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Voltage losses during discharge have been quantitatively investigated in a coulombically balanced biphenyl (Bp)|sodium-polysulfide (Na2Sx) organic redox flow battery. The individual half-cell electrochemical impedance spectroscopy (EIS) response was studied using a flow cell with an in-situ sodium/sodium-ion reference electrode. The anode, consisting of Bp/Bp− couple, contributed approximately 58% of the total cell overpotential during discharge. Further investigation revealed that kinetic overpotential dominating both anode and cathode voltage losses during discharge. The EIS response for the sodium-polysulfide half-cell exhibits two semicircles at high and low frequencies. Since there is limited literature relating the high-frequency semicircle to a physical process, this work extends the investigation of cathode high-frequency EIS features using in-situ and ex-situ electrochemical diagnostic tools. The Bp Nyquist plot consisted of a single semi-circle due to its simpler redox reaction relative to the more complicated Na2Sx. Tafel analysis was used to calculate exchange current density values, with Bp having a lower exchange current density than Na2Sx. This finding explains the relatively higher Bp kinetic voltage loss as compared to Na2Sx. 

Quadcopters are increasingly popular for robotics applications. Being able to efficiently calculate the set of positions reachable by a quadcopter within a time budget enables collision avoidance and pursuit-evasion strategies.This paper examines the set of positions reachable by a quadcopter within a specified time limit using a simplified 2D model for quadcopter dynamics. This popular model is used to determine the set of candidate optimal control sequences to build the full 3D reachable set. We calculate the analytic equations that exactly bound the set of positions reachable in a given time horizon for all initial conditions. To further increase calculation speed, we use these equations to derive tight upper and lower spherical bounds on the reachable set. 

Wetlands cover a small portion of the world, but have disproportionate influence on global carbon (C) sequestration, carbon dioxide and methane emissions, and aquatic C fluxes. However, the underlying biogeochemical processes that affect wetland C pools and fluxes are complex and dynamic, making measurements of wetland C challenging. Over decades of research, many observational, experimental, and analytical approaches have been developed to understand and quantify pools and fluxes of wetland C. Sampling approaches range in their representation of wetland C from short to long timeframes and local to landscape spatial scales. This review summarizes common and cutting-edge methodological approaches for quantifying wetland C pools and fluxes. We firstdefineeach of the major C pools and fluxes and providerationalefor their importance to wetland C dynamics. For each approach, we clarifywhatcomponent of wetland C is measured and its spatial and temporal representativeness and constraints. We describe practical considerations for each approach, such aswhereandwhenan approach is typically used,whocan conduct the measurements (expertise, training requirements), andhowapproaches are conducted, including considerations on equipment complexity and costs. Finally, we reviewkey covariatesandancillary measurementsthat enhance the interpretation of findings and facilitate model development. The protocols that we describe to measure soil, water, vegetation, and gases are also relevant for related disciplines such as ecology. Improved quality and consistency of data collection and reporting across studies will help reduce global uncertainties and develop management strategies to use wetlands as nature-based climate solutions.