Shock Metamorphism in Impact Melt Rocks from the Gow Lake Impact Structure, Saskatchewan, Canada

Meteorite impact craters are the dominant surface feature on most terrestrial planetary bodies [1] and are gathering increased interest with the continued exploration of the Solar System. It is worth, then, taking a fresh look at impact craters on Earth, in particular those which have not yet been studied in great detail, like Gow Lake, in order to see if new techniques will shed light on some of the remaining questions about them

Oxidation of austenitic and duplex stainless steels during primary processing

During manufacturing, stainless steels will experience high temperatures at many steps: continuous casting, reheat, rolling and annealing. After continuous casting, it is usual for the ascast metal to cool to ambient temperatures. In order to achieve successful hot forming, the metal must then be reheated to a suitable temperature. This process is called "reheat", and commonly takes place in large, propane-fired walking beam furnaces at temperatures in excess of 1200°C for times of 2 or more hours. During reheat, a thick oxide scale will form which, if left in place during cold working, may cause damage to the surface of the final cold rolled product. As a result, manufacturers generally apply a mechanical descaling procedure immediately prior to rolling. In order to study the effect of reheat conditions on the oxide scale formation, austenitic grades (Types 316L and 304) and duplex grades (Types S32101 and S32205) were oxidised. The temperatures used ranged from 700°C through to 1300°C for times up to, and including, 5 hours. The results of the heat treatments were investigated using a range of analytical techniques including: scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy and site specific cross-section preparation using focused ion beam for both SEM investigation and transmission electron microscopy analysis. The use of these techniques has provided a thorough description of oxides that are expected to form at a variety of temperatures and conditions. On austenitic grades a number of sub-surface oxide structures form, such as dendritic internal oxide particles and sub-surface oxide layering, which may pose great challenges to the mechanical descaling processes. External oxidation has not been neglected in this study and complex chemical and phase distributions within external oxide scales have been characterised. The presence of an as-cast oxide scale during reheat does not have a substantial effect on the reheat oxide formed, however, the as-cast microstructure may contribute to the formation of subsurface oxide banding. Duplex stainless steels produce oxides which are highly dependant on the phase distribution and surface finish of the substrate. Large scale oxide nodules have been found to form only on the austenite with an apparently protective thinner oxide present on the ferrite. The formation of these nodules has been studied from the initial stages of oxidation by the use of environmental SEM and site-specific preparation of important features to reveal that nodules form where the thin, protective chromium rich layer chemically fails during oxidation enabling local breakaway regions to form

Experimental Impacts into Feldspar Phenocrysts

Meteorite impact craters are the dominant surface feature on most terrestrial planetary bodies [1]. The extreme temperatures and pressures generated by hypervelocity impact events produce a variety of microscopic shock metamorphic effects in minerals, as well as non-exclusive shock-related features such as pervasive fracturing and brecciation.<p></p> Studies of shock effects in feldspar group minerals have been limited due to the the comparatively rapid rate at which feldspars weather, and the complexity of their microtextures which renders them difficult to study using conventional optical techniques. However, feldspars are becoming increasingly investigated for use as shock barometers due to their importance in planetary studies and meteoritics, where rocks often contain little or no quartz [e.g., 2]. This provides the motivation to examine more closely the effects of high-velocity impact of a projectile, in the method of [3], into a feldspathic target, in order to the resultant microstructural variation.<p></p&gt

On the predictability of extremes: Does the butterfly effect ever decrease?

This is the peer reviewed version of the following article: Sterk, A. E., Stephenson, D. B., Holland, M. P. and Mylne, K. R. (2015), On the predictability of extremes: Does the butterfly effect ever decrease?. Quarterly Journal of the Royal Meteorological Society, which has been published in final form at http://dx.doi.org/10.1002/qj.2627. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving: http://olabout.wiley.com/WileyCDA/Section/id-820227.html#termsThis study investigates whether or not predictability always decreases for more extreme events. Predictability is measured by the Mean Squared Error (MSE), estimated here from the difference of pairs of ensemble forecasts, conditioned on one of the forecast variables (the 'pseudo-observation') exceeding a threshold. Using an exchangeable linear regression model for pairs of forecast variables, we show that the MSE can be decomposed into the sum of three terms: a threshold-independent constant, a mean term that always increases with threshold, and a variance term that can either increase, decrease, or stay constant with threshold. Using the generalised Pareto distribution to model wind speed excesses over a threshold, we show that MSE always increases with threshold at sufficiently high threshold. However, MSE can be a decreasing function of threshold at lower thresholds but only if the forecasts have finite upper bounds. The methods are illustrated by application to daily wind speed forecasts for London made using the 24 member Met Office Global and Regional Ensemble Prediction System from 1 January 2009 to 31 May 2011. For this example, the mean term increases faster than the variance term decreases with increasing threshold, and so predictability decreases for more extreme events.Engineering and Physical Sciences Research Council (EPSRC)Netherlands Organisation for Scientific Research (NWO

Experimental Impacts into Feldspar Phenocrysts

Meteorite impact craters are the dominant surface feature on most terrestrial planetary bodies [1]. The extreme temperatures and pressures generated by hypervelocity impact events produce a variety of microscopic shock metamorphic effects in minerals, as well as non-exclusive shock-related features such as pervasive fracturing and brecciation. Studies of shock effects in feldspar group minerals have been limited due to the the comparatively rapid rate at which feldspars weather, and the complexity of their microtextures which renders them difficult to study using conventional optical techniques. However, feldspars are becoming increasingly investigated for use as shock barometers due to their importance in planetary studies and meteoritics, where rocks often contain little or no quartz [e.g., 2]. This provides the motivation to examine more closely the effects of high-velocity impact of a projectile, in the method of [3], into a feldspathic target, in order to the resultant microstructural variation.</p

Palynomorph preservation in volcaniclastic rocks of the Miocene Tepoztlan formation (Central Mexico) and implications for paleoenvironmental reconstruction

Palynomorph preservation in sedimentary rocks is strongly affected by various taphonomic factors related to transport, deposition, diagenesis and preservation potential. The palynological record may contribute to distinguish different taphonomic factors and also displays changes in paleoenvironment, especially in volcanic settings where a very complex interaction of eruptive, gravitational and fluvial processes in time and space can be observed. Herein, we report on new palynological data from the Miocene Tepoztlán Formation. The 800 m thick formation mainly consists of pyroclastic rocks, mass flow units (lahars) and fluvial deposits. It is part of the southern Transmexican Volcanic Belt, cropping out south of the Valley of Mexico and within the two states of Morelos and Mexico State. The volcaniclastic succession records various stages of recovery of vegetation related to a wide variety of disturbance factors and mechanisms. During the entire period of deposition, mixed mesophytic forests appear to have been widespread in the lowlands along streams and midaltitude uplands surrounding the valley. Pollen assemblages were repeatedly reset by volcanic eruptions or their secondary effects (lahars) to more limited assemblages with gradual recoveries to the initial stages before the eruption. A clear distinction can be made between samples taken from different transport regimes (fluvial, lahar and pyroclastic flow transport). The highest percentages of well-preserved, amorphous, and crumpled palynomorphs can be found in fluvial sediments while the highest percentage of fragmented palynomorphs is characteristic of lahar deposits. In contrast, the highest percentage of corroded palynomorphs can be found in deposits originating from pyroclastic flows.http://palaios.sepmonline.orghb201

Water sorption and hydration in spray-dried milk protein powders: Selected physicochemical properties

peer-reviewedLow and high protein dairy powders are prone to caking and sticking and can also be highly insoluble; with powder storage conditions an important factor responsible for such issues. The aim of this study focused on the bulk and surface properties of anhydrous and humidified spray-dried milk protein concentrate (MPC) powders (protein content ~40, 50, 60, 70 or 80%, w/w). Water sorption isotherms, polarized light and scanning electron micrographs showed crystallized lactose in low protein powders at high water activities. High protein systems demonstrated increased bulk diffusion coefficients compared to low protein systems. Glass transition temperatures, α-relaxation temperatures and structural strength significantly decreased with water uptake. CLSM measurements showed that humidified systems have slower real time water diffusion compared to anhydrous systems. Overall, the rate of water diffusion was higher for low protein powders but high protein powders absorbed higher levels of water under high humidity conditions

Data-Driven Audiogram Classification for Mobile Audiometry

Recent mobile and automated audiometry technologies have allowed for the democratization of hearing healthcare and enables non-experts to deliver hearing tests. The problem remains that a large number of such users are not trained to interpret audiograms. In this work, we outline the development of a data-driven audiogram classification system designed specifically for the purpose of concisely describing audiograms. More specifically, we present how a training dataset was assembled and the development of the classification system leveraging supervised learning techniques. We show that three practicing audiologists had high intra- and inter-rater agreement over audiogram classification tasks pertaining to audiogram configuration, symmetry and severity. The system proposed here achieves a performance comparable to the state of the art, but is signific

Frequency drift in MR spectroscopy at 3T

Purpose Heating of gradient coils and passive shim components is a common cause of instability in the B0 field, especially when gradient intensive sequences are used. The aim of the study was to set a benchmark for typical drift encountered during MR spectroscopy (MRS) to assess the need for real-time field-frequency locking on MRI scanners by comparing field drift data from a large number of sites. Method A standardized protocol was developed for 80 participating sites using 99 3T MR scanners from 3 major vendors. Phantom water signals were acquired before and after an EPI sequence. The protocol consisted of: minimal preparatory imaging; a short pre-fMRI PRESS; a ten-minute fMRI acquisition; and a long post-fMRI PRESS acquisition. Both pre- and post-fMRI PRESS were non-water suppressed. Real-time frequency stabilization/adjustment was switched off when appropriate. Sixty scanners repeated the protocol for a second dataset. In addition, a three-hour post-fMRI MRS acquisition was performed at one site to observe change of gradient temperature and drift rate. Spectral analysis was performed using MATLAB. Frequency drift in pre-fMRI PRESS data were compared with the first 5:20 minutes and the full 30:00 minutes of data after fMRI. Median (interquartile range) drifts were measured and showed in violin plot. Paired t-tests were performed to compare frequency drift pre- and post-fMRI. A simulated in vivo spectrum was generated using FID-A to visualize the effect of the observed frequency drifts. The simulated spectrum was convolved with the frequency trace for the most extreme cases. Impacts of frequency drifts on NAA and GABA were also simulated as a function of linear drift. Data from the repeated protocol were compared with the corresponding first dataset using Pearson's and intraclass correlation coefficients (ICC). Results Of the data collected from 99 scanners, 4 were excluded due to various reasons. Thus, data from 95 scanners were ultimately analyzed. For the first 5:20 min (64 transients), median (interquartile range) drift was 0.44 (1.29) Hz before fMRI and 0.83 (1.29) Hz after. This increased to 3.15 (4.02) Hz for the full 30 min (360 transients) run. Average drift rates were 0.29 Hz/min before fMRI and 0.43 Hz/min after. Paired t-tests indicated that drift increased after fMRI, as expected (p < 0.05). Simulated spectra convolved with the frequency drift showed that the intensity of the NAA singlet was reduced by up to 26%, 44 % and 18% for GE, Philips and Siemens scanners after fMRI, respectively. ICCs indicated good agreement between datasets acquired on separate days. The single site long acquisition showed drift rate was reduced to 0.03 Hz/min approximately three hours after fMRI. Discussion This study analyzed frequency drift data from 95 3T MRI scanners. Median levels of drift were relatively low (5-min average under 1 Hz), but the most extreme cases suffered from higher levels of drift. The extent of drift varied across scanners which both linear and nonlinear drifts were observed.publishedVersio