The expansion of clusters of particles under the action of atmospheric macroturbulence

Summary Making use of a 500 mb numerical forecast some problems of atmospheric large-scale diffusion are investigated. The expansion of various sets of clusters of particles is compared with the predictions based on the similarity theory of homogeneous turbulence. The spreading rates were in the beginning of the period of the forecast in a good agreement with the theoretical prediction, but later on they fell to the values considerable smaller than the predicted ones. The reasons of such behaviour are discussed. Furthermore the difference in zonal and meridional expansion of the clusters is demonstrated, the zonal expansion rates being more than one order of magnitude greater than the meridional ones.This work is part of the research on atmospheric macroturbulence, which has been sponsored partly by the Cambridge Research Laboratories, O.A.R. through the European Office, Aerospace Research, USAF.     

Isotopic variation of fishes in freshwater and estuarine zones of a large subtropical coastal lagoon

We used stable C and N isotope ratios of tissues from 29 fish species from a large subtropical lagoon in southern Brazil to examine spatial variability in isotopic composition and vertical trophic structure across freshwater and estuarine habitats. Nitrogen isotope ratios indicated a smooth gradation in trophic positions among species, with most fishes occupying the secondary and tertiary consumer level. Fish assemblages showed a significant shift in their carbon isotopic signatures between freshwater and estuarine sites. Depleted carbon signatures (from −24.7‰ to −17.8‰) were found in freshwater, whereas more enriched signatures (from −19.1‰ to −12.3‰) were obtained within the estuarine zone downstream. Based on our survey of the C₃ and C₄ plants and isotopic values for phytoplankton and benthic microalgae reported for ecosystems elsewhere, we hypothesized that the observed δ¹³C differences in the fish assemblage between freshwater and estuarine sites is due to a shift from assimilating organic matter ultimately derived from C₃ freshwater marsh vegetation and phytoplankton at the freshwater site (δ¹³C ranging from −25‰ to −19‰), to C₄ salt-marsh (e.g. Spartina) and widgeon grass (Ruppia maritima), benthic microalgae and marine phytoplankton at the estuarine sites (from −18‰ to −12‰). Our results suggested that fish assemblages are generally supported by autochthonous primary production. Freshwater fishes that likely were displaced downstream into the estuary during periods of high freshwater discharge had depleted δ¹³C values that were characteristic of the upper lagoon. These results suggest that spatial foodweb subsidies can occur within the lagoon.     

Biogeochemical impacts due to mesoscale eddy activity in the Sargasso Sea as measured at the Bermuda Atlantic Time-series Study (BATS)

A comparison of monthly biogeochemical measurements made from 1993 to 1995, combined with hydrography and satellite altimetry, was used to assess the impacts of nine eddy events on primary productivity and particle flux in the Sargasso Sea. Measurements of primary production, thorium-234 flux, nitrate+nitrite, and photosynthetic pigments made at the US JGOFS Bermuda Atlantic Time-series Study (BATS) site were used. During the 3 years of this study, four out of six high thorium-234 flux events occurred during the passage of an eddy. Primary production nearly as high as the spring bloom maximum was observed in two mode-water eddies (May 1993 and July 1995). The 1994 spring bloom at BATS was suppressed by the passage of an anticyclone. Distinct phytoplankton community shifts were observed in mode-water eddies, which had an increased percentage of diatoms and dinoflagellates, and in cyclones, which had an increased percentage of Synechococcus. These variations in species composition within mode-water eddies and cyclones may be associated with the ages of the sampled eddies, and/or differences in physical, chemical, and biological factors in these two distinct eddy types. In general, eddies that were 1–2 months old elicited a large biological response; eddies that were 3 months old may show a biological response and were accompanied by high thorium flux; eddies that were 4 months old or older did not show a biological response or high thorium flux. A conceptual model depicting temporal changes during eddy upwelling, maturation, and decay can explain the observations in all seven upwelling eddies present in the time-series investigated herein.     

Glucuronidation in the polar bear (Ursus maritimus)

Polar bears bioaccumulate lipophilic pollutants, including polychlorinated biphenyls (PCBs), into their bodies from their exclusive diet of marine organisms. Hydroxylated PCB metabolites (OH-PCBs) have been found in plasma, presumably due to CYP-dependent biotransformation of PCBs in liver. Little is known about the phase 2 metabolism of hydroxylated xenobiotics in polar bears. The objective of this study was to examine UDP-glucuronosyltransferase (UGT) activity with OH-PCBs and a hydroxylated polycyclic aromatic hydrocarbon, 3-hydroxy-benzo(a)pyrene (3-OH-BaP), in polar bear liver. Samples of frozen polar bear liver were used to prepare microsomes. UGT activity with 3-OH-BaP in Brij-treated microsomes, measured by a fluorescence assay, was readily measurable with protein concentrations in assay tubes of up to 10 g/ml, but dropped off very sharply at higher protein concentrations. The apparent Km for 3-OH-BaP was 1.71 +/- 0.04 microM, and Vmax 1.26 +/- 0.16 nmol/min/mg protein (mean +/- SD, n=3). UGT activities with a model tetrachloro-OH-PCB (4'-OH-CB72) and a model hexachloro-OH-PCB (4'-OH-CB159) were assayed with [14-C]-UDPGA and separation of the [14-C]-glucuronide by ion-pair extraction and thin-layer chromatography. [14-C]-glucuronide conjugates were readily formed by polar bear liver microsomes in the absence of added substrate, apparently from contaminants present in liver. This phenomenon was not observed using hepatic microsomes from laboratory-held catfish. Glucuronidation efficiency was much higher with 4'-OH-CB72 (Km 7.3 microM; Vmax 1.55 nmol/min/mg) than 4'-OH-CB159 (Km 16.1 microM; Vmax 0.46 nmol/min/mg). The identities of the aglycones present in polar bear liver are not known, but could include OH-PCBs or hydroxylated metabolites of other persistent organic pollutants. This study demonstrates that UGT with high activity for 3-OH-BaP and other substrates is present in polar bear liver.     

Observed foundation behaviour of concrete gravity platforms installed in the North Sea 1973–1978

Available measurements of foundation behaviour of the 13 concrete gravity platforms installed in the North Sea in the years 1973–1978 are presented. The measurements cover both the installation phase and the early part of the operation period. For the installation phase, measurements of dowel and skirt penetration resistance, base contact stresses, tilt, piping and erosion, are presented. For the operation period, the presentation includes measurements of settlements, pore water pressures, base contact stresses, permanent lateral displacements, cyclic displacements, dynamic behaviour and erosion. The measurements are used to back calculate soil properties and to evaluate the adequacy of the design procedures which have been used. The observations give valuable experience with respect to the foundation performance of offshore gravity platforms.     

Nannoplankton of the Atlantic Ocean from sediment trap samples

Calcareous nannoplankton from sediment trap samples collected at six sites in the Atlantic Ocean from 23° S to 73° N (cruise 20 of R/V Vityaz’ and cruise 33 and 34 of R/V Akademik Mstislav Keldysh). Those samples were studied with a scanning electron microscope. In the coastal and open-sea regions of the North and South Atlantic and in the subarctic region of the Norwegian Sea, the conditions are significantly different. In the shelf area of the Benguela upwelling, 11 species were recognized; some of them were agglutinated by diatoms and tintinnides or covered the surface of pellets. The Broken Spur and TAG pelagic areas of the North Atlantic contained up to 43 coccolith species. They included holococcoliths, large pelagic, and delicate easily soluble species distributed over the entire water column. The presence of coccoliths in the high-latitude area of the Norwegian Sea is related to their supply with the warmer North Atlantic waters. These assemblages are distinguished by a low species diversity and an enhancement of the coccolith solubility with the depth increase.     

Dynamics of an elastically moored floating body by the three-dimensional infinite element method

The three-dimensional problem of the dynamics of a moored floating object under the action of regular waves is solved numerically as a boundary value problem by use of the finite-infinite element method. The cross-sectional shape of the floating body and the mooring arrangements may all be arbitrary. The mathematical formulations of the problem and procedures of the numerical method are presented in this paper. A corresponding computer program WALOAD has been developed, which is capable of computing wave forces on fixed and floating structures. Numerical computations using this program could give very accurate results, even though rather coarse meshes were used. The program is easy to use and is readily applicable in many practical situations.     

Simulation of green water flow on deck using non-linear dam breaking theory

Experiments carried out with models of floating production, storage and offloading platforms (FPSOs) showed that the flow of water over the deck edge, onto the deck resembled a suddenly released wall of water rather than a breaking wave. Therefore green water flow onto the deck was simulated using dam breaking theory, but the theory’s shallow-water assumptions may be limiting. In this paper a non-linear dam breaking problem is formulated. Equations of motion in the Lagrangian form are used and the solution is sought as an infinite series in time. Comparisons with the shallow water approximation are carried out.     

Robust adaptive control of underactuated ships on a linear course with comfort

This paper addresses an important problem in ship control application—the robust stabilization of underactuated ships on a linear course with comfort. Specifically, we develop a multivariable controller to stabilize ocean surface ships without a sway actuator on a linear course and to reduce roll and pitch simultaneously. The controller adapts to unknown parameters of the ship and constant environmental disturbances induced by wave, ocean current and wind. It is also robust to time-varying environmental disturbances, time-varying change in ship parameters and other motions of the ship such as surge and heave. The roll and pitch can be made arbitrarily small while the heading angle and sway are kept to be in reasonably small bounds. The controller development is based on Lyapunov’s direct method and backstepping technique. A Lipschitz continuous projection algorithm is used to update the estimate of the unknown parameters to avoid the parameters’ drift due to time-varying environmental disturbances. Simulations on a full-scale catamaran illustrate the effectiveness of our proposed controller.     

Evidence of NW extension of the North Anatolian Fault Zone in the Marmara Sea: a new interpretation of the Marmara Sea (Izmit) earthquake on 17 August 1999

Active faults aligning in NW–SE direction and forming flower structures of strike-slip faults were observed in shallow seismic data from the shelf offshore of Avcılar in the northern Marmara Sea. By following the parallel drainage pattern and scarps, these faults were traced as NW–SE-directed lineaments in the morphology of the northern onshore sector of the Marmara Sea (eastern Thrace Peninsula). Right-lateral displacements in two watersheds of drainage and on the coast of the Marmara Sea and Black Sea are associated with these lineaments. This right-lateral displacement along the course of these faults suggests a new, active strike-slip fault zone located at the NW extension of the northern boundary fault of the ?ınarcık Basin in the Marmara Sea. This new fault zone is interpreted as the NW extension of the northern branch of the North Anatolian Fault Zone (NAFZ), extending from the ?ınarcık Basin of the Marmara Sea to the Black Sea coast of the Thrace Peninsula, and passing through B üy ük ?ekmece and K ü ? ük ?ekmece lagoons. These data suggest that the rupture of the 17 August 1999 earthquake in the NAFZ may have extended through Avcılar. Indeed, Avcılar and İzmit, both located on the Marmara Sea coast along the rupture route, were strongly struck by the earthquake whereas the settlements between Avcılar and İzmit were much less affected. Therefore, this interpretation can explain the extraordinary damage in Avcılar, based on the newly discovered rupture of the NAFZ in the Marmara Sea. However, this suggestion needs to be confirmed by further seismological studies.