Modeling Time's Arrow

Quantum gravity, the initial low entropy state of the Universe, and the problem of time are interlocking puzzles. In this article, we address the origin of the arrow of time from a cosmological perspective motivated by a novel approach to quantum gravitation. Our proposal is based on a quantum counterpart of the equivalence principle, a general covariance of the dynamical phase space. We discuss how the nonlinear dynamics of such a system provides a natural description for cosmological evolution in the early Universe. We also underscore connections between the proposed non-perturbative quantum gravity model and fundamental questions in non-equilibrium statistical physics.Comment: 18 page

Influential Publications in Ecological Economics: A Citation Analysis

We assessed the degree of influence of selected papers and books in ecological economics using citation analysis. We looked at both the internal influence of publications on the field of ecological economics and the external influence of those same publications on the broader academic community. We used four lists of papers and books for the analysis: (1) 92 papers nominated by the Ecological Economics (EE) Editorial Board; (2) 71 papers that were published in EE and that received 15 or more citations in all journals included in the Institute for Scientific Information (ISI) Citation Index; (3) 57 papers that had been cited in EE 15 or more times; and (4) 77 monographs and edited books that had been cited in EE 15 or more times. For each publication we counted the total number of ISI citations as well as the total number of citations in EE. We calculated the average number of citations/yr to each paper since its publication in both the ISI database and in EE, along with the percentage of the total ISI citations that were in EE. Ranking the degree of influence of the publications can be done in several ways, including using the number of ISI citations, the number of EE citations or both. We discuss both the internal and external influence of publications and show how these influences might be considered jointly. We display and analyze the results in several ways. By plotting the ISI citations against the EE citations we can identify those papers that are mainly influential in EE with some broader influence, those that are mainly influential in the broader literature but have also had influence on EE, and other patterns of influence. There are both overlaps and interesting lacunae among the four lists that give us a better picture of the real influence of publications in ecological economics versus perceptions of those publications' importance. By plotting the number of citations vs. date of publication, we can identify those publications that are projected to be most influential. Plots of the time series of citations over the 1990-2003 period show a generally increasing trend (contrary to what one would expect for an "average" paper) for the top papers. We suggest that this pattern of increasing citations (and thus influence) over time is one hallmark of a "foundational" paper.

Block matrix formulations for evolving networks

Many types of pairwise interaction take the form of a fixed set of nodes with edges that appear and disappear over time. In the case of discrete-time evolution, the resulting evolving network may be represented by a time-ordered sequence of adjacency matrices. We consider here the issue of representing the system as a single, higher dimensional block matrix, built from the individual time-slices. We focus on the task of computing network centrality measures. From a modeling perspective, we show that there is a suitable block formulation that allows us to recover dynamic centrality measures respecting time's arrow. From a computational perspective, we show that the new block formulation leads to the design of more effective numerical algorithms.Comment: 18 pages, 2 figure

Rangeland Resources Monitoring: Concepts and Practical Applications

How does one person manage and monitor a half million acres of rangelands towards a sustainable future? Through a journey that begins with the understanding of sustainability, I explore the monitoring concept, two -of its applications, and summarize with an emphasis on the art and science of management. Sustainability is a concept that confuses many managers because it is so complex. However, if one considers adaptability as the complement to sustainability, and realizes that an adaptable organism is a sustainable organism, then a manager can relate because the emphasis shifts from that of stability for the future to that of uncertainty for today. The need for monitoring becomes self-evident as it is used to observe the environment and warn people against the presence of variables thought to be harmful. Interestingly, professionals who monitor rangelands have not adopted statistical power analysis to aid in change detection. Moreover, range professionals do not have many tools to monitor a half million acres in a statistically and biologically meaningful way. I explored the role of power analysis in evaluating range trend data. In addition, I tested a low aerial photography method for monitoring vegetation cover across rangeland landscapes. The investigations revealed that when monitoring is used as a feedback loop, the information acquired would likely facilitate adaptability and therefore sustainability of resources and people. However, most monitoring programs offer limited information of low statistical power at an inappropriate scale. Therefore, monitoring information should be used with ancillary scientific information to direct decisions, not drive them. We will continue to rely upon both the art and science of management to keep us following a path towards sustainability

Multi-scale modelling for simulating marine activities under heterogeneous environmental constraints

International audienceThis paper describes the concepts behind the implementation of a multi-agents model aimed to explore how marine activities respond to various environmental constraints. The methodology takes advantage on a responsive agent-based structure, and treats the environment as a set of forcing variables (biophysical, socio-economic and regulatory data). A first experiment in the Iroise Sea area shows a great potential in assessing the intensity and the variability of marine activities at different scales level. The whole methodology is presented in this paper in order to completely analyze the contributions and limitations concerning the SIMARIS prototype

The Grip of History and the Scope for Novelty: Some Results and Open Questions on Path Dependence in Economic Processes

-Path dependence, irreversibility, increasing returns, learning, lock-in.