Cometary atmosphere (gas and dust)

There is important progress now in the identifications and measurements of primary (parent) molecules in the inner coma of Comet Halley. H₂O, CO₂ and CO are definitely in the list, CH and some complicate organic molecules are suspected. Gas production rate for water vapor is Q_H2O 10³⁰ s⁻¹. The bulk of data doesn't contradict to the Whipple model of nucleus (with clathrate modification). Pronounced spatial structure of gaseous flow in the coma was observed, but in general measured properties of neutral gas in the coma of Comet Halley are not very different from predicted. Situation for dust is different. In situ dust measurements show that size spectrum and optical properties of particles in coma are substantively declining from predicted on the base of groundbased photometry. However there are discrepancies between Vega and Giotto dust counter data. Dust in the inner coma didn't prevent the succesful imaging of nucleus by TV on Vega 1 and 2.     

Microlesions: theory and reality.

Efforts to assess radiation risk in space have been complicated by the considerable unknowns regarding the biological effects of the heavy ion component (HZE particles) of the cosmic rays. The attention has focused primarily on the assignation of a quality factor (Q) which would take into account the greater effectiveness of heavy ions vis-a-vis other forms of ionizing radiation. If however, as the so-called "Microlesion Theory" allows, the passage of HZE particles through living tissue produces unique biological damage, the traditional use of Q becomes meaningless. Therefore, it is critical to determine if microlesions, in fact, do exist. While the concept does not necessarily require detectable morphological damage, "tunnel-lesions" or holes in ocular tissues have been cited as evidence of microlesions. These data, however, are open to reinterpretation. On-going light, scanning and transmission electron microscopic studies of the corneas, lenses and retinas of rat eyes exposed to 450 MeV/amu 56Fe ions thus far have not revealed tunnel-lesion damage. The morphological effects of the heavy ions have been found to be qualitatively similar to the changes following other kinds of ionizing radiation.     

The influence of radiation quality on the formation of DNA breaks.

We have aimed to present a comprehensive review of our understanding to date of the formation of DNA strand breaks induced by high LET radiation. We have discussed data obtained from DNA in solution as well as from the formation and "repair" of strand breaks in cell DNA. There is good agreement, qualitatively, between these two systems. Results were evaluated for two parameters: (1) effectivity per particle, the cross section (sigma) in micrometers 2/particle; and (2) the strand break induction frequency as number of breaks per Gy per unit DNA (bp or dalton). A series of biological effects curves (one for each Z-number) is obtained in effectivity versus LET plots. The relationships between induction frequencies of single-strand breaks, or double-strand breaks, or the residual "irrepairable" breaks and LET-values have been evaluated and discussed for a wide spectrum of heavy ions, both for DNA in solution and for DNA in the cell. For radiation induced total breaks in cell DNA, the RBE is less than one, while the RBE for the induction of DSBs can be greater than one in the 100-200 keV/micrometers range. The level of irrepairable strand breaks is highest in this same LET range and may reach 25 percent of the initial break yield. The data presented cover results obtained for helium to uranium particles, covering a particle incident energy range of about 2 to 900 MeV/u with a corresponding LET range of near 16 to 16000 keV/micrometers.     

Hypervelocity acceleration techniques: A review of exisiting capabilities and prospects for future developments

During the last few decades various techniques have made it possible to accelerate microparticles (10⁻⁶ – 10⁻¹⁵ gr) up to tens of km/sec and macroparticles (1 gr or so) up to 10 km/sec, thus furthering our understanding of many impact related phenomena occurring on the surfaces of celestial bodies.

This review will deal with existing techniques for the acceleration of hypervelocity projectiles. The performance of electrostatic accelerators, electromagnetic rail guns and related systems, plasma drag accelerators, light gas guns and explosive accelerating techniques is reviewed, and the capabilities and limitations of each type are briefly discussed. An attempt is made to assess the future promise of existing techniques and the realism of some current suggestions.     

Observation of fundamental magnetoplasma emissions excited in magnetosphere by modulated electron beams

There were several cases when modulated electron beam had been injected from APEX satellite into an otherwise unmodified ionospheric plasma. The beams were formed from 2 μs pulses repeated at a rate of 40kHz. Injections took place in the altitude range 400–1100km over Europe. The onboard receiver connected to the dipole antenna swept the frequency interval 1–10 MHz in 1 sec. Due to a relatively narrow receiver bandwidth (15 kHz), moderate frequency step (50 kHz), slow changes of f_n and f_c (local electron plasma and gyro frequencies) fine structure of excited emissions was detected. In many cases, a very prominent doublet could be convincingly identified as a (f_n,f_u=sqrt(f_n^*f_n+f_c^*f_c)) band, with f_n practically equal to the local plasma frequency in the unperturbed ionosphere. Determination of plasma frequency is of prime importance in analysis of complex structures composed from various harmonics f_n,f_c,f_u. Complexity is manifested as coalescing of various harmonics with maxima shifted from nominal frequencies or splitting them into components due to mixing of local and propagation effects. Despite the existence of strong emissions on frequencies characteristic for the unperturbed ionosphere, very strong broadcasting transmissions are frequently cut off, even when the beam is directed upward. Most typical spectra are discussed.     

The chemical profiles of polar ice on Earth and Mars: What we read from the first; what we could read from the second

An analogy is drawn between the current knowledge on terrestrial snow and ice-cap chemistry and the possible composition of snowfall and ice caps of Mars. Terrestrial snowfall reflects the composition of the Earth's atmosphere. Snow cover further interacts with the atmosphere and is the recipient of aerosol and particulate fall-out. The snow is transformed to firn and ice and the chemical signatures become locked into the perennial ice sheets. The chemical profiles of ice thus constitute environmental records of the Earth's past. By considering the present knowledge on the hydrologie cycle of Mars and the chemistry of the atmosphere, a simple analogous model for the chemical profile of the North polar ice cap is proposed. Three major constituents of the ice are discussed: water ice, dust, and occluded air bubbles. The seasonal fluctuations and interannual variability of these components are examined as possible chemical signatures for the dating of ice, elucidating hydrologie processes, and recording long-term climatic change. The model of the north polar cap in summer consists of water-ice fine-dust layers (30–200 m thick) sandwiched between annual dust layers of variable size distribution and thickness (< 1m– > 66 m). The water ice is subjected to metamorphism and grain growth. The interpretation of the physico-chemical profile could lead to increased knowledge on the recent climatic past (1,000–2,000 years), hydrologic reservoirs, and seasonal cycles in the atmospheric dynamics of the planet.     

Study of shaping strategies for blisk vane channels by a cup tool

This paper deals with roughing milling of vane channels for axial blisks by a cup tool. The effect of the shaping strategy on waviness of the surfaces being machined and allowance for subsequent operations is determined.     

Theory of physical libration of the Moon with the liquid core: Forced librations

For a two-layer model of the Moon that consists of a solid nonspherical mantle and an ellipsoidal homogeneous liquid core, a theory of forced librations under the effect of gravitational Earth’s moments has been developed. The motion of the Moon over its orbit has been described by the high-accuracy theory of DE/LE-4 orbital motion. Tables have been constructed that present forced librations of the Moon caused by the second harmonic of its force function, in the neighborhood of its motion according to the generalized Cassini laws. Disturbances of the first-order with respect to dynamic compressions of the Moon and its core are obtained in analytical form for Andoyer variables and Poincare variables and for the projection of the angular velocity vector of Moon’s mantle rotation and the Poincare coordinate system (relative to which core’s liquid accomplishes simple motion) on its major central axes of inertia, as well as for the classical variables in the Moon libration theory, etc. Constructed tables of the forced librations theory give the amplitudes and periods of librations and combinations of arguments of the orbital motion theory that correspond to libration parameters. The interpretation of basic variations has been given and a comparison with the previous theories has been carried out, in particular with the modern empirical theory constructed based on the laser observation data.     

Study of the variability of blazars gamma-ray emission

The γ-ray emission of blazar jets shows a pronounced variability and this feature provides limits to the size and to the speed of the emitting region. We study the γ-ray variability of bright blazars using data from the first 18 months of activity of the Large Area Telescope on the Fermi Gamma-Ray Space Telescope. From the daily light-curves of the blazars characterized by a remarkable activity, we firstly determine the minimum variability time-scale, giving an upper limit for the size of the emitting region of the sources, assumed to be spheroidal blobs in relativistic motion. These regions must be smaller than ∼10⁻³ parsec. Another interesting time-scale is the duration of the outbursts. We conclude that they cannot correspond to radiation produced by a single blob moving relativistically along the jet, but they are either the signature of emission from a standing shock extracting energy from a modulated jet, or the superposition of a number of flares occurring on a shorter time-scale. We also derive lower limits on the bulk Lorentz factor needed to make the emitting region transparent for gamma-rays interacting through photon–photon collisions.     

A technique of shaping the barrel-type parts

In this paper, a new technique for shaping the thin-walled barrel-type parts is presented.