On the fully developed tube flow of a class of non-linear viscoelastic fluids

The fully developed pipe flow of a class of non-linear viscoelastic fluids is investigated. Analytical expressions are derived for the stress components, the friction factor and the velocity field. The friction factor which depends on the Deborah and Reynolds numbers is substantially smaller than the corresponding value for the Newtonian flow field with implications concerning the volume flow rate. We show that non-affine models in the class of constitutive equations considered such as Johnson-Segalman and some versions of the Phan-Thien-Tanner models are not representative of physically realistic flow fields for all Deborah numbers. For a fixed value of the slippage factor they predict physically admissible flow fields only for a limited range of Deborah numbers smaller than a critical Deborah number. The latter is a function of the slippage.     

A stochastic model for investments in different technologies for electricity production in the long period

We present a single stage stochastic mixed integer linear model for determining the optimal mix of different technologies for electricity generation, ranging from coal, nuclear and combined cycle gas turbine to hydroelectric, wind and photovoltaic, taking into account the existing plants, the cost of investment in new plants, maintenance costs, purchase and sale of ${CO}_2$ emission trading certificates and green certificates, in order to satisfy regulatory requirements. The power producer is assumed to be a price-taker. Stochasticity of future fuel prices, which affect the generation variable costs, is included in the model by means of a set of scenarios. The main contribution of the paper, beyond considering stochasticity in the future fuel prices, is the introduction of CVaR risk measure in the objective function in order to limit the possibility of low profits in bad scenarios with a fixed confidence level.     

Inhibitory activities on mammalian central nervous system receptors and computational studies of three sesquiterpene lactones from Coriaria ruscifolia subsp. ruscifolia

The electrophysiological characterization of sesquiterpene lactones from Coriaria ruscifolia subsp. ruscifolia has been tested on hippocampal neurons. The results for glycinergic rat hippocampal transmission and native γ-aminobutyric acid (GABA)ergic transmission on neurons (13DIV) are remarkably different for tutin, coriamyrtin, and dihydrotutin, being tutin the most potent inhibitor and dihydrotutin the least potent one. To understand the applied mechanism of action, we discuss the structural and electronic requirements for inhibitory activity by these sesquiterpene lactones when modulating receptors of the central nervous system. The structural and electrostatic properties of these compounds were compared to those of more active metabolites like picrotoxins. The minimal energy level of these structures was calculated and then optimized at the ab initio B3LYP/DGDZVP level of theory using Gaussian 03W software. This allowed calculation of the corresponding vibrational circular dichroism spectrum of coriamyrtin which rendered the molecular absolute configuration after comparison with an experimental spectrum. These results are consistent with those from studies of other models that provide the basis for the activity on the presence of the lactone at carbons 3 and 5, the presence of the hydroxyl group at position 6, and the different electronic distributions observed in tutin and coriamyrtin. The latter has an isopropenyl moiety at carbon 4 in contrast to the dihydrotutin isopropyl group at the same position, which could explain the difference in activity between dihydrotutin and tutin or coriamyrtin. The presence of the hydroxyl group at carbon 2 is not decisive since this functionality is present in tutin, the most active compound, and in dihydrotutin, the less active one.     

Elliptic Reflection Structures, K-Loop Derivations and Triangle-Inequality

This paper is a part of our general aim to study properties of elliptic and ordered elliptic geometries and then using some of these properties to introduce new concepts and develop their theories. If ${(P,\mathfrak{G}, \equiv,\tau)}$ denotes an elliptic geometry ordered via a separation ?? then there are polar points o and ?? and on the line ${ \overline{K} := \overline{\infty,o}}$ there can be established an operation ??+?? such that ${(\overline{K},+)}$ becomes a commutative group and the map ${ a^+ :\overline{K}\to \overline{K} ; x \mapsto a + x}$ is a motion on ${\overline{K}}$ . The separation ?? induces on ${\overline{K}}$ a cyclic order ?? with [o, e, ??] = 1 such that ${(\overline{K},+,\omega)}$ becomes a cyclic ordered group. For ${a,b \in K := \overline{K} {\setminus}\{\infty\}}$ we set ${a < b :\Longleftrightarrow [a,b,\infty] =1}$ and for all ${a\in K\,a < \infty}$ . Then (K,?<) is a totally ordered set. We show there is a surjective distance function: $$ \lambda : P \times P \to \overline{K}_+ := \{x \in \overline{K}\,|\,o \leq x\leq\infty\}, $$ with ?? ${\lambda(a,b) = \lambda(c,d) \ \Longleftrightarrow (a,b) \equiv (c,d)}$ ??. We prove in the first part of our project like (cf. Gr?ger in Mitt Math Ges Hamburg 11:441?C457, 1987) the following triangle-inequality: (cf. Theorem 8.2). If (a, b, c) is a triangle consisting of pairwise not polar points with ??(a, c), ??(b, c) < e then ??(a, b) ?? ??(a, c) + ??(b, c) < ??.