Thermodynamic properties and phase equilibria in alloys of Bi—Tm system

The thermochemical properties of the melts of the Bi—Tm system at a temperature of 1100 K in the range of compositions 0 ≤ xTm ≤ 0,2 were determined for the first time by the calorimetry method. It is established that the minimum value of the enthalpy of mixing of these liquid alloys is equal to –75,7 ± 0,5 kJ / mol at xTm = 0,65. = = –150,7 ± 16,7 kJ / mol, = –230,9 ± 21,8 kJ / mol. The activities of the components and molar particles of associates were calculated according to the model of an ideal associated solution (IAR), using data on the thermochemical properties of melts of the Bi—Tm system. It was found that the activities of the components in these metallic solutions show very large negative deviations from ideal solutions with a high content of TmBi and Tm2Bi associates. The obtained dependences of the first i i melts of the Bi—Tm system on temperature showed a large steepness of the Bi Bi curve in contrast to the gradual decrease of exothermic values Tm of Tm. This indicates large changes in the structure of the Bi atom with increasing temperature. Excess integral and partial Gibbs energies of Bi-Tm system melt mixing calculated from component activities The absolute values of G in the whole concentration range are smaller than H (G min = –41,8 kJ / mol at xTm = 0,58), and the function G of is more asymmetric, which is caused by the entropy contribution (entropy of mixing of the studied melts is negative, and Smin min = −30,5 J / mol ∙ K at xTm = 0,65). Keywords: thermochemical properties, compounds, melts, Bi, Tm.

Short Range Order Modeling in Alloys

The Short and Long Range Orders in alloys can be considered based on a new expression for the combinatorial factor. This expression is more convenient and intuitive than the traditionally used form and can be directly applied to reproduce the results of several good known statistical-thermodynamic models that usually are considered completely independent or even inconsistent.The short list includes quasichemical theory, associated solution model, surrounded atom model, cluster site approximation.As result, the formalism and interpretation of these models are significantly clarified, allowing simultaneously to identify and fix several long standing errors that otherwise could be left unnoticed.Multicomponent generalization of listed models is also critically simplified.For the systems experiencing a phase transition, the advanced version of theory provides a mechanism allowing to reproduce the correct critical temperature of conversion and at the same time to increase significantly the precision of thermodynamic functions.

Critical perturbations of elliptic operators by lower order terms

In this work we study issues of existence and uniqueness of solutions of certain boundary value problems for elliptic equations in the upper half-space. More specifically we treat the Dirichlet, Neumann, and Regularity problems for the general second order, linear, elliptic operator under a smallness assumption on the coefficients in certain critical Lebesgue spaces. Our results are perturbative in nature, asserting that if a certain operator L[subscript 0] has good properties (as far as boundedness and invertibility of certain associated solution operators), then the same is true for L[subscript 1], whenever the coefficients of these two operators are close in certain L[subscript p] spaces. Our approach is through the theory of layer potentials, though the lack of good estimates for solutions of L [equals] 0 force us to use a more abstract construction of these objects, as opposed to the more classical definition through the fundamental solution. On the other hand, these more general objects suggest a wider range of applications for these techniques. The results contained in this thesis were obtained in collaboration with Simon Bortz, Steve Hofmann, Svitlana Mayboroda, and Bruno Poggi. The resulting publications can be found in [BHL+a] and [BHL+b].

Analysis of thermodynamic properties of Ca – Si – Fe melt

The model of ideal associated solutions was used for the analysis of thermodynamic properties of the Ca – Si – Fe melt. Chemical equilibrium, as per the law of mass conservation between associates and monomers in the assumed model version, was performed without consideration of mole fractions of these particles in solution but with consideration of the absolute number of their moles. It allows taking account the changes in the associated solution mole composition depending on the concentration of its components. The understudied binary sub-system Ca – Si was analyzed most comprehensively. Using the latest data of temperature dependency of heat capacity for five types of intermetallics of this sub-system, types of stable associates in it were defined, i.e. Са2Si, СаSi in the solution range with low contents of silicon in solution and СаSi, СаSi2 in the solution range with high contents of silicon in solution. Thermodynamic properties of the corresponding intermetallics in the databases Terra, Astra and HSC notably differ from the computed properties of the associates. The reason of disagreement of experimental and reference data consists apparently in the inaccurate reference information based on the previous underestimated studies of intermetallics’ heat capacities. Analysis of mixing energy of Ca – Si alloy components has shown that concentration and temperature dependencies of excessive free energy closely follow the so-called pseudosubregular model of binary solutions. Only two types of stable associates were defined for the other sub-system Fe – Si, i.e. Fe3Si and FeSi. On the whole, energies of formation of these associates and respective intermetallics agree well. The third sub-system Ca – Fe was not considered because of the very limited mutual solubility of its components. Thus, only three associates, i.e. CaSi, CaSi2 , FeSi, are valid out of five possible in the triple system Ca – Si – Fe in the range with high concentrations of silicon. A calculation under this condition of thermodynamic properties of calcium silicon melts for CK10 – CK30 grades has shown that activity of silicon in them at temperature 1873 K constituted 0.6 – 0.7, whereas activities of other components do not exceed 0.01.

Modelling thermodynamic properties of binary Cu–Eu and ternary Al–Cu–Eu melts

Model calculations of the whole set of thermodynamic properties of liquid alloys for the binary Cu–Eu and ternary Al–Cu–Eu systems have been performed. Authors used the ideal associated solution model (IAS model) for calculation of the entropies and excess Gibbs energies of mixing for these systems. The binaries were given as the Redlich-Kister polynomials. The thermodynamic properties for the ternary system are described using the Redlich-Kister-Muggianu formalism. A comparison of the surfaces of excess Gibbs energy and entropy of mixing for liquid Al–Cu–Eu alloys at 1350 K demonstrates that the ordering related to the formation of rather strong associates in the Al–Eu system significantly affects the concentration dependence of the excess Gibbs energy of mixing in the liquid phase at this temperature.

Melting of nucleobases. Getting the cutting edge of “Walden's Rule”

Surprisingly high melting temperatures of the five nucleobases have been measured using a specially developed fast scanning calorimetry method that prevents decomposition. Results are rationalized in terms of an “ideal associated solution”.

Fixed-order ℋ∞ controller design for MIMO systems via polynomial approach

This paper presents a fixed-order [Formula: see text]∞ controller design based on linear matrix inequalities for multi-input–multi-output systems. The main difficulty in the development of a fixed-order controller design is that the associated solution set of the problem is defined in a non-convex cluster, and that makes the problem computationally intractable. The convex inner approximation is used to deal with this non-convexity. The proposed controller design approach is applied to some elegant numerical problems taken from various previous works. To show the effectiveness of the proposed method, the full-order [Formula: see text]∞ controller and fixed-order controllers are constructed for these models using the traditional method and popular toolboxes, respectively. Furthermore, in this paper, some strategies for choosing the central polynomial, which is the main conservatism of the proposed method, are discussed.

Developing Secure Software Using UML Patterns

This chapter presents a security engineering process based on UML security problem frames and concretized UML security problem frames. Both kinds of frames constitute patterns for analyzing security problems and associated solution approaches. They are arranged in a pattern system that makes dependencies between them explicit. The authors describe step-by-step how the pattern system can be used to analyze a given security problem and how solution approaches can be found. Then, solution approaches are specified by generic security components and generic security architectures, which constitute architectural patterns. Finally, the generic security components and the generic security architecture that composes them are refined, and the result is a secure software product built from existing and/or tailor-made security components.