Photoluminescence emissions of ceramics: a marker of production technology

Photoluminescence (PL) measurements have been performed on different sets of ceramic shards; the results obtained from the ceramic bodies of lustred majolicas produced in Iraq, Italy and Spain are reported. Non-lustred samples are analysed for comparison. The spectra obtained from all the lustred samples show PL emission bands that are attributed to the presence of α-quartz and diopside. The photoluminescence of the lustre-decorated ceramics is possibly a fingerprint of the particular production technology of lustre. PACS 81.05.Mh; 78.55.Hx     

Inflation of correlation in the pursuit of drug-likeness

Drug-likeness is a frequently invoked, although not always precisely defined, concept in drug discovery. Opinions on drug-likeness are to a large extent shaped by the relationships that are observed between surrogate measures of drug-likeness (e.g. aqueous solubility; permeability; pharmacological promiscuity) and fundamental physicochemical properties (e.g. lipophilicity; molecular size). This article draws on examples from the literature to highlight approaches to data analysis that exaggerate trends in data and the term correlation inflation is introduced in the context of drug discovery. Averaging groups of data points prior to analysis is a common cause of correlation inflation and results from analysis of binned continuous data should always be treated with caution.     

Propositional interval neighborhood logics: Expressiveness, decidability, and undecidable extensions

In this paper, we investigate the expressiveness of the variety of propositional interval neighborhood logics (PNL), we establish their decidability on linearly ordered domains and some important subclasses, and we prove the undecidability of a number of extensions of PNL with additional modalities over interval relations. All together, we show that PNL form a quite expressive and nearly maximal decidable fragment of Halpern–Shoham’s interval logic HS.     

Turbo codes: the phase transition

Turbo codes are a very efficient method for communicating reliably through a noisy channel. There is no theoretical understanding of their effectiveness. In reference [1] they are mapped onto a class of disordered spin models. The analytical calculations concerning these models are reported here. We prove the existence of a no-error phase and compute its local stability threshold. As a byproduct, we gain some insight into the dynamics of the decoding algorithm. Received 14 March 2000     

Neutron irradiation effects on martensitic iron-nickel alloys

Summary Iron-nickel alloys in the range from 29 to 32 wt.% Ni have been irradiated with an integral flux of 3·10¹⁸ n cm⁻² and then subjected to martensitic transformation. the resistivity, magnetoresistivity and Hall-effect measurements performed on the irradiated samples allow us to support the formation of iron-rich or nichel-rich ordered microstructures and additional α-phase from the supersaturated γ-matrix. The nickel content of the above-ordered region, is evaluated from the behaviour of the anomalous Hall effect in the irradiated specimens with different composition.

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Riassunto Leghe di ferro-nichel, con contenuto in Ni variabile dal 29% al 32%, sono state irradiate con un fascio di neutroni avente flusso integrale di 3·10¹⁸ n cm⁻² a 80°C e sono state successivamente sottoposte a trasformazione martensitica mediante raffreddamento. Le misure di resistività, di magnetoresistenza e di effetto Hall compiute sui campioni irradiati consentono di fare l'ipotesi della presenza nella fase supersatura γ di microstrutture ordinate, ricche di Fe o di Ni, oltre ad una fase α addizionale. Dal comportamento dell'effetto Hall anomalo nei campioni irradiati si è valutato il contenuto di Ni presente nelle regioni ordinate.

     

Microscopic description of aging dynamics: fluctuation-dissipation relations,effective temperature,and heterogeneities

We consider the dynamics of a diluted mean-field spin glass model in the aging regime. The model presents a particularly rich heterogeneous behavior. In order to catch this behavior, we perform a spin-by-spin analysis for a given disorder realization. We confirm the connection between statics and dynamics at the level of single degrees of freedom. Moreover, working with single-site quantities, we can introduce a new response-vs-correlation plot, which clearly shows how heterogeneous degrees of freedom undergo coherent structural rearrangements. We discuss the general scenario which emerges from our work and (possibly) applies to more realistic glassy models. Interestingly enough, some features of this scenario can be understood recurring to thermometric considerations.     

Studies for a Diastereoselective Synthesis of the Tetracyclic Diterpenic Diol Stemarin: A Model Study for a New Preparation of the Key Intermediate and the Synthesis of (+)-18-Deoxystemarin

Methods for a stereoselective preparation of compounds of type 2b , a key intermediate of a previous synthesis of the tetracyclic diterpene stemarin ( la ), have been tested on model compounds 5a, 5c , and 8a . Thus, (±)-(1RS,6SR,8SR,11SR)-hydroxytricyclo[6.2.2.0^l,6]dodecan-9-one ( 5a ) was transformed by the Mitsunobu reaction into (±)-(1RS,6SR,8SR,11RS)-11-(benzoyloxy)tricyclot[6.2.2.0^1,6]dodecan-9-one ( 6b ; Scheme 2). The latter was also obtained from (±)-(1RS,6SR,8SR,11RS)-11-[(4)-toluenesulfonyloxy]tricyclo[6.2.2.0^1,6]dodecan-9-one ( 5c ) by the action of Et₄N (PhCOO) in acetone. Compound 6b was then converted into (±)-(1RS,6RS,8RS,9RS)-tricyclo[6.2.2.0^1,6]dodecan-9-ol ( 8b ), a model for 2b . Compound 8b was also prepared from its epimer 8a by the Mitsunobu reaction via ester 7b . The inversion of configuration of bicyclo[2.2.2]octan-2-ols or derivates was not previously described. The model studies paved the way to the diastereoselective synthesis of (+)-18-deoxystemarin ( 1b ) via 12β-hydroxy-13-methyl-9β,13β-ethano-9β-podocarpan-15-one ( 10a ) and 13-methyl-9β,13β-ethano-9β-podpcarpan-12α-ol ( 11b ).     

Glassy phases in random heteropolymers with correlated sequences

We develop an analytic approach for the study of lattice heteropolymers and apply it to copolymers with correlated Markovian sequences. According to our analysis, heteropolymers present three different dense phases depending upon the temperature, the nature of the monomer interactions, and the sequence correlations: (i) a liquid phase, (ii) a "soft glass" phase, and (iii) a "frozen glass" phase. The presence of the intermediate "soft glass" phase is predicted, for instance, in the case of polyampholytes with sequences that favor the alternation of monomers. Our approach is based on the cavity method, a refined Bethe-Peierls approximation adapted to frustrated systems. It amounts to a mean-field treatment in which the nearest-neighbor correlations, which are crucial in the dense phases of heteropolymers, are handled exactly. This approach is powerful and versatile; it can be improved systematically and generalized to other polymeric systems.