A setup for integral measurements of multiple scattering angular distributions by 10- to 100-keV electrons

A dedicated setup has been developed to study the angular distributions of electrons traversing thin films employing the low-energy beam available from the gun of the São Paulo Microtron. In this first stage, only integral measurements are possible using the fraction of the electron beam current collected in a Faraday cup and in a ring surrounding the entrance of the former. The overall normalisation is provided by measuring the beam current collected by the scattering chamber as well, thus covering the full solid angle. In this work, important construction specifications are presented. The experience gained by operating this system is also discussed regarding its critical aspects like: avoiding cross talk between the cup and the ring both at the physical and electronic levels, measurements of small charges deposited on large objects (the chamber in particular), and conditioning of the various surfaces involved. Finally, some selected results are compared to the well-known theory by Goudsmit and Saunderson with good agreement

Teaching friction at university level through an experiment with images

The experiment with images described here contributes to the scarce literature about the experimental approach to the classical problem of oblique launching on the surface of an inclined plane. It is directed at an intermediate physics course, with the aim of contextualizing the teaching of the laws of friction and empirical modeling in Classical Mechanics. We used a video of a two-dimensional real motion of a coin sliding on an inclined plane, a case where the net force varies continuously. The video frames were separated and each one was assigned a time code by a computational process. The resulting set of images was used to analyze the dynamical evolution of the system, by recording the coin positions at known instants. All the images and laboratory manuals can be accessed at http://www.fep.if.usp.br/∼fisfoto/translacao/planoInclinado/index.php. Realizing that the resistive force can be interpreted as the kinetic friction force, according to Amontons’ laws, it is possible to build a theoretical model able to predict the trajectory through a first order numerical method, and then fit its parameters to the observed trajectory. This proposal reconciles the laboratory with Information and Communication Digital Technologies (ICDT). It also favors a deeper discussion about the role of laws, models and hypotheses in the physical sciences, which could be particularly interesting in the case of teacher education.Fil: Leite, Marcos L.. Universidade de Sao Paulo; BrasilFil: Maidana, Nora L.. Universidade de Sao Paulo; BrasilFil: Fonseca, Monaliza. Universidade de Sao Paulo; BrasilFil: Barros, Suelen F.. Universidade de Sao Paulo; Brasil. Instituto Federal de Educação, Ciência e Tecnologia de São Paulo; BrasilFil: Aduriz Bravo, Agustin. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Formación e Investigación en Enseñanza de las Ciencias; ArgentinaFil: Vanin, Vito R.. Universidade de Sao Paulo; Brasi

Dismantling Brazil's science threatens global biodiversity heritage

In the middle of a political and fiscal crisis, the Brazilian government is applying successive budget cuts, including in science funding. Recent cuts radically affect research programs on biodiversity that are crucial components for the design and monitoring of public policies for nature conservation and sustainable development. We analyze the consequences of such cuts on the Research Program on Biodiversity (PPBio), the largest biodiversity research network in Brazil (626 researchers, nine networks in all Brazilian biomes). Brazil holds a substantial part of the world's biodiversity and of tropical forests that play a significant role for regional and global climate stability. If underfunding is maintained, the dismantling of the Brazilian PPBio will have consequences that go beyond biodiversity knowledge itself but affect society as a whole. Brazil will likely fail to reach the National Targets for Biodiversity 2011–2020, and it will be difficult to fulfill the restoration target of the Brazilian NDC and to advance with the sustainable development goals. © 2017 Associação Brasileira de Ciência Ecológica e Conservaçã