Resumo A utilização de experimentos é uma das formas mais eficientes para o ensino de física, uma vez que os alunos tornam-se mais motivados quando conceitos teóricos fundamentais são associados a aplicações tecnológicas. O desenvolvimento de carros, aeronaves e foguetes, por exemplo, requer o conhecimento detalhado dos escoamentos de fluidos ao redor e no interior desses veículos. O presente artigo descreve os fundamentos da óptica geométrica em meios heterogêneos e apresenta as técnicas ópticas shadowgraph e schlieren que são amplamente utilizadas em centros de pesquisa, universidades e empresas no estudo da aerodinâmica e dos escoamentos em geral. Esses métodos ópticos são baseados na deflexão dos raios de luz causada por variações na massa específica do escoamento. O método schlieren-Toepler é apresentado e discutido em detalhes, derivando-se equações para o contraste, sensibilidade e o alinhamento óptico. Uma implementação do método shadowgraph direto para uso em sala de aula é demonstrada e, ao longo do artigo, são apresentadas diversas imagens obtidas pelos métodos ópticos descritos.

Abstract The use of experiments is one of the most efficient ways to teach physics, since students become more motivated when fundamental theoretical concepts are associated with technological applications. The development of cars, aircraft and rockets, for example, requires detailed knowledge of the flow of fluids around and inside these vehicles. This article describes the fundamentals of geometric optics in heterogeneous media and presents the shadowgraph and schlieren optical techniques that are widely used in research centers, universities and companies in the study of aerodynamics and flows in general. These optical methods are based on the deflection of the light rays caused by variations in the flow density. The schlieren-Toepler method is discussed in detail, deriving equations for contrast, sensitivity and optical alignment. An implementation of the direct shadowgraph method for classroom use is demonstrated and, throughout the article, several images obtained by the described optical methods are presented.

The effect of the application of constant temperatures (isothermal plateau) and variables (cooling ramp) during the overaging (OA) stage of the continuous annealing cycle in the microstructural characteristics and mechanical properties of a TRIP steel of the class of 780 MPa was investigated. It was simulated six overaging conditions in the equipment Gleeble. The microstructures presented variable fractions of ferrite, bainite, retained austenite and a small martensite portion. All the conditions achieved the minimum strength of 780 MPa it is possible to highlight the conditions for initial OA temperature of 440 °C where presented the best results of mechanical properties and typical TRIP steels behaviors.

ABSTRACT: Nitrous oxide is a monopropellant with potential for use in propulsion systems for orbit correction, positioning and attitude control of satellites. This paper presents experimental results with a 2N thruster prototype employing nitrous oxide gas decomposed by a rhodium oxide catalyst supported on alumina. Initially, the thruster design, the test bench and test procedures are described. Then the main experimental results, including thrust curves, mass flow rates, pressures and temperatures along the thruster are presented for pulsed operation. At the end specific impulses, characteristic velocities and thruster efficiencies are determined, thus indicating a catalytic decomposition efficiency of about 88%.

ABSTRACT: Hydrogen peroxide is a non toxic, low cost, green monopropellant with a significant potential for applications in satellite microthrusters. It presents a density-specific impulse similar to hydrazine. A new bulk mixed oxide catalyst for decomposition of hydrogen peroxide has been developed and tested in a 2 N thruster with modular parts, allowing the use of catalytic beds with different diameters and lengths. A method of experiment design with a star configuration was implemented to optimize the catalytic bed geometry, in order to yield complete peroxide decomposition, reduce thruster size and volume and provide maximum thrust.

ABSTRACT: Concerns about the rising fuel price and environmental changes have led to the search for alternative fuels and energy sources. The interest in improving the performance of power generation, with the aim of reducing costs, increasing operating efficiency, and reducing the emissions of pollutants, has driven the scientific community to work on new burning technologies. Flameless combustion is one of the best alternative new technologies for a clean and efficient one. The burning of liquid fuels in power generation and propulsion systems depends on the effective atomization to increase the surface area of the fuel and thus to achieve high rates of mixing and evaporation. This work described the spray characteristics of hydrous ethanol in a blurry injector for applications in a flameless compact combustion chamber. The experimental results are obtained over a range of relatively low flow rates with different air-toliquid mass flow ratios.

This work determines the preliminary mass distribution of hybrid rockets using 98% H2O2 and solid paraffin mixed with aluminum as propellants. An iterative process is used tocalculate the rocket performance characteristics and to determine the inert mass fractionfrom given initial conditions. It is considered a mission to place a 20 kg payload into a 300 km circular equatorial orbit by air launched and ground launched hybrid rockets usingthree stages. The results indicate total initial masses of about 7800 kg for a groundlaunched hybrid rocket and 4700 kg for an air launched hybrid rocket.

OBJETIVO: Avaliar os efeitos da pressão positiva expiratória final e da intervenção fisioterápica na fase I da reabilitação cardiovascular sobre o comportamento da função pulmonar e da força muscular inspiratória e sobre o pós-operatório de cirurgia cardíaca. MÉTODO: Estudo prospectivo, randomizado, com 24 pacientes, separados em 2 grupos: GEP (n=8), que realizaram exercícios respiratórios com pressão positiva expiratória nas vias aéreas associados à intervenção fisioterápica; e GFI (n=16), que realizaram somente a intervenção fisioterápica. A função pulmonar foi avaliada pela espirometria no pré e 5º dia pós-operatório; a força muscular inspiratória pela pressão inspiratória máxima no pré, 1º e 5º dias pós-operatório. RESULTADOS: As variáveis espirométricas mostraram reduções significativas do pré para o 5º dia pós-operatório no GFI, porém no GEP, observou-se redução apenas para capacidade vital (p<0,05). Com relação às diferenças entre os tratamentos, foram observados menores valores no GFI para o pico de fluxo no 5º dia pós-operatório. Foram observadas reduções significativas da pressão inspiratória máxima do pré para 1º dia pós-operatório em ambos os grupos. A pressão inspiratória máxima mostrou reduções significativas da situação pré para o 5º pós-operatório somente no GFI (p<0,05). CONCLUSÕES: Estes dados sugerem que a cirurgia cardíaca produz reduções da força muscular inspiratória, dos volumes e fluxos pulmonares e que a pressão positiva associada à intervenção fisioterápica foi mais eficiente em minimizar essas alterações do que quando a fisioterapia foi realizada de forma isolada. Entretanto, os volumes pulmo nares não foram completamente restabelecidos até o 5º dia pós-operatório em ambos os grupos, sendo necessária a continuidade dos tratamentos após a convalescença hospitalar.

PURPOSE: To evaluate the effects of positive end expiratory pressure and physiotherapy intervention during Phase I of cardiac rehabilitation on the behavior of pulmonary function and inspiratory muscle strength in postoperative cardiac surgery. METHODS: A prospective randomized study, in which 24 patients were divided in 2 groups: a group that performed respiratory exercises with positive airway expiratory pressure associated with physiotherapy intervention (GEP, n = 8) and a group that received only the physiotherapy intervention (GPI, n = 16). Pulmonary function was evaluated by spirometry on the preoperative and on the fifth postoperative days; inspiratory muscle strength was measured by maximal inspiratory pressure on the same days. RESULTS: Spirometric variables were significantly reduced from the preoperative to the fifth postoperative day for the GPI, while the GEP had a significant reduction only for vital capacity (P < .05). When the treatments were compared, smaller values were observed in the GPI for peak flow on the fifth postoperative day. Significant reductions of maximal inspiratory pressure from preoperative to the first postoperative day were found in both groups. However, the reduction in maximal inspiratory pressure from the preoperative to the fifth postoperative day was significant only in the GPI (P < .05). CONCLUSIONS: These data suggest that cardiac surgery produces a reduction in inspiratory muscle strength, pulmonary volume, and flow. The association of positive expiratory pressure with physiotherapy intervention was more efficient in minimizing these changes, in comparison to the physiotherapy intervention alone. However, in both groups, the pulmonary volumes were not completely reestablished by the fifth postoperative day, and it was necessary to continue the treatment after hospital convalescence.