Neurophysiological Model of the Normal and Abnormal Human Pupil

A model of the pathways controlling the size of the human pupil is presented. Computer simulation of this model demonstrates the role played by each of the elements in the pupil pathways. Simulations of the effects of drugs and a few common abnormalities in the system also help to illustrate the workings of the internal processes. Computer models of this type can be used as teaching aids or as tools for testing of hypotheses regarding the system.     

Longitudinal waves in liquid-filled tubes—I: Theory

Pulse propagation in axisymmetric elastic and viscoelastic tubes has been analyzed on the basis of extensions of existing one-dimensional bar-like and membrane-shell theories upon addition of viscous behavior of the components. A combined analytical-experimental procedure has also been developed for the determination of relevant mechanical properties. It has been found that, for the range of parameters considered, the fluid viscosity can be ignored, whereas that of the container plays a significant role; on the other hand, the radial inertia can be neglected. In a companion paper, the predictions of the theory are found to be in good correspondence with experimental results.     

Pulse transmission in elastic exponential and conical shells

A theoretical and experimental investigation was conducted to ascertain the response of an axisymmetric exponential shell and of a hollow cone with identical terminal dimensions and lengths, both composed of aluminum, to central longitudinal impact by steel spheres. The principal tests were concerned with loading at the small end and an open distal section; in a few cases, the large end was covered by a relatively thin aluminum plate and subjected to central impact by the various strikers. The range of initial velocities for the 3.175, 6.35 and 12.7 mm diameter pneumatically-fired steel spheres was from 7.6 to 60 m/s, while 23.7 and 50.8 mm steel balls were propelled in a pendulum arrangement at about 1.2 m/s. The input was monitored by a quartz crystal, while the waves were detected by a set of foil gages. A one- and a two-dimensional numerical analysis were executed for a typical set of experimental conditions of the first wave transit in both systems when struck at the small end: the results were in good correspondence with experimental data. The exponential shell exhibited the theoretically predicted cut-off behavior beyond a certain pulse duration which was also found previously in the case of a geometrically similar solid exponential rod. Correspondingly, the conical shell evidenced enormous attenuation, but not complete cut-off beyond such critical impact duration when the wave process was initiated at the small end. The much greater dispersion and attenuation relative to that of the solid bars is primarily due to wall bending of the specimens.     

Elastic wave propagation in an exponential rod

A theoretical and experimental investigation was undertaken to study wave propagation in an exponential rod composed of aluminum when subjected to impact by steel spheres with diameters from 3·175 to 50·8 mm at velocities up to about 60 m/s. Strain measurements were effected at three gage stations and force inputs were obtained in some cases by sandwiched quartz crystals located at the impact point. Corresponding data were obtained for a 17·8° cone of the same length and material. One-dimensional predictions concerning wave shapes in the rod were obtained employing an analytical representation that neglected the effects of radial inertia and numerical finite difference methods that either neglected or incorporated the effects of this parameter. Good correspondence was found between the predicted and measured strain histories during first pulse passage; subsequent correlation showed increasing divergence both with shorter pulse durations and increasing propagation distance.