Mechanisms of superconductivity investigated by nuclear radiation

Investigation focused on the behavior of superconducting magnet and its constituent materials during and after exposure to nuclear radiation. The results will indicate the feasibility of their use in diverse applications and various environments

Vascular Dysfunction and Posttraumatic Stress Disorder: Examining the Role of Oxidative Stress and Sympathetic Activity

Purpose: The physiological manifestations of posttraumatic stress disorder (PTSD) have been associated with an increase in risk of cardiovascular disease (CVD) independent of negative lifestyle factors. The goal of the study was to better elucidate the mechanisms behind the increased CVD risk by examining peripheral vascular function, a precursor to CVD. Moreover, this study sought to determine the role of oxidative stress and sympathetic nervous system (SNS) activity in PTSD-induced vascular dysfunction. Methods: Sixteen individuals with PTSD (10 women, 6 men; age 24 ± 4 years), and twenty-four healthy controls (CTRL; 15 women, 9 men, 24 ± 4 years), participated in the study. The PTSD group participated in two visits, consuming either a placebo or antioxidant cocktail (AO - vitamins C and E and alpha lipoic acid) prior to their visits, in a randomized order. Arm vascular function was assessed via the reactive hyperemia- induced flow mediated dilation of the brachial artery (BAFMD) technique and evaluated with Doppler ultrasonography. Brachial artery and arm microvascular function were determined by percent change of diameter from baseline normalized for BA shear rate (BAD/Shear), and blood flow area under the curve (BF AUC), respectively. Heart rate variability (HRV) was used to assess autonomic nervous system activity. Results: BF AUC was significantly lower (p = 0.02) and SNS activity was significantly higher (p = 0.02) in the PTSD group when compared to the CTRL group. BAD/Shear was not different between groups. Following the acute AO supplementation, BF AUC was augmented to which it was no longer significantly different (p = 0.16) when compared to the CTRL group. SNS activity within the PTSD group was significantly reduced (p=.007) following the AO supplementation when compared to the PL condition, and the difference between PTSD and CTRL was no longer significant (p=.41). Conclusion: Young individuals with PTSD demonstrated lower arm microvascular, but not brachial artery, function as well as higher sympathetic activity when compared to healthy controls matched for age, sex, and physical activity level. Furthermore, this microvascular dysfunction and SNS activity was attenuated by an acute AO supplementation to the level of the healthy controls. Taken together, this study revealed that the modulation of oxidative stress, via an acute AO supplementation, improved vascular dysfunction in individuals with PTSD, potentially by reducing the substantial SNS activity associated with this disorder.https://scholarscompass.vcu.edu/gradposters/1084/thumbnail.jp

Bichromatic Driving of a Solid State Cavity QED System

The bichromatic driving of a solid state cavity quantum electrodynamics system is used to probe cavity dressed state transitions and observe coherent interaction between the system and the light field. We theoretically demonstrate the higher order cavity-dressed states, supersplitting, and AC stark shift in a solid state system comprised of a quantum dot strongly coupled to a photonic crystal cavity for on- and far off-resonant cases. For the off-resonant case, phonons mediate off-resonant coupling between the quantum dot and the photonic resonator, a phenomenon unique to solid state cavity quantum electrodynamics.Comment: 8 pages 6 figure

The Effects of a High Fat Meal on Blood Flow Regulation during Arm Exercise

A diet high in saturated fats results in endothelial dysfunction and can lead to atherosclerosis, a precursor to cardiovascular disease. Exercise training is a potent stimulus though to mitigate the negative effects of a high saturated fat diet; however, it is unclear how high-saturated fat meal (HSFM) consumption impacts blood flow regulation during a single exercise session. PURPOSE: This study sought to examine the impact of a single HSFM on peripheral vascular function during an acute upper limb exercise bout. METHODS: Ten young healthy individuals completed two sessions of progressive handgrip exercise. Subjects either consumed a HSFM (0.84 g of fat/kg of body weight) 4 hours prior or remained fasted before the exercise bout. Progressive rhythmic handgrip exercise (6kg, 12kg, 18kg) was performed for 3 minutes per stage at rate of 1 Hz. The brachial artery (BA) diameter and blood velocity was obtained using Doppler Ultrasound (GE Logiq e) and BA blood flow was calculated with these values. RESULTS: BA blood flow and flow mediated dilation (normalized for shear rate) during the handgrip exercise significant increased from baseline in all workloads, but no differences were revealed in response to the HSFM consumption. CONCLUSION: Progressive handgrip exercise augmented BA blood flow and flow mediated dilation in both testing days; however, there was no significant differences following the HSFM consumption. This suggests that upper limb blood flow regulation during exercise is unaltered by a high fat meal in young healthy individuals.https://scholarscompass.vcu.edu/gradposters/1060/thumbnail.jp

Strong Coupling Theory of Two Level Atoms in Periodic Fields

We present a new convergent strong coupling expansion for two-level atoms in external periodic fields, free of secular terms. As a first application, we show that the coherent destruction of tunnelling is a third-order effect. We also present an exact treatment of the high-frequency region, and compare it with the theory of averaging. The qualitative frequency spectrum of the transition probability amplitude contains an effective Rabi frequency.Comment: 4 pages with 3 figure

Physical Electronics

Contains research objectives and reports on two research projects

Band Gaps for Atoms in Light based Waveguides

The energy spectrum for a system of atoms in a periodic potential can exhibit a gap in the band structure. We describe a system in which a laser is used to produce a mechanical potential for the atoms, and a standing wave light field is used to shift the atomic levels using the Autler-Townes effect, which produces a periodic potential. The band structure for atoms guided by a hollow optical fiber waveguide is calculated in three dimensions with quantised external motion. The size of the band gap is controlled by the light guided by the fiber. This variable band structure may allow the construction of devices which can cool atoms. The major limitation on this device would be the spontaneous emission losses.Comment: 7 pages, four postscript figures, uses revtex.sty, available through http://online.anu.edu.au/Physics/papers/atom.htm

Anomalous Sliding Friction and Peak Effect near the Flux Lattice Melting Transition

Recent experiments have revealed a giant "peak effect" in ultrapure high $T_c$ superconductors. Moreover, the new data show that the peak effect coincides exactly with the melting transition of the underlying flux lattice. In this work, we show using dynamical scaling arguments that the friction due to the pinning centers acting on the flux lattice develops a singularity near a continuous phase transition and can diverge for many systems. The magnitude of the nonlinear sliding friction of the flux lattice scales with this atomistic friction. Thus, the nonlinear conductance should diverge for a true continuous transition in the flux lattice or peak at a weakly first order transition or for systems of finite size.Comment: 4 pages, to appear in Phys. Rev.

Physical Electronics

Contains research objectives and reports on four research projects

Magnetic Pinning of Vortices in a Superconducting Film: The (anti)vortex-magnetic dipole interaction energy in the London approximation

The interaction between a superconducting vortex or antivortex in a superconducting film and a magnetic dipole with in- or out-of-plane magnetization is investigated within the London approximation. The dependence of the interaction energy on the dipole-vortex distance and the film thickness is studied and analytical results are obtained in limiting cases. We show how the short range interaction with the magnetic dipole makes the co-existence of vortices and antivortices possible. Different configurations with vortices and antivortices are investigated.Comment: 12 pages, 12 figures. Submitted to Phys. Rev.