Equivalent oxygen percentage as a function of hydration in hydrogel lenses: an in vivo study

Although many investigations have examined the parameters of hydrogel lens hydration loss, the in vivo effect (in humans) on lens oxygen behavior has not been characterized previously. Human subjects wore 2 different lenses (a thin, 38% water polymacon lens and a thin, 55% water bufilcon lens) for 5-min periods under either fully hydrated (i.e., with saline regularly applied to the lens) or partially hydrated (i.e., with "normal" wear of 1 blink every 5 s) conditions. An equivalent oxygen percentage (EOP) technique and a gravimetric method were used to determine lens oxygen behavior and hydration, respectively. The hydration results demonstrate that significant lens dehydration occurs during the partially hydrated (normal blink rate) condition compared to the in situ, fully hydrated situation. A corresponding, statistically significant diminution in oxygen equivalency was also observed.     

New class of microminiature Joule — Thomson refrigerator and vacuum package

Progress is reported on the development of a two-stage, fast cooldown Joule — Thomson refrigerator using nitrogen gas and a nitrogen — hydrocarbon gas mixture as the refrigerants. The refrigerator incorporates a microminiature Venturi pump to reduce the pressure of the exhaust of the main boiler to bring the operating temperature of the cold stage to < 70 K in as little as 10 s. The vacuum package for the refrigerator contains no organic materials and is designed to provide a ten year shelf life. Special glass strengthening techniques are being used to achieve cooler survival of acceleration tests of up to 100 000g.     

Degradation of mechanical properties after 100° to 250 °c storage of 25 μm Al-1 pct Si microelectronic interconnect wire

Degradation of mechanical properties of 25 μm Al-1 pct Si wire stored at 100° to 250 °C in an air atmosphere has been investigated utilizing mechanical, structural, and kinetic approaches. Forty pct of the strength of wires stored at 100 °C and 90 pct of the strength of wires stored at 250 °C disappeared within the first twenty-four (24) hours. Elongation measurements showed that the wire can be embrittled at temperatures as low as 200 °C within twenty-four (24) hours, and elongation can decrease to less than 1 pct within this time at 200 °C. Scanning electron micrographs of electro-polished wire revealed particles distributed throughout the wire which increase in size as a function of annealing time and temperature. A kinetic analysis showed that the particle coarsening was controlled by a 97 ±34 kJ/mole activation energy process. These observations are consistent with earlier findings^1,2,3 that silicon coarsens in aluminum with an activation energy of 118 ±8 kJ/mole. We therefore attribute the degradation of mechanical properties to the coarsening of silicon in aluminum wire. It has not been previously shown that this process proceeds during air storage and in the 100° to 250 °C temperature ranee.     

Monitoring land use and cover around parks: A conceptual approach

Many of the habitats and resources which influence ecological functioning within National Parks, and protected areas in general, are located outside of their borders in unprotected areas. Hence, land use and land cover changes in surrounding areas may substantially influence the natural resources within parks. The US National Park Service has recognized these threats and incorporated land use and land cover monitoring into its Inventory and Monitoring Program. The purpose of this paper is to provide a framework based on a conceptual approach for planning and implementing monitoring within this Program. We present a conceptual model, based on ecological theory, which illustrates how land use and land cover change impact park resources, and helps to identify monitoring indicators that will measure relevant attributes of land use and land cover change. We also discuss potential sources of data for quantifying indicators of land use and land cover change over time, including remote sensing data and ancillary spatial datasets. Finally, we describe steps for analyzing monitoring data so that the intensity and direction of changes in land use and land cover over time are quantified, as well as trends in the status of important park resources impacted by these changes. Integration of land use and land cover monitoring data and park resource data will allow for analysis of change from past to present, and can be used to project trends into the future to provide knowledge about potential land use and land cover change scenarios and ecological impacts. We illustrate our monitoring approach with an example from the Inventory and Monitoring Program's Greater Yellowstone Network.