Due to traumatic brain injury (TBI), numerous studies have focused on comprehensively determining the mechanical properties of the brain. This study examined the strain rate dependence of porcine brain under compression, and the microstructural damage was quantified using a confocal microscope and graphical user interface (GUI). The selected strain rates were 0.10 s-1, 0.025 s-1, and 0.00625 s-1 while the strain levels targeted for confocal imaging were 15%, 30%, and 40%. This study also characterized the stress-state dependence at a strain rate and strain level of 0.10 s-1 and 40%, respectively, under compression, tension, and shear. Strain rate dependency data exhibited viscoelastic behavior, and the analysis parameters correlated with increasing strain rate and strain level. Stress-state dependency data demonstrated distinct nonlinear behavior, and disparities were observed in the analysis parameters between different testing modes. Finite element procedures can implement this supplementary data for devising more realistic models.

Predicting fatigue failure is a critical design element for many engineering components and structures subject to complex service conditions. In high-temperature and corrosive environments, many materials exhibit rate dependent phenomena that can significantly alter safe service life predictions. Existing cycle processing techniques such as Peak Counting, Simple Range, and the Rain Flow method are able to resolve complex service histories into sets of simple cycles, but these methods are unable to handle time-related parameters such as engage rate and cycle sequence. To address this, a cycle processor was written in FORTRAN 95 later termed the Multi-Algorithm Cycle Counter (MACC). This code was utilized as a platform to develop, test, and study various methods of extracting and interpreting rate parameters extracted from cycles defined by existing counting algorithms.

In-vivo dosimetry with diode detectors is used in radiation therapy as a quality assurance tool. The diode sensitivity under radiation depends upon temperature, dose rate and SDD (source-to-detector distance), field size, beam angle, and energy. This dissertation presents the first systematic and quantitative study of dosimetric characteristics for most of the commercial radiation diodes (n-type and p-type) under different radiation beams.In the temperature dependence study, the systematic study on the dose rate dependence of svwt (sensitivity variation with temperature) was performed. It was concluded that sufficient preirradiation can eliminate dose rate dependence of svwt. However, preirradiation cannot eliminate dose rate dependence of the diode sensitivity, S, itself. In the dose rate and SDD dependence study, it was shown that the p-type diodes do not always show less dose rate dependence than the n-type diodes. Preirradiation does not always reduce diode dose rate dependence. SDD dependence of diode sensitivity can be explained by the instantaneous dose rate dependence if sufficient buildup is provided to eliminate electron contamination. An empirical formula was proposed to fit the dose rate dependence of diode sensitivity. In the energy dependence study, the energy dependence diode detectors are quantified. The empirical theory to quantify this effect was developed. Monte Carlo simulation and the cavity theory are used to predict the energy dependence. It was concluded that the energy dependence does not depend on whether the diode is n- or p- type but rather depends mainly on the material around the die (buildup and its geometry). A systematic study of the correction factors for accurate diode dosimetry is presented in this dissertation.This dissertation has established a theoretical foundation for the modeling of the transient electric and radiation properties of the diode detectors, separately. We believe that the Monte Carlo simulations code for radiation transport should be coupled with the continuity equations to describe the charge transport in the diode detector, and thus provides a complete quantitative description of dosimetric characteristics of the diode detectors. The ultimate goal is to use the diode detector as an absolute dosimeter, rather than as a relative dosimeter.

Teacher absenteeism is a major concern in many school districts around the country. There have been numerous studies on the topic, but we as educators are still dealing with the problems of teacher absenteeism. To get a good understanding of teacher and administrator perceptions of this problem, a quantitative research approach was used. Quantitative data was gathered using a questionnaire with 28 Likert scale questions. One hundred teachers and three administrators participated in this part of the study. In addition, structured questions were used to interview three teachers and three administrators. Multiple regression analyses were conducted to determine which predictor variables presented in the demographic section of the questionnaire contributed to variation in the various dependent variables, e.g. attendance. All multiple regression analyses were performed at the .05 level of statistical significance. The t-test for attendance indicated that the predictor variable, age, was statistically significant and could be concluded that the older the teacher, the less absenteeism. The t-test for attendance indicated that the predictor variable, degree, was statistically significant and could be concluded that the higher the degree, the less absenteeism. The t-test for operating procedures indicated that the predictor variable, years of experience, was statistically significant and could be concluded that the more experience, the more familiar were teachers with the operating procedures of the school. The t-test for training indicated that the predictor variable, years experience, was statistically significant and could be concluded that the more experience, the more inclined regular teachers were for substitute teacher training. The survey responses revealed many similarities between the teachers and administrators. Teachers and administrators believe there is reduced student achievement taking place when there are substitute teachers in the classroom. Because of this, all teachers and administrators feel the need for extensive professional development for substitute teachers. Teachers and administrators agree that student attendance is affected by substitute teachers in the classrooms. From all points of view, it is strongly believed that operational procedures are greatly affected when several regular teachers are absent at the same time and substitutes are in their classrooms.

While traumatic aortic injury (TAI) and rupture (TAR) continue to be a major cause of morbidity and mortality in motor vehicle accidents, its underlying mechanisms are still not well understood. Different mechanisms such as increase in intraluminal pressure, relative movement of aorta with respect to mediastinal structures, direct impact to bony structures have been proposed as contributing factors to TAI/TAR. At the tissue level, TAI is assumed to be the result of a complex state of supra-physiological, high rate, and multi-axial loading. A major step to gain insight into the mechanisms of TAI is a characterization of the aortic tissue mechanical and failure properties under loading conditions that resemble traumatic events. While the mechanical behavior of arteries in physiological conditions have been investigated by many researchers, this dissertation was motivated by the scarcity of reported data on supra-physiological and high rate loading conditions of aorta. Material properties of the porcine aortic tissue were characterized and a Fung-type constitutive model was developed based on ex-vivo inflation-extension of aortic segments with intraluminal pressures covering a range from physiological to supra-physiological (70 kPa). The convexity of the material constitutive model was preserved to ensure numerical stability. The increase in ë_è from physiological pressure (13 kPa) to 70 kPa was 13% at the outer wall and 22% at the inner wall while in this pressure range, the longitudinal stretch ratio ë_z increased 20%. A significant nonlinearity in the material behavior was observed as in the same pressure range, the circumferential and longitudinal Cauchy stresses at the inner wall were increased 16 and 18 times respectively. The effect of strain-rate on the mechanical behavior and failure properties of the tissue was characterized using uniaxial extension experiments in circumferential and longitudinal directions at nominal strain rates of 0.3, 3, 30 and 400 s-1. Two distinct states of failure initiation (FI) and ultimate tensile strength (UTS) were identified at both directions. Explicit direct relationships were derived between FI and UTS stresses and strain rate. On the other hand, FI and UTS strains were rate independent and therefore strain was proposed as the main mechanism of failure. On average, engineering strain at FI was 0.85±0.03 for circumferential direction and 0.58±0.02 for longitudinal direction. The engineering strain at UTS was not different between the two directions and reached 0.89±0.03 on average. Tissue pre-failure linear moduli showed an average of 60% increase over the range of strain rates. Using the developed material model, mechanical stability of aorta was studied by varying the loading parameters for two boundary conditions, namely pinned-pinned boundary condition (PPBC) and clamped-clamped boundary condition (CCBC). The critical pressure for CCBC was three times higher than PPBC. It was shown that the relatively free segment of aorta at the isthmus region may become unstable before reaching the peak intraluminal pressures that occur during a trauma. The mechanical instability mechanism was proposed as a contributing factor to TAI, where elevations in tissue stresses and strains due to buckling may increase the risk of injury. / Mechanical Engineering

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ヘテロ構造組織を有する鉄・非鉄金属の組織形態に注目して,微視的構造やその挙動が巨視的現象(変形特性,成形性)として発現するメカニズムを解明することを目的とした.鉄系金属ではDual Phase型高張力鋼のスプリングバック現象のひずみ速度依存性,非鉄系金属では半凝固鋳造法と強ひずみ加工を組み合わせた亜共晶アルミニウム合金の衝撃後方押出し成形性に注目した.これらの検討によりいずれの試料においても,結晶粒界よりもスケールの大きいヘテロ構造に由来した変形機構が支配的であることが明らかになった. / 博士(工学) / Doctor of Philosophy in Engineering / 同志社大学 / Doshisha University