530 Physik
Refine
Has Fulltext
- no (156)
Year of publication
- 2020 (156) (remove)
Document Type
- Article (156) (remove)
Language
- English (156)
Is part of the Bibliography
- yes (156)
Keywords
- diffusion (7)
- anomalous diffusion (4)
- dynamics (3)
- model (3)
- non-fullerene acceptors (3)
- Aluminum alloys (2)
- Kuramoto (2)
- coupled rotators (2)
- first-passage (2)
- fractional Brownian motion (2)
- gamma rays: general (2)
- hysteresis (2)
- impact (2)
- methods: numerical (2)
- neutron (2)
- noisy systems (2)
- organic photovoltaics (2)
- organic solar cells (2)
- perovskite solar cells (2)
- photocurrent generation (2)
- random diffusivity (2)
- stars: atmospheres (2)
- stars: low-mass (2)
- subdwarfs (2)
- surface (2)
- synchronization transition (2)
- 2D perovskites (1)
- 3D printing (1)
- AG (1)
- APCI (1)
- Absorption (1)
- Amazon rainforest (1)
- Answer Set Programming (1)
- Aromatic compounds (1)
- Astrophysics (1)
- Atlantic meridional overturning circulation (1)
- BESSY II (1)
- BL Lacertae objects: individual (1)
- Bessel functions (1)
- Black– Scholes model (1)
- Bloch-Torrey equation (1)
- Boundary value problem (1)
- Brownian motion (1)
- CRNS (1)
- Caccioppoli inequality (1)
- Cattaneo equation (1)
- Ce/Zr (1)
- Computational chemistry (1)
- Creep (1)
- Crystal lattices (1)
- CuI (1)
- Diffusion (1)
- Diffusion NMR (1)
- Dislocation motion (1)
- Dispersion force (1)
- DoS (1)
- Donor-Acceptor (DA) interface (1)
- Dynamical systems (1)
- Energy (1)
- Explainable AI (1)
- Femtosecond lasers (1)
- Flims (1)
- Fluorescence (1)
- Fokker– Planck equation (1)
- Fox H-function (1)
- Fox H-functions (1)
- Fractal (1)
- Genetic programming (1)
- Green function (1)
- Green's function (1)
- Greenland (1)
- HALS (1)
- Hermite polynomial expansion (1)
- Heterostructures (1)
- Hodge theory (1)
- Hydrocarbons (1)
- Hydrogen activation (1)
- IMD (1)
- ISM (1)
- ISM: clouds (1)
- ISM: supernova remnants (1)
- ISOS-L-1I protocol (1)
- Kalman filtering (1)
- Kuramoto model (1)
- LIBS (1)
- Levy walk (1)
- Localization regime (1)
- MHD (1)
- Machine learning control (1)
- Magellanic Cloud (1)
- Molecules (1)
- Monomers (1)
- Motivation (1)
- NTF (1)
- Neumann problem (1)
- Non-perturbative analysis (1)
- Oligomers (1)
- Ornstein–Uhlenbeck process (1)
- PEDOT:PSS (1)
- Perovskite solar cells (1)
- Phonons (1)
- Photoexcitations (1)
- Plasma Physics (1)
- Reaction mechanisms (1)
- Reactive adsorption (1)
- Resolved and unresolved sources as a function of wavelength (1)
- Schottky junction (1)
- Schrodinger operators (1)
- Schrödinger equation (1)
- Shnol theorem (1)
- Shockley-Read-Hall (1)
- Small (1)
- Spin-echo (1)
- Strain measurement (1)
- Surface properties (1)
- Synchronization control (1)
- Thermal effects (1)
- Ti-6Al-4V (1)
- Ultrafast X-rays (1)
- WAAM (1)
- X-ray (1)
- X-ray emission (1)
- X-ray photoelectron spectroscopy (1)
- X-ray refraction (1)
- absorption (1)
- acceptance (1)
- actuators (1)
- adaptation and mitigation (1)
- additive manufacturing (1)
- aggregation (1)
- amphiphilic side chains (1)
- and governance (1)
- anomalous (or non-Fickian) diffusion (1)
- anomalous heat conduction (1)
- astroparticle physics (1)
- astrophysical plasmas (1)
- asynchronous design (1)
- atomic force microscopy (AFM) (1)
- authentication (1)
- authentication protocol (1)
- axial next nearest neighbour Ising chains (1)
- background (1)
- barrier escape (1)
- basis-sets (1)
- battery (1)
- battery-depletion attack (1)
- binaries: general (1)
- blade (1)
- boron-10 (1)
- built-in potential (1)
- bulk-heterojunction solar cells (1)
- bumps (1)
- capacitance spectroscopy (1)
- carrier density (1)
- cesium lead halides (1)
- chains (1)
- channel (1)
- charge (1)
- charge carrier density (1)
- charge carrier extraction (1)
- charge collection (1)
- charge injection across hybrid interfaces (1)
- charge transport layers (1)
- charge-transfer (1)
- chimera states (1)
- circumstellar matter (1)
- classification (1)
- climate (1)
- cohomology (1)
- coma (1)
- comets (1)
- complex networks (1)
- composites (1)
- computed tomography (1)
- conductivity (1)
- conformational and hydrodynamic characteristics (1)
- conjugated polymers (1)
- consequences (1)
- continuous time random walk (1)
- convolutional neural networks (1)
- cooperation (1)
- copper iodide (1)
- copper minerals (1)
- costs (1)
- creep (1)
- critical adsorption (1)
- crossover dynamics (1)
- crystal (1)
- crystal orientation (1)
- data assimilation (1)
- de Rham complex (1)
- deep learning (1)
- delay faults (1)
- denial-of-service attack (1)
- density (1)
- dependent velocity (1)
- design for Testability (1)
- detector (1)
- dielectric (1)
- diffraction (1)
- diffusing diffusivity (1)
- dimension independent bound (1)
- diselenide (1)
- dislocations (1)
- donor (1)
- driven (1)
- driving force (1)
- droughts (1)
- dust (1)
- dynamical systems (1)
- dynamo (1)
- ecology and biodiversity (1)
- ecosystems (1)
- efficiency (1)
- electret polymers (1)
- electro-electrets (1)
- electron flux (1)
- electron localization (1)
- electron-transfer (1)
- electrons (1)
- electrostatics (1)
- elevated-temperature effects on the operation of dielectric-elastomer (1)
- emission factor (1)
- empirical modeling (1)
- enacted PCK (1)
- energetic disorders (1)
- energy (1)
- energy decarbonization (1)
- energy-level alignments (1)
- ensemble and time averaged mean squared displacement (1)
- ensemble methods (1)
- entropy production (1)
- excitonic materials (1)
- expanding medium (1)
- expectation maximisation algorithm (1)
- exploit (1)
- extremal values (1)
- extrusion (1)
- fastest first-passage time of N walkers (1)
- ferroelectricity and piezoelectricity in polymers (1)
- field experience (1)
- filter (1)
- flagellum (1)
- flexibility (1)
- fluorinated organic spacer (1)
- fluorination (1)
- formal specification (1)
- formal verification (1)
- formation (1)
- fractal (1)
- fractional dynamic equations (1)
- fullerenes (1)
- functional materials (1)
- functionalization (1)
- fungus (1)
- galaxies (1)
- galaxies: high-redshift (1)
- gamma rays: (1)
- gamma rays: diffuse (1)
- gamma-rays: general (1)
- gas (1)
- gas chromatography (1)
- generalized eigenfunction (1)
- genomic DNA conformation (1)
- geometric Brownian motion (1)
- global surface warming (1)
- gradient boosting (1)
- grafted polymers (1)
- graphs (1)
- greenhouse gas (1)
- ground state (1)
- helium-3 alternative (1)
- heteroatoms (1)
- heterojunction silicon solar cells (1)
- high dimensional (1)
- hole (1)
- human behaviour (1)
- humidity (1)
- hybrid manufacturing (1)
- hybrid material (1)
- hybrid metal oxides (1)
- hybrid synthesis (1)
- impedance spectroscopy (1)
- implantable medical device (1)
- implants (1)
- individual (1)
- inorganic perovskites (1)
- instabilities (1)
- instability (1)
- instructional (1)
- instructional explanation (1)
- interfaces (1)
- inversion (1)
- ion mobility spectrometry (1)
- iron (1)
- iron cyanides (1)
- land use (1)
- light photocontrol (1)
- localisation (1)
- low (1)
- low donor content (1)
- machine learning (1)
- magnetic fields (1)
- magnetosphere (1)
- manipulation (1)
- mass (1)
- matrix composites (1)
- maximum and range (1)
- metal (1)
- metal halide perovskites (1)
- metal species (1)
- methane localization (1)
- methods: observational (1)
- microstructure-property relations (1)
- mobility (1)
- modelling (1)
- modular logic programs (1)
- mold (1)
- molecular bottle brushes (1)
- molecular brushes (1)
- molecular crystals (1)
- molecular hydrodynamics and (1)
- molecular overcrowding (1)
- molecular weight (1)
- molecules (1)
- nanoparticles (1)
- natural resources (biological and non-biological) (1)
- nebulae: general (1)
- networks (1)
- neural networks (1)
- non-Gaussianity (1)
- non-Langevin reduction factors (1)
- non-integer dimension (1)
- non-repudiation (1)
- nonfullerene acceptors (1)
- nonlinear (1)
- numerical simulations (1)
- ocean heat uptake (1)
- on-farm evaluation (1)
- optics (1)
- option pricing (1)
- organic interfaces (1)
- organic solar cell (1)
- origins (1)
- p-type (1)
- parameter (1)
- phase purity (1)
- phase transition (1)
- phase transitions (1)
- phase-transition boundary (1)
- photochemistry (1)
- photoexcited hole transfer (1)
- photoisomerization (1)
- photoluminescence (1)
- photon recycling (1)
- photostability (1)
- photovoltaics (1)
- physics education (1)
- piezoelectrets (1)
- planetary (1)
- planetary nebulae: individual: SwSt1 (1)
- plasma flows (1)
- policies (1)
- politics (1)
- poly(vinylidenefluoride-trifluoroethylene) P(VDF-TrFE) (1)
- polyelectrolytes (1)
- polymer ferroelectrets (1)
- polymer solar cells (1)
- populations (1)
- pore orientation (1)
- porous carbon materials (1)
- positive solutions (1)
- power conversion efficiency (1)
- power spectrum (1)
- practicum (1)
- pre-service teachers (1)
- prediction (1)
- preferred orientation (1)
- printed electroacoustic thin-film transducers (1)
- printing (1)
- professional knowledge (1)
- projections (1)
- protocols (1)
- quality (1)
- quantum (1)
- quantum correlations (1)
- quantum mechanics (1)
- quasi-Fermi level (1)
- quasi-particles (1)
- quasi-steady-state photoinduced absorptions (1)
- radiation belts (1)
- random forest (1)
- readout electronics (1)
- recombination order (1)
- recombinations (1)
- regional equity (1)
- regression (1)
- remote monitoring (1)
- repertory grid (1)
- resetting (1)
- residual stress (1)
- resonant inelastic X-ray scattering (1)
- scalability (1)
- school internship (1)
- screen (1)
- segmentations (1)
- self-sufficiency (1)
- sensors and actuators (1)
- seperation (1)
- sequence-controlled polymers (1)
- shock waves (1)
- silver (1)
- single chain folding (1)
- single trajectories (1)
- smart card (1)
- soft X-ray (1)
- soft X-ray absorption (1)
- soft X-ray beamline (1)
- soft X-ray spectroscopy (1)
- soft electro-active materials (1)
- soft matter (1)
- soil moisture (1)
- solar coronal mass ejections (1)
- solar storm (1)
- solvation (1)
- space-dependent diffusivity (1)
- spectrometry (1)
- spectroscopy (1)
- spin-crossover (1)
- splitting (1)
- stability and accuracy (1)
- stars (1)
- stars: AGB and post-AGB (1)
- stars: abundances (1)
- stars: evolution (1)
- stars: fundamental parameters (1)
- stars: horizontal branch (1)
- stars: late-type (1)
- stars: massive (1)
- stars: rotation (1)
- stars: solar-type (1)
- stars: variables: general (1)
- state space modelling (1)
- stationary stochastic process (1)
- statistics (1)
- stellar content (1)
- stellar coronal mass ejections (1)
- stochastic dynamics (1)
- stochastic processes (1)
- stress exponent (1)
- structure (1)
- structures (1)
- stuck-at faults (1)
- subdiffusion (1)
- superdiffusion and (1)
- support vector machines (1)
- surface recombination (1)
- synchronization (1)
- synthesis (1)
- tandem solar cells (1)
- telegrapher's equation (1)
- telluride (1)
- tellurium (1)
- temperature (1)
- temperature dependence (1)
- thermal stimulation of (1)
- thermally enhanced actuators (1)
- thermodynamics (1)
- thermoelectrics (1)
- thick junctions (1)
- thin films (1)
- time (1)
- timing resilient design (1)
- trade (1)
- tranfer excited-state (1)
- transfer dynamics (1)
- transmission (1)
- transparent conductors (1)
- vibrational spectroscopy (1)
- voltage losses (1)
- water-interface (1)
- water-methane films (1)
- weak ergodicity breaking (1)
- weighted (1)
- work function (1)
- x-ray-absorption (1)
- zero-power defense (1)
- когомологии (1)
- комплекс де Рама (1)
- проблема Неймана (1)
- теория Ходжа (1)
Institute
- Institut für Physik und Astronomie (137)
- Institut für Chemie (10)
- Institut für Mathematik (4)
- Department Linguistik (1)
- Hasso-Plattner-Institut für Digital Engineering GmbH (1)
- Hasso-Plattner-Institut für Digital Engineering gGmbH (1)
- Institut für Informatik und Computational Science (1)
- Institut für Umweltwissenschaften und Geographie (1)
- Mathematisch-Naturwissenschaftliche Fakultät (1)
- Sozialwissenschaften (1)
The passive and active motion of micron-sized tracer particles in crowded liquids and inside living biological cells is ubiquitously characterised by 'viscoelastic' anomalous diffusion, in which the increments of the motion feature long-ranged negative and positive correlations. While viscoelastic anomalous diffusion is typically modelled by a Gaussian process with correlated increments, so-called fractional Gaussian noise, an increasing number of systems are reported, in which viscoelastic anomalous diffusion is paired with non-Gaussian displacement distributions. Following recent advances in Brownian yet non-Gaussian diffusion we here introduce and discuss several possible versions of random-diffusivity models with long-ranged correlations. While all these models show a crossover from non-Gaussian to Gaussian distributions beyond some correlation time, their mean squared displacements exhibit strikingly different behaviours: depending on the model crossovers from anomalous to normal diffusion are observed, as well as a priori unexpected dependencies of the effective diffusion coefficient on the correlation exponent. Our observations of the non-universality of random-diffusivity viscoelastic anomalous diffusion are important for the analysis of experiments and a better understanding of the physical origins of 'viscoelastic yet non-Gaussian' diffusion.
We consider the emerging dynamics of a separable continuous time random walk (CTRW) in the case when the random walker is biased by a velocity field in a uniformly growing domain. Concrete examples for such domains include growing biological cells or lipid vesicles, biofilms and tissues, but also macroscopic systems such as expanding aquifers during rainy periods, or the expanding Universe. The CTRW in this study can be subdiffusive, normal diffusive or superdiffusive, including the particular case of a Lévy flight. We first consider the case when the velocity field is absent. In the subdiffusive case, we reveal an interesting time dependence of the kurtosis of the particle probability density function. In particular, for a suitable parameter choice, we find that the propagator, which is fat tailed at short times, may cross over to a Gaussian-like propagator. We subsequently incorporate the effect of the velocity field and derive a bi-fractional diffusion-advection equation encoding the time evolution of the particle distribution. We apply this equation to study the mixing kinetics of two diffusing pulses, whose peaks move towards each other under the action of velocity fields acting in opposite directions. This deterministic motion of the peaks, together with the diffusive spreading of each pulse, tends to increase particle mixing, thereby counteracting the peak separation induced by the domain growth. As a result of this competition, different regimes of mixing arise. In the case of Lévy flights, apart from the non-mixing regime, one has two different mixing regimes in the long-time limit, depending on the exact parameter choice: in one of these regimes, mixing is mainly driven by diffusive spreading, while in the other mixing is controlled by the velocity fields acting on each pulse. Possible implications for encounter–controlled reactions in real systems are discussed.
Stochastic models based on random diffusivities, such as the diffusing-diffusivity approach, are popular concepts for the description of non-Gaussian diffusion in heterogeneous media. Studies of these models typically focus on the moments and the displacement probability density function. Here we develop the complementary power spectral description for a broad class of random-diffusivity processes. In our approach we cater for typical single particle tracking data in which a small number of trajectories with finite duration are garnered. Apart from the diffusing-diffusivity model we study a range of previously unconsidered random-diffusivity processes, for which we obtain exact forms of the probability density function. These new processes are different versions of jump processes as well as functionals of Brownian motion. The resulting behaviour subtly depends on the specific model details. Thus, the central part of the probability density function may be Gaussian or non-Gaussian, and the tails may assume Gaussian, exponential, log-normal, or even power-law forms. For all these models we derive analytically the moment-generating function for the single-trajectory power spectral density. We establish the generic 1/f²-scaling of the power spectral density as function of frequency in all cases. Moreover, we establish the probability density for the amplitudes of the random power spectral density of individual trajectories. The latter functions reflect the very specific properties of the different random-diffusivity models considered here. Our exact results are in excellent agreement with extensive numerical simulations.
The Ornstein–Uhlenbeck process is a stationary and ergodic Gaussian process, that is fully determined by its covariance function and mean. We show here that the generic definitions of the ensemble- and time-averaged mean squared displacements fail to capture these properties consistently, leading to a spurious ergodicity breaking. We propose to remedy this failure by redefining the mean squared displacements such that they reflect unambiguously the statistical properties of any stochastic process. In particular we study the effect of the initial condition in the Ornstein–Uhlenbeck process and its fractional extension. For the fractional Ornstein–Uhlenbeck process representing typical experimental situations in crowded environments such as living biological cells, we show that the stationarity of the process delicately depends on the initial condition.
This work focuses on the dynamics of particles in a confined geometry with position-dependent diffusivity, where the confinement is modelled by a periodic channel consisting of unit cells connected by narrow passage ways. We consider three functional forms for the diffusivity, corresponding to the scenarios of a constant (D ₀), as well as a low (D ₘ) and a high (D d) mobility diffusion in cell centre of the longitudinally symmetric cells. Due to the interaction among the diffusivity, channel shape and external force, the system exhibits complex and interesting phenomena. By calculating the probability density function, mean velocity and mean first exit time with the Itô calculus form, we find that in the absence of external forces the diffusivity D d will redistribute particles near the channel wall, while the diffusivity D ₘ will trap them near the cell centre. The superposition of external forces will break their static distributions. Besides, our results demonstrate that for the diffusivity D d, a high dependence on the x coordinate (parallel with the central channel line) will improve the mean velocity of the particles. In contrast, for the diffusivity D ₘ, a weak dependence on the x coordinate will dramatically accelerate the moving speed. In addition, it shows that a large external force can weaken the influences of different diffusivities; inversely, for a small external force, the types of diffusivity affect significantly the particle dynamics. In practice, one can apply these results to achieve a prominent enhancement of the particle transport in two- or three-dimensional channels by modulating the local tracer diffusivity via an engineered gel of varying porosity or by adding a cold tube to cool down the diffusivity along the central line, which may be a relevant effect in engineering applications. Effects of different stochastic calculi in the evaluation of the underlying multiplicative stochastic equation for different physical scenarios are discussed.
Optical excitation of spin-ordered rare earth metals triggers a complex response of the crystal lattice since expansive stresses from electron and phonon excitations compete with a contractive stress induced by spin disorder. Using ultrafast x-ray diffraction experiments, we study the layer specific strain response of a dysprosium film within a metallic heterostructure upon femtosecond laser-excitation. The elastic and diffusive transport of energy to an adjacent, non-excited detection layer clearly separates the contributions of strain pulses and thermal excitations in the time domain. We find that energy transfer processes to magnetic excitations significantly modify the observed conventional bipolar strain wave into a unipolar pulse. By modeling the spin system as a saturable energy reservoir that generates substantial contractive stress on ultrafast timescales, we can reproduce the observed strain response and estimate the time- and space dependent magnetic stress. The saturation of the magnetic stress contribution yields a non-monotonous total stress within the nanolayer, which leads to unconventional picosecond strain pulses.