Efficient Representation of Laguerre Mosaics with an Application to Microstructure Simulation of Complex Ore

Mathematical Geosciences - Laguerre mosaics have been an important modeling approach in astronomy, physics, crystallography, geology and mathematics for several decades. In materials science, they...     

Contrasting transient and steady-state rivers crossing active normal faults: new field observations from the Central Apennines, Italy

We present detailed data on channel morphology, valley width and grain size for three bedrock rivers crossing active normal faults which differ in their rate, history and spatial distribution of uplift. We evaluate the extent to which downstream changes in unit stream power correlate with footwall uplift, and use this information to identify which of the channels are likely to be undergoing a transient response to tectonics, and hence clarify the key geomorphic features associated with this signal. We demonstrate that rivers responding transiently to fault slip-rate increase are characterised by significant long-profile convexities (over-steepened reaches), a loss of hydraulic scaling, channel aspect ratios which are a strong non-linear function of slope, narrow valley widths, elevated coarse-fraction grain-sizes and reduced downstream variability in channel planform geometry. We are also able to quantify the steady-state configurations of channels, that have adjusted to differing spatial uplift fields. The results challenge the application of steady-state paradigms to transient settings and show that assumptions of power-law width scaling are inappropriate for rivers, that have not reached topographic steady state, whatever exponent is used. We also evaluate the likely evolution of bedrock channels responding transiently to fault acceleration and show that the headwaters are vulnerable to beheading if the rate of over-steepened reach migration is low. We estimate that in this setting the response timescale to eliminate long-profile convexity for these channels is ∼1 Myr, and that typical hydraulic scaling is regained within 3 Myr.     

Floodplain sedimentation rates in an alpine watershed determined by radionuclide techniques

Vertical profiles of the activities of ¹³⁷Cs and ²¹⁰Pb were measured on floodplain sediment cores and upland soil cores along the Soda Butte Creek and the Yellowstone River to determine floodplain sedimentation rates. The position of mine tailings from a 1950 impoundment failure was used as a stratigraphic marker to estimate the sedimentation rates and to make comparisons with rates provided by radionuclide‐based methods. Mass accumulation (sedimentation) rates calculated from the position of the mine tailings ranged from 0·00 to 0·17 g cm^?2 yr^?1 and were in good agreement with sedimentation rates calculated from the inventories of ¹³⁷Cs and ²¹⁰Pb. Sedimentation rates calculated from the position of the ¹³⁷Cs peak generally overestimated the sedimentation rates, probably because of increased downward migration of ¹³⁷Cs caused by the low pH of water moving through the mine tailings or the high permeability of floodplain sediments relative to upland reference soils. This study demonstrates that the ¹³⁷Cs and ²¹⁰Pb inventory methods for determining sedimentation rates can be applied to an alpine floodplain where sedimentation events are episodic and where orographic effects on precipitation generate strong downstream gradients in the delivery of atmospheric radionuclides. Copyright © 2007 John Wiley & Sons, Ltd.     

The response of ozone to solar activity variations: A review

Observational evidence and theoretical predictions of the response of ozone to solar variations are reviewed. Short-term solar proton effects, possible effects of galactic cosmic rays modulated by the Sun, and the effects of 27-day solar rotation and 11-year solar cycle variations are discussed. Solar proton effects on HO _x chemistry in the mesosphere and NO _x chemistry in the stratosphere with resulting catalytic destruction of O₃ help validate present day photochemical models. If there is an 11-year solar cycle variation in global ozone, the large dynamical effects at individual locations and the lack of good global coverage of ground based and in situ measurements can disguise it. Recently, with the global coverage of satellites, it has become possible to accurately determine global mean ozone. It has been found that variations in global mean ozone filtered for seasonal variations are highly correlated with variations of the 10.7 cm solar activity index and that global mean ozone responds rapidly to solar activity index variations. Photochemical models indicate that the observed 3% variations in global mean ozone over the solar cycle can be accounted for by solar UV variations which are not inconsistent with recent solar measurements.Proceedings of the 14th ESLAB Symposium on Physics of Solar Variations, 16–19 September 1980, Scheveningen, The Netherlands.     

Stratigraphy of the Caloris basin,Mercury

The 1300-km-diameter Caloris impact basin is surrounded by well-defined ejecta units that can be recognized from more than 1000 km, radially outward from the basin edge. A formal rock stratigraphic nomenclature is proposed for the Caloris ejecta units, which are collectively called the Caloris Group. Each of the individual formations within the Group are described and compared to similar rock units associated with the lunar Imbrium and Orientale basins. A crater degradation chronology, linked the the Caloris event, is also proposed to assist in stratigraphic correlation on a Mercury-wide basis.     

Six-color observations of the Eclipsing binary AR Cas

Depths and phases of both minima of AR Cas in six colors in 1959 are presented. Analysis leads to a color distribution for the secondary component which corresponds to spectral type A5–A7.