Competition for Open-Access Resources: A Class Exercise that Demonstrates the Tragedy of the Commons

Open-access resources, such as fisheries, often suffer from overexploitation due to competition among individuals. To help students appreciate this phenomenon, we developed a laboratory exercise that uses a computer model of a commercial fishery to illustrate the inevitability of overexploiting open-access resources. Our model contained two identical populations that were fished simultaneously: one on an individual, competitive basis and the other on a collective, cooperative basis. Both populations were governed by identical relationships for recruitment and catch-per-effort, and had constant growth and natural mortality rates. Competition within the individually-run fishery invariably led to population collapse whereas the cooperative group usually maintained sustained yields. This exercise demonstrated that optimal resource use was impossible in a purely competitive fishery and helped students understand fish population biology and commercial fishing strategies. The exercise can show how changes in regulations or population parameters influence yields from a fishery. It can be adapted for use in workshops and other professional settings, even for participants with little background in fisheries.This work was supported in part by the Ohio State University, Department of Zoology, and by the University of Wisconsin Sea Grant Institute under grants from the National Sea Grant College Program, National Oceanic and Atmospheric Administration, U.S. Department of Commerce, and from the State of Wisconsin. Federal grant NA84AA-D-00065, project R/GB-24

Multisensory Integration Produces an Initial Response Enhancement

The brain has evolved the ability to integrate information across the senses in order to improve the detection and disambiguation of biologically significant events. This multisensory synthesis of information leads to faster (and more accurate) behavioral responses, yet the underlying neural mechanisms by which these responses are speeded are as yet unclear. The aim of these experiments was to evaluate the temporal properties of multisensory enhancement in the physiological responses of neurons in the superior colliculus (SC). Of specific interest was the temporal evolution of their responses to individual modality-specific stimuli as well as to cross-modal combinations of these stimuli. The results demonstrate that cross-modal stimuli typically elicit faster, more robust, and more reliable physiological responses than do their modality-specific component stimuli. Response measures sensitive to the time domain showed that these multisensory responses were enhanced from their very onset, and that the acceleration of the enhancement was greatest within the first 40ms (or 50% of the response). The latter half of the multisensory response was typically only as robust and informative as predicted by a linear combination of the unisensory component responses. These results may reveal some of the key physiological changes underlying many of the SC-mediated behavioral benefits of multisensory integration

Temporal Profiles of Response Enhancement in Multisensory Integration

Animals have evolved multiple senses that transduce different forms of energy as a way of increasing their sensitivity to environmental events. Each sense provides a unique and independent perspective on the world, and very often a single event stimulates several of them. In order to make best use of the available information, the brain has also evolved the capacity to integrate information across the senses (“multisensory integration”). This facilitates the detection, localization, and identification of a given event, and has obvious survival value for the individual and the species. Multisensory responses in the superior colliculus (SC) evidence shorter latencies and are more robust at their onset. This is the phenomenon of initial response enhancement in multisensory integration, which is believed to represent a real time fusion of information across the senses. The present paper reviews two recent reports describing how the timing and robustness of sensory responses change as a consequence of multisensory integration in the model system of the SC

Computation of p-Adic Heights and Log Convergence

This paper is about computational and theoretical questions regarding p-adic height pairings on elliptic curves over a global field K. The main stumbling block to computing them efficiently is in calculating, for each of the completions Kv at the places v of K dividing p, a single quantity: the value of the p-adic modular form E2 associated to the elliptic curve. Thanks to the work of Dwork, Katz, Kedlaya, Lauder and Monsky-Washnitzer we offer an efficient algorithm for computing these quantities, i.e., for computing the value of E2 of an elliptic curve. We also discuss the p-adic convergence rate of canonical expansions of the p-adic modular form E2 on the Hasse domain. In particular, we introduce a new notion of log convergence and prove that E2 is log convergent.Mathematic

Non-Stationarity in Multisensory Neurons in the Superior Colliculus

The superior colliculus (SC) integrates information from multiple sensory modalities to facilitate the detection and localization of salient events. The efficacy of “multisensory integration” is traditionally measured by comparing the magnitude of the response elicited by a cross-modal stimulus to the responses elicited by its modality-specific component stimuli, and because there is an element of randomness in the system, these calculations are made using response values averaged over multiple stimulus presentations in an experiment. Recent evidence suggests that multisensory integration in the SC is highly plastic and these neurons adapt to specific anomalous stimulus configurations. This raises the question whether such adaptation occurs during an experiment with traditional stimulus configurations; that is, whether the state of the neuron and its integrative principles are the same at the beginning and end of the experiment, or whether they are altered as a consequence of exposure to the testing stimuli even when they are pseudo-randomly interleaved. We find that unisensory and multisensory responses do change during an experiment, and that these changes are predictable. Responses that are initially weak tend to potentiate, responses that are initially strong tend to habituate, and the efficacy of multisensory integration waxes or wanes accordingly during the experiment as predicted by the “principle of inverse effectiveness.” These changes are presumed to reflect two competing mechanisms in the SC: potentiation reflects increases in the expectation that a stimulus will occur at a given location relative to others, and habituation reflects decreases in stimulus novelty. These findings indicate plasticity in multisensory integration that allows animals to adapt to rapidly changing environmental events while suggesting important caveats in the interpretation of experimental data: the neuron studied at the beginning of an experiment is not the same at the end of it

The potential for decentralized community industries.

Massachusetts Institute of Technology. Dept. of Urban Studies and Planning. Thesis. 1974. Ph.D.Vita.Bibliography: leaves 264-282.Ph.D

The receptor protein tyrosine phosphatase PTPRB negatively regulates FGF2-dependent branching morphogenesis

PTPRB is a transmembrane protein tyrosine phosphatase known to regulate blood vessel remodelling and angiogenesis. Here we demonstrate that PTPRB negatively regulates branching morphogenesis in the mammary epithelium. We show that Ptprb is highly expressed in adult mammary stem cells and also, although at lower levels, in estrogen receptor positive luminal cells. During mammary development Ptprb expression is down-regulated during puberty, a period of extensive of ductal outgrowth and branching. In vivo shRNA knockdown of Ptprb in the cleared mammary fat pad transplant assay resulted in smaller epithelial outgrowths with an increased branching density and also increased branching in an in vitro organoid assay. Organoid branching was dependent on stimulation by FGF2, and Ptprb knockdown in mammary epithelial cells resulted in a higher level of FGFR activation and ERK1/2 phosphorylation, both at baseline and following FGF2 stimulation. Therefore, PTPRB regulates branching morphogenesis in the mammary epithelium by modulating the response of the FGFR signalling pathway to FGF stimulation. Considering the importance of branching morphogenesis in multiple taxa, our findings have general importance outside mammary developmental biology

Refugee Repatriation During Conflict A New Conventional Wisdom.

Draft of a paper presented at a conference on "Refugee Repatriation During Conflict: A New Conventional Wisdom." Addis Ababa, Ethiopia. Disaster Studies (General Aspects)/Repatriation. (80.2C)The digital Cuny Archive was made available in part through funding assistance from USAID.The Center for the Study of Societies in Crisi