Solid-state proton nuclear magnetic resonance (NMR) has been used to investigate the structure and dynamics of a thermoplastic polyurethane elastomer (TPE) filled with carbon nanofibers (CNF's) for shapememory applications. The TPE soft segments are above their glass transition temperature (T g ) at ambient temperature and give rise to relatively narrow (∼2 kHz) signals in the solid-state proton spectrum. The introduction of CNF's leads to a concentration-dependent shifting and broadening of the signals, while the proton spin-lattice and spin-spin relaxation times are not significantly altered, showing that the broadening is inhomogeneous and related to the difference in magnetic susceptibility between the TPE and the CNF's. Proton spin diffusion experiments reveal the onset of stress-induced crystallinity as the samples are stretched to 60%, and stretching to 1000% leads to crystallization at the CNF surface and increased separation between the CNF's and the mobile amorphous phase of the TPE. The implications for the mixing of polymers and CNF's are considered.
Biologically templated nanoparticles are of interest for a variety of biological applications and for controlling the porosity and other properties in nanocomposites. Solid-state NMR has been used to characterize polypeptide/silica composites templated from the poly(l-lysine) solutions in the α-helix, β-sheet, and random coil conformations. The results show that the poly(l-lysine) retains its solution conformation in the nanocomposites when templating from the α-helix or β-sheet conformation, but the random coil conformation is partially converted to the α-helical form during nanocomposite formation. The dynamics of poly(l-lysine) are restricted by incorporation into the composite compared to bulk poly(l-lysine) at the equivalent relative humidity. Bulk and film poly(l-lysine) samples undergo transitions from the random coil to the β-sheet to the α-helix conformation with increasing relative humidity, but these transitions are suppressed in the silica composite. {1H-31P} NMR studies show that inorganic phosphate is incorporated into the random coil-templated composite and that part of the phosphate is closely associated with the poly(l-lysine). The implications for biomimetic nanocomposites formation are considered.
The primary purpose of this effort was to review several forms of nontraditional (NT) training programs, including heavy lower extremity strength training, CrossFit training, kettlebell training, and agility training, and discuss the effects of these exercise regimens on physical performance. The secondary purpose was to evaluate NT fitness training programs for evidence that they may provide beneficial options to help airmen improve their fitness scores. A search of the literature for 1980-2010 was performed using the Franzello Aeromedical Library, Public Medicine, and Air Force Institute of Technology search engines. There were 50 articles located and the authors selected 29 articles that specifically addressed the primary and secondary purposes of this literature review. This review indicates that an NT training approach is warranted in the general Air Force population. Heavy leg strength training and agility training show promise in enhancing aerobic fitness and improving fitness scores, particularly among members who have difficulty passing a physical fitness test. Most of the nontraditional forms of physical training are not supported in the scientific literature, with the exception of heavy leg strength training and agility training. However, even these NT forms of training require further investigation.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.