Dion Harmon

Attractors and Democratic Dynamics

Cellular transcription networks are conceptualized as distributed control systems that regulate gene expression.

Dynamic Optimality—Almost

We present an O(lg lg n)-competitive online binary search tree, improving upon the best previous (trivial) competitive ratio of O(lg n). This is the first major progress on Sleator and Tarjans dynamic optimality conjecture of 1985 that O(1)-competitive binary search trees exist.

Anticipating Economic Market Crises Using Measures of Collective Panic

Predicting panic is of critical importance in many areas of human and animal behavior, notably in the context of economics. The recent financial crisis is a case in point. Panic may be due to a specific external threat or self-generated nervousness. Here we show that the recent economic crisis and earlier large single-day panics were preceded by extended periods of high levels of market mimicry—direct evidence of uncertainty and nervousness, and of the comparatively weak influence of external news. High levels of mimicry can be a quite general indicator of the potential for self-organized crises.

Computationally tractable pairwise complexity profile

Quantifying the complexity of systems consisting of many interacting parts has been an important challenge in the field of complex systems in both abstract and applied contexts. One approach, the complexity profile, is a measure of the information to describe a system as a function of the scale at which it is observed. We present a new formulation of the complexity profile, which expands its possible application to high-dimensional real-world and mathematically defined systems. The new method is constructed from the pairwise dependencies between components of the system. The pairwise approach may serve as both a formulation in its own right and a computationally feasible approximation to the original complexity profile. We compare it to the original complexity profile by giving cases where they are equivalent, proving properties common to both methods, and demonstrating where they differ. Both formulations satisfy linear superposition for unrelated systems and conservation of total degrees of freedom (sum rule). The new pairwise formulation is also a monotonically nonincreasing function of scale. Furthermore, we show that the new formulation defines a class of related complexity profile functions for a given system, demonstrating the generality of the formalism.

Good Fences: The Importance of Setting Boundaries for Peaceful Coexistence

We consider the conditions of peace and violence among ethnic groups, testing a theory designed to predict the locations of violence and interventions that can promote peace. Characterizing the models success in predicting peace requires examples where peace prevails despite diversity. Switzerland is recognized as a country of peace, stability and prosperity. This is surprising because of its linguistic and religious diversity that in other parts of the world lead to conflict and violence. Here we analyze how peaceful stability is maintained. Our analysis shows that peace does not depend on integrated coexistence, but rather on well defined topographical and political boundaries separating groups, allowing for partial autonomy within a single country. In Switzerland, mountains and lakes are an important part of the boundaries between sharply defined linguistic areas. Political canton and circle (sub-canton) boundaries often separate religious groups. Where such boundaries do not appear to be sufficient, we find that specific aspects of the population distribution guarantee either sufficient separation or sufficient mixing to inhibit intergroup violence according to the quantitative theory of conflict. In exactly one region, a porous mountain range does not adequately separate linguistic groups and that region has experienced significant violent conflict, leading to the recent creation of the canton of Jura. Our analysis supports the hypothesis that violence between groups can be inhibited by physical and political boundaries. A similar analysis of the area of the former Yugoslavia shows that during widespread ethnic violence existing political boundaries did not coincide with the boundaries of distinct groups, but peace prevailed in specific areas where they did coincide. The success of peace in Switzerland may serve as a model to resolve conflict in other ethnically diverse countries and regions of the world.

Dynamic optimality - almost [competitive online binary search tree]

We present an O(lg lg n)-competitive online binary search tree, improving upon the best previous (trivial) competitive ratio of O(lg n). This is the first major progress on Sleator and Tarjans dynamic optimality conjecture of 1985 that O(1)-competitive binary search trees exist.

Vulnerability analysis of high dimensional complex systems

Complex systems experience dramatic changes in behavior and can undergo transitions from functional to dysfunctional states. An unstable system is prone to dysfunctional collective cascades that result from self-reinforcing behaviors within the system. Because many human and technological civilian and military systems today are complex systems, understanding their susceptibility to collective failure is a critical problem. Understanding vulnerability in complex systems requires an approach that characterizes the coupled behaviors at multiple scales of cascading failures. We used neuromorphic methods, which are modeled on the pattern-recognition circuitry of the brain and can find patterns in high-dimensional data at multiple scales, to develop a procedure for identifying the vulnerabilities of complex systems. This procedure was tested on microdynamic Internet2 network data. The result was a generic pipeline for identifying extreme events in high dimensional datasets.

Advanced Mathematical Science of Ethnic Violence

Advancing peace and conflict studies into a quantitative science requires advanced mathematical methods and concepts. Lim, Metzler and Bar-Yam (2007, “LMB”) provide a wavelet based method for predicting the location of violence in a country based upon the hypothesis that well mixed or well separated groups do not engage in violence, but intermediate sized groups without clear boundaries between them do. Wiedmann and Toft (2010, “WT”) consider the remarkable quantitative success of LMB and question whether the methods used correctly evaluate their effectiveness. Here we provide some additional tests to address questions raised by WT. We confirm the quantitative success of LMB. Moreover, despite claiming to criticize LMB’s policy implications that suggest the separation of groups as a method of promoting peace, WT affirm that homogenous populations are not susceptible to violence. WT’s statement itself could be used to motivate a policy of separation. In contrast, LMB provide scientific precision that can guide policy makers in a choice of policy options in terms of geographical distributions and political boundaries, or the alternative of promoting the mixing of ethnic populations. Here we point to additional scientific support for the key policy implications.

The Geography of Ethnic Violence

We consider the conditions of peace and violence among ethnic groups, testing a theory designed to predict the locations of violence and interventions that can promote peace. Violence arises at boundaries between regions that are not sufficiently well defined. We model cultural differentiation as a separation of groups whose members prefer similar neighbors with a characteristic group size at which violence occurs. Application of this model to the area of the former Yugoslavia and to India accurately predicts the locations of reported conflict. Characterizing the model’s success in predicting peace requires examples where peace prevails despite diversity. Switzerland is recognized as a country of peace, stability, and prosperity. This is surprising because of its linguistic and religious diversity that in other parts of the world lead to conflict and violence. Here we analyze how peaceful stability is maintained. Our analysis shows that peace does not depend on integrated coexistence, but rather on well-defined topographical and political boundaries separating linguistic and religious groups, respectively. In exactly one region, a porous mountain range does not adequately separate linguistic groups and violent conflict has led to the recent creation of the canton of Jura. Our analysis supports the hypothesis that violence between groups can be inhibited by both physical and political boundaries. A similar analysis of the area of the former Yugoslavia shows that during widespread ethnic violence existing political boundaries did not coincide with the boundaries of distinct groups, but peace prevailed in specific areas where they did coincide.

Opportunities in Delivery of Preventive Services in Retail Settings

Improving the US healthcare system requires not only providing care to the uninsured but also addressing a set of linked organizational and motivational issues, including enhancing the role of wellness and prevention. It is widely acknowledged that system organization is key to healthcare improvement [1]. Previous studies [2, 3] have pointed to separating wellness and prevention services from acute care as a central component of healthcare transformation. Even while chronic and preventable diseases have become the dominant cause of loss of life, incentives and perceptions limit the delivery of services that could prevent them [2]. A complex systems analysis implies that the optimal organizational structure depends critically on the scale of repetition and complexity of tasks to be performed. Applied to health care, the separation of acute care from selected preventive services should enable improved matching of organizational structure to function [3–5].