In arid regions, water vapor diffusion predominates the total water migration in unsaturated soil, which significantly influences agriculture and engineering applications. With the aim of revealing the diffusion mecha...In arid regions, water vapor diffusion predominates the total water migration in unsaturated soil, which significantly influences agriculture and engineering applications. With the aim of revealing the diffusion mechanism of water vapor in unsaturated soil, a water vapor migration test device was developed to conduct the water vapor migration indoor test. The test results demonstrate that the characteristics of water vapor diffusion in unsaturated soil conformed to Fick’s second law. A mathematical model for water vapor diffusion under isothermal conditions in unsaturated soil was established based on Fick’s law. Factors including the initial moisture content gradient, initial moisture content distribution, soil type and temperature that affect the water vapor diffusion coefficient were analyzed. The results show that there was good agreement between the moisture content calculated by the mathematical model and obtained by the indoor experiment. The vapor diffusion coefficient increased with increasing initial moisture content gradient and temperature. When the initial moisture content gradient is constant, the vapor diffusion coefficient increases with the increase of matrix suction ratio in dry and wet soil section. The effect of soil type on the water vapor diffusion coefficient was complex, as both the moisture content and soil particle sizes affected the water vapor diffusion.展开更多
基金Projects(51878064, 51378072) supported by the National Natural Science Foundation of ChinaProjects(300102218408, 300102219108) supported by the Fundamental Research Funds for the Central Universities, China。
文摘In arid regions, water vapor diffusion predominates the total water migration in unsaturated soil, which significantly influences agriculture and engineering applications. With the aim of revealing the diffusion mechanism of water vapor in unsaturated soil, a water vapor migration test device was developed to conduct the water vapor migration indoor test. The test results demonstrate that the characteristics of water vapor diffusion in unsaturated soil conformed to Fick’s second law. A mathematical model for water vapor diffusion under isothermal conditions in unsaturated soil was established based on Fick’s law. Factors including the initial moisture content gradient, initial moisture content distribution, soil type and temperature that affect the water vapor diffusion coefficient were analyzed. The results show that there was good agreement between the moisture content calculated by the mathematical model and obtained by the indoor experiment. The vapor diffusion coefficient increased with increasing initial moisture content gradient and temperature. When the initial moisture content gradient is constant, the vapor diffusion coefficient increases with the increase of matrix suction ratio in dry and wet soil section. The effect of soil type on the water vapor diffusion coefficient was complex, as both the moisture content and soil particle sizes affected the water vapor diffusion.
文摘目的使用MRI时间依赖扩散诊断指标判断新诊断胶质母细胞瘤O6-甲基鸟嘌呤-脱氧核糖核酸甲基转移酶(O^(6)-methylguanine deoxyribonucleic acid methyltransferase,MGMT)启动子甲基化状态。材料与方法对22例甲基化MGMT启动子(methylated MGMT,mMGMT)和29例非甲基化MGMT启动子(unmethylated MGMT,uMGMT)新诊断胶质母细胞瘤患者进行诊断分析以及对14例mMGMT和14例uMGMT新诊断胶质母细胞瘤患者进行应用验证。使用3 T MRI震荡梯度回波和脉冲梯度回波进行时间依赖扩散扫描。基于两室模型获取MRI时间依赖扩散微结构诊断指标,包括细胞内容积分数(f_(in))、细胞外扩散率(D_(ex))、细胞直径(d)、细胞密度(cellularity)、不同频率的扩散率(D_(0Hz)、D_(15Hz)和D_(30Hz))。比较mMGMT和uMGMT两组胶质母细胞瘤之间以上指标的差异。首先使用单因素逻辑回归分析各指标区分两组胶质母细胞瘤的能力,然后使用多因素逻辑回归分析确定是否存在构建逻辑回归联合诊断模型的可能。两两比较各诊断指标区分两组胶质母细胞瘤的能力。结果相对于uMGMT胶质母细胞瘤,mMGMT胶质母细胞瘤表现出更高的f_(in),D_(ex)和cellularity(P<0.05)以及更低的D0 Hz(P=0.018)。f_(in)对于区分两组胶质母细胞瘤诊断能力最佳,曲线下面积(area under the curve,AUC)值为0.95,敏感度和特异度分别为95%和90%,且与其他诊断指标两两比较差异均具统计学意义(P<0.05)。多因素逻辑回归分析显示f_(in)为独立影响变量,因此无联合诊断模型的构建。以f_(in)>0.16作为诊断阈值进行应用验证,准确度为82.14%。结论MRI时间依赖扩散诊断指标f_(in)对于判断新诊断胶质母细胞瘤MGMT启动子甲基化状态表现出较好的应用价值。
