The energy absorption capacity of a series of axially crushed composite tubes fabricated from high tow count graphite fiber is compared with those of similar tubes fabricated from aerospace-grade fiber to determine the viability of considering the use of such fibers in automotive applications. To that end, graphite-epoxy tubular specimens with circular and square cross-sectional geometries; stacking sequences with ±45° fibers and with both ±45° and 0° fibers; and two different fiber types were fabricated and crushed both statically and dynamically to examine the energy absorption characteristics. The fiber types, in the form of preimpregnated tow (towpreg) from Thiokol, were Akzo Fortafil 50k fiber and aerospace-grade T300 12k fiber. Using the towpreg, sixteen tubes were filament wound on aluminum mandrels. Three specimens were cut from each of these tubes for a total of forty-eight specimens. Twenty-four of these specimens were crushed statically in a load frame and twenty-four were crushed dynamically in a drop fixture. In order to characterize the tubes and specimens, a number of measurements were taken. These measurements included length, wall thickness, cross-sectional dimensions, volume, and mass. Two important energy absorption measures were examined: the specific energy absorption (SEA) and the ratio of the peak load to the average load. The geometry had a significant effect on the energy absorption but the stacking sequence did not. It was also found that the 50k material was less effective at absorbing energy than the 12k material, but the 50k still may be acceptable. / Master of Science

The present study is part of the Long Term Bridge Performance Program (LTBP) funded by the Federal Highway Administration. The objectives of this program are to create a comprehensive database of quantitative information of the long-term performance of selected pilot bridges and to develop a methodology to assess bridge performance. Finite element (FE) modeling of the pilot bridges is an intrinsic part of the LTBP program and is intended to not only assist with instrumentation decisions, but also to provide further insight into the behavior of these bridges, which cannot be achieved solely from field testing of the bridges. This thesis provides a comprehensive study of a plethora of issues associated with the development of reliable and accurate FE models of bridges. The first objective of this investigation was to develop reliable finite element models with a variety of levels of refinement and to study the effect of the inclusion of various bridge parameters in the model, such as bridge skew, degree of composite action, thermal gradient and level of support restraint, on the response of bridges. First, the suitability of different modeling techniques and of elements used to model the primary bridge components was assessed using simple models for which analytical solutions are readily available. From these studies, it was concluded that shell elements are adequate to model the bridge deck, and beam and shell elements are both satisfactory to model the bridge girders. From the dynamic analyses of theWildcat Creek River Bridge and the Colquitz River Bridge, flexural modes of vibration were found to be highly sensitive to support restraints and to how the guardrails were modeled and less sensitive to the inclusion of bracing and thermal gradients in the model. The finite element models using extreme boundary conditions were successful in bracketing the field response. The factors identified from these analyses were considered in the analysis of the Virginia pilot bridge. Different support restraints, and the inclusion of skew and level of composite action in the model had noticeable impact on both the static and dynamic responses of the bridge. The results from these analyses were used to assist with instrumentation decisions prior to field-testing. The developed model will also be used to help researchers further understand the bridge's behavior and to help explain a variety of phenomena observed in the field. / Master of Science

Considerable attention has been paid to the design of low-power, high-performance SRAMs (Static Random Access Memories) since they are a critical component in both hand-held devices and high-performance processors. A key in improving the performance of the system is to use an optimum sized SRAM. In this thesis, an SRAM compiler has been developed for the automatic layout of memory elements in the ASIC environment. The compiler generates an SRAM layout based on a given SRAM size, input by the user, with the option of choosing between fast vs. low-power SRAM. Array partitioning is used to partition the SRAM into blocks in order to reduce the total power consumption. Experimental results show that the low-power SRAM is capable of functioning at a minimum operating voltage of 2.1 V and dissipates 17.4 mW of average power at 20 MHz. In this report, we discuss the implementation of the SRAM compiler from the basic component to the top-level SKILL code functions, as well as simulation results and discussion. / Master of Science

No

A guaranteed minimum income benefit (GMIB) is a long-dated option that can be embedded in a deferred variable annuity. The GMIB is attractive because, for policyholders who plan to annuitize, it offers protection against poor market performance during the accumulation phase, and adverse interest rate experience at annuitization. The GMIB also provides an upside equity guarantee that resembles the benefit provided by a lookback option. We price the GMIB, and determine the fair fee rate that should be charged. Due to the long dated nature of the option, conventional hedging methods, such as delta hedging, will only be partially successful. Therefore, we are motivated to find alternative hedging methods which are practicable for long-dated options. First, we measure the effectiveness of static hedging strategies for the GMIB. Static hedging portfolios are constructed based on minimizing the Conditional Tail Expectation of the hedging loss distribution, or minimizing the mean squared hedging loss. Next, we measure the performance of semi-static hedging strategies for the GMIB. We present a practical method for testing semi-static strategies applied to long term options, which employs nested Monte Carlo simulations and standard optimization methods. The semi-static strategies involve periodically rebalancing the hedging portfolio at certain time intervals during the accumulation phase, such that, at the option maturity date, the hedging portfolio payoff is equal to or exceeds the option value, subject to an acceptable level of risk. While we focus on the GMIB as a case study, the methods we utilize are extendable to other types of long-dated options with similar features.

A guaranteed minimum income benefit (GMIB) is a long-dated option that can be embedded in a deferred variable annuity. The GMIB is attractive because, for policyholders who plan to annuitize, it offers protection against poor market performance during the accumulation phase, and adverse interest rate experience at annuitization. The GMIB also provides an upside equity guarantee that resembles the benefit provided by a lookback option. We price the GMIB, and determine the fair fee rate that should be charged. Due to the long dated nature of the option, conventional hedging methods, such as delta hedging, will only be partially successful. Therefore, we are motivated to find alternative hedging methods which are practicable for long-dated options. First, we measure the effectiveness of static hedging strategies for the GMIB. Static hedging portfolios are constructed based on minimizing the Conditional Tail Expectation of the hedging loss distribution, or minimizing the mean squared hedging loss. Next, we measure the performance of semi-static hedging strategies for the GMIB. We present a practical method for testing semi-static strategies applied to long term options, which employs nested Monte Carlo simulations and standard optimization methods. The semi-static strategies involve periodically rebalancing the hedging portfolio at certain time intervals during the accumulation phase, such that, at the option maturity date, the hedging portfolio payoff is equal to or exceeds the option value, subject to an acceptable level of risk. While we focus on the GMIB as a case study, the methods we utilize are extendable to other types of long-dated options with similar features.

Le chargement électrostatique d’un avion en vol peut mener à des perturbations électromagnétiques sur les systèmes de communication et navigation à bord. Ce phénomène est appelé Precipitation Static (P-Static). Cette thèse vise à développer un outil capable de localiser la source des perturbations pour ainsi réduire le coût et la durée des missions d’investigation spécifiques en compagnie aérienne. Les principaux objectifs sont : •Comprendre les mécanismes de charge et décharge électrique d’un avion en vol. •Développer une instrumentation capable de mesurer les émissions des sources de P-Static et qui soit conforme à une installation sur avion. •Développer une méthode de localisation capable d’estimer la position de la source. Le comportement électrostatique d’un avion en vol a été étudié. Le défi de la mesure temporelle de l’impulsion générée par des décharges sur avion a été relevé à l’aide des antennes VHF, d’une chaine d’amplification à fort gain, de filtres sélectifs, d’un déclenchement de mesure automatique et de l’exploitation de nombreuses mesures. Les retards mesurés entre les impulsions ont été utilisés comme entrée de la méthode inverse de localisation développée. Cette méthode repose sur une base de données de retards, construite par modélisation de la propagation, permettant après comparaison avec la mesure, de déterminer la position de la source. Les tests effectués au laboratoire et sur avion au sol ont montré des résultats prometteurs puisque les zones estimées contenant la source correspondent à une zone réduite sur la surface de l’avion. / The static charging of an aircraft in flight may lead to electrostatic discharges that in turn lead to electromagnetic disturbances on aircraft radio and avionic systems. This phenomenon is called Precipitation Static (P-Static). This thesis aims to develop a tool capable of narrowing down the location of the source of disturbances in order to reduce the cost and duration of specific troubleshooting missions in airlines. The main objectives are : •To understand the electrical charging and discharging dynamics of an aircraft. •To develop an instrumentation capable of measuring the electromagnetic emissions of P-Static sources and that is compliant to aircraft installation constraints. •To develop a location method capable of estimating the position of the source. The electrostatic behaviour of an aircraft has been studied. The challenge in measuring the pulse generated by discharges on an aircraft was achieved by the combination of VHF antennas, a high gain amplifier chain, selective filters, automated triggering and numerous acquisitions. The delays obtained between the three pulses serve as input for the location inverse method developed. This method is based on a database of delays, built using propagation models, allowing after comparison with measurements, to determine the source position. The tests performed in laboratory and on aircraft on ground show promising results as the estimated zones containing the source correspond to a reduced zone on the surface of the aircraft.

Context. Name-bounded analysis is a type of static analysis that allows us to take a concurrent program, abstract away from it, and check for some interesting properties, such as deadlock-freedom, or watching the propagation of variables across different components or layers of the system. Objectives. In this study we investigate the difficulties of giving a representation of computer programs in a name-bounded variation of π-calculus. Methods. A preliminary literature review is conducted to assess the presence (or lack thereof) of other successful translations from real-world programming languages to π-calculus, as well for the presence of relevant prior art in the modelling of concurrent systems. Results. This thesis gives a novel translation going from a relevant subset of the Java programming language, to its corresponding name-bounded π-calculus equivalent. In particular, the strengths of our translation are being able to dispose of names representing inactive objects when there are no circular references, and a transparent handling of polymorphism and dynamic method resolution. The resulting processes can then be further transformed into their Petri-Net representation, enabling us to check for important properties, such as reachability and coverability of program states. Conclusions. We conclude that some important properties that are not, in general, easy to check for concurrent programs, can be in fact be feasibly determined by giving a more constrained model in π-calculus first, and as Petri Nets afterwards. / +49 151 52966429

Indiana University-Purdue University Indianapolis (IUPUI) / The number of smart mobile devices has grown at a significant rate in recent years. This growth has resulted in an exponential number of publicly available mobile Apps. To help the selection of suitable Apps, from various offered choices, the App distribution platforms generally rank/recommend Apps based on average star ratings, the number of installs, and associated reviews ― all the external factors of an App. However, these ranking schemes typically tend to ignore critical internal factors (e.g., bugs, security vulnerabilities, and data leaks) of the Apps. The AppStores need to incorporate a holistic methodology that includes internal and external factors to assign a level of trust to Apps. The inclusion of the internal factors will describe associated potential security risks. This issue is even more crucial with newly available Apps, for which either user reviews are sparse, or the number of installs is still insignificant. In such a scenario, users may fail to estimate the potential risks associated with installing Apps that exist in an AppStore. This dissertation proposes a security-related and evidence-based ranking framework, called SERS (Security-related and Evidence-based Ranking Scheme) to compare similar Apps. The trust associated with an App is calculated using both internal and external factors (i.e., security flaws and user reviews) following an evidence-based approach and applying subjective logic principles. The SERS is formalized and further enhanced in the second part of this dissertation, resulting in its enhanced version, called as E-SERS (Enhanced SERS). These enhancements include an ability to integrate any number of sources that can generate evidence for an App and consider the temporal aspect and reputation of evidence sources. Both SERS and E-SERS are evaluated using publicly accessible Apps from the Google PlayStore and the rankings generated by them are compared with prevalent ranking techniques such as the average star ratings and the Google PlayStore Rankings. The experimental results indicate that E-SERS provides a comprehensive and holistic view of an App when compared with prevalent alternatives. E-SERS is also successful in identifying malicious Apps where other ranking schemes failed to address such vulnerabilities. In the third part of this dissertation, the E-SERS framework is used to propose a trust-aware composition model at two different granularities. This model uses the trust score computed by E-SERS, along with the probability of an App belonging to the malicious category, as the desired attributes for selecting a composition as the two granularities. Finally, the trust-aware composition model is evaluated with the average star rating parameter and the trust score. A holistic approach, as proposed by E-SERS, to computer a trust score will benefit all kinds of Apps including newly published Apps that follow proper security measures but initially struggle in the AppStore rankings due to a lack of a large number of reviews and ratings. Hence, E-SERS will be helpful both to the developers and users. In addition, the composition model that uses such a holistic trust score will enable system integrators to create trust-aware distributed systems for their specific needs.

A non-contact angular measurement system for Pitch Static Attitude (PSA) and Roll Static Attitude (RSA) of hard disk drive sliders is designed and built. Real-time sampling at over 15 KHz is achieved with accuracy of +/- 0.05 degrees over a range of approximately 2-3 degrees. Measuring the PSA and RSA is critical for hard drive manufacturers to control and improve the quality and reliability of hard drives. Although the hard drive industry is able to measure the PSA and RSA at the subassembly level at this time, there is no system available that is able to measure PSA/RSA at the final assembly level. This project has successfully demonstrated a methodology that the PSA/RSA can be reliably measured in-situ using a laser and position sensitive detector (PSD) technology. A prototype of the measurement system has been built using simple and inexpensive equipment. This device will allow a continuous measurement between the parked position on the ramp and the loading position just off of the disk surface. The measured data can be used to verify manufacturing processes and reliability data.