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We have been studying the effects of an external Coriolis force on the dynamics and bifurcation behavior of Taylor-Couette flow. Our work had three motivations. The first motivation was the body of work that has been carried out investigating the effects of an external field on fluid flows.1,2 Second, in our system the axisymmetry of the base flow is broken, whereas in systems studied previously, the external field does not break the fundamental symmetry of the system. 1–4 Finally, we wanted to introduce a second control parameter5 to the Taylor-Couette system, in the form of an external field, to explore how the dynamics are affected. Our experiments have revealed an unexpected array of bifurcation phenomena.6 This paper will explain the techniques used to discover the bifurcations in the flow, present a bifurcation map of the Taylor-Couette system subject to a Coriolis force, and finally, discuss some of the more interesting features revealed by the map.

Taylor-Couette flow subjected to a Coriolis force is a rich pattern-forming system.1–5 The Coriolis force is applied by rotating a Couette apparatus so that the axis of rotation for the system is. orthogonal to the common axis of the cylinders (see figure 1). This orientation produces a nonaxisymmetric Coriolis force through the interaction of the rotation of the system with the (primarily) azimuthal base flow. Experimentally, a small Coriolis force is found to stabilize the base flow against Taylor vortex formation. In other words, the Coriolis force increases the critical value of the Reynolds number R c for the onset of instability in the base flow. At the transition to secondary flow, the Taylor vortices are tilted out of the plane normal to the cylinders’ axis. But the flow is still time-independent. This tilted Taylor vortex flow is an example of a novel pattern which arises as a result of the nonaxisymmetric Coriolis force. Several other novel patterns also arise. At somewhat large system rotation rates, there is a direct transition from the base flow to strong spatiotemporal turbulence. At small values of Ω (where Ω is a dimensionless measure of the angular frequency of the rotating system) there is nonhysteretic re-emergent order at Reynolds numbers not far from the threshold for instability.3 In a medium gap system, there is a Hopf bifurcation from the base flow to axially travelling tilted Taylor vortices.4

This paper presents an analysis of third order autoregressive time series. The parameter regions, in the three dimensional parameter space, that produce the six separate types of power spectral density are analyzed. The study reveals that when a particular two dimensional cross section of the three dimensional parameter space is taken, the region of stability is always triangular. Within each triangular stability region in this two dimensional space, subregions which produce the six possible types of spectral shape are indicated. From these subregions it is possible to approximately choose the parameters necessary to model a process whose power spectral density contains at most two critical frequencies (maxima and minima).

Emission tests were conducted in Colorado to determine the contribution automobiles make to air pollution and to see if there is any correlation between carbon monoxide (CO) or hydrocarbon (HC) emissions and vehicle characteristics. The study used statistical regression analysis to compare model years, odometer readings, and engine displacements with emissions. Car model year and maintenance standards were found to be significant variables. Since neither HC nor CO emissions can be accurately predicted from the other, it is recommended that both be measured as a way to reduce maintenance costs.

International audience; It is well-known that few object-oriented programming languages allow objects to change their nature at run-time. In this paper we discuss the need for object-oriented programming languages to reflect the dynamic nature of problems, particularly those arising in a mathematical context. It is from this context that we present a framework, together with a Java-like implementation of that framework, that realistically represents the dynamic and evolving characteristic of problems and algorithms.