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Scattered and free waves over periodic beds (2003)

Porter, R. ; Porter, D.

Cambridge University Press

In: Journal of Fluid Mechanics. 2003; 483: 129-163. Published 2003 May 25. doi: 10.1017/s0022112003004208.

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Publikationsdatum: 2003-05-25

Beschreibung: The behaviour of water waves over periodic beds is considered in a two-dimensional context and using linear theory. Three cases are investigated: the scattering of waves by a finite section of periodic topography; the Bloch problem for infinite periodic topography; and sloshing motions over periodic topography confined between vertical boundaries. Connections are established between these problems. A transfer matrix method incorporating evanescent modes is developed for the scattering problem, which reduces the computation to that required for a single period, without compromising full linear theory. The problem of the existence of Bloch waves can also be posed on a single period, leading to a close relationship between it and the scattering problem. Sloshing motions over periodic beds, which may be regarded as special cases of the Bloch problem, are also found to have a significant connection with wave scattering. Integral equations methods allied to the Galerkin approximation are used to resolve the three problems numerically. In particular, the full linear solution for Bragg resonance is presented, allowing the accuracy of existing approximations to this phenomenon to be assessed. The selection of results given illustrates the main features of the work.

Print ISSN: 0022-1120

Digitale ISSN: 1469-7645

Thema: Maschinenbau , Physik

Publiziert von Cambridge University Press

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Digitale Medien

HERBICIDES AND TRANSFORMATION PRODUCTS IN SURFACE WATERS OF THE MIDWESTERN UNITED STATES (2003)

Battaglin, William A. ; Thurman, Earl M. ; Kalkhoff, Stephen J. ; [weitere]

Oxford, UK : Blackwell Publishing Ltd

Journal of the American Water Resources Association 39 (2003), S. 0

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ISSN: 1752-1688

Quelle: Blackwell Publishing Journal Backfiles 1879-2005

Thema: Architektur, Bauingenieurwesen, Vermessung , Geographie

Notizen: : Most herbicides applied to crops are adsorbed by plants or transformed (degraded) in the soil, but small fractions are lost from fields and either move to streams in overland runoff, near surface flow, or subsurface drains, or they infiltrate slowly to ground water. Herbicide transformation products (TPs) can be more or less mobile and more or less toxic in the environment than their source herbicides. To obtain information on the concentrations of selected herbicides and TPs in surface waters of the Midwestern United States, 151 water samples were collected from 71 streams and five reservoir outflows in 1998. These samples were analyzed for 13 herbicides and 10 herbicide TPs. Herbicide TPs were found to occur as frequently or more frequently than source herbicides and at concentrations that were often larger than their source herbicides. Most samples contained a mixture of more than 10 different herbicides or TPs. The ratios of TPs to herbicide concentrations can be used to determine the source of herbicides in streams. Results of a two-component mixing model suggest that on average 90 percent or more of the herbicide mass in Midwestern streams during early summer runoff events originates from the runoff and 10 percent or less comes from increased ground water discharge.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1111/j.1752-1688.2003.tb04402.x

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Digitale Medien

Kakadumycins, novel antibiotics from Streptomyces sp. NRRL 30566, an endophyte of Grevillea pteridifolia (2003)

Castillo, Uvidelio ; Harper, James K ; Strobel, Gary A ; [weitere]

Oxford, UK : Blackwell Publishing Ltd

FEMS microbiology letters 224 (2003), S. 0

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ISSN: 1574-6968

Quelle: Blackwell Publishing Journal Backfiles 1879-2005

Thema: Biologie

Notizen: An endophytic streptomycete (NRRL 30566) is described and partially characterized from a fern-leaved grevillea (Grevillea pteridifolia) tree growing in the Northern Territory of Australia. This endophytic streptomycete produces, in culture, novel antibiotics – the kakadumycins. Methods are outlined for the production and chemical characterization of kakadumycin A and related compounds. This antibiotic is structurally related to a quinoxaline antibiotic, echinomycin. Each contains, by virtue of their amino acid compositions, alanine, serine and an unknown amino acid. Other biological, spectral and chromatographic differences between these two compounds occur and are given. Kakadumycin A has wide spectrum antibiotic activity, especially against Gram-positive bacteria, and it generally displays better bioactivity than echinomycin. For instance, against Bacillus anthracis strains, kakadumycin A has minimum inhibitory concentrations of 0.2–0.3 μg ml−1 in contrast to echinomycin at 1.0–1.2 μg ml−1. Both echinomycin and kakadumycin A have impressive activity against the malarial parasite Plasmodium falciparum with LD50s in the range of 7–10 ng ml−1. In macromolecular synthesis assays both kakadumycin A and echinomycin have similar effects on the inhibition of RNA synthesis. It appears that the endophytic Streptomyces sp. offer some promise for the discovery of novel antibiotics with pharmacological potential.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1016/S0378-1097(03)00426-9

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Digitale Medien

IMPACTS OF URBANIZATION ON NUTRIENT CONCENTRATIONS IN SMALL SOUTHEASTERN COASTAL STREAMS (2003)

Tufford, Daniel L. ; Samarghitan, Carmen L. ; McKellar, Hank N. ; [weitere]

Oxford, UK : Blackwell Publishing Ltd

Journal of the American Water Resources Association 39 (2003), S. 0

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ISSN: 1752-1688

Quelle: Blackwell Publishing Journal Backfiles 1879-2005

Thema: Architektur, Bauingenieurwesen, Vermessung , Geographie

Notizen: : Coastal watersheds in the southeastern United States are rapidly changing due to population growth and attendant increases in residential development, industry, and tourism related commerce. This research examined spatial and temporal patterns of nutrient concentrations in streams from 10 small watersheds (〈 4 km2) that drain into Murrells Inlet (impacted) and North Inlet (pristine), two high salinity estuaries along the South Carolina coast. Monthly grab samples were collected during baseflow during 1999 and analyzed for total and dissolved inorganic and organic forms of nitrogen and phosphorus. Data were grouped into forested wetland creeks (representing predevelopment reference sites), urban creeks, and urban ponds. DON and NH4 concentrations were greater in forested streams than in urban streams. NO3 and TP concentrations were greatest in urban streams. Seasonally, concentrations were highest during summer for TN, NH4, DON, and TP, while NO3 concentrations were greatest during winter. Nutrient ratios clearly highlighted the reduction in organic nitrogen due to coastal development. Multiple regression models to predict instream nutrient concentrations from land use in Murrells Inlet suggest that effects are not significant (small r2). The findings indicate that broad land use/land cover classes cannot be used to predict nutrient concentrations in streams in the very small watersheds in our study areas.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1111/j.1752-1688.2003.tb04385.x

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