2,359 research outputs found
Controlling uranyl oxo group interactions to group 14 elements using polypyrrolic Schiff-base macrocyclic ligands
Heterodinuclear uranyl/group 14 complexes of the aryl- and anthracenyl-linked Schiff-base macrocyclic ligands LMe and LA were synthesised by reaction of UO2(H2L) with M{N(SiMe3)2}2 (M = Ge, Sn, Pb). For complexes of the anthracenyl-linked ligand (LA) the group 14 metal sits out of the N4-donor plane by up to 0.7 Ă
resulting in relatively short MâŻOUO distances which decrease down the group; however, the solid state structures and IR spectroscopic analyses suggest little interaction occurs between the oxo and group 14 metal. In contrast, the smaller aryl-linked ligand (LMe) enforces greater interaction between the metals; only the PbII complex was cleanly accessible although this complex was relatively unstable in the presence of HN(SiMe3)2 and some organic oxidants. In this case, the equatorial coordination of pyridine-N-oxide causes a 0.08 Ă
elongation of the endo UO bond and a clear interaction of the uranyl ion with the Pb(II) cation in the second donor compartment
Hydrothermal activity lowers trophic diversity in Antarctic sedimented hydrothermal vents
Sedimented hydrothermal vents are those in which hydrothermal fluid vents through sediment and are among the least studied deep-sea ecosystems. We present a combination of microbial and biochemical data to assess trophodynamics between and within hydrothermally active and off-vent areas of the Bransfield Strait (1050â1647âm depth). Microbial composition, biomass and fatty acid signatures varied widely between and within vent and non-vent sites and provided evidence of diverse metabolic activity. Several species showed diverse feeding strategies and occupied different trophic positions in vent and non-vent areas and stable isotope values of consumers were generally not consistent with feeding structure morphology. Niche area and the diversity of microbial fatty acids reflected trends in species diversity and was lowest at the most hydrothermally active site. Faunal utilisation of chemosynthetic activity was relatively limited but was detected at both vent and non-vent sites as evidenced by carbon and sulphur isotopic signatures, suggesting that the hydrothermal activity can affect trophodynamics over a much wider area than previously thought
Uranyl to Uranium(IV) Conversion through Manipulation of Axial and Equatorial Ligands
The controlled manipulation of the axial oxo and equatorial halide ligands in the uranyl dipyrrin complex, UO2Cl(L), allows the uranyl reduction potential to be shifted by 1.53 V into the range accessible to naturally occurring reductants that are present during uranium remediation and storage processes. Abstraction of the equatorial halide ligand to form the uranyl cation causes a 780 mV positive shift in the UV/UIV reduction potential. Borane functionalization of the axial oxo groups causes the spontaneous homolysis of the equatorial UâCl bond and a further 750 mV shift of this potential. The combined effect of chloride loss and borane coordination to the oxo groups allows reduction of UVI to UIV by H2 or other very mild reductants such as Cp*2Fe. The reduction with H2 is accompanied by a BâC bond cleavage process in the oxo-coordinated borane
Reproductive control via eviction (but not the threat of eviction) in banded mongooses
Considerable research has focused on understanding variation in reproductive skew in cooperative animal societies, but the pace of theoretical development has far outstripped empirical testing of the models. One major class of model suggests that dominant individuals can use the threat of eviction to deter subordinate reproduction (the ârestraintâ model), but this idea remains untested. Here, we use long-term behavioural and genetic data to test the assumptions of the restraint model in banded mongooses (Mungos mungo), a species in which subordinates breed regularly and evictions are common. We found that dominant females suffer reproductive costs when subordinates breed, and respond to these costs by evicting breeding subordinates from the group en masse, in agreement with the assumptions of the model. We found no evidence, however, that subordinate females exercise reproductive restraint to avoid being evicted in the first place. This means that the pattern of reproduction is not the result of a reproductive âtransactionâ to avert the threat of eviction. We present a simple game theoretical analysis that suggests that eviction threats may often be ineffective to induce pre-emptive restraint among multiple subordinates and predicts that threats of eviction (or departure) will be much more effective in dyadic relationships and linear hierarchies. Transactional models may be more applicable to these systems. Greater focus on testing the assumptions rather than predictions of skew models can lead to a better understanding of how animals control each other's reproduction, and the extent to which behaviour is shaped by overt acts versus hidden threats
The Origin of the 24-micron Excess in Red Galaxies
Observations with the Spitzer Space Telescope have revealed a population of
red-sequence galaxies with a significant excess in their 24-micron emission
compared to what is expected from an old stellar population. We identify 900
red galaxies with 0.15<z<0.3 from the AGN and Galaxy Evolution Survey (AGES)
selected from the NOAO Deep Wide-Field Survey Bootes field. Using Spitzer/MIPS,
we classify 89 (~10%) with 24-micron infrared excess (f24>0.3 mJy). We
determine the prevalence of AGN and star-formation activity in all the AGES
galaxies using optical line diagnostics and mid-IR color-color criteria. Using
the IRAC color-color diagram from the IRAC Shallow Survey, we find that 64% of
the 24-micron excess red galaxies are likely to have strong PAH emission
features in the 8-micron IRAC band. This fraction is significantly larger than
the 5% of red galaxies with f24<0.3 mJy that are estimated to have strong PAH
emission, suggesting that the infrared emission is largely due to
star-formation processes. Only 15% of the 24-micron excess red galaxies have
optical line diagnostics characteristic of star-formation (64% are classified
as AGN and 21% are unclassifiable). The difference between the optical and
infrared results suggest that both AGN and star-formation activity is occurring
simultaneously in many of the 24-micron excess red galaxies. These results
should serve as a warning to studies that exclusively use optical line
diagnostics to determine the dominant emission mechanism in the infrared and
other bands. We find that ~40% of the 24-micron excess red galaxies are edge-on
spiral galaxies with high optical extinctions. The remaining sources are likely
to be red galaxies whose 24-micron emission comes from a combination of
obscured AGN and star-formation activity.Comment: ApJ, accepted; 11 pages, 7 figures; corrected reference to IRAC
Shallow Survey in abstrac
A call to action: A need for initiatives that increase equitable access to COVID-19 therapeutics
Structural racism is endemic in the United States and causes inequitable health outcomes that have been amplified throughout the COVID-19 pandemic. Non-Hispanic Black, Hispanic/Latino, and Native American individuals have been disproportionately affected, and are twice as likely to be hospitalized or die from COVID-19 or related morbidities when compared to White Americans. Social determinants of health inequities contribute to these disparate outcomes, given that minoritized individuals are more likely to occupy essential worker roles and to live in high-density settings. Despite their higher risk of severe COVID-19 illness, racially and ethnically minoritized individuals are less likely to receive potentially lifesaving COVID-19 therapeutics.3 While several state health departments attempted to implement race-conscious interventions and narrow the disparities, these efforts have been met with fallacious claims of âreverse racismâ and the reversal of the proposed implementations
The SPLASH Survey: A Spectroscopic Analysis of the Metal-Poor, Low-Luminosity M31 dSph Satellite Andromeda X
Andromeda X (And X) is a newly discovered low-luminosity M31 dwarf spheroidal
galaxy (dSph) found by Zucker et al. (2007) in the Sloan Digital Sky Survey
(SDSS - York et al. 2000). In this paper, we present the first spectroscopic
study of individual red giant branch stars in And X, as a part of the SPLASH
Survey (Spectroscopic and Photometric Landscape of Andromeda's Stellar Halo).
Using the Keck II telescope and multiobject DEIMOS spectrograph, we target two
spectroscopic masks over the face of the galaxy and measure radial velocities
for ~100 stars with a median accuracy of sigma_v ~ 3 km/s. The velocity
histogram for this field confirms three populations of stars along the sight
line: foreground Milky Way dwarfs at small negative velocities, M31 halo red
giants over a broad range of velocities, and a very cold velocity ``spike''
consisting of 22 stars belonging to And X with v_rad = -163.8 +/- 1.2 km/s. By
carefully considering both the random and systematic velocity errors of these
stars (e.g., through duplicate star measurements), we derive an intrinsic
velocity dispersion of just sigma_v = 3.9 +/- 1.2 km/s for And X, which for its
size, implies a minimum mass-to-light ratio of M/L =37^{+26}_{-19} assuming the
mass traces the light. Based on the clean sample of member stars, we measure
the median metallicity of And X to be [Fe/H] = -1.93 +/- 0.11, with a slight
radial metallicity gradient. The dispersion in metallicity is large,
sigma([Fe/H]) = 0.48, possibly hinting that the galaxy retained much of its
chemical enrichment products. We discuss the potential for better understanding
the formation and evolution mechanisms for M31's system of dSphs through
(current) kinematic and chemical abundance studies, especially in relation to
the Milky Way sample. (abridged version)Comment: Accepted for Publication in Astrophys. J. 14 pages including 7
figures and 2 tables (journal format
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