Kirsch problem and the lower natural frequencies of a clamped square-plate

A clamped square-plate is subjected to a uniform state of stress in the x-direction. The present study deals with the basic question of determining the variation of the lower natural frequencies of transverse vibration of a plate as a small diameter, central hole is made in it, introducing a stress concentration field.     

Dynamics of the long-period tides

The long-period tides are a tool for understanding oceanic motions at low frequencies and large scales. Here we review observations and theory of the fortnightly, monthly and pole tide constitutents. Observations have been plagued by low signal-to-noise ratios and theory by the complex lateral geometry and great sensitivity to bottom slopes. A new spectral element model is used to compute the oceanic response to tidal forcing at 2-week and monthly periods. The general response is that of a heavily damped (Q ≈ 5) system with both the energy input from the moon and the dissipation strongly localized in space. The high dissipation result is probably generally applicable to all low frequency barotropic oceanic motions. Over much of the ocean, the response has both the character of a large-scale and a superposed Rossby wave-like character, thus vindicating two apparently conflicting earlier interpretations. To the extent that free waves are excited they are consistent with their being dominated by Rossby and topographic Rossby wave components, although gravity modes are also necessarily excited to some degree. In general, a modal representation is not very helpful. The most active regions are the Southern Ocean and the western and northern North Atlantic. These results are stable to changes in geometry, topography, and tide period. On a global average basis, the dynamical response of Mm is closer to equilibrium than is Mf.     

A phase-resolving cross shore sediment transport model for beach profile evolution

A phase-resolving wave transformation module is combined with an intra-wave sediment transport module to calculate the on-/offshore sediment transport rates. The wave module is based on the Boussinesq equations extended into the surf zone. The vertical variation of the mean undertow and the intra-wave sediment concentrations are calculated. The net sediment transport rates are calculated, and the equation for conservation of sediment is solved to predict the beach profile evolution. The results of the present paper showed that the undertow contribution to the sediment transport rates is not dominating in all parts of the surf zone, even for eroding beaches, suggesting that other contributions should not be neglected. The present model also showed that for the same offshore wave energy the time series of the oscillatory motion is important and that the effect of wave groups cannot be disregarded.     

Harmonic generation past a submerged porous step

Experiments were conducted in a wave flume to study the differences between harmonic evolution of monochromatic waves as they propagate over a submerged impermeable or porous step under non-breaking conditions. Results are used as a preliminary analysis to establish some engineering design criteria on harmonic generation on submerged porous structures. The root-mean-squared wave height evolution is also studied and compared to linear models as a first approximation. It is shown that porous structure increases the effective relative depth and decreases the relative wave height, resulting in a lower Ursell number and a lower chance to generate harmonics. The effective water depth over a step as defined in the paper, provides information to evaluate the potential harmonic generation.     

Primary production and plankton stocks in the Pacific Ocean and their seasonal variation according to remote sensing and field observations

Data collected from 20 years of observations by the P. P. Shirshov Institute of Oceanology (about 250 comprehensive ecosystem stations) are summarized to evaluate the primary production and biomass of the principal groups of plankton in the Pacific Ocean. The stations were classified into geographical regions according to satellite determined criteria. The areas of these regions were evaluated according to CZCS data from 1978 to 1986. The total value of primary production was evaluated as 26·9 Gt C year⁻¹. Taking the “bottle effect” correction into account, this value may be as high as 45.6 Gt C year⁻¹. Total biomass values of phytoplankton (134 Mt C), bacteria (86 Mt C), protozoa (26 Mt C) and mesoplankton (184 Mt C) were also calculated. Seasonal variabilities of all these values were remarkably insignificant.     

Fine-grained sediments in deep water: An overview of processes and facies models

There appears to be a continuum of processes affecting the transport and deposition of fine-grained sediments in the deep sea. This results in a facies continuum within which we can recognize three broadly different facies groups: turbidites, contourites, and pelagites/hemipelagites. Several distinct facies models can be defined for each group on the basis of their chief structural, textural, and compositional attributes.     

On the origin of glauconitic and chamositic granules

Glauconitic minerals range from green smectite to 10Å glauconite, occur mainly in peloids (most of which were fecal pellets), and apparently were produced largely by neoformation replacing several kinds of substrate. Chamositic minerals, berthierine and chamosite, occur in Recent and ancient peloids, but mostly in ancient ooids, and they developed by alteration of a precursor Al-rich clay mineral. Ooid sheaths were built by rolling of cores on ue sea floor. Glauconitic greensands and chamositic oolitic ironstones are condensed sequences deposited as sandwaves during long periods of reduced influx of sediment. Some are associated with hardgrounds.     

Alkaline Phosphatase Activity in the Red-Tide Dinoflagellate, Ptychodiscus brevis

Abstract. Alkaline phosphatase activity (APA) was found in a nearshore, natural population of the red-tide dinoflagellate Ptychodiscus brevis. Initial hydrolysis rates were enhanced by two orders of magnitude within 24 h upon addition of ammonium. Other nutrient (additions) or no additions also lead to a higher, although less pronounced increase in activity. Enhanced growth after nutrient additions combined with specific APA indicated that the bloom was both N and P limited. Since the natural population was a mixture of diatoms and the dinoflagellate, APA was also measured in unialgal cultures of P. brevis. APA was not reduced but enhanced by the addition of low concentrations of orthophosphate (0.5 and 1 μM). Higher orthophosphate concentrations (5 to 20 μM) reduced APA, although activity returned to control levels within 2 to 6h. Repression occurred within 30 sec after a 20 μM orthophosphate addition. Cells which had APA repressed by an orthophosphate addition regained their initial activity within 2 h after washing with phosphate-free media. Phosphorus-deficient cells of P. brevis possess an alkaline phosphatase system which is capable of continued activity at low in situ orthophosphate levels.     

Effects of pulp bleach plant effluents on hepatic xenobiotic biotransformation enzymes in fish: Laboratory and field studies

The present preliminary report on studies of the influence of pulp bleach plant effluents on hepatic biotransformation enzymes in fish is a part of a major characterisation of biochemical and physiological effects of effluents from pulp industries in Sweden. Our studies on the xenobiotic biotransformation enzymes demonstrate, so far, that the pulp effluents have the potential to strongly induce 7-ethoxyresorufin-O-deethylase activity (EROD) in fish liver and that fish living in the receiving water of an effluent from a pulp bleach plant have induced hepatic EROD activities as well as higher hepatic UDP glucuronyltransferase activities than those living in an unpolluted area. It is thus apparent that measures of induction of biotransformation enzymes in fish liver may be a useful approach in monitoring the presence of potential hazardous compounds released from pulp industries.