The automated array assembly task of the low-cost silicon solar array project, phase 2

Several specific processing steps as part of a total process sequence for manufacturing silicon solar cells were studied. Ion implantation was identified as the preferred process step for impurity doping. Unanalyzed beam ion implantation was shown to have major cost advantages over analyzed beam implantation. Further, high quality cells were fabricated using a high current unanalyzed beam. Mechanically masked plasma patterning of silicon nitride was shown to be capable of forming fine lines on silicon surfaces with spacings between mask and substrate as great as 250 micrometers. Extensive work was performed on advances in plated metallization. The need for the thick electroless palladium layer was eliminated. Further, copper was successfully utilized as a conductor layer utilizing nickel as a barrier to copper diffusion into the silicon. Plasma etching of silicon for texturing and saw damage removal was shown technically feasible but not cost effective compared to wet chemical etching techniques

Effects of Parkinson’s disease on optic flow perception for heading direction during navigation

Visuoperceptual disorders have been identified in individuals with Parkinson’s disease (PD) and may affect the perception of optic flow for heading direction during navigation. Studies in healthy subjects have confirmed that heading direction can be determined by equalizing the optic flow speed (OS) between visual fields. The present study investigated the effects of PD on the use of optic flow for heading direction, walking parameters, and interlimb coordination during navigation, examining the contributions of OS and spatial frequency (dot density). Twelve individuals with PD without dementia, 18 age-matched normal control adults (NC), and 23 young control adults (YC) walked through a virtual hallway at about 0.8 m/s. The hallway was created by random dots on side walls. Three levels of OS (0.8, 1.2, and 1.8 m/s) and dot density (1, 2, and 3 dots/m2) were presented on one wall while on the other wall, OS and dot density were fixed at 0.8 m/s and 3 dots/m2, respectively. Three-dimensional kinematic data were collected, and lateral drift, walking speed, stride frequency and length, and frequency, and phase relations between arms and legs were calculated. A significant linear effect was observed on lateral drift to the wall with lower OS for YC and NC, but not for PD. Compared to YC and NC, PD veered more to the left under OS and dot density conditions. The results suggest that healthy adults perceive optic flow for heading direction. Heading direction in PD may be more affected by the asymmetry of dopamine levels between the hemispheres and by motor lateralization as indexed by handedness.Published versio

Aerosol chemical composition and distribution during the Pacific Exploratory Mission (PEM) Tropics

Distributions of aerosol-associated soluble ions over much of the South Pacific were determined by sampling from the NASA DC-8 as part of the Pacific Exploratory Mission (PEM) Tropics campaign. The mixing ratios of all ionic species were surprisingly low throughout the free troposphere (2-12 km), despite the pervasive influence from biomass burning plumes advecting over the South Pacific from the west during PEM-Tropics. At the same time, the specific activity of 7Be frequently exceeded 1000 fCi m-3 through much of the depth of the troposphere. These distributions indicate that the plumes must have been efficiently scavenged by precipitation (removing the soluble ions), but that the scavenging must have occurred far upwind of the DC-8 sampling regions (otherwise 7Be activities would also have been low). This inference is supported by large enhancements of HNO3 and carboxylic acids in many of the plumes, as these soluble acidic gases would also be readily scavenged in any precipitation events. Decreasing mixing ratios of NH4 + with altitude in all South Pacific regions sampled provide support for recent suggestions that oceanic emissions of NH3 constitute a significant source far from continents. Our sampling below 2 km reaffirms the latitudinal pattern in the methylsulfonate/non-sea-salt sulfate (MSA/nss SO4 =) molar ratio established through surface-based and shipboard sampling, with values increasing from \u3c0.05 in the tropics to nearly 0.6 at 70°S. However, we also found very high values of this ratio (0.2-0.5) at 10 km altitude above the intertropical convergence zone near 10°N. It appears that wet convective pumping of dimethylsulfide from the tropical marine boundary layer is responsible for the high values of the MSA/nss SO4 = ratio in the tropical upper troposphere. This finding complicates use of this ratio to infer the zonal origin of biogenic S transported long distances. Copyright 1999 by the American Geophysical Union

Elevated atmospheric sulfur levels off the Peruvian coast

Elevated levels of non‐sea‐salt sulfate and SO2 in samples collected off the west coast of South America indicate that there is a major source of atmospheric sulfur in the region of southern Peru and northern Chile. During a 1983 cruise, observed concentrations of non‐sea‐salt sulfur, SO2, selenium, arsenic, and antimony were comparable to levels reported for moderately polluted urban air. In contrast, methanesulfonic acid levels were typical of coastal marine air. Clearly, the elevated atmospheric sulfur levels in this region cannot be ascribed to oceanic organosulfur emissions. The major inputs are tentatively attributed to the smelting of sulfide ores which is a major industry in this region. The transport of smelter derived aerosols to this region may have a number of consequences for the atmospheric and oceanic chemistry of the Peruvian upwelling area

Adaptively-refined overlapping grids for the numerical solution of systems of hyperbolic conservation laws

Adaptive mesh refinement (AMR) in conjunction with higher-order upwind finite-difference methods have been used effectively on a variety of problems in two and three dimensions. In this paper we introduce an approach for resolving problems that involve complex geometries in which resolution of boundary geometry is important. The complex geometry is represented by using the method of overlapping grids, while local resolution is obtained by refining each component grid with the AMR algorithm, appropriately generalized for this situation. The CMPGRD algorithm introduced by Chesshire and Henshaw is used to automatically generate the overlapping grid structure for the underlying mesh

A dynamical approach to gestural patterning in speech production.

In this article, we attempt to reconcile the linguistic hypothesis that speech involves an underlying sequencing of abstract, discrete, context-independent units, with the empirical observation of continuous, context-dependent interleaving of articulatory movements. To this end, we first review a previously proposed task-dynamic model for the coordination and control of the speech articulators. We then describe an extension of this model in which invariant speech units (gestural primitives) are identified with context-independent sets of parameters in a dynamical system having two functionally distinct but interacting levels. The intergesturallevel is defined according to a set of activation coordinates; the interarticulator level is defined according to both model articulator and tract-variable coordinates. In the framework of this extended model, coproduction effects in speech are described in terms of the blending dynamics defined among a set of temporally overlapping active units; the relative timing of speech gestures is formulated in terms of the serial dynamics that shape the temporal patterning of onsets and offsets in unit activations. Implications of this approach for certain phonological issues are discussed, and a range of relevant experimental data on speech and limb motor control is reviewed