Most students’ initial exposure to physics is in the context of kinematics and dynamics. An understanding of how these topics relate to each other requires the ability to reason about vectors that represent forces and kinematic quantities. We present data that suggest that after traditional instruction in mechanics many students lack this ability. Modifications to instruction can significantly improve student performance on questions about vector addition and subtraction and increase the likelihood that students employ vectors in their attempt to solve mechanics problems. However, an increased emphasis on these topics has so far been only moderately successful in promoting the level of proficiency required to understand the connection between force and acceleration as vector quantities. We describe some of the procedural and reasoning difficulties we have observed in students’ use of vectors.

The photocatalytic reduction of nitrobenzene (ethanol + TiO 2 + UV-light) in non-aqueous suspension yielded aniline and acetaldehyde as main products. However, various by-products as intermediates of nitrobenzene photoreduction (i.e. nitrosobenzene and hydroxyaniline) and others (i.e. indoles and quinolines) were also detected. These last results were explained in terms of reactions between aniline and oxidation products of ethanol.

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The chemical synthesis of gold nanoparticles (NP) by using gold (III) chloride trihydrate (HAuCl∙3H2O) and sodium citrate as a reducing agent in aqueous conditions at 100 °C is presented here. Gold nanoparticles areformed by a galvanic replacement mechanism as described by Lee and Messiel. Morphology of gold-NP was analyzed by way of high-resolution transmission electron microscopy; results indicate a six-fold icosahedral symmetry with an average size distribution of 22 nm. In order to understand the mechanical behaviors, like hardness and elastic moduli, gold-NP were subjected to nanoindentation measurements—obtaining a hardness value of 1.72 GPa and elastic modulus of 100 GPa in a 3–5 nm of displacement at the nanoparticle’s surface.

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