Self-diffusion in binary blends of cyclic and linear polymers

A lattice model is used to estimate the self-diffusivity of entangled cyclic and linear polymers in blends of varying compositions. To interpret simulation results, we suggest a minimal model based on the physical idea that constraints imposed on a cyclic polymer by infiltrating linear chains have to be released, before it can diffuse beyond a radius of gyration. Both, the simulation, and recently reported experimental data on entangled DNA solutions support the simple model over a wide range of blend compositions, concentrations, and molecular weights.Comment: 10 pages, 2 figure

Topological effects in ring polymers: A computer simulation study

Unconcatenated, unknotted polymer rings in the melt are subject to strong interactions with neighboring chains due to the presence of topological constraints. We study this by computer simulation using the bond-fluctuation algorithm for chains with up to N=512 statistical segments at a volume fraction \Phi=0.5 and show that rings in the melt are more compact than gaussian chains. A careful finite size analysis of the average ring size R \propto N^{\nu} yields an exponent \nu \approx 0.39 \pm 0.03 in agreement with a Flory-like argument for the topologica interactions. We show (using the same algorithm) that the dynamics of molten rings is similar to that of linear chains of the same mass, confirming recent experimental findings. The diffusion constant varies effectively as D_{N} \propto N^{-1.22(3) and is slightly higher than that of corresponding linear chains. For the ring sizes considered (up to 256 statistical segments) we find only one characteristic time scale \tau_{ee} \propto N^{2.0(2); this is shown by the collapse of several mean-square displacements and correlation functions onto corresponding master curves. Because of the shrunken state of the chain, this scaling is not compatible with simple Rouse motion. It applies for all sizes of ring studied and no sign of a crossover to any entangled regime is found.Comment: 20 Pages,11 eps figures, Late

Restating the Case: How Revisiting the Development of the Case Method Can Help Us Think Differently About the Future of the Business School

© Academy of Management Learning & Education. Although supportive of calls for business schools to learn the lessons of history to address contemporary challenges about their legitimacy and impact, we argue that our ability to learn is limited by the histories we have created. Through contrasting the contested development of the case method of teaching at Harvard Business School and the conventional history of its rise, we argue that this history, which promotes a smooth linear evolution, works against reconceptualizing the role of the business school. To illustrate this, we develop a "counterhistory" of the case method-one that reveals a contested and circuitous path of development-and discuss how recognizing this would encourage us to think differently. This counterhistory provides ameans of stimulating debate and innovative thinking about how business schools can address their legitimacy challenges, and, in doing so, have a more positive impact on society

Democratizing corporate governance: Compensating for the democratic deficit of corporate political activity and corporate citizenship

This article addresses the democratic deficit that emerges when private corporations engage in public policy, either by providing citizenship rights and global public goods (corporate citizenship) or by influencing the political system and lobbying for their economic interests (strategic corporate political activities). This democratic deficit is significant, especially when multinational corporations operate in locations where national governance mechanisms are weak or even fail, where the rule of law is absent and there is a lack of democratic control. This deficit may lead to a decline in the social acceptance of the business firm and its corporate political activities and, thus, to a loss of corporate legitimacy. Under these conditions corporations may compensate for the emerging democratic deficit and reestablish their legitimacy by internalizing democratic mechanisms within their organizations, in particular in their corporate governance structures and procedures. The authors analyze the available corporate governance models with the help of a typology and discuss the possible contributions of a new form of democratic corporate governance