KPI Science News

SINGLE-STAGE AND SIMPLE FABRICATION OF PE FILMS DECORATED WITH HALLOYSITE NANOTUBES

2024-01-19T15:59:27+02:00

Background. Environmental pollution with plastic waste is a global problem that requires the search for effective and safe ways of disposal or processing of secondary raw materials. The use of catalysts for this purpose is a promising direction for research.

Objective. In this work, a method of introduction of nanomaterials on the surface of a polyethylene film by partially dissolving the upper layer of the polymer in a heated nanomaterial suspension, namely aluminosilicate halloysite nanotubes in cyclohexane, was developed.

Methods. Thermogravimetric, optical, and dynamic mechanical analyses of synthesised samples were carried out, and their properties were compared with reference samples of pure polyethylene and treated without the addition of nanomaterial.

Results. It was achieved by the introduction of halloysite nanotubes in the amount of a maximum of 2.83 % by mass after immersion of the film in the suspension at a temperature of 50 °C for 120 seconds. The resulting film showed a wetting angle value of 77.11o, while for the reference sample without HNT it was 99.24o, which indicates the presence of hydrophilic nanotubes in the PE surface layer.

Conclusions. At the same time, the synthesised samples showed a significant decrease in mechanical properties, such as elasticity and tensile strength, due to the destructive effect of the solvent on the polymer.

Analysis of the influence of local electrodeposition conditions on the accuracy of electrochemical 3D-printing

2023-10-19T16:23:10+03:00

Problem. Additive manufacturing of metal parts by local electrodeposition is a new promising area with several unique features. The use of electrolysis makes it possible to manufacture metal parts at room temperature with high accuracy and low energy consumption. The accuracy and speed of electrochemical 3D printing are inversely related, and therefore it is important to find optimal electrodeposition conditions at maximum speed without degrading accuracy.

The aim of the study. The purpose of this work was to analyse the influence of electrodeposition parameters (electrode distance, electrical conductivity and electrolyte polarization) on the accuracy of metal deposit formation in a computer model and to conduct experimental verification of optimal conditions for electroforming a real object from copper sulphate electrolyte.

Methodology of implementation. To achieve the goals of the study, computer simulation of the electrochemical deposition process in the COMSOL Multiphysics software and electrochemical measurements of the characteristics of copper sulphate electrolytes were used.

Research results. Computer simulation established optimal conditions: the distance between the edge of the capillary and the surface on which deposition occurs is not more than 0.5 mm, the electrolyte in which the inverse slope of the cathode polarization curve is not lower than 2000 mA/(V×cm²) and the electrical conductivity is not higher than 0.02 S/сm. The influence of the electrolyte composition on the inverse polarization of the cathode process and its electrical conductivity was investigated. The optimal composition of the electrolyte was selected, containing 200 g/L CuSO₄, 60 g/L H₂SO₄, 0.2 g/L KCl and RUBIN T-200 additive. In the selected electrolyte, the value of the inverse slope of the cathode polarization curve is 2120 mA/(V×cm²). Verification of the process of local electrodeposition in the selected electrolyte during the electroformation of a cylindrical object with a diameter of 4 mm and a height of 100 μm was carried out. It was determined that no more than 5 % of metal was deposited outside the capillary of the working electrode.

Conclusions. The results of the work can be used to create an electrochemical 3D printing system. Further research should be aimed at approbation of the obtained parameters of local electrodeposition in an installation that simulates the operation of a 3D printer and establish the accuracy and speed of printing of a three-dimensional object.

Key words: additive manufacturing, electrical conductivity, electrolyte composition, polarization, local electrodeposition.

FINITE APPROXIMATION OF NONCOOPERATIVE 2-PERSON GAMES PLAYED IN STAIRCASE-FUNCTION CONTINUOUS SPACES

2022-12-26T14:45:59+02:00

V. Romanuke

Finite approximation of noncooperative 2-person games played in staircase-function continuous spaces

Background. There is a known method of approximating continuous noncooperative 2-person games, wherein an approximate solution (an equilibrium situation) is considered acceptable if it changes minimally by changing the sampling step minimally. However, the method cannot be applied straightforwardly to a 2-person game played with staircase-function strategies. Besides, the independence of the player’s sampling step selection should be taken into account.

Objective. The objective is to develop a method of finite approximation of 2-person games played in staircase-function continuous spaces by taking into account that the players are likely to independently sample their pure strategy sets.

Methods. To achieve the said objective, a 2-person game, in which the players’ strategies are staircase functions of time, is formalized. In such a game, the set of the player’s pure strategies is a continuum of staircase functions of time, and the time is thought of as it is discrete. The conditions of sampling the set of possible values of the player’s pure strategy are stated so that the game becomes defined on a product of staircase-function finite spaces. In general, the sampling step is different at each player and the distribution of the sampled points (function-strategy values) is non-uniform.

Results. A method of finite approximation of 2-person games played in staircase-function continuous spaces is presented. The method consists in irregularly sampling the player’s pure strategy value set, finding the best equilibria in “smaller” bimatrix games, each defined on a subinterval where the pure strategy value is constant, and stacking the equilibrium situations if they are consistent. The stack of the “smaller” bimatrix game equilibria is an approximate equilibrium in the initial staircase game. The (weak) consistency of the approximate equilibrium is studied by how much the payoff and equilibrium situation change as the sampling density minimally increases by the three ways of the sampling increment: only the first player’s increment, only the second player’s increment, both the players’ increment. The consistency is decomposed into the payoff, equilibrium strategy support cardinality, equilibrium strategy sampling density, and support probability consistency. It is practically reasonable to consider a relaxed payoff consistency.

Conclusions. The suggested method of finite approximation of staircase 2-person games consists in the independent samplings, solving “smaller” bimatrix games in a reasonable time span, and stacking their solutions if they are consistent. The finite approximation is regarded appropriate if at least the respective approximate (stacked) equilibrium is -payoff consistent.

INFLUENCE OF CARBONATE TYPE ON TRANSPORT CHARACTERISTICS OF SiC-BASED CERAMIC MEMBRANES

2023-11-23T17:15:25+02:00

Background. Ceramic membranes have recently attracted particular attention due to their thermal and chemical resistance, ability to be used in aggressive environments, and long service life. Among ceramic membranes, silicon carbide membranes deserve special attention due to their high strength. However, the high cost of such membranes and the controllability of porous characteristics, which significantly affect the transportation characteristics, remain an unresolved problem. Therefore, it is extremely important to investigate ways to reduce the annealing temperature of SiC membranes and control their porosity.

Objective. The aim of this work is to determine the effect of the type of carbonate on the physicochemical properties and transport characteristics of ceramic membranes based on silicon carbide. The ceramic membranes were obtained by pressing, to which borax (to reduce the annealing temperature) and carbonates (as a pore forming agent) were added.

Methods. Method of pressing and sintering with different composition of carbonates. Analysis of the obtained ceramic membranes by the diffraction method and scanning electron microscopy.

Results. It has been shown that the addition of sodium carbonate results in the formation of a new phase, sodium aluminosilicate, while no new phases were detected when ammonium bicarbonate was used. The morphology of the synthesized ceramic membranes has a granular structure characterized by pores ranging in size from 13 to 21 μm and a specific surface area of 1.5–1.9 m³/g. The investigated transport characteristics of ceramic membranes indicate that the use of ammonium bicarbonate allows to obtain a ceramic membrane with a sufficiently high throughput, which can be recommended for use in the field of microfiltration.

Conclusions. Ammonium bicarbonate is a more promising pore-forming additive for ceramic membranes based on silicon carbide. Further research will focus on studying the effect of the defoamer content on the transport and mechanical properties of ceramic membranes.

Adaptive control at the channel level of the packet radio networks with a rigid strategy for accessing the radio channel

2023-03-01T11:34:17+02:00

Background. Development of methods and means of the adaptive management control of the bandwidth radio networks with competitive access to the radio channel.

Objective.

Determination of the effect of packets length on the effective transmission speed of radio networks taking into account the parameters, formats and procedures of the physical and channel levels when using six possible strategies of the adaptive CSMA protocol with a rigid strategy of competitive access to the radio channel.

Methods.

The goal is achieved by creating and analyzing a mathematical model of effective transmission speed in radio network. The model is described by the equation of the effective transmission rate, which is a function of the probability of conflict-free transmission of the adaptive CSMA protocol for rigid strategy and the deviation coefficient of the size of data packets from the optimal LLC protocol, taking into account the probability of packet damage due to interference in the radio channel.

Results.

With the help of this mathematical model, it is proved that of the six packet length management strategies for adaptive CSMA protocols with a rigid strategy, only the first, third and sixth strategies have practical significance from the point of view of increasing the effective transmission speed, provided that the influence of the parameters of the physical and LLC levels is taken into account. For these strategies can be calculated according to this model the optimal size of the length of data packets for each set of system parameters, such as the transmission speed, the probability of damaging one bit of information due to interference in the radio channel, and the structure of the packet of the LLC protocol.

Conclusions.

The proposed mathematical model is a tool for calculating the bandwidth of radio networks and the optimal size of data packets during adaptive management of competitive access to a radio channel with a hard strategy in conditions of significant fluctuations in traffic intensity and changes in the intensity of interference in the radio channel.

Use of implementations of arbitrary bitness permutations for cryptographic transformations

2022-08-19T16:33:21+03:00

Background. Cryptographic transformations have always aroused the interest of the educated part of humanity and are an integral part of modern communications. A lot of different cryptographic algorithms exist for different tasks and requirements. Permutation functions are useful for cases where transformation speed is more critical than theoretical secrecy. Hardware implementation of such substitutions is quite simple.

Objective. Investigate the model and combinational circuits for hardware implementation. Investigate algorithms for permutation functions software implementation. Investigate attack algorithms and cracking of permutation functions for cryptanalysis.

Methods. The paper reviews algorithms of cryptographic transformations and their cryptanalysis for bijective permutations implemented by means of regular combinational structures of linear complexity. The proposed algorithms provide the rate of processing up to gigabits per second. The paper clarifies the algorithm of formation of elements of regular structures of permutations, specifies volumes of public and private data, reviews data formats, methods of their transfer and hardware implementation of one of the methods. The paper reviews attack types and permutation regular structure schemes cracking algorithms with experimental calculation of necessary operations quantity. The software implementation of the proposed algorithms for results calculation was developed.

Results. Numerical results of the number of keys, the amount of memory required for hardware implementation and the number of required operations for cryptanalysis were obtained.

Conclusions. The results show that the proposed algorithms for cryptographic transformations have a sufficient level of protection with a high-speed encryption and decryption.

REASONS AND REGULARITIES OF THE INFLUENCE OF MAGNETIC FIELDS ON THE MECHANICAL PROPERTIES AND STRUCTURE OF DEFORMABLE METALS

2024-05-22T22:58:09+03:00

Background. The strength of metals greatly limits the possibility of obtaining products by plastic deformation. The electromagnetic nature of the processes of structure formation and plastic deformation provided the basis for the application of additional influence of the magnetic field. A fairly large volume of research material has been accumulated on the topic of additional influence of the magnetic field on ferro-, dia- and paramagnetic metals. The researches of recent years have an applied nature of studying the magnetoplasticity of technical alloys. Their generalization will make it possible to move from laboratory research to the development of equipment and technologies for combined pressure processing of metal products in a weak magnetic field.

Objective. Generalization and analysis of the results of laboratory and theoretical studies of the additional application of the magnetic field in the processes of mechanical testing of metals and alloys.Methods. Literary review of materials of articles, monographs, dissertations.

Results. Reasonable use of a magnetic field for plastic deformation of metals. The explanation of the mechanism of the influence of the magnetic field on the structural elements of metals based on the effect of magnetoplasticity has been made. The description of changes in the mechanical properties of metals and alloys under the additional influence of a magnetic field is given.

Conclusions. The phenomenon of magnetoplasticity has been studied for a wide range of materials such as pure metals and their alloys, including industrial steels and alloys. Various types of positive effects of a magnetic field on the mechanical properties of metals have been established: a decrease in the yield strength and deformation resistance, an increase in strain, relaxation of internal stresses, and a decrease in dislocation density. There is also a reverse, negative effect of the influence of a magnetic field: increased rate of hardening, embrittlement, increased creep of metals. What will be the effect of a magnetic field on a specific metal cannot be guaranteed with high accuracy.

Analysis of the technology of manufacturing a semi-finished part for a hollow part of a complex geometric form using the technology of hot volume stamping

2024-05-25T21:30:04+03:00

Abstract. Background. Today, the actual issues in the production of metal products are the saving of materials and the productivity of production, as this has a significant impact on the cost of finished products. This especially applies to hollow products with a complex geometric shape. Such products include parts or semi-finished products that have hollow cavities and additional elements in the design in the form of flanges, or variable wall thickness along the height of the product. Such parts are widely distributed in mechanical engineering, aircraft construction and in the production of special purpose products, in particular in the field of ammunition production. Therefore, the manufacturing technology of such parts should ensure mass production and have an economic effect.

Goal. By calculation, using the finite element method (FEM) in the DEFORM software environment, determine the option of stamping, from blanks of different diameters, a semi-finished product of a hollow part of a complex geometric shape using the technology of hot three-dimensional stamping, and analyze the proposed technological process of obtaining a semi-finished product.

Methodology of implementation. Using MSE in the DEFORM software environment, simulation of hot three-dimensional stamping of a semi-finished product was carried out for a hollow part of a complex geometric shape made of blanks of different diameters. In this way, the option of obtaining a semi-finished product with a minimum number of transitions and a guaranteed possibility of implementing the technological process of mold formation was chosen. For the selected option, an analysis of the force modes of forming, normal stresses on the contact surfaces of the workpiece with the tool, and the stress-strain state of the deformed metal was performed.

The results. A semi-finished product manufacturing technology for a hollow part of a complex geometric shape using hot three-dimensional stamping technology is proposed. This technology will be implemented in the production of the adapter housing part, which is used in the design of the 120 mm mine. By calculation, with the help of MSE in the DEFORM software environment, the variant of semi-finished product molding for the "Body-adapter" part was determined using the technology of hot three-dimensional stamping, and an analysis of the technological operation of semi-finished product molding was carried out. The temperature regime of the process, technological efforts, parameters of the stress-strain state of the deformed material, the distribution of normal stresses on the deforming tool are determined. The results of the conducted computer modeling make it possible to take into account the design features and select the necessary technological equipment for mass production.

Conclusions. The technology for serial production of semi-finished products by hot volumetric stamping has been developed and substantiated. This technology made it possible to increase the rate of material utilization by two times compared to the technology of obtaining a part by mechanical processing from graded rolled steel.

Conceptual model of the NLP-system for searching for the relevant legal position on the multiple court decisions of the judiciary of Ukraine

2024-08-21T14:27:35+03:00

Problems. An applied problem of automating the search for relevant legal positions on a set of court decisions in the judiciary of Ukraine. The possibility of developing a high-quality NLP system for searching for a relevant, contextually justified legal position on a set of court decisions in the judiciary of Ukraine, which, based on the user's request, produces expert answers to the user's request by applying a reasoning-search algorithm based on large language models.

Objective. To develop and formalize the concept and conceptual model of the NLP system for finding legal positions on the basis of interdisciplinary knowledge of a technical and philosophical direction, which covers the existence of a person, community, enterprises, institutions and organizations, state authorities, and also substantiates the formation of a legal position on the basis of a plurality . legislative acts and court decisions.

Methodology of implementation. The method of implementation of the NLP system for searching for a context-based legal position lies in the interaction of the essences of tasks related to the judiciary of Ukraine, tools for analysis, processing, text generation and available available court decisions of the judiciary of Ukraine based on the Erikson-Penker business profile and large language models .

Results. The proposed interdisciplinary model of the concept of the NLP system of finding a solution to the problem, tasks and tasks of searching court documents for more rendering of court decisions and/or formation of a legal position in the form of a Venn diagram as a set of entities and their cooperation, which integrates philosophical, legal and technical knowledge. The Erikson-Penker business profile of the conceptual model of the NLP system for searching for a context-based legal position is formalized. A formalized model of the work process of the NLP system of searching for a context-based legal position based on the RAG method. A conceptual model of the NLP system for searching for a context-based legal position has been developed in the form of a structural mapping based on a component diagram and a dynamic mapping based on an activity diagram with a description of the internal structure of the components.

Conclusions. A number of important philosophical, legal and technical problems have been identified in the process of searching for legal positions on many court decisions. The interdisciplinary nature of the problem of developing the concept and conceptual model of the NLP system for finding a context-based legal position on a set of court decisions and the need to automate the process of finding a legal position for judicial practice has been established. At the meta levels, the concept of the NLP system for finding context-based legal positions on Venn diagrams and the conceptual model of the NLP system based on the modified Erikson-Penker business profile as a system of entities and cooperation are formalized. A conceptual model of the NLP system for finding a context-based legal position has been developed in the form of a structural mapping based on a diagram of components and a dynamic mapping based on an activity diagram with a description of the internal structure of the components. The functionality of the NLP system was compared with other main existing systems for searching court decisions in the judiciary and it was established that the developed system, at least, is not implemented in terms of functionality of existing systems and has additional opportunities for users.