Distributed Management of Massive Data: an Efficient Fine-Grain Data Access Scheme

This paper addresses the problem of efficiently storing and accessing massive data blocks in a large-scale distributed environment, while providing efficient fine-grain access to data subsets. This issue is crucial in the context of applications in the field of databases, data mining and multimedia. We propose a data sharing service based on distributed, RAM-based storage of data, while leveraging a DHT-based, natively parallel metadata management scheme. As opposed to the most commonly used grid storage infrastructures that provide mechanisms for explicit data localization and transfer, we provide a transparent access model, where data are accessed through global identifiers. Our proposal has been validated through a prototype implementation whose preliminary evaluation provides promising results

Studies of Quaternary Depositional Systems of the Coastal Plain and Inner Continental Shelf along the Georgia Bight: South Carolina and Georgia, U.S.A.

The Quaternary stratigraphy of the continental shelf offshore of South Carolina consists of stratigraphic units deposited in coastal plain, shallow marine, and shelfal environments bound by composite erosional surfaces that developed in response to numerous glacioeustatic cycles and overprinted by regional uplift. These units are commonly distributed laterally rather than stacked vertically, a function of the long-term, low shelf gradient and the resulting lack of accommodation. This study integrates high-resolution geological and geophysical data sets acquired offshore and onshore with existing data onshore into a comprehensive conceptual model describing the Quaternary geologic evolution of the coastal plain and continental shelf within a study area of approximately 8,000 km2. We use seismic facies and core analysis to define stratigraphic units associated with transgressive, regressive, and lowstand systems offshore. Regressive systems include progradational wave- and river-dominated deltaic and shoreface deposits. Lowstand systems consist of a complex network of paleo-incisions produced by regional, Piedmont-draining fluvial systems and smaller coastal-plain rivers. Transgressive systems include paleochannel-fill successions dominated by mud-rich, tidally-influenced backbarrier deposits, cuspate and linear shelf sand ridges; and transgressive sand sheets and shoals. The low-accommodation setting of the continental shelf influences the stratigraphic record in several key ways: 1) the geometry of progradational coastal lithosomes; 2) the development of composite allogenic erosional surfaces; 3) the deposition of widespread, thin transgressive sand sheets; and 4) the restriction of thicker transgressive deposits to paleo-incisions. In this setting, the use of a hierarchical bounding surface scheme is preferable to the more common sequence stratigraphic or allostratigraphic conventions for several reasons: 1) major erosional bounding surfaces are commonly amalgamated; 2) lower-order surfaces capture internal variability which is key to the genetic interpretation of stratigraphic units; and 3) stratal stacking patterns typically used to define a sequence stratigraphic framework are rare

Doctor of Philosophy

dissertationMicrobial bioherms constitute some of the earliest forms of life on Earth. Although the primary form of life on earth during the Proterozoic (Hoffman, 1994), modern occurrences that spread over an area greater than a few square kilometers are rare. Microbial bioherms in Great Salt Lake were reported more than 75 years ago (Eardley, 1938); however, no additional studies have been done on the extent of these structures nor on how environmental factors may influence their distribution. This dissertation documents the development of a methodology to examine the occurrence and spatial distribution of microbial bioherms in Great Salt Lake, Utah, using multiple lines of evidence including marine acoustic technologies, various spatial and aspatial analyses, Geographic Information Systems (GIS) technologies, and in situ verification of bioherm occurrence. Microbial bioherms occupy an estimated area of more than 700 km2 in the south part of the lake and more than 300 km2 along the margins of the north part of Great Salt Lake. Distributions vary from statistically dispersed to clustered and are closely associated with structurally controlled, positive, microtopographical changes in the benthos. Individuals typically are circular to oblate and range in size from centimeters to over 2 meters in diameter. In some areas of the lake, bioherm heights were measured at more than 1.5 meters above adjacent substrate. Observations, videography, and samples of microbial bioherms from the south part of Great Salt Lake, in modern conditions of salinity averaging about 15 percent, are dark green in color, the result of an abundant surface-based phototrophic community that populates the highly rugose surface of the bioherms. Exposed shallow-water bioherms in the north part of the lake are white and not populated by either surface-based phototrophic communities or macroinvertebrate grazers. The environmental conditions in the north part of Great Salt Lake, averaging about 27 percent salinity, have exceeded the ability of bioherm-forming microbial communities to survive. Great Salt Lake provides a glimpse into what Earth was like during the first 3 billion years of its existence and before the emergence of more complex life forms. This investigation has identified how tectonics and environmental conditions influence the initiation and growth of microbially induced carbonates in saline environments and places important constraints on the conditions for microbial life during the present and during early Earth history

Characterization of Quaternary stratigraphy in the Mississippi Sound to evaluate the influence of geologic heterogeneity on submarine groundwater transport and discharge

Submarine Groundwater Discharge (SGD) through seafloor sediments is gaining recognition as an important component of coastal water quality. Stratigraphic features creating geologic heterogeneity, such as incised paleochannels, may influence preferential pathways for SGD. The central Mississippi Sound is underlain by paleochannels that were incised into Pleistocene sediments while the area was subaerially exposed during the last glacial maximum and are now buried by transgressive Holocene deposits. In this thesis, newly collected chirp, previously published seismic reflection, and sediment core data are used to characterize the three-dimensional structure of the Holocene-Pleistocene contact. Results indicate that Pleistocene paleochannels cross-cut the study area, exhibiting depths from 7.3–23.4 m, widths from 0.2–2.5 km, infilling with higher acoustic impedance fluvial sediments, and burial by transgressive Holocene sediments. Results suggest that this shallow subsurface stratigraphy may mediate locations of SGD and aid in predicting SGD pathways and associated contaminant loading into the coastal ocean

Repeated (4D) marine geophysical surveys as a tool for studying the coastal environment and ground-truthing remote-sensing observations and modeling

Sandy beaches and the nearshore environment are dynamic coastal systems characterized by sediment mobilization driven by alternating stormy and mild wave conditions. However, this natural behavior of beaches can be altered by coastal defense structures. Repeated surveys carried out with autonomous surface vehicles (ASVs) may represent an interesting tool for studying nearshore dynamics and testing the effects of mitigation strategies against erosion. We present a one-year experiment involving repeated stratigraphic and morpho-bathymetric surveys of a nearshore environment prone to coastal erosion along the Emilia-Romagna coast (NE Italy), the Lido di Dante beach, carried out between October 2020 and December 2021 using an ASV. Seafloor and subseafloor “snapshots” collected at different time intervals enabled us to delineate the seasonal variability and shed light on key controlling variables, which could be used to integrate and calibrate remote-sensing observations and modeling. The results demonstrated that repeated surveys could be successfully employed for monitoring coastal areas and represent a promising tool for studying coastal dynamics on a medium/short (years/months) timescale

Multi-band Multi-site GNSS RFI Monitoring Results after a Year of Operation

An international network of Radio Frequency Interference (RFI) monitoring stations covering all L-band Global Navigation Satellite System (GNSS) signals has provided large amounts of data on the occurrence rates and characteristics of the detected sources. As the stations are primarily deployed by roadways the measurements include a large number of Personal Privacy Device (PPD) style jammers as well as an unexpectedly large contingent of spurious emissions and co-authorized users. Important results include the high levels of variability in month-to-month activity levels of sites indicating that site survey activities must be conducted over longer periods to obtain accurate occurrence rate information.acceptedVersio

Geologic framework of the northern North Carolina, USA inner continental shelf and its influence on coastal evolution

© The Author(s), 2013. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Marine Geology 348 (2014): 113-130, doi:10.1016/j.margeo.2013.11.011.The inner continental shelf off the northern Outer Banks of North Carolina was mapped using sidescan sonar, interferometric swath bathymetry, and high-resolution chirp and boomer subbottom profiling systems. We use this information to describe the shallow stratigraphy, reinterpret formation mechanisms of some shoal features, evaluate local relative sea-levels during the Late Pleistocene, and provide new constraints, via recent bedform evolution, on regional sediment transport patterns. The study area is approximately 290 km long by 11 km wide, extending from False Cape, Virginia to Cape Lookout, North Carolina, in water depths ranging from 6 to 34 m. Late Pleistocene sedimentary units comprise the shallow geologic framework of this region and determine both the morphology of the inner shelf and the distribution of sediment sources and sinks. We identify Pleistocene sedimentary units beneath Diamond Shoals that may have provided a geologic template for the location of modern Cape Hatteras and earlier paleo-capes during the Late Pleistocene. These units indicate shallow marine deposition 15–25 m below present sea-level. The uppermost Pleistocene unit may have been deposited as recently as Marine Isotope Stage 3, although some apparent ages for this timing may be suspect. Paleofluvial valleys incised during the Last Glacial Maximum traverse the inner shelf throughout the study area and dissect the Late Pleistocene units. Sediments deposited in the valleys record the Holocene transgression and provide insight into the evolutionary history of the barrier-estuary system in this region. The relationship between these valleys and adjacent shoal complexes suggests that the paleo-Roanoke River did not form the Albemarle Shelf Valley complex as previously proposed; a major fluvial system is absent and thus makes the formation of this feature enigmatic. Major shoal features in the study area show mobility at decadal to centennial timescales, including nearly a kilometer of shoal migration over the past 134 yr. Sorted bedforms occupy ~ 1000 km2 of seafloor in Raleigh Bay, and indicate regional sediment transport patterns between Capes Hatteras and Lookout that help explain long-term sediment accumulation and morphologic development. Portions of the inner continental shelf with relatively high sediment abundance are characterized by shoals and shoreface-attached ridges, and where sediment is less abundant, the seafloor is dominated by sorted bedforms. These relationships are also observed in other passive margin settings, suggesting a continuum of shelf morphology that may have broad application for interpreting inner shelf sedimentation patterns.Funding for this research was provided by the USGS Coastal and Marine Geology Program

Configuration of the Pleistocene Surface Beneath Cat Island, Mississippi and Implications for Barrier Island Formation and Evolution

The mechanism of Holocene barrier formation aids in determining island geomorphologic responses to modifying climatic processes of the surrounding environment. The geometry and composition of local antecedent topography plays a role in barrier formation by providing an elevated base, nucleus for sedimentation and local sediment supply. Investigation of barriers\u27 subsurface geology provides insight into island formation and evolution. High-resolution shallow seismic data acquired in the island\u27s nearshore zone and interior canals, correlated with existing drillcore data, reveal that Cat Island, MS is situated over an Oxygen Isotope Stage 3 Phase 3 paleochannel located between two topographic high-grounds of the Pleistocene surface. Beach ridge strandplain sets on Cat Island provide additional evidence supporting the island\u27s formation over a relict depocenter. A new, 4-stage model for Cat Island development and evolution incorporating the influence of pre-existing topographic high-grounds and abundant local sediment supply provided by a backfilling fluvial channel is presented here