@article{WensauerSteffensSuhrkeetal., author = {Wensauer, Andreas and Steffens, Oliver and Suhrke, Michael and R{\"o}ssler, Ulrich}, title = {Laterally coupled few-electron quantum dots}, series = {Physical Review B}, volume = {62}, journal = {Physical Review B}, number = {4}, doi = {10.1103/PhysRevB.62.2605}, pages = {2605}, abstract = {We present ground-state calculations for laterally coupled quantum dots containing 2, 4, and 8 electrons. As our emphasis is on spin effects our results are obtained by applying spin-density functional theory (SDFT). By varying the distance between the centers of the coupled quantum dots, the transition from weak to strong coupling situation is realized. For the 2-electron system we also apply the Heitler-London approximation and analytical concepts to check the reliability of SDFT calculations in this case. In addition we discuss the features of the Coulomb staircase of laterally coupled quantum dots in the weak and strong coupling regimes in comparison to that of a circular parabolic quantum dot.}, language = {en} } @inproceedings{Steffens, author = {Steffens, Oliver}, title = {"Gr{\"u}nes Denkmal" - Denkmalpflege und Erneuerbare Energien erg{\"a}nzen sich}, series = {Vorsicht Baudenkmal! Konfliktfelder Umwelt - Nutzung - Geschichte. Beitr{\"a}ge des 28. Regensburger Herbstsymposions f{\"u}r Kunst, Geschichte und Denkmalpflege vom 22. bis 24. November 2013}, booktitle = {Vorsicht Baudenkmal! Konfliktfelder Umwelt - Nutzung - Geschichte. Beitr{\"a}ge des 28. Regensburger Herbstsymposions f{\"u}r Kunst, Geschichte und Denkmalpflege vom 22. bis 24. November 2013}, editor = {Trapp, Eugen}, publisher = {Regensburg}, address = {Morsbach-Verl.}, isbn = {978-3-937527-77-2}, pages = {9 -- 17}, subject = {Denkmalpflege}, language = {de} } @inproceedings{SteffensSuhrkeRoessler, author = {Steffens, Oliver and Suhrke, Michael and R{\"o}ssler, Ulrich}, title = {Correlation in few-electron quantum dots: Spin effects and spontaneous currents}, series = {24rd International Conference on the Physics of Semiconductors (ICPS 24), Jerusalem, Israel, August 2-7, 1998}, booktitle = {24rd International Conference on the Physics of Semiconductors (ICPS 24), Jerusalem, Israel, August 2-7, 1998}, editor = {Gershoni, David}, publisher = {World Scientific}, address = {Singapore}, isbn = {978-981-02-3613-7}, language = {en} } @article{SzaboSteffensLenzetal., author = {Szab{\´o}, Peter and Steffens, Oliver and Lenz, Michael and Farkas, G{\´a}bor}, title = {Transient junction-to-case thermal resistance measurement methodology of high accuracy and high repeatability}, series = {IEEE Transactions on Components and Packaging Technologies}, volume = {28}, journal = {IEEE Transactions on Components and Packaging Technologies}, number = {4}, issn = {1521-3331}, doi = {10.1109/TCAPT.2005.859768}, pages = {630 -- 636}, abstract = {High-power packages show a characteristic three-dimensional heat flow resulting in large lateral changes in chip and case surface temperature. This paper proposes an unambiguous definition for the R/sub thJC/ junction-to-case thermal resistance as a key parameter of such packages based on a transient measurement technique ensuring high repeatability even at very low R/sub th/ values. The technique is illustrated on thermal transient measurements of high-power MOSFET devices. It is also presented how the same measurement results can be used for die attach quality analysis. Finally, a comparative method is shown for measuring the differences of R/sub th/ values among samples with many times higher resolution compared with a direct R/sub thJC/ measurement.}, language = {en} } @techreport{SchaubeckSteffensRechenauer, author = {Schaubeck, Simon and Steffens, Oliver and Rechenauer, Christian}, title = {Integration eines kostenoptimierten, wirtschaftlich rentablen Blockheizkraftwerks mit mittlerer thermischer Leistung in ein genossenschaftliches Wohnquartier}, language = {de} } @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} } @book{Steffens, author = {Steffens, Oliver}, title = {Einfluss der Potentialmodulation auf Magnetotransport und Quantenchaos in lateralen Halbleiter-{\"U}bergittern}, publisher = {Tectum-Verl.}, address = {Marburg}, isbn = {978-3-89608-726-3}, pages = {113}, language = {de} } @techreport{Steffens, author = {Steffens, Oliver}, title = {Saisonale W{\"a}rmespeicherung von opaken Bauteilen im Massivbau}, 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} } @unpublished{Steffens, author = {Steffens, Oliver}, title = {Binomial Distribution Nomogram after Larson}, abstract = {Following an idea of Larson (1966) we construct a nomogram for cumulative binomial distribution that can be used to perform hypothesis testing, quality management (e.g. test design) and other statistical tasks. The nomogram can be printed and directly used with a simple ruler to read the results. It is instructive and as an analog computing device continuous changes are easily visible.}, language = {en} } @unpublished{MalzSindersbergerMonkmanetal., author = {Malz, Sebastian and Sindersberger, Dirk and Monkman, Gareth J. and Steffens, Oliver and Kusterle, Wolfgang}, title = {Determination of the Water Content within Tunnel Linings to Assess Fire Safety}, series = {SSRN Electronic Journal}, journal = {SSRN Electronic Journal}, doi = {10.2139/ssrn.4390700}, pages = {22}, abstract = {Fires in tunnels are known to lead to explosive spalling of the tunnel linings, mainly due to rapid expansion of water as a result of vaporization in the concrete. In order to determine water content and assess fire safety within tunnel linings a novel measurement system has been developed. The development process includes the calibration of the sensor system via both direct and indirect approaches. This work compares both calibration methods and shows the differences that can occur due to measurement uncertainty. This work presents the measured water content within the Inntal tunnel, Austria as a representative tunnel from a total of four investigated tunnels. The obtained water content is compared to that found in the literature, and recommendations for practical work in terms of fire safety is given.}, 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} }