8,641 research outputs found
The conceptual structure of evolutionary biology: A framework from phenotypic plasticity
In this review, I approach the role of phenotypic plasticity as a key aspect of the conceptual framework of evolutionary biology. The concept of phenotypic plasticity is related to other relevant concepts of contemporary research in evolutionary biology, such as assimilation, genetic accommodation and canalization, evolutionary robustness, evolvability, evolutionary capacitance and niche construction. Although not always adaptive, phenotypic plasticity can promote the integration of these concepts to represent some of the dynamics of evolution, which can be visualized through the use of a conceptual map. Although the use of conceptual maps is common in areas of knowledge such as psychology and education, their application in evolutionary biology can lead to a better understanding of the processes and conceptual interactions of the complex dynamics of evolution. The conceptual map I present here includes environmental variability and variation, phenotypic plasticity and natural selection as key concepts in evolutionary biology. The evolution of phenotypic plasticity is important to ecology at all levels of organization, from morphological, physiological and behavioral adaptations that influence the distribution and abundance of populations to the structuring of assemblages and communities and the flow of energy through trophic levels. Consequently, phenotypic plasticity is important for maintaining ecological processes and interactions that influence the complexity of biological diversity. In addition, because it is a typical occurrence and manifests itself through environmental variation in conditions and resources, plasticity must be taken into account in the development of management and conservation strategies at local and global levels
Fine Tuning in Quintessence Models with Exponential Potentials
We explore regions of parameter space in a simple exponential model of the
form that are allowed by observational
constraints. We find that the level of fine tuning in these models is not
different from more sophisticated models of dark energy. We study a transient
regime where the parameter has to be less than and the
fixed point has not been reached. All values of the parameter
that lead to this transient regime are permitted. We also point out
that this model can accelerate the universe today even for , leading to a halt of the present acceleration of the universe in the
future thus avoiding the horizon problem. We conclude that this model can not
be discarded by current observations.Comment: 15 pages, 8 figure
Dipole-induced anomalous top quark couplings at the LHC
We consider direct bounds on the coefficients of higher dimensional top quark
dipole operators from their contributions to anomalous top couplings that
affect some related processes at the LHC. Several observables are studied. In
particular, we incorporate for the first time in this type of analysis the
recently measured associated production, which is currently the
only measured direct observable sensitive to the dipole operator involving the
hypercharge field. We perform a Bayesian analysis to derive the
confidence level (CL) intervals on these coefficients.Comment: 9 pages, 1 figure, 1 table; references added. Version accepted for
publication in PR
Flux-vector model of spin noise in superconducting circuits: Electron versus nuclear spins and role of phase transition
Superconducting Quantum Interference Devices (SQUIDs) and other
superconducting circuits are limited by intrinsic flux noise with spectral
density with whose origin is believed to be due to
spin impurities. Here we present a theory of flux noise that takes into account
the vectorial nature of the coupling of spins to superconducting wires. We
present explicit numerical calculations of the flux noise power (spectral
density integrated over all frequencies) for electron impurities and lattice
nuclear spins under several different assumptions. The noise power is shown to
be dominated by surface electron spins near the wire edges, with bulk lattice
nuclear spins contributing % of the noise power in aluminum and niobium
wires. We consider the role of electron spin phase transitions, showing that
the spin-spin correlation length (describing e.g. the average size of
ferromagnetic spin clusters) greatly impacts the scaling of flux noise with
wire geometry. Remarkably, flux noise power is exactly equal to zero when the
spins are polarized along the flux vector direction, forming what we call a
poloidal state. Flux noise is non-zero for other spin textures, but gets
reduced in the presence of correlated ferromagnetic fluctuations between the
top and bottom wire surfaces, where the flux vectors are antiparallel. This
demonstrates that engineering spin textures and/or inter-surface correlation
provides a method to reduce flux noise in superconducting devices.Comment: New version accepted in PRB. Contains new discussion about the
poloidal stat
Higgs Pair Production at the LHC in Models with Universal Extra Dimensions
In this letter we study the process of gluon fusion into a pair of Higgs
bosons in a model with one universal extra dimension. We find that the
contributions from the extra top quark Kaluza-Klein excitations lead to a Higgs
pair production cross section at the LHC that can be significantly altered
compared to the Standard Model value for small values of the compactification
scale.Comment: 10 pages, 6 figures. LHC cross section computed, 2 new figure
- …