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- Murari, A., et al.
(författare)
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A control oriented strategy of disruption prediction to avoid the configuration collapse of tokamak reactors
- 2024
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Ingår i: Nature Communications. - 2041-1723 .- 2041-1723. ; 15:1
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Tidskriftsartikel (refereegranskat)abstract
- The objective of thermonuclear fusion consists of producing electricity from the coalescence of light nuclei in high temperature plasmas. The most promising route to fusion envisages the confinement of such plasmas with magnetic fields, whose most studied configuration is the tokamak. Disruptions are catastrophic collapses affecting all tokamak devices and one of the main potential showstoppers on the route to a commercial reactor. In this work we report how, deploying innovative analysis methods on thousands of JET experiments covering the isotopic compositions from hydrogen to full tritium and including the major D-T campaign, the nature of the various forms of collapse is investigated in all phases of the discharges. An original approach to proximity detection has been developed, which allows determining both the probability of and the time interval remaining before an incoming disruption, with adaptive, from scratch, real time compatible techniques. The results indicate that physics based prediction and control tools can be developed, to deploy realistic strategies of disruption avoidance and prevention, meeting the requirements of the next generation of devices.
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| 5. |
- Romagnoni, A, et al.
(författare)
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Comparative performances of machine learning methods for classifying Crohn Disease patients using genome-wide genotyping data
- 2019
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Ingår i: Scientific reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 9:1, s. 10351-
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Tidskriftsartikel (refereegranskat)abstract
- Crohn Disease (CD) is a complex genetic disorder for which more than 140 genes have been identified using genome wide association studies (GWAS). However, the genetic architecture of the trait remains largely unknown. The recent development of machine learning (ML) approaches incited us to apply them to classify healthy and diseased people according to their genomic information. The Immunochip dataset containing 18,227 CD patients and 34,050 healthy controls enrolled and genotyped by the international Inflammatory Bowel Disease genetic consortium (IIBDGC) has been re-analyzed using a set of ML methods: penalized logistic regression (LR), gradient boosted trees (GBT) and artificial neural networks (NN). The main score used to compare the methods was the Area Under the ROC Curve (AUC) statistics. The impact of quality control (QC), imputing and coding methods on LR results showed that QC methods and imputation of missing genotypes may artificially increase the scores. At the opposite, neither the patient/control ratio nor marker preselection or coding strategies significantly affected the results. LR methods, including Lasso, Ridge and ElasticNet provided similar results with a maximum AUC of 0.80. GBT methods like XGBoost, LightGBM and CatBoost, together with dense NN with one or more hidden layers, provided similar AUC values, suggesting limited epistatic effects in the genetic architecture of the trait. ML methods detected near all the genetic variants previously identified by GWAS among the best predictors plus additional predictors with lower effects. The robustness and complementarity of the different methods are also studied. Compared to LR, non-linear models such as GBT or NN may provide robust complementary approaches to identify and classify genetic markers.
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| 9. |
- Croitoru, MD, et al.
(författare)
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Electroluminescence spectra of an STM-tip-induced quantum dot
- 2003
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 68:19
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Tidskriftsartikel (refereegranskat)abstract
- We analyze the electroluminescence spectrum of an STM-tip-induced quantum dot in a GaAs surface layer. A flexible model has been developed that combines analytical and numerical methods and describes the key features of many-particle states in the STM-tip-induced quantum dot. The dot is characterized by its depth and lateral width, which are experimentally controlled by the bias and current. We find, in agreement with experiment, that increasing the voltage on the STM tip results in a redshift of the electroluminescence peaks, while the peak positions as a function of electron tunneling current through the STM tip reveal a blueshift.
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| 10. |
- Croitoru, MD, et al.
(författare)
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Electroluminescence spectra of an STM-tip-induced quantum dot
- 2004
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Ingår i: Physica. E, Low-Dimensional systems and nanostructures. - : Elsevier. - 1386-9477 .- 1873-1759. ; 21:2-4, s. 270-274
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Tidskriftsartikel (refereegranskat)abstract
- We analyze the electroluminescence spectrum of an STM-tip-induced quantum dot in a GaAs surface layer. A flexible model has been developed, that combines analytical and numerical methods and describes the key features of many-particle states in the STM-tip-induced quantum dot. The dot is characterized by its depth and lateral width, which are experimentally controlled by the bias and the tunneling current. We find, in agreement with experiment, that increasing voltage on the STM-tip results in a red shift of the electroluminescence peaks, while the peak positions as a function of the electron tunneling current through the STM-tip reveal a blue shift. (C) 2003 Elsevier B.V. All rights reserved.
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| 11. |
- Croitoru, MD, et al.
(författare)
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Influence of the characteristics of the STM-tip on the electroluminescence spectra
- 2005
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Ingår i: Physica. E, Low-Dimensional systems and nanostructures. - : Elsevier. - 1386-9477 .- 1873-1759. ; 27:1-2, s. 13-20
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Tidskriftsartikel (refereegranskat)abstract
- We analyze the influence of the characteristics of the STM-tip (applied voltage, tip radius) on the electroluminescence spectra from an STM-tip-induced quantum dot. We find that positions of electroluminescence peaks, attributed to the electron-hole recombination in the quantum dot, are very sensitive to the characteristics of the tip, namely increasing voltage on the STM-tip results in a red shift of the electroluminescence peaks, while the peak positions as a function of the tip radius reveal a non-monotonous behavior. (c) 2004 Elsevier B.V. All rights reserved.
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| 13. |
- Söderholm, Johan D, 1958-, et al.
(författare)
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Increased epithelial uptake of protein antigens in the ileum of Crohn's disease mediated by tumour necrosis factor α
- 2004
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Ingår i: Gut. - : BMJ. - 0017-5749 .- 1468-3288. ; 53:12, s. 1817-1824
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Tidskriftsartikel (refereegranskat)abstract
- Background and aims: The exact nature of the epithelial barrier defect in Crohn's disease remains to be elucidated. Previously we showed increased permeability to proteins in ileal Crohn's disease. Our aims were to study if this barrier defect (a) involves endocytotic uptake of antigens and (b) is related to low grade inflammation not detectable by histology. Methods: Macroscopically normal segments of distal ileum of Crohn's disease patients (n = 10) were subgrouped into non-inflamed (histologically unaffected) and slightly inflamed tissues and studied in Ussing chambers, with normal ileal specimens from colon cancer patients (n = 9) as controls. Endocytotic uptake into enterocytes of the protein antigen horseradish peroxidase was assessed by measuring the area of horseradish peroxidase containing endosomes in electron photomicrographs. Mucosal tumour necrosis factor α (TNF-α) mRNA was quantified using real time polymerase chain reaction. For comparison, the effects of low doses of TNF-α on endosomal uptake of horseradish peroxidase were studied in cultured T84 cells grown on filter supports. Results: The area of horseradish peroxidase containing endosomes was increased (p<0.001) in enterocytes of non-inflamed ileum of Crohn's disease (2.8 (0.7) μm2/300 μm2) compared with control ileum (0.6 (0.06)). In non-inflamed mucosa, a significant association between endosomal uptake and mucosal expression of TNF-α mRNA (p = 0.03) was found. Low concentrations of TNF-α (0.25-1.0 ng/ml) enhanced the endosomal uptake of horseradish peroxidase in polarised T84 cells, without affecting transepithelial electrical resistance. Conclusions: Our findings suggest increased endosomal uptake of antigens in ileal Crohn's disease that may be mediated by TNF-α. These data highlight the transcellular route of antigen uptake in barrier dysfunction and implicate the interaction between epithelial cells and the innate immune system in the development of mucosal inflammation.
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