Lithium hydride in the early universe and in protogalactic clouds

We examine the processes of formation and destruction of LiH molecules in the primordial gas at temperatures T \leq 5000 K in the framework of standard Friedmann cosmological models and we compute the optical depth of the Universe due to Thomson scattering of cosmic background photons on LiH. With the help of a simple model of evolution of a spherical density perturbation we follow the linear growth and the subsequent collapse of protogalactic clouds of various masses, evaluating consistently their physical characteristics and chemical composition. We determine the expected level of anisotropy of the cosmic background radiation due to the presence of LiH molecules in high-redshift protogalactic clouds. We conclude that LiH spectral features generated in the primordial gas are hardly detectable with current techniques and instrumentation.Comment: 10 pages (LaTeX), 7 Figures to be published in Monthly Notices of the Royal Astronomical Societ

Cosmological Recombination of Lithium and its Effect on the Microwave Background Anisotropies

The cosmological recombination history of lithium, produced during Big--Bang nucleosynthesis, is presented using updated chemistry and cosmological parameters consistent with recent cosmic microwave background (CMB) measurements. For the popular set of cosmological parameters, about a fifth of the lithium ions recombine into neutral atoms by a redshift $z\sim 400$. The neutral lithium atoms scatter resonantly the CMB at 6708 \AA and distort its intensity and polarization anisotropies at observed wavelengths around $\sim 300 \mu$m, as originally suggested by Loeb (2001). The modified anistropies resulting from the lithium recombination history are calculated for a variety of cosmological models and found to result primarily in a suppression of the power spectrum amplitude. Significant modification of the power spectrum occurs for models which assume a large primordial abundance of lithium. While detection of the lithium signal might prove difficult, if offers the possibility of inferring the lithium primordial abundance and is the only probe proposed to date of the large-scale structure of the Universe for $z\sim 500-100$.Comment: 20 pages, 7 figure

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

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

Formazione, tecnologia e mercati nel contesto di una multinazionale

The present paper discusses the hypothesis of a new understanding of the traditional and academic paths in the history of science and technology, trying to introduce a multi-sited and multi-centred approach that overtakes the prevalent current narrations. The hypothesis is discussed considering a relevant case study connected with issues in higher education, scientific and technological competencies and global markets. The paper presents the controversies that emerge within a high level training program provided by a multinational corporation operating in the area of energy production, and targeted to local middle eastern operators. The training program in advanced technology and related applicative competences remains framed inside a market oriented strategy, and it responds to logic of asymmetric power typical of a post colonial scenario. The higher education program becomes a pretext to hide persistent cultural and gender prejudices and to enforce existing or newly established relations of subalternity.  The presented case study offers also the possibility of discussing an example of re-appropriation and re-signification in the historic and scientific tradition of the West, providing a basis for challenging the hypothesis outlined above.</p