Chip-scale photonic devices such as microdisks, photonic crystal cavities and slow-light photonic crystal waveguides possess strong light localization and long photon lifetime, which will significantly enhance the light-matter interactions and can be used to implement new functionalities for both classical and quantum information processing, optical computation and optical communication in integrated nanophotonic circuits. This thesis will focus on three topics about light matter interactions and quantum information processing with chip-scale photonic devices, including 1) Design and characterization of asymmetric resonate cavity with radiation directionality and air-slot photonic crystal cavity with ultrasmall effective mode volume, 2) Exciton-photon interactions between quantum dots and photonic crystal devices and non-classical photon source from a single quantum dot, and 3) Quantum controlled phase gate and phase switching based on quantum dots and photonic crystal waveguide. The first topic is engineered control of radiation directionality and effective mode volume for optical mode in chip-scale silicon micro-/nano-cavities. High quality factor (Q), subwavelength mode volume (V) and controllable radiation directionality are the major properties for optical cavities designs. In Chapter 2, asymmetric resonant cavities with rational caustics are proposed and interior whispering gallery modes in monolithic silicon mesoscopic microcavities are experimentally demonstrated. These microcavities possess unique robustness of cavity quality factor against roughness Rayleigh scattering. In Chapter 3, air-slot mode-gap photonic crystal cavities with quality factor of 10^4 and effective mode volume ~ 0.02 cubic wavelengths are experimentally demonstrated. The origin of the high Q air-slot cavity mode is the mode-gap effect from the slotted photonic crystal waveguide mode with negative dispersion. The second topic is exciton-photon coupling between quantum dots and twodimensional photonic crystal nanocavities and waveguide localized modes, including Purcell effect in weak coupling regime and vacuum Rabi splitting in strong coupling regime. In Chapter 4, micro-photoluminescence measurements of PbS quantum dots coupled to air-slot mode-gap photonic crystal cavities with potentially high qualify factor and small effective mode volume are presented. Purcell factor due to ultrahigh Q/V ratios are critical for applications in non-classical photon sources, cavity QED, nonlinear optics and sensing. In Chapter 5, the observation of subpoisson photon statistics from a single InAs quantum dot emission is presented from both continuous wave and pulsed Hanbury Brown and Twiss measurement. Furthermore, strong coupling between single quantum dot exciton line and photonic crystal waveguide localized mode is demonstrated experimentally and theoretically analyzed with master equations, which can be used as a great implementation platform for realizing future solid-state quantum computation. The third topic is quantum controlled phase gate and phase switching operations based on quantum dots and photonic crystal slow-light waveguide. In Chapter 6, we propose a scheme to realize controlled phase gate between two single photons through a single quantum dot embedded in a photonic crystal waveguide. Enhanced Purcell factor and large β factor lead to high gate fidelity over broadband frequencies compared to cavity-assisted system. The excellent physical integration of this photonic crystal waveguide system provides tremendous potential for large-scale quantum information processing. In Chapter 7, dipole induced transparency can be achieved in a system which consists of two quantum dots properly located in silicon photonic crystal waveguide. Furthermore, we describe how this effect can be useful for designing full Ï€ phase switching in a hetero-photonic crystal waveguide structure just by a small amount of photons.

Hindbrain glucagon-like peptide 1 (GLP-1) neurons project to numerous forebrain areas, including the lateral septum (LS). Here, we propose this pathway represents a direct link between satiation processing and food reward, as LS-projecting GLP-1 neurons directly connect vagal afferent signaling to a reward-related brain region. The four studies presented in this dissertation broadly address the contribution of LS GLP-1 receptors (GLP-1R) in the control of feeding behavior under both non-stressed and stressed conditions in rats and mice. We first confirmed that pharmacologic activation of LS GLP-1R suppresses feeding. When we blocked these receptors rats and mice, we found that endogenous activation of LS GLP-1R promotes satiety. Because the LS is known to play a role in motivation, we next investigated the role of LS GLP-1R in motivation for food by examining operant responding for sucrose on a progressive ratio (PR) schedule. Our findings here suggest that GLP-1R in the dorsal subregion of the LS (dLS) affect motivation for food in both rats and mice. While we initially focused on the role of GLP-1 under normal, non-stressed conditions, central GLP-1 is also involved in behavioral and endocrine responses to stress. Here we demonstrated for the first time that restraint stress robustly activates hindbrain GLP-1-producing neurons in mice and found that LS GLP-1R blockade attenuates 30-min restraint stress-induced hypophagia in both rats and mice. LS neurons project to several other brain regions known to play a critical role in the control of food intake. In the final study, we determined the distinct axonal targets of LS GLP-1R bearing neurons. This anatomical analysis begins to unravel the downstream circuitry of GLP-1 signaling in the LS and has revealed candidate neural pathways through which LS GLP-1 signaling may alter food intake and other behavioral responses to stress. Together, the results presented in this dissertation provide clear evidence that there is in fact significant overlap in the neural pathways that mediate satiation signaling and food reward. / A Dissertation submitted to the Department of Psychology in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Spring Semester 2019. / February 27, 2019. / food intake, food reward, glucagon-like peptide 1, lateral septum, obesity, stress / Includes bibliographical references. / Diana Williams, Professor Directing Dissertation; Lynn Panton, University Representative; Alan Spector, Committee Member; Debra Fadool, Committee Member; Chris Schatschneider, Committee Member.

Biological cells are filled with a variety of pores and channels that transport ions and molecules across the cell membrane. These passageways are vital to cell function and remarkably effective due to their high selectivity, high flux, and sensitivity to environmental stimuli. This level of control is extremely attractive for applications ranging from biotechnology to energy and the environment. In this thesis, the unique properties of two dimensional materials are utilized to create solid-state nanopores that closely mimic the function of biological ion channels. Ionic conductance measurements were used to demonstrate that nanopores introduced into graphene membranes exhibit K+/Na+ selectivity and can modulate the ionic current with an applied gate voltage. These devices are shown to respond to low gate voltages (<500 mV) at biologically relevant concentrations (up to 1M). Cation-anion selectivity, concentration dependence, and pH dependence were also investigated. We propose the observed behavior is dependent on the presence of surface adsorbates that modify the surface energy of the membrane and near the pore, creating a gaseous barrier that is modulated via electro-wetting. Additionally, we work toward creating light responsive MoS2 nanopores operating in solution, by monitoring the current through a MoS2 nanopore while the device is exposed to a focused laser beam. / 2018-07-09T00:00:00Z

Hindbrain glucagon-like peptide 1 (GLP-1) neurons project to numerous feeding-relevant forebrain areas. One such region is the lateral septum (LS), which plays a role in learning, motivation, and stress. We hypothesized that stimulation of GLP-1R in the LS affects food intake. Rats were implanted with unilateral cannulas targeting the LS, and intra-LS injections were made 30 min before dark cycle onset. We examined the effects of the GLP-1R agonist Exendin 4 (Ex4) at doses subthreshold for effect when delivered to the lateral ventricle (0.01 or 0.025 µg). Ex4 had no effect on feeding at 2 and 4 h into the dark phase, but the 0.025 µg dose suppressed overnight intake. We then assessed the effects of ventricle-subthreshold doses (1.0, 2.5, 5.0, or 10.0 µg) of the GLP-1R antagonist Exendin (9-39) (Ex9) vs vehicle injected into the LS. Ex9 increased chow intake at 2, 4, and 20 hours post-dark onset relative to vehicle. We assessed the role of LS GLP-1R in motivation for food by examining operant responding for sucrose on progressive ratio (PR) schedule. Intra-LS injections of Ex9 (10.0 µg) or vehicle were made 45 min prior to the start of the PR session. We also tested PR responding after a nutrient preload designed to maximize GLP-1 neuron activation. The preload strongly suppressed PR responding, but blockade of LS GLP-1R did not affect motivation for sucrose in either preload condition. The Ensure preload significantly suppressed 24-hour chow intake relative to no preload condition. However, intra-LS Ex9 treatment significantly reduced this compensatory reduction in chow intake after the preload. These experiments suggest that the LS is a relevant site for neuronal GLP-1 influence on food intake. / A Thesis submitted to the Department of Psychology in partial fulfillment of the requirements for the degree of Master of Science. / Fall Semester, 2014. / October 1, 2014. / Food Intake, GLP-1, Lateral Septum / Includes bibliographical references. / Diana Williams, Professor Directing Thesis; Alan Spector, Committee Member; Colleen Kelley, Committee Member.

It is well known that exposure to severe stress increases the risk for developing mood disorders. Currently, the neurobiological and genetic mechanisms underlying the functional effects of psychological stress are poorly understood. Presenting a major obstacle to the study of psychological stress is the inability of current animal models of stress to distinguish between physical and psychological stressors. A novel paradigm recently developed by Warren et al., is able to tease apart the effects of physical and psychological stress in adult mice by allowing these mice to "witness," the social defeat of another mouse thus removing confounding variables associated with physical stressors. Using this ‘witness’ model of stress and RNA-Seq technology, the current study aims to study the genetic effects of psychological stress. After, witnessing the social defeat of another mouse, VTA tissue was extracted, sequenced, and analyzed for differential expression. Since genes often work together in complex networks, a pathway and gene ontology (GO) analysis was performed using data from the differential expression analysis. The pathway and GO analyzes revealed a perturbation of the glutamatergic synapse pathway and an enrichment of positive excitatory post-synaptic potential regulation. This is consistent with the excitatory synapse theory of depression. Together these findings demonstrate a dysregulation of the mesolimbic reward pathway at the gene level as a result of psychological stress potentially contributing to depressive like behaviors. / A Thesis submitted to the Department of Psychology in partial fulfillment of the requirements for the degree of Master of Science. / Fall Semester 2016. / November 21, 2016. / Pathway and GO analysis of VTA tissue after psychological stress / Includes bibliographical references. / James F. Johnson, Professor Directing Thesis; Jiang Feng, Committee Member; Michelle Arbeitman, Committee Member.

Schizophrenia is a neurological disorder associated with cognitive impairments, and clinical symptoms of hallucinations and delusions. Recent imaging and behavioral studies have repeatedly shown aberrant brain activity in the hippocampal regions in relation to episodic memory impairments associated with schizophrenia. These findings have warranted further research to elucidate the neural processes associated with episodic memory. Therefore, the current study examined activity in a priori brain regions associated with episodic memory using the face-name paired-associates fMRI task to determine whether there was reliable activation patterns observed in healthy subjects and patients with self-reported schizophrenia. This was evaluated by using ROI analysis and whole brain analysis to examine activity between subjects during a session, and by using Pearson’s R correlation coefficients to examine test-retest reliability over time. 30 schizophrenic (SZ) patients and 31 healthy control (HC) volunteers underwent a series of assessments including the fMRI behavioral task, face-name paired-associates task. The tests were conducted twice with a 14-day interval for the subjects. The results indicated no reliable brain activation in the hippocampus between scanning sessions for either the SZ or HC groups. However, distinct activation patterns were observed within sessions for both groups. These patterns were observed in the hippocampus, and regions of the frontal lobe and occipital lobe. Future studies should further explore these brain activity patterns across sessions in SZ patients compared to HC subjects to determine whether these patterns are due to pathological mechanisms associated with schizophrenia.

Calcific Aortic Valve Disease (CAVD) is the most common acquired valvular disorder in developed countries, and is estimated to affect more than 5 million Americans. In its severe form, the disease results in hemodynamically significant aortic stenosis, which causes a variety of negative physiological impacts to patients. All told, the physiological consequences of the disease mean that the heart must work harder to pump blood throughout the body, causing the heart muscle to weaken and putting patients at a significantly greater risk of cardiovascular event. However, no clinical imaging method currently available has the ability to reliably detect early CAVD, necessarily delaying diagnosis until patients are symptomatic and the disease has progressed to its late stages. Despite the extensive cost, recovery time, and heightened risk of post-surgical complications to patients, surgical approaches are often the only option for patients with aortic stenosis due to late diagnosis of the condition. The lack of diagnostic imaging techniques capable of detecting and monitoring early-stage disease is a major unmet need in the development of new treatments of CAVD. To address this problem, we have developed a novel contrast agent for MRI to aid in earlier detection of CAVD by using chemically modified and targeted superparamagnetic iron oxide nanoparticles (SPIONs) targeted to hydroxyapatite (HA). We have characterized the in vitro physiochemical and binding properties of these SPIONs as well as the selectivity of their targeted binding. We have also done work to optimize the binding and MRI contrast properties of the SPIONs. Finally, we have assessed the medically-relevant properties of the SPIONs, including their potential for toxicity and systemic effects and their binding to excised human aortic valve samples. Our results show that these HA-targeted SPIONs can be successfully fabricated via a fairly simple reaction scheme, and that they bind selectively to HA even in the presence of serum proteins. We have also determined that the reaction scheme for the addition of the poly(ethylene glycol) (PEG) is of particular importance in optimizing the MRI contrast properties of the SPIONs. Having a hydrophilic group linking the PEG to the SPIONs yields particles with the highest contrast. Additional studies indicated that these SPIONs do not have cytotoxic properties, and that they are not expected to interfere systemically with bone homeostasis, as they neither inhibit nor encourage HA nucleation and formation. We have confirmed that these particles are able to cross an endothelial barrier, and to bind to HA subsequently. Finally, we have demonstrated targeted binding of SPIONs to sites of calcification in excised human aortic valve tissue. All together, these studies indicate that these HA-targeted SPIONs are suitable for further development as an MRI contrast agent for the early detection of CAVD. / 2021-06-04T00:00:00Z

The properties of materials change in interesting ways when they are structured at the mesoscopic limit between macroscopic and molecular length scales. The mesoscopic properties of polymers in particular present a rich set of behavior because they potentially involve contributions that depend on numerous length scales such as the monomer size, persistence length of the polymer chain, the radius of gyration of polymer chains, and the average distance separating cross links between different polymer chains. It is critical to understand and leverage these size-dependent phenomena in order to realize the potential of polymers in nanotechnology applications spanning electronics, biomedicine, and soft robotics. Here, we explore a combined experimental and computational method to investigate the mechanical properties of nanoconfined polymers. At a high level this process entails seeking regions where experiments disagree with continuum models such as finite element analysis (FEA) as these identify regions where mesoscopic structuring is potentially affecting material properties. For instance, we perform nanoindentation experiments of thin films that are understood to differ from bulk experiments due to the presence of a rigid support. Thus, we compute a correction factor to account for the influence of the substrate effect using finite element analysis (FEA), and provide a path for using nanoindentation to extract the modulus of both relatively stiff glassy polymer films and soft elastomer films. Comprehensive studies of glassy polymer films found that they consistently became more compliant when confined to films thinner than 100 nm, in agreement with molecular dynamic results. However, elastomer films were observed to stiffen when thinner than 1 μm. We propose a surface crosslinking model in which the films have a crosslink density that varies with depth because of surface oxidation and find this model to be in agreement with the observed increase in modulus of elastomers. In addition to fundamental studies of polymer film mechanics, we explore the use of polymer thin films as photoactuators. In particular, composites of polydimethylsiloxane (PDMS) and carbon nanotubes (CNT) are known to physically deform when illuminated, however the mechanism of this effect is the subject of debate. We prepared thin films of PDMS-CNT composites and systematically studied their out- of-plane motion when illuminated. By constructing a FEA-based model that accurately predicts the observed actuation dynamics and magnitude based upon a photothermal mechanism, we confirm that photothermal actuation is the cause of composite motion. These results have led to both an understanding of photoactuation of PDMS-CNT thin films and an ability to optimize thin film actuators for nanolithography applications. These results have also led us to propose and test novel structured actuators for enhanced actuation efficiency. Having defined a combined experimental and computational approach for studying the mechanics of nanoconfined polymers and their photoactuation behavior, this work has provided a more general understanding of polymers and how nanoscale confinement can be leveraged to improve our utilization of soft materials. / 2020-10-31T00:00:00Z

No description available.

No description available.