Delft University of Technology

About: Delft University of Technology is a education organization based out in Delft, Zuid-Holland, Netherlands. It is known for research contribution in the topics: Computer science & Catalysis. The organization has 37681 authors who have published 94404 publications receiving 2741710 citations. The organization is also known as: TU-Delft & Technische Hogeschool Delft.

How to make a living from anaerobic ammonium oxidation.

Abstract: Anaerobic ammonium-oxidizing (anammox) bacteria primarily grow by the oxidation of ammonium coupled to nitrite reduction, using CO2 as the sole carbon source. Although they were neglected for a long time, anammox bacteria are encountered in an enormous species (micro)diversity in virtually any anoxic environment that contains fixed nitrogen. It has even been estimated that about 50% of all nitrogen gas released into the atmosphere is made by these ‘impossible’ bacteria. Anammox catabolism most likely resides in a special cell organelle, the anammoxosome, which is surrounded by highly unusual ladder-like (ladderane) lipids. Ammonium oxidation and nitrite reduction proceed in a cyclic electron flow through two intermediates, hydrazine and nitric oxide, resulting in the generation of proton-motive force for ATP synthesis. Reduction reactions associated with CO2 fixation drain lectrons from this cycle, and they are replenished by the oxidation of nitrite to nitrate. Besides ammonium or nitrite, anammox bacteria use a broad range of organic and inorganic compounds as electron donors. An analysis of the metabolic opportunities even suggests alternative chemolithotrophic lifestyles that are independent of these compounds. We note that current concepts are still largely hypothetical and put forward the most intriguing questions that need experimental answers.

On the numerical integration of interface elements

Abstract: SUMMARY Eigenmode analyses of the element stiffness matrices have been used to assess the impact of the applied integration scheme on the stress predictions of two- and three-dimensional plane interface elements. It is demonstrated that large stress gradients over the element and coupling of the individual node-sets of the interface element may result in an oscillatory type of response. For line elements and linear plane interface elements the performance can be improved by using either a nodal lumping scheme or Newton-Cotes or Lobatto integration schemes instead of the more traditional Gauss scheme. For quadratic interface elements the same holds true except for a nodal lumping scheme. Interface elements are a powerful tool in the modelling of geometrical discontinuities in different kinds of structures. In finite element analysis of civil engineering structures a large variety of applications for interface elements is present. Interface elements can be used to model soil reinforcement interaction,' to model the intermediate layer between rock and concrete, e.g. in arch dam or in the analysis of rock joints.536 Applications in concrete mechanics cover the modelling of discrete cracking,'~~ aggregate interlock9 and bond between concrete and reinforcement."-I4 In rubber parts, interface elements can be of importance when disintegration of rubber and texture is concerned, e.g. in conveyor belts. Furthermore, interface elements are suited to model delamination in layered composite structures' ', or frictional contact in forming processes. Interface elements can bc divided into two elementary classes. The first class contains the continuous interface elements (line, plane and shell interface^),^-^^"-'*, 2"+23 whereas the second class of elements contains the nodal or point interface elernent~,'~'~,~ ~ which, to a certain extent, are identical to spring elements. In this contribution we shall only consider the numerically and lumped integrated continuous interface elements, since nodal interfaces are integrated explicitly. A basic requirement of interface elements is that during the elastic mge of the loading process no significant additional deformations occur due to the presence of these elements in the finite element model. Therefore, a sufficiently high initial dummy stiffness has to be supplied for the interface elemenls. Depending upon the applied numerical integration scheme, this high dummy stiffness may result in undesired spurious oscillations of the stress field. In this paper th'e impact of Gauss, Newton-Cotes, Lobatto and lumped integration schemes on the stress prediction in interfaces is investigated for three-dimensional linear and non-linear analyses. Eigenvalue analyses of the linear elastic and non-linear element stiffness matrices have been carried out to explain the observed oscillatory performance of interface elements. Since we shall focus on 0029-598 1/93/010043+ 24$17.00 0 1993 by John Wiley & Sons, Ltd.

Socio-economic status, dietary intake and 10 y trends: the Dutch National Food Consumption Survey.

Abstract: Objective: To study differences in dietary intake between adults with different socioeconomic status (SES) and trends over time. Design: Cross-sectional study based on data of three Dutch National Food Consumption Surveys (DNFCS-1 1987/88; DNFCS-2 1992; DNFCS-3 1997/98), obtained from a panel by a stratified probability sample of the non-institutionalized Dutch population. Subjects: A total of 6008 men and 6957 women aged 19 y and over. Methods: Dietary intake was assessed with a 2 day dietary record. Background information was obtained by structured questionnaire. Sociodemographic variables were available from panel information. SES, based on educational level, occupation and occupational position was categorized into (very) low, middle and high. Analysis of variance with age as covariable was used to explore the effects of SES on dietary intake and anthropometry. Statistical tests for trend were carried out with models in which week-weekend-day effects and an interaction term of time with SES were also included. Results: The prevalence of obesity and skipping of breakfast was higher among people with a low SES. In all three surveys, subjects in the (very) low SES group reported having a higher consumption of potatoes, meat and meat products, visible fats, coffee and soft drinks (men only). Subjects with a high SES reported consuming more vegetables, cheese and alcohol. As regards nutrients, in all surveys a higher SES was associated with higher intake of vegetable protein, dietary fibre and most micronutrients. A higher SES was also associated with a lower fat intake but the differences between social classes were rather small and not consistent when the contribution of alcohol to energy intake was taken into account. Conclusion: In general, dietary intake among subjects in higher SES groups tended to be closer to the recommendations of the Netherlands Food and Nutrition Council and this phenomenon was quite stable over a period of 10y.

Auxetic mechanical metamaterials

Abstract: The surge of interest in so-called “designer materials” during the last few years together with recent advances in additive manufacturing (3D printing) techniques that enable fabrication of materials with arbitrarily complex nano/micro-architecture have attracted increasing attention to the concept of mechanical metamaterials. Owing to their rationally designed nano/micro-architecture, mechanical metamaterials exhibit unusual properties at the macro-scale. These unusual mechanical properties could be exploited for the development of materials with advanced functionalities, with applications in soft robotics, biomedicine, soft electronics, acoustic cloaking, etc. Auxetic mechanical metamaterials are identified by a negative Poisson's ratio and are perhaps the most widely studied type of mechanical metamaterials. Similar to other types of mechanical metamaterials, the negative Poisson's ratio of auxetics is generally a direct consequence of the topology of their nano/micro-architecture. This paper therefore focuses on the topology–property relationship in three main classes of auxetic metamaterials, namely re-entrant, chiral, and rotating (semi-) rigid structures. While the deformation mechanisms in the above-mentioned types of structures and their relationship with the large-scale mechanical properties receive most attention, the emerging concepts in design of auxetics such as the use of instability in soft matter and origami-based structures are discussed as well. Furthermore, the data available in the literature regarding the elastic properties of auxetic mechanical metamaterials are systematically analyzed to identify the spread of Young's modulus–Poisson's ratio duos achieved in the auxetic materials developed to date.

Metabolic engineering of a xylose-isomerase-expressing Saccharomyces cerevisiae strain for rapid anaerobic xylose fermentation

Abstract: After an extensive selection procedure, Saccharomyces cerevisiae strains that express the xylose isomerase gene from the fungus Piromyces sp. E2 can grow anaerobically on xylose with a μmax of 0.03 h−1. In order to investigate whether reactions downstream of the isomerase control the rate of xylose consumption, we overexpressed structural genes for all enzymes involved in the conversion of xylulose to glycolytic intermediates, in a xylose-isomerase-expressing S. cerevisiae strain. The overexpressed enzymes were xylulokinase (EC 2.7.1.17), ribulose 5-phosphate isomerase (EC 5.3.1.6), ribulose 5-phosphate epimerase (EC 5.3.1.1), transketolase (EC 2.2.1.1) and transaldolase (EC 2.2.1.2). In addition, the GRE3 gene encoding aldose reductase was deleted to further minimise xylitol production. Surprisingly the resulting strain grew anaerobically on xylose in synthetic media with a μmax as high as 0.09 h−1 without any non-defined mutagenesis or selection. During growth on xylose, xylulose formation was absent and xylitol production was negligible. The specific xylose consumption rate in anaerobic xylose cultures was 1.1 g xylose (g biomass)−1 h−1. Mixtures of glucose and xylose were sequentially but completely consumed by anaerobic batch cultures, with glucose as the preferred substrate.