CUTLASS: Coral Reef, Underwater Terrain, and Littoral Archaeological Site Surveyor

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Description

Undersea scientific ocean exploration and research only began in earnest approximately150 years ago. Much has been learned and discovered in that time, but there are also gaps in understanding of the ocean depths. One source of the knowledge gap is…

Undersea scientific ocean exploration and research only began in earnest approximately150 years ago. Much has been learned and discovered in that time, but there are also gaps in understanding of the ocean depths. One source of the knowledge gap is the relative lack of crewed exploration in some regions of the ocean. This work presents a vehicle that provides divers with longer time at deeper depths than is currently available in an unpressurized environment, reduces diver workload, and improves situational awareness. Working in collaboration with the scientific diver community, top-level requirements were defined, and a Concept of Operations was developed. This effort is followed up with a vehicle design which provides the capability for two divers to complete unpressurized dives to 200 meters, remain there for 20 minutes, and return to the surface within 12 hours. Additional functionality provided by the vehicle includes significant cargo capacity, voice and data communication with the surface, geolocation capabilities, and automated maneuvering and decompression management. Analysis of the hull shape and propulsion system is presented which demonstrates that the vehicle can reach its velocity and acceleration performance requirements. A virtual environment is then presented which has the potential to allow for end-to-end mission performance evaluation. Finally, the constraints on the life support system are discussed and source code for a simulation is presented. The final chapter of this work examines a hypothetical mission to 200 meters depth. The various phases of the mission are discussed as well as the potential consumption of both oxygen and electricity. Two life support gas mixtures are examined, and the resulting decompression profiles are presented. The final analysis shows that it is possible to conduct dives to 200 meters, perform 20 minutes of work, and return to the surface within 12 hours using the CUTLASS vehicle that is presented.

Date Created
2022
Agent

The Dependence of Star Formation Quenching and of Lyman Alpha Escape on Galaxy Structural Properties

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Description
Galaxy structural properties such as size, morphology, and surface brightness bear the imprint of galaxies' evolutionary histories, and so are related with other properties such as stellar mass, star formation rate, and emergent spectra. In this dissertation, I present three…

Galaxy structural properties such as size, morphology, and surface brightness bear the imprint of galaxies' evolutionary histories, and so are related with other properties such as stellar mass, star formation rate, and emergent spectra. In this dissertation, I present three studies exploring such relationships. In the first, I investigated the relationships between 4000 Å break (D4000) strength, colors, stellar masses, and morphology in a sample of 352 galaxies at intermediate redshifts based on photometric and spectroscopic data from the Hubble Space Telescope (HST). I explored several diagrams such as UVJ color space combined with the D4000 strengths and the structural parameters of sample galaxies. The analysis shows that the presence of a bulge component is a necessary but not sufficient requirement for star formation quenching at intermediate redshifts. In the second study, I investigated the central 250 pc UV star formation intensity (SFI, star formation rate per unit area) of a sample of 40 Green Pea (GP) galaxies and 15 local Lyman Break Galaxy Analogs (LBAs) to understand the Lyα escape mechanisms and the associations with the SFI in Lyα-emitters (LAEs). I utilized the Cosmic Origins Spectrograph near-ultraviolet (COS/NUV) images from the HST. I found that the Lyα equivalent width (EW(Lyα)) and the Lyα escape fraction are positively correlated with the ratio of SFI to galaxy stellar mass. These correlations suggest the importance of the central SFI in Lyα photon escape. In the third study, I investigated the UV photometric properties of a sample of 40 GPs and the possible associations with Lyα escape mechanisms. I measured the UV-continuum size and luminosity of the sample galaxies by employing the COS/NUV images. The circularized half-light radius of GPs shows compact sizes and it further shows the statistically significant anti-correlations with EW(Lyα) and the Lyα escape fraction. The size comparison of GPs to those of high-redshift LAEs shows that their sizes are similar, once spatial resolution effects are properly considered. These results show that a compact size is crucial for escape of Lyα photons, and that Lyα emitters show constant characteristic size independent of their redshift. Therefore, the results presented in this dissertation emphasize the importance of galaxy structural properties in star formation quenching and in Lyα escape.
Date Created
2020
Agent
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