Exploring conformations of comb-like polymers with varying grafting density in dilute solutions.

Comb-like polymers have shown potential as advanced materials for a diverse palette of applications due to the tunability of their polymer architecture. To date, however, it still remains a challenge to understand how the conformational properties of these polymers arise from the interplay of their architectural parameters. In this work, extensive simulations were performed using dissipative particle dynamics to investigate the effect of grafting density, backbone length, and sidechain length on the conformations of comb-like polymers immersed in a good solvent. To quantify the effect of these architectural parameters on polymer conformations, we computed the asphericity, radius of gyration, and backbone and sidechain end-to-end distances. Bond-bond correlation functions and effective Kuhn lengths were computed to quantify the topological stiffness induced by sidechain-sidechain interactions. Simulation results reveal that the effective Kuhn length increases as grafting density and sidechain length increase, in agreement with previous experimental and theoretical studies. This increase in stiffness results in comb-like polymers adopting extended conformations as grafting density and sidechain length increase. Simulation results regarding the radius of gyration of comb-like polymers as a function of grafting density are compared with scaling theory predictions based on a free energy proposed by Morozova and Lodge [ACS Macro Lett. 6, 1274-1279 (2017)] and scaling arguments by Tang et al. [Macromolecules 55, 8668-8675 (2022)].

Exploring design variations of the Titian Stradivari violin using a finite element model.

Because violins are traditionally hand-crafted using wood, each one is unique. This makes the design of repeatable experiments studying some aspects of its dynamic behavior unfeasible. To tackle this problem, an adjustable finite element (FE) model of a violin soundbox using the geometry and behavior of the "Titian" Stradivari was developed in this paper. The model is parametric, so its design and material properties can be varied for before/after comparisons in both the frequency and time domains. Systematic simulations revealed that f-holes set lower in the top, as seen in some Stradivari violins (e.g., Hellier, Cremonese), raise the frequency of the Hill (a feature in the bridge mobility); conversely, the higher set f-holes seen in some Guarneri violins (e.g., Principe Doria) reduces such frequency. This agrees with the widespread belief that the high-frequency response of Stradivari violins is stronger than Guarneri violins. Changes in the response of the system were quantified once each part of the design was added, calling attention to the influence of the blocks on the behavior of signature modes, especially in the frequency and shape of B1 +. A text file of the FE model is available in supplemental materials; it runs in ANSYS (free version), for which guides are included.

Diaphragmatic Ultrasonography, a Novel Approach in Critical Care: A Proposal for a New Weaning Index.

The evaluation of the diaphragm in critically ill patients is simple and noninvasive and has shown good repeatability. The aim of the study was to generate a predictive index for successful weaning (ULDIMex) from invasive mechanical ventilation (IMV) based on an ultrasonographic diaphragmatic assessment before performing a spontaneous breathing test. We recruited patients who required IMV and who were candidates for weaning from ventilation. The measurement of diaphragmatic excursion and time during inspiration and expiration was obtained with a 3- to 5-MHz probe in the M mode. Using the formula (a + b)c/2, the value for the ULDIMex was obtained to evaluate its impact on predicting the successful weaning of IMV, where a is the time during the inspiratory phase, b is the time during expiration, and c is the diaphragmatic excursion during the inspiratory phase, which corresponds to the highest point of the curve from the baseline. We recruited 114 patients, of whom 86 (76%) were successfully weaned from IMV. The patients who were successfully weaned from the IMV had a cutoff value greater than 4.06 cm/s for the ULDIMex index, with a sensitivity of 92.8% (95% confidence interval, 76.5-99.1), specificity of 63.9% (95% confidence interval, 52.9-74.0), positive predictive value of 45.6%, and negative predictive value of 96.5%. The ULDIMex index demonstrated a good level of discrimination for successful weaning prediction. Considering the excellent negative likelihood ratio of the ULDIMex index of greater than 4.06, this index may be considered before performing an spontaneous breathing test to identify critically ill adult patients who will extubate successfully.