A step forward in the study of the electroerosion by optical methods

This work develops two theoretical models of surfaces to explain the behavior of the light scattered by samples that suffers some alteration.

In a first model, it is evaluated the mean intensity scattered by the sample, analyzing the different curves obtained as function of the eroded/total surface ratio. The theoretical results are compared with those obtained experimentally. It can be seen that there exists a strong relation between the electroerosion level and the light scattered by the sample.

A second model analyzes a surface with random changes in its roughness. A translucent surface with its roughness changing in a controlled way is studied. Then, the correlation coefficient variation as function of the roughness variation is determined by the transmission speckle correlation method. The obtained experimental values are compared with those obtained with this model.

In summary, it can be shown that the first- and second-order statistics properties of the transmitted or reflected light by a sample with a variable topography can be taken account as a parameter to analyze these morphologic changes.     

Sur la structure projective d'espace fibré

Résumé Dans cet article nous introduisons d'abord un espace fibré principal B(M), P), oú M est une variété différentiable et P est un sous-groupe du groupe d'homographique générale, et nous étudierons ensuite des propriétés géométriques de quelques constructions qui se rattachent la connexion relative cet espace. à M. Enrico Bompiani pour son Jubilé scientifique     

Microstructural changes in amorphous Si/crystalline Al thin bilayer films upon annealing

Microstructural changes occurring in a sputter deposited Si (150 nm, amorphous)/Al (50 nm, crystalline); {111} fibre textured bilayer, upon annealing at 523 K for 60 min in a vacuum of 2.0×10^-4 Pa, were analyzed employing X-ray diffraction, Auger electron spectroscopy, scanning electron microscopy, atomic force microscopy and focused-ion beam imaging. After the annealing the Al and Si sublayers had largely exchanged their locations in the bilayer; i.e. the Si layer was adjacent to the substrate after annealing. Simultaneously, the amorphous Si layer had crystallized into an aggregate of {111} oriented nanocrystals, with a crystallite size of about 15 nm. The Al layer, now adjacent to the surface, had formed a uniformly net-shaped layer in association with an increase of the surface roughness. Upon this rearrangement, the already initially present Al {111} fibre texture had become stronger, the Al crystallites had grown laterally and the macrostress in the Al layer had relaxed. An extensive analysis of thermodynamic driving forces for the transformation indicated that the largest gain in energy upon transformation is due to the crystallization of the amorphous Si. The only identifiable driving force for the layer exchange appears to be the release of elastic energy upon the rearrangement of the Si and Al phases in the layer. PACS 61.43.D; 61.72.C; 62.40; 65.70; 68.55.J; 68.60.BThis revised version was published online in September 2004. Due to technical problems the PDF of the previous version was incomplete.     

Thermostatistics of the g-on gas

In this study, the particles of the quantum gases, namely bosons and fermions are called g-ons by using the parameter of the fractional exclusion statistics g, where . With this point of departure, the distribution function of the g-on gas is obtained by the variational, steepest descent and statistical methods. The distribution functions which are found by means of these three methods are compared. It is shown that the thermostatistical formulations of quantum gases can be unified. By suitable choices of g, standard relations of statistical mechanics of the Bose and Fermi systems are recovered.Received: 26 March 2003, Published online: 22 September 2003PACS: 05.20.-y Classical statistical mechanics - 03.65.-w Quantum mechanics     

Structure formation and instability in a tube of sand

A new instability in the combined flow of fine grains and gas is investigated by means of experiments, simulations, and analytic techniques. When a bubble of air rises through a granular packing in a tube, a sequence of smaller bubbles spontaneously forms in front of it. The existence of this instability is shown from the experiments, simulations, and theoretical considerations. Moreover, the simulations and experiments agree on the quantitative level. In particular, when the tube is tilted away from the vertical the experiments and the simulations show the same increase in the speed of the rising bubble.     

Synthesis and characterization of phenoxarsin-10-yl 2-R2N-cyclopent-1-ene-1-carbodithioate (R = H,C2H5, cyclo-C6H11CH2) and the crystal and molecular structure of the 2-amino (R = H) derivative

Phenoxarsin-10-yl derivatives of 2-amino-cyclopent-1-ene-1-carbodithioic acid, (ACDA), and its N-alkyl derivativesO(C₆H₄)₂ AsS₂C—C₅H₆— NHR-2 (R = H, CH₂CH₃, CH₂C₆H₁₁,), have been prepared by reacting O(C₆H₄)₂AsCI with the corresponding ACDA 1,1-dithioic acid. The compounds were obtained by stirring stoichiometric amounts of the reagents in ethanol, over 24 h, at room temperature. The scale of the preparations were in the order of 2 mmol and the yields of the compounds ca 75%. The reactions were carried out in absolute ethanol. The compounds were characterized by IR, mass and NMR (¹H, ¹³C) spectroscopy. The molecular structure of O(C₆H₄)₂AsS₂C—C₅H₆—NH₂-2 was determined using X-ray diffractometry, achieving an R-value of 6.3%; this compound is monomeric and contains an asymmetric monometallic biconnective 1,1-dithiolato ligand [As—S(1) 2.272(2) å, As … S(2) 3.125(2) å]. An intramolecular hydrogen bond is established between one hydrogen atom of the NH₂ group and the sulfur [S(2)] atom involved in the secondary interaction to arsenic. The dihedral angle (150.3(3)°) of the phenoxarsine moiety is practically unaffected by substitution of chlorine on arsenic by the carbodithioato ligand.     

Measurement of the polarization of the recoil proton from the photoproduction of neutral pions on hydrogen in the region of the first resonance. I

The polarization of the recoil proton from the reactionγ+p→π ⁰+p has been measured using liquid helium as polarization analyser. The photon energy has been varied between 250 and 360 MeV, the pion angle (CM) between 58° and 100°.