A discussion of interplanetary post-shock flows with two examples

Plasma and magnetometer observations are described for two flare-associated shock flows and the comparison of them with models. One represents a class of flows where the shock is followed by a stream and separated from it by a region in which density temperature and speed decrease monotonically. The other is characterized by a complex region between the shock and the following stream, which has many discontinuities and fluctuations, but in which there is no increase in helium concentration. These two types of flow can be distinguished using ground magnetograms, since the former shows no sudden impulses following the shock, whereas the latter shows many

Acceleration of protons by interplanetary shocks

Acceleration of protons by interplanetary shock

A self-sustaining nonlinear dynamo process in Keplerian shear flows

A three-dimensional nonlinear dynamo process is identified in rotating plane Couette flow in the Keplerian regime. It is analogous to the hydrodynamic self-sustaining process in non-rotating shear flows and relies on the magneto-rotational instability of a toroidal magnetic field. Steady nonlinear solutions are computed numerically for a wide range of magnetic Reynolds numbers but are restricted to low Reynolds numbers. This process may be important to explain the sustenance of coherent fields and turbulent motions in Keplerian accretion disks, where all its basic ingredients are present.Comment: 4 pages, 7 figures, accepted for publication in Physical Review Letter

The pancreas: studies in its development, pathology, and relative metabolism

SECTION I. A quantitative estimation of The pancreatic islet tissue. | SECTION II. The pancreatic islets in Obese subjects. | SECTION III. Sugar tolerance in geese: a review of sixty-five cases | SECTION IV. Diabetcgenic and pancreotropic Actions of ox anterior pituitary extract in rabbits. | SECTION V. 'growth' and the diabetogenic and pancreotropic actions of anterior pituitary extract. | SECTION VI. The aetiology of diabetes mellitus. | SECTION VII. The effect cf anterior pituitary extract in alloxan diabetes. 324 | SECTION VIII. Further observations on the effect of anterior pituitary extract in alloxan diabetes | SECTION IX. Duodenal diverticula and their complications with particular Reference to acute pancreatic necrosis

Study by animal experiment of the nature and distribution of the pathological changes produced in the tissues by corrosive sublimate: with special reference to the early phases of cell-degeneration and to changes in the blood-fat (illustrated)

Several years ago two cases of mercurial poisoning came to autopsy in the Royal Infirmary, Edinburgh. Microscopic examination of the liver in each of those cases revealed the presence of a fairly marked degree of mitosis. Such mitosis could manifestly be explained in either of two ways. On the one hand, it might be regarded as a direct effect of the mercury whereby the nuclei of the liver -cells are stimulated to divide. On the other hand, it might be looked upon as merely the sequel to a destruction of liver -cells produced by the toxic action of the mercury: in this case mitosis would be a purely regenerative phenomenon secondary to degeneration of liver-tissue. The immediate aim of this research was to discover which of these views is the correct one. If it could be shown that mercury does really exert a specific influence on the cells of the liver whereby their nuclei are stimulated to undergo mitosis, we would, indeed, be in possession of a fact of prime importance. For then we would be in a position to say that in mercury we had a drug capable of controlling the growth of liver-cells in so far as by administering it we could at will produce their division and proliferation. While working out the answer to this question 1 simultaneously made an investigation into the nature and distribution of the pathological changes produced by mercury in most of the other organs, kidney, heart, spleen, intestine, etc. Particular attention has been paid to the earliest phases of degeneration. For example, a special endeavour was made to define the relation between the various kinds of granules which appear in the cells of the kidney when that org- :an is subjected to intoxication - the granules of ordinary cloudy swelling, the mitochondrial granules and those of fatty degeneration. Such an investigation is timely, for as Lorrain Smith states - "It is clear that the interrelations of the granules which appear in degenerative conditions of the protoplasm, to each other, and to the normal structure, must be Lt he subject of much more investigation before we can reach a conception of their relation to those changes in metabolism from which degeneration results." Further, wherever phenomena have been encountered involving fundamental pathological principles an attempt has been made to interpret the phenomena observed with a view to increasing our knowledge of these principles. This is .exemplified in the case of certain changes in the spleen. As a result, moreover, of observations made in the earlier stages of the research my attention was ultimately directed to certain alterations produced by mercury in the amount of fat in the circulating blood. The findings hereafter recorded in this connection constitute, perhaps, the most interesting of my contributions to the pathology of mercurial intoxication. I have discussed the etiology of these changes in blood-fat so far as is possible and have indicated lines along which further research may with advantage be directed. Corrosive sublimate, being one of the best known mercurial compounds and one of the easiest to administer, was chosen as the drug whose effects were to be investigated

Linear and non-linear theory of a parametric instability of hydrodynamic warps in Keplerian discs

We consider the stability of warping modes in Keplerian discs. We find them to be parametrically unstable using two lines of attack, one based on three-mode couplings and the other on Floquet theory. We confirm the existence of the instability, and investigate its nonlinear development in three dimensions, via numerical experiment. The most rapidly growing non-axisymmetric disturbances are the most nearly axisymmetric (low m) ones. Finally, we offer a simple, somewhat speculative model for the interaction of the parametric instability with the warp. We apply this model to the masing disc in NGC 4258 and show that, provided the warp is not forced too strongly, parametric instability can fix the amplitude of the warp.Comment: 14 pages, 6 figures, revised version with appendix added, to be published in MNRA

Dissipative effects on the sustainment of a magnetorotational dynamo in Keplerian shear flow

The magnetorotational (MRI) dynamo has long been considered one of the possible drivers of turbulent angular momentum transport in astrophysical accretion disks. However, various numerical results suggest that this dynamo may be difficult to excite in the astrophysically relevant regime of magnetic Prandtl number (Pm) significantly smaller than unity, for reasons currently not well understood. The aim of this article is to present the first results of an ongoing numerical investigation of the role of both linear and nonlinear dissipative effects in this problem. Combining a parametric exploration and an energy analysis of incompressible nonlinear MRI dynamo cycles representative of the transitional dynamics in large aspect ratio shearing boxes, we find that turbulent magnetic diffusion makes the excitation and sustainment of this dynamo at moderate magnetic Reynolds number (Rm) increasingly difficult for decreasing Pm. This results in an increase in the critical Rm of the dynamo for increasing kinematic Reynolds number (Re), in agreement with earlier numerical results. Given its very generic nature, we argue that turbulent magnetic diffusion could be an important determinant of MRI dynamo excitation in disks, and may also limit the efficiency of angular momentum transport by MRI turbulence in low Pm regimes.Comment: 7 pages, 6 figure