| 1. |
- Aharonian, Felix, et al.
(författare)
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Hitomi X-ray studies of giant radio pulses from the Crab pulsar
- 2018
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Ingår i: Publications of the Astronomical Society of Japan. - : Oxford University Press (OUP). - 0004-6264 .- 2053-051X. ; 70:2
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Tidskriftsartikel (refereegranskat)abstract
- To search for giant X-ray pulses correlated with the giant radio pulses (GRPs) from the Crab pulsar, we performed a simultaneous observation of the Crab pulsar with the X-ray satellite Hitomi in the 2-300 keV band and the Kashima NICT radio telescope in the 1.4-1.7 GHz band with a net exposure of about 2 ks on 2016 March 25, just before the loss of the Hitomi mission. The timing performance of the Hitomi instruments was confirmed to meet the timing requirement and about 1000 and 100 GRPs were simultaneously observed at the main pulse and inter-pulse phases, respectively, and we found no apparent correlation between the giant radio pulses and the X-ray emission in either the main pulse or inter-pulse phase. All variations are within the 2 sigma fluctuations of the X-ray fluxes at the pulse peaks, and the 3 sigma upper limits of variations of main pulse or inter-pulse GRPs are 22% or 80% of the peak flux in a 0.20 phase width, respectively, in the 2-300 keV band. The values for main pulse or inter-pulse GRPs become 25% or 110%, respectively, when the phase width is restricted to the 0.03 phase. Among the upper limits from the Hitomi satellite, those in the 4.5-10 keV and 70-300 keV bands are obtained for the first time, and those in other bands are consistent with previous reports. Numerically, the upper limits of the main pulse and inter-pulse GRPs in the 0.20 phase width are about (2.4 and 9.3) x 10(-11) erg cm(-2), respectively. No significant variability in pulse profiles implies that the GRPs originated from a local place within the magneto-sphere. Although the number of photon-emitting particles should temporarily increase to account for the brightening of the radio emission, the results do not statistically rule out variations correlated with the GRPs, because the possible X-ray enhancement may appear due to a > 0.02% brightening of the pulse-peak flux under such conditions.
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| 2. |
- Algaba, Juan-Carlos, et al.
(författare)
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Broadband Multi-wavelength Properties of M87 during the 2017 Event Horizon Telescope Campaign
- 2021
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8213 .- 2041-8205. ; 911:1
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Forskningsöversikt (refereegranskat)abstract
- In 2017, the Event Horizon Telescope (EHT) Collaboration succeeded in capturing the first direct image of the center of the M87 galaxy. The asymmetric ring morphology and size are consistent with theoretical expectations for a weakly accreting supermassive black hole of mass ∼6.5 × 109 M o˙. The EHTC also partnered with several international facilities in space and on the ground, to arrange an extensive, quasi-simultaneous multi-wavelength campaign. This Letter presents the results and analysis of this campaign, as well as the multi-wavelength data as a legacy data repository. We captured M87 in a historically low state, and the core flux dominates over HST-1 at high energies, making it possible to combine core flux constraints with the more spatially precise very long baseline interferometry data. We present the most complete simultaneous multi-wavelength spectrum of the active nucleus to date, and discuss the complexity and caveats of combining data from different spatial scales into one broadband spectrum. We apply two heuristic, isotropic leptonic single-zone models to provide insight into the basic source properties, but conclude that a structured jet is necessary to explain M87's spectrum. We can exclude that the simultaneous γ-ray emission is produced via inverse Compton emission in the same region producing the EHT mm-band emission, and further conclude that the γ-rays can only be produced in the inner jets (inward of HST-1) if there are strongly particle-dominated regions. Direct synchrotron emission from accelerated protons and secondaries cannot yet be excluded.
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| 3. |
- Attié, David, et al.
(författare)
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A time projection chamber with GEM-based readout
- 2017
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Ingår i: Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. - : Elsevier BV. - 0168-9002. ; 856, s. 109-118
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Tidskriftsartikel (refereegranskat)abstract
- For the International Large Detector concept at the planned International Linear Collider, the use of time projection chambers (TPC) with micro-pattern gas detector readout as the main tracking detector is investigated. In this paper, results from a prototype TPC, placed in a 1. T solenoidal field and read out with three independent Gas Electron Multiplier (GEM) based readout modules, are reported. The TPC was exposed to a 6. GeV electron beam at the DESY II synchrotron. The efficiency for reconstructing hits, the measurement of the drift velocity, the space point resolution and the control of field inhomogeneities are presented.
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| 4. |
- Kim, Yong Suk, et al.
(författare)
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Greenhouse gas emissions after a prescribed fire in white birch-dwarf bamboo stands in northern Japan, focusing on the role of charcoal
- 2011
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Ingår i: European Journal of Forest Research. - : Springer Science and Business Media LLC. - 1612-4669 .- 1612-4677. ; 130:6, s. 1031-1044
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Tidskriftsartikel (refereegranskat)abstract
- Forest fires affect both carbon (C) and nitrogen (N) cycling in forest ecosystems, and thereby influence the soil-atmosphere exchange of major greenhouse gases (GHGs): carbon dioxide (CO(2)), methane (CH(4)), and nitrous oxide (N(2)O). To determine changes in the soil GHG fluxes following a forest fire, we arranged a low-intensity surface fire in a white birch forest in northern Japan. We established three treatments, having four replications each: a control plot (CON), a burned plot (BURN), and a plot burned with removal of the resulting charcoal (BURN-CHA). Soil GHG fluxes and various properties of the soil were determined on four or five occasions during a period that spanned two growing seasons. We observed increased concentrations of ammonium-N (NH(4)-N) in BURN and BURN-CHA after the fire, while nitrate-N (NO(3)-N) concentration was only increased in BURN-CHA after the fire. The soil CO(2) flux was significantly higher in CON than in BURN or BURN-CHA, but there was no difference in soil CH(4) uptake between the three treatments. Moreover, the N(2)O flux from BURN-CHA soil was slightly greater than in CON or BURN. In BURN-CHA, the soil N(2)O flux peaked in August, but there was no peak in BURN. We found temporal correlations between soil GHG fluxes and soil variables, e.g. soil temperature or NO(3)-N. Our results suggest that environmental changes following fire, including the increased availability of N and the disappearance of the litter layer, have the potential to change soil GHG fluxes. Fire-produced charcoal could be significant in reducing soil N(2)O flux in temperate forests.
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| 5. |
- Kitamura, Keiko, et al.
(författare)
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Decline in gene diversity and strong genetic drift in the northward-expanding marginal populations of Fagus crenata
- 2015
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Ingår i: Tree Genetics & Genomes. - : Springer Science and Business Media LLC. - 1614-2942 .- 1614-2950. ; 11:3
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Tidskriftsartikel (refereegranskat)abstract
- The species distribution of Fagus crenata, or Japanese beech, in the Japanese archipelago shifted northward during phytogeographical changes that occurred during the Pleistocene and Holocene epochs. Presently, the continuous natural distribution of beech reaches north to the Kuromatsunai-Depression of Hokkaido Island, Japan. In addition, dozens of marginal patches and isolated individuals north of the continuous distribution have been observed. F. crenata grows remarkably well among these small-scattered northern marginal populations, which must have originated from seeds dispersed beyond the northern limit of the continuous beech forest. It is conceivable that the distribution of F. crenata is still in the process of expanding northward. We investigated the genetic structure of 33 beech populations to evaluate the population gene diversity at the leading northern edge of the range expansion. We analyzed 12 nuclear microsatellite loci in each of the 1,693 individuals. Genetic diversity parameters such as expected heterozygosity and allelic richness were clearly lower in the northernmost populations. We found genetic differentiation in the northernmost distribution range (F-ST=0.045, G(ST)'=0.242). STRU CTURE analysis revealed that the southwestern continuous populations consisted of homogeneous ancestral clusters. However, northeastern marginal populations consisted of mixtures of highly differentiated clusters with higher levels of genetic drift than found in the continuous populations.
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| 6. |
- Klaminder, Jonatan, et al.
(författare)
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Physical mixing between humus and mineral matter found in cryoturbated soils increases short-term heterotrophic respiration rates
- 2013
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Ingår i: Soil Biology and Biochemistry. - : Elsevier BV. - 0038-0717 .- 1879-3428. ; 57, s. 922-924
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Tidskriftsartikel (refereegranskat)abstract
- Cryoturbation is an important mechanism in the most recent large-scale model describing the build-up of soil organic carbon (SOC) in arctic soils. In this paper, we hypothesize that the physical mixing of humus and mineral soil generated by this process causes previously unconsidered effects on respiration rates. Through laboratory incubations we found that mixing of humus into mineral soil from cryoturbated soils primed heterotrophic respiration rates by about 40%, which was of the same magnitude as the effect generated by a rise in soil temperature from 5 degrees C to 10 degrees C. Our result indicates that cryogenic mixing, if complete, may generate short-term positive effects on heterotrophic respiration rates as long as the mixing does not translocate carbon into much colder soil layers. (C) 2012 Elsevier Ltd. All rights reserved.
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| 7. |
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| 8. |
- Kobayashi, Makoto, et al.
(författare)
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Bark-beetle-attacked trees produced more charcoal than unattacked trees during a forest fire on the Kenai Peninsula, Southern Alaska
- 2012
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Ingår i: Scandinavian Journal of Forest Research. - : Informa UK Limited. - 0282-7581 .- 1651-1891. ; 27:1, s. 30-35
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Tidskriftsartikel (refereegranskat)abstract
- Alaskan boreal forests frequently suffer from outbreaks of bark beetles and fires, factors that appear to combine to alter charcoal production. Charcoal (black carbon) production in forest ecosystems is an important pathway to clarify for a more complete understanding of the effects of fire on carbon cycling in boreal forests. In this study, we aimed to clarify the effects of prevalent outbreaks of the spruce beetle, Dendroctonus rufipennis (Kirby), on charcoal production during forest fires in boreal forests. Snags with prefire damage by the spruce beetle (infested snags) have significantly more charcoal than those undamaged before fire (noninfested snags). This increased amount of charcoal in spruce beetle-damaged trees was probably the result of dried biomass in the canopies of these trees. The results of this study suggest that with changing environmental conditions, the proliferation of insect damage in the boreal forest can modify the effects of fire on carbon sink via a change in the amount of charcoal production.
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| 9. |
- Krab, Eveline J., et al.
(författare)
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Winter warming effects on tundra shrub performance are species-specific and dependent on spring conditions
- 2018
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Ingår i: Journal of Ecology. - : John Wiley & Sons. - 0022-0477 .- 1365-2745. ; 106:2, s. 599-612
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Tidskriftsartikel (refereegranskat)abstract
- Climate change-driven increases in winter temperatures positively affect conditions for shrub growth in arctic tundra by decreasing plant frost damage and stimulation of nutrient availability. However, the extent to which shrubs may benefit from these conditions may be strongly dependent on the following spring climate. Species-specific differences in phenology and spring frost sensitivity likely affect shrub growth responses to warming. Additionally, effects of changes in winter and spring climate may differ over small spatial scales, as shrub growth may be dependent on natural variation in snow cover, shrub density and cryoturbation. We investigated the effects of winter warming and altered spring climate on growing-season performance of three common and widespread shrub species in cryoturbated non-sorted circle arctic tundra. By insulating sparsely vegetated non-sorted circles and parts of the surrounding heath with additional snow or gardening fleeces, we created two climate change scenarios: snow addition increased soil temperatures in autumn and winter and delayed snowmelt timing without increasing spring temperatures, whereas fleeces increased soil temperature similarly in autumn and winter, but created warmer spring conditions without altering snowmelt timing. Winter warming affected shrub performance, but the direction and magnitude were species-specific and dependent on spring conditions. Spring warming advanced, and later snowmelt delayed canopy green-up. The fleece treatment did not affect shoot growth and biomass in any shrub species despite decreasing leaf frost damage in Empetrum nigrum. Snow addition decreased frost damage and stimulated growth of Vaccinium vitis-idaea by c. 50%, while decreasing Betula nana growth (p < .1). All of these effects were consistent the mostly barren circles and surrounding heath. Synthesis. In cryoturbated arctic tundra, growth of Vaccinium vitis-idaea may substantially increase when a thicker snow cover delays snowmelt, whereas in longer term, warmer winters and springs may favour E. nigrum instead. This may affect shrub community composition and cover, with potentially far-reaching effects on arctic ecosystem functioning via its effects on cryoturbation, carbon cycling and trophic cascading. Our results highlight the importance of disentangling effects of winter and spring climate change timing and nature, as spring conditions are a crucial factor in determining the impact of winter warming on plant performance.
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| 10. |
- Kusano, Miyako, et al.
(författare)
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Application of a metabolomic method combining one-dimensional and two-dimensional gas chromatography-time-of-flight/mass spectrometry to metabolic phenotyping of natural variants in rice
- 2007
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Ingår i: Journal of chromatography. B. - Amsterdam : Elsevier. - 1570-0232 .- 1873-376X. ; 855:1, s. 71-79
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Tidskriftsartikel (refereegranskat)abstract
- We have developed a comprehensive method combining analytical techniques of one-dimensional (I D) and two-dimensional (GC x GC) gas chromatography-time-of-flight (TOF)-mass spectrometry. This method was applied to the metabolic phenotyping of natural variants in rice for the 68 world rice core collection (WRC) and two other varieties. Ten metabolites were selected as metabolite representatives, and the selected ion current of each metabolite peak obtained from both techniques were statistically compared. Our method of combining I D- and GC x GC-TOF/MS is useful for the metabolic phenotyping of natural variants in rice for further studies in breeding programs.
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