@inproceedings{RechenauerNeuleitnerSteffens, author = {Rechenauer, Christian and Neuleitner, Nikolaus and Steffens, Oliver}, title = {Empirische Untersuchung und Optimierung der Performance eines Modellprojekts f{\"u}r ein Effizienzhaus Plus mit solarthermischem Energiekonzept}, series = {Fachforum Effizienzhaus Plus, 14.07.2015}, booktitle = {Fachforum Effizienzhaus Plus, 14.07.2015}, address = {Hamburg}, language = {de} } @techreport{Steffens, author = {Steffens, Oliver}, title = {Saisonale W{\"a}rmespeicherung von opaken Bauteilen im Massivbau}, language = {de} } @article{RaithSchmidlingWindisch, author = {Raith, Lea and Schmidling, Anja and Windisch, Bastian}, title = {Bauteiltemperierung}, address = {Regensburg}, language = {de} } @article{SteffensSuhrkeRotteretal., author = {Steffens, Oliver and Suhrke, Michael and Rotter, Peter and R{\"o}ssler, Ulrich}, title = {From Landau levels to universal fluctuations: Level statistics for lateral superlattices}, series = {Physical Review B}, volume = {55}, journal = {Physical Review B}, number = {7}, doi = {10.1103/PhysRevB.55.4486}, pages = {4486 -- 4493}, abstract = {We study the energy-level statistics for electrons in a lateral two-dimensional superlattice in dependence on the strength of the modulation potential at a given perpendicular magnetic field. The interminiband statistics at some selected point in the magnetic Brillouin zone shows a transition from degenerate Landau levels to universal spectral correlations while the corresponding classical dynamics displays a crossover from regular cyclotron orbits to chaotic motion. In terms of the nearest-neighbor spacing distribution, we observe the occurrence of level repulsion for all nonzero modulation amplitudes, which indicates a discontinuous transition to universal fluctuations for the smallest level spacings when the rotational invariance of the system is broken by a finite superlattice potential. In order to test the universality of the transition on larger scales, we propose a random matrix model with one transition parameter for comparison. Confirmed by two different types of potential shapes, we detect an explicit influence of the potential shape on the level spacing distributions, which hence cannot be described by the one-parameter model. Using the spectral rigidity, however, universal long-range fluctuations in the regime of negligible Landau-level mixing are found, in agreement with our random matrix model.}, language = {en} } @article{SteffensWensauerSuhrke, author = {Steffens, Oliver and Wensauer, Andreas and Suhrke, Michael}, title = {Collective excitations in quantum dots: Calculated Raman spectra}, series = {physica status solidi (b)}, volume = {215}, journal = {physica status solidi (b)}, publisher = {Wiley}, doi = {10.1002/(SICI)1521-3951(199909)215:1<365::AID-PSSB365>3.0.CO;2-C}, pages = {365 -- 371}, abstract = {Electronic Raman scattering provides information on excited states, whose collective character as being related to the charge or spin density can be distinguished by using different polarization configurations. We employ time-dependent spin-density functional theory to calculate Raman spectra for circular semiconductor quantum dots with up to 10 electrons for the polarized and depolarized configuration and in dependence on an external magnetic field and the momentum transfer. Our results demonstrate an increase of the collective (or many-particle) character of the excitations with increasing momentum transfer and a mixing of spin- and charge-density modes for excitations from ground states with finite spin density. These results have predictive character, because corresponding experiments on few-electron dots have not yet been performed.}, language = {en} } @article{SuhrkeSteffensRotteretal., author = {Suhrke, Michael and Steffens, Oliver and Rotter, Peter and R{\"o}ssler, Ulrich}, title = {Quantum chaos and magnetotransport in lateral superlattices: The transition from weak to strong modulation potential}, series = {Physica E: Low-dimensional Systems and Nanostructures}, volume = {1}, journal = {Physica E: Low-dimensional Systems and Nanostructures}, number = {1-4}, issn = {1386-9477}, doi = {10.1016/S1386-9477(97)00060-X}, pages = {281 -- 287}, abstract = {Magnetotransport in lateral superlattices covers a variety of apparently different physics dependent on the amplitude of the modulation potential relative to the Fermi energy ranging from the weakly modulated 2DEG to the antidot lattice. Here we investigate the transition between weak modulation and antidots within the quantum-mechanical theory by studying (i) the single-particle spectrum with respect to quantum signatures of classical chaos and (ii) the change of characteristic features in the magnetoresistance starting from the Kubo formula.}, language = {en} } @techreport{SteffensRoesslerSuhrke, author = {Steffens, Oliver and R{\"o}ssler, Ulrich and Suhrke, Michael}, title = {Comment on "Shell Filling and Spin Effects in a Few Electron Quantum Dot"}, series = {Physical Review Letters}, volume = {77}, journal = {Physical Review Letters}, pages = {3613}, abstract = {We briefly report on calculated addition spectra for electrons in a circular quantum dot with perpendicular magnetic field. We compare our current density functional theory calculations with recent experiments by Tarucha et al. [PRL 77, 3613 (1996)]. We find a very good qualitative agreement of the structures and find an additional effect caused by Hund's first rule in magnetic field, which gives rise to new substructures not discussed in the paper by Tarucha.}, language = {en} } @article{Steffens, author = {Steffens, Oliver}, title = {Energetische Modernisierung und Restaurierung historisch wertvoller Stadtquartiere. Regenerative Energieversorgung als Schwerpunkt einer nachhaltigen Modernisierung historisch wertvoller Stadtquartiere (RENARHIS)}, series = {Zukunft bauen. Forschungsinitiative Zukunft Bau 2016}, journal = {Zukunft bauen. Forschungsinitiative Zukunft Bau 2016}, number = {5}, publisher = {Bundesministerium f{\"u}r Umwelt, Naturschutz, Bau und Reaktorsicherheit (BMUB)}, pages = {62 -- 65}, language = {de} } @misc{SteffensSaller, author = {Steffens, Oliver and Saller, Tobias}, title = {Modernisierungskonzepte f{\"u}r das denkmalgesch{\"u}tzte Ensemble am Jahn-Stadion Regensburg Pr{\"u}feninger Straße 47-52}, language = {de} } @inproceedings{HoellerSteffens, author = {H{\"o}ller, Christoph and Steffens, Oliver}, title = {Bauphysikalische Grundlagenausbildung an der OTH Regensburg w{\"a}hrend der COVID-19-Pandemie}, series = {Tagungsband DAGA 2021: 47. Jahrestagung f{\"u}r Akustik, 15.-18. August 2021, Wien und Online}, booktitle = {Tagungsband DAGA 2021: 47. Jahrestagung f{\"u}r Akustik, 15.-18. August 2021, Wien und Online}, publisher = {Deutsche Gesellschaft f{\"u}r Akustik e.V.}, isbn = {978-3-939296-18-8}, language = {de} } @inproceedings{RiegerDaeubleSchecketal., author = {Rieger, Anna and D{\"a}uble, Lukas and Scheck, Jochen and Zeitler, Berndt and H{\"o}ller, Christoph}, title = {Experimental study on using transient excitation signals in the prediction of sound pressure levels from building services according to EN 12354-5 and EN 15657}, series = {Proceedings of DAS|DAGA 2025, 51st Annual Meeting on Acoustics, March 17-20, 2025, Copenhagen}, booktitle = {Proceedings of DAS|DAGA 2025, 51st Annual Meeting on Acoustics, March 17-20, 2025, Copenhagen}, address = {Berlin}, organization = {Deutsche Gesellschaft f{\"u}r Akustik e.V. (DEGA), Berlin}, isbn = {978-3-939296-23-2}, doi = {10.71568/dasdaga2025.526}, pages = {372 -- 375}, abstract = {EN 12354-5:2023 describes a calculation procedure to predict the sound pressure levels from building service equipment. The procedure uses the blocked force of the source as input data. This quantity can be determined using the reception plate method according to EN 15657:2017. The methods have been developed and validated for stationary excitation signals (Leq). Real structure-borne sound sources often have time-varying excitation signals. In addition, the requirements for sound insulation against noise from building service equipment in Germany (DIN 4109) are given in terms of the maximum, time-weighted sound pressure level (LFmax). This contribution investigates the suitability of the methods described in EN 12354-5 and EN 15657 for structure-borne sound sources with transient excitation signals. A measurement series with time signals ranging from stationary to highly transient was conducted in a building-like laboratory. The reverberation time of the receiving room was adjusted to three different values. The calculations were processed using Leq values, LFmax values and short-time Leq values. The results show the uncertainties that can arise in the prediction of signals with varying transient characteristics compared to stationary excitation signals.}, language = {en} } @inproceedings{HoellerParzingerSchanda, author = {H{\"o}ller, Christoph and Parzinger, Michael and Schanda, Ulrich}, title = {The Sound Reduction Index of Homogeneous Building Elements according to Annex B of ISO 12354-1 - Discussion and Proposal for Changes}, series = {Proceedings of DAS|DAGA 2025, 51st Annual Meeting on Acoustics, March 17-20, 2025, Copenhagen}, booktitle = {Proceedings of DAS|DAGA 2025, 51st Annual Meeting on Acoustics, March 17-20, 2025, Copenhagen}, address = {Berlin}, organization = {Deutsche Gesellschaft f{\"u}r Akustik e.V. (DEGA), Berlin}, isbn = {978-3-939296-23-2}, doi = {10.71568/dasdaga2025.147}, pages = {312 -- 315}, abstract = {Annex B of ISO 12354-1:2017 describes a procedure for the calculation of the frequency-dependent sound reduction index of homogeneous building elements such as concrete floors or masonry walls. With the introduction of EN 12354-5:2023 and an upcoming change in DIN 4109-2 regarding the calculation of sound levels due to service equipment, it is anticipated that the practical relevance and usage of Annex B will increase in the future. For this reason, the procedure has recently been investigated by an informal working group of academics from several German universities. It was found that Annex B contains some errors, missing references, and ambiguities in the calculation procedure. Based on these discussions, some changes were proposed to the committee responsible for the standard (CEN/TC 126/WG 2). While the general calculation procedure was left unchanged, the proposed changes focus on the influence of shear deformation, the radiation factor for free waves, a moving average function to limit the variability in the coincidence region, and the calculation examples provided in the annex. This contribution provides an overview of the procedure, presents some background information on the underlying theory, and discusses the proposed changes.}, language = {en} } @inproceedings{BaeumlerHoeller, author = {B{\"a}umler, Georg and H{\"o}ller, Christoph}, title = {Modifying a Wall Transmission Suite to Measure Diffuse Field Sound Absorption Coefficients - A Case Study}, series = {Proceedings of DAS|DAGA 2025, 51st Annual Meeting on Acoustics, March 17-20, 2025, Copenhagen}, booktitle = {Proceedings of DAS|DAGA 2025, 51st Annual Meeting on Acoustics, March 17-20, 2025, Copenhagen}, address = {Berlin}, organization = {Deutsche Gesellschaft f{\"u}r Akustik e.V. (DEGA), Berlin}, isbn = {978-3-939296-23-2}, doi = {10.71568/dasdaga2025.291}, pages = {1191 -- 1194}, abstract = {The determination of the diffuse field sound absorption coefficient is carried out in reverberation chambers that comply with the requirements of the corresponding standard, ISO 354. No such chamber exists at OTH Regensburg University of Applied Sciences, but a new wall transmission suite according to ISO 10140 is available. This student project investigates the possibility of using the wall transmission suite to measure absorption coefficients for teaching and research purposes.To assess the suitability of the room, the diffusivity was evaluated using the standard deviation of both the reverberation times and the equivalent continuous sound pressure levels at multiple positions within the room. These results, along with a comparison with expected values for a diffuse sound field, guided the design of reflector panels to introduce diffuse reflections. The implementation features acrylic (PMMA) as the primary material in combination with dense viscoelastic damping sheets, resulting in a low vibration solution. Suspended from the ceiling of the chamber, these improved the diffusivity of the sound field, making the room suitable for absorption measurements across a broad frequency range.}, language = {en} } @incollection{MuehlbergerSchoplocherSteffens, author = {M{\"u}hlberger, Thomas and Schoplocher, Paul Dragos and Steffens, Oliver}, title = {Thermische Geb{\"a}udesimulation: aktuelle Anwendungen und Erweiterungen mittels der Finite-Elemente-Methode}, series = {Bauphysik-Kalender 2025: Simulationen, BIM und KI}, booktitle = {Bauphysik-Kalender 2025: Simulationen, BIM und KI}, editor = {Fouad, Nabil A.}, publisher = {Ernst \& Sohn}, address = {Berlin}, isbn = {9783433034514}, doi = {10.1002/9783433612095.ch12}, pages = {435 -- 468}, abstract = {Nach einem kurzen historischen Abriss der Entwicklung der Geb{\"a}udesimulation wird die aktuell {\"u}bliche gleichungsbasierte Kompaktmodell-Simulation beschrieben und deren praktische Anwendung aufgezeigt. Dabei wird auf die Bedeutung der Validierung von Simulationstools und auf etablierte Validierungsstandards eingegangen. Geb{\"a}udesimulation dient der Optimierung des Bauens in allen Planungsphasen. Mit Praxisbeispielen vom sommerlichen W{\"a}rmeschutz bis hin zur Modellierung innovativer Konstruktionen werden unterschiedliche Einsatzbereiche demonstriert. Im zweiten Teil wird die Verwendung der Finite-Elemente-Methode (FEM) f{\"u}r die bauphysikalische Modellierung vorgestellt. Anhand von Beispielen zeigen wir, dass die (rechenzeitintensive) FEM aufgrund einer detaillierteren Modellierung von Geometrie, Strahlung und Konvektion pr{\"a}zisere Simulationsergebnisse liefert. Zum Abschluss werden Wege vorgeschlagen, wie dies zur Erweiterung der schnelleren Kompaktmodell-Simulation eingesetzt werden kann.}, language = {de} } @inproceedings{BuchnerWagnerHoeller, author = {Buchner, Stefan and Wagner, Marcus and H{\"o}ller, Christoph}, title = {Inverse Acoustic Characterization of Rigid Porous Media using Artificial Neural Networks}, series = {Proceedings of DAS|DAGA 2025, 51st Annual Meeting on Acoustics, March 17-20, 2025, Copenhagen}, booktitle = {Proceedings of DAS|DAGA 2025, 51st Annual Meeting on Acoustics, March 17-20, 2025, Copenhagen}, address = {Berlin}, organization = {Deutsche Gesellschaft f{\"u}r Akustik e.V. (DEGA), Berlin}, isbn = {978-3-939296-23-2}, doi = {10.71568/dasdaga2025.142}, pages = {847 -- 850}, abstract = {Porous sound absorbers can be described by the isotropic Biot model, and its fluid phase can be represented by the Champoux-Allard model. To apply these models to a given absorber material, the five acoustical and the four mechanical material parameters must be known. The direct measurement of these parameters is complex and requires cost-intensive measurement equipment. Current inverse methods to obtain these material parameters solve an optimization problem, trying to fit the absorption or impedance curve of the material model to the impedance tube measurement data. Solving this optimization problem, i.e. finding the global minimum, is not guaranteed in an acceptable amount of time, as the optimization problem possesses a multitude of local minima. This work proposes an alternative, data driven approach using artificial neural networks to obtain the material parameters necessary for the characterization of open porous materials. The approach only requires the results of standard impedance tube measurements. The characterization of rigid- and elastic frame materials has been investigated. The datasets were generated using the rigid and elastic frame models for porous absorbers. The approach shows good results for impedance curves generated by the analytical models, the validation with real-world impedance tube measurement data is currently under investigation.}, language = {en} }