Passive solar reflector satellite revisited

Passive light weight reflectors in space which direct the incident solar energy to a specified location on the Earth surface are proposed as an alternative system for the solar power satellite to overcome conversion losses and to avoid the need for photovoltaic cells. On Earth, either photovoltaic cells or a steam turbine alternator on a solar tower, or a similar conventional, relatively high efficiency cycle are used for electricity generation. The constraints which apply to the design of the optical system if a single satellite is placed in geostationary orbit are outlined. A single lens and a two lens system are discussed

Letters between Mary E. Polk and W. J. Kerr

Letters concerning a position at Utah Agricultural College

Letters between W. J. Kerr and Mary E. Polk

Letters concerning a position at Utah Agricultural College

The Statistics of the Environment Affect the Functional Architecture of Vision in Adulthood: A Reduce d Alphanumeric Category Effect in Canadian Mail Sorters

Letters are detected more efficiently among digits than among letters. This alphanumeric category effect suggests an architectural distinction between letter and number representation in human vision and dissociations between letter and number recognition following brain damage support this interpretation. Because letter and number recognition are not innate, this implies that experience can shape the functional architecture of vision. A possible explanation is that letters co-occur with letters in the environment while numbers co-occur with numbers; such statistics cause segregation of letter and number representations in artificial neural networks. To test the general hypothesis that environmental statistics affect the architecture of vision, and the specific hypothesis that within-category cooccurrence causes the alphanumeric category effect, we measured the effect in foreign mail sorters who process Canadian zip codes (which violate the co-occurrence statistics) and in control subjects. As predicted, foreign mail sorters showed a smaller category effec

A Simple Co-Occurrence Explanation for the Developmen t of Abstract Letter Identities

Evidence suggests that an early representation in the visual processing of orthography is neither visual nor phonological, but codes abstract letter identities (ALIs) independent of case, font, size, etc. How could the visual systeai come to develop such a representation? W e propose that, because many letters look similar regardless of case, font, etc., different visual forms of the same letter tend to appear in visually similar contexts (e.g., in the same words written in different ways) and that correlationbased learning in visual cortex picks up on this similarity among contexts to produce ALIs. W e present a simple selforganizing Hebbian neural network model that illustrates how this idea could work and that produces ALIs when presented with appropriate input

Scanning optical pyrometer for measuring temperatures in hollow cathodes

Life-limiting processes in hollow cathodes are determined largely by the temperature of the electron emitter. To support cathode life assessment, a noncontact temperature measurement technique which employs a stepper motor-driven fiber optic probe was developed. The probe is driven inside the hollow cathode and collects light radiated by the hot interior surface of the emitter. Ratio pyrometry is used to determine the axial temperature profile. Thermocouples on the orifice plate provide measurements of the external temperature during cathode operation and are used to calibrate the pyrometer system in situ with a small oven enclosing the externally heated cathode. The diagnostic method and initial measurements of the temperature distribution in a hollow cathode are discussed

Evidence for ion acceleration by oscillations in the discharge plasma of ion engines

The hollow cathode discharge plasma in ion engines is highly non-uniform, geometrically complex, and confined by a magnetic field; elucidating the mechanisms responsible for producing ions with anomalously high energies observed in the downstream regions of hollow cathodes will contribute to understanding the behavior of complex plasmas. Ions with energies in excess of ten times greater than the energy associated with electrostatic acceleration from the largest steady-state potential difference in the plasma discharge of ion engines have been detected