On the parabolic equation method in internal wave propagation

A parabolic equation for the propagation of periodic internal waves over varying bottom topography is derived using the multiple-scale perturbation method. Some computational aspects of the numerical implementation are discussed. The results of numerical experiments on propagation of an incident plane wave over a circular-type shoal are presented in comparison with the analytical result, based on Born approximation.Comment: Submitted to Coastal Engineering. 16 pages, 5 figures. One figure was excluded from article because of size problem

Rapid ascent of rhyolitic magma at Chaitén volcano, Chile

International audienceAlthough rhyolite magma has fuelled some of the Earth's largest explosive volcanic eruptions, our understanding of these events is incomplete due to the previous lack of direct observation of these eruptions. On 1 May 2008, Chaitén volcano in Chile erupted rhyolite magma unexpectedly and explosively. Here, petrological and experimental data are presented that indicate that the hydrous rhyolite magma at Chaitén ascended very rapidly from storage depth to near-surface, with velocities of the order of one metre per second

The potential for plant-based Meat in Africa - a proposed new approach using a system design methodology

Thesis: S.M. in Engineering and Management, Massachusetts Institute of Technology, System Design and Management Program, February, 2021Cataloged from the official version of thesis.Includes bibliographical references (pages 55-58).This Thesis explores the potential application of new plant-based protein technologies to Sub-Saharan Africa. It demonstrates the use of a system design methodology to evaluate, assess and select a new approach to protein production. This is an important topic, because global protein production systems are under pressure to reduce their environmental footprint. It is an interesting topic right now, because new protein technologies are emerging which have the potential to soon disrupt industrial livestock farming. The system design approach means thinking in terms of protein production as a system consisting of individual parts (farms, value chain, retail outlets etc.) and their interactions, which together deliver value to the protein consumers. The stakeholders and users of the system are analyzed in order to understand and prioritize their needs in terms of the system goals. This approach allows us to creatively examine the individual parts for alternatives, whilst assessing expected system performance in terms of the overall value delivered over time. The Thesis focuses on Africa's fast-growing and fast-urbanizing populations with their growing demand for protein. A common operating factor is malnourished populations, due to diets based on low-quality plant sources, and existing protein production systems which are inefficient, unsustainable and harming the environment. The work thoroughly analyses published research on the technical and operational aspects of new and old protein production. Interviews were conducted with experts in both protein and Africa. The comparison of new techniques for producing proteins suggest that new plant-based methods have the most immediate potential. The proposed system is based upon three simple ideas, which together lead to an interesting outcome: -- Product Platform Architecture - firstly, a product should use a Platform Architecture in order to keep development costs low, and yet allow the product to be adapted to different local markets in Africa -- Franchise Model - the best way to achieve scale is to work with local entrepreneurs through franchising, an approach which enables allocating responsibilities and risks within the system hierarchy -- Lean Operating Model - finally, the operating entity has to be exceptionally lean by design, in order to ensure an affordable product for consumers - an idea known as a Base of the Pyramid (BOP) strategy A case study of Southern Nigeria illustrates the concept.by Thomas Llewellin Smith.S.M. in Engineering and ManagementS.M.inEngineeringandManagement Massachusetts Institute of Technology, System Design and Management Progra

New carbon-hybrid nanoporous materials for enhanced hydrogen storage: synthesis and characterization

International audienceThe world is running out of fossil fuels and the products of their burning in air (mostly CO2) have already impacted global climate. Therefore, we still need a lot effort to search how to convert the global energy economy towards cleaner and renewable fuels (like hydrogen), in particular, for mobile applications. It is clear now, that to efficiently store hydrogen at ambient temperature and not too high pressures, we need to develop hydrogen sorbent and optimize simultaneously both its specific surface and adsorption energy. In this project we propose to explore the potential effectiveness of arc-discharge procedure to synthetize nanoporous, carbon based sorbents with characteristics required in vehicular applications. The technique was successfully used in the past to synthetize fullerenes and nanotubes. Therefore we have assumed that we can adjust the synthesis parameters to prepare other graphene-based structures, with a variety graphene fragment sizes, forms, and interconnections between them. In addition, arc-discharge technique provides a relatively easy way to incorporate heteroatoms into pure carbon structures.The first characterizations of boron-substituted carbons obtained by this method are promising: the energy of hydrogen adsorption is the highest ever observed experimentally in carbon-based sorbents. However, the specific surface is relatively low, ~ 200 m2/g, suggesting that the samples need to be activated to increase their accessible for adsorption surface and, in consequence, their capacity to store hydrogen