| 1. |
- Ersmark, Tore, et al.
(författare)
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Geant4 Monte Carlo simulations of the galactic cosmic ray radiation environment on-board the international space station/columbus
- 2007
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Ingår i: IEEE Transactions on Nuclear Science. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9499 .- 1558-1578. ; 54:No 5, s. 1854-1862
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Tidskriftsartikel (refereegranskat)abstract
- A characterization of the Galactic Cosmic Ray (GCR) induced radiation environment on-board Columbus and the Inter-national Space Station (ISS) has been carried out using the Geant4 Monte Carlo particle transport toolkit and detailed geometry models of Columbus and ISS. Dose and dose equivalent rates, as well as penetrating particle spectra are presented. Simulation results indicate that the major part of the dose rates due to GCR protons are associated with secondary particles produced in the hull of ISS. Neutrons contribute about 15% of the GCR proton dose equivalent rate and mesons about 10%. More than 40% of the simulated GCR proton dose and dose equivalent rates are due to protons in the energy range above 10 GeV. Protons in the energy range above 50 GeV contribute only 5% to the dose rates. The total simulated dose and dose equivalent rates at solar maximum are 63 mu Gy/d and 123 mu Sv/d, respectively. The dose equivalent rate underestimates measurements made during the 2001 solar maximum. The discrepancy can be attributed to deficiencies in hadronic ion-nuclei interaction models for heavy ions and to the lack of such models above 10 GeV/N in Geant4.
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| 2. |
- Kole, Merlin, 1986-
(författare)
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Background Studies for the Balloon-Borne Hard X-ray Polarimeter PoGOLite
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The polarisation degree and angle of the X-ray flux emitted by astrophysical objects holds valuable information on the responsible emission mechanisms and on the emission environments. PoGOLite is a balloon-borne hard X-ray polarimeter designed to measure polarisation using a segmented plastic scintillator array. The instrument was launched for its first scientific, near-circumpolar, flight in July 2013 from the Esrange Space Centre in Northern Sweden. The primary observation target for this flight, the Crab, was observed during the first 2 days of flight. One of the main challenges for PoGOLite is the relatively high measurement background, predicted to be induced by atmospheric neutrons. No measurement data on the neutron environment for the flight conditions of PoGOLite is however available, making exact predictions impossible. This environment was therefore studied in detail. A Monte Carlo based model of the atmospheric neutron flux was developed. This model is capable of providing differential neutron energy spectra for all altitudes, latitudes and solar activities. The predictions of this model were found to be in good agreement both with measurement data, measured by high altitude aircraft, and with predictions by location and time specific models. The results from the model were verified with data recorded by a purpose-build balloon-borne neutron detector, PoGOLino. The PoGOLino instrument uses novel neutron sensitive LiCAF scintillators sandwiched between BGO crystals which serve as an anti-coincidence system. PoGOLino was launched from the Esrange Space Centre to an altitude of 31 km on March 20th 2013 and performed the first successful measurements of the neutron flux for the PoGOLite flight conditions. Using the developed model the background as measured by the PoGOLite mission in 2013 was studied. Monte Carlo simulations were used to confirm that the PoGOLite background during flight is dominated by neutrons. The simulated neutron induced signal rate and its variations with time were furthermore found to be in good agreement with measurements. Based on these results the implications of the background on the polarisation measurements of the Crab were studied. Lastly, based on the acquired knowledge of the background, changes to the instrument geometry for potential future flight of PoGOLite were studied along with the expected achievable improvement in performance for such flights.
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| 3. |
- Kosonen, Joonas P., et al.
(författare)
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Injury-related cell death and proteoglycan loss in articular cartilage : Numerical model combining necrosis, reactive oxygen species, and inflammatory cytokines
- 2023
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Ingår i: PLoS Computational Biology. - : Public Library of Science (PLoS). - 1553-734X .- 1553-7358. ; 19:1
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Tidskriftsartikel (refereegranskat)abstract
- Osteoarthritis (OA) is a common musculoskeletal disease that leads to deterioration of articular cartilage, joint pain, and decreased quality of life. When OA develops after a joint injury, it is designated as post-traumatic OA (PTOA). The etiology of PTOA remains poorly understood, but it is known that proteoglycan (PG) loss, cell dysfunction, and cell death in cartilage are among the first signs of the disease. These processes, influenced by biomechanical and inflammatory stimuli, disturb the normal cell-regulated balance between tissue synthesis and degeneration. Previous computational mechanobiological models have not explicitly incorporated the cell-mediated degradation mechanisms triggered by an injury that eventually can lead to tissue-level compositional changes. Here, we developed a 2-D mechanobiological finite element model to predict necrosis, apoptosis following excessive production of reactive oxygen species (ROS), and inflammatory cytokine (interleukin-1)-driven apoptosis in cartilage explant. The resulting PG loss over 30 days was simulated. Biomechanically triggered PG degeneration, associated with cell necrosis, excessive ROS production, and cell apoptosis, was predicted to be localized near a lesion, while interleukin-1 diffusion-driven PG degeneration was manifested more globally. Interestingly, the model also showed proteolytic activity and PG biosynthesis closer to the levels of healthy tissue when pro-inflammatory cytokines were rapidly inhibited or cleared from the culture medium, leading to partial recovery of PG content. The numerical predictions of cell death and PG loss were supported by previous experimental findings. Furthermore, the simulated ROS and inflammation mechanisms had longer-lasting effects (over 3 days) on the PG content than localized necrosis. The mechanobiological model presented here may serve as a numerical tool for assessing early cartilage degeneration mechanisms and the efficacy of interventions to mitigate PTOA progression.
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