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Sharp Step (sharp + step)
Selected AbstractsGully processes and gully dynamicsEARTH SURFACE PROCESSES AND LANDFORMS, Issue 14 2009M. J. Kirkby Abstract This synthetic review of gully morphology and genesis focuses on incised semi-permanent gully systems rather than on shallow ephemeral gullies. It examines the conditions for gully formation; a sharp step to initiate a headcut, a sufficiently low effective bedload fraction to evacuate eroded material, and the potential to maintain steep sidewalls, usually dominated by mass movement processes. Gully formation is also favoured by an indurated surface layer which maintains steep sideslopes, often with armouring material from the capping layer, and a sharp headcut which does not diffuse away. Two different approaches towards the areal modelling of gully system development agree in treating the ratio of advective (channel) to diffusive (sideslope) processes as a key determinant of the morphology of a gully system as it evolves. Implications for gully prevention and remediation are briefly discussed. Copyright © 2009 John Wiley & Sons, Ltd. [source] Modification of impact craters in the northern plains of Mars: Implications for Amazonian climate historyMETEORITICS & PLANETARY SCIENCE, Issue 10 2006M. A. Kreslavsky Two of the 130 craters have unusually rough ejecta; they are deep, have steep walls, and are apparently the youngest in the population. Icy mantles filling the local subkilometer-scale topographic lows is the main contribution to ejecta smoothing, which occurs at a time scale on the order of tens of Myr. Wall degradation and crater shallowing generally occur at longer time scales, comparable to the duration of the Amazonian period. Many craters are shallow due to filling of the crater with specific ice-rich material of uncertain origin. We use our collected data to infer the nature of the past climate back through the Amazonian, a period prior to ,10,20 Myr ago, when orbital parameter solutions are chaotic and one must rely on geological data to infer climate conditions. We conclude that moderately high obliquity and wide obliquity variations were probable during the last 40,160 Myr. We tentatively conclude that high obliquity peaks (>40,45°) may have occurred episodically through the last 210,430 Myr. A sharp step in the frequency distribution of wall steepness at 20° may indicate a geologically long period prior to that time where obliquity never exceeded 40,45°. [source] Synthesis of phase-pure SnS particles employing dithiocarbamate organotin(IV) complexes as single source precursors in thermal decomposition experimentsAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 9 2010D. C. Menezes Abstract Preparation of tin(II) sulfide, semiconductor material, has been accomplished by thermal decomposition of easily prepared organotin dithiocarbamate complexes: [Sn{S2CNEt2}2Ph2] (1), [Sn{S2CNEt2}Ph3] (2), [Sn{S2CNEt2}3Ph] (3) and [Sn{S2CN(C4H8)}2Bu2] (4). Phase-pure tin(II) sulfide has been obtained by pyrolysis of these precursors at 350 °C in N2. Thermogravimetric analysis, X-ray powder diffraction, scanning electron microscopy, X-ray electron probe microanalysis and 119Sn Mössbauer spectroscopy revealed that the complexes decompose in a single and sharp step (1 and 2), or in pseudo-single stage (3 and 4), to produce SnS. We have also measured the bandgap energies of the residues using electronic spectroscopy in the solid state and the result relates well to that in the literature for SnS, 1.3 eV. A decomposition mechanism was also proposed for each complex based on electrospray ionization tandem mass spectrometric results. The synthetic method used in this work might be useful for the preparation of pure SnS on a large scale. Copyright © 2010 John Wiley & Sons, Ltd. [source] Mapping of unstressed lattice parameters using pulsed neutron transmission diffractionJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 4 2002Javier Roberto Santisteban Stress measurement by neutron diffraction depends critically on knowledge of the unstressed lattice parameter (a0) of the specimen under study. As a result, measurement of stress profiles in components where a0 is not homogeneous throughout the sample, such as welds or carburized surfaces, can be particularly difficult. An efficient solution to this problem is proposed based on the pulsed neutron transmission diffraction technique. This technique exploits the sharp steps in intensity, the so-called Bragg edges, appearing in the transmitted neutron spectra of polycrystalline materials, such steps being produced by coherent scattering from lattice planes. The position of these Bragg edges as defined by the time-of-flight technique is used to determine precisely local interplanar distances. In this work it is shown that the unstressed lattice parameter of thin specimens subjected to plane stress fields can be defined by recording transmission spectra at different sample inclinations, in complete analogy with the sin2, technique used in X-ray diffraction. Moreover, by using an array of detectors it is possible to produce a radiographic `image' of a0 for plane specimens or thin sections out of three-dimensional ones. The capability of the technique is exemplified by mapping the changes in a0 for a ferritic weld that was used as a round robin sample in an international program for standardization of stress measurements by neutron diffraction. [source] | ||||||||||