| 21. |
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| 22. |
- Zasowski, G., et al.
(författare)
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APOGEE DR14/DR15 Abundances in the Inner Milky Way
- 2019
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Ingår i: Astrophysical Journal. - : Institute of Physics Publishing (IOPP). - 0004-637X .- 1538-4357. ; 870:2
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Tidskriftsartikel (refereegranskat)abstract
- We present an overview of the distributions of 11 elemental abundances in the Milky Way's (MW) inner regions, as traced by APOGEE stars released as part of the Sloan Digital Sky Survey Data Release. 14/15 (DR14/DR15), including O, Mg, Si, Ca, Cr, Mn, Co, Ni, Na, Al, and K. This sample spans similar to 4000 stars with R-GC <= 4.0 kpc, enabling the most comprehensive study to date of these abundances and their variations within the innermost few kiloparsecs of the MW. We describe the observed abundance patterns ([X/Fe]-[Fe/H]), compare to previous literature results and to patterns in stars at the solar Galactocentric radius (R-GC), and discuss possible trends with DR14/DR15 effective temperatures. We find that the position of the [Mg/Fe]-[Fe/H] "knee" is nearly constant with R-GC, indicating a well-mixed star-forming medium or high levels of radial migration in the early inner Galaxy. We quantify the linear correlation between pairs of elements in different subsamples of stars and find that these relationships vary; some abundance correlations are very similar between the alpha-rich and alpha-poor stars, but others differ significantly, suggesting variations in the metallicity dependencies of certain supernova yields. These empirical trends will form the basis for more detailed future explorations and for the refinement of model comparison metrics. That the inner MW abundances appear dominated by a single chemical evolutionary track and that they extend to such high metallicities underscore the unique importance of this part of the Galaxy for constraining the ingredients of chemical evolution modeling and for improving our understanding of the evolution of the Galaxy as a whole.
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| 23. |
- Zastrow, K. D., et al.
(författare)
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Tritium transport experiments on the JET tokamak
- 2004
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Ingår i: Plasma Physics and Controlled Fusion. - 0741-3335 .- 1361-6587. ; 46, s. B255-B265
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Tidskriftsartikel (refereegranskat)abstract
- An overview is given of the experimental method, the analysis technique and the results for trace tritium experiments conducted on the JET tokamak in 2003. Observations associated with events such as sawtooth collapses, neo-classical tearing modes and edge localized modes are described. Tritium transport is seen to approach neo-classical levels in the plasma core at high density and low q(95), and in the transport barrier region of internal transport barrier (ITB) discharges. Tritium transport remains well above neo-classical levels in all other cases. The correlation of the measured tritium diffusion coefficient and convection velocity for normalized minor radii r/a = [0.65, 0.80] with the controllable parameters q95 and plasma density are found to be consistent for all operational regimes (ELMy H-mode discharges with or without ion cyclotron frequency resonance heating, hybrid scenario and ITB discharges). Scaling with local physics parameters is best described by gyro-Bohm scaling with an additional inverse beta dependence.
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| 25. |
- Zastruzny, Sebastian F., et al.
(författare)
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Accelerated permafrost thaw and increased drainage in the active layer : Responses from experimental surface alteration
- 2023
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Ingår i: Cold Regions Science and Technology. - 0165-232X. ; 212
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Tidskriftsartikel (refereegranskat)abstract
- Erosion and infrastructure in the Arctic can change the thickness of the active layer which can subsequently alternate the thermal-hydrological regime and change the drainage patterns on slopes. Previous studies have shown that drainage can either decrease due to the movement of water occurring in deeper soil layers with lower permeability or increase due to the formation of features like gullies and channels. In a field experiment conducted in Qaanaaq, Greenland, the surface topography was altered by adding 35 cm soil in one treatment, removing 33 cm in another, while an untreated plot measuring 10 × 10 m was maintained for comparison purposes. The temperature and water content of these plots were monitored in the three following years. Based on field measurements, a 1-dimensional model was set up in CoupModel to simulate the field experiment and quantify changes in the thickness of the saturated zone and drainage as a consequence of the treatment. Both field observations and simulations show that the addition and removal of soil changed the thickness of the saturated layer in the active layer, which changed the thermal properties in the soil and, thus, the response of thawing or recovery of permafrost. The simulations showed that during the summer depressions there were higher water contents, which accelerated warming of the soil and increased permafrost thawing of 35.7 cm in depth. In contrast, raising the soil surface aggregated only 19.8 cm of permafrost due to higher buffering from lower water contents. Changed active layer thickness altered the thickness of the saturated zone, leading to changed drainage patterns: In depressions, first drainage occurs three days earlier, and maximum daily drainage is increased by 154% as compared to ambient conditions. In contrast, raising the surface delayed the runoff from the plot by up to eight days, and decreased the maximum daily drainage to 72%. Effects of the treatment were most pronounced during the first year after the experiment, with diminishing effects during the consecutive year as the system equilibrated to the new state. Results from our study can advance our understanding of impacts of both natural and human-induced surface alterations on active layer thickening and water movement in permafrost-affected areas, which ultimately affect the entire ecosystem and the living conditions for local communities.
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| 26. |
- Zatcepin, Artem, et al.
(författare)
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Regional desynchronization of microglial activity is associated with cognitive decline in Alzheimer's disease
- 2024
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Ingår i: MOLECULAR NEURODEGENERATION. - 1750-1326. ; 19:1
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Tidskriftsartikel (refereegranskat)abstract
- BackgroundMicroglial activation is one hallmark of Alzheimer disease (AD) neuropathology but the impact of the regional interplay of microglia cells in the brain is poorly understood. We hypothesized that microglial activation is regionally synchronized in the healthy brain but experiences regional desynchronization with ongoing neurodegenerative disease. We addressed the existence of a microglia connectome and investigated microglial desynchronization as an AD biomarker.MethodsTo validate the concept, we performed microglia depletion in mice to test whether interregional correlation coefficients (ICCs) of 18 kDa translocator protein (TSPO)-PET change when microglia are cleared. Next, we evaluated the influence of dysfunctional microglia and AD pathophysiology on TSPO-PET ICCs in the mouse brain, followed by translation to a human AD-continuum dataset. We correlated a personalized microglia desynchronization index with cognitive performance. Finally, we performed single-cell radiotracing (scRadiotracing) in mice to ensure the microglial source of the measured desynchronization.ResultsMicroglia-depleted mice showed a strong ICC reduction in all brain compartments, indicating microglia-specific desynchronization. AD mouse models demonstrated significant reductions of microglial synchronicity, associated with increasing variability of cellular radiotracer uptake in pathologically altered brain regions. Humans within the AD-continuum indicated a stage-depended reduction of microglia synchronicity associated with cognitive decline. scRadiotracing in mice showed that the increased TSPO signal was attributed to microglia.ConclusionUsing TSPO-PET imaging of mice with depleted microglia and scRadiotracing in an amyloid model, we provide first evidence that a microglia connectome can be assessed in the mouse brain. Microglia synchronicity is closely associated with cognitive decline in AD and could serve as an independent personalized biomarker for disease progression.
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| 27. |
- Zaton, Michal, et al.
(författare)
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Earliest Triassic metazoan bioconstructions from East Greenland reveal a pioneering benthic community in the immediate aftermath of the end-Permian mass extinction
- 2018
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Ingår i: Global and Planetary Change. - : ELSEVIER SCIENCE BV. - 0921-8181 .- 1872-6364. ; 167, s. 87-98
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Tidskriftsartikel (refereegranskat)abstract
- Marine benthic ecosystems collapsed during the catastrophic end-Permian mass extinction, and subsequently endured a protracted phase of biotic recovery under harsh environmental conditions. In particular, metazoan reef communities almost totally disappeared and were replaced by microbe-dominated mounds during the latest Permian-earliest Triassic. Here we report the stratigraphically oldest exclusively metazoan bioconstructions from earliest Triassic (mid-Induan) strata in East Greenland - these formed within the first ca 300 ka after the Permian-Triassic boundary. Unlike the multitaxic sponge-microbe and bivalve-based buildups recorded from the Early Triassic peri-paleoequatorial Panthalassan and Tethyan margins, the East Greenland bioaccumulations developed within a restricted Boreal mid-paleolatitude seaway, and comprised a monospecific primary framework of microconchid 'lophophorate tubes with shell fragments and phosphatic debris cemented by biogenic calcite. Prostrate growth of the microconchids likely facilitated their accretion into successive sheet-like biostromes and small bioherms. These are associated with a regional paleoenvironmental shift towards well-oxygenated bottom waters, and locally punctuated sedimentation that created a favorable habitat. Although microconchids were both abundant and geographically widespread throughout the earliest Triassic, such buildups formed solely by these metazoans have not been reported from that time frame outside the Boreal Realm. These apparently flourished in the absence of more stable complex communities, and suggest that a locally variable, rather than ubiquitously sequential revival of metazoan bioconstruction activity took place in the immediate aftermath of the end-Permian extinction. However, these may also suggest that ecological recovery of benthic marine ecosystems following the end-Permian mass extinction might have started earlier in higher paleolatitudes.
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| 28. |
- Zaton, Michal, et al.
(författare)
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The first direct evidence of a Late Devonian coelacanth fish feeding on conodont animals
- 2017
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Ingår i: The Science of Nature. - : Springer Berlin/Heidelberg. - 0028-1042 .- 1432-1904. ; 104:3-4
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Tidskriftsartikel (refereegranskat)abstract
- We describe the first known occurrence of a Devonian coelacanth specimen from the lower Famennian of the Holy Cross Mountains, Poland, with a conodont element preserved in its digestive tract. A small spiral and phosphatic coprolite (fossil excrement) containing numerous conodont elements and other unrecognized remains was also found in the same deposits. The coprolite is tentatively attributed to the coelacanth. Although it is unclear whether the Late Devonian coelacanth from Poland was an active predator or a scavenger, these finds provide the first direct evidence of feeding on conodont animals by early coelacanth fish, and one of the few evidences of feeding on these animals known to date. It also expands our knowledge about the diet and trophic relations between the Paleozoic marine animals in general.
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