7 research outputs found
Survivability in layered networks
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2011.Cataloged from PDF version of thesis.Includes bibliographical references (p. 195-204).In layered networks, a single failure at the lower (physical) layer may cause multiple failures at the upper (logical) layer. As a result, traditional schemes that protect against single failures may not be effective in layered networks. This thesis studies the problem of maximizing network survivability in the layered setting, with a focus on optimizing the embedding of the logical network onto the physical network. In the first part of the thesis, we start with an investigation of the fundamental properties of layered networks, and show that basic network connectivity structures, such as cuts, paths and spanning trees, exhibit fundamentally different characteristics from their single-layer counterparts. This leads to our development of a new crosslayer survivability metric that properly quantifies the resilience of the layered network against physical failures. Using this new metric, we design algorithms to embed the logical network onto the physical network based on multi-commodity flows, to maximize the cross-layer survivability. In the second part of the thesis, we extend our model to a random failure setting and study the cross-layer reliability of the networks, defined to be the probability that the upper layer network stays connected under the random failure events. We generalize the classical polynomial expression for network reliability to the layered setting. Using Monte-Carlo techniques, we develop efficient algorithms to compute an approximate polynomial expression for reliability, as a function of the link failure probability. The construction of the polynomial eliminates the need to resample when the cross-layer reliability under different link failure probabilities is assessed. Furthermore, the polynomial expression provides important insight into the connection between the link failure probability, the cross-layer reliability and the structure of a layered network. We show that in general the optimal embedding depends on the link failure probability, and characterize the properties of embeddings that maximize the reliability under different failure probability regimes. Based on these results, we propose new iterative approaches to improve the reliability of the layered networks. We demonstrate via extensive simulations that these new approaches result in embeddings with significantly higher reliability than existing algorithms.by Kayi Lee.Ph.D
Doctor of Philosophy
dissertationThis dissertation adds to the literature on campus climate in higher education in the United States, by 1) focusing on international students, especially those from China and Saudi Arabia, and their perceptions of the classroom climate as the racialized Other, in particular, their feelings of being welcomed or not welcomed; and 2) examining their perceptions of, and reactions to, pedagogical practices and peer behaviors that marginalized and/or included them. The mixed-methods study was conducted at three predominantly White institutions in the Intermountain West, utilizing the theoretical framework of campus climate and the White racial frame. Qualitative and quantitative data found the international students to be somewhat ambivalent in their perceptions of the campus climate, reporting that it was both welcoming and unwelcoming. Perceptions of the classroom climate were found to be associated with those of the campus climate, with the role of the professor as essential to their fee
A theory of reference for product design: the semantics of product ideation
The present research focuses on the way designers make sense of things while developing their design concepts. The idea was to investigate whether the use of an appropriate segmentation of the meaningful aspects comprising products could help designers to work more consciously and more effectively in their exploration of ideas for design concepts. To this aim a methodology based on the inclusion of different forms of knowledge to understand design situations (Cross, 2002) and design themes (Margolin, 2005) was developed, with semiotics as its modelling paradigm and cognitive psychology as its experimental counterpart. Such an inclusive methodology allowed: (1) the identification of key issues and notions about concept formation (in general and within design), (2) a quite comprehensive review of the contributions of semiotic and non-semiotic theories to the understanding of meaning in products, (3) the formulation of a theoretical model about the meaningful aspects of products, and (4) the development of an experimental method to test the feasibility of this model. The last three points aforementioned are indeed the contributions of the present research to knowledge.
This dissertation is organised in five chapters. The first chapter introduces the reader to the subject of this research, the relevance of researching about this subject in design and the methodological aspects involved. The second chapter presents the literature review of design concepts and the theoretical positions about the construction of meaning in products. The third chapter outlines the theoretical notions and considerations that are needed to formulate a theory of concept ideation as a preamble to chapter four, in which the theoretical model is developed. This model is mainly inspired by the work of Roman Jakobson, and it suggests the existence of six meaningful dimensions for the ideation of design concepts. The last chapter presents the results and discussion of eight experimental carried out with 20 industrial design students and three studies developed to test the practical feasibility of the theoretical model formulated as part of this research. The conclusions show that the proposed division of meaning for concept ideation into six dimensions is quite feasible