Intermittent behavior at the time scale synchronization boundary

The intermittent behavior observed at the time scale synchronization boundary of interacting random oscillators operating in time scale synchronization mode is analyzed. Analysis of statistical characteristics (distributions of laminar segment lengths and the dependence of the average laminar segment length on the supercriticality parameter) shows that the observed intermittent behavior is ring intermittency.     

Investigation of deformation instability of Au/Cu multilayers by indentation

Plastic deformation behavior of Au/Cu multilayers with individual layer thicknesses of 25–250 nm was investigated via microindentation experiments. It was found that plastic instability of the Au/Cu multilayer exhibits strong length scale (individual layer thickness and grain size) dependence. The smaller the length scale, the easier shear bands form. In other words, plastic deformation becomes unstable with decreasing length scale. Cross-sectional observation along with plan-view indicates that the occurrence of plastic deformation instability corresponds to transformation of the deformation mechanism associated with geometrical configuration and length scale of the material. At nanometer scale, buckling-assisted interface crossing of dislocations results in local shear band, while, at submicron scale or above, local dislocation pileup-induced interface offset leads to plastic instability. Theoretical analysis is conducted to understand the length scale-dependent plastic deformation behavior of the multilayer.     

Roughness evolution of highly ordered nanoporous anodic aluminum oxide films

In this paper, we report on the surface roughness evolution of highly ordered anodic aluminum oxide (AAO) films based on an atomic force microscopy (AFM) study. Root mean square of the surface roughness was measured on AFM images taken from highly ordered AAO films produced by two-step anodization under different conditions including electrolyte type, anodization voltage, and anodization time. Surface roughness of highly ordered AAO films increases step by step through the two-step anodizing process including electropolishing, first-step anodization, dissolution, and second-step anodization. However, increase of the surface roughness is proportional to the anodization voltage and time. The surface roughness of AAO films changes as a function of length scale until it finally approaches a maximum termed the saturation roughness. The variation of roughness of the growth of AAO could be scaled with an anomalous dynamic behavior as it saturates over a critical length scale while the saturation roughness is dependent on the anodizing time and voltage.     

Scaling theory and morphometrics for a coarsening multiscale surface, via a principle of maximal dissipation

We consider the coarsening dynamics of multiscale solutions to a dissipative singularly perturbed partial differential equation which models the evolution of a thermodynamically unstable crystalline surface. The late-time leading-order behavior of solutions is identified, through the asymptotic expansion of a maximal-dissipation principle, with a completely faceted surface governed by an intrinsic dynamical system. The properties of the resulting piecewise-affine dynamic surface predict the scaling law L(Mu) approximately t(1/3), for the growth in time of a characteristic morphological length scale L(Mu). A novel computational geometry tool which directly simulates a million-facet piecewise-affine dynamic surface is also introduced. Our computed data are consistent with the dynamic scaling hypothesis, and we report a variety of associated morphometric scaling functions.     

Measurement of turbulence decorrelation during transport barrier evolution in a high-temperature fusion plasma

A low power polychromatic beam of microwaves is used to diagnose the behavior of turbulent fluctuations in the core of the JT-60U tokamak during the evolution of the internal transport barrier. A continuous reduction in the size of turbulent structures is observed concomitant with the reduction of the density scale length during the evolution of the internal transport barrier. The density correlation length decreases to the order of the ion gyroradius, in contrast with the much longer scale lengths observed earlier in the discharge, while the density fluctuation level remain similar to the level before transport barrier formation.     

Time domain analysis: an alternative way to interpret PGSE experiment.

We report a theoretical development which aims at interpreting Pulsed Gradient Spin Echo data for diffusing fluids in saturated porous media. It consists in analyzing the time dependence of PGSE amplitudes for each single gradient strength, and introduces a new diffusion coefficient D(q) as being continuously dependent on the length scale in the material. Both experimental measurements on water saturated bead packings and simulated experiments in 2D and 3D model systems are interpreted with this approach. D(q) is shown to give a new insight in the micro-macro transition. Its evolution vs. the length scale is non trivial, and can be sensitive to local slow kinetic effects.     

Thickness-dependent effective surface resistances of nearly ferroelectric superconductors

The effective surface resistance of nearly ferroelectric superconducting film in the dielectriclike response is theoretically investigated based on the electrodynamics of the nearly ferroelectric superconductors. We calculate the intrinsic film surface resistance for isolated thin film and the effective surface resistance for a superconductor/dielectric layered structure. It is found that the thickness-dependent surface resistance has two different behaviors separated by a critical film thickness being equal to the London penetration length. That is, a nonresonant dependence is seen when the film thickness is less than the London penetration length, and an anomalously resonant behavior is found when the film thickness is larger than the London penetration length. The nonresonant dependence is similar to that of a cuprate superconductor and it further is characterized by some other critical thicknesses. As for the anomalous resonant region it is seen only in a nearly ferroelectric superconductor.     

Improved models of optical fiber birefringence—Part II

In this paper, we employ several general models (introduced in Part I) for the evolution of optical fiber birefringence with longitudinal distance to analyze, both theoretically and numerically, the behavior of the polarization mode dispersion (PMD) in single mode fibers. We find that while the probability distribution function of the differential group delay varies along the fiber length as in existing models, the dependence of the root mean square differential group delay (DGD) on fiber length differs noticeably from earlier predictions.     

Anomalous band formation in arrays of terahertz nanoresonators

We investigate band formation in one-dimensional periodic arrays of rectangular holes which have a nanoscale width but a length of 100 μm. These holes are tailored to work as resonators in the terahertz frequency regime. We study the evolution of the electromagnetic response with the period of the array, showing that this dependence is not monotonic due to both the oscillating behavior of the coupling between holes and its long-range character.     

The influence of size on coercive field of ultra soft magnetic materials

We report here a size dependence of the coercive field in the millimeter–centimeter range length scale of ribbon like samples prepared from ultra soft amorphous and nanocrystalline alloys. A model is proposed where surface pinned domain walls are considered having an effective stiffness constant linearly increasing with the demagnetization factor.     

Quantum relaxation after a quench in systems with boundaries

We study the time dependence of the magnetization profile, m(l)(t), of a large finite open quantum Ising chain after a quench. We observe a cyclic variation, in which starting with an exponentially decreasing period the local magnetization arrives to a quasistationary regime, which is followed by an exponentially fast reconstruction period. The nonthermal behavior observed at near-surface sites turns over to thermal behavior for bulk sites. In addition to the standard time and length scales a nonstandard time scale is identified in the reconstruction period.     

Macroscopic channel-size effect of nonequilibrium electron distributions in quantum Hall conductors

We have studied the channel-size dependence of nonequilibrium electrons excited into higher Landau levels in a quantum Hall conductor, by mapping cyclotron emission in Hall bars of different sizes. The images obtained reveal that the spatial evolution of the nonequilibrium electrons with current density significantly depends on the channel width of the Hall bar on a macroscopic scale of several hundred microms. This observation provides clear evidence of a macroscopic channel-size effect, which can be reasonably understood as originating from a very long equilibrium length of the excited electrons.     

Segmental dynamics of poly(methyl phenyl siloxane) confined to nanoporous glasses

The effect of a nanometer confinement on the molecular dynamics of poly(methyl phenyl siloxane) (PMPS) was studied by dielectric spectroscopy (DS), temperature modulated DSC (TMDSC) and neutron scattering (NS). Nanoporous glasses with pore sizes of 2.5–20 nm have been used. DS and TMDSC experiments show that for PMPS in 7.5 nm pores the molecular dynamics is faster than in the bulk which originates from an inherent length scale of the underlying molecular motions. For high temperatures the temperature dependence of the relaxation rates for confined PMPS crosses that of the bulk state. Besides finite states effects also the thermodynamic state of nano-confined PMPS is different from that of the bulk. At a pore size of 5 nm the temperature dependence of the relaxation times changes from a Vogel/Fulcher/Tammann like to an Arrhenius behavior where the activation energy depends on pore size. This is in agreement with the results obtained by NS. The increment of the specific heat capacity at the glass transition depends strongly on pore size and vanishes at a finite length scale between 3 and 5 nm which can be regarded as minimal length scale for glass transition to appear in PMPS.     

Morphology of growing interfacial patterns

A study is made of the morphology of the interfacial patterns in the solid-on-solid model evolving from initial states very far from equilibrium. Monte Carlo simulation is used to study the time dependence of the length, the diffuseness, and the width of the interface during such evolution in the absence as well as in the presence of quenched random field. Moreover, the technique of Walsh-Fourier transform is introduced for analyzing the noise level in such interfacial patterns. A quantity is also introduced that characterizes the interfacial structure locally on a very short length scale. Finally, the latter technique is also applied to the kinetic Ising model evolving from a random initial configuration.     

Temperature evolution,flame behavior and extinction inside compartment with a ceiling vent under the ambient wind

This article presents an experimental and CFD simulation investigation and analysis on temperature evolution and flame behavior inside compartment with a ceiling vent under ambient wind. Experiments were conducted employing a reduced-scale model containing a cubic fire compartment with a ceiling vent under the external wind generated by a wind tunnel. The temperature of windward and leeward inside compartment as well as the flame behavior were recorded for various vent dimensions, heat release rates and wind speeds for a total of 720 test conditions. Results show that there are two types of fire behavior regimes inside the compartment for relatively small- (Bernoulli flow regime) or large vents (oscillatory exchange flow regime). With a relatively small vent, the flame is located at the center of compartment and the temperatures of windward and leeward are almost the same with or without the ambient wind. Then the flame turns to extinct due to lack of oxygen with increasing of fuel supply. However, with a relatively large vent, there is a flame transition from windward to leeward accompanied by the transition of temperature distribution with increasing of fuel supply when subject to ambient wind. Such extinction and transition mechanisms are interpreted by the aid of CFD simulation of global equivalence ratio and flow/oxygen field inside compartment. The critical heat release rate for the occurrence of flame transition decreases with raising wind speed while increases with vent size. Their complex dependence is found to be well represented in terms of a non-dimensional heat release rate as a function of the wind Froude number, employing the vent area-equivalent characteristic diameter as length scale. These new findings facilitate the understanding of the compartment fire evolution with a ceiling vent subject to ambient wind.     

Excitation of 2D plasmons in a Cs/W(110) system

The evolution of surface photoemission spectra was investigated for a Cs/W(110) system with metastable Cs coatings larger than a monolayer. It is demonstrated that 2D plasmons can be detected by threshold photoemission spectroscopy. Three photoemission peaks were observed, whose dependence on the Cs adsorption dose showed a complicated behavior. The peaks may be due to the photoinduced excitation of a plasmon in quasi-2D Cs clusters, a surface Cs plasmon, or an interface Cs-W plasmon.     

Role of molecular architecture on the vitrification of polymer thin films

We show that thin film star-shaped macromolecules exhibit significant differences in their average vitrification behavior, in both magnitude and thickness dependence, from their linear analogs. This behavior is dictated by a combination of their functionality and arm length. Additionally, the glass transition temperature at the free surface of a star-shaped molecule film may be higher than that of the interior, in contrast to their linear analogs where the opposite is true. These findings have implications for other properties, due largely to the origins, entropic, of this behavior.     

A review of fractality and self-similarity in complex networks

We review recent findings of self-similarity in complex networks. Using the box-covering technique, it was shown that many networks present a fractal behavior, which is seemingly in contrast to their small-world property. Moreover, even non-fractal networks have been shown to present a self-similar picture under renormalization of the length scale. These results have an important effect in our understanding of the evolution and behavior of such systems. A large number of network properties can now be described through a set of simple scaling exponents, in analogy with traditional fractal theory.     

Length scales at which classical elasticity breaks down for various materials

At what characteristic length scale does classical continuum elasticity cease to accurately describe small deformation mechanical behavior? The two dominant physical mechanisms that lead to size dependency of elastic behavior at the nanoscale are surface energy effects and nonlocal interactions. The latter arises due to the discrete structure of matter and the fluctuations in the interatomic forces that are smeared out within the phenomenological elastic modulus at coarser sizes. While surface energy effects have been well characterized in the literature, little is known about the length scales at which nonlocal effects manifest for different materials. Using a combination of empirical molecular dynamics and lattice dynamics (empirical and ab initio), we provide estimates of nonlocal elasticity length scales for various classes of materials: semiconductors, metals, amorphous solids, and polymers.