Formation of defects in multirow Wigner crystals

We study the structural properties of a quasi-one-dimensional classical Wigner crystal, confined in the transverse direction by a parabolic potential. With increasing density, the one-dimensional crystal first splits into a zigzag crystal before progressively more rows appear. While up to four rows the ground state possesses a regular structure, five-row crystals exhibit defects in a certain density regime. We identify two phases with different types of defects. Furthermore, using a simplified model, we show that beyond nine rows no stable regular structures exist.Comment: 11 pages, 8 figure

Optical exciton Aharonov-Bohm effect, persistent current, and magnetization in semiconductor nanorings of type I and II

The optical exciton Aharonov-Bohm effect, i. e. an oscillatory component in the energy of optically active (bright) states, is investigated in nanorings. It is shown that a small effective electron mass, strong confinement of the electron, and high barrier for the hole, achieved e. g. by an InAs nanoring embedded in an AlGaSb quantum well, are favorable for observing the optical exciton Aharonov-Bohm effect. The second derivative of the exciton energy with respect to the magnetic field is utilized to extract Aharonov-Bohm oscillations even for the lowest bright state unambiguously. A connection between the theories for infinitesimal narrow and finite width rings is established. Furthermore, the magnetization is compared to the persistent current, which oscillates periodically with the magnetic field and confirms thus the non-trivial (connected) topology of the wave function in the nanoring.Comment: 12 pages, 11 figure

Some Exact Solutions For The Classical Hall Effect In Inhomogeneous Magnetic Field

The classical Hall effect in inhomogeneous systems is considered for the case of one-dimensional inhomogeneity. For a certain geometry of the problem and for the magnetic field linearly depending on the coordinate the density of current distribution corresponds to the skin-effect.Comment: 5 pages, LaTe

Doctor of Philosophy

dissertationHypertension is a common diagnosis for American veterans. Despite years of research investigating how to improve antihypertensive medication adherence, suboptimal adherence still results in uncontrolled blood pressure leading to hospitalizations and complications. Connelly's model of Self-Care in Chronic Illness was used to compare veterans with hypertension, with and without post-traumatic stress disorder (PTSD) for health motivation, perceptions of the seriousness of illness, psychological status, and social support. Alcohol intake was added due to previous research suggesting it influences medication adherence in veterans with PTSD. A cross-sectional design was conducted among 428 veterans. 1,199 surveys were mailed with good response (n=428, 35.7%). The sample was comprised of 417 (97.4%) males and 11 (2.6%) females. Mean age was 76 years for participants with HTN and 66.7 years for participants with both HTN and PTSD (p<.01). Veterans with PTSD had higher rates of divorce or separation (28.8%), and higher mean blood pressure readings of 94.04 (p=.01). Medication adherence was very high in both groups with means of 7.14 (SD=1.30) and 6.48 (SD=1.97), respectively, for veterans with HTN and veterans with PTSD. Path analysis was used to evaluate associations of variables with medication adherence. However, the data did not fit the proposed model, thus modification indices were used with improved model fit. Among veterans with PTSD, less alcohol intake (β = -15), less health distress (β = -.36), and more social support (β = .27) were indirectly associated with medication adherence. Among veterans without PTSD the degree of comorbidity (β = -.15), less health distress (β = -.27), and more social support (β = .26), were indirectly associated with medication adherence. The path model explained a very small amount of the variance on medication adherence therefore nurses caring for veterans with HTN should assess for these variables but also be alert to other issues that may impact antihypertensive medication adherence. Future studies on antihypertensive medication adherence should recruit less adherent participants, and include more female veterans and other military subgroups at risk for PTSD to enhance the cardiovascular health of those who have served and protected our country

Quantum phase transition in quantum wires controlled by an external gate

We consider electrons in a quantum wire interacting via a long-range Coulomb potential screened by a nearby gate. We focus on the quantum phase transition from a strictly one-dimensional to a quasi-one-dimensional electron liquid, that is controlled by the dimensionless parameter $n x_0$, where $n$ is the electron density and $x_0$ is the characteristic length of the transverse confining potential. If this transition occurs in the low-density limit, it can be understood as the deformation of the one-dimensional Wigner crystal to a zigzag arrangement of the electrons described by an Ising order parameter. The critical properties are governed by the charge degrees of freedom and the spin sector remains essentially decoupled. At large densities, on the other hand, the transition is triggered by the filling of a second one-dimensional subband of transverse quantization. Electrons at the bottom of the second subband interact strongly due to the diverging density of states and become impenetrable. We argue that this stabilizes the electron liquid as it suppresses pair-tunneling processes between the subbands that would otherwise lead to an instability. However, the impenetrable electrons in the second band are screened by the excitations of the first subband, so that the transition is identified as a Lifshitz transition of impenetrable polarons. We discuss the resulting phase diagram as a function of $n x_0$.Comment: 18 pages, 8 figures, minor changes, published versio