44 research outputs found
Non-equilibrium h-2 formation in the early universe: energy exchanges, rate coefficients, and spectral distortions
Energy exchange processes play a crucial role in the early universe, affecting the thermal balance and the dynamical evolution of the primordial gas. In the present work we focus on the consequences of a non-thermal distribution of the level populations of H2: first, we determine the excitation temperatures of vibrational transitions and the non-equilibrium heat transfer; second, we compare the modifications to chemical reaction rate coefficients with respect to the values obtained assuming local thermodynamic equilibrium; and third, we compute the spectral distortions to the cosmic background radiation generated by the formation of H2 in vibrationally excited levels. We conclude that non-equilibrium processes cannot be ignored in cosmological simulations of the evolution of baryons, although their observational signatures remain below current limits of detection. New fits to the equilibrium and non-equilibrium heat transfer functions are provided
Adaptively Transforming Graph Matching
Recently, many graph matching methods that incorporate pairwise constraint
and that can be formulated as a quadratic assignment problem (QAP) have been
proposed. Although these methods demonstrate promising results for the graph
matching problem, they have high complexity in space or time. In this paper, we
introduce an adaptively transforming graph matching (ATGM) method from the
perspective of functional representation. More precisely, under a
transformation formulation, we aim to match two graphs by minimizing the
discrepancy between the original graph and the transformed graph. With a linear
representation map of the transformation, the pairwise edge attributes of
graphs are explicitly represented by unary node attributes, which enables us to
reduce the space and time complexity significantly. Due to an efficient
Frank-Wolfe method-based optimization strategy, we can handle graphs with
hundreds and thousands of nodes within an acceptable amount of time. Meanwhile,
because transformation map can preserve graph structures, a domain
adaptation-based strategy is proposed to remove the outliers. The experimental
results demonstrate that our proposed method outperforms the state-of-the-art
graph matching algorithms
Efficient Algorithms for Image and High Dimensional Data Processing Using Eikonal Equation on Graphs
International audienceIn this paper we propose an adaptation of the static eikonal equation over weighted graphs of arbitrary structure using a framework of discrete operators. Based on this formulation, we provide explicit solu- tions for the L1,L2 and L∞ norms. Efficient algorithms to compute the explicit solution of the eikonal equation on graphs are also described. We then present several applications of our methodology for image processing such as superpixels decomposition, region based segmentation or patch- based segmentation using non-local configurations. By working on graphs, our formulation provides an unified approach for the processing of any data that can be represented by a graph such as high-dimensional data
Effects of primordial chemistry on the cosmic microwave background
Previous works have demonstrated that the generation of secondary CMB
anisotropies due to the molecular optical depth is likely too small to be
observed. In this paper, we examine additional ways in which primordial
chemistry and the dark ages might influence the CMB. We present a detailed and
updated chemical network and give an overview of the interactions of molecules
with the CMB. We consider the optical depth due to line absorption,
photoionization, photodissociation and free-free processes, and estimate the
resulting changes in the CMB temperature and its power spectrum. The most
promising results are obtained for the negative hydrogen ion \HM and the \HeHII
molecule. The free-free process of \HM yields a relative change in the CMB
temperature of up to , and leads to a frequency-dependent
change in the power spectrum of the order at 30 GHz. With a change of
the order in the power spectrum, our result for the bound-free
process of \HM is significantly below a previous suggestion. \HeHII efficiently
scatters CMB photons and smears out primordial fluctuations, leading to a
change in the power spectrum of the order . Improvements in the
accuracy of future CMB experiments may thus help to constrain and finally
detect these interesting signals from the dark ages of the universe.Comment: 16 pages, 15 figures, accepted for publication at A&A. Discussion
section update
Nonlinear Multilayered Representation of Graph-Signals
We propose a nonlinear multiscale decomposition of signals defined on the vertex set of a general weighted graph. This decomposition is inspired by the hierarchical multiscale (BV, L 2) decomposition of Tadmor, Nezzar, and Vese (Multiscale Model. Simul. 2(4):554–579, 2004). We find the decomposition by iterative regularization using a graph variant of the classical total variation regularization (Rudin et al, Physica D 60(1–4):259–268, 1992). Using tools from convex analysis, and in particular Moreau’s identity, we carry out the mathematical study of the proposed method, proving the convergence of the representation and providing an energy decomposition result. The choice of the sequence of scales is also addressed. Our study shows that the initial scale can be related to a discrete version of Meyer’s norm (Meyer, Oscillating Patterns in Image Processing and Nonlinear Evolution Equations, 2001) which we introduce in the present paper. We propose to use the recent primal-dual algorithm of Chambolle and Pock (J. Math. Imaging Vis. 40:120–145, 2011) in order to compute both the minimizer of the graph total variation and the corresponding dual norm. By applying the graph model to digital images, we investigate the use of nonlocal methods to the multiscale decomposition task. Since the only assumption needed to apply our method is that the input data is living on a graph, we are also able to tackle the task of adaptive multi
Deep Learning Using Havrda-Charvat Entropy for Classification of Pulmonary Optical Endomicroscopy
International audienc
FAST LiH DESTRUCTION IN REACTION WITH H: QUANTUM CALCULATIONS AND ASTROPHYSICAL CONSEQUENCES
Patch-based potentials for interactive contour extraction
International audienceThe problem of interactive contour extraction of targeted objects of interest in images is challenging and finds many applications in image editing tasks. Several methods have been proposed to address this problem with a common objective: performing an accurate contour extraction with minimum user effort. For minimal paths techniques, achieving this goal depends critically on the ability of the so-called potential map to capture edges. In this context we propose new patch-based potentials designed to have small values at the boundary of the targeted object. To evaluate these potentials, we consider the livewire framework and quantify their abilities in terms of number of needed seed points. Both visual and quantitative results demonstrated the strong capability of our proposed potentials in reducing the user's interaction while preserving a good accuracy of extraction