| 1. |
- Eriksson, Johan, 1987, et al.
(författare)
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An atom probe tomography study of the chemistry of radiation-induced dislocation loops in Zircaloy-2 exposed to boiling water reactor operation
- 2021
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Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115. ; 550
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Tidskriftsartikel (refereegranskat)abstract
- This study is complementary to previous atom probe tomography (APT) studies of irradiation effects in the zirconium alloy Zircaloy-2. Using APT in voltage pulse mode, a difference in morphology was observed between clusters of Fe and Ni and clusters of Fe and Cr in Zircaloy-2 exposed to a high fast neutron fluence in a commercial boiling water reactor. The Fe–Ni clusters were disc-shaped with a diameter of 5–15 nm, whereas the Fe–Cr clusters were spheroidal with a diameter of approximately 5 nm. Both types of clusters appeared to be located at irradiation-induced -type dislocation loops aligned in layers normal to the -direction. The concentration of Fe was higher in the Fe–Cr clusters than in the Fe–Ni clusters. The dilute Fe–Ni clusters, which seem to be segregation of Fe and Ni inside the loops, had formed on all three families of first-order prismatic planes with some deviation from perfect -axis alignment. The Fe–Cr clusters might be very small precipitates with a nucleation associated with the loops.
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| 2. |
- Eriksson, Johan, 1987
(författare)
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Atom probe tomography of Zircaloy-2 exposed to boiling water reactor operation
- 2021
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Zirconium alloys are used as cladding tubes for the fuel in nuclear reactors. In boiling water reactors (BWRs), the alloy Zircaloy-2, which contains the alloying elements Sn, Fe, Cr, Ni, and O, is commonly used. In this thesis, results from atom probe tomography studies of Zircaloy-2 exposed to three and nine annual cycles of BWR operation are presented. The alloying elements were observed to be redistributed after reactor exposure. Clusters of Fe and Cr or Fe and Ni were observed at expected positions of radiation-induced type dislocation loops. Regions containing mainly Fe–Cr clusters were much more common than regions containing mainly Fe–Ni clusters. The Fe–Cr clusters appeared dense and spheroidal, whereas the Fe–Ni clusters appeared dilute and disc-shaped. The Fe–Ni discs occupied planes that correspond to all three families of first-order prismatic planes but with deviation from perfect axis alignment. Many grain boundaries were observed, and there were large grain-to-grain variations in cluster number density and cluster composition. Regarding cluster number density, there was on average no difference between three cycles and nine cycles. After nine cycles the clusters were on average larger and contained more Cr. Sn was observed to cluster in regions where there were no Fe–Cr or Fe–Ni clusters. Enrichment of Sn and Fe and small amounts of Cr and Ni was observed at grain boundaries. After nine cycles, but not after three cycles, enrichment of Sn, Fe, and Ni at ring-shaped features interpreted to be radiation-induced component loops was observed. Hydrogen was observed to be preferentially located outside a partially dissolved Zr(Fe,Cr)2 second phase particle that also contained Ni and Si. The present work demonstrates that the well-known dislocation loops have a chemistry, in the form of clusters of different types and shapes, that might substantially affect mechanisms degrading the cladding tubes, e.g. irradiation growth, corrosion, and hydrogen pickup.
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| 3. |
- Malik, Rameez Saeed, 1987-, et al.
(författare)
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Ultrafast magnetization dynamics in the half-metallic Heusler alloy Co2FeAl
- 2021
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 104:10
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Tidskriftsartikel (refereegranskat)abstract
- We report on optically induced, ultrafast magnetization dynamics in the Heusler alloy Co2FeAl, probed by time-resolved magneto-optical Kerr effect. Experimental results are compared to results from electronic structure theory and atomistic spin-dynamics simulations. Experimentally, we find that the demagnetization time (tau(M)) in films of Co2FeAl is almost independent of varying structural order, and that it is similar to that in elemental 3d ferromagnets. In contrast, the slower process of magnetization recovery, specified by tau(R), is found to occur on picosecond time scales, and is demonstrated to correlate strongly with the Gilbert damping parameter (alpha). Based on these results we argue that for Co2FeAl the remagnetization process is dominated by magnon dynamics, something which might have general applicability.
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| 4. |
- Naesström, Matilda, 1987-
(författare)
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Deep brain stimulation in obsessive-compulsive disorder
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Deep brain stimulation (DBS) is under investigation for severe obsessive-compulsive disorder (OCD) resistant to other therapies. As a crucial part of the anxiety circuit in the brain, the bed nucleus of stria terminalis (BNST) has been proposed as a target for DBS in OCD. However, the mechanism of action of BNST DBS in OCD is not yet fully understood. In our studies, the aim was to evaluate the effect and side effects of DBS in the BNST in severe OCD, to investigate which anatomical areas are being affected by the stimulation and what could be the potential mechanism of action of DBS in this target. We also explored the knowledge and concerns regarding DBS in OCD among psychiatrists, psychotherapists and patients suffering from the disorder. We investigate clinical outcomes and safety of DBS in the BNST in a series of 11 participants with severe therapy-refractory OCD. The primary outcome was a change in the Yale-Brown Obsessive-Compulsive Scale (YBOCS) scores one year after surgery. Using image and stimulation parameter data from the study above, we investigate through participant-specific simulation of the electric field, which anatomical areas are affected by the electric field, and if this can be related to the clinical results. Six of the participants were evaluated with symptom provocation fMRI pre-operatively and in DBS ON and OFF conditions. A web-based study surveyed psychiatrists, patients, and cognitive-behavioural therapists regarding previous knowledge of DBS, source of knowledge, attitudes, and concerns towards the therapy.At baseline, the mean±SD YBOCS score was 33±3.0. One year after DBS, mean±SD YBOCS score was 20±4.8 (38% improvement (range 10- 60%) p <0.01). Of the 11 participants, six were considered responders (decrease in YBOCS ≥35%) and four partial responders (decrease in YBOCS 25-34%). Surgical adverse events included one case of skin infection leading to reimplantation. The most common transient stimulation-related side-effects were anxiety and insomnia. The individual electric stimulation fields by stimulation in the BNST were similar at the 12 and 24-months follow up, involving mainly the anterior limb of the internal capsule (ALIC), genu of the internal capsule, BNST, fornix, anteromedial globus pallidus externa (GPe) and the anterior commissure. A statistically significant correlation (p < 0.05) between clinical effect measured by the YBOCS and simulation was found at the 12-month follow-up in the ventral ALIC and anteromedial GPe. A significant decrease in anxiety-related brain activity in the pre-supplementary motor area (pre-SMA) and the anterior insula was seen in 3/6 participants, with a comparable reduction (below significance level) in the other three participants. Results from the survey found that the primary source of information was from scientific sources among psychiatrists and psychotherapists. The patients' primary source of information was the media. Common concerns among the groups included complications from surgery, anaesthesia, stimulation side effects, and the novelty of the treatment. Specific concerns for the groups included; personality changes mentioned by patients and psychotherapists and ethical concerns among psychiatrists.BNST DBS is a promising therapy in severe therapy-refractory OCD. Our results are in line with previous publications regarding effect and safety profiles. We hypothesise that possible mechanisms of BNST DBS in OCD could be modulation of anxiety-related activity in the pre-SMA and anterior insula, two regions that play an important role in the pathophysiology of OCD. Many of the targets under investigation for OCD are in anatomical proximity, and as seen in our study, offtarget effects overlap. Therefore, DBS in the region of ALIC, NA, and BNST may perhaps be considered to be stimulation of the same target. DBS challenges in obsessive-compulsive disorder consist of source and quality of information, potential long-term adverse effects and eligibility. A broad research agenda is needed for studies as we advance in this field.
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