17,213 research outputs found
A Hybrid Mode Model of the Blazhko Effect, Shown to Accurately Fit Kepler Data for RR Lyr
The waveform for Blazhko stars can be substantially different during the
ascending and descending parts of the Blazhko cycle. A hybrid model, consisting
of two component oscillators of the same frequency, is proposed as a means to
fit the data over the entire cycle. One component exhibits a sawtooth-like
velocity waveform while the other is nearly sinusoidal. One method of
generating such a hybrid is presented: a nonlinear model is developed for the
first overtone mode, which, if excited to large amplitude, is found to drop
strongly in frequency and become highly non-sinusoidal. If the frequency drops
sufficiently to become equal to the fundamental frequency, the two can become
phase locked and form the desired hybrid. A relationship is assumed between the
hybrid mode velocity and the observed light curve, which is approximated as a
power series. An accurate fit of the hybrid model is made to actual Kepler data
for RR Lyr. The sinusoidal component may tend to stabilize the period of the
hybrid which is found in real Blazhko data to be extremely stable. It is
proposed that the variations in amplitude and phase might result from a
nonlinear interaction with a third mode, possibly a nonradial mode at 3/2 the
fundamental frequency. The hybrid model also applies to non-Blazhko RRab stars
and provides an explanation for the light curve bump. A method to estimate the
surface gravity is also proposed.Comment: No major changes. Emphasizes the ability of the hybrid mode to
explain changes in the pulsation waveform throughout the Blazhko cycle that
may otherwise be problematic. Notes that first-overtone/fundamental
combination is just one possible means to generate the hybrid and suggests
alternatives. Notes similarity of bump generation in this model to the
resonance mechanism in bump Cepheid
Digital controller for a Baum folding machine
A digital controller for controlling the operation of a folding machine enables automatic folding of a desired number of sheets responsive to entry of that number into a selector. The controller includes three decade counter stages for corresponding rows of units, tens and hundreds push buttons. Each stage including a decimal-to-BCD encoder, a buffer register, and a digital or binary counter. The BCD representation of the selected count for each digit is loaded into the respective decade down counters. Pulses generated by a sensor and associated circuitry are used to decrease the count in the decade counters. When the content of the decade counter reaches either 0 or 1, a solenoid control valve is actuated which interrupts operation of the machine. A repeat switch, when actuated, prevents clearing of the buffer registers so that multiple groups of the same number of sheets can be folded without reentering the number into the selector
Flight test validation of a design procedure for digital autopilots
Commercially available general aviation autopilots are currently in transition from an analogue circuit system to a computer implemented digital flight control system. Well known advantages of the digital autopilot include enhanced modes, self-test capacity, fault detection, and greater computational capacity. A digital autopilot's computational capacity can be used to full advantage by increasing the sophistication of the digital autopilot's chief function, stability and control. NASA's Langley Research Center has been pursuing the development of direct digital design tools for aircraft stabilization systems for several years. This effort has most recently been directed towards the development and realization of multi-mode digital autopilots for GA aircraft, conducted under a SPIFR-related program called the General Aviation Terminal Operations Research (GATOR) Program. This presentation focuses on the implementation and testing of a candidate multi-mode autopilot designed using these newly developed tools
Advanced symbology for general aviation approach to landing displays
A set of flight tests designed to evaluate the relative utility of candidate displays with advanced symbology for general aviation terminal area instrument flight rules operations are discussed. The symbology was previously evaluated as part of the NASA Langley Research Center's Terminal Configured Vehicle Program for use in commercial airlines. The advanced symbology included vehicle track angle, flight path angle and a perspective representation of the runway. These symbols were selectively drawn on a cathode ray tube (CRT) display along with the roll attitude, pitch attitude, localizer deviation and glideslope deviation. In addition to the CRT display, the instrument panel contained standard turn and bank, altimeter, rate of climb, airspeed, heading, and engine instruments. The symbology was evaluated using tracking performance and pilot subjective ratings for an instrument landing system capture and tracking task
Music and dance as a coalition signaling system
Evidence suggests that humans have neurological specializations for music processing, but a compelling adaptationist account of music and dance is lacking. The sexual selection hypothesis cannot easily account for the widespread performance of music and dance in groups (especially synchronized performances), and the social bonding hypothesis has severe theoretical difficulties. Humans are unique among the primates in their ability to form cooperative alliances between groups in the absence of consanguineal ties. We propose that this unique form of social organization is predicated on music and dance. Music and dance may have evolved as a coalition signaling system that could, among other things, credibly communicate coalition quality, thus permitting meaningful cooperative relationships between groups. This capability may have evolved from coordinated territorial defense signals that are common in many social species, including chimpanzees. We present a study in which manipulation of music synchrony significantly altered subjects’ perceptions of music quality, and in which subjects’ perceptions of music quality were correlated with their perceptions of coalition quality, supporting our hypothesis. Our hypothesis also has implications for the evolution of psychological mechanisms underlying cultural production in other domains such as food preparation, clothing and body decoration, storytelling and ritual, and tools and other artifacts
Performance of the Lester battery charger in electric vehicles
Tests are performed on an improved battery charger. The primary purpose of the testing is to develop test methodologies for battery charger evaluation. Tests are developed to characterize the charger in terms of its charge algorithm and to assess the effects of battery initial state of charge and temperature on charger and battery efficiency. Tests show this charger to be a considerable improvement in the state of the art for electric vehicle chargers
Development and study of chemical vapor deposited tantalum base alloys
A technique for the chemical vapor deposition of alloys was developed. The process, termed pulsing, involves the periodic injection of reactant gases into a previously-evacuated reaction chamber where they blanket the substrate almost instantaneously. Formation of alternating layers of the alloy components and subsequent homogenization allows the formation of an alloy of uniform composition with the composition being determined by the duration and relative numbers of the various cycles. The technique has been utilized to produce dense alloys of uniform thickness and composition (Ta- 10 wt % W) by depositing alternating layers of Ta and W by the hydrogen reduction of TaCl5 and WCl6. A similar attempt to deposit a Ta - 8 wt % W - 2 wt% Hf alloy was unsuccessful because of the difficulty in reducing HfCl4 at temperatures below those at which gas phase nucleation of Ta and W occurred
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