Nonlinear physics of the ionosphere and LOIS/LOFAR

The ionosphere is the only large-scale plasma laboratory without walls that we have direct access to. From results obtained in systematic, repeatable experiments in this natural laboratory, where we can vary the stimulus and observe its response in a controlled, repeatable manner, we can draw conclusions on similar physical processes occurring naturally in the Earth's plasma environment as well as in parts of the plasma universe that are not easily accessible to direct probing. Of particular interest is electromagnetic turbulence excited in the ionosphere by beams of particles (photons, electrons) and its manifestation in terms of secondary radiation (electrostatic and electromagnetic waves), structure formation (solitons, cavitons, alfveons, striations), and the associated exchange of energy, linear momentum, and angular momentum. We present a new diagnostic technique, based on vector radio allowing the utilization of EM angular momentum (vorticity), to study plasma turbulence remotely.Comment: Six pages, two figures. To appear in Plasma Physics and Controlled Fusio

Utilization of photon orbital angular momentum in the low-frequency radio domain

We show numerically that vector antenna arrays can generate radio beams which exhibit spin and orbital angular momentum characteristics similar to those of helical Laguerre-Gauss laser beams in paraxial optics. For low frequencies (< 1 GHz), digital techniques can be used to coherently measure the instantaneous, local field vectors and to manipulate them in software. This opens up for new types of experiments that go beyond those currently possible to perform in optics, for information-rich radio physics applications such as radio astronomy, and for novel wireless communication concepts.Comment: 4 pages, 5 figures. Changed title, identical to the paper published in PR

The contribution of lumbar sympathetic neurones activity to rat’s skin blood flow oscillations

Skin blood flow on the rat’s paws using laser Doppler flowmeter, electrical activity of the heart (ECG) and respiration were measured simultaneously. The signals were recorded for 20 minutes, both before and after denervation, at core temperature 37°C and 38.5°C, that was maintained constant during the recordings. Spinal nerve fibres, at the level L3–L4, were transected. Experiments were performed on 15 adult Wistar rats under general anaesthesia. The oscillations in the measured signals were analysed in the time-frequency domain using wavelet transform. On the frequency region from 0.7Hz to 5Hz two characteristic peaks were observed in the skin blood flow spectrum. They correspond to the main peaks in the spectra of the ECG (around 3.3Hz) and respiration (around 1.3Hz). Several additional peaks were observed in the low frequency region, from 0.01 to 0.7Hz, in all measured signals. In this frequency region the relative energy contribution of the blood flow oscillations decreased after denervation only in the denervated left hind paw. This difference was not statistically significant at 37°C (p=0.098, Kruskal-Wallis test) but became statistically significant at 38.5°C (p=0.017). Relative energy contribution of the low frequency region, from 0.01 to 0.7Hz, decreased 2.5-fold in the blood flow of the denervated paw. Within this region the relative energy contribution decreased significantly in two intervals, from 0.01 to 0.08Hz and from 0.08 to 0.2Hz (p=0.023). In the higher frequency region, from 0.7 to 5Hz, o statistically significant differences were obtained in any paws when compared before and after denervation at the same core temperature. We conclude that the activity of lumbar sympathetic neurones contributes to low frequency skin blood flow oscillations

Fluctuations and interactions between brain waves during deep and shallow anesthesia

Using gold plated electrodes, inserted into the rat's head above the dura of the left and right parietal cortex, we recorded EEG during deep and shallow anesthesia with either pentobarbital (PB) or ketamine-xylazine (KX). The fluctuations in time series were then analyzed using wavelet transforms and the spectral power was determined within 7 frequency intervals (slow wave 2, S2, 0.0067-0.0167 Hz; slow wave 1, S1, 0.02-0.19 Hz; delta, 0.2-3.9 Hz; theta, 4-7.9 Hz; alpha, 8-12.9 Hz; beta, 13-24.9 Hz and gamma, 25-34.9 Hz). In addition, the coupling strengths between individual oscillatory components during deep and shallow anesthesia were evaluated for both anesthetics. We show specific changes for both anesthetics indicating that during deep anesthesia PB reduces high and low frequency activity (0.2-35 Hz) and enhances coupling especially between delta, theta and alpha waves, while KX reduces low frequency activity (0.005 to 0.2 Hz) and enhances coupling between frequency waves alpha, beta and gamma. Our results, using two anesthetics known to block different ion channels, provide an insight into brain dynamics and could have wide implications in creating biomarkers for detecting various neurophysiological modifications, such as in Alzheimer and Parkinson's disease or Autism spectrum disorder, as well as in providing more realistic models of brain dynamics