The spatial growth of the disturbance in the boundary layer is directly numerically simulated, and the receptivity of the Blasius basic flow to the local two-dimensional （2-D） sustainable micro-vibration is investig...The spatial growth of the disturbance in the boundary layer is directly numerically simulated, and the receptivity of the Blasius basic flow to the local two-dimensional （2-D） sustainable micro-vibration is investigated. Results show that the disturbance velocity presents the sine vibration features with the change of time, and the vibration period is identical to the vibration of the local wall. The disturbance velocity presents the fluctuation feature downstream, and the streamwise wave length approximates to the results from the Orr-Sommerfeld equation （OSE）. The growth rate from direct numerical simulation（DNS） is a little greater than that from OSE, and their trends are almost consistent. Under the condition of Re= 2 800, the disturbance amplitude gradually grows in the given computational region with the period T=30. However, it firstly increases and then decreases with the period T= 20. The disturbance harmonic of the former is obviously larger than that of the latter. The maximum streamwise and vertical disturbance velocities from DNS do not fully coincide with those from OSE at the vicinity of the local vibration wall, but coincide well with the former when they travel downstream. The 2-D disturbance induced by the local micro-vibration represents the form of Tollmien-Schlichting （T-S） wave on the boundary layer.展开更多
In the present research,by using a numerical model,some analyses were performed on flows around a T-shape spur dike and a support structure located at its upstream under different wing to length ratios of T-shape spur...In the present research,by using a numerical model,some analyses were performed on flows around a T-shape spur dike and a support structure located at its upstream under different wing to length ratios of T-shape spur dike in the order of 0.25,0.50,0.75 and 1.00.In order to verify numerical model,physical model data were used in presence of a single T shape spur dike.Results from numerical model are desirably in agreement with those of physical one because the regression between both data is 0.86 up to 0.92.In this research,all hydraulic parameters of flows,streamlines and dimensions of flow separation zones were studied in order to select the most practical model.Increased W/L results in 7%–12%increase in the length of flow separation zone and in 2%increase in the width of this zone compared to W/L=0.25.展开更多
Bubble formation in an opposite-flowing T-shaped microchannel with 40 μm in depth and 120 μm in width was real-time visualized and investigated experimentally by means of a high speed camera. N2 bubbles were generat...Bubble formation in an opposite-flowing T-shaped microchannel with 40 μm in depth and 120 μm in width was real-time visualized and investigated experimentally by means of a high speed camera. N2 bubbles were generated in glycerol-water mixtures with different concentrations of surfactant sodium dodecyl sulfate (SDS). And the images were captured by the high speed camera linked to a computer. Results indicated that the bubble formation process can be distinguished into three consecutive stages, i.e., expansion, collapse and pinching off. The bubble size decreases with the increase of liquid flow rate and viscosity of liquid phase as well as the decrease of gas flow rate. The surface tension of the liquid phase has no measurable influence on the bubble size. Moreover, a new approach to predicting the size of bubbles formed in the T-shaped microchannel is proposed. And the predicted values agree well with the experimental data.展开更多
Objective To investigate prognostic predictors of long-term survival of patients with cardiac amyloidosis （CA）, and to determine predictive value of high-sensitivity cardiac troponin T （hs-cTnT） in CA patients. Me...Objective To investigate prognostic predictors of long-term survival of patients with cardiac amyloidosis （CA）, and to determine predictive value of high-sensitivity cardiac troponin T （hs-cTnT） in CA patients. Methods We recruited 102 consecutive CA cases and followed these patients for 5 years. We described their clinical characteristics at presentation and used a new, high-sensitivity assay to determine the concentration of cTnT in plasma samples from these patients. Results The patients with poor prognosis showed older age （56 ±12 years vs. 50 ±15 years, P=0.022）, higher incidences of heart failure （36.92%vs. 16.22%, P=0.041）, pericardial effusion （60.00%vs. 35.14%, P=0.023）, greater thickness of interventricular septum （IVS） （15 ±4 mm vs. 13 ±4 mm, P=0.034）, higher level of hs-cTnT （0.186 ±0.249 ng/mL vs. 0.044 ±0.055 ng/mL, P=0.001） and higher NT-proBNP （N-terminal pro-B-type natriuretic pep-tide） levels （11,742 ± 10,464 pg/mL vs. 6,031 ± 7,458 pg/mL, P=0.006）. At multivariate Cox regression analysis, heart failure （HR：1.78, 95%CI：1.09-2.92, P=0.021）, greater wall thickness of IVS （HR：1.44, 95%CI：1.04-3.01, P=0.0375） and higher hs-cTnT level （HR：6.16, 95%CI：2.20-17.24, P=0.001） at enrollment emerged as independent predictors of all-cause mortality. Conclusions We showed that hs-cTnT is associated with a very ominous prognosis, and it is also the strongest predictor of all-cause mortality in multivariate analysis. Examination of hs-cTnT concentrations provides valuable prognostic information concerning long-term outcomes.展开更多
The shear-stress transport(SST)turbulence model is incorporated into Navier-Stokes equations to simulate a turbomachinery flowfield.A staggered finite volume method is used to make the mean flow equations and turbulen...The shear-stress transport(SST)turbulence model is incorporated into Navier-Stokes equations to simulate a turbomachinery flowfield.A staggered finite volume method is used to make the mean flow equations and turbulence model equations strongly coupled and enhance the stability of the numerical computation.The implicit treatment of the source terms is applied to the SST model.A steady state solution is obtained using five-stage Runge-Kutta time-stepping scheme with local time stepping and residual smoothing to accelerate convergence. The wall distance d,a key parameter in the SST model,is solved by a partial differential equation.The validations of the code are conducted on rotor 37,wp11 at design and off-design conditions by comparison with measurements and the Spalart-Allmaras(SA)turbulence model.The flow within the tip is calculated with a multi-block grid.展开更多
Conjugate gradient methods have played a special role in solving large scale nonlinear problems. Recently, the author and Dai proposed an efficient nonlinear conjugate gradient method called CGOPT, through seeking the...Conjugate gradient methods have played a special role in solving large scale nonlinear problems. Recently, the author and Dai proposed an efficient nonlinear conjugate gradient method called CGOPT, through seeking the conjugate gradient direction closest to the direction of the scaled memoryless BFGS method. In this paper, we make use of two types of modified secant equations to improve CGOPT method. Under some assumptions, the improved methods are showed to be globally convergent. Numerical results are also reported.展开更多
New statistics are proposed to estimate and test the structural change when the data dimension is comparable to or larger than the sample size. Consistency of the new statistic in estimating the change point position ...New statistics are proposed to estimate and test the structural change when the data dimension is comparable to or larger than the sample size. Consistency of the new statistic in estimating the change point position is established under the alternative hypothesis. The asymptotic distribution of the new statistic in testing the existence of a change point is obtained under the null hypothesis. Some simulation results are presented which show that the numerical performance of our method is satisfactory. The method is illustrated via the analysis of the house price index of US.展开更多
基金Supported by the National Natural Science Foundation of China(10672052)the Advanced TalentStart-Up Foundation of Jiangsu University(08JDG018)~~
文摘The spatial growth of the disturbance in the boundary layer is directly numerically simulated, and the receptivity of the Blasius basic flow to the local two-dimensional （2-D） sustainable micro-vibration is investigated. Results show that the disturbance velocity presents the sine vibration features with the change of time, and the vibration period is identical to the vibration of the local wall. The disturbance velocity presents the fluctuation feature downstream, and the streamwise wave length approximates to the results from the Orr-Sommerfeld equation （OSE）. The growth rate from direct numerical simulation（DNS） is a little greater than that from OSE, and their trends are almost consistent. Under the condition of Re= 2 800, the disturbance amplitude gradually grows in the given computational region with the period T=30. However, it firstly increases and then decreases with the period T= 20. The disturbance harmonic of the former is obviously larger than that of the latter. The maximum streamwise and vertical disturbance velocities from DNS do not fully coincide with those from OSE at the vicinity of the local vibration wall, but coincide well with the former when they travel downstream. The 2-D disturbance induced by the local micro-vibration represents the form of Tollmien-Schlichting （T-S） wave on the boundary layer.
文摘In the present research,by using a numerical model,some analyses were performed on flows around a T-shape spur dike and a support structure located at its upstream under different wing to length ratios of T-shape spur dike in the order of 0.25,0.50,0.75 and 1.00.In order to verify numerical model,physical model data were used in presence of a single T shape spur dike.Results from numerical model are desirably in agreement with those of physical one because the regression between both data is 0.86 up to 0.92.In this research,all hydraulic parameters of flows,streamlines and dimensions of flow separation zones were studied in order to select the most practical model.Increased W/L results in 7%–12%increase in the length of flow separation zone and in 2%increase in the width of this zone compared to W/L=0.25.
基金Supported by National Natural Science Foundation of China (No. 20876107)Open Project of State Key Laboratory of Chemical Engineering (No. SKL-ChE-08B06) Program of Introducing Talents of Discipline to Universities (No. B06006)
文摘Bubble formation in an opposite-flowing T-shaped microchannel with 40 μm in depth and 120 μm in width was real-time visualized and investigated experimentally by means of a high speed camera. N2 bubbles were generated in glycerol-water mixtures with different concentrations of surfactant sodium dodecyl sulfate (SDS). And the images were captured by the high speed camera linked to a computer. Results indicated that the bubble formation process can be distinguished into three consecutive stages, i.e., expansion, collapse and pinching off. The bubble size decreases with the increase of liquid flow rate and viscosity of liquid phase as well as the decrease of gas flow rate. The surface tension of the liquid phase has no measurable influence on the bubble size. Moreover, a new approach to predicting the size of bubbles formed in the T-shaped microchannel is proposed. And the predicted values agree well with the experimental data.
文摘Objective To investigate prognostic predictors of long-term survival of patients with cardiac amyloidosis （CA）, and to determine predictive value of high-sensitivity cardiac troponin T （hs-cTnT） in CA patients. Methods We recruited 102 consecutive CA cases and followed these patients for 5 years. We described their clinical characteristics at presentation and used a new, high-sensitivity assay to determine the concentration of cTnT in plasma samples from these patients. Results The patients with poor prognosis showed older age （56 ±12 years vs. 50 ±15 years, P=0.022）, higher incidences of heart failure （36.92%vs. 16.22%, P=0.041）, pericardial effusion （60.00%vs. 35.14%, P=0.023）, greater thickness of interventricular septum （IVS） （15 ±4 mm vs. 13 ±4 mm, P=0.034）, higher level of hs-cTnT （0.186 ±0.249 ng/mL vs. 0.044 ±0.055 ng/mL, P=0.001） and higher NT-proBNP （N-terminal pro-B-type natriuretic pep-tide） levels （11,742 ± 10,464 pg/mL vs. 6,031 ± 7,458 pg/mL, P=0.006）. At multivariate Cox regression analysis, heart failure （HR：1.78, 95%CI：1.09-2.92, P=0.021）, greater wall thickness of IVS （HR：1.44, 95%CI：1.04-3.01, P=0.0375） and higher hs-cTnT level （HR：6.16, 95%CI：2.20-17.24, P=0.001） at enrollment emerged as independent predictors of all-cause mortality. Conclusions We showed that hs-cTnT is associated with a very ominous prognosis, and it is also the strongest predictor of all-cause mortality in multivariate analysis. Examination of hs-cTnT concentrations provides valuable prognostic information concerning long-term outcomes.
基金supported by the National Natural Science Foundation of China under Contract 50676004 and 50736007
文摘The shear-stress transport(SST)turbulence model is incorporated into Navier-Stokes equations to simulate a turbomachinery flowfield.A staggered finite volume method is used to make the mean flow equations and turbulence model equations strongly coupled and enhance the stability of the numerical computation.The implicit treatment of the source terms is applied to the SST model.A steady state solution is obtained using five-stage Runge-Kutta time-stepping scheme with local time stepping and residual smoothing to accelerate convergence. The wall distance d,a key parameter in the SST model,is solved by a partial differential equation.The validations of the code are conducted on rotor 37,wp11 at design and off-design conditions by comparison with measurements and the Spalart-Allmaras(SA)turbulence model.The flow within the tip is calculated with a multi-block grid.
基金supported by National Natural Science Foundation of China(Grant Nos.10831006 and 10971017)
文摘Conjugate gradient methods have played a special role in solving large scale nonlinear problems. Recently, the author and Dai proposed an efficient nonlinear conjugate gradient method called CGOPT, through seeking the conjugate gradient direction closest to the direction of the scaled memoryless BFGS method. In this paper, we make use of two types of modified secant equations to improve CGOPT method. Under some assumptions, the improved methods are showed to be globally convergent. Numerical results are also reported.
基金supported by National Natural Science Foundation of China (Grant No. 11571337)the Ministry of Education of Singapore (Grant No. # ARC 14/11)the National University of Singapore (Grant No. R-155-151-112)
文摘New statistics are proposed to estimate and test the structural change when the data dimension is comparable to or larger than the sample size. Consistency of the new statistic in estimating the change point position is established under the alternative hypothesis. The asymptotic distribution of the new statistic in testing the existence of a change point is obtained under the null hypothesis. Some simulation results are presented which show that the numerical performance of our method is satisfactory. The method is illustrated via the analysis of the house price index of US.
