An empirical model for vortex-induced vibrations

Through an analytical-empirical approach, the vortex-excited transverse oscillations of flexibly-mounted circular cylinders in a uniform flow is studied. A new model is derived, assuming spanwise constant flow velocity within the sub-critical range of Reynolds numbers and using only experimental data obtained from forced cylinders in water. The steady-state response of flexibly-mounted cylinders is obtained as a function of the structural system and flow parameters and its stability is analyzed. Several characteristics observed experimentally and also present in the model response are discussed. The resultant model's capability for predicting structural response for a wide range of fluid mediums is illustrated through comparisons between model predictions and results obtained experimentally from flexibly-mounted cylinders in air and in water. This model developed is expected to yield better results for structures in water, by virtue of being based only on experimental results obtained in water

Capacidade de dispersão de Trichogramma em tomateiro estaqueado Dispersion capacity of Trichogramma pretiosum in propped up tomato

Estudou-se a capacidade de dispersão de Trichogramma pretiosum Riley em ovos de Anagasta kuehniella (Zeller), na cultura do tomateiro, em diferentes estágios fenológicos e sistemas de condução das plantas. A dispersão de T. pretiosum, 24 horas após a liberação, foi de 7,37 a 7,94 m. A área de dispersão foi de 120,20 a 138,72 m². O parasitismo foi de 53,1% a 87,3%, e significativo de acordo com o estágio fenológico da cultura. A liberação dos parasitóides para o controle de Tuta absoluta (Meyrick) deve ser feita em 75 pontos por hectare.<br>The dispersion capacity of Trichogramma pretiosum Riley was studied on Anagasta kuehniella (Zeller) eggs, in tomato field in different phenological stages and systems of conduction of the plants. The dispersion of T. pretiosum, 24 hours after the liberation, attained 7.37 to 7.94 m. The dispersion area was 120.20 to 138.72 m². Parasitism varies from 53.1% to 87.3% and it is significant according to the phenological stage of the crop. The parasitoids liberation for the control of Tuta absoluta (Meyrick) should be done in 75 points per hectare