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The manuscripts should contain only unpublished data in the respective scientific field.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> „Prof. Marin Drinov“ Academic Publishing House en-US Proceedings of the Bulgarian Academy of Sciences 1310-1331 <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> Characterizable and V-characterizable groups <p>Let <em>G</em> be a finite group. The spectrum π<sub>e</sub>(G) is the set of all element orders of <em>G</em>. A vanishing element of <em>G</em> is an element g∈<em>G</em> such that χ(g)= 0 for some irreducible complex character χ of <em>G</em>. Denote by Vo(<em>G</em>) the set of the orders of vanishing elements of <em>G</em>. For a set Ω of positive integers, let h(Ω) (v(Ω)) be the number of isomorphism classes of finite group G such that <em>π<sub>e</sub></em>(<em>G</em>)= Ω Vo(<em>G</em>)= Ω, respectively). A group <em>G</em> is called characterizable (V-characterizable) if h(π<sub>e</sub>(<em>G</em>))= 1 (v(Vo(<em>G</em>))= 1, respectively). In this note, we discuss the relation between characterizable and V-recognizable. Moreover, by an application of the the relation, we prove that the group <em>M</em><sub>22</sub> is V-characterizable.</p> <p> </p> Jinshan Zhang Xiu Liu Dandan Liu Yanhua Huang Copyright (c) 2022 Proceedings of the Bulgarian Academy of Sciences 2022-11-30 2022-11-30 75 11 1551 1558 10.7546/CRABS.2022.11.01 Decay in Energy Space for the Solutions of Generalized Schrödinger-Hartree Equation Perturbed by a Potential <p>We prove, in any space dimension <em>d≥3</em>, the decay in the energy space for the defocusing Schrödinger–Hartree (SCH) equations with mass-energy intercritical non-local nonlinearities and perturbed by a potential. We will show also new Morawetz inequalities and estimates, generalizing the previous results appearing in [<sup>1</sup>].</p> Elena Nikolova Mirko Tarulli George Venkov Copyright (c) 2022 Proceedings of the Bulgarian Academy of Sciences 2022-11-30 2022-11-30 75 11 1559 1572 10.7546/CRABS.2022.11.02 The Endogenous Cannabinoid System and Nitric Oxide Interact in Modulation of Cold Stress-induced Analgesia <p>The aim of the present study was to estimate 1) whether the endogenous cannabinoid and the nitric oxide-ergic systems' interaction affects cold stress-induced analgesia (c-SIA), and 2) whether the possible interaction (and its impact on c-SIA) differs before and after cold-stress exposure.</p> <p>Male Wistar rats have been injected with CB1-receptor agonist anandamide (AEA) and the nitric oxide (NO) precursor L-arginine before and after 1 hour of cold stress (1 h CS) exposure; CB1 antagonist AM251, the nitric oxide synthase inhibitor L-NAME, and the NO-donor SIN-1 were additionally applied in order to further elucidate the interaction between the two systems.</p> <p>Results obtained suggest that endocannabinoids and NO differently interact before and after stress: applied before stress, the two systems were antagonistic between them with AEA exerting an analgesic effect, while NO decreased analgesia; a synergistic effect of endocannabinoids and NO resulted instead in application after 1 h CS.</p> Hristina Nocheva Eleonora Encheva-Stoykova Georgi Bogdanov Roman Tashev Rumen Nikolov Copyright (c) 2022 Proceedings of the Bulgarian Academy of Sciences 2022-11-30 2022-11-30 75 11 1672 1679 10.7546/CRABS.2022.11.15 Research of the Genetic Diversity of TT Viruses in Bulgaria <p>Torque teno viruses (TTVs) are a member of the newly formed family Anelloviridae and contain single stranded circular DNA genome. It is believed that these viruses chronically infect people of any age, yet it is not clear what is their pathogenic potential. Our previous research has shown spread of TT viruses at least 61.87% in voluntary blood donors, 62.74% in patients with respiratory diseases, 65.21% in cases of hepatitis, 62.96% in unknown cases of pathology, 66.66% in patients with brain tumour and 64.28% in patients with renal transplantation. It was the first report demonstrating TT viruses in Bulgaria. The purpose of this work is identification of the main genotypes of TT viruses circulating in Bulgaria. The original viral DNA was isolated from blood samples from clinically healthy blood donors, a HBsAg positive sample and a patient with unexplained febrile condition. Phylogenetic tree analysis shows that most of our sequences are genetically related, highly correlated, and fall into a single cluster. The analysis shows that they are close relatives and most likely have a common ancestor. Part of the sequences could also be a separate cluster or the start of a new clone within that cluster, together with the reference sequences clustered by literature data in genotype 1.</p> Kalina Shishkova Iliya Tsekov Rumen Popov Stoyan Shishkov Zlatko Kalvatchev Copyright (c) 2022 Proceedings of the Bulgarian Academy of Sciences 2022-11-30 2022-11-30 75 11 1680 1686 10.7546/CRABS.2022.11.16 Secreted Factors from Umbilical Cord-Mesenchymal Stem Cells Affect CD86 Expression on B Lymphocytes and Increase CCL5 Chemokine Secretion by Healthy Donors' PBMC <p>A growing number of autoimmune diseases, allergies, and atopic conditions in recent years are calling for the development of innovative therapies, such as those using stem cells with immunoregulatory activity. Because of the few and often conflicting results in the scientific literature, it is still uncertain whether mesenchymal stem cells (MSC) could be a useful therapeutic strategy for targeting B lymphocytes and be helpful in treating autoimmune and allergy patients or those with a variety of viral infections. In connection with the aforementioned, our team investigated the influence of umbilical cord MSC-secreted factors on healthy donors' B-cell CD86 expression and CCL5 secretion by peripheral blood mononuclear cells (PBMC) in vitro. When healthy donors' PBMC were cultivated with conditioned medium derived from umbilical cord MSC, CD86 density on the B-cell membrane statistically decreased, but the percentage of B cells expressing this co-stimulatory molecule was slightly but significantly increased. We also found significantly increased secretion of the chemokine CCL5 by PBMC under the influence of the MSC secretome.</p> Adelina Yordanova Dobroslav Kyurkchiev Mariana Ivanova Kalina Tumangelova-Yuzeir Kalina Belemezova Ekaterina Ivanova-Todorova Copyright (c) 2022 Proceedings of the Bulgarian Academy of Sciences 2022-11-30 2022-11-30 75 11 1687 1695 10.7546/CRABS.2022.11.17 Advantages of Real-time PCR and RD4-PCR as Molecular Methods for Rapid Detection of Bovine Tuberculosis in Bulgaria <p>Representatives of <em>Mycobacterium tuberculosis</em> complex (MTBC) are potential causative agents of tuberculosis in animals and humans, and <em>Mycobacterium bovis</em> is considered a major one among domestic and wild ruminants. In the last twenty years, the role of another representative of MTBC – <em>Mycobacterium caprae</em>, has been proven in the countries of Central and Southern Europe. Study sample included 121 diagnostic materials from lymph nodes and lungs from cattle, positively and doubtfully PPD tuberculin-reacted, originating from 6 farms belonging to the 4 regions in Northern and Southern Bulgaria. The bacteriological examination showed typical growth for mycobacteria for 110 (90.9%) samples, which was confirmed by qPCR. By RD4-PCR we proved that 102 (92.7%) of the mycobacterial strains were <em>M. caprae </em>and the remaining 8 strains (7.3%) were <em>M. bovis</em>. This defines <em>M. caprae</em> as a dominant species in the etiology of tuberculosis in cattle in Bulgaria.</p> <p>In conclusion, we confirmed that the application of real-time PCR is an accurate and convenient method for rapid detection of <em>M. bovis</em> from cattle in the Bulgarian settings. RD4-PCR provides a sufficiently high differentiation and can be used for first-line typing of <em>M. bovis</em> isolates in Bulgaria. This proves the need for the simultaneous application of both methods in the diagnosis of bovine tuberculosis in Bulgaria.</p> Tanya Savova-Lalkovska Violeta Valcheva Albena Dimitrova Hristo Najdenski Magdalena Bonovska Copyright (c) 2022 Proceedings of the Bulgarian Academy of Sciences 2022-11-30 2022-11-30 75 11 1696 1704 10.7546/CRABS.2022.11.18 Antimicrobial Resistance and Whole Genome Sequencing Analysis of Neisseria gonorrhoeae Isolates in Bulgaria, 2019 <p><em>Neisseria gonorrhoeae</em> is evolving into a superbug with resistance to previously and currently recommended antimicrobials for treatment of gonorrhoea, which creates a significant public health concern globally. Antimicrobial resistance (AMR) poses a great threat; it causes longer duration of illness and treatment, and increases health care costs and the social, psychological and financial burden to families and societies. In response to this worrying situation laboratory research should be strengthened with implementation of newer molecular methods for monitoring and detecting AMR, and evaluation of the correlation of obtained genetic data with corresponding phenotypes.</p> <p>This study aimed to implement whole genome sequencing analysis for the first time of <em>N. gonorrhoeae</em> isolates from Bulgaria and to acquire molecular epidemiological and AMR information linked with phenotypic resistance data.</p> <p>Although the tested strains were susceptible to current recommended dual therapy, genetic analysis showed the presence of several mutations responsible for reducing susceptibility to third generation cephalosporins, namely the presence of genotype G1407 strains in the Bulgarian population. Regarding previously recommended antimicrobials, penicillin resistance and intermediate sensitivity to tetracyclines was demonstrated in all strains, and fluoroquinolone resistance in two strains.</p> <p>The obtained results showed that the use of whole genome sequencing was feasible, could describe current circulating gonococcal strains and predict and infer transmission of antimicrobial resistance. Therefore, gonococcal infections prevention and control programmes will be aided to target interventions where needed and to revise treatment guidelines that will help improve patient care.</p> Ivva Philipova Viktoryia Levterova Ivan Simeonovski Todor Kantardjiev Copyright (c) 2022 Proceedings of the Bulgarian Academy of Sciences 2022-11-30 2022-11-30 75 11 1579 1587 10.7546/CRABS.2022.11.04 Quercetin Influences Phospholipase A2 Products in A549 Adenocarcinoma Cells <p>The effect of quercetin on phospholipase A2 activity and its products has been investigated in A549 adenocarcinoma cells. Quercetin is a polyphenol of medico-biological significance, which has been reported to show antioxidant and anti-tumour beneficial effects. Phospholipids are functionally active molecules, which participate in various cellular processes, acting as second messengers, enzyme activators, membrane transporters, etc. Although there are many studies dealing with the influence of quercetin on the lipid metabolism of different types of cancer cells, the mechanism of this effect</p> <p>remains largely unclear. The present study showed that quercetin treatment of A549 cells induced activation of phospholipase A2 (PLA2) activity, the latter being known as a source of pro-inflammatory intermediate metabolites. The phospholipid analysis of membranes from A549 cells revealed reduction of</p> <p>phosphatidylcholine (PC) and an increase of the level of lysophosphatidylcholine (LPC). In addition, acyl chain analysis showed an elevation of some polyunsaturated fatty acids, such as arachidonic acid (AA), the latter being a major product of PLA2. The content of lipid peroxides was also elevated in membranes from quercetin-treated A549 cells, which we presume is related to the higher content of polyunsaturated fatty acids, which are an excellent target of oxidative destruction.</p> <p>In conclusion, the present results show that treatment of A549 adenocarcinoma cells with the polyphenol quercetin induces activation of membrane-bound PLA2, which is a source polyunsaturated fatty acids, the</p> <p>latter producing lipid peroxides. We presume that this mechanism underlies the reported by other authors elevation of oxidative stress, which is induced by quercetin treatment of cancerous cells.</p> Biliana Nikolova Roumen Pankov Galya Staneva Nikolai Krastev Tania Markovska Stefan Pankov Evgenia Vassileva Dimo Krastev Albena Momchilova Copyright (c) 2022 Proceedings of the Bulgarian Academy of Sciences 2022-11-30 2022-11-30 75 11 1588 1594 10.7546/CRABS.2022.11.05 Barcoding and Morphological Characterization of Mycena cupressina (Agaricales, Fungi), a Little-known and Controversially Treated Member of Section Supinae <p>The author presents recent collections of &nbsp;<em>Mycena cupressina</em>, a corticolous species on <em>Cupressus sempervirens</em>, described from the Mediterranean area and sometimes treated as conspecific with <em>M. juniperina</em>. The first ITS nrDNA sequence of the species from Balkan material was obtained. Its analysis demonstrated the affinity of the sequenced collection to section <em>Supinae</em>, although the results could not be unambiguously interpreted and suggest that in this section the ITS marker may be less informative, similarly to some other groupings of the genus. Description of <em>M. cupressina</em> is provided, based on Balkan collections. The studied <em>Cupressus</em>-affiliated specimens share smooth stipitipellis hyphae, deemed to be diagnostic character of the species, suggesting that for the time being the two are better retained as separate taxa. The first records for Bulgaria of four other species of the section, namely <em>M. juniperina, M. meliigena, M. pseudocorticola</em> &nbsp;and <em>M. supina</em>, are also included.</p> Boris Assyov Copyright (c) 2022 Proceedings of the Bulgarian Academy of Sciences 2022-11-30 2022-11-30 75 11 1595 1603 10.7546/CRABS.2022.11.06 On the Sensitivity Estimation of the Symmetric Matrix Riccati Differential Equation <p>In this paper, we consider three already known perturbation estimates of the solution to the symmetric&nbsp; matrix Riccati differential equation. The aim of the paper is to analyse experimentally&nbsp; the effectiveness of the bounds considered, to compare their sharpness for problems with increasing conditioning, and to specify the area of application of the bounds analysed. The analytical solution to the scalar Riccati differential equation of one of the experimental models is proved in theorem. The results suggest a new field of research.</p> Vera Angelova Todor Balabanov Ivan Popchev Copyright (c) 2022 Proceedings of the Bulgarian Academy of Sciences 2022-11-30 2022-11-30 75 11 1638 1646 10.7546/CRABS.2022.11.11 Accident Severity Estimation from Environmental Factors with the Proposed Dataset Separation Method <p>Traffic accidents can be thought of as being the whole combination of events that usually occur due to reasons caused by humans, vehicles, roadway, and environment, which are the basic elements of transportation, and these events most likely result in injuries, death, and huge financial damage. In this study, by making use of a dataset, received from the New Zealand Transportation Agency, it is estimated whether or not traffic accidents occurring on roads end up with minor or serious damage. Predictions are made by exploiting machine learning algorithms. A new method has been proposed for separating the dataset and the classification success results made in this way gave the most successful scores by 89%. Based on the high performance rates, it is shown that such methods can be used to assist in preventing possible traffic accidents</p> Kerim Karadağ Mehmet Çetin Copyright (c) 2022 Proceedings of the Bulgarian Academy of Sciences 2022-11-30 2022-11-30 75 11 1647 1655 10.7546/CRABS.2022.11.12 The Influence of Steel and Cast Iron as Substrate Materials on the Microstructure, Microhardness and Wear Resistance of Nickel-base Ti-Al Plasma Spray Coatings <p>This paper studies the influence of different substrate materials on the phase composition, microstructure, microhardness, and wear resistance of Ni-Cr-B-Si-C-Ti-Al plasma spray coatings. Two types of substrate metals were studied – AISI 1045 steel and Pig-P3 Si grey cast iron. It has been found that in the as-coated condition the surface layers have a phase composition of γ-Ni, Cr<sub>23</sub>C<sub>6</sub>, γ-TiAl, TiN, and α-Ti(N, O) on steel substrate, and γ-Ni, α-Ti, TiN, Ni<sub>3</sub>B, CrB, Cr<sub>23</sub>C<sub>6</sub>, α-Ti(N, O), Ni<sub>3</sub>Si on cast iron. The microhardness and wear resistance of the plasma sprayed Ni-Cr-B-Si-C-Ti-Al coatings is tested. The wear volume of the coatings has been tested for up to 60 min. The deposits on cast iron substrates demonstrate lower wear than those on the steel substrate.</p> Hristo Skulev Deyan Veselinov Copyright (c) 2022 Proceedings of the Bulgarian Academy of Sciences 2022-11-30 2022-11-30 75 11 1656 1662 10.7546/CRABS.2022.11.13 Novel DE-based Optimization Technique for the Renewable Sources' Integration <p>Ever since the thermal generation units, once a foundation of a large number of the power systems, were marked as one of the main emitters of greenhouse gases and, therefore, undesirable in the modern systems, the renewable energy sources are taking over their share in the generation mix. Although this process is going fast, it might still not be efficient enough to reach the climate goals, set with short deadlines. In accordance with that, every measure that enhances the integration of renewable sources into the grid and makes the application process for the new investors simple and straightforward is welcome. To aid that cause, this paper proposes the method for determining the optimal location of the new wind power plant in the predefined geographical area, taking into account both the characteristics of the power system in that region and the relevant climatic indicators. This technique was developed by utilizing the differential evolution mechanism, while introducing a novel space search formula that ensures the avoidance of the local optima. For the mapping of the solutions and switching between the discrete and continuous values, the georeferencing principle was implemented. This method was illustrated on the part of the Serbian real-life system.</p> Vladan Ristic Darko Sosic Copyright (c) 2022 Proceedings of the Bulgarian Academy of Sciences 2022-11-30 2022-11-30 75 11 1663 1671 10.7546/CRABS.2022.11.14 Statistical Model of Temperature Anomalies Using a New Instability Index <p>A statistical model (relationship) between a new circulation instability index and the registered temperature anomalies in two regions of Europe has been proposed and tested. The average values of this index, calculated at levels of 850 hPa and 500 hPa, were used as predictors in the modelling of temperature anomalies by months for the period 2011–2020. The average monthly values of temperature and geopotential during this period were utilized to calculate the index and anomalies in these regions. For each of them, the following statistical characteristics were calculated: correlation, root mean square error, and the coefficient of determination (R-squared). They evaluate the performance of the statistical model. The obtained results demonstrate the principal applicability of the instability index in a similar way as the well established circulation estimator North Atlantic Oscillation.</p> Hristo Chervenkov Valery Spiridonov Copyright (c) 2022 Proceedings of the Bulgarian Academy of Sciences 2022-11-30 2022-11-30 75 11 1621 1627 10.7546/CRABS.2022.11.09 North Atlantic Oscillation and Variations of Geomagnetic Field <p>The North Atlantic Oscillation is one of the most influential climatic modes in the Northern Hemisphere. However, the mechanism(s) standing behind its wide spectra of variations is still unknown despite its numerous investigations. This paper presents evidence for a synchronization between secular variations of geomagnetic field intensity and NAO long-term variability. Analysis of the connectivity between geomagnetic secular variations and the sea-level pressure – point by point, in a grid with resolution 10 [deg] in latitude and longitude – reveals that the strength of their relation is unevenly distributed over the Northern Hemisphere. Based on the machine learning analysis over the period 1900–2019, we found that there are two centres of significant geomagnetic-pressure relations – the weaker of them is placed slightly north of Iceland, and the stronger one is in a close proximity to Azores islands. The suggested mechanism for geomagnetic influence on the near surface climatic conditions includes the geomagnetic modulation of energetic particles precipitating in Earth's atmosphere, and their impact on the lower stratospheric ozone. The analysis of ozone-pressure relation shows, in addition, reasonable similarities with the spatial patterns of geomagnetic-pressure relations.</p> Natalya Kilifarska Antonia Mokreva Tsvetelina Velichkova Copyright (c) 2022 Proceedings of the Bulgarian Academy of Sciences 2022-11-30 2022-11-30 75 11 1628 1637 10.7546/CRABS.2022.11.10 Santonian-Campanian Boundary Interval in the Kyunetsa Section, Western Srednogorie Zone, Bulgaria <p>The Kyunetsa section, 2.5 km west of Kosharevo, exposes mainly pelagic Upper Cretaceous marly limestones and marls of the Srednogorie Zone, part of the intermediate Balkanides in Bulgaria. The Melove Formation of Coniacian to early Campanian age involves a prominent Santonian-Campanian boundary interval of grey and reddish sediments, including CORBs (Cretaceous Oceanic Red Beds). The base of the Campanian can be discerned in bed 7c by the first rare (single) occurrence of the nannofossil <em>Broinsonia</em> (<em>Aspidolithus</em>) <em>parca parca</em>. A positive carbon isotope peak below, and a field magnetic susceptibility peak above may enhance correlation to other Tethyan sites such as the proposed GSSP at Bottaccione (Italy), the Postalm section (Austria) and the Mudurnu-Göynük Basin (Turkey).</p> Michael Wagreich Docho Dochev Polina Pavlishina Veronika Koukal Copyright (c) 2022 Proceedings of the Bulgarian Academy of Sciences 2022-11-30 2022-11-30 75 11 1604 1612 10.7546/CRABS.2022.11.07 Hydrochemical Characteristics of the Large Karst Springs in the Catchment of Mesta River (Bulgaria) <p>Mesta river is a cross-border river with Greece, whose catchment area includes parts of Rila, Pirin and the Rhodope Mountains. The karst is developed in pre-Paleozoic marble that forms isolated outcrops with different basins. The largest of them forms two alpine karst basins located in Northern Pirin and Slavyanka Mountains. In the Rhodopes region, the marble outcrops are fragmented and embedded in non-karstic rocks. They are drained from springs with relatively low flow rates. The largest karst springs drain different hydrodynamic zones of the karst massif of Northern Pirin. From the karst basin of Slavyanka Mountain, only the large subthermal spring near the village of Musomishta falls into the catchment area of the Mesta river. The data on the chemical composition of some of the karst springs are summarized, paying attention to the largest of them. An analysis of the changes in the chemical composition and comparison is made. The changes of the hydrochemical parameters of the springs draining different vertical zones in Northern Pirin are compared. The obtained results prove that the main role in the formation of the chemical composition of karst waters has natural factors - interaction between water and marbles. It was found that the waters are unsaturated to carbonate minerals, which proves that even now there are active processes of karst formation.</p> Boyka Mihaylova Konstantin Kostov Aleksey Benderev Copyright (c) 2022 Proceedings of the Bulgarian Academy of Sciences 2022-11-30 2022-11-30 75 11 1613 1620 10.7546/CRABS.2022.11.08 Optimal Signal Shaping in Solid State Detector Spectrometers <p>The performance of the most widely used shapers in solid state detector spectrometers is investigated in respect to noise suppression and count rate ability. Three shaper types have been experimentally checked with two detector types – X-ray Silicon Drift Detector and HPGe gamma detector. The results show small difference in noise line width and negligible difference in obtainable energy resolution while the high count rate performance depends noticeably on shaper type selected. This allows for simultaneous optimization of noise and count rate performance.</p> Mikhail Mikhailov Lilianna Panteleev-Simeonova Copyright (c) 2022 Proceedings of the Bulgarian Academy of Sciences 2022-11-30 2022-11-30 75 11 1573 1578 10.7546/CRABS.2022.11.03