Le Spectre de L'Alcool Propargylique en Fonction du pH. Un Exemple de Transferts Protoniques Complexes sur un Diacide Organique

Dimethyl sulphoxide (DMSO) is used as a solvent to investigate the kinetic acidity of very weak organic diacids by ¹H d.n.m.r. An inspection of the spectrum of propargyl alcohol as a function of the pH allows the assignment of various proton transfer mechanisms:      

Antifilarial activity in vitro of polycarpol and 3-O-acetyl aleuritolic acid from cameroonian medicinal plants against Onchocerca gutturosa

Previous results have revealed the antifilarial activities of crude extracts and pure compounds from some Cameroonian medicinal plants against Onchocerca volvulus and Onchocerca gutturosa. In our efforts to find new filaricidal agents against adult male O. gutturosa worms, we have isolated and screened three compounds: polycarpol and polyveoline from Polyalthia suaveolens (Annonaceae) and 3-O-acetyl aleuritolic acid from Discoglypremna caloneura (Euphorbiaceae). Only polycarpol and 3-O-acetyl aleuritolic acid exhibited significant inhibitory activities on the vitality of adult male worms of O. gutturosa using Amocarzine as positive control compound. The motility reduction values were 28.6 and 57.1%, and the inhibition of MTT reduction values 80.0 and 64.8% respectively.     

Nonlinear vibrations of a mechanical system with non-regular nonlinearities and uncertainties

This paper presents the concept of the Stochastic Multi-dimensional Harmonic Balance Method (Stochastic-MHBM) in order to solve dynamical problems with non-regular non linearities in presence of uncertainties. To treat the nonlinearity in the stochastic and frequency domains, the Alternate Frequency-Time method with Probabilistic Collocation (AFTPC) is proposed. The approach is demonstrated using nonlinear two-degree-of-freedom model with different types of nonlinearities (cubic nonlinearity, contact/no contact, friction). The quasi-periodic stochastic dynamic response is evaluated considering uncertainties in linear and nonlinear parts of the mechanical system. The results are compared with those obtained from the classical Monte Carlo Simulation (MCS). For various numerical tests, it is found that the results agreed very well whilst requiring significantly less computation.     

Tool replacement policy for one-sided processes with low fraction defective

In most manufacturing industries, tool replacement policy is essential for minimizing the fraction defective and the manufacturing cost. Tool wear is caused by the action of sliding chips in the shear zone, and the friction generated between the tool flank and workpiece. This wear, apparently, is a dominant and irremovable component of variability in many machining processes, which is a systematic assignable cause. As the tool wear occurs in the machining processes, the fraction of defectives would gradually become significant. When the fraction defective reaches a certain level, the tool must be replaced. Therefore, detecting suitable time for tool replacement operation becomes essential. In this paper, we present an analytical approach for unilateral processes based on the one-sided process capability index C _PU (or C _PL ) to find the appropriate time for tool replacement. Accurate process capability must be calculated, particularly, when the data contains assignable cause variation. By calculating the index C _PU (or C _PL ) in a dynamical environment, we propose estimators of C _PU (or C _PL ) and obtain exact form of the sampling distribution in the presence of systematic assignable cause. The proposed procedure is then applied to a real manufacturing process involving tool wear problem, to demonstrate the applicability of the proposed approach.     

Determination of γ-γ' lattice misfit in a single-crystal nickel-based superalloy using convergent beam electron diffraction aided by finite element calculations

In single-crystal nickel-based superalloys, the lattice mismatch associated with interface coherency between γ matrix and γ' precipitates has a strong influence on mechanical properties. The unconstrained lattice misfit in a single-crystal of the MC2 nickel-based superalloy is determined using convergent beam electron diffraction measurements and finite element calculations. The apparent lattice parameters of both constrained phases are obtained in thin foils, using a new multi-pattern approach, which allows for unambiguous determination of all the lattice parameters considering the real symmetry of the strained crystals. Finite element calculations are used to establish relations between the constrained and unconstrained lattice parameters, with the stress relaxation resulting from the thin foil geometry taken into account.     

A mathematical programming model for the fuzzy analytic network process—applications of international investment

Currently, the analytic network process (ANP) method is widely employed to consider the multiple criteria analysis problems with dependence and feedback effects. However, in order to extend the ANP to resolve the problem of uncertainty or human subjective judgment, the concepts of fuzzy numbers should be incorporated into the ANP to represent the subjective uncertain pairwise judgments. In this paper, therefore, we propose a novel fuzzy analytic network process (FANP) model by solving a mathematical programming problem. Unlike other FANPs, the proposed method does not require the reciprocity assumption of the weight ratios between criteria, and it can derive local and global weights simultaneously in a single model. Two numerical examples of international investment problems are used to demonstrate the proposed method.     

Synthesis of novel β-lactams bearing an anthraquinone moiety,and evaluation of their antimalarial activities

A novel series of β-lactams bearing an anthraquinone moiety have been synthesized from imines derived from anthraquinone-2-carbaldehyde and ketenes by a [2+2] cycloaddition reaction. The cycloadducts were fully characterized and evaluated for their antimalarial activities against Plasmodium falciparum K14 resistant strain and showed moderate to excellent EC₅₀ values varying from 9 to 50 μM.     

The destabilization paradox applied to friction-induced vibrations in an aircraft braking system

Mechanisms of friction are known as an important source of vibrations in a large variety of engineering systems, where the emergence of oscillations is noisy and can cause severe damage to the system. The reduction or elimination of these vibrations is then an industrial issue that requires the attention of engineers and researchers together. Friction-induced vibrations have been the matter of several investigations, considering experimental, analytical, and numerical approaches. An aircraft braking system is a complex engineering system prone to friction-induced vibrations, and is the subject herein. By considering experimental observations and by evaluating the mechanisms of friction involved, a complete nonlinear model is built. The nonlinear contact between the rotors and the stators is considered. The stability analysis is performed by determining the eigenvalues of the linearized system at the equilibrium point. Parametric studies are conducted in order to evaluate the effects of various system parameters on stability. Special attention will be given to the understanding the role of damping and the associated destabilization paradox in mode-coupling instabilities.     

Hindered rotation around the aryl-to-nitrogen bond of n-acetyl,n-ethoxycarbonylmethyl-2-amino, 5-nitrothiophen

Two stereoisomers of the title compound are observed by H NMR at 10°. Their spectra coalesce at higher temperature (10°-90°). The equilibrium and rate constants K and k, strongly dependent on the solvent used (1,4-dioxane, tetrahydrofuran, acetone, chloroform); typical values for these parameters and the related thermodynamic functions are: K(25°)= 0.170; k(25°)=23.2s^?1; ΔH_R and ΔH^≠=4.94 and 17.9 kcal.mol.^?1; ΔS_R and ΔS^≠ =13.1 and 7.7 e.u, in a 0.2 molar solution in 1,4-dioxane. The two isomers are shown to result from a hindered rotation around the aryl-to-nitrogen bond, presumably due to a direct resonance effect between the amide and nitro groups. The more abundant isomer was assigned a planar molecular structure in which the O atom of the amide group is close to the S atom of the thiophen ring, presumably on account of an electrostatic interaction between these two atoms which bear partial electrical charges of opposite sign.     

Asymmetric hydrogenation of α-amino acid precursors with a new chiral diphosphine (dioxop) derived from 1,6-D-anhydroglucose

High optical yields are obtained in the hydrogenation of α-amino acid precursors rising [Rh(COD)dioxop] + ClO₄^? in presence of triethylamine as catalyst.