Large Liquid Hydrogen (LH2) storage tanks are vital infrastructure for NASA. Eventually, air may leak into the evacuated and perlite filled annular region of these tanks. Although the vacuum level is monitored in this region, the extremely cold temperature causes all but the helium and neon constituents of air to freeze. A small, often unnoticeable pressure rise is the result. As the leak persists, the quantity of frozen air increases, as does the thermal conductivity of the insulation system. Consequently, a notable increase in commodity boiloff is often the first indicator of an air leak. Severe damage can then result from normal draining of the tank. The warming air will sublimate which will cause a pressure rise in the annulus. When the pressure increases above the triple point, the frozen air will begin to melt and migrate downward. Collection of liquid air on the carbon steel outer shell may chill it below its ductility range, resulting in fracture. In order to avoid a structural failure, as described above, a method for the safe removal of frozen air is needed. Two potential methods for air removal are evaluated here. The first method discussed is the connection of a vacuum pump to the annulus which provides pumping in parallel with drainage of LH2. The goal is to keep the annular pressure below the triple point so that the air continues to sublimate, thus eliminating the threat that liquefaction poses. The second method discussed is the application of heat to the bottom of the outer tank during tank drain. Though liquefaction in the annular space will occur, the goal of the heater design is to keep the outer shell above the embrittlement temperature, so that cracking will not occur. In order to evaluate these methods, it is first necessary to characterize some the physical properties and changes that take place in the system. A thermal model of the storage tank was created in SINDA/FLUINT (C&R Technologies, 2014) to identify locations where air can freeze. This model shows the volume that is capable of freezing air under varying conditions. It is also necessary to characterize the changes in thermal conductivity of perlite which has nitrogen frozen into its interstitial spaces. The details and results of an experiment designed for that purpose is outlined. All data, including operational data from existing LH2 tanks, is compiled and a physics-based evaluation of the two proposed air removal techniques is performed. Due to small pumping capacities at low pressure and the large quantity of air inside the annulus, the pumping option is not deemed feasible. It would take many years to remove a significant amount of air by pumping while maintaining the annular pressure below the necessary triple point. Application of heating devices is a feasible option. For a specific case, it is shown that approximately 105 kilowatts of power would be required to vaporize the air in the annulus and keep the temperature of the outer tank wall above the freezing point of water. Several engineering solutions to accomplish this are also discussed. There are many unknowns and complexities in addressing the problem of safely removing frozen air from the annulus of an LH2 storage sphere. The work that follows utilized: research, modeling, experimentation, analysis, and data from existing tanks to arrive at possible solutions to the problem. Heating solutions may be implemented immediately and could result in significant savings to the user.

Membrane durability is one of the limiting factors for proton exchange membrane fuel cell (PEMFC) commercialisation by limiting the lifetime of the membrane via electrochemical / mechanical / thermal degradation. Lower internal humidity in the membrane at high temperature ( > 100 °C) and low relative humidity (25-50 %RH) operating conditions leads to increased resistance, lowering of performance and higher degradation rate. One of the promising candidates is composite proton exchange membranes (CPEMs) which have heteropoly acid (HPA) e.g. Phosphotungstic acid (PTA) doped throughout the Nafion® matrix. HPA is primarily responsible for carrying intrinsic water which reduces the external water dependence. The role of relative humidity during membrane casting was studied using surface analysis tools such as Xray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Thermo-gravimetric analysis (TGA), and Scanning electron microscopy (SEM) / Energy dispersive spectrometer (EDS). Membrane casting at lower relative humidity (30% approx.) results in finer size, and better PTA incorporation in the composite membrane. The effect of increase in PTA concentration in the Nafion matrix was studied with regards to conductivity, performance and durability. In-plane conductivity measurements were performed at 80 oC and 120 oC. During theses measurements, relative humidity was varied from 20% to 100% RH. Membrane conductivity invariably increases on increasing the relative humidity or operating temperature of the cell. Membrane conductivity increases with increasing PTA content from 3% to 25% PTA but never reaches the conductivity of membrane with 0% PTA. Possible explanation might be the role of cesium in PTA stabilisation process. Cesium forms a complex compound with PTA inside host matrix, rendering the PTA incapable of holding water. In plane conductivity measurements only measure surface conductivity, hence another reason might be the existence of a PTA skin on the membrane surface which is not truly representative of the whole membrane. XRD revealed that the structure of the composite membrane changes significantly on addition of PTA. Membrane with 3% PTA has structure similar to Nafion® and does not exhibit the characteristic 25o and 35o 2Ө peaks while membrane with 15% PTA and 25% PTA have strong characteristic PTA peaks. Also the membrane structure with 25% PTA matches well with that of PTA.6H2O. By applying the Scherer formula, PTA particle size was calculated from Full width half maximum (FWHM) studies at 17o 2Ө peak of the membranes. Particles coalesce on increasing the PTA concentration in the membrane leading to larger particles but still all particles were in nanometer range. Also the FWHM of membranes decreased at 17o 2Ө peak on increasing the PTA concentration, leading to higher crystallinity in the membrane. Structure analysis by FTIR indicated increase in PTA signature intensity dips, as the PTA concentration in membrane increases from 0-25%. Also by FTIR studies, it was found that some PTA is lost during the processing step as shown by comparison of as cast and protonated spectra. Possible reasoning might be that some amount of PTA does not gets cesium stabilized which gets leached away during processing. TGA studies were performed which showed no signs of early thermal degradation (temperature > 300 °C); hence the assumption that all membranes are thermally robust for intended fuel cell applications. The membranes with different amounts of PTA were then catalyst coated and tested for 100-hour at open circuit voltage (OCV), 30% RH and 90 oC. By increasing the PTA in the host Nafion® matrix, the percent change in fuel crossover decreases, percent change in ECA increases, cathode fluoride emission rate decreases, and percent change in OCV decreases after the 100 hour test. Possible reasons for decreasing percentage of fuel crossover might be the increased internal humidity of the membrane due to increasing PTA incorporation. It is reported that during higher relative humidity operation, there is decrease in fuel crossover rate. Increasing ECA percentage loss might be due to the fact that HPA in the membrane can get adsorbed on the catalyst sites, rendering the sites inactive for redox reaction. Decrease in cathode fluorine emission rate (FER) might be due to the fact that there is more water available internally in the membrane as compared to Nafion®. It is reported that at higher relative humidity, FER decreases. ECA and crossover both contribute to the OCV losses. Higher component of OCV is crossover loss, which results in mixed potentials. Hence decreasing percentage of crossover might be the reason behind the decreasing OCV loss. Initial performance of fuel cell increases with increasing PTA concentration, but after the 100 hour test, higher PTA membrane exhibited highest performance loss. Increasing initial fuel cell performance can be due to the lowering of resistance due to PTA addition. Increasing ECA losses might be responsible for the increasing performance losses on adding more PTA to host membrane.

This project encompasses the design and development of a pretreatment microfluidic device for samples of physiological conductivity, namely a saline solution. The conductivity was reduced through the combination of dilution and ion removal using electric fields to enable downstream electro kinetic manipulations. The two major parts of this project include (1) designing a pretreatment protocol to reduce the conductivity of the sample solution to an acceptable level and (2) designing /fabricating a microchip that will effectively allow aim (1) to be performed on chip. This project is one of the first to observe the effects of an electric field, used in the application of ion removal, to reduce the conductivity of a sample. Through the combination of sample and low conductivity buffer, as well as the presence of an electric field, a conductivity pretreatment chip is created. Since biomarkers and analytes of interest are difficult to detect in complex raw samples, such as blood, this chip is a necessary preliminary step that allows for successive separations. Using previous literature from the field of capillary electrophoresis, a design and pretreatment protocol was developed to pretreat a sample into a target conductivity range. A PMMA device was fabricated using a laser photoablation system located on the Cal Poly campus. Off-chip electrodes were used to induce electrophoretic movement of ions across a membrane and out of the sample. The combination of dilution and electrical fields yielded samples that had their conductivity reduced 80%. Dilution was found to be more effective in a chip designed with a short process time and continuous flow. Ultimately, we wish to incorporate this device with other pre-fabricated pretreatment and electrokinetic devices to optimize certain bioseparations.

Poor emergence of sorghum [(Sorghum bicolor (L) Moench] affects the stand and potential yields. The major objective of this research was to find correlations among field emergence data and laboratory seed vigor tests. Thirty-two and 30 hybrids of sorghum were planted at three Virginia locations in 1995 and 1996, respectively. Field emergence was subsequently compared with results from laboratory tests that included: 1) standard germination; 2) osmotic-stress using polyethylene glycol 8000 (mw); 3) heat-shock using 2 hr at 50°C stress; 4) electrical conductivity of steep water of germinating seeds; and 5) seed mass. Field emergence of grain sorghum differed among hybrids, years and locations. Mean emergence across years and locations was 67.5%, whereas mean germination in the laboratory was 87.8%. There were interaction between hybrid and location and between hybrid and year. Germination under optimal conditions (standard germination test) and with osmotic or heat-shock stress differed among hybrids. Regression analyses showed a weak correlation between laboratory germination (with or without stress) and field emergence in both years. The fresh weight of seedlings whether from standard germination or stress tests also differed among hybrids in both years, and the associations with field emergence were weakly correlated in 1996. Hybrids showed significant differences in radicle length when grown under laboratory stress in both years following standard germination. There was a weak correlation with field emergence and radicle length following heat-shock treatment in 1996. The measurement of electrical conductivity in the seed steep water showed significant differences among hybrids. A weak correlation with field emergence was seen in 1996. Conductivity values per gram of seed and per cm² of seed area revealed differences among hybrids. The correlation of these parameters with field emergence was higher than conductivity per seed. Seed mass varied among hybrids in both years , but was no correlation between seed mass and emergence. Of the laboratory parameters examined, germination proved to be the most consistent predictor of variations in field emergence of sorghum hybrids. / Ph. D.

Traditionally, geothermal boreholes have utilized the ground energy for space heating and cooling. In this system, a circulation loop is placed in a small-diameter borehole typically extending to a depth of 200-300 ft. The hole is then backfilled with a mixture of sand, bentonite and/or cement. The loop is connected to a geothermal heat pump and the fluid inside the loop is circulated. The heat energy is fed into the ground for cooling in the summer and withdrawn from the ground for heating in the winter. Geothermal heat pumps work more efficiently for space heating and cooling compared to air-source heat pumps.  The reason is ground-source systems use the ground as a constant temperature source which serves as a more favorable baseline compared to the ambient air temperature. A significant cost associated with any deep geothermal borehole is the drilling required for installation. Because Energy Piles perform the dual function of exchanging heat and providing structural support, and are only installed at sites where pile foundations are already required, these systems provide the thermal performance of deep geothermal systems without the additional drilling costs. Low maintenance, long lifetime, less variation in energy supply compared to solar and wind power, and environmental friendliness have been cited as additional Energy Pile advantages. Case studies show that they can significantly lower heating/cooling costs and reduce the carbon footprint. Energy cost savings for typical buildings outfitted with Energy Piles could be as much as 70 percent. The use of Energy Piles has rapidly increased over the last decade, especially in Europe where more than 500 applications are reported. Primary installations have been in Germany, Austria, Switzerland and United Kingdom. Notable projects include the 56-story high Frankfurt Main Tower in Germany, Dock E Terminal Extension at Zurich International Airport in Switzerland and the One New Change building complex in London U.K. Energy piles have seen very little use in the North America, only a handful of completed projects are known; Marine Discovery Center in Ontario, Canada, Lakefront Hotel in Geneva, New York and the Art Stable building in Seattle, Washington. Energy Piles are typically installed with cast-in-place technology (i.e. drilled shafts, continuous flight auger piles, micropiles etc.) while some driven pile applications are also reported. Other types of geotechnical structures in contact with the ground, such as shallow foundations, retaining walls, basement walls, tunnel linings and earth anchors, also offer significant potential for harnessing near-surface geothermal energy. Energy Pile design needs to integrate geotechnical, structural and heat exchange considerations. Geotechnical characteristics of the foundation soils and the level of the structural loads are typically the deciding factors for the selection and dimensioning of the pile foundations. The geothermal heat exchange capacity of an Energy Pile is a key parameter to be considered in design. Thermal characteristics of the ground as well as the heating and cooling loads from the structure need to be considered for the number of piles that will be utilized as heat exchangers. Therefore, the thermal properties of the site need to be evaluated for an Energy Pile application in addition to the traditional geotechnical characterization for foundation design. Energy Piles bring new challenges to geotechnical pile design. During a heat exchange operation, the pile will expand and contract relative to the soil as heat is injected and extracted, respectively. These relative movements have the potential to alter the shear transfer mechanism at the pile-soil interface.  Furthermore, the range of temperature increases near the pile surface, though limited by practical operational guidelines, can have a significant effect on pore pressures generation and soil strength. This dissertation provides answers for several research questions including the long-term performance of Energy Piles, the applicability of the thermal conductivity tests to Energy Piles.  Furthermore, it presents the results and a detailed discussion about the full scale in-situ thermo-mechanical pile load test conducted at Virginia Tech. / Ph. D.

<p> Highly orientated BaTi1-xNbx03 thin films, spanning the entire range of x, have been successfully deposited on (001) MgAl20 4 substrates by the pulsed laser deposition (PLD) method. The structure of the films is characterized with a range of techniques. It is found that increasing x gives rise to a Ti4+ to Ti3+ transformation in the oxidation state accompanied by increased conductivity with a semiconductormetal transition near x = 0.2. Temperature dependent magnetic measurements show an anomalous rise in the spin moment. In order to further reduce the lattice mismatch and keep the conductivity at the same time, a partial strontium-for-barium substitution, (Ba1-ySry)Ti0.5Nb0.5O3 withy = 0, 0.4, 0.5 and 0.6, were used. Such a substitution provides a means for independently tuning the lattice parameter and conductivity over a significant range of compositions. The y = 0.6 composition show a sharp interface with flawless epitaxy and good quality films. We attribute the improvements in the film quality to a decrease in the lattice misfit strain made possible through the superior lattice match to the substrate obtained through strontium substitution. Electronic structure calculations were carried out by the 1st principle method using the WIEN2k program in order to understand the electronic structure of these compounds. Based on the assumed ordered structures, the Fermi level of BaTi1-xNbxO3 gradually moved to the lower energies as x increase, while the valence bands were not significantly altered with the Nb ions substitutions. The fraction of each Ti4+ and Ti3+ component in BaTi1-xNbxO3 samples was extracted by the linear profile fitting of the corresponding Ti-L2,3 edge obtained by the electron energy loss spectra. The fitting results indicate a high fraction of Ti3+ is present than excepted as Nb content increase, which could arise from the loss of oxygen stoichiometry. The electron energy loss spectra of the 0-K edge is analyzed by comparison to the partial density of states calculation. The evolutions of 0-K edge features are explained in terms of the decrease of the Ti 3d band contribution and the increase of the Nb 4d band contribution as the Nb content increase.</p> / Thesis / Doctor of Philosophy (PhD)

<p> An investigation has been made of the microwave reflections from the surface of a semiconducting medium with complex permittivity (^ε = εrεo -jσ/ω) at the open end of an empty rectangular waveguide. The approximate and exact solutions of the reflection coefficients at the surfaces of both finite and semi-infinite media have been found as a function of the complex permittivity of the medium. The computations of the reflection coefficients are made at the 10 and 35 GHz ranges. Measurements, which confirm these calculations, have been performed with n-type germanium, selectron, and air at the open end of a rectangular waveguide using a reflection type microwave bridge. The investigation has shown that it is possible to devise a convenient method of measuring the conductivity and dielectric constant of semiconductors.</p> <p> The theory of operation of the microwave reflection bridge together with the setting-up (matching) procedure of a practical form of the bridge has been presented. A method is also described for the correction of the measurement error which arises from the scattering coefficients at the input ports of the precision attenuator.</p> <p> A theoretical and experimental study has also been made of the small- signal microwave conductivity of n-type germanium at room temperature in the presence of a high electric field, directed at an angle θ to the microwave field. The study has shown that at frequencies such as 10 GHz, the microwave conductivity becomes anisotropic with respect to the direction of the d.c. field vector. Measurements are made on an 11.4 ohm cm, n-type germanium sample at 9.381 GHz with applied electric fields up to 1.8 KV/cm for θ = 0°, 40°, and 90°. The ''open-end-waveguide measuring technique", which allows the angle between the microwave and d.c. field vectors to be varied, was employed to measure the microwave conductivity. The results of measurements which agree with predictions, confirm the feasibility of operation of a new microwave device based on the anisotropic effect.</p> / Thesis / Doctor of Philosophy (PhD)

<p> A method for the measurement of the microwave conductivity of a semiconductor subjected to a high electric field is described, which provides for varying angles between the microwave and applied electric field vectors. The results of measurements on 10 ohm-em. n-type germanium at 9.522 GHz with applied electric fields up to 3KV/cm are given. </p> <p> The measurements show that the microwave conductivity is controlled by the differential carrier mobility (∂V/∂E) for the condition of microwave and applied electric field vectors parallel. For the case of the fields at right angles the microwave conductivity is controlled by a carrier mobility intermediate between the d. c. mobility (v/B) and the differential mobility (∂V/∂E). </p> <p> Theoretical expressions for the performance of a proposed "Hot Electron Microwave Rotator" are developed. </p> / Thesis / Master of Engineering (MEngr)

<p> A number of microwave measuring techniques for the measurement of the complex permittivity (^ɛ = ɛo ɛr - j σ/ω) have been investigated and a new method based on the replacement of the narrow wall of a rectangular wave-guide by a block of semi-conductor has been developed. This technique is shown to be suitable for the measurement of σ when σ >> ωɛo ɛr and for the measurement of σ and ɛr for σ ≃ ωɛo ɛr. </p> <p> An investigation has been made of the propagation characteristics of a rectangular wave-guide containing a centrally placed slab of semi-conductor parallel to the narrow walls of the guide. A comparison of exact solutions for the propagation constant in such a structure with the approximate solutions normally used has shown that the conditions for the validity of the approximate solutions are much more stringent than has been reported previously. It is further shown that under certain conditions the structure offers a convenient method of measuring the conductivity of a semi-conductor. In addition, a theoretical and experimental investigation of the effects of the higher order modes excited at the interface of such a structure with an empty wave-guide has been made. The study has shown that under certain conditions, the effects of these modes can be significant.</p> <p> A theoretical and experimental study has also been made of the effects of temperature, frequency and doping on the complex permittivity of lightly doped n-type germanium. Measurements of these effects which have not been reported previously have been made over a temperature range 100°K - 500°K at frequencies 9.25 and 34.5 GHz and confirm the theoretical model used.</p> / Thesis / Doctor of Philosophy (PhD)

Hydropower regulation of rivers exhibits a threat to the riverine ecosystems. Fragmentation of flow, landscape disturbances, and water retention are key features of regulated catchments, resulting in reduced floods and geochemical tr¬ansport, non-natural water level fluctuations, and thus disturbed exchange between the river and the aquifer. Storing of water in reservoirs reduces peak flow and turbidity, which increases particle settling and sometimes favours enhanced primary production and formation of a clogging layer. This in turn alters the interaction between surface water and groundwater, with potential secondary effects on the entire watershed. In Scandinavia, only eight large rivers (16%) remain entirely unregulated. The Lule River, the primary focus of this study, belongs to the most regulated rivers of Eurasia with a degree of regulation (i.e. the volume of water that can be stored in the reservoirs and used for regulation) of 72%, and is exposed to both seasonal and short-time regulation.Using hydrogeochemical analysis of two adjacent boreal rivers (pristine Kalix and regulated Lule River) discharging into the Gulf of Bothnia, the effects of regulation on river geochemistry were investigated. For the Lule River, the average maximum runoff was almost halved while the average minimum runoff was tripled as a result of the regulation. The winter transport fraction of total organic carbon, Fe, Si, suspended Mn and P in the Lule River was at least two to three times higher than in the pristine river. During summer, the suspended C/N ratio in the regulated river was 10-20, compared to &lt;10 for the pristine river, suggesting a presence of predominantly decaying organic material due to longer residence times for the regulated river. This was supported by a virtually constant suspended P/Fe ratio throughout the year in the Lule River, indicating low abundance of phytoplankton. Hence, a pronounced impact on the ecosystem of the river, the hyporheic/riparian zone, and the Gulf of Bothnia is expected.In spite of vast anthropogenic pressure on riverine ecosystems, the knowledge regarding the hyporheic zone (the interface between rivers and aquifers where exchange between surface water and groundwater occurs) is limited for regulated rivers. Therefore, this study was extended to also cover the hyporheic exchange along the Lule River. Temporal changes in hyporheic fluxes across the river channel (rates and directions) were determined using seepage measurements and continuous observations of water stages, temperatures, and electrical conductivity for both the river and the groundwater. While the river water level changed frequently (typically twice a day with up to ± 0.5 m), the river remained gaining 90% of the time, and the largest number of observed changes in flow direction (observed at 5 m orthogonal distance from the river) was six times per week. Flow velocities ≤10-4 m d-1 ( zero flow) constituted 1.5% of the total observation time.Although no changes in water temperature were observed for the hyporheic zone, effects of river level variations were detected up to 5 m inland, where electrical conductivity occasionally decreased to surface water levels indicating infiltration of river water into the aquifer (negative fluxes). River discharge regulation may therefore have severe implications on biogeochemical processes and deteriorate the hydroecological functions of the hyporheic zone.