The diffusion properties of water in polyelectrolyte multilayers (PEM) are investigated by pulsed field gradient diffusion NMR. The dependence of the mean-square displacement on the observation time does not agree to Gaussian diffusion, suggesting restricted diffusion in a porous structure. However, the extraction of a pore size in a model of restricted diffusion yields a very large pore size of several micrometers. The additional influence of cross-relaxation of water and polymer spins is investigated in Goldman-Shen experiments. These demonstrate a strong influence of cross-relaxation rates on diffusion echo decays, such that pore sizes obtained from the model of restricted diffusion have to be corrected. Corrected pore sizes are about 4 microm and reflect the existence of domains of lower polymer density and thus faster water diffusion. These heterogeneities occur upon PEM preparation at high salt content for large layer numbers and are detected in the surface morphology, too.
Vol. 59 hibit the same agreement in the PVT behavior of the ortho and para forms of the gas.A recently published paper by Schafer [Z. physik. Chem., 36, 85 (1937) ] describes a similar investigation of the data of state of normal and para hydrogen, his results agreeing very well with ours, although calculated differently.
Background: River surfing (also called “rapid surfing”) involves surfing on stationary waves that are artificially created or placed in rivers and is gaining popularity, especially among surfers in landlocked areas but also among athletes without experience in ocean surfing. Different wave setups, types of boards, and types of fins, as well as the use of safety equipment, can lead to overuse and injuries. Purpose: To analyze the incidence, mechanisms, and risk factors of river surfing–related injuries for different types of waves and to evaluate the usage and appropriateness of safety equipment. Study Design: Descriptive epidemiology study. Methods: An online survey was distributed via social media to river surfers in German-speaking countries to collect information on demographics, injury history for the previous 12 months, wave site attended, use of (safety) equipment, and health issues. The survey was accessible between November 2021 and February 2022. Results: A total of 213 participants completed the survey: 195 participants from Germany, 10 from Austria, 6 from Switzerland, and 2 from other countries. The mean age was 36 years (range, 11-73 years), 72% (n = 153) were male, and 10% (n = 22) took part in competitions. Overall, 60% (n = 128) of surfers experienced 741 surfing-related injuries over the previous 12 months. The most common mechanisms of injury were contact with the bottom of the pool/river (n = 75 [35%]), with the board (n = 65 [30%]), and with the fins (n = 57 [27%]). The most frequent injury types were contusions/bruises (n = 256), cuts/lacerations (n = 159), abrasions (n = 152), and overuse (n = 58). Injuries affected mainly the feet/toes (n = 90), head/face (n = 67), hand/fingers (n = 51), knee (n = 49), lower back (n = 49), and thighs (n = 45). Earplugs were used by 50 (24%) participants, and a helmet was used regularly by 38 (18%) participants and never by 175 (82%) participants. Conclusion: The most frequent types of injury in river surfers were contusions/bruises, cuts/lacerations, and abrasions. The main mechanisms of injury were contact with the bottom of the pool/river, with the board, or with the fins. The feet/toes were more prone to injuries, followed by the head/face and hand/fingers.
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