7 research outputs found
CONVERGENT AND DIVERGENT ANGLES OF A SOLID-FUEL ROCKET NOZZLE AND ITS INFLUENCES ON THE MOTOR’S THRUST CURVE
The main goal of this work is to investigate how the angles of a convergent-divergent rocket nozzle influence the thrust curve of a solid-propulsion rocket. The work has been conducted within an academic rocketry team. As there is not clear reasoning on how to define these angles, the present research provides insights on how these geometrical parameters influence the performance of a rocket motor. A 2D-axisymmetric CFD domain is considered, comprising the fluid domain inside and outside the nozzle, to give room for the shock waves to happen and also accommodate the flow. The study comprises a baseline geometry and twelve modified designs, varying the convergent and the divergent angles of the nozzle. Since the convergent diameter must match the chamber diameter, it is fixed. For the divergent diameter, there is no such restriction; therefore, there are two possibilities: a divergent section with the same divergent diameter or with the same length as the baseline. The benchmark thrust curve is generated with a MATLAB code based on solid-fuel modeling and the De Laval theory. The curve is divided into six steady-state simulations, using boundary conditions of mass flow, pressure and temperature at the inlet and pressure and temperature at the outlet. The baseline geometry is simulated in Ansys Fluent and normalized by the MATLAB benchmark. A mesh study selects which mesh and turbulence model to use based on this normalization. The modified geometries are then compared to the baseline. The main quantity of interest is the thrust but quantities such as static pressure and average velocity at the nozzle exit aid the understanding of the changes in thrust
Avaliação da capacidade preditiva da circunferência da cintura para obesidade global e hipertensão arterial em mulheres residentes na Região Metropolitana de Belo Horizonte, Brasil
Avaliou-se a capacidade que a Circunferência da Cintura (CC) tem em identificar valores de IMC ≥25 (sobrepeso) e ≥30 (obesidade) a partir de níveis de ação recomendados internacionalmente. Setecentas e noventa e uma mulheres entre 15-59 anos foram recrutadas. Foram calculadas a sensibilidade e a especificidade no diagnóstico de sobrepeso e obesidade e a sensibilidade e especificidade na predição da hipertensão, a partir de valores de CC. As associações foram testadas por análise de regressão linear e regressão logística controlando para o efeito de fatores de confusão. A CC ≥80 e ≥88cm discriminou corretamente 89,8% de mulheres com IMC ≥25 e 88,5% com IMC ≥30. A obesidade abdominal (CC ≥88cm) esteve associada significativamente com a hipertensão na análise multivariada (OR = 2,88, IC 95%: 1,77-4,67). A hipertensão foi identificada com sensibilidade de 63,8 e 42,8% e especificidade de 68,0 e 83,3% para CC ≥80 e ≥88, respectivamente. A obesidade abdominal nos pontos de corte propostos pode discriminar adequadamente indivíduos em risco de se tornarem obesos, no entanto, apresenta um poder apenas moderado para discriminar indivíduos com níveis pressóricos altos. _______________________________________________________________________________ ABSTRACTThis study examined the capacity of waist circumference (WC) to identify subjects with overweight (BMI ≥25) and obesity (BMI ≥30), in agreement with internationally recommended levels of action. Data were obtained from 791 women, 15-59 years old. After identifying overweight and obesity according to WC values, sensitivity and specificity were calculated to verify whether WC could be a good risk predictor for hypertension. Associations were tested by linear regression and logistic regression, controlling for confounding.WC cut-off points of 80cm and 88cm correctly identified 89.8% and 88.5% of women with overweight and obesity, respectively. Abdominal obesity (WC ≥88cm) was statistically associated with hypertension in the multivariate analysis (OR = 2.88; 95% CI: 1.77-4.67). Hypertension was identified with a sensitivity of 63.8% and 42.8%, and with a specificity of 68.0% and 83.3%, for WC ≥80 and ≥88, respectively. The proposed cut-off points for abdominal obesity can potentially distinguish individuals at risk for future obesity, but has only moderate power to predict individuals with high blood pressure
Comparative study of tubular diameter and quantity for human and bovine dentin at different depths
A fluorose dentária no Brasil: uma revisão crítica Dental fluorosis in Brazil: a critical review
Discute-se neste trabalho a pertinência de se considerar a fluorose dentária como um problema de saúde pública no Brasil, utilizando como método a revisão dos estudos epidemiológicos publicados no país sobre prevalência e severidade da doença e dos seus possíveis fatores de risco. Os resultados sugerem que já são encontradas freqüências mais altas que as esperadas, embora com poucos casos de maior severidade. São necessárias, então, medidas de vigilância à saúde bucal.<br>This paper discusses dental fluorosis as a relevant public health problem, using a review of epidemiological studies published in the last 10 years on the disease's prevalence, severity, and risk factors. The results suggest that there are already more cases than expected, although few studies refer to major severity. Thus, measures are needed for the prevention and surveillance of dental fluorosis