Recent Submissions

  • Journal Article

    Full NLO corrections to 3-jet production and R32 at the LHC 

    Reyer, Max; Schönherr, Marek; Schumann, Steffen
    The European Physical Journal C 2019; 79(4): Art. 321
    We present the evaluation of the complete set of NLO corrections to three-jet production at the LHC. To this end we consider all contributions of O(αnsαm) with n+m=3 and n+m=4. This includes in particular also subleading Born contributions of electroweak origin, as well as electroweak virtual and QED real-radiative corrections. As an application we present results for the three- over two-jet ratio R32. While the impact of non-QCD corrections on the total cross section is rather small, they can exceed −10% for high jet transverse momenta. The R32 observable turns out to be very stable against electroweak corrections, receiving absolute corrections below 5% even in the high-pT region.
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  • Journal Article

    Extreme velocity gradients in turbulent flows 

    Buaria, Dhawal; Pumir, Alain; Bodenschatz, Eberhard; Yeung, P. K.
    New Journal of Physics 2019; 21(4): Art. 043004
    Fully turbulent flows are characterized by intermittent formation of very localized and intense velocity gradients. These gradients can be orders of magnitude larger than their typical value and lead to many unique properties of turbulence. Using direct numerical simulations of the Navier–Stokes equations with unprecedented small-scale resolution, we characterize such extreme events over a significant range of turbulence intensities, parameterized by the Taylor-scale Reynolds number (Rl). Remarkably, we find the strongest velocity gradients to empirically scale as t l - Rb K 1 , with b »  0.775 0.025,where tK is theKolmogorov time scale (with its inverse, t-K1, being the rms of velocity gradient fluctuations). Additionally, we observe velocity increments across very small distances r  h,where η is theKolmogorov length scale, to be as large as the rms of the velocity fluctuations. Both observations suggest that the smallest length scale in the flow behaves as h l R-a,with a = b - 1 2 , which is at odds with predictions from existing phenomenological theories.Wefind that extreme gradients are arranged in vortex tubes, such that strain conditioned on vorticity grows on average slower than vorticity, approximately as a power law with an exponent g < 1, which weakly increaseswith Rl.Using scaling arguments,we get b = (2 - g)-1,which suggests that βwould also slowly increasewith Rl.We conjecture that approaching themathematical limit of infinite Rl, strain and vorticity would scale similarly resulting in g = 1and hence extreme events occurring at a scale h l R-1/2 corresponding to b = 1.
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  • Journal Article

    Eigenstate thermalization and quantum chaos in the Holstein polaron model 

    Jansen, David; Stolpp, Jan; Vidmar, Lev; Heidrich-Meisner, Fabian
    Physical Review B 2019; 99(15): Art. 155130
    The eigenstate thermalization hypothesis (ETH) is a successful theory that provides sufficient criteria for ergodicity in quantum many-body systems. Most studies were carried out for Hamiltonians relevant for ultracold quantum gases and single-component systems of spins, fermions, or bosons. The paradigmatic example for thermalization in solid-state physics are phonons serving as a bath for electrons. This situation is often viewed from an open-quantum-system perspective. Here, we ask whether a minimal microscopic model for electron-phonon coupling is quantum chaotic and whether it obeys ETH, if viewed as a closed quantum system. Using exact diagonalization, we address this question in the framework of the Holstein polaron model. Even though the model describes only a single itinerant electron, whose coupling to dispersionless phonons is the only integrability-breaking term, we find that the spectral statistics and the structure of Hamiltonian eigenstates exhibit essential properties of the corresponding random-matrix ensemble. Moreover, we verify the ETH ansatz both for diagonal and off-diagonal matrix elements of typical phonon and electron observables, and show that the ratio of their variances equals the value predicted from random-matrix theory.
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  • Journal Article

    A Theoretical Framework to Derive Simple, Firing-Rate-Dependent Mathematical Models of Synaptic Plasticity 

    Lappalainen, Janne; Herpich, Juliane; Tetzlaff, Christian
    Frontiers in Computational Neuroscience 2019; 13: Art. 26
    Synaptic plasticity serves as an essential mechanism underlying cognitive processes as learning and memory. For a better understanding detailed theoretical models combine experimental underpinnings of synaptic plasticity and match experimental results. However, these models are mathematically complex impeding the comprehensive investigation of their link to cognitive processes generally executed on the neuronal network level. Here, we derive a mathematical framework enabling the simplification of such detailed models of synaptic plasticity facilitating further mathematical analyses. By this framework we obtain a compact, firing-rate-dependent mathematical formulation, which includes the essential dynamics of the detailed model and, thus, of experimentally verified properties of synaptic plasticity. Amongst others, by testing our framework by abstracting the dynamics of two well-established calcium-dependent synaptic plasticity models, we derived that the synaptic changes depend on the square of the presynaptic firing rate, which is in contrast to previous assumptions. Thus, the here-presented framework enables the derivation of biologically plausible but simple mathematical models of synaptic plasticity allowing to analyze the underlying dependencies of synaptic dynamics from neuronal properties such as the firing rate and to investigate their implications in complex neuronal networks.
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  • Journal Article

    Time-resolved x-ray phase-contrast tomography of sedimenting micro-spheres 

    Ruhlandt, A; Salditt, T
    New Journal of Physics 2019; 21(4): Art. 043017
    We have implemented a time-dependent (dynamic) x-ray tomography of sedimenting micro-spheres suspended in water. To achieve phase contrast at high magnification we use the divergent and highly coherent beam emitted from an x-ray waveguide. Holograms are recorded with 5 ms acquisition time while the sample is rotated at 1 Hz, over a run of 40 s. We show that under these conditions, more than 20 000 individual particle trajectories can be tracked. The analysis of the trajectories shows apparent super-diffusive behavior due to collective flow patterns, as also further evidenced by plotting the temporal averaged spatial distribution of particle densities and velocities.
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  • Journal Article

    Magnetic-Field-Induced Suppression of Jahn-Teller Phonon Bands in (La0.6Pr0.4)0.7Ca0.3MnO3: the Mechanism of Colossal Magnetoresistance shown by Raman Spectroscopy 

    Merten, S.; Shapoval, O.; Damaschke, B.; Samwer, K.; Moshnyaga, V.
    Scientific Reports 2019; 9(1): Art. 2387
    A long-standing issue in the physics of the colossal magnetoresistance is the role of electron-phonon coupling, which manifests itself as Jahn-Teller polarons. The origin and architecture of polarons makes it possible to study their behavior by Raman spectroscopy, which allows to analyze the polaronic behavior in an applied magnetic field. We performed magnetic-field-dependent Raman spectroscopy on thin films of (La0.6Pr0.4)0.7Ca0.3MnO3 in a range of H = 0-50 kOe and compared the obtained Raman spectra with the magnetic field behavior of the electrical resistivity. In the vicinity of the Curie temperature, TC = 197 K, the intensity of the Jahn-Teller stretching mode at 614 cm-1 and of the bending mode at 443 cm-1 was found to be suppressed and enhanced, respectively. This observed behavior has a remarkable similarity with the field and temperature dependence of the colossal magnetoresistance in (La0.6Pr0.4)0.7Ca0.3MnO3. Our work provides direct evidence that the reduction of the amount of Jahn-Teller polarons at the phase transition is the main mechanism underlying the colossal magnetoresistance.
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  • Journal Article

    Monomerization of the photoconvertible fluorescent protein SAASoti by rational mutagenesis of single amino acids 

    Solovyev, Ilya D.; Gavshina, Alexandra V.; Katti, Aditya S.; Chizhik, Alexey I.; Vinokurov, Leonid M.; Lapshin, Grigory D.; Ivashina, Tatiana V.; Khrenova, Maria G.; Kireev, Igor I.; Gregor, Ingo; et al.
    Enderlein, JörgSavitsky, Alexander P.
    Scientific Reports 2018; 8(1): Art. 15542
    Photoconvertible fluorescent proteins (PCFPs) are widely used as markers for the visualization of intracellular processes and for sub-diffraction single-molecule localization microscopy. Although wild type of a new photoconvertible fluorescent protein SAASoti tends to aggregate, we succeeded, via rational mutagenesis, to obtain variants that formed either tetramers or monomers. We compare two approaches: one is based on the structural similarity between SAASoti and Kaede, which helped us to identify a single point mutation (V127T) at the protein's hydrophobic interface that leads to monomerization. The other is based on a chemical modification of amino groups of SAASoti with succinic anhydride, which converts the protein aggregates into monomers. Mass-spectrometric analysis helped us to identify that the modification of a single ε-amino group of lysine K145 in the strongly charged interface AB was sufficient to convert the protein into its tetrameric form. Furthermore, site-directed mutagenesis was used to generate mutants that proved to be either monomeric or tetrameric, both capable of rapid green-to-red photoconversion. This allows SAASoti to be used as a photoconvertible fluorescent marker for in vivo cell studies.
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  • Journal Article

    Near-Edge Soft X-ray Absorption Mass Spectrometry of Protonated Melittin 

    Egorov, Dmitrii; Bari, Sadia; Boll, Rebecca; Dörner, Simon; Deinert, Sascha; Techert, Simone; Hoekstra, Ronnie; Zamudio-Bayer, Vicente; Lindblad, Rebecka; Bülow, Christine; et al.
    Timm, Martinvon Issendorff, BerndLau, J. TobiasSchlathölter, Thomas
    Journal of The American Society for Mass Spectrometry 2018; 29(11) p.2138-2151
    We have investigated the photoionization and photofragmentation yields of gas-phase multiply protonated melittin cations for photon energies at the K-shell absorption edges of carbon, nitrogen, and oxygen. Two similar experimental approaches were employed. In both experiments, mass selected [melittin+qH]q+ (q=2-4) ions were accumulated in radiofrequency ion traps. The trap content was exposed to intense beams of monochromatic soft X-ray photons from synchrotron beamlines and photoproducts were analyzed by means of time-of-flight mass spectrometry. Mass spectra were recorded for fixed photon energies, and partial ion yield spectra were recorded as a function of photon energy. The combination of mass spectrometry and soft X-ray spectroscopy allows for a direct correlation of protein electronic structure with various photoionization channels. Non-dissociative single and double ionization are used as a reference. The contribution of both channels to various backbone scission channels is quantified and related to activation energies and protonation sites. Soft X-ray absorption mass spectrometry combines fast energy deposition with single and double ionization and could complement established activation techniques. Graphical Abstractᅟ.
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  • Journal Article

    Strong modification of the transport level alignment in organic materials after optical excitation 

    Stadtmüller, Benjamin; Emmerich, Sebastian; Jungkenn, Dominik; Haag, Norman; Rollinger, Markus; Eich, Steffen; Maniraj, Mahalingam; Aeschlimann, Martin; Cinchetti, Mirko; Mathias, Stefan
    Nature Communications 2019; 10(1): Art. 1470
    Organic photovoltaic devices operate by absorbing light and generating current. These two processes are governed by the optical and transport properties of the organic semiconductor. Despite their common microscopic origin-the electronic structure-disclosing their dynamical interplay is far from trivial. Here we address this issue by time-resolved photoemission to directly investigate the correlation between the optical and transport response in organic materials. We reveal that optical generation of non-interacting excitons in a fullerene film results in a substantial redistribution of all transport levels (within 0.4 eV) of the non-excited molecules. As all observed dynamics evolve on identical timescales, we conclude that optical and transport properties are completely interlinked. This finding paves the way for developing novel concepts for transport level engineering on ultrafast time scales that could lead to novel functional optoelectronic devices.
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  • Journal Article

    Experimental Study of the Bottleneck in Fully Developed Turbulence 

    Küchler, Christian; Bewley, Gregory; Bodenschatz, Eberhard
    Journal of Statistical Physics p.1-23
    The energy spectrum of incompressible turbulence is known to reveal a pileup of energy at those high wavenumbers where viscous dissipation begins to act. It is called the bottleneck effect (Donzis and Sreenivasan in J Fluid Mech 657:171–188, 2010; Falkovich in Phys Fluids 6:1411–1414, 1994; Frisch et al. in Phys Rev Lett 101:144501, 2008; Kurien et al. in Phys Rev E 69:066313, 2004; Verma and Donzis in Phys A: Math Theor 40:4401–4412, 2007). Based on direct numerical simulations of the incompressibleNavier-Stokes equations, results from Donzis and Sreenivasan (657:171–188, 2010) pointed to a power-law decrease of the strength of the bottleneck with increasing intensity of the turbulence, measured by the Taylor micro-scale Reynolds number Rλ. Here we report the first experimental results on the dependence of the amplitude of the bottleneck as a function of Rλ in a wind-tunnel flow. We used an active grid (Griffin et al. in Control of long-range correlations in turbulence, arXiv:1809.05126, 2019) in the variable density turbulence tunnel (VDTT) (Bodenschatz et al. in Rev Sci Instrum 85:093908, 2014) to reach Rλ > 5000, which is unmatched in laboratory flows of decaying turbulence. The VDTT with the active grid permitted us to measure energy spectra from flows of different Rλ, with the small-scale features appearing always at the same frequencies. We relate those spectra recorded to a common reference spectrum, largely eliminating systematic errors which plague hotwire measurements at high frequencies. The data are consistent with a power law for the decrease of the bottleneck strength for the finite range of Rλ in the experiment.
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  • Journal Article

    Associated production of a top quark pair with a heavy electroweak gauge boson at NLO+NNLL accuracy 

    Kulesza, Anna; Motyka, Leszek; Schwartländer, Daniel; Stebel, Tomasz; Theeuwes, Vincent
    The European Physical Journal C 2019; 79(3): Art. 249
    We perform threshold resummation of soft gluon corrections to the total cross sections and the invariant mass distributions for production of a top-antitop quark pair associated with a heavy electroweak boson V = W+,W− or Z in pp collisions at the Large Hadron Collider. The resummation is carried out at next-to-next-to-leading-logarithmic (NNLL) accuracy using the direct QCDMellin space technique in the three-particle invariant mass kinematics. It is found that for the t ¯t Z process the soft gluon resummation introduces significant corrections to the next-to-leading order (NLO) results. For the central scale equal to the t ¯t Z invariant mass the corrections reach nearly 30%. For this process, the dominant theoretical uncertainty of the cross section due to the scale choice is significantly reduced at the NLO+NNLL level with respect to the NLO results. The effects of resummation are found to be less pronounced in the t ¯tW± case. The obtained results are compared to recent measurements performed by CMS and ATLAS collaborations at the LHC.
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  • Journal Article

    Evidence of a structure in K¯0Λ+c consistent with a charged Ξc(2930)+ , and updated measurement of B¯0→K¯0Λ+cΛ¯−c at Belle 

    Li, Y. B.; Shen, C. P.; Adachi, I.; Aihara, H.; Al Said, S.; Asner, D. M.; Aushev, T.; Ayad, R.; Babu, V.; Badhrees, I.; et al.
    Bahinipati, S.Ban, Y.Bansal, V.Behera, P.Beleño, C.Bhardwaj, V.Bhuyan, B.Biswal, J.Bobrov, A.Bozek, A.Bračko, M.Browder, T. E.Cao, L.Červenkov, D.Chang, P.Chekelian, V.Chen, A.Cheon, B. G.Chilikin, K.Cho, K.Choi, S.-K.Choi, Y.Choudhury, S.Cinabro, D.Cunliffe, S.Dash, N.Di Carlo, S.Dingfelder, J.Doležal, Z.Dong, T. V.Drásal, Z.Eidelman, S.Epifanov, D.Fast, J. E.Fulsom, B. G.Garg, R.Gaur, V.Gabyshev, N.Garmash, A.Gelb, M.Giri, A.Goldenzweig, P.Golob, B.Haba, J.Hayasaka, K.Hirose, S.Hou, W.-S.Iijima, T.Inami, K.Inguglia, G.Ishikawa, A.Itoh, R.Iwasaki, M.Iwasaki, Y.Jacobs, W. W.Jaegle, I.Jeon, H. B.Jia, S.Jin, Y.Joo, K. K.Kaliyar, A. B.Kang, K. H.Kato, Y.Kawasaki, T.Kim, D. Y.Kim, J. B.Kim, S. H.Kinoshita, K.Kodyš, P.Korpar, S.Kotchetkov, D.Križan, P.Kroeger, R.Krokovny, P.Kuhr, T.Kwon, Y.-J.Lange, J. S.Lee, I. S.Lee, S. C.Li, L. K.Li Gioi, L.Libby, J.Liventsev, D.Luo, T.Matvienko, D.Merola, M.Miyata, H.Mizuk, R.Moon, H. K.Mori, T.Mussa, R.Nakano, E.Nanut, T.Nath, K. J.Natkaniec, Z.Nayak, M.Nisar, N. K.Nishida, S.Nishimura, K.Ogawa, K.Okuno, S.Ono, H.Pakhlov, P.Pakhlova, G.Pal, B.Pardi, S.Park, H.Paul, S.Pedlar, T. K.Pestotnik, R.Piilonen, L. E.Popov, V.Prencipe, E.Rostomyan, A.Russo, G.Sakai, Y.Salehi, M.Sandilya, S.Santelj, L.Sanuki, T.Savinov, V.Schneider, O.Schnell, G.Schwanda, C.Seino, Y.Senyo, K.Seon, O.Sevior, M. E.Shibata, T.-A.Shiu, J.-G.Solovieva, E.Starič, M.Strube, J. F.Sumihama, M.Sumiyoshi, T.Takizawa, M.Tamponi, U.Tanida, K.Tenchini, F.Uchida, M.Uglov, T.Unno, Y.Uno, S.Usov, Y.Van Hulse, C.Van Tonder, R.Varner, G.Varvell, K. E.Vorobyev, V.Waheed, E.Wang, B.Wang, C. H.Wang, M.-Z.Wang, P.Wang, X. L.Watanuki, S.Widmann, E.Won, E.Ye, H.Yelton, J.Yin, J. H.Yuan, C. Z.Yusa, Y.Zhang, Z. P.Zhilich, V.Zhukova, V.Zhulanov, V.Belle Collaboration
    The European Physical Journal C 2018; 78(11)
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  • Journal Article

    Searching for flavored gauge bosons 

    Chun, Eung Jin; Das, Arindam; Kim, Jinsu; Kim, Jongkuk
    Journal of High Energy Physics 2019; 2019(2)
    Standard Model may allow an extended gauge sector with anomaly-free flavored gauge symmetries, such as Li −Lj , Bi −Lj , and B −3Li, where i, j = 1, 2, 3 are flavor indices. We investigate phenomenological implications of the new flavored gauge boson Z′ in the above three classes of gauge symmetries. Focusing on the gauge boson mass above 5 GeV, we use the lepton universality test in the Z and τ /μ decays, LEP searches, LHC searches, neutrino trident production bound, and LHC Z → 4μ searches to put constraints on the g′ −MZ′ plane. When L1 is involved, the LEP bounds on the e−e+ → ℓ−ℓ+ processes give the most stringent bounds, while the LHC bound becomes the strongest constraints in the large MZ′ region when Bi is involved. The bound from Z → 4μ productions, which is applicable for L2-involved scenarios, provides stringent bounds in the small MZ′ region. One exception is the B − 3L2 scenario, in which case only a small region is favored due to the lepton universality.
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  • Journal Article

    A case study for the formation of stanene on a metal surface 

    Maniraj, M.; Stadtmüller, B.; Jungkenn, D.; Düvel, M.; Emmerich, S.; Shi, W.; Stöckl, J.; Lyu, L.; Kollamana, J.; Wei, Z.; et al.
    Jurenkow, A.Jakobs, S.Yan, B.Steil, S.Cinchetti, M.Mathias, S.Aeschlimann, M.
    Communications Physics 2019; 2(1)
    The discovery and realization of graphene as an ideal two-dimensional (2D) material has triggered extensive efforts to create similar 2D materials with exciting spin-dependent properties. Here, we report on a novel Sn 2D superstructure on Au(111) that shows similarities and differences to the expected electronic features of ideal stanene. Using spin- and angle-resolved photoemission spectroscopy, we find that a particular Sn/Au superstructure reveals a linearly dispersing band centered at the Γ-point and below the Fermi level with antiparallel spin polarization and a Fermi velocity of vF ≈ 1×106 m/s, the same value as for graphene. We attribute the origin of the band structure to the hybridization between the Sn and the Au orbitals at the 2D Sn-Au interface. Considering that free-standing stanene simply cannot exist, our investigated structure is an important step towards the search of useful stanene-like overstructures for future technological applications.
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  • Journal Article

    Interpretation of heliocentric water production rates of comets 

    Marshall, D.; Rezac, L.; Hartogh, P.; Zhao, Y.; Attree, N.
    Astronomy & Astrophysics 2019; 623: Art. A120
    Aims. We investigate the influence of three basic factors on water production rate as a function of heliocentric distance: nucleus shape, the spin axis orientation, and the distribution of activity on a comet’s surface. Methods. We used a basic water sublimation model driven by solar insolation to derive total production rates for different nuclei shapes and spin axis orientations using the orbital parameters of 67P/Churyumov-Gerasimenko. We used known shape models derived from prior missions to the Jupiter Family and short period comets. The slopes of production rates versus heliocentric distance were calculated for the different model setups. Results. The standard (homogeneous) outgassing model confirms the well-known result regarding the heliocentric dependence of water production rate that remains invariant for different nuclei shapes as long as the rotation axis is perpendicular to the orbital plane. When the rotation axis is not perpendicular, the nucleus shape becomes a critically important factor in determining the water production curves as the illuminated cross section of the nucleus changes with heliocentric distance. Shape and obliquity can produce changes in the illuminated cross section of up to 50% over an orbit. In addition, different spin axis orientations for a given shape can dramatically alter the pre- and post-perihelion production curves, as do assumptions about the activity distribution on the surface. If, however, the illuminated cross section of the nucleus is invariant, then the dependence on the above parameters is weak, as demonstrated here with the 67P/Churyumov-Gerasimenko shape. The comets Hartley 2 and Wild 2 are shown to yield significantly different production curve shapes for the same orbit and orientation as 67P/CG, varying by as much as a factor of three as a result of only changing the nucleus shape. Finally, we show that varying just three basic parameters, shape, spin axis orientation, and active spots distribution on the surface can lead to arbitrary deviations from the expected inverse square law dependence of water production rates near 1 au. Conclusions. With the results obtained, we cannot avoid the conclusion that, without prior knowledge of basic parameters (shape, spin axis orientation, activity locations), it is difficult to reveal the nature of cometary outgassing from the heliocentric water production rates. Similarly, the inter-comparison of water production curves of two such comets may not be meaningful.
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  • Journal Article

    Dark matter in (partially) composite Higgs models 

    Alanne, Tommi; Franzosi, Diogo Buarque; Frandsen, Mads T.; Rosenlyst, Martin
    Journal of High Energy Physics 2018; 2018(12)
    We construct composite and partially composite Higgs models with complex pseudo-Nambu-Goldstone (pNGB) dark matter states from four-dimensional gauge-Yukawa theories with strongly interacting fermions. The fermions are partially gauged under the electroweak symmetry, and the dynamical electroweak symmetry breaking sector is minimal. The pNGB dark matter particle is stable due to a U(1) technibaryon-like symmetry, also present in the technicolor limit of the models. However, the relic density is particle anti-particle symmetric and due to thermal freeze-out as opposed to the technicolor limit where it is typically due to an asymmetry. The pNGB Higgs is composite or partially composite depending on the origin of the Standard Model fermion masses, which impacts the dark matter phenomenology. We illustrate the important features with a model example invariant under an SU(4) × SU(2) × U(1) global symmetry.
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  • Journal Article

    Mutation-induced alterations of intra-filament subunit organization in vimentin filaments revealed by SAXS 

    Brennich, Martha E.; Vainio, Ulla; Wedig, Tatjana; Bauch, Susanne; Herrmann, Harald; Köster, Sarah
    Soft Matter 2019; 15(9) p.1999-2008
    Vimentin intermediate filaments constitute a distinct filament system in mesenchymal cells that is instrumental for cellular mechanics and migration. In vitro, the rod-like monomers assemble in a multi-step, salt-dependent manner into micrometer long biopolymers. To disclose the underlying mechanisms further, we employed small angle X-ray scattering on two recombinant vimentin variants, whose assembly departs at strategic points from the normal assembly route: (i) vimentin with a tyrosine to leucine change at position 117; (ii) vimentin missing the non-α-helical carboxyl-terminal domain. Y117L vimentin assembles into unit-length filaments (ULFs) only, whereas ΔT vimentin assembles into filaments containing a higher number of tetramers per cross section than normal vimentin filaments. We show that the shape and inner structure of these mutant filaments is significantly altered. ULFs assembled from Y117L vimentin contain more, less tightly bundled vimentin tetramers, and ΔT vimentin filaments preserve the number density despite the higher number of tetramers per filament cross-section.
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  • Journal Article

    Human blood platelets contract in perpendicular direction to shear flow 

    Hanke, Jana; Ranke, Christiane; Perego, Eleonora; Köster, Sarah
    Soft Matter 2019; 15(9) p.2009-2019
    In their physiological environment, blood platelets are permanently exposed to shear forces caused by blood flow. Within this surrounding, they generate contractile forces that eventually lead to a compaction of the blood clot. Here, we present a microfluidic chamber that combines hydrogel-based traction force microscopy with a controlled shear environment, and investigate the force fields platelets generate when exposed to shear flow in a spatio-temporally resolved manner. We find that for shear rates between 14 s-1 to 33 s-1, the general contraction behavior in terms of force distribution and magnitude does not differ from no-flow conditions. The main direction of contraction, however, does respond to the externally applied stress. At high shear stress, we observe an angle of about 90° between flow direction and main contraction axis. We explain this observation by the distribution of the stress acting on the adherent cell: the observed angle provides the most stable situation for the cell experiencing the shear flow, as supported by a finite element method simulation of the stresses along the platelet boundary.
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  • Journal Article

    Functional Macromolecular Systems: Kinetic Pathways to Obtain Tailored Structures 

    Abetz, Volker; Kremer, Kurt; Müller, Marcus; Reiter, Günter
    Macromolecular Chemistry and Physics 2018; 220(2): Art. 1800334
    This article aims to stimulate research on non-equilibrium macromolecular systems, as nowadays a large toolbox to synthesize tailored macromolecules is available. A large variety of characterization methods covering a broad spectrum of length and timescales allows researchers to follow and also manipulate macromolecular systems on their paths toward equilibrium. These possibilities are paralleled by the development of new concepts of the statistical physics of non-equilibrium phenomena in macromolecular systems as well as new models and algorithms for computer simulation.
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  • Journal Article

    Energy-Reduced Arrhythmia Termination Using Global Photostimulation in Optogenetic Murine Hearts 

    Quiñonez Uribe, Raúl A.; Luther, Stefan; Diaz-Maue, Laura; Richter, Claudia
    Frontiers in Physiology 2018; 9: Art. 1651
    Complex spatiotemporal non-linearity as observed during cardiac arrhythmia strongly correlates with vortex-like excitation wavelengths and tissue characteristics. Therefore, the control of arrhythmic patterns requires fundamental understanding of dependencies between onset and perpetuation of arrhythmia and substrate instabilities. Available treatments, such as drug application or high-energy electrical shocks, are discussed for potential side effects resulting in prognosis worsening due to the lack of specificity and spatiotemporal precision. In contrast, cardiac optogenetics relies on light sensitive ion channels stimulated to trigger excitation of cardiomyocytes solely making use of the inner cell mechanisms. This enables low-energy, non-damaging optical control of cardiac excitation with high resolution. Recently, the capability of optogenetic cardioversion was shown in Channelrhodopsin-2 (ChR2) transgenic mice. But these studies used mainly structured and local illumination for cardiac stimulation. In addition, since optogenetic and electrical stimulus work on different principles to control the electrical activity of cardiac tissue, a better understanding of the phenomena behind optogenetic cardioversion is still needed. The present study aims to investigate global illumination with regard to parameter characterization and its potential for cardioversion. Our results show that by tuning the light intensity without exceeding 1.10 mW mm-2, a single pulse in the range of 10-1,000 ms is sufficient to reliably reset the heart into sinus rhythm. The combination of our panoramic low-intensity photostimulation with optical mapping techniques visualized wave collision resulting in annihilation as well as propagation perturbations as mechanisms leading to optogenetic cardioversion, which seem to base on other processes than electrical defibrillation. This study contributes to the understanding of the roles played by epicardial illumination, pulse duration and light intensity in optogenetic cardioversion, which are the main variables influencing cardiac optogenetic control, highlighting the advantages and insights of global stimulation. Therefore, the presented results can be modules in the design of novel illumination technologies with specific energy requirements on the way toward tissue-protective defibrillation techniques.
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