A theory of retinal burnsVos, J. J.
doi: 10.1007/BF02477421pmid: 13926801
Abstract Retinal burns may be accidental in origin (eclipse blindness, flash burns) or intentional (in the operative technique of photocoagulation). An attempt is made to come to a quantitative understanding of the thermal events involved in the production of these burns. The results of experiments by Hamet al. (Am. J. Ophth.,46, 700–723, 1958) on retinal flash burns in rabbit eyes were therefore analyzed. It is concluded that the findings of these authors cannot be explained in the simple terms of a critical temperature beyond which burns are produced: the temperature is raised beyond the boiling point of the tissue fluid, and the production of steam must be taken into consideration. In fact, it appears from the computed amount of steam production. However, it is also obvious that functional damage might occur at a much lower level of irradiation too, since somewhere between 45° and 60°C. the albumins begin to coagulate. It even seems plausible that a still smaller temperature increase of only a few degrees centigrade might produce at least temporary lesions after prolonged exposure, by the process of “metabolic poisoning,” which occurs when the waste products of the accelerated metabolic processes cannot be removed quickly enough.
Variation of pressure with cycle length and duration of systole in the two-chambered cardiovascular modelRoston, Sidney
doi: 10.1007/BF02477422pmid: N/A
Abstract Variation in the heart rate and the duration of systole modifies the pressures in the two-chambered model of the cardiovascular system by several mechanisms. The theoretical results indicate that prediction of chamber pressures would require moment-to-moment knowledge of the resistances peripheral to each chamber in addition to the cardiac output per cycle, cycle length, and duration of systole. Lengthening of systole with increase in cycle length—a physiologically observed relationship—theoretically stabilizes the end-diastolic pressure in the ascending aorta and may be a homeostatic mechanism to steady blood flow through the coronary arteries.
Un modèle du neuroneNelson, Pierre P.
doi: 10.1007/BF02477424pmid: N/A
Abstract Expressions which describe the variations of the membrane potential are introduced. They consist of a second-order differential equation and of a threshold condition. The behavior of this differential equation is studied graphically in the phase plane. This formulation permits the description of certain properties which depend on time. In particular the excitability curve and the possibilities of synchronization are obtained, in agreement with observation. A simple extrapolation leads to the introduction of facilitation phenomena.
The equivalent generator components of uniform double layersBrody, Daniel A.; Bradshaw, J. Carl
doi: 10.1007/bf02477425pmid: 13873329
An analytic approach is described for resolving a uniform double layer with known rim configuration into a series of equivalent generator components. Using the principles developed in this report, it should be possible to estimate the intrinsic electrocardiographic characteristics of ventricular depolarization in the dog heart from available physiological data. In the case of a double layer with planar rim, the first three orders of approximation (dipolar, quadripolar, and octapolar) can be completely specified from the following properties of the plane area enclosed by the rim: magnitude of the area, direction cosines of a normal line, location of the center of gravity, and the momental ellipse of the area. All quadripolar components and position-variable octapolar components disappear when the coordinate origin coincides with the centroid of the rim area. In the non-planar case, an electrical center is specified for which three of the five quadripolar components vanish, and the residual second-order effects due to non-planarity may be equated withX-,Y-, andZ-oriented axial quadripoles. Non-planarity affects octapolar components also, but in a less easily defined manner.
On multipole representation of current generatorsYeh, Gordon C. K.
doi: 10.1007/BF02477426pmid: 14009078
Abstract In Yeh, Martinek, and de Beaumont (Bull. Math. Biophysics,20, 203–216, 1958), multipole representations of current generators in a volume conductor are used, based upon the Taylor series expansion of the potential function. In Yeh, (Bull. Math. Biophysics,23, 263–276, 1961) multipole representations of current generators in a spherical volume conductor are used, based upon the spherical harmonic expansion. This paper correlates these two systems of multipole representations so that formulations in terms of one system of the representations may be readily transformed into formulations in terms of the other system. Since the Taylor series representation is more graphic, whereas the spherical harmonic representation is more compact, such a transformation between these two systems of formulations can serve useful purposes in the application of the theory of electrocardiography.
On mutant setsMullin, A. A.
doi: 10.1007/BF02477427pmid: N/A
Abstract This paper sketches the outline of a new, general mathematical theory concerning the nature of a relative anti-closure property for subsets of general algebraic systems. It thus quite naturally fits into any exhaustive theory of relations and, in particular, into a theory of relations for abstract mathematical molecular biology. In addition, the theory possesses certain intuitive, but naive relationships to basic analytical studies of biological mating and mutation. At the purely mathematical level one can produce an abundance of theorems from the theory with interpretations in the context of the frequently appearing mathematical structures of groups and rings, among other algebraic structures.
A note on energy expenditure in walking on level ground and uphillRashevsky, N.
doi: 10.1007/BF02477428pmid: 14490429
Abstract In walking, energy is wasted in the process of up-and-down movement of the center of gravity of the body during each step, as well as in the kinetic energy involved in the swinging forward of each extrèmity. In this paper the frictional loss in muscles is not considered. It is shown that for a prescribed available amount of metabolic power expenditure there exists an optimal size of the step and an optimal (maximal) speed of walking for the size of the step. Calculated values are of the correct order of magnitude. In walking uphill there exists a type of step for which there is no “lost” up-and-down motion of the center of gravity of the body. This step is optimal for walking up a hill of a given incline.
On the function and design of the lungRashevsky, N.
doi: 10.1007/BF02477429pmid: 14490432
Abstract The purpose of this paper is to explore further the possibilities of a theory of structure (form) as determined by function. The paper is preliminary in nature and emphasis is placed more on the methodological approach than on immediately verifiable conclusions. An approximate mathematical treatment of diffusion between alveoli and blood is given, taking into account the periodic variations of the concentration of gases in the lung and in the bloodstream due to the periodicity of breathing. Expressions for the blood concentration and the alveolar concentration of oxygen as functions of time are derived in terms of the frequency of breathing and of some structural geometric parameters of the lung. It is then shown what tentative conclusions can be drawn from such considerations in regard to the structure of the lung.