Simulation of stellar instabilities with vastly different timescales using domain decomposition

Strange mode instabilities in the envelopes of massive stars lead to shock waves, which can oscillate on a much shorter timescale than that associated with the primary instability. The phenomenon is studied by direct numerical simulation using a, with respect to time, implicit Lagrangian scheme, which allows for the variation by several orders of magnitude of the dependent variables. The timestep for the simulation of the system is reduced appreciably by the shock oscillations and prevents its long term study. A procedure based on domain decomposition is proposed to surmount the difficulty of vastly different timescales in various regions of the stellar envelope and thus to enable the desired long term simulations. Criteria for domain decomposition are derived and the proper treatment of the resulting inner boundaries is discussed. Tests of the approach are presented and its viability is demonstrated by application to a model for the star P Cygni. In this investigation primarily the feasibility of domain decomposition for the problem considered is studied. We intend to use the results as the basis of an extension to two dimensional simulations.Comment: 15 pages, 10 figures, published in MNRA

Potential effects of atmospheric collapse on Martian heat flow and application to the InSight measurements

Heat flow is an important constraint on planetary formation and evolution. It has been suggested that Martian obliquity cycles might cause periodic collapses in atmospheric pressure, leading to corresponding decreases in regolith thermal conductivity (which is controlled by gas in the pore spaces). Geothermal heat would then build up in the subsurface, potentially affecting present–day heat flow — and thus the measurements made by a heat–flow probe such as the InSight HP3 instrument. To gauge the order of magnitude of this effect, we model the diffusion of a putative heat pulse caused by thermal conductivity changes with a simple numerical scheme and compare it to the heat–flow perturbations caused by other effects. We find that an atmospheric collapse to 300 Pa in the last 40 kyr would lead to a present–day heat flow that is up to larger than the average geothermal background. Considering the InSight mission with expected error bars on the HP3 measurement, this perturbation would only be significant in the best-case scenario of full instrument deployment, completed measurement campaign, and a well–modelled surface configuration. The prospects for detecting long-term climate perturbations via spacecraft heat–flow experiments remain challenging

How large are present-day heat flux variations across the surface of Mars?

International audienc

Four Dimensional CFT Models with Rational Correlation Functions

Recently established rationality of correlation functions in a globally conformal invariant quantum field theory satisfying Wightman axioms is used to construct a family of soluble models in 4-dimensional Minkowski space-time. We consider in detail a model of a neutral scalar field $\phi$ of dimension 2. It depends on a positive real parameter c, an analogue of the Virasoro central charge, and admits for all (finite) c an infinite number of conserved symmetric tensor currents. The operator product algebra of $\phi$ is shown to coincide with a simpler one, generated by a bilocal scalar field $V(x_1,x_2)$ of dimension (1,1). The modes of V together with the unit operator span an infinite dimensional Lie algebra $L_V$ whose vacuum (i.e. zero energy lowest weight) representations only depend on the central charge c. Wightman positivity (i.e. unitarity of the representations of $L_V$) is proven to be equivalent to $c \in N$.Comment: 28 pages, LATEX, amsfonts, latexsym. Proposition 2.3, and Conjecture in Sec. 6 are revised. Minor errors are correcte

Phobos Regolith Simulant for MMX Mission: Spectral Measurement for Remote Target Identification and Deconvolution System Training

The two natural satellites of Mars, Phobos and Deimos are both important targets for scientific investigation. The JAXA mission Martian Moons eXplorer (MMX) is designed to explore Phobos and Deimos, with a launch date scheduled for 2024. The MMX spacecraft will observe both Martian moons and will land on one of them (Phobos, most likely), to collect a sample and bring it back to Earth. The designs of both the landing and sampling devices depend largely on the surface properties of the target body and on how its surface is reacting to an external action in the low gravity conditions of the target. The Landing Operation Working Team (LOWT) of MMX started analyzing previous observations and theoretical/experimental considerations to better understand the nature of Phobos surface material, developing a Phobos regolith simulant material for the MMX mission [1]. At the Institute for Planetary Research of the German aerospace Center (DLR) in Berlin we performed a spectral characterization of the Phobos regolith simulant. Those data will be used to train an Artificial Neural Network (NN) to produce a system that could rapidly classify data during the mission and for endmember decomposition

The century of the incomplete revolution: searching for general relativistic quantum field theory

In fundamental physics, this has been the century of quantum mechanics and general relativity. It has also been the century of the long search for a conceptual framework capable of embracing the astonishing features of the world that have been revealed by these two ``first pieces of a conceptual revolution''. I discuss the general requirements on the mathematics and some specific developments towards the construction of such a framework. Examples of covariant constructions of (simple) generally relativistic quantum field theories have been obtained as topological quantum field theories, in nonperturbative zero-dimensional string theory and its higher dimensional generalizations, and as spin foam models. A canonical construction of a general relativistic quantum field theory is provided by loop quantum gravity. Remarkably, all these diverse approaches have turn out to be related, suggesting an intriguing general picture of general relativistic quantum physics.Comment: To appear in the Journal of Mathematical Physics 2000 Special Issu

Macro-Porosity and Grain Density of C-Type Asteroid (162173) Ryugu

The Macroporosity of (162173) Ryugu is estimated based on the observed boulder size-frequency distribution

Phobos Environment Model and Regolith Simulant for MMX Mission

Phobos and Deimos, the two moons of Mars, are considered to be scientifically important and potential human mission's target. Martian Moons eXplorer (MMX) is the JAXA's mission to explore Phobos (and/or Deimos), which is scheduled to be launched in 2024. The main spacecraft of MMX will perform in-situ observations of both Phobos and Deimos, land on one of them (most likely, Phobos), and bring samples back to Earth. Small landing modules may be included in the mission as for the Hayabusa-2 mission. The designs of both the landing and sampling devices depend largely on the surface conditions of the target body and on how this surface reacts to an external action in the low gravity conditions of the target. Thus, the Landing Operation Working Team (LOWT) of MMX, which is composed of both scientists and engineers, is studying Phobos' surface based on previous observations and theoretical/experimental considerations. Though engineering motivation initiated this activity, the results will be extremely useful for scientific purposes

Stratigraphy and Geologic History of the InSight Landing Site, Mars

We describe the local stratigraphy and geologic history of a regolith-covered lava plain at the InSight landing site using orbital and lander observations