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At least 55 records · Page 3Linked to original sources
PubMed1977

Respiratory control of body temperature: a theoretical model.

The two-compartment model of a ventilatory CO2 chemostat of Grodins et al. (1954) is modified to describe a ventilatory thermostat fitting the requirements of panting. Allowance for the extra heat production during panting leads to a second order third degree differential equation which by introducing the ventilation/perfusion ratio can be reduced to the second degree. From the steady-state solutions calculated for dogs using experimentally determined constants it is concluded that: (1) the ventilation/perfusion ratio has no influence; (2) the ambient temperature leads to a marked panting only above 30 degree C; (3) the relative humidity of the air increases the panting; (4) due to the oxygen cost of panting, the regulation of the body temperature is possible only within limits. The limitation depends upon the energy requirements of the respiratory muscles, upon the set-point temperature and the controller gain. The unsteady-state solution is given by approximation. The ventilatory reaction to the heat stress appears to be slow with a half-time of about 15 min for a 20 kg dog. All properties of the model are mainly determined by the high specific heat of tissues relative to expired air.

Animals↗
PubMed1979

A theoretical model for lipid mixtures, phase transitions, and phase diagrams.

We present a new model for the thermodynamic properties of lipid bilayers. The model consists of a system of hard cylinders of varying radii that correspond to the different molecular radii of lipids having different numbers of gauche rotations in their chains. Scaled particle theory is used to provide an accurate estimate of the entropy of packing of the cylinders. To apply the model to bilayers we introduce a semiempirical attractive potential energy. Once the form of this potential is chosen, we adjust one parameter, the interaction strength, so that the model fits the transition temperatures and entropies for various phospholipids. The model then agrees quite well with other published data for these systems. We also directly generalize our model to lipid mixtures, and we obtain phase diagrams that we compare to existing data for these systems. We use the model to describe lipid protein interactions in bilayers as well.

Lipid Bilayers↗
PubMed1976

Presynaptic calcium currents and their relation to synaptic transmission: voltage clamp study in squid giant synapse and theoretical model for the calcium gate.

A voltage clamp study of the presynaptic terminal in squid stellate ganglion has given quantitative results relating inward Ca2+ current to presynaptic membrane potential and postsynaptic response to inward Ca2+ current. The results indicate an S-shaped curve for the relationship between presynaptic potential and Ca2+ current and a linear relationship between Ca2+ current and postsynaptic potential. A similar S-shaped curve was found for the time-dependent properties of the Ca2+ conductance. Based on these results a mathematical model was developed which accounts for the experimental results in this and previously published papers by other authors. The model suggests that five subunits are involved in the Ca2+ gate and that the subunits change noncooperatively from an inactive to an active form upon membrane depolarization.

Animals↗
PubMed1977

Early chemical evolution of nucleic acids: a theoretical model.

Recent experimental work suggests a possible cyclical pathway for early prebiotic oligonucleotide formation that involves (i) dry-state (nontemplate) synthesis of random copolymers with mixed 2',5' and 3',5' bonds, (ii) passage of these oligomers into solution at low temperatures, and (iii) a preferential hydrolysis of the 2',5' bond in any short helices that have formed. This early system could have selected for complementary sequences that were largely 3',5'-linked, but may not have selected efficiently for a single enantiomer of ribose.

Cold Temperature↗
PubMed1979

Homosexual identity formation: a theoretical model.

A six-stage model of homosexual identity formation is outlined within the framework of interpersonal congruency theory. Stages are differentiated on the basis of the person's perceptions of his/her own behavior and the actions that arise as a consequence of this perception. The person is seen to have an active role in the acquisition of a homosexual identity. Alternative paths of development are proposed within each stage. The notion that people can accept homosexuality as a positively valued status is assumed. Several factors believed to be influential in determining whether a person takes one line of development or another are discussed. The model is intended to be applied to both female and male homosexuals.

Adaptation, Psychological↗
PubMedDate not supplied

[Theoretical model of homopolymer chain adsorption on a homogenous surface].

On the basis of I. M. Lifshitz's theory the adsorption of the homopolymer on the homogenous surface is considered. It is shown that the attraction of monomers to the surface may lead not only to adsorption of the globule or coil but also to the emergence of a new peculiar phase--dislike globule without the fringe, all the monomers of which are stuck to the surface. A two-dimensional phase-diagram is plotted.

Adsorption↗