Orb weavers intercept insects using non-hardening bioadhesive droplets, supported by two flagelliform fibers. Droplets contain an adhesive glycoprotein core and aqueous layer that confers hygroscopicity. The first study investigates the durability of these droplets to cycling, or repeatedly adhering, extending, and pulling off. Droplets of four species proved resilient, cycling 40 times. Cycling, coupled with droplet humidity responsiveness, qualifies them as smart materials. However, thread adhesion is complex, relying on an integrated performance of multiple droplets and the flagelliform fibers. As insects struggle, the flagelliform fibers bow and the droplets extend, forming a suspension bridge configuration whose biomechanics sum the adhesion of droplets and dissipate the energy of struggling insects. Given this performance, the second study predicts that the material properties of both thread components have evolved in a complementary way. Comparative phylogenetics of 14 study species revealed that their elastic moduli are correlated, with glycoproteins being six times more elastic than flagelliform fibers. Spider mass affects the amount of each material, but not their properties. Since glycoprotein performance changes with humidity, we hypothesized that orb weavers generate greater adhesion at their foraging humidity. After delimiting low and high humidity species groups (eight and six species, respectively), bridge force was determined as total contributing droplet adhesion at three humidities. Only three spiders generated greater adhesion outside of their foraging humidity. The distribution of force along a suspension bridge differed from a previously reported pattern. We also characterize the sheet configuration, which generates force similar to suspension bridges. / Master of Science / In nature, adhesives are used for a variety of functions. Many animals use adhesives use adhesives when climbing. Examples include toe pads of geckos, tarsal pads of ants, and tube feet of and sea urchins. Here, adhesion is repeatedly generated and released as the animal moves. However, some animals depend on permanent adhesives to anchor to surfaces. Marine mussels and barnacles, whose adult forms are sessile, use adhesives to resist the powerful action of waves and currents. Adhesion also plays a critical role in prey capture, where it prevents prey from escaping. The sticky droplets of a sundew plants and the adhesive capture threads of spider orb webs trap flies. Biologists and engineers study these bioadiehsives in search of inspiration and principles that will guide the development of new materials, including adhesives that function underwater, harden rapidly, or remaining pliable after adhering. This study investigated the material properties of capture threads spun by orb weaving spiders, which rely on non-hardening sticky droplets, supported by two protein fibers to capture insects. Inside each droplet is an adhesive core allows droplets to adhere to an insect and to extend as it struggles to escape. Surrounding this core is an aqueous layer that attracts atmospheric water, causing droplets to track changes in ambient humidity. A study of the cycling (or reusability) of four species' droplets repeatedly adhered a droplet to a surface and extending it to pull-off. These droplets were very resilient, cycling 40 times. Cycling, coupled with droplet humidity responsiveness, qualifies them as smart materials. However, prey capture is more complex, relying on the integration of multiple droplets and their supporting flagelliform fibers. As insects struggle, these fibers bow and the droplets extend, forming a suspension bridge configuration whose biomechanics sum the adhesion of droplets to resist an insect escape. The threads of 14 species were examined to test the hypothesis that material properties of both thread components have evolved in a complementary way to optimize adhesive performance. This revealed that the elasticities of the two capture thread components were correlated, with support fiber elasticity being greater. Capture threads generated the greatest adhesion at humidities during times that a spider feeds, although the distribution of this force across a suspension bridge showed different patterns among the species. The functional integration of a capture thread's components and its ability to respond to environmental humidity gives it exciting biomimicry potential.

The biosensing field has grown in importance and research efforts over the last few years for many reasons including point of care sensing devices and possible early detection of diseases in the body. Dopamine sensing is discussed in this paper and the development of a dopamine sensing platform would lead to early detection of diseases linked to its abundance or lack thereof in the brain such as Parkinson's disease. This work focuses on the electrochemical methods of biosensing, specifically dopamine sensing, and this method involves the use of electrodes as its sensing component. Multimaterial electrode-embedded fibers are used as the sensing electrode and the electrode material presented is platinum (Pt). Platinum is employed because of its biocompatibility property. The electrodes are placed in the fiber by the method of convergence fiber drawing and the fiber ends are stripped to expose the electrode for application. To make the proposed sensing platform more cost-effective, the platinum is electrodeposited onto the multimaterial fiber's embedded electrode. We discuss the use of a W/Pt modified electrode and a pure platinum wire in dopamine sensing and demonstrate that Pt is indeed a good candidate for dopamine sensing. The results show that the sensitivity of the W/Pt modified electrode to dopamine is higher than that of a pure Pt wire. This work has shown the promising application of electrodeposition in developing a cheaper flexible biosensing platform and opens up the possibility of the development of wearable flexible smart textile sensors because of the use of flexible multimaterial fibers. / Master of Science / The idea of sensing is important to our world and various scientific developments in this area have improved our way of life as humans. Biological sensing, which is what this thesis focuses on, detects the presence of various substances in the body, and developments in the area of biosensing have led to the creation of devices that can detect diseases or gather general information about a person's anatomical state. There has been increased interest in the detection of dopamine as more studies show that some diseases such as Parkinson's disease are related to the amounts of dopamine present in the brain. In this work, we present a potential platform for sensing dopamine in vitro using electrochemistry. Multimaterial fibers with embedded electrodes capable of measuring dopamine were fabricated using a thermal drawing technique. The electrode material in this fiber is the most important part of the sensing platform as it is what determines how sensitive the fiber is to an analyte. The two main topics discussed in this work are the modification of the electrode material using an electrodeposition technique and the sensing of dopamine with the modified electrode using the electrochemical methods of cyclic voltammetry and differential pulse voltammetry. The material involved in the electrodeposition process is Platinum (Pt) and the results show that platinum is a suitable material for dopamine sensing.

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Recently, a new class of sensors has emerged which have scalar outputs derived from distributed measurements over a significant gauge length; these sensors are known as distributed-effect sensors. The most familiar example of a distributed-effect sensor is the piezoelectric laminate PVDF film; other examples include holographic sensors and modal domain optical fiber sensors. Optical fiber sensors are particularly attractive for smart structure and materials applications because they have low mass, are flexible, and can be easily embedded in a variety of materials. Distributed-effect sensors can be fabricated with spatially varying sensitivity to the distributed measurand and act as spatial filters. The spatial variation in the sensor sensitivity, known as the sensor's weighting function, determines the measurement provided by the spatial filter. Spatial filters can be configured to measure a variety of structural parameters, such as modal amplitudes and traveling waves, that can not be measured directly using point sensors. The mathematical model of the sensor is described and incorporated into a state-space model of a flexible structure. Several criteria are described in this dissertation for selecting the weighting functions of distributed-effect sensors for structural control laws. The weighting function realized in the fabrication of a distributed-effect sensor may differ from the desired weighting function, causing the output of the manufactured sensor to differ from the desired measurement. In order to design reliable structural control laws, the nature and effects of errors in the implemented weighting functions of distributed-effect sensors must be understood. This dissertation describes several causes of errors in distributed-effect sensor weighting functions. Errors in the weighting functions of distributed-effect sensors are integrated into the mathematical models of the sensors, and the effects of these errors on the sensor outputs are examined. / Ph. D.

A novel bidirectional decomposition of exact solutions to the scalar wave equation has been shown to form a natural basis for synthesizing localized wave (LW) solutions that describe localized, slowly decaying transmission of energy in free space. In this work, we demonstrate the existence of LW solutions in optical fiber waveguides operated in the linear regime. In this sense, these solutions are fundamentally different from the non-linear, soliton-based communication systems. Despite the dielectric waveguiding constraints introduced by the fiber, solutions that resemble the free-space solutions can be obtained with broad bandwidth source spectra. As with the free-space case, these optical waveguide LW solutions propagate over very long distances, undergoing only local variations. Four different source modulation spectra that give rise to solutions similar to Focus Wave Modes (FWM’s), splash pulses, the scalar equivalent of Hillion’s spinor modes and the Modified Power Spectrum (MPS) pulses are considered. A detailed study of the MPS pulse is performed, practical issues regarding source spectra are addressed, and distances over which such LW solutions maintain their non-decaying nature are quantified. Present day state-of-the-art technology is not capable of meeting requirements that will make practical implementation of LW solution-based fiber optic systems a reality. We address futuristic technology issues and briefly describe efforts that could lead to efficient LW solution-based fiber optic systems. / Ph. D.

ln the last several years, considerable attention has been paid to the study of dispersion-flattened single-mode fibers which offer a high transmission capacity with low losses through a wide range of wavelengths. However, the existing designs are sensitive to bending and manufacturing tolerances, and are not truly single-mode at most wavelengths of interest. To remedy these problems a new series of broadband dispersion-flattened truly single-mode fiber designs are proposed. These fibers have both dispersion-shifted and dispersion-flattened features with low splice and bend losses. Results demonstrating a total dispersion of ±0.97 ps/km-nm over the entire spectral range between 1.31 μm to 1.66 μm are presented. Such dispersion-flattening is achieved while simultaneously maintaining a mode-field radius of 3 μm to 5 μm in the dispersion-flattened wavelength range. The most significant achievement is that the proposed muIti-clad fiber design is strictly single-mode and splice and bend losses are smaller than those of double-clad, triple-clad, and quadruple-clad fibers with the same value of dispersion. Ultralow dispersion fibers, whose chromatic dispersion and the first and second-order derivatives of the chromatic dispersion are zero at 1.5 μm or 1.55 μm, are described. This effectively increases the laser emission tolerance. Ultralow dispersion fibers open the way to wavelength multiplexing with currently available inexpensive multifrequency lasers, either in local or long distance networks. These fibers also have low splice and bend losses compared to double-clad, triple-clad, and quadruple-cIad fibers. An inverse waveguide synthesis program, which can trace multiple objective functions and optimize multiple parameters simultaneously, is developed. An objective function is applied, for the first time, to optimize the dispersion-flattened single-mode fiber index profile with respect to: (1) minimum dispersion, (2) the wavelengths of zero-dispersion, (3) maximum width of dispersion-flattened window, (4) maximum layer index difference less than 0.8%, and (5) layer thickness larger than 3.5 μm. The accuracy of chromatic dispersion calculations in dispersion-flattened fibers is evaluated. lt has been shown that the accuracy of approximate methods is influenced not only by the index differences, but also by their derivatives with respect to wavelength. The matrix method and direct numerical integration of the wave equation are used to compute the mode propagation constants, cutoff frequencies, field distributions, mode-field radius, and splice loss, and carry out production tolerance analysis for multi-clad step-index fibers and graded-index fibers, respectively. Detailed analysis and optimized fiber data are presented. / Ph. D.

The effect of anodization in NaOH, H₂SO₄, and amine salts on the surface chemistry of carbon fibers was examined by x-ray photoelectron spectroscopy (XPS). The surfaces of carbon fibers after anodization in NaOH and H₂SO₄ were examined by scanning transmission electron microscopy (STEM). angular dependent XPS, ultraviolet (UV) absorption spectroscopy of the anodization bath, secondary ion mass spectrometry, and polar/dispersive surface energy analysis. Hercules AS-4, Dexter Hysol XAS, and Union Carbide T-300 fibers were examined by STEM, angular dependent XPS, and breaking strength measurement before and after commercial surface treatment. The fibers from the three companies were anodized to create similar surface chemistry on each fiber. XPS was used to compare the surface chemistry after anodization. Adhesion of carbon fibers to polysulfone, polycarbonate, and polyetherimide was studied using the fiber critical length test. Oxygen and nitrogen were added to the fiber surfaces by anodization in amine salts. Analysis of the plasmon peak in the carbon 1s signal indicated that H₂SO₄ anodization affected the morphological structure of the carbon fiber surface. UV absorption spectra of the anodization bath, SIMS, and angular dependent XPS indicate that NaOH anodization removes amorphous carbon from the fiber. The oxygen and nitrogen content on the fiber surfaces were affected by commercial surface treatment. The Union Carbide fiber had much lower oxygen content after laboratory anodization than the Hercules or Dexter Hysol fibers. The breaking strength of all three fibers was increased by anodization. Laboratory anodization resulted in better fiber/matrix adhesion than the commercial surface treatment for the Hercules and Dexter Hysol fibers. Fiber/matrix adhesion was better for the commercially treated Union Carbide fiber than for the laboratory treated fiber. The work of adhesion of carbon fibers to thermoplastic resins was calculated using the geometric mean relationship. A correlation was observed between the dispersive component of the work of adhesion and the interfacial adhesion. / Ph. D. / incomplete_metadata

Since World War II, the military has sought methods for rapid stabilization of weak soils for support of its missions worldwide. Over the past 60 years, cement and lime have consistently been found to be among the most effective stabilizers for road and airfield applications, although recent developments show promise using nontraditional stabilizers. The purpose of this research is to determine the most effective stabilizers and dosage rates of stabilizers to increase the strength of soft clay soils (initial CBR = 2) within 72 hours for contingency airfields to support C-17 and C-130 aircraft traffic. Pavement design charts for various aircraft loading conditions were generated using the Pavement-Transportation Computer Assisted Structural Engineering Program, which was developed by the Engineering Research and Development Center to determine ranges of required strength and thickness for an underlying subbase layer and a top base layer, such as stabilized soil, crushed-aggregate, or aluminum matting. From laboratory studies, the required design strengths for many loading conditions were achieved by treating clay with 2%-4% pelletized quicklime for the underlying subbase layer, and treating clay with 2%-4% pelletized quicklime, 1% RSC15 fibers, and 11% Type III cement for the top base layer. While the base layer requires a minimum thickness of six inches, the required subbase layer thickness is often quite large and may be difficult to construct. However, newly developed construction equipment currently used for subgrade stabilization on civilian projects should be able to stabilize the soil down to these large required depths and make construction possible. / Master of Science

The present study was initiated to evaluate the pulmonary inflammatory and fibrotic responses induced by single and repeated exposures to glass fibers. Single and repeated intratracheal injections of glass fibers induced an acute inflammatory response which progressed to a chronic inflammatory and fibrotic response. Mice exposed to glass fibers in single or repeated doses demonstrated elevated numbers of eosinophils, neutrophils and macrophages and increases in cell-free protein in lung lavage fluid at five days post-exposure. These parameters, in addition to relative lung/body weight ratios and lung tissue hydroxyproline levels, were elevated in comparison to saline control animals at five weeks post-exposure. Although repeated exposures to glass fibers did not potentiate the cellular inflammatory response, they did induce a marked infiltration of eosinophils, a response not observed with either asbestos or silica exposures. These observations suggest that glass fibers may be more toxic to the lungs than previously thought.