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In-situ monitoring of vanadium dioxide formation using high-temperature XRD

Powder Diffraction

Rodriguez, Marko A.; Bell, Nelson S.; Griego, James J.M.; Edney, Cynthia E.; Clem, Paul G.

The monoclinic-to-tetragonal phase transition (∼70 °C) in vanadium dioxide (VO2) strongly impacts the infrared properties, which enables its use in applications such as smart window devices. Synthesis of VO 2 can be challenging due to the variability of vanadium oxide phases that may be formed. We have employed high-temperature X-ray diffraction (HTXRD) to monitor the reaction process of vanadium oxide precursor powders to form the desired tetragonal VO2 phase. Single-phase tetragonal VO2 was formed within 30 min at 420 °C in flowing N2 gas (∼50 ppm O2). The monoclinic-to-tetragonal phase transformation was observed via HTXRD at ∼70 °C with the typical ∼10 °C hysteresis (i.e. approached from above or below the transition). © International Centre for Diffraction Data 2014.

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Radar-cross-section reduction of wind turbines. part 1

McDonald, Jacob J.; Brock, Billy C.; Clem, Paul G.; Paquette, Joshua P.; Patitz, Ward E.; Calkins, David C.; Loui, Hung L.

In recent years, increasing deployment of large wind-turbine farms has become an issue of growing concern for the radar community. The large radar cross section (RCS) presented by wind turbines interferes with radar operation, and the Doppler shift caused by blade rotation causes problems identifying and tracking moving targets. Each new wind-turbine farm installation must be carefully evaluated for potential disruption of radar operation for air defense, air traffic control, weather sensing, and other applications. Several approaches currently exist to minimize conflict between wind-turbine farms and radar installations, including procedural adjustments, radar upgrades, and proper choice of low-impact wind-farm sites, but each has problems with limited effectiveness or prohibitive cost. An alternative approach, heretofore not technically feasible, is to reduce the RCS of wind turbines to the extent that they can be installed near existing radar installations. This report summarizes efforts to reduce wind-turbine RCS, with a particular emphasis on the blades. The report begins with a survey of the wind-turbine RCS-reduction literature to establish a baseline for comparison. The following topics are then addressed: electromagnetic model development and validation, novel material development, integration into wind-turbine fabrication processes, integrated-absorber design, and wind-turbine RCS modeling. Related topics of interest, including alternative mitigation techniques (procedural, at-the-radar, etc.), an introduction to RCS and electromagnetic scattering, and RCS-reduction modeling techniques, can be found in a previous report.

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A Summary of the Theory and Design Team Efforts for the Sandia Metamaterials Science and Technology Grand Challenge LDRD

Basilio, Lorena I.; Brener, Igal B.; Burckel, David B.; Shaner, Eric A.; Wendt, J.R.; Luk, Ting S.; Ellis, A.R.; Bender, Daniel A.; Clem, Paul G.; Rasberry, Roger D.; Langston, William L.; Ihlefeld, Jon I.; Dirk, Shawn M.; Warne, Larry K.; Peters, D.W.; El-Kady, I.; Reinke, Charles M.; Loui, Hung L.; Williams, Jeffery T.; Sinclair, Michael B.; McCormick, Frederick B.

Abstract not provided.

Results 76–100 of 179
Results 76–100 of 179