Stability Analysis of Piecewise Affine Systems with Multi-model Model Predictive Control

Constrained model predictive control (MPC) is a widely used control strategy, which employs moving horizon-based on-line optimisation to compute the optimum path of the manipulated variables. Nonlinear MPC can utilize detailed models but it is computationally expensive; on the other hand linear MPC may not be adequate. Piecewise affine (PWA) models can describe the underlying nonlinear dynamics more accurately, therefore they can provide a viable trade-off through their use in multi-model linear MPC configurations, which avoid integer programming. However, such schemes may introduce uncertainty affecting the closed loop stability. In this work, we propose an input to output stability analysis for closed loop systems, consisting of PWA models, where an observer and multi-model linear MPC are applied together, under unstructured uncertainty. Integral quadratic constraints (IQCs) are employed to assess the robustness of MPC under uncertainty. We create a model pool, by performing linearisation on selected transient points. All the possible uncertainties and nonlinearities (including the controller) can be introduced in the framework, assuming that they admit the appropriate IQCs, whilst the dissipation inequality can provide necessary conditions incorporating IQCs. We demonstrate the existence of static multipliers, which can reduce the conservatism of the stability analysis significantly. The proposed methodology is demonstrated through two engineering case studies.Comment: 28 pages 9 figure

Emergent management of complicated paraesophageal hernia due to distal gastrointestinal obstruction: three-case series

Background:The aim of this study is to describe the diagnostic evaluation and treatment in patients with complicated paraesophageal hernia (PEH) and distal gastrointestinal (GI) obstruction.Methods:Three cases with known PEH in the Department of Surgery of the General Hospital of Nea Ionia ‘’Constantopoulion-Patission’’, I woman 78 yrs, II man 88 and III man 78, underwent emergent open surgery for complicated PEH and GI obstruction. Cardiorespiratory distress in all and sepsis in I, were encountered. Case I had coexistent incarcerated abdominal hernia, II had a prepyloric lesion revealed by gastroscopy and III chronic constipation. X-rays and CT scan helped diagnosis. Operative findings: In case I, we found viable incarcerated bowel, gastric fundus and body strangulated in mediastinum, fundus ruptured, and antrum ischemic; total gastrectomy with esophageal and duodenal stapling were performed. In case II, the stomach with an obstructive prepyloric lesion was volvulized in mediastinum; distal gastrectomy, gastrojejunostomy,cruroraphy and fundopexy were performed. In case III, strangulation of the dolichosigmoid was the prominent feature, moreover, incarceration of gastric fundus and transverse colon in PEH sac were also found; reduction of PEH contents, limited resection of thick congenital bands, extended left colectomy, cruroraphy, fundopexyand caecopexy were performed.Results:Case I and II were transferred intubated to ICU. Case I was never stabilized, died after 50 hours; histology confirmed gastric necrosis. Case II was extubated on day 4, discharged on day 28; histology revealed antral ischemia and prepyloric pT2 adenocarcinoma. Case III had uneventful outcome; histology revealed dolichosigmoid ischemia. Follow-up of cases II and III (32 and 30 months respectively) has been uneventful.Conclusion:Obstructive conditions distal to large PEHs may lead to acute complications in hernia contents and emergent surgery is challenging. Obstructive conditions distal to large PEHs may lead to acute complications in hernia contents and emergent surgery is challenging

Microalgae strain catalogue:A strain selection guide for microalgae users: cultivation and chemical characteristics for high added-value products (3rd Edition)

The 3rd edition of this catalogue contains information on the cultivation and composition characteristics of 37 microalgae. Each entry includes relevant links to Atlantic Area stakeholders known to have a relevant connection with each of the species listed, be it in the form of culture collections, research expertise, technology developers, or biomass producers. We invite the readers to visit and/or join the EnhanceMicroAlgae Stakeholder database: an easily accessible, visual and open access database that brings together all the European Atlantic Area players working in the microalgae sector

Structured population balances to support microalgae-based processes: Review of the state-of-art and perspectives analysis

Design and optimization of microalgae processes have traditionally relied on the application of unsegregated mathematical models, thus neglecting the impact of cell-to-cell heterogeneity. However, there is experimental evidence that the latter one, including but not limited to variation in mass/size, internal composition and cell cycle phase, can play a crucial role in both cultivation and downstream processes. Population balance equations (PBEs) represent a powerful approach to develop mathematical models describing the effect of cell-to-cell heterogeneity. In this work, the potential of PBEs for the analysis and design of microalgae processes are discussed. A detailed review of PBE applications to microalgae cultivation, harvesting and disruption is reported. The review is largely focused on the application of the univariate size/mass structured PBE, where the size/mass is the only internal variable used to identify the cell state. Nonetheless, the need, addressed by few studies, for additional or alternative internal variables to identify the cell cycle phase and/or provide information about the internal composition is discussed. Through the review, the limitations of previous studies are described, and areas are identified where the development of more reliable PBE models, driven by the increasing availability of single-cell experimental data, could support the understanding and purposeful exploitation of the mechanisms determining cell-to-cell heterogeneity