Progenitors of Core-Collapse Supernovae

Massive stars have a strong impact on their surroundings, in particular when they produce a core-collapse supernova at the end of their evolution. In these proceedings, we review the general evolution of massive stars and their properties at collapse as well as the transition between massive and intermediate-mass stars. We also summarise the effects of metallicity and rotation. We then discuss some of the major uncertainties in the modelling of massive stars, with a particular emphasis on the treatment of convection in 1D stellar evolution codes. Finally, we present new 3D hydrodynamic simulations of convection in carbon burning and list key points to take from 3D hydrodynamic studies for the development of new prescriptions for convective boundary mixing in 1D stellar evolution codes.Comment: 10 pages, 5 figures, "SN 1987A, 30 years later", Proceedings IAU Symposium No. 331, 2017; A. Marcowith, G. Dubner, A. Ray, A. Bykov, & M. Renaud, ed

Gas flow in near surface comet like porous structures: Application to 67P/Churyumov-Gerasimenko

We performed an investigation of a comet like porous surface to study how sub-surface sublimation with subsequent flow through the porous medium can lead to higher gas temperatures at the surface. A higher gas temperature of the emitted gas at the surface layer, compared to the sublimation temperature, will lead to higher gas speeds as the gas expands into the vacuum thus altering the flow properties on larger scales (kilometres away from the surface). Unlike previous models that have used modelled artificial structures, we used Earth rock samples with a porosity in the range 24 – 92 % obtained from X-ray micro computed tomography (micro-CT) scans with resolution of some μm. Micro-CT scanning technology provides 3D images of the pore samples. The direct simulation Monte Carlo (DSMC) method for the rarefied gas dynamics is directly applied on the digital rock samples in an unstructured mesh to determine the gas densities, temperatures and speeds within the porous medium and a few centimetres above the surface. The thicknesses of the rock samples were comparable to the diurnal thermal skin depth (5cm). H2O was assumed to be the outgassing species. We correlated the coma temperatures and other properties of the flow with the rock porosities. The results are discussed as an input to analysis of data from the Microwave Instrument on Rosetta Orbiter (MIRO) on the 67P/Churyumov-Gerasimenko

Numerical Tests of the Fokas Method for Helmholtz-type Partial Differential Equations: Dirichlet to Neumann Maps

A method for solving boundary value problems for linear partial differential equations in convex polygons developed by A.S. Fokas in the late 1990s is introduced. In order to solve well-posed boundary value problems using the novel Fokas approach, certain global relations must be derived. These global relations yield so-called Dirichlet to Neumann maps which not only allow us to solve Helmholtz-type PDEs using the Fokas method, but they are also of interest in their own right. Given a convex polygon and a prescribed set of boundary conditions associated with a PDE, the Dirichlet to Neumann map enables us to numerically recover unknown boundary conditions with relatively high accuracy without solving the PDE on the interior. The numerical implementation of the Dirichlet to Neumann map is shown to be an efficient and accurate method for resolving unknown boundary conditions. The map is also analyzed and certain parameters are optimized. With an accurate Dirichlet to Neumann map, solving the modified Helmholtz and the Helmholtz equations via the Fokas method becomes possible

A study of two stochastic search methods for structural control

Abstract: Many engineering tasks involve the search for good solutions among many possibilities. In most cases, tasks are too complex to be modeled completely and their solution spaces often contain local minima. Therefore, classical optimization techniques cannot, in general, be applied effectively. This paper studies two stochastic search methods, one well-established �simulated annealing � and one recently developed �probabilistic global search Lausanne�, applied to structural shape control. Search results are applied to control the quasistatic displacement of a tensegrity structure with multiple objectives and interdependent actuator effects. The best method depends on the accuracy related to requirements defined by the objective function and the maximum number of evaluations that are allowed

High-Performance Data Mapping for BNNs on PCM-based Integrated Photonics

State-of-the-Art (SotA) hardware implementations of Deep Neural Networks (DNNs) incur high latencies and costs. Binary Neural Networks (BNNs) are potential alternative solutions to realize faster implementations without losing accuracy. In this paper, we first present a new data mapping, called TacitMap, suited for BNNs implemented based on a Computation-In-Memory (CIM) architecture. TacitMap maximizes the use of available parallelism, while CIM architecture eliminates the data movement overhead. We then propose a hardware accelerator based on optical phase change memory (oPCM) called EinsteinBarrier. Ein-steinBarrier incorporates TacitMap and adds an extra dimension for parallelism through wavelength division multiplexing, leading to extra latency reduction. The simulation results show that, compared to the SotA CIM baseline, TacitMap and EinsteinBarrier significantly improve execution time by up to ~154x and ~3113x, respectively, while also maintaining the energy consumption within 60% of that in the CIM baseline.Comment: To appear in Design Automation and Test in Europe (DATE), 202