Theoretical and numerical studies of chaotic mixing

Theoretical and numerical studies of chaotic mixing are performed to circumvent the difficulties of efficient mixing, which come from the lack of turbulence in microfluidic devices. In order to carry out efficient and accurate parametric studies and to identify a fully chaotic state, a spectral element algorithm for solution of the incompressible Navier-Stokes and species transport equations is developed. Using Taylor series expansions in time marching, the new algorithm employs an algebraic factorization scheme on multi-dimensional staggered spectral element grids, and extends classical conforming Galerkin formulations to nonconforming spectral elements. Lagrangian particle tracking methods are utilized to study particle dispersion in the mixing device using spectral element and fourth order Runge-Kutta discretizations in space and time, respectively. Comparative studies of five different techniques commonly employed to identify the chaotic strength and mixing efficiency in microfluidic systems are presented to demonstrate the competitive advantages and shortcomings of each method. These are the stirring index based on the box counting method, Poincare sections, finite time Lyapunov exponents, the probability density function of the stretching field, and mixing index inverse, based on the standard deviation of scalar species distribution. Series of numerical simulations are performed by varying the Peclet number (Pe) at fixed kinematic conditions. The mixing length (lm) is characterized as function of the Pe number, and lm ∝ ln(Pe) scaling is demonstrated for fully chaotic cases. Employing the aforementioned techniques, optimum kinematic conditions and the actuation frequency of the stirrer that result in the highest mixing/stirring efficiency are identified in a zeta potential patterned straight micro channel, where a continuous flow is generated by superposition of a steady pressure driven flow and time periodic electroosmotic flow induced by a stream-wise AC electric field. Finally, it is shown that the invariant manifold of hyperbolic periodic point determines the geometry of fast mixing zones in oscillatory flows in two-dimensional cavity

Comprehensive Microenvironment Monitoring for the Productivity and Welfare of Sows and Piglets

The world is facing increasing food demand and climate change. To improve piglet survivability and sow welfare through microenvironment management using precision technology, a USDA sponsored research project started in 2021 and is ongoing. A comprehensive yet low-cost system was designed and developed for continuous and real-time microenvironment monitoring in three rooms of Farrowing Building #1 at the Animal Sciences Research and Education Center, Purdue University. The system consists of two gas analyzers and 103 different sensors, including sensors in a weather station. The first trial of the project was conducted from Jan. 13 to Feb. 8, 2023, when the rooms were set at different temperatures, which were controlled by heating and ventilation. Preliminary results during the first trial revealed that the monitoring system can perform comprehensive and continues measurement of the indoor environment. They also demonstrated the dynamic nature and the interaction of different environmental variables in the three farrowing rooms. The results can be used to assist the assessment of sow and piglet productivity and welfare under different microenvironment conditions. Key words: Microenvironment monitoring, animal welfare, precision technolog

Hybrid Spam Filtering for Mobile Communication

Spam messages are an increasing threat to mobile communication. Several mitigation techniques have been proposed, including white and black listing, challenge-response and content-based filtering. However, none are perfect and it makes sense to use a combination rather than just one. We propose an anti-spam framework based on the hybrid of content-based filtering and challenge-response. There is the trade-offs between accuracy of anti-spam classifiers and the communication overhead. Experimental results show how, depending on the proportion of spam messages, different filtering %%@ parameters should be set.Comment: 6 pages, 5 figures, 1 tabl