A note on the magnetic spatial forcing of a ferrofluid layer

We report on the response of a thin layer of ferrofluid to a spatially modulated magnetic field. This field is generated by means of a constant current in a special arrangement of aluminum wires. The full surface profile of the liquid layer is recorded by means of the absorption of X-rays. The outcome is analyzed particularly with regard to the magnetic self focusing effect under a deformable fluid layer

Optimal decision making for sperm chemotaxis in the presence of noise

For navigation, microscopic agents such as biological cells rely on noisy sensory input. In cells performing chemotaxis, such noise arises from the stochastic binding of signaling molecules at low concentrations. Using chemotaxis of sperm cells as application example, we address the classic problem of chemotaxis towards a single target. We reveal a fundamental relationship between the speed of chemotactic steering and the strength of directional fluctuations that result from the amplification of noise in the chemical input signal. This relation implies a trade-off between slow, but reliable, and fast, but less reliable, steering. By formulating the problem of optimal navigation in the presence of noise as a Markov decision process, we show that dynamic switching between reliable and fast steering substantially increases the probability to find a target, such as the egg. Intriguingly, this decision making would provide no benefit in the absence of noise. Instead, decision making is most beneficial, if chemical signals are above detection threshold, yet signal-to-noise ratios of gradient measurements are low. This situation generically arises at intermediate distances from a target, where signaling molecules emitted by the target are diluted, thus defining a `noise zone' that cells have to cross. Our work addresses the intermediate case between well-studied perfect chemotaxis at high signal-to-noise ratios close to a target, and random search strategies in the absence of navigation cues, e.g. far away from a target. Our specific results provide a rational for the surprising observation of decision making in recent experiments on sea urchin sperm chemotaxis. The general theory demonstrates how decision making enables chemotactic agents to cope with high levels of noise in gradient measurements by dynamically adjusting the persistence length of a biased persistent random walk.Comment: 9 pages, 5 figure

Network permeability changes according to a quadratic power law upon removal of a single edge

We report an empirical power law for the reduction of network permeability in statistically homogeneous spatial networks upon removal of a single edge. We characterize this power law for plexus-like microvascular sinusoidal networks from liver tissue, as well as perturbed two- and three-dimensional regular lattices. We provide a heuristic argument for the observed power law by mapping arbitrary spatial networks that satisfies Darcy's law on an small-scale resistor network.Comment: 6 pages, 3 figure

Surfing along concentration filaments: sperm chemotaxis in physiological shear flows

Many motile biological cells navigate along concentration gradients of signaling molecules: This chemotaxis guides for instance sperm cells from marine invertebrates, which have to find egg cells in the ocean. While chemotaxis has been intensively studied for idealized conditions of rotationally symmetric gradients in still water, natural gradients are usually distorted, e.g., by turbulent flows in the ocean. Recent experiments and direct numerical simulations with sperm cells and bacteria surprisingly suggest the existence of an optimal flow strength at which chemotaxis is more effective than for still water. We use sperm chemotaxis in simple shear flow as a prototypical example to understand the origin of such an optimal flow strength theoretically: We quantify how flow accelerates spreading of signaling molecules released by the egg, but distorts the resulting concentration field into long and thin filaments. The competition between these two effects sets an optimal flow strength that maximizes sperm-egg encounter. We characterize how sperm cells `surf' along concentration filaments, typical for scalar turbulence, revealing a general navigation paradigm in the presence of flow. We compare both simulation and theory with previous experimental results and find good agreement.Comment: manuscript: 6 pages, 4 figures; SI: 11 pages, 8 figure

Sensorfusion und Regelung eines Roboters am kontinuierlich bewegten Band

Der Artikel beschreibt die Montage eines Anbauteils an ein kontinuierlich bewegtes Basisbauteil, dessen Bewegung durch unterschiedliche Sensoren gemessen wird. Dabei werden u. a. die Ergebnisse einer Bildverarbeitung mit den Auslenkungen eines nachgiebigen Kraft- Momentensensors fusioniert. Aus den Bahnpunkten wird dann eine geglättete Solltrajektorie für das Anbauteil bestimmt. Die Regelung des Roboters wird durch Vorsteuerungen ergänzt, die die dynamischen Verzögerungen und Schwingungen von Roboter und Endeffektor prädiktiv kompensieren

Empirical competence-testing: A psychometric examination of the German version of the Emotional Competence Inventory

The “Emotional Competence Inventory“ (ECI 2.0) by Goleman and Boyatzis assesses emotional intelligence (EI) in organizational context by means of 72 items in 4 clusters (self-awareness, self- management, social awareness, social skills) which at large consist of 18 competencies. Our study examines the psychometric properties of the first German translation of this instrument in two different surveys (N = 236). If all items are included in reliability analysis the ECI is reliable (Cronbach’s Alpha = .90), whereas the reliability of the four sub dimensions is much smaller (Alpha = .62 - .81). For 43 items the corrected item-total correlation with its own scale is higher than correlations with the other three clusters. Convergent validity was examined by using another EI instrument (Wong & Law, 2002). We found a significant correlation between the two instruments (r = .41). The German version of the ECI seems to be quite useful, although the high reliability is achieved by a large number of items. Possibilities of improvement are discussed

Emotional Intelligence and its consequences for occupational and life satisfaction - Emotional Intelligence in the context of irrational beliefs

According to Albert Ellis' theory of Rational Emotive Behavior Therapy irrational beliefs (IB) lead to maladaptive emotions. A central component of irrationality is the denial of one's own possibilities to control important aspects of life. A specific IB is that one cannot control and thus cannot avoid certain emotion states. Emotion research considers regulative emotion control a pivotal component of the concept of emotional intelligence (EI). A negative association between IB and EI can thus be theoretically derived from both concepts. Furthermore both should be related to life satisfaction. We examined the relationship between IB and EI using standardized questionnaire instruments and the predictive value of both concepts regarding life satisfaction. We found a significant negative correlation between both conceptions (r = -.21). Life satisfaction and occupational satisfaction are better predicted by IB. R² increases from .04 to .12 when both concepts are incorporated in regression analysis