10,595 research outputs found
Detecting filaments at z=3
We present the detection of a filament of Ly-alpha emitting galaxies in front
of the quasar Q1205-30 at z=3.04 based on deep narrow band imaging and
follow-up spectroscopy obtained at the ESO NTT and VLT. We argue that Ly-alpha
selection of high redshift galaxies with relatively modest amounts of observing
time allows the detection and redshift measurement of galaxies with
sufficiently high space densities that we can start to map out the large scale
structure at z=2-3 directly. Even more interesting is it that a 3D map of the
filaments will provide a new cosmological test for the value of the
cosmological constant, Omega_Lambda.Comment: 7 pages, 4 figures, contribution to the procedings of the conference
``Lighthouses of the Universe'' held in Garching (Germany), August 200
Deformations in VLBI antennas
A study is presented of deformations in antennas with the emphasis on their influence on VLBI measurements. The GIFTS structural analysis program has been used to model the VLBI antenna in Fairbanks (Alaska). The report identifies key deformations and studies the effect of gravity, wind, and temperature. Estimates of expected deformations are given
Constraints on (Omega_m,Omega_Lambda) using distributions of inclination angles for high redshift filaments
In this paper we present a scale free method to determine the cosmological
parameters (Omega_m, Omega_Lambda). The method is based on the requirement of
isotropy of the distribution of orientations of cosmological filaments. The
current structure formation paradigm predicts that the first structures to form
are voids and filaments, causing a web-like structure of the matter
distribution at high redshifts. Recent observational evidence suggests that the
threads, or filaments, of the cosmic web most easily are mapped in Ly-alpha
emission. We describe how such a 3D map can be used to constrain the
cosmological parameters in a way which, contrary to most other cosmological
tests, does not require the use of a standard rod or a standard candle. We
perform detailed simulations in order to define the optimal survey parameters
for the definition of an observing programme aimed to address this test, and to
investigate how statistical and observational errors will influence the
results. We conclude that observations should target filaments of comoving size
15-50 Mpc in the redshift range 2-4, and that each filament must be defined by
at least four Ly-alpha emitters. Detection of 20 filaments will be sufficient
to obtain a result, while 50 filaments will make it possible to place
significant new constraints on the values of Omega_m and Omega_Lambda permitted
by the current supernova observations. In a future paper we study how robust
these conclusions are to systematic velocities in the survey box.Comment: 8 pages, 6 figures, accepted for publication in A&
Simultaneous chromatic dispersion, polarization-mode-dispersion and OSNR monitoring at 40Gbit/s
A novel method for independent and simultaneous monitoring of chromatic dispersion ( CD), first-order PMD and OSNR in 40Gbit/s systems is proposed and demonstrated. This is performed using in-band tone monitoring of 5GHz, optically down-converted to a low intermediate-frequency (IF) of 10kHz. The measurement provides a large monitoring range with good accuracies for CD (4742 +/- 100ps/nm), differential group delay (DGD) (200 +/- 4ps) and OSNR (23 +/- 1dB), independently of the bit-rate. In addition, the use of electro-absorption modulators (EAM) for the simultaneous down-conversion of all channels and the use of low-speed detectors makes it cost effective for multi-channel operation. (C) 2008 Optical Society of Americ
Radiation effects in MOS integrated circuits
High energy electron irradiation effects on field effect transistors in integrated circuit device
Electronic and phononic Raman scattering in detwinned YBaCuO and YCaBaCuO: s-wave admixture to the -wave order parameter
Inelastic light (Raman) scattering has been used to study electronic
excitations and phonon anomalies in detwinned, slightly overdoped
YBaCuO and moderately overdoped
YCaBaCuO single crystals. In both samples
modifications of the electronic pair-breaking peaks when interchanging the a-
and b-axis were observed. The lineshapes of several phonon modes involving
plane and apical oxygen vibrations exhibit pronounced anisotropies with respect
to the incident and scattered light field configurations. Based on a
theoretical model that takes both electronic and phononic contributions to the
Raman spectra into account, we attribute the anisotropy of the
superconductivity-induced changes in the phonon lineshapes to a small s-wave
admixture to the pair wave-function. Our theory allows us to
disentangle the electronic Raman signal from the phononic part and to identify
corresponding interference terms. We argue that the Raman spectra are
consistent with an s-wave admixture with an upper limit of 20 percent.Comment: accepted in Phys. Rev. B, 11 page
- …