The lambda-dimension of commutative arithmetic rings

It is shown that every commutative arithmetic ring $R$ has $lambda$-dimension $leq 3$. An example of a commutative Kaplansky ring with $lambda$-dimension 3 is given. If $R$ satisfies an additional condition then $lambda$-dim($R$

Estimating internal wave spectra using constrained models of the dynamic ocean

Multi-Channel Seismic method (MCS), with its ability to image events down to a lateral resolution of 10 m has been successfully applied to address questions in physical oceanography. However, to date, these analyses have overlooked an important detail; the imaged boundaries are dynamic and move on a timescale that can be resolved by the MCS method. An important step in understanding the effect of the movement is calibration against constrained models. We demonstrate in this paper that it is possible using careful interpolation to take high resolution models of dynamic water (160 m x 2 m spatial resolution and 15 min temporal resolution) and generate models for synthetic seismic simulations (20 m x 4 m spatial resolution and 20 sec temporal resolution). We show that moving water, when ignored, will distort analyses of wavenumber spectra estimated from seismic data since the relative movement of water masses and the seismic acquisition vessel will change the apparent slope of spectra. Citation: Vsemirnova, E., R. Hobbs, N. Serra, D. Klaeschen, and E. Quentel (2009), Estimating internal wave spectra using constrained models of the dynamic ocean, Geophys. Res. Lett., 36, L00D07, doi: 10.1029/2009GL039598

Detecting and characterizing mesoscale and submesoscale structures of Mediterranean water from joint seismic and hydrographic measurements in the Gulf of Cadiz

International audienceMarine seismic and hydrographic data from the GO cruise in the Gulf of Cadiz acquired in April 2007 are analyzed to determine the physical nature and geometric characteristics of acoustic reflectors in the water column. Seismic data show strong reflectors near the surface, above Mediterranean water (MW) undercurrents, above a meddy, and within a submesoscale MW structure. These reflectors are associated with thermohaline layering. Wavelet analysis of seismic and hydrographic data (both in terms of reflectivity) shows strong signals with 12-48 m vertical wavelength scales. Hydrological data with its high vertical resolution, capture weaker signals with shorter wavelengths. At the edge of a meddy, lateral intrusions of fresher water are revealed by reflectors with 25-75 m thickness. Analyses of marine seismic data allow detection of submesoscale eddies that hydrographic sections identify only occasionally

Assisted Ion Transfer at Organic Film-Modified Electrodes

International audienceAn experimental and theoretical study of a complex electrochemical mechanism at three-phase and thin organic film-modified electrodes, where the coupled electron–ion transfer reaction is complicated by complexation reaction of the transferring ion, is reported. The transfer of monovalent and divalent cations across water|nitrobenzene interface, coupled with the complexation reactions with the ionophore valinomycin, is studied. Both types of electrodes are assembled of an edge plane pyrolytic graphite electrode modified with a nitrobenzene solution of lutetium bis(tetra-tert-butylphthalocyaninato) as a redox mediator and valinomycin as an ionophore. The reversible redox transformations of the redox mediator to either a monovalent hydrophobic anion or cation serve to drive the ion transfer across the liquid|liquid interface. In contact of the modified electrode with an aqueous electrolyte containing alkali or earth alkaline metal cations, significant partition of the aqueous electrolyte is taking place, due to the interfacial complexation of the cation with valinomycin. Thus, the thermodynamics and kinetics of the interfacial complexation–partition reaction at the liquid|liquid interface affect markedly the overall electron–ion transfer reaction at the modified electrodes under voltammetric conditions. Experiments are qualitatively compared with theoretical data collected by simulation of two different electrochemical mechanisms coupled with chemical reactions under conditions of square-wave voltammetry. It has been concluded that the overall electrochemical mechanism at three-phase electrodes can be described as a specific CrE reaction scheme, where Cr represents the reversible interfacial complexation–partition reaction of the transferring ion with valinomycin at the liquid|liquid interface

Tsunami Hazard in La Reunion Island (SW Indian Ocean): Scenario-Based Numerical Modelling on Vulnerable Coastal Sites

Several major tsunamis have affected the southwest Indian Ocean area since the 2004 Sumatra event, and some of them (2005, 2006, 2007 and 2010) have hit La Réunion Island in the southwest Indian Ocean. However, tsunami hazard is not well defined for La Réunion Island where vulnerable coastlines can be exposed. This study offers a first tsunami hazard assesment for La Réunion Island. We first review the historical tsunami observations made on the coastlines, where high tsunami waves (2–3 m) have been reported on the western coast, especially during the 2004 Indian Ocean tsunami. Numerical models of historical scenarios yield results consistent with available observations on the coastal sites (the harbours of La Pointe des Galets and Saint-Paul). The 1833 Pagai earthquake and tsunami can be considered as the worst-case historical scenario for this area. In a second step, we assess the tsunami exposure by covering the major subduction zones with syntethic events of constant magnitude (8.7, 9.0 and 9.3). The aggregation of magnitude 8.7 scenarios all generate strong currents in the harbours (3–7 m s$^{-1}$) and about 2 m of tsunami maximum height without significant inundation. The analysis of the magnitude 9.0 events confirms that the main commercial harbour (Port Est) is more vulnerable than Port Ouest and that flooding in Saint-Paul is limited to the beach area and the river mouth. Finally, the magnitude 9.3 scenarios show limited inundations close to the beach and in the riverbed in Saint-Paul. More generally, the results confirm that for La Runion, the Sumatra subduction zone is the most threatening non-local source area for tsunami generation. This study also shows that far-field coastal sites should be prepared for tsunami hazard and that further work is needed to improve operational warning procedures. Forecast methods should be developed to provide tools to enable the authorities to anticipate the local effects of tsunamis and to evacuate the harbours in sufficient time when such an earthquake occursThis work was supported by the PREPARTOI project and by the LRC (Laboratoire de Recherche Commun Yves Rocard CEA-ENS Paris)

Gulf of Cadiz oceanography for comparison with seismic imaging

The GO project (European Union-NEST-Adventure funding; www.durac.uk/eu.go) aims to assess the potential of seismic imaging of the water column. a dedicated experiment (April-May 2007, gulf of Cadiz) looked at varying Mediterranean Outflow water (MOW) flow along and down the continental slope. Distinctive MOW properties provide strong reflection from seismic sounding. We aim to relate water properties to mixing and hence (e.g.) tides, internal waves, eddies. Physical oceanography results derive from 500 XBT casts, typical spacing 2km, and moorings: three ACDPs, three temperature strings and near-sea-bed turbulence in line on the north-eastern margin of Portimao Canyon (water depths 740-980m); a fourth ADCP-6 km along-slope in 1015 m depth. CTD and LADCP profiling on an IFM-Geomar research cruise, closely following the seismic sections, supplemented the GO measurements. We examine the structures observed on the principal line through the moorings (five surveys,) and compare with the contemporary seismic data that further constrain observed boundaries. The mooring data and profiles are analysed for tides and internal wave spectra, small-scale structure and turbulence to estimate diffusivity and mixing