Unital Quantum Channels - Convex Structure and Revivals of Birkhoff's Theorem

The set of doubly-stochastic quantum channels and its subset of mixtures of unitaries are investigated. We provide a detailed analysis of their structure together with computable criteria for the separation of the two sets. When applied to O(d)-covariant channels this leads to a complete characterization and reveals a remarkable feature: instances of channels which are not in the convex hull of unitaries can return to it when either taking finitely many copies of them or supplementing with a completely depolarizing channel. In these scenarios this implies that a channel whose noise initially resists any environment-assisted attempt of correction can become perfectly correctable.Comment: 31 page

"What's (the) Matter?", A Show on Elementary Particle Physics with 28 Demonstration Experiments

We present the screenplay of a physics show on particle physics, by the Physikshow of Bonn University. The show is addressed at non-physicists aged 14+ and communicates basic concepts of elementary particle physics including the discovery of the Higgs boson in an entertaining fashion. It is also demonstrates a successful outreach activity heavily relying on the university physics students. This paper is addressed at anybody interested in particle physics and/or show physics. This paper is also addressed at fellow physicists working in outreach, maybe the experiments and our choice of simple explanations will be helpful. Furthermore, we are very interested in related activities elsewhere, in particular also demonstration experiments relevant to particle physics, as often little of this work is published. Our show involves 28 live demonstration experiments. These are presented in an extensive appendix, including photos and technical details. The show is set up as a quest, where 2 students from Bonn with the aid of a caretaker travel back in time to understand the fundamental nature of matter. They visit Rutherford and Geiger in Manchester around 1911, who recount their famous experiment on the nucleus and show how particle detectors work. They travel forward in time to meet Lawrence at Berkeley around 1950, teaching them about the how and why of accelerators. Next, they visit Wu at DESY, Hamburg, around 1980, who explains the strong force. They end up in the LHC tunnel at CERN, Geneva, Switzerland in 2012. Two experimentalists tell them about colliders and our heroes watch live as the Higgs boson is produced and decays. The show was presented in English at Oxford University and University College London, as well as Padua University and ICTP Trieste. It was 1st performed in German at the Deutsche Museum, Bonn (5/'14). The show has eleven speaking parts and involves in total 20 people.Comment: 113 pages, 88 figures. An up to date version of the paper with high resolution pictures can be found at http://www.th.physik.uni-bonn.de/People/dreiner/Downloads/. In v2 the acknowledgements and a citation are correcte

Recent advances in organic synthesis using light-mediated n-heterocyclic carbene catalysis

The combination of photocatalysis with other ground state catalytic systems have attracted much attention recently due to the enormous synthetic potential offered by a dual activation mode. The use of N-heterocyclic carbene (NHC) as organocatalysts emerged as an important synthetic tool. Its ability to harness umpolung reactivity by the formation of the Breslow intermediate has been employed in the synthesis of thousands of biologically important compounds. However, the available coupling partners are relatively restricted, and its combination with other catalytic systems might improve its synthetic versatility. Thus, merging photoredox and N-heterocyclic carbene (NHC) catalysis has emerged recently as a powerful strategy to develop new transformations and give access to a whole new branch of synthetic possibilities. This review compiles the NHC catalyzed methods mediated by light, either in the presence or absence of an external photocatalyst, that have been described so far, and aims to give an accurate overview of the potential of this activation modeL.M. acknowledges the Autonomous Community of Madrid (CAM) for the financial support (PEJD-2019-PRE/AMB-16640 and SI1/PJI/ 2019-00237) and for an “Atracción de Talento Investigador” contract (2017-T2/AMB-5037

Machbarkeitsstudie zur Integration spezifischer Funktionalitäten von EUVISC in FLOWer

Für die vorliegende Machbarkeitsstudie wurden die im CFD-Code EUVISC implementierten Algorithmen mit denen des DLR-Strömungslösers FLOWer verglichen. Ziel dieses Vergleichs war die Beurteilung der Effektivität einer Integration der in EUVISC enthaltenen Funktionalitäten und algorithmischen Besonderheiten in den parallelen Mehrblockcode FLOWer. Der EUVISC-Code kann derzeit ausschließlich auf Monoblocktopologien arbeiten. Aufgrund erwarteter steigender Komplexitätsanforderungen bezüglich der mit EUVISC zu untersuchenden Konfigurationen wird eine derartige Einschränkung der einsetzbaren Netztopologie als unzureichend erachtet. Die EUVISC-Algorithmen wurden daher insbesondere bezüglich ihrer Erweiterbarkeit auf Mehrblocktopologien sowie auf eine mögliche Parallelisierbarkeit hin untersucht und beurteilt. Da es zudem als nicht sinnvoll erachtet wurde, EUVISC auf Mehrblocktopologien zu erweitern, wurde neben der genannten Beurteilung auch eine Abschätzung des Zeitaufwandes gemacht, der notwendig ist, um die untersuchten Algorithmen von EUVISC in FLOWer zu integrieren

Preparation and pH‐Dependent Properties of Hydrogels Based on Acidic Copolymers with PEG Side Chains and α‐Cyclodextrin

A variety of differently structured PEG‐based polymers can form physically cross‐linked PEG hydrogels with α‐cyclodextrin. The polymer structures strongly influence the properties of the hydrogel and its formation. Four different copolymers of methoxy PEG methacrylate and methacrylic acid are used together with α‐cyclodextrin to study hydrogel formation speed and gel strength. The hydrogels are formed within 1–25 min, and the formation process is examined in situ by dynamic light scattering. The gel formation time is pH dependent due to the methacrylic acid present in the polymers. The gel strength examined by texture analyzer also depends on the composition and pH. With prior mechanical destruction, all hydrogels are dissolvable in an excess of water, being a useful feature for an in vivo usage. By analyzing the structures of the hydrogels with confocal light microscopy (laser scanning confocal microscopy) and scanning electron microscope (SEM) after freeze etching, the different hydrogel structures can be observed

The guinea pig as model for high resolution ultrasound in small exotic mammals

Faßbender M, Trillmich F, Fritsch G, Cromarty L, Göritz F, Hildebrandt TB. The guinea pig as model for high resolution ultrasound in small exotic mammals. Erkrankungen der Zootiere. 2003;2003(41):273-278