No abstract

In this paper we report on an analysis of visual stimuli models by a wavelet function. The human visual process is compared with a wavelet transform. Wavelet functions have been built from the Haar function. Two stimuli were analyzed by a wavelet function: a sinusoidal luminance stimulus (spatial frequency ƒ) and a luminance-varying regular stimulus. The theoretical results obtained from the wavelet transform are compared with the physiological results of R. Blake [in Frontiers in Visual Science, S. J. Cool and E. L. Smith, eds. (Springer-Verlag, Berlin, 1978), pp. 209-219] and K. K. De Valois [in Frontiers in Science, S. J. Cool and E. L. Smith, eds. (Springer-Verlag, Berlin, 1978), pp. 277-285]. A theoretical curve conforms to the shape of the contrast sensitivity curves. Hence it can be concluded that the wavelet transform is a new approach to human visual mechanisms.

Thin films of calcium were evaporated under ultrahigh vacuum conditions (pressures less than 5 x 10(-10) Torr) onto quartz substrates to a thickness of 20 nm. The photoelectric yield and hence the work function of the layers were determined as a function of thickness. For film thicknesses greater than 10 nm, the work function was constant with a value of 2.87 +/- 0.06 eV. The work function suows minima at film thicknesses of about 2.5 nm and 5.5 nm. Results from films thicker from 5.5 are a good fit to the Fowler function; for thinner films, the results suggest the existence of a second photoelectric threshold with a corresponding work function ø(s). A theory based on the energy states of the surface electrons is proposed to explain both this second threshold and the ir absorption of thin calcium films.

No abstract

No abstract