Letters to the Editor
Jubilee: Milka Dzhidzhova, a Teacher [In Bulgarian}
M. Dobreva
Влезте в системата, за да прочетете пълната статияLetters to the Editor
Our Experience in Astronomy Learning [In Bulgarian]
S. Dimitrova
Влезте в системата, за да прочетете пълната статияEducation: Theory & Practice
Parametric Investigation of Optical Pulses in Nonlinear Isotropic Media
Резюме. In present work the parametric interaction of two optical waves presented by their slowly varying amplitude functions A1(z) and A2(z) in isotropic nonlinear medium is investigated. The corresponding system of nonlinear amplitude differential equations describes the processes of third-harmonic generation and THz generation in femtosecond region. It is found analytical solution of this system, characterizing the periodic exchange of energy between the two waves. The obtained result can be used for investigating different parametric processes in nonlinear dielectric medium, depending on the value of the wavenumber mismatch Delta k. These effects are directly related to modern communication systems and optical sensors.
Keywords: parametric interaction, narrow-band optical pulses, third-harmonic generation, four-wave mixing
A. Dakova, V. Slavchev, D. Dakova, L. Kovachev
Влезте в системата, за да прочетете пълната статияEducation: Theory & Practice
Investigation of Polymer Materials by Means of Electro-Acustical Pulse-Echo Method and Eddy Current Method [In Bulgarian]
Резюме. We have examined eight types of optical polymer plates including polymethyl methacrylate (PMMA) which is preferred material for ultrasonic purposes. Their longitudinal ultrasonic velocity and attenuation coefficient have been determined by means of pulse-echo technique. Comparison of acoustic properties of the investigated polymers and PMMA sample at 15MHz frequency. Obtained values of the ultrasonic attenuation coefficient and acoustic path length could be used to qualify homogeneity and isotropy of the polymer materials. Eddy current testing is based on the physics phenomenon of electromagnetic induction. The principle of the eddy current technique is based on the interaction between a magnetic field source and the test material. This interaction induces eddy currents in the test piece. The thickness of nonmetallic coatings on metals can be determined simply from the effect of liftoff on impedance. This method has used for measuring thickness and research a structure of thin walled non-conductive polymers.
Keywords: electro-acoustic, ultrasonic attenuation coefficient, pulse-echo method, eddy current method, optical polymers
R. Kasarov, S. Dinev
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Unifying the Analytical Solutions of the Geodesic Equations in Bondi-Gold-Hoyle Universe Model
Резюме. In this paper, we unify the study of the geodesics in the Bondi-Gold-Hoyle universe model. Thus, we obtain analytical solutions of the geodesic equations which describe the motion of space-like, time-like and light-like particles in the considered model. In the case of light-like geodesics, we get the solutions obtained by Marcheva & Ivanov, 2017.
Keywords: universe models, steady state theory, differential geometry, differential equations, geodesic equations
P.I. Narcheva, D.Y. Dakova, S.I. Ivanov
Влезте в системата, за да прочетете пълната статияEducation: Theory & Practice
Gamma Radiation and Its Effect on Desoxyribonucleic acid [In Bulgarian]
Резюме. A concise review of the effect of gamma radiation on the living organisms is presented. The medical topics of the problem are elucidated and commented.
Keywords: ionizing radiation, DNA, cell, Bergonie & Tribondeau rule
M. Vacheva, H. Stefanov, J. Gvozdejkova, Y. Eneva
Влезте в системата, за да прочетете пълната статияEducation: Theory & Practice
Radiation Protection
Резюме. In this article the classification of incidents and accidents when working with sources of ionizing radiation (SIR) is discussed. Also are considered the important measures and actions laid down in the Bulgarian legislation for prevention of nuclear incidents and accidents, as well as for minimizing the consequences thereof for people and environment.
Keywords: radioactivity, radiation protection, classification of incidents, Bulgarian legislation, nuclear accidents, human error
N. Ivanova, B. Manusheva
Education: Theory & Practice
Comparative Analysis of Containing Natural Radionuclides in the Herbs Calendula Officialis L. and Matrocaria Chamomilla L.[In Bulgarian]
Резюме. The healing power of many plants has been known since ancient times and it is used until nowadays all over the world. The herbs Calendula officinalis L. and Matricaria chamomilla L. are among the most commonly used herbs. The article mentions the biologically active substances and their usage in folk medicine. The content of the radionuclides in both plants and the soil, near the root system of the samples collected in June and July 2016 from the region of Yagnillo village, Varna district, has been investigated. Flowers and soil are cleaned from impurities, dried and levigated in fine powder. Gamma-spectrometric analysis was performed on the prepared samples. A low-frequency gamma-spectrometer set up by a Ge (Li) detector with multilayer protection is used. The collection of gamma-spectra was done for 86,400 s. A specialized software for gamma-spectra – ANGES – was used for their processing. The activities and specific activities of the detected natural radionuclides from the Uranium-radionuclide and Toric families are calculated. The transfer from soil to plant has been calculated. A comparative analysis of the radionuclides content in the plants and the soils on which they were grown has been made. The comparison shows qualitative and quantitative compatibility with the radionuclides found.
Keywords: medicinal plant, Matricaria chamomilla L., Calendula officinalis L., soil, radionuclides, transfer factor
S. Dimova, T. Stefanova, Y. Eneva, N. Arhangelova
Влезте в системата, за да прочетете пълната статияEducation: Theory & Practice
Some Physical Factors Influencing the Azobenzene Polymer Properties
Резюме. Photonisotropic materials can be divided into two main groups: inorganic and organic materials. Polymers containing organic dyes are the subject of multiple studies in both areas of physics and medicine. Optical storage in azobenzene-containing polymers is based on the alignment of the polymer chains initiated by the reorientation and ordering of the azobenzene groups. This process requires considerably high recording energies but elevated temperature eases the mobility of the molecules thus making possible their reorientation by lower light intensities. On the other hand, an attractive approach is to use light, both to report on and control signaling proteins in cells, because light can probe cells in real time with minimal damage. Of particular interest is the development of chemically engineered proteins that are directly sensitive to light. The aim of this work is to present some physical factors influencing the azobenzene polymers properties used in various fields of science.
Keywords: azobenzene polymers, photoisomerization, photoinduced optical birefringence, carriers of drugs
D. Ilieva
Влезте в системата, за да прочетете пълната статияEducation: Theory & Practice
Stability of Emulsions from Type Oil/Water with Congugated Linoleic Acid [In Bulgarian]
Резюме. The model emulsion systems from type oil / water with oil phase refined sunflower oil type „Classic“ and water phase – deionized water and conjugated acid (CLA) – have been studied. The purpose of this paper is to investigate the stability characteristics of model oil / water emulsions with conjugated linoleic acid and to develop sensory profiles of the texture consistency and taste. For this purpose, a spectroscopic method for dispersion analysis, microscopic method, rheology and sensory profile of the consistency indicator have been used. It has been found that with an increase in the oil phase from 30% to 60% at CLA content between 1% and 3%, the data on the coefficient of transmission is statistically indistinguishable and, in the case of low concentration of the oil phase (10% and 20%) there is a tendency to increase the transmission coefficient. The rheological studies of model emulsions have a deviation from the dependence on flow rate of pseudoplastic bodies for a gradient of 1.32 min-1 to 2 min-1. After 2 min-1 there is a dependence on flowing of pseudoplastic bodies. As the speed increases, the emulsions are restructured. Emulsions are not stable and a stabilizer should be used. According to the sensory analysis, it can be concluded that the recommended concentrations of CLA in mayonnaise for a gentle and non-acidic flavor product is 2%. The addition of CLA to low oil phase values is suitable for developing emulsion sauces and dressings.
Keywords: emulsion stability, conjugated acid (CLA), rheology, dispersion, sensory profile
I. Milkova-Tomova, D. Buhalova, K. Nikolova, J. Alexieva, I. Minchev, G. Runtolev
Влезте в системата, за да прочетете пълната статияEducation: Theory & Practice
The Effect of Extra Virgin Olive Oil on the Human Body and Quality Control by Using Optical Methods
Резюме. There are many substances in extra virgin olive oil (EVOO), of which many have a beneficial effect. One of the most interesting substances in EVOO is Oleocanthal. This substance is first recognised in 2005 and can only be found in EVOO. Under further investigations it was proven that in vitro Oleocanthal has an anti-inflammatory effect comparable to Ibuprofen. This is due to the fact that it is an inhibitor of cyclooxygenase. It is able to form prostanoids, including thromboxane, which takes part in formation of thrombosis, and prostaglandins including prostacyclin, which prevent the formation of the platelet plug during blood clotting and acts as a vasodilator. The quality control of an EVOO is very important, because most often refined oils such as olive-pomace oil, seed oils or synthetic oils are used. In some cases, this may lead to serious health problems after consumption. Such an incident happened 1981 in Spain (Spanish toxic Oil syndrome) where 20000 people were affected from which 330 died from aniline intoxication. Optical techniques are ideal for this purpose because they are simple, cost-effective, rapid and non-destructive. Fluorescence spectroscopy has different applications: detection of adulteration, geographic region, quantification of fluorescent components, monitoring of photo-oxidation and thermal and assessment of quality changes of olive oil during storage.
Keywords: olive oil, florescence, healthy eating, oxidation
C. Tottmann, V. Hedderich, P. Radusheva, K. Nikolova
Влезте в системата, за да прочетете пълната статияEducation: Theory & Practice
Infrared Thermography for Diagnostics of Focal Infection [In Bulgarian]
Резюме. Focal infection is a present hidden infection inside the body that is not strong enough to cause symptoms and most often patients don’t know about its presence. By the physiological paths the organism can suppress it, but when a decrease in the immune protection occurs (virus, stress, fatigue) the focus of infection overcomes local protection and affects by the connective tissue distant organs and systems (heart, kidneys, joints, eyes, skin). Focal infection can be the genuine cause for some diseases (ear infections, pyelonephritis, arthritis, alopecia areata) or aggravation factor for others. Very often even doctors consider directing patients for focal infection diagnostics, when have run out of therapeutic possibilities. That’s why focal infection is a major medical problem and both doctors and patients pay much more attention. Infrared thermography is a contemporary method for non-contact thermodiagnostics and for short time the whole body temperature can be registered as thermal pictures. This happens by infrared camera that is highly sensitive and hi-tech technology that registers the infrared spectrum radiating from the object of surveillance. After a thorough computer analysis, the different foci and their activity can be differentiated. As a contemporary method for focal diagnostics infrared thermography gives guidelines for finding focal infection in the whole body in unclarified cases. Moreover, it’s a method that distinguishes with detailed information, possibility for precise software analysis and direct digital data transfer that’s why infrared thermography has its important place in the diagnostics of focal infection.
Keywords: infrared thermography, focal infection
R. Grozdanova-Uzunova, T. Uzunov, P. Uzunova
Влезте в системата, за да прочетете пълната статияEducation: Theory & Practice
The Physics Experiment and Its Role in Forming of Practical Skills in Military Students [In Bulgarian]
Резюме. In 2017/2018 school year in the new curriculum of the subject „Protection of Population and Infrastructure“ for the first time will appear discipline „Applied Physics“. It focuses on practical-applied knowledge in physics and its application in different situations, sometimes in extreme conditions.Under the available state of the University’s material base, non-standard methods should be done to students and learners and to find ways to apply their knowledge and skills in various non-standard situations, sometimes even non-traditional. In the lab, each student will conduct his/her own experiment in which he she will apply his knowledge both in physics and related subjects.
Keywords: experiment, physics, laboratory exercise, knowledge, experience
N.P. Dolchinkov, B.E. Karaivanova-Dolchinkova
Влезте в системата, за да прочетете пълната статияEducation: Theory & Practice
Electrical Properties of Polylactic Acid Composite Films [Un Bulgarian]
Резюме. In the present study, some electrical properties of polylactic acid (PLA) composite films with different percentages of MgO – 0 wt%, 2 wt%, 4 wt% and 8 wt% were investigated. Composite films were prepared using a Brabender Plastograph EC Plus blender under controlled electric heating for 5 minutes at 190 ° C. The films obtained were charged by the corona discharge method using a tri-electrode system for 1 minute under room conditions. Positive or negative 5kV voltage was applied to the corona electrode. 1 kV voltage of the same polarity as that of the corona electrode was applied to the grid. The surface potential of the charged samples was measured by the vibrating electrode method with compensation. The time dependencies of surface potential were investigated. The results obtained show a significant change in the electret behavior of PLA composite films after insertion of MgO particles with different concentration. Some dielectric and impedance characteristics of composite films were also studied. Dielectric permittivity was calculated. The results obtained show a change in dielectric permittivity by increasing the concentration of the inserted MgO particles in the PLA matrix.
Keywords: polylactic acid, corona discharge, electrets
A. Viraneva, I. Bodurov, T. Yovcheva
Влезте в системата, за да прочетете пълната статияProblems
Nine Hypothetical Problems for Linkage between Qualitative Analysis and Stoichiometric Calculations
Резюме. On the science or the chemistry education, it is one from the most important problems for both the science teachers and the students to design the linkage between ones information and other information as well. The aim of this study is hypothetically to model the linkage between the qualitative analysis and the quantitative analysis with the chemical calculations. For this aim, it is preferred the precipitation reactions of first group cations (Ag1+, Pb2+,Hg2+) with HCl solution that is the group reagent in the qualitative analysis of inorganic samples in this study. On these precipitation reactions, it is offered the three sub model for teaching how to calculate the quantity of precipitate if the quantities of one or two reactants are given for the quantitative analysis. These sub models are consecutively called First Model, Second Model and Third Model. First Model: The aim of First Model is to teach how to calculate the mass of precipitate when the molarity and the volume of the solution of only one reactant is given in the problems. Second Model: The aim of Second Model is to teach how to calculate the mass of precipitate if two reactants react completely when the molarities and the volumes of the solution of them are given in the problems. Third Model: The aim of Third Model is to teach how to calculate the mass of precipitate if one of two reactants reacts completely and other remains unreacted when the molarities and the volumes of their solutions are given in the problems. The solutions of problems have been done by two different methods that are known as by the using formula and by the conversion factor. It can be said that the models are hypothetically suitable to investigate the relations between the qualitative analysis and the quantitative analysis with the chemical calculation in this context the reactions of first group cations with HCl that is the group reagent of them. The precipitation reactions are directly the linkage with gravimetric analysis and Mohr, Fajans and Volhard methods in this context of volumetric analysis as well.
Keywords: analytical chemistry education, qualitative analysis, quantitative analysis, quantitative precipitation, stoichiometry, chemical calculation, limiting reagent
S. Ergul
Влезте в системата, за да прочетете пълната статияFrom the Research Laboratories
Mathematical Modeling and Effect of Isothermal Drying on Mushrooms (Boletus pinophilus)
Резюме. Eleven kinds of mathematical models were used to obtained moisture data. From obtained results, the semi-theoretical models chosen in this work proved to be quite good to describe the drying behavior of isothermal drying. In the experiment,Modified Henderson and Pabis model was most appropriate for fitting MR − t curve of isothermal drying of hot-air drying, its correlation coefficients is above 0.999; for chi-square is below 0.0075; for root mean square error is below 0.0077.
Keywords: mushrooms; isothermal drying; mathematical model
M. Ivanova, P. Papazov, L. Dospatliev, N. Katrandzhiev
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