Individual Differences in Scotopic Visual Acuity and Contrast Sensitivity: Genetic and Non-Genetic Influences

Despite the large amount of variation found in the night (scotopic) vision capabilities of healthy volunteers, little effort has been made to characterize this variation and factors, genetic and non-genetic, that influence it. In the largest population of healthy observers measured for scotopic visual acuity (VA) and contrast sensitivity (CS) to date, we quantified the effect of a range of variables on visual performance. We found that young volunteers with excellent photopic vision exhibit great variation in their scotopic VA and CS, and this variation is reliable from one testing session to the next. We additionally identified that factors such as Circadian preference, iris color, astigmatism, depression, sex and education have no significant impact on scotopic visual function. We confirmed previous work showing that the amount of time spent on the vision test influences performance and that laser eye surgery results in worse scotopic vision. We also showed a significant effect of intelligence and photopic visual performance on scotopic VA and CS, but all of these variables collectively explain <30% of the variation in scotopic vision. The wide variation seen in young healthy volunteers with excellent photopic vision, the high test-retest agreement, and the vast majority of the variation in scotopic vision remaining unexplained by obvious non-genetic factors suggests a strong genetic component. Our preliminary genome-wide association study (GWAS) of 106 participants ruled out any common genetic variants of very large effect and paves the way for future, larger genetic studies of scotopic vision.     

Rheological behavior of heated starch dispersions in excess water: role of starch granule

Granule size and size distribution, measured by laser diffraction, affected the flow behavior at 20 °C of (2.6% w/w) corn and cowpea starch dispersions heated for various time intervals above their gelatinization temperatures. The standard deviation of the granules' size described the transition of flow behavior from shear thickening in the early stages of gelatinization to shear thinning in the latter stages and influenced the critical shear rate, y_c, for the onset of shear thickening in starch dispersions. The granules swelled to a maximum of about 3.5 times the raw starch granule mean diameter and 65% granule mass fraction. The consistency index of the dispersions increased with granule mean diameter. Modified waxy maize starch dispersions heated at 80 °C exhibited antithixotropic behavior at a shear rate of 200s⁻¹; both dynamic frequency data and Cox-Merz plots revealed their gel-like behavior.     

An evaluation of pyrolytic techniques with regard to the Apollo 11, 12 and 14 lunar samples analyses

Two different pyrolysis techniques have been used in the analysis of lunar fines. The first technique involved pyrolysis at 700°C under an inert atmosphere in a flowing He system at normal pressure. The products were collected at liquid N₂ temperature and then allowed to pass instantaneously into a combined capillary gas chromatograph-mass spectrometer. The second technique consisted of a vacuum pyrolysis where the sample was first degassed at 150°C and then pyrolyzed at 500°C and 1000°C consecutively. The products were again collected at liquid N₂ temperature and then they were directly introduced to the ion source of the mass spectrometer through a modified gas inlet system.An evaluation of the two techniques based on control experiments has shown that the probability of secondary reactions is greater in the inert atmosphere pyrolysis method. Pyrolysis of benzene in He under atmospheric pressure at 600°C showed the presence of small quantities of biphenyl and trace amounts of naphthalene. Biphenyl pyrolyzed under vacuum at 600, 700, 800 and 900°C by passing through a hot zone containing a quartz wool plug showed the presence of a wide range of synthesis and breakdown products as the temperature increased.These experiments have shown the importance of taking into account the factors that influence pyrolytic degradation and/or the synthesis of products. These can be diffusion effects, involving sample size, sample form, pyrolysis pressure conditions; temperature, catalytic effects from the pyrolysis vessel, contamination, perhaps other factors. Pyrolysis is an effective method of analysis if used under carefully controlled conditions. Pyrolysis of Apollo 14 lunar fines and scrapings from an astronaut's glove gave different products by mass spectrometry and showed different looking flaky materials upon scanning electron microscopy.     

A Simplified Bacterial Spore Stain

A simplification of the Schaeffer-Fulton spore stain for bacteria is presented. It is shown that omission of the heating step during staining with malachite green resulted in spore stains as good as when the heat was applied. The simplified procedure involves (1) heat fixation of the smear by 20 passages through the flame, (2) staining with saturated aqueous malachite green for 10 minutes, (3) rinsing, and (4) counterstaining with 0.25% aqueous safranin for 15 seconds. The omission of the heating step in staining has obvious advantages, particularly in the classroom.     

Changes in Antimicrobial Susceptibility of Native Enterococcus faecium in Chickens Fed Virginiamycin

The extent of transfer of antimicrobial resistance from agricultural environments to humans is controversial. To assess the potential hazard posed by streptogramin use in food animals, this study evaluated the effect of virginiamycin exposure on antimicrobial resistance in Enterococcus faecium recovered from treated broilers. Four consecutive broiler feeding trials were conducted using animals raised on common litter. In the first three trials, one group of birds was fed virginiamycin continuously in feed at 20 g/ton, and a second group served as the nontreated control. In the fourth trial, antimicrobial-free feed was given to both groups. Fecal samples were cultured 1 day after chickens hatched and then at 1, 3, 5, and 7 weeks of age. Isolates from each time point were tested for susceptibility to a panel of different antimicrobials. Quinupristin/dalfopristin-resistant E. faecium appeared after 5 weeks of treatment in trial 1 and within 7 days of trials 2 to 4. Following removal of virginiamycin in trial 4, no resistant isolates were detected after 5 weeks. PCR failed to detect vat, vgb, or erm(B) in any of the streptogramin-resistant E. faecium isolates, whereas the msr(C) gene was detected in 97% of resistant isolates. In an experimental setting using broiler chickens, continuous virginiamycin exposure was required to maintain a stable streptogramin-resistant population of E. faecium in the animals. The bases of resistance could not be explained by known genetic determinants.