Recent Improvements to IERS Bulletin A Combination and Prediction

Driven by a need for increased accuracy in real-time Earth orientation parameters (EOPs), the Bulletin A (Rapid Servce and Predictions) of the International Earth Rotation Service (IERS) has recently made several major changes to its combination and prediction procedures. Changes to the process ob combining multi-technique results include creation of a daily Bulletin A updata, inclusion of several new data sets, and use of polar motion rantes for the latest epoch. Notably, the contributions from GPS observations have grown steadily in significance, both for polar motion and Universal Time (UT1). The prediction procedure has, in turn, benefited from these changes as well as improvements to the polar motion prediction model. As a result, demanding real-time applications, such as for satellite orbit extrapolations should observe a major improvement in the accuracy of our real-time EOP products. All results, together with supporting and diagnostic information, are available at the website http://maia.usno.navy.mil. The maximum EOP errors (root-mean-squared sense) that a real-time user would experience using the latest available update of Bulletin A are currently estimated to be ∼0.9 milliarcseconds (mas) for polar motion and ∼0.15 milliseconds (ms) for UT1-UTC. The data latency (the lag since the most recent observations) for EOP predictions need not exceed ∼41 hours for users who avail themselves of the daily updates. Over the past four years, the accuracy for real-time applications has improved by nearly a factor of 4 in polar motion and a factor of 10 in UT1. This is primarily due to the large reduction in data latency, which in turn is mostly possible due to the Rapid product delivery of the International GPS Service (IGS) (see Mireault et al, 1999). ? 2001 John Wiley & Sons, Inc.     

Correlation studies using the equivalent base horizontal acceleration method

The equivalent base horizontal acceleration concept was developed for calculating the response of test structures to shaking table excitations, to account for pitching interaction effects of the table. Using the procedure, analysis-experiment comparisons were made of the shaking table tests of a 0–3-scale model of a six-storey concentrically K-braced steel structure. The correlation of the analytical and experimental results was excellent in both the elastic and inelastic ranges of structural response.     

Fixed-ammonium in clays associated with crude oils

The association of ammonium (NH₄⁺) silicates with organic-rich sedimentary environments has stimulated interest in the chemical cycle of N, and its possible application as an indicator of in situ organic maturation reactions or crude oil migration. Fixed-NH₄ in clay minerals was determined from three hydrocarbon occurrences of similar depositional environment but different ages, depth and thermal maturity, to determine whether anomalously high NH₄-substitution occurs near mature hydrocarbons. Results show higher fixed-NH₄ concentrations in marginally mature mudstones than in immature sediments. The highest fixed-NH₄ concentrations were found in clays from sandstone reservoirs containing migrated crude oil.Fixed-NH₄ in clays from Holocene oil seep sediments in the Gulf of Mexico continental slope, offshore Louisiana, averages 0.08 wt % and increases with depth in shallow cores (420 cm), reflecting an early diagenetic trend that is apparently not influenced by migrating crude oil. Programmed pyrolysis shows that the sediments are thermally immature (av.T_max = 419°C). High Hydrogen Index values (av.= 359mg/g) are the result of biodegraded crude oil, and a high Oxygen Index (av.= 182mg/g) reflects the presence of authigenic carbonate.Fixed-NH₄ averages 0.16 wt % in Wilcox Group (Eocene) mudstones enclosing two sandstone reservoirs at Fordoche Field, onshore Louisiana. In comparison to these mudstones, anomalously high NH₄-fixation appears to occur in reservoir clay minerals. Pyrolysis shows that the sediments are marginally mature for crude oil generation (av.T_max = 432°C). Average Hydrogen Index (187 mg/g) and Oxygen Index values (75 mg/g) are consistent with oil-prone Type II and Type III kerogen. Increased pyrolysis Production Index values and solvent extraction shows the presence of migrated crude oil. This suggests that a reaction which releases NH₃ during crude oil generation or migration is recorded byNH₄⁺ substitution in clays.Fixed-NH₄ and total organic carbon (TOC) at Fordoche Field show no statistically significant correlation, suggesting that NH₄⁺ substitution in clay minerals is not simply related to the amount of organic matter in the section, but is also influenced by the presence of crude oil. Once NH₄⁺ has been fixed in clays, it is a more stable hydrocarbon proximity indicator than pore fluid tracers, because it is less influenced by later chemical or geological changes.     

Summary of taxa and morphological adaptations of the Desmostylia

Abstract Desmostylians from the Pacific coasts of Japan and North America are compared and taxonomy and adaptations in the mammalian order Desmostylia discussed. The taxonomy is based mainly on teeth and skulls. Feeding adaptations and habitat are discussed using teeth and restored skeletons, respectively. In the extinct order two families, six genera and 10 species can now be recognized. Each genus is distinguished by a set of tooth characters. The three species of the genus Paleoparadoxia have different body sizes. Two species of the genus Desmostylus can be distinguished on morphological differences in the cranium. As a result it is clear that both species, D. hesperus , which had long been recognized only in North America, and D. japonicus , which has hitherto been recognized only in Japan, inhabited both coasts of the Pacific. All genera of the Order Desmostylia share a common and distinctive body form, interpreted by Inuzuka as having a laterally placed limb posture. Based on this body form, the optimum habitat is thought to have been an intertidal sandy beach. The dental morphology is variable, and derived species show an adaptation for wear by an abrasive diet. In conclusion, we theorize that the Order Desmostylia was adapted for a coastal habitat from its inception, with each genus adapting to a different sort of herbivorous diet.     

Defining success in fisheries and conflicts in objectives

The traditional fisheries management objectives of maximizing yield and employment lead to heavily exploited stocks. Many current high-profile disputes arise from conflicting objectives, and the proposed solutions to “the fisheries problem” are primarily particular stakeholders’ efforts to have managers implement their own objectives. I suggest many “failures” are in fact successes for other objectives. Fisheries objectives, as reflected in management actions, are changing. Two current trends are the acceptance of objectives that value less disturbed ecosystems and acceptance of fisheries allocation through dedicated access to improve the fisheries’ economic efficiency. I suggest that increased use of dedicated access will result in more congruent objectives and less conflict.     

Critical properties of spherically symmetric accretion in a fractal medium

Spherically symmetric transonic accretion of a fractal medium has been studied in both the stationary and the dynamic regimes. The stationary transonic solution is greatly sensitive to infinitesimal deviations in the outer boundary condition, but the flow becomes transonic and stable when its evolution is followed through time. The evolution towards transonicity is more pronounced for a fractal medium than it is for a continuum, and in the former case the static sonic condition is met on relatively larger length scales. The dynamic approach also shows that there is a remarkable closeness between an equation  of motion for a perturbation in the flow, and the metric of an analogue acoustic black hole. The stationary inflow solutions of a fractal medium are as much stable under the influence of linearized perturbations as they are for the fluid continuum.     

Nuclear Morphology and Lysosomal Stability of Molluskan Hemocytes as Possible Biomarkers of Arsenic Toxicity

The frequency of nuclear aberrations and neutral red retention time of hemocytes in the mollusk Lamellidens marginalis were recorded under exposure to sublethal concentrations of sodium arsenite in order to examine the sensitivity and effectiveness of these inexpensive assays for screening the toxicity of As³⁺ in a freshwater ecosystem. A dose and time dependent increase in the density of micronucleated and binucleated hemocytes and gill cells was indicative of the pronounced genotoxic effect of arsenic on this animal. The disruption of intrahemocyte homeostasis imposed by this natural toxicant was evident from a dose and time dependent reduction in the lysosomal stability of the hemocytes of the animal. The tested parameters are indicative of arsenic toxicity in L. marginalis in the freshwater systems of the arsenic affected geographical areas of West Bengal, India.     

Suspended sediment transport and deposition over a dune: Río Paraná, Argentina

Field data from the Rio Paraná, Argentina, are used to examine patterns of suspended sediment transport over a sand dune. Measurements of three‐dimensional velocity are made with an acoustic Doppler current profiler whilst suspended sediment concentration and particle size have been quantified using a laser in situ sediment scattering transmissometer. Suspended sediment concentration and streamwise and vertical sediment flux are highest close to the bed, with an upward vertical flux over the stoss side of the dune and downward flux over the lee side. Suspended sediment concentrations are higher over the crest compared with the trough and suspended sediment is coarsest near the bed. About 17% of the suspended‐load transported over the crest is deposited in the lee side before it reaches the trough. Most of this deposited sand is coarser sediment that originates close to the bed over the crest, a result consistent with simulations based on the model of Mohrig and Smith (Water Resources Research 1996; 32: 3207–3217) for the excursion lengths of sediment dispersed in the lee side of a dune. Copyright © 2009 John Wiley & Sons, Ltd.