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The development of open well-mixed chemical reactors led to tremendous advances in the understanding of the temporal behavior of nonlinear chemical systems. For instance, many transitions between different asymptotic states of the system are now well understood in terms of bifurcation theory. However, for spatially extended (unmixed) reactions, only closed systems were experimentally available, and theoretical investigation of such systems naturally focused on matters other than bifurcations between the asymptotic states of the system. The recent introduction of open, unmixed chemical systems has now thrown open the door to theoretical investigation of these systems in terms of the different asymptotic states available to the system, as well as how and when the system can undergo transitions from one state to another. We have formulated models for several such open chemical systems, and have used both analytic and numerical methods to study various aspects of their dynamical behavior. We examine the bifurcations that occur between the different kinds of spatio-temporal structures that can appear in these systems. We will consider the effects that spatial inhomogeneities, both intended and not, can have on the dynamical behavior of these structures. We will also examine in several contexts the connection between the complex spatio-temporal structures in the extended system and the underlying local behavior of the chemistry. This will lead to a qualitative understanding of why the system is doing what it is. We will also examine the process of convection-enhanced diffusion, which is used in some open spatially-extended chemical systems to increase the size of the spatial patterns occurring in the system.

In this paper we compare two methods for estimating the size of personal networks using a nationally representative sample of the United States. Both methods rely on the ability of respondents to estimate the number of people they know in specific subpopulations of the U.S. (e.g., diabetics, Native Americans) and people in particular relation categories (e.g., immediate family, coworkers). The results demonstrate a remarkable similarity between the average network size generated by both methods (approximately 291). Similar results were obtained with a separate national sample. An attempt to corroborate our estimates by replication among a population we suspect has large networks (clergy), yielded a larger average network size. Extensive investigation into the existence of response effects showed some preference for using certain numbers when making estimates, but nothing that would significantly affect the estimate of network size beyond about 6 percent. We conclude that both methods for estimating personal network size yield valid and reliable proxies for actual network size, but questions about accuracy remain.

We seek to explain on what basis people choose to tell stigmatizing information about themselves to others. In particular, are there any rules governing how such decisions are made? We asked 70 HIV-positive individuals whether they knew various items of knowledge about their network members, and vice versa. These items range from things which might be known easily (e.g., marital status), things which are more difficult to know (e.g., blood type), to potentially stigmatizing information such as criminal record and HIV status. The information that one person knows about another may predict whether the latter's HIV status is also known. We examine this question using a combination of ethnography and decision trees. Even an apparently simple decision - whether or not to tell someone that you are seropositive - turns out to be complicated; yet the complexity can be extracted from open-ended interviews.

I agree with \"Taming NY's Medicaid beast\" [Editorial, May 8] that New York needs to stop Medicaid abuse. The elderly shouldn't be able to qualify as \"poor\" after simply transferring assets to family members. Well-off spouses should pay a share of nursing care. I found it ironic that, in the same issue, Lynn Brenner, in her Family Finance column, gave an elderly couple with a $250,000 apartment and a $40,000-a-year income \"Medicaid planning\" advice on how to protect their assets and qualify for Medicaid.