With the increased prevalence of roundabouts in the United States, there is a need to evaluate the performance of roundabouts relative to other intersection control strategies. Few studies have compared roundabouts with other intersection control strategies in a systematic fashion. Consequently, this Thesis compares four types of intersection control strategies considering a single lane approach with a 58 km/hr speed limit and equal demand on all approaches. The study demonstrates that vehicle delay is minimized with the use of a roundabout intersection control for all demand levels below 500 veh/hr/approach. Above this point if the left turn percentage exceeds 70% traffic signal control is more efficient. The roundabout alternative also produces the fewest vehicle stops for low demand levels, low left turn demand and high right turn demand, however a TWSC alternative produces the least number of vehicle stops when the through and total demand is high. This study illustrates that fuel consumption and carbon dioxide, carbon monoxide, hydrocarbon and nitrogen oxide emissions can be improved with roundabout control over other intersection control strategies. The research presented here demonstrates that for low traffic demand levels roundabouts should be part of design alternatives considered for isolated intersection control. / Master of Science

Audio acquisition and recording can benefit from directional reception of the acoustic signals. Current acoustic designs of highly-directional microphones are bandwidth limited and physically large. A microphone array used in conjunction with a beamforming algorithm can acquire and spatially filter the signal, but traditionally this has suffered from limitations similar to those of the purely acoustic designs. The work presented in this paper attempts to overcome these limitations by producing and analyzing three atypical techniques for broadband beamforming. The last and most successful technique employs an algorithm which calculates the difference in group delay of the acquired signals and uses that information to determine the direction of the incoming signals as a function of frequency.

In dieser Studie führten 37 adulte Patienten mit einer Aufmerksamkeitsdefizit-/Hyperaktivitätsstörung (ADHS) ein Delay Discounting (DD) - Paradigma aus, während gleichzeitig mittels Funktioneller-Nahinfrarotspektroskopie (fNIRS) die Gehirnaktivität der „Regions of Interest“ (ROIs) des Orbitofrontalen-Kortex (OFC) und des Dorsolateralen-Präfrontalen-Kortex (dlPFC) gemessen wurde. Mittels Fragebögen und eines Delay Discounting Tasks (DDT) wurden zusätzlich Verhaltensparameter erhoben und flossen in den Auswertungsprozess mit ein. Vorausgegangene Untersuchungen weisen auf ein hypofunktionel-les dopaminerges System bei ADHS-Patienten hin, welches mit der ADHS-Pathogenese in Zusammenhang gebracht wird. Vor allem im Präfrontalen-Kortex (PFC), bestehend unter anderem aus OFC und dlPFC, erfolgt die Metabolisierung von Dopamin durch die Catechol-O-Methyltransferase (COMT). Hierbei hängt die Metabolisierungsgeschwindigkeit vom genetischen COMT-Val158Met- Polymorphismus ab. Die Einflussnahme dieses COMT-Val158Met-Polymorphismus auf die kortikale Aktivität der ROIs und Impulsivität ist ebenfalls Gegenstand dieser Dissertation („Imaging Genetics“). Adulte ADHS Patienten zeigten eine verstärkte Aktivität des OFC der Entscheidungskategorie „verzögert“ im Verhältnis zu der Entscheidungskategorie „sofort“. Die gemessene Impulsivität korrelierte mit der kortikalen Gehirnaktivität „DD-Kontrast“. Es konnte kein Zusammenhang zwischen Verhaltensparameter und Gehirnaktivität mit dem COMT-Polymorphismus gezeigt werden. Die erhöhte Aktivität des OFC bei der Entscheidungskategorie verzögert unterstützt die These der „Delay Aversion“ des „Dual Pathway Model“. Eine enge Konnektivität der stark dopaminerg innervierten kortiko-striataler Strukturen in Form des OFC und der Amygdala, welche Einfluss auf die ADHS-Pathogenese nehmen, erscheint somit plausibel. / In this study 37 adult subjects with ADHD (Attention Deficit Hyperactivity Disorder) performed a validated Delay Discounting (DD) paradigm. By using near-infrared-spectroskopy (NIRS) functional brain activation in the regions of interest (ROIs) was measured. The ROIs are represented by the Orbito-Frontal-Cortex (OFC) and the Dorsolateral Prefrontal Cortex (dlPFC). Additionally questionnaires with relation to behaviour and a Delay Discounting Task (DDT) were interpreted. Former studies indicate a hypo-functional dopaminergic system in ADHD pathology. Mainly the Prefrontal Cortex (PFC), including the OFC and the dlPFC, metabolizes dopamine with the Catechol-O-Methyltransferase (COMT). Velocity of this metabolism depends on the COMT-Val158Met-polymorphism. This effect is generally known by the term “imaging genetics”. Adult ADHD subjects showed a stronger activation in the OFC in the DD category “delayed” than in the category “now”. Measured impulsivity correlated with the cortical brain activity “DD-Kontrast”. No significant relation between the COMT polymorphism an the cortical brain activity or behaviour could be shown. The stronger activation of the OFC in the category “delayed” underlines the thesis of “Delay Aversion” from the “Dual Pathway Model”. A close connectivity between the dopaminergic corticostriatal brain regions of the amygdala and the OFC, which have an influence to the ADHD pathology, seem to be a plausible approach.

Testing of delay defects is necessary in deep submicron (DSM) technologies. High coverage delay tests produced by automatic test pattern generation (ATPG) can be applied during wafer and package tests, but are difficult to apply during the board test, due to limited chip access. Delay testing at the board level is increasingly important to diagnose failures caused by supply noise or temperature in the board environment. An alternative to ATPG is the built-in self test (BIST). In combination with the insertion of test points, BIST is able to achieve high coverage of stuck-at and transition faults. The quality of BIST patterns on small delay defects is an open question. In this work we analyze the application of BIST to small delay defects using resistive short and open models in order to estimate the coverage and correlate the coverage to traditional delay fault models.

The analysis and design of passive broadband negative group delay (NGD) transmission line phase shifters is presented. By extending the metamaterial transmission line concept to include loss, a NGD unit cell is proposed. Phase shifters are supplemented with NGD unit cells to produce a flattened phase response significantly increasing phase bandwidths. The design methodology of a NGD phase shifter is presented with consideration of nominal phase, frequency, impedance, maximum insertion loss and bandwidth. The relation between gain, bandwidth and group delay signifies a fundamental design limitation and tradeoff. A significant application of NGD phase shifters for removing beam squint in series fed antenna arrays is discussed. Several NGD phase shifters are fabricated and experimentally verified in the UHF band upwards of 1 GHz using planar microstrip transmission lines loaded with passive surface mount RF components with both positive and negative phase shifts.

The analysis and design of passive broadband negative group delay (NGD) transmission line phase shifters is presented. By extending the metamaterial transmission line concept to include loss, a NGD unit cell is proposed. Phase shifters are supplemented with NGD unit cells to produce a flattened phase response significantly increasing phase bandwidths. The design methodology of a NGD phase shifter is presented with consideration of nominal phase, frequency, impedance, maximum insertion loss and bandwidth. The relation between gain, bandwidth and group delay signifies a fundamental design limitation and tradeoff. A significant application of NGD phase shifters for removing beam squint in series fed antenna arrays is discussed. Several NGD phase shifters are fabricated and experimentally verified in the UHF band upwards of 1 GHz using planar microstrip transmission lines loaded with passive surface mount RF components with both positive and negative phase shifts.

Construction delays are one of the biggest issues facing the construction industry and affecting delivery in terms of time, budget and the required quality. The characteristics of delay factors and their level of impact vary from project to project, ranging from a few days to years. They have significant financial, environmental and social impacts in construction projects; therefore, it is vital to investigate the causes of delay and analyse their impact. In this context, the research study was initiated to develop a new methodology for analysing and quantifying the impacts of delay factors on construction projects. A comprehensive literature survey was conducted to build up general background knowledge of delay factors in construction projects and particular attention was paid to identifying the potential differences in delay factors between Libya and the UK. A construction industry survey was conducted through a semi-structured questionnaire amongst contractors, consultants and owners. A total of 116 out of 300 responses (38.66%) were received from both countries. Statistical tests including T-test and Wilkinson rank test were executed to analyse the responses and present the findings from the survey. Following the findings from the literature review and an industry survey, a framework of Delay Analysis System (DAS) augmented with simulation model was developed by integrating the importance weight (IW) of each delay factor associated with critical activities using @risk tool. The key function of the system is the flexibility to analyse and quantify the impact in project duration, considering the IW of each delay factor independently. The system was evaluated through two case studies from building projects in Libya using the developed system. The analysis of case study 1 using DAS found that the building project might be delayed by 97 to 103 days when considering the delay factors identified from Libya whereas the project might be delayed by 80 to 85 days when considering the delay factors identified from the UK. The evaluation results from the case study revealed that the impact of delay factors in Libya is higher than in the UK. This confirms that the impact of delay in construction projects is higher in developing countries than in developed ones and varies from project to project in the same country. Finally, it is concluded that the system is a decision-supporting tool that helps to make government departments and decision-makers aware of the significance of delays in construction projects in terms of economic growth and the development processes. The key contribution of this study is the development of a strategy (delay analysis system) for analysing the impact of delay factors in the Libyan construction industry through better investigated, understood and documented reports. The system is expected to help policymakers, decision-makers and others stakeholders within the construction industry to gain a fuller understanding of the industry and to formulate short- and long-term construction strategies and policies that aim to improve the industry’s processes and operations.

Nowadays, Multi-GHz analog-to-digital converters (ADCs) are becoming more and more popular in radar systems, software-de ned radio (SDR) and wideband communications, because they can realize much higher operation speed through using many interleaved sub-ADCs to relax ADC sampling rates. Although the time interleaved ADC has some issues such as gain mismatch, o set mismatch and timing skew between each ADC channel, these deterministic errors can be solved by previous works such as digital calibration technique. However, time-interleaved ADCs require a precise sample clock to achieve an acceptable e ective-numberof- bits (ENOB) which can be degraded by jitter in the sample clock. The clock generation circuits presented in this work achieves sub-picosecond jitter performance in 180nm CMOS which is suitable for time-interleaved ADC. Two di erent test chips were fabricated in 180nm CMOS to investigate the low jitter design technique. The low jitter delay line in two chips were designed in two di erent ways, but both of them utilized the low jitter design technique. In rst test chip, the measured RMS jitter is 0.1061ps for each delay stage. The second chip uses the proposed low jitter Delay-Locked Loop can work from 80MHz to 120MHz, which means it can provide the time interleaved ADC with 2.4GHz to 3.6GHz low jitter sample clock, the measured delay stage jitter performance in second test chip is 0.1085ps.

In this research, statistical models of airport delay and single flight arrival delay were developed. The models use the Airline On-Time Performance Data from the Federal Aviation Administration (FAA) and the Surface Airways Weather Data from the National Climatic Data Center (NCDC). Multivariate regression, ANOVA, neural networks and logistic regression were used to detect the pattern of airport delay, aircraft arrival delay and schedule performance. These models are then integrated in the form of a system for aircraft delay analysis and airport delay assessment. The assessment of an airport¡¯s schedule performance is discussed. The results of the research show that the daily average arrival delay at Orlando International Airport (MCO) is highly related to the departure delay at other airports. The daily average arrival delay can also be used to evaluate the delay performance at MCO. The daily average arrival delay at MCO is found to show seasonal and weekly patterns, which is related to the schedule performance. The precipitation and wind speed are also found contributors to the arrival delay. The capacity of the airport is not found to be significant. This may indicate that the capacity constraint is not an important problem at MCO. This research also investigated the delays at the flight level, including the flights with delay ¡Ý0 minute and the flights with delay ¡Ý15min, which provide the delay pattern of single arrival flights. The characteristics of single flight and their effect on flight delay are considered. The precipitation, flight distance, season, weekday, arrival time and the time spacing between two successive arriving flights are found to contribute to the arrival delay. We measure the time interval of two consecutive flights spacing and analyze its effect on the flight delay and find that for a positively delayed flight, as the time space increases, the probability of the flights being delayed will decrease. While it was possible to calculate the immediate impact of originating delays, it is not possible to calculate their impact on the cumulative delay. If a late departing aircraft has no empty space in its down line schedule, it will continue to be late. If that aircraft enters a connecting airport, it can pass its lateness on to another aircraft. In the research we also consider purifying only the arrival delay at MCO, excluding the flights with originating delay >0. The model makes it possible to identify the pattern of the aircraft arrival delay. The weather conditions are found to be the most significant factors that influence the arrival delay due to the destination airport.

Ultrawideband (UWB) is one of the most promising communication technologies in recent times with the promise of high data rates and spectral reuse. This work analyses the outdoor and outdoor-to-indoor propagating characteristics of the UWB pulse, which can be of the order of a few gigahertz in bandwidth. The aim of the thesis is to provide the parameters needed in order to develop a channel model for such cases. The channel model would then play an important role in determining physical layer (PHY) solutions to optimally exploit these characteristics. The measurements carried out on the Virginia Tech campus are used to compute parameters such as path loss, penetration loss and delay statistics. These are carried out in multiple frequency bands and the results are compared across frequency bands to determine effect of different frequency levels on the parameters. Finally the results are analyzed with respect to similar parameters obtained in other measurement campaigns in an attempt to evaluate the performance of Ultrawideband vis-à-vis narrowband systems. / Master of Science