The accurate characterization of thermal electron transport and the determination of heating by suprathermal electrons in laser driven solid targets are both issues of great importance to the current experiments being performed at the National Ignition Facility, which aims to achieve thermonuclear fusion ignition using lasers. Ionization, induced by electronic heat conduction, can cause the opacity of a material to drop significantly once bound-free photoionization is no longer energetically possible. We show that this drop in opacity enables measurements of the transmission of extreme ultraviolet (EUV) laser pulses at 13.9 nm to act as a signature of the heating of thin (50 nm) iron layers with a 50-nm thick parylene-N (CH) overlay irradiated by 35-fs pulses at irradiance $3\times {10}^{16}$ Wcm${}^{-2}$. Comparing EUV transmission measurements at different times after irradiation to fluid code simulations shows that the target is instantaneously heated by hot electrons (with approximately 10$\%$ of the laser energy), followed by thermal conduction with a flux limiter of $\approx$0.05.

We report on a series of measurements on the microscopic structure and the magneto-optical properties of a calamitic liquid crystalline compound in its nematic phase. Structural studies show the existence of short-range, tilted smectic order consistent with pretransitional effects above an underlying smectic phase. Concomitantly, magneto-optical results exhibit the existence of an optic axis not collinear with the uniaxial director. This apparent biaxial nature is discussed within the context of coupling between the tensor nematic and the smectic order parameters.

I evaluate the thermodynamic curvature $R$ for fourteen pure fluids along their liquid-vapor coexistence curves, from the critical point to the triple point, using thermodynamic input from the NIST Chemistry WebBook. In this broad overview, $R$ is evaluated in both the coexisting liquid and vapor phases. $R$ is an invariant whose magnitude $\left|R\right|$ is a measure of the size of mesoscopic organized structures in a fluid, and whose sign specifies whether intermolecular interactions are effectively attractive ($R<0$) or repulsive ($R>0$). I discuss five principles for $R$ in pure fluids: (1) Near the critical point, the attractive part of the interactions forms loose structures of size $\left|R\right|$ proportional to the correlation volume ${\xi }^3$, and the sign of $R$ is negative. (2) In the vapor phase, there are instances of compact clusters of size $\left|R\right|$ formed by the attractive part of the interactions and prevented from collapse by the repulsive part of the interactions, and the sign of $R$ is positive. (3) In the asymptotic critical point regime, the $R$'s in the coexisting liquid and vapor phases are equal to each other, i.e., commensurate. (4) Outside the asymptotic critical-point regime incommensurate $R$'s may be associated with metastability. (5) The compact liquid phase has $\left|R\right|$ on the order of the volume of a molecule, with the sign of $R$ being negative for a liquidlike state held together by attractive interactions and the sign of $R$ being positive for a solidlike state held up by repulsive interactions. These considerations amplify and extend the application of thermodynamic curvature in pure fluids.

We study the surface scaling behavior of a semi-infinite $d$-dimensional $\text{O}\left(N\right)$ spin system in the presence of a quenched random field and random anisotropy disorders. It is known that above the lower critical dimension $d_{\mathrm{LC}}=4$ the infinite models undergo a paramagnetic-ferromagnetic transition for $N>N_c$ ($N_c=2.835$ for the random field and $N_c=9.441$ for random anisotropy). For $N<N_c$ and $d<d_{\mathrm{LC}}$ there exists a quasi-long-range-order phase with a zero order parameter and a power-law decay of spin correlations. Using a functional renormalization group, we derive the surface scaling laws that describe the ordinary surface transition for $d>d_{\mathrm{LC}}$ and the long-range behavior of spin correlations near the surface in the quasi-long-range-order phase for $d<d_{\mathrm{LC}}$. The corresponding surface exponents are calculated to one-loop order. The obtained results can be applied to the surface scaling of periodic elastic systems in disordered media, amorphous magnets, and ${}^3$He-$A$ in aerogel.

Using computer simulations, we investigate hysteresis loops and return-point memory for artificial square and kagome spin ice systems by cycling an applied bias force and comparing microscopic effective spin configurations throughout the hysteresis cycle. Return-point memory loss is caused by motion of individual defects in kagome ice or of grain boundaries in square ice. In successive cycles, return-point memory is recovered rapidly in kagome ice. Memory is recovered more gradually in square ice due to the extended nature of the grain boundaries. Increasing the amount of quenched disorder increases the defect density but also enhances the return-point memory since the defects become trapped more easily.

Condensed matter systems with topological defects in the ground states range from the Abrikosov phases in superconductors, to various blue phases and twist grain boundary phases in liquid crystals, and to phases of skyrmion lattices in chiral ferromagnets and Bose-Einstein condensates. In nematic and chiral nematic liquid crystals, which are true fluids with long-range orientational ordering of constituent molecules, point and line defects spontaneously occur as a result of symmetry-breaking phase transitions or due to flow, but they are unstable, hard to control, and typically annihilate with time. Here we describe the optical generation of two-dimensional crystalline, quasicrystalline, and arbitrary ensembles of particlelike structures manifesting both skyrmionlike and Hopf fibration features—dubbed “torons”—composed of looped double twist cylinders and point defects embedded in a uniform director field. In these two-dimensional lattices, we then introduce various dislocations, defects in positional ordering of the torons. We show that the periodic defect lattices with and without dislocation are light- and voltage-tunable reconfigurable two-dimensional diffraction gratings and can be used to generate various controlled phase singularities in the diffracted laser beams. The results of computer simulations of optical images, diffraction patterns, and phase distributions with optical vortices are in a good agreement with the corresponding experimental findings.

A poorly understood phenomenon seen in complex systems is diffusion characterized by Hurst exponent $H\approx 1/2$ but with non-Gaussian statistics. Motivated by such empirical findings, we report an exact analytical solution for a non-Markovian random walk model that gives rise to weakly anomalous diffusion with $H=1/2$ but with a non-Gaussian propagator.

It has been proposed that a first-order phase transition driven to happen in the metastable region exhibits scaling and universality near an instability point controlled by an instability fixed point of a ${\varphi }^3$ theory. However, this fixed point has an imaginary value and the renormalization-group flow of the ${\varphi }^3$ coupling diverges at a finite scale. Here combining a momentum-space RG analysis and a nucleation theory near the spinodal point, we show that imaginary rather than real values are physical counterintuitively and thus the imaginary fixed point does control the scaling.

Cluster heterogeneity, the number of clusters of mutually distinct sizes, has been recently studied for explosive percolation and standard percolation [H. K. Lee et al., Phys. Rev. E 84, 020101(R) (2011); J. D. Noh et al., Phys. Rev. E 84, 010101(R) (2011)]. In this work we study the scaling of various quantities related with cluster heterogeneity in a broader context of two-dimensional $q$-state Potts model. We predict, via an analytic approach, the critical exponents for most of the measured quantities, and confirm these predications for various $q$ values using extensive Monte Carlo simulations.

The electric-double-layer structure in an electrolyte close to a solid substrate near the three-phase contact line is approximated by considering the linearized Poisson-Boltzmann equation in a wedge geometry. The mathematical approach complements the semianalytical solutions reported in the literature by providing easily available characteristic information on the double-layer structure. In particular, the model contains a length scale that quantifies the distance from the fluid-fluid interface over which this boundary influences the electric double layer. The analysis is based on an approximation for the equipotential lines. Excellent agreement between the model predictions and numerical results is achieved for a significant range of contact angles. The length scale quantifying the influence of the fluid-fluid interface is proportional to the Debye length and depends on the wall contact angle. It is shown that for contact angles approaching 90${}^{\circ }$ there is a finite range of boundary influence.

Spin models of neural networks and genetic networks are considered elegant as they are accessible to statistical mechanics tools for spin glasses and magnetic systems. However, the conventional choice of variables in spin systems may cause problems in some models when parameter choices are unrealistic from a biological perspective. Obviously, this may limit the role of a model as a template model for biological systems. Perhaps less obviously, also ensembles of random networks are affected and may exhibit different critical properties. We consider here a prototypical network model that is biologically plausible in its local mechanisms. We study a discrete dynamical network with two characteristic properties: Nodes with binary states 0 and 1, and a modified threshold function with ${\Theta }_0\left(0\right)=0$. We explore the critical properties of random networks of such nodes and find a critical connectivity $K_c=2.0$ with activity vanishing at the critical point. Finally, we observe that the present model allows a more natural implementation of recent models of budding yeast and fission yeast cell-cycle control networks.

In this paper, we study the impact of the preference of an individual for public transport on the spread of infectious disease, through a quantity known as the public mobility. Our theoretical and numerical results based on a constructed model reveal that if the average public mobility of the agents is fixed, an increase in the diversity of the agents’ public mobility reduces the epidemic threshold, beyond which an enhancement in the rate of infection is observed. Our findings provide an approach to improve the resistance of a society against infectious disease, while preserving the utilization rate of the public transportation system.

We present a multiparameter family of a soliton on a background solution to the Sasa-Satsuma equation. The solution is controlled by a set of several free parameters that control the background amplitude as well as the soliton itself. This family of solutions admits a few nontrivial limiting cases that are considered in detail. Among these special cases is the nonlinear Schrödinger equation limit and the limit of rogue wave solutions.

We investigated the stress-strain behavior of sand with and without small amounts of liquid under steady and oscillatory shear. Since dry sand has a lower shear modulus, one would expect it to deform more easily. Using a new technique to quasistatically push the sand through a tube with an enforced parabolic (Poiseuille-like) profile, we minimize the effect of avalanches and shear localization. We observe that the resistance against deformation of the wet (partially saturated) sand is much smaller than that of the dry sand, and that the latter dissipates more energy under flow. This is also observed in large-amplitude oscillatory shear measurements using a rotational rheometer, showing that the effect is robust and holds for different types of flow.

High resolution quasielastic neutron scattering measurements have been used to study the effects of applied electric field on the dynamics of water molecules confined in the pores of folded silica sheet material FSM-12 with an average pore diameter (apd) of 16 Å. In the absence of field, there is a significant slowing down of the water molecule diffusion as the temperature is lowered, in agreement with previous observations. The application of a moderate electric field of 2.5 kV/mm remarkably enhances the translational diffusion of water molecules. We interpret this as being due to a disruption of the hydrogen bonding by the electric field. This new observation suggests that existing theories valid at large electric field strengths may have to be corrected at moderate fields.

Shear can impart a high degree of orientational order to supported block copolymer thin films containing one or more layers of cylindrical microdomains, leading to a striped pattern with a period of tens of nanometers extending over macroscopic (centimeter-squared) areas. Though the as-deposited films have a polygrain structure, after shearing at sufficiently high stresses the only defects which remain are isolated dislocations, and the orientational order can be quite high (nematic or twofold orientational order parameter >0.99, as measured by tapping-mode atomic force microscopy). The effect of isolated dislocations on orientational order is adequately captured by an isotropic elastic continuum model of the structure surrounding the dislocation, producing a linear decrease of order parameter with dislocation density. Even at zero dislocation density, however, the order parameter does not quite reach unity, due to small-amplitude undulations of the cylinders about their axes which persist in the transverse direction over several cylinder periods.

We study the possibility of modifying collisions in the lattice Boltzmann method to keep the proper entropy balance. We demonstrate that in the space of distributions operated on by lattice Boltzmann methods which respect a Boltzmann type $H$ theorem, there exists a vicinity of the equilibrium where collisions with entropy balance are possible and, at the same time, there exists a region of nonequilibrium distributions where such collisions are impossible. In particular, for a strictly concave and uniformly bounded entropy function with positive equilibria, we show that proper entropy balance is always possible sufficiently close to the local equilibrium and it is impossible sufficiently far from it, where additional dissipation has to appear. We also present some nonclassical entropies that do not share this concern. The cases where the distribution enters the region far from equilibrium typically occur in flows with low viscosity and/or high Mach number flows and in simulations on coarse grids.

We have performed orbital-free and quantum molecular dynamics simulations on plastic ablator along two isochores, namely 7 and 9 g cm${}^{-3}$, from 5 to 40 eV. These thermodynamic conditions correspond to those encountered during inertial confinement fusion capsule implosion when hydrodynamic instabilities can take place. The coupling between orbital-free and quantum approaches allowed us to compute an exhaustive set of microscopic coefficients, i.e., equation-of-state, ionic diffusion coefficients, thermal and electrical conductivities, spanning phenomena that can mitigate the growth of classical Rayleigh-Taylor instability. Comparisons to widely used models in hydrodynamics codes are developed.

We address here a special, extreme case of the quadratic pair interaction potential between classical, $D_{2h}$-symmetric particles (the generalized Straley model) on a three-dimensional simple cubic lattice. The model involves predominant antinematic couplings and it has been studied by Monte Carlo simulation and a molecular field treatment. The obtained results show a second-order transition between the isotropic phase and the low-temperature one, exhibiting uniaxial antinematic order.

Nematic shells are colloidal particles coated with nematic liquid crystal molecules, which may freely glide and rotate on the colloid's surface while keeping their long axis on the local tangent plane. Molecular dynamics simulations on a nanoscopic spherical shell indicate that under appropriate adhesion conditions for the molecules on the equator, the equilibrium nematic texture exhibits at each pole a pair of $+\frac{1}{2}$ defects so close to one another to be treated as one $+1$ defect. Spirals connect the polar defects, though the continuum limit of the interaction potential would not feature any elastic anisotropy. A molecular averaging justifies an anchoring defect energy that feels the geodesics emanating from the defect. All our observations are explained by such a geodesic anchoring, which vanishes on flat manifolds.