Biomedical subjects

Pascal Picart

Publications and source records attributed to Pascal Picart.

6 recordsLinked to original sources

PubMed2005

Full-field vibrometry with digital Fresnel holography.

A setup that permits full-field vibration amplitude and phase retrieval with digital Fresnel holography is presented. Full reconstruction of the vibration is achieved with a three-step stroboscopic holographic recording, and an extraction algorithm is proposed. The finite temporal width of the illuminating light is considered in an investigation of the distortion of the measured amplitude and phase. In particular, a theoretical analysis is proposed and compared with numerical simulations that show good agreement. Experimental results are presented for a loudspeaker under sinusoidal excitation; the mean quadratic velocity extracted from amplitude evaluation under two different measuring conditions is presented. Comparison with time averaging validates the full-field vibrometer.

Journal Article↗

PubMed2005

Some opportunities for vibration analysis with time averaging in digital Fresnel holography.

Features offered by the combination of time averaging and digital Fresnel holography are investigated. In particular, we introduce the concept of the zero-crossing phase of Bessel fringes, which allows a highly contrasted determination of the dark fringes in the hologram. We discuss some particularities of the digital reconstruction and show how time-averaged digital holography can be used to study vibration drifts. Experiment results are presented in the case of a loudspeaker under a sinusoidal excitation; digital and analogical holography are also compared.

Journal Article↗

PubMed2004

Development of a biosensor for the detection of tributyltin.

A biosensor (LUMISENS I), based on the inducible bioluminescence of the Escherichia coli strain TBT3 (Ec::luxAB TBT3), was developed for the detection of the biocide tributyltin. LUMISENS I was set up with a minibioreactor and additional equipment for growth monitoring and light acquisition. The 100-mL minibioreactor has allowed us to establish a stable and reproducible environment for the bacteria (regulation of the growth rate, temperature, pH, and oxygenation), as well as for in situ contact with the xenobiotic. The optical components of the transducer were chosen according to the spectral emission of the strain being studied using a highly sensitive spectrophotometer that was initially devoted to Raman scattering. LUMISENS I was patented according to the in situ, automatic, and simultaneous measurement of the cell density and bioluminescence in the bioreactor. The first results showed that cells cultivated in a synthetic glucose medium provided a better detection limit than did those cultivated in a complex Luria-Bertani (LB) medium (0.02 and 1.5 microM of tributyltin, respectively). Cells maintained at a high growth rate (0.9 h(-1)) led to maximum bioluminescence. Moreover, air bubbling was efficient enough to provide suitable quantities of oxygen for both growth and light emission. When the TBT3 strain used the luxAB genes on its own, decanal, a long-chain aldehyde, had to be added to obtain the bioluminescence reaction. We found that the continuous addition of decanal was the most effective means of obtaining this reaction. The monitoring of the bioluminescence after tributyltin induction showed that the aldehyde was not toxic up to 300 microM during a 7-day experiment. Measurement of tributyltin with LUMISENS I was performed, which showed significant response up to 0.125 microM without any effect on optical density. Even though optimization of the performance of LUMISENS I is still under development, because of its original design, this biosensor is already in use as a warning system for the online monitoring of tributyltin.

Biosensing Techniques↗

PubMed2003

Time-averaged digital holography.

We demonstrate that it is possible to study the modal structures of a vibrating object with digitally recorded holograms by use of the time-averaging principle. We investigate the numerical reconstruction from a theoretical point of view, and we show that the numerically reconstructed object from a digital hologram is modulated by the zeroth-order Bessel function. Results of experiments in time-averaged digital holography are presented.

Journal Article↗

PubMed2003

Twin-sensitivity measurement by spatial multiplexing of digitally recorded holograms.

We present an all-numeric multiplexing/demultiplexing technique for digitally recorded holograms that allow the simultaneous determination of the in-plane and the out-of-plane components of the displacement vector of an object submitted to some loading. The twin-sensitivity measurement is obtained from two different illumination directions that give two sensitivity vectors. The spatial multiplexing is achieved by an incoherent mixing of two duplets of coherent waves that produce holograms carried with orthogonal polarized reference waves. The spatial demultiplexing uses the autocorrelation function of the multiplexed holograms as a position estimator. The estimator then enables the determination of the pixel-to-pixel correspondence between the holograms for the double component determination. Results of the experiment are presented.

Journal Article↗

PubMedDate not supplied

Comparison of the spectral emission of lux recombinant and bioluminescent marine bacteria.

The purpose of the present paper was to study the influence of bacteria harbouring the luciferase-encoding Vibrio harveyi luxAB genes upon the spectral emission during growth in batch-culture conditions. In vivo bioluminescence spectra were compared from several bioluminescent strains, either naturally luminescent (Vibrio fischeri and Vibrio harveyi) or in recombinant strains (two Gram-negative Escherichia coli::luxAB strains and a Gram-positive Bacillus subtilis::luxAB strain). Spectral emission was recorded from 400 nm to 750 nm using a highly sensitive spectrometer initially devoted to Raman scattering. Two peaks were clearly identified, one at 491-500 nm (+/- 5 nm) and a second peak at 585-595 (+/- 5 nm) with the Raman CCD. The former peak was the only one detected with traditional spectrometers with a photomultiplier detector commonly used for spectral emission measurement, due to their lack of sensitivity and low resolution in the 550-650 nm window. When spectra were compared between all the studied bacteria, no difference was observed between natural or recombinant cells, between Gram-positive and Gram-negative strains, and growth conditions and growth medium were not found to modify the spectrum of light emission.

Bacillus subtilis↗