The peculiarities of cross-correlation between two secondary precursors - radon and magnetic field variations, induced by stress transfer changes

A model of precursor manifestation mechanisms, stimulated by tectonic activity and some peculiarities of observer strategy, whose main task is the effective measurement of precursors in the spatial area of their occurrence on the Earth's daylight, are considered. In particular, the applicability of Dobrovolsky's approximation is analyzed, when an unperturbed medium (characterized by the simple shear state) and the area of tectonic activity (local inhomogeneity caused by the change only of shear modulus) are linearly elastic, and perturbation, in particular, surface displacement is calculated as a difference of the solutions of two independent static problems of the theory of elasticity with the same boundary condition on the surface. Within the framework of this approximation a formula for the spatial distribution (of first component) of magnetic field variations caused by piezomagnetic effect in the case of perturbed regular medium, which is in simple shear state is derived. Cogent arguments in favor of linear dependence between the radon spatial distribution and conditional deformation are obtained. Changes in magnetic field strength and radon concentrations were measured along a tectonomagnetic profile of the total length of 11 km in the surroundings of the "Academician Vernadsky" Station on the Antarctic Peninsula (W 64{\deg}16', S 65{\deg}15'). Results showed a positive correlation between the annual surface radon concentration and annual changes of magnetic field relative to a base point, and also the good coincidence with theoretical calculation.Comment: 27 pages, 11 figures, 3 tables (a substantially revised and extended edition; v3 -- some analysis of recent publications added

Clinical application of a new sars-cov-2 antigen detection kit (Colloidal gold) in the detection of covid-19

The precise diagnosis of COVID-19 is of outmost importance in order to effectively treat patients and prevent SARS-CoV-2 transmission. Herein, we evaluated the sensitivity and specificity of the COVID-19 Antigen Detection Kit (Colloidal Gold—CG) compared with PCR in nasopharyngeal and nasal samples. A total of 114 positive and 244 negative nasopharyngeal specimens confirmed by PCR were used in this comparative study. When the PCR positive Cycle Threshold (Ct) value was ≤25, CG sensitivity was 100%. When the PCR positive Ct value was ≤33, CG sensitivity was 99%. When the PCR positive Ct value was ≤40, CG sensitivity was 89.47%. Regarding nasal swabs, a total of 109 positive and 250 negative specimens confirmed by PCR were used. When the PCR positive Ct value was ≤25, CG sensitivity was 100%. When the PCR positive Ct value was ≤33, CG sensitivity was 96.12%. When the PCR positive Ct value was ≤37, CG sensitivity was 91.74%. Specificity was above 99% regardless of the Ct value of PCR positivity for both nasopharyngeal and nasal specimens. Overall, the CG showed high sensitivity and specificity when the PCR Ct value was less than 33. Therefore, CG can be used for screening early in the disease course. Confirmatory PCR is essential when a false negative result is suspected. © 2021 by the authors. Licensee MDPI, Basel, Switzerland

The multichord stellar occultation on 2019 October 22 by the trans-Neptunian object (84922) 2003 VS

Context. Stellar occultations have become one of the best techniques to gather information about the physical properties of trans-Neptunian objects (TNOs), which are critical objects for understanding the origin and evolution of our Solar System. Aims. The purpose of this work is to determine, with better accuracy, the physical characteristics of the TNO (84922) 2003 VS2 through the analysis of the multichord stellar occultation on 2019 October 22 and photometric data collected afterward. Methods. We predicted, observed, and analyzed the multichord stellar occultation of the Second Gaia Data Release (Gaia DR2) source 3449076721168026624 (mυ = 14.1 mag) by the plutino object 2003 VS2 on 2019 October 22. We performed aperture photometry on the images collected and derived the times when the star disappeared and reappeared from the observing sites that reported a positive detection. We fit the extremities of such positive chords to an ellipse using a Monte Carlo method. We also carried out photometric observations to derive the rotational light curve amplitude and rotational phase of 2003 VS2 during the stellar occultation. Combining the results and assuming a triaxial shape, we derived the 3D shape of 2003 VS2. Results. Out of the 39 observatories involved in the observational campaign, 12 sites, located in Bulgaria (one), Romania (ten), and Serbia (one), reported a positive detection; this makes it one of the best observed stellar occultations by a TNO so far. Considering the rotational phase of 2003 VS2 during the stellar occultation and the rotational light curve amplitude derived (Am = 0.264 ± 0.017 mag), we obtained a mean area-equivalent diameter of $\left( {{D_{{{\rm{A}}_{{\rm{eq}}}}}}} \right)$ = 545 ± 13 km and a geometric albedo of 0.134 ± 0.010. By combining the rotational light curve information with the stellar occultation results, we derived the best triaxial shape for 2003 VS2, which has semiaxes a = 339 ± 5 km, b = 235 ± 6 km, and c = 226 ± 8 km. The derived aspect angle of 2003 VS2 is θ = 59° ± 2° or its supplementary θ = 121° ± 2°, depending on the north-pole position of the TNO. The spherical-volume equivalent diameter is $\left( {{D_{{{\rm{V}}_{{\rm{eq}}}}}}} \right)$ = 524 ± 7 km. If we consider large albedo patches on its surface, the semi-major axis of the ellipsoid could be ~ 10 km smaller. These results are compatible with the previous ones determined from the single-chord 2013 and four-chord 2014 stellar occultations and with the effective diameter and albedo derived from Herschel and Spitzer data. They provide evidence that 2003 VS2’s 3D shape is not compatible with a homogeneous triaxial body in hydrostatic equilibrium, but it might be a differentiated body and/or might be sustaining some stress. No secondary features related to rings or material orbiting around 2003 VS2 were detected