Magnetic recording stability of taenite-containing meteorites

Abstract Sub‐μm taenite and tetrataenite grains observed in a number of (stony‐)iron meteorite groups are promising sources of paleomagnetic records in meteorites. While slowly‐cooled meteorites form tetrataenite—an extremely good recorder—, fast‐cooled meteorites may contain fine‐grained taenite, which was considered unsuitable for paleomagnetic studies. In this work, however, we show that nm‐sized taenite grains are stable over billion‐year timescales, indicating that taenite‐bearing meteorites are reliable sources of paleomagnetic information. We find a range of sizes for which taenite forms stable single‐domain structures, which coincides with the grain sizes observed in the cloudy zone of most fast cooled IVA meteorites. These meteorites, therefore, can provide reliable paleomagnetic information recorded as a stable crystallization remanent magnetization as taenite grains grown. Vortex states observed in larger (>50 nm) grain sizes are also highly stable, indicating that coarse‐grained taenite observed in meteoritic microstructures can also provide reliable records of paleomagnetic fields

Reliable paleomagnetic records from single-vortex iron particles

Dusty olivine containing Fe-rich kamacite grains in chondrules can faithfully record the early solar magnetic fields. To retrieve paleointensity estimates, most experimental protocols are based on the dominance of uniformly magnetized single-domain (SD) particles. However, direct observation shows that most particles adopt a non-uniform magnetic structure. This inconsistency potentially represents a major impediment in reliably reconstructing ancient magnetic fields. Here we present a micromagnetic based model, the State Group Algorithm, that enables efficient simulations of thermoremanence acquisition in magnetic particles with single-vortex (SV) domain states. Our results show that these particles can acquire a thermoremanence that is linear proportional to the external field up to μ. They also have cooling rate effects that are generally weaker than those of SD particles. Notably, a small subset of SV particles can exhibit negative cooling rate effects, leading to underestimates in paleointensity. We conclude that SV particles are reliable paleomagnetic recorders

Propositional Tree Automata

In the paper, we introduce a new tree automata framework, called propositional tree automata, capturing the class of tree languages that are closed under an equational theory and Boolean operations. This framework originates in work on developing a sufficient completeness checker for specifications with rewriting modulo an equational theory. Propositional tree automata recognize regular equational tree languages. However, unlike regular equational tree automata, the class of propositional tree automata is closed under Boolean operations. This extra expressiveness does not affect the decidability of the membership problem. This paper also analyzes in detail the emptiness problem for propositional tree automata with associative theories. Though undecidable in general, we present a semi-algorithm for checking emptiness based on machine learning that we have found useful in practice

Co-design and refinement for safety critical systems

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Set-Based Analysis for Logic Programming and Tree Automata

. Compile-time program analysis aims to extract from a program properties useful for efficient implementations and sofware verification. A property of interest is the computational semantics of a program. For decidability reasons, only an approximation of this semantics can be computed. Set-based analysis [Hei92a] provides an elegant and accurate method for this. In the logic programming framework, this computation can be related to type inference [MR85]. In [FSVY91], a simpler presentation based on program transformation and algorithms on alternating tree automata is proposed. Unfortunately, the authors focussed on type checking (i:e: a membership test to the approximate semantics). We propose in this paper a new method to achieve set-based analysis reusing the main transformation described in [FSVY91]. The main tool for both computation and representation of the result of set-based analysis is tree automata. This leads to a global and coherent presentation of the problem of set-based..

Prolog program transformations and meta-interpreters

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Termination induction by means of an abstract OLDT resolution

National audienc

Toward optimization of full Prolog programs guided by abstract interpretation

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