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Search Results: 1 - 10 of 737 matches for " Rick Lytel "
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Dressed quantum graphs with optical nonlinearities approaching the fundamental limit
Rick Lytel,Mark G. Kuzyk
Physics , 2013, DOI: 10.1142/S0218863513500410
Abstract: We dress bare quantum graphs with finite delta function potentials and calculate optical nonlinearities that are found to match the fundamental limits set by potential optimization. We show that structures whose first hyperpolarizability is near the maximum are well described by only three states, the so-called three-level Ansatz, while structures with the largest second hyperpolarizability require four states. We analyze a very large set of configurations for graphs with quasi-quadratic energy spectra and show how they exhibit better response than bare graphs through exquisite optimization of the shape of the eigenfunctions enabled by the existence of the finite potentials. We also discover an exception to the universal scaling properties of the three-level model parameters and trace it to the observation that a greater number of levels are required to satisfy the sum rules even when the three-level Ansatz is satisfied and the first hyperpolarizability is at its maximum value, as specified by potential optimization. This exception in the universal scaling properties of nonlinear optical structures at the limit is traced to the discontinuity in the gradient of the eigenfunctions at the location of the delta potential. This is the first time that dressed quantum graphs have been devised and solved for their nonlinear response, and it is the first analytical model of a confined dynamic system with a simple potential energy that achieves the fundamental limits.
Scaling and universality in nonlinear optical quantum graphs containing star motifs
Rick Lytel,Shoresh Shafei,Mark G. Kuzyk
Physics , 2013,
Abstract: Quantum graphs have recently emerged as models of nonlinear optical, quantum confined systems with exquisite topological sensitivity and the potential for predicting structures with an intrinsic, off-resonance response approaching the fundamental limit. Loop topologies have modest responses, while bent wires have larger responses, even when the bent wire and loop geometries are identical. Topological enhancement of the nonlinear response of quantum graphs is even greater for star graphs, for which the first hyperpolarizability can exceed half the fundamental limit. In this paper, we investigate the nonlinear optical properties of quantum graphs with the star vertex topology, introduce motifs and develop new methods for computing the spectra of composite graphs. We show that this class of graphs consistently produces intrinsic optical nonlinearities near the limits predicted by potential optimization. All graphs of this type have universal behavior for the scaling of their spectra and transition moments as the nonlinearities approach the fundamental limit.
Dalgarno-Lewis perturbation theory for nonlinear optics
Sean Mossman,Rick Lytel,Mark G. Kuzyk
Physics , 2015,
Abstract: We apply the quadrature-based perturbation method of Dalgarno and Lewis to the evaluation of the nonlinear optical response of quantum systems. Through this method we derive exact expressions for the first three electronic polarizabilities by way of an operator substitution which requires only a good estimate of the ground state wave function, makes no explicit reference to the underlying Hamiltonian, and avoids complexities arising from excited state degeneracies. We apply this method to the half harmonic oscillator in one dimension and a quasi one-dimensional quantum graph to explore the effectiveness and numerical challenges of this approach. The accuracy and stability of this approach are also discussed.
Geometry-Controlled Nonlinear Optical Response of Quantum Graphs
Shoresh Shafei,Rick Lytel,Mark G. Kuzyk
Physics , 2012, DOI: 10.1364/JOSAB.29.003419
Abstract: We study for the first time the effect of the geometry of quantum wire networks on their nonlinear optical properties and show that for some geometries, the first hyperpolarizability is largely enhanced and the second hyperpolarizability is always negative or zero. We use a one-electron model with tight transverse confinement. In the limit of infinite transverse confinement, the transverse wavefunctions drop out of the hyperpolarizabilities, but their residual effects are essential to include in the sum rules. The effects of geometry are manifested in the projections of the transition moments of each wire segment onto the 2-D lab frame. Numerical optimization of the geometry of a loop leads to hyperpolarizabilities that rival the best chromophores. We suggest that a combination of geometry and quantum-confinement effects can lead to systems with ultralarge nonlinear response.
Optimization of eigenstates and spectra for quasi-linear nonlinear optical systems
Rick Lytel,Sean M. Mossman,Mark G. Kuzyk
Physics , 2015, DOI: 10.1142/S0218863515500186
Abstract: Quasi-one-dimensional quantum structures with spectra scaling faster than the square of the eigenmode number (superscaling) can generate intrinsic, off-resonant optical nonlinearities near the fundamental physical limits, independent of the details of the potential energy along the structure. The scaling of spectra is determined by the topology of the structure, while the magnitudes of the transition moments are set by the geometry of the structure. This paper presents a comprehensive study of the geometrical optimization of superscaling quasi-one-dimensional structures and provides heuristics for designing molecules to maximize intrinsic response. A main result is that designers of conjugated structures should attach short side groups at least a third of the way along the bridge, not near its end as is conventionally done. A second result is that once a side group is properly placed, additional side groups do not further enhance the response.
The influence of geometry and topology of quantum graphs on their nonlinear-optical properties
Rick Lytel,Shoresh Shafei,Julian H. Smith,Mark G. Kuzyk
Physics , 2012, DOI: 10.1103/PhysRevA.87.043824
Abstract: We analyze the nonlinear optics of quasi one-dimensional quantum graphs and manipulate their topology and geometry to generate for the first time nonlinearities in a simple system approaching the fundamental limits of the first and second hyperpolarizabilities. Changes in geometry result in smooth variations of the nonlinearities. Topological changes between geometrically-similar systems cause profound changes in the nonlinear susceptibilities that include a discontinuity due to abrupt changes in the boundary conditions. This work may inform the design of new molecules or nano- scale structures for nonlinear optics and hints at the same universal behavior for quantum graph models in nonlinear optics that is observed in other systems.
Phase disruption as a new design paradigm for optimizing the nonlinear-optical response
Rick Lytel,Sean M. Mossman,Mark G. Kuzyk
Physics , 2015,
Abstract: The intrinsic optical nonlinearities of quasi-one dimensional structures, including conjugated chain polymers and nanowires, are shown to be dramatically enhanced by the judicious placement of a side group or wire of sufficiently short length to create a large phase disruption in the dominant eigenfunctions along the main path of probability current. Phase disruption is proposed as a new general principle for the design of molecules, nanowires and any quasi-1D quantum system with large intrinsic response and does not require charge donors-acceptors at the ends.
Approaching the immunophysiology of steroid resistance
Rick Bucala
Arthritis Research & Therapy , 2012, DOI: 10.1186/ar3820
Abstract: In the current issue of Arthritis Research & Therapy, Wang and colleagues provide functional immunologic data on a molecular pathway for glucocorticoid resistance in systemic lupus erythematosus (SLE) [1]. Glucocorticoids have broad and powerful effects on the immune response and, despite the advent of biologic therapies, remain the most important and frequently used immunosuppressive agents in clinical practice [2]. Indeed, if it were not for their dose-limiting toxicity, glucocorticoids in all other respects would be ideal anti-inflammatory agents: orally absorbed, rapidly acting, and highly effective at shutting down a multitude of tissue-damaging, inflammatory pathways. Despite the clinical success of disease-modifying agents, concomitant steroid use remains an integral part of effective therapy as well as an established means for controlling disease exacerbations.Among practitioners focused on inflammatory disorders, whether rheumatologic or nonrheumatologic, there has long been the observation that some patients respond poorly to steroids or require high doses and prolonged treatment for disease control. These patients expectedly suffer most from the treatment-related complications of glucose intolerance, hypertension, obesity, osteoporosis, and myopathy. Even among patients maintained on low doses, the therapeutic objective remains the absolute minimalization or discontinuation of glucocorticoids. This goal has gained additional prominence with the recognition that accelerated atherosclerosis is an attendant consequence of systemic inflammation and a major cause of morbidity and mortality in rheumatoid arthritis and SLE [3]. The contributing effects of steroid-induced glucose intolerance and dyslipidemia add to the pathophysiology of atherogenesis and prompt continued investigation into more effective steroid-sparing agents and safer approaches to immunosuppression.Wang and colleagues provide evidence of a specific pathway for steroid resistance in patients w
Have microarrays failed to deliver for developmental biology?
Rick Livesey
Genome Biology , 2002, DOI: 10.1186/gb-2002-3-9-comment2009
Abstract: The cDNA microarray is a conceptually simple object, whether made on a glass slide within an academic lab or printed using complex technology in a commercial production setting. The best characterization of them is as glorified dot-blots (VG Cheung, personal communication), and this explains much of their appeal. Most life scientists have carried out a northern, Southern or in situ hybridization, and are therefore familiar with the main technology - hybridization - needed for microarray use. Yet it has proven difficult in some fields to translate the obvious promise of microarrays into tangible results. A pressing issue is why it appears that we are stuck in a 'proof of principle' stage, rather than a routine exploitation phase, especially in the field of developmental biology. The problem is that there have been few developmental biology microarray studies, indicating a very slow adoption of the technology in this field. Currently there appear to be two overriding concerns: access to the technology in a reliable form, and how best to apply the technology in a way that generates data that are useful in the short to medium term.Interesting and insightful developmental studies using microarrays have been published, but they are all the more striking for their infrequency. There have been several studies of Drosophila development [1,2,3], including one identifying targets of the mesoderm-specific transcription factor twist [4]. Similarly, there have been a number of genome-wide studies of worm development, almost all from the Kim lab at Stanford [5,6,7]. The situation appears more bleak when looking for published microarray studies of vertebrate development. Aside from some small-scale studies of retinal development in the mouse (including our own) [8,9] and mesoderm induction in Xenopus [10], there are very few. The predicted deluge of data has failed to materialize, and it is not immediately obvious why this is the case. Commercial arrays of worm, fly, human and mous
Tres proyectos en Arizona
ARQ (Santiago) , 2004, DOI: 10.4067/S0717-69962004005700008
Abstract: the dry air and gentle climate of certain parts of the american west made them an ideal setting for experimentation by architects like albert frey and rudolph schindler during the 20th century. various levels of relationship to the outside, innovative use of materials and new ways of handling light and shadow are some of the themes raised by these architectural incursions. the work of rick joy continues and expands upon these earlier explorations.
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