Past Research

Entropy and information transfer in cortex networks, in vitro

Based on experiments and information theory we showed that balanced interactions between excitatory (E) and inhibitory (I) neurons in the cortex result in maximized information capacity. We also show that this optimal E/I balance results in minimal information loss between stimulus and response. The project is a collaboration between University of Maryland and National Institutes of Health with H. Yang, R. Roy, and D. Plenz.  click here to view a talk on this research

Article:  JNeurosci

Regulation of neural synchrony by exciation and inhibition, in vitro

We studied how the dynamics of phase synchrony in a population of cortical neurons depends in the relative influence of excitatory versus inhibitory signalling. We showed that variability of synchrony is maximized near the onset of synchrony, which occurs for an intermediate level of network excitability. The project was a collaboration between University of Maryland and National Institutes of Health with H. Yang, R. Roy, and D. Plenz.

Article: JNeurosci

Dynamic range or cortex networks, in vitro

We study the ability of brain circuits in vivo (and in vitro) to process sensory (and electrical) stimuli. We use micro-electrode arrays and network level computer models. We are testing the hypothesis that a brain operating near the critical point of a phase transition is optimally able to process sensory input. The project is a collaboration between University of Maryland and National Institutes of Health with H. Yang, R. Roy, T. Petermann and D. Plenz. A collaboration with Juan Restrepo and Dan Larremore at U Colorado has shed light on the theoretical underpinnings of this phenomenon.

Articles:  JNeurosci PRL Chaos

Simultaneous two-photon imaging and microelectrode array recording

Combined two-photon microscopy and micro-electrode arrays (MEA) recording, by developing a method to remove from the MEA signal the electrical artifact caused by the imaging laser. Used this new method to study spontaneous neural activity in rat cortex slices. (with D. Plenz and T. Bellay at National Institutes of Health)

Article: JNM


Smart Particles: Lagrangian measurements of temperature

We have developed flow tracing particles with on-board temperature sensors and wireless communications systems. We have made measurements of Lagrangian heat transport of thermal plumes in Rayleigh-Benard convection. (with Y. Gasteuil, M. Gibert, and J.-F. Pinton at ENS Lyon)

Articles: PRL RSI


Spiraling and zigzagging bubbles 

Continuous ultrasound and high speed cameras are used to measure the three dimensional trajectory of air bubbles in water. The ultrasound method provides direct and very sensitive velocity measurements. We deduce quantitative measurementsof the forces on the bubbles from the peculiar zigzagging and spiraling bubble trajectories. We have developed a simple dynamical model for these motions based on our measurements. We have also explored viscoelastic effects on these dynamics with bubbles rising in non-Newtonian fluids. (with J.-F. Pinton at ENS Lyon)

Articles: PRL JFM JSTAT






Experimental model of Earth's core

The motion of the molten iron of Earth's outer core was modelled with a 60 cm diameter, rapidly rotating, spherical convection experiment. The titanium vessel contained 100 liters of molten sodium and rotated at rotation rates up to 30 RPS and sustained up to 5 kW of heat transfer. Our results allowed us to estimate the size of convective velocities, time and length scales, ohmic dissipation, as well as the Rayleigh number for the Earth's outer core. (with D. P. Lathrop at UMD)

Articles: PEPI My PhD



Magneto-turbulence

Molten sodium was driven into a highly turbulent state in the presence of large magnetic fields (up to 0.2 T). As the applied magnetic field is increased, Lorentz forces become large enough to significantly suppress the turbulence. For large enough magnetic fields, instabilities arise in the interactions between the fluid flow and the magnetic field, exhibiting regular patterns in the induced magnetic field. These instabilities may be a laboratory manifestation of the magneto-rotational instability. (with D. R. Sisan & D. P. Lathrop at UMD)

Article: PEPI

Suppressing chaos with disorder in coupled oscillator experiments

An experimental array of 10 coupled pendulums with sinusoidal forcing was used to explore the control of chaos in spatially extended systems. It was found that the system behaved chaotically when all the pendulums were identical and could be pushed into a periodic state by randomly adjusting their lengths; adding disorder tames the chaos. (with J. F. Lindner at COW)

Article: AJP

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