The determination of the direction of the optic axis of uniaxial crystalline materials

The birefringence of crystalline substances in general, and of sapphire in particular, is described. A test is described whose purpose is to determine the direction of the optic axis of a cylindrically machined single crystal of sapphire. This test was performed on the NASA Lewis sapphire cylinder and it was found that the optic axis made an angle of 18 deg with the axis of symmetry of the cylinder

Incident Beam Polarization for Laser Doppler Velocimetry Employing a Sapphire Cylindrical Window

For laser Doppler velocimetry studies employing sapphire windows as optical access ports, the birefringency of sapphire produces an extra beam intersection volume which serves to effectively smear the acquired velocity flow field data. It is shown that for a cylindrical window geometry, the extra beam intersection volume may be eliminated with minimal decrease in the fringe visibility of the remaining intersection volume by suitably orienting the polarizations of the initial laser beams. For horizontally incident beams, these polarizations were measured at three intersection locations within the cylinder. It was found that the measured polarization angles agreed with the theoretical predictions

Genomic variations associated with attenuation in Mycobacterium avium subsp paratuberculosis vaccine strains

BACKGROUND: Mycobacterium avium subspecies paratuberculosis (MAP) whole cell vaccines have been widely used tools in the control of Johne's disease in animals despite being unable to provide complete protection. Current vaccine strains derive from stocks created many decades ago; however their genotypes, underlying mechanisms and relative degree of their attenuation are largely unknown. RESULTS: Using mouse virulence studies we confirm that MAP vaccine strains 316 F, II and 2e have diverse but clearly attenuated survival and persistence characteristics compared with wild type strains. Using a pan genomic microarray we characterise the genomic variations in a panel of vaccine strains sourced from stocks spanning over 40 years of maintenance. We describe multiple genomic variations specific for individual vaccine stocks in both deletion (26-32 Kbp) and tandem duplicated (11-40 Kbp) large variable genomic islands and insertion sequence copy numbers. We show individual differences suitable for diagnostic differentiation between vaccine and wild type genotypes and provide evidence for functionality of some of the deleted MAP-specific genes and their possible relation to attenuation. CONCLUSIONS: This study shows how culture environments have influenced MAP genome diversity resulting in large tandem genomic duplications, deletions and transposable element activity. In combination with classical selective systematic subculture this has led to fixation of specific MAP genomic alterations in some vaccine strain lineages which link the resulting attenuated phenotypes with deficiencies in high reactive oxygen species handling

Children\u27s Voices: Perspectives on Using Assistive Technology

Rarely are the views of children with learning disabilities elicited. In this study, we used focus groups involving eight students with learning disabilities to explore their self-perceptions as learners and writers using assistive technology (AT). Three groups of two to three Grade 4–8 students and their parents participated in the qualitative study. Both student and parent responses provided data for thematic analysis that resulted in three themes: (a) changes in students’ self-perceptions as learners; (b) student and parental self-reported benefits of using assistive technology; and (c) inconsistencies in approaches to using assistive technology in schools. The implications for education are greater attention to the views of elementary school children; greater focus on the use of AT in the classroom; and greater AT training for teachers in order to better support the use of AT by students with LD

Compressible Flow Through a Tube Connecting a Continuum and a Vacuum

This report addresses the compressible flow through a tube connecting a continuum and a vacuum

Compressible flow through a tube connecting a continuum and a vacuum

This report addresses the compressible flow through a tube connecting a continuum and a vacuum

Comparison of measurements of the outer scale of turbulence by three different techniques

We have made simultaneous and nearly simultaneous measurements of L0, the outer scale of turbulence, at the Palomar Observatory by using three techniques: angle-of-arrival covariance measurements with the Generalized Seeing Monitor (GSM), differential-image-motion measurements with the adaptive-optics system on the Hale 5-m telescope, and fringe speed measurements with the Palomar Testbed Interferometer (PTI). The three techniques give consistent results, an outer scale of approximately 10-20 m, despite the fact that the spatial scales of the three instruments vary from 1 m for the GSM to 100 m for the PTI