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Search Results: 1 - 10 of 95385 matches for " George W. Hanson "
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Dyadic Green's Functions and Guided Surface Waves for a Surface Conductivity Model of Graphene
George W. Hanson
Physics , 2007, DOI: 10.1063/1.2891452
Abstract: An exact solution is obtained for the electromagnetic field due to an electric current in the presence of a surface conductivity model of graphene. The graphene is represented by an infinitesimally-thin, local and isotropic two-sided conductivity surface. The field is obtained in terms of dyadic Green's functions represented as Sommerfeld integrals. The solution of plane-wave reflection and transmission is presented, and surface wave propagation along graphene is studied via the poles of the Sommerfeld integrals. For isolated graphene characterized by complex surface conductivity, a proper transverse-electric (TE) surface wave exists if and only if the imaginary part of conductivity is positive (associated with interband conductivity), and a proper transverse-magnetic (TM) surface wave exists when the imaginary part of conductivity is negative (associated with intraband conductivity). By tuning the chemical potential at infrared frequencies, the sign of the imaginary part of conductivity can be varied, allowing for some control over surface wave properties.
Soft-boundary graphene nanoribbon formed by a graphene sheet above a perturbed ground plane: conductivity profile and SPP modal current distribution
Ebrahim Forati,George W. Hanson
Physics , 2013, DOI: 10.1088/2040-8978/15/11/114006
Abstract: An infinite sheet of graphene lying above a perturbed ground plane is studied. The perturbation is a two dimensional ridge, and a bias voltage is applied between the graphene and the ground plane, resulting in a graphene nanoribbonlike structure with a soft-boundary (SB) The spatial distribution of the graphene conductivity forming the soft-boundary is studied as a function of the ridge parameters and the bias voltage. The current distribution of the fundamental TM surface plasmon polariton (SPP) is considered. The effect of the ridge parameters and shape of the soft boundary on the current distributions are investigated, and the conditions are studied under which the mode remains confined to the vicinity of the ridge region.
Surface plasmon polaritons on soft-boundary graphene nanoribbons and their application as voltage controlled plasmonic switches and frequency demultiplexers
Ebrahim Forati,George W. Hanson
Physics , 2013, DOI: 10.1063/1.4822044
Abstract: A graphene sheet gated with a ridged ground plane, creating a soft-boundary (SB) graphene nanoribbon, is considered. By adjusting the ridge parameters and bias voltage a channel can be created on the graphene which can guide TM surface plasmon polaritons (SPP). Two types of modes are found; fundemental and higher-order modes with no apparent cutoff frequency and with energy distributed over the created channel, and edge modes with energy concen-trated at the soft-boundary edge. Dispersion curves, electric near-field patterns, and current distributions of these modes are determined. Since the location where energy is concentrated in the edge modes can be easily controlled electronically by the bias voltage and frequency, the edge-mode phenomena is used to propose a novel voltage controlled plasmonic switch and a plasmonic frequency demultiplexer.
Graphene as a tunable THz reservoir for shaping the Mollow triplet of an artificial atom via plasmonic effects
Ebrahim Forati,George W. Hanson,Stephen Hughes
Physics , 2014, DOI: 10.1103/PhysRevB.90.085414
Abstract: Using a realistic quantum master equation we show that the resonance fluorescence spectra of a two-level artificial atom (quantum dot) can be tuned by adjusting its photonic local density of states via biasing of one or more graphene monolayers. The structured photon reservoir is included using a photon Green function theory which fully accounts for the loss and dispersion. The field-driven Mollow triplet spectrum can be actively controlled by the graphene bias in the THz frequency regime. We also consider the effect of a dielectric support environment, and multiple graphene layers, on the emitted fluorescence. Finally, thermal bath effects are considered and shown to be important for low THz frequencies.
A planar hyperlens based on a modulated graphene monolayer
Ebrahim Forati,George W. Hanson,Alexander B. Yakovlev,Andrea Alu
Physics , 2013, DOI: 10.1103/PhysRevB.89.081410
Abstract: The canalization of terahertz surface plasmon polaritons using a modulated graphene monolayer is investigated for subwavelength imaging. An anisotropic surface conductivity formed by a set of parallel nanoribbons with alternating positive and negative imaginary conductivities is used to realize the canalization regime required for hyperlensing. The ribbons are narrow compared to the wavelength, and are created electronically by gating a graphene layer over a corrugated ground plane. Good quality canalization of surface plasmon polaritons is shown in the terahertz even in the presence of realistic loss in graphene, with relevant implications for subwavelength imaging applications.
Quantum plasmonic excitation in graphene and robust-to-loss propagation
George W. Hanson,S. A. Hassani Gangaraj,Changhyoup Lee,Dimitris G. Angelakis,Mark Tame
Physics , 2015, DOI: 10.1103/PhysRevA.92.013828
Abstract: We investigate the excitation of quantum plasmonic states of light in graphene using end-fire and prism coupling. In order to model the excitation process quantum mechanically we quantize the transverse-electric and transverse-magnetic surface plasmon polariton (SPP) modes in graphene. A selection of regimes are then studied that enable the excitation of SPPs by photons and we show that efficient coupling of photons to graphene SPPs is possible at the quantum level. Futhermore, we study the excitation of quantum states and their propagation under the effects of loss induced from the electronic degrees of freedom in the graphene. Here, we investigate whether it is possible to protect quantum information using quantum error correction techniques. We find that these techniques provide a robust-to-loss method for transferring quantum states of light in graphene over large distances.
Transient and steady-state entanglement mediated by three-dimensional plasmonic waveguides
S. Ali Hassani Gangaraj,Andrei Nemilentsau,George W. Hanson,Stephen Hughes
Physics , 2015, DOI: 10.1364/OE.23.022330
Abstract: Entanglement between two qubits (two level atoms) mediated by surface plasmons in three-dimensional plasmonic waveguides is studied using a quantum master equation formalism. Two types of waveguides, a nanowire and a V-shaped channel cut in a flat metal plane, are considered. The Green functions for the waveguides, which rigorously describes the dissipative qubit environment, are calculated numerically using a direct finite-difference time-domain (FDTD) solution of Maxwell's equations. Finite-length effects are shown to play a crucial role in enhancing entanglement, and resonant-length plasmonic waveguides can provide higher entanglement between qubits than infinite-length waveguides. It is also shown that coupling slots can improve entanglement via stronger qubit-waveguide coupling, for both the infinite- and finite-waveguide cases.
Black Phosphorus and Two-Dimensional Hyperbolic Materials: Tunable Surface Plasmons, Green Function and Complex-Plane Analysis
S. Ali Hassani Gangaraj,Tony Low,Andrei Nemilentsau,George W. Hanson
Physics , 2015,
Abstract: We study the electromagnetic response of twoand quasi-two-dimensional hyperbolic materials, on which a simple dipole source can excite a well-confined and tunable surface plasmon polariton (SPP). The analysis is based on the Green function for an anisotropic two-dimensional surface, which nominally requires the evaluation of a two-dimensional Sommerfeld integral. We show that for the SPP contribution this integral can be evaluated efficiently in a mixed continuousdiscrete form as a continuous spectrum contribution (branch cut integral) of a residue term, in distinction to the isotropic case, where the SPP is simply given as a discrete residue term. The regime of strong SPP excitation is discussed, and complex-plane singularities are identified, leading to physical insight into the excited SPP. Examples are presented using graphene strips to form a hyperbolic metasurface, and thin-film black phosphorus (BP). The green function and complex-plane analysis developed allows for the exploration of hyperbolic plasmons in general 2D materials.
Global burden of trauma: Need for effective fracture therapies
Mathew George,Hanson Beate
Indian Journal of Orthopaedics , 2009,
Abstract: Orthopedic trauma care and fracture management have advanced significantly over the last 50 years. New developments in the biology and biomechanics of the musculoskeletal system, fixation devices, and soft tissue management have greatly influenced our ability to care for musculoskeletal injuries. Many therapies and treatment modalities have the potential to transform future orthopedic treatment by decreasing invasive procedures and providing shorter healing times. Promising results in experimental models have led to an increase in clinical application of these therapies in human subjects. However, for many modalities, precise clinical indications, timing, dosage, and mode of action still need to be clearly defined. In order to further develop fracture management strategies, predict outcomes and improve clinical application of newer technologies, further research studies are needed. Together with evolving new therapies, the strategies to improve fracture care should focus on cost effectiveness. This is a great opportunity for the global orthopedic community, in association with other stakeholders, to address the many barriers to the delivery of safe, timely, and effective care for patients with musculoskeletal injuries in developing countries.
Do clinical guidelines reduce clinician dependent costs?
George Kosimbei, Kara Hanson, Mike English
Health Research Policy and Systems , 2011, DOI: 10.1186/1478-4505-9-24
Abstract: Globally, health care expenditures have increased tremendously in the last decade raising concerns over their sustainability[1-4]and value for money. This increased investment is being made by both households and governments and represents a potential pool of resources that could be used elsewhere in the economy[2,4]. Such an increase in expenditure if resulting in improved health status would appear to be justified. However, there are concerns that extra spending on health is not yielding the anticipated health returns[1,5,6]. Therefore, there is an increasing interest in maximizing the efficiency of health care spending while at the same time increasing the effectiveness of service provision. One commonly used approach to improving the effectiveness of health care is to develop guidelines for the health care workers based on the best available evidence of what works[7-9]. Often such guidelines aim to improve outcomes through use of optimal treatment approaches and to reduce or limit costs by therapies or procedures. The degree to which guidelines work to change practices depends usually on the extent to which health workers change their behaviour in response to the guidelines as suggested in the Grimshaw 2004 review[7].The cost consequence of such interventions has received less attention in the literature. The degree to which costs can be expected to change in response to clinical guideline adoption will depend on both the responsiveness of health worker behaviour, and on the share of patient costs that are attributable to decisions made by health workers. We have coined the term "clinician-dependent costs"to describe the costs of care that are under the discretion of the healthcare provider. These costs include the costs of drugs, tests and investigations, and discretionary outpatient visits and inpatient stays. Changes in CDCs may arise from interventions such as clinical guidelines that aim to alter health workers use of available resources. We are therefore i
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