M.S.

Groundwater is one of the least studied environments, yet many people rely on groundwater for their sole drinking water supply. Little is known about the indigenous microflora, but it is believed to be similar to oceanic planktobacteria due to the low nutrient concentrations occurring in both ecosystems. That is, groundwater microorganisms are atypically small, mostly Gram-negative cells. Also like the oceanic planktobacteria, they may have no affinity for surface attachment and may rely on dissolved low molecular weight organic substrates in dilute solution for their nutrition. Periods of metabolic dormancy may occur when natural substrate concentrations drop below the level required to sustain vegetative cell function. In these studies total cells present were determined by 4'6-diamidino-2-phenylindole (DAPI) epifluorescent counts. The percentage of those bacteria which were metabolically active was determined by a modification of the 2-(p-iodophenyl)-3-(p- nitrophenyl)- 5-phenyl tetrazolium chloride (INT) reduction method. Advantages of this method over others include more specific fluorochrome staining, ease of transfer of the cells to the slide, time saved, and ease of microscopic viewing. Heterotrophic uptake of aspartate, succinate, glucose and fructose by indigenous bacteria was measured and calculations of maximum uptake velocity (V_max) and a constant (K_t + S_n) equalling the natural substrate concentration (S_n) plus the half-saturation concentration (K_t) were made based on net assimilation (cellular retention) of radiolabeled substrate. Total counts by DAPI staining were 4-12.1 x 10⁴ cells/ml of which 17.4 to 20.85% were metabolically active (INT+). Mean maximum uptake velocities ranged from 1.73 to 2000 nmol/l/hr with aspartate being taken up at the highest rate followed by fructose, succinate and glucose. / Master of Science

The design of unmanned material collection systems requires a great deal of foresight and innovative design on the engineer's part in order to produce solutions to problems operators may encounter in the field. In this thesis, the development of a particulate collection system for use onboard a lightweight, helicopter deployable ground robot is presented. The Unmanned Systems Laboratory at Virginia Tech is developing a ground sampling robot to be carried in the payload pod of a Yamaha RMAX unmanned aerial vehicle. The robot's ultimate objective is to collect material samples from a hazardous environment. The pneumatic system presented here is a novel design developed to collect particulate without draining the resources of the robot. Vacuum samplers have been developed in the past, but they are large and cumbersome and require large amounts of electrical energy to operate. The pneumatic particulate collection system utilizes the kinetic energy from the release of compressed air to transport the particulate to a collection chamber. Consideration is given to the drop in pressure of the air supply tank as it empties, and a feasible air supply tank design is presented. Two forms of particulate collection are investigated experimentally: jet impingement and particle entrainment (i.e. steep attack angle and parallel flow). Turbulent, free jet characteristics and critical velocities of particles are studied. Ultimately, a final design is presented that effectively collects particulate material from the top 5/8" layer of both thick and thin particle beds. / Master of Science

In recent years, the subject of wide-area synchronized measurements has gained a significant amount of attention from the power system researchers. All of this started with the introduction of the Phasor Measurement Unit (PMU), which added a new perspective in the field of wide-area measurement systems (WAMS). With the ever evolving technologies over the years and the need for a more cost effective solution for synchronized frequency measurements, the Frequency Monitoring Network (FNET) was developed and introduced by the Power IT laboratory at Virginia Tech. The FNET is comprised of many Frequency Disturbance Recorders (FDR) geographically distributed throughout the United States. The FDR is a dedicated data acquisition device deployed at the distribution level, which allows for a lower cost and easily deployable WAMS solution. With Internet connectivity and GPS timing synchronization, the FDR provides high accuracy frequency, voltage magnitude and voltage angle data to the remote servers. Although the current FDR design is up to the standard in terms of the measurement accuracy and portability, it is of interest to further the research into alternative architectures and leverage the ever advancing technologies in high speed computing. One of the purposes of this dissertation is to present novel design options for a new generation of FDR hardware design. These design options will allow for more flexibility and to lower reliance on some vendor specific components. More importantly, the designs seek to allow for more computation processing capabilities so that more accurate frequency and angle measurements may be obtained. Besides the fact that the accuracy of frequency and angle measurement is highly dependent on the hardware and the algorithm, much can be said about the role of timing synchronization and its effects on accurate measurements. Most importantly, the accuracy of the frequency and angle estimation is highly dependent on the sampling time of local voltage angles. The challenges to accurate synchronized sampling are two folds. One challenge has to do with the inherent fallbacks of the GPS receiver, which is relatively high cost and limited in availability when the satellite signal is degraded. The other challenge is related to the timing inaccuracies of the sampling pulses, which is attributed to the remainder that results from the imperfect division of the processor counter. This dissertation addresses these issues by introducing the implementation of the high sensitivity (indoor) GPS and network timing synchronization, which aims to increase the availability of frequency measurements in locations that would not have been possible before. Furthermore, a high accuracy timing measurement system is introduced to characterize the accuracy and stability of the conventional crystal oscillator. To this end, a new method is introduced in close association with some prior work in generating accurate sampling time for FDR. Finally, a new method is introduced for modeling the FDR based on the sampling time measurements and some results are presented in order to motivate for more research in this area. / Ph. D.

Aerobic degradation of hydrocarbon contaminants in anaerobic ground water would be enhanced by oxygenating the water. However, when a contaminated ground water contains high concentrations of reduced iron, competition for oxygen may occur. This study was designed to study this competition. The oxidation of iron and biodegradation of organics was studied in a 12 in X 2.5 in soil column by injecting either oxygen microbubbles or hydrogen peroxide into the soil matrix to provide a source of oxygen. The effluent concentrations of organic and inorganic constituents and the head losses were monitored after injecting oxygen. First, iron oxidation alone was studied. Second, biodegradation of the organic compound was studied. Finally, the simultaneous iron oxidation and biodegradation of organic compound was carried out. The effect of different Fe2+ concentrations in water on the biodegradation of the organic contaminants was evaluated. It was intended to determine whether iron oxidation or biodegradation of organic compound would cause more plugging in soil. The oxidation efficiencies using oxygen microbubbles and peroxide were compared. It was concluded that at high concentrations of Fe2+ in water, iron is rapidly oxidized utilizing most of the available oxygen. At low Fe2+ concentrations, biodegradation efficiency was high. Oxygen microbubbles were found to be slightly more effective than hydrogen peroxide in transferring oxygen to ground water and oxidizing iron or biodegrading organic contaminants. Soil plugging was found to occur regardless of the method of oxygen delivery. The use of coarse media removal system seemed to solve the problem. / Master of Science

Combinatorial control of transcription is a well established phenomenon in the cell. Multiple transcription factors often bind to the same transcriptional control region of a gene and interact with each other to control the expression of the gene. It is thus necessary to consider the joint conservation of sequence pairs in order to identify combinations of binding sites to which the transcription factors bind. Conventional motif finding algorithms fail to address this issue. We propose a novel biclustering algorithm based on random sampling to identify candidate binding site combinations. We establish bounds on the various parameters to the algorithm and study the conditions under which the algorithm is guaranteed to identify candidate binding sites. We analyzed a yeast cell cycle gene expression data set using our algorithm and recovered certain novel combinations of binding sites, besides those already reported in the literature. / Master of Science

A detailed statistical study was performed on molluscan fossil assemblages collected from the Pliocene Morgarts Beach Member of the Yorktown Formation, located in Isle of Wight County, southeast Virginia. The principal objectives of this study were to examine potential sampling problems and biases inherent in paleontological research. This has been accomplished by statistically testing for the homogeneity, or lack thereof, in species assemblages obtained from samples collected from three localities within the Morgarts Beach Member. Multivariate analysis of variance, two-way analysis of variance, multiple comparison tests and cluster analysis were performed on data collected from a five horizon by five section sampling grid (18 feet [5.5 meters] high, 21 feet [6.4 meters] long) located at Morgarts Beach, Virginia. The results of this analysis demonstrate that the relative abundances of species present in the five horizons are significantly different, whereas the relative abundances of species present in the five sections are not significantly different. Results from cluster analysis show that species assemblages contained in samples collected from the Morgarts Beach Member located at Rushmere are substantially different from the Morgarts Beach type area assemblages, in terms of relative abundances of species. The reason for the lack of faunal similarity relates to the documented facies change between the two localities. The results demonstrate that there is no reliable method to obtain accurate census data (frequency abundance curves) from biostratigraphic or lithostratigraphic units deposited during anything but a restricted time interval. In addition, replicate sampling was found to be unnecessary when attempting to determine the relative abundances of species contained in closely spaced sections within the Morgarts Beach Member. Species accumulation curves were constructed from the data collected from the Morgarts Beach Member. Examination of these curves demonstrate that many rare species will not be found unless extensive collecting is undertaken. / Master of Science

Street trees are a subpopulation of the urban forest resource and exist in the rights-of-way adjacent to public roads in a municipality. Benefit-cost analyses have shown that the annual benefits provided by the average street tree far outweigh the costs of planting and maintenance. City and municipal foresters spend a majority of their time and resources managing street tree populations. Sample street tree inventories are a common method of estimating municipal street tree populations for the purposes of making urban forest policy, planning, and management decisions. i-Tree Streets is a suite of software tools capable of producing estimates of street tree abundance and value from a sample of street trees taken along randomly selected sections (segments) of public streets. During sample street tree inventories conducted by Virginia Tech Urban Forestry, it was observed that the lengths of the sample streets recommended by i-Tree varied greatly within most municipalities leading to concern about the impact of street length variation on sampling precision. This project was conducted to improve i-Tree Streets by changing the recommended sampling protocol without altering the software. Complete street tree censuses were obtained from 7 localities and standardized using GIS. The effects of standardizing street segments to 3 different lengths prior to sampling on the accuracy and precision of i-Tree Streets estimates were investigated though computer simulations and analysis of changes in variation in number of trees per street segment as a basis for recommending procedural changes. It was found that standardizing street segments significantly improved the precision of i-Tree Streets estimates. Based on the results of this investigation, it is generally recommended that street segments be standardized to 91m (300 ft) prior to conducting a sample inventory. Standardizing to 91m will significantly reduce the number of trees, the number of street segments, and the percentage of total street segments that must be sampled to achieve an estimate with a 10% relative standard error. The effectiveness of standardization and the associated processing time can be computed from municipal attributes before standardization so practitioners can gauge the marginal gains in field time versus costs in processing time. Automating standardization procedures or conducting an optimization study of segment length would continue to increase the efficiency and marginal gains associated with street segment standardization. / Master of Science

The hemlock woolly adelgid (HWA), Adelges tsugae Annand (Hemiptera: Adelgidae), is an invasive pest from Japan that is causing significant hemlock mortality in the eastern U.S. The most promising control method is biological control. Beetles in the genus Laricobius are adelgid specialists. In 2005, Laricobius osakensis, was discovered in Japan and in 2010 was approved for release in the eastern United States and there have now been more than 60 releases. In 2014, the polar vortex resulted in significant HWA mortality in the eastern U.S., depleting the food source for L. osakensis, which resulted in low field recoveries of them. In the 2015-2016 field season, there were 14 larvae recovered from the field, and the 2016-2017 field season yielded 90 larvae. A significant correlation was found between Laricobius beetles recovered and HWA density, between HWA density and plant hardiness zone, and a negative correlation between Laricobius beetles recovered and average tree health. Understanding more about the supercooling point of L. osakensis gave insight to its ability to survive subfreezing temperatures as occurred in 2014. Comparison of the supercooling point between the northern and southern populations of L. osakensis, and to the other released HWA predator, L. nigrinus, will allow us to determine which biological control agent is best suited for release in the coldest regions. The overall mean supercooling points of northern L. osakensis was -13.52 oC, southern L. osakensis was -13.42 oC, and L. nigrinus was -13.57 oC. There were no significant differences between species or populations. / Master of Science in Life Sciences

M. S.