@article{MalzKrenkelSteffens, author = {Malz, Sebastian and Krenkel, Walter and Steffens, Oliver}, title = {Infrared Reflective Wall Paint in Buildings: Energy Saving Potentials and Thermal Comfort}, series = {Energy and Buildings}, volume = {224}, journal = {Energy and Buildings}, number = {October}, publisher = {Elsevier}, issn = {0378-7788}, doi = {10.1016/j.enbuild.2020.110212}, abstract = {The reduction of the energy demand of existing buildings is the main objective of building refurbishment. Managing the heat radiation properties of the wall construction is a possible way to develop highly effective and resource efficient insulation materials and concepts. The application of infrared reflective wall paints and coatings has been studied since the latter half of the 20th century. A brief review of the literature gives an account of the current research status. One has to realise that the conclusions are not uniformly consistent but depend strongly on the specific boundary conditions and investigated parameters. The study presented here discusses the usage of infrared reflective wall paint in conjunction with heat insulation for historic brick masonry. The possible energy savings are linked to the resulting thermal comfort. We identify critical parameters that must be taken into account when using infrared reflective wall paint and derive recommended design rules for the refurbishment of such building types. The findings prove that infrared reflective wall paint can decrease heat losses by 18\% and up to 22\% if comfort conditions are considered. Increasing energy savings can also cause the negative effect of high radiative asymmetry. Thus, each configuration must be observed in detail.}, language = {en} } @book{Steffens, author = {Steffens, Oliver}, title = {On Media, typewriters, logic and truth: Essays}, address = {Regensburg}, doi = {10.35096/othr/pub-5838}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:898-opus4-58380}, publisher = {Ostbayerische Technische Hochschule Regensburg}, pages = {77}, abstract = {Essays on the Media Revolution in the 19th Century, when sound recording, film and typewriter changed the way of communication, literature, and arts; on the societal impact and role models that came along with the invention and success of the typewriting machine; on early mathematical and mechanistic ways of reasoning the medieval philosopher Ram{\´o}n Llull, Leibniz's idea of binary numbers and the advent of artificial intelligence.}, language = {en} } @unpublished{Steffens, author = {Steffens, Oliver}, title = {The Media Revolution in the 19th Century: How Sound Recording, Motion Pictures and Writing Machines affected human perception, thinking, and our society until today}, address = {Regensburg}, doi = {10.13140/RG.2.2.29059.53283}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:898-opus4-58376}, pages = {17}, abstract = {Which influence had the sudden appearance of sound recording, film, and typewriters at the end of the 19th century on the human perception of and our thinking about what we consider "reality"? How did our society change with these technological innovations? After millennia of speech and the culture of writing, a fundamental disruption occurred when Thomas Alva Edison introduced his "phonograph" in 1877. In his book "Grammophon, Film, Typewriter" (Brinkmann \& Bose, Berlin 1986), Friedrich Kittler (1943-2011) discusses this question from his perspective as literary scholar and media theorist, reviewing contemporary authors to let them bear witness to their experiences and impressions of the then-new media. This essay intends to be a short extract of Kittler's book, meandering between additional sources of historians, writers, commentators, yet always coming back to Kittler's fascinating panopticon.}, language = {en} } @unpublished{Steffens, author = {Steffens, Oliver}, title = {Leibniz, Llull and the Logic of Truth: Precursors of Artificial Intelligence}, address = {Regensburg}, doi = {10.13140/RG.2.2.28425.06243}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:898-opus4-58399}, pages = {10}, abstract = {Mankind has always been confronted with limited knowledge about Nature and many people devoted their lives and intellects to the very question: How to gain knowledge, confirm ideas and theories, and understand the world we live in? Religion was one fundamental base for explanations and existential questions. Philosophy and Science were the other. Nowadays, science and technology dominate our daily lives, religion and metaphysics have lost their former dominance, while our thoughts and factual knowledge are increasingly governed by the digitised versions of conversation and discussion, filtered and guided by the algorithms of social networks. Today, "artificial intelligence" is a phenomenon in information technology which takes over everyday routines. A new ideal, a new promise, and at the same time used as a stratagem by political and economic systems to guide and manipulate our thinking, values, and behaviour. But nothing is so new that one could not find its precursors in earlier times. Science and mathematics has kindled many brilliant ideas. Can we describe the world by numbers, find truth and explanation in mathematical structures? This essay is devoted to early ideas by the medieval philosopher Ram{\´o}n Llull, the great rationalist G.W. Leibniz, and early approaches to combinations, number theory. and information processing. Llull's thinking machine and subsequent endeavours to find methods of mechanical reasoning and inference paved the way to modern-day concepts of artificial intelligence.}, language = {en} } @techreport{Steffens, author = {Steffens, Oliver}, title = {Report on a Vernier (Nonius Rule) for Non-Linear Scales}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:898-opus4-58926}, pages = {7}, abstract = {The vernier or nonius (in other languages) goes back to a measuring tool used in navigation and astronomy named after its inventor Pedro Nunes (1502-1578; Latin: Petrus Nonius), a Portuguese mathematician and navigator. The nonius was created in 1542 to take finer measurements on circular instruments such as the astrolabe. In 1631 the French mathematician Pierre Vernier (1580-1637) adapted and simplified the system which was later denoted "vernier". We present a method to construct a vernier-like scale for logarithmic scales (as used for typical slide rules), which results in variable tick spacings. The idea is to put the non-linear scale on a spiral. The method can be applied to any non-linear scale, not only logarithmic scales.}, language = {en} } @inproceedings{LangSteinbornSteffensetal., author = {Lang, Christian and Steinborn, Florian and Steffens, Oliver and Lang, Elmar Wolfgang}, title = {Electricity Load Forecasting - An Evaluation of Simple 1D-CNN Network Structures}, series = {International Conference on Time Series and Forecasting (ITISE 2019), Proceedings of Papers Vol. 2, 25-27 September 2019, Granada (Spain)}, booktitle = {International Conference on Time Series and Forecasting (ITISE 2019), Proceedings of Papers Vol. 2, 25-27 September 2019, Granada (Spain)}, isbn = {978-84-17970-78-9}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:898-opus4-16649}, pages = {797 -- 806}, abstract = {This paper presents a convolutional neural network (CNN)which can be used for forecasting electricity load profiles 36 hours intothe future. In contrast to well established CNN architectures, the inputdata is one-dimensional. A parameter scanning of network parameters isconducted in order to gain information about the influence of the kernelsize, number of filters, and dense size. The results show that a goodforecast quality can already be achieved with basic CNN architectures.The method works not only for smooth sum loads of many hundredconsumers, but also for the load of apartment buildings}, language = {en} } @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} } @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} } @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} } @article{SteffensSuhrkeRoessler, author = {Steffens, Oliver and Suhrke, Michael and R{\"o}ssler, Ulrich}, title = {Shell structure and exchange-related spin effects for quantum dots in a magnetic field}, series = {Physica B}, volume = {256-258}, journal = {Physica B}, doi = {10.1016/S0921-4526(98)00557-2}, pages = {147 -- 151}, abstract = {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.}, language = {en} } @article{SteffensRoesslerSuhrke, author = {Steffens, Oliver and R{\"o}ssler, Ulrich and Suhrke, Michael}, title = {Generalized Hund's rule in the addition spectrum of a quantum dot}, series = {EPL (Europhysics Letters)}, volume = {42}, journal = {EPL (Europhysics Letters)}, number = {5}, doi = {10.1209/epl/i1998-00276-4}, pages = {529 -- 534}, abstract = {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.}, language = {en} } @article{SteffensSuhrkeRoessler, author = {Steffens, Oliver and Suhrke, Michael and R{\"o}ssler, Ulrich}, title = {Spontaneously-broken time-reversal symmetry in quantum dots}, series = {EPL (Europhysics Letters)}, volume = {44}, journal = {EPL (Europhysics Letters)}, issn = {1286-4854}, doi = {10.1209/EPL/I1998-00460-0}, pages = {222 -- 228}, abstract = {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.}, language = {en} } @incollection{LangSteinbornSteffensetal., author = {Lang, Christian and Steinborn, Florian and Steffens, Oliver and Lang, Elmar Wolfgang}, title = {Applying a 1D-CNN Network to Electricity Load Forecasting}, series = {Theory and Applications of Time Series Analysis}, booktitle = {Theory and Applications of Time Series Analysis}, editor = {Valenzuela, O. and Rojas, F. and Herrera, L.J. and Pomares, H. and Rojas, I.}, publisher = {Springer}, doi = {10.1007/978-3-030-56219-9_14}, pages = {205 -- 218}, abstract = {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.}, language = {en} } @inproceedings{TheussElianFinketal., author = {Theuss, Horst and Elian, Klaus and Fink, Markus and Fries, M. and Kalz, Franz-Peter and Schwabe, B. and Vaupel, M. and Jaroschek, C. and Schubert, A. and Hummel, H. and Steffens, Oliver}, title = {Mechanical Stress Impact of Assembly Processes onto a Stress-sensitive Testchip}, series = {44th International Symposium on Microelectronics (IMAPS 2011), October 9 - 13, 2011, Long Beach, California, USA}, booktitle = {44th International Symposium on Microelectronics (IMAPS 2011), October 9 - 13, 2011, Long Beach, California, USA}, number = {1}, publisher = {International Microelectronics \& Packaging}, address = {Washington}, isbn = {978-1-61839-850-5}, doi = {10.4071/isom-2011-WA5-Paper3}, pages = {619 -- 626}, abstract = {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.}, language = {en} } @article{MalzSteiningerDawoudetal., author = {Malz, Sebastian and Steininger, Peter and Dawoud, Belal and Krenkel, Walter and Steffens, Oliver}, title = {On the Development of a Building Insulation using Air Layers with Highly Reflective Interfaces}, series = {Energy and Buildings}, journal = {Energy and Buildings}, number = {236, April}, publisher = {Elsevier}, doi = {10.1016/j.enbuild.2021.110779}, abstract = {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.}, language = {en} } @inproceedings{SteffensSzaboLenzetal., author = {Steffens, Oliver and Szab{\´o}, Peter and Lenz, Michael and Farkas, G{\´a}bor}, title = {Thermal transient characterization methodology for single-chip and stacked structures}, series = {Semiconductor Thermal Measurement and Management Symposium, 2005}, booktitle = {Semiconductor Thermal Measurement and Management Symposium, 2005}, publisher = {IEEE}, issn = {1065-2221}, doi = {10.1109/STHERM.2005.1412198}, pages = {313 -- 321}, abstract = {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.}, language = {en} } @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{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} } @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} } @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} } @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} }