Aluminum-26 in meteorites—VII. Ureilites,their unique radiation history

Cosmogenic ²⁶A1 activities have been measured by γ-γ coincidence counting in the three ureilites which had not previously been studied. The values in dpm/kg are: Dingo Pup Donga, 38.4 ± 2.4; North Haig, 39.3 ± 4.8; Dyalpur, 55.8 ± 4.8. Five of the six known ureilites thus have lower ²⁶A1 contents, 63 per cent to 77 per cent, than the calculated saturation values, in marked contrast to most other stony meteorites. This cannot be attributed to short cosmic ray exposure ages. Nor do size and depth effects account for the narrow range of ²⁶A1 activities, because a nuclear particle track study indicates that preatmospheric radii were highly variable, from ≥ 40 cm for Goalpara to only a few cm for Dingo Pup Donga. By default, the most likely explanation is that the ureilites had much smaller or much larger orbits than all other stony meteorites.     

On the origin of solar metric type II bursts

The vast majority of solar flares are not associated with metric Type II radio bursts. For example, for the period February 1980–July 1982, corresponding to the first two and one-half years of the Solar Maximum Mission, 95% of the 2500 flares with peak >25 keV count rates >100 c s^–1lacked associated Type II emission. Even the 360 largest flares, i.e., those having >25 keV peak count rates >1000 c s^–1, had a Type II association rate of only 24%. The lack of a close correlation between flare size and Type II occurrence implies the need for a 'special condition' that distinguishes flares that are accompanied by metric Type II radio bursts from those of comparable size that are not. The leading candidates for this special condition are: (1) an unusually low Alfvén speed in the flaring region; and (2) fast material motion. We present evidence based on SMM and GOES X-ray data and Solwind coronagraph data that argues against the first of these hypotheses and supports the second. Type II bursts linked to flares within 30° of the solar limb are well associated (64%; 49/76) with fast (>400 km s^–1) coronal mass ejections (CMEs); for Type II flares within 15° of the limb, the association rate is 79% (30/38). An examination of the characteristics of 'non-CME' flares associated with Type IIs does not support the flare-initiated blast wave picture that has been proposed for these events and suggests instead that CMEs may have escaped detection. While the degree of Type II–CME association increases with flare size, there are notable cases of small Type II flares whose outstanding attribute is a fast CME. Thus we argue that metric Type II bursts (as well as the Moreton waves and kilometric Type II bursts that may accompany them) have their root cause in fast coronal mass ejections.     

The occurrence frequency of white-light flares

We derive an occurrence frequency for white-light flares (WLF) of 15.5 ± 4.5 yr^?1 during a 2.6 year period following the maximum of solar cycle 21. This compares with a frequency 5–6 yr^?1 derived by McIntosh and Donnelly (1972) during solar cycle 20. We find that the higher frequency of the more recently observed WLFs is due to the availability of patrol data at shorter wavelengths (λ ? 4000 Å), where the contrast of the flare emission is increased; the improved contrast has allowed less energetic (and hence more frequently occurring) events to be classified as WLFs. We find that sufficient conditions for the occurrence of a WLF are: active region magnetic class = delta; sunspot penumbra class = K, with spot group area ≥ 500 millionths of the solar hemisphere; 1–8 Å X-ray burst class ≥ X2.     

U.S. Mussel Watch: 1977–1978 results on trace metals and radionuclides

The results of the U.S. Mussel Watch Monitoring Program for the period 1976–1978 for trace metals and artificial radionuclides in bivalves are presented. The substances analysed included Ag, Cu, Zn, Cd, Ni, Pb, ²³⁸Pu, ^239+240Pu and ²⁴¹Am. The analyses of organic substances will be presented elsewhere. The concentrations of these substances in the bivalves may reflect upwelling processes, anthropogenic inputs or natural levels. Off the California coast, mussels show markedly elevated Pu and Cd concentrations in coastal areas adjacent to the most intensive upwelling zones. Elevated levels of Pb, for example, are found in organisms living adjacent to highly urbanized places. The general patterns of distribution repeat themselves year after year at a given site. Thus, it is concluded that annual monitoring activities may not be necessary and that a frequency of sampling of several or so years may be more appropriate to identify pollution problems. Finally, national or regional baselines for metal concentrations in bivalves from unpolluted waters are proposed. National baselines for Pb in the west coast mussels of 1·0 parts 10^?6 and for Ag in east coast mussels of 0·05 parts 10^?6 are suggested.     

Visual classification of very fine-grained sediments: Evaluation through univariate and multivariate statistics

Classifying very fine-grained rocks through fabric elements provides information about depositional environments, but is subject to the biases of visual taxonomy. To evaluate the statistical significance of an empirical classification of very fine-grained rocks, samples from Devonian shales in four cored wells in West Virginia and Virginia were measured for 15 variables: quartz, illite, pyrite and expandable clays determined by X-ray diffraction; total sulfur, organic content, inorganic carbon, matrix density, bulk density, porosity, silt, as well as density, sonic travel time, resistivity, and -ray response measured from well logs. The four lithologic types comprised: (1) sharply banded shale, (2) thinly laminated shale, (3) lenticularly laminated shale, and (4) nonbanded shale. Univariate and multivariate analyses of variance showed that the lithologic classification reflects significant differences for the variables measured, difference that can be detected independently of stratigraphic effects. Little-known statistical methods found useful in this work included: the multivariate analysis of variance with more than one effect, simultaneous plotting of samples and variables on canonical variates, and the use of parametric ANOVA and MANOVA on ranked data.     

CANADIAN ARCTIC METEORITE SEARCH: 1981

The recovery of several thousand meteorite fragments from Antarctica has led to speculation that accumulations may occur on the Earth's other major ice caps. Meteorites falling over the past 80,000 years on the Devon Island ice cap in the Canadian Arctic may be exposed at the surface near the ice cap margin. From the terrestrial meteorite flux, ice movement rates, and fragmentation factors it is calculated that 12,560 samples of 150 g mass are potentially concentrated in a 65 km² zone along the northwest margin. A search of this region on foot and by helicopter in July, 1981, failed to recover any specimens. Although metre-sized gneissic boulders, plucked from the underlying Precambrian basement, were concentrated in this zone it is postulated that the unseasonal 30 cm snow cover on the ice prohibited the recognition of possible meteorite specimens, which may average only 5 cm in diameter.     

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.     

Spatially explicit measures of production of young alewives in Lake Michigan: Linkage between essential fish habitat and recruitment

The identification and protection of essential habitats for early life stages of fishes are necessary to sustain fish stocks. Essential fish habitat for early life stages may be defined as areas where fish densities, growth, survival, or production rates are relatively high. To identify critical habitats for young-of-year (YOY) alewives (Alosa pseud oharengus) in Lake Michigan, we integrated bioenergetics models with GIS (Geographic Information Systems) to generate spatially explicit estimates of potential population production (an index of habitat quality). These estimates were based upon YOY alewife bioenergetic growth rate potential and their salmonine predators’ consumptive demand. We compared estimates of potential population production to YOY alewife yield (an index of habitat importance). Our analysis suggested that during 1994–1995, YOY alewife habitat quality and yield varied widely throughout Lake Michigan. Spatial patterns of alewife yield were not significantly correlated to habitat quality. Various mechanisms (e.g., predator migrations, lake circulation patterns, alternative strategies) may preclude YOY alewives from concentrating in areas of high habitat quality in Lake Michigan.