Characterization of molecular motions in polymer gel networks using intensity-fluctuation spectroscopy

This work seeks to investigate the intrinsic dynamics of synthetic polymer gel networks in terms of cooperative submolecular motions, which give rise to autocorrelation functions, observed by intensity fluctuation spectroscopy. Poly(dimethyl siloxane) samples were purified and chemically crosslinked to three levels of crosslink density. The resulting networks were swollen in toluene. Light scattering data were obtained over a range of swelling ratios from each sample as well as from the uncrosslinked polymer in solution. Due to a large amount of extraneous scattering, indicating the presence of a large component of static scattering, a "background" normalization technique was devised which allowed extraction of the desired correlation function. Also, a computer program utilizing the "method of cumulants" was developed to obtain diffusion coefficients from nonlinear autocorrelation decay data. The "diffusion coefficient" DT calculated for the uncrosslinked polymer in solution indicates scattering entities of about 6 A. This corresponds to a molecular weight of about 16,, considerably less than the molecular weight of the polymer (16,). The values for the diffusion coefficient were found to increase with increasing concentration, contrary to intuition. A similar increase in DT with polymer concentration was observed in swollen crosslinked gels. Also, there was evidence that the diffusion coefficient decreases with increasing degrees of crosslinking. A qualitative model was developed which describes a system of cooperative submolecular scatterers, consistent with the observed changes in D. The results of the light scattering measurements were also compared to mechanical measurements of the tensile elastic modulus for the different crosslinked systems. These tests indicate that not all of the available sites were utilized in the crosslinking reactions

TRUNK ANGLE EFFECTS ON QUADRICEPS:HAMSTRING RATIO DURING BODYWEIGHT SQUATS

Penny Schulken, John Fox. Methodist University, Fayetteville, NC. BACKGROUND: Anterior cruciate ligament (ACL) ruptures occur in up to 250,000 people per year. Neuromuscular activation imbalance between the quadriceps and hamstrings may be a significant contributor to ACL injury. It has been demonstrated that a quadriceps/hamstring ratio (QHR) closer to one reduces the risk of ACL injury. The purpose of this study was to determine the trunk angle or angles that produced a hamstring dominant QHR during a bilateral body-weight squat. METHODS: A cross-sectional design with repeated measures was used in which a sample of 10 subjects performed three repetitions of squats with trunk flexion of 15, 30, 45, and 60 degrees relative to the horizontal plane. A bilateral squat was performed until the subject’s thighs were parallel with the ground. During each squat repetition Delsys Trigno® wireless surface electrodes (Delsys Inc., Natick MA) were placed bilaterally over the biceps femoris, semitendinosus, vastus lateralis, and vastus medialis muscles. Mean EMG activity was estimated for each muscle on each leg during each repetition. The ratio of the mean activity of the vastus medialis to semitendinosus was estimated for the right and left legs (RQHRM and LQHRM, respectively). The ratio of the mean activity of the vastus lateralis to the biceps femoris was estimated for the right and left legs (RQHRL and LQHRL, respectively). The Friedman Rank Sum Test was used to evaluate the interaction of trunk angle on QHR. RESULTS: Friedman Rank Sum Test demonstrated trunk angle had a significant effect on RQHRL (Χ2=11.76, p=0.008), RQHRM (Χ2=14.04, p=0.003), and LQHRM (Χ2=13.8, p=0.003). Pairwise comparisons showed significant differences between the 15° and 60° conditions for RQHRL (p=.009), RQHRM (p=.001), and LQHRM (p=.001), and between the 30° and 60° conditions for RQHRL (p=.035). CONCLUSIONS: No trunk lean angle resulted in a hamstring dominant QHR but 60-degree trunk lean reduced the dominance of the quadriceps during squatting. The results suggest clinicians can manipulate neuromuscular activation of quadriceps and hamstrings by cueing the amount of trunk lean during squatting. This has application with the rehabilitation of individuals following ACL injury

Strategy for the multiplicity of degrowth

This chapter starts with outlining a degrowth vision for social-ecological transformation. It then traces the existing discussion on strategy in the degrowth movement and explains why it is important to think about strategy. Its key contribution is a conceptualiation strategy, which builds on and is closely aligned with our understanding of degrowth. Finally, it introduces the book and its structure, followed by a conclusion