Heliopause stability revisited: dispersion analysis and numerical simulations

The heliopause, a surface separating the tenuous hot heliosheath flow and the dense, strongly magnetized interstellar flow, is subject to instabilities of the Rayleigh–Taylor and Kelvin–Helmholtz types. The dynamic evolution of this discontinuity is of considerable importance for understanding the neutral atom and cosmic-ray filtration at the interface. Here, we investigate the stability of the upwind heliopause in the presence of charge exchange collisions using both an analytic (dispersion relation) approach and a numerical model that includes the interstellar magnetic field. The linear analysis yields a cubic dispersion relation that admits imaginary solutions for the full range of wavenumbers, implying that the stagnation point on the heliopause is unconditionally Rayleigh–Taylor unstable to small perturbations propagating parallel to the discontinuity surface. We confirm this result by following the nonlinear development of the instability with a time-dependent simulation using a four fluid MHD-neutral numerical code. For the typical solar wind and LISM conditions, we obtain cyclical evolution of the upwind heliopause with a period of the order of 100 years. We also identify two areas of space physics where the instability may have important implications.     

Fluxes of low-energy particles in quiet periods of solar activity and the <Emphasis Type="Italic">MgII</Emphasis> index

Low fluxes of protons with energies 0.3–10 MeV were studied during 21–23 solar cycles as a function of the MgII index using the data of the instruments CPME, EIS (IMP8), and EPHIN (SOHO). It has been shown that a) during quiet time of solar activity the fluxes of protons (background protons) have a positive correlation with the MgII index value throughout the solar cycle, b) specific features of variations of the MgII index during the solar minima of 1986–1987 and 1996–1997 can be considered, as well as variations of background fluxes of low energy charged particles, to be manifestations of the 22-year magnetic cycle of the Sun, and c) periods of the lowest value of the MgII index are also characterized by the smaller values of the ratio of intensities of protons and helium nuclei than in other quiet periods. A hypothesis is put forward that acceleration in a multitude of weak solar flares is one of the sources of background fluxes of low energy particles in the interplanetary space.     

Nonlinear decoupling sliding mode control and attitude control ofspacecraft

Control of a class of uncertain nonlinear systems which can be decoupled by state-variable feedback is considered. A variable-structure-control (VSC) law is derived so that in the closed-loop system the output variables asymptotically track given output trajectories in spite of any uncertainty in the system. On the basis of this result, a control law is derived for the attitude control of an orbiting spacecraft in the presence of uncertainty using reaction jets. The controlled outputs are the three Euler angles which describe the orientation of the spacecraft relative to an orbital frame. Simulation results are presented to show that, in the closed-loop system, precise attitude control is accomplished in spite of the uncertainty in the system     

Plant cell plasma membrane structure and properties under clinostatting.

Structural-functional organization of plasma membrane of pea roots seedling was investigated by methods of chemiluminescence, fluorescence probes, chromatography and freeze-fracture studies under normal conditions and clinostatting. Phase character of lipid peroxidation intensity was fixed. The initial phase of this process is characterized by lipid peroxidation decreasing with its next induction. The primary changes depending on free-radical mechanisms of lipid peroxidation were excellently revealed by chemiluminescence. Plasmalemma microviscosity increased on the average of 15-20% under microgravity at the initial stages of its phenomenon. There were major changes of phosphatidilcholine and phosphatidilethanolamine contents. The total quantity of phospholipids remained rather stable. Changes of phosphatide acid concentration point to degradation and phospholipids biosynthesis. There were increases of unsaturated fatty acids mainly at the expense of linoleic and linolenic acids and also a decrease of saturated fatty acid content at the expense of palmitic and stearic acids. Unsaturation index of fatty acids increased as well. On the whole fatty acid composition was variable in comparison with phospholipids. Probably it is one of mechanisms of maintaining of microviscosity within definite limits. Considerable structural changes in organization of plasmalemma protein-lipid complex were not revealed by the freeze-fracture studies.     

Long-term preservation of microbial ecosystems in permafrost.

It has been established that significant numbers (up to 10 million cells per gram of sample) of living microorganisms of various ecological and morphological groups have been preserved under permafrost conditions, at temperatures ranging from -9 to -13 degrees C and depths of up to 100 m, for thousands and sometimes millions of years. Preserved since the formation of permafrost in sand-clay sediments of the Pliocene-Quaternary period and in paleosols and peats buried among them, these cells art the only living organisms that have survived for a geologically significant period of time. The complexity of the microbial community preserved varies with the age of the permafrost. Eukaryotes are found only in Holocene sediments; while prokaryotes are found to greater ages, i.e., Pliocene and Pleistocene. The diversity of microorganisms decreases with increasing age of sediments, and as a result cocci and corynebacteria are predominant. Enzyme activity (catalase and hydrolytic enzymes) and photosynthetic pigments (chlorophyll and pheophytin have also been detected in permafrost sediments. These results permit us to outline some approaches to the search for traces of life in the permafrost of Martian sediments by borehole core sampling. It is in the deep horizons (and not on the planet surface), isolated by permafrost from the external conditions, that results similar to those obtained on Earth can be expected.     

Control of complex nonlinear vibrations of sandwich beams

Complex vibrations of the Bernoulli-Euler sandwich beams are considered. The solution is performed by the numerical methods of finite elements in the Bubnov-Galerkin form and finite differences of the second order of accuracy. The approaches for control of chaotic vibrations in the Bernoulli-Euler sandwich beams are proposed.     

Sikkim's Teesta River fog, mist and dust particle monitoring using monostatic LIDAR

Fog, mist, and atmospheric dust particles, having the dimension of one micrometer or less, play an important role in the deterioration of visibility, as well as in causing local warming in the atmosphere. With an attempt to reduce the deterioration, a scientific approach has to be taken to determine their origins. A monostatic LIDAR may be one of the best instruments for such work. The authors are tempted to develop such a LIDAR for fog, mist, and dust particle monitoring over River Teesta at Sikkim. LIDAR is an acronym for Light Detection And Ranging. What can we do with LIDAR? Measure distance, measure speed, measure rotation, measure chemical composition and concentration, and measure cross-sections of the targets. The digital technique is always utilized for its development which results in better security, lower power consumption, higher power efficiency, higher reliability, lower transmitter power, lower multipath effect, higher interference suppression as compared to an analog system. The commercial systems like disdometer, rain radar, mobile robot, etc., utilizing LIDAR principles are operational in different parts of the world. The authors are highly motivated for such LIDAR development and their development effort follows.     

Dynamic trapping of electrons in the porcupine ionospheric ion beam experiment

Electrons are needed to maintain quasineutrality in a case where positive ions are injected across the magnetic field into a limited volume in a magnetized plasma. In the absence of collisions, a positive potential builds up and traps the electrons which enter the region along the magnetic field. If the added density of ions exceeds the ambient density, large potential differences along the magnetic field can be maintained this way. The process explains several features of the Porcupine xenon ion beam injection experiment, where strong magnetic-field-aligned electric fields were measured in the vicinity of a xenon ion beam which was injected into the ambient ionosphere from a spinning subpayload.