Raman spectroscopy is employed by NASA, and many others, to detect trace amounts of substances. Unfortunately, the Raman signal is generally too weak to detect when very small, but non-trivial, amounts of molecules are present. One way around this weak signal is to use surface enhanced Raman spectroscopy (SERS). When used as substrates for SERS, metallic nanorods grown using physical vapor deposition (PVD) provide a large enhancement factor to the Raman signal, as much as 1012. However, Silver (Ag) nanorods that give high enhancement suffer from rapid degradation as a function of time and exposure to harsh environment. Exposure to harsh environments is an enormous issue for NASA; considering all environments experienced during space missions will be drastically different from Earth regarding atmosphere pressure, atmosphere composition, and environmental temperature. Au and Ag nanorods suffer from a thermochemical kinetic phenomenon where the surface atoms diffuse and cause the nanostructures to coalesce towards bulk structure. When in bulk, SERS enhancement is lost and the substrate becomes useless. A stable structure for SERS detection is designed through engineering the barriers to surface diffusion. Aluminum (Al) nanorods are forced to undergo surface diffusion through thermal annealing and form rough mounds with a stable terminating oxide layer. When Ag is deposited on top of this Al structure, it becomes kinetically bound and changes to physical structure become impeded. Using this paradigm, samples are grown with varied lengths of Ag and are then characterized using scanning electron microscopy (SEM) and Ultraviolet-Visible spectroscopy. The performance of the samples are then tested using SERS experiments for the detection of trace amounts of rhodamine 6G, a ‘gold standard’ analyte. Characterization shows the effectiveness of the Raman substrates remains stable up to 500°C. Transitioning to basic scientific investigation, next is to strive to isolate the individual impacts of chemical and physical changes to the Ag nanostructure and how they affect the Raman signal. Substrates are compared over the course of a month long experiment to determine the effects of vacuum storage and addressing the effects of chemical adsorbance. Additionally, this was attempted by comparing the signal degradation of Ag nanorods to that of Au, which is known to be chemically inert, allowing for the separation of chemical and physical effects. Although Ag and Au have similar melting points, Ag physically coarsened significantly more. FTIR also showed significant chemical contamination of the Ag, but not Au. A hypothesis is proposed for future investigations into the chemical changes and how they are coupled with and promote the physical changes in nanostructures. Overall, the novel SERS substrate engineered here may enable the detection of trace amounts of molecules in harsh environments and over long timescales. Conditions such as those found on space missions, where substrates will experience months or years of travel, high vacuum environments, and environments of extreme temperatures.

The growing global demand for energy and environmental implications have created a need to further develop the current energy generation technologies (solar, wind, geothermal, etc.). Recovering energy from low grade energy sources such as waste heat is one of the methods for improving the performance of thermodynamic cycles. The objective of this work was to achieve long-term steady state operation of a Free-Piston Linear Expander (FPLE) and to compare the FPLE with the currently existing expander types for use in low temperature energy recovery systems. A previously designed FPLE with a single piston, two chambers, and linear alternator was studied and several modifications were applied on the sealing and over expansion. An experimental test bench was developed to measure the inlet and outlet temperatures, inlet and outlet pressures, flow rate, and voltage output. A method of thermodynamic analysis was developed by using the first and second law of thermodynamics with air as the working fluid. The experimental tests were designed to evaluate the performance of the FPLE with varying parameters of inlet air pressure, inlet air temperature, and electrical resistance. The initial and steady-state operation of the FPLE were successfully achieved. An uncertainty analysis was conducted on the measured values to determine the accuracies of the calculated parameters. The trends of several output parameters such as frequency, average root mean square (RMS) voltage, volumetric efficiency, electrical-mechanical conversion efficiency, isentropic efficiency, irreversibility, actual expander work, and electrical power were presented. Results showed that the maximum expander frequency was found to be 44.01 Hz and the frequency tended to increase as the inlet air pressure increased. The FPLE achieved the maximum isentropic efficiency of 21.5%, and produced maximum actual expander work and electrical work of 75.13 W and 3.302 W, respectively.

The focus of this study is to investigate the cracking of concrete bridge decks and the sealants used in repairing transverse cracks. Cracking could occur in both hardened mature concrete and early age concrete. Several factors affect concrete cracking, such as age-dependent material properties, thermal- and moisture-related stresses and strains, material viscoelastic behavior, restraints, concrete expansion and contraction, casting sequence, formwork, material characteristics, and environmental exposure. The causes of early age cracking are primarily attributed to effects such as plastic shrinkage, temperature effects, autogenous shrinkage, and drying shrinkage. This deck cracking could greatly reduce durability, lead to a loss of functionality, loss of stiffness, and ultimately the loss of structural safety. The study investigates the deck cracking in general and also the transverse cracks developed in hardened concrete at early ages before service loads application. Both experimental and analytical investigations were performed. The experimental study included testing of 9 reinforced concrete slab specimens (18”x 48”x 5.5”). Cracks were induced in the slabs with different crack widths and lengths, sealed with 4 different materials of sealants, and tested under static loading. The study also included tensile testing of dry hardened samples of sealants. In addition, field application was performed on a bridge, where transverse deck cracks were sealed using 4 different sealant materials; cores were taken and tested according to ASTM-C496. The results of the testing showed that the 3-part HMWM was the best performing sealer for cracks between 0.01 and 0.019 inches of width with the epoxy sealer performing the best for cracks wider than 0.02 inches.

In this study, a non-linear Finite Element (FE) model was created and analyzed to determine the pressure distribution between the residual limb and the prosthetic socket of a transfemoral amputee. This analysis was performed in an attempt to develop a process allowing healthcare providers and engineers to simulate the fit and comfort of transfemoral prosthetics to reduce the number of re-fittings needed for the amputees. The analysis considered the effects of interference due to insertion of the limb into the prosthesis, referred to as donning, and also the effects due to the body weight of the amputee. A non-linear finite element static implicit analysis method was utilized. This analysis implemented multiple finite element techniques, including geometric non-linearity due to large deflections, non-linear contacts due to friction between the contact surfaces of the residual limb and the socket, and non-linear hyper-elastic material properties for the residual limb’s soft tissue. This non-linear static analysis was carried out in two time-steps. The first step involved solving the interference fit analysis to study the pre-stresses developed due to the effect of donning. The donning process results in soft tissue displacement to accommodate the internal geometry of the prosthesis. In the second load application time-step, an additional load of half the person’s body weight was applied to the femur. The maximum normal stress (contact pressure) of 84 kPa was observed due to the combined effect of the donning procedure and body weight application, comparable to the studies performed by other researchers. The procedure developed through this work can be used by future researchers and prosthetic designers in understanding how to better design transfemoral prosthesis.

As Florida’s population continues to grow and urbanization increases, traditional freshwater sources are in danger of being exhausted. Wastewater reuse programs offer a way to create a potable offset in order to protect these freshwater sources and the environments in which they are found. Reuse regulations for the disinfection of wastewater are increasingly becoming more stringent. In addition to tough regulations, operating costs have also become a driving force behind a movement to assess new and potentially economical chemicals and processes for disinfection. The objective of this thesis is to assess the disinfection performance of peracetic acid (PAA), an alternative chemical that can be used for the disinfection of wastewater in reuse programs. A pilot study was conducted at the Miller St. Wastewater Treatment Plant (WWTP) located near Orange Park, Florida. The pilot study consisted of three phases that were designed to determine the dosage of PAA required to meet Florida’s reuse regulations for treatment plants that provide high-level disinfection, quantify disinfection by-product (DBP) formation and aquatic toxicity, and investigate the effectiveness of utilizing multiple chemical injection points in series with smaller doses of acid. The results showed that the disinfection performance of PAA were comparable with the chlorination system currently in use at the plant when the proper dosage was used. In addition to its disinfection performance, the study showed that disinfection with PAA did not produce harmful amounts of DBP that are normally associated with chlorine-based disinfection.

Long term sustainability in salt marsh and mangroves is dependent on dominant species, such as Spartina alterniflora, to capture organic and inorganic sediment. The research analyzes that sustainability. This work demonstrates the prediction of hydrodynamics and biomass density of salt marsh to provide useful information for the planning and mitigation of sea-level rise impacts on marsh sustainability in the Guana Tolomato Matanzas National Estuarine Research Reserve (GTMNERR), Florida. An advanced circulation code was applied to simulate hydrodynamics (i.e., shallow water equations) in the GTMNERR. The model used a set of parameters and conditions based on the GTMNERR domain to predict tides for present-day conditions, which was validated using tidal data from eight monitoring stations within the GTMNERR. The hydrodynamic model results (i.e., MLW and MHW) were then coupled with a marsh equilibrium model to assess year-to-year biomass density for saltmarsh cordgrass (Spartina alterniflora). Vegetative data were obtained from the staff of the GTMNERR and organized for future work towards validation of biomass density predictions. Simulations were then performed with sea-level rise scenarios of 0.13 m, 0.22 m and 0.51 m, which are standardized cases of mild, moderate, and extreme rise for the northeast coast of Florida. The simulation results show nonlinear increase of tidal datums for given sea-level rise, thus leading to nonlinear change in biomass productivity. The modeling tool has engineering implications in the way of assisting the planning of dredging spoils to be laid over the marsh to sustain existing marsh against rising sea levels. The modeling tool further provides information about marsh migration due to sea-level rise, whereby coastal planners can use this information to designate and preserve existing uplands/wetlands that will house salt marsh in the future, as the marshes will migrate into such upland/wetlands areas.

Aluminum alloy 6061-T6 is a common engineering material used in aerospace, automotive, structural applications. Despite its wide use, little has been published about the effects of damage from surface corrosion on its fatigue life. An investigation was performed where 6061-T6 extrusions were exposed to a 3.5% NaCl solution at pH 2 for 2 days and 24 days. The length of time and pH were chosen in order to create distinct surface flaws. The effect of these flaws on the fatigue life was then investigated and analyzed using scanning electron microscopy (SEM) and Weibull statistics. It was determined that samples corroded for both 2-days and 24-days exhibit fatigue lives that can be described using a 3-parameter Weibull distribution. The result of which was the determination of a threshold value for fatigue as well a general understanding of flaw geometry.

The use of the empirical deck design method has increased its acceptance due to the economic advantages that it presents when compared to its counterpart, the traditional method. This can be attributed to the fact that the empirical method provides an appropriate design where the deck withstands stress not only due to the steel reinforcement but to an implicit arching membrane stress set-up as an effect of the lateral restraint surrounding the deck slab known as Compressive Membrane Action (CMA). It has been proved through research that most design codes underestimate the strength of laterally restrained slabs. However, there is still a lack of acceptance in practical bridge design codes. This thesis presents an analysis addressing the influence that the lateral stiffness of the support beams has on the overall bridge deck performance. The lateral stiffness behavior was assessed through a programmed electronic spreadsheet where a comparison with different current code requirements and an additional approach was made. Through this analysis it was determined that not only does the support beam lateral stiffness plays an important role in the overall bridge deck slab ultimate capacity, but mapping out this influence is a priority that may also be useful in setting the basis for future design criteria.

In the bus transit community, driving long hours or spending extra hours at work are very common. This is true in the State of Florida, where bus transit is a very popular mode of public transportation. Although the correlation between a bus driver’s schedule and a crash event appears intuitive, further study regarding the effects of operator driving schedules on accident rates is needed to evaluate safety measures. The focus of this research is on the examination of bus driver schedules, and the effects of scheduling on accident rates in Florida. Data were collected at five bus transit agencies including Jacksonville Transportation Authority (JTA), Central Florida Regional Transportation Authority (LYNX), Hillsborough Area Regional Transit Authority (HART), Miami-Dade Transit (MDT) and StarMetro in Tallahassee. Data collected included bus operator work schedules, accident data, and a voluntary questionnaire survey. The results indicate that the number of working hours significantly affect driving quality and increase the likelihood of driver involvement in a bus crash. Based upon 410 surveys obtained from operators, over 21% of drivers were concerned about the effects of split-time on fatigue. In addition to split-time considerations, the study revealed that nearly 15% of operators who completed the survey had a secondary driving job. The review of operator schedules also indicated that drivers involved in preventable accidents spent longer hours at work than on actual driving duty, primarily due to extended split-time. Consequently, drivers who had more than two hours of break had a higher probability of being involved in a preventable collision compared to drivers with less than two hours of split-time.

A failure associated with steel corrosion was identified in early 2011 in a bridge external post-tensioned tendon, approximately eight years after construction. Large voids in the grout and pockets of non-homogeneous material were identified. The non-homogeneous grout was characterized by high moisture content, and in most cases, the chloride content was lower than conservative threshold values. The non-homogeneous grout also had high pH and high content of sulfates (approximately in the range of 10,000-ppm). As a result, there was an interest in the study of possible corrosion development in repaired systems in which the affected tendons have been re-grouted with dissimilar grouts. The presence of two distinct grouting materials, manifested by the existing/simulated base grout and a newly introduced repair grout, provided the dissimilar grout condition studied. Corrosion activity was monitored in un-stressed mock up assemblies, in sections retrieved from the failed tendon, and in samples immersed in simulated pore solution. Corrosion activity was monitored through macrocell current, linear polarization resistance, open circuit potential, potentiodynamic scans, and electrochemical impedance spectroscopy. Samples in simulated pore solutions were studied at various pH levels and constituent concentrations. All samples were repaired or built with commercially available grouts. After analysis, no evidence of corrosion development was found when both existing and repair grout were free of material deficiencies. Corrosion activity was noted in the presence of nonhomogeneous grout and an increase in rate was observed due to macrocell coupling with sections containing normal grout. Results suggest that early exposure to sulfate to hydroxyl ion ratio as low 0.35 may prevent steel passivation and result in early high corrosion rates. Otherwise, sulfate to hydroxyl ratios as high as three may not be sufficient to initiate corrosion after formation of passive layer.