Turbulent mixing in stratified fluids : layer formation and energetics

Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 1993A turbulent mixing experiment was conducted to observe the dynamics and the energetics of layer formation along with the region of layer formation in the Reynolds number (Re) and the overall Richardson number (Rio) space. A salt stratified fluid was mixed uniformly throughout its depth with a vertical rod that moved horizontally at a constant speed. The evolution of density was measured with a conductivity probe. As the instability theory of Phillips (1972) and Posmentier (1977) shows, an initially uniform density profile turns into a series of steps when Rio is larger than a critical value Ric, which forms a stability boundary. For fixed Re, as Rio decreases to Ric, the steps get weaker; the density difference across the interface and the difference of density gradient between layers and interfaces become small. Ric increases as Re increases with a functional relation log Ric ≈ Re/900. The steps evolve over time, with small steps forming first, and larger steps appearing later through merging and decay of the interfaces. After some time the interior seems to reach an equilibrium state and the evolution of the interior steps stops. The length scale of the equilibrium step, ls, is a linear function of U /Ni, where U is the speed of the rod and Ni is the buoyancy frequency of the initial profile. The functional relationship is ls = 2.6U / Ni + l.Ocm. For Rio < Ric, the mixing efficiency, Rf, monotonically decreases to the end of a run. However, for Rio > Ric, the evolution of Rf is closely related to the evolution of the density field. Rf changes rapidly during the initiation of the steps. For Rio » Ric, R1 increases initially, while for Rio ≥ Ric, Rf ecreases initially. When the interior reaches an equilibrium state, Rf becomes uniform. Posmentier (1977) theorized that when steps reach an equilibrium state, a density flux is independent of the density gradient. The present experiments show a uniform density flux in the layered interior irrespective of the density structure, and this strongly supports the theory of Posmentier. The density flux generated in the bottom boundary mixed layer goes through the interior all the way to the top boundary mixed layer without changing the interior density structure. Thus, turbulence can transport scalar properties further than the characteristic length scale of active eddies without changing a density structure. When the fluid becomes two mixed layers, the relation between Rf and Ril was found for Ril > 1. Here, Ril is the local Richardson number based on the thickness of the interface. R, does decrease as Ril increases, which is the most crucial assumption of the instability theory

Rotating convection driven by differential bottom heating and its application

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1996.Includes bibliographical references (leaves 133-137).by Young-Gyu Park.Ph.D

Estimation of Water Quality Index for Coastal Areas in Korea Using GOCI Satellite Data Based on Machine Learning Approaches

In Korea, most industrial parks and major cities are located in coastal areas, which results in serious environmental problems in both coastal land and ocean. In order to effectively manage such problems especially in coastal ocean, water quality should be monitored. As there are many factors that influence water quality, the Korean Government proposed an integrated Water Quality Index (WQI) based on in situ measurements of ocean parameters(bottom dissolved oxygen, chlorophyll-a concentration, secchi disk depth, dissolved inorganic nitrogen, and dissolved inorganic phosphorus) by ocean division identified based on their ecological characteristics. Field-measured WQI, however, does not provide spatial continuity over vast areas. Satellite remote sensing can be an alternative for identifying WQI for surface water. In this study, two schemes were examined to estimate coastal WQI around Korea peninsula using in situ measurements data and Geostationary Ocean Color Imager (GOCI) satellite imagery from 2011 to 2013 based on machine learning approaches. Scheme 1 calculates WQI using estimated water quality-related factors using GOCI reflectance data, and scheme 2 estimates WQI using GOCI band reflectance data and basic products(chlorophyll-a, suspended sediment, colored dissolved organic matter). Three machine learning approaches including Random Forest (RF), Support Vector Regression (SVR), and a modified regression tree(Cubist) were used. Results show that estimation of secchi disk depth produced the highest accuracy among the ocean parameters, and RF performed best regardless of water quality-related factors. However, the accuracy of WQI from scheme 1 was lower than that from scheme 2 due to the estimation errors inherent from water quality-related factors and the uncertainty of bottom dissolved oxygen. In overall, scheme 2 appears more appropriate for estimating WQI for surface water in coastal areas and chlorophyll-a concentration was identified the most contributing factor to the estimation of WQI.ope

Thiol-linked peroxidase activity of human ceruloplasmin

AbstractHuman ceruloplasmin exhibited different antioxidant effects according to the electron donors in a metal-catalyzed oxidation system. Purified ceruloplasmin did not play a significant role in the protection of DNA strand breaks in the ascorbate/Fe3+/O2 system. However, when ascorbates were replaced with a thiol-reducing equivalent such as dithiothreitol, DNA strand breaks were significantly prevented by the same amount of ceruloplasmin. Ceruloplasmin did not catalyze the decomposition of H2O2 in the absence of reduced glutathione. On the contrary, ceruloplasmin showed a potent peroxidase ability to destroy H2O2 in the presence of reduced glutathione. In conclusion, the removal of H2O2 by human ceruloplasmin is not simply stoichiometric but thiol-dependent