Computational models of collective foraging.

In this paper the behaviour of a bee colony is modelled as society of communicating agents acting in parallel and synchronising their behaviour. Two computational approaches for defining the agents behaviour are introduced and compared. Their common features as well as the complementary aspects making them suitable for merging together into a more complex model.     

Effect of stressor factors on the behavior of monkeys. III. The behavior of rhesus macaques during immobilization stress

The three-hour immobilizational stress in two groups of males of rhesus monkeys at the age of 7-8 and 10-12 years has been investigated. The reaction on the stress has been established to depend on the age of animals. The young males bear the stress easier, their behaviour after it is practically normal. The normal behaviour of the elder animals restores during 24 hours after immobilization. A comparative analysis of hamadryas baboons and rhesus monkeys behaviour during this type of stress has been carried out. These species differ by their reaction on stress: Papio hamadryas serve as a model of hard depressive stress, the rhesus monkeys--a model of slight-stimulative stress. The peculiarities of stress bearing depend on the selected species, age of the animal, the type of social organization and individual features of behaviour.     

Chemo-klino-kinesis in planarian food location.

The effects of a homologous series of buffered fatty acid solutions on planarian behaviour were measured as the change in klino-kinetic activity. On the basis of the results obtained a model demonstrating the function of this behaviour pattern in the food-locating response was proposed. The model suggested that qualitative rather than quantitative gradients were effective in stimulating klino-kinetic orientation.     

Mechanical model of the inspiratory pump.

The inspiratory pump (inspiratory muscles and the rib cage) translates inspiratory commands in alveolar ventilation by applying expanding forces to the lungs. Its functioning is of paramount importance to the physiology of breathing and of many pathological situations. Major difficulties in studying its function in relationship with its structure arise from the extremely complex geometrical disposition of its active and passive elements. We herein describe a two-compartment model of the inspiratory pump, with model parameters identification derived from actual measurements obtained by magnetic resonance imaging in normal humans. The equations governing the model are presented. Numerical simulations validate the model by showing a behaviour similar to physiological observations. This opens the possibility of predicting the behaviour of the respiratory system during diseases involving changes in its mechanical or geometrical characteristics.     

A model of social grooming among adult female monkeys.

Grooming networks among adult female monkeys exhibit two similar features across a number of different species. High-ranking animals receive more grooming than others, and the majority of grooming occurs between females of adjacent rank. A theoretical model which duplicates these features is presented, and the properties of the model are used to explain the possible causation and function of female grooming behaviour. The model illustrates how relatively simple principles governing the behaviour of individuals may be used to explain more complex aspects of the social structure of non-human primate groups.     

Adolescent transition to coitus and premarital childbearing in Sudan: a biosocial context.

This paper examines the biosocial basis of premarital sexual and reproductive behaviour among women in Sudan. It applies Udry's biosocial perspective, which attempts to reconcile the biological and sociological models of premarital sexual and reproductive behaviour. World Fertility Survey (WFS) data were used to study premarital first motherhood. Early puberty was found to be paramount in determining childbearing in a separate biological model, but also in a biosocial model constructed to take account of social controls. This finding suggests that social controls do not influence the biological predisposition to premarital sexual behaviour. However, given the limitations of the WFS data, conclusive evidence must await a more appropriately designed study of reproductive behaviour in Sudan.     

Bubonic plague: a metapopulation model of a zoonosis.

Bubonic plague (Yersinia pestis) is generally thought of as a historical disease; however, it is still responsible for around 1000-3000 deaths each year worldwide. This paper expands the analysis of a model for bubonic plague that encompasses the disease dynamics in rat, flea and human populations. Some key variables of the deterministic model, including the force of infection to humans, are shown to be robust to changes in the basic parameters, although variation in the flea searching efficiency, and the movement rates of rats and fleas will be considered throughout the paper. The stochastic behaviour of the corresponding metapopulation model is discussed, with attention focused on the dynamics of rats and the force of infection at the local spatial scale. Short-lived local epidemics in rats govern the invasion of the disease and produce an irregular pattern of human cases similar to those observed. However, the endemic behaviour in a few rat subpopulations allows the disease to persist for many years. This spatial stochastic model is also used to identify the criteria for the spread to human populations in terms of the rat density. Finally, the full stochastic model is reduced to the form of a probabilistic cellular automaton, which allows the analysis of a large number of replicated epidemics in large populations. This simplified model enables us to analyse the spatial properties of rat epidemics and the effects of movement rates, and also to test whether the emergent metapopulation behaviour is a property of the local dynamics rather than the precise details of the model.     

Electromagnetic properties of biological solutions. - II. Methodological considerations on microwave spectroscopy of human sera

A wide-band analysis is proposed about the behaviour of the dielectric constant of human sera, using a proper mathematical model. Each serum is identified by two parameters. There is a good agreement between theoretical and experimental data.     

A study of general practitioners' reasons for changing their prescribing behaviour.

OBJECTIVES--To explore general practitioners'' reasons for recent changes in their prescribing behaviour. DESIGN--Qualitative analysis of semistructured interviews. SETTING--General practice in south east London. SUBJECTS--A heterogeneous sample of 18 general practitioners. RESULTS--Interviewees were able to identify between two and five specific changes that had occurred in their prescribing in the preceding six months. The most frequently mentioned changes related to fluoxetine, angiotensin converting enzyme inhibitors, and the antibiotic treatment of Helicobacter pylori. Three models of change were identified: an accumulation model, in which the volume and authority of evidence were important; a challenge model, in which behaviour change followed a dramatic or conflictual clinical event; and a continuity model, in which change took place against a background of willingness to change, modulated by other factors such as cost pressures and the comprehensible therapeutic action of a drug. Behaviour change was reinforced and sustained by experiences with individual patients. CONCLUSIONS--Multiple factors are involved in general practitioners'' decisions to change their prescribing habits. Three models of change can be identified which have important implications for the design and evaluation of interventions aimed at behaviour change.     

Rheological properties of extracellular polysaccharide, Pestan, produced by Pestalotiopsis sp.

Summary The fluid behaviour of Pestan produced from Pestalotiopsis sp. KCTC 8637P was as a non-Newtonian fluid. The rheological behaviour of Pestan solution was examined by Power-law model, Herschel-Bulkley model and Arrhenius equation. As the result, Pestan solution was pseudoplastic behaviour with yield stress. According to increase of Pestan concentration, its flow index was decreased. Thus, low concentrations of Pestan solution were well exposed pseudoplastic property. Apparent viscosity of 0.2 % Pestan solution was 268.2 cP at 14.3 sec^–1 and was higher about 2.8 times than that of Xanthan gum solution. Apparent viscosity of Pestan solution was stable over a wide pH and was maximum at pH 8. Also, consistency index of Pestan solution was very stable over wide temperature than that of Xanthan gum solution.     

Large strain behaviour of brain tissue in shear: some experimental data and differential constitutive model.

In this paper, some experimental measurements of the behaviour of bovine brain tissue under large shear strains in vitro are reported, and a constitutive model which is consistent with the data is developed. It was determined that brain tissue is not strain-time separable, showing slower relaxation at higher strains, and that the stresses in shear are not linear with increasing shear strain. The new constitutive model is a differential model, including both an "elastic" term, of the Mooney type and a nonlinear viscoelastic term. The latter allows for the change in relaxation behaviour with strain, by modifying an upper convected multimode Maxwell model with a damping function. The model shows good agreement with the experimental shear results and could be used to describe other types of data.     

A model for oscillating chemical reactions.

A simple theoretical model for a class of oscillating chemical reactions is investigated, which is inspired by Degn's analysis of the mechanism of Belousov-Zhabotinsky reactions. Although the model involves only one auto-catalytic path, as distinct from models presented hitherto, a limit-cycle behaviour is found for the concentrations, corresponding to a definite region in the space of controllable parameters. Characteristics of the coherent oscillations are investigated together with the behaviour in the induction period. The critical slowing-down around the onset of instability is shown to behave very much like that found in the equilibrium phase transition. The existence of an "anti-Curie" point is found as well as the Curie point, corresponding to the fact that the domain for sustained oscillation is closed in certain directions. Possible extensions of the model and ways of improving the theory are discussed.     

Kinetic properties and regulation by L-ornithine of chicken liver arginase induced by insulin.

After injection of insulin into chickens, a new form of arginase with a 16-fold increase of activity appears in the liver. The new form has a different chromatographic behaviour on DEAE-cellulose. The low activity enzyme has a very high Km value (60mM), and is poorly inhibited by L-ornithine. The induced form of arginase is strongly inhibited by L-ornithine and has an allosteric behaviour which can be described by a Monod-Wyman-Changeux model. 1,4-Diaminobutane, spermine have practically no effect on either form of arginase.     

The kinetics of E. coli RNA polymerase.

Using an assay specific for chain elongation of E. coli RNA polymerase the kinetics of this propagation reaction have been studied. The kinetic behaviour is consistent woth the mathematical model formulated for this multisubstrate enzyme. The effect of increasing salt concentration on the kinetics of the reaction indicated that DNA unwinding is probably a necessary step in the propagation step, although this may not be the rate limiting step under all conditions.     

A distributed model of exchange processes within the osteon.

In order to understand various exchange processes within the osteon, a mathematical model to describe the system has been developed which allows for concentration gradients in the axial and radial directions as well as cellular consumption and binding to bone surface. The normal values for the model parameter are discussed and the effects of the model parameters on the behaviour of the model are investigated. This model supports the idea that diffusion alone may be an inefficient mechanism in transport between blood and osteocytes.     

Computer modelling and experimental evidence for two steady states in the photosynthetic Calvin cycle.

We present observations of photosynthetic carbon dioxide assimilation, and leaf starch content from genetically modified tobacco (Nicotiana tabacum) plants in which the activity of the Calvin cycle enzyme, sedoheptulose-1,7-bisphosphatase, is reduced by an antisense construct. The measurements were made on leaves of varying ages and used to calculate the flux control coefficients of sedoheptulose-1,7-bisphosphatase over photosynthetic assimilation and starch synthesis. These calculations suggest that control coefficients for both are negative in young leaves, and positive in mature leaves. This behaviour is compared to control coefficients obtained from a detailed computer model of the Calvin cycle. The comparison demonstrates that the experimental observations are consistent with bistable behaviour exhibited by the model, and provides the first experimental evidence that such behaviour in the Calvin cycle occurs in vivo as well as in silico.     

Measurement and interpretation of fluorescence polarisations in phospholipid dispersions.

An instrument that measures the temperature dependence of fluorescence polarisation and intensity directly and continuously is described. The behaviour of four fluorescent probes bound to a number of well characterised model systems was then examined. The motional properties of the probes were determined from the polarisation and intensity data and were found to be sensitive to the crystalline-liquid crystalline phase transitions in phospholipid vesicles of dimyristoly and dipalmitoly phosphatidylcholine. Binary mixture of dilauroyl and dipalmitoyl phosphatidylcholine show lateral phase separation and in this system the probes parition preferentially into the more 'fluid' phase. In systems that have been reported to contain 'short range order' or 'liquid clustering', such as dioleoyl phosphatidylcholine and liquid paraffin, the motion of the probes was found to have anomalous Arrhenius behaviour consistent with the idea that homogeneous phases were not being sampled. The significance of these findings for the interpretation of the behaviour of fluorescent probes bound to natural membranes is discussed.     

Organization of brain complexity--synapse proteome form and function.

Proteomic study of the synapse has generated an extensive list of molecular components, revealing one of the most complex functional systems currently known to cell biology. While fundamental to neural information processing, behaviour and disease, the molecular organisation of the synapse and its relation to higher-level function has yet to be clearly understood. Neurotransmitter receptor complexes, such as the N-methyl-D-aspartate receptor complex (NRC/MASC), are major components of the synaptic proteome. We have recently completed a detailed study of MASC, its functional organisation and involvement in behaviour and disease. This pointed to simple design principles underlying synaptic organisation. Drawing together the results of proteomic and analytical study, we sketch out a model for synaptic functional organisation.     

Finite element model of the human neck during omni-directional impacts. Part II: relation between cervical curvature and risk of injury

A detailed 3D FE model of the human neck was used to assess a possible relationship between risk of injury and cervical spine curvature for various impacts. A FE model was previously developed, representing the head and neck of a 50th percentile human with a normal lordotic curvature. The model behaviour was omni-directionally validated for various impacts using published results. For the present study, the model was deformed in order to obtain a straight and a kyphotic curvature, and for each geometry, rear-end, frontal, lateral and oblique impact were simulated. Although results showed similar kinematic patterns, significant differences were found in the distribution and peak values of ligament elongations, forces and moments along the cervical spine for the three configurations. It was concluded that the variability observed on the curvature of the human cervical spine may have a significant influence both on the behaviour and on the risk of injury of the neck during impact.