7,738 research outputs found
Control of complex networks requires both structure and dynamics
The study of network structure has uncovered signatures of the organization
of complex systems. However, there is also a need to understand how to control
them; for example, identifying strategies to revert a diseased cell to a
healthy state, or a mature cell to a pluripotent state. Two recent
methodologies suggest that the controllability of complex systems can be
predicted solely from the graph of interactions between variables, without
considering their dynamics: structural controllability and minimum dominating
sets. We demonstrate that such structure-only methods fail to characterize
controllability when dynamics are introduced. We study Boolean network
ensembles of network motifs as well as three models of biochemical regulation:
the segment polarity network in Drosophila melanogaster, the cell cycle of
budding yeast Saccharomyces cerevisiae, and the floral organ arrangement in
Arabidopsis thaliana. We demonstrate that structure-only methods both
undershoot and overshoot the number and which sets of critical variables best
control the dynamics of these models, highlighting the importance of the actual
system dynamics in determining control. Our analysis further shows that the
logic of automata transition functions, namely how canalizing they are, plays
an important role in the extent to which structure predicts dynamics.Comment: 15 pages, 6 figure
The Real Anatomy of Complex Linear Superfields
Recent work on classicication of off-shell representations of N-extended
worldline supersymmetry without central charges has uncovered an unexpectedly
vast number--trillions of even just (chromo)topology types--of so called
adinkraic supermultiplets. Herein, we show by explicit analysis that a
long-known but rarely used representation, the complex linear supermultiplet,
is not adinkraic, cannot be decomposed locally, but may be reduced by means of
a Wess-Zumino type gauge. This then indicates that the already unexpectedly
vast number of adinkraic off-shell supersymmetry representations is but the
proverbial tip of the iceberg.Comment: 21 pages, 4 figure
Analyses of the dynamic docking test system for advanced mission docking system test programs
Results are given of analytical studies performed in support of the design, implementation, checkout and use of NASA's dynamic docking test system (DDTS). Included are analyses of simulator components, a list of detailed operational test procedures, a summary of simulator performance, and an analysis and comparison of docking dynamics and loads obtained by test and analysis
Economic Benefits of American Lobster Fishery Management Regulations
A simulation model is used to compare measures for future management identified in the American lobster fishery management plan; specifically, increases in the minimum legal size and a modest reduction in aggregate fishing mortality are evaluated. The analysis differs from previous work in that the distributional aspects of the alternative management regulations are quantified. The results indicate that (1) both an increased minimum size and a reduction in fishing mortality are economically justified in the sense that net benefits are positive; (2) increasing the minimum size without an adjunct regulation to prohibit entry will cause present fishermen to suffer an initial short-term reduction in revenues for which there will be no long-term gain; (3) because increased minimum size can be justified on the basis of consumer benefits alone, arguments favoring its increase to prevent recruitment failure are moot as far as a test of national economic efficiency is concerned; and (4) a program of effort reduction which reduces by 20% the fraction of available lobsters captured annually is projected to generate SI of producer benefits for every pound of lobster landed. Reducing the annual harvest fraction by 20% results in a level of fishery benefits greater than increasing the minimum size to 89 mm (3^-in.), and increases the coincidence of short-run costs and long-term benefits among those impacted by fishery management.Environmental Economics and Policy, Resource /Energy Economics and Policy,
Modularity and the spread of perturbations in complex dynamical systems
We propose a method to decompose dynamical systems based on the idea that
modules constrain the spread of perturbations. We find partitions of system
variables that maximize 'perturbation modularity', defined as the
autocovariance of coarse-grained perturbed trajectories. The measure
effectively separates the fast intramodular from the slow intermodular dynamics
of perturbation spreading (in this respect, it is a generalization of the
'Markov stability' method of network community detection). Our approach
captures variation of modular organization across different system states, time
scales, and in response to different kinds of perturbations: aspects of
modularity which are all relevant to real-world dynamical systems. It offers a
principled alternative to detecting communities in networks of statistical
dependencies between system variables (e.g., 'relevance networks' or
'functional networks'). Using coupled logistic maps, we demonstrate that the
method uncovers hierarchical modular organization planted in a system's
coupling matrix. Additionally, in homogeneously-coupled map lattices, it
identifies the presence of self-organized modularity that depends on the
initial state, dynamical parameters, and type of perturbations. Our approach
offers a powerful tool for exploring the modular organization of complex
dynamical systems
Nanocrystal seeding: A low temperature route to polycrystalline Si films
A novel method is presented for growth of polycrystalline silicon films on amorphous substrates at temperatures of 540–575 °C. Grain nucleation and grain growth are performed in two steps, using Si nanocrystals as nuclei ("seeds"). The nanocrystal seeds are produced by excimer laser photolysis of disilane in a room temperature flow cell. Film (grain) growth occurs epitaxially on the seeds in a separate thermal chemical vapor deposition (CVD) step, with growth rates 10–100 times higher than similar CVD growth rates on crystal Si. Grain size and CVD growth rates are dependent on seed coverage, for seed coverage <0.2 monolayers
Comparison of Some Exact and Perturbative Results for a Supersymmetric SU() Gauge Theory
We consider vectorial, asymptotically free supersymmetric
SU() gauge theories with copies of massless chiral super fields in
various representations and study how perturbative predictions for the lower
boundary of the infrared conformal phase, as a function of , compare with
exact results. We make use of two-loop and three-loop calculations of the beta
function and anomalous dimension of the quadratic chiral super field operator
product for this purpose. The specific chiral superfield contents that we
consider are copies of (i) , (ii) , (iii) ,
and (iv) , where , , , and denote,
respectively, the fundamental, adjoint, and symmetric and antisymmetric rank-2
tensor representations. We find that perturbative results slightly overestimate
the value of relative to the respective exact results for these
representations, i.e., slightly underestimate the interval in for which
the theory has infrared conformal behavior. Our results provide a measure of
how closely perturbative calculations reproduce exact results for these
theories.Comment: 16 pages, 3 figure
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Marriage, Registration and Dissolution by Same-Sex Couples in the U.S.
This study analyzes data from states that have extended legal recognition to same-sex couples. Analyses show that same-sex couples want and use these new legal statuses. Furthermore, they react more enthusiastically when marriage is possible. More than 40% of same-sex couples have formed legal unions in states where such recognition is available. Same-sex couples prefer marriage over civil unions or domestic partnerships. In the first year that marriage was offered in Massachusetts, 37% of same-sex couples there married. In states that offered civil unions, only 12% of same-sex couples took advantage of this status in the first year and only 10% did so in states with domestic partnership registrie
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