Morphological and Mechanical Investigation of Double-Layer Reciprocal Structures

The simple connection conditions of reciprocal structures means that technological constraints become geometrical constraints and bending moments are increased. Geometrical constraints can be dealt by using form-finding methods such as a dynamic relaxation algorithm, but resisting bending moments to gain stiffness is difficult to accomplish without increasing the weight of the structure. For standard reticulated structures, common strategies consist in introducing curvature in the structure and/or modifying the structure into a double-layer space structure. The proposed paper is thus an attempt to apply these strategies to reciprocal structures and to develop spherical domes with a structural thickness. Several configurations will be investigated and compared in term of geometrical feasibility and structural performance.     

Real-time infinite horizon tracking with data fusion for augmented reality in a maritime operations context

In this paper, we propose a method for real-time horizon tracking (i.e., separation line between the sky and the sea) in a maritime operations context. We present the fusion of an image processing algorithm with the data obtained from the inertial measurement unit (IMU). The initial aim is to filter out environmental conditions using inertial information in order to combine a video stream with onboard electronic charts. This is achieved by the detection of the horizon with an image processing algorithm in an area defined by the IMU. We then present an evaluation of the algorithm with regard to the rate of detection of the horizon and the impact of the image resolution on the computational time. The purpose of developing this method is to create an augmented reality maritime operations application. We combine the video stream with electronic charts in a single display. We use the position of the horizon in the image to split the display into different areas. Then, we use transparency to display the video, the electronic charts or both.     

Convergence of real per capita GDP within COMESA countries: A panel unit root evidence

This article examines the absolute and conditional convergence of real GDP per capita in the Common Market for Eastern and Southern Africa (COMESA) during the period 1950?C2003. Income departures across countries were evaluated from several panel data unit root tests. We find no evidence supporting the existence of convergence process for the income in the COMESA. Nevertheless, applying economic development criterion allows to identity two absolute convergence clubs into the COMESA, one for the most four developed countries (Egypt, Libya, Mauritius, Seychelles), and one other for the fourteen less developed ones. Thus, we show that most economies of COMESA are locked into a sustained poverty trap process.     

Using pore space 3D geometrical modelling to simulate biological activity: Impact of soil structure

This study is the follow-up to a previous one devoted to soil pore space modelling. In the previous study, we proposed algorithms to represent soil pore space by means of optimal piecewise approximation using simple 3D geometrical primitives: balls, cylinders, cones, etc. In the present study, we use the ball-based piecewise approximation to simulate biological activity. The basic idea for modelling pore space consists in representing pore space using a minimal set of maximal balls (Delaunay spheres) recovering the shape skeleton. In this representation, each ball is considered as a maximal local cavity corresponding to the “intuitive” notion of a pore as described in the literature. The space segmentation induced by the network of balls (pores) is then used to spatialise biological dynamics. Organic matter and microbial decomposers are distributed within the balls (pores). A valuated graph representing the pore network, organic matter and microorganism distribution is then defined. Microbial soil organic matter decomposition is simulated by updating this valuated graph. The method has been implemented and tested on real data. As far as we know, this approach is the first one to formally link pore space geometry and biological dynamics. The long-term goal is to define geometrical typologies of pore space shape that can be attached to specific biological dynamic properties. This paper is a first attempt to achieve this goal.     

High‐Temperature Creep Behavior of Dense SiOC‐Based Ceramic Nanocomposites: Microstructural and Phase Composition Effects

In this work, dense monolithic polymer‐derived ceramic nanocomposites (SiOC, SiZrOC, and SiHfOC) were synthesized via hot‐pressing techniques and were evaluated with respect to their compression creep behavior at temperatures beyond 1000°C. The creep rates, stress exponents as well as activation energies were determined. The high‐temperature creep in all materials has been shown to rely on viscous flow. In the quaternary materials (i.e., SiZrOC and SiHfOC), higher creep rates and activation energies were determined as compared to those of monolithic SiOC. The increase in the creep rates upon modification of SiOC with Zr/Hf relies on the significant decrease in the volume fraction of segregated carbon; whereas the increase of the activation energies corresponds to an increase of the size of the silica nanodomains upon Zr/Hf modification. Within this context, a model is proposed, which correlates the phase composition as well as network architecture of the investigated samples with their creep behavior and agrees well with the experimentally determined data.     

MDO: assessment and direction for advancement—an opinion of one international group

This paper is a summary of topics presented and discussed at the 2006 European–U.S. Multidisciplinary Optimization (MDO) Colloquium in Goettingen, Germany, attended by nearly seventy professionals from academia, industry, and government. An attempt is made to accurately reflect the issues discussed by this diverse group, qualified by interest, experience, and accomplishment to present an opinion about the state-of-the-art, trends, and developments in Multidisciplinary Design Optimization. As such, its main purpose is to provide suggestions and stimulus for future research in the field. The predominant content of the colloquium was centered on aerospace, with a few contributions from the automotive industry, and this is reflected in the article. Due to the timeframe that has passed since the conclusion of the workshop, the authors have updated topics where appropriate to reflect observed developments over the past 3 years. Finally, rather than dwelling extensively on past accomplishments and current capabilities in MDO we focus on the needs and identified shortcomings from the colloquium which lead to potential future research directions. A brief MDO background is provided to set the discussion in its proper context.     

Low speed lifting cable diagnosis using instantaneous angular speed

Journal of Mechanical Science and Technology - This paper describes an experimental study of lifting cable fault diagnostic based on instantaneous angular speed (IAS) technique. During the study...