21,129 research outputs found
Optical Turbulence Measurements and Models for Mount John University Observatory
Site measurements were collected at Mount John University Observatory in 2005
and 2007 using a purpose-built scintillation detection and ranging system.
profiling indicates a weak layer located at 12 - 14 km above sea
level and strong low altitude turbulence extending up to 5 km. During calm
weather conditions, an additional layer was detected at 6 - 8 km above sea
level. profiling suggests that tropopause layer velocities are nominally
12 - 30 m/s, and near-ground velocities range between 2 -- 20 m/s, dependent on
weather. Little seasonal variation was detected in either and
profiles. The average coherence length, , was found to be cm for
the full profile at a wavelength of 589 nm. The average isoplanatic angle,
, was arcsec. The mean turbulence altitude,
, was found to be km above sea level. No average in the
Greenwood frequency, , could be established due to the gaps present in the
\vw\s profiles obtained. A modified Hufnagel-Valley model was developed to
describe the profiles at Mount John, which estimates at 6 cm
and at 0.9 arcsec. A series of models were developed, based
on the Greenwood wind model with an additional peak located at low altitudes.
Using the model and the suggested model for moderate ground
wind speeds, is estimated at 79 Hz.Comment: 14 pages; accepted for publication in PAS
Factors affecting consistency and accuracy in identifying modern macroperforate planktonic foraminifera
Planktonic foraminifera are widely used in biostratigraphic, palaeoceanographic and evolutionary studies, but the strength of many study conclusions could be weakened if taxonomic identifications are not reproducible by different workers. In this study, to assess the relative importance of a range of possible reasons for among-worker disagreement in identification, 100 specimens of 26 species of macroperforate planktonic foraminifera were selected from a core-top site in the subtropical Pacific Ocean. Twenty-three scientists at different career stages – including some with only a few days experience of planktonic foraminifera – were asked to identify each specimen to species level, and to indicate their confidence in each identification. The participants were provided with a species list and had access to additional reference materials. We use generalised linear mixed-effects models to test the relevance of three sets of factors in identification accuracy: participant-level characteristics (including experience), species-level characteristics (including a participant’s knowledge of the species) and specimen-level characteristics (size, confidence in identification). The 19 less experienced scientists achieve a median accuracy of 57 %, which rises to 75 % for specimens they are confident in. For the 4 most experienced participants, overall accuracy is 79 %, rising to 93 % when they are confident. To obtain maximum comparability and ease of analysis, everyone used a standard microscope with only 35× magnification, and each specimen was studied in isolation. Consequently, these data provide a lower limit for an estimate of consistency. Importantly, participants could largely predict whether their identifications were correct or incorrect: their own assessments of specimen-level confidence and of their previous knowledge of species concepts were the strongest predictors of accuracy
Detection/estimation of the modulus of a vector. Application to point source detection in polarization data
Given a set of images, whose pixel values can be considered as the components
of a vector, it is interesting to estimate the modulus of such a vector in some
localised areas corresponding to a compact signal. For instance, the
detection/estimation of a polarized signal in compact sources immersed in a
background is relevant in some fields like astrophysics. We develop two
different techniques, one based on the Neyman-Pearson lemma, the Neyman-Pearson
filter (NPF), and another based on prefiltering-before-fusion, the filtered
fusion (FF), to deal with the problem of detection of the source and estimation
of the polarization given two or three images corresponding to the different
components of polarization (two for linear polarization, three including
circular polarization). For the case of linear polarization, we have performed
numerical simulations on two-dimensional patches to test these filters
following two different approaches (a blind and a non-blind detection),
considering extragalactic point sources immersed in cosmic microwave background
(CMB) and non-stationary noise with the conditions of the 70 GHz \emph{Planck}
channel. The FF outperforms the NPF, especially for low fluxes. We can detect
with the FF extragalactic sources in a high noise zone with fluxes >=
(0.42,0.36) Jy for (blind/non-blind) detection and in a low noise zone with
fluxes >= (0.22,0.18) Jy for (blind/non-blind) detection with low errors in the
estimated flux and position.Comment: 11 pages, 5 figure
An adaptive stereo basis method for convolutive blind audio source separation
NOTICE: this is the author’s version of a work that was accepted for publication in Neurocomputing. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in PUBLICATION, [71, 10-12, June 2008] DOI:neucom.2007.08.02
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