Calculation of transport coefficient profiles in modulation experiments as an inverse problem

The calculation of transport profiles from experimental measurements belongs in the category of inverse problems which are known to come with issues of ill-conditioning or singularity. A reformulation of the calculation, the matricial approach, is proposed for periodically modulated experiments, within the context of the standard advection-diffusion model where these issues are related to the vanishing of the determinant of a 2x2 matrix. This sheds light on the accuracy of calculations with transport codes, and provides a path for a more precise assessment of the profiles and of the related uncertainty.Comment: V2: two typos correcte

Myotonic dystrophy type 1 and high ventricular vulnerability at the electrophysiological evaluation: ICD yes or not?

A significant number of sudden death (SD) is observed in myotonic dystrophy (DM1) despite pacemaker implantation and some consider the ICD to be the preferential device in patients with conduction disease. According to the latest guidelines, prophylactic ICD implantation in patients with neuromuscular disorder should follow the same recommendations of non-ischemic dilated cardiomyopathy, being reasonable when pacing is needed. We here report a case of DM1 patient who underwent ICD implantation even in the absence of conduction disturbances on ECG and ventricular dysfunction/fibrosis at cardiac magnetic resonance. The occurrence of syncope, non-sustained ventricular tachycardias at 24-Holter ECG monitoring and a family history of SD resulted associated with ventricular fibrillation inducibility at electrophysiological study, favouring ICD implantation. On our advice, DM1 patient with this association of SD risk factors should be targeted for ICD implantation

Ground state magnetic dipole moment of 35K

The ground state magnetic moment of 35K has been measured using the technique of nuclear magnetic resonance on beta-emitting nuclei. The short-lived 35K nuclei were produced following the reaction of a 36Ar primary beam of energy 150 MeV/nucleon incident on a Be target. The spin polarization of the 35K nuclei produced at 2 degrees relative to the normal primary beam axis was confirmed. Together with the mirror nucleus 35S, the measurement represents the heaviest T = 3/2 mirror pair for which the spin expectation value has been obtained. A linear behavior of gp vs. gn has been demonstrated for the T = 3/2 known mirror moments and the slope and intercept are consistent with the previous analysis of T = 1/2 mirror pairs.Comment: 14 pages, 5 figure

Elasto-viscoplastic modeling of subsidence above gas fields in the Adriatic Sea

Abstract. From the analysis of GPS monitoring data collected above gas fields in the Adriatic Sea, in a few cases subsidence responses have been observed not to directly correlate with the production trend. Such behavior, already described in the literature, may be due to several physical phenomena, ranging from simple delayed aquifer depletion to a much more complex time-dependent mechanical response of subsurface geomaterials to fluid withdrawal. In order to accurately reproduce it and therefore to be able to provide reliable forecasts, in the last years Eni has enriched its 3D finite element geomechanical modeling workflow by adopting an advanced constitutive model (Vermeer and Neher, 1999), which also considers the viscous component of the deformation. While the numerical implementation of such methodology has already been validated at laboratory scale and tested on synthetic hydrocarbon fields, the work herein presents its first application to a real gas field in the Adriatic Sea where the phenomenon has been observed. The results show that the model is capable to reproduce very accurately both GPS data and other available measurements. It is worth remarking that initial runs, characterized by the use of model parameter values directly obtained from the interpretation of mechanical laboratory tests, already provided very good results and only minor tuning operations have been required to perfect the model outcomes. Ongoing R&D projects are focused on a regional scale characterization of the Adriatic Sea basin in the framework of the Vermeer and Neher model approach

Implementation of an elasto-viscoplastic constitutive law in Abaqus/Standard for an improved characterization of rock materials

Subsidence modeling is an important activity in the oil and gas industry, for the environmental and operational implications associated to this phenomenon. Abaqus/Standard has been used for many years in Eni as the main numerical simulator for studying the geomechanical behavior of reservoirs. The results of a large campaign of acquisition of subsidence monitoring data in conjunction with the advanced analysis of laboratory experiments have shown that, in some cases, an improved mechanical characterization can be tailored to better capture the complex behavior of the reservoir rock under the effect of underground fluid withdrawal. In this work we first present an implementation in Abaqus/Standard of an elasto-viscoplastic model – namely the Vermeer and Neher model – as user defined material by means of the UMAT subroutine. Next, we provide the results of various simulations of laboratory tests that were performed to investigate its capability to identify the main features of the behavior of reservoir sands, also including time dependency. Finally, we show a preliminary application to a synthetic, nonetheless realistic, reservoir model that has been performed to assess the capabilities of the elasto-viscoplastic model in the simulation of subsidence evolution

Multifractal properties of return time statistics

Fluctuations in the return time statistics of a dynamical system can be described by a new spectrum of dimensions. Comparison with the usual multifractal analysis of measures is presented, and difference between the two corresponding sets of dimensions is established. Theoretical analysis and numerical examples of dynamical systems in the class of Iterated Functions are presented.Comment: 4 pages, 3 figure