Dynamic phase diagram of plastically deformed amorphous solids at finite temperature

The yielding transition that occurs in amorphous solids under athermal quasistatic deformation has been the subject of many theoretical and computational studies. Here, we extend this analysis to include thermal effects at finite shear rate, focusing on how temperature alters avalanches. We derive a nonequilibrium phase diagram capturing how temperature and strain rate effects compete, when avalanches overlap, and whether finite-size effects dominate over temperature effects. The predictions are tested through simulations of an elastoplastic model in two dimensions and in a mean-field approximation. We find a new scaling for temperature-dependent softening in the low-strain rate regime when avalanches do not overlap, and a temperature-dependent Herschel-Bulkley exponent in the high strain rate regime when avalanches do overlap.Comment: 12 pages, 10 figures, 1 table. Updated to second version June 22, 202

Ascent of Ultrahigh-Pressure Rocks in Southeastern Papua New Guinea, as Revealed by Ti-in-Quartz Thermometry and Rb-Sr Dating

Debate concerns the timing of ultra-high pressure (UHP) metamorphism and the kinematics of exhumation of the world’s youngest known eclogite-facies rocks (U-Pb ages of 4 – 8 Ma) in the Woodlark Rift of southeastern Papua New Guinea. End-member kinematic models that have been proposed for the crustal exhumation of metamorphic gneiss domes that host these young eclogites include detachment-related (asymmetric) gneiss doming (metamorphic core complexes), and pure shear-dominated (symmetric or diapiric) gneiss doming. The former is predicted to exhume the deepest structural levels of the domes adjacent to a major normal fault. The latter is predicted to yield a concentric pattern of exhumation levels with the deepest rocks located near the center of the domes. As far as can be determined, there are no mappable field gradients with respect to either the high-pressure metamorphism or the later pervasive amphibolite-facies overprint in the lower crust. This apparent uniformity contributes to uncertainty regarding the distribution of vertical strain in the body, and thus to the mode of dome emplacement. To delineate spatial differences in exhumation and cooling rates, I measured Ti content in quartz for 90 samples of quartzofeldspathic gneiss and eclogite distributed across four migmatitic gneiss domes using laser ablation inductively coupled plasma mass spectrometry. I calculated paleo-temperatures from these data using the Ti-in-quartz geothermometer (Thomas et al., 2010; Wark and Watson, 2006). The Ti concentration in quartz in these samples ranges from 10 to 20 ppm, corresponding to an apparent temperature range of 500°C to 600°C (calculated using the Wark and Watson, 2006 calibration). As the apparent temperatures do not have a clear correlation with lithology and the quartz grains exhibit amoeboid grain boundaries, I infer that the Ti content in the quartz grains is capturing information related to quartz recrystallization and grain growth during the final stages of dynamic recrystallization by high-temperature grain-boundary migration (GBM). The presence of pervasive partial melt in the rocks and of chessboard microstructures in the quartz grains implies that the rocks in the D’Entrecasteaux Islands once attained temperatures of >630°C; however the 93% of the apparent temperatures calculated here are <630°C. Based on the pervasive GBM and the Ti-in-quartz apparent temperatures, I infer that the mean Ti content in these quartz grains was chiefly dependent on the relative rates of cooling and recrystallization as the body ascended through the crust. If the recrystallization rate was less spatially variable relative to the cooling rates across the gneiss domes, more quickly exhumed rocks would retain a larger relict fraction of unrecrystallized, hightemperature quartz grains. Ti content in quartz can therefore be used to map spatial changes in mean exhumation rate. As a rule, Ti concentrations in quartz in the D’Entrecasteaux Islands increase concentrically inward from 2.5 – 25 ppm at the dome margins to 20 – >100 ppm in the core of the domes. Based on this apparent increase in Ti content in quartz, I interpret the most rapidly cooled and exhumed rocks to occur today near the center of the gneiss domes. Thus, the Ti content in quartz data presented here indicate that the gneiss domes were emplaced in the crust by predominantly pure-shear symmetric doming. The timing of rock fabric development at the (U)HP conditions and during the main amphibolite-facies retrogression at lower crustal depths in the D’Entrecasteaux Islands has not been dated. To that end, I present nine Rb-Sr internal mineral isochrons for samples of eclogite, quartzofeldspathic gneiss, and granitic rock from four gneiss domes. Rb-Sr internal mineral isochrons for two samples of eclogites from the core zone of the Mailolo gneiss dome (Fergusson Island) date the timing of the (U)HP eclogite-facies metamorphism at mantle depths to 5.7 ± 2.0 Ma and 5.6 ± 1.6 Ma (2σ), respectively. One sample preserves coesite and the other contains radial fractures around quartz inclusions in garnet, implying that coesite was once been present in this rock. From this data, I infer that the eclogites in the Mailolo dome were metamorphosed at UHP depths of >90 km at 5.6 ± 1.2 Ma (approximate 95% confidence interval for the weighted mean of the two samples). The Rb-Sr isochron ages of amphibolite-facies rock fabric development in a granodioritic orthogneiss and quartzofeldspathic gneiss from the Mailolo and Goodenough dome are 2.4 ± 1.4 Ma (2σ) and 2.38 ± 0.3 Ma (2σ) respectively. This similarity in these Rb-Sr ages implies that deformation at amphibolite-facies conditions took place nearly simultaneously in these gneiss domes. A granodiorite >40 km to the south of the Mailolo granodioritic orthogneiss yielded a Rb-Sr age of 3.90 ± 0.44 Ma. This latter age is 1.5 ± 1.1 Ma (approximate 95% confidence interval) older then the Mailolo and Goodenough samples, indicating an apparent westward younging in the age of the amphibolite-facies metamorphism in the northwestern D’Entrecasteaux Islands. Five samples of quartzofeldspathic gneiss and quartzose rock were analyzed for pressure and temperature estimates using the garnet-plagioclase-muscovite-quartz barometer, the garnet- Al2SiO5-plagioclase-quartz barometer, and the garnet-phengite exchange thermometer. These data indicate a temperature range of 640 – 720 °C and a corresponding pressure range of 10 – 17 kbar for the amphibolite-facies metamorphic overprint in the D’Entrecasteaux Islands. This pressure estimate is higher then previous estimates (7 – 11 kbar) by ~3 – 6 kbar, which implies the HP body was thicker then previously inferred when it ponded at the lower crust. Combining these new Rb-Sr ages with U-Pb zircon ages by Gordon et al. (in review), I calculate a time lag of 2.2 ± 1.2 Ma (approximate 95% confidence interval) between eclogite-facies deformation in the mantle and amphibolite-facies foliation development in the lower crust for rocks in the Mailolo dome. This time lag, when combined with the amphibolite-facies pressure estimates presented here and pressure estimates consistent with the preservation of coesite in one sample, implies a minimum unroofing rate of 19 ± 11 mm yr-1 (approximate 95% confidence interval) for the (U)HP body from the mantle to the lower crust. This minimum unroofing rate strongly supports previous inferences that the exhumation from the mantle to the surface of the gneiss domes in the D’Entrecasteaux Islands took place at plate tectonic rates

Releasing hope—Women’s stories of transition from prison to community

This article embodies two key narratives among many that have emerged from a 14-year research project. The first narrative is of a community-engaged solution, a peer health mentor program, which was imagined during a prison participatory health and university research project, as described in Arresting Hope. The second is the narrative of Releasing Hope, a collection of writings by women with incarceration experience sharing their experiences, their challenges, and the barriers they face as they seek to heal from fractured and interrupted lives. A unique form of collaboration, innovation, research creation, and knowledge dissemination, Releasing Hope invites readers to reconsider communal perceptions, attitudes, and resistance towards those with incarceration experience, who struggle each day to be seen, not as former criminals, but as women capable of reimagining and enacting new lives. These two narratives illustrate the possibilities present when women are empowered with voice and agency. In the article, we aim to capture the spirit of both projects, in the interspersing of text and image, a collage of voices that speak to the experiences and learning that emerged through these two research ventures

Tectonic Mode Switches Recorded at the Northern Edge of the Australian Plate During the Pliocene and Pleistocene

We report new data from medium‐high grade metamorphic rocks found at the northern margin of the Lengguru Fold Belt in West Papua. The study involved a systematic analysis of cross‐cutting structures to establish the relative timing of deformation, together with isotopic dating to define when these tectono‐thermal events occurred. These data show that the region underwent multiple episodes of deformation within the last six million years. Metamorphic mineral growth was associated with the development of ductile shear zones. This episode occurred during a phase of crustal stretching associated with the formation of a metamorphic core complex. Metamorphic zircon growth at 4.9 to 5.3 Ma was documented in two of the dated samples. These data are interpreted to post‐date the peak pressure and temperature conditions of the phase of regional crustal stretching. The shear fabrics associated with the metamorphic core complex were later overprinted by at least two generations of folds. The change in mode from crustal extension to shortening reflects a tectonic mode switch. A subsequent mode switch is documented by numerous brittle extensional faults that cross‐cut the earlier formed ductile fabrics. We interpret ca. 0.75-1.51 Ma (U-Th)/He age data to reflect cooling associated with the later stages of crustal shortening (marked by folds) or the later extensional unroofing of the peninsula. This work demonstrates that an orogen can record multiple tectonic mode switches within several million years. These outcomes should be considered in studies of ancient orogens where analytical uncertainties associated with isotopic dating may mask short‐lived mode switches

Choose your cell model wisely: The in vitro nanoneurotoxicity of differentially coated iron oxide nanoparticles for neural cell labeling

Currently, there is a large interest in the labeling of neural stem cells (NSCs) with iron oxide nanoparticles (IONPs) to allow MRI-guided detection after transplantation in regenerative medicine. For such biomedical applications, excluding nanotoxicity is key. Nanosafety is primarily evaluated in vitro where an immortalized or cancer cell line of murine origin is often applied, which is not necessarily an ideal cell model. Previous work revealed clear neurotoxic effects of PMA-coated IONPs in distinct cell types that could potentially be applied for nanosafety studies regarding neural cell labeling. Here, we aimed to assess if DMSA-coated IONPs could be regarded as a safer alternative for this purpose and how the cell model impacted our nanosafety optimization study. Hereto, we evaluated cytotoxicity, ROS production, calcium levels, mitochondrial homeostasis and cell morphology in six related neural cell types, namely neural stem cells, an immortalized cell line and a cancer cell line from human and murine origin. The cell lines mostly showed similar responses to both IONPs, which were frequently more pronounced for the PMA-IONPs. Of note, ROS and calcium levels showed opposite trends in the human and murine NSCs, indicating the importance of the species. Indeed, the human cell models were overall more sensitive than their murine counterpart. Despite the clear cell type-specific nanotoxicity profiles, our multiparametric approach revealed that the DMSA-IONPs outperformed the PMA-IONPs in terms of biocompatibility in each cell type. However, major cell type-dependent variations in the observed effects additionally warrant the use of relevant human cell models.status: publishe

Branding and design for small business: effectively developing and managing brands through design

Bibliography: p. 115-124Some pages are in colour

Ascent of Ultrahigh-Pressure Rocks in Southeastern Papua New Guinea, as Revealed by Ti-in-Quartz Thermometry and Rb-Sr Dating

Debate concerns the timing of ultra-high pressure (UHP) metamorphism and the kinematics of exhumation of the world’s youngest known eclogite-facies rocks (U-Pb ages of 4 – 8 Ma) in the Woodlark Rift of southeastern Papua New Guinea. End-member kinematic models that have been proposed for the crustal exhumation of metamorphic gneiss domes that host these young eclogites include detachment-related (asymmetric) gneiss doming (metamorphic core complexes), and pure shear-dominated (symmetric or diapiric) gneiss doming. The former is predicted to exhume the deepest structural levels of the domes adjacent to a major normal fault. The latter is predicted to yield a concentric pattern of exhumation levels with the deepest rocks located near the center of the domes. As far as can be determined, there are no mappable field gradients with respect to either the high-pressure metamorphism or the later pervasive amphibolite-facies overprint in the lower crust. This apparent uniformity contributes to uncertainty regarding the distribution of vertical strain in the body, and thus to the mode of dome emplacement

The Universal Critical Dynamics of Noisy Neurons

The criticality hypothesis posits that the brain operates near a critical point. Typically, critical neurons are assumed to spread activity like a simple branching process and thus fall into the universality class of directed percolation. The branching process describes activity spreading from a single initiation site, an assumption that can be violated in real neurons where external drivers and noise can initiate multiple concurrent and independent cascades. In this thesis, I use the network structure of neurons to disentangle independent cascades of activity. Using a combination of numerical simulations and mathematical modelling, I show that criticality can exist in noisy neurons but that the presence of noise changes the underlying universality class from directed to undirected percolation. Directed percolation describes only small scale distributions of activity, on larger scales cascades can merge together and undirected percolation is the appropriate description