On the Evolution of Stars that Form Electron‐degenerate Cores Processed by Carbon Burning. IV. Outward Mixing During the Second Dredge‐up Phase and Other Properties of a 10.5M☉Model Star

Pd-Pt catalysts supported on carbon preheated to 1600°C have been reinvestigated in CHFCl2 hydrodechlorination. An additionally adopted catalyst oxidation at 350-400°C produced an order of magnitude increase in the catalytic activity of Pd/C. This increase is not caused by changes in metal dispersion or possible decontamination of the Pd surface from superficial carbon, but rather by unlocking the active surface, originally inaccessible in metal particles tightly packed in the pores of carbon. Burning carbon from the pore walls attached to the metal changes the pore structure, providing easier access for the reactants to the entire palladium surface. As upon calcination the performance of the rest of the Pd-Pt/C catalysts changes less than for Pd/C, the relation between the turnover frequency and alloy composition does not confirm the Pd-Pt synergy invoked in our previous work. The use of even higher-preheated carbon (1800°C), completely free of micropores, results in a Pd/C catalyst that does not need to be oxidized to achieve high activity and excellent selectivity up to CH2F2 (>90%).

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Hypothesis of Twin Deficits in Cote d’Ivoire: The Nonlinear Effect Analysis with a Smooth Transition Autoregression Model (STAR)

Applied Economics and Finance ◽

10.11114/aef.v8i1.5108 ◽

2020 ◽

Vol 8 (1) ◽

pp. 59

Author(s):

GREKOU Gahié Lopez

Keyword(s):

Current Account ◽

Cote D'ivoire ◽

Côte D’Ivoire ◽

Smooth Transition ◽

Budget Balance ◽

Cote D’Ivoire ◽

Effect Analysis ◽

Côte D'ivoire ◽

Model Star ◽

Double Deficit

This paper tests the hypothesis of double deficit in Côte d'Ivoire in non-linear aid framework, using an autoregressive smooth transition model (STAR). The main results validate the hypothesis of double deficit in Côte d' Ivoire. The effect of current balance on budget balance is greater than budget balance on current balance. Moreover, the rapid effects of current account instability on fiscal balance reveal the lack of expectation by economic agents that leads to current account deterioration compared to the deterioration of budget balance. Thus, economic policies aimed at influencing the effect on current balance would be more effective than those aimed at the effect on budget balance. In other words, Ivorian economy adopts a Keynesian performance in the event of current account shocks and performance that tend to be more or less Ricardian in presence of fiscal policy shock.

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On the Electrochemistry and Spectroelectrochemistry of Small Model Star-Shaped Compounds: 1,3,5-Triaryl-1-Methoxybenzenes and 2,4,6-Triaryl-1,3,5-Trimethoxybenzenes

ChemPhysChem ◽

10.1002/cphc.201200127 ◽

2012 ◽

Vol 13 (9) ◽

pp. 2322-2330 ◽

Cited By ~ 6

Author(s):

Peter Rapta ◽

Vladimír Lukeš ◽

Krzysztof R. Idzik ◽

Rainer Beckert ◽

Lothar Dunsch

Keyword(s):

Model Star ◽

Small Model

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Resonance Effects in Carbon Burning Process on Type Ia Supernovae

EPJ Web of Conferences ◽

10.1051/epjconf/201818402011 ◽

2018 ◽

Vol 184 ◽

pp. 02011

Author(s):

Kanji Mori ◽

Michael Famiano ◽

Toshitaka Kajino

Keyword(s):

Reaction Rate ◽

Low Energy ◽

Type Ia Supernovae ◽

Resonance Strength ◽

Resonance Effects ◽

Type Ia ◽

Binary Mergers ◽

Standard Rate ◽

Ia Supernovae ◽

Carbon Burning

The 12C+12C reaction plays an important role in type Ia supernovae. However, its cross section with astrophysical low energy has not been measured. If there is an unknown resonance in the low energy region, the reaction rate is enhanced and can affect astrophysics. We impose an upper limit to the resonance strength using the Wigner limit and find that the reaction rate can be larger than a standard rate by ~ 103 times in astrophysical temperature. We apply this enhanced reaction rate to binary mergers of two white dwarfs (WDs). We find that the fate of WD-WD mergers changes due to the resonance. The accretion induced collapse to neutron stars becomes more likely to occur, while it becomes more diffcult to explain SNe Ia from WD-WD mergers.

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The evolution of ultra-massive white dwarfs

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833822 ◽

2019 ◽

Vol 625 ◽

pp. A87 ◽

Cited By ~ 22

Author(s):

María E. Camisassa ◽

Leandro G. Althaus ◽

Alejandro H. Córsico ◽

Francisco C. De Gerónimo ◽

Marcelo M. Miller Bertolami ◽

...

Keyword(s):

Phase Separation ◽

White Dwarf ◽

White Dwarfs ◽

Outer Boundary ◽

Asymptotic Giant Branch ◽

Type Ia ◽

Chemical Profiles ◽

Supernova Explosions ◽

Carbon Burning ◽

The Impact

Ultra-massive white dwarfs are powerful tools used to study various physical processes in the asymptotic giant branch (AGB), type Ia supernova explosions, and the theory of crystallization through white dwarf asteroseismology. Despite the interest in these white dwarfs, there are few evolutionary studies in the literature devoted to them. Here we present new ultra-massive white dwarf evolutionary sequences that constitute an improvement over previous ones. In these new sequences we take into account for the first time the process of phase separation expected during the crystallization stage of these white dwarfs by relying on the most up-to-date phase diagram of dense oxygen/neon mixtures. Realistic chemical profiles resulting from the full computation of progenitor evolution during the semidegenerate carbon burning along the super-AGB phase are also considered in our sequences. Outer boundary conditions for our evolving models are provided by detailed non-gray white dwarf model atmospheres for hydrogen and helium composition. We assessed the impact of all these improvements on the evolutionary properties of ultra-massive white dwarfs, providing updated evolutionary sequences for these stars. We conclude that crystallization is expected to affect the majority of the massive white dwarfs observed with effective temperatures below 40 000 K. Moreover, the calculation of the phase separation process induced by crystallization is necessary to accurately determine the cooling age and the mass-radius relation of massive white dwarfs. We also provide colors in the Gaia photometric bands for our H-rich white dwarf evolutionary sequences on the basis of new model atmospheres. Finally, these new white dwarf sequences provide a new theoretical frame to perform asteroseismological studies on the recently detected ultra-massive pulsating white dwarfs.

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Massive stars burning helium: the numbers of WR stars and red supergiants in galaxies

International Astronomical Union Colloquium ◽

10.1017/s0252921100094896 ◽

1981 ◽

Vol 59 ◽

pp. 283-287

Author(s):

A. Maeder

Keyword(s):

Mass Loss ◽

Massive Stars ◽

Short Note ◽

Evolutionary Models ◽

Helium Burning ◽

Red Supergiants ◽

Low Mass ◽

Age Sequence ◽

Carbon Burning ◽

Loss Rates

We have calculated evolutionary models of massive stars in the range 15-120 Mʘ from the zero-age sequence up to the end of the carbon burning stage (Maeder, 1981). Three sets of models with different mass loss rates Ṁ have been computed; the adopted parametrisation of Ṁ is fitted on the observations and thus the expression for Ṁ differs according to the location of the stars in the HRD.In this short note we concentrate on the location of the He-burning stars in the HRD. The helium burning phase, which lasts 8 to 10% of the MS phase, is spent mainly as red supergiants (RSG) and as WR stars (note that for low mass loss, the time spent as A-G supergiants becomes longer).

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Evolution with Neutrino Loss of a Massive Star until the Onset of Carbon Burning.

The Astronomical Journal ◽

10.1086/109424 ◽

1964 ◽

Vol 69 ◽

pp. 140 ◽

Cited By ~ 3

Author(s):

Chushiro Hayashi ◽

Robert C. Cameron

Keyword(s):

Massive Star ◽

Carbon Burning

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