6,634 research outputs found
Improving the Parallel Execution of Behavior Trees
Behavior Trees (BTs) have become a popular framework for designing
controllers of autonomous agents in the computer game and in the robotics
industry. One of the key advantages of BTs lies in their modularity, where
independent modules can be composed to create more complex ones. In the
classical formulation of BTs, modules can be composed using one of the three
operators: Sequence, Fallback, and Parallel. The Parallel operator is rarely
used despite its strong potential against other control architectures as Finite
State Machines. This is due to the fact that concurrent actions may lead to
unexpected problems similar to the ones experienced in concurrent programming.
In this paper, we introduce Concurrent BTs (CBTs) as a generalization of BTs in
which we introduce the notions of progress and resource usage. We show how CBTs
allow safe concurrent executions of actions and we analyze the approach from a
mathematical standpoint. To illustrate the use of CBTs, we provide a set of use
cases in robotics scenarios
Anharmonic properties from a generalized third order ab~initio approach: theory and applications to graphite and graphene
We have implemented a generic method, based on the 2n+1 theorem within
density functional perturbation theory, to calculate the anharmonic scattering
coefficients among three phonons with arbitrary wavevectors. The method is used
to study the phonon broadening in graphite and graphene mono- and bi-layer. The
broadening of the high-energy optical branches is highly nonuniform and
presents a series of sudden steps and spikes. At finite temperature, the two
linearly dispersive acoustic branches TA and LA of graphene have nonzero
broadening for small wavevectors. The broadening in graphite and bi-layer
graphene is, overall, very similar to the graphene one, the most remarkable
feature being the broadening of the quasi acoustical ZO' branch. Finally, we
study the intrinsic anharmonic contribution to the thermal conductivity of the
three systems, within the single mode relaxation time approximation. We find
the conductance to be in good agreement with experimental data for the
out-of-plane direction but to underestimate it by a factor 2 in-plane
Well-posedness of the Two-dimensional Nonlinear Schr\"odinger Equation with Concentrated Nonlinearity
We consider a two-dimensional nonlinear Schr\"odinger equation with
concentrated nonlinearity. In both the focusing and defocusing case we prove
local well-posedness, i.e., existence and uniqueness of the solution for short
times, as well as energy and mass conservation. In addition, we prove that this
implies global existence in the defocusing case, irrespective of the power of
the nonlinearity, while in the focusing case blowing-up solutions may arise.Comment: 39 pages, pdfLaTex. Final version to appear in Ann. I. H. Poincar\'e
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3D numerical modelling of twisting cracks under bending and torsion of skew notched beams
The testing of mode III and mixed mode failure is every so often encountered in the dedicated literature of mechanical characterization of brittle and quasi-brittle materials. In this work, the application of the mixed strain displacement e-ue-u finite element formulation to three examples involving skew notched beams is presented. The use of this FE technology is effective in problems involving localization of strains in softening materials.
The objectives of the paper are: (i) to test the mixed formulation in mode III and mixed mode failure and (ii) to present an enhancement in terms of computational time given by the kinematic compatibility between irreducible displacement-based and the mixed strain-displacement elements.
Three tests of skew-notched beams are presented: firstly, a three point bending test of a PolyMethyl MethaAcrylate beam; secondly, a torsion test of a plain concrete prismatic beam with square base; finally, a torsion test of a cylindrical beam made of plain concrete as well. To describe the mechanical behavior of the material in the inelastic range, Rankine and Drucker-Prager failure criteria are used in both plasticity and isotropic continuum damage formats.
The proposed mixed formulation is capable of yielding results close to the experimental ones in terms of fracture surface, peak load and global loss of carrying capability. In addition, the symmetric secant formulation and the compatibility condition between the standard irreducible method and the strain-displacement one is exploited, resulting in a significant speedup of the computational procedure.Peer ReviewedPostprint (author's final draft
Programmable interactions with biomimetic DNA linkers at fluid membranes and interfaces
At the heart of the structured architecture and complex dynamics of
biological systems are specific and timely interactions operated by
biomolecules. In many instances, biomolecular agents are spatially confined to
flexible lipid membranes where, among other functions, they control cell
adhesion, motility and tissue formation. Besides being central to several
biological processes, \emph{multivalent interactions} mediated by reactive
linkers confined to deformable substrates underpin the design of
synthetic-biological platforms and advanced biomimetic materials. Here we
review recent advances on the experimental study and theoretical modelling of a
heterogeneous class of biomimetic systems in which synthetic linkers mediate
multivalent interactions between fluid and deformable colloidal units,
including lipid vesicles and emulsion droplets. Linkers are often prepared from
synthetic DNA nanostructures, enabling full programmability of the
thermodynamic and kinetic properties of their mutual interactions. The coupling
of the statistical effects of multivalent interactions with substrate fluidity
and deformability gives rise to a rich emerging phenomenology that, in the
context of self-assembled soft materials, has been shown to produce exotic
phase behaviour, stimuli-responsiveness, and kinetic programmability of the
self-assembly process. Applications to (synthetic) biology will also be
reviewed.Comment: 63 pages, revie
Flavour violation in supersymmetric SO(10) unification with a type II seesaw mechanism
We study flavour violation in a supersymmetric SO(10) implementation of the
type II seesaw mechanism, which provides a predictive realization of triplet
leptogenesis. The experimental upper bounds on lepton flavour violating
processes have a significant impact on the leptogenesis dynamics, in particular
they exclude the strong washout regime. Requiring successful leptogenesis then
constrains the otherwise largely unknown overall size of flavour-violating
observables, thus yielding testable predictions. In particular, the branching
ratio for mu -> e gamma lies within the reach of the MEG experiment if the
superpartner spectrum is accessible at the LHC, and the supersymmetric
contribution to epsilon_K can account for a significant part of the
experimental value. We show that this scenario can be realized in a consistent
SO(10) model achieving gauge symmetry breaking and doublet-triplet splitting in
agreement with the proton decay bounds, improving on the MSSM prediction for
alpha_3(m_Z), and reproducing the measured quark and lepton masses.Comment: 40 pages, 10 figures. Accepted for publication in JHE
Long-Range Communications in Unlicensed Bands: the Rising Stars in the IoT and Smart City Scenarios
Connectivity is probably the most basic building block of the Internet of
Things (IoT) paradigm. Up to know, the two main approaches to provide data
access to the \emph{things} have been based either on multi-hop mesh networks
using short-range communication technologies in the unlicensed spectrum, or on
long-range, legacy cellular technologies, mainly 2G/GSM, operating in the
corresponding licensed frequency bands. Recently, these reference models have
been challenged by a new type of wireless connectivity, characterized by
low-rate, long-range transmission technologies in the unlicensed sub-GHz
frequency bands, used to realize access networks with star topology which are
referred to a \emph{Low-Power Wide Area Networks} (LPWANs). In this paper, we
introduce this new approach to provide connectivity in the IoT scenario,
discussing its advantages over the established paradigms in terms of
efficiency, effectiveness, and architectural design, in particular for the
typical Smart Cities applications
Ab initio variational approach for evaluating lattice thermal conductivity
We present a first-principles theoretical approach for evaluating the lattice
thermal conductivity based on the exact solution of the Boltzmann transport
equation. We use the variational principle and the conjugate gradient scheme,
which provide us with an algorithm faster than the one previously used in
literature and able to always converge to the exact solution. Three-phonon
normal and umklapp collision, isotope scattering and border effects are
rigorously treated in the calculation. Good agreement with experimental data
for diamond is found. Moreover we show that by growing more enriched diamond
samples it is possible to achieve values of thermal conductivity up to three
times larger than the commonly observed in isotopically enriched diamond
samples with 99.93% C12 and 0.07 C13
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