Formation, preservation and extinction of high-pressure minerals in meteorites: temperature effects in shock metamorphism and shock classification

The goal of classifying shock metamorphic features in meteorites is to estimate the corresponding shock pressure conditions. However, the temperature variability of shock metamorphism is equally important and can result in a diverse and heterogeneous set of shock features in samples with a common overall shock pressure. In particular, high-pressure (HP) minerals, which were previously used as a solid indicator of high shock pressure in meteorites, require complex pressure–temperature–time (P–T–t) histories to form and survive. First, parts of the sample must be heated to melting temperatures, at high pressure, to enable rapid formation of HP minerals before pressure release. Second, the HP minerals must be rapidly cooled to below a critical temperature, before the pressure returns to ambient conditions, to avoid retrograde transformation to their low-pressure polymorphs. These two constraints require the sample to contain large temperature heterogeneities, e.g. melt veins in a cooler groundmass, during shock. In this study, we calculated shock temperatures and possible P–T paths of chondritic and differentiated mafic–ultramafic rocks for various shock pressures. These P–T conditions and paths, combined with observations from shocked meteorites, are used to constrain shock conditions and P–T–t histories of HP-mineral bearing samples. The need for rapid thermal quench of HP phases requires a relatively low bulk-shock temperature and therefore moderate shock pressures below ~ 30 GPa, which matches the stabilities of these HP minerals. The low-temperature moderate-pressure host rock generally shows moderate shock-deformation features consistent with S4 and, less commonly, S5 shock stages. Shock pressures in excess of 50 GPa in meteorites result in melt breccias with high overall post-shock temperatures that anneal out HP-mineral signatures. The presence of ringwoodite, which is commonly considered an indicator of the S6 shock stage, is inconsistent with pressures in excess of 30 GPa and does not represent shock conditions different from S4 shock conditions. Indeed, ringwoodite and coexisting HP minerals should be considered as robust evidence for moderate shock pressures (S4) rather than extreme shock (S6) near whole-rock melting.

FAST continuum mapping of the SNR VRO 42.05.01

The relativistic electrons rotate in the enhanced magnetic field of the supernova remnants and emit the synchrotron radio emission.We aim to use the Five-hundred-meter Aperture Spherical radio Telescope (FAST) to obtain a sensitive continuum map of the SNR VRO 42.05.01 (G166.0+4.3) at 1240 MHz. The 500 MHz bandwidth is divided into low and high-frequency bands centered at 1085 and 1383 MHz to investigate the spectral index variations within the remnant, together with the Effelsberg 2695 MHz data. We obtained an integrated flux density of 6.2±0.4 Jy at 1240 MHz for VRO 42.05.01, consistent with previous results. The spectral index found from TT-plot between 1240 and 2695 MHz agrees with previous values from 408 MHz up to 5 GHz. The three-band spectral index distribution shows a clear flatter value of α ∼ −0.33 in the shell region and steeper index of α = −0.36 − −0.54 in the wing region. The flatter spectral index in the shell region could be attributed to a second-order Fermi process in the turbulent medium in the vicinity of the shock and/or a higher compression ratio of shock and a high post-shock density than that in elsewhere.

Spectral Evolution of the X-Ray Remnant of SN 1987A: A High-resolution Chandra HETG Study

Based on observations with the Chandra X-ray Observatory, we present the latest spectral evolution of the X-ray remnant of SN 1987A (SNR 1987A). We present a high-resolution spectroscopic analysis using our new deep (∼312 ks) Chandra HETG observation taken in 2018 March as well as archival Chandra grating spectroscopic data taken in 2004, 2007, and 2011 with similarly deep exposures (∼170–350 ks). We perform detailed spectral model fits to quantify changing plasma conditions over the last 14 yr. Recent changes in electron temperatures and volume-emission measures suggest that the shocks moving through the inner ring have started interacting with less dense circumstellar material, probably beyond the inner ring. We find significant changes in the X-ray line-flux ratios (among H- and He-like Si and Mg ions) in 2018, consistent with changes in the thermal conditions of the X-ray-emitting plasma that we infer based on the broadband spectral analysis. Post-shock electron temperatures suggested by line-flux ratios are in the range ∼0.8–2.5 keV as of 2018. We do not yet observe any evidence of substantial abundance enhancement, suggesting that the X-ray emission component from the reverse-shocked metal-rich ejecta is not yet significant in the observed X-ray spectrum.

Abstract 11901: CPR Quality During the COVID-19 Pandemic - More Evidence of Collateral Damage During Out-of-Hospital Cardiac Arrest

Introduction: Many regions around the world have reported declining survival rates from out-of-hospital cardiac arrest (OHCA) during the COVID-19 pandemic. This has been attributed to COVID-19 infection and overwhelmed healthcare services in some regions and imposed social restrictions in others. However, the effect of the pandemic period on CPR quality, which has the potential to impact outcomes, has not yet been described. Methods: A retrospective observational study was performed using data collected in an established OHCA registry in Victoria, Australia. During a pre-pandemic period (11 February 2019-31 January 2020) and the COVID-19 pandemic period (1 February 2020-31 January 2021), 1,111 and 1,349 cases with attempted resuscitation had complete CPR quality data, respectively. The proportion of cases where CPR targets (chest compression fraction [CCF]≥90%, compression depth 5-10cm, compression rate 100-120 per minute, pre-shock pauses <6 seconds, post-shock pauses <5 seconds) were met was compared between the pre-pandemic and pandemic periods. Logistic regression was performed to identify the independent effect of the COVID-19 pandemic on achieving CPR targets. Results: The proportion of arrests where CCF≥90% significantly decreased during the pandemic (57% vs 74% in the pre-pandemic period, p<0.001) as did the proportion with pre-shock pauses <6 seconds (54% vs 62%, p=0.019) and post-shock pauses <5 seconds (68% vs 82%, p<0.001). However, the proportion within target compression rate significantly increased during the pandemic (64% vs 56%, p<0.001). Following multivariable adjustment, the COVID-19 pandemic period was independently associated with a decrease in the odds of achieving a CCF≥90% (adjusted odds ratio [AOR] 0.47 [95% CI 0.40, 0.56]), a decrease in the odds of achieving pre-shock pauses<6 seconds (AOR 0.71 [95% CI 0.52, 0.96]), and a decrease in the odds of achieving post-shock pauses<5 seconds (AOR 0.49 [95% CI 0.34, 0.71]). Conclusion: CPR quality was impacted during the COVID-19 pandemic period which may have contributed to a decrease in OHCA survival previously identified. These findings reinforce the importance of maintaining effective resuscitation practices despite changes to clinical context.

Abstract 13358: Pediatric Defibrillation; Safety and Efficacy of Shocks in Both Ventricular Fibrillation and Sinus Rhythm in a Porcine Model

Introduction: Pediatric sudden cardiac arrest may require the delivery of a defibrillating shock to promote return of spontaneous circulation (ROSC). Fear of harm is a barrier for the use of automated external defibrillators by lay personnel, particularly when the patient is a child. The aim of this study was to observe the effects of delivering pediatric defibrillation shocks to pediatric weight swine who are in a perfusing rhythm or ventricular fibrillation (VF). Methods: Eight swine (10.3-26.8 kg) were studied under anesthesia. Up to 30 shocks were applied using modified samaritan AEDs (HeartSine, UK) to animals either in sinus rhythm or after 30 seconds of VF. Shocks delivered in sinus rhythm were unsynchronized. Four different shock types were applied, utilizing two different waveforms (Waveform-A at 50 J, Waveform-A at 75 J, Waveform-A at 90J and Waveform-B at 50 J). Left ventricular (LV) pressures were recorded invasively (Millar, USA). If the shock was successful, the animal entered a rest period of approximately 5 minutes, after which the next shock was applied. Results: Data presented in Table 1. Out of a total of 77 shocks delivered in sinus rhythm, 2 (2.6%) resulted in conversion to a cardiac arrest rhythm. Analysis of LV pressures demonstrated no significant differences in the change of LV dP/dt from baseline at 1, 10 and 60 seconds post-shock. There was no significant difference in shock success or ROSC between the shock types for defibrillation of VF. Analysis of LV pressures demonstrated no significant differences in the change of LV dP/dt from baseline at at 1, 10 and 60 seconds post-shock between the groups. Conclusions: The results of this study indicate defibrillation shocks applied to swine in sinus rhythm rarely result in conversion to an arrhythmia. Additionally, the variety of shock types demonstrated similar levels of safety and efficacy in this porcine model.

Investors’ Delight? Climate Risk in Stock Valuation during COVID-19 and Beyond

We use the COVID-19 pandemic period in 2020 as an exogenous shock event to assess in how far climate risks measured by carbon exposure have entered and established themselves in the valuation of global stocks. In addition to descriptive analyses, we conduct cross-sectional panel regressions to assess the influence of carbon intensity levels on return and risk characteristics during and after the shock period. Furthermore, a difference-in-differences model setup allows us to infer whether these influences were significantly different when comparing pre-shock, shock, and post-shock periods. We find that carbon intensity affected returns significantly and negatively during a time of high uncertainty. In fact, high-emitting stocks suffered significantly more compared to the pre-crisis period. However, they could make up for their additional losses in the recovery period. In line with their high-risk exposure towards stranded assets and climate policy uncertainty, carbon-intensive stocks face higher risk levels in more stable economic times, thus justifying a carbon premium.

Does Livelihood and Asset Diversification Contribute to Pastoralist Resilience?: the Case of Il Chamus, Baringo County, Kenya, 1980-2018

In studies of pastoralism, the concept of resilience has normally been applied to the analyses of post-shock recoveries ('bounce backs') within an ecological framework and and limited time and spatial perspectives. When temporal and spatial parameters are relaxed to span multiple decades and geographies with widespread social changes and numerous shocks and recovery periods, understanding what resilience for pastoralists should look like is exceedingly complex and challenging. This article examines livelihood and asset diversification among Il Chamus of Baringo County, Kenya over a 35+ year period (1980-2018) in the context of significant changes. It suggests that 'successful resilience' among pastoralists involves much more than the continuity of a pastoralist livelihood in a particular place. By addressing diversification trends among households both in towns and rural spaces, the study shows that both better-off and poor households pursue non-pastoral strategies and assets, and that livestock remains an important real and symbolic form of capital even for those who work in towns. Finally, the article concludes that studies of pastoralist resilience should consider long-term continuities and changes associated with market expansion and the strengthening of rural-town linkages, in order to understand how pastoral livelihoods evolve not just in response to short-term shocks but also to challenges and opportunities that wider socio-economic changes present.

Supplying angular momentum to the jittering jets explosion mechanism using inner convection layers

We conduct one-dimensional stellar evolution simulations in the mass range 13 − 20M⊙ to late core collapse times and find that an inner vigorous convective zone with large specific angular momentum fluctuations appears at the edge of the iron core during the collapse. The compression of this zone during the collapse increases the luminosity there and the convective velocities, such that the specific angular momentum fluctuations are of the order of $j_{\rm conv} \simeq 5 \times 10^{15} {~\rm cm}^2 {~\rm s}^{-1}$. If we consider that three-dimensional simulations show convective velocities that are three to four times larger than what the mixing length theory gives, and that the spiral standing accretion shock instability in the post-shock region of the stalled shock at a radius of $\simeq 100 {~\rm km}$ amplify perturbations, we conclude that the fluctuations that develop during core collapse are likely to lead to stochastic (intermittent) accretion disks around the newly born neutron star. In reaching this conclusion we also make two basic assumptions with uncertainties that we discuss. Such intermittent disks can launch jets that explode the star in the frame of the jittering jets explosion mechanism.

Formation, preservation and extinction of high-pressure minerals in meteorites: temperature effects in shock metamorphism and shock classification

The goal of classifying shock metamorphic features in meteorites is to estimate the corresponding shock pressure conditions. However, the temperature variability of shock metamorphism is equally important and can result in a diverse and heterogeneous set of shock features in samples with a common overall shock pressure. In particular, high-pressure (HP) minerals, which were previously used as a solid indicator of high shock pressure in meteorites, require complex pressure-temperature-time (P-T-t) histories to form and survive. First, parts of the sample must be heated to the melting temperatures, at high pressure, to enable rapid formation of HP minerals before pressure release. Second, the HP minerals must be rapidly cooled to below a critical temperature, before the pressure returns to ambient conditions, to avoid retrograde transformation to their low-pressure polymorphs. These two constraints require the sample to contain large temperature heterogeneities, e.g. melt veins in a cooler groundmass, during shock. In this study, we calculated shock temperatures and possible P-T paths of chondritic and differentiated mafic rocks for various shock pressures. These P-T conditions and paths, combined with observations from shocked meteorites, are used to constrain shock conditions and P-T-t histories of HP-mineral bearing samples. The need for rapid thermal quench of HP phases requires a relatively low bulk-shock temperature and therefore moderate shock pressures below ~ 30 GPa, which matches the stabilities of these HP minerals. The low-temperature moderate-pressure host rock generally shows moderate shock-deformation features consistent with S4 and, less commonly, S5 shock stages. Shock pressures in excess of 50 GPa in meteorites result in melt breccias with high overall post-shock temperatures that anneal out HP-mineral signatures. The presence of ringwoodite, which is commonly considered an indicator of the S6 shock stage, is inconsistent with pressures in excess of 30 GPa and does not represent shock conditions different from S4 shock conditions. Indeed, ringwoodite and coexisting HP minerals should be considered as robust evidence for moderate shock pressures (S4) rather than extreme shock (S6) near whole-rock melting.

Impact of the ISM magnetic field on GRB afterglow polarization

Linear polarization has been measured in several GRB afterglows. After a few days, polarization arises from the forward shock emission which depends on the post-shock magnetic field. The latter can originate both from compression of existing fields, here the ISM magnetic field, and from shock generated instabilities. For short GRBs, previous modelling of the polarization arising from the forward shock considered a random field fully or partially confined to the shock plane. However, the ISM magnetic field likely consists of both random and ordered components. Here we study the impact of a more realistic magnetic field having both ordered and random components. We present our semi-analytical model and compute polarization curves arising for different magnetic field configurations. We find that the presence of an ordered component, even significantly weaker than the random one, has distinct signatures that could be detectable. In the presence of an ordered component not in the observer plane, we show that: i) for an observer inside the jet, the polarization angle θp either remains constant during all the afterglow phase or exhibits variations smaller than the 90○ swing expected from a random component solely, ii) for an off-axis observer, the polarization angle evolves from $\theta _p^{\max }$, before the jet break to its opposite after the jet break. We also find that the upper limit polarization for GRB170817 requires a random field not fully confined to the shock plane and is compatible with an ordered component as large as half the random one.