A5082232920- Fluid Dynamics and Turbulent Flows
- Plant Water Relations and Carbon Dynamics
- Magnetic properties of thin films
- Nonlinear Dynamics and Pattern Formation
- Electric Motor Design and Analysis
- Magnetic Bearings and Levitation Dynamics
- Meteorological Phenomena and Simulations
- Fluid Dynamics and Vibration Analysis
- Wind and Air Flow Studies
- Theoretical and Computational Physics
- Innovative Microfluidic and Catalytic Techniques Innovation
- Physics of Superconductivity and Magnetism
- Magnetic Properties and Applications
- Quantum chaos and dynamical systems
- Geomagnetism and Paleomagnetism Studies
- Quantum and electron transport phenomena
- Chaos control and synchronization
- Complex Systems and Time Series Analysis
- Electrowetting and Microfluidic Technologies
- Particle Dynamics in Fluid Flows
- Aerodynamics and Acoustics in Jet Flows
- Tribology and Lubrication Engineering
- Sensorless Control of Electric Motors
- Fluid Dynamics and Thin Films
- Magneto-Optical Properties and Applications
École Polytechnique Fédérale de Lausanne
2016-2025
Paderborn University
2006-2024
Deutsches Zentrum für Luft- und Raumfahrt e. V. (DLR)
2021-2024
Berlin Heart (Germany)
2023
Helmholtz-Zentrum Dresden-Rossendorf
2015-2021
Chemnitz University of Technology
2016-2021
NXP (Germany)
2021
University of Wuppertal
2015-2021
University of California, Riverside
2021
Polytechnic Institute of Porto
2019
Pipe flow is a prominent example among the shear flows that undergo transition to turbulence without mediation by linear instability of laminar profile. Experiments on pipe flow, as well plane Couette and Poiseuille show triggering depends sensitively initial conditions, between turbulent states there exists no intermediate state with simple spatial or temporal characteristics, not persistent, i.e., it can decay again, if observation time long enough. All these features consistently be...
High-speed applications involve technical and economical advantages because, as direct drives, they avoid the gear an additional mechanical drive component. Permanent-magnet synchronous machines (PMSMs) are attracting growing attention for high-speed drives. Surface-mounted PMSMs request a glass- or carbon-fiber bandage to fasten magnets rotor surface at high speed. At rotors with "buried" magnets, iron itself fixes magnets. This paper presents simple calculation strategies discusses their...
The linear stability of pipe flow implies that only perturbations sufficient strength will trigger the transition to turbulence. In order determine this threshold in perturbation amplitude we study edge chaos which separates decay towards laminar profile and Using lifetime as an indicator methods developed Skufca et al., Phys. Rev. Lett. 96, 174101 (2006), show superimposed on overall 1/Re scaling predicted studied previously there are small, nonmonotonic variations reflecting folds chaos....
We demonstrate the existence of a large number exact solutions plane Couette flow, which share topology known periodic but are localized in one spatial dimension. Solutions different size organized snakes-and-ladders structure strikingly similar to that observed for simpler pattern-forming partial differential equations. These new step towards extending dynamical systems view transitional turbulence spatially extended flows.
In the growing field of $m\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}g\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}c\phantom{\rule{0}{0ex}}s$, spin waves (magnons) are manipulated as information carriers, particularly for data processing. Thus controlling propagation is paramount interest here. This investigation considers a ferromagnetic bilayer with dipolar coupling potential nonreciprocal magnonic device, in...
We measure the response of cylindrical shells to poking and identify a stability landscape, which fully characterizes perfect imperfect ones in case where single defect dominates. show that landscape is independent loading protocol poker geometry. Our results suggest complex reduces low dimensional description. Tracking ridges valleys this defines natural phase-space coordinates for describing shells.
The Birman–Williams theorem gives a connection between the collection of unstable periodic orbits (UPOs) contained within chaotic attractor and topology that attractor, for three-dimensional systems. In certain cases, fractal dimension in partial differential equation (PDE) is less than three, even though embedded an infinite-dimensional space. Here, we study Kuramoto–Sivashinsky PDE at onset chaos. We use two different dimensionality-reduction techniques—proper orthogonal decomposition...
In this paper we present the foundation of a unified, object-oriented, three-dimensional biomodelling environment, which allows us to integrate multiple submodels at scales from subcellular those tissues and organs. Our current implementation combines modified discrete model statistical mechanics, Cellular Potts Model, with continuum reaction–diffusion state automaton well-defined conditions for cell differentiation transitions genetic regulation. This environment rapidly compactly create...
We apply the iterated edge-state tracking algorithm to study boundary between laminar and turbulent dynamics in plane Couette flow at $\mathrm{Re}=400$. Perturbations that are not strong enough become fully or weak relaminarize tend toward a hyperbolic coherent structure state space, termed edge state, which seems be unique up obvious continuous shift symmetries. The results reported here show cases where fixed point has only one unstable direction, such as for lower-branch solution flow,...
Flows through pipes and channels are the most common means to transport fluids in practical applications equally occur numerous natural systems. In general, transfer of is energetically far more efficient if motion smooth laminar because friction losses lower. However, even at moderate velocities pipe channel flows sensitive minute disturbances, practice turbulent. Investigating spatial distribution vortices, we uncovered an amplification mechanism that constantly feeds energy from mean...
We study the turbulence transition of plane Couette flow in large domains where localised perturbations are observed to generate growing turbulent spots. Extending previous studies on boundary between laminar and dynamics we determine invariant structures intermediate flow. In wide but short find states that spanwise direction, long also downstream direction. These act as critical nuclei for spatially extended domains.
Energy loss due to ohmic heating is a major bottleneck limiting down-scaling and speed of nano-electronic devices, harvesting heat for signal processing challenge in modern electronics. Here we demonstrate that thermal gradients arising from can be utilized excitation coherent auto-oscillations magnetization generation tunable microwave signals. The heat-driven dynamics observed $\mathrm{Y_{3}Fe_{5}O_{12}/Pt}$ bilayer nanowires where the Pt layer results injection pure spin current into...
Fluorescence-activated droplet sorting (FADS) is one of the most important features provided by droplet-based microfluidics. However, to date, it does not allow compete with high-throughput multiplexed capabilities offered flow cytometery. Here, we demonstrate use a dielectrophoretic-based FADS, allowing sort up five different populations simultaneously. Our system provides means select droplets phenotypes in single experimental run separate initially heterogeneous populations. results are...
A theoretical approach has been developed to study the spin-wave dynamics of magnetization-graded ferromagnetic films, where magnetic properties change along film thickness. The theory is based on a multilayer approach, influence both long-range dipolar interactions and interlayer exchange coupling between sublayers included. This allows for instance describe films with continuous variation saturation magnetization systematic carried out in order analyze different profiles magnetization,...
Periodically patterned metamaterials are known for exhibiting wave properties similar to the ones observed in electronic band structures crystal lattices. In particular, periodic ferromagnetic materials characterized by presence of bands and gaps their spin-wave spectrum at tunable GHz frequencies. Recently, fabrication magnets hosting Dzyaloshinskii-Moriya interactions has been pursued with high interest since properties, such as stabilization chiral spin textures nonreciprocal propagation,...
A survey on recently installed or developed permanent magnet (PM) synchronous generators for energy conversion in regenerative and alternative power supply systems is given. Its focus low speed machines geared gearless PM generator wind plants small hydro coupling. For distributed co-generation of heat electrical by micro gas turbines specially designed high are necessary. Design example both given along with application examples
High speed drives offer advantages such as small size, low noise, integrated and thus compact design for many industrial applications due to the fact, that direct they avoid mechanical gear. Inverter supply provides variable speed, which allows high efficient operation compressors pumps. A wide power range from 0.1 kW up 80 MW is covered with circumference speeds of 100 ... 250 m/s. Recent progress discussed details electric machinery are addressed, electromagnetic utilization, loss...
Plane Couette flow and pressure-driven pipe are two examples of flows where turbulence sets in while the laminar profile is still linearly stable. Experiments numerical studies have shown that transition has features compatible with formation a strange saddle rather than an attractor. In particular, depends sensitively on initial conditions turbulent state not persistent but exponential distribution lifetimes. Embedded within dynamics coherent structures, which transiently show up temporal...
Numerical and experimental studies of transitional pipe flow have shown the prevalence coherent structures that are dominated by downstream vortices. They attract special attention because they contribute predominantly to increase Reynolds stresses in turbulent flow. In present study we introduce a convenient detector for these states, calculate fraction time appear flow, Markov model transition between structures. The states show vortical exceeds 24% number about $\mathrm{Re}=2200$, it...
Direct numerical simulation of transitional pipe flow is carried out in a long computational domain order to characterize the dynamics within saddle region phase space that separates laminar from turbulent intermittency. For Reynolds numbers ranging $\mathrm{Re}=1800$ 2800, shoot and bisection method used compute critical trajectories. The chaotic or edge state approached by these trajectories studied detail. $\mathrm{Re}\ensuremath{\le}2000$ corresponding intermittent puff are shown share...
Turbulent-laminar banded patterns in plane Poiseuille flow are studied via direct numerical simulations a tilted and translating computational domain using parallel version of the pseudospectral code Channelflow. 3D visualizations streamwise vorticity an instantaneous time-averaged pattern presented, as well 2D average velocity field turbulent kinetic energy. Simulations for 2300 ⩾ Reb 700 show gradual development from uniform turbulence to with wavelength 20 half-gaps at ≈ 1900, 40 1300...
Biological filaments driven by molecular motors tend to experience tangential propulsive forces also known as active follower forces. When such a filament encounters an obstacle, it deforms, which reorients its and alters entire motion. If the pushes cargo, friction on cargo can be enough deform filament, thus affecting transport properties of cargo. Motivated cytoskeletal motility assays, we study dynamic buckling instabilities two-dimensional slender elastic through dissipative medium in...