Browsing by Subject "DISPLACEMENT"

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  • Dominguez-Gutierrez, F. J.; Byggmastar, J.; Nordlund, K.; Djurabekova, F.; von Toussaint, U. (2021)
    In this work, we study the damage in crystalline molybdenum material samples due to neutron bombardment in a primary knock-on atom (PKA) range of 0.5-10 keV at room temperature. We perform classical molecular dynamics (MD) simulations using a previously derived machine learning (ML) interatomic potential based on the Gaussian approximation potential (GAP) framework. We utilize a recently developed software workflow for fingerprinting and visualizing defects in damaged crystal structures to analyze the Mo samples with respect to the formation of point defects during and after a collision cascade. As a benchmark, we report results for the total number of Frenkel pairs (a self-interstitial atom and a single vacancy) formed and atom displacements as a function of the PKA energy. A comparison to results obtained using an embedded atom method (EAM) potential is presented to discuss the advantages and limits of the MD simulations utilizing ML-based potentials. The formation of Frenkel pairs follows a sublinear scaling law as xi ( b ) where b is a fitting parameter and xi = E (PKA)/E (0) with E (0) as a scaling factor. We found that the b = 0.54 for the GAP MD results and b = 0.667 for the EAM simulations. Although the average number of total defects is similar for both methods, the MD results show different atomic geometries for complex point defects, where the formation of crowdions by the GAP potential is closer to the DFT-based expectation. Finally, ion beam mixing results for GAP MD simulations are in a good agreement with experimental mixing efficiency data. This indicates that the modeling of atom relocation in cascades by machine learned potentials is suited to interpret the corresponding experimental findings.
  • Quist, Liina-Maija; Nygren, Anja (2019)
    Marine extraction accounts for one third of the world's hydrocarbon production. Several analyses suggest that seismic surveys employed in oil exploration harm marine life; however, their long-term impacts have not been extensively studied. We examine debates between fishers, the oil industry, and governmental authorities over the effects of oil explorations in Tabasco, Mexico. The study employs ideas from historical ontology in tracing the contested production of truth-claims about exploration in the context of scientific uncertainty. It shows how actors, through their different engagements with the sea, and with different degrees of power, frame claims about the relations between exploration and fish. We argue that fishers, through their efforts to "think like fish" produce situated knowledges about the effects of oil exploration. They explain a disappearance of fish by their understanding that seismic surveys disturb fish migration, impair the hearing of fish and cause fish death. Oil company and governmental representatives frame the impacts of oil exploration as insignificant by separating environmental and social dimensions, by isolating individual exploration events, and by arguing that possible effects are transitional. Due to scientific indeterminacy, oil exploration is malleable in the hands of powerful political representations that understate its possible impacts on marine socio-environments.
  • Fridlund, C.; Lopez-Cazalilla, A.; Nordlund, K.; Djurabekova, F. (2021)
    Structures consisting of a single Si nanodot buried within an insulating nanometric SiO2 layer stacked between two Si layers show promising properties for room temperature operational single-electron transistors. Moreover, such structures are highly compatible with modern complementary metal-oxide semiconductor technologies. Metastable SiOx phase separates into a Si nanodot and insulating, homogeneous SiO2 during annealing, providing a solid path towards the desired structure. However, achieving the necessary amount of excessive Si, dissolved in the SiO2 for correct concentrations of SiOx, remains a technological challenge. In this work, we investigate ion-induced atom mixing in pre-built Si/SiO2/Si nanopillars, which is considered to be a technologically promising way to produce the necessary concentrations of spatially confined SiOx in a controlled manner. During the high-fluence ion irradiation, we notice a significant shortening of the nanopillar and preferential loss of O atoms. Both sputtering and nanoscale ion hammering are found to be the cause of the deformation. The ion-hammering effect on nanoscale is explained by multiple small displacements, strongly enhanced after the nanopillar was rendered completely amorphous. The methods presented here can be used to determine the ion-fluence threshold for sufficient atom mixing in spatially confined regions before the large structural deformations are formed.
  • Saari, Sina; Andjelkovic, Ana; Garcia, Geovana S.; Jacobs, Howard T.; Oliveira, Marcos T. (2017)
    Background: Mitochondrial alternative respiratory-chain enzymes are phylogenetically widespread, and buffer stresses affecting oxidative phosphorylation in species that possess them. However, they have been lost in the evolutionary lineages leading to vertebrates and arthropods, raising the question as to what survival or reproductive disadvantages they confer. Recent interest in using them in therapy lends a biomedical dimension to this question. Methods: Here, we examined the impact of the expression of Ciona intestinalis alternative oxidase, AOX, on the reproductive success of Drosophila melanogaster males. Sperm-competition assays were performed between flies carrying three copies of a ubiquitously expressed AOX construct, driven by the a-tubulin promoter, and wild-type males of the same genetic background. Results: In sperm-competition assays, AOX conferred a substantial disadvantage, associated with decreased production of mature sperm. Sperm differentiation appeared to proceed until the last stages, but was spatially deranged, with spermatozoids retained in the testis instead of being released to the seminal vesicle. High AOX expression was detected in the outermost cell-layer of the testis sheath, which we hypothesize may disrupt a signal required for sperm maturation. Conclusions: AOX expression in Drosophila thus has effects that are deleterious to male reproductive function. Our results imply that AOX therapy must be developed with caution.
  • Alenius, Teija Helena; Gerasimov, Dmitry; Sapelko, Tatiana V; Ludikova, Anna; Kuznetsov, Denis; Golyeva, A; Nordqvist, Kerkko (2020)
    This paper presents the results of pollen, diatom, charcoal, and sediment analyses from Lake Bol'shoye Zavetnoye, situated between the Gulf of Finland and Lake Ladoga on the Karelian Isthmus, north-western Russia. The main goal is to contribute to the discussion of Neolithic land use in north-eastern Europe. The article aims to answer questions related to Stone Age hunter-gatherer economy, ecology, and anthropogenic environmental impact through a comprehensive combination of multiple types of palaeoecological data and archaeological material. According to diatom data, Lake Bol'shoye Zavetnoye was influenced by the water level oscillations of Ancient Lake Ladoga during much of the Holocene. Intensified human activity and prolonged human occupation become visible in the Lake Bol'shoye Zavetnoye pollen data between 4480 BC and 3250 BC. During the final centuries of the Stone Age, a new phase of land use began, as several anthropogenic indicators, such asTriticum, Cannabis, andPlantago lanceolataappear in the pollen data and a decrease inPinusvalues is recorded. In general, the results indicate that socio-cultural transformations could have taken place already from the mid-5th millennium BC onwards, including new ways of utilizing the environment, perhaps also in the field of subsistence, even though the livelihood was based on foraging throughout the period.
  • Levo, E.; Granberg, F.; Fridlund, C.; Nordlund, K.; Djurabekova, F. (2017)
    Single-phase multicomponent alloys of equal atomic concentrations ("equiatomic") have proven to exhibit promising mechanical and corrosion resistance properties, that are sought after in materials intended for use in hazardous environments like next-generation nuclear reactors. In this article, we investigate the damage production and dislocation mobility by simulating irradiation of elemental Ni and the alloys NiCo, NiCoCr, NiCoFe and NiFe, to assess the effect of elemental composition. We compare the defect production and the evolution of dislocation networks in the simulation cells of two different sizes, for all five studied materials. We find that the trends in defect evolution are in good agreement between the different cell sizes. The damage is generally reduced with increased alloy complexity, and the dislocation evolution is specific to each material, depending on its complexity. We show that increasing complexity of the alloys does not always lead to decreased susceptibility to damage accumulation under irradiation. We show that, for instance, the NiCo alloy behaves very similarly to Ni, while presence of Fe or Cr in the alloy even as a third component reduces the saturated level of damage substantially. Moreover, we linked the defect evolution with the dislocation transformations in the alloys. Sudden drops in defect number and large defect fluctuations from the continuous irradiation can be explained from the dislocation activity. (C) 2017 Elsevier B.V. All rights reserved.
  • Simons, T.; Soderlund, T.; Handolin, L. (2017)
    Purpose Pediatric prehospital endotracheal intubation (PHETI) is a difficult and rarely performed procedure that remains the gold standard for prehospital airway management when ventilation and/or anesthesia is required, but high complications rates, including malposition continue to concern. We reviewed the experience in our institution of pediatric intubations with particular emphasis on the position of the endotracheal tube (ETT) tip within the trachea and related complications. Method Intubated pediatric patients presenting directly from the scene to our level 1 trauma center, between 2006 and 2014, were included in our study. Patient records and radiographs were retrospectively reviewed to identify the ETT tip-to-carina distance and possible intubation-related complications. ETT tips identified beyond the carina on radiographs or by clinical diagnosis were defined as misplaced. Because head movement causes a significant ETT movement within the trachea, which is age related, we also defined ETT tip placement (1) less than 2 cm above the carina in children younger than 8 and (2) less than 3 cm above the carina in children 8 years or older as "near miss" intubations. Results From a total of 34 cases, ETT misplacement was identified in seven cases. Diagnosis was made radiologically in five cases and clinically in two cases. Four of these patients had left lung atelectasis due to tube misplacement. Tube thoracotomy was performed in two of these patients without concurrent evidence of chest injury. "Near miss" intubations accounted for 7/9 and 9/25 in children <8 years and >= 8 years old, respectively, totaling 16/34, with two of these leading to late displacements. Conclusions Pediatric endotracheal tube intubation carries a high rate of tube malposition and left lung atelectasis in our experience of pediatric trauma patients, with less than a third of ETTs placed in a safe position.
  • Alekseychik, P. K.; Korrensalo, A.; Mammarella, I.; Vesala, Timo; Tuittila, E. -S. (2017)
    Leaf area index (LAI) is an important parameter in natural ecosystems, representing the seasonal development of vegetation and photosynthetic potential. However, direct measurement techniques require labor-intensive field campaigns that are usually limited in time, while remote sensing approaches often do not yield reliable estimates. Here we propose that the bulk LAI of sedges (LAI(s)) can be estimated alternatively from a micrometeorological parameter, the aerodynamic roughness length for momentum (z(0)). z(0) can be readily calculated from high-response turbulence and other meteorological data, typically measured continuously and routinely available at ecosystem research sites. The regressions of LAI versus z(0) were obtained using the data from two Finnish natural sites representative of boreal fen and bog ecosystems. LAI(s) was found to be well correlated with z(0) and sedge canopy height. Superior method performance was demonstrated in the fen ecosystem where the sedges make a bigger contribution to overall surface roughness than in bogs.
  • Levo, Emil; Granberg, Fredric; Nordlund, Kai; Djurabekova, Flyura (2021)
    Multiprincipally designed concentrated solid solution alloys, such as high entropy alloys (HEA) and equiatomic multi-component alloys (EAMC-alloys) have shown much promise for use as structural components in future nuclear energy production concepts. The irradiation tolerance in these novel alloys has been shown to be superior to that in more conventional metals used in current nuclear reactors. However, studies involving irradiation of HEAs and EAMC-alloys have usually been performed at room temperature. Hence, in this study the irradiation damage is investigated computationally in two different Ni-based EAMC-alloys and pure Ni at four different temperatures, ranging from 138 K to 800 K. The irradiation damage was studied by analyzing point defects, defect cluster sizes and dislocation networks in the materials. Dislocation loop mobility calculations were performed to help understanding the formation of different dislocation networks in the irradiated materials. Utilizing the knowledge of the depth distribution of damage, and using simulations of Rutherford backscattering in channeling conditions (RBS/c), we can relate our results to experimental data. The main findings are that the alloys have superior irradiation tolerance at all temperatures as compared to pure Ni, and that the damage is reduced in all materials with an increase in temperature.