• Reinvestigation of the scaling law of the windblown sand launch velocity with a wind tunnel experiment

    分类: 环境科学技术及资源科学技术 >> 环境科学技术基础学科 提交时间: 2019-10-26 合作期刊: 《干旱区科学》

    摘要: Windblown sand transport is a leading factor in the geophysical evolution of arid and semi-arid regions. The evolution speed is usually indicated by the sand transport rate that is a function of launch velocity of sand particle, which has been investigated by the experimental measurement and numerical simulation. However, the obtained results in literatures are inconsistent. Some researchers have discovered a relation between average launch velocity and wind shear velocity, while some other researchers have suggested that average launch velocity is independent of wind shear velocity. The inconsistence of launch velocity leads to a controversy in the scaling law of the sand transport rate in the windblown case. On the contrary, in subaqueous case, the scaling law of the sand transport rate has been widely accepted as a cubic function of fluid shear velocity. In order to explain the debates surrounding the windblown case and the difference between windblown and subaquatic cases, this study reinvestigates the scaling law of the vertical launch velocity of windblown transported sand particles by using a dimensional analysis in consideration of the compatibility of the characteristic time of sand particle motion and that of air flow. Then a wind tunnel experiment is conducted to confirm the revisited scaling law, where the sand particle motion pictures are recorded by a high-speed camera and then the launch velocity is solved by the particle tracking velocimetry. By incorporating the results of dimensional analysis and wind tunnel experiment, it can be concluded that, the ratio of saltons number to reptons number determines the scaling law of sand particle launch velocity and that of sand transport rate, and using this ratio is able to explain the discrepancies among the classical models of steady sand transport. Moreover, the resulting scaling law can explain the sand sieving phenomenon: a greater fraction of large grains is observed as the distance to the wind tunnel entrance becomes larger.

  • A micro E-DNA sensor for selective detection of dopamine in presence of ascorbic acid

    分类: 物理学 >> 核物理学 提交时间: 2023-06-18 合作期刊: 《Nuclear Science and Techniques》

    摘要: In this paper, a novel method for selectively detection of dopamine (DA) in the interference of ascorbic acid (AA) is described. A nanometer-sized gold flower microelectrode (NGFME) is prepared by flame-etching and electrochemical deposition. The electrode tip was characterized by scanning electron microscope (SEM). The NGFME is sized at about 100 μm and dimensions of thorns of the electrode were in nanometers. By modifying with DA aptamer on the surface, the prepared aptasensor can selectively detect DA even in the presence of high concentration AA. Experimental results show that this NGFME has no response to AA. As a comparison, the carbon fiber electrode without DA aptamer modification is unable to effectively detect DA in the presence of AA. The NGFME is easy-to-prepare, selective and sensitive for DA detection down to 25 μm. The electrode can be expected to detect DA in vivo and in real biological samples.