For understanding the rock microscopic damage and dynamic mechanical properties subjected to recurrent freeze-thaw cycles, experiments for five groups of homogeneous sandstone under different freeze-thaw cycles were c...For understanding the rock microscopic damage and dynamic mechanical properties subjected to recurrent freeze-thaw cycles, experiments for five groups of homogeneous sandstone under different freeze-thaw cycles were conducted. After freezethaw, nuclear magnetic resonance(NMR) tests and impact loading tests were carried out, from which microscopic damage characteristics of sandstone and dynamic mechanical parameters were obtained. The results indicate that the porosity increases with the increase of cycle number, the rate of porosity growth descends at the beginning of freeze-thaw, yet accelerates after a certain number of cycles. The proportion of pores with different sizes changes dynamically and the multi-scale distribution of pores tends to develop on pore structure with the continuing impact of freeze-thaw and thawing. Dynamic compressive stress-strain curve of sandstone undergoing freeze-thaw can be divided into four phases, and the phase of compaction is inconspicuous compared with the static curve. Elastic modulus and dynamic peak intensity of sandstone gradually decrease with freeze-thaw cycles, while peak strain increases. The higher the porosity is, the more serious the degradation of dynamic intensity is. The porosity is of a polynomial relationship with the dynamic peak intensity.展开更多
丁酸类代谢物广泛存在于动物、植物和微生物中,且具有多种重要的生理功能,但它们的固体核磁共振参数、分子动力学性质及其结构依赖性并未得到清楚的认识.该文使用高分辨交叉极化与魔角旋转核磁共振(13 C CPMAS)实验技术,分析了一系列固...丁酸类代谢物广泛存在于动物、植物和微生物中,且具有多种重要的生理功能,但它们的固体核磁共振参数、分子动力学性质及其结构依赖性并未得到清楚的认识.该文使用高分辨交叉极化与魔角旋转核磁共振(13 C CPMAS)实验技术,分析了一系列固体丁酸类代谢物的13C化学位移,发现了这些代谢物的13 C化学位移与其分子结构的一些相关性规律.另外还发现,固体丁酸类代谢物与其在溶液中的13 C化学位移有显著的差异.这些代谢物中甲基参与的疏水作用以及羟基、氨基和羧基参与的氢键作用均对其化学位移大小有重要的影响.上述结果为认识代谢物的结构和功能以及功能对结构的依赖性提供了重要信息.展开更多
基金Project(2013YQ17046310)supported by the National Key Scientific Instrument and Equipment Development Project of ChinaProject(2013M542138)supported by China Postdoctoral Science FoundationProjects(20130162110010,20130162120012)supported by Specialized Research Fund for the Doctoral Program of Higher Education of China
文摘For understanding the rock microscopic damage and dynamic mechanical properties subjected to recurrent freeze-thaw cycles, experiments for five groups of homogeneous sandstone under different freeze-thaw cycles were conducted. After freezethaw, nuclear magnetic resonance(NMR) tests and impact loading tests were carried out, from which microscopic damage characteristics of sandstone and dynamic mechanical parameters were obtained. The results indicate that the porosity increases with the increase of cycle number, the rate of porosity growth descends at the beginning of freeze-thaw, yet accelerates after a certain number of cycles. The proportion of pores with different sizes changes dynamically and the multi-scale distribution of pores tends to develop on pore structure with the continuing impact of freeze-thaw and thawing. Dynamic compressive stress-strain curve of sandstone undergoing freeze-thaw can be divided into four phases, and the phase of compaction is inconspicuous compared with the static curve. Elastic modulus and dynamic peak intensity of sandstone gradually decrease with freeze-thaw cycles, while peak strain increases. The higher the porosity is, the more serious the degradation of dynamic intensity is. The porosity is of a polynomial relationship with the dynamic peak intensity.
文摘丁酸类代谢物广泛存在于动物、植物和微生物中,且具有多种重要的生理功能,但它们的固体核磁共振参数、分子动力学性质及其结构依赖性并未得到清楚的认识.该文使用高分辨交叉极化与魔角旋转核磁共振(13 C CPMAS)实验技术,分析了一系列固体丁酸类代谢物的13C化学位移,发现了这些代谢物的13 C化学位移与其分子结构的一些相关性规律.另外还发现,固体丁酸类代谢物与其在溶液中的13 C化学位移有显著的差异.这些代谢物中甲基参与的疏水作用以及羟基、氨基和羧基参与的氢键作用均对其化学位移大小有重要的影响.上述结果为认识代谢物的结构和功能以及功能对结构的依赖性提供了重要信息.
