Transport and deposition of suspended particles in saturated porous media: hydrodynamic effect

A laboratory study was undertaken to determine the transport and deposition rate of suspended particles in columns of saturated porous media (gravel and glass beads), where the porous media were subjected to steady-state flow. Silt particles with a mode of 14 μm diameter (used as the suspended particles) and fluorescein (as the conservative tracer) were injected into the columns in short pulses. The breakthrough curves were competently described with the analytical solution of a convection–dispersion equation with a first-order deposition rate. The experiments were performed using different flow rates. The suspended particle size distribution, the porous media, and the flow rates themselves were the main factors retained in this study to investigate the mechanisms governing the transport and deposition kinetics in detail. The results showed the existence of a flow rate, beyond which suspended particles travel faster than the conservative tracer. A decrease of the deposition rate of suspended particles beyond a critical flow velocity was also observed. Such behaviour led to consideration of the couple hydrodynamic-gravity forces at high flow rates. As the hydrodynamic force increases, particle deposition rates are reduced due to the effect of hydrodynamic forces inhibiting the deposition.     

Brest sea level record: a time series construction back to the early eighteenth century

The completeness and the accuracy of the Brest sea level time series dating from 1807 make it suitable for long-term sea level trend studies. New data sets were recently discovered in the form of handwritten tabulations, including several decades of the eighteenth century. Sea level observations have been made in Brest since 1679. This paper presents the historical data sets which have been assembled so far. These data sets span approximately 300 years and together constitute the longest, near-continuous set of sea level information in France. However, an important question arises: Can we relate the past and the present-day records? We partially provide an answer to this question by analysing the documents of several historical libraries with the tidal data using a ‘data archaeology’ approach advocated by Woodworth (Geophys Res Lett 26:1589–1592, 1999b). A second question arises concerning the accuracy of such records. Careful editing was undertaken by examining the residuals between tidal predictions and observations. It proved useful to remove the worst effects of timing errors, in particular the sundial correction to be applied prior to August 1, 1714. A refined correction based on sundial literature [Savoie, La gnomique, Editions Les Belles Lettres, Paris, 2001] is proposed, which eliminates the systematic offsets seen in the discrepancies in timing of the sea level measurements. The tidal analysis has also shown that shallow-water tidal harmonics at Brest causes a systematic difference of 0.023 m between mean sea level (MSL) and mean tide level (MTL). Thus, MTL should not be mixed with the time series of MSL because of this systematic offset. The study of the trends in MTL and MSL however indicates that MTL can be used as a proxy for MSL. Three linear trend periods are distinguished in the Brest MTL time series over the period 1807–2004. Our results support the recent findings of Holgate and Woodworth (Geophys Res Lett) of an enhanced coastal sea level rise during the last decade compared to the global estimations of about 1.8 mm/year over longer periods (Douglas, J Geophys Res 96:6981–6992, 1991). The onset of the relatively large global sea level trends observed in the twentieth century is an important question in the science of climate change. Our findings point out to an ‘inflexion point’ at around 1890, which is remarkably close to that in 1880 found in the Liverpool record by Woodworth (Geophys Res Lett 26:1589–1592, 1999b).     

A computer simulation study of natural silicate melts. Part I: Low pressure properties

In implementing into a molecular dynamics simulation code a simple interionic potential developed to describe the nine component system K₂O-Na₂O-CaO-MgO-FeO-Fe₂O₃-Al₂O₃-TiO₂-SiO₂ (KNCMFATS), it has been possible to reproduce satisfactorily a number of thermodynamic, structural and transport properties of a representative set of natural silicate melts. An important conclusion reached in this study is the good transferability of the potential from felsic to ultramafic compositions although this transferability becomes less accurate with high silica contents (rhyolitic composition and beyond) and with very iron-rich silicates (e.g. fayalite). A key feature of the simulation is to make the link between macroscopic properties of the melt and its microscopic structure and dynamics. We thus obtain a relationship between the molar volume of the melt, the number of network modifiers and the oxygen coordination number. The simulation also allows one to quantify the coordination environment around the cations as function of the melt composition. Furthermore, the electrical conductivity of the high temperature liquid is investigated.     

Single GPS receiver time-relative positioning with loop misclosure corrections

Time-relative positioning makes use of observations taken at two different epochs and stations with a single global positioning system (GPS) receiver to determine the position of the unknown station with respect to the known station. The limitation of this method is the degradation over time of the positioning accuracy due to the temporal variation of GPS errors (ionospheric delay, satellite clock corrections, satellite ephemerides, and tropospheric delay). The impact of these errors is significantly reduced by adding to the one-way move from the known to the unknown station, a back move to the known station. A loop misclosure is computed from the coordinates obtained at the known station at the beginning and at the end of the loop, and is used to correct the coordinates of the unknown station. The field tests, presented in this paper, show that using the loop misclosure corrections, time-relative positioning accuracy can be improved by about 60% when using single frequency data, and by about 40% with dual frequency data. For a 4-min processing interval (an 8-min loop) and a 95% probability level, errors remain under 20 cm for the horizontal components and 36 cm for the vertical component with single frequency data; and under 11 cm for the horizontal components and 29 cm for the vertical component with dual frequency data.     

GETEMME—a mission to explore the Martian satellites and the fundamentals of solar system physics

GETEMME (Gravity, Einstein??s Theory, and Exploration of the Martian Moons?? Environment), a mission which is being proposed in ESA??s Cosmic Vision program, shall be launched for Mars on a Soyuz Fregat in 2020. The spacecraft will initially rendezvous with Phobos and Deimos in order to carry out a comprehensive mapping and characterization of the two satellites and to deploy passive Laser retro-reflectors on their surfaces. In the second stage of the mission, the spacecraft will be transferred into a lower 1500-km Mars orbit, to carry out routine Laser range measurements to the reflectors on Phobos and Deimos. Also, asynchronous two-way Laser ranging measurements between the spacecraft and stations of the ILRS (International Laser Ranging Service) on Earth are foreseen. An onboard accelerometer will ensure a high accuracy for the spacecraft orbit determination. The inversion of all range and accelerometer data will allow us to determine or improve dramatically on a host of dynamic parameters of the Martian satellite system. From the complex motion and rotation of Phobos and Deimos we will obtain clues on internal structures and the origins of the satellites. Also, crucial data on the time-varying gravity field of Mars related to climate variation and internal structure will be obtained. Ranging measurements will also be essential to improve on several parameters in fundamental physics, such as the Post-Newtonian parameter ?? as well as time-rate changes of the gravitational constant and the Lense-Thirring effect. Measurements by GETEMME will firmly embed Mars and its satellites into the Solar System reference frame.     

Leaching of lead metallurgical slags and pollutant mobility far from equilibrium conditions

Lead metallurgical slags are partially vitrified materials containing residual amounts of Zn, Pb, Cr, Cd and As. These hazardous materials are generally buried on heaps exposed to weathering. In this study, leaching behavior of lead blast furnace slags has been tested using pure water and open flow experiments. It appears that in such far from equilibrium and slightly acidic conditions, the main phase to be altered is the vitreous phase. As for lunar, basaltic and nuclear glasses, alkalis/proton exchanges prevail and lead to the formation of a non-protective altered layer enriched in Si, Fe and Al. The composition of the altered layer is quite constant except for Si whose concentration decreases towards the leachate interface. Owing to their sizes, micrometric Pb droplets are not always totally dissolved at the slag surface. Nevertheless, nanometric Pb droplets are instantaneously dissolved while a surrounding altered layer is formed. This leads to high Pb releases in open flow systems. Leachate chemistry and dissolution rates of the vitreous phase are closely comparable to previous leaching tests with basaltic and nuclear glasses in conditions far from equilibrium. Moreover, this study confirms that Fe is a stable element in such conditions.     

Recursive algorithms for the computation of the potential harmonic coefficients of a constant density polyhedron

The gravitational potential of a constant density general polyhedron can be expressed both in terms of a closed analytical expression and as a series expansion involving the corresponding spherical harmonic coefficients. The latter can be obtained from two independent algorithms, which differ not only in their algorithmic architecture but in their efficiency and overall performance, especially when computing the coefficients of higher degree and order. In the present paper a comparative study of all these three approaches is carried out focusing on the numerical implementation of the recursive relations appearing in the two algorithms for the computation of the polyhedral potential harmonic coefficients. The performed numerical investigations show that the linear algorithm proposed by Jamet and Thomas (Proceedings of the second international GOCE user workshop, ‘GOCE, The Geoid and Oceanography’, ESA-ESRIN, Frascati, Italy, 8–10 March 2004, ESA SP-569, 2004), but so far not implemented, achieves a reasonable accuracy at a computational expense that opens to practical applications, for instance in the field of satellite gravimetry/gradiometry interpretation. The convergence behavior of the linear recursion algorithm is studied thoroughly and a computational procedure is proposed that enables the stable computation of potential harmonic coefficients up to degree 60 when referring to an arbitrarily shaped polyhedral body.