Lin S.,Miteq Inc. |
Fathy A.E.,University of Tenn
2011 IEEE 12th Annual Wireless and Microwave Technology Conference, WAMICON 2011 | Year: 2011
A 50 to 550 MHz wideband gallium nitride (GaN) HEMT power amplifier with over 20 W output power and 63% drain efficiency has been successfully developed. The demonstrated wideband power amplifier utilizes two GaN HEMTs and operates in a push-pull voltage mode Class D (VMCD). The design is based on a large signal simulation to optimize the power amplifier's output power and efficiency. To assure a wideband operation, a coaxial line impedance transformer has been used as part of the input matching network; meanwhile, a wideband a 11 ferrite loaded balun and low pass filters are utilized on the amplifier's output side instead of the conventional serial harmonic termination. © 2011 IEEE.
Masek J.G.,NASA |
Hayes D.J.,Oak Ridge National Laboratory |
Hayes D.J.,University of Tenn |
Joseph Hughes M.,University of Tenn |
And 2 more authors.
Forest Ecology and Management | Year: 2015
Sustaining forest resources requires a better understanding of forest ecosystem processes, and how management decisions and climate change may affect these processes in the future. While plot and inventory data provide our most detailed information on forest carbon, energy, and water cycling, applying this understanding to broader spatial and temporal domains requires scaling approaches. Remote sensing provides a powerful resource for "upscaling" process understanding to regional and continental domains. The increased range of available remote sensing modalities, including interferometric radar, lidar, and hyperspectral imagery, allows the retrieval of a broad range of forest attributes. This paper reviews the application of remote sensing for upscaling forest attributes from the plot scale to regional domains, with particular emphasis on how remote sensing products can support parameterization and validation of ecosystem process models. We focus on four key ecological attributes of forests: composition, structure, productivity and evapotranspiration, and disturbance dynamics. For each attribute, we discuss relevant remote sensing technologies, provide examples of their application, and critically evaluate both strengths and challenges associated with their use. © 2015 Published by Elsevier B.V.
Ziock K.-P.,Oak Ridge National Laboratory |
Ziock K.-P.,University of Tenn |
Braverman J.B.,University of Tenn |
Fabris L.,Oak Ridge National Laboratory |
Harrison M.J.,Oak Ridge National Laboratory
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012
Coded apertures were originally developed by the high-energy astrophysical community for use in imaging high-energy photons (x- and γ-rays) for which focusing optics are ineffective. We are now taking what was developed as a tool for use in the extreme far field at high energies to encode spatial information at optical wavelengths in the extreme near field to enhance the performance of position-sensitive x- and gamma-ray scintillator detectors. Spatial resolution for events within bulk scintillators is limited by the size of the light "spot" available at the sides of the scintillator, where phototransducers convert the light to an electrical signal. The ability to localize an event is determined by how well one can determine the centroid and the size of the spot. Generally, performance is limited to many millimeters in all three spatial dimensions, and one cannot resolve simultaneous events that are closer together than the width of the light spot (frequently of order 10 mm). For this reason, many applications requiring the finest spatial resolution subdivide the scintillator into tiny elements and use a digital approach to determine event location. However, that technique significantly complicates the overall instrument and sacrifices energy resolution because the light collection efficiency varies with event location within the subdivided scintillator. We are building a device that overcomes these shortcomings by using an optical coded-aperture shadow mask between a bulk crystal and a position-sensitive phototransducer. Simulations indicate that we can achieve millimeter-scale localization in all three spatial dimensions while resolving simultaneous energy depositions. The technique and progress toward its realization will be presented. © 2012 SPIE.