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The role of extensional rheology in polymer processing
Baird, Donald G. The Korean Society of Rheology 1999 Korea-Australia rheology journal Vol.11 No.4
The shear behavior of polymers obtained by means of devices such as capillary and cone-and-plate rheo-meters is commonly used to assess their processing performance and as a characterization tool. However, the number of instances when two polymers have the same shear properties but perform differently during certain types of processing operations (e.g. film blowing and sheet extrusion) indicate that shear properties alone may not be sufficient to characterize polymeric fluids. We begin by defining the kinematics of shear-free or extensional flow and the associated material functions. The extensional and shear behavior of three different types of polyethylene (PE) are then compared to illustrate the points that one cannot ascertain the extensional properties of polymer melts from their shear properties and, furthermore, there may not be a simple relation between properties obtained from one type of extensional flow and those of another type. The kinematics of most processing flows are extensional rather than shear in nature, and , hence, the performance of polymers during processes such as fiber spinning, film casting, film blowing, thermoforming, blow molding, and even extrusion is more readily accounted for through extensional viscosity measurements. Methods for carrying out extensional flow measurements are then reviewed including approximate methods. To illustrate the sensitivity of extensional viscosity measurements to subtle changes in the molecular architecture of PEs, results are presented for samples with a narrow molecular weight distribution but with varying numbers of long chain branches. Finally, constitutive equations which allow one to separate shear and extensional flow behavior are discussed as any attempts to simulate the subtle processing differences between two polymers will require constitutive equations of this nature.
Ian G. Baird 서강대학교 동아연구소 2017 TRaNS(Trans –Regional and –National Studies of Sou Vol.5 No.2
Although biographical and life history approaches are potentially important tools for historical geographers, biographical methodologies have rarely been used to specifically investigate borderland dynamics. In this article, I argue that biography can be useful for understanding the ways in which borders have been recognised and negotiated historically. As a case study, I examine the life of Chao Sone Bouttarobol, a member of the Champassak Royal House, who was born in 1895 and died in 1979. As his life story illustrates, the emergence of new national borders had a significant impact on Sone, although family ties and relationships allowed him to cross the national administrative borders that now exist between Thailand, Laos, and Cambodia, often with relative ease. Studying one individual makes it possible to explore the ways in which he interacted and negotiated with borders that cut across the Champassak Royal House's traditional space of influence.
( Eunbae Lee ),( Timothy D. Baird ) 한국교육공학회 2021 Educational Technology International Vol.22 No.2
It is commonly understood that students’ autonomous motivation and individualistic orientations and instructors’ autonomy support are important for student-centered learning (SCL). However, few studies have examined this assumption. To help researchers and practitioners design more engaging SCL experiences across diverse cultural contexts, this study examines the associations of these factors with SCL engagement and how these associations compare in different cultures. University students in South Korea and the United States participated in a bold SCL assignment, called Pink Time, in which students decide what and how they learn. Linear, multivariate models were estimated in each context to identify and compare relationships between SCL engagement and student characteristics and perceptions. We found that engagement was high in both contexts. Autonomous motivation, individualism, and perceived instructor support each had significant associations with SCL engagement in South Korea. In the US, which had a smaller sample size, only perceived instructor support was significantly associated. These findings suggest that SCL strategies can be effective across cultures. Also, the narrower classroom context, specifically instructors’ support, may be a stronger driver of engagement than the broader societal context. This study contributes to the scholarly discussion regarding SCL in diverse settings and offers several implications for instructors.
Dane E. Klett,Bryce Baird,Colleen T. Ball,Chandler D. Dora 대한비뇨의학회 2021 Investigative and Clinical Urology Vol.62 No.6
Purpose: Previously published studies have shown small prostate size, capsular perforation and intraoperative bladder distension are associated with failed trial without a catheter (TWOC) after HoLEP. The study objective was to determine the relationship between MOSES pulse modulation versus standard laser technology and short-term catheter reinsertion following failed TWOC. Materials and Methods: The study included 487 patients who underwent HoLEP, using standard holmium laser settings (180 patients) or MOSES pulse modulation (255 patients), between August 2018 and February 2021. Catheter reinsertion defined as reinsertion following failed TWOC within 30 days of surgery. Association of pulse modulation with catheter reinsertion was examined using single and multivariable logistic regression models. Comparisons of pre and intraoperative characteristics between patients treated without and with pulse modulation were made using a Wilcoxon rank sum test for numeric characteristics or Fisher’s exact test for categorical characteristics. Results: Short-term catheter reinsertion occurred in 14% (26/180) of the standard laser setting group as compared with 10% (24/252) of the pulse modulation group. There was no statistically significant association with short-term catheter reinsertion in single (unadjusted OR [standard settings vs. pulse modulation], 1.60; 95% CI, 0.80–2.91; p=0.12) or multivariable analysis adjusting for specimen weight and operative time (adjusted OR [standard settings vs. pulse modulation], 1.44; 95% CI, 0.77–2.68; p=0.25). Conclusions: In this study, we found no association between post-HoLEP short-term catheter reinsertion following failed TWOC and MOSES pulse modulation. Although MOSES pulse modulation offers several well-documented advantages, catheter reinsertion events appear to be attributable to other factors.