Вісник Київського національного університету імені Тараса Шевченка. Серія: фізико-математичні науки
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Introducing Security to Efficient Tree-based Self-organizing Protocol
Get PDFWireless sensor networks are widely used in many modern settings. In order to build substantial networks each sensor must be cheap. So it follows that, since resources of individual sensor are limited, there is a need to create protocols that would use them sparingly and evenly in order to maximize lifetime of the network. To reach this goal some useful self-organizing tree-based protocols were created that use different properties of the network nodes, such as number of children, number of hops from the ultimate sink, distance and remaining energy, to optimally select and reselect parent node in a network. However, there is also a challenge of providing security of the network. In this paper we propose a way of integrating a simple security method akin to iterative filtering into the protocol and discuss corresponding trade-off between attack prevention and increase of energy consumption.Key words: wireless sensor network, security, protocol, tree.Pages of the article in the issue: 76 - 79Language of the article: Ukrainia
Automated analysis of the educational-professional program "Informatics", implemented at the faculty of computer science and cybernetics, with the programs of other institutions of higher education in the specialty 122 "Computer Science"
Get PDFThe article presents a comparative analysis of the educational and professional program "Informatics" of the first (bachelor\u27s) level of higher education in the field of knowledge 12 "Information Technology", specialty 122 "Computer Science", which is implemented at the Faculty of Computer Science and Cybernetics Taras Shevchenko National University of Kyiv with educational and professional programs of the same level and specialties of other institutions of higher education in Ukraine. During the analysis, they were compared with the approved standard of the first (bachelor\u27s) level of higher education in the specialty 122 "Computer Science".In order to conduct a comparative analysis, the authors developed and completed a educational program database. The result of the study is checking the educational program for completeness, that is lack of competencies that are not provided by any discipline and sufficiency, that is the lack of disciplines that do not provide any competence. The ratio of competencies and disciplines in different programs in a common specialty is analyzed.Key words: computer science, informatics, database, educational program.Pages of the article in the issue: 49 - 62Language of the article: Ukrainia
Limits theorem of first passages times to regenerative processes
Get PDFThe current work continues the author’s investigation in the field of extreme values analysis. The investigation is concerned with the first passage time of a level u for a wide class of regenerative random processes. The common statement of the problem in most of works in the field under consideration dealt with cases when time of observation, t, and u tend to infinity. Alternatively, we investigate the case when t tends to infinity, whereas u is a fixed number. We establish a general limit theorem for the first passage time of a level u by a regenerative process. This topic is closely associated with the asymptotic behavior of extreme values of regenerative processes. In proving the main result, we establish an important lemma concerning the asymptotic behavior of probabilities for a class of random sums, which may be of independent interest. Necessity of the study of such sums occurs in many areas: mathematical reliability theory, queuing theory, some statistical physics problems. In addition, the work provides examples of applications of the obtained general results to some problems, which arise in applied areas: model of counters of type Geiger-Muller, estimation of the reliability of a redundant system with recovery, the problem of the first passage time of a level u by queue length in the queuing system M/M/1.Key words: regenerative processes, random sums, queuing systems.Pages of the article in the issue: 57 - 67Language of the article: Ukrainia
Sieve sorting algorithm
Get PDFThe purpose of this paper is to present a sorting algorithm that allows parallel execution of comparison operations, analysing complexity and runtime of the algorithm, discussing about a virtual process for this algorithm, and the implementation of the C++ program that simulates such a virtual process. The following problems were solved in this paper: the algorithm of sieve sorting was proposed, the correctness of its execution were proved, the complexity and timing of this algorithm were investigated, the structure of the virtual process implementing this algorithm was proposed, the C ++ program that simulates such a virtual process was discussed. Program code may be taken from the authors. The improvement for the algorithm also provided and correctness of such improvement proved. In the process of problem solving the inconvenience of classical UNIX-like implementation for working with the mechanisms of piping and the processes creating was found out.Key words: sieve sorting, virtual process.Pages of the article in the issue: 92-95Language of the article: EnglishThe purpose of this paper is to present a sorting algorithm that allows parallel execution of comparison operations, analysing complexity and runtime of the algorithm, discussing about a virtual process for this algorithm, and the implementation of the C++ program that simulates such a virtual process. The following problems were solved in this paper: the algorithm of sieve sorting was proposed, the correctness of its execution were proved, the complexity and timing of this algorithm were investigated, the structure of the virtual process implementing this algorithm was proposed, the C ++ program that simulates such a virtual process was discussed. Program code may be taken from the authors. The improvement for the algorithm also provided and correctness of such improvement proved. In the process of problem solving the inconvenience of classical UNIX-like implementation for working with the mechanisms of piping and the processes creating was found out.Key words: sieve sorting, virtual process.Pages of the article in the issue: 92 - 95Language of the article: Englis
Conservation laws in dynamic fracture tasks
Get PDFTwo fracture model under elastic wave action are considered: with energy dissipation while fracturing and without energy dissipation. The conservation of integrals of the complete mechanical energy and the quantities of motion of the fragments of the rod is investigated. For the model of fracture without energy dissipation, the complete mechanical energy is stored. For a fracture model involving energy dissipation, the complete mechanical energy decreases, although the motion of the inertia center remains. Therefore, dynamic fracture occurs due to the dissipation of the energy of the wave process in the rod. The application of the models is illustrated by an example of a study of quasistatic fracture by the propagation of a brittle crack. The dependence of the fracture energy on the crack size as well as the complete fracture energy were obtained.Key words: dynamic fracture, wave propagation, energy of fracture.Pages of the article in the issue: 38 - 43Language of the article: Ukrainia
Some peculiarities of the drilling rigs elements movement
Get PDFThis paper deals with investigatson of the process of drill bit whirling on the rough plane of the well bottom. Nonholonomic kinematic models of the mechanical interaction of contacting bodies with defects at the initial stage of system self-excitation are applied. On the basis of the results of experimental studies, it is believed that one of the main factors influencing on the whirlings vibrations is the geometry of the bit. The bit is considered to be an absolutely rigid ellipsoidal body, the well bottom surface is supposed to be a plane. The resulting oscillations are associated with spontaneous bending deformations of the drill string, which are accompanied by continuous contact of the bit and the rock. The equations of motion of the bit in the linear approximation are obtained. The analysis of the solution of the linearized equations is carried out, and the frequencies of the arising periodic motions are found. The forms of oscillations under different geometrical parameters of an ellipsoidal bit are analyzed. It is shown that the bit can rotate in backward direction, moving at angular velocities that exceed the angular frequency of the drill string. The research results can be used in the development of new types of drilling rigs.Key words: deep drilling, ellipsoidal bits, nonholonomic dynamics, forward and backward whirling.Pages of the article in the issue: 57 - 60Language of the article: Ukrainia
Features of heat and mass exchange in laminar flows of micro and nanofluids in tubes and channels
Get PDFIn recent years, high efficiency of using suspensions of nanoparticles for cooling of the operating systems compared to a homogeneous liquid has been shown, and the parameters of suspensions effective for various specific devices have been selected in experiments. A brief review of the relevant experimental data, as well as mathematical models of the flow of micro- and nanofluids, based on the incompressible Navier-Stokes equations with boundary conditions accounting for tangential momentum transfer of the particles and temperature jump due to diffuse reflection at rough walls, are presented. For the case of a laminar flow between infinite parallel plates with constant heat fluxes through the plates, an analytical solution is obtained for the velocity and temperature fields. Numerical calculations showed that with an increase in the momentum transfer coefficients at the plates, the flow accelerates significantly, which contributes to an increase in volumetric flow with the same pressure drop across the channel due to a decrease in the shear stress at the wall. Correspondingly, the heat transfer through the plates and the heat removal with the fluid flow increase. Based on the obtained analytical relationships, it is possible to select the parameters of the plate surfaces in such a way as to optimize the system, for example, to reduce the energy loss due to viscous and thermal dissipation or to obtain uniform temperature distributions in the liquid with asymmetric heat flows through the plates.Key words: microfluidic, nanofluidics, heat and mass transfer, laminar flows. Pages of the article in the issue: 62-67Language of the article: UkrainianIn recent years, high efficiency of using suspensions of nanoparticles for cooling of the operating systems compared to a homogeneous liquid has been shown, and the parameters of suspensions effective for various specific devices have been selected in experiments. A brief review of the relevant experimental data, as well as mathematical models of the flow of micro- and nanofluids, based on the incompressible Navier-Stokes equations with boundary conditions accounting for tangential momentum transfer of the particles and temperature jump due to diffuse reflection at rough walls, are presented. For the case of a laminar flow between infinite parallel plates with constant heat fluxes through the plates, an analytical solution is obtained for the velocity and temperature fields. Numerical calculations showed that with an increase in the momentum transfer coefficients at the plates, the flow accelerates significantly, which contributes to an increase in volumetric flow with the same pressure drop across the channel due to a decrease in the shear stress at the wall. Correspondingly, the heat transfer through the plates and the heat removal with the fluid flow increase. Based on the obtained analytical relationships, it is possible to select the parameters of the plate surfaces in such a way as to optimize the system, for example, to reduce the energy loss due to viscous and thermal dissipation or to obtain uniform temperature distributions in the liquid with asymmetric heat flows through the plates.Key words: microfluidic, nanofluidics, heat and mass transfer, laminar flows.Pages of the article in the issue: 62 - 67Language of the article: Ukrainia
Named entity recognition in texts with the help of part of speech tagging
No full textWe analyze neural network architectures that yield state of the art results on named entity recognition task and propose a number of new architectures for improving results even further. We have analyzed a number of ideas and approaches that researchers have used to achieve state of the art results in a variety of NLP tasks. In this work, we present a few architectures which we consider to be most likely to improve the existing state of the art solutions for named entity recognition task and part of speech tasks. The architectures are inspired by recent developments in multi-task learning. This work tests the hypothesis that NER and POS are related tasks and adding information about POS tags as input to the network can help achieve better NER results. And vice versa, information about NER tags can help solve the task ofPOS tagging. This work also contains the implementation of the network and results of the experiments together with the conclusions and future work.Key words: neural networks, named entity recognition, regularization, generalizability, part of speech tagging, multi-task learning.Pages of the article in the issue: 74-83Language of the article: UkrainianWe analyze neural network architectures that yield state of the art results on named entity recognition task and propose a number of new architectures for improving results even further. We have analyzed a number of ideas and approaches that researchers have used to achieve state of the art results in a variety of NLP tasks. In this work, we present a few architectures which we consider to be most likely to improve the existing state of the art solutions for named entity recognition task and part of speech tasks. The architectures are inspired by recent developments in multi-task learning.This work tests the hypothesis that NER and POS are related tasks and adding information about POS tags as input to the network can help achieve better NER results. And vice versa, information about NER tags can help solve the task of POS tagging.This work also contains the implementation of the network and results of the experiments together with the conclusions and future work.Key words: neural networks, named entity recognition, regularization, generalizability, part of speech tagging, multi-task learning.Pages of the article in the issue: 74 - 83Language of the article: Ukrainia
Optical properties of PEDOT:PSS-silicon solar cells
Get PDFWe study the optical and electrical losses in PEDOT:PSS/n-Si solar cells using spectroscopic ellipsometry and current-voltage measurements. The optical constants and thickness of the PEDOT:PSS films were studied using spectroscopic ellipsometry performed by a SE-2000 SEMILAB ellipsometer spanning the NIR–VIS–UV range with a resolution of 5 nm. The results were analyzed using a four-layer model involving the ntype silicon (001) substrate, interfacial layer between Si and polymer films, PEDOT:PSS thin film, and a surface roughness layer. The key to understand the origin of the losses is that the studied junctions have an interfacial layer between organic (PEDOT:PSS) and inorganic substrates. The dielectric functions of the PEDOT:PSS were fitted with the known thickness and the assumption of a negligible roughness (i.e. that the roughness is much smaller than the wavelength). Using the complex dielectric function, the optical constants (refractive index n and extinction coefficient k) were calculated. In addition to real and imaginary part of the refractive index, the absorption coefficient was calculated. The produced hybrid solar cells show efficiencies around 7%.Key words: PEDOT:PSS/n-Si solar cells, spectroscopic ellipsometry, interfacial layer, optical constants.Pages of the article in the issue: 118-121Language of the article: UkrainianWe study the optical and electrical losses in PEDOT:PSS/n-Si solar cells using spectroscopic ellipsometry and current-voltage measurements. The optical constants and thickness of the PEDOT:PSS films were studied using spectroscopic ellipsometry performed by a SE-2000 SEMILAB ellipsometer spanning the NIR–VIS–UV range with a resolution of 5 nm. The results were analyzed using a four-layer model involving the ntype silicon (001) substrate, interfacial layer between Si and polymer films, PEDOT:PSS thin film, and a surface roughness layer. The key to understand the origin of the losses is that the studied junctions have an interfacial layer between organic (PEDOT:PSS) and inorganic substrates. The dielectric functions of the PEDOT:PSS were fitted with the known thickness and the assumption of a negligible roughness (i.e. that the roughness is much smaller than the wavelength). Using the complex dielectric function, the optical constants (refractive index n and extinction coefficient k) were calculated. In addition to real and imaginary part of the refractive index, the absorption coefficient was calculated. The produced hybrid solar cells show efficiencies around 7%.Key words: PEDOT:PSS/n-Si solar cells, spectroscopic ellipsometry, interfacial layer, optical constants.Pages of the article in the issue: 118 - 121Language of the article: Ukrainia
Modelling of technical reserves of an insurance company
Get PDFIn the modern rapidly evolving society, the science and the business are facing new needs and challenges constantly. The insurance industry and its mathematical foundation, the actuarial science, are not exceptions. Currently, the greatest challenge that the insurance system has to cope with is the issue of the new international financial standard that affects the calculation of reserves among other things. So far, insurers have mainly used common classical deterministic methods. However, the new standard emphasizes the necessity of the realistic prognosis that is best achieved with stochastic modelling tools since deterministic models do not represent the uncertainty and the random nature of future possible losses. This article considers the advantage of using stochastic modelling for reserve calculation in comparison to the deterministic approach.The article consists of five sections.In the first section, we briefly present the technique that lies in the basis of technical reserves calculation.The second section is devoted to such deterministic methods of reserve calculation as the Bornhuetter-Ferguson method and the chain-ladder method.In the third section, we consider modifications of two stochastic models – the Mack method and the bootstrapping technique.The fourth section considers the adjustment of reserves for the time value of money and inflation.In the fifth section, the results of modelling in the programming language R are presented.Key words: reserve calculation, Mack method, bootstrapping, Bornhuetter-Ferguson method, chainladder method.Pages of the article in the issue: 46 - 51Language of the article: Englis