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| 2. |
- Connor, J W, et al.
(författare)
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High-m kink/tearing modes in cylindrical geometry
- 2014
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 1361-6587 .- 0741-3335. ; 56:12
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Tidskriftsartikel (refereegranskat)abstract
- The global ideal kink equation, for cylindrical geometry and zero beta, is simplified in the high poloidal mode number limit and used to determine the tearing stability parameter, Δ'. In the presence of a steep monotonic current gradient, Δ' becomes a function of a parameter, σ0, characterising the ratio of the maximum current gradient to magnetic shear and xs, characterising the separation of the resonant surface from the maximum of the current gradient. In equilibria containing a current 'spike', so that there is a non-monotonic current profile, Δ' also depends on two parameters: κ, related to the ratio of the curvature of the current density at its maximum to the magnetic shear and xs, which now represents the separation of the resonance from the point of maximum current density. The relation of our results to earlier studies of tearing modes and to recent gyrokinetic calculations of current driven instabilities, is discussed, together with potential implications for the stability of the tokamak pedestal.
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| 3. |
- Catto, P. J., et al.
(författare)
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Kinetic effects on a tokamak pedestal ion flow, ion heat transport and bootstrap current
- 2013
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 1361-6587 .- 0741-3335. ; 55:4
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Tidskriftsartikel (refereegranskat)abstract
- We consider the effects of a finite radial electric field on ion orbits in a subsonic pedestal. Using a procedure that makes a clear distinction between a transit average and a flux surface average we are able to solve the kinetic equation to retain the modifications due to finite E X B drift orbit departures from flux surfaces. Our approach properly determines the velocity space localized, as well as the nonlocal, portion of the ion distribution function in the banana and plateau regimes in the small aspect ratio limit. The rapid variation of the poloidal ion flow coefficient and the electrostatic potential in the total energy modify previous banana regime evaluations of the ion flow, the bootstrap current, and the radial ion heat flux in a subsonic pedestal. In the plateau regime, the rapid variation of the poloidal flow coefficient alters earlier results for the ion flow and bootstrap current, while leaving the ion heat flux unchanged since the rapid poloidal variation of the total energy was properly retained.
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| 4. |
- Holmberg, Lars, et al.
(författare)
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A comparison of prostate cancer survival in England, Norway and Sweden : A population-based study
- 2012
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Ingår i: Cancer Epidemiology. - : Elsevier BV. - 1877-7821 .- 1877-783X. ; 36:1, s. e7-e12
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Tidskriftsartikel (refereegranskat)abstract
- Purpose The objective of the study was to compare patterns of survival 2001-2004 in prostate cancer patients from England, Norway and Sweden in relation to age and period of follow-up. Subjects and methods Excess mortality in men with prostate cancer was estimated using nation-wide cancer register data using a period approach for relative survival. 179,112 men in England, 23,192 in Norway and 59,697 in Sweden were included. Results In all age groups, England had the lowest survival, particularly so among men aged 80+. Overall age-standardised five-year survival was 76.4%, 80.3% and 83.0% for England, Norway and Sweden, respectively. The majority of the excess deaths in England were confined to the first year of follow-up. Conclusion The results indicate that a small but important group of older patients present at a late stage and succumb early to their cancers, possibly in combination with severe comorbidity, and this situation is more common in England than in Norway or Sweden.
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| 5. |
- Jeronimo, Carmen, et al.
(författare)
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Epigenetics in Prostate Cancer: Biologic and Clinical Relevance
- 2011
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Ingår i: European Urology. - : Elsevier BV. - 1873-7560 .- 0302-2838. ; 60:4, s. 753-766
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Tidskriftsartikel (refereegranskat)abstract
- Context: Prostate cancer (PCa) is one of the most common human malignancies and arises through genetic and epigenetic alterations. Epigenetic modifications include DNA methylation, histone modifications, and microRNAs (miRNA) and produce heritable changes in gene expression without altering the DNA coding sequence. Objective: To review progress in the understanding of PCa epigenetics and to focus upon translational applications of this knowledge. Evidence acquisition: PubMed was searched for publications regarding PCa and DNA methylation, histone modifications, and miRNAs. Reports were selected based on the detail of analysis, mechanistic support of data, novelty, and potential clinical applications. Evidence synthesis: Aberrant DNA methylation (hypo-and hypermethylation) is the best-characterized alteration in PCa and leads to genomic instability and inappropriate gene expression. Global and locus-specific changes in chromatin remodeling are implicated in PCa, with evidence suggesting a causative dysfunction of histone-modifying enzymes. MicroRNA deregulation also contributes to prostate carcinogenesis, including interference with androgen receptor signaling and apoptosis. There are important connections between common genetic alterations (eg, E twenty-six fusion genes) and the altered epigenetic landscape. Owing to the ubiquitous nature of epigenetic alterations, they provide potential biomarkers for PCa detection, diagnosis, assessment of prognosis, and post-treatment surveillance. Conclusions: Altered epigenetic gene regulation is involved in the genesis and progression of PCa. Epigenetic alterations may provide valuable tools for the management of PCa patients and be targeted by pharmacologic compounds that reverse their nature. The potential for epigenetic changes in PCa requires further exploration and validation to enable translation to the clinic. (C) 2011 European Association of Urology. Published by Elsevier B. V. All rights reserved.
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| 6. |
- Catto, Peter J., et al.
(författare)
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A unified treatment of kinetic effects in a tokamak pedestal
- 2011
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 1361-6587 .- 0741-3335. ; 53, s. 054004-
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Tidskriftsartikel (refereegranskat)abstract
- We consider the effects of a finite pedestal radial electric field on ion orbits using a unified approach. We then employ these modified orbit results to retain finite E×B drift departures from flux surfaces in an improved drift-kinetic equation. The procedure allows us to make a clear distinction between transit averages and flux surface averages when solving this kinetic equation. The technique outlined here is intended to clarify and unify recent evaluations of the banana regime decrease and plateau regime alterations in the ion heat diffusivity; the reduction and possible reversal of the poloidal flow in the banana regime, and its augmentation in the plateau regime; the increase in the bootstrap current; and the enhancement of the residual zonal flow regulation of turbulence.
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| 7. |
- Kagan, G., et al.
(författare)
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Neoclassical Theory of Pedestal Flows and Comparison with Alcator C-Mod Measurements
- 2012
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Ingår i: Contributions to Plasma Physics. - : Wiley. - 0863-1042 .- 1521-3986. ; 52:5-6, s. 365 - 371
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Tidskriftsartikel (refereegranskat)abstract
- Neoclassical implications of the strong radial electric field, inherently present in an H-mode tokamak pedestal, are considered. The main ion poloidal flow in the pedestal is predicted to be reduced in magnitude, or even reversed, compared with its core counterpart. The resulting change in the neoclassical formula for the impurity flow is shown to result in improved agreement with boron measurements in the Alcator C-Mod pedestal. In addition, due to the ion flow being modified, the bootstrap current is expected to be enhanced in the pedestal over conventional predictions.
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| 8. |
- Landreman, M., et al.
(författare)
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Global delta-f neoclassical calculations in a pedestal
- 2013
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Ingår i: 55th Annual Meeting of the APS Division of Plasma Physics, Denver CO, USA, Bulletin of the American Physical Society. ; 58:16, s. PP8.00036-
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Konferensbidrag (refereegranskat)abstract
- Conventional calculations of neoclassical flows, current, and fluxes may not be valid in the pedestal since the strong gradients violate the assumed ordering, yet accurate calculation of these quantities is important for understanding edge stability and confinement. We have therefore developed a new radially global continuum neoclassical code PERFECT [1] which allows some radial scale lengths to be as small as the poloidal ion gyroradius. A strong radial electric field with strong shear is also included. In contrast to conventional neoclassical calculations, sources of particles and energy must be determined self-consistently to find the correction to the Maxwellian. The full linearized Fokker-Planck collision operator is implemented, arbitrary collisionality is allowed, and an arbitrary number of species are permitted. Efficiency is aided by a new spectral discretization for velocity space [2] and a preconditioned Krylov-space solver. At large aspect ratio, precise agreement is obtained between the code and recent analytic theory that accounts for finite orbit width effects. At realistic aspect ratio, strong poloidal asymmetries can arise in the flow, breaking the usual form for flows on a flux surface. [1] PPCF 54, 115006 (2012). [2] J Comp Phys 243, 130 (2013).
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| 9. |
- Pusztai, Istvan, 1983, et al.
(författare)
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A current-driven electromagnetic mode in sheared and toroidal configurations
- 2014
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 1361-6587 .- 0741-3335. ; 56:3
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Tidskriftsartikel (refereegranskat)abstract
- The induced electric field in a tokamak drives a parallel electron current flow. In an inhomogeneous, finite beta plasma, when this electron flow is comparable to the ion thermal speed, the Alfven mode wave solutions of the electromagnetic gyrokinetic equation can become nearly purely growing kink modes. Using the new 'low-flow' version of the gyrokinetic code GS2 developed for momentum transport studies (Barnes et al 2013 Phys. Rev. Lett. 111 055005), we are able to model the effect of the induced parallel electric field on the electron distribution to study the destabilizing influence of current on stability. We identify high mode number kink modes in GS2 simulations and make comparisons to analytical theory in sheared magnetic geometry. We demonstrate reassuring agreement with analytical results both in terms of parametric dependences of mode frequencies and growth rates, and regarding the radial mode structure.
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| 10. |
- Pusztai, Istvan, 1983, et al.
(författare)
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Current driven instability in finite beta plasmas
- 2013
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Ingår i: 55th Annual Meeting of the APS Division of Plasma Physics, Denver CO, USA, Bulletin of the American Physical Society. ; 58:16, s. PP8.00102-
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Konferensbidrag (refereegranskat)abstract
- The induced electric field in a tokamak drives a parallel electron current flow. In an inhomogeneous, finite beta plasma, when this electron flow is non-negligible compared to the ion thermal speed, the Alfv\'{e}n mode wave solutions of the electromagnetic gyrokinetic equation can become an almost purely growing kink mode. Using the new ``low-flow'' version of the gyrokinetic code GS2 developed for momentum transport studies [Barnes et al 2013 to appear in Phys. Rev. Lett., arXiv: 1304.3633], we are able to model the effect of the induced parallel electric field on the electron distribution to study the impact of a current on stability. We identify high mode number kink modes in GS2 simulations and make comparisons to analytical theory in a sheared magnetic geometry. We find a reassuring agreement with analytical results both in terms of parametric dependences of mode frequencies and growth rates, and regarding the radial mode structure.
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