Fourier Acceleration Research Articles

Comprehensive ground-motion characterization of the 6 February 2023 \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\:{\\varvec{M}}_{\\varvec{W}}$$\\end{document} 7.8 Pazarcık earthquake in Kahramanmaraş, Türkiye: insights into attenuation effects, site responses and source properties

The devastating \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\:{M}_{W}$$\\end{document} 7.8 Pazarcık earthquake on February 6, 2023, profoundly impacted a large region in south-central Türkiye and northwestern Syria, resulting in over 50,000 casualties and widespread damage. To better understand source properties and wave-propagation effects of this event, we analyze the strong ground-motion data recorded at ~ 230 stations. We determine the regional distance-dependent attenuation using the horizontal RotD50 Fourier acceleration amplitude spectrum (FAS) in the frequency range of 0.1–20 Hz. We find an apparent near-source saturation effect which needs to incorporate an additional finite-fault factor for the distance scaling. Uncertainty and sensitivity analyses are considered by variable decay rates in the geometric spreading model. For each decay rate, we derive a corresponding \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\:Q\\left(f\\right)$$\\end{document} model to account for the frequency-dependent anelastic attention. Significant duration of ground motions is modelled for two different measurements based on Arias intensity (\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\:{I}_{A}$$\\end{document}). For site amplification, we construct a model containing both \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\:{V}_{S30}$$\\end{document}-scaling and peak ground acceleration (PGA)-scaling. Source parameters are then determined using a reference Fourier source spectrum at 1.0 km. Specifically, we estimate the mean corner-frequency as \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\:{f}_{0}$$\\end{document}= 0.036 Hz, Brune stress drop as Δσ = 4.79 MPa and the reference rock site κ0 = 0.051 s. By analyzing near-source pulse-like waveforms, we demonstrate that the mismatch of peak ground velocity (PGV) between our model and close-distance observations is due to the rupture directivity effect. Finally, we compare ground motions of the 2023 \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\:{M}_{W}$$\\end{document} 7.8 event to those of the 2023 \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\:{M}_{W}$$\\end{document} 7.6 Elbistan and the 2020 \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\:{M}_{W}$$\\end{document} 6.7 Sivrice earthquakes. Attenuation effects estimated for the three events are found to be identical between ~ 0.2 and 6.0 Hz, with slight differences in site responses above ~ 5.0 Hz. Source spectra comparisons indicate that the source properties are complicated for all three events. Our comprehensive ground-motion analyses contribute to understanding and modeling regional properties of attenuation, site response, and event-based source characteristics that are important for future region-specific seismic hazard assessment.

Model-based iterative reconstruction for direct imaging with point spread function encoded echo planar MRI

BackgroundEcho planar imaging (EPI) is a fast measurement technique commonly used in magnetic resonance imaging (MRI), but is highly sensitive to measurement non-idealities in reconstruction. Point spread function (PSF)-encoded EPI is a multi-shot strategy which alleviates distortion, but acquisition of encodings suitable for direct distortion-free imaging prolongs scan time. In this work, a model-based iterative reconstruction (MBIR) framework is introduced for direct imaging with PSF-EPI to improve image quality and acceleration potential. MethodsAn MBIR platform was developed for accelerated PSF-EPI. The reconstruction utilizes a subspace representation, is regularized to promote local low-rankedness (LLR), and uses variable splitting for efficient iteration. Comparisons were made against standard reconstructions from prospectively accelerated PSF-EPI data and with retrospective subsampling. Exploring aggressive partial Fourier acceleration of the PSF-encoding dimension, additional comparisons were made against an extension of Homodyne to direct PSF-EPI in numerical experiments. A neuroradiologists' assessment was completed comparing images reconstructed with MBIR from retrospectively truncated data directly against images obtained with standard reconstructions from non-truncated datasets. ResultsImage quality results were consistently superior for MBIR relative to standard and Homodyne reconstructions. As the MBIR signal model and reconstruction allow for arbitrary sampling of the PSF space, random sampling of the PSF-encoding dimension was also demonstrated, with quantitative assessments indicating best performance achieved through nonuniform PSF sampling combined with partial Fourier. With retrospective subsampling, MBIR reconstructs high-quality images from sub-minute scan datasets. MBIR was shown to be superior in a neuroradiologists' assessment with respect to three of five performance criteria, with equivalence for the remaining two. ConclusionsA novel image reconstruction framework is introduced for direct imaging with PSF-EPI, enabling arbitrary PSF space sampling and reconstruction of diagnostic-quality images from highly accelerated PSF-encoded EPI data.

Investigation of Site Response in Xinjiang, Northwestern China, from S–Lg Fourier Amplitude Spectra

ABSTRACT Abundant seismic waveforms have been collected in Xinjiang since 2007, following the deployment of permanent stations by the China National Seismic Network and the Xinjiang Seismic Network. We investigated regional attenuation of the S–Lg phase in the crustal waveguide and site response in Xinjiang using broadband recordings at 44 stations from 118 earthquakes with magnitudes of 4.4–7.0 occurring in Xinjiang and adjacent areas between January 2009 and February 2022. We used linear regression analysis of the Fourier acceleration amplitude spectra in 18 frequency bands from 0.1 to 24.86 Hz to estimate site response terms and distance-dependent anelastic attenuation quality factor Q in the crustal waveguide at regional distances. The regression site terms of stations located in the Tarim and Junggar Basins show significant amplification at low frequencies and strong attenuation at higher frequencies due to the presence of thick sedimentary deposits. We quantified the linear behavior of the logarithms of the high-frequency site terms versus frequency using the zero distance attenuation parameter κ0 (Anderson and Hough, 1984). A positive correlation was observed between κ0 and the thickness of the sedimentary layers in Xinjiang. We observed some consistent patterns in the behavior of the site response terms as a function of sediment thickness over the frequency range of 0.1–24.86 Hz. Linear functions of sediment thickness were used to model the site response in Xinjiang at each of the 18 frequencies. An alternative approach that adopted the κ0 model as a function of sediment thickness can be used to estimate site responses at high frequencies (≥5.66 Hz). The results of this study demonstrate the nature of site effects on earthquake ground motions caused by the thick sedimentary deposits in Xinjiang and provide a preliminary site response model as a function of sediment thickness for this region.

Hybrid Monte Carlo simulation with Fourier acceleration of the N = 2 principal chiral model in two dimensions

Motivated by the similarity to QCD, specifically the property of asymptotic freedom, we simulate the dynamics of the SU(2) × SU(2) model in two dimensions using the Hybrid Monte Carlo algorithm. By introducing Fourier Acceleration, we show that critical slowing down is largely avoided and increases the simulation efficiency by up to a factor of 300. This yields numerical predictions at a precision exceeding that of existing studies and allows us to verify the onset of asymptotic scaling.

Ground motion simulations of the 1887 Pinal de Amoles (MW = 5.53) and the 1989 Landa de Matamoros (MW = 4.94) earthquakes, Querétaro, Mexico

Ground motions characteristics of the 1887 Pinal de Amoles (MW = 5.53) and the 1989 Landa de Matamoros (MW = 4.94) Querétaro earthquakes were studied. For this purpose, the specific barrier model (SBM) was implemented in the context of the stochastic ground motion representation of earthquakes. The SBM was calibrated by modeling the peak ground acceleration (PGA) and the Fourier acceleration spectra (FAS) of the 11 May 2016 (MW = 4.80) Guadalajara earthquake. The calibration results showed that the SBM and selected source and path parameters were able to reproduce synthetic PGA and spectra in good agreement with observed waveforms; in particular, a stress drop of 160 bars fits the results better. Several rupture scenarios for the 1887 and 1989 events were performed by obtaining synthetic seismograms considering different values of stress drop (10, 30, 50, 100, 150, 200, 300, and 500 bars). For a typical stress-drop value of 100 bars, the PGA at distances of 10 and 200 km are in the following intervals: 2.57–295 cm/s2 and 1.72–186 cm/s2 for the Pinal de Amoles and Landa de Matamoros earthquakes, respectively. The results obtained in this study contribute toward a better understanding of strong ground motions in the region.

Simulation of Ground Motion From Finite‐Fault Modeling Incorporating the Influence of Duration

AbstractOn 21 May 2021 (local time), an Mw 6.1 earthquake struck the Yangbi County, Yunnan Province, China. The finite fault stochastic simulation approach is usually used to simulate ground motions in high‐frequency band (f > 1 Hz). Model parameters needed for earthquake ground motion simulation mainly include source, path, and site. In the high‐frequency ground motion simulation program widely used in earthquake engineering, the reciprocal of corner frequency is typically used to define the source rise time; however, the complete step‐wise derivation process is unavailable. In deriving the static corner frequency f0, source rise time is typically estimated to be the time required for the rupture to reach 50% of the final location, and the source rise time then can be obtained as 0.27/f0, which is consistent with the hypothesis of corner frequency and rupture velocity, and the correlation and integrity between parameters are established. This study also focuses on the influence of different source rise times and path durations on the simulation results, such as Fourier acceleration spectrum, pseudo‐spectral acceleration, and peak ground acceleration. The results show that the source rise time recommended in this simulation can improve the accuracy of near‐fault ground motion simulations. This study provides suggestions for a reasonable selection of path duration in different engineering applications.

Physically Based and Empirical Ground Motion Prediction Equations for Multiple Intensity Measures (PGA, PGV, Ia, FIV3, CII, and Maximum Fourier Acceleration Spectra) on Sakhalin Island

In the present study, empirical attenuation relations for multiple ground motion intensity measures (PGA, PGV, Ia, FIV3, CII, and MFAS) were developed for Sakhalin Island (in the far east of Russia). A recorded strong motion dataset was used, making GMPEs applicable in active crustal regions with an earthquake magnitude range of 4–6 and a distance range of up to 150 km. The hypocentral distance was used as a basic distance metric. For the first time in the research, an analytical representation of Arias intensity (Ia) was obtained in the framework of a multi-asperity source model. Asperities are considered as sub-sources of high-frequency incoherent radiation. The physical representation of the attenuation model in our study was based on a stress drop on the asperities and the ratio of the total rupture area to the combined area of asperities. The average stress drop on asperities for the examined earthquakes was approximately 13.4 MPa, and the ratio of the total rupture area to the asperity area was 0.22, which is generally close to similar estimates for crustal earthquakes. The coefficients and statistical scattering of the attenuation models were also analyzed. Moreover, a magnitude scale based on a modified Arias intensity is proposed in the present study. The new magnitude scale has an explicit physical meaning and is characterized by its simplicity of measurement. It is associated with the acceleration source spectrum level and can be successfully used in early warning systems.

Stochastic Ground-Motion Simulation of the 2021 Mw 5.9 Woods Point Earthquake: Facilitating Local Probabilistic Seismic Hazard Analysis in Australia

ABSTRACT The 2021 Mw 5.9 Woods Point event is the largest onshore earthquake that has occurred in the recorded history of southeastern Australia since European settlement. To study its source and ground-motion characteristics and to extract information for local seismic hazard analysis, we employ a stochastic finite-fault simulation approach to simulate ground motions for this event based on the observations collected from 36 onshore stations. We determine the regional distance-dependent attenuation parameters using the horizontal Fourier acceleration amplitude spectrum in the frequency range of 0.1–20 Hz. We parameterize path parameters using different models to consider uncertainties and sensitivities. To investigate local site effects, we construct a VS30-based site amplification model. Source parameters are then determined by fitting the theoretical Brune’s ω2 model with a reference Fourier source spectrum at 1.0 km. The κ0 value for the reference rock site is estimated as κ0=0.01 s, and dynamic stress drop is found to be 41.0 MPa by minimizing the overall absolute residual of 5% damped pseudospectral acceleration. We validate the simulations by comparing simulated and observed ground motions in terms of various intensity measurements; analyses of residuals show that the simulations are in good agreement with observations (average residual is close to 0). To facilitate future probabilistic seismic hazard analysis, six selected ground-motion models are ranked using the deviance information criteria based on an independent data set consisting of field observations and simulated ground motions.

Investigation of Site Amplification and Attenuation Effects in the Changjiang Delta

Abstract Site response in the Changjiang Delta in eastern China was studied using Lg Fourier amplitude spectra. We used broadband seismograms recorded at 70 stations from 62 earthquakes with magnitude (Ms) varying from 3.5 to 5.0 during 2009–2021. The crustal quality factor Q and site response in the Changjiang Delta were obtained simultaneously from regression of Lg Fourier acceleration amplitude versus frequency. The κ0 of each individual station was subsequently calculated from a regression of the high-frequency site terms versus frequency. The site terms exhibit obvious dependence on sediment thickness in the Changjiang Delta. The site amplification factor reaches ∼7–10 for stations overlying sediments ∼8–9 km thick in the northern Jiangsu basin. The site terms were found to behave consistently as a function of sediment thickness over the frequencies of 0.56–24.86 Hz. Site amplification shows a positive correlation with sediment thickness at lower frequencies (<7.26 Hz) but transitions to a negative correlation as frequency increases to 12.86 Hz and higher. Linear functions versus sediment thickness were used to model the site response terms at individual frequencies. We also showed that site terms calculated using the κ0 model as a function of sediment thickness fit the site response terms well at frequencies higher than 9.66 Hz. Results of this study can be incorporated in ground-motion prediction models for the Changjiang Delta. In addition, the site response estimates determined here can be used to reduce bias due to site effects in studies of earthquake source parameters.

Ground Motion Simulations for the 19 January 2020 Jiashi, China, Earthquake Using Stochastic Finite‐Fault Approach

AbstractA 6.0‐magnitude (Mw) earthquake was reported to have occurred in Jiashi County, Xinjiang at 21:27 on 19 January 2020, Beijing time (13:27 UTC). This study applied a stochastic finite‐fault approach based on the dynamic corner frequency (EXSIM) to simulate 23 near‐field stations within a distance of 120 km from the epicenter. The stochastic finite‐fault approach is the simplest and most effective method for simulating high‐frequency ground motions. According to studies and empirical relationships, we estimated a region‐specific parameter (κ0) for use in simulations. In this study, two different slip models, namely, random and inverted slip models, were used to explain their influence on the simulation results. For most stations, the simulated seismic characteristics, such as the peak ground acceleration (PGA), pseudo spectral acceleration ,and Fourier acceleration spectrum, are highly compatible with the observed values in the frequency range (f > 1 Hz), indicating that the stochastic finite‐fault approach is not highly sensitive to input slip distributions and fault dimensions. The simulation results indicated no significance between the two slip models under high‐frequency conditions. Finally, based on the predicted PGA values of 1891 field points selected near the fault, the acceleration field of the Jiashi earthquake is plotted. The results show that the use of the acceleration time history predicted by modified EXSIM is feasible and practical in the high‐frequency band above 1 Hz.

Region- and Site-Specific Measurements of Kappa (κ0) and Associated Variabilities for Iran

ABSTRACT Spectral parameter kappa (κ) is widely used to model the decay slope of the Fourier acceleration spectrum at high frequencies. This study presents estimates of κ0, often referred to as the site-related contribution in κ, for the Iranian strong-motion dataset. For our analysis, we use 2798 acceleration time histories from 325 earthquakes (between 1976 and 2020, inclusive) in the magnitude range M 3–7.4 and recorded over 285 stations at distances up to 100 km. The main objective of this study is to estimate κ0 and associated uncertainties at Iranian strong-motion stations. We investigate different sources of uncertainty that contribute to the higher scatter in the station-specific measurements of κ0. According to our results, the choice of frequency range used to approximate linear decay of acceleration spectrum contributes significantly to measurement-related uncertainty. Moreover, our measurements exhibit regional variations in (average) κ0 within Iran; in particular, for Zagros, the average κ0(=0.036) is found to be lower than that for northern Iran (κ0=0.044) and central-eastern Iran (κ0=0.04). In terms of between-station variability, there is a weak negative correlation between κ0 and VS30. The within-station uncertainty (i.e., standard deviation of κ0 values at individual stations) is also found to be decreasing with increasing VS30. The fundamental frequency of the site (f0) also appears to affect both measurement-related uncertainty and between-station variability at stations that exhibit significant 1D soil response behavior.

Vehicle-induced dynamic response characteristics of a new subway tunnel closely undercrossing the existing subway

Due to the limited underground space in the city, it is inevitable that the new subway may undercross the existing subway during the construction process. The current research mainly focuses on the dynamic response of single tunnel or the construction mechanics and ground motion response of tunnels with short-distance, while there is little research on the dynamic characteristics of subway tunnels undercrossing the existing subway with zero-distance. Therefore, in this paper, relying on a subway tunnel closely undercrossing the existing Line 1 with zero distance in Chengdu, using on-site test and numerical calculation, the vehicle-induced dynamic response characteristics of the new subway tunnel is analyzed under the moving train load of the existing Line 1, and the dynamic response differences of the new subway tunnel under different vehicle speeds and operation modes of the existing Line 1 is also discussed. The results show that the relationship between the acceleration of each part of the new subway tunnel is: roof > the middle wall > side wall > floor. For the horizontal acceleration, since the thickness of the side wall is larger than that of the middle wall, and the difference in the boundary constraints between the middle wall and side wall, the acceleration peak value of the middle wall is larger than that of the side wall. The dynamic response of the new subway increases with vehicle speeds, and the increasing rate of the vehicle speed in the range of 40–60 km/h is greater than that of 60–80 km/h. Compared with one-way operation, the two-way meeting has a certain superimposed effect on the acceleration response of the new subway tunnel and has the greatest impact on the acceleration response of the middle wall. The Fourier acceleration spectrum shows the strongest response around 60 Hz and 130 Hz. It is also found the operation of existing subway has adverse impact on the new subway, and certain vibration reduction measures should be taken to ensure the stability of new subway.

Assessment of Kappa Values in the Chilean Subduction Zone for Interface and In-Slab Events

Abstract One way to study the physical process that occurs behind earthquakes and how they affect different sites depending on the source type and the geological structure of the site is the shape of the Fourier spectrum. A parameter related to the shape of the spectrum is the spectral decay factor—kappa (κ), which characterizes how the amplitude of the Fourier acceleration spectrum decays at high frequencies. The parameter κ can be important in the characterization and estimation of the surface seismic demand, being useful in, for example, the adjustment of ground-motion prediction equations. We calculate the values of κ and its site component κ​0 from 36 seismic stations of the National Seismological Network of Chile to determine the dependence that this parameter has to the site conditions as well as to the properties of the path in which greater values of κ are observed for subduction earthquakes that occur in the interface between the Nazca and the South American plates, compared with the values obtained from events occurring inside the subducting plate, known as in-slab earthquakes. We find that κ​0, calculated using the hypocentral distance correlates more closely with the site fundamental frequency f​0, rather than the commonly used V​S30 (time-averaged shear-wave velocity in the top 30 m). Our kappa value results are field estimates of near-surface attenuation, which can be used to calculate the minimum site-specific damping or crustal attenuation in seismological models that have a strong impact on seismic site characterization, particularly, in subduction settings.

Fast and scalable quantum Monte Carlo simulations of electron-phonon models.

We introduce methodologies for highly scalable quantum Monte Carlo simulations of electron-phonon models, and we report benchmark results for the Holstein model on the square lattice. The determinant quantum Monte Carlo (DQMC) method is a widely used tool for simulating simple electron-phonon models at finite temperatures, but it incurs a computational cost that scales cubically with system size. Alternatively, near-linear scaling with system size can be achieved with the hybrid Monte Carlo (HMC) method and an integral representation of the Fermion determinant. Here, we introduce a collection of methodologies that make such simulations even faster. To combat "stiffness" arising from the bosonic action, we review how Fourier acceleration can be combined with time-step splitting. To overcome phonon sampling barriers associated with strongly bound bipolaron formation, we design global Monte Carlo updates that approximately respect particle-hole symmetry. To accelerate the iterative linear solver, we introduce a preconditioner that becomes exact in the adiabatic limit of infinite atomic mass. Finally, we demonstrate how stochastic measurements can be accelerated using fast Fourier transforms. These methods are all complementary and, combined, may produce multiple orders of magnitude speedup, depending on model details.

Solving quantum rotor model with different Monte Carlo techniques

We systematically test the performance of several Monte Carlo update schemes for the (2 + 1)d XY phase transition of quantum rotor model. By comparing the local Metropolis (LM), LM plus over-relaxation (OR), Wolff-cluster (WC), hybrid Monte Carlo (HM), hybrid Monte Carlo with Fourier acceleration (FA) schemes, it is clear that among the five different update schemes, at the quantum critical point, the WC and FA schemes acquire the smallest autocorrelation time and cost the least amount of CPU hours in achieving the same level of relative error, and FA enjoys a further advantage of easily implementable for more complicated interactions such as the long-range ones. These results bestow one with the necessary knowledge of extending the quantum rotor model, which plays the role of ferromagnetic/antiferromagnetic critical bosons or Z 2 topological order, to more realistic and yet challenging models such as Fermi surface Yukawa-coupled to quantum rotor models.

A New Method for Estimating High Frequency Attenuation Parameter of Kappa

The Fourier amplitude spectrum of acceleration will drop rapidly in the high frequency range. Anderson and Hough quantitatively studied the attenuation law of the acceleration Fourier spectrum above the corner frequency, and proposed the high-frequency attenuation parameter Kappa ( ) to describe this phenomenon. It has important applications in the field of engineering earthquakes, and is widely used by seismologists and engineers in the work of ground motion simulation and attenuation relations. Based on the Anderson method, this paper proposed a method of first smoothing the Fourier acceleration spectrum with a 0.4 Hz Parzen window and then fitting the solution value. The Fukushima earthquake data from Japan’s KiK-net seismic network on February 13, 2021 was used to verify the reliability of the method. The results showed that when the width of the Parzen window was set to 0.4 Hz, the calculation accuracy of the value was effectively improved.

Diagnosis and Resolution of Vibration Issues in Vertical Centrifugal Pump

Centrifugal pumps are more popular for industrial and domestic applications because of small in size, less in capital cost, easy to maintain, able to work at medium to low heads and low viscous fluids when compared to other pumps. Present problem is to diagnosis and resolution of vibration issues of the vertical centrifugal pump at Visakhapatnam steel plant by using experimental and numerical vibration analysis methods. The power, speed, discharge and pressure head of vertical centrifugal pump used in present analysis are 75 kW, 3572 rpm, 150 m3/h and 190 m, respectively. Experimental vibration analysis and modal analysis are carried with the help of fast Fourier transformation analyser, impact hammer and acceleration sensor. The dimensions of various parts of domestic vertical centrifugal pump are obtained using reverse engineering method. Vertical centrifugal pump parts like motor, pump shaft, motor shaft, coupling, coupling cover, pump, tie rods and base frame are modelled and assembled using CATIA. The solid model of vertical centrifugal pump is exported into ANSYS to carry out numerical modal and harmonic analysis to find natural frequencies and vibration levels, respectively. Numerical modal and harmonic analysis results of existing vertical centrifugal pump are compared with experimental results and found that there is good agreement between the results (the maximum error is 5.6%). From the experimental vibration analysis, peak vibration velocity of 12.3 mm/s is observed at coupling cover. From the experimental natural frequency test, the natural frequency of coupling cover of vertical centrifugal pump is observed at 59.3 Hz and it is close to operating speed. So, problem in vertical centrifugal pump is identified at coupling cover. Structural modifications are carried out on coupling cover of vertical centrifugal pump to increase the natural frequencies to reduce the vibration levels. Numerical modal and harmonic analysis are carried out on modified pump to find the natural frequency and vibration levels to quantify the reduction in vibration levels. From this analysis, it is observed that natural frequency is increased to 137.5 Hz and vibration levels are reduced to 0.7 mm/s.

Estimation of Source Spectra, Attenuation, and Site Responses from Strong-Motion Data Recorded in the 2019 Changning Earthquake Sequence

ABSTRACTThis study used 306 accelerograms recorded at 22 strong-motion stations to investigate the source parameters, quality factor (Q), and site effects of S-wave Fourier acceleration amplitude spectrum (FAS) of the 2019 MS 6.0 Changning earthquake sequence in China with surface-wave magnitudes (MS) of 4.1–6.0. The generalized inversion technique (GIT) was adopted. The inverted stress drop of the mainshock was 1.15 MPa, and those of the aftershocks varied from 0.11 to 1.04 MPa with an average value of 0.43 MPa. The MS of these earthquakes were larger than Mw with an average magnitude difference of 0.22. The inverted Q values increase rapidly with frequencies at 0.5–4.0 Hz from 62 to 2920 and become less dependent at 4.0–25.0 Hz. Such a phenomenon indicates that the propagation path attenuation mechanism transited to intrinsic at high frequencies. A bilinear Q(f) model for which Q(f)=237.6f1.27 (Q<1280) and Q=1280 at higher frequencies was obtained. The high-frequency attenuation model of the study area was κ=0.0420+0.0001262R. The inverted site responses of the 22 stations were compared with those calculated using the horizontal-to-vertical spectral ratio (HVSR) method. In general, the amplification curves of most stations obtained with the GIT were similar to those of HVSR, and the amplification levels were relatively higher. Contrarily, obvious discrepancies were observed between the results estimated from the two methods at several stations. Such effects were attributed to the limitation that the majority of the stations were distributed along the boundary of the basin and mountainous areas, and the inverted Q values were representative of the specific area rather than the pure basin and mountainous areas. Finally, a nonlinear soil site effect was observed at 51GXT in earthquakes with peak ground acceleration greater than 300 cm/s2. The nonlinearity obviously aggravated the site amplification at 1.0–5.0 Hz.

Multi-spin echo T2 relaxation imaging with compressed sensing (METRICS) for rapid myelin water imaging.

Myelin water imaging (MWI) provides a valuable biomarker for myelin, but clinical application has been restricted by long acquisition times. Accelerating the standard multi-echo T2 acquisition with gradient echoes (GRASE) or by 2D multi-slice data collection results in image blurring, contrast changes, and other issues. Compressed sensing (CS) can vastly accelerate conventional MRI. In this work, we assessed the use of CS for in vivo human MWI, using a 3D multi spin-echo sequence. We implemented multi-echo T2 relaxation imaging with compressed sensing (METRICS) and METRICS with partial Fourier acceleration (METRICS-PF). Scan-rescan data were acquired from 12 healthy controls for assessment of repeatability. MWI data were acquired for METRICS in 9m:58s and for METRICS-PF in 7m:25s, both with 1.5×2×3mm3 voxels, 56 echoes, 7ms ΔTE, and 240×240×170mm3 FOV. METRICS was compared with a novel multi-echo spin-echo gold-standard (MSE-GS) MWI acquisition, acquired for a single additional subject in 2h:2m:40s. METRICS/METRICS-PF myelin water fraction had mean: repeatability coefficient 1.5/1.1, coefficient of variation 6.2/4.5%, and intra-class correlation coefficient 0.79/0.84. Repeatability metrics comparing METRICS with METRICS-PF were similar, and both sequences agreed with reference values from literature. METRICS images and quantitative maps showed excellent qualitative agreement with those of MSE-GS. METRICS and METRICS-PF provided highly repeatable MWI data without the inherent disadvantages of GRASE or 2D multi-slice acquisition. CS acceleration allows MWI data to be acquired rapidly with larger FOV, higher estimated SNR, more isotropic voxels and more echoes than with previous techniques. The approach introduced here generalizes to any multi-component T2 mapping application.

Quantum Monte Carlo with the Langevin Equation: Coupled Bose-Fermi Systems

We describe the algorithmic details and a performance evaluation of a Langevin approach to a strongly interacting electron-phonon system, and show it has a near linear scaling with lattice size Ns. Many of the limitations of previous attempts to employ such methods to condensed matter lattice Hamiltonians are absent. In particular, the iterative linear algebra solution remains well behaved at strong coupling and low temperatures. The use of Fourier Acceleration is crucial for efficiency, and its use makes the method competitive with the widely-used local update methods, which scale as for on-site interactions and for long range electron-phonon coupling, even on rather small lattice sizes.