A small contribution to the giant problem

We present a simple analytic model of a composite polytropic star, which exhibits a limiting Scho¨nberg–Chandrasekhar core mass fraction strongly analogous to the classic numerical result for an isothermal core, a radiative envelope and a μ-jump (i.e. a molecular weight jump) at the interface. Our model consists of an n _c = 5 core, an n _e = 1 envelope and a μ-jump by a factor ≥ 3; the core mass fraction cannot exceed 2/π. We use the classic U V plane to show that composite models will exhibit a Scho¨nberg–Chandrasekhar limit only if the core is 'soft', i.e. has n _c ≥ 5, and the envelope is 'hard', i.e. has n _e < 5; in the critical case ( n _c = 5), the limit only exists if the μ-jump is sufficiently large, ≥ 6/( n _e + 1).     

Comparison of Late Pleistocene and Modern Glacier Extents in Central Nepal Based on Digital Elevation Data and Satellite Imagery

Late Pleistocene and modern ice extents in central Nepal are compared to estimate equilibrium line altitude (ELA) depressions. New techniques are used for determining the former extent of glaciers based on quantitative, objective geomorphic analyses of a 90-m resolution digital elevation model (DEM). For every link of the drainage network, valley form is classified as glacial or fluvial based on cross-valley shape and slope statistics. Down-valley transitions from glacial to fluvial form indicate the former limits of glaciation in each valley. Landsat Multispectral Scanner imagery for the same region is used to map current glacier extents. For both full-glacial and modern cases, ELAs are computed from the glacier limits using the DEM and a toe-to-headwall altitude ratio of 0.5. Computed ELA depressions range from 100–900 m with a modal value of 650 m and a mean of 500 m, values consistent with previously published estimates for the central Himalaya but markedly smaller than estimates for many other regions. We suggest that this reflects reduced precipitation, rather than a small temperature depression, consistent with other evidence for a weaker monsoon under full-glacial conditions.     

Nick Rast and the recognition of the Avalonian Arc

Recognition of the eastern (Avalonian) margin of the northern Appalachian orogen as a Late Precambrian microcontinental arc terrane, rather than the opposing passive margin of the Proto-Atlantic (Iapetus) Ocean to that of eastern Laurentia, constituted a fundamental advance in Appalachian geology that profoundly influenced subsequent models for the orogen's plate tectonic evolution. This advance was first clearly articulated by Nick Rast and his students in 1976, who, by correlating rocks of the Avalon Platform with those of the British Midlands, established the Avalonian volcanic belt as a Japan-like microcontinent. Contrary to contemporary views of the Avalon Platform, which favored an extensional, Basin and Range-like setting for its volcanism, Rast argued on the basis of this correlation that the association of Avalonian volcanism with compressional orogeny, widespread calc-alkaline plutonism and, in Angelsey, with blueschists and ophiolitic rocks, indicated a convergent plate margin setting. Rast further proposed that the Avalonian volcanic belt was ensialic, and was bordered to the northwest and southeast by Precambrian oceanic domains. Contemporary reconstructions of the Avalonian and Cadomian belts as fragments of a Cordilleran-like accretionary orogen that developed along an active margin of Neoproterozoic Gondwana owe their origin to these early ideas and, while far removed from the tectonic model that Rast envisaged, are a direct heritage of his recognition of the Avalonian volcanic belt as a microcontinental arc terrane.     

On the relationship of radar backscatter to wind speed and fetch

The physics of the interaction of electromagnetic waves with the ocean surface has been an active area of research for a number of years. We present here the results of satellite and aircraft experiments to investigate the ability of active microwave radars to infer surface wind speeds remotely. Data obtained from the recent National Aeronautics and Space Administration (NASA) Skylab experiment are compared with surface wind speeds measured by low-flying aircraft and ships-of-opportunity and found to give useful estimates of the oceanic wind field. We also investigate the influence of varying wave height on radar measurements of wind speed by measuring the backscattering cross-section for constant wind speed but variable wave conditions. We conclude that this effect is of little importance.     

Jet drop enrichment of bacteria,virus, and dissolved organic material

Four parameters that control the enrichment of bacteria in jet drops are bubble scavenging, drop size, drop position in the jet set, and the type of bacteria. Without the scavenging of bacteria as a bubble rises through the water it is doubtful that the observed enrichment factors, EF, greater than 1000 could be obtained. There is a maximum in EF as a function of top jet drop size, and the EF decreases from the top to the bottom drop of the jet set. The efficiency by which bubbles scavenge bacteria varies with species. Presumably these parameters apply in some degree to the EF of virus in jet drops. Dissolved organic material in natural waters can adsorb to bubbles and contribute to a large EF in jet drops, but there is a feedback mechanism whereby changes in bubble surface free energy modify the jet drop-size distribution. However, there is reason to believe this will not significantly influence the jet drop-size distribution produced by bubbles in the sea.     

The dynamics of offshore gravity platforms: Some insights afforded by a two degree of freedom model

This paper presents some findings of an investigation into the dynamic behaviour of offshore gravity platforms excited by waves. Results obtained from a finite element model are presented in the form of dynamic magnification factor curves for two structures typical of current concrete platform designs. In order to facilitate interpretation of these results a simple two degree of freedom model is developed and the equivalent results presented. These are found to be very similar to those obtained from the more detailed idealization, and it is therefore concluded that the principal mechanisms involved in the dynamic behaviour of offshore gravity structures are adequately represented in the simple model. Several useful insights into this behaviour are then achieved by closer examination of the two degree of freedom configuration.     

Chemical balance of the Earth's crust

The chemical composition and lithologic proportions of average sedimentary and igneous rocks are analyzed by a linear least squares regression. The best set of internally consistent data for sediments in geosynclines, continental platforms, deep ocean basin and the average igneous and sedimentary rock are shown below. These results are based on published estimates of the chemical composition of igneous and sedimentary rocks and the relative volume of sediments on the continents and in the deep ocean basins.

$\text{SiO}{}_2\text{A1}{}_2\text{O}{}_3\text{Fe(total)}\text{MgO}\text{CaO}\text{Na}{}_2\text{O}\text{K}{}_2\text{O}\text{CO}{}_2\text{Geosynclines}\text{55.2}\text{12.0}\text{3.6}\text{3.2}\text{8.3}\text{1.0}\text{2.4}\text{8.6}\text{Platforms}\text{49.5}\text{10.7}\text{3.2}\text{3.3}\text{12.3}\text{0.9}\text{2.2}\text{10.8}\text{Av. sed.}\text{55.9}\text{13.8}\text{4.4}\text{3.6}\text{5.8}\text{1.2}\text{2.6}\text{5.2}\text{Av. ig.}\text{59.0}\text{15.0}\text{5.0}\text{3.6}\text{7.0}\text{3.4}\text{3.2}$

The lithologic proportions are: geosyncline—24% sandstone, 58% shale, and 16% carbonate; platform—23% sandstone, 49% shale and 26% carbonate; average sedimentary rock—13% sandstone, 33% shale, 12% carbonate, and 41% pelagic; average igneous rock is approximately 2/3 granodiorite and 1/3 tholeiite. These data indicate a chemical balance of major elements in the Earth's upper crust during the last 1.5 b.y.     

Hard Burst Emission from the Soft Gamma Repeater SGR 1900+14

We present evidence for burst emission from SGR 1900+14 with a power-law high-energy spectrum extending beyond 500 keV. Unlike previous detections of high-energy photons during bursts from soft gamma repeaters (SGRs), these emissions are not associated with extraordinarily bright flares. Not only is the emission hard, but the spectra are better fitted by D. Band's gamma-ray burst (GRB) function rather than by the traditional optically thin thermal bremsstrahlung model. We find that the spectral evolution within these hard events obeys a hardness/intensity anticorrelation. Temporally, these events are distinct from typical SGR burst emissions in that they are longer ( approximately 1 s) and have relatively smooth profiles. Despite a difference in peak luminosity of greater, similar1011 between these bursts from SGR 1900+14 and cosmological GRBs, there are striking temporal and spectral similarities between the two kinds of bursts, aside from spectral evolution. We outline an interpretation of these events in the context of the magnetar model.     

Geology of Santa Fe island: The oldest galapagos volcano

Santa Fe Island was a volcanic center when it emerged 3.9 ± 0.6 m.y. ago. Later upfaulting of a horst along the central axis of the island dominates its present morphology. Santa Fe is made up of evolved transitional lavas that are not related by fractional crystallization alone. Source heterogeneties, differing degrees of melting, or open-system magma chambers may explain the observed trace element variations.Santa Fe, Baltra, and Española make up a geologic subprovince in the central Galapagos: they are older than the other islands, and their lavas are compositionally similar. At the time of their emergence, the three islands were in a tectonic setting similar to that of the young western and central Galapagos Island.     

The life and times of Big Bertha: lunar breccia 14321

The lithic units of polymict breccia 14321 (Big Bertha) have been grouped according to composition, texture, degree of metamorphism, and additional criteria based on a systematic study of the interrelationships of all clast-matrix pairs. From this information it has been possible to reconstruct the assembly and metamorphic history of this breccia. The earliest formed fragmental component of 14321 (microbreccia-1) is dominated by KREEP-rich norite, extruded and subsequently brecciated and lithified in an ejecta blanket at approximately 1000°C in the general region of Mare Imbrium after the Serenitatis impact but prior to the Imbrium impact. This early microbreccia component and lesser amounts of mare-type basalt, microgranite, rhyolite glass, anorthosite and olivine microbreccia were assembled at the Apollo 14 site as part of the Fra Mauro ejecta blanket from the Imbrium impact. The resulting microbreccia-3 incorporates all the lithic types above and accretionary lapilli structures (microbreccia-2) in a dark matrix annealed at approximately 700°C. A later impact on the Fra Mauro excavated and mutually abraded microbreccia-3 and a local, 14321-type, basalt which were assembled into polymict breccia 14321. Final placement of 14321 at its sampling location was accomplished during the minor Cone Crater impact event.