1,860 research outputs found
Mantle formation, coagulation and the origin of cloud/core-shine: II. Comparison with observations
Many dense interstellar clouds are observable in emission in the near-IR,
commonly referred to as "Cloudshine", and in the mid-IR, the so-called
"Coreshine". These C-shine observations have usually been explained with grain
growth but no model has yet been able to self-consistently explain the dust
spectral energy distribution from the near-IR to the submm. We want to
demonstrate the ability of our new core/mantle evolutionary dust model THEMIS
(The Heterogeneous dust Evolution Model at the IaS), which has been shown to be
valid in the far-IR and submm, to reproduce the C-shine observations. Our
starting point is a physically motivated core/mantle dust model. It consists of
3 dust populations: small aromatic-rich carbon grains; bigger core/mantle
grains with mantles of aromatic-rich carbon and cores either made of amorphous
aliphatic-rich carbon or amorphous silicate. We assume an evolutionary path
where these grains, when entering denser regions, may first form a second
aliphatic-rich carbon mantle (coagulation of small grains, accretion of carbon
from the gas phase), second coagulate together to form large aggregates, and
third accrete gas phase molecules coating them with an ice mantle. To compute
the corresponding dust emission and scattering, we use a 3D Monte-Carlo
radiative transfer code. We show that our global evolutionary dust modelling
approach THEMIS allows us to reproduce C-shine observations towards dense
starless clouds. Dust scattering and emission is most sensitive to the cloud
central density and to the steepness of the cloud density profile. Varying
these two parameters leads to changes, which are stronger in the near-IR, in
both the C-shine intensity and profile. With a combination of aliphatic-rich
mantle formation and low-level coagulation into aggregates, we can
self-consistently explain the observed C-shine and far-IR/submm emission
towards dense starless clouds.Comment: Paper accepted for publication in A&A with companion paper "Mantle
formation, coagulation and the origin of cloud/core-shine: I. Dust scattering
and absorption in the IR", A.P Jones, M. Koehler, N. Ysard, E. Dartois, M.
Godard, L. Gavila
Ballet des papillons = Butterfly dance : op. 69
https://digitalcommons.library.umaine.edu/mmb-vp/1277/thumbnail.jp
Towards the noise reduction of piezoelectrical-driven synthetic jet actuators
This paper details an experimental investigation aimed at reducing the noise output of piezoelectrical-driven synthetic jet actuators without compromising peak jet velocity. Specifically, the study considers double-chamber ('back-to-back') actuators for anti-phase noise suppression and corrugated-lobed orifices as a method to enhance turbulent mixing of the jets to suppress jet noise. The study involved the design, manufacture and bench test of interchangeable actuator hardware. Hot-wire anemometry and microphone recordings were employed to acquire velocity and noise measurements respectively for each chamber configuration and orifice plate across a range of excitation frequencies and for a fixed input voltage. The data analysis indicated a 32% noise reduction (20 dBA) from operating a singlechamber, circular orifice SJA to a double-chamber, corrugated-lobed orifice SJA at the Helmholtz resonant frequency. Results also showed there was a small reduction in peak jet velocity of 7% (~3 m/s) between these two cases based on orifices of the same discharge area. Finally, the electrical-to-fluidic power conversion efficiency of the double-chamber actuator was found to be 15% across all orifice designs at the resonant frequency; approximately double the efficiency of a single-chamber actuator. This work has thus demonstrated feasible gains in noise reduction and power efficiency through synthetic jet actuator design
Discovery of interstellar mercapto radicals (SH) with the GREAT instrument on SOFIA
We report the first detection of interstellar mercapto radicals, obtained
along the sight-line to the submillimeter continuum source W49N. We have used
the GREAT instrument on SOFIA to observe the 1383 GHz Doublet Pi 3/2 J = 5/2 -
3/2 lambda doublet in the upper sideband of the L1 receiver. The resultant
spectrum reveals SH absorption in material local to W49N, as well as in
foreground gas, unassociated with W49N, that is located along the sight-line.
For the foreground material at velocities in the range 37 - 44 km/s with
respect to the local standard of rest, we infer a total SH column density ~ 2.6
E+12 cm-2, corresponding to an abundance of ~ 7 E-9 relative to H2, and
yielding an SH/H2S abundance ratio ~ 0.13. The observed SH/H2S abundance ratio
is much smaller than that predicted by standard models for the production of SH
and H2S in turbulent dissipation regions and shocks, and suggests that the
endothermic neutral-neutral reaction SH + H2 -> H2S + H must be enhanced along
with the ion-neutral reactions believed to produce CH+ and SH+ in diffuse
molecular clouds.Comment: Accepted for publication in Astronomy and Astrophysics (SOFIA/GREAT
special issue
Petrology and Geochemistry of Serpentinites Associated with the Ultra-High Pressure Lago di Cignana Unit (ItalianWestern Alps)
In the Western Alps, the ophiolitic Zermatt–Saas Zone (ZSZ) and the Lago di Cignana Unit (LCU) record oceanic lithosphere subduction to high (540°C, 2·3GPa) and ultra-high pressure (600°C, 3·2GPa), respectively. The top of the Zermatt–Saas Zone in contact with the Lago di Cignana Unit consists of olivine þ Ti-clinohumite-bearing serpentinites (the Cignana serpentinite) hosting olivine þ Ti-clinohumite veins and dykelets of olivine þ Ti-chondrodite þ Ti-clinohumite. The composition of this serpentinite reveals a refertilized oceanic mantle peridotite protolith that became subsequently enriched in fluid-mobile elements (FME) during oceanic serpentinization. The olivine þ Ti-clinohumite veins in the Cignana serpentinite display Rare Earth Element (REE) and FME compositions quite similar to the host-rock, which suggests closed-system dehydration of this serpentinite during subduction. The Ti-chondrodite-bearing dykelets are richer in REE and FME than the
host-rock and the dehydration olivine þ Ti-clinohumite veins: their Nd composition points to a mafic protolith, successively overprinted by oceanic metasomatism and by subduction zone recrystallization. These dykelets are comparable in composition to eclogites within the ultra-high pressure LCU that derive from subducted oceanic mafic crust. Different from the LCU, serpentinites from the core domains of the ZSZ display REE compositions indicating a depleted mantle protolith. The oceanic serpentinization of these rocks led to an increase in FME and to seawater-like Sr isotope compositions. The serpentinites sampled at increasing distance from the ultra-high pressure LCU reveal different mantle protoliths, still preserve an oceanic geochemical imprint and contain mafic dykelets affected by oceanic metasomatism. The subduction zone history of these rocks thus occurred under relatively closed system conditions, the only possible change during subduction being an enrichment in As and Sb recorded by the serpentinites closer to the crustal LCU. The ZSZ
and Cignana serpentinites thus likely evolved in a slab setting and were weakly exposed to interaction with slab-derived fluids characteristic of plate interface settings. Our data suggest two possible scenarios for the evolution of the studied ZSZ and Cignana serpentinites. They are either part of a coherent ophiolite unit whose initial lithospheric mantle was variably affected by depletion and re-fertilization processes, or they belong to separate tectonic slices derived from two different oceanic mantle sections. In the Cignana serpentinite atop the ZSZ, the presence of Ti-chondrodite dykelets similar in composition to the LCU eclogites suggests these two domains were closely associated in the oceanic lithosphere and shared the same evolution to ultra-high pressure conditions during Alpine subduction
A Very Low Resource Language Speech Corpus for Computational Language Documentation Experiments
Most speech and language technologies are trained with massive amounts of
speech and text information. However, most of the world languages do not have
such resources or stable orthography. Systems constructed under these almost
zero resource conditions are not only promising for speech technology but also
for computational language documentation. The goal of computational language
documentation is to help field linguists to (semi-)automatically analyze and
annotate audio recordings of endangered and unwritten languages. Example tasks
are automatic phoneme discovery or lexicon discovery from the speech signal.
This paper presents a speech corpus collected during a realistic language
documentation process. It is made up of 5k speech utterances in Mboshi (Bantu
C25) aligned to French text translations. Speech transcriptions are also made
available: they correspond to a non-standard graphemic form close to the
language phonology. We present how the data was collected, cleaned and
processed and we illustrate its use through a zero-resource task: spoken term
discovery. The dataset is made available to the community for reproducible
computational language documentation experiments and their evaluation.Comment: accepted to LREC 201
High-resolution absorption spectroscopy of the OH 2Pi 3/2 ground state line
The chemical composition of the interstellar medium is determined by gas
phase chemistry, assisted by grain surface reactions, and by shock chemistry.
The aim of this study is to measure the abundance of the hydroxyl radical (OH)
in diffuse spiral arm clouds as a contribution to our understanding of the
underlying network of chemical reactions. Owing to their high critical density,
the ground states of light hydrides provide a tool to directly estimate column
densities by means of absorption spectroscopy against bright background
sources. We observed onboard the SOFIA observatory the 2Pi3/2, J = 5/2 3/2 2.5
THz line of ground-state OH in the diffuse clouds of the Carina-Sagittarius
spiral arm. OH column densities in the spiral arm clouds along the sightlines
to W49N, W51 and G34.26+0.15 were found to be of the order of 10^14 cm^-2,
which corresponds to a fractional abundance of 10^-7 to 10^-8, which is
comparable to that of H_2O. The absorption spectra of both species have similar
velocity components, and the ratio of the derived H_2O to OH column densities
ranges from 0.3 to 1.0. In W49N we also detected the corresponding line of
^18OH
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