Correlation Inequalities for Spin Glasses

We prove a correlation type inequality for spin systems with quenched symmetric random interactions. This gives monotonicity of the pressure with respect to the strength of the interaction for a class of spin glass models. Consequences include existence of the thermodynamic limit for the pressure and bounds on the surface pressure. We also describe other conjectured inequalities for such systems. Submitted: January 6, 2007. Accepted: May 10, 2007.     

Structural and electronic properties of laser irradiated pure iron

The surface of a pure iron sample irradiated with a high power pulsed laser has been studied by UHV electron spectroscopies in the reflection mode (AES, EELS and EELFS) in order to verify the experimental hint of a laser induced non-crystalline surface layer.Our results point out that the local arrangement of atoms in the laser irradiated surface is not disorder-like: no significant differences in structural and electronic properties between irradiated and non-irradiated samples have been detected in the short-range limit (up to the fourth coordination shell).This result agrees with a theoretical computer calculation which predicts, for pure metals, a cooling rate of the order of 10¹⁰ K sec^?1 after the laser pulse, not sufficient to avoid recrystallization.     

Parallel ODE solvers based on block BVMs

In this paper we deal with Boundary Value Methods (BVMs), which are methods recently introduced for the numerical approximation of initial value problems for ODEs. Such methods, based on linear multistep formulae (LMF), overcome the stability limitations due to the well-known Dahlquist barriers, and have been the subject of much research in the last years. This has led to the definition of a new stability framework, which generalizes the one stated by Dahlquist for LMF. Moreover, several aspects have been investigated, including the efficient stepsize control [17,25,26] and the application of the methods for approximating different kinds of problems such as BVPs, PDEs and DAEs [7,23,41]. Furthermore, a block version of such methods, recently proposed for approximating Hamiltonian problems [24], is able to provide an efficient parallel solver for ODE systems [3].     

Solution properties of exocellular polysaccharides of rhizobium leguminosarum. Static and dynamic light-scattering: Characterization in dilute solution

Three polysaccharides, Rhizobium leguminosarum 8002 EPS(I), Rhizobium trifolii TA1-EPS (II), Rhizobium leguminosarum 127K87 EPS (III), produced by bacteria of Rhizobium genus have been investigated by static and dynamic light scattering combined with chirooptical measurements. All three polymers have the same backbone but differ in the length of the side chains and in the content of minor substituents. An isothermal conformational transition coil → helix was observed with I and II by adding salt (NaCl). The molecular parameters of the polysaccharides in the ordered state were determined by light-scattering data. Increasing the ionic strength a shrinking of the helix was observed accompanied by a corresponding decrease in the radius of gyration. An extraordinary chain stiffness in terms of Kuhn segment lengths was found in both cases, similar to that already observed for other microbial polysaccharides. In the case of III no disorder → order transition was induced by the salt, and the scattering behavior corresponds to that of a rather flexible polymer with a characteristic ratio C_∞ = 24. The incapability of III to form a helical structure is attributed to the effect of the very long side chain. The analysis of the time correlation functions revealed typical flexible chain behavior for all three polysaccharides. This behavior for the two ordered polymers is in agreement with a recent theory by Maggs and is due to bending modes of the rods. ©1995 John Wiley & Sons, Inc.     

Nonlinear evolution inclusions arising from phase change models

The paper is devoted to the analysis of an abstract evolution inclusion with a non-invertible operator, motivated by problems arising in nonlocal phase separation modeling. Existence, uniqueness, and long-time behaviour of the solution to the related Cauchy problem are discussed in detail. The Italian authors would like to point out financial support from theMIUR-COFIN 2002 research program on “Free boundary problems in applied sciences”. The second author was supported by GA ČR under Grant No. 201/02/1058, and by GNAMPA of INDAM during his stay at Pavia in May 2003: in this respect, the kind hospitality of the Department of Mathematics in Pavia is gratefully acknowledged as well. The work also benefited from partial support of the IMATI of CNR in Pavia, Italy.     

Unexpected one-step synthesis of 3-benzoyl-2-phenylbenzofurans under Wittig conditions

The reaction of 2-hydroxybenzyltriphenylphosphonium bromide with substituted benzoyl chlorides under Wittig conditions, led to 2-phenylbenzofuran derivatives 4a–p and the unexpected formation of 3-benzoyl-2-phenylbenzofuran derivatives 5a–p. Benzoyl chlorides possessing electron-withdrawing groups afforded 3-benzoyl-2-phenylbenzofuran derivatives in higher yields than those with electron-donating groups. This reaction represents a simple and regioselective, one-pot route towards the preparation of deactivated 3-benzoyl-2-phenylbenzofuran compounds which are difficult to obtain by the direct acylation of 2-phenylbenzofurans.     

cEST: a flexible tool for calorimetric data analysis

Journal of Thermal Analysis and Calorimetry - The pyrolysis characteristics and kinetics of lignocellulosic biomass (cotton stalk) and seaweed (Gracilaria lemaneiformis) were studied comparatively....     

Oxidative Polymerization of the Pheomelanin Precursor 5-Hydroxy-1,4-benzothiazinylalanine: A New Hint to the Pigment Structure

Biosynthetic studies have shown that pheomelanins, the distinctive pigments of red human hair, arise from oxidative polymerization of cysteinyldopas via 1,4-benzothiazinylalanine intermediates. However, the mode of formation of the pigment polymer remains controversial. To address this point, we have investigated the conversion of the major biosynthetic precursor 5-S-cysteinyldopa (2a) to pheomelanin under biomimetic conditions. Peroxidase/H(2)O(2) oxidation of 2a was shown to lead in the early stages to the 1,4-benzothiazinylalanine 8a, which rapidly declines with concomitant formation of a distinct pattern of oligomeric products. Reduction of the reaction mixture at this stage allowed the isolation of dimer 17 in 10% yield, along with trimers 18 and 19 in smaller amounts. A restricted rotation about the ethereal C-O bond of 17 was apparent by the presence of two NMR-detectable conformational isomers, separated by an activation energy barrier of 17.83 +/- 0.03 kcal mol(-)(1). Under similar oxidation conditions, the model catechol 2b gave the related dimers 15 and 16. The structure of oligomers 17-19, all characterized by C-C and C-O bonds between the benzothiazine units, would suggest that the peroxidase-promoted polymerization proceeds by phenol-type coupling of an aryloxy radical generated by initial one-electron oxidation of 8a. Overall, these results point to a structural model for the pheomelanin polymer which is basically different from that proposed on the basis of degradative studies.     

Gemini pyridinium surfactants: synthesis and conductometric study of a novel class of amphiphiles1

A new series of pyridinium cationic gemini surfactants was prepared by quaternization of the 2,2'-(alpha,omega-alkanediyl)bispyridines with N-alkylating agents, whose reactivity is briefly discussed. Particularly useful was the use of long-chain alkyl triflates (trifluoromethanesulfonates) for both overcoming the sterical hindrance in the pyridines and obtaining higher synthetic yields. Well-known 4,4'-(alpha,omega-alkanediyl)bis(1-alkylpyridinium) structures showed narrow temperature ranges for practical applications, due to their high Krafft points, while the new 2,2'-(alpha,omega-alkanediyl)bis(1-alkylpyridinium) series, accounted for good surface active properties. Due to the Krafft points below 0 degrees C, they could be exploited as solutions in water at any temperature. The characterization of the behavior of the series was performed by conductivity measurements. Some of the proposed structures exhibited unusual surface active behavior, which was interpreted in terms of particular conformational arrangements.     

Molecular orbital study of hyperfine splitting constants in ethyl and cyclohexadienyl radicals

Hyperconjugated models are used for a m.o. calculation of proton h.f.s. constants in Ethyl and Cyclohexadienyl radicals. A slightly modified Pariser-Parr-Pople SCF method is employed including extensive configuration interaction. The calculated spin densities for the hyperconjugated protons are in good agreement with experiment.

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Zusammenfassung Zur Berechnung von Protonenhyperfeinstrukturkonstanten von Äthyl- und Cyclohexadienyl-Radikalen werden Modelle mit Hyperkonjugation verwendet. Die Rechnung gründet sich auf eine leicht modifizierte Pariser-Parr-Pople-Methode einschließlich ausgedehnter Konfigurationswechselwirkung. Die berechneten Spin-Dichten für die hyperkonjugierten Protonen stimmen mit experimentell ermittelten Werten gut überein.

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Résumé Des modèles tenant compte à la hyperconjugaison sont usés pour le calcul des constantes de structure hyperfine protonique des radicaux éthyl et Cyclohexadiényl. Le calcul se base sur une méthode Pariser-Parr-Pople un peu modifiée et comprenant une interaction de configurations extensive. Les densités de spin calculées pour les protons hyperconjugués sont en bon accord avec des valeurs expérimentales.

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We thank the Italian National Research Council (Chemistry Committee, Research Group IV) for financial support. One of us (P.L.N.) thanks Sicedison S.p.A. for a grant.