Biomedical subjects

S J Duff

Publications and source records attributed to S J Duff.

8 recordsLinked to original sources

PubMed2001

A sex difference on a novel spatial working memory task in humans.

Neurophysiological and behavioral evidence suggests that the prefrontal cortex (PFC) may be sexually differentiated in nonhuman primates. The present study examined whether there are sex differences in working memory in humans that might reflect sexual differentiation of human PFC. Male and female undergraduates were administered a novel multitrial spatial working memory task (SPWM) and a verbal working memory task. In three experiments, females committed significantly fewer working memory errors and took significantly less time to reach criterion than males on the SPWM task. The female advantage was not accounted for by differences in general intellectual ability, attention, perceptual speed, incidental memory, or speed of verbal access. In Study 3, a sex difference was also observed on a measure of verbal working memory. The findings suggest that some prefrontal functions may be sexually differentiated in humans.

Adult↗

PubMed2001

Effect of oxygen delignification on the rate and extent of enzymatic hydrolysis of lignocellulosic material.

In this study, we examined the effect of oxygen delignification on the rate and extent of enzymatic hydrolysis (using commercial cellulase and beta-glucosidase) of a number of lignocellulosic substrates, including kraft pulp (model substrate), pulp mill primary clarifier sludge (PCS) and steam-exploded Douglas fir chips. Oxygen delignification removed up to 67% of the lignin from softwood pulp and improved the rate of, and yield from, hydrolysis by up to 111% and 174%, respectively. Glucose yield varied linearly with fractional lignin removal. Oxygen delignification of primary clarifier sludge improved hydrolysis yield by up to 90%. However steam-exploded Douglas fir was very resistant to hydrolysis at low enzyme loading, and oxygen delignification decreased hydrolysis rate and yield.

Atmospheric Pressure↗

PubMed2001

A solid waste audit and directions for waste reduction at the University of British Columbia, Canada.

A novel design for a solid waste audit was developed and applied to the University of British Columbia, Canada, in 1998. This audit was designed to determine the characteristics of the residual solid waste generated by the campus and provide directions for waste reduction. The methodology was constructed to address complications in solid waste sampling, including spatial and temporal variation in waste, extrapolation from the study area, and study validation. Accounting for spatial effects decreased the variation in calculating total waste loads. Additionally, collecting information on user flow provided a means to decrease daily variation in solid waste and allow extrapolation over time and space. The total annual waste estimated from the experimental design was compared to documented values and was found to differ by -18%. The majority of this discrepancy was likely attributable to the unauthorised disposal of construction and demolition waste. Several options were proposed to address waste minimisation goals. These included: enhancing the current recycling program, source reduction of plastic materials, and/or diverting organic material to composting (maximum diversion: approximately 320, approximately 270, and approximately 1510 t yr(-1), respectively). The greatest diversion by weight would be accomplished through the diversion of organic material, as it was estimated to comprise 70% of the projected waste stream. The audit methodology designed is most appropriate for facilities/regions that have a separate collection system for seasonal wastes and have a means for tracking user flow.

British Columbia↗

PubMed2000

A beneficial effect of estrogen on working memory in postmenopausal women taking hormone replacement therapy.

Recent neurophysiological data suggest that the prefrontal cortex (PFC) may be susceptible to modulation by estrogen. In humans, the PFC mediates a number of cognitive processes that contribute to memory function, particularly working memory. The present study examined whether memory tasks that recruit PFC-dependent information processing might exhibit estrogen sensitivity in women. Performance on several memory tasks, including measures of working memory, was evaluated in three groups of postmenopausal women: (1) women who were tested when taking estrogen only (n = 38, M(age) = 55.1 years), (2) women who were tested when taking estrogen and a progestin concurrently (n = 23, M(age) = 55.9 years), and (3) women who were not taking hormone replacement therapy (n = 35, M(age) = 56.0 years). Estrogen users exhibited significantly better performance on a verbal task and on a spatial task, each with a prominent working memory component, but did not differ from nonusers on control tasks involving simple passive recall. These findings are consistent with the hypothesis that estrogen is active within PFC and is capable of influencing functions dependent on this region. The results of this study raise the possibility that estrogen may play a role in maintaining certain frontal lobe functions in women.

Affect↗

PubMed1997

Thermostability and irreversible activity loss of exoglucanase/xylanase Cex from Cellulomonas fimi.

The activity of the beta-1,4-glycanase Cex (EC 3.2.1.91) from Cellulomonas fimi is investigated in connection with its industrial application in cellulose hydrolysis and its potential use in cellosaccharide synthesis. Catalytic activity measurements as a function of temperature, complemented with differential scanning calorimetry (DSC) data, are used to characterize the thermostability of the protein and the influence of interdomain interactions. The data suggest that the enzyme is irreversibly deactivated in one of two possible ways: (1) through a low-temperature route characterized by first-order kinetics; or (2) through a high-temperature route characterized by an initial reversible step followed by an irreversible step. Melting temperatures (Tm) of Cex and p-33 (the isolated catalytic domain of Cex) as estimated by DSC are 64.2 and 64.0 degrees C, respectively, suggesting that the binding and catalytic domains of the protein fold independently. Kinetic parameters (Km, kcat, and kcat/Km) of Cex for the hydrolysis of p-nitrophenyl beta-D-cellobioside (pNPC) were determined at temperatures ranging from 15 to 80 degrees C. As demanded by reversible mass-action thermodynamics, the Tm of Cex in the presence of excess ligand as determined from activity-temperature data is ca. 66.55 degrees C, more than 2 degrees C higher than the Tm for Cex under ligand-free conditions. The effect of temperature on the rate constant has been determined using Arrhenius plots. Combined with irreversible deactivation half-life data and DSC data, the results are used to evaluate a model, based on a theory developed by Hei et al. (1993), for predicting the time-dependent activity and active-state stability of the protein under a range of potential operating conditions.

Algorithms↗

PubMed1997

Comparison of industrial yeast strains for fermentation of spent sulphite pulping liquor fortified with wood hydrolysate.

Ethanol production from spent sulphite pulping liquor (SSL) was compared for four different yeasts. A second strain of S. cerevisiae as well as a 2-deoxyglucose-resistant strain formed through protoplast fusions between S. uvarum and S. diastaticus produced up to 27% more ethanol from SSL fortified with hydrolysis sugars than was produced by S. cerevisiae. The incremental improvement in ethanol yield appeared to vary with the degree of fortification, ranging from 5.8% for unfortified SSL, to 27% for the highest level of fortification tested. Decreasing fermentation rates were observed for SSL fortified with glucose, mannose and galactose, respectively. Sugar uptake rates in SSL fortified with glucose, galactose and mannose were 6.8, 2.8 and 2.0 g L-1 h-1, respectively. However, when these sugars were fermented along with a glucose cosubstrate, the rate at which the combined glucose/mannose medium was fermented was nearly identical to that of the glucose control.

Cellulose↗

PubMed1985

Effect of Colloidal Materials on Cellulase Production by Trichoderma reesei Rut-C30.

The addition of positively charged colloidal materials to the growth medium markedly increased the concentration of cellulase enzymes produced by Trichoderma reesei Rut-C30. Filter paper activities of up to 4 and 13 IU/ml have been achieved by the addition of colloidal materials, using 3% lactose and 3% cellulose, respectively, as a substrate. The particles exert their effect by binding soluble sugars and slowing their uptake by the organism.

Journal Article↗

PubMed1981

Enhanced Production of Surfactin from Bacillus subtilis by Continuous Product Removal and Metal Cation Additions.

The lipopeptide, surfactin, is produced by Bacillus subtilis. A study has been made on large-scale production of this surfactant. A good yield was obtained from a glucose substrate fermentation by continuously removing the product by foam fractionation. The surfactin could be easily recovered from the collapsed foam by acid precipitation. The yield was also improved by the addition of either iron or manganese salts. Hydrocarbon addition to the medium, which normally increases biosurfactant production, completely inhibited surfactin production by B. subtilis.

Journal Article↗