Percolation on fitness-dependent networks with heterogeneous resilience

Copyright @ 2014 American Physical SocietyThe ability to understand the impact of adversarial processes on networks is crucial to various disciplines. The objects of study in this article are fitness-driven networks. Fitness-dependent networks are fully described by a probability distribution of fitness and an attachment kernel. Every node in the network is endowed with a fitness value and the attachment kernel translates the fitness of two nodes into the probability that these two nodes share an edge. This concept is also known as mutual attractiveness. In the present article, fitness does not only serve as a measure of attractiveness, but also as a measure of a node's robustness against failure. The probability that a node fails increases with the number of failures in its direct neighborhood and decreases with higher fitness. Both static and dynamic network models are considered. Analytical results for the percolation threshold and the occupied fraction are derived. One of the results is that the distinction between the dynamic and the static model has a profound impact on the way failures spread over the network. Additionally, we find that the introduction of mutual attractiveness stabilizes the network compared to a pure random attachment. © 2014 American Physical Society

Mutual selection in time-varying networks

Copyright @ 2013 American Physical SocietyTime-varying networks play an important role in the investigation of the stochastic processes that occur on complex networks. The ability to formulate the development of the network topology on the same time scale as the evolution of the random process is important for a variety of applications, including the spreading of diseases. Past contributions have investigated random processes on time-varying networks with a purely random attachment mechanism. The possibility of extending these findings towards a time-varying network that is driven by mutual attractiveness is explored in this paper. Mutual attractiveness models are characterized by a linking function that describes the probability of the existence of an edge, which depends mutually on the attractiveness of the nodes on both ends of that edge. This class of attachment mechanisms has been considered before in the fitness-based complex networks literature but not on time-varying networks. Also, the impact of mutual selection is investigated alongside opinion formation and epidemic outbreaks. We find closed-form solutions for the quantities of interest using a factorizable linking function. The voter model exhibits an unanticipated behavior as the network never reaches consensus in the case of mutual selection but stays forever in its initial macroscopic configuration, which is a further piece of evidence that time-varying networks differ markedly from their static counterpart with respect to random processes that take place on them. We also find that epidemic outbreaks are accelerated by uncorrelated mutual selection compared to previously considered random attachment

The Revival of Climate Change Science in U.S. Courts

Science never has been the obstacle to the recognition of climate change. Since Arhennius did his original calculations in 1896, the scientific world was quite aware of the prospect that industrial-age levels of carbon dioxide pollution would result in increasing global temperatures and acidification of the world’s oceans. The brilliant—and striking—graphical display that we know today as the Keeling Curve started in 1957, and year after year it records the relentless upward march of these atmospheric pollutant loadings. Through the years, necessarily, a vast number of scientific warnings, publications, findings, and predictions would be offered to the public at large, urging action to combat climate change. The pages in this journal devoted to the issue of ocean acidification are but the latest manifestation of this relentless march of science towards more understanding and deeper appreciation of the gravity of these issues. In contrast to the slow (if erratic) march of science, the political response to climate change—particularly in the United States—has been enthusiastically absent. Even the sufferers from this political nullification policy have tipped their hats, conceding an insidious effectiveness of “just say no” tactics. There is an eerie concordance of interest between the corporate takeover of Washington, D.C. by lobbyists and the conspicuous inaction on climate change. This political denial of climate change in Washington, D.C., has endured for close to thirty years

The Revival of Climate Change Science in U.S. Courts

Science never has been the obstacle to the recognition of climate change. Since Arhennius did his original calculations in 1896, the scientific world was quite aware of the prospect that industrial-age levels of carbon dioxide pollution would result in increasing global temperatures and acidification of the world’s oceans. The brilliant—and striking—graphical display that we know today as the Keeling Curve started in 1957, and year after year it records the relentless upward march of these atmospheric pollutant loadings. Through the years, necessarily, a vast number of scientific warnings, publications, findings, and predictions would be offered to the public at large, urging action to combat climate change. The pages in this journal devoted to the issue of ocean acidification are but the latest manifestation of this relentless march of science towards more understanding and deeper appreciation of the gravity of these issues. In contrast to the slow (if erratic) march of science, the political response to climate change—particularly in the United States—has been enthusiastically absent. Even the sufferers from this political nullification policy have tipped their hats, conceding an insidious effectiveness of “just say no” tactics. There is an eerie concordance of interest between the corporate takeover of Washington, D.C. by lobbyists and the conspicuous inaction on climate change. This political denial of climate change in Washington, D.C., has endured for close to thirty years

Laid Off: American Workers and Employers Assess a Volatile Labor Market

This Work Trends survey shows that despite economic growth, worker concern for the economy, their job security, and the threat of terrorism is increasing; workers and employers express fear about outsourcing jobs abroad

An Investigation of the Interest for a Nurse Re-entry Program in Southeastern Ohio

In the United States and throughout the world there is a serious concern in the growing nursing shortage. Many recruitment and retention techniques are currently being used to ease the nursing shortage. One such avenue is a nurse re-entry program. The primary purpose of this study was to determine the interest for a RN re-entry program in southeastern Ohio. The data collected during the investigation used both qualitative and quantitative research techniques. Information was received through two survey questionnaires and two focus groups. The instruments were designed with the purpose of determining how many registered nurses were not working in a hospital setting and the number interested in returning to acute care through a nurse re-entry program. The results showed a significant number of nurses (n=40) interested in returning to nursing. However, the number willing to commit to a nurse re-entry program was much less (n=13). Further research of interest in a re-entry program is suggested after definite re-entry course criteria has been established and a more expanded needs assessment by the local college is accomplished

Network growth model with intrinsic vertex fitness

© 2013 American Physical SocietyWe study a class of network growth models with attachment rules governed by intrinsic node fitness. Both the individual node degree distribution and the degree correlation properties of the network are obtained as functions of the network growth rules. We also find analytical solutions to the inverse, design, problems of matching the growth rules to the required (e.g., power-law) node degree distribution and more generally to the required degree correlation function. We find that the design problems do not always have solutions. Among the specific conditions on the existence of solutions to the design problems is the requirement that the node degree distribution has to be broader than a certain threshold and the fact that factorizability of the correlation functions requires singular distributions of the node fitnesses. More generally, the restrictions on the input distributions and correlations that ensure solvability of the design problems are expressed in terms of the analytical properties of their generating functions

Characteristics of Feedback that Influence Student Confidence and Performance during Mathematical Modeling

This study focuses on characteristics of written feedback that influence students’ performance and confidence in addressing the mathematical complexity embedded in a Model-Eliciting Activity (MEA). MEAs are authentic mathematical modeling problems that facilitate students’ iterative development of solutions in a realistic context. We analyzed 132 first-year engineering students’ confidence levels and mathematical model scores on aMEA(pre and post feedback), along with teaching assistant feedback given to the students. The findings show several examples of affective and cognitive feedback that students reported that they used to revise their models. Students’ performance and confidence in developing mathematical models can be increased when they are in an environment where they iteratively develop models based on effective feedback

Tropical Pacific Decadal Variability and its relation to decadal modulations of ENSO

The decadal-scale variability in the tropical Pacific has been analyzed herein by means of observations and numerical model simulations. The two leading modes of the sea surface temperature (SST) variability in the central western Pacific are a decadal mode with a period of about 10 yr and the ENSO mode with a dominant period of about 4 yr. The SST anomaly pattern of the decadal mode is ENSO like. The decadal mode, however, explains most variance in the western equatorial Pacific and off the equator. A simulation with an ocean general circulation model (OGCM) forced by reanalysis data is used to explore the origin of the decadal mode. It is found that the variability of the shallow subtropical–tropical overturning cells is an important factor in driving the decadal mode. This is supported by results from a multicentury integration with a coupled ocean–atmosphere general circulation model (CGCM) that realistically simulates tropical Pacific decadal variability. Finally, the sensitivity of the shallow subtropical–tropical overturning cells to greenhouse warming is discussed by analyzing the results of a scenario integration with the same CGCM