James E. Raynolds

Ohmic loss in frequency-selective surfaces

The present study was undertaken in order to quantify absorption effects due to ohmic loss in frequency-selective surfaces (FSS) at infrared frequencies. The structures considered in this work act as electromagnetic filters, and as such, are of interest for use as thermophotovoltaic spectral control devices. For this application, absorption is of primary concern since it leads to reduced filter efficiency. This work focuses on the behavior of single-layer, free-standing FSS arrays comprised of circular apertures (holes) and circular loop apertures (rings). Numerical calculations of the transmission, reflection, and absorption characteristics of various arrays were carried out for wavelengths between 1 and 15 μm using a commercial finite-element software package. Absorption effects were included using measured optical properties as input parameters to a surface impedance boundary condition. Analytical techniques were then employed to determine the absorption behavior in the static limit. An interesting res...

Two-dimensional computer modeling of single junction a-Si:H solar cells

A two dimensional physically-based computer simulation of single junction pin amorphous silicon solar cells is presented using Sentaurus, Technology Computer-Aided Design (TCAD). The simulation program solves the Poisson, the continuity, and the current density equations by using a standard procedure for amorphous materials, including the continuous density of state model, Shockley-Read-Hall and Auger recombination mechanisms, and computes the generation function of electron-hole pairs from the optical parameters of each layer. The dependence of these optical parameters with the photon energy has been included, taking into account the doping level, thickness of each layer and their effect on cell efficiency. The simulator is applied to the analysis of a p-i-n single junction a-SiC:H/a-Si:H/a-Si:H solar cell, obtaining results comparable to one dimensional simulation results using AMPS (analysis of microelectronic and photonic structure)-1D. More advanced simulation models for novel solar cell devices such as tandem cells are in progress, with the aim of achieving an optimal design of solar cells based on amorphous materials or micro-/nanocrystalline layers.

Improving performance of cryogenic power electronics

Cryogenic Power Electronics (CPE) provides promising benefits for power conditioning system compared to their room-temperature counterparts in terms of reduced size and weight (increased power density), improved efficiency, improved switching speed, and improved reliability. Active devices such as semiconductor switches can exhibit performance improvements such as reduced conduction losses, higher switching speed, reduced diode reverse recovery, greater device gain, higher over-current capability, and increased power levels. Passive devices (inductors, capacitors, interconnects) will also improve by the lowered resistance of their constituent metal conductors or the use of superconductors. This paper aims to review the present status of CPE and to provide an outlook on emerging device technologies that are gaining in interest. Advanced power electronic packaging/interconnect methods that adapt well to cryogenics and help further improve system performance is discussed. Given improved and known device and interconnect properties, the system designer can develop the best circuit topologies for maximum CPE system performance.

Gate control of a quantum dot single-electron spin in realistic confining potentials: Anisotropy effects

Among recent proposals for next-generation non-charge-based logic is the notion that a single electron can be trapped and its spin can be manipulated through the application of gate potentials. In this paper, we present numerical simulations of such spins in single-electron devices for realistic (asymmetric) confining potentials in two-dimensional electrostatically confined quantum dots. Using analytical and numerical techniques we show that breaking the in-plane rotational symmetry of the confining potential leads to a significant effect on the tunability of the

Applications of Conformal Computing techniques to problems in computational physics : the Fast Fourier Transform

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Spin echo dynamics under an applied drift field in graphene nanoribbon superlattices

factor with applied gate potentials. In particular, anisotropy extends the range of tunability to larger quantum dots.

Fabry-perot opitcal switch having a saturable absorber

Abstract The techniques of Conformal Computing are introduced with an application to the Fast Fourier Transform. Conformal Computing is a design methodology, based on a rigorous mathematical foundation, which provides a systematic approach to the most efficient organization of all levels of the software and hardware design hierarchy from high-level software constructs all the way down to the design of the integrated circuits. We show that using these general design principles, without any specialized optimization, leads to portable, scalable, code that is competitive with other well-tuned machine specific routines. Further improvements are straightforward within our formalism by taking into account specific hardware details (e.g., cache loops) in a portable parametric way. We also argue that the present theory constitutes a uniform way of reasoning about physics and the data structures that define physics on computers.

Optical switch having a saturable absorber

We investigate the evolution of spin dynamics in graphene nanoribbon superlattices (GNSLs) with armchair and zigzag edges in the presence of a drift field. We determine the exact evolution operator and show that it exhibits spin echo phenomena due to rapid oscillations of the quantum states along the ribbon. The evolution of the spin polarization is accompanied by strong beating patterns. We also provide detailed analysis of the band structure of GNSLs with armchair and zigzag edges.