CONTEMPORARY MATERIALS

OVERVIEW OF THE ELECTROPHYSIOLOGICAL MODELS FOR THE LEFT VENTRICLE SIMULATIONS

2024-06-26T12:17:22+02:00

Electrophysiological models play a crucial role in understanding the complex dynamics of the heart, particularly the left ventricle. These models provide insights into the mechanisms underlying cardiac function and are essential for developing treatments for cardiac diseases. This paper presents an overview of various electrophysiological models used for simulating the left ventricle, including the van der Pol oscillator, the FitzHugh-Nagumo model, the Luo-Rudy model, and the O’Hara-Rudy model. By exploring the historical development, applications, and future directions of these models, this paper aims to highlight their significance and potential in advancing cardiac research and clinical practice.

MEASUREMENT AND ANALYSIS OF THE SPECTRAL EMISSION OF DIFFERENT TYPES OF DOMESTIC LAMPS IN THE BLUE LIGHT HAZARD WAVELENGTH RANGE

2024-06-26T12:19:21+02:00

In recent years, research on the photobiological impact of light on humans has been expanding and deepening. A significant part of this research is aimed at harmful effects such as the blue light hazard (BLH) on the retina of the human eye, for which there are standardized indicators in international normative documents. The current research presents laboratory measurements and results for the spectral emission in blue light hazard wavelength range for several domestic lamps: conventional tungsten filament lamps, halogen and metal halide lamps, compact fluorescent lamps, and state-of-the-art LED lamps. The measurements are conducted in a specialised laboratory in the Technological Park of the Technical University - Gabrovo using a photometer with a spectroradiometer in an integrating sphere and are processed with specialised software. Graphical comparisons of the spectral distributions of lamps in the visible part of the electromagnetic spectrum with the dangerous blue light wavelength range are shown. Data on the main photometric and colour characteristics - luminous flux, light efficacy, chromaticity coordinates, colour temperature, colour rendering index, and indicators for assessing the presence of dangerous blue light - blue light (weighted power) and blue light hazard factor (weighted power/ lux), for the different types of lamps, are shown in tables. Conclusions and recommendations regarding the choice of the type of domestic lamp and its colour characteristics to limit the level of dangerous blue light are made.

CHROMATOGRAPHIC APPROACH IN THE ASSESSMENT OF LIPOPHILICITY OF CHLOROACETAMIDE DERIVATIVES

2024-06-26T12:23:15+02:00

Chloroacetamides are widely used and highly effective herbicides. However, in addition to the positive aspects of application, their residues and metabolites remain in water and soil for a long time, which is why they represent a threat to the ecosystem. Lipophilicity, as the most important physico-chemical parameter closely related to bioavailability or potential biological activity of compounds for the newly synthesized chloroacetamide derivatives was determined computationally by using appropriate software packages, as well as experimentally, by using thin-layer chromatography on reversed phases, RPTLC C18/ UV254s in a mixture of water and four organic modifier, separately. It was found that the chromatographic behavior of the studied derivatives of chloroacetamide is affected to a small extent by the applied organic modifier, and to a greater extent by the total number of carbon atoms in the structure of their molecules, as well as by the type of hydrocarbon substituents. Dependence between the chromatographic parameters and the software-derived values of the partition coefficient as a standard measure of lipophilicity, as well as the relevant parameters of acute ecotoxicity, was examined by using the linear regression analysis. The reliable application of chromatographic parameters in the assessment of lipophilicity and ecotoxicity of the tested chloroacetamide derivatives was confirmed by the obtained mathematical models.

CHARGING AND DISCHARGING PROCESSES IN GRAPHITE-ZEOLITE/NaCl/MgCl2 SYSTEMS

2024-06-26T12:26:02+02:00

The most important characteristics of stationary battery installations are environmental friendliness and low price. Therefore, widely available and acceptable materials such as zeolite should be the focus of research in this field of science. The properties of a simple system consisting of graphite electrodes and zeolite/water/NaCl/MgCl2 electrolytes were tested. Energy density and recoverable energy storage were improved by adding a small amount of NaCl and MgCl2 to the zeolite/water electrolyte. The energy efficiency of the examined electro-capacitive systems in the DC electric field is generally below 10%.

GROWTH OF THE SUBURBAN AREAS DUE TO THE UNFAVORABLE CONDITIONS IN THE CITY - CASE STUDY THE CITY OF BIJELJINA

2024-06-26T12:28:13+02:00

This research includes several aspects of relocation of people from urban to suburban and rural areas. Those include the growth of population in the city which leads to massive construction, increased number of vehicles, converting of green areas to residential, one floor houses to multi floor buildings, etc. All mentioned led to the increase of temperature in city itself and made Bijeljina a heat island. The analyzed parameters in this research were number of inhabitants, land use of the area and thermal comfort for the period of 19 years (2005–2023) for the summer period when the temperatures are the highest. Obtained results show the three directions of suburban growth, and allocation of the population to the neighboring settlements. All three directions record intense growth of the population in its areas, with also the increase of business facilities, while still the agriculture being the dominant as the population income in most of the settlements.

TREATMENT OF WASTEWATER FROM CYANIDE-FREE ZINC PLATING

2024-06-26T12:29:42+02:00

Wastewater from the electroplating process often contains high concentrations of heavy metals, and must be treated before being discharged into public sewage systems or natural recipients. In this research, rinsing wastewater after acid and alkaline zinc electroplating process was treated by the electrocoagulation process. The experiments were performed in a batch electrochemical reactor made of polypropylene with a volume of 250 cm³. During all treatments constant mixing was performed at a speed of 200 rpm. Different electrode pairs (anode-cathode) were used: Fe-Fe, Al-Al, Fe-stainless steel (SS), Fe-Cu, Al-SS, Al-Cu. The success of the electrocoagulation process, in terms of zinc removal from cyanide-free electroplating rinsing wastewater, achieved with electrode pairs was: Fe-SS > Fe-Cu > Fe-Fe, respectively. The initial concentration of zinc in the wastewater was 173.5 mg/L, and after 60 minutes of treatment with the Fe-SS electrode pair it was achieved removal efficiency of 99.8%, while the specific energy consumption was 6.10 kWh per mᶟ of treated wastewater, or 8.74 kWh per kg of removed zinc.

COLORIMETRIC CHARACTERISTICS OF ULTRASOUND DYED TEXTILES WITH EXTRACTS OF Reynoutria japonica AND COPPER-BASED MORDANTS

2024-06-26T12:40:47+02:00

In this study, the influence of the type of extract (leaf and rhizome of R. japonica) and the type of copper-based mordant (copper (I) oxide - Cu2O and copper (II) sulfate - CuSO4) on the spectroscopic and antimicrobial properties of dyed wool knitwear was investigated. The antimicrobial activity of all samples was tested against the bacteria Staphylococcus aureus and Escherichia coli and the yeast Candida albicans. It was observed that knitted fabrics dyed with R. Japonica leaf extract and Cu2O show a better antimicrobial effect on S. aureus bacteria compared to knitted fabrics dyed with the addition of CuSO4. However, in the case of knitwear dyed with R. Japonica rhizome extract, we have the opposite case; CuSO4 proved to be better as a mordant. Conductance was measured using the dielectric spectroscopy method in the frequency range from 20 Hz to 100 kHz. The highest increase in conductivity was observed in the sample dyed with the rhizome extract of R. Japonica and Cu2O, where the increase at the frequency of 24 kHz was 20 times higher compared to the initial sample. The obtained results of the coloration spectrophotometric analysis of the samples show that the highest colour strength (K/S) was achieved with the sample dyed with R. Japonica leaf extract and CuSO4. The obtained results indicate the possibility of using the tested knitwear for antimicrobial as well as electro protection.

INFLUENCE OF CURRENT DENSITY ON MORPHOLOGY AND ROUGHNESS OF SONOELECTRODEPOSITED Zn-Co-Al2O3 NANOCOMPOSITE COATINGS

2024-06-26T12:43:41+02:00

Nanocomposite Zn-Co-Al2O3 coatings were electrodeposited from three different solutions, at 1, 2, 4 and 6A/dm2 current densities. Electrodeposition time was same for all samples, 15 minutes. Steel plates were used as cathodes while the anode was made of 99.99% pure zinc. All samples were mechanically and chemically prepared before electrochemical deposition of the Zn-Co-Al2O3 nanocomposite coating. Electroplating solutions were prepared from the chemicals of p.a. purity and aluminium oxide nanoparticles. All solutions possesed the same chemical composition, they differed only in the concentration of Al2O3. Solution R1 was without Al2O3, while solutions R2 and R3 contained 2g/dm3 and 5g/dm3 Al2O3, respectively. All experiments were performed in an electrochemical cell, with a volume of 100cm3 at room temperature and atmospheric pressure. The surface of the obtained coatings was examined by Leica EZ4 HD optical microscope at a 100x magnification, while the roughness was measured by TR200 device. Based on the obtained results, it can be concluded that the thickness of the obtained Zn-Co-Al2O3 coatings depends on the current density, but also on the composition of the solution. With increasing current density, the thickness of the coating increases, as well as the roughness of the deposited coatings, while the current utilization decreases with increasing current density, no matter of plating solution composition. The morphology of the coatings was generally uniform and compact with good adhesion.

THE STATIC ANALYSIS OF OPTIMUM CLOSURES OF THIN-WALLED CYLINDERS

2024-06-26T12:47:37+02:00

This paper deals with the problem of optimal vessel end closures subjected to internal pressure. This research aims to analyse the shapes of the middle surfaces in the case of one-arc and two-arc domes. The optimal solutions seek to minimize design complexity while satisfying geometric and strength requirements. For one-arc closures, meridional profiles are defined by a generalized ellipse as well as a Bezier polynomial of the 5th degree, while in the case of two-arc closures, they are represented by Bezier polynomials of the 3rd and 5th degree. The static analysis was conducted using the finite elements method implemented in the Simcenter Femap software package. Appropriate conclusions were derived by assessing equivalent stresses and criterion functions.

WATER QUALITY MANAGEMENT OF SOUTH MORAVA RIVER AND CRITERIA FOR ENVIRONMENTAL STATUS

2024-06-26T12:49:31+02:00

Water quality management is primarily performed through the control function. Water quality control in the South Morava is performed on a monthly basis by chemical and physical methods. Controlling is done at two measuring points from which the samples are taken, namely the village of Mezgraje, near the Railway Bridge, and the site of Mramora Novo Selo. Tests of water samples from the South Morava River included determination of: general parameters, nutrients, salinity, organic substances and microbiological parameters. Measured values of the investigated physicochemical parameters at the sampling location at Mezgraja village level, with the Railway Bridge, dominantly correspond to class I, except for BOD5 corresponding to class V, HPC corresponding to class IV, TOC, phenolic compounds and total nitrogen corresponding to class II, nitrites, orthophosphates, ammonium ion, copper and iron content corresponding to Class III. At the same location, the measured values of microbiological parameters correspond to Class IV. The water of South Morava River, from the physico-chemical aspect, has a mixed excellent to poor environmental status, while from a microbiological point of view it has a moderate environmental status at Mramor (Novo Selo) or poor environmental status at the level of the village of Mezgraja, at the Railway Bridge. The results of the water quality control tests show that the water is nutrient-poor and has microbiological parameters present in MPN/100 ml. Research in the field of water quality is one of the most important starting points in the proper conception of water management.

GENOTOXIC EFFECT OF NEWLY SYNTHESIZED NANOMATERIALS FOR POTENTIAL DENTAL APPLICATION

2024-06-26T12:51:03+02:00

Introduction: Biocompatibility is the property of a material to fulfill its function in the body without causing harmful side effects. To confirm biocompatibility, all newly synthesized materials must undergo numerous in vitro and clinical tests. The starting point is cytotoxicity and genotoxicity tests. This study aimed to determine the genotoxicity of newly synthesized nanomaterials based on calcium aluminates and calcium silicates with additional hydroxyapatite. Material and methods: The research was conducted at the Institute of Oncology in Belgrade. An alkaline version of the Comet test was used, following the recommendation of the international standard ISO / DIS 10993-3, and MRC-5 (normal human lung fibroblasts) was used as a cell line. Cells were grown in monolayer culture, in a complete nutrient medium, at a temperature of 37 °C in air enriched with 5% CO2 and saturated water vapor. The genotoxicity of calcium aluminate and mixtures of hydroxyapatite and calcium silicate was investigated. and untreated cells were used as controls. A 40x lens on a fluorescence microscope was used to visualize the DNA damage. Comet Assay IV (Perceptive Instruments) was used to statistically process the results. Results: ALBO-CA extract did not show a genotoxic effect, that is, the percentage of DNA damage at the highest applied concentration of cement of 100 mg / mL, was 9.6%. ALBO-CS-HA extract showed genotoxic potential at concentrations ≥ of 25 mg / mL Conclusion: Nanostructured calcium aluminate did not show genotoxic potential on human lung fibroblasts, unlike ALBO-CSHA, with recommendations for further studies.

COMPARATIVE ANALYSIS OF SUBCUTANEOUS CONNECTIVE TISSUE RESPONSES TO CALCIUM ALUMINATE AND NANOSTRUCTURED TRICALCIUM SILICATE NANOMATERIALS IN MOUSE MODELS

2024-06-26T12:54:13+02:00

This study aimed o evaluate connective tissue reaction to experimental nanomaterial based on calcium aluminate (ALBO-CA) and commercial nanostructured tricalcium silicate DiaRoot Bioaggregate (DiaDent Group International, Burnaby, BC, Canada) in Wistar rats.The study included 36 rats aged from 10 to 11 weeks. In all animals, an incision took place on the back and two pockets of 15 mm in depth were made, in which sterile polyethylene tubes with test materials (ALBO-CA -Group F, Diaroot Bioaggregat- Group C) were implemented. The empty half of the tubes represented a negative control. After 7, 15, and 30 days (n=12), the animals were euthanized, and the tissues were processed for histological evaluation using hematoxylin-eosin (H&E) staining. Patohystological analysis included: inflammation, bleeding, fibrous capsule, and tissue integrity around the implanted material. Data were analyzed by the Mann -Whitney U test.ALBO-CA induced a statically significantly less inflammatory response after 15 (U=42.000, Z=-2.460, p=0.014) and after 30 days (U=42.000, Z=-2.198 p=0.028). At the end observation period significantly less vascular congestion (U=42.000, Z=-2.460, p=0.014) and significantly greater preservation of connective tissue integrity was noted (U =36.000, Z=-2.769, p=0.006) after ALBO-CA implantation compared to Diaroot Bioaggregate. There were no statistically significant difference in the fibrous capsule formation between the tested materials across all observation periods. The tested materials proved to be biologically acceptable, with the experimental nanostructured ALBO-CA showing a slightly better tissue response after subcutaneous implantation in rats.