Hybrid Planning and Control for Multiple Fixed-Wing Aircraft under Input Constraints

This paper presents a novel hybrid control protocol for de-conflicting multiple vehicles with constraints on control inputs. We consider turning rate and linear speed constraints to represent fixed-wing or car-like vehicles. A set of state-feedback controllers along with a state-dependent switching logic are synthesized in a hybrid system to generate collision-free trajectories that converge to the desired destinations of the vehicles. The switching law is designed so that the safety can be guaranteed while no Zeno behavior can occur. A novel temporary goal assignment technique is also designed to guarantee convergence. We analyze the individual modes for safety and the closed-loop hybrid system for convergence. The theoretical developments are demonstrated via simulation results.Comment: Best Student Paper Finalist, AIAA-SciTech GNC Conference, 201

Multiscale formulation for material failure accounting for cohesive cracks at the macro and micro scales

This contribution presents a two-scale formulation devised to simulate failure in materials with het- erogeneous micro-structure. The mechanical model accounts for the activation of cohesive cracks in the micro-scale domain. The evolution/propagation of cohesive micro-cracks can induce material instability at the macro-scale level. Then, a cohesive crack is activated in the macro-scale model which considers, in a homogenized sense, the constitutive response of the intricate failure mode taking place in the smaller length scale.The two-scale model is based on the concept of Representative Volume Element (RVE). It is designed following an axiomatic variational structure. Two hypotheses are introduced in order to build the foundations of the entire two-scale theory, namely: (i) a mechanism for transferring kinematical information from macro- to-micro scale along with the concept of “Kinematical Admissibility”, relating both primal descriptions, and (ii) a Multiscale Variational Principle of internal virtual power equivalence between the involved scales of analysis. The homogenization formulae for the generalized stresses, as well as the equilibrium equations at the micro-scale, are consequences of the variational statement of the problem.The present multiscale technique is a generalization of a previous model proposed by the authors and could be viewed as an application of a general framework recently proposed by the authors. The main novelty in this article lies on the fact that failure modes in the micro-structure now involve a set of multiple cohesive cracks, connected or disconnected, with arbitrary orientation, conforming a complex tortuous failure path. Tortuosity is a topic of decisive importance in the modelling of material degradation due to crack propagation. Following the present multiscale modelling approach, the tortuosity effect is introduced in order to satisfy the “Kinematical Admissibility” concept, when the macro-scale kinematics is transferred into the micro-scale domain. There- fore, it has a direct consequence in the homogenized mechanical response, in the sense that the proposed scale transition method (including the tortuosity effect) retrieves the correct post-critical response.Coupled (macro-micro) numerical examples are presented showing the potentialities of the model to sim- ulate complex and realistic fracture problems in heterogeneous materials. In order to validate the multiscale technique in a rigorous manner, comparisons with the so-called DNS (Direct Numerical Solution) approach are also presented

MERCURY SPECIATION BY ELECTROCHEMICAL SEPARATION AND COLD-VAPOR ATOMIC-ABSORPTION SPECTROMETRY

Mercury speciation in aqueous solutions containing inorganic mercury and methylmercury has been demonstrated using electrochemical separation prior to determination by cold-vapour atomic absorption spectrometry. Approximately 95% of the inorganic mercury was electro-deposited on a Pt electrode at –0.1 V, whereas for methylmercury –0.2 V or even more negative potentials were required. Organic mercury was determined by NaBH4 reduction after electrochemical separation. Inorganic mercury was determined in the original solution by SnCl2 reduction

DETERMINATION OF CEFTRIAXONE IN AQUEOUS-HUMOR AND SERUM SAMPLES BY DIFFERENTIAL-PULSE ADSORPTIVE STRIPPING VOLTAMMETRY

Differential-pulse adsorptive stripping voltammetry was used to determine ceftriaxone in serum and aqueous humour samples. The method involved extraction of the ceftriaxone from serum samples with an Amberlite XAD-2 column followed by elution with methanol. The recovery was 97.6% with a relative standard deviation of 3.3% at a ceftriaxone concentration of 90.9 mu g l(-1). Peak currents of ceftriaxone were measured with a hanging mercury drop electrode at -0.78 V versus an Ag-AgCl reference electrode in pH 3.0 Britton-Robinson buffer. The calibration graph was linear from 0.02 to 1300 mu g l(-1). The method was applied to cataract cases and ceftriaxone levels were measured in aqueous humour and serum samples from patients who had received 1 or 2 g of ceftriaxone intravenously. Aqueous humour was added to the polarographic cell directly. The amounts of ceftriaxone in the aqueous humour and serum samples with respect to time were measured. The pharmacokinetic profiles for 1 and 2 g were compared