Abstract Improved understanding of how vortices develop and propagate under pulsatile ow can shed important light on the mixing and transport processes occurring in such systems, including the transition to turbulent regime. For example, the characterization of pulsatile ows in obstructed artery models serves to encourage research into ow-induced phenomena associated with changes in morphology, blood viscosity, wall elasticity and Mow rate. In this work, an axisymmetric rigid model was used to study the behaviour of the ow pattern with varying degrees of constriction (d0) and mean Reynolds (Re) and Womersley numbers. Velocity elds were obtained experimentally using Digital Particle Image Velocimetry, and generated numerically. For the acquisition of data, Re was varied from 385 to 2044, d0 was 1.0 cm and 1.6 cm, and was varied from 17 to 33 in the experiments and from 24 to 50 in the numerical simulations. Results for the Reynolds numbers considered showed that the ow pattern consisted of two main structures: a central jet around the tube axis and a recirculation zone adjacent to the inner wall of the tube, where vortices shed. Using the vorticity elds, the trajectory of vortices was tracked and their displacement over their lifetime calculated. The analysis led to a scaling law equation for maximum vortex displacement as a function of a dimensionless variable dependent on the system parameters.

Recentemente, os sensores disponíveis em vários modelos de smartphones, iPads ou tablets têm-se revelado muito úteis em laboratórios de física. Em particular, tem sido proposto o uso de acelerômetros em muitas experiências. Em virtude do princípio da equivalência, um sensor fixado em um sistema de referência não-inercial não pode discernir entre um campo gravitacional e um sistema com aceleração. Assim, os valores de aceleração medidos por este sensor devem ser corrigidos considerando-se o componente gravitacional. Neste trabalho um pêndulo físico é estudado e a aceleração absoluta e o ângulo de rotação são obtidos a partir de medições feitas com o acelerômetro e o sensor de rotação. Os resultados obtidos pelos sensores são comparados com as medições obtidas a partir da análise do vídeo do movimento. Finalmente são discutidas as limitações dos vários sensores.

Acceleration sensors built into smartphones, i-pads or tablets can conveniently be used in the physics laboratory. By virtue of the equivalence principle, a sensor fixed in a non-inertial reference frame cannot discern between a gravitational field and an accelerated system. Accordingly, acceleration values read by these sensors must be corrected for the gravitational component. A physical pendulum was studied by way of example, and absolute acceleration and rotation angle values were derived from the measurements made by the accelerometer and gyroscope. Results were corroborated by comparison with those obtained by video analysis. The limitations of different smartphone sensors are discussed.

In this paper, viscoelastic liquids spray emission generated by vibration and the influence of their physical properties are studied. The fluid contained in a cell is subjected to a field of periodic vertical forces, for which the excitation amplitude and frequency are controlled. Different mixtures of kerosene with viscoelastic polymer were used and results were modelled using equations applicable to Newtonian fluids with acceptable results within the values of the operating conditions considered. Also, the dependence of drop size with the quantity of polymer added, the acceleration and the frequency applied was determined. It is concluded that Newtonian fluids models can be applied to liquids with characteristics similar to those studied in this work.

En este trabajo se estudia la emisión de spray de liquidos viscoelasticos generada mediante vibración, asi como la influencia de sus propiedades físicas en el tamaño de las gotas. El recipiente conteniendo el fluido es sometido a un campo de fuerzas vertical periódico, del cual se controlan la amplitud de la excitación y la frecuencia del mismo. Se utilizaron diferentes mezclas de queroseno con agregado de polímero viscoelástico, resultando validos los modelos aplicados a fluidos Newtonianos dentro de las condiciones de trabajo. Tambien se obtuvo la dependencia del tamaño de gota con la cantidad de polimero agregado, la aceleracion y la frecuencia aplicadas. Se concluye que los modelos desarrollados para fluidos Newtonianos pueden ser aplicados a liquidos de características similares a los utilizados en estas experiencias.