Mass transport in a two-layer wave boundary layer

The transport of a chemical species under the pure action of surface progressive waves in the benthic boundary layer which is loaded with dense suspended sediments is studied theoretically. The flow structure of the boundary layer is approximated by that of a two-layer Stokes boundary layer with a sharp interface between clear water and a heavy fluid. The simplest model of constant eddy diffusivities is adopted and the exchange of matter with the bed is ignored. For a thin layer of heavy fluid, whose thickness is comparable to the surface wave amplitude and the Stokes boundary layer thickness, effective transport equations are deduced using an averaging technique based on the method of homogenization. The effective advection velocity is found to be equal to the depth-averaged mass transport velocity, while the dispersion coefficient can be shown to be positive definite. Explicit expressions for the transport coefficients are obtained as functions of fluid properties and flow kinematics. Physical discussions on their relations are also presented.     

Behavioral response of Indo-Pacific humpback dolphin (Sousa chinensis) to vessel traffic

A series of land-based surveys were conducted at two vantage points of known dolphin abundance in Hong Kong. The purpose of this study was to determine the behavioral response of Indo-Pacific humpback dolphin (Sousa chinensis) to vessel traffic. Results indicated that dolphins dove for a longer duration in areas of heavy vessel traffic or when there was the presence of an oncoming vessel. Dependent upon the type of vessel and the relative distance, dolphins might flee, continue their ongoing activity, perform a new activity, or approach the vessel. Whilst slow-moving vessels appeared not to cause immediate stress on the dolphin community, fast-moving vessels often cause disruption of behavior and social life. In order to ensure a better environment for the animals, we suggest that proactive conservation measures such as the creation of a marine park, rules and regulations for dolphin watching activities, and regional control of vessel speed should be implemented.     

On the chemical mass-balance in estuaries

A general model is presented for mixing processes between river and ocean water in which are established criteria for the identification of any non-conservative behavior of the dissolved constituents involved. A review of previous data shows that in no case has removal of silica been demonstrated unambiguously in estuarine regimes. New data for iron which show highly non-conservative behavior are used in an example of the application of the model.     

Natural concentrations of lead in ancient Arctic and Antarctic ice

Concentrations of Pb and K were determined in a series of veneer layers chiseled in sequence from the outside toward the center of each of the five 1500–5500yr old ice core sections that had been drilled in Greenland and Antarctic ice. They were analogs of very old ice samples analyzed earlier by Herronet al. (1977) and Craginet al. (1975), who reported high concentrations of Pb in them. Lead contamination, existing at exterior concentrations of about 10⁶ ng/kg ice, had intruded to the centers of the cores, establishing interior values of at least 1.4 ng/kg ice in three electromechanically drilled Camp Century core sections taken from fluid filled drill holes. Corresponding Pb concentration changes were 3 × 10⁴ ng/kg ice to 1.2 ng/kg ice in two thermally drilled New Byrd Station core sections taken from non-fluid filled drill holes. Contamination made the lowest center concentrations serve only as upper limits to the original concentrations of Pb in the ice.Potassium concentrations decreased from exterior values of about 5 × 10⁵ ng/kg ice to an interior value of 2 × 10³ ng/kg ice in the Camp Century core sections and from 8 × 10⁴ ng/kg ice to 9 × 10² ng/kg ice in New Byrd Station core sections. Potassium contamination effects were not large within the central portions of the cores.These data verify earlier findings by Murozumiet al. (1969) and extend to a broader geographical significance the general validity of their observation of a ~ 300-fold increase of Pb concentrations in the Greenland ice sheet during the past 3000 yr. Our findings refute claims by Herronet al. (1977) and Craguinet al. (1975) that 100-fold excesses of natural Pb exist in 800 yr old Greenland ice above levels contributed by silicate dusts. Our new data also show that average Pb concentrations of 26 ng Pb/kg ice, claimed by Boutron and Lorius (1979) to be natural and present for 60 yr in snow strata in Antarctica, did not exist in old Antarctic ice, and that Pb concentrations have increased at least 10-fold in that ice during the past century.Virtually all of the present day ~300-fold excess of Pb above natural levels in Greenland ice can be shown to be caused by industrial Pb emissions to the atmosphere on the basis of the following factors: (1) the historic increase of Pb in snow strata coincides with the historic increase of industrial Pb production and atmospheric emissions (2) mass inventories of industrial emissions can account for the excess Pb in polar snow (3) new quantitative measurements of Pb emissions from volcanic plumes by Buat-Menard and Arnold (1978), Pattersonet al. (1981), and Buat-Menardet al. (1981), and from sea spray by Ng and Patterson (1981) and Settle and Patterson (1981). show that these natural sources cannot account for 99% of the excess Pb above contributions by silicate dusts observed today in the atmosphere; and (4) the historic increase of Pb in snow strata is paralleled by analogous increases of excess Pb shown by isotopic tracers to be industrial in water-laid sediments in a remote continental region (Shirahataet al., 1980). It is now known, however, that snows display about a 10-fold greater excess of industrial Pb above crustal silicate concentrations than exists in the air above the snows.     

Particle shape effect on macro‐ and micro‐behaviors of monodisperse ellipsoids

The microscopic and macroscopic behaviors of assemblages of monodisperse ellipsoids with different particle shapes were studied using the discrete element method. Four samples were created with 1170 identical prolate ellipsoids. The samples were compressed isotropically to 100 kPa. Then triaxial compression tests were carried out to very large strains until the ultimate state was reached. This paper presents typical macroscopic result including stress–strain relationship and volumetric behavior. In addition, the fabric of the samples was examined at the initial state, at the peak shear strength state, and at the ultimate state. We studied the evolution of three vector‐typed micromechanical arguments with strain including the particle orientation, branch vector, and normal contact force. The normal contact force (micromechanical argument) was found to have a direct relationship with the principal stress ratio (macroscopic parameter). The angles between these vectors were also investigated. The maximum angle between vectors is related to particle shape. The results indicate that the distributions and the maximum values of these angles do not change with loading. Copyright © 2008 John Wiley & Sons, Ltd.     

Influence of discontinuities on the stability of cut slopes in weathered meta-sedimentary rocks

The meta-sedimentary rocks along Pos Selim Highway in Perak State, Malaysia showed a gradational weathering profile based on differences particularly in textures, hardness, lateral changes in colour and consistency of material extension. Both large and small scale discontinuities observed in the investigated rocks reduce the physical and mechanical properties of the rocks, and provide slip surfaces for failures. Rock and soil samples were tested using established standards to determine their characteristics and responses under a wide variety of disturbances. Kinematic analyses were also carried out to determine the modes and likely modes of failures.

Petrographic analyses revealed associated micro-structures, and the implications of these micro-structures showed shearing components along planes of weakness. From the determined index properties of the tested soil samples, the weathered quartz mica schist is not suitable for structural support. Further study involving unconsolidated undrained direct shear box tests carried out under total stress, revealed a non-uniform response of the rocks to shearing disturbance along discontinuity planes, and the rate and depth of deformation. The shear strength components of the investigated rocks were thereby prescribed in terms of cohesion and friction angle. From the kinematic analyses across this extended cut slope, there are possibilities of wedge and planar failures.     

Frame transformation of spherical-harmonic coefficients of differential particle intensity

We present a general second-order-correct frame transformation on spherical-harmonic coefficients of differential particle intensity. The transformation, valid for relativistic particles as well, provides a clear view of the Compton-Getting effect. It shows explicitly how each transformed harmonic coefficient depends on a subset of the original harmonic coefficients. The general expression for the first-order Compton-Getting vector anisotropy is derived and interpreted. In addition, we show how the new transformation allows one to simplify a current procedure for determining the directional intensity in a comoving frame. This involves the directional particle data measured on a spacecraft.