1,092 research outputs found
Sulfur Degassing From Volcanoes: Source Conditions, Surveillance, Plume Chemistry and Earth System Impacts
International audienceDespite its relatively minor abundance in magmas (compared with H2O and CO2), sulfur degassing from volcanoes is of tremendous significance. It can exert substantial influence on magmatic evolution (potentially capable of triggering eruptions); represents one of the most convenient opportunities for volcano monitoring and hazard assessment; and can result in major impacts on the atmosphere, climate and terrestrial ecosystems at a range of spatial and temporal scales. The complex behavior of sulfur in magmas owes much to its multiple valence states (-II, 0, IV, VI), speciation (e.g., S2, H2S, SO2, OCS and SO3 in the gas phase; S2-, SO42- and SO32- in the melt; and non-volatile solid phases such as pyrrhotite and anhydrite), and variation in stable isotopic composition (32S, 33S, 34S and 36S; e.g., MĂ©trich and Mandeville 2010). Sulfur chemistry in the atmosphere is similarly rich involving gaseous and condensed phases and invoking complex homogeneous and heterogeneous chemical reactions. Sulfur degassing from volcanoes and geothermal areas is also important since a variety of microorganisms thrive based on the redox chemistry of sulfur: by reducing sulfur, thiosulfate, sulfite and sulfate to H2S, or oxidizing sulfur and H2S to sulfate (e.g., Takano et al. 1997; Amend and Shock 2001; Shock et al. 2010). Understanding volcanic sulfur degassing thus provides vital insights into magmatic, volcanic and hydrothermal processes; the impacts of volcanism on the Earth system; and biogeochemical cycles. Here, we review the causes of variability in sulfur abundance and speciation in different geodynamic contexts; the measurement of sulfur emissions from volcanoes; links between subsurface processes and surface observations; sulfur chemistry in volcanic plumes; and the consequences of sulfur degassing for climate and the environment
Radiation Pressure Driven Galactic Winds from Self-Gravitating Discs
(Abridged) We study large-scale winds driven from uniformly bright
self-gravitating discs radiating near the Eddington limit. We show that the
ratio of the radiation pressure force to the gravitational force increases with
height above the disc surface to a maximum of twice the value of the ratio at
the disc surface. Thus, uniformly bright self-gravitating discs radiating at
the Eddington limit are fundamentally unstable to driving large-scale winds.
These results contrast with the spherically symmetric case, where
super-Eddington luminosities are required for wind formation. We apply this
theory to galactic winds from rapidly star-forming galaxies that approach the
Eddington limit for dust. For hydrodynamically coupled gas and dust, we find
that the asymptotic velocity of the wind is v_\infty ~ 1.5 v_rot and that
v_\infty SFR^{0.36}, where v_rot is the disc rotation velocity and SFR is the
star formation rate, both of which are in agreement with observations. However,
these results of the model neglect the gravitational potential of the
surrounding dark matter halo and an old passive stellar bulge or extended disc,
which act to decrease v_\infty. A more realistic treatment shows that the flow
can either be unbound, or bound, forming a "fountain flow" with a typical
turning timescale of t_turn ~ 0.1-1 Gyr. We provide quantitative criteria and
scaling relations for assessing whether or not a rapidly star-forming galaxy of
given properties can drive unbound flows via the mechanism described in this
paper. Importantly, we note that because t_turn is longer than the star
formation timescale in the rapidly star-forming galaxies and ULIRGs for which
our theory is most applicable, if rapidly star-forming galaxies are selected as
such, they may be observed to have strong outflows, even though their winds are
eventually bound on large scales.Comment: 10 pages, 6 figures, Accepted for publication in MNRA
A galaxy as the source of a Civ absorption system close to the epoch of reionization
We find a bright (L_{UV}=2.5 L*_{z=6}) Lyman alpha emitter at redshift
z=5.719 at a projected distance of 79 physical kpc from a strong triply ionized
carbon (Civ) absorption system at redshift z=5.7238 previously reported in the
spectrum of the z_{em} = 6.309 QSO SDSS J1030+0524. This is the highest
redshift galaxy-absorber pair detected to-date, supporting the idea that
galaxy-wide outflows were already in place at the end of the epoch of
reionization. The proximity of this object makes it the most likely source of
metals, consistent with models of outflows at lower redshift where significant
observational evidence relates metal absorption systems with galaxies hosting
outflows.
In a typical outflow scenario, a wind of 200 km/s, active since the universe
was only 0.6 Gyr old (z ~8.4), could eject metals out to 79 kpc at z=5.719.
Although the origin of metals in the intergalactic medium (IGM) is still under
debate, our results are consistent with predictions from cosmological
simulations which reproduce the evolution of the cosmic density of Civ, from z
~ 6 to the present day based on outflow-driven enrichment of the IGM.
We also report two more Lyman alpha emitters in this field, at z=5.973\pm
0.002 and z=5.676\pm 0.002 respectively, the former confirming the original
identification by Stiavelli et al. Our results suggest that the colour cut
typically used to identify i-dropouts (i_{775}-z_{850}>1.3) misses a
non-negligible fraction of blue galaxies with faint UV continuum at z \geq 5.7.Comment: Accepted for publication in MNRAS, 9 pages, 3 figures, 1 tabl
Development and application of an optimised Bayesian shrinkage prior for spectroscopic biomedical diagnostics
Background and objective: Classification of vibrational spectra is often challenging for biological substances containing similar molecular bonds, interfering with spectral outputs. To address this, various approaches are widely studied. However, whilst providing powerful estimations, these techniques are computationally extensive and frequently overfit the data. Shrinkage priors, which favour models with relatively few predictor variables, are often applied in Bayesian penalisation techniques to avoid overfitting.Methods: Using the logit-normal continuous analogue of the spike-and-slab (LN–CASS) as the shrinkage prior and modelling, we have established classification for accurate analysis, with the established system found to be faster than conventional least absolute shrinkage and selection operator, horseshoe or spike-and-slab. These were examined versus coefficient data based on a linear regression model and vibrational spectra produced via density functional theory calculations. Then applied to Raman spectra from saliva to classify the sample sex.Results: Subsequently applied to the acquired spectra from saliva, the evaluated models exhibited high accuracy (AUC>90 %) even when number of parameters was higher than the number of observations. Analyses of spectra for all Bayesian models yielded high-classification accuracy upon cross-validation. Further, for saliva sensing, LN–CASS was found to be the only classifier with 100 %-accuracy in predicting the output based on a leave-one-out cross validation.Conclusions: With potential applications in aiding diagnosis from small spectroscopic datasets and are compatible with a range of spectroscopic data formats. As seen with the classification of IR and Raman spectra. These results are highly promising for emerging developments of spectroscopic platforms for biomedical diagnostic sensing systems
Tracing the Reionization-Epoch Intergalactic Medium with Metal Absorption Lines
IGM metal absorption lines observed in z>6 spectra offer the opportunity to
probe early feedback processes, the nature of enriching sources, and the
topology of reionization. We run high-resolution cosmological simulations
including galactic outflows to study the observability and physical properties
of 5 ions (C II, C IV, O I, Si II, Si IV) in absorption between z=8->5. We
apply three cases for ionization conditions: Fully neutral, fully reionized,
and a patchy model based on the flux from the nearest galaxy. We find that our
simulations broadly fit available z~5-6 IGM metal-line data, although all
observations cannot be accommodated with a single ionization condition.
Variations in O I absorbers among sight lines seen by Becker et al. (2006)
suggest significant neutral IGM patches down to z~6. Strong C IV absorbers at
z~6 may be the result of ionization by their parent galaxy. Our outflows have
typical speeds of ~200 km/s and mass loading factors of ~6. Such high mass
loading is critical for enriching the IGM to the observed levels while
curtailing star formation to match the observed z~6 rest-frame UV luminosity
function. The volume filling factor of metals increases during this epoch, but
only reaches ~1% for Z>10^(-3) Zsolar by z=5. C IV is an ideal tracer of IGM
metals at z~5-6, with dropping global ionization fractions to either higher or
lower redshifts. This results in a strongly increasing global Omega(C IV) from
z=8->5, in contrast to its relative constancy from z=5->2. Our simulations do
not support widespread early IGM enrichment from e.g. Pop III stars. High-z
absorbers arise from metals on their first outward journey from galaxies, at
distances less than 50 kpc. The galaxies responsible for early IGM enrichment
have typical M*=10^(7.0-8.5) Msolar.Comment: Accepted to MNRAS, 34 pages, 24 figures, 1 table (Sections 5.5,
6.3.1, & 6.3.2 added as well as 5 figures and 1 table
The Nature and Origin of Low-Redshift O VI Absorbers
The O VI ion observed in quasar absorption line spectra is the most
accessible tracer of the cosmic metal distribution in the low redshift (z<0.5)
intergalactic medium (IGM). We explore the nature and origin of O VI absorbers
using cosmological hydrodynamic simulations including galactic outflows. We
consider the effects of ionization background variations, non-equilibrium
ionization and cooling, uniform metallicity, and small-scale (sub-resolution)
turbulence. Our main results are 1) IGM O VI is predominantly photo-ionized
with T= 10^(4.2+/-0.2) K. A key reason for this is that O VI absorbers
preferentially trace over-enriched regions of the IGM at a given density, which
enhances metal-line cooling such that absorbers can cool within a Hubble time.
As such, O VI is not a good tracer of the WHIM. 2) The predicted O VI
properties fit observables only if sub-resolution turbulence is added. The
required turbulence increases with O VI absorber strength such that stronger
absorbers arise from more recent outflows with turbulence dissipating on the
order of a Hubble time. The amount of turbulence is consistent with other
examples of turbulence observed in the IGM and galactic halos. 3) Metals traced
by O VI and H I do not trace exactly the same baryons, but reside in the same
large-scale structure. Observed alignment statistics are reproduced in our
simulations. 4) Photo-ionized O VI traces gas in a variety of environments, and
is not directly associated with the nearest galaxy, though is typically nearest
to ~0.1L* galaxies. Weaker O VI components trace some of the oldest cosmic
metals. 5) Very strong absorbers are more likely to be collisionally ionized,
tracing more recent enrichment (<2 Gyr) within or near galactic halos.Comment: 33 pages, 18 figures, accepted to MNRAS. Two new figures adde
Advanced Tuneable Micronanoplatforms for Sensitive and Selective Multiplexed Spectroscopic Sensing via Electro-Hydrodynamic Surface Molecular Lithography
Micro- and nanopatterning of materials, one of the cornerstones of emerging technologies, has transformed research capabilities in lab-on-a-chip diagnostics. Herein, a micro- and nanolithographic method is developed, enabling structuring materials at the submicron scale, which can, in turn, accelerate the development of miniaturized platform technologies and biomedical sensors. Underpinning it is the advanced electro-hydrodynamic surface molecular lithography, via inducing interfacial instabilities produces micro- and nanostructured substrates, uniquely integrated with synthetic surface recognition. This approach enables the manufacture of design patterns with tuneable feature sizes, which are functionalized via synthetic nanochemistry for highly sensitive, selective, rapid molecular sensing. The development of a high-precision piezoelectric lithographic rig enables reproducible substrate fabrication with optimum signal enhancement optimized for functionalization with capture molecules on each micro- and nanostructured array. This facilitates spatial separation, which during the spectroscopic sensing, enables multiplexed measurement of target molecules, establishing the detection at minute concentrations. Subsequently, this nano-plasmonic lab-on-a-chip combined with the unconventional computational classification algorithm and surface enhanced Raman spectroscopy, aimed to address the challenges associated with timely point-of-care detection of disease-indicative biomarkers, is utilized in validation assay for multiplex detection of traumatic brain injury indicative glycan biomarkers, demonstrating straightforward and cost-effective micro- and nanoplatforms for accurate detection.</p
Shaping the galaxy stellar mass function with supernova- and AGN-driven winds
Cosmological hydrodynamical simulations of galaxy formation in representative
regions of the Universe typically need to resort to subresolution models to
follow some of the feedback processes crucial for galaxy formation. Here, we
show that an energy-driven outflow model in which the wind velocity decreases
and the wind mass loading increases in low-mass galaxies, as suggested by
observations, can produce a good match to the low-mass end of the observed
galaxy stellar mass function. The high-mass end can be recovered simultaneously
if feedback from active galactic nuclei (AGN) and a correction for diffuse
stellar light plausibly missed in observations are included. At the same time,
our model is in good agreement with the stellar mass functions at redshifts z=1
and z=2, and with the observed redshift evolution of the cosmic star formation
rate density. In addition, it accurately reproduces the observed gas to stellar
mass ratios and specific star formation rates of galaxies as a function of
their stellar mass. This agreement with a diverse set of data marks significant
progress in hydrodynamically modelling the formation of a representative galaxy
population. It also suggests that the mass flux in real galactic winds should
strongly increase towards low-mass galaxies. Without this assumption, an
overproduction of galaxies at the faint-end of the galaxy luminosity function
seems inevitable in our models.Comment: 14 pages, 9 figures, submitted to MNRA
Feedback and Recycled Wind Accretion: Assembling the z=0 Galaxy Mass Function
We analyse cosmological hydrodynamic simulations that include
observationally-constrained prescriptions for galactic outflows. If these
simulated winds accurately represent winds in the real Universe, then material
previously ejected in winds provides the dominant source of gas infall for new
star formation at redshifts z<1. This recycled wind accretion, or wind mode,
provides a third physically distinct accretion channel in addition to the "hot"
and "cold" modes emphasised in recent theoretical studies. Because of the
interaction between outflows and gas in and around halos, the recycling
timescale of wind material (t_rec) is shorter in higher-mass systems, which
reside in denser gaseous environments. In these simulations, this differential
recycling plays a central role in shaping the present-day galaxy stellar mass
function (GSMF). If we remove all particles that were ever ejected in a wind,
then the predicted GSMFs are much steeper than observed; galaxy masses are
suppressed both by the direct removal of gas and by the hydrodynamic heating of
their surroundings, which reduces subsequent infall. With wind recycling
included, the simulation that incorporates our favoured momentum-driven wind
scalings reproduces the observed GSMF for stellar masses 10^9 < M < 5x10^10
Msolar. At higher masses, wind recycling leads to excessive galaxy masses and
excessive star formation rates relative to observations. In these massive
systems, some quenching mechanism must suppress the re-accretion of gas ejected
from star-forming galaxies. In short, as has long been anticipated, the form of
the GSMF is governed by outflows; the unexpected twist here for our simulated
winds is that it is not primarily the ejection of material but how the ejected
material is re-accreted that governs the GSMF.Comment: 16 pages, 7 figures, accepted by MNRA
Climate change and postglacial human dispersals in southeast Asia
Modern humans have been living in Island Southeast Asia (ISEA) for at least 50,000 years. Largely because of the influence of linguistic studies, however, which have a shallow time depth, the attention of archaeologists and geneticists has usually been focused on the last 6,000 years--in particular, on a proposed Neolithic dispersal from China and Taiwan. Here we use complete mitochondrial DNA (mtDNA) genome sequencing to spotlight some earlier processes that clearly had a major role in the demographic history of the region but have hitherto been unrecognized. We show that haplogroup E, an important component of mtDNA diversity in the region, evolved in situ over the last 35,000 years and expanded dramatically throughout ISEA around the beginning of the Holocene, at the time when the ancient continent of Sundaland was being broken up into the present-day archipelago by rising sea levels. It reached Taiwan and Near Oceania more recently, within the last approximately 8,000 years. This suggests that global warming and sea-level rises at the end of the Ice Age, 15,000-7,000 years ago, were the main forces shaping modern human diversity in the region
- …