Unifying Sparsest Cut, Cluster Deletion, and Modularity Clustering Objectives with Correlation Clustering

Graph clustering, or community detection, is the task of identifying groups of closely related objects in a large network. In this paper we introduce a new community-detection framework called LambdaCC that is based on a specially weighted version of correlation clustering. A key component in our methodology is a clustering resolution parameter, $\lambda$, which implicitly controls the size and structure of clusters formed by our framework. We show that, by increasing this parameter, our objective effectively interpolates between two different strategies in graph clustering: finding a sparse cut and forming dense subgraphs. Our methodology unifies and generalizes a number of other important clustering quality functions including modularity, sparsest cut, and cluster deletion, and places them all within the context of an optimization problem that has been well studied from the perspective of approximation algorithms. Our approach is particularly relevant in the regime of finding dense clusters, as it leads to a 2-approximation for the cluster deletion problem. We use our approach to cluster several graphs, including large collaboration networks and social networks

Quantitative real-time RT-PCR determining extracellular matrix protein expression in osteogenesis imperfecta murine (oim) thoracic aortas [abstract]

Abstract only availableFaculty Mentor: Dr. Charlotte Phillips, Biochemistry and Child HealthPrimary components of the thoracic aorta critical for tissue integrity are collagen and elastin. Collagen, a rod-like protein contributes to aortic strength and stiffness, while elastin, a highly extensible protein contributes to aortic compliance. Type I collagen, the predominate collagen in aortic tissue, is normally a heterotrimeric molecule composed of two proalpha 1(I) chains and one proalpha 2(I) chain. The osteogenesis imperfecta murine (oim) model is an exceptional system to study type I collagen's affect on aortic integrity because it is a functional null for the proalpha 2(I) collagen gene, synthesizing only homotrimeric type I collagen molecules composed of three proalpha 1(I) chains. Our biomechanical studies of oim mice demonstrate that the absence of proalpha 2(I) collagen chains significantly reduces thoracic aortic breaking strength and stiffness. Histological analysis suggested reduced collagen staining in oim/oim and heterozygote aortas. To further investigate the mechanism of reduced collagen staining, HPLC analysis was done to determine total collagen and crosslinking content. Results demonstrated a significant reduction of collagen content per tissue content and an increase of collagen crosslinks in oim/oim and heterozygote aortas compared to wildtype. The reduced collagen content and increased collagen crosslinks of oim/oim and heterozygote aortas prompted us to examine the pre-translational amounts of aortic extracellular matrix protein mRNAs. We determined the COL1A1, COL1A2, COL3A1, ELASTIN, LYSYL OXIDASE, and TUBULIN mRNA levels in thoracic aortas of oim/oim, heterozygote, and wildtype mice at 3, 8, and 18 months of age using quantitative real-time RT-PCR.Life Sciences Undergraduate Research Opportunity Progra

An American Word for War

Jesse is in his early twenties and stuck in Salinas, California. He works at Lenscrafters, making glasses, making decent money and he is comfortable. The novel opens when Jesse’s high school friend, Ben, is visiting from Los Angeles, where he is a screenwriter. The two go to a party for another old acquaintance, Ian, who has just returned from a tour in Iraq. Their encounter with Ian sets the rest of the novel in motion. They are exposed to something big in the world (the machinery of a war that up to that point had been nothing more than words in magazines and pictures in newspapers). The two, who feel unaccomplished, decide that they want to do big things--important things. They decide to combat crime in Salinas, to become vigilantes, like Marvel Comics\u27 The Punisher. They decide to do this despite the fact that neither of them can think of a time that he has seen or met a real criminal. Jesse’s paternal grandparents are from Spain, and their story is told from a limited third-person perspective. This part of the novel is about the experiences of Jesse’s grandparents during the Spanish Civil War, about being Nationalists behind Republican lines, and about being on the wrong side of a war. Parallels are drawn between Franco’s war in Spain and the American war in Iraq. Ultimately, this novel is a coming-of-age story that explores themes of alienation, disenfranchisement, helplessness, and perspective

Engineering the Climate: Geoengineering as a Challenge to International Governance

The challenge of global climate change has attracted recommendations for remediation from a number of professions, including engineering. The possibilities suggested for “geoengineering” the climate generally fall into one of two categories: (1) removing gaseous carbon dioxide from the air and storing it in long-term repositories (“carbon dioxide removal”); and (2) limiting or reducing the intensity of incoming electromagnetic waves from the sun (“solar radiation management”). Specific and often controversial proposals include the aerial dispersion of aerosols, launching reflective gratings into orbit around the Earth, and seeding the oceans with iron filings. These proposals share the following characteristics: (1) they can be undertaken within the territorial jurisdiction of a single state or in areas beyond national jurisdiction; (2) they are likely to, and are intended to, have extrajurisdictional—indeed, global— effects; and (3) they are largely unregulated at the international level. This Essay examines the existing international governance structures to address geoengineering and concludes that they are inadequate to the task. After reviewing those modest international measures that have been adopted to regulate climate geoengineering proposals, the Essay makes recommendations for structural adaptations in international governance to address the problem of climate change