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45 results on '"Muller, Steffen"'

1. Towards a Holographic Realization of Homes' Law

Author

Erdmenger, Johanna, Kerner, Patrick, and Muller, Steffen

Subjects
High Energy Physics - Theory, Condensed Matter - Superconductivity
Abstract

Gauge/gravity duality has proved to be a very successful tool for describing strongly coupled systems in particle physics and heavy ion physics. The application of the gauge/gravity duality to quantum matter is a promising candidate to explain questions concerning non-zero temperature dynamics and transport coefficients. To a large extent, the success of applications of gauge/gravity duality to the quark-gluon plasma is founded on the derivation of a universal result, the famous ratio of shear viscosity and entropy density. As a base for applications to condensed matter physics, it is highly desirable to have a similar universal relation in this context as well. A candidate for such a universal law is given by Homes' law: High Tc superconductors, as well as some conventional superconductors, exhibit a universal scaling relation between the superfluid density at zero temperature and the conductivity at the critical temperature times the critical temperature itself. In this work we describe progress in employing the models of holographic superconductors to realize Homes' law and to find a universal relation governing strongly correlated quantum matter. We calculate diffusive processes, including the backreaction of the gravitational matter fields on the geometry. We consider both holographic s-wave and p-wave superconductors. We show that a particular form of Homes' law holds in the absence of backreaction. Moreover, we suggest further steps to be taken for holographically realizing Homes' law more generally in the presence of backreaction., Comment: 32 pages, 9 figures and 1 table

Published
2012
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2. On Stability and Transport of Cold Holographic Matter

Author

Ammon, Martin, Erdmenger, Johanna, Lin, Shu, Muller, Steffen, O'Bannon, Andy, and Shock, Jonathan P.

Subjects
High Energy Physics - Theory
Abstract

We use gauge-gravity duality to study the stability of zero-temperature, finite baryon density states of N=4 supersymmetric SU(Nc) Yang-Mills theory coupled to a single massive fundamental-representation N=2 hypermultiplet in the large-Nc and large-coupling limits. In particular, we study the spectrum of mesons. The dual description is a probe D7-brane in anti-de Sitter space with a particular configuration of worldvolume fields. The meson spectrum is dual to the spectrum of fluctuations of worldvolume fields about that configuration. We use a combination of analytical and numerical techniques to compute the spectrum, including a special numerical technique designed to deal with singular points in the fluctuations' equations of motion. Despite circumstantial evidence that the system might be unstable, such as a finite entropy density at zero temperature and the existence of instabilities in similar theories, we find no evidence of any instabilities, at least for the ranges of frequency and momenta that we consider. We discover a pole on the imaginary frequency axis in a scalar meson two-point function, similar to the diffusive mode in the two-point function of a conserved charge., Comment: 40 pages, 7 figures

Published
2011
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3. Reliability of Deep Neural Networks for an End-to-End Imitation Learning-Based Lane Keeping

Author

Liu, Shen and Muller, Steffen

Abstract

In recent years, end-to-end imitation learning-based deep neural networks (DNN) have been successfully applied to several autonomous driving tasks. Meanwhile, however, the large uncertainties with respect to the reliability of the DNN’s decision-making mechanism significantly limit the application of DNN-based approaches in the safety-critical domain of autonomous driving. In this work, a comprehensive analytical method of the DNN’s decision-making mechanism is proposed for developing a reliable imitation learning-based end-to-end visual solution for automated lane keeping on the highway in a co-simulation environment. During the mechanism analysis, three progressive and crucial questions covering from the DNN’s decision-making basis to decision itself can be explicitly answered using the modified algorithms of Explainable artificial intelligence (XAI) and the theoretical knowledge of vehicle dynamics; During the model development, the DNN’s architecture is stepwise improved based on the intermediate analytical and test results in the imperfect and failure cases, aimed at increasing the DNN’s lane keeping imitation accuracy and robustness from a superficial point of view as well as enhancing the reliability of the DNN’s decision-making mechanism from an essential point of view. The DNN’s lane keeping performance is quantitatively evaluated based on a proposed evaluation method considering 3 vital perspectives regarding vehicle dynamics. The ultimate test results show that the final proposed DNN model, which has a reliable decision-making mechanism, achieves a satisfactory lane keeping performance with a high imitation accuracy and robustness, and outperforms the state-of-the-art lane keeping approaches based on the end-to-end DNN models and the traditional modular solution.

Published
2023
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13. Estimation of the maximum tire-road friction coefficient

Author

Muller, Steffen, Uchanski, Michael, and Hedrick, Karl

Subjects
Dynamical systems -- Research, Engineering and manufacturing industries, Science and technology
Abstract

We develop and test a 'slip-based' method to estimate the maximum available tire-road friction during braking. The method is based on the hypothesis that the low-slip, low-[mu] parts of the slip curve used during normal driving can indicate the maximum tire-road friction coefficient, [[mu].sub.max]. We find support for this hypothesis in the literature and through experiments. The friction estimation algorithm uses data from short braking maneuvers with peak accelerations of 3.9 m/[s.sup.2] to classify the road surface as either dry. ([[mu].sub.max][approximately equal to] 1) or lubricated ([[mu].sub.max][approximately equal to] 0.6). Significant measurement noise makes it difficult to detect the subtle effect being measured, leading to a misclassification rate of 20%.

Published
2003

16. Transcriptional regulation of genes encoding the selenium-free (NiFe)-hydrogenases in the archaeon Methanococcus voltae involves positive and negative control elements

Author

Noll, Izabela, Muller, Steffen, and Klein, Albrecht

Subjects
Genetic regulation -- Research, Nitrogen compounds -- Research, Hydrogenation -- Research, Microbial enzymes -- Genetic aspects, Biological sciences
Abstract

Methanococcus voltae harbors genetic information for two pairs of homologous [NiFe]-hydrogenases. Two of the enzymes contain selenocysteine, while the other two gene groups encode apparent isoenzymes that carry cysteinyl residues in the homologous positions. The genes coding for the selenium-free enzymes, frc and vhc, are expressed only under selenium limitation. They are transcribed out of a common intergenic region. A series of deletions made in the intergenic region localized a common negative regulatory element for the vhc and frc promoters as well as two activator elements that are specific for each of the two transcription units. Repeated sequences, partially overlapping the frc promoter, were also detected. Mutations in these repeated heptanucleotide sequences led to a weak induction of a reporter gene under the control of the frc promoters in the presence of selenium. This result suggests that the heptamer repeats contribute to the negative regulation of the frc transcription unit.

Published
1999

23. Kinetic resolution of homoaldols via catalytic asymmetric transacetalization

Author

Coric, Ilija, Muller, Steffen, and List, Benjamin

Subjects
Chemical reaction, Rate of -- Analysis, Fructosediphosphate aldolase -- Chemical properties, Catalysts -- Analysis, Chemistry
Abstract

A transacetalization reaction was applied to achieve the highly enantioselective kinetic resolution of homoaldols. The transformation was performed in the presence of a novel phosphoric acid, STRIP, based on a spirocyclic 1,1'-spirobiindane backbone designed and identified as a superior catalyst.

Published
2010

41. CVD Diamond Detectors - R&D Status and New Results

Author

BERDERMANN, Elèni, primary, De Boer, Wim, additional, Ciobanu, M., additional, Dunst, Stefan, additional, Kis, M., additional, Koenig, W., additional, Moritz, P., additional, Morse, J., additional, Muller, Steffen, additional, Nociforo, C., additional, Pomorski, Michal, additional, Schreck, Matthias, additional, Rahman, M. S., additional, Traeger, M., additional, and Weick, H., additional

Published
2010
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43. Development of diamond tracking detectors for high luminosity experiments at LHC

Author

Barbero, M., Mathes, M., Velthuis, J., Wermes, N., Bellini, V., Potenza, R., Sutera, C., Tuve, C., Gorisek, A., Pernegger, H., Roe, S., Weilhammer, P., Frais-Kolbl, H., Griesmayer, E., Schreiner, T., Bruzzi, M., Lagomarsino, S., Menichelli, D., Miglio, S., Sciortino, Silvio, Eusebi, R., Mishina, M., Berdermann, E., Pomorski, M., Schmidt, C., Traeger, M., Eremin, V., Dulinski, W., Golubev, A., Grigoriev, E., Kuleshov, S., Martemyanov, A., Vladimir Cindro, Dolenc, I., Kramberger, G., Mandic, I., Mikuz, M., Bol, Johannes, Boer, Wim, Furgeri, A., Muller, Steffen, Bergonzo, P., Belyaev, V., Hartjes, F., Gan, K. K., Kagan, H., Kass, R., Smith, S., Schnetzer, S., Stone, R., Fizzotti, F., Lo Giudice, A., Manfredotti, C., Vittone, E., Trischuk, W., Dong, P., Schrupp, C., and Wallny, R.

Subjects
Detectors and Experimental Techniques
Abstract

During 2006 detectors based on new polycrystalline CVD (pCVD) material were produced as candidates for use in LHC experiments. The first full size diamond pixel module with ATLAS specifications using a $2 \times 6$ cm$^2$ pCVD sample was characterized in the 2006 CERN test beam. Radiation damage studies performed outside of CERN corroborate the radiation hardness of this material. Radiation hardness studies at CERN using the highest quality diamond were deferred until 2007 due to the PS magnet problem. ATLAS, CMS, ALICE and LHCb are planning to use diamond for their beam conditions monitoring systems. Construction of the BCM system for ATLAS was completed in 2006 and the BCM modules were characterized in 2006 CERN test beams. Similar devices are under construction for the CMS, ALICE and LHCb experiments. Single-crystal CVD (scCVD) samples were produced and made available to RD42 institutes. The first scCVD diamond pixel device was constructed and tested in the 2006 CERN test beams. In this report we present the progress and work done by the RD42 collaboration on the development of CVD diamond material for radiation detectors.

44. RD39 status report 2006

Author

Rouby, X., Militaru, O., Piotrzkowski, K., Vladimir Cindro, Mandic, I., Mikuz, M., Zavrtanik, M., Anbinderis, P., Anbinderis, T., Gaubas, E., Kalesinskas, V., Vaitkus, J., D Ambrosio, N., Buontempo, S., Pagano, S., Bates, R., Buttar, C., O Shea, V., Parkes, C., Boer, Wim, Bol, Johannes, Furgeri, A., Heising, S., Krause, M., Muller, Steffen, Reinhardt, S., Borchi, E., Bruzzi, M., Menichelli, D., Pirollo, S., Chen, W., Li, Z., Eremin, V., Ilyashenko, I., Verbitskaya, E., Grigoriev, E., Harkonen, J., Luukka, P., Tuominen, E., Tuovinen, E., Heijne, E., Niinikoski, T. O., Pusa, P., Raisanen, J., and Vayrynen, S.

Subjects
Detectors and Experimental Techniques

45. Sensitivity of Extensive Air Showers to Features of Hadronic Interactions at Ultra-High Energies

Author

Ulrich, Ralf, Engel, Ralph, Muller, Steffen, Tanguy Pierog, Schussler, Fabian, and Unger, Michael

Subjects
High Energy Astrophysical Phenomena (astro-ph.HE), Astrophysics::High Energy Astrophysical Phenomena, Astrophysics::Instrumentation and Methods for Astrophysics, FOS: Physical sciences, High Energy Physics::Experiment, Astrophysics - High Energy Astrophysical Phenomena
Abstract

We study the dependence of extensive air shower development on the first hadronic interactions at ultra-high energies occurring in the startup phase of the air shower cascade. The interpretation of standard air shower observables depends on the characteristics of these interactions. Thus, it is currently difficult to draw firm conclusions for example on the primary cosmic ray mass composition from the analysis of air shower data. On the other hand, a known primary mass composition would allow us to study hadronic interactions at center of mass energies well above the range that is accessible to accelerators measurements., Submitted to the 31th ICRC, Lodz, Poland, 2009

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