Description: 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 1989

Description: This thesis studies mixing and convection in a rectangular basin driven by a specified heat flux at the surface. A numerical model is constructed for this purpose. The main focus of the study is on the density and circulation structure resulting from the thermal forcing. In chapter two, a simple vertical one-dimensional model is developed to examine the mixing processes under a given surface heat flux. In order to simulate strong vertical mixing in the region where stratification is unstable, turbulent processes are modeled by a convective overturning parameterization of eddy viscosity and diffusivity. The results show that the density structure is strongly affected by the convective overturning adjustment as surface cooling prevails, and the resulting density field is nearly depth independent. In chapter three, a more complicated two-dimensional model is constructed to simulate mixing and circulation in a vertical rectangular basin with rigid boundaries. The aspect ratio of the basin ranges from 1 to 0.001 and Rayleigh number from 104 to 2 x 1012. It is found that the circulation pattern is dominated by these two important numbers. The roles of density overturning and density-momentum overturning mixing are further investigated. The results show that the convective overturning not only homogenizes the density field in the unstably stratified region but also contributes to increase the circulation. A crude scale analysis of the system shows that the characteristics of the density and momentum fields from the analysis agree well with the numerical results.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 1992

Description: This study concerns the barotropic interactions between a mesoscale eddy and a straight monotonic bottom topography. Through simple to relatively complicated modeling effort, some of the fundamental properties of the interaction are investigated. In chapter two, the fundamental aspects of the interaction are examined using a simple contour dynamics model. With the simplest model configuration of an ideal vortex and a step topography, the basic dynamical features of the observed oceanic eddy-topography interaction are qualitatively reproduced. The results consist of eddy-induced cross-topography exchange, formation of topographic eddies, eddy propagation and generation of topographic waves. In chapter three, a more complicated primitive equation model is used to investigate a mesoscale eddy interacting with an exponential continental shelf/slope topography on both f and β-planes. The f-plane model recasts the important features of chapter two. The roles of the eddy size and strength and the geometry of topography are studied. It is seen that the multiple anticyclonic eddy-slope interactions strongly affect the total cross-slope volume transport and the evolution of both the original anticyclone and the topographic eddy. Since a cyclone is trapped at the slope and eventually moves on to the slope, it is most effective in causing perturbation on the shelf and slope. The responses on the shelf and slope are mainly wavelike with dispersion relation obeying that of the free shelf-trapped wave modes. On the β-plane, the problem of an eddy colliding onto a continental shelf/slope from a distance with straight or oblique incident angles is investigated. It is found that the straight eddy incident is more effective in achieving large onslope eddy penetration distance than the oblique eddy incident. The formation of a dipole-like eddy pair consisting of the original anticyclone and the topographic cyclone acts to suppress the eddy decay due to long Rossby wave radiation. A weak along-slope current near the edge of the slope is found, which is part of a outer slope circulation cell originated from the Rossby wave wake trailing the propagating eddy. Model-observation comparisons in_chapter four show favorable qualitative agreement of the model results with some of the observed events in the eastern U.S. continental margins and in the Gulf of Mexico. The model results give dynamical interpretations to some observed features of the oceanic eddy-topography interactions and provide enlightening insight into the problem.

Description: Purpose To investigate the diffusion abnormalities in the brain of children with idiopathic generalized epilepsy (IGE) with generalized tonic-clonic seizure (GTCS) by using diffusion kurtosis imaging (DKI). Materials and Methods Twenty-one IGE children with GTCS and 16 controls were recruited. DKI was performed and maps of radial diffusivity (λ ⊥ ), axial diffusivity (λ // ), mean diffusivity (MD), fractional anisotropy (FA), radial kurtosis (K ⊥ ), axial kurtosis (K // ) and mean kurtosis (MK) were calculated. Voxel-based analyses were employed to compare diffusion metrics in epilepsy versus the controls. Results In the case group, MD was found significantly higher in the right temporal lobe, the right occipital lobe, hippocampus, and some subcortical regions, while FA increased in bilateral supplementary motor area and the left superior frontal lobe (false discovery rate corrected P  〈 0.05). Analysis of λ ⊥ and λ // showed that the increased MD was mainly due to the elevated λ // . Significantly decreased MK was also detected in bilateral temporo-occipital regions, the right hippocampus, the left insula, the left post-central area, and some subcortical regions (false discovery rate corrected P  〈 0.05). In most regions the changed MK were due to the decreased K // . Conclusion The kurtosis parameters (K ⊥ , K // , and MK) reflect different microstructural information in the IGE children with GTCS, and this support the value of DKI in studying children GTCS. J. Magn. Reson. Imaging 2014 . © 2014 Wiley Periodicals, Inc .

Description: [1]  One of the primary goals for the Visible Infrared Imaging Radiometer Suite (VIIRS) onboard the Suomi National Polar-orbiting Partnership (SNPP) is to provide the science and user communities with the data continuity of the Environmental Data Records (EDR) (or Level-2 products) over global oceanic waters for various research and applications, including assessment of climatic and environmental variations. The ocean color EDR is one of the most important products derived from VIIRS. Since ocean color EDR is processed from the upstream Sensor Data Records (SDR) (or Level-1B data), the objective of this study is to evaluate the impact of the SDR on the VIIRS ocean color EDR. The quality of the SDR relies on pre-launch sensor characterizations as well as on-orbit radiometric calibrations, which are used to develop the sensor F-factor lookup tables (F-LUTs). VIIRS F-LUTs derived from solar and lunar calibrations have been used in processing data from the VIIRS Raw Data Records (RDR) (or Level-0 data) to SDR. In this study, three sets of F-LUTs with different generation schemes have been used to reprocess the SDR and then the ocean color EDR for product evaluations. VIIRS ocean color products are compared with in situ data from the Marine Optical Buoy (MOBY) and products from the Moderate Resolution Imaging Spectroradiometer (MODIS) on the satellite Aqua. It is found that the data quality of VIIRS operational ocean color products before 6 February 2012 is poor due to the inappropriate use of the at-launch F-LUTs for the SDR calibration, and that the recently updated VIIRS F-LUTs have significantly improved the SDR and ocean color EDR. Using reprocessed SDR with updated F-LUTs and including vicarious calibration, VIIRS ocean color EDR products are consistent with those from MODIS-Aqua in global deep waters. Although there are still some significant issues with VIIRS ocean color EDR, e.g., poor data quality over coastal regions, our results demonstrate that VIIRS has great potential to provide the science and user communities with consistently high quality global ocean color data records that are established from heritage ocean color sensors such as MODIS-Aqua.

Description: AmyP is a raw-starch-degrading α-amylase newly identified from a marine metagenome library. It shares low sequence similarity with characterized glycoside hydrolases and was classified into a new subfamily of GH13. In particular, it showed preferential degradation to raw rice starch. Full-length AmyP was cloned and overexpressed in Escherichia coli , then purified and crystallized in the presence of its substrate analogue β-cyclodextrin. X-ray diffraction data were collected to a resolution of 2.1 Å. The crystal belonged to space group P 2 1 2 1 2, with unit-cell parameters a = 129.824, b = 215.534, c = 79.699 Å, α = β = γ = 90°, and was estimated to contain two molecules in one asymmetric unit.

Description: Abstract. The asymmetrical crystal [Na(15C5) 2 ][Na(15C5)] 2 (AsMo 12 O 40 )] · CH 3 CN ( 1 ) was synthesized. Interestingly, the huge α-keggin ion AsMo 12 is distorted by introduction of CH 3 CN molecules and adopts a chiral assembly with space group P 4 . In contrast, the analogous compound AsW 12 co-crystallizes with trace H 2 O molecules. The hydrogen atoms of H 2 O are positionally disordered with 50 % occupation to correlate with AsW 12 in space group P 4/ m . Solid and solution CD spectra indicate that the crystals of 1 are in R configuration. This leads to the conclusion that molybdenum has greater affinity toward organic CH 3 CN, whereas tungsten has greater affinity to inorganic H 2 O. Additionally, AsMo 12 shows greater deformability than AsW 12 . It is suggested that POMo shows a greater potential as chiral material than POW because of the flexibility of Mo. As a highlight, CH 3 CN can function as a general chiral inducer for the innovation of other chiral crystals, if fixed along one dimension.

Description: P-n junction BiOBr/ZnO composites were prepared by a facile solvothermal process with double Br sources of CTAB and KBr. The samples were characterized by XRD, XPS, SEM, TEM, HRTEM, DRS, BET and PL. The BiOBr/ZnO composites exhibited much higher photocatalytic activity than single BiOBr and ZnO for the degradation of phenol under simulated sunlight irradiation. The enhanced photocatalytic activity of BiOBr/ZnO composites could be mainly ascribed to the high-efficiency separation of photogenerated electron-hole pairs through BiOBr/ZnO p-n junction. The reaction mechanism for the removal of phenol was also discussed. Hole and ·OH were the main reactive species. Moreover, the influence of disparate ratios of double Br sources to BiOBr/ZnO composites was also investigated. The results indicated that the BiOBr/ZnO composites prepared by double Br sources showed better photocatalytic activities than the sample prepared by single Br source. P-n junction BiOBr/ZnO composites were prepared by a facile solvothermal process with double Br sources and the composites exhibited higher photocatalytic activity than BiOBr and ZnO for the degradation of phenol, which could be ascribed to two reasons. One reason may be the high efficient separation of photogenerated electron-hole pairs through BiOBr/ZnO p-n junction. Another one would be the high surface area achieved by adjusting the content of CTAB.

Description: The cloud water content (CWC) in rainy clouds is a crucial parameter to determine the onset and the growth rate of precipitation, and to quantify the associated latent heating rate. No direct retrieval of CWC in rainy cloud from satellite observations is reported due to the difficulties of separating cloud particles from precipitation sized particles. However, based on multiple cloud simulations from the Weather and Research Forecasting (WRF) model, we have found that the CWC profile in warm rains can be well determined by three macro-physical cloud properties of cloud water path (CWP), cloud top height (CTH), and cloud bottom height (CBH). The CBH can be estimated using CWP, CTH and near surface rain rate. We proposed an algorithm with a lookup table for estimating the CWC profile using CWP, CTH and near surface rain rate as inputs. The performance of this algorithm was tested with WRF model simulations and a real drizzle case observed by the CloudSat satellite. Testing verified that the algorithm can retrieve the vertical distribution of CWC correctly with few errors at different spatiotemporal scales. In addition, the algorithm is not confined to particular microphysics schemes and is valid for multiple cloud systems in different areas over the world. This algorithm is expected to improve current knowledge of cloud water content in rainy clouds.

Description: Unusual cold filaments are uncovered during the spring intermonsoon season in the South China Sea (SCS) using a suite of satellite observations. They have a width of about 100 km on average and extend several hundreds of kilometers offshore on the sea surface, providing significant cross-shelf transport of heat and nutrients. The eastward current associated with mesoscale eddies in spring in the western SCS is found to play an important role in the filament formation by advecting coastal cold waters far offshore. The meridional location of the cold filament displays considerable interannual variability ranging between 9 o N and 18 o N, which can be attributed to the interannual south-north shift of the eastward current associated with eddies. It is also found that in the spring, cold filaments have profound effects on the chlorophyll a concentration in the upper ocean and the overlying atmosphere. These findings provide new insights into the role of eddies in cross-shelf exchange and mesoscale air-sea interaction in the marginal seas.

Description: Agricultural production, rural areas, and farmers are three key aspects of agriculture related to sustainable economic and social development in China. Rural development is a process of multi-participation, which involves actors from governments, village committees, villagers, rural economic cooperatives, enterprises, financing institutions, and non-government organizations (NGOs). Based on social network analysis (SNA), this article analyzes the social network structures and characteristics of various actors in different stages of rural development in Yanhe village, Hubei Province, China. The results show that both the village committee and villagers have great influence on rural development; NGOs are the leaders of rural environmental improvement; village cooperatives are the promoters of rural economic development; enterprises are the accelerators of rural construction and development. The study outlines the rural development model in Yanhe village where the village committee is the leader and multiple forms of participation and cooperation are present; there are excellent partnerships and communication mechanisms among the participants. The endogenous and sustainable development model identified from Yanhe village is valuable for other villages in China to adopt.