The current methodologies in body scanning diagnostic uses different simultaneous imaging modalities like Ultrasound (US), magnetic resonance imaging (MRI), single photon emission tomography (SPECT) and positron emission tomography (PET). The field requires combination of different modalities for effective use in clinical diagnostics. Such incorporation of different modalities has already been achieved. For example, PET-CT hybrid scanner is designed to acquire align functional and anatomical images and recently US-MRI scanner has successfully shown to improve diagnosis of prostate cancer. The non ionizing radiation hybrid US-MRI is of great interest in health care industry. Further these US and MRI modalities uses different contrast agents like micro-sized gas bubbles (MBs) encapsulated by surfactant for US and superparamagnetic nanoparticles for MRI imaging modalities to further enables new diagnostic opportunities and therapeutic applications. Recently in our 3MiCRON project, we have developed the multimodal contrast agent that could be supported for both US and MRI. This was achieved by coating the magnetic nanoparticles to the poly vinyl alcohol (PVA) surfactant shelled MBs. The nanoparticles in the shell effect the structure can alter the MBs performance as an ultrasound contrast agent. The present thesis is conducted to examine the acoustic and mechanical properties of such multimodal contrast agents. These multimodal contrast agents were prepared by coating the surface of PVA-shelled MBs by two following strategies: (1) The superparamagnetic iron oxide (Fe3O4) nano-particles (SPIONs) were chemically anchored to the surface of poly vinyl alcohol (PVA) shelled MBs namely MBs-chem and (2) in the second strategy the SPIONs were physical entrapped into the PVA shell while formation of PVA surface on the gas bubble were named as MBs-phys. To understand the scattering efficiency and viscoelastic properties of these modified agents, we investigated the backscattering power, attenuation coefficient and phase velocity measurements. Our acoustic experimental results indicate that both the modified MBs and non-modified plain PVA-shelled ultrasound contrast agents have the same echogenic response. The investigation of mechanical properties of modified MBs revealed that the attached SPIONs on the PVA shell has reduced the stiffness of MBs-chem shell, while, the SPIONs inside the shell has increased MBs-phys stiffness. As a result, MBs-chem exhibits soft shell behavior under ultrasound exposure than both MBs-phys. Finally, the images were obtained through the MRI investigations at the department of Radiology, Karolinksa Institute, has demonstrated that both MB types have enough magnetic susceptibility that further provides good detectability in vitro and in vivo. As an outlook, the modified magnetic gas bubbles, i.e. both MBs-chem and MBs-phys can be proposed as a potential contrast agent for both US and MR imaging and can be further utilized in potential therapeutic applications. / <p>QC 20131126</p>

Earlier research has demonstrated that downstream of combustion in a rotating detonation engine, exhaust flow periodically reverses circumferential direction. For small periods, the circumferential flow reaches velocity magnitudes rivaling the bulk flow of exhaust, manifesting as a swirl. The minimization of this swirl is critical to maximizing thrust and engine performance for rocket propulsion. During this study, numerous nozzle contours were iteratively designed and analyzed for losses analytically. Once a nozzle was chosen, further losses were validated through computational fluid dynamics simulations and then tested experimentally. Three different configurations were run with the RDRE: no nozzle, a nozzle without a spike, and a nozzle with a spike. Images of the exhaust quality were recorded using OH* chemiluminescence in high-speed cameras. One camera was used to confirm the existence of a detonation and the frequency of detonation. The second camera is pointed perpendicular to the exhaust flow to capture the quality of exhaust. Quantitative results of the turbulent velocity fluctuations were obtained through particle image velocimetry of the side-imaging frames. All frames in each case were exported and converted to several time-averaged frames whereupon the time-averaged turbulent velocity fluctuation profiles could be compared between cases for swirl attenuation.

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Extreme flooding and excess nutrient pollution have been detrimental to river health under increased environmental stress from human activities (e.g., agriculture, urbanization). Riverine flooding can be detrimental to human life and infrastructure yet provides important habitat and ecosystem services. Traditional flood control approaches (e.g., levees, dams) negatively impact habitat and ecosystem services, and cause flooding elsewhere along the river. Prior studies have shown that stream restoration can enhance flood attenuation, and increased exchange of water between the channel and floodplain can improve water quality. However, the effects of floodplain restoration during small and sub annual recurrence interval storms have not been thoroughly studied, nor have cumulative impacts of floodplain restoration on water quality at watershed scales. We used HEC-RAS to perform 1D unsteady simulations on a 2nd-order generic stream from the Chesapeake Bay Watershed to study flood attenuation under small and sub-annual recurrence interval storms (i.e., 2-year, 1-year, 0.5-year, and monthly). In HEC-RAS we varied percent of channel restored, location of restoration, bank height of restoration, floodplain width, and floodplain Manning's n. Overall, stream restoration reduced peak flow (up to 37%) and decreased time to peak (up to 93%). We found the timing of tributary inflows could obscure the attenuation achieved, and even reverse the trends with certain parameters in the sensitivity analysis. The greatest exchange with the floodplains (greater volume and exchange under more recurrence interval storms) was observed from Stage 0 restoration, which reduces bank height more than other approaches. We also conducted a quantitative literature synthesis of nitrate removal rates from stream restoration projects. We focused on how removal rates varied with properties relevant at watershed scales, such as effects of stream order. The resulting database will aid in determining which stream restoration parameters better reduce nutrient loads and in simulating the effects of stream restoration on water quality at watershed scales. Floodplain restoration practices, and particularly Stage 0 approaches, enhance flood attenuation which can help to counteract urban hydrologic effects. / Master of Science / Extreme flooding and excess nutrient pollution have been detrimental to river health under increased environmental stress from human activities (e.g., agriculture, urbanization). Riverine flooding can be detrimental to human life and infrastructure yet provides important habitat and ecosystem services. Traditional flood control approaches (e.g., levees, dams) negatively impact habitat and ecosystem services, and cause flooding elsewhere along the river. Prior studies have shown that stream restoration can enhance flood attenuation and aid in removal of excess nutrients. Previous studies have shown that stream restoration helps to transport nutrients to highly reactive soils and increases time for reactions. However, the effects of floodplain restoration during small and sub annual recurrence interval storms have not been thoroughly studied, nor have cumulative impacts of floodplain restoration on water quality at watershed scales. To fill these knowledge gaps, increased understanding of stream restoration design parameters and watershed level characteristics (e.g., tributary inflows, nutrient loads, etc.) is necessary. We used HEC-RAS to study flood attenuation via stream restoration under small and sub-annual recurrence interval storms on a generic stream from the Chesapeake Bay Watershed. In HEC-RAS we varied percent of channel restored, location of restoration, bank height of restoration, floodplain width, and floodplain Manning's n (surface roughness). Overall, stream restoration did reduce peak flow and decrease time to peak, which means that restoration can diminish negative flooding effects. The greatest exchange with the floodplains was observed under Stage 0 restoration, which reduces bank height more than other approaches. We also conducted a quantitative literature synthesis to collect nitrate removal rates from stream restoration projects. We focused on how removal rates varied with properties relevant at watershed scales, such as effects of stream order. The resulting database will aid in determining which stream restoration parameters better reduce nutrient loads and in simulating the effects of stream restoration on water quality at watershed scales. These efforts will help to inform practitioners how to construct stream restoration projects that are more efficient for flood control and nutrient reduction. Floodplain restoration practices, particularly Stage 0 approaches, enhance flood attenuation and exchange which can help to counteract urban hydrologic effects.

Fade and inter-fade duration data obtained from the three beacons at 12, 20, and 30 GHz aboard the OLYMPUS satellite were analyzed. The different types of signal impairments and their causes were highlighted and a literature survey conducted. Twelve months of fade and inter-fade data were analyzed and the results of these statistics are presented in the form of tables and figures. The analysis was done on both the monthly and annual data. These tables and figures show that at the higher fade levels, the number of fade events and the fade time is smaller than at the lower thresholds. For the same fade level the number of fade events and the fade time goes down as the fade duration which it exceeds is increased. Inter-fade durations also showed similar results. The fades exhibited seasonal dependencies. The number of fades (and consequently the fade time) were much higher for the months of May through August and for the months of March and December. The other months showed very little fade activity. A model was also constructed that can predict the fade time as a function of frequency, attenuation level, and fade duration interval. The predicted fade times agree well with the measured fade duration data. An alternate simplified version of the model is also presented. / Master of Science

Frequency scaling of attenuation is the prediction of attenuation at a desired frequency from attenuation values at a base frequency. The attenuation at the base frequency is often known from prior measurements. Frequency scaling of attenuation is of interest because of the eventual need to exploit higher frequency bands. Most satellite communications traffic now use C-band (4-8 GHz) and Ku-band (12-18 GHz). The next approved, yet largely unused, frequency allocation for domestic use is in the K-band (18-27 GHz) to Ka-band (27-40 GHz). At these higher frequencies, however, earth-space radio links suffer atmospherically induced impairments as frequency increases. In particular, rain causes severe fading. Consequently, satellite systems in these higher bands are very susceptible to outages due to rain-induced fades. Reliable frequency scaling models are needed in system design to estimate the effect of these rain-induced fades. Between August 1990 and August 1992, V.P.I. & S.U.'s SATCOM Group performed extensive measurements of slant path attenuation using the 12, 20, and 30 GHz beacon signals (in the Ku/Ka-bands) of the European OLYMPUS experimental satellite. The experimental results are used to evaluate the usefulness of scaling models proposed by other researchers, both for instantaneous and statistical purposes. New models are presented for accurate scaling of attenuation within the Ku/Ka-bands. / Master of Science

This thesis reports the results of a thorough study into the effects of rain and ice on the polarization reuse technique for earth-space communications. Precipitation in the form of rain and ice leads to significant depolarization and attenuation of dual polarized signals above about 10 GHz. The depolarization versus attenuation relationship is examined in depth using a rigorous multiple scattering model. This relationship for rain is expressed in the form of a simple function similar to that used by the CCIR. Prediction accuracy using this simple model is quantified by comparisons to measured data and other model values. The impact of depolarization effects on the carrier-to-noise ratio for digital PSK systems is also addressed. Preliminary results for ice layer effects are presented. / Master of Science

Diesel #2 is used to heat nearly 400,000 dwellings in Virginia. Home heating oil released from leaking underground tanks located adjacent to homes and residing in unsaturated soil adjacent to houses poses a potentially serious health risk. Specifically, the migration of hazardous vapors into buildings, known as vapor intrusion, can negatively impact indoor air quality in homes and public buildings (USEPA 2015). In this look-back study, we assessed the potential for petroleum vapor intrusion by sampling soil vapor at 25 previously remediated spill sites. Residual contaminants, in particular total petroleum hydrocarbons (TPH) and naphthalene, were detected in approximately 1/3 of the samples. Concentration levels were correlated to site variables (building type, remediation time, physiographic region) including previous abatement measures. Spill category as assigned by the remediation contractor was investigated in conjunction with these three site variables. Remediation time was the most promising predictive site variable, with visible trends downward in DEQ Category 2 sites with increased remediation time. Higher contaminant concentrations were found near basement-style dwellings, which we hypothesize is due to the wall of the basement blocking horizontal migration of contaminants and the flow of oxygen to the release source zone. We found that many sites exceeded the sub-slab risk target threshold in naphthalene concentration, which has negative implications on previous abatement strategy efficacy. / Master of Science

Human land use practices such as urbanization and agriculture contribute excess nutrients (nitrogen and phosphorus) and runoff volumes to rivers that degrade aquatic ecosystems and cause a loss of river functions such as nutrient processing and flood attenuation. Floodplain restoration increases floodplain exchange and is commonly implemented to improve water quality and reduce flood impacts at watershed scales. However, the effect of multiple restoration projects at the watershed scale is not well studied. We addressed this knowledge gap by two studies. The first study evaluated the impact of cumulative and spatially varying Stage-0 and bankfull floodplain restoration on nitrate removal in a generic 4th-order Virginia Piedmont watershed for small and sub-annual storm sizes (i.e. 2-year, 1-year, half-year, and monthly recurrence intervals). We used HEC-RAS hydraulics results from a prior study together with a nitrate removal model coded in R. Results indicated that watershed nitrate removal varied depending on the location of restoration in the watershed and where removal was evaluated. The greatest reductions in nitrate loads were observed in the same part of the river network where restoration occurred, with diminished impacts downstream. Removal also increased with increasing stream order/river size. However, removal was generally of small magnitude, with up to 1% or 19% of the watershed load removed for median or 90th-percentile removal rates, respectively. We estimated removal for our restoration scenarios under the Chesapeake Bay Program Protocols and found the removal rate to also be a critical factor in determining the efficiency of restoration project. Other controlling factors for nitrate removal were the amount of restoration and storm size. The second study entailed modeling cumulative restoration in a case study watershed to assess the impacts on nutrient removal and flood attenuation. We built a 1D HEC-RAS model of the 4th-order Gwynns Falls watershed near Baltimore MD using georeferenced HEC-RAS model geometries from the Maryland Department of the Environment and simulated unsteady stormflow hydraulics due to cumulative Stage-0 floodplain restoration for small and sub-annual storms. Restoration actually increased peak flow on the main channel (up to 0.9%) due to slowing of the flood wave on the main channel which was then better synchronized with tributary inflows. Restoration increased nitrate removal but at low levels (up to 0.12% or 2.6% removal for a median and 90th-percentile removal rate respectively) due to the small footprint of restoration in the watershed (up to 21.4% of the main channel was restored). These small and sometimes adverse outcomes occurred in response to what would be expensive restoration. Therefore, we argue for large-scale solutions to address watershed-scale water quality and flooding issues yet acknowledge re-evaluation of restoration goals against other societal priorities may be necessary. Overall, our results highlight the potential value and limitations of floodplain restoration in reducing flooding and nitrate exports at the channel network scale and provide practical insight for application of floodplain modeling at the watershed scale. / Master of Science / Human land use practices such as building cities and farms adds nutrients (nitrogen and phosphorus) and increase storm flows in rivers downstream. While nutrients and flows are needed for humans and wildlife, too much of either can harm aquatic organisms and endanger people and property. Floodplain restoration is a common river engineering technique that increases exchange between the river channel and low-lying areas next to rivers known as floodplains. Floodplains are natural features, but people have reduced river flows between channels and floodplains in many ways. For example, by allowing sediments to build up in floodplains or building levees that separate channels from adjacent floodplains. Increasing floodplain exchange by floodplain restoration is commonly implemented to improve water quality and reduce the impact of flooding in watersheds, which are large areas that drain to a single river. However, while the goals of restoration are often at watershed scales, the effect of multiple restoration projects at that watershed scale is not well studied. We addressed this knowledge gap by two studies. The first study evaluated the impact of multiple restoration projects and project locations in a generic (average/typical) watershed on nitrate removal. We used a nitrate removal model and the results from a prior study that modeled the stormflow behavior resulting from floodplain restoration. Results indicated that watershed nitrate removal varied depended on the location of restoration in the watershed and where removal was evaluated. The most nitrate was removed where restoration occurred, with less removal downstream in the watershed. Removal also increased with increasing river size. However, removal was generally small with up to 1% or 19% of the watershed load removed for a smaller and larger nitrate removal rate, respectively. Other factors that changed the amount of nitrate removed were the amount of restoration, nitrate removal rate in the floodplains, and storm size. The second study entailed modeling cumulative restoration in a case study watershed to assess the impacts on nitrate removal and reducing flooding. We modeled stormflow for multiple hypothetical restoration projects in the Gwynns Falls watershed and found that restoration can actually increase peak flow when placed in certain locations. Restoration increased removal but at low levels (up to 0.12% or 2.6% for a smaller and larger removal rate) due to the small amount of restoration simulated. These small and sometimes adverse outcomes occurred in response to what would be expensive restoration projects to construct. Therefore, we argue for large-scale solutions to address watershed-scale water quality and flooding issues yet acknowledge that re-evaluation of restoration goals against other societal priorities may be necessary. Overall, our results highlight the potential value and limitations of using floodplain restoration to reduce flooding and nutrient exports and provide practical insight for using our modeling techniques in managing watershed flows and pollution.