Natural hazards and geomagnetic disturbances can generate a combination of atmospheric and ionospheric waves of different scales. The carrier phase of signals of global navigation satellite system ...(GNSS) can provide the highest efficiency to detect and study the weak ionospheric disturbances in contrast to total electron content (TEC) and TEC-based indices. We consider the border between the informative part of the carrier phase spectrum and the uninformative noises—the deviation frequency—as the promising means to improve the GNSS-based disturbance detection algorithms. The behavior of the deviation frequency of the carrier phase spectra was studied under quiet and disturbed geomagnetic conditions. The results showed that the deviation frequency value increases under magnetic storms. This effect was revealed for all GNSS constellations and signals regardless the GNSS type, receiver type/make and data rate (50 or 100 Hz). For the 100 Hz data, the most probable values of the deviation frequency grouped within ~28–40 Hz under quiet condition and shifted to ~37–48 Hz during the weak geomagnetic storms. Additionally, the lower values of deviation frequency of ~18–25 Hz almost disappear from the distribution of the deviation frequencies as it becomes narrower during geomagnetic storms. Considering that the small-scale irregularities shift the deviation frequencies, we can use this indicator as a “red alert” for weakest small-scale irregularities when the deviation frequency reaches ~35–50 Hz.
The term deviation frequency (fd) denotes the boundary between the variable part of the amplitude and phase scintillation spectrum and the part of uninformative noises. We suggested the concept of ...the “characteristic deviation frequency” during the observation period. The characteristic deviation frequency is defined as the most probable value of the deviation frequency under current local conditions. Our case study involved GPS, GLONASS, Galileo and SBAS data under quiet and weakly disturbed geomagnetic conditions (geomagnetic storm on 16 April 2021, Kpmax = 5, SYM-Hmin = −57 nT) at the mid-latitude GNSS station. Our results demonstrated that the deviation frequency for all signal components of GPS, GLONASS and Galileo varies within 15–22 Hz. The characteristic deviation frequency was 20 Hz for the mentioned GNSS signals. The SBAS differs from other systems: deviation frequency varies within 13–20 Hz. The characteristic deviation frequency is lower and equal to 18 Hz. We suggest the characteristic deviation frequency to determine the optimal sampling rate of the GNSS carrier phase data for the ionospheric studies. In turn, the deviation frequency can be considered as a promising index to estimate the boundary of non-variability of the ionosphere.
The study is focused on the analysis of total electron content (TEC)
variations during six geomagnetic storms of different intensity: from
Dstmin=-46 nT to Dstmin=-223 nT. The values of TEC ...deviations from its 27-day median value
(δTEC) were calculated during the periods of the storms along three
meridians: American, Euro-African and Asian-Australian. The following results
were obtained. For the majority of the storms almost simultaneous occurrence
of δTEC maximums was observed along all three meridians at the
beginning of the storm. The transition from a weak storm to a superstorm (the
increase of magnetic activity) almost does not affect the intensity of the
δTEC maximum. The seasonal effect was most pronounced along the
Asian-Australian meridian, less often along the Euro-African meridian and was
not revealed along the American meridian. Sometimes the seasonal effect can
penetrate to the opposite hemisphere. The character of average δTEC
variations for the intense storms was confirmed by GOES satellite data.
Though there are some common features of TEC variation revealed during each
storm phase, in general no clear dependence of TEC responses on the storm
phases was found: the effects were different during each storm at different
locations. The behavior of the correlation coefficient (R) between δTEC values along the three meridians was analyzed for each storm. In
general, R>0.5 between δTEC values averaged along each meridian.
This result is new. The possible reasons for the exceptions (when R<0.5)
were provided: the complexity of phenomena during the intense storms and
discordance in local time of the geomagnetic storm beginning along different
meridians. Notwithstanding the complex dependence of R on the intensity of
magnetic disturbance, in general R decreased with the growth of storm
intensity.
Based on the previously developed approach, hybrid recombinant proteins containing short conformational epitopes (a.a. 144-153, 337-346, 414-425, 496-507) of the receptor-binding domain (RBD) of ...SARS-CoV-2 Spike protein (S protein) were synthesized in
Escherichia coli
cells as potential components of epitope vaccines. Selected epitopes are involved in protein–protein interactions in the S protein complexes with neutralizing antibodies and ACE2 (angiotensin-converting enzyme 2). The recombinant proteins were used for immunization of mice (three doses with 2-week intervals), and the immunogenicity of protein antigens and ability of the resulting sera to interact with inactivated SARS-CoV-2 and RBD produced in eukaryotic cells were examined. All recombinant proteins showed high immunogenicity; the highest titer in the RBD binding assay was demonstrated by the serum obtained after immunization with the protein containing epitope 414-425. At the same time, the titers of sera obtained against other proteins in the RBD and inactivated virus binding assays were significantly lower than the titers of sera obtained with the previously produced four proteins containing the loop-like epitopes 452-494 and 470-491, the conformation of which was fixed with a disulfide bond. We also studied activation of cell-mediated immunity by the recombinant proteins that was monitored as changes in the levels of cytokines in the splenocytes of immunized mice. The most pronounced increase in the cytokine synthesis was observed in response to the proteins containing epitopes with disulfide bonds (452-494, 470-491), as well as epitopes 414-425 and 496-507. For some recombinant proteins with short conformational epitopes, adjuvant optimization allowed to obtained mouse sera displaying virus-neutralizing activity in the microneutralization assay with live SARS-CoV-2 (hCoV-19/Russia/StPetersburg-3524/2020 EPI_ISL_415710 GISAID). The results obtained can be used to develop epitope vaccines for prevention of COVID-19 and other viral infections.
Inactivated vaccines are promising tools for tackling the COVID-19 pandemic. We applied several protocols for SARS-CoV-2 inactivation (by β-propiolactone, formaldehyde, and UV radiation) and examined ...the morphology of viral spikes, protein composition of the preparations, and their immunoreactivity in ELISA using two panels of sera collected from convalescents and people vaccinated by Sputnik V. Transmission electron microscopy (TEM) allowed us to distinguish wider flail-like spikes (supposedly the S-protein's pre-fusion conformation) from narrower needle-like ones (the post-fusion state). While the flails were present in all preparations studied, the needles were highly abundant in the β-propiolactone-inactivated samples only. Structural proteins S, N, and M of SARS-CoV-2 were detected via mass spectrometry. Formaldehyde and UV-inactivated samples demonstrated the highest affinity/immunoreactivity against the convalescent sera, while β-propiolactone (1:2000, 36 h) and UV-inactivated ones were more active against the sera of people vaccinated with Sputnik V. A higher concentration of β-propiolactone (1:1000, 2 h) led to a loss of antigenic affinity for both serum panels. Thus, although we did not analyze native SARS-CoV-2 for biosafety reasons, our comparative approach helped to exclude some destructive inactivation conditions and select suitable variants for future animal research. We believe that TEM is a valuable tool for inactivated COVID-19 vaccine quality control during the downstream manufacturing process.
The carrier phase observable is the most preferable means for observation of ionospheric scintillation events. As the ionospheric scintillations show different features at different GNSS frequencies ...the single-frequency data should be used for complex analysis and data interpretation. The second-order derivative of the GPS signal carrier phase is suggested as a promising means to detect small-scale ionospheric disturbances. The high-rate L1 phase data with no additional processing are used for this purpose. Modeling and experimental results proved the hypothesis. It was revealed the strict dependence of sensitivity of the second-order derivative parameter on GPS receiver hardware features and carrier phase sampling rate.
Space Weather (SW) hazards are discussed in terms of the operation of national SW services and global SW centers for the International Civil Aviation Organization (ICAO). The definition of threshold ...values of monitored parameters which are used to identify moderate and severe SW events is one of the critical problems. Due to the lack of both physical data on severe events and user feedback, we tried to approach the problem statistically. In particular, we pursued the answer to the question about what intensity of ionospheric storms and flare effects should be reported by national and global SW entities to their users. We also discussed the possible role of an active region on the Sun, and the cosmic rays’ issues that may be helpful regarding SW operational work. The presented considerations are based on examples of the ionosphere state assessment for the low-latitude American sector with a focus on the Mexican region. This work attempts to argue the possible approaches to resolve the tasks that the SW national services and global centers face.
The COVID-19 pandemic has uncovered the high genetic variability of the SARS-CoV-2 virus and its ability to evade the immune responses that were induced by earlier viral variants. Only a few ...monoclonal antibodies that have been reported to date are capable of neutralizing a broad spectrum of SARS-CoV-2 variants. Here, we report the isolation of a new broadly neutralizing human monoclonal antibody, iC1. The antibody was identified through sorting the SARS-CoV-1 RBD-stained individual B cells that were isolated from the blood of a vaccinated donor following a breakthrough infection. In vitro , iC1 potently neutralizes pseudoviruses expressing a wide range of SARS-CoV-2 Spike variants, including those of the XBB sublineage. In an hACE2-transgenic mouse model, iC1 provided effective protection against the Wuhan strain of the virus as well as the BA.5 and XBB.1.5 variants. Therefore, iC1 can be considered as a potential component of the broadly neutralizing antibody cocktails resisting the SARS-CoV-2 mutation escape.
Manifestations of two solar flares of March 2022 were studied over Mexico. The flare effects in the lower ionosphere had a ~3 min delay from the X1.3-flare onset and ~5 min from the M9.6-flare onset. ...The maximal impact on the HF signal amplitude was ~(14–15) min after the onset of both flares. The X1.3-flare provoked the shortwave fadeout during ~6 min. The effects in the lower ionosphere lasted longer than the flares and the effects at the F2 region and higher altitudes only during the flares. The interpretation of results showed the following. (1) Based on the absorption level estimated with minimum frequency and signal amplitude on ionograms, the major role of X-ray radiation in the electron concentration increase in the lower ionosphere was confirmed. At the same time, the EUV radiation impact on the lower ionosphere cannot be totally discarded. The lower ionosphere recovery began before and lasted after the X1.3-flare end, being more rapid at Eglin than in Mexico. During M9.6-flare, the responses at the two observation points were rather synchronized due to the more similar illumination conditions at the two meridians. (2) According to the dI variations characterizing the F2 region and higher, the M9.6-flare provoked medium-scale and the X1.3-flare provoked both medium- and small-scale ionospheric irregularities. The response duration corresponded to the dI series filtered with (10–20) min windows. The dI curve during the flares was characterized by the И-form and depended more on the active region position and the flare class than on the solar zenith angle. The available data do not allow us to unambiguously identify the reason for the negative dI: the applied filtering procedure or the physical effect. (3) During both flares, the major EUV impact on the lower ionosphere was by the flux at 133.5 nm and on the F2 region and higher altitudes at 25.6 nm. In addition, during the M9.6-flare, EUV 28.4, 30.4 and 121.6 nm spectral bands also played an important role in the F2 response. During the X1.3-flare, the EUV 25.6 nm flux and X-ray flux impacts on the F2 region were of the same level. The weakest impact was caused by the emission in the EUV 28.4 nm spectral band on the absorption in the lower ionosphere during both flares and on the electron density in the F2 region and higher during the X1.3-flare.
A Global Navigation Satellite System (GNSS) receiver is, to some extent, a “black box” when its data is used for ionospheric studies. Our results based on Javad, Septentrio, Trimble, and Leica GNSS ...receivers have proven that the accuracy of the slant Total Electron Content (TEC) calculation can differ significantly depending on the GNSS receiver type/model, because TEC measurements depend on the carrier phase tracking technique applied in a receiver. The correlation coefficient between carrier phase noise in L1 and L2 channels is considered as a possible indicator that shows if the L1-aided tracking technique or independent tracking is applied inside a receiver. An empirical model of the TEC noise component was provided to determine the TEC noise value in different types/models of GNSS receivers.
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