iDEA Collection: Drexel Theses and Dissertations

Roles, expectations, and influence: high-risk behaviors among groups of emerging adults

Wed, 06 Aug 2008 12:01:02 GMT

Title: Roles, expectations, and influence: high-risk behaviors among groups of emerging adults

Authors: Woodson, Jennifer Christi

Abstract: This study investigated the differences between younger and older college students with respect to perceptions of engaging in high-risk group behaviors. The sample consisted of 106 college students fiom Drexel University. Overall, the results did not confirm the hypotheses and revealed that (1) younger students did not report significantly higher levels of willingness to engage in high-risk behaviors compared to older students; (2) older students did not report significantly higher levels of expected risk in high-risk behaviors compared to younger students; (3) older students did not report significantly lower levels of expected benefits in high-risk behaviors compared to younger students; and (4) older students did not report significantly lower levels of expected involvement in high-risk behaviors when compared to younger students. This study supplements previous research on perceptions of expected high-risk behavior, and the present analyses revealed trends that lend support to the hypotheses.

GPU-accelerated deformable registration of cone-beam CT images: design and implementation in the compute unified device architecture

Wed, 06 Aug 2008 12:00:28 GMT

Title: GPU-accelerated deformable registration of cone-beam CT images: design and implementation in the compute unified device architecture

Authors: Jain, Nakul

Abstract: This thesis describes a stream-processing model for the demons deformable registration algorithm, suitable for use on a graphics processing unit (GPU). The streaming version of the demons algorithm is developed using the Compute Unified Device Architecture (CUDA) and executed on NVidia‘s 8800 GTS GPU. Performance results using cone-beam CT data of a preserved swine lung indicate that the GPU-based implementation achieves a substantial speedup of 60 times when compared to an optimized reference implementation on a 2.8 GHz Intel processor. In addition, the accuracy of the GPU-based implementation was found to be excellent, with an RMS difference of less than 0.1 mm when compared with the reference implementation.

Locomotion of magnetic objects in fluids

Wed, 06 Aug 2008 11:58:32 GMT

Title: Locomotion of magnetic objects in fluids

Authors: Bhat, Shubham K.

Abstract: Manipulation of magnetic objects in fluids is a promising technology for many applications including targeted drug delivery, sorting and analysis of biological objects. Most prior work employed magnetic field gradients achieving limited control over assembly and manipulation of magnetic and non-magnetic micro-particles. However, many important questions related to magnetic manipulation technology remain open. One such issue is the controllability of positioning multiple objects during manipulation. Positioning controllability of even the simplest system such as a pair of spherical beads seems to have been largely ignored. The main goal of this thesis is to begin addressing the question of controllability of multiple magnetic objects during their manipulation. Although the ultimate applications may involve many multiple objects, only two spherical linearly magnetizable beads are considered in this thesis in order to identify important issues and potential problems. As a first step, the manipulation problem is formulated using only magnetic interactions between the beads and their interactions with a simple source of external field gradient, while neglecting hydrodynamic interactions between the beads. Newtonian behavior of the fluid is assumed and effects of boundaries are also ignored. Such a model is typical in magnetic separation literature. It is demonstrated theoretically that positions of the beads are locally controllable (in a linearized system) by using uniform field as the input only when the beads are sufficiently close to each other. This analysis clearly demonstrates that magnetic interactions between the different objects is not necessarily a nuisance, but could in fact help to control the system. It also reveals that controllability is possible only in close proximity to a source of gradient. Placing the beads in close proximity to a source of gradient is not possible in many applications such as magnetically guided drug delivery. To circumvent difficulties with the gradients, the possibility of locomotion of the bead-pair system using only uniform magnetic field as the input is considered. The advantage of such a strategy is that the external magnetic field delivers energy for the movements of the beads but no net force. The inspiration for this comes from the motility of living organisms such as leukocytes and bacteria. It is known from previous work on swimming of living and artificial swimmers that hydrodynamic interactions play a critical role. For this reason, movement of beads subject to both, magnetic and hydrodynamic interactions is considered in the second part of this thesis. Using a simple model of hydrodynamic interactions, it is demonstrated theoretically that the beads can move as a pair in any desired direction and their final positions are completely controllable using only uniform magnetic field. Subsequently, the thesis focuses on experimental demonstrations of locomotion of a pair of beads using two different types of experimental set-ups. In one, the magnetic beads are suspended in a non-magnetic fluid using thin threads. In the other, a pair of non-magnetic beads is suspended in a magnetic fluid (ferrofluid). Locomotion is demonstrated experimentally in both test-beds. In fact, it is also shown that in the second system, where the beads are suspended magnetically, the direction and magnitude of locomotion agrees quantitatively with the proposed theoretical model. Thus, the main novel and useful contribution of this thesis is that it demonstrates using both, theoretical analysis and experimental validation, that positions of beads in a pair can be controlled to a significant extent using only uniform magnetic fields. On the one hand, this suggests future strategies by which positioning of more than two objects could possibly be magnetically guided and controlled. On the other, the work carried out in this thesis is likely to find direct applications even if it proves difficult to control more than two objects. One of the most exciting of such applications involves movements of two objects inside the body for the purpose of delivery of drugs, therapies, minimally invasive surgeries and others. Although the work carried out in this thesis is only the beginning for such medical applications, the results obtained so far offer a significant hope of success.

Structurally colored biopolymer thin films for detection of dissolved metal ions in aqueous solution

Mon, 14 Jul 2008 16:04:08 GMT

Title: Structurally colored biopolymer thin films for detection of dissolved metal ions in aqueous solution

Authors: Cathell, Matthew David

Abstract: Natural polymers, such as the polysaccharides alginate and chitosan, are noted sorbents of heavy metals. Their polymer backbone structures are rich in ligands that can interact with metal ions through chelation, electrostatics, ion exchange and nonspecific mechanisms. These water-soluble biopolymer materials can be processed into hydrogel thin films, creating high surface area interfaces ideal for binding and sequestering metal ions from solution. By virtue of their uniform nanoscale dimensions (with thicknesses smaller than wavelengths of visible light) polymer thin films exhibit structure-based coloration. This phenomenon, frequently observed in nature, causes the transparent and essentially colorless films to reflect light in a wide array of colors. The lamellar film structures act as one-dimensional photonic crystals, allowing selective reflection of certain wavelengths of light while minimizing other wavelengths by out-of-phase interference. The combination of metal-binding and reflective properties make alginate and chitosan thin films attractive candidates for analyte sensing. Interactions with metal ions can induce changes in film thicknesses and refractive indices, thus altering the path of light reflected through the film. Small changes in dimensional or optical properties can lead to shifts in film color that are perceivable by the unaided eye. These thin films offer the potential for optical sensing of toxic dissolved materials without the need for instrumentation, external power or scientific expertise. With the use of a spectroscopic ellipsometer and a fiber optic reflectance spectrometer, the physical and optical characteristics of biopolymer thin films have been characterized in response to 50 ppm metal ion solutions. It has been determined that metal interactions can lead to measurable changes in both film thicknesses and effective refractive indices. The intrinsic response behaviors of alginate and chitosan, as well as the responses of modified derivatives of these materials, have been investigated. It has been found that the natural metal selectivity of biopolymer films can be tuned and refined by adjusting the ligand environment through backbone modification. Other investigations have also been undertaken, including in situ monitoring of biopolymer-metal interactions and quantification of thin film metal-binding capacities.

A novel approach to programmable imaging using MOEMS

Mon, 14 Jul 2008 16:03:40 GMT

Title: A novel approach to programmable imaging using MOEMS

Authors: Nasis, Vasileios T.

Abstract: New advancements in science are frequently sparked by the invention of new instruments. Possibly the most important scientific instrument of the past fifty years is the digital computer. Among the computers many uses and impacts, digital imaging has revolutionized images and photography, merging computer processing and optical images. In this thesis, we merge an additional reconfigurable micro-mechanical domain into the digital imaging system, introducing a novel imaging method called Programmable Imaging. With our imaging method, we selectively sample the object plane, by utilizing state-of-the-art Micro-Optical-Electrical-Mechanical Systems (MOEMS) of mirror arrays. The main concept is to use an array of tiny mirrors that have the ability to tilt in different directions. Each mirror acts as an “eye” which images a scene. The individual images from each mirror are then reassembled, such that all of the information is placed into a single image. By exact control of the mirrors, the object plane can be sampled in a desired fashion, such that post-processing effects, such as image distortion and digital zoom, that are currently performed in software can now be performed in real time in hardware as the image gets captured. It is important to note that even for different sampling or imaging functions, no hardware components or settings are changed in the system. In this work, we present our programmable imaging system prototype. The MOEMS chipset used in our prototype is the Lucent LambdaRouter mirror array. This device contains 256 individually-controlled micro-mirrors, which can be tilted on both the x and y axes ±8o. We describe the theoretical model of our system, including a system model, capacity model, and diffraction results. We experimentally prototype our programmable imaging system using both a single mirror, followed by multiple mirrors. With the single mirror imaging, we explore examples related to single projection systems and give details of our required mirror calibration. Using this technique, we show mosaic images, as well as images in which a single pixel was extracted for every mirror tilt. Using this single pixel approach, the greatest capabilities of our programmable imaging are realized. When using multiple mirrors to image an object, new features of our system are demonstrated. In this case, the object plane can be viewed from different perspectives. From these multi-perspective images, virtual 3-D images can be created. In addition, stereo depth estimation can be performed to calculate the distance between the object and the image plane. This depth measurement is significant, as the depth information is taken with only one image from only one camera.

Multifunctional polymers via incorporation of ionic groups at molecular and mesoscopic length scales

Mon, 14 Jul 2008 16:03:13 GMT

Title: Multifunctional polymers via incorporation of ionic groups at molecular and mesoscopic length scales

Authors: Rahmathullah, Mohamed Aflal Mohamed

Abstract: Multifunctional polymer systems with specific functionality and strength are developed by integrating diverse polymers into physically and chemically compatible composite structures. The concept has been achieved repeatedly in nature in examples such as the human skin or stimuli-responsive plants, where sensory or actuating mechanisms are part of a structurally sound system. Similar ideas can be extended to polymeric materials by incorporating hydrophilic ionic groups within hydrophobic non-ionic polymers to achieve desired functionality and mechanical strength respectively. This notion has been the focus of this work that is broadly categorized into investigations at the molecular and mesoscopic length scales. At the molecular scale, three strategies were investigated for thermoset functionalization. First, ionic groups were grafted on nanoporous and hydrophobic epoxy-amine thermosets via sulfonation. Second, copolymerization of hydrophobic diglycidyl ether of bisphenol A vinyl ester (VE) and hydrophilic 2-Acrylamido-2-methyl-1-propanesulfonic acid (AMPS) was investigated. Reactivity ratios were used to determine the distribution of VE and AMPS in a copolymer network based on the Mayo-Lewis terminal model. Links between structure and properties such as water uptake, proton conductivity, and proton mobility were elucidated. Fuel cell performance was evaluated and compared to Nafion®117. Third, functionalized epoxy thermosets were prepared by the encapsulation of reactive or non-reactive ionic liquids. 1-ethyl 3-methyl imidazolium dicyandiamide exhibited thermally latent cure behavior and tunable network hydrophilicity, modulus, and glass transition temperatures. At the mesoscopic length scale, two strategies were investigated in developing polymer-polymer composites. First, fiber-thermoplastic matrix composites were developed as selective permeation membranes and proton conductive membranes. This was achieved by encapsulating, within a thermoplastic matrix, either hydrophobic fibers with grafted ionic groups or hydrophilic fibers. A combination of microscopy, permeability measurements and proton conductivity were used to assess composite performance. Correlations between the spatial location of ionic groups and proton mobility were developed and extended to understand the effects of polymer structure. Second, ionomer-thermoset composites were developed as potential self-healing materials designed to combine crack-repair characteristics of the ionomer with the mechanical strength of the thermoset. Since an unmodified epoxy-amine thermoset also exhibits significant healing, a fundamental understanding on the crack-healing behavior of epoxy-amine thermosets was developed.

Quantitative analysis of cell-surface interactions and cell adhesion process in real-time

Fri, 11 Jul 2008 18:21:55 GMT

Title: Quantitative analysis of cell-surface interactions and cell adhesion process in real-time

Authors: Hong, Soonjin

Abstract: The cell adhesion process and cellular interactions with extracellular matrix (ECM) proteins were quantitatively evaluated using a thickness shear mode (TSM) sensor. For understanding cell-surface interactions, specific effects of receptor-mediated adhesion, the glycocalyx, and surface charge on initial cell-surface attachment and steady state adhesion of bovine aortic endothelial cells (BAECs) were investigated. The result showed that integrin binding determines the kinetics of initial cell attachment while heparan sulfate proteoglycan (HSPG) modulates steady state adhesion strength. Coating the sensor surface with the positively charged poly-D-lysine (PDL) enhanced the initial interaction with substratum. In order to relate sensor data to the adhesion of the cells, we performed independent measures of cell spreading and adhesion strength. The adhesive interactions of human mammary epithelial cells, MCF-10A, with a fibronectin coated sensor were altered by overexpressing Her2/Neu oncogene and by blocking integrin function with soluble GRGDS. Correlation of ΔR with cell spreading and adhesion measurements revealed three phases: adhesion, spreading and structural reorganization. In the initial adhesion phase, ΔR increases rapidly as the cells bind to the substratum and began to flatten. The rate of change of ΔR is proportional to the adhesion strength. As the cells spread beyond their initial projected area, ΔR increased in proportion to the change in area. In the final phase, as the cells approach their final spread area, further increases in ΔR reflect structural changes, possibly indicating maturation of cytoskeleton and focal adhesion formation. In order to see the effect of cell deformability on the initial adhesion, the elastic modulus of spherical cells were evaluated. The calculation of Young’s moduli showed that oncogene expressing cells were more compliant than normal cells (1.09kPa±0.36 vs. 2.95kPa±0.34), which was reflected to the initial increase of ΔR. The real time monitoring capability of this technique with high temporal resolution provides more detailed information on the kinetics of the different stages of the adhesion process. The analysis of adhesion properties of normal versus transformed mammary epithelia correlates with changes in integrin expression, demonstrating the usefulness of TSM sensor measurement system for understanding adhesion characteristics in real time as it relates to phenotypic variations.

The effects of multiple discounts on consumers’ product judgments

Fri, 11 Jul 2008 18:15:54 GMT

Title: The effects of multiple discounts on consumers’ product judgments

Authors: Cai, Zhen (Jane)

Abstract: The concept of multiple discounts refers to the situation when two or more discounts are combined together resulting in a discount larger than any of the individual discounts. Despite the increasing popularity of this practice in the marketplace, past research provides little evidence about the relative effectiveness of such discounts. For instance, compared to single discounts, offers using multiple-discounts generally require more cognitive effort by consumers to process price information. This research presents a conceptualization that explains the effect of multiple discounts on consumers’ evaluation of discount offers by examining the economic, informational, and affective dimensions of such discounts. A set of hypotheses were developed regarding multiple discounts’ effect on consumers’ perception of savings and product quality, compared to an economically equivalent single discount. Two experimental studies investigated the way that double discounts affect product evaluations. Participants who encounter price information along with discount(s) information evaluated perception of savings, product quality, monetary sacrifice, and value. The following are some major findings: 1. The product’s price level may motivate different evaluation processes of the double discounts. Specifically, participants seemed to rely more on the anchoring-andadjustment heuristic when the price level is high, which results in lower perceptions of savings with double discounts than with a single discount. When the price level is low, participants process the double discounts information more thoroughly and hence no difference on perceptions of savings was found between a single discount and double discounts. 2. Double discounts interrupt the price-perceived quality linkage by making the price information more complex and harder to process. In contrast, a single discount still maintains a positive relationship between price and perception of product quality. Therefore, a high price point led to higher perceptions of product quality than a low price point. 3. Emotional reactions partially mediated the effect of discount format on perceptions of savings, especially for hedonic products. Double discounts created lower positive emotions than a single discount, which led to lower perceptions of savings.

The effect of posttraumatic stress disorder psychoeducation on the nature and severity of traumatic stress symptoms in a Burundian sample

Fri, 11 Jul 2008 18:14:54 GMT

Title: The effect of posttraumatic stress disorder psychoeducation on the nature and severity of traumatic stress symptoms in a Burundian sample

Authors: Yeomans, Peter Douglass

Abstract: Post-Traumatic Stress Disorder (PTSD) was recognized in the Diagnostic and Statistical Manual of Mental Disorders (DSM–III) in 1980 as a syndrome associated with the experience of a traumatic event (APA, 1980). In recent years, the diagnosis of PTSD has been increasingly applied to diverse cultural settings, even as the validity of the construct sparks controversy and debate. Argument continues over whether the symptoms of PTSD are more driven by universal biological response or cultural factors. A review of the literature that documents recent efforts to identify and treat posttraumatic stress symptoms in diverse populations is provided. Given evidence for the suggestive and iatrogenic effects of some PTSD treatment methods and other interventions, as well as the theoretical support for the presence of social influences germane to cross-cultural research and treatment, it was proposed that PTSD-specific psychoeducation in pre-industrialized settings might diminish otherwise beneficial treatment effects. The present project drew on an indigent, rural Burundian sample and used an experimental design to examine the influence of PTSD psychoeducation on the nature and severity of traumatic stress symptoms reported. Participants were randomized to three conditions: A reconciliation workshop with psychoeducation, a reconciliation workshop without psychoeducation, and a waitlist control. Results showed that participants in the psychoeducation condition experienced a diminished reduction of PTSD symptoms relative to other conditions. There was no differential effect by condition on more general symptoms of anxiety, depression, and somatization symptoms. Secondary hypotheses predicting relationships at baseline between prior exposure to trauma models developed in industrialized societies and the nature and severity of posttraumatic stress symptoms were not supported. The findings are discussed in terms of how they might inform intervention development for traumatic stress in non-industrialized cultural settings

“Just the facts Ma’am?” a contextual approach to the legal information use environment

Fri, 11 Jul 2008 18:13:48 GMT

Title: “Just the facts Ma’am?” a contextual approach to the legal information use environment

Authors: Jones, Yolanda Patrice

Abstract: The purpose of this study was to develop a conceptual framework for legal information behavior in the law clinic setting. A strong conceptual framework for legal information behavior can be used to improve legal information systems, instruction, and services. This study examined academic law school researchers from a Farmworker Legal Aid Clinic. Student teams were observed in the law clinic as they constructed legal theories and located legal materials. The conceptual framework for this study is Solomon's Discovering Information in Context, which allows for multiple perspectives in gaining a rich, “round” view of information behavior, and puts forth Activity Theory as a possible tool for exploring how people discover information. Activity Theory was used to examine the systems, users, and the context of information use in the law clinic. Data collection involved naturalistic observations, “think-alouds,” post-observation interviews and examination of client file documents. Analyses involved situating the activities of the clinic historically, mapping the activities observed in the clinic within a “web of activities” using the Activity Theory matrix, looking for “breakdown situations,” and considering other information behavior theories and models which might “fit” the activities observed within the clinic. The findings showed the deeply collaborative nature of research in the law clinic, and how various sources of memory were used (individual, organizational, group, and artifacts such as books and databases). Information behavior models, if seen in terms of memory, each contribute useful perspectives on information behavior. While many information behavior models rely on an individual view of memory and knowledge, it is argued that models which take into account social and collaborative aspects of memory and behavior are more robust and were more useful in accounting for the behaviors observed in the clinic. In the law clinic, information behavior was embedded in a context of collaboration which had an impact, either directly or indirectly, on almost every aspect of information seeking and use. Thinking of information behavior and memory tools “in the round” allows you to consider the people, their work, the systems they use, and the environment in which they use them as they engage in information behavior.