The results of extensive nonequilibrium molecular dynamics simulations of flow and transport of a pure fluid, as well as a binary fluid mixture, through a porous material composed of a macropore, a mesopore, and a nanopore, in the presence of an external pressure gradient, are reported. We find that under supercritical conditions, unusual phenomena occur that give rise to direction-dependent and pressure-dependent permeabilities for the fluids’ components. The results, which are also in agreement with a continuum formulation of the problem, indicate that the composite nature of the material, coupled with condensation, give rise to the direction-dependent permeabilities. Therefore, modeling flow and transport of fluids, in the supercritical regime, in porous materials with the type of morphology considered in this paper (such as supported porous membranes) would require using effective permeabilities that depend on both the external pressure drop and the direction along which it is applied to the materials.

We offer a method to study transport of fast electrons in dense hot media. The technique relies on temporal profiling of the laser induced magnetic fields and offers a unique capability to map the hot electron currents and their neutralization (or lack of it) by the return currents in the plasma. We report direct quantitative measurements of strong electric inhibition in insulators and turbulence induced anomalous stopping of hot electrons in conductors. The present technique can prove extremely important from the point of view of fast ignition scheme, which relies on the penetration of fast electrons into the fusion core.

We investigate modulation instability (MI) in negative-index material (NIM) with a Kerr nonlinear polarization based on a derived $(3+1)$-dimensional nonlinear Schrödinger equation for ultrashort pulse propagation. By a standard linear stability analysis, we obtain the expression for instability gain, which unifies the temporal, spatial, and spatiotemporal MI. It is shown that negative refraction not only brings some new features to MI, but also makes MI possible in ordinary material in which it is otherwise impossible. For example, spatial MI can occur in the defocusing regime, while it only occurs in the focusing regime in ordinary material. Spatiotemporal MI can appear in NIM in the case of anomalous dispersion and defocusing nonlinearity, while it cannot appear in ordinary material in the same case. We believe that the difference between the MI in NIM and in ordinary material is due to the fact that negative refraction reverses the sign of the diffraction term, with the signs of dispersion and nonlinearity unchanged. The most notable property of MI in NIM is that it can be manipulated by engineering the self-steepening effect by choosing the size of split-ring resonator circuit elements. To sum up the MI in ordinary material and in NIM, MI may occur for all the combinations of dispersion and nonlinearity.

The Fermi-Pasta-Ulam (FPU) problem consists of the nonequipartition of energy among normal modes of a weakly anharmonic atomic chain model. In the harmonic limit, each normal mode corresponds to a periodic orbit in phase space and is characterized by its wave number $q$. We continue normal modes from the harmonic limit into the FPU parameter regime and obtain persistence of these periodic orbits, termed here $q$-breathers (QB). They are characterized by time periodicity, exponential localization in the $q$-space of normal modes, and linear stability up to a size-dependent threshold amplitude. Trajectories computed in the original FPU setting are perturbations around these exact QB solutions. The QB concept is applicable to other nonlinear lattices as well.

For more than a century the possibility of imaging the structure of a medium with diffracting wave fields has been limited by the tradeoff between resolution and imaging depth. While long wavelengths can penetrate deep into a medium, the resolution limit precludes the possibility of observing subwavelength structures. Near-field microscopy has recently demonstrated that the resolution limit can be overcome by bringing a probing sensor within one wavelength distance from the surface to be imaged. This paper extends the scope of near-field microscopy to the reconstruction of subwavelength structures from measurements performed in the far-field. It is shown that the distortion undergone by a wave field as it travels through an inhomogeneous medium and the subsequent generation of local evanescent fields encode subwavelength information in the far-field due to multiple scattering within the medium. This argument is proved theoretically and supported by a limited view experiment performed with elastic waves in which an image with a resolution better than a third of the wavelength is achieved.

A different retroreflective effect which parallels that encountered with dihedral corner reflectors is found in the scattering response of a penetrable left-handed media $\epsilon =\mu =-1$ right angle prism. More significantly, no diffraction from the vertex is found to exist and hence no field singularity for the right angle wedge. Although the results are illustrated with microwaves, the concept finds applications in optics, acoustics, elasticity, and other media characterized by negative index wave propagation.

Using a Fourier approach we offer a general solution to calculations of slip velocity within the circuit description of the electrohydrodynamics in a binary electrolyte confined by a plane surface with a modulated surface potential. We consider the case with a spatially constant intrinsic surface capacitance where the net flow rate is, in general, zero while harmonic rolls as well as time-averaged vortexlike components may exist depending on the spatial symmetry and extension of the surface potential. In general, the system displays a resonance behavior at a frequency corresponding to the inverse $RC$ time of the system. Different surface potentials share the common feature that the resonance frequency is inversely proportional to the characteristic length scale of the surface potential. For the asymptotic frequency dependence above resonance we find a ${\omega }^{-2}$ power law for surface potentials with either an even or an odd symmetry. Below resonance we also find a power law ${\omega }^{\alpha }$ with $\alpha$ being positive and dependent of the properties of the surface potential. Comparing a tanh potential and a sech potential we qualitatively find the same slip velocity, but for the below-resonance frequency response the two potentials display different power-law asymptotics with $\alpha =1$ and $\alpha \sim 2$, respectively.

Kye et al. [Phys. Rev. E 68, 025201 (2003)] have recently claimed that, before the onset of chaotic phase synchronization in coupled phase coherent oscillators, there exists a temporally coherent state called periodic phase synchronization (PPS). Here we give evidence that some of their numerical calculations are flawed, while we provide theoretical arguments that indicate that PPS is not to be expected generically in this type of systems.

The phase difference in coupled chaotic oscillators exhibits a small noiselike fast fluctuation in long-term phase dynamics. The fast fluctuation can cause an error in the measurement of the period of the temporary phase locking state. We discuss why we should filter out the fast fluctuation on determination of periodic phase synchronization.

We predict a temperature-driven phase transition of DNA below the melting transition. The additional, intermediate phase exists for repetitive sequences, when the two strands have different lengths. In this phase, the excess bases of the longer strand are completely absorbed as bulge loops inside the helical region. When the temperature is lowered, the excess bases desorb into overhanging ends, resulting in a contour length change. This continuous transition is in many aspects analogous to Bose–Einstein condensation. When the sequence is weakly disordered, the contour length changes discontinuously with temperature.

The single file diffusion in a circular channel of millimetric charged balls is studied. The evolution in time of the mean square displacement is shown to be subdiffusive, but slower than the powerlike $t^{1∕2}$ behavior observed in circular colloidal systems or predicted in one-dimensional infinite systems.

In the present paper, the nature of the fragility of liquids with a developed H-bond network is investigated. It is shown that the effective activation energy of the shear viscosity $\eta$ and the fragility parameter defined as $m={\phantom{\mid }d\log \eta ∕d(T_g∕T)\mid }_{T=T_g^{+}}$ are immediately connected with the average number $n_{\mathrm{H}}\left(T\right)$ of the H-bond per molecule. The consistency of the macroscopic $\left(m\right)$ and the microscopic [$M={\phantom{\mid }d(u_0^2∕{⟨{\vec{u}}^2⟩}_{\mathrm{loc}})∕d(T_g∕T)\mid }_{T=T_g^{+}}$, where ${⟨{\vec{u}}^2⟩}_{\mathrm{loc}}={⟨{\vec{u}}^2⟩}_{\mathrm{anharm}}-{⟨{\vec{u}}^2⟩}_{\mathrm{harm}}$] definitions of the fragility is established.

We have found that the ability of long thin rods to jam into a solidlike state in response to a local perturbation depends upon both the particle aspect ratio and the container size. The dynamic phase diagram in this parameter space reveals a broad transition region separating granular stick-slip and solidlike behavior. In this transition region the pile displays both solid and stick-slip behavior. We measure the force on a small object pulled through the pile, and find the fluctuation spectra to have power law tails with an exponent characteristic of the region. The exponent varies from $\beta =-2$ in the stick-slip region to $\beta =-1$ in the solid region. These values reflect the different origins—granular rearrangements vs dry friction—of the fluctuations. Finally, the packing fraction shows only a slight dependence on container size, but depends on aspect ratio in a manner predicted by mean-field theory and implies an aspect-ratio-independent contact number of $⟨c⟩=5.25\pm 0.03$.

The Pore-Cor void network model is used to construct stochastic realizations of the void structures of five sandstone samples of varying lithography. A close match was achieved to experimental porosity and mercury intrusion curves. The samples were resin impregnated and the fragments of voids revealed in thin sections photographed by backscatter electron microscopy at two magnifications. The sizes of these pore fragments matched those derived from a simulated microtoming of the network model much more closely than the sizes derived from the traditional capillary bundle approximation. Absolute permeabilities of the network were calculated by finding the flow capacity of the entire flow network, based on parametrized Navier Stokes equations with Klinkenberg correction, applied to each pore-throat-pore arc. A match to the experimental trend was obtained, although the network model considerably underestimated the experimental values. The results were also compared with the semiempirical equations of Thomson et al. and Kozeny and Carmen modified to accept thin section image analysis. Finally, the simulated pore and throat size distributions were compared to proton NMR transverse $\left(T_2\right)$ spin-echo relaxation times. Although the shapes of the distributions differed markedly, the mean values trended together. The capillary bundle approximation, however, gave a poor match to the NMR data.

The angular dependence of the intensity of x-rays scattered from binary and ternary hard sphere mixtures is investigated and compared to the predictions of two scattering models. Mixture ratio and total volume fraction dependent effects are investigated for size ratios equal to 0.51 and 0.22. Comparisons of model predictions with experimental results indicate the significant impact of the role of particle size distributions in interpreting the angular dependence of the scattering at wave vectors probing density fluctuations intermediate between the sizes of the particles in the mixture.

Motivated by the original Lothe-Pound prescription, we derive a formula for the replacement partition function that is suitable for vapor to liquid phase nucleation in terms of the classical phase integral. The resulting expression was evaluated for truncated and shifted Lennard-Jones fluids by means of computer simulation. The corresponding Lothe-Pound correction factor, which is to multiply the classical expression for the nucleation rate, decreases significantly with increasing temperature and decreasing cluster size, and is in the range of ${10}^9\text{–}{10}^{13}$ for the temperatures and the cluster sizes we studied. This is somewhat smaller than the original estimate of ${10}^{17}$ by Lothe and Pound.

The field-induced Berezinskii-Kosterlitz-Thouless (BKT) transition in the ground state of the triangular antiferromagnetic Ising model is studied by the level-spectroscopy method. We analyze dimensions of operators around the BKT line, and estimate the BKT point $H_{\mathrm{c}}\simeq 0.5229\pm 0.001$, which is followed by the level-consistency check to demonstrate the accuracy of our estimate. Further we investigate the anisotropic case to clarify the stability of the field-induced string-density plateau against an incommensurate liquid state by the density-matrix renormalization-group method.

We show that optical wave propagation in discrete boundary geometries can be effectively analyzed using the method of images. Such semi-infinite and finite discrete systems include, for example, waveguide arrays as well as coupled resonator optical waveguides. In the linear domain, the diffraction properties of one- and two-dimensional bounded array structures are considered in detail. The possibility of using the method of images to numerically investigate nonlinear semi-infinite lattices is also discussed.