In the centres of stars where the temperature is high enough, three alpha-particles (helium nuclei) are able to combine to form 12C because of a resonant reaction leading to a nuclear excited state. (Stars with masses greater than approximately 0.5 times that of the Sun will at some point in their lives have a central temperature high enough for this reaction to proceed.) Although the reaction rate is of critical significance for determining elemental abundances in the Universe, and for determining the size of the iron core of a star just before it goes supernova, it has hitherto been insufficiently determined. Here we report a measurement of the inverse process, where a 12C nucleus decays to three alpha-particles. We find a dominant resonance at an energy of approximately 11 MeV, but do not confirm the presence of a resonance at 9.1 MeV (ref. 3). We show that interference between two resonances has important effects on our measured spectrum. Using these data, we calculate the triple-alpha rate for temperatures from 10(7) K to 10(10) K and find significant deviations from the standard rates. Our rate below approximately 5 x 10(7) K is higher than the previous standard, implying that the critical amounts of carbon that catalysed hydrogen burning in the first stars are produced twice as fast as previously believed. At temperatures above 10(9) K, our rate is much less, which modifies predicted nucleosynthesis in supernovae.
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Sci Rep
December 2024
School of architecture, Ocean and energy power engineering, Wuhan University of Technology, Wuhan, 430070, China.
During maritime operations, extreme events such as explosions, grounding, and seal failures can cause water ingress into lubricant compartments, forming oil-water emulsions that significantly affect the lubrication performance of ship stern bearings. Existing studies mainly focus on low water content, with limited exploration of the impact of high water content on lubrication performance. To address this gap, viscosity measurements of oil-water mixtures were conducted, and an emulsification viscosity equation applicable to varying water contents was derived.
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December 2024
Department of Electrical Engineering, College of Engineering, King Saud University, Riyadh, 11421, Saudi Arabia.
The world is moving towards the utilization of hydrogen vehicle technology because its advantages are uniformity in power production, more efficiency, and high durability when compared to fossil fuels. So, in this work, the Proton Exchange Membrane Fuel Stack (PEMFS) device is selected for producing the energy for the hydrogen vehicle. The merits of this fuel technology are the possibility of operating less source temperature, and more suitability for stationery and transportation applications.
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December 2024
Faculty of Natural Sciences, Institute of Biology, Biotechnology and Environmental Protection, University of Silesia in Katowice, Jagiellońska 28, 40-032, Katowice, Poland.
Studies of in situ plant response and adaptation to complex environmental stresses, are crucial for understanding the mechanisms of formation and functioning of ecosystems of anthropogenically transformed habitats. We study short- and long-term responses of photosynthetic apparatus (PSA) and anti-oxidant capacity to complex abiotic stresses of common plants Calamagrostis epigejos and Solidago gigantea in semi-natural (C) and heavy metal contaminated habitats (LZ). We found significant differences in leaf pigment content between both plant species growing on LZ plots and their respective C populations.
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December 2024
Graduate School of Engineering, University of Hyogo, Himeji, 671-2280, Japan.
The effect of hot isostatic pressing (HIP) on the thermoelectric power factor of zinc oxide (ZnO) has been examined. ZnO is expected to be a potential n-type oxide thermoelectric material that could enhance the thermoelectric conversion efficiency. The HIP treatment is useful for densifying the material and controlling crystal defects in the material by applying high temperatures and pressures simultaneously.
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December 2024
School of Civil and Hydraulic Engineering, Chongqing University of Science & Technology, Chongqing, 400074, China.
The CRTS (China Railway Track System) II slab ballastless track is widely utilized in high-speed railway construction owing to its excellent structural integrity. However, its interfacial performance deteriorates under high-temperature conditions, leading to significant damage in structural details. Furthermore, the evolution of its performance under these conditions has not been comprehensively studied.
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