551 research outputs found
Remote sensing of near-infrared chlorophyll fluorescence from space in scattering atmospheres: implications for its retrieval and interferences with atmospheric CO_2 retrievals
With the advent of dedicated greenhouse gas space-borne spectrometers sporting high resolution spectra in the O_2 A-band spectral region (755â774 nm), the retrieval of chlorophyll fluorescence has become feasible on a global scale. If unaccounted for, however, fluorescence can indirectly perturb the greenhouse gas retrievals as it perturbs the oxygen absorption features. As atmospheric CO_2 measurements are used to invert net fluxes at the landâatmosphere interface, a bias caused by fluorescence can be crucial as it will spatially correlate with the fluxes to be inverted. Avoiding a bias and retrieving fluorescence accurately will provide additional constraints on both the net and gross fluxes in the global carbon cycle. We show that chlorophyll fluorescence, if neglected, systematically interferes with full-physics multi-band X_(CO_2) retrievals using the O_2 A-band. Systematic biases in X_(CO_2) can amount to +1 ppm if fluorescence constitutes 1% to the continuum level radiance. We show that this bias can be largely eliminated by simultaneously fitting fluorescence in a full-physics based retrieval.
If fluorescence is the primary target, a dedicated but very simple retrieval based purely on Fraunhofer lines is shown to be more accurate and very robust even in the presence of large scattering optical depths. We find that about 80% of the surface fluorescence is retained at the top-of-atmosphere, even for cloud optical thicknesses around 2â5. We further show that small instrument modifications to future O_2 A-band spectrometer spectral ranges can result in largely reduced random errors in chlorophyll fluorescence, paving the way towards a more dedicated instrument exploiting solar absorption features only
Successful treatment of a solitary skull metastasis in a child with Wilms' Tumor
This report presents the successful treatment of a child with a solitary metastatic lesion to the calvarium following treatment for Stage III anaplastic Wilmsâ Tumor
Inferring metabolic mechanisms of interaction within a defined gut microbiota
The diversity and number of species present within microbial communities create the potential for a multitude of interspecies metabolic interactions. Here, we develop, apply, and experimentally test a framework for inferring metabolic mechanisms associated with interspecies interactions. We perform pairwise growth and metabolome profiling of co-cultures of strains from a model mouse microbiota. We then apply our framework to dissect emergent metabolic behaviors that occur in co-culture. Based on one of the inferences from this framework, we identify and interrogate an amino acid cross-feeding interaction and validate that the proposed interaction leads to a growth benefit in vitro. Our results reveal the type and extent of emergent metabolic behavior in microbial communities composed of gut microbes. We focus on growth-modulating interactions, but the framework can be applied to interspecies interactions that modulate any phenotype of interest within microbial communities
Tropospheric sources and sinks of gas-phase acids in the Colorado Front Range
We measured organic and inorganic gas-phase acids in the
Front Range of Colorado to better understand their tropospheric sources and
sinks using a high-resolution time-of-flight chemical ionization mass
spectrometer. Measurements were conducted from 4 to 13 August 2014 at the
Boulder Atmospheric Observatory during the Front Range Air Pollution and
Photochemistry Ăxperiment. Diurnal increases in mixing ratios are
consistent with photochemical sources of HNO3, HNCO, formic, propionic,
butyric, valeric, and pyruvic acid. Vertical profiles taken on the 300 m
tower demonstrate net surface-level emissions of alkanoic acids, but net
surface deposition of HNO3 and pyruvic acid. The surface-level alkanoic
acid source persists through both day and night, and is thus not solely
photochemical. Reactions between O3 and organic surfaces may contribute
to the surface-level alkanoic acid source. Nearby traffic emissions and
agricultural activity are a primary source of propionic, butyric, and
valeric acids, and likely contribute photochemical precursors to HNO3
and HNCO. The combined diel and vertical profiles of the alkanoic acids and
HNCO are inconsistent with dry deposition and photochemical losses being the
only sinks, suggesting additional loss mechanisms.</p
Sources and Secondary Production of Organic Aerosols in the Northeastern United States during WINTER
Most intensive field studies investigating aerosols have been conducted in summer, and thus, wintertime aerosol sources and chemistry are comparatively poorly understood. An aerosol mass spectrometer was flown on the National Science Foundation/National Center for Atmospheric Research Câ130 during the Wintertime INvestigation of Transport, Emissions, and Reactivity (WINTER) 2015 campaign in the northeast United States. The fraction of boundary layer submicron aerosol that was organic aerosol (OA) was about a factor of 2 smaller than during a 2011 summertime study in a similar region. However, the OA measured in WINTER was almost as oxidized as OA measured in several other studies in warmer months of the year. Fiftyâeight percent of the OA was oxygenated (secondary), and 42% was primary (POA). Biomass burning OA (likely from residential heating) was ubiquitous and accounted for 33% of the OA mass. Using nonvolatile POA, one of two default secondary OA (SOA) formulations in GEOSâChem (v10â01) shows very large underpredictions of SOA and O/C (5Ă) and overprediction of POA (2Ă). We strongly recommend against using that formulation in future studies. Semivolatile POA, an alternative default in GEOSâChem, or a simplified parameterization (SIMPLE) were closer to the observations, although still with substantial differences. A case study of urban outflow from metropolitan New York City showed a consistent amount and normalized rate of added OA mass (due to SOA formation) compared to summer studies, although proceeding more slowly due to lower OH concentrations. A box model and SIMPLE perform similarly for WINTER as for Los Angeles, with an underprediction at ages \u3c6 hr, suggesting that fast chemistry might be missing from the models
A Correlation Between the Ionization State of the Inner Accretion Disk and the Eddington Ratio of Active Galactic Nuclei
X-ray reflection features observed from the innermost regions of accretion
disks in Active Galactic Nuclei (AGNs) allow important tests of accretion
theory. In recent years it has been possible to use the Fe K line and
reflection continuum to parametrize the ionization state of the irradiated
inner accretion disk. Here, we collect 10 measurements of xi, the disk
ionization parameter, from 8 AGNs with strong evidence for reflection from the
inner accretion disk and good black hole mass estimates. We find strong
statistical evidence (98.56% confidence) for a nearly linear correlation
between xi and the AGN Eddington ratio. Moreover, such a correlation is
predicted by a simple application of alpha-disk accretion theory, albeit with a
stronger dependence on the Eddington ratio. The theory shows that there will be
intrinsic scatter to any correlation as a result of different black hole spins
and radii of reflection. There are several possibilities to soften the
predicted dependence on the Eddington ratio to allow a closer agreement with
the observed correlation, but the current data does not allow for an unique
explanation. The correlation can be used to estimate that MCG-6-30-15 should
have a highly ionized inner accretion disk, which would imply a black hole spin
of ~0.8. Additional measurements of xi from a larger sample of AGNs are needed
to confirm the existence of this correlation, and will allow investigation of
the accretion disk/corona interaction in the inner regions of accretion disks.Comment: 21 pages, 2 figures, accepted by Ap
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