Dylan Walker

Assessing the Vulnerability of Eco-Environmental Health to Climate Change

International Journal of Environmental Research and Public Health, 2010

There is an urgent need to assess the vulnerability of eco-environmental health to climate change... more There is an urgent need to assess the vulnerability of eco-environmental health to climate change. This paper aims to provide an overview of current research, to identify knowledge gaps, and to propose future research needs in this challenging area. Evidence shows that climate change is affecting and will, in the future, have more (mostly adverse) impacts on ecosystems. Ecosystem degradation, particularly the decline of the life support systems, will undoubtedly affect human health and wellbeing. Therefore, it is important to develop a framework to assess the vulnerability of eco-environmental health to climate OPEN ACCESS J.; Sauerimuttu, T.; Tong, S.

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Identifying Social Influence in Networks Using Randomized Experiments

IEEE Expert / IEEE Intelligent Systems, 2011

... 91 Published by the IEEE Computer Society CYBER-PHYSICAL-SOCIAL SYSTEMS Editor: Daniel Zeng, ... more

Identifying Peer Influence in Massive Online Social Networks: A Platform for Randomized Experimentation on Facebook

Identifying peer to peer influence in social networks is a difficult and fundamental problem in n... more Identifying peer to peer influence in social networks is a difficult and fundamental problem in numerous disciplines including network theory, marketing, epidemiology and diffusion research. It is widely believed that the cleanest way to examine the magnitude of peer effects and the social, structural and personal circumstances under which influence is more or less pronounced is to observe large scale, real world randomized trials of person to person communications intended to influence particular economic decisions. In this research we explore this approach to the identification of peer effects using random experiments in a massive online social network.

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Creating Social Contagion Through Viral Product Design: A Randomized Trial of Peer Influence in Networks

... Sinan Aral acknowledges generous financial support from Microsoft, the National Science Found... more

CiteRank: A Google-inspired ranking algorithm for citation networks

Due to their rapid growth, many information networks have become untenable to navigate without so... more Due to their rapid growth, many information networks have become untenable to navigate without some sort of ranking scheme. One solution to the problem of ranking exists in the form of Google's PageRank algorithm. In this work, we extend PageRank ideas to another example of an information network, namely, citation networks. Unlike hyperlinks, citations cannot be updated after the point of publication. Because of this, citation networks exhibit strong aging characteristics [1],[2] that make direct application of the PageRank algorithm unfavorable. To account for this, we modify the PageRank algorithm to a new ranking method, CiteRank. The advantages and performance of CiteRank over the conventional method of ranking citation networks are assessed. We optimize parameters of our algorithm to achieve the best correlation with actual citation accrual for two different citation networks. Despite the variation between the two citation networks considered, we find universal behavior in the correlation between rank and citation accrual.

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Fluctuations in Mass-Action Equilibrium of Protein Binding Networks

Physical Review Letters, 2008

We consider two types of fluctuations in the mass-action equilibrium in protein binding networks.... more We consider two types of fluctuations in the mass-action equilibrium in protein binding networks. The first type is driven by relatively slow changes in total concentrations (copy numbers) of interacting proteins. The second type, to which we refer to as spontaneous, is caused by quickly decaying thermodynamic deviations away from the equilibrium of the system. As such they are amenable to methods of equilibrium statistical mechanics used in our study. We investigate the effects of network connectivity on these fluctuations and compare them to their upper and lower bounds. The collective effects are shown to sometimes lead to large power-law distributed amplification of spontaneous fluctuations as compared to the expectation for isolated dimers. As a consequence of this, the strength of both types of fluctuations is positively correlated with the overall network connectivity of proteins forming the complex. On the other hand, the relative amplitude of fluctuations is negatively correlated with the abundance of the complex. Our general findings are illustrated using a real network of protein-protein interactions in bakers yeast with experimentally determined protein concentrations.

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Ranking Scientific Publications Using a Simple Model of Network Traffic

Computing Research Repository, 2006

To account for strong aging characteristics of citation networks, we modify Google's PageRank alg... more To account for strong aging characteristics of citation networks, we modify Google's PageRank algorithm by initially distributing random surfers exponentially with age, in favor of more recent publications. The output of this algorithm, which we call CiteRank, is interpreted as approximate traffic to individual publications in a simple model of how researchers find new information. We develop an analytical understanding of traffic flow in terms of an RPA-like model and optimize parameters of our algorithm to achieve the best performance. The results are compared for two rather different citation networks: all American Physical Society publications and the set of highenergy physics theory (hep-th) preprints. Despite major differences between these two networks, we find that their optimal parameters for the CiteRank algorithm are remarkably similar.

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Ranking scientific publications using a model of network traffic

Journal of Statistical Mechanics-theory and Experiment, 2007

To account for strong aging characteristics of citation networks, we modify Google's PageRank alg... more To account for strong aging characteristics of citation networks, we modify Google's PageRank algorithm by initially distributing random surfers exponentially with age, in favor of more recent publications. The output of this algorithm, which we call CiteRank, is interpreted as approximate traffic to individual publications in a simple model of how researchers find new information. We develop an analytical understanding of traffic flow in terms of an RPA-like model and optimize parameters of our algorithm to achieve the best performance. The results are compared for two rather different citation networks: all American Physical Society publications and the set of highenergy physics theory (hep-th) preprints. Despite major differences between these two networks, we find that their optimal parameters for the CiteRank algorithm are remarkably similar.

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Distribution, encounter rates, and habitat characteristics of toothed cetaceans in the Bay of Biscay and adjacent waters from platform-of-opportunity data

Ices Journal of Marine Science, 2007

Data on the distribution and habitat utilization of oceanic marine mammals are difficult to colle... more Data on the distribution and habitat utilization of oceanic marine mammals are difficult to collect and yet such information is beneficial for many conservation and management purposes. Data collected during ferry-based cetacean surveys in the English Channel and Bay of Biscay between 1998 and 2002 were analysed to investigate the distribution, encounter rate, and habitat characteristics of toothed cetaceans there. In all, 17 873 nautical miles were surveyed, and 1008 encounters of 13 identified species, including delphinids, ziphiids, harbour porpoise, and sperm whale, were recorded. The common dolphin was the commonest species, followed in decreasing occurrence by striped and bottlenose dolphins, pilot whale, harbour porpoise, Cuvier's beaked whale, and sperm whales. The distribution of harbour porpoises was restricted to the shallow waters of the western English Channel. Common and bottlenose dolphins were distributed mainly over the continental shelf, although there were some encounters along the shelf edge and in the open ocean. Striped dolphins and pilot whales were sighted in oceanic waters in the central and southern Bay of Biscay. Cuvier's beaked whales and sperm whales were recorded in the deep oceanic waters of the southern Bay of Biscay. Bathymetry clearly plays a significant role in the distribution and habitat partitioning of toothed cetaceans in the region.

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Diversity, distribution and occurrence of toothed cetaceans in the Bay of Biscay and western English Channel (1998- 2002

Data on diversity, distribution and occurrence of pelagic cetaceans are generally difficult to co... more Data on diversity, distribution and occurrence of pelagic cetaceans are generally difficult to collect. Such information is beneficial for most management and conservation purposes. Data collected during ferry-based surveys in the western English Channel and Bay of Biscay between 1998 and 2002 were analysed to investigate the occurrence, diversity and distribution of toothed cetaceans in these waters. More than 17,800 nautical miles were surveyed and 1,008 encounters of mono-specific groups (20,481 individuals) were recorded. Thirteen species, including delphinids (Delphinus delphis, Stenella coeruleoalba, Tursiops truncatus, Globicephala melas, Grampus griseus, Orcinus orca, Pseudorca crassidens), ziphiids (Ziphius cavirostris, Hyperoodon ampullatus, Mesoplodon bidens, Mesoplodon mirus), the harbour porpoise (Phocoena phocoena) and the sperm whale (Physeter macrocephalus). The common dolphin was the most frequently encountered species, followed in decreasing occurrence by striped and bottlenose dolphins, long-finned pilot whale, harbour porpoise, Cuvier's beaked whale and sperm whale. This study underlines an exceptional toothed cetacean diversity and this may be attributable to the presence of a wide range of potential habitats in the Bay of Biscay. In addition, the Bay of Biscay is probably an interface for both cold temperate species (such as the harbour porpoise, the long-finned pilot whale and the northern bottlenose whale) and warm temperate species (striped dolphin and Cuvier's beaked whale). As many interactions between fisheries and small cetaceans are known to occur in the Bay of Biscay and western English Channel, these data provide preliminary evidence on the importance of this area for toothed cetaceans.

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