Examination of the effect of the fibrous structure of a lens on the optical characteristics of the human eye: a computer-simulated model.

We introduce a model of the human eye for which we take into consideration the laminated nature of lens fibers. The thickness of each lamina is 5.6 µm; thus the lens comprises 300 eccentric lenses of minute dimensions. The index gradient of the lens is such that the index of refraction increases exponentially from the lens core to its peripheral zone. A vector ray-tracing technique is employed to study the optical haracteristics of the system. Both paraxial and marginal rays are simulated, and the angles of incidence vary from 0° to ±20°. Special attention is given to the meridional caustic surfaces as well as the wave-front distortion of the refracted rays. A quasi-Newton optimization technique is employed to obtain the best parameters for the system. A computer modeling program, written in FORTRAN 77, is used to simulate a ray's refraction through the multisurfaces of the eye. The results show full agreement with previous data and that the cornea is responsible for eliminating possible spherical aberration of the system.

Magnetic field interaction with streaming potentials in cancellous bone.

The effect of applying a DC magnetic field on the streaming potential developed across cancellous bone samples is reported. Electrolyte fluid (0.95 mM NaCl) was made to flow at different rates through a thin disc sample while a DC magnetic field was applied normal and parallel to the direction of the flow. The results may confirm the existence of the streaming potential hypothesis yet no significant correlation was observed between the magnetic field at two different orientations and the streaming potential.

Spatial and vacancy effects on the stabilising mechanisms of two-dimensional free growth.

A Monte-Carlo simulation technique is introduced to study the spatial considerations of cellular distribution that affect the overall asynchronous process of population growth. The stochastic nature of cellular characteristics such as mitotic time, loss rate and direction of growth is considered. The fluctuation of these values from one generation to the next and from one cell to the other, is illustrated. Cells are assumed to grow in a two-dimensional honeycomb-like network such that a central cell is always surrounded with six equally distant sites. The modes of cellular growth are controlled mainly and simply by the existence of a definite number of neighbouring vacancies. An IBM-compatible PC-AT computer was used and a program written in Pascal is employed to simulate and follow up the growth of a single stem cell in a 40,000-sites network. The results of the proposed stochastic model illustrate the importance of the spatial interaction among growing cellular modes such that vacancies act as local sensors for a negative feedback mechanism regulating the overall growth pattern. The role of the resting mode (G0) in stabilising the overall growth pattern is discussed.