First-fourth order pial branches of the median cerebral artery were studied by biomicroscopy in male Wistar rats aged 1 and 12 months. Irrespective of age, CO-mediated mechanisms are involved in the ...regulation of the basal tone of pial vessels of various diameters (more so of arteries with well-developed muscular tunic). Injection of hemin confirmed that endogenous production of CO maintained vasodilatation and this effect was most pronounced in large pial branches of young animals, while zinc protoporphyrin IX blocked this effect in all cases. On the other hand, zinc IX protoporphyrin did not modify NO-mediated reaction caused by injection of L-arginine, while hemin compensated (though not completely) vasoconstriction induced by NO synthase blocker L-NAME. In contrast to NO, the effect of CO on blood vessels was not so rapid and potent, but more lasting. Other targets for CO were arteries with well-developed muscular tunic, while targets for NO were small vessels. The vasomotor effects of both gas transmitters were more pronounced in young animals.
Multi-instrument observations of two filament eruptions on 24 February and 11 May 2011 suggest the following updated scenario for eruptive flare, coronal mass ejection (CME), and shock wave ...evolution. An initial destabilization of a filament results in stretching out of the magnetic threads belonging to its body that are rooted in the photosphere along the inversion line. Their reconnection leads to i) heating of parts of the filament or its environment, ii) an initial development of the flare cusp, arcade, and ribbons, iii) an increasing similarity of the filament to a curved flux rope, and iv) to its acceleration. Then the pre-eruption arcade enveloping the filament becomes involved in reconnection according to the standard model and continues to form the flare arcade and ribbons. The poloidal magnetic flux in the curved rope developing from the filament progressively increases and forces its toroidal expansion. This flux rope impulsively expands and produces a magnetohydrodynamical disturbance, which rapidly steepens into a shock. The shock passes through the arcade that expands above the filament and then freely propagates for some time ahead of the CME like a decelerating blast wave. If the CME is slow, then the shock eventually decays. Otherwise, the frontal part of the shock changes into the bow-shock regime. This was observed for the first time in the 24 February 2011 event. When reconnection ceases, the flux rope relaxes and constitutes the CME core–cavity system. The expanding arcade develops into the CME frontal structure. We also found that reconnection in the current sheet of a remote streamer forced by the shock passage results in a running flare-like process within the streamer responsible for a type II burst. The development of dimming and various associated phenomena are discussed.
The locations of heme oxygenase-2 (HO-2) and heme oxygenase-1 (HO-1) in the walls of 1st- to 4th-order arterial branches in the pia mater were studied in normotensive rats and in animals with induced ...renovascular hypertension (RVH). Immunohistochemical detection of heme oxygenase was performed on 40 Wistar rats. The vasomotor function of carbon monoxide (CO) in 3rd- to 5th-order arteries was found to be associated mainly with the endothelium, while in 1st- and 2nd-order arteries it was associated with myocytes. In normotensive animals, HO-2 was involved in forming CO, while both HO-2 and HO-1 had roles in hypertensive animals. The largest number of vessels expressing HO-1 was seen in week 16 of RVH, when the proportion of vessels positive for HO-2 was minimal, which is consistent with the time at which arterial pressure stabilizes at the new, higher, level.
First to fourth-order branches of the uterine artery in sexually mature female Wistar rats were studied by biomicroscopy. After administration of a CO donor hemin (60 mM), the diameters of large ...uterine branches with a well-developed muscle layer markedly increased, while the increase in diameter of small vessels with one often interrupted layer of smooth muscle cells increased insignificantly. Zinc protoporphyrin IX (30 mM) in all cases blocked this effect. However, zinc protoporphyrin IX does not affect NO-mediated reaction of the branches of the uterine artery caused by administration of L-arginine (60 mM), and L-NAME did not significantly affect reactivity of uterine artery branches associated with the hemoxygenase—CO system. In contrast to NO, CO produced less potent and rapid, but more sustained effect. The target for the hemoxygenase—CO system is mainly arteries with developed muscular layer, while the target for the NO synthase—NO is small vessels where endothelium plays a Rdecisive role in the regulation of vasomotor reactions.
The capillaries containing MMP-2 and its tissue inhibitor TIMP-2 were examined in cerebral cortex and white matter obtained from intact Wistar rats (
n
=5) and the rats with progressing experimental ...renovascular hypertension (
n
=35). In hypertensive rats, the changes in intensity of the immunohistochemical reaction and in the density of capillaries expressing TIMP-2 significantly differed from the corresponding values in MMP-2-positive capillaries, which resulted in pronounced deviation of MMP-2/TIMP-2 index from the control level (especially in cerebral cortex) probably attesting to enhanced risk of complications in cases with arterial hypertension.
We show examples of the excitation of coronal waves by flare-related abrupt eruptions of magnetic rope structures. The waves presumably rapidly steepened into shocks and freely propagated afterwards ...like decelerating blast waves that showed up as Moreton waves and EUV waves. We propose a simple quantitative description for such shock waves to reconcile their observed propagation with drift rates of metric type II bursts and kinematics of leading edges of coronal mass ejections (CMEs). Taking account of different plasma density falloffs for propagation of a wave up and along the solar surface, we demonstrate a close correspondence between drift rates of type II bursts and speeds of EUV waves, Moreton waves, and CMEs observed in a few previously studied events.
The distribution of two enzymes involved in the formation of carbon monoxide, heme oxygenases 1 and 2, in the pial branches of orders I-V of the middle cerebral artery basin and in intracerebral ...vessels was studied in adult Wistar rats. Immunohistochemical studies detected hemeoxygenase-2 in the endothelium of the small pial and intracerebral arterioles and in myocytes of pial branches I-III. Heme oxygenase 1, an inducible form of the enzyme, is normally not expressed in the cerebral vessels, but the enzyme is expressed in response to sodium metaarsenite. In this case, heme oxygenase markers are detected in myocytes of pial arteries I-II and in the endothelium of small pial and intracerebral vessels. Sodium meta-arsenite is inessential for immunolocation and quantitative distribution of heme oxygenase 2 in the vessels.
This is the first of four companion papers, which comprehensively analyze a complex eruptive event of 18 November 2003 in active region (AR) 10501 and the causes of the largest Solar Cycle 23 ...geomagnetic storm on 20 November 2003. Analysis of a complete data set, not considered before, reveals a chain of eruptions to which hard X-ray and microwave bursts responded. A filament in AR 10501 was not a passive part of a larger flux rope, as usually considered. The filament erupted and gave origin to a coronal mass ejection (CME). The chain of events was as follows: i) a presumable eruption at 07:29 UT accompanied by a not reported M1.2 class flare probably associated with the onset of a first southeastern CME (CME1), which most likely is not responsible for the superstorm; ii) a confined eruption (without a CME) at 07:41 UT (M3.2 flare) that destabilized the large filament; iii) the filament acceleration around 07:56 UT; iv) the bifurcation of the eruptive filament that transformed into a large “cloud”; v) an M3.9 flare in AR 10501 associated to this transformation. The transformation of the filament could be due to the interaction of the eruptive filament with the magnetic field in the neighborhood of a null point, located at a height of about 100 Mm above the complex formed by ARs 10501, 10503, and their environment. The CORONAS-F/SPIRIT telescope observed the cloud in 304 Å as a large Y-shaped darkening, which moved from the bifurcation region across the solar disk to the limb. The masses and kinematics of the cloud and the filament were similar. Remnants of the filament were not clearly observed in the second southwestern CME (CME2), previously regarded as a source of the 20 November geomagnetic storm. These facts do not support a simple scenario, in which the interplanetary magnetic cloud is considered as a flux rope formed from a structure initially associated with the pre-eruption filament in AR 10501. Observations suggest a possible additional eruption above the bifurcation region close to solar disk center between 08:07 and 08:17 UT, which could be the source of the 20 November superstorm.
We study large‐scale activity on the solar disk associated with a 24–26 November 2000 series of six recurrent major flares and “halo” coronal mass ejections (CMEs). The analysis is based mainly on ...the SOHO/EIT data, particularly by using properly rotated difference full‐disk images with 12‐min intervals at 195 Å as well as with 6‐hour intervals at 171, 195, 284, and 304 Å. We demonstrate that these eruptive events were homologous not only by their flare and CME characteristics, as Nitta and Hudson 2001 showed, but also in terms of their large‐scale CME‐associated manifestations in the EUV corona. These include long and narrow channeled dimmings, some transequatorial; anisotropic coronal waves, propagating in a restricted angular sector; and additional quasi‐stationary emitting fronts. As a whole, in all of these six events, the homologous CME‐associated disturbances covered a considerable portion of the solar disk. The homology tendency appears to be due to significant disturbance, partial eruption, and relatively fast restoration of the same large‐scale structures involved in the repeating CME events. We briefly discuss the implications of the analysis in connection with the nature of coronal equilibrium.
This study aims at the early diagnostics of the geoeffectiveness of coronal mass ejections (CMEs) from quantitative parameters of the accompanying EUV dimming and arcade events. We study events of ...the 23th solar cycle, in which major non-recurrent geomagnetic storms (GMS) with Dst<−100 nT are sufficiently reliably identified with their solar sources in the central part of the disk. Using the SOHO/EIT 195 Å images and MDI magnetograms, we select significant dimming and arcade areas and calculate summarized unsigned magnetic fluxes in these regions at the photospheric level. The high relevance of this eruption parameter is displayed by its pronounced correlation with the Forbush decrease (FD) magnitude, which, unlike GMSs, does not depend on the sign of the
B
z
component but is determined by global characteristics of ICMEs. Correlations with the same magnetic flux in the solar source region are found for the GMS intensity (at the first step, without taking into account factors determining the
B
z
component near the Earth), as well as for the temporal intervals between the solar eruptions and the GMS onset and peak times. The larger the magnetic flux, the stronger the FD and GMS intensities are and the shorter the ICME transit time is. The revealed correlations indicate that the main quantitative characteristics of major non-recurrent space weather disturbances are largely determined by measurable parameters of solar eruptions, in particular, by the magnetic flux in dimming areas and arcades, and can be tentatively estimated in advance with a lead time from 1 to 4 days. For GMS intensity, the revealed dependencies allow one to estimate a possible value, which can be expected if the
B
z
component is negative.
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