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Journal articles on the topic 'Inverted reflector'
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Desta, Derese, Rita Rizzoli, Caterina Summonte, Rui N. Pereira, Arne Nylandsted Larsen, Peter Balling, and Sanjay K. Ram. "Nanomolded buried light-scattering (BLiS) back-reflectors using dielectric nanoparticles for light harvesting in thin-film silicon solar cells." EPJ Photovoltaics 11 (2020): 2. http://dx.doi.org/10.1051/epjpv/2019011.
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The article presents a nanoparticle-based buried light-scattering (BLiS) back-reflector design realized through a simplified nanofabrication technique for the purpose of light-management in solar cells. The BLiS structure consists of a flat silver back-reflector with an overlying light-scattering bilayer which is made of a TiO2 dielectric nanoparticles layer with micron-sized inverted pyramidal cavities, buried under a flat-topped silicon nanoparticles layer. The optical properties of this BLiS back-reflector show high broadband and wide angular distribution of diffuse light-scattering. The efficient light-scattering by the buried inverted pyramid back-reflector is shown to effectively improve the short-circuit-current density and efficiency of the overlying n-i-p amorphous silicon solar cells up to 14% and 17.5%, respectively, compared to the reference flat solar cells. A layer of TiO2 nanoparticles with exposed inverted pyramid microstructures shows equivalent light scattering but poor fill factors in the solar cells, indicating that the overlying smooth growth interface in the BLiS back-reflector helps to maintain a good fill factor. The study demonstrates the advantage of spatial separation of the light-trapping and the semiconductor growth layers in the photovoltaic back-reflector without sacrificing the optical benefit.
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Yatsyshen, V. V., and A. Yu Gordeev. "Electrodynamic target selection techniques." Journal of «Almaz – Antey» Air and Space Defence Corporation, no. 1 (March 30, 2016): 61–68. http://dx.doi.org/10.38013/2542-0542-2016-1-61-68.
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We examine a new electrodynamic approach to target selection. The study shows that in the case of p-polarisation, a topological portrait of two types of angle reflectors is in a certain sense inverted in relation to that of the s-polarisation case, and consequently, evident polarisation dependence of angle reflector topological portraits may be traced.
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Park, Kibeom, Jingon Joung, Sungjoon Lim, and Han Lim Lee. "A Compact Crossed Inverted-V Antenna with a Common Reflector for Polarization Diversity in the IoT." Electronics 8, no. 6 (June 6, 2019): 637. http://dx.doi.org/10.3390/electronics8060637.
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This article presented a compact and high gain antenna with reconfigurable polarization based on two inverted-V dipoles fabricated in a crossed configuration, and with a common planar reflector. The proposed antenna could generate four different types of polarizations, such as vertical polarization (VP), horizontal polarization (HP), right-hand circular polarization (RHCP), and left-hand circular polarization (LHCP). A pair of inverted-V dipoles drove the polarization diversity, where each dipole had an integrated matching circuit and a microstrip balun. Using a crossed inverted-V configuration with a ground plane as the common reflector, we could achieve compactness in size, high directivity, and a wider beamwidth than a normal dipole antenna. To verify the performance of the proposed antenna, we fabricated a sub-6GHz antenna with a Taconic TLX-9 substrate, which had a relative permittivity of 2.5. The proposed antenna showed a measured 10-dB impedance bandwidth of 752 MHz (5.376 GHz to 6.128 GHz). The peak gains for the VP, HP, RHCP and LHCP operations at 5.8 GHz were about 5.2 dBi, 4.61 dBi, 5.25 dBic, and 5.51 dBic, respectively. In addition, the half-power beamwidth (HPBW) for all the polarizations were greater than 78° in the operation band.
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Zhang, Dan-Dan, Xiao-Chen Jiang, Rong Wang, Hao-Jun Xie, Guo-Fu Ma, Qing-Dong Ou, Yuan-Li Chen, Yan-Qing Li, and Jian-Xin Tang. "Enhanced Performance of Semitransparent Inverted Organic Photovoltaic Devices via a High Reflector Structure." ACS Applied Materials & Interfaces 5, no. 20 (October 4, 2013): 10185–90. http://dx.doi.org/10.1021/am402872u.
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Stunff, Yves Le, Vladimir Grechka, and Ilya Tsvankin. "Depth‐domain velocity analysis in VTI media using surface P-wave data: Is it feasible?" GEOPHYSICS 66, no. 3 (May 2001): 897–903. http://dx.doi.org/10.1190/1.1444979.
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The main difficulties in anisotropic velocity analysis and inversion using surface seismic data are associated with the multiparameter nature of the problem and inherent trade‐offs between the model parameters. For the most common anisotropic model, transverse isotropy with a vertical symmetry axis (VTI media), P-wave kinematic signatures are controlled by the vertical velocity V0 and the anisotropic parameters ε and δ. However, only two combinations of these parameters—NMO velocity from a horizontal reflector Vnmo(0) and the anellipticity coefficient η—can be determined from P-wave reflection traveltimes if the medium above the reflector is laterally homogeneous. While Vnmo(0) and η are sufficient for time‐domain imaging in VTI media, they cannot be used to resolve the vertical velocity and build velocity models needed for depth migration. Here, we demonstrate that P-wave reflection data can be inverted for all three relevant VTI parameters (V0, ε and δ) if the model contains nonhorizontal intermediate interfaces. Using anisotropic reflection tomography, we carry out parameter estimation for a two‐layer medium with a curved intermediate interface and reconstruct the correct anisotropic depth model. To explain the success of this inversion procedure, we present an analytic study of reflection traveltimes for this model and show that the information about the vertical velocity and reflector depth was contained in the reflected rays which crossed the dipping intermediate interface. The results of this work are especially encouraging because the need for depth imaging (such as prestack depth migration) arises mostly in laterally heterogeneous media. Still, we restricted this study to a relatively simple model and constrained the inversion by assuming that one of the layers is isotropic. In general, although lateral heterogeneity does create a dependence of P-wave reflection traveltimes on the vertical velocity, there is no guarantee that for more complicated models all anisotropic parameters can be resolved in a unique fashion.
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Grechka, Vladimir, and Ilya Tsvankin. "3-D description of normal moveout in anisotropic inhomogeneous media." GEOPHYSICS 63, no. 3 (May 1998): 1079–92. http://dx.doi.org/10.1190/1.1444386.
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We present a new equation for normal‐moveout (NMO) velocity that describes azimuthally dependent reflection traveltimes of pure modes from both horizontal and dipping reflectors in arbitrary anisotropic inhomogeneous media. With the exception of anomalous areas such as those where common‐midpoint (CMP) reflection time decreases with offset, the azimuthal variation of NMO velocity represents an ellipse in the horizontal plane, with the orientation of the axes determined by the properties of the medium and the direction of the reflector normal. In general, a minimum of three azimuthal measurements is necessary to reconstruct the best‐fit ellipse and obtain NMO velocity in all azimuthal directions. This result provides a simple way to correct for the azimuthal variation in stacking velocity often observed in 3-D surveys. Even more importantly, analytic expressions for the parameters of the NMO ellipse can be used in the inversion of moveout data for the anisotropic coefficients of the medium. For homogeneous transversely isotropic media with a vertical axis of symmetry (VTI media), our equation for azimuthally dependent NMO velocity from dipping reflectors becomes a relatively simple function of phase velocity and its derivatives. We show that the zero‐dip NMO velocity Vnmo(0) and the anisotropic coefficient η are sufficient to describe the P-wave NMO velocity for any orientation of the CMP line with respect to the dip plane of the reflector. Using our formalism, Vnmo(0) and η (the only parameters needed for time processing) can be found from the dip‐dependent NMO velocity at any azimuth or, alternatively, from the azimuthally dependent NMO for a single dipping reflector. We also apply this theory to more complicated azimuthally anisotropic models with the orthorhombic symmetry used to describe fractured reservoirs. For reflections from horizontal interfaces in orthorhombic media, the axes of the normal moveout ellipse are aligned with the vertical symmetry planes. Therefore, azimuthal P-wave moveout measurements can be inverted for the orientation of the symmetry planes (typically determined by the fracture direction) and the NMO velocities within them. If the vertical velocity is known, symmetry‐plane NMO velocities make it possible to estimate two anisotropic parameters equivalent to Thomsen’s coefficient δ for transversely isotropic media.
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Islam, Mohammad, Md Ullah, Touhidul Alam, Mandeep Singh, and Mengu Cho. "Microwave Imaging Sensor Using Low Profile Modified Stacked Type Planar Inverted F Antenna." Sensors 18, no. 9 (September 5, 2018): 2949. http://dx.doi.org/10.3390/s18092949.
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Microwave imaging is the technique to identify hidden objects from structures using electromagnetic waves that can be applied in medical diagnosis. The change of dielectric property can be detected using microwave antenna sensor, which can lead to localization of abnormality in the human body. This paper presents a stacked type modified Planar Inverted F Antenna (PIFA) as microwave imaging sensor. Design and performance analysis of the sensor antenna along with computational and experimental analysis to identify concealed object has been investigated in this study. The dimension of the modified PIFA radiating patch is 40 × 20 × 10 mm3. The reflector walls used, are 45 mm in length and 0.2-mm-thick inexpensive copper sheet is considered for the simulation and fabrication which addresses the problems of high expenses in conventional patch antenna. The proposed antenna sensor operates at 1.55–1.68 GHz where the maximum realized gain is 4.5 dB with consistent unidirectional radiation characteristics. The proposed sensor antenna is used to identify tumor in a computational human tissue phantom based on reflection and transmission coefficient. Finally, an experiment has been performed to verify the antenna’s potentiality of detecting abnormality in realistic breast phantom.
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Sinha, Mrinal, and Gerard T. Schuster. "Interferometric full-waveform inversion." GEOPHYSICS 84, no. 1 (January 1, 2019): R45—R60. http://dx.doi.org/10.1190/geo2018-0047.1.
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Velocity errors in the shallow part of the velocity model can lead to erroneous estimates of the full-waveform inversion (FWI) tomogram. If the location and topography of a reflector are known, then such a reflector can be used as a reference reflector to update the underlying velocity model. Reflections corresponding to this reference reflector are windowed in the data space. Windowed reference reflections are then crosscorrelated with reflections from deeper interfaces, which leads to partial cancellation of static errors caused by the overburden above the reference interface. Interferometric FWI (IFWI) is then used to invert the tomogram in the target region, by minimizing the normalized waveform misfit between the observed and predicted crosscorrelograms. Results with synthetic and field data with static errors above the reference interface indicate that an accurate tomogram can be inverted in areas lying within several wavelengths of the reference interface. IFWI can also be applied to synthetic time-lapse data to mitigate the nonrepeatability errors caused by time-varying overburden variations. The synthetic- and field-data examples demonstrate that IFWI can provide accurate tomograms when the near surface is ridden with velocity errors.
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YAMAMOTO, Kazuhisa, Kiminori MIZUUCHI, Hisako HARA, Yasuo KITAOKA, and Makoto KATO. "Frequency Doubling of a Laser Diode Using a Domain-Inverted LiTaO3Waveguide with a Monolithic Bragg Reflector." Optical Review 1, no. 1 (November 1994): 88–90. http://dx.doi.org/10.1007/s10043-994-0088-1.
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Ordoñez, Alba, Walter Söllner, Tilman Klüver, and Leiv J. Gelius. "Subsurface reflectivity estimation from imaging of primaries and multiples using amplitude-normalized separated wavefields." GEOPHYSICS 81, no. 3 (May 2016): S101—S117. http://dx.doi.org/10.1190/geo2015-0385.1.
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Several studies have shown the benefits of including multiple reflections together with primaries in the structural imaging of subsurface reflectors. However, to characterize the reflector properties, there is a need to compensate for propagation effects due to multiple scattering and to properly combine the information from primaries and all orders of multiples. From this perspective and based on the wave equation and Rayleigh’s reciprocity theorem, recent works have suggested computing the subsurface image from the Green’s function reflection response (or reflectivity) by inverting a Fredholm integral equation in the frequency-space domain. By following Claerbout’s imaging principle and assuming locally reacting media, the integral equation may be reduced to a trace-by-trace deconvolution imaging condition. For a complex overburden and considering that the structure of the subsurface is angle-dependent, this trace-by-trace deconvolution does not properly solve the Fredholm integral equation. We have inverted for the subsurface reflectivity by solving the matrix version of the Fredholm integral equation at every subsurface level, based on a multidimensional deconvolution of the receiver wavefields with the source wavefields. The total upgoing pressure and the total filtered downgoing vertical velocity were used as receiver and source wavefields, respectively. By selecting appropriate subsets of the inverted reflectivity matrix and by performing an inverse Fourier transform over the frequencies, the process allowed us to obtain wavefields corresponding to virtual sources and receivers located in the subsurface, at a given level. The method has been applied on two synthetic examples showing that the computed reflectivity wavefields are free of propagation effects from the overburden and thus are suited to extract information of the image point location in the angular and spatial domains. To get the computational cost down, our approach is target-oriented; i.e., the reflectivity may only be computed in the area of most interest.
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Jangid, K. G., P. K. Jain, B. R. Sharma, V. K. Saxena, V. S. Kulhar, and D. Bhatnagar. "Triple-Notched Band CPW fed UWB Antenna with Metallic Reflector for High Gain Performance." Advanced Electromagnetics 6, no. 4 (October 22, 2017): 15–21. http://dx.doi.org/10.7716/aem.v6i4.506.
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This paper exhibits the design and performance of a coplanar waveguide (CPW) fed triple notched band ultra-wide band (UWB) antenna. Proposed prototype has two U-shaped slots on the patch and an inverted U slot in feed line with a metal reflector beneath the radiating element. Proposed structure renders wider impedance bandwidth extended between frequencies 2.71GHz to 12.92 GHz for VSWR < 2 with three rejection bands in the frequency ranges 3.456 to 3.988 GHz (WI-MAX IEEE 802.16), 5.27 to 6.032 GHz (WLAN IEEE 802.11 a/h/j/n) and 7.88 to 8.65 GHz (X-band down link satellite system) for VSWR > 2. The utmost simulated gain of proposed antenna with reflector is close to 9.9dBi at 7.4GHz. A sharp reduction observed in the efficiency values of the proposed structure at stop bands. Perhaps, this structure proved as a useful tool for various applications in modern communication systems including UWB.
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Ayache, Ahmed, and Othman Echi. "The envelope of a subcategory in topology and group theory." International Journal of Mathematics and Mathematical Sciences 2005, no. 21 (2005): 3387–404. http://dx.doi.org/10.1155/ijmms.2005.3387.
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A collection of results are presented which are loosely centered around the notion of reflective subcategory. For example, it is shown that reflective subcategories are orthogonality classes, that the morphisms orthogonal to a reflective subcategory are precisely the morphisms inverted under the reflector, and that each subcategory has a largest “envelope” in the ambient category in which it is reflective. Moreover, known results concerning the envelopes of the category of sober spaces, spectral spaces, and jacspectral spaces, respectively, are summarized and reproved. Finally, attention is focused on the envelopes of one-object subcategories, and examples are considered in the category of groups.
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Grechka, Vladimir, and Ilya Tsvankin. "3-D moveout velocity analysis and parameter estimation for orthorhombic media." GEOPHYSICS 64, no. 3 (May 1999): 820–37. http://dx.doi.org/10.1190/1.1444593.
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Orthorhombic symmetry describes several azimuthally anisotropic models typical for fractured formations, such as those containing two orthogonal crack systems or parallel vertical cracks in a VTI (transversely isotropic with a vertical symmetry axis) background. Here, we present a methodology for inverting multiazimuth P-wave reflection traveltimes for the parameters of vertically inhomogeneous orthorhombic media. Our approach is based on the general analytic representation of normal‐moveout (NMO) velocity as an ellipse in the horizontal plane. A minimum of three differently oriented common‐midpoint (CMP) lines (or a “wideazimuth” 3-D survey) is needed to reconstruct the ellipse and thus obtain NMO velocity in any azimuthal direction. Then, the orientation and the semiaxes of the NMO ellipse, which are dependent on both anisotropy and heterogeneity, can be inverted for the medium parameters. Our analytic and numerical study shows that for the model of a homogeneous orthorhombic layer above a dipping reflector, the exact P-wave NMO velocity is determined by the symmetry‐plane orientation and five parameters: the NMO velocities from a horizontal reflector measured in the symmetry planes [[Formula: see text]] and three anisotropic coefficients η(1,2,3) introduced by analogy with the Alkhalifah‐Tsvankin parameter η for VTI media. The importance of the medium parameterization in terms of the η coefficients goes well beyond the NMO-velocity function. By generating migration impulse responses, we demonstrate that the parameters [Formula: see text] and η(1,2,3) are sufficient to perform all time processing steps (normal‐moveout and dip‐moveout corrections, prestack and poststack time migration) in orthorhombic models. The velocities [Formula: see text] and the orientation of the vertical symmetry planes can be found using the azimuthally dependent NMO velocity from a horizontal reflector. Then the NMO ellipse of at least one dipping event is additionally needed to obtain the coefficients η(1,2,3) that control the dip dependence of normal moveout. We discuss the stability of the inversion procedure and specify the constraints on the dip and azimuth of the reflector; for instance, for all three η coefficients to be resolved individually, the dip plane of the reflector should not coincide with either of the symmetry planes. To carry out parameter estimation in vertically inhomogeneous orthorhombic media, we apply the generalized Dix equation of Grechka, Tsvankin and Cohen, which operates with the matrices responsible for interval NMO ellipses rather than with the NMO velocities themselves. Our algorithm is designed to find the interval values of [Formula: see text] and η(1,2,3) using moveout from horizontal and dipping reflectors measured at different vertical times (i.e., only surface P-wave data are needed). Application to a synthetic multiazimuth P-wave data set over a layered orthorhombic medium with depth‐varying orientation of the symmetry planes verifies the accuracy of the inversion method.
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Shinozaki, K., Y. Miyamoto, H. Okayama, T. Kamijoh, and T. Nonaka. "Second‐harmonic generation device with integrated periodically domain‐inverted regions and distributed Bragg reflector in a LiNbO3channel waveguide." Applied Physics Letters 58, no. 18 (May 6, 1991): 1934–36. http://dx.doi.org/10.1063/1.105050.
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Chen, Zhi-Hui, Na Qiao, Yang Wang, Li Liang, Yibiao Yang, Han Ye, and Shaoding Liu. "Efficient broadband energy absorption based on inverted-pyramid photonic crystal surface and two-dimensional randomly patterned metallic reflector." Applied Energy 172 (June 2016): 59–65. http://dx.doi.org/10.1016/j.apenergy.2016.03.098.
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Moreira, F. J. S., A. Prata, and M. A. Thorburn. "Minimization of the plane-wave scattering contribution of inverted-Y strut tripods to the noise temperature of reflector antennas." IEEE Transactions on Antennas and Propagation 44, no. 4 (April 1996): 492–99. http://dx.doi.org/10.1109/8.489300.
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Reddy, K. S., and K. Ravi Kumar. "Estimation of convective and radiative heat losses from an inverted trapezoidal cavity receiver of solar linear Fresnel reflector system." International Journal of Thermal Sciences 80 (June 2014): 48–57. http://dx.doi.org/10.1016/j.ijthermalsci.2014.01.022.
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Li, Hong Mei, Jin Yue Wang, Li Kun Xing, Xin Yu Cao, and Tie Xin Yang. "A Design of EBG-PIFA for RFID Applications in UHF Band." Applied Mechanics and Materials 427-429 (September 2013): 1141–44. http://dx.doi.org/10.4028/www.scientific.net/amm.427-429.1141.
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One of the longstanding problems in planar inverted F antenna (PIFA) is its efficiency, which reduces as PIFA is placed too close to the ground. In this paper a kind of mushroom-like Electromagnetic band gap (EBG) structure with three conductor layers is designed In the UHF band, which has smaller unit cells and thinner thickness compared to classical ones. This kind of mushroom-like EBG structure is used as the reflector of PIFA with capacitor structure. It is demonstrated that PIFAs with EBG grounds have higher radiation efficiency than those with PEC ground. At the same time, no significant changes in the antenna resonance frequency and the radiation patterns are found. The theoretical prediction is well verified by results of both simulation and experiment.
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Isabella, O., S. Solntsev, D. Caratelli, and M. Zeman. "3-D optical modeling of single and multi-junction thin-film silicon solar cells on gratings." MRS Proceedings 1426 (2012): 149–54. http://dx.doi.org/10.1557/opl.2012.897.
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ABSTRACTThree-dimensional (3-D) optical modeling based on Finite Element Method of single, double, and triple junction thin-film silicon solar cells is presented. The combination of front periodic gratings with optimal geometrical parameters and rear ZnO/Ag reflector constitutes an efficient light trapping scheme for solar cells in superstrate (pin) configuration. The application of optimized trapezoidal 1-D and 2-D gratings resulted in 25.5% (1-D case) and 32.5% (2-D case) increase in photo-current density with respect to the flat solar cell. The application of inverted pyramidal 2-D gratings in double and triple junction silicon solar cells with very thin absorber layers resulted in a photo-current density > 11 mA/cm2 and > 9 mA/cm2, respectively.
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Feng, Botao, Weijun Hong, Shufang Li, Wenxing An, and Sixing Yin. "A Dual-Wideband Double-Layer Magnetoelectric Dipole Antenna with a Modified Horned Reflector for 2G/3G/LTE Applications." International Journal of Antennas and Propagation 2013 (2013): 1–9. http://dx.doi.org/10.1155/2013/509589.
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A novel dual-wideband double-layer magnetoelectric dipole unidirectional antenna with a modified horned reflector for 2G/3G/LTE applications is proposed. Firstly, a double-layer electric dipole structure is presented to provide a dualwideband, whose folded lower layer mainly serves the lower frequency band while the inclined upper layer works for the upper frequency band. In addition, to reduce the size of the antenna and improve impedance matching, a new feeding structure designed with inverted U-shaped and tapered line is introduced. Finally, a modified horn-shaped reflector, instead of a ground plane, is employed to achieve stable and high gains. The antenna prototype can achieve a bandwidth of 24.4% (790 MHz–1010 MHz) with a stable gain of 7.2 ± 0.6 dBi for the lower band, and a bandwidth of 67.3% (1.38 GHz–2.78 GHz) with a gain of 7.5 ± 0.8 dBi for the upper band covering all the frequency bands for 2G/3G/LTE systems. To the best of our knowledge, it is the first double-layer magnetoelectric dipole antenna proposed. Compared with the existing ME dipole antennas, the proposed antenna, which is completely made of copper, can be easily fabricated at low cost and thus is practicable for 2G/3G/LTE applications.
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Contreras, Pedro, Vladimir Grechka, and Ilya Tsvankin. "Moveout inversion of P-wave data for horizontal transverse isotropy." GEOPHYSICS 64, no. 4 (July 1999): 1219–29. http://dx.doi.org/10.1190/1.1444628.
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The transversely isotropic model with a horizontal symmetry axis (HTI media) has been extensively used in seismological studies of fractured reservoirs. In this paper, a parameter‐estimation technique originally developed by Grechka and Tsvankin for the more general orthorhombic media is applied to horizontal transverse isotropy. Our methodology is based on the inversion of azimuthally‐dependent P-wave normal‐moveout (NMO) velocities from horizontal and dipping reflectors. If the NMO velocity of a given reflection event is plotted in each azimuthal direction, it forms an ellipse determined by three combinations of medium parameters. The NMO ellipse from a horizontal reflector in HTI media can be inverted for the azimuth β of the symmetry axis, the vertical velocity [Formula: see text], and the Thomsen‐type anisotropic parameter δ(V). We describe a technique for obtaining the remaining (for P-waves) anisotropic parameter η(V) (or ε(V)) from the NMO ellipse corresponding to a dipping reflector of arbitrary azimuth. The interval parameters of vertically inhomogeneous HTI media are recovered using the generalized Dix equation that operates with NMO ellipses for horizontal and dipping events. High accuracy of our method is confirmed by inverting a synthetic multiazimuth P-wave data set generated by ray tracing for a layered HTI medium with depth‐varying orientation of the symmetry axis. Although estimation of η(V) can be carried out by the algorithm developed for orthorhombic media, for more stable results the HTI model has to be used from the outset of the inversion procedure. It should be emphasized that P-wave conventional‐spread moveout data provide enough information to distinguish between HTI and lower‐symmetry models. We show that if the medium has the orthorhombic symmetry and is sufficiently different from HTI, the best‐fit HTI model cannot match the NMO ellipses for both a horizontal and a dipping event. The anisotropic coefficients responsible for P-wave moveout can be combined to estimate the crack density and predict whether the cracks are fluid‐filled or dry. A unique feature of the HTI model that distinguishes it from both vertical transverse isotropy and orthorhombic media is that moveout inversion provides not just zero‐dip NMO velocities and anisotropic coefficients, but also the true vertical velocity. As a result, reflection P-wave data acquired over HTI formations can be used to build velocity models in depth and perform anisotropic depth processing.
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van der Burg, Dennis, Arie Verdel, and Kees Wapenaar. "Ray-based stochastic inversion of prestack seismic data for improved reservoir characterization." GEOPHYSICS 74, no. 5 (September 2009): R85—R97. http://dx.doi.org/10.1190/1.3190131.
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Trace inversion for reservoir parameters is affected by angle averaging of seismic data and wavelet distortion on the migration image. In an alternative approach to stochastic trace inversion, the data are inverted prestack before migration using 3D dynamic ray tracing. This choice makes it possible to interweave trace inversion with Kirchhoff migration. The new method, called ray-based stochastic inversion, is a generalization of current amplitude versus offset/amplitude versus angle (AVO/AVA) inversion techniques. The new method outperforms standard stochastic inversion techniques in cases of reservoir parameter estimation in a structurally complex subsurface with substantial lateral velocity variations and significant reflector dips. A simplification of the method inverts the normal-incidence response from reservoirs with approximately planar layering at the subsurface target locations selected for inversion. It operates along raypaths perpendicular to the reflectors, the direction that offers optimal resolution to discern layering in a reservoir. In a test on field data from the Gulf of Mexico, reservoir parameter estimates obtained with the simplified method, the estimates found by conventional stochastic inversion, and the actual values at a well drilled after the inversion are compared. Although the new method uses only 2% of the prestack data, the result indicates it improves accuracy on the dipping part of the reservoir, where conventional stochastic inversion suffers from wavelet stretch caused by migration.
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Sun, Minao, Liangguo Dong, Jizhong Yang, Chao Huang, and Yuzhu Liu. "Elastic least-squares reverse time migration with density variations." GEOPHYSICS 83, no. 6 (November 1, 2018): S533—S547. http://dx.doi.org/10.1190/geo2017-0517.1.
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Elastic least-squares reverse time migration (ELSRTM) is a powerful tool to retrieve high-resolution subsurface images of the earth’s interior. By minimizing the differences between synthetic and observed data, ELSRTM can improve spatial resolution and reduce migration artifacts. However, conventional ELSRTM methods usually assume constant density models, which cause inaccurate amplitude performance in resulting images. To partially remedy this problem, we have developed a new ELSRTM method that considers P- and S-wave velocity and density variations. Our method can simultaneously obtain P- and S-wave velocity and density images with enhanced amplitude fidelity and suppressed parameter crosstalk. In addition, it can provide subsurface elastic impedance images by summing the inverted velocity images with the density image. Compared with the conventional ELSRTM method, our method can improve the quality of final images and provide more accurate reflectivity estimates. Numerical experiments on a horizontal reflector model and a Marmousi-II model demonstrate the effectiveness of this method.
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Zhang, Zhi-Ya, Jia-Yue Zhao, Qiongqiong Liu, and Guang Fu. "Dual-Polarized Cross Bowtie Dipole for 3G and LTE Applications." International Journal of Antennas and Propagation 2013 (2013): 1–6. http://dx.doi.org/10.1155/2013/341563.
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A dual-polarized cross bowtie dipole element with parasitical circular patch and vertical metal cylinders for base station antennas is presented. A pair of orthogonal cross bowtie dipoles, with a reflector ground plane, is used to obtain the two linear polarizations. Besides two inverted L-shaped feed strips and two shorted feed baluns, parasitical circular patch is introduced to improve the impendence bandwidth and vertical metal cylinders are employed to decrease the lateral dimensions of the antenna. A wideband impedance characteristic of about 45.6% for VSWR ≤ 1.5 (+45° polarization) and VSWR ≤ 1.5 (−45° polarization) ranging from 1.76 to 2.80 GHz is obtained. Moreover, the stable peak gain, unidirectional radiation patterns, high isolation between the two orthogonal polarizations, and low cross-polarization over the whole operating band are also achieved. The proposed antenna is very suitable for potential base station applications in mobile communication such as TD-SCDMA, WCDMA, and CDMA2000 and LTE applications.
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Linde, Niklas, and Laust B. Pedersen. "Characterization of a fractured granite using radio magnetotelluric (RMT) data." GEOPHYSICS 69, no. 5 (September 2004): 1155–65. http://dx.doi.org/10.1190/1.1801933.
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We applied tensor radio magnetotellurics (RMT) in the 10–250 kHz frequency range to study major fracture zones on Ävrö, a small island (1.6 × 1.2 km2) in southeastern Sweden with bedrock dominated by highly resistive granite. The interpretation of a 950‐m RMT profile was facilitated by seismic reflection and borehole data but was complicated (1) by possible 3D effects of the surrounding sea and (2) because the quasi‐static assumption is violated. Inversions based on the quasi‐static assumption give severely distorted models in this type of environment. Inversion codes that include displacement currents are restricted to 1D structures. Therefore, 2D inversions were applied to lower frequencies only. The central part of the inverted profile showed a 30–40‐m‐thick weathered layer over an almost intact bedrock down to a depth of at least 200 m, where higher salinity and/or fracturing yielded higher conductivities. The first 200 m of the profile revealed a major fracture zone, which coincided with a seismic reflector. We used 3D forward modeling to understand the sea effect and to model the conductor in three dimensions. We believe that 3D forward modeling is a highly valuable tool to distinguish known 3D effects (i.e., the sea) from regional 2D features of interest. We suggest that water flow at Ävrö is dominated by a few major fracture zones.
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Tharimela, Raghava, Adolpho Augustin, Marcelo Ketzer, Jose Cupertino, Dennis Miller, Adriano Viana, and Kim Senger. "3D controlled-source electromagnetic imaging of gas hydrates: Insights from the Pelotas Basin offshore Brazil." Interpretation 7, no. 4 (November 1, 2019): SH111—SH131. http://dx.doi.org/10.1190/int-2018-0212.1.
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Mapping of natural gas hydrate systems has been performed successfully in the past using the controlled-source electromagnetic (CSEM) method. This method relies on differentiating resistive highly saturated free gas or hydrate-bearing host sediment from a less resistive low-saturated gas or brine-bearing host sediments. Knowledge of the lateral extent and resistivity variations (and hence the saturation variations) within sediments that host hydrates is crucial to be able to accurately quantify the presence of saturated gas hydrates. A 3D CSEM survey (PUCRS14) was acquired in 2014 in the Pelotas Basin offshore Brazil, with hydrate resistivity mapping as the main objective. The survey was acquired within the context of the CONEGAS research project, which investigated the origin and distribution of gas hydrate deposits in the Pelotas Basin. We have inverted the acquired data using a proprietary 3D CSEM anisotropic inversion algorithm. Inversion was purely CSEM data driven, and we did not include any a priori information in the process. Prior to CSEM, interpretation of near-surface geophysical data including 2D seismic, sub-bottom profiler, and multibeam bathymetry data indicated possible presence of gas hydrates within features identified such as faults, chimneys, and seeps leading to pockmarks, along the bottom simulating reflector and within the gas hydrate stability zone. Upon integration of the same with CSEM-derived resistivity volume, the interpretation revealed excellent spatial correlation with many of these features. The interpretation further revealed new features with possible hydrate presence, which were previously overlooked due to a lack of a clear seismic and/or multibeam backscatter signature. In addition, features that were previously mapped as gas hydrate bearing had to be reinterpreted as residual or low-saturated gas/hydrate features, due to the lack of significant resistivity response associated with them. Furthermore, we used the inverted resistivity volume to derive the saturation volume of the subsurface using Archie’s equation.
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Reuber, Kyle R., Jim Pindell, and Brian W. Horn. "Demerara Rise, offshore Suriname: Magma-rich segment of the Central Atlantic Ocean, and conjugate to the Bahamas hot spot." Interpretation 4, no. 2 (May 1, 2016): T141—T155. http://dx.doi.org/10.1190/int-2014-0246.1.
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The Demerara Rise is a prominent bathymetric feature that has been considered as a broad expression of shallow continental basement and used in conjunction with the Guinea Plateau as a pinning point for circum-Atlantic plate reconstructions. Previously, shallow-penetration, poorly imaged seismic data over the Demerara Rise were modeled with the lower sequences interpreted as continental crust at relatively shallow depths. However, new long-offset, deeply penetrating seismic data provide evidence that basement nearly or entirely comprises excessively thick volcanic strata (approximately 21 km). Seismic character and geometry, 2D gravity modeling, and volcanic margin analogs were used to identify unfaulted, convex-upward seaward dipping reflector (SDR) packages. These steeply dipping (approximately 20°) igneous successions are westwardly divergent, and occur as offlapping reflector sets in trains as long as 250 km. This rift-related volcanism now recognized at the Demerara Rise was probably conjugate to syn-rift volcanism in South Florida/Great Bahama Bank, and from this we have predicted a volcanic element for the Guinea Plateau. This volcanism could be linked to a Bahamas hot spot at the initial opening of the Central Atlantic. Six SDR packages have been interpreted below the Late Jurassic-Early Cretaceous carbonate section of the rise, indicating that the early volcanism produced a marine substrate upon which the subsequent carbonate bank section developed. We have inferred that this Early Cretaceous volcanic/carbonate margin continued into the Guinea Plateau of West Africa. The pre-Aptian section was inverted and peneplained with a strong angular unconformity prior to the Early Cretaceous opening of the Equatorial Atlantic seaway. The newly identified Central Atlantic volcanic margin of the Demerara Rise holds implications of a volcanic origin for its conjugate margins. We have confirmed a voluminous magma-rich opening of the southeastern Central Atlantic.
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Jacobel, Robert W., Knut Christianson, Adam C. Wood, Kevin J. Dallasanta, and Rebecca M. Gobel. "Morphology of basal crevasses at the grounding zone of Whillans Ice Stream, West Antarctica." Annals of Glaciology 55, no. 67 (2014): 57–63. http://dx.doi.org/10.3189/2014aog67a004.
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AbstractThe transition from limited-slip conditions at the base of grounded ice to free-slip conditions beneath floating ice occurs across the few-kilometers-wide grounding zone. This region involves either an elastic flexural transition from bedrock to hydrostatically supported elevations (often tidally influenced), a transition from thicker to thinner ice over a flat bed, or some combination of these two processes. In either case, ice must flow across a changing stress field, often resulting in brittle deformation, manifested as basal crevassing. Thus the position and morphology of basal crevasses reveal important information about the stress state across this transition. Our gridded ground-based radar surveys on Whillans Ice Stream, West Antarctica, indicate a complex pattern of basal crevasses, but most are associated with regions where the surface elevation gradient is steepest. Due to the high reflectivity of sea water, we image many off-nadir crevasses from a corner-reflector geometry involving reflections from the ice/sea-water interface and then from the crevasse, producing echoes with an inverted phase that could be misinterpreted as subglacial returns. Our results indicate that basal crevasses offer a rich dataset for diagnosing stress state and salient processes across grounding zones, and that special care is needed when interpreting subglacial returns in radar data.
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Chauris, Hervé, Mark S. Noble, Gilles Lambaré, and Pascal Podvin. "Migration velocity analysis from locally coherent events in 2‐D laterally heterogeneous media, Part I: Theoretical aspects." GEOPHYSICS 67, no. 4 (July 2002): 1202–12. http://dx.doi.org/10.1190/1.1500382.
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We present a new method based on migration velocity analysis (MVA) to estimate 2‐D velocity models from seismic reflection data with no assumption on reflector geometry or the background velocity field. Classical approaches using picking on common image gathers (CIGs) must consider continuous events over the whole panel. This interpretive step may be difficult—particularly for applications on real data sets. We propose to overcome the limiting factor by considering locally coherent events. A locally coherent event can be defined whenever the imaged reflectivity locally shows lateral coherency at some location in the image cube. In the prestack depth‐migrated volume obtained for an a priori velocity model, locally coherent events are picked automatically, without interpretation, and are characterized by their positions and slopes (tangent to the event). Even a single locally coherent event has information on the unknown velocity model, carried by the value of the slope measured in the CIG. The velocity is estimated by minimizing these slopes. We first introduce the cost function and explain its physical meaning. The theoretical developments lead to two equivalent expressions of the cost function: one formulated in the depth‐migrated domain on locally coherent events in CIGs and the other in the time domain. We thus establish direct links between different methods devoted to velocity estimation: migration velocity analysis using locally coherent events and slope tomography. We finally explain how to compute the gradient of the cost function using paraxial ray tracing to update the velocity model. Our method provides smooth, inverted velocity models consistent with Kirchhoff‐type migration schemes and requires neither the introduction of interfaces nor the interpretation of continuous events. As for most automatic velocity analysis methods, careful preprocessing must be applied to remove coherent noise such as multiples.
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Aldawood, Ali, Emad Hemyari, Ilya Silvestrov, and Andrey Bakulin. "Imaging ahead of and around the bit in a desert environment: DrillCAM field trial with wireless geophones and top-drive sensor." Leading Edge 40, no. 5 (May 2021): 374–81. http://dx.doi.org/10.1190/tle40050374.1.
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Advanced seismic-while-drilling (SWD) technologies are being utilized to steer drilling operations and provide high-resolution subsurface images around and ahead of the bit. We present a case study of SWD imaging using a recently acquired field data set from a desert environment with a complex near surface. Data acquisition is performed with wireless geophones and top-drive sensors using continuous real-time recording. The drill-bit noise data are analyzed while continuously recording in real time by using a specialized workflow that combines elements of SWD and conventional vertical seismic profiling processing with controlled seismic sources. First, the workflow enhances the direct wavefield to retrieve accurate first-break picks for traveltime tomographic inversion along east–west- and north–south-striking walkaway lines. Then, it extracts and enhances upgoing reflection events, illuminating parts of the subsurface around and ahead of the bit. During the final step, these upgoing reflections are imaged using the inverted velocity model to reconstruct a migrated subsurface image around the well. As is the case for land surface seismic in the presence of a complex near surface, we observe a significant variation of data quality for the orthogonal receiver lines. As a result, each line provides a robust image of a different part of the subsurface. The east–west-striking line's migrated image delineates a major shallow reflector that serves as a marker for predicting the drilling depth of a deeper horizon. Likewise, migrating upgoing reflections from the north–south line accurately maps a deeper target horizon ahead of the bit. The obtained SWD images assist in setting the casing points accurately and provide a more precise ahead-of-the-bit depth for different horizons with significantly less uncertainty than surface seismic.
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Li, Yubing, and Hervé Chauris. "Coupling direct inversion to common-shot image-domain velocity analysis." GEOPHYSICS 83, no. 5 (September 1, 2018): R497—R514. http://dx.doi.org/10.1190/geo2017-0825.1.
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Migration velocity analysis is a technique used to estimate the large-scale structure of the subsurface velocity model controlling the kinematics of wave propagation. For more stable results, recent studies have proposed to replace migration, adjoint of Born modeling, by the direct inverse of the modeling operator in the context of extended subsurface-offset domain. Following the same strategy, we have developed a two-way-wave-equation-based inversion velocity analysis (IVA) approach for the original surface-oriented shot gathers. We use the differential semblance optimization (DSO) objective function to evaluate the quality of inverted images depending on shot positions and to derive the associated gradient, an essential element to update the macromodel. We evaluate the advantages and limitations through applications of 2D synthetic data sets, first on simple models with a single-reflector embedded in various background velocities and then on the Marmousi model. The direct inverse attenuates migration smiles by compensating for geometric spreading and uneven illuminations. We slightly modified the original DSO objective function to remove spurious oscillations around interface positions in the velocity gradient. These oscillations are related to the fact that the locations of events in the image domain depend on the macromodel. We pay attention to the presence of triplicated wavefields. It appears that IVA is robust even if artifacts are observed in the seismic migrated section. The velocity gradient leads to a stable update, especially after a Gaussian smoothing over a wavelength distance. Coupling common-shot direct inversion to velocity analysis offers new possibilities for the extension to 3D in the future.
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Che, Yanbo, Guojian Liu, Jianmei Xu, and Yuancheng Zhao. "Modeling and Analysis of 12-Pulse Inverter in Shipboard or Aircraft." Polish Maritime Research 24, s3 (November 27, 2017): 136–42. http://dx.doi.org/10.1515/pomr-2017-0116.
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Abstract With the development of DC distribution system within the isolated power system of a ship or an aircraft, more constant frequency loads will be supplied by inverters connected to DC main bus. In the operating mode conversion process of an isolated power system, inverters will inevitably suffer from serious disturbance and affect the stability of the system. Therefore, it is important to establish a model of the inverter that reflects its dynamic characteristics and based on which to conduct the stability analysis. This paper proposes a 12-pulse inverter model based on the generalized state space averaging (GSSA) method. This model can overcome the limitations of 12-pulse inverter state space averaging (SSA) model in transient analysis with good accuracy and fast analysis ability effectively. Three kinds of models for a 12-pulse aircraft inverter are built in MATLAB, namely GSSA model, SSA model and detail device model. The simulation results show the high accuracy of GSSA model in stability analysis. This study provides an effective analytical tool for stability analysis of 12-pulse inverter and also provides a reference for inverter modeling research of isolated power system such as in aircraft or ship.
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Ojha, Maheswar, and Ranjana Ghosh. "Assessment of gas hydrate using prestack seismic inversion in the Mahanadi Basin, offshore eastern India." Interpretation 9, no. 2 (March 11, 2021): SD15—SD26. http://dx.doi.org/10.1190/int-2020-0139.1.
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The Indian National Gas Hydrate Program Expedition-01 in 2006 has discovered gas hydrate in the Mahanadi offshore basin along the eastern Indian margin. However, well-log analysis, pressure core measurements, and infrared anomalies reveal that gas hydrates are distributed as disseminated within the fine-grained sediment, unlike massive gas hydrate deposits in the Krishna-Godavari Basin. The 2D multichannel seismic section, which crosses holes NGHP-01-9A and 19B located at approximately 24 km apart, indicates a continuous bottom-simulating reflector (BSR) along it. We aim to investigate the prospect of gas hydrate accumulation in this area by integrating well-log analysis and seismic methods with rock-physics modeling. First, we estimate gas hydrate saturation at these two holes from the observed impedance using the three-phase Biot-type equation. Then, we establish a linear relationship between the gas hydrate saturation and the impedance contrast with respect to the water-saturated sediment. Using this established relation and impedance obtained from prestack inversion of seismic data, we produce a 2D gas hydrate-distribution image over the entire seismic section. The gas hydrate saturation estimated from resistivity and sonic data at well locations varies within 0%–15%, which agrees well with the available pressure core measurements at hole 19. However, the 2D map of gas hydrate distribution obtained from our method indicates that the maximum gas hydrate saturation is approximately 40% just above the BSR between the common-depth points of 1450 and 2850. The presence of gas-charged sediments below the BSR is one of the reasons for the strong BSR observed in the seismic section, which is depicted as low impedance in the inverted impedance section. Closed sedimentary structures above the BSR are probably obstructing the movements of free-gas upslope, for which we do not see the presence of gas hydrate throughout the seismic section above the BSR.
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Grechka, Vladimir, and Ilya Tsvankin. "Feasibility of nonhyperbolic moveout inversion in transversely isotropic media." GEOPHYSICS 63, no. 3 (May 1998): 957–69. http://dx.doi.org/10.1190/1.1444407.
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Inversion of reflection traveltimes in anisotropic media can provide estimates of anisotropic coefficients required for seismic processing and lithology discrimination. Nonhyperbolic P-wave moveout for transverse isotropy with a vertical symmetry axis (VTI media) is controlled by the parameter η (or, alternatively, by the horizontal velocity Vhor), which is also responsible for the influence of anisotropy on all time‐processing steps, including dip‐moveout (DMO) correction and time migration. Here, we recast the nonhyperbolic moveout equation, originally developed by Tsvankin and Thomsen, as a function of Vhor and normal‐moveout (NMO) velocity Vnmo and introduce a correction factor in the denominator that increases the accuracy at intermediate offsets. Then we apply this equation to obtain Vhor and η from nonhyperbolic semblance analysis on long common midpoint (CMP) spreads and study the accuracy and stability of the inversion procedure. Our error analysis shows that the horizontal velocity becomes relatively well‐constrained by reflection traveltimes if the spreadlength exceeds twice the reflector depth. There is, however, a certain degree of tradeoff between Vhor and Vnmo caused by the interplay between the quadratic and quartic term of the moveout series. Since the errors in Vhor and Vnmo have opposite signs, the absolute error in the parameter η (which depends on the ratio Vhor/Vnmo) turns out to be at least two times bigger than the percentage error in Vhor. Therefore, the inverted value of η is highly sensitive to small correlated errors in reflection traveltimes, with moveout distortions on the order of 3–4 ms leading to errors in η up to ±0.1—even in the simplest model of a single VTI layer. Similar conclusions apply to vertically inhomogeneous media, in which the interval horizontal velocity can be obtained with an accuracy often comparable to that of the NMO velocity, while the interval values of η are distorted by the tradeoff between Vhor and Vnmo that gets amplified by the Dix‐type differentiation procedure. We applied nonhyperbolic semblance analysis to a walkaway VSP data set acquired at Vacuum field, New Mexico, and obtained a significant value of η = 0.19 indicative of nonnegligible anisotropy in this area. Then we combined moveout inversion results with the known vertical velocity to resolve the anisotropic coefficients ε and δ. However, in agreement with our modeling results, η estimation was significantly compounded by the scatter in the measured traveltimes. Certain instability in η inversion has no influence on the results of anisotropic poststack time migration because all kinematically equivalent models obtained from nonhyperbolic moveout give an adequate description of long‐spread reflection traveltimes. Also, inversion of nonhyperbolic moveout provides a relatively accurate horizontal‐velocity function that can be combined with the vertical velocity (if it is available) to estimate the anisotropic coefficient ε. However, η represents a valuable lithology indicator that can be obtained from surface P-wave data. Therefore, for purposes of lithology discrimination, it is preferable to find η by means of the more stable DMO method of Alkhalifah and Tsvankin.
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James, Melissa S., Stuart J. Johnstone, and William G. Hayward. "Event-Related Potentials, Configural Encoding, and Feature-Based Encoding in Face Recognition." Journal of Psychophysiology 15, no. 4 (October 2001): 275–85. http://dx.doi.org/10.1027//0269-8803.15.4.275.
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Abstract The effects of manipulating configural and feature information on the face recognition process were investigated by recording event-related potentials (ERPs) from five electrode sites (Fz, Cz, Pz, T5, T6), while 17 European subjects performed an own-race and other-race face recognition task. A series of upright faces were presented in a study phase, followed by a test phase where subjects indicated whether inverted and upright faces were studied or novel via a button press response. An inversion effect, illustrating the disruption of upright configural information, was reflected in accuracy measures and in greater lateral N2 amplitude to inverted faces, suggesting that structural encoding is harder for inverted faces. An own-race advantage was found, which may reflect the use of configural encoding for the more frequently experienced own-race faces, and feature-based encoding for the less familiar other-race faces, and was reflected in accuracy measures and ERP effects. The midline N2 was larger to configurally encoded faces (i. e., own-race and upright), possibly suggesting configural encoding involves more complex processing than feature-based encoding. An N400-like component was sensitive to feature manipulations, with greater amplitude to other-race than own-race faces and to inverted than upright faces. This effect was interpreted as reflecting increased activation of incompatible representations activated by a feature-based strategy used in processing of other-race and inverted faces. The late positive complex was sensitive to configural manipulation with larger amplitude to other-race than own-race faces, and was interpreted as reflecting the updating of an own-race norm used in face recognition, to incorporate other-race information.
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Salo, Edward L., and Gerard T. Schuster. "Traveltime inversion of both direct and reflected arrivals in vertical seismic profile data." GEOPHYSICS 54, no. 1 (January 1989): 49–56. http://dx.doi.org/10.1190/1.1442576.
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Traveltimes from both direct and reflected arrivals in a VSP data set (Bridenstein no. 1 well in Oklahoma) are inverted in a least‐squares sense for velocity structure. By comparing the structure from inversion to the sonic log, we conclude that the accuracy of the reconstructed velocities is greater than that found when only the direct arrivals are used. Extensive tests on synthetic VSP data confirm this observation. Apparently, the additional reflection traveltime equations aid in averaging out the traveltime errors, as well as reducing the slowness variance in reflecting layers. These results are consistent with theory, which predicts a decrease in a layer’s slowness variance with an increase in the number and length of terminating reflected rays. For the Bridenstein data set, 130 direct traveltimes and 399 primary reflection traveltimes were used in the inversion.
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P, Maithili, and Kanakaraj J. "Transformer Less Self-Commutated PV Inverter." Regular issue 10, no. 8 (June 30, 2021): 1–4. http://dx.doi.org/10.35940/ijitee.g9037.0610821.
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The power demand is increased day by day and generation of electrical energy from non-renewable sources are not able to meet the demand. An alternate energy sources are the only solution to meet the power demand. The power generation from solar energy with photovoltaic effect is plays a major role. This Solar PV system has low efficiency. The power semiconductor devices and converter circuit along with inductive / magnetic circuit. The Inverter circuit have an influence on photovoltaic power generation to improve the level of output voltage along with efficiency. In this paper a new transformer less DC-AC converter is proposed, and it has high efficiency, requires less cost when compares with conventional inverter with transformer. Transformer less self-commutated photovoltaic inverter is reflected the advantages of central and string inverters. It gives high output power and low-cost converter. These transformer less DC-AC converter is connect with Boost/Buck-Boost converter for the better output. So, this proposed DC-AC converter topology is not required mechanical switching and it is lighter in size. The PV technology has low efficiency and utilize more cost for generation of power. The proposed transformer less PV inverter is the better choice to increase the usefulness and reduce the charge rate of this PV system.
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Yao, Zhi Lei, Lan Xiao, and Jing Xu. "Performance Improvement of SVPWM-Based Three-Phase Grid-Connected Inverters." Advanced Materials Research 732-733 (August 2013): 1261–64. http://dx.doi.org/10.4028/www.scientific.net/amr.732-733.1261.
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An improved control strategy for three-phase grid-connected inverters with space vector pulse width modulation (SVPWM) is proposed. When the grid current contains harmonics, the d-and q-axes grid currents is interacted in the traditional control method, and the waveform quality of the grid current is poor. As the reference output voltage cannot directly reflect the change of the reference grid current with the traditional control strategy, the dynamic response of the grid-connected inverter is slow. In order to solve the aforementioned problems, the d-and q-axes grid currents in the decoupled components of the grid current controller are substituted by the d-and q-axes reference grid currents, respectively. The operating principles of the traditional and proposed control methods are illustrated. Experimental results show that the grid-connected inverter with the improved control strategy has high waveform quality of the grid current and fast dynamic response.
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Scherbaum, Frank. "Seismic imaging of the site response using microearthquake recordings. Part II. Application to the Swabian Jura, southwest Germany, Seismic network." Bulletin of the Seismological Society of America 77, no. 6 (December 1, 1987): 1924–44. http://dx.doi.org/10.1785/bssa0770061924.
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Abstract The subsurface site structure of the Swabian Jura, southwest Germany, seismic network has been modeled from the inversion of locally recorded SH wave microearthquake seismograms. The observed records have been deconvolved from the effects of apparent source pulse broadening due to the combined influence of frequency bandlimited source signals, absorption, peg leg multiple reflections, and the recording system following the procedure of Scherbaum and Stoll (1985). Corresponding pseudo-reflection seismograms were calculated based on the Kunetz-Claerbout relation for SH waves and inverted using a Levison recursion algorithm. The final structural models have been optimized in terms of numbers of layers and depth resolution using Ferber's (1985) noise stabilization technique. The resulting impedance models for the Swabian Jura, southwest Germany, seismic network show some strongly correlated reflectors in the uppermost layers, which are well understood in terms of the local stratigraphy. The comparison of the inverted impedance model HSN with the P-wave velocity log from a nearby exploration drilling (Trochtelfingen, BEB) shows a high degree of similarity of the dominating reflectors down to a depth of several hundred meters. As a consequence, the coda-generating process for the early part of the coda of the observed Swabian Jura microearthquake seismograms (Wood-Anderson magnitude MWA < 3.0) can be completely interpreted as an effect of the local subsurface structure.
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Hu, Kezhong, Li Chen, Anupam Madhukar, Ping Chen, Chris Kyriakakis, Zaheed Karim, and Armand R. Tanguay. "Inverted cavity GaAs/InGaAs asymmetric Fabry–Perot reflection modulator." Applied Physics Letters 59, no. 14 (September 30, 1991): 1664–66. http://dx.doi.org/10.1063/1.106261.
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Butt, Haider, Qing Dai, Ranjith Rajasekharan, Timothy D. Wilkinson, and Gehan A. J. Amaratunga. "Enhanced reflection from arrays of silicon based inverted nanocones." Applied Physics Letters 99, no. 13 (September 26, 2011): 133105. http://dx.doi.org/10.1063/1.3633119.
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Lee, Woochan, and Dukju Ahn. "Wireless Power Transfer under Wide Distance Variation Using Dual Impedance Frequency." Electronics 9, no. 1 (January 7, 2020): 110. http://dx.doi.org/10.3390/electronics9010110.
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A dual-impedance operation, where coil impedance is controlled by operating frequency selection, is proposed to maintain optimum reflected impedance across coupling variation. More specifically, this work focuses on how high coupling between coils presents excessively high reflected resistance to transmitter (Tx) inverters, degrading the efficiency and output power of the inverter. To overcome this problem, the proposed system is equipped with dual-impedance coil and selects high- or low-impedance coil based on the ability to operate both at 200 kHz and 6.78 MHz frequencies. The reactive impedances of 6.78 MHz coils are designed to be higher than that of 200 kHz coils. Since the reflected resistance is proportional to the coil impedances and coupling squared, at close distance with high coupling coefficient, 200 kHz coils with low coil impedances are activated to prevent an excessive rise in reflected resistance. On the other hand, at large distance spacing with low coupling coefficient, 6.78 MHz coils with high coil impedances are activated so that sufficient reflected resistance is obtained even under the small coupling. The proposed system’s advantages are the high efficiency and the elimination of bulky mechanical relay switches. Measured efficiencies are 88.6–50% across 10 coupling variations.
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Bakulin, Andrey, Vladimir Grechka, and Ilya Tsvankin. "Estimation of fracture parameters from reflection seismic data—Part I: HTI model due to a single fracture set." GEOPHYSICS 65, no. 6 (November 2000): 1788–802. http://dx.doi.org/10.1190/1.1444863.
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The simplest effective model of a formation containing a single fracture system is transversely isotropic with a horizontal symmetry axis (HTI). Reflection seismic signatures in HTI media, such as NMO velocity and amplitude variation with offset (AVO) gradient, can be conveniently described by the Thomsen‐type anisotropic parameters [Formula: see text] [Formula: see text] and [Formula: see text] Here, we use the linear slip theory of Schoenberg and co‐workers and the models developed by Hudson and Thomsen for pennyshaped cracks to relate the anisotropic parameters to the physical properties of the fracture network and to devise fracture characterization procedures based on surface seismic measurements. Concise expressions for [Formula: see text] [Formula: see text] and [Formula: see text] linearized in the crack density, show a substantial difference between the values of the anisotropic parameters for isolated fluid‐filled and dry (gas‐filled) penny‐sh aped cracks. While the dry‐crack model is close to elliptical with [Formula: see text] for thin fluid‐filled cracks [Formula: see text] and the absolute value of [Formula: see text] for typical [Formula: see text] ratios in the background is close to the crack density. The parameters [Formula: see text] and [Formula: see text] for models with partial saturation or hydraulically connected cracks and pores always lie between the values for dry and isolated fluid‐filled cracks. We also demonstrate that all possible pairs of [Formula: see text] and [Formula: see text] occupy a relatively narrow triangular area in the [Formula: see text] [Formula: see text]plane, which can be used to identify the fracture‐induced HTI model from seismic data. The parameter [Formula: see text] along with the fracture orientation, can be obtained from the P-wave NMO ellipse for a horizontal reflector. Given [Formula: see text] the NMO velocity of a dipping event or nonhyperbolic moveout can be inverted for [Formula: see text] The remaining anisotropic coefficient, [Formula: see text] can be determined from the constraint on the parameters of vertically fractured HTI media if an estimate of the [Formula: see text] ratio is available. Alternatively, it is possible to find [Formula: see text] by combining the NMO ellipse for horizontal events with the azimuthal variation of the P-wave AVO gradient. Also, we present a concise approximation for the AVO gradient of converted (PS) modes and show that all three relevant anisotropic coefficients of HTI media can be determined by the joint inversion of the AVO gradients or NMO velocities of P- and PS-waves. For purposes of evaluating the properties of the fractures, it is convenient to recalculate the anisotropic coefficients into the normal [Formula: see text] and tangential [Formula: see text] weaknesses of the fracture system. If the HTI model results from penny‐shaped cracks, [Formula: see text] gives a direct estimate of the crack density and the ratio [Formula: see text] is a sensitive indicator of fluid saturation. However, while there is a substantial difference between the values of [Formula: see text] for isolated fluid‐filled cracks and dry cracks, interpretation of intermediate values of [Formula: see text] for porous rocks requires accounting for the hydraulic interaction between cracks and pores.
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Lei, Biao, Hongzhong Liu, Weitao Jiang, Bangdao Chen, Yongsheng Shi, Lei Yin, and Xiaokang Liu. "Transparent film with inverted conical microholes array for reflection enhancement." Applied Surface Science 369 (April 2016): 143–50. http://dx.doi.org/10.1016/j.apsusc.2016.02.055.
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Guo, Qiang, and Tariq Alkhalifah. "Elastic reflection-based waveform inversion with a nonlinear approach." GEOPHYSICS 82, no. 6 (November 1, 2017): R309—R321. http://dx.doi.org/10.1190/geo2016-0407.1.
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Full-waveform inversion (FWI) is a highly nonlinear problem due to the complex reflectivity of the earth, and this nonlinearity only increases under the more expensive elastic assumption. In elastic media, we need a good initial P-wave velocity and even better initial S-wave velocity models with accurate representation of the low model wavenumbers for FWI to converge. However, inverting for the low-wavenumber components of P- and S-wave velocities using reflection waveform inversion (RWI) with an objective to fit the reflection shape, rather than produce reflections, may mitigate the limitations of FWI. Because FWI, performing as a migration operator, is preferred of the high-wavenumber updates along reflectors. We have developed an elastic RWI that inverts for the low-wavenumber and perturbation components of the P- and S-wave velocities. To generate the full elastic reflection wavefields, we derive an equivalent stress source made up by the inverted model perturbations and incident wavefields. We update the perturbation and propagation parts of the velocity models in a nested fashion. Applications on the synthetic isotropic models and field data indicate that our method can efficiently update the low- and high-wavenumber parts of the models.
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Beretta, Matteo Mario, Giancarlo Bernasconi, and Giuseppe Drufuca. "AVO and AVA inversion for fractured reservoir characterization." GEOPHYSICS 67, no. 1 (January 2002): 300–306. http://dx.doi.org/10.1190/1.1451802.
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Seismic wave reflection amplitudes are used to detect fluids and fracture properties in reservoirs. This paper studies the characterization of a vertically fractured fluid‐filled reservoir by analyzing the reflection amplitudes of P‐waves with varying incident and azimuthal angles. The reservoir is modeled as a horizontal transversely isotropic medium embedded in an isotropic background, and the linearized P‐waves reflection coefficient are considered. The conditioning of the inverse problem is analyzed, and fracture density is found to be the best conditioned parameter. Using diffraction tomography under the Born approximation, an inversion procedure is proposed in the transformed k–ω domain to detect fracture density variations within the reservoir. Seismic data are rearranged in pairs of incident and reflected plane waves, enlightening only one spectral component of the fracture density field at a time. Only the observable spectral components are inverted. Moreover, working in the transformed domain, picking reflection amplitudes is not required. An example of the inversion applied to a synthetic data set is presented. The limitation of source and receiver numbers and the finite bandwidth of the wavelet produce a loss of resolution, but the overall fracture density variations are recovered correctly.
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Mora, Peter. "Elastic wave‐field inversion of reflection and transmission data." GEOPHYSICS 53, no. 6 (June 1988): 750–59. http://dx.doi.org/10.1190/1.1442510.
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Elastic inversion of multioffset seismic data by wave‐ field fitting yields a maximum probability P-wave and S-wave velocity and density model of the Earth. Theoretically, the inversion accounts for all elastic waves including reflected and transmitted waves, mode conversions, shear waves, head waves, Rayleigh waves, etc. These different wave types tend to resolve different components of the Earth properties. By inverting two‐ component synthetic data, I show that reflection data mainly resolve high wavenumbers, while transmission data mainly resolve low wavenumbers of the P-wave and S-wave velocity model. The inversion of reflection data (shot gathers) yields a result that looks like a prestack elastic migration but the meaning of the inverted data is not simply reflectivity: it is the P-wave and S-wave velocity perturbation. The inversion of transmission data (VSPs) yields a solution that contains useful interval velocity information and is comparable to an elastic diffraction tomography result.
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Nabanja, Sheila P., Leslie A. Kolodziejski, and Gale S. Petrich. "Lateral Oxidation of AlAs for Circular and Inverted Mesa Saturable Bragg Reflectors." IEEE Journal of Quantum Electronics 49, no. 9 (September 2013): 731–38. http://dx.doi.org/10.1109/jqe.2013.2268536.
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Kaufhold, Elias, Simon Grandl, Jan Meyer, and Peter Schegner. "Feasibility of Black-Box Time Domain Modeling of Single-Phase Photovoltaic Inverters Using Artificial Neural Networks." Energies 14, no. 8 (April 10, 2021): 2118. http://dx.doi.org/10.3390/en14082118.
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This paper introduces a new black-box approach for time domain modeling of commercially available single-phase photovoltaic (PV) inverters in low voltage networks. An artificial neural network is used as a nonlinear autoregressive exogenous model to represent the steady state behavior as well as dynamic changes of the PV inverter in the frequency range up to 2 kHz. The data for the training and the validation are generated by laboratory measurements of a commercially available inverter for low power applications, i.e., 4.6 kW. The state of the art modeling approaches are explained and the constraints are addressed. The appropriate set of data for training is proposed and the results show the suitability of the trained network as a black-box model in time domain. Such models are required, i.e., for dynamic simulations since they are able to represent the transition between two steady states, which is not possible with classical frequency-domain models (i.e., Norton models). The demonstrated results show that the trained model is able to represent the transition between two steady states and furthermore reflect the frequency coupling characteristic of the grid-side current.
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HERRERÍAS-AZCUÉ, F., A. GONZÁLEZ-VEGA, J. TORRES-ARENAS, and G. GUTIÉRREZ-JUÁREZ. "SOLUTION FOR THE PHOTOACOUSTIC WAVE EQUATION WITH A SINGLE SPATIAL DEGREE OF FREEDOM, BEER'S LAW ABSORPTION OF RADIATION AND MECHANICAL BARRIERS." Modern Physics Letters B 27, no. 18 (July 11, 2013): 1350135. http://dx.doi.org/10.1142/s0217984913501352.
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A photoacoustic model with one degree of freedom in the spatial coordinates for a plane sample is studied. The model proposed considers a sample with Beer's law absorption immersed in a fluid with different acoustical impedance. An analytical solution for this problem is given. It is shown that the generated PA wave is composed of a pressure peak followed by a reflected and inverted pulse with diminished magnitude. It is also remarked that the form described for the pulse has a periodicity related to the sample's width and attenuated by the reflection coefficient. It is noted that, due to this attenuation, information about the sample's width is more easily detected at the irradiation side. Border cases are taken for equal impedances and infinite sample width.