Aggregation of SiC-X Grains in Supernova Ejecta

We present a model for the formation of silicon carbide aggregates within the expanding and cooling supernova remnant. Many SiC-X grains have been found to be aggregates of smaller crystals which are isotopically homogenous. The initial condensation of SiC in the ejecta occurs within a interior dense shell of material which is created by a reverse shock which rebounds from the core-envelope interface. A subsequent reverse shock accelerates the grains forward, but the gas drag from the ejecta on the rapidly moving particles limits their travel distance. By observing the effects of gas drag on the travel distance of grains, we propose that supernova grain aggregates form from material that condensed in a highly localized region, which satisfies the observational evidence of isotopic homogeneity in SiC-X grains.Comment: 9 pages, 5 figures, To be published in the Astrophysical Journa

Time-trends and treatment gaps in the antithrombotic management of patients with atrial fibrillation after percutaneous coronary intervention: Insights from the CHUM AF-STENT Registry.

BACKGROUND: The management of atrial fibrillation and flutter (AF) patients undergoing percutaneous coronary intervention (PCI) has undergone a rapid recent evolution. In 2016, the Canadian Cardiovascular Society (CCS) published expert recommendations to help guide clinicians in balancing bleeding and thrombotic risks in these patients. HYPOTHESIS: Antithrombotic regimen prescriptions for AF patients undergoing PCI evolved after the publication of the 2016 CCS AF guidelines. METHODS: A prospective cohort of AF patients undergoing PCI with placement of a coronary stent from a single tertiary academic center was analyzed for the recommended antithrombotic regimen at discharge. Prescribing behavior was compared between three time periods (Cohort A [2010-2011]; Cohort B [2014-2015]; Cohort C [2017]) using the χ2 test. In addition, antithrombotic management in Cohorts B and C were compared to guideline-recommended therapy. RESULTS: A total of 459 patients with AF undergoing PCI were identified. Clinical and procedural characteristics were similar between cohorts, with the exception of an increase in drug-eluting stent (DES) use over time (P < .01). Overall, the rate of oral anticoagulation (OAC) increased over time (P < .01), associated with an increase in nonvitamin K OAC prescription (P < .01) and a concomitant decrease in vitamin K antagonist prescription (P < .01). Despite this, the overall rate of anticoagulation remains below what would be predicted with perfect guideline compliance (75% vs 94%, P < .01). CONCLUSION: There has been a dramatic shift in clinical practice for AF patients requiring PCI, with increases in prescription of OAC even in the context of an increase in the use of DES. However, room for further practice optimization still exists

Supernova Reverse Shocks: SiC Growth and Isotopic Composition

We present new mechanisms by which the isotopic compositions of X-type grains of presolar SiC are altered by reverse shocks in Type II supernovae. We address three epochs of reverse shocks: pressure wave from the H envelope near t ¼ 106 s, reverse shock from the presupernova wind near 108–109 s, and reverse shock from the interstellar medium near 1010 s. Using one-dimensional hydrodynamics we show that the first creates a dense shell of Si and C atoms near 106 s in which the SiC surely condenses. The second reverse shock causes precondensed grains to move rapidly forward through decelerated gas of different isotopic composi-tion, during which implantation, sputtering, and further condensation occur simultaneously. The third reverse shock causes only further ion implantation and sputtering, which may affect trace element isotopic compositions. Using a 25 M supernova model we propose solutions to the following unsolved questions: Where does SiC condense? Why does SiC condense in preference to graphite? Why is condensed SiC 28Si-rich? Why is O-richness no obstacle to SiC condensation? How many atoms of each isotope are impacted by a grain that condenses at time t0 at radial coordinate r0? These many considerations are put forward as a road map for interpreting SiC X grains found in meteorites and their meaning for supernova physics

Supernova Reverse Shocks and SiC Growth

We present new mechanisms by which the isotopic compositions of X-type grains of presolar SiC are altered by reverse shocks in Type II supernovae. We address three epochs of reverse shocks: pressure wave from the H envelope near t = 10$^6$s; reverse shock from the presupernova wind near 10$^8-10^9$s; reverse shock from the ISM near 10$^{10}$s. Using 1-D hydrodynamics we show that the first creates a dense shell of Si and C atoms near 10$^6$s in which the SiC surely condenses. The second reverse shock causes precondensed grains to move rapidly forward through decelerated gas of different isotopic composition, during which implantation, sputtering and further condensation occur simultaneously. The third reverse shock causes only further ion implantation and sputtering, which may affect trace element isotopic compositions. Using a 25M$_{\odot}$ supernova model we propose solutions to the following unsolved questions: where does SiC condense?; why does SiC condense in preference to graphite?; why is condensed SiC $^{28}$Si-rich?; why is O richness no obstacle to SiC condensation?; how many atoms of each isotope are impacted by a grain that condenses at time t$_0$ at radial coordinate r$_0$? These many considerations are put forward as a road map for interpreting SiC X grains found in meteorites and their meaning for supernova physics.Comment: 28 pages, 14 figures, animation for Figure 3 and machine-readable Table 3 can be found at http://antares.steelangel.com/~edeneau/supernova/DHC_2003, Submitted to Ap

Growth of Carbon Grains in Supernova Ejecta

We present a chemical reaction network that describes the condensation chemistry of carbon dust grains in an expanding supernova shell. We assume that the region of interest consists solely of gaseous free carbon and oxygen atoms and that the buildup of CO is counteracted by the radioactive decay of 56Co, which breaks up the CO mol-ecule and allows C to condense into solids. Our chemical model takes C to first form linear chains, which, at some critical length, transition into ringed isomers. These isomers are more resistant to oxidation than linear chains. These ringed isomers form the nuclei for the growth of larger carbon solids. The effect of the disruption of CO on grain growth is displayed, leading to a rethinking of previous assumptions on the importance of CO disruption. How the abundance and size distribution of grains are affected by various parameters of the ejecta is also studied, providing insight into the possible sites of grain condensation

Condensation of Carbon in Radioactive Supernova Gas

The chemistry of carbon molecules leading to the formation of large carbon-bearing molecules and dust in the interior of an expanding supernova is explored and the equations governing their abundances are solved. A steady state between production and destruction is set up early and evolves adiabatically as the supernova evolves. Simple solutions for that steady state limit yield the abundance of each linear carbon molecule and its dependence on the C/O atomic ratio in the gas. Carbon dust condenses from initially gaseous C and O atoms because Compton electrons produced by the radioactivity cause dissociation of the CO molecules, which would otherwise form and limit the supply of C atoms. The resulting free C atoms enable carbon dust to grow faster by C association than its destruction by oxidation for various C/O ratios. Nucleation for graphite growth occurs when linear Cn molecules transition to ringed Cn molecules. We survey the dependence of the abundances of these molecules on the C/O ratio and on several other kinetic rate parameters. The concept of population control is significant for the maximum sizes of carbon particles grown during supernova expansion. Interpretation of presolar micrometer-sized carbon solids found in meteorites and of infrared emission from supernova is relaxed to allow O to be more abundant than C, but the maximum grain size depends upon that ratio

Global Climate Action 2022: How have international initiatives delivered, and what more is possible

Contains fulltext : 285265.pdf (Publisher’s version ) (Open Access)This report is the latest stocktake of international cooper- ative climate action. International cooperative initiatives (ICIs) have been a major feature of international climate governance ever since the UNFCCC started recording them in 2013. These partnerships engage a wide range of non- state and subnational actors, including businesses, inves- tors, civil society, national governments, and international organizations. We identified 601 ICIs launched since 2013 with more than 70,000 instances1 of participation by cities and regions, businesses, and by domestic and international NGOs. The total number of ICIs covered in this study has more than doubled compared to previous analyses as a result of examining outcomes from all major climate summits and campaigns since 2014. The growth of active initiatives (85% of all ICIs launched since 2013) has flat- tened since 2019. This is partly explained by the expiration of many initiatives that were launched prior or around the UN Climate Conference in Paris in 2015. The outbreak of the COVID 19 pandemic may also explain lower growth of new initiatives, especially in 2020. Overall productivity of initiatives is trending downwards. Through assessing the extent whether initiatives’ outputs (e.g., infrastructure, research, new installations) are consist- ent with their functions (e.g., training, norm-/standard set- ting, technical on-the-ground implementation), we observed a higher share of low or non-performing initiatives in both mitigation and adaptation since 2019. Overall productivity of initiatives is also trending downwards. ICIs have been launched without further implementation and operation- alization of commitments. This gap between commitments and implementation risks to undermine the credibility of ICIs and the campaigns and summits that convene them. The downwards trend in productivity may be explained by ICIs initially picking ‘low-hanging fruit’ and subsequently having to take more difficult measures. Moreover, the COVID-19 pandemic has likely affected the performance of ICIs. During the pandemic, ICIs’ production of outputs that are location-specific (such as in-person trainings, and new infrastructure or installations) decreased at a faster rate than those that are not location specific (such as websites, online platforms, and research publications). Conversely, we observe a rapid growth of webcasted events, which may reflect a replacement of physical activities by virtual ones. Our analysis suggests a strong and growing underrep- resentation of the Global South. Although ICIs have great potential to contribute to sustainable development in devel- oping countries, studies have consistently shown a strong underrepresentation of the Global South. Implementation disproportionately takes place in the Global North. In line with previous assessments our analysis shows the under- representation of funders, leaders, and participants of ICIs based in non-OECD countries. Moreover, since 2015 the share of outputs produced in the Global North has steadily grown. Some imbalances are to be expected as they appro- priately and reflect differentiated responsibilities and the need for a strong focus on climate mitigation. Nonetheless, the benefits of ICIs, particularly adaptation and resilience building, should also accrue to developing countries. Summit and campaign organizers should steer towards higher performance by setting requirements for ICIs, particularly among initiatives that are launched at cli- mate conferences, summits and by COP presidencies. For instance, before featuring ICIs at climate conferences, organizers should require ICIs to provide evidence that they are making progress against targets and/or have capacities and resources to deliver on pledges. Possible measures identified in the literature include the appointment of dedi- cated staff and/or a secretariat, regular reporting, credible budgets, and openness for new partners to join an initiative, while facilitating interfaces between non-state, subnational actors, policymakers and funders. The report assessed the potential contributions of 12 international sector initiatives launched around and during COP26 (hereinafter, ‘Glasgow initiatives’) on future green- house gas (GHG) emission reductions. We found that the theoretical coverage of these Glasgow initiatives is large: they cover sectors that could potentially lead to 11 GtCO2e lower emissions in 2030 compared to the aggregate of NDCs, addressing a considerable part of the ‘ambition gap’ between the NDC scenario and the benchmark 1.5°C scenario (Figure ES-1). However, not all governments have signed up and impact of signatories is quite small because many already have the action included in their NDC: There- fore, a full implementation of the initiatives’ 1.5°C-aligned goals by the current signatories would only lead to about 5 GtCO2e of emission reductions additional to the NDC scenario (Figure ES- 1). Ambition can be raised in two ways based on these results: First, the biggest potential lies in additional governments signing up to initiatives that have not yet done so (6 GtCO2e). The theory of change of the initiatives is to put non-signatories on the spot, but membership since the Glasgow COP has changed only marginally. Second, govern- ments that have signed up have not yet fully taken these actions into account in their NDCs and therefore could increase the ambition in their NDCs (5 GtCO2e). Future COPs could generate momentum in sectors not covered by the Glasgow initiatives. Although the Glasgow initiatives’ emission reduction potential is substantial, there are still sectors in which momentum for rapid transition toward decarbonisation is needed, including the buildings sector and heavy industry sectors other than steel, such as chemicals and cement. These sectors have not been well covered by ICIs, especially by those that involve large emitting countries and established international institutions. The presidencies of the next few COPs as well as the UN Climate Change High-Level Champions may take the leader- ship to generate momentum to accelerate decarbonisation in these sectors. We also compared these Glasgow initiatives to those pre- viously launched at major international conferences, which have shown mixed performance results , in terms of, for example, financing and reporting requirements. The lim- ited literature indicates that there continues to be a lack of enforcement mechanisms in some Glasgow initiatives. However, there are also noticeable improvements in other Glasgow initiatives , such as annual progress assessment mandated to international organisations and, more impor- tantly, securing finance for implementation. Continued political drive from national governments can help realize the Glasgow initiatives’ potential. The political drive as shown by the UK Presidency has been crucial for establishing the Glasgow initiatives with their launch. Continued political drive is required for the poten- tial impact of the initiatives to materialise and expand. Upcoming COP Presidencies and UN Climate Change High- Level Champions may represent this political drive and generate more leadership, particularly among large emitting countries, in order to maintain momentum and credibility after COP27 and to drive towards more signatories and implementation of global climate action.28 p

Child-father attachment in early childhood and behavior problems: A meta-analysis

This meta-analytic study examined the associations between child-father attachment in early childhood and children's externalizing and internalizing behavior problems. Based on 15 samples (N = 1,304 dyads), the association between child-father attachment insecurity and externalizing behaviors was significant and moderate in magnitude (r = 0.18, 95% CI: 0.10, 0.27 or d = 0.37, 95% CI: 0.20, 0.55). No moderators of this association were identified. Based on 12 samples (N = 1,073), the association between child-father attachment insecurity and internalizing behaviors was also significant, albeit smaller in magnitude (r = 0.09, 95% CI: 0.02, 0.15; or d = 0.17, 95% CI: 0.03, 0.31). Between-study heterogeneity was insufficient to consider moderators. When compared to the effect sizes of prior meta-analyses on child-mother attachment and behavior problems, the quality of the attachment relationship with fathers yields a similar magnitude of associations to children's externalizing and internalizing behaviors. Results support the need to consider the role of the attachment network, which notably includes attachment relationships to both fathers and mothers, to understand how attachment relationships contribute to child development

Dust and the type II-Plateau supernova 2004dj

We present mid-infrared (MIR) spectroscopy of a Type II-plateau supernova, SN 2004dj, obtained with the Spitzer Space Telescope, spanning 106--1393 d after explosion. MIR photometry plus optical/near-IR observations are also reported. An early-time MIR excess is attributed to emission from non-silicate dust formed within a cool dense shell (CDS). Most of the CDS dust condensed between 50 d and 165 d, reaching a mass of 0.3 x 10^{-5} Msun. Throughout the observations much of the longer wavelength (>10 microns) part of the continuum is explained as an IR echo from interstellar dust. The MIR excess strengthened at later times. We show that this was due to thermal emission from warm, non-silicate dust formed in the ejecta. Using optical/near-IR line-profiles and the MIR continua, we show that the dust was distributed as a disk whose radius appeared to be slowly shrinking. The disk radius may correspond to a grain destruction zone caused by a reverse shock which also heated the dust. The dust-disk lay nearly face-on, had high opacities in the optical/near-IR regions, but remained optically thin in the MIR over much of the period studied. Assuming a uniform dust density, the ejecta dust mass by 996 d was 0.5 +/- 0.1) x 10^{-4} Msun, and exceeded 10^{-4}Msun by 1393 d. For a dust density rising toward the center the limit is higher. Nevertheless, this study suggests that the amount of freshly-synthesized dust in the SN 2004dj ejecta is consistent with that found from previous studies, and adds further weight to the claim that such events could not have been major contributors to the cosmic dust budget.Comment: ApJ in press; minor changes c.f. v