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

Computational simulation of probabilistic lifetime strength for aerospace materials subjected to high temperature, mechanical fatigue, creep and thermal fatigue

This report presents the results of a fourth year effort of a research program, conducted for NASA-LeRC by the University of Texas at San Antonio (UTSA). The research included on-going development of methodology that provides probabilistic lifetime strength of aerospace materials via computational simulation. A probabilistic material strength degradation model, in the form of a randomized multifactor interaction equation, is postulated for strength degradation of structural components of aerospace propulsion systems subject to a number of effects or primitive variables. These primitive variables may include high temperature, fatigue or creep. In most cases, strength is reduced as a result of the action of a variable. This multifactor interaction strength degradation equation has been randomized and is included in the computer program, PROMISS. Also included in the research is the development of methodology to calibrate the above-described constitutive equation using actual experimental materials data together with regression analysis of that data, thereby predicting values for the empirical material constants for each effect or primitive variable. This regression methodology is included in the computer program, PROMISC. Actual experimental materials data were obtained from industry and the open literature for materials typically for applications in aerospace propulsion system components. Material data for Inconel 718 has been analyzed using the developed methodology

An objective check list for the evaluation of student councils in secondary schools

Thesis (M.A.)--Boston University, 1949. This item was digitized by the Internet Archive

A Summary of the Facts and a Restatement of the Theory of Sound Localization

Experimentation has repeatedly demonstrated that phase, time and intensity, as physical variants, function in much the same manner in determining the directional localization of sound. Their effects are alike; the relationship of the angular displacement to the differences in the stimuli in each case is approximately the same; each factor has its optimal effectiveness; the very slight differences in the stimuli in each case are not perceived as differences in phase, time and intensity as such; and each factor may modify the effectiveness of the others. But, in the complex conditions of ordinary hearing, does either of these factors predominate in determining the directional localization, or are all of these factors reducible to some common factor, or do they each and all contribute to a pattern of effects that results in directional perception

A Modern Approach to Elementary Analysis

Recall, on the one hand, that mathematics has grown up in the past one hundred fifty years. With the acceptance of non-euclidean geometrics, of algebraic structures beginning with groups, and of symbolic logic, the very idea of what mathematics is had to change. It took a while for mathematicians to digest the ideas of men like Lobachevski, Galois, and Boole. The Bourbaki notion of mathematics as a \u27storehouse of structures\u27 is new in the last few decades

The Phase-Theory as a Time Theory in Sound Localization

In a preliminary study of the phenomena of localization by the method of temporal difference of arrival of sound at the two ears, we find results which so nearly coincide with results obtained by Stewart (1) and by Halverson (3) who studied the problem by means of continuous sounds of varying phase relations at the ears, that we feel justified in presenting here the phase-theory as a time-theory in sound localization

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

Stellar abundances and molecular hydrogen in high-redshift galaxies -the far-ultraviolet view

FUSE spectra of star-forming regions in nearby galaxies are compared to composite spectra of Lyman-break galaxies (LBGs), binned by strength of Lyman alpha emission and by mid-UV luminosity. Several far-UV spectral features, including lines dominated by stellar wind and by photospheric components, are very sensitive to stellar abundances. Their measurement in Lyman-break galaxies is compromised by the strong interstellar absorption features, allowing in some cases only upper limits. The derived C and N abundances in the LBGs are no higher than half solar (scaled to oxygen abundance for comparison with emission-line analyses), independent of the strength of Lyman alpha emission. P V absorption indicates abundances as low as 0.1 solar, with an upper limit near 0.4 solar in the reddest and weakest-emission galaxies. Unresolved interstellar absorption components would further lower the derived abundances. Trends of line strength, and derived abundances, are stronger with mid-UV luminosity than with Lyman-alpha strength. H2 absorption in the Lyman and Werner bands is very weak in the LBGs. Template H2 absorption spectra convolved to appropriate resolution show that strict upper limits N(H2)< 10^18 cm^-2 apply in all cases, with more stringent values appropriate for the stronger-emission composites and for mixes of H2 level populations like those on Milky Way sight lines. Since the UV-bright regions are likely to be widespread in these galaxies, these results rule out massive diffuse reservoirs of H2, and suggest that the dust/gas ratio is already fairly large at z~3.Comment: Astron J., in press (June 2006