arXiv subjects

K. Wiesner

Publications and source records attributed to K. Wiesner.

6 recordsLinked to original sources

arXiv2017

Haematopietic stem cells -- entropic landscapes of differentiation

The metaphor of a potential epigenetic differentiation landscape broadly suggests that during differentiation a stem cell follows the steepest descending gradient toward a stable equilibrium state which represents the final cell type. It has been conjectured that there is an analogy to the concept of entropy in statistical mechanics. In this context, in the undifferentiated state the entropy would be large since fewer constraints exist on the gene expression programs of the cell. As differentiation progresses, gene expression programs become more and more constrained and thus the entropy would be expected to decrease. Such an entropy decrease would, in analogy to statistical mechanics, require some form of free energy to decrease accordingly. In order to assess these predictions, we compute the Shannon entropy for time-resolved single-cell gene expression data in two different experimental setups of haematopoietic differentiation. We find that the behaviour of this entropy measure is in contrast to these predictions. In particular, we find that the Shannon entropy is not a decreasing function of developmental pseudo-time but instead it increases toward the point of commitment before decreasing again. This behaviour is consistent with an increase in gene expression disorder observed in populations sampled at the point of commitment. Single cells in these populations exhibit different combinations of regulator activity that suggest the presence of multiple configurations of a potential differentiation network as a result of multiple entry points into the committed state.

q-bio.CB↗

arXiv2017

Pulsar Searches with the SKA

The Square Kilometre Array will be an amazing instrument for pulsar astronomy. While the full SKA will be sensitive enough to detect all pulsars in the Galaxy visible from Earth, already with SKA1, pulsar searches will discover enough pulsars to increase the currently known population by a factor of four, no doubt including a range of amazing unknown sources. Real time processing is needed to deal with the 60 PB of pulsar search data collected per day, using a signal processing pipeline required to perform more than 10 POps. Here we present the suggested design of the pulsar search engine for the SKA and discuss challenges and solutions to the pulsar search venture.

astro-ph.IM↗

arXiv2017

The careless use of language in quantum information

An imperative aspect of modern science is that scientific institutions act for the benefit of a common scientific enterprise, rather than for the personal gain of individuals within them. This implies that science should not perpetuate existing or historical unequal social orders. Some scientific terminology, though, gives a very different impression. I will give two examples of terminology invented recently for the field of quantum information which use language associated with subordination, slavery, and racial segregation: 'ancilla qubit' and 'quantum supremacy'.

physics.soc-ph↗

arXiv2014

Entanglement gives rise to Pareto optimality in the generalised quantum Hawk-Dove Game

We quantise the generalised Hawk-Dove Game. By restricting the strategy space available to the players, we show that every game of this type can be extended into the quantum realm to produce a Pareto optimal evolutionarily stable strategy. This equilibrium replaces the inefficient classical one when the entanglement prepared in the game exceeds a critical threshold value, which we derive analytically.

quant-ph↗

arXiv2008

Quantum Cellular Automata

Quantum cellular automata (QCA) are reviewed, including early and more recent proposals. QCA are a generalization of (classical) cellular automata (CA) and in particular of reversible CA. The latter are reviewed shortly. An overview is given over early attempts by various authors to define one-dimensional QCA. These turned out to have serious shortcomings which are discussed as well. Various proposals subsequently put forward by a number of authors for a general definition of one- and higher-dimensional QCA are reviewed and their properties such as universality and reversibility are discussed.

quant-ph↗

arXiv2004

Core excitation in Ozone localized to one of two symmetry-equivalent chemical bonds - molecular alignment through vibronic coupling

Core excitation from terminal oxygen O$_T$ in O$_3$ is shown to be an excitation from a localized core orbital to a localized valence orbital. The valence orbital is localized to one of the two equivalent chemical bonds. We experimentally demonstrate this with the Auger Doppler effect which is observable when O$_3$ is core-excited to the highly dissociative O$_{T}$1s$^{-1}$7a$_1^1$ state. Auger electrons emitted from the atomic oxygen fragment carry information about the molecular orientation relative to the electromagnetic field vector at the moment of excitation. The data together with analytical functions for the electron-peak profiles give clear evidence that the preferred molecular orientation for excitation only depends on the orientation of one bond, not on the total molecular orientation. The localization of the valence orbital "7a$_1$" is caused by mixing of the valence orbital "5b$_2$" through vibronic coupling of anti-symmetric stretching mode with b$_2$-symmetry. To the best of our knowledge, it is the first discussion of the localization of a core excitation of O$_3$. This result explains the success of the widely used assumption of localized core excitation in adsorbates and large molecules.

physics.chem-ph↗