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Dynamics of Current Redistribution in Insulated REBCO Tape Stacks
No full textFor the design of new high-field magnets, it is essential to understand the properties and limits of the constituent superconductors. One of the most exciting and currently-researched classes is superconductors is Rare-Earth Barium Copper Oxide (REBCO), which are exclusively fabricated in a tape geometry. This paper discusses new methods that allow for higher maximum current loads in stacks of REBCO tapes in a dipole magnet. The focus of this paper is on current redistribution, in which current enters a REBCO tape stack in varying amounts to maximize the total critical current. A general introduction to superconductivity and REBCO superconductors is shared in this paper as well. The theory behind current redistribution is discussed, and the experimental methods used to test this theory are shown. A custom test dipole was designed and fabricated in order to accurately test the effects of current redistribution. Different tests of the Hall probes used to indirectly measure the current in the REBCO tapes are presented. This paper discusses results of a test to measure the effect of current redistribution. The prominence of this effect is compared to the effect of current sharing, where current flows from one REBCO tape to another. A test is designed and carried out with electrical isolation between each REBCO tape to isolate the effect of current redistribution and eliminate current sharing effects. Also presented are possible future implementations of this effect. Namely, the increase in maximum critical current in a REBCO tape stack allows REBCO tape stacks to be aligned with the direction of the external magnetic field, taking advantage of REBCO tape���s natural anisotropy. This fact is used in the design of an 18 Tesla accelerator magnet proposed in a previous paper. This high-field accelerator magnet would allow for higher-energy particle accelerators, which could discover new fundamental physics. Additionally, high-field magnets are widely used in medical applications such as MRIs and proton therapy. Higher-field magnets utilizing current redistribution and current sharing could be used in these applications as well
Genotyping Through Allorecognition In Mesophotic Coral Restoration
Get PDFAnthropogenic stressors continue to threaten and diminish coral reefs worldwide, and natural recovery rates may not be fast enough to compete with these changes. Restoration efforts, then, are required to ensure reef ecosystem stability and active intervention has been proven to positively impact recovery. The gorgonian species Swiftia exserta and Diodogorgia nodulifera form part of mesophotic reef ecosystems that have experienced extensive injury due to the 2010 Deepwater Horizon oil spill This study aims to aid restoration efforts of mesophotic reefs by creating a field-based genotyping method with the potential to accelerate and broaden coral-focused restoration projects. Given the innate ability of many corals like S. exserta to rapidly recognize self vs non-self through physical contact, known as allorecognition, I designed a grafting experiment using D. nodulifera to understand its immune response to non-self . I predicted that isografts would fuse, while allografts would reject upon tissue contact points as was observed in S. exserta. The results, however, demonstrated a slow and minor immune response in D. nodulifera. Among the different genotypes, reactivity was either not observed, led to the indentation of one branch into the other, or was able to partially fuse across membranes for both isografts and allografts. Given that reaction times were protracted in D. nodulifera relative to S. exserta, I propose that: (a) a more thorough characterization of species-specific allorecognition responses are necessary before deploying this genotyping tool universally, and (b) that the degree of sensitivity for non-self recognition may widely vary in cnidarians based on life history patterns
The Effects of Resonant Vibrations on Dropwise Condensation and Droplet Size Distribution
No full textA study has been conducted to determine the effects of resonant vibrations on droplet motion and sliding on surfaces experiencing dropwise condensation. This study set out to determine the effects of resonant vibrations on the amount of condensate shed from a surface, and the effects these vibrations have on the droplet size distribution present on the same surface. Additionally, the effect of vibrations at varying accelerations was also investigated. Resonant vibration based dropwise condensation has the potential to become an efficient and rugged method of improving heat transfer in condensers by using tuned vibrations.
Copper and PTFE surfaces were cooled and vibrated at frequencies between 50-90Hz at accelerations of 0.2g. The amount of condensate shed from each surface at each vibration was recorded, and a high-speed camera was used to capture photos of the droplets on the surface. The number and size of the droplets were then measured from the images to determine the corresponding droplet size distributions. It was found that the optimum amount of condensate was shed from a copper surface when vibrated at 60-70Hz, while optimum condensation rate on a PTFE surface was obtained at 90Hz. While the vibrated copper surface was observed to have an increase in condensate shed of 137% at the imposed frequencies, the PTFE surface was extremely responsive to the vibration at 90Hz yielding over 3 times the condensate shed compared to the PTFE control.
The droplet size distribution in most cases was predominately exponentially distributed. At higher frequencies, the distribution would tend to become bimodal, with the PTFE surface becoming significantly more bimodal than the comparative copper cases. It was also found that by imposing a range of sweeping frequencies, from a high frequency to a low frequency, a very strong bimodal distribution could be observed. These high to low frequency sweeps also shed the least amount of condensate from both surfaces.
A single frequency case for each surface was also performed at accelerations of 0.1g, 0.2g, and 0.3g. The results show that the 0.2g case yielded more shed condensate from both surfaces than at the other two frequencies. This, combined with the results from the varied frequency vibrations provides new insight into the effects of resonant vibrations on droplet size distribution. This further suggests that an optimal acceleration and frequency should be imposed on a surface to improve droplet shedding