A PRACTICAL APPLICATION OF A NUMERICAL OPTIMIZATION TECHNIQUE IN THE FEEDMILL INDUSTRY

The cow model of Meijer describes a mathematical relation between the predicted daily milk production and the corresponding feed intake needed for lactating cows. The milk production is a function of several parameters defined for each cow. Used in least cost calculations of daily rations, an optimization problem is obtained, which consists of one highly non-linear equality constraint, together with several linear inequality constraints. Their number required in the optimization can vary and depends on the user's choice. The cost function itself gives a linear relation between the prices of the different forages mixed in the optimal blend. The optimization result has been implemented with the aid of Augmented Lagrange Functions with a view to apply the program in the feedmill industry.     

Alcohol deterpenation of black pepper oil

The alcohol extraction of black pepper oil using three different oil to 60%-alcohol ratios was studied. Quantitative composition of the oils was established through their physical constants and gas-liquid chromatography. The 1:2 oil to 60% ethanol ratio showed the lowest oil recovery but resulted in sesquiterpeneless oil with the lowest terpene content and closest in sensory profile to the original oil.     

Is ionic dialysance useful for early detection of vascular access dysfunction? Six illustrative cases

Continuous ionic dialysance monitoring is a useful clinical tool to determine the dialysis dose in real time in each hemodialysis session. We followed up 49 patients for 16 months. Six patients with a Kt reduction of ≥20% in >3 consecutive hemodialysis sessions were identified. Fistulography demonstrated significant stenosis in all 6 patients. Angioplasty was performed in 5 with an excellent angiographic result and optimal Kt levels were restored. Unexplained and persistent Kt reduction in patients with stable chronic kidney disease under hemodialysis could represent, together with an accurate vascular access examination, a practical and additional indirect method for the early detection of vascular access dysfunction.     

Adaptive control with discontinuous σ-factor and saturation for improved robustness

An adaptive control law is proposed to improve the robustness of the adaptive system with respect to fast unmodelled dynamics represented by a singular perturbation. The new law is based on saturation of the regressor and control parameter vector with inclusion of a discontinuous σ-factor. The analysis of the resulting system is presented and the conclusions are illustrated by simulations. The introduction of a discontinuous σ-factor represents an extension of an earlier work. The advantages of this extension include global stability, with less restrictive assumptions, and better transient behaviour.     

Mechanisms of Salt Tolerance Conferred by Overexpression of the HAL1 Gene in Saccharomyces cerevisiae

Overexpression of the HAL1 gene improves the tolerance of Saccharomyces cerevisiae to NaCl by increasing intracellular K⁺ and decreasing intracellular Na⁺. The effect of HAL1 on intracellular Na⁺ was mediated by the PMR2/ENA1 gene, corresponding to a major Na⁺ efflux system. The expression level of ENA1 was dependent on the gene dosage of HAL1 and overexpression of HAL1 suppressed the salt sensitivity of null mutants in calcineurin and Hal3p, other known regulators of ENA1 expression. The effect of HAL1 on intracellular K⁺ was independent of the TRK1 and TOK1 genes, corresponding to a major K⁺ uptake system and to a K⁺ efflux system activated by depolarization, respectively. Overexpression of HAL1 reduces K⁺ loss from the cells upon salt stress, a phenomenon mediated by an unidentified K⁺ efflux system. Overexpression of HAL1 did not increase NaCl tolerance in galactose medium. NaCl poses two types of stress, osmotic and ionic, counteracted by glycerol synthesis and sodium extrusion, respectively. As compared to glucose, with galactose as carbon source glycerol synthesis is reduced and the expression of ENA1 is increased. As a consequence, osmotic adjustment through glycerolsynthesis, a process not affected by HAL1, is the limiting factor for growth on galactose under NaCl stress. © 1997 John Wiley & Sons, Ltd.     

MICROMECHANICS: SIMULATING THE ELASTIC BEHAVIOR OF ONION EPIDERMIS TISSUE

A generic modeling approach is introduced that allows for dynamical simulations of cellular biological tissue. It is derived from the discrete element approach in the sense that the tissue is discretized such that histological aspects like cell geometry and the cellular arrangement within the tissue can be fully incorporated into the model. This makes dynamical simulations of arbitrarily shaped cellular tissues feasible in an elegant and a robust way. The validity of this simulation technique is demonstrated by a case study on the unicellular epidermis layer of onion (Allium cepa). The parameters of a two‐dimensional model are determined using published stress–strain data from a tension test on longitudinal strips. The model is then validated quantitatively against the data for transversal strips.