Leuven, Belgium
Leuven, Belgium

Time filter

Source Type

Miao S.,Center for Surface Chemistry and Catalysis | Leeman H.,Center for Surface Chemistry and Catalysis | De Feyter S.,Celestijnenlaan | Schoonheydt R.A.,Center for Surface Chemistry and Catalysis
Chemistry - A European Journal | Year: 2010

The Langmuir-Blodgett (L- B) technique has been employed for the construction of hybrid films consisting of three components: surfactant, clay, and lysozyme (Lys). The surfactants are octadecylammonium chloride (ODAH) and octadecyl ester of rhodamine B (RhB18). The clays include saponite and laponite. Surface pressure versus area isotherms indicate that lysozyme is adsorbed by the surfactant- clay L-B film at the air-water interface without phase transition. The UV-visible spectra of the hybrid film ODAH- saponite-Lys show that the amount of immobilized lysozyme in the hybrid film is (1.3±0.2) ngmm-2. The average surface area (Ω) per molecule of lysozyme is approximately 18.2 nm2 in the saponite layer. For the multilayer film (ODAH-saponite-Lys)n, the average amount of lysozyme per layer is (1.0± 0.1) ngmm-2. The amount of lysozyme found in the hybrid films of ODAH-laponite- Lys is at the detection limit of about 0.4 ngmm-2. Attenuated total reflectance (ATR) FTIR spectra give evidence for clay layers, ODAH, lysozyme, and water in the hybrid film. The octadecylammonium cations are partially oxidized to the corresponding carbamate. A weak 1620 cm-1 band of lysozyme in the hybrid films is reminiscent of the presence of lysozyme aggregates. AFM reveals evidence of randomly oriented saponite layers of various sizes and shapes. Individual lysozyme molecules are not resolved, but aggregates of about 20 nm in diameter are clearly seen. Some aggregates are in contact with the clay mineral layers, others are not. These aggregates are aligned in films deposited at a surface pressure of 20 mNm-1. © 2010 Wiley-VCH Verlag GmbH&Co. KGaA, Weinheim.

Miao S.,Center for Surface Chemistry and Catalysis | Leeman H.,Center for Surface Chemistry and Catalysis | De Feyter S.,Celestijnenlaan | Schoonheydt R.A.,Center for Surface Chemistry and Catalysis
Journal of Materials Chemistry | Year: 2010

Water-soluble protein monolayers have been prepared by spreading protein (lysozyme (Lys) and bovine serum albumin (BSA)) aqueous solutions over water and diluted clay (saponite) dispersions in a Langmuir-Blodgett (LB) trough. LB films of protein and hybrid protein-clay were prepared by vertical upstroke deposition at a desired surface pressure. Surface pressure-time (π-t) curves and surface pressure-area isotherms (π-A) indicate that the equilibrium time between the injection and compression plays an important role in forming a protein monolayer. Atomic force microscopy (AFM) suggests that heterogeneous films, consisting of regions of protein clusters and regions of saponite layers covered with protein clusters, are obtained. Both lysozyme and BSA accumulate particularly well at the edges of the saponite layers. The main difference is that the positively charged lysozyme is much more efficient in attracting negatively charged saponite layers at the air-water interface. The amount of lysozyme immobilized (nS) is 0.2-0.4 ng mm-2 for the water-lysozyme film and 0.5-0.6 ng mm-2 for the saponite-lysozyme film, as determined using UV-Vis spectroscopy. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) confirmed the presence of clay and proteins in the hybrid LB films. No significant change in the position of amide I or II bands was observed, suggesting little or no conformational changes upon immobilization of the proteins. © 2010 The Royal Society of Chemistry.

Van Den Broeck L.,Celestijnenlaan | Diehl M.,Kasteelpark Arenberg | Swevers J.,Celestijnenlaan
Mechatronics | Year: 2011

This paper presents a new model predictive control method for time-optimal point-to-point motion control of mechatronic systems. The formulation of time-optimal behavior within the model predictive control framework and the structure of the underlying optimization problem are discussed and modifications are presented in order to decrease the computational load of the numerical solution method such that sampling rates in the millisecond range and long prediction horizons for large point-to-point motions are feasible. An extensive experimental validation on a linear motor drive and an overhead crane setup demonstrates the advantages of the developed time-optimal model predictive control approach in comparison with traditional model predictive control. © 2011 Elsevier Ltd. All rights reserved.

Demol J.,Celestijnenlaan | Lambrechts D.,Celestijnenlaan | Geris L.,Celestijnenlaan | Schrooten J.,Kasteelpark Arenberg | Van Oosterwyck H.,Celestijnenlaan
Biomaterials | Year: 2011

The in vitro culture of hydrogel-based constructs above a critical size is accompanied by problems of unequal cell distribution when diffusion is the primary mode of oxygen transfer. In this study, an experimentally-informed mathematical model was developed to relate cell proliferation and death inside fibrin hydrogels to the local oxygen tension in a quantitative manner. The predictive capacity of the resulting model was tested by comparing its outcomes to the density, distribution and viability of human periosteum derived cells (hPDCs) that were cultured inside fibrin hydrogels in vitro. The model was able to reproduce important experimental findings, such as the formation of a multilayered cell sheet at the hydrogel periphery and the occurrence of a cell density gradient throughout the hydrogel. In addition, the model demonstrated that cell culture in fibrin hydrogels can lead to complete anoxia in the centre of the hydrogel for realistic values of oxygen diffusion and consumption. A sensitivity analysis also identified these two parameters, together with the proliferation parameters of the encapsulated cells, as the governing parameters for the occurrence of anoxia. In conclusion, this study indicates that mathematical models can help to better understand oxygen transport limitations and its influence on cell behaviour during the in vitro culture of cell-seeded hydrogels. © 2010 Elsevier Ltd.

Depraetere B.,Celestijnenlaan | Pinte G.,FMTC | Symens W.,FMTC | Swevers J.,Celestijnenlaan
Mechatronics | Year: 2011

This paper discusses the application of Iterative Learning Control (ILC) algorithms for the engagement of wet clutches. A two-level control scheme is presented, consisting of a high level ILC-type algorithm which iteratively updates parameterized reference trajectories which are tracked by the low level tracking control. At this low level, two standard ILC controllers are used to first track a pressure reference in the filling phase and afterwards a slip reference in the slip phase of the clutch engagement. The performance and robustness of the presented approach are validated on an experimental test setup. It is shown that both levels are crucial to achieve good engagement quality during normal machine operation. Through the use of this ILC control scheme, it is possible to avoid time-consuming and cumbersome experimental (re)calibrations, which are nowadays used to achieve and maintain good performance despite the complex and time-varying dynamics of wet clutches. © 2011 Elsevier Ltd. All rights reserved.

Mojid M.A.,Bangladesh Agricultural University | Wyseure G.C.L.,Celestijnenlaan | Biswas S.K.,Bangladesh Agricultural University | Hossain A.B.M.Z.,Bangladesh Agricultural University
Agricultural Water Management | Year: 2010

By interviewing farmers in twelve peri-urban and two sugar mill areas information was collected on the use of urban wastewater. In all cases, untreated sewage water was used without primary treatment. The domestic polluted water originated from household kitchen, cloth wash, bathroom shower, and other municipal sources (e.g., supermarkets, restaurants, offices). Moreover it was often diluted by urban storm-water drainage. Major quality parameters of the wastewater were determined. The boron, iron, sodium, nitrogen, phosphate and zinc content along with the electrical conductivity and pH of the wastewater, with few exceptions, were lower than their safe limits for irrigation. The manganese content always exceeded the recommended threshold limit. Most farmers irrigated rice (Oryza sativa L.), and, in few locations, potato (Solanum tuberosum L.), wheat (Triticum aestium L.) and vegetables (e.g., tomato; Lycopersicon esculentum L.) with wastewater. At one peri-urban area, farmers stopped irrigating with wastewater after having (free) access to freshwater. The farmers at another area were very concerned of its negative impact on human and soil health. Because of high temperature and impurities, only few farmers used wastewater for irrigating sugarcane (Saccharum sp. L.) and rice by diluting it during the scarcity of freshwater at one sugar mill area, and only some tail-end farmers directly used it for irrigating rice at the other area. In this manuscript, the word 'wastewater' refers to 'untreated sewage water'. In Bangladesh, water treatment is rare.Farmers articulated two opposing attitudes for irrigating with wastewater. They recognized fertility, reliability and low cost of wastewater in one extent, and viewed, as negative elements, the presence of solid wastes, fecal matter, engine oil, grease, diesel, molasses, and harmful chemicals in the other extent. Also the social acceptability of wastewater was low. While working with wastewater, farmers faced multi-facet problems of blistering, skin infection, injury to hands and lower legs, bad smell, mosquito nuisance and damage to low-lift pumps due to solid wastes. Important considerations for preferring wastewater were to avoid high cost of pumping groundwater and to save on chemical fertilizers. Also, farmers did not perceive any problem with the quality of the yield. The farmers strongly felt a necessity of primary treatment of wastewater to remove solid wastes, heavy ones by settling and suspended ones by separation, before irrigation. Although aware of the fertility value of wastewater, most farmers lacked knowledge on how to adjust its doses. All these demonstrated a necessity of proper policy, training, and more information on health precautions as well as on food safety in using urban wastewater. © 2010 Elsevier B.V.

Allaerts D.,Celestijnenlaan | Meyers J.,Celestijnenlaan
Journal of Physics: Conference Series | Year: 2014

In this study we consider large wind farms in a conventionally neutral atmospheric boundary layer. In large wind farms the energy extracted by the turbines is dominated by downward vertical turbulent transport of kinetic energy from the airflow above the farm. However, atmospheric boundary layers are almost always capped by an inversion layer which slows down the entrainment rate and counteracts boundary layer growth. In a suite of large eddy simulations the effect of the strength of the capping inversion on the boundary layer and on the performance of a large wind farm is investigated. For simulations with and without wind turbines the results indicate that the boundary layer growth is effectively limited by the capping inversion and that the entrainment rate depends strongly on the inversion strength. The power output of wind farms is shown to decrease for increasing inversions. © Published under licence by IOP Publishing Ltd.

Kellens K.,Celestijnenlaan | Rodrigues G.C.,Celestijnenlaan | Dewulf W.,Celestijnenlaan | Duflou J.R.,Celestijnenlaan
Physics Procedia | Year: 2014

Due to increasing energy and resource costs at the one hand and upcoming regulations on energy and resource efficiency at the other, a growing interest of machine tool builders in the environmental performance of their machine tools can be observed today. The last decade, academic as well as industrial research groups started to assess the environmental aspects of discrete part manufacturing processes and indicated a significant potential for improvement [1]. This paper provides an overview of the environmental performance (energy and resource efficiency) of different types of laser cutting systems and derived performance improving strategies. © 2014 The Authors. Published by Elsevier B.V.

Chys P.,Catholic University of Leuven | Gielens C.,Catholic University of Leuven | Meersman F.,Celestijnenlaan
Biochimica et Biophysica Acta - Proteins and Proteomics | Year: 2011

An alkali-pretreated gelatin (pI ~ 4.9) was fractionated by means of alcohol coacervation and semi-preparative gel chromatography. The thermal responses of the isolated α fractions, the coacervate and the total gelatin were investigated by 2D-correlation FTIR spectroscopy in the amide I band region (1600-1700 cm- 1). The gelation temperature was the same for all examined samples (24.5 °C) while the melting temperature of the α2 fraction was lower (30 °C) than that of the other samples (32.5 °C). The 2D COS plots indicate that on cooling (gelation) the core sequence of conformational changes is the same for all samples. On heating, however, the α2 fraction deviates from the α1-containing samples and shows an earlier disappearance of the triple helix signal in the event sequence. The lower melting temperature (less thermostable gelatin gel) of the α2 fraction thus results from a different conformational cascade of the α2 chains upon melting. In all samples the initial conformational changes take place in the β-turns, providing further evidence for the models proposed previously. © 2010 Elsevier B.V. All rights reserved.

Van Snick S.,Celestijnenlaan | Dehaen W.,Celestijnenlaan
Organic and Biomolecular Chemistry | Year: 2012

A new synthetic pathway towards 2,8-difunctionalised indolo[3,2-b] carbazoles was investigated. The presented method offers a short and high yielding route towards 2,8-dibromo-5,11-dihexyl-6,12-diphenyl-indolo[3,2-b] carbazole. It is demonstrated that the latter compound is a versatile building block, enabling the synthesis of a number of previously unreported 5,11-dialkyl-6,12-diphenyl-indolo[3,2-b]carbazoles in moderate to good yields, using Suzuki and Sonogashira cross-coupling reaction. Furthermore it is shown that 2,8-dibromo-5,11-dihexyl-6,12-diphenyl-indolo[3,2-b]carbazole can be easily formylated, giving rise to the 2,8-diformyl-5,11-dihexyl-6,12-diphenyl-indolo- [3,2-b]carbazole. The latter compound was successfully subjected to condensation reactions.

Loading Celestijnenlaan collaborators
Loading Celestijnenlaan collaborators