http://idea.library.drexel.edu/handle/1860/1 Search the Channel search http://idea.library.drexel.edu/simple-search http://idea.library.drexel.edu/handle/1860/3192 Title: Preignition and autoignition behavior of the xylene isomers <br/> <br/>Authors: Natelson, Robert Harris <br/> <br/>Abstract: The relative preignition and autoignition reactivity of the xylene isomers (o-, mand p-xylene, or 1,2-, 1,3-, and 1,4-dimethylbenzene) has been studied. The principal objectives were to determine the relative reactivity among the isomers and the key oxidation branching pathways. Preignition experiments were conducted in a pressurized flow reactor facility at 600-850 K temperatures, 8 atm pressure, and lean equivalence ratios. Online analysis of the data included carbon monoxide and carbon dioxide measurements using a nondispersive infrared analyzer and molecular oxygen measurements using an electrochemical oxygen cell. Offline analysis, for identification and quantification of intermediate species, was performed using gas chromatography with flame ionization detection and coupling to a mass spectrometer. Additional experiments were conducted in a single cylinder research engine. Neat o- and m-xylene were oxidized in the PFR under preignition conditions. They showed no reactivity, so mixtures of each isomer with n-dodecane were tested and compared, and intermediate species were identified. This data helped resolve a recent controversy regarding the relative reactivity of the xylene isomers. Additionally, a mixture of p-xylene / n-dodecane was studied. To study the autoignition of the xylenes, the isomers neat, in binary mixtures with n-decane, and in six-component JP-8 surrogates were tested in the single cylinder research engine. The experimental data were analyzed and compared to existing chemical kinetic models, and it was concluded that at lower temperatures (<850 K), the xylenes show similar reactivity, and at higher temperatures, o-xylene is the more reactive isomer. The data can be used for the improvement of xylene chemical kinetic models, and the conclusions from this study will aid in the selection of the appropriate xylene isomer for JP-8 surrogate fuels. Mon, 08 Mar 2010 16:26:38 GMT http://idea.library.drexel.edu/handle/1860/3191 Title: Behavioral and lifestyle treatment options post myocardial infarction: an exploratory analysis of patients’ preferences for treatment <br/> <br/>Authors: Tiernan, Kristin A. <br/> <br/>Abstract: Treatment post-MI is best suited when tailored to the individual’s needs (Williams, 2001). This study was conducted as an exploratory analysis of patients’ preferences for behavioral and lifestyle treatment options after a myocardial infarction (MI). Specifically, whether there were differences in men’s and women’s preferences for treatment. There were no significant differences in men’s and women’s preferences for treatment, although women tended to rate their preferences the same or lower then the men for each treatment option. By looking at patients’ preferences across various demographic variables, this exploratory analysis can assist physicians when explaining and offering treatment options to their patients’ post-MI. Mon, 08 Mar 2010 16:06:38 GMT http://idea.library.drexel.edu/handle/1860/3189 Title: Combinatorial investigation of nanolaminate ternary carbide thin films <br/> <br/>Authors: Scabarozi, Theodore H., Jr. <br/> <br/>Abstract: MAX phases have shown a combination of metal- and ceramic-like properties making them candidates in aerospace and other high-performance applications currently dominated by superalloys. The MAX phases follow the general formula Mn+1AXn, where M is an early transition metal, A is an A-group element, X is C and/or N, and n = 1 to 3. The hexagonal structure consists of edge sharing M6X octahedra interleaved with Agroup element layers. This layered structure, referred to as nanolaminate, leads to the unique and interesting properties. With more than fifty MAX phases already identified, an almost unlimited number of solid solution possibilities exist. Combinatorial methods provide a technique which allows for a large number of thin film samples to be generated with minimal time and expense. In this research, investigations of thin film MAX phase ternary carbides synthesized by magnetron sputtering in the temperature range of RT-1000 °C are reported. The ultimate goal was to synthesize MAX phase thin film solid solutions by a combinatorial method in an attempt to identify enhanced properties. The M2AC MAX phases that formed in the following systems, Ti-Nb-Al-C, V-Cr-Al-C, V-Cr-Ge-C, were examined. In all solutions, only mixing of the M elements was investigated. All textured films grew epitaxially (c-axis) on c-sapphire substrates or deposited binary carbide buffer layers. The lowest synthesis temperature resulting in textured growth was for V2AlC at 600 °C, however; formation of nanocrystalline Cr2AlC was observed at 550 °C as indicated by Raman spectroscopy. High temperature X-ray diffraction of amorphous Cr-Al-C and Cr-Ge-C films showed textured growth of the MAX phase occurred around 650 °C, and 725 °C, respectively. All combinatorial studies were performed at 850 °C with (Ti1-xNbx)2AlC films grown on TiC buffer layers while (V1-xCrx)2AlC and (V1-xCrx)2GeC grown directly on sapphire. Complete solubility across the entire range of x was observed for all systems. Additionally, new thin film phases of V3AlC2, V4AlC3, Nb5Al3Cx, Cr5Ge3Cx, (Ti1-xNbx)3AlC2, (Ti1-xNbx)4AlC3, and (V1-xCrx)4AlC3 were discovered. The M-element impacts many different properties of MAX phase films. The surface of most films were rough, some containing large hexagonal crystals. Yet, this work has demonstrated that the surface roughness can be tuned using elemental substitutions on the M-sites. While friction testing found all films to have relatively low coefficients of friction (<0.12), this too was found to be influenced by the M-element. Raman spectroscopy of (Ti1-xNbx)2AlC films indicates possible stiffening around x = 0.75 explicitly demonstrating the role of the M-element in this solid solution. All films were good electrical conductors with metal-like conduction down to 2K with magnitude and temperature dependence of the resistance tunable through composition. The Hall coefficient and magnetoresistance were also controlled by M-element substitution. While dramatic changes have not been observed, it is clear that the application of combinatorial methods has improved the understanding of the role of the M-element in determining the properties of MAX phases improving the ability to use the materials for thin film applications and beyond. Mon, 15 Feb 2010 16:57:23 GMT http://idea.library.drexel.edu/handle/1860/3188 Title: Thermoacoustic convection and transport in supercritical fluids under normal and micro-gravity conditions <br/> <br/>Authors: Lei, Zhiheng <br/> <br/>Abstract: The generation, propagation and dissipation of thermally induced and mechanically driven acoustic waves in supercritical nitrogen and carbon dioxide were studied. Supercritical fluids are widely used in various industrial and laboratory processes as substitutes for organic solvents. These fluids also have high compressibilities, high thermal conductivities, low viscosities, and low thermal diffusivities. As the thermal diffusivity tends to zero near the critical point, acoustic waves are believed to be the primary reason for fast thermal equilibration in supercritical fluids. The compressible form of Navier-Stokes equations for Newtonian fluids was considered to model the supercritical fluids. A high-order explicit numerical scheme (FCT: flux-corrected transport, along with an accurate wall density boundary condition, was applied to accurately track the acoustic waves. The property variations (pressure, internal energy, viscosity, and thermal conductivity) of the supercritical fluids (carbon dioxide and nitrogen) as functions of temperature and density were obtained from the NIST Standard Reference Database 12 instead of simplified equations for real gases. Both one-and two-dimensional computational fluid dynamics models were developed for predicting the temporal evolution of pressure, density, temperature and flow field in supercritical fluids due to thermal and mechanical excitations. The flow fields and heat transport induced by thermally induced acoustic waves and buoyancy in supercritical fluids were investigated numerically under normal and reduced gravity conditions. The flow fields induced by mechanically driven acoustic waves in an enclosure driven by a vibrating wall were also numerically studied. The model developed was also used to investigate the interaction of thermally induced acoustic waves and mass transfer in supercritical fluids (naphthalene dissolution in supercritical carbon dioxide). The generation and propagation of thermally induced acoustic waves due to rapid heating of a solid wall in a confined supercritical fluid layer were also experimentally investigated. A high-pressure experimental facility was constructed to characterize the generation and decay of acoustic waves in supercritical nitrogen and supercritical carbon dioxide in an enclosure due to rapid heating of an end wall. The underlying physics of the ‘piston effect’ (fast thermal equilibration of supercritical fluids with high compressibilities) were studied and explained in detail. To the author’s knowledge, this is the first attempt where detailed simulations of thermally induced and mechanically driven acoustic waves in supercritical fluids have been conducted with accurate equations of state and property functions. Better understanding of these problems will help the tailoring and optimizing the operating conditions for industrial and laboratory processes for supercritical fluids. Mon, 15 Feb 2010 16:56:05 GMT http://idea.library.drexel.edu/handle/1860/3186 Title: The Philadelphia Obstetrics Crisis: Etiology, Implications, and Solutions For Maintaining Quality Obstetric Care and The Viability of Academic Medicine <br/> <br/>Authors: Croft, Damien J <br/> <br/>Abstract: The Philadelphia area has been the site of an unprecedented number of maternity unit closures over the past 15 years. Staring with the closure of the maternity floor at Medical College of Pennsylvania Hospital in 1997 and culminating this summer with the closure of Northeastern Hospital planned for June 2009, a total of 16 providers of obstetrical care will have been eliminated. This has lead to nearly a 35 percent decrease in the number of staffed maternity beds in the city. The reasons postulated have been identified as a combination of high malpractice and low reimbursement. Thus far all of the 15 closures have been community hospitals in the area, many of which have provided obstetrical care to the city of Philadelphia for the last 50-100 years. In contrast, the six remaining providers of maternity care in the city of Philadelphia are all academic medical centers. The strengths, weaknesses and missions of community versus academic medical facilities play a significant role in this outcome. The questions to be examined in this paper are what are the reasons for these closures. If it is due to malpractice and reimbursement issues, why have academic medical centers thus far persevered in the face of this environment? What are the implications for both maternity care and medical training at institutions in the city if this situation is not resolved? Lastly is the current situation sustainable and what are some possible solutions to the crisis for the area. Fri, 12 Feb 2010 15:55:45 GMT http://idea.library.drexel.edu/handle/1860/3185 Title: Monitoring fitness of caged mussels (elliptio complanata) to assess and prioritize streams for restoration in Southeastern Pennsylvania <br/> <br/>Authors: Gray, Matthew W <br/> <br/>Abstract: Freshwater mussels (Order: Unionidae) are currently the most imperiled organisms in North America. Restoration of these animals is becoming an increasing research interest for conservationists and resource managers. Historically, restoration methods have yielded less than optimal survival rates due in part to an inability to identify suitable habitat for these organisms. Through the use of caged mussels as bioindicators, a method was developed to identify suitable habitat for supporting mussel fitness prior to beginning actual restoration efforts. To assess the effectiveness of Elliptio complanata to serve as a bioindicator of stream suitability, its physiological plasticity was also examined. Mussels were caged and reciprocally transferred between two source streams in Southeastern Pennsylvania (Brandywine Creek and Ridley Creek). Mussel condition index and proximate biochemical composition (protein, carbohydrate, lipid) were monitored seasonally and related to expected seasonal nutritional demands for the different biochemical constituents. Controls consisted of caged mussels from source streams that were deployed back into their source streams, and the physiological response to caging was determined in contrast to that of uncaged mussels from the same source beds. No caging effects were observed. The physiology of this species was found to be quite plastic, showing rapid adaptation to varying environmental conditions in the new streams. Additionally, the seasonal variation in condition index was similar in some aspects to that of marine species, but did not always follow the expected pattern. To test candidate restoration streams for suitability, mussels from Brandywine Creek were deployed in five candidate streams for restoration. Four of the five streams supported the same or even greater mussel fitness than in Brandywine Creek, which was the main source stream that still harbors extant populations of Elliptio complanata, suggesting that those streams (Chester, White Clay East Branch, White Clay Middle Branch, Red Clay) are suitable for restoration; whereas, West Branch Brandywine Creek was not found to be suitable for mussels. The proximate biochemical composition of stream seston (i.e. microparticulate food for filter-feeders) was also analyzed to partially explain disparities in stream suitability for mussels. Hydrological and water chemistry data were also collected and contrasted among source and indicator streams. Food quality varied widely among studied streams, suggesting that seston biochemical composition was likely to have affected in the suitability of these streams for sustaining healthy mussels. Candidate restoration streams were ranked for their suitability. Since the Ridley Creek source population was significantly more fit than the Brandywine population, I recommend that this population be targeted for special protection and possible enhancement since it appears to serve as the best healthy reference population within the study area. Although mussels still exist in Brandywine Creek, there are indications that the population is not naturally reproducing and this mussel bed may benefit from enhancement and restoration. Mussels have been extirpated from Chester and White Clay drainages, but water quality and food conditions appear suitable there for sustaining mussels that could be restored. Middle Branch White Clay, East Branch White Clay and Chester Creek were found to be similar or greater in suitability than Brandywine Creek. In particular, Middle Branch White Clay was found to have the greatest food quality of any candidate stream and mussels held in this stream were found to be more fit than that of any other candidate stream. At this time, restoration is not prioritized for Red Clay and West Branch Brandywine due to inadequate water quality and habitat conditions for mussels. Since mussels are long-lived and excellent bioindicators of stream conditions, this caging methodology could be used for bioassessment as well as for gauging stream readiness for mussel restoration. Wed, 20 Jan 2010 19:32:41 GMT http://idea.library.drexel.edu/handle/1860/3184 Title: Characterization of chemical-mechanical planarization Pads with X-Ray microtomography and finite element modeling <br/> <br/>Authors: Sexton, Michael John <br/> <br/>Abstract: Modeling the mechanical behavior of realistic porous structures with finite element models generated from x-ray tomography scan data has been a recent interest for various fields including metallic foams [1], bone and biomedical scaffolds [2], and even bread [3]. This work studies the feasibility of using x-ray micro-computed tomography (μCT) and finite element analysis (FEA) to model the structural deformation and mechanical properties of Chemical-Mechanical Planarization (CMP) pads in compression. The electronics industry uses CMP pads to polish and flatten the surface of integrated circuit chip die wafers in between steps of the lithography process. Non-uniformity of material removal impairs the performance of CMP pads. This is believed to be in part due to the internal porosity of the pad and its interaction with the abrasive slurry. In-situ μCT compression experiments were carried out to map the structural deformation of internal porosity and measure its effect on the global and local stress-strain behavior of CMP pads. Scan data of unloaded samples were used to develop finite element simulations of the material. The reported results of experiments and simulations exhibit the strength of μCT and FEA as characterization techniques for CMP pads. This work provides insight into the compressive behavior of the pad material and the response of the actual structure. This work may also serve as a foundation for a more complete study of the CMP process and materials. Wed, 20 Jan 2010 19:14:56 GMT http://idea.library.drexel.edu/handle/1860/3183 Title: Subject specific models of the hindfoot reveal a relationship between morphology and passive mechanical properties <br/> <br/>Authors: Toy, Jason Robert <br/> <br/>Abstract: The morphology of the bones, articular surfaces, and ligaments, as well as the passive mechanical characteristics of the ankle complex were reported to vary greatly among individuals. The goal of this study was to test the hypothesis that the variations observed in the passive mechanical properties of the healthy and injured ankle complex are strongly influenced by morphological variations. To evaluate this hypothesis, six numerical models of the ankle joint complex were developed from morphological data obtained from magnetic resonance images of six cadaveric lower limbs, and from average reported data on the mechanical properties of ligaments and articular cartilage. The passive mechanical behavior of each model, under a variety of loading conditions, was found to closely match the experimental data obtained from each corresponding specimen. Since all models used identical material properties and were subjected to identical loads and boundary conditions, it was concluded that the observed variations in passive mechanical characteristics were due to variations in morphology, thus confirming the hypothesis. In addition, the average and large variations in passive mechanical behavior observed between the models were similar to those observed experimentally between cadaveric specimens. The results suggested that individualized subject specific treatment procedures for ankle complex disorders are potentially superior to a one size fits all approach. Tue, 19 Jan 2010 20:32:11 GMT http://idea.library.drexel.edu/handle/1860/3182 Title: Exploiting polymer single crystals to assemble and functionalize nanomaterials <br/> <br/>Authors: Li, Bing <br/> <br/>Abstract: Nanomaterials are fundamental building blocks for nanoscience and nanotechnology. They can generally be categorized into three classes: zero-dimensional (0D) (e.g. nanoparticles), onedimensional (1D) (e.g. carbon nanotubes) and two-dimensional (2D) (e.g. thin films) nanomaterials. Assembly of nanomaterials is the key step to transfer their fascinating mechanical, electronic and optical properties from nano- to micro- or macro- scale. Among all types of assemblies, assembling across different nanomaterial classes is of particular interest. For example, assembling 0D nanoparticles with 1D nanotubes or 2D thin films. These assembled structures have the advantage of possessing properties from both classes of nanomaterials. Functionalization of nanomaterials is important from both scientific and technological points of view. A newly developed field of functionalization is called “patchy particles”. Multiple types of functional molecules form different domains on particle surface. Each domain contains only one type of functional molecules. These domains are called patches. These patchy particles are advanced building blocks, which may assemble into useful complex structures. In this thesis, polymer single crystals are exploited to assemble and functionalize nanomaterials. Polymer single crystals have a lamellar structure. Since the thickness of these lamellae is ~10 nm, polymer single crystals are introduced as a new type of 2D nanomaterials. Different from the traditional 2D nanomaterials such as Langmuir-Blodgett films, self-assembled monolayers and thin films made by Layer-by-Layer technique, these polymer single crystals are free-standing, which means no substrate is needed. Furthermore, the surface of these polymer single crystals can be readily functionalized by crystallizing end-functionalized polymers. Based on the studied polymers, this thesis is divided into two parts. The first part is focused on single crystals of poly(ethylene oxide) (PEO). Thiol-terminated PEO is used to make functional lamellar single crystals. Assembling 0D nanoparticles with these 2D lamellae leads to nanoparticles sheets with three different structures: monolayer, bilayer and sandwich. Furthermore, by assembling nanoparticles during crystallization of PEO, nanoparticle sheets with frame-like patterns are obtained. The morphology of these frames can be readily controlled by tuning experimental parameters. Finally, as nanoparticles sheets form, patchy nanoparticles are produced as well. Structures like “bilines” and nanowires are formed by self-assembly of these patchy nanoparticles. The second part deals with single crystals of polyethylene-block-poly(ethylene oxide) (PE-b-PEO). Single crystals of PE-b-PEO are used to functionalize carbon nanotubes and assemble nanoparticles with these nanotubes. Alternating patterns are formed on carbon nanotube surface by thin film crystallization of PE-b-PEO. As a result, the surface of a carbon nanotube is uniformly divided into many sub-10 nm pieces along the tube axis. This functionalization opens the door to periodical functionalization of carbon nanotubes at nanoscale. By employing thiolterminated PE-b-PEO, thiol groups are introduced to the alternating patterns. These periodically functionalized 1D carbon nanotubes are used to assemble 0D nanoparticles into periodical parallel nanoparticle chains. Tue, 19 Jan 2010 20:31:49 GMT http://idea.library.drexel.edu/handle/1860/3181 Title: Elucidation of levels of bacterial viability post-non-equilibrium dielectric barrier discharge plasma treatment <br/> <br/>Authors: Cooper, Moogega <br/> <br/>Abstract: As a solution to chemically and thermally destructive sterilization methods currently used for spacecraft, non-equilibrium atmospheric pressure Dielectric Barrier Discharge (DBD) plasma is proposed to treat surfaces inoculated with everyday and extremophile bacteria. The purpose of this study is to show that non-thermal plasma has the ability to completely destroy bacteria to the DNA level on the surface of spacecraft materials without thermal degradation of the material. This is achieved by a threefold approach: physical, biological, and chemical. The physical approach involves characterizing plasma discharges in varying regimes to understand the properties of the discharge. The biological approach entails gathering evidence of reduction in bacterial load due to dielectric barrier discharge plasma treatment and understanding the sequence of events leading to a microorganism’s death when exposed to plasma. Polymerase Chain Reaction, Gel Electrophoresis, florescent assays and colony counts are among the techniques needed for this facet. The chemical approach adds understanding of sterilization mechanisms via the analysis of chemical reactions caused by UV photons, ions, and other components of plasma. This facet requires, in addition to biological assays, the use of a scanning electron microscope (SEM) to determine the morphological changes of the bacteria with increased plasma dose. This threefold approach has shown that plasma succeeds in achieving complete disintegration of bacteria and alluded to the possible mechanisms. This will ultimately aide in preventing both forward contamination of planets and moons and reverse contamination of Earth for future NASA space missions. Tue, 19 Jan 2010 18:39:42 GMT