Viscous to inertial crossover in liquid drop coalescence

Using an electrical method and high-speed imaging, we probe drop coalescence down to 10?ns after the drops touch. By varying the liquid viscosity over two decades, we conclude that, at a sufficiently low approach velocity where deformation is not present, the drops coalesce with an unexpectedly late crossover time between a regime dominated by viscous and one dominated by inertial effects. We argue that the late crossover, not accounted for in the theory, can be explained by an appropriate choice of length scales present in the flow geometry.     

Jumping nanodroplets: a new route towards metallic nano-particles

The dewetting process, which appears upon laser-induced melting of flat nanostructures and leads to a jumping of the droplets off the surface, is used for deposition of nano-particles onto a second substrate. Limitations in materials and particle sizes are discussed and experimentally verified. The experiments show that a variety of metals can be deposited in a size ranging from tens up to several hundreds of nanometers.     

Lattice Boltzmann simulations of drop coalescence and chemical mixing

The results of a lattice Boltzmann simulation for collisions between two liquid drops in an immiscible liquid in a linear Stokes flow will be presented. The results will be compared with existing experimental results and asymptotic solutions. The mixing of a contaminant that is initially contained in one of the drops will also be discussed and compared with particle tracking simulations.     

Statistical properties of one-dimensional inversion for the wave field diffracted by a two-dimensional phase screen

We study theoretically the statistical properties of one-dimensional wave-field inversions. We show that the real and imaginary parts of the logarithm of the normalized coherence function are the invariants of the inverted field if the field is measured on the statistical symmetry axis. Using these invariants, one can easily reconstruct two-point statistical moments of the phase distribution on the screen. We derive equations for the reconstruction of phase-distribution moments in the general case. Numerical simulations show that these equations can be solved by an iterative technique. The convergence range of the iteration method with variation in the parameters is studied. A. M. Obukhov Institute for Physics of the Atmosphere of the Russian Academy of Sciences, Moscow, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 43, No. 3, pp. 234–242, March., 2000.     

Exact treatment of interface fluctuations in a two-dimensional emulsion

Summary We present a model for a polydisperse ensemble of two-dimensional droplets wich accounts for the effects of arbitrarily large distortions of the droplet shape. Interactions within a droplet include bending rigidity and spontaneous curvature. Interactions between droplets are omitted. Even at high temperatures, the effects of the shape fluctuations on the droplet size distribution remain small, as they are dominated by the contributions from the mixing entropy. In contrast, shape fluctuations lead to a pronounced peak in thermodynamic quantities like specific heat. This peak occurs at temperatures where thermal excitations become of the order of the bending energies of the droplet surface. The fluctuation-dominated regime extends to temperatures far lower than expected from a mean-field calculation. Paper presented at the I International Conference on Scaling, Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994.     

Propagation loss in a two-dimensional triangular photonic crystal waveguide

By means of a plane-wave-based transfer-matrix method, we present an extensive study of propagation loss in two-dimensional (2D) photonic crystal waveguides with limited cladding wall thickness. We examine the dependence of propagation loss on both the propagation direction and the waveguide wall thickness. It is shown that the propagation loss is a function of excitation frequency, wall thickness and waveguide outermost surface morphology. The conclusion that the propagation loss essentially decays exponentially with respect to the cladding wall thickness of a waveguide is valid only to a certain degree. In addition, we find that the propagation loss exhibit very complex behavior with respect to the excitation frequency.     

Quantum emulsion: a glassy phase of bosonic mixtures in optical lattices

We numerically investigate mixtures of two interacting bosonic species with unequal parameters in one-dimensional optical lattices. In large parameter regions full phase segregation is seen to minimize the energy of the system, but the true ground state is masked by an exponentially large number of metastable states characterized by microscopic phase separation. The ensemble of these quantum emulsion states, reminiscent of emulsions of immiscible fluids, has macroscopic properties analogous to those of a Bose glass, namely, a finite compressibility in absence of superfluidity. Their metastability is probed by extensive quantum Monte Carlo simulations generating rich correlated stochastic dynamics. The tuning of the repulsion of one of the two species via a Feshbach resonance drives the system through a quantum phase transition to the superfluid state.     

Unconventional metallic state in a two-dimensional system with broken inversion symmetry

We present a model that explains two phenomena, recently observed in high-mobility Si-MOS structures: (1) the strong enhancement of metallic conduction at low temperatures, T<2 K, and (2) the occurrence of a metal-insulator transition in the 2D electron system. Both effects are ascribed to the spin-orbit interaction anomalously enhanced by the broken inversion symmetry of the confining potential well. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 3, 168–172 (10 August 1997) Published in English in the original Russian journal. Edited by Steve Torstveit.     

One-dimensional phase transitions in a two-dimensional optical lattice

A phase transition for bosonic atoms in a two-dimensional anisotropic optical lattice is considered. If the tunnelling rates in two directions are different, the system can undergo a transition between a two-dimensional superfluid and a one-dimensional Mott insulating array of strongly coupled tubes. The connection to other lattice models is exploited in order to better understand the phase transition. Critical properties are obtained using quantum Monte Carlo calculations. These critical properties are related to correlation properties of the bosons and a criterion for commensurate filling is established.     

Quantum phase transition in a two-dimensional system of dipoles

The ground-state phase diagram of a two-dimensional Bose system with dipole-dipole interactions is studied by means of a quantum Monte Carlo technique. Our calculation predicts a quantum phase transition from a gas to a solid phase when the density increases. In the gas phase, the condensate fraction is calculated as a function of the density. Using the Feynman approximation, the collective excitation branch is studied and the appearance of a roton minimum is observed. The results of the static structure factor at both sides of the gas-solid phase are also presented. The Lindemann ratio at the transition point becomes gamma=0.230(6). The condensate fraction in the gas phase is estimated as a function of the density.     

Nucleation efficiency of R134a as a sensitive liquid for superheated drop emulsion detector

Superheated emulsion detector is known to detect neutrons, γ-rays and other charged particles. The present work includes the study of nucleation efficiency of superheated drops of one of the CFC-free liquids, R134a (C₂H₂F₄), to fast neutrons, its response to γ-rays from ²⁴¹Am and ¹³⁷Cs and compare its nucleation efficiency with that of R12. The observation indicates that because of the presence of hydrogen, the nucleation efficiency is less in R134a than in R12 in the present neutron energy range of consideration. R134a is one of the most environment-friendly, commercially available liquid that is suitable for superheated drop detector, specially in neutron dosimetry and one needs to investigate it in detail.     

The complement: a solution to liquid drop finite size effects in phase transitions

The effects of the finite size of a liquid drop undergoing a phase transition are described in terms of the complement, the largest (but mesoscopic) drop representing the liquid in equilibrium with the vapor. Vapor cluster concentrations, pressure, and density from fixed mean density lattice gas (Ising) calculations are explained in terms of the complement generalization of Fisher's model. Accounting for this finite size effect is important for extracting the infinite nuclear matter phase diagram from experimental data.     

Plasma waves in two-dimensional electron channels: Propagation and trapped modes

Plasma waves in two-dimensional electron channels with nontrivial geometry and governing electrodes are described by the hydrodynamical equations combined with the Poisson equation for the self-consistent electric potential. If the amplitudes of the oscillations of the velocity, the concentration, and the potential are much smaller than the stationary values of these variables, then the hydrodynamical equation for oscillations can be linearized and transformed to the wave equation on a two-dimensional network. We consider the scattering problem for the wave equation and develop a semi-analytic method to calculate the transmission coefficients through the junction. The formulas for the transmission coefficients have resonance character and can be used in design of manipulated 2D-networks of plasma channels. Dedicated to the memory of V. A. Geyler On leave from the Dep. of Mathematics, the University of Auckland, Private Bag 92019, Auckland, New Zealand. On leave from the Institute of Physics and Technology RAS, Moscow, 117218 Russia.     

Finite-temperature phase transitions in a two-dimensional boson Hubbard model

We study finite-temperature phase transitions in a two-dimensional boson Hubbard model with zero-point quantum fluctuations via Monte Carlo simulations of a quantum rotor model and construct the corresponding phase diagram. Compressibility shows a thermally activated gapped behavior in the insulating regime. Finite-size scaling of the superfluid stiffness clearly shows the nature of the Kosterlitz-Thouless transition. The transition temperature T(c) confirms a scaling relation T(c) proportional, rho(0)(x), with x=1.0. Some evidence of anomalous quantum behavior at low temperatures is presented.     

Electrical switching of wetting states on superhydrophobic surfaces: a route towards reversible Cassie-to-Wenzel transitions

We demonstrate that the equilibrium shape of the composite interface between superhydrophobic surfaces and drops in the superhydrophobic Cassie state under electrowetting is determined by the balance of the Maxwell stress and the Laplace pressure. Energy barriers due to pinning of contact lines at the edges of the hydrophobic pillars control the transition from the Cassie to the Wenzel state. Barriers due to the narrow gap between adjacent pillars control the lateral propagation of the Wenzel state. We demonstrate how reversible switching between the two wetting states can be achieved locally using suitable surface and electrode geometries.