Seismic response of heavily damped base isolation systems

The development of an efficient energy-dissipating mechanism that works in conjunction with laminated elastomeric bearings in order to reduce the lateral deformation of the isolation system has always been a goal of base isolation research. Theoretically, this deformation will be reduced to the minimum if damping augmentation of the isolation system can reach a critical value. However, augmenting the isolation damping may cause some unwanted side effects. The purpose of this paper is to study the influence of isolation damping on the seismic response of heavily damped base-isolated buildings. The base isolation system is assumed to be linearly viscoelastic and is analysed using the complex mode method. Solutions derived by using perturbation techniques for a two-degree-of-freedom system and the computer simulation for a multiple-degree-of-freedom system reveal that augmenting the isolation damping can reduce efficiently the deformation of the isolation system, but at the price of increasing the high-frequency vibration in the superstructure. When the damping ratio of the isolation system is beyond some level, increasing the isolation damping will enlarge the extreme values of the base and superstructural accelerations. It is also found that approximate solutions derived from the use of classical damping and classical modes of vibration in the seismic analysis of heavily damped base isolation systems can be substantially in error.     

X-ray absorption spectroscopy identifies calcium-uranyl-carbonate complexes at environmental concentrations

Current research on bioremediation of uranium-contaminated groundwater focuses on supplying indigenous metal-reducing bacteria with the appropriate metabolic requirements to induce microbiological reduction of soluble uranium(VI) to poorly soluble uranium(IV). Recent studies of uranium(VI) bioreduction in the presence of environmentally relevant levels of calcium revealed limited and slowed uranium(VI) reduction and the formation of a Ca-UO₂-CO₃ complex. However, the stoichiometry of the complex is poorly defined and may be complicated by the presence of a Na-UO₂-CO₃ complex. Such a complex might exist even at high calcium concentrations, as some UO₂-CO₃ complexes will still be present. The number of calcium and/or sodium atoms coordinated to a uranyl carbonate complex will determine the net charge of the complex. Such a change in aqueous speciation of uranium(VI) in calcareous groundwater may affect the fate and transport properties of uranium. In this paper, we present the results from X-ray absorption fine structure (XAFS) measurements of a series of solutions containing 50 μM uranium(VI) and 30 mM sodium bicarbonate, with various calcium concentrations of 0-5 mM. Use of the data series reduces the uncertainty in the number of calcium atoms bound to the UO₂-CO₃ complex to approximately 0.6 and enables spectroscopic identification of the Na-UO₂-CO₃ complex. At nearly neutral pH values, the numbers of sodium and calcium atoms bound to the uranyl triscarbonate species are found to depend on the calcium concentration, as predicted by speciation calculations.     

Episodes of late Holocene aridity recorded by stalagmites from Devil's Icebox Cave, central Missouri, USA

Two stalagmites from Devil's Icebox Cave, central Missouri, display similar δ¹³C and δ¹⁸O values and trends during the late Holocene. Positive δ¹³C excursions at 3.5-2.6 ka and 1.2-0.9 ka are interpreted to reflect drier conditions. These elevated stalagmite δ¹³C values could have plausibly been driven by increasing C₄ plant abundances over the cave or an increased contribution of bedrock carbon, both of which could reflect decreased effective moisture. A lack of corresponding oxygen isotopic anomalies during these intervals suggests that neither mean annual temperature nor the seasonality of precipitation changed concomitantly with dryness. Both of the δ¹³C excursions identified in our stalagmite record are roughly coincident with dry intervals from a number of sites located across the Great Plains.     

Renewable energy strategies in England, Australia and New Zealand

The development of renewable energy sources is of prime interest to many countries seeking to pursue greenhouse gas emission reduction obligations. The increased use of renewables offers the possibility of not only contributing to emission reduction, but at the same time improving energy supply diversity and security, and developing employment and business in related supply industries. Two main mechanisms are in common use, one a quota (quantity) instrument often associated with tradable certificates, and the other a prescribed pricing mechanism. This paper considers the renewable energy development strategies of three countries (the UK, Australia, and New Zealand) all using a variant of the quota/certificate approach as the central instrument in their programs. The regulatory frameworks defining the application of the certificate systems differ notably, and the likely differing outcomes suggest that these regulatory settings may be at least as important as the selection of the basic policy instrument, in determining the overall success of programs of this nature.     

The influence of human activity in the Arctic on climate and climate impacts

Human activities in the Arctic are often mentioned as recipients of climate-change impacts. In this paper we consider the more complicated but more likely possibility that human activities themselves can interact with climate or environmental change in ways that either mitigate or exacerbate the human impacts. Although human activities in the Arctic are generally assumed to be modest, our analysis suggests that those activities may have larger influences on the arctic system than previously thought. Moreover, human influences could increase substantially in the near future. First, we illustrate how past human activities in the Arctic have combined with climatic variations to alter biophysical systems upon which fisheries and livestock depend. Second, we describe how current and future human activities could precipitate or affect the timing of major transitions in the arctic system. Past and future analyses both point to ways in which human activities in the Arctic can substantially influence the trajectory of arctic system change.     

A comparative mineralogical and geochemical study of sulfide mine tailings at two sites in New Mexico, USA

A comparative study of sulfide mine tailings from two sites near Silver City in southwest New Mexico has shown the need for environmental monitoring in a geological context. The Cyprus-Piños Altos and Cleveland deposits consist of Cu and Zn skarn mineralization in the Piños Altos Mountains of New Mexico. Primary ore minerals in both deposits include chalcopyrite, sphalerite, and galena. The Cyprus-Piños Altos Mine ceased operation in 1995 and the Cleveland Mill closed in 1950. The deposits have similar mineralogical characteristics; however, the tailings are different in terms of age, degree of oxidation and method of disposal. The Cyprus-Piños Altos tailings (CPAT) are stored in a lined, bermed impoundment. They are dominantly water-saturated and exhibit no secondary-phase formation. The grains are not cemented and show no evidence of primary-mineral dissolution. The geochemical data show a predominantly primary signature. The tailings pond water is neutral to slightly alkaline (pH?from 7 to 8.3), partly as a result of processing methods. The Cleveland mill tailings (CMT) were deposited in a valley at the headwaters of an ephemeral stream. They are highly oxidized and differentially cemented. They have undergone numerous wet/dry cycles resulting in extensive oxidation. Secondary minerals predominate, and consist mainly of jarosite, goethite, hematite, and Fe-oxyhydroxides and -oxyhydroxysulfates. The pH of the stream draining the CMT is as high as 2.15. Maximum metal contents in the stream immediately downstream from the tailings are 5305?ppm Zn, 454?ppm Cu, 1.16?ppm Pb, 17.5?ppm Cd, 1.4?ppm As, and 0.01?ppm Hg.     

The C/CO ratio in B335 and the decaying dark matter neutrino hypothesis

C¹⁸O J  = 2–1, C¹⁷O J  = 2–1 and [C  I ] ³P₁–³P₀ emission from the dense cold cloud B335 has been observed and modelled in order to determine the C/CO ratio. The observed ratio is compared with a prediction by Tarafdar who assumes a mechanism in which the CO dissociation is caused by photons of energy ∼ 13.8 eV. These were postulated by Sciama to result from the decay of dark matter neutrinos. Our value for the C/CO ratio sets an upper limit to the strength of the neutrino decay dissociation process, thus providing a significant datum for interstellar chemistry theory.     

Magmatic and hydrothermal inclusions in carbonatite of the Magnet Cove Complex,Arkansas

The carbonatite at Magnet Cove, Arkansas, USA contains a great variety and abundance of magmatic and hydrothermal inclusions that provide an informative, though fragmentary, record of the original carbonatite melt and of late hydrothermal solutions which permeated the complex in postmagmatic time. These inclusions were studied by optical and scanning electron microscopy. Primary magmatic inclusions in monticellite indicate that the original carbonatite melt contained approximately 49.7 wt% CaO, 16.7% CO₂, 15.7% SiO₂, 11.4% H₂O, 4.4% FeO+Fe₂O₃, 1.1% P₂O₅ and 1.0% MgO. The melt was richer in SiO₂ and iron oxides than the carbonatite as now exposed; this is attributed to crystal settling and relative enrichment of calcite at shallower levels. The density of the carbonatite melt as revealed by the magmatic inclusions was approximately 2.2–2.3 g/cc. Such a light melt should separate rapidly from any denser parent material and could be driven forcibly into overlying crustal rocks by buoyant forces alone. Fluid inclusions in apatite suggest that a separate (immiscible) phase composed of supercritical CO₂ fluid of low density coexisted with the carbonatite magma, but the inclusion record in this mineral is inconclusive with respect to the nature of any other coexisting fluids. Maximum total pressure during CO₂ entrapment was about 450 bars, suggesting depths of 1.5 km or less for apatite crystallization and supporting earlier proposals of a shallow, subvolcanic setting for the complex. Numerous secondary inclusions in the Magnet Cove calcite contain an intriguing variety of daughter minerals including some 19 alkali, alkaline earth and rare earth carbonates, sulfates and chlorides few of which are known as macroscopic phases in the complex. The exotic fluids from which the daughter minerals formed are inferred to have cooled and diluted through time by progressive mixing with local groundwaters. These fluids may be responsible for certain late veins and elemental enrichments associated with the complex.     

Environmental effects on the reproduction and fecundity of the introduced calcareous sponge Paraleucilla magna in Rio de Janeiro,Brazil

The calcareous sponge Paraleucilla magna (Porifera, Calcarea) has been the subject of several studies in the last decade. It was first described along the Brazilian coast, where it is considered cryptogenic, and was subsequently found in the Mediterranean, where it is considered invasive. The wide artificial distribution of this species allows us to compare different aspects of the biology of an introduced species in different locations. Here, we analysed the effects of selected environmental parameters on the reproductive dynamics of P. magna in Rio de Janeiro (Brazil) over 18 months and compared our results with those obtained for the same species in the Mediterranean Sea. Specimens were collected monthly and analysed through histological methods. The density of reproductive elements in each month was calculated, and the effects of environmental parameters (photoperiod, precipitation, temperature, phytoplankton and bacterioplankton) were analysed using a regression tree analysis. Paraleucilla magna was reproductive throughout the study period. The densities of the reproductive elements (oocytes, embryos and larvae) showed no seasonality, and this species presented one of the highest reproductive efforts documented to date in the phylum Porifera (99.0 oocytes · mm^?3; 89.0 embryos · mm^?3; 319.0 larvae · mm^?3). The main environmental parameters related to the reproduction of P. magna were temperature, photoperiod and bacterioplankton. Temperature was the main driver associated with the densities of oocytes and embryos, while bacterioplankton was the main driver of larvae (positive relationships). In Rio de Janeiro, larvae were present and continuously released. This strategy is different from that observed in the Mediterranean, where a larger larval output was observed but only during the summer months. Our results show that P. magna is a species with a strong invasive potential, considering its high and continuous reproductive effort. This high fecundity stimulated by high temperatures may be a key factor contributing to the growth of P. magna populations and its invasion of new areas.