Biomedical subjects

Thomas L Carroll

Publications and source records attributed to Thomas L Carroll.

6 recordsLinked to original sources

PubMed2006

Using a phase space statistic to identify resonant objects.

The identification of resonant objects in radar or sonar, important for object identification, is difficult because existing methods require that the signal have a large signal-to-noise ratio. It is shown in this article that a modified version of the Kaplan-Glass (KG) statistic, a phase space statistic used to determine if a signal is deterministic, is sensitive to the properties of resonant objects. The modified KG statistic can be used to detect the presence of a resonant object even when the radar or sonar signal does not come from a deterministic dynamical system. The use of the modified KG statistic both numerically and in a simple experiment is also demonstrated.

Journal Article↗

PubMed2005

Analysis of multiple time scales in a transistor amplifier.

It was shown previously in an experiment that when high frequency signals (on the order of 1 MHz) were injected into this low frequency amplifier, the nonlinearities of the pn junctions caused period doubling, chaos, and very low frequency oscillations (on the order of 1 Hz). In this paper we present theory and simulations to explain the existence of the low frequency oscillations.

Journal Article↗

PubMed2005

Chaotic systems that are robust to added noise.

While added noise can destroy synchronization in synchronized chaotic systems, it was shown that some chaotic systems were not sensitive to added noise. In this paper, the mechanism for this noise resistance is explored. It is seen that part of the chaotic system acts like it is resonant, reducing the noise sensitivity of the system. By comparing to a model of a neuron, it is speculated that similar mechanisms may also be present in biological systems.

Algorithms↗

PubMed2005

Chaotic system for self-synchronizing Doppler measurement.

In a radar system, it is necessary to measure both range and velocity of a target. The movement of the target causes a Doppler shift of the radar signal, and the size of the Doppler shift is used to measure the velocity of the target. In this work, a chaotic drive-response system is simulated that detects a Doppler shift in a chaotic signal. The response system can detect Doppler shifts in more than one signal at a time.

Computers↗

PubMed2005

Bistability in a complementary metal oxide semiconductor inverter circuit.

Radiofrequency signals can disrupt the operation of low frequency circuits. A digital inverter circuit would seem to be immune to such disruption, because its output state usually jumps abruptly between 0 and 5 V. Nevertheless, when driven with a high frequency signal, the inverter can have two coexisting stable states (which are not at 0 and 5 V). Slow switching between these states (by changing the rf signal) will produce a low frequency signal. I demonstrate the bistability in a circuit experiment and in a simple model of the circuit.

Artifacts↗

PubMed2005

Multiple time scale chaos in a Schmitt trigger circuit.

It is known that stray radio frequency signals can produce nonlinear effects that disrupt the operation of circuits, but the mechanisms by which this disruption occurs are not well known. In this paper, an emitter coupled Schmitt trigger circuit is driven with a high-frequency signal to look for disruptive effects. As the circuit makes a transition between mode locked states (period 2 and period 3, for example), there is a region of chaos in which the largest peak in the power spectrum is in between the mode-locked frequencies, and is not related to the driving frequency by an integer multiple. This chaos resembles the chaos seen during a period adding sequence, except that it contains frequencies ranging over many orders of magnitude, from the driving frequencies on the order of megahertz, down to a few hertz. It is found that only a one-transistor circuit is necessary to produce this extremely broadband chaos, and true quasiperiodicity is not seen in this circuit. The single-transistor circuit is then simulated to confirm the frequency conversion effects.

Artifacts↗