Using computers to explore ecological issues: A simple limits-to-growth educational program

Educational-level software allows students to interactively conduct their own research on Earth's ecology by using a much-simplified version of the Forrester computer model on which the landmark 1972 limits-to-growth studies were based. Default values of all variables (including the Earth's population, food supply, natural resources, industrialization, and pollution), and simple difference equations relating them, are provided so that the program can be immediately run by novice users. Both variable values and equations can be easily altered to observe the consequences of users' assumptions or proposed policies.In keeping with its educational objectives, SPACESHIP EARTH has been placed in the public domain and an IBM PC-compatible version can be obtained without charge by sending a formatted diskette (3.5 or 5.25 inch) to the author.     

Approximating the equilibrium quantity traded and welfare in large markets

We consider the efficient outcome of a canonical economic market model involving buyers and sellers with independent and identically distributed random valuations and costs, respectively. When the number of buyers and sellers is large, we show that the joint distribution of the equilibrium quantity traded and welfare is asymptotically normal. Moreover, we bound the approximation rate. The proof proceeds by constructing, on a common probability space, a representation consisting of two independent empirical quantile processes, which in large markets can be approximated by independent Brownian bridges. The distribution of interest can then be approximated by that of a functional of a Gaussian process. This methodology applies to a variety of mechanism design problems.     

Use of satellite data in agricultural surveys

A major application of satellite remote sensing is the estimation of the acreage of agricultural crops. The potential for crop yield estimation using satellite remote sensing exists, but research in this area is still in its early stages. In this paper we survey the methodology for using remotely sensed data in agricultural surveys, based primarily on research conducted during the Large Area Crop Inventory Experiment (LACIE) and the follow-on program Agricultural Research and Inventory Surveys Through Aerospace Remote Sensing (AgRISTARS). The data obtained from multispectral scanner (MSS) and thematic mapper (TM) sensors onboard the Landsat series of satellites are described. Approaches for preprocessing, transferring, and modeling these data for understanding the relationship between their temporal behavior and crop growth cycles are discussed. Finally, techniques for crop identification and area and yield estimation are briefly described     

"Walking the Walk" of Public Service Motivation: Public Employees and Charitable Gifts of Time, Blood, and Money

Research generally indicates that public employees "talk thetalk," but do they also "walk the walk" of the public servicemotive (PSM)? Are public service employees more likely thanothers to engage in public service activities? The behavioralimplications of PSM are addressed by studying the involvementin charitable activities of public, nonprofit, and private workers.Using data from the 2002 General Social Survey, multivariatelogistic regression models are estimated to examine self-reportedgifts of time, blood, and money to charitable organizations.It is found that government employees are more likely to volunteerfor charity and to donate blood than for-profit employees are.Additionally, nonprofit workers are also more likely than theirfor-profit counterparts to volunteer. However, no differenceis found among public service and private employees in termsof individual philanthropy. These findings generally lend supportfor the hypothesis that PSM is more prominent in public servicethan in private organizations, especially as it pertains togovernment personnel.     

A program of research with Hispanic and African American families: three decades of intervention development and testing influenced by the changing cultural context of Miami

In this article we summarize work with poor, inner-city Hispanic and African American families conducted at the University of Miami Center for Family Studies. We elucidate ways in which this research program has paralleled the treatment development paradigm and has been responsive to changes in local demographics. Specific cultural issues pertaining to Hispanics and African Americans are discussed in light of treatment development and implementation. Future directions and challenges for working with poor, inner-city minority families are addressed.     

Parental Linguistic Input and Its Relation to Toddlers’ Visual Attention in Joint Object Play: A Comparison Between Children with Normal Hearing and Children With Hearing Loss

Parent–child interactions are multimodal, often involving coordinated exchanges of visual and auditory information between the two partners. The current work focuses on the effect of children's hearing loss on parent–child interactions when parents and their toddlers jointly played with a set of toy objects. We compared the linguistic input received by toddlers with hearing loss (HL) and their chronological age‐matched (CA) and hearing age‐matched (HA) normal‐hearing peers. Moreover, we used head‐mounted eye trackers to examine how different parental linguistic input affected children's visual attention on objects when parents either led or followed children's attention during joint object play. Overall, parents of children with HL provided comparable amount of linguistic input as parents of the two normal‐hearing groups. However, the types of linguistic input produced by parents of children with HL were similar to the CA group in some ways and similar to the HA group in other ways. Interestingly, the effects of different types of linguistic input on extending the attention of children with HL qualitatively resembled the patterns seen in the CA group, even though the effects were less pronounced in the HL group. We discuss the implications of these results for our understanding of the reciprocal, dynamic, and multi‐factored nature of parent–child interactions.