Longitudinal Excitation Research Articles

Assessment and mitigation on near-fault earthquake wave effects on seismic responses and pile-soil interactions of soil-pile-bridge model

A 1/70-scale soil-pile-bridge model was designed and constructed according to an extremely long-span cable-stayed bridge with a 1400 m-main span. Shaking table tests were performed to estimate the effects of the near-fault earthquake waves on the seismic responses and pile-soil interactions of the bridge model under near-fault and far-field earthquake waves in the longitudinal direction. A three-dimensional analytical model was established to represent the test results and track the response variations resulting from the near-fault earthquake waves. Finally, both control strategies were numerically studied to decrease the effects of the near-fault earthquake waves on the seismic responses of the bridge model. The results showed that the longitudinal near-fault earthquake excitation significantly increased the acceleration and displacement of the towers and girder, and augmented the curvature and strain at the bottom of the towers as compared to the far-field earthquake excitation, resulting in the bridge model suffering from more severe damage. The near-fault earthquake excitation considerably amplified the pile-soil interaction effects on the seismic responses of the towers and piers. Additionally, the analytical model could approximately represent the test results and reliably take the response variations induced by the near-fault earthquake waves. The elastic cables and supporting piers control strategies could effectively mitigate the effects of the near-fault earthquake waves on the seismic responses the bridge model except for the longitudinal acceleration and vertical displacement of the girder, preventing the towers from experiencing more significant damage.

Total Moment Sum Rule for Magnets in the Vicinity of Quantum Critical Point

It is known that the longitudinal and transverse excitation modes can exist in the vicinity of a quantum critical point in the ordered phase of quantum magnetic systems. The total moment sum rule for such systems is derived on the basis of the extended spin-wave theory, where both longitudinal and transverse magnetic excitations are taken into account. The sum rule is resolved into elastic, one-magnon, and two-magnon components. The formulation is applicable to spin systems with the longitudinal mode, such as $S=1$ systems with single-ion anisotropy of easy-plane type and spin dimer systems. The result helps us analyze and understand measured data of inelastic neutron scattering.

Experimental study on the effect of centrally positioned vertical baffles on sloshing noise in a rectangular tank

Liquid sloshing in fuel tanks has become a major source of noise in hybrid vehicles under various driving conditions. Flow dampening devices like baffles proved to be a good solution to control sloshing induced loads on the tank walls. But their effect on sloshing noise is yet to be understood clearly. This study provides insights into generation mechanisms of sloshing noise in a rectangular tank, in the presence of vertical baffles, in different sloshing regimes. Three types of vertical baffle configurations, placed at the center of the tank are considered for this study, which are immersed bottom-mounted, flush mounted and surface-piercing bottom mounted baffle configurations. Different sloshing regimes are created by applying longitudinal periodic excitation at various frequencies to the tank. The synchronized measurement of parameters like dynamic pressure on the tank walls and sound pressure level is done along with high-speed camera images of fluid motion. This study helps in understanding the effect of vertical baffles on sloshing noise, for various fill levels in different sloshing regimes.

Про демпфовані усталені резонансні коливання рідини в контейнері кругового перерізу для довільних періодичних непараметричних збурень

Nonlinear modal Narimanov-Moiseev—type equations are investigated to study resonant sloshing in a vertical cylindrical tank. The tank moves periodically in the space with the forcing frequency close to the lowest natural sloshing frequency. We show that the considered sloshing problem can to within the higher-order asymptotic terms be reduced to the case of orbital tank motions in the horizontal plane. Analytical solutions of the secular system which couples the dominant amplitudes of the steady-state sloshing are analytically solved. Effect of viscous damping is accounted. The results are compared with experimental measurements conducted by diverse authors for longitudinal and circular orbital tank excitations. A parametric analysis of the amplitude curves is done to clarify how the steady-state wave regimes and their stability change versus the forcing frequency and the semi-axes ratio of the elliptic orbit. The main result consists of confirming the experimental disappearance of the counter-directed swirling wave mode (relative to the elliptic orbit direction) when passaging to the circular orbit.

Dynamic modelling, simulation and experiments of a micro-cutter with applications to cell perforation

The nonlinear three-dimensional dynamic equations of motion of a micro-cutter driven longitudinally at ultrasonic operating frequencies are derived using Kane's method. The micro-cutter is assumed to be immersed in a fluid, and in contact with an oocyte, which is to be perforated by the micro-cutter. The micro-cutter is modelled as an Euler-Bernoulli cantilever beam attached to a moving base. The shear and rotary inertia effects are neglected by considering a slender-shaped beam with homogeneous and isotropic material properties. It is assumed that there is no slip between the micro-cutter tip and the embryo membrane. The model presented demonstrates that the longitudinal excitation input of a micropipette results in excitation of out-of-plane, lateral motion due to the nonlinear dynamic coupling of the dynamics. Experimental results of membrane perforation are presented in the work supporting oocyte micro-cutter observations regarding suitable frequencies of excitation for effective oocyte membrane perforation.

First ESR Detection of Higgs Amplitude Mode and Analysis with Extended Spin-Wave Theory in Dimer System KCuCl$$_3$$

KCuCl$_3$ is known to show a quantum phase transition from the disordered to antiferromagnetically ordered phases by applying pressure. There is a longitudinal excitation mode (Higgs amplitude mode) in the vicinity of the quantum critical point in the ordered phase. To detect the Higgs amplitude mode, high-pressure ESR measurements are performed in KCuCl$_3$. The experimental data are analyzed by the extended spin-wave theory on the basis of the vector spin chirality. We report the first ESR detection of the Higgs amplitude mode and the important role of the electric dipole described by the vector spin chirality.

Two-Photon Excited Fluorescence Dynamics in NADH in Water-Methanol Solutions: The Role of Conformation States.

The dynamics of polarized fluorescence in reduced nicotinamide adenine dinucleotide (NADH) at 460 nm under two-photon excitation at 720 nm by femtosecond laser pulses in water-methanol solutions has been studied experimentally and theoretically as a function of methanol concentration. A number of fluorescence parameters have been determined from experiment by means of the global fit procedure and then compared with the results reported by other authors. A comprehensive analysis of experimental errors was made. Ab initio calculations of the structure of NADH in water and methanol and of β-nicotinamide mononucleotide (NMNH) in vacuum have been carried out for clarifying the role of decay time heterogeneity. The main results obtained are as follows. An explanation of the heterogeneity in the measured fluorescence decay times in NADH has been suggested based on the influence of the internal molecular electric field in the nicotinamide ring on nonradiative decay rates. We suggest that different charge distributions in the cis and trans configurations result in different internal electrostatic field distributions that lead to the decay time heterogeneity. A slight but noticeable rise of the fluorescence decay times τ1 and τ2 with methanol concentration was observed and treated as a minor effect of a nonradiative relaxation slowing due to the decrease in solution polarity. Relative concentrations of the folded and unfolded NADH conformations in solutions have been determined using a new method of analysis of the rotational diffusion time τr as a function of methanol concentration on the basis of the Stokes-Einstein-Debye equation. The analysis of the fluorescence anisotropy parameters obtained under linearly and circularly polarized excitation and the parameter Ω has been carried out and resulted in the determination of the two-photon excitation tensor components and suggested the existence of two excitation channels with comparable intensities. These were the longitudinal excitation channel dominated by the diagonal tensor component Szz and the mixed excitation channel dominated by the off-diagonal tensor components |Sxz2 + Syz2|1/2.

Vibrational density of states of amorphous solids with long-ranged power-law-correlated disorder in elasticity

.A theory of vibrational excitations based on power-law spatial correlations in the elastic constants (or equivalently in the internal stress) is derived, in order to determine the vibrational density of states D(omega) of disordered solids. The results provide the first prediction of a boson peak in amorphous materials where spatial correlations in the internal stresses (or elastic constants) are of power-law form, as is often the case in experimental systems, leading to a logarithmic enhancement of (Rayleigh) phonon attenuation. A logarithmic correction of the form sim -omega^{2}lnomega is predicted to occur in the plot of the reduced excess DOS for frequencies around the boson peak in 3D. Moreover, the theory provides scaling laws of the density of states in the low-frequency region, including a simomega^{4} regime in 3D, and provides information about how the boson peak intensity depends on the strength of power-law decay of fluctuations in elastic constants or internal stress. Analytical expressions are also derived for the dynamic structure factor for longitudinal excitations, which include a logarithmic correction factor, and numerical calculations are presented supporting the assumptions used in the theory.Graphical abstract

Longitudinal response of buried pipeline under non-uniform seismic excitation from multi-point shaking table tests

The spatial variability of ground motion has a significant influence on the seismic response of long infrastructure and is considered the primary cause of pipeline damage during earthquakes. In this study, a series of three-dimensional shaking table tests were carried out to investigate the influence of non-uniform seismic excitation on the pipeline response using a scaled pipeline model installed in sand. The pipeline-soil model was enclosed in a suspension continuum soil box situated on three shaking tables that can induce uniform and non-uniform seismic excitations. Accelerometers were distributed along the soil profile, and strain gauges and accelerometers were attached to the pipeline to monitor the dynamic response of the pipeline-soil system during the shaking. The pipeline-soil model was subjected to a series of uniform and non-uniform excitations with gradually increasing intensity. The testing results demonstrated that the pipeline experienced tensile and compressive strains due to the longitudinal seismic excitation because the phase and waveform of the seismic waves were almost the same at the strain measuring points around the pipeline profile. The acceleration response of the pipeline under non-uniform seismic excitation was larger than that of the surrounding soil. The pipeline strain response under non-uniform seismic excitation was approximately twice that under uniform seismic excitation. The soil-pipeline interaction exhibited complex behavior; sliding may occur with the increase of loading intensity, and more likely to occur under non-uniform seismic excitation. These results indicate that the dynamic response of the pipeline-soil system is sensitive to non-uniform ground motion, which should be properly considered in the seismic design of pipeline.

Longitudinal Spin Dynamics in the Heisenberg Antiferromagnet: Two-Magnon Excitations

Understanding the ultrafast spin dynamics in magnetically ordered materials is important for the comprehenssion of fundamental limits in spin-based magnetic electronics – magnonics. We have studied a microscopic model of magnetization dynamics in a two-sublattice antiferromagnet with the emphasis on longitudinal spin excitations. The diagrammatic technique for spin operators has been used to overcome limitations typical of phenomenological approaches. The graphical representations of spin wave propagators allow us to summing up the infinite series of distinctive diagrams. Its sum is transformed into an analytic expression for the longitudinal spin susceptibility xzz (q, w) applicable in all regions of the frequency w and wave vector q spaces beyond the hydrodynamical and critical regimes. It is found that the longitudinal magnetization dynamics consists of two types of excitations, which have different dependences on the temperature and wave vector q. The obtained result could be important for understanding the physics of nonequilibrium magnetic dynamics under the effect of ultrafast laser pulses in antiferromagnetic materials.

Shake Table Test of Long Span Cable-Stayed Bridge Subjected to Near-Fault Ground Motions Considering Velocity Pulse Effect and Non-Uniform Excitation

This paper presents the results of shake table tests of a scaled long span cable-stayed bridge (CSB). The design principles of the scaled CSB are first introduced. The first six in-plane modes are then identified by the stochastic subspace identification (SSI) method. Furthermore, shake table tests of the CSB subjected to the non-pulse near-field (NNF) and velocity-pulse near-fault (PNF) ground motions are carried out. The tests indicated that: (1) the responses under longitudinal uniform excitation are mainly contributed by antisymmetric modes; (2) the maximum displacement of the tower occurs on the tower top node, the maximum acceleration response of the tower occurs on the middle cross beam, and the maximum bending moment of the tower occurs on the bottom section; (3) the deformation of the tower and girder subjected to uniform excitation is not always larger than that subjected to non-uniform excitation, and therefore the non-uniform case should be considered in the seismic design of CSBs.

Delocalization of Longitudinal Acoustic-Like Excitations in DNA Due to Structural Effects

Terahertz-frequency phonon-like modes in DNA have been widely studied both experimentally and theoretically in recent years. However, current theoretical models turn out to fail to reproduce some basic properties of these modes. Using a generalized hydrodynamics approach and the results of inelastic X-ray scattering measurements, we propose a model to describe structural effects due to wavenumber dependence of the static structure factor in the dynamics of longitudinal acoustic-like excitations in DNA. Our analysis qualitatively suggests that on a length scale corresponding to a wavenumber region between the positions of the maximum and the minimum of the dispersion relation for the excitation frequency, structural effects may induce a tendency of delocalization of the dynamics. This proposal is consistent with the recent experimental observations of delocalized terahertz-frequency DNA phonon-like modes that seem to be relevant to biological function.

Direct evaluation of the physical characteristics of Yukawa fluids based on a simple approximation for the radial distribution function

We propose a simple analytical approximation for the radial distribution function (RDF) in a single-component Yukawa fluid. The proposed RDF depends on the two input parameters – the non-ideality parameter Γ and the structure (screening) parameter κ, which determine the thermodynamic state of Yukawa systems. We demonstrate that various physical properties can be directly calculated using the proposed RDF. In particular, the internal energy and pressure, the excess entropy in the pair approximation, and the dispersion relation of longitudinal acoustic-like collective excitations are calculated. These theoretical results are compared with the results from molecular dynamics simulations and good overall agreement is observed in the investigated regime of screening and coupling parameters.

Nonlinear soil response under non-uniform seismic excitation from multi-point shaking table tests

The soil response to large earthquakes is strongly nonlinear, which has a significant influence on the performance of buried infrastructure as well as input motion to superstructures. This paper reports on uniform and non-uniform multi-point shaking table tests to elucidate the effect of soil non-linearity on free-field soil response. Emphasis was placed on investigating the effect of the non-uniform seismic excitation in different directions on the soil response. The tests were conducted on scaled sand deposits enclosed in a suspension continuum soil box using three shaking tables that can induce uniform and non-uniform seismic excitations. Quantitative analyses were performed to study the ground motion response characteristics and variation of free-field soil characteristics underground motions with different intensity, frequency content and directions. The analyses evaluated the soil dynamic characteristics and their variation with strain level, as well as soil acceleration and settlement responses. The results demonstrated that the soil nonlinear behavior is influenced by the ground motion intensity, direction (longitudinal or transverse) and uniformity. Non-uniform ground motion may lead to more pronounced changes of soil structure, which would decrease the soil profile natural frequency and increase its damping ratio. The variation of soil shear modulus with strain also reflected the soil plastic response. The longitudinal excitation had a more pronounced effect on the soil vertical settlement compared with the transverse excitation. However, non-uniform excitation had a minor effect on the soil vertical settlement.

Liquid Vibrations in Cylindrical Tanks with and Without Baffles Under Lateral and Longitudinal Excitations

The paper is devoted to issues of estimating free surface elevations in rigid cylindrical fluid-filled tanks under external loadings. The possibility of baffles installation is provided. The liquid vibrations caused by lateral and longitudinal harmonic loadings are under consideration. Free, forced and parametrical vibrations are examined. Modes of the free liquid vibrations are considered as basic functions for the analysis of forced and parametric vibrations. The modes of the free liquid vibrations in baffled and un-baffled cylindrical tanks are received by using single-domain and multi-domain boundary element methods. Effects of baffle installation are studied. The problems of forced vibrations are reduced to solving the systems of second order ordinary differential equations. For parametric vibrations the system of Mathieu equations is obtained. The numerical simulation of free surface elevations at different loadings and baffle configurations is accomplished. Beat phenomena effects are considered under lateral harmonic excitations. The phenomenon of parametric resonance is examined under longitudinal harmonic excitations.

Realization of an ultrawide stop band in a 2-D elastic metamaterial with topologically optimized inertial amplification mechanisms

The aim of this study is to design a two-dimensional solid structure with embedded inertial amplification mechanisms that shows an ultrawide stop band (band gap) at low frequencies. First of all, a unique compliant inertial amplification mechanism is suggested. The compliant (flexure) hinge connections are designed and the topology of the beams in the unit cell mechanism are optimized to achieve the maximum possible stop band width. Then, a two-dimensional periodic structure is formed by using this topologically optimized inertial amplification mechanism. Thereafter, the formed periodic structure is manufactured. Experimental and finite element analyses show that an ultrawide stop band between 29 Hz and 590 Hz is obtained for both longitudinal and transverse excitations. This outcome reveals a phononic gap whose upper and lower limits have a ratio that exceeds 20 (i.e., arithmetic mean normalized bandwidth of 181% or geometric mean normalized bandwidth of 429%). This much bandwidth has not been achieved in the literature for two dimensions, so far.

Transverse acoustic phonon excitations in liquid metals

Abstract In this article, transverse acoustic (TA) phonon excitations in various liquid metals are reviewed. Low-frequency TA phonon excitations were investigated on liquid Ga, Sn, Fe, Cu, Zn, and Bi, by using high energy resolution inelastic X-ray scattering (IXS). The current correlation functions obtained from the IXS spectra were analyzed by using two Gaussians to evaluate the excitation energies and widths of the longitudinal acoustic and TA excitation modes, which are consistent with ab initio molecular dynamics simulations. The lifetimes and propagating lengths of the TA modes were determined, and may respectively correspond to the lifetimes and sizes of cages instantaneously formed in each liquid metal. The microscopic elastic constants were estimated and characteristic differences from macroscopic polycrystalline values were found in Poisson’s ratios. Future experimental and analytical problems to be solved in the near future are addressed.

Transverse acoustic phonon excitations in liquid metals

Abstract In this article, transverse acoustic (TA) phonon excitations in various liquid metals are reviewed. Low-frequency TA phonon excitations were investigated on liquid Ga, Sn, Fe, Cu, Zn, and Bi, by using high energy resolution inelastic X-ray scattering (IXS). The current correlation functions obtained from the IXS spectra were analyzed by using two Gaussians to evaluate the excitation energies and widths of the longitudinal acoustic and TA excitation modes, which are consistent with ab initio molecular dynamics simulations. The lifetimes and propagating lengths of the TA modes were determined, and may respectively correspond to the lifetimes and sizes of cages instantaneously formed in each liquid metal. The microscopic elastic constants were estimated and characteristic differences from macroscopic polycrystalline values were found in Poisson’s ratios. Future experimental and analytical problems to be solved in the near future are addressed.

Wave-passage effects on seismic responses of pile–soil–cable-stayed bridge model under longitudinal non-uniform excitation: shaking table tests and numerical simulations

A pile–soil–cable-stayed 1/70-scale bridge model was designed and constructed to represent an extremely long-span cable-stayed bridge with a 1400-m central span. Shaking table tests were conducted to investigate the wave-passage effects on the seismic responses of the pile–soil–cable-stayed bridge model under uniform and non-uniform longitudinal excitations. Additionally, the acceleration frequency spectra and seismic responses of the bridge model were separately evaluated to compare the effects of uniform and non-uniform excitation. Finally, a 3-D finite element model in OpenSees was built for comparison with the test results. The results showed that the longitudinal wave-passage excitations considerably impacted the acceleration frequency spectra in the vertical direction of the girder and the modal participation factor, which resulted in the symmetric vertical bending mode shapes of the girder to increasingly affect the seismic response as the wave-propagation velocity decreased. The longitudinal wave-passage excitations increased the vertical responses at the 1/2-span of the girder, whereas they generally decreased the longitudinal responses of the girder and tower, as compared with uniform excitation. The longitudinal wave-passage excitations had different impacts on the pile–soil interaction effects for the three studied structural systems of the pile–soil–cable-stayed bridge model. Moreover, the dynamic characteristics and seismic responses obtained from the numerical simulations were consistent with the experimental results.

The localized surface plasmon resonance on noble metal-semiconductor: Au nanosphere-ZnO nanorod

In this work, we have investigated the localized surface plasmon resonance of metal-semiconductor model. The raw materials are gold nanosphere (Au-NP) and ZnO nanorod (ZnO-NR). The nanoparticles were surrounded by air with refractive index constant (1.0+0i). Moreover, the diameter and aspect ratio of Au-NP and ZnO-NR were 40 nm and 4, respectively. Then, we designed the nanoparticle in two different configurations. First, Au-NP was placed at the sides of ZnO-NR and second, Au-NP was placed at the tip of nanorod. Next, we varied the gap-distance among them from 0 nm to 40 nm with 10 nm increment. The photon wavelength used were from 300 nm to 1200 nm within two different excitations (transverse and longitudinal excitation). Furthermore, our result suggests that on the longitudinal excitation, when the gap-distance increases, the resonance peak of second configuration remains at constant value and the intensity significantly decreases compared to the first configuration. However, on the transverse excitation, the first configuration has a high intensity and the resonance peaks is slightly red-shifted. In addition, based on the near-field mapping which reflects the energy density of electromagnetic field by LSPR, the LSPR of Au-NP stands to aid the exciton production to enhance the photocatalytic activity.