On propagators and vertices of Landau gauge Yang-Mills theory

We calculate the three-point functions of pure Landau gauge QCD and investigate their influence on the propagators. As expected, the ghost-gluon vertex leads only to minor modifications, while the three-gluon vertex has a sizeable impact on the mid-momentum regime of the gluon propagator. We describe an effective model of the three-gluon vertex that includes contributions from the neglected two-loop diagrams and thus allows to obtain propagators in good agreement with lattice results. We also determine the three-gluon vertex from these propagators and find good agreement with lattice results as well. In turn, these results allow us to assess the effect of the missing two-loop diagrams in the gluon propagator equation. Finally, we present the first self-consistent calculation that includes all two-and three-point functions.Comment: 12 pages, 10 figs., contribution to "QCD-TNT-III: From quarks and gluons to hadronic matter: A bridge too far?", 2-6 Sept 2013, ECT*, Trento, Ital

Mott metal-insulator transition on compressible lattices

The critical properties of the finite temperature Mott endpoint are drastically altered by a coupling to crystal elasticity, i.e., whenever it is amenable to pressure tuning. Similar as for critical piezoelectric ferroelectrics, the Ising criticality of the electronic system is preempted by an isostructural instability, and long-range shear forces suppress microscopic fluctuations. As a result, the endpoint is governed by Landau criticality. Its hallmark is thus a breakdown of Hooke's law of elasticity with a non-linear strain-stress relation characterized by a mean-field exponent. Based on a quantitative estimate, we predict critical elasticity to dominate the temperature range DeltaT/Tc ~ 8% close to the Mott endpoint of kappa-(BEDT-TTF)2X.Comment: 4 pages, 6 figure

Untersuchung des Zusammenhangs von Presence und User Experience in der Virtuellen Realität als Grundlage für die Entwicklung von Trainingssystemen und Medizinprodukten in der Chirurgie

Die Dissertation untersucht grundlegende psychologische Faktoren für die Nutzbarmachung der Potentiale von Virtueller Realität für die chirurgische Ausbildung und Medizinprodukteentwicklung.:I Abkürzungsverzeichnis .................................................................................................................... 4 II Abbildungsverzeichnis..................................................................................................................... 5 1 Einführung in die Thematik ............................................................................................................. 6 1.1 Einsatz von Virtual Reality in Medizin und Chirurgie .............................................................. 6 1.1.1 Virtual Reality für chirurgisches Training und Telechirurgie ........................................... 6 1.1.2 Virtual Reality in der Therapie und Rehabilitation.......................................................... 7 1.2 Presence, User Experience und Usability ................................................................................ 8 1.2.1 Begriffe ............................................................................................................................ 8 1.2.2 Verwendete Messmethoden für Presence, User Experience und Usability ................. 10 1.3 Potentiale von Virtual Reality in der Medizinproduktentwicklung....................................... 11 1.4 Motivation und Ziele der Arbeit............................................................................................ 13 1.5 Experimenteller Aufbau ........................................................................................................ 16 1.5.1 Studienaufbau ............................................................................................................... 16 1.5.2 Experimentaltechnik...................................................................................................... 20 2 Publikationsmanuskripte............................................................................................................... 22 2.1 Brade, J., Lorenz, M. et al. (2017). Being there again – Presence in real and virtual environments and its relation to usability and user experience using a mobile navigation task..... 22 2.2 Lorenz, M. et al. (2018). Presence and User Experience in a Virtual Environment under the Influence of Ethanol: An Explorative Study....................................................................................... 35 2.3 Diskussion.............................................................................................................................. 51 3 Zusammenfassung der Arbeit ....................................................................................................... 53 3.1 Hintergrund ........................................................................................................................... 53 3.2 Ziele ....................................................................................................................................... 53 3.3 Methoden.............................................................................................................................. 54 3.4 Ergebnisse.............................................................................................................................. 54 3.5 Schlussfolgerungen................................................................................................................ 55 4 Literaturverzeichnis....................................................................................................................... 56 III Darstellung des eigenen Beitrags.................................................................................................. 64 IV Erklärung über die eigenständige Abfassung der Arbeit............................................................... 66 V Wissenschaftliche Veröffentlichungen und Vorträge ................................................................... 67 VI Danksagung ................................................................................................................................... 7

Micro-electromechanical affinity sensor for the monitoring of glucose in bioprocess media

An affinity-viscometry-based micro-sensor probe for continuous glucose monitoring was investigated with respect to its suitability for bioprocesses. The sensor operates with glucose and dextran competing as binding partner for concanavalin A, while the viscosity of the assay scales with glucose concentration. Changes in viscosity are determined with a micro-electromechanical system (MEMS) in the measurement cavity of the sensor probe. The study aimed to elucidate the interactions between the assay and a typical phosphate buffered bacterial cultivation medium. It turned out that contact with the medium resulted in a significant long-lasting drift of the assay’s viscosity at zero glucose concentration. Adding glucose to the medium lowers the drift by a factor of eight. The cglc values measured off-line with the glucose sensor for monitoring of a bacterial cultivation were similar to the measurements with an enzymatic assay with a difference of less than ±0.15 g·L−1. We propose that lectin agglomeration, the electro-viscous effect, and constitutional changes of concanavalin A due to exchanges of the incorporated metal ions may account for the observed viscosity increase. The study has demonstrated the potential of the MEMS sensor to determine sensitive viscosity changes within very small sample volumes, which could be of interest for various biotechnological applications.DFG, 325093850, Open Access Publizieren 2017 - 2018 / Technische Universität Berli

Certifiers Make Neural Networks Vulnerable to Availability Attacks

To achieve reliable, robust, and safe AI systems, it is vital to implement fallback strategies when AI predictions cannot be trusted. Certifiers for neural networks are a reliable way to check the robustness of these predictions. They guarantee for some predictions that a certain class of manipulations or attacks could not have changed the outcome. For the remaining predictions without guarantees, the method abstains from making a prediction, and a fallback strategy needs to be invoked, which typically incurs additional costs, can require a human operator, or even fail to provide any prediction. While this is a key concept towards safe and secure AI, we show for the first time that this approach comes with its own security risks, as such fallback strategies can be deliberately triggered by an adversary. In addition to naturally occurring abstains for some inputs and perturbations, the adversary can use training-time attacks to deliberately trigger the fallback with high probability. This transfers the main system load onto the fallback, reducing the overall system's integrity and/or availability. We design two novel availability attacks, which show the practical relevance of these threats. For example, adding 1% poisoned data during training is sufficient to trigger the fallback and hence make the model unavailable for up to 100% of all inputs by inserting the trigger. Our extensive experiments across multiple datasets, model architectures, and certifiers demonstrate the broad applicability of these attacks. An initial investigation into potential defenses shows that current approaches are insufficient to mitigate the issue, highlighting the need for new, specific solutions

Electronic properties of curved few-layers graphene: a geometrical approach

We show the presence of non-relativistic L\'evy-Leblond fermions in flat three- and four-layers graphene with AB stacking, extending the results obtained in [Curvatronics2017] for bilayer graphene. When the layer is curved we obtain a set of equations for Galilean fermions that are a variation of those of L\'evy-Leblond with a well defined combination of pseudospin, and that admit L\'evy-Leblond spinors as solutions in an approriate limit. The local energy of such Galilean fermions is sensitive to the intrinsic curvature of the surface. We discuss the relationship between two-dimensional pseudospin, labelling layer degrees of freedom, and the different energy bands. For L\'evy-Leblond fermions an interpretation is given in terms of massless fermions in an effective 4D spacetime, and in this case the pseudospin is related to four dimensional chirality. A non-zero energy band gap between conduction and valence electronic bands is obtained for surfaces with positive curvature.Comment: 16 pages, 4 figures. Matches the published version. Refined theory that describes the unique combination of isospin states ocurring in curved bilayer graphene sheet

Lessons Learned from OSIRIS-Rex Autonomous Navigation Using Natural Feature Tracking

The Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer (Osiris-REx) spacecraft is scheduled to launch in September, 2016 to embark on an asteroid sample return mission. It is expected to rendezvous with the asteroid, Bennu, navigate to the surface, collect a sample (July 20), and return the sample to Earth (September 23). The original mission design called for using one of two Flash Lidar units to provide autonomous navigation to the surface. Following Preliminary design and initial development of the Lidars, reliability issues with the hardware and test program prompted the project to begin development of an alternative navigation technique to be used as a backup to the Lidar. At the critical design review, Natural Feature Tracking (NFT) was added to the mission. NFT is an onboard optical navigation system that compares observed images to a set of asteroid terrain models which are rendered in real-time from a catalog stored in memory on the flight computer. Onboard knowledge of the spacecraft state is then updated by a Kalman filter using the measured residuals between the rendered reference images and the actual observed images. The asteroid terrain models used by NFT are built from a shape model generated from observations collected during earlier phases of the mission and include both terrain shape and albedo information about the asteroid surface. As a result, the success of NFT is highly dependent on selecting a set of topographic features that can be both identified during descent as well as reliably rendered using the shape model data available. During development, the OSIRIS-REx team faced significant challenges in developing a process conducive to robust operation. This was especially true for terrain models to be used as the spacecraft gets close to the asteroid and higher fidelity models are required for reliable image correlation. This paper will present some of the challenges and lessons learned from the development of the NFT system which includes not just the flight hardware and software but the development of the terrain models used to generate the onboard rendered images

Concurrent segregation and erosion effects in medium-energy iron beam patterning of silicon surfaces

This paper is part of: Special Issue on Surfaces Patterned by Ion SputteringWe have bombarded crystalline silicon targets with a 40 keV Fe+ ion beam at different incidence angles. The resulting surfaces have been characterized by atomic force, current-sensing and magnetic force microscopies, scanning electron microscopy, and x-ray photoelectron spectroscopy. We have found that there is a threshold angle smaller than 40 degrees for the formation of ripple patterns, which is definitely lower than those frequently reported for noble gas ion beams. We compare our observations with estimates of the value of the critical angle and of additional basic properties of the patterning process, which are based on a continuum model whose parameters are obtained from binary collision simulations. We have further studied experimentally the ripple structures and measured how the surface slopes change with the ion incidence angle. We explore in particular detail the fluence dependence of the pattern for an incidence angle value (40 degrees) close to the threshold. Initially, rimmed holes appear randomly scattered on the surface, which evolve into large, bug-like structures. Further increasing the ion fluence induces a smooth, rippled background morphology. By means of microscopy techniques, a correlation between the morphology of these structures and their metal content can be unambiguously established.This research is supported by the MINECO/FEDER (Spain/UE) grants Nos. MAT2017-85089-C2-1-R, MAT2016-80394-R, FIS2015-66020-C2-1-P, FIS2015-73337-JIN, FIS2016-78883-C2-2-P, and BIO2016-79618-R, and by Comunidad de Madrid grant NANOAVANSENS ref. S2013/MIT-3029. We want to thank C. Ballesteros and B. Galiana for their help in the SEM measurements. ARC acknowledges the Ramón y Cajal contract number RYC-2015-18047 and KL thanks FCT, Portugal, for her grant as Investigador FCT