@techreport{BergmannHaugRechenaueretal., author = {Bergmann, Anja and Haug, Sonja and Rechenauer, Christian and Saller, Tobias and Schaubeck, Simon and Scheuerer (Scheuerer-Lenzen), Birgit and Schr{\"o}ter, Sonja and Schulz-Brize, Thekla and Steffens, Oliver and Vernim, Matthias and Matthias, Wittmann and Zeitler, Annika and Zimmermann, Patrick}, title = {Nachhaltige energetische Modernisierung und Restaurierung historisch wertvoller Stadtquartiere. Forschungsprojekt RENARHIS - Endbericht und Leitfaden. Zukunft Bau Projekt Nr. II 3-F20-11-1-038 (BBSR)}, editor = {Steffens, Oliver}, address = {Regensburg}, organization = {Ostbayerische Technische Hochschule Regensburg}, doi = {10.13140/RG.2.1.2465.7364}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:898-opus4-20766}, pages = {338}, abstract = {Dieser Bericht in Gestalt eines Leitfadens f{\"u}r eine nachhaltige energetische Modernisierung von historischen Stadtquartieren mit besonderem architektonischen Wert ist das Ergebnis eines Forschungsprojekts an der Ostbayerischen Technischen Hochschule Regensburg, das vom Bundesinstitut f{\"u}r Bau-, Stadt- und Raumforschung im Rahmen der F{\"o}rderinitiative „Zukunft Bau" (Projekt Nr. II 3-F20-11-1-038 / SWD-10.08.18.7-12.21) in den Jahren 2012 bis 2014 gef{\"o}rdert wurde. Im Projekt RENARHIS („Regenerative Energieversorgung als Schwerpunkt einer nachhaltigen Modernisierung historischer Stadtquartiere") wurden am Modell eines genossenschaftlichen Wohnquartiers aus den 1920er Jahren Restaurierungs- und Modernisierungsstrategien erarbeitet. Das „Plato-Wild-Ensemble" liegt im Regensburger Stadtosten, außerhalb der mittelalterlichen Altstadt. Es steht nicht unter Denkmalschutz, kann aber gleichwohl aus architektonischen und sozialgeschichtlichen Gr{\"u}nden als Beispiel f{\"u}r musterg{\"u}ltigen und sch{\"a}tzenswerten genossenschaftlichen Wohnungsbau gelten. In diesem Leitfaden sollen aus den Erfahrungen und L{\"o}sungsans{\"a}tzen des Projekts allgemeine Handlungsgrund Orientierungshilfen geboten werden, die den Horizont des eigentlichen Projekts erweitern auf eine Vielzahl {\"a}hnlicher Bestandssituationen.}, language = {de} } @incollection{FalterGoldbergGuentheretal., author = {Falter, Thomas and Goldberg, Boris and G{\"u}nther, Swen and Steffens, Oliver}, title = {Transfererfolg messbar machen}, series = {Erfolgreicher Transfer in der Arbeitsgestaltung}, booktitle = {Erfolgreicher Transfer in der Arbeitsgestaltung}, editor = {Borowski, Esther and Cernavin, Oleg and Hees, Frank and Joerißen, Theresa}, publisher = {Waxmann}, address = {M{\"u}nster}, doi = {10.31244/9783830998082}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:898-opus4-67568}, publisher = {Ostbayerische Technische Hochschule Regensburg}, pages = {173 -- 187}, abstract = {Hochschulen f{\"u}r angewandte Wissenschaften (HAW) kommt als regionalen Innovationstreibern eine gesellschaftliche Verantwortung durch ihre Zusammenarbeit mit Unternehmen und Gesellschaft zu. Diese Zusammenarbeit geschieht im Rahmen von Aktivit{\"a}ten des Wissens- und Technologietransfers. Die Beurteilung des Erfolgs dieser Transferaktivit{\"a}ten verursacht jedoch regelm{\"a}ßig Schwierigkeiten, da geeignete Indikatoren zur Erfolgsmessung fehlen. Im Rahmen des vom Bundesministerium f{\"u}r Bildung und Forschung (BMBF) gef{\"o}rderten Verbundforschungsprojektes Transfer_i wurde ein Modell zur Objektivierung und Messung von Forschungsleistung, forschungsbasiertem Transfer sowie dessen Umsetzung am Markt in Form von Innovationen erarbeitet. Mit dem Forschungsprojekt wurden kausale Zusammenh{\"a}nge f{\"u}r das Gelingen von Transfer identifiziert und daraufhin entsprechende Indikatoren definiert, um auf dieser Basis die Steuerung von Transferprozessen zu erm{\"o}glichen. In diesem Beitrag werden zwei im Projekt Transfer_i entwickelte Modelle und Indikatoren vorgestellt, die die Voraussetzungen f{\"u}r einen erfolgreichen Transferprozess abbilden k{\"o}nnen. Auf dieser Grundlage zeigen wir anhand eines Projekts (MAGGIE) der Ostbayerischen Technischen Hochschule (OTH) Regensburg mit mehreren regionalen Partnern, wie die vorher definierten Modelle und Indikatoren in einem konkreten Anwendungsfall verwendet werden k{\"o}nnen. Abschließend beschreiben wir die erforderlichen Rahmenbedingungen f{\"u}r die erfolgreiche Umsetzung von Transfer an Hochschulen und wie darauf bezogene Indikatoren effektiv eingef{\"u}hrt werden k{\"o}nnen.}, subject = {Angewandte Forschung}, language = {de} } @article{SteffensSuhrke, author = {Steffens, Oliver and Suhrke, Michael}, title = {Novel spin features in Raman spectra of few-electron quantum dots}, series = {Physical Review Letters}, volume = {82}, journal = {Physical Review Letters}, number = {19}, publisher = {American Physical Society}, doi = {10.1103/PhysRevLett.82.3891}, pages = {3891 -- 3894}, abstract = {We employ a self-consistent, dynamic spin-density functional concept beyond the dipole approximation in order to calculate the collective modes of few-electron quantum dots with partial spin polarization. Because of Hund's rule in a magnetic field the mode energies exhibit characteristic discontinuities in their magnetic-field dependence, which is a manifestation of ground-state transitions between different spin configurations. A finite ground-state spin density couples collective charge- and spin-density excitations. We predict their observability in state-of-the-art Raman experiments.}, language = {en} } @incollection{SteffensSuhrkeRoessler, author = {Steffens, Oliver and Suhrke, Michael and R{\"o}ssler, Ulrich}, title = {Ground state and collective excitations of quantum dots: Correlation effects and Hund's rule in magnetic field}, series = {Advances in Solid State Physics}, volume = {39}, booktitle = {Advances in Solid State Physics}, editor = {Kramer, Bernhard}, publisher = {Friedr. Vieweg \& Sohn}, address = {Braunschweig}, isbn = {978-3-540-44553-1}, doi = {10.1007/BFb0107469}, pages = {111 -- 120}, abstract = {We review ground-state properties and collective excitations of semiconductor quantum dots in a magnetic field obtained from current-spin density-functional theory. Due to exchange-correlation, a generalized Hund's rule in magnetic field can be established which leads to spin alignment in partially occupied energy shells at the Fermi energy. This results, in distinct spin structures in single-electron addition spectra. Current-dependent exchange-correlation modifies the magnetic-field dependence of the ground state configuration and leads to deviations from plain spin-density calculations. Moreover it gives rise to spontaneous current textures at zero magnetic field. Collective excitation spectra, explicitly calculated for inelastic light scattering, exhibit novel features in their magnetic field dependence due to a finite ground-state spin density.}, language = {en} } @misc{SteffensSaller, author = {Steffens, Oliver and Saller, Tobias}, title = {Restaurierungskonzepte f{\"u}r St. Oswald in Regensburg}, language = {de} } @article{StierstorferWellnitzSteffens, author = {Stierstorfer, Johannes and Wellnitz, Felix and Steffens, Oliver}, title = {Conservation of historic building fabric through integrated building research and digital simulation}, series = {Bauphysik}, volume = {39}, journal = {Bauphysik}, number = {2}, publisher = {ERNST \& SOHN}, doi = {10.1002/bapi.201710016}, pages = {135 -- 143}, abstract = {The abbey of Weltenburg monastery, a late baroque icon, designed by the Asam brothers and today's world heritage, has been subject to a constant need for repair and restoration due to its geological, climatological, and exposed location on the banks of the river Danube. To solve the hygric problems within the church, an exceptional restoration concept has been executed in the last decade. This research project analyses and verifies the building-physical and indoor climatic effects of the restoration measures with focus on the improvement of the central space climate. With this case study the question is raised whether appropriate measures exist that allow a contemporary and sustainable usage of historic buildings with respect to the preservation of the historic building fabric.}, language = {en} } @unpublished{Steffens, author = {Steffens, Oliver}, title = {Nomograms for Quadratic and Cubic Equations}, doi = {10.13140/RG.2.2.12187.48168}, language = {en} } @techreport{SteffensNeuleitner, type = {Working Paper}, author = {Steffens, Oliver and Neuleitner, Nikolaus}, title = {Einfluss der W{\"a}rmespeicherf{\"a}higkeit von Massivbauteilen in der Geb{\"a}udeh{\"u}lle und im Inneren von Geb{\"a}uden auf Energiebedarf und Behaglichkeit}, language = {de} } @article{SteiningerGadererSteffensetal., author = {Steininger, Peter and Gaderer, Matthias and Steffens, Oliver and Dawoud, Belal}, title = {Experimental and Numerical Study on the Heat Transfer Characteristics of a Newly-Developed Solar Active Thermal Insulation System}, series = {Buildings}, volume = {11}, journal = {Buildings}, number = {3}, publisher = {MDPI}, doi = {10.3390/buildings11030123}, pages = {1 -- 22}, abstract = {A newly-developed solar active thermal insulation system (SATIS) is introduced with the main objective to accomplish a highly-dependent total solar transmittance on the irradiation angle. SATIS is also designed to obtain the maximum transmittance at a prescribed design irradiation angle and to reduce it remarkably at higher irradiation angles. A purely mineral thermal insulation plaster with micro hollow glass spheres is applied to manufacture the investigated SATIS prototype. Light-conducting elements (LCEs) have been introduced into SATIS and suitable closing elements have been applied. The SATIS prototype has been investigated both experimentally and numerically. It turned out that the contributions of conduction, radiation and convection to the effective thermal conductivity of SATIS, without the closing elements (49 mWmK), amount to 86.2\%, 13.2\% and 0.6\%, respectively. The angle-dependent short-wave radiation exchange within the LCE has been investigated via ray tracing. At the incidence angle of 19\% (design angle), 27\% of the radiation within the LCE is absorbed by the absorber plate, resulting in measured and computed total solar energy transmittances of 11.2\%/11.7\%, respectively. For a typical summer irradiation angle of 60\%, 98\% of the incident radiation is absorbed by the surfaces at the entrance of the LCE. The corresponding total solar energy transmittance amounts to 2.9\%.}, language = {en} } @article{SchloplocherEttengruberSteffens, author = {Schloplocher, Paul Dragos and Ettengruber, Stefan and Steffens, Oliver}, title = {Improvements for building-performance simulations by a comparative finite-element method analysis}, series = {Energy and Buildings}, volume = {278}, journal = {Energy and Buildings}, publisher = {Elsevier}, doi = {10.1016/j.enbuild.2022.112563}, pages = {1 -- 12}, abstract = {This paper presents a method to improve building-performance simulations (BPS) by the comparison and analysis of different approaches based on finite-element method (FEM) models. The lumped parameter method (LPM) is used in several BPS programs and tools. It has the advantage of fast computing times and comparably good accuracy for thermal and energy loads. With the help of detailed FEM simulations, it is possible to further improve the degree of detail and accuracy while maintaining the high simulation speed. In this work, we compare time-dependent results for local temperatures in a generic reference room within a given periode of time. In a second step, the differences between the models with respect to various physical effects are analyzed and used to introduce additional equations into the LPM model in order to improve its accuracy. Thus, we discuss potentials for improvement for BPS and demonstrate a method of a practical implementation. The results show minor differences of less than 0.1 K for radiation and heat transfer, so their level of detail in BPS is appropriate. In these terms, no improvements were pursued within the work. However, the FEM simulation is capable of calculating the internal convective heat transfer and thermal bridges more accurately due to the use of computational fluid dynamics (CFD) and the geometrically precise representation of the FEM model. Here, deviations of up to 1 K in room temperature (convective heat transfer) and up to 0.5 K in wall temperatures (thermal bridges) were pointed out. By improving the LPM with equations obtained from the FEM, these deviations can be reduced to less than 0.2 K, which is a considerable improvement in accuracy.}, language = {en} } @article{SteffensSchloesserRotteretal., author = {Steffens, Oliver and Schl{\"o}sser, Tilman and Rotter, Peter and Ensslin, Klaus and Suhrke, Michael and Kotthaus, J{\"o}rg and R{\"o}ssler, Ulrich and Holland, M.}, title = {From the two-dimensional electron gas to antidot superlattices: Magnetoresistance effects in the transition regime}, series = {Journal of Physics: Condensed Matter}, volume = {10}, journal = {Journal of Physics: Condensed Matter}, number = {17}, issn = {0953-8984}, doi = {10.1088/0953-8984/10/17/016}, pages = {3859 -- 3872}, abstract = {Magnetoresistance measurements and theoretical calculations for two-dimensional electron systems under a perpendicular magnetic field are presented which illuminate transport effects due to a periodic electrostatic potential modulation. We focus on features arising from the resolution of the magnetic miniband structure which are beyond the perturbative regime governed by the dispersion of Landau bands. Our non-perturbative quantum-mechanical calculations reveal that the dispersion of individual minibands is responsible for the complicated behaviour of the magnetoresistance in the regime of intermediate modulation strength. In particular, the interplay between miniband and scattering contributions to the conductivity leads to an almost structureless magnetoresistance in this regime followed by the formation of antidot peaks due to the miniband conductivity.}, language = {en} }