448 research outputs found
Weaving the fabric of science: Dynamic network models of science's unfolding structure
AbstractScience is a complex system. Building on Latour's actor network theory, we model published science as a dynamic hypergraph and explore how this fabric provides a substrate for future scientific discovery. Using millions of abstracts from MEDLINE, we show that the network distance between biomedical things (i.e., people, methods, diseases, chemicals) is surprisingly small. We then show how science moves from questions answered in one year to problems investigated in the next through a weighted random walk model. Our analysis reveals intriguing modal dispositions in the way biomedical science evolves: methods play a bridging role and things of one type connect through things of another. This has the methodological implication that adding more node types to network models of science and other creative domains will likely lead to a superlinear increase in prediction and understanding
Link and subgraph likelihoods in random undirected networks with fixed and partially fixed degree sequence
The simplest null models for networks, used to distinguish significant
features of a particular network from {\it a priori} expected features, are
random ensembles with the degree sequence fixed by the specific network of
interest. These "fixed degree sequence" (FDS) ensembles are, however, famously
resistant to analytic attack. In this paper we introduce ensembles with
partially-fixed degree sequences (PFDS) and compare analytic results obtained
for them with Monte Carlo results for the FDS ensemble. These results include
link likelihoods, subgraph likelihoods, and degree correlations. We find that
local structural features in the FDS ensemble can be reasonably well estimated
by simultaneously fixing only the degrees of few nodes, in addition to the
total number of nodes and links. As test cases we use a food web, two protein
interaction networks (\textit{E. coli, S. cerevisiae}), the internet on the
autonomous system (AS) level, and the World Wide Web. Fixing just the degrees
of two nodes gives the mean neighbor degree as a function of node degree,
, in agreement with results explicitly obtained from rewiring. For
power law degree distributions, we derive the disassortativity analytically. In
the PFDS ensemble the partition function can be expanded diagrammatically. We
obtain an explicit expression for the link likelihood to lowest order, which
reduces in the limit of large, sparse undirected networks with links and
with to the simple formula . In a
similar limit, the probability for three nodes to be linked into a triangle
reduces to the factorized expression .Comment: 17 pages, includes 11 figures; first revision: shortened to 14 pages
(7 figures), added discussion of subgraph counts, deleted discussion of
directed network
A quantitative workflow for modeling diversification in material culture.
Questions about the evolution of material culture are widespread in the humanities and social sciences. Statistical modeling of long-term changes in material culture is less common due to a lack of appropriate frameworks. Our goal is to close this gap and provide robust statistical methods for examining changes in the diversity of material culture. We provide an open-source and quantitative workflow for estimating rates of origination, extinction, and preservation, as well as identifying key shift points in the diversification histories of material culture. We demonstrate our approach using two distinct kinds of data: age ranges for the production of American car models, and radiocarbon dates associated with archaeological cultures of the European Neolithic. Our approach improves on existing frameworks by disentangling the relative contributions of origination and extinction to diversification. Our method also permits rigorous statistical testing of competing hypotheses to explain changes in diversity. Finally, we stress the value of a flexible approach that can be applied to data in various forms; this flexibility allows scholars to explore commonalities between forms of material culture and ask questions about the general properties of cultural change
Not by transmission alone : the role of invention in cultural evolution
We are grateful to the Templeton World Charity Foundation, Inc. for funding this work and to the Diverse Intelligences research community for valuable conversations around these themes. S. Nöbel acknowledges IAST funding from the French National Research Agency (ANR) under the Investissements dâAvenir program, grant ANR-17-EUR-0010 and support by the Laboratoires dâExcellence TULIP (ANR-10-LABX-41). EA and MS acknowledge support from the US Army Research Office (W911NFâ17â1â0017 to EA).Innovationâthe combination of invention and social learningâcan empower species to invade new niches via cultural adaptation. Social learning has typically been regarded as the fundamental driver for the emergence of traditions and thus culture. Consequently, invention has been relatively understudied outside the human lineageâdespite being the source of new traditions. This neglect leaves basic questions unanswered: what factors promote the creation of new ideas and practices? What affects their spread or loss? We critically review the existing literature, focusing on four levels of investigation: traits (what sorts of behaviours are easiest to invent?), individuals (what factors make some individuals more likely to be inventors?), ecological contexts (what aspects of the environment make invention or transmission more likely?), and populations (what features of relationships and societies promote the rise and spread of new inventions?). We aim to inspire new research by highlighting theoretical and empirical gaps in the study of innovation, focusing primarily on inventions in non-humans. Understanding the role of invention and innovation in the history of life requires a well-developed theoretical framework (which embraces cognitive processes) and a taxonomically broad, cross-species dataset that explicitly investigates inventions and their transmission. We outline such an agenda here. This article is part of the theme issue âFoundations of cultural evolutionâ.Publisher PDFPeer reviewe
Scaling Behavior of Cyclical Surface Growth
The scaling behavior of cyclical surface growth (e.g. deposition/desorption),
with the number of cycles n, is investigated. The roughness of surfaces grown
by two linear primary processes follows a scaling behavior with asymptotic
exponents inherited from the dominant process while the effective amplitudes
are determined by both. Relevant non-linear effects in the primary processes
may remain so or be rendered irrelevant. Numerical simulations for several
pairs of generic primary processes confirm these conclusions. Experimental
results for the surface roughness during cyclical electrodeposition/dissolution
of silver show a power-law dependence on n, consistent with the scaling
description.Comment: 2 figures adde
Roughness Scaling in Cyclical Surface Growth
The scaling behavior of cyclical growth (e.g. cycles of alternating
deposition and desorption primary processes) is investigated theoretically and
probed experimentally. The scaling approach to kinetic roughening is
generalized to cyclical processes by substituting the time by the number of
cycles . The roughness is predicted to grow as where is
the cyclical growth exponent. The roughness saturates to a value which scales
with the system size as , where is the cyclical
roughness exponent. The relations between the cyclical exponents and the
corresponding exponents of the primary processes are studied. Exact relations
are found for cycles composed of primary linear processes. An approximate
renormalization group approach is introduced to analyze non-linear effects in
the primary processes. The analytical results are backed by extensive numerical
simulations of different pairs of primary processes, both linear and
non-linear. Experimentally, silver surfaces are grown by a cyclical process
composed of electrodeposition followed by 50% electrodissolution. The roughness
is found to increase as a power-law of , consistent with the scaling
behavior anticipated theoretically. Potential applications of cyclical scaling
include accelerated testing of rechargeable batteries, and improved
chemotherapeutic treatment of cancerous tumors
Dosing Regimen of Enrofloxacin Impacts Intestinal Pharmacokinetics and the Fecal Microbiota in Steers
Objective: The intestinal concentrations of antimicrobial drugs that select for resistance in fecal bacteria of cattle are poorly understood. Our objective was to associate active drug concentrations in the intestine of steers with changes in the resistance profile and composition of the fecal microbiome.Methods: Steers were administered either a single dose (12.5 mg/kg) or 3 multiple doses (5 mg/kg) of enrofloxacin subcutaneously every 24 h. Enrofloxacin and ciprofloxacin concentrations in intestinal fluid were measured over 96 h, and the abundance and MIC of E. coli in culture and the composition of the fecal microbiota by 16S rRNA gene sequencing were assessed over 192 h after initial treatment.Results: Active drug concentrations in the ileum and colon exceeded plasma and interstitial fluid concentrations, but were largely eliminated by 48 h after the last dose. The concentration of E. coli in the feces significantly decreased during peak drug concentrations, but returned to baseline by 96 h in both groups. The median MIC of E. coli isolates increased for 24 h in the single dose group, and for 48 h in the multiple dose group. The median MIC was higher in the multiple dose group when compared to the single dose group starting 12 h after the initial dose. The diversity of the fecal microbiota did not change in either treatment group, and taxa-specific changes were primarily seen in phyla commonly associated with the rumen.Conclusions: Both dosing regimens of enrofloxacin achieve high concentrations in the intestinal lumen, and the rapid elimination mitigates long-term impacts on fecal E. coli resistance and the microbiota
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