Element Geochemical Analysis of the Contribution of Aeolian Sand to Suspended Sediment in Desert Stream Flash Floods

The interaction of wind and water in semiarid and arid areas usually leads to low-frequency flash flood events in desert rivers, which have adverse effects on river systems and ecology. In arid zones, many aeolian dune-fields terminate in stream channels and deliver aeolian sand to the channels. Although aeolian processes are common to many desert rivers, whether the aeolian processes contribute to fluvial sediment loss is still unknown. Here, we identified the aeolian-fluvial cycling process responsible for the high rate of suspended sediment transport in the Sudalaer desert stream in the Ordos plateau of China. On the basis of element geochemistry data analysis, we found that aeolian sand was similar to suspended sediment in element composition, which suggests that aeolian sand contributes to suspended sediment in flash floods. Scatter plots of some elements further confirm that aeolian sand is the major source of the suspended sediment. Factor analysis and the relation between some elements and suspended sediment concentration prove that the greater the aeolian process, the higher the suspended sediment concentration and the greater the contribution of aeolian sand to suspended sediment yield. We conclude that aeolian sand is the greatest contributor to flash floods in the Sudalaer desert stream

Recovering both the wave speed and the source function in a time-domain wave equation by injecting high contrast bubbles

Dealing with the inverse source problem for the scalar wave equation, we have shown recently that we can reconstruct the spacetime dependent source function from the measurement of the wave, collected on a single point $x$ and a large enough interval of time, generated by a small scaled bubble, enjoying large contrasts of its bulk modulus, injected inside the domain to image. Here, we extend this result to reconstruct not only the source function but also the variable wave speed. Indeed, from the measured waves, we first localize the internal values of the travel time function by looking at the behavior of this collected wave in terms of time. Then from the Eikonal equation, we recover the wave speed. Second, we recover the internal values of the wave generated only by the background (in the absence of the small particles) from the same measured data by inverting a Volterra integral operator of the second kind. From this reconstructed wave, we recover the source function at the expense of a numerical differentiation.Comment: 28 page

Development of a low inertia drumless tether management system

Oceanography winch system is a very important piece of equipment for ocean research. It is capable of managing cable and towing lines that are connected to the scientific research equipment. Traditional drummed winch systems exhibits issues such as large drum inertia that causes slow response, cable kink and high power consumption. In this thesis, an innovative low inertia drumless winch system that winds cable into a Figure "1" shape was proposed and prototypes were designed and fabricated to prove the concept. To estimate the power requirement for the winch system with regard to sensor towing applications, a dynamic mathematical model of the tow cable in two dimensions was developed using lumped parameter modelling. The model was implemented in Matlab, and simulations were done for different towing speeds. Towing forces including analysis of drag on cable, and relative sensor position under varying towing conditions could be estimated from the model. Two prototypes were designed and built to prove the concept. The first prototype was designed to be a two module system which was planned to achieve reeling, twisting and directing the cable separately by the two modules. Dry running tests of the cable manipulation was performed. Second prototype which consisted of Cable Manipulation Unit and Cable Storage Unit was also designed and built. All three geared DC servo motors are feedback loop controlled using PID controllers, and PID parameters were manually tuned. Cable winding tests were performed. Prototype one failed at twisting and changing the direction of cable.Prototype two successfully reels in and out the cable and can also change the direction while reeling it, but failed at twisting the cable while it was being reeled. Test results and problems encountered were discussed, possible solutions and future work on how to solve the problems and improve the performance of the system were also discussed