Reconstruction of a multi-vent kimberlite eruption from deposit and host rock characteristics: Jericho kimberlite, Nunavut, Canada

The Jericho kimberlite (173.1. ±. 1.3. Ma) is a small (~. 130. ×. 70. m), multi-vent system that preserves products from deep (>. 1. km?) portions of kimberlite vents. Pit mapping, drill core examination, petrographic study, image analysis of olivine crystals (grain size distributions and shape studies), and compositional and mineralogical studies, are used to reconstruct processes from near-surface magma ascent to kimberlite emplacement and alteration. The Jericho kimberlite formed by multiple eruptions through an Archean granodiorite batholith that was overlain by mid-Devonian limestones ~. 1. km in thickness. Kimberlite magma ascended through granodiorite basement by dyke propagation but ascended through limestone, at least in part, by locally brecciating the host rocks. After the first explosive breakthrough to surface, vent deepening and widening occurred by the erosive forces of the waxing phase of the eruption, by gravitationally induced failures as portions of the vent margins slid into the vent and, in the deeper portions of the vent (>. 1. km), by scaling, as thin slabs burst from the walls into the vent. At currently exposed levels, coherent kimberlite (CK) dykes (<. 40. cm thick) are found to the north and south of the vent complex and represent the earliest preserved in-situ products of Jericho magmatism. Timing of CK emplacement on the eastern side of the vent complex is unclear; some thick CK (15-20. m) may have been emplaced after the central vent was formed. Explosive eruptive products are preserved in four partially overlapping vents that are roughly aligned along strike with the coherent kimberlite dyke. The volcaniclastic kimberlite (VK) facies are massive and poorly sorted, with matrix- to clast-supported textures. The VK facies fragmented by dry, volatile-driven processes and were emplaced by eruption column collapse back into the volcanic vents. The first explosive products, poorly preserved because of partial destruction by later eruptions, are found in the central-east vent and were formed by eruption column collapse after the vent was largely cleared of country rock debris. The next active vent was either the north or south vent. Collapse of the eruption column, linked to a vent widening episode, resulted in coeval avalanching of pipe margin walls into the north vent, forming interstratified lenses of country rock-rich boulder breccias in finer-grained volcaniclastic kimberlite. South vent kimberlite has similar characteristics to kimberlite of the north vent and likely formed by similar processes. The final eruptive phase formed olivine-rich and moderately sorted deposits of the central vent. Better sorting is attributed to recycling of kimberlite debris by multiple eruptions through the unconsolidated volcaniclastic pile and associated collapse events. Post-emplacement alteration varies in intensity, but in all cases, has overprinted the primary groundmass and matrix, in CK and VK, respectively. Erosion has since removed all limestone cover.

Aerodynamics of delta wings with flaps at hypersonic speeds

Control surface effectiveness is an important parameter for any aeroplane. For a hypersonic aircraft, though the power required to operate the flaps is determined by low speed flying conditions, it is imperative to know the effect of flaps at hypersonic speeds. Hence, studies have been done on this topic by aerodynamicists for over 40 years. In spite of this, only a limited data is available in the literature on this subject. This paper discusses the experimental study of the effect of sweep on the aerodynamic characteristics of thin slab delta wings with flaps at hypersonic speeds. For the purpose of this investigation, a novel special thin six-component balance, which has a thickness of 4mm and can be housed inside wings with 8mm thickness, has been designed. The wings had a sweep of 76degrees, 70degrees and 65degrees, t/c of 0.053 and flaps with 12% of wing area and 12% of wing chord. Testing were done at Mach 8.2, Re number of 2.13 x 10(6) (based on chord), from alpha = -12degrees to 12degrees and flap angle of 20degrees, 30degrees and 40degrees. Separation lengths, measured from Schlieren pictures, clearly show that there is 'no appreciable' effect of sweep on them. Also, using a simple local flow field calculation, the separation has been identified to be transitional in nature. These features of separation reflect in the force data. Because of the small separation length, the flaps (inspite of their small size) were very effective in generating additional C-N, C-M and C-l, which increased with increase in flap angle. In general, the C-N, C-M and X-CP were unaffected by sweep for symmetric flap deflection at positive incidences and asymmetric flap case, For symmetric flap case at negative incidences, only C-N was not influenced by the sweep but C-M decreased and X-CP moved upstream as the sweep is decreased, The wing with lower sweep produces higher CA and lower (L/D)(max) for both symmetric and asymmetric flaps. The rolling moment and adverse yaw increased with decrease in sweep for asymmetric flap deflection. Newtonian theory is shown to be incapable of predicting the effect of sweep on C-l, C-n and on the incremental values of C-N, C-M and C-A. In conclusion, it can be said that a small flap is generally adequate for hypersonic aeroplanes provided they operate at altitudes where transitional and turbulent separation can be expected to occur. This would make the flaps effective and thus enable ample control authority.

Wallner lines, crack velocity and mechanisms of crack nucleation and growth in a brittle bulk metallic glass

Mode I fracture experiments were conducted on brittle bulk metallic glass (BMG) samples and the fracture surface features were analyzed in detail to understand the underlying physical processes. Wollner lines, which result from the interaction between the propagating crack front and shear waves emanating from a secondary source, were observed on the fracture surface and geometric analysis of them indicates that the maximum crack velocity is similar to 800 m s(-1), which corresponds to similar to 0.32 times the shear wave speed. Fractography reveals that the sharp crack nucleation at the notch tip occurs at the mid-section of the specimens with the observation of flat and half-penny-shaped cracks. On this basis, we conclude that the crack initiation in brittle BMGs is stress-controlled and occurs through hydrostatic stress-assisted cavity nucleation ahead of the notch tip. High magnification scanning electron and atomic force microscopies of the dynamic crack growth regions reveal highly organized, nanoscale periodic patterns with a spacing of similar to 79 nm. Juxtaposition of the crack velocity with this spacing suggests that the crack takes similar to 10(-10) s for peak-to-peak propagation. This, and the estimated adiabatic temperature rise ahead of the propagating crack tip that suggests local softening, is utilized to critically discuss possible causes for the nanocorrugation formation. Taylor's fluid meniscus instability is unequivocally ruled out. Then, two other possible mechanisms, viz. (a) crack tip blunting and resharpening through nanovoid nucleation and growth ahead of the crack tip and eventual coalescence, and (b) dynamic oscillation of the crack in a thin slab of softened zone ahead of the crack-tip, are critically discussed. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Experimental observation of negative lateral displacements of microwave beams transmitting through dielectric slabs

It was theoretically predicted that when a beam of light travels through a thin slab of optically denser medium in the air, the emerging beam from the slab will suffer a lateral displacement that is different from the prediction of geometrical optics, that is, the Snell's law of refraction and can be zero and negative as well as positive. These phenomena have been directly observed in microwave experiments in which large angles of incidence are chosen for the purpose of obtaining negative lateral displacements. (C) 2005 Elsevier B.V. All rights reserved.

Molekulardynamik-Simulationen zu Oberflächeneigenschaften von Siliziumdioxid-Schmelzen

Molekulardynamik-Simulationen zu OberflächeneigenschaftenvonSiliziumdioxid-Schmelzen In der vorliegenden Arbeit werdenMolekulardynamik-Computersimulationenzur Untersuchung der statischen und dynamischenOberflächeneigenschafteneiner Siliziumdioxid (SiO$_2$)-Schmelze durchgeführt.Als Modellpotential verwenden wirein in der Literatur als BKS-Potential bezeichnetesPaarpotential.Wir betrachten in dieser Arbeit zwei Systemgeometrien: zumeinenSysteme aus 432, 1536 und 4608 Atomen ohne periodischeRandbedingungen(Tropfen), zum anderen ein System aus 1152 Atomen mitperiodischen Randbedingungen in zwei Richtungen (dünnerFilm).Für beide Geometrien finden wir im Inneren der Systemekonstante Dichten.Direktan der Oberfläche halten sich ausschließlich Sauerstoffatomeauf.Die Strukturan der Oberfläche erscheint weniger ausgeprägt mit mehrDefekten, als im Inneren des Systems.Es erweist sich,daß viele Eigenschaften statischer Größen, die wir an derOberfläche im Vergleich zum Inneren finden, aufdas Vorhandensein von Zweierringen zurückzuführen sind.Bei der Betrachtung der dynamischen Größen finden wir eineerhöhteBeweglichkeit der Atome an der Oberfläche gegenüber demSysteminneren.

Estimation of concentration-dependent diffusion coefficient in drying process from the space-averaged concentration versus time with experimental data

The estimation of a concentration-dependent diffusion coefficient in a drying process is known as an inverse coefficient problem. The solution is sought wherein the space-average concentration is known as function of time (mass loss monitoring). The problem is stated as the minimization of a functional and gradient-based algorithms are used to solve it. Many numerical and experimental examples that demonstrate the effectiveness of the proposed approach are presented. Thin slab drying was carried out in an isothermal drying chamber built in our laboratory. The diffusion coefficients of fructose obtained with the present method are compared with existing literature results.

Single dipole mode photonic crystal laser on InGaAsP/InP QW waveguide slab - art. no. 698436

Single point defect microcavity possesses only the degenerate dipole modes under certain photonic crystal structure parameters. By deforming lattice structure, the degeneracy of the dipole modes has been broken. Theoretical simulation shows the large splitting of 65nm between the splitted x-mode and y-mode, approximate to the luminescent gain spectrum, which benefits for the single mode lasing. Experimentally the single dipole mode lasing, y-mode, is achieved in the deformed microcavity.

On thin ice: surface order and disorder during pre-melting

The effect of temperature on the structure of the ice Ih (0001) surface is considered through a series of molecular dynamics simulations on an ice slab. At relatively low temperatures (200K) a small fraction of surface self-interstitials (i.e. admolecules) appear that are formed exclusively from molecules leaving the outermost bilayer. At higher temperatures (ca. 250 K), vacancies start to appear in the inner part of the outermost bilayer exposing the underlying bilayer and providing sites with a high concentration of the dangling hydrogen bonds. Around 250-260 K aggregates of molecules formed on top of the outermost bilayer from self-interstitials become more mobile and have diffusivities approaching that of liquid water. At similar to 270-280 K the inner bilayer of one surface noticeably destructures and it appears that at above 285 K both surfaces are melting. The observed disparity in the onset of melting between the two sides of the slab is rationalised by considering the relationship between surface energy and the spatial distribution of protons at the surface; thermodynamic stability is conferred on the surface by maximising separations between dangling protons at the crystal exterior. Local hotspots associated with a high dangling proton density are suggested to be susceptible to pre-melting and may be more efficient at trapping species at the external surface than regions with low concentrations of protons thus potentially helping ice particles to catalyse reactions. A preliminary conclusion of this work is that only about 10-20 K below the melting temperature of the particular water potential employed is major disruption of the crystalline lattice noted which could be interpreted as being "liquid", the thickness of this film being about a nanometre.

Investigation of RuO2/Ta2O5 thin film evolution by thermogravimetry combined with mass spectrometry

The thermal evolution process of RuO2–Ta2O5/Ti coatings with varying noble metal content has been investigated under in situ conditions by thermogravimetry combined with mass spectrometry. The gel-like films prepared from alcoholic solutions of the precursor salts (RuCl3·3H2O, TaCl5) onto titanium metal support were heated in an atmosphere containing 20% O2 and 80% Ar up to 600 °C. The evolution of the mixed oxide coatings was followed by the mass spectrometric ion intensity curves. The cracking of retained solvent and the combustion of organic surface species formed were also followed by the mass spectrometric curves. The formation of carbonyl- and carboxylate-type surface species connected to the noble metal was identified by Fourier transform infrared emission spectroscopy. These secondary processes–catalyzed by the noble metal–may play an important role in the development of surface morphology and electrochemical properties. The evolution of the two oxide phases does not take place independently, and the effect of the noble metal as a combustion catalyst was proved.