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T Ross

Publications and source records attributed to T Ross.

At least 55 records · Page 3Linked to original sources
PubMed1999

Validating and comparing predictive models.

The bias and accuracy factors introduced by Ross [Ross, T., 1996. Indices for performance evaluation of predictive models in food microbiology. J. Appl Bacteriol. 81, 501-508] for the evaluation of the performance of models in 'predictive food microbiology' are refined by basing the calculation of those measures on the mean square differences between predictions and observations. The use of the indices is extended by presenting formulae and methods which enable evaluation of the difference between alternative models for growth of an organism of interest over a domain of environmental factors. This is done by calculating the integral mean of the square differences between the models under investigation over the domain of the environmental variables common to those models, or a sub-region of it. The use of the techniques is exemplified by evaluating the difference between four published models for the growth rate of psychrotrophic pseudomonads.

Bias↗
PubMed1999

Feature selection for optimized skin tumor recognition using genetic algorithms.

In this paper, a new approach to computer supported diagnosis of skin tumors in dermatology is presented. High resolution skin surface profiles are analyzed to recognize malignant melanomas and nevocytic nevi (moles), automatically. In the first step, several types of features are extracted by 2D image analysis methods characterizing the structure of skin surface profiles: texture features based on cooccurrence matrices, Fourier features and fractal features. Then, feature selection algorithms are applied to determine suitable feature subsets for the recognition process. Feature selection is described as an optimization problem and several approaches including heuristic strategies, greedy and genetic algorithms are compared. As quality measure for feature subsets, the classification rate of the nearest neighbor classifier computed with the leaving-one-out method is used. Genetic algorithms show the best results. Finally, neural networks with error back-propagation as learning paradigm are trained using the selected feature sets. Different network topologies, learning parameters and pruning algorithms are investigated to optimize the classification performance of the neural classifiers. With the optimized recognition system a classification performance of 97.7% is achieved.

Algorithms↗
PubMed1999

Behaviour of Listeria monocytogenes under combined chilling processes.

The behaviour of Listeria monocytogenes under chilling processes was investigated. Growth kinetics were measured at 7 degrees C in TSBYE culture medium as a function of pH (7.2 and 6.2), pre-incubation temperatures (4 or 7 degrees C), cooling (0.05 or 0.1 degree C min-1) and freezing (0 and -5 degrees C) treatments. Growth curves generated were fitted by Gompertz and Baranyi functions. The Baranyi function gave better parameter estimation values than the Gompertz equation which over-estimated the specific growth rate values. Listeria monocytogenes grew at 7 degrees C without a lag phase, except when the sub-culture was performed at 37 degrees C, whereas the specific growth rate was affected by the chilling processes. In fact, L. monocytogenes grew slightly faster at 7 degrees C when a 4 degrees C pre-incubation treatment was applied than with a 7 degrees C pre-incubation treatment. These results suggest that to mimic the processes of contamination in industry, predictive microbiology studies with L. monocytogenes should be performed with organisms cultured at low temperatures.

Food Technology↗
PubMed1999

Physicochemical parameters for growth of the sea ice bacteria Glaciecola punicea ACAM 611(T) and Gelidibacter sp. strain IC158.

The water activity and pH ranges for growth of Glaciecola punicea (a psychrophile) were extended when this organism was grown at suboptimal rather than optimal temperatures. No such extension was observed for Gelidibacter sp. strain IC158 (a psychrotolerant bacterium) at analogous temperatures. Salinity and pH may be primary physicochemical parameters controlling bacterial community development in sea ice.

Antarctic Regions↗
PubMed1999

Computer-supported diagnosis of melanoma in profilometry.

Laser profilometry offers new possibilities to improve non-invasive tumor diagnostics in dermatology. In this paper, a new approach to computer-supported analysis and interpretation of high-resolution skin-surface profiles of melanomas and nevocellular nevi is presented. Image analysis methods are used to describe the profile's structures by texture parameters based on co-occurrence matrices, features extracted from the Fourier power spectrum, and fractal features. Different feature selection strategies, including genetic algorithms, are applied to determine the best possible subsets of features for the classification task. Several architectures of multilayer perceptrons with error back-propagation as learning paradigm are trained for the automatic recognition of melanomas and nevi. Furthermore, network-pruning algorithms are applied to optimize the network topology. In the study, the best neural classifier showed an error rate of 4.5% and was obtained after network pruning. The smallest error rate in all, of 2.3%, was achieved with nearest neighbor classification.

Diagnosis, Differential↗
PubMed1998

Final optical density and growth rate; effects of temperature and NaCl differ from acidity.

Most predictive models used in food microbiology accurately describe microbial growth rate responses to conditions in the environment, but do not improve understanding of mechanisms. The effects of temperature, water activity and acid constraints on the growth of Escherichia coli are investigated using substrate-limited batch culture experiments. Final optical densities of substrate-limited batch cultures indicate the efficiency of substrate conversion to biomass and, therefore, the relative energetic burdens that different environmental conditions pose for microbial growth. Typical growth rate responses are observed. At suboptimal temperatures, the square root of growth rate declines linearly with temperature. With increasingly stringent water activity conditions, the growth rate declines linearly. It also declines linearly (but only slightly) with increasing hydrogen-ion concentration. Similar deltaOD (the change in optical density from the initial value to the value where the final population density is reached) responses are observed for temperature and water activity (adjusted using sodium chloride). Over most of the growth permissive ranges, the deltaOD remains high for both factors. Close to the growth boundaries, however, at the low water activity extreme and at the low and high temperature extremes, cell production declines to zero suddenly. The influence of water activity on growth rate is partly relieved by the compatible solute betaine. However, the main influence of betaine on deltaOD is to extend (to a lower water activity value) the water activity growth boundary and, therefore, the water activity value where cell production declines suddenly. In contrast to the temperature and water activity responses, the deltaOD declines steadily with increasing hydrogen-ion concentration. This indicates that temperature and water activity constraints, despite their marked influence on growth rate, may not impose large energetic burdens. However, when acid stress is applied, the efficiency of substrate conversion to biomass appears to be reduced.

Betaine↗
PubMed1998

Applicability of a model for non-pathogenic Escherichia coli for predicting the growth of pathogenic Escherichia coli.

A model was developed for the temperature dependence of growth rate of a non-pathogenic Escherichia coli strain. The suitability of that model for predicting the growth rate of pathogenic E. coli strains was assessed. Growth rates of pathogenic strains were found to be adequately described by the model. Model predictions were also found to describe sufficiently well-published growth rate data for non-pathogenic E. coli on mutton carcase surfaces and E. coli O157:H7 in ground roasted beef, milk, and on cantaloupes and water melons. In addition, E. coli O157:H7 was found to grow in the region of 44-45 degrees celsius.

Escherichia coli↗
PubMed1998

Modelling the growth limits (growth/no growth interface) of Escherichia coli as a function of temperature, pH, lactic acid concentration, and water activity.

The form of a previously developed Bĕlehrádek type of growth rate model was used to develop a probability model for defining the growth/no growth interface as a function of temperature (10 to 37 degrees C), pH (pH 2.8 to 6.9), lactic acid concentration (0 to 500 mM), and water activity (0.955 to 0.999; NaCl was used as the humectant). Escherichia coli was unable to grow in broth in which the undissociated lactic acid concentration exceeded 11 mM or, with two exceptions, at a pH of 3.9 or less with no lactic acid present. Under experimental conditions at which the pH and the undissociated acid concentrations were the major growth-limiting factors, the growth/no growth interface was essentially independent of temperature at temperatures ranging from 15 to 37 degrees C. The interface between conditions that allowed growth and conditions at which growth did not occur was abrupt. The inhibitory effect of combinations of water activity and pH varied with temperature. Predictions of the model for the growth/no growth interface were consistent with 95% of the experimental data set.

Escherichia coli↗
PubMed1998

Image analysis and pattern recognition for computer supported skin tumor diagnosis.

A new approach to computer supported recognition of melanoma and naevocytic naevi based on high resolution skin surface profiles is presented. Profiles are generated by sampling an area of 4 x 4 mm2 at a resolution of 125 sample points per mm with a laser profilometer at a vertical resolution of 0.1 micron. With image analysis algorithms Haralick's texture parameters, Fourier features and features based on fractal analysis are extracted. Genetic algorithms are employed successfully to select good feature subsets for the following classification process. As quality measure for feature subsets, the error rate of the nearest neighbor classifier estimated with the leaving-one-out method is used. Classification is performed with feed forward back-propagation network and the nearest neighbor classifier. Classification performance of the neural classifier is optimized using different topologies, learning parameters and pruning algorithms. The best neural classifier achieved an error rate of 4.5% and was found after network pruning. The best result with an error rate of 2.3% was obtained with the nearest neighbor classifier.

Algorithms↗
PubMed1998

Care activities and outcomes of patients cared for by acute care nurse practitioners, physician assistants, and resident physicians: a comparison.

BACKGROUND: Little information is available on the practice of acute care nurse practitioners and physician assistants in acute care settings. OBJECTIVES: To compare the care activities performed by acute care nurse practitioners and physician assistants and the outcomes of their patients with the care activities and patients' outcomes of resident physicians. METHODS: Sixteen acute care nurse practitioners and physician assistants and a matched group of resident physicians were studied during a 14-month period. Data on the subjects' daily activities and on patients' outcomes were collected 4 times. RESULTS: Compared with the acute care nurse practitioners and physician assistants, residents cared for patients who were older and sicker, cared for more patients, worked more hours, took a more active role in patient rounds, and spent more time in lectures and conferences. The nurse practitioners and physician assistants were more likely than the residents to discuss patients with bedside nurses and to interact with patients' families. They also spent more time in research and administrative activities. Few of the acute care nurse practitioners and physician assistants performed invasive procedures on a regular basis. Outcomes were assessed for 187 patients treated by the acute care nurse practitioners and physician assistants and for 202 patients treated by the resident physicians. Outcomes did not differ markedly for patients treated by either group. The acute care nurse practitioners and physician assistants were more likely than the residents to include patients' social history in the admission notes. CONCLUSIONS: The tasks and activities performed by acute care nurse practitioners and physician assistants are similar to those performed by resident physicians. However, residents treat patients who are sicker and older than those treated by acute care nurse practitioners and physician assistants. Patients' outcomes are similar for both groups of subjects.

Acute Disease↗
PubMed1997

Development and evaluation of a predictive model for the effect of temperature and water activity on the growth rate of Vibrio parahaemolyticus.

The growth rates of four strains of Vibrio parahaemolyticus were measured and compared in a model broth system. The results for the fastest growing strain, based on 77 combinations of temperature and water activity (aw) using NaCl as the humectant, were summarised in the form of a predictive mathematical model. The model, of the square-root type includes a novel term to describe the effects of super-optimal water activity, and can be used to predict generation times for the temperature range (8-45 degrees C) and water activity range (0.936-0.995) which permit growth of Vibrio parahaemolyticus. Predicted generation times from the model were compared to literature data, using bias and accuracy factors, for both laboratory media and foods. The model was shown to give realistic growth estimates, with a bias value of 1.01, and an accuracy factor of 1.38.

Models, Biological↗
PubMed1997

The likely financial effects on individuals, industry and commerce of the use of genetic information.

In this paper I look at the financial implications of genetic testing, particularly in the employment and pensions fields. I have generally not covered life insurance, as that is covered in other papers in this Discussion Meeting. However, the issues are similar, although the emphasis is different. Inevitably there is an element of speculation involved; genetic testing is in its infancy and so we cannot predict either what information we will be able to obtain through genetic testing, nor the uses that may be devised for this information.

Adult↗
PubMed1997

Development of a predictive model to describe the effects of temperature and water activity on the growth of spoilage pseudomonads.

A combined temperature and water activity model for the growth of psychrotrophic pseudomonads was developed using turbidimetric data. Psychrotrophic pseudomonads were isolated from various modified and whole milks. The fastest growing strain was identified and used to develop the model. Generation time estimates calculated by turbidimetric and viable count data differed but this difference was constant with respect to temperature and was incorporated into the modelling process so that all models are constructed to predict generation times equivalent to those calculated by viable counts, the standard method for enumerating microorganisms in food products.

Animals↗
PubMed1997

Validation of a model describing the effects of temperature and water activity on the growth of psychrotrophic pseudomonads.

The reliability of the predictive model for the growth of psychrotrophic pseudomonads was evaluated both under controlled laboratory conditions and in industry conditions using various milks, milk-based products, meat and meat products. The validation process involved monitoring the growth of pseudomonads at various temperatures and comparing the observed generation times to those predicted by the model using bias and accuracy factors. For fluctuating temperatures bias and accuracy factors were used to compare the predicted and observed times to reach various population densities. The psychrotrophic pseudomonad model was shown to predict accurately the growth of pseudomonads in the products tested. In some instances knowledge of the lag phase duration was required to maximise the performance of the model.

Animals↗
PubMed1997

Acid habituation of Escherichia coli and the potential role of cyclopropane fatty acids in low pH tolerance.

A reversible adaptive tolerance to low pH termed 'acid habituation' is demonstrated for five strains of Escherichia coli. Superimposed upon the intrinsic acid tolerance of individual strains, acid habituation significantly enhances the survival of exponential phase cultures exposed to a lethal acid challenge (pH 3.0), and minimises inter-strain variability in acid tolerance. The fatty acid composition of acid habituated, non-habituated, and de-habituated exponential phase cultures is also reported. During acid habituation, monounsaturated fatty acids (16:1 omega 7c and 18:1 omega 7c) present in the phospholipids of E. coli are either converted to their cyclopropane derivatives (cy17:0 and cy19:0), or replaced by saturated fatty acids. The acid tolerance of individual strains of E. coli appears to be correlated with membrane cyclopropane fatty acid content and, thus, it is postulated that increased levels of cyclopropane fatty acids may enhance the survival of microbial cells exposed to low pH. The results presented illustrate the remarkable capacity of E. coli to adapt to environmental challenges, and have significant implications for the survival of spoilage and pathogenic bacteria, and hence for food safety.

Adaptation, Physiological↗
PubMed1997

Modelling the growth rate of Escherichia coli as a function of pH and lactic acid concentration.

The growth rate responses of Escherichia coli M23 (a nonpathogenic strain) to suboptimal pH and lactic acid concentration were determined. Growth rates were measured turbidimetrically at 20 degrees C in the range of pH 2.71 to 8.45. The total concentration of lactic acid was fixed at specific values, and the pH was varied by the addition of a strong acid (hydrochloric) or base (sodium hydroxide) to enable the determination of undissociated and dissociated lactic acid concentrations under each condition. In the absence of lactic acid, E. coli grew at pH 4.0 but not at pH 3.7 and was unable to grow in the presence of > or = 8.32 mM undissociated lactic acid. Growth rate was linearly related to hydrogen ion concentration in the absence of lactic acid. In the range 0 to 100 mM lactic acid, growth rate was also linearly related to undissociated lactic acid concentration. A mathematical model to describe these observations was developed based on a Bĕlehrádek-like model for the effects of water activity and temperature. This model was expanded to describe the effects of pH and lactic acid by the inclusion of novel terms for the inhibition due to the presence of hydrogen ions, undissociated lactic acid, and dissociated lactic acid species. Preliminary data obtained for 200 and 500 mM total lactic acid concentrations show that the response to very high lactic acid concentrations was less well described by the model. However, for 0 to 100 mM lactic acid, the model described well the qualitative and quantitative features of the response.

Cell Division↗