This study adds to current understandings of the relationship between socioeconomic conditions and health by examining the influence of work-family strain on health in the context of the recent Great Recession and the preceding and following years in the United States. Analyses used data from the 2002 and 2008 National Survey of the Changing Workforce (NSCW) and 2002, 2006 and 2010 General Social Survey's Quality of Working Life modules. Findings suggest that work-family strain in general increased during the Great Recession compared to non-recessionary periods, that people who experience lower levels of work-family strain enjoy better health, and that health tends to be better during non-recessionary periods compared to recessionary periods. Work-family strain was shown to mediate a small portion of the impact of macroeconomic condition on health. While work-family strain does not appear to be a primary mediator of the relationship macroeconomic condition and health it remains significant and also a very alterable condition. Findings suggest that positive workplace environments can significantly lessen the negative impacts of work-family strain on health of employees. Improvements of workplace environments and conscious efforts to reduce work-family strain for employees could have significant impact on the health of the working US population with minimal costs during both recessionary and non-recessionary periods. / Ph. D.

Sensing has been essential for the investigation, understanding, exploitation, and utilization of physical phenomena. Traditional single-point sensing methods are being challenged by the multi-point or distributed sensing capabilities afforded by optical fiber sensors. A powerful technique available for distributed sensing involves the use of the Optical Frequency Domain Reflectometry (OFDR). This work focuses on using OFDR as a means of obtaining distributed vibration measurements using the Rayleigh scatter along a single-mode optical fiber. The effort begins by discussing various distributed measurement techniques currently in use before discussing the OFDR technique. Next, a thorough discussion on how high spatially resolved Rayleigh measurements are acquired and how such measurements can be used to make static strain measurements is presented. A new algorithm to resolve strain at regions of high spatial gradient is developed. This results in enhanced measurement performance of systems using the Rayleigh scatter to determine static strain or temperature measurements by improving measurement fidelity at the high gradient locations. Next, discussions on how dynamic strain (vibration) couples to optical fiber in a single point and in a distributed setting are presented. Lessons learned are then used to develop a new and unique distributed vibration measurement algorithm. Various consequential benefits are then reviewed before concluding remarks are stated. A simulation model was developed and used to supplement this investigation in every step of the discussion. The model was used to gain insight on how various physical phenomena interact with the optical fiber. The simulation was also used to develop and optimize the high gradient and vibration algorithms developed herein. Simple experiments were then used to validate the theory and the simulation models. / Ph. D.

This thesis is concerned with both the static and dynamic analysis of parabolic arches. In the dynamic part, special attention is given to the free vibration of such arches. The following procedure is followed. The loading conditions are assumed and a infinitesimal segment of the arch is taken so as the differential equations relating deflections and slope changes on both ends of the segment are developed. These obtain a set of general equations for elastic parabolic arches. In dynamics, the equations of general curved structure are developed through considerations of dynamic equilibrium. A sudden removal of loading is assumed to cause the structure to vibrate freely. Then, a method of separating variables for partial differential equations is used to get the equations of deflection components. Each special characteristic function is derived for each special set of boundary conditions so as to get an unlimited number of modes of free vibrations. The Fourier series is employed to determine the coefficients of the dynamic equations, and to get a series-form solution for deflections. Finally, two numerical examples are given to represent the practical application. Two kinds of parabolic arches, one with two-hinged supports and the other with fixed-ends are considered in each procedure. / Master of Science

The Virginia Tech Transportation Institute is recognized for being a pioneer in naturalistic driving studies. These studies determine driving behavior, and its correlation to safety critical events, by equipping participant's vehicles with data acquisition systems and recording them for a period of time. The driver's habits and responses to certain scenarios and events are analyzed to determine trends and opportunities to improve overall driver safety. One of these studies installed strain gauges on the front and rear brake levers of motorcycles to record the frequency and magnitude of brake presses. The recorded data was sampled at 10 hertz and had a significant amount of noise introduced from temperature and electromagnetic interference. This thesis proposes a peak detection algorithm, written in MATLAB, that can parallel process the 40,000 trips recorded in this naturalistic driving study. This algorithm uses an iterative LOWESS regression to eliminate the offset from zero when the strain gauge is not stressed, as well as a cumulative sum and statistical concepts to separate brake activations from the rest of the noisy signal. This algorithm was verified by comparing its brake activation detection to brake activations that were manually identified through video reduction. The algorithm had difficulty in accurately identifying activations in files where the amplitude of the noise was close to the amplitude of the brake activations, but this only described 2% of the sampled data. For the rest of the files, the peak detection algorithm had an accuracy of over 90%. / Master of Science

The purpose of this study was to develop material properties of human rib cortical bone using dynamic tension coupon testing. This study presents 117 human rib cortical bone coupon tests from six cadavers, three male and three female, ranging in age from 18 to 67 years old. The rib sections were taken from the anterior, lateral, and posterior regions on ribs 1 through 12 of each cadaver's rib cage. The cortical bone was isolated from each rib section with a low speed diamond saw, and milled into dog bone shaped tension coupons using a small computer numerical control machine. A high-rate servo-hydraulic Material Testing System equipped with a custom slack adaptor, to provide constant strain rates, was used to apply tension loads to failure at an average rate of 0.5 strains/sec. The elastic modulus, yield stress, yield strain, ultimate stress, ultimate strain, and strain energy density were determined from the resulting stress versus strain curves. The overall average of all cadaver data gives an elastic modulus of 13.9 GPa, a yield stress of 93.9 MPa, a yield strain of 0.883 %, an ultimate stress of 124.2 MPa, an ultimate strain of 2.7 %, and a strain energy density of 250.1 MPa-strain. For all cadavers, the plastic region of the stress versus strain curves was substantial and contributed approximately 60 strain % to the overall response and over 80 strain % in the tests with the 18 year old cadaver. The rib cortical bone becomes more brittle with increasing age, shown by an increase in the modulus (p < 0.01) and a decrease in peak strain (p < 0.01). In contrast to previous three-bending tests on whole rib and rib cortical bone coupons, there were no significant differences in material properties with respect to rib region or rib level. When these results are considered in conjunction with the previous three-point bending tests, there is regional variation in the structural response of the human rib cage, but this variation appears to be primarily a result of changes in the local geometry of each rib while the material properties remain nearly constant within an individual. / Master of Science

Since the Eighteenth century, a great amount of research has been done using the elastic analysis technique in the field of curved structures. Recently the question of behavior beyond the yielding range has become increasingly important. By applying the methods of plastic analysis, the collapse load of a structure can be determined, and also the stress distribution and the deflection, just before collapse, can be calculated. However the evolution of the stress distribution and the deflection at any section of the structure between the load causing first yielding and the collapse load is still an unsolved problem. Concerning the problem of evolution of the stress distribution in the inelastic range, most literature relies on the simple plastic theory in which the effect of the axial force on the formation of a plastic hinge is neglected. In fact this conception is in serious error in some cases, especially when the curved structure is a shallow arch, the stresses developed are apparently governed by the axial force. Literature considering the combined effects of bending moment and axial force is very rare. In this thesis, the author proposes a new method, incorporating effects of both axial force and bending moment, of determining the evolution of stress distributions and the deflections in the inelastic range. The thesis includes three parts. In the first to parts, the theory for the stress analysis and for the deflection of a rectangular section is presented. The third part contains three examples to illustrate the use of the new method in practical engineering problems. / Master of Science

Collagen type I is an extracellular matrix (ECM) protein that affords tensile strength and biological scaffolding to numerous vertebrate and invertebrate tissues. This strength has been attributed to the triple-helical structure of the collagen type I molecules, their organization into fibrils, and the presence of inter-molecular, covalent, enzymatic crosslinks. There are several different types of these crosslinks; their composition is tissue-specific and dependent upon factors such as age and health. Furthermore, these enzymatic crosslinks tend to form specifically at amino/N- and carboxy/C-terminal crosslinking sites. The mechanical behavior of collagen type I has been investigated, via experiment and theory, at the level of the molecule, microfibril, fibril, and fiber. However, the influence of different enzymatic crosslinks and their location (e.g., N- vs. C-site) on the mechanics of collagen type I has not been investigated in the literature. We employed molecular dynamics to model the mechanical behavior of uncrosslinked and crosslinked ~23-nm-long molecular segments and ~65-nm-long microfibril units of collagen type I. We then used these molecular simulations to construct a model of a single collagen type I fibril by considering the ~65-nm-long microfibril units arranged in series and then in parallel. When a uniaxial deformation was applied along the long axis of the molecular models, N-crosslinks aligned rapidly at lower strains followed by C-crosslinks more gradually at higher strains, leading to a two-stage crosslink recruitment. Then when comparing the influence of different enzymatic crosslinks, significant differences were observed for the high-strain elastic moduli of our microfibril unit models, namely and in increasing order, uncrosslinked, immature crosslinked (HLKNL and deH-HLNL), mature HHL-crosslinked, and mature PYD-crosslinked. At the fibril level, our low- and high-strain elastic moduli were in good agreement with some literature data, but in over-estimation of several other literature reports. Future work will seek to address simplifications and limitations in our modeling approach. A model such as this, accounting for different enzymatic crosslink types, may allow for the prediction of the mechanics of collagen fibrils and collagenous tissues, in representation of healthy and diseased states. / Ph. D.

The brain, like many parts of the human body, can experience swelling, also known as cerebral edema. Cerebral edema may occur because of an injury, health related issues, tumors, or even high altitudes[1]. When cerebral edema occurs, a rise in intracranial pressure (ICP) becomes prevalent and may cause a serious threat. Without immediate treatment, increased intracranial pressure can prevent blood from flowing to the brain and depriving it of necessary oxygen it needs to function. A normal ICP is usually between 5-15 mmHg (666 Pa - 1333Pa). Any ICP observed to be above 20 mmHg (2666Pa) can be associated with brain ischemia and is usually treated[2, 3]. If prolonged, high intracranial pressures can be fatal. Current methods of measuring increased ICP are invasive and may involve drilling into the skull. Extreme invasive measures are not always suitable for certain situations. This thesis presents a study of a non-invasive sensor using piezoelectric PVDF wire to measure the ICP. The PVDF wire sensor is wrapped around the outer portion of the human head to measure the integrated hoop strain. Using this hoop strain, the pressure is then calculated from a known coupling factor of strain to pressure outputted from finite element modeling simulations. The coupling factor is then incorporated into a final calibration factor to calibrate the piezoelectric PVDF wire sensor from charge (Picocoulomb) to pressure (Pascal). These calibration factors are proven to be primarily dependent on the circumference of the human skull. Furthermore, part of this study analyzed the effectiveness and validity of the sensor due to asymmetries in the human skull. A comparison of analytical analysis results versus computational results using finite element modeling simulations show that the PVDF wire sensor neglects any asymmetries presented within the test subject. The results of this study show that this sensor will output correct ICP measurements of different subjects using appropriate calibration factors and is a viable option for measuring ICP non-invasively. / Master of Science

Blindness due to ocular trauma is a significant problem in the United States considering that each year approximately 500,000 years of eyesight are lost. The most likely sources of eye injuries include sports related impacts, automobile accidents, consumer products, and military combat. Out of the 1.9 million total eye injuries in the country, more than 600,000 sports injuries occur each year and 40,000 of them require emergency care. In 2007, approximately 66,000 people suffered from vehicle related eye injuries in the United States. Of the vehicle occupants sustaining an eye injury during a crash, as many as 15% to 25% sustained severe eye injuries and it was shown that within these severe eye injuries as many as 45% resulted in globe rupture. The purpose of this thesis is to characterize the biomechanical response of the human eye to dynamic loading. A number of test series were conducted with different loading conditions to gather data. A drop tower pressurization system was used to dynamically increase intraocular pressure until rupture. Results for rupture pressure, stress and strain were reported. Water streams that varied in diameter and velocity were developed using a customized pressure system to impact eyes. Intraocular pressure, normalized energy and eye injury risk were reported. A Facial and Ocular Countermeasure Safety (FOCUS) headform was used to measure the force applied to a synthetic eye during each hit from projectile shooting toys. The risk of eye injury for each impact was reported. These data provide new and significant research to the field of eye injury biomechanics to further the understanding of eye injury thresholds. / Master of Science

As supported by ecological systems theory and the family stress model of economic hardship, socioeconomic status can directly be related to adolescent adjustment outcomes including self-regulation, academic performance, and substance use as well as be indirectly related to these outcomes through the mediator of parental monitoring. Data obtained from 220 adolescent (male = 55%, female = 45%, mean age = 15.12 years) and primary caregiver dyads participated in the study to examine the relationship between these variables. Analyses were conducted using Structural Equation Modeling, and the results of the study demonstrate that economic hardship is directly related to adolescent academic performance and also indirectly related to this outcome through maternal monitoring. Parental monitoring was also positively related to adolescent self-regulation. Therefore, this study highlights the importance of high levels of parental monitoring for beneficial adolescent self-regulation, academic, and substance use outcomes. / Master of Science