In contrast to the rapid dissociative adsorption of diatomic gases on the transition metals, chem... more In contrast to the rapid dissociative adsorption of diatomic gases on the transition metals, chemisorption of methane and ethane occurs slowly and with an appreciable activation energy. In order to explore the molecular events in this activated adsorption we have examined the interaction of methane with a rhodium crystal, using a field emission microscope equipped with a variable temperature molecular beam source. From studies on clean surfaces prepared by field evaporation it appears that activation of the gas alone is sufficient to bring about adsorption, and that the activation energy for this process is 7 kcal/mol. Measurements have also been carried out on variously deuterated methanes. These reveal that for methane, excitation of the gas to higher vibrational states is the significant step in the passage over the barrier to disociative chemisorption.
Compact LCD projectors require a high efficiency light source that has the smallest possible spat... more Compact LCD projectors require a high efficiency light source that has the smallest possible spatial extent. The objective of the lamp design must be to preserve the system etendue to ensure excellent screen illuminance. We present the results of the development of projection lighting systems that produce 1,500 to 3,000 lumens, have luminous efficacious of >= 1m/W and source sizes
Compact LCD projectors require a high efficiency light source that has the smallest possible spat... more Compact LCD projectors require a high efficiency light source that has the smallest possible spatial extent. Further, they require optical systems that preserve the etendue. Current projector illumination systems have aberrations that produce a light beam whose etendue far exceeds the intrinsic etendue of the light source itself. As a result both efficiency and uniformity fall short of what is theoretically possible. We provide a theoretical framework for understanding these aberrations and the magnitude of their effect. We also present results showing the efficiency, uniformity, and other performance gains which are possible when these aberrations are corrected. This work also describes the performance of long-life, short-arc metal halide lighting systems that are able to increase screen brightness of compact projectors several fold without any increase in system power or heat. With these systems it has been possible to design and validate lamps operating at 50 Watts, producing > 3,000 lumens and having excellent lumen maintenance throughout their 4,000 hour life. The benefits of the combination of an improved etendue-preserving optical system and a short-arc metal halide lamp will be demonstrated.
Compact LCD projectors require compact, low power metal halide lamps to achieve maximum screen br... more Compact LCD projectors require compact, low power metal halide lamps to achieve maximum screen brightness. We have previously described such lighting systems, taking into account ballast stability, source étendue, and collection optics. Metal halide sources have a significant advantage over high pressure xenon, high pressure mercury, and halogen sources in that the spectral power distribution (SPD) of the source can be optimized for the projection system. This is in addition to the inherently greater luminous efficacy of metal halide sources. We present the result of recent studies on chemical dose composition in 50 Watt, 1.2 mm arc gap, long life (4,000 hr.) metal halide lamps. Through designed experiments on chemical species, dose weight, and molar composition we were able to increase the luminous output by as much as 50% in some cases. The optimized metal halide lamp has 50% more red radiation than a 50 Watt, 1.3 mm gap high pressure mercury lamp and also produces a preferred color temperature. Knowledge of the significant factors that effect color allows us to design virtually any color gamut. It was possible to match the filter characteristics of a number of projection systems.
Dynamics of activated chemisorption: Methane on rhodium. [The Journal of Chemical Physics 62, 467... more Dynamics of activated chemisorption: Methane on rhodium. [The Journal of Chemical Physics 62, 4672 (1975)]. Charles N. Stewart, Gert Ehrlich. Abstract. Chemisorption of methane has been examined on highly perfect rhodium ...
In contrast to the rapid dissociative adsorption of diatomic gases on the transition metals, chem... more In contrast to the rapid dissociative adsorption of diatomic gases on the transition metals, chemisorption of methane and ethane occurs slowly and with an appreciable activation energy. In order to explore the molecular events in this activated adsorption we have examined the interaction of methane with a rhodium crystal, using a field emission microscope equipped with a variable temperature molecular beam source. From studies on clean surfaces prepared by field evaporation it appears that activation of the gas alone is sufficient to bring about adsorption, and that the activation energy for this process is 7 kcal/mol. Measurements have also been carried out on variously deuterated methanes. These reveal that for methane, excitation of the gas to higher vibrational states is the significant step in the passage over the barrier to disociative chemisorption.
Compact LCD projectors require a high efficiency light source that has the smallest possible spat... more Compact LCD projectors require a high efficiency light source that has the smallest possible spatial extent. The objective of the lamp design must be to preserve the system etendue to ensure excellent screen illuminance. We present the results of the development of projection lighting systems that produce 1,500 to 3,000 lumens, have luminous efficacious of >= 1m/W and source sizes
Compact LCD projectors require a high efficiency light source that has the smallest possible spat... more Compact LCD projectors require a high efficiency light source that has the smallest possible spatial extent. Further, they require optical systems that preserve the etendue. Current projector illumination systems have aberrations that produce a light beam whose etendue far exceeds the intrinsic etendue of the light source itself. As a result both efficiency and uniformity fall short of what is theoretically possible. We provide a theoretical framework for understanding these aberrations and the magnitude of their effect. We also present results showing the efficiency, uniformity, and other performance gains which are possible when these aberrations are corrected. This work also describes the performance of long-life, short-arc metal halide lighting systems that are able to increase screen brightness of compact projectors several fold without any increase in system power or heat. With these systems it has been possible to design and validate lamps operating at 50 Watts, producing > 3,000 lumens and having excellent lumen maintenance throughout their 4,000 hour life. The benefits of the combination of an improved etendue-preserving optical system and a short-arc metal halide lamp will be demonstrated.
Compact LCD projectors require compact, low power metal halide lamps to achieve maximum screen br... more Compact LCD projectors require compact, low power metal halide lamps to achieve maximum screen brightness. We have previously described such lighting systems, taking into account ballast stability, source étendue, and collection optics. Metal halide sources have a significant advantage over high pressure xenon, high pressure mercury, and halogen sources in that the spectral power distribution (SPD) of the source can be optimized for the projection system. This is in addition to the inherently greater luminous efficacy of metal halide sources. We present the result of recent studies on chemical dose composition in 50 Watt, 1.2 mm arc gap, long life (4,000 hr.) metal halide lamps. Through designed experiments on chemical species, dose weight, and molar composition we were able to increase the luminous output by as much as 50% in some cases. The optimized metal halide lamp has 50% more red radiation than a 50 Watt, 1.3 mm gap high pressure mercury lamp and also produces a preferred color temperature. Knowledge of the significant factors that effect color allows us to design virtually any color gamut. It was possible to match the filter characteristics of a number of projection systems.
Dynamics of activated chemisorption: Methane on rhodium. [The Journal of Chemical Physics 62, 467... more Dynamics of activated chemisorption: Methane on rhodium. [The Journal of Chemical Physics 62, 4672 (1975)]. Charles N. Stewart, Gert Ehrlich. Abstract. Chemisorption of methane has been examined on highly perfect rhodium ...
Uploads
Papers by Chuck Stewart