Fakultät für Physik
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Time and frequencyresolved fluorescence with a single TCSPC detector via a Fouriertransform approach
Optics Express 2018; 26(3): Art. 2270We introduce a broadband singlepixel spectrotemporal fluorescence detector, combining timecorrelated single photon counting (TCSPC) with Fourier transform (FT) spectroscopy. A birefringent commonpath interferometer (CPI) generates two timedelayed replicas of the sample's fluorescence. Via FT of their interference signal at the detector, we obtain a twodimensional map of the fluorescence as a function of detection wavelength and emission time, with high temporal and spectral resolution. Our instrument is remarkably simple, as it only requires the addition of a CPI to a standard singlepixel TCSPC system, and it shows a readily adjustable spectral resolution with inherently broad bandwidth coverage. 
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Topology determines force distributions in onedimensional random spring networks
Physical Review E 2018; 97(2): Art. 022306etworks of elastic fibers are ubiquitous in biological systems and often provide mechanical stability to cells and tissues. Fiberreinforced materials are also common in technology. An important characteristic of such materials is their resistance to failure under load. Rupture occurs when fibers break under excessive force and when that failure propagates. Therefore, it is crucial to understand force distributions. Force distributions within such networks are typically highly inhomogeneous and are not well understood. Here we construct a simple onedimensional model system with periodic boundary conditions by randomly placing linear springs on a circle. We consider ensembles of such networks that consist of N nodes and have an average degree of connectivity z but vary in topology. Using a graphtheoretical approach that accounts for the full topology of each network in the ensemble, we show that, surprisingly, the force distributions can be fully characterized in terms of the parameters (N,z). Despite the universal properties of such (N,z) ensembles, our analysis further reveals that a classical meanfield approach fails to capture force distributions correctly. We demonstrate that network topology is a crucial determinant of force distributions in elastic spring networks. 
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Combined ForwardBackward Asymmetry Measurements in TopAntitop Quark Production at the Tevatron
Physical Review Retters 2018; 120(4): Art. 042001The CDF and D0 experiments at the Fermilab Tevatron have measured the asymmetry between yields of forward and backwardproduced top and antitop quarks based on their rapidity difference and the asymmetry between their decay leptons. These measurements use the full data sets collected in protonantiproton collisions at a centerofmass energy of sqrt[s]=1.96 TeV. We report the results of combinations of the inclusive asymmetries and their differential dependencies on relevant kinematic quantities. The combined inclusive asymmetry is A_{FB}^{tt[over ¯]}=0.128±0.025. The combined inclusive and differential asymmetries are consistent with recent standard model predictions. 
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Photodissociation of aligned CH3I and C6H3F2I molecules probed with timeresolved Coulomb explosion imaging by siteselective extreme ultraviolet ionization.
Structural Dynamics 2018; 5(1): Art. 014301We explore timeresolved Coulomb explosion induced by intense, extreme ultraviolet (XUV) femtosecond pulses from a freeelectron laser as a method to image photoinduced molecular dynamics in two molecules, iodomethane and 2,6difluoroiodobenzene. At an excitation wavelength of 267 nm, the dominant reaction pathway in both molecules is neutral dissociation via cleavage of the carboniodine bond. This allows investigating the influence of the molecular environment on the absorption of an intense, femtosecond XUV pulse and the subsequent Coulomb explosion process. We find that the XUV probe pulse induces local innershell ionization of atomic iodine in dissociating iodomethane, in contrast to nonselective ionization of all photofragments in difluoroiodobenzene. The results reveal evidence of electron transfer from methyl and phenyl moieties to a multiply charged iodine ion. In addition, indications for ultrafast charge rearrangement on the phenyl radical are found, suggesting that timeresolved Coulomb explosion imaging is sensitive to the localization of charge in extended molecules. 
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Constraining scalar resonances with topquark pair production at the LHC
Journal of High Energy Physics 2018; 2018(3): Art. 22Constraints on models which predict resonant topquark pair production at the LHC are provided via a reinterpretation of the Standard Model (SM) particle level measurement of the topantitop invariant mass distribution, m(t t). We make use of stateof theart Monte Carlo event simulation to perform a direct comparison with measurements of m(t t) in the semileptonic channels, considering both the boosted and the resolved regime of the hadronic top decays. A simpli ed model to describe various scalar resonances decaying into topquarks is considered, including CPeven and CPodd, colorsinglet and coloroctet states, and the excluded regions in the respective parameter spaces are provided. 
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An ensemble framework for time delay synchronization
Quarterly Journal of the Royal Meteorological Society 2018; 144(711) p.305316Synchronization based state estimation tries to synchronize a model with the true evolution of a system via the observations. In practice, an extra term is added to the model equations which hampers growth of instabilities transversal to the synchronization manifold. Therefore, there is a very close connection between synchronization and data assimilation. Recently, synchronization with timedelayed observations has been proposed, in which observations at future times are used to help synchronize a system that does not synchronize using only present observations, with remarkable successes. Unfortunately, these schemes are limited to smalldimensional problems. In this article, we lift that restriction by proposing an ensemblebased synchronization scheme. Tests were performed using the Lorenz’96 model for 20, 100 and 1000dimension systems. Results show global synchronization errors stabilizing at values of at least an order of magnitude lower than the observation errors, suggesting that the scheme is a promising tool to steer model states to the truth. While this framework is not a complete data assimilation method, we develop this methodology as a potential choice for a proposal density in a more comprehensive data assimilation method, like a fully nonlinear particle filter. 
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Partially composite Higgs models: phenomenology and RG analysis
Journal of High Energy Physics 2018; 2018(1): Art. 51Abstract: We study the phenomenology of partially compositeHiggs models where electroweak symmetry breaking is dynamically induced, and the Higgs is a mixture of a composite and an elementary state. The models considered have explicit realizations in terms of gaugeYukawa theories with new strongly interacting fermions coupled to elementary scalars and allow for a very SMlike Higgs state. We study constraints on their parameter spaces from vacuum stability and perturbativity as well as from LHC results and nd that requiring vacuum stability up to the compositeness scale already imposes relevant constraints. A small part of parameter space around the classically conformal limit is stable up to the Planck scale. This is however already strongly disfavored by LHC results. In different limits, the models realize both (partially) compositeHiggs and (bosonic) technicolor models and a dynamical extension of the fundamental GoldstoneHiggs model. Therefore, they provide a general framework for exploring the phenomenology of composite dynamics. 
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Microfluidic device for chemical and mechanical manipulation of suspended cells
Journal of Physics D: Applied Physics 2018; 51(4)Microfluidic devices have proven to be useful and versatile for cell studies. We here report on a method to adapt microfluidic stickers made from UVcurable optical adhesive with inserted permeable hydrogel membrane microwindows for mechanical studies of suspended cells. The windows were fabricated by optical projection lithography using scanning confocal microscopy. The device allows us to rapidly exchange embedding medium while observing and probing the cells. We characterize the device and demonstrate the function by exposing cultured fibroblasts to varying osmotic conditions. Cells can be shrunk reversibly under osmotic compression. 
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Neon ion beam induced pattern formation on amorphous carbon surfaces
AIP Advances 2018; 8(2): Art. 025205We investigate the ripple pattern formation on amorphous carbon surfaces at room temperature during low energy Ne ion irradiation as a function of the ion incidence angle. Monte Carlo simulations of the curvature coefficients applied to the BradleyHarper and CaterVishnyakov models, including the recent extensions by HarrisonBradley and Hofsäss predict that pattern formation on amorphous carbon thin films should be possible for low energy Ne ions from 250 eV up to 1500 eV. Moreover, simulations are able to explain the absence of pattern formation in certain cases. Our experimental results are compared with prediction using current linear theoretical models and applying the crater function formalism, as well as Monte Carlo simulations to calculate curvature coefficients using the SDTrimSP program. Calculations indicate that no patterns should be generated up to 45° incidence angle if the dynamic behavior of the thickness of the ion irradiated layer introduced by Hofsäss is taken into account, while pattern formation most pronounced from 50° for ion energy between 250 eV and 1500 eV, which are in good agreement with our experimental data. 
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Rhombic organization of microvilli domains found in a cell model of the human intestine
PlOS ONE 2018; 13(1): Art. e0189970Symmetry is rarely found on cellular surfaces. An exception is the brush border of microvilli, which are essential for the proper function of transport epithelia. In a healthy intestine, they appear densely packed as a 2Dhexagonal lattice. For in vitro testing of intestinal transport the cell line Caco2 has been established. As reported by electron microscopy, their microvilli arrange primarily in clusters developing secondly into a 2Dhexagonal lattice. Here, atomic force microscopy (AFM) was employed under aqueous buffer conditions on Caco2 cells, which were cultivated on permeable filter membranes for optimum differentiation. For analysis, the exact position of each microvillus was detected by computer vision; subsequent Fourier transformation yielded the type of 2Dlattice. It was confirmed, that Caco2 cells can build a hexagonal lattice of microvilli and form clusters. Moreover, a second type of arrangement was discovered, namely a rhombic lattice, which appeared at submaximal densities of microvilli with (29 ± 4) microvilli / μm2. Altogether, the findings indicate the existence of a yet undescribed pattern in cellular organization. 
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The MUSE Hubble Ultra Deep Field Survey. IV. Global properties of CIII] emitters
Astronomy & Astrophysics 2017; 608 p.116: Art. A4The CIII] 1907, 1909 emission doublet has been proposed as an alternative to Lyman in redshift confirmations of galaxies at z & 6 since it is not attenuated by the largely neutral intergalactic medium at these redshifts and is believed to be strong in the young, vigorously starforming galaxies present at these early cosmic times. We present a statistical sample of 17 CIII]emitting galaxies beyond z 1:5 using 30 h deep VLT/MUSE integral field spectroscopy covering 2 square arcminutes in the Hubble Deep Field South (HDFS) and Ultra Deep Field (UDF), achieving C III] sensitivities of 2 1017 erg s1 cm2 in the HDFS and 7 1018 erg s1 cm2 in the UDF. The restframe equivalent widths range from 2 to 19 Å. These 17 galaxies represent 3% of the total sample of galaxies found between 1:5 . z . 4. They also show elevated star formation rates, lower dust attenuation, and younger massweighted ages than the general population of galaxies at the same redshifts. Combined with deep slitless grism spectroscopy from the HST/WFC3 in the UDF, we can tie the restframe ultraviolet C III] emission to restframe optical emission lines, namely [O III] 5007, finding a strong correlation between the two. Down to the flux limits that we observe ( 1 1018 erg s1 cm2 with the grism data in the UDF), all objects with a restframe [O III] 4959, 5007 equivalent width in excess of 250 Å, the socalled extreme emission line galaxies, have detections of CIII] in our MUSE data. More detailed studies of the C III]emitting population at these intermediate redshifts will be crucial to understand the physical conditions in galaxies at early cosmic times and to determine the utility of C III] as a redshift tracer. 
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The MUSE Hubble Ultra Deep Field Survey. II. Spectroscopic redshifts and comparisons to color selections of highredshift galaxies
Astronomy & Astrophysics 2017; 608 p.126: Art. A2We have conducted a twolayered spectroscopic survey (10 10 ultra deep and 30 30 deep regions) in the Hubble Ultra Deep Field (HUDF) with the Multi Unit Spectroscopic Explorer (MUSE). The combination of a large field of view, high sensitivity, and wide wavelength coverage provides an order of magnitude improvement in spectroscopically confirmed redshifts in the HUDF; i.e., 1206 secure spectroscopic redshifts for Hubble Space Telescope (HST) continuum selected objects, which corresponds to 15% of the total (7904). The redshift distribution extends well beyond z > 3 and to HST/F775W magnitudes as faint as 30 mag (AB, 1 ). In addition, 132 secure redshifts were obtained for sources with no HST counterparts that were discovered in the MUSE data cubes by a blind search for emissionline features. In total, we present 1338 high quality redshifts, which is a factor of eight increase compared with the previously known spectroscopic redshifts in the same field.We assessed redshifts mainly with the spectral features [O ii] at z < 1:5 (473 objects) and Ly at 2:9 < z < 6:7 (692 objects). With respect to F775W magnitude, a 50% completeness is reached at 26:5 mag for ultra deep and 25:5 mag for deep fields, and the completeness remains &20% up to 28–29 mag and 27 mag, respectively.We used the determined redshifts to test continuum color selection (dropout) diagrams of highz galaxies. The selection condition for F336W dropouts successfully captures 80% of the targeted z 2:7 galaxies. However, for higher redshift selections (F435W, F606W, and F775W dropouts), the success rates decrease to 20–40%. We empirically redefine the selection boundaries to make an attempt to improve them to 60%. The revised boundaries allow bluer colors that capture Ly emitters with high Ly equivalent widths falling in the broadbands used for the colorcolor selection. Along with this paper, we release the redshift and line flux catalog. 
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The MUSE Hubble Ultra Deep Field Survey. III. Testing photometric redshifts to 30th magnitude
Astronomy & Astrophysics 2017; 608 p.123: Art. A3We tested the performance of photometric redshifts for galaxies in the Hubble Ultra Deep field down to 30th magnitude. We compared photometric redshift estimates from three spectral fitting codes from the literature (EAZY, BPZ and BEAGLE) to high quality redshifts for 1227 galaxies from the MUSE integral field spectrograph. All these codes can return photometric redshifts with bias j(zMUSE pz)=(1 + zMUSE)j < 0:05 down to F775W = 30 and spectroscopic incompleteness is unlikely to strongly modify this statement. We have, however, identified clear systematic biases in the determination of photometric redshifts: in the 0:4 < z < 1:5 range, photometric redshifts are systematically biased low by as much as (zMUSE pz)=(1 + zMUSE) = 0:04 in the median, and at z > 3 they are systematically biased high by up to (zMUSE pz)=(1 + zMUSE) = 0:05, an o set that can in part be explained by adjusting the amount of intergalactic absorption applied. In agreement with previous studies we find little di erence in the performance of the di erent codes, but in contrast to those we find that adding extensive groundbased and IRAC photometry actually can worsen photoz performance for faint galaxies.We find an outlier fraction, defined through j(zMUSE pz)=(1 + zMUSE)j > 0:15, of 8% for BPZ and 10% for EAZY and BEAGLE, and show explicitly that this is a strong function of magnitude. While this outlier fraction is high relative to numbers presented in the literature for brighter galaxies, they are very comparable to literature results when the depth of the data is taken into account. Finally, we demonstrate that while a redshift might be of high confidence, the association of a spectrum to the photometric object can be very uncertain and lead to a contamination of a few percent in spectroscopic training samples that do not show up as catastrophic outliers, a problem that must be tackled in order to have su ciently accurate photometric redshifts for future cosmological surveys. 
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The MUSE Hubble Ultra Deep Field Survey. I. Survey description, data reduction, and source detection
Astronomy & Astrophysics 2017; 608 p.120: Art. A1We present the MUSE Hubble Ultra Deep Survey, a mosaic of nine MUSE fields covering 90% of the entire HUDF region with a 10h deep exposure time, plus a deeper 31h exposure in a single 1.15 arcmin2 field. The improved observing strategy and advanced data reduction results in datacubes with subarcsecond spatial resolution (00:065 at 7000 Å) and accurate astrometry (00:007 rms). We compare the broadband photometric properties of the datacubes to HST photometry, finding a good agreement in zeropoint up to mAB = 28 but with an increasing scatter for faint objects. We have investigated the noise properties and developed an empirical way to account for the impact of the correlation introduced by the 3D drizzle interpolation. The achieved 3 emission line detection limit for a point source is 1:5 and 3:1 1019 erg s1 cm2 for the single ultradeep datacube and the mosaic, respectively. We extracted 6288 sources using an optimal extraction scheme that takes the published HST source locations as prior. In parallel, we performed a blind search of emission line galaxies using an original method based on advanced test statistics and filter matching. The blind search results in 1251 emission line galaxy candidates in the mosaic and 306 in the ultradeep datacube, including 72 sources without HST counterparts (mAB > 31). In addition 88 sources missed in the HST catalog but with clear HST counterparts were identified. This data set is the deepest spectroscopic survey ever performed. In just over 100 h of integration time, it provides nearly an order of magnitude more spectroscopic redshifts compared to the data that has been accumulated on the UDF over the past decade. The depth and high quality of these datacubes enables new and detailed studies of the physical properties of the galaxy population and their environments over a large redshift range. 
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Affluence and emission tradeoffs: evidence from Indonesian households' carbon footprint
Environment and Development Economics 2017; 22(05) p.546570This study estimates Indonesian households’ carbon emissions that are attributed to their expenditures in 2005 and 2009 to analyze the pattern, distribution and drivers of their carbon footprint. Employing an inputoutputemissionexpenditure framework, the authors find a significant difference in household carbon emissions between different affluence levels, regions and educational levels. They also find that, while many household characteristics influence emissions, total expenditure is by far the most important determinant of household emissions, both across households and over time. Consequently, emissions inequality is very similar to expenditure inequality across households. The decomposition analysis confirms that changes in emissions are predominantly due to rising expenditures between the two periods, while expenditure elasticities analysis suggests that the rise in household emissions is mainly caused by the overall rise in total household expenditure, and not by shifting consumption shares among consumption categories. The paper discusses policy options for Indonesia to reduce this very strong expenditure–emissions link. 
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Efficient scheduling of astronomical observations
Astronomy & Astrophysics 2017; 604 p.116: Art. A87Context. Targeted spectroscopic exoplanet surveys face the challenge of maximizing their planet detection rates by means of careful planning. For a large planet survey, the number of possible observation combinations, i.e., the sequence of observations night after night, both in total time and amount of targets, is enormous. Aims. Sophisticated scheduling tools and the improved understanding of the exoplanet population are employed to investigate an e cient and optimal way to plan the execution of observations. This is applied to the CARMENES instrument, which is an optical and infrared highresolution spectrograph that has started a survey of about 300 Mdwarf stars in search of terrestrial exoplanets. Methods. We used evolutionary computation techniques to create an automatic scheduler that minimizes the idle periods of the telescope and distributes the observations among all the targets using configurable criteria.We simulated the case of the CARMENES survey with a realistic sample of targets, and we estimated the e ciency of the planning tool both in terms of telescope operations and planet detection. Results. Our scheduling simulations produce plans that use about 99% of the available telescope time (including overheads) and optimally distribute the observations among the di erent targets. Under such conditions, and using current planet statistics, the optimized plan using this tool should allow the CARMENES survey to discover about 65% of the planets with radialvelocity semiamplitudes greater than 1 ms1 when considering only photon noise. Conclusions. The simulations using our scheduling tool show that it is possible to optimize the survey planning by minimizing idle instrument periods and fulfilling the science objectives in an e cient manner to maximize the scientific return. 
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Kepler observations of the asteroseismic binary HD 176465
Astronomy & Astrophysics 2017; 601 p.116: Art. A82Binary star systems are important for understanding stellar structure and evolution, and are especially useful when oscillations can be detected and analysed with asteroseismology. However, only four systems are known in which solarlike oscillations are detected in both components. Here, we analyse the fifth such system, HD 176465, which was observed by Kepler. We carefully analysed the system’s power spectrum to measure individual mode frequencies, adapting our methods where necessary to accommodate the fact that both stars oscillate in a similar frequency range. We also modelled the two stars independently by fitting stellar models to the frequencies and complementary parameters.We are able to cleanly separate the oscillation modes in both systems. The stellar models produce compatible ages and initial compositions for the stars, as is expected from their common and contemporaneous origin. Combining the individual ages, the system is about 3:0 0:5 Gyr old. The two components of HD 176465 are young physicallysimilar oscillating solar analogues, the first such system to be found, and provide important constraints for stellar evolution and asteroseismology. 
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Computational helioseismology in the frequency domain: acoustic waves in axisymmetric solar models with flows
Astronomy & Astrophysics 2017; 600 p.123: Art. A35Context. Local helioseismology has so far relied on semianalytical methods to compute the spatial sensitivity of wave travel times to perturbations in the solar interior. These methods are cumbersome and lack flexibility. Aims. Here we propose a convenient framework for numerically solving the forward problem of timedistance helioseismology in the frequency domain. The fundamental quantity to be computed is the crosscovariance of the seismic wavefield. Methods.We choose sources of wave excitation that enable us to relate the crosscovariance of the oscillations to the Green’s function in a straightforward manner. We illustrate the method by considering the 3D acoustic wave equation in an axisymmetric reference solar model, ignoring the e ects of gravity on the waves. The symmetry of the background model around the rotation axis implies that the Green’s function can be written as a sum of longitudinal Fourier modes, leading to a set of independent 2D problems. We use a highorder finiteelement method to solve the 2D wave equation in frequency space. The computation is embarrassingly parallel, with each frequency and each azimuthal order solved independently on a computer cluster. Results. We compute traveltime sensitivity kernels in spherical geometry for flows, sound speed, and density perturbations under the first Born approximation. Convergence tests show that travel times can be computed with a numerical precision better than one millisecond, as required by the most precise traveltime measurements. Conclusions. The method presented here is computationally effcient and will be used to interpret traveltime measurements in order to infer, e.g., the largescale meridional flow in the solar convection zone. It allows the implementation of (fullwaveform) iterative inversions, whereby the axisymmetric background model is updated at each iteration. 
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Computational helioseismology in the frequency domain: acoustic waves in axisymmetric solar models with flows
Astronomy & Astrophysics 2017; 600 p.123: Art. A35Context. Local helioseismology has so far relied on semianalytical methods to compute the spatial sensitivity of wave travel times to perturbations in the solar interior. These methods are cumbersome and lack flexibility. Aims. Here we propose a convenient framework for numerically solving the forward problem of timedistance helioseismology in the frequency domain. The fundamental quantity to be computed is the crosscovariance of the seismic wavefield. Methods.We choose sources of wave excitation that enable us to relate the crosscovariance of the oscillations to the Green’s function in a straightforward manner. We illustrate the method by considering the 3D acoustic wave equation in an axisymmetric reference solar model, ignoring the e ects of gravity on the waves. The symmetry of the background model around the rotation axis implies that the Green’s function can be written as a sum of longitudinal Fourier modes, leading to a set of independent 2D problems. We use a highorder finiteelement method to solve the 2D wave equation in frequency space. The computation is embarrassingly parallel, with each frequency and each azimuthal order solved independently on a computer cluster. Results. We compute traveltime sensitivity kernels in spherical geometry for flows, sound speed, and density perturbations under the first Born approximation. Convergence tests show that travel times can be computed with a numerical precision better than one millisecond, as required by the most precise traveltime measurements. Conclusions. The method presented here is computationally e cient and will be used to interpret traveltime measurements in order to infer, e.g., the largescale meridional flow in the solar convection zone. It allows the implementation of (fullwaveform) iterative inversions, whereby the axisymmetric background model is updated at each iteration. 
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Mechanistic Parameters of Electrocatalytic Water Oxidation on LiMn2O4 in Comparison to Natural Photosynthesis
ChemSusChem 2017; 10(22) p.44794490Targeted improvement of the low efficiency of water oxidation during the oxygen evolution reaction (OER) is severely hindered by insufficient knowledge of the electrocatalytic mechanism on heterogeneous surfaces. We chose LiMn2O4 as a model system for mechanistic investigations as it shares the cubane structure with the active site of photosystem II and the valence of Mn3.5+ with the darkstable S1 state in the mechanism of natural photosynthesis. The investigated LiMn2O4 nanoparticles are electrochemically stable in NaOH electrolytes and show respectable activity in any of the main metrics. At low overpotential, the key mechanistic parameters of Tafel slope, Nernst slope, and reaction order have constant values on the RHE scale of 62(1) mV dec−1, 1(1) mV pH−1, −0.04(2), respectively. These values are interpreted in the context of the wellstudied mechanism of natural photosynthesis. The uncovered difference in the reaction sequence is important for the design of efficient bioinspired electrocatalysts.