IMF effect on sporadic-E layers at two northern polar cap sites: Part I ? Statistical study

International audienceIn this paper we investigate the relationship between polar cap sporadic-E layers and the direction of the interplanetary magnetic field (IMF) using a 2-year database from Longyearbyen (75.2 CGM Lat, Svalbard) and Thule (85.4 CGM Lat, Greenland). It is found that the MLT distributions of sporadic-E occurrence are different at the two stations, but both are related to the IMF orientation. This relationship, however, changes from the centre of the polar cap to its border. Layers are more frequent during positive By at both stations. This effect is particularly strong in the central polar cap at Thule, where a weak effect associated with Bz is also observed, with positive Bz correlating with a higher occurrence of Es. Close to the polar cap boundary, at Longyearbyen, the By effect is weaker than at Thule. On the other hand, Bz plays there an equally important role as By, with negative Bz correlating with the Es occurrence. Since Es layers can be created by electric fields at high latitudes, a possible explanation for the observations is that the layers are produced by the polar cap electric field controlled by the IMF. Using electric field estimates calculated by means of the statistical APL convection model from IMF observations, we find that the diurnal distributions of sporadic-E occurrence can generally be explained in terms of the electric field mechanism. However, other factors must be considered to explain why more layers occur during positive than during negative By and why the Bz dependence of layer occurrence in the central polar cap is different from that at the polar cap boundary

CMC is more than a measure of corticospinal tract integrity in acute stroke patients

In healthy subjects, motor cortex activity and electromyographic (EMG) signals from contracting contralateral muscle show coherence in the beta (15-30 Hz) range. Corticomuscular coherence (CMC) is considered a sign of functional coupling between muscle and brain. Based on prior studies, CMC is altered in stroke, but functional significance of this finding has remained unclear. Here, we examined CMC in acute stroke patients and correlated the results with clinical outcome measures and corticospinal tract (CST) integrity estimated with diffusion tensor imaging (DTI). During isometric contraction of the extensor carpi radialis muscle, EMG and magneto encephalographic oscillatory signals were recorded from 29 patients with paresis of the upper extremity due to ischemic stroke and 22 control subjects. CMC amplitudes and peak frequencies at 13-30 Hz were compared between the two groups. In the patients, the peak frequency in both the affected and the unaffected hemisphere was significantly (p < 0.01) lower and the strength of CMC was significantly (p < 0.05) weaker in the affected hemisphere compared to the control subjects. The strength of CMC in the patients correlated with the level of tactile sensitivity and clinical test results of hand function. In contrast, no correlation between measures of CST integrity and CMC was found. The results confirm the earlier findings that CMC is altered in acute stroke and demonstrate that CMC is bidirectional and not solely a measure of integrity of the efferent corticospinal tract.Peer reviewe

EISCAT and Cluster observations in the vicinity of the dynamical polar cap boundary

The dynamics of the polar cap boundary and auroral oval in the nightside ionosphere are studied during late expansion and recovery of a substorm from the region between Tromsø (66.6&amp;deg; cgmLat) and Longyearbyen (75.2&amp;deg; cgmLat) on 27 February 2004 by using the coordinated EISCAT incoherent scatter radar, MIRACLE magnetometer and Cluster satellite measurements. During the late substorm expansion/early recovery phase, the polar cap boundary (PCB) made zig-zag-type motion with amplitude of 2.5&amp;deg; cgmLat and period of about 30 min near magnetic midnight. We suggest that the poleward motions of the PCB were produced by bursts of enhanced reconnection at the near-Earth neutral line (NENL). The subsequent equatorward motions of the PCB would then represent the recovery of the merging line towards the equilibrium state (Cowley and Lockwood, 1992). The observed bursts of enhanced westward electrojet just equatorward of the polar cap boundary during poleward expansions were produced plausibly by particles accelerated in the vicinity of the neutral line and thus lend evidence to the Cowley-Lockwood paradigm. &lt;br&gt;&lt;br&gt; During the substorm recovery phase, the footpoints of the Cluster satellites at a geocentric distance of 4.4 &lt;I&gt;R&lt;sub&gt;E&lt;/sub&gt;&lt;/I&gt; mapped in the vicinity of EISCAT measurements. Cluster data indicate that outflow of H&lt;sup&gt;+&lt;/sup&gt; and O&lt;sup&gt;+&lt;/sup&gt; ions took place within the plasma sheet boundary layer (PSBL) as noted in some earlier studies as well. We show that in this case the PSBL corresponded to a region of enhanced electron temperature in the ionospheric F region. It is suggested that the ion outflow originates from the F region as a result of increased ambipolar diffusion. At higher altitudes, the ions could be further energized by waves, which at Cluster altitudes were observed as BBELF (broad band extra low frequency) fluctuations. &lt;br&gt;&lt;br&gt; The four-satellite configuration of Cluster revealed a sudden poleward expansion of the PSBL by 2&amp;deg; during ~5 min. The beginning of the poleward motion of the PCB was associated with an intensification of the downward FAC at the boundary. We suggest that the downward FAC sheet at the PCB is the high-altitude counterpart of the Earthward flowing FAC produced in the vicinity of the magnetotail neutral line by the Hall effect (Sonnerup, 1979) during a short-lived reconnection pulse

Guiding and reflecting light by boundary material

We study effects of finite height and surrounding material on photonic crystal slabs of one- and two-dimensional photonic crystals with a pseudo-spectral method and finite difference time domain simulation methods. The band gap is shown to be strongly modified by the boundary material. As an application we suggest reflection and guiding of light by patterning the material on top/below the slab.Comment: 12 pages, 7 figure

Автономизация вузов в Украине как драйвер перехода к образовательной модели медицинского предпринимательского университета

УНИВЕРСИТЕТ 3.0ПРЕДПРИНИМАТЕЛЬСКИЕ КОМПЕТЕНЦИИОБРАЗОВАНИЕ МЕДИЦИНСКОЕСТУДЕНТЫ МЕДИЦИНСКИХ УЧЕБНЫХ ЗАВЕДЕНИЙОБРАЗОВАТЕЛЬНЫЕ МОДЕЛИПРЕДПРИНИМАТЕЛЬСКИЕ УНИВЕРСИТЕТЫУКРАИН

On large plasmoid formation in a global magnetohydrodynamic simulation

Peer reviewe