilibria in Anonymous Games
We study the computation of equilibria of anonymous games, via algorithms
that may proceed via a sequence of adaptive queries to the game's payoff
function, assumed to be unknown initially. The general topic we consider is
\emph{query complexity}, that is, how many queries are necessary or sufficient
to compute an exact or approximate Nash equilibrium.
We show that exact equilibria cannot be found via query-efficient algorithms.
We also give an example of a 2-strategy, 3-player anonymous game that does not
have any exact Nash equilibrium in rational numbers. However, more positive
query-complexity bounds are attainable if either further symmetries of the
utility functions are assumed or we focus on approximate equilibria. We
investigate four sub-classes of anonymous games previously considered by
\cite{bfh09, dp14}.
Our main result is a new randomized query-efficient algorithm that finds a
-approximate Nash equilibrium querying
payoffs and runs in time . This improves on the running
time of pre-existing algorithms for approximate equilibria of anonymous games,
and is the first one to obtain an inverse polynomial approximation in
poly-time. We also show how this can be utilized as an efficient
polynomial-time approximation scheme (PTAS). Furthermore, we prove that
payoffs must be queried in order to find any
-well-supported Nash equilibrium, even by randomized algorithms
Scattering a pulse from a chaotic cavity: Transitioning from algebraic to exponential decay
The ensemble averaged power scattered in and out of lossless chaotic cavities
decays as a power law in time for large times. In the case of a pulse with a
finite duration, the power scattered from a single realization of a cavity
closely tracks the power law ensemble decay initially, but eventually
transitions to an exponential decay. In this paper, we explore the nature of
this transition in the case of coupling to a single port. We find that for a
given pulse shape, the properties of the transition are universal if time is
properly normalized. We define the crossover time to be the time at which the
deviations from the mean of the reflected power in individual realizations
become comparable to the mean reflected power. We demonstrate numerically that,
for randomly chosen cavity realizations and given pulse shapes, the probability
distribution function of reflected power depends only on time, normalized to
this crossover time.Comment: 23 pages, 5 figure
TRIAD - Preliminary design of an operational earth resources survey system. 1969 summer faculty fellowship program in engineering systems design
TRIAD, preliminary design of operational earth resources survey syste
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