scholarly journals Development and Validation of a Predictive Model for the Growth of Vibrio vulnificus in Postharvest Shellstock Oysters

2012 ◽  
Vol 78 (6) ◽  
pp. 1675-1681 ◽  
Author(s):  
Ligia DaSilva ◽  
Salina Parveen ◽  
Angelo DePaola ◽  
John Bowers ◽  
Kathy Brohawn ◽  
...  
Keyword(s):  
Growth Rate ◽  
Chesapeake Bay ◽  
Predictive Model ◽  
Growth Rates ◽  
Vibrio Vulnificus ◽  
Assessment Model ◽  
Mobile Bay ◽  
Content Type ◽  
Wide Range ◽  
Eastern Oysters

ABSTRACTPostharvest growth ofVibrio vulnificusin oysters can increase risk of human infection. Unfortunately, limited information is available regardingV. vulnificusgrowth and survival patterns over a wide range of storage temperatures in oysters harvested from different estuaries and in different oyster species. In this study, we developed a predictive model forV. vulnificusgrowth in Eastern oysters (Crassostrea virginica) harvested from Chesapeake Bay, MD, over a temperature range of 5 to 30°C and then validated the model againstV. vulnificusgrowth rates (GRs) in Eastern and Asian oysters (Crassostrea ariakensis) harvested from Mobile Bay, AL, and Chesapeake Bay, VA, respectively. In the model development studies,V. vulnificuswas slowly inactivated at 5 and 10°C with average GRs of −0.0045 and −0.0043 log most probable number (MPN)/h, respectively. Estimated average growth rates at 15, 20, 25, and 30°C were 0.022, 0.042, 0.087, and 0.093 log MPN/h, respectively. With respect to Eastern oysters, bias (Bf) and accuracy (Af) factors for model-dependent and -independent data were 1.02 and 1.25 and 1.67 and 1.98, respectively. For Asian oysters,BfandAfwere 0.29 and 3.40. Residual variations in growth rate about the fitted model were not explained by season, region, water temperature, or salinity at harvest. Growth rate estimates for Chesapeake Bay and Mobile Bay oysters stored at 25 and 30°C showed relatively high variability and were lower than Food and Agricultural Organization (FAO)/WHOV. vulnificusquantitative risk assessment model predictions. The model provides an improved tool for designing and implementing food safety plans that minimize the risk associated withV. vulnificusin oysters.

scholarly journals Dynamics in Copy Numbers of Five Plasmids of a DairyLactococcus lactisStrain under Dairy-Related Conditions Including Near-Zero Growth Rates

2018 ◽  
Vol 84 (11) ◽  
Author(s):  
Oscar van Mastrigt ◽  
Marcel M. A. N. Lommers ◽  
Yorick C. de Vries ◽  
Tjakko Abee ◽  
Eddy J. Smid
Keyword(s):  
Nutrient Limitation ◽  
Lactococcus Lactis ◽  
Growth Rates ◽  
Copy Number ◽  
Plasmid Copy ◽  
Content Type ◽  
Copy Numbers ◽  
Wide Range ◽  
Zero Growth ◽  
The Impact

ABSTRACTLactic acid bacteria can carry multiple plasmids affecting their performance in dairy fermentations. The expression of plasmid-borne genes and the activity of the corresponding proteins are severely affected by changes in the numbers of plasmid copies. We studied the impact of growth rate on the dynamics of plasmid copy numbers at high growth rates in chemostat cultures and down to near-zero growth rates in retentostat cultures. Five plasmids of the dairy strainLactococcus lactisFM03-V1 were selected, and these varied in size (3 to 39 kb), in replication mechanism (theta or rolling circle), and in putative (dairy-associated) functions. The copy numbers ranged from 1.5 to 40.5, and the copy number of theta-type replicating plasmids was negatively correlated to the plasmid size. Despite the extremely wide range of growth rates (0.0003 h−1to 0.6 h−1), the copy numbers of the five plasmids were stable and only slightly increased at near-zero growth rates, showing that the plasmid replication rate was strictly controlled. One low-copy-number plasmid, carrying a large exopolysaccharide gene cluster, was segregationally unstable during retentostat cultivations, reflected in a complete loss of the plasmid in one of the retentostat cultures. The copy number of the five plasmids was also hardly affected by varying the pH value, nutrient limitation, or the presence of citrate (maximum 2.2-fold), signifying the stability in copy number of the plasmids.IMPORTANCELactococcus lactisis extensively used in starter cultures for dairy fermentations. Important traits for the growth and survival ofL. lactisin dairy fermentations are encoded by genes located on plasmids, such as genes involved in lactose and citrate metabolism, protein degradation, oligopeptide uptake, and bacteriophage resistance. Because the number of plasmid copies could affect the expression of plasmid-borne genes, it is important to know the factors that influence the plasmid copy numbers. We monitored the plasmid copy numbers ofL. lactisat near-zero growth rates, characteristic for cheese ripening. Moreover, we analyzed the effects of pH, nutrient limitation, and the presence of citrate. This showed that the plasmid copy numbers were stable, giving insight into plasmid copy number dynamics in dairy fermentations.

Combustion Instabilities Damping System Development for Dry Low NOx Emissions Operability Enhancement of a Heavy-Duty Gas Turbine

2019 ◽  
Author(s):  
Matteo Cerutti ◽  
Nicola Giannini ◽  
Bruno Schuermans ◽  
Riccardo Brenci ◽  
Alessandro Marini ◽  
...  
Keyword(s):  
Growth Rate ◽  
Gas Turbine ◽  
Growth Rates ◽  
Fine Tuning ◽  
Optimized Design ◽  
Nox Emissions ◽  
Preliminary Design ◽  
Heavy Duty ◽  
Wide Range ◽  
Heavy Duty Gas Turbine

Abstract This paper describes the development phases of a damping system for combustion instability reduction in an annular type combustor for heavy-duty gas turbine applications. As reported by the authors in a previous paper, the full scale annular test rig allowed for an extensive characterization of the combustor with realistic acoustic boundaries at engine-relevant conditions. Emissions and operability assessment over a wide range of load conditions was performed, allowing the evaluation of the response of the system near the thermo-acoustic instability onset. The instability is quantified by its acoustic growth rate. This quantity is a crucial input in the design process of dampers. A methodology has been used to extract these growth rates form measured pulsation data. Experimentally determined growth rates have been evaluated for different fuel flow rate split between the main and the pilot injections, providing input to dampers preliminary design. Given current combustor architecture constraints, a first attempt configuration has been proposed and performances evaluated in the full annular rig. Dampers have been equipped with dynamic sensors and thermocouples with the purpose of measuring the growth rate abatement and the consequent NOx emissions reduction. A dedicated numerical toolbox, in-house developed by GE Power, has been used for both dampers preliminary design and growth rate reduction evaluation. Fine tuning of dampers elements as well as design assumptions adjustments required additional experimental evaluations and design iterations. Encouraged by the successful test in the concept phase, an optimized design for engine implementation was defined, that featured a significant increased damper volume, involving combustor parts re-design. The optimized configuration was finally tested in full annular rig and results demonstrated an important enhancement of operability while maintaining NOx emissions below the target levels.

Growth Characteristics and Development of a Predictive Model for Bacillus cereus in Fresh Wet Noodles with Added Ethanol and Thiamine

2011 ◽  
Vol 74 (4) ◽  
pp. 658-664 ◽  
Author(s):  
BO-YEON KIM ◽  
JI-YOUNG LEE ◽  
SANG-DO HA
Keyword(s):  
Growth Rate ◽  
Response Surface Methodology ◽  
Bacillus Cereus ◽  
Predictive Model ◽  
Response Surface ◽  
Growth Rates ◽  
Vitamin B1 ◽  
Growth Characteristics ◽  
Quadratic Polynomial ◽  
Polynomial Model

Response surface methodology was used to determine growth characteristics and to develop a predictive model to describe specific growth rates of Bacillus cereus in wet noodles containing a combination of ethanol (0 to 2% [vol/wt]) and vitamin B1 (0 to 2 g/liter). B. cereus F4810/72, which produces an emetic toxin, was used in this study. The noodles containing B. cereus were incubated at 10°C. The growth curves were fitted to the modified Gompertz equation using nonlinear regression, and the growth rate values from the curves were used to establish the predictive model using a response surface methodology quadratic polynomial equation as a function of concentrations of ethanol and vitamin B1. The model was shown to fit the data very well (r2 = 0.9505 to 0.9991) and could be used to accurately predict growth rates. The quadratic polynomial model was validated, and the predicted growth rate values were in good agreement with the experimental values. The polynomial model was found to be an appropriate secondary model for growth rate (GR) and lag time (LT) based on the correlation of determination (r2 = 0.9899 for GR, 0.9782 for LT), bias factor (Bf = 1.006 for GR, 0.992 for LT), and accuracy factor (Af = 1.024 for GR, 1.011 for LT). Thus, this model holds great promise for use in predicting the growth of B. cereus in fresh wet noodles using only the bacterial concentration, an important contribution to the manufacturing of safe products.

scholarly journals Campylobacter Colonization and Proliferation in the Broiler Chicken upon Natural Field Challenge Is Not Affected by the Bird Growth Rate or Breed

2014 ◽  
Vol 80 (21) ◽  
pp. 6733-6738 ◽  
Author(s):  
Fraser J. Gormley ◽  
Richard A. Bailey ◽  
Kellie A. Watson ◽  
Jim McAdam ◽  
Santiago Avendaño ◽  
...  
Keyword(s):  
Growth Rate ◽  
Growth Rates ◽  
Consumer Preferences ◽  
Pure Line ◽  
Public Health Perspective ◽  
Content Type ◽  
Commercial Flock ◽  
Significant Difference ◽  
Commercial Broiler ◽  
Market Needs

ABSTRACTThe zoonotic association betweenCampylobacterbacteria in poultry and humans has been characterized by decades of research which has attempted to elucidate the epidemiology of this complex relationship and to reduce carriage within poultry. While much work has focused on the mechanisms facilitating its success in contaminating chicken flocks (and other animal hosts), it remains difficult to consistently excludeCampylobacterunder field conditions. Within the United Kingdom poultry industry, various bird genotypes with widely varying growth rates are available to meet market needs and consumer preferences. However, little is known about whether any differences inCampylobactercarriage exist across this modern broiler range. The aim of this study was to establish if a relationship exists between growth rate or breed and cecalCampylobacterconcentration after natural commercial flockCampylobacterchallenge. In one investigation, four pure line genotypes of various growth rates were grown together, while in the second, eight different commercial broiler genotypes were grown individually. In both studies, theCampylobacterconcentration was measured in the ceca at 42 days of age, revealing no significant difference in cecal load between birds of different genotypes both in mixed- and single-genotype pens. This is important from a public health perspective and suggests that other underlying reasons beyond genotype are likely to control and affectCampylobactercolonization within chickens. Further studies to gain a better understanding of colonization dynamics and subsequent proliferation are needed, as are novel approaches to reduce the burden in poultry.

scholarly journals Attenuated Virulence and Biofilm Formation in Staphylococcus aureus following Sublethal Exposure to Triclosan

2012 ◽  
Vol 56 (6) ◽  
pp. 3092-3100 ◽  
Author(s):  
Joe Latimer ◽  
Sarah Forbes ◽  
Andrew J. McBain
Keyword(s):  
Staphylococcus Aureus ◽  
Growth Rate ◽  
Growth Rates ◽  
Biofilm Formation ◽  
Galleria Mellonella ◽  
Concentration Gradients ◽  
Content Type ◽  
Small Colony Variant ◽  
Small Colony ◽  
Repeated Passage

ABSTRACTSubeffective exposure ofStaphylococcus aureusto the biocide triclosan can reportedly induce a small-colony variant (SCV) phenotype.S. aureusSCVs are characterized by low growth rates, reduced pigmentation, and lowered antimicrobial susceptibility. While they may exhibit enhanced intracellular survival, there are conflicting reports regarding their pathogenicity. The current study reports the characteristics of an SCV-like strain ofS. aureuscreated by repeated passage on sublethal triclosan concentrations.S. aureusATCC 6538 (the passage 0 [P0] strain) was serially exposed 10 times to concentration gradients of triclosan to generate strain P10. This strain was then further passaged 10 times on triclosan-free medium (designated strain ×10). The MICs and minimum bactericidal concentrations of triclosan for P0, P10, and ×10 were determined, and growth rates in biofilm and planktonic cultures were measured. Hemolysin, DNase, and coagulase activities were measured, and virulence was determined using aGalleria mellonellapathogenicity model. Strain P10 exhibited decreased susceptibility to triclosan and characteristics of an SCV phenotype, including a considerably reduced growth rate and the formation of pinpoint colonies. However, this strain also had delayed coagulase production, had impaired hemolysis (P< 0.01), was defective in biofilm formation and DNase activity, and displayed significantly attenuated virulence. Colony size, hemolysis, coagulase activity, and virulence were only partially restored in strain ×10, whereas the planktonic growth rate was fully restored. However, ×10 was at least as defective in biofilm formation and DNase production as P10. These data suggest that although repeated exposure to triclosan may result in an SCV-like phenotype, this is not necessarily associated with increased virulence and adapted bacteria may exhibit other functional deficiencies.

Trends and determinants of IT-BPM exports in India

2016 ◽  
Vol 7 (2) ◽  
pp. 212-232 ◽  
Author(s):  
Manzoor Hassan Malik ◽  
Nirmala Velan
Keyword(s):  
Information Technology ◽  
Growth Rate ◽  
Growth Rates ◽  
Labour Productivity ◽  
Domestic Market ◽  
Export Growth ◽  
Annual Data ◽  
Average Growth ◽  
Content Type ◽  
Export Revenue

Purpose The purpose of this paper is to present an overview of trends of Indian information technology and business processing management (IT-BPM) sector and to analyse the determinants of IT-BPM sector during the period 1991-2014. Design/methodology/approach The study is based on annual data collected from National Association of Software and Service Companies and Department of Electronic and Information Technology for the period 1991 to 2014. The methodology adopted for studying the objectives are simple averages, percentages, ratios, growth rates, graphs prepared on the basis of data from the IT-BPM sector and regression analysis. Trends and patterns in key variables, such as total revenue, domestic revenue, export revenue, employment and exports of the IT-BPM sector have been examined. Factors influencing IT-BPM export growth have been analysed using ordinary least square multiple regression model, with growth rates of gross domestic product (GDP), labour productivity, exchange rate and previous year’s export, as the explanatory variables. Findings The export revenue from IT-BPM sector increased continuously over the years, at an average growth rate of 36.60 per cent during the period 1991 to 2014. Similarly, domestic revenue of IT-BPM sector also increased, but at a lower growth rate. This is because domestic market in India is captured by multinational giants against Indian firms, which do not possess full comparative advantage in the case of IT-BPM sector. Indian firms are producing low skill activities required for production, mainly concentrated only in the export sector. Direct employment, excluding hardware from IT-BPM sector, has grown at an average rate of 18.08 per cent over the study period. The determinants of IT-BPM exports indicated previous year’s export demand to be significantly contributing the highest to export growth rate. This was followed by GDP growth rate, implying that overall growth of the economy leads to significant increase in export growth. Increased labour productivity followed next in significantly encouraging export growth. Research limitations/implications Generalization of the results may not be possible, as Indian conditions and policies vary. Practical implications The paper has implications for the expansion of domestic market, diversification of trade and products, innovations for increasing competitiveness and sustainability in the global market in the wake of stiff competitions from new competitors. Originality/value This paper focuses on originality in analysis of determinants of export growth.

scholarly journals Comparison of the Effects of Environmental Parameters on Growth Rates of Vibrio vulnificus Biotypes I, II, and III by Culture and Quantitative PCR Analysis

2011 ◽  
Vol 77 (12) ◽  
pp. 4200-4207 ◽  
Author(s):  
Eva Chase ◽  
Valerie J. Harwood
Keyword(s):  
Quantitative Pcr ◽  
Growth Rates ◽  
Environmental Changes ◽  
Vibrio Vulnificus ◽  
Environmental Parameters ◽  
Defined Medium ◽  
Pcr Analysis ◽  
Human Pathogens ◽  
Content Type ◽  
Specific Growth Rates

ABSTRACTVibrio vulnificusis a natural inhabitant of estuarine waters. The three known biotypes include (i) most human pathogens, (ii) primarily eel pathogens, and (iii) pathogens associated with fish and with human wound infections in Israel. Despite the frequently lethal consequences ofV. vulnificusinfections, the growth rates of the various biotypes and their response to environmental changes are not well characterized. We compared the specific growth rates (μ) of a representative of each biotype by culture and quantitative PCR (qPCR) analysis in a defined medium under varied pH, temperature, and salinity. Growth rates based on culturable concentrations were always higher than those based on qPCR estimates; however, both enumeration methods yielded comparable results on the influence of environmental factors on growth rates. Temperature (25°C, 30°C, 37°C), pH (7.0, 8.0), and salinity (5 to 40‰) all had significant effects on the μ of each biotype. Temperature had the greatest effect on the μ of biotype 1 (CMCP6), whereas salinity had the greatest effect on the μ of biotypes 2 (ATCC 33147) and 3 (302/99). The biotypes' growth rates varied significantly; biotype 1 grew most rapidly, while biotype 3 grew most slowly. The highest growth rates were achieved at 37°C, pH 7.0, and salinities of 15 to 30‰ (μ = 4.0, 2.9, and 2.4 generations h−1for biotypes 1, 2, and 3, respectively). Other strains of the biotypes yielded comparable results, suggesting that the physiological responses of the biotypes are differentially affected by parameters that are highly variable both in estuarine environments and between the free-living and pathogen states ofV. vulnificus.

scholarly journals Kinetic and Surface Mechanisms to Growth of Hexagonal Boron Nitride

2002 ◽  
Vol 750 ◽  
Author(s):  
Patrícia R. R. Barreto ◽  
Alan E. Kull ◽  
Mark A. Cappelli
Keyword(s):  
Growth Rate ◽  
Boron Nitride ◽  
Gas Phase ◽  
Growth Rates ◽  
Hexagonal Boron Nitride ◽  
Great Influence ◽  
Theoretical Data ◽  
State Theory ◽  
Elementary Reactions ◽  
Wide Range

ABSTRACTA mechanism is presented for the gas-phase chemistry and surface reactions describing the growth of boron nitride films. The gas phase mechanism includes 33 species and 216 elementary reactions. Rate parameters for 117 elementary reactions were obtained from published experimental/theoretical data and those for the other 99 were determined using transition state theory. The mechanism examined here is an extension and update of a previous mechanism that contained 26 species and 67 elementary reactions. Standard reaction flux/pathway and gradient sensitivity analysis techniques are used to identify important reaction pathways. The calculations were handled through the use of the ChemKin software package. The model was applied to the growth of hexagonal boron nitride in an arcjet plasma source operating on mixture of BF3, H2 and N2. From the growth rate and experimental conditions for such reactors, this work demonstrates that species with mole fractions in the range of 1 × 10-10 − 2 × 10-4 (easily generated by gas-phase conditions) can account for the measured growth rate. A comparison of the predicted mole fractions of the gas-phase species present for the experimental residence times with those required to account for the measured film growth rates allows us to identify possible growth precursors. At the experimental settings, it is found that the residence time of the reacting species does not allow the flow to reach the chemical equilibrium, and that many radicals other than the source gases can account for the measured BN growth rate. The gas-phase is shown to be removed from thermodynamic equilibrium. For comparison, the equilibrium mole fractions were also calculated using an available equilibrium chemistry solver, STANJAN. Growth rates of 10-9 to 10-6 kg m-1 s-1 were measured for a wide range of H2, BF3 and NF3 flux. Both the finite-rate kinetics and equilibrium calculations confirm the importance of added hydrogen to facilitate boron nitride condensation from the gas phase. A simple surface mechanism with 7 steps is proposed with rate constants chosen to best fit the experimental growth kinetics. The results of the model, with surface rate coefficients determined from analogous gas-phase reactions, tuned slightly to agree with the experimental growth rates for BFx, x = 1, 2 or 3, as the rate-limiting growth precursor. It is also shown that the hydrogen atom has a great influence in the growth rate and that fluorine atom etches the hBN films.

Cleaning during Initial Stages of Epitaxial Growth in an Ultrahigh Vacuum Rapid Thermal Chemical Vapor Deposition Reactor

1993 ◽  
Vol 334 ◽  
Author(s):  
Mahesh K. Sanganeria ◽  
Katherine E. Violette ◽  
Mehmet C. ÖZtÜRk ◽  
Gari Harris ◽  
C. Archie Lee ◽  
...  
Keyword(s):  
Growth Rate ◽  
Epitaxial Growth ◽  
Oxygen Concentration ◽  
Growth Rates ◽  
Oxygen Absorption ◽  
Substrate Interface ◽  
Wide Range ◽  
Order Of Magnitude ◽  
Si Films ◽  
Water Rinse

AbstractIn this paper, we report our results on surface preparation for the growth of epitaxial Si films. Hydrogen passivated surfaces are currently being investigated for application in Si epitaxy to eliminate the high temperature in-situ bake necessary to remove the native oxide. Hydrogen passivation is obtained by a dilute HF dip before the substrate is loaded in the process chamber. However the passivation is partially lost when the HF dip is followed by a water rinse which results in oxygen absorption on the substrate. It was found that the peak oxygen concentration at the epitaxy substrate interface increase by an order of magnitude due to a five minute water rinse. We report here that oxygen and carbon at the epitaxy substrate interface can be desorbed during initial stage of epitaxial growth by reducing epitaxial growth rate. In this work, epitaxial Si films were deposited over a wide range of growth rates obtained by varying Si2H6 flow rates. The peak oxygen concentration decreases by an order of magnitude by changing the growth rate from 3000 to 700Å/kminute for a deposition temperature of 800°C. We believe that at higher growth rates Si overgrows on absorbed oxygen maintaining epitaxial alignment reflected in the good electrical quality of the epitaxial films. However, at low growth rates oxygen has sufficient time to desorb before overgrowth can take place, improving the epitaxy substrate interface quality.

Digital divide in the major regions of the world and the possibility of convergence

2021 ◽  
Vol 34 (1) ◽  
pp. 68-85
Author(s):  
Henry Egbezien Inegbedion
Keyword(s):  
Growth Rate ◽  
Digital Divide ◽  
Growth Rates ◽  
Quantitative Research ◽  
Internet Usage ◽  
The Other ◽  
Empirical Literature ◽  
The Internet ◽  
Content Type ◽  
The World

Purpose The purpose of this paper is to investigate the nature of the inequalities in the usage of the internet and inequalities in the growth rate in the usage of the internet, and thus ascertain the possibility of convergence of the digital divide between the major regions of the world. Design/methodology/approach The design was a longitudinal study of the usage of internet and growth rate in the usage of the internet in the different regions of the world for the period 2009–2019. The quantitative research method was used. Simple percentages and F-test were used in data analysis. Findings The usage of internet in Asia and Europe is higher than all the other regions in the world but there is no significant difference in usage between the other regions. The results further showed that some of the digitally disadvantaged regions had higher growth rates in the usage of the internet and these digitally disadvantage states are not disadvantaged in access to smartphones and the emerging 5G technology, thus suggesting the possibility of imminent convergence in access to the internet given the increasing usage of smartphones for the internet subscription. Research limitations/implications The focus on internet usage in the major regions of the world without recourse to the variability of the usage and growth rate of internet usage within the regions. The dearth of the empirical literature on quantitative research on the research problem was another constraint. Finally, restriction in available statistics on digital divide constrained the use of 2009–2019 as the periodic scope of the study. Practical implications Inclusion of ICT in the school curricula of the component states to acquaint them with information and communication technology (ICT) usage at an early stage, as well as provision of the enabling environment for business to thrive and through a national culture that will encourage businesses to be vibrant, and thus lay a foundation for future convergence. Social implications Enhancement in employment opportunities through the increased investment in the ICT facilities and the subsequent reduction in social vices. Originality/value Use of secondary data through a longitudinal design to categorically indicate the differences between the different regions of the world in terms of internet usage, as well as the empirical determination of the discrepancies between the growth rates in the access to internet and usage of internet by different regions of the world, especially as regard some of the digitally disadvantaged regions having higher growth rates in the usage of the internet than the perceived digitally advantaged regions.

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