Design principles for cognitive artifacts

Modern designs are more than ever before required to be understandable and usable by their intended audience. As machines get ever more complex, it becomes essential for designers to provide a user-centered design that focuses upon the needs and abilities of the user. This paper presents an analysis of cognitive artifacts—devices designed to maintain, display, or operate upon information in order to serve a representational function. An important design consideration is the human action cycle which means that artificial devices must support both execution and evaluation.     

A systematic approach to the search for variational principles for plane steady flows

Using Vainberg's theorem of nonlinear potential operators, alternate potential principles associated with the differential equations governing the gasdynamics of plane steady irrotational diabatic flow and isoenergetic rotational adiabatic flow are formulated and their equivalence with Bateman's principle is established. Further, the advantage usefulness of treating a single nonlinear equation for the existence and hence formulation of a functional over the equivalent system for the same problem is brought into sharper focus.     

General slow viscous flows in a two-fluid system

Summary A general solution of the creeping flow equations suitable for a flow that is bounded by a nondeforming planar interface is presented. New compact representations for the velocity and pressure fields are given in terms of two scalar functions which describe arbitrary Stokes flow. A general reflection theorem is derived for a fluid-fluid interface problem containing Lorentz reflection formula as a particular case. The theorem allows a better interpretation of the image system for various singularities in the presence of a planar interface. The general solution is further used to describe the first-order approximation of the deformed interface by performing normal stress balance. It is found that the normal stress imbalance and the interface displacement are independent of the viscosity ratio of two fluids (!) and only depend on the location of initial singularity.