Disruptive colouration is a visual camouflage composed of false edges and boundaries. Many disruptively camouflaged animals feature enhanced edges; light patches are surrounded by a lighter outline and/or a dark patches are surrounded by a darker outline. This camouflage is particularly common in amphibians, reptiles and lepidopterans. We explored the role that this pattern has in creating effective camouflage. In a visual search task utilising an ultra-large display area mimicking search tasks that might be found in nature, edge enhanced disruptive camouflage increases crypsis, even on substrates that do not provide an obvious visual match. Specifically, edge enhanced camouflage is effective on backgrounds both with and without shadows; i.e. this is not solely due to background matching of the dark edge enhancement element with the shadows. Furthermore, when the dark component of the edge enhancement is omitted the camouflage still provided better crypsis than control patterns without edge enhancement. This kind of edge enhancement improved camouflage on all background types. Lastly, we show that edge enhancement can create a perception of multiple surfaces. We conclude that edge enhancement increases the effectiveness of disruptive camouflage through mechanisms that may include the improved disruption of the object outline by implying pictorial relief.

No abstract

Calculations are made on specific DNA-type compleles using refined e\pressions for electrostatic and polariiation energies. Dispersion and repulsive terms are included in the evaluation of the total interaction energy. It is shown that the expansion of the electrostatic potential to include multipole moments up to octopole is necessary to achieve convergence of first-order energies. Polarization energies are not as sensitive to this expansion. The calculations also support the usefulness of the hard sphere model for DNA hydrogen bonds and indicate how stacking interactions are influenced by second-order energies.

A set of building and displaying programs has been written and applied to serve as tools in the study of the interaction of proteins with DNA and RNA. This study, which has involved the use of a variety of computers, is a collaborative project between the group at RPMI, Buffalo, New York, and NASA-Ames, California. The RPMl system, which is currently running on the Univac 70 computer, is easily adaptable to any computer, with or without sophisticated graphics hardware. Hence we emphasize the availability of an easy to handle and inexpensive means for building, displaying, and manipulating molecules. The RPMl system also includes an automated, noninteractive program for fast construction of specified molecular structures. The NASA system is running on an Evans and Sutherland display system which has sophisticated hardware and which is capable of continuously rotating the molecule with constant adjustment of perspective and intensity.

No abstract