Determination of parameters in surface limited hydrogen permeation through metal membrane

Hydrogen permeation through metal membranes at low upstream pressures is considered in the regime where the permeation rate is limited by the surface processes and not by diffusion in the bulk. The mathematical model for the hydrogen permeation through asymmetric membrane in the surface limited regime (SLR) is briefly introduced. For this model, we show that it is not possible to determine the unknown hydrogen-related membrane parameters by measuring the permeation flux through the membrane only in one direction. As an alternative to experiments on permeation in both directions, we describe an innovative and simple experimental technique that enables measurement of the permeation and outgassing rates of the membrane. All fluxes are determined from the upstream pressure change. For the proposed technique, we give a mathematical model and procedure that allows to extract all hydrogen-related membrane parameters from the experimental data without any fitting, solving of differential equations and without relying on the published parameters. The error of the obtained parameters introduced by the calculational procedure is only a few percents.     

Identification of the effective distribution function for determination of the distributed activation energy models using the maximum likelihood method: Isothermal thermogravimetric data

The new procedure for identification of the effective distribution function for determination of the distributed activation energy models, which is based on use the maximum likelihood method (MLM), was established. The five different continuous probability functions (exponential, logistic, normal, gamma, and Weibull probability functions (the extended set of distributions)) were used for searching the best reactivity model for two heterogeneous processes: (a) the isothermal reduction process of nickel oxide under hydrogen atmosphere and (b) the isothermal degradation process of bisphenol‐A polycarbonate (Lexan) under nitrogen atmosphere. The MLM showed that for both processes, the most suitable reactivity model represents the Weibull distribution model. It was concluded that the values of Arrhenius parameters (ln A and E_a), evaluated from the Weibull distribution model, represent the effective kinetic values for both considered processes. This procedure enables identification the suitable distribution model for considered process only from the experimental data (based on the shapes of obtained integral kinetic curves), and this fact represents the advantage of established analysis. The established mathematical procedure, which is based on the MLM, can be applied as the preliminary analysis for evaluating the distribution of activation energies for complex heterogeneous processes. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 41: 27–44, 2009     

A solid-liquid extraction approach to elucidate the chemical availability of metals in soil and sediment assuming Langmuir isotherm behaviour

In an earlier paper (Anal. Chim. Acta 514 (2004) 137) we claimed that the maximal extractability of a metal from soil or sediment for a user-defined extractant, i.e. the chemical availability in that particular extractant, may be biased as a result of inadequate volume to mass (V/m) ratios. Correcting for that artifact using an implementation of the simple linear isotherm model gave good results although we cautioned the general applicability. In this paper we will theoretically derive the limitations of that approach based on the more general assumption that sorption processes are described by a Langmuir isotherm.NIST reference material 8704 was extracted with 1 mol l⁻¹ NaOAc (adjusted to pH 5) to experimentally verify the applicability of the Langmuir isotherm approach and illustrate the deviations obtained for some metals using the linear isotherm approach. Of the seven metals measured (Cr, Co, Ni, Cu, Zn, Cd, and Ba) only for Cr and Cu severe discrepancies between both approaches were found, which could be traced back to non-linear isotherm behaviour. Moreover, the Langmuir isotherm approach showed that the above mentioned extractability artifact is even more serious than earlier assumed applying the linear isotherm approach.     

Coloring-flow duality of embedded graphs

Let be a directed graph embedded in a surface. A map is a tension if for every circuit , the sum of on the forward edges of is equal to the sum of on the backward edges of . If this condition is satisfied for every circuit of which is a contractible curve in the surface, then is a local tension. If holds for every , we say that is a (local) -tension. We define the circular chromatic number and the local circular chromatic number of by and , respectively. The invariant is a refinement of the usual chromatic number, whereas is closely related to Tutte's flow index and Bouchet's biflow index of the surface dual .

From the definitions we have . The main result of this paper is a far-reaching generalization of Tutte's coloring-flow duality in planar graphs. It is proved that for every surface and every 0$">, there exists an integer so that holds for every graph embedded in with edge-width at least , where the edge-width is the length of a shortest noncontractible circuit in .

In 1996, Youngs discovered that every quadrangulation of the projective plane has chromatic number 2 or 4, but never 3. As an application of the main result we show that such `bimodal' behavior can be observed in , and thus in for two generic classes of embedded graphs: those that are triangulations and those whose face boundaries all have even length. In particular, if is embedded in some surface with large edge-width and all its faces have even length , then . Similarly, if is a triangulation with large edge-width, then . It is also shown that there exist Eulerian triangulations of arbitrarily large edge-width on nonorientable surfaces whose circular chromatic number is equal to 5.

     

Reactions of N-heteroarylformamide oximes and N-heteroarylacetamide oximes with N,N-dimethylformamide dimethyl acetal. Synthesis of 2-methyl-s-triazolo[1,5-x]azines and N-methylcyanoaminoazines

N-Heteroarylformamide oximes 3 (R ? H) were converted with N,N-dimethylformamide dimethyl acetal (DMFDMA) into N-heteroaryl-N-methylcyanoamino compounds 5 , as the main products. In some instances N-heteroarylcyanoamino compounds 4 , cyanoimino compounds 7 , and some other products, such as 9 and 10 were also formed. On the other hand, N-heteroarylacetamide oximes 3 (R ? CH₃) were cyclized under the same reaction conditions into 2-methyl-s-triazolo[1,5-x]azines ( 6 ). N-Heteroarylacetamide O-methyl oximes 11 and 12 were prepared from the corresponding acetamidines 2 (R ? CH₃) and O-methylhydroxylamine.     

The norm of a symmetric elementary operator

The norm of the operator on (or on any prime C-algebra ) is computed for all and is shown to be equal to the completely bounded norm.

     

Non-linear waves in heterogeneous elastic rods via homogenization

We consider the propagation of a planar loop on a heterogeneous elastic rod with a periodic microstructure consisting of two alternating homogeneous regions with different material properties. The analysis is carried out using a second-order homogenization theory based on a multiple scale asymptotic expansion.     

Thermal analysis testing and natural radioactivity characterization of kaolin as building material

Journal of Thermal Analysis and Calorimetry - Kaolins are used in a multiplicity of industries because of unique physical and chemical properties. Relationships between thermal and radioactivity...     

Halogen Bonding between Anions and Iodoperfluoroorganics: Solution‐Phase Thermodynamics and Multidentate‐Receptor Design

The interactions of iodoperfluoroarenes and ‐alkanes with anions in organic solvent were studied. The data indicates that favorable halogen‐bonding interactions exist between halide anions and the monodentate model compounds C₆F₅I and C₈F₁₇I. These data served as a basis for the development of preorganized multidentate receptors capable of high‐affinity anion recognition. Several new receptor architectures were prepared, and the multidentate‐iodoperfluorobenzoate‐ester design, as described in a preliminary communication, was evaluated in more detail. Computation was employed to better interpret the structure–activity relationships arising from these studies. Investigations of the thermodynamics of anion binding (by van't Hoff analysis) and solvent effects reveal details of these halogen bonding interactions.