Kinetics of Recrystallization and Grain Growth in Cu2O

The kinetics of recrystallization and grain growth in Cu₂O prepared by oxidation of Cu at 1030°C were studied. A critical strain of 8% at 700°C is necessary to cause recrystallization during subsequent annealing at 1020°C. Grain-growth kinetics fit the expression D³–D₀³= kt with an activation energy of 83±2 kcal/mol.     

Tutorial paper Robust performance specifications for uncertain stable SISO systems

A new method is presented for defining the bounds on achieveable robust performance for stable SISO systems which can be described by approximate linear models. The method provides a tutorial presentation on the use of the H _∞-formulation to define performance specifications which can be guaranteed despite the degree of uncertainty in the model. The parametric uncertainty associated with the linear process model is used to contruct a region of achievable performance in performance weight parameter space, which can be used to characterize bandwidth and underdampedness in the achievable closed-loop response. This region is bounded by locii of ‘best performance guaranteeing robustness’ and ‘worst necessary performance’ and also by robust stability constraints. The position and size of the region depends greatly on the level of model uncertainty. Using the performance bounds thus generated, the designer can pick a performance weight which will guarantee robust performance while incorporating his own preferences regarding controller type and response characteristics.     

Smith predictor design for robust performance

A method is outlined for designing Smith predictor controllers that provide robust performance despite real parameter uncertainties in the process model. Insight into the design process is gained by viewing the Smith predictor from the perspective of internal model control. Performance requirements are written in terms of a frequency-domain weight restricting the magnitude of the closed-loop sensitivity function. A general method for approximating multiple parameter uncertainties by a single multiplicative uncertainty is developed—an exact bound is derived for the magnitude of multiplicative uncertainty used to approximate simultaneous uncertainties in process gain, time-constant, and time-delay. Three different tuning methods are demonstrated; each is applied to a wide range of parameter uncertainties in a first-order with time-delay model. The first tuning method locates loop transfer-function uncertainty regions to test for robust performance—real parameter uncertainties are considered exactly. The second tuning method approximates real parameter uncertainties by multiplicative uncertainty and uses structured singular value analysis to guarantee robust performance. The third is a ‘quick design’ method that considers the unit magnitude crossing of the multiplicative uncertainty. Finally, the Smith predictor controller is compared with the structured-singular-value-optimal controller.     

Integrating planning and learning: the PRODIGY architecture

Abstract

Planning is a complex reasoning task that is well suited for the study of improving performance and knowledge by learning, i.e. by accumulation and interpretation of planning experience. PRODIGY is an architecture that integrates planning with multiple learning mechanisms. Learning occurs at the planner's decision points and integration in PRODIGY is achieved via mutually interpretable knowledge structures. This article describes the PRODIGY planner, briefly reports on several learning modules developed earlier along the project, and presents in more detail two recently explored methods to learn to generate plans of better quality. We introduce the techniques, illustrate them with comprehensive examples, and show preliminary empirical results. The article also includes a retrospective discussion of the characteristics of the overall PRODIGY architecture and discusses their evolution within the goal of the project of building a large and robust integrated planning and learning system.     

PATHOGEN DETECTION IN FOOD MICROBIOLOGY LABORATORIES: AN ANALYSIS OF QUALITATIVE PROFICIENCY TEST DATA, 1999–2007

The objective of this study was to assess laboratories' ability to detect or rule out the presence of four common food pathogens: Escherichia coli O157:H7, Salmonella spp., Listeria monocytogenes and Campylobacter spp. To do this, qualitative proficiency test data provided by one proficiency test provider from 1999 to 2007 were examined. The annual and cumulative 9-year percentages of false-negative and false-positive responses were calculated.
The cumulative 9-year false-negative rates were 7.8% for E. coli O157:H7, 5.9% for Salmonella spp., 7.2% for L. monocytogenes and 13.6% for Campylobacter spp. Atypical strains and low concentrations of bacteria were more likely to be missed, and the data showed no trend of improving performance over time. Percentages of false-positive results were below 5.0% for all four pathogens.

PRACTICAL APPLICATIONS

The results imply that food testing laboratories often fail to detect the presence of these four food pathogens in real food specimens. To improve pathogen detection, supervisors should ensure that testing personnel are adequately trained, that recommended procedures are followed correctly, that samples are properly prepared, that proper conditions (temperature, atmosphere and incubation time) are maintained for good bacterial growth and that recommended quality control procedures are followed. Supervisors should also always investigate reasons for unsatisfactory proficiency test results and take corrective action. Finally, more research is needed into testing practices and proficiency test performance in food testing laboratories.     

MICROBIOLOGICAL RISK FACTORS ASSOCIATED WITH FOOD HANDLERS IN ELEMENTARY SCHOOLS FROM BRAZIL

A total of 44 food handlers who work in elementary schools from Governador Valadares, Minas Gerais, Brazil, were subjected to the examination of the nasal carriers of Staphylococcus aureus and of hand carriers of Enterobacteriaceae and Pseudomonas aeruginosa. A simple method using the eosine-methilene-blue media to isolate enterobacteria from the hands was performed. Among the total number of food handlers, 29.5% were S. aureus nasal carriers . The following percentages were obtained for enterobacteria isolation from the hand carriers: Enterobacter spp. (54.5%), Serratia spp. (9.0%), Shigella spp. (9.0%), E. coli (6.8%), Salmonella spp. (2.3%) and Yersinia spp. (2.3%). Pseudomonas aeruginosa was isolated from the hands of 2.3% food handlers. Our results demonstrated the necessity of performing evaluation of S. aureus and Enterobacteriaceae in food handlers from elementary schools and also indicated that the method is useful to identify sources of food poisoning in epidemiological studies and in investigations of food contamination sources. Our data also showed that authorities may allot more attention to alerting the community about food problems.

PRACTICAL APPLICATIONS

The methods used in this work could be a valuable and low-cost tool to verify the microbiological risk factors associated with food handlers, including Staphylococcus aureus and enterobacteriaceae.     

Behaviour of power-factor meters under non-sinusoidal current and voltage

Different types of analogue and digital power-factor meters used for low frequencies are studied. Their errors are calculated when the current or voltage waveform is distorted. It is shown that large errors appear under these working conditions. A new measuring instrument is proposed. It has very small errors, even under highly distorted waveforms, having low-pass filters at the inputs to prevent errors generated by high frequency harmonics.     

A phenological description of Iberian vegetation using short wave vegetation index imagery

Abstract

The phenology of Iberian vegetation is described using twelve full resolution Advanced Very High Resolution Radiometer short wave vegetation index images for the period April to October 1985 and 1986. The characteristics of the most appropriate vegetation classification scheme for use with these data are discussed.     

THE ENHANCEMENT OF PRODUCTION OF PHENYLALANINE BY EXTRACTIVE FERMENTATION WITH POLYMERIC BEADS

Extractive fermentation using uncharged polymeric beads (Amberlite XAD-16) was used for phenylalanine production. By compensating the adsorption of the hydrophobic nutrients by the polymeric beads, production of phenylalanine was increased due to the removal of phenylalanine inhibition on the growth of the bacteria. When the fed batch culture was performed at low bead concentration, the production of the phenylalanine increased about 30% compared to the control fermentation. An increase of production can be also achieved by using the pre-saturated beads with the hydrophobic nutrients. In addition, the adsorption isotherm in the fermentation medium was investigated. It was found that the adsorption of phenylalanine onto the beads decreased because the adsorption sites can be occupied by nutrients, but this competitive adsorption is not so drastic as to affect the adsorption of phenylalanine during fermentation. This knowledge will be useful when this technology is applied to actual commercial operation.