Liquid fragility characterizes how steeply the viscosity of a glass-forming liquid decreases with increasing temperature above the glass transition. It is one of the most fundamental properties of a liquid, with high importance for science and application. Yet, its origin is unclear. Here we show that it is directly related to the structural coherence of the medium-range order (MRO) in liquid defined by the decay of the pair-distribution function with distance. The MRO can also be evaluated from the first peak of the structure function determined by x-ray or neutron diffraction, and it is a measure of the cooperativity of atomic motion in a diffusive event in supercooled liquids. These findings shed light on the mechanism of atomic transport in supercooled liquids.

This paper reports the pattern formation and evolution in a high-frequency dielectric regime observed in the AC-driven electroconvection of nematic liquid crystals (NLCs). It is determined that prewavy (PW) instability is essential for the formation and evolution. Specifically, in a twisted-aligned NLC cell, we observe a unique pattern that is comparable to the dielectric chevrons (DCVs) typically observed in a conventional planarly aligned pattern. It is determined to be a combined PW pattern with dielectric normal rolls (DNRs). Moreover, the power indices $({\alpha }_{\mathrm{PW}},$ ${\alpha }_{\mathrm{DNR}}, \mathrm{and} {\alpha }_{\mathrm{DCV}})$ are determined from the frequency-dependent thresholds $(V_{\mathrm{th}}\propto f^{\alpha })$ of PW, DNR, and DCV. By taking into account the appearance of PW and the different power indices, the pattern evolution scenarios for DCV are proposed, which can well explain the previous experimental results. Specifically, the PW-originated DCV2 clearly differs from the defect-mediated DCV1, which is known as a typical pattern evolution.

We analyze a recent generalized free-energy for liquid crystals posited by Virga and falling in the class of quartic functionals in the spatial gradients of the nematic director. We review some known interesting solutions, i.e., uniform heliconical structures, and we find new liquid crystal configurations, which closely resemble some novel, experimentally detected, structures called Skyrmion tubes. These new configurations are characterized by a localized pattern given by the variation of the conical angle. We study the equilibrium differential equations and find numerical solutions and analytical approximations.

In this paper we derive an exact expression for the mean heat flux at the wall for the compressible turbulent channel flow. In the expression, the heat flux at the wall can be decomposed into four parts, including the contribution from the turbulent heat transfer, the contribution from the molecular heat transfer, the contribution from the pressure work, and the contribution from the work from viscous stress (VW). The decomposition is validated in compressible turbulent channel flows with isothermal walls at three different Reynolds and Mach numbers, and the results match very well with the direct estimations at the wall. The data also show that the VW term dominates the contributions (around $90\%$) in the decomposition while around $90\%$ of VW is from the near-wall region $(y/h<0.2)$, illustrating the importance of the viscous stress work in the near-wall region.

Influences of surface nanotubes at high temperatures are investigated on droplet impact dynamics and Leidenfrost effect. Five distinct regimes of impact droplets are found on the nanotube surface, including contact boiling, film levitation, central jet levitation, central jet, and Leidenfrost phenomenon. The regimes of film levitation, central jet levitation, and central jet are characterized by either film levitation and/or liquid central jet. The regime of Leidenfrost phenomenon is characterized by droplet bounce-off behavior free of any liquid jets. Film levitation is driven by the vaporization of two parts of the droplet, with one as the droplet bottom layer over the contact area above the nanotube structure, and the other as the hemiwicking liquid in nanotubes. Both the vaporization is impaired by increasing the surface temperature, which is attributed to the reduced contact time and less extent of spread of the droplet at a higher surface temperature. The central jet phenomenon is driven by the vapor stream produced by hemiwicking liquid in the central area upon impact. It is enhanced and then suppressed by elevating the surface temperature, resulting from the collective effects of the vapor pressure in nanotubes which increases with the surface temperature, and the cross-sectional area of the vapor stream, which increases and then decreases with the surface temperature. At a high Weber number, the Leidenfrost temperature can be increased by ${125}^{\circ }\mathrm{C}$ on the nanotube surface, implying a great potential in heat transfer enhancement for droplet-based applications.

The transport properties of warm dense neon (Ne) and krypton (Kr) are studied by combining self-consistent fluid variational theory (SFVT) with linear response theory (LRT). The components are determined using the SFVT, and the transport parameters, including the electrical conductivity, thermal conductivity, and thermopower, are calculated with the LRT. The relevant scattering mechanisms, including electron-ion, electron-electron, and electron-atom scatterings, are taken into account. An effective potential model in combination with the Muffin-tin model is introduced to further improve the description for electron-atom scattering, which not only includes static, exchange, and polarization interactions but also considers the plasma environmental effects. It is found that for electron-atom scattering, the influence of the plasma density is significant at lower scattering energies but the effects are different for electron-Ne and electron-Kr scattering. For electron-Kr scattering, a plasma density-dependent Ramsauer-Townsend minimum is observed. The obtained transport parameters are compared with the available experiments and other simulations. The plasma phase transition of warm dense Kr is revisited from multiple perspectives based on the numerical simulation results for the electrical conductivity and thermopower. These observations may help one to better understand the transport properties of warm dense noble gases and are an important guide for future experimental designs and theoretical developments.

Spin-polarized fuels are promising for inertial confinement fusion due to the enhanced fusion cross section. One significant concern of spin-polarized inertial confinement fusion is whether the nuclei polarization could survive in the implosions and contribute to ignitions. Here we present numerical simulation methods and results of spin dynamics of polarized deuterium-tritium fuels in strong self-generated magnetic fields during the implosions of dense cylindrical shells. The magnetic field generation and evolution is modeled with generalized Ohm's laws combined with hydrodynamic equations. The spin dynamics is investigated with a particle-tracking method, by solving the spin precession equations of tracked particles. Rayleigh-Taylor instabilities and Richtmyer-Meshkov instabilities are found to be the main cause of depolarization. Hydrodynamic instabilities lead to depolarization of nuclei near the hot-spot shell interface, and an asymmetric shock front leads to depolarization of nuclei inside a hot spot. Deuterium polarization is more stable than tritium polarization due to its smaller gyromagnetic ratio. Low-mode perturbations can lead to higher depolarization inside a hot spot than high-mode perturbations. In the multimode simulations, the modes around 16–32 are significant for hot-spot depolarization.

Many systems with propagation dynamics, such as spike propagation in neural networks and spreading of infectious diseases, can be approximated by autoregressive models. The estimation of model parameters can be complicated by the experimental limitation that one observes only a fraction of the system (subsampling) and potentially time-dependent parameters, leading to incorrect estimates. We show analytically how to overcome the subsampling bias when estimating the propagation rate for systems with certain nonstationary external input. This approach is readily applicable to trial-based experimental setups and seasonal fluctuations as demonstrated on spike recordings from monkey prefrontal cortex and spreading of norovirus and measles.

Using numerical exact diagonalization, we study matrix elements of a local spin operator in the eigenbasis of two different nonintegrable quantum spin chains. Our emphasis is on the question to what extent local operators can be represented as random matrices and, in particular, to what extent matrix elements can be considered as uncorrelated. As a main result, we show that the eigenvalue distribution of band submatrices at a fixed energy density is a sensitive probe of the correlations between matrix elements. We find that, on the scales where the matrix elements are in a good agreement with all standard indicators of the eigenstate thermalization hypothesis, the eigenvalue distribution still exhibits clear signatures of the original operator, implying correlations between matrix elements. Moreover, we demonstrate that at much smaller energy scales, the eigenvalue distribution approximately assumes the universal semicircle shape, indicating transition to the random-matrix behavior, and in particular that matrix elements become uncorrelated.

We study the dynamics of the statistics of the energy transferred across a point along a quantum chain which is prepared in the inhomogeneous initial state obtained by joining two identical semi-infinite parts thermalized at two different temperatures. In particular, we consider the transverse field Ising and harmonic chains as prototypical models of noninteracting fermionic and bosonic excitations, respectively. Within the so-called hydrodynamic limit of large space-time scales we first discuss the mean values of the energy density and current, and then, aiming at the statistics of fluctuations, we calculate exactly the scaled cumulant generating function of the transferred energy. From the latter, the evolution of the associated large deviation function is obtained. A natural interpretation of our results is provided in terms of a semiclassical picture of quasiparticles moving ballistically along classical trajectories. Similarities and differences between the transferred energy scaled cumulant and the large deviation functions in the cases of noninteracting fermions and bosons are discussed.

We investigate the nonlinear dynamics of a recent architecture of an optoelectronic oscillator, where the emitting laser and the receiving diode are connected in a head-to-tail configuration via an optical fiber delay line. The resulting nonlinear transfer function is a piecewise linear profile, and its interplay with the delay leads to many complex behaviors such as relaxation oscillations and deterministic chaos. This system belongs to a recent class of optoelectronic oscillators where the nonlinearity does not originate from the sinusoidal transfer function of an imbalanced interferometer, and, in particular, it is a simple optoelectronic oscillator configuration that is capable of displaying a chaotic behavior. The results of the analytic study are confirmed by numerical simulations and experimental measurements.

Experiments have shown that, in an aqueous environment, lipids and membrane proteins can self-assemble into membrane protein polyhedral nanoparticles (MPPNs). MPPNs are closed, spherical vesicles composed of a lipid bilayer membrane and membrane proteins, with a polyhedral arrangement of membrane proteins. The observed symmetry and size of MPPNs can be understood from the interplay of protein-induced lipid bilayer deformations in MPPNs, topological defects in protein packing necessitated by the spherical shape of MPPNs, and thermal fluctuations in MPPN self-assembly. We explore here the effect of protein steric constraints on MPPN shape. The protein steric constraints considered here may arise from a well-defined shape of protein domains outside the membrane, entropic repulsion between membrane proteins with flexible domains outside the membrane, or binding of other molecules to membrane proteins. Calculating MPPN self-assembly diagrams under protein steric constraints we find that protein steric constraints can strongly affect MPPN self-assembly. Depending on the specific scenario considered, protein steric constraints can leave large portions of the MPPN self-assembly diagrams with no clearly defined MPPN symmetry or substantially expand the regions of MPPN self-assembly diagrams dominated by highly symmetric MPPN states, such as MPPNs with icosahedral or snub cube symmetry. Our results suggest that modification of protein steric constraints may allow the directed self-assembly of MPPNs with specified symmetry, size, and protein composition and may thus facilitate the further utilization of MPPNs for membrane protein structural analysis or targeted drug delivery.

In this work, we present results from experiments capable of producing and measuring the propagation of multiple successive, copropagating shocks across an unstable planar interface, where the shocks are independently driven and separately controllable, enabling the study of this important phenomenon. Copropagating shocks play a significant role in a wide range of systems involving stratified media subject to a shock, and exhibit different physical characteristics compared to counterpropagating shocks. Existing techniques, however, preclude copropagating shocks, so experiments to date have been limited to the study of counterpropagating shocks. We address this previous limitation and open a physical parameter space for study using a new hohlraum platform on the National Ignition Facility. Initial experimental results are presented together with comparisons from numerical simulations.

Ground-state structures of a two-dimensional (2D) system composed of superparamagnetic charged particles are investigated by means of molecular dynamics simulation. The charged particles trapped in a quadratic potential interact with each other via the repulsive, attractive, and magnetic dipole-dipole forces. Simulations are performed within two regimes: a one-component system and a two-component system where the charged particles have the identical charge-to-mass ratio. The effects of magnetic dipole-dipole interaction, mixing ratio of the two species and confinement frequency on the ground-state structures are discussed. It is found that as the strength of the magnetic dipole increases, the charged particles tend to self-organize into chainlike structures. The two species particles exhibit different structural features, depending on the competition of electrostatic repulsive interaction, magnetic dipole-dipole interaction and confinement force. The potential lanes are observed through analyzing the global potential of the magnetic particles, which guide the unmagnetic particles aligning themselves in the direction of the potential lanes.

The contact process with diffusion (PCPD) defined by the binary reactions $B+B\to B+B+B, B+B\to \varnothing$ and diffusive particle spreading exhibits an unusual active to absorbing phase transition whose universality class has long been disputed. Multiple studies have indicated that an explicit account of particle pair degrees of freedom may be required to properly capture this system's effective long-time, large-scale behavior. We introduce a two-species representation for the PCPD in which single particles $B$ and particle pairs $A$ are dynamically coupled according to the stochastic reaction processes $B+B\to A, A\to A+B, A\to \varnothing$, and $A\to B+B$, with each particle type diffusing independently. Mean-field analysis reveals that the phase transition of this model is driven by competition and balance between the two species. We employ Monte Carlo simulations in one, two, and three dimensions to demonstrate that this model consistently captures the pertinent features of the PCPD. In the inactive phase, $A$ particles rapidly go extinct, effectively leaving the $B$ species to undergo pure diffusion-limited pair annihilation kinetics $B+B\to \varnothing$. At criticality, both $A$ and $B$ densities decay with the same exponents (within numerical errors) as the corresponding order parameters of the original PCPD, and display mean-field scaling above the upper critical dimension $d_c=2$. In one dimension, the critical exponents for the $B$ species obtained from seed simulations also agree well with previously reported exponent value ranges. We demonstrate that the scaling properties of consecutive particle pairs in the PCPD are identical with that of the $A$ species in the coupled model. This two-species picture resolves the conceptual difficulty for seed simulations in the original PCPD and naturally introduces multiple length scales and timescales to the system, which are also the origin of strong corrections to scaling. The extracted moment ratios from our simulations indicate that our model displays the same temporal crossover behavior as the PCPD, which further corroborates its full dynamical equivalence with our coupled model.

The spectral form factor is a dynamical probe for level statistics of quantum systems. The early-time behavior is commonly interpreted as a characterization of two-point correlations at large separation. We argue that this interpretation can be too restrictive by indicating that the self-correlation imposes a constraint on the spectral form factor integrated over time. More generally, we indicate that each expansion coefficient of the two-point correlation function imposes a constraint on the properly weighted time-integrated spectral form factor. We discuss how these constraints can affect the interpretation of the spectral form factor as a probe for ergodicity. We propose a probe, which eliminates the effect of the constraint imposed by the self-correlation. The use of this probe is demonstrated for a model of randomly incomplete spectra and a Floquet model supporting many-body localization.

Liquid crystal networks combine the orientational order of liquid crystals with the elastic properties of polymer networks, leading to a vast application potential in the field of responsive coatings, e.g., for haptic feedback, self-cleaning surfaces, and static and dynamic pattern formation. Recent experimental work has further paved the way toward such applications by realizing the fast and reversible surface modulation of a liquid crystal network coating upon in-plane actuation with an AC electric field [Liu, Tito, and Broer, Nat. Commun. 8, 1526 (2017)]. Here, we construct a Landau-type theory for electrically-responsive liquid crystal networks and perform molecular dynamics simulations to explain the findings of these experiments and inform on rational design strategies. Qualitatively, the theory agrees with our simulations and reproduces the salient experimental features. We also provide a set of testable predictions: the aspect ratio of the nematogens, their initial orientational order when cross-linked into the polymer network, and the cross-linking fraction of the network all increase the plasticization time required for the film to macroscopically deform. We demonstrate that the dynamic response to oscillating electric fields is characterized by two resonances, which can likewise be influenced by varying these parameters, providing an experimental handle to fine-tune device design.

We carry out numerical simulations to study the behavior of an athermal mixture of frictionless circular disks and elongated rods in two dimensions, under three different types of global linear deformation at a finite strain rate: (i) simple shearing, (ii) pure shearing, and (iii) isotropic compression. We find that the fluctuations induced by such deformations lead to depletion forces that cause rods to group in parallel oriented clusters for the cases of simple and pure shear, but not for isotropic compression. For simple shearing, we find that as the fraction of rods increases, this clustering increases, leading to an increase in the average rate of rotation of the rods, and a decrease in the magnitude of their nematic ordering.

We study a ballistic agglomeration process in the reaction-controlled limit. Cluster densities obey an infinite set of Smoluchowski rate equations, with rates dependent on the average particle energy. The latter is the same for all cluster species in the reaction-controlled limit and obeys an equation depending on densities. We express the average energy through the total cluster density that allows us to reduce the governing equations to the standard Smoluchowski equations. We derive basic asymptotic behaviors and verify them numerically. We also apply our formalism to the agglomeration of dark matter.

Formation of bands of macroscopic strain localization during staircase creep in an AlMg polycrystal is studied by the acoustic emission (AE) technique and high-speed video recording with an image acquisition rate up to 50 000 frames per second. The simultaneous measurements by two methods allow us to distinguish different types of embryo deformation bands and concomitant AE signals, and to establish correlations between the band evolution and the acoustic response. It is found that the fastest stages of band formation, associated with its emergence to the surface and subsequent accelerated expansion, generate complex AE bursts in the frequency band ∼0.05–1 MHz. The correlations hidden in the complex structure of an individual acoustic burst are investigated by methods of statistical and fractal analysis. On the other hand, relationships between average parameters of various physical responses to discontinuous creep are assessed. Particularly, a close correspondence is found between the envelope of the acoustic burst and the rate of stress change during formation of a single deformation band. Evolution of dynamical behavior of embryo bands with increasing creep stress is discussed. Notably, a qualitative change in the AE waveform observed on approaching the ultimate stress is considered from the viewpoint of anticipation of the oncoming fracture.