Site Occupancy and Lattice Parameters in Sigma-Phase Co-Cr alloys

Neutron diffraction technique was used to study distribution of Co and Cr atoms over different lattice sites as well as lattice paramaters in sigma-phase Co100-xCrx compounds with x = 57.0, 62.7 and 65.8. From the diffractograms recorded in the temperature range of 4.2 - 300 K it was found that all five sites A, B, C, D and E are populated by both kinds of atoms. Sites A and D are predominantly occupied by Co atoms while sites B, C and E by Cr atoms. The unit cell parameters a and c, hence the unit cell volume, increase with x, the increase being characteristic of the lattice paramater and temperature. Both a and c show a non-linear increase with temperature.Comment: 5 figure

Debye temperature of disordered bcc-Fe-Cr alloys

Debye temperature, TD, of Fe100-xCrx disordered alloys with 0<x<99.9 was determined from the temperature dependence of the centre shift of 57Fe Mossbauer spectra recorded in the temperature range of 80-300K. Its compositional dependence shows an interesting non-monotonous behaviour. For 0<x<~45 as well as for ~75<x<~95 the Debye temperature is enhanced relative to its value of a metallic iron, and at x=~3 there is a local maximum having a relative height of ~12% compared to a pure iron. For ~45~95 the Debye temperature is smaller than the one for the metallic iron, with a local minimum at x=~55 at which the relative decrease of TD amounts to ~12%. The first maximum coincides quite well with that found for the spin-waves stiffness coefficient, D0, while the pretty steep decrease observed for x>~95 which is indicative of a decoupling of the probe Fe atoms from the underlying chromium matrix is likely related to the spin-density waves which constitute the magnetic structure of chromium in that interval of composition. The harmonic force constant calculated from the Debye temperature of the least Fe-concentrated alloy (x>99.9) amounts to only 23% of the one characteristic of a pure chromium.Comment: 15 pages, 7 figures, 26 reference

Magnetic ordering above room temperature in the sigma-phase of Fe66V34

Magnetic properties of four sigma-phase Fe_(100-x)V_x samples with 34.4<x<55.1 were investigated by Mossbauer spectroscopy and magnetic measurements in the temperature interval 5-300 K. Four magnetic quantities viz. hyperfine field, Curie temperature, magnetic moment and susceptibility were determined. The sample containing 34.4 at% V was revealed to exhibit the largest values found up to now for the sigma-phase for average hyperfine field, B = 12.1 T, average magnetic moment per Fe atom, m = 0.89 mB, and Curie temperature, TC = 315.5 K. The quantities were shown to be strongly correlated with each other. In particular, TC is linearly correlated with m with a slope of 406.5 K/mB, as well as B is so correlated with m yielding 14.3 T/mB for the hyperfine coupling constant.Comment: 15 pages, 11 figures, 1 tabl

Sigma-phase in Fe-Cr and Fe-V alloy systems and its physical properties

A review is presented on physical properties of the sigma-phase in Fe-Cr and Fe-V alloy systems as revealed both with experimental -- mostly with the Mossbauer spectroscopy -- and theoretical methods. In particular, the following questions relevant to the issue have been addressed: identification of sigma and determination of its structural properties, kinetics of alpha-to-sigma and sigma-to-alpha phase transformations, Debye temperature and Fe-partial phonon density of states, Curie temperature and magnetization, hyperfine fields, isomer shifts and electric field gradients.Comment: 26 pages, 23 figures and 83 reference

Finite-time blowup in a supercritical quasilinear parabolic-parabolic Keller-Segel system in dimension 2

In this paper we prove finite-time blowup of radially symmetric solutions to the quasilinear parabolic-parabolic two-dimensional Keller-Segel system for any positive mass. This is done in case of nonlinear diffusion and also in the case of nonlinear cross-diffusion provided the nonlinear chemosensitivity term is assumed not to decay. Moreover, it is shown that the above-mentioned lack of non-decay assumption is essential with respect to keeping the dichotomy finite-time blowup against boundedness of solutions. Namely, we prove that without the non-decay assumption possible asymptotic behaviour of solutions includes also infinite-time blowup.Comment: 14 page

Long-time behavior of an angiogenesis model with flux at the tumor boundary

This paper deals with a nonlinear system of partial differential equations modeling a simplified tumor-induced angiogenesis taking into account only the interplay between tumor angiogenic factors and endothelial cells. Considered model assumes a nonlinear flux at the tumor boundary and a nonlinear chemotactic response. It is proved that the choice of some key parameters influences the long-time behaviour of the system. More precisely, we show the convergence of solutions to different semi-trivial stationary states for different range of parameters.Comment: 17 page

Narzędzia rachunkowości w praktyce działania regulatora sektorowego w telekomunikacji

Telecommunications has a direct impact on the development and competitiveness of the economy and quality of each citizen’s life. It is a basic infrastructure sector. Many telecommunications markets can be lead by even one entrepreneur in an economically efficient way. The subject of this research are sectoral regulator interventions – of the President of the Office of Electronic Communications. The main method of this research is to analyze the regulatory decisions. The use of ex - ante sector regulation requires recognition of the competitiveness level of the markets. The assessment requires an economic analysis. This evaluation shows the relations between telecommunications companies. The method of analysis results from the description in the legislation regulatory mandate. It is the result of applied regulatory practice. For this assessment both quantitative and qualitative criteria are used. Some of them are supported by accounting and finance instruments. The aim of this paper is to demonstrate the practical use of the accounting in the assessment of the competitiveness of the telecommunications markets by the sectoral regulator.Telekomunikacja ma bezpośredni wpływ na rozwój i konkurencyjność gospodarki oraz jakość życia obywateli. Jest podstawowym sektorem infrastrukturalnym. Na wielu rynkach telekomunikacyjnych działalność w sposób efektywny ekonomicznie prowadzić może jeden przedsiębiorca. Przedmiotem badań są interwencje regulatora sektorowego – Prezesa UKE. Główna metoda badań polega na analizie rozstrzygnięć regulacyjnych. Wykorzystanie wyprzedzającej regulacji sektorowej wymaga rozpoznania poziomu konkurencyjności rynków. Przeprowadzenie oceny wymaga dokonania analizy ekonomicznej. Ocena ta pokazuje, jakie relacje zachodzą między przedsiębiorcami. Sposób przeprowadzania analiz wynika z opisanego w przepisach prawa mandatu regulacyjnego. Jest on efektem stosowanej praktyki regulacyjnej. Do tej oceny wykorzystywane są kryteria ilościowe i jakościowe. Wybrane z nich wspomagane są instrumentami rachunkowości i finansów. Celem opracowania jest ukazanie praktycznego wykorzystania rachunkowości, w ocenie konkurencyjności rynków telekomunikacyjnych przez organ administracji publicznej

Well-posedness for a model of individual clustering

25 pagesInternational audienceWe study the well-posedness of a model of individual clustering. Given p > N ≥ 1 and an initial condition in W 1,p (Ω), the local existence and uniqueness of a strong solution is proved. We next consider two specific reproduction rates and show global existence if N = 1, as well as, the convergence to steady states for one of these rates