Global existence for a class of generalized systems for irreversible phase changes

A nonlinear evolution system is investigated. It can describe a wide class of phase transition phenomena, including irreversible phase changes. The nonlinearities are of various kind and two maximal monotone graphs appear in the phase relaxation equation. An existence result is established for the related Cauchy-Neumann problem by using regularization, truncation, and monotonicity techniques.     

Study of a system for the isothermal separation of components in a binary alloy with change of phase

An isothermal model describing the separation of the componentsof a binary metallic alloy is considered. A process of phasetransition is also assumed to occur in the solder; hence, thestate of the material is described by two order parameters,i.e. the concentration c of the first component and the phasefield . A physical derivation is provided starting from energybalance considerations. The resulting system of PDEs consistsof a rather regular second-order parabolic equation for coupledwith a fourth-order relation of Cahn–Hilliard type forc with constraint and solution-dependent mobility. Global existenceof solutions is proved and several regularity properties arediscussed under more restrictive assumptions on the physicalparameters. Continuous dependence on data is shown in a specialcase. An asymptotic analysis of the model is also performed,yielding at the limit step a coupling of the original phasefield equation with a Stefan-like system for c.     

Erkennung eines Alkoholgehaltes in Aether

Ohne Zusammenfassung     

Attractors for Gradient Flows of Nonconvex Functionals and Applications

This paper addresses the long-time behaviour of gradient flows of nonconvex functionals in Hilbert spaces. Exploiting the notion of generalized semiflows by J. M. Ball, we provide some sufficient conditions for the existence of a global attractor. The abstract results are applied to various classes of nonconvex evolution problems. In particular, we discuss the long-time behaviour of solutions of quasistationary phase field models and prove the existence of a global attractor.     

Platinum porphyrins as ionophores in polymeric membrane electrodes

A comparative study of Pt(II)- and Pt(IV)-porphyrins as novel ionophores for anion-selective polymeric membrane electrodes is performed. Polymeric membranes of different compositions, prepared by varying plasticizers, cationic and anionic additives and Pt porphyrins, have been examined by potentiometric and optical techniques. Pt porphyrin-based devices were found to exhibit enhanced potentiometric selectivity toward iodide ion compared to electrodes based on a typical anion-exchanger (e.g. tridodecylmethylammonium chloride). It is shown that Pt(II)-porphyrins function as neutral anion carriers within the electrode membranes, while those based on Pt(IV)TPPCl(2) operate via a mixed mode carrier mechanism, evidencing also a partial reduction of the starting ionophore to Pt(II)TPP. Spectrophotometric measurements of thin polymeric films indicate that no spontaneous formation of hydroxide ion bridged porphyrin dimers occurs in the membrane plasticized both with high or low dielectric constant plasticizer, due to a low oxophilicity of central Pt. The computational study of various anion-Pt(IV)TPPCl(2) complex formation by means of semi-empirical and density functional theory (DFT) methods revealed a good correlation between calculated and measured ionophore selectivity.     

Magnetic shape-memory alloys: thermomechanical modelling and analysis

A phenomenological model for the coupled thermo-electro-magneto-mechanical and phase-transformation behaviour of magnetic shape-memory alloys is advanced in small strains and eddy current approximation. The corresponding system of strongly nonlinear relations is tackled via a suitable enthalpy-like transformation. A fully implicit regularized time-discretization scheme is devised and proved to be stable and convergent. In particular, the convergence proof for discrete solutions entails that a suitably weak, energy-conserving solution to the continuous nonlinear system exists. Moreover, several particular models as e.g. ferro/paramagnetic transformation in ferromagnetic materials, martensitic transformation in shape memory allows, or just a simple thermistor problem are covered just as special cases.     

A three-dimensional model describing stress-induced solid phase transformation with permanent inelasticity

The employment of shape memory alloys (SMA) in a large number of applications in the fields of aeronautical, biomedical, and structural engineering has been the motivation for an increasing interest in the direction of a correct and exhaustive modeling of their macroscopic behaviour.     

Evaluation of the reproducibility standard deviation in the pesticide multi-residue methods on olive oil from past proficiency tests

Accreditation and Quality Assurance - The data reported in the frame of proficiency testing (PT) exercises organized from 2007 to 2016 have been statistically re-evaluated using Algorithm A of the...     

Use of enzymatic catalysis with E.C. 1.2.3.2 xanthine oxidase for the kinetic determination of V(V) at low concentrations

An enzymatic kinetic method for the determination of V(V) is described, based on the activation of xanthine oxidase-catalysed NADH oxidation, in the presence of xanthine, dithiothreitol and Ag(+) ions. Under these conditions the activating power of V(V) was found to be enhanced. The linear relationship between relative enzyme activity and V(V) concentration allows the enzymatic determination of vanadium in the concentration range 20-500 ng ml , the maximum relative error being +/- 3%, and relative standard deviation less than +/- 2.2%. Possible interferences have been studied.