laboratoire de physique statistique
 
 
laboratoire de physique statistique

Publications

Rechercher
REVIEW OF SCIENTIFIC INSTRUMENTS 


4
P U B L I C A T I O N S

S E L E C T I O N N E R
P A R M I :



 
2014
Design, fabrication and characterization of a monolithic focusing piezoceramic transducer for an anisotropic material - Souris, Fabien and Grucker, Jules and Garroum, Nabil and Leclercq, Arnaud and Isac, Jean-Michel and Dupont-Roc, Jacques and Jacquier, Philippe
REVIEW OF SCIENTIFIC INSTRUMENTS 85 (2014)

Abstract : Piezoceramic transducers shaped as spherical caps are widely used to focus ultrasound waves in isotropic materials. For anisotropic materials, the sound wave surface is not spherical and the transducer surface should be adjusted to reproduce a portion of this wave surface to focus the emitted sound properly. In this article, we show how to design such a transducer and how to fabricate it in lab on a standard machine from a rod of raw piezo ceramic material. The main features of its electrical impedance response are well reproduced by a numerical model, allowing the identification of most of its vibrational modes. We finally measured the sound field emitted by such a transducer and found its focusing efficiency similar to that of spherical caps in isotropic media. (C) 2014 AIP Publishing LLC.
 
2012
Monitoring microbial population dynamics at low densities - Julou, Thomas and Desprat, Nicolas and Bensimon, David and Croquette, Vincent
REVIEW OF SCIENTIFIC INSTRUMENTS 83 (2012)

Abstract : We propose a new and simple method for the measurement of microbial concentrations in highly diluted cultures. This method is based on an analysis of the intensity fluctuations of light scattered by microbial cells under laser illumination. Two possible measurement strategies are identified and compared using simulations and measurements of the concentration of gold nanoparticles. Based on this comparison, we show that the concentration of Escherichia coli and Saccharomyces cerevisiae cultures can be easily measured in situ across a concentration range that spans five orders of magnitude. The lowest measurable concentration is three orders of magnitude (1000x) smaller than in current optical density measurements. We show further that this method can also be used to measure the concentration of fluorescent microbial cells. In practice, this new method is well suited to monitor the dynamics of population growth at early colonization of a liquid culture medium. The dynamic data thus obtained are particularly relevant for microbial ecology studies. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4729796]
 
2011
Soft magnetic tweezers: A proof of principle - Mosconi, Francesco and Allemand, Jean Francois and Croquette, Vincent
REVIEW OF SCIENTIFIC INSTRUMENTS 82 (2011)

Abstract : We present here the principle of soft magnetic tweezers which improve the traditional magnetic tweezers allowing the simultaneous application and measurement of an arbitrary torque to a deoxyribonucleic acid (DNA) molecule. They take advantage of a nonlinear coupling regime that appears when a fast rotating magnetic field is applied to a superparamagnetic bead immersed in a viscous fluid. In this work, we present the development of the technique and we compare it with other techniques capable of measuring the torque applied to the DNA molecule. In this proof of principle, we use standard electromagnets to achieve our experiments. Despite technical difficulties related to the present implementation of these electromagnets, the agreement of measurements with previous experiments is remarkable. Finally, we propose a simple way to modify the experimental design of electromagnets that should bring the performances of the device to a competitive level. (C) 2011 American Institute of Physics. [doi:10.1063/1.3531959]
Fiber optic probe hydrophone for the study of acoustic cavitation in water - Arvengas, Arnaud and Davitt, Kristina and Caupin, Frederic
REVIEW OF SCIENTIFIC INSTRUMENTS 82 (2011)

Abstract : We use focused ultrasound bursts to submit a liquid to mechanical tension. When the pressure in the sound wave reaches a sufficiently low value, vapor bubbles are nucleated in the bulk liquid. According to nucleation theory, increasing the ultrasound frequency increases the cavitation threshold by a calculable amount. To check this, we have built a fiber optic probe hydrophone based on one originally proposed by Staudenraus and Eisenmenger [Ultrasonics 31, 267 (1993)]. We have adapted the pressure calibration and data analysis of this tool to make it appropriate for precise measurements of tension in liquids. We are able to resolve the fractional change in the pressure threshold for cavitation in water that results from a twofold increase in the frequency. This provides a test of nucleation theory in general. (C) 2011 American Institute of Physics. [doi:10.1063/1.3557420]