Electrical & Computer Engineering
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Item Bleaching Kinetics of Visual Pigments(1977) Resnik, Judith Arlene; Zajac, Felix E. III; Electrical & Computer Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)A rapid scanning microspectrophotometer (RMSP) has been developed and utilized to study the photoproducts resulting from the bleaching of rhodopsin in the isolated retina of the frog. The RMSP is capable of measuring absorption spectra at multiple wavelengths within the milliseconds and longer time domain. The unusual characteristic of the instrument is the use of a special cathode ray tube as a measuring light source. Spectral scanning is accomplished electronically, with a sampling interval of 600 microseconds for each waveband. A lock-in amplifier system enables the RMSP to be utilized as either a single or dual beam instrument. The results discussed in this dissertation have shown that hydrogen ion availability is a primary cofactor in determining the relative concentration of the metarhodopsin III photoproduct, with less appearing, in lieu of greater free retinal formation, at low pH levels. Metabolic factors have also been shown to influence the pathways of photoproduct decay. The most significant effect has been observed in nonacidic intracellular environments, with deficiencies in metabolic energy production also favoring the direct formation of free retinal from metarhodopsin II. The half-times of formation and decay of metarhodopsin III have also been observed to vary, depending on the extracellular environment of photoreceptor cells. In general, both halftimes tend to be greater when proportionately more metarhodopsin III 1s formed. The ratio of the two half-times, however, remains relatively constant, except in anoxic conditions, in which the decay half-time is significantly prolonged with respect to the formation half-time. Several problems associated with the control of experimental conditions have been discussed as they relate to photoproduct sequence and kinetics. The elimination of as many metabolic, ionic, and other insufficiently controlled conditions as possible has been pointed out as a necessary requirement for obtaining meaningful quantitative results. In addition, the baseline magnitude of the optical density of the retina, which is, in part, a quantification of light scattering, has been shown to be significantly larger in conditions of low intracellular pH or insufficient substrate supply. The utilization of this parameter as an indirect indicator of the probably sequence of photoproducts has been discussed. In conclusion, this research has provided a greater insight into the mechanisms affecting the later, slow photoproduct processes in isolated retinas. In particular, the interaction of hydrogen ions and metabolic factors influences the pathways of photoproduct decay in isolated retinas, subsequent to metarhodopsin II. The results and methods described here should be useful in establishing a context in which to study the faster mechanisms involved in photochemical and electrical transduction in photoreceptor cells. In addition, these results may become important in understanding the normal and pathological functionings of the eye.Item Sunspots, and the Solar Influence Upon High Frequency Radio Communications(1960) Jacobs, George; Reed, Henry R.; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)Item PRESENTATION OF A NEW HIGH-FREQUENCY COMMUNICATION SYSTEM PERFORMANCE PREDICTION TECHNIQUE(1965) Gatts, Thomas Fiscus Jr.; Reed, Henry R.; Electrical & Computer Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)The prediction technique developed by the National Bureau of Standards has been used extensively by high-frequency communicators. An adaption of this technique is used to demonstrate the type of results obtained when applied to the Buffalo, N.Y. to Boston, Mass. (B/B) link for January and July 1965. A new prediction technique is presented which will allow the HF communicator to predict system performance between the maximum useable frequency (MUF) and the lowest useable frequency (LUF) and which is flexible enough to allow system parameter changes to be made and the effect on the overall system determined. The new technique is demonstrated by applying it to the B/B link for January and July 1965 and displaying the results in the form of relative gain contours, which show the effect on communication capability of reducing the LUF by increasing system gain and the increase in process gain that may be achieved for the purpose of raising the data rate or decreasing transmission error rate. Some of the many applications of the results of this new technique are presented. The results are used: (1) to facilitate the selection of necessary operating frequencies to provide communication throughout a 24-hour period, (2) to estimate the severity and length of occurrence of multipath, (3) to investigate possible frequency adaption, and (4) to investigate possible power adaption.Item A Set of Karnaugh Map Manipulation Computer Routines for Use in Logic Design(1968) Shub, Charles Martin; Marcovitz, Alan B.; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)The Karnaugh map provides a convenient visual aid for the manipulation of switching functions for both the design engineer and the student of logic design. Algorithms for the minimization of switching functions by the manipulation of information displayed on a Karnaugh map are presented, along with a method of obtaining more information than was previously possible from the Karnaugh map. A dynamic, flexible, and easy to use collection of computer subroutines written in the MAD language to accomplish such manipulations as a subset of an entire logic design system of computer programs is described. A user's manual for the entire system is included, as well as descriptions of the programs used in conjunction with the map manipulation process. Several examples are included.Item Some Characteristics of Broadband Delta-Sigma Modulation(1971) Biegalski, Robert J.; Tretter, Steven; Electrical and Computer Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)This paper presents an analysis using correlation techniques of an idealized Delta-Sigma Modulation system. An analytical assumption of errors with a marginally Gaussian distribution is shown to yield accurate results for broadband modulation with a maximum input-output cross correlation. It is also shown that this maximum is greatest for the degenerate case of only "hard limiting" with no feedback and no integration. A case of highly correla~ed inputs for Delta- Sigma Modulation is also discussed to compare it with broad- band performance and "hard limiting."Item Study of a UHF Command Destruct Missile Antenna System(1960) Mullins, Elwood Hatcher; Schuchard, E.A.; Electrical and Computer Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)