| 467971. |
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| 467972. |
- Karkin, A. E., et al.
(författare)
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Monitoring an insulator-metal transition in icosahedral AlPdRe by neutron irradiation
- 2002
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 66:9
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Tidskriftsartikel (refereegranskat)abstract
- The intrinsic disorder effect on the electrical resistivity and magnetoresistance (MR) of icosahedral AlPdRe is studied by use of high-energy neutron irradiation. The icosahedral phase is preserved under irradiation with a decrease of x-ray peak intensity and volume of the coherent icosahedral phase. An insulator-metal transition, as observed in the MR, can be driven by the irradiation and is monitored by the resistance ratio R[=rho(4.2 K)/rho(295 K)]. The relation of MR vs R was found to be similar for samples of a widely different history.
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| 467973. |
- Karkin, I. N., et al.
(författare)
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Effect of Ni and Al on the Decomposition Kinetics and Stability of Cu-Enriched Precipitates in Fe-Cu-Ni-Al Alloys : Results of MD plus MC Simulation
- 2021
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Ingår i: Physics of metals and metallography. - : MAIK NAUKA/INTERPERIODICA/SPRINGER. - 0031-918X .- 1555-6190. ; 122:5, s. 498-503
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Tidskriftsartikel (refereegranskat)abstract
- To understand the effects of doping elements on the formation and structure of Cu-enriched precipitates, different stages of Fe-Cu-Ni-Al alloy decomposition are studied using the combined MC + MD approach, which includes the Monte Carlo (MC) and molecular dynamics (MD) simulations. It is shown that the surface of the precipitates enriches in the doping elements at early stages of the decomposition, which is significant for the structure stability against the bcc -> 9R transition of the copper enriched precipitates.
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| 467974. |
- Kar'kin, I. N., et al.
(författare)
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Kinetics of Early Decomposition Stages in Diluted bcc Fe-Cu-Ni-Al Alloy : MC plus MD Simulation
- 2019
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Ingår i: Physics of the solid state. - : PLEIADES PUBLISHING INC. - 1063-7834 .- 1090-6460. ; 61:4, s. 601-608
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Tidskriftsartikel (refereegranskat)abstract
- A combined approach including the Monte Carlo and molecular-dynamics simulation, decomposition kinetics and segregation formation in the multicomponent low-alloy Fe-1.5Cu-2Ni-1.5Al (at %) alloy is studied. It is shown that the formation of Cu nanoparticles surface-enriched with Ni and Al (coprecipitation mode) includes several stages: (i) the formation of clusters consisting of several Cu atoms, (ii) their enrichment with Ni and Al atoms, and (iii) redistribution of Ni and Al atoms with the formation of a surface layer providing stabilization of Cu nanoparticles. Observed structural features of segregations and their stability in Fe-Cu-Ni-Al alloys is discussed.
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| 467975. |
- Kar'kin, I. N., et al.
(författare)
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Monte Carlo Simulation of the Kinetics of Decomposition and the Formation of Precipitates at Grain Boundaries of the General Type in Dilute BCC Fe-Cu Alloys
- 2017
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Ingår i: Physics of the solid state. - : MAIK NAUKA/INTERPERIODICA/SPRINGER. - 1063-7834 .- 1090-6460. ; 59:1, s. 106-113
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Tidskriftsartikel (refereegranskat)abstract
- The kinetics of decomposition of a polycrystalline Fe-Cu alloy and the formation of precipitates at the grain boundaries of the material have been investigated theoretically using the atomistic simulation on different time scales by (i) the Monte Carlo method implementing the diffusion redistribution of Cu atoms and (ii) the molecular dynamics method providing the atomic relaxation of the crystal lattice. It has been shown that, for a small grain size (D similar to 10 nm), the decomposition in the bulk of the grain is suppressed, whereas the copper-enriched precipitates coherently bound to the matrix are predominantly formed at the grain boundaries of the material. The size and composition of the precipitates depend significantly on the type of grain boundaries: small precipitates (1.2-1.4 nm) have the average composition of Fe-40 at % Cu and arise in the vicinity of low-angle grain boundaries, while larger precipitates that have sizes of up to 4 nm and the average composition of Fe-60 at % Cu are formed near grain boundaries of the general type and triple junctions.
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| 467976. |
- Karkin, I. N., et al.
(författare)
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Segregation of Mg to generic tilt grain boundaries in Al : Monte Carlo modeling
- 2015
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Ingår i: Materials Physics and Mechanics. - : Institute of Problems of Mechanical Engineering. - 1605-2730 .- 1605-8119. ; 24:3, s. 201-210
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Tidskriftsartikel (refereegranskat)abstract
- The formation of equilibrium segregations at tilt grain boundaries of several different types in Al-Mg alloys has been investigated in the framework of a combined approach, which includes molecular dynamics simulation and thermodynamic Monte Carlo modeling. The concentration profile of Mg distribution in GB vicinity was calculated in dependence on the alloy concentration and temperature. We found that width of segregation on generic GB determined by feature of their structure and is match bigger in comparison with special lowenergy GB. It is shown that segregation formation is control not only energy gain due to moving solute on GB but also interaction between solute atoms; as results, maximal enrichment of GB is not exceed 25 at.%. Possible origins of the formation of extended segregation on GB in materials subjected by severe plastic deformation have been discussed.
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| 467977. |
- Karkina, L. E., et al.
(författare)
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Solute-grain boundary interaction and segregation formation in Al : First principles calculations and molecular dynamics modeling
- 2016
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Ingår i: Computational materials science. - : Elsevier. - 0927-0256 .- 1879-0801. ; 112, s. 18-26
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Tidskriftsartikel (refereegranskat)abstract
- The interaction between solute atoms (Mg, Si, Ti) and grain boundaries (GBs) of different types in Al are investigated using two approaches: first principles total energy calculations and large scale atomistic simulations. We have found that both deformation (size effect) and electronic (charge transfer) mechanisms play an important role in solute-GB interaction. The deformation and electronic contributions to GB segregation energy for the considered solutes have been analyzed in dependence on the impurity and the GB type. Mg and Si atoms are calculated to segregate to GBs, while Ti atoms to repel from, GBs in Al. For the case of a symmetric special-type GB the interaction is found to be short-ranged. For a general-type GB the range of GB-solute interaction is found to be considerably longer. A method to estimate the segregation capacity of a GB has been proposed, which takes into account the solute-solute interactions, and shown to be able to correctly describe the GB enrichment in alloying elements. The features of the segregation formation in fine-grained materials produced by severe plastic deformation are discussed.
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| 467978. |
- Karkkainen, Elina, et al.
(författare)
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Optotracing for live selective fluorescence-based detection of Candida albicans biofilms
- 2022
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Ingår i: Frontiers in Cellular and Infection Microbiology. - : Frontiers Media SA. - 2235-2988. ; 12
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Tidskriftsartikel (refereegranskat)abstract
- Candida albicans is the most common fungal pathogen in humans, implicated in hospital-acquired infections, secondary infections in human immunodeficiency virus (HIV) patients, and is a significant contributor to the global antimicrobial resistance (AMR) burden. Early detection of this pathogen is needed to guide preventative strategies and the selection and development of therapeutic treatments. Fungal biofilms are a unique heterogeneous mix of cell types, extracellular carbohydrates and amyloid aggregates. Perhaps due to the dominance of carbohydrates in fungi, to date, few specific methods are available for the detection of fungal biofilms. Here we present a new optotracing-based method for the detection and analysis of yeast and biofilms based on C. albicans SC5314 as a model. Using commercial extracts of cell wall carbohydrates, we showed the capability of the optotracer EbbaBiolight 680 for detecting chitin and beta-glucans. The sensitivity of this tracer to these carbohydrates in their native environment within fungal cells enabled the visualization of both yeast and hyphal forms of the microbe. Analysis of optotracer fluorescence by confocal laser scanning microscopy revealed extensive staining of fungi cell walls as well as the presence of intracellular amyloid aggregates within a subpopulation of cells within the biofilm. Further analysis of the photophysical properties of bound tracers by spectroscopy and spectral imaging revealed polymorphisms between amyloid aggregates within yeast and hyphal cells and enabled their differentiation. With exceptional spatial and temporal resolution, this assay adds a new technique that facilitates future understanding of fungal biofilms and their formation, and enables direct, unbiased diagnostics of these medically relevant biofilms, as well as the development of antifungal strategies.
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| 467979. |
- Karkkainen, K, et al.
(författare)
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Density-functional theory of multicomponent quantum dots
- 2004
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 70:19
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Tidskriftsartikel (refereegranskat)abstract
- Quantum dots with conduction electrons or holes originating from several bands are considered. We assume the particles are confined in a harmonic potential and assume the electrons (or holes) belonging to different bands to be different types of fermions with isotropic effective masses. The density-functional method with the local density approximation is used. The increased number of internal (Kohn-Sham) states leads to a generalization of Hund's first rule at high densities. At low densitites the formation of Wigner molecules is favored by the increased internal freedom.
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| 467980. |
- Karkkainen, K, et al.
(författare)
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Electron-hole bilayer quantum dots: phase diagram and exciton localization
- 2004
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Ingår i: Solid State Communications. - : Elsevier BV. - 1879-2766 .- 0038-1098. ; 130:3-4, s. 187-191
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Tidskriftsartikel (refereegranskat)abstract
- We studied a vertical 'quantum dot molecule', where one of the dots is occupied by electrons and the other by holes. We find that different phases occur in the ground state, depending on the carrier density and the interdot distance. When the system is dominated by shell structure, orbital degeneracies can be removed either by Hund's rule, or by Jahn-Teller deformation. Both mechanisms can lead to a maximum of the addition energy at mid-shell. At low densities and large interdot distances, bound electron-hole pairs are formed. (C) 2004 Elsevier Ltd. All rights reserved.
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