High pressure synthesis and crystal structure of a new series of perovskite-like compounds CMn7O12 (C = Na,Ca, Cd,Sr, La,Nd)

A new series of perovskite-like compounds CMn₇O₁₂ have been synthesized under high pressure and high temperature conditions. C is a large divalent or trivalent cation such as Ca, Cd, Sr, La and Nd. The structures of the quenched materials have been determined from powder X-ray data. They are distortions of the NaMn₇O₁₂ cubic structure. The [C²⁺Mn³⁺₃](Mn³⁺₃Mn⁴⁺)O₁₂ compounds are trigonal ($\text{R}\text{3}$). The C²⁺ and Mn³⁺ as well as the Mn³⁺ and Mn⁴⁺ cations are ordered on the corresponding A and B sites of the perovskite structure, respectively. The [C³⁺Mn³⁺₃] (Mn³⁺₄)O₁₂ compounds are monoclinic ($\text{I}\text{2}\text{m}$). In these compounds the order exists only in the A sites. It is shown that the lower symmetry may be the result of a cooperative Jahn-Teller effect of the Mn³⁺ cations occupying the B sites.     

Simultaneous Determination of Carvedilol,Enalaprilat, and Perindoprilat in Human Plasma Using LC–MS/MS and Its Application to a Pharmacokinetic Pilot Study

Chromatographia - A method for the extraction and quantification of carvedilol, enalaprilat, and perindoprilat in 50 µL human plasma, using high-performance liquid chromatography with...     

Coordination of α,β-unsaturated aldehydes on d Ru and Rh complexes: A DFT study

The coordination modes of various α,β-unsaturated aldehydes on d⁶ ML₄ and ML₅ complexes of rhodium and ruthenium have been compared by means of density functional theory (DFT) calculations. The studied aldehydes were acrolein, crotonaldehyde, prenal and cinnamaldehyde and the metallic fragments RuH₂(PH₃)₂, RuH₂(PH₃)₃ and RhH₂Cl(PH₃)₂. On the d⁶ ML₄ Ru fragment, the best coordination geometry is η⁴, where both double bonds are involved. On the d⁶ ML₅ Ru fragment, the η²CC geometry is preferred to the η¹O and to the η²CO ones. Finally on the d⁶ ML₅ Rh fragment, the η²CO mode is not stable and only η¹O and η²CC exist, the former being favored. In conclusion, the η²CO coordination geometry is never favored even if the energy gap between η²CC and η²CO is reduced by the use of bulky ligands (PPh₃) or alkyl substituents on the CC bond. The Ru and Rh complexes behave differently: in the case of Ru, η²CC and η²CO can be in competition and in the case of Rh, the best form is η¹O. This different behavior can explain the results obtained in the hydrogenation reaction of α,β-unsaturated aldehydes.     

Some multicolor bipartite Ramsey numbers involving cycles and a small number of colors

For bipartite graphs $G_1,G_2,\dots ,G_k$, the bipartite Ramsey number $b(G_1,G_2,\dots ,G_k)$ is the least positive integer $b$ so that any coloring of the edges of $K_{b,b}$ with $k$ colors will result in a copy of $G_i$ in the $i$th color for some $i$. In this paper, our main focus will be to bound the following numbers: $b(C_{2t_1},C_{2t_2})$ and $b(C_{2t_1},C_{2t_2},C_{2t_3})$ for all $t_i\ge 3,$$b(C_{2t_1},C_{2t_2},C_{2t_3},C_{2t_4})$ for $3\le t_i\le 9,$ and $b(C_{2t_1},C_{2t_2},C_{2t_3},C_{2t_4},C_{2t_5})$ for $3\le t_i\le 5.$ Furthermore, we will also show that these mentioned bounds are generally better than the bounds obtained by using the best known Zarankiewicz-type result.     

On some optimisation models in a fuzzy-stochastic environment

This paper is on fuzzy stochastic optimisation, an area that is quickly coming to the forefront of mathematical programming under uncertainty. An even stronger motivating factor for the growing interest in this area can be found in the ubiquitous nature of decision problems involving hybrid imprecision. More precisely, we consider a range of situations in which random factors and fuzzy information co-occur in an optimisation setting. Related hybrid optimisation models are discussed and converted into deterministic terms through appropriate tools like probabilistic set, uncertain probability, and fuzzy random variable, making good use of uncertainty principles. We also discuss ways to deal with the resulting problems. Numerical examples carried out using class optimisation software demonstrate the efficiency of the proposed approaches. We shall end this article by pointing out some of the challenges that currently occupy researchers in this emerging field.     

Etude cristallochimique des phases de type perovskite du systeme Th0.25 NbO3NaNbO3

The compound Th_0.25 NbO₃ melts congruently at 1390°C. Single crystals obtained by slow cooling from the melt are transparent and show uniaxial optical properties. A single-crystal X-ray analysis confirms the tetragonal cell found by Kovba and Trunov from a powder data and gives a = 3.90 Å and c = 7.85 Å. No systematic absence of the hkl reflections is observed on precession films. The relative intensities of the main reflections are characteristic of a perovskite-like arrangement ABO₃ whose large dodecahedral A sites are only partly occupied. Several domains have been found in the perovskite-type solid solution (1 ? x) Th_0.25NbO₃-x NaNbO₃. For 0 ? x ? 0.5 the phases have a tetragonal cell with $\text{a ? a}{}_0$ and $\text{c ? 2a}{}_0$ as in pure Th_0.25 NbO₃. When 0.6 ? x ? 0.8 the corresponding phases crystallize with a small cubic cell ($\text{a}{}_0\text{? 3.9}$Å), while phases with 0.9 ? x ? 1 have an orthorhombic cell ($\text{a ? 2}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{a}{}_0\text{, b ? 2}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{a}{}_0\text{, c ? a}{}_0$).     

Synthese et structure cristalline d'un nouvel oxyde mixte “FeV3O8” (FexV1−xO2; x ⋍ 0.25)

Single crystals of a new oxide “FeV₃O₈” ($\text{Fe}{}_{\mathrm{x}}\text{V}{}_{\mathrm{1?x}}\text{O}{}_2\text{: x ? 0.25}$) have been synthesized by slowly cooling a melted mixture with the composition, 8VO₂, 3V₂O₅, Fe₂O₃. The chemical formula has been determined by electron microprobe analysis. The compound, isostructural with AlNbO₄ and VO₂(B), has a monoclinic symmetry, space group $\text{C2}\text{m}$; the unit cell dimensions are a = 12.13Å, b = 3.679 Å, c = 6.547 Å, β = 106.85°. A structural refinement based on single crystal data has been carried out. It gave an R-factor of 1.9%. This refinement indicated that the iron and vanadium cations are partially ordered, although the average cation-oxygen distances for the two six-coordinated cations were exactly the same (1.961 Å). This conjecture was supported by the calculation of the cation valences.