CONTEMPORARY MATERIALS

MECHANICAL DEFORMATION OF CARBON NANOTUBES FOLLOWED BY LOCAL ELECTRON TRANSFER

Zoran P. Popović, Milan Damnjanović, Ivanka Milošević — Tue, 24 Dec 2024 00:00:00 +0100

Structure and geometry, modeling of carbon nanotubes enable to generate whole system from a single representative atom, by symmetry transformation. Hence, symmetry can be used to reduce calculations and prediction of electronics and wide range other relevant physical properties. Homogeneous mechanical deformation, that preserves symmetry, causes Hamiltonian reparameterization that influences change of energy bands change. For semiconducting carbon nanotubes, the most significant changes occur around Fermi level, where the process involves conducting and valence bands with the same angular quantum number. Deformations can be varied until bands come close to each other. Inside Brillouin zone bands approach always in two points symmetrical with respect to gamma point during homogeneous deformation of carbon nanotube. In accordance with the non-crossing rule, valence and conducted states never intersect if they have all quantum numbers the same, even in the moment they take cone-like shape when it comes to the change of Berry phase. This is interpreted as the change of average positions of two electrons simultaneously by tunneling from the onsite position toward the intermediate position between two neighbor sites or vice versa, despite that nanotube is semiconductor.

EXPLORING THE ADSORPTION POTENTIAL OF CARBON NANOTUBES AS EFFICIENT ADSORBERS FOR DRUG MOLECULES

Tue, 24 Dec 2024 00:00:00 +0100

This research observed the interaction between carbon nanotubes (CTs) and ephedrine (EH) molecules through a comprehensive utilization of density functional theory (DFT) and density functional tight-binding (DFTB) calculations applied to both periodic and isolated structures. EH, as a prevalent pharmaceutical pollutant, interacts with CTs and prominent organic nanostructures, prompting a meticulous examination of CTs’ potential as EH adsorbents. Multiple models of CTs were systematically scrutinized to elucidate their interaction with EH in detail. Given the substantial complexity of systems involving 122-187 atoms, the DFTB methodology was used for geometric optimizations. DFT computations were subsequently employed to procure accurate total energies, enabling the precise evaluation of binding energies between EH and nanotubes. The binding energies, ranging from ‒0.46 eV to ‒0.53 eV, confirm significant non-covalent interactions between CTs and EH. The shortest distance between EH and CT in all observed systems involves the hydrogen atom in the vicinity of the oxygen atom which is also crucial for non-covalent interactions. The outcomes underscore the propensity of CTs to adsorb EH molecules with notable binding energies, striking a balance between robust adhesion and facilitation of desorption under plausible experimental conditions. These findings not only shed light on the fundamental mechanisms governing the CT-EH interaction but also offer promising insights for the practical application of CTs in environmental remediation strategies targeting pharmaceutical pollutants.

ENVIRONMENTAL EFFICIENCY OF UV-ACTIVATED TiO2-MODIFIED ACRYLIC SELF-CLEANING SURFACES

Tue, 24 Dec 2024 00:00:00 +0100

Raising awareness of the importance of protecting the environment generates ever-increasing efforts of chemists and material scientists who seek new chemical compounds, production methods, and new types of surfaces and materials with self-cleaning abilities. Taking into consideration the data on increasing pollutant levels in the environment, materials that degrade pollutants could be an acceptable, sustainable solution to improve self-cleaning materials, especially when functionalizing large surfaces characteristic of building materials. The development of building materials that degrade polluting chemicals and carry out the mineralization of pollutant loads has now become a necessity. This work aimed to analyze the environmental performance of TiO2-modified acrylic surfaces under UV‒LED irradiation through the oxidative processes taking place on the illuminated surfaces. The simple approach of synthesis yielded highly affordable self-cleaning surfaces. The self-cleaning properties of these surfaces were tested against three frequently used textile dyes, rhodamine B, methylene blue, and methyl orange. It was demonstrated that rhodamine B was still present after 10 h of irradiation, while methylene blue and methyl orange were successfully self-cleaned after 3 h and 5 h, respectively.

THE MAP OF SOLAR RADIATION FOR FIVE MUNICIPALITIES LOCATED IN THE SOUTHEASTERN AND EASTERN PART OF THE REPUBLIC OF SRPSKA

Tue, 24 Dec 2024 00:00:00 +0100

The world’s transition process to renewable energy sources emerged as its commitment to limit global warming, mainly caused by the greenhouse gas emissions. Solar energy drives most of the processes on the planet, and it can be directly converted into electricity by using photovoltaic technologies. This way of electricity generation proves to be one of the most promising in the achieving the aforementioned goal. Among all renewables, Bosnia and Herzegovina mostly exploits hydropower, whereas its solar potential is almost untouched. In this paper, we produce the map of solar radiation for five municipalities located in the southeastern and eastern part of the Republic of Srpska. The map is obtained by using the Photovoltaic Geographical Information System (PVGIS) database. For selected towns, we present average daily irradiation, average monthly and yearly global horizontal irradiation, direct normal irradiation, global irradiation at optimum angle as well as diffuse to global ratio and average temperature. Besides, we give estimates of electricity that could be generated by solar power plants of 5 kWp nominal power, installed on the rooftops of households or buildings. These estimates may guide householders in their decisions to harvest solar energy as independent energy producers.

THE INHIBITIVE EFFECT OF THYMUS SERPYLLUM EXTRACT ON CORROSION OF STEEL

Tue, 24 Dec 2024 00:00:00 +0100

The study examined the inhibitive effect of thyme extract as a green inhibitor on the corrosion of two steel types, steel 1 - DC01 and steel 2 - X5 CrNi 18-10, in a 3% NaCl solution. Four test solutions were used: 1) blank 3% NaCl, 2) 3% NaCl + 0.5 g/L thyme extract, 3) 3% NaCl + 1.0 g/L thyme extract, and 4) 3% NaCl + 1.5 g/L thyme extract. Steel samples (3x3x0.2 cm) underwent chemical treatment before being exposed to the non-inhibited and inhibited solutions. Weight loss and electrochemical techniques, i.e. electrochemical impedance spectroscopy, were employed to investigate the corrosion rate and the inhibitive effect of thyme extract. All experiments were obtained on room temperature. After chemical treatment samples were immersed in blank and inhibited solutions for 2h, 4h, 6h, 8h, 24h, 48h и 168h. Based on the weight loss in steel samples for the time spent in prepared solutions, negative mass index of corrosion, Km - (g/m2h), depth corrosion indicator, π (mm/year), and degree of efficiency, protection factor, z (%), were calculated. The results of the gravimetric and electrochemical measurements showed that thyme extract had an inhibitive effect on the corrosion of the tested steels, but not sufficient to be recommended for commercial application. The average corrosion inhibition efficiency of thyme extract was below 60% for both steel types. For steel 1, the protection factor was above 80% only in solution 4 after 48h and 168h, while for steel 2, the protection factor was greater than 80% for all three inhibited solutions only after 168h. These findings suggest a very slow adsorption of phytochemicals from thyme extract on the surface of the tested steels.

IMPACT ANALYSIS OF HIGH-SPEED PROJECTILES ON GRANULAR MATERIAL

Tue, 24 Dec 2024 00:00:00 +0100

To enhance ballistic protection, this paper explores the benefits of granular materials compared to traditional materials used in this field. Currently, ballistic protection employs various materials either individually or in combination, such as armored steels, ceramic layers, composite materials, and granular structures. This study investigates the interaction of projectiles with each type of material, as well as the effects of combining different material layers. Granular materials consist of macroscopic particles, each with its own degrees of freedom. Collisions between these particles transfer energy from the solid body to individual particles, leading to energy dissipation that can halt the motion of particles within the granular material. The primary objective of this research is to analyze the results of projectile impacts on various material obstacles using a mathematical model for image processing.

CRITERIA AND INDICATORS OF FOREST MANAGEMENT IN THE REPUBLIC OF SRPSKA: CASE STUDY FOR KOTORVAROŠKO FOREST MANAGEMENT AREA AND KALINOVAČKO FOREST MANAGEMENT AREA

Zoran Govedar — Tue, 24 Dec 2024 00:00:00 +0100

Successful monitoring of forest management is based on criteria and indicators of the quality of forest ecosystems. In this sense, methods of comparing specific forests with reference models or the remaining old forest communities are used. Several parameters are used as indicators (quantity and quality of volume and volume increment, health status, degree of renewal, origin and method of establishment of forests, etc.). The indicators provide feedback based on which decisions can be made on future activities in order to improve the general condition and functions of forests. To implement the strategic goals of sustainable development of the European Union’s forestry, criteria are used that enable the adoption of forestry policy, forest management plans and the development of cross-sectoral cooperation. At the level of the European Union, six pan-European criteria have been defined, and due to the specifics of forestry and the regional character of the forests of the Republic of Srpska, for the purpose of drafting a new Forestry Development Strategy, harmonization was carried out on the basis of 40 sub-criteria and 70 indicators were defined. This paper includes quantitative indicators related to the silvicultural quality of stands.

SHOCK RESISTANCE OF SERBIAN SPRUCE WOOD FROM NATURAL AND PLANTED FORESTS

Tue, 24 Dec 2024 00:00:00 +0100

Among other things, the origin of the stand has a great influence on the quality of wood as a material. One of the important indicators of wood quality is the impact strength, because a large number of wood products crack under the influence of dynamic and not under the influence of static load. The aim of this work is to show the values of the impact bending strength (shock resistance) of Serbian spruce wood originating from natural stands and wood originating from planted forests, i.e. plantations. Correlations between impact bending strength and ring width, late wood content and wood density were determined by regression analysis.

CORRELATION ANALYSIS OF FORCE PARAMETERS ASSIGNED TO TIME SERIES DATA

Dragana Malivuk Gak, Zoran Rajilić — Tue, 24 Dec 2024 00:00:00 +0100

In a complex system, determinism without chaos, determinism with chaos, and stochasticity are intertwined, making the behavior of such a system difficult to predict. In this model, time series data are linked to time-dependent force parameters using Newton’s second law. The correlations between these force parameters are calculated, and a correlation matrix is created. The values of the determinants of the correlation matrix are then computed. The relationship between the determinant values and the prediction of the behavior of the complex system is considered. This type of rough forecasting model can be valuable for studying earthquakes, movements in stock markets and stock indices, as well as predicting fluctuations in daily and monthly temperatures.

CLINICAL EVALUATION OF THREE DIFFERENT SELF-ADHERING MATERIALS IN CLASS I RESTORATIONS

Tue, 24 Dec 2024 00:00:00 +0100

Introduction: Self-adhering flowable composite (Vertise Flow, Kerr, USA) simplified the long-lasting restorative procedure and opened a new chapter in conservative dentistry. This study aimed to evaluate the clinical effect of VF in comparison with resin-modified glass ionomer (Fuji II LC, GC, Japan) and glass carbomer (Glass Fill, GCP Dental, Vianen, Netherlands) in cavities of I class. Material and methods: Thirty patients with initial occlusal caries lesions were recruited in the study. For each patient, three restorations of I class were placed, one each with each examined material. All materials were applied according to the manufacturer’s instructions. The restoration was evaluated after one month and after 6 months using the modified United States Public Health Service criteria measuring (retention, postoperative sensitivity, color match, marginal adaptation, and marginal discoloration). For statistical analysis, Fisher’s test, Student’s test, Mann-Whitney, and Chi-square test were used to investigate changes in the follow-up periods. Results: After one month and after 6 months, there was no statistically significant difference between the three materials for all the parameters tested (p<0.05). Conclusion: VF showed a clinical effect similar to resin-modified glass ionomer (Fuji II LC, GC, Japan) and glass carbomer (Glass Fill, GCP Dental, Vianen, Netherlands) in cavities of I class after 6- months of follow-up.

COMBINED ORTHODONTIC - SURGICAL TREATMENT OF SEVERE SKELETAL CLASS III MALOCLUSSION

Tue, 24 Dec 2024 00:00:00 +0100

Severe skeletal Class III caused by mandibular prognathism often requires a combined orthodontic and surgical treatment to ensure a stable therapeutic outcome. This case presents the therapeutic approach for a male patient who had a 1/2 / Class III malocclusion, an anterior open bite of 3 mm, anterior crossbite and a concave profile before initiating orthodontic treatment. The initial lateral cephalogram indicated mandibular prognathism (SNB 83°), a skeletal Class III (ANB -1°) with a tendency towards an open bite (B 31°), proclination of the upper incisors (I/SpP 59°), and retroclination of the lower incisors (i/ MP 92°). Additionally, an increased mandibular corpus length of 4 mm was observed. The second lateral cephalogram, taken immediately before surgical intervention indicated a skeletal Class III (ANB -3°), an increased mandibular corpus by 5.85 mm, and corrected inclinations of the upper and lower incisors. Presurgical treatment with fixed appliances lasted 36 months, followed by bimaxillary surgery. Postsurgical orthodontic treatment lasted 8 months, during which the patient wore vertical intermaxillary elastics to establish a stable occlusion. At the end of the treatment, Class I occlusion was achieved with proper overbite and overjet, and a harmonious facial profile. The post-surgical lateral cephalogram showed correction from Class III to Class I skeletal relationship, proper inclination of the upper and lower incisors, and corrected mandibular corpus length. Combined orthodontic - surgical treatment can effectively correct severe skeletal discrepancies caused by mandibular overdevelopment.

THERAPY OF SKELETAL OPEN BITE AND SKELETAL CLASS III USING BIONATOR ACCORDING TO BALTERS TYPE III

Tue, 24 Dec 2024 00:00:00 +0100

In the period of puberty growth spurt, functional therapy can be successfully performed using the Bionator according to Balters. This case report aims to show the successful treatment of a skeletally open bite and overbite in a 13- year-old girl. The clinical examination revealed an enlarged lower third of the face, an open bite in the area of the frontal teeth (1.5 mm), and occlusion of / class III. Analyzing the initial profile teleradiograph, she was diagnosed with skeletal class III (ANB= -2°), skeletal open bite (B= 31°)), increased corpus of the mandible (by 8 mm), and a tendency towards a vertical type of facial growth (Bjork=400°). Balters type III bionator was indicated. The active phase of therapy lasted 19 months. During this period, the patient wore the appliance continuously during the day and night. Control examinations were performed every 6 weeks. After finishing the active phase of therapy, the value of the ANB angle on the control profile teleradiograph was 1°, with the presence of a vertical growth tendency (Bjork= 402°) and an enlarged body of the mandible of 3.3 mm. Clinical examination revealed a stable Class I occlusion and a flap depth of 2 mm. A bionator according to Balters, is a tooth-worn functional appliance, that gives a successful therapeutic result by affecting the change in the position and activity of the tongue while suppressing the excessive sagittal growth of the lower jaw.