Scaling laws for the movement of people between locations in a large city

Large scale simulations of the movements of people in a ``virtual'' city and their analyses are used to generate new insights into understanding the dynamic processes that depend on the interactions between people. Models, based on these interactions, can be used in optimizing traffic flow, slowing the spread of infectious diseases or predicting the change in cell phone usage in a disaster. We analyzed cumulative and aggregated data generated from the simulated movements of 1.6 million individuals in a computer (pseudo agent-based) model during a typical day in Portland, Oregon. This city is mapped into a graph with $181,206$ nodes representing physical locations such as buildings. Connecting edges model individual's flow between nodes. Edge weights are constructed from the daily traffic of individuals moving between locations. The number of edges leaving a node (out-degree), the edge weights (out-traffic), and the edge-weights per location (total out-traffic) are fitted well by power law distributions. The power law distributions also fit subgraphs based on work, school, and social/recreational activities. The resulting weighted graph is a ``small world'' and has scaling laws consistent with an underlying hierarchical structure. We also explore the time evolution of the largest connected component and the distribution of the component sizes. We observe a strong linear correlation between the out-degree and total out-traffic distributions and significant levels of clustering. We discuss how these network features can be used to characterize social networks and their relationship to dynamic processes.Comment: 18 pages, 10 figure

Quadratic Forms in Singular Normal Variables

16 pages, 1 article*Quadratic Forms in Singular Normal Variables* (Rodhe, C. A.; Urquhart, N. S.; Searle, S. R.) 16 page

Seasonal Degree-day Statistics for the United States

11 pages, 1 article*Seasonal Degree-day Statistics for the United States* (Thom, H. C. S.) 11 page

Estimating Variance Components of Binomial Frequencies

16 pages, 1 article*Estimating Variance Components of Binomial Frequencies* (Searle, S. R.; Gates, C. E.) 16 page

Self-Modeling Regression with Random Effects Using Penalized Splines

20 pages, 1 article*Self-Modeling Regression with Random Effects Using Penalized Splines* (Altman, Naomi S.; Villarreal, Julio C.) 20 page

On the Modelling of Epidemics

18 pages, 1 article*On the Modelling of Epidemics* (Castillo-Chavez, C.; Cooke, K.; Levin, S. A.) 18 page

Stagewise Discrimination Algorithms for Selecting a Subset of Groups of Discriminant Variables

18 pages, 1 article*Stagewise Discrimination Algorithms for Selecting a Subset of Groups of Discriminant Variables* (Evans, John C.; Robson, Douglas S.; Schwager, Steven J.) 18 page

HCI as a means to prosociality in the economy

HCI research often involves intervening in the economic lives of people, but researchers only rarely give explicit consideration to what actually constitutes prosociality in the economy. Much has been said previously regarding sustainability but this has largely focused on environmental rather than interpersonal relations. This paper provides an analysis of how prosocial HCI has been discussed and continues to be defined as a research field. Based on a corpus of published works, we describe a variety of genres of work relating to prosocial HCI. Key intellectual differences are explored, including the epistemological and ethical positions involved in designing for prosocial outcomes as well as how HCI researchers posit economic decision-making. Finally, emerging issues and opportunities for further debate and collaboration are discussed in turn

On the Homogeneity of Sequential Quota-Samples of Clusters: A Parameter-Free Distribution

6 pages, 1 article*On the Homogeneity of Sequential Quota-Samples of Clusters: A Parameter-Free Distribution* (Wood, C. L.; Robson, D. S.) 6 page

Low power coordination in wireless ad-hoc networks

ABSTRACT Distributed wireless ad-hoc networks @WANs) pose numerous technical Among them, two are widely conthese problems, two are of dominating importance: (i) low energy and Operation and (ii) autonomous localized operation and decision making. Recent studies have shown sidered as crucial: autonomous localized operation and minimization of energy consumption. We address the fundamental problem of how to maximize life-time of the network by using only local information while preserving network connectivity, We start by introducing the Care-Ree Sleep (CS) Theorem that provides provably optimal necessary and nodes are not required for addressing the current network cient conditions for a node to turn off its radio while ensuring and Although there have been a number of efforts to deterthat global connectivity is not affected. The cS theorem is the basis for an efficient localized almine the conditions for a node to enter sleep state using gorithm that decides which node will turn its radio off, and only locally available information while preserving the overfor how long, The effectiveness of the approach is demonall connectivity of the network, only heuristic answers have sleep coordination problem. The sleep coordination problem the algorithm over a wide range of network parameters. is interesting and challenging from several view points: 0 Complexity of the Problem. The nodes that stay Categories and Subject Descriptors awake to preserve the connectivity of the network form a [ C O M P U T E R -C O M M U N I C A T I O N N E T W O R K S ] : connected dominating set on the network graph. Finding Network Protocols; C.4 [ P E R F O R M A N C E OF S Y S - the minimum connected dominating set can be proven to be TEMS]: [Reliability, availability, and serviceability] NP-complete. Therefore, even in cases where we do have the complete graph information about the whole network, finding the optimal solution in polynomial time is unlikely. Furthermore, setting the proper sleep times t o the nodes to maximize the overall network's lifetime, adds a new dimension to the NP-complete minimum connected dominating 0 Scope of the Problem. For a sleep coordination procedure, making a globally sound decision using only local information is a challenging task. Changing the status of even one node can potentially impact any node in the network ill terms Of its CODneCtiVity and energy consumption. 0 Guaranteed Connectivity. There is a need to determine under which conditions, a Particular node can sleep, while still guaranteeing that the network is connected. 0 Protocol Design. The autonomous operation of the nodes in DWANs has several advantages including fault tolerance, fast response to changes, and non-PrePlanned network structure. However, interaction and collaboration between the nodes and existence of shared resources, dictates a need for a protocol that can handle concurrency and synchronization of the autonomous ad-hoc node decisions. The power saving coordination strategy introduced here attempts to address these challenges. we start by introducing the care-nee sleep (CS) theorem that establishes provably optimal necessary and sufficient conditions for a given node to enter sleep state without disconnecting the network. strated using numerous simulations of the performance of been Presented [17, 3~ ' 1. we refer to this Problem as the General Terms Algorithms, Design, Performance Keywords set problem. Wireless ad-hoc network, low-power, coordinatio