Relative effects of bacterial and protozoan predators on survival of Escherichia coli in estuarine water samples

The relative effect of protozoan and bacterial predators on the survival of Escherichia coli in estuarine water samples was examined. Predacious protozoa exerted their major influence on E. coli destruction during the first 2 days of a 10-day-decline period. Inhibition of protozoa after day 2 had little effect on E. coli survival. Bacterial predators also contributed to E. coli destruction but in natural estuarine water samples were maintained at lower levels due to "grazing" by predacious protozoa.     

Effect of water immersion on the microtopography of the skin of chicken carcasses

Water-immersion cleaning and chilling of poultry carcasses caused the skin to swell and exposed deep channels and crevices in the skin surface as a result of water uptake. These changes were demonstrated by electron microscopy and were shown to be dependent on the time of immersion and the temperature of the water. Addition of sodium chloride to the immersion medium and manipulation of the medium pH did not markedly affect or prevent these changes. The implications of these changes for microbial contamination during water-immersion chilling are discussed.     

Predictive microbiology: providing a knowledge-based framework for change management

This contribution considers predictive microbiology in the context of the Food Micro 2002 theme, "Microbial adaptation to changing environments". To provide a reference point, the state of food microbiology knowledge in the mid-1970s is selected and from that time, the impact of social and demographic changes on microbial food safety is traced. A short chronology of the history of predictive microbiology provides context to discuss its relation to and interactions with hazard analysis critical control point (HACCP) and risk assessment. The need to take account of the implications of microbial adaptability and variable population responses is couched in terms of the dichotomy between classical versus quantal microbiology introduced by Bridson and Gould [Lett. Appl. Microbiol. 30 (2000) 95]. The role of population response patterns and models as guides to underlying physiological processes draws attention to the value of predictive models in development of novel methods of food preservation. It also draws attention to the paradox facing today's food industry that is required to balance the "clean, green" aspirations of consumers with the risk, to safety or shelf life, of removing traditional barriers to microbial development. This part of the discussion is dominated by consideration of models and responses that lead to stasis and inactivation of microbial populations. This highlights the consequence of change on predictive modelling where the need is now to develop interface and non-thermal death models to deal with pathogens that have low infective doses for general and/or susceptible populations in the context of minimal preservation treatments. The challenge is to demonstrate the validity of such models and to develop applications of benefit to the food industry and consumers as was achieved with growth models to predict shelf life and the hygienic equivalence of food processing operations.     

Small-spot interference pattern for single-step 2D integration and wide wavelength detuning of planar Bragg gratings

A single-step technique for defining 2D channel waveguide structures with internal Bragg gratings in photosensitive germanosilica-on-silicon using two interfering focused UV beams is presented. Through software control, grating detuning across the S-, C-, and L-wavelength bands is also demonstrated.     

Crystallization Kinetics and Morphology Control of Formamidinium–Cesium Mixed‐Cation Lead Mixed‐Halide Perovskite via Tunability of the Colloidal Precursor Solution

The meteoric rise of the field of perovskite solar cells has been fueled by the ease with which a wide range of high‐quality materials can be fabricated via simple solution processing methods. However, to date, little effort has been devoted to understanding the precursor solutions, and the role of additives such as hydrohalic acids upon film crystallization and final optoelectronic quality. Here, a direct link between the colloids concentration present in the [HC(NH₂)₂]_0.83Cs_0.17Pb(Br_0.2I_0.8)₃ precursor solution and the nucleation and growth stages of the thin film formation is established. Using dynamic light scattering analysis, the dissolution of colloids over a time span triggered by the addition of hydrohalic acids is monitored. These colloids appear to provide nucleation sites for the perovskite crystallization, which critically impacts morphology, crystal quality, and optoelectronic properties. Via 2D X‐ray diffraction, highly ordered and textured crystals for films prepared from solutions with lower colloidal concentrations are observed. This increase in material quality allows for a reduction in microstrain along with a twofold increase in charge‐carrier mobilities leading to values exceeding 20 cm² V^?1 s^?1. Using a solution with an optimized colloidal concentration, devices that reach current–voltage measured power conversion efficiency of 18.8% and stabilized efficiency of 17.9% are fabricated.     

Diffraction efficiency of random binary-amplitude diffracting screens

The diffraction characteristics of random binary-amplitude diffracting screens are investigated. It is shown that, for such a random diffracting screen with complex amplitude transmittance t equal to either 0 or 1, the diffraction efficiency of the screen is maximized when 50% of the screen has transmittance t = 1, independent of other characteristics of the screen. The maximum diffraction efficiency equals ?. For this result to hold the screen must be adequately modeled by a stationary binary random process.     

Performance evaluation of a model describing the effects of temperature,water activity,pH and lactic acid concentration on the growth of Escherichia coli

A square root-type model for Escherichia coli growth in response to temperature, water activity, pH and lactic acid was developed by Ross et al. [Int. J. Food Microbiol. (2002).]. Predicted generation times from the model were compared to the literature data using bias and accuracy factors, graphical comparisons and plots of residuals for data obtained from both liquid growth media and foods. The model predicted well for 1025 growth rate estimates reported in the literature after poor quality or unrepresentative data (n=215) was excluded, with a bias factor of 0.92, and an accuracy factor of 1.29. In a detailed comparison to two other predictive modes for E. coli growth, Pathogen Modeling Program (PMP) and Food MicroModel (FMM), the new model generally performed better. The new model consistently gave better predictions than the other models at generation times 相似文献