University of Potsdam

About: University of Potsdam is a education organization based out in Potsdam, Germany. It is known for research contribution in the topics: Population & Computer science. The organization has 9629 authors who have published 26740 publications receiving 759745 citations. The organization is also known as: Universität Potsdam.

Microsaccades Keep the Eyes' Balance During Fixation

Abstract: During fixation of a stationary target, small involuntary eye movements exhibit an erratic trajectory-a random walk. Two types of these fixational eye movements are drift and microsaccades (small-amplitude saccades). We investigated fixational eye movements and binocular coordination using a statistical analysis that had previously been applied to human posture control. This random-walk analysis uncovered two different time scales in fixational eye movements and identified specific functions for microsaccades. On a short time scale, microsaccades enhanced perception by increasing fixation errors. On a long time scale, microsaccades reduced fixation errors and binocular disparity (relative to pure drift movements). Thus, our findings clarify the role of oculomotor processes during fixation.

Schmidt measure as a tool for quantifying multiparticle entanglement

Abstract: We present a measure of quantum entanglement which is capable of quantifying the degree of entanglement of a multipartite quantum system. This measure, which is based on a generalization of the Schmidt rank of a pure state, is defined on the full state space, and is shown to be an entanglement monotone, that is, it cannot increase under local quantum operations with classical communication and under mixing. For a large class of mixed states this measure of entanglement can be calculated exactly, and it provides a detailed classification of mixed states.

Effects of the electronic spin transitions of iron in lower mantle minerals: implications for deep mantle geophysics and geochemistry

Abstract: [1] We have critically reviewed and discussed currently available information regarding the spin and valence states of iron in lower mantle minerals and the associated effects of the spin transitions on physical, chemical, and transport properties of the deep Earth. A high-spin to low-spin crossover of Fe2+ in ferropericlase has been observed to occur at pressure-temperature conditions corresponding to the middle part of the lower mantle. In contrast, recent studies consistently show that Fe2+ predominantly exhibits extremely high quadrupole splitting values in the pseudo-dodecahedral site (A site) of perovskite and post-perovskite, indicative of a strong lattice distortion. Fe3+ in the A site of these structures likely remains in the high-spin state, while a high-spin to low-spin transition of Fe3+ in the octahedral site of perovskite occurs at pressures of 15–50 GPa. In post-perovskite, the octahedral-site Fe3+ remains in the low-spin state at the pressure conditions of the lowermost mantle. These changes in the spin and valence states of iron as a function of pressure and temperature have been reported to affect physical, chemical, rheological, and transport properties of the lower mantle minerals. The spin crossover of Fe2+ in ferropericlase has been documented to affect these properties and is discussed in depth here, whereas the effects of the spin transition of iron in perovskite and post-perovskite are much more complex and remain debated. The consequences of the transitions are evaluated in terms of their implications to deep Earth geophysics, geochemistry, and geodynamics including elasticity, element partitioning, fractionation and diffusion, and rheological and transport properties.