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- Kröll, Th, et al.
(författare)
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Quadrupole Collectivity of neutron-rich nuclei around 132Sn
- 2008
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Ingår i: Frontiers in Nuclear Structure, Astrophysics, and Reactions, FINUSTAR 2007. - : AIP. - 9780735405325 ; 1012, s. 296-299
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Konferensbidrag (refereegranskat)abstract
- We report on the "safe" Coulomb excitation of neutron-rich Cd, Xe, and Ba isotopes in the vicinity of the doubly-magic nucleus 132Sn. The radioactive nuclei have been produced by ISOLDE at CERN and postaccelerated by the REX-ISOLDE facility. The γ-decay of excited states has been detected by the MINIBALL array. The presented preliminary results for the B(E2) values are consistent with expectations from phenomenological systematics and will be compared with theoretical calculations.
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| 4. |
- Cartier, Rosine, et al.
(författare)
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Hydrological changes in Yellowstone Lake (USA) during the Holocene based on the analysis of oxygen isotopes in diatoms
- 2019
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Ingår i: Hydrological changes in Yellowstone Lake (USA) during the Holocene based on the analysis of oxygen isotopes in diatoms.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Northern Yellowstone Lake is on the southeast edge of the 631-ka Yellowstone caldera and is an area with high heat flow, high seismicity, and an abundance of active hydrothermal features and structures. Several large hydrothermal explosions since the last glacial recession formed craters of more than 100 m in diameter. These large craters raise the question on how climate and hydrological changes have affected the hydrothermal system and the lake ecosystem at millennial timescales.This study focuses on an 11.6-m-long core collected in 2016 in the Lake Hotel graben covering the last 9,900 cal years according to radiocarbon ages. Past hydrological changes were inferred from oxygen isotopes values of biogenic silica that comprises the cell wall of the diatoms. d 18O values reflect silica-lake water fractionation during diatom growth. The d 18O values vary according to changes in sources of precipitation, supply of runoff by tributaries, lake water temperature, and evaporation. Currently, precipitation occurs mainly as winter snow from weather systems originating in the Pacific.Periods of high d 18O in diatoms (enrichment in the heavy isotope) occur from the base of the record 9900 to ca. 7500 cal years BP, from 4500 to 3000 cal years BP and ca. 1000 cal years BP. These isotopic enrichments have been interpreted as to be mostly the result of increased water evaporation and/or reduced snowmelt flowing into the lake from the Yellowstone River and other tributaries. This inference is supported by d 18O measurements from water samples showing that lake water is progressively more evaporated with increased distance from the Yellowstone River inlet . The base of the record also is characterized by lower abundance of Pinus pollen suggesting a more open Pinus contorta forest until 5800 cal years BP, with more-frequent fire than today. Additionally, a long-term decrease in d 18Odiatomin the record and a progressive increase in the duration of spring water mixing shown by diatom assemblages (i.e. higher A. subarctica/S. minutulusratio) are associated with decreased summer insolation during the Holocene. These results compare well with other paleoclimatic records from the Yellowstone region that show a transition to cool, wet conditions in the late Holocene.
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| 8. |
- Loarer, T., et al.
(författare)
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Fuel retention in L and H mode experiments in JET
- 2007
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Ingår i: 34th EPS Conference on Plasma Physics 2007, EPS 2007 - Europhysics Conference Abstracts. - 9781622763344 ; , s. 13-16
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Konferensbidrag (refereegranskat)abstract
- The fuel retention has been studied out in JET in L mode, Type III and Type I ELMy H-modes using gas balance in series of repetitive pulses with an overall accuracy of about 1.2%. The short term (dynamic) retention is important for both L mode and Type III ELMy H-mode over the heating phases (respectively 13 and 17 sec) but decreases already significantly during the pulse. It becomes small already after 6 sec for the Type I ELMy H-mode conditions. In all the cases, the recovery after the pulse contributes for a weak part in the gas balance and in the overall fuel retention. The absolute long term fuel retention (on the time basis of typically 5 hours) for the different plasma conditions is between 1.3 and 2.8 1021Ds-1 (averaged over the plasma heating time) and in reasonable agreement with the value deduced from post mortem tile analysis of about 5 1020Ds-1 considering the additional long term outgassing, conditioning and disruptions included in the post mortem analysis. The increase of the long term retention observed from L mode to Type I ELMy H-mode is associated to the increase of the recycling flux and the ELM energy. This larger long term retention is attributed to an enhanced carbon erosion and transport in the SOL leading to stronger carbon deposition and fuel codeposition. The results confirm the strong concerns about fuel retention in a carbon clad tokamak and a possible full carbon wall ITER which could reach the T-inventory limit in only a small number of high performance shots. A reasonable ITER operation time depends thus on a significant reduced T codeposition under the different ITER material conditions (which has to be confirmed in a relevant tokamak experiment such as the JET ILW project) and an effective routine T removal technique.
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| 9. |
- Mangat, Jasvinder, et al.
(författare)
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A study of the image quality of CT brain adaptive statistical iterative reconstructed (ASIR) images using subjective and objective methods
- 2015
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Ingår i: Optimisation in X-ray and Molecular Imaging 2015 - the Fourth Malmö Conference on Medical Imaging, Gothenburg, Sweden, 28-30 May 2015.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Purpose: The aim of this study was to investigate the image quality of ASIR reconstructed brain images using subjective, observer-based assessment and objective metrics to elucidate trends and possible alternatives to the current standard protocol featuring 40%ASIR and a noise index of 11.20, possibly facilitating a dose decrease. Method: An audit of image quality of patient brain scans (n=55) was performed using Visual Grading Assessment (VGA) by two radiologist-observers, using CEC image criteria of retrospectively reconstructed images at 0% -70% & 100% ASIR-levels originally scanned using the standard protocol. Analysis was conducted using Visual Grading Characteristics (VGC). Empirical phantom-based assessments of high-contrast spatial resolution (HCSR) and Noise Power Spectrum (NPS) with 0-100%ASIR increments and decrementing tube currents (565-235mA), were also conducted. Results: VGC analysis showed that the mid-range increments (50%-70%ASIR) were not significantly different to 40%ASIR (p>0.05). Low-contrast spatial resolution (LCSR) showed slight, non-significant improvement with 70% and 60%ASIR increments compared with 40%ASIR (p>0.05). Subjective image noise remained constant across this range, but was slightly worse than 40%ASIR (p>0.05). However, 70%ASIR reconstructions were found to be overly susceptible to artefact appearance. Hence pairwise-analysis was performed using 60% & 50%ASIR, which showed 60%ASIR was the preferred increment. Phantom-based HCSR investigations showed MTF50 and MTF10 increases of up-to 4.1% and 3.0%, respectively (p<0.05) for ASIR reconstructed images as compared to those produced using FBP. MTF50 and MTF10 showed a linearly improving relationship with increasing %ASIR. With tube current, MTF behaviour was more complex with a rapid increase up to 305mA, a plateau between 305 and 420mA and then a rapid fall off. The NPS study revealed peak-frequency decreased linearly with increasing %ASIR and remained constant with tube current. Peak-variance decreased non-linearly with %ASIR and tube current. Empirical ranges for MTF50, MTF10, peak frequency NPS & peak variance NPS of (0.370- 0.375mm-1), (0.617- 0.622mm-1), (0.199- 0.176mm-1) & (99.28- 84.92mm-1) respectively, were obtained for the standard protocol for the mid-range ASIR increments. Conclusion: This study demonstrated the trends for objective and subjective image quality metrics with ASIR increment and tube-current. 60%ASIR with a tube current of 305mA (NI=12.20) was proposed as an alternative to the current standard, as it was the best fit with these empirical ranges, producing a possible dose saving of 16.1%.
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