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  • 1
    Electronic Resource
    Electronic Resource
    Seismic character of gas hydrates on the Southeastern U.S. continental margin (1994)
    Springer
    Marine geophysical researches 16 (1994), S. 163-184 
    Details
    ISSN: 1573-0581
    Keywords: bottom simulating reflection ; gas hydrate ; amplitude blanking ; seismic characteristics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Gas hydrates are stable at relatively low temperature and high pressure conditions; thus large amounts of hydrates can exist in sediments within the upper several hundred meters below the sea floor. The existence of gas hydrates has been recognized and mapped mostly on the basis of high amplitude Bottom Simulating Reflections (BSRs) which indicate only that an acoustic contrast exists at the lower boundary of the region of gas hydrate stability. Other factors such as amplitude blanking and change in reflection characteristics in sediments where a BSR would be expected, which have not been investigated in detail, are also associated with hydrated sediments and potentially disclose more information about the nature of hydratecemented sediments and the amount of hydrate present. Our research effort has focused on a detailed analysis of multichannel seismic profiles in terms of reflection character, inferred distribution of free gas underneath the BSR, estimation of elastic parameters, and spatial variation of blanking. This study indicates that continuous-looking BSRs in seismic profiles are highly segmented in detail and that the free gas underneath the hydrated sediment probably occurs as patches of gas-filled sediment having variable thickness. We also present an elastic model for various types of sediments based on seismic inversion results. The BSR from sediments of high ratio of shear to compressional velocity, estimated as about 0.52, encased in sediments whose ratios are less than 0.35 is consistent with the interpretation of gasfilled sediments underneath hydrated sediments. This model contrasts with recent results in which the BSR is explained by increased concentrations of hydrate near the base of the hydrate stability field and no underlying free gas is required.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01237512
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  • 2
    Electronic Resource
    Electronic Resource
    Petrov-Galerkin finite element methods with a hinged test space for singularly perturbed problems (1985)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 21 (1985), S. 1803-1812 
    Details
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In this paper we introduce finite element methods of Petrov-Galerkin type for the approximate solution of two-point boundary-value problems for singularly perturbed, second-order, ordinary, linear differential equations. We write down Petrov-Galerkin methods on a uniform mesh which have asymptotic error estimates, as the mesh size tends to zero, whose magnitude is independent of the singular perturbation parameter. This is in marked contrast to standard finite element methods which do not possess such a property on a uniform mesh. For these, typically, the error on a fixed uniform mesh blows up as the singular perturbation parameter tends to zero.This robust behaviour of these Petrov-Galerkin methods for singularly perturbed problems is achieved by choosing trial spaces of standard piecewise polynomial type, while the test spaces consist of hinged piecewise polynomials.We consider self-adjoint and non-self-adjoint two-point boundary-value problems with Dirichlet boundary conditions. We define hinged test spaces for both types of problem. We then introduce a number of sample problems and we present numerical solutions of these sample problems using a Petrov-Galerkin method with the appropriate hinged test space.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/nme.1620211007
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  • 3
    Electronic Resource
    Electronic Resource
    Dispersal ofAleochara bilineata [Col.: Staphylinidae] following inundative releases in urban gardens (1992)
    Springer
    BioControl 37 (1992), S. 55-63 
    Details
    ISSN: 1573-8248
    Keywords: Staphylinidae ; Aleochara bilineata ; beneficial arthropods ; dispersal ; predation ; biological control ; arthropodes utiles ; dissémination ; prédation ; lutte biologique ; Staphylinidae ; Aleochara bilineata
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Description / Table of Contents: Résumé Aleochara bilineata (Gyllenhal) [Coleoptera: Staphylinidae] est un prédateur et un parasite courants de la mouche des racines [Diptera: Anthomyiidae] dans les cultures commerciales et les jardins potagers. Pour évaluer l'activité de dissémination deA. bilineata dans les jardins potagers, on a lâché des coléoptères marqués à raison de 0 et de 1000 en 1987, et de 0, 250, 500, et 1000/jardin potager/semaine en 1988. Trois pour cent des coléoptères ainsi marqués ont été recapturés dans les jardins potagers d'origine. Les populations naturelles deA. bilineata sont très faibles dans tous les jardins potagers et on ne constate aucune augmentation décelable de 1987 à 1988. Les recaptures sont proportionnelles aux taux de lâchers. On n'observe aucune différence significative dans les taux de recapture entre les sexes. Les recaptures et les distributions non uniformes deA. bilineata marqués dans les jardins potagers révèlent qu'ils ont pu voler au moins à 5 km de distance dans les conditions urbaines et choisir certains jardins plutôt que d'autres comme emplacements propices à l'accouplement, la quête de nourriture et l'oviposition.
    Notes: Abstract Aleochara bilineata (Gyllenhal) [Coleoptera: Staphylinidae] is a common predator and endoparasite of root maggot [Diptera: Anthomyiidae] in both commercial crops and home gardens. To test dispersal activity ofA. bilineata in home gardens, marked beetles were released at rates of 0 and 1,000 in 1987 and 0, 250, 500, and 1,000/gardens/wk in 1988. Three percent of marked beetles were recaptured in release gardens. NaturalA. bilineata populations were very small in all gardens, and there was no detectable increase from 1987 to 1988. Recaptures were proportional to release rates. There was no significant difference in recapture rates between sexes. Recaptures and non-uniform distributions of markedA. bilineata in control gardens revealed that they were capable of flying at least 5 km under urban conditions, and of selecting particular gardens as suitable mating, foraging, and oviposition sites.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02372974
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