University of Konstanz

About: University of Konstanz is a education organization based out in Konstanz, Baden-Württemberg, Germany. It is known for research contribution in the topics: Population & Visualization. The organization has 12115 authors who have published 27401 publications receiving 951162 citations. The organization is also known as: University of Constance & Universität Konstanz.

Constraints on the distribution and energetics of fast radio bursts using cosmological hydrodynamic simulations

Abstract: We present constraints on the origins of fast radio bursts (F RBs) using one of the largest currently available cosmological hydrodynamic simulations. We use these simulations to calculate contributions to the dispersion measures (DMs) of FRBs from the Milky Way, from the local Universe out to � 100 Mpc, from cosmological large-scale structure and from potential FRB host galaxies, and we then compare the results of these simulations to the DMs for observed FRBs. We find that the foreground Milky Way contr ibution has previously been underestimated by a factor of � 2, and that the the distribution of foreground-subtracted DMs is consistent with a cosmological origin, corresponding to a population of sources observable out to a maximum redshift z � 0.6 0.9. We consider models for the spatial distribution and occurrence of FRBs in which they are randomly distributed in the Universe, track the star-formation rate of their host galaxies, track total ste llar mass, or require the presence of a central supermassive black hole. While the current data (nine extragalactic FRBs) do not allow us to distinguish between these possibilities, we show that the predicted distributions of DM for these different models will differ considerably once we begin detecting significant fractions of FRBs at higher DMs and higher redshifts. We additionally consider the distribution of fluences for observed FRBs, and show that the observations are consistent with the hypothesis that FRBs are standard candles, each burst producing the same radiated isotropic energy. Comparing the combined DM and fluence distributions with our cosmological model, we find that the data are consistent with a constant isotropic burst energy of � 4 × 10 40 erg if FRBs are embedded in host galaxies, or two times higher if FRBs are randomly distributed over the cosmic volume. These energies are a factor of 10‐100 times larger than had previously been inferred. Within the limited constraints of the available s mall sample of data, our analysis favours FRB mechanisms for which the isotropic burst energy has a narrow distribution in excess of 10 40 erg.

Kinetic properties of ion carriers and channels

Abstract: A unified description of ion carriers, channels, and pumps seems possible based on the concept of channels with multiple conformational states. The notion of a channel with variable energy profile is suggested by recent work on the dynamics of proteins. With the exception of mobile, translatory carriers of the valinomycin type which represent a separate class of ion translocators, most transport systems in biological membranes seem to be built-in proteins. Transmembrane proteins may differ in their mode of operation by the extent to which conformational changes are involved in the translocation of the permeant. While carriers and channels in the usual sense are limiting cases of a multistate channel, many real transport systems probably function by an intermediate mechanism.

Space, sympatry and speciation

Abstract: Sympatric speciation remains controversial. ‘Sympatry’ originally meant ‘‘in the same geographical area’’. Recently, evolutionists have redefined ‘sympatric speciation’ non-spatially to require panmixia (m = 0.5) between a pair of demes before onset of reproductive isolation. Although panmixia is a suitable starting point in models of speciation, it is not a useful definition of sympatry in natural populations, because it becomes virtually impossible to find or demonstrate sympatry in nature. The newer, non-spatial definition fails to address the classical debate about whether natural selection within a geographic overlap regularly causes speciation in nature, or whether complete geographic isolation is usually required. We therefore propose a more precise spatial definition by incorporating the population genetics of dispersal (or ‘cruising range’). Sympatric speciation is considerably more likely under this spatial definition than under the demic definition, because distance itself has a powerful structuring effect, even over small spatial scales comparable to dispersal. Ecological adaptation in two-dimensional space often acts as a ‘magic trait’ that causes pleiotropic reductions of gene flow. We provide examples from our own research.