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152. The Reversed Field Pinch toward magnetic order: a genuine self-organization.

Author

Cappello, S., Bonfiglio, D., Escande, D. F., Guo, S. C., Alfier, A., and Lorenzini, R.

Subjects
MAGNETIC traps, EQUILIBRIUM, TURBULENCE, FLUID dynamics, MAGNETICS
Abstract

During the last decade, experimental and theoretical results induced a change of paradigm for the Reversed Field Pinch, (RFP). Indeed, experiments in present generation devices back up the new theoretical understanding of this alternative configuration for magnetic confinement: the basic nature of the system can be described as a self-organized helical state corresponding to the nonlinear saturation of a kink-tearing mode. This perspective was somewhat anticipated by older pioneering 3D nonlinear MHD. Very importantly from a theoretical point of view and with respect to confinement properties, the existence of RFP equilibrium with perfectly conserved helical confining magnetic surfaces comes into play. This is at variance with the previous traditional idea of the RFP as a relaxed axis-symmetric state, which, by theoretical arguments, requires the action of turbulence to accomplish and to maintain relaxation. In this presentation we propose a summary and discussion of the achievements in this subject, including results from 3D nonlinear MHD simulations, related transport effects and present open issues. Major relevant experimental facts are also surveyed. [ABSTRACT FROM AUTHOR]

Published
2008
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153. New insights into MHD dynamics of magnetically confined plasmas from experiments in RFX

Author

Martin, P, primary, Martini, S, additional, Antoni, V, additional, Apolloni, L, additional, Bagatin, M, additional, Baker, W, additional, Barana, O, additional, Bartiromo, R, additional, Bettini, P, additional, Boboc, A, additional, Bolzonella, T, additional, Buffa, A, additional, Canton, A, additional, Cappello, S, additional, Carraro, L, additional, Cavazzana, R, additional, Chitarin, G, additional, Costa, S, additional, D'Angelo, F, additional, Bello, S. Dal, additional, Lorenzi, A. De, additional, Desideri, D, additional, Escande, D, additional, Fattorini, L, additional, Fiorentin, P, additional, Franz, P, additional, Gaio, E, additional, Garzotti, L, additional, Giudicotti, L, additional, Gnesotto, F, additional, Grando, L, additional, Guo, S.C, additional, Innoccente, P, additional, Intravaia, A, additional, Lorenzini, R, additional, Luchetta, A, additional, Malesani, G, additional, Manduchi, G, additional, Marchiori, G, additional, Marrelli, L, additional, Martines, E, additional, Maschio, A, additional, Masiello, A, additional, Milani, F, additional, Moresco, M, additional, Murari, A, additional, Nielsen, P, additional, O'Gorman, M, additional, Ortolani, S, additional, Paccagnella, R, additional, Pasqualotto, R, additional, Pégourié, B, additional, Peruzzo, S, additional, Piovan, R, additional, Pomaro, N, additional, Ponno, A, additional, Preti, G, additional, Puiatti, M.E, additional, Rostagni, G, additional, Sattin, F, additional, Scarin, P, additional, Serianni, G, additional, Sonato, P, additional, Spada, E, additional, Spizzo, G, additional, Spolaore, M, additional, Taliercio, C, additional, Telesca, G, additional, Terranova, D, additional, Toigo, V, additional, Tramontin, L, additional, Valisa, M, additional, Vianello, N, additional, Viterbo, M, additional, Zabeo, L, additional, Zaccaria, P, additional, Zanca, P, additional, Zaniol, B, additional, Zanotto, L, additional, Zilli, E, additional, and Zollino, G, additional

Published
2002
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154. High-order harmonic generation processes in classical and quantum anharmonic oscillators

Author

Balcou, P, L'Huillier, Anne, Escande, D, Balcou, P, L'Huillier, Anne, and Escande, D

Abstract

We present a theoretical study of high-order harmonic generation by a slowly driven ''Duffing'' anharmonic oscillator. The power spectra are shown to display a plateau of high harmonics, which ends up with a sharp cutoff. The classical dynamics is analyzed with the adiabatic invariance theorem, which yields a simple interpretation to this characteristic behavior. We compare with the quantum case by solving numerically the time-dependent Schrodinger equation, and outline the similarity between classical damping and quantum-mechanical ionization processes. This allows us, in particular, to interpret the existence of intrinsic phases between high harmonics and the driving field. We further discuss the implication of these relaxation processes on the coherence of high harmonics, as well as the existence of interference processes yielding quasiresonant structures in intensity dependences.

Published
1996

156. Transport mechanisms and enhanced confinement studies in RFX

Author

Antoni, V, primary, Valisa, M, additional, Apolloni, L, additional, Bagatin, M, additional, Baker, W, additional, Barana, O, additional, Bartiromo, R, additional, Bettini, P, additional, Boboc, A, additional, Bolzonella, T, additional, Buffa, A, additional, Canton, A, additional, Cappello, S, additional, Carraro, L, additional, Cavazzana, R, additional, Chitarin, G, additional, Costa, S, additional, D'Angelo, F, additional, Bello, S. Dal, additional, Lorenzi, A. De, additional, Desideri, D, additional, Escande, D, additional, Fattorini, L, additional, Fiorentin, P, additional, Franz, P, additional, Gaio, E, additional, Garzotti, L, additional, Giudicotti, L, additional, Gnesotto, F, additional, Grando, L, additional, Guo, S.C, additional, Innocente, P, additional, Intravaia, A, additional, Lorenzini, R, additional, Luchetta, A, additional, Malesani, G, additional, Manduchi, G, additional, Marchiori, G, additional, Marrelli, L, additional, Martin, P, additional, Martines, E, additional, Martini, S, additional, Maschio, A, additional, Masiello, A, additional, Milani, F, additional, Moresco, M, additional, Murari, A, additional, Nielsen, P, additional, O'Gorman, M, additional, Ortolani, S, additional, Paccagnella, R, additional, Pasqualotto, R, additional, P gouri, B, additional, Peruzzo, S, additional, Piovan, R, additional, Pomaro, N, additional, Ponno, A, additional, Preti, G, additional, Puiatti, M.E, additional, Rostagni, G, additional, Sattin, F, additional, Scarin, P, additional, Serianni, G, additional, Sonato, P, additional, Spada, E, additional, Spizzo, G, additional, Spolaore, M, additional, Taliercio, C, additional, Telesca, G, additional, Terranova, D, additional, Toigo, V, additional, Tramontin, L, additional, Vianello, N, additional, Viterbo, M, additional, Zabeo, L, additional, Zaccaria, P, additional, Zanca, P, additional, Zaniol, B, additional, Zanotto, L, additional, Zilli, E, additional, and Zollino, G, additional

Published
2001
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160. Quasi-Single-Helicity Reversed-Field-Pinch Plasmas

Author

Escande, D. F., primary, Martin, P., additional, Ortolani, S., additional, Buffa, A., additional, Franz, P., additional, Marrelli, L., additional, Martines, E., additional, Spizzo, G., additional, Cappello, S., additional, Murari, A., additional, Pasqualotto, R., additional, and Zanca, P., additional

Published
2000
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161. Quasi-single helicity states in the reversed field pinch: Beyond the standard paradigm

Author

Martin, P., primary, Buffa, A., additional, Cappello, S., additional, D’Angelo, F., additional, Escande, D. F., additional, Franz, P., additional, Marrelli, L., additional, Martines, E., additional, Ortolani, S., additional, Spizzo, G., additional, Bilato, R., additional, Bolzonella, T., additional, Costa, S., additional, Murari, A., additional, Paccagnella, R., additional, Pasqualotto, R., additional, Terranova, D., additional, and Zanca, P., additional

Published
2000
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162. Recent progress in reversed field pinch research in the RFX experiment

Author

Bartiromo, R, primary, Buffa, A, additional, Antoni, V, additional, Apolloni, L, additional, Bagatin, M, additional, Baker, W, additional, Bellina, F, additional, Bettini, P, additional, Bilato, R, additional, Bolzonella, T, additional, Canton, A, additional, Cappello, S, additional, Carraro, L, additional, Cavazzana, R, additional, Chitarin, G, additional, Costa, S, additional, D'Angelo, F, additional, Lorenzi, A. De, additional, Pol, G. De, additional, Desideri, D, additional, Escande, D, additional, Fiorentin, P, additional, Franz, P, additional, Gaio, E, additional, Garzotti, L, additional, Giudicotti, L, additional, Gnesotto, F, additional, Gregoratto, D, additional, Guo, S.C, additional, Innocente, P, additional, Intravaia, A, additional, Luchetta, A, additional, Malesani, G, additional, Manduchi, G, additional, Marchiori, G, additional, Marrelli, L, additional, Martin, P, additional, Martines, E, additional, Martini, S, additional, Maschio, A, additional, Masiello, A, additional, Milani, F, additional, Moresco, M, additional, Murari, A, additional, Ortolani, S, additional, Paccagnella, R, additional, Pasqualotto, R, additional, Peruzzo, S, additional, Piovan, R, additional, Pomaro, N, additional, Pugno, R, additional, Puiatti, M.E, additional, Rostagni, G, additional, Sattin, F, additional, Scarin, P, additional, Serianni, G, additional, Sonato, P.G, additional, Spada, E, additional, Spizzo, G, additional, Spolaore, M, additional, Taliercio, C, additional, Telesca, G, additional, Terranova, D, additional, Toigo, V, additional, Tramontin, L, additional, Valisa, M, additional, Viterbo, M, additional, Vitturi, S, additional, Zaccaria, P, additional, Zanca, P, additional, Zilli, E, additional, and Zollino, G, additional

Published
1999
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179. Three-dimensional equilibria and transport in RFX-mod: A description using stellarator tools.

Author

Gobbin, M., Bonfiglio, D., Boozer, A. H., Cooper, A. W., Escande, D. F., Hirshman, S. P., Lore, J., Lorenzini, R., Marrelli, L., Martin, P., Martines, E., Momo, B., Pomphrey, N., Predebon, I., Puiatti, M. E., Sanchez, R., Spizzo, G., Spong, D. A., and Terranova, D.

Subjects
PLASMA diffusion, STELLARATORS, FUSION (Phase transformation), THERMODYNAMIC equilibrium, PARTICLES (Nuclear physics), COLLISIONS (Nuclear physics), CHAOS theory, TURBULENCE
Abstract

RFX-mod self-organized single helical axis (SHAx) states provide a unique opportunity to advance 3D fusion physics and establish a common knowledge basis in a parameter region not covered by stellarators and tokamaks. The VMEC code has been adapted to the reversed-field pinch (RFP) to model SHAx equilibria in fixed boundary mode with experimental measurements as constraint. The averaged particle diffusivity over the helical volume, estimated with the Monte Carlo code ORBIT, has a neoclassical-like dependence on collisionality and does not show the 1/ν trend of un-optimized stellarators. In particular, the helical region boundary, corresponding to an electron transport barrier with zero magnetic shear and improved confinement, has been investigated using numerical codes common to the stellarator community. In fact, the DKES/PENTA codes have been applied to RFP for local neoclassical transport computations, including radial electric field, to estimate thermal diffusion coefficients in the barrier region for typical RFX-mod temperature and density profiles. A comparison with power balance estimates shows that residual chaos due to secondary tearing modes and small-scale turbulence still contribute to drive anomalous transport in the barrier region. [ABSTRACT FROM AUTHOR]

Published
2011
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188. Dynamic analysis of the QT interval in long QT1 syndrome patients with a normal phenotype.

Author

Lande, G., Kyndt, F., Baró, I., Chabannes, D., Boisseau, P., Pony, J.-C., Escande, D., and Le Marec, H.

Abstract

Aims In families with the long QT syndrome penetrance may be low: up to 70% of gene carriers may have a normal QTc interval. These patients require therapy, similar to that in those with longer QTc intervals, but identifying them, using molecular analysis, is difficult to apply on a large scale. A large French family affected by the long QT1 syndrome was followed-up over a 25-year period. In adult males but not in females, the QTc interval normalized after puberty. We aimed to find clinical criteria, based on ambulatory ECG recordings so that we could improve diagnosis in affected members with a normal QTc.Methods and Results Linkage analysis and direct sequencing were an indicator of the long QT1 gene in our family. Reverse transcription-polymerase chain reaction analysis demonstrated abnormal transcripts in lymphocytes from silent gene carriers. The functional profile of mutated protein isoforms was investigated using the patch–clamp technique. Dynamic analysis of ventricular depolarization was conducted using Holter recordings in patients, and in sex- and age-matched controls. Circadian variations of the QTc interval and the QT/RR relationship were assessed. Sensitivity, specificity, and predictive values were evaluated for proposed clinical criteria. We found that dynamic analysis of the QT interval permitted individual diagnosis in mutation carriers even when the QTc interval was normal (adult males).Conclusion Dynamic analysis of the QT interval is of diagnostic value in the long QT1 syndrome in patients with a normal phenotype. Clinical implications include improvement in screening and patient management. [ABSTRACT FROM PUBLISHER]

Published
2001
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190. Effects of quinidine on ventricular repolarization.

Author

BRUGADA, J., SASSINE, A., ESCANDE, D., MASSE, C., and PUECH, P.

Abstract

The possibility that an asynchronous increase in the ventricular monophasic action potential duration is the basis of the quinidine-induced torsade de pointes, has led us to study the electrophysiological effects of increasing doses of intravenous quinidine. We measured the monophasic action potential duration and the ventricular effective refractory period at several right ventricular myocardial sites in the anaesthetized dog. Our results showed that quinidine induces a dose-dependent prolongation in ventricular effective refractory period and in ventricular monophasic action potential duration. These increases were uniform throughout the right ventricle. No variations in repolarization or in refractoriness were observed between the four ventricular sites studied. The results suggest that quinidine does not have a direct effect on dispersion of repolarization, and that mechanisms other than its direct electrophysiological action are involved in the development of torsade de pointes. [ABSTRACT FROM PUBLISHER]

Published
1987
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195. beta3-adrenoceptor control the cystic fibrosis transmembrane conductance regulator through a cAMP/protein kinase A-independent pathway.

Author

Leblais, V, Demolombe, S, Vallette, G, Langin, D, Baró, I, Escande, D, and Gauthier, C

Abstract

In human cardiac myocytes, we have previously identified a functional beta3-adrenoceptor in which stimulation reduces action potential duration. Surprisingly, in cardiac biopsies obtained from cystic fibrosis patients, beta3-adrenoceptor agonists produced no effects on action potential duration. This result suggests the involvement of cystic fibrosis transmembrane conductance regulator (CFTR) chloride current in the electrophysiological effects of beta3-adrenoceptor stimulation in non-cystic fibrosis tissues. We therefore investigated the control of CFTR activity by human beta3-adrenoceptors in a recombinant system: A549 human cells were intranuclearly injected with plasmids encoding CFTR and beta3-adrenoceptors. CFTR activity was functionally assayed using the 6-methoxy-N-(3-sulfopropyl)quinolinium fluorescent probe and the patch-clamp technique. Injection of CFTR-cDNA alone led to the expression of a functional CFTR protein activated by cAMP or cGMP. Co-expression of CFTR (but not of mutated DeltaF508-CFTR) with high levels of beta3-adrenoceptor produced an increased halide permeability under base-line conditions that was not further sensitive to cAMP or beta3-adrenoceptor stimulation. Patch-clamp experiments confirmed that CFTR channels were permanently activated in cells co-expressing CFTR and a high level of beta3-adrenoceptor. Permanent CFTR activation was not associated with elevated intracellular cAMP or cGMP levels. When the expression level of beta3-adrenoceptor was lowered, CFTR was not activated under base-line conditions but became sensitive to beta3-adrenoceptor stimulation (isoproterenol plus nadolol, SR 58611, or CGP 12177). This later effect was not prevented by protein kinase A inhibitors. Our results provide molecular evidence that CFTR but not mutated DeltaF508-CFTR is regulated by beta3-adrenoceptors expression through a protein kinase A-independent pathway.

Published
1999

198. Apparent competition between ATP and the potassium channel opener RP 49356 on ATP-sensitive K+ channels of cardiac myocytes.

Author

Thuringer, D and Escande, D

Abstract

The mechanism whereby RP 49356, a novel potassium channel opener, activates ATP-sensitive K+ channels (K+-ATP channels) in isolated cardiac cells was investigated with the patch-clamp technique. When directly applied onto the inner face of an inside-out membrane patch, RP 49356 (300 microM) had no effect on K+ channels opened in an ATP-free solution. In contrast, the same concentration of the drug reactivated K+-ATP channels that had experienced spontaneous "run-down" of their activity following long recording periods. In cell-attached experiments, externally applied RP 49356 (300 microM) opened K+-ATP channels at 35 degrees in spite of the high intracellular ATP concentration, which was sufficient to prevent channel openings in the absence of the drug. In control conditions, the dose-response relation for ATP closing the channels had a Hill coefficient of 2.37 and a half-inhibition concentration of 56 microM. With 30 microM RP 49356 present in the intracellular medium, the slope factor of this relation was unchanged but the curve was shifted to the right, with a half-inhibition concentration of 515 microM. Conversely, the dose-response relation of RP 49356 activating K+-ATP channels was shifted to the right in a parallel manner under the influence of increasing concentrations of ATP. It is concluded that RP 49356 acts on cardiac K+-ATP channels by decreasing their sensitivity to ATP. Our results are consistent with an apparent competition between ATP and RP 49356.

Published
1989

199. A long lasting Ca2+ -activated outward current in guinea-pig atrial myocytes

Author

Baró, I. and Escande, D.

Abstract

Among other characteristics, the steady-state current-voltage relationship of patch-clamped single atrial myocytes from guinea-pig hearts is defined by an outward current hump in the potential region -15 to +40mV. This hump was reversibly suppressed by Co2+ (3 mM) or nitrendipine (5 µM) and enhanced by Bay K 8644 (5 µM). The maintained outward current component suppressed by Co2+ extended between -15.2±1.9 mV and +39.5 ±1.7 mV (mean±SEM of 14 cells) and has an amplitude of 95.7±9.4 pA at +10 mV. In isochronal I-V curves, the hump was already visible at 400 ms with essentially the same amplitude as at 1500 ms. The Co2+ -sensitive outward current underlying the hump was poorly time-dependent during 1.5 s voltage pulses but slowly relaxed upon repolarization. Tail currents reversed near the K+ equilibrium potential under our experimental conditions. The current hump of the steady-state I-V curve was also abolished by caffeine (10 mM) or ryanodine (3 µM), both drugs that interfere with sarcoplasmic reticulum function. Apamin (1 µM) or quinine (100 µM) but not TEA (5–50 mM) markedly reduced its amplitude. However, at similar concentrations as required to inhibit the hump, both apamin and quinine appeared to be poorly specific for Ca2+ -activated K+ currents in heart cells since they also inhibited the L-Type Ca2+ current. It is concluded that a long lasting Ca2+ -activated outward current, probably mainly carried by K+ ions but not sensitive to TEA, exists in atrial myocytes which is responsible for the current hump of the background I-V curve.

Published
1990
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