6,903 research outputs found

    Adaptively time stepping the stochastic Landau-Lifshitz-Gilbert equation at nonzero temperature: implementation and validation in MuMax3

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    Thermal fluctuations play an increasingly important role in micromagnetic research relevant for various biomedical and other technological applications. Until now, it was deemed necessary to use a time stepping algorithm with a fixed time step in order to perform micromagnetic simulations at nonzero temperatures. However, Berkov and Gorn have shown that the drift term which generally appears when solving stochastic differential equations can only influence the length of the magnetization. This quantity is however fixed in the case of the stochastic Landau-Lifshitz-Gilbert equation. In this paper, we exploit this fact to straightforwardly extend existing high order solvers with an adaptive time stepping algorithm. We implemented the presented methods in the freely available GPU-accelerated micromagnetic software package MuMax3 and used it to extensively validate the presented methods. Next to the advantage of having control over the error tolerance, we report a twenty fold speedup without a loss of accuracy, when using the presented methods as compared to the hereto best practice of using Heun's solver with a small fixed time step.Comment: 9 pages, 9 figure

    Postural adjustments in catching: on the interplay between segment stabilization and equilibrium control

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    The purpose of this study was to investigate postural adjustments in one-handed ball catching. Specifically, the functional role of anticipatory postural adjustments (APA) during the initial arm raising and subsequent postural adjustments (SPA) for equilibrium control and ball-hand impact were scrutinized. Full-body kinematics and kinetics allowed an analysis of the mechanical consequences of raising up the arm and preparing for ball-hand impact. APA for catching were suggested to be for segment stabilization. SPA had a functional role for equilibrium control by an inverted pendulum mechanism but were also involved in preparing for the impact of the ball on the hand, which was illustrated by an increased postural response at the end of the movement. These results were compared with raising up the arm in a well-studied reaction-time task, for which an additional counter rotation equilibrium mechanism was observed. Together, our findings demonstrate that postural adjustments should be investigated in relation to their specific functional task constraints, rather than generalizing the functional role of these postural adjustments over different tasks

    Intraguild predation between lady beetles and lacewings: outcomes and consequences vary with focal prey and arena of interaction

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    Citation: Noppe, Christophe, J. P. Michaud, and Patrick De Clercq. 2012. “Intraguild Predation Between Lady Beetles and Lacewings: Outcomes and Consequences Vary With Focal Prey and Arena of Interaction.” Annals of the Entomological Society of America 105 (4): 562–71. https://doi.org/10.1603/AN11165.We examined reciprocal intraguild predation (IGP) and cannibalism among various combinations of Coleomegilla maculata DeGeer and Chrysoperla carnea Stephens larvae as they developed feeding on greenbugs, Schizaphis graminum Rondani, on sorghum plants in microcosms. Pairs of C. maculata larvae suppressed aphids better than pairs of C. carnea larvae or heterospecific larval pairs and yielded the highest rate of plant survival. IGP by C. carnea larvae occurred mostly in the first instar, whereas C. maculata larvae were more aggressive in later instars. Although C. carnea was the superior intraguild predator, winning 62.7% of contests in microcosms, this value increased to 88.9% when the experiment was repeated in petri dishes without plant material, regardless of whether greenbugs or eggs of Ephestia kuehniella Zeller were offered as focal prey. Provision in petri dishes of the sessile, higher quality prey (Ephestia) as opposed to greenbugs, improved the survival of solitary larvae and delayed cannibalism and IGP until later developmental stages in both species. Larvae of C. maculata that cannibalized took longer to develop and weighed less at pupation, independent of the arena or prey offered. Although larvae of C. carnea did not pay a cost for cannibalism or IGP in microcosms, there were some negative developmental effects of IGP in petri dishes, particularly on the Ephestia diet. These results illustrate how the plant, as a substrate, can mediate the strength of IGP interactions and how the relative suitability of the focal prey can influence both the timing and consequences of cannibalism and IGP

    The internationalization of small and medium-sized firms: the role of organizational learning effort and entrepreneurial orientation

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    This paper contributes to the existing research by integrating the notions of organizational learning and entrepreneurial orientation into the body of international entrepreneurship. Our primary framework combines learning theory and the new venture theory of internationalization to study the extent to which small and medium-sized companies engage in international activities. In order to focus on firms likely to engage in significant cross-border activity, we used a survey instrument to collect data from small and medium-sized firms located in Belgium. We found that the firms' international learning effort and entrepreneurial orientation are positively associated with internationalization intent whereas domestic learning effort is negatively related with internationalization intent. Overall, our results suggest (1) that intensive knowledge renewal and exploitation regarding foreign markets and the internationalization process itself may increase internationalization by affecting the perceptions of opportunities offered by further international expansion, and (2) that firms with an entrepreneurial mindset may be more likely to develop a long-term, substantial presence in the international arena, compared to firms that are more reactive or conservative. However, our results also suggest that firms that invest in domestic learning activities, as opposed to international learning activities, may be less likely to internationalize further

    Selective inhibitory effects of (S)-9-(3-hydroxy-2-phosphonyl-methoxypropyl)adenine and 1-(2'-deoxy-

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    From a selection of 25 antiviral compounds with specific anti-herpes activity or broad-spectrum antiviral properties, two compounds, namely (S)-9-(3-hydroxy-2-phosphonyl-methoxypropyl)adenine and 1-(2'-deoxy-2'-fluoro-beta-D-arabinofuranosyl)-5-iodouracil, appeared particularly effective in inhibiting the cytopathogenicity of seal herpesvirus (phocid herpesvirus 1)

    Eddy-induced cross currents in the Westerschelde estuary: numerical simulation, physical driving mechanisms and navigation assistance

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    The Westerschelde estuary is located in The Netherlands and is a major shipping route connecting the North Sea to the Port of Antwerp (Belgium). Cross currents up to three knots occur at high water during extreme spring tides and are increasingly hampering navigation in the Westerschelde near Hansweert resulting in one major incident leaving a container vessel stranded on a nearby sand bank.This study aimed at the simulation, prediction and assessment of a large eddy (stretching over the complete navigation channel) which produces these cross currents. A numerical model was set up and a detailed calibration of the hydrodynamic model was executed. A good agreement was obtained between model and measured data on the location of the eddy and the strength of the cross currents. Flow fields produced by the numerical model subsequently have been implemented in a nautical simulator in which pilots are trained on sailing in these exceptional conditions.Currently, a warning is sent out to Traffic Control whenever at least one of two parameters is being foreseen to pass a critical value according to forecasting models (high water level and water level gradient). This system has been proven to yield false negatives in some cases. The simulation results and analysis have clarified the conditions in which the eddy grows sufficiently (2 km across) to cause cross currents in the navigation channel. A new criterion for sending out a navigation warning is proposed. It shows a better correlation with the occurrence of cross currents, hence pilots will have a higher probability to be warned in case of cross currents.</p
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