Nucleation of magnetic bubble domains in iron garnet films by means of an electric probe

The possibility of the local nucleation of magnetic bubble domains from a single-domain state in an arbitrary region of a iron garnet film ((210) crystallographic orientation) by means of an electrically charged tip electrode has been experimentally demonstrated. The size of magnetic bubble domains nucleated near the contact point between the probe and sample depends on the magnitude of a DC voltage supplied to the probe. After the removal of the voltage, magnetic bubble domains move away from the probe, decreasing to the equilibrium radius.     

Crossover dynamics in bond disordered lattices

The asymptotic dynamics of the percolation model for a bond disordered lattice is studied. The velocity autocorrelation function (VACF) is investigated for arbitrary concentration of disorder in two and three dimensions using an effective medium approximation (EMA). Corrections to the long time tails away from the percolation threshold and to the percolation tails at the threshold are calculated. A characteristic time scale for the long time tails is identified and found to diverge at the threshold. Sufficiently close to the threshold the two types of asymptotic dynamics can be identified clearly for times greater than and less than this characteristic time, respectively. An approximate scaling of the EMA equation is obtained near the threshold for investigation of the crossover region. More generally, the EMA equation is solved numerically for arbitrary concentration in two dimensions to exhibit the complete time dependence of the VACF in all domains near and far from the threshold.     

On Scaling in Relation to Singular Spectra

This paper relates uniform α-H?lder continuity, or $\alpha$-dimensionality, of spectral measures in an arbitrary interval to the Fourier transform of the measure. This is used to show that scaling exponents of exponential sums obtained from time series give local upper bounds on the degree of H?lder continuity of the power spectrum of the series. The results have applications to generalized random walk, numerical detection of singular continuous spectra and to the energy growth in driven oscillators. Received: 3 July 1996 / Accepted: 11 September 1996     

GENERALIZED SCALING LAWS IN THRESHOLD PKENOMENA OF NON-EQUILIBRIUM SYSTEMS

A general discussion on threshold phenomena, namely exponent behaviors of abrupt transitions between steady states near a threshold for a non-equilibrium system satisfying potential condition and having the arbitrary values of z and c, both characteristic parameters of the system, is given. It is shown that the scaling hypothesis in general homogeneous function form holds for threshold phenomena. The expressions of the threshold exponents,β,δ,γ^′ and α^′of the threshold amplitudes, B, D, Γ^′ and A^′,and the generalized scaling laws obeyed by them are all obtained. These Iaws reduce to the same as the scaling laws in critical phenomena when z=c=1.The results support, in respect of exponent behaviors of transitions, the statement on the great similarity between the phase transitions in equilibrium systems and the abrupt transitions of steady states in non-equilibrium systems.     

Diffusion in a metallic melt at the critical temperature of mode coupling theory

According to mode coupling theory, liquidlike motion becomes frozen at a critical temperature T(c) well above the caloric glass transition temperature T(g). Here, for the first time, we report on radiotracer diffusion in a supercooled Pd43Cu27Ni10P20 alloy from T(g) to the equilibrium melt. Liquidlike motion is seen to set in exactly above T(c) as evidenced by a gradual drop of the effective activation energy. This strongly supports the mode coupling scenario. Isotope effect measurements, which have never been carried out near T(c) in any material, show atomic transport up to the equilibrium melt to be far away from the hydrodynamic regime of uncorrelated binary collisions.     

Point-contact tunneling spectroscopy between a Nb tip and an ideal topological insulator Sn-doped Bi_(1.1)Sb_(0.9)Te_2S

The lightly Sn-doped Bi_(1.1)Sb_(0.9)Te_2S is a good material to investigate the pure topological surface state because the bulk bands are far away from the Fermi level. By measuring point-contact tunneling spectra on the topological insulator Bi_(1.08)Sn_(0.02)Sb_(0.9)Te_2S samples with a superconducting Nb tip, we observed the suppression of differential conductance near zero bias, instead of the enhancement due to Andreev reflection on the spectra. The fitting to the measured spectrum results in a superconducting gap of more than 4 meV, and this value is much larger than the superconducting gap of the bulk Nb. The gaped feature exists at temperatures even above the critical temperature of bulk Nb, and is visible when the magnetic field is as large as 9 T at 3 K. We argue that such behaviors may be related to the pressure induced superconductivity by the tip in the junction area, or just some novel phenomena arising from the junction between an s-wave superconductor and an ideal topological insulator.     

Thermal and non-thermal fluctuations in active polar gels

We discuss general features of noise and fluctuations in active polar gels close to and away from equilibrium. We use the single-component hydrodynamic theory of active polar gels built by Kruse and coworkers to describe the cytoskeleton in cells. Close to equilibrium, we calculate the response function of the gel to external fields and introduce Langevin forces in the constitutive equations with correlation functions respecting the fluctuation-dissipation theorem. We then discuss the breakage of the fluctuation-dissipation theorem due to an external field such as the activity of the motors. Active gels away from equilibrium are considered at the scaling level. As an example of application of the theory, we calculate the density correlation function (the dynamic structure factor) of a compressible active polar gel and discuss possible instabilities.     

Grain-boundary grooving and agglomeration of alloy thin films with a slow-diffusing species

We present a general phase-field model for grain-boundary grooving and agglomeration of polycrystalline alloy thin films. In particular, we study the effects of slow-diffusing species on the grooving rate. As the groove grows, the slow species becomes concentrated near the groove tip so that further grooving is limited by the rate at which it diffuses away from the tip. At early times the dominant diffusion path is along the boundary, while at late times it is parallel to the substrate. This change in path strongly affects the time dependence of grain-boundary grooving and increases the time to agglomeration. The present model provides a tool for agglomeration-resistant thin film alloy design.     

Subdiffraction‐limited chemical imaging of patterned phthalocyanine films using tip‐enhanced near‐field optical microscopy

A tip‐enhanced near‐field optical microscope, based on a shear‐force atomic force microscope with plasmonic tip coupled to an inverted, confocal optical microscope, has been constructed for nanoscale chemical (Raman) imaging of surfaces. The design and validation of the instrument, along with its application to near‐field Raman mapping of patterned organic thin films (coumarin‐6 and Cu(II) phthalocyanine), are described. Lateral resolution of the instrument is estimated at 50 nm (better than λ/10), which is roughly dictated by the size of the plasmonic tip apex. Additional observations, such as the distance scaling of Raman enhancement and the inelastic scattering background generated by the plasmonic tip, are presented. Copyright © 2016 John Wiley & Sons, Ltd.     

n:m phase synchronization with mutual coupling phase signals

We generalize the n:m phase synchronization between two chaotic oscillators by mutual coupling phase signals. To characterize this phenomenon, we use two coupled oscillators to demonstrate their phase synchronization with amplitudes practically noncorrelated. We take the 1:1 phase synchronization as an example to show the properties of mean frequencies, mean phase difference, and Lyapunov exponents at various values of coupling strength. The phase difference increases with 2pi phase slips below the transition. The scaling rules of the slip near and away from the transition are studied. Furthermore, we demonstrate the transition to a variety of n:m phase synchronizations and analyze the corresponding coupling dynamics. (c) 2002 American Institute of Physics.     

Phase transitions in experimental systems

Scaling functions of the support and of the measure have been used to characterize the scaling behavior of a dynamical system. While scaling functions for the scaling of the measure, ƒ(), have been calculated for a number of experimental systems, examples of scaling functions φ(λ) for the scaling of the support are difficult to obtain. In this contribution, we report on a phase-transition-like effect of an experimental p-doped germanium semiconductor sample. It is found that the results obtained from the dynamical scaling function agree with those obtained by Horita et al. from model maps, indicating that scaling functions for the scaling of the support are a powerful method of characterizing experimental dynamical systems.     

Global aspects of turbulence induced by heteroclinic cycles in competitive diffusion Lotka-Volterra equation

This paper presents detailed numerical results of the competitive diffusion Lotka-Volterra equation (May-Leonard type). First, we derive the global phase diagrams of attractors in the parameter space including the system size, where transition lines between simple attractors are clearly obtained in accordance with the results of linear stability analysis, but the transition borders become complex when multi-basin structures appear. The complex aspects of the transition borders are studied in the case when the system size decreases. Next, we show the statistical aspects of the turbulence with special attention to the onset of the supercritical Hopf bifurcation. Several characteristic quantities, such as correlation length, correlation time, Lyapunov spectra and Lyapunov dimension, are investigated in detail near the onset of turbulence. Our data show the critical scaling law near the onset only in the restricted parameter domain. However even when the critical indices are not determined accurately, it is shown that the empirical scaling relations are obtained in a wide parameter domain far from the onset point and those scaling indices satisfy several relations. These scaling relations are discussed in comparison with the result derived by the phase reduction method. Lastly, we make a conjecture about the stability of an ecosystem based on the bifurcation diagram: the ecosystem obeying the Lotka-Volterra equation in the case of May-Leonard type is stabilized more as the system size increases.     

Differentiability at the Tip of Arnold Tongues for Diophantine Rotations: Numerical Studies and Renormalization Group Explanations

We study numerically the regularity of Arnold tongues corresponding to Diophantine rotation numbers of circle maps at the edge of validity of KAM theorem. This serves as a good test for the numerical stability of two different algorithms. We find empirically that Arnold tongues are only finitely differentiable at the tip. We also find several scaling properties of the Sobolev norms of the conjugacy near the breakdown. We also provide a renormalization group explanation of the regularity at the tip and the scaling behaviors of the Sobolev regularity. We also uncover empirically some other patterns which require explanation.     

Taylor expansions in Hartree-Fock and isoscalar nuclear shifts

We consider changes in the bulk properties of a nucleus when a particle is added to an even system. The main thing we show is that one can determine these changes by doing a Hartree-Fock calculation on the even system only. We must, however, also examine what happens away from equilibrium, or at least get derivates at equilibrium, in the even system. We get expressions for E0 isoscalar effective charges which involve, but do not determine, the nuclear compressibility, likewise expressions for E2 effective charges which involve but do not determine the quadrupolarizability. Illustrative examples using simple interactions are presented. E0 effective charge corrections in a major shell are larger by roughly a factor of two in orbits with high radial quantum number and E2 effective charge corrections are near unity. Finally, we consider simultaneous changes in the radial and quadrupole shapes.     

Momentum dependence of charge excitations in the electron-doped superconductor Nd1.85 Ce0.15 CuO4: a resonant inelastic x-ray scattering study

We report a resonant inelastic x-ray scattering (RIXS) study of charge excitations in the electron-doped high-T(c) superconductor Nd1.85 Ce0.15 CuO4. The intraband and interband excitations across the Fermi energy are separated for the first time by tuning the experimental conditions properly to measure charge excitations at low energy. A dispersion relation with q-dependent width emerges clearly in the intraband excitation, while the intensity of the interband excitation is concentrated around 2 eV near the zone center. The experimental results are consistent with theoretical calculation of the RIXS spectra based on the Hubbard model.     

Studies on convergence and scaling law of Thomson backscattering spectra in strong fields

With the saddle point analysis method for the Bessel function structure and property, the convergence problem and the scaling laws of Thomson backscattering spectra are solved and studied in both cases that are for the plane wave laser field without and with applied external constant magnetic field. Some unclear points appeared in previous work are clarified. The extension of the method to a general situation for the laser field with an arbitrary polarization is discussed. We also make a simple analysis and discussion about the optimal spectra dependence of field parameters and its implication to practical applications.     

Transient response in flexure to general uni-directional loads of variable cross-section beam with concentrated tip inertias immersed in a fluid

This paper presents a method for solving problems of transient response in flexure due to general unidirectional dynamic loads of beams of variable cross section with tip inertias. An elastodynamic theory which includes effects of continuous mass and rigidity of the beam has been applied. In the analysis the general dynamic load is expanded into a Fourier series and the beam is divided into many small uniform thickness segments. The equation of motion of each segment is mapped onto the complex domain by use of the Laplace transform method. The solutions of each set of adjoining segments are related to each other at the boundaries by the use of the transfer matrix method. The displacement, the bending slope, the bending moment and the shearing force at each boundary and at arbitrary time are obtained from the Laplace transform inversion integral by using the residue theorem. The theoretical results given in this paper are applicable to problems of dynamic response due to arbitrary loads varying with time of beams of arbitrary shape with concentrated tip inertias. As applications of the present theoretical results, numerical calculations have been carried out for two cases: a uniform beam with a tip inertia and a non-uniform beam (a truncated cone) with a tip inertia. Both are immersed in a fluid and subjected to large waves such as cnoidal waves.     

Phonon spectrum and related thermodynamic properties of microcrack in bcc-Fe

The phonon spectrum and the related thermodynamic properties of microcracks in bcc-Fe are studied with the recursion method by using the Finnis--Sinclair (F--S) N-body potential. The initial configuration of the microcracks is established from an anisotropic linear elastic solution and relaxed to an equilibrium by molecular dynamics method. It is shown that the local vibrational density of states of the atoms near a crack tip is considerably different from the bulk phonon spectrum, which is closely associated with the local stress field around the crack tip; meanwhile, the local vibrational energies of atoms near the crack tip are higher than those of atoms in a perfect crystal. These results imply that the crack tip zone is in a complex stress state and closely related to the structure evolution of cracks. It is also found that the phonon excitation is a kind of local effect induced by microcracks. In addition, the microcrack system has a higher vibrational entropy, which reflects the character of phonon spectrum related to the stress field induced by cracks.     

Short-time behavior of the kinetic spherical model with long-ranged interactions

The kinetic spherical model with long-ranged interactions and an arbitrary initial order m₀ quenched from a very high temperature to T is solved. In the short-time regime, the bulk order increases with a power law in both the critical and phase-ordering dynamics. To the latter dynamics, a power law for the relative order is found in the intermediate time-regime. The short-time scaling relations of small m₀ are generalized to an arbitrary m₀ and all the time larger than . The characteristic functions for the scaling of m₀ and for are obtained. The crossover between scaling regimes is discussed in detail. Received 17 September 1999     

Attachment structure of a non-premixed laminar methane flame

The stoichiometry and the flame structure of the leading edge, an anchor point, of a non-premixed methane flame were investigated. Local equivalence ratio at an anchor point was measured using local chemiluminescence spectra with a high spatial resolution of 17 × 450 μm. Spatially and spectrally resolved chemiluminescence measurements were carried out along the centerline and radius of the non-premixed laminar flame. The chemiluminescence spectra measured at the flame tip contained very strong luminous spectra, while these continuous background spectra disappeared at the blue flame tip region. The chemiluminescence spectra below the blue flame region were very similar to those measured in laminar premixed methane/air flames. Based on these results, the local equivalence ratio near the anchor point was calculated. Therefore, we measure the anchor point location, its shape, and stoichiometry using the flame spectra. At the anchor point, there was an island of lower equivalence ratio of 0.65, which can be estimated as the lower flammable limit of premixed laminar flame. The size of the anchor point was of horizontal elliptical shape less than 0.6 and 0.4 mm in vertical length, which located at 1.2 mm above the burner rim and inside of the rim.