RESUMO
There is growing interest in creating solids that are responsive to various stimuli. Herein we report the first molecular-level mechanistic picture of the thermochromic polymorphic transition in a series of MAN-NI dyad crystals that turn from orange to yellow upon heating with minimal changes to the microscopic morphology following the transition. Detailed structural analyses revealed that the dyads assemble to create an alternating bilayer type structure, with horizontal alternating alkyl and stacked aromatic layers in both the orange and yellow forms. The observed dynamic behavior in the solid state moves as a yellow wavefront through the orange crystal. The overall process is critically dependent on a complex interplay between the layered structure of the starting crystal, the thermodynamics of the two differently colored forms, and similar densities of the two polymorphs. Upon heating, the orange form alkyl chain layers become disordered, allowing for some lateral diffusion of dyads within their own layer. Moving to either adjacent stack in the same layer allows a dyad to exchange a head-to-head stacking geometry (orange) for a head-to-tail stacking geometry (yellow). This transition is unique in that it involves a nucleation and growth mechanism that converts to a faster cooperative wavefront mechanism during the transition. The fastest moving of the wavefronts have an approximately 38° angle with respect to the long axis of the crystal, corresponding to a nonconventional C-H···O hydrogen bond network of dyad molecules in adjacent stacks that enables a transition with cooperative character to proceed within layers of orange crystals. The orange-to-yellow transition is triggered at a temperature that is very close to the temperature at which the orange and yellow forms exchange as the more stable, while being lower than the melting temperature of the original orange, or final yellow, solids.
RESUMO
Objective: The current multi-university, multi-disaster study examined the impact of natural disaster exposure on identity-related distress through life stressors and posttraumatic stress symptoms (PTSS). Participants: Young adult university students (n = 665, 77% female, M = 20.5 years old) participated in Wave (W) 1. Half provided contact information for follow-up, and 136 university students participated in W2. Method: University students in the mainland U.S. and Puerto Rico were asked about disaster exposure, life stressors, PTSS, and identity-related distress at W1 (M = 9.7 months post-disaster) and identity-related distress at W2 (M = 12.4 months after W1). Two serial mediation models assessed the indirect effect of disaster exposure on W1 and W2 identity-related distress through life stressors and PTSS. Results: Disaster exposure impacted identity-related distress concurrently and longitudinally through increasing life stressors since disaster and PTSS. Conclusion: Potential supportive services should address identity-related distress among disaster-exposed young adults with PTSS.
RESUMO
Community-Based Participatory Research promotes the inclusion of diverse voices in the research process and in decision-making processes. However, there are very few research studies that collaborate with children, especially within the context of schools. Promoting child participation has benefits both for children as well as for schools. Nonetheless, this may depend on how adults react to such participation. The present study is part of a broader study on school violence prevention. Our objective is to explore school personnel's concept of childhood and how it relates to their opinions about child school participation. We conducted a discussion group with nineteen (19) faculty and non-faculty members of a public school to ask them questions about the topic. We categorized participants' answers and analyzed relationships among them. Results suggest that participants' concept of childhood is linked to socio-cultural and historical factors and that it impacts their opinions about child participation. Also, school personnel recognize that child participation has benefits for children, the school and the wider society. This contrasts with deficiencies on how to articulate this participation beyond traditional classroom strategies. We discuss the implications of these results for pedagogical practice and for participatory research as promoters of children voices in context.