Mechanics, cosmology and Mach's principle

It is pointed out that recent cosmological findings seem to support the view that the mass/energy distribution of the universe defines the Newtonian inertial frames as originally suggested by Mach. The background concepts of inertial frame, Newton's second law, and fictitious forces are clarified. A precise definition of Mach's principle is suggested. Then an approximation to general relativity discovered by Einstein, Infeld, and Hoffmann is used and it is found that this precise formulation of Mach's principle is realized provided the mass/energy density of the universe has a specific value. This value turns out to be twice the critical density. The implications of this approximate result is put into context.Comment: 9 pages, 34 references, 0 figure

La gestión de cadenas productivas: desarrollos recientes y aplicabilidad del concepto

El concepto central de este artículo se refiere a "sistemas productivos estrictamente coordinados" (slrictlycoordinaledsupplysystems-SCSS). basado en la teoría de la integración vertical, propuesta por Williamson (1985). Su objetivo principal es exponer elementos clave en la gestión de las cadenas productivas, ya que la literatura reciente en este campo está avanzando hacia el desarrollo de una les la sólida sobre este tema, y además los sectores productivos (público y privado) han mostrado interés en conocer instrumentos que puedan ayudar a gestionar Iqs sistemas productivos. Para cumplir este propósito, se encuentra dividido en cinco partes, asi: introducción o marco de referencia, ubicación del concepto de sistema productivo en un marco "coasiano", análisis del concepto de coordinación y sus límites, problemática de la falta de coordinación y teoría de la gestión de los sistemas productivos. Por último, se presentan las conclusiones y se identifican algunos conceptos que requieren especial atención

How might educational research into children’s ideas about light be of use to teachers?

This paper offers a synthesis of research evidence around teaching light to primary and secondary school pupils, as part of the Institute of Physics (IOP) Promoting and Interpreting Physics Education Research (PIPER) project. Conceptual change literature describes many difficulties young people have with understanding the phenomenon of light, and this knowledge can be useful in the classroom. Pupil teacher dialogue is used to illustrate some of the pedagogical challenges teachers face in this topic. This paper highlights a range of influences on pupils from everyday life and from the classroom, with a view to promoting teacher awareness of conceptual change research evidence