Computational Steering of Cluster Formation in Brownian Suspensions

We simulate cluster formation of model colloidal particles interacting via DLVO (Derjaguin, Landau, Vervey, Overbeek) potentials. The interaction potentials can be related to experimental conditions, defined by the pH-value, the salt concentration and the volume fraction of solid particles suspended in water. The system shows different structural properties for different conditions, including cluster formation, a glass-like repulsive structure, or a liquid suspension. Since many simulations are needed to explore the whole parameter space, when investigating the properties of the suspension depending on the experimental conditions, we have developed a steering approach to control a running simulation and to detect interesting transitions from one region in the configuration space to another. The advantages of the steering approach and the restrictions of its applicability due to physical constraints are illustrated by several example cases.Comment: 9 pages, 4 figures, submitted to Proceedings of the Fourth International Conference on Mesoscopic Methods in Engineering and Science (ICMMES) 2007 (Munich, Germany), revised version, 2 figures exchanged, some parts rephrase

Bid early and get it cheap - Timing effects in Internet auctions

Most internet auction sites, like eBay, use a proxy bidding system where bidders can put in their maximum bid and let a proxy bidder (a computer) bid for them. Yet many bidders speculate about how to bid and employ bidding strategies. This paper examines how the timing of bids can affect the final price. In a unique data set of 17,000 Scandinavian furniture auctions it turns out that early price increases, i.e. much early bidding, scare off bidders and therefore result in lower prices, whereas much late bidding results in higher prices. Sniping is therefore not a successful strategy to avoid bidding wars.Internet auctions, Auction fever, Pseudo-endowment, Bidding behavior, eBay, Strategies, WTP

Learning to bid, but not to quit – Experience and Internet auctions

A classic argument in economics is that experience in the market place will eliminate mistakes and cognitive biases. Internet auctions are a popular market were some bidders gather extensive experience. In a unique data set from a Scandinavian auction site I question if and what bidders learn. At face value experienced bidders do adapt better bidding strategies. However, the so-called pseudo-endowment effect does not disappear. Regardless of their experience, bidders will be inclined to increase their willingness to pay as a response to having had “ownership” (the leading bid) before being outbid. Thus, this data can confirm that feedback, and especially negative feedback, seems to be a critical component in learning.Experience, Learning, Internet auctions, Reference-Dependent Preferences, Endowment Effect, Bidding behavior, eBay.

Texture dependence of motion sensing and free flight behavior in blowflies

Lindemann JP, Egelhaaf M. Texture dependence of motion sensing and free flight behavior in blowflies. Frontiers in Behavioral Neuroscience. 2013;6:92.Many flying insects exhibit an active flight and gaze strategy: purely translational flight segments alternate with quick turns called saccades. To generate such a saccadic flight pattern, the animals decide the timing, direction, and amplitude of the next saccade during the previous translatory intersaccadic interval. The information underlying these decisions is assumed to be extracted from the retinal image displacements (optic flow), which scale with the distance to objects during the intersaccadic flight phases. In an earlier study we proposed a saccade-generation mechanism based on the responses of large-field motion-sensitive neurons. In closed-loop simulations we achieved collision avoidance behavior in a limited set of environments but observed collisions in others. Here we show by open-loop simulations that the cause of this observation is the known texture-dependence of elementary motion detection in flies, reflected also in the responses of large-field neurons as used in our model. We verified by electrophysiological experiments that this result is not an artifact of the sensory model. Already subtle changes in the texture may lead to qualitative differences in the responses of both our model cells and their biological counterparts in the fly's brain. Nonetheless, free flight behavior of blowflies is only moderately affected by such texture changes. This divergent texture dependence of motion-sensitive neurons and behavioral performance suggests either mechanisms that compensate for the texture dependence of the visual motion pathway at the level of the circuits generating the saccadic turn decisions or the involvement of a hypothetical parallel pathway in saccadic control that provides the information for collision avoidance independent of the textural properties of the environment

Every simple compact semiring is finite

A Hausdorff topological semiring is called simple if every non-zero continuous homomorphism into another Hausdorff topological semiring is injective. Classical work by Anzai and Kaplansky implies that any simple compact ring is finite. We generalize this result by proving that every simple compact semiring is finite, i.e., every infinite compact semiring admits a proper non-trivial quotient.Comment: 6 page

Pooling of Income and Sharing of Consumption within Households

There are extensive literatures within economics and economic psychology on the allocation of household income within the household. These two literatures are largely disjoint but both use a concept of ‘income pooling’. In economics this refers to the independence of household decisions from who receives the income within the household. In economic psychology it refers to the management of household finances. This article uses a new Danish expenditure survey that gives information on both concepts and on the assignment of expenditures to consider the link between the two. More importantly, we investigate whether either type of pooling is related to the sharing of expenditures between the two partners. We find that sharing does depend on who receives the income within non-pooling households, but not on the economic psychological income pooling regime per se.household production and intra-household allocation; personal income; wealth and their distributions; methodology for collecting, estimating, and organizing microeconomic data; marriage and family