Shear induced morphology of semicrystalline block copolymers

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1994.Includes bibliographical references (leaves 98-100).by Peter Kofinas.Ph.D

Black Holes on Thin 3-branes of Codimension-2 and their Extension into the Bulk

We discuss black hole solutions in six-dimensional gravity with a Gauss-Bonnet term in the bulk and an induced gravity term on a thin 3-brane of codimension-2. We show that these black holes can be localized on the brane, and they can further be extended into the bulk by a warp function. These solutions have regular horizons and no other curvature singularities appear apart from the string-like ones. The projection of the Gauss-Bonnet term on the brane imposes a constraint relation which requires the presence of matter in the extra dimensions.Comment: 23 pages, no figures, minor corrections, version to appear in Nuclear Physics

Quintom Cosmology: Theoretical implications and observations

We review the paradigm of quintom cosmology. This scenario is motivated by the observational indications that the equation of state of dark energy across the cosmological constant boundary is mildly favored, although the data are still far from being conclusive. As a theoretical setup we introduce a no-go theorem existing in quintom cosmology, and based on it we discuss the conditions for the equation of state of dark energy realizing the quintom scenario. The simplest quintom model can be achieved by introducing two scalar fields with one being quintessence and the other phantom. Based on the double-field quintom model we perform a detailed analysis of dark energy perturbations and we discuss their effects on current observations. This type of scenarios usually suffer from a manifest problem due to the existence of a ghost degree of freedom, and thus we review various alternative realizations of the quintom paradigm. The developments in particle physics and string theory provide potential clues indicating that a quintom scenario may be obtained from scalar systems with higher derivative terms, as well as from non-scalar systems. Additionally, we construct a quintom realization in the framework of braneworld cosmology, where the cosmic acceleration and the phantom divide crossing result from the combined effects of the field evolution on the brane and the competition between four and five dimensional gravity. Finally, we study the outsets and fates of a universe in quintom cosmology. In a scenario with null energy condition violation one may obtain a bouncing solution at early times and therefore avoid the Big Bang singularity. Furthermore, if this occurs periodically, we obtain a realization of an oscillating universe. Lastly, we comment on several open issues in quintom cosmology and their connection to future investigations.Comment: 105 pages, 36 figures, version published at Physics Report

The costs of power sharing : community involvement in Canadian porcupine caribou co-management

Co-management arrangements are commonly framed with the theoretical assumption that community management systems function with a minimum of transaction costs and government-community power sharing lowers overall costs of management. Commonly overlooked both practically and theoretically are costs to communities. This dissertation investigates the involvement of three northern indigenous communities in a wildlife co-management arrangement to delineate community costs of power sharing. The subject of the study is the internationally migratory Porcupine Caribou Herd, Canada's three primary Porcupine Caribou user communities (Old Crow, YT, Aklavik, NT, and Fort McPherson, NT), and the resource regime established by the Canadian Porcupine Caribou Management Agreement and The Agreement between the Governments of Canada and the United States for the Conservation of Porcupine Caribou. Using multiple sources of evidence and drawing on the ethnographic method, the study documents emergent communication linkages between co-management boards and communities, analyzes locals' perceptions of caribou management information and scientific research activities, identifies patterns of interaction between researchers and hunters, and illustrates the constraints of choice available to hunters of the Canadian ' Porcupine Caribou co-management system. Presented is an account of the "1993 Caribou Crisis," a critical co-management incident in which hunters confront caribou researchers and face the dilemma of violating cultural traditions in order to stop proposed hydrocarbon development. Fundamentally, the study examines the consequence of interfacing authority systems and power dynamics of a formal co-management arrangement. The study also points to the limitations of rational choice perspectives when conducting institutional analysis, and the need to consider group identity, perspectives on uncertainty, and styles of learning when delineating transaction costs. From a more applied perspective, delineating anticipated and incurred community transaction costs of power sharing brings attention to the impediments to local involvement, how community members invest their energies in a co-management process, and who and by what method they bear the costs of shared decision making. Porcupine Caribou user communities make sacrifices when seeking to exercise authority in shared decision-making. The transaction costs of co-management associated with community involvement come at the price of time commitments and imposed schedules, restructuring of former traditions of leadership, and engaging with government agencies in bureaucratic processes. Internalizing authority in caribou management means that community members and leaders must decipher new information, interact with a host of players, engage in lobbying, and become involved in conflicts which are at times turbulent and controversial, as well as divisive to community. In some cases, the costs of power sharing are perceived to violate customary and traditional institutions regarding human-human, and human- caribou relations and in turn, undermine the well-being of the caribou resource and the relationships of those who depend on it.Science, Faculty ofResources, Environment and Sustainability (IRES), Institute forGraduat

Polymer nanomaterials for use as adjuvant surgical tools

Materials employed in the treatment of conditions encountered in surgical and clinical practice frequently face barriers in translation to application. Shortcomings can be generalized through their reduced mechanical stability, difficulty in handling, and inability to conform or adhere to complex tissue surfaces. To overcome an amalgam of challenges, research has sought the utilization of polymer-derived nanomaterials deposited in various fashions and formulations to improve the application and outcomes of surgical and clinical interventions. Clinically prevalent applications include topical wound dressings, tissue adhesives, surgical sealants, hemostats, and adhesion barriers, all of which have displayed the potential to act as superior alternatives to current materials used in surgical procedures. In this review, emphasis will be placed not only on applications, but also on various design strategies employed in fabrication. This review is designed to provide a broad and thought-provoking understanding of nanomaterials as adjuvant tools for the assisted treatment of pathologies prevalent in surgery.https://doi.org/10.1002/wnan.188