Application of flexible recipes for model building, batch process optimization and control

Unlike the traditionally fixed recipes in batch process operation, flexible recipes allow the adjustment of some of its relevant recipe items. These adjustments can either be predefined in cases of planned experimentation, or suggested by a formal process optimization or control algorithm on the basis of actual information. In both the response surface methodology and the simplex evolutionary operation (EVOP), some well-known methods for empirical model building and process optimization, flexible recipes are involved. Another application of flexible recipes arises in a feedforward quality control strategy of batch processes when variations in market or process conditions are known a priori. The experimental results of these strategies are presented for the batchwise production of benzylalcohol on a pilotplant scale. Experiments have been performed to obtain a reliable model of the yield. On the basis of this model, better process conditions have been suggested, which substantially deviate from the final simplex resulted from experiments within simplex EVOP. Finally, an adaptive feedforward control strategy has been applied for a priori known disturbances in the process inputs

Using dissolved oxygen concentrations to determine mixed layer depths in the Bellingshausen Sea

Concentrations of oxygen (O<sub>2</sub>) and other dissolved gases in the oceanic mixed layer are often used to calculate air-sea gas exchange fluxes. The mixed layer depth (<i>z</i><sub>mix</sub>) may be defined using criteria based on temperature or density differences to a reference depth near the ocean surface. However, temperature criteria fail in regions with strong haloclines such as the Southern Ocean where heat, freshwater and momentum fluxes interact to establish mixed layers. Moreover, the time scales of air-sea exchange differ for gases and heat, so that <i>z</i><sub>mix</sub> defined using oxygen may be different than <i>z</i><sub>mix</sub> defined using temperature or density. Here, we propose to define an O<sub>2</sub>-based mixed layer depth, <i>z</i><sub>mix</sub>(O<sub>2</sub>), as the depth where the relative difference between the O<sub>2</sub> concentration and a reference value at a depth equivalent to 10 dbar equals 0.5 %. This definition was established by analysis of O<sub>2</sub> profiles from the Bellingshausen Sea (west of the Antarctic Peninsula) and corroborated by visual inspection. Comparisons of <i>z</i><sub>mix</sub>(O<sub>2</sub>) with <i>z</i><sub>mix</sub> based on potential temperature differences, i.e., <i>z</i><sub>mix</sub>(0.2 °C) and <i>z</i><sub>mix</sub>(0.5 °C), and potential density differences, i.e., <i>z</i><sub>mix</sub>(0.03 kg m<sup>−3</sup>) and <i>z</i><sub>mix</sub>(0.125 kg m<sup>−3</sup>), showed that <i>z</i><sub>mix</sub>(O<sub>2</sub>) closely follows <i>z</i><sub>mix</sub>(0.03 kg m<sup>−3</sup>). Further comparisons with published <i>z</i><sub>mix</sub> climatologies and <i>z</i><sub>mix</sub> derived from World Ocean Atlas 2005 data were also performed. To establish <i>z</i><sub>mix</sub> for use with biological production estimates in the absence of O<sub>2</sub> profiles, we suggest using <i>z</i><sub>mix</sub>(0.03 kg m<sup>−3</sup>), which is also the basis for the climatology by de Boyer Montégut et al. (2004)

Uncertainty propagation and speculation in projective forecasts of environmental change: a lake-eutrophication example

The issue of whether models developed for current conditions can yield correct predictions when used under changed control, as is often the case in environmental management, is discussed. Two models of different complexity are compared on the basis of performance criteria, but it appears that good performance at the calibration stage does not guarantee correctly predicted behavior. A requirement for the detection of such a failure of the model is that the prediction uncertainty range is known. Two techniques to calculate uncertainty propagation are presented and compared: a stochastic first-order error propagation based on the extended Kalman filter (EKF), and a newly developed and robust Monte Carlo set-membership procedure (MCSM). The procedures are applied to a case study of water quality, generating a projective forecast of the algal dynamics in a lake (Lake Veluwe) in response to management actions that force the system into a different mode of behavior. It is found that the forecast from the more complex model falls within the prediction uncertainty range, but its informative value is low due to large uncertainty bounds. As a substitute for time-consuming revisions of the model, educated speculation about parameter shifts is offered as an alternative approach to account for expected but unmodelled changes in the system

Mechanisms of deterioration of nutrients

The retention of flavor during freeze drying was studied with model systems. Mechanisms by which flavor retention phenomena is explained were developed and process conditions specified so that flavor retention is optimized. The literature is reviewed and results of studies of the flavor retention behavior of a number of real food products, including both liquid and solid foods are evaluated. Process parameters predicted by the mechanisms to be of greatest significance are freezing rate, initial solids content, and conditions which result in maintenance of sample structure. Flavor quality for the real food showed the same behavior relative to process conditions as predicted by the mechanisms based on model system studies

Mechanisms of deterioration of nutrients

Methods for improving the quality of freeze-dried foods were investigated. Areas discussed include: (1) microstructure of freeze-dried systems, (2) structural changes in freeze-dried systems, (3) artificial food matrices, and (4) osmotic preconcentration to yield improved freeze-dried products

Retention and intentions of professional accountants

This paper enhances understanding of factors underlying professional accountants’ high turnover rates. Various researchers, institutions and government bodies have identified accountants’ retention is of concern. However, traditional explanations, such as job satisfaction and organizational commitment, do not sufficiently account for the turnover rates observed in the accounting profession. A New Zealand (NZ) sample of professional accountants enabled us to identify a range of factor. Intentions to stay were very low, 50% of accountants expected to leave their current employer within 3 years of the survey date. Satisfaction with two core job characteristics, feedback and skill variety, in addition to work life balance (WLB) accounted for 65% of the variance of overall job satisfaction. WLB, or at least a lack of access to flexible work arrangements was strongly indicated as the primary consideration when choosing to remain with the present employer

Non-conventional approaches to food processing in CELSS, 1. Algal proteins: Characterization and process optimization

Protein isolate obtained from green algae cultivated under controlled conditions was characterized. Molecular weight determination of fractionated algal proteins using SDS-polyacrylamide gel electrophoresis revealed a wide spectrum of molecular weights ranging from 15,000 to 220,000. Isoelectric points of dissociated proteins were in the range of 3.95 to 6.20. Amino acid composition of protein isolate compared favorably with FAO standards. High content of essential amino acids leucine, valine, phenylalanine and lysine make algal protein isolate a high quality component of closed ecological life support system diets. To optimize the removal of algal lipids and pigments supercritical carbon dioxide extraction (with and without ethanol as a co-solvent) was used. Addition of ethanol to supercritical carbon dioxide resulted in more efficient removal of algal lipids and produced protein isolate with a good yield and protein recovery. The protein isolate extracted by the above mixture had an improved water solubility

Libéralisme égalitariste, républicanisme critique et reconnaissance identitaire

In Liberalism’s religion, Laborde defends a liberal egalitarian position and tackles, from a new perspective, some issues dealt with in his republican writings. This article examines some of these issues, paying attention to the place that the recognition of identities occupies both in her republican and in her liberal theories, as well as the type of justification advanced in both cases. The article shows that the recognition of identities has gone from having a peripheral and instrumental role in her republican writings to having a central role in her liberal theory