Edison — the international infrared space observatory

Edison is planned as a 1.7m telescope to be deployed at L2, and cooled non-cryogenically so that its lifetime would be from a minimum 3 years to possibly in excess of 10 years. Scientific projects have been proposed by 87 scientists from 11 countries. Due to its planned sensitivity and long lifetime it would be an excellent telescope to do comprehensive targeted searches for many different types of astronomical phenomena.     

Open boundaries in short wave simulations — A new approach

A new way of implementing radiation boundary conditions in finite difference schemes is reported. Instead of prescribing the incident field at the model boundary, waves are generated inside the model boundary. All outgoing waves are absorbed at open boundaries using so-called “sponge” layers.     

Stability criteria in many-body systems

The stability parameters developed and discussed in the first paper of this series (Walkeret al., 1980) are used to determine empirically, by means of numerical integration experiment, regions of stability for corotational, coplanar, hierarchical three-body systems. The initially circular case of these systems is studied: the components of the close binary are taken to move initially in circular orbits with respect to their common mass-centre, the third mass initially moving in a circular orbit with respect to the same mass-centre such that its orbit lies wholly outside those of the former two masses. The stability of these systems is then studied by reference to the empirical stability parameters and the initial ratio of the semi-major axes of the orbit of the close binary to that of the third mass about the binary's mass-centre, which is less than unity. For given values of the stability parameters it is determined how the stability of a system is affected by changes in the ratio of the semi-major axes. It is found that an upper limit to this ratio exists which determines the region of stability for such systems. It is also found possible, in the region of instability, to predict how unstable a system will be i.e. crudely speaking, the number of orbits it may be expected to execute before some gross instability sets in. The effect commensurabilities in mean motion have on the stability of these systems is also considered. It is generally found that these commensurabilities enhance the stability of these systems. The predictive powers of the method are then tested: using many test cases it is seen how accurately the stability or instability of a system may be predicted.     

Empirical studies of the peak surge due to tropical storms at Hong Kong

Correlation studies of the peak surges at a particular location in Hong Kong due to tropical storms with differing storm tracks and landfall positions relative to Hong Kong are presented. Empirical equations relating the peak surge with the central pressure of storm and the local maximum wind speed have been determined and these could be used for the further prediction of storm surges.     

Sampling and computational design of nutrient flux from a southeastern U.S. saltmarsh

A sampling and computational approach for estimating nutrient fluxes from a salt marsh ecosystem is presented. Extensive and intensive sampling of tidal velocities, water depths, and nutrient concentrations was made synoptically across three tidal creeks, connecting a 34 km² South Carolina salt marsh with surrounding coastal waters. An estimate of nutrient exchange over each sampling period is based on measurements over four tidal cycles during a neap and spring tidal regime. The computation of instantaneous fluxes of NO₃^?NO₂^?, NH₄⁺, and o-PO₂^4? was based on the cross-multiplication of concentration, velocity, and integrated over the cross-sectional area of each tidal creek. The net flux of nutrients was estimated using a least-squares regression model which included periodic functions simulating tidal and diurnal cycles. This computational approach allows for a rigorous test of the statistical significance of the measured nutrient fluxes and a basis on which interpretations of the ecological significance of the exchange can be made.Tidal patterns in inorganic nutrient concentrations and the corresponding exchanges are presented for a spring time sampling. Nitrate-nitrite was exported consistently from the marsh to the coastal ocean with a mean value of 8.0 kg per tidal cycle for the neap sampling set and 15.6 kg per tidal cycle for the spring set. This corresponded to high concentrations of nitrate-nitrite (0.6 μM) on the ebb tide with low concentrations (0.1 μM) on the flood tide. Ammonia flux was variable and did not portray a consistent tidal concentration pattern. Concentrations ranged from 1 to 6 μM. Ammonia flux was exported to the coastal ocean only during the spring tidal set with a mean value of 114 kg per tidal cycle. Ortho-phosphate was also exported only on the spring tidal set with a mean flux of 40.0 kg per tidal cycle. A tidal concentration pattern of high concentrations (0.6 μM) on the ebb tide and low concentrations (0.05 μM) on the flood was consistent for ortho-phosphate during both neap and spring tidal sets.     

Glacier response to climatic change during the Loch Lomond Stadial and early Flandrian: Geomorphological and palynological evidence from the Isle of Skye,Scotland

The deglaciation of Skye at the close of the Loch Lomond Stadial is assessed on the basis of detailed geomorphological mapping and pollen-stratigraphic correlations. It is concluded that deglaciation proceeded in two distinct stages. The first was marked by numerous glacier stillstands and readvances, while uninterrupted retreat and local glacier stagnation occurred during the second and final stage. The pollen evidence indicates that the first stage was well advanced before the marked thermal improvement at the start of the Flandrian, and it is inferred that initial glacier retreat occurred in response to a decline in precipitation in the later part of the Loch Lomond Stadial. The first stage of glacier retreat continued into the early Flandrian, during which climatic amelioration was interrupted briefly. Final deglaciation appears to have occurred rapidly in response to sustained temperature increases. The collective evidence also indicates spatial variations in the timing of deglaciation, which appear to reflect differences in glacier morphology.     

Five years of photometry ofσ geminorum

Five years of photoelectric photometry of this bright K1 III RS CVn binary has been obtained at thirteen different observatories. Except for one year, the light curve has shown two minima, separated by roughly a half cycle. At the epoch of discovery (1977.2) one minimum was shallower but as of 1980.2 the two became comparable in depth. During the 1979–80 season the light curve changed shape rapidly, the shallower minimum becoming as deep as the other within about 80 days or perhaps less. Times of both minima can be fit with a photometric period of 19 ^d .423, which is 0.9% shorter than the 19 ^d .603 orbital period. The overall brightness range during the five years has been 4 ^m .13<V<4 ^m .29.Guest Observer, Kitt Peak National Observatory, operated by the Association of Universities for Research in Astronomy, under contract with the National Science Foundation.     

Ureilite Compaction

Abstract— Experimental partial melting of Allende in a modest thermal gradient produces compacted crystalline residues on the cold side and silicate liquid segregations on the hot side of the gradient. The mechanism leading to this segregation is a type of zone refining: thermal migration. Chemical diffusion produces relative migration of phases along a saturation gradient induced by a temperature gradient. The compacted crystals have many features reminiscent of ureilite meteorites: olivine major element compositions, surface-equilibrium-controlled adcumulus textures, ripened grain sizes, virtually complete silicate melt removal, and textural elongation. Sulfide melt fails to segregate from crystals by this mechanism. If thermal migration is responsible for the textural features of ureilite compaction, then often-assumed constraints about ambient gravity fields and cooling regimes do not apply to ureilite origins irrespective of whether the compaction is of a melting residue or a cumulus crystal pile. Certain ingrained expectations relating the geochemistry of complementary liquids to these crystals also will be unsatisfied. Because virtually any crystal consolidation regime operates through a thermal gradient, it is likely that thermal migration must play at least a small role in the process. It would be a particularly appropriate mechanism for consolidating ureilites within planetesimals undergoing vigorous primordial heating by radioactivity or electromagnetic induction—circumstances in which the efficacy of the process is not truncated by cooling. The possible existence of this mechanism does not invalidate less unusual suggestions for the origin of ureilites. However, some of the constraints on ureilite origin and complementary liquid geochemistry are now considerably relaxed.     

The change in satellite orbital inclination caused by a rotating atmosphere with day-to-night density variation

The theory specifying the change i in a satellite's orbital inclination due to atmospheric rotation, in terms of the decrease in orbital period T, has been extended to an atmosphere with sinusoidal variation of density between day and night. It is found that with certain special sets of values for the orbital parameters, the day-to-night variation in the Earth's atmosphere can alter the equation for i/T by as much as 25% though only for a few days. Appreciable changes in i/T persisting for several months can only occur for certain resonant orbits: the maximum change is then about 8%. Near-resonance is very unlikely, but the resonance conditions are derived so that orbits can be recognised and avoided.