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The dramatic increase in the amount of content available in digital forms gives rise to large-scale digital libraries, targeted to support millions of users and terabytes of data. Retrieving information from a system of this scale in an efficient manner is a challenging task due to the size of the collection as well as the index. This research deals with the design and implementation of an inverted index that supports searching for information in a large-scale digital library, implemented atop a massively parallel storage system. Inverted index partitioning is studied in a simulation environment, aiming at a terabyte of text. As a result, a high performance partitioning scheme is proposed. It combines the best qualities of the term and document partitioning approaches in a new Hybrid Partitioning Scheme. Simulation experiments show that this organization provides good performance over a wide range of conditions. Further, the issues of creation and incremental updates of the index are considered. A disk-based inversion algorithm and an extensible inverted index architecture are described, and experimental results with actual collections are presented. Finally, distributed algorithms to create a parallel inverted index partitioned according to the hybrid scheme are proposed, and performance is measured on a portion of the equipment that normally makes up the 100 node Virginia Tech PetaPlex™ system. NOTE: (02/2007) An updated copy of this ETD was added after there were patron reports of problems with the file. / Ph. D.

The inverted-T bridge system is a rapid bridge construction technique that consists of precast inverted-T girders placed adjacent to one another and covered with a cast-in-place deck. This system was first implemented in the U.S. by the Minnesota Department of Transportation (Mn/DOT). This research focuses on improving the constructability of the Mn/DOT system while maintaining the system's structural performance characteristics. To accomplish this goal, five sub-assemblage specimens were cast and tested in the structures laboratory at Virginia Tech. These tests focused on identifying an improved precast girder geometry and transverse sub-assemblage connection for this system. From this study it was found that all of the proposed specimens behaved adequately at service load and strength. From these results, it is recommended to further evaluate a specimen with a tapered profile and no physical connection between precast girders for use in a Virginia Department of Transportation bridge near Richmond, VA. / Master of Science

The inverted T-beam bridge system is a bridge construction technique that follows accelerated bridge construction processes. The system was discovered in France and first adopted in the U.S. by the Minnesota Department of Transportation. In 2012 the system was modified and adopted by Virginia, with research being carried out at Virginia Polytechnic Institute and State University (Virginia Tech). The research focused on multiple items involving the system, but the most relevant one is that regarding the transverse bending behavior of the system for different geometries, and joint types between adjacent precast beam members. The study found that using a joint system without any mechanical connection between adjacent beams was most efficient, and gave adequate performance under monotonic loading. The study recommended cyclic load testing be carried out on this joint type, as well as a welded joint similar to those found in decked bulb-T systems. The research contained herein presents the setup and results of this testing. From the work it was found that the no-connection joint behaves adequately under cyclic loading at service loads, however surface roughening between precast and cast-in-place concrete must be adequate. The welded connection behaves well, granted the surfaces to be welded are properly prepared. From these results it is recommended to evaluate different surface roughening techniques, and repeat the cyclic testing using the best. The surface roughening technique chosen should be used to provide guidance on this aspect of construction with inverted T-beams. / Master of Science / The inverted T-beam bridge system is a new type of bridge system intended for use in short to medium length bridges. The system was discovered in France in 2004, where a similar type was being used. It was first modified slightly, and adopted in the in Minnesota. In 2012, the system was again modified to increase its strength and its construction speed, and was then adopted in Virginia. The modifications to the system in Virginia focused on the connections between the individual units making up the bridge, and the geometry of each of these units. The focus of this research was to quantify the long-term performance of two of the connection types currently used on bridges in Virginia. This was achieved by subjecting a test specimen to repeated loads in the laboratory at Virginia Tech. The loading used in the laboratory represented the conditions that a real bridge of this type would be subjected to. The research showed that the two connection types performed well under the repeated loading conditions. However, it was concluded that the concrete surfaces which are in contact with one another must be properly roughened, so that the system maintains its strength. The importance of this research is due to the fact that the large costs associated with maintaining the nation’s bridge infrastructure can be substantially reduced due to this system’s quick and simple construction. In addition to this, road users experience less disruption because of the shortened construction times.

With balance assessment being essential to the prediction of fall risk and detection and assessment of motor disorders, increasing clinical accessibility to objective balance metrics is essential. Work has been done validating center of mass (COM) acceleration metrics against well regarded force plate center of pressure (COP) position standards for mobile device data acquisition systems, but most research is restricted to devices being close to the COM or strapped in a harness configuration. Through the use of rigid body kinematics and the inverted pendulum model, this study develops novel methodology for calculating COM acceleration using mobile devices in arbitrary positions, as well as a novel approach to validation through direct comparison of COP position predictions to force plate measurements. Validation of this methodology included comparison of smartphone and force plate results for COM accelerations and COP positions. Results showed good analysis performance for both approaches during subject intentional swaying, but results were limited in cases of little motion where good balance was observed.

In recent years, the demand for compact handheld communication devices has grown significantly. Devices having internal antennas have appeared to fill this need. Antenna size is a major factor that limits device miniaturization. In the past few years, new designs based on the microstrip antennas (MSA) and planar inverted-F antennas have been used for handheld wireless devices because these antennas have low-profile geometry and can be embedded into the devices. New wireless applications requiring operation in more than one frequency band are emerging. Dual-band and tri-band phones have gained popularity because of the multiple frequency bands used for wireless applications. One prominent application is to include bluetooth, operating band at 2.4 GHz, for short-range wireless use. This thesis examines two antennas that are potential candidates for small and low-profile structures: microstrip antennas and planar inverted-F antennas. Two techniques for widening the antenna impedance bandwidth are examined by adding parasitic elements. Reducing antenna size generally degrades antenna performance. It is therefore important to also examine the fundamental limits and parameter tradeoffs involved in size reduction. In the handheld environment, antennas are mounted on a small ground plane. Ground plane size effects on antennas are investigated and the results from a thorough numerical study on the performance of a PIFA with various ground planes sizes and shapes is reported. Finally, a new wideband compact PIFA antenna (WC-PIFA) is proposed. Preliminary work is presented along with numerical and experimental results for various environments such as free space, plastic casing, and the proximity of a hand. This new antenna covers frequencies from 1700 MHz to 2500 MHz, which basically include the following operating bands: DCS-1800m PCS-1900, IMT-2000, ISM, and Bluetooth. / Master of Science

Spinal cord injury and stroke affect many people each year and can result in the loss of muscle function. Current research attempts to correct muscle paralysis through the use of mechanical braces or through open-loop stimulation methods. However, prosthetic systems that use closed-loop control strategies can offer improved functionality by accounting for the changing dynamics associated with the human body and external disturbances. In particular, closed-loop functional electrical stimulation (FES) offers the possibility of moving paralyzed muscles in a predetermined manner, allowing a paraplegic individual to regain the ability to perform some tasks. An experimental setup was designed for the development and testing of a closed-loop FES control system, as well as the characterization of muscle properties. Due to the complexities associated with using a human subject, an inverted pendulum model is utilized for this preliminary study. This model is a basic engineering control problem often used when studying postural control in humans. In particular, electrical stimuli will be applied to the gastrocnemius muscle of a frog in order to produce a contraction force that will drive an inverted pendulum and maintain its desired angle. The stimulation signal will be determined by control algorithms applied through the use of Matlab® and implemented in real-time with a data acquisition system. This setup will help provide an understanding of the muscle behavior and can be used to establish the validity of proposed controller methods.

This thesis investigates the impact of interface surface treatment methods for use in the Virginia Inverted T-Beam bridge system. The specific system consists of precast beams with thin bottom flanges placed next to one another, with a cast-in-place slab on top. Previous research has shown that the strength of this system after cyclic loading is highly dependent upon the shear strength of the interface between the precast and cast-in-place sections, especially for the adhesion-based connection configuration. The approval of this bridge system for use in bridges with high daily traffic volumes hinges on the verification of its strength and durability for a 50-year lifespan. The shear strength of ten different surface textures was tested using push-off tests to determine which interface roughening methods would prove adequate for use in the bridge system. The strength was found to depend on both the amplitude and the geometry of the undulations on the beam-to-slab interface. Using this information, a texture was selected for a new trial of the adhesion-based connection configuration, and a test specimen was constructed. After completing cyclic loading to simulate the design life of the bridge, it was found that the system achieved a strength similar to previous monotonically loaded specimens. It was concluded that the bridge is safe for use in high daily traffic areas provided that a surface roughening with adequate shear strength is used. / Master of Science / The Virginia Inverted T-Beam bridge system was initially designed to be more durable and economical than other types of bridges. The bridge is constructed by arranging prefabricated beams side-by-side across the span before placing fresh concrete overtop. In the most economical version of the system, the only connection between the beams is the newly placed concrete. For the beams and topping to act together, the bond between them must be strong. Roughening the surface of the prefabricated beams increases the strength of the bond, although different roughening patterns achieve different levels of strength. Past tests of the bridge system have utilized inadequate roughing patterns which lead to low bridge failure loads after many loading cycles. This low-cost configuration is currently only approved for use in low daily traffic areas. The goal of this research was to determine a roughening pattern that would result in a high bridge failure load which would allow the low-cost configuration to be approved for high daily traffic areas. Several roughening patterns were investigated and the patterns producing the highest shear strengths were determined. The best pattern was chosen to be used for the bridge configuration and a sub-section of the bridge was constructed. This specimen was subjected to a loading protocol that simulated the traffic that an actual bridge would be subjected to over its life span. The failure load was then measured and found to be high enough to warrant the use of the specific system in high daily traffic areas.

In this thesis we focus on two elementary unstable quantum systems, the inverted harmonic oscillator and the inverse square potential, using the methods of effective field theory (EFT) and the renormalization group (RG). We demonstrate that the phenomenon of fall to the centre associated with the inverse square potential is an example of a PT symmetry breaking transition. We also demonstrate a mapping between the inverted harmonic oscillator and the inverse square potential including a one-to-one mapping between the quantum states and boundary conditions using an EFT framework in a renormalization group invariant way. We apply these methods to the phenomenon of Schwinger pair production and study finite size effects using the RG scheme for the quantum inverted harmonic oscillator. / Thesis / Doctor of Philosophy (PhD)

<p>The economic development and industrialization that has taken place in many parts of the world during the past century has brought about a huge increase in economic welfare. During this process, it has repeatedly been debated whether the gains from economic development are shared by everyone or just a few. In the field of economics, vast research has been conducted on this particular subject ever since the 1950’s. The most famous contribution might be said to be Simon Kuznets article, Growth and Income Inequality from 1955 and the ”inverted U”-hypothesis that was formulated on the basis of that article. The essence of the hypothesis is that a country, during its development, moves from agricultural to industrial production. At first, income inequality increases and then, at the end of the process, decreases.</p><p>The aim of this paper has been to investigate the relationship between income distribution and economic development in a particular region, namely the countries of the former Soviet Union, during 1992-2003. Also, we have tested whether Kuznets theory and the “inverted U”-hypothesis hold true for our sample. The investigations method is a survey, which uses secondary data collected from the World Bank’s database of World Development Indicators. Regression-analysis has been employed to conduct cross-sections between 20 countries over 4 periods in Eastern Europe and Central Asia. The number of observations equals to 62. The variables that we use are: the Gini index, GDP per capita and the agricultural sector’s share of GDP.</p><p>The results of the regression do not indicate any resemblance to the pattern of the “inverted U”-hypothesis. The curve we get is that of a “positive U”. Countries with high GDP per capita as well as countries with low GDP per capita have high income inequality. Countries with mediate GDP per capita levels have low income inequality. Our analysis concludes that the countries in our sample might have had a very unique economic development following the fall of the Soviet Union. Only 7 countries partly follow the Kuznets theory if tested individually. Since these seven countries seem to have a reversed development with increasing agricultural sector and the remainder of the countries show increasing income inequality, we reject the “inverted U”-hypothesis and question the ability of Kuznets’ theory to explain income distribution for our sample.</p>