Abdulsamad F.,CNRS Transfers and Interactions in Hydrosystems and Soils |
Florsch N.,CNRS Transfers and Interactions in Hydrosystems and Soils |
Florsch N.,Paris-Sorbonne University |
Schmutz M.,Bordeaux INP |
Camerlynck C.,CNRS Transfers and Interactions in Hydrosystems and Soils
Journal of Applied Geophysics | Year: 2016
During the last decades, the usage of spectral induced polarization (SIP) measurements in hydrogeology and detecting environmental problems has been extensively increased. However, the physical mechanisms which are responsible for the induced polarization response over the usual frequency range (typically 1. mHz to 10-20. kHz) require better understanding. The phase shift observed at high frequencies is sometimes attributed to the so-called Maxwell-Wagner polarization which takes place when charges cross an interface. However, SIP measurements of tap water show a phase shift at frequencies higher than 1. kHz, where no Maxwell-Wagner polarization may occur. In this paper, we enlighten the possible origin of this phase shift and deduce its likely relationship with the types of the measuring electrodes. SIP Laboratory measurements of tap water using different types of measuring electrodes (polarizable and non-polarizable electrodes) are carried out to detect the origin of the phase shift at high frequencies and the influence of the measuring electrodes types on the observed complex resistivity. Sodium chloride is used to change the conductivity of the medium in order to quantify the solution conductivity role. The results of these measurements are clearly showing the impact of the measuring electrodes type on the measured phase spectrum while the influence on the amplitude spectrum is negligible. The phenomenon appearing on the phase spectrum at high frequency (>. 1. kHz) whatever the electrode type is, the phase shows an increase compared to the theoretical response, and the discrepancy (at least in absolute value) increases with frequency, but it is less severe when medium conductivity is larger. Additionally, the frequency corner is shifted upward in frequency. The dependence of this phenomenon on the conductivity and the measuring electrodes type (electrode-electrolyte interface) seems to be due to some dielectric effects (as an electrical double layer of small relaxation time formed at the electrodes interface). Therefore, this dielectric response should be taken into account at high frequency to better analytically separate the medium own response from that linked to the measuring electrodes used. We modeled this effect by adding a capacitance connected in parallel with the traditional equivalent electric circuit used to describe the dielectric response of medium. © 2016 Elsevier B.V.
Kouadio T.,University of Bordeaux 1 |
Meziane A.,University of Bordeaux 1 |
Pradere C.,French National Center for Scientific Research |
Bacon C.,Bordeaux INP |
And 2 more authors.
Quantitative InfraRed Thermography Journal | Year: 2014
A new method for the thermal characterisation of homogeneous materials is proposed. This method, specifically designed to measure the thermal diffusivity in the plane of thin specimens, is based on a low-order weak formulation (LOWF) method of the heat equation using a virtual test function. In this formulation, the spatial derivatives of temperature are coupled with an analytical expression less dependent on measurement noise. In this way, it is shown that the LOWF method leads to a robust method for the estimation of thermal diffusivity. The LOWF method is numerically tested on a two-dimensional model and validated on a homogeneous material using infrared thermography. © 2014 Taylor & Francis.
Ben Slimene Ben Amor I.,RIADI Laboratory |
Chehata N.,Bordeaux INP |
Lagacherie P.,French National Institute for Agricultural Research |
Bailly J.-S.,Agro ParisTech |
Farah I.R.,RIADI Laboratory
International Geoscience and Remote Sensing Symposium (IGARSS) | Year: 2015
Active learning (AL) has shown a great potential in the field of remote sensing to improve the efficiency of the classification process while keeping a limited training dataset. Active learning uses heuristics to select the most informative pixels in each iteration. In literature, there are several metrics and selection criteria. In this paper, we focus on the uncertainty heuristics for large margin active learning. Existing uncertainty metrics are presented and combined to new ones using support vector machine learning algorithm. Besides, a new methodology is proposed, which automates a priori the choice of the best uncertainty heuristic. This contribution is evaluated on hyperspectral datasets while varying two parameters: class mixing and class balance. Finally discussion and conclusion are drawn. © 2015 IEEE.
Rummens F.,University of Bordeaux 1 |
Renaud S.,French National Center for Scientific Research |
Lewis N.,Bordeaux INP
Conference Proceedings - 13th IEEE International NEW Circuits and Systems Conference, NEWCAS 2015 | Year: 2015
We present a CMOS differential neural amplifier with high input impedance, which topology is inspired by the instrumentation amplifier. The miniaturization of the MEAs goes with an increase of the electrodes impedance and necessitates high input impedance neural amplifiers; otherwise it results in a significant loss of signal and low SNR. The circuit presented here is designed on a 0.35 μm CMOS technology. Two versions are described which capacitive input impedance is 1 pF. One is robust to high input offset and consumes 13.5 μA; the other one is more sensitive to offset but consumes only 3.7 μA. Both generate less than 7 μVRMS input-referred noise and their NEF figures are respectively 8.4 and 3.66. These features are competitive in view of the literature on neural amplifiers, while the circuit was specifically designed to present a high input impedance. © 2015 IEEE.
Lanusse P.,Bordeaux INP |
Sabatier J.,French National Center for Scientific Research |
Oustaloup A.,Bordeaux INP
IFAC Proceedings Volumes (IFAC-PapersOnline) | Year: 2014
This paper presents how common PID controllers have been generalized to fractional order PID controllers and how the additional tuning parameters can be used to meet more requirements. It is shown that the first generation CRONE control-system design methodology is able to provide robust fractional order PID for uncertain gain perturbed plants. © IFAC.