The pion quasiparticle in the low-temperature phase of QCD

We investigate the properties of the pion quasiparticle in the low-temperature phase of two-flavor QCD on the lattice with support from chiral effective theory. We find that the pion quasiparticle mass is significantly reduced compared to its value in the vacuum, by contrast with the static screening mass, which increases with temperature. By a simple argument, near the chiral limit the two masses are expected to determine the quasiparticle dispersion relation. Analyzing two-point functions of the axial charge density at non-vanishing spatial momentum, we find that the predicted dispersion relation and the residue of the pion pole are simultaneously consistent with the lattice data at low momentum. The test, based on fits to the correlation functions, is confirmed by a second analysis using the Backus-Gilbert method.Comment: 22 pages, 8 figure

Chiral dynamics in the low-temperature phase of QCD

We investigate the low-temperature phase of QCD and the crossover region with two light flavors of quarks. The chiral expansion around the point $(T, m_q = 0)$ in the temperature vs. quark-mass plane indicates that a sharp real-time excitation exists with the quantum numbers of the pion. We determine its dispersion relation and test the applicability of the chiral expansion. The time-dependent correlators are also analyzed using the Maximum Entropy Method (MEM), yielding consistent results. Finally, we test the predictions of ordinary chiral perturbation theory around the point $(T = 0, m_q = 0)$ for the temperature dependence of static observables. Around the crossover temperature, we find that all quantities considered depend only mildly on the quark mass in the considered range 8MeV $\leq \bar{m}^{\bar{\text{MS}}} \leq$ 15MeV.Comment: 7 pages, 5 figures, talk presented at the 32nd International Symposium on Lattice Field Theory (Lattice 2014), 23 - 28 June, 2014 Columbia University New York, NY, US

Supernova Feedback in Molecular Clouds: Global Evolution and Dynamics

We use magnetohydrodynamical simulations of converging warm neutral medium flows to analyse the formation and global evolution of magnetised and turbulent molecular clouds subject to supernova feedback from massive stars. We show that supernova feedback alone fails to disrupt entire, gravitationally bound, molecular clouds, but is able to disperse small--sized (~10 pc) regions on timescales of less than 1 Myr. Efficient radiative cooling of the supernova remnant as well as strong compression of the surrounding gas result in non-persistent energy and momentum input from the supernovae. However, if the time between subsequent supernovae is short and they are clustered, large hot bubbles form that disperse larger regions of the parental cloud. On longer timescales, supernova feedback increases the amount of gas with moderate temperatures (T~300-3000 K). Despite its inability to disrupt molecular clouds, supernova feedback leaves a strong imprint on the star formation process. We find an overall reduction of the star formation efficiency by a factor of 2 and of the star formation rate by roughly factors of 2-4.Comment: 16 pages, 12 figures (2 in appendix), revised version, submitted to MNRA

Numerical simulation of growth of Escherichia coli in unsaturated porous media

A model for the aerobic and anaerobic growth of Escherichia coli (HB101 K12 pGLO) depending on the concentration of oxygen and DOC as substrate has been developed based on laboratory batch experiments. Using inverse modelling to obtain optimal sets of parameters, it could be shown that a model based on a modified double Contois kinetic can predict cell densities, organic carbon utilisation, oxygen transfer and utilisation rates for a large number of experiments under aerobic and anaerobic conditions with a single unique set of parameters. The model was extended to describe growth of E. coli in unsaturated porous media, combining diffusion, phase exchange and microbiological growth. Experiments in a Hele-Shaw cell, filled with quartz sand, were conducted to study bacterial growth in the capillary fringe above a saturated porous medium. Cell density profiles in the Hele-Shaw cell were predicted with the growth model and the parameters from the batch experiments without any further calibration. They showed a very good qualitative and quantitative agreement with cell densities determined from samples taken from the Hele-Shaw cell by re-suspension and subsequent counting. Thus it could be shown, that it is possible to successfully transfer growth parameters from batch experiments to porous media for both aerobic and anaerobic conditions.Comment: Minor changes in conclusions, results unchange

Isospin breaking in pion-deuteron scattering and the pion-nucleon scattering lengths

In recent years, high-accuracy data for pionic hydrogen and deuterium have become the primary source of information on the pion-nucleon scattering lengths. Matching the experimental precision requires, in particular, the study of isospin-breaking corrections both in pion-nucleon and pion-deuteron scattering. We review the mechanisms that lead to the cancellation of potentially enhanced virtual-photon corrections in the pion-deuteron system, and discuss the subtleties regarding the definition of the pion-nucleon scattering lengths in the presence of electromagnetic interactions by comparing to nucleon-nucleon scattering. Based on the pi^{+/-} p channels we find for the virtual-photon-subtracted scattering lengths in the isospin basis a^{1/2}=(170.5 +/- 2.0) x 10^{-3} mpi^{-1} and a^{3/2}=(-86.5 +/- 1.8) x 10^{-3} mpi^{-1}.Comment: 6 pages, 1 figure, Proceedings for the 7th International Workshop on Chiral Dynamics, Newport News, Virginia, USA, August 6-10, 201

Is Information Systems Research Concerned with Societal Grand Challenges?

“Grand challenges” can provide an important orientation regarding whether research deals with societally relevant problems. Yet, many IS scholars have claimed that IS research is often dealing with issues that are of rather little relevance to societal grand challenges. In this “research-in-progress” study, we examine to which degree IS research is concerned with societal grand challenges. We approach this question by thus far analyzing 329 papers published in the leading AIS ‘Basket of Eight’ (AIS 8) IS journals in the year 2020. Using coding analysis rooted in justification theory to clarify why IS research was performed, we map the justifications given in those papers against the grand challenges as set out in the United Nations (UN) Sustainable Development Goals. The findings indicate that IS research seems to be contributing to some societal challenges (e.g., industrial innovation, economic growth or health), while neglecting many others (e.g., societal equality, environmental sustainability and challenges in developing countries)