Magnetocaloric Effects in Pr0.6−x Er x Sr0.4MnO3 (0.0≤x≤0.2) Manganese Oxides

The effects of partial substitution of praseodymium by erbium on the structural, magnetic, and magnetocaloric properties of Pr_0.6?x Er _x Sr_0.4MnO₃ (0.0≤x≤0.2) powder samples have been studied. Our polycrystalline compounds were synthesized by the conventional solid state reaction at high temperature. Rietveld refinement of the X-ray diffraction patterns using Fullprof program shows that all our samples are single phase and crystallize in the orthorhombic structure with the Pnma space group. The unit cell volume decreased with increasing the Er amount. Magnetic measurements show that all our samples exhibit a paramagnetic–ferromagnetic transition with decreasing temperature. The Curie temperature T _C shifts to lower values with increasing Er content. From the magnetization isotherms at different temperatures, magnetic entropy changes ΔS _M and relative cooling power RCP have been evaluated. The maximum of the magnetic entropy changes for the Pr_0.45Er_0.15Sr_0.4MnO₃ sample is found to be $| \Delta S_{M}^{\max } | = 2.66~\mathrm{J}\,\mathrm{kg}^{-1}\,\mathrm{K}^{-1}$ under a magnetic applied field change of 2 T.     

STUDY OF SOME UNIQUE FEATURES OF RATIO-DEPENDENT MODELS FOR PREDATOR-PREY-SUBSTRATE INTERACTIONS IN CONTINUOUS CULTURES

This article studies the dynamics of ratio-dependent models for continuous bioreactors involving interactions between predator, prey, and a limiting substrate. Ratio-dependent models, for which the growth rate of predator is a function of the ratio of prey to predator abundance, have recently received growing attention and were shown to exhibit more interesting behavior than the classical (strictly) prey-dependent models. It is shown that in addition to predicting areas of predator washout and areas of total washout, the studied examples of ratio-dependent models predict areas for which the species coexist either at steady state or in oscillatory mode for any initial population values. The studied models also predict a unique feature for which the interacting species can coexist or wash out depending on their initial values. The objective of this article is to study in some detail this interesting behavior that makes ratio-dependent models better candidates in predicting predator-prey interactions in real biological life.     

A surrogate model to assess the whole body SAR induced by multiple plane waves at 2.4?GHz

The assessment of the exposure to electromagnetic waves is nowadays a key question. Dealing with the relationship between exposure and incident field, most of previous investigations have been performed with a single plane wave. Realistic exposure in the far field can be modeled as multiple plane waves with random direction of arrival, random amplitude, and random phase. This paper, based on numerical investigations, studies the whole body specific absorption rate (SAR) linked to the exposure induced by five random plane waves having uniformly distributed angles of arrival in the horizontal plane, log-normal distributed amplitudes, and uniformly distributed phases. A first result shows that this random heterogeneous exposure generates maximal variations of ??25% for the whole body specific absorption. An important observation is that the exposure to a single plane wave arriving face to the body, used for the guidelines, does not constitute the worst case. We propose a surrogate model to assess the distribution of the whole body SAR in the case of an exposure to multiple plane waves. For a sample of 30 values of whole body SAR induced by five plane waves at 2.4?GHz, this simple approach, considering the resulting SAR as the sum of the SAR induced by each isolated plane wave, leads to an estimated distribution of whole body SAR following the real distribution with a p value of 76% according to the Kolmogorov statistical test.     

Unexploited Thapsia garganica,Orlaya maritima,and Retama raetam Seeds: Potential Sources of Unsaturated Fatty Acid and Natural Antioxidants

Total lipid contents, fatty acid compositions, phenolic profiles and antioxidants activities of seeds from Thapsia garganica, Orlaya maritima, and Retama raetam were investigated. The oil values were more than 26 %, except seeds of R. raetam (ca. 3 %). Unsaturated fatty acids accounted for the majority of the fatty acids (more than 75 %). Oleic and linoleic acid were the predominant fatty acids. Total phenolic compounds (24–104 mg GAE g^?1 DR), total flavonoids (4–102 mg QE g^?1g DR), total tannins (28–85 mg GAE g^?1 DR) and condensed tannins (0.62–131 mg CE g^?1 DR) were also determined. The antioxidant activities using different assays were evaluated. The predominant detected classes were the phenolic acids (42–85 %) and the flavonoids (11–48 %). The major phenolic acids were caffeic, trans‐4‐hydroxy‐3‐methoxycinnamic, p‐coumaric, and gallic acid. The predominant flavonoids were quercetin, luteolin, naringin, apigenin, and kaempferol. This study brings attention to the medicinal importance of these species as a source of oil and antioxidant molecules.     

Sulfated Zirconia-Based Strong Solid-Acid Catalysts: Recent Progress

This review article deals with recent progress in the preparation of sulfated zirconia (SZ)-bassed, strong solid-acid catalysts, the characterization of their physicochemical properties and the evaluation of their catalytic performance in various promising applications. Strong emphasis was put on discussion of controversial issues such as the strength of acid sites, the nature of active sites, the reaction mechanism, and the role and state of supported platinum. An important part of this work was devoted to recent catalytic applications.     

Facile synthesis route to monodispersed platelet-like SBA-15 silica

We here report a facile synthesis route to monodispersed platelet-like SBA-15 mesoporous silica employing kinetically controlled micelles as templates. In previous preparations of SBA-15 silica, it was believed that thermodynamically equilibrated micelles were used as templates. The kinetically controlled micelle has never been used before to generate periodic mesoporous materials with unique morphology. Monodispersed hexagonal platelet-like SBA-15 microparticles were prepared via a very facile synthesis route by tuning the micelle formation process, i.e. the stirring rate and the time of dissolution of the triblock copolymer and formation of the micelles. Shorter micelle formation time and faster stirring are essential to generate platelet-like SBA-15 silica particles. It is expected to apply in the synthesis of a wide variety of mesophase materials.     

Cyclic polymers in good solvents

This paper deals with the effects of excluded volume interactions on the thermodynamic and structural properties of cyclic polymers in good solvents. Several thermodynamic properties are discussed with particular emphasis on excluded volume interactions and their effects on the radii of gyration and the form factors. An empirical model describing the mean square distance between two points along a cyclic polymer is proposed and its predictions compared with those of other models. Comparison between cyclic and linear chain properties highlights the effects of chain closure under good solvent conditions. © 2000 Society of Chemical Industry