Because of their high surface areas, crystallinity, and tunable properties, metal–organic frameworks (MOFs) have attracted intense interest as next-generation materials for gas capture and storage. While much effort has been devoted to the discovery of new MOFs, a vast catalog of existing MOFs resides within the Cambridge Structural Database (CSD), many of whose gas uptake properties have not been assessed. Here we employ data mining and automated structure analysis to identify, “cleanup,” and rapidly predict the hydrogen storage properties of these compounds. Approximately 20 000 candidate compounds were generated from the CSD using an algorithm that removes solvent/guest molecules. These compounds were then characterized with respect to their surface area and porosity. Employing the empirical relationship between excess H2 uptake and surface area, we predict the theoretical total hydrogen storage capacity for the subset of ∼4000 compounds exhibiting nontrivial internal porosity. Our screening identifies several overlooked compounds having high theoretical capacities; these compounds are suggested as targets of opportunity for additional experimental characterization. More importantly, screening reveals that the relationship between gravimetric and volumetric H2 density is concave downward, with maximal volumetric performance occurring for surface areas of 3100–4800 m2/g. We conclude that H2 storage in MOFs will not benefit from further improvements in surface area alone. Rather, discovery efforts should aim to achieve moderate mass densities and surface areas simultaneously, while ensuring framework stability upon solvent removal.

Zourdos, MC, Goldsmith, JA, Helms, ER, Trepeck, C, Halle, JL, Mendez, KM, Cooke, DM, Haischer, MH, Sousa, CA, Klemp, A, and Byrnes, RK. Proximity to failure and total repetitions performed in a set influences accuracy of intraset repetitions in reserve-based rating of perceived exertion. J Strength Cond Res 35(2S): S158–S165, 2021—The aim of this study was to assess the accuracy of predicting repetitions in reserve (RIR) intraset using the RIR-based rating of perceived exertion (RPE) scale. Twenty-five men (age: 25.3 ± 3.3 years, body mass: 89.0 ± 14.7 kg, height: 174.69 ± 6.7 cm, and training age: 4.7 ± 3.2 years) reported to the laboratory. Subjects performed a 1 repetition maximum (1RM) squat followed by one set to failure at 70% of 1RM. During the 70% set, subjects verbally indicated when they believed they were at a 5RPE (5RIR), 7RPE (3RIR), or 9RPE (1RIR), and then continued to failure. The difference between actual repetitions performed and participant-predicted repetitions was calculated as the RIR difference (RIRDIFF). The average load used for the 70% set was 123.10 ± 24.25 kg and the average repetitions performed were 16 ± 4. The RIRDIFF was lower (RPEs were more accurate) closer to failure (RIRDIFF at 9RPE = 2.05 ± 1.73; RIRDIFF at 7RPE = 3.65 ± 2.46; and RIRDIFF at 5RPE = 5.15 ± 2.92 repetitions). There were significant relationships between total repetitions performed and RIRDIFF at 5RPE (r = 0.65, p = 0.001) and 7RPE (r = 0.56, p = 0.004), but not at 9RPE (r = 0.01, p = 0.97). Thus, being farther from failure and performing more repetitions in a set were associated with more inaccurate predictions. Furthermore, a multiple linear regression revealed that more repetitions performed per set was a significant predictor of RIR prediction inaccuracy at the called 5 (p = 0.003) and 7 (p = 0.011) RPEs, while training age (p > 0.05) was not predictive of rating accuracy. These data indicate RIR predictions are improved during low to moderate repetition sets and when there is close proximity to failure.

This Letter describes molecular dynamics simulations of pressureinduced flow of water and aqueous salt solutions through model nanopores. The systems studied are comprised of (n,n) carbon nanotubes (CNT) that span a membrane constructed of parallel graphene walls separating two solution reservoirs. We employ this system as an idealized model of surface-modified nanoporous membranes, and thus, both native hydrophobic CNT and nanotubes with artificial surface partial charge patterns are considered. The dependence of the fluxes of water and ions on the nanopore size, nanopore charge patterns, and pressure difference are explored using nonequilibrium molecular dynamics simulation. We demonstrate size-and structure-dependent salt rejection and show evidence of salt flux rectification for our asymmetric nanopore model.

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Purpose: To examine the validity of 2 linear position transducers, the Tendo Weightlifting Analyzer System (TWAS) and Open Barbell System (OBS), compared with a criterion device, the Optotrak Certus 3-dimensional motion-capture system (OC3D). Methods: A total of 25 men (age, 25 [3] y; height, 174.0 [6.7] cm; body mass, 89.0 [14.7] kg; squat 1-repetition maximum [1RM], 175.8 [34.7] kg) with ≥2 y of resistance-training experience completed a back 1RM and 1 set to failure at 70% of 1RM. Average concentric velocity (ACV) and peak concentric velocity (PCV) were recorded by all 3 devices during the final warm-up set, all 1RM attempts, and every repetition during the 70% set. Results: In total, 575 samples were obtained. Bland–Altman plots, mountain plots, a 1-way analysis of variance, SEM, and intraclass correlation coefficients were used to analyze validity. The analysis of variance showed no difference (P = .089) between devices for ACV. However, for PCV, TWAS was significantly different (ie, inaccurate) from OC3D (P < .001) and OBS (P = .001), but OBS was similar (P = .412) to OC3D. For ACV, intraclass correlation coefficients were higher for OBS than for TWAS. Bland–Altman plots showed agreement for ACV for both devices against OC3D but large limits of agreement for PCV for both devices. Mountain plots showed valid ACV for both devices, however, but slightly greater ACV and PCV accuracy with OBS than TWAS. Conclusions: Both devices may provide valid ACV measurements, but some metrics suggest more accurate ACV with OBS vs TWAS. For PCV, neither device is particularly accurate; however, OBS seems to be more accurate than TWAS.

The close association between f b and RPE throughout the run at CHR - 5 and during the last 50 % of the run at CHR + 5 indicated that muscle afferents may have provided feedback from metabolic and mechanical stimuli that contributed to the perceptual responses. In addition, only RPE consistently indicated exhaustion and the current findings supported its use to monitor exercise performed at a constant HR.

This paper describes nonequilibrium molecular dynamics simulations of pressure induced transport of liquid water through model nanopores. We consider a simple model for a porous membrane consisting of a slab of water molecules held in a rigid ice structure and penetrated by a pore of nanometer scale dimensions. Both hydrophilic membranes composed of conventional TIP3P water and hydrophobic membranes consisting of modified water with the model partial charges set to zero are treated. Molecular dynamics simulation is employed to investigate the rate of water flow through the pore induced by a pressure difference across the membrane. The results are compared with the predictions of continuum hydrodynamics. We find that the flow rate of water through hydrophilic pores is much less than the continuum predictions, while the flux through hydrophobic pores can significantly exceed the continuum theory. Finally, we show asymmetric behavior in the flux vs. pressure difference for a conical nanopore, which thus acts as a Brownian ratchet.

The mathematical model used to estimate critical power has been applied to heart rate (HR) measurements during cycle ergometry to derive a fatigue threshold called the critical heart rate (CHR). This study had 2 purposes: (a) determine if the CHR model for cycle ergometry could be applied to treadmill running and (b) examine the times to exhaustion (Tlim) and the VO2 responses during constant HR runs at the CHR. Thirteen runners (mean ± SD; age = 23 ± 3 years) performed an incremental treadmill test to exhaustion. On separate days, 4 constant velocity runs to exhaustion were performed. The total number of heart beats (HBlim) for each velocity was calculated as the product of the average 5-second HR and Tlim. The CHR was the slope coefficient of the HBlim vs. Tlim relationship. The Tlim and VO2 responses were recorded during a constant HR run at the CHR. Polynomial regression analyses were used to examine the patterns of responses for VO2 and velocity. The HBlim vs. Tlim relationship (r = 0.995-1.000) was described by the linear equation: HBlim = a + CHR (Tlim). The CHR (176 ± 7 b·min, 91 ± 3% HRpeak) was maintained for 47.84 ± 11.04 minutes. There was no change in HR but quadratic decreases in velocity and VO2. These findings indicated that the CHR model for cycle ergometry was applicable to treadmill running and represented a sustainable (30-60 minutes) intensity but cannot be used to demarcate exercise intensity domains.