54 research outputs found
The contribution of insects to global forest deadwood decomposition
The amount of carbon stored in deadwood is equivalent to about 8âper cent of the global forest carbon stocks. The decomposition of deadwood is largely governed by climate with decomposer groupsâsuch as microorganisms and insectsâcontributing to variations in the decomposition rates. At the global scale, the contribution of insects to the decomposition of deadwood and carbon release remains poorly understood. Here we present a field experiment of wood decomposition across 55 forest sites and 6 continents. We find that the deadwood decomposition rates increase with temperature, and the strongest temperature effect is found at high precipitation levels. Precipitation affects the decomposition rates negatively at low temperatures and positively at high temperatures. As a net effectâincluding the direct consumption by insects and indirect effects through interactions with microorganismsâinsects accelerate the decomposition in tropical forests (3.9% median mass loss per year). In temperate and boreal forests, we find weak positive and negative effects with a median mass loss of 0.9âper cent and â0.1âper cent per year, respectively. Furthermore, we apply the experimentally derived decomposition function to a global map of deadwood carbon synthesized from empirical and remote-sensing data, obtaining an estimate of 10.9â±â3.2âpetagram of carbon per year released from deadwood globally, with 93âper cent originating from tropical forests. Globally, the net effect of insects may account for 29âper cent of the carbon flux from deadwood, which suggests a functional importance of insects in the decomposition of deadwood and the carbon cycle
Measurement of the cosmogenic neutron yield in Super-Kamiokande with gadolinium loaded water
Cosmic-ray muons that enter the Super-Kamiokande detector cause hadronic
showers due to spallation in water, producing neutrons and radioactive
isotopes. Those are a major background source for studies of MeV-scale
neutrinos and searches for rare events. Since 2020, gadolinium was introduced
in the ultra-pure water in the Super-Kamiokande detector to improve the
detection efficiency of neutrons. In this study, the cosmogenic neutron yield
was measured using data acquired during the period after the gadolinium
loading. The yield was found to be at
259 GeV of average muon energy at the Super-Kamiokande detector.Comment: 10 pages, 10 figures, 3 table
Search for astrophysical electron antineutrinos in Super-Kamiokande with 0.01wt% gadolinium-loaded water
We report the first search result for the flux of astrophysical electron
antineutrinos for energies O(10) MeV in the gadolinium-loaded Super-Kamiokande
(SK) detector. In June 2020, gadolinium was introduced to the ultra-pure water
of the SK detector in order to detect neutrons more efficiently. In this new
experimental phase, SK-Gd, we can search for electron antineutrinos via inverse
beta decay with efficient background rejection and higher signal efficiency
thanks to the high efficiency of the neutron tagging technique. In this paper,
we report the result for the initial stage of SK-Gd with a exposure at 0.01% Gd mass concentration. No significant excess
over the expected background in the observed events is found for the neutrino
energies below 31.3 MeV. Thus, the flux upper limits are placed at the 90%
confidence level. The limits and sensitivities are already comparable with the
previous SK result with pure-water () owing
to the enhanced neutron tagging
Termite sensitivity to temperature affects global wood decay rates.
Deadwood is a large global carbon store with its store size partially determined by biotic decay. Microbial wood decay rates are known to respond to changing temperature and precipitation. Termites are also important decomposers in the tropics but are less well studied. An understanding of their climate sensitivities is needed to estimate climate change effects on wood carbon pools. Using data from 133 sites spanning six continents, we found that termite wood discovery and consumption were highly sensitive to temperature (with decay increasing >6.8 times per 10°C increase in temperature)-even more so than microbes. Termite decay effects were greatest in tropical seasonal forests, tropical savannas, and subtropical deserts. With tropicalization (i.e., warming shifts to tropical climates), termite wood decay will likely increase as termites access more of Earth's surface
Atmospheric neutrino oscillation analysis with neutron tagging and an expanded fiducial volume in Super-Kamiokande IâV
We present a measurement of neutrino oscillation parameters with the Super-Kamiokande detector using atmospheric neutrinos from the complete pure-water SK IâV (April 1996âJuly 2020) dataset, including events from an expanded fiducial volume. The dataset corresponds to 6511.3 live days and an exposure of 484.2 kiloton-years. Measurements of the neutrino oscillation parameters Îm322, sin2Ξ23, sin2Ξ13, ÎŽCP, and the preference for the neutrino mass ordering are presented with atmospheric neutrino data alone, and with constraints on sin2Ξ13 from reactor neutrino experiments. Our analysis including constraints on sin2Ξ13 favors the normal mass ordering at the 92.3% level
Performance of SK-Gdâs upgraded real-time supernova monitoring system
Among multimessenger observations of the next Galactic core-collapse supernova, Super-Kamiokande (SK) plays a critical role in detecting the emitted supernova neutrinos, determining the direction to the supernova (SN), and notifying the astronomical community of these observations in advance of the optical signal. In 2022, SK has increased the gadolinium dissolved in its water target (SK-Gd) and has achieved a Gd concentration of 0.033%, resulting in enhanced neutron detection capability, which in turn enables more accurate determination of the supernova direction. Accordingly, SK-Gd's real-time supernova monitoring system has been upgraded. SK_SN Notice, a warning system that works together with this monitoring system, was released on 2021 December 13, and is available through GCN Notices. When the monitoring system detects an SN-like burst of events, SK_SN Notice will automatically distribute an alarm with the reconstructed direction to the supernova candidate within a few minutes. In this paper, we present a systematic study of SK-Gd's response to a simulated Galactic SN. Assuming a supernova situated at 10 kpc, neutrino fluxes from six supernova models are used to characterize SK-Gd's pointing accuracy using the same tools as the online monitoring system. The pointing accuracy is found to vary from 3° to 7° depending on the models. However, if the supernova is closer than 10 kpc, SK_SN Notice can issue an alarm with three-degree accuracy, which will benefit follow-up observations by optical telescopes with large fields of view
Performance of SK-Gd's upgraded real-time supernova monitoring system
Among multi-messenger observations of the next galactic core-collapse supernova, Super-Kamiokande (SK) plays a critical role in detecting the emitted supernova neutrinos, determining the direction to the supernova (SN), and notifying the astronomical community of these observations in advance of the optical signal. On 2022, SK has increased the gadolinium dissolved in its water target (SK-Gd) and has achieved a Gd concentration of 0.033%, resulting in enhanced neutron detection capability, which in turn enables more accurate determination of the supernova direction. Accordingly, SK-Gd's real-time supernova monitoring system (Abe te al. 2016b) has been upgraded. SK_SN Notice, a warning system that works together with this monitoring system, was released on December 13, 2021, and is available through GCN Notices (Barthelmy et al. 2000). When the monitoring system detects an SN-like burst of events, SK_SN Notice will automatically distribute an alarm with the reconstructed direction to the supernova candidate within a few minutes. In this paper, we present a systematic study of SK-Gd's response to a simulated galactic SN. Assuming a supernova situated at 10 kpc, neutrino fluxes from six supernova models are used to characterize SK-Gd's pointing accuracy using the same tools as the online monitoring system. The pointing accuracy is found to vary from 3-7â depending on the models. However, if the supernova is closer than 10 kpc, SK_SN Notice can issue an alarm with three-degree accuracy, which will benefit follow-up observations by optical telescopes with large fields of view
Measurements of the charge ratio and polarization of cosmic-ray muons with the Super-Kamiokande detector
We present the results of the charge ratio (R) and polarization (PÎŒ0) measurements using the decay electron events collected from 2008 September to 2022 June by the Super-Kamiokande detector. Because of its underground location and long operation, we performed high precision measurements by accumulating cosmic-ray muons. We measured the muon charge ratio to be R=1.32±0.02 (stat.+syst.) at EÎŒcosΞZenith=0.7+0.3â0.2 TeV, where EÎŒ is the muon energy and ΞZenith is the zenith angle of incoming cosmic-ray muons. This result is consistent with the Honda flux model while this suggests a tension with the ÏK model of 1.9Ï. We also measured the muon polarization at the production location to be PÎŒ0=0.52±0.02 (stat.+syst.) at the muon momentum of 0.9+0.6â0.1 TeV/c at the surface of the mountain; this also suggests a tension with the Honda flux model of 1.5Ï. This is the most precise measurement ever to experimentally determine the cosmic-ray muon polarization near 1 TeV/c. These measurement results are useful to improve the atmospheric neutrino simulations
Characterization and modelling of spring-in effect on Z-shape composite part
International audienceIn this study, a simple finite-element model is developed to predict the spring-in of Z-section composite parts made of carbon fiber/ epoxy resin manufactured with resin transfer molding process. The different mechanisms occurring during manufacturing and effective in the formation of residual stresses and shape distortions are implemented. They are mainly the thermal effect and the chemical shrinkage of the resin during the cross-linking polymerization reaction. A dedicated experimental procedure allowing separation of strains to cure shrinkage and thermal expansion is presented to characterize the resin cure shrinkage. Cure kinetic properties of the resin are determined with differential scanning calorimetry measurements. The spring-in angles predicted by the finite element analysis are compared to the angles measured on the Z-section specimens of various thicknesses
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