Wave speeds in the corona and the dynamics of mass ejections

A disturbance or coronal mass ejection being advected by the solar wind will expand at the fastest local characteristic speed - typically approximately the fast-mode speed. To estimate this characteristic wave speed and the velocity field in the ambient corona, it is necessary to know the magnetic field, temperature, and density. Only the density is known from coronal observations. The temperature, magnetic field, and velocity are not yet directly measured in the outer corona and must be estimated from a model. In this study, it is estimated that the magnetic field, solar wind velocity, and characteristic speeds use the MHD model of coronal expansion between 1 and 5 solar radii (R solar radii) with a dipole magnetic field at the base. This model, for a field strength of about 2 gauss at the base, gives flow speeds at low latitudes (near the heliospheric current sheet) of 250 km/s at 5 R solar radii and, 50 km/s at 2 solar radii, and fast-mode speeds to 400 to 500 km/s everywhere between 2 and 5 solar radii. This suggests that the outer edge of a velocity of mass ejection reported by MacQueen and Fisher (1983) and implies that the acceleration mechanism for coronal mass ejections is other than simple entrainment in the solar wind

Influences on Handedness of Local Application of Acetylcholine with Glutamic Acid to Cerebral Cortex of the Rat

This study was undertaken to determine the effects on handedness in the rat upon application of glutamic acid and acetylcholine to the cortex

Constituents of Castilleja rhexifolia, Mahonia repens and Oncidium cebolleta, The

1981 Spring.Includes bibliographical references.Covers not scanned.Print version deaccessioned 2022.A total of 54 species of plants from 21 different plant families were collected throughout the subalpine region of the Colorado Rocky Mountains. These plants were tested for antitumor activity, alkaloid content and grasshopper antifeedant activity. Although none of the plants showed significant antitumor activity, 13 showed the presence of alkaloids and eight showed activity in the grasshopper antifeedant screen. One of the plants that showed the presence of alkaloids was Castilleja rhexifolia Rydb. Investigation of C. rhexifolia extracts led to the isolation of senecionine, a previously reported hepatoxic, pyrrolizidine alkaloid. This is the first report of a pyrrolizidine alkaloid in the Scrophulariaceae, and the first alkaloid isolated from Castilleja. The constituents of Mahonia repens (Lindl.) G. Don, a plant used by the Ramah Navajo of the Southwest in folk medicine, were also investigated. The leaves of M. repens contained four known aporphine alkaloids: isocorydine, corydine, thaliporphine and glaucine. The stems and roots of M. repens contained one known aporphine alkaloid (magnoflorine), four known bisbenzylisoquinoline alkaloids (obaberine, thalrugosine, oxyacanthine and obamegine), four known protoberberine alkaloids (palmatine, berberine, jatrorrhizine and columbamine), the known lignan, syringaresinol, and the sugar, sucrose. The isolation of these secondary metabolites allows a chemotaxonomic comparison of M. repens to the other Mahonia sp. studied, and also to the closely related genus, Berberis. As part of a continuing study to clarify the spectral data of 1,2,10,11-dihydroxydimethoxyaporphines, N-methylisocorytuberine was synthesized by the Pomeranz-Fritsch reaction and Pschorr cyclization. Spectral and thin layer chromatography data for N-methylisocorytuberine were then compared to two other reported isomers, magnoflorine and N,N-dimethyllindcarpine. The orchid, Oncidium cebolleta (Jacq.) Sw., is used by the Tarahumara Indians of Mexico as an important substitute for peyote. The chloroform extract of O. cebolleta was found to contain five previously unreported phenanthrenes and 9,10-dihydrophenanthrenes. Four of these compounds were identified as 2,3-dihydroxy-4,6,7 -trimethoxyphenanthrene, 2,3-dihydroxy-4,6,7-trimethoxy-9,10-dihydrophenanthrene, 2,7-dihydroxy-3,4-dimethoxyphenanthrene and 2,8- dihydroxy-4,7-dimethoxyphenanthrene. Although it is not known if these compounds are responsible for the hallucinogenic activity of O. cebolleta, their structural similarity to tetrahydrocannabinol makes this conceivable

Thermal stability of metastable magnetic skyrmions: Entropic narrowing and significance of internal eigenmodes

We compute annihilation rates of metastable magnetic skyrmions using a form of Langer's theory in the intermediate-to-high damping (IHD) regime. For a N\'eel skyrmion, a Bloch skyrmion, and an antiskyrmion, we look at two possible paths to annihilation: collapse and escape through a boundary. We also study the effects of a curved vs. a flat boundary, a second skyrmion and a non-magnetic defect. We find that the skyrmion's internal modes play a dominant role in the thermally activated transitions compared to the spin-wave excitations and that the relative contribution of internal modes depends on the nature of the transition process. Our calculations for a small skyrmion stabilized at zero-field show that collapse on a defect is the most probable path. In the absence of a defect, the annihilation is largely dominated by escape mechanisms, even though in this case the activation energy is higher than that of collapse processes. Escape through a flat boundary is found more probable than through a curved boundary. The potential source of stability of metastable skyrmions is therefore found not to lie in high activation energies, nor in the dynamics at the transition state, but comes from entropic narrowing in the saddle point region which leads to lowered attempt frequencies. This narrowing effect is found to be primarily associated with the skyrmion's internal modes.Comment: 14 pages, 9 figure

The 2-D magnetohydrostatic configurations leading to flares or quiescent filament eruptions

To investigate the cause of flares and quiescent filament eruptions the quasi-static evolution of a magnetohydrostatic (MHS) model was studied. The results lead to a proposal that: the sudden disruption of an active-region filament field configuration and the accompanying flare result from the lack of a neighboring equilibrium state as magnetic shear is increased above the critical value; and a quiescent filament eruption is due to an ideal MHD kink instability of a highly twisted detached flux tube formed by the increase of plasma current flowing along the length of the filament. A numerical solution was developed for the 2-D MHS equation for the self-consistent equilibrium of a filament and overlying coronal magnetic field. Increase of the poloidal current causes increase of magnetic shear. As shear increases past a critical point, there is a discontinuous topological change in the equilibrium configuration. It was proposed that the lack of a neighboring equilibrium triggers a flare. Increase of the axial current results in a detached tube with enough helical twist to be unstable to ideal MHD kink modes. It was proposed that this is the condition for the eruption of a quiescent filament

Path sampling for lifetimes of metastable magnetic skyrmions and direct comparison with Kramers' method

We perform a direct comparison between Kramers' method in many dimensions -- i.e., Langer's theory -- adapted to magnetic spin systems, and a path sampling method in the form of forward flux sampling, as a means to compute collapse rates of metastable magnetic skyrmions. We show that a good agreement is obtained between the two methods. We report variations of the attempt frequency associated with skyrmion collapse by three to four orders of magnitude when varying the applied magnetic field by 5$\%$ of the exchange strength, which confirms the existence of a strong entropic contribution to the lifetime of skyrmions. This demonstrates that in complex systems, the knowledge of the rate prefactor, in addition to the internal energy barrier, is essential in order to properly estimate a lifetime.Comment: 5 pages, 5 figures (main text), 8 pages including supplemental materia

On the formation of coronal cavities

A theoretical study of the formation of a coronal cavity and its relation to a quiescent prominence is presented. It is argued that the formation of a cavity is initiated by the condensation of plasma which is trapped by the coronal magnetic field in a closed streamer and which then flows down to the chromosphere along the field lines due to lack of stable magnetic support against gravity. The existence of a coronal cavity depends on the coronal magnetic field strength; with low strength, the plasma density is not high enough for condensation to occur. Furthermore, we suggest that prominence and cavity material is supplied from the chromospheric level. Whether a coronal cavity and a prominence coexist depends on the magnetic field configuration; a prominence requires stable magnetic support

Regulation of nitric oxide signaling by formation of a distal receptor-ligand complex.

The binding of nitric oxide (NO) to the heme cofactor of heme-nitric oxide/oxygen binding (H-NOX) proteins can lead to the dissociation of the heme-ligating histidine residue and yield a five-coordinate nitrosyl complex, an important step for NO-dependent signaling. In the five-coordinate nitrosyl complex, NO can reside on either the distal or proximal side of the heme, which could have a profound influence over the lifetime of the in vivo signal. To investigate this central molecular question, we characterized the Shewanella oneidensis H-NOX (So H-NOX)-NO complex biophysically under limiting and excess NO conditions. The results show that So H-NOX preferably forms a distal NO species with both limiting and excess NO. Therefore, signal strength and complex lifetime in vivo will be dictated by the dissociation rate of NO from the distal complex and the rebinding of the histidine ligand to the heme