Physics Commons^™

Measurement Of Polarization Observables PZ, PSZ, And PCZ In Double-Pion Photoproduction Off The Proton, Yuqing Mao

Theses and Dissertations

Meson production from excited nucleons is important in the study of baryon resonances and pion photoproduction is attracting much attention. To date a rather large amount of unpolarized cross-section measurements have been reported for both single- and double-pion photoproduction. However, polarization observables provide complementary information as they probe different combinations of transition amplitudes. The database for polarization observables remains quite sparse. Double-pion photoproduction have been studied in Hall B at Jefferson Lab with linearly polarized tagged photon beams incident on longitudinally polarized protons. The experiment covered center-of-mass energies between 1.4 GeV and 2.3 GeV. The target was a FROzen Spin …

Network Analysis And Cluster Detection Using Markov Theory, John William Campbell

Theses and Dissertations

Networks are a vital part of nature and society, yet many aspects of how networks function are still largely unknown. From understanding the internet to biology, chemistry, and physics, networks play a role, but even some of the most basic questions about networks can be difficult to answer. How are two networks alike or different? How do networks within networks form and how can clusters be detected? As networks change with time, how can we monitor those changes? The answers to these questions are vitally important to humans’ understanding of the world. Better understanding of networks allows for things like …

Physical And Magnetic Properties Of Magnetic Nanoparticle Arrays, Abdul Rahman Mohtasebzadeh

Theses and Dissertations

Using Scanning Electron Microscope (SEM) , Atomic Force Microscope (AFM) and Vibrating Sample Magnetometer (VSM) I studied magnetic-field directed self-assembly of magnetic nanoparticles into patterned arrays on the surface of perpendicular magnetic recording media. A controllable machine was used to coat super paramagnetic nano particles onto the surface of perpendicular recording media for different time intervals. Self assembled nano particles on the surface of the media, were transferred to a polymer layer to observe physical properties. Results from imaging shows that the average width and height of arrays is increasing as a function of time. Width of arrays varies with …

Galaxies In Absorption: A Study Of Chemical And Kinematic Properties Of Sub-Damped Lyman-Alpha Quasar Absorbers, Debopam Som

Theses and Dissertations

Study of the chemical composition of the interstellar medium (ISM) in galaxies over cosmic time is essential for a coherent understanding of galaxy formation and evolu- tion. Absorption lines in the spectra of quasars can be used as powerful, luminosity- independent probes of the properties of gas in and around galaxies and have been used extensively to study galaxies, the circumgalactic medium (CGM) and the intergalac- tic medium (IGM). The Damped Lyman-α systems (DLAs), with neutral hydrogen column densities of log NHI & 20.3, and sub-Damped Lyman-α systems (sub-DLAs) with 19.0 . log NHI < 20.3 are the highest NHI quasar absorbers and contain the most of the neutral gas available for star formation in the high-redshift Universe. These systems are believed to trace the progenitors of present-day galaxies and ac- curately probe chemical abundances in the ISM over ∼ 90% of the cosmic history. In contradiction with the cosmic chemical evolution models which predict the mean metallicity of galaxies to rise from low metallicities at high-z to a near-solar level at z ∼ 0, the DLAs are typically found to be metal-poor at all redshifts, showing little or no evolution. Interestingly, past work showed that the sub-DLAs at 0.6 . z . 1.5 are more metal-rich on average than DLAs, and evolve consistently with the chemical evolution models in this redshift range. This suggests that the DLAs and sub-DLAs may be tracing the progenitors of different populations of present-day galaxies. How- ever, chemical evolution of sub-DLAs is poorly constrained outside of the redshift range 0.6 < z < 1.5 which hinders a better understanding of galaxy evolution traced by DLAs and sub-DLAs.

This dissertation presents chemical abundance measurements …

On The Electrovacuum Solutions To The Einstein-Maxwell System In General Relativity, Nelson Camilo Posada Aguirre

Theses and Dissertations

In this masters thesis, we will present the analysis of the solution to the Einstein field equation, known as electrovac universe. In this model, an electric charge is located somewhere in an empty universe. An important result from this scenario, is that there is a functional relation between the electrostatic potential and the metric components, asumming a comformastat metric. On the other hand, the Einstein’s equations implies that the metric function satisfy the Laplace equation. We extended this model considering the Einstein’s equation with cosmological constant, which increased the complexity of the equations. The metric function satisfies now a nonlinear …

Nonlinear Magnetic Dynamics And The Switching Phase Diagrams In Spintronic Devices, Shu Anthoney Yan

Theses and Dissertations

Spin-transfer torque induced magnetic switching, by which the spin-polarized current transfers its magnetic moment to the ferromagnetic layer and changes its magnetization, holds great promise towards faster and smaller magnetic bits in data-storage applications due to the lower power consumption and better scalability.

We propose an analytic approach which can be used to calculate the switching phase diagram of a nanomagnetic system in the presence of both magnetic field and spin-transfer torque in an exact fashion. This method is applied to the study of switching conditions for the uniaxial, single domain magnetic layers in different spin-transfer devices. In a spin …

Next Discoveries In Neutrino Mixing: Electron Neutrino Appearance, Hongyue Duyang

Theses and Dissertations

The discovery of neutrino oscillation is a clear evidence of new physics beyond the Standard Model. Measurements of electron neutrino ($\nu_e$) and electron anti-neutrino $\bar{\nu}_{e}$ appearances are the most important channels to complete the neutrino mixing matrix. In a $ \nu_{e} $/$\bar{\nu}_{e}$ appearance experiment, a near detector (ND) is used to constrain the neutrino flux and measure the backgrounds to the signal. Backgrounds to the $ \nu_{e} $ appearance comes from Neutral Current Muon Neutrino Interactions ($\nu_{\mu}$-NC), Charged Current Muon Neutrino Interactions ($\nu_{\mu}$-CC), beam $ \nu_{e} $ events and outside backgrounds. The background components are then extrapolated to the far …

Timewalk Correction Analysis With Fadcs, Saptaparnee Chaudhuri

Theses and Dissertations

The upgraded CLAS12 (12 GeV) detector is built around a six-coil toroidal magnet that divides the active detection area into six azimuthal sectors. The Forward Time-of-Flight system (FTOF) is a major component of the CLAS 12 detector. It is used to measure the time-of-flight of the charged particles emerging from the interaction of the probing particle and the target. In each of the six sectors of the CLAS12, the FTOF system is comprised of three arrays of counters referred to as panel-1a, panel-1b, panel-2b. Panel-1b arrays consists of 62 counters each. This research focuses on the "timewalk corrections" analysis of …