Dragoljub Lj. Mirjanić

Phonon Participation in Thermodynamics and Superconductive Properties of Thin Ceramic Films

Jovan P. Setrajcic1, Vojkan M. Zoric1, Nenad V. Delic1, Dragoljub Lj. Mirjanic2 and Stevo K. Jacimovski3 1University of Novi Sad, Faculty of Sciences, Department of Physics, Novi Sad 2University of Banja Luka, Faculty of Medicine, Banja Luka, Academy of Sciences and Arts of the Republic of Srpska, Banja Luka 3Academy of Criminology and Police, Belgrade 1Vojvodina− Serbia, 2Republic of Srpska − B&H 3Serbia

Electron spectra in low-dimensional crystalline systems

Considering the models of spatially bounded structures and with broken translational symmetry (ultrathin films, quantum wires and dots), we have found the electron spectra using the method of two-time anticommutator Greens functions. The electron spectra are distinctly discrete and possess gaps (which we the consequence of the spatial boundedness of the system). Using the definition of the activation temperature of the electron subsystem we connected these results with better superconductive properties of micro samples, which can be a possible explanation of high critical temperature of HTC ceramics.

Energy efficiency of PV solar plant in real climate conditions in Banja Luka

In this paper comparison of experimentally obtained results of energy efficiency of PV solar plant of 2.08 kWp installed on the roof of the Academy of Sciences and Arts (ASARS) in Banja Luka (Republic of Srpska) in the real climate conditions in 2013 and 2014 are given. It was found that energy efficiency of PV solar plant from April till November 2013 was 12.28%, and in same period in 2014 was 13.03%. Also, it was found that the increase in the ambient temperature by 1°C, PV solar plant efficiency decreases by 0.43% from April till November 2013, and by 0.27% in the same period in 2014.

ASSESSMENT OF THE POSSIBILITIES OF BUILDING INTEGRATED PV SYSTEMS OF 1 kW ELECTRICITY GENERATION IN BANJA LUKA

The paper focuses on the analysis and assessment of the possibilities of building integrated PV (BIPV) systems of 1 kW electricity generation in Banja Luka in the Republic of Srpska. Special attention was paid to average monthly sum of global solar irradiation per square meter received by horizontally, optimally and vertically inclined and south-oriented solar modules of 1kW BIPV system and total for year electricity production from 1 kW BIPV system with horizontally, optimally and vertically inclined and south-oriented solar modules of different materials for Banja Luka, obtained by PVGIS. In addition, comparison was made of total for year electricity production of 1kW BIPV system with horizontal, optimal and vertical inclination and south-oriented solar modules of monocrystalline silicon, CdTe and CIS in Banja Luka. The research estimated the proportion of BIPV systems power generation according to different types of PV modules and installation methods. The data could serve as a useful reference for the application of BIPV systems in buildings.

Adaption and application of the Green function method to research on molecular ultrathin film optical properties

Interest in the study of the exciton subsystem in crystalline structures (in this case nanostructures, i.e. thin films) occurred because dielectric, optical, photoelectric and other properties of materials can be explained by means of it. The basic question to be solved concerning theoretical research into the spatially strongly bounded structures is the inability to apply the standard mathematical tools: differential equations and Fourier analysis. In this paper, it is shown how the Green function method can also be efficiently applied to crystalline samples so constrained that quantum size effects play a significant role on them. For the purpose of exemplification of this methods application, we shall consider a molecular crystal of simple cubic structure: spatially unbounded (bulk) and strongly bounded alongside one direction (ultrathin film).

Dielectric properties of molecular crystalline films

A microscopic theory of dielectrical properties of thin molecular films, was formulated in bosonic and nearest-neighbor approximation. The dispersion law of harmonic exciton states were calculated using the method of two-time, temperature dependent Greens functions. It has been shown that two types of excitations can be occur: bulk and surface exciton states. Exciton spectral weights and space distribution along the direction of broken symmetry were analyzed as well. Calculating dynamical permitivity by the single-pole Greens functions it was shown that the threshold of light absorption can be moved along frequencies, changing the film thickness and the intensity of boundary perturbations. This can give a great contribution to practical ultrathin film engineering.

Electron spectra in crystal films

The dispersion law of electrons in film structures was derived by the method of two-time temperature dependent Greens functions. In variance from unbounded structures, the electron energy spectra in films possesses a gap and the zone of electron energies is narrower and strictly discrete. The magnitude of the gap and the zone width depend on film thickness and increase quickly as a function of it. These results allow us to make a breakthrough in nanoelectronics.

Thermodynamical characteristics of thin ferroelectric films

Abstract Thermodynamic characteristics of the KDP type ferroelectrics are analysed in the paper. Dispersion laws of the ferroelectric excitations in the thin ferroelectric films are considered. The ordering parameter was investigated at the low temperatures and at the temperatures near the phase transition temperature. The analysis shows that the spontaneous polarization in the film decreases more slowly with increase of the temperature than in the bulk structure. This conclusion is important for practical application because the thin films keep the ferroelectric properties at significantly higher temperatures than the bulk structures.

Theory and smart practice in the reduction of negative effects of urban heat island

Urban environment could be considered as a complex biotechnical system. Multidisciplinary, interdisciplinary, and intradisciplinary analyses are required in order to achieve sustainable urban communities and healthier cities, especially in the era of climate changes. The main goal of this paper is to investigate, select, and review the theories and smart practices in negative effects of urban areas heat problems reduction and to define the objective function of the issue. The objective function could be treated as the force, with magnitude and direction of influence that operates in a certain space, which is considered to control certain factors and parameters, including time as a dimension. Spatial and temporal gradient of canyon effect are defined with nodes canyon effects interaction. The thermal islands are analyzed by its volume, sources of heat, thermal gradient, with the goal to select strategies to reduce the negative effects of heat islands. Positive smart practice in the world is discussed. The purpose of this study is to find, by literature review and by holistic methodological approach application, better practice and adequate solutions for building, energy, water, and carbon balance in urban environment. The results are expected in the movement towards the blue and green cities.

Short History of Biomaterials Used in Hip Arthroplasty and Their Modern Evolution

The hip joint is one of the largest joints in the body and is a major weight-bearing joint. The function of the hip is to withstand body weight during standing and walking; during single leg stance the hip joint must carry a load three times greater the body weight. However, Joint degeneration is the final phase of the joint cartilage destruction, leading to severe pain, loss of mobility, and sometimes even angular deformity of the limbs. The primary reasons for a large number of total hip replacements are osteoarthritis and osteoporosis of the femoral neck, which often leads to hip fractures. One of the most successful techniques to restore function of a degenerated joint is the total joint replacement. In this surgical procedure, diseased cartilage and parts of the bone are removed and replaced with an appropriate joint prosthesis. Several types of materials and techniques have been developed for this purpose: glass, polymer, metal alloy, ceramics, etc. Earliest prosthesis designs and biomaterials that have been developed to treat osteoarthritic hip degenerated joint surfaces were for the most part empirical and unsuccessful. Joint replacement heralded a revolution after the materials and replacement procedures developed by Sir John Charnley. A modern total hip prosthesis consists of a femoral and acetabular component, where the femoral head is made of cobalt-chrome alloy, alumina or zirconium, and the stem component is now usually made of Ti- or Co-Cr-based alloy. The search for improved designs and new hip implant biomaterials with better biocompatibility and more desirable mechanical properties is still underway.