An energy approach to sliding of single-span simply supported slab-on-girder steel highway bridges with damaged bearings

This paper investigates the non-linear inelastic seismic response of existing single-span simply supported bridges having bearings which can remain stable and slide after their anchor bolts are ruptured. A simplified equivalent model is developed for the inelastic analysis of these single-span simply supported bridges. Non-linear inelastic time-history analyses are conducted for various acceleration inputs. It is found that narrower bridges with longer spans may have considerable sliding displacements and fall off their supports if adequate seat width is not provided. It is also found that for the same ratio of friction coefficient to peak ground acceleration, the sliding displacement of a structural system is linearly proportional to the amplitude of the peak ground acceleration beyond a certain threshold value. This is also demonstrated analytically from an energy approach point of view. The distribution of the energy content of an earthquake, which is related to its velocity time history, can be an indication of the propensity of an earthquake to cause high sliding displacements. Ground motions with high frequency content or high A_p/V_p ratio may produce smaller sliding displacements than ground motions with relatively lower A_p/V_p ratios.     

Temperature variability in the Bay of Biscay during the past 40 years,from an in situ analysis and a 3D global simulation

A global in situ analysis and a global ocean simulation are used jointly to study interannual to decadal variability of temperature in the Bay of Biscay, from 1965 to 2003. A strong cooling is obtained at all depths until the mid-1970's, followed by a sustained warming over ～30 years. Strong interannual fluctuations are superimposed on this slow evolution. The fluctuations are intensified at the surface and are weakest at ～500 m. A good agreement is found between the observed and simulated temperatures, in terms of mean values, interannual variability and time correlations. Only the decadal trend is significantly underestimated in the simulation. A comparison to satellite sea surface temperature (SST) data over the last 20 years is also presented. The first mode of interannual variability exhibits a quasi-uniform structure and is related to the inverse winter North Atlantic Oscillation (NAO) index. Regarding the vertical structure, most cool and warm anomalies are generated at the surface, with the strongest ones penetrating down to 700 m and lasting up to 5 years. The complete heat budget from 1965 to 2004 is presented, including the contributions of vertical transport, freshwater flux and surface elevation. Interannual anomalies are mainly generated by the surface heat flux, while oceanic transports may become more important at longer time scales.     

New insights on the interior of solar-like pulsators thanks to CoRoT: the case of HD 49385

The high performance photometric data obtained with space mission CoRoT offer the opportunity to efficiently constrain our models for the stellar interior of solar-like pulsating stars. On the occasion of the analysis of the oscillations of solar-like pulsator HD 49385, a G0-type star in an advanced stage of evolution, we revisit the phenomenon of the avoided crossings. Christensen-Dalgaard proposed a simple analogy to describe an avoided crossing between two modes. We here present an extension of this analogy to the case of n modes, and show that it should lead, in certain cases, to a characteristic behavior of the eigenfrequencies, significantly different from the n=2 case. This type of behavior seems to be observed in HD 49385, from which we infer that the star should be in a Post Main Sequence phase.     

Biogenic carbon flows through the planktonic food web of the Amundsen Gulf (Arctic Ocean): A synthesis of field measurements and inverse modeling analyses

Major pathways of biogenic carbon (C) flow are resolved for the planktonic food web of the flaw lead polynya system of the Amundsen Gulf (southeast Beaufort Sea, Arctic Ocean) in spring-summer 2008. This period was relevant to study the effect of climate change on Arctic marine ecosystems as it was characterized by unusually low ice cover and warm sea surface temperature. Our synthesis relied on a mass balance estimate of gross primary production (GPP) of 52.5 ± 12.5 g C m⁻² calculated using the drawdown of nitrate and dissolved inorganic C, and a seasonal f-ratio of 0.64. Based on chlorophyll a biomass, we estimated that GPP was dominated by phytoplankton (93.6%) over ice algae (6.4%) and by large cells (>5 μm, 67.6%) over small cells (<5 μm, 32.4%). Ancillary in situ data on bacterial production, zooplankton biomass and respiration, herbivory, bacterivory, vertical particle fluxes, pools of particulate and dissolved organic carbon (POC, DOC), net community production (NCP), as well as selected variables from the literature were used to evaluate the fate of size-fractionated GPP in the ecosystem. The structure and functioning of the planktonic food web was elucidated through inverse analysis using the mean GPP and the 95% confidence limits of every other field measurement as lower and upper constraints. The model computed a net primary production of 49.2 g C m⁻², which was directly channeled toward dominant calanoid copepods (i.e. Calanus hyperboreus 20%, Calanus glacialis 10%, and Metridia longa 10%), other mesozooplankton (12%), microzooplankton (14%), detrital POC (18%), and DOC (16%). Bacteria required 29.9 g C m⁻², a demand met entirely by the DOC derived from local biological activities. The ultimate C outflow comprised respiration fluxes (82% of the initial GPP), a small sedimentation (3%), and a modest residual C flow (15%) resulting from NCP, dilution and accumulation. The sinking C flux at the model limit depth (395 m) supplied 60% of the estimated benthic C demand (2.8 g C m⁻²), suggesting that the benthos relied partly on other C sources within the bottom boundary layer to fuel its activity. In summary, our results illustrate that the ongoing decline in Arctic sea ice promotes the growth of pelagic communities in the Amundsen Gulf, which benefited from a ∼80% increase in GPP in spring-summer 2008 when compared to 2004 – a year of average ice conditions and relatively low GPP. However, 53% of the secondary production was generated within the microbial food web, the net ecological efficiency of zooplankton populations was not particularly high (13.4%), and the quantity of biogenic C available for trophic export remained low (6.6 g C m⁻²). Hence it is unlikely that the increase in lower food web productivity, such as the one observed in our study, could support new harvestable fishery resources in the offshore Beaufort Sea domain.     

Simultaneous Determination of Fluorine,Chlorine, Bromine and Iodine in Six Geochemical Reference Materials Using Pyrohydrolysis,Ion Chromatography and Inductively Coupled Plasma‐Mass Spectrometry

Concentrations of halogens (fluorine, chlorine, bromine and iodine) were determined in six geochemical reference materials (BHVO‐2, GS‐N, JG‐1, JR‐1, JB‐1b, JB‐2). Halogens were first extracted from powdered samples using a pyrohydrolysis technique, then hydrolysis solutions were analysed by ion chromatography for F and Cl and inductively coupled plasma‐mass spectrometry for Br and I. The detection limits in solutions were 100 μg l^?1 for both F and Cl and 10 ng l^?1 for Br and I. Considering the extraction procedure, performed on a maximum of 500 mg of sample and producing 100 ml of pyrohydrolysis solution, detection limits in rock samples were 20 mg kg^?1 for F and Cl and 2 μg kg^?1 for Br and I. The mean analytical errors on the studied composition ranges were estimated at 10 mg kg^?1 for F and Cl, 100 μg kg^?1 for Br and 25 μg kg^?1 for I. The concentration values, based on repeated (generally > 10) sample analysis, were in good agreement generally with published values and narrowed the mean dispersion around mean values. Large dispersions are discussed in terms of samples heterogeneity and contaminations during sample preparation. Basaltic RMs were found to be more suitable for studies of halogen compositions than differentiated rock material, especially granites – the powders of which were heterogeneous in halogens at the 500 mg level.     

Synthetic SH seismograms in a laterally varying medium by the discrete wavenumber method

Summary. We present a new method to calculate the SH wavefield produced by a seismic source in a half-space with an irregular buried interface. The diffracting interface is represented by a distribution of body forces. The Green's functions needed to solve the boundary conditions are evaluated using the discrete wavenumber method. Our approach relies on the introduction of a periodicity in the source-medium configuration and on the discretization of the interface at regular spacing. The technique developed is applicable to boundaries of arbitrary shapes and is valid at all frequencies. Some examples of calculation in simple configurations are presented showing the capabilities of the method.     

Comparaison de catalogues de crateres lunaires

Résumé La partie systématique des différences entre les positions des cratères de plusieurs catalogues est développée en harmoniques sphériques. L'application du test en ² détermine l'ordre du développement. La méthode a été appliquée pour comparer le système de référence de Arthur avec les catalogues de Schrutka-Rechtenstamm et Gavrilov. On obtient les surfacesf (l, b) des différences systématiques de ces catalogues. La zone centrale de la face visible de la lune (± 40° en latitude et longitude) est bien déterminée, mais la zone marginale présente des différences systématiques qui peuvent atteindre le kilomètre.

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The systematic part of the differences between positions in crater catalogues is expanded into spherical harmonics. The application of the ² test determines the highest order of the expansion. The method was applied to compare the Arthur System with the Schrutka-Rechtenstamm and Gavrilov catalogues. The surfacesf (l, b) of systematic differences from these catalogues were obtained. The central zone of the near side of the Moon (± 40° in latitude and longitude) is well determined but the marginal zone presents systematic differences that can be as large as one kilometer.