255 research outputs found
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
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