2,603 research outputs found
Combinational logic for generating gate drive signals for phase control rectifiers
Control signals for phase-delay rectifiers, which require a variable firing angle that ranges from 0 deg to 180 deg, are derived from line-to-line 3-phase signals and both positive and negative firing angle control signals which are generated by comparing current command and actual current. Line-to-line phases are transformed into line-to-neutral phases and integrated to produce 90 deg phase delayed signals that are inverted to produce three cosine signals, such that for each its maximum occurs at the intersection of positive half cycles of the other two phases which are inputs to other inverters. At the same time, both positive and negative (inverted) phase sync signals are generated for each phase by comparing each with the next and producing a square wave when it is greater. Ramp, sync and firing angle controls signals are than used in combinational logic to generate the gate firing control signals SCR gate drives which fire SCR devices in a bridge circuit
Measurement of neutron spectra in liquid hydrogen Quarterly progress report, period ending Dec. 17, 1965
Neutron spectra measurement in liquid hydrogen, water cooled fast neutron source, thermal neutron measurements, and liquid hydrogen facility checkout using nitroge
Measurement of neutron spectra in liquid hydrogen final report
Neutron spectrum measurement in liquid hydrogen and wate
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On the wrong track : equal access to knowledge and ability grouping in secondary social studies classes.
Gamma and neutron dose measurements for a thermal tungsten nuclear rocket critical experiment
Measurements of gamma and neutron dose distributions in core of thermal tungsten nuclear rocket experimen
Aeolian sand transport over a wet, sandy beach
Abstract Quantifying aeolian transport within the intertidal zone is critical to understanding feedbacks between aeolian and nearshore processes in coastal environments. Here, we report a field study of aeolian transport over a wet bed in the intertidal zone. Predominate winds and beach orientation were aligned during all field observations. Mean grain size of bed samples were 0.18 mm and moisture content ranged from 16 to 17%. Velocity profiles were measured with a vertical array of cup anemometers. Sustained wind velocities were 9.5 m/s at 93 cm above the bed with gusts reaching 13.5 m/s. Five saltation traps captured particles in transport from the bed to a height of 15 cm. Particles in transport were wet and the highest moisture content of trapped sediments was found in the lowest saltation trap. Vertical flux profiles show a higher concentration of flux closer to the bed (81 to 89% below 5 cm) than those measured over dry beds. Power and exponential decay functions were fit to our vertical flux profiles; the exponential decay function best fit flux profiles with larger β coefficients and smaller α estimates than those fit to dry bed profiles. Total flux models predict transport below Belly's (1964) fluid threshold of motion for moist beds and model performance improves when using a threshold for dry sand. Our results suggest transport over wet beds is fundamentally different from transport over dry beds. However, more research is needed to discern the mechanics driving deviations in flux profiles over wet beds in field environments
Deep space experiment to measure
Responding to calls from the National Science Foundation (NSF) for new
proposals to measure the gravitational constant , we offer an interesting
experiment in deep space employing the classic gravity train mechanism. Our
setup requires three bodies: a larger layered solid sphere with a cylindrical
hole through its center, a much smaller retroreflector which will undergo
harmonic motion within the hole and a host spacecraft with laser ranging
capabilities to measure round trip light-times to the retroreflector but
ultimately separated a significant distance away from the sphere-retroreflector
apparatus. Measurements of the period of oscillation of the retroreflector in
terms of host spacecraft clock time using existing technology could give
determinations of nearly three orders of magnitude more accurate than
current measurements here on Earth. However, significant engineering advances
in the release mechanism of the apparatus from the host spacecraft will likely
be necessary. Issues with regard to the stability of the system are briefly
addressed.Comment: 13 pp, 3 figs, accepted CQ
Possible Observational Criteria for Distinguishing Brown Dwarfs from Planets
The difference in formation process between binary stars and planetary
systems is reflected in their composition as well as their orbital
architecture, particularly orbital eccentricity as a function of orbital
period. It is suggested here that this difference can be used as an
observational criterion to distinguish between brown dwarfs and planets.
Application of the orbital criterion suggests that with three possible
exceptions, all of the recently-discovered substellar companions discovered to
date may be brown dwarfs and not planets. These criterion may be used as a
guide for interpretation of the nature of sub-stellar mass companions to stars
in the future.Comment: LaTeX, 11 pages including 2 figures, accepted for publication in the
Astrophysical Journal Letter
Measurement of neutron spectra in liquid hydrogen Quarterly progress report, period ending Mar. 17, 1966
Measurement of neutron spectra in liquid hydroge
Reevaluation and analysis of neutron spectra in liquid hydrogen Final report
Neutron spectra for various thicknesses of liquid hydroge
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