975 research outputs found
Simulation of aromatic SOA formation using the lumping model integrated with explicit gas-phase kinetic mechanisms and aerosol-phase reactions
The Unified Partitioning-Aerosol phase Reaction (UNIPAR) model has been
developed to predict the secondary organic aerosol (SOA) formation through
multiphase reactions. The model was evaluated with aromatic SOA data produced
from the photooxidation of toluene and 1,3,5-trimethylbenzene (135-TMB) under
various concentrations of NO<sub>x</sub> and SO<sub>2</sub> using an outdoor
reactor (University of Florida Atmospheric PHotochemical Outdoor Reactor
(UF-APHOR) chamber). When inorganic species (sulfate, ammonium and water)
are present in aerosol, the prediction of both toluene SOA and 135-TMB SOA,
in which the oxygen-to-carbon (O : C) ratio is lower than 0.62, are approached
under the assumption of a complete organic/electrolyte-phase separation below
a certain relative humidity. An explicit gas-kinetic model was employed to
express gas-phase oxidation of aromatic hydrocarbons. Gas-phase products are
grouped based on their volatility (6 levels) and reactivity (5 levels) and
exploited to construct the stoichiometric coefficient (α<sub>i,j</sub>)
matrix, the set of parameters used to describe the concentrations of organic
compounds in multiphase. Weighting of the α<sub>i,j</sub> matrix as a function
of NO<sub>x</sub> improved the evaluation of NO<sub>x</sub> effects on aromatic
SOA. The total amount of organic matter (OM<sub>T</sub>) is predicted by two modules
in the UNIPAR model: OM<sub>P</sub> by a partitioning process and OM<sub>AR</sub> by
aerosol-phase reactions. The OM<sub>AR</sub> module predicts multiphase reactions of
organic compounds, such as oligomerization, acid-catalyzed reactions, and
organosulfate (OS) formation. The model reasonably simulates SOA formation
under various aerosol acidities, NO<sub>x</sub> concentrations, humidities and
temperatures. Furthermore, the OS fractions in the SOA predicted by the model
were in good agreement with the experimentally measured OS fractions
The EoR Sensitivity of the Murchison Widefield Array
Using the final 128 antenna locations of the Murchison Widefield Array (MWA),
we calculate its sensitivity to the Epoch of Reionization (EoR) power spectrum
of red- shifted 21 cm emission for a fiducial model and provide the tools to
calculate the sensitivity for any model. Our calculation takes into account
synthesis rotation, chro- matic and asymmetrical baseline effects, and excludes
modes that will be contaminated by foreground subtraction. For the fiducial
model, the MWA will be capable of a 14{\sigma} detection of the EoR signal with
one full season of observation on two fields (900 and 700 hours).Comment: 5 pages, 4 figures, 1 table, Accepted for publication in MNRAS
Letters. Supplementary material will be available in the published version,
or by contacting the author
Recommended from our members
The impact of mental health recovery narratives on recipients experiencing mental health problems: Qualitative analysis and change model.
BACKGROUND: Mental health recovery narratives are stories of recovery from mental health problems. Narratives may impact in helpful and harmful ways on those who receive them. The objective of this paper is to develop a change model identifying the range of possible impacts and how they occur. METHOD: Semi-structured interviews were conducted with adults with experience of mental health problems and recovery (n = 77). Participants were asked to share a mental health recovery narrative and to describe the impact of other people's recovery narratives on their own recovery. A change model was generated through iterative thematic analysis of transcripts. RESULTS: Change is initiated when a recipient develops a connection to a narrator or to the events descripted in their narrative. Change is mediated by the recipient recognising experiences shared with the narrator, noticing the achievements or difficulties of the narrator, learning how recovery happens, or experiencing emotional release. Helpful outcomes of receiving recovery narratives are connectedness, validation, hope, empowerment, appreciation, reference shift and stigma reduction. Harmful outcomes are a sense of inadequacy, disconnection, pessimism and burden. Impact is positively moderated by the perceived authenticity of the narrative, and can be reduced if the recipient is experiencing a crisis. CONCLUSIONS: Interventions that incorporate the use of recovery narratives, such as peer support, anti-stigma campaigns and bibliotherapy, can use the change model to maximise benefit and minimise harms from narratives. Interventions should incorporate a diverse range of narratives available through different mediums to enable a range of recipients to connect with and benefit from this material. Service providers using recovery narratives should preserve authenticity so as to maximise impact, for example by avoiding excessive editing
Ocean variability contributing to basal melt rate near the ice front of Ross Ice Shelf, Antarctica
Author Posting. © American Geophysical Union, 2014. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 119 (2014): 4214–4233, doi:10.1002/2014JC009792.Basal melting of ice shelves is an important, but poorly understood, cause of Antarctic ice sheet mass loss and freshwater production. We use data from two moorings deployed through Ross Ice Shelf, ∼6 and ∼16 km south of the ice front east of Ross Island, and numerical models to show how the basal melting rate near the ice front depends on sub-ice-shelf ocean variability. The moorings measured water velocity, conductivity, and temperature for ∼2 months starting in late November 2010. About half of the current velocity variance was due to tides, predominantly diurnal components, with the remainder due to subtidal oscillations with periods of a few days. Subtidal variability was dominated by barotropic currents that were large until mid-December and significantly reduced afterward. Subtidal currents were correlated between moorings but uncorrelated with local winds, suggesting the presence of waves or eddies that may be associated with the abrupt change in water column thickness and strong hydrographic gradients at the ice front. Estimated melt rate was ∼1.2 ± 0.5 m a−1 at each site during the deployment period, consistent with measured trends in ice surface elevation from GPS time series. The models predicted similar annual-averaged melt rates with a strong annual cycle related to seasonal provision of warm water to the ice base. These results show that accurately modeling the high spatial and temporal ocean variability close to the ice-shelf front is critical to predicting time-dependent and mean values of meltwater production and ice-shelf thinning.The Woods Hole Oceanographic
Institution (WHOI) participation in the
ANDRILL Coulman High Program was
supported by the National Science
Foundation Office of Polar Programs
(NSF ANT-0839108) through a
subcontract from the University of
Nebraska, Lincoln (UNL 25-0550-0004-004). I. Arzeno was
supported as a 2011 WHOI Summer
Student Fellow through the NSF
Research Experiences for
Undergraduates program (OCE-
0649139). L. Padman and S. Springer
were supported by NASA grant
NNX10AG19G to Earth & Space
Research (ESR). M. Williams and C.
Stewart were supported by the New
Zealand National Institute of Water
and Atmosphere (NIWA) core funding
under the National Climate Centre,
and the Ministry of Business,
Innovation, and Employment (Contract
CO5X1001).2015-01-0
A new layout optimization technique for interferometric arrays, applied to the MWA
Antenna layout is an important design consideration for radio interferometers
because it determines the quality of the snapshot point spread function (PSF,
or array beam). This is particularly true for experiments targeting the 21 cm
Epoch of Reionization signal as the quality of the foreground subtraction
depends directly on the spatial dynamic range and thus the smoothness of the
baseline distribution. Nearly all sites have constraints on where antennas can
be placed---even at the remote Australian location of the MWA (Murchison
Widefield Array) there are rock outcrops, flood zones, heritages areas,
emergency runways and trees. These exclusion areas can introduce spatial
structure into the baseline distribution that enhance the PSF sidelobes and
reduce the angular dynamic range. In this paper we present a new method of
constrained antenna placement that reduces the spatial structure in the
baseline distribution. This method not only outperforms random placement
algorithms that avoid exclusion zones, but surprisingly outperforms random
placement algorithms without constraints to provide what we believe are the
smoothest constrained baseline distributions developed to date. We use our new
algorithm to determine antenna placements for the originally planned MWA, and
present the antenna locations, baseline distribution, and snapshot PSF for this
array choice.Comment: 12 pages, 6 figures, 1 table. Accepted for publication in MNRA
Recommended from our members
Johnston Island light scattering and transmission data : a data report
The data contained in this report represents over 3000 individual scattering measurements taken in the equatorial Pacific in the vicinity of Johnston Island. The purpose of the measurements was to obtain data that would aid in the determination of a correct model for the mixing processes in the vicinity of the island. Consequently a majority of the measurements are vertical profiles of the volume scattering function accompanying standard hydrographic data of salinity, temperature, and depth
Gridded and direct Epoch of Reionisation bispectrum estimates using the Murchison Widefield Array
We apply two methods to estimate the 21~cm bispectrum from data taken within
the Epoch of Reionisation (EoR) project of the Murchison Widefield Array (MWA).
Using data acquired with the Phase II compact array allows a direct bispectrum
estimate to be undertaken on the multiple redundantly-spaced triangles of
antenna tiles, as well as an estimate based on data gridded to the -plane.
The direct and gridded bispectrum estimators are applied to 21 hours of
high-band (167--197~MHz; =6.2--7.5) data from the 2016 and 2017 observing
seasons. Analytic predictions for the bispectrum bias and variance for point
source foregrounds are derived. We compare the output of these approaches, the
foreground contribution to the signal, and future prospects for measuring the
bispectra with redundant and non-redundant arrays. We find that some triangle
configurations yield bispectrum estimates that are consistent with the expected
noise level after 10 hours, while equilateral configurations are strongly
foreground-dominated. Careful choice of triangle configurations may be made to
reduce foreground bias that hinders power spectrum estimators, and the 21~cm
bispectrum may be accessible in less time than the 21~cm power spectrum for
some wave modes, with detections in hundreds of hours.Comment: 19 pages, 10 figures, accepted for publication in PAS
- …