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    Neural and Response Correlations to Complex Natural Sounds in the Auditory Midbrain. 

    Lyzwa, Dominika; Wörgötter, Florentin
    Frontiers in neural circuits 2016; 10: Art. 89
    How natural communication sounds are spatially represented across the inferior colliculus, the main center of convergence for auditory information in the midbrain, is not known. The neural representation of the acoustic stimuli results from the interplay of locally differing input and the organization of spectral and temporal neural preferences that change gradually across the nucleus. This raises the question of how similar the neural representation of the communication sounds is across these gradients of neural preferences, and whether it also changes gradually. Analyzed neural recordings were multi-unit cluster spike trains from guinea pigs presented with a spectrotemporally rich set of eleven species-specific communication sounds. Using cross-correlation, we analyzed the response similarity of spiking activity across a broad frequency range for neurons of similar and different frequency tuning. Furthermore, we separated the contribution of the stimulus to the correlations to investigate whether similarity is only attributable to the stimulus, or, whether interactions exist between the multi-unit clusters that lead to neural correlations and whether these follow the same representation as the response correlations. We found that similarity of responses is dependent on the neurons' spatial distance for similarly and differently frequency-tuned neurons, and that similarity decreases gradually with spatial distance. Significant neural correlations exist, and contribute to the total response similarity. Our findings suggest that for multi-unit clusters in the mammalian inferior colliculus, the gradual response similarity with spatial distance to natural complex sounds is shaped by neural interactions and the gradual organization of neural preferences.
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    Mechanisms of vortices termination in the cardiac muscle. 

    Hornung, D; Biktashev, V N; Otani, N F; Shajahan, T K; Baig, T; Berg, S; Han, S; Krinsky, V I; Luther, S
    Royal Society open science 2017-03; 4(3): Art. 170024
    We propose a solution to a long-standing problem: how to terminate multiple vortices in the heart, when the locations of their cores and their critical time windows are unknown. We scan the phases of all pinned vortices in parallel with electric field pulses (E-pulses). We specify a condition on pacing parameters that guarantees termination of one vortex. For more than one vortex with significantly different frequencies, the success of scanning depends on chance, and all vortices are terminated with a success rate of less than one. We found that a similar mechanism terminates also a free (not pinned) vortex. A series of about 500 experiments with termination of ventricular fibrillation by E-pulses in pig isolated hearts is evidence that pinned vortices, hidden from direct observation, are significant in fibrillation. These results form a physical basis needed for the creation of new effective low energy defibrillation methods based on the termination of vortices underlying fibrillation.
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    Four dimensional material movies: High speed phase-contrast tomography by backprojection along dynamically curved paths. 

    Ruhlandt, A.; Töpperwien, M.; Krenkel, M.; Mokso, R.; Salditt, T.
    Scientific reports 2017-07-26; 7(1): Art. 6487
    We present an approach towards four dimensional (4d) movies of materials, showing dynamic processes within the entire 3d structure. The method is based on tomographic reconstruction on dynamically curved paths using a motion model estimated by optical flow techniques, considerably reducing the typical motion artefacts of dynamic tomography. At the same time we exploit x-ray phase contrast based on free propagation to enhance the signal from micron scale structure recorded with illumination times down to a millisecond (ms). The concept is demonstrated by observing the burning process of a match stick in 4d, using high speed synchrotron phase contrast x-ray tomography recordings. The resulting movies reveal the structural changes of the wood cells during the combustion.
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    Three-dimensional mouse brain cytoarchitecture revealed by laboratory-based x-ray phase-contrast tomography. 

    Töpperwien, Mareike; Krenkel, Martin; Vincenz, Daniel; Stöber, Franziska; Oelschlegel, Anja M.; Goldschmidt, Jürgen; Salditt, Tim
    Scientific reports 2017-02-27; 7: Art. 42847
    Studies of brain cytoarchitecture in mammals are routinely performed by serial sectioning of the specimen and staining of the sections. The procedure is labor-intensive and the 3D architecture can only be determined after aligning individual 2D sections, leading to a reconstructed volume with non-isotropic resolution. Propagation-based x-ray phase-contrast tomography offers a unique potential for high-resolution 3D imaging of intact biological specimen due to the high penetration depth and potential resolution. We here show that even compact laboratory CT at an optimized liquid-metal jet microfocus source combined with suitable phase-retrieval algorithms and a novel tissue preparation can provide cellular and subcellular resolution in millimeter sized samples of mouse brain. We removed water and lipids from entire mouse brains and measured the remaining dry tissue matrix in air, lowering absorption but increasing phase contrast. We present single-cell resolution images of mouse brain cytoarchitecture and show that axons can be revealed in myelinated fiber bundles. In contrast to optical 3D techniques our approach does neither require staining of cells nor tissue clearing, procedures that are increasingly difficult to apply with increasing sample and brain sizes. The approach thus opens a novel route for high-resolution high-throughput studies of brain architecture in mammals.
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    Modeling observations of solar coronal mass ejections with heliospheric imagers verified with the Heliophysics System Observatory 

    Möstl, C.; Isavnin, A.; Boakes, P. D.; Kilpua, E. K. J.; Davies, J. A.; Harrison, R. A.; Barnes, D.; Krupar, V.; Eastwood, J. P.; Good, S. W.; et al.
    Forsyth, R. J.Bothmer, V.Reiss, M. A.Amerstorfer, T.Winslow, R. M.Anderson, B. J.Philpott, L. C.Rodriguez, L.Rouillard, A. P.Gallagher, P.Nieves-Chinchilla, T.Zhang, T. L.
    Space Weather 2017; 15(7) p.955-970
    We present an advance toward accurately predicting the arrivals of coronal mass ejections (CMEs) at the terrestrial planets, including Earth. For the first time, we are able to assess a CME prediction model using data over two thirds of a solar cycle of observations with the Heliophysics System Observatory. We validate modeling results of 1337 CMEs observed with the Solar Terrestrial Relations Observatory (STEREO) heliospheric imagers (HI) (science data) from 8 years of observations by five in situ observing spacecraft. We use the self-similar expansion model for CME fronts assuming 60° longitudinal width, constant speed, and constant propagation direction. With these assumptions we find that 23%–35% of all CMEs that were predicted to hit a certain spacecraft lead to clear in situ signatures, so that for one correct prediction, two to three false alarms would have been issued. In addition, we find that the prediction accuracy does not degrade with the HI longitudinal separation from Earth. Predicted arrival times are on average within 2.6 ± 16.6 h difference of the in situ arrival time, similar to analytical and numerical modeling, and a true skill statistic of 0.21. We also discuss various factors that may improve the accuracy of space weather forecasting using wide-angle heliospheric imager observations. These results form a first-order approximated baseline of the prediction accuracy that is possible with HI and other methods used for data by an operational space weather mission at the Sun-Earth L5 point.
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    Evidence for photometric activity cycles in 3203 Kepler stars 

    Reinhold, Timo; Cameron, Robert H.; Gizon, Laurent
    Astronomy & Astrophysics 2017; 603: Art. A52
    Context. In recent years it has been claimed that the length of stellar activity cycles is determined by the stellar rotation rate. It has been observed that the cycle period increases with rotation period along two distinct sequences, known as the active and inactive sequences. In this picture the Sun occupies a solitary position between the two sequences. Whether the Sun might undergo a transitional evolutionary stage is currently under debate. Aims. Our goal is to measure cyclic variations of the stellar light curve amplitude and the rotation period using four years of Kepler data. Periodic changes in the light curve amplitude or the stellar rotation period are associated with an underlying activity cycle. Methods. Using a recent sample of active stars we compute the rotation period and the variability amplitude for each individual Kepler quarter and search for periodic variations of both time series. To test for periodicity in each stellar time series we consider Lomb-Scargle periodograms and use a selection based on a false alarm probability (FAP). Results. We detect amplitude periodicities in 3203 stars between 0.5 < Pcyc < 6 yr covering rotation periods between 1 < Prot < 40 days. Given our sample size of 23 601 stars and our selection criteria that the FAP is less than 5%, this number is almost three times higher than that expected from pure noise. We do not detect periodicities in the rotation period beyond those expected from noise. Our measurements reveal that the cycle period shows a weak dependence on rotation rate, slightly increasing for longer rotation periods. We further show that the shape of the variability deviates from a pure sine curve, consistent with observations of the solar cycle. The cycle shape does not show a statistically significant dependence on effective temperature. Conclusions. We detect activity cycles in more than 13% of our final sample with a FAP of 5% (calculated by randomly shuffling the measured 90-day variability measurements for each star). Our measurements do not support the existence of distinct sequences in the Prot−Pcyc plane, although there is some evidence for the inactive sequence for rotation periods between 5–25 days. Unfortunately, the total observing time is too short to draw sound conclusions on activity cycles with similar lengths to that of the solar cycle.
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    Evolution of the Sun’s non-axisymmetric toroidal field 

    Martin-Belda, D.; Cameron, R. H.
    Astronomy & Astrophysics 2017; 603
    Aims.We aim to infer the sub-surface distribution of the Sun’s non-axisymmetric azimuthal magnetic flux from observable quantities, such as the surface magnetic field and the large scale plasma flows. Methods. We have built a kinematic flux transport model of the solar dynamo based on the Babcock-Leighton framework. We constructed the source term for the poloidal field using SOLIS magnetograms spanning three solar cycles. Based on this source we calculated the azimuthal flux below the surface. The flux transport model has two free parameters which we constrained using sunspot observations from cycle 22. We compared the model results with observations from cycle 23. Results. The structure of the azimuthal field is mainly axisymmetric. The departures from axisymmetry represent, on average, 3% of the total azimuthal flux. Owing to its relative weakness, the non-axisymmetric structure of the azimuthal field does not have a significant impact on the location in which the emergences appear or on the amount of flux contained in them. We find that the probability of emergence is a function of the ratio between the flux content of an active region and the underlying azimuthal flux.
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    Helicity decoupling in the massless limit of massive tensor fields 

    Mund, Jens; Rehren, Karl-Henning; Schroer, Bert
    Nuclear Physics B 2017; 924 p.699-727
    Massive and massless potentials play an essential role in the perturbative formulation of particle inter-actions. Many difficulties arise due to the indefinite metric in gauge theoretic approaches, or the increase with the spin of the UV dimension of massive potentials. All these problems can be evaded in one stroke: modify the potentials by suitable terms that leave unchanged the field strengths, but are not polynomial in the momenta. This feature implies a weaker localization property: the potentials are “string-localized”. In this setting, several old issues can be solved directly in the physical Hilbert space of the respective parti-cles: We can control the separation of helicities in the massless limit of higher spin fields and conversely we recover massive potentials with 2s+1degrees of freedom by a smooth deformation of the massless potentials (“fattening”). We construct stress–energy tensors for massless fields of any helicity (thus evading the Weinberg–Witten theorem). We arrive at a simple understanding of the van Dam–Veltman–Zakharov discontinuity concerning, e.g., the distinction between a massless or a very light graviton. Finally, the use of string-localized fields opens new perspectives for interacting quantum field theories with, e.g., vector bosons or gravitons.
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    Relations between positivity, localization and degrees of freedom: The Weinberg–Witten theorem and the van Dam–Veltman–Zakharov discontinuity 

    Mund, Jens; Rehren, Karl-Henning; Schroer, Bert
    Physics Letters B 2017; 773 p.625-631
    The problem of accounting for the quantum degrees of freedom in passing from massive higher-spin potentials to massless ones, and the inverse problem of “fattening” massless tensor potentials of helicity ±hto their massive s =|h|counterparts, are solved – in a perfectly ghost-free approach – using “string-localized fields”. This approach allows to overcome the Weinberg–Witten impediment against the existence of massless |h|≥2energy–momentum tensors, and to qualitatively and quantitatively resolve the van Dam–Veltman–Zakharov discontinuity concerning, e.g., very light gravitons, in the limit m →0.
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    Small Molecule Accurate Recognition Technology (SMART) to Enhance Natural Products Research. 

    Zhang, Chen; Idelbayev, Yerlan; Roberts, Nicholas; Tao, Yiwen; Nannapaneni, Yashwanth; Duggan, Brendan M.; Min, Jie; Lin, Eugene C.; Gerwick, Erik C.; Cottrell, Garrison W.; et al.
    Gerwick, William H.
    Scientific reports 2017-10-27; 7(1): Art. 14243
    Various algorithms comparing 2D NMR spectra have been explored for their ability to dereplicate natural products as well as determine molecular structures. However, spectroscopic artefacts, solvent effects, and the interactive effect of functional group(s) on chemical shifts combine to hinder their effectiveness. Here, we leveraged Non-Uniform Sampling (NUS) 2D NMR techniques and deep Convolutional Neural Networks (CNNs) to create a tool, SMART, that can assist in natural products discovery efforts. First, an NUS heteronuclear single quantum coherence (HSQC) NMR pulse sequence was adapted to a state-of-the-art nuclear magnetic resonance (NMR) instrument, and data reconstruction methods were optimized, and second, a deep CNN with contrastive loss was trained on a database containing over 2,054 HSQC spectra as the training set. To demonstrate the utility of SMART, several newly isolated compounds were automatically located with their known analogues in the embedded clustering space, thereby streamlining the discovery pipeline for new natural products.
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    Search for Dark Matter Produced in Association with a Higgs Boson Decaying to b¯b Using 36  fb−1 of pp Collisions at √s=13  TeV with the ATLAS Detector 

    Aaboud, M. et al. (ATLAS Collaboration)
    Physical Review Letters 2017; 119: Art. 181804
    Several extensions of the standard model predict associated production of dark-matter particles with a Higgs boson. Such processes are searched for in final states with missing transverse momentum and a Higgs boson decaying to a b¯b pair with the ATLAS detector using 36.1 fb−1 of pp collisions at a center-ofmass energy of 13 TeVat the LHC. The observed data are in agreement with the standard model predictions and limits are placed on the associated production of dark-matter particles and a Higgs boson.
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    Divide and update: towards single-shot object and probe retrieval for near-field holography. 

    Hagemann, Johannes; Salditt, Tim
    Optics express 2017-09-04; 25(18) p.20953-20968
    We present a phase reconstruction scheme for X-ray near-field holographic imaging based on a separability constraint for probe and object. In order to achieve this, we have devised an algorithm which requires only two measurements - with and without an object in the beam. This scheme is advantageous if the standard flat-field correction fails and a full ptychographic dataset can not be acquired, since either object or probe are dynamic. The scheme is validated by numerical simulations and by a proof-of-concept experiment using highly focused undulator radiation of the beamline ID16a of the European Synchrotron Radiation Facility (ESRF).
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    Imaging of neuronal tissues by x-ray diffraction and x-ray fluorescence microscopy: evaluation of contrast and biomarkers for neurodegenerative diseases. 

    Carboni, Eleonora; Nicolas, Jan-David; Töpperwien, Mareike; Stadelmann-Nessler, Christine; Lingor, Paul; Salditt, Tim
    Biomedical optics express 2017-10-01; 8(10) p.4331-4347
    We have used scanning X-ray diffraction (XRD) and X-ray fluorescence (XRF) with micro-focused synchrotron radiation to study histological sections from human substantia nigra (SN). Both XRF and XRD mappings visualize tissue properties, which are inaccessible by conventional microscopy and histology. We propose to use these advanced tools to characterize neuronal tissue in neurodegeneration, in particular in Parkinson's disease (PD). To this end, we take advantage of the recent experimental progress in x-ray focusing, detection, and use automated data analysis scripts to enable quantitative analysis of large field of views. XRD signals are recorded and analyzed both in the regime of small-angle (SAXS) and wide-angle x-ray scattering (WAXS). The SAXS signal was analyzed in view of the local myelin structure, while WAXS was used to identify crystalline deposits. PD tissue scans exhibited increased amounts of crystallized cholesterol. The XRF analysis showed increased amounts of iron and decreased amounts of copper in the PD tissue compared to the control.
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    Scalar production and decay to top quarks including interference effects at NLO in QCD in an EFT approach 

    Franzosi, Diogo Buarque; Vryonidou, Eleni; Zhang, Cen
    Journal of High Energy Physics 2017; 2017(10): Art. 96
    Scalar and pseudo-scalar resonances decaying to top quarks are common predictions in several scenarios beyond the standard model (SM) and are extensively searched for by LHC experiments. Challenges on the experimental side require optimising the strategy based on accurate predictions. Firstly, QCD corrections are known to be large both for the SM QCD background and for the pure signal scalar production. Secondly, leading order and approximate next-to-leading order (NLO) calculations indicate that the interference between signal and background is large and drastically changes the lineshape of the signal, from a simple peak to a peak-dip structure. Therefore, a robust prediction of this interference at NLO accuracy in QCD is necessary to ensure that higher-order corrections do not alter the lineshapes. We compute the exact NLO corrections, assuming a point-like coupling between the scalar and the gluons and consistently embedding the calculation in an effective field theory within an automated framework, and present results for a representative set of beyond the SM benchmarks. The results can be further matched to parton shower simulation, providing more realistic predictions. We find that NLO corrections are important and lead to a significant reduction of the uncertainties. We also discuss how our computation can be used to improve the predictions for physics scenarios where the gluon-scalar loop is resolved and the effective approach is less applicable.
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    Physical probing of cells 

    Rehfeldt, Florian; Schmidt, Christoph F.
    Journal of Physics D: Applied Physics 2017; 50(46): Art. 463001
    In the last two decades, it has become evident that the mechanical properties of the microenvironment of biological cells are as important as traditional biochemical cues for the control of cellular behavior and fate. The field of cell and matrix mechanics is quickly growing and so is the development of the experimental approaches used to study active and passive mechanical properties of cells and their surroundings. Within this topical review we will provide a brief overview, on the one hand, over how cellular mechanics can be probed physically, how different geometries allow access to different cellular properties, and, on the other hand, how forces are generated in cells and transmitted to the extracellular environment. We will describe the following experimental techniques: atomic force microscopy, traction force microscopy, magnetic tweezers, optical stretcher and optical tweezers pointing out both their advantages and limitations. Finally, we give an outlook on the future of the physical probing of cells.
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    Reconstructing mode mixtures in the optical near-field. 

    Hagemann, Johannes; Salditt, Tim
    Optics express 2017-06-26; 25(13) p.13973-13989
    We propose a reconstruction scheme for hard x-ray inline holography, a variant of propagation imaging, which is compatible with imaging conditions of partial (spatial) coherence. This is a relevant extension of current full-field phase contrast imaging, which requires full coherence. By the ability to reconstruct the coherent modes of the illumination (probe), as demonstrated here, the requirements of coherence filtering could be relaxed in many experimentally relevant settings. The proposed scheme is built on the mixed-state approach introduced in [Nature494, 68 (2013)], combined with multi-plane detection of extended wavefields [Opt. Commun.199, 65 (2001), Opt. Express22, 16571 (2014)]. Notably, the diversity necessary for the reconstruction is generated by acquiring measurements at different defocus positions of the detector. We show that we can recover the coherent mode structure and occupancy numbers of the partial coherent probe. Practically relevant quantities as the transversal coherence length can be computed from the reconstruction in a straightforward way.
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    Magnetisation switching of FePt nanoparticle recording medium by femtosecond laser pulses 

    John, R.; Berritta, M.; Hinzke, D.; Müller, C.; Santos, T.; Ulrichs, H.; Nieves, P.; Walowski, J.; Mondal, R.; Chubykalo-Fesenko, O.; et al.
    McCord, J.Oppeneer, P. M.Nowak, U.Münzenberg, M.
    Scientific Reports 2017; 7: Art. 4114
    Manipulation of magnetisation with ultrashort laser pulses is promising for information storage device applications. The dynamics of the magnetisation response depends on the energy transfer from the photons to the spins during the initial laser excitation. A material of special interest for magnetic storage are FePt nanoparticles, for which switching of the magnetisation with optical angular momentum was demonstrated recently. The mechanism remained unclear. Here we investigate experimentally and theoretically the all-optical switching of FePt nanoparticles. We show that the magnetisation switching is a stochastic process. We develop a complete multiscale model which allows us to optimize the number of laser shots needed to switch the magnetisation of high anisotropy FePt nanoparticles in our experiments. We conclude that only angular momentum induced optically by the inverse Faraday effect will provide switching with one single femtosecond laser pulse.
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    ESTIMATION OF PARAMETERS IN A PLANAR SEGMENT PROCESS WITH A BIOLOGICAL APPLICATION 

    Beneš, Viktor; Večeřa, Jakub; Eltzner, Benjamin; Wollnik, Carina; Rehfeldt, Florian; Králová, Veronika; Huckemann, Stephan
    Image Analysis & Stereology 2017; 36(1) p.25-33
    The paper deals with modeling of segment systems in a bounded planar set (a cell) by means of random segment processes. Two models with a density with respect to the Poisson process are presented. In model I interactions are given by the number of intersections, model II includes the length distribution and takes into account distances from the centre of the cell. The estimation of parameters of the models is suggested based on Takacz-Fiksel method. The method is tested first using simulated data. Further the real data from fluorescence imaging of stress fibres in mesenchymal human stem cells are evaluated. We apply model II which is inhomogeneous. The degree-of-fit testing of the model using various characteristics yields quite satisfactory results.
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    Nanotip-based photoelectron microgun for ultrafast LEED 

    Storeck, Gero; Vogelgesang, Simon; Sivis, Murat; Schäfer, Sascha; Ropers, Claus
    Structural Dynamics 2017; 4(4): Art. 044024
    We present the design and fabrication of a micrometer-scale electron gun for the implementation of ultrafast low-energy electron diffraction from surfaces. A multi-step process involving photolithography and focused-ion-beam nanostructuring is used to assemble and electrically contact the photoelectron gun, which consists of a nanotip photocathode in a Schottky geometry and an einzel lens for beam collimation. We characterize the low-energy electron pulses by a transient electric field effect and achieve pulse durations of 1.3 ps at an electron energy of 80 eV. First diffraction images in a backscattering geometry (at 50 eV electron energy) are shown.
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    Jitter-correction for IR/UV-XUV pump-probe experiments at the FLASH free-electron laser 

    Savelyev, Evgeny; Boll, Rebecca; Bomme, Cédric; Schirmel, Nora; Redlin, Harald; Erk, Benjamin; Düsterer, Stefan; Müller, Erland; Höppner, Hauke; Toleikis, Sven; et al.
    Müller, JostKristin Czwalinna, MarieTreusch, RolfKierspel, ThomasMullins, TerenceTrippel, SebastianWiese, JossKüpper, JochenBrauβe, FelixKrecinic, FarukRouzée, ArnaudRudawski, PiotrJohnsson, PerAmini, KasraLauer, AlexandraBurt, MichaelBrouard, MarkChristensen, LaugeThøgersen, JanStapelfeldt, HenrikBerrah, NoraMüller, MariaUlmer, AnatoliTechert, SimoneRudenko, ArtemRolles, Daniel
    New Journal of Physics 2017; 19(4) p.1-13: Art. 043009
    In pump-probe experiments employing a free-electron laser (FEL) in combination with a synchronized optical femtosecond laser, the arrival-time jitter between the FEL pulse and the optical laser pulse often severely limits the temporal resolution that can be achieved. Here, we present a pump-probe experiment on the UV-induced dissociation of 2,6-difluoroiodobenzene (C6H3F2I) molecules performed at the FLASH FEL that takes advantage of recent upgrades of the FLASH timing and synchronization system to obtain high-quality data that are not limited by the FEL arrival-time jitter. We discuss in detail the necessary data analysis steps and describe the origin of the time-dependent effects in the yields and kinetic energies of the fragment ions that we observe in the experiment.
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