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Master of Engineering (Research) / This thesis presents a new approach to ensuring fair service for highly concurrent requests. Our design uses the advantages of staged event-driven architecture (SEDA) to support high-concurrent loadings and makes use of control theory to manage the system performance. In order to guarantee the quality of service is fairly made to each request, based on SEDA, the control system for fairness is developed as a combination of a global control framework and a set of local self-tune stags. The global control framework is used to control the performance of the whole staged network at the top-level, aimed at coordinating the performance of the stages in the network. On the other hand, each self-tune stage under the control framework is built on the thread pool model, and will use automatic control theory to adjust its performance locally in order to meet the overall target performance. The automatic control system in each stage consists of an automatic modeling mechanism and a feedback module, which optimizes the controller parameters in the system automatically and guarantees the quality of performance (service rate here) for the stage at runtime. Based on mathematical proof and simulation results, our designs are implemented in a SEDA-based web server running in a dynamic loading environment. Results demonstrate that the performance of the new system in the real world is almost the same as the theoretical results. It demonstrates that the design is able to adaptively ensure the quality of service to the high-concurrent requests fairly. Compared to the original SEDA design, our design is an effective and handy approach to significantly enhancing the performance of SEDA in a variety of aspects, including fairer service, faster convergent speed, better robustness, higher accuracy and ease of deployment in various practical applications.

Time-resolved electroluminescence has been primarily and widely applied in the field of optoelectronic devices and phosphor materials. Here we use the method to measure the response time and phase difference of green light-emitting diode. In our experiment, which is essentially dominated by pulsed signal from function generator¡Bhigh spatial resolution from laser scanning microscopic and phase-lock characteristic from lock-in amplifier to complete our experimental result. We are capable to detect relative carrier information within any point or any surface region from epi-layer of green light-emitting diode. Otherwise, the carrier transport of the sample is able to be observed through time-resolved characteristic measurement. Laser cutting would be beneficial for obvious phase-difference observation and mobility acquirement.

Efficiency and power conservation are critical issues in the design of cluster systems because these two parameters have direct implications on the user experience and the global need to conserve power. Widely adopted, distributor-based systems forward client requests to a balanced set of waiting servers in complete transparency to the clients. The policy employed in forwarding requests from the front-end distributor to the backend servers plays an important role in the overall system performance. Existing research separately addresses server performance and power conservation. The locality-aware request distribution (LARD) scheme improves the system response time by having the requests served by web servers which have the data in their cache. The power-aware request distribution aims at reducing the power consumption by turning the web servers OFF and ON according to the load. This research tries to achieve power conservation while preserving the performance of the system. First, we prove that using both power-aware and locality-aware request distribution together provides optimum power conservation, while still maintaining the required QoS of the system. We apply the usage of pinned memory in the backend servers to boost performance along with a request distributor design based on power and locality considerations. Secondly, we employ an intelligent-proactive-distribution policy at the front-end to improve the distribution scheme and complementary pre-fetching at the backend server nodes. The proactive distribution depends on both online and offline analysis of the website log files, which capture user navigation patterns on the website. The prefetching scheme pre-fetches the web pages into the memory based on a confidence value of the web page predicted by backend using the log file analysis. Designed to work with the prevailing web technologies, such as HTTP 1.1, our scheme provides reduced response time to the clients and improved power conservation at the backend server cluster. Simulations carried out with traces derived from the log files of real web servers witness performance boost of 15-45% and 10-40% power conservation in comparison to the existing distribution policies.

Master of Engineering (Research) / This thesis presents a new approach to ensuring fair service for highly concurrent requests. Our design uses the advantages of staged event-driven architecture (SEDA) to support high-concurrent loadings and makes use of control theory to manage the system performance. In order to guarantee the quality of service is fairly made to each request, based on SEDA, the control system for fairness is developed as a combination of a global control framework and a set of local self-tune stags. The global control framework is used to control the performance of the whole staged network at the top-level, aimed at coordinating the performance of the stages in the network. On the other hand, each self-tune stage under the control framework is built on the thread pool model, and will use automatic control theory to adjust its performance locally in order to meet the overall target performance. The automatic control system in each stage consists of an automatic modeling mechanism and a feedback module, which optimizes the controller parameters in the system automatically and guarantees the quality of performance (service rate here) for the stage at runtime. Based on mathematical proof and simulation results, our designs are implemented in a SEDA-based web server running in a dynamic loading environment. Results demonstrate that the performance of the new system in the real world is almost the same as the theoretical results. It demonstrates that the design is able to adaptively ensure the quality of service to the high-concurrent requests fairly. Compared to the original SEDA design, our design is an effective and handy approach to significantly enhancing the performance of SEDA in a variety of aspects, including fairer service, faster convergent speed, better robustness, higher accuracy and ease of deployment in various practical applications.

Due to the need for advanced computer-controlled functionality in distributed embedded systems the requirements on network communication are becoming overly intricate. This dissertation targets the requirements that are concerned with real-time guarantees, run-time adaptation, resource utilization and flexibility during the development. The Flexible Time-Triggered Switched Ethernet (FTT-SE) and Hard Real-Time Ethernet Switching (HaRTES) network architectures have emerged as two promising solutions that can cater for these requirements. However, these architectures do not support multi-hop communication as they are originally developed for single-switch networks. This dissertation presents a fundamental contribution in multi-hop real-time communication over the FTT-SE and HaRTES architectures targeting the above mentioned requirements. It proposes and evaluates various solutions for scheduling and forwarding the traffic through multiple switches in these architectures. These solutions preserve the ability of dynamic adaptation without jeopardizing real-time properties of the architectures. Moreover, the dissertation presents schedulability analyses for the timeliness verification and evaluation of the proposed solutions as well as several protocols to support run-time adaptation in the multi-hop communication. Finally, the work led to an end-to-end resource reservation framework, based on the proposed multi-hop architectures, to support flexibility during the development of the systems. The efficiency of the proposed solutions is evaluated on various case studies that are inspired from industrial systems.

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Concerns about increased emergency vehicle response times in the Washington D.C. Region, especially during peak periods, have led to the implementation of signal preemption systems to facilitate the efficient and safe movement of emergency vehicles. However, to date only limited research has been carried out on the travel characteristics of emergency vehicles. This paper presents an analysis of emergency vehicle characteristics to enhance our understanding of emergency vehicle operations and impacts and to assist public agencies and other stakeholders in the planning and deployment of emergency vehicle preemption systems. Emergency vehicle characteristics that merit special attention include temporal and spatial distribution of emergency vehicle travel; frequency and duration of preemption requests; platoon responses; and crashes involving emergency vehicles. Data on major corridors in Fairfax County, Virginia and Montgomery County, Maryland are used in the analysis. The analysis indicates that such data are useful to assess the need for a preemption system along major arterials. Moreover, the analysis demonstrates the importance of considering emergency vehicle preemption impacts regarding delay to other vehicles. It is also important to note that there is some variability in the emergency vehicle characteristics depending on the proximity of a firehouse to an intersection and other factors. It is proposed that future efforts build upon this research to develop warrants to be used in determining the appropriateness of installing preemption systems at signalized intersections. / Master of Science

The purpose of this research was to determine if personality type and system response time have any effect on state anxiety and user response time. The sample for this study consisted of senior and graduate level college students who possessed basic know 1 edge of a text editor. Each test subject was administered the Jenkins Activity Survey to determine scores for Type A versus Type B, speed and impatience, involvement, and competitiveness. The test subjects were randomly assigned to one of three treatment groups (good, variable, and poor system response time). They were required to edit a text file which contained multiple errors. The test subjects were provided hard copies of the file with errors (errors highlighted) and the file as should appear without the errors. The test situation for each test subject was identical, except for changes in system response time. The A-state scale of the State-Trait Anxiety Inventory (STAI) was administered to the test subjects immediately prior to the edit task in order to determine pre-task state anxiety levels. The A-state scale of the STAI was again administered immediately after the edit task in order to determine post-task state anxiety levels. Analysis of variance, analysis of covariance, regression, and two sample t-tests were used to analyze the data collected. All hypotheses were tested at the alpha .05 level. The most significant finding of this study was the positive relationship between state anxiety and system response time. It was originally predicted that the Type A personality would experience a greater increase in state anxiety than the Type B personality. However, that was not found to be true. Both Type A and Type B individuals experience an increase in state anxiety during periods of poor or variable system response time. This study also confirms prior research regarding user and system response time. There is a significant positive relationship between user response time and system response time. Personality type, specifically the Type A personality, contributes toward this relationship.