Method accurately measures mean particle diameters of monodisperse polystyrene latexes

Photomicrographic method determines mean particle diameters of monodisperse polystyrene latexes. Many diameters are measured simultaneously by measuring row lengths of particles in a triangular array at a glass-oil interface. The method provides size standards for electronic particle counters and prevents distortions, softening, and flattening

Internal and ancestral controls of cell-generation times

Lateral and longitudinal correlations between related cells reveal associations between the generation times of cells for an intermediate period /three generations in bacteral cultures/. Generation times of progeny are influenced by nongenetic factors transmitted from their ancestors

SIRTF/IRS cryogenic grating drive mechanism (ARC second positioning at 4 K)

The requirements, design, and test results of a grating drive mechanism for the Infrared Spectrograph (IRS) science instrument on the proposed superfluid helium-cooled Space Infrared Telescope Facility (SIRTF) are described. The IRS grating drive mechanism, tested in the fall of 1989, satisfied all performance requirements in vacuum at 4 K. Measured mechanism performance included: 1.4 arc sec root-mean-square (rms) error positioning resolution; 2.2 arc sec rms position repeatability error, less than 10 millijoules/deg dissipated power; and 170 deg angular range of travel. Mechanisms that precisely position optical elements at very low cryogenic temperatures (at/below 4 K) are vital to the operating success of a number of proposed infrared scientific instruments like those in SIRTF

School Sector, School Poverty, and the Catholic School Advantage

Equality of educational opportunity is threatened by long-standing gaps in student achievement by race, gender, and student poverty, as well as by school sector and school poverty. The true magnitude of these gaps cannot be understood, however, unless these factors are considered simultaneously. While accounting for the effects of demographic characteristics, this article focuses on the effects of school sector and school poverty on gains in academic achievement. Analyses from a longitudinal study of public and Catholic middle school students in and around the city of Chicago show that neither the public nor Catholic sector has a consistent advantage in increasing student achievement in sixth and eighth grade reading and mathematics. School poverty has a deleterious effect on student achievement, although this effect is considerably mitigated for students in Catholic schools

Orion Optical Navigation for Loss of Communication Lunar Return Contingencies

The Orion Crew Exploration Vehicle (CEV) will replace the Space Shuttle and serve as the next-generation spaceship to carry humans back to the Moon for the first time since the Apollo program. For nominal lunar mission operations, the Mission Control Navigation team will utilize radiometric measurements to determine the position and velocity of Orion and uplink state information to support Lunar return. However, in the loss of communications contingency return scenario, Orion must safely return the crew to the Earth's surface. The navigation design solution for this loss of communications scenario is optical navigation consisting of lunar landmark tracking in low lunar orbit and star- horizon angular measurements coupled with apparent planetary diameter for Earth return trajectories. This paper describes the optical measurement errors and the navigation filter that will process those measurements to support navigation for safe crew return