A multivariate generalized long memory model

In this Note, we propose a new flexible multivariate long memory process which is a self-similar model with the ability to capture short-range dependence, seasonality and long-range dependence characteristics. Specifically, we extend the multivariate ARFIMA model proposed by Sowell (1989) [8], and investigate some of its statistical properties.     

Analysis of geological standards with PIXE and PIGE technioues applications to volcanic rocks

Geological standards are analyzed using PIXE and PIGE techniques. The concentrations of up to 26 elements are determined and compared with those obtained by other methods. PIXE and PIGE techniques are also applied to different volcanic rock samples. Their sensitivity, accuracy, and speed of data collection and reduction, are of great interest in the study of volcanic phenomena.     

119Sn Mössbauer spectroscopy: a powerful tool to unfold the reaction mechanism in advanced electrodes for lithium-ion batteries

Cobalt–tin intermetallic compounds with different particle size have been obtained and characterized by using ¹¹⁹Sn Mössbauer spectroscopy as a main tool. The electrochemical behavior of the Co–Sn compounds has been evaluated in lithium test cells. The Lamb–Mössbauer factors for CoSn with different crystallite sizes have been calculated. The results f _nano???CoSn(300 K) = 0.19 and f _{coarse???CoSn}(300 K) = 0.55 are obtained. Nano-CoSn exhibits larger capacity to react with lithium than coarse-CoSn.     

Physical properties of mixed-valence Tl 3 I TlIIICl6 investigated by conductivity and positron annihilation lifetime measurements: Effect of crushing the crystals

For a better understanding of isotope exchange in solid Tl₄Cl₆ the effects of crushing the crystals were investigated by conductivity and by positron annihilation lifetime measurements. As in untreated Tl₄Cl₆, the conductivity variation with temperature shows a break at about 450 K. The activation energies, 0.53 eV and 0.70 eV, respectively, below and above 450 K, are very close to those in the untreated material but the absolute values of conductivity are lower after crushing which is attributed to the trapping of the mobile defects of dislocation. The positron lifetime variation with increasing temperature shows some contribution of extrinsic defects, annealing at about 413 K. On further heating or cooling cycles, the lifetime changes are controlled by the production of intrinsic cation vacancies, whose formation enthalpy, 0.39 eV, is close to that derived for untreated Tl₄Cl₆. The shape of the initial part of the curves would indicate that crushing does not directly create appreciable concentrations of cation vacancies but would rather produce annealable defects, possibly dislocations, favouring the formation and/or trapping of such vacancies.     

Tin oxalate as a precursor of tin dioxide and electrode materials for lithium-ion batteries

Tin(II) oxalate was studied as a novel precursor for active electrode materials in lithium-ion batteries. The discharge of lithium cells using tin oxalate electrodes takes place by three irreversible steps: tin reduction, forming a lithium oxalate matrix; solvent decomposition to form a passivating layer; and oxalate reduction in a two-electron process. These are followed by reversible alloying of tin with lithium, leading to a maximum discharge of 11 F/mol. Cycling of the cells showed reversible capacities higher than 600 mAh/g during the first five cycles and ca. 200 mAh/g after 50 cycles. Tin oxalate was converted to tin dioxide by thermal decomposition at 450 °C and also by a chemical method by dissolving tin oxalate powder in 33% v/v hydrogen peroxide at room temperature. The ultrafine nature of the tin dioxide powders obtained by this procedure allow their use as electrodes in lithium cells. The best capacity retention during the first five cycles was achieved for a sample heat treated to 250 °C to eliminate surface water. Electronic Publication