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- Aharonian, Felix, et al.
(author)
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Solar abundance ratios of the iron-peak elements in the Perseus cluster
- 2017
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In: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 551:7681, s. 478-
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Journal article (peer-reviewed)abstract
- The metal abundance of the hot plasma that permeates galaxy clusters represents the accumulation of heavy elements produced by billions of supernovae(1). Therefore, X-ray spectroscopy of the intracluster medium provides an opportunity to investigate the nature of supernova explosions integrated over cosmic time. In particular, the abundance of the iron-peak elements (chromium, manganese, iron and nickel) is key to understanding how the progenitors of typical type Ia supernovae evolve and explode(2-6). Recent X-ray studies of the intracluster medium found that the abundance ratios of these elements differ substantially from those seen in the Sun(7-11), suggesting differences between the nature of type Ia supernovae in the clusters and in the Milky Way. However, because the K-shell transition lines of chromium and manganese are weak and those of iron and nickel are very close in photon energy, highresolution spectroscopy is required for an accurate determination of the abundances of these elements. Here we report observations of the Perseus cluster, with statistically significant detections of the resonance emission from chromium, manganese and nickel. Our measurements, combined with the latest atomic models, reveal that these elements have near-solar abundance ratios with respect to iron, in contrast to previous claims. Comparison between our results and modern nucleosynthesis calculations(12-14) disfavours the hypothesis that type Ia supernova progenitors are exclusively white dwarfs with masses well below the Chandrasekhar limit (about 1.4 times the mass of the Sun). The observed abundance pattern of the iron-peak elements can be explained by taking into account a combination of near-and sub-Chandrasekhar-mass type Ia supernova systems, adding to the mounting evidence that both progenitor types make a substantial contribution to cosmic chemical enrichment(5,15,16).
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- Douglas, Peter M. J., et al.
(author)
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Clumped Isotopes Link Older Carbon Substrates With Slower Rates of Methanogenesis in Northern Lakes
- 2020
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In: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 47:6
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Journal article (peer-reviewed)abstract
- The release of long-stored carbon from thawed permafrost could fuel increased methanogenesis in northern lakes, but it remains unclear whether old carbon substrates released from permafrost are metabolized as rapidly by methanogenic microbial communities as recently produced organic carbon. Here, we apply methane (CH4) clumped isotope (Delta(18)) and C-14 measurements to test whether rates of methanogenesis are related to carbon substrate age. Results from culture experiments indicate that Delta(18) values are negatively correlated with CH4 production rate. Measurements of ebullition samples from thermokarst lakes in Alaska and glacial lakes in Sweden indicate strong negative correlations between CH4 Delta(18) and the fraction modern carbon. These correlations imply that CH4 derived from older carbon substrates is produced relatively slowly. Relative rates of methanogenesis, as inferred from Delta(18) values, are not positively correlated with CH4 flux estimates, highlighting the likely importance of environmental variables other than CH4 production rates in controlling ebullition fluxes. Plain Language Summary There is concern that carbon from thawed permafrost will be emitted to the atmosphere as methane (CH4). It is currently uncertain whether old organic carbon from thawed permafrost can be converted to CH4 as rapidly as organic carbon recently fixed by primary producers. We address this question by combining radiocarbon and clumped isotope measurements of CH4 from lakes in permafrost landscapes. Radiocarbon (C-14) measurements indicate the age of CH4 carbon sources. We present data from culture experiments that support the hypothesis that clumped isotope values are dependent on microbial CH4 production rate. In lake bubble samples, we observe a strong correlation between these two measurements, which implies that CH4 formed from older carbon is produced relatively slowly. We also find that higher rates of CH4 production, as inferred from clumped isotopes, are not linked to higher rates of CH4 emissions, implying that variables other than CH4 production rate strongly influence emission rates.
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| 17. |
- Douglas, P. M. J., et al.
(author)
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Diverse origins of Arctic and Subarctic methane point source emissions identified with multiply-substituted isotopologues
- 2016
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In: Geochimica et Cosmochimica Acta. - : Elsevier BV. - 0016-7037 .- 1872-9533. ; 188, s. 163-188
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Journal article (peer-reviewed)abstract
- Methane is a potent greenhouse gas, and there are concerns that its natural emissions from the Arctic could act as a substantial positive feedback to anthropogenic global warming. Determining the sources of methane emissions and the biogeochemical processes controlling them is important for understanding present and future Arctic contributions to atmospheric methane budgets. Here we apply measurements of multiply-substituted isotopologues, or clumped isotopes, of methane as a new tool to identify the origins of ebullitive fluxes in Alaska, Sweden and the Arctic Ocean. When methane forms in isotopic equilibrium, clumped isotope measurements indicate the formation temperature. In some microbial methane, however, non-equilibrium isotope effects, probably related to the kinetics of methanogenesis, lead to low clumped isotope values. We identify four categories of emissions in the studied samples: thermogenic methane, deep subsurface or marine microbial methane formed in isotopic equilibrium, freshwater microbial methane with non-equilibrium clumped isotope values, and mixtures of deep and shallow methane (i.e., combinations of the first three end members). Mixing between deep and shallow methane sources produces a non-linear variation in clumped isotope values with mixing proportion that provides new constraints for the formation environment of the mixing end-members. Analyses of microbial methane emitted from lakes, as well as a methanol-consuming methanogen pure culture, support the hypothesis that non-equilibrium clumped isotope values are controlled, in part, by kinetic isotope effects induced during enzymatic reactions involved in methanogenesis. Our results indicate that these kinetic isotope effects vary widely in microbial methane produced in Arctic lake sediments, with non-equilibrium Delta(18) values spanning a range of more than 5 parts per thousand.
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| 18. |
- Emerson, Joanne B., et al.
(author)
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Diverse sediment microbiota shape methane emission temperature sensitivity in Arctic lakes
- 2021
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In: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 12
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Journal article (peer-reviewed)abstract
- Northern post-glacial lakes are significant, increasing sources of atmospheric carbon through ebullition (bubbling) of microbially-produced methane (CH4) from sediments. Ebullitive CH4 flux correlates strongly with temperature, reflecting that solar radiation drives emissions. However, here we show that the slope of the temperature-CH4 flux relationship differs spatially across two post-glacial lakes in Sweden. We compared these CH4 emission patterns with sediment microbial (metagenomic and amplicon), isotopic, and geochemical data. The temperature-associated increase in CH4 emissions was greater in lake middles—where methanogens were more abundant—than edges, and sediment communities were distinct between edges and middles. Microbial abundances, including those of CH4-cycling microorganisms and syntrophs, were predictive of porewater CH4 concentrations. Results suggest that deeper lake regions, which currently emit less CH4 than shallower edges, could add substantially to CH4 emissions in a warmer Arctic and that CH4 emission predictions may be improved by accounting for spatial variations in sediment microbiota.
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| 19. |
- Fischer, Hakan, et al.
(author)
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Right-sided human prefrontal brain activation during acquisition of conditioned fear.
- 2002
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In: Emotion. - : American Psychological Association (APA). - 1528-3542 .- 1931-1516. ; 2:3, s. 233-41
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Journal article (peer-reviewed)abstract
- This H2(15)O positron emission tomography (PET) study reports on relative regional cerebral blood flow (rCBF) alterations during fear conditioning in humans. In the PET scanner, subjects viewed a TV screen with either visual white noise or snake videotapes displayed alone, then with electric shocks, followed by final presentations of white noise and snakes. Autonomic nervous system responses confirmed fear conditioning only to snakes. To reveal neural activation during acquisition, while equating sensory stimulation, scans during snakes with shocks and white noise alone were contrasted against white noise with shocks and snakes alone. During acquisition, rCBF increased in the right medial frontal gyrus, supporting a role for the prefrontal cortex in fear conditioning to unmasked evolutionary fear-relevant stimuli.
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| 20. |
- Hagberg, L, et al.
(author)
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Determination of biomechanical characteristics of restrictive adhesions and of functional impairment after flexor tendon surgery : a methodological study of rabbits.
- 1991
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In: Journal of Biomechanics. - 0021-9290 .- 1873-2380. ; 24:10, s. 935-42
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Journal article (peer-reviewed)abstract
- Formation of restrictive adhesions is one of the main obstacles in rehabilitation following hand surgery. Most experimental work, however, involves only a macroscopic and/or histologic evaluation of the amount of adhesions, and their functional characteristics are poorly described. The aim of this study was to develop an experimental technique for characterization of the biomechanical properties of the finger-tendon unit. An instrument was developed for continuous and simultaneous recording of tensile load, tendon excursion and angular rotation in the distal interphalangeal joint of rabbit digits. Utilizing this instrument, it was revealed that the first 50 degrees of flexion required virtually no tensile load either in unoperated digits or immediately after tenorrhaphy. Thereafter, the load required to obtain further flexion was progressively increased. The strength of adhesions, determined 2 weeks after tenorrhaphy, was best expressed as the maximum tensile load recorded before 50 degrees of flexion was reached. This measurement could also be used to register the strength of the tendon repair and to detect partial tendon rupture during the measurement. The technique allows both adequate measurements of the strength of the adhesions and of the tendon gliding ability after flexor tendon surgery.
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| 23. |
- Solorzano, Leslie, 1989-, et al.
(author)
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Machine learning for cell classification and neighborhood analysis in glioma tissue
- 2021
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In: Cytometry Part A. - : Wiley. - 1552-4922 .- 1552-4930. ; 99:12, s. 1176-1186
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Journal article (peer-reviewed)abstract
- Multiplexed and spatially resolved single-cell analyses that intend to study tissue heterogeneity and cell organization invariably face as a first step the challenge of cell classification. Accuracy and reproducibility are important for the downstream process of counting cells, quantifying cell-cell interactions, and extracting information on disease-specific localized cell niches. Novel staining techniques make it possible to visualize and quantify large numbers of cell-specific molecular markers in parallel. However, due to variations in sample handling and artifacts from staining and scanning, cells of the same type may present different marker profiles both within and across samples. We address multiplexed immunofluorescence data from tissue microarrays of low-grade gliomas and present a methodology using two different machine learning architectures and features insensitive to illumination to perform cell classification. The fully automated cell classification provides a measure of confidence for the decision and requires a comparably small annotated data set for training, which can be created using freely available tools. Using the proposed method, we reached an accuracy of 83.1% on cell classification without the need for standardization of samples. Using our confidence measure, cells with low-confidence classifications could be excluded, pushing the classification accuracy to 94.5%. Next, we used the cell classification results to search for cell niches with an unsupervised learning approach based on graph neural networks. We show that the approach can re-detect specialized tissue niches in previously published data, and that our proposed cell classification leads to niche definitions that may be relevant for sub-groups of glioma, if applied to larger data sets.
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| 24. |
- Tapp, I, et al.
(author)
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Homogenous scoring of single nucleotide polymorphism markers: The 5´-nuclease
- 2000
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In: Biotechniques. ; 28, s. 732-
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Journal article (peer-reviewed)abstract
- An exceptional disposition of the elongation factor genes is observed in Rickettsia prowazekii, in which there is only one tuf gene, which is distant from the lone firs gene, In contrast, the closely related bacterium Agrobacterium tumefaciens has the nor
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| 25. |
- Wadström, J, et al.
(author)
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An in vivo method for studies of traumatic vasospasm.
- 1990
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In: Microsurgery. - 0738-1085 .- 1098-2752. ; 11:3, s. 197-203
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Journal article (peer-reviewed)abstract
- A study was undertaken to develop a model for investigations of traumatically induced vasospasm. The left ear of the rabbit was denervated under short anesthesia. With the animal under light sedation, spasm of the central ear artery was repeatedly induced with a clip applying forceps. To evaluate the vasospasm, the vessel was transilluminated with cold light, and the internal diameter was continuously measured. The spasm was assessed in terms of its duration, intensity (reduction of initial diameter) and severity (integrated change in diameter over time). Repetitive application of the forceps on the same vessel segment shortened the spasm duration. With prolonged pinch duration, the spasm duration was lengthened. The preparation was stable for at least 3 hours. This model was effective for manipulating small vessels and producing spasm and is of potential value for studying the treatment of vasospasm by topical local intra-arterial and systemic methods.
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| 26. |
- Wintoft, P, et al.
(author)
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Predictions of local ground geomagnetic field fluctuations during the 7-10 November 2004 events studied with solar wind driven models
- 2005
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In: Annales Geophysicae. - 1432-0576. ; 23:9, s. 3095-3101
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Journal article (peer-reviewed)abstract
- The 7-10 November 2004 period contains two events for which the local ground magnetic field was severely disturbed and simultaneously, the solar wind displayed several shocks and negative B-z periods. Using empirical models the 10-min RMS Delta X and Delta Y at Brorfelde (BFE, 11.67 degrees E, 55.63 degrees N), Denmark, are predicted. The models are recurrent neural networks with 10-min solar wind plasma and magnetic field data as inputs. The predictions show a good agreement during 7 November, up until around noon on 8 November, after which the predictions become significantly poorer. The correlations between observed and predicted log RMS Delta X is 0.77 during, 7-8 November but drops to 0.38 during 9-10 November. For RMS Delta Y the correlations for the two periods are 0.71 and 0.41, respectively. Studying the solar wind data for other L1-spacecraft (WIND and SOHO) it seems that the ACE data have a better agreement to the near-Earth solar wind during the first two days as compared to the last two days. Thus, the accuracy of the predictions depends on the location of the spacecraft and the solar wind flow direction. Another finding, for the events studied here, is that the Delta X and Delta Y models showed a very different dependence on B-z The Delta X model is almost independent of the solar wind magnetic field B-z except at times when B-z is exceptionally large or when the overall activity is low. On the contrary, the Delta Y model shows a strong dependence on B-z at all times.
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