Particle deposition onto a flat plate with various slopes

In this work, a numerical simulation of the deposition of small suspended particles onto a flat plate with various degrees of inclination is performed. The particle deposition rates are obtained for various Reynolds and Rayleigh number groups

O projeto DACHOR: Dinâmica multicorpo e controlo de ortóteses híbridas activas

Fundação para a Ciência e a Tecnologia pelo financiamento concedido no âmbito do projecto MIT-PVBSHHMS/0042/200

An efficient muscle fatigue model for forward and inverse dynamic analysis of human movements

AbstractThe aim of this work is to present the integration of a simple and yet efficient dynamic muscle fatigue model in a multibody formulation with natural coordinates. The fatigue model considers the force production history of each muscle to estimate its fitness level by means of a three-compartment theory approach. The model is easily adapted to co-operate with standard Hill-type muscle models, allowing the simulation and analysis of the redundant muscle forces generated in the presence of muscular fatigue. This has particular relevance in the design of orthotic devices to support human locomotion and manipulation

Particle deposition in airway bifurcations in different breathing conditions

In this paper, particle deposition in a rigid double bifurcation airway is studied experimentally. The effect of particle size and breathing conditions in the deposition are analyzed. Besides, the effect of airway obstruction (local reduction of airway diameter) that can be originated by some respiratory disorders is also studied. The experiments were performed in conditions of humidity near saturation in order to account for the conditions occurring in the respiratory tree

Fast optimum-predictive control and capacitor voltage balancing strategy for bipolar back-to-back NPC converters in high-voltage direct current transmission systems

Multilevel power converters have been introduced as the solution for high-power high-voltage switching applications where they have well-known advantages. Recently, full back-to-back connected multilevel neutral point diode clamped converters (NPC converter) have been used inhigh-voltage direct current (HVDC) transmission systems. Bipolar-connected back-to-back NPC converters have advantages in long-distance HVDCtransmission systems over the full back-to-back connection, but greater difficulty to balance the dc capacitor voltage divider on both sending and receiving end NPC converters. This study shows that power flow control and dc capacitor voltage balancing are feasible using fast optimum-predictive-based controllers in HVDC systems using bipolar back-to-back-connected five-level NPC multilevel converters. For both converter sides, the control strategytakes in account active and reactive power, which establishes ac grid currents in both ends, and guarantees the balancing of dc bus capacitor voltages inboth NPC converters. Additionally, the semiconductor switching frequency is minimised to reduce switching losses. The performance and robustness of the new fast predictive control strategy, and its capability to solve the DC capacitor voltage balancing problem of bipolar-connected back-to-back NPCconverters are evaluated

Characterization of additives of PVAc and acrylic waterborne dispersions and paints by analytical Py-GC-MS and Py-Silylation-GC-MS

[EN] Commercial formulations of poly(vinyl acetate) (PVAc) and acrylic dispersions and paints commonly used by artists include a number of additives such as surfactants, coalescing agents, defoamers and thickeners, which are designed for improving shelf-life, as well as chemical and physical properties of the resulting product. Recent studies have shown that additives present in paints play an important role in the alteration processes undergone by the painting during ageing and further in cleaning tasks planed in conservation interventions. However, the identification of additives is a difficult task due to the elusive character of these substances present at low concentration in the paint. In this context, a four-step approach is proposed that includes analysis of paint samples together with analysis of their water extracted products by pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) and pyrolysis-silylation-gas chromatography-mass spectrometry (Py-silylation-GC-MS). This analytical strategy enables a better characterization of common additives present in commercial PVAc and acrylic paints and dispersions. In particular, the analysis of water soluble extracts, which are mainly composed by paint additives, avoids the interference of the major polymer pyrolizates. Experimental conditions concerning sample preparation and instrumental working conditions of both Py-GC techniques are optimized. Both acrylic and PVAc paints presented poly(ethylene oxide) (POE) type fragments dominating the background of their pyrograms, especially when derivatized by means of hexamethyldisilazane (HMDS). For the first time, additives such as alkyl sulfate and alkyl ether sulfate with C-10 and C-12 alkyl chains, poly(ethoxylate) fatty alcohol and octylphenyl poly(ethoxylate) surfactants were identified, as well as polyvinyl alcohol (PVOH) protective colloids, hydrophobically modified ethoxylated urethane (HEUR) thickeners an defoamers. Their major fragments and corresponding mass spectra are discussed. (C) 2015 Elsevier B.V. All rights reserved.Financial support from the MINECO Projects CTQ2011-28079-CO3-01 and CTQ2014-53736-C3-1-P, which are supported with ERDF funds, is gratefully acknowledged.Silva, MF.; Domenech Carbo, MT.; Osete Cortina, L. (2015). Characterization of additives of PVAc and acrylic waterborne dispersions and paints by analytical Py-GC-MS and Py-Silylation-GC-MS. Journal of Analytical and Applied Pyrolysis. 113:606-620. https://doi.org/10.1016/j.jaap.2015.04.011S60662011

Optimal observational scheduling framework for binary and multiple stellar systems

The optimal instant of observation of astrophysical phenomena for objects that vary on human time-sales is an important problem, as it bears on the cost-effective use of usually scarce observational facilities. In this paper we address this problem for the case of tight visual binary systems through a Bayesian framework based on the maximum entropy sampling principle. Our proposed information-driven methodology exploits the periodic structure of binary systems to provide a computationally efficient estimation of the probability distribution of the optimal observation time. We show the optimality of the proposed sampling methodology in the Bayes sense and its effectiveness through direct numerical experiments. We successfully apply our scheme to the study of two visual-spectroscopic binaries, and one purely astrometric triple hierarchical system. We note that our methodology can be applied to any time-evolving phenomena, a particularly interesting application in the era of dedicated surveys, where a definition of the cadence of observations can have a crucial impact on achieving the science goals.Comment: Accepted for publication to PASP. 23 pages, 2 Tables, 9 Figures, 2 Appendice

HVDC transmission systems: Bipolar back-to-back diode clamped multilevel converter with fastoptimum-predictive control and capacitor balancing strategy

Voltage source multilevel power converter structures are being considered for high power high voltage applications where they have well known advantages. Recently, full back-to-back connected multilevel neutral diode clamped converters (NPC) have been used in high voltage direct current (HVDC) transmission systems. Bipolar back-to-back connection of NPCs have advantages in long distance HVDC transmission systems, but highly increased difficulties to balance the dc capacitor voltage dividers on both sending and receiving end NPCs. This paper proposes a fast optimum-predictive controller to balance the dc capacitor voltages and to control the power flow in a long distance HVDCsystem using bipolar back-to-back connected NPCs. For both converter sides, the control strategy considers active and reactive power to establish ac grid currents on sending and receiving ends, while guaranteeing the balancing of both NPC dc bus capacitor voltages. Furthermore, the fast predictivecontroller minimizes the semiconductor switching frequency to reduce global switching losses. The performance and robustness of the new fast predictive control strategy and the associated dc capacitors voltage balancing are evaluated. (C) 2011 Elsevier B.V. All rights reserved