Wheelchair propulsion test: development and measurement properties of a new test for manual wheelchair users.

OBJECTIVE: To develop and assess some of the measurement properties of a simple and inexpensive test that can be used to evaluate the wheelchair mobility of manual wheelchair users. DESIGN: The initial phase of the study was developmental and descriptive. For the assessment of reliability and validity, correlations and comparisons were carried out using within-participant and subgroup comparisons. SETTING: Rehabilitation center. PARTICIPANTS: Manual wheelchair users (N=58), a sample of convenience. INTERVENTION: The Wheelchair Propulsion Test (WPT) consists of wheeling 10m while time is recorded with a stopwatch, and the number of cycles and propulsion methods are recorded by observation. The WPT was administered once to each participant. Participants in subgroups involved in the assessment of reliability, construct, and concurrent validity had an additional WPT on the same occasion. MAIN OUTCOME MEASURES: Derived measures-speed (m/s), push frequency (cycles per second) and effectiveness (meters per cycle)-from the WPT and, for concurrent validity, an instrumented rear wheel. RESULTS: Regarding intra- and interrater reliability, intraclass correlation coefficients ranged from .72 to .96. Content validity was qualitatively good. For construct validity, on univariate or multivariate analyses, we found statistically significant relations between WPT measures and age, sex, duration of wheelchair use, type of wheelchair frame, and rolling surface. For concurrent validity, the WPT and instrumented wheel variables were highly correlated (r range, .92-.99), and there were no clinically significant differences between them. CONCLUSIONS: The WPT appears to be a simple and inexpensive test with good measurement properties that can be used for people who use hand and/or foot propulsion. However, further study is needed before widespread implementation can be recommended.

3D Asymmetric Bilayer Garnet-Hybridized High-Energy-Density Lithium-Sulfur Batteries.

Lithium garnet Li7La3Zr2O12 (LLZO), with high ionic conductivity and chemical stability against a Li metal anode, is considered one of the most promising solid electrolytes for lithium-sulfur batteries. However, an infinite charge time resulting in low capacity has been observed in Li-S cells using Ta-doped LLZO (Ta-LLZO) as a solid electrolyte. It was observed that this cell failure is correlated with lanthanum segregation to the surface of Ta-LLZO that reacts with a sulfur cathode. We demonstrated this correlation by using lanthanum excess and lanthanum deficient Ta-LLZO as the solid electrolyte in Li-S cells. To resolve this challenge, we physically separated the sulfur cathode and LLZO using a poly(ethylene oxide) (PEO)-based buffer interlayer. With a thin bilayer of LLZO and the stabilized sulfur cathode/LLZO interface, the hybridized Li-S batteries achieved a high initial discharge capacity of 1307 mA h/g corresponding to an energy density of 639 W h/L and 134 W h/kg under a high current density of 0.2 mA/cm2 at room temperature without any indication of a polysulfide shuttle. By simply reducing the LLZO dense layer thickness to 10 µm as we have demonstrated before, a significantly higher energy density of 1308 W h/L and 257 W h/kg is achievable. X-ray diffraction and X-ray photoelectron spectroscopy indicate that the PEO-based interlayer, which physically separates the sulfur cathode and LLZO, is both chemically and electrochemically stable with LLZO. In addition, the PEO-based interlayer can adapt to the stress/strain associated with sulfur volume expansion during lithiation.