The dynamics of traffic assignment and traffic control: A theoretical study

The paper considers traffic assignment, with traffic controls, in an increasingly dynamic way. First, a natural way of introducing the responsive policy, P_o, into steady state traffic assignment is presented. Then it is shown that natural stability results follow within a dynamical version of this static equilibrium model (still with a constant demand). We are able to obtain similar stability results when queues are explicitly allowed for, provided demand is constant. Finally we allow demand to vary with time; we consider the dynamic assignment problem with signal-settings now fixed. Here we assume that vehicles are very short and that deterministic queueing theory applies, and show that the time-dependent queueing delay at the bottleneck at the end of a link is a monotone function of the time-dependent input profile to the bottleneck. We have been unable to obtain results when dynamic demand and responsive signal control are combined.     

Coupled transport-reaction pathways and distribution patterns between siliciclastic-carbonate sediments at the Ria de Vigo

This paper examines the linkages between the space-distribution of grain sizes and the relative percentage of the amount of mineral species that result from the mixing process of siliciclastic and carbonate sediments at the Ria de Vigo (NW of Spain).The space-distribution of minerals was initially determined, starting from a detailed mineralogical study based on XRD-Rietveld analysis of the superficial sediments. Correlations between the maps obtained for grain sizes, average fractions of either siliciclastic or carbonates, as well as for individual-minerals, were further stabilised. From this analysis, spatially organized patterns were found between carbonates and several minerals involved in the siliciclastic fraction. In particular, a coupled behaviour is observed between plagioclases and carbonates, in terms of their relative percentage amounts and the grain size distribution.In order to explain these results a conceptual model is proposed, based on the interplay between chemical processes at the seawater–sediment interface and hydrodynamical factors. This model suggests the existence of chemical control mechanisms that, by selective processes of dissolution-crystallization, constrain the mixed environment's long-term evolution, inducing the formation of self-organized sedimentary patterns.     

SLENIUM FROM BEEF IS HIGHLY BIOAVAILABLE AS ASSESSED BY LIVER GLUTATHIONE PEROXIDASE （EC1．11．1．9） ACTIVITY AND TISSUE SELENI

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On the axial force induced on a duct by a propulsor

The axial force induced on a duct (duct thrust) which surrounds a propulsor is, by means of an energy conservation argument, expressed in terms of the thrust and power of the propulsor and the kinetic energy losses per unit of time of the propulsor and the duct. Emphasis is put on the linear theory of an axisymmetric ducted actuator disk, where it is shown that the work done by the duct thrust is equal to the extra work done by the actuator disk when it is surrounded by the duct. This simplified model gives more insight into the interaction between the propeller and the duct and on the limits of linearization.     

Pb and Pu in the Northeast Water Polynya, Greenland: particle dynamics and sediment mixing rates

Distributions of the radionuclides ²¹⁰Pb and ^239,240Pu in sediment cores from the Northeast Water Polynya, Greenland, showed that these nuclides reached depths of 5–15 cm by particle mixing and sediment accumulation. End-member average values of the particle mixing coefficient and sediment accumulation rate were 0.13 cm² y⁻¹ and 0.06 cm y⁻¹, obtained from the ²¹⁰Pb profiles by assuming that each process is dominant relative to the other. Both ²¹⁰Pb and ^239,240Pu were measured on four cores; using the Pu data to constrain mixing rates produced corrected sediment accumulation rates that were 20–80% of the values calculated by neglecting mixing. Organic carbon burial in the polynya sediments was ≤0.4 mmol m⁻² d⁻¹, based on measured POC values at depth in the sediments and sediment accumulation rates corrected for mixing. This value is about 1% of the independently measured POC flux leaving the euphotic zone and compares with benthic carbon remineralization rates of 7% calculated by others from O₂ uptake in the sediments.The inventories of excess ²¹⁰Pb in the sediments ranged from 6 to 28 dpm cm⁻². Relative to the atmospheric input of ²¹⁰Pb and in situ production from decay of ²²⁶Ra, approximately 5 dpm cm⁻² of ²¹⁰Pb was being removed from the water column. The difference between the removal from the water column and sediment inventories suggests a net import of ²¹⁰Pb to the polynya. This may occur by input of dissolved ²¹⁰Pb from offshore waters or by input of ²¹⁰Pb carried by sea ice. Particulate matter in land-derived fast ice adjacent to the polynya contained 330 ± 14 dpm of excess ²¹⁰Pb g⁻¹. If particles transported in sea ice are comparable to those extracted from fast ice, then sea ice transport into the polynya followed by melting may be an important source of excess ²¹⁰Pb to the area. Fast ice also may contribute ²¹⁰Pb if portions break off and melt within the polynya, as occurred in 1993.     

The coastal edge of the Northeast Water polynya in spring 1993

Multidisciplinary, marine ecological observations were conducted at the shallow water edge of the Northeast Water in June, 1993. Although variable in size and shape, a small polynya was constantly present at Eskimonaes, at the fast-ice edge of Ingolfsfjord. A shallow stratified layer developed at the water sufface at negative water and air temperatures—an effect of sea ice melting in cold water early in the season. Nutrients were recorded in considerable quantities, although by mid July NO₃ had become depleted. The chlorophyll and phytoplankton maxima at 8–12 m depth had peak values of 2 mg chl a m⁻³, typical for Arctic algal blooms. The phytoplankton included over 90 species and was dominated by the Fragillariopsis group. Zooplankton was poor in biomass and density, but over 23 taxa were found, with the copepods Oithona similis and Pseudocalanus acuspes being numerically dominant. Sedimentation was approximately 0.2 g dry weight m⁻² d⁻¹ and suspended matter concentrations ranged from 4 to 19 mg l⁻¹. The benthos was represented by hard bottom forms only, with a surprisingly dense cover of macrophytes. Juvenile sea urchins (Strongylocentrotus droebachiensis), brittle stars (Ophiocten sericeum) and amphipods were dominant. Higher trophic levels were represented by benthic feeders, such as eiders and walruses. The area observed was more similar to high Arctic fjord ecosystems than to the offshore central Northeast Water polynya.     

Eddies around Madagascar — The retroflection re-considered

The Agulhas Current with its retroflection and attendant eddy-shedding is the cause of some of the greatest mesoscale variability in the ocean. This paper considers the area to the south and east of Madagascar, which provides some of the source waters of the Agulhas Current, and examines the propagating sea surface height signals in altimetry and output from a numerical model, OCCAM. Both show bands of variability along the axis of the East Madagascar Current (EMC) and along a zonal band near 25°S. Sequences of images plus associated temperature data suggest that a number of westward-propagating eddies are present in this zonal band. The paper then focuses on the region to the south of the island, where ocean colour and infra-red imagery are evocative of an East Madagascar Retroflection. The synthesis of data analysed in this paper, however, shows that remotely observed features in this area can be explained by anticyclonic eddies moving westward through the region, and this explanation is consistent with numerical model output and the trajectories of drifting buoys.     

Second-order perturbation added mass fluctuation on vertical vibration of tension leg platforms

Total motion in waves can be considered as a superposition of the motion of the body in still water and the forces on the restrained body. In this study the effect of added mass fluctuation on vertical vibration of tension leg platforms (TLP) in the case of vibration in still water for both free and forced vibration subjected to axial load at the top of the leg is presented. This effect is more important when the amplitude of vibration is large. Also this is important in fatigue life study of tethers. The structural model used here is very simple. Perturbation method is used to formulate and solve the problem. First- and second-order perturbations are used to solve the free and forced vibrations, respectively.     

Ground truthing sediment profile imagery with traditional benthic survey data along an established disturbance gradient

Macrobenthic surveys are an expensive, slow and labour intensive means to establish the health of benthic communities. Sediment profile imagery (SPI) is a means of rapid reconnaissance for monitoring large areas of the benthos. SPI has often been used to monitor gross anthropogenic disturbance. The aim of this study is to determine if SPI can be used as a tool to reliably map change in communities along natural estuarine gradients. Macrobenthic sampling was carried out at five stations along an established estuarine gradient. This faunal data was analysed using standard multivariate techniques and to ground truth a concurrent SPI survey. Faunal analysis showed that habitat quality in Inner Galway Bay was generally good, with some localised disturbance from the River Corrib and the sewage out flow exterior to the city dock. Four distinct groups were identified with a degree of overlap occurring between stations 3 and 4. While existing SPI indices mapped habitat quality in the same manner as the faunal data for end member stations, the level of distinction between the habitats of an intermediate staging was found to be poor. This lack of distinction amongst the stage 2 and 3 stations was overcome by developing a tailored index, the Galway Bay index of habitat quality (GBHQ). This index was derived from the 5 observed variables in the SPI data that were determined to best match the faunal distribution by permutative mantel testing. The 5 observed variables from the SPI data were the depth of the apparent redox potential discontinuity (aRPD), the depth of penetration by the prism, and the presence/absence of infauna, surface faecal pellet layer and biogenic mounding. The GBHQ was able to distinguish between the 5 stations to a greater extent than previously described indices, showing clearly the separate groupings defined by the faunal data. The index was tested on a follow up SPI survey and shown to be applicable in mapping a broader range of habitats in Galway Bay. Indices generated for localised mapping of estuarine gradients should be derived from observed features and be ground truthed using faunal data. Some aspects of the GBHQ should be generally applicable to fine grained boreal estuarine sediments (aRPD/penetration), while others may be of limited utility in other locations depending on the digging characteristics of the particular SPI camera, and local factors influencing the persistence of biogenic features in the profile. This derivation technique provides a simple way to optimise SPI to particular studies and localities.