A study of impulsively started flow over cylindrical objects is made using the particle image velocimetry (PIV) technique for Reynolds numbers of Re = 200, 500 and 1000 in an X-Y towing tank. The cylindrical objects studied were a circular cylinder of diameter, D = 25.4 mm, and square and diamond cylinders each with side length, D = 25.4 mm. The aspect ratio, AR (= L/D) of the cylinders was 28 and therefore they were considered infinite. The development of the recirculation zone up to a dimensionless time of t* = 4 following the start of the motion was examined. The impulsive start was approximated using a dimensionless acceleration parameter, a*, and in this research, the experiments were conducted for five acceleration parameters, a* = 0.5, 1, 3, 5 and 10. The study showed that conditions similar to impulsively started motion were attained once a* ¡Ý 3.<p> A recirculation zone was formed immediately after the start of motion as a result of flow separation at the surface of the cylinder. It contained a pair of primary eddies, which in the initial stages (like in this case) were symmetrical and rotating in opposite directions. The recirculation zone was quantified by looking at the length of the zone, LR, the vortex development, both in terms of the streamwise location and the cross-stream spacing of the vortex centers, a and b, respectively, as well as the circulation (strength) of the primary vortices, ¦£.<p> For all types of cylinders examined, the length of the recirculation zone, the streamwise location of the primary eddies and the circulation of the primary eddies increase as time advances from the start of the impulsive motion. They also increase with an increase in the acceleration parameter, a*, until a* = 3, beyond which there is no more change, since the conditions similar to impulsively started conditions have been achieved. The cross-stream spacing of the primary vortices is relatively independent of Re, a* and t* but was different for different cylinders.<p> Irrespective of the type of cylinder, the growth of the recirculation zone at Re = 500 and 1000 is smaller than at Re = 200. The recirculation zone of a diamond cylinder is much larger than for both square and circular cylinders. The square and diamond cylinders have sharp edges which act as fixed separation points. Therefore, the cross-stream spacing of the primary vortex centers are independent of Re, unlike the circular cylinder which shows some slight variation with changes in Reynolds number.<p> The growth of the recirculation is more dependent on the distance moved following the start of the impulsive motion; that is why for all types of cylinders, the LR/D, a/D and ¦£/UD profiles collapse onto common curves when plotted against the distance moved from the start of the motion.

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The evaluation of freeway service quality is crucial work, and thus, transportation professionals have developed numerous measures including traffic volume, speed, and density. However, recent research efforts have indicated that such traditional measures may not fully reflect the quality of roadway service from the perspective of individual drivers, necessitating the development of alternative approaches that complement or replace the current service quality measures. As an alternative approach, the speed variation of a vehicle has been suggested as a promising indicator of traffic flow quality perceived by individual drivers. In particular, acceleration noise, defined by the standard deviation of the acceleration of a vehicle, has been often studied as a measure of the degree of speed variation. However, previous studies have been limited to the experimental level due to the difficulty in collecting high-resolution vehicle speed profiles for computing acceleration noise. In this dissertation, the characteristics of speed variation, measured by acceleration noise, are investigated using the rich set of GPS data collected from the instrumented vehicles driven by the participants of the Commute Atlanta research program. The employment of the real-world vehicle activity data, composed of every second of vehicle operation, renders this research effort unique and provides an opportunity to investigate the various aspects of acceleration noise in the real-world context. The investigation is performed by relating acceleration noise to its three influential factors: traffic conditions, roadway, and driver/vehicles. In addition, a fuzzy inference system-based methodology, combining vehicle speed and acceleration noise from instrumented vehicles, is proposed as an approach to evaluating traffic flow quality.

We use the elitist and extinction policies to improve the simple genetic algorithm in this study. We expect that the search technique can avoid falling into the local maximum due to the premature convergence, and the chance of finding the near-optimal parameter in the larger searching space could be obviously increased. The accelerometer is then taken as the sensor for output measurement, and the designed controller is implemented to actively suppress the vibration of the plain that is due to the excitation effect of the high-speed and precision positioning of the linear motor. From the computer simulations and the experimented results, it is obvious that the near-optimal controller designed by using genetic approach with elitist and extinction can improve the effect of vibration suppression; the settling time is also decrease. For the vibration suppressions of high-speed precision positioning problems, the results are satisfactory in the cases of short, middle and long distance.

<p>This thesis deals with the reliability and life-time ofelectronic components and ways to determine these factors.Plastic encapsulated and open test circuits were assessed atdifferent humidity and temperature conditions. From the resultsan acceleration factor could be derived using the Arrheniusrelation. This factor is used to determine failure rates atdifferent drift conditions under accelerated test conditions. Aformula for the factor containing both relative humidity andtemperature could be established and was found to hold also formeasurements published by others.</p><p>Electrostatic discharge (ESD) transients were studiedexperimentally and by simulation with good agreement. A verysensitive method to detect latent failures of two kinds wasintroduced by nonlinearity measurements utilizing the thirdharmonic of a test signal. The ESD-susceptibility dependence ondesign and technology is shown and can be used to improvebuilt-in reliability.</p><p>Influences in the performance of semiconductor devices fromdefects like fixed charges and ions were interpreted for thefirst time by simulation using a 2D- finite element componentprogram. Significant results gave an application to a MOSFETdevice showing parameter derating, especially the change of thethreshold value. A short description of later development insimulation methods with new, more powerful tools improvingcomponent performance and reliability is given.</p><p>Charged thin films of Teflon, so called<i>electrets</i>, are used as microphone membranes. Theelectret voltage is a suitable reliability factor. Fromexperimental results a mathematical relation including thetemperature was established for the rate of decay of theelectret voltage with time. A method to charge the electretswith radioactive sources is outlined and described in apatent.</p><p>Finally an attempt was done to analyze the reliability ofthin film circuits by mathematical methods. Bell Labsintroduced<i>RC</i>-feedback filters realized in tantalum thin filmtechnology. The phase shift of the filter is about π or180°. A mathematical apparatus was developed to calculatethe change in frequency and attenuation from small componentvariations in resistors and capacitors. First and higher ordercorrections were derived, using expansion by the Taylor seriesfor the higher order.</p><p><b>Keywords:</b>reliability, failure mechanism, accelerationtests, ESD, latent failure, plastic encapsulation, electret,thin film</p>

Thesis (D. of Education)--University of Texas at Austin, 1999. / Vita. Includes bibliographical references (leaves 121-128). Available also in a digital version from Dissertation Abstracts.

Thesis (Ph. D.)--School of Aerospace Engineering, Georgia Institute of Technology, 2004. Directed by Dewey H. Hodges. / Vita. Includes bibliographical references (leaves 162-176).

Thesis (Ph. D.)--University of Texas at Austin, 1999. / Vita. Includes bibliographical references (leaves 161-178). Available also in a digital version from Dissertation Abstracts.

The incidence of falls in the elderly population is a growing concern in the healthcare industry as associated morbidity is high, particularly morbidity associated with falls from bed. Bedrails were implemented as a device intended to reduce the incidence of falls from bed; however, recent evidence may indicate that bedrails contribute to adverse events including entrapment and entanglement. As such, efforts have been madeto reduce the use of bedrails and implement alternatives including height adjustable beds and floor mats. An instrumented anthropomorphic test dummy was used in the current study to measure the deceleration profiles of the head, thorax, and pelvis upon impact onto a tile surface or floor mat. The height of the fall was varied by using a height adjustable bed, and the impact site was varied by head or feet first falls. The deceleration profiles were used to determine mean maximum values across repeated trials and to calculate injury criteria at the head (HIC), thorax (TIC), and pelvis (PIC). The mean maximum values were further used to estimate the effect of adding bedrails. Injury severity was then predicted from the injury criteria calculated for the head. From this study, the mean maximum values were found to significantly increase with an increase in height regardless of fall direction. As such, the addition of bedrails consequently increased these values. Furthermore, the use of a floor mat significantly reduced the mean maximum values at the head and pelvis during head first falls and at the head and thorax during feet first falls. Injury criteria were also calculated for each body region and found to be significantly increased with an increase in height and decreased with the use of the floor mat.

To address the pervasive concerns of educators about the social and emotional effects of mathematics acceleration on students and the paucity of findings on those issues, 6 students who had participated in 6 years of accelerated mathematics courses were purposefully identified and interviewed in this longitudinal study. Through a qualitative research design, using phenomenological methods, and accompanying descriptive statistics, the author elicited the students’ descriptions of their learning experiences. Major findings in this study were that all students described great benefits from the experience, negative effects were minor, and key factors contributing to success were work ethic, motivation, parents and teachers. The researcher examines a subset of able and promising students who experienced increased mathematics expectations, and she gives parents, educators and policymakers insight into how that population responded to those challenges. In the ever-shifting arena of higher learning expectations for all students under No Child Left Behind legislation and the poor showing of U.S. students on international tests, these results provide information about the possible responses that other students, those struggling and unmotivated, might have to those demands.