DFG-Abschlussberichte
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- ItemFinal report on the DFG Heisenberg project "Quantum Gravity from String Theory"(Hannover : Technische Informationsbibliothek, 2025) Plauschinn, Erik
- ItemReport on the DFG Project "Approaching Superconductor/Cold Atom Hybrid Quantum Circuits " (KL 930_16-1)(Hannover : Technische Informationsbibliothek, 2025-06-10) Kleiner, Reinhold; Fortagh, JozsefThe project was intended to realize superconductor-cold atom hybrid systems, whereby the atoms are captured and manipulated in the vicinity of a superconducting chip. The chip should operate in the millikelvin range, which enables both subsystems to operate in the quantum regime. The vision: In this geometry, the methods of solid-state physics and quantum optics can be combined to manipulate the atoms or solid-state circuits directly or via photons from microwave to optical frequencies. If successful, the hybrid system offers unique opportunities to study the coupling between macroscopic objects (superconducting qubits, resonators) and natural atoms. In the context of quantum information, one can imagine a hybrid in which the superconducting circuit acts as a processor and the atoms act as a quantum memory. Cold atoms coupled to superconducting resonators could also enable the realization of new quantum gates. At the start of the project, a cold atom/superconductor setup was already in operation, working at a bath temperature of 4.2 K. Measurement systems were also available that allow superconducting microwave structures to be examined in the absence of cold atoms. In these setups, concepts for atom-superconductor coupling could be developed and tested. On the atom side, the focus was on Rydberg atoms, which offer a variety of resonant transitions and enable strong electrical dipole coupling to the superconducting devices. On the superconducting side, chips have been developed that contain resonators optimized for coupling to Rydberg atoms and can be combined with structures to trap the atoms. Originally, magnetic trap structures were considered but, as the project progressed, the focus went to optical dipole traps. A UHV millikelvin system was also available at the start of the project and was designed to incorporate the superconductor-cold atom hybrid systems. In this cryostat, part of the transport path for capturing the atoms and transporting them magnetically to the millikelvin level was demonstrated as part of a previous project. The transport path was completely rebuilt in the project, including the necessary laser and microwave components. A suitable superconducting chip was also installed at the end of the transport path. Unfortunately, the construction of the coil system required for transport turned out to be considerably more difficult than expected and took until the end of the project. The system is now functional, although the actual experiments on the coupled superconductor-cold atom hybrid systems are reserved for further projects.
- ItemReport on the DFG project "Optimization of different strategies for designing an energy harvester based on spin-torque diodes" (BE 2464/21-1)(Hannover : Technische Informationsbibliothek, 2025-06-04) Berkov, DmitrySteadily growing demand for cheap and green energy has caused a rapid development of so called ‘energy harvesting’ devices for producing dc-power from the ambient microwave radiation from various sources like TV and mobile-phone networks, Wi-Fi routers etc. The energy density of this radiation ranges from 1 to 1000 nW/cm^2, so that corresponding technology could be successfully used by low-power applications (digital thermometer, smoke detectors, some sensors in medicine etc.). The main goal of this project was the optimization of various designs for energy harvesters based on spin-torque-diodes (STDs), i.e. devices where dc-voltage is generated when an ac-current flows through a magnetic tunnel junction (MTJ). Using computer simulations, we have studied and optimized three main types of MTJ-based nanodevices: (i) ‘standard’ MTJ nanopillars of the resonant type employing quasi-homogeneous in-plane magnetization oscillations; (ii) MTJs in the out-of-plane precession regime for broadband rectification and (iii) multilayer stacks with the in-plane shape designed for oscillation of domains walls. As the results of this project we have determined optimal geometric and magnetic parameters for all three kinds of spin-torque-based energy harvesters listed above, and predicted corresponding maximal rectification efficiencies in ambient conditions.
- ItemAbschlussbericht zum DFG-Transferprojekt "Simulationsgestützte Werkzeug- und Prozessauslegung beim Microfinishen mit metallisch gebundenen Honwerkzeugen"(Hannover : Technische Informationsbibliothek, 2025) Biermann, Dirk; Wiederkehr, Petra; Heining, Ines; Tilger, MeikInnerhalb des Ergebnistransferprojektes sollten aufbauend auf den bisherigen Ergebnissen Untersuchungen zur Herstellung konvexer Konturen mittels Microfinishen durchgeführt und Simulationsmodelle zur prototypischen Prozess- und Werkzeugauslegung entwickelt werden. Die aus den vorhergehenden Grundlagenprojekten gewonnenen Erkenntnisse sollten im Rahmen des Transferprojektes prototypisch auf eine industrielle Anwendung und ein neues Werkzeugkonzept übertragen werden. Hierzu haben das Institut für Spanende Fertigung (ISF) und der Lehrstuhl Virtual Machining (VM) gemeinsam mit den Firmen NAGEL Maschi- nen- und Werkzeugfabrik GmbH, ELGAN-Diamantwerkzeuge GmbH & Co. KG und der Alicona Imaging GmbH die im Rahmen des Transfervorhabens notwendigen Forschungs- und Entwicklungsarbeiten durchgeführt. Es erfolgten experimentelle Untersuchungen zur Konditionierung von metallisch gebundenen Honwerkzeugen, um eine geeignete Prozess- kette für das Profilieren, Schärfen sowie das Einlaufen der Werkzeuge zu definieren. Parallel zu den technologischen Untersuchungen erfolgte die Entwicklung einer geometrisch- physikalischen Honsimulation. Das Ziel der Simulationsentwicklung war es, unterschiedliche Werkzeugkonfigurationen, bspw. durch eine Variation der Korngröße oder der Werkzeugges- talt, und Prozesskenngrößen im Hinblick auf die resultierende Kontur der bearbeiteten Wel- lenabsätze analysieren und mittels Microfinishbearbeitung gezielt einstellen zu können. Zur detaillierten Abbildung der komplexen Prozessführung wurden neben der Modellierung der Kraftregelung auf Einzelkornbasis neue Modelle entwickelt, welche zum einen bei der Be- rechnung der Einzelkornkraft die Orientierung der Korntopographie in Relation zur Schnitt- richtung berücksichtigten und zum anderen die explizite Beschreibung der Bindung und die Berücksichtigung der Bindungsverschleißmechanismen im Werkzeugmodell ermöglichten. Zur Validierung des entwickelten Simulationssystems wurden verschiedene Parameterkonfi- gurationen zunächst simulativ systematisch untersucht und anschließend experimentelle Untersuchungen für ausgewählte Werkzeug- und Prozesskonfigurationen durchgeführt. Die Ergebnisse der experimentellen Werkzeug- und Prozessanalyse konnten hierbei dazu ein- gesetzt werden, die Simulationsparametrierung zu optimieren und den Einfluss unterschied- licher Werkzeugkonfigurationen auf die resultierende Werkstückgestalt zu analysieren. Durch die gewonnenen Erkenntnisse konnten die Projektpartner zum einen reproduzierbare Ergeb- nisse für die Werkzeugkonditionierung durch die neu entwickelten Methoden erzielen. Zum anderen tragen die Ergebnisse der experimentellen und simulationsgestützten Untersuchun- gen zu einem verbesserten Prozessverständnis bei. Zusätzlich konnte das Potenzial aufge- zeigt werden, durch eine simulationsgestützte Werkzeugauslegung den ökonomische Auf- wand bei der Werkzeugentwicklung für die Projektpartner perspektivisch zu reduzieren.
- ItemCavitation Control using Mesoscale Surface Structuring in Marine Engineering and Hydraulic Systems(Hannover : Technische Informationsbibliothek, 2025-06-02) el Moctar, Bettar Ould; Kadivar, EbrahimWe propose a passive cavitation control method to mitigate undesirable effects, such as structural vibration in the context of marine engineering and hydraulic systems. For this aim, we used different mesoscale surface structures, such as scalloped and sawtooth riblet structures, finned and roughness structures to control the cavitating flow around circular cylinders, and hydrofoils. We performed extensive experiments to investigate the effects of wall roughness and riblet structures on the dynamics of cavitation, cavitation instability and turbulence structures in the cross flow around and in the wake of a circular cylinder, and a hydrofoil at different cavitating regimes and various Reynolds numbers. We used high-speed cameras to visualize the cavitation structure and a Particle Image Velocimetry (PIV) method to measure the velocity fields. In addition, we measured the forces acting on the smooth cylinder and on the cylinders with different mesoscale surface structures, and we also performed an acoustic measurement, using a hydrophone located downstream of the cylinders. Finally, we numerically studied the dynamics of the cavitation flow around a benchmark hydrofoil with and without passive control methods and compared our numerical results with our experimental data. Our results showed that the mesoscale surface structures were very efficient in suppressing or mitigating cavitation. The cavitation-induced vibration exciting forces acting on the cylinders and hydrofoils with riblet structures were significantly reduced compared to the cases without cavitation control. Furthermore, a substantial reduction in the cavitation volume and the sound pressure level in the low- and middle-frequency ranges were observed for the hydrofoils with riblet structures. The large-scale cloud cavity on the hydrofoil with scalloped and sawtooth riblets was changed to a small-scale cavity, which modified the cavitation dynamics on the hydrofoil surface and controlled unsteady cloud cavitation.