694 research outputs found
Nitrogen removal in marine environments: recent findings and future research challenges
Respiratory reduction of nitrate (denitrification) is recognized as the most important process converting biologically available (fixed) nitrogen to N2. In current N cycle models, a major proportion of global marine denitrification (50â70%) is assumed to take place on the sea floor, particularly in organic rich continental margin sediments. Recent observations indicate that present conceptual views of denitrification and pathways of nitrate reduction and N2 formation are incomplete. Alternative N cycle pathways, particularly in sediments, include anaerobic ammonium oxidation to nitrite, nitrate and N2 by Mn-oxides, and anaerobic ammonium oxidation coupled to nitrite reduction and subsequent N2 mobilization. The discovery of new links and feedback mechanisms between the redox cycles of, e.g., C, N, S, Mn and Fe casts doubt on the present general understanding of the global N cycle. Recent models of the oceanic N budget indicate that total inputs are significantly smaller than estimated fixed N removal. The occurrence of alternative N reaction pathways further exacerbates the apparent imbalance as they introduce additional routes of N removal. In this contribution, we give a brief historical background of the conceptual understanding of N cycling in marine ecosystems, emphasizing pathways of aerobic and anaerobic N mineralization in marine sediments, and the implications of recently recognized metabolic pathways for N removal in marine environments
Cryostratigraphy, sedimentology, and the late Quaternary evolution of the Zackenberg River delta, northeast Greenland
The Zackenberg River delta is located in northeast Greenland (74°30âČâŻN, 20°30âČâŻE) at the outlet of the Zackenberg fjord valley. The fjord-valley fill consists of a series of terraced deltaic deposits (ca. 2âŻkm2) formed during relative sea-level (RSL) fall. We investigated the deposits using sedimentological and cryostratigraphic techniques together with optically stimulated luminescence (OSL) dating. We identify four facies associations in sections (4 to 22âŻm in height) exposed along the modern Zackenberg River and coast. Facies associations relate to (I) overriding glaciers, (II) retreating glaciers and quiescent glaciomarine conditions, (III) delta progradation in a fjord valley, and (IV) fluvial activity and niveo-aeolian processes. Pore, layered, and suspended cryofacies are identified in two 20âŻm deep ice-bonded sediment cores. The cryofacies distribution, together with low overall ground-ice content, indicates that permafrost is predominately epigenetic in these deposits. Fourteen OSL ages constrain the deposition of the cored deposits to between approximately 13 and 11âŻka, immediately following deglaciation. The timing of permafrost aggradation was closely related to delta progradation and began following the subaerial exposure of the delta plain (ca. 11âŻka). Our results reveal information concerning the interplay between deglaciation, RSL change, sedimentation, permafrost aggradation, and the timing of these events. These findings have implications for the timing and mode of permafrost aggradation in other fjord valleys in northeast Greenland
The second-âharmonic generation in chalcogenide glass-âceramic doped with CdS nanocrystals
International audienceAn innovative way is proposed here to synthesize chalcogenide glass-âCdS nanocrystal composites by hot-âpressing a combination of Ge20Sb12S68 glassy powder and nonlinear CdS nanoparticles. The cadmium sulfide nanoparticles, which possess the second-âharmonic generation property, were synthesized from basic cadmium soln. strongly complexed by amine. The obtained nanocomposites present a homogeneous distribution of the crystals. The transmission reaches 30â% at 5 ÎŒm and up to 60â% at 10.6 ÎŒm. The second-âharmonic generation at 0.9 ÎŒm has been detected. This technique can overcome the uncontrollable hetero-âcrystn. which tends to occur in the glass-âceramics prepd. by the conventional thermal treatment method
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Cryostratigraphy, sedimentology, and the late Quaternary evolution of the Zackenberg River delta, northeast Greenland
The Zackenberg River delta is located in northeast Greenland (74°30âČâŻN, 20°30âČâŻE) at the outlet of the Zackenberg fjord valley. The fjord-valley fill consists of a series of terraced deltaic deposits (ca. 2âŻkm2) formed during relative sea-level (RSL) fall. We investigated the deposits using sedimentological and cryostratigraphic techniques together with optically stimulated luminescence (OSL) dating. We identify four facies associations in sections (4 to 22âŻm in height) exposed along the modern Zackenberg River and coast. Facies associations relate to (I) overriding glaciers, (II) retreating glaciers and quiescent glaciomarine conditions, (III) delta progradation in a fjord valley, and (IV) fluvial activity and niveo-aeolian processes. Pore, layered, and suspended cryofacies are identified in two 20âŻm deep ice-bonded sediment cores. The cryofacies distribution, together with low overall ground-ice content, indicates that permafrost is predominately epigenetic in these deposits. Fourteen OSL ages constrain the deposition of the cored deposits to between approximately 13 and 11âŻka, immediately following deglaciation. The timing of permafrost aggradation was closely related to delta progradation and began following the subaerial exposure of the delta plain (ca. 11âŻka). Our results reveal information concerning the interplay between deglaciation, RSL change, sedimentation, permafrost aggradation, and the timing of these events. These findings have implications for the timing and mode of permafrost aggradation in other fjord valleys in northeast Greenland
Effect of co-administered lopinavir/ritonavir and sulfamethoxazole/trimethoprim on cardiac function and architecture of albino rats
Background: Lopinavir/ritonavir (LPV/r) could be associated with adverse cardiac event. Antiretroviral drugs containing LPV/r are used concurrently with sulfamethoxazole/trimethoprim (SMX/TMP) which may also be associated with adverse cardiac events in the management of human immunodeficiency virus and co-infection. The concurrent use of these drugs may precipitate synergistic adverse cardiac events. This work, therefore, evaluates the possible toxicological interaction of co administered LPV/r and SMX/TMP on cardiac function and architecture of albino rats.Methods: Seventy five (75) animals which were divided into five groups (A-E) of fifteen (15) animals each were used in this study. Animals in Group A, which served as the control, were treated with 1% ethanol orally. Animals in Group (B-E) were treated with oral doses of SMX/TMP (11.2/2.3Â mg/kg), LPV/r (11.4/2.9Â mg/kg), and combine doses of SMX/TMP+LPV/r for 2-8Â weeks, respectively. Blood sample was collected and evaluated for pack cell volume, hemoglobin, red blood cell and white blood cell. Cardiac tissues were evaluated for malondialdehyde (MDA), superoxide dismutase (SOD), glutathione peroxidase (GSHPX), and histopathological changes.Results: Treatment with SMX/TMP LPV/r and their combine doses produced no significant effect on cardiac weight. SMX/TMP significantly decreased red blood cell and hemoglobin while LPV/r produced no significant hematologic effect. Combine doses of these agents produced no synergistic hematologic effects. Treatment with a single and combine doses of these agents produced time-dependent decrease in SOD, GSHPX and increase in MDA, but no synergistic effects were produced by their combine doses. Normal cardiac myocytes with patchy collection of mononuclear inflammatory cells infiltration of the interstitium were observed after treatment with single and combined doses of these agents but without any synergistic effect when agents were co-administered.Conclusion: In this study, the co-administration of SMX/TMP and LPV/r did not produce any significant synergistic effects on all the evaluated parameters; hence, the concurrent use of these agents in the management of HIV and co-infections may be safe on cardiac function and structure
Similar self-organizing scale-invariant properties characterize early cancer invasion and long range species spread
Occupancy of new habitats through dispersion is a central process in nature.
In particular, long range dispersal is involved in the spread of species and
epidemics, although it has not been previously related with cancer invasion, a
process that involves spread to new tissues. We show that the early spread of
cancer cells is similar to the species individuals spread and that both
processes are represented by a common spatio-temporal signature, characterized
by a particular fractal geometry of the boundaries of patches generated, and a
power law-scaled, disrupted patch size distribution. We show that both
properties are a direct result of long-distance dispersal, and that they
reflect homologous ecological processes of population self-organization. Our
results are significant for processes involving long-range dispersal like
biological invasions, epidemics and cancer metastasis.Comment: 21 pages, 2 figure
Resolution of the type material of the Asian elephant, Elephas maximus Linnaeus, 1758 (Proboscidea, Elephantidae)
The understanding of Earthâs biodiversity depends critically on the accurate identification and nomenclature of
species. Many species were described centuries ago, and in a surprising number of cases their nomenclature or type
material remain unclear or inconsistent. A prime example is provided by Elephas maximus, one of the most iconic
and well-known mammalian species, described and named by Linnaeus (1758) and today designating the Asian
elephant. We used morphological, ancient DNA (aDNA), and high-throughput ancient proteomic analyses to
demonstrate that a widely discussed syntype specimen of E. maximus, a complete foetus preserved in ethanol, is
actually an African elephant, genus Loxodonta. We further discovered that an additional E. maximus syntype,
mentioned in a description by John Ray (1693) cited by Linnaeus, has been preserved as an almost complete skeleton
at the Natural History Museum of the University of Florence. Having confirmed its identity as an Asian elephant
through both morphological and ancient DNA analyses, we designate this specimen as the lectotype of E. maximus
KELT-3b: A Hot Jupiter Transiting a V=9.8 Late-F Star
We report the discovery of KELT-3b, a moderately inflated transiting hot
Jupiter with a mass of 1.477 (-0.067, +0.066) M_J, and radius of 1.345 +/-
0.072 R_J, with an orbital period of 2.7033904 +/- 0.000010 days. The host
star, KELT-3, is a V=9.8 late F star with M_* = 1.278 (-0.061, +0.063) M_sun,
R_* = 1.472 (-0.067, +0.065) R_sun, T_eff = 6306 (-49, +50) K, log(g) = 4.209
(-0.031, +0.033), and [Fe/H] = 0.044 (-0.082, +0.080), and has a likely proper
motion companion. KELT-3b is the third transiting exoplanet discovered by the
KELT survey, and is orbiting one of the 20 brightest known transiting planet
host stars, making it a promising candidate for detailed characterization
studies. Although we infer that KELT-3 is significantly evolved, a preliminary
analysis of the stellar and orbital evolution of the system suggests that the
planet has likely always received a level of incident flux above the
empirically-identified threshold for radius inflation suggested by Demory &
Seager (2011).Comment: 12 pages, 12 figures, accepted to Ap
Ultra-bright single photon source based on an atomically thin material
Solid-state single photon sources are central building blocks in quantum
communication networks and on-chip quantum information processing. Atomically
thin crystals were established as possible candidates to emit non-classical
states of light, however, the performance of monolayer-based single photon
sources has so far been lacking behind state-of-the-art devices based on volume
crystals. Here, we implement a single photon source based on an atomically thin
sheet of WSe2 coupled to a spectrally tunable optical cavity. It is
characterized by a high single photon purity with a value as low
as and a record-high first lens brightness of linearly
polarized photons as large as . Interestingly, the high
performance of our devices allows us to observe genuine quantum interference
phenomena in a Hong-Ou-Mandel experiment. Our results demonstrate that open
cavities and two-dimensional materials constitute an excellent platform for
ultra-bright quantum light sources: the unique properties of such
two-dimensional materials and the versatility of open cavities open an
inspiring avenue for novel quantum optoelectronic devices.Comment: 12 pages, 7 figure
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