318 research outputs found
Associative -categories
We define novel fully combinatorial models of higher categories. Our
definitions are based on a connection of higher categories to "directed
spaces". Directed spaces are locally modelled on manifold diagrams, which are
stratifications of the n-cube such that strata are transversal to the flag
foliation of the n-cube. The first part of this thesis develops a combinatorial
model for manifold diagrams called singular n-cubes. In the second part we
apply this model to build our notions of higher categories.
Singular n-cubes are "directed triangulations" of space together with a
decomposition into a collection of subspaces or strata. Singular n-cubes can be
naturally organised into two categories. The first, whose morphisms are bundles
themselves, is used for the inductive definition of singular (n+1)-cubes. The
second, whose morphisms are "open" base changes, admits an (epi,mono)
factorisation system. Monomorphisms will be called embeddings of cubes.
Epimorphisms will be called collapses and describe how triangulations can be
coarsened. Each cube has a unique coarsest triangulation called its normal
form. The existence of normal forms makes the equality relation of
(combinatorially represented) manifold diagrams decidable.
As the main application of the resulting combinatorial framework for manifold
diagrams, we give algebraic definitions of various notions of higher
categories. Namely, we define associative n-categories, presented associative
n-categories and presented associative n-groupoids. All three notions will have
strict units and associators; the only weak coherences are homotopies, but we
develop a mechanism for recovering the usual coherence data of weak
n-categories, such as associators and pentagonators and their higher analogues.
This will motivate the conjecture that the theory of associative higher
categories is equivalent to its fully weak counterpart.Comment: 499 page
Robust monomer-distribution biosignatures in evolving digital biota
Because organisms synthesize component molecules at rates that reflect those
molecules' adaptive utility, we expect a population of biota to leave a
distinctive chemical signature on their environment that is anomalous given the
local (abiotic) chemistry. We observe the same effect in the distribution of
computer instructions used by an evolving population of digital organisms, and
characterize the robustness of the evolved signature with respect to a number
of different changes in the system's physics. The observed instruction
abundance anomaly has features that are consistent over a large number of
evolutionary trials and alterations in system parameters, which makes it a
candidate for a non-Earth-centric life-diagnosticComment: 22 pages, 4 figures, 1 table. Supplementary Material available from
C
Monomer abundance distribution patterns as a universal biosignature: Examples from terrestrial and digital life
Organisms leave a distinctive chemical signature in their environment because
they synthesize those molecules that maximize their fitness. As a result, the
relative concentrations of related chemical monomers in life-bearing
environmental samples reflect, in part, those compounds' adaptive utility. In
contrast, rates of molecular synthesis in a lifeless environment are dictated
by reaction kinetics and thermodynamics, so concentrations of related monomers
in abiotic samples tend to exhibit specific patterns dominated by small, easily
formed, low-formation-energy molecules. We contend that this distinction can
serve as a universal biosignature: the measurement of chemical concentration
ratios that belie formation kinetics or equilibrium thermodynamics indicates
the likely presence of life. We explore the features of this biosignature as
observed in amino acids and carboxylic acids, using published data from
numerous studies of terrestrial sediments, abiotic (spark, UV, and high-energy
proton) synthesis experments, and meteorite bodies. We then compare these data
to the results of experimental studies of an evolving digital life system. We
observe the robust and repeatable evolution of an analogous biosignature in a
digital lifeform, suggesting that evolutionary selection necessarily constrains
organism composition and that the monomer abundance biosignature phenomenon is
universal to evolved biosystems.Comment: 35 pages, 5 figures. Supplementary material (two movie files)
available upon request. To appear in J. Mol. Evo
A Flexible Approach Towards Self-Adapting Process Recommendations
A company's ability to flexibly adapt to changing business requirements is one key factor to remain competitive. The required flexibility in people driven processes is usually achieved through ad-hoc workflows which are naturally highly unstructured. Effective guidance in ad-hoc workflows therefore requires a simultaneous consideration of multiple goals: support of individual work habits, classification of unstructured messages, exploration of crowd process knowledge, and automatic adaptation to changes. This paper presents a flexible approach towards the mapping of unstructured messages onto processes as well as patterns for self-adjusting and context-sensitive process recommendations based on the analysis of user behavior, crowd processes, and continuous application of process detection. Specifically, we classify users as eagles (i.e., specialists) or flock. The approach is evaluated in the context of the European research project Commius
Balanced Knowledge Distribution among Software Development Teams -- Observations from Open-Source and Closed-Source Software Development
In software development teams, developer turnover is among the primary
reasons for project failures as it leads to a great void of knowledge and
strain for the newcomers. Unfortunately, no established methods exist to
measure how knowledge is distributed among development teams. Knowing how this
knowledge evolves and is owned by key developers in a project helps managers
reduce risks caused by turnover. To this end, this paper introduces a novel,
realistic representation of domain knowledge distribution: the ConceptRealm. To
construct the ConceptRealm, we employ a latent Dirichlet allocation model to
represent textual features obtained from 300k issues and 1.3M comments from 518
open-source projects. We analyze whether the newly emerged issues and
developers share similar concepts or how aligned the developers' concepts are
with the team over time. We also investigate the impact of leaving members on
the frequency of concepts. Finally, we evaluate the soundness of our approach
to closed-source software, thus allowing the validation of the results from a
practical standpoint. We find out that the ConceptRealm can represent the
high-level domain knowledge within a team and can be utilized to predict the
alignment of developers with issues. We also observe that projects exhibit many
keepers independent of project maturity and that abruptly leaving keepers harm
the team's concept familiarity.Comment: 33 pages, 17 figures, journal submissio
Are landscape structures insurmountable barriers for foraging bees? A mark-recapture study with two solitary pollen specialist species
To investigate whether landscape structures act as insurmountable barriers for foraging bees, we conducted mark-recapture studies with two pollen-specialist solitary species. Foraging options of the bees were confined to host plant stands across different landscape structures. Differences in altitude of more than 130 m were overcome and forests covering a distance of up to 480 m were crossed by Chelostoma florisomne. A broad river and a motorway with intense traffic did not represent insurmountable barriers for Hoplitis adunca. For C. florisomne, total foraging distances of up to 650 m were measured, but foraging females were recorded predominantly on host plant patches available in relatively close vicinity to their nesting site. While landscape structures might impede foraging in endangered bees, the investigated landscape structures clearly did not act as insurmountable physical barriers for the two common solitary bee species tested in our stud
Comparative study of gp130 cytokine effects on corticotroph AtT-20 cells - Redundancy or specificity of neuroimmunoendocrine modulators?
Objective: This comparative in vitro study examined the effects of all known gp130 cytokines on murine corticotroph AtT-20 cell function. Methods: Cytokines were tested at equimolar concentrations from 0.078 to 10 nM. Tyrosine phosphorylation of the signal transducer and activator of transcription ( STAT) 3 and STAT1, the STAT-dependent suppressor of cytokine signaling (SOCS)-3 promoter activity, SOCS-3 gene expression, STAT-dependent POMC promoter activity and adrenocorticotropic hormone ( ACTH) secretion were determined. Results: Leukemia inhibitory factor (LIF), human oncostatin M (OSM) and cardiotrophin (CT)-1 (LIFR/gp130 ligands), as well as ciliary neurotrophic factor ( CNTF) and novel neurotrophin1/B-cell stimulating factor-3 (CNTFRalpha/LIFR/gp130 ligands) are potent stimuli of corticotroph cells in vitro. In comparison, interleukin (IL)-6 (IL-6R/gp130 ligand) and IL-11 (IL-11R/gp130 ligand) exhibited only modest direct effects on corticotrophs, while murine OSM (OSMR/gp130 ligand) showed no effect. Conclusion: (i) CNTFR complex ligands are potent stimuli of corticotroph function, comparable to LIFR complex ligands; (ii) IL-6 and IL-11 are relatively weak direct stimuli of corticotroph function; (iii) differential effects of human and murine OSM suggest that LIFR/gp130 (OSMR type I) but not OSMR/gp130 (OSMR type II) are involved in corticotroph signaling. (iv) CT-1 has the hitherto unknown ability to stimulate corticotroph function, and (v) despite redundant immuno-neuroendocrine effects of different gp130 cytokines, corticotroph cells are preferably activated through the LIFR and CNTFR complexes. Copyright (C) 2004 S. Karger AG, Basel
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