Optimum control of deterministic and stochastic distributed populations with intra-species competition†

Most of the literature devoted to the study of dynamic populations with predators is focused on the use of the so-called ‘population law’ discovered by Verhulst in 1937, and generalized later by several authors. Basically this model deals with the total number of individuals in the population, irrespective of their distribution over the geographical space of definition. In contrast, the present paper suggests a distributed approach to populations with intra-species competitions, which explicitly takes into account the distributed parameter, for instance the age, of the individuals. Two models are given: a distributed version of the logistic law and a generalization of the transfer equation, and two frameworks are considered: the deterministic case and the stochastic one. The equations so obtained are mainly distributed differential integral equations; one considers The optimum control or such systems and necessary optimality conditions are given. The covariance of the deviation from a steady state in the presence of random fluctuations is derived. This model applies not only to biological populations, but also to social and economic systems, and it may be used as a basis for general studies on populations with intra-species competitions.     

Nouvelle méthode pour améliorer la précision du premier harmonique†

In this paper, we give first a contribution to the ‘dual input describing function’ of West et al. (1956); we show how it is possible to define by means of the characteristic curve of the non-linearity alone, without knowing the mathematical expression for it. Secondly, we give a new method for determining the self-oscillation of a non-linear system dependent on reactive energy considerations. Lastly, we extend the theory to non-linear multivariable systems.

On donne une contribution à la notion de ‘double fonetion de transfert équivalente’ de West et al. (1956), et on montre comment il est possible déterminer uniquement à l'aide de la courbe de gain g(x), sans connaicirc;tre son expression mathématique. On donne une nouvelle méthode pour améliorer la précision du premier harmonique, basée sur des considérations relatives à l'énergie réactive du systéme.     

ALPHA-TOCOPHEROL EFFECTS ON COLOR AND SENSORY CHARACTERISTICS OF GROUND PORK DURING RETAIL DISPLAY

To assess the effects of a-tocopherol addition on lipid and pigment oxidation of ground pork, 10, 100 or 1000 ppm was added directly to ground pork in a food grade carrier (2% Medium Chain Triglyceride Oil) then pork was overwrapped with polyvinyl-chloride film and displayed at 4C for three days. Addition of α-tocopherol to ground pork had limited effects on color and sensory characteristics. Display time and light present during display had detrimental effects on a* value, total color, red color contributed by oxymyoglobin, percent of myoglobin, metmyoglobin and oxymyoglobin, visual red and grey colors.     

Sodium Lactate/Sodium Chloride Effects on Aerobic Plate Counts and Color of Aerobically Packaged Ground Pork

Ground pork (15% fat) was formulated to contain 0% to 3.0% sodium chloride and/or 0% to 3.0% sodium lactate (SL) resulting in 28 treatment combinations. Five replications consisted of two with low initial microbial loads (< 10³ CFU/g) and three with high initial loads (> 10⁵ CFU/ g). Ground pork (454g) was overwrapped in PVC and stored (4°C) aerobically for 21 d. A significant salt × SL interaction existed for redness of samples with low initial aerobic plate count (APC). Red color was best preserved by 2.0% or 3.0% SL. Initial pH values of low and high initial APC samples were similar. Initial product pH was best maintained by higher SL levels in low initial load samples and by higher sodium chloride levels in high initial load samples. Samples containing 3.0% SL had the lowest APC regardless of salt level.     

Sustainable Architecture and the Pluralist Imagination

In our review of the literature concerning sustainable architecture, we find a remarkably diverse constellation of ideas that defy simple categorization. But rather than lament the apparent inability to standardize a singular approach to degraded environmental and social conditions, we celebrate pluralism as a means to contest technological and scientific certainty. At the same time, we reject epistemological and moral relativism. These twin points of departure lead us to propose a research agenda for an architecture of reflective engagement that is sympathetic to the pragmatist tradition.     

Energy Catabolism in Rabbit Muscle as Affected by Brine Injection: 31P NMR Studies

The energy catabolism in brine-injected muscles was examined by ³¹P Nuclear Magnetic Resonance (NMR) spectroscopy. Immediately after death of rabbits, brines containing NaCl, with or without pyrophosphate, were injected into the arterial system. ³¹P NMR spectra at 4°revealed marked heterogeneity in postmortem catabolism due to brine diffusion. The heterogeneity of the Pi signal for injected muscles reflected the existence of muscle areas with different intracellular pH values. This observation suggested an increase in rate of glycolysis for fibers experiencing brine. The heterogeneity of brine diffusion seemed to be affected by method of injection.     

Swelling Control in Uranium Carbide

Fine particles were dispersed in a fuel structure to trap fission gases as very small bubbles and thereby reduce fuel swelling. The dispersions were made by adding 1.5 to 3.0 wt% W to the UC; the specimens were irradiated to a maximum of ∼2 at.% burnup. Density changes were used as the measure of swelling; there was much scatter in the results. Tungsten reduced the swelling when it was uniformly dispersed. For some samples having excess U and W or a segregated structure, W increased the swelling. The results tentatively confirm that fine particles are of value in reducing fission-gas swelling of carbide fuels.     

Effect of Melting History on the Mechanical Properties of Glass: I, Role of Melting Time and Atmosphere

The pristine strength of 0.5Li₂O·0.5K₂O·2SiO₂ glass measured in 3-point bending under liquid nitrogen was studied as a function of melting time and atmosphere at a constant melting temperature. The atmosphere over the melt was one of the most important parameters affecting the pristine strength. The most significant time-dependent melting effects and the highest strengths resulted from melting in a dry atmosphere of O₂ or air. In contrast, vacuum-melted and Ar-melted glasses had the lowest strengths. Melting in N₂ or CO₂ led to intermediate strengths. The presence of water vapor in the atmosphere during melting was detrimental to strength in those cases where very high strengths had been obtained with dry gases. The introduction of water vapor into those gases which in the dry state had led to low-strength glasses did not significantly affect the strength. The effects of the atmosphere in leading to oxygen-deficient or excess-oxygen glasses on the formation or dissolution of microheterogeneous regions were correlated with the pristine strengths of the glasses.