To analyze previous experimental data of suspended sediment concentration for silty sediment with different sediment particle sizes due to waves, a new stratification correction coefficient is presented. The suspended...To analyze previous experimental data of suspended sediment concentration for silty sediment with different sediment particle sizes due to waves, a new stratification correction coefficient is presented. The suspended sediment concentration gradient and sediment particle diameter are selected as parameters. Furthermore, a diffusion coefficient model with a stratification effect over the whole water depth for silty sediment suspension under waves is developed. The comparison between the suspended sediment concentration calculated by the presented model and several groups of experimental data shows that the model can reasonably reflect the vertical distribution of silty sediment suspension.The stratification effect calculated by the present model decreases with an increase in the sediment particle diameter,which indicates that the model can be extended to describe the suspended sediment concentration of fine to medium sand when the near-bottom sediment concentration is not very high. Although the original model needs to be iteratively solved, the approximate method without iteration is recommended for applications when the near bottom sediment concentration is between 10 and 20 kg/m~3 due to the small difference between the non-iterative and iterative solution for near bed layer suspended sediment concentration, which plays a major role in sediment transport.展开更多
The structure of double diffusive convec-tion in a circular cylinder cavity has been numerically studied. The numerical results exhibit some new characters of non-horizontal stratifications of thermal and solutal fiel...The structure of double diffusive convec-tion in a circular cylinder cavity has been numerically studied. The numerical results exhibit some new characters of non-horizontal stratifications of thermal and solutal fields: in the stratification state, the iso-thermal lines near the sidewall are higher than that near the symmetry axis, while the isoconcentration lines near the symmetry axis are relatively high. The mechanism of these non-horizontal stratifications is illustrated by comparing double-diffusive convection with natural convection driven by thermal buoyancy or solutal buoyancy alone. The effects of Lewis number Le and buoyancy ratio N on the non-hor- izontal stratifications of thermal and solutal fields are also investigated. The results show that: at a given time (t = 0.2), with an increase in Le (Le = 0-15), the area influenced by solute diffusion decreases; for isothermal line, the gradients of it initially increase, but it tends to be horizontal at the top of the cavity when the Lewis number is higher than 10. When N varies from 0 to 2, the isoconcentration lines tend to be horizontal while the gradients of isothermal line increase.展开更多
目的评估双参数磁共振成像(biparametric magnetic resonance imaging,bpMRI)的表观扩散系数(apparent diffusion coefficients,ADC)对前列腺癌(prostate cancer,PCa)进行预后相关的国际泌尿病理学会(International Society of Urologic...目的评估双参数磁共振成像(biparametric magnetic resonance imaging,bpMRI)的表观扩散系数(apparent diffusion coefficients,ADC)对前列腺癌(prostate cancer,PCa)进行预后相关的国际泌尿病理学会(International Society of Urological Pathology,ISUP)分级分组(grading group,GG)的能力,并且对最小表观扩散系数(minimum apparent diffusion coefficients,ADCmin)及平均表观扩散系数(mean apparent diffusion coefficients,ADCmean)的诊断效能进行比较。材料与方法回顾性分析91名患者的bpMRI图像和数据,计算主要病灶的ADCmin及ADCmean,绘制受试者工作特征(receiver operating characteristic,ROC)曲线确定ADC诊断界值并计算ROC曲线下面积(area under the curve,AUC),分析ADC对PCa的诊断效能。比较良恶性病变的ADC差异,依据风险分层比较低危与中高危病变的ADC差异。采用Spearman分析对ADC和ISUP GG之间的相关性进行分析。结果91例患者中48例为PCa(52.7%),43例为良性病变(47.3%)。PCa组的ADCmin及ADCmean的中位数均明显低于良性病变组,良性病变与恶性病变差异有统计学意义(P<0.05)。中高危PCa(intermediateand high-risk PCa,ihPCa)的ADCmin及ADCmean中位数显著低于良性组和低危组,差异均有统计学意义(P<0.05)。以0.49×10^(-3)mm^(2)/s(b=2000)为诊断界值,ADCmin诊断ihPCa的特异度、阳性预测值(positive predictive value,PPV)、Youden指数和AUC分别为88%、84%、68%、0.87。而以0.64×10^(-3)mm^(2)/s(b=2000)为诊断界值,ADCmean诊断ihPCa的特异度、PPV、Youden指数和AUC分别为85%、78%、59%、0.83。ADCmin及ADCmean值的大小与ISUP GG数值呈负性相关(ρ=-0.661,P<0.01)。结论随着ADC值降低,PCa的预后风险增高;bpMRI的ADC参数在诊断ihPCa时有较高的特异度和PPV,且ADCmin的诊断性能优于ADCmean。bpMRI的ADC参数可用于无创评估PCa预后相关风险分层,为PCa患者的风险预测和个体化治疗提供有效工具,并且建议影像医师在诊断中可以更偏重对ADCmin的使用。展开更多
基金financially supported by NSFC—Shandong Joint Fund Project (Grant No. U1906231)。
文摘To analyze previous experimental data of suspended sediment concentration for silty sediment with different sediment particle sizes due to waves, a new stratification correction coefficient is presented. The suspended sediment concentration gradient and sediment particle diameter are selected as parameters. Furthermore, a diffusion coefficient model with a stratification effect over the whole water depth for silty sediment suspension under waves is developed. The comparison between the suspended sediment concentration calculated by the presented model and several groups of experimental data shows that the model can reasonably reflect the vertical distribution of silty sediment suspension.The stratification effect calculated by the present model decreases with an increase in the sediment particle diameter,which indicates that the model can be extended to describe the suspended sediment concentration of fine to medium sand when the near-bottom sediment concentration is not very high. Although the original model needs to be iteratively solved, the approximate method without iteration is recommended for applications when the near bottom sediment concentration is between 10 and 20 kg/m~3 due to the small difference between the non-iterative and iterative solution for near bed layer suspended sediment concentration, which plays a major role in sediment transport.
文摘The structure of double diffusive convec-tion in a circular cylinder cavity has been numerically studied. The numerical results exhibit some new characters of non-horizontal stratifications of thermal and solutal fields: in the stratification state, the iso-thermal lines near the sidewall are higher than that near the symmetry axis, while the isoconcentration lines near the symmetry axis are relatively high. The mechanism of these non-horizontal stratifications is illustrated by comparing double-diffusive convection with natural convection driven by thermal buoyancy or solutal buoyancy alone. The effects of Lewis number Le and buoyancy ratio N on the non-hor- izontal stratifications of thermal and solutal fields are also investigated. The results show that: at a given time (t = 0.2), with an increase in Le (Le = 0-15), the area influenced by solute diffusion decreases; for isothermal line, the gradients of it initially increase, but it tends to be horizontal at the top of the cavity when the Lewis number is higher than 10. When N varies from 0 to 2, the isoconcentration lines tend to be horizontal while the gradients of isothermal line increase.
