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 - JOUR A1 - Szabó, Peter A1 - Steffens, Oliver A1 - Lenz, Michael A1 - Farkas, Gábor T1 - Transient junction-to-case thermal resistance measurement methodology of high accuracy and high repeatability JF - IEEE Transactions on Components and Packaging Technologies N2 - 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. KW - Thermal resistance KW - Electrical resistance measurement KW - Temperature KW - Packaging KW - Cold plates KW - MOSFET circuits KW - Semiconductor device measurement KW - Surface resistance KW - Microassembly KW - Thermal conductivity Y1 - 2005 U6 - https://doi.org/10.1109/TCAPT.2005.859768 SN - 1521-3331 VL - 28 IS - 4 SP - 630 EP - 636 ER - TY - RPRT A1 - Schaubeck, Simon A1 - Steffens, Oliver A1 - Rechenauer, Christian T1 - Integration eines kostenoptimierten, wirtschaftlich rentablen Blockheizkraftwerks mit mittlerer thermischer Leistung in ein genossenschaftliches Wohnquartier BT - TWO-Projekt (Technologie- und Wissenschaftsnetzwerk Oberpfalz), Endbericht 08 / 2015 Y1 - 2015 ER - TY - CHAP A1 - Rechenauer, Christian A1 - Neuleitner, Nikolaus A1 - Steffens, Oliver T1 - Empirische Untersuchung und Optimierung der Performance eines Modellprojekts für ein Effizienzhaus Plus mit solarthermischem Energiekonzept T2 - Fachforum Effizienzhaus Plus, 14.07.2015 Y1 - 2015 CY - Hamburg ER - TY - BOOK A1 - Steffens, Oliver T1 - Einfluss der Potentialmodulation auf Magnetotransport und Quantenchaos in lateralen Halbleiter-Übergittern Y1 - 1996 SN - 978-3-89608-726-3 N1 - Mikrofiche-Ausg. PB - Tectum-Verl. CY - Marburg ER -