Interplay of low-energy phonons and magnetic excitations in the Kondo insulator YbB12

Peculiarities in the lattice dynamics of the Kondo insulator Y bB(12) have been studied by inelastic neutron scattering. Selected phonon modes were traced above and below the temperature region (T ~ 50 K) where the gap opens in the electron density of states. The intensities of some low-energy modes exhibit an anomalous temperature dependence for q vectors close to the Brillouin zone boundary, suggesting a renormalization of the phonon eigenvectors. This effect is thought to arise from a coupling with magnetic excitations of the same symmetry, which exist at nearby energies. It is argued that this magnetovibrational coupling may in turn play a role in the steep temperature crossover existing in Y bB(12) between the low-temperature (Kondo insulator) and high-temperature (incoherent spin-fluctuation) regimes, which is rapidly suppressed by lighter Zr substitution.     

The economics of a closed-loop supply chain with remanufacturing

This study deals with joint decisions on pricing and production lot-sizing in a closed-loop supply chain consisting of manufacturing and remanufacturing operations. This study emphasizes the economic analysis of this hybrid system with substitution between the new and the remanufactured versions of the same product. We develop analytical models under a newsvendor framework bearing the following questions in mind. Can a hybrid system operate cost-effectively? Can it outperform the manufacturing-only system? If yes, to what extent and under what conditions? If not, what are the key factors that cause underperformance? This study formulates a multi-variable optimization problem and performs mathematical and numerical analysis. Results show that the hybrid system does not outperform the manufacturing-only system under a generic setting, but achieves better performance under conditions with a higher degree of substitution and/or a lower remanufacturing cost. In this scenario, participating in remanufacturing is not only an issue of environmental responsibility, but a profit-boosting option.     

Solvated calcium ions in charged silica nanopores

Hydroxyl surface density in porous silica drops down to nearly zero when the pH of the confined aqueous solution is greater than 10.5. To study such extreme conditions, we developed a model of slit silica nanopores where all the hydrogen atoms of the hydroxylated surface are removed and the negative charge of the resulting oxygen dangling bonds is compensated by Ca(2+) counterions. We employed grand canonical Monte Carlo and molecular dynamics simulations to address how the Ca(2+) counterions affect the thermodynamics, structure, and dynamics of confined water. While most of the Ca(2+) counterions arrange themselves according to the so-called "Stern layer," no diffuse layer is observed. The presence of Ca(2+) counterions affects the pore filling for strong confinement where the surface effects are large. At full loading, no significant changes are observed in the layering of the first two adsorbed water layers compared to nanopores with fully hydroxylated surfaces. However, the water structure and water orientational ordering with respect to the surface is much more disturbed. Due to the super hydrophilicity of the Ca(2+)-silica nanopores, water dynamics is slowed down and vicinal water molecules stick to the pore surface over longer times than in the case of hydroxylated silica surfaces. These findings, which suggest the breakdown of the linear Poisson-Boltzmann theory, provide important information about the properties of nanoconfined electrolytes upon extreme conditions where the surface charge and ion concentration are large.     

Stochastic games without perfect monitoring

A two-person zero-sum stochastic game with finitely many states and actions is considered. The classical assumption of perfect monitoring is relaxed. Instead of being informed of the previous action of his opponent, each player receives a random signal, the law of which depending on both previous actions and on the previous state. We prove the existence of the max-min and dually of the min-max, thus extending both the result of Mertens-Neyman about the existence of the value in case of perfect monitoring and a theorem obtained by the author on a subclass of stochastic games: the absorbing games. It is a pleasure to thank J. Filar and V. Gaitsgory for their friendly hospitality at the School of Mathematics, University of South-Australia, where this work was initiated. There, the author was supported by a grant from the Australian Research Council no. A69703141. I would like also to thank S. Sorin for his keen interest and finally an anonymous referee for his careful reading of the proof.     

Relationship between the structural and catalytic properties of mechanosynthesized lithiated manganese oxides

The relationship between the structural and catalytic properties of lithiated spinel manganese oxides was investigated by means of X-ray diffraction, Infrared and Xanes spectroscopies, thermogravimetric analysis, and by evaluating two catalytic oxidation tests, namely the carbon black combustion and the toluene conversion. Li-Mn-O catalysts were prepared from stoichiometric (Li₂O + MnO₂) mixtures, either by the classical high temperature ceramic method or by mechanochemistry. For both catalytic tests, some spectacular temperature reductions were measured as a function of grinding. A remarkable decrease of 210 °C (from 650 °C to 440 °C) in the carbon black combustion temperature was obtained when using mechanosynthesized Li-Mn-O spinel prepared from a mixture of Li₂O and MnO₂ ground for 3 hours, whereas a 100 % toluene conversion rate was achieved for a temperature lower than 200 °C for the 5 hours milled ceramic LiMn₂O₄ while the as-made ceramic was inactive. The enhancement of the performances (i.e. decrease in carbon black combustion temperature Tc and decrease in toluene conversion temperature T_95%) is due both to an increase in grain boundaries and in specific BET surface area and to the nano-crystallite size nature of the material. Besides, the spinel stoichiometry (both in oxygen or in cations) reflected by the lattice parameter variation plays a significant role in the catalytic reaction mechanism.     

Measurements of isomeric cross-section ratios for neutron capture in the resonances region

The creation of isomeric nuclei by neutron capture in the resonances energy range was studied with the lead slowing-down assembly CIRENE. The isomeric-ratio measurement of 8 nuclei allows to determine the spin of the compound nucleus at the binding energy. An experiment on ¹⁷⁷Lu underlines the role of the spin of a resonance on the isomeric-state feeding probability.     

Infinite ordered sets spanned by finitely many chains

We say that an ordered set P is spanned by a family C of chains if P=(P, ) is the transitive closure of {(C, | C) C C. It is shown that there is a function h: such that if P is spanned by k< chains, then P has a finite cutset-number h(k) (i.e. for any xP, there is a finite set F of size |F|h(k)–1, such that the elements of F are incomparable with x and {x}F meets every maximal chain of P). The function h is exponentially bounded but eventually dominates any polynomial function, even if it is only required that there are at most h(k) pairwise disjoint maximal chains in P, whenever P is spanned by k< chains.     

Convergent solid phase peptide synthesis vi : synthesis by the fmoc procedure with a modified protocol of two protected segments, sequence 5-17 and 18-31 of the neurotoxin ii of the scorpion androctonus australis hector.

Synthesis of two protected peptides thirteen and fourteen residues long, sequence 5-17, i.e. Fmoc-Tyr(cHex)- Ile-Val-Asp(Bzl)-Asp(Bzl)-Val-Asn-Cys(Acm)-Thr(Bzl)-Tyr(cHex)- Phe-Cys(Acm)-Gly-OH, and 18-31, i.e. Fmoc-Arg (Tos)-Asn-Ala- Tyr(cHex)-Cys(Acm )-Asn-Glu(Bzl)-Glu(Bzl)-Cys(Acm)-Thr(Bzl)- Lys(Z)-Leu-Lys(Z)-Gly-OH, of the scorpion neurotoxin II from , was performed by the solid phase method. The hydroxymethylphenoxymethyl copoly(styrene - 1% -divinylbenzene) type resin was used in combination with Fmoc-amino acids for both syntheses. A general protocol minimizing side reactions has been developed for the use of the base labile Fmoc--amino protecting group. The time of reaction with piperidine (50% in N,N'-dimethylformamide) has been shortened to three times one minute and coupling was performed mainly in methylene chloride with just dicyclohexyl or diisopropyl-carbodiimide. The side chain protecting groups of the Fmoc--amino acids were of the hydrogen fluoride labile type, which permitted, after trifluoroacetic acid cleavage of the peptide to resin ester bond, obtainment of protected peptides. The crude segments, precipitated from N,N'-dime- thylacetamide with water, were highly purified by HPLC and chemically characterized for future use in convergent solid phase assembling.     

Chain-Extension of Carbohydrates. II1 Stereospecific Ethynylation of Protected Pyrano- and Furano- Dialdoses

Abstract

Stereospecific high-yielding ethynylation of protected dialdoses is described.     

Diversity of the surface properties of Lactococci and consequences on adhesion to food components

Bacteria possess surface properties, related to their charge, hydrophobicity and Lewis acid/base characteristics, that are involved in the attachment processes of microorganisms to surfaces. Fermentation bulks and food matrixes are complex heterogeneous media containing various components with different physicochemical characteristics. The aim of the present study was to investigate whether (i) bacteria present in a food matrix, interacted physicochemically at their surface level with the other constituents and (ii) the diversity of bacterial surface properties could result in a diversity of microbial adhesion to components and thus in a diversity of tolerance to toxic compounds. The surface properties of 20 lactic acid bacteria were characterized by the MATS method showing their relatively hydrophilic and various basic characteristics. The results obtained from a set of representative strains showed that (i) the strains with higher affinity for apolar solvents adsorbed more to lipids and hydrophobic compounds, (ii) the more the strains adsorbed to a toxic solvent, the less they were tolerant to this solvent. A diversity of bacterial surface properties was observed for the strains in the same species showing the importance of choosing bacteria according to their surface properties in function of technological objectives.