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Item Anti-Coronavirus Activity of Chitosan-Stabilized Liposomal Nanocarriers Loaded with Natural Extracts from Bulgarian Flora(2024-09-01) Gyurova A.; Milkova V.; Iliev I.; Lazarova-Zdravkova N.; Rashev V.; Simeonova L.; Vilhelmova-Ilieva N.Disease’s severity, mortality rates, and common failures to achieve clinical improvement during the unprecedented COVID-19 pandemic exposed the emergency need for new antiviral therapeutics with higher efficacy and fewer adverse effects. This study explores the potential to encapsulate multi-component plant extracts in liposomes as optimized delivery systems and to verify if they exert inhibitory effects against human seasonal betacoronavirus OC43 (HCoV-OC43) in vitro. The selection of Sambucus nigra, Potentilla reptans, Allium sativum, Aesculus hippocastanum, and Glycyrrhiza glabra L. plant extracts was based on their established pharmacological and antiviral properties. The physicochemical characterization of extract-loaded liposomes was conducted by DLS and electrokinetics. Encapsulated amounts of the extract were evaluated based on the total flavonoid content (TFC) and total polyphenol content (TPC) by colorimetric methods. The BALB 3T3 neutral red uptake (NRU) phototoxicity/cytotoxicity assay was used to estimate compounds’ safety. Photo irritation factors (PIFs) of the liposomes containing extracts were <2 which assigned them as non-phototoxic substances. The antiviral capacities of liposomes containing medicinal plant extracts against HCoV-OC43 were measured by the cytopathic effect inhibition test in susceptible HCT-8 cells. The antiviral activity increased by several times compared to “naked” extracts’ activity reported previously. A. hippocastanum extract showed 16 times higher inhibitory properties reaching a selectivity index (SI) of 58.96. Virucidal and virus-adsorption effects were investigated using the endpoint dilution method and ∆lgs comparison with infected and untreated controls. The results confirmed that nanoparticles do not directly affect the viral surface or cell membrane, but only serve as carriers of the active substances and the observed protection is due solely to the intracellular action of the extracts.Item Influence of the support on the morphology of Co-Sn, Ni-Sn, Co-Ni nanoparticles synthesized through a borohydride reduction method applying a template technique(2018-01-01) Markova I.N.; Piskin M.B.; Zahariev I.Z.; Hristoforou E.; Milanova V.L.; Ivanova D.I.; Fachikov L.B.Intermetallic (Co-Sn, Ni-Sn, Co-Ni) nanoparticles have been synthesized through a borohydride reduction with NaBH4 in aqueous solutions of the chloride salts of Co, Ni, Sn at room temperature using a template technique with a carbon support. As a result nanocomposite materials have been obtained in situ. The ratio of the metallic components has been chosen according the phase diagrams of the relevant binary (Co-Sn, Ni-Sn, Co-Ni) systems: Co:Sn=35:65, Ni:Sn=45:55, Co:Ni=50:50. As carbon supports have been used graphite and carbon powder. To avoid the nanoparticle's aggregation β-cyclodextrin has been added to the reaction solutions. To study the influence of the supports used on the morphology, specific surface area, elemental and phase composition of the synthesized intermetallic nanoparticles and their carbon nanocomposites SEM, EDS, BET, and XRD investigation techniques have been used. The particle's morphology varies with the different supports, but in the all cases it is typical for alloyed materials. The nanoparticles are different in shape and size and exhibit a tendency to aggregate. The last-one is due to the unsaturated nanoparticle's surface and the existing magnetic forces. Regardless of the elemental composition, the nanosized particles are characterized by a relatively high specific surface area (SSA). The Ni-Sn nanoparticle have the largest SSA (80 m2/g), while the Co-Sn particles have the lowest SSA (69 m2/g). The use of a carrier modifies the SSA of the resulting nanocomposites differently depending on the size and shape of the carrier's particles. The studies conducted on the intermetallic nanoparticles synthesized with various carriers demonstrate that the particle's morphology, size, and specific surface area for the different supports are suitable for use as catalysts, electrode materials in Li-ion batteries and as magnetic materials for biomedical applications.Item Predicting Petroleum SARA Composition from Density, Sulfur Content, Flash Point, and Simulated Distillation Data Using Regression and Artificial Neural Network Techniques(2024-08-01) Shiskova I.; Stratiev D.; Sotirov S.; Sotirova E.; Dinkov R.; Kolev I.; Stratiev D.D.; Nenov S.; Ribagin S.; Atanassov K.; Yordanov D.; van den Berg F.The saturate, aromatic, resin, and asphaltene content in petroleum (SARA composition) provides valuable information about the chemical nature of oils, oil compatibility, colloidal stability, fouling potential, and other important aspects in petroleum chemistry and processing. For that reason, SARA composition data are important for petroleum engineering research and practice. Unfortunately, the results of SARA composition measurements reported by diverse laboratories are frequently very dissimilar and the development of a method to assign SARA composition from oil bulk properties is a question that deserves attention. Petroleum fluids with great variability of SARA composition were employed in this study to model their SARA fraction contents from their density, flash point, sulfur content, and simulated distillation characteristics. Three data mining techniques: intercriteria analysis, regression, and artificial neural networks (ANNs) were applied. It was found that the ANN models predicted with higher accuracy the contents of resins and asphaltenes, whereas the non-linear regression model predicted most accurately the saturate fraction content but with an accuracy that was lower than that reported in the literature regarding uncertainty of measurement. The aromatic content was poorly predicted by all investigated techniques, although the prediction of aromatic content was within the uncertainty of measurement. The performed study suggests that as well as the investigated properties, additional characteristics need to be explored to account for complex petroleum chemistry in order to improve the accuracy of SARA composition prognosis.Item Utilization Perspectives of Lignin Biochar from Industrial Biomass Residue(2023-06-01) Naydenova I.; Radoykova T.; Petrova T.; Sandov O.; Valchev I.The present study aimed at utilizing technically hydrolyzed lignin (THL), industrial biomass residue, derived in high-temperature diluted sulfuric acid hydrolysis of softwood and hardwood chips to sugars. The THL was carbonized in a horizontal tube furnace at atmospheric pressure, in inert atmosphere and at three different temperatures (500, 600, and 700 °C). Biochar chemical composition was investigated along with its HHV, thermal stability (thermogravimetric analysis), and textural properties. Surface area and pore volume were measured with nitrogen physisorption analysis often named upon Brunauer–Emmett–Teller (BET). Increasing the carbonization temperature reduced volatile organic compounds (40 ÷ 96 wt. %), increased fixed carbon (2.11 to 3.68 times the wt. % of fixed carbon in THL), ash, and C-content. Moreover, H and O were reduced, while N- and S-content were below the detection limit. This suggested biochar application as solid biofuel. The biochar Fourier-transform infrared (FTIR) spectra revealed that the functional groups were gradually lost, thus forming materials having merely polycyclic aromatic structures and high condensation rate. The biochar obtained at 600 and 700 °C proved having properties typical for microporous adsorbents, suitable for selective adsorption purposes. Based on the latest observations, another biochar application was proposed—as a catalyst.Item On the concentration unsteadiness of chemical vapour deposition with a precursor sublimated from packed bed of solid source. Problems with multicomponent coatings(2013-01-01) Peev G.; Tsibranska I.In some CVD processes the precursor is introduced into the reactor as vapor obtained by sublimation from particles of solid source forming packed bed in a column, where through a carrier gas passes. A typical example is the deposition of metal or metal oxide using its carbonyl compound. The study evaluates by mathematical modeling the effect of particle size reduction due to sublimation on the composition of the gas phase entering the reactor. A set of differential equations describing the convective solid to gas mass transfer process in the column is formulated. Equations for precursor equilibrium partial pressure, mass transfer coefficient, diffusivity and axial dispersion coefficient found from literature are added and the model is solved numerically by the method of finite differences. On the example of W(CO)6 the influence of the carrier gas flow rate, temperature and CVD duration on the change of the precursor concentration is revealed. The calculated alterations are significant and may spoil the running experiments. As to prevent this problem three approaches are suggested allowing the maintenance of the reactor inlet precursor concentration in reasonable limits: (i) to use a sufficiently high initial bed for saturation of the carrier gas during the entire particular experiment; (ii) to increase step-bystep in time the bed temperature; (iii) to increase step-by-step in time the carrier gas velocity in the column on the account of its stream by-passing the column. In all three approaches the model allows to calculate the necessary factors, i.e. the sufficient bed height, the temperature and velocity increment in time. Some numerical experiments employing the suggested approaches with approximately constant precursor concentrations are illustrated. Approaches how to proceed when multicomponent coating is to be deposited are discussed. The main conclusion is that the CVD processes should be carefully prepared accounting for a possible unsteadiness and the concentration of the precursor at the reactor inlet should be monitored.. © 2013 The Authors.Item Density Functional Theory Prediction of Laser Dyes–Cucurbit[7]uril Binding Affinities(2024-09-01) Petkova V.; Dobrev S.; Kircheva N.; Nazarova D.; Nedelchev L.; Nikolova V.; Dudev T.; Angelova S.Among a variety of diverse host molecules distinguished by specific characteristics, the cucurbit[n]uril (CB) family stands out, being widely known for the attractive properties of its representatives along with their increasingly expanding area of applications. The presented herewith density functional theory (DFT)-based study is inspired by some recent studies exploring CBs as a key component in multifunctional hydrogels with applications in materials science, thus considering CB-assisted supramolecular polymeric hydrogels (CB-SPHs), a new class of 3D cross-linked polymer materials. The research systematically investigates the inclusion process between the most applied representative of the cavitand family CB[7] and a series of laser dye molecules as guests, as well as the possible encapsulation of a model side chain from the photoanisotropic polymer PAZO and its sodium-containing salt. The obtained results shed light on the most significant factors that play a key role in the recognition process, such as binding mode, charge, and dielectric constant of the solvent. The observed findings provide valuable insights at a molecular level for the design of dye–CB[7] systems in various environments, with potential applications in intriguing and prosperous fields like photonics and material science.Item DESIGN IMPROVEMENT OF THE STEP-WEDGE DIES AND EXPERIMENTAL STUDY OF THE FORGING PROCESS OF 45 STEEL BILLETS(2024-01-01) Tolkushkin A.; Naizabekov A.; Panin E.; Yordanova R.; Shvarts D.; Tsyba P.; Volokitina I.; Rovin S.; Esbolat A.In this paper, a forging tool of a new design is proposed, which allows to implement shear and alternating strain in the entire volume of the deformed billet with a smaller change in its initial dimensions. To confirm the effectiveness of the proposed new forging tool in obtaining billets and forgings of the plates and slabs type of the required quality, a laboratory experiment was conducted. During the laboratory experiment, the forging of billets made of the steel 45 was carried out in such forging tools as step-wedge dies of two different variants (proposed and previously known) and in step dies. Analysis of the shape change of billets and the evolution of the microstructure of steel after two deformation cycles showed that the use of the step-wedge dies with a wedge protrusion on the upper die and a wedge cavity on the lower die is more promising for forging billets and forgings of the plates and slabs type with a given level of mechanical properties, since it allows to obtain a fine-grained structure with a smaller change in the initial dimensions of the billet.Item Synthesis and analgesic activity of new analogs of FELL tetrapeptide containing D-Phe in the first position(2024-01-01) Borisova B.; Nocheva H.; Iliev I.; Laronze-Cochard M.; Gérard S.; Petrin S.; Danalev D.Pain, whether acute or chronic, is one of the most unpleasant experiences. It can have different origins and long-term effects on the body starting from the trivial once such as physical discomfort, accompanying by emotional distress and going to the more serious like depression, anxiety, and social isolation. The removal and proper treatment of the pain is a problem highly dependent on both the source and the individual features of each organism. Herein the view is turned on investigation of activity of new analogs of natural FELL peptide as a promising alternative of the existing antipain molecules. All targeted compounds are obtained by means of conventional peptide synthesis on solid support using standard Fmoc/OtBu approach and their analgesic activity was evaluated by Paw-pressure (Randall-Selitto) test. Determination of the in vivo analgesic activity of the newly synthesized substances showed that the substitution of both Leu (BB11) with Val residues (BB8) increased PPT of the experimental animals on the 10th min, compared to the values after the nonmodified parent molecule injection. On the 20th and the 30th min, BB8 analgesic activity was comparable to BB11 and further a decrease in the PPT was observed. In addition, compared to the controls, analgesia exists until the end of the monitored period of 50 min. The other three newly synthesized substances including Nle (BB6), Ile (BB7) and triple Leu (BB5) instead of double Leu residues showed time-varying short-term analgesic activity, which did not reach that of the parent molecule BB11. Final results show that D-Phe in a first position of the molecule, combined with both Leu residues in the third and fourth positions are the best combination concerning analgesic activity. In addition, lengthening the peptide chain by adding one more hydrophobic residue has also a positive effect on the obtained analgesia. Cytotoxicity of final molecules is significantly lower than those of the positive control SLS, combined with complete hydrolytic stability, which allows their safety use in pharmacy.Item A note on a transverse magnetic field controlled co-current bubble column Barbotažna kolona sa istostrujnim tokom faza u transferzalnom magnetnom polju(2024-10-04) Hristov J.Y.; Pešić R.D.An experimental study has been carried out investigating the fluidization behavior of a bubble column with a bottom magnetic particle bed controlled by an external transverse magnetic field. The magnetization-first/gas-scanning mode was applied, at up to 45 kA m-1 field intensity, with liquid superficial velocities of up to 20 mm s-1 and with a gas flowrate of up to 8 m3 h-1. Particle fractions of two different sizes of up to 1 mm were used. The focus has been both on the three-phase magnetic particle bed expansion playing the role of a gas distributor and the gas holdup of the abovepositioned two-phase section, as well as related column parameters. Piezometric measurements have been performed that provided detection of the position of the interface between the two column sections without visual observation, as well as the gas holdup in the two-phase zone. The bed expansion was strongly affected by the bed state created by the initially established liquid flow rate. The results showed that the intensity of the field applied to the magnetic solids allows control both of bed expansion and internal bed structure, so the applicability of magnetically assisted three-phase beed as a gas distributor in bubble column seems promising.Item Chemical and technological characterization of medieval glass bracelets from South-East Bulgaria(2014-01-01) Georgieva R.; Detcheva A.; Dimitriev Y.The present paper deals with chemical and physicochemical characterization of seven glass fragments of medieval glass bracelets from South-East Bulgaria. Samples were investigated by Fourier-transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM) and differential thermal analysis (DTA). Gravimetric chemical analysis was used for silica assessment. Flame photometry was applied to determine sodium and potassium content while aluminium, calcium and magnesium were determined by flame atomic absorption spectrometry after dissolution using a mixture of acids. All investigated artefacts are soda-lime-silica glasses and when produced two different recipe norms were used. Important technological parameters of glass manufacturing were determined and discussed. This investigation throws light on the technological development and production of glass during medieval times. ©Versita Sp. z o.o.Item Attenuation of 1-chloro-2, 4-dinitrobenzene-induced inflammation in atopic dermatitis-like skin lesions in rats by a pyrrole containing FELL-NH2 bioconjugate: Cannabinoid receptor type 1 involvement(2024-01-01) Papadakis K.; Bezirci K.; Borisova B.; Vladimirova S.; Danalev D.; Handjieva-Darlenska T.; Tafradjiiska-Hadjiolova R.; Nocheva H.Atopic dermatitis (AD) is a chronic inflammatory skin condition of significant health and social importance, which justifies the search for new means of treatment. Since the endogenous cannabinoid system appears to be involved in the pathogenesis of AD, the proposed article summarizes the clinical impact on skin inflammation in a rat model of 1-chloro-2, 4-dinitrobenzene-induced atopic dermatitis-like condition after exogenous systemic administration of the cannabinoid receptor type 1 (CB1r) agonist anandamide, as well as after local treatment with a newly synthesized pyrrole moiety containing bioconjugate of FELL tetrapeptide with CB1r-dependent analgesic activity. The changes in skin lesions and ear thickness were estimated along with the CB1r expression immunohistochemically determined on skin punch biopsies. The results showed attenuation of skin lesions by anandamide and lack of positive effect after introduction of CB1r antagonist, accompanied by a change in CB1r expression, suggesting the involvement of the cannabinoid system in the defensive functions of the skin. The topically applied newly synthesized bioconjugate also favorably affected skin manifestations of inflammation, but without a change in CB1r expression, suggesting the involvement of other mechanisms in the reported effects.Item TREATMENT OF COPPER FLUE DUST FROM FLASH FURNACE WASTE HEAT BOILER FOR IMPURITIES CONTROL(2024-01-01) Kadiyski M.; Angelov N.; Iliev P.; Stefanov E.; Semerdzhiev T.; Sopotenska I.During the pyrometallurgical processing of copper sulphide raw materials, part of the charge leaves the furnace space together with the exhaust gases in the form of dust entrainment. Volatile components also pass into the dust-gas flow, due to which it is enriched with impurities, some of which are harmful to the technological process. The formed dust-gas flow passes through dust collection equipment, where the main part of it is captured. Most often, the captured dust is recirculated, which leads to a decrease in the productivity of the furnace unit and a gradual increase in the content of impurities in the condensed products of the smelting. To overcome these disadvantages, it is necessary to take part or all the recirculating dust out of the melting cycle and process it independently to extract the valuable metals and dispose of the harmful substances. In metallurgical practice, industrial application for the processing of recirculating dust entrainment has mainly been accomplished by hydrometallurgical methods based on treating the flue dust in aqueous solutions of acid or alkaline reagents. In the present research work, laboratory results on hydrometallurgical leaching of flue dust from a flash furnace waste heat boiler (FF-WHB) are presented. The effect of the main technological parameters affecting the degrees of recovery of the main metals in solution was studied. Based on the experimental results, the optimal conditions for hydrometallurgical treatment of the FF-WHB flue dust were determined. By treating the dust under optimal conditions, the main tasks of the research are achieved - removal of impurities harmful to the technological process and reduction of the amount of flue dust processed in the flash furnace.Item The Influence of Artificial Intelligence on the Automation of Processes in Electronic Commerce La influencia de la inteligencia artificial en la automatización de procesos en el comercio electrónico(2024-01-01) Halachev P.Objective: this study explores the transformative impact of Artificial Intelligence (AI) on automating business processes in electronic commerce (e-commerce), with a focus on enhancing efficiency and customer experience. Method: the research employs Deep Learning (DL) and Machine Learning (ML) as primary analytical tools to process and analyze data from e-commerce transaction records and customers’ browsing histories. Techniques such as data preprocessing, normalization, sentiment analysis, and advanced predictive models using Convolutional Neural Networks (CNNs), Recurrent Neural Networks (RNNs), and Support Vector Machines (SVMs) are utilized. Data collection was conducted using web scraping tools like Beautiful Soup and Scrapy, along with APIs from Amazon and Google. Results: the application of AI in e-commerce has led to significant improvements in inventory control, fraud prevention, and customer relations. ML algorithms have enhanced the estimation of product demand and personalized customer interactions, while DL has strengthened product recommendation systems and fraud detection mechanisms. The findings indicate that AI contributes to a more secure, faster, and smarter operational environment in e-commerce. Conclusion: this research highlights the substantial benefits and broad potential of AI in optimizing e-commerce operations, demonstrating that the integration of advanced AI technologies not only streamlines transactions but also reinforces platforms against fraudulent activities.Item How to avoid concentration unsteadiness with a CVD precursor delivery system employing bubbler?(2016-11-15) Peev G.; Peshev D.An approach of great certainty is suggested as to avoid concentration unsteadiness with a CVD delivery system employing bubbler. Assuming that the carrier gas has to be saturated of precursor vapour during the entire CVD experiment a set of equations has been selected from the literature for calculating the height of liquid layer in the bubbler which is necessary to this aim. The selection is made on the prerequisites that gas bubbles are spherical, diffusion of precursor vapour in them is molecular and it takes place during their rising only, which has a velocity equal to the terminal bubble velocity of rising. The errors at levels lower than the one for saturation are discussed. Heights of Al(CH3)3 calculated using the approach are compared to those at which the bubbler controlling LED indicator of Dow Electronic Materials lights green, amber or red.Item Influence of bis(triethoxysilylpropyl) tetrasulfide amount on the properties of silica-filled epoxidized natural rubber-based composites(2016-07-01) Al-Hartomy O.A.; Al-Ghamdi A.A.; Al Said S.A.F.; Dishovsky N.; Mihaylov M.The aim of the present article is to investigate the influence of the amount of bis(triethoxysilylpropyl) tetrasulfide on the curing characteristics and mechanical and dynamic properties of rubber composites based on epoxidized natural rubber (Epoxyprene 50) filled with 70 phr silica. The obtained results showed that although the interaction between the epoxy groups of epoxidized natural rubber and the silanol groups of silica through hydrogen bonds improves the dispersion of filler in the rubber matrix, the presence of silane coupling agents is necessary to obtain rubber compounds and vulcanizates with good vulcanization characteristics and mechanical and dynamic properties.Item Application of electron beam melting method for recycling of tantalum scrap(2024-10-01) Vutova K.; Stefanova V.; Iliev P.The paper presents a study on the refining efficiency of tantalum scrap when applying the electron beam melting method to recycle tantalum material. Thermodynamic analysis and experimental tests were carried out at different technological regimes to determine the optimal conditions for obtaining tantalum with high purity. The behavior of the controlled impurities (W, Nb, Mn, Ce, Cr, Mo, Al, Fe, etc) and the influence of the thermodynamic and kinetic technological parameters (temperature, melting time) on the refining efficiency of the studied material were investigated. At a temperature of 3700 K and a melting time of 10 min, the highest overall degree of refinement of 98.82% and the highest tantalum purity of 99.987% were achieved.Item Mechanism of Anodic Dissolution of Tungsten in Sulfate–Fluoride Solutions(2024-09-01) Bojinov M.; Penkova Y.; Betova I.; Karastoyanov V.Thin passive films on tungsten play an important role during the surface levelling of the metal for various applications and during the initial stages of electrochemical synthesis of thick, nanoporous layers that perform well as photo-absorbers and photo-catalysts for light-assisted water splitting. In the present work, the passivation of tungsten featuring metal dissolution and thin oxide film formation is studied by a combination of in situ electrochemical (voltammetry and impedance spectroscopy) and spectro-electrochemical methods coupled with ex situ surface oxide characterization by XPS. Voltametric and impedance data are successfully reproduced by a kinetic model featuring oxide growth and dissolution coupled with the recombination of point defects, as well as a multistep tungsten dissolution reaction at the oxide/electrolyte interface. The model is in good agreement with the spectro-electrochemical data on soluble oxidation products and the surface chemical composition of the passive oxide.Item ANALYSIS AND EVALUATION OF TRADE WITH CHEMICAL PRODUCTS(2024-01-01) Terzieva A.The purpose of this article is to analyse the trade with chemical products based on statistical data. The analysis and assessment were carried out on a database for the period 2015 - 2021 related to production, import, export in the “Chemical Products Manufacturing” sector. The main export and import partners by country are presented. Based on the analysis, conclusions were drawn regarding production of chemical products, the main export and import partners by country, and the importance of the considered industry for the development of the country’s economy.Item Producing bleached microcrystalline cellulose by two-stage dilute acid hydrolysis(2020-01-01) Valchev I.; Yavorov N.; Todorova D.This study investigates the process of producing microcrystalline cellulose (MCC) through two-stage acid hydrolysis with intermediate washing and removal of dissolved sugars. The temperature–time dependence shows fast xylose extraction in the initial phase of the process, while the glucose increases slowly and permanently over the period. After the second stage of hydrolysis, a cleaning effect and an increase in pulp brightness is observed. This method allows obtaining MCC, with high brightness and properties appropriate for usage in the pharmaceutical, cosmetics and food industries, as well as in the chemical industry, from paper grade pulp, which contains large amounts of hemicelluloses.Item SEM and EDX Study of Stainless Steels, Suggested as Human Body Implants(2018-06-12) Simitchiiska R.; Ivanova D.; Fachikov L.The most important requirement for any material used as an implant is to be biocompatible and not to cause undesirable effects in the human body. Corrosion of implants is included in the topic of biocompatibility because it is a determining factor in their sustainability and seamless fulfillment of their functional purpose. The work presents the results obtained in the comparative study of two austenitic stainless steels (Cr18Ni9 and Cr18Mn12N) in two models of artificial saliva, accepted as environments for testing the corrosion behavior of materials for these aims. The nature of the corrosion attack, the composition of the corrosion products at 37°C and the pH 5.5 and pH 6.75 of the model media were determined using physical methods such as SEM and EDX of investigation and analysis. It was found that Cr18Mn12N steel (0.61 % N), exhibits higher corrosion resistance.