4 results
Nudging-based data assimilation of the turbulent flow around a square cylinder
- M. Zauner, V. Mons, O. Marquet, B. Leclaire
-
- Journal:
- Journal of Fluid Mechanics / Volume 937 / 25 April 2022
- Published online by Cambridge University Press:
- 03 March 2022, A38
-
- Article
- Export citation
-
We investigate the estimation of the turbulent flow around a canonical square cylinder at $Re=22\,000$ based on temporally resolved but spatially sparse velocity data and solving the unsteady Reynolds-averaged Navier–Stokes (URANS) equations. Flow reconstruction from sparse data is achieved through the application of a nudging data assimilation technique. It involves the introduction of a feedback control term in the momentum equations which allows us to drive URANS predictions towards reference data, which are here extracted from a direct numerical simulation. Such a data assimilation approach induces negligible supplementary computational cost compared with that of a standard URANS simulation. The influence of the spatial resolution of the reference data on the reconstruction performances is systematically investigated. Using a spacing of the order of one cylinder length between data points, we already observe synchronisation of the low-frequency vortex shedding between the full reference flow and the one that is estimated by URANS. The present data assimilation procedure allows us to compensate for deficiencies in standard URANS calculations and leads to a significant decrease in temporal and spectral errors as computed by spectral proper orthogonal decomposition. Furthermore, high accuracy in terms of mean-flow prediction by URANS is achieved. When considering spacings between measurements that are of the order of the wavelength of the Kelvin–Helmholtz vortices, such phenomena in the shear layers at the top and bottom of the cylinder are correctly estimated, while they are not self-sustained in standard URANS. The influence of the structure of the feedback control term in the data assimilation procedure is also investigated.
Selective extinction of late Neogene bivalves on the temperate Pacific coast of South America
- Marcelo M. Rivadeneira, Pablo A. Marquet
-
- Journal:
- Paleobiology / Volume 33 / Issue 3 / Summer 2007
- Published online by Cambridge University Press:
- 20 May 2016, pp. 455-468
-
- Article
- Export citation
-
We assessed selective extinction patterns in bivalves during a late Neogene mass extinction event observed along the temperate Pacific coast of South America. The analysis of 99 late Neogene and Quaternary fossil sites (recorded from 7°S to 55°S), yielding ∼2800 occurrences and 118 species, revealed an abrupt decline in Lyellian percentages during the late Neogene–Pleistocene, suggesting the existence of a mass extinction that decimated ∼66% of the original assemblage. Using the late Neogene data set (n = 59 species, 1346 occurrences), we tested whether the extinction was nonrandom according to taxonomic structure, life habit, geographic range, and body size. Our results showed that the number of higher taxa that went extinct was not different than expected by random. At first sight, extinction was selective only according to life habit and geographic range. Nevertheless, when phylogenetic effects were accounted for, body size also showed significant selectivity. In general, epifaunal, small-sized (after phylogenetic correction), and short-ranged species tended to have increased probability of extinction. This is verified by strong interactions between the variables herein analyzed, suggesting the existence of nonlinear effects on extinction chances. In the heavily decimated epifaunal forms, survival was not enhanced by widespread ranges or larger body sizes. Conversely, the widespread and large-sized infaunal forms tended to have lower probability of extinction. Overall, the ultimate extinction of late Neogene bivalve species along the Pacific coast of South America seems to have been determined by a complex interplay of ecological and historical (phylogenetic) effects.
10 - Human Susceptibility to Visceral Leishmaniasis (Leishmania donovani) and to Schistosomiasis (Schistosoma mansoni) Is Controlled by Major Genetic Loci
-
- By A. Dessein, Immunology and Genetics of Parasitic Diseases, INSERM, U. 399, Marseille, France, B. Bucheton, Immunology and Genetics of Parasitic Diseases, INSERM, U. 399, Marseille, France, L. Argiro, Immunology and Genetics of Parasitic Diseases, INSERM, U. 399, Marseille, France, N. M. A. Elwali, Institute of Nuclear Medicine and Molecular Biology, University of Gezira, Wad Medani, Sudan, V. Rodrigues, Laboratory of Immunology, University of Medicine, Triangulo Miniero, Uberaba, Brazil, C. Chevillard, Immunology and Genetics of Parasitic Diseases, INSERM, U. 399, Marseille, France, S. Marquet, Immunology and Genetics of Parasitic Diseases, INSERM, U. 399, Marseille, France, H. Dessein, Immunology and Genetics of Parasitic Diseases, INSERM, U. 399, Marseille, France, S. H. El-Safi, Institute for Tropical Medicine, PO Box 1304, Khartoum, Sudan, L. Abel, Laboratory of Human Genetics of Infectious Diseases, INSERM, U. 550, Paris, France
- Edited by Krishna R. Dronamraju, Foundation for Genetic Research, Houston, Texas
-
- Book:
- Infectious Disease and Host-Pathogen Evolution
- Published online:
- 10 August 2009
- Print publication:
- 05 April 2004, pp 241-262
-
- Chapter
- Export citation
-
Summary
SUSCEPTIBILITY TO SEVERE DISEASE DURING AN OUTBREAK OF VISCERAL LEISHMANIASIS IN A SUDANESE VILLAGE
Visceral leishmaniasis (VL) is caused by protozoan parasites of the Leishmania genus that are transmitted to humans by infected sandflies (Figure 10.1a). Parasites rapidly invade host phagocytes and multiply inside phagolysosomes. Clinical disease is primarily due to the uncontrolled multiplication of the parasite in many organs including the spleen and the liver; clinical symptoms include recurrent fever, considerable splenomegaly, hepatomegaly, and adenopathy (1). Death is certain if the patient is left untreated. Violent outbreaks of VL have occurred in regions of eastern Africa (2) (Kenya, Sudan) and in India (Bihar). VL is endemic in South America and in the Mediterranean basin. VL is caused by three Leishmania species: Leishmania donovani, L. chagasi/infantum, and L. archibaldi (L. donovani being the most pathogenic) (3). To identify the principal risk factors in VL, we carried out a five-year longitudinal study on 1,600 subjects from a village located on the Sudanese–Ethiopian border. The study was initiated in 1995 when the number of VL cases had just begun to rise in the village (4). Within five years, 28% of the population had been affected by VL. Most of these VL patients were treated and cured. Unfortunately, a small percentage either failed to respond to treatment or were not treated because of the difficulties involved in reaching them during the rainy season.
The Genetic Production of Synthetic Crystalline Protein Polymers
- Joseph Cappello, J. Crissman, M. Dorman, M. Mikolajczak, G. Textor, M. Marquet, F. A. Ferrari
-
- Journal:
- MRS Online Proceedings Library Archive / Volume 174 / 1989
- Published online by Cambridge University Press:
- 21 February 2011, 267
- Print publication:
- 1989
-
- Article
- Export citation
-
Genetic and protein engineering are components of a new polymer chemistry which provide the tools for producing macromolecular polyamide copolymers of diversity and precision far beyond the current capabilities of synthetic polymer chemistry. The genetic machinery allows molecular control of chemical and physical chain properties. Nature utilizes this control to formulate protein polymers into materials with extraordinary mechanical properties such as the strength and toughness of silk and the elasticity and resilience of mammalian elastin. The protein chains which make up these fibers consist of extensive repeating oligopeptide sequences. By producing synthetically designed protein chains containing many tandem repeats of only one repetitive sequence block (homoblock polymers), we are able to evaluate the inherent contribution of each repeat to the overall material properties. Using biotechnology, we produced homoblock protein polymers consisting exclusively of silklike crystalline blocks in quantities sufficient for material evaluation studies (10–100 grams). Silk-like homoblock polymers, as produced by microbial fermentation, exhibited measurable crystallinity both in solution and in solid state. The chain properties of the homoblock polymer were changed by adding blocks of amino acids designed to contribute different structural or functional properties. We produced alternating copolymers of various amounts of silk-like and elastin-like blocks ranging from a ratio of 1:4 to 2:1, respectively. The crystallinity of each copolymer varied with the extent of crystalline block interruption. The substitution of the elastin block with one containing the amino acids from human fibronectin responsible for mammalian cell attachment, produced a highly active silk-like copolymer with biological activity. The ability to specifically engineer the mechanical and functional properties of a fiber material is a potential outcome of this technology.