PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “COMPUTERS, ANALOG”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 973 records · Page 54Linked to original sources
PubMed1970

X-ray diffraction of myelin membrane. II. Determination of the phase angles of the frog sciatic nerve by heavy atom labeling and calculation of the electron density distribution of the membrane.

The phase signs of the five main X-ray reflections from normal frog sciatic nerve have been determined as all positive using a technique of labeling with very small amounts of heavy metal. The changes in intensity of the individual reflections were studied as a function of uptake of metal label by the membrane. The possible localization of the metal label was decided from computer-analogue studies and from Patterson calculations. These phases are different from those determined by previous workers using techniques of trial of the best set of phases, or a step model, to give the best fit of the combined intensity data of normal and swollen myelin membranes. The electron density map has been calculated using eight reflections and their experimentally determined phases. The map shows an inner low electron density region which is different from that shown by earlier calculations. The center of the low electron density region shows a small region of increased electron density. However, without fixing absolute electron density levels in the map, it is not yet possible to allocate regions of low electron density to pure lipid or lipoprotein. The map shows the two sides of the membranes to be different in molecular structure without significant water spaces between the membranes.

Animals↗
PubMed1970

A physical model for muscular behavior.

A model for muscular behavior has been developed by a generalization of the laws governing the viscoelastic behavior of polymeric materials. The model simulates events thought to take place during stretch, loading, and stimulation of muscle, whether smooth or striated. The equations of motion were solved with an analogue computer for several types of perturbation, and stress, strain, and strainrate curves were generated. Model parameters were selected by fitting experimental stress-relaxation data. The resulting equations predicted the frequency dependence of dynamic modulus and phase angle within experimental error. With appropriate boundary conditions and suitable values for model parameters, the computed results also closely resembled experimental curves of contraction velocity vs. time, isometric tension development vs. time, force-velocity curves, and temperature-tension relationships. These results call attention to the relationship between the behavior of various kinds of muscle and open the way for quantifying muscular behavior in general.

Animals↗
PubMed1972

Computer simulation of after-inhibition in crayfish slowly adapting stretch receptor neuron.

A theoretical model is described which is able to mimic the responses of slowly adapting stretch receptor neurons of crayfish to applied currents. Its principal feature is postspike inhibition, in which each nerve impulses produces a small inhibitory current that decays with a simple exponential time-course that is long compared with normal interspike intervals. The model was simulated with both an analogue and a digital computer. Parameters for particular model neurons were determined both by an analysis of experimental data obtained from adaptation to constant injected currents, and by matching computer output to the data. Parameter values estimated by the two techniques agreed within +/-10%. Model parameters determined from adaptation data successfully predicted the magnitude and time-course of posttetanic hyperpolarization (PTH) in the stretch receptor neuron. In addition, model neurons were able to reproduce posttetanic depression (PTD) as seen in stretch receptor cells.

Animals↗
PubMed1975

Continuous infusion urography in unilateral hydronephrosis.

In cases of unilateral hydronephrosis the urine concentration of contrast medium, for example diatrizoate, depends on the remaining renal function, the rate of turnover in the obstructed renal pelvis and the function of the contralateral kidney. Contrast medium for a single injection or a short infusion time is rapidly excreted by the normal contraleteral kidney, without allowing high enough plasma levels long enough for sufficient urine concentrations in the hydronephrotic kidney. This excretion rate can be compensated for by continuous infusion urography for several hours with large doses of contrast medium (up to 1,250 ml. 30 per cent diatrizoate). This method was theoretically computerized, tested in animals experiments and clinically used in 11 patients. It can improve the diagnostic possibilites of excretory urography, especially in cases of unilateral obstruction, and can minimize the need for retrograde pyelography with its known complications.

Aged↗