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The universities in Bulgaria operate in a very dynamic environment. The Ministry of Education and Science (MES) changes annually the requirements that their systems must meet. Changes can be small and affect only parts of the information systems in use or impose fundamental changes. To cope with this challenge, each university has a choice - either to move to a high level of digitalization or to maintain a minimum digitization of processes, so that no correction is needed in them, thus increasing the hours of work...

A directional coupler is a passive device designed to divide the power between its outputs in a given ratio. The value of this ratio depends on the resistances of the segments with which the device is assembled. It is important to understand how the miniaturization efficiency of a 3 dB directional coupler varies at different operating frequencies. Modeling and calculation of the characteristics of the devices was carried out in a specialized program Cadence AWR. The first step in the work was the design of taps ac...

The fixture of optical elements in optomechanical assemblies is a field that develops depending on ever-increasing demands on optical systems, namely on their performance, the accuracy of the fit for the lenses, on the installation space, the resistance of the assemblies, etc. Equally important is the view in terms of the production demand for such a system, which is also growing. The article presented here deals with a theoretical understanding of the issues concerning the free bonding of lenses, i.e. fitting the...

The matrix of silicon carbide (SiC) is sufficiently rigid and strong, but in order to fully realize its potential capabilities, it is necessary to reduce its fragility and increase its reliability when used under shock loading conditions, which is achieved by creating ceramic composites based on it. Zirconia (ZrO2) was chosen as a hardening additive, since it has very high resistance to crack propagation and thermal, electrical, optical, strength, and other properties. Stabilization of the cubic phase of zirconia ...

The article reports on detection of toxic effect of nanosized magnesium oxide on brain tissue of laboratory animals that have been given the substances via inhalation and orally. The experiment was performed on mature adult male Wistar rats (weight 250±15 g) and on BALB/C mice (weight 25±2 g). Detection of the nanoscale magnesium oxide toxic effects on brain tissue was conducted using multifractal image analysis of histology preparations with application of the binarization and constructing Voronoi diagrams from g...

Paper presents usage of viscoelastic material in the body of turning tool holder in order to damp the vibrations in the turning process. The standard approach to designing is the strength and stiffness based designing resulting from static material properties. However, each dynamically loaded structure is the subject of vibrations. Thus the dynamic material properties (damping measures) are of equal importance as vibrations are a part of the machines and devices performance. Their occurrence cannot be prevented be...

Currently, the urgent task associated with the development and production of new, cheaper, building materials. Rocks have a reserve of free internal energy, which is determined by the method of their formation. The use of this energy reserve can reduce the work that needs to be done during the technological transformation of raw materials in the production of building materials. In this paper, it is proposed to evaluate the efficiency of using various finely dispersed systems to use as a criterion - surface activi...

One of the most important parameters of pavement serviceability in terms of view road safety is without doubt skid resistance. By now, a number of different methods and devices have been developed for both friction and texture evaluation. However, while measurements of friction coefficients tend to be subject to a large number of boundary conditions, texture measurements are affected by device limits without the possibility of detecting surface irregularities at the microtexture level, which appears to be crucial ...

Based on the nanomaterials market research, the global production of cobalt (II, III) oxide (Co3O4), aluminum oxide (Al2O3) and magnesium oxide (MgO) nanoparticles is large-scale (> 100 tons/year), which leads to their contamination of environmental objects and accumulation in organisms. Research and scientific forecasting of the potential hazard and the features of the accumulation of Co3O4, Al2O3, and MgO nanoparticles have been carried out. According to the research results of the physical properties of the tes...

The work is devoted to the synthesis of epoxy derivatives based on hexachlorocyclotriphosphazene. The aim of this study is to synthesize a new epoxyphosphazene binder with reduced functionality, due to which the mass fraction of phosphorus in the synthesized compound increases, as well as its viscosity decreases, which makes it possible to fine-tune the density of the network formed during the curing of the binder. To achieve this aim, the tasks of choosing of mono- and difunctional substituents of chlorine atoms ...

This article presents the results of the studies that were conducted by the authors for determining the influence of the cycles of heat treatments on the structure and mechanical properties of dual-phase steel with a low manganese content. For the research in discussion, was used an alloy with 0.094% C and 0.53% Mn which was subjected to several cycles of heat treatments (consisting of full annealing, normalizing, subcritical annealing, full quenching, intercritical quenching). The metallographic analyzes were per...

The article presents results of the studies conducted by the authors for determining the influence of the structure succession on the volume fraction of martensite and ferrite microhardness in a dual-phase steel with low manganese content. For the research in discussion, an alloy with 0.094% C and 0.53% Mn (Si, Cr, Ni, Mo, Al, Cu, P, and S below 0.1%) was used. This alloy was subjected to several cycles of heat treatments (consisting of full annealing, normalizing, subcritical annealing, full quenching, intercriti...

Purified natural clinoptilolite as well as clinoptilolite converted into hydrogen and sodium form have been contacted with 0.1 mol/L silver nitrate solution at a ratio solid to liquid equal to 1 to 20, in order to load silver ions (Ag+) on the zeolite support. It has been found that sodium modified clinoptilolite exchanged in highest degree Ag+ ions, followed by natural zeolite. Preliminary transformation of natural clinoptilolite into hydrogen form leads to decreasing of zeolite ability to bind Ag+ ions. The kine...

Nanoparticles, due to small size and capacity to remain in suspension, are very efficient to remediate aquifers contaminated. However, due to their small size, while nanoparticles are traveling through porous media, they can rapidly aggregate, causing their settling and deposition. These phenomena produce issues for in situ remediation, such as the loss in chemical reactivity and the unknowing about the nanoparticles distribution when they are injected in situ. Laboratory experiment has been carried out with groun...

Silicon carbide is a promising material for heat-loaded units due to its high strength at elevated (up to 1500 °C) temperatures and excellent thermal conductivity. Silicon carbide ceramics is widely used for structural applications, yet production of such materials belongs to extremely energy-consuming industries, thus it becomes an important task to carefully adjust ceramics compositions and methods of manufacturing. The present paper discusses the correlation between mechanical behaviour (dependent variable, cal...

One of the possible ways of transition to the eco-friendly energy is widening the use of the solar cells. It requires the enhancement of their efficiency and the reduction of the cost of manufacture. One of the most common tools for producing silicon films for the solar cells is the Plasma Enhanced Chemical Vapor Deposition (PECVD). The present paper describes a new Particle-In-Cell code for simulation of the PECVD reactor. The goal of the research is the optimization of real PECVD reactor by means of the simulati...

Large territories in many countries of the world are occupied by tailings after placer gold excavation, including Russia (the Urals, Altai, Yakutia, Chukotka, etc.). The technologies of gold excavation for placers were intended for extraction of the most wide-spread gold grains. As a result, small gold particles were often removed in tailings. Long period of staying of fine gold particles in tailings has been accompanying the process of ?new? metal (secondary gold) origin. Detailed investigations of ?new? gold (gr...

The cement industry, along with metallurgy, electric power, chemistry, and mechanical engineering, determines the economic potential and level of industrial development of any country. The role of cement in modern construction is very large, at the moment it cannot be replaced by anything equivalent. At the same time, cement production is extremely resource-and energy consumption industry, and its production accompanied by a large amount of greenhouse gases. According to forecasts of scientists, emissions of carbo...

Various eco-friendly and cost-effective hydrocarbons clean-up methods based on natural sorbents were developed and tested, in order to prevent the massive environmental damage due to the petroleum spills. Among these sorbents, natural zeolitic tuffs are easily available and have numerous adsorptive properties that make them appropriate for the removal of petroleum substances. This study aims to preliminary investigate the sorption capacity of natural zeolites from a deposit located at Racos, Brasov County, Romania...

At present, the issue of environmental protection is very important in the world. In Portland cement production a large amount of greenhouse gas is released, namely 8 % of all world anthropogenic emissions. CO2 emissions from cement production are associated with fuel combustion and decomposition of limestone during firing of the raw mixture. Scientists around the world are trying to reduce the amount of carbon dioxide released by replacing the main component of cement ? clinker with various additives. In recent y...

The research and evaluation of calcium oxide nanoparticles? (CaO) accumulation and toxicity when ingested orally were carried out. The results, obtained after the study of CaO nanopowder by scanning electron microscopy method, demonstrate, that a large proportion of particles in its composition have a size of up to 100 nm, a rounded shape and a smooth surface, while the microparticles of the chemical analog have a cubic shape with a rough surface. According to the death rate, LD50 values were calculated for male W...

In a study over a two-month period, identifying the volatile compounds of potential odorous substances (hydrogen sulfide, ammonia, benzene, toluene, xylene, etc.), which periodically spread in the area adjacent to the Free Port of Riga and have a negative impact on the quality of life and health of residents of these areas. Potential sources of odours were identified as far as possible and the results obtained were assessed in the context of complaints from citizens and the results obtained in the reference measur...

The aim of this work is to experimentally study the synthesis of carbon nanotubes and nanofibers by catalytic pyrolysis of methane-hydrogen mixtures, as well as to develope a kinetic scheme that takes into account the accelerating and suppressing effect of hydrogen on pyrolysis. Carbon nanotubes were synthesized in a laboratory kinetic setup with a vertical quartz reactor at a temperature of 700?. The oxide system (Fe0.45Co0.15Al0.40)2O3 obtained by combustion method was taken as a catalyst. The hydrogen concentra...

The research of 2D carbon-based nanomaterials has become very intensive since the discovery of graphene. Many different preparation procedures of graphene and graphene derivatives have been reported. The aim of this paper was to prepare and characterize partially oxidized graphite oxides, which were prepared from nanographite by adding different amounts of potassium permanganate as an oxidizing agent. The C/O ratio was evaluated from X-ray photoelectron spectroscopy, energy dispersive spectroscopy, and elemental a...

Being released into the environment, the nanosized particles are present in it in the form of a colloid. At the same time, the colloid has an ability to change its properties, including its dimensionality, depending on the physical conditions, as well as composition of the dispersing medium. Nevertheless, this circumstance is irrelevant when assessing the risk associated with the spread of nanosized particles in the environment. The conditions under which the colloid retains its property of nanoscale dimensionalit...