228 research outputs found
Heterogeneous Timed Machines
International audienceWe present an algebra of discrete timed input/output au- tomata that execute in the context of different clock granularities -- timed machines -- as models of systems that can be dynamically inter- connected at run time in a heterogeneous context. We show how timed machines can be refined to a lower granularity of time and how timed machines with different clock granularities can be composed. We propose techniques for checking whether timed machines are consistent or feasi- ble. Finally, we investigate how consistency and feasibility of composition can be proved at run-time without computing products of automata
Slow Switching in Globally Coupled Oscillators: Robustness and Occurrence through Delayed Coupling
The phenomenon of slow switching in populations of globally coupled
oscillators is discussed. This characteristic collective dynamics, which was
first discovered in a particular class of the phase oscillator model, is a
result of the formation of a heteroclinic loop connecting a pair of clustered
states of the population. We argue that the same behavior can arise in a wider
class of oscillator models with the amplitude degree of freedom. We also argue
how such heteroclinic loops arise inevitably and persist robustly in a
homogeneous population of globally coupled oscillators. Although the
heteroclinic loop might seem to arise only exceptionally, we find that it
appears rather easily by introducing the time-delay in the population which
would otherwise exhibit perfect phase synchrony. We argue that the appearance
of the heteroclinic loop induced by the delayed coupling is then characterized
by transcritical and saddle-node bifurcations. Slow switching arises when the
system with a heteroclinic loop is weakly perturbed. This will be demonstrated
with a vector model by applying weak noises. Other types of weak
symmetry-breaking perturbations can also cause slow switching.Comment: 10 pages, 14 figures, RevTex, twocolumn, to appear in Phys. Rev.
Scenario analysis can guide aquaculture planning to meet sustainable future production goals
Marine aquaculture holds great promise for meeting increasing demand for healthy protein that is sustainably produced, but reaching necessary production levels will be challenging. The ecosystem approach to aquaculture is a framework for sustainable aquaculture development that prioritizes multiple-stakeholder participation and spatial planning. These types of approaches have been increasingly used to help guide sustainable, persistent, and equitable aquaculture planning, but most countries have difficulties in setting or meeting longer-term development goals. Scenario analysis (SA) for future planning uses similar approaches and can complement holistic methods, such as the ecosystem approach to aquaculture framework, by providing a temporal analogue to the spatially robust design. Here we define the SA approach to planning in aquaculture, outline how SA can benefit aquaculture planning, and review how this tool is already being used. We track the use of planning tools in the 20 International Council for the Exploration of the Sea member nations, with particular attention given to Norway’s development goals to 2050. We conclude that employing a combination of an ecosystem framework with scenario analyses may help identify the scale of development aquaculture goals over time, aid in evaluating the feasibility of the desired outcomes, and highlight potential social-ecological conflicts and trade-offs that may otherwise be overlooked.Versión del editor2,27
Alpha scattering and capture reactions in the A = 7 system at low energies
Differential cross sections for He- scattering were measured in
the energy range up to 3 MeV. These data together with other available
experimental results for He and H scattering were
analyzed in the framework of the optical model using double-folded potentials.
The optical potentials obtained were used to calculate the astrophysical
S-factors of the capture reactions HeBe and
HLi, and the branching ratios for the transitions into
the two final Be and Li bound states, respectively. For
HeBe excellent agreement between calculated and
experimental data is obtained. For HLi a value
has been found which is a factor of about 1.5 larger than the adopted value.
For both capture reactions a similar branching ratio of has been obtained.Comment: submitted to Phys.Rev.C, 34 pages, figures available from one of the
authors, LaTeX with RevTeX, IK-TUW-Preprint 930540
Covariant description of inelastic electron--deuteron scattering:predictions of the relativistic impulse approximation
Using the covariant spectator theory and the transversity formalism, the
unpolarized, coincidence cross section for deuteron electrodisintegration,
, is studied. The relativistic kinematics are reviewed, and simple
theoretical formulae for the relativistic impulse approximation (RIA) are
derived and discussed. Numerical predictions for the scattering in the high
region obtained from the RIA and five other approximations are presented
and compared. We conclude that measurements of the unpolarized coincidence
cross section and the asymmetry , to an accuracy that will distinguish
between different theoretical models, is feasible over most of the wide
kinematic range accessible at Jefferson Lab.Comment: 54 pages and 24 figure
Helium Clustering in Neutron-Rich Be Isotopes
Measurements of the helium-cluster breakup and neutron removal cross sections
for neutron-rich Be isotopes A=10-12,14 are presented. These have been studied
in the 30 to 42 MeV/u energy range where reaction measurements are proposed to
be sensitive to the cluster content of the ground-state wave-function. These
measurements provide a comprehensive survey of the decay processes of the Be
isotopes by which the valence neutrons are removed revealing the underlying
alpha-alpha core-cluster structure. The measurements indicate that clustering
in the Be isotopes remains important up to the drip-line nucleus 14^Be and that
the dominant helium-cluster structure in the neutron-rich Be isotopes
corresponds to alpha-Xn-alpha.Comment: 5 pages, 2 tables and 3 figure
Missing values: sparse inverse covariance estimation and an extension to sparse regression
We propose an l1-regularized likelihood method for estimating the inverse
covariance matrix in the high-dimensional multivariate normal model in presence
of missing data. Our method is based on the assumption that the data are
missing at random (MAR) which entails also the completely missing at random
case. The implementation of the method is non-trivial as the observed negative
log-likelihood generally is a complicated and non-convex function. We propose
an efficient EM algorithm for optimization with provable numerical convergence
properties. Furthermore, we extend the methodology to handle missing values in
a sparse regression context. We demonstrate both methods on simulated and real
data.Comment: The final publication is available at http://www.springerlink.co
Accessory proteins are vital for the functional expression of certain G protein-coupled receptors
Looking forward through the past: identification of 50 priority research questions in palaeoecology
1. Priority question exercises are becoming an increasingly common tool to frame future agendas in conservation and ecological science. They are an effective way to identify research foci that advance the field and that also have high policy and conservation relevance. 2. To date, there has been no coherent synthesis of key questions and priority research areas for palaeoecology, which combines biological, geochemical and molecular techniques in order to reconstruct past ecological and environmental systems on time-scales from decades to millions of years. 3. We adapted a well-established methodology to identify 50 priority research questions in palaeoecology. Using a set of criteria designed to identify realistic and achievable research goals, we selected questions from a pool submitted by the international palaeoecology research community and relevant policy practitioners. 4. The integration of online participation, both before and during the workshop, increased international engagement in question selection. 5. The questions selected are structured around six themes: human–environment interactions in the Anthropocene; biodiversity, conservation and novel ecosystems; biodiversity over long time-scales; ecosystem processes and biogeochemical cycling; comparing, combining and synthesizing information from multiple records; and new developments in palaeoecology. 6. Future opportunities in palaeoecology are related to improved incorporation of uncertainty into reconstructions, an enhanced understanding of ecological and evolutionary dynamics and processes and the continued application of long-term data for better-informed landscape management
Validation of the GROMOS force-field parameter set 45A3 against nuclear magnetic resonance data of hen egg lysozyme
- …