Evolution of Wear Characteristics and Frictional Behavior in MEMS Devices

A surface-micromachined nanotractor device has been used to investigate the tribological behavior of MEMS devices made of polycrystalline silicon. An accelerated wear test, spanning several hundreds of thousands of cycles, was developed to monitor the evolution of wear characteristics and frictional behavior during its operational lifetime. Postmortem microscopic observations of the wear surfaces revealed features that can be categorized into two regimes of wear: (i) adhesion-dominated wear and (ii) third-body wear. The former was characterized by asperity blunting, plastic deformation of asperity peaks, and smearing of fine wear debris into a thin-surface film. With an increased number of wear cycles, the wear mechanism transitioned to the latter regime which consisted of debris agglomeration and material removal through scratches induced by these agglomerates. Finally, it was theorized that one of the agglomerates grows to a large size, adheres to one of the contact surfaces and causes severe wear in a localized region on the counter surface to lock the two surfaces and cause device failure.     

Exploitation of Chemical Signaling by Parasitoids: Impact on Host Population Dynamics

Chemical information mediates species interactions in a wide range of organisms. Yet, the effect of chemical information on population dynamics is rarely addressed. We designed a spatio-temporal parasitoid—host model to investigate the population dynamics when both the insect host and the parasitic wasp that attacks it can respond to chemical information. The host species, Drosophila melanogaster, uses food odors and aggregation pheromone to find a suitable resource for reproduction. The larval parasitoid, Leptopilina heterotoma, uses these same odors to find its hosts. We show that when parasitoids can respond to food odors, this negatively affects fruit fly population growth. However, extra parasitoid responsiveness to aggregation pheromone does not affect fruit fly population growth. Our results indicate that the use of the aggregation pheromone by D. melanogaster does not lead to an increased risk of parasitism. Moreover, the use of aggregation pheromone by the host enhances its population growth and enables it to persist at higher parasitoid densities.     

Influence of the uterine environment on the development of in vitro-produced equine embryos

The necessity for early interaction between the embryo and the oviductal and/or uterine environment in the horse is reflected by several striking differences between equine embryos that develop in vivo and those produced in vitro. Better understanding of the salient interactions may help to improve the efficiency of in vitro equine embryo production. In an initial experiment, cleavage-stage in vitro-produced (IVP) equine embryos were transferred into the uterus of recipient mares that had ovulated recently to determine whether premature placement in this in vivo environment would improve subsequent development. In a second experiment, an important element of the uterine environment was mimicked by adding uterocalin, a major component of the endometrial secretions during early pregnancy, to the culture medium. Intrauterine transfer of cleavage-stage IVP equine embryos yielded neither ultrasonographically detectable pregnancies nor day 7 blastocysts, indicating that the uterus is not a suitable environment for pre-compact morula stage horse embryos. By contrast, exposure to uterocalin during IVP improved capsule formation, although it did not measurably affect the development or expression of a panel of genes known to differ between in vivo and in vitro embryos. Further studies are required to evaluate whether uterocalin serves purely as a carrier protein or more directly promotes improved capsule development.     

A statistical data-processing methodology of Py-GC/MS data for the simulation of flash co-pyrolysis reactor experiments

Practically it is extremely difficult to collect observations following a fully sound statistical design, typically encompassing a high number of repetitions, of an intensive and elaborate experimental procedure such as flash pyrolysis reactor experiments. Pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) is an extremely useful analytical technique in order to simulate a high number of repetitive pyrolysis experiments in an acceptable time span. Combining Py-GC/MS experiments and statistical data processing, conclusions can be drawn on the pyrolysis behaviour of any input material, supplying crucial information on its respective behaviour during the actual flash pyrolysis experiments.In this research Py-GC/MS experiments combined with a tailored statistical data processing methodology strongly indicate the occurrence of synergetic interactions during the flash co-pyrolysis of willow/polyhydroxybutyrate (PHB) blends. Such interactions are also indicated by pattern recognition and by the analysis of the condensable and noncondensable pyrolytic gases obtained from Py-GC/MS. Accordingly, the actual influence of the flash co-pyrolysis of willow and PHB, executed with a semi-continuous pyrolysis reactor, on the pyrolytic oil features is investigated by GC/MS. Based on these experiments an explanation for the observed synergy during flash co-pyrolysis of willow and PHB is proposed.     

Dutch wind power policy: Stagnating implementation of renewables

Since 1985 the official goal for wind power development in the Netherlands is 1000 MW by the year 2000. About 200 MW had been installed in 1995 and in 2000 only about 300 MW appears to be feasible, which is far behind the official goal. Essential government choices that have made policy less effective are relying on large-scale application by utilities, stimulating capacity instead of energy yield, entanglement of energy policy and industrial policy and most of all aloofness in the process of obtaining sites. There was no programme on making sites available and there were no instruments to stimulate crucial actors in the process of decision making of sites. This started a vicious circle: economic feasibility has not been reached, because there is no mass production of turbines, which in turn is a result of the lack of available sites.     

On the Significance of Digits in Interval Notation

We review the various interval notations as starting point for the analysis of the significance of the decimals used for interval bounds. As intervals are used to indicate that a number is known with a certain degree of uncertainty, we also review the rules used in physics to ensure the significance of the decimals used in recording a measurement. It turns out that according to these rules, commonly used interval notation carries too many decimals. To be able to investigate whether rules similar to those used in physics can be used to improve interval notation, we use information theory to determine the information content of the last decimals of the numerals used to denote the interval's bounds. We introduce the Law of One Tenth, stating that in many situations this content diminishes by a factor of ten on average for successive decimals. The law is especially useful in conjunction with a novel and little-used way of writing intervals that we call “factored notation.” The law implies that it is usually futile to write more than two or three decimals inside the brackets of factored notation. This revised version was published online in June 2006 with corrections to the Cover Date.     

A Trichome-Specific Linoleate Lipoxygenase Expressed During Pyrethrin Biosynthesis in Pyrethrum

The lipid precursor alcohols of pyrethrins—jasmolone, pyrethrolone and cinerolone—have been proposed as sharing parts of the oxylipin pathway with jasmonic acid. This implies that one of the first committed steps of pyrethrin biosynthesis is catalyzed by a lipoxygenase, catalyzing the hydroperoxidation of linolenic acid at position 13. Previously, we showed that the expression and activity of chrysanthemyl diphosphate synthase (TcCDS), the enzyme catalyzing the first committed step in the biosynthesis of the acid moiety of pyrethrins, is trichome-specific and developmentally regulated in flowers. In the present study we characterized the expression pattern of 25 lipoxygenase EST contigs, and subsequently carried out the molecular cloning of two pyrethrum lipoxygenases, TcLOX1 and TcLOX2, that have a similar pattern to TcCDS. Only recombinant TcLOX1 catalyzed the peroxidation of the linolenic acid substrate. Just as TcCDS, TcLOX1, are exclusively expressed in trichomes. Phylogenetic analysis showed that the enzyme shared the highest homology with chloroplast-localized 13-type-lipoxygenases that are involved in maintaining basal levels of jasmonate.     

Efficient model learning methods for actor-critic control

We propose two new actor-critic algorithms for reinforcement learning. Both algorithms use local linear regression (LLR) to learn approximations of the functions involved. A crucial feature of the algorithms is that they also learn a process model, and this, in combination with LLR, provides an efficient policy update for faster learning. The first algorithm uses a novel model-based update rule for the actor parameters. The second algorithm does not use an explicit actor but learns a reference model which represents a desired behavior, from which desired control actions can be calculated using the inverse of the learned process model. The two novel methods and a standard actor-critic algorithm are applied to the pendulum swing-up problem, in which the novel methods achieve faster learning than the standard algorithm.     

Crossover in Grammatical Evolution

We present an investigation into crossover in Grammatical Evolution that begins by examining a biologically-inspired homologous crossover operator that is compared to standard one and two-point operators. Results demonstrate that this homologous operator is no better than the simpler one-point operator traditionally adopted.An analysis of the effectiveness of one-point crossover is then conducted by determining the effects of this operator, by adopting a headless chicken-type crossover that swaps randomly generated fragments in place of the evolved strings. Experiments show detrimental effects with the utility of the headless chicken operator.Finally, the mechanism of crossover in GE is analysed and termed ripple crossover, due to its defining characteristics. An experiment is described where ripple crossover is applied to tree-based genetic programming, and the results show that ripple crossover is more effective in exploring the search space of possible programs than sub-tree crossover by examining the rate of premature convergence during the run. Ripple crossover produces populations whose fitness increases gradually over time, slower than, but to an eventual higher level than that of sub-tree crossover.     

A response surface based optimisation algorithm for the calculation of fuzzy envelope FRFs of models with uncertain properties

This paper describes a response surface based optimisation technique for the calculation of envelope frequency response functions (FRFs) of imprecisely defined structures using the interval and fuzzy finite element method.The authors developed a hybrid - global optimisation and interval arithmetic - procedure for interval and fuzzy envelope FRF calculation. This hybrid approach reduces the computational cost of the analysis compared to a full global optimisation approach and reduces the conservatism on the envelope FRF compared to a full interval arithmetic approach.Still, the optimisation step is the computationally most expensive part of the algorithm. To handle industrially sized applications, a very efficient optimisation procedure is imperative. The response surface based procedure described in this paper decreases the computational cost of a fuzzy envelope FRF calculation with a factor 50 or more compared to the commonly used two-level full factorial design of experiments, while giving a comparable accuracy.