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The manuscripts should contain only unpublished data in the respective scientific field.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> Intuitionistic Logics of Confirmation and Discouragement <p>We analyse intuitionistic logics of confirmation and discouragement. This means that our acceptance of some formula <em>φ</em> in a possible world <em>w</em> gets an additional support or disapprovement. We use pre-ordered neighbourhood frames to model this situation. Our systems have certain connection with so-called logics of false belief and unknown truths.</p> Tomasz Witczak Copyright (c) 2022 Proceedings of the Bulgarian Academy of Sciences 2022-07-29 2022-07-29 75 7 945 951 10.7546/CRABS.2022.07.01 A More Flexible Counterpart of a Huang–Kotz's Copula-type <p>We propose a more flexible symmetric counterpart of the Huang–Kotz’s copula of the 1st type. Both the counterpart and Huang–Kotz’s copula of the 1st type provide the same improvement in the correlation level. Moreover, the proposed copula includes special cases of many other extensions of the Farlie–Gumbel–Morgenstern (FGM) copula.</p> Haroon Barakat Metwally Alawady Islam Husseiny Mohamed Elgawad Copyright (c) 2022 Proceedings of the Bulgarian Academy of Sciences 2022-07-29 2022-07-29 75 7 952 958 10.7546/CRABS.2022.07.02 UHPLC-HRMS Based Saponin and Flavonoid Profiling of Chenopodium bonus-henricus L. Roots and Prolipase Activity of the Main Saponins <p>UHPLC-HRMS profiling method was used for a comprehensive study of flavonoid and saponin-rich fractions from the MeOH extract of <em>C. bonushenricus</em> L. roots. Thirty-one compounds, respectively, 16 saponins of five sapogenins (oleanoic acid, 2-hydroxyoleanoic acid, medicagenic acid, bayogenin, and phytolaccagenin), together with 15 flavonoid glycosides of 6-methoxykaempferol, isorhamnetin, spinacetin, and patuletin were detected. Lipase modulatory activities of the main saponins were established by measuring the levels of the released 4-nitrophenol using LC-MS. All saponins exhibited prolipase activity and could find application in the treatment of cachexia.</p> Zlatina Kokanova-Nedialkova Paraskev Nedialkov Copyright (c) 2022 Proceedings of the Bulgarian Academy of Sciences 2022-07-29 2022-07-29 75 7 982 991 10.7546/CRABS.2022.07.06 A study of Genetic Relationships of Crocus Taxa, Series Biflori (Iridaceae) from Bulgaria by ISSR Markers <p>The taxonomy of the genus <em>Crocus ser. Nudiscapus</em> and the relationship between species in the genus are complicated and often contradictory. In this study, the genetic diversity and molecular markers’ pattern variation among members of the <em>C. biflorus</em> group in Bulgaria were evaluated. For this study, five <em>Crocus</em> L. species from 15 natural populations were collected and assessed using the ISSR marker system. The data obtained was consolidated in a consensus tree, revealing a high degree of genetic variability among the studied species, as well as among the specimens inside the group.</p> Elena Apostolova Tsvetanka Raycheva Kiril Stoyanov Samir Naimov Copyright (c) 2022 Proceedings of the Bulgarian Academy of Sciences 2022-07-29 2022-07-29 75 7 992 999 10.7546/CRABS.2022.07.07 On the Reproductive Biology of Alkanna tinctoria (Boraginaceae) <p>In the present study main parameters of reproductive biology as features of embryological structures and processes as well as the pollen and seed viability of <em>Alkanna tinctoria</em>, an endangered useful species of Bulgarian flora were established. In its studied Bulgarian populations pollen viability above 90% and seed viability – between 32% and 64% were determined. The anthers are tetrasporangiate and their wall develops according to Dicotyledonous-type, consisting of an epidermis, fibrous endothecium, an ephemeral middle layer and secretory tapetum. The microsporogenesis is simultaneous and in the anthers tetrahedral and isobilateral microspore tetrads are formed. The mature pollen is threecelled at shedding stage. The ovule is anatropous, teniunucellate, unitegmic. Embryo sac (ES) develops according to the Polygonum (monosporic)-type. The embryo development follows the Asterad-type. The endosperm in the mature seeds has been completely consumed. As a result of the present study <em>A. tinctoria</em> is characterized as a sexually reproducing species.</p> Elina Yankova Petka Grancharova Rozalia Nikolova Copyright (c) 2022 Proceedings of the Bulgarian Academy of Sciences 2022-07-29 2022-07-29 75 7 1000 1008 10.7546/CRABS.2022.07.08 Production of Functional Recombinant Human Interferon-gamma by RTX CPD-fusion Technology <p>Human interferon-gamma (hIFNγ) is an important pleiotropic cytokine with therapeutic application. Recombinant hIFNγ has been shown to be an effective pharmaceutical against a wide range of viral, immuno-suppressive diseases with promising prospects in cancer immunotherapy resulting in a strong increase in demand and price. The aim of this study was to develop an efficient method for production of soluble and active hIFNγ. To this end a fusion gene encoding hIFNγ and a C-terminally located His<sub>10</sub>-tagged RTX CPD was constructed by two-step PCR. The fusion gene was cloned in an expression vector under inducible promoter and expressed in different <em>E. coli</em> strains such as Rosetta (appropriate for expression of eukaryotic genes containing rare codons), and two chaperone containing strains – BL21(DE3)/pG-KJE8 and BL21(DE3)/pG-Tf2. The transformed bacteria were cultivated at 24℃ to favour proper folding of the recombinant protein. Under these conditions the strain BL21(DE3)/pG-KJE8 was chosen as more suitable for production of soluble hIFNγ. The latter was purified by Ni<sup>2+</sup>- based affinity chromatography, the peak fractions were subjected to affinity chromatography combined with a direct on-column digestion to release hIFNγ, which was further purified by ion exchange chromatography. It is worth mentioning that this strategy, employing auto-cleaving and solubility-enhancing CPD tag, combined with on-column tag digestion was applied for the first time for production of hIFNγ.</p> Elena Krachmarova Genoveva Nacheva Copyright (c) 2022 Proceedings of the Bulgarian Academy of Sciences 2022-07-29 2022-07-29 75 7 1009 1017 10.7546/CRABS.2022.07.09 Establishment and Biochemical Characterization of a Multidrug-resistant Promyelocytic Leukemia Cell Line HL-60/CDDP <p>The present study reports on the establishment, validation and biochemical characterization of a novel chemoresistant variant of the HL-60 acute myeloid leukemia (AML) cell line developed at the Laboratory of Experimental Chemotherapy at the Faculty of Pharmacy of MU-Sofia. Selection of the chemoresistant strain (HL-60/CDDP) has been carried out by prolonged serial exposures of the parent chemosensitive HL-60 cell line to gradually increasing concentrations of the metal complex. In its final variant, the resultant HL-60/CDDP test system showed significantly altered chemosensitivity profiles to the Pt(II)-based drugs cisplatin, carboplatin, oxaliplatin and was maintained in an RPMI-1640 medium containing 25 μM cisplatin. The promyelocytic cells also showed diminished susceptibility to differentiation therapy with arsenic trioxide As<sub>2</sub>O<sub>3</sub>. The emergence of the multiresistant phenotype is suggested to be most likely due to common biochemical properties of the screened compounds, including their strong affinity and high reactivity with sulfhydryl SH-groups. The presented study is focused on elucidating the multidrug resistance patterns in the newly established leukemic model that can be used as a potential test system for exploring the drug-resistance reversal capacity of various drugs and experimental compounds.</p> Rositsa Mihaylova Ivelina Zhelezova Rumiana Simeonova Georgi Momekov Copyright (c) 2022 Proceedings of the Bulgarian Academy of Sciences 2022-07-29 2022-07-29 75 7 1045 1052 10.7546/CRABS.2022.07.13 Effects of Metformin on Body Weight Management and Markers of the Metabolic Syndrome in Persons with Normal Glucose Tolerance <p>Treatment of the metabolic syndrome (MS) is essential for prevention of type 2 diabetes mellitus (T2DM) and cardiovascular disease (CVD). The purpose of this open-label prospective one year observational clinical study was to examine the effects of metformin 2.55 ± 0.3 g/d on body weight management and markers of the MS in normal glucose tolerant persons with hyperinsulinaemia. Body weight was reduced by 6.8% at 6 months and by 11.1% at 1 year. The body weight reduction was 7.2 ± 3.4 kg at 6 months and 11.7 ± 4.7 kg (mean ± SD) at 1 year. We found a significant correlation of reduction of body weight at 1 year with initial body weight, body mass index, waist circumference and homeostasis model assessment of insulin resistance (HOMA-IR), all <em>p</em> &lt; 0:001. At 1 year of metformin treatment HOMA-IR, total cholesterol, low-density lipoprotein cholesterol, triglycerides, systolic and diastolic blood pressure were significantly reduced, all <em>p</em> &lt; 0:001 and high-density lipoprotein cholesterol was significantly increased, <em>p</em> = 0:004. Our study shows that treatment with metformin alone, without intensive diet and physical activity, could reduce visceral obesity, insulin resistance, dyslipidaemia and arterial hypertension and supports the hypothesis that it could be applied for prevention of T2DM and CVD.</p> Petya Kamenova Georgi Kirilov Copyright (c) 2022 Proceedings of the Bulgarian Academy of Sciences 2022-07-29 2022-07-29 75 7 1053 1062 10.7546/CRABS.2022.07.14 Effectiveness and Safety of Treatment with Nucleo(s)tide Analogues in Patients with Hepatitis B-related Cirrhosis <p>Data from Bulgaria are limited on the long-term effects of nucleo(s)tide analogues (NAs) to patients with hepatitis B-related cirrhosis. The study aimed to evaluate the overall efficacy and renal safety of NAs in such cohort of patients, comparing treated with high to low-barrier NAs. We retrospectively analyzed 58 patients with HBV cirrhosis (74.1% in compensated stage) for a period of 5 years. Thirty-five patients received NAs with high-barrier of resistance: Tenofovir disoproxil fumarate and Entecavir (followed up for 51.63 ± 30.3) and 23 received NAs with low-barrier of resistance: Lamivudine and Telbivudine (followed up for 56.7 ± 48.4). After a median treatment time of 53.7 months virological response (VR) rates (HBV DNA&lt;10 IU/ml) were 91.4% in high barrier and 87.0% in low barrier NAs groups. Undetectability of HBVDNA was influenced most by the treatments’ duration. Serological response reached 57.1%, similar for the two treatment groups. One patient (1.7%) cleared HBsAg and discontinued NAs (TDF). Multidrug resistance (MDR) occurred in 15.5% of LAM recipients only. One-, 3-, 5-, 8- year MDR rates were 0.0%; 11.1%; 33.3% and 77.6%. A slight improvement of the renal function was observed in 85.7% and 69.6% of the patients treated with high and low-barrier NAs. Dose reduction for renal toxicity was required in 1.7%. Decompensated cirrhosis and T2DM were the main risk factors for renal function decline. Long-term therapy with high and low barrier NAs was equally effective and renally safe in patients with HBV-related cirrhosis.</p> Klimentina Gerdzhikova Ivo Donkov Teodora Komitova Jordan Genov Borislav Vladimirov Rumyana Mitova Milena Chetirska Boryana Asenova Ali Bedran Kaloyan Pavlov Copyright (c) 2022 Proceedings of the Bulgarian Academy of Sciences 2022-07-29 2022-07-29 75 7 1063 1071 10.7546/CRABS.2022.07.15 A Field Study on Fertility Traits of Holstein Heifer and Cows Artificially Inseminated with Sexed Belgian Blue Sperm and Growth Characteristics of Crossbreed Belgian Blue × Holstein (F1) Male Calves <p>The study was conducted to investigate some reproductive traits of Holstein cattle inseminated with imported sexed male Belgian Blue semen and the growth characteristics of calves in Aydın province of Turkey. Totally 82 Holstein cattle including 29 heifers and 53 cows were inseminated. After the inseminations, some reproductive (the number of insemination per conception, conception rate, the dystocia rate, the rate of stillbirth) values were determined in the enterprises. The birth weights of the male calves were determined and in the following periods, the chest girth and body length values were determined for 6 months of age. In the study, it was observed that the average age of the first insemination was 14.05 months for heifers and 38.11 months for cows (<em>P</em> &lt; 0:05). While more than half of the cows (52.08%) became pregnant in the first insemination, a great majority of the pregnancies (69.03%) of heifers occurred in the second inseminations (<em>P</em> &lt; 0:05). The number of inseminations per conception were 2.13 and 1.79 for heifers and cows, respectively. While the conception rate was determined as 47.76% and 55.62% for heifers and cows respectively, dystocia rate were 43.10% and 25.75%, respectively. The average birth weight of the male calves were found as 42.75 kg and the 90th and 180th day live weights were 106.22 kg and 154.16 kg, respectively. While, the height at withers, body length and chest girth values were detected as 80.60 cm, 78.28 cm, 81.04 cm at birth, the same measurements were 94.45 cm, 94.22 cm and 109.79 cm; 108.46 cm, 110.88 cm and 129.45 cm for the 90th and 180th day, respectively. The corresponding study has clearly shown that the application in the project can create a dramatical meaning in dairy farms. This application can be used in dairy farms in a certain period to whole herd or a part of it. </p> Aykut Akbaş Mehmet Sari Zafer Usta Mustafa Saatci Copyright (c) 2022 Proceedings of the Bulgarian Academy of Sciences 2022-07-29 2022-07-29 75 7 1072 1081 10.7546/CRABS.2022.07.16 Sex-dependent Differences of Emotional Status in a Rat Model of Prenatal Stress <p>Untoward events during pregnancy negatively affect offspring mental development. We investigated sex-dependent differences of emotional problems in offspring with a history of prenatal stress (PNS). Female rats demonstrated decreased anxiety-like behaviour in comparison to male controls, shown in the light-dark test. Male and female offspring of prenatally stressed mothers were characterized by higher anxiety levels, compared to unstressed controls. PNS induced depression-like behaviour in both sexes without differences among them, indicated with decreased intake of sweet solution in the sucrose consumption tests and increased immobility time spent in the forced swim test. Control females showed higher plasma corticosteroid (CORT) concentrantions after acute stress and decreased recovery (120 min after the stressor) than control males. Both male and female PNS-offspring were with elevated levels of CORT in the plasma, which remained high 120 min after application of the stressogenic procedure. This study evidenced that the unfavourable effect of PNS on emotional state correlated with impaired feedback mechanism of the hypothalamic-pituitary-adrenal (HPA) axis function both in male and female offspring.</p> Natasha Ivanova Zlatina Nenchovska Milena Atanasova Rumyana Mitreva Tzveta Stoynova Lidia Kortenska Jana Tchekalarova Copyright (c) 2022 Proceedings of the Bulgarian Academy of Sciences 2022-07-29 2022-07-29 75 7 1082 1088 10.7546/CRABS.2022.07.17 Chemometric Approach to the Elemental Composition of Ethereal Oil Plant Materials <p>The aim of the present study is the effective application of chemometric approach to the elemental composition of a data set of ten ethereal oil plant materials. The contents of 28 essential and toxic mineral elements at main, minor and trace level are determined in each sample by means of direct solid sampling electrothermal vapourization inductively coupled plasma optical emission spectrometry (ETV-ICP-OES) and are subjected to hierarchical and non-hierarchical cluster analysis and principal component analysis. Z-transformation of the raw data, Ward’s method of linkage and squared Euclidean distance as similarity measure are used in order to discover appropriate linkage between the plant materials and between the chemical parameters characterizing them. Thus, the investigated plant samples are classified, depending on their chemical composition. On the other hand, the mineral elements are categorized into several patterns which are related to the specific soil characteristics.&nbsp;</p> Albena Detcheva Vasil Simeonov Lidia Ivanova Caroline Hommel Paunka Vassileva Copyright (c) 2022 Proceedings of the Bulgarian Academy of Sciences 2022-07-29 2022-07-29 75 7 966 973 10.7546/CRABS.2022.07.04 Separation and Determination of Matrine, Oxymatrine and Sophoridine in Composite Preparations by Non-aqueous Capillary Electrophoresis <p>A new, simple, and quick method for the simultaneous determination of three alkaloids (matrine, sophoridine, and oxymatrine) in composite preparations by nonaqueous capillary electrophoresis has been developed. A running buffer composed of 60% acetonitrile + 0.75% acetic acid + 25 mM ammonium acetate in methanol was found to be the most suitable for this separation. The limits of detection for three alkaloids were over the range of 0.45–0.6 μg/ml. In the tested concentration range, good linear relationships between peak areas and concentrations of the analytes were obtained. This method has been successfully applied to simultaneous determination of the three alkaloids with recoveries over the range of 95.6 to 97.2%. This new non-aqueous capillary electrophoresis method established has been successfully used for the simultaneous separation and determination of sophoridine, matrine and oxymatrine in complex preparations in 5 minutes.</p> Cunhong Li Tianlin Zhu Copyright (c) 2022 Proceedings of the Bulgarian Academy of Sciences 2022-07-29 2022-07-29 75 7 974 981 10.7546/CRABS.2022.07.05 Global System for Space Monitoring of Environmental Littering <p>As a result of human activity, a huge number of landfills and industrial waste is formed. For timely intervention in the process of environmental pollution from unauthorized landfills and industrial waste, it is necessary to have a global automated (automatic) space monitoring system. A model of such a global system for landfill monitoring is proposed using remote sensing methods from space. Modern methods for designing information systems are applied. Several innovative methodologies have been developed and used in the proposed model. The use of different images from the following satellites is classified: QuickBird; Ikonos; IRS-1C/1D; Landsat 8; RapidEye; WorldView2; NOAA; Terra; Meteor-3M and Radarsat-1.</p> Maretta Kazaryan Mihail Shakhramanyan Andrey Richter Petar Getsov Pavlin Gramatikov Copyright (c) 2022 Proceedings of the Bulgarian Academy of Sciences 2022-07-29 2022-07-29 75 7 1028 1036 10.7546/CRABS.2022.07.11 Microsomal P450-related Electron Transfer Components, Glutathione and Glutathione S-transferase Contribution in Stress Response of Herbicide-treated Wheat to Drought and Waterlogging <p>The activities of some plant microsomal P450-related electron transfer components (NADPH-cytochrome P450 reductase, CPR and NADH-cytochrome b5 reductase, B5R), glutathione S-transferase (GST) together with the content of reduced (GSH) and oxidized (GSSG) glutathione were determined in wheat (Triticum aestivum L., cv. Sadovo 1) treated with herbicide Serrate<sup>®</sup> prior to drought or waterlogging. Both stresses, especially drought, increased the content of glutathione and the activities of CPR and B5R during the stress, while GST activity was rather decreased. Herbicide application alone increased substantially most of the parameters, especially at the beginning of the experimental period. Serrate<sup>®</sup>+drought/waterlogging (S+D/W), amplified the observed alterations (except for GST), which were more significant after drought. The decrease in ratio GSH to GSSG after 4 days of recovery for all treatment groups except Serrate<sup>®</sup> signifies disrupted buffer capacity in cells. After 4 days of recovery the activities of CPR and B5R dropped below the control, while the glutathione pool and GST activity remained increased in drought and S+D treated plants. Contrariwise, the levels of glutathione, CPR and B5R remained closer to control in waterlogged plants, while S+W kept higher levels of P450-related enzymes. The herbicide application prior to drought or waterlogging did not affect negatively detoxification and oxidative status of wheat plants compared to those subjected to water stress alone.</p> Liliana Brankova Ljudmila Dimitrova Elena Shopova Zornitsa Katerova Iskren Sergiev Dessislava Todorova Copyright (c) 2022 Proceedings of the Bulgarian Academy of Sciences 2022-07-29 2022-07-29 75 7 1089 1096 10.7546/CRABS.2022.07.18 Enhanced Feature Selection Method Using Wrapper-based Random Search Strategy and Mutual Information for Remote Sensing Image Classification <p>Remote sensing image classification is one of the useful image processing tasks and finds application in many real-life scenarios. Image feature is important and unavoidable in classification. It is impossible to get a clear classification result without proper features. So after feature extraction, selecting an efficient and relevant feature is inevitable. Thus, our system proposes a new way of selecting features by a wrapper-based method that works using a randomized search strategy. The process is done in an orderly manner. In each step, the features that contribute less to classification are rejected to bring out the most relevant features. Three steps are followed: (1) Randomized selection (2) Warm start and (3) Cool down. The Randomized selection selects relevant features based on the random search method from the full feature set. Among the selected features, the important features are selected, based on the Mutual Information using the Warm start. Some important features, missed out in Randomized selection, are picked up in Cool down. The system finds out 25% of the most relevant features with greater classification accuracy when compared with classification accuracy obtained using 100% features. The proposed system has been checked for its efficiency with the help of remote sensing-based datasets from the UCI repository and it is found to be more efficient than the other existing methods. The results produced with the selected features are of high accuracy and low computational cost.</p> T. Nisia S. Rajesh Copyright (c) 2022 Proceedings of the Bulgarian Academy of Sciences 2022-07-29 2022-07-29 75 7 1037 1044 10.7546/CRABS.2022.07.12 BEPU Analyses for the Postulated Loss-of-cooling Accident Scenario in the Spent Fuel Pool at the Fukushima Daiichi Unit 4 <p>The aim of the paper is to present the results obtained from the study devoted on the Best Estimate plus Uncertainty (BEPU) Methods application. To this end, the simulation of the Loss of cooling accident (LOCA) scenario in the Fukushima Daiichi spent fuel pool was carried out. Special attention was paid on the uncertainty analysis with the domain fission products release. The work presented herein was carried out by using the ASTECv2.2b/SUNSET in the coupling mode. A brief description of the ASTECv2.2b/SUNSET coupling is provided and a short discussion concerning the BEPU methodology is also presented.</p> Petya Petrova Pavlin Groudev Petya Vryashkova Copyright (c) 2022 Proceedings of the Bulgarian Academy of Sciences 2022-07-29 2022-07-29 75 7 959 965 10.7546/CRABS.2022.07.03 REE and Trace Elements Distribution in the Deep-sea Sediments from the Interoceanmetal (IOM) Polymetallic Nodule Exploration Area in the Clarion-Clipperton Fractures Zone, NE Pacific <p>Geochemical features of the deep-sea sediments from a high polymetallic nodule area in the eastern part of the Clarion-Clipperton Fractures Zone (CCZ), NE Pacific were studied. Box-corer samples from six stations in individual depth layers 0–3, 3–5, 5–10, 10–20 cm were collected from 4300–4500 m depth. The deep-sea sediments were classified as clayey-siliceous oozes according to the mineral and grain-size analyses. The chemical composition of the studied samples is compatible with that of pelagic sediments. Manganese content varies from 0.16% to 0.70% being the highest in the geochemically active layer (top 7–12 cm) and decreases with depth. The Mn/Fe ratio, Ba, Co, Ni and Cu have the highest values in the first (0–3) and second (3–5) layers and decrease with depth. REE range is 195.84–357.79 ppm showing low variation between the layers. PAAS-normalized REE patterns show significant enrichment of MREE and HREE with strong negative Ce anomaly and weak positive Eu and Y anomalies. The geochemical characteristics of the studied sediments infer polygenic origin. The redox sensitive oxides and barite presense, Eh values and negative Ce anomaly, indicate oxidizing environment of sediment formation. </p> Atanas Hikov Zlatka Milakovska Valcana Stoyanova Elitsa Stefanova Tomasz Abramowski Silvia Chavdarova Milen Stavrev Copyright (c) 2022 Proceedings of the Bulgarian Academy of Sciences 2022-07-29 2022-07-29 75 7 1018 1027 10.7546/CRABS.2022.07.10