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- Barnes, A. T., et al.
(författare)
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LEGO - II. A 3mm molecular line study covering 100 pc of one of the most actively star-forming portions within the Milky Way disc
- 2020
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 497:2, s. 1972-2001
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Tidskriftsartikel (refereegranskat)abstract
- The current generation of (sub)mm-telescopes has allowed molecular line emission to become a major tool for studying the physical, kinematic, and chemical properties of extragalactic systems, yet exploiting these observations requires a detailed understanding of where emission lines originate within the Milky Way. In this paper, we present 60'' (similar to 3pc) resolution observations of many 3mm-band molecular lines across a large map of the W49 massive star-forming region (similar to 100x100pc at 11kpc), which were taken as part of the 'LEGO' IRAM-30m large project. We find that the spatial extent or brightness of the molecular line transitions are not well correlated with their critical densities, highlighting abundance and optical depth must be considered when estimating line emission characteristics. We explore how the total emission and emission efficiency (i.e. line brightness per H-2 column density) of the line emission vary as a function of molecular hydrogen column density and dust temperature. We find that there is not a single region of this parameter space responsible for the brightest and most efficiently emitting gas for all species. For example, we find that the HCN transition shows high emission efficiency at high column density (10(22)cm(-2)) and moderate temperatures (35K), whilst e.g. N2H+ emits most efficiently towards lower temperatures (10(22)cm(-2); <20K). We determine XCO(1-0)similar to 0.3 x 10(20)cm(-2)(Kkms(-1))(-1), and alpha(HCN(1-0))similar to 30M(circle dot)(Kkms(-1)pc(2))(-1), which both differ significantly from the commonly adopted values. In all, these results suggest caution should be taken when interpreting molecular line emission.
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- Aberg, S., et al.
(författare)
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Nuclear Structure Effects in Fission
- 2023. - 1
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Ingår i: Journal of Physics: Conference Series. - 1742-6588. ; 2586
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Konferensbidrag (refereegranskat)abstract
- Three examples of nuclear structure effects in fission dynamics are discussed: (i) The appearance of a super-short symmetric mode in the fission of nuclei around 264Fm leading to two double-magic 132Sn, (ii) Fission of some super-heavy elements where the heavy cluster is focused around double-magic 208Pb, and (iii) A saw-tooth distribution in angular momenta versus the fission fragment mass in the fission of 239U. The Metropolis random walk method is used to simulate the strongly damped fission dynamics on a 5D deformation grid. The dynamics is driven by pairing-, shape- and energy-dependent level densities. When available, a good agreement with experimental data is obtained.
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- Albertsson, Anna-Maj, et al.
(författare)
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γδ T cells contribute to injury in the developing brain.
- 2018
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Ingår i: The American journal of pathology. - : Elsevier BV. - 1525-2191 .- 0002-9440. ; 188:3, s. 757-767
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Tidskriftsartikel (refereegranskat)abstract
- Brain injury in premature infants, especially periventricular leukomalacia, is an important cause of neurological disabilities. Inflammation contributes to the development of perinatal brain injury, but the essential mediators leading to brain injury in early life remain largely unknown. Neonates have reduced capacity for mounting conventional αβT-cell responses. However γδT-cells are already functionally competent during early development and are important in early life immunity. We investigated the potential contribution of γδT-cells to preterm brain injury by using postmortem brains from human preterm infants with periventricular leukomalacia and two animal models of preterm brain injury-the hypoxic-ischemic mouse model and a fetal sheep asphyxia model. Large numbers of γδT-cells were observed in the brains of mice, sheep, and postmortem preterm infants after injury, and depletion of γδT-cells provided protection in the mouse model. The common γδT-cell associated cytokines interferon-γ and interleukin (IL)-17A were not detectable in the brain. Although there were increased mRNA levels of Il17f and Il22 in the mouse brains after injury, neither IL-17F nor IL-22 cytokines contributed to preterm brain injury. These findings highlight unique features of injury in the developing brain where, unlike injury in the mature brain, γδT-cells function as important initiators of injury independently of common γδT-cell associated cytokines. This new finding will help to identify therapeutic targets for preventing or treating preterm infants with brain injury.
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- Albertsson, M., et al.
(författare)
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Correlation studies of fission-fragment neutron multiplicities
- 2021
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Ingår i: Physical Review C. - 2469-9985. ; 103:1
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Tidskriftsartikel (refereegranskat)abstract
- We calculate neutron multiplicities from fission fragments with specified mass numbers for events having a specified total fragment kinetic energy. The shape evolution from the initial compound nucleus to the scission configurations is obtained with the metropolis walk method on the five-dimensional potential-energy landscape, calculated with the macroscopic-microscopic method for the three-quadratic-surface shape family. Shape-dependent microscopic level densities are used to guide the random walk, to partition the intrinsic excitation energy between the two proto-fragments at scission, and to determine the number of neutrons evaporated from the fragments. The contribution to the total excitation energy of the resulting fragments from statistical excitation and shape distortion at scission is studied. Good agreement is obtained with available experimental data on neutron multiplicities in correlation with fission fragments from U235(nth,f). With increasing neutron energy a superlong fission mode grows increasingly prominent, which affects the dependence of the observables on the total fragment kinetic energy.
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- Albertsson, M., et al.
(författare)
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Excitation energy partition in fission
- 2020
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Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 803
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Tidskriftsartikel (refereegranskat)abstract
- The transformation of an atomic nucleus into two excited fission fragments is modeled as a strongly damped evolution of the nuclear shape. As in previous studies, it is assumed that the division of mass and charge is frozen in at a critical neck radius of c0=2.5fm. In order to also determine the energetics, we follow the system further until scission occurs at a smaller neck radius, at which point the shapes of the proto-fragments are extracted. The statistical energy available at scission is then divided on the basis of the respective microscopic level densities. This approach takes account of important (and energy-dependent) finite-size effects. After the fragments have been fully accelerated and their shapes have relaxed to their equilibrium forms, they undergo sequential neutron evaporation. The dependence of the resulting mean neutron multiplicity on the fragment mass, ν¯(A), including the dependence on the initial excitation energy of the fissioning compound nucleus, agrees reasonably well with observations, as demonstrated here for 235U(n, f), and the sawtooth appearance of ν¯(A) can be understood from shell-structure effects in the level densities.
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- Albertsson, M., et al.
(författare)
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Super-short fission mode in fermium isotopes
- 2021
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Ingår i: Physical Review C. - 2469-9985. ; 104:6
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Tidskriftsartikel (refereegranskat)abstract
- The so-called super-short fission mode, in which a nucleus divides nearly symmetrically into two unusually energetic fragments, competes favorably with the standard asymmetric fission mode for spontaneous fission of a limited number of nuclei near Fm264 but it quickly fades away at finite excitations. We investigate the energy-dependent competition between those two fission modes for even fermium isotopes from Fm254 to Fm268, using the Metropolis method to simulate the strongly damped fission dynamics being driven by shape- and energy-dependent level densities. The origin of the super-short mode is discussed and its effects on the fragment mass distribution, the total fragment kinetic energy, and the neutron multiplicity are calculated. Generally good agreement with the available data is obtained.
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