Source Orientation Research Articles

Guided Wave Studies for Enhanced Acoustic Emission Inspection

ABSTRACT Fundamental elements of wave mechanics are covered with respect to Acoustic Emission (AE) analysis in Nondestructive Evaluation (NDE) and Structural Health monitoring (SHM). Emphasis is placed on aspects of Ultrasonic Guided Waves that travel in a structure due to elastic wave emissions from a defect source as defects continue to grow. The AE Method is based on the emission of elastic waves from a particular source as failure is initiated – crack, corrosion, leak, and so on. The AE signal received is a function of the source orientation and location as well as wave velocities in the structure, sensor types and positions, arrival time differences, thicknesses of the structure, and specimen structural variations. Such topics as Guided wave physical and theoretical considerations, Ultrasonic Guided wave accomplishments, and enhanced AE by considering various guided wave concepts are discussed. The topic of Acousto-Ultrasonics and its impact on guided wave understanding is also reviewed. This paper illustrates how principles in Ultrasonic Guided waves can be applied to Acoustic Emission. Besides basic issues, Acoustic Emission enhancement possibilities are based on recent studies of Ultrasonic Guided Waves and the use of Shear Horizontal guided waves in Acoustic Emission along with an omni-directional shear horizontal wave transducer. Editor’s note: Joseph L. Rose, PhD, is the recipient of the 2021 ASNT Research Recognition for Sustained Excellence. Rose presented on “Guided Wave Studies for Enhanced Acoustic Emission Inspection” during the ASNT Research Symposium which was held 27–29 April 2021.

Robust Estimation of Contact Force and Location for Magnetic-Field-Based Soft Tactile Sensor Considering Magnetic Source Inconsistency.

Flexible magnetic-field-based tactile sensors (FMFTS) have numerous advantages including low cost, ease of manufacture, simple wiring, high sensitivity, and so on. Flexible magnetic-field-based tactile sensors need to be calibrated before use to build accurate mapping between contact force and magnetic field intensity measured by magnetic sensors; however, when considering remanence inconsistency of magnetic source, each FMFTS needs to be calibrated independently to enhance accuracy, and the complex preparation prevents FMFTS from being used conveniently. A robust estimation method of contact force and location that can tolerate remanence inconsistency of magnetic source in FMFTS is proposed. Firstly, the position and orientation of magnetic source were tracked using the Levenberg–Marquart algorithm, and the tracking results were insensitive to the remanence of magnetic source with appropriate cost function. Secondly, the mapping between magnitude and location of contact force and position and orientation of magnetic source was built with calibration of one sensor; the mapping only depends on the structural response of flexible substrate, and thus can be extended to estimate external force and location for other sensors with the same structure. The proposed method was evaluated in both simulations and experiments, and the results confirm that the estimation of magnitude and location of external force for FMFTS with the same structure and different remanence could reach acceptable accuracy, depending on single calibration. The proposed method can be used to simplify the calibration procedure and remove the barrier for large-scale application of FMFTS and replacement of damaged FMFTS.

Near-field strain in distributed acoustic sensing-based microseismic observation

Microseismic monitoring with surface or downhole geophone arrays has commonly been used in tracking subsurface deformation and fracture networks during hydraulic fracturing operations. Recently, the use of fiber-optic distributed acoustic sensing (DAS) technology has improved microseismic acquisition to a new level with unprecedentedly high spatial resolution and low cost. Deploying fiber-optic cables in horizontal boreholes allows for very close observation of these microsize earthquakes and captures their full wavefield details. We have found that DAS-based microseismic profiles present a seldomly reported near-field strain signal between the P- and S-wave arrivals. This near-field signal indicates a monotonically increasing (or decreasing) temporal variation, which resembles the previously reported near-field observations of large earthquakes. To understand the near-field strain behavior, we use a mathematical expression of the analytic normal strain solution that reveals the near-field, intermediate-near-field, intermediate-far-field, and far-field components. Synthetic DAS strain records of hydraulic-fracture-induced microseismic events can be generated using this analytic solution with the Brune source model. The polarity sign patterns of the near-field and far-field terms in these synthetics are linked to the corresponding source mechanism’s radiation patterns. These polarity sign patterns are demonstrated to be sensitive to the source orientations by rotating the moment tensor in different directions. A field data example is compared to the synthetic result, and a qualitative match is shown. The microseismic near-field signals detected by DAS have potential value in hydraulic fracture monitoring by providing a means to better constrain microseismic source parameters that characterize the source magnitude, source orientation, and temporal source evolution and therefore better reflect the geomechanical response of the hydraulically fractured environment in the unconventional reservoirs.

A fast LED calibration method under near field lighting based on photometric stereo

We proposed and experimentally demonstrate a calibration method to estimate the position and the orientation of the anisotropic near point LED light source from a single view. In this work, a Lambertian sphere is used as the calibration target, where the reflection model of the Lambertian sphere under the illumination of LED with given radiant intensity distribution is analyzed theoretically to establish the relationship between the recorded image intensity and the observed surface. Based on this relationship, the geometrical principle of the calibration is researched and an iteration method is presented to calculate the LED position and orientation with a cost function through minimizing the estimation error. The accuracy of the proposed method is verified by simulations with the mean estimation error lower than 5.8mm and 1.7deg for near field lighting. The experiments are performed by measuring the plaster models using the presented system, which proves the effectiveness of the proposed calibration approach.

Loreto Intermediate Depth Earthquake of 26 May 2019 (Northeast Peru): Source Parameters by Inversion of Local to Regional Waveforms and Strong-Motion Observations

AbstractThe Loreto earthquake of 26 May 2019 occurred below the extreme northeast part of Peru at a depth of 140 km within the subducting Nazca plate at a distance of 700 km from the trench Peru–Chile. The orientation of the seismic source was obtained from waveform inversion in the near field using velocity and strong-motion data. The rupture occurred in normal faulting corresponding to a tensional process with T axis oriented in east–west direction similar to the direction of convergence between the Nazca and South America plates. The analysis of the strong-motion data shows that the levels of ground shaking are very heterogeneous with values greater than 50 Gal up to distances of 300 km; the maximum recorded acceleration of 122 Gal at a distance of 100 km from the epicenter. The Loreto earthquake is classified as a large extensional event in the descending Nazca slab in the transition from flat-slab geometry to greater dip.

Sensitivity functions of space-borne gravitational wave detectors for arbitrary time-delay interferometry combinations regarding nontensorial polarizations

Direct observation of gravitational waves offers us numerous novel possibilities to further explore the Universe. In practice, the efficiency of the experimental facility for a given gravitational wave source can be measured in terms of the sensitivity function of the instrument. The latter essentially indicates the least incident amplitude required in order to achieve the desired level of the signal-to-noise ratio. Among others, the resultant sensitivity function depends on the specific polarization state of the incident gravitational wave as well as the spatial layout of the detector and its orientation to the wave source. Theoretically, Einstein's general relativity predicts two tensor polarization modes, from a total of six possible modes arising from an arbitrary perturbation of the spacetime metric. Therefore, in this context, the feasibility of measuring nontensorial polarization states provides access to an alternative theory of gravity. In the present study, we analytically evaluate the response functions for arbitrary time-delay interferometry combinations while enumerating all possible polarization modes. The derivation is accomplished by separating the average on the all-sky solid angle from the remaining expression, which, in turn, gives rise to a few factors independent of the time-delay interferometry combination in question. Moreover, we applied the obtained results to the LISA and TianQin missions, and the asymptotic behavior of the resultant sensitivity functions is analyzed and discussed. Among others, it is observed that, for Sagnac combinations, the averaged response function of the breathing mode attains zero at specific discrete frequencies. Such a frequency value corresponds to a multiple of the reciprocal of the one-way light propagation time along the detector arm, irrelevant to the orientation of the wave source. For all six polarization modes, the present findings can be readily applied to an arbitrary time-delay interferometry combination with improved efficiency and accuracy.

The Quadrature Method: A Novel Dipole Localisation Algorithm for Artificial Lateral Lines Compared to State of the Art.

The lateral line organ of fish has inspired engineers to develop flow sensor arrays—dubbed artificial lateral lines (ALLs)—capable of detecting near-field hydrodynamic events for obstacle avoidance and object detection. In this paper, we present a comprehensive review and comparison of ten localisation algorithms for ALLs. Differences in the studied domain, sensor sensitivity axes, and available data prevent a fair comparison between these algorithms from their original works. We compare them with our novel quadrature method (QM), which is based on a geometric property specific to 2D-sensitive ALLs. We show how the area in which each algorithm can accurately determine the position and orientation of a simulated dipole source is affected by (1) the amount of training and optimisation data, and (2) the sensitivity axes of the sensors. Overall, we find that each algorithm benefits from 2D-sensitive sensors, with alternating sensitivity axes as the second-best configuration. From the machine learning approaches, an MLP required an impractically large training set to approach the optimisation-based algorithms’ performance. Regardless of the data set size, QM performs best with both a large area for accurate predictions and a small tail of large errors.

Media Literacy Research During COVID-19 Pandemic: Social Network Screening

The article presents screening of Facebook and Instagram news pages for the degree of media literacy of modern recipients in the perception and further dissemination of information about COVID-19. We state that in most cases modern recipients do not check the information obtained from media sources (as confirmation, we present the results of an electronic survey). Nowadays most respondents do not pay attention to the information provided and are ready to repost the material on their social media pages. The data obtained confirm this thesis: 45.8 % partially 23.7 % fully do not check the information from media sources, therefore, almost two thirds of respondents trust the facts presented in media. We associate low media literacy with the rapid globalization of modern media, due to which the flow of information is uncontrolled, especially in Internet communication. Another reason for low media literacy is the skill of journalists to mislead recipients through bright headlines. It is proved that a bright headline, compositionally organized as an interrogative or exclamatory sentence, has a greater impact than a narrative construction. According to our survey, headlines with lexical manipulative resources are the most popular (44 %), while headlines with phonetic manipulative means are less affected by the recipient. Most of the interviewed recipients are still ready to check the factuality of the information in a media text (we emphasize that we have deliberately selected fake news). Some recipients (22 %) pay attention to fake news because of a bright headline (or trusting a verified media resource) and are ready to repost the news without verification. Due to the resonance of the news related to COVID-19 journalists have used not only objective but also fake news as a tool to influence the recipient. The questionnaire clearly indicates that media literacy of modern recipients is influenced by the political orientation of a media source, as well as the recklessness of recipients to verify the facts and trust any information obtained from official sources and interpreted in media. Copyright © 2021 by Academic Publishing House Researcher s.r.o.

A novel beamformer-based imaging of phase–amplitude coupling (BIPAC) unveiling the inter-regional connectivity of emotional prosody processing in women with primary dysmenorrhea

Objective. Neural communication or the interactions of brain regions play a key role in the formation of functional neural networks. A type of neural communication can be measured in the form of phase–amplitude coupling (PAC), which is the coupling between the phase of low-frequency oscillations and the amplitude of high-frequency oscillations. This paper presents a beamformer-based imaging method, beamformer-based imaging of PAC (BIPAC), to quantify the strength of PAC between a seed region and other brain regions. Approach. A dipole is used to model the ensemble of neural activity within a group of nearby neurons and represents a mixture of multiple source components of cortical activity. From ensemble activity at each brain location, the source component with the strongest coupling to the seed activity is extracted, while unrelated components are suppressed to enhance the sensitivity of coupled-source estimation. Main results. In evaluations using simulation data sets, BIPAC proved advantageous with regard to estimation accuracy in source localization, orientation, and coupling strength. BIPAC was also applied to the analysis of magnetoencephalographic signals recorded from women with primary dysmenorrhea in an implicit emotional prosody experiment. In response to negative emotional prosody, auditory areas revealed strong PAC with the ventral auditory stream and occipitoparietal areas in the theta–gamma and alpha–gamma bands, which may respectively indicate the recruitment of auditory sensory memory and attention reorientation. Moreover, patients with more severe pain experience appeared to have stronger coupling between auditory areas and temporoparietal regions. Significance. Our findings indicate that the implicit processing of emotional prosody is altered by menstrual pain experience. The proposed BIPAC is feasible and applicable to imaging inter-regional connectivity based on cross-frequency coupling estimates. The experimental results also demonstrate that BIPAC is capable of revealing autonomous brain processing and neurodynamics, which are more subtle than active and attended task-driven processing.

Auto-calibration of cone beam geometries from arbitrary rotating markers using a vector geometry formulation of projection matrices

An efficient method for the determination of the projection geometry of cone beam micro computed tomography systems based on two or more fiducial markers of unknown position within the field of view is derived. By employing the projection matrix formalism commonly used in computer graphics, a very clear presentation of the resulting self consistent calibration problem can be given relating the sought-for matrix to observable parameters of the markers’ projections. Both an easy to implement solution procedure for both the unknown projection matrix and the marker assembly as well as the mapping from projection matrices to real space positions and orientations of source and detector relative to the rotational axis are provided. The separate treatment of the calibration problem in terms of projection matrices on the one hand and the independent transformation to a more intuitive geometry representation on the other hand proves to be very helpful with respect to the discussion of the ambiguities occurring in reference-free calibration. In particular, a link between methods based on knowledge on the sample and those based on knowledge solely on the detector geometry can be drawn. This further provides another intuitive view on the often reported difficulty in the estimation of the detector tilt towards the rotational axis. A simulation study considering 106 randomly generated cone beam imaging configurations and fiducial marker distributions within a range of typical scenarios is performed in order to assess the stability of the proposed technique. An experimental example supports the simulation results.

The role of early and late reflections on perception of source orientation.

Sound radiation of most natural sources, like human speakers or musical instruments, typically exhibits a spatial directivity pattern. This directivity contributes to the perception of sound sources in rooms, affecting the spatial energy distribution of early reflections and late diffuse reverberation. Thus, for convincing sound field reproduction and acoustics simulation, source directivity has to be considered. Whereas perceptual effects of directivity, such as source-orientation-dependent coloration, appear relevant for the direct sound and individual early reflections, it is unclear how spectral and spatial cues interact for later reflections. Better knowledge of the perceptual relevance of source orientation cues might help to simplify the acoustics simulation. Here, it is assessed as to what extent directivity of a human speaker should be simulated for early reflections and diffuse reverberation. The computationally efficient hybrid approach to simulate and auralize binaural room impulse responses [Wendt et al., J. Audio Eng. Soc. 62, 11 (2014)] was extended to simulate source directivity. Two psychoacoustic experiments assessed the listeners' ability to distinguish between different virtual source orientations when the frequency-dependent spatial directivity pattern of the source was approximated by a direction-independent average filter for different higher reflection orders. The results indicate that it is sufficient to simulate effects of source directivity in the first-order reflections.

Validation of a Fast and Accurate Magnetic Tracker Operating in the Environmental Field

We characterize the performance of a system based on a magnetoresistor array. This instrument is developed to map the magnetic field, and to track a dipolar magnetic source in the presence of a static homogeneous field. The position and orientation of the magnetic source with respect to the sensor frame is retrieved together with the orientation of the frame with respect to the environmental field. A nonlinear best-fit procedure is used, and its precision, time performance, and reliability are analyzed. This analysis is performed in view of the practical application for which the system is designed that is an eye-tracking diagnostics and rehabilitative tool for medical purposes, which require high speed (≥100 Sa/s) and sub-millimetric spatial resolution. A throughout investigation on the results makes it possible to list several observations, suggestions, and hints, which will be useful in the design of similar setups.

Vertex-degree based topological indices of digraphs

Let Dn be the set of digraphs with n non-isolated vertices. Let D∈Dn and denote by du+ and du− the outer degree and inner degree, respectively, of the vertex u of D. We define the vertex-degree-based (VDB, for short) topological index φ induced by the real numbers φij, as φD=12∑1≤i,j≤n−1aijφij,where aij is the number of arcs in D of the form uv, where du+=i and dv−=j. We show in this paper that this is a generalization of the concept of VDB topological indices of graphs. In the case φij=1ij, we obtain the Randić index of digraphs, which we denote by χ. We find the extremal values of χ over Dn. We also find the extremal values of χ over OT(n), the set of all oriented trees with n vertices. On the other hand, given a graph G, we consider the set OG of all orientations of G, and show that when G is a bipartite graph, the sink–source orientations of G uniquely attain the minimal value of χ over OG. We find the extremal values of χ over OPn and OCn, where Pn and Cn are the path and the cycle with n vertices, respectively. Finally, we find the extremal values of χ over OHd, the set of all orientations of the hypercube Hd of dimension d.

Natural convection and wall radiation in a cubical cavity with different discrete heat source configurations: Geometric parameters effect

The heat transfer by natural convection and wall radiation in filled air partially heated 3-D cavity is a problem related to different practical situations. In this study, the effects of several geometric parameters (form, orientation, size, position) of a discreet heat source on the flow structure and heat transfer characteristics are discussed for a wide range of the Rayleigh number 103≤Ra≤107 and the different wall-emissivities 0≤ε≤1. The heater is maintained at a high-temperature and positioned on a given vertical or horizontal passive wall of the enclosure. The right vertical surface of the cavity is completely isothermal at a fixed cold temperature. Flow and thermal fields were exhibited using of velocity vectors (or streamlines) and isotherms, respectively. The local and average Nusselt numbers were also presented. A numerical procedure based on both the finite volume and the discrete ordinate methods are used to solve the governing equations. It is found that the rate of heat transfer is not so sensitive to the form and the orientation of the discreet heat source. On the other hand, the position and the size of the heater are found to play a significant role in the global Nusselt number.

Effects of explant position and orientation, medium ph and nitrogen sources on micropropagation of blackberry

Composition of the medium and the explant origin are factors that interfere on success of micropropagation of Rubus species. For blackberry cultivar LochNess it was not investigated yet how the position and orientation of explant, pH levels and nitrogen source interfere on micropropagation. In this work, focused on the establishment of in vitro culture, variables were studied on R. fruticosus cv Loch Ness, such as the choice of the explants depending on their original position on the mother plant, pH level and nitrogen sources of the culture medium. For the first time in vitro on Rubus, the downward orientation (capogatto) of shoot tips explants was compared with the normal upward orientation. The highest weight and length values were recorded for the shoots proliferated from basal and nodal explants. For the initiation medium, the best multiplication rate were obtained in pH adjusted to 4.5. Shoot length was influenced by the nitrogen source; when associated with an increased light intensity, the complete substitution of ammonium by nitrate allowed results comparable with those obtained with the control medium containing both sources. The use of aminoacids did not improve the results. Apex orientation did not affect anatomical parameters or rooting rates of wild Rubus, but more efforts should be devoted on in vitro capogatto technique considering that advantages like reduction of plant growth regulators, cultivation on the same medium culture for more time and easily rooting can be established.

Variability of room acoustic parameters with thermo-hygrometric conditions

The variation of the room acoustic parameters measured in an auditorium is influenced by many variables such as the equipment, the operator, the position and orientation of the sound source and the microphones, and the post-processing method used for the calculation. An influence of fundamental importance is due to the thermo-hygrometric variables, which is commonly neglected. In this article, an experimental analysis concerning the influence of the temperature, relative humidity, and air velocity on acoustic parameters is presented. Thermo-hygrometric variables have been varied and the variation of several room acoustic parameters has been analized. A statistical analysis of the correlations has been obtained and used for the evaluation of the variation of the acoustic parameters by changing the thermo-hygrometric variables. Finally, a statistical analysis has been conducted to find correlations between room acoustic parameters and thermo-hygrometric parameters.

Conspiracy vs science: A large-scale analysis of online discussion cascades.

With the emergence and rapid proliferation of social media platforms and social networking sites, recent years have witnessed a surge of misinformation spreading in our daily life. Drawing on a large-scale dataset which covers more than 1.4M posts and 18M comments from an online social media platform, we investigate the propagation of two distinct narratives–(i) conspiracy information, whose claims are generally unsubstantiated and thus referred as misinformation to some extent, and (ii) scientific information, whose origins are generally readily identifiable and verifiable. We find that conspiracy cascades tend to propagate in a multigenerational branching process whereas science cascades are more likely to grow in a breadth-first manner. Specifically, conspiracy information triggers larger cascades, involves more users and generations, persists longer, and is more viral and bursty than science information. Content analysis reveals that conspiracy cascades contain more negative words and emotional words which convey anger, fear, disgust, surprise and trust. We also find that conspiracy cascades are much more concerned with political and controversial topics. After applying machine learning models, we achieve an AUC score of nearly 90% in discriminating conspiracy from science narratives using the constructed features.We further investigate user’s role during the growth of cascades. In contrast with previous assumption that misinformation is primarily driven by a small set of users, we find that conspiracy cascades are more likely to be controlled by a broader set of users than science cascades, imposing new challenges on the management of misinformation. Although political affinity is thought to affect the consumption of misinformation, there is very little evidence that political orientation of the information source plays a role during the propagation of conspiracy information; Instead, we find that conspiracy information from media outlets with left or right orientation triggers smaller cascades and is less viral than information from online social media platforms (e.g., Twitter and Imgur) whose political orientations are unclear. Our study provides complementing evidence to current misinformation research and has practical policy implications to stem the propagation and mitigate the influence of misinformation online.

Convolutional Neural Network for Voltage Sag Source Azimuth Recognition in Electrical Internet of Things

Recognition and analytics at the edge enable utility companies to predict and prevent problems in real time. Clearing the voltage sag disturbance source by the positioning method is the most effective way to solve and improve the voltage sag. However, for different grid structures and fault types, the existing methods usually achieve a sag source location based on the single feature of monitoring data extraction. However, due to the effectiveness and applicability of the existing method features, this paper proposes a multidimensional feature of the voltage sag source positioning method of the matrix. Based on the analysis of the characteristics of the voltage sag event caused by the fault, this paper proposes a multidimensional feature matrix for voltage sag source location, based on the convolutional neural network to establish the mapping relationship between the feature matrix and the voltage sag position, thus achieving multiple points based on multiple points. The voltage sag source orientation is identified by the monitoring data. Finally, the voltage sag event caused by the short‐circuit fault is simulated in the IEEE14 node model, and the effectiveness of the proposed method is verified by simulation data. The simulation results show that the proposed method has higher accuracy than the traditional method, and the method can be applied to different grid structures and different types of faults.

Fast, Cheap, and Scalable Magnetic Tracker with an Array of Magnetoresistors

We present the hardware of a cheap multi-sensor magnetometric setup, where a relatively large set of magnetic field components is measured in several positions by calibrated magnetoresistive detectors. The setup is developed to map the (inhomogeneous) field generated by a known magnetic source, which is measured and then discerned from the background (homogeneous) geomagnetic field. The data output from this hardware can be successfully and reliably used to retrieve the position and orientation of the magnetic source with respect to the sensor frame, together with the orientation of the frame with respect to the environmental field. Possible applications of the setup are briefly discussed, and a synthetic description of the methods of data elaboration and analysis is provided.

Electrokinetic Contributions to Self‐Potential Signals From Magmatic Stressing

AbstractPre‐eruptive electrical signals at active volcanoes are generally interpreted in terms of electrokinetic processes. Spatio‐temporal self‐potential (SP) signals can be caused by strain‐induced fluid flow in volcanic aquifers, however, previous studies lack the quantitative assessments of these phenomena and the underpinning poroelastic responses. Here we use Finite‐Element Analysis to study poroelastic responses induced by subsurface stressing from sill and dike sources by jointly solving for ground displacements, pore pressure, and SP signals. We evaluate the influence of pressure source orientation on the poroelastic response in two different volcanic aquifers (pyroclastic and lava flow) to provide insights on emergent geodetic and SP signals and their sensitivity to governing parameters. Strain‐induced SP amplitudes deduced from a reference parameter set vary in both aquifer models and are of negative polarity (−0.35 and −22.6 mV) for a pressurized dike and of positive polarity (+4 and +20 mV) for a pressurized sill. Importantly, we find uniquely different SP and ground displacement patterns from either sill or dike intrusions. Our study shows that SP signals are highly sensitive to the subsurface Young's modulus, streaming potential coupling coefficient and electrical conductivity of the poroelastic domains. For the set of parameters tested, the dike model predicts SP amplitudes of up to −947 mV which are broadly representative of recorded amplitudes from active volcanoes. Our study demonstrates that electrokinetic processes reflect magma‐induced stress and strain variations and highlights the potential of joint geodetic and SP studies to gain new insights on causes of volcanic unrest.