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- Lakens, Daniel, et al.
(författare)
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Justify your alpha
- 2018
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Ingår i: Nature Human Behaviour. - : Nature Publishing Group. - 2397-3374. ; 2:3, s. 168-171
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Tidskriftsartikel (refereegranskat)abstract
- In response to recommendations to redefine statistical significance to P ≤ 0.005, we propose that researchers should transparently report and justify all choices they make when designing a study, including the alpha level.
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| 5. |
- Thorn, D. B., et al.
(författare)
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Polarization and anisotropic emission of K-shell radiation from heavy few electron ions
- 2011
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Ingår i: Canadian journal of physics (Print). - 0008-4204 .- 1208-6045. ; 89:5, s. 513-519
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Tidskriftsartikel (refereegranskat)abstract
- The population of magnetic sublevels in hydrogen-like uranium ions has been investigated in relativistic ion-atom collisions by observing the subsequent X-ray emission. Using the gas target at the experimental storage ring facility we observed the angular emission of Lyman-alpha radiation from hydrogen-like uranium ions. The alignment parameter for three different interaction energies was measured and found to agree well with theory. In addition, the use of different gas targets allowed for the electron-impact excitation process to be observed.
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| 7. |
- Reggiani, M, et al.
(författare)
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Discovery of a point-like source and a third spiral arm in the transition disk around the Herbig Ae star MWC 758
- 2018
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 611
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Tidskriftsartikel (refereegranskat)abstract
- Context. Transition disks offer the extraordinary opportunity to look for newly born planets and to investigate the early stages of planet formation. Aims. In this context we observed the Herbig A5 star MWC 758 with the L'-band vector vortex coronagraph installed in the near-infrared camera and spectrograph NIRC2 at the Keck II telescope, with the aim of unveiling the nature of the spiral structure by constraining the presence of planetary companions in the system. Methods. Our high-contrast imaging observations show a bright (Delta L' = 7.0 +/- 0.3 mag) point-like emission south of MWC 758 at a deprojected separation of similar to 20 au (r = 0 ''.111 +/- 0 ''.004) from the central star. We also recover the two spiral arms (southeast and northwest), already imaged by previous studies in polarized light, and discover a third arm to the southwest of the star. No additional companions were detected in the system down to 5 Jupiter masses beyond 0 ''.6 from the star. Results. We propose that the bright L'-band emission could be caused by the presence of an embedded and accreting protoplanet, although the possibility of it being an asymmetric disk feature cannot be excluded. The spiral structure is probably not related to the protoplanet candidate, unless on an inclined and eccentric orbit, and it could be due to one (or more) yet undetected planetary companions at the edge of or outside the spiral pattern. Future observations and additional simulations will be needed to shed light on the true nature of the point-like source and its link with the spiral arms.
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- Thomas, Richard D., et al.
(författare)
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The double electrostatic ion ring experiment : A unique cryogenic electrostatic storage ring for merged ion-beams studies
- 2011
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 82:6, s. 065112-
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Tidskriftsartikel (refereegranskat)abstract
- We describe the design of a novel type of storage device currently under construction at Stockholm University, Sweden, using purely electrostatic focussing and deflection elements, in which ion beams of opposite charges are confined under extreme high vacuum cryogenic conditions in separate rings and merged over a common straight section. The construction of this double electrostatic ion ring experiment uniquely allows for studies of interactions between cations and anions at low and well-defined internal temperatures and centre-of-mass collision energies down to about 10 K and 10 meV, respectively. Position sensitive multi-hit detector systems have been extensively tested and proven to work in cryogenic environments and these will be used to measure correlations between reaction products in, for example, electron-transfer processes. The technical advantages of using purely electrostatic ion storage devices over magnetic ones are many, but the most relevant are: electrostatic elements which are more compact and easier to construct; remanent fields, hysteresis, and eddy-currents, which are of concern in magnetic devices, are no longer relevant; and electrical fields required to control the orbit of the ions are not only much easier to create and control than the corresponding magnetic fields, they also set no upper mass limit on the ions that can be stored. These technical differences are a boon to new areas of fundamental experimental research, not only in atomic and molecular physics but also in the boundaries of these fields with chemistry and biology. For examples, studies of interactions with internally cold molecular ions will be particular useful for applications in astrophysics, while studies of solvated ionic clusters will be of relevance to aeronomy and biology.
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| 10. |
- Absil, Oliver, et al.
(författare)
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Three years of harvest with the vector vortex coronagraph in the thermal infrared
- 2016
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Ingår i: Ground-Based and Airborne Instrumentation for Astronomy VI. - : SPIE - International Society for Optical Engineering. - 9781510601963 ; , s. 1-14
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Konferensbidrag (refereegranskat)abstract
- For several years, we have been developing vortex phase masks based on sub-wavelength gratings, known as Annular Groove Phase Masks. Etched onto diamond substrates, these AGPMs are currently designed to be used in the thermal infrared (ranging from 3 to 13 μm). Our AGPMs were first installed on VLT/NACO and VLT/VISIR in 2012, followed by LBT/LMIRCam in 2013 and Keck/NIRC2 in 2015. In this paper, we review the development, commissioning, on-sky performance, and early scientific results of these new coronagraphic modes and report on the lessons learned. We conclude with perspectives for future developments and applications.
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| 12. |
- Gumberidze, A., et al.
(författare)
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Electron- and Proton-Impact Excitation of Hydrogenlike Uranium in Relativistic Collisions
- 2013
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 110:21, s. 213201-
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Tidskriftsartikel (refereegranskat)abstract
- The K shell excitation of H-like uranium (U91+) in relativistic collisions with different gaseous targets has been studied at the experimental storage ring at GSI Darmstadt. By performing measurements with different targets as well as with different collision energies, we were able to observe for the first time the effect of electron-impact excitation (EIE) process in the heaviest hydrogenlike ion. The large fine-structure splitting in H-like uranium allowed us to unambiguously resolve excitation into different L shell levels. State-of-the-art calculations performed within the relativistic framework which include excitation mechanisms due to both protons (nucleus) and electrons are in good agreement with the experimental findings. Moreover, our experimental data clearly demonstrate the importance of including the generalized Breit interaction in the treatment of the EIE process.
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| 14. |
- Mahmood, Sultan, et al.
(författare)
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RECOMBINATION RATE COEFFICIENTS OF BORON-LIKE Ne
- 2013
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 771:2, s. 78-
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Tidskriftsartikel (refereegranskat)abstract
- Recombination of Ne5+ was measured in a merged-beam type experiment at the heavy-ion storage ring CRYRING. In the collision energy range 0-110 eV resonances due to 2s(2)2p -> 2s2p(2) (Delta n=0) and 2s(2)2p -> 2s(2)3l (Delta n=1), core excitations were observed. The experimentally derived rate coefficients agree well with the calculations obtained using AUTOSTRUCTURE. At low energies, recombination is dominated by resonances belonging to the spin-forbidden 2s2p(2)(P-4(J))nl series. The energy-dependent rate coefficients were convoluted with a Maxwell-Boltzmann electron energy distribution to obtain plasma recombination rate coefficients. The data from the literature deviate from the measured results at low temperature.
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| 18. |
- Pradhan, Ajay, 1983-, et al.
(författare)
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Activation of NF-kappa B Protein Prevents the Transition from Juvenile Ovary to Testis and Promotes Ovarian Development in Zebrafish
- 2012
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Ingår i: Journal of Biological Chemistry. - : The American Society for Biochemistry and Molecular Biology. - 0021-9258 .- 1083-351X. ; 287:45, s. 37926-37938
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Tidskriftsartikel (refereegranskat)abstract
- Testis differentiation in zebrafish involves juvenile ovary to testis transformation initiated by an apoptotic wave. The molecular regulation of this transformation process is not fully understood. NF-kappa B is activated at an early stage of development and has been shown to interact with steroidogenic factor-1 in mammals, leading to the suppression of anti-Mullerian hormone (Amh) gene expression. Because steroidogenic factor-1 and Amh are important for proper testis development, NF-kappa B-mediated induction of anti-apoptotic genes could, therefore, also play a role in zebrafish gonad differentiation. The aim of this study was to examine the potential role of NF-kappa B in zebrafish gonad differentiation. Exposure of juvenile zebrafish to heat-killed Escherichia coli activated the NF-kappa B pathways and resulted in an increased ratio of females from 30 to 85%. Microarray and quantitative real-time-PCR analysis of gonads showed elevated expression of NF-kappa B-regulated genes. To confirm the involvement of NF-kappa B-induced anti-apoptotic effects, zebrafish were treated with sodium deoxycholate, a known inducer of NF-kappa B or NF-kappa B activation inhibitor (NAI). Sodium deoxycholate treatment mimicked the effect of heat-killed bacteria and resulted in an increased proportion of females from 25 to 45%, whereas the inhibition of NF-kappa B using NAI resulted in a decrease in females from 45 to 20%. This study provides proof for an essential role of NF-kappa B in gonadal differentiation of zebrafish and represents an important step toward the complete understanding of the complicated process of sex differentiation in this species and possibly other cyprinid teleosts as well.
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| 19. |
- Reinhed, Peter, et al.
(författare)
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Precision lifetime measurements of He- in a cryogenic electrostatic ion-beam trap
- 2009
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 103:21, s. 213002-
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Tidskriftsartikel (refereegranskat)abstract
- We have developed a small purely electrostatic ion-beam trap which may be operated in thermal equilibrium at precisely controlled temperatures down to 10 K. Thus, we avoid magnetic field induced mixing of quantum states and may effectively eliminate any influence from absorption of photons from black-body radiation. We report the first correction free measurements of the lifetimes of the 1s2s2p 4PoJ state of 4He- and the high precision result 359.0±0.7 μs for the J=5/2 level. The lifetimes for the J=3/2 and J=1/2 levels are determined to be 12.3±0.5 and 7.8±1.0 μs, respectively.
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