Shocks in dense clouds. IV. Effects of grain-grain processing on molecular line emission

Grain-grain processing has been shown to be an indispensable ingredient of shock modelling in high density environments. For densities higher than \sim10^5 cm-3, shattering becomes a self-enhanced process that imposes severe chemical and dynamical consequences on the shock characteristics. Shattering is accompanied by the vaporization of grains, which can directly release SiO to the gas phase. Given that SiO rotational line radiation is used as a major tracer of shocks in dense clouds, it is crucial to understand the influence of vaporization on SiO line emission. We have developed a recipe for implementing the effects of shattering and vaporization into a 2-fluid shock model, resulting in a reduction of computation time by a factor \sim100 compared to a multi-fluid modelling approach. This implementation was combined with an LVG-based modelling of molecular line radiation transport. Using this model we calculated grids of shock models to explore the consequences of different dust-processing scenarios. Grain-grain processing is shown to have a strong influence on C-type shocks for a broad range of magnetic fields: they become hotter and thinner. The reduction in column density of shocked gas lowers the intensity of molecular lines, at the same time as higher peak temperatures increase the intensity of highly excited transitions compared to shocks without grain-grain processing. For OH the net effect is an increase in line intensities, while for CO and H2O it is the contrary. The intensity of H2 emission is decreased in low transitions and increased for highly excited lines. For all molecules, the highly excited lines become sensitive to the value of the magnetic field. Although vaporization increases the intensity of SiO rotational lines, this effect is weakened by the reduced shock width. The release of SiO early in the hot shock changes the excitation characteristics of SiO radiation.Comment: Published in Astronomy and Astrophysics (2013). 26 pages, 16 figures, 14 table

Real-Time Rough Extraction of Foreground Objects in MPEG1,2 Compressed Video

This paper describes a new approach to extract foreground objects in MPEG1,2 video streams, in the framework of “rough indexing paradigm”, that is starting from rough data obtained by only partially decoding the compressed stream. In this approach we use both P-frame motion information and I-frame colour information to identify and extract foreground objects. The particularity of our approach with regards to the state of the art methods consists in a robust estimation of camera motion and its use for localisation of real objects and filtering of parasite zones. Secondly, a spatio-temporal filtering of roughly segmented objects at DC resolution is fulfilled using motion trajectory and gaussian-like shape characteristic function. This paradigm results in content description in real time, maintaining a good level of details

Evaluation of Explanation Methods of AI -- CNNs in Image Classification Tasks with Reference-based and No-reference Metrics

The most popular methods in AI-machine learning paradigm are mainly black boxes. This is why explanation of AI decisions is of emergency. Although dedicated explanation tools have been massively developed, the evaluation of their quality remains an open research question. In this paper, we generalize the methodologies of evaluation of post-hoc explainers of CNNs' decisions in visual classification tasks with reference and no-reference based metrics. We apply them on our previously developed explainers (FEM, MLFEM), and popular Grad-CAM. The reference-based metrics are Pearson correlation coefficient and Similarity computed between the explanation map and its ground truth represented by a Gaze Fixation Density Map obtained with a psycho-visual experiment. As a no-reference metric, we use stability metric, proposed by Alvarez-Melis and Jaakkola. We study its behaviour, consensus with reference-based metrics and show that in case of several kinds of degradation on input images, this metric is in agreement with reference-based ones. Therefore, it can be used for evaluation of the quality of explainers when the ground truth is not available.Comment: Due to a bug found in the code, all tables and figures were redone. The new results did not change the main conclusion, except for the best explainer. FEM has performed better than MLFEM; 25 pages, 16 tables, 16 figures; Submitted to "Advances in Artificial Intelligence and Machine Learning" (ISSN: 2582-9793

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

The abundances of nitrogen-containing molecules during pre-protostellar collapse

We have studied the chemistry of nitrogen--bearing species during the initial stages of protostellar collapse, with a view to explaining the observed longevity of N2H+ and NH3 and the high levels of deuteration of these species. We followed the chemical evolution of a medium comprising gas and dust as it underwent free--fall gravitational collapse. Chemical processes which determine the relative populations of the nuclear spin states of molecules and molecular ions were included explicitly, as were reactions which lead ultimately to the deuteration of the nitrogen--containing species N2H+ and NH3. The freeze-out of `heavy' molecules onto grains was taken into account. We found that the timescale required for the nitrogen--containing species to attain their steady--state values was much larger than the free--fall time and even comparable with the probable lifetime of the precursor molecular cloud. However, it transpires that the chemical evolution of the gas during gravitational collapse is insensitive to its initial composition. If we suppose that the grain--sticking probabilities of atomic nitrogen and oxygen are both less than unity (S less than 0.3), we find that the observed differential freeze--out of nitrogen- and carbon--bearing species can be reproduced by the model of free--fall collapse when a sufficiently large grain radius (a_{g}= 0.5 micron) is adopted. Furthermore, the results of our collapse model are consistent with the high levels of deuteration of N2H+ and NH3 which have been observed in L1544 providing that 0.5<a_{g}<1 micron. We note that the o/p H2D+ ratio and fractional abundance of ortho-H2D+ should be largest when ND3 is most abundant

Crack fronts and damage in glass at the nanometer scale

We have studied the low speed fracture regime for different glassy materials with variable but controlled length scales of heterogeneity in a carefully mastered surrounding atmosphere. By using optical and atomic force microscopy (AFM) techniques we tracked in real-time the crack tip propagation at the nanometer scale on a wide velocity range (mm/s - pm/s and below). The influence of the heterogeneities on this velocity is presented and discussed. Our experiments reveal also -for the first time- that the crack progresses through nucleation, growth and coalescence of nanometric damage cavities within the amorphous phase. This may explain the large fluctuations observed in the crack tip velocities for the smallest values. This behaviour is very similar to what is involved, at the micrometric scale, in ductile fracture. The only difference is very likely due to the related length scales (nanometric instead of micrometric). Consequences of such a nano-ductile fracture mode observed at a temperature far below the glass transition temperature in glass is finally discussed.Comment: 12 pages, 8 figures, submitted to Journal of Physics: Condensed Matter; Invited talk at Glass and Optical Materials Division Fall 2002 Meeting, Pittsburgh, Pa, US

3D Convolutional Networks for Action Recognition: Application to Sport Gesture Recognition

3D convolutional networks is a good means to perform tasks such as video segmentation into coherent spatio-temporal chunks and classification of them with regard to a target taxonomy. In the chapter we are interested in the classification of continuous video takes with repeatable actions, such as strokes of table tennis. Filmed in a free marker less ecological environment, these videos represent a challenge from both segmentation and classification point of view. The 3D convnets are an efficient tool for solving these problems with window-based approaches.Comment: Multi-faceted Deep Learning, 202

The chemistry and excitation of H2 and HD in the early Universe

We have critically reviewed the literature pertaining to reactions that are significant for the chemistry of hydrogen-, deuterium-, and helium-bearing species in the homogeneous early Universe. For each reaction rate coefficient, we provide a fit in the modified-Arrhenius form, specifying the corresponding uncertainty and temperature range. This new network, limited to 21 reactions, should be the most reliable to date. Combined with accurate state-to-state rate coefficients for inelastic and reactive collisions involving H2 and HD, it allows us for the first time to follow the evolution of the abundances of atomic and molecular species, level populations of H2 and HD, and the ortho:para ratio (OPR) of H2, in a self-consistent fashion during the adiabatic expansion of the universe. The abundances of H2 and HD change only marginally compared to previous models, indicating that the uncertainties on the main reaction rate coefficients have essentially been removed. We also find that the adiabatic expansion has a dramatic effect on the OPR of H2, which freezes-out at redshifts z ≲ 50. In contrast, at higher redshifts, the populations of the rotational levels of H2 and HD are predicted to be fully thermalized at the temperature of the cosmic background radiation field, a result that conflicts with some recent, independent calculations. This new network allows the chemistry of primordial gas to be followed during the early phase of collapse towards Population III star progenitors