1,355,134 research outputs found
Advances in understanding the relationship between rock wettability and high-frequency dielectric response
No full textPrevious studies have shown that wettability has an effect on the complex permittivity of rock in a wide frequency interval. At low frequencies ( < 10 kHz), the dielectric behaviour is primarily controlled by the connectivity of the water phase. At higher frequencies (10 kHz-10 GHz), the governing parameter is the shape of the water inclusions, i.e. large-surface inclusions, typical of a water wet system, and small-surface inclusions, generally associated with oil wet situations, show markedly different electrical responses. Maxwell-Wagner-Sillars polarisation governs these high-frequency effects, which are relatively independent of the level of water saturation of the system, allowing direct and easier determination of wettability. Several experiments carried out on synthetic porous media and reservoir rocks made strongly oil wet using a sylanisation process have been published by the authors [Rev. Inst. Fr. Pet. 53 (1994) 771; Bona, N., Rossi, E., Capaccioli, S., 1999a. Wettability and dielectric constant. Proc. of the 1999 Int. Symp. of the Society of Core Analysts, Golden, Colorado, paper SCA 9925; Bona, N., Rossi, E., Capaccioli, S., 1999b. Electrical measurements in the 100 Hz-10 GHz frequency range for efficient rock wettability evaluation. Proc. of the 1999 SPE Int. Symp. on Oilfield Chemistry, Houston, paper SPE 50720, 207-217; J. Phys. D: Appl. Phys. 33 (2000) 1036]. This paper summarizes the results obtained on "fresh-state" rocks with preserved wettability. Two reservoirs were studied. One is a fractured oil reservoir, with a permeability so low that it cannot be investigated using the conventional wettability test techniques. The other is a carbonate reservoir, with Arnott test results available. While the second reservoir was found to be strongly water wet, the first showed the coexistence of water wet and oil wet zones, which were clearly recognised by two distinct relaxation peaks in the dielectric spectra. Air-mercury pore size distribution measurements and CryoSEM analyses were also carried out. All the collected data were used to build a consistent model of the behaviour of the rock. (C) 2002 Elsevier Science B.V. All rights reserved
Reply to "Comment on 'Correlation between configurational entropy and structural relaxation time in glass-forming liquids' "
No full textIn this Reply we show that contrary to the statements of Goldstein, the empirical function we proposed [D. Prevosto, M. Lucchesi, S. Capaccioli, R. Casalini, and P. A. Rolla, Phys. Rev. B 67, 174202 (2003)] for the pressure and temperature dependencies of the configurational entropy is mathematically and physically valid. Specifically we demonstrate that the condition of equal second derivatives, necessary for the configurational entropy to be a function of state, has physically reasonable solutions without the necessity of imposing implausible constraints
Change of caged dynamics at T-g in hydrated proteins: Trend of mean squared displacements after correcting for the methyl-group rotation contribution
No full textThe question whether the dynamics of hydrated proteins changes with temperature on crossing the glass transition temperature like that found in conventional glassformers is an interesting one. Recently, we have shown that a change of temperature dependence of the mean square displacement (MSD) at T-g is present in proteins solvated with bioprotectants, such as sugars or glycerol with or without the addition of water, coexisting with the dynamic transition at a higher temperature T-d. The dynamical change at T-g is similar to that in conventional glassformers at sufficiently short times and low enough temperatures, where molecules are mutually caged by the intermolecular potential. This is a general and fundamental property of glassformers which is always observed at or near T-g independent of the energy resolution of the spectrometer, and is also the basis of the dynamical change of solvated proteins at T-g. When proteins are solvated with bioprotectants they show higher T-g and T-d than the proteins hydrated by water alone, due to the stabilizing action of excipients, thus the observation of the change of T-dependence of the MSD at T-g is unobstructed by the methyl-group rotation contribution at lower temperatures [S. Capaccioli, K. L. Ngai, S. Ancherbak, and A. Paciaroni, J. Phys. Chem. B 116, 1745 (2012)]. On the other hand, in the case of proteins hydrated by water alone unambiguous evidence of the break at T-g is hard to find, because of their lower T-g and T-d. Notwithstanding, in this paper, we provide evidence for the change at T-g of the T-dependence of proteins hydrated by pure water. This evidence turns out from (i) neutron scattering experimental investigations where the sample has been manipulated by either full or partial deuteration to suppress the methyl-group rotation contribution, and (ii) neutron scattering experimental investigations where the energy resolution is such that only motions with characteristic times shorter than 15 ps can be sensed, thus shifting the onset of both the methyl-group rotation and the dynamic transition contribution to higher temperatures. We propose that, in general, coexistence of the break of the elastic intensity or the MSD at T-g with the dynamic transition at T-d in hydrated and solvated proteins. Recognition of this fact helps to remove inconsistency and conundrum encountered in interpreting data of hydrated proteins that thwart progress in understanding the origin of the dynamic transition. (C) 2013 AIP Publishing LLC
Major axis kinematics of 15 early-type galaxies in the Fornax cluster.
No full textMajor axis rotation curves and velocity dispersions profiles, extending out to about one effective radius, are presented for 15 ellipticals and S0's out of the photometric sample of Fornax cluster galaxies studied by Caon et al. (1994). A brief description of the spectroscopic and photometric characteristics of each galaxy is provided, together with a comparison with previous studies. Six of the nine E's are possibly misclassified S0's or ellipticals harboring a disk-like component. Two galaxies (NGC 1399 and 1404) show a hint of counter-rotation. Evidence is given that the bright and the ordinary families of early-type galaxies, first introduced by Capaccioli et al. (1992), look distinct also in term of the anisotropy parameter (V_m_/σ)*
Including Plastic Strain Into the Discrete Preisach-Mayergoyz Space: Application to Granular Media
No full textThe Preisach-Mayergoyz (PM) model describes hysteretic behavior in several fields. For fractured rocks, a discretized version of the PM model successfully models nonlinear hysteretic elasticity under multiple loading cycles. In addition to hysteresis, granular media are subjected to large irreversible (plastic) deformation. To account for plastic deformation, we propose a modification of the PM density matrix, in which we include negative opening pressure. We associate negative opening pressure with rearrangements of the contact network. We apply the model to three sand samples undergoing multiple isotropic loading cycles. Calibrating the model parameters from quasi-static measurements of volumetric deformation, we estimate the quality of prediction of the dynamic bulk modulus. When this elastoplastic PM model is compared to the classic PM model, strong improvements are found both in matching the strain path and in the estimation of the dynamic bulk modulus
Sull'evoluzione dei sistemi stellari: un passo fondamentale verso lo sfruttamento scientifico di VST (COFIN 2004, progetto biennale)
No full textIl Progetto finanziato dal MIUR (No. 2004020323004) ha consentito di completare le simulazioni necessarie a consentire lo sfruttamento scientifico dei dati ottenibili con il telescopio VST (Verylarge Survey Telescope) dell'ESO (European Southern Observatory). Il coordinatore nazionale del Progetto e' stato il Prof. M. Capaccioli.
Il finanziamento assegnato dal MIUR al Progetto e' stato i Euro 380000
VST processing facility: first astronomical applications
No full textVST–Tube is a new software package designed to process optical astronomical images. It is an automated pipeline to go from the raw exposures to fully calibrated co-added images, and to extract catalogs with aperture and PSF photometry. A set of tools allow the data administration and the quality check of the intermediate and final products. VST-Tube comes with a Graphical User Interface to facilitate the interaction between data and user. We outline here the VST–Tube architecture and show some applications enlightening some of the characteristics of the pipeline
Predicting the Pressure Dependence of Elastic Velocities of Dry Granular Assemblies Using a Modified GCT Model
No full textEvaluating abnormal pore pressure (overpressure zones) is a major safety issue in well drilling for oil and gas exploration. Nevertheless, presently, the problem of assessing the dependence of elastic moduli with pressure in unconsolidated media is still an open question even for the simple case of dry materials and packing of identical spherical grains. This is because the effective medium theory (EMT) based on the Hertz-Mindlin contact theory fails to predict the measured trend in laboratory data. To overcome this issue, we test a modified grain contact theory (GCT) model that fits elastic moduli with pressure proposed by Saul et al. (2013). We optimized this method by allowing a non linear relation between the calibration parameter and porosity and a simpler relation between pressure and porosity. We show that this model can predict the Vp and Vs pressure trends using published laboratory datasets by performing a blind test on Santa Cruz agglomerate samples
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