First results of absolute measurements of solar flux at the Irkutsk Incoherent Scatter Radar (IISR)

The Irkutsk Incoherent Scatter Radar (IISR) allows us to carry out passive radio observations of the Sun and other powerful radio sources. We describe a method for absolute measurements of spectral flux density of solar radiation at IISR. The absolute measurements are meant to determine the flux density in physical units [W·m–2·Hz–1]. The IISR antenna is a horn with frequency beam steering, therefore radio sources can be observed at different frequencies. Also there is a polarization filter in the antenna aperture, which passes only single (horizontal) polarization. To acquire flux density absolute values, the IISR receiver is calibrated by the Cygnus-A radiation. Since the Sun’s position in the IISR antenna pattern is determined by a frequency differing from the Cygnus-A observation frequency, we perform an additional calibration of the frequency response in the 154–162 MHz operation frequency range, using the background sky noise. The solar disk size is comparable with the main beam width in the north—south direction, hence the need to take into account the shape of the brightness distribution in the operation frequency range. The average flux density of the quiet-Sun radiation was ~5 sfu (solar flux units, 10–22 W·m–2·Hz–1) at the 161 MHz frequency

Ultrasound detection of cerebral microembolism in carotid stenoses: progress and perspective (A review of the literature)

The review summarizes available information regarding the method of Transcranial doppler sonography (TCD) usage to record microembolism in patients with carotid artery stenosis, search for information was carried out in literature 1997–2020 (PUBMED, MEDLINE). History overview of TCD with embolodetection implementation is presented, as well as ways of its technical and methodological improvement. Evidence-based studies of the method clinical relevance in atherosclerotic carotid stenoses and their surgical treatment are outlined. Observation results of the intraoperative cerebral embolization during carotid endarterectomy and carotid artery stenting are presented along with comparison of TCD-embolodetection data, neuroimaging and clinical outcomes. Individual centres and multicenter study ACES data on prognostic value of registration of embolic signals in asymptomatic carotid stenosis, risk assessment of vascular events in diffe-rent groups of patients and in varying degrees of stenosis of the vessel lumen was analyzed. The role of embolodetection in predicting repeated cerebrovascular disorders in symptomatic carotid stenosis and its importance for monitoring antiplatelet therapy is set out (multicenter study CARESS). The evidence of the reliability of TCD embolodetection as tool for verificarion of at-risk patients with carotid stenosis who may benefit ftom surgical treatment is presented. Recent advances in ultrasound and other imaging techniques for assessing unstable plague are outlined along with prospects for the use of TCD monitoting for cerebrovascular disorders forecasting

Interferometric observation of Cygnus-А discrete radiosource scintillations at Irkutsk Incoherent Scatter radar

We propose a new method for analyzing data from the Irkutsk Incoherent Scatter Radar. The method allows us to accomplish interferometric observation of discrete cosmic radio source characteristics. In this study, we analyze ionospheric scintillations of the radio source Cygnus-A. Observations were made in 2013 during regular radar sessions within 5–15 days for different seasons; the effective time of observation was 15–30 minutes per day. For interferometric analysis, the properties of correlation (coherence) coefficient of two independent recording channels were used. The statistical analysis of data from the independent channels allows us to construct two-dimensional histograms of radio source brightness distribution with a period of 18 s and to determine parameters (the maximum position and the histogram width) representing position and angular size of the radio source for each histogram. It is shown that the change of statistical characteristics does not correlate with fluctuations in power (scintillations) of the signal induced by radio wave propagation through ionospheric irregularities