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Desai, Priyanka S.,Kang, Beom-Goo,Katzarova, Maria,Hall, Ryan,Huang, Qifan,Lee, Sanghoon,Shivokhin, Maksim,Chang, Taihyun,Venerus, David C.,Mays, Jimmy,Schieber, Jay D.,Larson, Ronald G. American Chemical Society 2016 Macromolecules Vol.49 No.13
<P>We compare predictions of two of the most advanced versions of the tube model, namely the 'Hierarchical model' by Wang et al. [J. Rheol. 2010, 54, 223] and the BoB (branch-on-branch) model by Das et al. [J. Rheol. 2006, SO, 207], against linear viscoelastic G' and G '' data of binary blends of nearly monodisperse 1,4-polybutadiene 4-arm star polymer of arm molar mass 24 000 g/mol with a monodisperse linear 1,4-polybutadiene of molar mass 58 000 g/mol. The star was carefully synthesized and characterized by temperature gradient interaction chromatography and by linear rheology over a wide frequency region through time temperature superposition. We found large failures of both the Hierarchical and BoB models to predict the terminal relaxation behavior of the star/linear blends, despite their success in predicting the rheology of the pure star and pure linear polymers. This failure occurred regardless of the choices made concerning constraint release, such as assuming arm retraction in 'fat' or 'skinny' tubes. Allowing for 'disentanglement relaxation' to cut off the constraint release Rouse process at long times does lead to improved predictions for our blends, but leads to much worse predictions for other star/linear blends described in the literature, especially those of Shivokhin et al. [Macromolecules 2014, 47, 2451]. In addition, our blends and those of Shivokhin et al. were also tested against a coarse-grained slip-link model, the 'clustered fixed slip-link model (CFSM)' of Schieber and co-workers [J. Rheol. 2014, 58, 723], in which several Kuhn steps are clustered together for computational efficiency. The CFSM with only two molecular-weight- and chain-architecture-independent parameters was able to give very good agreement with all experimental data for both of these sets of blends. In light of its success, the CFSM slip-link model may be used to address the constraint release issue more rigorously and potentially help develop improved tube models.</P>
Hall, Ryan,Desai, Priyanka S.,Kang, Beom-Goo,Huang, Qifan,Lee, Sanghoon,Chang, Taihyun,Venerus, David C.,Mays, Jimmy,Ntetsikas, Konstantinos,Polymeropoulos, George,Hadjichristidis, Nikos,Larson, Ronal American Chemical Society 2019 Macromolecules Vol.52 No.20
<P>We blend newly synthesized nearly monodisperse four-arm star 1,4-polybutadienes with various well-entangled linear polymers, confirming the conclusions in Desai et al. [<I>Macromolecules</I>201649 (13)49644977] that advanced tube models, namely, the hierarchical 3.0 and branch-on-branch models [Wang, Z.; <I>J. Rheol.</I>201054 (2)223260], fail to predict the linear rheological data when the pure linear polymers have shorter relaxation times, but within 3-4 orders of magnitude of the star polymer. However, when the linear polymer has a longer relaxation time than the star, our new work, surprisingly, finds that non-monotonic dependence of terminal relaxation behavior on composition is both observed experimentally and captured by the models. Combined with previous data from the literature, we present results from over 50 1,4-polybutadiene star-linear blends, suitable for thorough testing of rheological models of entangled polymers.</P> [FIG OMISSION]</BR>
Sujit J. Kshirsagar,Anandkumar H,Sanyogita V. Naik,Alok Yadav,Ruchira M. Sakhala,Sangharsh M. Salve,Aysath Nuhaimah,Priyanka Desai 대한중환자의학회 2024 Acute and Critical Care Vol.39 No.1
Background: Optic nerve sheath diameter (ONSD) is an emerging non-invasive, easily accessible, and possibly useful measurement for evaluating changes in intracranial pressure (ICP). The utilization of bedside ultrasonography (USG) to measure ONSD has garnered increased attention due to its portability, real-time capability, and lack of ionizing radiation. The primary aim of the study was to assess whether bedside USG-guided ONSD measurement can reliably predict increased ICP in traumatic brain injury (TBI) patients.Methods: A total of 95 patients admitted to the trauma intensive care unit was included in this cross sectional study. Patient brain computed tomography (CT) scans and Glasgow Coma Scale (GCS) scores were assessed at the time of admission. Bedside USG-guided binocular ONSD was measured and the mean ONSD was noted. Microsoft Excel ) was used for statistical analysis.Results: Patients with low GCS had higher mean ONSD values (6.4±1.0 mm). A highly significant association was found among the GCS, CT results, and ONSD measurements (p < 0.001). Compared to CT scans, the bedside USG ONSD had 86.42% sensitivity and 64.29% specificity for detecting elevated ICP. The positive predictive value of ONSD to identify elevated ICP was 93.33%, and its negative predictive value was 45.00%. ONSD measurement accuracy was 83.16%.Conclusions: Increased ICP can be accurately predicted by bedside USG measurement of ONSD and can be a valuable adjunctive tool in the management of TBI patients.