Nikolaj Višniakov - Academia.edu (original) (raw)

Papers by Nikolaj Višniakov

Mathematics, 2021

A model of the heat exchange process in the heat exchanger of the cardiopulmonary bypass device i... more A model of the heat exchange process in the heat exchanger of the cardiopulmonary bypass device is proposed which allows for automation of the process of temperature regulation in the cardiopulmonary bypass with an accuracy of ±1 °C during cardiac surgery under controlled cooling and warming of the patient’s heart and brain. The purpose of this research is to create a concept and model of the temperature control circuit using the MSC Easy5 system, the creation of mathematical models of blocks of the temperature control circuit, and the description of the principle of temperature control in the cardiopulmonary bypass circuit. The model of the temperature control loop in the heat exchanger of the heart-lung machine was created using the MSC Easy5 system with a programmable microcontroller. The microcontroller implements a specialized temperature control algorithm in the C language. The model allows the creation of a full-fledged virtual prototype of a temperature control device in a h...

Materialwissenschaft und Werkstofftechnik, 2018

The main objective of this work is to explore the possibility of applying electron beams to conne... more The main objective of this work is to explore the possibility of applying electron beams to connect copper-niobium conductors. Electron beam welding of copperniobium microcomposite wires was investigated. The evaluation of welded joint properties was carried out according to the same methodology applied to contact electrical connections. The major electrical and mechanical properties of welded joints were established. The microscopic examination of the joint cross-section showed that welded joints of copper-niobium conductors have minimal thermal effects on the structure of the conductor and on the propagation of welding defects thanks to the welding in a vacuum. According to the non-destructive radiographic test, the joint structure does not have welding defects. The difference in electrical resistances of the conductor and welded joint was below 20 %. The welded joint can withstand the maximum load, which is equal to 31.25 % of the load-bearing capacity of microcomposite conductor. Keywords: Electron beam welding / copper-niobium microcomposite / welding joint / electric cable / electrical contact connection Das Hauptziel dieser Arbeit besteht in der Erforschung der Mö glichkeiten zur Anwendung von Elektronenstrahlen zur Verbindung von Kupfer-Niob-Leitern. Dazu wurde die Elektronenstrahlschweißtechnik bei Mikro-Verbunddrä hten aus Kupfer und Niob untersucht. Entsprechend der bei elektrischen Kontaktverbindungen angewandten Methode wurden die wichtigsten elektrischen und mechanischen Eigenschaften der Schweißfugen ermittelt. Durch mikroskopische Untersuchung des Fugenquerschnitts wurde nachgewiesen, dass durch das Schweißen im Vakuum sowohl die thermische Wirkung der Schweißfugen auf die Struktur von Kupfer-Niob-Leitern als auch die Ausbreitung von Schweißfehlern minimal ist. Die zerstörungsfreie Rö ntgenprü fung zeigte keine Schweißfehler an der Struktur der Schweißfuge. Die Differenz zwischen den Widerstandswerten des Leiters und der Schweißfuge lag unter 20 %. Die Schweißfuge hä lt den maximalen Laststrom in Hö he von 31,25 % der Belastbarkeit des Mikro-Verbundleiters aus.

Materials, 2021

In the present study, pulsed laser post-processing was applied to improve the properties of the t... more In the present study, pulsed laser post-processing was applied to improve the properties of the thermally sprayed NiCrCoFeCBSi/40 wt.% WC coatings. The powder mix was deposited onto a mild steel substrate by flame spray method and then the as-sprayed coatings were processed by Nd:YAG laser. The peak power density applied was between 4.00 × 106 and 5.71 × 106 W/cm2, and the laser operating speed ranged between 100 and 400 mm/min, providing processing in a melting mode. Scanning electron microscopy, energy dispersive spectroscopy, Knop hardness measurements, and “ball-on-disc” dry friction tests were applied to study the effect of the processing parameters on the geometry of laser pass and microstructure, hardness, and tribology of the processed layers. The results obtained revealed that pulsed laser processing provides a monolithic remelted coating layer with the microstructure of ultrafine, W-rich dendrites in Ni-based matrix, where size and distribution of W-rich dendrites periodic...

Applied Sciences, 2020

A method for the preliminary processing of MRI images of the heart that allows for the eliminatio... more A method for the preliminary processing of MRI images of the heart that allows for the elimination of fluctuation and impulse noise from useful signals is proposed. These types of noise are due to the regular geometric structure of the photoelectric elements of the MRI scanner matrix and the structure of the signal transmission channel. The aim of this work is to develop a comprehensive mathematical model for eliminating noise in the signal of an MRI scanner. In this work, mathematical models of linear and median filtering of impulse noise, fluctuation, and geometric noise are implemented. The mathematical models consist of the combined use of linear and median filters for recording MRI images of the heart. In the experiments, real MRI images of the heart from six patients with different diseases were used after noise was added to them. We were able to eliminate the impulse noise, geometric noise, and fluctuation noise in the MRI images by applying our filtering techniques. The filt...

Metals, 2020

This paper presents the experimental results of Cu-Nb wire joining upon applying flash welding te... more This paper presents the experimental results of Cu-Nb wire joining upon applying flash welding technology. The present research is aimed at investigating the structure, electrical and mechanical properties of butt welding joints of Cu-Nb conductors, usable for coils of pulsed magnetic systems. The butt joint structure was found to be free of welding defects. The structure of the butt welded joint provides an insignificant increase in electrical resistance and sufficient ultimate strength and plasticity of the joint. The tensile strength of the welded sample reaches 630 MPa.

Tehnicki vjesnik - Technical Gazette, 2018

In this work we have evaluated the feasibility of the magnetic field pressing technology for form... more In this work we have evaluated the feasibility of the magnetic field pressing technology for formation of Cu-Nb joints for further pulsed power applications. The electrical and mechanical properties of joints have been investigated. The structure of Cu-Nb conductors joints was investigated using optical and scanning electron microscopy. The mechanical characteristics have been evaluated using tensile tests. It has been determined that the maximum tensile strength of 350 MPa could be achieved, which is 30,4 % of a Cu-Nb wire strength. The applied pressing technology allowed minimizing the defects in the microcomposite structure due to solid-state joining process, however the resultant decrease of conductivity by 10 % influenced an increase of the Joule heating. After a 2 min 200 A current flow the difference of 54,4 °C between the conductor and the joint area was observed. It was concluded that the Cu-Nb joints formed by magnetic field pressing are applicable for pulsed magnet setups where non-destructive joints are required.

Journal of Mechanics in Medicine and Biology, 2018

This paper discusses the dynamics of oxygen partial pressure in intercellular fluid upon a limite... more This paper discusses the dynamics of oxygen partial pressure in intercellular fluid upon a limited load and a subsequent post-ischemic hyperemia in healthy individuals and individuals with vascular pathologies of the lower limbs. Within the framework of the phenomenological approach, which takes into consideration the qualitative peculiarities of the gas exchange processes in the body, a formal theory describing the dynamics of oxygen ([Formula: see text]) concentration dependently on the conditions of blood supply to the tissues has been developed. It was shown that certain parameters, for instance the relaxation time upon the conditions of artificial ischemia and the characteristic time of return of spontaneous blood circulation in the post-ischemic period, depend on the degree of pathology of the vascular system and may be used for assessing the functional status of a biological body.

Technology and Health Care, 2018

BACKGROUND: In this paper a method is proposed to evaluate the heart's coronary vessels' status b... more BACKGROUND: In this paper a method is proposed to evaluate the heart's coronary vessels' status based on the elimination of large coronary branches from IR-thermal image. This method makes it possible to determine nutrient cardiac blood circulation by calculation of the rate of heat spreading in small coronary vessels in the myocardium at hypothermia and hyperthermia under the conditions of artificial blood circulation. OBJECTIVE: The objective of the paper includes a theoretical substantiation of the proposed method for evaluation of the heart's coronary vessels' status and an experimental investigation of the efficiency of the method. METHODS: In the experiment, the dynamics of temperature distribution in the myocardium were registered by using thermal imaging cameras Flir i7 and Thermo Cam E300. RESULTS: Processing of the myocardium's thermographic images and the results of heat spreading modeling make it possible to single out the temperature profiles of the visible myocardium zones and to establish the presence of coronary arteries in them. CONCLUSIONS: The method makes it possible to monitor the heart temperature at hypothermia and hyperthermia; additionally, it makes it possible to evaluate the efficiency of the coronary artery bypass graft surgery performed during open heart operation.

Materialwissenschaft und Werkstofftechnik, 2019

The laser welding of copper-niobium microcomposite wires was investigated. It was determined that... more The laser welding of copper-niobium microcomposite wires was investigated. It was determined that the joint structure does not have welding defects, while microscopic examination of the joint cross-section showed that the microstructure of the autogenous weld consists mainly of a copper-based solid solution strengthened by niobium-rich precipitations. The weld obtained with use of filler material consists of two distinct zones, which are formed due to melting of filler wire and microcomposite wire. This structure of the joint provides an insignificant increase in electrical resistance and sufficient ultimate strength and plasticity of the joint. The tensile strength of the sample welded without filler material reaches 335 MPa, but such welded joints are very brittle due to very low ductility. However, an autogenous laser welding joint has about 1.6 times better ductility, and the tensile strength of the joint depends on the applied filler material and is equal to the tensile strength of this material.

Technology and Health Care, 2019

BACKGROUND: Monitoring of temperature changes and accurately determining the moment of electrode ... more BACKGROUND: Monitoring of temperature changes and accurately determining the moment of electrode removal during open heart operations is not well recognized. OBJECTIVE: We investigated the temperature fields distribution in the biological tissues affected by electrosurgery upon use of an infrared thermograph. METHODS: The dynamics of temperature distribution in the tissue was registered by the thermal imaging camera FLIR i7. Measurement of the temperature between electrode couples was carried out for two operation modes: coagulation (100% power) and coagulation (50% power). RESULTS: The most important result of the applied method of temperature monitoring is a determination of the moment for electrodes removal that ensures the avoidance of carbonization of the cardiac tissues during their ablation. CONCLUSIONS: Temperature monitoring for connection of soft live biological tissues by welding allows the power to be fed in the amount sufficient for a formation of continuous ablation of the myocardium tissue.

Metals, 2018

The paper presents the study of the influence of mechanical damage on the safe operation of gas t... more The paper presents the study of the influence of mechanical damage on the safe operation of gas transmission pipelines. The main types of pipeline damage with the actual parameters and their influence on the operational parameters are analysed. The damaged fractures of the section of the pipeline Kaunas (Lithuania)-Kaliningrad (Russia) were investigated in the laboratory. The main operational characteristics and the structure of the pipeline's metal after the period of long-term operation were determined using various research and experimental methods. The influence of the pipeline's damage was modelled by using the Finite Element Method and the ANSYS code. The predictions of the failure pressure were made, taking into consideration the actual properties of the pipeline's metal. Techniques including the hardness and microhardness measurement, chemical analysis, the impact strength test, and metallography analysis with an optical microscope, were used in the experimental study.

Mokslas - Lietuvos ateitis, 2017

High magnetic fields systems is widely used in fundamental and applied research in variuos branch... more High magnetic fields systems is widely used in fundamental and applied research in variuos branches of science and industry. The most famous examples of such magnetic systems are tokomaks, stellators, superconducting magnets, CERN collider, ITER reactor, levitation systems. The key component of magnetic systems is inductor (solenoid). At this moment, the record magnetic fields reaches 100 T. The creation of a strong magnetic field is no longer enough just to improve designs for inductor (solenoid). Traditional electrotechnical materials and conductors can no longer withstand the huge mechanical and thermal loads, therefore, them changes to an entirely new advanced materials, for example Cu-Nb microcomposite conductors. These materials are characterized by a unique structure, excellent mechanical properties and good electrical conductivity. One of the most important and unresolved problems of high magnetic fields systems are reliable non-destructive joints and joining technologies cr...

Science – Future of Lithuania, 2014

Nowadays, complex and potentially dangerous structures are usually welded. Manufacturers need to ... more Nowadays, complex and potentially dangerous structures are usually welded. Manufacturers need to measure welding deformations and residual stresses. Tensometric stations are widely used for control and monitoring of such deformations and stresses. The article discusses a low-cost computer-aided measurement system.

International Journal of Materials Research, 2017

Thermite welding of Cu–Nb microcomposite wires was investigated. Suitable compositions of thermit... more Thermite welding of Cu–Nb microcomposite wires was investigated. Suitable compositions of thermite material and slag were determined from the equation of the exothermic combustion synthesis reaction. The phase compositions of the thermite mixture and slag determined by X-ray diffraction analysis correspond to those assessed from the equation. According to non-destructive radiographic testing, the joint structure does not have welding defects. Microstructural examination of the joint cross-section with scanning electron microscopy showed that the Cu–Nb wire retained its shape and microstructure and only a thin surface layer of wire was melted during welding. The difference in electrical resistances of the conductor and welded joint was below 20 %. The thermite joint can withstand a maximum load equal to 62.5 % of the load-bearing capacity of microcomposite conductor.

British Journal of Applied Science & Technology, 2015

The paper considers the possibility of a theoretical definition of the natural frequencies of vib... more The paper considers the possibility of a theoretical definition of the natural frequencies of vibrations of thermoelectric coolers with a different number of stages and different configurations in the design phase. Determination of natural frequencies of vibrations in parallel was carried out for products, taking into account the damping produced by a number of structural elements as well - without taking into account the damping capacity of the solder layers at the ends of thermocouples. The analysis and comparison of the theoretical results were carried out. The results of the calculation determining the natural vibration frequencies of thermoelectric coolers (TEC) through a system of Lagrange equations of the 2nd kind were compared with the calculated values obtained by using the method of electrodynamic analogies.

Materials Science, 2015

The paper presents studies of vibratory treatment effect on the microstructure and hardness of th... more The paper presents studies of vibratory treatment effect on the microstructure and hardness of thermally sprayed and refused Ni-based coatings. Ni-Cr-B-Si-Fe-C system powder has been deposited on the S235 steel substrate and re-melted with the simultaneous introduction of the horizontal mechanical vibrations of frequency from 50 Hz to 400 Hz and of amplitude from 25 µm to 185 µm. The microstructure of obtained coatings has been studied along with the microhardness. The grain refinement effect accompanied by the hardness increase up to 20 % has been obtained in vibrated coatings, and frequency from 100 Hz to 200 Hz has been established as the range of the most intensive effect. No visible influence of vibratory treatment on the phase composition has been established.

Sensors, 2015

In the paper, an opportunity for the development of multichannel transcutaneous raster matrixes f... more In the paper, an opportunity for the development of multichannel transcutaneous raster matrixes for sensors of oxygen on the basis of an electrochemical cell sensor is described. An analysis of the influence of heat sources on the distribution of the temperature pattern of a raster matrix for sensors of oxygen had been carried out, and their optimum configuration had been found. The application of such matrixes will enable one to obtain information about the distribution of the partial pressure of oxygen from the skin cover of the object of research in dynamics, to assess its functional health pattern in a more comprehensive way and to control the effect of possible remedial actions.

Solid State Phenomena, 2015

The corrosion of exploited motor vehicles and important or potentially dangerous structures is no... more The corrosion of exploited motor vehicles and important or potentially dangerous structures is not a new problem of engineering [1]. However, nowadays, it still remains one of the most burning questions of manufacturing welding structures. There are a number of established methods and technological solutions allowing improvements to the premature corrosion resistance of exploited welded joints and structural elements. In the majority of cases, different protective coatings are used. However, protective coatings are not applicable for some structures in food and medical industry as well as for some other big dissimilar-material structures of a complicated shape. In such cases, the corrosion resistance of welded structures may be provided by other technological means. The present research is aimed at investigating the efficiency of such methods. Several different welding technological solutions and post-weld surface treatments have been applied. The corrosion resistance of the obtaine...

Leidinį sudaro šie studijų programos metodikos nurodymų ir laboratorinių darbų leidiniai: Irmanta... more Leidinį sudaro šie studijų programos metodikos nurodymų ir laboratorinių darbų leidiniai: Irmantas Gedzevičius. Dangų technologijos: laboratorinių darbų metodikos nurodymai; Irmantas Gedzevičius.Suvirinimo įrenginiai: laboratorinių darbų metodikos nurodymai; Irmantas Gedzevičius.Suvirinimo technologijos: laboratorinių darbų metodikos nurodymai; Jevgenijus Ščemeliovas. Pramoninė integruota gamyba: metodikos nurodymai; Nikolaj Višniakov. Polimerinių, kompozitinių ir keraminių medžiagų jungimas: laboratorinių darbų metodikos nurodymai; Olegas Černašėjus, Raimonda Lukaiskaitė. Metalų korozija ir apsaugos būdai: laboratorinių darbų metodikos nurodymai; Olegas Černašėjus. Inžinerinės konstrukcijos. Virintinių jungčių skaičiavimas: pratybų metodikos nurodymai; Vitalijus Rudzinskas, Ivanas Višniakas. Suvirintinių jungčių kontrolė: laboratorinių darbų metodikos nurodymai

Nanomaterials

Foodborne pathogens are frequently associated with risks and outbreaks of many diseases; therefor... more Foodborne pathogens are frequently associated with risks and outbreaks of many diseases; therefore, food safety and processing remain a priority to control and minimize these risks. In this work, nisin-loaded magnetic nanoparticles were used and activated by alternating 10 and 125 mT (peak to peak) magnetic fields (AMFs) for biocontrol of bacteria Listeria innocua, a suitable model to study the inactivation of common foodborne pathogen L. monocytogenes. It was shown that L. innocua features high resistance to nisin-based bioactive nanoparticles, however, application of AMFs (15 and 30 min exposure) significantly potentiates the treatment resulting in considerable log reduction of viable cells. The morphological changes and the resulting cellular damage, which was induced by the synergistic treatment, was confirmed using scanning electron microscopy. The thermal effects were also estimated in the study. The results are useful for the development of new methods for treatment of the dr...