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  1. Ultrasensitive feedback control can improve robust gene expressions in cell populations, yet it usually requires large chemical productions that cause severe burden to cells. Inspired by `division-of-labor' in heterogeneous populations, we propose a bistable switch circuit that utilizes quorum sensing systems to coordinate heterogeneous phenotypes' behaviors. We show that ultrasensitivity emerges from a collection of parallel bistable switches in individual cells. When applied to feedback control of population level expressions, it can achieve robust reference tracking and adaptation to disturbances. In particular, we demonstrate that molecular sequestration enables tunable hysteresis in single switches, leading to a wide range of stablemore »population level expressions.« less
  2. Lightning increases the atmosphere’s ability to cleanse itself by producing nitric oxide (NO), leading to atmospheric chemistry that forms ozone (O3) and the atmosphere’s primary oxidant, the hydroxyl radical (OH). Our analysis of a 2012 airborne study of deep convection and chemistry demonstrates that lightning also directly generates the oxidants OH and the hydroperoxyl radical (HO2). Extreme amounts of OH and HO2were discovered and linked to visible flashes occurring in front of the aircraft and to subvisible discharges in electrified anvil regions. This enhanced OH and HO2is orders of magnitude greater than any previous atmospheric observation. Lightning-generated OH in allmore »storms happening at the same time globally can be responsible for a highly uncertain, but substantial, 2 to 16% of global atmospheric OH oxidation.

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