TY - GEN A1 - Richter, Sebastian A1 - Bestehorn, Michael T1 - Thin-film Faraday patterns in three dimensions T2 - The European Physical Journal Special Topics N2 - We investigate the long time evolution of a thin fluid layer in three spatial dimensions located on a horizontal planar substrate. The substrate is subjected to time-periodic external vibrations in normal and in tangential direction with respect to the plane surface. The governing partial differential equation system of our model is obtained from the incompressible Navier-Stokes equations considering the limit of a thin fluid geometry and using the long wave lubrication approximation. It includes inertia and viscous friction. Numerical simulations evince the existence of persistent spatially complex surface patterns (periodic and quasiperiodic) for certain superpositions of two vertical excitations and initial conditions. Additional harmonic lateral excitations cause deformations but retain the basic structure of the patterns. Horizontal ratchet-shaped forces lead to a controllable lateral movement of the fluid. A Floquet analysis is used to determine the stability of the linearized system. KW - Thin Film Instabilities Y1 - 2017 UR - https://link.springer.com/article/10.1140/epjst/e2016-60234-4 U6 - https://doi.org/10.1140/epjst/e2016-60234-4 SN - 1951-6401 SN - 1951-6355 VL - 226 IS - 6 SP - 1253 EP - 1261 ER - TY - GEN A1 - Richter, Sebastian A1 - Bestehorn, Michael T1 - Direct numerical simulations of liquid films in two dimensions under horizontal and vertical external vibrations T2 - Physical Review Fluids N2 - We consider Newtonian liquid films on a horizontal substrate with a free and deformable surface. The substrate is subjected to oscillatory accelerations in the normal or in the horizontal direction. An algorithm based on a nonlinear coordinate transformation is presented that allows for direct numerical solutions of the fully nonlinear Navier-Stokes equations and appropriate boundary conditions. No surface tracking is necessary. Normal oscillations generate the traditional subharmonic and harmonic Faraday patterns. Lateral oscillations cause a pattern formation scenario qualitatively similar to spinodal dewetting, namely the disintegration of the film into isolated drops followed by coarsening or fusion, the stabilization of a “precursor” film, and no rupture. Ratchet-like lateral excitations break the horizontal mirror symmetry x→−x and give the patterns a preferred direction. We show that drops formed due to instability of the flat film start to travel in a distinguished direction. For thin films, the results are in good agreement to those of a recently studied lubrication-based dimension-reduced model [Bestehorn et al., Phys. Rev. E 88, 023025 (2013); Bestehorn, Phys. Fluids 25, 114106 (2013)]. KW - Flow instability KW - Interfacial Flows KW - Naviar-Stokes equation KW - Nonlinear Dynamics KW - Fluid Dynamics Y1 - 2019 UR - https://journals.aps.org/prfluids/abstract/10.1103/PhysRevFluids.4.044004 U6 - https://doi.org/10.1103/PhysRevFluids.4.044004 SN - 2469-990X VL - 4 IS - 4 SP - 044004-1 EP - 044004-21 ER - TY - GEN A1 - Borcia, Ion-Dan A1 - Borcia, Rodica A1 - Richter, Sebastian A1 - Xu, Wenchao A1 - Bestehorn, Michael A1 - Harlander, Uwe T1 - Horizontal Faraday instability in a circular channel T2 - Proceedings in Applied Mathematics and Mechanics (PAMM) N2 - We study surface waves in a circular channel placed on a rotating table. The tank can rotate with constant velocity and/or can oscillate. For a glycerin‐water‐solution with high viscosity, oscillation amplitudes about 20 cm and frequencies of 0.5 Hz, we observe surface patterns generated by a parametric instability. The circular geometry of the channel assures in a natural way the periodic lateral boundary conditions often used in the numerical simulations. Up to our knowledge this is the first experiment which evidences the horizontal Faraday instability in a container without walls blocking the flow in the oscillation direction. Experimental and numerical results are compared and discussed. KW - Faraday instability KW - Numerical solutions Y1 - 2019 UR - https://onlinelibrary.wiley.com/doi/abs/10.1002/pamm.201900242 U6 - https://doi.org/10.1002/pamm.201900242 SN - 1617-7061 VL - 19 IS - 1 ER - TY - GEN A1 - Borcia, Ion-Dan A1 - Borcia, Rodica A1 - Xu, Wenchao A1 - Bestehorn, Michael A1 - Richter, Sebastian A1 - Harlander, Uwe T1 - Undular bores in a large circular channel T2 - European Journal of Mechanics - B/Fluids N2 - An experimental device previously developed for studying rotating baroclinic flows has been used to investigate undular bores formation, propagation and collision. Up to our knowledge this is the first experimental study of undular bores in a circular channel. For a setup without barriers, this geometry accomplishes in a natural way the periodic lateral boundary conditions, very often used in numerical simulations. An excellent agreement between the experiment and simulation has been achieved. The spatio-temporal structure of bores is well reproduced for the first few reflections or collisions. KW - Undular bores KW - Bore collision KW - Periodical boundary conditions Y1 - 2020 UR - https://www.sciencedirect.com/science/article/pii/S0997754619300706?via%3Dihub U6 - https://doi.org/10.1016/j.euromechflu.2019.09.003 SN - 0997-7546 VL - 79 SP - 67 EP - 73 ER - TY - GEN A1 - Strobel, Carsten A1 - Alvarado Chavarin, Carlos A1 - Leszczynski, Sebastian A1 - Richter, Karola A1 - Knaut, Martin A1 - Reif, Johanna A1 - Völkel, Sandra A1 - Albert, Matthias A1 - Wenger, Christian A1 - Bartha, Johann Wolfgang A1 - Mikolajick, Thomas T1 - Improved Graphene-base Heterojunction Transistor with Different Collector Semi-conductors for High-frequency Applications T2 - Advanced Materials Letters N2 - A new kind of transistor device with a graphene monolayer embedded between two n-type silicon layers is fabricated and characterized. The device is called graphene-base heterojunction transistor (GBHT). The base-voltage controls the current of the device flowing from the emitter via graphene to the collector. The transit time for electrons passing by the ultrathin graphene layer is extremely short which makes the device very promising for high frequency RF-electronics. The output current of the device is saturated and clearly modulated by the base voltage. Further, the silicon collector of the GBHT is replaced by germanium to improve the device performance. This enabled the collector current to be increased by almost three orders of magnitude. Also, the common-emitter current gain (Ic/Ib) increased from 10-3 to approximately 0.3 for the newly designed device. However, the ON-OFF ratio of the improved germanium based GBHT has so far been rather low. Further optimizations are necessary in order to fully exploit the potential of the graphene-base heterojunction transistor. KW - Graphene KW - transistor Y1 - 2022 U6 - https://doi.org/10.5185/amlett.2022.011688 SN - 0976-3961 VL - 13 IS - 1 ER - TY - GEN A1 - Eisenhauer, Nico A1 - Frank, Karin A1 - Weigelt, Alexandra A1 - Bartkowski, Bartosz A1 - Beugnon, Rémy A1 - Liebal, Katja A1 - Mahecha, Miguel A1 - Quaas, Martin A1 - Al‐Halbouni, Djamil A1 - Bastos, Ana A1 - Bohn, Friedrich J. A1 - Brito, Mariana Madruga de A1 - Denzler, Joachim A1 - Feilhauer, Hannes A1 - Fischer, Rico A1 - Fritsche, Immo A1 - Guimaraes‐Steinicke, Claudia A1 - Hänsel, Martin A1 - Haun, Daniel B. M. A1 - Herrmann, Hartmut A1 - Huth, Andreas A1 - Kalesse‐Los, Heike A1 - Koetter, Michael A1 - Kolleck, Nina A1 - Krause, Melanie A1 - Kretschmer, Marlene A1 - Leitão, Pedro J. A1 - Masson, Torsten A1 - Mora, Karin A1 - Müller, Birgit A1 - Peng, Jian A1 - Pöhlker, Mira L. A1 - Ratzke, Leonie A1 - Reichstein, Markus A1 - Richter, Solveig A1 - Rüger, Nadja A1 - Sánchez‐Parra, Beatriz A1 - Shadaydeh, Maha A1 - Sippel, Sebastian A1 - Tegen, Ina A1 - Thrän, Daniela A1 - Umlauft, Josefine A1 - Wendisch, Manfred A1 - Wolf, Kevin A1 - Wirth, Christian A1 - Zacher, Hannes A1 - Zaehle, Sönke A1 - Quaas, Johannes T1 - A belowground perspective on the nexus between biodiversity change, climate change, and human well‐being T2 - Journal of Sustainable Agriculture and Environment N2 - Soil is central to the complex interplay among biodiversity, climate, and society. This paper examines the interconnectedness of soil biodiversity, climate change, and societal impacts, emphasizing the urgent need for integrated solutions. Human‐induced biodiversity loss and climate change intensify environmental degradation, threatening human well‐being. Soils, rich in biodiversity and vital for ecosystem function regulation, are highly vulnerable to these pressures, affecting nutrient cycling, soil fertility, and resilience. Soil also crucially regulates climate, influencing energy, water cycles, and carbon storage. Yet, climate change poses significant challenges to soil health and carbon dynamics, amplifying global warming. Integrated approaches are essential, including sustainable land management, policy interventions, technological innovations, and societal engagement. Practices like agroforestry and organic farming improve soil health and mitigate climate impacts. Effective policies and governance are crucial for promoting sustainable practices and soil conservation. Recent technologies aid in monitoring soil biodiversity and implementing sustainable land management. Societal engagement, through education and collective action, is vital for environmental stewardship. By prioritizing interdisciplinary research and addressing key frontiers, scientists can advance understanding of the soil biodiversity–climate change–society nexus, informing strategies for environmental sustainability and social equity. Y1 - 2024 U6 - https://doi.org/10.1002/sae2.12108 SN - 2767-035X VL - 3 IS - 2 PB - Wiley ER - TY - GEN A1 - Borcia, Ion-Dan A1 - Richter, Sebastian A1 - Borcia, Rodica A1 - Schön, Franz-Theo A1 - Harlander, Uwe A1 - Bestehorn, Michael T1 - Wave propagation in a circular channel: sloshing and resonance T2 - The European Physical Journal Special Topics N2 - Surface wave resonance of a liquid (water) layer confined in a circular channel is studied both experimentally and numerically. For the experiment, eight unevenly distributed ultrasonic distance sensors measure the local height of the wave surface. The resonance curves show maxima only for odd multiples of the fundamental resonance frequency . We explained this behavior using a simple intuitive “ping-pong” like model. Collision of wave fronts can be observed for higher frequencies. Also, the wave reflection on the walls can be treated as wave collision with itself. The non-linearity seems to be weak in our study so the delay in the wave propagation before and after the collision is small. Time-space plots show localized propagating waves with high amplitudes for frequencies near resonance. Between the peaks low amplitude and harmonic patterns are observed. However, for higher frequencies, the frequency band for localized waves becomes wider. In the Fourier space-time plane, this can be observed as a point for the harmonic patterns or a superposition of two lines: one line parallel to wave-vector k axis corresponding to the excitation frequency and a second line with inclination given by wave propagation velocity . For planned future work, this result will help us to reconstruct the whole water surface elevation using time-series from only a few measurement points Y1 - 2023 UR - https://link.springer.com/article/10.1140/epjs/s11734-023-00790-z U6 - https://doi.org/10.1140/epjs/s11734-023-00790-z SN - 1951-6401 SN - 1951-6355 VL - Vol. 232 IS - 4 SP - 461 EP - 468 ER - TY - GEN A1 - Piriz, S. A. A1 - Piriz, Antonio R. A1 - Tahir, Naeem A. A1 - Richter, Sebastian A1 - Bestehorn, Michael T1 - Rayleigh-Taylor instability in elastic-plastic solid slabs bounded by a rigid wall T2 - Physical Review E N2 - The linear evolution of the incompressible Rayleigh-Taylor instability for the interface between an elastic-plastic slab medium and a lighter semi-infinite ideal fluid beneath the slab is developed for the case in which slab is attached to a rigid wall at the top surface. The theory yields the maps for the stability in the space determined by the initial perturbation amplitude and wavelength, as well as for the transition boundary from the elastic to the plastic regimes for arbitrary thicknesses of the slab and density contrasts between the media. In particular, an approximate but very accurate scaling law is found for the minimum initial perturbation amplitude required for instability and for the corresponding perturbation wavelength at which it occurs. These results allows for an interpretation of the recent experiments by Maimouni et al. [Phys. Rev. Lett. 116, 154502 (2016)]. KW - Rayleigh-Taylor instability KW - Research Areas Flow instability KW - Research Areas Nonlinear phenomena in plasmas KW - Plasma instabilities Plasma macroinstabilities Y1 - 2021 UR - https://journals.aps.org/pre/abstract/10.1103/PhysRevE.103.023105 U6 - https://doi.org/10.1103/PhysRevE.103.023105 SN - 2470-0045 VL - 103 IS - 2 SP - 023105-1 EP - 023105-12 ER -