A structure for maturing intelligent tutoring system student models

A special structure is examined for evolving a detached model of the user of an intelligent tutoring system. Tutoring is used in the context of education and training devices. A detached approach to populating the student model data structure is examined in the context of the need for time dependent reasoning about what the student knows about a particular concept in the domain of interest. This approach, to generating a data structure for the student model, allows an inference engine separate from the tutoring strategy determination to be used. This methodology has advantages in environments requiring real-time operation

Josiah Parsons Cooke Jr.: Epistemology in the Service of Science, Pedagogy, and Natural Theology

Josiah Parsons Cooke established chemistry education at Harvard University, initiated an atomic weight research program, and broadly impacted American chemical education through his students, the introduction of laboratory instruction, textbooks, and influence on Harvard's admissions requirements. The devoutly Unitarian Cooke also articulated and defended a biogeochemical natural theology, which he defended by arguing for commonalities between the epistemologies of science and religion. Cooke's pre-Mendeleev classification scheme for the elements and atomic weight research were motivated by his interest in numerical order in nature, which reflected his belief in a divine lawgive

Tools for Verifying Classical and Quantum Superintegrability

Recently many new classes of integrable systems in n dimensions occurring in classical and quantum mechanics have been shown to admit a functionally independent set of 2n-1 symmetries polynomial in the canonical momenta, so that they are in fact superintegrable. These newly discovered systems are all separable in some coordinate system and, typically, they depend on one or more parameters in such a way that the system is superintegrable exactly when some of the parameters are rational numbers. Most of the constructions to date are for n=2 but cases where n>2 are multiplying rapidly. In this article we organize a large class of such systems, many new, and emphasize the underlying mechanisms which enable this phenomena to occur and to prove superintegrability. In addition to proofs of classical superintegrability we show that the 2D caged anisotropic oscillator and a Stackel transformed version on the 2-sheet hyperboloid are quantum superintegrable for all rational relative frequencies, and that a deformed 2D Kepler-Coulomb system is quantum superintegrable for all rational values of a parameter k in the potential

Can disorder enhance incoherent exciton diffusion?

Recent experiments aimed at probing the dynamics of excitons have revealed that semiconducting films composed of disordered molecular subunits, unlike expectations for their perfectly ordered counterparts, can exhibit a time-dependent diffusivity in which the effective early time diffusion constant is larger than that of the steady state. This observation has led to speculation about what role, if any, microscopic disorder may play in enhancing exciton transport properties. In this article, we present the results of a model study aimed at addressing this point. Specifically, we present a general model, based upon F\"orster theory, for incoherent exciton diffusion in a material composed of independent molecular subunits with static energetic disorder. Energetic disorder leads to heterogeneity in molecule-to-molecule transition rates which we demonstrate has two important consequences related to exciton transport. First, the distribution of local site-specific diffusivity is broadened in a manner that results in a decrease in average exciton diffusivity relative to that in a perfectly ordered film. Second, since excitons prefer to make transitions that are downhill in energy, the steady state distribution of exciton energies is biased towards low energy molecular subunits, those that exhibit reduced diffusivity relative to a perfectly ordered film. These effects combine to reduce the net diffusivity in a manner that is time dependent and grows more pronounced as disorder is increased. Notably, however, we demonstrate that the presence of energetic disorder can give rise to a population of molecular subunits with exciton transfer rates exceeding that of subunits in an energetically uniform material. Such enhancements may play an important role in processes that are sensitive to molecular-scale fluctuations in exciton density field.Comment: 15 pages, 3 figure

"Whither the Middle Class'? A Dynamic View"

Research using cross-sectional survey 'snapshots' of household income taken over the past quarter century reveals a growing inequality in the distribution of annual money income of households in the United States (Thurow, 1987; Levy, 1987; Levy and Michel, 1991; Michel, 1991; Karoly, 1990; Center on Budget and Policy Priorities, 1990; Easterlin, MacDonald and Macunovich, 1990), prompting some to argue that the U.S. middle class is disappearing (Phillips, 1990; Bradbury, 1986). Aggregate data from the National Accounts and from wealth surveys (Wolff, 1989; Eargle, 1991) reinforce this conclusion by showing a growing share of income from capital, a falling share for earnings, and a slightly increasing concentration of wealth among upper-income groups. Also well-documented is greater inequality in the size distribution of earnings and wages in the late 1980s as compared to one or two decades before (GottschaLk and Danziger, 1989; Burtless, 1989; Blackbum et al., this volume). Despite the consistency of these results, their almost universal reliance on data drawn from cross-sectional snapshots leaves unanswered many important questions regarding the nature of the changes taking place in the distribution of income and wealth. Most importantly, cross-sectional snapshots provide information only on net changes in economic position and thus reveal little about the extent and nature of movement into and out of the middle class.. Are increasing numbers of families 'falling from grace', as Katherine Newman (1988) puts it? If so, who are they and what events are linked to their income losses? Or is mobility into the middle class declining? And, if so, does this affect in particular young families? What avenues for upward mobility are disappearing? These are the types of questions we seek to address for adults crossing either the lower or the upper boundary of the middle class. A second set of issues we address involves linkages between changes in income and changes in wealth. We analyze trends in the transitions of prime age (25-54 years old) adults into and out of the middle class using 22 years of data from the Panel Study of Income Dynamics. We begin by reviewing the methodology and measurement procedures that we employ to define the middle class and transitions into and out of middle-class status. Next we present our basic findings which, in fact, show a persistent 'withering' of the middle class since about 1980. We then search for clues as to who moved into and out of the middle-income groups and the source of such changes. Because notions of 'class' are usually based on measures of wealth as well as income, we also investigate longitudinal changes in the wealth distribution in the 1980s for these same individuals. Our findings on wealth reinforce those based on income. The paper concludes with a brief discussion of the policy implications of our findings.