Physics Commons^™

Molecular Dynamics Studies Of Interactions Of Phospholipid Membranes With Dehydroergosterol And Penetrating Peptides, Amir Mohsen Pourmousa Abkenar

Electronic Thesis and Dissertation Repository

We have performed molecular modeling of membrane and peptide systems by employing the classical molecular dynamics method and force field parameterizations. In this thesis, our main interest is the interaction of sterols as well as peptides with membranes. The thesis consists of three related projects. The first project focuses on cholesterol (CHOL) and dehydroergosterol (DHE) interacting with palmitoyl-oleoyl phosphatidylcholine (POPC) lipid bilayers. We study the effects of both sterols on the bilayer and compare them with each other. We first study the condensing and ordering effect of these sterols. Then, we study their orientations within the bilayer and relate them …

Quantum Coherence And Interference In Metallic Photonic Crystals And Hybrid Systems, Ali Hatef

Electronic Thesis and Dissertation Repository

In the first part of the thesis, we study the absorption coefficient of quantum dots doped in metallic photonic crystals under different circumferences. We study numerically the temporal evolution of the absorption coefficient profile where a probe field is applied to monitor the absorption process in two cases, when quantum dots are embedded lightly and densely. We also studied the effect of a changing plasma frequency on the absorption profile of quantum dots two possible field configurations. We show that the changes in plasma energy can take the system from the absorption region to the transparent and gain region.

As …

High Power Systems For Dynamic Field Control And Shielding In The Mr Environment, Dustin W. Haw

Electronic Thesis and Dissertation Repository

This thesis addresses several aspects of gradient and shim coil design and fabrication. New design techniques are coupled with experimental construction methods to expand small animal insert gradient and shim technology. The design techniques are also applied to other areas of magnetic resonance hardware.

A custom 2-axis gradient insert coil is designed and fabricated for the purpose of eddy current characterization. The construction tolerances were examined via bench top inductance measurements and eddy currents measurement inside a 7.0 T head-only MR system. A great deal of freedom is available when positioning shielding coils with respect to their corresponding primary coils …

Convection Due To Spatially Distributed Heating, Mohammad Zakir Hossain

Electronic Thesis and Dissertation Repository

Convection in an infinite horizontal slot subject to spatially distributed heating has been investigated for a wide range of Prandtl numbers. The primary flow response consists of convection in the form of rolls. When heating wave number alpha is sufficiently large the convection is found to be limited to a layer adjacent to lower wall and a uniform conductive layer emerges at upper section of the slot.

Conditions leading to the emergence of secondary convection have been identified using linear stability of the above primary convection. The secondary convection gives rise to longitudinal, or transverse, or oblique rolls; or to …

The Polylogarithm And The Lambert W Functions In Thermoelectrics, Muralikrishna Molli, Kamisetty Venkataramaniah, Sree Ram Valluri

Physics and Astronomy Publications

In this work, we determine the conditions for the extremum of the figure of merit, theta², in a degenerate semiconductor for thermoelectric (TE) applications. We study the variation of the function theta² with respect to the reduced chemical potential mu* using relations involving polylogarithms of both integral and nonintegral orders. We present the relevant equations for the thermopower, thermal, and electrical conductivities that result in optimizing theta² and obtaining the extremum equations. We discuss the different cases that arise for various values of r, which depends on the type of carrier scattering mechanism present in the …

A Study Of The Orbits Of The Logarithmic Potential For Galaxies, Sree Ram Valluri, Paul Wiegert, John Drozd, Matt Dasilva

Physics and Astronomy Publications

The logarithmic potential is of great interest and relevance in the study of the dynamics of galaxies. Some small corrections to the work of Contopoulos & Seimenis (1990) who used the method of Prendergast (1982) to find periodic orbits and bifurca- tions within such a potential are presented. The solution of the orbital radial equation for the purely radial logarithmic potential is then considered using the p-ellipse (pre- cessing ellipse) method pioneered by Struck (2006). This differential orbital equation is a special case of the generalized Burgers equation. The apsidal angle is also deter- mined, both numerically as well as …

Electronic And Magnetic Excitations In Graphene And Magnetic Nano-Ribbons, Maher Zakaria Ahmed Selim

Electronic Thesis and Dissertation Repository

The discovery of graphene - a 2D material with superior physical properties - in 2004 was important for the intensive global research to find alternatives to three-dimensional (3D) semiconductor materials in industry. At the same time there have been exciting advances for 2D magnetic materials on the nanometer scale. The superior properties of graphene are mainly attributed to its crystal structure and its relatively short-range interactions. These properties show that natural and artificial 2D materials are promising for new applications.

In this thesis we have carried out a comprehensive investigation of the effects of the 2D lattice structures, the roles …

Hyperthermal H2 Induced C–H Bond Cleavage: A Novel Approach To Cross-Linking Of Organic Molecules, Tomas Trebicky

Electronic Thesis and Dissertation Repository

The development of simple and effective methods of incorporating molecular moieties with desirable properties into new functional materials is one of the ultimate goals of material scientists. The work presented in this thesis demonstrates an easy way to accomplish this using a beam of gaseous H₂, which we call hyperthermal hydrogen induced cross-linking (HHIC). We prove theoretically and experimentally that when the kinetic energy of H₂ is raised to ~20 eV, it becomes a light-mass projectile which is energetic enough to knock hydrogen atoms off of organic molecules, but not other heavier atoms. By developing a reactor …

Exploring Bacterial Nanowires: From Properties To Functions And Implications, Kar Man Leung

Electronic Thesis and Dissertation Repository

The discovery of electrically conductive bacterial nanowires from a broad range of microbes provides completely new insights into microbial physiology. Shewanella oneidensis strain MR-1, a dissimilatory metal-reducing bacterium, produces extracellular bacterial nanowires up to tens of micrometers long, with a lateral dimension of ~10 nm. The Shewanella bacterial nanowires are efficient electrical conductors as revealed by scanning probe techniques such as CP-AFM and STM.

Direct electrical transport measurements along Shewanella nanowires reveal a measured nanowire resistivity on the order of 1 Ω∙cm. With electron transport rates up to 10⁹/s at 100 mV, bacterial nanowires can serve as a …

Validation And Application Of Wind Profiler Measurements Of Atmospheric Turbulence, Armin Dehghan

Electronic Thesis and Dissertation Repository

This thesis focuses on the investigation of the reliability of turbulence measurements by radars when the spectral-width method is used. This method employs the spectral widths observed by radar (experimental spectral width) to determine turbulence. However, the experimental width can be affected by non-turbulent effects, including radar geometry. Therefore, the spectral width due to non-turbulent effects (theoretical spectral width) must be removed from the experimental width. This can occasionally lead to negative values of turbulence.

It is our aim (1) to study the effects of both experimental and theoretical spectral widths on the accuracy of turbulence measurements, (2) to study …

Rational Design And Advanced Fabrication Of Metallic Nanostructures For Surface-Enhanced Raman Spectroscopy, Betty Cristina Galarreta

Electronic Thesis and Dissertation Repository

One of the main challenges in analytical science and technology is to develop devices that provide unambiguously the chemical nature of the material of interest with the minimum intrusiveness, the smallest amount of analyte, and the shortest acquisition time. Among the promising methods for such purpose, optical spectroscopy such as surface-enhanced Raman scattering is considered a suitable option. This spectroscopic technique takes advantage of the interaction between an optical field and metallic nanostructures to magnify the electromagnetic field in the vicinity of the nanostructure, resulting in an amplified signal of the vibrational fingerprints of the adsorbed molecules onto the metallic …

Microrheology And Microstructure Of Poly(Vinyl Alcohol)-Based Physical Gels, Nan Yang

Electronic Thesis and Dissertation Repository

We study the microrheology and microstructure of physically cross-linked poly(vinyl alcohol) (PVA) gels using atomic force microscopy, dynamic light scattering and particle tracking. We compare the microscopic rheological properties with the bulk properties measured using conventional shear rheometry, and correlate the rheological properties to the structure of the materials.

We develop a new technique for investigating the viscoelastic properties of soft materials using the atomic force microscope. The electronic feedback of an atomic force microscope is modified by adding a small oscillatory voltage to the deflection signal, and the amplitude and phase of the motion of the sample stage is …

Structure And Strength: Anisotropic Polyvinyl Alcohol Hydrogels And Spider Mite Silk Fibres, Stephen Hudson

Electronic Thesis and Dissertation Repository

Polyvinyl alcohol (PVA) is a hydrophilic, biocompatible polymer which can be made into physically cross-linked hydrogels by freezing and thawing PVA solution. These hydrogels can be made with anisotropic mechanical properties closely matching those of porcine aorta, making them a promising material for producing artificial heart valves and heart valve stents.

Small- and ultra small-angle neutron scattering has been used to study the structure of isotropic and anisotropic PVA hydrogels at length-scales of 2 nm to 10 μm. By supplementing the neutron data with data from atomic force microscopy, a large range of length-scales have been probed, within which structural …

Thermodynamics, Hydrodynamics And Critical Phenomena In Strongly Coupled Gauge Theories, Christopher Pagnutti

Electronic Thesis and Dissertation Repository

The gauge theory / string theory correspondence has led to great progress in the study of strongly-coupled gauge theories. In this work, we start with a detailed treatment of some simple examples of this correspondence in order to establish some of the concepts and techniques are used on a more complicated system. We then consider a (3+1)-dimensional theory of gravity with a translationally invariant horizon, that is assumed to be dual to a (2+1)-dimensional non-conformal gauge theory at finite temperature. We study the thermodynamics of this model and find that there exists an exotic type of second-order phase transition wherein …

Pushing The Boundaries In Gradient And Shim Design For Mri, Parisa Hudson

Electronic Thesis and Dissertation Repository

High performance gradient and shim coils are highly interested for high-field magnetic resonance imaging and spectroscopy to correct for large B₀ inhomogeneities created by the magnetic susceptibility differences between tissues, bone, and air. In chapter two, complete sets of high-performance gradient and shim coils are designed using two different methods: the minimum inductance and the minimum power target field methods. A quantitative comparison of shim performance in terms of merit of inductance, ML, and merit of resistance, MR, is made for shim coils designed using the minimum inductance and the minimum power design algorithms. The coils designed …

Hemodynamics In The Stenosed Carotid Bifurcation With Plaque Ulceration, Emily Y. Wong

Electronic Thesis and Dissertation Repository

The presence of irregular plaque surface morphology or ulceration of the atherosclerotic lesion has been identified as an independent risk factor for ischemic stroke. Doppler ultrasound (DUS) is the most commonly performed non-invasive technique used to assess patients suspected of having carotid artery disease, but currently does not incorporate the diagnosis of plaque ulceration. Advanced Doppler analyses incorporating quantitative estimates of flow disturbances may result in diagnostic indices that identify plaque ulcerative conditions. A technique for the fabrication of DUS-compatible flow phantoms was developed, using a direct-machining method that is amenable to comprehensive DUS investigations. In vitro flow studies in …

A Perspective On Space Programs Beyond North America, Raymond Francis

Planetary Science & Exploration Research Forum

The popular image of space programs today is dominated by the activities of NASA, even here in Canada where our own space agency has a relatively low profile. But space exploration is a global effort, and numerous national governments undertake space activities without being well known to North Americans. This talk, originally a public lecture for the Royal Astronomical Society of Canada, revisits the history of national space programs, and discusses examples of established, emerging, and new space actors from around the globe, including the motives of governments in undertaking them. It concludes with a survey of the activities of …