Network Kriging

Network service providers and customers are often concerned with aggregate performance measures that span multiple network paths. Unfortunately, forming such network-wide measures can be difficult, due to the issues of scale involved. In particular, the number of paths grows too rapidly with the number of endpoints to make exhaustive measurement practical. As a result, it is of interest to explore the feasibility of methods that dramatically reduce the number of paths measured in such situations while maintaining acceptable accuracy. We cast the problem as one of statistical prediction--in the spirit of the so-called `kriging' problem in spatial statistics--and show that end-to-end network properties may be accurately predicted in many cases using a surprisingly small set of carefully chosen paths. More precisely, we formulate a general framework for the prediction problem, propose a class of linear predictors for standard quantities of interest (e.g., averages, totals, differences) and show that linear algebraic methods of subset selection may be used to effectively choose which paths to measure. We characterize the performance of the resulting methods, both analytically and numerically. The success of our methods derives from the low effective rank of routing matrices as encountered in practice, which appears to be a new observation in its own right with potentially broad implications on network measurement generally.Comment: 16 pages, 9 figures, single-space

Metaphysical accounts of modality: A comparative evaluation of Lewisian and neo-Aristotelian modal metaphysics

In this essay I comparatively evaluate two realist metaphysical accounts of modality: David Lewis’ (1986) genuine modal realism (GMR), and neo-Aristotelian modal realism (AMR) as put forth by Alexander Pruss (2011). GMR offers a reductive analysis of modal claims of possibility and necessity in terms of claims quantifying over concrete worlds and counterparts, and is in this way committed the existence of a plurality of concrete worlds other than the actual world; AMR, on the other hand, offers an analysis of modal claims in terms of claims about the causal powers of existing objects in the actual world, and identifies these powers and powerful properties as the truthmakers for modal truths of possibility and necessity. I consider two objections to GMR; firstly, that it leads to ethical paradoxes, and secondly, that the counterparts it offers as truthmakers for modal claims are fundamentally irrelevant to the de re modal properties of objects. I argue that AMR bears a prima facie advantage over GMR by reason of its avoidance of those two objections, before evaluating two objections faced by AMR itself, namely, that its analysis is not genuinely explanatory, and secondly, that the ontology of powers fails to account for the full range of metaphysical possibility. I argue that AMR has the resources to avoid these objections, that AMR on balance is more attractive, and that therefore AMR is worthy of serious consideration by advocates of GMR. References LEWIS, DAVID K. (1986). On the plurality of worlds. New York, NY, USA: B. Blackwell. PRUSS, ALEXANDER R. (2011). Actuality, Possibility, and Worlds. London: Continuum

Finite element modelling of the expanson of small tubular parts by internal pressure

A stent is a device that is used to support arterial walls to alleviate the blockage of arteries by plaque. The slotted tube stent is one of the most common stent designs being widely used in many patients today. The amount of stent implantations is growing each year and for this it is becoming increasingly important in interventional cardiology. One of the reasons is that the use of stents has proved more effective in the therapy of coronary stenosis. However, it is evidenced that the success of the stent implantation is limited by re-stenosis, which is discussed almost entirely in terms of medical and biological reasons. This work is concerned with investigating the deformation mechanism with variable conditions during slotted tube expansion processes using numerical simulation. The simulations were run and analysed using commercial finite element software. A nonlinear explicit solution method was used in each case. The processes chosen for simulation were: slotted tube expansion without balloon catheter, slotted tube expansion with balloon catheter, scaling the stent size, stent production defect and slotted tube expansion with the presence of artery and plaque. A number of process parameters were varied for balloon catheter (i.e. balloon length, thickness and friction factor) and the subsequent effects on the process were identified. Some trial experimental tests were carried out to verify the finite element results from the computer simulations. From the results obtained it was concluded that higher rate of pressure increase results in higher stresses in stent for similar levels of expansion. Deployment of higher magnitude pressure might increase the expansion in radial direction but it does not necessarily increase the uniformity of the slotted tube. Appropriate balloon length has to be chosen to obtain a uniform expansion. Friction could reduce the foreshortening of the stent. When scaling down the stent, displacement deceases proportionally for similar deployment pressure and stent geometry. It was found from the simulations that the tubular stent is not very sensitive to imperfections. Altering sent strut configuration and number has practical effects on the clinical use of vascular stents, as the magnitude of expansion will change. The deformation characteristic of the slotted tube during deployment is affected by the presence of artery and plaque

Guest Artist Recital, David Tayloe, tenor

David Tayloe, tenor Emily Yap Chua, pian

Legal Consciousness Reconsidered

Legal consciousness is a vibrant research field attracting growing numbers of scholars worldwide. Yet differing assumptions about aims and methods have generated vigorous debate, typically resulting from a failure to recognize that three different clusters of scholars—identified here as the Identity, Hegemony, and Mobilization schools—are pursuing different goals and deploying the concept of legal consciousness in different ways. Scholarship associated with these three schools demonstrates that legal consciousness is actually a flexible paradigm with multiple applications rather than a monolithic approach.Furthermore, a new generation of scholars has energized the field in recent years, focusing on marginalized peoples and non-Western settings. Through their findings, and as a result of broader trends across the social sciences, relational legal consciousness has taken on greater importance. Legal consciousness research should be imagined on a continuum ranging from individualistic conceptualizations of thought and action to interactive, co-constitutive approaches

Making design pedagogical content knowledge visible within design reviews

Design pedagogical content knowledge (PCK) is the content-specific specialized teacher knowledge that connects the how (pedagogical knowledge) and what (content knowledge) of teaching design. In this study, we make visible the design PCK in three student design reviews: choreography, undergraduate industrial design, and mechanical engineering. We use cognitive apprenticeship and teaching-as-improvisation frameworks to characterize PK, and design judgment, design task strategies, and process management strategies to characterize CK. We identify and describe four patterns of design PCK: scaffolded articulation, driving for meaning and guidance, breaking the 4th wall to create a teaching moment, and “suggest don’t tell”. Theoretical implications of this work include translating theories of social learning to the context of design reviews and showing design-specific teaching approaches design coaches use to support and instruct students as learners of design. We summarize practical implications for design students, new design coaches, and more experienced design coaches