Eun-Kyung Lim

Persistent Horizontal Flows and Magnetic Support of Vertical Threads in a Quiescent Prominence

There has been some controversy as to whether the magnetic fields of vertical threads seen in quiescent prominences are predominantly vertical or horizontal. We report finding special patterns of flow in a quiescent prominence observed by the Solar Optical Telescope aboard Hinode. This prominence is a small hedgerow prominence composed of many vertical threads. To one side of it, we found a pattern of persistent horizontal flows of Hα-emitting plasma. These flows originated from a region in the chromosphere, rose to coronal heights, and then extended horizontally for a long distance until they reached the main body of the prominence. In the higher altitudes the flows either moved across vertical threads or lifted them up, while in the lower altitudes they often formed bright blobs of plasma and shed them, resulting in a sudden change of flow direction from horizontal to vertical. The observed persistent horizontal flows support a configuration of initially horizontal magnetic fields, and our results appear to be consistent with the traditional theory that vertical threads in quiescent prominences are stacks of plasma supported against gravity by the sagging of initially horizontal magnetic field lines.

A Check for Consistency between Different Magnetic Helicity Measurements Based on the Helicity Conservation Principle

Magnetic helicity is a useful quantity in characterizing the magnetic systems of solar active regions. The purpose of the present work is to check for consistency between the local correlation tracking (LCT) method used to measure helicity injection through the photosphere, and the linear force-free field (LFFF) method used to determine helicity in the corona, based on the principle of helicity conservation in the solar corona. We have calculated the amount of magnetic helicity injected through the photosphere during the first disk passage of AR 10696 using the LCT method initially described by Chae. We have also measured the coronal magnetic helicity as a function of time using the LFFF method. With a value for the force-free α, the coronal field is constructed from the extrapolation of the Solar and Heliospheric Observatory (SOHO) MDI magnetograms, then compared with the coronal loops in the EUV images taken by the SOHO EIT. The force-free α that best fits the loops is used to calculate the coronal helicity. From a careful comparison of different helicity measurements during each time interval, we have reached the core conclusion that our measurements follow the helicity conservation principle with an uncertainty of ~15% and hence support the consistency between the two different methods with the same amount of uncertainty.

Vascular smooth muscle dysfunction induced by monomethylarsonous acid (mmaiii): a contributing factor to arsenic-associated cardiovascular diseases

While arsenic in drinking water is known to cause various cardiovascular diseases in human, exact mechanism still remains elusive. Recently, trivalent-methylated arsenicals, the metabolites of inorganic arsenic, were shown to have higher cytotoxic potential than inorganic arsenic. To study the role of these metabolites in arsenic-induced cardiovascular diseases, we investigated the effect of monomethylarsonous acid (MMA III), a major trivalent-methylated arsenical, on vasomotor tone of blood vessels. In isolated rat thoracic aorta and small mesenteric arteries, MMA III irreversibly suppressed normal vasoconstriction induced by three distinct agonists of phenylephrine (PE), serotonin and endothelin-1. Inhibition of vasoconstriction was retained in aortic rings without endothelium, suggesting that MMA III directly impaired the contractile function of vascular smooth muscle. The effect of MMA III was mediated by inhibition of PE-induced Ca2+ increase as found in confocal microscopy and fluorimeter in-lined organ chamber technique. The attenuation of Ca2+ increase was from concomitant inhibition of release from intracellular store and extracellular Ca2+ influx via L-type Ca2+ channel, which was blocked by MMA III as shown in voltage-clamp assay in Xenopus oocytes. MMA III did not affect downstream process of Ca2+, as shown in permeabilized arterial strips. In in vivo rat model, MMA III attenuated PE-induced blood pressure increase indeed, supporting the clinical relevance of these in vitro findings. In conclusion, MMA III-induced smooth muscle dysfunction through disturbance of Ca2+ regulation, which results in impaired vasoconstriction and aberrant blood pressure change. This study will provide a new insight into the role of trivalent-methylated arsenicals in arsenic-associated cardiovascular diseases.

CHIRALITY OF INTERMEDIATE FILAMENTS AND MAGNETIC HELICITY OF ACTIVE REGIONS

Filaments that form either between or around active regions (ARs) are called intermediate filaments. Even though there have been many theoretical studies, the origin of the chirality of filaments is still unknown. We investigated how intermediate filaments are related to their associated ARs, especially from the point of view of magnetic helicity and the orientation of polarity inversion lines (PILs). The chirality of filaments has been determined based on the orientations of barbs observed in full-disk Hα images taken at Big Bear Solar Observatory during the rising phase of solar cycle 23. The sign of magnetic helicity of ARs has been determined using /inverse- shaped sigmoids from Yohkoh SXT images. As a result, we have found good correlation between the chirality of filaments and the magnetic helicity sign of ARs. Among 45 filaments, 42 filaments have shown the same sign as helicity sign of nearby ARs. It has been also confirmed that the role of both the orientation and the relative direction of PILs to ARs in determining the chirality of filaments is not significant, against a theoretical prediction. These results suggest that the chirality of intermediate filaments may originate from magnetic helicity of their associated ARs.

THE FORMATION OF A MAGNETIC CHANNEL BY THE EMERGENCE OF CURRENT-CARRYING MAGNETIC FIELDS

A magnetic channel-a series of polarity reversals separating elongated flux threads with opposite polarities-may be a manifestation of a highly non-potential magnetic configuration in active regions. To understand its formation, we have carried out a detailed analysis of the magnetic channel in AR 10930 using data taken by the Solar Optical Telescope/Hinode. As a result, we found upflows (-0.5 to -1.0 km s{sup -1}) and downflows (+1.5 to +2.0 km s{sup -1}) inside and at both tips of the thread, respectively, and a pair of strong vertical currents of opposite polarity along the channel. Moreover, our analysis of the nonlinear force-free fields constructed from the photospheric magnetic field indicates that the current density in the lower corona may have gradually increased as a result of the continuous emergence of the highly sheared flux along the channel. With these results, we suggest that the magnetic channel originates from the emergence of the twisted flux tube that has formed below the surface before the emergence.

Three-minute Sunspot Oscillations Driven by Magnetic Reconnection in a Light Bridge

We report a different type of three-minute chromospheric oscillations above a sunspot in association with a small-scale impulsive event in a light bridge. During our observations, we found a transient brightening in the light bridge. The brightening was composed of elementary bursts that may be a manifestation of fast repetitive magnetic reconnections in the light bridge. Interestingly, the oscillations in the nearby sunspot umbra were impulsively excited when the intensity of the brightening reached its peak. The initial period of the oscillations was about 2.3 minutes and then gradually increased to 3.0 minutes with time. In addition, we found that the amplitude of the excited oscillations was twice the amplitude of oscillations before the brightening. Based on our results, we propose that magnetic reconnection occurring in a light bridge can excite of oscillations in the nearby sunspot umbra.

A NEW METHOD TO DETERMINE THE TEMPERATURE OF CMES USING A CORONAGRAPH FILTER SYSTEM

The coronagraph is an instrument that enables the investigation of faint features in the vicinity of the Sun, particularly coronal mass ejections (CMEs). So far coronagraphic observations have been mainly used to determine the geometric and kinematic parameters of CMEs. Here, we introduce a new method for the determination of CME temperature using a two filter (4025 A and 3934 A) coronagraph system. The thermal motion of free electrons in CMEs broadens the absorption lines in the optical spectra that are produced by the Thomson scattering of visible light originating in the photosphere, which affects the intensity ratio at two different wavelengths. Thus the CME temperature can be inferred from the intensity ratio measured by the two filter coronagraph system. We demonstrate the method by invoking the graduated cylindrical shell (GCS) model for the 3-dimensional CME density distribution and discuss its significance.

Methylated Organic Metabolites of Arsenic and their Cardiovascular Toxicities

Recently, arsenic-toxicity has become the major focus of strenuous assessment and dynamic research from the academy and regulatory agency. To elucidate the cause and the mechanism underlying the serious adverse health effects from chronic ingestion of arsenic-contaminated drinking water, numerous studies have been directed on the investigation of arsenic-toxicity using various in vitro as well as in vivo systems. Neverthless, some questions for arsenic effects remain unexplained, reflecting the contribution of unknown factors to the manifestation of arsenic-toxicity. Interestingly, very recent studies on arsenic metabolites have discovered that trivalent methylated arsenicals show stronger cytotoxic and genotoxic potentials than inorganic arsenic or pentavalent metabolites, arguing that these metabolites could play a key role in arsenic-associated disorders. In this review, recent progress and literatures are summarized on the metabolism of trivalent methylated metabolites and their toxicity on body systems including cardiovascular system in an effort to provide an insight into the future research on arsenic-associated disorders.