14,165 research outputs found

    Speeding up liquid crystal SLMs using overdrive with phase change reduction

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    Nematic liquid crystal spatial light modulators (SLMs) with fast switching times and high diffraction efficiency are important to various applications ranging from optical beam steering and adaptive optics to optical tweezers. Here we demonstrate the great benefits that can be derived in terms of speed enhancement without loss of diffraction efficiency from two mutually compatible approaches. The first technique involves the idea of overdrive, that is the calculation of intermediate patterns to speed up the transition to the target phase pattern. The second concerns optimization of the target pattern to reduce the required phase change applied to each pixel, which in addition leads to a substantial reduction of variations in the intensity of the diffracted light during the transition. When these methods are applied together, we observe transition times for the diffracted light fields of about 1 ms, which represents up to a tenfold improvement over current approaches. We experimentally demonstrate the improvements of the approach for applications such as holographic image projection, beam steering and switching, and real-time control loops

    Research study of some RAM antennas Final report, 18 Nov. 1964 - 18 Jun. 1965

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    Input impedance and radiation pattern determinations for cylindrical gap, waveguide excited and circular waveguide slot antenna array

    Cross sections for the excitation of isovector charge-exchange resonances in 208Tl

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    The Glauber approximation for the treatment of heavy-ion scattering, has already been shown to give reliable predictions for the reaction cross section in the particular case of intermediate energy charge-exchange processes. In the present work, we couple a Glauber-type model to microscopic Random Phase Approximation calculations of the charge-exchange excitations of 208^{208}Pb. The aim is to solve the longstanding question whether the very elusive charge-exchange isovector monopole has been really identified in the past experiments, or other multipoles were prevalent in the observed spectra.Comment: text + 4 figures; accepted for publication in Phys. Rev.

    A study of acute respiratory disease in families exposed to different levels of Air pollution in the Great Salt Lake basin, Utah, 1971-1972 and 1972-1973.

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    The reported incidence of acute respiratory illness in families exposed to different concentrations of air pollution was studied during two consecutive school years. The purpose of the study was to determine the effect of increased exposure to sulfur dioxide and suspended particulate matter. In each of four study communities, the mothers of approximately 250 white families were contacted biweekly to obtain information regarding the occurrence of respiratory symptoms in each family member. Annual mean ambient sulfur dioxide concentrations in one community for the three years included in the study (1971-1973) were well above the current air quality standard of 80 micrograms/m3, while in the other three communities the annual sulfur dioxide concentrations were much lower (usually less than 40 micrograms/m3). Suspended particulate matter concentrations in high sulfur dioxide community were close to the limit designated by the annual standard (75 micrograms/m3) but actual exposures in the four communities probably were not excessive. Regression analyses of the data collected showed inconsistent associations between illness rates and educational attainment of the head of household, crowding in the home, bronchitis in parents or smoking of parents. However, once the effects of these factors were removed the adjusted rates showed little association with community of residence. It was concluded that the higher concentrations of sulfur dioxide in the Utah atmosphere could not be the cause of increases in acute respiratory illness in the exposed populations

    Reconnaissance Study of Pleistocene Lake and Fluvial Deposits In and Near Ancestral Yellowstone Lake, Wyoming

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    Seven sequences of Pleistocene strata, five of them predominantly lacustrine, are described from outcrops north of Yellowstone Lake. These are (1) Turbid Lake sequence, 30–50 feet of white pumiceous claystone and tuff with carbonaceous partings and a distinctive compositional pattern of excesses and deficiencies of many elements; (2) Yellowstone Falls sequence, 75 feet or more of varved white claystone and tuff containing pollen and diatoms, overlain by gray conglomerate and sandstone; (3) Hayden Valley sequence, 200 feet or more of gray and white silt and claystone containing sparse diatoms; (4) Alum Creek sequence, 30 feet or more of bedded sand and gravel with lesser amounts of clay; (5) Mudkettle sequence, 150 feet or more of light gray to white, soft clay and claystone with lesser amounts of sandstone and conglomerate, moderately lithified in part, and containing some pollen and diatoms; (6) Astringent Creek Sand (newly named), a gray, commonly unlithified sand as much as 300 feet thick and containing abundant volcanic debris; and (7) Pelican Valley sequence, 120 feet or more of light gray to white, soft clay, silt, sand, and some pumice pebble conglomerate and shard beds; finer grained beds contain diatoms, pollen, and carbonaceous debris that has a radiocarbon date of 7,550 ±350 years. Other localized deposits with radiocarbon dates and abundant diatoms consist of white carbonaceous tuffaceous clay and sand with an age of 9,440±300 years, in Gibbon Canyon, and a gray and white carbonaceous clay, silt, and sand with an age of 3,750+300 years at Bannock Ford in Yellowstone Canyon. Slight arching of the Upper Basin Member of the Plateau Rhyolite caused the Yellowstone River to develop an antecedent course across it. Uplift of the Pelican Valley area during the last 7,500 years averaged about one foot in 50 years

    Reconnaissance Study of Pleistocene Lake and Fluvial Deposits In and Near Ancestral Yellowstone Lake, Wyoming

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    Seven sequences of Pleistocene strata, five of them predominantly lacustrine, are described from outcrops north of Yellowstone Lake. These are (1) Turbid Lake sequence, 30–50 feet of white pumiceous claystone and tuff with carbonaceous partings and a distinctive compositional pattern of excesses and deficiencies of many elements; (2) Yellowstone Falls sequence, 75 feet or more of varved white claystone and tuff containing pollen and diatoms, overlain by gray conglomerate and sandstone; (3) Hayden Valley sequence, 200 feet or more of gray and white silt and claystone containing sparse diatoms; (4) Alum Creek sequence, 30 feet or more of bedded sand and gravel with lesser amounts of clay; (5) Mudkettle sequence, 150 feet or more of light gray to white, soft clay and claystone with lesser amounts of sandstone and conglomerate, moderately lithified in part, and containing some pollen and diatoms; (6) Astringent Creek Sand (newly named), a gray, commonly unlithified sand as much as 300 feet thick and containing abundant volcanic debris; and (7) Pelican Valley sequence, 120 feet or more of light gray to white, soft clay, silt, sand, and some pumice pebble conglomerate and shard beds; finer grained beds contain diatoms, pollen, and carbonaceous debris that has a radiocarbon date of 7,550 ±350 years. Other localized deposits with radiocarbon dates and abundant diatoms consist of white carbonaceous tuffaceous clay and sand with an age of 9,440±300 years, in Gibbon Canyon, and a gray and white carbonaceous clay, silt, and sand with an age of 3,750+300 years at Bannock Ford in Yellowstone Canyon. Slight arching of the Upper Basin Member of the Plateau Rhyolite caused the Yellowstone River to develop an antecedent course across it. Uplift of the Pelican Valley area during the last 7,500 years averaged about one foot in 50 years
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