Modeling of the ionosphere has been a highly interesting subject within the scientific community due to its effects on the propagation of electromagnetic waves. The development of the Global Positioning System (GPS) and creation of extensive ground-based GPS networks started a new period in observation of the ionosphere, which resulted in several studies on GPS-based modeling of the ionosphere. However, software studies on the subject that are open to the scientific community have not progressed in a similar manner and the options for the research community to reach ionospheric modeling results are still limited. Being aware of this need, a new MATLAB&reg / based ionosphere modeling software, i.e. TECmapper is developed within the study. The software uses three different algorithms for the modeling of the Vertical Total Electron Content (VTEC) of the ionosphere, namely, 2D B-spline, 3D B-spline and spherical harmonic models. The study includes modifications for the original forms of the B-spline and the spherical harmonic approaches. In order to decrease the effect of outliers in the data a robust regression algorithm is utilized as an alternative to the least squares estimation. Besides, two regularization methods are employed to stabilize the ill-conditioned problems in parameter estimation stage. The software and models are tested on a real data set from ground-based GPS receivers over Turkey. Results indicate that the B-spline models are more successful for the local or regional modeling of the VTEC. However, spherical harmonics should be preferred for global applications since the B-spline approach is based on Euclidean theory.

In this paper, a mixed boundary value problem for the Laplace-Beltrami operator is considered for spherical domains in $R^3$, i.e. for domains on the unit sphere. These domains are parametrized by spherical coordinates (\varphi, \theta), such that functions on the unit sphere are considered as functions in these coordinates. Careful investigation leads to the introduction of a proper finite element space corresponding to an isotropic triangulation of the underlying domain on the unit sphere. Error estimates are proven for a Clément-type interpolation operator, where appropriate, weighted norms are used. The estimates are applied to the deduction of a reliable and efficient residual error estimator for the Laplace-Beltrami operator.

Thermal energy storage (TES) is one of the most attractive and cost effective solutions to the intermittent generation systems like solar, wind and other renewable sources, compared to alternatives. It creates a bridge between the power supply and demand during peak hours or at times of emergency to ensure the continuous supply of energy. Among all the TES systems, latent heat thermal energy storage (LHTES) draws lots of interests as it has high energy density and can store or retrieve energy isothermally. Two major technical challenges associated with the LHTES are low thermal conductivity of the phase change materials (PCMs), and corrosion tendency of the containment vessel with the PCMs. Macro-encapsulation of the PCM is one of the techniques to encounter the low thermal conductivity issue as it will maximize the heat transfer area for the given volume of the PCM and restrict the PCMs to get in contact with the containment vessel. However, finding a suitable encapsulation technique that can address the volumetric expansion problem and compatible shell material are significant barriers of this approach. In the present work, an innovative technique to encapsulate PCMs that melt in the 100-350 oC temperature range was developed for industrial and private applications. This technique did not require a sacrificial layer to accommodate the volumetric expansion of the PCMs on melting. The encapsulation consisted of coating a non-reactive polymer over the PCM pellet followed by deposition of a metal layer by a novel non-vacuum metal deposition technique. The fabricated spherical capsules were tested in different heat transfer fluid (HTF) environments like air, oil and molten salt (solar salt). Thermophysical properties of the PCMs were investigated by DSC/TGA, IR and weight change analysis before and after the thermal cycling. Also, the constrained melting and solidification of sodium nitrate PCM inside the spherical capsules of different sizes were compared to explore the charging and discharging time. To accomplish this, three thermocouples were installed vertically inside the capsule at three equidistant positions. Low-density graphene was dispersed in the PCM to increase its conductivity and compared with pure PCM capsules. A laboratory scale packed-bed LHTES system was designed and built to investigate the performance of the capsules. Sodium nitrate (m.p. 306oC) was used as the PCM and air was used as the heat transfer fluid (HTF). The storage system was operated between 286oC and 326oC and the volumetric flow rate of the HTF was varied from 110 m3/h to 151 m3/h. The temperature distribution along the bed (radially and axially) and inside the capsules was monitored continuously during charging and discharging of the system. The effect of the HTF mass flow rate on the charging and discharging time and on the pressure drop across the bed was evaluated. Also, the energy and exergy efficiencies were calculated for three different flow rates. Finally, a step-by-step trial manufacturing process was proposed to produce large number of spherical capsules.

Single-probe formation testers have been used since the 1950s to measure pore pressure and estimate mobility in fluid-bearing formations penetrated by a well. They are widely used in the oil and gas industry, with tens of measurements often made in every newly drilled well as part of the formation evaluation program. Each measurement consists of placing the tool in the wellbore in direct contact with the face of the formation, extracting a small amount of fluid (from 1 to 50 cc) from the rock and analyzing the fluid pressure response of the system. Pressure interpretation is based on models that assume that temperature within the formation tester flowline remains constant during the tool operation. However, formation pressure measurement involves relatively fast volume and pressure changes within the flowline, which result in temperature changes. These temperature changes are modeled semi-analytically and their effect on pressure transients is analyzed. Temperature variations are accounted for by describing the pressure and temperature dependence of fluid density in the continuity equation, and that temperature varies with both space and time. It is considered here that once a temperature change is imposed on the system, the primary mechanism of thermal transport to achieve equilibrium is conduction. Including temperature in the analysis requires taking into account flowline geometry, and well environmental conditions during the measurement-- namely, wellbore temperature and type of drilling fluid in the wellbore, all of which are immaterial in the isothermal analysis. Arguably, pressure behavior during formation tester measurements could be influenced by several factors. All previous studies related to formation testers assume perfect tool performance and provide explanations to pressure behaviors from the reservoir point of view (e.g., Stewart and Witmmann, 1979; Phelps et al., 1984; Proett and Chin, 1996, etc.). The approach followed here is diametrically opposite. The formation is considered `perfect' from the point of view of pressure measurement, and physical phenomena (thermal transients) that may affect the measured pressure signal are studied. The focus is to understand fundamental aspects of the tool performance that can be studied analytically while minimizing, as much as possible, external parameters that add uncertainty. This dissertation was motivated by inconsistencies observed between the pressure behavior in field measurements and existing (isothermal) theory. For instance, false buildups, buildup overshoots and long time required to reach pressure equilibration, have puzzled those involved in the interpretation of formation tester pressure transients for many years. These behaviors can be reproduced in pressure computations when accounting for temperature variations. The focus of this dissertation is on modeling the tool capability to sense pressure transients associated with recompression of formation fluids several inches away from the wellbore, accounting for temperature variations during the measurement. This is relevant because it is desirable to characterize formation properties beyond the region affected by drilling mud filtrate invasion. In practice, a discrepancy is often observed between formation mobility obtained from drawdown, which depends mostly on formation properties near the wellbore, and mobility obtained from the analysis of late-time buildup pressure, which in theory depends on formation properties farther from the wellbore (Moran and Finklea, 1962). This dissertation examines the influence of late-time tool storage effects caused by thermal equilibration of the flowline fluid on the pressure equilibration and buildup mobility interpretation. It was found that in some cases such late-time storage effects could exhibit a behavior that resembles that expected from spherical flow, that is, the flow regime characteristic of single-probe formation testers; and could therefore invalidate mobility determined by isothermal transient pressure analysis. Formation tester flowline and probe design, test parameters (rate and volume), and environmental conditions during the measurement, mostly type of drilling fluid and wellbore temperature, are important variables in determining the magnitude of late-time storage effects, and hence the tool capability to detect a deep formation signal (spherical flow). Temperature variations affecting late-buildup pressure transients were observed to be more pronounced (listed in order of importance): as wellbore temperature increases; drilling fluid is oil-based mud; flowline with large radius components (e.g. > 1 cm); large flowline volume; small probe radius (< 1 cm); and, large drawdown rate. Temperature effects on the late-buildup also tend to be more significant when mobility is in the 0.1 to 10 md/cp range, that is for those formations more likely, in theory, to exhibit spherical flow regime during buildup. / text

Compliant mechanism theory permits a procedure called rigidbody replacement, in which two or more rigid links of the mechanism are replaced by a compliant flexure with equivalent motion. Methods for designing flexure with equivalent motion to replace rigid links are detailed in Pseudo-Rigid-Body Models (PRBMs). Such models have previously been developed for planar mechanisms. This thesis develops the first PRBM for spherical mechanisms. In formulating this PRBM for a spherical mechanism, we begin by applying displacements are applied to a curved beam that cause it todeflect in a manner consistent with spherical kinematics. The motion of the beam is calculated using Finite Element Analysis. These results areanalyzed to give the PRBM parameters. These PRBM parameters vary with the arc length and the aspect ratio of the curved beam.

Fast algorithms for potential evaluation in N-body problems often tend to be extremely abstract and complex. This thesis presents a simple, hierarchical approach to solving the potential evaluation problem in O(n) time. The approach is developed in the field of electrostatics and can be extended to N-body problems in general. Herein, the potential vector is expressed as a product of the potential matrix and the charge vector. The potential matrix itself is a product of component matrices. The potential function satisfies the Laplace equation and is hence expressed as a linear combination of spherical harmonics, which form the general solutions of the Laplace equation. The orthogonality of the spherical harmonics is exploited to reduce execution time. The duality of the various lists in the algorithm is used to reduce storage and computational complexity. A smart tree-construction strategy leads to efficient parallelism at computation intensive stages of the algorithm. The computational complexity of the algorithm is better than that of the Fast Multipole Algorithm, which is one of the fastest contemporary algorithms to solve the potential evaluation problem. Experimental results show that accuracy of the algorithm is comparable to that of the Fast Multipole Algorithm. However, this approach uses some implementation principles from the Fast Multipole Algorithm. Parallel efficiency and scalability of the algorithms are studied by the experiments on IBM p690 multiprocessors.

No description available.

While much research has been done regarding different Nonnegative Matrix Factorization (NMF) algorithms, less time has been spent looking at initialization techniques. In this thesis, four different initializations are considered. After a brief discussion of NMF, the four initializations are described and each one is independently examined, followed by a comparison of the techniques. Next, each initialization's performance is investigated with respect to the changes in the size of the data set. Finally, a method by which smaller data sets may be used to determine how to treat larger data sets is examined.

No description available.

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