scholarly journals SNe Ia from double detonations: Impact of core-shell mixing on the carbon ignition mechanism

2020 ◽  
Vol 635 ◽  
pp. A169 ◽  
Author(s):  
Sabrina Gronow ◽  
Christine Collins ◽  
Sebastian T. Ohlmann ◽  
Rüdiger Pakmor ◽  
Markus Kromer ◽  
...  
Keyword(s):  
Detonation Wave ◽  
Three Dimensions ◽  
Core Shell ◽  
The Core ◽  
Ignition Mechanism ◽  
Type Ia ◽  
Shock Mechanism ◽  
Set Up ◽  
Ia Supernovae ◽  
The Impact

Sub-Chandrasekhar mass white dwarfs accreting a helium shell on a carbon-oxygen core are potential progenitors of normal Type Ia supernovae. This work focuses on the details of the onset of the carbon detonation in the double detonation sub-Chandrasekhar model. In order to simulate the influence of core-shell mixing on the carbon ignition mechanism, the helium shell and its detonation are followed with an increased resolution compared to the rest of the star treating the propagation of the detonation wave more accurately. This significantly improves the predictions of the nucleosynthetic yields from the helium burning. The simulations were carried out with the AREPO code. A carbon-oxygen core with a helium shell was set up in one dimension and mapped to three dimensions. We ensured the stability of the white dwarf with a relaxation step before the hydrodynamic detonation simulation started. Synthetic observables were calculated with the radiative transfer code ARTIS. An ignition mechanism of the carbon detonation was observed, which received little attention before. In this “scissors mechanism”, the impact the helium detonation wave has on unburnt material when converging opposite to its ignition spot is strong enough to ignite a carbon detonation. This is possible in a carbon enriched transition region between the core and shell. The detonation mechanism is found to be sensitive to details of the core-shell transition and our models illustrate the need to consider core-shell mixing taking place during the accretion process. Even though the detonation ignition mechanism differs form the converging shock mechanism, the differences in the synthetic observables are not significant. Though they do not fit observations better than previous simulations, they illustrate the need for multi-dimensional simulations.

Enhancing team performance through transactive memory

2016 ◽  
Vol 30 (4) ◽  
pp. 13-16 ◽  
Author(s):  
Srabasti Chatterjee
Keyword(s):  
Team Performance ◽  
Individual Performance ◽  
Transactive Memory ◽  
Three Dimensions ◽  
Major Focus ◽  
Content Type ◽  
Organizational Settings ◽  
Current Scenario ◽  
Set Up ◽  
The Impact

Purpose The major focus in the current scenario in organizational settings has shifted from individual performance to team performance. The current study investigates team performance and its antecedents from both social and cognitive dimensions and hence provides a qualitative and synopsis of the same. There is one such antecedent transactive memory which collectively looks into both the facets. For more than a decade after the very emergence of this concept, a plethora of work has been done to relate team performance and transactive memory. In an attempt to understand both these multi-dimensional constructs, and to comprehend the interrelationships in a better way, this paper aims to analyze the impact of transactive memory on team performance and how to improve it in organizations. Design/methodology/approach The paper is purely conceptual. So it uses other earlier studies to make necessary propositions. Findings The present study tries to qualitatively analyze the impact of transactive memory on team performance with respect to the various dimensions of team performance both task process and relational performance. The results of the study show a positive relationship between the three dimensions of transactive memory – credibility, consensus and specilaization and team performance. The study also provides recommendations to improvise transactive memory in organizations. Research limitations/implications The paper is not empirical, so further empirical analysis could enrich the results. Originality/value The paper is original in terms of giving solutions to increase transactive memory in organizational set up.

WD+AGB star systems as the progenitors of type Ia supernovae

2018 ◽  
Vol 14 (S343) ◽  
pp. 540-541
Author(s):  
Bo Wang
Keyword(s):  
Type Ia Supernovae ◽  
Population Synthesis ◽  
Final Phase ◽  
Common Envelope ◽  
The Core ◽  
Delay Times ◽  
Careful Treatment ◽  
Type Ia ◽  
Ia Supernovae ◽  
Synthesis Approach

AbstractWD+AGB star systems have been suggested as an alternative way for producing type Ia supernovae (SNe Ia), known as the core-degenerate (CD) scenario. In the CD scenario, SNe Ia are produced at the final phase during the evolution of common-envelope through a merger between a carbon-oxygen (CO) WD and the CO core of an AGB secondary. However, the rates of SNe Ia from this scenario are still uncertain. In this work, I carried out a detailed investigation on the CD scenario based on a binary population synthesis approach. I found that the Galactic rates of SNe Ia from this scenario are not more than 20% of total SNe Ia due to more careful treatment of mass transfer, and that their delay times are in the range of ∼90 − 2500 Myr, mainly contributing to the observed SNe Ia with short and intermediate delay times.

Synthesis Technology of Silica Aerogels/Polystyrene Core-Shell Composite Materials

2010 ◽  
Vol 168-170 ◽  
pp. 1833-1836
Author(s):  
Gang Qiang Geng ◽  
Jing Tao Guo ◽  
Jun Jun Zou ◽  
Gong Xun Bian
Keyword(s):  
Composite Materials ◽  
Polymerization Process ◽  
System Component ◽  
Core Shell ◽  
Ultrasound Technique ◽  
The Core ◽  
Optimum Reaction ◽  
The Impact ◽  
Shell Composite

In order to obtain super aerogels heat insulating composite materials with silane coupling agent on the in-situ surface treatment. The core-shell structure composite materials have been prepared by dispersion polymerization process of polystyrene grafted on the SiO2 particles. By TEM on these samples the impact of the system components initiator polymerization parameters and dispersion process was discussed. The results showed that the system component of the greatest impact on conversion rate is the ratio of aerogels /St ,the optimum reaction temperature is 75 °C.With organic initiator KPS as initiator after a unique ultrasound technique to obtain the core-shell composite materials structure which coating is 70%.

scholarly journals Sensitivity of Type Ia supernovae to electron capture rates

2019 ◽  
Vol 624 ◽  
pp. A139 ◽  
Author(s):  
E. Bravo
Keyword(s):  
Weak Interactions ◽  
Dynamical Evolution ◽  
Sensitivity Study ◽  
Decay Rates ◽  
Type Ia Supernovae ◽  
Thermonuclear Explosion ◽  
Type Ia ◽  
Long Time ◽  
Ia Supernovae ◽  
The Impact

The thermonuclear explosion of massive white dwarfs is believed to explain at least a fraction of Type Ia supernovae (SNIa). After thermal runaway, electron captures on the ashes left behind by the burning front determine a loss of pressure, which impacts the dynamics of the explosion and the neutron excess of matter. Indeed, overproduction of neutron-rich species such as 54Cr has been deemed a problem of Chandrasekhar-mass models of SNIa for a long time. I present the results of a sensitivity study of SNIa models to the rates of weak interactions, which have been incorporated directly into the hydrodynamic explosion code. The weak rates have been scaled up or down by a factor ten, either globally for a common bibliographical source, or individually for selected isotopes. In line with previous works, the impact of weak rates uncertainties on sub-Chandrasekhar models of SNIa is almost negligible. The impact on the dynamics of Chandrasekhar-mass models and on the yield of 56Ni is also scarce. The strongest effect is found on the nucleosynthesis of neutron-rich nuclei, such as 48Ca, 54Cr, 58Fe, and 64Ni. The species with the highest influence on nucleosynthesis do not coincide with the isotopes that contribute most to the neutronization of matter. Among the latter, there are protons, 54, 55Fe, 55Co, and 56Ni, while the main influencers are 54, 55Mn and 55 − 57Fe, in disagreement with Parikh et al (2013, A&A, 557, A3), who found that SNIa nucleosynthesis is most sensitive to the β+-decay rates of 28Si, 32S, and 36Ar. An increase in all weak rates on pf-shell nuclei would affect the dynamical evolution of burning bubbles at the beginning of the explosion and the yields of SNIa.

The dividends of investing in computational software design: A case study

2017 ◽  
Vol 33 (2) ◽  
pp. 322-331 ◽  
Author(s):  
Anshu Dubey ◽  
Petros Tzeferacos ◽  
Don Q Lamb
Keyword(s):  
High Energy ◽  
High Energy Density ◽  
Core Collapse ◽  
Fluid Structure Interactions ◽  
Research Areas ◽  
Type Ia ◽  
Scientific Results ◽  
Ia Supernovae ◽  
The Impact

A significant fraction of computational software for scientific research grows through accretion. In a common scenario, a small group develops a code for a specific purpose. Others find the software useful, so they add to it for their own use. The software grows to the point where its management becomes intractable and scientific results obtained from it become unreliable. This is in stark contrast with a small number of scientific codes that have undergone a design process, be it due to an upfront investment, or when haphazardly grown codes have reset and started again. At a minimum, these codes reduce the time to obtain research results for the communities they serve because individual researchers do not have to develop their own codes. They provide further benefits; the results they produce are more reproducible due to greater scrutiny, leading to better science. One of the more overlooked benefits, which is perhaps of greater significance, is that a well-designed code can expand to serve communities beyond the ones it was designed for. Thus, research communities with similar computational requirements can symbiotically improve computation-based research for each other. In this article, we present a case study of FLASH, a code that was designed and developed for simulating thermonuclear runaways such as novae and type Ia supernovae in astrophysics. Designed to be modular and extensible, users from several diverse research areas have added capabilities to it and adapted it for their own communities. Examples include cosmology, high-energy density physics, core-collapse supernovae, star formation, fluid–structure interactions, and chemical combustion. We give a summary of design features that facilitated the expansion and quantify the effort needed to expand into some of the above-mentioned fields. We also quantify the impact on different communities by mining the database of publications using FLASH, collected by its developers.

Overview of astroparticle physics and dark matter searches

2007 ◽  
Vol 22 (31) ◽  
pp. 5735-5746
Author(s):  
Nathalie Palanque-Delabrouille
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Acoustic Oscillation ◽  
Type Ia Supernovae ◽  
Clusters Of Galaxies ◽  
Astroparticle Physics ◽  
The Status ◽  
Type Ia ◽  
Ia Supernovae ◽  
The Impact

We present a general overview of recent results in the searches for dark matter and dark energy. We discuss the observation of the collision between two clusters of galaxies, and the impact this has on the relevance of dark matter. We then present the final results from microlensing experiments, which aimed at detecting dark baryonic objects in the halo of our galaxy, and the status of direct searches for WIMPs. We present the evidence for dark energy which initially comes from experiments dedicated to the study of distant type Ia supernovae. The measure of the baryon acoustic oscillation, an independent probe of the evolution of our universe that has recently brought interesting constraints, is finally described.

scholarly journals A minority view on the majority: A personal meeting summary on the explosion mechanism of supernovae

2017 ◽  
Vol 12 (S331) ◽  
pp. 131-140
Author(s):  
Noam Soker
Keyword(s):  
Feedback Mechanism ◽  
Core Collapse ◽  
Negative Feedback Mechanism ◽  
The Core ◽  
Type Ia ◽  
Explosion Mechanism ◽  
Personal Meeting ◽  
Minority View ◽  
Ia Supernovae ◽  
Evolutionary Route

AbstractI present my minority view that the majority (or even all) of core collapse supernovae (CCSNe) are driven by jets rather than by neutrinos, and that the majority of type Ia supernovae (SN Ia) reach their explosion via the core degenerate scenario. New simulations presented at the meeting did not achieve an explosion of CCSNe. I critically examine other arguments that where presented in support of the neutrino-driven model, and present counter arguments that support the jet-driven explosion mechanism. The jets operate via a negative jet feedback mechanism (JFM). The negative feedback mechanism explains the explosion energy being several times the binding energy of the core in most CCSNe. We do not know yet what mechanism explodes massive stars and we do not know yet what evolutionary route leads white dwarfs to explode as SN Ia, and so we must be open to different ideas and critically examine old notions.

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