The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Beny Neta - One of the best experts on this subject based on the ideXlab platform.
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high order non reflecting boundary conditions for the linearized 2 d euler equations no mean flow case
Wave Motion, 2009Co-Authors: John R Dea, Francis X Giraldo, Beny NetaAbstract:Higdon-type non-reflecting boundary conditions (NRBCs) are developed for the 2-D linearized Euler equations with Coriolis forces. This implementation is applied to a simplified form of the equations, with the NRBCs applied to all four sides of the domain. We demonstrate the validity of the NRBCs to high order. We close with a list of areas for further research.
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application of high order higdon non reflecting boundary conditions to linear shallow water models
Communications in Numerical Methods in Engineering, 2007Co-Authors: Beny Neta, John R Dea, Vince Van Joolen, Dan GivoliAbstract:SUMMARY A shallow water model with linear time-dependent dispersive waves in an unbounded domain is considered. The domain is truncated with artificial boundaries B where a sequence of high-order non-reflecting boundary conditions (NRBCs) proposed by Higdon are applied. Methods devised by Givoli and Neta that afford easy implementation of Higdon NRBCs are refined in order to reduce computational expenses. The new refinement makes the computational effort associated with the boundary treatment quadratic rather than exponential (as in the original scheme) with the order. This allows for implementation of NRBCs of higher orders than previously. A numerical example for a semi-infinite channel truncated on one side is presented. Finite difference schemes are used throughout. Copyright q 2007 John Wiley & Sons, Ltd.
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high order non reflecting boundary conditions for dispersive waves in cartesian cylindrical and spherical coordinate systems
International Journal of Computational Fluid Dynamics, 2003Co-Authors: Vince Van Joolen, Dan Givoli, Beny NetaAbstract:Among the many areas of research that Professor Kawahara has been active in is the subject of open boundaries in which linear time-dependent dispersive waves are considered in an unbounded domain. The infinite domain is truncated via an artificial boundary B on which an open boundary condition (OBC) is imposed. In this paper, Higdon OBCs and Hagstrom–Hariharan (HH) OBCs are considered. Higdon-type conditions, originally implemented as low-order OBCs, are made accessible for any desired order via a new scheme. The higher-order Higdon OBC is then reformulated using auxiliary variables and made compatible for use with finite element (FE) methods. Methodologies for selecting Higdon parameters are also proposed. The performances of these schemes are demonstrated in two numerical examples. This is followed by a discussion of the HH OBC, which is applicable to non-dispersive media on cylindrical and spherical geometries. The paper extends this OBC to the “slightly dispersive” case.
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high order non reflecting boundary scheme for time dependent waves
Journal of Computational Physics, 2003Co-Authors: Dan Givoli, Beny NetaAbstract:A new non-reflecting boundary scheme is proposed for time-dependent wave problems in unbounded domains. The linear time-dependent wave equation, with or without a dispersive term, is considered in a semi-infinite wave guide. The infinite domain is truncated via an artificial boundary B, and a high-order non-reflecting boundary condition (NRBC) is imposed on B. Then the problem is solved numerically in the finite domain bounded by B. The new boundary scheme is based on a reformulation of the sequence of NRBCs proposed by Higdon. In contrast to the original formulation of the Higdon conditions, the scheme constructed here does not involve any high derivatives beyond second order. This is made possible by introducing special auxiliary variables on B. As a result, the new NRBCs can easily be used up to any desired order. They can be incorporated in a finite element or a finite difference scheme; in the present paper the latter is used. The parameters appearing in the NRBC are chosen automatically via a special procedure. Numerical examples concerning a semi-infinite wave guide are used to demonstrate the performance of the new method.
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high order non reflecting boundary conditions for dispersive waves
Wave Motion, 2003Co-Authors: Dan Givoli, Beny NetaAbstract:Problems of linear time-dependent dispersive waves in an unbounded domain are considered. The infinite domain is truncated via an artificial boundary B, and a high-order non-reflecting boundary condition (NRBC) is imposed on B. Then the problem is solved by a finite difference (FD) scheme in the finite domain bounded by B. The sequence of NRBCs proposed by Higdon is used. However, in contrast to the original low-order implementation of the Higdon conditions, a new scheme is devised which allows the easy use of a Higdon-type NRBC of any desired order. In addition, a procedure for the automatic choice of the parameters appearing in the NRBC is proposed. The performance of the scheme is demonstrated via numerical examples.
J. A. C. Nicol - One of the best experts on this subject based on the ideXlab platform.
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On the eye of the Goldeye Hiodon alosoides (Teleostei: Hiodontidae)
Journal of Zoology, 2009Co-Authors: A. C. G. Best, J. A. C. NicolAbstract:In the eye of the Goldeye the photoreceptors are arranged in bundles and the pigment epithelium contains a massive reflector or tapetum lucidum. Photoreceptor bundles are arranged in parallel rows, the bundles alternating in position from row to row. Each bundle contains about 60 photoreceptors, of which 30 or so are cones. Rod outer segments lie in the scleral half of the outer retinal region of the light-adapted eye. Processes of the pigment epithelium cells extend vitread almost to the external limiting membrane; they envelop the bundles of rods and cones, and a ring of four processes surrounds each bundle. A process contains two kinds of reflecting crystals (composed of uric acid). A large part of the epithelium cell is packed with small disc-shaped crystals (crystallites) enclosed in thin membranes; the tip of the process, in the region of the photoreceptor bundle, contains orderly arrays of small rod-shaped crystals (rodlets). It is suggested that the crystallites form a diffuse reflector backscattering light into the rods; and that the rodlets reflect light regularly from their surfaces into the photoreceptor bundles. In the light-adapted state, rods are enveloped by pigment and crystallites. The organization is compared with that of other fishes that have photoreceptors in bundles (grouped retinae) and tapeta lucida.
Gino Sardella - One of the best experts on this subject based on the ideXlab platform.
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mercury and other metals in muscle and ovaries of goldeye Hiodon alosoides
Environmental Toxicology and Chemistry, 2010Co-Authors: David B Donald, Gino SardellaAbstract:Concentrations of 24 trace metals were assessed in gravid ovaries and in muscle of female juvenile and adult female goldeye (Hiodon alosoides), a fish with both low annual growth (16 g/year as adults) and a long life span (maximum longevity of 30 years). It was hypothesized that adult fish with these life-history characteristics would maintain stable concentrations of metals in their tissues with higher levels of essential elements compared with those that are potentially toxic. As hypothesized, the concentration of most metals in muscle of adult female goldeye was similar at all ages, suggesting that uptake and excretion of metals was equal. Mercury was a notable exception. Total Hg concentrations in muscle of adults increased throughout life from a mean of 206 ng/g wet weight at age 8 to 809 ng/g at age 28, or by 26.2 ng/g/year. Concentrations of Hg were low in ovaries (mean 21.1 ng/g wet wt) compared to the mean for muscle, only 7% of the concentration in muscle. This was the lowest percent of muscle concentration of all 24 metals. Concentrations of Al, Ba, La, V, and Mn were significantly greater in muscle of juveniles and in ovaries than in muscle of adults. Concentrations of 13 metals were higher in ovaries relative to muscle, seven were similar, and four were depleted. Silver was enriched by over 50-fold in ovaries. Overall, the present study suggests that low concentrations of some metals in muscle of adult female goldeye, relative to concentrations in female juveniles and ovaries, may be maintained in part by transfer of metals to the external environment in eggs at spawning.
Alison M Murray - One of the best experts on this subject based on the ideXlab platform.
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the late eocene early oligocene ichthyofauna from the eastend area of the cypress hills formation saskatchewan canada
Journal of Vertebrate Paleontology, 2015Co-Authors: Julien D Divay, Alison M MurrayAbstract:ABSTRACT The Eocene through Miocene Cypress Hills Formation of Saskatchewan and Alberta has been the basis of studies on sedimentology, paleobotany, herpetofauna, avifauna, and mammalian local faunas. We describe the ichthyofauna from the Eastend area of the formation, representing late Eocene Chadronian to early Oligocene Whitneyan deposits. This fauna is diverse, including at least 14 fish taxa: Lepisosteus, Amiinae, aff. Hiodon, at least three cypriniforms among which is a Ptychocheilus-like leuciscine and at least one catostomid, two ictalurids, both ascribed to Astephus, a probable salmoniform, an amblyopsid-like percopsiform, Mioplosus, a probable moronid, a centrarchid, and at least one other perciform of uncertain affinity. The formation may therefore represent the first fossil record of the Amblyopsidae, and the first North American occurrence of the Moronidae. The composition of the ichthyofauna suggests higher temperatures during the Eocene—Oligocene transition than at present. Paleotemperature...
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a mid miocene ichthyofauna from the wood mountain formation saskatchewan canada
Journal of Vertebrate Paleontology, 2013Co-Authors: Julien D Divay, Alison M MurrayAbstract:ABSTRACT The southern Saskatchewan mid-Miocene Wood Mountain Formation has been the basis of studies describing its mammalian and herpetofaunas; here we present the description of the fish material from the formation. The fauna, of probable Barstovian age, would have been isolated from the western side of the continent, in an area draining towards the northeast. Sixteen taxa are recognized to specific orders or lower taxonomic levels, although this number is approximate because some identifications are tentative. The fauna includes a lepisosteid (Lepisosteus), an amiine, a probable Hiodontiform osteoglossomorph, a Hiodontid (Hiodon), at least two unidentified cypriniforms and a leuciscine, three ictalurids (Ameiurus, Ictalurus, and cf. Noturus), an esocid Esox sp. more closely related to pikes than to pikerels, a possible moronid perciform, a centrarchid (cf. Pomoxis), two percids (including Stizostedion sp.), and an unidentified teleost. This fauna includes the earliest North American percids, the last o...
Julian Junker - One of the best experts on this subject based on the ideXlab platform.
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structural genomic variation leads to genetic differentiation in lake tanganyika s sardines
Molecular Ecology, 2020Co-Authors: Julian Junker, Jessica A Rick, Peter B Mcintyre, Ismael A Kimirei, Emmanuel A Sweke, Julieth B Mosille, Bernhard Wehrli, Christian DinkelAbstract:Identifying patterns in genetic structure and the genetic basis of ecological adaptation is a core goal of evolutionary biology and can inform the management and conservation of species that are vulnerable to population declines exacerbated by climate change. We used reduced-representation genomic sequencing methods to gain a better understanding of genetic structure among and within populations of Lake Tanganyika's two sardine species, Limnothrissa miodon and Stolothrissa tanganicae. Samples of these ecologically and economically important species were collected across the length of Lake Tanganyika, as well as from nearby Lake Kivu, where L. miodon was introduced in 1959. Our results reveal differentiation within both S. tanganicae and L. miodon that is not explained by geography. Instead, this genetic differentiation is due to the presence of large sex-specific regions in the genomes of both species, but involving different polymorphic sites in each species. Our results therefore indicate rapidly evolving XY sex determination in the two species. Additionally, we found evidence of a large chromosomal rearrangement in L. miodon, creating two homokaryotypes and one heterokaryotype. We found all karyotypes throughout Lake Tanganyika, but the frequencies vary along a north-south gradient and differ substantially in the introduced Lake Kivu population. We do not find evidence for significant isolation by distance, even over the hundreds of kilometres covered by our sampling, but we do find shallow population structure.
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structural genomic variation leads to unexpected genetic differentiation in lake tanganyika s sardines
bioRxiv, 2020Co-Authors: Julian Junker, Jessica A Rick, Peter B Mcintyre, Ismael A Kimirei, Emmanuel A Sweke, Julieth B Mosille, Bernhard Wehrli, Christian DinkelAbstract:Abstract Identifying patterns in genetic structure and the genetic basis of ecological adaptation is a core goal of evolutionary biology and can inform the management and conservation of species that are vulnerable to population declines exacerbated by climate change. We used reduced representation genomic sequencing methods to gain a better understanding of genetic structure among and within populations of Lake Tanganyika’s two sardine species, Limnothrissa miodon and Stolothrissa tanganicae. Samples of these ecologically and economically important species were collected across the length of Lake Tanganyika, as well as from nearby Lake Kivu, where L. miodon was introduced in 1959. Our results reveal unexpected differentiation within both S. tanganicae and L. miodon that is not explained by geography. Instead, this genetic differentiation is due to the presence of large sex-specific regions in the genomes of both species, but involving different polymorphic sites in each species. Our results therefore indicate rapidly evolving XY sex determination in the two species. Additionally, we found evidence of a large segregating inversion in L. miodon. We found all inversion karyotypes throughout Lake Tanganyika, but the frequencies vary along a north-south gradient, and differ substantially in the introduced Lake Kivu population. We do not find evidence for significant isolation-by-distance, even over the hundreds of kilometers covered by our sampling, but we do find shallow population structure.