Detection and mapping of mineralized areas in the Cortez-Uinta Belt, Utah-Nevada, using computer-enhanced ERTS imagery

The author has identified the following significant results. Preliminary analysis indicates that mineralogical differences between altered rocks and most unaltered rocks in south-central Nevada cause visible and near infrared spectral reflectance differences, which can be used to discriminate these broad categories of rocks in multispectral images. The most important mineralogical differences are the increased abundance of goethite, hematite, and jarosite, and the presence of alunite, montmorillonite, and kaolinite in the altered rock. The technique to enhance subtle spectral differences combines ratioing of the MSS bands and contrast stretching. The stretched ratio values are used to produce black and white images that depict materials according to spectral reflectance; rationing minimizes the influence of topography and overall albedo on the grouping of spectrally similar materials. Field evaluation of color-ratio composite shows that, excluding alluvial areas, approximately 80 percent of the green and brown color patterns are related to hydrothermal alternation. The remaining 20 percent consists mainly of pink hematitic crystallized tuff, a result of vapor phase crystallization, and of tan and red ferruginous shale and siltstone

Cold galaxies

We use 350 mu angular diameter estimates from Planck to test the idea that some galaxies contain exceptionally cold (10-13 K) dust, since colder dust implies a lower surface brightness radiation field illuminating the dust, and hence a greater physical extent for a given luminosity. The galaxies identified from their spectral energy distributions as containing cold dust do indeed show the expected larger 350 mu diameters. For a few cold dust galaxies where Herschel data are available we are able to use submillimetre maps or surface brightness profiles to locate the cold dust, which as expected generally lies outside the optical galaxy.Comment: 9 pages, 15 figures. Accepted for publication MNRA

The impact of resolution on the adjustment and decadal variability of the Atlantic Meridional Overturning Circulation in a coupled climate model

Variations in the Atlantic Meridional Overturning Circulation (MOC) exert an important influence on climate, particularly on decadal time scales. Simulation of the MOC in coupled climate models is compromised, to a degree that is unknown, by their lack of fidelity in resolving some of the key processes involved. There is an overarching need to increase the resolution and fidelity of climate models, but also to assess how increases in resolution influence the simulation of key phenomena such as the MOC. In this study we investigate the impact of significantly increasing the (ocean and atmosphere) resolution of a coupled climate model on the simulation of MOC variability by comparing high and low resolution versions of the same model. In both versions, decadal variability of the MOC is closely linked to density anomalies that propagate from the Labrador Sea southward along the deep western boundary. We demonstrate that the MOC adjustment proceeds more rapidly in the higher resolution model due the increased speed of western boundary waves. However, the response of the Atlantic Sea Surface Temperatures (SSTs) to MOC variations is relatively robust - in pattern if not in magnitude - across the two resolutions. The MOC also excites a coupled ocean-atmosphere response in the tropical Atlantic in both model versions. In the higher resolution model, but not the lower resolution model, there is evidence of a significant response in the extratropical atmosphere over the North Atlantic 6 years after a maximum in the MOC. In both models there is evidence of a weak negative feedback on deep density anomalies in the Labrador Sea, and hence on the MOC (with a time scale of approximately ten years). Our results highlight the need for further work to understand the decadal variability of the MOC and its simulation in climate models

Thermodynamics and phase behavior of the lamellar Zwanzig model

Binary mixtures of lamellar colloids represented by hard platelets are studied within a generalization of the Zwanzig model for rods, whereby the square cuboids can take only three orientations along the $x$, $y$ or $z$ axes. The free energy is calculated within Rosenfeld's ''Fundamental Measure Theory'' (FMT) adapted to the present model. In the one-component limit, the model exhibits the expected isotropic to nematic phase transition, which narrows as the aspect ratio $\zeta=L/D$ ($D$ is the width and $L$ the thickness of the platelets) increases. In the binary case the competition between nematic ordering and depletion-induced segregation leads to rich phase behaviour.Comment: 9 pages, 6 figure

Suramin inhibits the early effects of PLA(2) neurotoxins at mouse neuromuscular junctions: a twitch tension study

Several phospholipase A(2) (PLA(2)) neurotoxins from snake venoms can affect acetylcholine release at the neuromuscular junction. In isolated nerve-muscle preparations three distinct phases have been described for this phenomenon: An initial transient decrease in twitch tension; a second facilitatory phase during which twitch height is greater than control twitch height; and the last phase which causes a reduction in twitch height that finally results in paralysis. Suramin has been reported to inhibit the toxic effects of β-bungarotoxin and another PLA(2) neurotoxin, crotoxin in vitro and in vivo. We have further examined the effects of suramin on the three phases of the effects of the presynaptic PLA(2) neurotoxins β-bungarotoxin, taipoxin and ammodytoxin on mouse phrenic nerve-hemidiaphragm preparations. When preparations were pre-treated with suramin (0.3mM), the early biphasic effects (depression followed by facilitation) were abolished, and the time taken for final blockade induced by β-bungarotoxin, taipoxin and ammodytoxin A was significantly prolonged. In contrast, suramin did not significantly affect the facilitation induced by the potassium channel blocking toxin dendrotoxin I when applied under the same conditions. In addition, application of 0.3mM suramin did not prevent the facilitatory actions of 3,4-diaminopyridine (3,4-DAP) and tetraethylammonium chloride (TEA). Overall, the mechanism whereby suramin reduces the effects of PLA(2) neurotoxins remains elusive. Since suramin reduces both enzyme-dependent and enzyme-independent effects of the toxins, suramin is not acting as a simple enzyme inhibitor. Furthermore, the observation that suramin does not affect actions of standard K(+) channel blockers suggests that suramin does not stabilise nerve terminals

Iron-absorption band analysis for the discrimination of iron-rich zones

There are no author-identified significant results in this report

Nonexistence of large nuclei in the liquid drop model

We give a simplified proof of the nonexistence of large nuclei in the liquid drop model and provide an explicit bound. Our bound is within a factor of 2.3 of the conjectured value and seems to be the first quantitative result.Comment: 3 pages; new version with improved bound and simplified proo

Structural geologic analysis of Nevada using ERTS-1 images: A preliminary report

Structural analysis of Nevada using ERTS-1 images showns several previously unrecognized lineaments which may be the surface manifestations of major fault or fracture zones. Principle trends are NE, NW, NNE-NNW, and ENE. Two lineament zones, the Walker Lane and Midas Trench lineament system, transect the predominantly NNE-NNW trending mountain ranges for more than 500 km. 50 circular features have been delineated. Comparison with known Tertiary volcanic centers and reference to geologic maps suggest 8 new centers. Preferred distribution of mines and Tertiary volcanic centers along some of the major lineament suggests a genetic relationship. The intersection of three previously unmapped lineaments in northwestern Nevada is the location of a highly productive metallogenic district. In the Walker Lane, ENE-trending lineament appear to be related to the occurrence of productive ore deposits

Shocks, cooling and the origin of star formation rates in spiral galaxies

Understanding star formation is problematic as it originates in the large scale dynamics of a galaxy but occurs on the small scale of an individual star forming event. This paper presents the first numerical simulations to resolve the star formation process on sub-parsec scales, whilst also following the dynamics of the interstellar medium (ISM) on galactic scales. In these models, the warm low density ISM gas flows into the spiral arms where orbit crowding produces the shock formation of dense clouds, held together temporarily by their external pressure. Cooling allows the gas to be compressed to sufficiently high densities that local regions collapse under their own gravity and form stars. The star formation rates follow a Schmidt-Kennicutt \Sigma_{SFR} ~ \Sigma_{gas}^{1.4} type relation with the local surface density of gas while following a linear relation with the cold and dense gas. Cooling is the primary driver of star formation and the star formation rates as it determines the amount of cold gas available for gravitational collapse. The star formation rates found in the simulations are offset to higher values relative to the extragalactic values, implying a constant reduction, such as from feedback or magnetic fields, is likely to be required. Intriguingly, it appears that a spiral or other convergent shock and the accompanying thermal instability can explain how star formation is triggered, generate the physical conditions of molecular clouds and explain why star formation rates are tightly correlated to the gas properties of galaxies.Comment: 13 pages, 12 figures. MNRAS in pres

The Global Star Formation Rate from the 1.4 GHz Luminosity Function

The decimetric luminosity of many galaxies appears to be dominated by synchrotron emission excited by supernova explosions. Simple models suggest that the luminosity is directly proportional to the rate of supernova explosions of massive stars averaged over the past 30 Myr. The proportionality may be used together with models of the evolving 1.4 GHz luminosity function to estimate the global star formation rate density in the era z < 1. The local value is estimated to be 0.026 solar masses per year per cubic megaparsec, some 50% larger than the value inferred from the Halpha luminosity density. The value at z ~ 1 is found to be 0.30 solar masses per year per cubic megaparsec. The 10-fold increase in star formation rate density is consistent with the increase inferred from mm-wave, far-infrared, ultra-violet and Halpha observations.Comment: 10 pages, 2 figures, Astrophysical Journal Letters (in press); new PS version has improved figure placemen