Attainable-Set Model Predictive Control for AUV Formation Control

In this article, we focus on the motion control of an AUV formation in order to track a given path along which data will be gathered. A computationally efficient architecture enables the conciliation of onboard resources optimization with state feedback control - to deal with the typical a priori high uncertainty - while managing the formation with a low computational and power budgets. To meet these very strict requirements, a novel Model Predictive Control (MPC) scheme is used. The key idea is to pre-compute data which is known to be time invariant for a number of likely scenarios and store it on-board in appropriate look-up tables. Then, as the mission proceeds, sampled motion sensor data, and communicated data is processed in each one of the AUVs and fed to the onboard proposed MPC scheme implemented with the dynamics of the formation that, by combining with information extracted from the pertinent on-board look-up tables, determine the best control action with inexpensive computational operations

Digital ocular fundus imaging: a review

Ocular fundus imaging plays a key role in monitoring the health status of the human eye. Currently, a large number of imaging modalities allow the assessment and/or quantification of ocular changes from a healthy status. This review focuses on the main digital fundus imaging modality, color fundus photography, with a brief overview of complementary techniques, such as fluorescein angiography. While focusing on two-dimensional color fundus photography, the authors address the evolution from nondigital to digital imaging and its impact on diagnosis. They also compare several studies performed along the transitional path of this technology. Retinal image processing and analysis, automated disease detection and identification of the stage of diabetic retinopathy (DR) are addressed as well. The authors emphasize the problems of image segmentation, focusing on the major landmark structures of the ocular fundus: the vascular network, optic disk and the fovea. Several proposed approaches for the automatic detection of signs of disease onset and progression, such as microaneurysms, are surveyed. A thorough comparison is conducted among different studies with regard to the number of eyes/subjects, imaging modality, fundus camera used, field of view and image resolution to identify the large variation in characteristics from one study to another. Similarly, the main features of the proposed classifications and algorithms for the automatic detection of DR are compared, thereby addressing computer-aided diagnosis and computer-aided detection for use in screening programs.Fundação para a Ciência e TecnologiaFEDErPrograma COMPET

Hydrogen uptake and release in carbon nanotube electrocatalysts

Funding Information: Acknowledgments: This work was financed by national funds registered in the budget of FCT— Foundation for Science and Technology within the scope of the Research Unit CTS—Center for Technology and Systems, under the reference UIDB/00066/2020. FCT-MCTES Portugal through SFRH/BSAB/135131/2017 is also gratefully acknowledged.The recent technique of molecular beam-thermal desorption spectrometry was used here for monitoring hydrogen uptake and release from carbon nanotube networks, after electrochemical hydrogen uptake. This way, an accurate determination of the hydrogen mass absorbed in electrodes made from those assemblies can be achieved by significantly improving the signal-to-noise ratio. The hydrogen desorption mass spectra account for the enhanced surface capability for hydrogen adsorption in the electrodes and enable a comparison with the performance of a palladium electrode in similar conditions. A comparative study involving different carbon nanotube electrodes, in similar hydrogen uptake/desorption conditions, clearly confirmed the expectations about their enhanced hydrogen storage capacity and points to the great potential of carbon nanotube assemblies in replacing the heavier metal alloys as electrocatalysts.publishersversionpublishe

Hydrogen nanometrology in advanced carbon nanomaterial electrodes

This work is financed by national funds registered in the budget of FCT-Foundation for Science and Technology within the scope of the Research Unit CTS-Center for Technology and Systems, under the reference UIDB/00066/2020. FCT-MCTES Portugal through SFRH/BSAB/135131/2017 is also gratefully acknowledged.A comparative experimental study between advanced carbon nanostructured electrodes, in similar hydrogen uptake/desorption conditions, is investigated making use of the recent molecular beam-thermal desorption spectrometry. This technique is used for monitoring hydrogen uptake and release from different carbon electrocatalysts: 3D-graphene, single-walled carbon nanotube networks, multi-walled carbon nanotube networks, and carbon nanotube thread. It allows an accurate determination of the hydrogen mass absorbed in electrodes made from these materials, with significant enhancement in the signal-to-noise ratio for trace hydrogen avoiding recourse to ultra-high vacuum procedures. The hydrogen mass spectra account for the enhanced surface capability for hydrogen adsorption in the different types of electrode in similar uptake conditions, and confirm their enhanced hydrogen storage capacity, pointing to a great potential of carbon nanotube threads in replacing the heavier metals or metal alloys as hydrogen storage media.publishersversionpublishe

Gestão de sistemas: problemas e soluções baseados em casos de estudo

Durante a última década, os computadores pessoais invadiram os ambientes empresariais substituindo soluções centralizadas e mudando a aquisição, processamento, fluxo e armazenamento de informação dentro de organizações. Esta explosão de novos sistemas, se por um lado dotou os utilizadores finais de mais e melhores ferramentas, por outro elevou grandemente os custos de operação e manutenção. Neste artigo discutem-se alguns do problemas inerentes à democratização dos computadores pessoais, descrevem-se dois casos de estudo e apontam-se soluções e resultados de como lidar com esta complexidade

A macro-physics model of depreciation rate in economic exchange

This article aims at a new approach for a known fundamental result: barter or trade increases economic value. It successfully bridges the gap between the theory of value and the exchange process attached to the transition from endowments to the equilibrium in the core and contract curve. First, we summarise the theory of value; in Section 2, we present the Edgeworth (1881) box and an axiomatic approach and in Section 3, we apply our pure exchange model. Finally (in Section 4), using our open econo-physics pure barter (EPB) model, we derive an improvement in value, which means that pure barter leads to a decline in depreciation rate

An impulsive framework for the control of hybrid systems

An impulsive control formulation suitable for analyzing hybrid systems is presented. Besides a continuous evolution, the trajectory of an impulsive control system may also exhibit jumps. The jump trajectory is well characterized in this impulsive framework. These jumps can be interpreted as the discrete evolution of an hybrid system. Several examples of hybrid systems modeled in the impulsive framework are given. An impulsive formulation of a formation control problem, regarded as an hybrid system is detailed. Finally, an overview of important classes of control results available for impulsive control systems, notably, stability and optimality, attest the importance of this paradigm for the control of hybrid systems. These results are essential to investigate the properties of model predictive control schemes for hybrid systems