Measuring the two-point correlation function of the galaxies in the Universe gives access to the underlying dark matter distribution, which is related to cosmological parameters and to the physics of ...the primordial Universe. The estimation of the correlation function for current galaxy surveys makes use of the Landy-Szalay estimator, which is supposed to reach minimal variance. This is only true, however, for a vanishing correlation function. We study the Landy-Szalay estimator when these conditions are not fulfilled and propose a new estimator that provides the smallest variance for a given survey geometry. Our estimator is a linear combination of ratios between pair counts of data and/or random catalogues (DD, RR, and DR). The optimal combination for a given geometry is determined by using lognormal mock catalogues. The resulting estimator is biased in a model-dependent way, but we propose a simple iterative procedure for obtaining an unbiased model-independent estimator. Our method can be easily applied to any dataset and requires few extra mock catalogues compared to the standard Landy-Szalay analysis. Using various sets of simulated data (lognormal, second-order LPT, and N-body), we obtain a 20–25% gain on the error bars on the two-point correlation function for the SDSS geometry and ΛCDM correlation function. When applied to SDSS data (DR7 and DR9), we achieve a similar gain on the correlation functions, which translates into a 10–15% improvement over the estimation of the densities of matter Ωm and dark energy ΩΛ in an open ΛCDM model. The constraints derived from DR7 data with our estimator are similar to those obtained with the DR9 data and the Landy-Szalay estimator, which covers a volume twice as large and has a density that is three times higher.
In the underground waste isolation projects such as the ANDRA'one in the site of Bure, the transport properties of the surrounding rock mass is of fundamental importance. To measure very low ...permeability, we use the modified version of the pulse test proposed by Hsieh et al. Hsieh, P.A., Tracy, J.V., Neuzil, C.E., Bredehoeft, J.D., Silliman, S.E., 1981. A transient laboratory method for determining the hydraulic properties of ‘tight’ rocks — I. Theory. Int. J. Rock Mech. Min. Sci. Geomech. Abstr. Vol. 18, pp. 245–252 which enables the intrinsic permeability,
k, and the specific storage coefficient,
S
s, of rocks such as mudstone to be characterized. In this paper, the special effort performed on the laboratory apparatus design, to ensure a good sensitivity of the rock response with respect to both parameters,
k and
S
s, is presented. In addition, two parameters identification procedures are proposed: the graphical method given by Hsieh et al. Hsieh, P.A., Tracy, J.V., Neuzil, C.E., Bredehoeft, J.D., Silliman, S.E., 1981. A transient laboratory method for determining the hydraulic properties of ‘tight’ rocks — I. Theory. Int. J. Rock Mech. Min. Sci. Geomech. Abstr. Vol. 18, pp. 245–252 and a parameter identification based on the solution of an inverse problem. The efficiency of the apparatus design and the parameters identification procedures is then demonstrated though some pulse tests performed on the Meuse/Haute-Marne mudstone.
This paper deals with the methods of determination of permeability in saturated and partially saturated conditions for low permeable porous rocks such as argillites. The modified version of the pulse ...test proposed by Hsieh et al. Int. J. Rock Mech. Min. Sci. Geomech. Abstr. 18 (1981) 245 has been used to characterize permeability in the saturated case. It enables the hydraulic diffusivity and then the intrinsic permeability and the specific storage coefficient to be characterized. In partially saturated conditions the method of saline solution to impose relative humidity and then capillary pressure has been used. The permeability in the partially saturated range can be deduced form measurements of transient weight loss and deformations of a sample submitted to a decrease of relative humidity in an hermetic chamber. In the two cases, pulse and drying tests, original experimental devices have been developed. The parameter-identification procedure based on the solution of corresponding inverse problems is presented. First approach explicit or semi-explicit solutions for the direct problems are used. It shows that the simplified linear approach is useful to obtain correct order of magnitude of unknowns parameters.
The clay minerals are among the first silicated minerals to be transformed physically and chemically during changes of temperature, pressure, relative humidity and fluid composition. One of the first ...physical processes, extremely rapid, is the hydration and/or dehydration of swelling clays minerals. These processes could generate changes of the clay structure and consequently the texture of an argillaceous rock. In order to observe in situ structural modifications on a deep argillaceous rock “argillite” (Parisian basin, in France) according hydration–dehydration cycles, an Environmental Scanning Electron Microscope (ESEM) was used. This instrument allows the possibility to observe geological samples in their natural state without preliminary preparation or modification. Two types of samples were prepared, parallel and perpendicular to the lithology. Then, each sample was submitted to three water condensation/evaporation cycles.
The observed samples were from the Callovo-Oxfordian formations in HTM 80743, HTM 983, HTM 02618 and EST 2159 cores. ESEM observations show that the water sensitivity of these bulk samples depends directly on the clay mineral proportion in the rock, and on the clay family present. It is also obvious that the water sensitivity depends on the anisotropy of the pore structure and the particle size and total porosity. The main structural modifications observed were the cracking of the surface, particles aggregation/disaggregating and opening/closing of pores and/or cracks.
Seismic behavior of inclined piles has been considered detrimental for years. However, recent researches show that battered piles can have a beneficial effect. In this framework, a series of ...centrifuge tests on an inclined pile group is performed. The analysis is based on the comparative response of two 2×1 simplified pile groups: one with vertical piles and the other with one vertical and one inclined pile. The response of these pile groups to repeated earthquakes or sinusoidal inputs is analyzed through the response frequencies, the envelop curves of bending moment profiles, the axial loads measured in both piles and the kinematic response of the cap. Results highlight that the effect of inclined pile is highly influenced by the frequency content of the input. In addition, the inclined pile induces non-negligible residual bending moments, higher horizontal stiffness at the pile cap and larger rotation.
► Seismic centrifuge tests are performed to highlight the effect of inclined pile. ► Cap response and pile stresses are measured during seismic and sinusoidal events. ► The effects of inclined pile are largely influenced by the input frequency. ► Presence of inclined pile increases residual bending moments. ► Inclined pile induces larger lateral stiffness and larger rotation of the footing.
A major advance in accurate electron beam polarization measurement has been achieved at Jlab Hall A with a Compton polarimeter based on a Fabry–Perot cavity photon beam amplifier. At an electron ...energy of 4.6
GeV and a beam current of 40
μ
A, a total relative uncertainty of 1.5% is typically achieved within 40
min of data taking. Under the same conditions monitoring of the polarization is accurate at a level of 1%. These unprecedented results make Compton polarimetry an essential tool for modern parity-violation experiments, which require very accurate electron beam polarization measurements.
The European Quaker project has been a powerful opportunity to accelerate the development of the ability to carry out earthquake simulations at reduced scale in the centrifuge in LCPC—France. This ...paper summarizes the main original technologies of this simulator. The quality of the checked performances is demonstrated in terms of ability to perform since earthquakes as well as to simulate scaled records of real earthquakes. The consistancy of the results is presented in the time and in the frequency domains.
The combination of galaxy-galaxy lensing (GGL) and redshift space distortion of galaxy clustering (RSD) is a privileged technique to test general relativity predictions and break degeneracies between ...the growth rate of structure parameter f and the amplitude of the linear power spectrum σ8. We performed a joint GGL and RSD analysis on 250 sq. deg using shape catalogues from CFHTLenS and CFHT-Stripe 82 and spectroscopic redshifts from the BOSS CMASS sample. We adjusted a model that includes non-linear biasing, RSD, and Alcock–Paczynski effects. We used an N-body simulation supplemented by an abundance matching prescription for CMASS galaxies to build a set of overlapping lensing and clustering mocks. Together with additional spectroscopic data, this helps us to quantify and correct several systematic errors, such as photometric redshifts. We find f(z = 0.57) = 0.95 ± 0.23, σ8(z = 0.57) = 0.55 ± 0.07 and Ωm = 0.31 ± 0.08, in agreement with Planck cosmological results 2018. We also estimate the probe of gravity EG = 0.43 ± 0.10, in agreement with ΛCDM−GR predictions of EG = 0.40. This analysis reveals that RSD efficiently decreases the GGL uncertainty on Ωm by a factor of 4 and by 30% on σ8. We make our mock catalogues available on the Skies and Universe database.
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