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Biomedical subjects

T A Roberts

Publications and source records attributed to T A Roberts.

At least 19 recordsLinked to original sources
PubMed1998

Effect of microfiller fraction and silane treatment on resin composite properties.

A series of microfilled resin composites were formulated by incrementally mixing either agglomerated 20 nm or unagglomerated 50 nm silica microfillers into monomers composed of diphenyloxymethacrylate and TEGDMA. The microfiller particles were prepared with and without a gamma-methacryloxypropyl-trimethoxy silane coupling agent. Following polymerization, five material properties were tested: uniaxial tensile strength, Young's modulus in slow compression, Knoop hardness, water sorption, and toothbrush abrasion resistance. Results from these tests indicated that microfiller content clearly was the most influential parameter affecting material property performance. Composites containing 20 nm particles demonstrated greater water sorption, higher Knoop hardness, and better resistance to toothbrush wear. Surprisingly, the application of silane to microfiller surfaces did not greatly improve composite performance for most of the material properties tested in this study. However, water sorption behavior over a 3-year period was observed to be more stable for materials possessing silane-treated particles. Future evaluation of coupling agents should include long-term water storage prior to conducting mechanical tests.

Biocompatible Materials↗
PubMed1998

That swimsuit becomes you: sex differences in self-objectification, restrained eating, and math performance.

Objectification theory (B. L. Fredrickson & T. Roberts, 1997) posits that American culture socializes women to adopt observers' perspectives on their physical selves. This self-objectification is hypothesized to (a) produce body shame, which in turn leads to restrained eating, and (b) consume attentional resources, which is manifested in diminished mental performance. Two experiments manipulated self-objectification by having participants try on a swimsuit or a sweater. Experiment 1 tested 72 women and found that self-objectification increased body shame, which in turn predicted restrained eating. Experiment 2 tested 42 women and 40 men and found that these effects on body shame and restrained eating replicated for women only. Additionally, self-objectification diminished math performance for women only. Discussion centers on the causes and consequences of objectifying women's bodies.

Adolescent↗
PubMed1997

Predictive modelling of growth of Listeria monocytogenes. The effects on growth of NaCl, pH, storage temperature and NaNO2.

The effect of NaCl concentration (5.0 115.0 g/l). pH value (4.0-7.2), temperature (1-35 degrees C) and NaNO2 concentration (0 200 mg/l) on the growth responses of Listeria monocytogenes, in laboratory medium was investigated. The growth curves generated within this matrix of conditions were fitted using the function of Baranyi and Roberts (1994) and the growth responses modelled using a quadratic polynomial to produce response surfaces. Growth curves could then be regenerated for any set of conditions within the experimental matrix and values predicted for the growth rate, doubling time, lag time and time to 1000-fold increase. The model was validated using data from published literature and was found to give realistic predictions for doubling times in foods, including meat and meat products, milk, dairy products and vegetables. Predictions from this model (Baranyi and Roberts. 1994) compared favourably with those from the models of Buchanan and Phillips (1990), Murphy et al. (1996) and the Food MicroModel.

Hydrogen-Ion Concentration↗
PubMed1995

A response surface study on the role of some environmental factors affecting the growth of Saccharomyces cerevisiae.

The combined effect of pH, ethanol and fructose on the growth of Saccharomyces cerevisiae at 25 degrees C was studied by the standard Response Surface Methodology. Canonical analysis of the obtained response surface led to the conclusion that the effects of ethanol and fructose can be described by a single factor, the value of water activity, which can be calculated from the other two. Therefore the number of explanatory variables can be reduced. The computational usefulness of the transformation bw = square root of (1-aw) is demonstrated.

Ethanol↗
PubMed1995

Mathematics of predictive food microbiology.

Commonly encountered problems related to modelling bacterial growth in food are analysed from a mathematical point of view. Modelling techniques and terms, some misused, are discussed and an attempt is made to clarify how, and under what conditions, they may be used. A theoretical framework is given to provide a basis in which mathematical models having been used in predictive microbiology can be embedded. By using several simplifying idealizations as a compromise between the complexity of the biological system and the available data, a practically usable model becomes available.

Bacteria↗
PubMed1994

Predictive modelling of growth of Staphylococcus aureus: the effects of temperature, pH and sodium chloride.

The growth responses of Staphylococcus aureus as affected by NaCl concentration, pH value and storage temperature were studied in laboratory medium. Growth curves at concentrations of NaCl in the range 0.5-13.5% (w/v), pH values in the range 4.0-7.0 and storage temperatures in the range 10-30 degrees C were fitted using the Gompertz routine and the derived parameters modelled. Growth curves could then be regenerated for any set of conditions within the matrix studied and values for growth rate, generation time, lag time and time to 1000-fold increase predicted. The model was validated against data from the literature and was found to give realistic estimates of generation time for media and a range of foods including milk, cheese, starch-based foods and cooked meats but not for mayonnaise or Wiltshire bacon. All predictions were consistently 'fail-safe'.

Animals↗
PubMed1994

Computer aided microbial safety design of food processes.

To reduce the time required for product development, to avoid expensive experimental tests, and to quantify safety risks for fresh products and the consequence of processing there is a growing interest in computer aided food process design. This paper discusses the application of hybrid object-oriented and rule-based expert system technology to represent the data and knowledge of microbial experts and food engineers. Finite element models for heat transfer calculation routines, microbial growth and inactivation models and texture kinetics are combined with food composition data, thermophysical properties, process steps and expert knowledge on type and quantity of microbial contamination. A prototype system has been developed to evaluate changes in food composition, process steps and process parameters on microbiological safety and textual quality of foods.

Computer-Aided Design↗
PubMed1994

Modelling the growth, survival and death of microorganisms in foods: the UK food micromodel approach.

Techniques for the development of mathematical models in the area of predictive microbiology have greatly improved recently, allowing better and more accurate descriptions of microbial responses to particular environmental conditions, thus enabling predictions of those responses to be made with greater confidence. Recognising the potential value of applying these techniques in the food industry, the Ministry of Agriculture, Fisheries and Food (MAFF) initiated a nationally coordinated five-year programme of research into the growth and survival of microorganisms in foods, with the aim of developing a computerised Predictive Microbiology Database in the UK. This initiative has resulted in the systematic generation of data, through protocols which ensure consistency of methodology, so that data in the database are truly comparable and compatible, and lead to reliable predictive models. The approaches taken by scientists involved in this programme are described and the various stages in the development of mathematical models summarized. It is hoped that this initiative and others being developed in the USA, Australia, Canada and other countries, will encourage a more integrated approach to food safety which will influence all stages of food production and, eventually, result in the development of an International Predictive Microbiology Database.

Bacteria↗
PubMed1994

A dynamic approach to predicting bacterial growth in food.

A new member of the family of growth models described by Baranyi et al. (1993a) is introduced in which the physiological state of the cells is represented by a single variable. The duration of lag is determined by the value of that variable at inoculation and by the post-inoculation environment. When the subculturing procedure is standardized, as occurs in laboratory experiments leading to models, the physiological state of the inoculum is relatively constant and independent of subsequent growth conditions. It is shown that, with cells with the same pre-inoculation history, the product of the lag parameter and the maximum specific growth rate is a simple transformation of the initial physiological state. An important consequence is that it is sufficient to estimate this constant product and to determine how the environmental factors define the specific growth rate without modelling the environment dependence of the lag separately. Assuming that the specific growth rate follows the environmental changes instantaneously, the new model can also describe the bacterial growth in an environment where the factors, such as temperature, pH and aw, change with time.

Bacteria↗
PubMed1994

Predicting fungal growth: the effect of water activity on Aspergillus flavus and related species.

Growth of four species belonging to Aspergillus Section Flavi (A. flavus, A. oryzae, A. parasiticus and A. nomius) was studied at 30 degrees C at ten water activities (aw) between 0.995 and 0.810 adjusted with equal mixtures of glucose and fructose. Colony diameters were measured at intervals and plotted against time. A flexible growth model describing the change in colony diameter (mm) with respect to time was first fitted to the measured growth data and from the fitted curves the maximum colony growth rates were calculated. These values were then fitted with respect to aw to predict colony growth rates at any aw within the range tested. The optimum aw for each species and time to reach a colony diameter of 3 mm were also calculated.

Aspergillus flavus↗
PubMed1993

Effect of crosslinking agent content, monomer functionality, and repeat unit chemistry on properties of unfilled resins.

Seven mechanical/physical properties were used to evaluate 10 unfilled resins: eight aromatic dimethacrylates and two urethane dimethacrylates. Physical property tests included compressive strength, Young's modulus in compression, uniaxial tensile strength, intrinsic yield point, toothbrush abrasion, Knoop hardness, and water sorption. Controlled changes were made in the following four material parameters: amount of crosslinking diluent present in the uncured monomer, functionality of the monomer, repeat unit chemistry of the monomer (urethane vs. aromatic structure) and mode of activation (chemical vs. visible light). Polymers containing a high concentration of crosslinking agent (50 wt%) were found to be tougher and to possess lower hardness than materials containing lesser amounts of crosslinking agent. This was attributed to the flexible nature of the triethylene glycol dimethacrylate crosslinking molecule. Exposure to water plasticized the highly crosslinked materials to the degree that the yield point and elastic modulus were effectively lowered. Most of the tested properties were unaffected by differences in functionality except resistance to toothbrush abrasion, which was enhanced for polymers derived from high functionality monomers. The urethane-based polymers sorbed substantially more water than the aromatic-based materials, which presumably resulted in lower values for surface hardness. However, the urethane resins were very tough, and excellent resistance to toothbrush abrasion was observed. Property differences caused by differences in activation mode were small, although the visible light materials did sorb more water.

Absorption↗
PubMed1993

A predictive model for the combined effect of pH, sodium chloride and storage temperature on the growth of Brochothrix thermosphacta.

Growth of Brochothrix thermosphacta was observed under ranges of pH (5.6-6.8), NaCl (0.5-8.0% w/v) and incubation temperature (1-30 degrees C). In order to compare different approaches, two models were used to fit growth curves to viable count data, and to calculate parameters from those fitted curves. Growth responses as a function of pH, NaCl and temperature were described with a quadratic function which was then used to predict growth within the limits where growth was observed. The predictions of the model show good agreement with published observations from other laboratories.

Cell Division↗
PubMed1993

Modelling bacterial growth of Listeria monocytogenes as a function of water activity, pH and temperature.

Temperature, pH and water activity are important factors controlling the microbiological safety of foods. To describe the growth rate of Listeria monocytogenes in relation to these factors, two equations have been developed. Both equations are based upon the Ratkowsky equation for temperature and growth rate. The first equation predicts growth rate at sub-optimal pH values, sub-optimal temperatures and sub-optimal water activities, the second model predicts growth throughout the entire pH range. The first model may be used to predict growth rates between pH 4.6-6.7, temperature range 5-35 degrees C and a water activity range of 0.95-0.997. The second model is valid throughout the pH range of 4.6-7.4 and the same temperature and water activity range as the first model.

Cell Division↗
PubMed1992

Sequence of the gene encoding type F neurotoxin of Clostridium botulinum.

Primers designed to conserved regions of botulinum and tetanus clostridial toxins were used to amplify DNA fragments from non-proteolytic Clostridium botulinum type F (202F) DNA using polymerase chain reaction technology. The fragments were cloned and the complete nucleotide sequence of the gene encoding type F toxin determined. Analysis of the nucleotide sequence demonstrated the presence of an open frame encoding a protein of 1274 amino acids, similar to other botulinum neurotoxins. Upstream of the toxin gene is the end of an open reading frame which encodes the C-terminus of a protein with homology to non-toxic-non-hemagglutinin component of type C progenitor toxin.

Amino Acid Sequence↗
PubMed1992

Taxonomic studies on a psychrophilic Clostridium from vacuum-packed beef: description of Clostridium estertheticum sp. nov.

Taxonomic studies were performed on an anaerobic Gram-positive, spore-forming, psychrophilic bacterium originally isolated from spoiled vacuum-packed refrigerated beef. Based on the present finding it is proposed that this unknown psychrophilic bacterium be classified as a new species of the genus Clostridium, as Clostridium estertheticum sp. nov. The type strain is NCIMB 12511.

Animals↗
PubMed1991

The effects of temperature, pH, sodium chloride and sodium nitrite on the growth of Listeria monocytogenes.

An automated turbidimetric system using multiwelled plates was used to examine the effects of different combinations of NaCl (0.5-8.0% w/v), NaNO2 (0-400 micrograms/ml) pH (4.6-7.4) and temperature (5-30 degrees C) on the growth of Listeria monocytogenes in tryptone soya broth. The data presented clearly illustrate the combinations that permit visible growth of the organism. The ability of L. monocytogenes to grow at low pH levels was strongly influenced by incubation temperature as well as NaNO2 concentration. At 20 degrees C and below, no visible growth was detected, even with 50 micrograms/ml NaNO2 at pH 5.3 (or below) within 21 days. At pH 6.0 and above, NaNO2 had little effect in delaying visible growth except at higher concentrations and also at lower incubation temperatures.

Colony Count, Microbial↗
PubMed1991

Gender and the influence of evaluations on self-assessments in achievement settings.

This article reviews evidence for a gender difference in responsiveness to others' evaluations in achievement situations. Studies show that women's self-evaluations are more responsive to the valence of the evaluative feedback they receive than are men's. A number of possible explanations for this effect are then discussed, with the best evidence pointing to men's and women's differing construals of the informational value of others' evaluations in such situations. Research on the behavioral consequences of women's lower status as well as on children's experiences with evaluative feedback provides potential explanations for this effect. A more proximal explanation, however, lies in men's and women's different approaches to evaluative achievement situations. Men may be particularly likely to respond to the competitive nature of evaluative achievement and hence to adopt a self-confident approach that leads them to deny the informational value of others' evaluations. Women may be particularly likely to approach such situations as opportunities to gain information about their abilities.

Achievement↗