Response of a nuclear power plant on aseismic bearings to horizontally propagating waves

The nuclear island of Koeberg with a large basemat, a non-linear base isolation effective in the horizontal direction only, founded on rock, is analysed for inclined body waves and for a combination of surface and body waves associated with prescribed horizontal and vertical components of the control motion. When compared to vertical incidence, an additional rocking component arises, generated by the horizontally propagating vertical component. As the aseismic bearings do not isolate against this rocking component, the corresponding horizontal response bears comparison with that of a conventional structure. The ratio of the response for horizontally propagating waves and that for vertically incident waves is thus considerably larger for the base-isolated structure than for a conventional one. However, the actual design incorporating other loading cases is affected much less.     

Tropical cyclones in the SW Indian Ocean. Part 2: structure and impacts at the event scale

The southwest Indian Ocean (5°–20°S, 45°–70°E) experiences frequent tropical cyclones (TC) in the December–March season. In this paper, TC composite and case-study structure and impacts are studied using daily oceanic and atmospheric fields from model-reanalyzed data, satellite remote sensing, and in situ station data. The TC environment is characterized according to mean track: W-, SW-, and S-moving. Case studies of TC are investigated, and impacts such as storm surge and rainfall are evaluated through comparison of ‘real’ and ‘model’ datasets in the period since 1998. The northern sub-tropical jet stream is found to influence the intensity and track of TC in the SWIO. The composite SW-moving TC maintains intensity compared to the other tracks, which decline in strength. Variability is found in TC rainfall distribution, with maximum intensity in a spiral band 1–2 days before peak intensity, based on satellite estimates. There is a re-establishment of equatorial rainfall in the case of southward moving TC after peak intensity. The W-moving TC lacks monsoon inflow compared to the recurving TC. Comparisons are made between low-resolution model-estimated rainfall, various satellite products, and station-observed rainfall. TC spiral rain-band intensity is found to be similar to that reported elsewhere in the tropics, based on a limited sample of TRMM PR data and station reports. The satellite-derived daily rainfall out-performs NCEP reanalysis due to low resolution and underestimated diabatic heating. Similarly, the circulation within a 300-km radius of the composite TC is poorly resolved by re-analysis; winds, swells, and storm surges are too low by a factor of two compared with QuikSCAT and in situ measurements. This work will offer ways to adjust operational forecasts of winds, rainfall, and swells around tropical cyclones, so that TC risk and impacts are better managed.     

The palaeomagnetism and magnetic fabric of cave sediments from Grønligrotta and Jordbrugrotta, Norway

Summary. Twenty-four oriented specimens of laminated clay were obtained from vertical sections in two caves in northern Norway. Studies of the magnetic remanence and susceptibility anisotropy show that the magnetization is depositional in origin and due to magnetite. The palaeomagnetic record in one section is correlated with results from a Swiss lake sediment core to suggest an age of 9600–6800 yr bp for the cave clay. It is shown that the susceptibility lineation produced on gently sloping surfaces was predominantly controlled by gravity and cannot therefore be used directly to estimate the palaeoflow or palaeofield directions.     

Extreme subsidence in the Agulhas-Benguela air mass transition

Analysis of three-dimensional wind profiles recorded by an acoustic sounder near Cape Town has indicated that extreme subsidence (-35 cm s^-1) is a mean feature throughout the atmospheric boundary layer (50–1000m) during summertime southerly winds. Over the SW Cape coast, the atmospheric subsidence translates into a N-S gradient of the mean summer water deficit (-20 to -32 cm month^-1). The rapid drying out of the air mass along a northward trajectory is linked to a number of factors including synoptic-scale divergence of the surface wind and the effects of the local orography which produce a hydraulic jump of the southerly wind. The along-coast reduction in sea surface temperature provides a major constraint on the height of the moist marine layer. As the depth of the marine air mass shrinks, its potential for inland penetration becomes limited. In addition, dry air is entrained towards the surface as evidenced by aerial survey data. A model is formulated which indicates the importance of the surface heat fluxes in reducing the depth of the Agulhas air mass as it passes northward over the SW tip of Africa during summer.     

Complementary Investigative Techniques for Site Assessment with Low-Level Contaminants

A remedial investigation (RI) was performed in an area downgradient from an abandoned missile silo at Vandenberg Air Force Base, California, as part of the United States Air Force Installation Restoration Program (IRP). A number of complementary investigative techniques were used to assure a reliable assessment of site contamination. These included the review of aerial photographs, the use of an organic vapor analyzer (OVA) and carbon adsorption/mass spectrometer (MS) method to conduct a soil-gas survey; magnetic and electromagnetic geophysical surveys; bedrock permeability testing; and the chemical analysis of soil, sediment, surface water, and ground water samples. The results from this investigation revealed the presence of an undocumented landfill and a small trichloroethylene plume in ground water at concentrations ranging from 6.7 ppb to 31 ppb. The investigation also identified local ground water flow direction, provided strong evidence of the location of potential sources of contamination, and defined the downgradient extent of ground water contamination. Because the identified contaminants have not as yet reached the environmentally sensitive wetland at the base of the slope below this facility, there is still time to propose remedial alternatives that would serve to protect this environmentally sensitive area.     

SPICES: spectro-polarimetric imaging and characterization of exoplanetary systems

SPICES (Spectro-Polarimetric Imaging and Characterization of Exoplanetary Systems) is a five-year M-class mission proposed to ESA Cosmic Vision. Its purpose is to image and characterize long-period extrasolar planets and circumstellar disks in the visible (450?C900 nm) at a spectral resolution of about 40 using both spectroscopy and polarimetry. By 2020/2022, present and near-term instruments will have found several tens of planets that SPICES will be able to observe and study in detail. Equipped with a 1.5 m telescope, SPICES can preferentially access exoplanets located at several AUs (0.5?C10?AU) from nearby stars (<25 pc) with masses ranging from a few Jupiter masses to Super Earths (??2 Earth radii, ??10 M_??) as well as circumstellar disks as faint as a few times the zodiacal light in the Solar System.     

Short-term variability of suspended sediment and phytoplankton in Tampa Bay,Florida: Observations from a coastal oceanographic tower and ocean color satellites

We examined short-term phytoplankton and sediment dynamics in Tampa Bay with data collected between 8 December 2004 and 17 January 2005 from optical, oceanographic, and meteorological sensors mounted on a coastal oceanographic tower and from satellite remote sensing. Baseline phytoplankton (chlorophyll-a, Chl) and sediment concentrations (particle backscattering coefficient at 532 nm, bbp(532)) were of the order of 3.7 mg m⁻³ and 0.07 m⁻¹, respectively, during the study period. Both showed large fluctuations dominated by semidiurnal and diurnal frequencies associated with tidal forcing. Three strong wind events (hourly averaged wind speed >8.0 m s⁻¹) generated critical bottom shear stress of >0.2 Pa and suspended bottom sediments that were clearly observed in concurrent MODIS satellite imagery. In addition, strong tidal current or swells could also suspend sediments in the lower Bay. Sediments remained suspended in the water column for 2–3 days after the wind events. Moderate Chl increases were observed after sediment resuspension with a lag time of ˜1–2 days, probably due to release of bottom nutrients and optimal light conditions associated with sediment resuspension and settling. Two large increases in Chl with one Chl > 12.0 mg m⁻³ over ˜2 days, were observed at neap tides. For the study site and period, because of the high temporal variability in phytoplankton and sediment concentrations, a monthly snapshot can be different by −50% to 200% from the monthly “mean” chlorophyll and sediment conditions. The combination of high-frequency observations from automated sensors and synoptic satellite imagery, when available, is an excellent complement to limited field surveys to study and monitor water quality parameters in estuarine environments.     

Nb/Zr fractionation on the Moon and the search for extinct Nb

A comprehensive Zr isotopic study was conducted on eleven lunar basalts and highland rocks to search for evidence of the extinct nuclide ⁹²Nb, which decays to ⁹²Zr with a half-life of 36 Ma. Internal isochrons were determined for two early highland rocks, 77215 and 60025. No resolvable Zr isotopic variations were detected in this wide range of lunar samples and thus there is no evidence for the former existence of live ⁹²Nb on the Moon. The Nb/Zr ratios of lunar ilmenites and bulk rock samples vary by only a factor of two to three relative to the chondritic Nb/Zr ratio. No evidence for larger Nb/Zr fractionation was found. This limited fractionation and late isotopic closure of the source region prevents the formation of measurable ⁹²Zr anomalies in high-Ti mare basalts. As a consequence, it is not possible to draw conclusions from the ⁹²Nb-⁹²Zr chronometer about the timing of early lunar differentiation and to constrain the role of ilmenite in the source region of high-Ti mare basalts. However, the fractionation is still sufficient to deduce an upper limit for the initial ⁹²Nb/⁹³Nb ratio of the solar system of <5 × 10⁻⁴.     

Foraging across ecosystems: diet diversity and social foraging spanning aquatic and terrestrial ecosystems by an invertebrate

Ecosystems are fundamentally connected to one another, although empirical documentation of the links between them, especially the links between marine and terrestrial ecosystems, has been limited. This study examined the foraging behavior and ecology of an understudied invertebrate, the hermit crab Coenobita compressus, which is remarkably abundant at the nexus of marine, terrestrial, and freshwater ecosystems. Data collected between 2008 and 2011 in the Osa Peninsula of Costa Rica revealed that C. compressus plays a generalist scavenger role across ecosystems. Beach almond fruits (Terminalia catappa) were a staple of the crabs’ diet, but the crabs also commonly consumed a variety of other fruit species and various parts of plants (nuts, seeds, flowers, husk, stems, buds) as well as algae, fungus, animal feces, and the carcasses of insects, jellyfish, conspecifics, other crustacean species, freshwater and saltwater fish, sea turtles (eggs and adults), and mammals. The crabs fed on these resources in prominent social aggregations, also forming such aggregations as they exchanged the aquatically derived gastropod shells that they use as homes while roaming the land. The size of the crabs’ aggregations around plant versus animal resources and around terrestrial versus aquatic resources did not differ, underscoring the species’ generalist foraging behavior. Broadly, these results suggest that C. compressus has one of the most diverse diets of any crustacean and plays a critical role in recycling organic matter and nutrients. This species might also mediate the passage of resources across different ecosystems, although further research is needed to explore this possibility.     

Lacustrine records of Holocene flood pulse dynamics in the Upper Paraguay River watershed (Pantanal wetlands,Brazil)

The Pantanal is the world's largest tropical wetland and a biodiversity hotspot, yet its response to Quaternary environmental change is unclear. To address this problem, sediment cores from shallow lakes connected to the Upper Paraguay River (PR) were analyzed and radiocarbon dated to track changes in sedimentary environments. Stratal relations, detrital particle size, multiple biogeochemical indicators, and sponge spicules suggest fluctuating lake-level lowstand conditions between ~ 11,000 and 5300 cal yr BP, punctuated by sporadic and in some cases erosive flood flows. A hiatus has been recorded from ~ 5300 to 2600 cal yr BP, spurred by confinement of the PR within its channel during an episode of profound regional drought. Sustained PR flooding caused a transgression after ~ 2600 cal yr BP, with lake-level highstand conditions appearing during the Little Ice Age. Holocene PR flood pulse dynamics are best explained by variability in effective precipitation, likely driven by insolation and tropical sea-surface temperature gradients. Our results provide novel support for hypotheses on: (1) stratigraphic discontinuity of floodplain sedimentary archives; (2) late Holocene methane flux from Southern Hemisphere wetlands; and (3) pre-colonial indigenous ceramics traditions in western Brazil.