1,720,977 research outputs found
Effects of temperature and Hydrostatic pressure on routine oxygen uptake of the bloater (Coregonus hoyi)
No full textWe present the first measurements of routine oxygen uptake (VO2) of the bloater (Coregonus hoyi), including the effects of temperature and hydrostatic pressure. For temperature experiments, ten 24 hour trials were conducted each at 10.5°C and 7°C, using flow-through respirometry. Average routine VO2 was approximately 130 mg O2/(kg*hr) at 10.5°C and approximately 120 mg O2/(kg*hr) at 7°C. These values did not differ significantly, probably because we used temperatures spanning the thermal range of bloater, within which this species may conserve routine metabolism. Derivations of daily food ration for bloater were calculated and compared with a previous bioenergetics model. For pressure experiments, the diel vertical migrations bloater undertake in the wild were simulated using a flow-through respirometer that could be pressurized. Ten 3-day trials were conducted, consisting of an overnight acclimation to the respirometer, a 12-hour pressure regime, and a day of recovery. The pressure regime involved a compression from 1 atm (atmospheric pressure) to 4 atm over 6 hours and a subsequent decompression of the same magnitude and duration. Increases in hydrostatic pressure elicited a rise in bloater VO2 and motor activity; conversely, the subsequent decrease in hydrostatic pressure caused a return of oxygen uptake and motor activity to baseline values at 1 atm. We hypothesize that pressure-induced compression of the gas bladder explain the changes in VO2, because increased swimming (causing increased VO2) is needed to maintain station when the swimbladder is compressed.Source type: Electronic(1
Hypoxia tolerance in fishes : cardiorespiratory performance and metabolism
No full textCardiac failure occurs in most vertebrates including humans following even short hypoxia exposure due to an inability to match cardiac energy demand to the limited energy supply. In contrast, hypoxia-tolerant ectothermic vertebrates show the remarkable ability to maintain cardiac energy balance and stable cardiac function during prolonged exposure to severe hypoxia (cardiac hypoxia tolerance, CHT). I investigated how CHT is achieved and its relationship to whole-animal hypoxia tolerance using measurements at multiple physiological levels in two study models: 1) tilapia, a hypoxia-tolerant teleost, and 2) a two-species comparison of elasmobranchs with different hypoxia tolerance.
I tested the hypothesis that CHT depends upon the depression of cardiac power output (PO) (i.e., cardiac energy demand) to a level lower than the cardiac maximum glycolytic potential (MGP). All species showed a hypoxic PO depression via bradycardia and my work generally supports this hypothesis. However, in tilapia, hypoxic PO depression is not necessarily required to maintain cardiac energy balance, contrary to previous suggestions, because of an exceptionally high MGP. Thus, in certain species, PO depression may primarily benefit CHT by minimizing fuel use and waste production.
I also tested the hypothesis that greater hypoxia tolerance is associated with enhanced hypoxic O₂ supply and consequently enhanced cardiovascular function (i.e., less PO depression and improved cardiac energy balance). My work on elasmobranchs supported this hypothesis and also suggested a role for strategic cardiac O₂ supply via O₂ sparing resulting from metabolic rate depression (MRD) in non-essential tissues. Finally, my work on elasmobranchs showed that critical oxygen tension (Pcrit) predicts hypoxic blood O₂ transport, supporting the use of Pcrit as an indicator of hypoxia tolerance.
Next, I tested the hypothesis that hypoxic PO depression is associated with the depression of whole-animal O₂ consumption rate below Pcrit. I found that this occurred in all species, suggesting that modulation of peripheral demand for blood flow (e.g., via MRD) may influence CHT.
Finally, my work on in vivo and in situ cardiac responses in tilapia provided little evidence for the hypothesis that hypoxic modulation of aerobic energy production pathways, including provision of aerobic fuels (specifically, fatty acids), contributes to CHT.Science, Faculty ofZoology, Department ofGraduat
Seawater carbonate chemistry and behaviour of coral reef fishes
No full textThe partial pressure of CO2 in the oceans has increased rapidly over the past century, driving ocean acidification and raising concern for the stability of marine ecosystems. Coral reef fishes are predicted to be especially susceptible to end-of-century ocean acidification on the basis of several high-profile papers that have reported profound behavioural and sensory impairments—for example, complete attraction to the chemical cues of predators under conditions of ocean acidification. Here, we comprehensively and transparently show that—in contrast to previous studies—end-of-century ocean acidification levels have negligible effects on important behaviours of coral reef fishes, such as the avoidance of chemical cues from predators, fish activity levels and behavioural lateralization (left–right turning preference). Using data simulations, we additionally show that the large effect sizes and small within-group variances that have been reported in several previous studies are highly improbable. Together, our findings indicate that the reported effects of ocean acidification on the behaviour of coral reef fishes are not reproducible, suggesting that behavioural perturbations will not be a major consequence for coral reef fishes in high CO2 oceans
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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