Theses and Dissertations from UMD
Permanent URI for this communityhttp://hdl.handle.net/1903/2
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
More information is available at Theses and Dissertations at University of Maryland Libraries.
Browse
3 results
Search Results
Item 3D ENGINEERING OF VIRUS-BASED PROTEIN NANOTUBES AND RODS: A TOOLKIT FOR GENERATING NOVEL NANOSTRUCTURED MATERIALS(2018) Brown, Adam Degen; Culver, James N; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Technological innovation at the nanometer scale has the potential to improve a wide range of applications, including energy storage, sensing of environmental and medical signals, and targeted drug delivery. A key challenge in this area is the ability to create complex structures at the nanometer scale. Difficulties in meeting this challenge using traditional fabrication methods have prompted interest in biological processes, which provide inspiration for complex structural organization at nanometer to micrometer length scales from self-assembling components produced inexpensively from common materials. From that perspective, a system of targeted modifications to the primary amino acid structure of Tobacco mosaic virus (TMV) capsid protein (CP) has been developed that induces new self-assembling behaviors to produce nanometer-scale particles with novel architectures. TMV CPs contain several negatively charged carboxylate residues which interact repulsively with those of adjacent CP subunits to destabilize the assembled TMV particle. Here, the replacement of these negatively charged carboxylate residues with neutrally charged or positively charged residues results in the spontaneous assembly of bacterially expressed CP into TMV virus-like particles (VLPs) with a range of environmental stabilities and morphologies and which can be engineered to attach perpendicularly to surfaces and to display functional molecular patterns such as target-binding peptide chains or chemical groups for attachment of functional targets. In addition, the distinct electrostatic surface charges of these CP variants enable the higher-level coassembly of TMV and VLP into continuous rod-shaped nanoparticles with longitudinally segregated distribution of functionalities and surface properties. Furthermore, the unique, novel, environmentally responsive assembly and disassembly behaviors of the modified CPs are shown to act as simple mechanisms to control the fabrication of these hierarchically structured functional nanoparticles.Item EMPIRICAL STUDIES BASED ON HONEYPOTS FOR CHARACTERIZING ATTACKERS BEHAVIOR(2015) Sobesto, Bertrand; Cukier, Michel; Reliability Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The cybersecurity community has made substantial efforts to understand and mitigate security flaws in information systems. Oftentimes when a compromise is discovered, it is difficult to identify the actions performed by an attacker. In this study, we explore the compromise phase, i.e., when an attacker exploits the host he/she gained access to using a vulnerability exposed by an information system. More specifically, we look at the main actions performed during the compromise and the factors deterring the attackers from exploiting the compromised systems. Because of the lack of security datasets on compromised systems, we need to deploy systems to more adequately study attackers and the different techniques they employ to compromise computer. Security researchers employ target computers, called honeypots, that are not used by normal or authorized users. In this study we first describe the distributed honeypot network architecture deployed at the University of Maryland and the different honeypot-based experiments enabling the data collection required to conduct the studies on attackers' behavior. In a first experiment we explore the attackers' skill levels and the purpose of the malicious software installed on the honeypots. We determined the relative skill levels of the attackers and classified the different software installed. We then focused on the crimes committed by the attackers, i.e., the attacks launched from the honeypots by the attackers. We defined the different computer crimes observed (e.g., brute-force attacks and denial of service attacks) and their characteristics (whether they were coordinated and/or destructive). We looked at the impact of computer resources restrictions on the crimes and then, at the deterrent effect of warning and surveillance. Lastly, we used different metrics related to the attack sessions to investigate the impact of surveillance on the attackers based on their country of origin. During attacks, we found that attackers mainly installed IRC-based bot tools and sometimes shared their honeypot access. From the analysis on crimes, it appears that deterrence does not work; we showed attackers seem to favor certain computer resources. Lastly, we observed that the presence of surveillance had no significant impact on the attack sessions, however surveillance altered the behavior originating from a few countries.Item ENGINEERING OF SELF-ASSEMBLED MULTIFERROIC NANOSTRUCTURES IN PbTiO3-CoFe2O4 THIN FILMS(2006-01-31) Li, jianhua; Roytburd, Alexander L; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Multiferroic materials which display a coexistence of ferroelectric and ferromagnetic properties attract considerable interest for their potential for novel device applications as well as for the interesting physics and materials science underlying their functional responses. In multiferroic composite, electromagnetic coupling facilitate elastic interaction between ferroelectric and ferromagnetic components via piezoeffect and magnetostriction. The major goal of our research is designing the transverse epitaxial multiferroic nanostructures with controlled morphologies. The PbTiO3-CoFe2O4 system was selected for this study because of the (i) large spontaneous strain associated with the ferroelectric phase transition in PbTiO3 (6.5%), which should create strong elastic interactions between the two phases accompanying the piezoelectric effect, and (ii) large magnetostriction of ferrimagnetic CoFe2O4. We successfully fabricate self-assembling multiferroic nanostucture films of CoFe2O4-PbTiO3 by PLD deposition on SrTiO3 substrates of different orientations. X-ray and TEM characterization show that all films have columnar architecture and 3D epitaxial relationships between phases and each phase and substrates. The morphology of nanostructures has been controlled by changing orientation of a substrate. It has been shown that it is possible to obtain the ferromagnetic (CoFe2O4) rods with a diameter about 10-20 nm in the ferroelectric PbTiO3 matrix in (001) films of composition 0.67PbTiO3-0.33CoFe2O4, and vise versa: ferroelectric rods in ferrimagnetic matrix in (111) films of composition 0.33PbTiO3-0.67CoFe2O4. The lamellate morphology with a specific crystallographic orientation of lamellae corresponding to {111} planes has been obtained in (110) films. The measurements of lattice parameters of the constitutive phases at different temperature allows us to determine the level of internal stresses due to misfit between phases. The measurements of piezo- and magnetic responses of the films prove that the films are ferroelectric and ferromagnetic simultaneously. The piezo- and magnetic responses are considerable suppressed due to mutual constraints between phases. This suppression indicates the strong elastic interactions between the phases which allows us to suggest the strong electro-magnetic coupling in the films. Combining theoretical and experimental studies of self-assembled multiferroic nanostructures in epitaxial films has revealed that the elastic interactions caused by epitaxial stresses play the dominate role in defining the morphology of the nanostructures and their magnetic and electric responses.