Pràctica 9. El desenvolupament psicomotor del xiquet (primer cicle d'Educació Infantil)

El començament del desenvolupament del xiquet està dominat essencialment per la motricitat. En els primers mesos d’edat del nadó, els moviments són veritables manifestacions del seu desenvolupament psicològic. Aquesta motricitat es desenvoluparà amb més precisió i seguretat si creem un ambient segur i de llibertat per als xiquets, on el rol de l’adult és d’acompanyament no invasiu i testimoni dels seus èxits. Els treballs d’investigació de l’Institut Lóczy i de la doctora Emmi Pikler ens indiquen que la intervenció directa de l’adult durant els primers estadis del desenvolupament motor no és una condició prèvia per a l’adquisició d’aquests estadis, perquè en condicions favorables els xiquets aconsegueixen regular-se per si mateixos, per la seua pròpia iniciativa, amb moviments de bona qualitat, ben equilibrats i cada vegada més complexos (Pikler, 1985).

On the forbidden gap of finite graphene nanoribbons

The electronic structure of isolated finite graphene nanoribbons is investigated by solving, at the Hartree-Fock (HF) level, the Pariser, Parr and Pople (PPP) many-body Hamiltonian. The study is mainly focused on 7-AGNR and 13-AGNR (Armchair Graphene Nano-Ribbons), whose electronic structures have been recently experimentally investigated. Only paramagnetic solutions are considered. The characteristics of the forbidden gap are studied as a function of the ribbon length. For a 7-AGNR, the gap monotonically decreases from a maximum value of ~6.5 eV for short nanoribbons to a very small value of ~0.12 eV for the longer calculated systems. Gap edges are defined by molecular orbitals that are spatially localized near the nanoribbon extremes, that is, near both zig-zag edges. On the other hand, two delocalized orbitals define a much larger gap of about 5 eV. Conductance measurements report a somewhat smaller gap of ~3 eV. The small real gap lies in the middle of the one given by extended states and has been observed by STM and reproduced by DFT calculations. On the other hand, the length dependence of the gap is not monotonous for a 13-AGNR. It decreases initially but sharply increases for lengths beyond 30 Å remaining almost constant thereafter at a value of ~2.1 eV. Two additional states localized at the nanoribbon extremes show up at energies 0.31 eV below the HOMO (Highest Occupied Molecular Orbital) and above the LUMO (Lowest Unoccupied Molecular Orbital). These numbers compare favorably with those recently obtained by means of STS for a 13-AGNR sustained by a gold surface, namely 1.4 eV for the energy gap and 0.4 eV for the position of localized band edges. We show that the important differences between 7- and 13-AGNR should be ascribed to the charge rearrangement near the zig-zag edges obtained in our calculations for ribbons longer than 30 Å, a feature that does not show up for a 7-AGNR no matter its length.