67 research outputs found
Toward an internally consistent astronomical distance scale
Accurate astronomical distance determination is crucial for all fields in
astrophysics, from Galactic to cosmological scales. Despite, or perhaps because
of, significant efforts to determine accurate distances, using a wide range of
methods, tracers, and techniques, an internally consistent astronomical
distance framework has not yet been established. We review current efforts to
homogenize the Local Group's distance framework, with particular emphasis on
the potential of RR Lyrae stars as distance indicators, and attempt to extend
this in an internally consistent manner to cosmological distances. Calibration
based on Type Ia supernovae and distance determinations based on gravitational
lensing represent particularly promising approaches. We provide a positive
outlook to improvements to the status quo expected from future surveys,
missions, and facilities. Astronomical distance determination has clearly
reached maturity and near-consistency.Comment: Review article, 59 pages (4 figures); Space Science Reviews, in press
(chapter 8 of a special collection resulting from the May 2016 ISSI-BJ
workshop on Astronomical Distance Determination in the Space Age
Two-sided Grassmann-Rayleigh quotient iteration
The two-sided Rayleigh quotient iteration proposed by Ostrowski computes a
pair of corresponding left-right eigenvectors of a matrix . We propose a
Grassmannian version of this iteration, i.e., its iterates are pairs of
-dimensional subspaces instead of one-dimensional subspaces in the classical
case. The new iteration generically converges locally cubically to the pairs of
left-right -dimensional invariant subspaces of . Moreover, Grassmannian
versions of the Rayleigh quotient iteration are given for the generalized
Hermitian eigenproblem, the Hamiltonian eigenproblem and the skew-Hamiltonian
eigenproblem.Comment: The text is identical to a manuscript that was submitted for
publication on 19 April 200
Impact ionization induced negative far-infrared photoconductivity inn-GaAs
Far-infrared photoconductivity ofn-GaAs epitaxial layers showing impact ionization breakdown has been investigated by molecular lasers at photon energies below the 1s-2p shallow donor transition energy. Negative photoconductivity was observed if a magnetic field was applied to the crystals and if impact ionization of donors by the electric bias field was the dominant electron excitation mechanism. The experimental results are qualitatively explained on the basis of the generation-recombination kinetics of electrons bound to donors. Negative photoconductivity is attributed to optically induced free to bound transitions of electrons from theN=0 Landau band to donor levels shifted by the magnetic field above the low energy edge of the conduction band
Improved lateral force calibration based on the angle conversion factor in atomic force microscopy
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