Studies of the magnetic axis switching in magnetite

The influence of the external magnetic field on magnetic and crystallographic structure of magnetite was studied. We have confirmed, by means of vibrating sample magnetometer measurements, that external magnetic field can switch the easy magnetic axis to the new crystallographic direction. We have also proved by the direct observation of the crystalline structure that this phenomenon is strictly related to the crystallographic structure relaxation

Mathematical modelling and stationary characteristics of a two - phase fluidised - bed bioreactor with external aeration

A mathematical model for a two-phase fluidised bed bioreactor with liquid d recirculation and an external aerator was proposed. A stationary nonlin ear analysis of such a bioreactor for an aerobic process with double-substrate kinetics was carried out. The influences of a volumetric fraction of solid carriers in the liquid phase, the rate of active e biomass transfer from the biofilm to the liquid, the concentration of carbonaceous substrate, the mean residence time of the liquid and the efficiency of the external aerator on the steady state characteristics of the bioreactor were described. A method for determination of the minimal recirculation ratio related to oxygen demand and fluidised bed conditions was presented. On the basis of the obtained results, it is possible to choose reasonable operating conditions of such plants and to determine constraints, while considering acceptable concentrations of a toxic substrate being degraded

Conditions for employing fluidized-bed bioreactors in aerobic processes

W pracy przedstawiono warunki stosowalności dwu- i trójfazowych bioreaktorów fluidyzacyjnych w procesach aerobowych. Zaproponowano metodę wyznaczania granicznych wartości współczynnika recyrkulacji, stopnia przereagowania substratu i czasu przebywania płynu w instalacji. Przedstawiona metoda ma charakter ogólny i może być stosowana dla dowolnego procesu aerobowego.Conditions for the application of two- and three-phase fluidized bed bio-reactors in aerobic processes are presented in the paper. A method for the determination of recirculation ratio boundary values, substrate conversion degree and mean residence time of liquid in the installation is proposed. The presented method has a general nature and may be used for any aerobic process

Nonlinear Dynamics of a Controlled Stirred Tank Bioreactor With Predator-Prey Relationship

The paper presents the dynamic characteristics of a continuous tank bioreactor for microbiological process, with a developed predator-prey food chain. The presence of the predator microorganism considerably influences the position and stability character of steady-states. There appears to exist a wide range of unstable steady-states and high-amplitude oscillations of state variables. Without automatic control, the system can operate only in unsteady conditions. From technological point of view, this circumstance is unfavorable. It was shown that oscillations can be removed by employing automatic control with continuous P or PI controllers. Moreover, the use of a controller with integrating element causes removal of the predator from the bioreactor. The paper discusses an application of this phenomenon for practical purposes

Magnetic and structural studies of magnetite at the Verwey transition

Abstract Studies of the Verwey transition in zinc doped magnetite (Fe 3−x Zn x O 4 , x = 0, 0.0097, 0.011, 0.036) by simultaneous ac magnetic susceptibility (χ) and electric resistance measurements are presented. The temperature hysteresis of the Verwey transition increases from 0.03 K for stoichiometric magnetite to 0.5 K for Zn doped samples, despite the continuous character of the transition. The results of introductory observations of structural changes are also presented

Transport properties and doping evolution of the Fermi surface in cuprates

Abstract Measured transport properties of three representative cuprates are reproduced within the paradigm of two electron subsystems, itinerant and localized. The localized subsystem evolves continuously from the Cu 3d $$^9$$ 9 hole at half-filling and corresponds to the (pseudo)gapped parts of the Fermi surface. The itinerant subsystem is observed as a pure Fermi liquid (FL) with material-independent universal mobility across the doping/temperature phase diagram. The localized subsystem affects the itinerant one in our transport calculations solely by truncating the textbook FL integrals to the observed (doping- and temperature-dependent) Fermi arcs. With this extremely simple picture, we obtain the measured evolution of the resistivity and Hall coefficients in all three cases considered, including LSCO which undergoes a Lifshitz transition in the relevant doping range, a complication which turns out to be superficial. Our results imply that prior to evoking polaronic, quantum critical point, quantum dissipation, or even more exotic scenarios for the evolution of transport properties in cuprates, Fermi-surface properties must be addressed in realistic detail

Взаимодействие частиц и излучения с веществом № УД-858/р

Using density functional theory, we study the lattice dynamical properties of magnetite (Fe$_3$O$_4$) in the high-temperature cubic and low-temperature monoclinic phases. The calculated phonon dispersion curves and phonon density of states are compared with the available experimental data obtained by inelastic neutron, inelastic x-ray, and nuclear inelastic scattering. We find a very good agreement between the theoretical and experimental results for the monoclinic $Cc$ structure revealing the strong coupling between charge-orbital (trimeron) order and specific phonon modes. For the cubic phase, clear discrepancies arise which, remarkably, can be understood assuming that the strong trimeron-phonon coupling can be extended above the Verwey transition, with lattice dynamics influenced by the short-range trimeron order instead of the average cubic structure. Our results establish the validity of trimerons (and trimeron-phonon coupling) in explaining the physics of magnetite much beyond their original formulation.Comment: 11 pages, 9 figures, 1 tabl