Quasi-periodic burst structure at 2.8 GHz and its relationship to burst morphological parameters

Fifteen examples of quasi-periodic 2.8 GHz burst emission observed at the La Posta Astrogeophysical Observatory during the period December 1966 through May 1973 were identified. The periods of these events and those of 22 additional events previously reported in the literature were plotted against burst morphological parameters. The relationship between period and event energy was found to be considerably weaker than initially reported by Cribbens and Matthews.     

A note on frame transformations with applications to geodetic datums

Rigorous equations in compact symbolic matrix notation are introduced to transform coordinates and velocities between ITRF frames and modern GPS-based geocentric geodetic datums. The theory is general but, after neglecting higher than second-order terms, it is shown that the equations revert to the formulation currently applied in most major continental datums. We discuss several examples: the North American Datum of 1983 (NAD83), the European Terrestrial Reference System of 1989 (ETRS89), the Geodetic Datum of Australia of 1994 (GDA94), and the South American Geocentric Reference System (SIRGAS). Electronic Publication     

Application of multiple sublethal stress indicators to assess the health of fish in Pamlico Sound following extensive flooding

Multiple indicators of sublethal stress (bioindicators) were used to assess the health and condition of two important estuarine fish species in the Pamlico Sound estuary following extensive flooding from three sequential hurricanes that occurred during early fall 1999. Bioindicators ranging from the biochemical to the reproductive and organism-level were used to assess the health of southern flounder and spot in Pamlico Sound compared to the health of these same species sampled from a relatively unaffected references site in lower Core Sound. Many of the physiological, reproductive, immunological, histopathological, and general condition indices suggested that both species, and particularly spot, in Pamlico Sound were sublethally stressed and in poorer condition than fish sampled from Core Sound. The major environmental stressors causing these sublethal stress responses in Pamlico Sound fish appears to be those related to episodic hypoxic exposure or a combination of effects associated with hypoxic conditions such as alterations in preferred habitat and food availability. Although fish populations in Pamlico Sound do not appear to be severely damaged or impaired at this time, organisms that are sublethally stressed can incur increased vulnerability to additional or future stressors such as modified physicochemical regimes, changes in food and habitat availability, and increases in infectious pathogens. Because of the low flushing rate (～1 yr) of Pamlico Sound, recovery rate may be exceptionally slow, prolonging any adverse effects of altered nutrient regimes (such as hypoxia) on the health and fitness of resident fish populations. Flooding from the 1999 hurricanes may have contributed to the short-term health and condition of finfish species in Pamlico Sound and also influenced longer-term recovery and ecological status of this system. Longer-term manifestation of effects from flooding may be of particular concern as the frequency of hurricanes is expected to increase over the next few years and the accelerated uses of the coastal zone places further stress on estuarine resources.     

Pressure dependence of hydrogen bonding in metal deuteroxides: a neutron powder diffraction study of Mn(OD)2 and β-Co(OD)2.

The structures of deuterated pyrochroite, Mn(OD)₂ and β−Cο(OD)₂ have been refined using the Rietveld method and neutron powder diffraction data collected in an opposed-anvil high pressure (Paris-Edinburgh) cell from room pressure to 9 GPa. The equation of state for Mn(OD)₂ was determined (K=41(3) GPa for fixed K′=4.7) and found to be consistent with previous studies of the isostructural brucite, Mg(OD)₂. The compressibility of β−Cο(OD)₂ on the other hand is apparently anomalous. The c-axis initially decreases at 3 times the rate of decrease of the a-axis; the ratio decreases to about 1.5 at an estimated 6 GPa before increasing again beyond this pressure. There is no obvious corresponding anomaly in the details of the atomic structure. In both materials there is an increase in the D-site disorder with pressure. A split-site model for the D-positions best fits the data at pressures above 8 GPa. There is no statistically significant increase in the O-D interatomic distance at increased pressure while the hydrogen bonding interaction D...O appears to increase as this distance decreases and the O-D...O angle increases. The intramolecular O-D bond valences, determined indirectly from the intermolecular D...O distances, decrease steadily for both materials as pressure is increased. Received: 31 October 1996 / Revised, accepted: 27 February 1997     

Uplift rates of the Loyalty Islands as determined by 230Th234U dating of raised coral terraces

Uplift rates of the Loyalty Islands (S.W. Pacific) have been determined from ${}^{230}\text{Th}{}^{234}\text{U}$ dating of raised coral terraces standing 2 to 7.5 m above sea level. The ages of the terraces on Ouvéa and Lifou correspond closely to previously documented periods of high sea levels at 120,000 and 180,000 yr BP. A +2-m terrace on Beautemps-Beaupré is considered to be beyond the range of the dating technique. The uplift rates of the various islands show a decrease toward the west. This lends support to the hypothesis of a lithospheric bulge of the leading edge of the Australian plate prior to its subduction at the level of the New Hebrides trench.     

Recrystallization and peristerite formation in albite

Plagioclase in the range An₂-An₁₀ in a relatively undeformed Quartz—feldspar pegmatite is compared with similar material in a strongly deformed and recrystallized shear zone. Optical and transmission electron microscope observations and chemical data are discussed in terms of established mechanisms of strain induced recrystallization.Recrystallization occurs by the formation of subgrains from recovery, and their subsequent growth by boundary migration or coalescence by rotation. It is suggested that the recrystallization and grain growth are enhanced by a small increase in the anorthite content. Peristerite formation in the recrystallized grains is associated with the migration of high angle boundaries under upper greenschist facies conditions.     

Transmission electron microscope study of the domain structures associated with the b-, c-, d-, e- and f-reflections in plagioclase feldspars

Ten specimens of plagioclase feldspars (An₁₀₀ to An₂₅) have been examined by transmission electron microscopy using dark field and direct lattice imaging. The specimens are classified into two groups: (i) those that have been quenched from the melt (synthetic An₁₀₀, An₉₅, An₆₆ and An₅₀) and (ii) those that have been cooled relatively slowly (An₉₄, An₇₇, An₇₅, An₅₂, An₃₂ and An₂₆). The observed contrast is interpreted in detail using the two-beam dynamical theory of electron diffraction contrast. The fault vectors of the antiphase boundaries (APBs) observed in An₁₀₀ and An₇₇ are determined. Direct resolution of the sublattice and superlattice in specimens of intermediate composition (An₇₅ to An₂₅) indicates that the superlattice is not a regular array of out-of-step faults and is probably due to a simple sinusoidal distortion of the structure. Only three specimens (An₁₀₀, An₇₇ and An₅₀) exhibited a single structural type. All the remaining specimens consisted of intergrowths of two structural types. The structural type present in any particular specimen depends upon its An-content and thermal history. The rate of transformation from any structural type to a lower-temperature structural type appears to decrease with decreasing An-content.     

Dives into outer Coronado Canyon System

Dives in Lockheed's submarine “Deep Quest” followed the floor of the fan valley and outer gorge of Coronado Canyon, southwest of the California—Baja California border. Both the fan valley and outer gorge have meandering courses. Basin depressions and intermittent steep descents characterize the outer gorge. No indications were found of recent activity of turbidity currents at either location, but a sand layer 30 cm below the surface is interpreted as related to a lower stand of sea level at the close of the last ice age. Abundant organisms were seen on the valley floor and in the overlying water.     

A Late‐glacial chironomid record from Hawes Water,northwest England

This paper presents the results of a high‐resolution Late‐glacial chironomid stratigraphy from Hawes Water, a small carbonate lake in northern Lancashire. The samples were from a core taken from the terrestrialised margin of the present lake, which represents an intermediate depth between the true littoral and the profundal. The chironomid assemblage showed a high degree of sensitivity to both broad‐scale and short‐term temperature changes. Comparison with an existing proxy temperature record (δ¹⁸O) for the site confirmed the presence of four temperature inversions within the Late‐glacial Interstadial. A mean July air temperature inference model, derived from acid, soft‐water lakes in Norway and Svalbard, was applied to the data. Despite the absence of carbonate lakes within the Norwegian training set, there was a close similarity between trends in estimated July air temperature and the δ¹⁸O trace, with a particularly strong correspondence in the periods of clay deposition. This suggests that this model is highly robust. The inferred maximum Interstadial temperature was 13.4°C, dropping initially to 7.5°C in the Loch Lomond Stadial. Temperatures reach a maximum of nearly 10°C in this period, cool for a short period before rising rapidly to 13.2°C at the start of the Holocene. These temperatures are similar to but slightly higher than those estimated for Whitrig Bog, southeast Scotland, and lower than those inferred from coleopteran‐based models for sites in South Wales. Copyright © 2004 John Wiley & Sons, Ltd.