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Sökning: WFRF:(Maaskant Koen)

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1.
  • Follette, Katherine B., et al. (författare)
  • SEEDS ADAPTIVE OPTICS IMAGING OF THE ASYMMETRIC TRANSITION DISK OPH IRS 48 IN SCATTERED LIGHT
  • 2015
  • Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 798:2
  • Tidskriftsartikel (refereegranskat)abstract
    • We present the first resolved near-infrared imagery of the transition disk Oph IRS 48 (WLY 2-48), which was recently observed with ALMA to have a strongly asymmetric submillimeter flux distribution. H-band polarized intensity images show a similar to 60 AU radius scattered light cavity with two pronounced arcs of emission, one from northeast to southeast and one smaller, fainter, and more distant arc in the northwest. K-band scattered light imagery reveals a similar morphology, but with a clear third arc along the southwestern rim of the disk cavity. This arc meets the northwestern arc at nearly a right angle, revealing the presence of a spiral arm or local surface brightness deficit in the disk, and explaining the east-west brightness asymmetry in the H-band data. We also present 0.8-5.4 mu m IRTF SpeX spectra of this object, which allow us to constrain the spectral class to A0 +/- 1 and measure a low mass accretion rate of 10(-8.5) M-circle dot yr(-1), both consistent with previous estimates. We investigate a variety of reddening laws in order to fit the multiwavelength spectral energy distribution of Oph IRS 48 and find a best fit consistent with a younger, higher luminosity star than previous estimates.
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3.
  • Iupikov, Oleg, 1983, et al. (författare)
  • A Dual-Fed PIFA Antenna Element With Nonsymmetric Impedance Matrix for High-Efficiency Doherty Transmitters: Integrated Design and OTA-Characterization
  • 2020
  • Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X. ; 68:1, s. 21-32
  • Tidskriftsartikel (refereegranskat)abstract
    • A single planar inverted F-antenna is proposed employing two input ports to optimally power-combine the output signals of two nonlinear power amplifiers inside the metal-only low-loss antenna structure. High power-added efficiency (PAE) at back-off power levels is reached through a Doherty combiner architecture, where the optimal power combination is seen to generally require the synthesis of a nonsymmetric antenna input impedance matrix. The dual-fed antenna is compact and exhibits close to single-mode radiation properties; it has a relatively stable gain pattern despite the nonequal Doherty power amplifier (PA) output powers. An integrated active prototype has been designed, fabricated, and characterized over-the-air in both an anechoic and a reverberation chamber. Good agreement is observed and an uncertainty analysis is performed. The Doherty transmitter features a max-PAE of 58 at 2.14 GHz and a 6 dB back-off PAE of 52; a minimum system power gain of 9.5 dB (max 12 dB); and a maximum system output power of 43.5 dBm.
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