TY - RPRT A1 - Bergmann, Anja A1 - Haug, Sonja A1 - Rechenauer, Christian A1 - Saller, Tobias A1 - Schaubeck, Simon A1 - Scheuerer (Scheuerer-Lenzen), Birgit A1 - Schröter, Sonja A1 - Schulz-Brize, Thekla A1 - Steffens, Oliver A1 - Vernim, Matthias A1 - Matthias, Wittmann A1 - Zeitler, Annika A1 - Zimmermann, Patrick ED - Steffens, Oliver T1 - Nachhaltige energetische Modernisierung und Restaurierung historisch wertvoller Stadtquartiere. Forschungsprojekt RENARHIS - Endbericht und Leitfaden. Zukunft Bau Projekt Nr. II 3-F20-11-1-038 (BBSR) BT - Langtitel: RENARHIS - Dezentrale regenerative Energieversorgung als Schwerpunkt einer nachhaltigen Restaurierung historisch bedeutender Stadtquartiere des frühen 20. Jahrhunderts N2 - Dieser Bericht in Gestalt eines Leitfadens für 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 für Bau-, Stadt- und Raumforschung im Rahmen der Förderinitiative „Zukunft Bau“ (Projekt Nr. II 3-F20-11-1-038 / SWD-10.08.18.7-12.21) in den Jahren 2012 bis 2014 gefördert 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 Gründen als Beispiel für mustergültigen und schätzenswerten genossenschaftlichen Wohnungsbau gelten. In diesem Leitfaden sollen aus den Erfahrungen und Lösungsansätzen des Projekts allgemeine Handlungsgrund Orientierungshilfen geboten werden, die den Horizont des eigentlichen Projekts erweitern auf eine Vielzahl ähnlicher Bestandssituationen. Y1 - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:898-opus4-20766 CY - Regensburg ER - TY - JOUR A1 - Steffens, Oliver A1 - Suhrke, Michael T1 - Novel spin features in Raman spectra of few-electron quantum dots JF - Physical Review Letters N2 - 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. Y1 - 1999 U6 - https://doi.org/10.1103/PhysRevLett.82.3891 VL - 82 IS - 19 SP - 3891 EP - 3894 PB - American Physical Society ER - TY - CHAP A1 - Steffens, Oliver A1 - Suhrke, Michael A1 - Rössler, Ulrich ED - Kramer, Bernhard T1 - Ground state and collective excitations of quantum dots: Correlation effects and Hund’s rule in magnetic field T2 - Advances in Solid State Physics N2 - 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. KW - Spin Density KW - Fermi Energy KW - Collective Excitation KW - Addition Spectrum KW - Inelastic Light Scattering Y1 - 1999 SN - 978-3-540-44553-1 U6 - https://doi.org/10.1007/BFb0107469 VL - 39 SP - 111 EP - 120 PB - Friedr. Vieweg & Sohn CY - Braunschweig ER - TY - GEN A1 - Steffens, Oliver A1 - Saller, Tobias T1 - Restaurierungskonzepte für St. Oswald in Regensburg BT - Studienarbeiten Gebäudemodernisierung Sommer 2015 Y1 - 2015 ER - TY - JOUR A1 - Stierstorfer, Johannes A1 - Wellnitz, Felix A1 - Steffens, Oliver T1 - Conservation of historic building fabric through integrated building research and digital simulation JF - Bauphysik N2 - 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. Y1 - 2017 U6 - https://doi.org/10.1002/bapi.201710016 VL - 39 IS - 2 SP - 135 EP - 143 PB - ERNST & SOHN ER - TY - RPRT A1 - Steffens, Oliver A1 - Neuleitner, Nikolaus T1 - Einfluss der Wärmespeicherfähigkeit von Massivbauteilen in der Gebäudehülle und im Inneren von Gebäuden auf Energiebedarf und Behaglichkeit BT - Gutachterliche Stellungsnahme Y1 - 2016 ER - TY - JOUR A1 - Steininger, Peter A1 - Gaderer, Matthias A1 - Steffens, Oliver A1 - Dawoud, Belal T1 - Experimental and Numerical Study on the Heat Transfer Characteristics of a Newly-Developed Solar Active Thermal Insulation System JF - Buildings N2 - 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%. KW - angle-dependent total solar energy transmittance KW - effective thermal conductivity KW - experimental investigation KW - numerical simulation KW - ray tracing KW - solar active thermal insulation system (SATIS) Y1 - 2021 U6 - https://doi.org/10.3390/buildings11030123 N1 - Corresponding author: Belal Dawoud VL - 11 IS - 3 SP - 1 EP - 22 PB - MDPI ER - TY - JOUR A1 - Schloplocher, Paul Dragos A1 - Ettengruber, Stefan A1 - Steffens, Oliver T1 - Improvements for building-performance simulations by a comparative finite-element method analysis JF - Energy and Buildings N2 - 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. KW - Lumped parameter model KW - Finite-element method KW - Building performance simulation Y1 - 2023 U6 - https://doi.org/10.1016/j.enbuild.2022.112563 N1 - Corresponding author: Dragos Paul Schoplocher VL - 278 SP - 1 EP - 12 PB - Elsevier ER - TY - JOUR A1 - Steffens, Oliver A1 - Schlösser, Tilman A1 - Rotter, Peter A1 - Ensslin, Klaus A1 - Suhrke, Michael A1 - Kotthaus, Jörg A1 - Rössler, Ulrich A1 - Holland, M. T1 - From the two-dimensional electron gas to antidot superlattices: Magnetoresistance effects in the transition regime JF - Journal of Physics: Condensed Matter N2 - 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. Y1 - 1998 U6 - https://doi.org/10.1088/0953-8984/10/17/016 SN - 0953-8984 VL - 10 IS - 17 SP - 3859 EP - 3872 ER - TY - JOUR A1 - Steffens, Oliver A1 - Suhrke, Michael A1 - Rössler, Ulrich T1 - Shell structure and exchange-related spin effects for quantum dots in a magnetic field JF - Physica B N2 - Ground-state calculations based on current spin density-functional theory for circular parabolic quantum dots are presented which reveal interesting spin effects in dependence on an external magnetic field: Hund's first rule (well-known from atomic physics for zero magnetic field) is related to the level occupancy near the Fermi energy and determines the spin configuration of the ground state in finite magnetic field. Consequently, the addition spectrum of the quantum dot exhibits a specific non-monotonous dependence on magnetic field, which is visible in recent quantum transport experiments. KW - Quantum dot KW - Current spin density-functional theory KW - Exchange correlation Y1 - 1998 U6 - https://doi.org/10.1016/S0921-4526(98)00557-2 VL - 256-258 SP - 147 EP - 151 ER - TY - JOUR A1 - Steffens, Oliver A1 - Rössler, Ulrich A1 - Suhrke, Michael T1 - Generalized Hund's rule in the addition spectrum of a quantum dot JF - EPL (Europhysics Letters) N2 - We report on ground-state calculations based on current-spin density-functional theory for circular parabolic quantum dots. Hund's first rule, well-known from atomic physics, applies not only at zero magnetic field; analogous rules, related to the level occupancy near the Fermi energy, determine the spin configuration of the ground state in finite magnetic field. Consequently, the addition spectrum of the quantum dot exhibits a specific non-monotonous dependence on magnetic field. We discuss our results with focus on recent experiments which may already contain indications of this new feature. Y1 - 1998 U6 - https://doi.org/10.1209/epl/i1998-00276-4 VL - 42 IS - 5 SP - 529 EP - 534 ER - TY - JOUR A1 - Steffens, Oliver A1 - Suhrke, Michael A1 - Rössler, Ulrich T1 - Spontaneously-broken time-reversal symmetry in quantum dots JF - EPL (Europhysics Letters) N2 - We present current-spin density-functional calculations for circular parabolic quantum dots in zero magnetic field. We find the possibility for broken time-reversal symmetry via exchange correlation with spontaneously induced orbital currents. For certain electron numbers, this results in new current textures which give rise to a finite magnetization even for ground states with vanishing total angular momentum. Y1 - 1998 U6 - https://doi.org/10.1209/EPL/I1998-00460-0 SN - 1286-4854 VL - 44 SP - 222 EP - 228 ER - TY - CHAP A1 - Lang, Christian A1 - Steinborn, Florian A1 - Steffens, Oliver A1 - Lang, Elmar Wolfgang ED - Valenzuela, O. ED - Rojas, F. ED - Herrera, L.J. ED - Pomares, H. ED - Rojas, I. T1 - Applying a 1D-CNN Network to Electricity Load Forecasting T2 - Theory and Applications of Time Series Analysis N2 - This paper presents a convolutional neural network (CNN) which can be used for forecasting electricity load profiles 36 hours into the future. In contrast to well established CNN architectures, the input data is one-dimensional. A parameter scanning of network parameters is conducted in order to gain information about the influence of the kernel size, number of filters and number of nodes. Furthermore, different dropout methods are applied to the CNN and are evaluated. The results show that a good forecast quality can already be achieved with basic CNN architectures, the dropout improves the forecast. The method works not only for smooth sum loads of many hundred consumers, but also for the load of single apartment buildings. KW - Energy load forecasting KW - STLF KW - Neural networks KW - CNN KW - Convolutional networks Y1 - 2020 U6 - https://doi.org/10.1007/978-3-030-56219-9_14 SP - 205 EP - 218 PB - Springer ER - TY - JOUR A1 - Reuther, Maike A1 - Steffens, Oliver T1 - Evaluation der Bauteiltemperierung für den Herzogskasten Abensberg JF - Bauphysik N2 - Die These, dass die Methode der direkten Temperierung von erdberührten oder anderweitig feuchtebelasteten Bauteilen zur Beseitigung von Feuchteschäden in Bestandsgebäuden auch die Energieeffizienz des Gebäudes erhöhen und sogar ohne weitere energetische Sanierungsmaßnahmen die Anforderungen der Energieeinsparverordnung (EnEV) erfüllen kann, wird anhand des als Museum genutzten Herzogskastens in Abensberg überprüft. In Verbindung mit einer Evaluation der Trocknungswirkung wird die Gebäude-Energieeffizienz durch Vergleich von Bedarfsberechnungen auf Basis der DIN V 18599 mit realen Verbrauchszahlen überprüft und diskutiert. KW - Bauteiltemperierung KW - energetische Sanierung KW - Gebäudeenergieeffizienz KW - Mauerwerkstrocknung KW - Denkmal KW - Restaurierung KW - DIN V 18599 KW - EnEV Y1 - 2015 U6 - https://doi.org/10.1002/bapi.201510010 VL - 37 IS - 2 SP - 96 EP - 99 PB - Ernst & Sohn, a Wiley Brand ER - TY - CHAP A1 - Theuss, Horst A1 - Elian, Klaus A1 - Fink, Markus A1 - Fries, M. A1 - Kalz, Franz-Peter A1 - Schwabe, B. A1 - Vaupel, M. A1 - Jaroschek, C. A1 - Schubert, A. A1 - Hummel, H. A1 - Steffens, Oliver T1 - Mechanical Stress Impact of Assembly Processes onto a Stress-sensitive Testchip T2 - 44th International Symposium on Microelectronics (IMAPS 2011), October 9 - 13, 2011, Long Beach, California, USA N2 - A semiconductor die typically undergoes a variety of assembly processes, each of them influencing the mechanical stress environment of the chip. We report on a stress-sensitive testchip and its application to measure and characterize the respective stress distributions across the die. Particularly in the field of MEMS and sensor devices, even low stresses might deteriorate the electrical performance of a device significantly, while higher stress levels may even cause cracks and irreversible damage. This is why the present methodology has a high potential to develop into a useful tool in the field of sensor package development. After a brief introduction to the sensing principle, we investigate the stress distribution in various sample assemblies – all of them targeting pressure sensors. Typical low stress packages use silicone based soft elastic encapsulations. Changing to a harder material with a young’s modulus comparable to standard mold compounds, we demonstrate an increase of the average stress level by more than one order of magnitude. Y1 - 2011 SN - 978-1-61839-850-5 U6 - https://doi.org/10.4071/isom-2011-WA5-Paper3 IS - 1 SP - 619 EP - 626 PB - International Microelectronics & Packaging CY - Washington ER - TY - JOUR A1 - Malz, Sebastian A1 - Steininger, Peter A1 - Dawoud, Belal A1 - Krenkel, Walter A1 - Steffens, Oliver T1 - On the Development of a Building Insulation using Air Layers with Highly Reflective Interfaces JF - Energy and Buildings N2 - In this work, a novel building insulation system implying wooden fiberboards and intermediate air layers with highly reflective interfaces for the reflection of longwave IR radiation is introduced. A wall test sample with a double air insulation layer has been built and experimentally investigated in a dedicated setup, which consists of a differential climatic chamber to simulate different indoor and outdoor conditions. The test results have been utilized in validating the developed simulation model. In addition, a thorough numerical parameter study has been conducted, through which the general design rules of the introduced insulation system for realizing the lowest possible effective thermal conductivity have been defined. Furthermore, a multi-air-layer-insulation concept is developed, and the energy saving potential is evaluated. It turned out that, emissivity, object size and air layer thickness are the most dominant design parameters which influence the thermal conductivity of the introduced insulation. A thermal conductivity of 0.033 W/(mK) has been estimated for a multi-air-layer insulation with 7 layers. The obtained results prove the high insulation potential of the introduced building insulation system compared with insulating materials available in the market while outlining their limitations. KW - Building insulation KW - Infrared-reflective KW - Air layers KW - Energy-saving potential KW - Heat radiation Y1 - 2021 U6 - https://doi.org/10.1016/j.enbuild.2021.110779 IS - 236, April PB - Elsevier ER - TY - CHAP A1 - Steffens, Oliver A1 - Szabó, Peter A1 - Lenz, Michael A1 - Farkas, Gábor T1 - Thermal transient characterization methodology for single-chip and stacked structures BT - Best Paper Award T2 - Semiconductor Thermal Measurement and Management Symposium, 2005 N2 - High-power semiconductor packages typically exhibit a 3D heat flow, resulting in large lateral changes in chip and case surface temperature. For single-chip devices we propose to use an unambiguous definition for the junction-to-case thermal resistance as a key parameter, based on a transient measurement technique with much higher repeatability, also for very low thermal resistances compared to a two-point thermal resistance measurement. The technique is illustrated on thermal transient measurements of power MOSFETs. A comparison between different thermal coupling to the ambient is used to demonstrate the method's capability to reveal even subtle internal details of the package. The concept is extended to multichip and stacked-chip structures, where transfer impedances have to be introduced. Here, the dynamic properties of the package are important and complex impedance mapping is the proper way to characterize the package. KW - Thermal resistance KW - Temperature KW - Electrical resistance measurement KW - Impedance KW - Assembly KW - Semiconductor device packaging KW - Surface resistance KW - Measurement techniques KW - MOSFETs Y1 - 2005 U6 - https://doi.org/10.1109/STHERM.2005.1412198 SN - 1065-2221 SP - 313 EP - 321 PB - IEEE ER - TY - JOUR A1 - Puff, Simone A1 - Seidel, Uwe M. A1 - Steffens, Oliver T1 - Pflege- und intensivmedizinische Bereiche im EnEV-Bewertungsverfahren JF - Bauphysik N2 - Die Anwendbarkeit des derzeit gültigen Verfahrens zur energetischen Bewertung von Nichtwohngebäuden gemäß aktueller Energieeinsparverordnung (EnEV 2014) in Verbindung mit DIN V 18599 als Planungs- und Bewertungstool auf Pflege- und intensiv-medizinische Bereiche von Krankenhäusern wird an einem beispielhaften, mittelgroßen Krankenhaus untersucht. Der Fokus liegt dabei auf der Praktikabilität der Abbildung von thermischen Lasten und Raumzuständen durch die Normnutzungsprofile aus DIN V 18599 Teil 10 im Vergleich zu realen, vor Ort erfassten Nutzungsbedingungen. Weitere Betrachtungen in einer einfachen thermischen Simulation (TRNSYSlite) erlauben eine methodische Kritik in Bezug auf die Aussagekraft der nach Norm berechneten EnEV-Ergebnisse. Es werden Empfehlungen für Maßnahmen zur Verbesserung der energetischen Performance und der Behaglichkeit in Krankenhäusern im Bereich der Planung erarbeitet. T2 - Energetic Evaluation of care and critical care units of hospitals according to EnEV 2014 KW - Energieeinsparungsverordnung KW - Krankenhaus Y1 - 2015 U6 - https://doi.org/10.1002/bapi.201510036 VL - 37 IS - 6 SP - 307 ER - TY - JOUR A1 - Wensauer, Andreas A1 - Steffens, Oliver A1 - Suhrke, Michael A1 - Rössler, Ulrich T1 - Laterally coupled few-electron quantum dots JF - Physical Review B N2 - 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. Y1 - 2000 U6 - https://doi.org/10.1103/PhysRevB.62.2605 VL - 62 IS - 4 SP - 2605 ER - TY - CHAP A1 - Steffens, Oliver ED - Trapp, Eugen T1 - "Grünes Denkmal" - Denkmalpflege und Erneuerbare Energien ergänzen sich T2 - Vorsicht Baudenkmal! Konfliktfelder Umwelt - Nutzung - Geschichte. Beiträge des 28. Regensburger Herbstsymposions für Kunst, Geschichte und Denkmalpflege vom 22. bis 24. November 2013 KW - Denkmalpflege KW - Denkmalschutz KW - Erneuerbare Energien Y1 - 2014 SN - 978-3-937527-77-2 SP - 9 EP - 17 PB - Regensburg CY - Morsbach-Verl. ER - TY - CHAP A1 - Steffens, Oliver A1 - Suhrke, Michael A1 - Rössler, Ulrich ED - Gershoni, David T1 - Correlation in few-electron quantum dots: Spin effects and spontaneous currents T2 - 24rd International Conference on the Physics of Semiconductors (ICPS 24), Jerusalem, Israel, August 2-7, 1998 Y1 - 1999 SN - 978-981-02-3613-7 PB - World Scientific CY - Singapore ER - TY - THES A1 - Gering, Stefan T1 - Thermische Detailsimulationen in der Bestandssanierung Y1 - 2014 CY - Regensburg ER -