Modeling and investigating the thermalization of microscopic objects with arbitrary shape from first principles is of fundamental interest and may lead to technical applications. Here, we study, over a large temperature range, the thermalization dynamics due to far-field heat radiation of an individual, deterministically produced silica fiber with a predetermined shape and a diameter smaller than the thermal wavelength. The temperature change of the subwavelength-diameter fiber is determined through a measurement of its optical path length in conjunction with an ab initio thermodynamic model of the fiber structure. Our results show excellent agreement with a theoretical model that considers heat radiation as a volumetric effect and takes the emitter shape and size relative to the emission wavelength into account.

We present a study of the energy transfer in the bulk of a turbulent flow with dilute long-chain polymer additives. Based on prior work by Tabor and de Gennes [Europhys. Lett. 2, 519 (1986); Physica (Amsterdam) 140A, 9 (1986)], we propose a theory on the energy flux into the elastic degrees of freedom of the polymer chains. This elastic energy flux, which increases as the length scale decreases, gradually reduces the energy transferred to smaller scales through turbulence cascade and hence suppresses small scale fluctuations. The balance of the elastic energy flux and the turbulence energy cascade gives an elastic length scale, which describes the effect of polymer elasticity on turbulence in the inertial range. Predictions of this new “energy flux balance theory” agree excellently with our experimental results.

Nonautonomous oscillatory systems with stable amplitudes and time-varying frequencies have often been treated as stochastic, inappropriately. We therefore formulate them as a new class and discuss how they generate complex behavior. We show how to extract the underlying dynamics, and we demonstrate that it is simple and deterministic, thus paving the way for a diversity of new systems to be recognized as deterministic. They include complex and nonautonomous oscillatory systems in nature, both individually and in ensembles and networks.

We address the partial wetting of liquid drops on ultrathin solid sheets resting on a deformable foundation. Considering the membrane limit of sheets that can relax compression through wrinkling at negligible energetic cost, we revisit the classical theory for the contact of liquid drops on solids. Our calculations and experiments show that the liquid-solid-vapor contact angle is modified from the Young angle, even though the elastic bulk modulus ($E$) of the sheet is so large that the ratio between the surface tension $\gamma$ and $E$ is of molecular size. This finding indicates a new elastocapillary phenomenon that stems from the high bendability of very thin elastic sheets rather than from material softness. We also show that the size of the wrinkle pattern that emerges in the sheet is fully predictable, thus resolving a puzzle in modeling “drop-on-a-floating-sheet” experiments and enabling a quantitative, calibration-free use of this setup for the metrology of ultrathin films.

Convective motions in a fluid layer are affected by its orientation with respect to the gravitational field. We investigate the long-term stability of a thermally stressed layer of a binary liquid mixture and show that pattern formation is strongly affected by marginal inclinations as small as a few milliradians. At small Rayleigh numbers, the mass transfer is dominated by the induced large scale shear flow, while at larger Rayleigh numbers, it is dominated by solutal convection. At the transition, the balance between the solutal and shear flows gives rise to drifting columnar flows moving in opposite directions along parallel lanes in a superhighway configuration.

Waves traveling through weakly random media are known to be strongly affected by their corresponding ray dynamics, in particular in forming linear freak waves. The ray intensity distribution, which, e.g., quantifies the probability of freak waves is unknown, however, and a theory of how it is approached in an appropriate semiclassical limit of wave mechanics is lacking. We show that this limit is not the usual limit of small wavelengths, but that of decoherence. Our theory, which can describe the intensity distribution for an arbitrary degree of coherence is relevant to a wide range of physical systems, as decoherence is omnipresent in real systems.

By introducing a processing delay in the coupling, we find that it can effectively annihilate the quenching of oscillation, amplitude death (AD), in a network of coupled oscillators by switching the stability of AD. It revives the oscillation in the AD regime to retain sustained rhythmic functioning of the networks, which is in sharp contrast to the propagation delay with the tendency to induce AD. This processing delay-induced phenomenon occurs both with and without the propagation delay. Further this effect is rather general from two coupled to networks of oscillators in all known scenarios that can exhibit AD, and it has a wide range of applications where sustained oscillations should be retained for proper functioning of the systems.

Drop rebound is a spectacular event that appears after impact on hydrophobic or superhydrophobic surfaces but can also be induced through the so-called Leidenfrost effect. Here we demonstrate that drop rebound can also originate from another physical phenomenon, the solid substrate sublimation. Through drop impact experiments on a superhydrophobic surface, a hot plate, and solid carbon dioxide (commonly known as dry ice), we compare drop rebound based on three different physical mechanisms, which apparently share nothing in common (superhydrophobicity, evaporation, and sublimation), but lead to the same rebound phenomenon in an extremely wide temperature range, from $300°\mathrm{C}$ down to even below $-79°\mathrm{C}$. The formation and unprecedented visualization of an air vortex ring around an impacting drop are also reported.

We present the optical response of two interacting metallic nanowires calculated for separation distances down to angstrom range. State-of-the-art local and nonlocal approaches are compared with full quantum time-dependent density functional theory calculations that give an exact account of nonlocal and tunneling effects. We find that the quantum results are equivalent to those from classical approaches when the nanoparticle separation is defined as the separation between centroids of the screening charges. This establishes a universal plasmon ruler for subnanometric distances. Such a ruler not only impacts the basis of many applications of plasmonics, but also provides a robust rule for subnanometric metrology.

We report on the onset of fluid entrainment when a contact line is forced to advance over a dry solid of arbitrary wettability. We show that entrainment occurs at a critical advancing speed beyond which the balance between capillary, viscous, and contact-line forces sustaining the shape of the interface is no longer satisfied. Wetting couples to the hydrodynamics by setting both the morphology of the interface at small scales and the viscous friction of the front. We find that the critical deformation that the interface can sustain is controlled by the friction at the contact line and the viscosity contrast between the displacing and displaced fluids, leading to a rich variety of wetting-entrainment regimes. We discuss the potential use of our theory to measure contact-line forces using atomic force microscopy and to study entrainment under microfluidic conditions exploiting colloid-polymer fluids of ultralow surface tension.

The impact of a drop onto a deep bath of an immiscible liquid is studied with emphasis on the drop fragmentation into a collection of noncoalescing daughter drops. At impact the drop flattens and spreads at the surface of the crater it transiently opens in the bath and reaches a maximum deformation, which gets larger with increasing impact velocity, before surface tension drives its recession. This recession can promote the fragmentation by two different mechanisms: At moderate impact velocity, the drop recession converges to the axis of symmetry to form a jet which then fragments by a Plateau-Rayleigh mechanism. At higher velocity the edge of the receding drop destabilizes and shapes into radial ligaments which subsequently fragment. For this latter mechanism the number $N\propto {\mathrm{We}}^3$ and the size distribution of the daughter drops $p(d)\propto d^{-4}$ as a function of the impact Weber number We are explained on the basis of the observed spreading of the drop. The universality of this model for the fragmentation of receding liquid sheets might be relevant for other configurations.

We provide direct measurements of the boundary layer properties in highly turbulent Taylor-Couette flow up to $\mathrm{Re}=2\times {10}^6$ ($\mathrm{Ta}=6.2\times {10}^{12}$) using high-resolution particle image velocimetry and particle tracking velocimetry. We find that the mean azimuthal velocity profile at the inner and outer cylinder can be fitted by the von Kármán log law $u^{+}=1/\kappa \ln y^{+}+B$. The von Kármán constant $\kappa$ is found to depend on the driving strength Ta and for large Ta asymptotically approaches $\kappa \approx 0.40$. The variance profiles of the local azimuthal velocity have a universal peak around $y^{+}\approx 12$ and collapse when rescaled with the driving velocity (and not with the friction velocity), displaying a log dependence of $y^{+}$ as also found for channel and pipe flows.

We study matter-wave bright solitons in spin-orbit coupled Bose-Einstein condensates with attractive interactions. We use a multiscale expansion method to identify solution families for chemical potentials in the semi-infinite gap of the linear energy spectrum. Depending on the linear and spin-orbit coupling strengths, the solitons may present either a ${\mathrm{sech}}^2$-shaped or a modulated density profile reminiscent of the stripe phase of spin-orbit coupled repulsive Bose-Einstein condensates. Our numerical results are in excellent agreement with our analytical findings and demonstrate the potential robustness of solitons for experimentally relevant conditions.

Molecular dynamics simulations are performed to investigate the water permeation across the single-walled carbon nanotube with the radial breathing mode (RBM) vibration. It is found that the RBM can play a significant role in breaking the hydrogen bonds of the water chain, accordingly increasing the net flux dramatically, and reducing drastically the average number of water molecules inside the tube with the frequency ranging from 5000 to 11 000 GHz, while far away from this frequency region the transport properties of water molecules are almost unaffected by the RBM. This phenomenon can be understood as the resonant response of the water molecule chain to the RBM. Our findings are expected to be helpful for the design of high-flux nanochannels and the understanding of biological activities, especially the water channelling.

Low-frequency currents induced by ultrashort laser-driven ionization can emit extremely broadband, single-cycle terahertz pulses. We present a model that predicts a strong wavelength dependence of the THz emission in good agreement with our experimental study. This reveals that the combined effects of plasma currents rising proportionally to the square of the pump wavelength and wavelength-dependent focusing conditions lead to 30 times higher THz emission at 1800 nm compared to an 800 nm wavelength. Unrivaled single-cycle electric field strengths of $4.4\mathrm{MV}/\mathrm{cm}$ are achieved with this compact table-top setup.

We investigate the coefficient of normal restitution as a function of the impact velocity, $\epsilon (v)$, for inelastic spheres. We observe oscillating behavior of $\epsilon (v)$ which is superimposed to the known decay of the coefficient of restitution as a function of impact velocity. This remarkable effect was so far unnoticed because under normal circumstances it is screened by statistical scatter. We detected its clear signature by recording large amounts of data using an automated experiment. The new effect may be understood as an interplay between translational and vibrational degrees of freedom of the colliders. Both characteristics of the oscillation, the wavelength and the amplitude, agree quantitatively with a theoretical description of the experiment.

We introduce a novel concept of the pseudo-parity-time (pseudo-$\mathcal{P}\mathcal{T}$) symmetry in periodically modulated optical systems with balanced gain and loss. We demonstrate that whether or not the original system is $\mathcal{P}\mathcal{T}$ symmetric, we can manipulate the property of the $\mathcal{P}\mathcal{T}$ symmetry by applying a periodic modulation in such a way that the effective system derived by the high-frequency Floquet method is $\mathcal{P}\mathcal{T}$ symmetric. If the original system is non-$\mathcal{P}\mathcal{T}$ symmetric, the $\mathcal{P}\mathcal{T}$ symmetry in the effective system will lead to quasistationary propagation that can be associated with the pseudo-$\mathcal{P}\mathcal{T}$ symmetry. Our results provide a promising approach for manipulating the $\mathcal{P}\mathcal{T}$ symmetry of realistic systems.

Chimera states occur spontaneously in populations of coupled photosensitive chemical oscillators. Experiments and simulations are carried out on nonlocally coupled oscillators, with the coupling strength decreasing exponentially with distance. Chimera states with synchronized oscillators, phase waves, and phase clusters coexisting with unsynchronized oscillators are analyzed. Irregular motion of the cores of asynchronous oscillators is found in spiral-wave chimeras.

We demonstrate 97%, 89%, and 76% transmission of sound amplitude in air through walls perforated with subwavelength holes of areal coverage fractions 0.10, 0.03, and 0.01, respectively, producing 94-, 950-, and 5700-fold intensity enhancements therein. This remarkable level of extraordinary acoustic transmission is achieved with thin tensioned circular membranes, making the mass of the air in the holes effectively vanish. Imaging the pressure field confirms incident-angle independent transmission, thus realizing a bona fide invisible wall. Applications include high-resolution acoustic sensing.

We present a new methodology for studying non-Hamiltonian nonlinear systems based on an information theoretical extension of a renormalization group technique using a modified maximum entropy principle. We obtain a rigorous dimensionally reduced description for such systems. The neglected degrees of freedom by this reduction are replaced by a systematically defined stochastic process under a constraint on the second moment. This then forms the basis of a computationally efficient method. Numerical computations for the generalized Kuramoto-Sivashinsky equation support our method and reveal that the long-time underlying stochastic process of the fast (unresolved) modes obeys a universal distribution that does not depend on the initial conditions and which we rigorously derive by the maximum entropy principle.