Simultaneous Sources Research Articles

Differences in cortical responses to spatial changes in foreground versus background auditory objects

Identifying neural markers related to the integration of auditory features—such as spectrum, temporal coherence, and lateral position—can help to reveal the mechanisms underlying how the auditory system processes simultaneous sound sources. For a stimulus that is composed of randomly chosen successive inharmonic tone complexes, a subset of tones can perceptually segregate from the other simultaneous tones if the subset repeats for a sufficient number of tokens. Listeners can reliably detect this repeating pattern as a figure sound object amidst a randomly changing background. An electroencephalogram was recorded while listeners performed the detection of changes in interaural time difference (ITD) cues that were attributed to either the figure or the background. Detection of ITD changes for either auditory object elicited a fronto-central early negativity (100–200 ms) and P300 event-related potentials (ERP) associated with identification of a behaviorally relevant event. However, the ERP amplitudes were larger for the ITD changes associated with the figure compared those associated with an ITD change of the background. This illustrates that the manner in which spectro-temporal features combine to form auditory objects can modulate cortical responses to spatial information. The result supports the notion that spatial features integrate subsequent to object formation.

Multiple partial discharge source discrimination with multiclass support vector machines

The costs of decommissioning high-voltage equipment due to insulation breakdown are associated to the substitution of the asset and to the interruption of service. They can reach millions of dollars in new equipment purchases, fines and civil lawsuits, aggravated by the negative perception of the grid utility. Thus, condition based maintenance techniques are widely applied to have information about the status of the machine or power cable readily available. Partial discharge (PD) measurements are an important tool in the diagnosis of power systems equipment. The presence of PD can accelerate the local degradation of insulation systems and generate premature failures. Conventionally, PD classification is carried out using the phase resolved partial discharge (PRPD) pattern of pulses. The PRPD is a two dimensional representation of pulses that enables visual inspection but lacks discriminative power in common scenarios found in industrial environments, such as many simultaneous PD sources and low magnitude events that can be hidden below noise. The literature shows several works that complement PRPD with machine learning detectors (neural networks and support vector machines) and with more sophisticated signal representations, like statistics captured in several modalities, wavelets and other transforms, etc. These methods improve the classification accuracy but obscure the interpretation of the results. In this paper, the use of a support vector machine (SVM) operating on the power spectrum density of signals is proposed to identify different pulses what could be used in an online tool in the maintenance decision-making of the utility. Particularly, the approach is based on an SVM endowed with a special kernel that operates in the frequency domain. The SVM is previously trained with pulses of different PD types (internal, surface and corona) and noise that are obtained with several test objects in the laboratory. The experimental results demonstrate that this technique is highly effective in identifying PD for cases where several sources are active or when the noise level is high. Thus, the early identification of critical events with this approach during normal operation of the equipment will help in the decision of decommissioning the asset with reduced costs and low impact to the grid reliability.

Control of nitrogen content and its effects on the electrochemical behavior of nitrogen-doped carbon nanofibers

Nitrogen-doped carbon nanofibers (N-CNFs) with different nitrogen contents were synthesized from vaporized acetonitrile as a simultaneous carbon and nitrogen source via the chemical vapor deposition method. N-CNF synthesis was conducted at 640°C for 2h, and the ratio of nitrogen and hydrogen mixture as reactant gas was adjusted to control the nitrogen content in the N-CNFs. The amount of hydrogen in the reactant gas was varied in the range from 0 to 40mLmin−1. The physical and electrochemical properties of the N-CNFs were characterized. The content of introduced nitrogen decreased with the ratio of supplied hydrogen, as opposed to the growth yield of the N-CNFs. Additionally, the nitrogen content and chemical states of the N-CNFs were examined and compared to reveal their correlations with the electrochemical behavior. The N-CNFs were found to have a noticeable electrochemical behavior such as capacitance and oxygen reduction reaction activity that was determined by the total nitrogen contents, especially those of pyridinic-nitrogen.

How do we adopt multiple cultural identities? A multidimensional operationalization of the sources of culture

Given the shortcomings of unidimensional accounts of culture that are based on nationality, this paper builds on and steps beyond current multidimensional conceptualizations of culture in order to provide first empirical evidence for a multidimensional operationalization of culture. It shows the multiple and simultaneous sources of cultural values (i.e., Family, Nationality, Urban/Rural Background, etc.) that individuals draw from in order to behave in accordance with their social setting. This contributes to our understanding of how and when individuals adopt multiple cultural identities. As the first attempt to operationalize the ‘mosaic’ framework of culture proposed by Chao and Moon (2005), this paper presents rich and detailed accounts from participants operating in various multinational organizations located in Munich, Germany and Cape Town/Johannesburg, South Africa. Findings reveal that the operationalization that was used in this study can determine which cultural facets are more influential than others in different settings. It further shows how some individuals willingly adopt distinct cultural identities in different social settings (i.e., home culture versus organizational culture), while others acquire permeable identities, bringing their home culture to work. Thus, we provide a multifaceted view of what constitutes culturally derived behaviour and how individuals' multiple cultural identities can be managed in the workplace.

Binary Sparse Coding of Convolutive Mixtures for Sound Localization and Separation via Spatialization

We propose a sparse coding approach to address the problem of source-sensor localization and speech reconstruction. This approach relies on designing a dictionary of spatialized signals by projecting the microphone array recordings into the array manifolds characterized for different locations in a reverberant enclosure using the image model. Sparse representation over this dictionary enables identifying the subspace of the actual recordings and its correspondence to the source and sensor locations. The speech signal is reconstructed by inverse filtering the acoustic channels associated to the array manifolds. We provide rigorous analysis on the optimality of speech reconstruction by elucidating the links between inverse filtering and source separation followed by deconvolution. This procedure is evaluated for localization, reconstruction and recognition of simultaneous speech sources using real data recordings. The results demonstrate the effectiveness of the proposed approach and compare favorably against beamforming and independent component analysis techniques.

Penning Plasma Based Simultaneous Light Emission Source of Visible and VUV Lights

Penning Plasma Based Simultaneous Light Emission Source of Visible and VUV Lights

Seismic character of possible buried grounding-zone wedges in the Late Ordovician glacial rocks of Algeria

A relatively brief ice age in the Late Ordovician, about 445 Ma ago, when North Africa was located near the South Pole led to the deposition of terrestrial and marine glacial sediments across northern Africa (e.g. Le Heron & Craig 2008). Several types of glacial landforms have been identified previously in these glacial rocks, including sedimentary features interpreted as ice-proximal fans and tunnel valleys produced by subglacial meltwater flow (e.g. Hirst 2012). These glacigenic rocks had been buried beneath about 2000 m of overlying sediment and have been deformed subsequently by multiple orogenic phases. A number of asymmetrical depocentres have been identified in three-dimensional (3D) reflection-seismic records from Illizi Basin, Algeria (Fig. 1). They are interpreted as grounding-zone wedges (GZWs), by analogy with similar features in Quaternary sediments on the Greenland margin (Dowdeswell & Fugelli 2012). Fig. 1. ( a , c , d ) Seismic profiles through the long axes of three Late Ordovician buried grounding-zone wedges (GZWs, blue lines mark upper surfaces) in Illizi Basin, Algeria. VE×25, ×10 and ×10, respectively. Time sections from ISS™ (Independent Simultaneous Sources). 3D survey shot in 2009. We acknowledge Sonatrach, BP's partner in Algeria, for its part in …

Polarization Control of Morphological Pattern Orientation During Light-Mediated Synthesis of Nanostructured Se-Te Films.

The template-free growth of well ordered, highly anisotropic lamellar structures has been demonstrated during the photoelectrodeposition of Se-Te films, wherein the orientation of the pattern can be directed by orienting the linear polarization of the incident light. This control mechanism was investigated further herein by examining the morphologies of films grown photoelectrochemically using light from two simultaneous sources that had mutually different linear polarizations. Photoelectrochemical growth with light from two nonorthogonally polarized same-wavelength sources generated lamellar morphologies in which the long axes of the lamellae were oriented parallel to the intensity-weighted average polarization orientation. Simulations of light scattering at the solution-film interface were consistent with this observation. Computer modeling of these growths using combined full-wave electromagnetic and Monte Carlo growth simulations successfully reproduced the experimental morphologies and quantitatively agreed with the pattern orientations observed experimentally by considering only the fundamental light-material interactions during growth. Deposition with light from two orthogonally polarized same-wavelength as well as different-wavelength sources produced structures that consisted of two intersecting sets of orthogonally oriented lamellae in which the relative heights of the two sets could be varied by adjusting the relative source intensities. Simulations of light absorption were performed in analogous, idealized intersecting lamellar structures and revealed that the lamellae preferentially absorbed light polarized with the electric field vector along their long axes. These data sets cumulatively indicate that anisotropic light scattering and light absorption generated by the light polarization produces the anisotropic morphology and that the resultant morphology is a function of all illumination inputs despite differing polarizations.

New insight into the correlations between land use and water quality in a coastal watershed of China: Does point source pollution weaken it?

Uncovering the associations between land use and river water quality is useful for managing land-based pollution in the catchment-coast continuum. However, it is not clear how land use affects water quality in the context of simultaneous point source (PS) pollution. In this study, we develop a self-organizing map (SOM)-based approach to explore the relationship between land use and water quality in the Minjiang River Watershed, Southeast China. Water samples from 139 headwater sub-watersheds were associated with six land use categories, namely, Woodland, Agriculture, Orchard, Built-up, Unused land and Water. Sampling sites are delineated into six clusters based on six water quality parameters: ammonium-N, nitrate-N, total nitrogen, soluble reactive phosphate, total phosphate and potassium permanganate index. Local relationships between land use and water quality among four clusters that have sufficient sample sizes are further identified. There is no significant land use-water quality correlation in one of the four clusters (including 37 sub-watersheds). And the greater the PS pollution is, the less significant the land use-water quality correlations are in clusters. The results demonstrate how PS pollution weakens the land use-water quality correlation. Our method can help to determine whether non-point source or PS pollution exerts greater influence on the quality of the water coming from watershed.

Simultaneous Low-Cost Carbon Sources and CO2 Valorizations through Catalytic Gasification

The inherent CO2 gasification reactivities of chars derived from a series of plentiful carbon sources, including petroleum coke (petcoke), coal with various ranks, biomass, and even municipal solid wastes, have been systematically investigated in this work. Among these, switchgrass char exhibits the best activity, while petcoke char behaves the worst toward CO production. The results from sample characterizations indicate that the inherent char reactivity during CO2 gasification is closely related to its physical properties such as the alkali metal and oxygen contents as well as the H/C atomic ratio. In addition, the effect of the reaction conditions (i.e., temperature, pressure, space velocity, particle size of char, and CO and CO2 concentrations in the gas feedstock) on char CO2 gasification has also been explored. Moreover, a set of supported catalysts have been developed to further promote the char reactivity toward CO2 gasification at moderate temperature, among which K–Ca/ZnO–CeO2 ranks at the top in terms of CO2 conversion and CO production and demonstrates excellent stability during a long-term cumulative run. Through careful analyses of the collected catalyst characterization results, a novel catalyst design composed of two redox metal/metal oxide pairs supported on an oxygen ion conductor, based on the reported K–Ca/ZnO–CeO2 system, has been proposed for future catalyst development with even better CO2 gasification performance for fluidized bed applications with much easier catalyst recovery and thus minimized catalyst loss.

Independent simultaneous source acquisition and processing

Seismic surveys are often constrained by the time needed to activate all the required sources so the source signals do not interfere with each other. Simultaneous source seismic acquisition, also referred to as blended acquisition, is an effective method for reducing the cost and improving the quality of seismic surveys by eliminating the requirement that the sources do not interfere with each other. Independent simultaneous shooting is a unique form of blended acquisition in which sources operate independently of each other and the receiver recording is continuous. This acquisition method is particularly efficient and robust in obtaining high-density source grids for land and marine surveys. Processing the simultaneous source data depends on the randomness of the shot times to create a situation where the signal is coherent, and the interference is random in common-receiver gathers. Although the older and simpler method of separating interfering shots with random noise attenuation works well when the residual interference noise left by the random noise attenuation is acceptable, higher separation quality is possible using a shot separation process based on sparse inversion and compressive sensing methodology. We found that the resulting simultaneous source surveys produced images that were equivalent to or better than conventional seismic surveys, while requiring less acquisition effort, thus reducing costs.

Fast simultaneous seismic source separation using Stolt migration and demigration operators

Stolt migration is a Fourier-domain imaging operator that assumes a constant-velocity media. We have developed a multivelocity version of the Stolt migration and demigration operators to derive a transform that can decompose seismic data into a sparse collection of coefficients in the image space. This Stolt-based transform is similar to the apex-shifted hyperbolic Radon transform (ASHRT). However, the Stolt-based transform is considerably faster than the classical ASHRT because it uses two fast operators (forward and inverse fast Fourier transforms) to estimate the data coefficients in the image space. We used this Stolt-based transform as a tool for simultaneous seismic source separation by removing erratic interference noise in common receiver gathers. Estimating the coefficients of interference-free seismic data using the Stolt-based transform was posed as an inverse problem. The solution of this inverse problem was found by minimizing a cost function that included a sparsity-promoting regularization term. In addition, the cost function incorporated a robust misfit function that was not sensitive to erratic interferences. Our tests on synthetic and field data examples determined that this new transform can efficiently remove interference noise and achieve fast simultaneous seismic source separation.

Taking signal and noise to new dimensions — Introduction

This special section covers present-day algorithms for seismic signal processing. In the last decade, important efforts were made in the development of signal processing methods that exploit the multidimensionality of seismic data. A stringent requirement for multidimensional seismic data processing is the elaboration of strategies to represent seismic data. This special section contains interesting examples of novel transformation for multidimensional seismic signal separation, seismic noise attenuation, and reconstruction. Examples are algorithms that use seislets, chirplets, local slant stacks, and apex shifted Radon transforms. In addition, this special section also offers results from a new family of algorithms that are inspired by the fields of compressive sensing, reduce-rank filtering, and dictionary learning. These algorithms can be used for data reconstruction, signal-to-noise-ratio enhancement and simultaneous source data processing. A special section on seismic signal processing cannot be complete without articles that tackle pervasive problems in seismic data exploration. As such, we also present papers on wavelet processing and sampling theory. We hope you enjoy reading this brew of papers as much as we have enjoyed assembling this special section. Chen and Fomel develop a novel approach to random noise attenuation that eliminates remaining coherent signal in the removed noise by using local signal and-noise orthogonalization. Local signal-and-noise orthogonalization can retrieve the leakage signal …

Separation of simultaneous sources using a structural-oriented median filter in the flattened dimension

Simultaneous-source shooting can help tremendously shorten the acquisition period and improve the quality of seismic data for better subsalt seismic imaging, but at the expense of introducing strong interference (blending noise) to the acquired seismic data. We propose to use a structural-oriented median filter to attenuate the blending noise along the structural direction of seismic profiles. The principle of the proposed approach is to first flatten the seismic record in local spatial windows and then to apply a traditional median filter (MF) to the third flattened dimension. The key component of the proposed approach is the estimation of the local slope, which can be calculated by first scanning the NMO velocity and then transferring the velocity to the local slope. Both synthetic and field data examples show that the proposed approach can successfully separate the simultaneous-source data into individual sources. We provide an open-source toy example to better demonstratethe proposed methodology.

Looking for Oil From More Angles

Seismic Data New generation of seismic promises big advances Selling new offshore seismic survey methods can be reduced to two goals: “We want more of everything at less cost.” That maxim was offered by Andrew Long, chief scientist of geoscience and engineering, imaging, and engineering for Petroleum Geo- Services, one of the players in this intensely competitive, economically depressed, technology-driven business. While the science behind using sound waves to image underground formations is baffling to outsiders, the two avenues for doing it better are not. There are improvements in data acquisition covering sound sources, receivers, and survey methods. And there is the mathematics and computer power needed to process and extract more information from the constantly growing amount of data gathered. Faster, Better Seismic Surveys by Making Many Sounds at Once The pace of a seismic survey can be measured by the number of shots taken per day. Huge onshore surveys have shown that allowing 10 or more sound sources working at the same time without any coordination can drastically reduce the time needed to gather data over a large area, and get better data as well. “One of the biggest surprises is we have gotten almost universally better data from our simultaneous source surveys,” said Craig Beasley, a Schlumberger Fellow and chief geophysicist at WesternGeco. More data are gathered from more angles for a more accurate picture of what is below, said Beasley, who explained that one flashlight can help you see in a dark basement, but it is better with two and more is better. The Hunger for the Lowest Frequencies Takes Data Gathering in New Directions The word “broadband” is used to sell a lot of what is new in offshore seismic. It can mean different things depending on who is speaking. But most often, it is applied to things used to gather scarce signals at the lowest frequencies. Gathering more low-frequency data is the “holy grail’ in broadband, said Craig Beasley, chief geophysicist at Western- Geco, which is part of Schlumberger. They are valuable for determining rock properties and imaging deep formations. Seemingly small gains can be big. “Moving down from “3 to 1.5 (Hz) does not sound like a lot. But in octaves, it is a whole other octave,” he said. Intractable Problem and Big Payoff Sell a Seismic Acquisition Innovation The Mad Dog field was a major discovery for BP in the late 1990s, but developing it looked like a high-risk proposition. The problem was the field was an early discovery beneath the thick layer of salt covering much of the deepwater US Gulf of Mexico. Shooting seismic through the salt resulted in murky images that increased the risk of development wells that produced little or nothing, which could turn a 4-billion-bbl field into a marginal investment. BP needed to solve the problem because it had leased a large number of deepwater blocks where the industry was drilling a growing number of dry holes due to poor subsurface imaging. “It was pretty common knowledge in the industry that you have this problem. But what are you going to do about it?” said John Etgen, a distinguished advisor in seismic imaging at BP. The problem is salt distorts sound waves as they travel down and are reflected back up. The salt is like broken eyeglasses. It acts as “big, very complex lens distorting the sound waves.”

Acoustic 2D full waveform inversion to solve gas cloud challenges

<p>The existing conventional inversion algorithm does not provide satisfactory results due to the complexity of propagated wavefield though the gas cloud. Acoustic full waveform inversion has been developed and applied to a realistic synthetic offshore shallow gas cloud feature with Student-t approach, with and without simultaneous sources encoding. As a modeling operator, we implemented the grid based finite-difference method in frequency domain using second order elastic wave equation. Jacobin operator and its adjoint provide a necessary platform for solving full waveform inversion problem in a reduced Hessian matrix. We invert gas cloud model in 5 frequency band selected from 1 to 12 Hz, each band contains 3 frequencies. The inversion results are highly sensitive to the misfit. The model allows better convergence and recovery of amplitude losses. This approach gives better resolution then the existing least-squares approach. In this paper, we implement the full waveform inversion for low frequency model with minimum number of iteration providing a better resolution of inversion results.</p>

The benefit of encoded source sequences for simultaneous source separation

We have developed a method for simultaneous source separation using time dithering and encoded source sequences. The source sequences are designed so that they are close to orthogonal to each other, having minimized crosscorrelation and optimal autocorrelation properties. We found that this additional encoding of time-dithered sources could be exploited with a multifrequency separation method. The separation method relies on a coherency-based approach and is solved by a sparse Radon inversion. Realistic synthetic data examples confirmed the importance of using the multifrequency method to take advantage of the sequence orthogonality and to deal with spatially aliased data. Our results demonstrate that source sequence encoding can significantly improve simultaneous source separation compared with using time dithering only.

Simultaneous head tissue conductivity and EEG source location estimation

Accurate electroencephalographic (EEG) source localization requires an electrical head model incorporating accurate geometries and conductivity values for the major head tissues. While consistent conductivity values have been reported for scalp, brain, and cerebrospinal fluid, measured brain-to-skull conductivity ratio (BSCR) estimates have varied between 8 and 80, likely reflecting both inter-subject and measurement method differences. In simulations, mis-estimation of skull conductivity can produce source localization errors as large as 3cm. Here, we describe an iterative gradient-based approach to Simultaneous tissue Conductivity And source Location Estimation (SCALE). The scalp projection maps used by SCALE are obtained from near-dipolar effective EEG sources found by adequate independent component analysis (ICA) decomposition of sufficient high-density EEG data. We applied SCALE to simulated scalp projections of 15cm2-scale cortical patch sources in an MR image-based electrical head model with simulated BSCR of 30. Initialized either with a BSCR of 80 or 20, SCALE estimated BSCR as 32.6. In Adaptive Mixture ICA (AMICA) decompositions of (45-min, 128-channel) EEG data from two young adults we identified sets of 13 independent components having near-dipolar scalp maps compatible with a single cortical source patch. Again initialized with either BSCR 80 or 25, SCALE gave BSCR estimates of 34 and 54 for the two subjects respectively. The ability to accurately estimate skull conductivity non-invasively from any well-recorded EEG data in combination with a stable and non-invasively acquired MR imaging-derived electrical head model could remove a critical barrier to using EEG as a sub-cm2-scale accurate 3-D functional cortical imaging modality.

Simultaneous source and attenuation reconstruction in SPECT using ballistic and single scattering data

In medical single-photon emission computed tomography (SPECT) imaging, we seek to simultaneously obtain the internal radioactive sources and the attenuation map using not only ballistic measurements but also first-order scattering measurements and assuming a very specific scattering regime. The problem is modeled using the radiative transfer equation by means of an explicit non-linear operator that gives the ballistic and scattering measurements as a function of the radioactive source and attenuation distributions. First, by differentiating this non-linear operator we obtain a linearized inverse problem. Then, under regularity hypothesis for the source distribution and attenuation map and considering small attenuations, we rigorously prove that the linear operator is invertible and we compute its inverse explicitly. This allows proof of local uniqueness for the non-linear inverse problem. Finally, using the previous inversion result for the linear operator, we propose a new type of iterative algorithm for simultaneous source and attenuation recovery for SPECT based on the Neumann series and a Newton–Raphson algorithm.

Sector-Based Parametric Sound Field Reproduction in the Spherical Harmonic Domain

This papers presents a parametric method for perceptual sound field recording and reproduction from a small-sized microphone array to arbitrary loudspeaker layouts. The applied parametric model has been found to be effective and well-correlated with perceptual attributes in the context of directional audio coding, and here it is generalized and extended to higher orders of spherical harmonic signals. Higher order recordings are used for estimation of the model parameters inside angular sectors that provide increased separation between simultaneous sources and reverberation. The perceptual synthesis according to the combined properties of these sector parameters is achieved with an adaptive least-squares mixing technique. Furthermore, considerations regarding practical microphone arrays are presented and a frequency-dependent scheme is proposed. A realization of the system is described for an existing spherical microphone array and for a target loudspeaker setup similar to NHK 22.2. It is demonstrated through listening tests that, compared to a reference scene, the perceived difference is greatly reduced with the proposed higher order analysis model. The results further indicate that, on the same task, the method outperforms linear reproduction with the same recordings available.