S��ntesi i propietats de vidres met��l���lics massissos i materials nanocomposites basats en Fe per aplicacions com a materials magn��tics tous

Estudi realitzat a partir d���una estada a l��� Institut f��r Komplexe Materialien, Leibniz-Institut f��r Festk��rper- und Werkstoffforschung Dresden, entre 2010 i 2011. S'ha explorat l'efecte de les condicions i influ��ncia dels elements d'aleaci�� en la capacitat de formaci�� de vidre, l'estructura i les propietats t��rmiques i magn��tiques de vidres met��l���lics massissos i materials nanocristal���lins en base Fe. La producci�� d'aquests materials en forma de cintes de unes 20 micres de gruix ha estat ��mpliament estudiada i s'ha vist que presenten unes propietats excel���lents com a materials magn��tics tous. El prop��sit general d'aquest projecte era l'obtenci�� de composicions ��ptimes amb alta capacitat de formar vidre i amb excel���lents propietats magn��tiques com a materials magn��tics tous combinat amb bones propietats mec��niques. El projecte prenia com a punt de partida l'aliatge [FeCoBSi]96Nb4 ja que ��s el que presenta millor capacitat de formar vidre i presenta una alta imantaci�� de saturaci�� i baix camp coercitiu. S'ha fet un estudi dels factors fonamentals que intervenen en la formaci�� de l'estat vitri. La composici�� abans esmentada ha estat variada amb l'addici�� d'altres elements per estudiar com afecten aquests nous elements a les propietats, la formaci�� de vidre i l'estructura dels aliatges resultants amb l'objectiu de millorar-ne les propietats magn��tiques i la capacitat de formaci�� de vidre. Entre altres s'ha usat el Zr, Mo, Y i el Gd per millorar la formaci�� de vidre; i el Co i el Ni per millorar les propietats magn��tiques a alta temperatura. S'han estudiat les relacions entre la capacitat de formaci�� de vidre i la seva estabilitat t��rmica, la resist��ncia a la cristal���litzaci�� i la estructura de l'aliatge resultant despr��s del proc��s de solidificaci��. Per aquest estudi s'han determinat els mecanismes que controlen la transformaci�� i la seva cin��tica aix�� com les fases que es formen durant el tractament t��rmic permetent la formulaci�� de models predictius.

Simulation methods with extended stability for stiff biochemical kinetics

Background: With increasing computer power, simulating the dynamics of complex systems in chemistry and biology is becoming increasingly routine. The modelling of individual reactions in (bio)chemical systems involves a large number of random events that can be simulated by the stochastic simulation algorithm (SSA). The key quantity is the step size, or waiting time, ��, whose value inversely depends on the size of the propensities of the different channel reactions and which needs to be re-evaluated after every firing event. Such a discrete event simulation may be extremely expensive, in particular for stiff systems where �� can be very short due to the fast kinetics of some of the channel reactions. Several alternative methods have been put forward to increase the integration step size. The so-called ��-leap approach takes a larger step size by allowing all the reactions to fire, from a Poisson or Binomial distribution, within that step. Although the expected value for the different species in the reactive system is maintained with respect to more precise methods, the variance at steady state can suffer from large errors as �� grows. Results: In this paper we extend Poisson ��-leap methods to a general class of Runge-Kutta (RK) ��-leap methods. We show that with the proper selection of the coefficients, the variance of the extended ��-leap can be well-behaved, leading to significantly larger step sizes.Conclusions: The benefit of adapting the extended method to the use of RK frameworks is clear in terms of speed of calculation, as the number of evaluations of the Poisson distribution is still one set per time step, as in the original ��-leap method. The approach paves the way to explore new multiscale methods to simulate (bio)chemical systems.

First-passage time in a bistable potential with colored noise

A precise digital simulation of a bistable system under the effect of colored noise is carried out. A set of data for the mean first-passage time is obtained. The results are interpreted and compared with presently available theories, which are revisited following a new insight. Discrepancies that have been discussed in the literature are understood within our framework.

Kinetic resolution: a powerful tool for the synthesis of planar-chiral ferrocenes

Since the serendipitous discovery of ferrocene by Pauson and Kealy in 1951, it has become one of the most important structures in Organic Chemistry. Lately, kinetic resolution has emerged as a useful tool for the synthesis of planar chiral ferrocenes. This review aims to cover and discuss the development of this topic.

Study and modeling of the desintegration kinetics of coated paper

The disintegration of recovered paper is the first operation in the preparation of recycled pulp. It is known that the defibering process follows a first order kinetics from which it is possible to obtain the disintegration kinetic constant (KD) by means of different ways. The disintegration constant can be obtained from the Somerville index results (%lsv and from the dissipated energy per volume unit (Ss). The %slv is related to the quantity of non-defibrated paper, as a measure of the non-disintegrated fiber residual (percentage of flakes), which is expressed in disintegration time units. In this work, disintegration kinetics from recycled coated paper has been evaluated, working at 20 revise rotor speed and for different fiber consistency (6, 8, 10, 12 and 14%). The results showed that the values of experimental disintegration kinetic constant, Ko, through the analysis of Somerville index, as function of time. Increased, the disintegration time was drastically reduced. The calculation of the disintegration kinetic constant (modelled Ko), extracted from the Rayleigh���s dissipation function, showed a good correlation with the experimental values using the evolution of the Somerville index or with the dissipated energy

Study and modeling of the desintegration kinetics of coated paper

The disintegration of recovered paper is the first operation in the preparation of recycled pulp. It is known that the defibering process follows a first order kinetics from which it is possible to obtain the disintegration kinetic constant (KD) by means of different ways. The disintegration constant can be obtained from the Somerville index results (%lsv and from the dissipated energy per volume unit (Ss). The %slv is related to the quantity of non-defibrated paper, as a measure of the non-disintegrated fiber residual (percentage of flakes), which is expressed in disintegration time units. In this work, disintegration kinetics from recycled coated paper has been evaluated, working at 20 revise rotor speed and for different fiber consistency (6, 8, 10, 12 and 14%). The results showed that the values of experimental disintegration kinetic constant, Ko, through the analysis of Somerville index, as function of time. Increased, the disintegration time was drastically reduced. The calculation of the disintegration kinetic constant (modelled Ko), extracted from the Rayleigh���s dissipation function, showed a good correlation with the experimental values using the evolution of the Somerville index or with the dissipated energy

Report on theorerical results of power generation and conversion

Experimental results of a new controller able to support bidirectional power flow in a full-bridge rectifier with boost-like topology are obtained. The controller is computed using port Hamiltonian passivity techniques for a suitable generalized state space averaging truncation system, which transforms the control objectives, namely constant output voltage dc-bus and unity input power factor, into a regulation problem. Simulation results for the full system show the essential correctness of the simplifications introduced to obtain the controller, although some small experimental discrepancies point to several aspects that need further improvement.

Hybrid model of a double-fed induction machine and back-to-back converter

This report details the port interconnection of two subsystems: a power electronics subsystem (a back-to-back AC/AC converter (B2B), coupled to a phase of the power grid), and an electromechanical subsystem (a doubly-fed induction machine (DFIM), coupled mechanically to a flywheel and electrically to the power grid and to a local varying load). Both subsystems have been essentially described in previous reports (deliverables D 0.5 and D 4.3.1), although some previously unpublished details are presented here. The B2B is a variable structure system (VSS), due to the presence of control-actuated switches: however from a modelling and simulation, as well as a control-design, point of view, it is sensible to consider modulated transformers (MTF in the bond-graph language) instead of the pairs of complementary switches. The port-Hamiltonian models of both subsystems are presents and coupled through a power-preserving interconnection, and the Hamiltonian description of the whole system is obtained; detailed bond-graphs of all the subsystems and the complete system are provided.

Study and modeling of the desintegration kinetics of coated paper

The disintegration of recovered paper is the first operation in the preparation of recycled pulp. It is known that the defibering process follows a first order kinetics from which it is possible to obtain the disintegration kinetic constant (KD) by means of different ways. The disintegration constant can be obtained from the Somerville index results (%lsv and from the dissipated energy per volume unit (Ss). The %slv is related to the quantity of non-defibrated paper, as a measure of the non-disintegrated fiber residual (percentage of flakes), which is expressed in disintegration time units. In this work, disintegration kinetics from recycled coated paper has been evaluated, working at 20 revise rotor speed and for different fiber consistency (6, 8, 10, 12 and 14%). The results showed that the values of experimental disintegration kinetic constant, Ko, through the analysis of Somerville index, as function of time. Increased, the disintegration time was drastically reduced. The calculation of the disintegration kinetic constant (modelled Ko), extracted from the Rayleigh���s dissipation function, showed a good correlation with the experimental values using the evolution of the Somerville index or with the dissipated energy

Application of Information Statistical Theory to the Description of the Effect of Heat Conduction on the Chemical Reaction Rate in Gases

The effect of the heat flux on the rate of chemical reaction in dilute gases is shown to be important for reactions characterized by high activation energies and in the presence of very large temperature gradients. This effect, obtained from the second-order terms in the distribution function (similar to those obtained in the Burnett approximation to the solution of the Boltzmann equation), is derived on the basis of information theory. It is shown that the analytical results describing the effect are simpler if the kinetic definition for the nonequilibrium temperature is introduced than if the thermodynamic definition is introduced. The numerical results are nearly the same for both definitions

Spontaneous Emergence of Chirality in the Limited Enantioselectivity Model: Autocatalytic Cycle Driven by an External Reagent

The emergence of chirality in enantioselective autocatalysis for compounds unable to transform according to the Frank-like reaction network is discussed with respect to the controversial limited enantioselectivity (LES) model composed of coupled enantioselective and non-enantioselective autocatalyses. The LES model cannot lead to spontaneous mirror symmetry breaking (SMSB) either in closed systems with a homogeneous temperature distribution or in closed systems with a stationary non-uniform temperature distribution. However, simulations of chemical kinetics in a two-compartment model demonstrate that SMSB may occur if both autocatalytic reactions are spatially separated at different temperatures in different compartments but coupled under the action of a continuous internal flow. In such conditions, the system can evolve, for certain reaction and system parameters, toward a chiral stationary state; that is, the system is able to reach a bifurcation point leading to SMSB. Numerical simulations in which reasonable chemical parameters have been used suggest that an adequate scenario for such a SMSB would be that of abyssal hydrothermal vents, by virtue of the typical temperature gradients found there and the role of inorganic solids mediating chemical reactions in an enzyme-like role.

Study and modeling of the desintegration kinetics of coated paper

The disintegration of recovered paper is the first operation in the preparation of recycled pulp. It is known that the defibering process follows a first order kinetics from which it is possible to obtain the disintegration kinetic constant (KD) by means of different ways. The disintegration constant can be obtained from the Somerville index results (%lsv and from the dissipated energy per volume unit (Ss). The %slv is related to the quantity of non-defibrated paper, as a measure of the non-disintegrated fiber residual (percentage of flakes), which is expressed in disintegration time units. In this work, disintegration kinetics from recycled coated paper has been evaluated, working at 20 revise rotor speed and for different fiber consistency (6, 8, 10, 12 and 14%). The results showed that the values of experimental disintegration kinetic constant, Ko, through the analysis of Somerville index, as function of time. Increased, the disintegration time was drastically reduced. The calculation of the disintegration kinetic constant (modelled Ko), extracted from the Rayleigh���s dissipation function, showed a good correlation with the experimental values using the evolution of the Somerville index or with the dissipated energy

Fotoluminiscencia visible debida a capas de SiO2. implantadas con silicio y carbono

Se ha n realizado implantaciones de silicio y de carbono + silicio en matrices aislantes de S��O2 t��rmico, las cuales, despu��s de un recocido a alta temperatura precipitan en forma de nanocristales de tama��os comprendidos entre 30 y 60 ��. Estas estructuras presentan una intensa fotoluminiscencia en el rojo profundo (1.4-1.6 eV) y el verde (2.0-2.2 eV). La energ��a e intensidad de las bandas depende fuertemente de la temperatura y duraci��n del recocido. Diferentes comportamientos se han encontrado para las bandas roja y verde, incluyendo la cinética de desexcitaci��n y el origen estructural. Los experimentos de absorci��n infrarroja, Raman y microscop��a electr��nica demuestran que los nanocristales son los responsables de la banda roja mientras que agregados amorfos de carbono son los responsables de la verde.

La calorimetr��a diferencial de barrido y su aplicaci��n a la Ciencia de Materiales

Se pone de manifiesto la idoneidad de la t��cnica de calorimetr��a diferencial de barrido para la caracterizaci��n de materiales. Se presentan ejemplos espec��ficos de aplicaci��n de dicha t��cnica en el estudio de los fen��menos ligados a la transici��n vitrea y cinética de cristalizaci��n de vidrios calcogenuros y met��licos as�� como en el estudio de la reordenaci��n de fases desordenadas metastables.