Open Access. Powered by Scholars. Published by Universities.®

Physical Sciences and Mathematics Commons

Open Access. Powered by Scholars. Published by Universities.®

2014

Masters Theses

Discipline
Institution
Keyword

Articles 1 - 30 of 91

Full-Text Articles in Physical Sciences and Mathematics

Investigating The Effects Of Urbanization On Residual Forest Soils In Knox Co., Tennessee, Benjamin Lee Reichert Dec 2014

Investigating The Effects Of Urbanization On Residual Forest Soils In Knox Co., Tennessee, Benjamin Lee Reichert

Masters Theses

As the process of urbanization advances across the country, so does the importance of urban forests, which include both trees and the soils in which they grow. Soil microbial biomass, which plays a critical role in nutrient transformation in urban ecosystems, is affected by factors such as soil type and the availability of water, carbon, and nitrogen. However, the microbial dynamics of urban forest soils remain largely unknown. A key mechanistic link between plant species diversity and ecosystem function is heterotrophic microbial communities that inhabit the soil and mediate principal processes that control ecosystem carbon (C) and nitrogen (N) cycling. …


Structural And Metamorphic Evolution Of The Haimanta Group: Insights From P-T-T-D Path Modeling Of Rocks Near The Leo Pargil Dome, Nw India, Kyle Vincent White Dec 2014

Structural And Metamorphic Evolution Of The Haimanta Group: Insights From P-T-T-D Path Modeling Of Rocks Near The Leo Pargil Dome, Nw India, Kyle Vincent White

Masters Theses

The metasedimentary rocks of the Haimanta Group in the upper Sutlej Valley, NW India, record an extensive history of Himalayan deformation and metamorphism. Situated beneath the low-grade metasediments of the Tethyan Sedimentary sequence in the hanging wall of the South Tibetan detachment system (STDS), these poly-deformed rocks record Eocene–Oligocene burial metamorphism, crustal thickening and shortening, decompression and mid-crustal melting in the early Miocene, and exhumation along extensional shear zones related to the orogen-parallel exhumation of the Leo Pargil dome (LPD). Low-pressure assemblages (cordierite + sillimanite + quartz) overgrow Barrovian porphyroblasts in Haimanta Group rocks in the NE portion of Sutlej …


Detecting Tropical Cyclone Signals In Tree Rings Of Longleaf Pine (Pinus Palustris Mill.), Valdosta, Georgia, U.S.A., Savannah Anne Collins Dec 2014

Detecting Tropical Cyclone Signals In Tree Rings Of Longleaf Pine (Pinus Palustris Mill.), Valdosta, Georgia, U.S.A., Savannah Anne Collins

Masters Theses

The study of past hurricanes to help interpret the patterns of current and future tropical storms is vital to our economy, society, and infrastructure. Understanding how hurricanes are influenced by a warm climate is critical, and hurricane reconstructions from former periods of the Holocene (the last ~11,500 yr) will be beneficial. Paleotempestology is the study of past tropical cyclones and uses historical, biological, and geological proxies to reconstruct tropical cyclone activity to create a record of historical hurricane patterns. A tropical cyclone (TC) is a chaotic weather event that is influenced by several elements, including warm ocean waters from which …


Laser-Induced Breakdown Spectroscopy For Analysis Of High Density Methane-Oxygen Mixtures, Matthew Dackman Dec 2014

Laser-Induced Breakdown Spectroscopy For Analysis Of High Density Methane-Oxygen Mixtures, Matthew Dackman

Masters Theses

The applicability of laser-induced breakdown spectroscopy (LIBS) toward greater than atmospheric density combustion diagnostics is examined. Specifically, this involves ascertaining the feasibility of measuring chemical equivalence ratios directly from atomic emission spectra at high density. The need for such measurement arises from the desire to quantify real time, localized combustion performance in weakly mixed flows. Insufficiently mixed flows generally result in unwanted byproducts, possess the propensity for overall combustion instability, and are increasingly likely to experience localized flame extinction.

We simulate methane/oxygen combustion in ambient pressures ranging 1 to 4 atmospheres, demonstrating these results to be analogous to what would …


A Remote Sensing Based Early Warning System For Algal Blooms In Kuwait Bay And Coastal Waters, Cameron Manche Dec 2014

A Remote Sensing Based Early Warning System For Algal Blooms In Kuwait Bay And Coastal Waters, Cameron Manche

Masters Theses

The Kuwait Bay and its coastal waters are being threatened by a perpetual hazard, the proliferation of harmful algal blooms (HABS). The frequency of HAB occurrences is a growing problem that is only reported subsequent to the onset of a HAB event. Little effort has been invested in investigating the spatial and temporal distribution of these events in Kuwait Bay and even less is known about their controlling factors. All previous studies within the Kuwait Bay have focused either on measuring nutrient availability and the biodiversity of algal species.

The overall study objective is four-fold: (1) to monitor the spatial …


Design And Model Of The Frame For Hagrid (Hybrid Array Of Gamma Ray Detectors), Santiago Munoz Dec 2014

Design And Model Of The Frame For Hagrid (Hybrid Array Of Gamma Ray Detectors), Santiago Munoz

Masters Theses

Transfer reactions in inverse kinematics have provided critical information in the study of exotic nuclei. However, transfer reactions with charged particles suffer from poor resolution. The measurement of gamma-rays offers several advantages: they provide not only good resolution in measurements but also other information about the nuclei like lifetimes of unstable states. The combination of these two methods would be the ideal situation to gather information about nuclear structure.

HAGRiD, which stands for The Hybrid Array of Gamma Ray Detectors, is a LaBr3(Ce) [lanthanum bromide crystal with a cerium activator] scintillation array to measure gamma rays from transfer reactions and …


Transport Of Fecal Pollution Indicators: Impacts From The Land Spreading Of Liquid Manure On Water Quality, Derek Lee Street Dec 2014

Transport Of Fecal Pollution Indicators: Impacts From The Land Spreading Of Liquid Manure On Water Quality, Derek Lee Street

Masters Theses

This thesis is a case study to determine if groundwater and/or drainage tiles are important pathways for fecal migration to streams resulting from the application of liquid manure to cropland at a small dairy farm, the Little River Animal and Environmental Unit, near Townsend, TN. Traditional biological indicators, coliforms and E.coli, were used in conjunction with a bovine specific Bacteroides assay to measure fecal microbes. Total nitrates, turbidity, and other chemical parameters for water quality also were used to identify related fecal contamination. This thesis covers three separate manure applications. The first manure application occurred in May 2013, the …


Estimating Streambank Erosion Using Gps-Based Watershed-Scale Video Mapping And Usepa Bancs For The Development Of Sediment Tmdls, Kelsey Jo Hensley Dec 2014

Estimating Streambank Erosion Using Gps-Based Watershed-Scale Video Mapping And Usepa Bancs For The Development Of Sediment Tmdls, Kelsey Jo Hensley

Masters Theses

According to the United States Environmental Protection Agency (USEPA), sediment is one of the most common water pollutants in the nation’s rivers. Consequently, the identification of streambank locations with high erosion potential is important in reducing sediment input via management and monitoring practices. Furthermore, the estimation of erosion rates and sediment loads can assist in the development of Total Maximum Daily Loads (TMDLs). The objective of this study was to integrate two USEPA-recommended approaches with the Streambank Video Mapping System (SVMS) in order to predict site-specific Total Daily Sediment Loads (TDSLs) and calculate sediment TMDLs for streambank erosion over several …


Metamorphic Evolution Of Eastern Blue Ridge Calc-Silicates In Southwestern North Carolina, Northeastern Georgia, And Northwestern South Carolina, Gina Brianne Smith Dec 2014

Metamorphic Evolution Of Eastern Blue Ridge Calc-Silicates In Southwestern North Carolina, Northeastern Georgia, And Northwestern South Carolina, Gina Brianne Smith

Masters Theses

Calc-silicate rocks in the eastern Blue Ridge of SW North Carolina, NE Georgia, and NW South Carolina are products of contact and regional metamorphism. Two types of calc-silicates occur in this area: Type A rocks occur as contact metamorphosed xenoliths in the ~336 Ma Rabun Granodiorite batholith, and Type B rocks occur as mappable thin, elongate, ribbon-like units in the Tallulah Falls Formation east of the Rabun batholith. Petrographic and geochemical data confirm similar composition for both types and mineral assemblages that includes amphibole, garnet, epidote, diopside, quartz, and plagioclase with accessory zircon, sphene, and opaque minerals. Calcite, however, is …


The Cumulative Impacts Of Climate Change And Land Use Change On Water Quantity And Quality In The Narragansett Bay Watershed, Evan R. Ross Nov 2014

The Cumulative Impacts Of Climate Change And Land Use Change On Water Quantity And Quality In The Narragansett Bay Watershed, Evan R. Ross

Masters Theses

Narragansett Bay, Rhode Island, is a valuable natural resource that suffers summer hypoxic events resulting from over a century of cultural eutrophication. Current efforts to reduce nitrogen loading from wastewater treatment facilities discharging into the Bay and its tributaries hold the promise of working towards ecological restoration. But, the efficacy of these efforts may be limited, or undone, if future changes in climate or land use increase nutrient and sediment loads to the Bay. This study developed a SWAT model of the upper Narragansett Bay watershed to simulate water quantity and quality. The baseline model was calibrated and validated to …


Sedimentological, Geochemical And Isotopic Evidence For The Establishment Of Modern Circulation Through The Bering Strait And Depositional Environment History Of The Bering And Chukchi Seas During The Last Deglaciation, Ben M. Pelto Nov 2014

Sedimentological, Geochemical And Isotopic Evidence For The Establishment Of Modern Circulation Through The Bering Strait And Depositional Environment History Of The Bering And Chukchi Seas During The Last Deglaciation, Ben M. Pelto

Masters Theses

Sea level regression during the Last Glacial Maximum exposed the Bering Land Bridge, and cut off the connection between the North Pacific and Arctic Ocean, ending the exchange of North Pacific Water through the Bering Strait. Exchange of North Pacific Water comprises a major portion of fresh water input to the Arctic Ocean, and is of vital importance to North Atlantic Deep Water formation, a vital component of Atlantic Meridional Overturning Circulation. Bering Strait throughflow thus plays an integral role in global climate stability. A suite of four cores was selected, three in the Bering Sea and one in the …


Estimating Prevalence From Complex Surveys, Sophie O'Brien Nov 2014

Estimating Prevalence From Complex Surveys, Sophie O'Brien

Masters Theses

Massachusetts passed legislation in the fall of 2012 to allow the construction of three casinos and a slot parlor in the state. The prevalence of problem gambling in the state and in areas where casinos will be constructed is of particular interest. The goal is to evaluate the change in prevalence after construction of the casinos, using a multi-mode address based sample survey. The objective of this thesis is to evaluate and describe ways of using statistical inference to estimates prevalence rates in finite populations. Four methods were considered in an attempt to evaluate the prevalence of problem gambling in …


Volatile Profiles And Resistance To Herbivory In Eastern Hemlock, Elizabeth A. Mckenzie Nov 2014

Volatile Profiles And Resistance To Herbivory In Eastern Hemlock, Elizabeth A. Mckenzie

Masters Theses

Eastern hemlock hosts the hemlock woolly adelgid, an introduced sap-feeding insect that causes rapid deterioration of the host. Like most conifers, eastern hemlock produces a variety of constitutive and induced defenses, primarily terpenoids. To explore the relationship of terpenoid defenses with adelgid infestations, we artificially infested hemlocks at a forest site and a plantation site, and compared their terpenoid concentrations to those in control trees. Infested trees showed lower terpenoid concentrations than control trees, suggesting that eastern hemlock not only fails to induce production of terpenoids in response to adelgid infestation, but becomes less able to produce carbon-based defenses due …


The Timing Of Deformation In The Four Peaks Area, Central Arizona, And Relevance For The Mazatzal Orogeny, Calvin A. Mako Nov 2014

The Timing Of Deformation In The Four Peaks Area, Central Arizona, And Relevance For The Mazatzal Orogeny, Calvin A. Mako

Masters Theses

The Mazatzal orogeny (1.66-1.60 Ga) is a key element of the tectonic evolution of the North American continent during the Proterozoic (Whitmeyer and Karlstrom, 2007). Recently, Mesoproterozoic detrital zircon grains (1.55-1.45 Ga) have been found in metasedimentary rocks that were thought to have been deformed during the Paleoproterozoic Mazatzal orogeny (Jones et al. 2011; Doe et al. 2012, 2013; Daniel et al. 2013). Some type examples Mazatzal deformation now seem to be too young to have been deformed in the accepted time of that orogeny (1.66-1.60 Ga) and may have been deformed in the younger, newly defined, Picuris orogeny. This …


Evolution Of Off-Fault Deformation Along Analog Strike-Slip Faults, Alexandra E. Hatem Nov 2014

Evolution Of Off-Fault Deformation Along Analog Strike-Slip Faults, Alexandra E. Hatem

Masters Theses

Strike-slip faults evolve to accommodate more fault slip, resulting in less off-fault deformation. In analog experiments, the measured fault slip to off-fault deformation ratios are similar to those measured in crustal strike-slip systems, such as the San Andreas fault system. Established planar faults have the largest fault slip to off-fault deformation ratio of ~0.98. In systems without a pre-existing fault surface, crustal thickness and basal detachment conditions affect shear zone width and roughness. However, once the applied plate displacement is 1-2 times the crustal thickness, partitioning of deformation between fault slip and off-fault distributed shear is >0.90, regardless of the …


From ~1.5 Ma To Today: Insights Into The Southern San Andreas Fault System From 3d Mechanical Models, Laura Fattaruso Nov 2014

From ~1.5 Ma To Today: Insights Into The Southern San Andreas Fault System From 3d Mechanical Models, Laura Fattaruso

Masters Theses

Three-dimensional mechanical simulations of the San Andreas fault (SAF) within the Coachella Valley in California produce deformation that match geologic observations and demonstrate the impact of fault geometry on uplift patterns. Most models that include the Coachella Valley segment of the SAF have assumed a vertical orientation, but recent studies suggest that this segment dips 60-70° northeast. We compare models with varied fault geometry and evaluate how well they reproduce observed uplift patterns. Our model with a dipping SAF matches geologic observations, while models containing a vertical fault do not. This suggests that the active Coachella Valley segment of the …


Modification Of Gold Nanoparticles For Sers Application In Emulsion And Lipid Systems, Michael J. Driver Nov 2014

Modification Of Gold Nanoparticles For Sers Application In Emulsion And Lipid Systems, Michael J. Driver

Masters Theses

Gold nanoparticles produced using the Turkevich method were able to have their hydrophobicity modified using octanethiol in a novel method for SERS application. Both amphiliphic GNPs and hydrophobic GNPs were produced and differentiated by Raman signals. The amphiliphic GNPs were able to enhance the SERS signals of the protein emulsifier in the emulsion in situ and the hydrophobic GNPs were able to enhance the SERS signals from canola oil. Further purification of the hydrophobic GNPs proved to have higher enhancement and sensitivity, but still poor consistency which is typical of SERS. Monitoring lipid oxidation using Raman and SERS using alternative …


Cell-Based Sensing Of Endocrine Disrupting Substances Using Fluorescent Protein-Gold Nanoparticle Complexes, Xian Wang Aug 2014

Cell-Based Sensing Of Endocrine Disrupting Substances Using Fluorescent Protein-Gold Nanoparticle Complexes, Xian Wang

Masters Theses

Developing a sensitive and effective in vitro bioassay to detect endocrine disrupting chemicals (EDCs) would reduce the cost, eliminate the possibility of low dose effects, detect the non-monotonic dose responses, and identify mechanisms of actions. The “chemical nose” sensing method using supramolecular complexes composed of cationic monolayer functionalized gold nanoparticles (AuNPs) and fluorescent proteins (FPs) can successfully distinguish serum proteins, mammalian cells, tissue lysates, and chemotherapeutic drug mechanisms. EDCs regulate target cells via genomic or non-genomic pathways in terms of proliferative effect and response time. In this thesis, green fluorescent protein-gold nanoparticle (GFP-AuNP) sensors were used to detect the proliferative …


Ecology And Conservation Of Endangered Species In Sumatra: Smaller Cats And The Sumatran Rhinoceros (Dicerorhinus Sumatrensis) As Case Studies, Wulan Pusparini Aug 2014

Ecology And Conservation Of Endangered Species In Sumatra: Smaller Cats And The Sumatran Rhinoceros (Dicerorhinus Sumatrensis) As Case Studies, Wulan Pusparini

Masters Theses

While we should celebrate the bicentennial of naming the Sumatran rhinoceros (SR), the only extant population on earth might be on the island of Sumatra. Since Strien's 1986 study in Mamas Valley, Leuser, very little more has been learned about how this species distributed and what factors are influencing its extirpation. This study is the first conducted in Sumatra at an Island-wide scale. Using hierarchical models, I estimate the occurrence rates (%) and indices of abundance of SR on three remaining population areas: Leuser Landscape (LL) in 2007 (2.77%, 26 (CI 12-61)), Way Kambas (WK) in 2008 (33.58%, 27 (CI …


Gpu-Accelerated Influenza Simulations For Operational Modeling, Peter Holvenstot Aug 2014

Gpu-Accelerated Influenza Simulations For Operational Modeling, Peter Holvenstot

Masters Theses

Simulations of influenza spread are useful for decision-making during public-health emergencies. Policy-makers use models to predict disease spread and estimate the effects of various intervention strategies. Effective modeling of targeted intervention strategies requires accurate modeling of individual-level behavior and transmission. However, this greatly increases the computational costs of these agent-based models. In addition, if the models are used as an outbreak progresses, some operational decisions must occur rapidly in order to contain the spread of the disease.

Graphics Processing Units (GPUs) are a type of specialized processor used to drive graphical displays. Many recent devices also allow users to write …


Electron Transfer In Pnicogen Bond, Liangyu Guan Aug 2014

Electron Transfer In Pnicogen Bond, Liangyu Guan

Masters Theses

Abstract is available for download as a separate file.


Comparison Of Triangle And Tetrad Discrimination Methodology In Applied, Industrial Manner, Sara Lyn Carlisle Aug 2014

Comparison Of Triangle And Tetrad Discrimination Methodology In Applied, Industrial Manner, Sara Lyn Carlisle

Masters Theses

The triangle method has been widely used in the food industry for many years when conducting sensory discrimination testing. Recently, however, another discrimination testing method, the tetrad, has begun to gain popularity. Based on currently published research, the tetrad method possesses statistical advantages over the triangle and would require fewer panelists, reduce testing time, and use less sample material. More testing is needed to confirm these advantages in an applied, industrial approach on a wider range of products. Over thirty triangles and thirty tetrads with untrained panelists have been completed in order to compare the two methods. Products tested ranged …


Data Analytics Of University Student Records, Mark Blaise Decotes Aug 2014

Data Analytics Of University Student Records, Mark Blaise Decotes

Masters Theses

Understanding the proper navigation of a college curriculum is a daunting task for students, faculty, and staff. Collegiate courses offer enough intellectual challenge without the unnecessary confusion caused by course scheduling issues. Administrative faculty who execute curriculum changes need both quantitative data and empirical evidence to support their notions about which courses are cornerstone. Students require clear understanding of paths through their courses and majors that give them the optimal chance of success. In this work, we re-envision the analysis of student records from several decades by opening up these datasets to new ways of interactivity. We represent curricula through …


Structure Analysis Of Sn Bilayer Films On Si (111), Weisong Tu Aug 2014

Structure Analysis Of Sn Bilayer Films On Si (111), Weisong Tu

Masters Theses

Chemical doping is a well-established method for controlling the electronic properties of bulk semiconductors and, e.g, complex oxide materials. In this process, dopant atoms are located at substitutional lattice locations, from where they introduce free charge carriers to the host material. These carriers greatly improve the electrical conductivity of the host material and can even induce an insulator-metal transition at high doping levels. Dopants, however, also introduce scattering centers that are detrimental to conductivity, especially in low-dimensional systems such as nanowires and ultrathin films. These problems can be overcome by using a modulation doping approach in which the dopant atoms …


Radiation-Induced Radicals In Polyurea-Crosslinked Silica Aerogel, Benjamin Michael Walters Aug 2014

Radiation-Induced Radicals In Polyurea-Crosslinked Silica Aerogel, Benjamin Michael Walters

Masters Theses

Free radicals are atoms or molecules with an odd number of electrons in an outer shell. Since electrons typically occur in pairs, this leaves one electron that is unpaired. In seek of another electron to pair with, free radicals react with and steal electrons from neighboring molecules, which then become free radicals themselves. This can start a chain reaction, cascading into large scale damage.

Ionizing radiation can tear through molecules, just as bullets can tear through things that we see. If free radicals can be detected, and seen to increase in a material upon radiation exposure, this can indicate molecular …


Mineralized Microbialites As Archives Of Environmental Evolution Of A Hypersaline Lake Basin: Laguna Negra, Catamarca Province, Argentina, Joy Buongiorno Aug 2014

Mineralized Microbialites As Archives Of Environmental Evolution Of A Hypersaline Lake Basin: Laguna Negra, Catamarca Province, Argentina, Joy Buongiorno

Masters Theses

Environmental fluctuations related to climate, biological productivity, and evaporation can be recorded by sedimentary archives within lacustrine depositional systems. Sediments within terminal, closed-basin lakes are amongst the most sensitive paleoenvironmental indicators, and have great potential for permitting detailed reconstruction of environmental conditions via a variety of geochemical and isotopic proxies. Microbialites, however, have been largely overlooked as repositories of paleoenvironmental data. Here, we investigate mineralized microbialites within Laguna Negra, a high-altitude (4100 meters above sea level) hypersaline, closed-basin lake in the Argentinian Puna region and explore the potential recovery of environmental signals from these unique sedimentary archives. Mineralized microbialites within …


Measuring Carbon Dioxide (Co2) Flux Of Agricultural Practices In Sub-Saharan Africa, Debra Blumberg O'Dell Aug 2014

Measuring Carbon Dioxide (Co2) Flux Of Agricultural Practices In Sub-Saharan Africa, Debra Blumberg O'Dell

Masters Theses

Agriculture has an important role in addressing two of the world’s most pressing problems: meeting global food demand and mitigating climate change. If agriculture is not practiced sustainably it will fail to meet future food demand and likely intensify the pace of global climate change. There are some agricultural practices, such as Conservation Agriculture, that can produce food sustainably and have the potential to mitigate climate change. However it is not clear which agricultural practices contribute to climate mitigation and by how much. By measuring the carbon dioxide (CO2) emissions of specific agricultural practices, the ability of practices to sequester …


Michigan's Clay Bluffs: The Description And Comparison Of An Erosion-Dependent Natural Community, Nathaniel G. Fuller Aug 2014

Michigan's Clay Bluffs: The Description And Comparison Of An Erosion-Dependent Natural Community, Nathaniel G. Fuller

Masters Theses

The clay bluffs of Michigan are a natural community found along the shores of the Great Lakes. Groundwater is found to be critical to sustaining the alkaline wetlands on the face of the bluff as well as the source of most erosion events. The clay bluffs are unusual in their vegetation, disturbance regime and geographical context. This thesis focuses primarily on describing seeping clay bluffs and exploring the comparison to other natural communities. The purpose of this is twofold, to better understand the ways in which natural communities are described as distinct from one another, and to assess the distinctness …


An Analysis Of The Suspended Sediment Rating Curve Parameters In The Upper Mississippi River Basin At The Monthly And Annual Levels, Vi Thi Tuong Tran Aug 2014

An Analysis Of The Suspended Sediment Rating Curve Parameters In The Upper Mississippi River Basin At The Monthly And Annual Levels, Vi Thi Tuong Tran

Masters Theses

Suspended sediment rating curve parameters were analyzed to investigate the relationship of suspended load and discharge in the Upper Mississippi River Basin (UMRB) at the annual and monthly levels. The rating curve parameters were obtained from the power function of load and discharge: Load = a × (Discharge)b [(Discharge)^b]. The function was solved by ordinary least squares regression on its logarithmic form.

The annual rating coefficient a and exponent b ranged from 0 to 0.25 (kg/s)(s/m3)b [(kg/s)(s/m^3)^b] and from 0.91 to 4.27, respectively. The monthly rating coefficient a and exponent b ranged from 0 to 0.239 …


Effects Of Road Salt On Asylum Lake Geochemistry, Davina A. Wyman Aug 2014

Effects Of Road Salt On Asylum Lake Geochemistry, Davina A. Wyman

Masters Theses

Several studies indicate that seasonal applications of road deicers can lead to saline runoff entering surface water and groundwater, which can in turn change the chemistry, density, and physical mixing patterns of urban lakes. An investigation at Asylum Lake, an urban lake located near three major roadways, was conducted to determine the degree of road salt contamination in the lake, to determine if salt loading disrupts seasonal mixing patterns, and to determine the extent of redox stratification present due to eutrophic conditions. Samples were collected monthly from the deepest point in Asylum Lake over a 19-month period and analyzed for …