University of Victoria

About: University of Victoria is a education organization based out in Victoria, British Columbia, Canada. It is known for research contribution in the topics: Population & Galaxy. The organization has 14994 authors who have published 41051 publications receiving 1447972 citations. The organization is also known as: Victoria College.

On the need to incorporate sensitivity to CO2 transfer conductance into the Farquhar–von Caemmerer–Berry leaf photosynthesis model

Abstract: Virtually all current estimates of the maximum carboxylation rate ( V cmax ) of ribulose-1,5-bisphosphate carboxylase/ oxygenase (Rubisco) and the maximum electron transport rate ( J max ) for C 3 species implicitly assume an infinite CO 2 transfer conductance ( g i ). And yet, most measurements in perennial plant species or in ageing or stressed leaves show that g i imposes a significant limitation on photosynthesis. Herein, we demonstrate that many current parameterizations of the photosynthesis model of Farquhar, von Caemmerer & Berry ( Planta 149, 78‐90, 1980) based on the leaf intercellular CO 2 concentration ( C i ) are incorrect for leaves where g i limits photosynthesis. We show how conventional A‐C i curve (net CO 2 assimilation rate of a leaf ‐ A n ‐ as a function of C i ) fitting methods which rely on a rectangular hyperbola model under the assumption of infinite g i can significantly underestimate V cmax for such leaves. Alternative parameterizations of the conventional method based on a single, apparent Michaelis‐Menten constant for CO 2 evaluated at C i [ K m (CO 2 ) i ] used for all C 3 plants are also not acceptable since the relationship between V cmax and g i is not conserved among species. We present an alternative A‐C i curve fitting method that accounts for g i through a non-rectangular hyperbola version of the model of Farquhar et al . (1980). Simulated and real examples are used to demonstrate how this new approach eliminates the errors of the conventional A‐C i curve fitting method and provides V cmax estimates that are virtually insensitive to g i . Finally, we show how the new A‐C i curve fitting method can be used to estimate the value of the kinetic constants of Rubisco in vivo is presented

Did Cooling Oceans Trigger Ordovician Biodiversification? Evidence from Conodont Thermometry

Abstract: The Ordovician Period, long considered a supergreenhouse state, saw one of the greatest radiations of life in Earth9s history. Previous temperature estimates of up to ∼70°C have spawned controversial speculation that the oxygen isotopic composition of seawater must have evolved over geological time. We present a very different global climate record determined by ion microprobe oxygen isotope analyses of Early Ordovician–Silurian conodonts. This record shows a steady cooling trend through the Early Ordovician reaching modern equatorial temperatures that were sustained throughout the Middle and Late Ordovician. This favorable climate regime implies not only that the oxygen isotopic composition of Ordovician seawater was similar to that of today, but also that climate played an overarching role in promoting the unprecedented increases in biodiversity that characterized this period.

The interactions of intensity, frequency and duration of exercise training in altering cardiorespiratory fitness

Abstract: This review has grouped many studies on different populations with different protocols to show the interactive effects of intensity, frequency and duration of training as well as the effects of initial fitness levels and programme length on cardiorespiratory fitness as reflected by aerobic power (VO2max). Within each level of exercise duration, frequency, programme length or initial fitness level, the greatest improvements in aerobic power occur when the greatest challenge to aerobic power occurs i.e., when intensity is from 90 to 100% of VO2max. The pattern of improvement where different intensities are compared with different durations suggests that when exercise exceeds 35 minutes, a lower intensity of training results in the same effect as those achieved at higher intensities for shorter durations. Frequencies of as low as 2 per week can result in improvements in less fit subjects but when aerobic power exceeds 50 ml/kg/min, exercise frequency of at least 3 times per week is required. As the levels of initial fitness improve, the changes in aerobic power decreases regardless of the intensity, frequency or duration of exercise. Although these pooled data suggest that maximal gains in aerobic power are elicited with intensities between 90 to 100% VO2max, 4 times per week with exercise durations of 35 to 45 minutes, it is important to note that lower intensities still produce effective changes and reduce the risks of injury in non-athletic groups.

Earth system models of intermediate complexity: closing the gap in the spectrum of climate system models

Abstract: We propose a new perspective on the hierarchy of climate models which goes beyond the ''classical'' climate modeling pyramid that is restricted mainly to atmospheric processes, Most notably, we introduce a new indicator, called ''integration'', which characterizes the number of interacting components of the climate system being explicitly described in a model. The location of several model types, from conceptual to comprehensive, is presented in a new spectrum of climate system models. In particular. the location of the Earth system Models of Intermediate Complexity (EMICs) in this spectrum is discussed in some detail and examples are given, which indicate that there is currently a broad range of EMICs in use. In some EMICs, the number of processes and/or the detail of description is reduced for the sake of simulating the feedbacks between as many components of the climate system as feasible. Others, with a lesser degree of interaction, or ''integration'', are used for long-term ensemble simulations to study specific aspects of climate variability. EMICs appear to be closer to comprehensive coupled models of atmospheric and oceanic circulation (CGCMs) than to ''conceptual'' or ''box'' models. We advocate that EMICs be considered as complementary to CGCMs and conceptual models, because we believe that there is an advantage of having a spectrum of climate system models which are designed to tackle specific aspects of climate and which together provide the proper tool for climate system modeling.

The feedback correct-related positivity: sensitivity of the event-related brain potential to unexpected positive feedback.

Abstract: The N200 and the feedback error-related negativity (fERN) are two components of the event-related brain potential (ERP) that share similar scalp distributions, time courses, morphologies, and functional dependencies, which raises the question as to whether they are actually the same phenomenon. To investigate this issue, we recorded the ERP from participants engaged in two tasks that independently elicited the N200 and fERN. Our results indicate that they are, in fact, the same ERP component and further suggest that positive feedback elicits a positive-going deflection in the time range of the fERN. Taken together, these results indicate that negative feedback elicits a common N200 and that modulation of fERN amplitude results from the superposition on correct trials of a positive-going deflection that we term the feedback correct-related positivity.