59 research outputs found
A Rapid Assessment of Coral Reefs Near Hopetown, Abaco Islands, Bahamas (Stony Corals and Algae)
Coral reefs at 13 sites ranging in depth from 1-16 m near Hopetown, Abaco Islands, Bahamas were surveyed utilizing the Atlantic and Gulf Rapid Reef Assessment (AGRRA) benthos protocol. A total of 35 species of scleractinian corals and 2 species of calcareous hydrocorals were observed. The overall coral cover averaged just over 14%. Among corals that were at least 10 cm in diameter, small colonies (\u3c 40 cm diameter) predominated in all sites except for the Fowl Cay pinnacles where 68% were larger than 60 cm in diameter. Large colonies (\u3e 40 cm diameter) were also found in the Lynyard Cay spur-and-groove formations and the Sandy Cay fore reef. Zero-4% of the colonies were affected by disease. Total (recent + old) partial-colony mortality ranged from 9-31% (both extreme values being found in outer reef crests). Turf algae were the most common algal functional group overall. Macroalgae were ubiquitous, however, with relative abundance values of about 25-47%. Macroalgal indices (a proxy for biomass) ranged from 64 in the Sandy Cay back reef to 184 in the Fowl Cay outer reef crest
JWST MIRI flight performance: The Medium-Resolution Spectrometer
The Medium-Resolution Spectrometer (MRS) provides one of the four operating
modes of the Mid-Infrared Instrument (MIRI) on board the James Webb Space
Telescope (JWST). The MRS is an integral field spectrometer, measuring the
spatial and spectral distributions of light across the 5-28 wavelength
range with a spectral resolving power between 3700-1300. We present the MRS's
optical, spectral, and spectro-photometric performance, as achieved in flight,
and we report on the effects that limit the instrument's ultimate sensitivity.
The MRS flight performance has been quantified using observations of stars,
planetary nebulae, and planets in our Solar System. The precision and accuracy
of this calibration was checked against celestial calibrators with well-known
flux levels and spectral features. We find that the MRS geometric calibration
has a distortion solution accuracy relative to the commanded position of 8 mas
at 5 and 23 mas at 28 . The wavelength calibration is accurate
to within 9 km/sec at 5 and 27 km/sec at 28 . The uncertainty in
the absolute spectro-photometric calibration accuracy was estimated at 5.6 +-
0.7 %. The MIRI calibration pipeline is able to suppress the amplitude of
spectral fringes to below 1.5 % for both extended and point sources across the
entire wavelength range. The MRS point spread function (PSF) is 60 % broader
than the diffraction limit along its long axis at 5 and is 15 % broader
at 28 . The MRS flight performance is found to be better than prelaunch
expectations. The MRS is one of the most subscribed observing modes of JWST and
is yielding many high-profile publications. It is currently humanity's most
powerful instrument for measuring the mid-infrared spectra of celestial sources
and is expected to continue as such for many years to come.Comment: 16 pages, 21 figure
JWST MIRI/MRS in-flight absolute flux calibration and tailored fringe correction for unresolved sources
Context. The Medium Resolution Spectrometer (MRS) is one of the four observing modes of JWST/MIRI. Using JWST in-flight data of unresolved (point) sources, we can derive the MRS absolute spectral response function (ASRF) starting from raw data. Spectral fringing, caused by coherent reflections inside the detector arrays, plays a critical role in the derivation and interpretation of the MRS ASRF. The fringe corrections implemented in the current pipeline are not optimal for non-extended sources, and a high density of molecular features particularly inhibits an accurate correction. Aims. In this paper, we present an alternative way to calibrate the MIRI/MRS data. Firstly, we derive a fringe correction that accounts for the dependence of the fringe properties on the MIRI/MRS pupil illumination and detector pixel sampling of the point spread function. Secondly, we derive the MRS ASRF using an absolute flux calibrator observed across the full 5- 28 \ub5m wavelength range of the MRS. Thirdly, we apply the new ASRF to the spectrum of a G dwarf and compare it with the output of the JWST/MIRI default data reduction pipeline. Finally, we examine the impact of the different fringe corrections on the detectability of molecular features in the G dwarf and K giant. Methods. The absolute flux calibrator HD 163466 (A-star) was used to derive tailored point source fringe flats at each of the default dither locations of the MRS. The fringe-corrected point source integrated spectrum of HD 163466 was used to derive the MRS ASRF using a theoretical model for the stellar continuum. A cross-correlation was run to quantify the uncertainty on the detection of CO, SiO, and OH in the K giant and CO in the G dwarf for different fringe corrections. Results. The point-source-tailored fringe correction and ASRF are found to perform at the same level as the current corrections, beating down the fringe contrast to the sub-percent level in the G dwarf in the longer wavelengths, whilst mitigating the alteration of real molecular features. The same tailored solutions can be applied to other MRS unresolved targets. Target acquisition is required to ensure the pointing is accurate enough to apply this method. A pointing repeatability issue in the MRS limits the effectiveness of the tailored fringe flats is at short wavelengths. Finally, resulting spectra require no scaling to make the sub-bands match, and a dichroic spectral leak at 12.2 \ub5m is removed
Novel Roles of Formin mDia2 in Lamellipodia and Filopodia Formation in Motile Cells
Actin polymerization-driven protrusion of the leading edge is a key element of cell motility. The important actin nucleators formins and the Arp2/3 complex are believed to have nonoverlapping functions in inducing actin filament bundles in filopodia and dendritic networks in lamellipodia, respectively. We tested this idea by investigating the role of mDia2 formin in leading-edge protrusion by loss-of-function and gain-of-function approaches. Unexpectedly, mDia2 depletion by short interfering RNA (siRNA) severely inhibited lamellipodia. Structural analysis of the actin network in the few remaining lamellipodia suggested an mDia2 role in generation of long filaments. Consistently, constitutively active mDia2 (ΔGBD-mDia2) induced accumulation of long actin filaments in lamellipodia and increased persistence of lamellipodial protrusion. Depletion of mDia2 also inhibited filopodia, whereas expression of ΔGBD-mDia2 promoted their formation. Correlative light and electron microscopy showed that ΔGBD-mDia2–induced filopodia were formed from lamellipodial network through gradual convergence of long lamellipodial filaments into bundles. Efficient filopodia induction required mDia2 targeting to the membrane, likely through a scaffolding protein Abi1. Furthermore, mDia2 and Abi1 interacted through the N-terminal regulatory sequences of mDia2 and the SH3-containing Abi1 sequences. We propose that mDia2 plays an important role in formation of lamellipodia by nucleating and/or protecting from capping lamellipodial actin filaments, which subsequently exhibit high tendency to converge into filopodia
The long coiled-coil protein NECC2 is associated to caveolae and modulates NGF/TrkA signaling in PC12 cells [corrected].
TrkA-mediated NGF signaling in PC12 cells has been shown to be compartimentalized in specialized microdomains of the plasma membrane, the caveolae, which are organized by scaffold proteins including the member of the caveolin family of proteins, caveolin-1. Here, we characterize the intracellular distribution as well as the biochemical and functional properties of the neuroendocrine long coiled-coil protein 2 (NECC2), a novel long coiled-coil protein selectively expressed in neuroendocrine tissues that contains a predicted caveolin-binding domain and displays structural characteristics of a scaffolding factor. NECC2 distributes in caveolae, wherein it colocalizes with the TrkA receptor, and behaves as a caveolae-associated protein in neuroendocrine PC12 cells. In addition, stimulation of PC12 cells with nerve growth factor (NGF) increased the expression and regulated the distribution of NECC2. Interestingly, knockdown as well as overexpression of NECC2 resulted in a reduction of NGF-induced phosphorylation of the TrkA downstream effector extracellular signal-regulated kinases 1 and 2 (ERK1/ERK2) but not of Akt. Altogether, our results identify NECC2 as a novel component of caveolae in PC12 cells and support the contribution of this protein in the maintenance of TrkA-mediated NGF signaling.journal articleresearch support, non-u.s. gov't20132013 09 06importe
MINDS. Abundant water and varying C/O across the disk of Sz 98 as seen by JWST/MIRI
MIRI/MRS on board the JWST allows us to probe the inner regions of
protoplanetary disks. Here we examine the disk around the classical T Tauri
star Sz 98, which has an unusually large dust disk in the millimetre with a
compact core. We focus on the HO emission through both its ro-vibrational
and pure rotational emission. Furthermore, we compare our chemical findings
with those obtained for the outer disk from Atacama Large
Millimeter/submillimeter Array (ALMA) observations. In order to model the
molecular features in the spectrum, the continuum was subtracted and LTE slab
models were fitted. The spectrum was divided into different wavelength regions
corresponding to HO lines of different excitation conditions, and the slab
model fits were performed individually per region. We confidently detect CO,
HO, OH, CO, and HCN in the emitting layers. The isotopologue
HO is not detected. Additionally, no other organics, including
CH, are detected. This indicates that the C/O ratio could be
substantially below unity, in contrast with the outer disk. The HO emission
traces a large radial disk surface region, as evidenced by the gradually
changing excitation temperatures and emitting radii. The OH and CO emission
are relatively weak. It is likely that HO is not significantly
photodissociated; either due to self-shielding against the stellar irradiation,
or UV-shielding from small dust particles. The relative emitting strength of
the different identified molecular features point towards UV-shielding of
HO in the inner disk of Sz 98, with a thin layer of OH on top. The majority
of the organic molecules are either hidden below the dust continuum, or not
present. In general, the inferred composition points to a sub-solar C/O ratio
(<0.5) in the inner disk, in contrast with the larger than unity C/O ratio in
the gas in the outer disk found with ALMA.Comment: Submitted to A&A on May 25 2023. 18 pages, 11 figure
MINDS. The detection of CO with JWST-MIRI indicates abundant CO in a protoplanetary disk
We present JWST-MIRI MRS spectra of the protoplanetary disk around the
low-mass T Tauri star GW Lup from the MIRI mid-INfrared Disk Survey (MINDS) GTO
program. Emission from CO, CO, HO, HCN,
CH, and OH is identified with CO being detected for
the first time in a protoplanetary disk. We characterize the chemical and
physical conditions in the inner few au of the GW Lup disk using these
molecules as probes. The spectral resolution of JWST-MIRI MRS paired with high
signal-to-noise data is essential to identify these species and determine their
column densities and temperatures. The -branches of these molecules,
including those of hot-bands, are particularly sensitive to temperature and
column density. We find that the CO emission in the GW Lup disk is
coming from optically thick emission at a temperature of 400 K.
CO is optically thinner and based on a lower temperature of
325 K, may be tracing deeper into the disk and/or a larger emitting
radius than CO. The derived /
ratio is orders of magnitude higher than previously derived for GW Lup and
other targets based on \textit{Spitzer}-IRS data. This high column density
ratio may be due to an inner cavity with a radius in between the HO and
CO snowlines and/or an overall lower disk temperature. This paper
demonstrates the unique ability of JWST to probe inner disk structures and
chemistry through weak, previously unseen molecular features.Comment: 15 pages, 10 figures. Accepted to ApJ
The Mid-infrared Instrument for JWST and Its In-flight Performance
The Mid-Infrared Instrument (MIRI) extends the reach of the James Webb Space Telescope (JWST) to 28.5 μm. It provides subarcsecond-resolution imaging, high sensitivity coronagraphy, and spectroscopy at resolutions of λ/Δλ ∼ 100-3500, with the high-resolution mode employing an integral field unit to provide spatial data cubes. The resulting broad suite of capabilities will enable huge advances in studies over this wavelength range. This overview describes the history of acquiring this capability for JWST. It discusses the basic attributes of the instrument optics, the detector arrays, and the cryocooler that keeps everything at approximately 7 K. It gives a short description of the data pipeline and of the instrument performance demonstrated during JWST commissioning. The bottom line is that the telescope and MIRI are both operating to the standards set by pre-launch predictions, and all of the MIRI capabilities are operating at, or even a bit better than, the level that had been expected. The paper is also designed to act as a roadmap to more detailed papers on different aspects of MIRI
The Science Performance of JWST as Characterized in Commissioning
This paper characterizes the actual science performance of the James Webb
Space Telescope (JWST), as determined from the six month commissioning period.
We summarize the performance of the spacecraft, telescope, science instruments,
and ground system, with an emphasis on differences from pre-launch
expectations. Commissioning has made clear that JWST is fully capable of
achieving the discoveries for which it was built. Moreover, almost across the
board, the science performance of JWST is better than expected; in most cases,
JWST will go deeper faster than expected. The telescope and instrument suite
have demonstrated the sensitivity, stability, image quality, and spectral range
that are necessary to transform our understanding of the cosmos through
observations spanning from near-earth asteroids to the most distant galaxies.Comment: 5th version as accepted to PASP; 31 pages, 18 figures;
https://iopscience.iop.org/article/10.1088/1538-3873/acb29
The James Webb Space Telescope Mission
Twenty-six years ago a small committee report, building on earlier studies,
expounded a compelling and poetic vision for the future of astronomy, calling
for an infrared-optimized space telescope with an aperture of at least .
With the support of their governments in the US, Europe, and Canada, 20,000
people realized that vision as the James Webb Space Telescope. A
generation of astronomers will celebrate their accomplishments for the life of
the mission, potentially as long as 20 years, and beyond. This report and the
scientific discoveries that follow are extended thank-you notes to the 20,000
team members. The telescope is working perfectly, with much better image
quality than expected. In this and accompanying papers, we give a brief
history, describe the observatory, outline its objectives and current observing
program, and discuss the inventions and people who made it possible. We cite
detailed reports on the design and the measured performance on orbit.Comment: Accepted by PASP for the special issue on The James Webb Space
Telescope Overview, 29 pages, 4 figure
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