Saudi Cultural Missions Theses & Dissertations
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Item Restricted Design and Implementation of a Delay-Compensated Pneumatic Brake Controller for Heavy Vehicles(University of Exeter, 2024-02-05) Aljuaid, Yazeed; Koonthalakadu Baby, DvikaHeavy Commercial Road Vehicles (HCRVs) are crucial to the effective transfer of products and people in modern transport systems. Economy of a country, as they rely on passenger and freight transportation, is depends highly on the HCRVs. Various Safety systems in the context of safety systems for vehicles, Collision Avoidance System (CAS) as well as Anti-Lock Braking System (ABS) etc., are some systems capable enough in assisting drivers to avoid accidents are of prime focus. However, challenges are there in design of safety systems for HCRVs. Considering pneumatic brake system various factors such as delay, significant variations of mass during different operations such as laden and unladed operation, and during braking the dynamic load transfer and all above factors are challenges faced during active safety system design. Pneumatic brake system is the traditional actuation system for HCRVs. For medium of actuation, compressed air is used. Compressibility of air, pipe length and valve response time are some of the factors that affects its dynamic response. These factors induce a delay in the system causing the stopping distance of vehicle and response time of brake system to increase. This time delay and its effects on the system in-turn affects the overall performance of the system. For the efficient and optimal performance of active safety system is very much dependent on the performance of the pneumatic brake system. Thus, a PID controller is created for a pneumatic brake system to enhance performance. The gains of the PID Controller are optimized using the Grey-Wolf Optimizer. The Padé Approximation is used to estimate the time delay since the system has a time delay. Then PID Controller is designed for this time delay approximate transfer function. Other Methods for delay compensation such as State -Prediction is also used. Controller other than PID such as Sliding Mode Control is also used. Performance of controllers incorporating time delay is compared with other controllers that include state predictors that are compensating for the time delay. Also, different controllers with state predictors are compared for performance evaluation of controllers. Performance of brake controllers is also evaluated by considering ABS operation. Two loop control design is used. Brake controllers will act as inner control loop. The purpose of this work for the controller design for ABS is to increase the braking effort and keep control during an emergency braking scenario. When traveling long distances on HCVRs, driver fatigue could be a risk. ABS adds an extra safety net. ABS is designed to assist the HCVRs in the event that the driver falls asleep.18 0Item Restricted STATISTICAL MODELING OF THE IMPACT OF MULTIPLICITY POOL TESTING AND THE ESTIMATION OF INFECTION AND RECOVERY RATES OF PARTIALLY KNOWN NETWORKS USING HYBRID SAMPLING(OhioLINK, 2023-12-15) Alsehibani, Razan; Omar, De La Cruz CabreraDetection and control of epidemic outbreaks require effective testing measures, identification of highly-connected members in social networks, as well as the estimation of important epidemic parameters. Pool testing have been proven to be an efficient testing approach to control epidemic spread by reducing the total number of tests. However, pool testing can also be used to improve the accuracy of the testing process. One objective of this thesis is to improve the accuracy of pool testing using the same number of tests as that of individual testing taking into consideration the probability of testing errors and pool multiplicity classification thresholds. Statistical models are developed to evaluate the impact of pool multiplicity classification thresholds on pool testing accuracy using the receiver operating characteristic (ROC) curve and the area under the curve (AUC). The findings indicate that under certain conditions, pool testing multiplicity yields superior testing accuracy compared to individual testing without additional cost. Modelling the spread of epidemics requires the identification of well-connected nodes in partially known networks where network sampling can be leveraged to detect important nodes in these networks. This thesis extends prior research by developing a hybrid sampling method based on simple random sampling and network sampling to identify well-connected nodes in partially known networks. The performance of the proposed method is evaluated in terms of the Perron eigenvalue of the sampled subnetwork using simulation. The performance evaluation shows that the hybrid sampling method yields significantly superior performance compared to that of simple random sampling. The performance of the different levels of the partial combinations of the hybrid sampling is also evaluated where we find that the different hybrid levels give differing results under varying conditions. The findings reveal that by sampling only a small proportion of the individuals, the hybrid sampling very efficiently identifies well-connected ones. Finally, recent developments in social networks research enabled researchers to model the spread of infectious diseases using network structures. This thesis develops statistical models to estimate the infection rate and recovery rate in partially known networks. A joint sampling infection process is implemented and its outcomes are fed as input to two back tracing algorithms to estimate the health status of individuals during the periods before they are sampled. The infection and recovery rates for partially known networks are then estimated. The findings reveal that the identification of well-connected nodes using the proposed hybrid sampling method leads to significantly lower total number of infections and lower infection peak rates. The results also indicate that one of the two fill-up methods performs better than the other but incurs extra computational time.21 0Item Restricted Accuracy of ultrasonography and computed tomography in the diagnosis of acute appendicitis(0023-03-09) Alqahtani, Yahya; Street, AngelaBackground: Acute appendicitis (AA) is a common reason for surgical intervention. Considering the high burden of AA, early and correct diagnosis is crucial. Two imaging modalities (i.e., ultrasonography and computed tomography) are frequently used for the diagnostic evaluation of AA. However, there is lack of clarity regarding their diagnostic accuracy. Choosing the most valid intervention to diagnose AA would have important clinical implications. Aim of Study: To assess the diagnostic accuracy of ultrasonography (US) and computed tomography (CT) in the diagnosis of AA in adolescents and adults. Methods: This structured literature review (SLR) was carried out using the components of the PICO framework. The literature search was conducted using Cochrane, Embase and PubMed databases. All steps in the SLR were followed, from searching for relevant studies to selecting them, extracting their data, assessing their quality, and synthesising their results. Results of the search process were recorded according to the Preferred Reporting Items for Systematic reviews and Meta-analyses (PRISMA) flow diagram. This SLR included studies on adolescents and adult patients (aged >14 years) with confirmed AA, that were diagnosed using both US and CT. Articles published before 2012, those published in languages other than English, or with no available full text were excluded. The quality assessment of the selected articles was done using the Critical Appraisal Skills Programme (CASP) checklist. Results: Five articles were included in this SLR. The highest reported sensitivity for US was 98.5%, while the lowest was 58.2%. The highest specificity of US was 97.3%, while the lowest was 54.2%. High diagnostic accuracy rates of US were reported by the included studies ranging from 83% and 93.14%. All included studies reported that CT had very high sensitivity for the diagnosis of AA, reaching 100% in one study, while slightly lower sensitivity rates were reported by other studies ranging from 96% to 98.9%. The specificity of CT was reported to be 100% by two studies, while other high specificity rates were reported by three studies (i.e., 97.2%, 89% and 88.9%). The diagnostic accuracy for CT was consistently higher than that of US. Conclusions and implications: The diagnostic accuracy of CT is higher than that of US. However, CT cannot be routinely used because of its high cost and the associated potentially harmful effects of ionizing radiation. Therefore, it is recommended that in cases clinically suspected to be AA, US can be used as the first-line diagnostic modality, followed by CT when the results of US are not conclusive. Keyword: Ultrasonography, Computed tomography, Acute appendicitis, Diagnostic Accuracy, Sensitivity, Specificity, Predictive Value, Validity.23 0