1,155 research outputs found
Evidence for ubiquitous carbon grain destruction in hot protostellar envelopes
Earth is deficient in carbon and nitrogen by up to orders of
magnitude compared with the Sun. Destruction of (carbon- and nitrogen-rich)
refractory organics in the high-temperature planet forming regions could
explain this deficiency. Assuming a refractory cometary composition for these
grains, their destruction enhances nitrogen-containing oxygen-poor molecules in
the hot gas (K) after the initial formation and sublimation of
these molecules from oxygen-rich ices in the warm gas (K). Using
observations of high-mass protostars with ALMA, we find that
oxygen-containing molecules (CHOH and HNCO) systematically show no
enhancement in their hot component. In contrast, nitrogen-containing,
oxygen-poor molecules (CHCN and CHCN) systematically show an
enhancement of a factor in their hot component, pointing to
additional production of these molecules in the hot gas. Assuming only thermal
excitation conditions, we interpret these results as a signature of destruction
of refractory organics, consistent with the cometary composition. This
destruction implies a higher C/O and N/O in the hot gas than the warm gas,
while, the exact values of these ratios depend on the fraction of grains that
are effectively destroyed. This fraction can be found by future chemical models
that constrain C/O and N/O from the abundances of minor carbon, nitrogen and
oxygen carriers presented here.Comment: Accepted for publication in ApJ Letter
Case Studies to Illustrate the Rotorcraft Certification by Simulation Process; CS 29/27 Category a Rejected Take-Off, Confined Area
IDLaS-NL – A platform for running customized studies on individual differences in Dutch language skills via the internet
We introduce the Individual Differences in Language Skills (IDLaS-NL) web platform, which enables users to run studies on individual differences in Dutch language skills via the internet. IDLaS-NL consists of 35 behavioral tests, previously validated in participants aged between 18 and 30 years. The platform provides an intuitive graphical interface for users to select the tests they wish to include in their research, to divide these tests into different sessions and to determine their order. Moreover, for standardized administration the platform provides an application (an emulated browser) wherein the tests are run. Results can be retrieved by mouse click in the graphical interface and are provided as CSV-file output via email. Similarly, the graphical interface enables researchers to modify and delete their study configurations. IDLaS-NL is intended for researchers, clinicians, educators and in general anyone conducting fundamental research into language and general cognitive skills; it is not intended for diagnostic purposes. All platform services are free of charge. Here, we provide a description of its workings as well as instructions for using the platform. The IDLaS-NL platform can be accessed at www.mpi.nl/idlas-nl
Economic values for ecosystem services:A global synthesis and way forward
This paper presents a global synthesis of economic values for ecosystem services provided by 15 terrestrial and marine biomes. Information from over 1,300 studies, yielding over 9,400 value estimates in monetary units, has been collected and organised in the Ecosystem Services Valuation Database (ESVD). This is a substantial expansion of data since the de Groot et al. (2012) description of the ESVD and provides an important juncture to explore developments in the use of valuation methods and the contexts in which valuations are conducted. In this paper we provide summary values for 23 ecosystem services from 15 biomes to represent the magnitude, variation and gaps in economic values. To enable the comparison and synthesis of values, estimates in the ESVD are standardised to a common set of units (Int$/ha/year at 2020 price levels). This data provides a basis for value transfers to inform decision-making in current policy contexts but requires due consideration and adjustment for context specific determinants of value. Although the coverage of the ESVD is global, the geographic distribution of data is not even. There is a particularly high representation of European ecosystems and relatively little information for Russia, Central Asia and North Africa. Therefore, the data are not globally representative of biophysical and socio-economic contexts. The distribution of data across ecosystem services is also far from even, with some services very well represented (e.g. recreation, wild fish and wild animals, ecosystem and species appreciation, air filtration and global climate regulation) and others with almost no value estimates (e.g. disease control, water baseflow maintenance, rainfall pattern regulation). In the past decade, there has been a notable increase in demand for information on the economic value of ecosystem services from both public and private institutions to improve the conservation and management of natural capital. The literature is developing to meet this demand but there is a need for targeted and refined valuation research to ensure sufficient certainty, comparability, and representativeness of the data, and to enable transferability and fill knowledge gaps. This paper concludes by identifying avenues for future development to further increase the amount, quality, representativeness and application of data on economic values for ecosystem services.</p
Temperature structures of embedded disks: young disks in Taurus are warm
The chemical composition of gas and ice in disks around young stars set the
bulk composition of planets. In contrast to protoplanetary disks (Class II),
young disks that are still embedded in their natal envelope (Class 0 and I) are
predicted to be too warm for CO to freeze out, as has been confirmed
observationally for L1527 IRS. To establish whether young disks are generally
warmer than their more evolved counterparts, we observed five young (Class 0/I
and Class I) disks in Taurus with the Atacama Large Millimeter/submillimeter
Array (ALMA), targeting CO , HCO , HDO
and CHOH transitions at resolution. The different freeze-out temperatures
of these species allow us to derive a global temperature structure. CO
and HCO are detected in all disks, with no signs of CO freeze-out in the
inner 100 au, and a CO abundance close to 10. HCO
emission originates in the surface layers of the two edge-on disks, as
witnessed by the especially beautiful V-shaped emission pattern in
IRAS~04302+2247. HDO and CHOH are not detected, with column density upper
limits more than 100 times lower than for hot cores. Young disks are thus found
to be warmer than more evolved protoplanetary disks around solar analogues,
with no CO freeze-out (or only in the outermost part of 100 au disks)
or CO processing. However, they are not as warm as hot cores or disks around
outbursting sources, and therefore do not have a large gas-phase reservoir of
complex molecules.Comment: Accepted for publication in ApJ. 19 pages, 11 figures, 3 tables (+
appendix
Complex organic molecules in low-mass protostars on Solar System scales -- II. Nitrogen-bearing species
The chemical inventory of planets is determined by the physical and chemical
processes that govern the early phases of star formation. The aim is to
investigate N-bearing complex organic molecules towards two Class 0 protostars
(B1-c and S68N) at millimetre wavelengths with ALMA. Next, the results of the
detected N-bearing species are compared with those of O-bearing species for the
same and other sources. ALMA observations in Band 6 ( 1 mm) and Band 5
( 2 mm) are studied at 0.5" resolution, complemented by Band 3
( 3 mm) data in a 2.5" beam. NH2CHO, C2H5CN, HNCO, HN13CO, DNCO,
CH3CN, CH2DCN, and CHD2CN are identified towards the investigated sources.
Their abundances relative to CH3OH and HNCO are similar for the two sources,
with column densities that are typically an order of magnitude lower than those
of O-bearing species. The largest variations, of an order of magnitude, are
seen for NH2CHO abundance ratios with respect to HNCO and CH3OH and do not
correlate with the protostellar luminosity. In addition, within uncertainties,
the N-bearing species have similar excitation temperatures to those of
O-bearing species ( 100 300 K). The similarity of most abundances
with respect to HNCO, including those of CH2DCN and CHD2CN, hints at a shared
chemical history, especially the high D/H ratio in cold regions prior to star
formation. However, some of the variations in abundances may reflect the
sensitivity of the chemistry to local conditions such as temperature (e.g.
NH2CHO), while others may arise from differences in the emitting areas of the
molecules linked to their different binding energies in the ice. The two
sources discussed here add to the small number of sources with such a detailed
chemical analysis on Solar System scales. Future JWST data will allow a direct
comparison between the ice and gas abundances of N-bearing species.Comment: Accepted to A&A, 41 pages, 37 figure
Identification of Radiopure Titanium for the LZ Dark Matter Experiment and Future Rare Event Searches
The LUX-ZEPLIN (LZ) experiment will search for dark matter particle
interactions with a detector containing a total of 10 tonnes of liquid xenon
within a double-vessel cryostat. The large mass and proximity of the cryostat
to the active detector volume demand the use of material with extremely low
intrinsic radioactivity. We report on the radioassay campaign conducted to
identify suitable metals, the determination of factors limiting radiopure
production, and the selection of titanium for construction of the LZ cryostat
and other detector components. This titanium has been measured with activities
of U~1.6~mBq/kg, U~0.09~mBq/kg,
Th~~mBq/kg, Th~~mBq/kg, K~0.54~mBq/kg, and Co~0.02~mBq/kg (68\% CL).
Such low intrinsic activities, which are some of the lowest ever reported for
titanium, enable its use for future dark matter and other rare event searches.
Monte Carlo simulations have been performed to assess the expected background
contribution from the LZ cryostat with this radioactivity. In 1,000 days of
WIMP search exposure of a 5.6-tonne fiducial mass, the cryostat will contribute
only a mean background of (stat)(sys) counts.Comment: 13 pages, 3 figures, accepted for publication in Astroparticle
Physic
Osmosis with active solutes
Despite much current interest in active matter, little is known about osmosis
in active systems. Using molecular dynamics simulations, we investigate how
active solutes perturb osmotic steady states. We find that solute activity
increases the osmotic pressure, and can also expel solvent from the solution -
i.e. cause reverse osmosis. The latter effect cannot be described by an
effective temperature, but can be reproduced by mapping the active solution
onto a passive one with the same degree of local structuring as the passive
solvent component. Our results provide a basic framework for understanding
active osmosis, and suggest that activity-induced structuring of the passive
component may play a key role in the physics of active-passive mixtures.Comment: 6 page
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