Structural investigation of the synthetic CaAn(PO4)2 (An = Th and Np) cheralite-like phosphates

The crystallographic structures of the synthetic cheralite, CaTh(PO₄)₂, and its homolog CaNp(PO₄)₂ have been investigated by X-ray diffraction at room temperature. Rietveld analyses showed that both compounds crystallize in the monoclinic system and are isostructural to monazite LnPO₄ (Ln = La to Gd). The space group is P2₁/n (I.T. = 14) with Z = 2. The refined lattice parameters of CaTh(PO₄)₂ are a = 6.7085(8) Å, b = 6.9160(6) Å, c = 6.4152(6) Å, and β = 103.71(1)° with best fit parameters R _wp = 4.87%, R _p = 3.69% and R _B = 3.99%. For CaNp(PO₄)₂, we obtained a = 6.6509(5) Å, b = 6.8390(3) Å, c = 6.3537(8) Å, and β = 104.12(6)° and R _wp = 6.74%, R _p = 5.23%, and R _B = 6.05%. The results indicate significant distortions of bond length and angles of the PO₄ tetrahedra in CaTh(PO₄)₂ and to a lesser extent in CaNp(PO₄)₂. The structural distortions were confirmed by Raman spectroscopy of CaTh(PO₄)₂. A comparison with the isostructural compounds LnPO₄ (Ln = Ce and Sm) confirmed that the substitution of the large rare earth trivalent cations with Ca²⁺ and Th⁴⁺ introduces a distortion of the PO₄ tetrahedra.     

Structure cristalline d'une ménéghinite naturelle pauvre en cuivre,Cu0,58Pb12,72(Sb7,04Bi0,24)S24Crystal structure of a Cu-poor natural meneghinite,Cu0.58Pb12.72(Sb7.04Bi0.24)S24

Cu-poor meneghinite from La Lauzière Massif (Savoy, France) has the composition (electron microprobe) (in wt%): Pb 59.50, Sb 20.33, Bi 1.19, Cu 0.87, Ag 0.05, Fe 0.03, S 17.62, Se 0.05, Total 99.64. Its crystal structure (X-ray on a single crystal) was solved with R1=0.0506, wR2=0.1026, with an orthorhombic symmetry, space group Pnma, and a=24.080(5) Å, b=4.1276(8) Å, c=11.369(2) Å, V=1130.0(4) Å³, Z=4. Relatively to the model of Euler and Hellner (1960), this structure shows a significantly lower site occupancy factor for the tetrahedral Cu site (0.146 against 0.25). Among the five other metallic sites, Bi appears in the one with predominant Sb. Developed structural formula: Cu_0.15Pb₂(Pb_0.53Sb_0.47)(Pb_0.46Sb_0.54)(Sb_0.75Pb_0.19Bi_0.06)S₆; the reduced one: Cu_0.58Pb_12.72(Sb_7.04Bi_0.24)S₂₄. The formation of such a Cu-poor variety seems to be related to specific paragenetic conditions (absence of coexisting galena), or to crystallochemical constraints (minor Bi). To cite this article: Y. Moëlo et al., C. R. Geoscience 334 (2002) 529–536.     

A Compilation of Silicon,Rare Earth Element and Twenty‐One other Trace Element Concentrations in the Natural River Water Reference Material SLRS‐5 (NRC‐CNRC)

The natural river water certified reference material SLRS‐5 (NRC‐CNRC) was routinely analysed in this study for major and trace elements by ten French laboratories. Most of the measurements were made using ICP‐MS. Because no certified values are assigned by NRC‐CNRC for silicon and 35 trace element concentrations (rare earth elements, Ag, B, Bi, Cs, Ga, Ge, Li, Nb, P, Rb, Rh, Re, S, Sc, Sn, Th, Ti, Tl, W, Y and Zr), or for isotopic ratios, we provide a compilation of the concentrations and related uncertainties obtained by the participating laboratories. Strontium isotopic ratios are also given.     

Numerical simulation of percussive drilling

This paper presents a novel dynamical model to analyze the long‐term response of a percussive drilling system. This departs from existing approaches that usually consider a single activation and bit/rock interaction cycle for the analysis of the process performance. The proposed model integrates the axial dynamics of an elastic piston and an elastic drill bit, a motion‐dependent pressure law to drive the piston, and a generalized bit/rock interaction law representative of the dynamic indentation taking place at the bit/rock interface. It applies to down‐the‐hole percussive drilling as well as top‐hole, with minor modifications. The model does not account for the angular motion or the hole cleaning, however. The model is first formulated mathematically; then, a finite‐dimensional approximation is proposed for computations. Numerical analyses of the model response, for a low‐size down‐the‐hole percussive system, follow. The period‐1 stationary response for the reference configuration is studied in detail, and parametric analyses assessing the influence on the rate of penetration of the bit/rock interaction parameters, the feed force, and the percussive activation parameters are conducted. These analyses reveal that the multiscale nature of the process is well captured by the model and recover expected trends for the influence of the parameters. They also suggest that a significant increase of the penetration rate can be achieved by increasing the percussive frequency. Copyright © 2015 John Wiley & Sons, Ltd.     

Analysis of the interannual variability of annual daily extreme water levels in the St Lawrence River and Lake Ontario from 1918 to 2010

We compared the interannual variability of annual daily maximum and minimum extreme water levels in Lake Ontario and the St Lawrence River (Sorel station) from 1918 to 2010, using several statistical tests. The interannual variability of annual daily maximum extreme water levels in Lake Ontario is characterized by a positive long‐term trend showing two shifts in mean (1929–1930 and 1942–1943) and a single shift in variance (in 1958–1959). In contrast, for the St Lawrence River, this interannual variability is characterized by a negative long‐term trend with a single shift in mean, which occurred in 1955–1956. As for annual daily minimum extreme water levels, their interannual variability shows no significant long‐term change in trend. However, for Lake Ontario, the interannual variability of these water levels shows two shifts in mean, which are synchronous with those for maximum water levels, and a single shift in variance, which occurred in 1965–1966. These changes in trend and stationarity (mean and variance) are thought to be due to factors both climatic (the Great Drought of the 1930s) and human (digging of the Seaway and construction of several dams and locks during the 1950s). Despite this change in means and variance, the four series are clearly described by the generalized extreme value distribution. Finally, annual daily maximum and minimum extreme water levels in the St Lawrence and Lake Ontario are negatively correlated with Atlantic multidecadal oscillation over the period from 1918 to 2010. Copyright © 2013 John Wiley & Sons, Ltd.     

Identifying influence areas with connectivity analysis – application to the local perturbation of heterogeneity distribution for history matching

Numerical representations of a target reservoir can help to assess the potential of different development plans. To be as predictive as possible, these representations or models must reproduce the data (static, dynamic) collected on the field. However, constraining reservoir models to dynamic data – the history-matching process – can be very time consuming. Many uncertain parameters need to be taken into account, such as the spatial distribution of petrophysical properties. This distribution is mostly unknown and usually represented by millions of values populating the reservoir grid. Dedicated parameterization techniques make it possible to investigate many spatial distributions from a small number of parameters. The efficiency of the matching process can be improved from the perturbation of specific regions of the reservoir. Distinct approaches can be considered to define such regions. For instance, one can refer to streamlines. The leading idea is to identify areas that influence the production behavior where the data are poorly reproduced. Here, we propose alternative methods based on connectivity analysis to easily provide approximate influence areas for any fluid-flow simulation. The reservoir is viewed as a set of nodes connected by weighted links that characterize the distance between two nodes. The path between nodes (or grid blocks) with the lowest cumulative weight yields an approximate flow path used to define influence areas. The potential of the approach is demonstrated on the basis of 2D synthetic cases for the joint integration of production and 4D saturation data, considering several formulations for the weights attributed to the links.     

Adaptation of the vertical resolution in the mixed layer for HYCOM

This paper focuses on the dynamics of the mixed layer. When the mixed layer depth increases, the vertical discretisation eventually becomes too sparse at the bottom of this layer to accurately resolve its evolution and strong numerical errors can appear. This is linked to the fact that the vertical resolution is concentrated in the upper part of the ocean and does not adapt to the deepening of the mixed layer.Knowing that the HYbrid Coordinate Ocean Model (HYCOM) is able to modify the distribution of the vertical levels, we suggest in this paper a method to adapt the resolution to the mixed layer extension. This method is tested in 1-D configurations for two academic atmospheric forcing conditions (strong convection and wind-mixing) and a realistic forcing extending over one year, with seasonal restratification following strong winter convection. The new method improves the results in all cases, and in particular when the mixed layer reaches deep layers.     

Identification of Gleissberg Cycles and a Rising Trend in a 315-Year-Long Series of Sunspot Numbers

We show in this short note that the method of singular spectrum analysis (SSA) is able to clearly extract a strong, clean, and clear component from the longest available sunspot (International Sunspot Number, ISN) time series (1700?–?2015) that cannot be an artifact of the method and that can be safely identified as the Gleissberg cycle. This is not a small component, as it accounts for 13% of the total variance of the total original signal. Almost three and a half clear Gleissberg cycles are identified in the sunspot number series. Four extended solar minima (XSM) are determined by SSA, the latest around 2000 (Cycle 23/24 minimum). Several authors have argued in favor of a double-peaked structure for the Gleissberg cycle, with one peak between 55 and 59 years and another between 88 and 97 years. We find no evidence of the former: solar activity contains an important component that has undergone clear oscillations of \(\approx90\) years over the past three centuries, with some small but systematic longer-term evolution of “instantaneous” period and amplitude. Half of the variance of solar activity on these time scales can be satisfactorily reproduced as the sum of a monotonous multi-secular increase, a \(\approx90\)-year Gleissberg cycle, and a double-peaked (\(\approx10.0\) and 11.0 years) Schwabe cycle (the sum amounts to 46% of the total variance of the signal). The Gleissberg-cycle component definitely needs to be addressed when attempting to build dynamo models of solar activity. The first SSA component offers evidence of an increasing long-term trend in sunspot numbers, which is compatible with the existence of the modern grand maximum.     

Test of the vibrational modelling for the λ-type transitions: Application to the α-β quartz transition

Vibrational modelling is at the present time the only known way to predict the heat capacities of the Earth's mantle minerals at high-pressure and high-temperature. To test the validity of this method for λ-type transitions, we have applied it to the α-β quartz transition (T ₀=846±1 K). Raman spectra of quartz were recorded up to 900 K. Measured frequency shifts of the α-quartz Raman modes were then used in conjunction with available high-pressure Raman data to calculate intrinsic mode anharmonicity, through the parameter a _i=(?Lnv_i/?T)_v. Vibrational modelling of the heat capacity at constant volume, Cv, and at constant pressure, Cp, including anharmonic corrections deduced from the a _i parameters, are compared to experimental data. Taking into account the soft-mode associated to the α-β quartz transition, the model reproduces the excess of Cp related to the transition. Then, this study confirms that detecting a soft-mode from vibrational data allows one to predict λ-type transitions. However, when modelling the thermodynamic properties, the contribution of a soft-mode cannot be established from spectroscopic data. Therefore, one needs first to determine this contribution in order to predict the heat capacities of Earth's mantle minerals displaying λ-type transitions. In α-quartz, this contribution has been determined as 0.007% of the total number of the optic modes in the model of the density of states.     

A Note on Extension Variances in IR2

Matheron (1971) proposed an approximation of the extension variance in IR. We propose in this note an extension of this formula in IR ² , based on a MacLaurin formula. Its application is shown in an example, the estimation of the maximum depressional storage of a soil surface.