Will jams get worse when slow cars move over?

Motivated by an analogy with traffic, we simulate two species of particles (`vehicles'), moving stochastically in opposite directions on a two-lane ring road. Each species prefers one lane over the other, controlled by a parameter $0 \leq b \leq 1$ such that $b=0$ corresponds to random lane choice and $b=1$ to perfect `laning'. We find that the system displays one large cluster (`jam') whose size increases with $b$, contrary to intuition. Even more remarkably, the lane `charge' (a measure for the number of particles in their preferred lane) exhibits a region of negative response: even though vehicles experience a stronger preference for the `right' lane, more of them find themselves in the `wrong' one! For $b$ very close to 1, a sharp transition restores a homogeneous state. Various characteristics of the system are computed analytically, in good agreement with simulation data.Comment: 7 pages, 3 figures; to appear in Europhysics Letters (2005

Simultaneous Influence of Geology and System Design on Drinking Water Quality in Private Systems

Abstract Between 2012 and 2014, almost 3,000 point-of-usewater samples from private water systems (e.g., wells, springs) in Virginiawere analyzed for common contaminants of human health and aestheticconcern. In addition, each sample was accompanied by a brief questionnairedetailing system characteristics. Approximately 55% of samples exceeded atleast one health-based drinking water standard. This study evaluated theinteractions between local geology and private system type to understandvariations in water quality, which is critical when evaluating and prioritizingefforts to protect public health. In the context of lead, sodium, and totalcoliform bacteria, this study illustrated the importance of considering localgeology as it dictates groundwater flow; private system type as it determinesthe source aquifer and raw groundwater quality; and household treatmentdevices as potential sources of additional water quality constituents

Engineered and Environmental Controls of Microbial Denitrification in Established Bioretention Cells

Bioretention cells (BRCs) are effective tools for treating urban stormwater, but nitrogen removal by these systems is highly variable. Improvements in nitrogen removal are hampered by a lack of data directly quantifying the abundance or activity of denitrifying microorganisms in BRCs and how they are controlled by original BRC design characteristics. We analyzed denitrifiers in twenty-three BRCs of different designs across three mid-Atlantic states (MD, VA, and NC) by quantifying two bacterial denitrification genes (<i>nirK</i> and <i>nosZ</i>) and potential enzymatic denitrification rates within the soil medium. Overall, we found that BRC design factors, rather than local environmental variables, had the greatest effects on variation in denitrifier abundance and activity. Specifically, denitrifying populations and denitrification potential increased with organic carbon and inorganic nitrogen concentrations in the soil media and decreased in BRCs planted with grass compared to other types of vegetation. Furthermore, the top layers of BRCs consistently contained greater concentrations and activity of denitrifying bacteria than bottom layers, despite longer periods of saturation and the presence of permanently saturated zones designed to promote denitrification at lower depths. These findings suggest that there is still considerable potential for design improvements when constructing BRCs that could increase denitrification and mitigate nitrogen export to receiving waters