RESUMO
Rayleigh-Taylor instability (RTI) under radiation background is commonly found in both engineering applications and natural phenomena. In the optically thin and incompressible limit, the corresponding problem can be simplified as an interface discontinuous acceleration (IDA) RTI problem, but to date has only been studied in the linear stage. In this paper, the entire IDA-RTI evolution was studied numerically and theoretically, particularly for the stages beyond the linear stage. The results show that the IDA-RTI problem is equivalent to the classical RTI with the effective acceleration g_{eff}^{*} that is introduced in this work. Moreover, our studies further show that IDA-RTI can occur if and only if g_{eff}^{*}>0 (from heavy fluid to light fluid). This criterion means that IDA-RTI can occur when (i) heavy fluid supports (or accelerates) the light fluid or (ii) the two fluids have the same density, in contrast to the classical RTI problem. Moreover, the quasisteady bubble and spike velocities are theoretically predicted with quantitative accuracy, showing good agreement with the results of numerical simulations in a wide range of density ratios and acceleration configurations.
RESUMO
OBJECTIVES: To investigate if hyperinsulinemia or insulin resistance could predict the elevation of blood pressure in non-diabetic adults. METHODS: One hundred and seventy non-diabetic adults (NGT 107, IGT 63) were included based on the screen by OGTT in 1986. Height, weight, blood pressure were measured. Plasma glucose and insulin concentration at 0.60 and 120 min during OGTT were determined at baseline. All the subjects were followed for six years with blood pressure and plasma glucose examined at the end of the study. Subjects worsening to diabetes were excluded. Insulin area under-curve (INSAUC) and insulin sensitivity index [IAI = (1/FINS x FPG)] were calculated. Stepwise regression analysis was performed to evaluate the effects of INSAUC and insulin sensitivity to the elevation of blood pressure. RESULTS: Both SBP and DBP levels at the end of the study were increased with increased INSAUC baseline. The SBP were (119.5 +/- 2.3), (122.1 +/- 2.5), (129.4 +/- 2.4) and (128.3 +/- 2.6) mmHg, and the DBP were (78.6 +/- 1.6), (79.7 +/- 1.7), (85.2 +/- 1.4) and (84.0 +/- 1.0) mmHg from the lowest to the highest quartiles of INSAUC respectively. Pearson correlation analysis showed Age, SBP, DBP, BMI, FINS, INS1h, INSAUC at baseline were positively correlated to blood pressure levels at the end of the study. After the adjustment of Age, sex, BMI, smoking, PG2 h and blood pressure at baseline, the INSAUC was significantly correlated to blood pressure six years later, while the insulin sensitivity index was not. CONCLUSION: The compensated hyperinsulinemia based on selective insulin resistance rather than insulin resistance to glucose per se could predict the elevation of blood pressure in nondiabetic adults.
