A definition of tool use due to Benjamin Beck has served the field of animal cognition well for over 25 years. This article proposes a new, more explanatory definition that accounts for tool use in terms of two complementary subcategories of behaviors: behaviors aimed at altering a target object by mechanical means and behaviors that mediate the flow of information between the tool user and the environment or other organisms in the environment. The conceptual foundation and implications of the new definition are contrasted with those of existing definitions, particularly Beck's. The new definition is informally evaluated with respect to a set of scenarios in which differences from Beck's definition and others in the literature can be seen.

We describe concepts to support the analysis of cell phone menu hierarchies, based on cognitive models of users and easy-to-use optimization techniques. We present an empirical study of user performance on five simple tasks of menu traversal on an example cell phone. Two of the models applied to these tasks, based on GOMS and ACT-R, give good predictions of behavior. We use the empirically supported models to create an effective evaluation and improvement process for menu hierarchies. Our work makes three main contributions: a novel and timely study of a new, very common HCI task; new versions of existing models for accurately predicting performance; and a search procedure to generate menu hierarchies that reduce traversal time, in simulation studies, by about a third.

Cell phone interfaces are now ubiquitous. In this paper, we describe concepts to support the analysis of cell phone menu hierarchies. We present an empirical study of user performance on five simple tasks of menu traversal on a cell phone. Two models we tested, based on GOMS and ACT-R, give very good predictions of behavior. We use the study results to motivate an effective evaluation process for menu hierarchies. Our work makes several contributions: a novel and timely study of a new, very common HCI task; new models for accurately predicting performance; novel development tools to support such modeling; and a search procedure to generate menu hierarchies that reduce traversal time, in simulation studies, by about a third.

The differential equations are derived for reflective optical surfaces in systems that give prescribed spatial irradiation from collimated sources. The equations are derived for axisymmetric configurations assuming specular reflective surfaces. The formulation considers general source radiant emittance distributions, general receiver shapes, and receiver irradiation distributions. The formulation of the differential equations is effected through the vector formulation of ray-trace equations for the systems, formulation of differential radiant energy balance equations, and appropriate differentiation of the ray-trace equations. The differential equations are derived for two configurations.

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