Digital Commons Network^™

Self -Assembly On Strained Metallic Interfaces, And, Novel Collective Excitations On Metal Surfaces, Bogdan Diaconescu

Doctoral Dissertations

Recent interest in novel physical properties of reduced dimensional systems is spurred by the advance of investigation methods at the nanoscale. Understanding bottom-up techniques for the growth of nanomaterials with novel physical, chemical, and mechanical properties require specialized investigation tools.

I am presenting a novel design and performance of an ultra high vacuum scanning tunneling microscope (STM) that allows for large scale (8 mum x 8 mum), fast scanning (3 s for a 100 A x 100 A frame), and atomically resolved studies of reduced dimensional systems on metallic surfaces. The STM proved excellent performance, allowing for variable temperature (100 …

Inclusive Scattering Of Polarized Electrons From Polarized Protons In The Delta-Excitation Region With Blast, Octavian Florin Filoti

Doctoral Dissertations

Inclusive scattering of polarized electrons from polarized protons has been studied using the BLAST detector at MIT-Bates Linear Accelerator Center. The Bates Large Acceptance Spectrometer Toroid (BLAST) is a detector designed to study in a comprehensive and precise way the spin-dependent electromagnetic response in one and few-body systems over a large kinematic range. It has been used to measure spin-dependent scattering from the elastic to the nucleon resonance region for hydrogen and deuterium using a longitudinally polarized electron beam at a beam energy of 850 MeV stored in the MIT-Bates South Hall Ring, and polarized internal gas targets of hydrogen …

Solar Wind Entry Into The Magnetosphere Under Northward Imf Conditions, Wenhui Li

Doctoral Dissertations

The state of the plasma sheet in the magnetosphere is usually observed to be hot (1-10 keV) and tenuous (∼0.1 cm-3). However, sometimes part of it is observed to be colder (< 1 keV) and denser (∼1 cm-3), and the plasma flow is almost stagnant. Much higher density (∼10 cm-3) plasma material (superdense plasma sheet) is also sometimes observed near the geosynchronous orbit. The cold dense plasma sheet (CDPS) is usually observed after a period of northward interplanetary magnetic field (IMF), which is also a necessary condition for the formation of a superdense plasma sheet (SDPS). Since the CDPS is generally absent of a cold O+ component, and the ionospheric outflow is strong only under southward IMF condition, the source of the CDPS is thought to be the solar wind.

Usually, solar wind plasma and energy entry into the magnetosphere is considered to occur mainly during the southward IMF condition through reconnection processes that first occur at the dayside magnetopause and then in the magnetotail. However, the formation of CDPS suggests that there are also certain processes that let solar wind enter the magnetosphere when the IMF is northward. The purpose of this dissertation study is to find …

Structural And Functional Pulmonary Imaging Using Hyperpolzarized Xenon-129, Iga Muradyan

Doctoral Dissertations

We describe applications of hyperpolarized 129 Xe to pulmonary imaging. Unique characteristics of this gas such as its polarizability and diffusibility in tissue allow probing important properties of the lungs. Three methods that study structure and function of the lungs, Chemical Shift Saturation Recovery (CSSR), Xenon polarization Transfer Contrast (XTC) and Dixon, and their application to human studies for the first time are the focus of this work.

CSSR measures the global fractional gas transport, F(t) in the lungs. Using this method the dynamics of gas exchange were studied. A model describing this process was derived and used to interpret …

Measurement Of Parity Violation In Thermal Neutron Capture On A Proton, Mikayel Dabaghyan

Doctoral Dissertations

The NPDGamma experiment is measuring the directional parity violating asymmetry in the emission of gamma rays from the capture of cold neutrons on protons. The asymmetry can be related in a straightforward way to effective couplings within an appropriate NN weak interaction theory, such as chiral perturbation based effective field theories.

Since this is a measurement within a two body system, the observables are calculable without uncertainties from few to many body (large nuclei) effects. The experiment consists of two phases. The first one, at the Los Alamos Neutron Science Center (LANSCE), has just been completed, providing a measurement of …

Ring Current -Atmosphere Interactions Model With Stormtime Magnetic Field, Alexander Emilov Vapirev

Doctoral Dissertations

An improved version of the ring current-atmosphere interactions kinetic model (RAM) is presented in this thesis. The recent stormtime empirical model T04s and the IGRF model are used to represent the Earth's external and internal magnetic fields respectively. Particle drifts, losses due to charge exchange with geocoronal hydrogen and atmospheric losses are included in the model as they are considered the main mechanisms of ring current development and its following decay. A numerical technique for bounce-averaging along the field lines is introduced and results for the calculated bounce-averaged hydrogen densities and magnetic gradient-curvature drift velocities (general case) for the moderate …