8,589 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
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
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&
The strength of the radial-breathing mode in single-walled carbon nanotubes
We show by ab initio calculations that the electron-phonon coupling matrix
element M of the radial breathing mode in single-walled carbon nanotubes
depends strongly on tube chirality. For nanotubes of the same diameter the
coupling strength |M|^2 is up to one order of magnitude stronger for zig-zag
than for armchair tubes. For (n,m) tubes M depends on the value of (n-m) mod 3,
which allows to discriminate semiconducting nano tubes with similar diameter by
their Raman scattering intensity. We show measured resonance Raman profiles of
the radial breathing mode which support our theoretical predictions
Integrated nitrogen input systems in Denmark
Cycling of N in agriculture through the use of mineral fertilizers, manures and N-fixing crops gives rise to many forms of N emissions to the environment, including nitrate (NO3) leaching, ammonia (NH3) volatilization and nitrous oxide (N2O) emissions, resulting in ground water pollution, eutrophication of surface waters, soil acidification and contributions to global warming. The high rates of N input in intensive North European agricultural systems have given rise to high loss rates, and the focus in Danish agriculture during the past two decades has been on increasing the N use efficiency with the aim of reducing losses. The N use efficiency at the system level can be increased by improved handling of manure, targeted application of fertilizers and manures, and through adjustments of the crop rotation
Pure-state quantum trajectories for general non-Markovian systems do not exist
Since the first derivation of non-Markovian stochastic Schr\"odinger
equations, their interpretation has been contentious. In a recent Letter [Phys.
Rev. Lett. 100, 080401 (2008)], Di\'osi claimed to prove that they generate
"true single system trajectories [conditioned on] continuous measurement". In
this Letter we show that his proof is fundamentally flawed: the solution to his
non-Markovian stochastic Schr\"odinger equation at any particular time can be
interpreted as a conditioned state, but joining up these solutions as a
trajectory creates a fiction.Comment: 4 page
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