Miniaturized triblock copolymers have been found to self-assemble into nanostructures that are highly regular in size and shape. Mushroom-shaped supramolecular structures of about 200 kilodaltons form by crystallization of the chemically identical blocks and self-organize into films containing 100 or more layers stacked in a polar arrangement. The polar supramolecular material exhibits spontaneous second-harmonic generation from infrared to green photons and has an adhesive tape-like character with nonadhesive-hydrophobic and hydrophilic-sticky opposite surfaces. The films also have reasonable shear strength and adhere tenaciously to glass surfaces on one side only. The regular and finite size of the supramolecular units is believed to be mediated by repulsive forces among some of the segments in the triblock molecules. A large diversity of multifunctional materials could be formed from regular supramolecular units weighing hundreds of kilodaltons.

Ⅲ This article examines the unfolding of experiences in youth programs

To create and sustain high quality youth development programs it is important to understand the challenging situations and dilemmas that emerge in program leaders' daily work with youth. In this research the experiences of leaders in 12 programs were followed over a 2-9 month period, which led to the identification of 250 dilemma situations. Qualitative analyses identified 5 categories and 12 subcategories of dilemmas that reflected distinct types of considerations (e.g., youth's personalities, relationships with the community). The analyses also found that the experienced leaders in the study typically responded to these dilemmas in ways that were youth-centered and that balanced multiple considerations. It is argued that researchers need to go beyond identifying features of high quality programs, and more fully examine how effective leaders create and sustain high quality in response to the challenging situations of practice.

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