Temporal evolution of magnetic molecular shocks I. Moving grid simulations

We present time-dependent 1D simulations of multifluid magnetic shocks with chemistry resolved down to the mean free path. They are obtained with an adaptive moving grid implemented with an implicit scheme. We examine a broad range of parameters relevant to conditions in dense molecular clouds, with preshock densities between 10^3 and 10^5 cm-3, velocities between 10 and 40 km/s, and three different scalings for the transverse magnetic field: B=0,0.1,1 \mu G \sqrt{n.cm3}. We first use this study to validate the results of Chi\`eze, Pineau des For\^ets & Flower (1998), in particular the long delays necessary to obtain steady C-type shocks, and we provide evolutionary time-scales for a much greater range of parameters. We also present the first time-dependent models of dissociative shocks with a magnetic precursor, including the first models of stationary CJ shocks in molecular conditions. We find that the maximum speed for steady C-type shocks is reached before the occurrence of a sonic point in the neutral fluid, unlike previously thought. As a result, the maximum speed for C-shocks is lower than previously believed. Finally, we find a large amplitude bouncing instability in J-type fronts near the H2 dissociation limit (u ~ 25-30 km/s), driven by H2 dissociation/reformation. At higher speeds, we find an oscillatory behaviour of short period and small amplitude linked to collisional ionisation of H. Both instabilities are suppressed after some time when a magnetic field is present. In a companion paper, we use the present simulations to validate a new semi-analytical construction method for young low-velocity magnetic shocks based on truncated steady-state models.Comment: A&A in pres

Dense molecular globulettes and the dust arc towards the runaway O star AE Aur (HD 34078)

Some runaway stars are known to display IR arc-like structures around them, resulting from their interaction with surrounding interstellar material. The properties of these features as well as the processes involved in their formation are still poorly understood. We aim at understanding the physical mechanisms that shapes the dust arc observed near the runaway O star AEAur (HD34078). We obtained and analyzed a high spatial resolution map of the CO(1-0) emission that is centered on HD34078, and that combines data from both the IRAM interferometer and 30m single-dish antenna. The line of sight towards HD34078 intersects the outer part of one of the detected globulettes, which accounts for both the properties of diffuse UV light observed in the field and the numerous molecular absorption lines detected in HD34078's spectra, including those from highly excited H2 . Their modeled distance from the star is compatible with the fact that they lie on the 3D paraboloid which fits the arc detected in the 24 {\mu}m Spitzer image. Four other compact CO globulettes are detected in the mapped area. These globulettes have a high density and linewidth, and are strongly pressure-confined or transient. The good spatial correlation between the CO globulettes and the IR arc suggests that they result from the interaction of the radiation and wind emitted by HD 34078 with the ambient gas. However, the details of this interaction remain unclear. A wind mass loss rate significantly larger than the value inferred from UV lines is favored by the large IR arc size, but does not easily explain the low velocity of the CO globulettes. The effect of radiation pressure on dust grains also meets several issues in explaining the observations. Further observational and theoretical work is needed to fully elucidate the processes shaping the gas and dust in bow shocks around runaway O stars. (Abridged)Comment: Accepted for publication in Astronomy & Astrophysic

Three-stream 3D/1D CNN for fine-grained action classification and segmentation in table tennis

This paper proposes a fusion method of modalities extracted from videothrough a three-stream network with spatio-temporal and temporal convolutionsfor fine-grained action classification in sport. It is applied to TTStroke-21dataset which consists of untrimmed videos of table tennis games. The goal isto detect and classify table tennis strokes in the videos, the first step of abigger scheme aiming at giving feedback to the players for improving theirperformance. The three modalities are raw RGB data, the computed optical flowand the estimated pose of the player. The network consists of three brancheswith attention blocks. Features are fused at the latest stage of the networkusing bilinear layers. Compared to previous approaches, the use of threemodalities allows faster convergence and better performances on both tasks:classification of strokes with known temporal boundaries and joint segmentationand classification. The pose is also further investigated in order to offerricher feedback to the athletes.<br

Collisional excitation of water by hydrogen atoms

We present quantum dynamical calculations that describe the rotational excitation of H$_2$O due to collisions with H atoms. We used a recent, high accuracy potential energy surface, and solved the collisional dynamics with the close-coupling formalism, for total energies up to 12 000 cm$^{-1}$. From these calculations, we obtained collisional rate coefficients for the first 45 energy levels of both ortho- and para-H$_2$O and for temperatures in the range T = 5-1500 K. These rate coefficients are subsequently compared to the values previously published for the H$_2$O / He and H$_2$O / H$_2$ collisional systems. It is shown that no simple relation exists between the three systems and that specific calculations are thus mandatory

Temporal evolution of magnetic molecular shocks II. Analytics of the steady state and semi-analytical construction of intermediate ages

In the first paper of this series (Paper I) we computed time dependent simulations of multifluid shocks with chemistry and a transverse magnetic field frozen in the ions, using an adaptive moving grid. In this paper, we present new analytical results on steady-state molecular shocks. Relationships between density and pressure in the neutral fluid are derived for the cold magnetic precursor, hot magnetic precursor, adiabatic shock front, and the following cooling layer. The compression ratio and temperature behind a fully dissociative adiabatic shock is also derived. To prove that these results may even hold for intermediate ages, we design a test to locally characterise the validity of the steady state equations in a time-dependent shock simulation. Applying this tool to the results of Paper I, we show that most of these shocks (all the stable ones) are indeed in a quasi-steady state at all times, i.e. : a given snapshot is composed of one or more truncated steady shock. Finally, we use this property to produce a construction method of any intermediate time of low velocity shocks (u < 20 km/s) with only a steady-state code. In particular, this method allows one to predict the occurrence of steady CJ-type shocks more accurately than previously proposed criteria.Comment: A&A in pres

Mumford dendrograms and discrete p-adic symmetries

In this article, we present an effective encoding of dendrograms by embedding them into the Bruhat-Tits trees associated to $p$-adic number fields. As an application, we show how strings over a finite alphabet can be encoded in cyclotomic extensions of $\mathbb{Q}_p$ and discuss $p$-adic DNA encoding. The application leads to fast $p$-adic agglomerative hierarchic algorithms similar to the ones recently used e.g. by A. Khrennikov and others. From the viewpoint of $p$-adic geometry, to encode a dendrogram $X$ in a $p$-adic field $K$ means to fix a set $S$ of $K$-rational punctures on the $p$-adic projective line $\mathbb{P}^1$. To $\mathbb{P}^1\setminus S$ is associated in a natural way a subtree inside the Bruhat-Tits tree which recovers $X$, a method first used by F. Kato in 1999 in the classification of discrete subgroups of $\textrm{PGL}_2(K)$. Next, we show how the $p$-adic moduli space $\mathfrak{M}_{0,n}$ of $\mathbb{P}^1$ with $n$ punctures can be applied to the study of time series of dendrograms and those symmetries arising from hyperbolic actions on $\mathbb{P}^1$. In this way, we can associate to certain classes of dynamical systems a Mumford curve, i.e. a $p$-adic algebraic curve with totally degenerate reduction modulo $p$. Finally, we indicate some of our results in the study of general discrete actions on $\mathbb{P}^1$, and their relation to $p$-adic Hurwitz spaces.Comment: 14 pages, 6 figure

Sports video: Fine-grained action detection and classification of table tennis strokes from videos for MediaEval 2021

This paper presents the baseline method proposed for the Sports Video task part of the MediaEval 2021 benchmark. This task proposes a stroke detection and a stroke classification subtasks. This baseline addresses both subtasks. The spatio-temporal CNN architecture and the training process of the model are tailored according to the addressed subtask. The method has the purpose of helping the participants to solve the task and is not meant to reach stateof-the-art performance. Still, for the detection task, the baseline is performing better than the other participants, which stresses the difficulty of such a task

The development of a resource-efficient photovoltaic system

This paper presents the measures taken in the demonstration of the photovoltaic case study developed within the European project ‘Towards zero waste in industrial networks’ (Zerowin), integrating the D4R (Design for recycling, repair, refurbishment and reuse) criteria at both system and industrial network level. The demonstration is divided into three phases. The first phase concerns the development of a D4R photovoltaic concept, the second phase focused on the development of a specific component of photovoltaic systems and the third phase was the demonstration of the D4R design in two complete photovoltaic systems (grid-connected and stand-alone). This paper includes a description of the installed photovoltaic systems, including a brief summary at component level of the lithium ion battery system and the D4R power conditioning system developed for the pilot installations. Additionally, industrial symbioses within the network associated with the photovoltaic systems and the production model for the network are described