McGill University

About: McGill University is a education organization based out in Montreal, Quebec, Canada. It is known for research contribution in the topics: Population & Poison control. The organization has 72688 authors who have published 162565 publications receiving 6966523 citations. The organization is also known as: Royal institution of advanced learning & University of McGill College.

Fishes as integrators of benthic and pelagic food webs in lakes

Abstract: Studies of lake ecosystems generally focus on pelagic food chains and processes. Recently, there has been an emerging recognition of the importance of benthic production and processes to whole-lake ecosystems. To examine the extent to which zoobenthos contribute to higher trophic level production in lakes, we synthesized diet data from 470 fish populations (15 species) and stable isotope data from 90 fish populations (11 species), all of which are common inhabitants of north-temperate lakes. Across all species considered, zoobenthos averaged 50% of total prey consumption. Indirect consumption of zoobenthos (i.e., feeding on zoobenthos-supported fishes) contributed another 15%, for a total of 65% reliance on benthic secondary production. Stable isotopes provided estimates of mean zoobenthivory ranging from 43% to 59%. For most fish species, consumption of zoobenthos was highly variable among populations. The overwhelming concern of ecologists with pelagic food chains and processes contrasts sharply with our finding that benthic secondary production plays a central role in supporting higher trophic level production. This extensive zoobenthivory can subsidize fish populations, leading to apparent competition and otherwise altering trophic dynamics and ecosystem processes in the pelagic zone. We argue for a more integrated view of lake ecosystems that recognizes the duality of benthic and pelagic production pathways. Food web models that explicitly consider energy flow from pelagic and benthic sources will provide a more realistic energy flow template for understanding the regulation of lake ecosystem functioning.

AAPM protocol for 40–300 kV x-ray beam dosimetry in radiotherapy and radiobiology

Abstract: The American Association of Physicists in Medicine (AAPM) presents a new protocol, developed by the Radiation Therapy Committee Task Group 61, for reference dosimetry of low- and medium-energy x rays for radiotherapy and radiobiology (40 kV or = 100 kV (the "in-phantom" method). The in-phantom method is not recommended for tube potentials < 100 kV. Guidelines are provided to determine the dose at other points in water and the dose at the surface of other biological materials of interest. The protocol is based on an up-to-date data set of basic dosimetry parameters, which produce consistent dose values for the two methods recommended. Estimates of uncertainties on the final dose values are also presented.

In-Vitro of Measurement of Static Pressure Distribution in Synovial Joints—Part I: Tibial Surface of the Knee

Abstract: In this first part of a two-part paper, the results of measurement of static pressure distribution on the tibial surface of the knee are presented. Results with intact menisci have been obtained from 18 specimens. Eight of these specimens were the subject of further measurements following medial meniscectomy. The study has been carried out at various flexion angles of the knee with the joint subjected to a compressive force, with or without an initial passive relative displacement between the joint members. The results indicate that a significant fraction of the joint compressive load is transmitted through the menisci and that total meniscectomy causes a drastic alteration in the pressure distribution on the tibial surface. Clinical implications of these results, in terms of post-meniscectomy degenerative changes and mechanism of meniscal lesions, have been discussed.

How adaptive behavior is produced: a perceptual-motivational alternative to response reinforcements

Abstract: The sway that the response-reinforcement framework (Spencer, Thorndike, Hull, Skinner) has held on the behavioral sciences for nearly a hundred years is finally ending. The strength of this framework lay in providing concepts and methods for studying the effects of hedonic (reinforcing) stimuli on the repetition of specified responses acquired in instrumental training situations of various kinds. Its weakness lay in the invalidity of its central assumptions, stimulus-response association and response-reinforcement, which could not deal with motor-equivalence and flexibility (or “intelligence”) in behavior. To the four decades of incisive criticism on particular theoretical and empirical grounds, a more comprehensive challenge to the response-reinforcement framework is now added by the newer ideas about the nature of cognitive, motivational, and response-production processes that have emerged from the work of ethologists, neuroscientists, and cognitive psychologists. An alternative framework, incorporating the newer ideas, is clearly needed.The particular framework proposed here is based on the ideas of perceptual learning of stimulus-stimulus correlations and of a motivational (rather than reinforcing) role of hedonic (incentive) stimuli. According to it, an act is produced when its act-assembly is activated by a pexgo (perceptual representation) of a certain eliciting stimulus complex (ES). When certain eliciting stimuli are correlated with incentive stimuli, they acquire motivational properties that serve to strengthen the pexgos generated by those eliciting stimuli and thereby increase the probability of activation of the corresponding act-assemblies. Motivation thus influences response production, not by directly instigating “existing” responses, but by modulating the strength of pexgos of eliciting stimuli for the succession of acts that comprise a response. Therefore, a response is always constructed afresh on the basis of current perceptions; not even a stable and stereotyped response occurs as a mere activation of a preformed motor program. The topography of any response that emerges is determined by the nature of the motivational state and the momentary spatiotemporal distribution of eliciting stimuli of changing motivational valence.By suggesting that the animal learns the overlapping and nested correlations between the stimulus events that commonly occur in a given situation, and by separating what is learned from the processes of response production, the proposed perceptual-motivational framework seems capable of dealing with the problems of motor equivalence and flexibility in adaptive behavior. Some implications of this approach for further behavioral and brain research on such problems as behavior modification, learning by observation of models, analysis of causality, and search for neural substrates of learning and response production, are outlined.