Ionization of Hydrogen and Helium Atoms in Collisions with Relativistic Structural Heavy Ions

Based on the eikonal approximation, cross sections for single and double ionization of hydrogen and helium atoms in collisions with structural multiply charged heavy ions moving with relativistic velocities are calculated. In the present paper, the structural ions are taken to mean the ions with partially filled electronic shells. It is demonstrated that a consideration of the ion charge extension may noticeably change the corresponding cross sections compared to the cross sections for ionization by point ions having the same charges and energies.     

Characterization of phospho-olivines as materials for Li-ion cell cathodes

Solid State Reaction was employed to prepare phospho-olivines LiMPO₄ (where M=Fe, Co) as pure phase and LiNiPO₄ in presence of foreign phases, as cathodic materials for lithiumions batteries. The relationship between structural, morphological and electrochemical properties were investigated in the case of LiFePO₄. Structural investigation has been carried out by means of X-ray powder diffraction (XRPD) and Rietveld refinement. The influence on the morphology of annealing temperature, different flowing gas mixture and addition of ascorbic acid during the synthesis, has been analysed via scanning electron microscopy. The electrochemical cycling performances on LiFePO₄ showed to be positively affected by the modifications of the experimental conditions. Cyclic voltammetry showed a good reversibility during insertion-extraction mechanism, in particular in presence of additives. LiCoPO₄ and LiNiPO₄ are interesting as high voltage cathode materials for Li-ion batteries and have been taken into account, but their electrochemical operating conditions are still to be optimised. In the case of LiNiPO₄ it is very difficult to obtain, by solid state synthesis, suitable purity powders, having a grain size small enough to exploit it usefully as cathodic material for Li-ion cells. Paper presented at the 8th EuroConference on Ionics, Carvoeiro, Algarve, Portugal, Sept. 16 – 22, 2000.     

Analysis of Static Simulated Annealing Algorithms

Generalized hill climbing (GHC) algorithms provide a framework for modeling local search algorithms to address intractable discrete optimization problems. This paper introduces a measure for determining the expected number of iterations to visit a predetermined objective function level, given that an inferior objective function level has been reached in a finite number of iterations. A variation of simulated annealing (SA), termed static simulated annealing (S²A), is analyzed using this measure. S²A uses a fixed cooling schedule during the algorithm execution. Though S²A is probably nonconvergent, its finite-time performance can be assessed using the finite-time performance measure defined in this paper.     

STM/AFM studies of the evolution of morphology of electroplated Ni/W alloys

The surface morphology evolution of Ni/W alloys was studied, as a function of the alloy composition. Using the modified plating baths developed in our laboratory recently, electroplated Ni/W alloys with different W content, in the range of 7–67 atom percent (a/o), can be obtained. This was found to lead to different structures, ranging from polycrystalline fcc-Ni type structure to amorphous, followed by orthorhombic with increasing W content in the alloy. Powder XRD was studied to determine the crystal structures. Ex situ STM, AFM and SEM were used to study in detail the surface morphologies of the different alloys, and their evolution with increasing W content.

The important findings are that a mixture of two crystalline forms can give rise to an amorphous structure. Hillocks that are usually a characteristic of epitaxial growth can also exist in the amorphous alloys. Oriented scratches caused by stress can also be formed.

Up to 20 a/o of W is deposited in the alloys in crystalline form, with the fcc-Ni type structure. Between 20 and about 40 a/o an amorphous structure is observed, and above that an orthorhombic crystal structure is seen, which is characteristic of the NiW binary alloy. Careful choice of the composition of the plating bath allowed us to deposit an alloy containing 67 a/o W, which corresponds to the composition NiW₂.     

Continuum Approaches in the Mechanics of Curved Composites and Associated Problems for Structural Members

A review is made of studies on the mechanics of curved composites carried out using continuum approaches. The relevant theory, problem formulations, and solution methods are considered and some typical results on the influence of structural distortion on the mechanical behavior of composites are analyzed. Subjects for near-term studies are proposed     

One-Parameter Fixed-Point Theory and Gradient Flows of Closed 1-Forms

We use the one-parameter fixed-point theory of Geoghegan and Nicas to get information about the closed orbit structure of transverse gradient flows of closed 1-forms on a closed manifold M. We define a noncommutative zeta function in an object related to the first Hochschild homology group of the Novikov ring associated to the 1-form and relate it to the torsion of a natural chain homotopy equivalence between the Novikov complex and a completed simplicial chain complex of the universal cover of M.     

Observation of hydrogen induced intermediate borides in PrFeB based alloys by Mössbauer effect spectroscopy

In the present work, a quantitative analysis of the phase compositions by Mössbauer effect spectroscopy of solid and conventional hydrogen disproportionated Pr_13.7Fe_80.3B_6.0 and Pr_13.7Fe_63.5Co_16.7Zr_0.1B_6.0 alloys was carried out. Significant amounts of intermediate borides t-Fe₃B and Pr(Fe, Co)₁₂B₆ were detected after solid hydrogen disproportionation treatment in Pr_13.7Fe_80.3B_6.0 and Pr_13.7Fe_63.5Co_16.7Zr_0.1B_6.0 alloys, respectively. After conventional hydrogenation–disproportionation–desorption–recombination treatment these phases were not detected and in no case residual Pr₂Fe₁₄B-phase was found. It was observed that the amount of intermediate borides after disproportionation can be correlated with the degree of texture after recombination at various temperatures.     

The Effect of Boundary Conditions on Gas-phase Synthesised Silver Nanoparticles

We have prepared spherical non-agglomerated silver nanoparticles by an evaporation–condensation–dilution/cooling technique. Silver was evaporated from a crucible in a tubular flow reactor. A porous tube diluter was used to quench the carrier gas at the outlet of the reactor to enhance the formation of small particles and to suppress agglomeration and other particle growth mechanisms. The number size distribution of the prepared particles was measured with a differential mobility analyser–condensation nucleus counter combination and the size and the shape of the particles were analysed with transmission electron microscope. The system was modelled using a sectional aerosol dynamics computer code to estimate the importance of different aerosol processes. In all conditions the particles obtained were non-agglomerated and spherical. The mean particle diameter varied from 4 to 10-nm depending on boundary conditions. From the modelling studies it can be concluded that the nucleation rate is the most important parameter controlling the final particle size.