Finite strip analysis of the dynamic response of beam and slab highway bridges

This paper presents a method of analysis for the dynamic response of a simply supported beam and slab bridge under the action of a moving vehicle. The bridge is idealized as an orthotropic plate and, in the analysis, is subdivided into a number of finite strips. The vehicle is idealized as a moving sprung mass. Viscous damping is taken into account for both bridge and vehicle. The results show that there is significant variation of response across transverse sections of the bridge. Furthermore the dynamic magnification is considerably greater than that predicted by a more approximate method in which the bridge is idealized as a simple prismatic beam.     

Nitrous oxide emission from Gulf Coast wetlands

Nitrous oxide evolution may contribute to partial destruction of the ozone layer in the stratosphere. A two year study of the release of N₂O from adjoining salt, brackish, and fresh marsh sediment indicates that the annual emission was 31, 48, and 55 mg N m^?2 respectively. Emission from open water area was less than the corresponding emission from the marsh sediment. In vitro experiments indicate that the N₂O emission was increased when the sediment was drained for extended periods of time. The addition of NO₃^? significantly increased the rate of N₂O evolution, indicating that a large potential for denitrification exists in the anoxic sediment. Appreciable losses of N₂O would only be expected when the marshes receive an extraneous source of nitrate such as sewage and/or wastewater.The contribution of the Gulf Coast wetlands to the atmospheric N₂O balance is estimated to be 3.3 × 10⁹ g N₂O. The maximum average daily emission was equivalent to 1.5 g N₂O-N ha^?1, which is less than the measured emission from uncultivated soils (Mosieret al., 1981) but greater than the estimates from noncropped land (CAST, 1976).     

The crystal chemistry of a naturally occurring magnesium hydroxide sulfate hydrate,a precipitate of heated seawater

The crystal chemistry of a naturally occurring magnesium hydroxide sulfate hydrate, $\text{MgSO}{}_4\text{·}\text{1}\text{3}\text{Mg(OH}{}_2\text{) ·}\text{1}\text{3}\text{H}{}_2\text{O}$ (designated MHSH($\text{2}\text{3}$)), and a number of existing and predicted compounds which are structurally related to MHSH($\text{2}\text{3}$) are discussed. An x-ray diffraction powder pattern for MHSH($\text{2}\text{3}$) is calculated from single crystal data to aid in the identification of this phase, recently found associated with active hydrothermal vents along the East Pacific Rise. It is suggested that this MHSH-type crystal structure can have a variable composition due to a novel chemical substitution, Mg²⁺ → 2 H⁺, which this particular structure may be able to accommodate. In relation to this, a method for determining the stoichiometry of MHSH crystals via density measurements is also proposed. Finally, the leaching properties of heated seawater, instrumental in the genesis of metalliferous deposits on the sea-floor, may be due in part to the growth of MHSH-type phases in certain seawater-rock systems.     

Sterane distribution of solid bitumen pyrolyzates. Changes with biodegradation of crude oil in the Ouachita Mountains,Oklahoma

Solid bitumens (grahamite and impsonite) of southeastern Oklahoma have been shown to originate from near-surface alteration of crude oil (Curiale, 1981; Curiale and Harrison, 1981). Pyrolysis of these solids has been employed to compare the sterane distribution of geographically proximate oils to that of the bitumens. The ratio of rearranged to regular steranes is higher in the pyrolyzates than in the oils, a finding consistent with a bitumen origin due to biodegradation of oil. The remaining presence of steranes, particularly regular steranes, in the bitumens suggests that sterane occlusion may have occurred prior to or during the alteration process, thus removing tetracyclic compounds from the influence of microbial attack. These data suggest that pyrolysis-$\text{GC}\text{MS}$ offers a viable approach to correlation problems involving solid bitumens.     

The effect of air flow rate on the kinetics of flotation. Part 2: The transfer of material from the froth over the cell lip

The flotation rate of galena was investigated as a function of air flow rate (AFR) and froth thickness (from 0 to 6 cm) in a batch flotation cell designed to produce a quiescent froth-liquid interface. This cell design limits mechanical breakage of the froth and prevents the hydraulic entrainment of fine particles into the froth phase. The overall transfer rate was characterized by a first-order rate constant, the overall rate constant (ORC). The ORC was found to increase with increasing AFR and with decreasing froth thickness. The transfer rate of material from the slurry to the froth was also determined as a function of AFR, and characterizes by its first-order rate constant, the flotation rate constant (FRC).The froth transport constant (FTC), the first-order constant which characterizes the transport of galena from the froth over the cell lip, was then determined from the ORC and the FRC. The FTC was found to increase with increasing AFR and decreasing froth thickness. For a froth thickness of 5 cm and low-to-intermediate AFR, the FTC was found to be significantly lower than the FRC.The FTC of galena particles of 0–12, 12–32 and 22–40 μm was also determined. At a froth thickness of 5 cm, the FTC decreased with increasing particle size over the full experimental range of AFRs.     

Pisolitic laterite geochemistry in the golden grove massive sulphide district, Western Australia

The two known massive Cu-Zn sulphide deposits in the steeply dipping strata of the Golden Grove District of Western Australia — the Gossan Hill Deposit and Scuddles Prospect — both have a multi-element secondary geochemical dispersion halo in the pisolitic layer of laterite of probable Tertiary age. The Gossan Hill geochemical anomaly is about 1.5 × 2 km and has a Bi-Sn-Mo-In-Sb-As-Cu-Au association. Mean compositions of pisolitic laterite samples range from 4 to 18 times background, with maxima for Bi, Sn and Mo reaching 90 to 100 times background. Relief of Gossan Hill, which rises some 80 m above the laterite plain, would have favoured dispersion during lateritization. Nevertheless at Scuddles, where the laterite surface has only a gentle slope across strike, an anomaly in pisolitic laterite measures 1 to 1.5 by 1.5 to 2.0 km. The anomalous association, Bi-Sn-Mo-Sb-As, is similar to that at Gossan Hill; the mean contents in pisolitic laterite samples from the Scuddles anomaly range from 2.3 to 8 times background, with maxima for Bi being 12 times background.At Gossan Hill, individual pisolites and the concretionary skins contain gossan fragments and cassiterite, indicating mechanical dispersion during interitization. However, anomalous Cu, Zn and As in goethites of the concretionary skins of pisolites and nodules from the centre of the anomaly indicate that there has also been hydromorphic dispersion.The geochemical characteristics of pisolitic laterite samples have been represented by empirically derived additive indices based on up to eleven chalcophile elements. One index is suggested as a method to increase anomaly size and simplify interpretation; a more specific index based on Bi, Sn and Se is suggested for defining more closely the actual centres of mineralization.For routine exploration of lateritic terrain where the dips of the host sequence are steep, 320-m spacing of samples on a triangular grid appears suitable for locating anomalies and generally defining their source. However, for reconnaissance exploration, the density of sampling could be significantly reduced for example to 1 km spacing.     

Analysis of high-voltage,high-resolution images of lattice defects in experimentally-deformed dolomite

Deformation-induced stacking defects in dolomite have been characterised following examination at the cation sublattice level using high-resolution electron microscopy at 500kV. Slip on c (≡{0001}) is observed to produce stacking faults, often de-localised laterally, which are terminated by partial dislocations with Burgers vectors of the form 1/3 [1 \(\overline 1 \) 00]: a model for the faulted dolomite lattice has been constructed which agrees with the image appearance. Slip on f (≡{10 \(\overline 1 \) 2}) produces long planar faults which are established as not being stacking faults, in the normal sense, since there appear to be no offsets of the cation sublattice across the faults, nor any general indication of any terminating partial dislocations: it is proposed that the contrast arises from rotational disorder in CO₃ groups which has resulted from the prior passage of partial dislocations during deformation.     

The decay of coastal forts in southeast Brazil and its implications for the conservation of colonial built heritage

The 500th anniversary of European arrival in Brazil was celebrated in 2000 and highlighted the need to review the condition of the countrys remaining colonial built heritage. This revision is particularly apposite in the adjacent cities of Rio de Janeiro and Niterói, where the heritage that survived twentieth century reconstruction has done so largely because of ownership by the church or military. However, whilst this may have protected buildings from demolition, detailed fabric can be neglected or abused. This paper investigates this possibility through an examination of two forts, built primarily of local augen gneiss, that guard the entrance to Guanabara Bay. Natural outcrops exposed to the same humid sub-tropical maritime environment show that this rock is susceptible to slow disaggregation through salt weathering. Surveys suggest that stonework in the forts that is sheltered from rainwash is heavily loaded with salt and has passed a threshold, wherein stresses accumulated over centuries of apparent stability, combined with the effects of a more recent increase in atmospheric pollution and apparently inappropriate intervention (re-pointing), have triggered rapid breakdown that requires immediate intervention.     

Modelling the sea ice-ocean seasonal cycle in Hudson Bay, Foxe Basin and Hudson Strait, Canada

The seasonal cycle of water masses and sea ice in the Hudson Bay marine system is examined using a three-dimensional coastal ice-ocean model, with 10 km horizontal resolution and realistic tidal, atmospheric, hydrologic and oceanic forcing. The model includes a level 2.5 turbulent kinetic energy equation, multi-category elastic-viscous-plastic sea-ice rheology, and two layer sea ice with a single snow layer. Results from a two-year long model simulation between August 1996 and July 1998 are analyzed and compared with various observations. The results demonstrate a consistent seasonal cycle in atmosphere-ocean exchanges and the formation and circulation of water masses and sea ice. The model reproduces the summer and winter surface mixed layers, the general cyclonic circulation including the strong coastal current in eastern Hudson Bay, and the inflow of oceanic waters into Hudson Bay. The maximum sea-ice growth rates are found in western Foxe Basin, and in a relatively large and persistent polynya in northwestern Hudson Bay. Sea-ice advection and ridging are more important than local thermodynamic growth in the regions of maximum sea-ice cover concentration and thickness that are found in eastern Foxe Basin and southern Hudson Bay. The estimate of freshwater transport to the Labrador Sea confirms a broad maximum during wintertime that is associated with the previous summers freshwater moving through Hudson Strait from southern Hudson Bay. Tidally driven mixing is shown to have a strong effect on the modeled ice-ocean circulation.