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Author: Schultz, T. ×

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    Experimental strategies for optical pump - Soft x-ray probe experiments at the LCLS
    (Bristol : Institute of Physics Publishing, 2014) McFarland, B.K.; Berrah, N.; Bostedt, C.; Bozek, J.; Bucksbaum, P.H.; Castagna, J.C.; Coffee, R.N.; Cryan, J.P.; Fang, L.; Farrell, J.P.; Feifel, R.; Gaffney, K.J.; Glownia, J.M.; Martinez, T.J.; Miyabe, S.; Mucke, M.; Murphy, B.; Natan, A.; Osipov, T.; Petrovic, V.S.; Schorb, S.; Schultz, T.; Spector, L.S.; Swiggers, M.; Tarantelli, F.; Tenney, I.; Wang, S.; White, J.L.; White, W.; Gühr, M.
    Free electron laser (FEL) based x-ray sources show great promise for use in ultrafast molecular studies due to the short pulse durations and site/element sensitivity in this spectral range. However, the self amplified spontaneous emission (SASE) process mostly used in FELs is intrinsically noisy resulting in highly fluctuating beam parameters. Additionally timing synchronization of optical and FEL sources adds delay jitter in pump-probe experiments. We show how we mitigate the effects of source noise for the case of ultrafast molecular spectroscopy of the nucleobase thymine. Using binning and resorting techniques allows us to increase time and spectral resolution. In addition, choosing observables independent of noisy beam parameters enhances the signal fidelity.
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    Correlated rotational alignment spectroscopy of isolated molecules and molecular mixtures
    (Les Ulis : EDP Sciences, 2013) Schröter, C.; Kosma, K.; Schultz, T.
    We present a novel multi-pulse spectroscopic method for the correlated analysis of molecular mass, rotational structure and electronic structure. First experiments investigate carbon disulfide and butadiene.
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    Probing nucleobase photoprotection with soft x-rays
    (Les Ulis : EDP Sciences, 2013) McFarland, B.K.; Farrell, J.P.; Berrah, N.; Bostedt, C.; Bozek, J.; Bucksbaum, P.H.; Coffee, R.; Cryan, J.; Fang, L.; Feifel, R.; Gaffney, K.; Glownia, J.; Martinez, T.; Mucke, M.; Murphy, B.; Miyabe, S.; Natan, A.; Osipov, T.; Petrovic, V.; Schorb, S.; Schultz, T.; Spector, L.; Tarantelli, F.; Tenney, I.; Wang, S.; White, W.; White, J.; Gühr, M.
    Nucleobases absorb strongly in the ultraviolet region, leading to molecular excitation into reactive states. The molecules avoid the photoreactions by funnelling the electronic energy into less reactive states on an ultrafast timescale via non-Born-Oppenheimer dynamics. Current theory on the nucleobase thymine discusses two conflicting pathways for the photoprotective dynamics. We present our first results of our free electron laser based UV-pump soft x-ray-probe study of the photoprotection mechanism of thymine. We use the high spatial sensitivity of the Auger electrons emitted after the soft x-ray pulse induced core ionization. Our transient spetra show two timescales on the order of 200 fs and 5 ps, in agreement with previous (all UV) ultrafast experiments. The timescales appear at different Auger kinetic energies which will help us to decipher the molecular dynamics.
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    Excited state dynamics of liquid water near the surface
    (Les Ulis : EDP Sciences, 2013) Buchner, F.; Ritze, H.-H.; Beutler, M.; Schultz, T.; Hertel, I.-V.; Lübcke, A.
    Time resolved photoelectron spectroscopy explores the excited state dynamics of liquid water in presence of cations close to the surface. A transient hydrated electroncation complex is observed.
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    Replication and Refinement of an Algorithm for Automated Drusen Segmentation on Optical Coherence Tomography
    (Berlin : Springer Nature, 2020) Wintergerst, M.W.M.; Gorgi Zadeh, S.; Wiens, V.; Thiele, S.; Schmitz-Valckenberg, S.; Holz, F.G.; Finger, R.P.; Schultz, T.
    Here, we investigate the extent to which re-implementing a previously published algorithm for OCT-based drusen quantification permits replicating the reported accuracy on an independent dataset. We refined that algorithm so that its accuracy is increased. Following a systematic literature search, an algorithm was selected based on its reported excellent results. Several steps were added to improve its accuracy. The replicated and refined algorithms were evaluated on an independent dataset with the same metrics as in the original publication. Accuracy of the refined algorithm (overlap ratio 36–52%) was significantly greater than the replicated one (overlap ratio 25–39%). In particular, separation of the retinal pigment epithelium and the ellipsoid zone could be improved by the refinement. However, accuracy was still lower than reported previously on different data (overlap ratio 67–76%). This is the first replication study of an algorithm for OCT image analysis. Its results indicate that current standards for algorithm validation do not provide a reliable estimate of algorithm performance on images that differ with respect to patient selection and image quality. In order to contribute to an improved reproducibility in this field, we publish both our replication and the refinement, as well as an exemplary dataset.