Living plant systems: How robust are they in the absence of gravity?

The following hierarchical levels can be recognised in plant systems: cells, organs, organisms and gamodemes (interbreeding members of a community). Each level in this ‘living hierarchy’ is both defined and supported by a similar set of sub-systems. Within this framework of plant organization, two complementary questions are relevant for interpreting plant-oriented space experiments: 1) What role, if any, does gravity play in enabling the development of each organizational level? and 2) Does abnormal development in an altered gravity environment indicate sub-system inefficiency? Although a few representatives of the various organizational levels in plant systems have already been the subject of microgravity experiments in space laboratories—from cells in culture to gamodemes, the latter being found in some Closed Environment Life Support Systems—it would be of interest to investigate additional systems with respect to their response to microgravity. Recognition of the sub-systems at each level might be relevant not only for a more complete understanding of plant development but also for the successful cultivation and propagation of plants during long-term space flights and the establishment of plants in extra-terrestrial environments.     

Sequences of Solar Events with Identical Decays as a Tool for Isolating Quasistationary States in the Interplanetary Space

Time profile of the fluxes of energetic solar particles generated by solar flares (including their phase of decline) is formed to a large extent by the structure of the interplanetary magnetic field and its irregularities that move away from the Sun with the solar wind velocity. When propagation is a pure diffusion, the solar particle fluxes decay after the maximum in a power-law manner. At the same time in many cases this decay is exponential, which is indicative of a considerable role played by the convective sweep of particles and their adiabatic deceleration in the expanding solar wind. In this paper we consider the events with long exponential decays and newly discovered series of successive events with identical exponential decays lasting for one to two weeks or more. They allow us to assume that the interplanetary space is stable and homogeneous during this period.     

Wave-particle interactions and their relevance to substorms

Wave-particle effects are implicit in most models of radial diffusion and energization of Van Allen belt particles; they were explicitly used in the wave turbulence model for trapped particle precipitation and trapped flux limitations by Kennel and Petschek, Cornwall and by many others. Liemohn used wave-particle interactions to work out a theory of path-integrated whistler amplification process to explain the lack of large per-hop attenuation of multiple-hop LF whistlers.Others have now used wave-particle interactions to construct theories of ELF and VLF chorus. In the present paper we shall review the observations and some of the pertinent theoretical interpretations of wave-particle effects as they relate to substorm and storm-time phenomena. If substorms develop as a result of magnetic merging, then it seems clear that wave-particle interactions in the dissipative or so-called diffusion region of the reconnection zone may be of great importance. The plasma sheet thinning and flow towards the Earth lead inevitably to the development of particle distribution functions that contain free energy in a pitch-angle anisotropy. Such free energy can be released via plasma wave instabilities. The subsequent wave-particle interactions can result in both strong and weak diffusion of particles into loss cones with consequent precipitation fluxes into the auroral zone. Ring current proton spectra also should be unstable against various plasma instabilities with consequent ring current decay and precipitations. Wave-particle interactions must play some important roles in auroral arcs, electrojets and other phenomena related to substorms. These aspects of wave-Paticle interaction will be covered     

Doppler tomography of O-type binaries: The physical properties of seven systems

We have analyzed UV photospheric lines of seven O-type binaries, by means of crosscorrelation and Doppler tomographic methods, with the goal of estimating the physical properties of the individual stars. These systems are HD 1337 (AO Cas), HD 47129 (Plaskett's star), HD 57060 (29 UW CMa), HD 37043 (Iota Ori), HD 215835 (DH Cep), HD 152218, and HD 152248. Mass ratios have been obtained primarily from a cross-correlation technique, but also by several other techniques. The tomographic techniques allow us to separate the spectra of the components. We then can estimate the individual spectral types and luminosity classes of the stars (and henceT _eff and logg, respectively), the luminosity ratio, and projected rotational velocities. We discuss the physical properties of these O-type binaries. These are some of the early results of a large scale project involving 36 O-type double-lined binary systems (from the catalog of Battenet al. 1989) which we will study using IUE and complementary ground-based data.     

Ground-Based and Space-Based Radio Observations of Planetary Lightning

We review radio detection of planetary lightning performed by Voyager, Galileo (including in-situ probe measurements), Cassini, and other spacecraft, and compare the information on the underlying physics derived from these observations—especially the discharge duration, at Jupiter and Saturn—with our knowledge of terrestrial lightning. The controversial evidence at Venus is discussed, as well as the prospects for lightning-like discharges in Martian dust-storms (and studies on terrestrial analogues). In addition, lightning sources provide radio beacons that allow us to probe planetary ionospheres. Ground-based observations of Saturn’s lightning have been attempted several times in the past and have been recently successful. They will be the subject of observations by the new generation of giant radio arrays. We review past results and future studies, focussing on the detection challenges and on the interest of ground-based radio monitoring, in conjunction with spacecraft observations or in standalone mode.