Opinion cascades and the unpredictability of partisan polarization.

"Culture wars" involve the puzzling alignment of partisan identity with disparate policy positions, lifestyle choices, and personal morality. Explanations point to ideological divisions, core values, moral emotions, and cognitive hardwiring. Two "multiple worlds" experiments (n = 4581) tested an alternative explanation based on the sensitivity of opinion cascades to the initial conditions. Consistent with recent studies, partisan divisions in the influence condition were much larger than in the control group (without influence). The surprise is that bigger divisions indicate less predictability. Emergent positions adopted by Republicans and opposed by Democrats in one experimental "world" had the opposite outcome in other parallel worlds. The unpredictability suggests that what appear to be deep-rooted partisan divisions in our own world may have arisen through a tipping process that might just as easily have tipped the other way. Public awareness of this counter-intuitive possibility has the potential to encourage greater tolerance for opposing opinions.

Practical aspects of MR imaging in the presence of conductive guide wires.

Various aspects of RF-induced heating of guide wires during their MRI guidance have been investigated in the past. However, the previous works focused on inducing tip heating in either fully immersed or tip-immersed (and otherwise free) wires of impractical lengths in small phantoms. This study simulates real clinical conditions using a product guide wire and a same-length conductive wire partially inserted into a torso-size phantom filled with saline solution. The purpose was to identify potential safety concerns relevant to real clinical applications, as opposed to identifying the worst-case heating scenario. Significant heating occurred at the insertion point, independent of tip heating, with a strong correlation with excitation frequency-dependent imaging parameters. Heat transfer through the wire was also demonstrated to be a safety concern. From these experiments, we have been able to demonstrate additional impacting factors that increase the complexity of safety considerations for the use of conductive guide wires during MR imaging. Safety under a particular set of conditions does not imply safety in all possible conditions that can be encountered during real MRI-guided interventions.