19,902 research outputs found
A user oriented computer program for the analysis of microwave mixers, and a study of the effects of the series inductance and diode capacitance on the performance of some simple mixers
A user oriented computer program for analyzing microwave and millimeter wave mixers with a single Schottky barrier diode of known I-V and C-V characteristics is described. The program first performs a nonlinear analysis to determine the diode conductance and capacitance waveforms produced by the local oscillator. A small signal linear analysis is then used to find the conversion loss, port impedances, and input noise temperature of the mixer. Thermal noise from the series resistance of the diode and shot noise from the periodically pumped current in the diode conductance are considered. The effects of the series inductance and diode capacitance on the performance of some simple mixer circuits using a conventional Schottky diode, a Schottky diode in which there is no capacitance variation, and a Mott diode are studied. It is shown that the parametric effects of the voltage dependent capacitance of a conventional Schottky diode may be either detrimental or beneficial depending on the diode and circuit parameters
Green-Schwarz Formulation of Self-Dual Superstring
The self-dual superstring has been described previously in a
Neveu-Schwarz-Ramond formulation with local N=2 or 4 world-sheet supersymmetry.
We present a Green-Schwarz-type formulation, with manifest spacetime
supersymmetry.Comment: 11 pg., (uuencoded dvi file) ITP-SB-92-5
Processing techniques development, volume 3. Part 2: Data preprocessing and information extraction techniques
There are no author-identified significant results in this report
Swift/UVOT Photometry of the Planetary Nebula WeBo 1: Unmasking A Faint Hot Companion Star
We present an analysis of over 150 ks of data on the planetary nebula WeBo 1
(PN G135.6+01.0) obtained with the Swift Ultraviolet Optical Telescope (UVOT).
The central object of this nebula has previously been described as a late-type
K giant barium star with a possible hot companion, most likely a young
pre-white dwarf. UVOT photometry shows that while the optical photometry is
consistent with a large cool object, the near-ultraviolet (UV) photometry shows
far more UV flux than could be produced by any late-type object. Using model
stellar atmospheres and a comparison to UVOT photometry for the pre-white dwarf
PG 1159-035, we find that the companion has a temperature of at least 40,000 K
and a radius of, at most, 0.056 R_sun. While the temperature and radius are
consistent with a hot compact stellar remnant, they are lower and larger,
respectively, than expected for a typical young pre-white dwarf. This likely
indicates a deficiency in the assumed UV extinction curve. We find that higher
temperatures more consistent with expectations for a pre-white dwarf can be
derived if the foreground dust has a strong "blue bump" at 2175 AA and a lower
R_V. Our results demonstrate the ability of Swift to both uncover and
characterize hot hidden companion stars and to constrain the UV extinction
properties of foreground dust based solely on UVOT photometry.Comment: 26 pages, 9 figure, accepted to Astronomical Journa
Broadband electromagnetic response and ultrafast dynamics of few-layer epitaxial graphene
We study the broadband optical conductivity and ultrafast carrier dynamics of
epitaxial graphene in the few-layer limit. Equilibrium spectra of nominally
buffer, monolayer, and multilayer graphene exhibit significant terahertz and
near-infrared absorption, consistent with a model of intra- and interband
transitions in a dense Dirac electron plasma. Non-equilibrium terahertz
transmission changes after photoexcitation are shown to be dominated by excess
hole carriers, with a 1.2-ps mono-exponential decay that reflects the
minority-carrier recombination time.Comment: 4 pages, 3 figures, final versio
UVOT Measurements of Dust and Star Formation in the SMC and M33
When measuring star formation rates using ultraviolet light, correcting for
dust extinction is a critical step. However, with the variety of dust
extinction curves to choose from, the extinction correction is quite uncertain.
Here, we use Swift/UVOT to measure the extinction curve for star-forming
regions in the SMC and M33. We find that both the slope of the curve and the
strength of the 2175 Angstrom bump vary across both galaxies. In addition, as
part of our modeling, we derive a detailed recent star formation history for
each galaxy.Comment: 6 pages, 5 figures, conference proceedings from Swift: 10 years of
Discovery, held in Rome (2-5 Dec. 2014
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