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Light scattering at random pyramid textures: Effects beyond geometric optics

AIP Conference Proceedings 2018年第1期1999卷

作者： Oliver Höhn Nico Tucher Armin Richter Martin Hermle Benedikt Bläsi 1Fraunhofer Institute for Solar Energy Systems ISE Heidenhofstraße 2 79100 Freiburg Germany 2Albert-Ludwigs-University Department of Sustainable Systems Engineering INATECH Georges-Köhler-Allee 103 79110 Freiburg Germany

The currently highest measured efficiency for both side contacted monocrystalline Silicon solar cells is 25.8%. The external quantum efficiency of these solar cells with random pyramids at the front side differs from results achieved with pure ray optical modeling. As is already known from literature, better agreement can be reached by introducing additional scattering into the modeled system. Within this paper we show that this scattering can be well explained using a Phong-like scatterer. What is more, we show that in the investigated high efficiency solar cells scattering at the rear side is a minor effect although it is often assumed as the origin of scattering. The relevant scattering instead is caused by the random pyramids themselves.

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On the Systematic Construction of Lyapunov Functions for Polynomial systems

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PAMM 2023年第1期23卷

作者： Lars Natkowski Daniel Gerbet Klaus Röbenack Fraunhofer Institute for Transportation and Infrastructure Systems IVI Zeunerstraße 38 01069 Dresden Germany Institute of Control Theory Faculty of Electrical and Computer Engineering TU Dresden Georg-Schumann-Straße 7A 01187 Dresden Germany

Lyapunov functions are a widely used tool to evaluate stability properties of nonlinear dynamical systems' equilibria. In this paper quantifier elimination is used to construct Lyapunov functions for polynomial systems from a parametric ansatz. Because the existing algorithms for quantifier elimination are inherently computationally expensive, a strategy is to simplify the quantifier elimination problem beforehand. A method is presented that may help simplifying the problem of finding suitable Lyapunov functions by deriving easier to evaluate necessary conditions. Finally, the introduced method is applied to an example system to show local asymptotic stability of an equilibrium point by constructing a Lyapunov function.

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Lock-in Thermography for the Development of New Materials

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Materials Today: Proceedings 2017年 4卷 S128-S134页

作者： Peter W. Nolte Timo Malvisalo A. Charlotte Rimbach Franziska Steudel Bernd Ahrens Stefan Schweizer Fraunhofer Application Center for Inorganic Phosphors Branch Lab of Fraunhofer Institute for Microstructure of Materials and Systems IMWS Lübecker Ring 2 59494 Soest Germany Department of Electrical Engineering South Westphalia University of Applied Sciences Lübecker Ring 2 59494 Soest Germany

Thermal management is one of the crucial concerns for mid- and high-power white light-emitting diodes (LEDs). Most of the currently available white LEDs on the market consist of a blue LED chip coated with a yellow phosphor-polymer composite. Besides the heat-induced degradation of the phosphor-polymer composite, the so-called thermal quenching, i.e. the decrease in light output upon increasing temperature, is also a pressing issue. Both result in an efficiency decrease and in a color change of the LED. In this work, a method to determine the thermal diffusivity and the thermal conductivity of phosphors is presented using lanthanide-doped glasses as test samples. In the quest for temperature-stable phosphors with a high thermal conductivity, such luminescent glasses might represent an attractive alternative. Thermal waves are introduced to the samples by periodical heating with a laser. Lock-in infrared thermography, a non-destructive method, is used to monitor even small changes in surface temperature. The phase delay of the thermal wave passing through the sample is analyzed at different lock-in frequencies and a mathematical fitting of the phase data then provides the coefficients required to determine the thermal diffusivity. Subsequently, the thermal conductivity is calculated from the thermal diffusivity, the mass density, and the specific heat capacity.

关键词： lock-in thermography thermal diffusivity thermal conductivity laser heating

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Characterization of thin-film structures of silicon heterojunction solar cells with inline reflectance spectroscopy

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AIP Conference Proceedings 2023年第1期2826卷

作者： Saravana Kumar Henri Vahlman Sebastian Pingel Ioan Voicu Vulcanean Anamaria Steinmetz Jonas Haunschild Stefan Rupitsch Stefan Rein Fraunhofer Institute for Solar Energy Systems ISE Heidenhofstr. 2 D-79110 Freiburg Germany Department of Microsystems Engineering University of Freiburg Georges-Köhler-Allee 106 D-79110 Freiburg Germany

In this work, we explore reflectance spectrophotometry as a fast, inline-compatible quality-assurance method to extract thin-film layer thicknesses on silicon heterojunction (SHJ) solar cell precursors. We develop an optical model based on the transfer-matrix method (TMM) and so-called rigorous polarization ray-tracing technique for the model-based fitting of experimental reflectance spectra. First, individual layers of both amorphous silicon (a-Si) and indium-doped tin-oxide (ITO) on planar surfaces are measured with both an inline and an offline spectrophotometer to compare the fit results and to understand the quality of the optical constants that are necessary as input parameters to perform the model-based fitting. We find that using effective optical constants based on spectral ellipsometry (SE) results in reliable fitted a-Si stack and ITO thicknesses in the case of individual layers on planar surfaces. Second, we analyze single layers of ITO on a textured surface, finding a reasonable agreement with a mean relative deviation of 5% between the thickness values based on inline and offline reflectance spectra. We also compare the results of the reflectance fits to thicknesses extracted from scanning electron microscopy (SEM) images, finding a mean relative deviation of 10.7% between the two methods. Third, we perform a reflectance analysis of a-Si/ITO stacks on textured surfaces typical for SHJ solar cells and find that while the ITO thickness can be fitted to an accuracy of 4% in mean relative deviation compared to SEM images, the a-Si stack thicknesses are overestimated by 18–51% compared to reference measurements based on SE. Subsequently, we discuss the reasons for the deviations between the model-based reflectance fitting and the reference methods, and consider possibilities to improve the agreement.

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Ir-Ru Supported Electrocatalysts for Oxygen Evolution Reaction in a PEM Water Electrolyzer

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ECS Meeting Abstracts 2011年第30期MA2011-01卷

作者： Roderick E. Fuentes Sebastian Rau Tom Smolinka John Weidner Department of Chemical Engineering University of South Carolina 301 Main St. Room 2C02 Columbia South Carolina 29208 Fraunhofer Institute for Solar Energy Systems University of South Carolina

Abstract not Available.

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Verification of a numerical model of the offshore wind turbine from the alpha ventus wind farm within OC5 phase III 37

Verification of a numerical model of the offshore wind turbi...

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ASME 2018 37th International Conference on Ocean, Offshore and Arctic engineering, OMAE 2018

作者： Popko, Wojciech Huhn, Matthias L. Robertson, Amy Jonkman, Jason Wendt, Fabian Muller, Kolja Kretschmer, Matthias Vorpahl, Fabian Hagen, Torbjørn Ruud Galinos, Christos Dreff, Jean-Baptiste Le Gilbert, Philippe Auriac, Bertrand Villora, Francisco Navarro Schunemann, Paul Bayati, Ilmas Belloli, Marco Oh, Sho Totsuka, Yoshitaka Qvist, Jacob Bachynski, Erin Sørum, Stian Høegh Thomassen, Paul E. Shin, Hyunkyoung Vittori, Felipe Galvan, Josean Molins, Climent Bonnet, Paul Van Der Zee, Tjeerd Bergua, Roger Wang, Kai Fu, Pengcheng Cai, Jifeng Fraunhofer Institute for Wind Energy Systems IWES Division Wind Turbine and System Technology Bremerhaven27572 Germany National Renewable Energy Laboratory GoldenCO United States University of Stuttgart Stuttgart Wind Energy Stuttgart Germany Senvion Osnabruck Germany OWEC Tower AS Oslo Norway Technical University of Denmark Department of Wind Energy Roskilde Denmark Electricite de France Recherche et Developpement Palaiseau France IFP Energies Nouvelles Solaize France Principia La Ciotat France Siemens Gamesa Renewable Energy Hamburg Germany University of Rostock Endowed Department of Wind Energy Technology Rostock Germany Politecnico di Milano Department of Mechanical Engineering Milan Italy Tokyo Japan Wind Energy Institute of Tokyo Inc. Tokyo Japan Subsea Hvalstad Norway Norwegian University of Science and Technology Department of Marine Technology Trondheim Norway Simis AS Trondheim Norway University of Ulsan School of Naval Architecture and Ocean Engineering Ulsan Korea Republic of Sarriguren Spain TECNALIA Derio Spain Polytechnic University of Catalonia Barcelona Spain Siemens Industry Software Cornella de Llobregat Spain Knowledge Centre WMC Wieringerwerf Netherlands Envision Energy Limited Shanghai China China General Certification Center Beijing China

ISBN: (纸本)9780791851319

The main objective of the Offshore Code Comparison Collaboration Continuation, with Correlation (OC5) project, is validation of aero-hydro-servo-elastic simulation tools for offshore wind turbines (OWTs) through comparison of simulated results to the response data of physical systems. Phase III of the OC5 project analyzes the Senvion 5M wind turbine supported by the OWEC Quattropod from the alpha ventus offshore wind farm. This paper shows results of the verification of the OWT models (code-to-code comparison). A subsequent publication will focus on their validation (comparison of simulated results to measured physical system response data). Based on the available data, the participants of Phase III set up numerical models of the OWT in their simulation tools. It was necessary to verify and to tune these models. The verification and tuning were performed against an OWT model available at the University of Stuttgart - Stuttgart Wind Energy (SWE) and documentation provided by Senvion and OWEC Tower. A very good match was achieved between the results from the reference SWE model and models set up by OC5 Phase III participants. © Copyright 2018 ASME.

关键词： Numerical models

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Enhanced dynamic performance evaluation method of line-concentrating solar collectors

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AIP Conference Proceedings 2018年第1期2033卷

作者： Annie Zirkel-Hofer Korbinian Kramer Anna Heimsath Stephan Scholl Werner Platzer 1Fraunhofer Institute for Solar Energy Systems ISE Heidenhofstr. 2 79110 Freiburg Germany 2Institute for Chemical and Thermal Process Engineering ICTV Technical University Braunschweig Langer Kamp 7 38106 Braunschweig Germany

This publication presents an enhanced dynamic performance testing method for line-concentrating solar thermal collectors. To fully exploit the potential of concentrating solar power and legitimize investments within this sector, a reliable and meaningful performance testing is essential. Dynamic testing is especially beneficial for outdoor testing, particularly on-site, lacking of laboratory facilities and therefore requiring in situ measurements. Those complex test conditions prevail for systems of larger dimensions such as concentrating collectors. The introduced comprehensive performance test method addresses diverse elements of reliable collector certification, such as sophisticated confidence interval computations allowing to properly assess the quality of test results. It moreover includes aspects concerning the selection of suitable measurement instrumentation as well as recommendations regarding an appropriate testing strategy. Both aspects may substantially increase the identification quality of the performance results. Exemplary evaluation results prove the capability, reliability, and high benefit of the introduced dynamic procedure. It allows for a significant reduction of testing time, effort, and consequently costs. Flexible and simultaneously reliable certification procedures are considered crucial for the further establishment of solar thermal technologies and their global acceptance.

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Pseudomagic Quantum States

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Physical Review Letters 2024年第21期132卷 210602-210602页

作者： Andi Gu Lorenzo Leone Soumik Ghosh Jens Eisert Susanne F. Yelin Yihui Quek Department of Physics Harvard University 17 Oxford Street Cambridge Massachusetts 02138 USA Department of Physics University of Massachusetts Boston 100 Morrissey Boulevard Boston Massachusetts 02125 USA Dahlem Center for Complex Quantum Systems Freie Universität Berlin 14195 Berlin Germany Department of Computer Science University of Chicago Chicago Illinois 60637 USA Helmholtz-Zentrum Berlin für Materialien und Energie 14109 Berlin Germany Fraunhofer Heinrich Hertz Institute 10587 Berlin Germany Department of Computer Science Harvard John A. Paulson School of Engineering and Applied Sciences 150 Western Ave Boston Massachusetts 02134 USA

Notions of nonstabilizerness, or “magic,” quantify how nonclassical quantum states are in a precise sense: states exhibiting low nonstabilizerness preclude quantum advantage. We introduce “pseudomagic” ensembles of quantum states that, despite low nonstabilizerness, are computationally indistinguishable from those with high nonstabilizerness. Previously, such computational indistinguishability has been studied with respect to entanglement, introducing the concept of pseudoentanglement. However, we demonstrate that pseudomagic neither follows from pseudoentanglement nor implies it. In terms of applications, the study of pseudomagic offers fresh insights into the theory of quantum scrambling: it uncovers states that, even though they originate from nonscrambling unitaries, remain indistinguishable from scrambled states to any physical observer. Additional applications include new lower bounds on state synthesis problems, property testing protocols, and implications for quantum cryptography. Our Letter is driven by the observation that only quantities measurable by a computationally bounded observer—intrinsically limited by finite-time computational constraints—hold physical significance. Ultimately, our findings suggest that nonstabilizerness is a “hide-able” characteristic of quantum states: some states are much more magical than is apparent to a computationally bounded observer.

关键词： Quantum algorithms & computation Quantum chaos Quantum computation Quantum information processing Quantum information theory Resource theories

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Dynamic performance evaluation of line-concentrating steam collectors

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AIP Conference Proceedings 2018年第1期2033卷

This publication presents a newly developed procedure for performance evaluation of direct steam generating collectors. Performance testing and evaluation of solar collectors operating with direct steam are not yet standardized, since accredited testing standard procedures do not foresee testing with compressible heat transfer media. Due to the existence of two-phase flow, the measurement concept as well as the collector simulation model needs to be adjusted. Two approaches of steady-state and dynamic performance evaluation are introduced. The corresponding methodology is applicable to small- and large-scale parabolic trough as well as linear Fresnel collectors. The application of the newly developed simulation model and evaluation procedure to measurement data proves the practicability and reliability of the introduced approach. On the basis of exemplary results, the benefits and remaining drawbacks of the procedure are thoroughly discussed. They particularly demonstrate the adapted testing method to be a valuable tool for fast and simple performance checks of steam generating systems. Meaningful performance testing is considered highly beneficial for a further dissemination and global acceptance of steam collectors and solar process heat in general.

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SatNEx - the European satellite communications network of excellence

SatNEx - the European satellite communications network of ex...

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IEEE Conference on Vehicular Technology (VTC)

作者： M. Werner A. Donner E. Lutz R. Sheriff F. Hu R. Rumeau H. Brandt G. Maral M. Bousquet B. Evans G. Corazza Deutsches Zentrum für Luftund Raumfahrt e.V. DLR Institute of Communications and Navigation Oberpfaffenhofen Germany School of Engineering Design and Technology University of Bradford West Yorkshire UK Centre National d''Etudes Spatiales Toulouse France Fraunhofer Institute for Open Communication Systems Berlin Germany Ecole Nationale Supérieure des TéIécommunications Toulouse France SUPAERO Le Départment Systèmes Electroniques Photoniques et Télécoms Toulouse France School of Electronics Computing and Mathematics University of Surrey Surrey UK DEISARCES University of Bologna Bologna Italy

Summary form only given. This paper outlines the primary goal of SatNEx which is to achieve long-lasting integration of the European research in satellite communications and to develop a common base of knowledge. Networks of excellence have been introduced as a new instrument within the 6/sup th/ IST framework program, and SatNEx is one of the first consortia to implement the new ideas and to overcome the fragmentation of European research. Through co-operation of outstanding universities and research organizations with excellent expertise in satellite communications, SatNEx will build a European virtual centre of excellence in satellite communications and contribute to the realization of the European Research Area (ERA) SatNEx will include an advisory board incorporating representatives of the European space industry, satellite service providers, and standardization and regulation organizations. SatNEx will collaborate with these players and put together a critical mass of resources and expertise needed for making Europe a world force in the field of satellite communications.

关键词： Satellite communication Satellite broadcasting Europe Mobile communication Artificial satellites Communication industry Instruments Industrial training Collaboration Design engineering

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