Filters

20183

More filters

20233
Reset filters

Settings

End date: 2018 × DDC: 530 × DDC: 550 × Publisher: College Park, Md. : APS ×

Search Results

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    Topology Counts: Force Distributions in Circular Spring Networks
    (College Park, Md. : APS, 2018) Heidemann, Knut M.; Sageman-Furnas, Andrew O.; Sharma, Abhinav; Rehfeldt, Florian; Schmidt, Christoph F.; Wardetzky, Max
    Filamentous polymer networks govern the mechanical properties of many biological materials. Force distributions within these networks are typically highly inhomogeneous, and, although the importance of force distributions for structural properties is well recognized, they are far from being understood quantitatively. Using a combination of probabilistic and graph-theoretical techniques, we derive force distributions in a model system consisting of ensembles of random linear spring networks on a circle. We show that characteristic quantities, such as the mean and variance of the force supported by individual springs, can be derived explicitly in terms of only two parameters: (i) average connectivity and (ii) number of nodes. Our analysis shows that a classical mean-field approach fails to capture these characteristic quantities correctly. In contrast, we demonstrate that network topology is a crucial determinant of force distributions in an elastic spring network. Our results for 1D linear spring networks readily generalize to arbitrary dimensions.
  • Thumbnail Image
    Item
    Three-Dimensional Shapes of Spinning Helium Nanodroplets
    (College Park, Md. : APS, 2018) Langbehn, Bruno; Sander, Katharina; Ovcharenko, Yevheniy; Peltz, Christian; Clark, Andrew; Coreno, Marcello; Cucini, Riccardo; Drabbels, Marcel; Finetti, Paola; Di Fraia, Michele; Giannessi, Luca; Grazioli, Cesare; Iablonskyi, Denys; LaForge, Aaron C.; Nishiyama, Toshiyuki; Oliver Álvarez de Lara, Verónica; Piseri, Paolo; Plekan, Oksana; Ueda, Kiyoshi; Zimmermann, Julian; Prince, Kevin C.; Stienkemeier, Frank; Callegari, Carlo; Fennel, Thomas; Rupp, Daniela; Möller, Thomas
    A significant fraction of superfluid helium nanodroplets produced in a free-jet expansion has been observed to gain high angular momentum resulting in large centrifugal deformation. We measured single-shot diffraction patterns of individual rotating helium nanodroplets up to large scattering angles using intense extreme ultraviolet light pulses from the FERMI free-electron laser. Distinct asymmetric features in the wide-angle diffraction patterns enable the unique and systematic identification of the three-dimensional droplet shapes. The analysis of a large data set allows us to follow the evolution from axisymmetric oblate to triaxial prolate and two-lobed droplets. We find that the shapes of spinning superfluid helium droplets exhibit the same stages as classical rotating droplets while the previously reported metastable, oblate shapes of quantum droplets are not observed. Our three-dimensional analysis represents a valuable landmark for clarifying the interrelation between morphology and superfluidity on the nanometer scale.
  • Thumbnail Image
    Item
    Robustness of Light-Transport Processes to Bending Deformations in Graded-Index Multimode Waveguides
    (College Park, Md. : APS, 2018) Boonzajer Flaes, Dirk E.; Stopka, Jan; Turtaev, Sergey; de Boer, Johannes F.; Tyc, Tomáš; Čižmár, Tomáš
    Light transport through a multimode optical waveguide undergoes changes when subjected to bending deformations. We show that optical waveguides with a perfectly parabolic refractive index profile are almost immune to bending, conserving the structure of propagation-invariant modes. Moreover, we show that changes to the transmission matrix of parabolic-index fibers due to bending can be expressed with only two free parameters, regardless of how complex a particular deformation is. We provide detailed analysis of experimentally measured transmission matrices of a commercially available graded-index fiber as well as a gradient-index rod lens featuring a very faithful parabolic refractive index profile. Although parabolic-index fibers with a sufficiently precise refractive index profile are not within our reach, we show that imaging performance with standard commercially available graded-index fibers is significantly less influenced by bending deformations than step-index types under the same conditions. Our work thus predicts that the availability of ultraprecise parabolic-index fibers will make endoscopic applications with flexible probes feasible and free from extremely elaborate computational challenges.