Synthesis, structure and magnetic properties in the Nd2O3-Gd2O3 mixed system synthesized at 1200 °C

Phase relation studies in the Gd₂O₃-Nd₂O₃ system have been performed on (Gd_1−xNd_x)₂O₃ samples (0?x?1) with the purpose of performing a systematic study of the composition effects on their structural and magnetic properties. All the samples were synthesized by calcination of the related oxalates at 1200 °C in order to ensure the complete decomposition of the oxalates. Five phase regions, namely an A-type hexagonal, a B-type monoclinic, a C-type cubic solid solution and two biphasic mixtures of the former three phase fields were detected in this system. The magnetic susceptibility measurements showed the presence of antiferromagnetic interactions in all samples. The Curie-Weiss temperature shows a nonlinear dependence on concentration. Deduced effective magnetic moments are close to the free ion values.     

Electrodeposition of white gold alloys: an electrochemical,spectroelectrochemical and structural study of the electrodeposition of Au-Sn alloys in the presence of 4-cyanopyridine

A bath for the electrodeposition of Au-Sn alloys is proposed and the properties of the deposit obtained have been studied, in view of applications in the field of white precious metal plating and electroforming. 4-Cyanopyridine has been employed as an organic additive to confer stability to the bath and compactness to the deposit. The electrochemical behaviour of the bath has been investigated by means of cyclic voltammetry, stripping potentiodynamic scans, open circuit potential decay measurements and potentiostatic transients. The nucleation behaviour of the system has been studied on glassy carbon electrodes. The electrodic behaviour of 4-cyanopyridine was investigated as a function of electrode potential by in situ Raman spectroscopy. The composition of the alloys was evaluated by electron dispersive spectroscopy, the crystalline structure by X-ray diffraction and the morphology by scanning electron microscopy. The effects of the additive on the crystalline structure and on the morphology of the electrodeposits have been highlighted. Potential-dependent adsorption, reorientation and cathodic reactivity of 4-cyanopyridine during the alloy electrodeposition process have been assessed.Presented at the 3rd International Symposium on Electrochemical Processing of Tailored Materials held at the 53rd Annual Meeting of the International Society of Electrochemistry, 15–20 September 2002, Düsseldorf, Germany     

Dynamic charges for photoexcited defects in trans (CH)x

We show that the dynamic charge for an arbitrary vibrational excitation of a photogenerated defect in (CH)_x vanishes in the SSH Hamiltonian for a band filling which is symmetric with respect to the interchange of electrons and holes. As a consequence solitonic excitons do not contribute to the infrared conductivity although dissociated charged defects do. Trapping of dissociated kinks at defects on the chain is suggested as a pinning mechanism.     

Gas phase kinetic and thermochemical data for endo- and exo-5-monosubstituted bicyclo[2.2.2]Oct-2-Enes

The thermal reactions of endo- and exo-5-Y bicyclo[2.2.2]oct-2-enes (NYBO and XYBO) where Y = methyl, ethyl, and isopropyl have been studied in the gas phase between 567 and 695 K. For both isomers they are parallel first-order retro-Diels-Alder reactions with elimination of ethene (E) and monosubstituted ethene (YE).The observed Arrhenius parameters are used to discuss the mechanism and to estimate the heats of formation and the entropies of NYBO and XYBO. Group values are proposed for estimation of these thermochemical data for compounds of the same type by means of the methods of Benson.     

Structure–reactivity correlations for gas-phase thermal Diels-Alder reactions of cyclohexa-1,3-diene with substituted ethenes and reverse reactions

Structure–reactivity correlations are developed and used to test a biradical mechanism for gas-phase thermal Diels-Alder reactions of cyclohexa-1,3-diene with substituted ethenes and reverse reactions. © 1994 John Wiley & Sons, Inc.     

Geometrical,spectroscopic, and magnetic properties of an oxygen atom adsorbed on the Ni(100) surface

Spin-polarized linear combinations of Gaussian-type orbital–model core potential–local spin density (LCGTO –MCP –LSD ) computations have been performed for oxygen chemisorption on a Ni(100) surface simulated by four different clusters. Results show that the oxygen atom chemisorbs preferentially on the fourfold hollow site with an equilibrium distance of 1.931 Å and a vertical vibrational frequency of 401 cm^?1. The corresponding experimental values are 1.960 Å and 423 or 430 cm^?1. A satisfactory agreement with experiment is also found for the adsorption energy (6.7 vs. 5.6 eV). The bridge position lies at only 0.4 eV above the fourfold hollow one. It is found that oxygen adsorption leaves the bare cluster total spin magnetic moment unchanged, but induces appreciable reductions of the local atomic moment on the surface nickel atoms. © 1993 John Wiley & Sons, Inc.     

The influence of measurement errors on the determination of the degrees of freedom of dynamic systems

We consider the influence of measurement errors on the experimental calculation of dimensions of possible turbulent flow attractors. For this purpose we considered a Gaussian noise and we carried out some tests showing the existence of a lower limit below which the operational definition of dimension is not reliable.

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Sommario In questo lavoro viene presentata una valutazione della influenza degli errori di misura sulla determinazione sperimentale delle dimensioni di eventuali attrattori di deflussi turbolenti. A tale scopo si considera un rumore Gaussiano. I test effettuati permettono di definire l'esistenza di un minimo al di sotto del quale la definizione operativa di dimensione formisce valori non attendibili.