An approximation method for the solution of diffusion and related problems

An approximation method is introduced which enables a number of diffusion-type problems to be solved in an approximate but simple manner. Many cases require only the solution of a simple first-order differential equation. The method is applied to a number of cases in which the exact solutions are available. A comparison shows that the method is quite satisfactory in these cases. The method is applied to diffusion problems with rate of consumption proportional to concentration or to the square of the concentration. In the latter case, the result obtained is essentially the same as that found by H. G. Landau (1950) after elaborate calculations.     

Outline of a matrix calculus for neural nets

The activity of a neural net is represented in terms of a matrix vector equation with a normalizing operator in which the matrix represents only the complete structure of the net, and the normalized vector-matrix product represents the activity of all the non-afferent neurons. The activity vectors are functions of a quantized time variable whose elements are zero (no activity) or one (activity). Certain properties of the structure matrix are discussed and the computational procedure which results from the matrix vector equation is illustrated by a specific example.     

An application of the theory of neural nets to the study of motion sickness

The results from a study by M. F. Morales on the labyrinthine response to motion are used, together with results of neural net theory, to enable one to calculate, in terms of a small number of parameters, the percentage of individuals who have motion sickness when exposed to rather general patterns of motion which may vary with time.     

Resistance to anoxia of Chironomus plumosus and Chironomus anthracinus (Diptera) larvae

Survival of the midge larvae Chironomus plumosus and C. anthracinus in anoxia at 4°C was investigated. C. plumosus survived about twice as long as C. anthracinus . The corresponding LT 50 values were ca 205 and 100 d. There was no statistically significant difference between the survival in anoxia and in aerated water, which indicates that the main reason for death in anoxia is not the absence of oxygen. This main reason is presumed to be starvation. The presence of undissociated H₂S in low concentrations (ca 1.2 mg 1⁻¹) did not influence the survival. In anoxia the larvae were usually motionless and did not feed but they increased in weight due to uptake of water. During 43 d C. plumosus and C. anthracinus increased ca. 10%.     

Discrimination between temporally separated stimuli

A mechanism is discussed which has the property that two temporally separated stimuli presented over a common path may be discriminated as though they had been presented simultaneously over separate paths.     

Comparison of models of insulin release

A model for insulin secretion with a storage and a labile compartment, as well as a provisionary factor, is combined with a signal model in which the signal can be the difference between an excitation and an inhibition, or the difference in concentrations inside and outside some cell components. The model, using a single set of values for the parameters, accounts in a semiquantitative manner for all of the regularly appearing features of the insulin secretion from thein vitro perfused pancreas to a wide range of patterns of glucose and tolbutamide stimulation. Among the features which can be accounted for are: early and late secretion of insulin as a function of glucose in terms of a single parameter; the apparent depletion and recovery during a pulsed pattern of stimulation by tolbutamide; the hypersecretion following a short period of rest during a prolonged stimulation by glucose; the negative spike which occurs when the concentration of glucose, which has been maintained for a period of time, is suddenly reduced to a lower level; and the appropriate responses to slow and fast ramp functions of glucose concentration.     

Note on oscillations in a closed chain of compartments with linear,unidirectional transport

A closed chain of compartments in which there is unidirectional transport between adjacent members can exhibit damped oscillations. For a system ofn equivalent compartments, the value ofn which gives the greatest difference between the first maximum and first minimum isn=11, the difference being 1.57%. The greatest difference between the first maximum value and the steady state value is 4% and is obtained whenn=25. The results are illustrated graphically forn equal to 5, 10, 25 and 100.     

Studies on the maturation of immune responsiveness in the mouse. II. Role of the spleen.

Experiments were designed to investigate the role of the spleen in the development of the murine immune system. By using mice splenectomized within 24 hr of birth, as well as mice with a hereditary, congenital absence of the spleen, the primary immune response to sheep erythrocytes was examined. The immunocompetence of lymph node cells from spleenless or control mice was assessed in vitro, in organ and in cell suspension cultures, and in vivo, by transfer into lethally irradiated syngeneic recipients followed by antigenic stimulation. The immunologic capacities of thymus and bone marrow cells were similarly tested by injection separately or in combination into irradiated syngeneic mice. Lymph node cells from spleenless animals appeared fully competent both in vitro and in transfer experiments. Neither neonatal splenectomy nor congenital absence of the spleen significantly reduced the capacity of bone marrow or thymus cells to participate in the immune response to sheep erythrocytes.