Radar detection of near-Earth Asteroids 1915 Quetzalcoatl, 3199 Nefertiti, 3757 (1982 XB), and 4034 (1986 PA)

We describe Arecibo (2380 MHz, 12.6 cm) Doppler-only radar detections of near-Earth Asteroids 1915 Quetzalcoatl, 3199 Nefertiti, 3757 (1982 XB), and 4034 (1986 PA) obtained between 1981 and 1989. Estimates of the echo spectral bandwidths, radar cross-sections, and circular polarization ratios of these objects constrain their sizes, radar albedos, surface roughnesses, taxonomic classes, rotation periods, and pole directions. Our radar constraints on the diameters of Quetzalcoatl and Nefertiti are most consistent with sizes determined using thermal-radiometry and the Fast Rotation Model (FRM); this consistency may indicate that these asteroids have surfaces of high thermal inertia (i.e., little or no regolith). Constraints on Quetzalcoatl's radar albedo rule out a “metallic M” classification. The radar constraints for Nefertiti are inconsistent with a rotation pole published by Kaasalainen et al. (2004, Icarus 167, 178). Our estimates of 1982 XB's size are consistent with previously published estimates. The radar bandwidth of 1986 PA places an upper bound of about 24 h on its rotation period.     

Discriminant trace-element analysis of strata in the Witwatersrand System

Powdered rock samples from strata of the Witwatersrand System's sedimentary succession have been analyzed by x-ray fluorescence and optical spectroscopy techniques for nineteen elements. Using discriminant analysis it is possible to identify strata based on their trace-element compositions.     

Resonant attitude instabilities for a symmetric satellite in a circular orbit

The roll-yaw attitude motion of a spinning symmetric satellite in a circular orbit is investigated with particular emphasis on the behavior near resonance. Resonance in circular orbit occurs if there is a low-order commensurability between the coupled roll-yaw attitude frequencies. For the so-called Delp region where the Hamiltonian describing the linearized attitude oscillations is not positive definite, there can exist, near resonance, a simultaneous growth or decay of the energy of the two normal modes. Two sections of the resonance line ₂=3 ₁ permitting the largest effects are determined and the equations of motion are integrated numerically as a check on the resonance theory. In particular, resonance-induced instabilities are confirmed.     

Escape from a gravitational system of positive energy

It is proved in this article that under the condition defined in Equation (6), whent, at least two particles must escape from a Newtonian gravitational system of positive energy.     

Late-Wisconsin vegetational changes in unglaciated Eastern North America

Recent pollen and macrofossil data from the Southeast is consistent with a displacement of boreal forest species by over 1000 km during full-glacial time. Data from west of the Appalachians suggests a displacement of some 600 km. Thus boreal forests were developed in a broad area south of the ice margin. Few deciduous forest elements persisted in that region. The displacement appears to have been azonal. There is good evidence to suggest a significant mid-Wisconsin interstadial (23,00036,000 BP) characterized by a more temperate biota.     

A reinterpretation of the Lateglacial environmental history of the Isle of Skye,Inner Hebrides,Scotland

This paper presents a major revision of the Late Devensian Lateglacial environmental history of the Isle of Skye, Scotland, based upon a combination of geomorphological, biostratigraphical and radiocarbon evidence. The distribution of glacial and periglacial landforms, and of raised shorelines, suggests that there was only one extensive readvance of local glaciers in southern Skye following the wastage of the Late Devensian ice sheet. Pollen-stratigraphic evidence from 10 sites inside and 4 sites outside the mapped ice limits indicates that this readvance occurred during the Loch Lomond Stadial. At that time over 180km² of the uplands of south-central Skye were covered by glacier ice, a much more extensive glaciation than previously envisaged. Palynological evidence from four Lateglacial profiles implies that degree of exposure to strong westerly winds was the principal factor determing vegetational contrasts on the island, and that regional differences in vegetational type were less pronounced than has hitherto been suggested. The glacial and palaeobotanical reconstructions reported here are more compatible with Lateglacial data from the Scottish mainland and Hebridean islands than were the previously-published accounts for the Isle of Skye.