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We reformulate the transport equation which determines the size, shape and orientation of innnitesimal light beams in arbitrary spacetimes. The behaviour of such light beams near vertices and conjugate points is investigated, with special attention to the singular behaviour of the optical scalars. We then specialize the general transport equation to the(More)
We present a new method for reconstructing two-dimensional mass maps of galaxy clusters from the image distortion of background galaxies. In contrast to most previous approaches , which directly convert locally averaged image ellip-ticities to mass maps (direct methods), our entropy-regularized maximum-likelihood method is an inverse approach. Albeit(More)
Gravitational light deeection can distort the images of distant sources by its tidal eeects. The population of faint blue galaxies is at suuciently high redshift so that their images are distorted near foreground clusters, with giant luminous arcs being the most spectacular evidence for this eeect. Much weaker distortions, however, can observationally be(More)
We present a novel method to reconstruct the mass distribution of galaxy clusters from their gravitational lens effect on background galaxies. The method is based on a least-␹ 2 fit of the two-dimensional gravitational cluster potential. The method combines information from shear and magnification by the cluster lens and is designed to easily incorporate(More)
A new concept for tunable and reduced size microwave circuits is presented based on barium-strontium-titanate (BST) varactors. The proposed design methodology relies on substitution of quarter-wavelength transmission line segments with their equivalent low-pass structures. The ferroelectric BST-varactors are used as tuning elements and allow for a frequency(More)
We present evidence for a coherent shear signal in a field containing the z = 1.2 radio-source PKS1508−05. Since there were no intervening mass concentrations known before targeting this field, we interpret this signal as due to weak lens-ing by large-scale structure. This result is the outcome of a re-analysis of the observations of Fort et al. (1996) in(More)
Re-ionization of the intergalactic medium occurred in the early Universe at redshift z ≈ 6-11, following the formation of the first generation of stars. Those young galaxies (where the bulk of stars formed) at a cosmic age of less than about 500 million years (z ≲ 10) remain largely unexplored because they are at or beyond the sensitivity limits of existing(More)
We use the very deep and homogeneous I-band selected dataset of the FORS Deep Field (FDF) to trace the evolution of the luminosity function over the redshift range 0.5 < z < 5.0. We show that the FDF I-band selection down to IAB = 26.8 misses of the order of 10 % of the galaxies that would be detected in a K-band selected survey with magnitude limit KAB =(More)
A simple model of thin film BST varactors for the use in commercial circuit simulators is presented. The model implies the varactor's nonlinear capacitance as well as the frequency and voltage dependency of the losses. For the use of BST based components in mobile communication systems low tuning voltages are required. This leads unfortunately to high(More)
The FORS Deep Field project is a multi-colour, multi-object spectroscopic investigation of a ∼ 7 ′ × 7 ′ region near the south galactic pole based mostly on observations carried out with the FORS instruments attached to the VLT telescopes. It includes the QSO Q 0103-260 (z = 3.36). The goal of this study is to improve our understanding of the formation and(More)