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Background: Strokes can cause a variety of cardiovascular complications. The underlying mechanisms are largely unknown but there is evidence that dysautonomia plays a role in stroke induced-heart injury (SIHI) and arrhythmias triggered by damage of specific brain regions involved in the autonomic regulation of cardiac functions. Understanding these mechanisms could aid in preventing these cardiovascular consequences. We hypothesize that compared to -patients with sinus rhythm (SR) or with cardiogenic atrial fibrillation known before the stroke (cKAF) or diagnosed after the stroke (cAFDAS), those with neurogenic AFDAS (nAFDAS) will show a specific pattern of autonomic functioning. Methods: We will prospectively evaluate 200 ischemic stroke patients at the London Health Sciences Center University Hospital. Participants will undergo continuous electrocardiographic monitoring during 14 days. Based on pre-specified criteria, patients with AFDAS will be classified into presumably neurogenic vs cardiogenic. We will assess autonomic function within 14 days after stroke onset by using the Autonomic Reflex Screening. We will compare markers of cardiac dysfunction with autonomic changes, as well as specific stroke topographies for SR, cKAF, cAFDAS, and nAFDAS. Results: We are currently performing an interim analysis. Conclusions: Characterizing the autonomic changes that occur after ischemic stroke and their relationship with heart injury will help to advance knowledge on the pathophysiology of SIHI.
We study the formation of elliptical galaxies and the bulges of disk galaxies as a result of the collisionless collapse of a rotating star cloud. At small amounts of rotation, this process is accompanied by the bar mode of the radial orbit instability slightly modified by rotation. We refer this case to (giant) ellipticals. For moderate rotation, when the radial orbit instability is suppressed, another mode takes over, which is the direct continuation of a strongly damping mode at the limit of almost radial orbits; it turns into a practically non-damping and long-lived mode (for many revolutions), and even a slowly rotating bar may eventually be formed. It is natural to refer this case to bulges and dwarf elipticals. Then spirals could be formed from the clouds with large amounts of rotation.
The paper aims at a demonstration of the principal differences between the oscillation spectra of multi-component systems and a one-component medium. The character of the mutual motions of components appears then to be of importance. Three cases are considered: (1) motionless components in the inertial frame of reference; (2) inertial subsystems moving at constant relative velocities; (3) a rotating n-component system. The oscillation spectra in these three cases have qualitative differences between each other and when compared with those of resting or rotating one-component systems.
The hydrodynamical conception of the spiral structure generation in the galaxies with a “kink” on the rotation curve is discussed. It treats the spirals as density waves in gas component of galactic disks. The main results of the fifteen-year study are presented. References are made to the papers of authors that prove a) the “gas” conception of the Galaxy spiral structure, b) the identity of equations for rotating shallow water and galactic gas disk, c) the method of laboratory modelling of galactic spirals induced by hydrodynamical mechanisms in shallow water experiments with the “Spiral” set up. The linear stability theory describes the mechanism of spiral arm formation and gives the parameters of the arms. Experiments agree with theory. Besides, they show banana-like vortices between the arms near the generator. Observational data on the galaxy NGC 1566 reveal a pronounced velocity kink and may be explained in terms of the spiral-vortex gas conception. The results of laboratory experiments and numerical simulations allow us to suggest certain hypothesis concerning observational evidences of the spiral-vortex structure.
We would like to draw attention to some observational data which should not be neglected, in our opinion, in developing spiral structure theories. Some of these results demonstrate Le Chatelier principle well-known in physics. According to this principle, any physical process is proceeding to cancel its cause. Localization of galactic disks near the marginal curves of various instabilities shown below indicates the important role that these instabilities play in evolutionary processes of disks.
In this report we present a possible scheme of short-term CME detection forecasting developed on the basis of statistical analysis of solar radio emission regularities prior to “isolated” solar Coronal Mass Ejections registered in 1998, 2003, 2009-2013.
It is shown that in flat gravitating systems, such as spiral galaxies, groups of galaxies and some superclusters (which have an axis ratio of, say, 1/5) there are nonlinear effects such as the formation of collapsars in disks which are stable according to Toomre's criterion; the formation of solitons (spiral and ring-shaped), which can move with supersonic as well as subsonic velocities depending on the characteristic parameters of the disk. in an isothermal gas, shock waves can only originate in spirals with two or more arms. in the background of two bright spiral arms one may be able to trace a weaker ring structure. in contrast to supersonic spirals, the velocity of the circular structure is subsonic. A bright ring structure can in principle indicate that in such systems for some reason the adiabatic index γ is close to that of an ideal gas γ ≈ 5/3. This last point can be of interest in the future if non-isothermal perturbations will be found as seems possible in some systems. A break-up instability will lead to practically uniform enhanced star formation all over the disk; it will have a tendency to simulate narrow rings and tightly wound spirals with one arm according to the law (δσ/σO)~(t-tO)−1.
We investigate numerically the transitions and oscillatory regimes in two-layer quasigeostrophic hetons and tripoles composed of patches of uniform potential vorticity (PV). The contour-surgery algorithms are employed, in which either some symmetries are preserved, or asymmetric evolution of the vortex structures is allowed, induced by generally asymmetric numerical noise. The fluid layers are assumed equally thick. First, the evolution of hetons is considered. A heton, a steadily translating pair of vortices residing in different layers, is antisymmetric in the sense that the two PV patches are opposite in sign and symmetric in shape about the axis of translation. A feebly stable heton, when exposed to weak antisymmetric perturbations, responds by developing an oscillation, which culminates in a transition to a new, substantially robust oscillating heton. The results obtained reinforce our earlier findings regarding the modon-to-modon transition (Kizner et al., J. Fluid Mech., vol. 468, 2002, pp. 239–270; Kizner, Phys. Fluids, vol. 18 (5), 2006, 056601; Kizner, UTAM Symposium on Hamiltonian Dynamics, Vortex Structures, Turbulence (ed. Borisov et al.), IUTAM Bookseries, vol. 6, 2008, pp. 125–133. Springer) and clarify the transition mechanism. Asymmetric perturbations might cause a heton-to-tripole transition. Next we consider the transitions and oscillations in carousel tripoles exposed to weak, generally asymmetric perturbations. A carousel tripole is a steadily rotating centrally symmetric ensemble of three PV patches, with the central vortex being located in one layer and the two remaining, satellite vortices in the other layer. Depending on the tripoles’ size, hence also on the shape of the satellite vortices, three different types of transition are revealed, the transition to a ringed (shielded) monopole being one of them. Whereas the transition of a ringed monopole into a tripole is a known phenomenon, the reverse transition in baroclinic flows is detected for the first time.
The analysis of the observational line-of-sight radial velocity field of molecular clouds, connecting with young stars, has strengthened the Fridman's hypothesis (1994) on the possible existence of anticyclone in the solar neighborhood. Anticyclones are located near corotation radius of the observed spiral arms, a number of which is equal to a number of vortices. Our calculations show that the four-vortices model fits observational data fairly well.
We shall not use any theoretical conception on the nature of spiral arms generation (bar, selfgravitational or hydrodynamical mechanisms, etc.). We shall base on the treatment of the observational data.
Observations show that in the solar neighborhood the velocity dispersions of disk stars increase with their age. In this work we present the results of a critical analysis of the existing interpretations of the data, as well as of previous theoretical explanations of the heating phenomenon. It is shown that different relaxation mechanisms based on star-cloud collisions can result in a wide set of age–velocity dispersion relations (AVDR). Thus the observed differing power laws of the heating of the stellar component can be a consequence of the different relaxation mechanisms.
The Fourier analysis of the observed velocity field of ionized gas in the inner 1.5 pc of the Galactic Center (obtained by Roberts and Goss, 1993) is made. As follows from the analysis, the observed field of residual velocities is dominated by the second Fourier harmonic. This fact can be treated as a consequence of the presence of an one-armed density wave with the density maximum along the Northern Arm plus the Western Arc structure. The wave nature of this structure is proved on the base of the behaviour of the phase of the second harmonic of line-of-sight velocity field in the whole region. The Fourier analysis shows also the presence of systematic radial velocity. We consider this flow as a quasi-stationary radial drift caused by one-armed nonlinear density wave (‘mini-spiral’).
We investigate a stability of the gaseous disk in the Milky Way. The rotation curve with smooth two kinks in the Solar vicinity (Fig.1) was adopted in accordance with the observations (Fridman et al., 1994a). Such a gaseous disk is unstable. The instability can generate the four-armed spiral (Fig.2) and four-vortex structure (Fig.3). The method of the analysis is described by Fridman et al., 1994b. The generation mechanism is similar to that described by Glatsel, 1987.
Line-of-sight and proper motions data for stars near the Galactic center have evolved in recent years (see, e.g. Eckart & Genzel). The data were used for determining the star velocity dispersions in different directions (with a result that the velocity distribution is isotropic to within the observational error). Here we note that there exists a possibility for determining the star phase density itself from such data. The method is based on the solution of the corrensponding integral equations with their left sides being calculated from radial velocities and proper motions. Remind that discussion of the problems connected with reconstruction of the phase density from the radial velocity data was started by Merritt. There is some difference in applying this approach to self-gravitating systems (open and globular clusters) and clusters within external gravitational field. Among the latter is, for example, the inner parts of the Galactic nuclear cluster: they are governed by the field of the central black hole. It follows from the proper motions data estimates for a mass within a radius of 0.16 pc and within 0.083 pc given by Eckart & Genzel (cited above). In the case of the cluster in the field of the black hole we have no need of information about the densities σ(s) (s is the projected radius) and ρ(r) (since the method uses only the gravitational potential Φ(r), which here is foregone: Φ(r) = −GMh/r). Unfortunately, the data on the stars around the central black hole are yet inadequate to derive the distribution function with satisfactory accuracy. (Obviously the necessary data will be available before long.) So we restrict ourselves to only testing the computer algorithms used on the example of the simplest (Plummer) model, for which f(E) ∞ (–E)7/2.
The innermost 2 pc contain a rotating ring (“circumnuclear disk”) of molecular gas, neutral hydrogen, and dust with an embedded H II region called Sgr A West; a dense stellar cluster; and a compact nonthermal radio source Sgr A∗ (for a recent review, see Blitz et al. 1993). The clumped, spiral-shaped morphology of Sgr A West, sometimes called lthe mini-spiral”, has been a subject of numerous speculations concerning its origin (for a review, see Genzel & Townes 1987). Lacy et al. (1991) demonstrated that both the kinematics and shape of a part of Sgr A West can be fairly well approximated using an one-armed density-wave model.
This report lists some of the major conferences that took place or were published during the current period in the areas of interest to Commission 33. It then presents in summary form some of the scientific highlights in these areas. An expanded version of this report, including more related conferences, full references and a report of activities from the former Soviet Union, appears on the mid-2000 WWW page of the Commission: http://msowww.anu.edu.au/~ kcf/kcf_ftp/IAU/comm33report_1999.html.
The paper is devoted to the interpretation of spectrographic data within the frequency range 8-12 GHz. Some spectral characteristics of weak solar steplike radio bursts are reported. To explain some parameters of the emission the ability to keep superthermal electrons in a magnetic trap with dense inhomogeneous plasma is theoretically studied. On the basis of this model we estimate the energy and number of accelerated electrons, and the flux density of precipitating electrons which are the source of enhanced plasma radiation. For the obtained efficiency of electron acceleration the calculated intensity of gyrosynchrotron emission proves to be less than the observed one.
Subject headings: acceleration of particles — radiation mechanisms: nonthermal — Sun: flares — Sun: radio radiation