Now showing 1 - 10 of 27
  • Publication
    Mechanical and electrical properties of the solid sapropel
    (2015) ;
    Josef Timmerberg
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    ;
    Paul Beckmann
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    Valentina Popa
    ;
    Regina Wagner
    In this paper are explored the mechanical (ultimate compression strength, ultimate strain, Young’s modulus, hardness) and the electrical (relative permittivity, specific electrical resistance, quality factor, their dependence on the electric field frequency in the range till 1MHz) properties of the solid sapropel. For the researches are used samples from the solid, monolith sapropel (obtained in the drying process) and samples from the sapropel powder that are pressed with a different force; before the measurements, a part of these samples were heated. There is explored the dependence of the relative permittivity on temperature. Are explored the methods for the forming of the products from the solid sapropel powder.
    Scopus© Citations 1
  • Publication
    EFFECT OF HEAT TREATMENT ON ELECTRICAL AND MECHANICAL PROPERTIES OF THE SOLID SAPROPEL
    (2017) ; ;
    Rene Castro
    ;
    Vladimir Solovyev
    ;
    Josef Timmerberg
    ;
    Alexander Cvetkov
    ;
    Sergey Gango
    ;
    Angelika Borkenstein
    ;
    Paul Beckmann
    ;
    Helmut Schütte
    ;
    Nikolai Puchkov
    ;
    Sergey Trifonov
    In this work changes of electrical and mechanical properties (hardness) of the solid sapropel after its heat treatment were researched. Changes of real and imaginary parts of dielectric permittivity, dielectric losses and specific electrical resistance depending on electrical field frequency in the range 0.01Hz- 1MHz were observed. Temperature dependences of AC (at 1 kHz) and DC electrical conductivity were studied. Chemical sample composition, IR spectra and structure of the solid sapropel were investigated. Heat treatment has a noticeable effect on the electrical characteristics of solid sapropel due to the strong influence of water on the charge transfer in this complex material. Charge transfer occurs predominantly due to ion migration and demonstrates strong dependence upon hydration - dehydration processes. After the heat treatment of the solid sapropel at the temperature of 1000C its hardness doesn’t change. If the sample of the solid sapropel is subjected to 20 min heat treatment at the temperature of 1500C, its hardness decreases by 5.4%, the number of C=C bonds decreases by 6.3±0.1%, the number of C=N bonds decreases by 2.2±0.1%, the number of C-C bonds decreases by 1,7±0.1%, the number of C-H bonds increases by 18.5±0.3%. It shows that in the temperature range 100-1500C destructive processes of the solid sapropel start, although visually (with optical microscope and with SEM) changes of structure are impossible to observe yet.
    Scopus© Citations 2
  • Publication
    Overview Of The River Basin Management Plans In The Baltic Region Under The Waterpraxis Project
    (2015)
    Māris Mednis
    ;
    Ivars Matisovs
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    ; ;
    Gundars Vaļģis
    The paper provides brief overview of the river basin district management plans in the Baltic region within the WATERPRAXIS project, linked to the EU Water Framework Directive. Latvian experience in completion of the river basin district management plans is emphasized comparing to other regional cooperation partners. Article is based on the report documents, analysis of the available data and review of the development projects subject to implementation. To some extent also potential issues for discussion are outlined. Certain Baltic countries have had difficulties complying with the EU Water Framework Directive,and there are some potential areas of contention, which should be taken into account in further activities. In course of the administrative and territorial reform and compliance with other EU directives (e.g. in the renewable energy sector) modifications can be made to the status of spatial and also river basin management plans and for the purpose of sustainable development in the region.
  • Publication
    A Method For Determination Of Specific Electrical Resistance Of Steel And Nano-Coating Sputtered On It
    (2015) ;
    Josef Timmerberg
    ;
    Konstantins Savkovs
    ;
    Aleksandrs Urbahs
    ;
    Paul Beckmann
    The paper describes methods developed to determine specific electrical conductivity and relative magnetic permeability of cylindrical steel items and nano-coatings deposited on them by sputtering. Research enables development of a new method for determination of thickness of vacuum deposited nano- coating that is based on application of skin effect.
  • Publication
    Does the energy transfer from Ar(1s) atoms to N2 lead to dissociation?
    (2020)
    Claus‐Peter Klages
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    ;
    Lars Bröcker
    ;
    Detlef Loffhagen
    Dielectric‐barrier discharges (DBDs) in Ar–N2 mixtures, with N2 fractions in 0.1–1% range, would be attractive alternatives to DBDs in pure N2 if energy‐transfer reactions between Ar(1s) atoms and N2 molecules were an efficient source of N atoms. Attempts to functionalize polyolefins in flowing postdischarges fed by such DBDs, as well as the search for the First Positive System in the emission spectrum, however, failed. Evidently, the energy‐transfer reactions do not produce N atoms. For Ar(1s3) and Ar(1s5) metastable states, this fact has already been reported in the literature. For Ar(1s2) and Ar(1s4) resonant states, a quantitative argument is derived in this paper: energy transfer from Ar(1s) atoms to N2 molecules is not an efficient source of N atoms.
    Scopus© Citations 3
  • Publication
    RESERCH OF LASER MARKING CHANEL GEOMETRICAL DIMENSIONS DEPENDENCE OF CHANGE OF LASER RADIATION PARAMETERS ON STAINLESS STEEL
    (2016-04-20)
    Dunkins, Vitālijs
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    Komkovs, Jurijs
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    Narica, Pavels
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    Valiniks, Jānis
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    ; ;
    Publication describes results of the stainless steel laser marking, which shows relationship between geometry of the treated surface and parameters of the laser radiation, such as power, pulse frequency, and processing speed.
  • Publication
    EXPERIMENTAL STUDYING OF MECHANICAL-AND- PHYSICAL PROPERTIES OF RUBBER DURING AGEING
    (2019)
    Svetlana Polukoshko
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    ;
    Elastomeric materials, both natural rubber and synthetic, are widely used in industry and civil engineering, due to their unique properties: high elasticity, low volume compressibility, capability to absorb and dissipate input energy, a linear relationship between stress and strain up to strain of 15% ÷ 20%, resistance to aggressive environmental factors. Different kind of compensation devices, vibration dampers, shock absorbers are fabricated from rubber materials.At the same time the elastomeric materials nonreversible change their properties over time, this disadvantage is called ageing.In given paper the results of experimental studying of the influence of aging on the physical-and-mechanical properties of polyurethane rubber is presented. The samples of cylindrical form were prepared from soft flexible polyurethane rubber Xenias PX30 and subjected to the artificial ageing. Accelerated aging of samples was fulfilled in accordance with European standard ISO 188:2011 (Rubber, vulcanized or thermoplastic - Accelerated ageing and heat resistance tests).The changing of volume, Shore A hardness, elastic rebound coefficient and static elasticity modulus under compression were investigated. Experiments showed the volume decrease, hardness shore increasing, elastic rebound increase and compression modulus under static loading increasing. This data are necessary for correct designing of the compensation devices to provide their working properties during all service life.
  • Publication
    Determination constants of 4-element reological model with rebound resilience method
    (2017) ;
    Svetlana Polukoshko
    ;
    Elvijs Apeinans
    ;
    In this paper an express-method and equipment for experimental determination of the 4-element rheological model constants (2 elastic modulus, 2 viscosity coefficients) for elastomers are developed. The method is based on rebound of falling hammer against an elastomer material. A mathematical model for describing this collision is elaborated and an algorithm for determination of the constants of the model was developed and realized in Matlab software. Time necessary for determination of the constants is until 5 minutes. It gives an opportunity to significantly accelerate the design and production process of elastomer-metal vibration isolator prototypes with defined parameters of stiffness and damping. The method allows to trace displacement, velocity and acceleration of the metal parts of the shock absorber throughout the collision; this may be realized with Matlab or an analogical program of numerical integration. For forecasting of the mechanical properties of the shock absorber during a long period (considering the aging of elastomer) it is necessary to know the rheological model parameter dependence on time, temperature, energy input and other factors; the proposed method allows to significantly accelerate these experimental studies.
    Scopus© Citations 2
  • Publication
    Laser hardening process optimization using FEM
    In given work a method for optimization of the process of laser hardening of steel parts is developed. The approach is based on the finite element method (FEM) using computer program “COMSOL Multiphysics” (module Heat Transfer in Solids) – software for multi-physical processes simulation. This method allows to reduce the number of laser hardening experiments, replacing them with numerical calculations, and to find the optimal parameters of the used laser equipment. To perform the calculations it is necessary to know the hardening temperature range of the particular steel grade, the martensite formation start temperature, the critical value of the cooling rate, the material density, the thermal conductivity k = k(T), the specific heat capacity Cp = Cp(T) and the surface reflectivity R = R(T, λ), where T temperature, λ – wavelength of laser beam. Depending on the laser power, the feed rates of the laser beam, the spot size and the distribution of energy in it, the temperature field is calculated for the steel part in different moments of time. Analysing these data it is possible to determine the thickness of the hardened layer or to predict damage to the material of a given steel part due to heat treatment. The method has been tested experimentally.
  • Publication
    Influence of rubber ageing on damping capacity of rubber vibration absorber
    (2018)
    Svetlana Polukoshko
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    ;
    The vibration dampers, shock absorbers, seismic isolation, bearing seals, compensation devices are widely applied in civil engineering, machine manufacturing and shipbuilding, aviation and aerospace engineering. For these details fabrication elastomeric materials are used. Rubber and rubber-like materials (elastomers) have the capability of absorbing input energy much better than other engineering materials. Elastomeric materials give many engineering advantages due to their high elasticity, good dynamic properties, low volume compressibility, a linear relationship between stress and strain at small and middle deformation, resistance to aggressive environmental factors. The disadvantage of elastomeric materials is ageing, i.e. changing their mechanical properties over time and lowering their operational capability. In given paper the influence of ageing of elastomeric materials on the damping properties of shock absorbers is considered based on the mechanical models of elastomers - Maxwell and Burgers modes.
    Scopus© Citations 6