Sub-scale coils are being manufactured and tested at Lawrence Berkeley National Laboratory in order to develop wind-and-react Bi2Sr2CaCu20, (Bi-2212) magnet technology for future graded accelerator magnet use. Previous Bi-2212 coils showed significant leakage of the conductors' core constituents to the environment, which can occur during the partial melt reaction around 890 °C in pure oxygen. The main origin of the observed leakage is intrinsic leakage of the wires, and the issue is therefore being addressed at the wire manufacturing level. We report on further compatibility studies, and the performance of new sub-scale coils that were manufactured using improved conductors. These coils exhibit significantly reduced leakage, and carry currents that are about 70% of the witness wire critical current (/ c ). The coils demonstrate, for the first time, the feasibility of round wire Bi-2212 conductors for accelerator magnet technology use. Successful high temperature superconductor coil technology will enable the manufacture of graded accelerator magnets that can surpass the, already closely approached, intrinsic magnetic field limitations of Nb-based superconducting magnets.

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Li−O 2 batteries can provide significantly higher gravimetric energy density than Li-ion batteries, but their practical use is limited by a number of fundamental issues associated with oxidizing discharge products such as Li 2 O 2 and LiOH during charging. Soluble inorganic redox mediators (RMs) like LiI and LiBr have been shown to enhance round-trip efficiency where different solvents can greatly shift the redox potential of the RMs, significantly altering the overpotential during charging, as well as their oxidizing power against the discharge product. Unfortunately, other design requirements like (electro)chemical stability with the electrode as well as reactive discharge products greatly constrain the selection of solvent, making it impractical to additionally design the solvent to provide optimal RM performance. In this work, we demonstrate that interhalide RMs based on LiI/LiBr and LiI/LiCl mixtures can enable tuning of the oxidizing power of the RM in a given solvent. I−Br interhalides I 2 Br − to IBr 2 − showed increasing chemical oxidizing power toward Li 2 O 2 and LiOH with increasing Br, and DEMS measurements during charging of Li−O 2 cells demonstrated that these I−Br interhalide RMs led to increased O 2 evolution with respect to LiI and reduced charging potential and CO 2 evolution with respect to LiBr.

Piezoelectric components offer several potential advantages to power conversion including high power density and efficiency capabilities compared to magnetics at small scales. Converter architectures have been developed for efficient utilization of piezoelectrics, but without fundamental criteria for designing the piezoelectric components themselves. In this paper, we derive figures of merit for the achievable efficiencies and power handling densities of piezoelectric materials and vibration modes based on realistic utilization in a power converter. These figures of merit are likewise accompanied by geometry conditions that serve as guidelines for high-efficiency, high-power-density piezoelectric resonator design. We demonstrate use of these metrics to evaluate commercially-available PZT and lithium niobate materials across seven vibration modes, and we validate the figures of merit and geometry conditions with numerical solutions of converter operation and experimental results. The proposed figures of merit are concluded to be highly representative metrics for the capabilities of piezoelectrics in power conversion, and these capabilities are shown to have favorable scaling properties for converter miniaturization.

Abstract:The following conjecture of Brualdi and Shen is proven in this paper: let n be partitioned into natural numbers no one of which is greater than ðn þ 1Þ=2. Then, given any sequence of wins for the players of some tournament among n players, there is a partition of the players into blocks with cardinalities given by those numbers, and a tournament with the given sequence of wins, that is transitive on the players within each block.