1,173 research outputs found
Velocity-aided Attitude Estimation for Accelerated Rigid Bodies
Two nonlinear observers for velocity-aided attitude estimation, relying on
gyrometers, accelerometers, magnetometers, and velocity measured in the
body-fixed frame, are proposed. As opposed to state-of-the-art body-fixed
velocity-aided attitude observers endowed with local properties, both observers
are (almost) globally asymptotically stable, with very simple and flexible
tuning. Moreover, the roll and pitch estimates are globally decoupled from
magnetometer measurements
The transition of small-scale coffee farming systems and new pathways for coffee production: A case study in the central highlands of Vietnam
The dynamics of agriculture in general and coffee farming systems need to be investigated to derive insights for policies and interventions to promote sustainable agriculture. Through a systematic approach, including historical and adaptive ones, the study aims to probe the spatial-temporal transition of coffee farming systems. We found evidence for the diverse adaptive capacity of the coffee farming systems in Dak Lak province in their response to various factors. Moreover, an economic comparison was made between coffee farming systems, including mono-coffee farms and coffee-based intercropped ones. The study showed that coffee-based intercropped farms yield higher returns than mono-cropping ones by productivity enhancement, land equity ratio, and gross margin. These findings provided empirical evidence to design appropriate policies for the sustainable development of coffee farming
Effect of size polydispersity versus particle shape in dense granular media
International audienceWe present a detailed analysis of the morphology of granular systems composed of frictionless pentagonal particles by varying systematically both the size span and particle shape irregularity, which represent two polydispersity parameters of the system. The microstructure is characterized in terms of various statistical descriptors such as global and local packing fractions, radial distribution functions, coordination number, and fraction of floating particles.We find that the packing fraction increases with the two parameters of polydispersity, but the effect of shape polydispersity for all the investigated structural properties is significant only at low size polydispersity where the positional and/or orientational ordering of the particles prevail.We focus in more detail on the class of side/side contacts, which is the interesting feature of our system as compared to a packing of disks. We show that the proportion of such contacts has weak dependence on the polydispersity parameters. The sideside contacts do not percolate but they define clusters of increasing size as a function of size polydispersity and decreasing size as a function of shape polydispersity. The clusters have anisotropic shapes but with a decreasing aspect ratio as polydispersity increases. This feature is argued to be a consequence of strong force chains (forces above the mean), which are mainly captured by side-side contacts. Finally, the force transmission is intrinsically multiscale, with a mean force increasing linearly with particle size
Bonded-cell model for particle fracture
Particle degradation and fracture play an important role in natural granular flows and in many applications of granular materials. We analyze the fracture properties of two-dimensional disklike particles modeled as aggregates of rigid cells bonded along their sides by a cohesive Mohr-Coulomb law and simulated by the contact dynamics method. We show that the compressive strength scales with tensile strength between cells but depends also on the friction coefficient and a parameter describing cell shape distribution. The statistical scatter of compressive strength is well described by the Weibull distribution function with a shape parameter varying from 6 to 10 depending on cell shape distribution. We show that this distribution may be understood in terms of percolating critical intercellular contacts. We propose a random-walk model of critical contacts that leads to particle size dependence of the compressive strength in good agreement with our simulation data
Degenerate epitaxy-driven defects in monolayer silicon oxide onto ruthenium
The structure of the ultimately-thin crystalline allotrope of silicon oxide,
prepared onto a ruthenium surface, is unveiled down to atomic scale with
chemical sensitivity, thanks to high resolution scanning tunneling microscopy
and first principle calculations. An ordered oxygen lattice is imaged which
coexists with the two-dimensional monolayer oxide. This coexistence signals a
displacive transformation from an oxygen reconstructed-Ru(0001) to silicon
oxide, along which latterally-shifted domains form, each with equivalent and
degenerate epitaxial relationships with the substrate. The unavoidable
character of defects at boundaries between these domains appeals for the
development of alternative methods capable of producing single-crystalline
two-dimensional oxides
Weld pool shape identification by using Bezier surfaces
International audienceThis paper deals with the heat transfer analysis in a welding process: A method is developed to determine the shape of the three-dimensional (3-D) phase change front and to estimate the temperature field within the solid part of the work piece. The problem is formulated and solved as an inverse phase-change problem by using an optimization method. The direct problem is solved in the torch frame and so formulated as an Eulerian approach. The interface between the weld pool and the solid region is parameterized by Bezier surfaces. The most important feature of the presented approach is that the liquid–solid interface as well as the temperature distribution within the solid region can be obtained from additional temperature data available in the solid region, without considering heat transfer and fluid flow in a molten zone. The estimate of these thermal characteristics then allows a thermomechanical calculation of the welded joint (calculation of the deformations and residual stresses). The validity of the numerical solution of the inverse problem is checked by comparing the results with the direct solution of the problem
Non-functional Data Collection for Adaptive Business Processes and Decision Making
International audienceMonitoring application services becomes more and more a transverse key activity in SOA. Beyond traditional human system administration and load control, new activities such as autonomic management as well as SLA enforcement raise the stakes over monitoring requirements. In this paper, we address a new monitoring-based activity which is selecting among competitive service offers based on their currently measured QoS. Starting from this use case, the late binding of service calls in SOA given the current QoS of a set of candidate services, we first elicit the requirements and then describe M4ABP (Monitoring for Adaptive Business Process), a middleware component for monitoring services and delivering monitoring data to business processes wishing to call them. M4ABP provides solutions for general requirements: flexibility as well as performance in data access for clients, coherency of data sets and network usage optimization. Lessons learned from this first use case can be applied to similar monitoring scenario, as well as to the larger field of context-aware computing
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