The Loop-of-Stencil-Reduce Paradigm

In this paper we advocate the Loop-of-stencil-reduce pattern as a way to simplify the parallel programming of heterogeneous platforms (multicore+GPUs). Loop-of-Stencil-reduce is general enough to subsume map, reduce, map-reduce, stencil, stencil-reduce, and, crucially, their usage in a loop. It transparently targets (by using OpenCL) combinations of CPU cores and GPUs, and it makes it possible to simplify the deployment of a single stencil computation kernel on different GPUs. The paper discusses the implementation of Loop-of-stencil-reduce within the FastFlow parallel framework, considering a simple iterative data-parallel application as running example (Game of Life) and a highly effective parallel filter for visual data restoration to assess performance. Thanks to the high-level design of the Loop-of-stencil-reduce, it was possible to run the filter seamlessly on a multicore machine, on multi-GPUs, and on both.

Multipair massive MIMO full-duplex relaying with MRC/MRT processing

We consider a multipair relay channel, where multiple sources communicate with multiple destinations with the help of a full-duplex (FD) relay station (RS). All sources and destinations have a single antenna, while the RS is equipped with massive arrays. We assume that the RS estimates the channels by using training sequences transmitted from sources and destinations. Then, it uses maximum-ratio combining/maximum-ratio transmission (MRC/MRT) to process the signals. To significantly reduce the loop interference (LI) effect, we propose two massive MIMO processing techniques: i) using a massive receive antenna array; or ii) using a massive transmit antenna array together with very low transmit power at the RS. We derive an exact achievable rate in closed-form and evaluate the system spectral efficiency. We show that, by doubling the number of antennas at the RS, the transmit power of each source and of the RS can be reduced by 1.5 dB if the pilot power is equal to the signal power and by 3 dB if the pilot power is kept fixed, while maintaining a given quality-of-service. Furthermore, we compare FD and half-duplex (HD) modes and show that FD improves significantly the performance when the LI level is low.

Makespaces: From Redistributed Manufacturing to a Circular Economy

Redistributed manufacturing is an emerging concept which captures the anticipated reshoring and localisation of production from large scale manufacturing plants to smaller-scale localised, customisable production units, largely driven by new additive digital production technologies. Critically, community based digital fabrication workshops, or makespaces, are anticipated to be the hothouse for this new era of localised production and as such are key to future sustainable design and manufacturing practices. In parallel, the concept of the circular economy (CE) conceptualises the move from a linear economy of take-make-waste to a closed loop system, through repair, remanufacturing, refurbishment and recycling which maintains the value of materials and resources. Despite the clear interplay between RdM and CE, there is limited research exploring this relationship. In light of these interconnected developments, the aim of this paper is to explore the role of makespaces in contributing to a circular economy through RdM activities. This is achieved through six semi-structured interviews with thought leaders on these topics. The research findings identify barriers and opportunities to both CE and RdM, uncover key overlaps between CE and RdM, and identify a range of future research directions that can support the coming together of these areas. The research contributes to a wider conversation on embedding circular practices within makespaces and their role in RdM.

Makespaces: From Redistributed Manufacturing to a Circular Economy

Redistributed manufacturing is an emerging concept which captures the anticipated reshoring and localisation of production from large scale mass manufacturing plants to smaller-scale localised, customisable production units, largely driven by new digital production technologies. Critically, community-based digital fabrication workshops, or makespaces, are anticipated to be one hothouse for this new era of localised production and as such are key to future sustainable design and manufacturing practices. In parallel, the concept of the circular economy conceptualises the move from a linear economy of take-make-waste to a closed loop system, through repair, remanufacturing, and recycling to ultimately extend the value of products and materials. Despite the clear interplay between redistributed manufacturing and circular economy, there is limited research exploring this relationship. In light of these interconnected developments, the aim of this paper is to explore the role of makespaces in contributing to a circular economy through redistributed manufacturing activities. This is achieved through six semi-structured interviews with thought leaders on these topics. The research findings identify barriers and opportunities to both circular economy and redistributed manufacturing, uncover overlaps between circular economy and redistributed manufacturing, and identify a range of future research directions that can support the coming together of these areas. The research contributes to a wider conversation on embedding circular practices within makespaces and their role in redistributed manufacturing.

Discrete-time positive periodic systems with state and control constraints

The aim of this paper is to provide an efficient control design technique for discrete-time positive periodic systems. In particular, stability, positivity and periodic invariance of such systems are studied. Moreover, the concept of periodic invariance with respect to a collection of boxes is introduced and investigated with connection to stability. It is shown how such concept can be used for deriving a stabilizing state-feedback control that maintains the positivity of the closed-loop system and respects states and control signals constraints. In addition, all the proposed results can be efficiently solved in terms of linear programming.

Fluctuations in and out of equilibrium: Thermalization, quantum measurements and Coulomb disorder

This purely theoretical thesis covers aspects of two contemporary research fields: the non-equilibrium dynamics in quantum systems and the electronic properties of three-dimensional topological insulators. In the first part we investigate the non-equilibrium dynamics in closed quantum systems. Thanks to recent technologies, especially from the field of ultracold quantum gases, it is possible to realize such systems in the laboratory. The focus is on the influence of hydrodynamic slow modes on the thermalization process. Generic systems in equilibrium, either classical or quantum, in equilibrium are described by thermodynamics. This is characterized by an ensemble of maximal entropy, but constrained by macroscopically conserved quantities. We will show that these conservation laws slow down thermalization and the final equilibrium state can be approached only algebraically in time. When the conservation laws are violated thermalization takes place exponential in time. In a different study we calculate probability distributions of projective quantum measurements. Newly developed quantum microscopes provide the opportunity to realize new measurement protocols which go far beyond the conventional measurements of correlation functions. The second part of this thesis is dedicated to a new class of materials known as three-dimensional topological insulators. Also here new experimental techniques have made it possible to fabricate these materials to a high enough quality that their topological nature is revealed. However, their transport properties are not fully understood yet. Motivated by unusual experimental results in the optical conductivity we have investigated the formation and thermal destruction of spatially localized electron- and hole-doped regions. These are caused by charged impurities which are introduced into the material in order to make the bulk insulating. Our theoretical results are in agreement with the experiment and can explain the results semi-quantitatively. Furthermore, we study emergent lengthscales in the bulk as well as close to the conducting surface.

Conception d’un mécanisme déployable à grand ratio d’expansion et de son système d’actionnement par roues d’inertie pour applications spatiales

Cette thèse propose de développer des mécanismes déployables pour applications spatiales ainsi que des modes d’actionnement permettant leur déploiement et le contrôle de l’orientation en orbite de l’engin spatial les supportant. L’objectif étant de permettre le déploiement de surfaces larges pour des panneaux solaires, coupoles de télécommunication ou sections de station spatiale, une géométrie plane simple en triangle est retenue afin de pouvoir être assemblée en différents types de surfaces. Les configurations à membrures rigides proposées dans la littérature pour le déploiement de solides symétriques sont optimisées et adaptées à l’expansion d’une géométrie ouverte, telle une coupole. L’optimisation permet d’atteindre un ratio d’expansion plan pour une seule unité de plus de 5, mais présente des instabilités lors de l’actionnement d’un prototype. Le principe de transmission du mouvement d’un étage à l’autre du mécanisme est revu afin de diminuer la sensibilité des performances du mécanisme à la géométrie de ses membrures internes. Le nouveau modèle, basé sur des courroies crantées, permet d’atteindre des ratios d’expansion plans supérieurs à 20 dans certaines configurations. L’effet des principaux facteurs géométriques de conception est étudié afin d’obtenir une relation simple d’optimisation du mécanisme plan pour adapter ce dernier à différents contextes d’applications. La géométrie identique des faces triangulaires de chaque surface déployée permet aussi l’empilement de ces faces pour augmenter la compacité du mécanisme. Une articulation spécialisée est conçue afin de permettre le dépliage des faces puis leur déploiement successivement. Le déploiement de grandes surfaces ne se fait pas sans influencer lourdement l’orientation et potentiellement la trajectoire de l’engin spatial, aussi, différentes stratégies de contrôle de l’orientation novatrices sont proposées. Afin de tirer profit d’une grande surface, l’actionnement par masses ponctuelles en périphérie du mécanisme est présentée, ses équations dynamiques sont dérivées et simulées pour en observer les performances. Celles-ci démontrent le potentiel de cette stratégie de réorientation, sans obstruction de l’espace central du satellite de base, mais les performances restent en deçà de l’effet d’une roue d’inertie de masse équivalente. Une stratégie d’actionnement redondant par roue d’inertie est alors présentée pour différents niveaux de complexité de mécanismes dont toutes les articulations sont passives, c’est-à-dire non actionnées. Un mécanisme à quatre barres plan est simulé en boucle fermée avec un contrôleur simple pour valider le contrôle d’un mécanisme ciseau commun. Ces résultats sont étendus à la dérivation des équations dynamiques d’un mécanisme sphérique à quatre barres, qui démontre le potentiel de l’actionnement par roue d’inertie pour le contrôle de la configuration et de l’orientation spatiale d’un tel mécanisme. Un prototype à deux corps ayant chacun une roue d’inertie et une seule articulation passive les reliant est réalisé et contrôlé grâce à un suivi par caméra des modules. Le banc d’essai est détaillé, ainsi que les défis que l’élimination des forces externes ont représenté dans sa conception. Les résultats montrent que le système est contrôlable en orientation et en configuration. La thèse se termine par une étude de cas pour l’application des principaux systèmes développés dans cette recherche. La collecte de débris orbitaux de petite et moyenne taille est présentée comme un problème n’ayant pas encore eu de solution adéquate et posant un réel danger aux missions spatiales à venir. L’unité déployable triangulaire entraînée par courroies est dupliquée de manière à former une coupole de plusieurs centaines de mètres de diamètre et est proposée comme solution pour capturer et ralentir ces catégories de débris. Les paramètres d’une mission à cette fin sont détaillés, ainsi que le potentiel de réorientation que les roues d’inertie permettent en plus du contrôle de son déploiement. Près de 2000 débris pourraient être retirés en moins d’un an en orbite basse à 819 km d’altitude.

Hydrothermal carbonization in the synthesis of sustainable porous carbon materials

Carbon materials are found versatile and applicable in wide range of applications. During the recent years research of carbon materials has focussed on the search of environmentally friendly, sustainable, renewable and low-cost starting material sources as well as simple cost-efficient synthesis techniques. As an alternative synthesis technique in the production of carbon materials hydrothermal carbonization (HTC) has shown a great potential. Depending on the application HTC can be performed as such or as a pretreatment technique. This technique allows synthesis of carbon materials i.e. hydrochars in closed vessel in the presence of water and self-generated pressure at relatively low temperatures (180-250 ˚C). As in many applications well developed porosity and heteroatom distribution are in a key role. Therefore in this study different techniques e.g. varying feedstock, templating and post-treatment in order to introduce these properties to the hydrochars structure were performed. Simple monosaccharides i.e. fructose or glucose and more complex compounds such as cellulose and sludge were performed as starting materials. Addition of secondary precursor e.g. thiophenecarboxaldehyde and ovalbumin was successfully exploited in order to alter heteroatom content. It was shown that well-developed porosity (SBET 550 m2/g) can be achieved via one-pot approach (i.e. exploitation of salt mixture) without conventionally used post-carbonization step. Nitrogen-enriched hydrochars indicated significant Pb(II) and Cr(VI) removal efficiency of 240 mg/g and 68 mg/g respectively. Sulphur addition into carbon network was not found to have enhancing effect on the adsorption of methylene blue or change acidity of the carbon material. However, these hydrochars were found to remove 99.9 % methylene blue and adsorption efficiency of these hydrochars remained over 90 % even after regeneration. In addition to water treatment application N-rich high temperature treated carbon materials were proven applicable as electrocatalyst and electrocatalyst support. Hydrothermal carbonization was shown to be workable technique for the production of carbon materials with variable physico-chemical properties and therefore hydrochars could be applied in several different applications e.g. as alternative low-cost adsorbent for pollutant removal from water.

A matlab-based toolbox for the simulation and design of L1 adaptive controllers

This thesis introduces the L1 Adaptive Control Toolbox, a set of tools implemented in Matlab that aid in the design process of an L1 adaptive controller and enable the user to construct simulations of the closed-loop system to verify its performance. Following a brief review of the existing theory on L1 adaptive controllers, the interface of the toolbox is presented, including a description of the functions accessible to the user. Two novel algorithms for determining the required sampling period of a piecewise constant adaptive law are presented and their implementation in the toolbox is discussed. The detailed description of the structure of the toolbox is provided as well as a discussion of the implementation of the creation of simulations. Finally, the graphical user interface is presented and described in detail, including the graphical design tools provided for the development of the filter C(s). The thesis closes with suggestions for further improvement of the toolbox.

Análise e proposição de estratégias de estimação e controle de velocidade para motores de indução trifásicos

This study presents a proposal of speed servomechanisms without the use of mechanical sensors (sensorless) using induction motors. A comparison is performed and propose techniques for pet rotor speed, analyzing performance in different conditions of speed and load. For the determination of control technique, initially, is performed an analysis of the technical literature of the main control and speed estimation used, with their characteristics and limitations. The proposed technique for servo sensorless speed induction motor uses indirect field-oriented control (IFOC), composed of four controllers of the proportional-integral type (PI): rotor flux controller, speed controller and current controllers in the direct and quadrature shaft. As the main focus of the work is in the speed control loop was implemented in Matlab the recursive least squares algorithm (RLS) for identification of mechanical parameters, such as moment of inertia and friction coefficient. Thus, the speed of outer loop controller gains can be self adjusted to compensate for any changes in the mechanical parameters. For speed estimation techniques are analyzed: MRAS by rotóricos fluxes MRAS by counter EMF, MRAS by instantaneous reactive power, slip, locked loop phase (PLL) and sliding mode. A proposition of estimation in sliding mode based on speed, which is performed a change in rotor flux observer structure is displayed. To evaluate the techniques are performed theoretical analyzes in Matlab simulation environment and experimental platform in electrical machinery drives. The DSP TMS320F28069 was used for experimental implementation of speed estimation techniques and check the performance of the same in a wide speed range, including load insertion. From this analysis is carried out to implement closed-loop control of sensorless speed IFOC structure. The results demonstrated the real possibility of replacing mechanical sensors for estimation techniques proposed and analyzed. Among these, the estimator based on PLL demonstrated the best performance in various conditions, while the technique based on sliding mode has good capacity estimation in steady state and robustness to parametric variations.

Controller system design using the coefficient diagram method

Coefficient diagram method is a controller design technique for linear time-invariant systems. This design procedure occurs into two different domains: an algebraic and a graphical. The former is closely paired to a conventional pole placement method and the latter consists on a diagram whose reading from the plotted curves leads to insights regarding closed-loop control system time response, stability and robustness. The controller structure has two degrees of freedom and the design process leads to both low overshoot closed-loop time response and good robustness performance regarding mismatches between the real system and the design model. This article presents an overview on this design method. In order to make more transparent the presented theoretical concepts, examples in Matlab®code are provided. The included code illustrates both the algebraic and the graphical nature of the coefficient diagram design method. © 2016, King Fahd University of Petroleum & Minerals.

Implante neural controlado em malha fechada

One of the challenges to biomedical engineers proposed by researchers in neuroscience is brain machine interaction. The nervous system communicates by interpreting electrochemical signals, and implantable circuits make decisions in order to interact with the biological environment. It is well known that Parkinson’s disease is related to a deficit of dopamine (DA). Different methods has been employed to control dopamine concentration like magnetic or electrical stimulators or drugs. In this work was automatically controlled the neurotransmitter concentration since this is not currently employed. To do that, four systems were designed and developed: deep brain stimulation (DBS), transmagnetic stimulation (TMS), Infusion Pump Control (IPC) for drug delivery, and fast scan cyclic voltammetry (FSCV) (sensing circuits which detect varying concentrations of neurotransmitters like dopamine caused by these stimulations). Some softwares also were developed for data display and analysis in synchronously with current events in the experiments. This allowed the use of infusion pumps and their flexibility is such that DBS or TMS can be used in single mode and other stimulation techniques and combinations like lights, sounds, etc. The developed system allows to control automatically the concentration of DA. The resolution of the system is around 0.4 µmol/L with time correction of concentration adjustable between 1 and 90 seconds. The system allows controlling DA concentrations between 1 and 10 µmol/L, with an error about +/- 0.8 µmol/L. Although designed to control DA concentration, the system can be used to control, the concentration of other substances. It is proposed to continue the closed loop development with FSCV and DBS (or TMS, or infusion) using parkinsonian animals models.

Alteration of the bone tissue material properties in type 1 diabetes mellitus: A Fourier transform infrared microspectroscopy study

International audience

Inverted decoupling internal model control for square stable multivariable time delay systems

This paper presents a new tuning methodology of the main controller of an internal model control structure for n×n stable multivariable processes with multiple time delays based on the centralized inverted decoupling structure. Independently of the system size, very simple general expressions for the controller elements are obtained. The realizability conditions are provided and the specification of the closed-loop requirements is explained. A diagonal filter is added to the proposed control structure in order to improve the disturbance rejection without modifying the nominal set-point response. The effectiveness of the method is illustrated through different simulation examples in comparison with other works.

Mode locking in a spatially extended neuron model: active soma and compartmental tree

Understanding the mode-locked response of excitable systems to periodic forcing has important applications in neuroscience. For example it is known that spatially extended place cells in the hippocampus are driven by the theta rhythm to generate a code conveying information about spatial location. Thus it is important to explore the role of neuronal dendrites in generating the response to periodic current injection. In this paper we pursue this using a compartmental model, with linear dynamics for each compartment, coupled to an active soma model that generates action potentials. By working with the piece-wise linear McKean model for the soma we show how the response of the whole neuron model (soma and dendrites) can be written in closed form. We exploit this to construct a stroboscopic map describing the response of the spatially extended model to periodic forcing. A linear stability analysis of this map, together with a careful treatment of the non-differentiability of the soma model, allows us to construct the Arnol'd tongue structure for 1:q states (one action potential for q cycles of forcing). Importantly we show how the presence of quasi-active membrane in the dendrites can influence the shape of tongues. Direct numerical simulations confirm our theory and further indicate that resonant dendritic membrane can enlarge the windows in parameter space for chaotic behavior. These simulations also show that the spatially extended neuron model responds differently to global as opposed to point forcing. In the former case spatio-temporal patterns of activity within an Arnol'd tongue are standing waves, whilst in the latter they are traveling waves.