Relaxation of Disordered Magnets in the Griffiths' Regime

We study the relaxation to equilibrium of discrete spin systems with random finite range (not necessarily ferromagnetic) interactions in the Griffiths' regime. We prove that the speed of convergence to the unique reversible Gibbs measure is almost surely faster than any stretched exponential, at least if the probability distribution of the interaction decays faster than exponential (e.g. Gaussian). Furthermore, if the interaction is uniformly bounded, the average over the disorder of the time–autocorrelation function, goes to equilibrium as (in d > 1), in agreement with previous results obtained for the dilute Ising model. Received: 12 June 1996 / Accepted: 23 January 1997     

Excitons in rare gas atoms and solids

Excitons in rare gas are described using the integral equation approach and an appropriate semi-empirical simplification of the short-range terms. In the solids, polarization effects are taken into account using a semi-continuum model in analogy with F-centre problem. Reasonable agreement with experiments is obtained for exciton binding energy shifts passing from atoms to crystals.     

Formation and decomposition of the rutile-type compound FeSbO4

The reaction between Fe₂O₃ (hematite) and Sb₂O₃ leading to the formation of the rutile-type compound FeSbO₄ was analysed by means of DTA and TG, performed under various O₂ partial pressures up to 1673 K. The reaction products were identified by means of XRD analysis. Three transformations occur in the analysed temperature range: 1. oxidation of Sb₂O₃ to Sb₂O₄ between 745 and 768 K; 2. formation of FeSbO₄ between 1226 and 1246 K; 3. decomposition of FeSbO₄ without melting above 1543-1591 K. The TG-DTA and XRD analysis results indicate that deviations from perfect stoichiometry are likely to exist inside FeSbO₄. This revised version was published online in July 2006 with corrections to the Cover Date.     

Oxidative decarboxylation of arylacetic acids by means of tetrabutylammonium periodate

Tetrabutylammonium periodate (TBAPI) in refluxing dioxane is able to convert arylacetic acids into the corresponding nor-aldehydes in good yields.     

Conformational studies of peptides in the presence of lanthanide shift reagent,Eu(DPM)3

The conformations of diastereomers of Z-Phe-Ala-OCH₃ were investigated by analyzing NMR and IR spectra in the presence and absence of Eu(DPM)₃. NMR ΔEu values and ratios of integral intensities for NH(bonded)/NH(free) confirm the stereochemistry of the time-averaged conformation for the peptide-Eu(DPM)₃ complex as that proposed by Bystrov for a dipeptide in solution. Total H-bonding by the peptide was increased by the presence of Eu(DPM)₃.     

Approach to equilibrium of Glauber dynamics in the one phase region

Various finite volume mixing conditions in classical statistical mechanics are reviewed and critically analyzed. In particular somefinite size conditions are discussed, together with their implications for the Gibbs measures and for the approach to equilibrium of Glauber dynamics inarbitrarily large volumes. It is shown that Dobrushin-Shlosman's theory ofcomplete analyticity and its dynamical counterpart due to Stroock and Zegarlinski, cannot be applied, in general, to the whole one phase region since it requires mixing properties for regions ofarbitrary shape. An alternative approach, based on previous ideas of Oliveri, and Picco, is developed, which allows to establish results on rapid approach to equilibrium deeply inside the one phase region. In particular, in the ferromagnetic case, we considerably improve some previous results by Holley and Aizenman and Holley. Our results are optimal in the sene that, for example, they show for the first time fast convergence of the dynamicsfor any temperature above the critical one for thed-dimensional Ising model with or without an external field. In part II we extensively consider the general case (not necessarily attractive) and we develop a new method, based on renormalizations group ideas and on an assumption of strong mixing in a finite cube, to prove hypercontractivity of the Markov semigroup of the Glauber dynamics.Work partially supported by grant SCi-CT91-0695 of the Commission of European Communities     

High-resolution structures of large ribosomal subunits from mesophilic eubacteria and halophilic archaea at various functional States

Structural analysis of the recently determined high resolution structures of the small and the large ribosomal subunits from three bacterial sources, assisted by the medium resolution structure of a complex of the entire ribosome with three tRNAs, led to a quantum jump in our understanding of the process of the translation of the genetic code into proteins. Results of these studies highlighted dynamic aspects of protein biosynthesis; illuminated the modes of action of several antibiotics; indicated strategies adopted by ribosomes for maximizing their functional activity and revealed a wealth of architectural elements, including long tails of proteins penetrating the particle s cores and stabilizing the intricate folds of the RNA chains. Binding of substrate analogues showed that the decoding and the peptide-bond formation are accomplished mainly by RNA. However, several proteins may be functionally relevant in directing the mRNA and in mediating the proper orientation of the tRNA molecules within the ribosomal rRNA frame. Elements involved in intersubunit contacts or in substrate binding are inherently flexible, but maintain well-ordered characteristic conformations in unbound particles. The ribosomes utilize this conformational variability for optimizing their efficiency and minimizing non-productive interactions, hence disorder of functionally relevant features may be linked to less active conformations or to far from physiological conditions. Clinically relevant antibiotics bind almost exclusively to rRNA. In the small subunit they affect the decoding accuracy or limit conformational mobility and in the large subunit they either interfere with substrate binding, by interacting with components of the peptidyl transferase cavity, or hinder the progression of the growing peptide chain.     

Identification of organic compounds by microscopy and X-ray diffractometry

Summary Primary and secondary crystallographic constants can be utilized conveniently for identifications of crystalline organic and inorganic materials by microscopy and X-ray diffractometry. Several specific properties can be measured under the petrographical microscope, including optic axial angle, character, dispersion, and in addition, refractive index directions can be established. The d spacings and their intensities as determined with the X-ray diffractometer serve to identify crystalline materials. The two instruments should be considered as supplementary tools for identifying crystals.Both instruments supply a means for identification and semiquantitative analysis of mixed crystal systems. Data are presented for the systems: acetic-propionic p-bromoanilides and acet-propion-2.4-dinitro-phenylhydrazones.

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Zusammenfassung Primäre und sekundäre kristallographische Konstanten können zur Identifizierung kristallisierter organischer und anorganischer Stoffe auf mikroskopischem Wege und durch Röntgendiffraktometrie gut herangezogen werden. Einzelne spezifische Eigenschaften können unter dem petrographischen Mikroskop gemessen werden, so der optische Achsenwinkel, der Charakter, die Dispersion. Außerdem kann man Angaben über den Brechungsindex erhalten. Die mit dem Röntgendiffraktometer bestimmten Netzebenenabstände d und deren Intensitäten dienen zur Identifizierung kristallisierter Stoffe. Die beiden Instrumente sind als Hilfsmittel zur Erkennung von Kristallen anzusehen.Sie bieten die Möglichkeit zur Identifizierung und halbquantitativen Analyse von Mischkristallsystemen. Daten für die Systeme Essigsäure-Propionsäure-p-Bromanilid und Acetaldehyd-Propionaldehyd-2,4-Dinitrophenylhydrazon werden mitgeteilt.

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Résumé Les constantes cristallographiques primaires et secondaires sont utilisables pour l'identification de composés cristallins organiques et minéraux par microscopie et diffractométrie de rayons X. Il est possible de mesurer diverses propriétés spécifiques sous le microscope pétrographique, savoir: l'angle des axes optiques, le caractère et la dispersion optiques. Il est en outre possible de déterminer les directions des indices de réfraction primaires. Les espacements «d» et leurs intensités déterminés par le diffractomètre à rayons X permettent d'identifier les substances cristallines. Les deux instruments doivent être considérés comme complémentaires pour l'identification de cristaux. Chacun d'entre eux fournit un moyen d'identification et d'analyse semi quantitative des systèmes de cristaux mixtes. On rend compte de résultats obtenus pour les systèmes: p-bromoanilides acétique et propionique ainsi que 2, 4-dinitro phénylhydrazones de l'acétaldéhyde et du propionaldéhyde.

     

Dioxolane-to-bridged acetal-to-spiroketal via ring-closing metathesis and rearrangement: a novel route to 1,7-dioxaspiro[5.5]undecanes

Several examples of 1,7-dioxaspiro[5.5]undecane spiroketal systems have been synthesized from the common bicyclic intermediate 1 via acid-catalyzed rearrangement. Intermolecular ketalization of C(2) symmetric diene diol 3 with ketone 9 and then desymmetrization by ring-closing metathesis rapidly constructs bicyclic acetal 1. The locked conformation and steric bias of 1 allow stereoselective functionalization of one or both double bonds before spiroketalization.     

Practical synthesis of the calcimimetic agent, cinacalcet

A practical synthesis of cinacalcet (Sensipar^®, Mimpara^®) is described. The synthesis starts from readily available starting materials and relies on safe and practical reaction conditions. The sequence comprises three synthetic steps and only one isolation point. The overall yield for the sequence is 85%.