Analysis of the effect of inoculum characteristics on the first stages of a growing yeast population in beer fermentations by means of an individual-based model.

The yeast Saccharomyces cerevisiae has a limited replicative lifespan. The cell mass at division is partitioned unequally between a larger, old parent cell and a smaller, new daughter cell. Industrial beer fermentations maintain and reuse yeast. At the end of fermentation a portion of the yeast is 'cropped' from the vessel for 'serial repitching'. Harvesting yeast may select a population with an imbalance of young and aged individuals, but the output of any bioprocess is dependent on the physiology of each single cell in the population. Unlike continuous models, individual-based modelling is an approach that considers each microbe as an individual, a unique and discrete entity, with characteristics that change throughout its life. The aim of this contribution is to explore, by means of individual-based simulations, the effects of inoculum size and cell genealogical age on the dynamics of virtual yeast fermentation, focussing on: (1) the first stages of population growth, (2) the mean biomass evolution of the population, (3) the rate of glucose uptake and ethanol production, and (4) the biomass and genealogical age distributions. The ultimate goal is to integrate these results in order to make progress in the understanding of the composition of yeast populations and their temporal evolution in beer fermentations. Simulation results show that there is a clear influence of these initial features of the inocula on the subsequent growth dynamics. By contrasting both the individual and global properties of yeast cells and populations, we gain insight into the interrelation between these two types of data, which helps us to deal with the macroscopic behaviour observed in experimental research.

Flocculation in brewing yeasts: a computer simulation study.

A new simulator, INDISIM-FLOC, based on the individual-based simulator INDISIM, is used to examine the predictions of two different models of yeast flocculation. The first, proposed by Calleja is known as the "addition" model. The second, proposed by Stratford is known as the "cascade" model. The simulations show that the latter exhibits a better qualitative agreement with available experimental data.

Simulation modelling of bacterial growth in yoghurt.

INDISIM, an individual-based simulator, was used to specifically study the influence of the shape and size of Streptococcus salivarius subsp. thermophilus and Lactobacillus delbrueckii subsp. bulgaricus in yoghurt processing. To this effect, two different sets of simulations were carried out. In the first set of simulations, it was assumed that the initial acidity of the medium has the same value as the acidity of the cytoplasm of the microorganisms. Hence, the differences in bacterial growth by the two species are only attributable to differences in their geometry. It was found that, in an optimum culture, the growth in biomass of S. salivarius subsp. thermophilus is larger than that of L. delbrueckii subsp. bulgaricus. An important factor for understanding this difference might be the larger mass-to-surface ratio of the former. In the second set of simulations, a simplified model of yoghurt, the parametrisation differs both in the geometry and the metabolism of the two species. The results of these simulations are in very good qualitative agreement with the experimental data of [Lait 69 (1989) 519]. Finally, by inhibiting the uptake of amino acids by S. salivarius subsp. thermophilus, the large relative importance of lactic acid in yoghurt processing was highlighted.

Persistent hyperplastic primary vitreous.

Persistent hyperplastic primary vitreous (PHPV) is a common congenital developmental anomaly of the eye that results following failure of the embryological, primary vitreous and hyaloid vasculature to regress. It typically presents unilaterally without associated systemic findings. Although the etiology is assumed to be identical in each of its three variants, PHPV is still subclassified into three presentations. The purely anterior presentation of PHPV is also known as persistent tunica vasculosa lentis and persistent posterior fetal fibrovascular sheath of the lens. It occurs in eyes with pathology of the anterior segment. This form typically involves cataract, glaucoma and a retrolenticular membrane. The purely posterior presentation of PHPV is termed falciform retinal septum and ablatio falcicormis congentia. It occurs in eyes with abnormalities confined to the posterior segment such as retinal folds, vitreal stalk, vitreal membranes, macular abnormalities and optic disc abnormalities. A combination of anterior and posterior presentations is the most commonly seen clinical presentation. Case report. We present a case in which an 11-year old male was referred to our office for reevaluation of a large angle esotropia, strabismic and deprivational amblyopia and previously diagnosed PHPV, OD. Conclusion. Without treatment, PHPV can produce recurrent intraocular hemorrhage, secondary glaucoma and eventually require enucleation. Early surgical intervention is necessary to prevent progressive pathologic changes and to obtain the best visual results. Finally, while PHPV is a documented source of leukocoria, clinicians should be aware of differential diagnoses which involve the white pupil (congenital cataract, retinoblastoma, Norrie's disease, retinopathy of prematurity, retinal detachment and Coat's disease).

Substance abuse and prostitution.

A study of 200 street prostitutes documented a high prevalence of alcohol and drug abuse in their family of origin, during the drift into prostitution and as part of prostitution. Additionally, the study documented a high prevalence of substance abuse among the child molesters and rapists of the subjects. The existence of a relationship between substance abuse and prostitution in and of itself does not imply causality. It is not clear whether substance abuse is one of the factors that pushed these women into prostitution (as noted earlier, 55% of the subjects reported being addicted prior to their prostitution involvement) or whether it was prostitution that caused their drug involvement (30% became addicted following and 15% concurrently with their prostitution involvement). Most likely, both prostitution and substance abuse are the behavioral translations of these women's endless cycles of victimization and severely disturbed backgrounds, as well as an expression of the self-destructive pull, the sense of hopelessness, helplessness, negative self-concept and psychological paralysis reported by almost every subject in the study.

Ageing and mental problems in the family context.

Family doctors have substantially contributed to extending life expectancy beyond the biblical allocation of three score years and ten, and, ironically, we may now find ourselves having to cope with problems in the aged for which our training has not adequately equipped us. The topic of mental disorders in the aged provides for discussion of various relevant issues in geriatric care such as diagnostic problems and difficulties (seen not only in their psychiatric context, but also in their medical and social contexts); difficulties in management; the significance of losses sustained in later life, both within the context of the family and in other support systems; the general practitioner's role in management; and, finally, the attitude of the doctor toward the aged.

Hexamethonium modification of cardiovascular adjustments during combined static-dynamic arm exercise in monkeys.

In weight lifting and rowing, essentially the same groups of muscles contract in isometric (static) and isotonic (dynamic) fashion. To approximate the combined static-dynamic arm movements involved in rowing or lifting weights, four rhesus monkeys were trained to pull a T-bar and thereby avoid tail shock. Each animal received 8 daily test sessions in which loads (0.4, 0.8, 1.2, 1.6 kg), total pulls (3, 6, 9, 12 at a constant pull frequency, 0.5 Hz) and alternate sessions of pulling after injection of hexamethonium chloride (7 mg/kg) or saline were factorially combined. Our data indicate that heart rate in this model is primarily influenced by the duration of the dynamic exercise component (number of pulls) in this specific exercise task whereas both dynamic and static components affect systolic and diastolic blood pressure. After ganglionic blockade, heart rate and diastolic pressure do not change appreciably during T-bar pulling while the rise in systolic pressure is attenuated and varies primarily as a function of the static exercise component. The clinical implications of these experiments are discussed.