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Theses and Dissertations

Theses/Dissertations

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Articles 61 - 70 of 70

Full-Text Articles in Nanoscience and Nanotechnology

Field Emission Of Thermally Grown Carbon Nanostructures On Silicon Carbide, Jonathon M. Campbell Mar 2012

Field Emission Of Thermally Grown Carbon Nanostructures On Silicon Carbide, Jonathon M. Campbell

Theses and Dissertations

CNTs are known to be excellent field emitter due to their unique physical and electrical properties. Because of their semi-metallic nature, CNT do not suffer the thermal runaway found in metallic emitters, and their near one-dimension shape make them an ideal emission sources. CNTs growth by thermal decomposition of silicon carbide does not utilize a catalyst, therefore relatively defect free. One drawback to this method, however is that the CNT grow in a very dense carpet. This very dense CNT carpet comes under the affect of field emission screening effects which dampen the field emission. In this thesis, silicon carbide …

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Providing A Theoretical Basis For Nanotoxicity Risk Analysis Departing From Traditional Physiologically-Based Pharmacokinetic (Pbpk) Modeling, Dirk P. Yamamoto Sep 2010

Providing A Theoretical Basis For Nanotoxicity Risk Analysis Departing From Traditional Physiologically-Based Pharmacokinetic (Pbpk) Modeling, Dirk P. Yamamoto

Theses and Dissertations

The same novel properties of engineered nanoparticles that make them attractive may also present unique exposure risks. But, the traditional physiologically-based pharmacokinetic (PBPK) modeling assumption of instantaneous equilibration likely does not apply to nanoparticles. This simulation-based research begins with development of a model that includes diffusion, active transport, and carrier mediated transport. An eigenvalue analysis methodology was developed to examine model behavior to focus future research. Simulations using the physicochemical properties of size, shape, surface coating, and surface charge were performed and an equation was determined which estimates area under the curve for arterial blood concentration, which is a surrogate …

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Fatigue Evaluation Of Nanocomposites As Lightweight Electronic Enclosures For Satellites' Applications, Javier Rodriguez Mar 2009

Fatigue Evaluation Of Nanocomposites As Lightweight Electronic Enclosures For Satellites' Applications, Javier Rodriguez

Theses and Dissertations

Existing nanocomposite materials used for satellite applications don't offer the required conductivity and electromagnetic shielding protection, requiring metal shields in order to survive in space. The AFRL Materials and Manufacturing Directorate in conjunction with the private sector have developed a material that promises to blend the attributes of nanocomposites and metal materials. The M55J/RS3 material consists of carbon fibers combined with a polyisocyanate matrix, in which Nickel nanostrandsTM are added. The research effort investigated the changes in the EMI and ESD of the material after being subjected to cyclic loads. Four configurations of a symmetric layup with fibers oriented …

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Patterning And Characterization Of Carbon Nanotubes Grown In A Microwave Plasma Enhanced Chemical Vapor Deposition Chamber, Mauricio Kossler Mar 2009

Patterning And Characterization Of Carbon Nanotubes Grown In A Microwave Plasma Enhanced Chemical Vapor Deposition Chamber, Mauricio Kossler

Theses and Dissertations

This research studies the growth of carbon nanotubes (CNT) from a nickel catalyst to be used on a field emission device. This thesis can be divided into three sections: the construction of a vacuum chamber for field emission testing, the design and fabrication of a triode structure to enable improved electron emission, and the pretreatment and growth of CNTs. To experimentally test the field emission of CNTs, a vacuum chamber must attain a vacuum of at least 10-5 torr. Our vacuum chamber designed and built achieved a maximum, final pressure of 10-8 torr. A triode structure was designed …

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Electrostatic Discharge Properties Of Irradiated Nanocomposites, Joshua D. Mcgary Mar 2009

Electrostatic Discharge Properties Of Irradiated Nanocomposites, Joshua D. Mcgary

Theses and Dissertations

Modernization in space systems requires employment of new light-weight, high performance composite materials that reduce bulk weight and increase structural integrity. This thesis explored the behavior of one such material prior to and following a 35-year simulated space radiation life-cycle. Select electrical properties of nickel nanostrandTM-carbon composites in seven configurations were characterized prior to electron irradiation via surface and bulk resistivity measurements and contact electrostatic discharge (ESD) measurements. Following irradiation at a fluence of 1016 e-/cm2 at an average energy of 500 keV, measurements were repeated and compared against pre-irradiation data. Configuration D is …

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Evaluation Of Nanocomposites As Lightweight Electronic Enclosures For Satellites' Applications, Benjamin T. Harder Jun 2008

Evaluation Of Nanocomposites As Lightweight Electronic Enclosures For Satellites' Applications, Benjamin T. Harder

Theses and Dissertations

The United States military is exploring the use of nanocomposite materials for satellite structural applications. Current composite spacecraft structures are nonconductive and must have expensive shielding materials applied in order to protect the spacecraft from catastrophic damage that can be caused by electromagnetic interference (EMI) and/or electrostatic discharge (ESD) which are characteristics of the space environment. Conductive nanocomposites are being developed for spacecraft structures that will provide ESD and EMI shielding protection without the need for expensive secondary shielding materials. This thesis studied one such material consisting of M55J/RS-3 composite combined with nickel nanostrands™. Four different configurations were tested for …

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Nano-Mechanical Properties Of Heat Inactivated Bacillus Anthracis And Bacillus Thuringiensis Spores, Jessica L. Poindexter Mar 2008

Nano-Mechanical Properties Of Heat Inactivated Bacillus Anthracis And Bacillus Thuringiensis Spores, Jessica L. Poindexter

Theses and Dissertations

B. thuringiensis spores must have similar properties to B. anthracis spores to be a good simulant in counter-proliferation studies. In particular, they must behave in a similar way when exposed to high temperatures for short periods of time as would be caused by an explosion. This research project compares surface elasticities for four different spore sample types, B. anthracis spores, heat inactivated B. anthracis spores, B. thuringiensis spores, and heat inactivated B. thuringiensis spores. Heat inactivated spores were exposed to a temperature just high enough that no spores were observed to germinate. Elasticity values for the spore surfaces were determined …

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Characterization Of The Field Emission Properties Of Carbon Nanotubes Formed On Silicon Carbide Substrates By Surface Decomposition, Michael C. Pochet Mar 2006

Characterization Of The Field Emission Properties Of Carbon Nanotubes Formed On Silicon Carbide Substrates By Surface Decomposition, Michael C. Pochet

Theses and Dissertations

Dense arrays of vertically aligned carbon nanotubes (CNTs) form on the surface of silicon carbide wafers during high temperature anneals under moderate vacuum conditions. The novelty of this growth method is that the CNTs form without the aid of a metal catalyst, allowing for potentially impurity-free CNTs to form. In this study, CNT films were grown by the surface decomposition of silicon carbide substrates. The associated field emission characteristics were investigated to determine if films grown using this method possessed advantages over films grown using metal-catalyzed methods. The associated turn-on and threshold voltages, maximum current density, and emission current stability …

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In Vitro Toxicity Of Aluminum Nanoparticles In Rat Alveolar Macrophages, Andrew J. Wagner Mar 2006

In Vitro Toxicity Of Aluminum Nanoparticles In Rat Alveolar Macrophages, Andrew J. Wagner

Theses and Dissertations

Nanomaterials, which are by definition in the 1 - 100 nanometer range, have numerous possible benefits to society, but currently there is a lack of data that characterizes these materials effects on human health and environment. In general nanomaterials are of interest to the Air Force because of their applications in electronics, sensors, munitions and energetic/reactive systems. Nanoparticles such as aluminum have been considered for enhancing propulsion in solid rocket fuel. To date, only a few studies have looked at the toxicological effects of direct exposure to nanoparticles, none with aluminum. It is important to increase the understanding of the …

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Classification Characteristics Of Carbon Nanotube Polymer Composite Chemical Vapor Detectors, Huynh A. Hinshaw Mar 2006

Classification Characteristics Of Carbon Nanotube Polymer Composite Chemical Vapor Detectors, Huynh A. Hinshaw

Theses and Dissertations

The first step in combating a chemical weapons threat is contamination avoidance. This is accomplished by the detection and identification of chemical agents. The Air Force has several instruments to detect chemical vapors, but is always looking for lighter, faster, and more accurate technology for a better capability. This research is focused on using carbon nanotube polymer composite sensors for chemical detection. More specifically, models are developed to classify three sets of sensor data according to vapor using various multivariate techniques. Also, prediction models of a mixed sensor output are developed using neural networks and regression analysis. The classifiers developed …

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