We describe the breakup of a confined gas thread in a cross-flowing stream of liquid at capillary numbers $\mathrm{Ca}<{10}^{-2}$. The breakup is initiated, not by a Plateau-Rayleigh instability, but by liquid that flows from the tip of the thread to the neck where pinch-off occurs. This flow, faster than previously estimated, is driven by different curvatures at the tip and neck and runs through large gaps between thread and channel walls. Understanding how these curvatures evolve during bubble formation leads to accurate predictions of the moment of pinch-off.

We propose a method for optical nanoimaging in which the structure of a three-dimensional inhomogeneous medium may be recovered from far-field power measurements. Neither phase control of the illuminating field nor phase measurements of the scattered field are necessary. The method is based on the solution to the inverse scattering problem for a system consisting of a weakly-scattering dielectric sample and a strongly-scattering nanoparticle tip. Numerical simulations are used to illustrate the results.

Wave turbulence in a thin elastic plate is experimentally investigated. By using a Fourier transform profilometry technique, the deformation field of the plate surface is measured simultaneously in time and space. This enables us to compute the wave-vector-frequency ($\mathbf{k}$, $\omega$) Fourier spectrum of the full space-time deformation velocity. In the 3D ($\mathbf{k}$, $\omega$) space, we show that the energy of the motion is concentrated on a 2D surface that represents a nonlinear dispersion relation. This nonlinear dispersion relation is close to the linear dispersion relation. This validates the usual wave-number-frequency change of variables used in many experimental studies of wave turbulence. The deviation from the linear dispersion, which increases with the input power of the forcing, is attributed to weak nonlinear effects. Our technique opens the way for many new extensive quantitative comparisons between theory and experiments of wave turbulence.

If a metal film, thick enough to be totally opaque, is perforated by tiny subwavelength holes in an orderly fashion, the transmission will be enhanced extraordinarily [T. W. Ebbesen, et al. Nature (London) 391, 667 (1998)]. Here, we investigate the transmission through an ultrathin semitransparent Au film with a square array of subwavelength holes and observe the opposite behavior: less light is transmitted through the pierced metal compared to the closed film.

We propose a model for a description of dynamics of cracklike processes that occur at the interface between two blocks prior to the onset of frictional motion. We find that the onset of sliding is preceded by well-defined detachment fronts initiated at the slider trailing edge and extended across the slider over limited lengths smaller than the overall length of the slider. Three different types of detachment fronts may play a role in the onset of sliding: (i) Rayleigh (surface sound) fronts, (ii) slow detachment fronts, and (iii) fast fronts. The important consequence of the precursor dynamics is that before the transition to overall sliding occurs, the initially uniform, unstressed slider is already transformed into a highly nonuniform, stressed state. Our model allows us to explain experimental observations and predicts the effect of material properties on the dynamics of the transition to sliding.

Here we consider stationary states for nonlinear Schrödinger equations in any spatial dimension $n$ with symmetric double well potentials. These states may bifurcate as the strength of the nonlinear term increases and we observe two different pictures depending on the value of the nonlinearity power: a supercritical pitchfork bifurcation, and a subcritical pitchfork bifurcation with two asymmetric branches occurring as the result of saddle-node bifurcations. We show that in the semiclassical limit, or for a large barrier between the two wells, the first kind of bifurcation always occurs when the nonlinearity power is less than a critical value; in contrast, when the nonlinearity power is larger than such a critical value then we always observe the second scenario. The remarkable fact is that such a critical value is a universal constant in the sense that it does not depend on the shape of the double well potential and on the dimension $n$.

We measure acceleration statistics of neutrally buoyant spherical particles with a diameter $0.4<d/\eta <27$ in intense turbulence ($400<R_{\lambda }<815$). High speed cameras image polystyrene tracer particles in a flow between counterrotating disks. The measurements of acceleration variance $⟨a^2⟩$ clearly resolve the transition from the tracer like behavior of small particles to the much smaller accelerations of large particles. Two models of this transition from small to large particle behavior are critically examined. For $d>5\eta$, $⟨a^2⟩$ decreases with the diameter as $d^{-2/3}$, in agreement with inertial range scaling arguments. Consistent with earlier work, we find that the scaled acceleration probability density function shows very little dependence on particle size.

We investigate the flow of various non-Newtonian fluids through three-dimensional disordered porous media by direct numerical simulation of momentum transport and continuity equations. Remarkably, our results for power-law (PL) fluids indicate that the flow, when quantified in terms of a properly modified permeability-like index and Reynolds number, can be successfully described by a single (universal) curve over a broad range of Reynolds conditions and power-law exponents. We also study the flow behavior of Bingham fluids described in terms of the Herschel-Bulkley model. In this case, our simulations reveal that the interplay of (i) the disordered geometry of the pore space, (ii) the fluid rheological properties, and (iii) the inertial effects on the flow is responsible for a substantial enhancement of the macroscopic hydraulic conductance of the system at intermediate Reynolds conditions.

Using a hydrogen-filled hollow-core photonic crystal fiber as a nonlinear optical gas cell, we study amplification of ns-laser pulses by backward rotational Raman scattering. We find that the amplification process has two characteristic stages. Initially, the pulse energy grows and its duration shortens due to gain saturation at the trailing edge of the pulse. This phase is followed by formation of a symmetric pulse with a duration significantly shorter than the phase relaxation time of the Raman transition. Stabilization of the Stokes pulse profile to a solitonlike hyperbolic secant shape occurs as a result of nonlinear amplification at its front edge and nonlinear absorption at its trailing edge (caused by energy conversion back to the pump field), leading to a reshaped pulse envelope that travels at superluminal velocity.

Isolated attosecond pulses are powerful tools for exploring electron dynamics in matter. So far, such extreme ultraviolet pulses have only been generated using high power, few-cycle lasers, which are very difficult to construct and operate. We propose and demonstrate a technique called generalized double optical gating for generating isolated attosecond pulses with 20 fs lasers from a hollow-core fiber and 28 fs lasers directly from an amplifier. These pulses, generated from argon gas, are measured to be 260 and 148 as by reconstructing the streaked photoelectron spectrograms. This scheme, with a relaxed requirement on laser pulse duration, makes attophysics more accessible to many laboratories that are capable of producing such multicycle laser pulses.

In conventional dropwise condensation on a hydrophobic surface, the condensate drops must be removed by external forces for continuous operation. This Letter reports continuous dropwise condensation spontaneously occurring on a superhydrophobic surface without any external forces. The spontaneous drop removal results from the surface energy released upon drop coalescence, which leads to a surprising out-of-plane jumping motion of the coalesced drops at a speed as high as $1\mathrm{m}/\mathrm{s}$. The jumping follows an inertial-capillary scaling and gives rise to a micrometric average diameter at steady state.

Efficient energy transfer between two ultrafast laser beams is reported. Energy transfer occurs when linearly polarized donor and acceptor beams are focused in air and intersect at an acute angle. This effect is attributed to plasma-mediated forward stimulated Raman scattering, facilitated by supercontinuum generation. Donor depletion as high as 57% is observed, with quantitative energy transfer from the donor to the acceptor beam. Amplification of the acceptor depends on the polarization directions of the two pulses and the delay between them. Interaction between the beams results also in compression and spectral broadening of the acceptor pulse.

We report theoretical and experimental results on 4-wave capillary wave turbulence. A system consisting of two immiscible and incompressible fluids of the same density can be written in a Hamiltonian way for the conjugated pair ($\eta$, $\Psi$). Adding the symmetry $z\to -z$, the set of capillary waves display a Kolmogorov-Zakharov spectrum $k^{-4}$ in wave vector space and $f^{-8/3}$ in the frequency domain. The wave system is studied experimentally with two immiscible fluids of almost equal densities (water and silicon oil) where the capillary surface waves are excited by a low-frequency random forcing. The probability density function of the local wave amplitude shows a quasi-Gaussian behavior and the power spectral density is shows a power-law behavior in frequency with a slope of $-2.75$. Theoretical and experimental results are in fairly good agreement with each other.

We consider the familiar problem of a bump, or ruck, in a rug. Under lateral compression, a rug bends to form a ruck—a localized region in which it is no longer in contact with the floor. We show that when the external force that created the ruck is removed, the ruck flattens out unless the initial compression is greater than a critical value, which we determine. We also study the inertial motion of a ruck that is generated when one end of the rug is moved rapidly. We show that the equations of motion admit a traveling ruck solution for which a linear combination of the tension and kinetic energy is determined by the ruck size. We confirm these findings experimentally. We end by discussing the potential implications of our work for the analogous propagation of localized slip pulses in the sliding of two bodies in contact.

The motion of a ruck in a rug is used as an analogy to explain the role of dislocations in crystalline solids. We take literally one side of this analogy and study the shape and motion of a bump, wrinkle or ruck in a thin sheet in partial contact with a rough substrate in a gravitational field. Using a combination of experiments, scaling analysis and numerical solutions of the governing equations, we quantify the static shape of a ruck on a horizontal plane. When the plane is inclined, the ruck becomes asymmetric and moves by rolling only when the inclination of the plane reaches a critical angle, at a speed determined by a simple power balance. We find that the angle at which rolling starts is larger than the angle at which the ruck stops; i.e., static rolling friction is larger than dynamic rolling friction. We conclude with a generalization of our results to wrinkles in soft adherent extensible films.

A lotus leaf retains water repellency after repeated condensation in nature but becomes sticky to water drops after condensation on a fixed cold plate. Our experiments show that mechanical vibration can be used to overcome the energy barrier for transition from the sticky Wenzel state to the nonsticking Cassie state, and the threshold for the dewetting transition follows a scaling law comparing the kinetic energy imparted to the drop with the work of adhesion. The vibration-induced Wenzel to Cassie transition can be used to achieve antidew superhydrophobicity.

We show that all the spatiotemporal degrees of freedom available in a complex medium can be harnessed and converted into spatial ones. This is demonstrated experimentally through an instantaneous spatial inversion, using broadband ultrasonic waves in a multiple scattering sample. We show theoretically that the inversion convergence is governed by the total number of degrees of freedom available in the medium for a fixed bandwidth and demonstrate experimentally its use for complex media investigation. We believe our approach has potential in sensing, imagery, focusing, and telecommunication.

Capillary filling dynamics of liquid $n$-tetracosane ($n\mathrm{\text{−}}{\mathrm{C}}_{24}{\mathrm{H}}_{50}$) in a network of cylindrical pores with 7 and 10 nm mean diameter in monolithic silica glass (Vycor) exhibit an abrupt temperature-slope change at $T_s=54°\mathrm{C}$, $\sim 4°\mathrm{C}$ above bulk and $\sim 16°\mathrm{C}$, $8°\mathrm{C}$, respectively, above pore freezing. It can be traced to a sudden inversion of the surface tension’s $T$ slope, and thus to a decrease in surface entropy at the advancing pore menisci, characteristic of the formation of a single solid monolayer of rectified molecules, known as surface freezing from macroscopic, quiescent tetracosane melts. The imbibition speeds, that are the squared prefactors of the observed square-root-of-time Lucas-Washburn invasion kinetics, indicate a conserved bulk fluidity and capillarity of the nanopore-confined liquid, if we assume a flat lying, sticky hydrocarbon backbone monolayer at the silica walls.

A unidirectional optical oscillator is built by using a liquid crystal light valve that couples a pump beam with the modes of a nearly spherical cavity. For sufficiently high pump intensity, the cavity field presents complex spatiotemporal dynamics, accompanied by the emission of extreme waves and large deviations from the Gaussian statistics. We identify a mechanism of spatial symmetry breaking, due to a hypercycle-type amplification through the nonlocal coupling of the cavity field.

A dynamic crack tip equation of motion is proposed based on the autonomy of the near-tip nonlinear zone of scale ${\ell }_{\mathrm{nl}}$, symmetry principles, causality, and scaling arguments. Causality implies that the asymptotic linear-elastic fields at time $t$ are determined by the crack path at a retarded time $t-{\tau }_d$, where the delay time ${\tau }_d$ scales with the ratio of ${\ell }_{\mathrm{nl}}$ and the typical wave speed $c_{\mathrm{nl}}$ within the nonlinear zone. The resulting equation is shown to agree with known results in the quasistatic regime. As a first application in the fully dynamic regime, an approximate analysis predicts a high-speed oscillatory instability whose characteristic scale is determined by ${\ell }_{\mathrm{nl}}$. This prediction is corroborated by experimental results, demonstrating the emergence of crack tip inertialike effects.