The Socio-Economic Value of the Shark-Diving Industry in Fiji

Based on a survey of divers, dive operators, resort managers, estimates business revenues from shark diving and related expenditures by area; tax revenues; and economic benefit to local communities

Quantum state of a free spin-1/2 particle and the inextricable dependence of spin and momentum under Lorentz transformations

We revise the Dirac equation for a free particle and investigate Lorentz transformations on spinors. We study how the spin quantization axis changes under Lorentz transformations, and evince the interplay between spin and momentum in this context.Comment: 14 pages, 3 figures, published as a Review in the IJQ

Desenvolvimento profissional para a ação docente em ciência-tecnologia-sociedade : a formação continuada de professores de física do ensino médio

Esta pesquisa ocorreu ao longo de um curso de formação continuada, envolvendo quatro professores de Física do ensino médio de escolas públicas do Rio de Janeiro, no Brasil. A ação de formação foi estruturada a partir de um trabalho colaborativo de construção de estratégias didáticas para abordagem do tema produção e consumo da energia elétrica, considerando-se a perspectiva do enfoque Ciência-Tecnologia-Sociedade (CTS) para o ensino de Física. Dentre os aspectos estudados, destacamos a relação entre a precariedade da situação profissional dos participantes e os desafios postos pelo enfoque CTS. Os resultados apontam para a necessidade de desenvolvimento de uma ‘autonomia em CTS’ e, o espaço de formação mostrou-se adequado para um desenvolvimento profissional na direção de práticas mais autônomas em relação papel do ‘educador CTS’

TRANSIENT MODELLING OF A NATURAL CIRCULATION LOOP UNDER VARIABLE PRESSURE

The objective of the present work is to model the transient operation of a natural circulation loop, which is one-tenth scale in height to a typical Passive Residual Heat Removal system (PRHR) of an Advanced Pressurized Water Nuclear Reactor and was designed to meet the single and two-phase ow similarity criteria to it. The loop consists of a core barrel with electrically heated rods, upper and lower plena inter- connected by hot and cold pipe legs to a seven-tube shell heat exchanger of countercurrent design, and an expansion tank with a descending tube. A long transient characterized the loop operation, during which a phenomenon of self-pressurization, without self-regulation of the pressure, was experimentally observed. This represented a unique situation, named natural circulation under variable pressure (NCVP). The self-pressurization was originated in the air trapped in the expansion tank and compressed by the loop water dilatation, as it heated up during each experiment. The mathematical model, initially oriented to the single-phase ow, included the heat capacity of the structure and employed a cubic polynomial approximation for the density, in the buoyancy term calculation. The heater was modelled taking into account the di erent heat capacities of the heating elements and the heater walls. The heat exchanger was modelled considering the coolant heating, during the heat exchanging process. The self-pressurization was modelled as an isentropic compression of a perfect gas. The whole model was computationally im-plemented via a set of nite di erence equations. The corresponding computational algorithm of solution was of the explicit, marching type, as for the time discretization, in an upwind scheme, regarding the space discretization. The computational program was implemented in MATLAB. Several experiments were carried out in the natural circulation loop, having the coolant ow rate and the heating power as control parameters. The variables used in the comparison between experimental and calculated data were some relevant loop temperatures and pressures. The results obtained from the computational model agree qualitatively well with the experimental NCVP data