Characterisation of a collection of perennial Panicum species

A collection of 74 perennial Panicum accessions, belonging to 6 different species, maintained at the field genebank of the International Livestock Research Institute, was described using 49 agromorphological characters in a multivariate analysis. Fifty-four accessions, for which coordinates of the collection site were available, were further characterised using environmental data obtained through use of geographic information systems. Three drought-tolerant species, P. antidotale, P. turgidum and P. phragmitoides, were very different agro-morphologically from the other species. Of these drought-tolerant species, P. phragmitoides appeared to have the best agromorphological attributes for use as forage in dry areas. P. maximum, P. coloratum and P. infestum appeared more similar, and were not entirely separated using cluster analysis. The accessions of these 3 species could be divided into 5 different clusters with similar characteristics. The majority of the P. maximum accessions belonged to 2 clusters, mainly differing in the size and robustness of the plants. A strong correlation was found between characters describing the robustness of the P. maximum plant and the annual precipitation at the collection site. Promising P. maximum accessions for use in cut-and-carry systems were identified

Extremum Seeking With Enhanced Convergence Speed for Optimization of Time-Varying Steady-State Behavior of Industrial Motion Stages

Recently, an extremum-seeking control (ESC) approach has been developed for optimization of generically time-varying steady-state responses of nonlinear systems. A generic filter structure was introduced, the so-called dynamic cost function, which has been instrumental in facilitating the use of ESC in the more generic, time-varying context. However, the dynamic cost function must operate sufficiently slow compared to the time-varying nature of the system responses, thereby compromising the convergence speed of the ESC scheme. In this work, a modified ESC approach is proposed that incorporates explicit knowledge about the user-defined dynamic cost function, able to enhance the convergence speed of the ESC scheme. Moreover, we provide a stability analysis for this extended approach. The main contribution of this work is the experimental demonstration of both ESC approaches for the performance optimal tuning of a variable-gain control (VGC) strategy employed on a high-accuracy industrial motion stage setup, exhibiting generically time-varying steady-state responses. VGC is able to enhance the system performance by balancing the typical linear control tradeoff between low-frequency disturbance suppression properties and sensitivity to high-frequency disturbances in a more desirable manner. We experimentally show that, for the unknown disturbance situation at hand, the variable-gain controller can be automatically tuned using both ESC approaches to achieve the optimal system performance. In addition, enhanced convergence speed with the modified ESC approach is evidenced experimentally.acceptedVersio

Optimal H∞ LMI-based model reduction by moment matching for linear time-invariant models

This paper proposes an approach to model order reduction of stable linear time-invariant (LTI) models. The proposed approach extends time-domain moment matching by the minimization of the H∞ norm of the error dynamics characterizing the difference between the full-order and reduced-order models given fixed interpolation points. The optimal H∞ moment matching problem is a constrained optimization problem with bilinear constraints. Introducing a novel numerical procedure, we minimize the approximation error, while respecting the constraints and, thereby, find a suboptimal H∞ reduced-order model. The effectiveness of the approach is illustrated in a numerical example

Error estimation in reduced basis method for systems with time-varying and nonlinear boundary conditions

Many physical phenomena, such as mass transport and heat transfer, are modeled by systems of partial differential equations with time-varying and nonlinear boundary conditions. Control inputs and disturbances typically affect the system dynamics at the boundaries and a correct numerical implementation of boundary conditions is therefore crucial. However, numerical simulations of high-order discretized partial differential equations are often too computationally expensive for real-time and many-query analysis. For this reason, model complexity reduction is essential. In this paper, it is shown that the classical reduced basis method is unable to incorporate time-varying and nonlinear boundary conditions. To address this issue, it is shown that, by using a modified surrogate formulation of the reduced basis ansatz combined with a feedback interconnection and a input-related term, the effects of the boundary conditions are accurately described in the reduced-order model. The results are compared with the classical reduced basis method. Unlike the classical method, the modified ansatz incorporates boundary conditions without generating unphysical results at the boundaries. Moreover, a new approximation of the bound and a new estimate for the error induced by model reduction are introduced. The effectiveness of the error measures is studied through simulation case studies and a comparison with existing error bounds and estimates is provided. The proposed approximate error bound gives a finite bound of the actual error, unlike existing error bounds that grow exponentially over time. Finally, the proposed error estimate is more accurate than existing error estimates

Error estimates for model order reduction of Burgers' equation

Burgers' equation is a nonlinear scalar partial differential equation, commonly used as a testbed for model order reduction techniques and error estimates. Model order reduction of the parameterized Burgers' equation is commonly done by using the reduced basis method. In this method, an error estimate plays a crucial rule in both accelerating the offline phase and quantifying the error induced after reduction in the online phase. In this study, we introduce two new estimates for this reduction error. The first error estimate is based on a Lur'e-type model formulation of the system obtained after the full-discretization of Burgers' equation. The second error estimate is built upon snapshots generated in the offline phase of the reduced basis method. The second error estimate is applicable to a wider range of systems compared to the first error estimate. Results reveal that when conditions for the error estimates are satisfied, the error estimates are accurate and work efficiently in terms of computational effort

Guideline versus non-guideline based management of rectal cancer in octogenarians

The number of octogenarians with rectal adenocarcinoma is growing. Current guidelines seem difficult to apply on octogenarians which may result in non-adherence. The aim of this retrospective cohort study is to give insight in occurrence of treatment-related complications, hospitalisations and survival among octogenarians treated according to guidelines versus octogenarians treated otherwise. 108 octogenarians with rectal adenocarcinoma were identified by screening of medical records. 22 patients were excluded for treatment process analysis because of stage IV disease or unknown stage. Baseline characteristics, diagnostic process, received treatment, motivation for deviation from guidelines, complications, hospitalisations and date of death were documented. Patients were divided in two groups depending on adherence to treatment guidelines. Differences in baseline characteristics, treatment-related complications and survival between both groups were evaluated. Diagnosis and treatment according to guidelines occurred in 95 and 54% of the patients, respectively. When documented, patient's preference and comorbidities were major reasons to deviate from guidelines. 66% of patients who were treated according to guidelines experienced complications versus 34% of those treated otherwise (p = 0.02). After adjustment for differences in age and polypharmacy, this association was not significant. Patients treated according to the guideline had better survival 18 months after diagnosis (80 versus 56%, p = 0.02). Treating octogenarians with rectal cancer according to guidelines seem to lead to better overall survival, but may lead to a high risk of complications. This may jeopardise quality of life. More and prospective studies in octogenarians with rectal cancer are needed to customize guidelines for these patients

Water vasthouden aan de bron: inzicht door modelberekeningen

De meest effectieve strategie voor de reductie van piekafvoeren, water vasthouden, is bergen van water bij de bron, waarbij de afstroming van water op perceelsniveau wordt bemoeilijkt. Om een onderbouwd inzicht in effect en relevantie van water vasthouden te krijgen zijn, in samenspraak met betrokken instanties, vijf maatregelen met behulp van de computercode SIMGRO geëvalueerd in de stroomgebieden Peelsche Loop, Groote Wetering en Raamsloop. Piekafvoeren kunnen met 3 tot 45% worden gereduceerd. De meest effectieve manier om water vast te houden is het voorkómen van maaiveldafvoer waarbij water tijdelijk op het maaiveld wordt geborgen, met als neveneffect structurele grondwaterstandverhogingen en effecten op de landbouw. Minder effectieve maatregelen hebben een marginaal effect op de regionale hydrologie. Inundaties verdwijnen sneller met goede drainage