A gamma ray telescope for the highest energies using radio waves

This paper considers the possibility of using pulsed and continuous wave radio sources to scatter or reflect a signal from the ionisation produced by an Extensive Air Shower (EAS) to provide a precise indication of the source co-ordinates of the primary gamma ray. It indicates the limits of such methods and suggests a route which may result in a significant improvement in the current precision of cosmic gamma ray source coordinates.     

Toward an automated system for a correctly registered bathymetricchart

A scheme has been developed for automated bathymetric registration of multiple overlapping swaths of data collected by a ship equipped with a multibeam echo-sounder device. Because each swath of data overlaps with several others, registration is performed both at local and global levels. The primitives used for local matching are contours of constant depth which are extracted from the data and are represented as a modified chain code. The main heuristic guiding the search for matching contours of equal depth is their proximity to the middle of the apparent (unregistered) overlapping region. The degree to which two contours match is determined by the correlation of their respective chain codes and the geometrical proximity of their nodes. All best matches are considered tentative until their geometrical implications are evaluated and a consistent majority has emerged. To do global matching. a cost function is constructed and minimized     

Boundary assessment under uncertainty: A case study

Estimating certain attributes within a geological body whose exact boundary is not known presents problems because of the lack of information. Estimation may result in values that are inadmissible from a geological point of view, especially with attributes which necessarily must be zero outside the boundary, such as the thickness of the oil column outside a reservoir. A simple but effective way to define the boundary is to use indicator kriging in two steps, the first for the purpose of extrapolating control points outside the body, the second to obtain a weighting function which expresses the uncertainty attached to estimations obtained in the boundary region.     

Wavy size distributions for collisional systems with a small-size cutoff

Dohnanyi's [J. geophys. Res. 74, 2531–2554, 1969; in Physical Studies of Minor Planets (edited by T. Gehrels), pp. 263–295. NASA-SP 267, 1971] theory predicts that a collisional system such as the asteroid population should rapidly relax to a power-law equilibrium size distribution, provided all the collisional response parameters are independent of size. However, we have found that Dohnanyi did not include in a consistent way in the theory the possible occurrence of a small-size cutoff in the distribution. We have carried out a number of numerical simulations of the collisional evolution process, showing that the cutoff results in a wavy pattern superimposed on Dohnanyi's equilibrium power law, which affects the distribution up to sizes of tens of km. The pattern arises because particles just above the cutoff are not removed by catastrophic impacts by smaller projectiles, and therefore are created by break-up of larger bodies faster than they are eliminated; larger particles are increasingly depleted up to the size where the smallest shattering projectile exceeds the cutoff, and beyond that the removal rate is reduced and the distribution flattens. Thus, to be effective in producing the waves, the cutoff (or any other persisting “discontinuity” in the particle properties) must be sharp over a size range corresponding to the threshold projectile-to-target ratio for fragmentation. The presence of a small-size cutoff in the real asteroid belt is an open question, since it may be generated by poorly known non-gravitational effects acting on μm-sized dust, and may be affected by influx of cometary debris. However, the observational evidence for a variable characteristic exponent of the size distribution of interplanetary bodies is now strong, and the cutoff effect may provide a simple explanation for this finding.     

The Jovian atmospheric window at 2.7 μm: A search for H2S

The atmospheric transmission window at 2.7 μm in Jupiter's atmosphere was observed at a spectral resolution of 0.1 cm^?1 from the Kuiper Airborne Observatory. From analysis of the CH₄ abundance (～80m-am) and the H₂O abundance (<0.0125cm-am) it was determined that the penetration depth of solar flux at 2.7 μm is near the base of the NH₃ cloud layer. The upper limit to H₂O at 2.7 μm and other recent results suggest that photolytic reactions in Jupiter's lower troposphere may not be as significant as was previously thought. The search for H₂S in Jupiter's atmosphere yielded an upper limit of ～0.1cm-am. The corresponding limit to the elemental abundance ratio [S]/[H] was ～1.7 × 10^?8, about 10^?3 times the solar value. Upon modeling the abundance and distribution of H₂S in Jupiter's atmosphere it was concluded that, contrary to expectations, sulfur-bearing chromophores are not present in significant amounts in Jupiter's visible clouds. Rather, it appears that most of Jupiter's sulfur is locked up as NH₄SH in a lower cloud layer. Alternatively, the global abundance of sulfur in Jupiter may be significantly depleted.     

Observations of Jet Diameter, Density and Dynamics

Collimated jets are believed to be an essential ingredient of the star formation process, and we are now able for the first time to test observationally the theories for their formation and propagation. The major advances achieved in recent years are reviewed, regarding the observed morphology, kinematics and excitation properties of jets, from the parsec-scale `giant outflows' down to the `microjets' from T Tauri stars. High angular resolution images and spectra have provided valuable estimates of jet diameter, space velocity, temperature, ionization fraction, electron and total density, both along and across the flow. We can thus calculate key physical quantites, as the shock excitation parameters, or the mass and momentum fluxes in the flow. The results obtained appear to validate the popular magneto-centrifugal models for jet launching, although some important issues are still under debate, as to the cause of knotty structures, observed wind thermal properties, and the dynamical relationship between jets and molecular outflows. Among the most interesting recent findings, we mention the observed indications for jet rotation, with inferred toroidal velocities consistent with the prescribed angular momentum balance between infall and outflow.     

The hydrocarbons in the Isla Vista marine seep environment

Hydrocarbon analyses on samples of sediment, interstitial water, and dissolved and particulate fractions of the water column from the vicinity of the Isla Vista seep near Santa Barbara, California, are presented. The results demonstrate that a very heterogeneous distribution of hydrocarbon composition and concentration exists in the seep environment and that the life-style and feeding habits of the organisms in this environment will have a dramatic effect on their hydrocarbon exposure.