Proceedings of the Bulgarian Academy of Sciences <p>Founded in 1948 by academician Georgy Nadjakov, "Comptes rendus de l’Académie bulgare des Sciences" is also known as "Доклади на БАН","Доклады Болгарской академии наук" and "Proceedings of the Bulgarian Academy of Sciences".</p> <p>If applicable, the name of the journal should be abbreviated as follows: C. R. Acad. Bulg. Sci. (according to ISO.)</p> <p><big><strong>Related subjects:</strong></big></p> <p class="condensed">Astronomy, Mathematics, Physics, Chemistry, Biology, Geology, Geophysics, Space Sciences, Engineering Sciences, Physical Geography, Medicine, Agricultural Sciences.</p> <p class="condensed">The manuscripts should contain only unpublished data in the respective scientific field. They can further be expanded to be published elsewhere. All manuscripts are subject to peer review and copy editing.</p> <p><strong><big>2002-2021 website:</big></strong></p> <p>The site with the archive of <em>Comptes rendus de l’Académie bulgare des Sciences</em> - 2002 to 2021 is <a href="" target="_blank" rel="noopener">still accessible at that address.</a></p> en-US <p>Copyright (c) 2022 Proceedings of the Bulgarian Academy of Sciences</p> <p>Copyright is subject to the protection of the <em>Bulgarian Copyright and Associated Rights Act</em>. The copyright holder of all articles on this site is Proceedings of the Bulgarian Academy of Sciences. If you want to reuse any part of the content, please, contact us.</p> (Ralitsa Boteva) (Ralitsa Boteva) Mon, 30 Jan 2023 22:11:25 +0200 OJS 60 Projective Embeddings of Ball Quotients, Birational to a Bi-elliptic Surface <p>For a neat lattice $$\Gamma &lt; SU(1,2)$$, whose quotient $${\mathbb B} / \Gamma$$ is birational to a bi-elliptic surface, we compute the dimensions of the cuspidal $$\Gamma$$-modular forms $$[ \Gamma,n]_o$$ and all modular forms $$[ \Gamma, n]$$ of weight $$n \geq 2. $$ The work provides a sufficient condition for a subspace $$V \subset [ \Gamma, n]$$ to determine a regular projective embedding of the Baily-Borel compactification $$\widehat{ {\mathbb B} / \Gamma}$$ and applies this criterion to a specific example.</p> Azniv Kasparian Copyright (c) 2023 Proceedings of the Bulgarian Academy of Sciences Mon, 30 Jan 2023 00:00:00 +0200 Geometry of CR-slant Warped Products in Nearly Trans-Sasakian Manifolds <p>A CR-slant warped product is considered a generalization of a CR-warped product. It was firstly introduced and studied in the field of Kaehler geometry. In this paper, we study CR-slant warped products in nearly trans-Sasakian manifolds. We obtain a general inequality related to the second fundamental form and the warping function in such warped products. The equality case is discussed.</p> Lamia S. Alqahtani, Mića S. Stanković Copyright (c) 2023 Proceedings of the Bulgarian Academy of Sciences Mon, 30 Jan 2023 00:00:00 +0200 Two New Modifications of the InterCriteria Analysis <p>In the present work two modifications of the InterCriteria Analysis are proposed in order to extend its theoretical foundation. The results obtained from the application of these methods over real data (from patients with prostate carcinoma) have been analyzed to determine the reliability of the calculated consonance and dissonance.</p> <p>The similarity scores obtained by the modified versions of the InterCriteria Analysis are close to those given by the classical InterCriteria Analysis, as well as to the values of the correlation coefficients between the considered criteria. This shows the reliability of the proposed modification with respect to determining the consonance and dissonance between criteria in different problems.</p> Peter M. Vassilev, Lyudmila P. Todorova, Elenko P. Popov, Radostina N. Georgieva, Chavdar K. Slavov, Krassimir T. Atanassov Copyright (c) 2023 Proceedings of the Bulgarian Academy of Sciences Mon, 30 Jan 2023 00:00:00 +0200 Simulation and Real-time Application of the Load Cell-based Segway <p>In this study, real-time application and simulation of the load cell-based Segway was carried out by using an STM32F103 microcontroller. The Brushless Direct Current Motor (BLDC) current and speed information was recorded on the SD card simultaneously during the real-time application of the vehicle. The BLDC parameters required for the simulation of the Segway were entered into the block diagram created in Matlab/Simulink interface. Then the load cell-based Segway was simulated. As a result of the simulation, the determined phase currents were compared with the real-time application results. In addition, the repetition test of the load cells was performed, and 99.9% correlation coefficients were obtained from the measurement of each load cell. As a result of this process, the measurement error rate of the load cells was determined as 0.01%. Finally, the currents of the BLDC motors were compared with the simulation study and the real-time application. The similarity of the currents with each other was obtained with an error rate of approximately 1.5–2%.</p> Muhammed Mustafa Kelek, Tolga Özer, Uğur Fidan, Yüksel Oğuz Copyright (c) 2023 Proceedings of the Bulgarian Academy of Sciences Mon, 30 Jan 2023 00:00:00 +0200 A Novel Neural Collaborative Filtering Recommendation Based on Side Information Fusion <p>It is difficult to accurately learn user's latent features using only one single data source. In order to solve these problems, we consider to utilize relevant side information of users or items as a supplement to rating information to enhance the performance of recommender systems, and propose a novel neural collaborative filtering recommendation model based on side information fusion. Extensive experiments on different datasets validate the efficiency and accuracy of our proposed framework.</p> Ruihui Mu Copyright (c) 2023 Proceedings of the Bulgarian Academy of Sciences Mon, 30 Jan 2023 00:00:00 +0200 Applying the VIKOR Method to Select the Optimal Underground Mining Technology <p>The selection of the most appropriate underground mining technology is not a simple process because it involves handling of a large amount of information about several potential methods. Multicriteria optimization approaches are proven useful tools for ranking alternatives, especially in cases where multiple complex criteria have to be considered simultaneously. An ore deposit is a complex system because of its geology, physical and mechanical properties, and hydrogeological conditions. As such, problem solving requires a heuristic approach and includes tasks involving expert judgement, intuition, estimation, and experience. Using a heuristic strategy to state a problem means that the analyst is placed in a position to apply past experience to a future situation and existing knowledge to new circumstances, as well as discover new avenues to creative problem solving. A complex algorithm was developed to pave the way to quality management of mining, by using the VIKOR method to rank various mining technologies relative to a set of criteria and select the optimum mining method that will primarily ensure profitable and safe mining.</p> Sanja Bajić, Dragoljub Bajić , Branko Gluščević, Vesna Ristić Vakanjac Copyright (c) 2023 Proceedings of the Bulgarian Academy of Sciences Mon, 30 Jan 2023 00:00:00 +0200 Antibacterial Activity of Combined Nanodiamonds and Snail Fractions with Biocompounds with MW below 10 kDa and above 30 kDa <p>The use of nanomaterials for enhancement of the antibacterial activity of different compounds is a new approach contributing to the efforts of overcoming the emerging antibiotics resistance. This study explores the combined antibacterial activity of nanodiamonds and snail peptides against <em>Brevibacillus laterosporus BT271</em>. Two peptide/protein fractions from <em>Cornu aspersum</em> mucus were used – with molecular weight (MW) below 10 kDa and with MW above 30 kDa. Four types of nanodiamonds (ND) were tested (positively charged, single digit and two types of detonation ND). Peptide fractions were characterized by using MALDI-TOF. The fraction with MW below 10 kDa consisted of many different peptides, while the fraction with proteins above 30 kDa showed proteins at m/z 26879.2 Da, 33903.11 Da, 43583.81 Da, 53986.81 Da, 79091.82 Da, 100650.42 Da, and 141 550.82 Da. When mixture peptides+ND was applied directly on the bacterial culture, the nanodiamonds showed enhanced antibacterial effect from 8% up to 42%. The combination of nanodiamonds and the mucus fraction with MW above 30 kDa had strongest bactericidal effect (1593.04 mm<sup>2</sup>/mgP*μL). The results demonstrated that ND have potential to enhance the antibacterial activity of the snail peptides but also highlighted that their effects should be carefully studied.</p> Elmira Daskalova, Mihaela Belouhova, Nellie Zheleva, Yana Topalova, Lyudmila Velkova, Aleksandar Dolashki, Pavlina Dolashka Copyright (c) 2023 Proceedings of the Bulgarian Academy of Sciences Mon, 30 Jan 2023 00:00:00 +0200 Chemical Composition, Scolicidal Effects and Antimicrobial Activities of Green Macroalga Ulva intestinalis <p>The aim of the study is to investigate the antimicrobial, biological, and scolicidal activities of <em>Ulva intestinalis</em> (<em>U. intestinalis</em>), which is one of the green algae. <em>U. intestinalis</em> was collected in appropriate amounts and some of the samples were distilled with water vapour to extract their essential oils, and some of them were extracted by Soxhlet extraction with hexane and dichloromethane. The values of lethal concentration doses (LD<sub>50</sub> and LD<sub>90</sub>) were calculated using the probit analysis. Antibacterial and scolicidal effects of the essential oil and solvent extracts of <em>U. intestinalis</em> against gram-positive, gram-negative and yeast microorganisms were studied. It was determined that essential oil and solvent extracts of <em>U. intestinalis</em> may have scolicidal effects. The highest scolicidal activity was observed in 15 000 µg/ml in all organic solvents. Antimicrobial activity was observed for <em>U. intestinalis</em>, with high potency with hexane extract against <em>Enterobacter aerogenes</em> and with dichloromethane extract against <em>Enterococcus faecalis</em> (inhibition zone ≥ 12 mm). It is suggested that controlled in vivo studies should be carried out in order to use this alga as a bactericidal and scolicidal medication.</p> Tuğba Cebeci Copyright (c) 2023 Proceedings of the Bulgarian Academy of Sciences Mon, 30 Jan 2023 00:00:00 +0200 Protein Amadoriase Activity of the Escherichia coli K-12 Glycolytic Enzyme Phosphoglucose Isomerase <p>The Maillard reaction (glycation) is a spontaneous non-enzymatic reaction between primary amines and carbonyl compounds, which affects proteins and DNA of both pro- and eukaryotes. In recent studies, we have shown that the glycolytic enzyme of <em>Escherichia coli</em> phosphoglucose isomerase (PGI) catalyzes in vitro the deglycation of DNA modified with glucose 6-phosphate (G6P)-derived Amadori products (APs). APs are early products of the Maillard reaction, which are formed not only on DNA but also on other amines including proteins. The aim of the current study was to test the <em>E. coli</em> PGI for protein deglycation (amadoriase) activity. To this end, we used chicken lysozyme glycated with G6P as a model protein. Treatment of the glycated lysozyme with protein extract from an <em>E. coli</em> PGI proficient but not deficient strain resulted in the release of G6P, which was indicative of PGI protein amadoriase activity. G6P-derived APs represent fructose 6-phosphate (F6P) residues bound to free amino groups of the model protein and because of that we compared the kinetic constants of the <em>E. coli</em> PGI for the glycated lysozyme and for free F6P. PGI demonstrated nearly two times higher affinity to the glycated lysozyme (K<sub>m</sub>' = 0.06 mM) than to free F6P (K<sub>m</sub>' = 0.1 mM). However, the apparent catalytic constant of the enzyme with the glycated lysozyme (K<sub>cat</sub>' = 93 s<sup>–1</sup>) was eight times lower than with F6P (K<sub>cat</sub>' = 736 s<sup>–1</sup>). Future studies are expected to shed light on the physiological relevance of the PGI protein amadoriase activity we report here.</p> Elitsa Boteva, Konstantin Doychev, Rositsa Tsekovska, Yordan Handzhyski, Ivan Ivanov, Roumyana Mironova Copyright (c) 2023 Proceedings of the Bulgarian Academy of Sciences Mon, 30 Jan 2023 00:00:00 +0200 Prioritization of Genetic Variants Predisposing to Alzheimer's Disease in Young Healthy Bulgarian Individuals Using Centenarian Exomes <p>The present study aims to identify pathogenic/risky variants in the exomes of healthy young individuals predisposing to Alzheimer's disease (AD) by their validation in centenarian's exomes. The group of Bulgarian centenarians included 32 individuals (mean age 102.4) without AD diagnosis and the matched control group of 61 young healthy individuals (mean age 21.9). Two DNA pools were constructed with equimolar amounts of DNA from each participant and whole exome sequencing analysis (WES) was performed. We examined the WES data for pathogenic or risky SNPs predisposing to AD. Of altogether 1929 variants selected from DisGeNet database for association with AD, only 174 (9.02%) were detected in our WES data. One hundred and fifty-two (152) SNPs were present in both studied groups, 8 in centenarians and 14 in controls only. Seven variants have significantly higher frequency in young individuals or absence in centenarians. Based on sufficiently unambiguous literature data, we nominated rs63750264 in <em>APP</em>, rs429358 in <em>APOE</em>, rs1800562 in <em>HFE</em> variants for predisposition to AD in young individuals. To a lesser extent, the carriership of rs2070045 in <em>SORL1</em>, rs6265 in <em>BDNF</em>, rs769449 in <em>APOE</em>, <em>rs4988514</em> in <em>SST</em> can increase the risk to AD development. These variants could find implication in the Alzheimer's disease estimation in young individuals before the onset of clinical symptoms.</p> Dragomira Nikolova, Lubomir Balabanski, Dimitar Serbezov, Shima Mehrabian, Maria Petrova, Latchezar Traykov, Draga Toncheva Copyright (c) 2023 Proceedings of the Bulgarian Academy of Sciences Mon, 30 Jan 2023 00:00:00 +0200 SEIR Model Analysis of the Omicron Variant Spread in Bulgaria – an Empirical Study <p>We provide a study of the Covid-19 spread in Bulgaria in the period starting December 15, 2021 until early February, 2022. In particular, we provide predictive scenarios for the peak of the pandemic. Based on these scenarios, we estimate the risks in terms of fatalities in the case no restrictive measures are imposed. The main challenge is distinguishing the influence of the Delta variant which is still dominating in December, 2021, while Omicron becomes dominant in early January, 2022.</p> Ognyan Kounchev, Georgi Boyadzhiev, Georgi Simeonov, Methody Kunchev, Zhana Kuncheva Copyright (c) 2023 Proceedings of the Bulgarian Academy of Sciences Mon, 30 Jan 2023 00:00:00 +0200 Radical Cystectomy as a Cause of an Increased Neuroendocrine Response <p>The present study compared the neuroendocrine response in patients undergoing conventional cystectomy with two postoperative pain management techniques: epidural analgesia (EA) and intermittent opioid analgesia (IOA) on adrenocorticotropic hormone (ACTH), cortisol, glucose levels for 48 hours. We hypothesize that appropriate analgesic regime can attenuate stress response reaction. Forty-four patients scheduled for radical conventional cystectomy were assigned to one of the two study groups: group A (n=22) with EA, group B (n=22) with IOA. The surgical stress factor induced significant hypothalamic-pituitary-adrenal (HPA) axis responses in both groups. The ACTH and cortisol levels were higher than baseline for both groups, but more significantly in group B. Blood glucose level was elevated few hours after the surgical intervention and was back to baseline level by the following morning. The results suggest that EA might have more advantages associated with reduced postoperative pain and attenuated neuroendocrine response when open access is the preferred operative technique. There is a need of randomized multicentre trials to evaluate the quality of life, the survival and the role of pain management at least 12 months after radical cystectomy.</p> Petya Hubenova, Plamen Krastev, Atanas Temelkov Copyright (c) 2023 Proceedings of the Bulgarian Academy of Sciences Mon, 30 Jan 2023 00:00:00 +0200 Comparison of the Effectiveness of Fluoride versus Grape Seed Extract in Biomimetic Remineralization of Dentin <p>This study aims to compare the remineralization efficiency of grape seed extract versus fluoride in artificial carious dentin lesions in the biomimetic remineralization procedure. One hundred and twelve extracted impacted human teeth were demineralized for 10 days and divided into 4 groups. Demineralization group (DM), remineralization group (RM group), remineralization fluoride group (RM F), remineralization grape seed extract group (RM GSE). Demineralization (DM) group were stored in physiological saline after demineralization. RM F was kept in 1000 ppm fluorine solution and RM GSE was kept in 6.5% grape seed extract for 10 min. RM, RM F, RM GSE groups were stored in simulated body fluid (SBF) with biomimetic analogues and Portland cement discs for 6 weeks. The specimens were evaluated by microhardness test, elasticity modulus measurement, and scanning electron microscope (SEM) analysis. Kruskal–Wallis H test with Bonferroni correction was used for between-group comparisons. Microhardness and elasticity modulus values differed significantly among the groups, with the highest values in the RM-GSE group, followed by the RM-F group, RM group, and DM group. SEM images showed granular structure formations in the RM-GSE and RM-F groups. It is concluded that although remineralization can occur by mineral precipitation in structures with high organic matrix density such as dentin, the collagen structure must be supported to increase the degree of remineralization.</p> Simge Vural, Zeynep Ökte Copyright (c) 2023 Proceedings of the Bulgarian Academy of Sciences Mon, 30 Jan 2023 00:00:00 +0200 Periodontal Status of Active Age Population in the Republic of Bulgaria <p>Periodontal health is an important component of oral health. Numerous studies prove the progressing nature of periodontal diseases and their dependence on a number of demographic and socio-economic factors.</p> <p>The purpose of the study is to examine the periodontal status of the active age population in the Republic of Bulgaria and to define its dependence on social and demographic factors.</p> <p>To accomplish the study goals epidemiological and survey cards were developed and approbated and epidemiological study was conducted, including clinical dental examination and anonymous survey among 416 Bulgarian citizens aged 18 to 65 years. The results were statistically analyzed to establish the dependencies between the periodontal status and socio-demographic factors.</p> <p>Only 69 (16.59%) of the study subjects have no periodontal problems (CPI = 0) in all sextants, while all other patients have different degrees of periodontal disease. One can witness an increase of the periodontal disease incidence, proportional to the age of the patients, as well as its decrease with increasing the frequency of dental visits on behalf of the patients and their oral health self-assessment. Healthy periodontal tissues prevail in young patients and urban population. Gingival inflammation and calculus are prevalent among middle-aged people, rural population as well as in individuals of lower educational level. Periodontal pockets of varying depths are being registered mostly among the older people and the subjects with low and average income. Higher severity of the periodontal pathology is observed in individuals of lower educational levels and lower income.</p> <p>These facts verify the conclusion about an inadequate state commitment as regards the dental health problems of the population, while bearing in mind that the treatment of periodontal conditions is not reimbursed by NHIF.</p> Stanislav Nenov, Petar Bozhinov, Boyko Bonev Copyright (c) 2023 Proceedings of the Bulgarian Academy of Sciences Mon, 30 Jan 2023 00:00:00 +0200 Estimation Chickpea Species and Productivity per Decare with Synthetic Data Generation Methods <p>Production increase in agriculture depends on some parameters such as improving arable land, activating spraying and irrigation activities. In addition to these, it is known that spraying and seed types have an effect on productivity. Therefore, proper selection of seed types is important. With the developing technology, big data consisting of scientific studies can be recorded digitally and used in the estimation or decision-making process. In this study, chickpea species diversity was made with classification process using machine learning methods by taking advantage of the characteristics of chickpea plant. In addition, productivity per decare was estimated by regression process. Accuracy was preferred as a success criterion for classification, and rmse success criterion was preferred for regression. The dataset was first used raw, and then experiments were made using synthetic data. To generate synthetic data, the synthetic minority oversampling technique method and also the n-shifting mean method proposed in this study were used. When the success rates of the results obtained were compared, the highest success rate was 90.6% in the classification made using only raw data. Likewise, the classification success rate of the dataset using the synthetic data created with the raw data was the highest 100%. For regression, the highest score was 0.17 for raw data and 0.16 for synthetic data. The high performance of the results showed that machine learning algorithms can be used in this field.</p> <p>&nbsp;</p> Kerim Karadağ, Fırat Keskinbıçak Copyright (c) 2023 Proceedings of the Bulgarian Academy of Sciences Mon, 30 Jan 2023 00:00:00 +0200 Growth Performance, Carcass Composition and Tenderness of Meat in Male Layer-type Chickens Slaughtered at Different Age <p>An experiment with male layer-type chickens was carried out in the Institute of Animal Science-Kostinbrod, aiming to investigate their growth performance and carcass composition, as well as the cooking loss and tenderness of the meat at the age of 5 and 9 weeks. The birds were reared in controlled microclimate, with initial stocking density of 22 birds/m<sup>2</sup>. After 5 weeks of age, fragmentation of the stocking density was applied and it was diminished to 7 birds/m<sup>2</sup>. Chickens were slaughtered at 5 and 9 weeks of age, and 10 chickens of each age group were subjected to carcass analysis. The average live weight of the birds at 5 weeks was 329 g, while the 9 weeks old chickens reached 1096 g. In order to attain the weight of the first age of slaughter (5 weeks) the chickens gained 294.03 g with a feed conversion ratio of 2.97, whereas for the whole period the feed conversion ratio was 2.91. The dressing percentage of the 5 weeks old chicks was 51.26%. For the 9 weeks old it was 77.62%. The age affected the yield of the main carcass components and the older birds had higher yield of breast (P=0.0035) and thighs (P&lt;0.0001). The cooking loss for both breast and thigh meat was higher in younger chickens (P&lt;0.0001). The tenderness measured as Warner-Bratzler shear force (WBSF) of breast and thigh remained unaffected by the age at slaughter. Its values classified the meat of the male layer-type chickens from this trial as “very tender”.</p> Teodora Popova, Evgeni Petkov, Maya Ignatova, Stefan Dragoev, Desislava Vlahova-Vangelova, Desislav Balev, Nikolay Kolev Copyright (c) 2023 Proceedings of the Bulgarian Academy of Sciences Mon, 30 Jan 2023 00:00:00 +0200 Characterization of Serpentine Soils from Eastern and Southern Rhodope Mountains (Bulgaria) <p>This work aims to characterize serpentine soils in Bulgaria and examine the biogeochemistry of pedogenic Ni and its relation to Ni available forms. Soils were collected from serpentine soils of the Eastern and Southern Rhodopes (Bulgaria). The chemical composition of serpentine soils is similar to serpentine soils from the Balkan Peninsula and is characterized by high contents of Ni (919.9–2397.2<sup>–1</sup>). The soils had a neutral to slightly alkaline reaction (pH 6.4 to 7.6) and a medium to high organic matter content. Of the primary minerals, those of the serpentine group (antigorite and lizardite), the talc group (willemseite), the amphibole group (riebeckite), the feldspar group (albite) and quartz are mainly present in the soil samples. The secondary minerals present in the samples include calcite and dolomite, and also representatives of the clay minerals, clinochlore and montmorillonite. The contents of free iron oxides (Fed), amorphous iron oxides (Feo), well-crystallized iron oxides (Fecr) (Fed-Feo) and activity index (Feo/Fed) showed significant differences (p&lt;0.05) among soils from different locations. In the soils from Dobromirtsi, Parvenets, and Golyamo Kamenyane Ni bound to Fe oxides were evenly distributed between the well-crystallized and amorphous phases. In the soils from Kardzhali, Chernichevo and Dyulitsa more than half of the Ni bound to Fe oxides were bound to or occluded in amorphous Fe oxides, while in the soils from Kazak were bound to well-crystallized Fe oxides. Pedogenesis, weathering intensity, and Fe geochemistry influence Ni availability in serpentine soils.</p> Violina Angelova, Daniela Kovacheva Copyright (c) 2023 Proceedings of the Bulgarian Academy of Sciences Mon, 30 Jan 2023 00:00:00 +0200 Application of CORSIMA (Cosmic Ray Spectrum and Intensity in Middle Atmosphere) Model for Solar Cosmic Rays. Case Study of the Extremes GLE 05 and GLE 69 <p>The new model CORSIMA (COsmic Ray Spectrum and Intensity in Middle Atmosphere) is presented. The spectra and intensities of solar cosmic rays (SCR) from GLE (Ground Level Enhancement) 05 on 23 February 1956 and GLE 69 on 20 January 2005 at different altitudes are calculated. For this purpose, the operational CORSIMA model is applied. In the final version of the CORSIMA program, an approximation in 6 characteristic energy intervals of the Bohr–Bethe–Bloch function is used, including the charge decrease interval. Analytical expressions for the contributions of the energy intervals are provided.</p> <p>For the first time we present a quantitative and qualitative appreciation of the impact of Solar Cosmic Rays (SCRs) from the Solar Particle Events (SPEs) on the ionosphere and middle atmosphere (30–80 km). These altitudes are above the Regener–Pfotzer maximum.</p> <p>Unlike Galactic Cosmic Rays (GCR), the differential spectra of SCR essentially vary in time. The SCR fluxes also differ from each other during the different events. The spectrum and intensity behaviour is explained considering the structure of the CORSIMA program. The calculation results are in agreement with the experimental data and show characteristic features of the propagation process for different altitudes and geomagnetic latitudes. The calculations are performed for geomagnetic latitudes 90° (cusp region). The development of this research is important for the processes and mechanisms of space weather.</p> Simeon Asenovski, Peter I. Y. Velinov, Lachezar Mateev Copyright (c) 2023 Proceedings of the Bulgarian Academy of Sciences Mon, 30 Jan 2023 00:00:00 +0200