Neural Network Trees And Simulation Databases: New Approaches For Signalized Intersection Crash Classification And Prediction

Intersection related crashes form a significant proportion of the crashes occurring on roadways. Many organizations such as the Federal Highway Administration (FHWA) and American Association of State Highway and Transportation Officials (AASHTO) are considering intersection safety improvement as one of their top priority areas. This study contributes to the area of safety of signalized intersections by identifying the traffic and geometric characteristics that affect the different types of crashes. The first phase of this thesis was to classify the crashes occurring at signalized intersections into rear-end, angle, turn and sideswipe crash types based on the traffic and geometric properties of the intersections and the conditions at the time of the crashes. This was achieved by using an innovative approach developed in this thesis Neural Network Trees . The first neural network model built in the Neural Network tree classified the crashes either into rear end and sideswipe or into angle and turn crashes. The next models further classified the crashes into their individual types. Two different neural network methods (MLP and PNN) were used in classification, and the neural network with a better performance was selected for each model. For these models, the significant variables were identified using the forward sequential selection method. Then a large simulation database was built that contained all possible combinations of intersections subjected to various crash conditions. The collision type of crashes was predicted for this simulation database and the output obtained was plotted along with the input variables to obtain a relationship between the input and output variables. For example, the analysis showed that the number of rear end and sideswipe crashes increase relative to the angle and turn crashes when there is an increase in the major and minor roadways\u27 AADT and speed limits, surface conditions, total left turning lanes, channelized right turning lanes for the major roadway and the protected left turning lanes for the minor roadway, but decrease when the light conditions are dark. The next phase in this study was to predict the frequency of different types of crashes at signalized intersections by using the geometric and traffic characteristics of the intersections. A high accuracy in predicting the crash frequencies was obtained by using another innovative method where the intersections were first classified into two different types named the safe and unsafe intersections based on the total number of lanes at the intersections and then the frequency of crashes was predicted for each type of intersections separately. This method consisted of identifying the best neural network for each step of the analysis, selecting significant variables, using a different simulation database that contained all possible combinations of intersections and then plotting each input variable with the average output to obtain the pattern in which the frequency of crashes will vary based on the changes in the geometric and traffic characteristics of the intersections. The patterns indicated that an increase in the number of lanes of the major roadway, lanes of the minor roadway and the AADT on the major roadway leads to an increased crashes of all types, whereas an increase in protected left turning lanes on the major road increases the rear end and sideswipe crashes but decreases the angle, turning and overall crash frequencies. The analyses performed in this thesis were possible due to a diligent data collection effort. Traffic and geometric characteristics were obtained from multiple sources for 1562 signalized intersections in Brevard, Hillsborough, Miami-Dade, Seminole and Orange counties and the city of Orlando in Florida. The crash database for these intersections contained 27,044 crashes. This research sheds a light on the characteristics of different types of crashes. The method used in classifying crashes into their respective collision types provides a deeper insight on the characteristics of each type of crash and can be helpful in mitigating a particular type of crash at an intersection. The second analysis carried out has a three fold advantage. First, it identifies if an intersection can be considered safe for different crash types. Second, it accurately predicts the frequencies of total, rear end, angle, sideswipe and turn crashes. Lastly, it identifies the traffic and geometric characteristics of signalized intersections that affect each of these crash types. Thus the models developed in this thesis can be used to identify the specific problems at an intersection, and identify the factors that should be changed to improve its safet

Retrospective study of dog bite cases at Ahmadu Bello University, Zaria, Nigeria and its environment

Aim: A 10-year retrospective study was undertaken to determine the prevalence of dog bites reported to the Veterinary Teaching Hospital (VTH), Ahmadu Bello University (ABU), Zaria, and to implement measures to control rabies exposure in the environment. Materials and Methods: Data on dog bite cases, reported to the VTH of ABU, Zaria, Nigeria between January, 2002 and December, 2011, were retrieved and analyzed using Statistical Package for Social Sciences version 17.0, Chicago, IL, USA. Result: A total of 236 dog bite-related cases was presented, of which 1.7% dogs died of rabies. The number of cases (59.7%) increased through time with the highest number (32) recorded in 2011. Majority of the cases were recorded between June and October of each year. Of the biting dogs, 22.5% were puppies (1-6 months) and 77.5% were adults (above 6 months). The human victims were 92.4%, while the dog victims were 7.6%. Eight of the dogs were stray dogs, while 228 (96.6%) were owned dogs. Of the owned dogs, 71.2% were free-roaming. Only 22% of the owned dogs were vaccinated. The most common offending breeds included the Nigerian Indigenous local breeds (73.3%), cross breeds (24.6%), Alsatians (0.8%), Terriers (0.8%), and Bulldogs (0.4%). Conclusion: In conclusion, rabies is endemic in Zaria, Nigeria, and the incidence of dog bites is on the rise. Strict measures including vaccination of the dogs and the leash law should be adopted to prevent dog bites

Experiments on Film Cooling of Gas Turbine Vane Passage Surfaces: The Effects of Various Distributions of Combustor Coolant and Endwall Injection Coolant

University of Minnesota M.S.M.E. thesis. August 2019. Major: Mechanical Engineering. Advisor: Terrence W. Simon. 1 computer file (PDF); xvi, 184 pagesThe efficiency of gas turbines is known to increase with the exit temperature of the combustor gases. However, this temperature is limited by the melting point of various equipment downstream of the combustor. To increase this limit, coolants injected at different locations form low-temperature films on the surfaces of these regions to avoid melting and thermal stress damage. This injection significantly changes the flow field in the vane passage. Therefore, there is a need to study the aerodynamic and thermal effects of combustor, transition duct and passage coolant injection, which can assist the designers of gas turbines to employ better cooling schemes with minimal use of coolant, thus increasing the efficiency and durability of turbines. The study presented in this thesis discusses experimental tests performed to understand the coolant effectiveness for cooling the endwall and vane surfaces of a nozzle guide vane cascade. The test section contains an engine representative combustor-turbine interface along with a contoured endwall. High turbulence intensity as well as high Reynolds numbers are achieved in the facility to closely simulate engine conditions. In addition to recording the surface effectiveness values, in-field thermal and aerodynamic measurements were taken. It has been previously discovered that the effusion and louver coolants, used to cool the combustor section, can also be credited in cooling the endwall and the vane surfaces. Therefore, this study is helpful to understand the effects of changing the mass flow ratios of different coolants injected upstream of the passage. Especially, louver coolant injection in the combustor transition duct region, due to its location and injection angle, is suspected to provide significant passage endwall cooling. In-field measurements provide insight to the coolant transport through the passage and its interaction with the mainstream. As the net combustor coolant momentum is higher than the film coolant momentum, the changes in the flow field due to its injection are more significant and are sustained to the end of the passage, giving more streamwise coverage than with a conventional film cooling setup. The film coolant mass flow ratio is varied in this study to see how the interaction of different coolants changes with changes of their injected momentum. The measurements reveal that the upstream coolant flow helps in keeping the film coolant attached to the endwall for most of the passage and also keeping the film thickness fairly uniform in the pitchwise direction. An increase in louver coolant mass flow rate shows higher endwall cooling effectiveness. The velocity contours show that a dominant vortex is present due to combustor coolant injection and that the passage vortex was, although present, diminished due to this other vortex. While changing the louver coolant mass flow rate did not change the intensity of these vortices, changes in the film coolant mass flow rate increased the intensity of the dominant vortex near the pressure surface. Also, the presence of this new vortex helps in film cooling the pressure surface, a region where, conventionally, the least amount of coolant coverage is recorded

Comparison of diurnal variations, gestational age and gender related differences in fetal heart rate (FHR) parameters between appropriate-for-gestational-age (AGA) and small-for-gestational-age (SGA) fetuses in the home environment

Objective To assess the influence of gender, time of the day and gestational age on fetal heart rate (FHR) parameters between appropriate-for-gestational-age (AGA) and small-for-gestational age (SGA) fetuses using a portable fetal ECG monitor employed in the home setting. Methods We analysed and compared the antenatal FHR data collected in the home setting on 61 healthy pregnant women with singleton pregnancies from 24 weeks gestation. Of the 61 women, 31 had SGA fetuses (estimated fetal weight below the tenth gestational centile) and 30 were pregnant with AGA fetuses. FHR recordings were collected for up to 20 h. Two 90 min intervals were deliberately chosen retrospectively with respect to signal recording quality, one during day-time and one at night-time for comparison. Results Overall, success rate of the fetal abdominal ECG in the AGA fetuses was 75.7% compared to 48.6% in the SGA group. Based on randomly selected episodes of heart rate traces where recording quality exceeded 80% we were able to show a marginal difference between day and night-time recordings in AGA vs. SGA fetuses beyond 32 weeks of gestation. A selection bias in terms of covering different representation periods of fetal behavioural states cannot be excluded. In contrast to previous studies, we neither controlled maternal diet and activity nor measured maternal blood hormone and heart rate as all mothers were monitored in the home environment. Conclusion Based on clinically unremarkable, but statistically significant differences in the FHR parameters between the AGA and SGA group we suggest that further studies with large sample size are required to assess the clinical value of antenatal fetal ECG monitoring

Predictive accuracy of cerebroplacental ratio for adverse perinatal and neurodevelopmental outcomes in suspected fetal growth restriction: systematic review and meta-analysis.

OBJECTIVE: The cerebroplacental ratio (CPR) has been proposed for the routine surveillance of pregnancies with suspected fetal growth restriction (FGR), but the predictive performance of this test is unclear. The aim of this study was to determine the accuracy of CPR for predicting adverse perinatal and neurodevelopmental outcomes in suspected FGR. METHODS: PubMed, EMBASE, CINAHL and Lilacs were searched from inception to 31 July 2017 for cohort or cross-sectional studies reporting on the accuracy of CPR for predicting adverse perinatal and/or neurodevelopmental outcomes in singleton pregnancies with FGR suspected antenatally based on sonographic parameters. Summary receiver-operating characteristics (ROC) curves, pooled sensitivities and specificities, and summary likelihood ratios (LRs) were generated. RESULTS: Twenty-two studies (including 4301 women) met the inclusion criteria. Summary ROC curves showed that the best predictive accuracy of CPR was for perinatal death and the worst was for neonatal acidosis, with areas under the summary ROC curves of 0.83 and 0.57, respectively. The predictive accuracy of CPR was moderate to high for perinatal death (pooled sensitivity and specificity of 93% and 76%, respectively, and summary positive and negative LRs of 3.9 and 0.09, respectively) and low for composite of adverse perinatal outcomes, Cesarean section for non-reassuring fetal status, 5-min Apgar score < 7, admission to the neonatal intensive care unit, neonatal acidosis and neonatal morbidity, with summary positive and negative LRs ranging from 1.1 to 2.5 and 0.3 to 0.9, respectively. An abnormal CPR result had moderate accuracy for predicting small-for-gestational age at birth (summary positive LR of 7.4). CPR had a higher predictive accuracy in pregnancies with suspected early-onset FGR. No study provided data for assessing the predictive accuracy of CPR for adverse neurodevelopmental outcome. CONCLUSION: CPR appears to be useful in predicting perinatal death in pregnancies with suspected FGR. Nevertheless, before incorporating CPR into the routine clinical management of suspected FGR, randomized controlled trials should assess whether the use of CPR reduces perinatal death or other adverse perinatal outcomes. Copyright © 2018 ISUOG. Published by John Wiley & Sons Ltd

A novel contact interaction formulation for voxel-based micro-finite-element models of bone

Voxel-based micro-finite-element (μFE) models are used extensively in bone mechanics research. A major disadvantage of voxel-based μFE models is that voxel surface jaggedness causes distortion of contact-induced stresses. Past efforts in resolving this problem have only been partially successful, ie, mesh smoothing failed to preserve uniformity of the stiffness matrix, resulting in (excessively) larger solution times, whereas reducing contact to a bonded interface introduced spurious tensile stresses at the contact surface. This paper introduces a novel "smooth" contact formulation that defines gap distances based on an artificial smooth surface representation while using the conventional penalty contact framework. Detailed analyses of a sphere under compression demonstrated that the smooth formulation predicts contact-induced stresses more accurately than the bonded contact formulation. When applied to a realistic bone contact problem, errors in the smooth contact result were under 2%, whereas errors in the bonded contact result were up to 42.2%. We conclude that the novel smooth contact formulation presents a memory-efficient method for contact problems in voxel-based μFE models. It presents the first method that allows modeling finite slip in large-scale voxel meshes common to high-resolution image-based models of bone while keeping the benefits of a fast and efficient voxel-based solution scheme