Publications

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Internet Protocol version 4 (IPv4) has been a mainstay of the both the Internet and corporate networks for delivering network packets to the desired destination. However, rapid proliferation of network appliances, evolution of corporate networks, and the expanding Internet has begun to stress the limitations of the protocol. Internet Protocol version 6 (IPv6) is the replacement protocol that overcomes the constraints of IPv4. As the emerging Internet network protocol, SNL needs to prepare for its eventual deployment in international, national, customer, and local networks. Additionally, the United States Office of Management and Budget has mandated that IPv6 deployment in government network backbones occurs by 2008. This paper explores the readiness of the Sandia National Laboratories network backbone to support IPv6, the issues that must be addressed before a deployment begins, and recommends the next steps to take to comply with government mandates. The paper describes a joint work effort of the Sandia National Laboratories ASC WAN project team and members of the System Analysis & Trouble Resolution, the Communication & Network Systems, and Network System Design & Implementation Departments.

A physical model of electrode polarization is applied to dielectric (impedance) data from two poly(methoxyethoxy-ethoxy phenoxyphosphazene) systems with nearly identical chemical structures, one composed of an ionomer with a single mobile cation and the other composed of a salt-doped polymer with mobile cation and mobile anion. Quantitative comparison of the ion mobility and mobile ion concentration, based on chemical structure, is achieved. Both conductivity and ion mobility are reduced to common curves by normalizing T with T g, indicating that Tg of the polymer matrix is a major factor controlling ion diffusion. Even with the use of normalized temperature, both the mobility of ions and the mobile ion concentration in the doped polymers are ∼ 10 times larger than those in the ionomers. These factors arise from faster diffusion of the anion and the local environment surrounding ion pairs. Also, Arrhenius and VFT parameters associated with mobile ion concentration and ion mobility, respectively, reveal differences in activation energies between ionomer and doped polymer that are due to interactions between the ion pairs and polymer segments. © 2007 American Chemical Society.

The radial distribution of the measured voltage drop across a sheath formed between a 300 mm electrode and an argon plasma discharge is shown to depend on the excitation radio frequency, under constant power and pressure conditions. At a lower frequency of 13.56 MHz, the voltage drop across the sheath is uniform across the 300 mm electrode, while at higher frequencies of 60 and 162 MHz the voltage drop becomes radially nonuniform. The magnitude and spatial extent of the nonuniformity become greater with increasing frequency. © 2007 American Institute of Physics.

We developed techniques to design higher efficiency diffractive optical elements (DOEs) with large numerical apertures (NA) for quantum computing and quantum information processing. Large NA optics encompass large solid angles and thus have high collection efficiencies. Qubits in ion trap architectures are commonly addressed and read by lasers1. Large-scale ion-trap quantum computing2 will therefore require highly parallel optical interconnects. Qubit readout in these systems requires detecting fluorescence from the nearly isotropic radiation pattern of single ions, so efficient readout requires optical interconnects with high numerical aperture. Diffractive optical element fabrication is relatively mature and utilizes lithography to produce arrays compatible with large-scale ion-trap quantum computer architectures. The primary challenge of DOEs is the loss associated with diffraction efficiency. This is due to requirements for large deflection angles, which leads to extremely small feature sizes in the outer zone of the DOE. If the period of the diffractive is between λ (the free space wavelength) and 10λ, the element functions in the vector regime. DOEs in this regime, particularly between 1.5λ and 4λ, have significant coupling to unwanted diffractive orders, reducing the performance of the lens. Furthermore, the optimal depth of the zones with periods in the vector regime differs from the overall depth of the DOE. We will present results indicating the unique behaviors around the 1.5λ and 4λ periods and methods to improve the DOE performance.

We present the design and initial fabrication for a wavelength-agile, high-speed modulator that enables a long-term vision for the THz Scannerless Range Imaging (SRI) sensor. This modulator takes the place of the currently utilized SRI micro-channel plate which is limited to photocathode sensitive wavelengths (primarily in the visible and near-IR regimes). The new component is an active Resonant Subwavelength Grating (RSG). An RSG functions as an extremely narrow wavelength and angular band reflector, or mode selector. Theoretical studies predict that the infinite, laterally-extended RSG can reflect 100% of the resonant light while transmitting the balance of the other wavelengths. Previous experimental realization of these remarkable predictions has been impacted primarily by fabrication challenges. Even so, we have demonstrated large-area (1.0mm) passive RSG reflectivity as high as 100.2%, normalized to deposited gold. In this work, we transform the passive RSG design into an active laser-line modulator.

We report a synthesis of FePt nanorods by confining decomposition of Fe(CO)5 and reduction of Pt(caca)2 in surfactant reverse cylindrical micelles. The controlled nucleation and growth kinetics in confined environment allows easy control over Fe/Pt composition, nanorod uniformity, and nanorod aspect ratio. The FePt nanorods tend to self-assemble into ordered arrays along three-dimensions. Directed assembly under external magnetic field leads to two-dimensional ordered arrays, parallel to the substrate magnetic field. We expect that with optimized external magnetic fields, we should be able to assemble these nanorods into orientated one or two-dimensional arrays, providing a uniform anisotropic magnetic platform for varied applications in enhanced data storage, magneto-electron transport, etc. Copyright © 2007 American Chemical Society.

Small platinum clusters have been prepared in zeolite hosts through ion exchange and controlled calcination/reduction processes. In order to enable electrochemical application, the pores of the Pt-zeolite were filled with electrically conductive carbon via infiltration with carbon precursors, polymerization, and pyrolysis. The zeolite host was then removed by acid washing, to leave a Pt/C electrocatalyst possessing quasi-zeolitic porosity and Pt clusters of well-controlled size. The electrocatalysts were characterized by TEM, XRD, EXAFS, nitrogen adsorption and electrochemical techniques. Depending on the synthesis conditions, average Pt cluster sizes in the Pt/C catalysts ranged from 1.3 to 2.0 nm. The presence of ordered porosity/structure in the catalysts was evident in TEM images as lattice fringes, and in XRD as a low-angle diffraction peak with d-spacing similar to the parent zeolite. The catalysts possess micro- and meso-porosity, with pore size distributions that depend upon synthesis variables. Finally, electroactive surface areas as high as 112 m² g_Pt^-1 have been achieved in Pt/C electrocatalysts which show oxygen reduction performance comparable to standard industrial catalysts.

We have numerically compared the performance of various designs for the core refractive-index (RI) and rare-earth-dopant distributions of large-mode-area fibers for use in bend-loss-filtered, high-power amplifiers. We first established quantitative targets for the key parameters that determine fiber-amplifier performance, including effective LP01 modal area (Aeff, both straight and coiled), bend sensitivity (for handling and packaging), high-order mode discrimination, mode-field displacement upon coiling, and index contrast (manufacturability). We compared design families based on various power-law and hybrid profiles for the RI and evaluated confined rare-earth doping for hybrid profiles. Step-index fibers with straight-fiber Aeff values > 1000 μm2 exhibit large decreases in Aeff and transverse mode-field displacements upon coiling, in agreement with recent calculations of Hadley et al. [Proc. of SPIE, Vol. 6102, 61021S (2006)] and Fini [Opt. Exp. 14, 69 (2006)]. Triangular-profile fibers substantially mitigate these effects, but suffer from excessive bend sensitivity at Aeff values of interest. Square-law (parabolic) profile fibers are free of modal distortion but are hampered by high bend sensitivity (although to a lesser degree than triangular profiles) and exhibit the largest mode displacements. We find that hybrid (combined power-law) profiles provide some decoupling of these tradeoffs and allow all design goals to be achieved simultaneously. We present optimized fiber designs based on this analysis.

Probability of Detection (POD) studies are typically conducted on EDM notches, "manufactured" crack specimens, or actual in-service crack specimens. The purpose of this paper is the education of the aerospace community in the subtle differences and benefits of using each specimen type. Data from previous POD studies are compared to data from teardown of a retired passenger aircraft, resulting in POD data from in-situ defects. Analysis of this data reveals similarities and differences between signals for four (4) types of specimens and four (4) nondestructive inspection (NDI) methods. Additionally, the paper provides an awareness of the assumptions used in each type of POD study, and potential consequences of violating such assumptions. © 2007 American Institute of Physics.

Sandia National Laboratories Airworthiness Assurance Nondestructive Inspection Validation Center (AANC) implemented two crack probability of detection (POD) experiments to compare in a quantitative manner the ability of Sonic Infrared (IR) Imaging and fluorescent penetrant inspection (FPI) to reliably detect cracks. Blind Sonic IR and FPI inspections were performed on titanium and Inconel® specimens having statistically relevant flaw profiles. Inspector hit/miss data was collected and POD curves for each technique were generated and compared. In addition, the crack lengths for a number of titanium and Inconel® reference standards were measured before and after repeated Sonic IR inspections to determine if crack growth occurred. © 2007 American Institute of Physics.

This is a pretty pretentious title, but I promised that I would write something autobiographical in this space, and I will do that. However, first I want to thank everyone who contributed to the Festschrift. When Stephen Klippenstein told me that he and Craig Taatjes had gotten approval for it (against my advice), I envisioned a situation where the issue had only two papers, both co-authored by Stephen. Luckily that turned out not to be the case. At the time of this writing there are forty-three manuscripts at various stages of review. I am extremely grateful to Craig and Stephen, to the editors of the journal, and to all the authors for the tribute. It is far and away the most flattering thing that anyone has ever done for me in my career.