07 Fakultät Konstruktions-, Produktions- und Fahrzeugtechnik
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/8
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Item Open Access Editorial - optical microscopic and spectroscopic techniques targeting biological applications(2021) Micó, Vicente; Pedrini, Giancarlo; Lei, Ming; Zuo, Chao; Gao, PengItem Open Access Improvement in systematic error in background-oriented schlieren results by using dynamic backgrounds(2021) Reichenzer, Frieder; Schneider, Mike; Herkommer, AloisThe use of electronic visual displays for background-oriented schlieren allows for the quick change of the reference images. In this study, we show that the quality of synthetic and background-oriented schlieren images can be improved by acquiring a set of images with different reference images and generating a median displacement field from it. To explore potential benefits, we studied different background changing strategies and their effect on the quality of the evaluation of the displacement field via artificial and experimental image distortions.Item Open Access Influence of pulse duration on X-ray emission during industrial ultrafast laser processing(2022) Holland, Julian; Weber, Rudolf; Sailer, Marc; Graf, ThomasSoft X-ray emissions during the processing of industrial materials with ultrafast lasers are of major interest, especially against the background of legal regulations. Potentially hazardous soft X-rays, with photon energies of >5 keV, originate from the fraction of hot electrons in plasma, the temperature of which depends on laser irradiance. The interaction of a laser with the plasma intensifies with growing plasma expansion during the laser pulse, and the fraction of hot electrons is therefore enhanced with increasing pulse duration. Hence, pulse duration is one of the dominant laser parameters that determines the soft X-ray emission. An existing analytical model, in which the fraction of hot electrons was treated as a constant, was therefore extended to include the influence of the duration of laser pulses on the fraction of hot electrons in the generated plasma. This extended model was validated with measurements of H (0.07) dose rates as a function of the pulse duration for a constant irradiance of about 3.5 × 1014 W/cm2, a laser wavelength of 800 nm, and a pulse repetition rate of 1 kHz, as well as for varying irradiance at the laser wavelength of 1030 nm and pulse repetition rates of 50 kHz and 200 kHz. The experimental data clearly verified the predictions of the model and confirmed that significantly decreased dose rates are generated with a decreasing pulse duration when the irradiance is kept constant.Item Open Access The effect of rod orientation on electrical anisotropy in silver nanowire networks for ultra-transparent electrodes(2016) Ackermann, Thomas; Neuhaus, Raphael; Roth, SiegmarTwo-dimensional networks made of metal nanowires are excellent paradigms for the experimental observation of electrical percolation caused by continuous jackstraw-like physical pathways. Such systems became very interesting as alternative material in transparent electrodes, which are fundamental components in display devices. This work presents the experimental characterization of low-haze and ultra-transparent electrodes based on silver nanowires. The films are created by dip-coating, a feasible and scalable liquid film coating technique. We have found dominant alignment of the silver nanowires in withdrawal direction. The impact of this structural anisotropy on electrical anisotropy becomes more pronounced for low area coverage. The rod alignment does not influence the technical usability of the films as significant electrical anisotropy occurs only at optical transmission higher than 99 %. For films with lower transmission, electrical anisotropy becomes negligible. In addition to the experimental work, we have carried out computational studies in order to explain our findings further and compare them to our experiments and previous literature. This paper presents the first experimental observation of electrical anisotropy in two-dimensional silver nanowire networks close at the percolation threshold.Item Open Access Numerical analysis of micro-optics based single photon sources via a combined physical optics and rigorous simulations approach(2023) Jimenez, Carlos; Hellmann, Christian; Toulouse, Andrea; Drozella, Johannes; Wyrowski, Frank; Herkommer, AloisItem Open Access Advantages of holographic imaging through fog(2023) Gröger, Alexander; Pedrini, Giancarlo; Claus, Daniel; Alekseenko, Igor; Gloeckler, Felix; Reichelt, StephanItem Open Access Data-driven development of sparse multi-spectral sensors for urological tissue differentiation(2023) Fischer, Felix; Frenner, Karsten; Granai, Massimo; Fend, Falko; Herkommer, AloisItem Open Access Stability of rigid body motion through an extended intermediate axis theorem : application to rockfall simulation(2021) Leine, Remco I.; Capobianco, Giuseppe; Bartelt, Perry; Christen, Marc; Caviezel, AndrinThe stability properties of a freely rotating rigid body are governed by the intermediate axis theorem, i.e., rotation around the major and minor principal axes is stable whereas rotation around the intermediate axis is unstable. The stability of the principal axes is of importance for the prediction of rockfall. Current numerical schemes for 3D rockfall simulation, however, are not able to correctly represent these stability properties. In this paper an extended intermediate axis theorem is presented, which not only involves the angular momentum equations but also the orientation of the body, and we prove the theorem using Lyapunov’s direct method. Based on the stability proof, we present a novel scheme which respects the stability properties of a freely rotating body and which can be incorporated in numerical schemes for the simulation of rigid bodies with frictional unilateral constraints. In particular, we show how this scheme is incorporated in an existing 3D rockfall simulation code. Simulations results reveal that the stability properties of rotating rocks play an essential role in the run-out length and lateral spreading of rocks.Item Open Access Flow visualisation and evaluation studies on metalworking fluid applications in manufacturing processes : methods and results(2023) Fritsching, Udo; Buss, Lizoel; Tonn, Teresa; Schumski, Lukas; Gakovi, Jurgen; Hatscher, Johnson David; Sölter, Jens; Avila, Kerstin; Karpuschewski, Bernhard; Gerken, Julian Frederic; Wolf, Tobias; Biermann, Dirk; Menze, Christian; Möhring, Hans-Christian; Tchoupe, Elio; Heidemanns, Lukas; Herrig, Tim; Klink, Andreas; Nabbout, Kaissar; Sommerfeld, Martin; Luther, Fabian; Schaarschmidt, Ingo; Schubert, Andreas; Richter, MarkusMetalworking operations rely on the successful application of metalworking fluids (MWFs) for effective and efficient operation. Processes such as grinding or drilling often require the use of MWFs for cooling, lubrication, and chip removal. Electrochemical machining processes require electrolyte flow to operate. However, in those machining operations, a fundamental understanding of the mode of action of MWF is lacking due to the unknown flow dynamics and its interaction with the material removal during the process. Important information on the behaviour of MWFs during machining can be obtained from specific experimental flow visualisation studies. In this paper, promising flow visualisation analysis techniques applied to exemplary machining processes (grinding, sawing, drilling, and electrochemical machining) are presented and discussed. Shadowgraph imaging and flow measurements, e.g., particle image velocimetry, allow the identification of typical flow and MWF operating regimes in the different machining processes. Based on the identification of these regimes, efficient machining parameters and MWF applications can be derived. In addition, detailed experimental analyses of MWFs provide essential data for the input and validation of model development and numerical simulations within the Priority Programme SPP 2231 FluSimPro.Item Open Access Design and realization of a miniaturized high resolution computed tomography imaging spectrometer(2023) Amann, Simon; Haist, Tobias; Gatto, Alexander; Kamm, Markus; Herkommer, Alois