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We describe a dual-class authentic learning experience (ALE) in which undergraduate upper-division physics students develop low-cost instruments, which are then used by students in a lower-division course to monitor water quality in rivers. The ALE bridges the experiences of lower- and upper-division physics majors by involving students across different stages of their college careers in a collaborative project. Lower-division physics students characterize, calibrate, and troubleshoot the instrument prototypes developed by their upper-division peers, and their work informs instrument modifications in future upper-division physics classes. This paper describes the first iteration of this project along with student perceptions. We find that lower-division students report an increase in their awareness of possible upper-division projects, an increased sense that their coursework has real-world applications, and a heightened understanding of how physicists can play a role in research on environmental issues. 

Polymer retention from the flow of a polymer solution through porous media results in substantial decrease of the permeability; however, the underlying physics of this effect is unknown. While the polymer retention leads to a decrease in pore volume, here we show that this cannot cause the full reduction in permeability. Instead, to determine the origin of this anomalous decrease in permeability, we use confocal microscopy to measure the pore-level velocities in an index-matched model porous medium.We show that they exhibit an exponential distribution and, upon polymer retention, this distribution is broadened yet retains the same exponential form. Surprisingly, the velocity distributions are scaled by the inverse square root of the permeabilities. We combine experiment and simulation to show these changes result from diversion of flow in the random porous-medium network rather than reduction in pore volume upon polymer retention.