5,689 research outputs found

    Phase of beta-frequency tACS over primary motor cortex modulates corticospinal excitability

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    The assessment of corticospinal excitability by means of transcranial magnetic stimulation-induced motor evoked potentials is an established diagnostic tool in neurophysiology and a widely used procedure in fundamental brain research. However, concern about low reliability of these measures has grown recently. One possible cause of high variability of MEPs under identical acquisition conditions could be the influence of oscillatory neuronal activity on corticospinal excitability. Based on research showing that transcranial alternating current stimulation can entrain neuronal oscillations we here test whether alpha or beta frequency tACS can influence corticospinal excitability in a phase-dependent manner. We applied tACS at individually calibrated alpha- and beta-band oscillation frequencies, or we applied sham tACS. Simultaneous single TMS pulses time locked to eight equidistant phases of the ongoing tACS signal evoked MEPs. To evaluate offline effects of stimulation frequency, MEP amplitudes were measured before and after tACS. To evaluate whether tACS influences MEP amplitude, we fitted one-cycle sinusoids to the average MEPs elicited at the different phase conditions of each tACS frequency. We found no frequency-specific offline effects of tACS. However, beta-frequency tACS modulation of MEPs was phase-dependent. Post hoc analyses suggested that this effect was specific to participants with low (<19 Hz) intrinsic beta frequency. In conclusion, by showing that beta tACS influences MEP amplitude in a phase-dependent manner, our results support a potential role attributed to neuronal oscillations in regulating corticospinal excitability. Moreover, our findings may be useful for the development of TMS protocols that improve the reliability of MEPs as a meaningful tool for research applications or for clinical monitoring and diagnosis. (C) 2018 Elsevier Ltd. All rights reserved

    Real non-degenerate two-step nilpotent Lie algebras of dimension eight

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    We classify the non-degenerate two-step nilpotent Lie algebras of dimension 8 over the field R of real numbers, using results of Galitski and Timashev over complex numbers. We write explicit structure constants for these real Lie algebras.Comment: 21 pages; comments are welcome

    An effective method to compute closure ordering for nilpotent orbits of θ\theta-representations

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    We develop an algorithm for computing the closure of a given nilpotent G0G_0-orbit in \g_1, where \g_1 and G0G_0 are coming from a Z\Z or a Z/mZ\Z/m\Z-grading \g= \bigoplus \g_i of a simple complex Lie algebra \g

    Superfluid vortex front at T -> 0: Decoupling from the reference frame

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    Steady-state turbulent motion is created in superfluid 3He-B at low temperatures in the form of a turbulent vortex front, which moves axially along a rotating cylindrical container of 3He-B and replaces vortex-free flow with vortex lines at constant density. We present the first measurements on the thermal signal from dissipation as a function of time, recorded at 0.2 Tc during the front motion, which is monitored using NMR techniques. Both the measurements and the numerical calculations of the vortex dynamics show that at low temperatures the density of the propagating vortices falls well below the equilibrium value, i.e. the superfluid rotates at a smaller angular velocity than the container. This is the first evidence for the decoupling of the superfluid from the container reference frame in the zero-temperature limit.Comment: 4 pages, 4 figure

    Spontaneous Charging and Crystallization of Water Droplets in Oil

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    We study the spontaneous charging and the crystallization of spherical micron-sized water-droplets dispersed in oil by numerically solving, within a Poisson-Boltzmann theory in the geometry of a spherical cell, for the density profiles of the cations and anions in the system. We take into account screening, ionic Born self-energy differences between oil and water, and partitioning of ions over the two media. We find that the surface charge density of the droplet as induced by the ion partitioning is significantly affected by the droplet curvature and by the finite density of the droplets. We also find that the salt concentration and the dielectric constant regime in which crystallization of the water droplets is predicted is enhanced substantially compared to results based on the planar oil-water interface, thereby improving quantitative agreement with recent experiments.Comment: 10 pages, 7 figures, submitted for publicatio

    Analyse du risque posé en santé animale par la présence de l'hydroxyméthylfurfural dans les sirops de nourrissement des abeilles domestiques

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    This paper discusses an incident that occurred in Belgium during winter 2009-2010, after which many honey bee colonies have been lost. Later analyses showed that these colonies had been fed during the winter with a inverted sugar syrup from sugar beet which had a high concentration of hydroxymethylfurfural (HMF). HMF concentrations ranged from 18.8 ppm to 365.6 ppm. Data from the scientific literature are quite limited, but several authors confirm the harmful effect of HMF on honey bee health. Other elements, however, may have played a role in this apparent mortality such as crystallization of syrups, resulting in unavailability of sugar for the honey bees, and thus the death of them from starvation. Pending the acquisition of new scientific knowledge on the subject, it is recommended to follow good beekeeping practices detailed in this article to minimize the formation of HMF in syrups for honey bee feeding. In addition, a draft action limit corresponding to a maximal concentration of 40 ppm of HMF is proposed in order to control the risk at the producer and distributor of syrups for honey bee feeding level
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