We study the interplay between the fluid-crystal transition and the glass transition of elastic sphere system with polydispersity using nonequilibrium molecular dynamics simulations. It is found that the end point of the crystal-fluid transition line, which corresponds to the critical polydispersity above which the crystal state is unstable, is on the glass transition line. This means that crystal and fluid states at the melting point becomes less distinguishable as polydispersity increases and finally they become identical state, i.e., marginal glass state, at critical polydispersity.

We present molecular dynamics simulations of the binary Kob-Andersen Lennard-Jones model, a model glass former, and consider the distributions of inherent energies and metabasins during aging. In addition to the typical protocol of performing a temperature jump from a high temperature to a low destination temperature, we consider the temporal evolution of the energy distributions after an “up-jump,” i.e., from a low to a high temperature. In this case, for times on the order of the relaxation time the distribution of metabasin energies exhibits a transient two-peak structure for a small system (65 particles). For a large system (1000 particles) no such two-peak structure appears because it is averaged out. The simulations show, however, that a clear signal of an intermediate two-peak structure survives in the thermodynamic limit, namely that the inherent energy distribution width goes through a maximum at intermediate times for temperature up jumps; no such maximum is found for temperature down jumps. These findings are qualitatively rationalized in terms of a simple trap model with a Gaussian distribution of energies, assuming that the liquid may be divided into non-interacting regions each of which is described by a trap model.

We present an approach to the energetics of a diode based on the Langevin equation for an ideal $RC$ circuit and establish a simple model consisting of two diodes switched in the same directions located in two heat reservoirs with different temperatures. We calculate the thermoelectric voltage and the efficiency of the diode system as a fluctuation rectifier and show the efficiency is always smaller than the Carnot value, thus, indicating the irreversible mode of operation. The Carnot efficiency is achieved only when the diode works as the normal resistor.

Amorphous solids that underwent a strain in one direction such that they responded in a plastic manner “remember” that direction also when relaxed back to a state with zero mean stress. We address the question “what is the order parameter that is responsible for this memory?” and is therefore the reason for the different subsequent responses of the material to strains in different directions. We identify such an order parameter which is readily measurable, we discuss its trajectory along the stress-strain curve, and propose that it and its probability distribution function must form a necessary component of a theory of elastoplasticity.

We derive expressions for the lowest nonlinear elastic constants of amorphous solids in athermal conditions (up to third order), in terms of the interaction potential between the constituent particles. The effect of these constants cannot be disregarded when amorphous solids undergo instabilities such as plastic flow or fracture in the athermal limit; in such situations the elastic response increases enormously, bringing the system much beyond the linear regime. We demonstrate that the existing theory of thermal nonlinear elastic constants converges to our expressions in the limit of zero temperature. We motivate the calculation by discussing two examples in which these nonlinear elastic constants play a crucial role in the context of elastoplasticity of amorphous solids. The first example is the plasticity-induced memory that is typical to amorphous solids (giving rise to the Bauschinger effect). The second example is how to predict the next plastic event from knowledge of the nonlinear elastic constants. Using the results of our calculations we derive a simple differential equation for the lowest eigenvalue of the Hessian matrix in the external strain near mechanical instabilities; this equation predicts how the eigenvalue vanishes at the mechanical instability and the value of the strain where the mechanical instability takes place.

An experimental research concerning highly underexpanded jets made of different gases from the surrounding ambient is here described. By selecting different species of gases, it was possible to vary the jet-to-ambient density ratio in the 0.04–12 range and observe its effect on the jet morphology. By adjusting the stagnation and ambient pressures, it has been possible to select the Mach number of the jets, independently from the density ratio. Each jet is therefore characterized by its maximum Mach number, ranging from 10 to 50. The Reynolds number range of the nozzle is ${10}^3–5\times {10}^4$. The spatial evolution of the jets was observed over a much larger scale than the nozzle diameter. The gas densities were evaluated from the light emission induced by an electron beam and the gas concentrations were obtained by analyzing the color of the emitted light. The results have shown that the morphology of the jets depends to a greater extent on the density ratio. Jets that are lighter than the ambient exhibit a more intense jet-ambient mixing than jets that are heavier than the ambient, while the effects of changing the jet Mach number do not seem to be too large in the explored range. These results can be expressed by means of two simple scaling laws relevant to the near field (pre-Mach-disk) and the mid-long term field (post-Mach-disk), respectively.

The long-term lateral migration of a two-dimensional elastic capsule in a microchannel is studied numerically in this paper. The numerical method combines a finite volume technique for solving the fluid problem with a front tracking technique for capturing and tracking the capsule membrane. The capsule is modeled as a liquid medium enclosed by a thin membrane which has linear elastic properties. The capsule, whose initial shape is circle and which starts from a near-center position or a near-wall position, experiences tilting and membrane tank-treading, and migrates laterally when moving along the surrounding flow. The lateral migration demonstrates the existence of lift effect of surrounding flow on moving capsule. Before capsule approaches to the microchannel centerline closely, lower membrane dilation modulus and lower viscosity ratio tend to result in faster lateral migration. The initial position also influences the performance behavior of capsule, despite the lateral migration of capsule is a quasisteady process. Small difference in capsule behavior when capsule is not near to the microchannel centerline might lead to significant difference in capsule behavior when capsule approaches closely to the centerline. When capsules are near to microchannel wall, the effect of the wall on capsule behavior might dominate, leading to relatively faster lateral migration. When capsules are not far from microchannel centerline, the effect of the nonlinearity of Poiseuille flow might dominate, resulting in relatively slower lateral movement. When capsules are located closely to the centerline, they behave differently, where the reason still remains poorly understood and it will be one of our future studies. The comparison between the capsule behavior from the present simulation and that by the migration law proposed by Coupier et al. [Phys. Fluids 20, 111702 (2008)] shows that the behavioral agreement for near-wall capsule is better than that for near-center capsule, and the best agreement occurs to the near-wall capsule with intermediate membrane dilation modulus and highest viscosity ratio.

Statistical behavior and scaling properties of isoheight lines in three different saturated two-dimensional grown surfaces with controversial universality classes are investigated using ideas from Schramm-Loewner evolution $\left({\text{SLE}}_{\kappa }\right)$. We present some evidence that the isoheight lines in the ballistic deposition (BD), Eden and restricted solid-on-solid (RSOS) models have conformally invariant properties all in the same universality class as the self-avoiding random walk (SAW), equivalently ${\text{SLE}}_{8/3}$. This leads to the conclusion that all these discrete growth models fall into the same universality class as the Kardar-Parisi-Zhang (KPZ) equation in two dimensions.

We investigate the zero-temperature glassy transitions in the square-lattice $\pm J$ Ising model, with bond distribution $P\left(J_{xy}\right)=p\delta \left(J_{xy}-J\right)+\left(1-p\right)\delta \left(J_{xy}+J\right)$; $p=1$ and $p=1/2$ correspond to the pure Ising model and to the Ising spin glass with symmetric bimodal distribution, respectively. We present finite-temperature Monte Carlo simulations at $p=4/5$, which is close to the low-temperature paramagnetic-ferromagnetic transition line located at $p\approx 0.89$, and at $p=1/2$. Their comparison provides a strong evidence that the glassy critical behavior that occurs for $1-p_0<p<p_0$, $p_0\approx 0.897$, is universal, i.e., independent of $p$. Moreover, we show that glassy and magnetic modes are not coupled at the multicritical zero-temperature point where the paramagnetic-ferromagnetic transition line and the $T=0$ glassy transition line meet. On the theoretical side we discuss the validity of finite-size scaling in glassy systems with a zero-temperature transition and a discrete Hamiltonian spectrum. Because of a freezing phenomenon which occurs in a finite volume at sufficiently low temperatures, the standard finite-size scaling limit in terms of $T{L}^{1/\nu }$ does not exist; the renormalization-group invariant quantity $\xi /L$ should be used instead as basic variable.

A microscopic formalism based on computing many-particle densities is applied to the analysis of the diffusion-controlled kinetics of pattern formation in oppositely charged molecules on surfaces or adsorbed at interfaces with competing long-range Coulomb and short-range Lennard-Jones interactions. Particular attention is paid to the proper molecular treatment of energetic interactions driving pattern formation in inhomogeneous systems. The reverse Monte Carlo method is used to visualize the spatial molecular distribution based on the calculated radial distribution functions (joint correlation functions). We show the formation of charge domains for certain combinations of temperature and dynamical interaction parameters. The charge segregation evolves into quasicrystalline clusters of charges, due to the competing long- and short-range interactions. The clusters initially co-exist with a gas phase of charges that eventually add to the clusters, generating ”fingers” or line of charges of the same sign, very different than the nanopatterns expected by molecular dynamics in systems with competing interactions in two dimensions, such as strain or dipolar versus van der Waals interactions.

Entanglements in a polymer network are like knots between the polymer chains, and they are at the root of many phenomena observed in polymer systems. When a polymer glass is strained, cracklike deformations called crazes may be formed and the study of these regions can reveal much about the nature of entanglements. We have studied crazes in systems that are blends of long polymer chains diluted with chains of various small molecular weights. The range of diluting chain lengths is such that a fraction of them have conformations leading to entanglements. It has been found that a system with more short chains added acts like one in which the entanglement density is smaller than that in an undiluted system. We propose a model that quantitatively predicts the density of effective entanglements of a polydisperse system of polymer chains which is consistent with our experimental data.

Recent experiments [J. van Mameren et al., Proc. Natl. Acad. Sci. U.S.A. 106, 18231 (2009)] provide a detailed spatial picture of overstretched DNA, showing that under certain conditions the two strands of the double helix separate at about 65 pN. It was proposed that this observation rules out the existence of an elongated, hybridized form of DNA (S-DNA). Here, we argue that the S-DNA picture is consistent with the observation of unpeeling during overstretching. We demonstrate that assuming the existence of S-DNA does not imply DNA overstretching to consist of the complete or near-complete conversion of the molecule from B to S form. Instead, this assumption implies in general a more complex dynamic coexistence of hybridized and unhybridized forms of DNA. We argue that such coexistence can rationalize several recent experimental observations.

Micropipette aspiration technique can be very useful for describing the shape transitions of lipid bilayer vesicles with fluid phase coexistence modulated by the line tension and the bending rigidity. For example, composition dependence of the line tension at the liquid-ordered and liquid-disordered phase interface has been investigated using this technique. Recently, using a very simple mechanical model, the instabilities that occur during suction and release experiments of aspirated vesicles have been discussed. Due to its simplicity the model could not predict the influence of the bending rigidity. In this work, we incorporate the contributions from Helfrich bending energy and the line energy in the vesicle free energy and investigate the shape transitions in micropipette aspirated vesicles. We discuss how the critical aspiration pressure depends on the bending moduli of the phases, the line tension at the interface, and the reduced volume of the vesicle. The ratio of the bending moduli that we predict using the critical aspiration pressure data from recent experiments agrees with the literature.

In this communication we address some hydrodynamic aspects of recently proposed drift mechanism of biogenic mixing in the ocean [K. Katija and J. O. Dabiri, Nature (London) 460, 624 (2009)]. The relevance of the locomotion gait at various spatial scales with respect to the drift is discussed. A hydrodynamic scenario of the drift based on unsteady inertial propulsion, typical for most small marine organisms, is proposed. We estimate its effectiveness by taking into account interaction of a swimmer with the turbulent marine environment. Simple scaling arguments are derived to estimate the comparative role of drift-powered mixing with respect to the turbulence. The analysis indicates substantial biomixing effected by relatively small but numerous drifters, such as krill or jellyfish.

We investigate the properties of and the transition to exploding dissipative solitons as they have been found by Akhmediev’s group for the cubic-quintic complex Ginzburg-Landau equation. Keeping all parameters fixed except for the distance from linear onset, $\mu$, we covered a large range of values of $\mu$ from very negative values to $\mu =0$, where the zero solution loses its linear stability. We find, with increasing values of $\mu$, stationary pulses, pulses with rapid oscillations, and pulses modulated with an additional small frequency. The transition to exploding solitons arises via a hysteretic transition involving symmetric and asymmetric pulses with two frequencies. As $\mu$ is increased in the regime of exploding solitons, the fraction of symmetric exploding solitons is increasing. At the transition from asymmetric two frequency pulses to exploding solitons, only asymmetric exploding solitons are found. We completed our analysis with an analytic study of the collapse time for the exploding solitons and found good agreement with our numerical results.

We propose a method for the control of synchronization in two oscillator populations interacting according to a drive-response coupling scheme. The response ensemble of oscillators, which gets synchronized because of a strong forcing by the intrinsically synchronized driving ensemble, is controlled by mixed nonlinear delayed feedback. The stimulation signal is constructed from the mixed macroscopic activities of both ensembles. We show that the suggested method can effectively decouple the interacting ensembles from each other, where the natural desynchronous dynamics can be recovered in a demand-controlled way either in the stimulated ensemble, or, intriguingly, in both stimulated and not stimulated populations. We discuss possible therapeutic applications in the context of the control of abnormal brain synchrony in loops of affected neuronal populations.

We have revised the value of the turbulent Prandtl number obtained in the model of a passive scalar advected by the velocity field driven by the stochastic Navier-Stokes equation which was calculated by L. Ts. Adzhemyan et al. [Phys. Rev. E 71, 056311 (2005)] by using the field-theoretic renormalization group approach within the two-loop approximation in the corresponding perturbative theory. It is shown that the correct two-loop contribution to the turbulent Prandtl number is essentially smaller than that calculated by Adzhemyan et al. and, as a result, the final two-loop value of the turbulent Prandtl number is ${\text{Pr}}_t=0.7051$ instead of ${\text{Pr}}_t=0.7693$. The source of discrepancy between our result and that obtained by Adzhemyan et al. is identified and discussed.

Excitable systems can have more than one response threshold, but accessing each of these is only facilitated by preferential choice of the appropriate components in the input noise. The coherence resonance phenomenon discovered by Pikovsky and Kurths [Phys. Rev. Lett. 78, 775 (1997)] utilizes only one response threshold, thus leaving the nature of the dynamics of a possible second threshold unspecified. Here we show using a FitzHugh-Nagumo excitable system that the second response threshold can be reached transiently by brief pulses in the negative noise component, leading to a coherence resonance phenomenon of its own. The resonance can occur both as a function of input amplitude and frequency. The phenomenon is also illustrated in more realistic Hodgkin-Huxley model equations, and analytical predictions are made using probabilistic considerations of the input. This phenomenon attributes more complex role noise can play in excitable systems.

Using analysis and simulation, we show how ordered arrays of microcapsules in solution can be harnessed to propagate chemical signals in directed and controllable ways, allowing the signals to be transmitted over macroscopic distances. The system encompasses two types of capsules that are localized on an adhesive surface. The “signaling” capsules release inducer molecules, which trigger “targets” to release nanoparticles. The released nanoparticles can bind to the underlying surface and thus, create adhesion gradients, which then propel the signaling capsules to shuttle between neighboring targets. This arrangement acts like a relay, so that triggering target capsules at a particular location in the array also triggers target capsules in adjacent locations. For an array containing two target columns, our simulations and analysis show that steady input signal leads to a sustained periodic output. For an array containing multiple target columns, we show that by introducing a prescribed ratio of nanoparticle release rates between successive target columns, a chemical signal can be propagated along the array without dissipation. We also demonstrate that similar signal transmission cannot be performed via diffusion alone.