We build an experiment system based on total reflection(TR) method to observe the evolution of real contact area of polymethyl methacrylate(PMMA) in the continual stick-slip movement. The bilateral friction is adopted...We build an experiment system based on total reflection(TR) method to observe the evolution of real contact area of polymethyl methacrylate(PMMA) in the continual stick-slip movement. The bilateral friction is adopted to overcome the bending moment in the lateral friction movement. Besides some classical phenomena of stick-slip movement such as periodical slow increase of frictional force in sticking phase and a sudden drop when slipping, a special phenomenon that the contact area increases with the tangential force is observed, which was called junction growth by Tabor in 1959.Image processing methods are developed to observe the variation of the junction area. The results show that the center of the strongest contact region will keep sticking under the tangential force until the whole slipping, the strongest point undergoes three stages in one cycle, which are named as sticking stage, fretting stage, and cracking stage, respectively. The combined analysis reveals a physical process of stick-slip movement: the tangential force causes the increase of the real contact area, which reduces the pressure between the contact spots and finally leads to the slipping. Once slipping occurs,the real contact area drops to the original level resulting in the pressure increase to the original level, which makes the sticking happen again.展开更多
The scaling relationship between leaf area and total mass of plant has important implications for understanding resource allocations in the plant.The model of West,Brown and Enquist(WBE model)considers that a 3/4 scal...The scaling relationship between leaf area and total mass of plant has important implications for understanding resource allocations in the plant.The model of West,Brown and Enquist(WBE model)considers that a 3/4 scaling exponent of metabolic rate versus total mass to be optimal for each plant and has been confirmed numerous times.Although leaf area is a better proxy of the metabolic rate than leaf mass,few studies have focused on the scaling exponent of leaf area versus total mass and even fewer have discussed the diversification of this scaling exponent across different conditions.Here,I analyzed the scaling exponent of leaf area versus total mass of sample plots across world plants.I found that as the plant grows,it allocates fewer resources to photosynthetic tissues than expected by the WBE model.The results also empirically show that this scaling exponent varies significantly for different plant leaf habit,taxonomic class and geographic region.Therefore,leaf strategy in response to environmental pressure and constraint clearly plays a significant role.展开更多
[Objectives] To determine the content of total flavonoids in Tetracera asiatica from different production areas in Guangxi and provide a basis for improving the quality standards of crude drug. [Methods] Using 50% eth...[Objectives] To determine the content of total flavonoids in Tetracera asiatica from different production areas in Guangxi and provide a basis for improving the quality standards of crude drug. [Methods] Using 50% ethanol as extractor,NaNO_2-Al(NO_3)_3-NaOH as chromogenic system and rutin as the reference substance,the content of total flavonoids from the crude drug was determined. [Results] A method for determining the content of total flavonoids was established,the content of total flavonoids was 11.35-21.35 mg·g^(-1),and the average content was 17.64 mg·g^(-1). [Conclusions] The method had high repeatability and stability,and the method was simple,rapid and sensitive and suitable for quantitative analysis.展开更多
An experimental method of measuring the real contact area of transparent blocks based on the principle of total internal reflection is presented, intending to support the investigation of friction characteristics, hea...An experimental method of measuring the real contact area of transparent blocks based on the principle of total internal reflection is presented, intending to support the investigation of friction characteristics, heat conduction, and energy dissipation at the contact interface. A laser sheet illuminates the contact interface, and the transmitted laser sheet is projected onto a screen. Then the contact information is acquired from the screen by a camera. An improved Otsu method is proposed to process the data of experimental images. It can compute the threshold of the overall image and filter out all the pixels one by one. Through analyzing the experimental results, we describe the relationship between the real contact area and the positive pressure during a continuous loading process, at different loading rates, with the polymethyl methacrylate（PMMA）material. A hysteresis phenomenon in the relationship between the real contact area and the positive pressure is found and explained.展开更多
High total dissolved solids （TDS） content is one of the most important pollution contributors in lakes in arid and semiarid areas. Ulansuhai Lake, located in Urad Qianqi, Inner Mongolia, China, was selected as the o...High total dissolved solids （TDS） content is one of the most important pollution contributors in lakes in arid and semiarid areas. Ulansuhai Lake, located in Urad Qianqi, Inner Mongolia, China, was selected as the object of study. Temperatures and TDS contents of both ice and under-ice water were collected together with corresponding ice thickness. TDS profiles were drawn to show the distribution of TDS and to describe TDS migration. The results showed that about 80% （that is 3.602x108 kg） of TDS migrated from ice to water during the whole growth period of ice. Within ice layer, TDS migration only occurred during initial ice-on period, and then perished. The TDS in ice decreased with increasing ice thickness, following a negative exponential-like trend. Within un- der-ice water, the TDS migrated from ice-water interface to the entire water column under the effect of concentra- tion gradient until the water TDS content was uniform. In winter, 6.044x 107 kg （16.78% of total TDS） TDS migrated from water to sedirnent, which indicated that winter is the best time for dredging sediment. The migration effect gives rise to TDS concentration in under-ice water and sediment that is likely to affect ecosystem and water quality of the Yellow River. The trend of transfer flux of ice-water and water-sediment interfaces is similar to that of ice growth rate, which reveals that ice growth rate is one of the determinants of TDS migration. The process and mechanism of TDS migration can be referenced by research on other lakes with similar TDS content in cold and arid areas.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant No.11872033)the Beijing Natural Science Foundation,China(Grant No.3172017)
文摘We build an experiment system based on total reflection(TR) method to observe the evolution of real contact area of polymethyl methacrylate(PMMA) in the continual stick-slip movement. The bilateral friction is adopted to overcome the bending moment in the lateral friction movement. Besides some classical phenomena of stick-slip movement such as periodical slow increase of frictional force in sticking phase and a sudden drop when slipping, a special phenomenon that the contact area increases with the tangential force is observed, which was called junction growth by Tabor in 1959.Image processing methods are developed to observe the variation of the junction area. The results show that the center of the strongest contact region will keep sticking under the tangential force until the whole slipping, the strongest point undergoes three stages in one cycle, which are named as sticking stage, fretting stage, and cracking stage, respectively. The combined analysis reveals a physical process of stick-slip movement: the tangential force causes the increase of the real contact area, which reduces the pressure between the contact spots and finally leads to the slipping. Once slipping occurs,the real contact area drops to the original level resulting in the pressure increase to the original level, which makes the sticking happen again.
文摘The scaling relationship between leaf area and total mass of plant has important implications for understanding resource allocations in the plant.The model of West,Brown and Enquist(WBE model)considers that a 3/4 scaling exponent of metabolic rate versus total mass to be optimal for each plant and has been confirmed numerous times.Although leaf area is a better proxy of the metabolic rate than leaf mass,few studies have focused on the scaling exponent of leaf area versus total mass and even fewer have discussed the diversification of this scaling exponent across different conditions.Here,I analyzed the scaling exponent of leaf area versus total mass of sample plots across world plants.I found that as the plant grows,it allocates fewer resources to photosynthetic tissues than expected by the WBE model.The results also empirically show that this scaling exponent varies significantly for different plant leaf habit,taxonomic class and geographic region.Therefore,leaf strategy in response to environmental pressure and constraint clearly plays a significant role.
基金Supported by Youth Fund Project of Guangxi Natural Science Foundation(2016GXNSFBA380014)Key Laboratory Project of Guangxi Zhuang and Yao Medicine(GuiKeJiZi201432)+5 种基金Collaborative Innovation Center Project of Zhuang and Yao Medicine(GuiJiaoKeYan201320)Guangxi Key Discipline(Zhuang Medicine Study)Project(GuiJiaoKeYan201316)Bagui Scholar Program"Innovation Theory and Efficacy Studies of Traditional Chinese Medicine"Special Traditional Chinese Medicine Science and Technology Project of Health Department of Guangxi Zhuang Autonomous Region(GZPT1204)Scientific Research Project of Guangxi’s Colleges and Universities(KY2015-YB160)Scientific Research Project of Guangxi University of Chinese Medicine in 2015(2015LX005)
文摘[Objectives] To determine the content of total flavonoids in Tetracera asiatica from different production areas in Guangxi and provide a basis for improving the quality standards of crude drug. [Methods] Using 50% ethanol as extractor,NaNO_2-Al(NO_3)_3-NaOH as chromogenic system and rutin as the reference substance,the content of total flavonoids from the crude drug was determined. [Results] A method for determining the content of total flavonoids was established,the content of total flavonoids was 11.35-21.35 mg·g^(-1),and the average content was 17.64 mg·g^(-1). [Conclusions] The method had high repeatability and stability,and the method was simple,rapid and sensitive and suitable for quantitative analysis.
基金Project supported by the National Natural Science Foundation of China(Grant No.11272171)the Beijing Natural Science Foundation,China(Grant No.3132030)the Education Ministry Doctoral Fund of China(Grant No.20120002110070)
文摘An experimental method of measuring the real contact area of transparent blocks based on the principle of total internal reflection is presented, intending to support the investigation of friction characteristics, heat conduction, and energy dissipation at the contact interface. A laser sheet illuminates the contact interface, and the transmitted laser sheet is projected onto a screen. Then the contact information is acquired from the screen by a camera. An improved Otsu method is proposed to process the data of experimental images. It can compute the threshold of the overall image and filter out all the pixels one by one. Through analyzing the experimental results, we describe the relationship between the real contact area and the positive pressure during a continuous loading process, at different loading rates, with the polymethyl methacrylate（PMMA）material. A hysteresis phenomenon in the relationship between the real contact area and the positive pressure is found and explained.
基金Financial support was provided by the National Natural Science Foundation of China (50569002,50669004 and 51069007)Natural Science Foundation of Inner Mongolia (200711020604)Key Project from Department of Water Resources of Inner Mongolia (20080105)
文摘High total dissolved solids （TDS） content is one of the most important pollution contributors in lakes in arid and semiarid areas. Ulansuhai Lake, located in Urad Qianqi, Inner Mongolia, China, was selected as the object of study. Temperatures and TDS contents of both ice and under-ice water were collected together with corresponding ice thickness. TDS profiles were drawn to show the distribution of TDS and to describe TDS migration. The results showed that about 80% （that is 3.602x108 kg） of TDS migrated from ice to water during the whole growth period of ice. Within ice layer, TDS migration only occurred during initial ice-on period, and then perished. The TDS in ice decreased with increasing ice thickness, following a negative exponential-like trend. Within un- der-ice water, the TDS migrated from ice-water interface to the entire water column under the effect of concentra- tion gradient until the water TDS content was uniform. In winter, 6.044x 107 kg （16.78% of total TDS） TDS migrated from water to sedirnent, which indicated that winter is the best time for dredging sediment. The migration effect gives rise to TDS concentration in under-ice water and sediment that is likely to affect ecosystem and water quality of the Yellow River. The trend of transfer flux of ice-water and water-sediment interfaces is similar to that of ice growth rate, which reveals that ice growth rate is one of the determinants of TDS migration. The process and mechanism of TDS migration can be referenced by research on other lakes with similar TDS content in cold and arid areas.
