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Full-Text Articles in Physics

Spontaneous Oscillations In Simple Fluid Networks, Nathaniel Karst, Brian Storey, John Geddes Jun 2014

Spontaneous Oscillations In Simple Fluid Networks, Nathaniel Karst, Brian Storey, John Geddes

John B. Geddes

Nonlinear phenomena including multiple equilibria and spontaneous oscillations are common in fluid networks containing either multiple phases or constituents. In many systems, such behavior might be attributed to the complicated geometry of the network, the complex rheology of the constituent fluids, or, in the case of microvascular blood flow, biological control. In this paper we investigate two examples of a simple three-node fluid network containing two miscible Newtonian fluids of differing viscosities, the first modeling microvascular blood flow and the second modeling stratified laminar flow. We use a combination of analytic and numerical techniques to identify and track saddle-node and ...


Laminar Flow Of Two Miscible Fluids In A Simple Network, Casey Karst, Brian Storey, John Geddes Mar 2013

Laminar Flow Of Two Miscible Fluids In A Simple Network, Casey Karst, Brian Storey, John Geddes

John B. Geddes

When a fluid comprised of multiple phases or constituents flows through a network, nonlinear phenomena such as multiple stable equilibrium states and spontaneous oscillations can occur. Such behavior has been observed or predicted in a number of networks including the flow of blood through the microcirculation, the flow of picoliter droplets through microfluidic devices, the flow of magma through lava tubes, and two-phase flow in refrigeration systems. While the existence of nonlinear phenomena in a network with many inter-connections containing fluids with complex rheology may seem unsurprising, this paper demonstrates that even simple networks containing Newtonian fluids in laminar flow ...


Boundary Effects In Large-Aspect-Ratio Lasers, G.K. Harkness, W.J. Firth, John B. Geddes, J.V Moloney, E.M. Wright Oct 2011

Boundary Effects In Large-Aspect-Ratio Lasers, G.K. Harkness, W.J. Firth, John B. Geddes, J.V Moloney, E.M. Wright

John B. Geddes

We study theoretically the effect of transverse boundary conditions on the traveling waves foundin infinitely extended and positively detuned laser systems. We find that for large-aspect-ratiosystems, well above threshold and away from the boundaries, the traveling waves persist. Sourceand sink defects are observed on the boundaries, and in very-large-aspect-ratio systems these defectscan also exist away from the boundaries. The transverse size of the sink defect, relative to the sizeof the transverse domain, is important in determining the final pattern observed, and so, close tothreshold, standing waves are always observed.


Extraction Of Signals From Chaotic Laser Data, John B. Geddes, Kevin Short, Kelly Black Oct 2011

Extraction Of Signals From Chaotic Laser Data, John B. Geddes, Kevin Short, Kelly Black

John B. Geddes

Several experimental groups have demonstrated communication with chaotic lasers. We analyzedata collected from a message-modulated erbium-doped fiber-ring laser (provided by VanWiggerenand Roy). We show that the transmitted signal is dominated by convolution of the message with theresponse function of the laser. A simple model based on the topology of the laser allows us to recovera hidden message. While prior estimates indicate that the laser dynamics are high dimensional, weshow that only four parameters are required, each of which can be recovered from the transmittedsignal alone.


Bistability In A Simple Fluid Network Due To Viscosity Contrast, John B. Geddes, Brian D. Storey, David Gardner, Russell T. Carr Jun 2011

Bistability In A Simple Fluid Network Due To Viscosity Contrast, John B. Geddes, Brian D. Storey, David Gardner, Russell T. Carr

John B. Geddes

We study the existence of multiple equilibrium states in a simple fluid network using Newtonian fluids and laminar flow. We demonstrate theoretically the presence of hysteresis and bistability, and we confirm these predictions in an experiment using two miscible fluids of different viscosity—sucrose solution and water. Possible applications include blood flow, microfluidics, and other network flows governed by similar principles.


Hexagons And Squares In A Passive Nonlinear Optical System, John Geddes, R.A. Indik, J.V. Moloney, Willie Firth Dec 1993

Hexagons And Squares In A Passive Nonlinear Optical System, John Geddes, R.A. Indik, J.V. Moloney, Willie Firth

John B. Geddes

Pattern formation is analyzed and simulated in a nonlinear optical system involving all three space dimensions as well as time in an essential way. This system, counterpropagation in a Kerr medium, is shown to lose stability, for sufficient pump intensity, to a nonuniform spatial pattern. We observe hexagonal patterns in a self-focusing medium, and squares in a self-defocusing one, in good agreement with analysis based on symmetry and asymptotic expansions.