Cluster-induced crater formation

Using molecular-dynamics simulation, we study the crater volumes induced by energetic impacts ($v= 1- 250$ km/s) of projectiles containing up to N=1000 atoms. We find that for Lennard-Jones bonded material the crater volume depends solely on the total impact energy $E$. Above a threshold \Eth, the volume rises linearly with $E$. Similar results are obtained for metallic materials. By scaling the impact energy $E$ to the target cohesive energy $U$, the crater volumes become independent of the target material. To a first approximation, the crater volume increases in proportion with the available scaled energy, $V=aE/U$. The proportionality factor $a$ is termed the cratering efficiency and assumes values of around 0.5.Comment: 9 page

Crater formation by fast ions: comparison of experiment with Molecular Dynamics simulations

An incident fast ion in the electronic stopping regime produces a track of excitations which can lead to particle ejection and cratering. Molecular Dynamics simulations of the evolution of the deposited energy were used to study the resulting crater morphology as a function of the excitation density in a cylindrical track for large angle of incidence with respect to the surface normal. Surprisingly, the overall behavior is shown to be similar to that seen in the experimental data for crater formation in polymers. However, the simulations give greater insight into the cratering process. The threshold for crater formation occurs when the excitation density approaches the cohesive energy density, and a crater rim is formed at about six times that energy density. The crater length scales roughly as the square root of the electronic stopping power, and the crater width and depth seem to saturate for the largest energy densities considered here. The number of ejected particles, the sputtering yield, is shown to be much smaller than simple estimates based on crater size unless the full crater morphology is considered. Therefore, crater size can not easily be used to estimate the sputtering yield.Comment: LaTeX, 7 pages, 5 EPS figures. For related figures/movies, see: http://dirac.ms.virginia.edu/~emb3t/craters/craters.html New version uploaded 5/16/01, with minor text changes + new figure

PIBID espanhol enquanto agente de contribuição social para os alunos do Colégio Estadual Governador Djenal Tavares de Queiróz

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPESO presente trabalho relata a importância do Programa Institucional de Bolsas de Iniciação à Docência (PIBID) da Universidade Federal de Sergipe (UFS), desenvolvido no Colégio Estadual Governador Djenal Tavares de Queiróz (CEGDTQ), na disciplina de Espanhol, objetivando incentivar a formação de professores de língua espanhola no nível superior, no qual, desde o início da formação acadêmica, estudantes são incluídos no ambiente das escolas públicas, para vivenciarem experiências como futuros professores de Espanhol. A pesquisa seguiu uma base qualitativa de cunho interpretativista, em que foram analisados documentos como os Parâmetros Curriculares Nacionais - PCN (1998, 2002) e as Orientações Curriculares Nacionais - OCEM (2006), que serviram para orientar no planejamento das aulas abordadas. Obtivemos como resultado o aprimoramento e desenvolvimento de práticas docentes, devido ao contato direto com a sala de aula. Diante disso, conclui-se como o PIBID é importante para que o discente desenvolva suas práticas pedagógicas e se familiarize com o ambiente de trabalho que fará parte do seu futuro.São Cristóvão, S