Ultrasound spatiotemporal despeckling via Kronecker wavelet-Fisz thresholding

We propose a novel framework for despeckling ultrasound image sequences while respecting the structural details. More precisely, we use thresholding in an adapted wavelet domain that jointly takes into account for the non-Gaussian statistics of the noise and the differences in spatial and temporal regularities. The spatiotemporal wavelet is obtained via the Kronecker product of two sparsifying wavelet bases acting, respectively, on the spatial and temporal domains. Besides enabling a structured sparse representation of the time–space plan, it also makes it possible to perform a variance stabilization routine on the spatial domain through a Fisz transformation. The proposed method enjoys adaptability, easy tuning and theoretical guaranties. We propose the corresponding algorithm together with results that demonstrate the benefits of the proposed spatiotemporal approach over the successive spatial treatment. Finally, we describe a data-driven extension of the proposed method that is based on temporal pre-filtering.     

Alternative patterns of the multidimensional Hilbert curve

Locality-preserving (distance preserving-mapping) is a useful property to manage multidimensional data. Close points in space remain -as much as possible- close after mapping on curve. That is why Hilbert space-filling curve is used in many domains and applications. Hilbert curve preserves well locality because from a construction aspect, it is guided by adajacency constraint on points ordering : the curve connects all points of a D-dimensional discrete space, without favoring any direction, under the constrainst that two successive points are separated by an unit distance. Originally defined in 2-D, all existing multidimensional extensions of the Hilbert curve satisfy adjacency by using the RBG pattern (based on Reflected Binary Gray code). The RBG pattern is then duplicated and arranged (geometrical transformations) to build the multidimensional Hilbert curve at a given order. In this paper, we emphasize that there are other patterns that can satisfy the adjacency. A formulation is given, an algorithm to find out solutions is provided and their respective level of locality preservation is estimated through a standard criterion. Results show that some new patterns can carry a comparable levels of locality and sometimes better than RBG. Moreover, selecting the best locality preserving pattern allows one to design, through orders, a new curve with a comparable overall locality preserving refer to Hilbert curve. The contribution of new patterns is experimented through a CBIR (Content-Based Image Retrieval) application. Large-scale image retrieval tests show that exploring the image feature space with an alternative way to the classical Hilbert curve can lead to improved image searching performances.

     

Persian Variations

The concept of variation is essential in geometric design. It is surprising that patterns very different may be variations of the same model. We define two families of pentagonal patterns with three kind of variations, and give some suggestions how to analyse these patterns and create in this style. We then search for self-similarity systems in a strict sense. Although from a systematic search, the two solutions proposed here can also generate some traditional 2-level patterns. In searching for subdivisions of the tiles into rhombuses, we found two solutions. Both can be compatible with the Binary Tiling (not with the Penrose Tiling). Then, using the concept of X-Tiles defined in a previous paper (Castera et al., http://castera.net/entrelacs/public/articles/Flying_Patterns.pdf, 2011), we find new relationship between the two families of pentagonal patterns. In the last chapter we show and comment some examples taken from traditional architecture in Iran, and infer a self-similar system for pattern with interlaces from a 2-level tiling in Isfahan. This paper reflect the point of view of a pattern designer.     

Quantile-based optimization under uncertainties using adaptive Kriging surrogate models

Uncertainties are inherent to real-world systems. Taking them into account is crucial in industrial design problems and this might be achieved through reliability-based design optimization (RBDO) techniques. In this paper, we propose a quantile-based approach to solve RBDO problems. We first transform the safety constraints usually formulated as admissible probabilities of failure into constraints on quantiles of the performance criteria. In this formulation, the quantile level controls the degree of conservatism of the design. Starting with the premise that industrial applications often involve high-fidelity and time-consuming computational models, the proposed approach makes use of Kriging surrogate models (a.k.a. Gaussian process modeling). Thanks to the Kriging variance (a measure of the local accuracy of the surrogate), we derive a procedure with two stages of enrichment of the design of computer experiments (DoE) used to construct the surrogate model. The first stage globally reduces the Kriging epistemic uncertainty and adds points in the vicinity of the limit-state surfaces describing the system performance to be attained. The second stage locally checks, and if necessary, improves the accuracy of the quantiles estimated along the optimization iterations. Applications to three analytical examples and to the optimal design of a car body subsystem (minimal mass under mechanical safety constraints) show the accuracy and the remarkable efficiency brought by the proposed procedure.     

Jacobians and Hessians of mean value coordinates for closed triangular meshes

Mean value coordinates provide an efficient mechanism for the interpolation of scalar functions defined on orientable domains with a nonconvex boundary. They present several interesting features, including the simplicity and speed that yield from their closed-form expression. In several applications though, it is desirable to enforce additional constraints involving the partial derivatives of the interpolated function, as done in the case of the Green coordinates approximation scheme (Ben-Chen, Weber, Gotsman, ACM Trans. Graph.:1–11, 2009) for interactive 3D model deformation. In this paper, we introduce the analytic expressions of the Jacobian and the Hessian of functions interpolated through mean value coordinates. We provide these expressions both for the 2D and 3D case. We also provide a thorough analysis of their degenerate configurations along with accurate approximations of the partial derivatives in these configurations. Extensive numerical experiments show the accuracy of our derivation. In particular, we illustrate the improvements of our formulae over a variety of finite differences schemes in terms of precision and usability. We demonstrate the utility of this derivation in several applications, including cage-based implicit 3D model deformations (i.e., variational MVC deformations). This technique allows for easy and interactive model deformations with sparse positional, rotational, and smoothness constraints. Moreover, the cages produced by the algorithm can be directly reused for further manipulations, which makes our framework directly compatible with existing software supporting mean value coordinates based deformations.     

Influence of BaCuO2 on the Sintering and the Properties of YBa2Cu3O7−δ-Based Ceramics

The preparation of YBa₂Cu₃O_{7 - δ}-based ceramics was made from a mixture of oxides taken in the molar proportions α:1:2 BaCuO₂:Y₂BaCuO₅:CuO(0.95 α 3). The densification of the ceramics is strongly dependent on the initial amount of BaCuO₂. The highest density is obtained when α= 1. All the ceramics present a superconducting transition. A sintering mechanism is proposed in which the densification is mainly governed by the appearance of a metastable BaCuO₂-based liquid at around 900°C.     

Influence of the Content and Distribution of Vanadium in the M1 Phase of the MoVTe(Sb)NbO Catalysts on their Catalytic Properties in Light Alkanes Oxidation

Phase-pure MoVTe(Sb)NbO mixed oxides, with an M1 structure, and various compositions were prepared, characterized and tested as catalysts for the oxidative dehydrogenation of ethane, in order to study the influence of vanadium content and its distribution over the crystallographic sites on the catalytic properties of these oxides. A linear variation in catalytic activity was observed, as a function of the total vanadium content. This property, which has already been demonstrated for propane oxidation, is shown to remain unaffected by the alkane reaction, the nature of the propene α-dehydrogenation elements (Te or Sb), the presence or absence of niobium. The use of XPS to study the surface composition of the catalysts allowed a direct proportionality to be established between the rate of ethane conversion and the V⁵⁺ surface content, thus explaining the first correlation observed with bulk V content. This result also emphasizes the fact that a maximum level of intrinsic catalytic activity can be found, and that high vanadium content might be detrimental to this activity, or to the stability of the catalysts. Finally, crystallographic data found in the literature are used to further interpret and discuss these results.     

Analysis of the historical collapse of an abandoned underground chalk mine in 1961 in Clamart (Paris,France)

In chalk mines, the method of room and pillar mining has been widely used in France. Yet, many large collapses have occurred during or after their exploitation, with the collapse of Clamart (south of Paris, France) being well known as one of the most catastrophic. Today, 50 years after the collapse, the main causes of the event are still not well understood. This paper presents a back-analysis of the case study, using both an empirical approach and a numerical approach. Based on a set of hypotheses, an empirical approach and 3D numerical modeling have indicated a plausible scenario that may explain the collapse: The large collapse may have been caused by a lack of bearing capacity of the pillars and the sudden rupture of a hard limestone bed on which the load would have accumulated until overload occurred. The bed weakness between the two mine levels may also have had an influence on the mine’s general lack of stability. Moreover, under the given hypothesis, the study shows a very low influence of the water table due to flooding of the mine.

     

Innovative design for agriculture in the move towards sustainability: scientific challenges

Agriculture is facing increasing innovation challenges to meet current societal expectations, yet very few design science studies are devoted to it. This paper highlights some of the particularities of the objects, reasoning and organization of design in agriculture that may open fruitful scientific dialogue between design scientists and agricultural scientists. We first provide an overview of the broad range of objects that are designed in agriculture and point out their specific characteristics with regard to design. We then identify some particular challenges of design activities in agriculture and review how they have been addressed up to now. Finally, we discuss how design challenges and characteristics in agriculture can contribute to current debate in the field of design science. We propose two main lines of enquiry and debate: enhancing the links between design reasoning and organization and further conceptualizing the status of use situations in design to deal with uncertainties and complexity in design processes.     

A polyamidoamine dendrimer as a selective colorimetric and ratiometric fluorescent sensor for Li+ cations in alkali media

In a DMF + NaOH medium, a polyamidoamine dendrimer having sixteen 1,8-naphthalimide fragments in its periphery, formed a complex only with Li⁺ ions, detected by a colour change from red to yellow and by a significant increase in fluorescence intensity. The dendrimer can be used as a selective sensor for Li⁺ ions in the presence of other alkali ions such as Na⁺ or K⁺.