Decomposition-based qualitative experiment design algorithms for a class of compartmental models.

Qualitative experiment design, to determine experimental input/output configurations that provide identifiability for specific parameters of interest, can be extremely difficult if the number of unknown parameters and the number of compartments are relatively large. However, the problem can be considerably simplified if the parameters can be divided into several groups for separate identification and the model can be decomposed into smaller submodels for separate experiment design. Model decomposition-based experiment design algorithms are proposed for a practical class of large-scale compartmental models representative of biosystems characterized by multiple input sources and unidirectional interconnectivity among subsystems. The model parameters are divided into three types, each of which is identified consecutively, in three stages, using simpler submodel experiment designs. Several practical examples are presented. Necessary and sufficient conditions for identifiability using the algorithm are also discussed.     

Individualized optimal release angles in discus throwing

The purpose of this study was to determine individualized optimal release angles for elite discus throwers. Three-dimensional coordinate data were obtained for at least 10 competitive trials for each subject. Regression relationships between release speed and release angle, and between aerodynamic distance and release angle were determined for each subject. These relationships were linear with subject–specific characteristics. The subject–specific relationships between release speed and release angle may be due to subjects’ technical and physical characteristics. The subject–specific relationships between aerodynamic distance and release angle may be due to interactions between the release angle, the angle of attack, and the aerodynamic distance. Optimal release angles were estimated for each subject using the regression relationships and equations of projectile motion. The estimated optimal release angle was different for different subjects, and ranged from 35° to 44°. The results of this study demonstrate that the optimal release angle for discus throwing is thrower-specific. The release angles used by elite discus throwers in competition are not necessarily optimal for all discus throwers, or even themselves. The results of this study provide significant information for understanding the biomechanics of discus throwing techniques.     

THE INTERACTION BETWEEN PERIPHERAL NERVE POLYANIONS AND ALCIAN BLUE

—A study of the staining characteristics of Alcian blue in mammalian peripheral myelinated nerve in the presence of added electrolyte has enabled a comparison to be made of polyanions, formerly shown to be present at nodes of Ranvier, with other chemically defined macromolecules present in the same tissue. Two types of polyanion were shown to exist at nodes, one probably carboxylated and the other containing in addition sulphate ester groups. The possible physiological functions of such materials are discussed in relation to the role played by the nodes of Ranvier in conduction of the nerve impulse.     

The hydrodynamic characteristics of six scallops of the Super Family Pectinacea, Class Bivalvia

Measurements have been made in a recirculating water channel of the lift and drag forces on the plaster casts of six scallops of the Super Family Pectinacea, Class Bivalvia, namely Chlamys varia, Amusium pleuronectes, Pecten irradians, Pecten senatorius, Pecten pallium and Pecten alba . The results have shown that the shape of the lift curve for the bi-convex shells is similar to that of a comparable aerofoil shape, a discus, although with lower values. The piano-convex shell had similar lift values but a lower stall angle.
All the shells produced more induced drag than the discus and also had a higher form drag. Generally there was a correlation between the form drag coefficient and the thickness to chord ratio of the shell.
It is suggested that Amusium pleuronectes would be the best adapted for swimming flight, because of its low drag characteristics, followed by Pecten senatorius and Pecten irradians . It is thought that, although Pecten alba was likely to be the worst swimmer of those tested, it was also likely to be best able to escape by its ability to develop lift.     

The living dead: transformative experiences in modelling natural selection

This study considers how students change their coherent conceptual understanding of natural selection through a hands-on simulation. The results show that most students change their understanding. In addition, some students also underwent a transformative experience and used their new knowledge in a leisure time activity. These transformative experiences appear in different categories where students find value both towards biological content, societal value and individual identity. Finally there is a discussion on how to transfer characteristics from the setting of this study to other educational settings in biology and science in general.     

The control of ventilation: a theoretical analysis of the response to transient disturbances

Serial measurements of respiration in infants from birth to 7 months have revealed a changing pattern of response with age to spontaneous transient disturbances (e.g. deep sighs). These responses may be interpreted in terms of changing stability of the respiratory control system. The simplest possible model of respiratory control is analysed here. The control system is described by a feedback loop comprising a lung compartment, central and peripheral CO2 detectors and a circulatory delay. The differential equations representing this model are analysed in terms of the phase portrait. First we define the bounds of the solutions in the phase space and the equilibrium points. Next we discuss the local stability and damping of the system under small displacements from these equilibrium points. This local stability can be described in terms of the solution of a linear approximation about the equilibrium points. The trajectories of the solution vector under larger displacements from the equilibrium points are discussed in terms of Taylor expansions. It is shown by this analyses that this simple model can account qualitatively for the observed patterns of respiration following a deep sigh and the changes in that response from birth to 7 months.     

Why is the choice of future climate scenarios for species distribution modelling important?

Species distribution models (SDMs) are common tools for assessing the potential impact of climate change on species ranges. Uncertainty in SDM output occurs due to differences among alternate models, species characteristics and scenarios of future climate. While considerable effort is being devoted to identifying and quantifying the first two sources of variation, a greater understanding of climate scenarios and how they affect SDM output is also needed. Climate models are complex tools: variability occurs among alternate simulations, and no single 'best' model exists. The selection of climate scenarios for impacts assessments should not be undertaken arbitrarily - strengths and weakness of different climate models should be considered. In this paper, we provide bioclimatic modellers with an overview of emissions scenarios and climate models, discuss uncertainty surrounding projections of future climate and suggest steps that can be taken to reduce and communicate climate scenario-related uncertainty in assessments of future species responses to climate change.     

Ladder network prediction of transients in linear spatially inhomogeneous cables

A numerical method is described for finding steady state and transient responses in electrically linear, spatially inhomogeneous cables. Spatial inhomogeneities are incorporated by representing the cable by a number of finite length uniform cylindrical segments, each having the radius and electrical characteristics of a small region along the cable. Input waveforms are approximated by truncated Fourier series of sinusoidal components. Output waveforms are produced by multiplying the input Fourier series sinusoids by their respective transfer functions between input and output points on the cable and summing the resultant output point sinusoids. The transfer functions, representing attenuation and phase shift for each input sinusoid, are obtained by numerical analysis of an electrical ladder network derived from the cylindrical segment model of the cable. Results are shown for application of this method to both cylindrical and expanding radius cable geometries.     

Parametric and non-parametric modeling of short-term synaptic plasticity. Part II: Experimental study

This paper presents a synergistic parametric and non-parametric modeling study of short-term plasticity (STP) in the Schaffer collateral to hippocampal CA1 pyramidal neuron (SC) synapse. Parametric models in the form of sets of differential and algebraic equations have been proposed on the basis of the current understanding of biological mechanisms active within the system. Non-parametric Poisson–Volterra models are obtained herein from broadband experimental input–output data. The non-parametric model is shown to provide better prediction of the experimental output than a parametric model with a single set of facilitation/depression (FD) process. The parametric model is then validated in terms of its input–output transformational properties using the non-parametric model since the latter constitutes a canonical and more complete representation of the synaptic nonlinear dynamics. Furthermore, discrepancies between the experimentally-derived non-parametric model and the equivalent non-parametric model of the parametric model suggest the presence of multiple FD processes in the SC synapses. Inclusion of an additional set of FD process in the parametric model makes it replicate better the characteristics of the experimentally-derived non-parametric model. This improved parametric model in turn provides the requisite biological interpretability that the non-parametric model lacks.     

Response characteristics of a neuron model to a periodic input

A mathematical neuron model defined by a difference equation was investigated when it was exposed to an environment of a periodic input stimulus. It is shown that pulse sequences constructed in advance by a particular method are actually realizable as the output of the system and the condition for the output sequence is also obtained with respect to the magnitude of the input. The results are interesting from a point of view of number theory.     

Optimal distance from the implement to the axis of rotation in hammer and discus throws.

It is a well-known fact that a dramatic improvement in the range of any projective throw can be achieved by increasing the release velocity. In this paper a simple model of a competitor with an implement (hammer or discus) in the turns is considered. The thrower is regarded as a rigid body, and the implement as a point mass. The transverse velocity component of the implement at the release moment is maximized. For finding the optimal distance of the implement from the axis of rotation optimal control theory is applied. According to the proposed model, the optimal hammer throwing technique requires constant and maximal distance of the implement from the axis of rotation, followed by the rapid shortening of the distance immediately prior to the release. In the discus throw, however, this shortening is useless.     

A Modeling Study on Responses of Alkaline Grassland Ecosystems to Climate Change in Light of Diversity and Spatial Patterns

Temporal variations of spatial coverage patterns of major plant species in the alkaline grasslands in northeast China subject to climate change were studied using a spatial simulation model. The model stressed the coupling between soil alkali and vegetation coverage. The modeled species coverage patterns were shown in close agreement with observations on a fenced one-hectare alkaline grassland from 1989 to 1993. The impacts of climate change on the species coverage were studied by subtracting the output patterns of the model under contemporary climate from those under altered climate. To relate the difference patterns to various landscape indices, the one-hectare region was divided into 25 subregions. The differencein species coverage between the present and altered climate and spatial pattern and diversity indices were computed for each subregion. A statistical analysis showed that for plants with wide ranges of tolerance to soil alkali and strong spatial migration capability, the impact of climate change was significantly related to spatial patterns, but not to diversity. However, for plants with narrow ranges of tolerance to soil alkali and less capability to migrate spatially, the impact of climate change was related to both diversity and spatial patterns.     

An intracellular factor that induces erythroid differentiation in mouse erythroleukemia (Friend) cells

We have previously shown that in vitro erythroid differentiation of mouse Friend cells is a result of a synergistic action of two distinctive intracellular reactions. We now have evidence that a factor in the cell free extract is involved in one of the reactions. This factor triggers erythroid differentiation when introduced into undifferentiated mouse Friend cells, provided the cells have been briefly exposed to dimethyl sulfoxide. The factor is induced in nonerythroid cells as well following treatment of the cells by agents that affect DNA replication. Cycloheximide inhibited the induction of the factor. The factor, which is in the cytoplasm, was partially purified and proteinaceous. When introduced into the cells the partially purified factor converts 60% to 70% of undifferentiated Friend cells to erythroid cells, at an efficiency almost equivalent to the efficiencies achieved by typical inducing agents. The factor's biochemical characteristics and possible role in erythroid differentiation are also discussed.     

Properties of central control of body temperature in the rabbit

The structure of the central temperature controller in rabbits has been analysed. On the one hand, experiments were carried out to obtain the necessary data for system analysis; on the other hand, a mathematical model of the passive system was developed which describes the thermal characteristics of the body in accordance with the experimental results. In applying the model, different controller equations for the effector mechanisms involved were tested to fit the experimental data best. They are compared with already existing models of metabolic control. In addition, mechanisms of the effector coordination are discussed. It is shown that the three effectors make use of a similar controller structure thet feeds core temperature as well as skin temperature back into the controller. The system is insensitive to variations of the controller gains, whereas a slight change in the controller reference temperature causes significant changes of the controlled core temperature. Furthermore it is shown that any mutual effector blockings are dispensible.     

Physiological background of the change point in VO2 and the slow component of oxygen uptake kinetics.

It is generally believed that oxygen uptake during incremental exercise--until VO2max, increases linearly with power output (see eg. Astrand & Rodahl, 1986). On the other hand, it is well established that the oxygen uptake reaches a steady state only during a low power output exercise, but during a high power output exercise, performed above the lactate threshold (LT), the oxygen uptake shows a continuous increase until the end of the exercise. This effect has been called the slow component of VO2 kinetics (Whipp & Wasserman, 1972). The presence of a slow component in VO2 kinetics implies that during an incremental exercise test, after the LT has been exceeded, the VO2 to power output relationship has to become curvilinear. Indeed, it has recently been shown that during the incremental exercise, the exceeding of the power output, at which blood lactate begins to accumulate (LT), causes a non-proportional increase in VO2 (Zoladz et al. 1995) which indicates a drop in muscle mechanical efficiency. The power output at which VO2 starts to rise non-proportionally to the power output has been called "the change point in VO2" (Zoladz et al. 1998). In this paper, the significance of the factors most likely involved in the physiological mechanism responsible for the change point in oxygen uptake (CP-VO2) and for the slow component of VO2 kinetics, including: increase of activation of additional muscle groups, intensification of the respiratory muscle activity, recruitment of type II muscle fibres, increase of muscle temperature, increase of the basal metabolic rate, lactate and hydrogen ion accumulation, proton leak through the inner mitochondrial membrane, slipping of the ATP synthase and a decrease in the cytosolic phosphorylation potential, are discussed. Finally, an original own model describing the sequence of events leading to the non-proportional increase of oxygen cost of work at a high exercise intensity is presented.     

Dynamic response of intraocular pressure and biomechanical effects of the eye considering fluid-structure interaction

The vibration characteristics of shell structures such as eyes have been shown to vary with intraocular pressure (IOP). Therefore, vibration characteristics of the eye have the potential to provide improved correlation to IOP over traditional IOP measurements. As background to examine an improved IOP correlation, this paper develops a finite element model of an eye subject to vibration. The eye is modeled as a shell structure filled with inviscid pressurized fluid in which there is no mean flow. This model solves a problem of a fluid with coupled structural interactions of a generally spherically shaped shell system. The model is verified by comparing its vibrational characteristics with an experimental modal analysis of an elastic spherical shell filled with water. The structural dynamic effects due to change in pressure of the fluid are examined. It is shown that the frequency response of this fluid-solid coupled system has a clear increase in natural frequency as the fluid pressure rises. The fluid and structure interaction is important for accurate prediction of system dynamics. This model is then extended to improve its accuracy in modeling the eye by including the effect of the lens to study corneal vibration. The effect of biomechanical parameters such as the thicknesses of different parts of the eye and eye dimensions in altering measured natural frequencies is investigated and compared to the influence of biomechanical parameters in Goldmann applanation tonometry models. The dynamic response of the eye is found to be less sensitive to biomechanical parameters than the applanation tonometry model.     

Utilization of carbohydrates by Thermomonospora sp. Grown on glucose,cellobiose, and cellulose

Thermomonospora sp. was grown on glucose, cellobiose, and in order to study its growth characteristics with different carbohydrate substrates and to assess the validity of some of the assumptions made in a previously proposed model for the cellulose fermentation with this microorganism. It was observed that the nitrogen and protein contents of the cells are essentially constant during the fermentation and independent of the carbon source when glucose or cellobiose are utilized. Under oxygen starvation conditions it was shown that unidentification organic compound(s) accumulate(s) in the culture broth. Culture fluorescence was shown to be an excellent variable for monitoring and control of the fermentation process. This microorganism showed a preference for crystalline cellulose (Avicel) as substrate although it grows readily on a more amorphous cellulose (Solka Floc). The production of extra cellular protein is shown to be growth related. Data were obtained confirming the decrease in the number of active adsorption sites as the cause for the decrease in the cellulose digestion rate. It is suggested that a future model should account for the time change of surface characteristics of the cellulose particles.     

Prenatal development of cutaneous afferent connections in the spinal cord of fetal sheep

In this study we have examined the physiological and neurochemical development of the cutaneous afferent pathways from the hindlimb to the spinal cord in fetal sheep. We have shown that somatosensory input from the hindlimb evokes activity in DRG neurons at 87d gestation and in cells in the dorsal horn at 92d (term, 146d). There is evidence of immunoreactivity for substance P, calcitonin gene-related peptide and glutamine several days prior to this at 77-80 days. The implication of these findings are discussed.