Invariant barriers to reactive front propagation in fluid flows

We present theory and experiments on the dynamics of reaction fronts in two-dimensional, vortex-dominated flows, for both time-independent and periodically driven cases. We find that the front propagation process is controlled by one-sided barriers that are either fixed in the laboratory frame (time-independent flows) or oscillate periodically (periodically driven flows). We call these barriers burning invariant manifolds (BIMs), since their role in front propagation is analogous to that of invariant manifolds in the transport and mixing of passive impurities under advection. Theoretically, the BIMs emerge from a dynamical systems approach when the advection-reaction-diffusion dynamics is recast as an ODE for front element dynamics. Experimentally, we measure the location of BIMs for several laboratory flows and confirm their role as barriers to front propagation.

Barriers to front propagation in ordered and disordered vortex flows

We present experiments on reactive front propagation in a two-dimensional (2D) vortex chain flow (both time-independent and time-periodic) and a 2D spatially disordered (time-independent) vortex-dominated flow. The flows are generated using magnetohydrodynamic forcing techniques, and the fronts are produced using the excitable, ferroin-catalyzed Belousov-Zhabotinsky chemical reaction. In both of these flows, front propagation is dominated by the presence of burning invariant manifolds (BIMs) that act as barriers, similar to invariant manifolds that dominate the transport of passive impurities. Convergence of the fronts onto these BIMs is shown experimentally for all of the flows studied. The BIMs are also shown to collapse onto the invariant manifolds for passive transport in the limit of large flow velocities. For the disordered flow, the measured BIMs are compared to those predicted using a measured velocity field and a three-dimensional set of ordinary differential equations that describe the dynamics of front propagation in advection-reaction-diffusion systems.

Does Mental Illness Affect Consumer Direction of Community-Based Care? Lessons From the Arkansas Cash and Counseling Program

Purpose: Previous research from the Cash and Counseling Demonstration and Evaluation (CCDE) in Arkansas, New Jersey, and Florida suggests that giving consumers control over their personal care greatly increases their satisfaction and improves their outlook on life. Still, some argue that consumerdirected care may not be appropriate for consumers with intellectual disabilities or mental health diagnoses. This study examined how Cash and Counseling— a new option allowing consumers to manage an individualized budget equivalent to what agencies would have spent on their care—changes the way consumers with mental health diagnoses meet their personal care needs and how that affects their wellbeing. Design and Methods: Using the Arkansas CCDE baseline and the 9-month follow-up data for individuals in the treatment and control groups, we compared and contrasted the experience of elderly consumers with and without mental health diagnoses utilizing logit regression. Results: After examining several outcome measures, including satisfaction with care arrangements and the paid caregiver’s reliability and schedule, unmet needs, and satisfaction with the relationship with paid caregivers, this study found evidence that, from the perspective of consumers, the Cash and Counseling program works well for participants with mental health diagnoses. Implications: Considering the growing need for long-term-care services and the limited resources available, a consumer-directed option makes sense, and it can be a valuable alternative for persons with mental health needs.