Energy and stability in the Full Two Body Problem

The conditions for relative equilibria and their stability in the Full Two Body Problem are derived for an ellipsoid–sphere system. Under constant angular momentum it is found that at most two solutions exist for the long-axis solutions with the closer solution being unstable while the other one is stable. As the non-equilibrium problem is more common in nature, we look at periodic orbits in the F2BP close to the relative equilibrium conditions. Families of periodic orbits can be computed where the minimum energy state of one family is the relative equilibrium state. We give results on the relative equilibria, periodic orbits and dynamics that may allow transition from the unstable configuration to a stable one via energy dissipation.      

Extreme value modelling of daily areal rainfall over Mediterranean catchments in a changing climate

Heavy rainfall events during the fall season are causing extended damages in Mediterranean catchments. A peaks‐over‐threshold model is developed for the extreme daily areal rainfall occurrence and magnitude in fall over six catchments in Southern France. The main driver of the heavy rainfall events observed in this region is the humidity flux (FHUM) from the Mediterranean Sea. Reanalysis data are used to compute the daily FHUM during the period 1958–2008, to be included as a covariate in the model parameters. Results indicate that the introduction of FHUM as a covariate can improve the modelling of extreme areal precipitation. The seasonal average of FHUM can improve the modelling of the seasonal occurrences of heavy rainfall events, whereas daily FHUM values can improve the modelling of the events magnitudes. In addition, an ensemble of simulations produced by five different general circulation models are considered to compute FHUM in future climate with the emission scenario A1B and hence to evaluate the effect of climate change on the heavy rainfall distribution in the selected catchments. This ensemble of climate models allows the evaluation of the uncertainties in climate projections. By comparison to the reference period 1960–1990, all models project an amplification of the mean seasonal FHUM from the Mediterranean Sea for the projection period 2070–2099, on average by +22%. This increase in FHUM leads to an increase in the number of heavy rainfall events, from an average of 2.55 events during the fall season in present climate to 3.57 events projected for the period 2070–2099. However, the projected changes have limited effects on the magnitude of extreme events, with only a 5% increase in the median of the 100‐year quantiles. Copyright © 2011 John Wiley & Sons, Ltd.     

Lead analysis of sediment cores from seven Connecticut lakes

Lead analyses were performed on sediment cores from seven Connecticut lakes by dilute acid leaching. The absolute concentrations of lead varied from core to core, but the lead profiles were similar in all of the cores, and each depicted a point where the concentration of lead sharply increased above background levels. The background lead concentrations observed in the bottom portions of the cores ranged from 12-54 g Pb/g sediment with a mean of 30 g Pb/g, and increased to a mean maximum of 310 g Pb/g. In six of the lakes significant increases above background levels were not noted until between 1924 and 1952, suggesting that, at least for Connecticut lakes, the point in a lake sediment core where the concentration of lead began to increase was after ca. 1924, and on average about 1930. Lead concentrations declined in the surface sediments of only three of the lakes, mostly since the 1980's, and presumably in response to the phasing out of leaded gasoline. However, significant declines in lead concentrations were not observed in the remaining cores, possibly due to increased motor vehicle use within the airshed of the lakes and/or changes in the export of lead to the lakes from their watersheds.     

An Overview of Electrokinetic Consolidation of Soils

Electrokinetic stabilization is one of the techniques that improve the geotechnical properties of the soils. It was pioneered by Casagrande in late 1940s and has not seen much development since then, especially in large-scale field applications. Some bench scale studies have been carried out during the past two decades and there have been some small scale field studies and limited field applications, mostly on soft soils. Due to lack of understanding of the physiochemical and electrochemical changes in the soil during electrokinetic stabilization, uncertain energy costs, loss of efficiency with time and the corrosion of electrodes, this method is usually considered as a last resort for large-scale practical applications. The objective of this paper is to highlight the critical parameters affecting electrokinetic consolidation, and to discuss their effects on the efficiency of the process. A better understanding of these critical parameters and their effects will enable geotechnical engineers to design the electrokinetic consolidation operation more effectively and make it an economically viable process for many situations.     

On harbour siltation in the fresh-salt water mixing region

In this paper a novel series of field measurements are presented, which are the first to elucidate the processes influencing siltation in Botlek Harbour. Botlek Harbour is situated at the limit of saline water intrusion in the Rotterdam Waterway. Normally, after the ebb tide fresher river waters are found in the Rotterdam Waterway at the location of Botlek Harbour. On the flooding tide, the tip of the salt wedge is advected along the Rotterdam Waterway towards the mouth of Botlek Harbour. Hence on flood, a lock-exchange mechanism operates between Botlek Harbour and the Rotterdam Waterway. On the flood tide, when there is a supply of suspended particulate matter (SPM) associated with the presence of the estuarine turbidity maximum (ETM) at the mouth of the harbour, the survey data show exchange of SPM into the harbour. This lock-exchange process is found to be the dominant cause for SPM transport into the harbour. This is further substantiated by an analysis of the mass transport mechanisms. In this analysis, the vertical profiles of the instantaneous velocity, salinity and SPM concentration fields, recorded during the surveys, were decomposed into advective and dispersive transport components. The results of this analysis indicate that the correlation between the lock-exchange mechanism on the flood tide with the availability of SPM for exchange and efficient trapping, dominate the total exchange of SPM (97%). Hence, the increase in measured near-bed SPM concentration within the harbour is ascribed to tidal advection of saline water and the ETM along the Rotterdam Waterway. Tidal advection controls the density difference between the estuary and harbour, as well as the availability of SPM for exchange at the entrance to Botlek Harbour. The location of the ETM at the tip of the salt wedge is a key factor in supplying SPM to Botlek Harbour. Consequently the timing of the availability of SPM at the mouth of the harbour needs to be considered in siltation studies. The survey data suggest that Botlek Harbour basin has a 100% trapping efficiency. Analysis of 5 months of data, from a measuring rig located within the harbour, show excursions of the limit of the salt wedge and ETM. These excursions are likely to affect siltation of upstream harbours. Salinity-induced density gradients control the transport and subsequent trapping of SPM in the estuary in close proximity to the harbour entrance, the exchange of SPM between the estuary and harbour, and the trapping of SPM in the harbour basin.     

Effects of the October 25, 2010, Mentawai tsunami in La Réunion Island (France): observations and crisis management

On October 25, 2010, a Mw = 7.7 magnitude earthquake was recorded in the Kepulauan Mentawai archipelago, in Indonesia. Following the earthquake, the Pacific Tsunami Warning Center issued a tsunami bulletin to the countries of the Indian Ocean informing them that a local tsunami watch was in effect for Indonesia. La Réunion Island, a French territory located 5,000 km southwest of the seismic source, did not trigger its tsunami early warning protocol, but did suffer the impact of this tsunami 7h20 post-earthquake. This paper presents the post-tsunami survey conducted in La Réunion Island a few days after the event, providing run-up measurements that reach 1.72 m locally as well as information about the material losses and the crisis management. It provides a time sequence of the observations along the coast and the reactions of the population and authorities in dealing with this crisis. This paper also shows the local authorities’ lack of action in managing this event—thus increasing human and material vulnerabilities—the consequences for victims and the impact on the credibility of the local early warning system. These results provide geophysicists with information to better describe the source of this tsunami through far-field inversion and provide local decision makers with a comprehensive assessment of the weaknesses of the local early warning system and protocols.     

The place of individuals in the politics of scale

Conceptualizations and re-conceptualizations of scale have been powerful tools for explaining spatial processes that transcend traditionally-bounded territories. Examining the role of individuals within a politics of scale can do even more to explain multi-scalar conflicts. This paper does so by examining struggles over airport expansion in the US, showing how an understanding of the various roles of individuals in the politics of scale – as sites of multiple scales, as actors constituting other scales, and as scales in and of themselves – better explains multi-scalar conflicts and offers more opportunities for resolving them.     

Bacterial dominance of phototrophic communities in a High Arctic lake and its implications for paleoclimate analysis

The phototrophic communities in meromictic, perennially ice-covered Lake A, on Ellesmere Island in the Canadian High Arctic, were characterized by pigment analysis using high performance liquid chromatography. Samples were taken to determine the vertical changes down the water column as well as a variation between years. These analyses showed that Lake A had distinct phototrophic communities in its oxic and anoxic layers. The pigment analyses indicated that phototrophic biomass in the upper, oxic waters was dominated by picocyanobacteria, while in the lower, anoxic layer photosynthetic green sulphur bacteria were dominant. Interannual variation in pigment concentrations was related to the penetration of photosynthetically active radiation in the water column, suggesting that light availability may be limiting the net accumulation of photosynthetic bacterial biomass in Lake A. Pigment analysis of the surface sediments indicated that deposition was dominated by the photosynthetic sulphur bacterial contribution. The sedimentary record of bacterial pigments in polar meromictic lakes offers a promising tool for the reconstruction of past changes in ice cover and therefore in climate.     

TOPOGRAPHIC EFFECTS ON VENTIFACT DEVELOPMENT,MOJAVE DESERT,CALIFORNIA

I nvestigations into processes of ventifact formation in the east-central Mojave Desert, California confirm the importance of topography as a control in the location, orientation, and intensity of ventifact abrasion. Ventifacts in the region appear to be relict in nature and probably formed during a period that ended several thousand years ago. Comparison of groove orientations with available wind data shows that regional flow direction has not changed in the recent past. Although west to northwest winds are the most frequent and intense, and therefore dictate the regional erosion pattern, low to moderate southeasterly flow is recorded on ventifacts near the crests of hills owing to the effects of velocity acceleration. Two conditions that affect ventifact development are considered in this paper: (1) wind acceleration through topographic constrictions; and (2) wind acceleration up the windward flanks of hills. Constrictions in the Barstow-Bristol trough allowed velocity increases that resulted in ventifaction on 70–90 percent of all exposed cobbles and boulders. Velocity acceleration towards the crests of hills caused a marked increase in sand transport and resultant abrasion, as expressed by increases in groove and pit dimensions. [Key words: Aeolian geomorphology, ventifacts, Mojave Desert, California.]