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

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

Effect of time and storing conditions on iron forms in ferrous gluconate and Ascofer

Antianemic medicament Ascofer and ferrous gluconate, its basic iron bearing ingredient, were studied with the use of Mossbauer spectroscopy. Room temperature spectra gave a clear evidence that two phases of iron were present viz. ferrous (Fe2+) as a major one with a contribution of 85+-5%, and ferric (Fe3+) whose contribution was found to be 15+-5%. However, the actual values of the contributions of the two kind of the iron ions in Ascofer depend on sample's age: the abundance of Fe2+ ions increases with time by 10% after 51 months, while that of Fe3+ decreases by the same amount. This means that an internal reduction of Fe3+ ions takes place. Ferrous ions were shown to occupy at least two different sites. In Ascofer, the relative abundance of the two sites does not depend on the age of sample, while in the gluconate the population of site 1 increases and that of site 2 decreases with the age of the sample.Comment: 14 pages, 13 figure

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

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

Anomalous behavior of the Debye temperature in Fe-rich Fe-Cr alloys

Debye temperature, $\Theta_D$, of Fe-rich Fe$_{100-x}$Cr$_x$ disordered alloys with $0\le x \le 22.3$ was determined from the temperature dependence of the central shift of M\"ossbauer spectra recorded in the temperature range of 60 -- 300 K. Its compositional dependence shows a maximum at $x \approx 5$ with a relative increase of $\sim 30$% compared to a pure iron. The composition at which the effect occurs correlates well with that at which several other quantities, e. g. the Curie temperature and the spin-wave stiffness coefficient, $D_0$, show their maxima, but the enhancement of $\Theta_D$ is significantly greater and comparable with the enhancement of the hyperfine field (spin-density of itinerant $s$-like electrons) in the studied system. The results suggest that the electron-phonon interaction is important in this alloy system

Stealth nanocarriers based sterosomes using PEG post-insertion process

Sterosomes (STEs), a new and promising non-phospholipidic liposome platform based on palmitic acid (PA) and cholesterol (Chol) mixtures, need to have polyethylene glycol (PEG) chains grafted to their surface in order to obtain long-circulating nanocarriers in the blood stream. A post-insertion method was chosen to achieve this modification. The post-insertion process of PEG-modified distearoylphosphoethanolamine (DSPE-PEG) was monitored using the zeta potential value of STEs. Various conditions including PEG chain length and the DSPE-PEG/PA-Chol ratio, were explored. Zeta potential of STEs changed from about -40mV for non-modified STEs to values close to 0 mV by the end of the process, i.e. for PEG-modified STEs. The kinetics of DSPE-PEG insertion and the stability of the resulting PEG-modified STEs were not considerably influenced, within the investigated range, by changes in PEG chain lengths and in DSPE-PEG/PA-Chol proportion. The post-insertion of PEG chains reduced in vitro complement activation as well as in vitro macrophage uptake compared to the non-modified STEs. Moreover, longer blood circulation time in mice was established for PEG-modified STEs intravenously injected compared to non-modified STEs. These results establish that post-insertion process of PEG chains to STEs is a promising strategy for developing long-term circulating drug delivery nanocarriers