The unitary conformal field theory behind 2D Asymptotic Safety

Being interested in the compatibility of Asymptotic Safety with Hilbert space positivity (unitarity), we consider a local truncation of the functional RG flow which describes quantum gravity in $d>2$ dimensions and construct its limit of exactly two dimensions. We find that in this limit the flow displays a nontrivial fixed point whose effective average action is a non-local functional of the metric. Its pure gravity sector is shown to correspond to a unitary conformal field theory with positive central charge $c=25$. Representing the fixed point CFT by a Liouville theory in the conformal gauge, we investigate its general properties and their implications for the Asymptotic Safety program. In particular, we discuss its field parametrization dependence and argue that there might exist more than one universality class of metric gravity theories in two dimensions. Furthermore, studying the gravitational dressing in 2D asymptotically safe gravity coupled to conformal matter we uncover a mechanism which leads to a complete quenching of the a priori expected Knizhnik-Polyakov-Zamolodchikov (KPZ) scaling. A possible connection of this prediction to Monte Carlo results obtained in the discrete approach to 2D quantum gravity based upon causal dynamical triangulations is mentioned. Similarities of the fixed point theory to, and differences from, non-critical string theory are also described. On the technical side, we provide a detailed analysis of an intriguing connection between the Einstein-Hilbert action in $d>2$ dimensions and Polyakov's induced gravity action in two dimensions.Comment: 64 page

Magneto-optical probing of weak disorder in a two-dimensional hole gas

In two-beam magneto-photoluminescence spectra of a two-dimensional valence hole gas we identify the three-level energy spectrum of a free positive trion with a field-induced singlet-triplet transition. The recombination spectrum of acceptor-bound trions is also detected, including a cyclotron replica corresponding to the hole shake-up process. The emergence of a shake-up peak at low temperature is shown to be a sensitive probe of the presence of a small number of impurities inside the high-mobility quantum well, and its relative position is directly related to the hole cyclotron mass.Comment: 4 pages, 5 figure

Transform-limited single photons from a single quantum dot

A semiconductor quantum dot mimics a two-level atom. Performance as a single photon source is limited by decoherence and dephasing of the optical transition. Even with high quality material at low temperature, the optical linewidths are a factor of two larger than the transform-limit. A major contributor to the inhomogeneous linewdith is the nuclear spin noise. We show here that the nuclear spin noise depends on optical excitation, increasing (decreasing) with increasing resonant laser power for the neutral (charged) exciton. Based on this observation, we discover regimes where we demonstrate transform-limited linewidths on both neutral and charged excitons even when the measurement is performed very slowly

Coexisting graphical and structured textual representations of requirements : insights and suggestions

[Context & motivation] Many requirements documents contain graphical and textual representations of requirements side-byside. These representations may be complementary but oftentimes they are strongly related or even express the same content. [Question/problem] Since both representation may be used on their own, we want to nd out why and how a combination of them is used in practice. In consequence, we want to know what advantages such an approach provides and whether challenges arise from the coexistence. [Principal ideas/results] To get more insights into how graphical and textual representations are used in requirements documents, we conducted eight interviews with stakeholders at Daimler. These stakeholders work on a system that is speci ed by tabular textual descriptions and UML activity diagrams. The results indicate that the di erent representations are associated with di erent activities. [Contribution] Our study provides insights into a possible implementation of a speci cation approach using mixed representations of requirements. We use these insights to make suggestions on how to apply the approach in a way that pro ts from its advantages and mitigates potential weaknesses. While we draw our conclusions from a single use case, some aspects might be applicable in general

A case study on a specification approach using activity diagrams in requirements documents

Rising complexity of systems has long been a major challenge in requirements engineering. This manifests in more extensive and harder to understand requirements documents. At the Daimler AG, an approach is applied that combines the use of activity diagrams with natural language specifications to specify system functions. The approach starts with an activity diagram that is created to get an early overview. The contained information is then transferred to a textual requirements document, where details are added and the behavior is refined. While the approach aims to reduce efforts needed to understand a system’s behavior, the application of the approach itself causes new challenges on its own. By examining existing specifications at Daimler, we identified nine categories of inconsistencies and deviations between activity diagrams and their textual representations. In a case study, we examined one system in detail to assess how often these occur. In a follow-up survey, we presented instances of the categories to different stakeholders of the system and let them asses the categories regarding their severity. Our analysis indicates that a coexistence of textual and graphical representations of models without proper tool support results in inconsistencies and deviations that may cause severe maintenance costs or even provoke faults in subsequent development steps

Post-exposure prophylaxis for rape survivors

CITATION: Pluddemann, A., Reuter, H. & Johnson, C. 2007. Post-exposure prophylaxis for rape survivors. South African Medical Journal, 97(1):12-13The original publication is available at http://www.samj.org.za[No abstract available]Publisher’s versio

Condition monitoring of machines by tapping data from existing sensors and retrofitting simple energy measurement technology to existing machines

The average metal and mechanical engineering company must spend around two per cent of its annual turnover on electricity and natural gas, and companies are expecting further price increases. As a result, the issue of energy saving is becoming more of a strategic factor than ever before. In order to save costs and ensure competitive advantages, it is necessary to introduce precise energy-saving measures. The first steps taken by most mechanical engineering companies are to replace lighting, heating, and ventilation systems, improve compressed air generation and raise employee awareness. However, there is also a great potential for optimization in machines with their individual electrical drives, fans, and units. In this case, though, it is necessary to look at the machine and its processes as a whole rather than the individual electrical energy consumers. In most cases, however, there is a lack of suitable interfaces for analyzing the measured values from sensors (e.g. temperature, pressure sensors, etc.) and drives, which concludes that this potential is not fully exploited