We present two pilot studies for the search and characterization of accretion events in star-forming dwarf galaxies. Our strategy consists of two complementary approaches: i) the direct search for stellar substructures around dwarf galaxies through deep wide-field imaging, and ii) the characterization of the chemical properties in these systems up to large galacto-centric distances. We show our results for two star-forming dwarf galaxies, the starburst irregular NGC 4449, and the extremely metal-poor dwarf DDO 68.

We continue the study of collisionless systems governed by additive $r^{-{\it\alpha}}$ interparticle forces by focusing on the influence of the force exponent ${\it\alpha}$ on radial orbital anisotropy. In this preparatory work, we construct the radially anisotropic Osipkov–Merritt phase-space distribution functions for self-consistent spherical Hernquist models with $r^{-{\it\alpha}}$ forces and $1\leqslant {\it\alpha}<3$. The resulting systems are isotropic at the centre and increasingly dominated by radial orbits at radii larger than the anisotropy radius $r_{a}$. For radially anisotropic models we determine the minimum value of the anisotropy radius $r_{ac}$ as a function of ${\it\alpha}$ for phase-space consistency (such that the phase-space distribution function is nowhere negative for $r_{a}\geqslant r_{ac}$). We find that $r_{ac}$ decreases for decreasing ${\it\alpha}$, and that the amount of kinetic energy that can be stored in the radial direction relative to that stored in the tangential directions for marginally consistent models increases for decreasing ${\it\alpha}$. In particular, we find that isotropic systems are consistent in the explored range of ${\it\alpha}$. By means of direct $N$-body simulations, we finally verify that the isotropic systems are also stable.

We describe some results obtained with N-MODY, a code for N-body simulations of collisionless stellar systems in modified Newtonian dynamics (MOND). We found that a few fundamental dynamical processes are profoundly different in MOND and in Newtonian gravity with dark matter. In particular, violent relaxation, phase mixing and galaxy merging take significantly longer in MOND than in Newtonian gravity, while dynamical friction is more effective in a MOND system than in an equivalent Newtonian system with dark matter.

The oxygen behaviour and its influence on the annealing properties of the TiO2/Si and Ti/TiO2/Si systems have been investigated. For the TiO2/Si system no reaction at all could be evidenced after vacuum annealing up to 900°C for 30'. In the Ti/TiO2/Si system metallic Ti reacts with the TiO2 film above 400°C and at 600°C a uniform oxygen solid solution at the solubility limit was obtained without any Si reaction. Silicide formation occurs for annealing temperatures higher than 650°C and causes oxygen expulsion from the reacted layer and consequently a rise in its concentration at the surface where Ti oxide precipitation takes place. This surface oxide layer prevents a further growth of the silicide up to 850°C. The reaction of the whole metal film is attained only by annealing at 900°C or above, when the oxide is completely reduced and an important oxygen loss takes place. A model explaining this behaviour is proposed.

The use of Q-switched ruby laser and multiscanning electron beam annealing (MEBA) to produce the reaction of thin Ti and Ni films deposited onto single crystal Si has been studied. Laser annealing produces a reaction at the interface between the metal and the semiconductor; the reacted layers are not uniform in composition and more similar to a mixture than to a well-defined phase. The silicide layers produced by MEBA results from the solid state reaction of whole metal layer and have well-defined compositions and sharp interfaces between phases and the underlying crystal. The observed thicknesses of the silicides produced by MEBA cannot be accounted for by the parabolic volume diffusion mechanism operating in the standard furnace annealing. Post annealing treatments in furnace showed that e-beam produced silicides have the same thermal stability as those produced by conventional heat treatments. The presence of a critical temperature for silicide formation in Ti/Si MEBA annealed samples has been confirmed and studied in detail.