scholarly journals Relative importance of convective uncertainties in massive stars

2020 ◽  
Vol 496 (2) ◽  
pp. 1967-1989 ◽  
Author(s):  
Etienne A Kaiser ◽  
Raphael Hirschi ◽  
W David Arnett ◽  
Cyril Georgy ◽  
Laura J A Scott ◽  
...  
Keyword(s):  
Convective Zone ◽  
Stellar Structure ◽  
Convective Boundary ◽  
Hydrogen Burning ◽  
Surface Evolution ◽  
Boundary Mixing ◽  
The Core ◽  
Boundary Location ◽  
Parameter Values ◽  
The Impact

ABSTRACT In this work, we investigate the impact of uncertainties due to convective boundary mixing (CBM), commonly called ‘overshoot’, namely the boundary location and the amount of mixing at the convective boundary, on stellar structure and evolution. For this we calculated two grids of stellar evolution models with the MESA code, each with the Ledoux and the Schwarzschild boundary criterion, and vary the amount of CBM. We calculate each grid with the initial masses of 15, 20, and $25\, \rm {M}_\odot$. We present the stellar structure of the models during the hydrogen and helium burning phases. In the latter, we examine the impact on the nucleosynthesis. We find a broadening of the main sequence with more CBM, which is more in agreement with observations. Furthermore, during the core hydrogen burning phase there is a convergence of the convective boundary location due to CBM. The uncertainties of the intermediate convective zone remove this convergence. The behaviour of this convective zone strongly affects the surface evolution of the model, i.e. how fast it evolves redwards. The amount of CBM impacts the size of the convective cores and the nucleosynthesis, e.g. the 12C to 16O ratio and the weak s-process. Lastly, we determine the uncertainty that the range of parameter values investigated introduces and we find differences of up to $70{{\ \rm per\ cent}}$ for the core masses and the total mass of the star.

scholarly journals 3D Simulations of Oxygen Shell Burning with and without Magnetic Fields

2021 ◽  
Author(s):  
Vishnu Varma ◽  
Bernhard Müller
Keyword(s):  
Magnetic Fields ◽  
Field Strength ◽  
Stress Tensor ◽  
Convective Flow ◽  
Core Collapse ◽  
Convective Boundary ◽  
Maxwell Stress Tensor ◽  
Boundary Mixing ◽  
Order Of Magnitude ◽  
The Impact

Abstract We present a first 3D magnetohydrodynamic (MHD) simulation of convective oxygen and neon shell burning in a non-rotating 18 M⊙ star shortly before core collapse to study the generation of magnetic fields in supernova progenitors. We also run a purely hydrodynamic control simulation to gauge the impact of the magnetic fields on the convective flow and on convective boundary mixing. After about 17 convective turnover times, the magnetic field is approaching saturation levels in the oxygen shell with an average field strength of $\mathord {\sim }10^{10}\, \mathrm{G}$, and does not reach kinetic equipartition. The field remains dominated by small to medium scales, and the dipole field strength at the base of the oxygen shell is only 109 G. The angle-averaged diagonal components of the Maxwell stress tensor mirror those of the Reynolds stress tensor, but are about one order of magnitude smaller. The shear flow at the oxygen-neon shell interface creates relatively strong fields parallel to the convective boundary, which noticeably inhibit the turbulent entrainment of neon into the oxygen shell. The reduced ingestion of neon lowers the nuclear energy generation rate in the oxygen shell and thereby slightly slows down the convective flow. Aside from this indirect effect, we find that magnetic fields do not appreciably alter the flow inside the oxygen shell. We discuss the implications of our results for the subsequent core-collapse supernova and stress the need for longer simulations, resolution studies, and an investigation of non-ideal effects for a better understanding of magnetic fields in supernova progenitors.

scholarly journals Linking 1D Stellar Evolution to 3D Hydrodynamic Simulations

2014 ◽  
Vol 9 (S307) ◽  
pp. 98-99 ◽  
Author(s):  
A. Cristini ◽  
R. Hirschi ◽  
C. Georgy ◽  
C. Meakin ◽  
D. Arnett ◽  
...  
Keyword(s):  
Stellar Evolution ◽  
Richardson Number ◽  
Front Propagation ◽  
Bulk Richardson Number ◽  
Convective Boundary ◽  
Hydrodynamic Simulations ◽  
Boundary Mixing ◽  
The Core ◽  
Convective Boundaries ◽  
Initial Results

AbstractIn this contribution we present initial results of a study on convective boundary mixing (CBM) in massive stellar models using the GENEVA stellar evolution code (Eggenbergeret al.2008). Before undertaking costly 3D hydrodynamic simulations, it is important to study the general properties of convective boundaries, such as the: composition jump; pressure gradient; and “stiffness”. Models for a 15M⊙star were computed. We found that for convective shells above the core, the lower (in radius or mass) boundaries are “stiffer” according to the bulk Richardson number than the relative upper (Schwarzschild) boundaries. Thus, we expect reduced CBM at the lower boundaries in comparison to the upper. This has implications on flame front propagation and the onset of novae.

Soziale Disziplinierung im flexiblen Kapitalismus

2004 ◽  
Vol 34 (136) ◽  
pp. 339-356
Author(s):  
Tobias Wölfle ◽  
Oliver Schöller
Keyword(s):  
Social Welfare ◽  
Second Step ◽  
Social Rights ◽  
Federal Law ◽  
Capitalist Development ◽  
The Core ◽  
The Past ◽  
The Impact ◽  
Municipal Level

Under the term “Hilfe zur Arbeit” (aid for work) the federal law of social welfare subsumes all kinds of labour disciplining instruments. First, the paper shows the historical connection of welfare and labour disciplining mechanisms in the context of different periods within capitalist development. In a second step, against the background of historical experiences, we will analyse the trends of “Hilfe zur Arbeit” during the past two decades. It will be shown that by the rise of unemployment, the impact of labour disciplining aspects of “Hilfe zur Arbeit” has increased both on the federal and on the municipal level. For this reason the leverage of the liberal paradigm would take place even in the core of social rights.

Heterotrophic Kinetic Parameter Estimation for Enhanced Biological Phosphorus Removal Processes Operated in Conventional and Membrane-Assisted Modes

2006 ◽  
Vol 41 (1) ◽  
pp. 72-83 ◽  
Author(s):  
Zhe Zhang ◽  
Eric R. Hall
Keyword(s):  
Parameter Estimation ◽  
Phosphorus Removal ◽  
Growth Yield ◽  
Pilot Scale ◽  
Enhanced Biological Phosphorus Removal ◽  
Biological Phosphorus Removal ◽  
Nitrogen And Phosphorus ◽  
Parameter Values ◽  
The Impact ◽  
Biological Phosphorus

Abstract Parameter estimation and wastewater characterization are crucial for modelling of the membrane enhanced biological phosphorus removal (MEBPR) process. Prior to determining the values of a subset of kinetic and stoichiometric parameters used in ASM No. 2 (ASM2), the carbon, nitrogen and phosphorus fractions of influent wastewater at the University of British Columbia (UBC) pilot plant were characterized. It was found that the UBC wastewater contained fractions of volatile acids (SA), readily fermentable biodegradable COD (SF) and slowly biodegradable COD (XS) that fell within the ASM2 default value ranges. The contents of soluble inert COD (SI) and particulate inert COD (XI) were somewhat higher than ASM2 default values. Mixed liquor samples from pilot-scale MEBPR and conventional enhanced biological phosphorus removal (CEBPR) processes operated under parallel conditions, were then analyzed experimentally to assess the impact of operation in a membrane-assisted mode on the growth yield (YH), decay coefficient (bH) and maximum specific growth rate of heterotrophic biomass (µH). The resulting values for YH, bH and µH were slightly lower for the MEBPR train than for the CEBPR train, but the differences were not statistically significant. It is suggested that MEBPR simulation using ASM2 could be accomplished satisfactorily using parameter values determined for a conventional biological phosphorus removal process, if MEBPR parameter values are not available.

Citizen Deliberation Online

2019 ◽  
pp. 689-712
Author(s):  
Patrícia Rossini ◽  
Jennifer Stromer-Galley
Keyword(s):  
Political Engagement ◽  
Future Research ◽  
The Internet ◽  
Digital Platforms ◽  
The Core ◽  
Political Conversation ◽  
Political Talk ◽  
Citizen Deliberation ◽  
The Impact

Political conversation is at the heart of democratic societies, and it is an important precursor of political engagement. As society has become intertwined with the communication infrastructure of the Internet, we need to understand its uses and the implications of those uses for democracy. This chapter provides an overview of the core topics of scholarly concern around online citizen deliberation, focusing on three key areas of research: the standards of quality of communication and the normative stance on citizen deliberation online; the impact and importance of digital platforms in structuring political talk; and the differences between formal and informal political talk spaces. After providing a critical review of these three major areas of research, we outline directions for future research on online citizen deliberation.

Static and dynamic response of sandwich beams with lattice and pantographic cores

2021 ◽  
pp. 109963622110338
Author(s):  
Yury Solyaev ◽  
Arseniy Babaytsev ◽  
Anastasia Ustenko ◽  
Andrey Ripetskiy ◽  
Alexander Volkov
Keyword(s):  
Mechanical Performance ◽  
Lattice Structure ◽  
Unit Length ◽  
Experimental Tests ◽  
Plane Geometry ◽  
Sandwich Beams ◽  
Static Tests ◽  
Three Point Bending ◽  
The Core ◽  
The Impact

Mechanical performance of 3d-printed polyamide sandwich beams with different type of the lattice cores is investigated. Four variants of the beams are considered, which differ in the type of connections between the elements in the lattice structure of the core. We consider the pantographic-type lattices formed by the two families of inclined beams placed with small offset and connected by stiff joints (variant 1), by hinges (variant 2) and made without joints (variant 3). The fourth type of the core has the standard plane geometry formed by the intersected beams lying in the same plane (variant 4). Experimental tests were performed for the localized indentation loading according to the three-point bending scheme with small span-to-thickness ratio. From the experiments we found that the plane geometry of variant 4 has the highest rigidity and the highest load bearing capacity in the static tests. However, other three variants of the pantographic-type cores (1–3) demonstrate the better performance under the impact loading. The impact strength of such structures are in 3.5–5 times higher than those one of variant 4 with almost the same mass per unit length. This result is validated by using numerical simulations and explained by the decrease of the stress concentration and the stress state triaxiality and also by the delocalization effects that arise in the pantographic-type cores.

Comparative crosstalk performance analysis of different configurations of heterogeneous multicore fiber

2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Umar Farooque ◽  
Rakesh Ranjan
Keyword(s):  
Refractive Index ◽  
Mode Coupling ◽  
The Other ◽  
Heterogeneous Multicore ◽  
Coupled Mode ◽  
The Core ◽  
Bending Radius ◽  
Multicore Fiber ◽  
The Impact ◽  
Core Pitch

AbstractIn order to select the heterogeneous multicore fiber (MCF) configuration with ultra-low crosstalk and low peak bending radius, comparative crosstalk analysis have been done for the three possible core configurations, namely, Configuration 1 - different refractive index (R.I.) and different radius, Configuration 2 - different R.I., and Configuration 3 - different radius. Using the coupled mode equation and the simplified expressions of mode coupling coefficient (MCC) for different configurations of heterogeneous cores, the crosstalk performance of all the heterogeneous MCF configurations along with the homogeneous MCF have been investigated analytically with respect to core pitch (D) and fiber bending radius (${R}_{b}$). Further, these expressions of MCC have been extended to obtain the simplified expressions of MCC for the estimation of crosstalk levels in respective trench-assisted (TA) heterogeneous MCF configurations. It is observed from the analysis that in Configuration 1, crosstalk level is lowest and the rate of decrease in the crosstalk with respect to the core pitch is highest compared to the other configurations of heterogeneous MCF. The values of crosstalk obtained analytically have been validated by comparing it with the values obtained from finite element method (FEM) based numerical simulation results. Further, we have investigated the impact of a fixed percent change (5%) in the core parameters (radius and/or R.I.) of one of the core of a homogeneous MCF, to realize the different heterogeneous MCF configurations, on the variations in crosstalk levels, difference in the mode effective refractive index of the core 1 and core 2 ($\Delta {n}_{eff}={n}_{eff1}-{n}_{eff2}$), and the peak bending radius (${R}_{pk}$). For the same percent variations (5%) in the core parameters (radius and/or R.I.) of different configurations of cores (Config. 1-Config. 3), Config. 1 MCF has highest variation in $\Delta {n}_{eff}$ value compared to other configurations of MCF. Further, this highest variation in $\Delta {n}_{eff}$ value of Config. 1 MCF results in smallest peak bending radius. The smaller value of peak bending radius allows MCF to bend into smaller radius. Therefore, Configuration 1 is the potential choice for the design of MCF with smaller peak bending radius and ultra-low crosstalk level compared to the other configurations of SI-heterogeneous MCF.

scholarly journals Formation of GW190521 from stellar evolution: the impact of the hydrogen-rich envelope, dredge-up and 12C(α, γ)16O rate on the pair-instability black hole mass gap

2020 ◽  
Author(s):  
Guglielmo Costa ◽  
Alessandro Bressan ◽  
Michela Mapelli ◽  
Paola Marigo ◽  
Giuliano Iorio ◽  
...  
Keyword(s):  
Stellar Evolution ◽  
Reaction Rate ◽  
Primary Component ◽  
Mass Reduction ◽  
Black Hole Mass ◽  
Core Mass ◽  
The Core ◽  
Mass Gap ◽  
M Stars ◽  
The Impact

Abstract Pair-instability (PI) is expected to open a gap in the mass spectrum of black holes (BHs) between ≈40 − 65 M⊙ and ≈120 M⊙. The existence of the mass gap is currently being challenged by the detection of GW190521, with a primary component mass of $85^{+21}_{-14}$ M⊙. Here, we investigate the main uncertainties on the PI mass gap: the 12C(α, γ)16O reaction rate and the H-rich envelope collapse. With the standard 12C(α, γ)16O rate, the lower edge of the mass gap can be 70 M⊙ if we allow for the collapse of the residual H-rich envelope at metallicity Z ≤ 0.0003. Adopting the uncertainties given by the starlib database, for models computed with the 12C(α, γ)16O rate −1 σ, we find that the PI mass gap ranges between ≈80 M⊙ and ≈150 M⊙. Stars with MZAMS > 110 M⊙ may experience a deep dredge-up episode during the core helium-burning phase, that extracts matter from the core enriching the envelope. As a consequence of the He-core mass reduction, a star with MZAMS = 160 M⊙ may avoid the PI and produce a BH of 150 M⊙. In the −2 σ case, the PI mass gap ranges from 92 M⊙ to 110 M⊙. Finally, in models computed with 12C(α, γ)16O −3 σ, the mass gap is completely removed by the dredge-up effect. The onset of this dredge-up is particularly sensitive to the assumed model for convection and mixing. The combined effect of H-rich envelope collapse and low 12C(α, γ)16O rate can lead to the formation of BHs with masses consistent with the primary component of GW190521.

scholarly journals A numerical study of the impact perforation of sandwich panels with graded hollow sphere cores

2021 ◽  
Vol 13 (4) ◽  
pp. 168781402110094
Author(s):  
Ibrahim Elnasri ◽  
Han Zhao
Keyword(s):  
Boundary Conditions ◽  
Hollow Sphere ◽  
Sandwich Panel ◽  
Numerical Study ◽  
Sandwich Panels ◽  
Hopkinson Bar ◽  
Core Density ◽  
The Core ◽  
The Impact ◽  
Force Displacement

In this study, we numerically investigate the impact perforation of sandwich panels made of 0.8 mm 2024-T3 aluminum alloy skin sheets and graded polymeric hollow sphere cores with four different gradient profiles. A suitable numerical model was conducted using the LS-DYNA code, calibrated with an inverse perforation test, instrumented with a Hopkinson bar, and validated using experimental data from the literature. Moreover, the effects of quasi-static loading, landing rates, and boundary conditions on the perforation resistance of the studied graded core sandwich panels were discussed. The simulation results showed that the piercing force–displacement response of the graded core sandwich panels is affected by the core density gradient profiles. Besides, the energy absorption capability can be effectively enhanced by modifying the arrangement of the core layers with unclumping boundary conditions in the graded core sandwich panel, which is rather too hard to achieve with clumping boundary conditions.

Development of a Commercial Wireline Retrievable Coring System

1998 ◽  
Vol 1 (06) ◽  
pp. 489-495 ◽  
Author(s):  
Tommy Warren ◽  
Jim Powers ◽  
David Bode ◽  
Eric Carre ◽  
Lee Smith
Keyword(s):  
Economic Evaluation ◽  
Coalbed Methane ◽  
Technical Conference ◽  
The Core ◽  
Core Recovery ◽  
Drilling Equipment ◽  
Original Manuscript ◽  
The Impact ◽  
Conventional Drilling ◽  
Target Depth

This paper (SPE 52993) was revised for publication from paper SPE 36536, first presented at the 1996 SPE Annual Technical Conference and Exhibition, Denver, 6-9 October. Original manuscript received for review 11 October 1996. Revised manuscript received 22 September 1998. Paper peer approved 23 September 1998. Summary A Wireline retrievable coring system for use with conventional drilling equipment is described. The coring system was developed and tested for application in evaluating coalbed methane prospects where a large quantity of core is required, and it is essential that the core is processed soon after it is cut. A drill plug allows for alternation between coring and drilling without tripping the drillstring. The system is particularly advantageous for coring long intervals, multiple zones relatively close together, or when the exact target depth is unknown. The system has been used to core more than 4940 m (15,057 ft) in Poland, Germany, and France, with a combined core recovery of 94%. In addition, the impact of varying rig costs on total savings is factored into the overall economic evaluation of the system. P. 489

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