8,202 research outputs found
Ad-Nilpotent Ideals of a Parabolic Subalgebra
We extend the results of Cellini-Papi on the characterizations of nilpotent
and abelian ideals of a Borel subalgebra to parabolic subalgebras of a simple
Lie algebra. These characterizations are given in terms of elements of the
affine Weyl group and faces of alcoves. In the case of a parabolic subalgebra
of a classical Lie algebra, we give formulas for the number of these ideals.Comment: Proof of 4.1 corrected and generalized to all types. Further
references and remarks adde
Degree Variance and Emotional Strategies Catalyze Cooperation in Dynamic Signed Networks
We study the problem of the emergence of cooperation in dynamic signed
networks where agent strategies coevolve with relational signs and network
topology. Running simulations based on an agent-based model, we compare results
obtained in a regular lattice initialization with those obtained on a
comparable random network initialization. We show that the increased degree
heterogeneity at the outset enlarges the parametric conditions in which
cooperation survives in the long run. Furthermore, we show how the presence of
sign-dependent emotional strategies catalyze the evolution of cooperation with
both network topology initializations.Comment: 16 Pages, Proceeding of the European Conference on Modelling and
Simumatio
Signed Networks, Triadic Interactions and the Evolution of Cooperation
We outline a model to study the evolution of cooperation in a population of
agents playing the prisoner's dilemma in signed networks. We highlight that if
only dyadic interactions are taken into account, cooperation never evolves.
However, when triadic considerations are introduced, a window of opportunity
for emergence of cooperation as a stable behaviour emerges.Comment: In Proceedings Wivace 2013, arXiv:1309.712
The Miracle of Peer Review and Development in Science: An Agent-Based Model
It is not easy to rationalize how peer review, as the current grassroots of
science, can work based on voluntary contributions of reviewers. There is no
rationale to write impartial and thorough evaluations. Consequently, there is
no risk in submitting low-quality work by authors. As a result, scientists face
a social dilemma: if everyone acts according to his or her own self-interest,
low scientific quality is produced. Still, in practice, reviewers as well as
authors invest high effort in reviews and submissions.
We examine how the increased relevance of public good benefits (journal
impact factor), the editorial policy of handling incoming reviews, and the
acceptance decisions that take into account reputational information can help
the evolution of high-quality contributions from authors. High effort from the
side of reviewers is problematic even if authors cooperate: reviewers are still
best off by producing low-quality reviews, which does not hinder scientific
development, just adds random noise and unnecessary costs to it. We show with
agent-based simulations that tacit agreements between authors that are based on
reciprocity might decrease these costs, but does not result in superior
scientific quality. Our study underlines why certain self-emerged current
practices, such as the increased importance of journal metrics, the
reputation-based selection of reviewers, and the reputation bias in acceptance
work efficiently for scientific development. Our results find no answers,
however, how the system of peer review with impartial and thorough evaluations
could be sustainable jointly with rapid scientific development.Comment: Submitted to Scientometric
Tribochemistry of graphene on iron and its possible role in lubrication of steel
Recent tribological experiments revealed that graphene is able to lubricate
macroscale steel-on-steel sliding contacts very effectively both in dry and
humid conditions. This effect has been attributed to a mechanical action of
graphene related to its load-carrying capacity. Here we provide further insight
into the functionality of graphene as lubricant by analysing its tribochemical
action. By means of first principles calculations we show that graphene binds
strongly to native iron surfaces highly reducing their surface energy. Thanks
to a passivating effect, the metal surfaces coated by graphene become almost
inert and present very low adhesion and shear strength when mated in a sliding
contact. We generalize the result by establishing a connection between the
tribological and the electronic properties of interfaces, which is relevant to
understand the fundamental nature of frictional forces.Comment: 19 pages, 6 figure
A fundamental mechanism for carbon-film lubricity identified by means of ab initio molecular dynamics
Different hypotheses have been proposed to explain the mechanism for the
extremely low friction coefficient of carbon coatings and its undesired
dependence on air humidity. A decisive atomistic insight is still lacking
because of the difficulties in monitoring what actually happens at the buried
sliding interface. Here we perform large-scale ab initio molecular dynamics
simulations of both undoped and silicon-doped carbon films sliding in the
presence of water. We observe the tribologically-induced surface hydroxylation
and subsequent formation of a thin film of water molecules bound to the
OH-terminated surface by hydrogen bonds. The comparative analysis of
silicon-incorporating and clean surfaces, suggests that this two-step process
can be the key phenomenon to provide high slipperiness to the carbon coatings.
The water layer is, in fact, expected to shelter the carbon surface from direct
solid-on-solid contact and make any counter surface slide extremely easily on
it. The present insight into the wettability of carbon-based films can be
useful for designing new coatings for biomedical and energy-saving applications
with environmental adaptability.Comment: 22 pages, 4 figures, 1 tabl
- …