143 research outputs found
Some Effects of 30 Years of Weir-Management on Coastal Marsh Aquatic Vegetation and Implications to Waterfowl Management
Aquatic vegetation was compared between weir-managed and unmanaged brackish marsh ponds at Marsh Island, Louisiana, parts of which have been weir-managed since 1958. Coverage by aquatic vegetation was greater in weir-managed ponds than in unmanaged ponds, but weir-management affected individual species differently. Eleocharis parvula was more common in unmanaged ponds than in managed ponds during the early 1960s but has not occurred in any ponds sampled since then. Ceratophyllum demersum and the dominant plants Myriophyllum spicatum and Ruppia maritima were more common in weir-managed ponds than in unmanaged ponds, although the magnitude of the difference varied greatly among sample dates. Because Myriophyllum spicatum and Ruppia maritima are important and preferred duck foods in Louisiana brackish marsh, it was concluded that weir-management improved habitat quality for migrant and resident ducks at Marsh Island. Weir-managed ponds contained more aquatic vegetation than unmanaged ponds in 1988, even though the crest of weirs had lost 15 cm of elevation relative to rising sea level and the accreting marsh surface. This suggests that aquatic vegetation can be increased with a greater degree of water exchange than previously believed, which is desired to reduce interference to juvenile fish and crustacean movement. Weir-managed and unmanaged ponds did not differ in pond depth, which suggests that weir-management did not affect sedimentation
How to estimate the differential acceleration in a two-species atom interferometer to test the equivalence principle
We propose a scheme for testing the weak equivalence principle (Universality
of Free Fall) using an atom-interferometric measurement of the local
differential acceleration between two atomic species with a large mass ratio as
test masses. A apparatus in free fall can be used to track atomic free-fall
trajectories over large distances. We show how the differential acceleration
can be extracted from the interferometric signal using Bayesian statistical
estimation, even in the case of a large mass and laser wavelength difference.
We show that this statistical estimation method does not suffer from
acceleration noise of the platform and does not require repeatable experimental
conditions. We specialize our discussion to a dual potassium/rubidium
interferometer and extend our protocol with other atomic mixtures. Finally, we
discuss the performances of the UFF test developed for the free-fall (0-g)
airplane in the ICE project (\verb"http://www.ice-space.fr"
Breakdown of Temporal Coherence in Photon Condensates
The temporal coherence of an ideal Bose gas increases as the system
approaches the Bose-Einstein condensation threshold from below, with coherence
time diverging at the critical point. However, counter-examples have been
observed for condensates of photons formed in an externally pumped, dye-filled
microcavity, wherein the coherence time decreases rapidly for increasing
particle number above threshold. This paper establishes intermode correlations
as the central explanation for the experimentally observed dramatic decrease in
the coherence time beyond critical pump power.Comment: 5 pages, 4 figure
Photon-photon correlation of condensed light in a microcavity
The study of temporal coherence in a Bose-Einstein condensate of photons can
be challenging, especially in the presence of correlations between the photonic
modes. In this work, we use a microscopic, multimode model of photonic
condensation inside a dye-filled microcavity and the quantum regression
theorem, to derive an analytical expression for the equation of motion of the
photon-photon correlation function. This allows us to derive the coherence time
of the photonic modes and identify a nonmonotonic dependence of the temporal
coherence of the condensed light with the cutoff frequency of the microcavity.Comment: 12 pages, 5 figure
I.C.E.: a Transportable Atomic Inertial Sensor for Test in Microgravity
We present our the construction of an atom interferometer for inertial
sensing in microgravity, as part of the I.C.E. (\textit{Interf\'{e}rom\'{e}trie
Coh\'{e}rente pour l'Espace}) collaboration. On-board laser systems have been
developed based on fibre-optic components, which are insensitive to mechanical
vibrations and acoustic noise, have sub-MHz linewidth, and remain frequency
stabilised for weeks at a time. A compact, transportable vacuum system has been
built, and used for laser cooling and magneto-optical trapping. We will use a
mixture of quantum degenerate gases, bosonic Rb and fermionic K,
in order to find the optimal conditions for precision and sensitivity of
inertial measurements. Microgravity will be realised in parabolic flights
lasting up to 20s in an Airbus. We show that the factors limiting the
sensitivity of a long-interrogation-time atomic inertial sensor are the phase
noise in reference frequency generation for Raman-pulse atomic beam-splitters
and acceleration fluctuations during free fall
Radio Observations of the Hubble Deep Field South region: I. Survey Description and Initial Results
This paper is the first of a series describing the results of the Australia
Telescope Hubble Deep Field South (ATHDFS) radio survey. The survey was
conducted at four wavelengths - 20, 11, 6, and 3 cm, over a 4-year period, and
achieves an rms sensitivity of about 10 microJy at each wavelength. We describe
the observations and data reduction processes, and present data on radio
sources close to the centre of the HDF-S. We discuss in detail the properties
of a subset of these sources. The sources include both starburst galaxies and
galaxies powered by an active galactic nucleus, and range in redshift from 0.1
to 2.2. Some of them are characterised by unusually high radio-to-optical
luminosities, presumably caused by dust extinction.Comment: Accepted by AJ. 32 pages, 4 tables, 3 figures. PDF with
full-resolution figures is on
http://www.atnf.csiro.au/people/rnorris/N197.pd
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