Combretins A and B,New Cycloartane‐Type Triterpenes from Combretum fragrans

The phytochemical studies on the leaves of the traditionally used medicinal plant Combretum fragrans F. Hoffm (Combretaceae) from Cameroon have led to the isolation of combretins A and B ( 1 and 2 , resp.), two new cycloartane‐type triterpenes from the AcOEt‐soluble subfraction along with β‐sitosterol ( 3 ), oleanolic acid ( 4 ), ursolic acid ( 5 ), and pratensein ( 6 ). The compounds 4  –  6 are reported for the first time from this species. The structures of the new triterpenes were elucidated by spectroscopic techniques including ¹H‐ and ¹³C‐NMR (DEPT), and 2D‐NMR experiments.     

Modèle multi-bulles pour la cavitation

In this study we propose new multi-bubble model for cavitation, in which, to simulate the interactions within a cloud of cavitation at the initial stage, the dynamic behaviour of two nonidentical bubbles localised in a volume of control is studied. The presence of two bubbles introduces an instability in which the exchange of volume seems an additional degree of freedom. Depending on the conditions of expansion, the small bubble can disappear or not. If the small bubble disappears, the volume of control is readjusted to introduce a new small bubble and to continue calculation in a new sequence. The model makes it possible for many small bubbles to disappear as in the appearance of cavitation, which is at the origin of certain phenomena observed in the zone of the appearance, such as emission of the noise. The model reveals especially the pressure rather like a result than a datum.The comparison of the size of the bubbles and the pressure varying in time, obtained with the model are coherent with the measurements taken by Ohl [Phys. Fluids 14 (10) (2002) 3512–3521]. To cite this article: M. Adama Maiga, D. Buisine, C. R. Mecanique 337 (2009).     

Bounds for the Castelnuovo–Mumford regularity of modules

We establish bounds for the Castelnuovo–Mumford regularity of a finitely generated graded module and its symmetric powers in terms of the degrees of the generators of the module and the degrees of their relations. We extend to modules (and improve) the known bounds for homogeneous ideals in a polynomial ring established by Galligo, Giusti, Caviglia and Sbarra.     

Correction non linéaire et principe du maximum avec des schémas hybrides pour la discrétisation dʼopérateurs de diffusion

We describe a nonlinear technique to eliminate oscillations appearing in the discretization of diffusion operators with hybrid schemes.     

Estimation par le minimum de distance de Hellinger dʼun processus ARFIMA

In this Note, we determine the minimum Hellinger distance estimate of an ARFIMA (AutoRegressive Fractionally Integrated Moving Average) process. The estimate minimizes the Hellinger distance between the probability density function of the innovation of the process and a parameterized random function. Under some assumptions, we establish the asymptotic properties of this estimate.     

Spectroscopic Investigations of Polymer Nanocomposites

The addition of an inorganic component to polymers leads to improvements in various physical and mechanical properties. Various examples on filled elastomeric networks will show that a mechanical characterization can be nicely combined with a spectroscopic investigation for a better understanding of the properties of the composite materials.     

Size,Shape, and Wavelength Effect on Photothermal Heat Elevation of Gold Nanoparticles: Absorption Coefficient Experimental Measurement

Complex-shaped nanoparticles as gold nanourchins (GNU) and nanorods (GNR) are very suitable agents in the case of photothermal therapy due to their photon-heat conversion ability in the red and near-infrared region (NIR). The quantification in heat generation of complex shaped nanostructures is an important key to predict the therapeutic effect of these nanoparticles. For that, the determination of the nanoparticles absorption cross section (σ_Abs) responsible for the heat generation is one of the important steps before any application. Although it is obvious to determine σ_Abs for spheres via Mie's theory, in the case of complex structures like GNU or GNR, this parameter is difficult to model. In this work, a new methodology is used to determine experimentally σ_Abs for both GNU and GNR. Experimental measurements of the photothermal properties of 100 nm size GNU and two different sizes of GNRs are studied regarding different parameters such as concentration, laser excitation wavelength, and exposure time. By using the heat transfer theory, the temperature elevation in the nanoparticles solutions is converted to temperature elevation at the nanoparticles surface and σ_Abs values are then calculated for both GNU and GNR in the NIR spectral region.     

Dictums for problem solving and approximation in mathematical acoustics: examples involving low-frequency vibration and radiation

A sequence of dictums for mathematical acoustics is given representing opinions intended to be regarded as authoritative, but not necessarily universally agreed upon. The dictums are presented in the context of the detailed solution for a class of problems involving the forced vibration of a long cylinder protruding half-way into a half-space bounded by a compliant surface (impedance boundary) characterized by a spring constant. One limiting case corresponds to a cylinder vibrating within an infinite rigid baffle, and another limiting case corresponds to a vibrating cylinder on the compliant surface of an incompressible fluid. The second limiting case is identified as analogous to that of a floating half-submerged cylinder whose vibrations cause water waves to propagate over the surface. Attention is focused on vibrations at very low frequencies. Difficulties with insuring a causal solution are pointed out and dictums are given as to how one overcomes such difficulties. Various approximation techniques are described. The derivations involve application of the theory of complex variables and the method of matched asymptotic expansions, and the results include the apparent entrained mass in the near field of the cylinder and the radiation resistance per unit length experienced by the vibrating cylinder.     

Flavonol Glycoside from Psorospermum androsaemifolium

A new flavonol glycoside, 3′‐(4′''‐(3′''',4′'''‐dihydroxyphenoxy)‐2′''‐hydroxyphenoxy)acanthophorin B ( 1a ) together with 3′‐(2′'',4′''‐dihydroxyphenoxy)acanthophorin B ( 1 ), acanthophorin B ( 2 ), vismiaquinone ( 3 ), rheochrysidin ( 3a ), lupeol acetate and fatty acid were isolated from the chloroform extract of the stem bark of Psorospermum androsaemifolium Baker (Clusiaceae). The structure of 1a was determined on the basis of detailed spectroscopic analysis and comparison with the literature. Compounds 1a and 3a showed moderate antimicrobial activity.     

Diastereoisomeric 1,2,5-trimethyl-4-mtolylpiperidin-4-ols and 2,5-dimethyl-4-m-tolylpyridine

The preparation of 1,2,5-trimethyl-4-m-tolypiperidin-4-ol and the isolation of three of its diastereoisomers are described. The passage from this piperidinol to 2,5-dimethyl-4-m-tolylpyridine has been effected. Some derivatives of the latter compound have been obtained.Translated from Khimiya Geterotsiklicheskikh Soedinii, Vol. 6, No. 6, pp. 782–786, June, 1970.