2,683 research outputs found
Kinematics of a Spacetime with an Infinite Cosmological Constant
A solution of the sourceless Einstein's equation with an infinite value for
the cosmological constant \Lambda is discussed by using Inonu-Wigner
contractions of the de Sitter groups and spaces. When \Lambda --> infinity,
spacetime becomes a four-dimensional cone, dual to Minkowski space by a
spacetime inversion. This inversion relates the four-cone vertex to the
infinity of Minkowski space, and the four-cone infinity to the Minkowski
light-cone. The non-relativistic limit c --> infinity is further considered,
the kinematical group in this case being a modified Galilei group in which the
space and time translations are replaced by the non-relativistic limits of the
corresponding proper conformal transformations. This group presents the same
abstract Lie algebra as the Galilei group and can be named the conformal
Galilei group. The results may be of interest to the early Universe Cosmology.Comment: RevTex, 7 pages, no figures. Presentation changes, including a new
Title. Version to appear in Found. Phys. Let
Mass Generation from Lie Algebra Extensions
Applied to the electroweak interactions, the theory of Lie algebra extensions
suggests a mechanism by which the boson masses are generated without resource
to spontaneous symmetry breaking. It starts from a gauge theory without any
additional scalar field. All the couplings predicted by the Weinberg-Salam
theory are present, and a few others which are nevertheless consistent within
the model.Comment: 11 pages; revtex; title and PACS have been changed; comments included
in the manuscrip
Plant growth promoting potential of rhizobacteria isolated from a contaminated area
info:eu-repo/semantics/publishedVersio
Communities of practice as a tool to support the GCIO function
A Community of Practice (CoP) allows practitioners of a clearly defined domain to share knowledge, experience,and best practices. It provides a social context for practitioners,often distributed across multiple organizations,and emerged over the last few decades as a fundamental mechanism for knowledge sharing, management,and generation within organizations. Best practices, innovations,and solutions to shared problems first emerge within CoPs. These are, and must be perceived as, an investmentin organizations’ future and competitiveness.Establishing a CoP is a straightforward process, the most challenging factor being the recruitment of members to attain critical mass. The challenge is to maintain the CoP active, with members contributing with high quality, innovative content. Increasing a CoP’smedium / long-termsurvival probabilities requires careful planning to avoid incurringinsome well-known pitfalls.This paper proposes and discusses a set of nine guidelines for establishing and maintaining a community of practice within the context of Electronic Governance (EGOV) and Government Chief Information Officers (GCIO). This research was motivated by the initiative of the government of a developing country. Results are based on a review of the relevant literature, together with the detailed analysis of interviews to members or coordinators of large communities of practice. This analysis was further validated against the opinions of public servantsdirectly involved on EGOV-GCIO-related functions during two focus groups meetingsSmartEGOV: Harnessing
EGOV for Smart Governance (Foundations, Methods, Tools)
NORTE-01-0145-FEDER-000037, supported by Norte Portugal
Regional Operational Programme (NORTE 2020), under the
PORTUGAL 2020 Partnership Agreement, through the European
Regional Development Fund (EFDR
NUTRITIVE VALUE, TOTAL PHENOLIC CONTENT AND RADICAL SCAVENGING ACTIVITY BEFORE AND AFTER DIGESTION OF THE LEAVES OF SIX GRAPEVINE (VITIS VINIFERA L.) CULTIVARS.
A L\'evy flight for electrons in graphene: superdiffusive-to-diffusive transport transition
In this work we propose an electronic L\'evy flight device, analogous to a
recent optical realization. To that end, we investigate the transmission of
electrons in graphene nanoribbons in the presence of circular electrostatic
clusters, whose diameter follow a power-law distribution. We analyze the effect
of the electrostatic clusters on the electronic transport regime of the
nanoribbons, in terms of its diffusion behavior. Our numerical calculations
show that the presence of circular electrostatic clusters induces a transition
from L\'evy (superdiffusive) to diffusive transport as the energy increases.
Furthermore, we argue that in our electronic L\'evy flight device,
superdiffusive transport is an exclusive feature of the low-energy quantum
regime, while diffusive transport is a feature of the semiclassical regime.
Therefore, we attribute the observed transition to the chiral symmetry
breaking, once the energy moves away from the Dirac point of graphene.Comment: Accepted for publication as a Regular Article in Physical Review
- …