Table of contents

The emergence and abundance of cooperation in animal and human societies is a challenging puzzle to evolutionary biology. Most research has focused on the imitation rules, but the update rules based uniquely on one's own payoff have received less attention so far. In this letter, we introduce a new yet simple update rule into a spatial voluntary public goods game where the agents located on a square lattice have longer memory and choose the successful strategies according to the game's earlier history. This introduction results in interesting dynamical properties and intriguing spatiotemporal patterns. In particular, this introduction can provide an explanation how microscopic agent-agent interactions may generate a spontaneous aggregate cooperation towards a more efficient outcome in the real-life situations. In addition, we found that the length of memory has a crucial effect on the average outcome of the population by this introduction.

We study the directed polymer of length t in a random potential with fixed endpoints in dimension 1+1 in the continuum and on the square lattice, by analytical and numerical methods. The universal regime of high temperature T is described, upon scaling "time"t∼T⁵/κ and space x=T³/κ (with κ=T for the discrete model) by a continuum model with δ-function disorder correlation. Using the Bethe Ansatz solution for the attractive boson problem, we obtain all positive integer moments of the partition function. The lowest cumulants of the free energy are predicted at small time and found in agreement with numerics. We then obtain the exact expression at any time for the generating function of the free-energy distribution, in terms of a Fredholm determinant. At large time we find that it crosses over to the Tracy-Widom distribution (TW) which describes the fixed-T infinite-t limit. The exact free-energy distribution is obtained for any time and compared with very recent results on growth and exclusion models.

The distribution function of the free-energy fluctuations in one-dimensional directed polymers with δ-correlated random potential is studied by mapping the replicated problem to a many-body quantum boson system with attractive interactions. Performing the summation over the entire spectrum of excited states the problem is reduced to the Fredholm determinant with the Airy kernel which is known to yield the Tracy-Widom distribution.

Momentum-conserving one-dimensional models are known to exhibit anomalous Fourier's law, with a thermal conductivity varying as a power law of the system size. Here we measure, by numerical simulations, several cumulants of the heat flux of a one-dimensional hard particle gas. We find that the cumulants, like the conductivity, vary as power laws of the system size. Our results also indicate that cumulants higher than the second follow different power laws when one compares the ring geometry at equilibrium and the linear case in contact with two heat baths (at equal or unequal temperatures).

We use computer simulations to study the microscopic dynamics of an athermal assembly of soft particles near the fluid-to-solid jamming transition. Borrowing tools developed to study dynamic heterogeneity near glass transitions, we discover a number of original signatures of the jamming transition at the particle scale. We observe superdiffusive, spatially heterogeneous, and collective particle motion over a characteristic scale which displays a surprising non-monotonic behavior across the transition. In the solid phase, the dynamics is an intermittent succession of elastic deformations and plastic relaxations, which are both characterized by scale-free spatial correlations and system size dependent dynamic susceptibilities. Our results show that dynamic heterogeneities in dense athermal systems and glass formers are very different, and shed light on recent experimental reports of "anomalous" dynamical behavior near the jamming transition of granular and colloidal assemblies.

We study the sensitivities of the centroid energy E0 of the isoscalar giant-monopole resonance and the centroid energy E1 of the isoscalar giant-dipole resonance to the effect of relaxation. We find that the energy ratio E1/E0 grows with the relaxation time approaching the experimental value (E1/E0)_exp=1.6±0.1.

We derive Maxwell's equations on the κ-deformed spacetime, valid up to first order in the deformation parameter, using Feynman's approach. We show that the electric-magnetic duality is a symmetry of these equations. It is also shown that the laws of electrodynamics are different for particles of equal charges, but with different masses. We show that the Poincaré angular momentum, required to maintain the usual Lorentz algebra structure, do not get any κ-dependent corrections.

The radiative damping rate and light emission pattern of electronic excitons in an infinite one-dimensional chain of atoms strongly deviates from independent atom excitations. Exciton emission in the far field is concentrated in cones centered around the chain. Long-wavelength excitons exhibit superradiance with excitation life time orders of magnitude shorter than a single atom. Short-wavelength excitons show reduced spontaneous emission depending on their polarization and beyond a critical wave number they even can get metastable with zero radiation damping rate. Such meta-stable excitations can propagate and mediate interactions over large distances or store photons in the lattice for a long time. While they cannot be directly optically excited, they can be created and read out via tailored evanescent fields from a nearby structured surface or an optical fiber.

We report an experimental investigation on the scattering of sound by the vortical wake flow created downstream a thin flat plate with a moving flap at the trailing edge. Two situations were examined: a) the free case, when the flap remained in a fixed horizontal position without external forcing and b) the harmonic forced case, when the flap is in continuous periodic motion of small amplitude. The sound scattering processes on both free- and forced-wake flows, provided a direct spectral measurement, in Fourier space, of the spatial and temporal modes of the wake as a function of the thickness-based Reynolds number.

The role of surface rheology in fundamental fluid dynamical systems, such as liquid coating flows and soap film formation, is poorly understood. We investigate the role of surface viscosity in the classical film-coating problem. We propose a theoretical model that predicts film thickening based on a purely surface-viscous theory. The theory is supported by a set of new experimental data that demonstrates slight thickening even at very high surfactant concentrations for which Marangoni effects are irrelevant. The model and experiments represent a new regime that has not been identified before.

A simple theoretical model is developed to study the properties of fullerites under varying conditions of pressure and temperature. The model is initially applied to study the compression behavior of C₇₀ and C₈₄ solids in the light of other relations as well as experimental data. The model performed in a better way as compared with the other relations. The results obtained are found to be encouraging. The model is therefore extended for the study of C₇₀ and C₈₄ solids under varying conditions of pressure and temperature. We have computed the pressure and temperature dependence of V/V₀, the coefficient of volume thermal expansion and the bulk modulus. The results are compared with the available experimental data. There is a good agreement between theory and experiment, which supports the validity of the model developed for fullerites.

We report the impact of post-deposition thermal annealing (in nitrogen ambient) on the evolution of an interfacial layer between a hydrogenated amorphous silicon nitride (a-SiN_x :H) thin film and a Si(100) substrate and its correlation with electrical properties. X-ray reflectivity measurements reveal that the SiN_x films under different post annealing temperatures demonstrate variation in the density, thickness and roughness. Also it is found that the interface state density (D_it) is directly related to the interfacial layer density of the film rather than to the surface and interface roughness.

Using large-scale molecular-dynamics simulation of a generic model, we study the mechanical behavior of thermoset/thermoplastic polymer alloys under shear. We investigate the effect of thermoplastic mass fraction Γ_l and the thermoplastic chain length N_l. Our results show two different fracture peaks in the stress-strain behavior. The first peak occurs at around 60% strain followed by a stress plateau, and the system fails at around 90% strain. This "slip-stick" fracture is independent of shear rate and only occurs when Γ_l is less than the threshold concentration Γ^* at which thermoplastic chains start to overlap. A micro-structural analysis suggests that the escape of thermoplastic chains from cavities near the fractured interfaces gives rise to slip-stick behavior. Slip-stick behavior has a strong chain length dependence and is only observed when N_l is greater than critical chain length N_l^c=40. Slip-stick fracture makes an alloy of Γ_l=4.7% more than 40% tougher than a neat thermoset.

The thermal fluctuations of the order parameter affect the transport of Bose gas above the superfluid transition. Using the time-dependent Ginzburg-Landau theory in the classical region, we calculate the fluctuation corrections to the coefficients of thermal conductivity and shear viscosity. Above the transition temperature T_c, the fluctuation contribution to the thermal conductivity diverges as (T−T_c)^-2+d/2 for dimensions d. The viscosity drops near T_c since the fluctuation contributes a correction which varies as − (T−T_c)^−2+d/2. The calculations are conducted under the condition that the fluctuation corrections are small compared with the normal part of the transport coefficients.

We add relaxation mechanisms that mimic the effect of temperature and non-equilibrium driving to the recently proposed spiral model which jams at a critical density ρ_c<1. This enables us to explore unjamming by temperature or driving at ρ_c<ρ<1. We numerically calculate the relaxation time of the persistence function and its spatial heterogeneity. We disentangle the three different relaxation mechanisms responsible for unjamming when varying density, temperature, and driving strength, respectively. We show that the spatial scale of dynamic heterogeneity depends on density much more strongly than on temperature and driving.

We perform a linear stability analysis of coherent epitaxy films on pre-strained substrates by incorporating the effect of long-range forces. We show that a proper pre-strain can increase or decrease the critical thickness and alter the fastest-growing unstable mode of the film. The result may provide a mechanism to control the morphology of the films in a mechanical way.

The surface nano-topography of the amorphous alloy Fe₇₇Ni₁Si₉B₁₃ was found to be anisotropic and fractal with the absolute values of Hurst exponent and fractal dimension close to those known for fracture surfaces of both conventional and amorphous metals. The tensile stress application causes the formation of shear bands (SBs), the highly prevailing orientation of which is normal to the stress applied. However, in very few cases, the SBs oriented at 45° to the stress direction detected. The latter SB orientation is typical for conventional (crystalline) metals where a specific dislocation mechanism determines the SBs orientation; the occurrence of 45°-oriented SBs in the amorphous alloy was attributed to the local, stress-induced extrinsic crystallization at the sample surface. In the region of heterogeneity of this kind, the scaling properties of surface relief were fully disturbed. The mechanism of the fractal roughness formation was related to the fractal geometry of thermal vibrations of walls of primary cavities during the new surface formation under critical conditions, such as that take place at fracturing or ultra high cooling.

Autophobic dewetting of a thin polystyrene (PS) layer on a cross-linked PS film has been studied with optical microscopy and neutron reflection. For two different cross-linking densities, the increase in contact angle and the fast decrease of both dewetting velocity and slippage length as a function of dewetting time indicate that the dewetting dynamics is controlled by the penetration of free linear polymer chains into the cross-linked film and the concomitant stretching of the network mesh: the loss of entropy of the network favors dewetting, while partial chain interdiffusion between the layers increases friction and eventually stabilizes the top film. In a second series of experiment, we modified the entropy of the network by swelling it with linear chains from a reservoir of identical polymers prior to depositing the top PS film. Once equilibrated, a stable interface without considerable interdiffusion between network and top film was achieved. Without such interdiffusion, a constant contact angle and a constant slippage length were observed.

Electron spin resonance microscopy (ESRM) was employed in the evaluation of diffusion characteristics of point defects (E' paramagnetic centers) in amorphous SiO₂. Samples were subjected to inhomogeneous γ-irradiation creating a heterogeneous distribution of E'-centers in SiO₂ substrates. The samples were measured by ESRM after preparation and following several heat treatment cycles. These measurements revealed pronounced changes in the distribution of the E'-centers due to the heat treatments. The defects' reorganization did not obey simple diffusion laws and they exhibited an attraction towards areas with higher initial concentration. This behavior was simulated by an empirical model, resulting in the evaluation of the defects' diffusion constant, its activation energy, and their characteristic attractive potential. This is the first time that ESR imaging is employed to directly obtain such type of fundamental information regarding the diffusion behavior and interaction of point defects.

We use three-dimensional phase-field simulations to investigate the dynamics of the two-phase composite patterns formed upon during solidification of eutectic alloys. Besides the spatially periodic lamellar and rod patterns that have been widely studied, we find that there is a large number of additional steady-state patterns which exhibit stable defects. The defect density can be so high that the pattern is completely disordered, and that the distinction between lamellar and rod patterns is blurred. As a consequence, the transition from lamellae to rods is not sharp, but extends over a finite range of compositions and exhibits strong hysteresis. Our findings are in good agreement with experiments.

We use the weak-coupling renormalization group method to examine the interplay between charge-density-wave and s-wave superconducting orders in a quasi–one-dimensional model of electrons interacting with acoustic phonons. The relative stability of both types of order is mapped out at arbitrary nesting deviations and Debye phonon frequency ω_D. We single out a power law increase of the superconducting T_c∼ω_D^0.7 from a quantum critical point of charge-density-wave order triggered by nesting alterations. The results capture the key features shown by the proximity between the two types of ordering in the phase diagram of the recently discovered Perylene-based organic superconductor under pressure. The impact of Coulomb interaction on the relative stability of the competing phases is examined and discussed in connection with the occurrence of s-wave superconductivity in low-dimensional charge-density-wave materials.

Competing interactions are often responsible for intriguing phase diagrams in correlated electron systems. Here we analyze the competition of instantaneous short-range Coulomb interaction U with the retarded electron-electron interaction induced by an electron-phonon coupling g as described by the Hubbard-Holstein model. The ground-state phase diagram of this model in the limit of large dimensions at half-filling is established. The study is based on dynamical mean-field theory combined with the numerical renormalization group. Depending on U, g, and the phonon frequency ω₀, the ground state is antiferromagnetically (AFM) or charge ordered (CO). We find quantum phase transitions from the AFM to CO state to occur when U-λ≃0, where λ characterizes the phonon-induced effective attraction. The transition is continuous for small couplings and large phonon frequencies ω₀ and becomes discontinuous for large couplings and small values of ω₀. We comment on the possible relevance of this work for Ba_{1- x}K_xBiO₃.

We report on the experimental and theoretical investigation of spin-wave tunnelling through a mechanical gap in a ferromagnetic film. Samples with different gap widths were fabricated and the transmission of spin-wave pulses through the gaps was studied. Transmission through the gaps is possible due to the long-range character of the dipole-dipole interaction underlying dynamics of long-wavelength spin waves. By comparing our experimental results with the developed theoretical model, we demonstrate, that the local inhomogeneity of the static magnetisation and the internal field has a significant impact on the transmission.

Non-monotonic dependence of anomalous Hall resistivity on temperature and magnetization, including a sign change, was observed in Fe/Gd bilayers. To understand the intriguing observations, we fabricated the Fe/Gd bilayers and single layers of Fe and Gd simultaneously. The temperature and field dependences of longitudinal resistivity, Hall resistivity and magnetization in these films have also been carefully measured. The analysis of these data reveals that these intriguing features are due to the opposite signs of Hall resistivity/or spin polarization and different Curie temperatures of Fe and Gd single-layer films.

Combining the transfer matrix method with Landauer-Büticker formalism, we study the spin-polarized transport in the current-perpendicular-to-the plane (CPP) geometry of a quasiperiodic magnetic multilayered structure consisting of a ferromagnet (FM) and a nonmagnet (NM) arranged in a Fibonacci sequence. The CPP giant magnetoresistance (GMR) in the quasiperiodic structure is found to be largely enhanced compared with that in the periodic one. It is also shown that there are the same and different properties in the variations of the relative conductivities and of the GMR with the number of bilayers between the quasiperiodic and periodic structures, implying that there exist common and different physical origins in them.

Magnetic impurities in neutral graphene provide a realization of the pseudogap Kondo model, which displays a quantum phase transition between phases with screened and unscreened impurity moment. Here, we present a detailed study of the pseudogap Kondo model with finite chemical potential μ. While carrier doping restores conventional Kondo screening at lowest energies, properties of the quantum critical fixed point turn out to influence the behavior over a large parameter range. Most importantly, the Kondo temperature T_K shows an extreme asymmetry between electron and hole doping. At criticality, depending on the sign of μ, T_K follows either the scaling prediction T_K∝|μ| with a universal prefactor, or T_K∝|μ|^x with x≈2.6. This asymmetry between electron and hole doping extends well outside the quantum critical regime and also implies a qualitative difference in the shape of the tunneling spectra for both signs of μ.

In this letter we obtain the finite-temperature structure of 180° domain walls in PbTiO₃ using a quasi-harmonic–lattice dynamics approach. We obtain the temperature dependence of the atomic structure of domain walls from 0 K up to room temperature. We also show that both Pb-centered and Ti-centered 180° domain walls are thicker at room temperature; domain wall thickness at T=300 K is about three times larger than that of T=0 K. Our calculations show that Ti-centered domain walls have a lower free energy than Pb-centered domain walls and hence are more likely to be seen at finite temperatures.

The zero-temperature Glauber dynamics of the random-field Ising model describes various ubiquitous phenomena such as avalanches, hysteresis, and related critical phenomena. Here, for a model on a random graph with a special initial condition, we derive exactly an evolution equation for an order parameter. Through a bifurcation analysis of the obtained equation, we reveal a new class of cooperative slow dynamics with the determination of critical exponents.

We report data on the Hall coefficient (R_H) of the carbon-substituted Mg(B_1−xC_x)₂ single crystals with x in the range from 0 to 0.1. The temperature dependences of R_H obtained for the substituted crystals differ systematically at low temperatures, but all of them converge to the value of 1.8×10⁻¹⁰ m³C⁻¹ at room temperature. The R_H(T) data together with results of the thermoelectric power and electrical-resistivity measurements are interpreted within a quasi-classical transport approach, where the presence of four different conducting sheets is considered. The main influence of the carbon substitution on the transport properties in the normal state is associated with enhanced scattering rates rather than modified concentration of charge carriers. Presumably the carbon substitution increases the electron-impurity scattering mainly in the π-band.

We consider the full driven quantum dynamics of a qubit realized as spin of electron in a one-dimensional double quantum dot with spin-orbit coupling. The driving perturbation is taken in the form of a single half-period pulse of electric field. Spin-orbit coupling leads to a nontrivial evolution in the spin and charge densities making the dynamics in both quantities irregular. As a result, the charge density distribution becomes strongly spin-dependent. The transition from the field-induced tunneling to the strong-coupling regime is clearly seen in the charge and spin channels. These results can be important for the understanding of the techniques for the spin manipulation in nanostructures.

We report a comparative study of the series Fe_1.1Te_1−xSe_x and the stoichiometric FeTe_1−xSe_x to bring out the difference in their magnetic, superconducting and electronic properties. The Fe_1.1Te_1−xSe_x series is found to be magnetic and its microscopic properties are elucidated through Mössbauer spectroscopy. The magnetic phase diagram of Fe_1.1Te_1−xSe_x is traced out and it shows the emergence of spin-glass state when the antiferromagnetic state is destabilized by the Se substitution. The isomer shift and quadrupolar splitting obtained from the Mössbauer spectroscopy clearly brings out the electronic differences in these two series.

We perform Brownian dynamics simulations of molecular motor-induced ordering and structure formations in semi-dilute cytoskeletal filament solutions. In contrast to the previously studied dilute case where binary filament interactions prevail, the semi-dilute regime is characterized by multiple motor-mediated interactions. Moreover, the forces and torques exerted by motors on filaments are intrinsically fluctuating quantities. We incorporate the influences of thermal and motor fluctuations into our model as additive and multiplicative noises, respectively. Numerical simulations reveal that filament bundles and vortices emerge from a disordered initial state. Subsequent analysis of motor noise effects reveals: i) Pattern formation is very robust against fluctuations in motor force; ii) bundle formation is associated with a significant reduction of the motor fluctuation contributions; iii) the time scale of vortex formation and coalescence decreases with increases in motor noise amplitude.

We propose a fluctuation analysis to quantify spatial correlations in complex networks. The approach considers the sequences of degrees along shortest paths in the networks and quantifies the fluctuations in analogy to time series. In this work, the Barabasi-Albert (BA) model, the Cayley tree at the percolation transition, a fractal network model, and examples of real-world networks are studied. While the fluctuation functions for the BA model show exponential decay, in the case of the Cayley tree and the fractal network model the fluctuation functions display a power law behavior. The fractal network model comprises long-range anticorrelations. The results suggest that the fluctuation exponent provides complementary information to the fractal dimension.

We employ parallel superposition rheology to study the dynamics of an aging colloidal glass in the presence of a mean-field stress σ_m. Over a range of intermediate stresses, the loss modulus exceeds the storage modulus at short times but develops a maximum concomitant with a crossover between the two as the system ages. This is attended by a narrowing of the loss peak on increasing stress. We show that this feature is characteristic of the structural arrest in these materials, which is made observable on reasonable timescales by the activating influence of the stress. The arrest time displays an exponential dependence on inverse stress. These results provide experimental validation of the role of stress as an effective temperature in soft glassy systems as has been advanced in recent theoretical frameworks.

We use grazing incidence X-ray scattering to study the surface micellization of charged amphiphilic diblock copolymers poly(styrene-block-acrylic acid) at the air-water interface. Scattering interference peaks are consistent with the formation of hexagonally packed micelles. The remarkable increase of inter-micelle distance upon compression is explained by a dissociation of micelles into a brush. Hence, surface micelles reorganize, whereas micelles of the same copolymers in solutions are "frozen". We show indeed that the energetic cost of unimer extraction from micelles is much lower for surface than for solution. Finally, a model combining electrostatic interactions and micelle/brush equilibrium explains surface pressure vs. area without free parameters.

We quantify random migration of the social ameba Dictyostelium discoideum. We demonstrate that the statistics of cell motion can be described by an underlying Langevin-type stochastic differential equation. An analytic expression for the velocity distribution function is derived. The separation into deterministic and stochastic parts of the movement shows that the cells undergo a damped motion with multiplicative noise. Both contributions to the dynamics display a distinct response to external physiological stimuli. The deterministic component depends on the developmental state and ambient levels of signaling substances, while the stochastic part does not.

It has recently been observed that there are no disc galaxies with masses less than 10⁹M_⊙ and this cutoff has not been explained. It is shown here that this minimum mass can be predicted using a model that assumes that 1) inertia is due to Unruh radiation, and 2) this radiation is subject to a Hubble-scale Casimir effect. The model predicts that as the acceleration of an object decreases, its inertial mass eventually decreases even faster stabilising the acceleration at a minimum value, which is close to the observed cosmic acceleration. When applied to rotating disc galaxies the same model predicts that they have a minimum rotational acceleration, i.e.: a minimum apparent mass of 1.1×10⁹M_⊙, close to the observed minimum mass. The Hubble mass can also be predicted. It is suggested that assumption 1 above could be tested using a cyclotron to accelerate particles until the Unruh radiation they see is short enough to be supplemented by manmade radiation. The increase in inertia may be detectable.