Symmetric Fluctuations Research Articles

Semi-compact skyrmion-like structures

We study three distinct types of planar, spherically symmetric and localized structures, one of them having non-topological behavior and the two others being of topological nature. The non-topological structures have energy density localized in a compact region in the plane, but are unstable against spherically symmetric fluctuations. The topological structures are stable and behave as vortices and skyrmions at larger distances, but they engender interesting compact behavior as one approaches their inner cores. They are semi-compact skyrmion-like spin textures generated from models that allow to control the internal behavior of such topological structures.

Resting-state hemodynamics are spatiotemporally coupled to synchronized and symmetric neural activity in excitatory neurons

Brain hemodynamics serve as a proxy for neural activity in a range of noninvasive neuroimaging techniques including functional magnetic resonance imaging (fMRI). In resting-state fMRI, hemodynamic fluctuations have been found to exhibit patterns of bilateral synchrony, with correlated regions inferred to have functional connectivity. However, the relationship between resting-state hemodynamics and underlying neural activity has not been well established, making the neural underpinnings of functional connectivity networks unclear. In this study, neural activity and hemodynamics were recorded simultaneously over the bilateral cortex of awake and anesthetized Thy1-GCaMP mice using wide-field optical mapping. Neural activity was visualized via selective expression of the calcium-sensitive fluorophore GCaMP in layer 2/3 and 5 excitatory neurons. Characteristic patterns of resting-state hemodynamics were accompanied by more rapidly changing bilateral patterns of resting-state neural activity. Spatiotemporal hemodynamics could be modeled by convolving this neural activity with hemodynamic response functions derived through both deconvolution and gamma-variate fitting. Simultaneous imaging and electrophysiology confirmed that Thy1-GCaMP signals are well-predicted by multiunit activity. Neurovascular coupling between resting-state neural activity and hemodynamics was robust and fast in awake animals, whereas coupling in urethane-anesthetized animals was slower, and in some cases included lower-frequency (<0.04 Hz) hemodynamic fluctuations that were not well-predicted by local Thy1-GCaMP recordings. These results support that resting-state hemodynamics in the awake and anesthetized brain are coupled to underlying patterns of excitatory neural activity. The patterns of bilaterally-symmetric spontaneous neural activity revealed by wide-field Thy1-GCaMP imaging may depict the neural foundation of functional connectivity networks detected in resting-state fMRI.

The Asymmetric Cyclical Behavior of the U.S. Labor Market

The U.S. employment rate fluctuates asymmetrically over the business cycle: it contracts deeply and sharply during recessions, but it recovers slowly and gradually during expansions. By contrast, output features nearly symmetric fluctuations. I explain these facts using a search-and-matching model with worker heterogeneity in skills. The model identifies endogenous job separation and cyclical fluctuations in the composition of the unemployment pool as key driving forces of the asymmetric cyclical behavior of the U.S. labor market and output.

Theoretical investigation on the magnetocaloric effect in amorphous [formula omitted] system

In this work, we investigated the magnetic and magnetocaloric properties of the amorphous system Eu80Au20. The magnetic state equation and entropy were considered in the framework of Handrich–Kaneyoshi model, which takes into account the amorphization through the symmetric exchange fluctuation in the mean field approximation. The exchange and structural fluctuations parameters were chosen based on the experimental data of Eu80Au20. The isothermal entropy change was calculated for several variations of external magnetic field. Furthermore, the adiabatic temperature change and the refrigerant capacity were calculated for a magnetic field change from 0 to 5T.

Role of the aperture in Z-scan experiments: A parametric study

In close-aperture Z-scan experiments, a small aperture is conventionally located in the far-field thereby enabling the detection of slight changes in the laser beam profile due to the Kerr-lensing effect. In this work, by numerically solving the Fresnel–Kirchhoff diffraction integrals, the amount of transmitted power through apertures has been evaluated and a parametric study on the role of the various parameters that can influence this transmitted power has been done. In order to perform a comprehensive analysis, we have used a nonlinear phase shift optimized for nonlocal nonlinear media in our calculations. Our results show that apertures will result in the formation of symmetrical fluctuations on the wings of Z-scan transmittance curves. It is further shown that the appearance of these fluctuations can be ascribed to the natural diffraction of the Gaussian beam as it propagates up to the aperture plane. Our calculations reveal that the nonlocal parameter variations can shift the position of fluctuations along the optical axis, whereas their magnitude depends on the largeness of the induced nonlinear phase shift. It is concluded that since the mentioned fluctuations are produced by the natural diffraction of the Gaussian beam itself, one must take care not to mistakenly interpret them as noise and should not expect to eliminate them from experimental Z-scan transmittance curves by using apertures with different sizes.

Statistical work-energy theorems in deterministic dynamics

We theoretically explore the Bochkov-Kuzovlev-Jarzynski-Crooks work theorems in a finite system subject to external control, which is coupled to a heat reservoir. We first elaborate the mechanical energy-balance between the system and the surrounding reservoir and proceed to formulate the statistical counterpart under the general nonequilibrium conditions. Consequently, a consistency condition is derived, underpinning the nonequilibrium equalities, both in the framework of the system-centric and nonautonomous Hamiltonian pictures and its utility is examined in a few examples. Also, we elucidate that the symmetric fluctuation associated with forward and backward manipulation of the nonequilibrium work is contingent on time-reversal invariance of the underlying mesoscopic dynamics.

Effect of fluctuations on time-averaged multi-line NO-LIF thermometry measurements of the gas-phase temperature

Multi-line NO laser-induced fluorescence (LIF) thermometry enables accurate gas-phase temperature imaging in combustion systems through least-squares fitting of excitation spectra. The required excitation wavelength scan takes several minutes which systematic biases the results in case of temperature fluctuations. In this work, the effect of various types (linear, Gaussian and bimodal) and amplitudes of temperature fluctuations is quantified based on simulated NO-LIF excitation spectra. Temperature fluctuations of less than ±5 % result in a negligible error of less than ±1 % in temperature for all cases. Bimodal temperature distributions have the largest effect on the determined temperature. Symmetric temperature fluctuations around 900 K have a negligible effect. At lower mean temperatures, fluctuations cause a positive bias leading to over-predicted mean temperatures, while at higher temperatures the bias is negative. The results of the theoretical analysis were applied as a guide for interpreting experimental multi-line NO-LIF temperature measurements in a mildly turbulent pilot-plant scale flame reactor dedicated for nanoparticle synthesis.

Generation of Alfvénic waves and turbulence in reconnection jets

AbstractThe magnetohydrodynamic linear stability with the localized bulk flow oriented parallel to the neutral sheet is investigated, by including the Hall effect and the guide magnetic field. We observe three different unstable modes: a “streaming tearing” mode at a slow flow speed, a “streaming sausage” mode at a medium flow speed, and a “streaming kink” mode at a fast flow speed. The streaming tearing and sausage modes have a standard tearing mode‐like structure with symmetric density fluctuations in the neutral sheet, while the kink mode has an asymmetric fluctuation. The growth rate of the streaming tearing mode decreases with increasing magnetic Reynolds number, while the growth rates of the sausage and kink modes do not depend strongly on the Reynolds number. The sausage and kink modes can be unstable for not only super‐Alfvénic flow but also sub‐Alfvénic flow when the lobe density is low. The wavelengths of these unstable modes are of the same order of magnitude as the thickness of the plasma sheet. Their maximum growth rates are higher than that of a standard tearing mode, and under a strong guide magnetic field, the growth rates of the sausage and kink modes are enhanced, while under a weak guide magnetic field, they are suppressed. For a thin plasma sheet with the Hall effect, the fluctuations of the streaming modes can exist over the plasma sheet. These unstable modes may be regarded as being one of the processes generating Alfvénic turbulence in the plasma sheet during magnetic reconnection.

Facilitated transport and efficiency optimization in a cross-correlated noise ratchet

We study the energetic efficiency of a Brownian particle moving in a spatially symmetric potential with temporally symmetric unbiased fluctuations, which is driven by cross-correlated multiplicative and additive noise. The analytical expressions of the current and efficiency at the quasi-steady state limit are presented. Based on the current and efficiency, it is found that: (i) there exists an optimal value of the temperatures and driving force, at which the current takes its maximum, which means that these parameters can facilitate the transport of Brownian particles; (ii) the efficiency shows a resonant-like phenomenon as a function of the temperatures, the load and the driving force, which implies that these parameters can induce optimized efficiency of energy transformation at finite values; and (iii) the efficiency optimization increases with the increase of the cross-correlation between two noises, i.e. the cross-correlation between two noises can enhance the efficiency optimization.

A New Proposed Return Guide Vane for Compact Multistage Centrifugal Pumps

For widely used multistage centrifugal pumps, their former structures are so bulky that nowadays growing interest has been shifted to the development of more compact structures. Following this trend, a compact pump structure is provided and analysed. To maintain the pump’s pressure recovery, as well as to meet the water flow from the impeller, a circumferential twisted return guide vane (RGV) is proposed. To validate this design method, the instantaneous CFD simulations are performed to investigate the rotor-stator interventions. Within the impeller, the pressure fluctuation is cyclic symmetry, where the impeller frequency dominates. At the zone where flow leaves impeller for RGV, the pressure fluctuation is nonperiodic, the impeller frequency is major, and the rotation frequency is secondary. Within RGV, the periodic symmetric fluctuation is recovered, where the rotation frequency is governing. The fluctuation decreases from seven cycles within impeller to two cycles within RGV, indicating that the flow from impeller is well handled by RGV. To examine the pump’s performance, a prototype multistage pump is designed. The testing shows that the pump efficiency is 57.5%, and the stage head is 9 m, which is comparable to former multistage centrifugal pumps. And this design is more advantageous in developing compact multistage centrifugal pumps.

Transport coefficients ofO(N)scalar field theories close to the critical point

We investigate the critical dynamics of $O(N)$-symmetric scalar field theories to determine the critical exponents of transport coefficients as a second-order phase transition is approached from the symmetric phase. A set of stochastic equations of motion for the slow modes is formulated, and the long-wavelength dynamics is examined for an arbitrary number of field components $N$ in the framework of the dynamical renormalization group within the $\ensuremath{\epsilon}$ expansion. We find that for a single component scalar field theory, $N=1$, the system reduces to the model C of critical dynamics, whereas for $N&gt;1$, the model G is effectively restored owing to dominance of $O(N)$-symmetric charge fluctuations. In both cases, the shear viscosity remains finite in the critical region. On the other hand, we find that the bulk viscosity diverges as the correlation length squared, for $N=1$, while it remains finite for $N&gt;1$.

Negro and Danube are mirror rivers

We study the European river Danube and the South American river Negro daily water levels. We present a fit for the Negro daily water level period and standard deviation. Unexpectedly, we discover that the river Negro and Danube are mirror rivers in the sense that the daily water levels fluctuations histograms are close to the universal non-parametric BHP and reversed BHP, respectively. Hence, the probability of a certain positive fluctuation range in the river Negro is, approximately, equal to the probability of the corresponding symmetric negative fluctuation range in the river Danube.

Nonequilibrium fluctuations in micro-MHD effects on electrodeposition

In copper electrodeposition under a magnetic field parallel to electrode surface, different roles of two kinds of nonequilibrium fluctuations for micro-magnetohydrodynamic (MHD) effects are discussed; symmetrical fluctuations are accompanied by the suppression of three dimensional (3D) nucleation by micro-MHD flows (the 1st micro-MHD effect), whereas asymmetrical fluctuations controlling 2D nucleation yield secondary nodules by larger micro-MHD flows (the 2nd micro-MHD effect). Though the 3D nucleation with symmetrical fluctuations is always suppressed by the micro-MHD flows, due to the change in the rate-determining step from electron transfer to mass transfer, the 2D nucleation with asymmetrical fluctuations newly turns unstable, generating larger micro-MHD flows. As a result, round semi-spherical deposits, i.e., secondary nodules are yielded. Using computer simulation, the mechanism of the 2nd micro-MHD effect is validated.

Spatial Fluctuations Affect the Dynamics of Motor Proteins

Motor proteins are active biological molecules that perform their functions by converting chemical energy into mechanical work. They move unidirectionally along rigid protein filaments or DNA and RNA molecules in discrete steps by hydrolyzing ATP (adenosine triphsophate) or related energy-rich compounds. Recent single-molecule experiments have shown that motor proteins experience significant spatial fluctuations during its motion, leading to broad step-size distributions. The effect of these spatial fluctuations is analyzed explicitly by considering discrete-state stochastic models that allow us to compute exactly all dynamic properties. It is shown that for symmetric spatial fluctuations there is no change in mean velocities for weak external forces, while dispersions and stall forces are strongly affected at all conditions. These results are illustrated by several simple examples. Our method is also applied to analyze the effect of step-size fluctuations on dynamics of myosin V motor proteins. It is argued that spatial fluctuations might be used to control and regulate the dynamics of motor proteins.

Soliton spin excitations and their perturbation in a generalized inhomogeneous Heisenberg ferromagnet

We investigate the nonlinear spin dynamics of a generalized inhomogeneous anisotropic Heisenberg ferromagnetic spin chain with bilinear and biquadratic exchange, octupole-dipole, and weak interactions in the semiclassical limit by using Glauber's coherent state method in combination with Holstein-Primakoff bosonic representation of spin operators. The dynamics is found to be governed by a generalized nonlinear Schroedinger equation in the continuum limit. We have identified several completely integrable spin models with soliton spin excitations for specific parametric choices. Finally, we carry out a multiple scale perturbation analysis to find the effect of discreteness and inhomogeneity on the soliton excitations in a more general case. The results show that the discreteness effect introduces symmetric fluctuations in the localized region of the soliton without altering its amplitude and velocity. On the other hand, the inhomogeneity introduces asymmetric fluctuations in the localized region with a decrease in the amplitude and velocity of the soliton with time. Further, the inhomogeneity reverses the velocity of the soliton after some time.

銅の電気めっきにおける磁場効果－スルーホールめっきへの応用－

In a magnetic field, an electrochemical reaction generates a macroscopic solution flow called MHD flow by the Lorentz force, which enhances mass transfer in the diffusion layer (MHD effect). In electroplating, the MHD effect comes from two-dimensional (2D) nucleation in an electrical double layer accompanied by the unstable growth of non-equilibrium fluctuations (called asymmetrical fluctuations). Electroplating under a magnetic field provides the other magnetic field effect called the micro-MHD effect, which emerges with micro-MHD flow and symmetrical non-equilibrium fluctuations in a diffusion layer, and suppresses three-dimensional (3D) nucleation. That is to say, the MHD effect acts as a positive catalyst, whereas the micro-MHD effect is employed as a negative catalyst, or inhibitor. Furthermore, owing to the strong penetration of the magnetic field into the materials, micro-MHD flows are effectively induced even in the inside of a complicated minute structure. Therefore, by controlling the magnetic field, we can expect high quality plating in the through-hole plating. In this paper, along with its application to through-hole plating, copper magneto-electroplating is examined from various aspects.

Quantum horizon fluctuations of an evaporating black hole

The quantum fluctuations of a black hole spacetime are studied within a low-energy effective field theory approach to quantum gravity. Our approach accounts for both intrinsic metric fluctuations and those induced by matter fields interacting with the gravitational field. Here we will concentrate on spherically symmetric fluctuations of the black hole horizon. Our results suggest that for a sufficiently massive evaporating black hole, fluctuations can accumulate over time and become significant well before reaching Planckian scales. In addition, we provide the sketch of a proof that the symmetrized two-point function of the stress-tensor operator smeared over a null hypersurface is actually divergent and discuss the implications for the analysis of horizon fluctuations. Finally, a natural way to probe quantum metric fluctuations near the horizon is briefly described.

Photon echo spectroscopy of porphyrins and heme proteins: Effects of quasidegenerate electronic structure on the peak shift decay

Three pulse photon echo peak shift spectroscopy and transient grating measurements on Zn-substituted cytochrome c, Zn-tetraphenylporphyrin, and Zn-protoporphyrin IX are reported. The effects of protein conformation, axial ligation, and solvent are investigated. Numerical simulations of the peak shift and transient grating experiments are presented. The simulations employed recently derived optical response functions for square-symmetric molecules with doubly degenerate excited states. Simulations exploring the effects of excited-state energy splitting, symmetric and asymmetric fluctuations, and excited-state lifetime show that the time scales of the peak shift decay in the three-level system largely reflect the same dynamics as in the two-level system. However, the asymptotic peak shift, which is a clear indicator of inhomogeneous broadening in a two-level system, must be interpreted more carefully for three-level systems, as it is also influenced by the magnitude of the excited-state splitting. The calculated signals qualitatively reproduce the data.

Method for measuring radial impurity emission profiles using correlations of line integrated signals

A method of determining radial impurity emission profiles is outlined. The method uses correlations between line integrated signals and is based on the assumption of cylindrically symmetric fluctuations. Measurements at the reversed field pinch EXTRAP T2R show that emission from impurities expected to be close to the edge is clearly different in raw as well as analyzed data to impurities expected to be more central. Best fitting of experimental data to simulated correlation coefficients yields emission profiles that are remarkably close to emission profiles determined using more conventional techniques. The radial extension of the fluctuations is small enough for the method to be used and bandpass filtered signals indicate that fluctuations below 10kHz are cylindrically symmetric. The novel method is not sensitive to vessel window attenuation or wall reflections and can therefore complement the standard methods in the impurity emission reconstruction procedure.

Self-Organization Process of Secondary Crystal Nodules from Individual Nuclei in Electrodeposition

Using nonequilibrium fluctuations in electrodeposition, the self-organization process of secondary crystal nodules from individual nuclei was examined. As a result, it was concluded that electrodeposition can be described by two types of fluctuation, i.e., symmetrical and asymmetrical fluctuations; the former yields three-dimensional (3D) nuclei, whereas the latter yields two-dimensional (2D) nuclei that determine the spatial distribution of the 3D nuclei. The complex self-organization of these two types of nuclei leads to the aggregation of each 3D nucleus. In the present paper, first, the instability of these fluctuations was discussed. Then, it was shown that asymmetrical fluctuations control the total reaction rate, and lead to nucleation currents in silver nucleation. Finally, the crystal morphology yielded by the symmetrical and asymmetrical fluctuations was visualized by computer calculation, and the aggregation process of 3D nuclei to secondary nodules was examined.