4,644 research outputs found
Big data analyses reveal patterns and drivers of the movements of southern elephant seals
The growing number of large databases of animal tracking provides an
opportunity for analyses of movement patterns at the scales of populations and
even species. We used analytical approaches, developed to cope with big data,
that require no a priori assumptions about the behaviour of the target agents,
to analyse a pooled tracking dataset of 272 elephant seals (Mirounga leonina)
in the Southern Ocean, that was comprised of >500,000 location estimates
collected over more than a decade. Our analyses showed that the displacements
of these seals were described by a truncated power law distribution across
several spatial and temporal scales, with a clear signature of directed
movement. This pattern was evident when analysing the aggregated tracks despite
a wide diversity of individual trajectories. We also identified marine
provinces that described the migratory and foraging habitats of these seals.
Our analysis provides evidence for the presence of intrinsic drivers of
movement, such as memory, that cannot be detected using common models of
movement behaviour. These results highlight the potential for big data
techniques to provide new insights into movement behaviour when applied to
large datasets of animal tracking.Comment: 18 pages, 5 figures, 6 supplementary figure
The role of Dark Matter interaction in galaxy clusters
We consider a toy model to analyze the consequences of dark matter
interaction with a dark energy background on the overall rotation of galaxy
clusters and the misalignment between their dark matter and baryon
distributions when compared to {\Lambda}CDM predictions. The interaction
parameters are found via a genetic algorithm search. The results obtained
suggest that interaction is a basic phenomenon whose effects are detectable
even in simple models of galactic dynamics.Comment: RevTeX 4.1, 5 pages, 3 figure
Verifying compliance with ballast water standards : a decision-theoretic approach
We construct credible intervals to estimate the mean organism (zooplankton and phytoplankton) concentration in ballast water via a decision-theoretic approach. To obtain the required optimal sample size, we use a total cost minimization criterion defined as the sum of the sampling cost and the Bayes risk either under a Poisson or a negative binomial model for organism counts, both with a gamma prior distribution. Such credible intervals may be employed to verify whether the ballast water discharged from a ship is in compliance with international standards. We also conduct a simulation study to evaluate the credible interval lengths associated with the proposed optimal sample sizes
The Covering-Assignment Problem for Swarm-powered Ad-hoc Clouds: A Distributed 3D Mapping Use-case
The popularity of drones is rapidly increasing across the different sectors
of the economy. Aerial capabilities and relatively low costs make drones the
perfect solution to improve the efficiency of those operations that are
typically carried out by humans (e.g., building inspection, photo collection).
The potential of drone applications can be pushed even further when they are
operated in fleets and in a fully autonomous manner, acting de facto as a drone
swarm. Besides automating field operations, a drone swarm can serve as an
ad-hoc cloud infrastructure built on top of computing and storage resources
available across the swarm members and other connected elements. Even in the
absence of Internet connectivity, this cloud can serve the workloads generated
by the swarm members themselves, as well as by the field agents operating
within the area of interest. By considering the practical example of a
swarm-powered 3D reconstruction application, we present a new optimization
problem for the efficient generation and execution, on top of swarm-powered
ad-hoc cloud infrastructure, of multi-node computing workloads subject to data
geolocation and clustering constraints. The objective is the minimization of
the overall computing times, including both networking delays caused by the
inter-drone data transmission and computation delays. We prove that the problem
is NP-hard and present two combinatorial formulations to model it.
Computational results on the solution of the formulations show that one of them
can be used to solve, within the configured time-limit, more than 50% of the
considered real-world instances involving up to two hundred images and six
drones
Heuristics for optimizing 3D mapping missions over swarm-powered ad hoc clouds
Drones have been getting more and more popular in many economy sectors. Both
scientific and industrial communities aim at making the impact of drones even
more disruptive by empowering collaborative autonomous behaviors -- also known
as swarming behaviors -- within fleets of multiple drones. In swarming-powered
3D mapping missions, unmanned aerial vehicles typically collect the aerial
pictures of the target area whereas the 3D reconstruction process is performed
in a centralized manner. However, such approaches do not leverage computational
and storage resources from the swarm members.We address the optimization of a
swarm-powered distributed 3D mapping mission for a real-life humanitarian
emergency response application through the exploitation of a swarm-powered ad
hoc cloud. Producing the relevant 3D maps in a timely manner, even when the
cloud connectivity is not available, is crucial to increase the chances of
success of the operation. In this work, we present a mathematical programming
heuristic based on decomposition and a variable neighborhood search heuristic
to minimize the completion time of the 3D reconstruction process necessary in
such missions. Our computational results reveal that the proposed heuristics
either quickly reach optimality or improve the best known solutions for almost
all tested realistic instances comprising up to 1000 images and fifteen drones
MobSIP: uma extensão SIP para suporte a handover em nível de aplicação em comunicações multimídia em tempo real com requisitos de mobilidade
In real-time multimedia, the overall time in Internet communications must be low and constant, in order to keep real-time sense and received media quality. When mobility is a basic requirement, efficient and flexible solutions should be adopted, avoiding harming time sensitive applications. In order to support real-time multimedia communications with mobility requirements on Internet backbones, a novel SIP extension is proposed, adding direct support to handover procedures in SIP clients. The procedures of that new extension, MobSIP, are specified and implemented, allowing formal and experimental verifications.Keywords: SIP, application layer mobility, handover procedures, real-time multimedia.Em comunicações multimídia em tempo real na Internet, o fator tempo deve ser baixo e constante, a fim de manter a noção de tempo real e a qualidade da mídia recebida. Quando a mobilidade é um requisito básico, soluções eficientes e flexíveis devem ser adotadas, evitando prejuízos às aplicações sensíveis ao tempo. A fim de suportar comunicações multimídia em tempo real com requisitos de mobilidade em backbones Internet, uma nova extensão SIP é proposta, adicionando suporte direto a procedimentos de handover em clientes SIP. Os procedimentos dessa nova extensão, MobSIP, são especificados e implementados, permitindo verificações formais e experimentais da solução.Palavras-chave: SIP, mobilidade em nível de aplicação, procedimentos de handover, multimídia em tempo real
Effect of water-soluble polymers, polyethylene glycol and poly(vinylpyrrolidone),on the gelation of aqueous micellar solutions of Pluronic copolymer F127
The micellization of F127 (E98P67E98) in dilute aqueous solutions of polyethylene glycol (PEG6000 and
PEG35000) and poly(vinylpyrrolidone) (PVP K30 and PVP K90) is studied. The average hydrodynamic
radius (rh,app) obtained from the dynamic light scattering technique increased with increase in PEG concentration
but decreased on addition of PVP, results which are consistent with interaction of the micelles
with PEG and the formation of micelles clusters, but no such interaction occurs with PVP. Tube inversion
was used to determine the onset of gelation. The critical concentration of F127 for gelation increased on
addition of PEG and of PVP K30 but decreased on addition of PVP K90. Small-angle X-ray scattering
(SAXS) was used to show that the 30 wt% F127 gel structure (fcc) was independent of polymer type
and concentration, as was the d-spacing and so the micelle hard-sphere radius. The maximum elastic
modulus (G0
max) of 30 wt% F127 decreased from its value for water alone as PEG was added, but was little
changed by adding PVP. These results are consistent with the packed-micelles in the 30 wt% F127 gel
being effectively isolated from the polymer solution on the microscale while, especially for the PEG, being
mixed on the macroscale
Listening to farmers
Extension officers in the Pacific are working with farmers to produce DVDs, printed guides and radio and TV programmes in order strengthen rural economie
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