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Khalil, Diaa. "Cascaded multimode interference phased array structures for dense wavelength division multiplexing applications". Optical Engineering 43, n.º 5 (1 de maio de 2004): 1060. http://dx.doi.org/10.1117/1.1695404.
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Turnbull, Daniel H., Paul K. Lum, Andrew T. Kerr e F. Stuart Foster. "Simulation of B-Scan Images from Two-Dimensional Transducer Arrays: Part I - Methods and Quantitative Contrast Measurements". Ultrasonic Imaging 14, n.º 4 (outubro de 1992): 323–43. http://dx.doi.org/10.1177/016173469201400401.
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Recently, theoretical investigations of the beamforming capability of two-dimensional (2-D) transducer arrays have characterized the array parameters required to steer a symmetrically focused ultrasound beam up to 45° off-axis. These investigations have also shown that the number of elements in a steered 2-D array can be dramatically reduced by using a sparse set of elements, randomly distributed throughout the aperture of the transducer. The penalty paid for the use of a sparse array is the development of a “pedestal” sidelobe in the beam profile, the amplitude of which increases as the number of elements in the array decreases. In this paper the potential of 2-D arrays for medical imaging is assessed by simulating B-scan images of spherical lesions, both cystic and scattering, embedded in a large random scattering volume. Similar contrast characteristics over a range of cyst sizes are demonstrated for a dense 2-D array and a sparse array with 1/8th the number of elements, both operating at 5 MHz. A 32nd order sparse array is shown to perform at a reduced level, producing unacceptable artifactual echoes within images of cysts. The 8th order sparse array pattern has been fabricated on a fixed-focus poly(vinylidene difluoride) transducer using photolithographic, techniques. Experimental images from this transducer are used to verify some of the theoretical predictions made in this paper. Comparisons between simulated B-scan images from linear and 2-D phased arrays are presented in a companion paper.
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Gangfeng, Zheng, Xia Wandong, Wu Xiaoming e Yan Yingchun. "A study of dense-medium cyclone inner-wall abrasion based on ultrasonic phased array technology". Measurement 126 (outubro de 2018): 58–64. http://dx.doi.org/10.1016/j.measurement.2018.05.013.
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Otsuka, Shigenori, Gulanbaier Tuerhong, Ryota Kikuchi, Yoshikazu Kitano, Yusuke Taniguchi, Juan Jose Ruiz, Shinsuke Satoh, Tomoo Ushio e Takemasa Miyoshi. "Precipitation Nowcasting with Three-Dimensional Space–Time Extrapolation of Dense and Frequent Phased-Array Weather Radar Observations". Weather and Forecasting 31, n.º 1 (1 de fevereiro de 2016): 329–40. http://dx.doi.org/10.1175/waf-d-15-0063.1.
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Abstract The phased-array weather radar (PAWR) is a new-generation weather radar that can make a 100-m-resolution three-dimensional (3D) volume scan every 30 s for 100 vertical levels, producing ~100 times more data than the conventional parabolic-antenna radar with a volume scan typically made every 5 min for 15 scan levels. This study takes advantage of orders of magnitude more rapid and dense observations by PAWR and explores high-precision nowcasting of 3D evolution at 1–10-km scales up to several minutes, which are compared with conventional horizontal two-dimensional (2D) nowcasting typically at O(100) km scales up to 1–6 h. A new 3D precipitation extrapolation system was designed to enhance a conventional algorithm for dense and rapid PAWR volume scans. Experiments show that the 3D extrapolation successfully captured vertical motions of convective precipitation cores and outperformed 2D nowcasting with both simulated and real PAWR data.
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Newman, Jennifer F., e Pamela L. Heinselman. "Evolution of a Quasi-Linear Convective System Sampled by Phased Array Radar". Monthly Weather Review 140, n.º 11 (1 de novembro de 2012): 3467–86. http://dx.doi.org/10.1175/mwr-d-12-00003.1.
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Abstract On 2 April 2010, a quasi-linear convective system (QLCS) moved eastward through Oklahoma during the early morning hours. Wind damage in Rush Springs, Oklahoma, approached (enhanced Fujita) EF1-scale intensity and was likely associated with a mesovortex along the leading edge of the QLCS. The evolution of the QLCS as it produced its first bow echo was captured by the National Weather Radar Testbed Phased Array Radar (NWRT PAR) in Norman, Oklahoma. The NWRT PAR is an S-band radar with an electronically steered beam, allowing for rapid volumetric updates (~1 min) and user-defined scanning strategies. The rapid temporal updates and dense vertical sampling of the PAR created a detailed depiction of the damaging wind mechanisms associated with the QLCS. Key features sampled by the PAR include microbursts, an intensifying midlevel jet, and rotation associated with the mesovortex. In this work, PAR data are analyzed and compared to data from nearby operational radars, highlighting the advantages of using high-temporal-resolution data to monitor storm evolution. The PAR sampled the events preceding the Rush Springs circulation in great detail. Based on PAR data, the midlevel jet in the QLCS strengthened as it approached Rush Springs, creating an area of strong midlevel convergence where it impinged on the system-relative front-to-rear flow. As this convergence extended to the lower levels of the storm, a preexisting azimuthal shear maximum increased in magnitude and vertical extent, and EF1-scale damage occurred in Rush Springs. The depiction of these events in the PAR data demonstrates the complex and rapidly changing nature of QLCSs.
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Zribi, Mehrez, Sekhar Muddu, Safa Bousbih, Ahmad Al Bitar, Sat Kumar Tomer, Nicolas Baghdadi e Soumya Bandyopadhyay. "Analysis of L-Band SAR Data for Soil Moisture Estimations over Agricultural Areas in the Tropics". Remote Sensing 11, n.º 9 (11 de maio de 2019): 1122. http://dx.doi.org/10.3390/rs11091122.
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The main objective of this study is to analyze the potential use of L-band radar data for the estimation of soil moisture over tropical agricultural areas under dense vegetation cover conditions. Ten radar images were acquired using the Phased Array Synthetic Aperture Radar/Advanced Land Observing Satellite (PALSAR/ALOS)-2 sensor over the Berambadi watershed (south India), between June and October of 2018. Simultaneous ground measurements of soil moisture, soil roughness, and leaf area index (LAI) were also recorded. The sensitivity of PALSAR observations to variations in soil moisture has been reported by several authors, and is confirmed in the present study, even for the case of very dense crops. The radar signals are simulated using five different radar backscattering models (physical and semi-empirical), over bare soil, and over areas with various types of crop cover (turmeric, marigold, and sorghum). When the semi-empirical water cloud model (WCM) is parameterized as a function of the LAI, to account for the vegetation’s contribution to the backscattered signal, it can provide relatively accurate estimations of soil moisture in turmeric and marigold fields, but has certain limitations when applied to sorghum fields. Observed limitations highlight the need to expand the analysis beyond the LAI by including additional vegetation parameters in order to take into account volume scattering in the L-band backscattered radar signal for accurate soil moisture estimation.
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Connor, L., J. van Leeuwen, L. C. Oostrum, E. Petroff, Y. Maan, E. A. K. Adams, J. J. Attema et al. "A bright, high rotation-measure FRB that skewers the M33 halo". Monthly Notices of the Royal Astronomical Society 499, n.º 4 (30 de setembro de 2020): 4716–24. http://dx.doi.org/10.1093/mnras/staa3009.
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ABSTRACT We report the detection of a bright fast radio burst, FRB 191108, with Apertif on the Westerbork Synthesis Radio Telescope. The interferometer allows us to localize the FRB to a narrow 5 arcsec × 7 arcmin ellipse by employing both multibeam information within the Apertif phased-array feed beam pattern, and across different tied-array beams. The resulting sightline passes close to Local Group galaxy M33, with an impact parameter of only 18 kpc with respect to the core. It also traverses the much larger circumgalactic medium (CGM) of M31, the Andromeda Galaxy. We find that the shared plasma of the Local Group galaxies could contribute ∼10 per cent of its dispersion measure of 588 pc cm−3. FRB 191108 has a Faraday rotation measure (RM) of +474 $\pm \, 3$ rad m−2, which is too large to be explained by either the Milky Way or the intergalactic medium. Based on the more moderate RMs of other extragalactic sources that traverse the halo of M33, we conclude that the dense magnetized plasma resides in the host galaxy. The FRB exhibits frequency structure on two scales, one that is consistent with quenched Galactic scintillation and broader spectral structure with Δν ≈ 40 MHz. If the latter is due to scattering in the shared M33/M31 CGM, our results constrain the Local Group plasma environment. We found no accompanying persistent radio sources in the Apertif imaging survey data.
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Rodriguez-Alvarez, Nereida, Erika Podest, Katherine Jensen e Kyle C. McDonald. "Classifying Inundation in a Tropical Wetlands Complex with GNSS-R". Remote Sensing 11, n.º 9 (4 de maio de 2019): 1053. http://dx.doi.org/10.3390/rs11091053.
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The use of global navigation satellite system reflectometry (GNSS-R) measurements for classification of inundated wetlands is presented. With the launch of NASA’s Cyclone Global Navigation Satellite System (CYGNSS) mission, space-borne GNSS-R measurements have become available over ocean and land. CYGNSS covers latitudes between ±38°, providing measurements over tropical ecosystems and benefiting new studies of wetland inundation dynamics. The GNSS-R signal over inundated wetlands is driven mainly by coherent scattering associated with the presence of surface water, producing strong forward scattering and a distinctive bistatic scattering signature. This paper presents a methodology used to classify inundation in tropical wetlands using observables derived from GNSS-R measurements and ancillary data. The methodology employs a multiple decision tree randomized (MDTR) algorithm for classification and wetland inundation maps derived from the phased-array L-band synthetic aperture radar (PALSAR-2) as reference for training and validation. The development of an innovative GNSS-R wetland classification methodology is aimed to advance mapping of global wetland distribution and dynamics, which is critical for improved estimates of natural methane production. The results obtained in this manuscript demonstrate the ability of GNSS-R signals to detect inundation under dense vegetation over the Pacaya-Samiria Natural Reserve, a tropical wetland complex located in the Peruvian Amazon. Classification results report an accuracy of 69% for regions of inundated vegetation, 87% for open water regions, and 99% for non-inundated areas. Misclassification of inundated vegetation, primarily as non-inundated area, is likely related to the combination of two factors: partial inundation within the GNSS-R scattering area, and signal attenuation from dense overstory vegetation, resulting in a low signal.
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Pedraza, Carlos, Nicola Clerici, Cristian Forero, América Melo, Diego Navarrete, Diego Lizcano, Andrés Zuluaga, Juliana Delgado e Gustavo Galindo. "Zero Deforestation Agreement Assessment at Farm Level in Colombia Using ALOS PALSAR". Remote Sensing 10, n.º 9 (13 de setembro de 2018): 1464. http://dx.doi.org/10.3390/rs10091464.
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Due to the fast deforestation rates in the tropics, multiple international efforts have been launched to reduce deforestation and develop consistent methodologies to assess forest extension and change. Since 2010 Colombia implemented the Mainstream Sustainable Cattle Ranching project with the participation of small farmers in a payment for environmental services (PES) scheme where zero deforestation agreements are signed. To assess the fulfillment of such agreements at farm level, ALOS-1 and ALOS-2 PALSAR fine beam dual imagery for years 2010 and 2016 was processed with ad-hoc routines to estimate stable forest, deforestation, and stable nonforest extension for 2615 participant farms in five heterogeneous regions of Colombia. Landsat VNIR imagery was integrated in the processing chain to reduce classification uncertainties due to radar limitations. Farms associated with Meta Foothills regions showed zero deforestation during the period analyzed (2010–2016), while other regions showed low deforestation rates with the exception of the Cesar River Valley (75 ha). Results, suggests that topography and dry weather conditions have an effect on radar-based mapping accuracy, i.e., deforestation and forest classes showed lower user accuracy values on mountainous and dry regions revealing overestimations in these environments. Nevertheless, overall ALOS Phased Array L-band SAR (PALSAR) data provided overall accurate, relevant, and consistent information for forest change analysis for local zero deforestation agreements assessment. Improvements to preprocessing routines and integration of high dense radar time series should be further investigated to reduce classification errors from complex topography conditions.
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Deka, Suruj S., Sizhu Jiang, Si Hui Pan e Yeshaiahu Fainman. "Nanolaser arrays: toward application-driven dense integration". Nanophotonics 10, n.º 1 (29 de setembro de 2020): 149–69. http://dx.doi.org/10.1515/nanoph-2020-0372.
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AbstractThe past two decades have seen widespread efforts being directed toward the development of nanoscale lasers. A plethora of studies on single such emitters have helped demonstrate their advantageous characteristics such as ultrasmall footprints, low power consumption, and room-temperature operation. Leveraging knowledge about single nanolasers, the next phase of nanolaser technology will be geared toward scaling up design to form arrays for important applications. In this review, we discuss recent progress on the development of such array architectures of nanolasers. We focus on valuable attributes and phenomena realized due to unique array designs that may help enable real-world, practical applications. Arrays consisting of exactly two nanolasers are first introduced since they can serve as a building block toward comprehending the behavior of larger lattices. These larger-sized lattices can be distinguished depending on whether or not their constituent elements are coupled to one another in some form. While uncoupled arrays are suitable for applications such as imaging, biosensing, and even cryptography, coupling in arrays allows control over many aspects of the emission behavior such as beam directionality, mode switching, and orbital angular momentum. We conclude by discussing some important future directions involving nanolaser arrays.
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Krieger, James D., Chen-Pang Yeang e Gregory W. Wornell. "Dense Delta-Sigma Phased Arrays". IEEE Transactions on Antennas and Propagation 61, n.º 4 (abril de 2013): 1825–37. http://dx.doi.org/10.1109/tap.2013.2241719.
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Nwobi, Chukwuebuka, Mathew Williams e Edward T. A. Mitchard. "Rapid Mangrove Forest Loss and Nipa Palm (Nypa fruticans) Expansion in the Niger Delta, 2007–2017". Remote Sensing 12, n.º 14 (21 de julho de 2020): 2344. http://dx.doi.org/10.3390/rs12142344.
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Mangrove forests in the Niger Delta are very valuable, providing ecosystem services, such as carbon storage, fish nurseries, coastal protection, and aesthetic values. However, they are under threat from urbanization, logging, oil pollution, and the proliferation of the invasive Nipa Palm (Nypa fruticans). However, there are no reliable data on the current extent of mangrove forest in the Niger Delta, its rate of loss, or the rate of colonization by the invasive Nipa Palm. Here, we estimate the area of Nipa Palm and mangrove forests in the Niger Delta in 2007 and 2017, using 567 ground control points, Advanced Land Observatory Satellite Phased Array L-band SAR (ALOS PALSAR), Landsat and the Shuttle Radar Topography Mission Digital Elevation Model 2000 (SRTM DEM). We performed the classification using Maximum Likelihood (ML) and Support Vector Machine (SVM) methods. The classification results showed SVM (overall accuracy 93%) performed better than ML (77%). Producers (PA) and User’s accuracy (UA) for the best SVM classification were above 80% for most classes; however, these were considerably lower for Nipa Palm (PA—32%, UA—30%). We estimated a 2017 mangrove area of 801,774 ± 34,787 ha (±95% Confidence Interval) ha and Nipa Palm extent of 11,447 ± 7343 ha. Our maps show a greater landward extent than other reported products. The results indicate a 12% (7–17%) decrease in mangrove area and 694 (0–1304)% increase in Nipa Palm. Mapping efforts should continue for policy targeting and monitoring. The mangroves of the Niger Delta are clearly in grave danger from both rapid clearance and encroachment by the invasive Nipa Palm. This is of great concern given the dense carbon stocks and the value of these mangroves to local communities for generating fish stocks and protection from extreme events.
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Lucas, Richard, Lisa-Maria Rebelo, Lola Fatoyinbo, Ake Rosenqvist, Takuya Itoh, Masanobu Shimada, Marc Simard et al. "Contribution of L-band SAR to systematic global mangrove monitoring". Marine and Freshwater Research 65, n.º 7 (2014): 589. http://dx.doi.org/10.1071/mf13177.
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Information on the status of and changes in mangroves is required for national and international policy development, implementation and evaluation. To support these requirements, a component of the Japan Aerospace Exploration Agency’s (JAXA) Kyoto and Carbon (K&C) initiative has been to design and develop capability for a Global Mangrove Watch (GMW) that routinely monitors and reports on local to global changes in the extent of mangroves, primarily on the basis of observations by Japanese L-band synthetic aperture radar (SAR). The GMW aims are as follows: (1) to map progression of change within or from existing (e.g. Landsat-derived) global baselines of the extent of mangroves by comparing advanced land-observing satellite 2 (ALOS-2) phased array L-band SAR 2 (PALSAR-2) data from 2014 with that acquired by the Japanese earth resources satellite (JERS-1) SAR (1992–1998) and ALOS PALSAR (2006–2011); (2) to quantify changes in the structure and associated losses and gains of carbon on the basis of canopy height and above-ground biomass (AGB) estimated from the shuttle radar topographic mission (SRTM; acquired 2000), the ice, cloud and land-elevation satellite (ICESAT) geoscience laser altimeter system (GLAS; 2003–2010) and L-band backscatter data; (3) to determine likely losses and gains of tree species diversity through reference to International Union for the Conservation of Nature (IUCN) global thematic layers on the distribution of mangrove species; and (4) to validate maps of changes in the extent of mangroves, primarily through comparison with dense time-series of Landsat sensor data and to use these same data to describe the causes and consequences of change. The paper outlines and justifies the techniques being implemented and the role that the GMW might play in supporting national and international policies that relate specifically to the long-term conservation of mangrove ecosystems and the services they provide to society.
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Wang, Baoping, e Junhao Zheng. "DOA Estimation Using Fourth-Order Cumulants in Nested Arrays with Structured Imperfections". Sensors 20, n.º 4 (12 de fevereiro de 2020): 994. http://dx.doi.org/10.3390/s20040994.
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Recently developed super nested array families have drawn much attention owing to their merits on keeping the benefits of the standard nested arrays while further mitigating coupling in dense subarray portions. In this communication, a new mutual coupling model for nested arrays is constructed. Analyzing the structure of the newly formed mutual coupling matrix, a transformation of the distorted steering vector to separate angular information from the mutual coupling coefficients is revealed. By this property, direction of arrival (DOA) estimates can be determined via a grid search for the minimum of a determinant function of DOA, which is induced by the rank reduction property. We also extend the robust DOA estimation method to accommodate the unknown mutual coupling and gain-phase mismatches in the nested array. Compared with the schemes of super nested array families on reducing the mutual coupling effects, the solutions presented in this paper has two advantages: (a) It is applicable to the standard nested arrays without rearranging the configuration to increase the inter-element spacing, alleviating the cross talk in dense uniform linear arrays (ULAs) as well as gain-phase errors in sparse ULA parts; (b) Perturbations in nested arrays are estimated in colored noise, which is significant but rarely discussed before. Simulations results corroborate the superiority of the proposed methods using fourth-order cumulants.
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Samajdar, Rhine, Wen Wei Ho, Hannes Pichler, Mikhail D. Lukin e Subir Sachdev. "Quantum phases of Rydberg atoms on a kagome lattice". Proceedings of the National Academy of Sciences 118, n.º 4 (19 de janeiro de 2021): e2015785118. http://dx.doi.org/10.1073/pnas.2015785118.
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We analyze the zero-temperature phases of an array of neutral atoms on the kagome lattice, interacting via laser excitation to atomic Rydberg states. Density-matrix renormalization group calculations reveal the presence of a wide variety of complex solid phases with broken lattice symmetries. In addition, we identify a regime with dense Rydberg excitations that has a large entanglement entropy and no local order parameter associated with lattice symmetries. From a mapping to the triangular lattice quantum dimer model, and theories of quantum phase transitions out of the proximate solid phases, we argue that this regime could contain one or more phases with topological order. Our results provide the foundation for theoretical and experimental explorations of crystalline and liquid states using programmable quantum simulators based on Rydberg atom arrays.
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Zhong, Minyan, e Zhongwen Zhan. "An array-based receiver function deconvolution method: methodology and application". Geophysical Journal International 222, n.º 1 (14 de março de 2020): 1–14. http://dx.doi.org/10.1093/gji/ggaa113.
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SUMMARY Receiver functions (RFs) estimated on dense arrays have been widely used for the study of Earth structures across multiple scales. However, due to the ill-posedness of deconvolution, RF estimation faces challenges such as non-uniqueness and data overfitting. In this paper, we present an array-based RF deconvolution method in the context of emerging dense arrays. We propose to exploit the wavefield coherency along a dense array by joint inversions of waveforms from multiple events and stations for RFs with a minimum number of phases required by data. The new method can effectively reduce the instability of deconvolution and help retrieve RFs with higher fidelity. We test the algorithm on synthetic waveforms and show that it produces RFs with higher interpretability than those by the conventional RF estimation practice. Then we apply the method to real data from the 2016 Incorporated Research Institutions for Seismology (IRIS) community wavefield experiment in Oklahoma and are able to generate high-resolution RF profiles with only three teleseismic earthquakes recorded by the temporary deployment. This new method should help enhance RF images derived from short-term high-density seismic profiles.
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Chmiel, Małgorzata, Philippe Roux, Marc Wathelet e Thomas Bardainne. "Phase-velocity inversion from data-based diffraction kernels: seismic Michelson interferometer". Geophysical Journal International 224, n.º 2 (28 de outubro de 2020): 1287–300. http://dx.doi.org/10.1093/gji/ggaa512.
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SUMMARY We propose a new surface wave tomography approach that benefits from densely sampled active-source arrays and brings together elements from active-source seismic-wave interferometry, full waveform inversion and dense-array processing. In analogy with optical interferometry, seismic Michelson interferometer (SMI) uses seismic interference patterns given by the data-based diffraction kernels in an iterative inversion scheme to image a medium. SMI requires no traveltime measurements and no spatial regularization, and it accounts for bent rays. Furthermore, the method does not need computation of complex synthetic models, as it works as a data-driven inversion technique that makes it computationally very fast. In an automatic way, it provides high-resolution phase-velocity maps and their error estimation. SMI can complete traditional surface wave tomography studies, as its use can be easily extended from land active seismic data to the virtual source gathers of ambient-noise-based studies with dense arrays.
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Gong, Pan, Tanveer Ahmed e Jianfeng Li. "Three-Dimensional Coprime Array for Massive MIMO: Array Configuration Design and 2D DOA Estimation". Wireless Communications and Mobile Computing 2020 (13 de janeiro de 2020): 1–14. http://dx.doi.org/10.1155/2020/2686257.
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In massive multiple-input multiple-output (MIMO) systems, it is critical to obtain the accurate direction of arrival (DOA) estimation. Conventional three-dimensional array mainly focuses on the uniform array. Due to the dense arrangement of the sensors, the array aperture is limited and severe mutual coupling effects arise. In this paper, a coprime cubic array (CCA) configuration design is presented, which is composed of two uniform cubic subarrays and can extend the interelement spacing with a selection of three pairs of coprime integers. Compared with uniform cubic array (UCA), CCA achieves the larger array aperture and less MC effects. And the analytical expression of Cramer–Rao Bound (CRB) for CCA is derived which verifies that the proposed CCA geometry outperforms the conventional UCA in two-dimensional (2D) DOA estimation performance in massive MIMO systems. Meanwhile, we propose a computationally efficient 2D DOA estimation algorithm with high accuracy for CCA. Specifically, we utilize array mapping to extract two uniform arrays from the nonuniform array by exploiting the relation derived from the signal subspace and the two directional matrices. Then, we operate a reduced dimension process on the uniform arrays and convert the 2D spectrum peak searching (SPS) problem into one-dimensional (1D) one, which significantly reduces the computational complexity. In addition, we employ the polynomial root finding technique with a lower complexity instead of 1D SPS to further relieve the computational complexity. Simultaneously, with coprime property, the phase ambiguity problem is solved, which results from the large interelement spacing. Numerical simulation results demonstrate that the proposed algorithm is very computationally efficient without degradation of DOA estimation performance.
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Iizuka, Kotaro, Yuichi S. Hayakawa, Takuro Ogura, Yasutaka Nakata, Yoshiko Kosugi e Taichiro Yonehara. "Integration of Multi-Sensor Data to Estimate Plot-Level Stem Volume Using Machine Learning Algorithms–Case Study of Evergreen Conifer Planted Forests in Japan". Remote Sensing 12, n.º 10 (21 de maio de 2020): 1649. http://dx.doi.org/10.3390/rs12101649.
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The development of new methods for estimating precise forest structure parameters is essential for the quantitative evaluation of forest resources. Conventional use of satellite image data, increasing use of terrestrial laser scanning (TLS), and emerging trends in the use of unmanned aerial systems (UASs) highlight the importance of modern technologies in the realm of forest observation. Each technology has different advantages, and this work seeks to incorporate multiple satellite, TLS- and UAS-based remote sensing data sets to improve the ability to estimate forest structure parameters. In this paper, two regression analysis approaches are considered for the estimation: random forest regression (RFR) and support vector regression (SVR). To collect the dependent variable, in situ measurements of individual tree parameters (tree height and diameter at breast height (DBH)) were taken in a Japanese cypress forest using the nondestructive TLS method, which scans the forest to obtain dense and accurate point clouds under the tree canopy. Based on the TLS data, the stem volume was then computed and treated as ground truth information. Topographic and UAS information was then used to calculate various remotely sensed explanatory variables, such as canopy size, canopy cover, and tree height. Canopy cover and canopy shapes were computed via the orthoimages derived from the UAS and watershed segmentation method, respectively. Tree height was computed by combining the digital surface model (DSM) from the UAS and the digital terrain model (DTM) from the TLS data. Topographic variables were computed from the DTM. The backscattering intensity in the satellite imagery was obtained based on L-band (Advanced Land Observing Satellite-2 (ALOS-2) Phased Array type L-band Synthetic Aperture Radar-2 (PALSAR-2)) and C-band (Sentinel-1) synthetic aperture radar (SAR). All satellite (10–25 m resolution), TLS (3.4 mm resolution) and UAS (2.3–4.6 cm resolution) data were then combined, and RFR and SVR were trained; the resulting predictive powers were then compared. The RFR method yielded fitting R2 up to 0.665 and RMSE up to 66.87 m3/ha (rRMSE = 11.95%) depending on the input variables (best result with canopy height, canopy size, canopy cover, and Sentinel-1 data), and the SVR method showed fitting R2 up to 0.519 and RMSE up to 80.12 m3/ha (rRMSE = 12.67%). The RFR outperformed the SVR method, which could delineate the relationship between the variables for better model accuracy. This work has demonstrated that incorporating various remote sensing data to satellite data, especially adding finer resolution data, can provide good estimates of forest parameters at a plot level (10 by 10 m), potentially allowing advancements in precision forestry.
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Xu, Y., S. Lebedev, T. Meier, R. Bonadio e C. J. Bean. "Optimized workflows for high-frequency seismic interferometry using dense arrays". Geophysical Journal International 227, n.º 2 (6 de julho de 2021): 875–97. http://dx.doi.org/10.1093/gji/ggab260.
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SUMMARY High-frequency seismic surface waves sample the top few tens of meters to the top few kilometres of the subsurface. They can be used to determine 3-D distributions of shear-wave velocities and to map the depths of discontinuities (interfaces) within the crust. Passive seismic imaging, using ambient noise as the source of signal, can thus be an effective tool of exploration for mineral, geothermal and other resources, provided that sufficient high-frequency signal is available in the ambient noise wavefield and that accurate, high-frequency measurements can be performed on this signal. Ambient noise imaging using the ocean-generated noise at 5–30 s periods is now a standard method, but less signal is available at frequencies high enough for deposit-scale imaging (0.2–30 Hz), and few studies have reported successful measurements in broad frequency bands. Here, we develop a workflow for the measurement of high-frequency, surface wave phase velocities in very broad frequency ranges. Our workflow comprises (1) a new noise cross-correlation procedure that accounts for the non-stationary properties of the high-frequency noise sources, removes bandpass filtering, replaces temporal normalization with short time window stacking, and drops the explicit spectral normalization by adopting cross-coherence; (2) a new phase-velocity measurement method that extends the bandwidth of reliable measurements by exploiting the (resolved) 2π ambiguity of phase-velocity measurements and (3) interstation-distance-dependent quality control that uses the similarity of subgroups of dispersion curves to reject outliers and identify the frequency ranges with accurate measurements. The workflow is highly automated and applicable to large arrays. Applying our method to data from a large-N array that operated for one month near Marathon, Ontario, Canada, we use rectangular subarrays with 150-m station spacing and, typically, 1 hr of data and obtain Rayleigh-wave phase-velocity measurements in a 0.5–30 Hz frequency range, spanning over 5.9 octaves, twice the typical frequency range of 1.5–3 octaves in previous studies. Phase-velocity maps and the subregion-average 1-D velocity models they constrain show a high-velocity anomaly consistent with the known, west-dipping gabbro intrusions beneath the area. The new structural information can improve our understanding of the geometry of the gabbro intrusions, hosting the Cu-PGE Marathon deposit.
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Mattias Borg, B., Jonas Johansson, Kristian Storm e Knut Deppert. "Geometric model for metalorganic vapour phase epitaxy of dense nanowire arrays". Journal of Crystal Growth 366 (março de 2013): 15–19. http://dx.doi.org/10.1016/j.jcrysgro.2012.12.142.
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Надточий, А. М., С. А. Минтаиров, Н. А. Калюжный, С. C. Рувимов, В. Н. Неведомский, М. В. Максимов e А. Е. Жуков. "Бимодальность в массивах гибридных квантово-размерных гетероструктур In-=SUB=-0.4-=/SUB=-Ga-=SUB=-0.6-=/SUB=-As, выращенных на подложках GaAs". Физика и техника полупроводников 52, n.º 1 (2018): 57. http://dx.doi.org/10.21883/ftp.2018.01.45319.8636.
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AbstractHybrid quantum-confined heterostructures grown by metal-organic vapor-phase epitaxy (MOVPE) via the deposition of In_0.4Ga_0.6As layers with various nominal thicknesses onto vicinal GaAs substrates are studied by photoluminescence spectroscopy and transmission electron microscopy. The photoluminescence spectra of these structures show the superposition of two spectral lines, which is indicative of the bimodal distribution of the size and/or shape of light-emitting objects in an array. The dominant spectral line is attributed to the luminescence of hybrid “quantum well–dot” nanostructures in the form of a dense array of relatively small quantum dots (QDs) with weak electron and hole localization. The second, lower intensity line is attributed to luminescence from a less dense array of comparatively larger QDs. Analysis of the behavior of the spectral line intensities at various temperatures showed that the density of larger QDs grows with increasing thickness of the InGaAs layer.
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Lin, En-Chiang, Jun Fang e Heiko O. Jacobs. "Gas Phase Electrodeposition: A Programmable Localized Deposition Method for Rapid Combinatorial Investigation of Nanostuctured Devices and 3D Bulk Heterojunction Photovoltaic Cells". MRS Proceedings 1439 (2012): 57–62. http://dx.doi.org/10.1557/opl.2012.846.
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ABSTRACTThis article applies a recently discovered gas phase nanocluster electrodeposition process to the formation and combinatorial improvement of 3D bulk heterojunction photovoltaic cells. The gas phase deposition process used here is a single reactor system that forms charged nanoclusters (gold, silver, tungsten, and platinum) at atmospheric pressure. The clusters deposit onto selected surface areas with sub 100 nm lateral resolution using a programmable concept similar to liquid phase electrodeposition such that biased electrodes turn ON or OFF deposition in selected areas. Continued deposition of the nanoparticles results in a tower array with different lengths and density on a single substrate which is used as contacts to the active organic layer of 3D bulk heterojunction photovoltaic cells. Applying a combinatorial approach identifies in a massively parallel way electrode designs and topologies that improve light scattering, absorption, and minority carrier extraction. We report photovoltaic cells with higher and denser nanocluster tower arrays that improve the power conversion efficiency of bulk heterojunction photovoltaic cells by approximately 47.7%.
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Barone, Ilaria, Emanuel Kästle, Claudio Strobbia e Giorgio Cassiani. "Surface wave tomography using 3D active-source seismic data". GEOPHYSICS 86, n.º 1 (1 de janeiro de 2021): EN13—EN26. http://dx.doi.org/10.1190/geo2020-0068.1.
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Surface wave tomography (SWT) is a powerful and well-established technique to retrieve 3D shear-wave (S-wave) velocity models at the regional scale from earthquakes and seismic noise measurements. We have applied SWT to 3D active-source data, in which higher modes and heterogeneous spatial sampling make phase extraction challenging. First, synthetic traveltimes calculated on a dense, regular-spaced station array are used to test the performance of three different tomography algorithms (linearized inversion, Markov chain Monte Carlo [MCMC], and eikonal tomography). The tests suggest that the lowest misfit to the input model is achieved with the MCMC algorithm, at the cost of a much longer computational time. Then, real phases were extracted from a 3D exploration data set at different frequencies. This operation included an automated procedure to isolate the fundamental mode from higher order modes, phase unwrapping in two dimensions, and the estimation of the zero-offset phase. These phases are used to compute traveltimes between each source-receiver couple, which are input into the previously tested tomography algorithms. The resulting phase-velocity maps show good correspondence, highlighting the same geologic structures for all three methods. Finally, individual dispersion curves obtained by the superposition of phase-velocity maps at different frequencies are depth inverted to retrieve a 3D S-wave velocity model.
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Frankel, Arthur. "Dense array recordings in the San Bernardino Valley of landers-big bear aftershocks: Basin surface waves, Moho reflections, and three-dimensional simulations". Bulletin of the Seismological Society of America 84, n.º 3 (1 de junho de 1994): 613–24. http://dx.doi.org/10.1785/bssa0840030613.
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Abstract Fourteen GEOS seismic recorders were deployed in the San Bernardino Valley to study the propagation of short-period (T ≈ 1 to 3 sec) surface waves and Moho reflections. Three dense arrays were used to determine the direction and speed of propagation of arrivals in the seismograms. The seismograms for a shallow (d ≈ 1 km) M 4.9 aftershock of the Big Bear earthquake exhibit a very long duration (60 sec) of sustained shaking at periods of about 2 sec. Array analysis indicates that these late arrivals are dominated by surface waves traveling in various directions across the Valley. Some energy is arriving from a direction 180° from the epicenter and was apparently reflected from the edge of the Valley opposite the source. A close-in aftershock (Δ = 25 km, depth = 7 km) displays substantial short-period surface waves at deep-soil sites. A three-dimensional (3D) finite difference simulation produces synthetic seismograms with durations similar to those of the observed records for this event, indicating the importance of S-wave to surface-wave conversion near the edge of the basin. Flat-layered models severely underpredict the duration and spectral amplification of this deep-soil site. I show an example where the coda wave amplitude ratio at 1 to 2 Hz between a deep-soil and a rock site does not equal the S-wave amplitude ratio, because of the presence of surface waves in the coda of the deep-soil site. For one of the events studied (Δ ≈ 90 km), there are sizable phases that are critically reflected from the Moho (PmP and SmS). At one of the rock sites, the SmS phase has a more peaked spectrum that the direct S wave.
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Tsingas, Constantinos, Mohammed S. Almubarak, Woodon Jeong, Abdulrahman Al Shuhail e Zygmunt Trzesniowski. "3D distributed and dispersed source array acquisition and data processing". Leading Edge 39, n.º 6 (junho de 2020): 392–400. http://dx.doi.org/10.1190/tle39060392.1.
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Numerous field acquisition examples and case studies have demonstrated the importance of recording, processing, and interpreting broadband land data. In most seismic acquisition surveys, three main objectives should be considered: (1) dense spatial source and receiver locations to achieve optimum subsurface illumination and wavefield sampling; (2) coverage of the full frequency spectrum, i.e., broadband acquisition; and (3) cost efficiency. Consequently, an effort has been made to improve the manufacturing of seismic vibratory sources by providing the ability to emit both lower (approximately 1.5 Hz) and higher frequencies (approximately 120 Hz) and of receivers by utilizing single, denser, and lighter digital sensors. All these developments achieve both operational (i.e., weight, optimized power consumption) and geophysical benefits (i.e., amplitude and phase response, vector fidelity, tilt detection). As part of the effort to reduce the acquisition cycle time, increase productivity, and improve seismic imaging and resolution while optimizing costs, a novel seismic acquisition survey was conducted employing 24 vibrators generating two different types of sweeps in a 3D unconstrained decentralized and dispersed source array field configuration. During this novel blended acquisition design, the crew reached a maximum of 65,000 vibrator points during 24 hours of continuous recording, which represents significantly higher productivity than a conventional seismic crew operating in the same area using a nonblended centralized source mode. Applying novel and newly developed deblending algorithms, high-resolution images were obtained. In addition, two data sets (i.e., low-frequency and medium-high-frequency sources) were merged to obtain full-bandwidth broadband seismic images. Data comparisons between the distributed blended and nonblended conventional surveys, acquired by the same crew during the same time over the same area, showed that the two data sets are very similar in the poststack and prestack domains.
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Li, Shiben, Yongyun Ji, Peng Chen, Linxi Zhang e Haojun Liang. "Surface-induced phase transitions in dense nanoparticle arrays of lamella-forming diblock copolymers". Polymer 51, n.º 21 (outubro de 2010): 4994–5001. http://dx.doi.org/10.1016/j.polymer.2010.08.019.
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Eason, P. D., e M. J. Kaufman. "Impurity Effects on the Environmental Stability of Powder Processed Intermetallic Alumino-Silicide Compounds". Journal of Materials Research 20, n.º 10 (outubro de 2005): 2691–704. http://dx.doi.org/10.1557/jmr.2005.0329.
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The evolution of nearly dense stoichiometric silicide compacts via powder processing is presented in this paper. For specific single-phase Mo(Si,Al)2 compacts, room-temperature environmental degradation, phenomenologically similar to the pesting behavior of binary MoSi2 was observed. This degradation occurs over a series of a few months and results in grain boundary decohesion, which leads to crumbling of polycrystalline compacts in air at room temperature. Auger electron spectroscopy, transmission electron microscopy, and energy dispersive spectroscopy of the boundaries revealed the presence of an array of lens-shaped particles each comprised of silicon carbide and aluminum. The reaction of these phases with atmospheric species was accelerated by the presence of humidity. The trace presence of carbon was unavoidable due to the use graphite pressing dies. Alloying additions were made to tie up carbon by forming more stable carbides while maintaining the desired matrix phase stoichiometry. The pest phenomenon and alloying remedy were proven applicable to other silicide systems through experimentation and ThermoCalc modeling.
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Frankel, Arthur, Susan Hough, Paul Friberg e Robert Busby. "Observations of Loma Prieta aftershocks from a dense array in Sunnyvale, California". Bulletin of the Seismological Society of America 81, n.º 5 (1 de outubro de 1991): 1900–1922. http://dx.doi.org/10.1785/bssa0810051900.
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Abstract A small aperture (≈300 m), four-station array was deployed in Sunnyvale, California for 5 days to record aftershocks of the Loma Prieta earthquake of October 1989. The purpose of the array was to study the seismic response of the alluvium-filled Santa Clara Valley and the role of surface waves in the seismic shaking of sedimentary basins. Strong-motion records of the Loma Prieta mainshock indicate that surface waves produced the peak velocities and displacements at some sites in the Santa Clara Valley. We use the recordings from the dense array to determine the apparent velocity and azimuth of propagation for various arrivals in the seismograms of four aftershocks with magnitudes between 3.6 and 4.4. Apparent velocities are generally observed to decrease with increasing time after the S wave in the seismograms. Phases arriving less than about 8 sec after the S wave have apparent velocities comparable to the S wave and appear to be body waves multiply reflected under the receiver site or reflected by crustal interfaces. For times 10 to 30 sec after the direct S wave, we observe long-period (1 to 6 sec) arrivals with apparent velocities decreasing from 2.5 to 0.8 km / sec. We interpret these arrivals to be surface waves and conclude that these surface waves produce the long duration of shaking observed on the aftershock records. Much of the energy in the 40 sec after the S-wave is coming approximately from the direction of the source, although some arrivals have backazimuths as much as 60° different from the backazimuths to the epicenters. Two of the aftershocks show arrivals coming from 30 to 40° more easterly than the epicenters. This energy may have been scattered from outcrops along the southeastern edge of the basin. In contrast, the deepest aftershock studied (d = 17 km) displays later arrivals with backazimuths 30 to 40° more westerly than the epicenter. A distinct arrival for one of the aftershocks propagates from the southwest, possibly scattered from the western edge of the basin. Synthetic seismograms derived from a plane-layered crustal model do not produce the long-period Love waves observed in the waveforms of the ML 4.4 aftershock. These Love waves may be generated by the conversion of incident S waves or Rayleigh waves near the edge of the basin.
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Wang, Yadong, Fan-Chi Lin e Kevin M. Ward. "Ambient noise tomography across the Cascadia subduction zone using dense linear seismic arrays and double beamforming". Geophysical Journal International 217, n.º 3 (27 de fevereiro de 2019): 1668–80. http://dx.doi.org/10.1093/gji/ggz109.
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SUMMARY In the summer of 2017, we deployed 174 three-component nodal geophones along a 130 km west–east line across the central Oregon forearc lasting about 40 d. Our goal was to evaluate the possibility of imaging the lithospheric structure in detail with a dense but short-duration sampling of passive seismic signals. In this study, we used passive recordings from the nodal array and the previous CASC93 broad-band array along the same line to calculate noise cross-correlations. Fundamental Rayleigh wave signals were observed in the cross-correlations between 3 and 15 s period. To enhance the signal and simultaneously measure the phase velocity, we employed a double beamforming method. At each period and location, a source beam and a receiver beam were selected and the cross-correlations between the two were shifted and stacked based on the presumed local velocities. A 2-D grid search was then used to find the best velocities at the source and receiver location. Multiple velocity measurements were obtained at each location by using different source and receiver pairs, and the final velocity and uncertainty at each location were determined using the mean and the standard deviation of the mean. All available phase velocities across the profile were then used to invert for a 2-D shear wave crustal velocity model. Well resolved shallow slow velocity anomalies are observed corresponding to the sediments within the Willamette Valley, and fast velocity anomalies are observed in the mid-to-lower crust likely associated with the Siletzia terrane. We demonstrate that the ambient noise double beamforming method is an effective tool to image detailed lithospheric structures across a dense and large-scale (>100 km) temporary seismic array.
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Lin, Fan-Chi, Dunzhu Li, Robert W. Clayton e Dan Hollis. "High-resolution 3D shallow crustal structure in Long Beach, California: Application of ambient noise tomography on a dense seismic array". GEOPHYSICS 78, n.º 4 (1 de julho de 2013): Q45—Q56. http://dx.doi.org/10.1190/geo2012-0453.1.
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Ambient noise tomography has proven to be effective in resolving shallow earth structure. We applied ambient noise tomography on a dense seismic array in Long Beach, California. The array was composed of more than 5200 stations with an average spacing close to 100 m. Three weeks of passive ambient noise were crosscorrelated between each station pair, which resulted in more than 13.5 million crosscorrelations within the area. Clear fundamental-mode Rayleigh waves were observed between 0.5 and 4 Hz, which were most sensitive to structure above 1-km depth. For each station pair, we applied frequency-time analysis to determine the phase traveltime dispersion, and, for each frequency, we applied eikonal tomography to determine the Rayleigh wave phase velocity map. The eikonal tomography accounted for ray bending by tracking the wavefront and allowed uncertainties to be estimated through statistical analysis. The compilation of phase velocity maps was then used to invert for 3D shear velocity structure. The inverted model showed clear correlation with the known geologic features such as the shallow south–north velocity dichotomy and a deeper fast anomaly associated with the Newport-Inglewood fault zone. Our results can potentially be used to complement traditional active source studies.
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Gao, Heming, Qi Chang e Xiaojuan Wang. "Particle velocity measurement method of dense-phase gas–solid flow based on an electrostatic sensor array". Measurement Science and Technology 30, n.º 3 (8 de fevereiro de 2019): 035301. http://dx.doi.org/10.1088/1361-6501/aaf901.
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Cao, Ruikun, Stephanie Earp, Sjoerd A. L. de Ridder, Andrew Curtis e Erica Galetti. "Near-real-time near-surface 3D seismic velocity and uncertainty models by wavefield gradiometry and neural network inversion of ambient seismic noise". GEOPHYSICS 85, n.º 1 (1 de janeiro de 2020): KS13—KS27. http://dx.doi.org/10.1190/geo2018-0562.1.
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With the advent of large and dense seismic arrays, novel, cheap, and fast imaging and inversion methods are needed to exploit the information captured by stations in close proximity to each other and produce results in near real time. We have developed a sequence of fast seismic acquisition for dispersion curve extraction and inversion for 3D seismic models, based on wavefield gradiometry, wave equation inversion, and machine-learning technology. The seismic array method that we use is Helmholtz wave equation inversion using measured wavefield gradients, and the dispersion curve inversions are based on a mixture of density neural networks (NNs). For our approach, we assume that a single surface wave mode dominates the data. We derive a nonlinear relationship among the unknown true seismic wave velocities, the measured seismic wave velocities, the interstation spacing, and the noise level in the signal. First with synthetic and then with the field data, we find that this relationship can be solved for unknown true seismic wave velocities using fixed point iterations. To estimate the noise level in the data, we need to assume that the effect of noise varies weakly with the frequency and we need to be able to calibrate the retrieved average dispersion curves with an alternate method (e.g., frequency wavenumber analysis). The method is otherwise self-contained and produces phase velocity estimates with tens of minutes of noise recordings. We use NNs, specifically a mixture density network, to approximate the nonlinear mapping between dispersion curves and their underlying 1D velocity profiles. The networks turn the retrieved dispersion model into a 3D seismic velocity model in a matter of seconds. This opens the prospect of near-real-time near-surface seismic velocity estimation using dense (and potentially rolling) arrays and only ambient seismic energy.
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Kim, Sang Il, Kyu Hyoung Lee, Hyeon A. Mun, Hyun Sik Kim, Sung Woo Hwang, Jong Wook Roh, Dae Jin Yang et al. "Dense dislocation arrays embedded in grain boundaries for high-performance bulk thermoelectrics". Science 348, n.º 6230 (2 de abril de 2015): 109–14. http://dx.doi.org/10.1126/science.aaa4166.
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The widespread use of thermoelectric technology is constrained by a relatively low conversion efficiency of the bulk alloys, which is evaluated in terms of a dimensionless figure of merit (zT). ThezTof bulk alloys can be improved by reducing lattice thermal conductivity through grain boundary and point-defect scattering, which target low- and high-frequency phonons. Dense dislocation arrays formed at low-energy grain boundaries by liquid-phase compaction in Bi0.5Sb1.5Te3(bismuth antimony telluride) effectively scatter midfrequency phonons, leading to a substantially lower lattice thermal conductivity. Full-spectrum phonon scattering with minimal charge-carrier scattering dramatically improved thezTto 1.86 ± 0.15 at 320 kelvin (K). Further, a thermoelectric cooler confirmed the performance with a maximum temperature difference of 81 K, which is much higher than current commercial Peltier cooling devices.
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Jin, Jiehong, Toma Stoica, Stefan Trellenkamp, Yang Chen, Nicklas Anttu, Vadim Migunov, Rudy M. S. Kawabata et al. "Dense, Regular GaAs Nanowire Arrays by Catalyst-Free Vapor Phase Epitaxy for Light Harvesting". ACS Applied Materials & Interfaces 8, n.º 34 (19 de agosto de 2016): 22484–92. http://dx.doi.org/10.1021/acsami.6b05581.
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Xia, Yong Mei, You Fa Zhang, Xin Quan Yu e Feng Chen. "Controllable Growth of Highly Oriented ZnO Nanorod Arrays on Copper by a Two-Step Route". Advanced Materials Research 1119 (julho de 2015): 137–41. http://dx.doi.org/10.4028/www.scientific.net/amr.1119.137.
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Highly oriented and well-aligned ZnO nanorod arrays were synthesized by low-temperature solution phase method on copper substrate under different conditions. Results illustrated that dense ZnO nanorods were vertically and uniformly distributed on the substrate. The effects of precursor concentration, growth temperature and time on the morphologies of nanorod arrays were investigated systematically. It is demonstrated that the controllable growth of well-aligned ZnO nanorods can be realized by readily adjusting the preparation parameters. The high quality ZnO nanorod arrays could be achieved via the chemical approach at low temperature.
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Chang, C. H., T. L. Lin, Y. M. Wu e W. Y. Chang. "Basement Imaging Using Sp Converted Phases from a Dense Strong-Motion Array in Lan-Yang Plain, Taiwan". Bulletin of the Seismological Society of America 100, n.º 3 (14 de maio de 2010): 1363–69. http://dx.doi.org/10.1785/0120090305.
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HORIUCHI, Shigeki, Noriko TSUMURA, Akira HASEGAWA, Syuichiro HORI e Kouichi NIDA. "An Observation System for a Dense Seismic Array Designed for Detecting Weak Reflected Phases from Deep Crust". Zisin (Journal of the Seismological Society of Japan. 2nd ser.) 45, n.º 2 (1992): 255–58. http://dx.doi.org/10.4294/zisin1948.45.2_255.
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Han, Fengqin, Ruizhi Jia e Yuanyuan V. Fu. "Love wave phase velocity models of the southeastern margin of Tibetan Plateau from a dense seismic array". Tectonophysics 712-713 (agosto de 2017): 125–31. http://dx.doi.org/10.1016/j.tecto.2017.05.013.
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Kang, Xue, Yiping Wang, Qunwu Huang, Yong Cui, Xusheng Shi e Yong Sun. "Study on direct-contact phase-change liquid immersion cooling dense-array solar cells under high concentration ratios". Energy Conversion and Management 128 (novembro de 2016): 95–103. http://dx.doi.org/10.1016/j.enconman.2016.09.073.
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Fu, Feifei, Ming Kong, Chuanlong Xu, Cai Liang e Shimin Wang. "Flow Characterization of Dense-Phase Pneumatic Conveying System of Pulverized Coal through Electrostatic Sensor Arrays". Advances in Mechanical Engineering 5 (janeiro de 2013): 656194. http://dx.doi.org/10.1155/2013/656194.
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Basu, Urbi, e Christine A. Powell. "Velocity and azimuthal anisotropy structure underneath the Reelfoot Rift region from Rayleigh wave phase velocity dispersion curves". Geophysical Journal International 228, n.º 1 (23 de agosto de 2021): 291–307. http://dx.doi.org/10.1093/gji/ggab337.
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SUMMARY Phase velocity and azimuthal anisotropy maps for fundamental mode Rayleigh waves are determined for a portion of the central United States including the seismically active Reelfoot Rift (RFR) and the enigmatic Illinois Basin. Dense seismic array installations of the Northern Embayment Lithosphere Experiment, the EarthScope transportable array and the Ozarks Illinois Indiana Kentucky array allow a detailed investigation of phase velocity and anisotropy in a broad period range (20–100s).We obtain more than 12 000 well-constrained, unique two-station paths from teleseismic events. The two-station method is used to determine dispersion curves and these are inverted for isotropic phase velocity maps and azimuthal anisotropy maps for each period. The presence of fast phase velocities at lower crustal and uppermost mantle depths is found below the RFR, and Ste. Genevieve and Wabash Valley fault zones. At periods of 30s and higher, the RFR is underlain by slow phase velocities and is flanked to the NW and SE by regions of fast velocity. Fast phase velocities are present below the centre of the Illinois Basin in the period range 75–100s. Anisotropy fast axis orientations display complex patterns for each period and do not trend parallel to the direction of absolute plate motion. Anisotropy fast directions are consistently parallel to the trend of the RFR from 50s to higher periods, suggesting the presence of either frozen-in anisotropic fabric or fabric related to material transport from a recently discovered, pronounced low velocity zone below the Mississippi Embayment.
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Apoloner, M. T., e G. Bokelmann. "Modeling and detection of regional depth phases at the GERES array". Advances in Geosciences 41 (31 de agosto de 2015): 5–10. http://dx.doi.org/10.5194/adgeo-41-5-2015.
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Abstract. The Vienna Basin in Eastern Austria is a region of low to moderate seismicity, and hence the seismological network coverage is relatively sparse. Nevertheless, the area is one of the most densely populated and most developed areas in Austria, so accurate earthquake location, including depth estimation and relation to faults is not only important for understanding tectonic processes, but also for estimating seismic hazard. Particularly depth estimation needs a dense seismic network around the anticipated epicenter. If the station coverage is not sufficient, the depth can only be estimated roughly. Regional Depth Phases (RDP) like sPg, sPmP and sPn have been already used successfully for calculating depth even if only observable from one station. However, especially in regions with sedimentary basins these phases prove difficult or impossible to recover from the seismic records. For this study we use seismic array data from GERES. It is 220 km to the North West of the Vienna Basin, which – according to literature – is a suitable distance to recover PmP and sPmP phases. We use array processing on recent earthquake data from the Vienna Basin with local magnitudes from 2.1 to 4.2 to reduce the SNR and to search for RDP. At the same time, we do similar processing on synthetic data specially modeled for this application. We compare real and synthetic results to assess which phases can be identified and to what extent depth estimation can be improved. Additionally, we calculate a map of lateral propagation behavior of RDP for a typical strike-slip earthquake in our region of interest up to 400 km distance. For our study case RDP propagation is strongly azimuthally dependent. Also, distance ranges differ from literature sources. Comparing with synthetic seismograms we identify PmP and PbP phases with array processing as strongest arrivals. Although the associated depth phases cannot be identified at this distance and azimuth, identification of the PbP phases limits possible depth to less than 20 km. Polarization analysis adds information on the first arriving Pn wave for local magnitudes above 2.5.
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Douglass, J. D., S. A. Pikuz, T. A. Shelkovenko, D. A. Hammer, S. N. Bland, S. C. Bott e R. D. McBride. "Structure of the dense cores and ablation plasmas in the initiation phase of tungsten wire-array Z pinches". Physics of Plasmas 14, n.º 1 (janeiro de 2007): 012704. http://dx.doi.org/10.1063/1.2431633.
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Lou, Cuijuan, Junjie Song, Liang Zhou, Yang Peng, Mingyue Ding e Ming Yuchi. "A Fast Contrast Improved Zero-Phase Filtered Delay Multiply and Sum in Ultrasound Computed Tomography". Journal of Medical Imaging and Health Informatics 8, n.º 9 (1 de dezembro de 2018): 1850–54. http://dx.doi.org/10.1166/jmihi.2018.2566.
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In linear array B-mode imaging, the zero-phase filtered delay multiply and sum beamforming (ZPF-DMAS) weighted by space-time smoothing coherence factor (StS-CF) has been proved to enhance the image contrast resolution than the traditional delay and sum method. However, the large number of virtual received signals may increase the computational cost of this method in ultrasound computed tomography (USCT) with ring array. Here, a method with less computation amount is proposed in USCT: the received signals are separated into different groups by their spatial lag; the groups form a new smaller size receive aperture; StS-CF is finally applied to the new receive aperture. CIRS model 055A is tested to compare the performances of the proposed method and ZPF-DMAS. The results show that the computational complexity has been reduced by N*B*D((M2–3M)/2+1) multiplications, supposing there are N ultrasound waves transmitted, B scan lines, D imaging points on each line and M-element receive aperture. StS-CF with a subarray size of L = 16 (far less than half the receive aperture) and P = 5 time samples gives the best result in USCT, which is different from that in linear array B-mode imaging. The proposed method can enhance contrast ratio about 6.3 dB and 5.7 dB for the cystic mass and dense mass than ZPF-DMAS, respectively.
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Du, Peixiao, Jing Wu, Yang Li, Jian Wang, Chunming Han, Mark Douglas Lindsay, Huaiyu Yuan, Liang Zhao e Wenjiao Xiao. "Imaging Karatungk Cu-Ni Mine in Xinjiang, Western China with a Passive Seismic Array". Minerals 10, n.º 7 (1 de julho de 2020): 601. http://dx.doi.org/10.3390/min10070601.
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Karatungk Mine is the second-largest Cu-Ni sulfide mine in China. However, the detailed structure beneath the mine remains unclear. Using continuous waveforms recorded by a dense temporary seismic array, here we apply ambient noise tomography to study the shallow crustal structure of Karatungk Mine down to ~1.3 km depth. We obtain surface-wave dispersions at 0.1–1.5 s by calculating cross-correlation functions, which are inverted for 3D shear-wave structure at the top-most (0–1.3 km) crust by a joint inversion of group and phase dispersions. Our results show that low-velocity zones beneath Y1 ore-hosting intrusion (hereafter called Y1) at 0–0.5 km depth and northwest of the Y2 ore-hosting intrusion (hereafter called Y2) at 0–0.6 km depth are consistent with highly mineralized areas. A relatively high-velocity zone is connected with a weakly mineralized area located to the southeast of Y2 and Y3 (hereafter called Y3) ore-hosting intrusions. Two high-velocity zones, distributed at 0.7–1.3 km depth in the northernmost and southernmost parts of the study area respectively, are interpreted to be igneous rocks related to early magma intrusion. Furthermore, the low-velocity zone at 0.7–1.3 km depth in the middle of the study area may be related to: a possible channel related to initial magma transport; mine strata or a potentially mineralized area. This study demonstrates a new application of dense-array ambient noise tomography to a mining area that may guide future studies of mineralized regions.
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Imtiaz, A., C. Cornou, P.-Y. Bard e M. Hobiger. "Diffracted wavefield decomposition and multidimensional site effects in the Argostoli valley, Greece". Geophysical Journal International 224, n.º 3 (5 de novembro de 2020): 1849–69. http://dx.doi.org/10.1093/gji/ggaa529.
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SUMMARY Effects of seismic ground motion induced by surface geology and geometry are known to be associated with the generation of a substantial proportion of surface waves. As a consequence, surface waves significantly contribute to ground-motion variability and site amplification. There is a growing body of literature recognizing that an understanding of physical patterns of the wavefield crossing a site is the key aspect to characterize and quantify them. However, this task remains technically challenging due to the complexity of such effects as well as the limitations of geophysical investigations, especially in case of small sedimentary valleys. The present study attempts to investigate the waves propagating across two 2-D dense seismic arrays from a number of earthquakes and explore the extent to which they are contributing to the multidimensional site effects. The arrays were deployed in the small-size, shallow alluvial valley of Koutavos-Argostoli, located in Cephalonia Island, Greece, and consisted of three-component velocimeters with interstation distances ranging from 5 to 160 m. A set of 46 earthquakes, with magnitudes between 2 and 5 and epicentral distances up to 200 km, was analysed by using an advanced seismic array processing technique, MUSIQUE. The phase velocity, backazimuth and energy of the dominant waves crossing the array were extracted, and their identification as Love or prograde/retrograde Rayleigh waves was obtained. The results clearly indicate a predominance of scattered surface waves (up to 60 per cent of total energy), mainly from the closest valley edges, above the fundamental frequency (∼1.5 Hz) of the valley. Love waves dominate the low-frequency wavefield (<3 Hz) while Rayleigh waves dominate some high-frequency bands. An excellent consistency is observed, in a given frequency range, among the dominance of the type of diffracted surface waves, group velocities estimated from the ground velocity structure and site amplification. The outcomes of this research provide a better understanding of the contribution of edge-diffracted surface waves and the 2-D/3-D site amplification at small and shallow alluvium valleys like Argostoli. The method applied here can be used to calibrate and validate 3-D models for simulating seismic ground motion.
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Tokan, Fikret, Daniele Cavallo e Andrea Neto. "A novel planar, broadband, high gain lateral wave antenna array for body scanning applications". Journal of Electrical Engineering 71, n.º 5 (1 de setembro de 2020): 308–16. http://dx.doi.org/10.2478/jee-2020-0042.
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Abstract Three-dimensional body scanning systems are increasingly used in sensitive public areas such as airports. By providing a high resolution image of a person from all sides, it is possible to detect potential metallic, ceramic and explosive threats. For these systems, it is essential to design broadband antennas with a fan beam, highly directional radiation in one plane and wide in the other plane, and characterized by phase center stability as a function of frequency. In this paper, the planar lateral wave antenna (LWA) array is proposed to achieve these radiation requirements. The LWA has two critical shortcomings: the flaring part and the dielectric matching layers (MLs), to operate over very broad frequency bands. In this work, these shortcomings are overcomed by forming a connected array of planar LWAs to improve broadband performance and by applying necessary perforations on the dense dielectric lens antenna to create different effective relative permittivity regions. An eight element connected and perforated LWA array is designed to operate in the 8–24 GHz frequency band. The drilled holes are proved to play a similar critical role of MLs in internal reflection suppression. The results emphasize all crucial demands for body scanning systems.
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Roux, Philippe, e Yehuda Ben-Zion. "Rayleigh phase velocities in Southern California from beamforming short-duration ambient noise". Geophysical Journal International 211, n.º 1 (28 de julho de 2017): 450–54. http://dx.doi.org/10.1093/gji/ggx316.
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Abstract Beamforming of ambient noise recorded by regional arrays of seismometers is presented as an alternative imaging approach to cross-correlations between pairs of sensors. The method is used to obtain phase velocities and propagation directions of Rayleigh surface waves around the first and second microseism peaks in southern California. The derived velocity maps and propagation directions correlate with major geological structures and changes of the coastal shape in the region. The results are consistent with and complementary to those obtained using cross-correlations of long-duration data between pairs of sensors. Significant advantages of the presented high-resolution adaptive beamforming method over point-to-point noise cross-correlations are the short time interval of required data (hours to days compared to a year) and robust performance with directive (rather than omnidirectional) noise propagation. Given the recent trend toward dense and large seismic arrays at various scales, the combination of beamforming and noise-correlation processing may provide an optimal strategy for performing noise-based tomography.
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Bešlić, I., A. T. Barnes, F. Bigiel, J. Puschnig, J. Pety, C. Herrera Contreras, A. K. Leroy et al. "Dense molecular gas properties on 100 pc scales across the disc of NGC 3627". Monthly Notices of the Royal Astronomical Society 506, n.º 1 (30 de junho de 2021): 963–88. http://dx.doi.org/10.1093/mnras/stab1776.
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ABSTRACT It is still poorly constrained how the densest phase of the interstellar medium varies across galactic environment. A large observing time is required to recover significant emission from dense molecular gas at high spatial resolution, and to cover a large dynamic range of extragalactic disc environments. We present new NOrthern Extended Millimeter Array (NOEMA) observations of a range of high critical density molecular tracers (HCN, HNC, HCO+) and CO isotopologues (13CO, C18O) towards the nearby (11.3 Mpc) strongly barred galaxy NGC 3627. These observations represent the current highest angular resolution (1.85 arcsec; 100 pc) map of dense gas tracers across a disc of a nearby spiral galaxy, which we use here to assess the properties of the dense molecular gas, and their variation as a function of galactocentric radius, molecular gas, and star formation. We find that the HCN(1–0)/CO(2–1) integrated intensity ratio does not correlate with the amount of recent star formation. Instead, the HCN(1–0)/CO(2–1) ratio depends on the galactic environment, with differences between the galaxy centre, bar, and bar-end regions. The dense gas in the central 600 pc appears to produce stars less efficiently despite containing a higher fraction of dense molecular gas than the bar ends where the star formation is enhanced. In assessing the dynamics of the dense gas, we find the HCN(1–0) and HCO+(1–0) emission lines showing multiple components towards regions in the bar ends that correspond to previously identified features in CO emission. These features are cospatial with peaks of Hα emission, which highlights that the complex dynamics of this bar-end region could be linked to local enhancements in the star formation.