Constrained Online Optimization Using Evolutionary Operation: A Case Study About Energy‐Optimal Robot Control

Optimization of full‐scale processes during regular production is a challenge that is often encountered in practice, requiring specialized approaches that only introduce small perturbations so that production does not need to be interrupted. Based on a case study, we discuss the potential of Evolutionary Operation (EVOP) derived methods. The case study relates to a badminton robot that has to perform point‐to‐point motions during a fixed time interval, based on two operation modes: time‐optimal motion, which ensures maximum precision but highest energy consumption, and energy‐optimal motion, which decreases the energy consumption, but as a trade‐off also lowers the precision. The current standard mode of operation is the energy‐optimal mode that is constructed from off‐line optimization on simulations. An online EVOP steepest ascent optimization to further reduce the energy consumption by fine‐tuning the implemented energy‐optimal mode was implemented. The constrained nature of the problem, where energy needs to be minimized subject to a time constraint, was transformed to an unconstrained single‐objective optimization using Derringer desirability functions. Two important contributions were made: (i) the online optimization of the energy‐optimal motion lowered the energy consumption by 4.7% while keeping the precision constant and (ii) the more stringent time‐constraints implemented in desirability functions lead to an operation mode with maximum precision and 51.7% less energy consumption than the current time‐optimal motion. Copyright © 2014 John Wiley & Sons, Ltd.     

Trehalose Analogues: Latest Insights in Properties and Biocatalytic Production

Trehalose (α-d-glucopyranosyl α-d-glucopyranoside) is a non-reducing sugar with unique stabilizing properties due to its symmetrical, low energy structure consisting of two 1,1-anomerically bound glucose moieties. Many applications of this beneficial sugar have been reported in the novel food (nutricals), medical, pharmaceutical and cosmetic industries. Trehalose analogues, like lactotrehalose (α-d-glucopyranosyl α-d-galactopyranoside) or galactotrehalose (α-d-galactopyranosyl α-d-galactopyranoside), offer similar benefits as trehalose, but show additional features such as prebiotic or low-calorie sweetener due to their resistance against hydrolysis during digestion. Unfortunately, large-scale chemical production processes for trehalose analogues are not readily available at the moment due to the lack of efficient synthesis methods. Most of the procedures reported in literature suffer from low yields, elevated costs and are far from environmentally friendly. “Greener” alternatives found in the biocatalysis field, including galactosidases, trehalose phosphorylases and TreT-type trehalose synthases are suggested as primary candidates for trehalose analogue production instead. Significant progress has been made in the last decade to turn these into highly efficient biocatalysts and to broaden the variety of useful donor and acceptor sugars. In this review, we aim to provide an overview of the latest insights and future perspectives in trehalose analogue chemistry, applications and production pathways with emphasis on biocatalysis.     

Epitaxy on Demand

Perovskite oxide heteroepitaxy is realized on the top of inorganic nanosheets that are covering the amorphous oxide surfaces of Si substrates. Utilizing pulsed laser deposition, thin films of SrRuO₃ in a (001)_pc and (110)_pc orientation on nanosheets of Ca₂Nb₃O₁₀ and Ti_0.87O₂ are grown, respectively. The two types of nanosheets are patterned to locally tailor the crystallographic orientation and properties of SrRuO₃. The success of our approach is demonstrated by electron backscatter diffraction and spatial magnetization maps. An unprecedented control of perovskite film growth on arbitrary substrates is illustrated in this work, and the methods that are developed to deposit SrRuO₃ thin films are a viable starting point for growth of artificial heteroepitaxial thin films that require a bottom electrode. Control is not just reached in the direction of film growth, as the crystal orientation and film properties are regulated laterally on the surface of micropatterned nanosheets. Local control of magnetic properties is illustrated, which holds out prospects for the fabrication of next‐generation devices like noncollinear magnetic random access memories.     

Boron‐doped selective silicon epitaxy: high efficiency and process simplification in interdigitated back contact cells

The present research and development activities in crystalline silicon photovoltaics include the exploration of doping technologies alternative to the mainstream diffusion process. The goal is to identify those technologies with potential to increase the solar cell efficiency and reduce the cost per watt peak. In that respect, this work presents the selective epitaxial growth of silicon as a candidate for boron doping; showing the results of the evaluation of boron‐doped silicon epitaxial emitters on slurry and diamond‐coated wire‐sliced Czochralski material, their integration in interdigitated back contact solar cells, and the development of a novel process sequence to create the interdigitated rear junction of these devices using selective epitaxial growth. Boron‐doped silicon epitaxy is demonstrated to perform in the high efficiency range (>22%), and the use of selective epitaxial growth is proposed as a route for the simplification of the interdigitated back contact solar cell flow. Copyright © 2013 John Wiley & Sons, Ltd.     

Evaluation of the influence of an embedded porous silicon layer on the bulk lifetime of epitaxial layers and the interface recombination at the epitaxial layer/porous silicon interface

Porous silicon plays an important role in the concept of wafer‐equivalent epitaxial thin‐film solar cells. Although porous silicon is beneficial in terms of long‐wavelength optical confinement and gettering of metals, it could adversely affect the quality of the epitaxial silicon layer grown on top of it by introducing additional crystal defects such as stacking faults and dislocations. Furthermore, the epitaxial layer/porous silicon interface is highly recombinative because it has a large internal surface area that is not accessible for passivation. In this work, photoluminescence is used to extract the bulk lifetime of boron‐doped (10¹⁶/cm³) epitaxial layers grown on reorganised porous silicon as well as on pristine mono‐crystalline, Czochralski, p⁺ silicon. Surprisingly, the bulk lifetime of epitaxial layers on top of reorganised porous silicon is found to be higher (~100–115 µs) than that of layers on top of bare p⁺ substrate (32–50 µs). It is believed that proper surface closure prior to epitaxial growth and metal gettering effects of porous silicon play a role in ensuring a higher lifetime. Furthermore, the epitaxial layer/porous silicon interface was found to be ~250 times more recombinative than an epitaxial layer/p⁺ substrate interface (S ≅ 10³ cm/s). However, the inclusion of an epitaxially grown back surface field on top of the porous silicon effectively shields minority carriers from this highly recombinative interface. Copyright © 2013 John Wiley & Sons, Ltd.     

A novel ball handling mechanism for the RoboCup middle size league

This paper presents the hardware design and control design of a novel ball handling mechanism in the RoboCup Middle Size League used by team Tech United Eindhoven. The ball handling mechanism consist of two levers with two actively driven wheels attached to it, to exert forces on the ball in order to control its position relative to the robot. The proposed design is fully compliant to the rules and regulations imposed by the RoboCup Middle Size League community. The control design consists of a cascaded velocity and position feedback loop in combination with a feedforward controller which compensates for the robots ego motion. The proposed design is validated on a robot used by the Tech United Eindhoven team.     

The inconceivable agenda

While the ‘unthinkable doctorate’ conference aimed at forming the ground for an inquiry that is at once legitimate, necessary and important, its premises, as articulated in the call for papers (see above: Introduction), failed to grasp the conceptual (and institutional, and historical) foundations of what its organisers considered to be ‘the current lack’ by posing this question through a rhetoric of ‘inconceivability’. In a direct response to the conference call, this essay argues that the classical separation of architectural science from architectural practice is all but productive as a starting point for rethinking and broadening the scope of the doctorate as a degree and as an academic process. Surpassing discursive and institutional frameworks upholding and consolidating the seemingly immutable division between architectural practice and the intellectualisation of architecture, we propose to position the doctorate as an investigatory ‘project’ implicating in equal measure both the university and the profession. ‘Thinking’ of ‘scientific work in architecture’ as a genuine architectural enterprise, we consider the doctorate as an institutionally authorised challenge to the disciplinary bases and techniques of architecture itself, that mobilises both theory and practice, however specific or traditional the individual project. The role of the doctorate is thus not simply to test the limits of architectural knowledge, but also the academic tools and media addressing that corpus.     

Rebuilding Ground Zero. The Politics of Performance

Some events have such an impact on society that it is unclear whether the standard rules of political decision making still apply. This paper analyses the planning process of rebuilding Ground Zero as a case in which politics was unhinged and new procedures were invented on the spot. The politics of planning was not only about what should be done on the site, but also about the sort of procedure that should be followed to take a legitimate decision. The paper conceives of the political process as a sequence of staged performances and introduces a model that analyses policy processes in terms of discourse, dramaturgy and deliberation. It describes the rebuilding of Ground Zero as a case of an ‘unhappy performance’ in which, as the process continued, the wider publicly-shared determination to create a bold symbolic response to terrorism lost out to uninspired political-economic reasoning. It argues that this analysis of policy processes as performance deserves a much wider application as today's world is full of situations in which decisions are made in networks marked by unclear rules as to how to arrive at a legitimate decision.     

Heat stress leads to superoxide formation in Bacillus cereus detected using the fluorescent probe MitoSOX

Bacillus cereus is a food-borne human pathogen and food spoilage organism. Spores and vegetative cells of B. cereus can be found almost everywhere and therefore often end up in food processing equipment and food products. To remove spores and vegetative cells from food or equipment, harsh treatments such as high temperatures are applied. The heat stress response of B. cereus and other organisms has been studied and it has been shown that reactive oxygen species may be involved in inactivating the bacterial cells. Using a novel approach with the fluorescent probe MitoSOX, the formation of superoxide in B. cereus cells upon exposure to heat has been confirmed. MitoSOX can be used in combination with other probes, including, SYTOX green, CYTO 9, and CFDA, showing superoxide formation in combination with damaged cell membranes, intact cell membranes, and esterase activity in cells with intact membranes, respectively. MitoSOX in combination with flow cytometry-assisted sorting showed three distinct populations, a low fluorescent population that was still viable, a highly fluorescent population that could not be recovered on agar plates, and a low fluorescent non-viable population that appeared after prolonged exposure to heat. This third population may include dead cells where MitoSOX binds to DNA without reacting with superoxide. Superoxide formation during exposure to lethal temperatures by B. cereus shows that superoxide plays a role in bacterial cell death and its generation may thus contribute to the efficiency of food preservation conditions.