Browsing by Subject "Gravity"
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Item A simulation study towards local mass anomaly estimation using GRACE data(2019-01-30) Köhne, Tobias; Bettadpur, Srinivas Viswanath, 1963-Since the dawn of spaceborne Earth Science missions like the Gravity Recovery and Climate Experiment (GRACE), our understanding of global geophysical processes has increased significantly. As measurements get more precise, it is necessary to improve the accuracy of our models to explain observations more precisely. In the case of GRACE-produced gravity solutions, postfit residuals show spatial patterns that indicate unmodeled influences and motivate further investigation. The purpose of this work is to assess the potential of dividing Earth into a grid and using GRACE observations to investigate local mass anomalies, in contrast to the global fields generated usually. Starting from the equations of motion of the N-body problem, a framework is developed and implemented to allow for the simulation of GRACE-like orbits, and generation of inter-satellite range measurements. After differentiating twice using a digital filter, the acceleration observables can be used to estimate excess or default mass, as they are proportional to the forces acting on the spacecraft. Using analytical formulations to generate the true inter-satellite range accelerations, grid-by-grid least squares solutions allow for the estimation of the respective local mass anomaly. However, as there is no knowledge about the true accelerations in reality, this only proves theoretical feasibility. When imitating the process flow of GRACE to generate observed range accelerations from range measurements, numerical insufficiencies stemming from a suboptimal orbit propagator are too large to yield accurate and stable estimates. A sensitivity analysis is included to determine the impact of several simulation parameters and inform future studies of critical design choices, if any emerge. Lastly, an effort is made to search for unmodeled forces in GRACE acceleration residuals. Applying the same grid-based models as used in the simulation setup, a curve is fit through the data spanning the entire mission. The result is a global, coarse estimate of the location and amplitude of model inaccuracies, serving as a starting point for future studies into their causes.Item Characterization of connection details for truss-diaphragm for use in full-scale experiments focused on lateral contribution of gravity connections in steel frames(2021-05-07) Schulz, Adam Carl; Clayton, Patricia M.Typical structures derive lateral strength and stiffness from only a limited number of lateral load resisting elements. Gravity framing normally accounts for the vast majority of members in a structure and is assumed not to contribute to the lateral resistance of the frame. This assumption is partly due to the perfect pin idealization for gravity connections. However, research has indicated that gravity framing offers a nonnegligible amount of lateral resistance both due to moment resistance in the connections and continuity of gravity columns. In aggregate, the moment resistance of gravity framing may substantially impact the lateral capacity of a structure. This thesis presents the details of a system-level test specimen that will be used to evaluate the contribution of gravity framing to the lateral resistance of a steel building structure. This overall research investigation is an extension of the work published by Donahue (2019) and employs many of the same details. The specimen described herein is a two-bay by three-bay structure that utilizes double-angle shear connections in the direction of loading. This structure represents one floor of a representative building with columns spanning from mid-height of the story below to mid-height of the story above. The specimen will be tested as a bare-steel frame to collect calibration data for forthcoming tests that include composite decking. In addition to explaining the geometry of the specimen, this thesis details computational and experimental testing completed to validate a horizontal-to-vertical connection between a knife plate and a WT section in a top truss diaphragm that is used to distribute lateral loads throughout the specimen. This connection was designed with the intent that the WT section will accommodate bending while limiting permanent deformations in the knife plate. While the knife plate was observed to experience substantial plastic strains in experimental subassembly testing, it was decided that the magnitude of residual deformation sustained by the knife plate would not substantially impact the constructability of subsequent test specimens. Therefore, the detail was used in the full-scale system-level specimen.Item Dynamical refinement in loop quantum gravity(2015-08) Hassan, Syed Asif; Matzner, Richard A. (Richard Alfred), 1942-; Dicus, Duane A; Freed, Daniel S; Morrison, Philip J; Weinberg, StevenIn Loop Quantum Gravity, a quantum state of the gravitational field has a semiclassical interpretation as a three-dimensional lattice discretization of space. We explore the possibility that the scale of the lattice is only as fine as it needs to be in order to carry the dominant frequency excitations of the auxiliary fields living on the lattice, by considering graph-changing transition amplitudes in the context of a pure gravity quantum theory. We define regular graphs that correspond to closed spatial slices of FLRW spacetime in a novel way, with coherent state labels that correspond to physical observables. This correspondence is obtained using the novel concept of a pseudoregular polyhedron which affords a dimensionless volume to surface area ratio in terms of the number of faces of the polyhedron. We normalize these regular graph states using a new method, employing a saddle point approximation based on the valence of the nodes rather than the large-scale semiclassical limit to obtain a result that holds in the quantum limit. Finally we employ the EPRL spin foam model to obtain a transition amplitude between single-node graphs of arbitrary valence that is valid in both the semiclassical and quantum regimes, using an improved method of normalizing the amplitude. We find that if we fix the scale factor and the fiducial volume of space the amplitude favors final states with infinitely large valence.Item An ensemble solution for the Earth's time-varying gravitational field from the NASA/DLR GRACE mission(2013-08) Sakumura, Carly Frances; Bettadpur, Srinivas Viswanath, 1963-Several groups produce estimates of the Earth's time-varying gravitational field with data provided by the NASA/DLR Gravity Recovery and Climate Experiment (GRACE) mission. These unprecedented highly accurate global data sets track the time-variable transport of mass across and underneath the surface of the Earth and give insight into secular, seasonal, and sub seasonal variations in the global water supply. Knowledge gained from these products can inform and be incorporated into ocean and hydrological models and advise environmental policy planning. Therefore, a complete understanding of the accuracy and variations between these different fields is necessary, and the most accurate possible solutions desired. While the various gravity fields are similar, differences in processing strategies and tuning parameters result in solutions with regionally specific variations and error patterns. This study analyzed the spatial, temporal, and spectral variations between four different gravity field products. The knowledge gained in this analysis was used to develop an ensemble solution that harnesses the best characteristics of each individual field to create an optimal model. Multiple methods were used to combine and analyze the individual and ensemble solutions. First a simple mean model was created; then the different solutions were weighted based on the formal error estimates as well as the monthly deviation from the arithmetic mean ensemble. These ensemble models as well as the four individual data center solutions were analyzed for bias, long term trend, and regional variations between the solutions, evaluated statistically to assess the noise and scatter within the solutions, and compared to independent hydrological models. Therefore, the form and cause of the deviations between the models, as well as the impact of these variations, is characterized. The three ensemble solutions constructed in this analysis were all effective at reducing noise in the models and better correlate to hydrological processes than any individual solution. However, the scale of these improvements is constrained by the relative variation between the individual solutions as the deviation of these individual data products from the hydrological model output is much larger than the variations between the individual and ensemble solutions.Item Essays on international trade(2010-05) French, Scott Thomas; Corbae, Dean; Abrevaya, Jason; Freitas, Kripa; Ramondo, Natalia; Ruhl, KimThis dissertation consists of three essays pertaining to the causes of the levels and composition of the international trade flows of nations, and the consequential implications for the levels of per capita income and welfare of their populations. The first of these documents a pattern of comparative advantage in product level, bilateral trade data that conventional quantitative trade models have difficulty explaining. It goes on to develop a theory of product level productivity differences based on endogenous differences in the allocation of research and development into product and process innovation across countries over time, and it shows that, when fitted to cross-country manufacturing wage data, the predicted product level technology distribution is consistent with the observed trade pattern. The second essay shows that the distribution of technology levels inferred in the first essay can help explain the inability of both ad-hoc and theoretically based gravity models of trade to account for the observed positive correlation between the percentage of manufacturing output that is traded and countries' per capita income. It derives a modified gravity equation based on a Ricardian model of trade with deterministic product level technology differences across countries. It then uses estimates from a product level gravity estimation to compute the component of this equation that differs from a conventional gravity equation in order to determine the extent to which the observed concentration of comparative advantage in a common set of products for low-income countries explains the small percentage of their output that is exported. The final essay shows that a simple model of firm profit maximization in the presence of sunk costs of entering the export market is broadly consistent with the observed persistence of exporting behavior in firm level data. It uses this simple model and moments from data on US manufacturing firms to estimate the value of the sunk export entry costs faced by these firms using an indirect inference strategy. These costs are shown to be substantial relative the revenue stream of a typical firm.Item Expected improvements in modeling Earth's time-variable gravity field using multiple GRACE-like satellite constellations(2018-08-20) Widner, Maxon Vaughn, IV; Bettadpur, Srinivas Viswanath, 1963-The Gravity Recovery and Climate Experiment (GRACE) mission has been a principal contributor in the study and quantification of Earth's time-varying gravity field. With continuing missions like GRACE Follow-On and the Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) capitalizing on improved technologies such as laser interferometry and drag-free flying systems, respectively, the temporal aliasing of high frequency geophysical processes is anticipated to be the primary source of errors for future missions. Micro-satellite technology has presented the feasibility of improving the architecture of future missions with the implementation of a constellation of satellites having similar characteristics as GRACE. Such a configuration is suggested and analyzed to help address these under-sampling errors. The initial series of simulations is designed to build off the current GRACE mission with a near polar orbit, 450 km altitude, but with each satellite spaced approximately 120 km apart. Because of atmospheric and residual ground interference the reliability of ranging data diminishes at greater distances and therefore scenarios involving distances between satellites greater than 1,100 km are not evaluated. A multi-satellite orbit determination package (MSODP) is used to simulate these configurations and the observations corresponding to their orbits. This data is then processed using the Center for Space Research's Advanced Equation Solver for Parallel Systems (AESoP) linear least squares estimator providing high degree and order gravity field map solutions for each case. A sensitivity analysis is performed by varying certain parameters including: satellite spacing, altitude, and technological improvements. The multiple case results are consolidated to help ascertain the most optimal configuration for error reduction. Another series of data is provided from simulations which represent a constellation of satellites in a similar orbit except for the orbital plane being inclined at 72° with the same methodology implemented. This data is then combined in various configurations with the original data set of measurements and compared with the data from the original polar orbit scenario to determine the impact of a second train of satellites and their mitigation of detrimental effects like longitudinal striping. An analysis is performed to quantify the improvements of these configurations and is then evaluated to find optimal parameters for single and multiplane constellations. These results are extrapolated to show their impact on assessing metrics that would most benefit the water market's interests.Item A generalized flow rate model for primary production and an analysis of gravity drainage through numerical simulation(2014-08) Vitter, Cameron Artigues; Balhoff, Matthew T.; Lake, Larry W.The age of “easy” oil has steadily declined through the years as many conventional land-based fields have been depleted to residual levels. Novel technologies, however, have reawakened old fields, allowing incremental oil to be added to their recoverable oil in place (ROIP). Underground Gravity Drainage (UGD), an example of one of these technologies, combines improved horizontal and deviated drilling technologies with the longstanding concept of gravity drainage. In this work, a better understanding of gravity drainage has been gained through (1) development of a numerical, three-dimensional, three-phase reservoir simulator (UT-EMPRES), (2) development of a universal, semi-empirical model of production rates through primary depletion, and (3) analysis of the important aspects of gravity drainage through simulation. UT-EMPRES is a new three-phase, finite-difference reservoir simulator, which utilizes a simple, easy-to-use Microsoft Excel interface to access MATLAB-programmed simulation code. This simulator produces nearly identical results to other well-established simulators, including UTCHEM and CMG. UT-EMPRES has some unique features, allows for easy post-processing in MATLAB, and has been utilized extensively in the other two areas of this thesis. The generalized flow rate model (GFRM) is a semi-empirical equation that is used to forecast the dynamic primary production rate of a reservoir with an arbitrary number of wells all operating at the same constant pressure condition. The model is an extension of the classic tank model, which is inherently a single flowing phase development. With the ability to make a priori predictions of production figures, users can screen various prospect assets on the basis of economic potential through optimization routines on the GFRM. Gravity drainage and its approximation through numerical simulation are analyzed. A sensitivity study was conducted on three-phase gravity drainage, leading to the conclusion that small changes in vertical permeability and portions of the relative permeability-saturation relationships can greatly affect production rates. Finally, two-phase (oil and air) and regions of three-phase (water, oil, air) flow simulations were found to exhibit exponential decline in phase production rates, which may enable the GFRM to be applicable to UGD-type processes.Item Geophysical investigations of the coastal evolution of the Totten Glacier System, East Antarctica(2015-11-24) Greenbaum, Jamin Stevens; Blankenship, Donald D.; Grand, Stephen; Heimbach, Patrick; Jackson, Charles; Sen, Mrinal; Wilson, Clark; Young, DuncanThe Sabrina Coast is the primary outlet of ice from the Aurora Subglacial Basin, draining more than 3.5 meters of eustatic sea level potential into the Indo-Pacific sector of the Southern Ocean. Recent work has shown that the Aurora Subglacial Basin has drained and filled many times since large scale glaciation began including evidence that it collapsed during the Pliocene. Ice predominantly flows from the interior to the coast through two outlet glaciers, Totten Glacier and the unnamed glacier feeding the Moscow University Ice Shelf. Steady thinning rates near the grounding line of Totten Glacier are the largest in East Antarctica and the nature of the thinning suggests that it is driven by enhanced basal melting due to ocean processes while thinning rates are modest for the glacier feeding the Moscow University Ice Shelf. Warm modified Circumpolar Deep Water (mCDW), which has been linked to glacier retreat in West Antarctica, has been observed in summer and winter on the Sabrina Coast continental shelf in the 300-600 m depth range. Here we show that entrances to the cavity deeper than this range of thermocline depths indicate that the TGIS is vulnerable to intrusions of mCDW. We relate areas of elevated basal specularity and reflectivity (flatness and brightness of the ice-ocean interface, respectively), supported by independent model predictions and ice flow divergence estimates of basal melt, to ice draft and ice thinning rates, demonstrating that the current climatological regime is enhancing melting of ice deeper than 800 mbsl in the cavity, possibly resulting in a bifurcated coastal ice thinning signal. For the first time in East Antarctica, and the first time using ice sounding radar, we identify large basal channels and flat terraces several kilometers wide and several hundred meters deep produced by complex ice-ocean melt processes in the deep, warm cavity waters. Finally, by analyzing new physical oceanographic data recently acquired along the Sabrina Coast, we show that the depths of deep, warm mCDW observed on the continental shelf relative to the coastal bathymetry control the coastal thinning of ice between the Moscow University Ice Shelf and Totten Glacier; moderate shoaling the average depth of the thermocline would allow the observed mCDW to breach this topography and enhance coastal melting. The lack of dense, cool Shelf Water at depth on the continental shelf indicates that that variability in heat content along the Sabrina Coast is driven by far-field oceanic boundary conditions, not to polynya activity as has been proposed. Predicting future change in this important area of the coastline requires improved knowledge of the sub-ice shelf boundary conditions and processes, and controls on continental shelf circulation and heat transfer.Item Improving the observation of time-variable gravity using GRACE RL04 data(2010-12) Bonin, Jennifer Anne; Tapley, Byron D.The Gravity Recovery and Climate Experiment (GRACE) project has two primary goals: to determine the Earth’s mean gravitational field over the lifetime of the mission and to observe the time-variable nature of the gravitational field. The Center for Space Research's (CSR) Release 4 (RL04) GRACE solutions are currently created via a least-squares process that assimilates data collected over a month using a simple boxcar window and determines a spherical harmonic representation of the monthly gravitational field. The nature of this technique obscures the time-variable gravity field on time scales shorter than one month and spatial scales shorter than a few hundred kilometers. A computational algorithm is developed here that allows increased temporal resolution of the GRACE gravity information, thus allowing the Earth's time-variable gravity to be more clearly observed. The primary technique used is a sliding-window algorithm attached to a weighted version of batch least squares estimation. A number of different temporal windowing functions are evaluated. Their results are investigated via both spectral and spatial analyses, and globally as well as in localized regions. In addition to being compared to each other, the solutions are also compared to external models and data sets, as well as to other high-frequency GRACE solutions made outside CSR. The results demonstrate that a GRACE solution made from at least eight days of data will provide a well-conditioned solution. A series of solutions made with windows of at least that length is capable of observing the expected near-annual signal. The results also indicate that the signals at frequencies greater than 3 cycles/year are often smaller than the GRACE errors, making detection unreliable. Altering the windowing technique does not noticeably improve the resolution, since the spectra of the expected errors and the expected non-annual signals are very similar, leading any window to affect them in the same manner.Item Interpreting the Earth's time varying geopotential as observed from space and comparisons to global models of hydrologic transport(2004) Thompson, Paul Frank; Tapley, Byron D.Measurements of temporal changes in Earthís gravitational field were measured using six years of satellite laser ranging (SLR) to Lageos-1 and Lagoes-2 and the results were compared to geophysical models of mass variability for the atmosphere, ocean, and continental hydrology. Annual estimates of spherical harmonic gravity coefficients (degree and order four expansion) derived from the SLR observations when compared to combinations of the mass models had degree correlations that generally exceeded the 90% confidence limit and agreed to about the 1 mm level in terms of geoid height anomaly. The Gravity Recovery and Climate Experiment (GRACE) is measuring Earthís gravitational field approximately every month at spatial scales of a few hundred kilometers. In order to achieve smaller temporal and spatial scales, it is necessary to account for the effects of short period, non-tidal, mass variability which was not previously included in other gravity determinations. Orbital simulations of GRACE showed that the highest degrees were impacted the most by unmodeled variability in the atmosphere, oceans, and continental hydrology (a factor of ~20 increase in degree error in the case of the atmosphere). The use of approximate models gave the greatest reduction in aliasing error for the mid-degrees and higher; however, the lowest degrees (~2-5) were dominated by the sensitivity of the GRACE processing system to systematic error. GRACE data processing that used a combined atmosphere-ocean de-aliasing (AOD) model showed improvement in the gravity estimates consistent with the simulations: the shorter spatial wavelengths (higher degrees) were improved while the longest spatial wavelengths (particularly important for time-variable gravity studies) were relatively unaffected. Monthly gravity solutions from GRACE resolved features on the order of 2-3 mm geoid height anomaly when smoothed to 400-km spatial scales. Comparisons with the Global Land Data Assimilation System (GLDAS) terrestrial water storage model indicated a high degree of correlation up to spatial wavelengths of 600 km or larger; a significant improvement over the spatial and temporal scales obtained with SLR observations. However, temporal variability in the degree 2 coefficients, particularly the zonal, seemed to be better resolved by SLR observations than by GRACE observations.Item Investigation of the role of extracellular nucleotide gradients in plant gravity responses(2016-12) Cannon, Ashley Elisabeth; Roux, Stanley J.; Browning, Karen S; Huq, Enamul; Levin, Donald A; Mehdy, MonaExtracellular ATP (eATP) was first identified as a neurotransmitter in animal systems decades ago, but has only recently been classified as a signaling molecule in plants. Previous studies have shown that exogenously applied ATP can disrupt gravitropism in roots, depolarize root hairs, and alter auxin distribution. These results support a clear role for this molecule as a regulatory signal in plants. To further define eATP as a signal in plants, Ceratopteris spores, a model system, were used to study gravity-directed cell polarization. This polarization begins with the uptake of Ca2+ through channels at the bottom of the spore, a process required for the cell’s gravity response. Previous data showing that mechanosensitive channels can release ATP and that eATP can induce the opening of Ca2+ channels led to the hypothesis that eATP could play a role in the gravity-directed polarization. Data described in this dissertation show that an eATP gradient, with significantly higher [ATP] outside the bottom of the cell, is present during and promotes gravity-directed polarization. To explore the link between eATP and Ca2+ in gravity-directed polarization of spores, microparticle bombardment was used to transform Ceratopteris cells with a FRET-based Ca2+ sensor, Yellow Cameleon 3.60. The success of this effort has generated a uniquely valuable tool that can be used to analyze intracellular Ca2+ dynamics and rapidly screen transformants in Ceratopteris, a primitive plant system. In addition to studying the role of eATP signaling in the gravity response of single cells, an assessment of its role in the gravity response of a multicellular system, primary roots of Arabidopsis, was carried out. By using ecto-luciferase-expressing seedlings, a gradient of eATP, with the highest concentration being along the bottom of the root, was visualized within 30 min of gravistimulation. When this gradient was disrupted by excess ATP or an eATP receptor antagonist, the gravity response was attenuated. These results characterize the role of eATP gradients in the gravity responses of single spore cells of ferns and multicellular primary roots of a flowering plant. They suggest that the preferential accumulation of eATP along the bottom of gravity-responding cells is an evolutionarily conserved mechanism for promoting gravity-directed development.Item Measuring frame-dragging with LARES, and other topics in gravity(2017-05) Nguyen, Phuc Hong; Matzner, Richard A. (Richard Alfred), 1942-; Fischler, Willy; Paban, Sonia; Kilic, Can; Sadun, LorenzoThis dissertation is divided into two conceptually distinct parts, which both fall under the broad umbrella of gravitational physics. In the first part, we describe work done on the LARES experiment whose goal is to measure the Lense-Thirring effect of general relativity. We first review the derivation of the Lense-Thirring effect, then review past experimental efforts to confirm it, and finally describe our work to help model one of the major error sources of the experiment. In the second part, we give two sample of work done in the area of holography. The first sample presents a toy model for Schwinger pair creation in de Sitter space. The second sample establishes a link between quantum complexity and the thermodynamic volume of black holes.Item Preliminary design of spacecraft trajectories for missions to outer planets and small bodies(2015-08) Lantukh, Demyan Vasilyevich; Russell, Ryan Paul, 1976-; Fowler, Wallace; Bettadpur, Srinivas; Guo, Yanping; Broschart, StephenMultiple gravity assist (MGA) spacecraft trajectories can be difficult to find, an intractable problem to solve completely. However, these trajectories have enormous benefits for missions to challenging destinations such as outer planets and primitive bodies. Techniques are presented to aid in solving this problem with a global search tool and additional investigation into one particular proximity operations option is discussed. Explore is a global grid-search MGA trajectory pathsolving tool. An efficient sequential tree search eliminates v∞ discontinuities and prunes trajectories. Performance indices may be applied to further prune the search, with multiple objectives handled by allowing these indices to change between trajectory segments and by pruning with a Pareto-optimality ranking. The MGA search is extended to include deep space maneuvers (DSM), v∞ leveraging transfers (VILT) and low-thrust (LT) transfers. In addition, rendezvous or nπ sequences can patch the transfers together, enabling automatic augmentation of the MGA sequence. Details of VILT segments and nπ sequences are presented: A boundaryvalue problem (BVP) VILT formulation using a one-dimensional root-solve enables inclusion of an efficient class of maneuvers with runtime comparable to solving ballistic transfers. Importantly, the BVP VILT also allows the calculation of velocity-aligned apsidal maneuvers (VAM), including inter-body transfers and orbit insertion maneuvers. A method for automated inclusion of nπ transfers such as resonant returns and back-flip trajectories is introduced: a BVP is posed on the v∞ sphere and solved with one or more nπ transfers – which may additionally fulfill specified science objectives. The nπ sequence BVP is implemented within the broader search, combining nπ and other transfers in the same trajectory. To aid proximity operations around small bodies, analytical methods are used to investigate stability regions in the presence of significant solar radiation pressure (SRP) and body oblateness perturbations. The interactions of these perturbations allow for heliotropic orbits, a stable family of low-altitude orbits investigated in detail. A novel constrained double-averaging technique analytically determines inclined heliotropic orbits. This type of knowledge is uniquely valuable for small body missions where SRP and irregular body shape are very important and where target selection is often a part of the mission design.Item Simulation study of surfactant transport mechanisms in naturally fractured reservoirs(2010-08) Abbasi Asl, Yousef; Pope, Gary A.; Mohanty, Kishore K.Surfactants both change the wettability and lower the interfacial tension by various degrees depending on the type of surfactant and how it interacts with the specific oil. Ultra low IFT means almost zero capillary pressure, which in turn indicates little oil should be produced from capillary imbibition when the surfactant reduces the IFT in naturally fractured oil reservoirs that are mixed-wet or oil-wet. What is the transport mechanism for the surfactant to get far into the matrix and how does it scale? Molecular diffusion and capillary pressure are much too slow to explain the experimental data. Recent dynamic laboratory data suggest that the process is faster when a pressure gradient is applied compared to static tests. A mechanistic chemical compositional simulator was used to study the effect of pressure gradient on chemical oil recovery from naturally fractured oil reservoirs for several different chemical processes (polymer, surfactant, surfactant-polymer, alkali-surfactant-polymer flooding). The fractures were simulated explicitly by using small gridblocks with fracture properties. Both homogeneous and heterogeneous matrix blocks were simulated. Microemulsion phase behavior and related chemistry and physics were modeled in a manner similar to single porosity reservoirs. The simulations indicate that even very small pressure gradients (transverse to the flow in the fractures) are highly significant in terms of the chemical transport into the matrix and that increasing the injected fluid viscosity greatly improves the oil recovery. Field scale simulations show that the transverse pressure gradients promote transport of the surfactant into the matrix at a feasible rate even when there is a high contrast between the permeability of the fractures and the matrix. These simulations indicate that injecting a chemical solution that is viscous (because of polymer or foam or microemulsion) and lowers the IFT as well as alters the wettability from mixed-wet to water-wet, produces more oil and produces it faster than static chemical processes. These findings have significant implications for enhanced oil recovery from naturally fractured oil reservoirs and how these processes should be optimized and scaled up from the laboratory to the field.Item Toward a theory of observation(2014-08) Carney, Daniel Joseph, Jr.; Fischler, Willy; Paban, SoniaQuantum mechanics is usually formulated in terms of a single Hilbert space and observables are defined as operators on this space. Attempts to describe entire spacetimes and their resident matter in this way often encounter paradoxes. For example, it has been argued that an observer falling into a black hole may be able to witness deviations from unitary, violations of semi-classical quantum field theory, and the like. This thesis argues that the essential problem is the insistence on the use of a single, global Hilbert space, because in general it may be that a physical observer cannot causally probe all of the information described by this space due to the presence of horizons. Instead, one could try to define unitary quantum physics directly in terms of the information causally accessible to particular observers. This thesis makes steps toward a systematization of this idea. Given an observer on a timelike worldline, I construct coordinates which (in good cases) cover precisely the set of events to which she can send and then receive a signal. These coordinates have spatial sections parametrized by her proper time, and the metric manifestly encodes the equivalence principle in the sense that it is flat along her worldline. To describe the quantum theory of fields according to these observers, I define Hilbert spaces in terms of field configurations on these spatial sections and show how to implement unitary time-evolution along proper time. I explain how to compare the observations of a pair of observers, and how to obtain the description according to some particular observer given some a priori global description. In this sense, the program outlined here constructs a manifestly unitary description of the events which the observer can causally probe. I give a number of explicit examples of the coordinates, and show how the quantum theory works for a uniformly accelerated observer in flat spacetime and for an inertial (co-moving) observer in an inflating universe.Item Utilization of simulated GRACE inter-satellite range-accelerations to estimate Earth's gravity field(2019-02-06) Smith, Matthew Scott; Bettadpur, Srinivas Viswanath, 1963-The Gravity Recovery and Climate Experiment (GRACE) provides high-precision K-band Ranging (KBR) data which has been instrumental in improving our understanding of the monthly mass redistribution within the Earth system, and consequently its static and time-varying gravity fields. In practice, estimation of the Earth's gravity field with data from GRACE-like missions is typically done via the range-rate pseudo-observations. This approach is widely used and produces high-quality solutions, however there does exist a well-known North-South striping error in the resulting gravity field. It is thought there may be a potential benefit from utilizing instead the range-acceleration pseudo-observations, which should be sensitive to more spatially-localized mass variations in the signal, thereby reducing the N-S errors in the gravity field and facilitating more precise estimation to higher degrees. Most solutions obtained from range-accelerations to date have been unusable at worst and lesser in quality at best when compared to range-rate derived gravity field solutions. Current understanding is that this is due to the time-differentiation of the KBR signal required to obtain the range-acceleration measurements. The differentiation process acts as a high-pass filter, degrading the signal-to-noise ratio (SNR) at high frequencies, and thus the quality of the solution. The purpose of this work, which explores variational methods solely, is to discover what conditions, if any, make it possible to generate feasible solutions via range-accelerations, and to compare them to one obtained via range-rate. A 180x180 range-rate based gravity field solution produced from simulated August 2008 data was used as a baseline for these comparisons. It is demonstrated that adjusting the parameters of the currently-used filter for obtaining the range-accelerations provides some improvement in the resulting solutions. Conversely, attempts with an alternative approach to filtering the range measurements yielded no benefit over the current method, and only served to degrade the solutions further. However, through an application of filtering the range residuals instead, this research suggests that the culprit is not solely the noise induced by differentiation, but the inclusion of other noisy measurements necessary for the computation of the range-acceleration measurement equation. Through this new method, it is shown that not only are range-accelerations viable for estimating the gravity field, but they can produce solutions more accurate at higher degrees than their range-rate counterparts. While these results are encouraging for processing the range-accelerations, the same technique can be applied to range-rate based solutions, which produces similar improvements and again establishes that quantity as the most suitable for estimating the gravity field, for now.Item Wind Work(2009-04) Barker, Daniel S.