Showing papers by "Daniel J. Gauthier published in 2009"

Controlling the Velocity of Light Pulses

Abstract: It is now possible to exercise a high degree of control over the velocity at which light pulses pass through material media. This velocity, known as the group velocity, can be made to be very different from the speed of light in a vacuum c. Specifically, the group velocity of light can be made much smaller than c, greater than c, or even negative. We present a survey of methods for establishing extreme values of the group velocity, concentrating especially on methods that work in room-temperature solids. We also describe some applications of slow light.

Boolean Chaos

Abstract: We observe deterministic chaos in a simple network of electronic logic gates that are not regulated by a clocking signal The resulting power spectrum is ultra-wide-band, extending from dc to beyond 2 GHz The observed behavior is reproduced qualitatively using an autonomously updating Boolean model with signal propagation times that depend on the recent history of the gates and filtering of pulses of short duration, whose presence is confirmed experimentally Electronic Boolean chaos may find application as an ultra-wide-band source of radio waves

Dynamics of Diastolic Sounds Caused by Partially Occluded Coronary Arteries

Abstract: The aim of this project is to improve the detection of coronary occlusions using an approach based on the recording and analysis of isolated diastolic heart sounds associated with turbulent blood flow in occluded coronary arteries. The nonlinear dynamic analysis method based on approximate entropy has been proposed for the analysis of diastolic heart sounds. A commercially available electronic stethoscope was used to record the diastolic heart sounds from patients diagnosed with or without coronary artery disease (CAD) based on their coronary angiography examination. The nonlinear dynamical analysis (approximate entropy) measures of the diastolic heart sounds recorded from 30 patients with coronary occlusions and ten normal subjects were estimated. Results suggest the presence of the high nonlinear (approximate entropy) values of diastolic heart sounds associated with CAD ( p < 0.05). This approach led to a sensitivity of 77%, a specificity of 80%, and an overall accuracy of 78%. As a summary, 23 out of 30 abnormal patients and eight out of ten normal patients were correctly detected.

Kinetic rate laws of Cd, Pb, and Zn vaporization during municipal solid waste incineration.

Abstract: The kinetic rate laws of heavy metal (HM) vaporization from municipal solid waste during its incineration were studied. Realistic artificial waste (RAW) samples spiked with Pb, Zn, and Cd were injected into a fluidized bed reactor. Metal vaporization was tracked by continuous measure of the above metals in exhaust gases. An inverse model of the reactor was used to calculate the metal vaporization rates from the concentration vs time profiles in the outlet gas. For each metal, experiments were carried out at several temperatures in order to determine the kinetic parameters and to obtain specific rate laws as functions of temperature. Temperature has a strong influence on the HM vaporization dynamics, especially on the vaporization kinetics profile. This phenomenon was attributed to internal diffusion control of the HM release. Two types of kinetic rate laws were established based on temperature: a fourth- or fifth-order polynomial rate law (r(x) = k0e−EA/RTp(x)) for temperatures lower than 740 °C and a fir...

Accurate description of optical precursors and their relation to weak-field coherent optical transients

Abstract: We study theoretically the propagation of a step-modulated optical field as it passes through a dispersive dielectric made up of a dilute collection of oscillators characterized by a single narrow-band resonance. The propagated field is given in terms of an integral of a Fourier type, which cannot be evaluated even for simple models of the dispersive dielectric. The fact that the oscillators have a low number density (dilute medium) and have a narrow-band resonance allows us to simplify the integrand. In this case, the integral can be evaluated exactly, although it is not possible using this method to separate out the transient part of the propagated field known as optical precursors. We also use an asymptotic method (saddle-point method) to evaluate the integral. The contributions to the integral related to the saddle points of the integrand give rise to the optical precursors. We obtain analytic expressions for the precursor fields and the domain over which the asymptotic method is valid. When combined to obtain the total transient field, we find that the agreement between the solutions obtained by the asymptotic and the exact methods is excellent. Our results demonstrate that precursors can persist for many nanoseconds and the chirp in the instantaneous frequency of the precursors can manifest itself in beats in the transmitted intensity. Our work strongly suggests that precursors have been observed in many previous experiments.

Causality in Superluminal Pulse Propagation

Abstract: The theory of electromagnetism for wave propagation in vacuum, as embodied by Maxwell’s equations, contains physical constants that can be combined to arrive at the speed of light in vacuum c. As shown by Einstein, consideration of the space–time transformation properties of Maxwell’s equations leads to the special theory of relativity. One consequence of this theory is that no information can be transmitted between two parties in a time shorter than it would take light, propagating through vacuum, to travel between the parties. That is, the speed of information transfer is less than or equal to the speed of light in vacuum c and information related to an event stays within the so-called light cone associated with the event. Hypothetical faster-than-light (superluminal) communication is very intriguing because relativistic causality would be violated. Relativistic causality is a principle by which an event is linked to a previous cause as viewed from any inertial frame of reference; superluminal communication would allow us to change the outcome of an event after it has happened.

Transient dynamics and momentum redistribution in cold atoms via recoil-induced resonances

Abstract: We use an optically dense, anisotropic magneto-optical trap to study recoil-induced resonances (RIRs) in the transient, high-gain regime. We find that two distinct mechanisms govern the atomic dynamics: the finite, frequency-dependent atomic response time, and momentum-space population redistribution. At low input probe intensities, the residual Doppler width of the atoms, combined with the finite atomic response time, result in a linear, transient hysteretic effect that modifies the locations, widths, and magnitudes of the resulting gain spectra depending on the sign of the scan chirp. When larger intensities (\textit{i.e.}, greater than a few $\mu$W/cm$^2$) are incident on the atomic sample for several $\mu$s, hole-burning in the atomic sample's momentum distribution leads to a coherent population redistribution that persists for approximately 100 $\mu$s. We propose using RIRs to engineer the atomic momentum distribution to enhance the nonlinear atom-photon coupling. We present a numerical model, and compare the calculated and experimental results to verify our interpretation.

Superradiance in an Ultracold Thermal Vapor

Abstract: We report on superradiant Rayleigh scattering in an anisotropic, cold thermal vapor. We identify threshold pump powers and atomic densities for entering the superradiant regime, and observe temporal correlations between light emitted in opposite directions.

Spatial heterogeneity of restitution properties and the onset of alternans

Abstract: Traditionally, it was believed that cardiac rhythm stability was governed by the slope of the restitution curve (RC), which relates the duration of an action potential to the preceding diastolic interval. However, a single RC does not exist; rate-dependence leads to multiple distinct RCs. We measure spatial differences in the steady-state action potential duration (APD), as well as in three different RCs: the S1-S2 (SRC), constant-basic-cycle-length (BRC), and dynamic (DRC), and correlate these differences with the tissue’s propensity to develop alternans. The results show that spatial differences in APD, SRC slope, and DRC slope are correlated with the tissue’s propensity to exhibit alternans. These results may lead to a new diagnostic approach to identifying patients with vulnerability to arrhythmias, which will involve pacing at slow rates and analyzing spatial differences in restitution properties.

Superluminal Communication in Quantum Mechanics

Abstract: 29. W. Keesom, M. Wolfke: Two different liquid states of helium. CPL 190b, 17–22 (1927) 30. A. Kozhevnikov: Piotr Kapitza and Stalin’s government: a study in moral choice. Historical Studies in the Physical and Biological Sciences 22, 131–163 (1992) 31. L. D. Landau: The theory of superfluidity of helium II. Journal of Physics (USSR), 5, 71–90 (1941); On the hydrodynamics of helium II, Ibid. 8, 1–3 (1944) 32. L. D. Landau: On the theory of superfluidity of Helium II. Journal of Physics (USSR), 11, 9–92 (1947) 33. L. D. Landau: On the theory of superfluidity. Physical Review 75, 884–885 (1949) 34. E. M. Lifshitz: Radiation of sound in helium II. Journal of Physics 8, 110–114 (1944) 35. E. Maxwell: Isotope effect in the superconductivity of mercury. Physical Review 78, 477 (1950) 36. L. Tisza: The theory of liquid helium. Physical Review 72, 838–854 (1947)

On the Origin of Chaos in Autonomous Boolean Networks

Abstract: We undertake a systematic study of the dynamics of Boolean networks to determine the origin of chaos observed in recent experiments. Networks with nodes consisting of ideal logic gates are known to display either steady states, periodic behavior, or an ultraviolet catastrophe where the number of logic-transition events circulating in the network per unit time grows as a power-law. In an experiment, non-ideal behavior of the logic gates prevents the ultraviolet catastrophe and may lead to deterministic chaos. We identify certain non-ideal features of real logic gates that enable chaos in experimental networks. We find that short-pulse rejection and the asymmetry between the logic states tends to engender periodic behavior, at least for the simplest networks. On the other hand, we find that a memory effect termed "degradation" can generate chaos. Our results strongly suggest that deterministic chaos can be expected in a large class of experimental Boolean-like networks. Such devices may find application in a variety of technologies requiring fast complex waveforms or flat power spectra, and can be used as a test-bed for fundamental studies of real-world Boolean-like networks.