RESUMEN
In this article, we experimentally investigate the nonlinear behaviour of a viscoplastic film flow down an inclined plane. We focus on the nonlinear instabilities that appear as roll waves. Roll waves are generated by perturbing a permanent flow of Herschel-Bulkley fluid (Carbopol 980) at low frequencies. To determine the local thickness of the film, we used a laser sensor and a camera to globally capture the transverse shape of the waves. For a regular forcing, the results show the existence of different regimes. First, we observe primary instabilities below the cut-off frequency at the entrance of the channel. After the exponential growth of the wave in the linear regime, we recognise the nonlinear dynamics with the existence of finite amplitude waves. This finite amplitude depends on the frequency, the Reynolds number and the inclination angle. The results show that this instability is supercritical. At moderate Reynolds numbers, the finite 2-D waves become sensitive to transverse perturbations, due to a secondary instability, and become 3-D waves. The experimental results illustrate a phenomenology of viscoplastic film flows similar to Newtonian fluids, except for the capillary waves.
RESUMEN
OBJECTIVES: Onchocerciasis is one of the most devastating neglected tropical diseases and it is mostly prevalent in Africa. The disease has important heavy social and economic burdens on the infected populations including low productivity, unemployment, social isolation, and stigma. A cross-sectional study was implemented using a well-established questionnaire to investigate the socio-economic impacts of Onchocerciasis elimination in Abu-Hamed, River Nile State, Sudan in 2015; 512 participants in ten affected communities were interviewed. RESULTS: Our findings revealed that these communities are recovering from the social and economic burden of the diseases. Ninety percent of the research participants reported general satisfaction about elimination of the disease in their community, 48.3% of them attended secondary school or university. Only 0.6% reported unemployment. Also, 25.3% and 24.7% of the participants were workers and farmers respectively. Except about the vector biting and nuisance, the majority of the respondents (90%) had no complain related to the disease after the elimination. Also, 90.5% of the participants reported either stable or increase in their work performance during the last 12 months. About 93.8% of the respondents were engaged in normal daily life activities and involved in happy events like marriage and giving birth during the last 12 months.
