Plovdiv University "Paisii Hilendarski"
  • Plovdiv, Plovdiv, Bulgaria
Recent publications
Ricci-like solitons with arbitrary potential are introduced and studied on Sasaki-like almost contact B-metric manifolds. A manifold of this type can be considered as an almost contact complex Riemannian manifold which complex cone is a holomorphic complex Riemannian manifold. The soliton under study is characterized and proved that its Ricci tensor is equal to the vertical component of both B-metrics multiplied by a constant. Thus, the scalar curvatures with respect to both B-metrics are equal and constant. In the 3-dimensional case, it is found that the special sectional curvatures with respect to the structure are constant. Gradient almost Ricci-like solitons on Sasaki-like almost contact B-metric manifolds have been proved to have constant soliton coefficients. Explicit examples are provided of Lie groups as manifolds of dimensions 3 and 5 equipped with the structures under study.
Background and Objectives: Despite the importance of life satisfaction for health and well-being, there is a paucity of cross-national comparative studies in life satisfaction related to the family environment. The present research examined the pathways of life satisfaction association with perceived family support and other family environment variables among adolescents aged from 11 to 15 years in 45 countries. Materials and Methods: Samples from the Health Behaviour in School-aged Children (HBSC) survey in 2017/2018 were analysed (n = 188,619). Path analysis was applied to evaluate the associations among the study variables. Results: A positive association between the life satisfaction score and high family support was identified in all 45 countries (standardized regression weight ranged from 0.067 to 0.420, p < 0.05). In majority of countries, living with both parents and higher levels of family affluence had a positive effect on adolescent life satisfaction both directly and indirectly through family support. In the described path model, the proportion of life satisfaction score variance that was accounted for by family support, family structure, family affluence, gender and age was up to 25.3%. The path models made it possible to group the participating countries into two clusters. In the first cluster (10 countries) the Eastern and Southern European countries dominated, while the second cluster (35 countries) united the countries of Western and Central Europe. Conclusions: There is evidence that countries with high level of adolescent life satisfaction differ in the high rate of intact family structure and the strong relation between family support and perceived life satisfaction.
The current study aimed to determine the major and minor nutritional constituents of Sorbus domestica L. fruits. It was revealed that palmitic acid was the most commonly occurring saturated fatty acid, while linoleic acid represented the major polyunsaturated fatty acid. The sterol fraction consisted mainly of β-sitosterol. Small amounts of lipophilic pigments were quantified. Potassium, iron, and boron were the most abundant macro-, micro-, and ultra-trace elements. The amino acid composition analysis suggested that the non-essential amino acids predominated over the essential ones. Soluble sugars (fructose and glucose) represented a large part of the total carbohydrate content, but pectin formed the major part of polysaccharides. Malic acid was the most abundant organic acid whereas quercetin-3-β-glucoside, neochlorogenic, and 3,4-dihydroxybenzoic acids were the major phenolic constituents. Fruits exhibited free-radical scavenging and protecting ability against peroxyl and hydroxyl radicals. Service tree fruits provided valuable bioactive constituents having a high nutritional value and potential health benefits.
The generalized proportional Caputo fractional derivative is a comparatively new type of derivative that is a generalization of the classical Caputo fractional derivative, and it gives more opportunities to adequately model complex phenomena in physics, chemistry, biology, etc. In this paper, the presence of noninstantaneous impulses in differential equations with generalized proportional Caputo fractional derivatives is discussed. Generalized proportional Caputo fractional derivatives with fixed lower limits at the initial time as well as generalized proportional Caputo fractional derivatives with changeable lower limits at each impulsive time are considered. The statements of the problems in both cases are set up and the integral representation of the solution of the defined problem in each case is presented. Ulam-type stability is also investigated and some examples are given illustrating these concepts.
It has been known that bulk La0.6Ca0.4MnO3 is an intermediate material of the first- and second-order characters with the tricritical-point exponents, and the doping of a metal ion in it usually causes a continuous second-order transition. The present work reports the re-entrance of a discontinuous first-order transition in orthorhombic La0.6-xYxCa0.4MnO3 (x = 0.03–0.09) compounds. This enhances the magnetocaloric effect. For the field H = 30 kOe, the maximum magnetic-entropy change (|ΔSmax|) and relative cooling power (RCP) have been evaluated being about 5.45–6.3 J/kg·K and 130–185 J/kg, respectively. If combining these compounds as refrigerant blocks in a rotary ring model, a magnetic cooling device can operate at temperatures T = 85–280 K, with |ΔSmax| ≈ 5.5 J/kg⋅K and RCP ≈ 1073 J/kg. Aside from the re-entranced first-order phase transition, the magnetization and structural analyses have proved the enhanced magnetocaloric effect in La0.6-xYxCa0.4MnO3 related to a Griffiths singularity, and local Jahn-Teller distortions of the perovskite structure (since the Mn³⁺/Mn⁴⁺ ratio and orthorhombic structural phase are unchanged vs. x).
This paper deals with multi-agent systems that, due to using the generalized proportional Caputo fractional derivative, possess memories. The information exchange between agents does not occur continuously but only at fixed given update times, and the lower limit of the fractional derivative changes according to the update times. Two types of multi-agent systems are studied, namely systems without a leader and systems with a leader. For a generalized proportional Caputo fractional model of multi-agent linear dynamic systems, sufficient conditions for exponential stability via impulsive control are obtained. In the case of the presence of a leader in the multi-agent system, we derive sufficient conditions for the leader-following consensus via impulsive control based on the leader’s influence. Simulation results are provided to verify the essential role of the generalized proportional Caputo fractional derivative and impulsive control in realizing the consensus of multi-agent systems.
Beekeepers have various options to control the parasitic mite Varroa destructor in honey bee colonies, but no empirical data are available on the methods they apply in practice. We surveyed 28,409 beekeepers maintaining 507,641 colonies in 30 European countries concerning Varroa control methods. The set of 19 different Varroa diagnosis and control measures was taken from the annual COLOSS questionnaire on honey bee colony losses. The most frequent activities were monitoring of Varroa infestations, drone brood removal, various oxalic acid applications and formic acid applications. Correspondence analysis and hierarchical clustering on principal components showed that six Varroa control options (not necessarily the most used ones) significantly contribute to defining three distinctive clusters of countries in terms of Varroa control in Europe. Cluster I (eight Western European countries) is characterized by use of amitraz strips. Cluster II comprises 15 countries from Scandinavia, the Baltics, and Central-Southern Europe. This cluster is characterized by long-term formic acid treatments. Cluster III is characterized by dominant usage of amitraz fumigation and formed by seven Eastern European countries. The median number of different treatments applied per beekeeper was lowest in cluster III. Based on estimation of colony numbers in included countries, we extrapolated the proportions of colonies treated with different methods in Europe. This suggests that circa 62% of colonies in Europe are treated with amitraz, followed by oxalic acid for the next largest percentage of colonies. We discuss possible factors determining the choice of Varroa control measures in the different clusters.
Extracts obtained from different Betonica species have been shown to possess important biological properties. The present study aimed to investigate the cytotoxicity, antitumor and immunomodulatory potential of the endemic plant Betonica bulgarica (Lamiaceae) and thus, reveal new aspects of its biological activity. Methods: Methanolic extract obtained from inflorescences was analyzed for cytotoxicity against mammalian cell lines. The antitumor potential of the sample was determined using human cervical and lung adenocarcinoma cells (HeLa and A549). Programmed cell death-inducing effects against HeLa cells and peripheral blood lymphocytes, as well as immunomodulatory properties of the extract were determined by flow cytometry analysis. Results: The research results demonstrated that the extract has significant inhibitory potential against HeLa cells (mean IC50 value 119.2 μg/mL). The sample selectively induced apoptotic death in tumor cells. Cytotoxic effects towards mouse cell lines were detected following treatment with high concentrations of Betonica bulgarica extract (200 and 250 μg/mL). Twenty-four-hour ex vivo incubation of peripheral blood leucocytes in growth medium containing plant extract induced prominent effects in distinct immune cell populations. They included elevated levels of CD25+ and CD56+ T cells’ lymphocytes, particularly CD4+CD25+ and CD8+CD56+ cells. Conclusions: The present study demonstrates that Betonica bulgarica inflorescence extract possesses potential beneficial antitumor and immunomodulatory activity and could serve as a source of bioactive compounds with biomedical application.
The purpose of the proposed article is to present the creation of ontologies for automatic generation of test questions from the Test Generation Environment, which was created as part of the Virtual Education Space. The ontologies presented in the article are in different fields and can be helpful to students in their exams or for self-study. The three ontologies are in the fields of botany, literature and history of Bulgaria, and architecture of Revival houses. The article presents examples of automatically generated questions for each of them.
Predicting trends is crucial for any business. No exception for education as well. Usually, this is a complex task that needs good planning and hard working to get to results. But sometimes luckily, a result from a study could be recognized as something that could reveal a potential trend, though it was not its primary goal, but spending some time digging deeper into data would pay off. This paper presents results from a study of the students’ trend for choosing favorite database type to learn and use, which was found during analyzing data from the software agents that work for our e-learning portal DeLC, serving as helpers for students and lecturers. These agents are there for very different purpose, but from the data they collect many interesting facts and behavioral patterns of our students could be revealed.
Interest in plant extracts as a natural source of antioxidants has grown significantly in recent years. The tree species Koelreuteria paniculata deserves attention due to its wide distribution, good adaptability, and growth to the degree of invasiveness in a number of European countries. The purpose of the present study was to analyze flavonoids and phenolic acids of the ethanol extracts from aerial parts of K. paniculata and to screen their antioxidant and DNA-protective activity. HPLC profiling revealed the presence of five flavonoids, with rutin (4.23 mg/g DW), hesperidin (2.97 mg/g DW), and quercetin (2.66 mg/g DW) as the major ones in the leaves, and (−)-epicatechin (2.69 mg/g DW) in the flower buds. Among the nine phenolic acids identified, rosmarinic, p-coumaric, salicylic, vanillic, and gallic acids were the best represented. All the extracts tested showed in vitro antioxidant activity that was determined by DPPH, ABTS, FRAP, and CUPRAC assays. The highest activity was recorded in the flower parts (in the range from 1133 to 4308 mmol TE/g DW). The DNA-protective capacity of the flower and stem bark extracts from the in vitro nicking assay performed, as well as the main diagnostic microscopic features of the plant substances, are given for the first time. According to the results obtained, the aerial parts of K. paniculata could be valuable sources of natural antioxidants.
Objectives: Ductal epithelial changes (lympho-epithelial lesions-LEL) in prostatic chronic inflammation (CI) are not well studied so far. Aim: to investigate LEL immediately adjacent to prostatic CI. Methods: We studied LEL in 144 prostatic surgical and autopsy specimens in various types of prostatic CI: NIH-category IV prostatitis (histologic prostatitis-HP), nonspecific granulomatous prostatitis (NSGP), and the reactive lymphoid infiltrates in the vicinity of benign prostatic hyperplasia (BPH) and prostate adenocarcinoma (PCa). CI is scored as low and high grade (LG, HG) according to the severity of inflammation. Results: LEL was identified in all types of prostatic specimens and in all types of prostatic CI: in 70.9% of patients with HP; in 100% of cases with NSGP; in 68.7% and in 80% adjacent to BPH and PCa respectively. Statistical analysis showed a significant correlation of the presence of LEL with HG CI (p<0.001). LEL showed strong membranous PD-L1 expression. Conclusions: The study presents the first attempt to examine LEL in inflammatory human prostate. PD-L1 positive LEL have no diagnostic organ specificity, although they are a constant histological finding in HG prostatic CI. LEL, inducible after birth by CI, are an integral part of prostate-associated lymphoid tissue (PALT) and of the inflammatory prostatic microenvironment.
In the present work, the formation of optical vortex in waveguides, with spatial dependence of the nonlinear refractive index, is studied. The propagation of such type of laser pulses is governed by a system of amplitude equations for x and y components of the electrical field in which the effects of second-order dispersion and self-phase modulation are taken into account. The corresponding system of equations is solved analytically. New class of exact solutions, describing the generation of vortex structures in the optical fibers with spatial dependence of the nonlinear refractive index and anomalous dispersion, are found. These optical vortices admit only amplitude type singularities. Their stability is a result of the delicate balance between diffraction and nonlinearity, as well as nonlinearity and angular distribution. This kind of singularities can be observed as a depolarization of the vector field in the laser spot.
In the present work the propagation of bright solitons under the influence of third-order of linear dispersion and self-steepening effect in single-mode fibers is analytically studied. Such optical pulses can be observed as a result of the dynamic balance between higher orders of dispersive and nonlinear phenomena. New analytical solutions of the nonlinear amplitude equation (NAE) in the form of cnoidal waves are found. The solutions are presented by Jacobi elliptic delta functions. It is shown that at certain values of the parameter k, representing modulus of ellipticity, the solutions can be reduced to sech-soliton.
The crystal structure of N-(2-benzoyl-4,5-dimethoxyphenethyl)-2-phenylacetamide indicates that the compound crystallizes in the monoclinic C2/c space group with eight molecules in the unit cell. The heteroatoms from the amide group form a chain of intermolecular N-H ··· O hydrogen bonds propagating along the b axis. The carbonyl group from the benzoyl substituent participates in short contacts with two H-atoms from the ethyl or phenyl groups.
The article describes a string recognition approach, engraved in the parsers generated by Tunnel Grammar Studio that use the tunnel parsing algorithm, of how a lexer and a parser can operate on the input during its recognition. Proposed is an addition of the augmented Backus-Naur form syntax that enables the formal language to be expressed with a parser grammar and optionally with an additional lexer grammar. The tokens outputted from the lexer are matched to the phrases in the parser grammar by their name and optionally by their lexeme, case sensitively or insensitively.
This study aimed to investigate how family structure varies and identify its time trends in European and North American countries using data from seven surveys conducted between 1994 and 2018 according to the Health Behaviour in School-aged Children (HBSC) study. The current family structure in 44 countries was described and time trend analysis of 28 countries was performed. Adolescents were asked whom they lived with in their home to describe family structures. Family structures showed distinct patterns and dynamics between countries. In 2018, in all countries, 73% of adolescents lived with both their mother and father; 14% and 5% of adolescents lived in a single-parent family and stepfamily, respectively; and around 9% of adolescents lived in another family type. In the period 1994–2018, the proportion of young people living in intact families decreased from 79.6% to 70.0%, on average about 10 percentage points. There were no significant changes in the prevalence of single-parent families and stepfamilies, but a significant increase in the number of adolescents living without either parent was revealed. The findings have implications for cross-national adjustment of adolescent health, well-being, and behaviours, and for critical analysis of socioeconomic family resources.
The purpose of this article is to explain the principle behind practice tests based on authentic short stories in English, describe their construction, and outline their ap­plication which aims to increase student knowledge and skills in a foreign language. The methodology employs digital practice tests created following a set of criteria for test development based on Bloom’s taxonomy. The results of the study indicate certain benefits of the practice tests: short stories introduce new vocabulary and the tests provide reinforcement, which both facilitates and motivates the students.
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891 members
Siyka Kovacheva
  • Department of Applied and Institutional Sociology
Ivan Ganchev
  • Faculty of Mathematics and Informatics
Ilia Iliev
  • Department of Biochemistry and Microbiology
Meglena Zlatkova
  • Department of Ethnology
Dimitar Mekerov
  • Department of Algebra and Geometry
"Tzar Asen" 24 str., 4000, Plovdiv, Plovdiv, Bulgaria