Search results for "Part"
showing 10 items of 22361 documents
Strain rate dependence for evolution of steady state grain sizes: Insights from high-strain experiments on ice
2019
Abstract Understanding of the microstructural evolution and equilibrium grain size development during steady state tertiary flow is essential in order to improve our knowledge of ice and rock deformation. This contribution presents results from in situ transmitted light deformation experiments of natural glacier ice, with the development of the microstructure in a tertiary flow regime. We conducted one relative slower ( 1 × 10 − 6 1/s) and two relative faster-strain rate ( 2 × 10 − 6 1/s) pure shear experiments at −10 °C, up to a shortening of ∼57%. Microstructure development was followed by time-lapse observations, and two new microstructure-based indicators, the ‘seeding rate’ and the ‘mi…
New P-T-X conditions for the formation of gem tsavorite garnet in the Voi area (southwestern Kenya)
2018
International audience; Tsavorite nodules-bearing deposits from southwestern Kenya are located in the Kurase Group, a metasedimentary unit of the Neoproterozoic Metamorphic Mozambique Belt. This unit is composed of graphitic paragneisses intercalated with metacarbonates and metaevaporites, surrounded by migmatites. The rocks underwent high grade metamorphism at 615-600 Ma. The main goal of this work is to link tsavorite formation to the metamorphic evolution of the Kurase Group. The new thermobarometric data indicate widespread granulite facies conditions at 800 +/- 50 degrees C and 10 +/- 1 kbar, with no significant difference between the tsavorite-bearing metasediments and the surrounding…
High-grade metamorphism and partial melting in Archean composite grey gneiss complexes
2016
Much of the exposed Archaean crust is composed of composite gneiss which includes a large proportion of intermediate to tonalitic material. These gneiss terrains were typically metamorphosed to amphibolite to granulite facies conditions, with evidence for substantial partial melting at higher grade. Recently published activity–composition (a-x) models for partial melting of metabasic to intermediate compositions allows calculation of the stable metamorphic minerals, melt production and melt composition in such rocks for the first time. Calculated P–T pseudosections are presented for six bulk rock compositions taken from the literature, comprising two metabasic compositions, two intermediate…
Ash-plume dynamics and eruption source parameters by infrasound and thermal imagery: The 2010 Eyjafjallajökull eruption
2013
During operational ash-cloud forecasting, prediction of ash concentration and total erupted mass directly depends on the determination of mass eruption rate (MER), which is typically inferred from plume height. Uncertainties for plume heights are large, especially for bent-over plumes in which the ascent dynamics are strongly affected by the surrounding wind field. Here we show how uncertainties can be reduced if MER is derived directly from geophysical observations of source dynamics. The combination of infrasound measurements and thermal camera imagery allows for the infrasonic type of source to be constrained (a dipole in this case) and for the plume exit velocity to be calculated (54–14…
On the Dependence of Cirrus Parametrizations on the Cloud Origin
2019
<p>Particle size distributions (PSDs) for cirrus clouds are important for both climate models as well as many remote sensing retrieval methods. Therefore, PSD parametrizations are required. This study presents parametrizations of Arctic cirrus PSDs. The dataset used for this purpose originates from balloon-borne measurements carried out during winter above Kiruna (Sweden), i.e. north of the Arctic circle. The observations are sorted into two types of cirrus cloud origin, either in-situ or liquid. The cloud origin describes the formation pathway of the ice particles. At temperatures below −38 °C, ice particles form in-situ from solution or ice nuclea…
Long-term stability of alpha particle damage in natural zircon
2005
Abstract We report the first discovery of radiation damage haloes generated by alpha particles in zircon. Proterozoic zircon crystals from a potassium-rich leucogranite from the Adirondack Mountains, New York State, have interior regions that are generally low in actinide elements (UO 2 + ThO 2 ≤ 0.02 wt.%) but show a remarkable pattern of heterogeneous metamictisation. The degree of radiation damage in these regions is not uniformly low, as would be expected if it corresponded to the observed actinide distribution patterns and age of the crystals. Rather, radiation damage is significantly increased in the outermost micro-areas of the low-actinide regions. The additional radiation damage …
Ray optics for absorbing particles with application to ice crystals at near-infrared wavelengths
2018
Abstract Light scattering by particles large compared to the wavelength of incident light is traditionally solved using ray optics which considers absorption inside the particle approximately, along the ray paths. To study the effects rising from this simplification, we have updated the ray-optics code SIRIS to take into account the propagation of light as inhomogeneous plane waves inside an absorbing particle. We investigate the impact of this correction on traditional ray-optics computations in the example case of light scattering by ice crystals through the extended near-infrared (NIR) wavelength regime. In this spectral range, ice changes from nearly transparent to opaque, and therefore…
Activity-composition relations for the calculation of partial melting equilibria in metabasic rocks
2020
A set of thermodynamic models is presented that, for the first time, allows partial melting equilibria to be calculated for metabasic rocks. The models consist of new activity–composition relations combined with end-member thermodynamic properties from the Holland & Powell dataset, version 6. They allow for forward modelling in the system Na (Formula presented.) O–CaO–K (Formula presented.) O–FeO–MgO–Al (Formula presented.) O (Formula presented.) –SiO (Formula presented.) –H (Formula presented.) O–TiO (Formula presented.) –Fe (Formula presented.) O (Formula presented.). In particular, new activity–composition relations are presented for silicate melt of broadly trondhjemitic–tonalitic compo…
A Search for IceCube Events in the Direction of ANITA Neutrino Candidates
2020
During the first three flights of the Antarctic Impulsive Transient Antenna (ANITA) experiment, the collaboration detected several neutrino candidates. Two of these candidate events were consistent with an ultra-high-energy up-going air shower and compatible with a tau neutrino interpretation. A third neutrino candidate event was detected in a search for Askaryan radiation in the Antarctic ice, although it is also consistent with the background expectation. The inferred emergence angle of the first two events is in tension with IceCube and ANITA limits on isotropic cosmogenic neutrino fluxes. Here, we test the hypothesis that these events are astrophysical in origin, possibly caused by a po…
Reactive oxygen species formed in aqueous mixtures of secondary organic aerosols and mineral dust influencing cloud chemistry and public health in th…
2017
Mineral dust and secondary organic aerosols (SOA) account for a major fraction of atmospheric particulate matter, affecting climate, air quality and public health. How mineral dust interacts with SOA to influence cloud chemistry and public health, however, is not well understood. Here, we investigated the formation of reactive oxygen species (ROS), which are key species of atmospheric and physiological chemistry, in aqueous mixtures of SOA and mineral dust by applying electron paramagnetic resonance (EPR) spectrometry in combination with a spin-trapping technique, liquid chromatography-tandem mass spectrometry (LC-MS/MS), and a kinetic model. We found that substantial amounts of ROS includi…