427 research outputs found
Organizing to Respond to External Research Opportunities: Dimensions of Concern for University Collective Action
Public Values Leadership
Instead of private gain or corporate profits, what if we set public values as the goal of leadership?Leadership means many things and takes many forms. But most studies of the topic give little attention to why people lead or to where they are leading us. In Public Values Leadership, Barry Bozeman and Michael M. Crow explore leadership that serves public valuesāthat is to say, values that are focused on the collective good and fundamental rights rather than profit, organizational benefit, or personal gain. While nearly everyone agrees on core public values, there is less agreement on how to obtain them, especially during this era of increased social and political fragmentation. How does public values leadership differ from other types of organizational leadership, and what distinctive skills does it require? Drawing on their extensive experience as higher education leaders, Bozeman and Crow wrestle with the question of how to best attain universally agreed-upon public values like freedom, opportunity, health, and security. They present conversations and interviews with ten well-known leadersāpeople who have achieved public values objectives and who are willing to discuss their leadership styles in detail. They also offer a series of in-depth case studies of public values leadership and accomplishment. Public values leadership can only succeed if it includes a commitment to pragmatism, a deep skepticism about government versus market stereotypes, and a genuine belief in the fundamental importance of partnerships and alliances. Arguing for a "mutable leadership," they suggest that different people are leaders at different times and that ideas about natural leaders or all-purpose leaders are off the mark. Motivating readers, including students of public policy administration and practitioners in public and nonprofit organizations, to think systematically about their own values and how these can be translated into effective leadership, Public Values Leadership is highly personal and persuasive
Power Transmission Control using Distributed Max-Flow
Existing maximum flow algorithms use one processor for all calculations or one processor per vertex in a graph to calculate the maximum possible flow through a graph\u27s vertices. This is not suitable for practical implementation. We extend the max-flow work of Goldberg and Tarjan to a distributed algorithm to calculate maximum flow where the number of processors is less than the number of vertices in a graph. Our algorithm is applied to maximizing electrical flow within a power network where the power grid is modeled as a graph. Error detection measures are included to detect problems in a simulated power network. We show that our algorithm is successful in executing quickly enough to prevent catastrophic power outages
Metastability and anomalous fixation in evolutionary games on scale-free networks
We study the influence of complex graphs on the metastability and fixation
properties of a set of evolutionary processes. In the framework of evolutionary
game theory, where the fitness and selection are frequency-dependent and vary
with the population composition, we analyze the dynamics of snowdrift games
(characterized by a metastable coexistence state) on scale-free networks. Using
an effective diffusion theory in the weak selection limit, we demonstrate how
the scale-free structure affects the system's metastable state and leads to
anomalous fixation. In particular, we analytically and numerically show that
the probability and mean time of fixation are characterized by stretched
exponential behaviors with exponents depending on the network's degree
distribution.Comment: 5 pages, 4 figures, to appear in Physical Review Letter
Adaptive evolution of molecular phenotypes
Molecular phenotypes link genomic information with organismic functions,
fitness, and evolution. Quantitative traits are complex phenotypes that depend
on multiple genomic loci. In this paper, we study the adaptive evolution of a
quantitative trait under time-dependent selection, which arises from
environmental changes or through fitness interactions with other co-evolving
phenotypes. We analyze a model of trait evolution under mutations and genetic
drift in a single-peak fitness seascape. The fitness peak performs a
constrained random walk in the trait amplitude, which determines the
time-dependent trait optimum in a given population. We derive analytical
expressions for the distribution of the time-dependent trait divergence between
populations and of the trait diversity within populations. Based on this
solution, we develop a method to infer adaptive evolution of quantitative
traits. Specifically, we show that the ratio of the average trait divergence
and the diversity is a universal function of evolutionary time, which predicts
the stabilizing strength and the driving rate of the fitness seascape. From an
information-theoretic point of view, this function measures the
macro-evolutionary entropy in a population ensemble, which determines the
predictability of the evolutionary process. Our solution also quantifies two
key characteristics of adapting populations: the cumulative fitness flux, which
measures the total amount of adaptation, and the adaptive load, which is the
fitness cost due to a population's lag behind the fitness peak.Comment: Figures are not optimally displayed in Firefo
Corrigendum: Collective search by ants in microgravity
The problem of collective search is a tradeoff between searching thoroughly and covering as much area as possible. This tradeoff depends on the density of searchers. Solutions to the problem of collective search are currently of much interest in robotics and in the study of distributed algorithms, for example to design ways that without central control robots can use local information to perform search and rescue operations. Ant colonies operate without central control. Because they can perceive only local, mostly chemical and tactile cues, they must search collectively to find resources and to monitor the colony's environment. Examining how ants in diverse environments solve the problem of collective search can elucidate how evolution has led to diverse forms of collective behavior. An experiment on the International Space Station in January 2014 examined how ants (Tetramorium caespitum) perform collective search in microgravity. In the ISS experiment, the ants explored a small arena in which a barrier was lowered to increase the area and thus lower ant density. In microgravity, relative to ground controls, ants explored the area less thoroughly and took more convoluted paths. It appears that the difficulty of holding on to the surface interfered with the antsā ability to search collectively. Ants frequently lost contact with the surface, but showed a remarkable ability to regain contact with the surface
Schwinger Boson Formulation and Solution of the Crow-Kimura and Eigen Models of Quasispecies Theory
We express the Crow-Kimura and Eigen models of quasispecies theory in a
functional integral representation. We formulate the spin coherent state
functional integrals using the Schwinger Boson method. In this formulation, we
are able to deduce the long-time behavior of these models for arbitrary
replication and degradation functions.
We discuss the phase transitions that occur in these models as a function of
mutation rate. We derive for these models the leading order corrections to the
infinite genome length limit.Comment: 37 pages; 4 figures; to appear in J. Stat. Phy
Developing patient-friendly genetic and genomic test reports: formats to promote patient engagement and understanding
10.1186/s13073-014-0058-6Genome Medicine675
Finite population size effects in quasispecies models with single-peak fitness landscape
We consider finite population size effects for Crow-Kimura and Eigen quasispecies
models with single-peak fitness landscape. We formulate accurately the iteration procedure for
the finite population models, then derive the Hamilton-Jacobi equation (HJE) to describe the
dynamic of the probability distribution. The steady-state solution of HJE gives the variance of
the mean fitness. Our results are useful for understanding the population sizes of viruses in which
the infinite population models can give reliable results for biological evolution problems
Large Fluctuations and Fixation in Evolutionary Games
We study large fluctuations in evolutionary games belonging to the
coordination and anti-coordination classes. The dynamics of these games,
modeling cooperation dilemmas, is characterized by a coexistence fixed point
separating two absorbing states. We are particularly interested in the problem
of fixation that refers to the possibility that a few mutants take over the
entire population. Here, the fixation phenomenon is induced by large
fluctuations and is investigated by a semi-classical WKB
(Wentzel-Kramers-Brillouin) theory generalized to treat stochastic systems
possessing multiple absorbing states. Importantly, this method allows us to
analyze the combined influence of selection and random fluctuations on the
evolutionary dynamics \textit{beyond} the weak selection limit often considered
in previous works. We accurately compute, including pre-exponential factors,
the probability distribution function in the long-lived coexistence state and
the mean fixation time necessary for a few mutants to take over the entire
population in anti-coordination games, and also the fixation probability in the
coordination class. Our analytical results compare excellently with extensive
numerical simulations. Furthermore, we demonstrate that our treatment is
superior to the Fokker-Planck approximation when the selection intensity is
finite.Comment: 17 pages, 10 figures, to appear in JSTA
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