Amplitude Reduction Factor Research Articles

BOUNDARY ELEMENT MODELING AND ANALYSIS OF THE INTERACTION OF A VERTICAL BARRIER WITH SURFACE WAVES IN A POROELASTIC FORMULATION

The paper studies the possibility of attenuating the wave intensity on the surface of a half-space by installing a barrier based on the solution of a three-dimensional problem of the dynamic theory of partially saturated poroelasticity using the boundary element method. The basic idea of using a wave barrier is to create an obstacle to the propagation of surface waves over the territory occupied by structures or constructions. Open or unfilled trenches can be effective when organizing this method of protection. In the paper, numerical modeling is performed using the boundary element method based on the combined use of boundary integral equations of the direct approach of the three-dimensional isotropic theory of poroelasticity and the integral Laplace transform. To describe the poroelastic medium, the Biot model of a poroelastic material in the case of partial saturation is used. The solution in the time domain is obtained using a method based on quadrature formulas for calculating the convolution integral and referred to hereinafter as the step method. The problem of the action of a dynamic load on a deformable partially saturated poroelastic half-space with a vertical barrier in the form of a trench is considered. To assess the efficiency of wave damping by a barrier on the surface of a half-space, the amplitude reduction factor is calculated for different values of the saturation coefficient of the poroelastic material of the half-space, geometric dimensions of the barrier and boundary conditions. Graphs and maps of the amplitude reduction factor are provided. The simulation results show that the presence of a barrier in the form of a trench leads to a decrease in the Rayleigh wave amplitude at points located behind the trench, for all considered values of the parameters under study. It is also shown that the condition of permeability or impermeability of the trench boundary does not have a noticeable effect on its properties in reducing the intensity of surface waves. The results obtained can be useful for developing effective methods for protecting buildings and structures from dynamic effects.

Transient scattering of a Rayleigh wave by a cluster of subwavelength resonators—Towards asymptotic modeling of seismic surface metabarriers

A seismic metabarrier (intended for surface waves mitigation effect) is modeled as a cluster of single-degree-of-freedom resonator units deposited on the surface of an isotropic homogeneous elastic half-space. It is assumed that each resonator has a frictionless flat rigid base of diameter much smaller than the wavelength of an incoming surface wave. The slow-motions asymptotic method is applied for constructing the first-order asymptotic model of multiple time-dependent scattering of a pulsed Rayleigh wave with respect to the vertical displacements of the resonators (including their rigid bases and inertial elements) and the normal contact forces (time-dependent integral characteristics of the contact reactions beneath the resonator bases). Both the stationary and transient multiple scattering scenarios are considered. The variation of the amplitude reduction factor due to the model parameters variation is studied in detail.

Exploring Platinum Speciation with X-ray Absorption Spectroscopy under High-Energy Resolution Fluorescence Detection Mode

Critical to interpreting platinum chemical speciation using X-ray absorption spectroscopy (XAS) is the availability of reference spectra of compounds with known Pt redox and coordination. Here we compare different techniques for Pt LIII-edge X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectral regions for a large set of Pt-O-Cl-S reference compounds of known structures. The measurements were conducted in HERFD (high-energy resolution fluorescence detection, high-resolution or HR) mode, as well as in two conventional modes such as transmission (TR) and nominal-resolution total fluorescence yield (TFY or NR). Samples analyzed here included Pt0 (TR), PtIIS (HR), PtIVS2 (TR), K2PtIICl4 (HR + TR), K2PtIVCl6 (HR + TR), PtIVO2 (HR + TR), C6H12N2O4PtII (HR + TR), and aqueous solutions of K2PtIICl4 and H2PtIVCl6 (NR + TR), as well as (NH4)2PtIV(S5)3 (HR + TR). XANES spectra in HERFD mode offer a better energy resolution than in conventional modes, allowing a more accurate identification of Pt redox state and coordination geometry. EXAFS spectra in all three modes for a given compound yield identical within errors values of Pt-neighbor interatomic distances and mean square relative displacement (MSRD, σ2) parameters. In contrast, both TR and NR spectra on the one hand and HR spectra on the other hand yield distinct amplitude reduction factor (S02) values, 0.76 ± 0.04 and 0.99 ± 0.07 (1 standard error), respectively. This study contributes to the development of an open-access XAS database SSHADE.

Estimation and prediction of screening efficiency of Sand Crumb Rubber (SCR) mix infill trench

ABSTRACT The present study investigates the efficiency of using sand crumb rubber mixture for vibration isolation and its prediction using machine learning. Safe disposal of waste rubber from tire industries is a matter of concern due to its detrimental effects. A two-dimensional finite element (FE) analysis was performed in ABAQUS, considering a strip foundation as the source of vibration. The effectiveness of the screening was evaluated by calculating the Amplitude Reduction Factor (Arf ) for open and infilled trench (OT and IFT) for different trench geometry (distance from the source, depth and width). In previous studies, modelling such screening problems has mostly been accomplished through regression models. The present study explored the Support Vector Regression (SVR) model since machine learning excels in modelling complex behaviours. The SVR model's optimum parameters were successfully determined by performing a grid search and selecting the best model using the Preferential Ranking Organization Method for Enrichment Evaluation (PROMETHEE) technique.

The Enhancement of Selectivity and Activity for Two-Electron Oxygen Reduction Reaction by Tuned Oxygen Defects on Amorphous Hydroxide Catalysts

Amorphous catalysts, thanks to their unique coordinately unsaturated properties and abundant of defect sites, incline to possess higher activity and selectivity than their crystalline counterparts....

Vibration mitigation efficiency of an inclined, curved, open trench

The vibration screening efficiency of a curved, inclined, open trench is investigated in this paper. An elastic, transversely isotropic half-space with hysteretic damping, acted upon by a harmonic vertical excitation, is assumed. Equations of motion with absorbing boundary conditions are presented and numerically integrated using FlexPDE software, based on the finite element method. The barrier efficiency is analysed in terms of the reduction of the vertical and horizontal components of the ground surface vibration. The results are presented for trenches with different geometric features based on the non-dimensional amplitude reduction factor. The trench inclination angle, the shape of the trench surface and the distance between the source of vibration and an obstacle are investigated as factors that can improve the trench reduction ability. It is demonstrated that a better attenuation of vibration is achieved with the proposed inclined trench than with its vertical counterpart. Moreover, the vibration mitigation effect is more significant in the case of a more horizontally located trench than for its vertical counterpart (even up to 5 times smaller displacement amplitudes for the vertical displacement component). Additionally, assuming the same trench depth, the vibration reduction effect is better in the case of a smaller number of rings used. The vibration attenuation efficiency is more visible if the trench is located closer to the vibration source.

Differences in local structures around zirconium atoms in Eu2Zr2O7 and La2Zr2O7

Extended X-ray absorption fine structure (EXAFS) analyses of the Eu2Zr2O7 and La2Zr2O7 pyrochlore composition oxides were performed to examine differences in the local structures around the Zr atoms. In the EXAFS analyses of Eu2Zr2O7, the amplitude reduction factor of Zr16c-O8a was considerably large, indicating that a part of the oxygen vacancy site (8a) was occupied by oxide ions. Furthermore, the occupancy of the 8a site determined by Rietveld refinement of the X-ray diffraction data for Eu2Zr2O7 was 0.32(2), which was consistent with the EXAFS results. From the EXAFS analyses of La2Zr2O7, oscillation in the high wavenumber k-range sharpened with decreasing temperature, and the mean square relative displacement (MSRD) values of the ZrO peak in the R-space were small compared to those of Eu2Zr2O7. Therefore, the disorder in the local structures around the Zr atoms of La2Zr2O7 was determined to be smaller than that of Eu2Zr2O7.

A novel vibration screening technique using bamboo: a numerical study

ABSTRACTIn vibration screening technique, the effectiveness of in-filled trenches in soil has been extensively studied over the years considering various synthetic in-filled materials. However, the application of natural but cheaper in-filled materials in vibration screening technique is still scarce. The present study investigates the efficiency and aptness of bamboo, a naturally available hollow and less expensive element, as a vibration barrier to mitigate the vibration induced by machine excitation. The vibration screening efficiency of the bamboo in-filled trench has been assessed based on two factors such as amplitude reduction factor (ARF) and system effectiveness (SE). Considering a vertical harmonic load as the source, three-dimensional finite element explicit dynamic analysis in the time domain has been performed assuming the soil as linearly elastic, isotropic, and homogeneous. The effect of various parameters such as the length and depth of the trench, the distance of the trench from the vibration source, the spacing between the bamboos, and the frequency of excitation on ARF and SE has been analyzed.

A proposal for vibration isolation of structures by using a wave generator

This paper describes a concept for vibration-mitigation techniques with the potential to reduce the ground vibration amplitudes by applying an additional vibration source. The idea is presented through the case of an impact load. Equations of motion for the transversally isotropic ground model with absorbing boundary conditions are presented and numerically integrated using FlexPDE software, based on the finite element method. The efficiency of the solution is analysed in terms of reducing the vertical and horizontal components of ground surface vibrations. Results in the form of a dimensionless amplitude reduction factor are presented for four different locations of a generator and different soil conditions. In each analysed case the vibration mitigation effect in a three-story building was achieved.

The Efficiency of an Active Generator in the Case of a Deep Foundation Location

Abstract This paper presents a concept for vibration-mitigation techniques with the potential to reduce ground vibration amplitudes by applying an additional vibration source. The idea of an additional generator is verified in the case of an impact load for the points located on the ground surface and below it. Equations of motion for the damped transversally isotropic ground model with the absorbing boundary conditions are presented and numerically integrated using FlexPDE software, based on the finite element method. The efficiency of the solution is analyzed in terms of reducing the vertical and horizontal components. Results are presented in the form of a dimensionless amplitude reduction factor. In each case being analyzed, a vibration mitigation effect in a three-story building was achieved.

The effects of oblateness and solar radiation pressure on halo orbits in the photogravitational Sun-Earth system

In this paper, we construct a third-order analytic approximate solution using the Lindstedt-Poincare method in the photogravitational circular restricted three body problem considering the Sun as a radiating source and the Earth as an oblate spheroid for computing halo orbits around the collinear Lagrangian points L1 and L2. Further, the well-known differential correction and continuation schemes are used to compute halo orbits and their families numerically. The effects of solar radiation pressure and oblateness on the orbit are studied around both Lagrangian points. From the study, it is noticed that time period of the halo orbit increases around L1 and L2 accounting oblateness of the Earth and solar radiation pressure of the Sun. It is also found that stability of halo orbits is a weak function of the out-of-plane amplitude and mass reduction factor.

A study of the reduction of ground vibrations by an active generator

This paper presents the concept of using an additional generator to prevent ground vibrations. A linear, transversally isotropic three dimensional half-space with the hysteretic damping model, acted upon by a harmonic vertical excitation is assumed. Equations of motion for the transversally isotropic ground model with the absorbing boundary conditions are presented and numerically integrated using FlexPDE software, based on the finite element method. The efficiency of the solution is analysed in terms of reducing the vertical and horizontal components of ground surface vibrations. Results in the form of a dimensionless amplitude reduction factor are presented for four different locations of a generator. The influence of the soil parameters and layers locations on the additional generator's efficiency is investigated. The vibration reduction efficiency in a four-story building is also presented.

Active screening for axi-symmetric machine loading using EPS geofoam

In this paper, the application potential of expanded polystyrene (EPS) geofoam as a vibration screening material in an in-filled trench has been investigated under circular machine loading. Circular machine foundations are commonly used for the foundations of reciprocating engines, compressors, turbines, generators etc. The numerical analysis is performed using two-dimensional finite element method under dynamic condition. The present analysis considers the foundation bed as linearly elastic, isotropic and homogeneous soil deposit. The inclination of the trench is also considered as a special parametric study. The vertical displacement amplitudes of the ground vibrations are analysed at different pick-up points along the ground surface to determine the amplitude reduction factor (ARF).

Intermittent geofoam in-filled trench for vibration screening considering soil non-linearity

The application of open as well as in-filled trenches as vibration screening technique has been considered in several situations. However, very few works have included the Expanded Polystyrene (EPS) geofoam as an in-filled material for the trench. The current study focuses on the effectiveness of the intermittent geofoam in-filled trench as vibration barrier in presence of machine induced ground vibration, where the geofoam blocks and the open air pockets are arranged alternately to form an effective vibration screening material. The screening efficiency of the geofoam in-filled trench is determined in terms of Amplitude Reduction Factor (ARF). The effect of the soil non-linearity under the propagating waves is also emphasized in the present study. Hyperbolic non-linear elastic Duncan and Chang (1970) soil model has been implemented in time domain finite element analysis. A parametric study is performed considering the geometric parameters of trench, excitation frequency, and stiffness of the soil.

Comparison of EXAFS foil spectra from around the world

The EXAFS spectra of Cu and Pd foil from many different beamlines and synchrotrons are compared to address the dependence of the amplitude reduction factor (S02) on beamline specific parameters. Even though S02 is the same parameter as the EXAFS coordination number, the value for S02 is given little attention, and is often unreported. The S02 often differs for the same material due to beamline and sample attributes, such that no importance is given to S02-values within a general range of 0.7 to 1.1. EXAFS beamlines have evolved such that it should now be feasible to use standard S02 values for all EXAFS measurements of a specific elemental environment. This would allow for the determination of the imaginary energy (Ei) to account for broadening of the EXAFS signal rather than folding these errors into an effective S02-value. To test this concept, we model 11 Cu-foil and 6 Pd-foil EXAFS spectra from around the world to compare the difference in S02- and Ei-values.

The Amplitude Reduction Factor and the Cumulant Expansion Method: Crucial Factors in the Structural Analysis of Alkoxide Precursors in Solution

The transition-metal alkoxide yttrium 2-methoxyethoxide Y(OEtOMe)(3) in solution is studied as a model system of the large class of alkoxide precursors used in the sol-gel process by means of EXAFS spectroscopy. The discussion is focused on the amplitude reduction factor S (2)(0) and the cumulant expansion method. If asymmetry is present in the radial distribution function, the determination of the correct structural model can only be achieved by balancing multiple Gaussian shell fits against only one shell fit with a third cumulant C3. A method to identify the best model, based on statistical parameters of the EXAFS fit, is proposed and checked with two well-known reference compounds, Y(5)O(O(i)Pr)(13) and Y(acac)(3).3H(2)O, and applied to the structurally unknown solution of Y(OEtOMe)(3) in 2-methoxyethanol. The two references are also used to discuss the transferability of S(2)(0) values, determined from reference compounds to unknown samples. A model-free procedure to identify the correct amplitude reduction factor S(2)(0) by making use of fits with different k-weighting schemes is critically investigated. This procedure, which does not require any crystallographic data, is used for the case of Y(OEtOMe)(3) in solution, where significant differences of the amplitude reducing factor of both the oxygen and yttrium shell in comparison to the reference Y(5)O(O(i)Pr)(13) were found. With such a detailed analysis of EXAFS data, a reliable characterization of Y(OEtOMe)3 in 2-methoxyethanol by means of EXAFS spectroscopy is possible. The decameric structure unit found in solid Y(OEtOMe)(3) is not preserved, but rather, a pentameric framework similar to that in Y5O(O(i)Pr)(13) is formed.

The Iron-Sulfur Cluster-free Hydrogenase (Hmd) Is a Metalloenzyme with a Novel Iron Binding Motif

The iron-sulfur cluster-free hydrogenase (Hmd) from methanogenic archaea harbors an iron-containing cofactor of yet unknown structure. X-ray absorption spectroscopy of the active, as isolated enzyme from Methanothermobacter marburgensis (mHmd) and of the active, reconstituted enzyme from Methanocaldococcus jannaschii (jHmd) revealed the presence of mononuclear iron with two CO, one sulfur and one or two N/O in coordination distance. In jHmd, the single sulfur ligand is most probably provided by Cys176, as deduced from a comparison of the activity and of the x-ray absorption and Mössbauer spectra of the enzyme mutated in any of the three conserved cysteines. In the isolated Hmd cofactor, two CO, one sulfur, and two nitrogen/oxygen atoms coordinate the iron, the sulfur ligand being most probably provided by mercaptoethanol, which is absolutely required for the extraction of the iron-containing cofactor from the holoenzyme and for the stabilization of the extracted cofactor. In active mHmd holoenzyme, the number of iron ligands increased by one when one of the Hmd inhibitors (CO or KCN) were present, indicating that in active Hmd, the iron contains an open coordination site, which is proposed to be the site of H2 interaction.

Rapid Loss of Structural Motifs in the Manganese Complex of Oxygenic Photosynthesis by X-ray Irradiation at 10–300 K

Structural changes upon photoreduction caused by x-ray irradiation of the water-oxidizing tetramanganese complex of photosystem II were investigated by x-ray absorption spectroscopy at the manganese K-edge. Photoreduction was directly proportional to the x-ray dose. It was faster in the higher oxidized S2 state than in S1; seemingly the oxidizing potential of the metal site governs the rate. X-ray irradiation of the S1 state at 15 K initially caused single-electron reduction to S0* accompanied by the conversion of one di-mu-oxo bridge between manganese atoms, previously separated by approximately 2.7 A, to a mono-mu-oxo motif. Thereafter, manganese photoreduction was 100 times slower, and the biphasic increase in its rate between 10 and 300 K with a breakpoint at approximately 200 K suggests that protein dynamics is rate-limiting the radical chemistry. For photoreduction at similar x-ray doses as applied in protein crystallography, halfway to the final Mn(II)4 state the complete loss of inter-manganese distances <3 A was observed, even at 10 K, because of the destruction of mu-oxo bridges between manganese ions. These results put into question some structural attributions from recent protein crystallography data on photosystem II. It is proposed to employ controlled x-ray photoreduction in metalloprotein research for: (i) population of distinct reduced states, (ii) estimating the redox potential of buried metal centers, and (iii) research on protein dynamics.

Synchrotron X-ray absorption of LaCoO 3 perovskite

LaCoO 3 perovskite was prepared at 700°C using citrate precursors. The product was then characterized with X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS). The powder XRD pattern indicates rhombohedral (R 3 ̄ c) or its monoclinic I2/ a subgroup symmetry. The electronic configuration and the short-range atomic structure of the LaCoO 3 perovskite at room temperature were investigated using synchrotron near-edge X-ray absorption spectroscopy (XANES) and extended X-ray absorption spectroscopy (EXAFS). From the XANES region of the XAS we conclude that Co(III) is at least partly in its intermediate- or high-spin state, which is in accordance with most of the published literature on LaCoO 3 perovskite. The EXAFS region of the LaCoO 3 perovskite spectrum, which up to now was almost not investigated, was simulated satisfactorily for the first two radial structure peaks in terms of the dominant scattering contributions generated with the FEFF8 code and the structural information available from crystallographic data. The best simulation results were obtained with I2/ a symmetry. The obtained amplitude reduction factor, zero-energy shift and Debye–Waller factors are useful reference values for data analyses of similar compounds like partly substituted LaCoO 3 perovskite, such as La 1− x Ca x CoO 3 or La 1− x Sr x CoO 3, which are materials of technical interest in catalyst and other applications.

Multiple-electron excitation in X-ray absorption: a simple generic model.

The probability of multiple-electron excitation in X-ray absorption is calculated using a simple generic model. The model permits calculations to be made for all atoms with little input data or computing effort. The high-energy limit of this probability, which gives the usual EXAFS amplitude reduction factor, is calculated in the 'sudden approximation' using Slater orbitals. Good agreement with experiment is found. The energy dependence of this probability is also calculated using a simple model form of perturbing potential and found to agree well with experiment for rare gas atoms. The effect on the X-ray absorption coefficient of including multiple-electron excitations is also determined and is found to be small, again in agreement with observation.