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Search Results: 1 - 10 of 325388 matches for " S. Kotrechko "
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Atomic structure and mechanical properties of carbyne
A. Timoshevskii,S. Kotrechko,Yu. Matviychuk
Physics , 2015, DOI: 10.1103/PhysRevB.91.245434
Abstract: The atomic structure and mechanical properties of the carbyne (monatomic linear chains), containing from 2 to 21 carbon atoms, are theoretically investigated by ab-initio methods. We demonstrate the existence of a stable cumulene-structure in the inner part of chains with the number of atoms N>=10. We present a general stress-strain diagram of chains until the moment when they break, which enables to determine their strength, elasticity and fragility. For chains with N>=4, the relationship between the strength of the chain and the binding energy of the edge atom in the chain is established. The existence of scale-effect and "even-odd" effect for such properties as strength, elasticity and fragility is observed. We demonstrate that the 5-atom carbon chains show the maximum strength value.
Mechanical stability paradigm for prediction of rpv service life
S. Kotrechko,Yu. Meshkov,I. Nekludov,V. Revka,L. Chyrko
Physics , 2012,
Abstract: In the framework of the engineering version of a Local approach to fracture the criterion of a fracture limit of RPV with crack-like flaw is derived. It has been shown that the level of ductile state stability (mechanical stability) of metal ahead of a crack governs the value of critical fluence. On this basis, the new paradigm of life-time prediction using the condition of exhaustion of mechanical stability of irradiated PV metal has been proposed. The technique of an end-of-life fluence assessment is developed, and predictive capabilities of this approach are demonstrated by the example of WWER-1000 pressure vessels
Temperature dependence of irradiation hardening due to dislocation loops and precipitates in RPV steels and model alloys
S. Kotrechko,V. Dubinko,N. Stetsenko,D. Terentyev,Xinfu He
Physics , 2014, DOI: 10.1016/j.jnucmat.2015.04.014
Abstract: A relative contribution to irradiation hardening caused by dislocation loops and solute-rich precipitates is established for RPV steels of WWER-440 and WWER-1000 reactors, based on TEM measurements and mechanical testing at reactor operating temperature of 563 K. The pinning strength factors evaluated for loops and precipitates are shown to be much lower than those obtained for model alloys based on the room temperature testing as well as those evaluated by means of atomistic simulations in the temperature range of 300 to 600 K. This discrepancy is explained in the framework of a model of thermally activated dislocation motion, which takes into account the difference in temperature and strain rate employed in atomistic simulations and in mechanical testing.
Radiation-induced softening of Fe and Fe-based alloys during in-situ electron irradiation under mechanical testing
V. I. Dubinko,D. Terentyev,A. N. Dovbnya,V. A. Kushnir,I. V. Hodak,S. V. Lebedev,S. A. Kotrechko,A. V. Dubinko
Physics , 2014,
Abstract: Defects formed under irradiation in the bulk act as additional pinning centers resulting in the well-known effect of radiation-induced hardening. On the other hand, there is a poorly understood but well-established effect of instant and reversible softening of metals subjected to various types of irradiation. This radiation-induced softening (RIS) effect should be taken into account both in the theory of radiation effects and in the engineering approach for technological applications. In the present paper, the RIS is investigated experimentally in polycrystalline technically pure iron (0.048%C) and in commercial ferritic steel. The effect of the electron beam on plastic deformation of bcc Fe is compared with that in fcc Al (99.5%). Electron energy ranged from 0.5 to 0.8 MeV. Reversible drop of the yield stress and radiation-induced reduction of the elongation to fracture are measured as functions of the electron current and specimen thickness. Rate theory of RIS is proposed, which takes into account the radiation-induced excitation of moving discrete breathers (DBs), recently proven to exist in bcc Fe, and their interaction with dislocations enhancing unpinning from structural defects. The behavior of the DBs is studied using classical MD simulations providing input for the modified rate theory, which eventually demonstrates a reasonable agreement with experimental data. The relevance of results to the in-reactor behavior of pressure vessel steels is discussed.
Relation between the strength and dimensionality of defect-free carbon crystals
Sergey Kotrechko,Andrey Timoshevskii,Eugene Kolyvoshko,Yuriy Matviychuk
Physics , 2015, DOI: 10.1186/s11671-015-0929-9
Abstract: On the basis of ab-initio simulations, the value of strength of interatomic bonds in one-, two- and three-dimensional carbon crystals is obtained. It is shown that decreasing in dimensionality of crystal gives rise to nearly linear increase in strength of atomic bonds. It is ascertained that growth of strength of the crystal with a decrease in it dimensionality is due to both a reduction in coordination number of atom and increase in the angle between the directions of atomic bonds. Based on these data, it is substantiated that the one-dimensional crystals have maximum strength, and strength of carbyne is the absolute upper limit of strength of materials
Inherent tensile strength of molybdenum nanocrystals
Anatoly P Shpak, Sergiy O Kotrechko, Tatjana I Mazilova and Igor M Mikhailovskij
Science and Technology of Advanced Materials , 2009,
Abstract: The strength of Mo nanorods was measured under uniaxial tension. Tensile tests of lang 110rang-oriented single-crystalline molybdenum rod-shaped specimens with diameters from 25 to 90 nm at the apex were conducted inside a field-ion microscope (FIM). The nanocrystals were free from dislocations, planar defects and microcracks, and exhibited the plastic mode of failure under uniaxial tension with the formation of a chisel-edge tip by multiple gliding in the (11ar{2})[111] and (112)[11ar{1}] deformation systems. The experimental values of tensile strength vary between 6.3 and 19.8 GPa and show a decrease with increasing nanorod diameter. A molecular dynamic simulation of Mo nanorod tension also suggests that the strength decreases from 28.8 to 21.0 GPa when the rod diameter increases from 3.1 to 15.7 nm. The maximum values of experimental strength are thought to correspond to the inherent strength of Mo nanocrystals under uniaxial tension (19.8 GPa, or 7.5% of Young's modulus).
Study of the Structural and Electrical Properties of Cr-Doped BiFeO3 Ceramic  [PDF]
S. S. Arafat, S. Ibrahim
Materials Sciences and Applications (MSA) , 2017, DOI: 10.4236/msa.2017.810051
Abstract: Multiferroic BiFe1-xCrxO3 (x = 0.2 and 0.4) ceramics were synthesized in a single phase. The effects of Cr3+ substitution on the crystal structure, dielectric permittivity and leakage current were investigated. Preliminary X-ray structural studies revealed that the samples had a rhombohedral perovskite crystal structure. The dielectric constant ε' significantly increased while the dielectric loss tanδ was substantially decreased with the increase in Cr3+ substitution. The temperature effect on the dielectric properties exhibited an anomaly corresponding to magneto-electric coupling in the samples and was shifted to lower temperatures with the increase in Cr3+ substitution. The leakage current density also reduced in magnitude with the increase in the Cr3+ substitution.
Degree Splitting of Root Square Mean Graphs  [PDF]
S. S. Sandhya, S. Somasundaram, S. Anusa
Applied Mathematics (AM) , 2015, DOI: 10.4236/am.2015.66086
Abstract: Let \"\" be an injective function. For a vertex labeling f, the induced edge labeling \"\" is defined by, \"\" or \"\"; then, the edge labels are distinct and are from \"\". Then f is called a root square mean labeling of G. In this paper, we prove root square mean labeling of some degree splitting graphs.
A Parameter Estimation Model of G-CSF: Mathematical Model of Cyclical Neutropenia  [PDF]
S. Balamuralitharan, S. Rajasekaran
American Journal of Computational Mathematics (AJCM) , 2012, DOI: 10.4236/ajcm.2012.21002
Abstract: We investigate the FFT (Fast Fourier Transform) model and G-CSF (granulocyte colony-stimulating factor) treatment of CN (Cyclical Neutropenia). We collect grey collies and normal dog’s data from CN and analyze the G-CSF treatment. The model develops the dynamics of circulating blood cells before and after the G-CSF treatment. This is quite natural and useful for the collection of laboratory data for investigation. The proposed interventions are practical. This reduces the quantity of G-CSF required for potential maintenance. This model gives us good result in treatment. The changes would be practical and reduce the risk side as well as the cost of treatment in G-CSF.
Synthesis, Thermal Behaviour, XRD, and Luminescent Properties of Lighter Lanthanidethiodipropionate Hydrates Containing Aminogunidine as Neutral Ligand  [PDF]
S. Packiaraj, S. Govindarajan
Open Journal of Inorganic Chemistry (OJIC) , 2014, DOI: 10.4236/ojic.2014.43006
Abstract:
Aminoguanidine lanthanide thiodipropionate hydrates of composition [Ln(Agun)2(tdp)3·nH2O], Agun = Aminoguanidine, tdp = thiodipropionic acid, where Ln = La, Pr, Nd and Sm if n = 2, have been prepared and characterized by physic-chemical techniques.
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