The Experts below are selected from a list of 297 Experts worldwide ranked by ideXlab platform
David A. Ratkowsky - One of the best experts on this subject based on the ideXlab platform.
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predictive microbiology towards the Interface and beyond
International Journal of Food Microbiology, 2002Co-Authors: Thomas A. Mcmeekin, David A. Ratkowsky, Joseph Olley, T RossAbstract:Abstract This review considers the concept and history of predictive microbiology and explores aspects of the modelling process including kinetic and probability modelling approaches. The “journey” traces the route from reproducible responses observed under close to optimal conditions for Growth, through recognition and description of the increased variability in responses as conditions become progressively less favourable for Growth, to defining combinations of factors at which Growth ceases (the Growth/no Growth Interface). Death kinetics patterns are presented which form a basis on which to begin the development of nonthermal death models. This will require incorporation of phenotypic, adaptive responses and may be influenced by factors such as the sequence in which environmental constraints are applied. A recurrent theme is that probability (stochastic) approaches are required to complement or replace kinetic models as the Growth/no Growth Interface is approached and microorganisms adopt a survival rather than Growth mode. Attention is also drawn to the Interfaces of predictive microbiology with microbial physiology, information technology and food safety initiatives such as HACCP and risk assessment.
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Quantifying the hurdle concept by modelling the bacterial Growth/no Growth Interface.
International journal of food microbiology, 2000Co-Authors: Thomas A. Mcmeekin, David A. Ratkowsky, T Ross, K Presser, M Salter, S TienungoonAbstract:The hurdle concept described eloquently over many years by Professor Leistner and his colleagues draws attention to the interaction of factors that affect microbial behaviour in foods. Under some circumstances these effects are additive. Under others the implication is that synergistic interactions lead to a combined effect of greater magnitude than the sum of constraints applied individually. Predictive modelling studies on the combined effects of temperature and water activity and temperature and pH suggest that the effect of these combinations on Growth rate is independent. Where the effect of the two factors is interactive rather than independent is at the point where Growth ceases--the Growth/no Growth Interface. An interesting and consistent observation is that a very sharp cut off occurs between conditions permitting Growth and those preventing Growth, allowing those combinations of factors to be defined precisely and modelled. Growth/no Growth Interface models quantify the effects of various hurdles on the probability of Growth and define combinations at which the Growth rate is zero or the lag time infinite. Increasing the stringency of one or more hurdles at the Interface by only a small amount will significantly decrease the probability of an organism growing. Understanding physiological processes occurring near the Growth/no Growth Interface and changes induced by moving from one side of the Interface to the other may well provide insights that can be exploited in a new generation of food preservation techniques with minimal impact on product quality.
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modelling the Growth limits Growth no Growth Interface of escherichia coli as a function of temperature ph lactic acid concentration and water activity
Applied and Environmental Microbiology, 1998Co-Authors: K A Presser, T Ross, David A. RatkowskyAbstract:The form of a previously developed Bělehradek 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°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°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.
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Modelling the Growth Limits (Growth/No Growth Interface) of Escherichia coli as a Function of Temperature, pH, Lactic Acid Concentration, and Water Activity
Applied and Environmental Microbiology, 1998Co-Authors: K A Presser, Tom Ross, David A. RatkowskyAbstract:The form of a previously developed Bělehradek 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°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°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.
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Modelling the bacterial Growth/no Growth Interface
Letters in Applied Microbiology, 1995Co-Authors: David A. Ratkowsky, Tom RossAbstract:A logistic regression model is proposed which enables one to model the boundary between Growth and no Growth for bacterial strains in the presence of one or more Growth controlling factors such as temperature, pH and additives such as salt and sodium nitrite. The form of the expression containing the Growth limiting factors may be suggested by a kinetic model, while the response at a given combination of factors may either be presence/absence (i.e. Growth/no Growth) or probabilistic (i.e. r successes in n trials). The approach described represents an integration of the probability and kinetic aspects of predictive microbiology, and a unification of predictive microbiology and the hurdle concept. The model is illustrated using data for Shigella flexneri.
K A Presser - One of the best experts on this subject based on the ideXlab platform.
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modelling the Growth limits Growth no Growth Interface of escherichia coli as a function of temperature ph lactic acid concentration and water activity
Applied and Environmental Microbiology, 1998Co-Authors: K A Presser, T Ross, David A. RatkowskyAbstract:The form of a previously developed Bělehradek 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°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°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.
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Modelling the Growth Limits (Growth/No Growth Interface) of Escherichia coli as a Function of Temperature, pH, Lactic Acid Concentration, and Water Activity
Applied and Environmental Microbiology, 1998Co-Authors: K A Presser, Tom Ross, David A. RatkowskyAbstract:The form of a previously developed Bělehradek 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°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°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.
T Ross - One of the best experts on this subject based on the ideXlab platform.
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predictive microbiology towards the Interface and beyond
International Journal of Food Microbiology, 2002Co-Authors: Thomas A. Mcmeekin, David A. Ratkowsky, Joseph Olley, T RossAbstract:Abstract This review considers the concept and history of predictive microbiology and explores aspects of the modelling process including kinetic and probability modelling approaches. The “journey” traces the route from reproducible responses observed under close to optimal conditions for Growth, through recognition and description of the increased variability in responses as conditions become progressively less favourable for Growth, to defining combinations of factors at which Growth ceases (the Growth/no Growth Interface). Death kinetics patterns are presented which form a basis on which to begin the development of nonthermal death models. This will require incorporation of phenotypic, adaptive responses and may be influenced by factors such as the sequence in which environmental constraints are applied. A recurrent theme is that probability (stochastic) approaches are required to complement or replace kinetic models as the Growth/no Growth Interface is approached and microorganisms adopt a survival rather than Growth mode. Attention is also drawn to the Interfaces of predictive microbiology with microbial physiology, information technology and food safety initiatives such as HACCP and risk assessment.
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Quantifying the hurdle concept by modelling the bacterial Growth/no Growth Interface.
International journal of food microbiology, 2000Co-Authors: Thomas A. Mcmeekin, David A. Ratkowsky, T Ross, K Presser, M Salter, S TienungoonAbstract:The hurdle concept described eloquently over many years by Professor Leistner and his colleagues draws attention to the interaction of factors that affect microbial behaviour in foods. Under some circumstances these effects are additive. Under others the implication is that synergistic interactions lead to a combined effect of greater magnitude than the sum of constraints applied individually. Predictive modelling studies on the combined effects of temperature and water activity and temperature and pH suggest that the effect of these combinations on Growth rate is independent. Where the effect of the two factors is interactive rather than independent is at the point where Growth ceases--the Growth/no Growth Interface. An interesting and consistent observation is that a very sharp cut off occurs between conditions permitting Growth and those preventing Growth, allowing those combinations of factors to be defined precisely and modelled. Growth/no Growth Interface models quantify the effects of various hurdles on the probability of Growth and define combinations at which the Growth rate is zero or the lag time infinite. Increasing the stringency of one or more hurdles at the Interface by only a small amount will significantly decrease the probability of an organism growing. Understanding physiological processes occurring near the Growth/no Growth Interface and changes induced by moving from one side of the Interface to the other may well provide insights that can be exploited in a new generation of food preservation techniques with minimal impact on product quality.
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modelling the Growth limits Growth no Growth Interface of escherichia coli as a function of temperature ph lactic acid concentration and water activity
Applied and Environmental Microbiology, 1998Co-Authors: K A Presser, T Ross, David A. RatkowskyAbstract:The form of a previously developed Bělehradek 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°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°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.
Sonia Marin - One of the best experts on this subject based on the ideXlab platform.
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Modelling the effect of temperature and water activity of Aspergillus flavus isolates from corn
International Journal of Food Microbiology, 2012Co-Authors: Andrea Astoreca, Graciela Vaamonde, A Dalcero, A J Ramos, Sonia MarinAbstract:The aim of this study was to model the effects of temperature (10-40°C) and aw(0.80-0.98), in two media (Czapek yeast agar: CYA; corn extract medium: CEM) on the Growth rates and Growth boundaries (Growth-no Growth Interface) of three strains of A. flavus isolated from corn in Argentina. Both kinetic and probability models were applied to colony Growth data. The Growth rates obtained in CYA were significantly (p
Tao Wang - One of the best experts on this subject based on the ideXlab platform.
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Modification of Growth Interface of CdZnTe crystals in THM process by ACRT
Journal of Crystal Growth, 2018Co-Authors: Boru Zhou, Tao Wang, Fan Yang, Binbin Zhang, Shouzhi Xi, Jiangpeng DongAbstract:Abstract The accelerated crucible rotation technique (ACRT) was introduced in the traveling heater method (THM) Growth process of detector-grade CdZnTe (CZT) crystals to regulate the convection in the melt and to modify the Growth Interface morphology. Several ingots with the diameter of 53 mm were grown by THM with/without ACRT. The ingots were quenched during the Growth to show both macroscopic and microscopic morphologies of the Growth Interfaces. The results show that by using ACRT the Growth Interface can be changed from a concave one to the flat or even convex one depending on the ACRT parameters, which is favorable for reducing nucleation in the melt to get larger CZT grains. Meanwhile, by using ACRT in THM process, the microscopic Interface was changed from a diffused one to cellular or even planar one (at suitable ACRT parameters), through which the trapped Te inclusions was decreased for one order. An ingot grown by THM with constant rotation rate of 40 rpm was also grown, which have also reduced the Interface curvature in macro-scale and Te inclusions to some extent, but the effects are not as significant as ACRT with high crucible rotation rate.
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Numerical simulation of the multicomponent mass transfer during Bridgman Growth of CdZnTe crystal using Maxwell-Stefan diffusion model
Journal of Wuhan University of Technology-materials Science Edition, 2017Co-Authors: Tao Wang, Boru Zhou, Fan YangAbstract:To reveal the complicated mechanism of the multicomponent mass transfer during the Growth of ternary compound semiconductors, a numerical model based on Maxwell-Stefan equations was developed to simulate the Bridgman Growth of CdZnTe crystal. The Maxwell-Stefan diffusion coefficients in the melt were estimated. Distributions of Zn, Cd, and Te were calculated with variable ampoule traveling rate and diffusion coefficients. The experimental results show that Zn in melt near the Growth Interface decreases and diffuses from the bulk melt to the Growth Interface. For Cd, the situation is just the opposite. The coupling effects of Zn and Cd diffusions result in an uphill diffusion of Te at the beginning of the Growth. Throughout the Growth, the concentration of Te in the melt keeps low near the Growth Interface but high far from the Growth Interface. Increasing the ampoule traveling rate will aggravate the segregation of Zn and Cd, and hence deteriorate the uniformity of Te. We also find that not only the diffusion coefficients but also the ratios between them have significant influence on the species diffusions.
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The transport phenomena during the Growth of ZnTe crystal by the temperature gradient solution Growth technique
Journal of Crystal Growth, 2017Co-Authors: Tao Wang, Boru Zhou, Fan YangAbstract:Abstract A numerical model is developed to simulate the temperature field, the thermosolutal convection, the solute segregation and the Growth Interface morphology during the Growth of ZnTe crystal from Te rich solution by the temperature gradient solution Growth (TGSG) technique. Effects of the temperature gradient on the transport phenomena, the Growth Interface morphology and the Growth rate are examined. The influences of the latent heat and the thermal conductivity of ZnTe crystal on the transport phenomena and the Growth Interface are also discussed. We find that the mass transfer of ZnTe in the solution is very slow because of the low diffusion coefficient and the lack of mixing in the lower part of the solution. During the Growth, dilute solution with high density and low Growth temperature accumulates in the central region of the Growth Interface, making the Growth Interface change into two distinct parts. The inner part is very concave, while the outer part is relatively flat. Growth conditions in front of the two parts of the Growth Interface are different. The crystalline quality of the inner part of the ingot is predicted to be worse than that of the outer part. High temperature gradient can significantly increase the Growth rate, and avoid the diffusion controlled Growth to some extent.
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Growth Interface of In-doped CdMnTe from Te solution with vertical Bridgman method under ACRT technique
Transactions of Nonferrous Metals Society of China, 2012Co-Authors: Yuan-yuan Du, Xin Zheng, Tao WangAbstract:Abstract CdMnTe (CMT) crystals were grown from Te solution with vertical Bridgman method under accelerated crucible rotation (ACRT) technique. Ingot in diameter of 30 mm and length of 60 mm was obtained. The result shows that as-grown CMT has fewer twins compared with the one grown by conventional vertical Bridgman method. However, IR microscopy shows that the microscopic Growth Interface morphology is non-uniform and irregular, which is attributed to higher Te inclusions density. Meanwhile, the laser confocal microscope images reveal that the Te phases are deposited randomly in the Te-rich CMT region with irregular shapes and voids. By optimizing the Growth parameters to obtain a smooth Interface, the Te solution vertical Bridgman technique can effectively reduce the twins in CMT crystal.
