32,176 research outputs found
A comparison of the results of dynamic wind-tunnel tests with theoretical predictions for an aeromechanical gust-alleviation system for light airplanes
Dynamic wind tunnel tests have been conducted on a 1/6-scale model of a general aviation airplane equipped with an all-mechanical gust alleviation system which uses auxiliary aerodynamic surfaces to drive the flaps. The longitudinal short period motions were studied under simulated gust conditions in order to verify the mathematical model used in a previous study to predict the performance of the full scale system and determine the amount of normal acceleration alleviation which could be attained. The model responses were measured for different configurations with the system active and without the system active for comparison. The tests confirmed the general relationships between the experimental variables and the model responses predicted by the mathematical model, but there were significant differences in the magnitudes of the responses. The experimental results for the model were used to estimate a reduction of 30 percent in the rms normal acceleration response of a similar full scale airplane in atmospheric turbulence
Development of sprayed ceramic seal systems for turbine gas path sealing
A ceramic seal system is reported that employs plasma-sprayed graded metal/ceramic yttria stabilized zirconium oxide (YSZ). The performance characteristics of several YSZ configurations were determined through rig testing for thermal shock resistance, abradability, and erosion resistance. Results indicate that this type of sealing system offers the potential to meet operating requirements of future gas turbine engines
Evolution of a localized thermal explosion in a reactive gas
Experimental observations of ignition in premixed gaseous reactants indicate that perfectly homogeneous initiation is practically unrealizable. Instead, combustion first sets in, as a rule, at small, discrete sites where inherent inhomogeneities cause chemical activity to proceed preferentially and lead to localized explosions. Combustion waves propagating away from these hot spots or reaction centers eventually envelop the remaining bulk. This study examines the spatial structure and temporal evolution of a hot spot for a model involving Arrhenius kinetics. The hot spot, characterized by peaks in pressure and temperature with little diminution in local density, is shown to have one of two possible self-similar structures. The analysis employs a combination of asymptotics and numerics, and terminates when pressure and temperature in the explosion have peaked
p-wave Feshbach molecules
We have produced and detected molecules using a p-wave Feshbach resonance
between 40K atoms. We have measured the binding energy and lifetime for these
molecules and we find that the binding energy scales approximately linearly
with magnetic field near the resonance. The lifetime of bound p-wave molecules
is measured to be 1.0 +/- 0.1 ms and 2.3 +/- 0.2 ms for the m_l = +/- 1 and m_l
= 0 angular momentum projections, respectively. At magnetic fields above the
resonance, we detect quasi-bound molecules whose lifetime is set by the
tunneling rate through the centrifugal barrier
Preliminary Performance of the Advanced Dental Admission Test (ADAT): Association Between ADAT Scores and Other Variables for Applicants to Residency Programs at a U.S. Dental School
Historically, dental residency programs have used numerical assessment criteria to evaluate and identify qualified candidates for admission. Recent elimination of such assessment tools has undermined many programs’ holistic evaluation process. The Advanced Dental Admission Test (ADAT) was developed and recently piloted in hopes of addressing this issue. The aim of this study was to evaluate the preliminary performance and validity of the ADAT by exploring the association between ADAT scores and other variables for a sample of applicants to residency programs. The WebAdMIT admissions database was used to identify the test scores and educational and demographic information of 92 individuals who completed the pilot ADAT and were seeking a 2017 postgraduate specialty position at Indiana University School of Dentistry. The results showed that the ADAT had strong to weak correlations with certain applicant variables (p<0.05). No significant differences were found for age, race, school location, or country of origin. However, males performed better than females (p<0.05), and non-Hispanics performed better than Hispanics (p<0.01). ADAT component scores were also higher for individuals with a history of research activity (p<0.05). This study found that significant associations existed between the ADAT and indices typically associated with competitive applicants. These findings suggest that the ADAT may serve as a useful numerical assessment instrument, with the potential to identify high-performing candidates. Furthermore, the ADAT seemed to be a plausible option for programs seeking to incorporate a quantitative assessment instrument as part of a holistic candidate selection process
Children's computation of complex linguistic forms: a study of frequency and imageability effects.
This study investigates the storage vs. composition of inflected forms in typically-developing children. Children aged 8-12 were tested on the production of regular and irregular past-tense forms. Storage (vs. composition) was examined by probing for past-tense frequency effects and imageability effects--both of which are diagnostic tests for storage--while controlling for a number of confounding factors. We also examined sex as a factor. Irregular inflected forms, which must depend on stored representations, always showed evidence of storage (frequency and/or imageability effects), not only across all children, but also separately in both sexes. In contrast, for regular forms, which could be either stored or composed, only girls showed evidence of storage. This pattern is similar to that found in previously-acquired adult data from the same task, with the notable exception that development affects which factors influence the storage of regulars in females: imageability plays a larger role in girls, and frequency in women. Overall, the results suggest that irregular inflected forms are always stored (in children and adults, and in both sexes), whereas regulars can be either composed or stored, with their storage a function of various item- and subject-level factors
TETRA Observation of Gamma Rays at Ground Level Associated with Nearby Thunderstorms
Terrestrial Gamma ray Flashes (TGFs) -- very short, intense bursts of
electrons, positrons, and energetic photons originating from terrestrial
thunderstorms -- have been detected with satellite instruments. TETRA, an array
of NaI(Tl) scintillators at Louisiana State University, has now been used to
detect similar bursts of 50 keV to over 2 MeV gamma rays at ground level. After
2.6 years of observation, twenty-four events with durations 0.02- 4.2 msec have
been detected associated with nearby lightning, three of them coincident events
observed by detectors separated by ~1000 m. Nine of the events occurred within
6 msec and 3 miles of negative polarity cloud-to-ground lightning strokes with
measured currents in excess of 20 kA. The events reported here constitute the
first catalog of TGFs observed at ground level in close proximity to the
acceleration site.Comment: To be published in Journal of Geophysical Research: Space Phys. 118,
Models of planetary rings
The Voyager occultations provide several uniform and high quality data sets for Saturn, Uranus, and Neptune. These data are intercompared, and theoretical models for the particle sizes and the particle transport are developed. The major topics covered include: ring size distribution, torques and resonances, and satellite wakes
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