Real-time control of a laboratory heat exchanger using the particle swarm optimisation algorithm

In the past decade, evolutionary based algorithms have been a popular research theme in many disciplinary areas like control systems. Although, due to the computational load required, this type of algorithms usually are applied off-line. In this paper, a stochastic search algorithm known as particle swarm is used as an optimisation tool for on-line control of a custom made laboratory thermodynamic system

Hardware-in-the-loop control using the particle swarm optimisation

In the last two decades, evolutionary based algorithms have proved to be an important tool in solving optimisation problems in many disciplinary areas namely in control system design. However one of its limitations, for some type of applications, is the usually high computational load required, which restricts its use for on-line control. This paper proposes the use of a stochastic search algorithm, known as particle swarm, as an optimisation tool for an on-line predictive control of a custom made thermodynamic system. Preliminary results are presented

Greenhouse air temperature control using the particle swarm optimisation algorithm

The particle swarm optimisation algorithm is proposed as a new method to design a model based predictive controller subject to restrictions. Its performance is compared with the one obtained by using a genetic algorithm for the environmental temperature control of a greenhouse. Controller outputs are computed in order to optimise future behaviour of the greenhouse environment, regarding set-point tracking and minimisation of the control effort over a prediction horizon of one hour with a one-minute sampling period

Greenhouse air temperature modelling

This paper describes two implementation approaches for modelling the air temperature of an automated greenhouse located in the campus of the University of Trás-os- Montes e Alto Douro. Linear models, based in the discretization of the heat transfer physical laws, and non-linear neural networks models are used. These models are describes as functions of the outside climate and control actions performed for heating and cooling. Results are presented to illustrate the performance of each model in the simulation and prediction of the greenhouse air temperature. The data used to compute the simulation models was collected with a PC-based acquisition and control system using a sampling time interval of 1 minute.The authors appreciate the support of the Portuguese Foundation for Science and Technology (FCT) through the project MGS/ 33906/2000

Valorização agrícola de resíduo orgânico produzido por empresa do sector têxtil

Comunicação oral da qual só está disponível o resumo.Valorização agrícola de resíduo orgânico produzido por empresa do sector têxtil

Operation of a perfusive catalytic membrane with nonlinear kinetics

Operation of a perfusive catalytic curved membrane is systematized into different transport-reaction regimes. The internal viscous permeation improves the catalyst performance, measured here by the effectiveness factor and by its enhancement relative to purely diffusive conditions. A theoretical analysis is presented for nonlinear kinetic expressions, which are suitable to describe the consumption of a reactant in many (bio)catalytic systems. The kinetic and transport parameters required to attain maximum enhancement are related by simple design rules, which depend on the form of the reaction rate law (namely on the order of reaction and dimensionless inhibition constant). For zero-order reactions, these optimum conditions correspond to attaining negligible concentration at a position inside the membrane, while may be interpreted in general as separating situations of severe mass transfer resistance from cases of high effectiveness. It is important to incorporate the correct form of the kinetic expression in the analysis, so that the predictions can be used in a quantitative manner. The results for the different regimes are compiled in enhancement plots and in Peclet–Thiele diagrams. Moreover, the study also yielded new results for the nonlinear reaction–diffusion problem in a curved membrane with its two surfaces exposed to different concentrations, a case of relevance in membrane reactors

The VMC survey III : Mass-loss rates and luminosities of LMC AGB stars

Context. Asymptotic giant branch (AGB) stars are major contributors to both the chemical enrichment of the interstellar medium and the integrated light of galaxies. Despite its importance, the AGB is one of the least understood phases of stellar evolution. The main difficulties associated with detailed modelling of the AGB are related to the mass-loss process and the 3rd dredge-up efficiency Aims. We provide direct measures of mass-loss rates and luminosities for a complete sample of AGB stars in the Large Magellanic Cloud, disentangling the C- and O-rich stellar populations. Methods. Dust radiative transfer models are presented for all 374 AGB stars candidates in one of the fields observed by the new VISTA survey of the Magellanic Clouds (VMC). Mass-loss rates, luminosities and a classification of C-and O-rich stars are derived by fitting the models to the spectral energy distribution (SED) obtained by combining VMC data with existing optical, near-, and mid-infrared photometry. Results. The classification technique is reliable at a level of - at worst -75% and significantly better for the reddest dusty stars. We classified none of the stars with a relevant mass-loss rate as O-rich, and we can exclude the presence of more than one dusty O-rich star at a similar to 94% level. The bolometric luminosity function we obtained is fully consistent with most of the literature data on the LMC and with the prediction of theoretical models, with a peak of the C-star distribution at M-bol similar or equal to -4.8 mag and no stars brighter than the classical AGB tip, at M-bol = -7.1 mag. Conclusions. This exploratory study shows that our method provides reliable mass-loss rates, luminosities and chemical classifications for all AGB stars. These results offer already important constraints to AGB evolutionary models. Most of our conclusions, especially for the rarer dust-enshrouded extreme AGB stars, are however strongly limited by the relatively small area covered by our study. Forthcoming VMC observations will easily remove this limitation.Peer reviewe

Phase Diversity For Speckle Reduction

B-mode ultrasound images are characterised by speckle artefact, which results from interference effects between returning echoes, and may make the interpretation of images difficult. Consequently, many methods have been developed to reduce this problematic feature. One widely used method, popular in both medical and non-destructive-testing applications, is a 1D method known as Split Spectrum Processing (SSP), or also as Frequency Diversity. Alhough this method was designed for speckle reduction applications, the final image experiences a resultant loss of resolution, impinging a trade-off between speckle reduction and resolution loss. In order to overcome this problem, we have developed a new method that is an extension of SSP to 2D data using directive filters, called Split Phase Processing (SPP). Instead of using ID narrow band-pass filters as in the SSP method, we use 2D directive filters to split the RF ultrasound image in a set of wide band images with different phases. The use of such filters substantially avoids the resolution loss usually associated with SSP for speckle reduction, because they effectively have the same bandwidth as the original image. It is concluded that the Split Phase Processing, as introduced here, provides a significant improvement over the conventional Split Spectrum Processing.5035414422Burckhardt, C.B., Speckle in ultrasound b-mode scans (1978) IEEE Trans. Sonics and Ultrasonics, 25 (1), pp. 1-6. , JanuaryChen, Y., Yin, R., Hynn, P., Broschat, S., Aggressive region growing for speckle reduction in ultrasound images (2003) Pattern Recognition Letters, 24 (4-5), pp. 677-691. , FebruaryGehlbach, S.M., (1983) Pulse Reflection Imaging and Acoustic Speckle, , Ph.D. dissertation, Stanford UniversityHealey, A.J., Leeman, S., Ferrari, L.A., Removing the ambiguity from single image speckle reduction techniques (1996) Acoustical Imaging, 22, pp. 145-150Li, P.C., Odonnell, M., Evaluational spatial compounding (1994) Ultrasonic Imaging, 16 (3), pp. 176-189Shankar, P.M., Newhouse, V.L., Speckle reduction with improved resolution in ultrasound images (1985) IEEE Trans. Sonics and Ultrasonics, 32 (4), pp. 537-543. , Jul

Nonuniqueness and derivative discontinuities in density-functional theories for current-carrying and superconducting systems

Current-carrying and superconducting systems can be treated within density-functional theory if suitable additional density variables (the current density and the superconducting order parameter, respectively) are included in the density-functional formalism. Here we show that the corresponding conjugate potentials (vector and pair potentials, respectively) are {\it not} uniquely determined by the densities. The Hohenberg-Kohn theorem of these generalized density-functional theories is thus weaker than the original one. We give explicit examples and explore some consequences.Comment: revised version (typos corrected, some discussion added) to appear in Phys. Rev.