Matching Items (181)
Description
Gold nanoparticles as potential diagnostic, therapeutic and sensing systems have a long history of use in medicine, and have expanded to a variety of applications. Gold nanoparticles are attractive in biological applications due to their unique optical, chemical and biological properties. Particularly, gold nanorods (GNRs) are increasingly used due to superior optical property in the near infrared (NIR) window. Light absorbed by the nanorod can be dissipated as heat efficiently or re-emitted by the particle. However, the limitations for clinical translation of gold nanorods include low yields, poor stability, depth-restricted imaging, and resistance of cancer cells to hyperthermia, are severe. A novel high-throughput synthesis method was employed to significantly increase in yields of solid and porous gold nanorods/wires. Stable functional nanoassemblies and nanomaterials were generated by interfacing gold nanorods with a variety of polymeric and polypeptide-based coatings, resulting in unique properties of polymer-gold nanorod assemblies and composites. Here the use of these modified gold nanorods in a variety of applications including optical sensors, cancer therapeutics, and nanobiomaterials were described.
ContributorsHuang, Huang-Chiao (Author) / Rege, Kaushal (Thesis advisor) / Sierks, Michael (Committee member) / Dai, Lenore (Committee member) / Ramakrishna, B (Committee member) / Vogt, Bryan (Committee member) / Arizona State University (Publisher)
Created2012
Description
Concrete design has recently seen a shift in focus from prescriptive specifications to performance based specifications with increasing demands for sustainable products. Fiber reinforced composites (FRC) provides unique properties to a material that is very weak under tensile loads. The addition of fibers to a concrete mix provides additional ductility and reduces the propagation of cracks in the concrete structure. It is the fibers that bridge the crack and dissipate the incurred strain energy in the form of a fiber-pullout mechanism. The addition of fibers plays an important role in tunnel lining systems and in reducing shrinkage cracking in high performance concretes. The interest in most design situations is the load where cracking first takes place. Typically the post crack response will exhibit either a load bearing increase as deflection continues, or a load bearing decrease as deflection continues. These behaviors are referred to as strain hardening and strain softening respectively. A strain softening or hardening response is used to model the behavior of different types of fiber reinforced concrete and simulate the experimental flexural response. Closed form equations for moment-curvature response of rectangular beams under four and three point loading in conjunction with crack localization rules are utilized. As a result, the stress distribution that considers a shifting neutral axis can be simulated which provides a more accurate representation of the residual strength of the fiber cement composites. The use of typical residual strength parameters by standards organizations ASTM, JCI and RILEM are examined to be incorrect in their linear elastic assumption of FRC behavior. Finite element models were implemented to study the effects and simulate the load defection response of fiber reinforced shotcrete round discrete panels (RDP's) tested in accordance with ASTM C-1550. The back-calculated material properties from the flexural tests were used as a basis for the FEM material models. Further development of FEM beams were also used to provide additional comparisons in residual strengths of early age samples. A correlation between the RDP and flexural beam test was generated based a relationship between normalized toughness with respect to the newly generated crack surfaces. A set of design equations are proposed using a residual strength correction factor generated by the model and produce the design moment based on specified concrete slab geometry.
ContributorsBarsby, Christopher (Author) / Mobasher, Barzin (Thesis advisor) / Rajan, Subramaniam D. (Committee member) / Neithalath, Narayanan (Committee member) / Arizona State University (Publisher)
Created2011
Description
Research shows that general parenting practices (e.g., support and discipline), influence adolescent substance use. However, socialization theory suggests that parental socialization occurs not only through general parenting practices, but also through parents' attempts to influence specific behaviors and values. A growing literature supports links between substance-specific parenting and adolescent substance use. For adolescent alcohol use, there are considerable limitations and gaps within this literature. To address these limitations, the present study examined the factor structure of alcohol-specific parenting, investigated the determinants of alcohol-specific parenting, and explored its association with nondrinking adolescents' attitudes about alcohol use. Using a high-risk sample of nondrinking adolescents and their parents, the current study found three dimensions of alcohol-specific parenting using both adolescent and parent reports, but also found evidence of non-invariance across reporters. Results also revealed complex roles of parental alcohol use disorder (AUD; including recovered and current AUD), family history of AUD, and current drinking as determinants of the three dimensions of anti-alcohol parenting behaviors. Moreover, the current study showed that the effects of these determinants varied by the reporter of the parenting behavior. Finally, the current study found the dimensions of alcohol-specific parenting to be unique and significant predictors of nondrinking adolescents' attitudes about alcohol, over and above general parenting practices, parent AUD, and parent current drinking. Given its demonstrated distinctness from general parenting practices, its link with adolescent alcohol attitudes, and its potential malleability, alcohol-specific parenting may be an important complement to interventions targeting parents of adolescents.
ContributorsHandley, Elizabeth D (Author) / Chassin, Laurie (Thesis advisor) / MacKinnon, David (Committee member) / Crnic, Keith (Committee member) / Sandler, Irwin (Committee member) / Arizona State University (Publisher)
Created2012
Description
Ultra-concealable multi-threat body armor used by law-enforcement is a multi-purpose armor that protects against attacks from knife, spikes, and small caliber rounds. The design of this type of armor involves fiber-resin composite materials that are flexible, light, are not unduly affected by environmental conditions, and perform as required. The National Institute of Justice (NIJ) characterizes this type of armor as low-level protection armor. NIJ also specifies the geometry of the knife and spike as well as the strike energy levels required for this level of protection. The biggest challenges are to design a thin, lightweight and ultra-concealable armor that can be worn under street clothes. In this study, several fundamental tasks involved in the design of such armor are addressed. First, the roles of design of experiments and regression analysis in experimental testing and finite element analysis are presented. Second, off-the-shelf materials available from international material manufacturers are characterized via laboratory experiments. Third, the calibration process required for a constitutive model is explained through the use of experimental data and computer software. Various material models in LS-DYNA for use in the finite element model are discussed. Numerical results are generated via finite element simulations and are compared against experimental data thus establishing the foundation for optimizing the design.
ContributorsVokshi, Erblina (Author) / Rajan, Subramaniam D. (Thesis advisor) / Neithalath, Narayanan (Committee member) / Mobasher, Barzin (Committee member) / Arizona State University (Publisher)
Created2012
Description
The current method of measuring thermal conductivity requires flat plates. For most common civil engineering materials, creating or extracting such samples is difficult. A prototype thermal conductivity experiment had been developed at Arizona State University (ASU) to test cylindrical specimens but proved difficult for repeated testing. In this study, enhancements to both testing methods were made. Additionally, test results of cylindrical testing were correlated with the results from identical materials tested by the Guarded Hot&ndashPlate; method, which uses flat plate specimens. In validating the enhancements made to the Guarded Hot&ndashPlate; and Cylindrical Specimen methods, 23 tests were ran on five different materials. The percent difference shown for the Guarded Hot&ndashPlate; method was less than 1%. This gives strong evidence that the enhanced Guarded Hot-Plate apparatus in itself is now more accurate for measuring thermal conductivity. The correlation between the thermal conductivity values of the Guarded Hot&ndashPlate; to those of the enhanced Cylindrical Specimen method was excellent. The conventional concrete mixture, due to much higher thermal conductivity values compared to the other mixtures, yielded a P&ndashvalue; of 0.600 which provided confidence in the performance of the enhanced Cylindrical Specimen Apparatus. Several recommendations were made for the future implementation of both test methods. The work in this study fulfills the research community and industry desire for a more streamlined, cost effective, and inexpensive means to determine the thermal conductivity of various civil engineering materials.
ContributorsMorris, Derek (Author) / Kaloush, Kamil (Thesis advisor) / Mobasher, Barzin (Committee member) / Phelan, Patrick E (Committee member) / Arizona State University (Publisher)
Created2011
Description
Electronic devices based on various stimuli responsive polymers are anticipated to have great potential for applications in innovative electronics due to their inherent intelligence and flexibility. However, the electronic properties of these soft materials are poor and the applications have been limited due to their weak compatibility with functional materials. Therefore, the integration of stimuli responsive polymers with other functional materials like Silicon is strongly demanded. Here, we present successful strategies to integrate environmentally sensitive hydrogels with Silicon, a typical high-performance electronic material, and demonstrate the intelligent and stretchable capability of this system. The goal of this project is to develop integrated smart devices comprising of soft stimuli responsive polymeric-substrates with conventional semiconductor materials such as Silicon, which can respond to various external stimuli like pH, temperature, light etc. Specifically, these devices combine the merits of high quality crystalline semiconductor materials and the mechanical flexibility/stretchability of polymers. Our innovative system consists of ultra-thin Silicon ribbons bonded to an intelligently stretchable substrate which is intended to interpret and exert environmental signals and provide the desired stress relief. As one of the specific examples, we chose as a substrate the standard thermo-sensitive poly(N-isopropylacrylamide) (PNIPAAm) hydrogel with fast response and large deformation. In order to make the surface of the hydrogel waterproof and smooth for high-quality Silicon transfer, we introduced an intermediate layer of poly(dimethylsiloxane) (PDMS) between the substrate and the Silicon ribbons. The optical microscope results have shown that the system enables stiff Silicon ribbons to become adaptive and drivable by the soft environmentally sensitive substrate. Furthermore, we pioneered the development of complex geometries with two different methods: one is using stereolithography to electronically control the patterns and build up their profiles layer by layer; the other is integrating different multifunctional polymers. In this report, we have designed a bilayer structure comprising of a PNIPAAm hydrogel and a hybrid hydrogel of N-isopropylacrylamide (NIPAAm) and acrylic acid (AA). Typical variable curvatures can be obtained by the hydrogels with different dimensional expansion. These structures hold interesting possibilities in the design of electronic devices with tunable curvature.
ContributorsPan, Yuping (Author) / Dai, Lenore (Thesis advisor) / Jiang, Hanqing (Thesis advisor) / Lind, Mary Laura (Committee member) / Arizona State University (Publisher)
Created2012
Description
Gels are three-dimensional polymer networks with entrapped solvent (water etc.). They bear amazing features such as stimuli-responsive (temperature, PH, electric field etc.), high water content and biocompatibility and thus find a lot of applications. To understand the complex physics behind gel's swelling phenomenon, it is important to build up fundamental mechanical model and extend to complicated cases. In this dissertation, a coupled large deformation and diffusion model regarding gel's swelling behavior is presented. In this model, free-energy of the total gel is constituted by polymer stretching energy and polymer-solvent mixing energy. In-house nonlinear finite element code is implemented with fast computational capability. Complex phenomenon such as buckling and healing of cracked gel by swelling are studied. Due to the wide coverage of polymeric materials and solvents, solvent diffusion in gels not only follows Fickian diffusion law where concentration map is continuous but also follows non-Fickian diffusion law where concentration map shows high gradient. Phenomenological model with viscoelastic polymer constitutive and concentration dependent diffusivity is created. The model well captures this special diffusion phenomenon such as sharp diffusion front and distinctive swollen and unswollen region.
ContributorsZhang, Jiaping (Author) / Jiang, Hanqing (Thesis advisor) / Peralta, Pedro (Committee member) / Dai, Lenore (Committee member) / Rajan, Subramaniam D. (Committee member) / Chawla, Nikhilesh (Committee member) / Arizona State University (Publisher)
Created2012
Description
The present study tested the factor structure of the externalizing disorders (e.g. attention-deficit hyperactivity disorder (ADHD), conduct disorder (SE), and substance experimentation (SE) ) in adolescence. In addition, this study tested the influence of the GABRA2 gene on the factors of the externalizing spectrum. Confirmatory factor analyses were used to test the factor structure of the externalizing spectrum. Specifically, three competing alternate confirmatory factor analytic models were tested: a one-factor model where all disorders loaded onto a single externalizing factor, a two-factor model where CD and SE loaded onto one factor and ADHD loaded onto another, and a three-factor model, where all three disorders loaded onto separate factors. Structural equation modeling was used to test the effect of a GABRA2 SNP, rs279858, on the factors of the externalizing spectrum. Analyses revealed that a three-factor model of externalizing disorders with correlated factors fit the data best. Additionally, GABRA2 had a significant effect on the SE factor in adolescence, but not on the CD or ADHD factors. These findings demonstrate that the externalizing disorders in adolescence share commonalities but also have separate sources of systematic variance. Furthermore, biological mechanisms may act as a unique etiological factor in the development of adolescent substance experimentation.
ContributorsWang, Frances L (Author) / Chassin, Laurie (Thesis advisor) / Lemery-Chalfant, Kathryn (Committee member) / Geiser, Christian (Committee member) / Arizona State University (Publisher)
Created2012
Description
The disordered nature of glass-forming melts results in two features for its dynamics i.e. non-Arrhenius and non-exponential behavior. Their macroscopic properties are studied through observing spatial heterogeneity of the molecular relaxation. Experiments performed in a low-frequency range tracks the flow of energy in time on slow degrees of freedom and transfer to the vibrational heat bath of the liquid, as is the case for microwave heating. High field measurements on supercooled liquids result in generation of fictive temperatures of the absorbing modes which eventually result in elevated true bath temperatures. The absorbed energy allows us to quantify the changes in the 'configurational', real sample, and electrode temperatures. The slow modes absorb energy on the structural relaxation time scale causing the increase of configurational temperature resulting in the rise of dielectric loss. Time-resolved high field dielectric relaxation experiments show the impact of 'configurational heating' for low frequencies of the electric field and samples that are thermally clamped to a thermostat. Relevant thermal behavior of monohydroxy alcohols is considerably different from the cases of simple non-associating liquids, due to their distinct origins of the prominent dielectric loss. Monohydroxy alcohols display very small changes due to observed nonthermal effects without increasing sample temperature. These changes have been reflected in polymers in our measurements.
ContributorsPathak, Ullas (Author) / Richert, Ranko (Thesis advisor) / Dai, Lenore (Thesis advisor) / Nielsen, David (Committee member) / Arizona State University (Publisher)
Created2012
Description
This dissertation provides a fundamental understanding of the properties of mesoporous carbon based materials and the utilization of those properties into different applications such as electrodes materials for super capacitors, adsorbents for water treatments and biosensors. The thickness of mesoporous carbon films on Si substrates are measured by Ellipsometry method and pore size distribution has been calculated by Kelvin equation based on toluene adsorption and desorption isotherms monitored by Ellipsometer. The addition of organometallics cobalt and vanalyl acetylacetonate in the synthesis precursor leads to the metal oxides in the carbon framework, which largely decreased the shrink of the framework during carbonization, resulting in an increase in the average pore size. In addition to the structural changes, the introduction of metal oxides into mesoporous carbon framework greatly enhances the electrochemical performance as a result of their pseudocapacitance. Also, after the addition of Co into the framework, the contraction of mesoporous powders decreased significantly and the capacitance increased prominently because of the solidification function of CoO nanoparticles. When carbon-cobalt composites are used as adsorbent, the adsorption capacity of dye pollutant in water is remarkably higher (90 mg/g) after adding Co than the mesoporous carbon powder (2 mg/g). Furthermore, the surface area and pore size of mesoporous composites can be greatly increased by addition of tetraethyl orthosilicate into the precursor with subsequent etching, which leads to a dramatic increase in the adsorption capacity from 90 mg/g up to 1151 mg/g. When used as electrode materials for amperometric biosensors, mesoporous carbons showed good sensitivity, selectivity and stability. And fluorine-free and low-cost poly (methacrylate)s have been developed as binders for screen printed biosensors. With using only 5wt% of poly (hydroxybutyl methacrylate), the glucose sensor maintained mechanical integrity and exhibited excellent sensitivity on detecting glucose level in whole rabbit blood. Furthermore, extremely high surface area mesoporous carbons have been synthesized by introducing inorganic Si precursor during self-assembly, which effectively determined norepinephrine at very low concentrations.
ContributorsDai, Mingzhi (Author) / Vogt, Bryan D (Thesis advisor) / La Belle, Jeffrey T (Committee member) / Dai, Lenore (Committee member) / Nielsen, David R (Committee member) / Torres, César I (Committee member) / Arizona State University (Publisher)
Created2012