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The Proton Spin Structure Function G2p At Low Momentum Transfer, Tobias Badman

Doctoral Dissertations

Over the past several decades Jefferson Lab National Accelerator Facility has proven to be extremely successful in its endeavor to study the polarized structure of nucleons. Measurements of these nucleon structure functions have proven to be powerful tools in testing and understanding a number of effective theories of QCD. The neutron spin structure functions, g1n and g2n, and the proton spin structure function, g1p, have been measured to very high precision over a wide kinematic range. However, the second proton structure function, g2p, remained largely unmeasured. The primary goal of Jefferson Lab Hall A experiment E08-027 was to perform an …

The G2p Experiment: A Measurement Of The Proton's Spin Structure Functions, Ryan Zielinski

Doctoral Dissertations

The E08-027 (g2p) experiment measured the spin structure functions of the proton at Jefferson Laboratory in Newport News, Va. Longitudinally polarized electrons were scattered from a transversely and longitudinally polarized solid ammonia target in Jefferson Lab's Hall A, with the polarized NH₃ acting as an effective proton target. Focusing on small scattering angle events at the electron energies available at Jefferson Lab, the experiment covered a kinematic phase space of 0.02 GeV² < Q² < 0.20 GeV² in the proton's resonance region. The spin structure functions, g₁^p(x,Q²) and g₂^p(x,Q²) , are …

A Dynamical-Systems Approach To Understanding Turbulence In Plane Couette Flow, Mimi Szeto

Doctoral Dissertations

Dynamical systems theory is used to understand the dynamics of low-dimensional spatio-temporal chaos. Our research aimed to apply the theory to understanding turbulent fluid flows, which could be thought of as spatio-temporal chaos in a very-high dimensional space. The theory explains a system's dynamics in terms of the local dynamics of its periodic solutions; these are the periodic orbits in state space. We considered the development of a model for the dynamics of plane Couette flow based on the theory. The proposed model is essentially a set of low-dimensional models for the local dynamics of the periodic orbits of the …

Modeling And Observation Of He+ Pickup Ions In The Inner Heliosphere, Junhong Chen

Doctoral Dissertations

Interstellar pickup ions constitute a charged particle population that originates from interstellar neutrals inside the heliosphere. They are produced by photoionization, charge exchange with solar wind ions, and electron impact ionization (EI). Once ionized, they are picked up by the interplanetary magnetic field (IMF) and rapidly swept outward with the solar wind. Typically, pickup ion distributions have been described in terms of a velocity distribution function that evolves through fast pitch angle scattering followed by adiabatic cooling during radial transport in the reference frame of the solar wind [e.g., Vasyliunas & Siscoe, 1976, VS76 hereafter].

In the VS76 model, the …

The Study Of Magnetotail Dynamics And Their Ionospheric Signatures Using Magnetohydrodynamic Simulation Model: Openggcm, Banafsheh Ferdousi Shahandashti

Doctoral Dissertations

In-situ measurements in the magnetotail are sparse and limited to single points. In the ionosphere, on the other hand, there is a broad range of observations, including magnetometers, aurora imagers, and radars . Since the ionosphere is the mirror of the plasmasheet, it can be used as a monitor of the magnetotail dynamics. Thus, it is of great importance to understand the coupling process between the ionosphere and the magnetosphere in order to interpret the ionosphere and ground observations properly. In this dissertation, the global magnetohydrodynamic simulation model, OpenGGCM model, is used to investigate two of such coupling processes. The …

A Study Of Reconnection Poleward Of The Cusp: Cluster And Polar, Fathima M. Muzamil

Doctoral Dissertations

Asymmetries in plasma density and the presence of a guide field significantly alter the structure of the ion diffusion region (IDR) in symmetric, collisionless reconnection. These features have been shown by numerical simulations under moderate density asymmetries (~10), and theoretical analyses. However, very few studies have addressed these issues with in-situ observations, particularly at high magnetic latitudes. By the structure of the IDR we refer to features such as the non-colocation of the X-line and stagnation line, the distortion of the Hall magnetic and electric fields, outflow speed, outflow density etc. We have compiled a collection of Cluster crossings of …