One of the major conundrums in oceanography for the past 20 y has been that, although the total flux of dissolved organic carbon (OC; DOC) discharged annually to the global ocean can account for the ...turnover time of all oceanic DOC (ca. 4,000–6,000 y), chemical biomarker and stable isotopic data indicate that there is very little terrestrially derived OC (TerrOC) in the global ocean. Similarly, it has been estimated that only 30% of the TerrOC buried in marine sediments is of terrestrial origin in muddy deltaic regions with high sedimentation rates. If vascular plant material—assumed to be highly resistant to decay—makes up much of the DOC and particulate OC of riverine OC (along with soil OC), why do we not see more TerrOC in coastal and oceanic waters and sediments? An explanation for this "missing" TerrOC in the ocean is critical in our understanding of the global carbon cycle. Here, I consider the origin of vascular plants, the major component of TerrOC, and how their appearance affected the overall cycling of OC on land. I also examine the role vascular plant material plays in soil OC, inland aquatic ecosystems, and the ocean, and how our understanding of TerrOC and "priming" processes in these natural systems has gained considerable interests in the terrestrial literature, but has largely been ignored in the aquatic sciences. Finally, I close by postulating that priming is in fact an important process that needs to be incorporated into global carbon models in the context of climate change.
I show here that the bulk of the dust mass in a galaxy can be equivalently estimated from i) the full spectral energy distribution of dust emission, using the approach of Draine & Li (2007, ApJ, 657, ...810) that includes a distribution of dust grains and a range of interstellar radiation field intensities; ii) the emission in the wavelength range 100 μm ≤ λ ≤ 500 μm (covered by the Herschel Space Observatory), by fitting a simpler single-temperature modified blackbody to the data. Recent claims to the contrary should be interpreted as a caveat in the simpler fits to use an absorption cross section which is consistent both in the normalization and in the spectral index β with that of the full dust model. I also show that the dust mass does not depend significantly on the choice of β, if both the dust mass and the absorption cross section are derived with the same assumption on β.
Aims. I present the Monte Carlo radiative transfer code TRADING (Transfer of RAdiation through Dust In Galaxies). The code self-consistently computes the extinction of radiation in a dusty medium ...(including absorption and scattering) and the dust emission. Methods. A binary-tree adaptive grid is used for the description of the dust distribution. Dust radiation is computed at thermal equilibrium or under stochastic heating conditions, for a distribution of grains of different radii and materials. The code is applied to the case of a clumpy galactic disk, including both diffuse dust and a distribution of spherical clouds modelled on the GMCs of local galaxies. Diffuse and localised sources of starlight are used, with independent spectra. Results. A model is provided for the edge-on galaxy NGC 891. The SED of the galaxy from the UV to the submm/mm range can be well reproduced by a bulge/disk configuration of old stars together with an extended dust disk, as suggested by the analysis of optical/near-infrared images; a clumpy dust distribution of the same mass as the diffuse dust disk, together with a UV emitting component, half of which is in the form of a diffuse disk and half in sources embedded in clouds. In total, it is found that about 35% of the bolometric radiation is absorbed (and emitted) by dust; that absorption of starlight from the old population contributes to about 60% of the dust emission. A significant component of the dust emission from clouds is due to absorption of diffuse radiation. Radial profiles of dust emission in a clumpy disk are almost independent of the wavelength, with the exception of the wavelength range on the Wien side of the thermal equilibrium peak.
Plastics in the Earth system Stubbins, Aron; Law, Kara Lavender; Muñoz, Samuel E. ...
Science (American Association for the Advancement of Science),
07/2021, Letnik:
373, Številka:
6550
Journal Article
Recenzirano
Plastic contamination of the environment is a global problem whose magnitude justifies the consideration of plastics as emergent geomaterials with chemistries not previously seen in Earth’s history. ...At the elemental level, plastics are predominantly carbon. The comparison of plastic stocks and fluxes to those of carbon reveals that the quantities of plastics present in some ecosystems rival the quantity of natural organic carbon and suggests that geochemists should now consider plastics in their analyses. Acknowledging plastics as geomaterials and adopting geochemical insights and methods can expedite our understanding of plastics in the Earth system. Plastics also can be used as global-scale tracers to advance Earth system science.
A
bstract
We show that the two-point function of protected bi-scalar operators in
N
= 4 SYM evaluated in dimensional regularization exhibits a uniform transcendental weight up to three-loop order. We ...conjecture that this property holds for the whole perturbative series and leverage the explicit results to postulate a prediction for the leading, order
ϵ
, correction to all loop orders. We also consider the soft limit of three-point functions of such operators in momentum space and point out a simple and surprising perturbative relation to two-point functions, which we also extrapolate to all loop orders.
A
bstract
We present the three-point function of two spin-two and one scalar twist-two operators in 𝒩 = 4 SYM up to three perturbative orders at weak coupling, obtained via a direct Feynman ...diagrammatic calculation.
This book is a comprehensive reference and practical guide on the technology and application of ultrasound to the musculoskeletal system. It is organized into two main sections. The first is devoted ...to general aspects, while the second provides a systematic overview of the applications of musculoskeletal ultrasound in different areas of the body. Each chapter of the second section provides an introduction on clinical anatomy and the essentials of clinical history and physical examination. Thereafter, performance of the ultrasound study is explained and the normal and pathological anatomy is reviewed. To assist in understanding, the ultrasound scans are correlated with drawings, photographs, images obtained using other modalities, and anatomic specimens. There is a generous complement of high-quality illustrations based on high-end equipment. This book contains a wealth of invaluable information.
The X-ray spectra of many active galactic nuclei (AGNs) show a soft X-ray excess below 1–2 keV on top of the extrapolated high-energy power law. The origin of this component is uncertain. It could be ...a signature of relativistically blurred, ionized reflection or the high-energy tail of thermal Comptonization in a warm (kT ~ 1 keV), optically thick (τ ≃ 10–20) corona producing the optical/UV to soft X-ray emission. The purpose of the present paper is to test the warm corona model on a statistically significant sample of unabsorbed, radio-quiet AGNs with XMM-Newton archival data, providing simultaneous optical/UV and X-ray coverage. The sample has 22 objects and 100 observations. We use two thermal Comptonization components to fit the broadband spectra, one for the warm corona emission and one for the high-energy continuum. In the optical/UV, we also include the reddening, the small blue bump, and the Galactic extinction. In the X-rays, we include a warm absorber and a neutral reflection. The model gives a good fit (reduced χ2 < 1.5) to more than 90% of the sample. We find the temperature of the warm corona to be uniformly distributed in the 0.1–1 keV range, while the optical depth is in the range ~10–40. These values are consistent with a warm corona covering a large fraction of a quasi-passive accretion disk, i.e., that mostly reprocesses the warm corona emission. The disk intrinsic emission represents no more than 20% of the disk total emission. According to this interpretation, most of the accretion power would be released in the upper layers of the accretion flow.
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