Standing kink waves in sigmoid coronal loops : implications for coronal seismology

Using full three-dimensional magnetohydrodynamic numerical simulations, we study the effects of magnetic field sigmoidity or helicity on the properties of the fundamental kink oscillation of solar coronal loops. Our model consists of a single denser coronal loop, embedded in a plasma with dipolar force-free magnetic field with a constant α-parameter. For the loop with no sigmoidity, we find that the numerically determined oscillation period of the fundamental kink mode matches the theoretical period calculated using WKB theory. In contrast, with increasing sigmoidity of the loop, the actual period is increasingly smaller than the one estimated by WKB theory. Translated through coronal seismology, increasing sigmoidity results in magnetic field estimates that are increasingly shifting toward higher values, and even surpassing the average value for the highest α value considered. Nevertheless, the estimated range of the coronal magnetic field value lies within the minimal/maximal limits, proving the robustness coronal seismology. We propose that the discrepancy in the estimations of the absolute value of the force-free magnetic field could be exploited seismologically to determine the free energy of coronal loops, if averages of the internal magnetic field and density can be reliably estimated by other methods

Sicherheit. Anspruch - Versprechen - Utopie

Zusammenfassung: Im Rahmen des Artikels wird das Phänomen der Unsicherheit auf Basis der Plessnerschen anthropologischen Perspektive aufgezeigt und der Umgang mit diesem Phänomen fokussiert: expliziert werden der unsicherheitskompensierende, utopische Gehalt von Selbst- und Gemeinschaftsentwürfen sowie gesellschaftspolitische Techniken. Ausgehend von den Schein-Handlungssicherheiten erzeugenden Maßnahmen im Kontext der Sozialen Arbeit wird das Sicherheitsversprechen in dem gesellschaftlichen Zusammenhang zwischen Markt, Staat und Zukunftsprognosen machttheoretisch verortet. Weiterhin wird aufgezeigt, wie diese paradoxalen Verflechtungen: das anthropologische Bedürfnis, Verlangen nach bzw. Anspruch auf Sicherheit, das Versprechen dieser Sicherheit mittels politischer Maßnahmen sowie die faktische Nichteinlösbarkeit dieses Versprechens, die Utopie der Sicherheit, eine Sicherheitsspirale generiere

Generalized phase mixing: Turbulence-like behaviour from unidirectionally propagating MHD waves

We present the results of three-dimensional (3D) ideal magnetohydrodynamics (MHD) simulations on the dynamics of a perpendicularly inhomogeneous plasma disturbed by propagating Alfv\'enic waves. Simpler versions of this scenario have been extensively studied as the phenomenon of phase mixing. We show that, by generalizing the textbook version of phase mixing, interesting phenomena are obtained, such as turbulence-like behavior and complex current-sheet structure, a novelty in longitudinally homogeneous plasma excited by unidirectionally propagating waves. This constitutes an important finding for turbulence-related phenomena in astrophysics in general, relaxing the conditions that have to be fulfilled in order to generate turbulent behavior

Investigating “Dark” Energy in the Solar Corona Using Forward Modeling of MHD Waves

It is now well established that Alfvénic waves are ubiquitous in the solar corona. However, the Alfvénic wave energy estimated from Doppler velocity measurements in the corona was found to be four orders of magnitude less than that estimated from nonthermal line widths. McIntosh & De Pontieu suggested that this discrepancy in energy might be due to the line-of-sight (LOS) superposition of several oscillating structures, which can lead to an underestimation of the Alfvénic wave amplitudes and energies. McIntosh & De Pontieu termed this coronal "dark" or "hidden" energy. However, their simulations required the use of an additional, unknown source of Alfvénic wave energy to obtain agreement with measurements of the coronal nonthermal line widths. In this study, we investigate the requirement of this unknown source of additional "dark" energy in the solar corona using gravitationally stratified 3D magnetohydrodynamic (MHD) simulations of propagating waves. We excite the transverse MHD waves and generate synthetic observations of the Fe xiii emission line. We establish that LOS superposition greatly reduces the Doppler velocity amplitudes and increases the nonthermal line widths. Importantly, our model generates the observed wedge-shape correlation between Doppler velocities and nonthermal line widths. We find that the observed wave energy is only 0.2%–1% of the true wave energy, which explains the 2–3 order-of-magnitude energy discrepancy. We conclusively establish that true wave energies are hidden in nonthermal line widths. Hence, our results rule out the requirement for an additional "dark" energy in the solar corona

Forward modeling of EUV and gyrosynchrotron emission from coronal plasmas with FoMo

Odysseus funding (FWO-Vlaanderen), IAPP7/08CHARM (Belspo), GOA-2015-014 (KULeuven), NAOJ Visiting Fellows Program. N Misa PhD student of the FWO-Vlaanderen.The FOMO code was developed to calculate the EUV and UV emission from optically thin coronal plasmas. The input data for FOMO consists of the plasma density, temperature and velocity on a 3D grid. This is translated to emissivity on the 3D grid, using CHIANTI data. Then, the emissivity is integrated along the line-of-sight (LOS) to calculate the emergent spectral line for synthetic spectrometer observations. The code also generates the emission channels for synthetic AIA imaging observations. Moreover, the code has been extended to model also the gyrosynchrotron emission from plasmas with a population of non-thermal particles. In this case, also optically thick plasmas may be modeled. The radio spectrum is calculated over a large wavelength range, allowing for the comparison with data from a wide range of radio telescopes.Publisher PDFPeer reviewe

Utódepolarizációk ionmechanizmusainak vizsgálata akciós potenciál clamp módszerrel = Afterdepolarization, Cellular electrophysiology, Action Potential Clamp

A project célja az volt, hogy megismerjük az utódepolarizációk által kiváltott ritmuszavarok hátterében álló ionmechanizmusokat. Hagyományos- és akciós potenciál feszültség clamp technika segítségével tanulmányoztuk az akciós potenciál alatt folyó ionáramok tulajdonságait emlős miocardiumban. Matematikai modellek alkalmazásával a tanulmányozott ionáramok viselkedése az akciós potenciál formájából prediktálható volt. - Vizualizáltuk és analizáltuk az akciós potenciál alatti lefutását a következő áramoknak: klorid áram, L-tipusú kalcium áram és a késői egyenirányító kálium áram lassú komponense. A klorid áram az akciós potenciál korai fázisában kifelé irányul, majd irányt vált. Gátlása az akciós potenciált nyújtja és fokozza az utódepolarizációk jelentkezésének gyakoriságát. Az L-tipusú kalcium áram az akciós potenciál első 20 milliszekunduma alatt eléri maximumát, majd platófázis nélkül igen gyorsan lecseng. Megfigyelésünk szerint a késői egyenirányító kálium áram lassú komponense a terminális repolarizáció igen fontos tényezője. - Vizsgáltuk az emlős szívizomzat ioncsatornáinak aszimmetrikus megoszlását. Összehasonlítottuk az ionáramokat és az akciós potenciál morfológiáját az szivizomzat különböző régióiban. Azt találtuk, hogy a tranziens outward K+ áram és a késői egyenirányító K+ áram lassú komponense jelentősen nagyobb az epicardiumban mint a midmyocardiumban mind humán mind kutya szívizom esetén. A Kv4.3, Kv1.4, KchIP2 és KvLQT1 csatornaproteinek expressziója ugyancsak jelentősen magasabb volt az epicardiumban. | The goal of this project was to obtain information on the ionic mechanism of cardiac arrhythmias caused different types of afterdepolarizations. We used traditional and action potential voltage clamp methods to understand the behavior of ionic currents during the action potential in mammalian myocardium. Using mathematical models we could predict the profile of ionic currents studied from the contour of action potential. - We visualized and analyzed the profile of the chloride current, the L-type calcium current and the slow component of delayed rectifier potassium current during the action potential. The chloride current showed an outward peak during the early phase of action potential, but later it became inward. Inhibition of the chloride current prolonged the action potential and facilitated the development of afterdepolarizations. The L-type calcium current showed an early peak during the firs 20 milliseconds of the action potential and decayed quickly without a plateau phase. The slow component of the delayed rectifier potassium current was found to be a crucial component of terminal repolarization. - We studied the asymmetrical distribution of ion channels in mammalian myocardium. We compared the ionic currents and the morphology of action potential in the different regions of the myocardium. We found that the amplitude of the transien outward K+ current and the slow componenet of the delayed rectifier K+ current was significanly larger in epicardiac than in midmyocardiac cells in both human and canine heart. Expression of Kv4.3, Kv1.4, KchIP2 and KvLQT1 was singificantly higher in epicardium

Effect of thymol on kinetic properties of Ca and K currents in rat skeletal muscle

BACKGROUND: Thymol is widely used as a general antiseptic and antioxidant compound in the medical practice and industry, and also as a stabilizer to several therapeutic agents, including halothane. Thus intoxication with thymol may occur in case of ingestion or improper anesthesia. In the present study, therefore, concentration-dependent effects of thymol (30–600 micro-grams) were studied on calcium and potassium currents in enzymatically isolated rat skeletal muscle fibers using the double vaseline gap voltage clamp technique. RESULTS: Thymol suppressed both Ca and K currents in a concentration-dependent manner, the EC(50 )values were 193 ± 26 and 93 ± 11 μM, with Hill coefficients of 2.52 ± 0.29 and 1.51 ± 0.18, respectively. Thymol had a biphasic effect on Ca current kinetics: time to peak current and the time constant for inactivation increased at lower (100–200 μM) but decreased below their control values at higher (600 μM) concentrations. Inactivation of K current was also significantly accelerated by thymol (200–300 μM). These effects of thymol developed rapidly and were partially reversible. In spite of the marked effects on the time-dependent properties, thymol caused no change in the current-voltage relationship of Ca and K peak currents. CONCLUSIONS: Present results revealed marked suppression of Ca and K currents in skeletal muscle, similar to results obtained previously in cardiac cells. Furthermore, it is possible that part of the suppressive effects of halothane on Ca and K currents, observed experimentally, may be attributed to the concomitant presence of thymol in the superfusate

Quantitative EEG in obstructive sleep apnea syndrome: a review of the literature

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