We report on experiments in which the Texas Petawatt laser irradiated a mixture of deuterium or deuterated methane clusters and helium-3 gas, generating three types of nuclear fusion reactions: D($d$,${}^3$He)$n$, D($d$,$t$)$p$, and ${}^3$He($d$,$p$)${}^4$He. We measured the yields of fusion neutrons and protons from these reactions and found them to agree with yields based on a simple cylindrical plasma model using known cross sections and measured plasma parameters. Within our measurement errors, the fusion products were isotropically distributed. Plasma temperatures, important for the cross sections, were determined by two independent methods: (1) deuterium ion time of flight and (2) utilizing the ratio of neutron yield to proton yield from D($d$,${}^3$He)$n$ and ${}^3$He($d$,$p$)${}^4$He reactions, respectively. This experiment produced the highest ion temperature ever achieved with laser-irradiated deuterium clusters.

The effects of ion mobility and positron fraction on the solitary waves of the laser field envelope and the potential of the electrostatic field in weak relativistic electron-positron-ion plasma are investigated. The parameter region for the existence of solitary waves is obtained analytically, and a reasonable choice of parameters is clarified. Both cases of mobile and immobile ions are considered. It is found that the amplitudes of solitary waves in the former case are larger compared to the latter case. For small plasma density, the localized solitary wave solutions in terms of the approximate perturbation analytical method are very consistent with those by exact numerical calculations. However, as the plasma density increases the analytical method loses its validity more and more. The influence of the positron fraction on the amplitudes of solitary waves shows a monotonous increasing relation. The implications of our results to particle acceleration are also discussed briefly.

We measure the propagation of guided acoustic waves in a nonlinear three-wave mixing experiment in a water-filled steel pipe. These waves exhibit a predicted phasing-dephasing behavior as a function of propagation distance due to the underlying velocity dispersion between the fundamentals and the nonlinearly generated waves. We extract the dimensionless nonlinear parameter, $\beta$, which is weakly frequency dependent.

This paper reports a super-resolution imaging approach based on orbital-angular-momentum diffraction tomography (OAM-DT), which makes an important breakthrough on the Rayleigh limit associated with conventional diffraction tomography (DT) technique. It is well accepted that orbital-angular momentum (OAM) provides additional electromagnetic degrees of freedom. This concept has been widely applied in science and technology. In this paper we revisit the DT problem extended with OAM, and demonstrate theoretically and numerically that there is no physical limit on imaging resolution with OAM-DT. The physical mechanism behind it is that either the near field or superoscillation of the transmitter is employed to super-resolve probed objects. This super-resolution OAM-DT imaging paradigm does not require near-field measurement, a subtle focusing lens, or complicated postprocessing, etc., thus providing an approach to realize the wave-field imaging of universal objects with subwavelength resolution.

The hydrodynamics of flexible slender bodies in Stokes flow is studied by taking into account the fluid-structure interaction through both forces and coupled moments. The fluid subjected to line sources of forces and moments is described by using integral equations. Meanwhile, the flexible slender body is modeled using finite beam elements. The two sides are linked through interfacial continuity conditions. Upon discretization, it results in a higher-order line element method for efficient and accurate solution of slender-body hydrodynamics. Four examples are presented to demonstrate the validity and efficiency of the present method: (a) hydrodynamics of a flexible slender rod subjected to a torque at one end, (b) hydrodynamics of a flexible slender rod subjected to a bending moment at one end, (c) hydrodynamics of a flexible slender rod subjected to a cyclic force, and (d) hydrodynamics of a flexible slender rod with a magnetized head within a rotating magnetic field. Examples (a) and (b) may serve as benchmark solutions and examples (c) and (d) show how planar and spiral waves can be excited in a slender body.

We introduce a simple method to estimate the accuracy of exact solutions under initial value conditions proposed by Petrov and Kudrin [Phys. Rev. Lett. 104, 190404 (2010)]. We demonstrate that even for a sufficiently weak nonlinearity, the initial value condition difference between linear and nonlinear case may be evident. Our result may be used as a criterion of employing the exact solution to deal with initial value problems of cylindrical electromagnetic wave propagation in a nonlinear nondispersive medium.

We consider an open two-level system driven by a piecewise constant periodic field and described by a rate equation with Fermi, Bose, and Arrhenius rates, respectively. We derive an analytical expression for the generating function and large deviation function of the work performed by the field and show that a work fluctuation theorem holds.

We study the consequences of different realizations of diffusion processes in relativistic Langevin simulations. We elaborate on the Ito-Stratonovich dilemma by showing how microscopically calculated transport coefficients as obtained from a Boltzmann–Fokker-Planck equation can be implemented to lead to an unambiguous realization of the Langevin process. Pertinent examples within the prepoint (Ito) and postpoint (Hänggi-Klimontovich) Langevin prescriptions are worked out explicitly. Deviations from this implementation are shown to generate variants of the Boltzmann distribution as the stationary (equilibrium) solutions. Finally, we explicitly verify how the Lorentz invariance of the Langevin process is maintained in the presence of an expanding medium, including the case of an “elliptic flow” transmitted to a Brownian test particle. This is particularly relevant for using heavy-flavor diffusion as a quantitative tool to diagnose transport properties of QCD matter as created in ultrarelativistic heavy-ion collisions.

In this paper, we study the effects of the interparticle interaction range on heat flow. We show that, by increasing the interaction range, we may amplify the thermal conductivity and even change the regime of heat transport. More importantly, considering a crucial problem of phononics, namely, the search of a suitable thermal diode, we investigate the range effects in some graded systems in which thermal rectification is a ubiquitous phenomenon. In such graded models, we show that long-range interactions may significatively increase the rectification power and may avoid its decay with the system size, thus solving relevant problems of the usual proposals of rectifiers. Our results indicate that graded materials are genuine candidates for the actual fabrication of thermal diodes.

Individual random trajectories of stochastic processes are often analyzed by using quadratic forms such as time averaged (TA) mean square displacement (MSD) or velocity auto-correlation function (VACF). The appropriate quadratic form is expected to have a narrow probability distribution in order to reduce statistical uncertainty of a single measurement. We consider the problem of finding the optimal quadratic form that minimizes a chosen cumulant moment (e.g., the variance) of the probability distribution, under the constraint of fixed mean value. For discrete noncentered Gaussian processes, we construct the optimal quadratic form by using the spectral representation of cumulant moments. Moreover, we obtain a simple explicit formula for the smallest achievable cumulant moment that may serve as a quality benchmark for other quadratic forms. We illustrate the optimality issues by comparing the optimal variance with the variances of the TA MSD and TA VACF of fractional Brownian motion superimposed with a constant drift and independent Gaussian noise.

This article deals with the characterization, using an acoustic technique, of the mechanical behavior of a dry dense granular medium under quasistatic loading. Ultrasound propagation through the contact-force network supporting the external load offers a noninvasive probe of the viscoelastic properties of such heterogeneous media. First the response of a glass bead packing is studied in an oedometric configuration during creep and relaxation tests. Quasilogarithmic increases of sound velocities are found in both mechanical tests. A model based on the mechanics of microcontacts between rough grains adequately reproduces our experimental results, especially for the evolution of elastic modulus. Another main experimental finding is that collective grain rearrangements within the packing also play a crucial role at the early stage of creep and relaxation.

Evanescent wave microscopy is used to study the dynamics of probe particles inside a laponite suspension, when the size of the latex probes is of the order of the diameter of the laponite disks. A correlation procedure is introduced that allows us to study quantitatively the diffusion of small probes. For all studied sizes, the motion exhibits two modes: a fast relaxation mode and a slow relaxation mode. In the fast relaxation mode, the probes diffuse in a viscous medium, whose viscosity does not depend on the diameter of the probes and is slightly larger than the viscosity of water. Then, the diffusion of the particles is restricted over distances larger than their diameters, which increase when the particle diameter decreases. In this regime, the probe particles experience the elasticity of the solution and the apparent elastic modulus increases when the diameter of the probe particle increases, whereas for large enough particles, the macroscopic behavior is recovered, in which the diffusing particles experience a homogeneous medium, and the macroscopic elastic modulus is recovered.

We study a phase oscillator network on a circle with an infinite-range interaction. First, we treat the Mexican-hat interaction with the zeroth and first Fourier components. We give detailed derivations of the auxiliary equations for the phases and self-consistent equations for the amplitudes. We solve these equations and characterize the nontrivial solutions in terms of order parameters and the rotation number. Furthermore, we derive the boundaries of the bistable regions and study the bifurcation structures in detail. Expressions for location-dependent resultant frequencies and entrained phases are also derived. Secondly, we treat a different interaction that is composed of $m$th and $n$th Fourier components, where $m<n$, and we study its nontrivial solutions. In both cases, the results of numerical simulations agree quite well with the theoretical results.

We use a lattice gas cellular automata model in the presence of random dynamic scattering sites and quenched disorder in the two-phase immiscible model with the aim of producing an interface dynamics similar to that observed in Hele-Shaw cells. The dynamics of the interface is studied as one fluid displaces the other in a clean lattice and in a lattice with quenched disorder. For the clean system, if the fluid with a lower viscosity displaces the other, we show that the model exhibits the Saffman-Taylor instability phenomenon, whose features are in very good agreement with those observed in real (viscous) fluids. In the system with quenched disorder, we obtain estimates for the growth and roughening exponents of the interface width in two cases: viscosity-matched fluids and the case of unstable interface. The first case is shown to be in the same universality class of the random deposition model with surface relaxation. Moreover, while the early-time dynamics of the interface behaves similarly, viscous fingers develop in the second case with the subsequent production of bubbles in the context of a complex dynamics. We also identify the Hurst exponent of the subdiffusive fractional Brownian motion associated with the interface, from which we derive its fractal dimension and the universality classes related to a percolation process.

Buoyantly unstable 3D chemical fronts were seen traveling through an iodate-arsenous acid reaction solution. The experiments were performed in channel reactors with rectangular cross sections, where the top of the reaction solution was in contact with air. A concave or convex meniscus was pinned to reactor lateral walls. Influence of the meniscus shape on front development was investigated. For the concave meniscus, an asymptotic shape of fronts holding negative curvature was observed. On the other hand, fronts propagating in the solution with the convex meniscus kept only positive curvature. Those fronts were also a bit faster than fronts propagating in the solution with the concave meniscus. A relation between the meniscus shape, flow distribution, velocity, and shape is discussed.

Based on the Boltzmann-BGK (Bhatnagar-Gross-Krook) equation, in this paper a discrete unified gas kinetic scheme (DUGKS) is developed for low-speed isothermal flows. The DUGKS is a finite-volume scheme with the discretization of particle velocity space. After the introduction of two auxiliary distribution functions with the inclusion of collision effect, the DUGKS becomes a fully explicit scheme for the update of distribution function. Furthermore, the scheme is an asymptotic preserving method, where the time step is only determined by the Courant-Friedricks-Lewy condition in the continuum limit. Numerical results demonstrate that accurate solutions in both continuum and rarefied flow regimes can be obtained from the current DUGKS. The comparison between the DUGKS and the well-defined lattice Boltzmann equation method (D2Q9) is presented as well.

Microfluidic obstacle arrays have been used in numerous applications, and their ability to sort particles or capture rare cells from complex samples has broad and impactful applications in biology and medicine. We have investigated the transport and collision dynamics of particles in periodic obstacle arrays to guide the design of convective, rather than diffusive, transport-based immunocapture microdevices. Ballistic and full computational fluid dynamics simulations are used to understand the collision modes that evolve in cylindrical obstacle arrays with various geometries. We identify previously unrecognized collision mode structures and differential size-based collision frequencies that emerge from these arrays. Previous descriptions of transverse displacements that assume unidirectional flow in these obstacle arrays cannot capture mode transitions properly as these descriptions fail to capture the dependence of the mode transitions on column spacing and the attendant change in the flow field. Using these analytical and computational simulations, we elucidate design parameters that induce high collision rates for all particles larger than a threshold size or selectively increase collision frequencies for a narrow range of particle sizes within a polydisperse population. Furthermore, we investigate how the particle Péclet number affects collision dynamics and mode transitions and demonstrate that experimental observations from various obstacle array geometries are well described by our computational model.

The reflection anisotropy spectroscopy profiles of a variant of cytochrome P450 reductase adsorbed at the Au(110)–phosphate buffer interface depend on the sequence of potentials applied to the Au(110) electrode. It is suggested that this dependence arises from changes in the orientation of the isoalloxazine ring structures in the protein with respect to the Au(110) surface. This offers a method of monitoring conformational change in this protein by measuring variations in the reflection anisotropy spectrum arising from changes in the redox potential.

In this paper, we provide a theory to pinpoint the role of electric double layer (EDL) interactions in governing the contact angle of an electrolyte drop on a charged solid in air or a bubble on a charged surface within an electrolyte solution. The EDL interactions are analytically solved by representing the three phase contact line as a wedge edge, with the wedge being formed by the solid-liquid and the air-liquid interfaces, and calculating the corresponding Maxwell stresses. We demonstrate that the EDL effects induce an “electrowetting-like” behavior, resulting in a lowering of the contact angle. As a specific example, we use this model to analyze the effect of added salt on preformed surface nanobubbles, and find, in contrast to what has been reported earlier, that even for most moderate conditions, added salt may have remarkable effect in altering the contact angle in preformed surface nanobubbles.

In spite of the increasing applications of the lattice Boltzmann method (LBM) in simulating various flow and transport systems in recent years, complex boundary conditions for the convection-diffusion and heat transfer processes in LBM have not been well addressed. In this paper, we propose an improved bounce-back method by using the midpoint concentration value to modify the bounced-back density distribution for LBM simulations of the concentration field. An accurate finite-difference scheme in the normal boundary direction has also been introduced for gradient boundary conditions. Compared with existing boundary methods, our method has a simple algorithm and can easily deal with boundaries with general geometries, motions, and surface conditions (the Dirichlet, Neumann, and mixed conditions). Carefully designed simulations are performed to examine the capacity and accuracy of this proposed boundary method. Simulation results are compared with those from theory and a representative boundary method, and an improved performance is observed. We have also simulated the effect of reference velocity on global accuracy to examine the performance of our model in preserving the fundamental Galilean invariance. These boundary treatments for concentration boundary conditions can be readily applied to other processes such as heat transfer systems.