Electrochemical monitoring of the Pseudomonas aeruginosa growth and the formation of a biofilm in TSB media.

Understanding and sensing microbial biofilm formation onto surfaces remains highly challenging for preventing corrosion and biofouling processes. For that purpose, we have thoroughly investigated biofilm formation onto glassy carbon electrode surfaces by using electrochemical technics. Pseudomonas aeruginosa was studied because of its remarkable ability to form biofilms in many environments. The modification of the electrode-solution interface during biofilm growth was monitored by in-situ measurement of the open-circuit potential and correlated with results obtained by electrochemical impedance spectroscopy, cyclic voltammetry, scanning electron microscopy and bioassays. The sensing of the biofilm formation hence suggests a multi-steps mechanism, which may include pre-formation of an insulating layer onto the surface prior to the bacteria adhesion and biofilm formation.

Development of a Resonant Microwave Sensor for Sediment Density Characterization.

In this study, a sensor based on the development of a planar antenna immersed in sediments dedicated to water content monitoring in this type of material is proposed and experimentally validated. It is produced by a conventional Printed Circuit Board (PCB) manufacturing process on a double-sided metalized FR4 substrate. The sensitivity of the sensor is ensured by the variation of the real part of the complex dielectric permittivity of sediments with water content at around 1 GHz. As shown, in this frequency range, electrode polarization and Maxwell-Wagner polarization effects become negligible, leading to only a bulk water polarization sensitivity. The sensor operates in the reflection mode by monitoring the variation of the resonant frequency as a function of the sediment density through the S11 reflection measurements. An experimental sensitivity of 820   MHz . g - 1 . cm 3 was achieved. Despite the simplification of data interpretation at the considered frequency, the influence of ionic species such as NaCl in sediments on the real part of the relative complex dielectric permittivity is highlighted. This demonstrates the importance of considering a second parameter such as the S11 level at low frequency or the electrical conductivity to extract the density from the frequency measurements.

Coherence of nondegenerate states studied by auger electron-photoelectron coincidence experiments in Kr.

The indirect double photoionization of Kr via the Kr+(3d(-1)(3/2,5/2)) states to the Kr2+(4s4p(5) (1)P(o)) final state has been studied by Auger electron-photoelectron angular resolved coincidence experiments. By tuning the incident photon energy, we succeeded in observing the coherence in the photoionization of two nondegenerate spin-orbit states. The observations have been described quantitatively by a model which accounts for the two pathways to the final state as well as for the indistinguishability of the two ejected electrons.

Experimental observation of post-collision interaction and interference effects in resonant double photoionization processes.

The combined effects of post-collision interaction in the final state and interference due to the indistinguishability of the two electrons have been studied in a selected case of resonant double photoionization of neon. In our coincidence experiments, the photo- and Auger-electron pair was measured when the two electrons have nearly equal energy and are ejected at small mutual angle. The obtained energy distributions exhibit a strong interplay of post-collision interaction and interference effects, in agreement with the theoretical prediction of Sheinerman and Schmidt [J. Phys. B 30, 1677 (1997)] made on beryllium.