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Articles de revues sur le sujet « CIRCULAR HARMONICS »

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Auteur : Grafiati

Publié le 11 septembre 2023

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1

Fan, Tingting, Patrik Grychtol, Ronny Knut, Carlos Hernández-García, Daniel D. Hickstein, Dmitriy Zusin, Christian Gentry et al. « Bright circularly polarized soft X-ray high harmonics for X-ray magnetic circular dichroism ». Proceedings of the National Academy of Sciences 112, n^o 46 (3 novembre 2015) : 14206–11. http://dx.doi.org/10.1073/pnas.1519666112.

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We demonstrate, to our knowledge, the first bright circularly polarized high-harmonic beams in the soft X-ray region of the electromagnetic spectrum, and use them to implement X-ray magnetic circular dichroism measurements in a tabletop-scale setup. Using counterrotating circularly polarized laser fields at 1.3 and 0.79 µm, we generate circularly polarized harmonics with photon energies exceeding 160 eV. The harmonic spectra emerge as a sequence of closely spaced pairs of left and right circularly polarized peaks, with energies determined by conservation of energy and spin angular momentum. We explain the single-atom and macroscopic physics by identifying the dominant electron quantum trajectories and optimal phase-matching conditions. The first advanced phase-matched propagation simulations for circularly polarized harmonics reveal the influence of the finite phase-matching temporal window on the spectrum, as well as the unique polarization-shaped attosecond pulse train. Finally, we use, to our knowledge, the first tabletop X-ray magnetic circular dichroism measurements at the N4,5 absorption edges of Gd to validate the high degree of circularity, brightness, and stability of this light source. These results demonstrate the feasibility of manipulating the polarization, spectrum, and temporal shape of high harmonics in the soft X-ray region by manipulating the driving laser waveform.

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Klemke, Nicolai, Nicolas Tancogne-Dejean, Giulio M. Rossi, Yudong Yang, Roland E. Mainz, Giuseppe Di Sciacca, Angel Rubio, Franz X. Kärtner et Oliver D. Mücke. « Polarization states of high-harmonics generated in silicon from elliptical drivers ». EPJ Web of Conferences 205 (2019) : 02022. http://dx.doi.org/10.1051/epjconf/201920502022.

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The polarization states of high-harmonics generated in silicon with elliptical excitation are studies. Circularly polarized harmonics are demonstrated with both circular and non-circular excitation, determined by crystal symmetry and the dynamical response of the system.

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3

Snape-Jenkinson, C. J., S. Crozier et L. K. Forbes. « NMR shim coil design utilising a rapid spherical harmonic calculation method ». ANZIAM Journal 43, n^o 3 (janvier 2002) : 375–86. http://dx.doi.org/10.1017/s1446181100012578.

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AbstractA rapid spherical harmonic calculation method is used for the design of Nuclear Magnetic Resonance shim coils. The aim is to design each shim such that it generates a field described purely by a single spherical harmonic. By applying simulated annealing techniques, coil arrangements are produced through the optimal positioning of current-carrying circular arc conductors of rectangular cross-section. This involves minimizing the undesirable harmonics in relation to a target harmonic. The design method is flexible enough to be applied for the production of coil arrangements that generate fields consisting significantly of either zonal or tesseral harmonics. Results are presented for several coil designs which generate tesseral harmonics of degree one.

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Xie, Duan, Yan Yin, Tongpu Yu, Hongyu Zhou et Dongxia Li. « High harmonic generation by co-rotating bi-circular laser fields interaction with relativistic plasmas ». Physics of Plasmas 29, n^o 10 (octobre 2022) : 103107. http://dx.doi.org/10.1063/5.0110746.

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We present an investigation of high harmonic generation (HHG) from relativistic plasmas driven by two-color co-rotating circularly polarized (CP) laser fields at various frequency ratios [Formula: see text]. The theoretical analysis and the particle-in-cell simulation results reveal that when [Formula: see text], CP harmonics with opposite helicities can appear simultaneously due to the relativistic mirror effect and the related conservation laws. Meanwhile, the harmonic spectra features (including the HHG efficiency, the allowed harmonic orders, and their polarization states) can be tuned through adjusting the frequency and intensity ratio of the two driving field components. This finding might be helpful for a consummate understanding of the bi-circular HHG technique.

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Khangale, Z. N., S. B. Potter, P. A. Woudt, D. A. H. Buckley, A. N. Semena, E. J. Kotze, D. N. Groenewald et al. « A spectroscopic, photometric, polarimetric, and radio study of the eclipsing polar UZ Fornacis : the first simultaneous SALT and MeerKAT observations ». Monthly Notices of the Royal Astronomical Society 492, n^o 3 (11 janvier 2020) : 4298–312. http://dx.doi.org/10.1093/mnras/staa080.

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ABSTRACT We present phase-resolved spectroscopy, photometry, and circular spectropolarimetry of the eclipsing polar UZ Fornacis. Doppler tomography of the strongest emission lines using the inside-out projection revealed the presence of three emission regions: from the irradiated face of the secondary star, the ballistic stream and the threading region, and the magnetically confined accretion stream. The total intensity spectrum shows broad emission features and a continuum that rises in the blue. The circularly polarized spectrum shows the presence of three cyclotron emission harmonics at ∼4500, 6000, and 7700 Å, corresponding to harmonic numbers 4, 3, and 2, respectively. These features are dominant before the eclipse and disappear after the eclipse. The harmonics are consistent with a magnetic field strength of ∼57 MG. We also present phase-resolved circular and linear photopolarimetry to complement the spectropolarimetry around the times of eclipse. MeerKAT radio observations show a faint source that has a peak flux density of 30.7 ± 5.4 $\mu$Jy beam−1 at 1.28 GHz at the position of UZ For.

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Holmes, Stewart. « Circular harmonics beamforming with spheroidal baffles ». Journal of the Acoustical Society of America 133, n^o 5 (mai 2013) : 3524. http://dx.doi.org/10.1121/1.4806335.

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Ahmad, Mahmoud, Najah Kabalan et Samar Omran. « An Analytical Study of the Diffraction of Light by a Circular Aperture Using Spherical Harmonics for n≤1 ». International Journal of Optics 2020 (9 juin 2020) : 1–10. http://dx.doi.org/10.1155/2020/3057674.

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Based on the importance of spherical harmonics and their applicability in many physical problems, this research aimed to study the diffraction pattern of light by a circular aperture starting from the first Rayleigh–Sommerfeld diffraction equation and to expand the polar radius of a point on the surface of the circular aperture based on spherical harmonics. We depended on this theoretical framework in our paper. We calculated the optical intensity compounds C00,C10,C11,C1−1 for n=0,1,m=−1,0,1. We studied the intensity distributions in three special cases (along the optical axis, at the geometrical focal plane, and along the boundary of the geometrical shadow). We presented numerical comparative examples to illustrate the variation of the intensity versus a ratio (Z/A is the ratio of the distance between the circular aperture and the observation plane to a radius of the circular aperture), and we used Maple program to represent these results. We noticed that the expansion we made using spherical harmonic analysis led to an increase in the number of fringes bright enough to be visible to the naked eye. We then concluded with a brief discussion of the results.

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Rylyuk, V. M. « Tunneling and multiphoton ionization of atoms in two-color linear and circular laser fields and possibility of coherent polarization control of terahertz waves ». International Journal of Modern Physics B 34, n^o 29 (28 octobre 2020) : 2050275. http://dx.doi.org/10.1142/s0217979220502756.

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The tunneling and multiphoton ionization of atoms in an intense two-color linearly and circularly polarized laser fields are discussed in the Keldysh theory framework. We use the “imaginary-time” method, where tunneling of the photoelectron is described by the classical equations of motion but with purely imaginary “time.” Together with using of the saddle-point method, this allows to obtain the dependence of the total ionization rate and the net photoelectron current, generated due to the interaction of an intense two-color laser field with an atom, on the ratio of the second and fundamental harmonic amplitudes, their relative phase and an angle between harmonics. Application of the “imaginary-time” method also allows us to specify the parameters maximizing the net photocurrent and to determine the Coulomb correction to the ionization rate. We investigate the properties of polarization and spectral intensity of terahertz (THz) radiation and also the possibility of the coherent control of THz waves polarization in two-color scheme, through the relative phase between harmonics. We theoretically demonstrate that the amplification of THz radiation in the case of parallel co-rotating circular laser pulses is greater than for a combination of circularly and linearly polarized harmonics and provides the most promising conditions for increasing the efficiency of THz emission and coherent control of the THz beam polarization.

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Buznikov, N. A., A. S. Antonov et A. A. Rakhmanov. « Bias Current Effect on Nonlinear Magnetoimpedance Response in Amorphous Wires with Circular Anisotropy ». Solid State Phenomena 152-153 (avril 2009) : 329–32. http://dx.doi.org/10.4028/www.scientific.net/ssp.152-153.329.

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The effect of bias current on the appearance of higher harmonics in the nonlinear mag¬netoimpedance in amorphous wires with a circular anisotropy is studied. The rotational model to calculate the voltage response in the case of a weak skin effect is proposed. It is shown that the ap¬plication of the bias current may lead to significant increase of the second harmonic amplitude in the voltage. The conditions of maximum field sensitivity of the second harmonic are found.

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Ghaffarian, Mohammad Saeid, Gholamreza Moradi et Reza Zaker. « Harmonic Suppressed Slot Antennas Using Rectangular/Circular Defected Ground Structures ». International Journal of Antennas and Propagation 2012 (2012) : 1–7. http://dx.doi.org/10.1155/2012/721565.

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Two wide rectangle-shaped microstrip-fed 2.6-GHz slot antennas using defected ground structures (DGSs) with a low design complexity are proposed to achieve wideband harmonic suppression. To accomplish this, two rectangular DGSs (RDGSs) in the first antenna and two circular DGSs (CDGSs) in the second one with various dimensions are etched into the ground plane, which could have a wideband-stop characteristic. Simulated and measured reflection coefficients indicate that the two proposed structures effectively suppress the second and third harmonics up to 23 dB between 3.5 and 10.5 GHz with a maximum ripple of 2.4 dB. In addition, the radiation patterns and peak gains of the antennas can be suppressed at least 17 dB and 7.1 dBi, respectively, at the third harmonic frequency of 7.86 GHz.

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Sabanca, M. « On wave harmonics of heated circular cylinders ». Computers & ; Fluids 36, n^o 5 (juin 2007) : 887–901. http://dx.doi.org/10.1016/j.compfluid.2006.06.004.

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Yamansarin, Ildar, Mikhail Salikov, Alexander Padeev et Dmitry Surkov. « An Approach to the Use of an External Magnetic Field As a Diagnostic Sign of an Asynchronous Motor Malfunction ». Известия высших учебных заведений. Электромеханика 64, n^o 3 (2021) : 18–23. http://dx.doi.org/10.17213/0136-3360-2021-3-18-23.

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The article deals with the issues related to the possibility of diagnosing the technical condition of an asyn-chronous electric motor by an external magnetic field. The justification of the problems associated with the di-agnosis of electric motors is given. The difficulties that arise when measuring the external magnetic field of electric motors, as well as the devices with which it is possible to carry out measurements, are described. The re-lationship between the EMF of the sensor and the external magnetic field is shown. The results of processing the EMF waveforms induced by an external magnetic field in an inductive sensor for various electric motors are presented. The processing was carried out by the fast Fourier transform method. The external magnetic field contains the first harmonic and various harmonics that are multiples of the combination of the stator teeth, or the sum of the stator and rotor teeth that fall on one pair of poles. The ratio of the amplitudes of the first and tooth harmonics is affected by the measurement location and the orientation of the sensor. Diagrams showing the ratio of the main and tooth harmonics at different points of the motor body are constructed. The depend-ences of the harmonic amplitudes on the magnitude of the magnetizing current of the stator are given. Changes in the amplitudes and spectrum of harmonics in the presence and absence of an inter-turn short circuit in the stator winding are shown. Diagrams of the circular external magnetic field for the main and higher harmonics are constructed. The study shows the possibility of using an external magnetic field to detect inter-turn short circuits of the stator winding.

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Rueda-Parada, Jorge Enrique. « Encryption using circular harmonic key ». DYNA 82, n^o 190 (11 mai 2015) : 70–73. http://dx.doi.org/10.15446/dyna.v82n190.42915.

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This work presents a study of variance to rotation key encryption processors based on the Fourier transform. It was determined that the key in rectangular coordinates allows a tolerance level of less than 0.2 degrees of rotation of the key in the decryption process. Thus, the solution is to build the key in polar coordinates, by means of circular harmonics expansion; in this way, the tolerance threshold rises to about 40 degrees of rotation of the key in the decryption process. This solution is an added value for optical encryption processors. I have developed a computational tool for simulations and results obtained in this study.

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Pirozhenko, A. V., A. I. Maslova et V. V. Vasyliev. « Analytical model of satellite motion in almost circular orbits under the influence of zonal harmonics of geopotential ». Kosmìčna nauka ì tehnologìâ 28, n^o 4 (9 août 2022) : 18–30. http://dx.doi.org/10.15407/knit2022.04.018.

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The article deals with the movement of satellites in low near-circular orbits of the Earth. An analytical model is constructed, which consists of formulas describing the change of the osculating elements and averaged equations. An algorithm for constructing a second approximation of the influence of zonal harmonics of the geopotential on the movement of satellites in almost circular orbits is presented. For the second and third zonal harmonics, formulas are given for the osculating and average elements describing the motion of the satellite in the second approximation in small parameters. The introduction of special variables for almost circular orbits made it possible to significantly simplify the procedure for constructing the second approximation of the influence of zonal harmonics. The article provides a justification for the accuracy of the analytical model for the considered orbits. The constructed model of changes in the average elements of the orbit describes the basic principles of motion. With a sufficiently high accuracy, this model describes the changes in the average elements of the orbit with simple analytical formulas and is convenient for analyzing the properties of orbits and pre-selecting a reference orbit for a specific mission.

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Silaev, A. A., A. A. Romanov et N. V. Vvedenskii. « The Use of Brunel Harmonics of Elliptically Polarized Laser Pulses for High-Resolved Detection of Terahertz and Mid-Infrared Radiation ». Journal of Physics : Conference Series 2494, n^o 1 (1 mai 2023) : 012004. http://dx.doi.org/10.1088/1742-6596/2494/1/012004.

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Abstract We study the generation of low-order harmonics during the interaction of helium atoms with intense elliptically-polarized laser pulses in the presence of a static electric field. Based on the solution of the three-dimensional time-dependent Schrödinger equation, the spectra of generated radiation are calculated for various pulse ellipticities, intensities, and static-field strengths. We show the possibility of using the second harmonic generation in the free-electron current density by laser pulses with arbitrary (even circular) polarization for high-resolved measuring the waveforms of terahertz and mid-infrared radiation.

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Brázda, Petr, et Lukas Palatinus. « Precise lattice parameters through distortions refinement using circular harmonics ». Acta Crystallographica Section A Foundations and Advances 77, a2 (14 août 2021) : C238. http://dx.doi.org/10.1107/s0108767321094447.

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Elko, Gary W., et Jens Meyer. « A circular microphone array beamformer based on spherical harmonics ». Journal of the Acoustical Society of America 140, n^o 4 (octobre 2016) : 3032. http://dx.doi.org/10.1121/1.4969408.

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Singh, Jagadish, et Achonu Joseph Omale. « Robe’s circular restricted three-body problem with zonal harmonics ». Astrophysics and Space Science 353, n^o 1 (12 juin 2014) : 89–96. http://dx.doi.org/10.1007/s10509-014-1995-7.

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Rajpoot, Rambabu, Amol R. Holkundkar et Jayendra N. Bandyopadhyay. « Polarization control of attosecond pulses using bi-chromatic elliptically polarized laser ». Journal of Physics B : Atomic, Molecular and Optical Physics 54, n^o 22 (17 novembre 2021) : 225401. http://dx.doi.org/10.1088/1361-6455/ac3f97.

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Abstract We study the high harmonic generation (HHG) using elliptically polarized two-color driving fields. The HHG via bi-chromatic counter-rotating laser fields is a promising source of circularly polarized ultrashort XUV radiation at the attosecond time scale. The ellipticity or the polarization of the attosecond pulses (APs) can be tweaked by modifying the emitted harmonics’ ellipticity, which can be controlled by varying the driver fields. A simple setup is used to control the polarization of the driving fields, which eventually changes the ellipticity of the APs. A well-defined scaling for the ellipticity of the AP as a function of the rotation angle of the quarter-wave plate is also deduced by solving the time-dependent Schrödinger equation in two dimensions. The scaling can further be explored to obtain the APs of the desired degree of polarization, ranging from linear to elliptical to circular polarization.

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Hong, Weijun, Yanjie Cao, Li Deng, Shufang Li, Mengmeng Li et Hongjie Liu. « A Circular Polarized Rectenna with Out-of-Band Suppression for Microwave Power Transmission ». International Journal of Antennas and Propagation 2016 (2016) : 1–7. http://dx.doi.org/10.1155/2016/8628496.

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A novel circular polarized rectenna with out-of-band suppression is proposed in this paper. The circular polarization is realized by corner perturbation on a rectangular radiation patch and enhanced by a diagonal slim slot etched at the center of the patch. An open stub connecting to the quarter wavelength impedance transformer is used to suppress out-of-band wave through harmonics notching. The results of simulations and experiments agree very well, which show that the rectenna obtained −19 dB return loss at 2.4 GHz and −15.5 dB, −18.1 dB, and −11.4 dB suppression on second, third, and fourth harmonic frequency bands, respectively. The reflection coefficient in overall out-of-band, up to 10 GHz, is limited up to −3 dB. Integrated with a voltage doubling rectification circuit, the proposed rectenna can obtain 75.5% RF-to-DC conversion efficiency.

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M.M., Ajith Kumar, Sheel Aditya et Ciersiang Chua. « Interaction Impedance for Space Harmonics of Circular Helix Using Simulations ». IEEE Transactions on Electron Devices 64, n^o 4 (avril 2017) : 1868–72. http://dx.doi.org/10.1109/ted.2017.2669332.

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Ma, Yuchen, Haijiao Yang, Junhong Wang, Ying Zhu, Chong Pan et Xiang Wu. « Circular Polarization Annular Leaky-Wave Antenna with Conical and Broadside Beams ». Electronics 12, n^o 13 (21 juin 2023) : 2761. http://dx.doi.org/10.3390/electronics12132761.

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In order to properly cover different scenarios, radiation patterns of antennas should be accordingly designed. However, most antennas are unable to provide either broadside beams or designable conical beams, which are the typically used radiation patterns for radio coverage, based on one single-structure format through adjusting parameters before fabrication. In this paper, a planar circular polarized (CP) annular leaky-wave antenna (LWA) is proposed, which is realized on an annular substrate-integrated waveguide (SIW). A broadside beam or a conical beam could be easily obtained through fabricating the LWA with different structural parameters. The operating frequency is 5.75 GHz. The LWA allows only the −1st spatial harmonic to radiate, while the fundamental wave and other spatial harmonics are suppressed in slow wave mode. In order to validate the design effectiveness, two examples for broadside beam and conical beam radiation are fabricated and measured. The measurement results show good agreement with the simulation results. The broadside beam LWA shows a gain of 9.75 dBic and the conical beam LWA with a beam angle of 13° has a gain of 7.93 dBic. The proposed LWA presents promising radiation performance and is a good candidate for wireless communication applications.

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Horng Shou Huang et Hung-Chun Chang. « Analysis of equilateral three-core fibers by circular harmonics expansion method ». Journal of Lightwave Technology 8, n^o 6 (juin 1990) : 945–52. http://dx.doi.org/10.1109/50.54514.

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Shabtai, Noam R., et Michael Vorländer. « Acoustic centering of a baffled piston in the circular harmonics domain ». Journal of the Acoustical Society of America 139, n^o 3 (mars 2016) : 1372–80. http://dx.doi.org/10.1121/1.4944691.

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Sghir, Elmahjouby, Ahmed Errkik, Jamal Zbitou, Larbi El abdellaoui, Abdelali Tajmouati et Mohamed Latrach. « A novel compact CPW Band-stop filter using O-DGS configuration ». International Journal of Electrical and Computer Engineering (IJECE) 9, n^o 6 (1 décembre 2019) : 4836. http://dx.doi.org/10.11591/ijece.v9i6.pp4836-4844.

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<p>A novel and compact multi-band stop filter using two different structures of circular DGS and circular DGS loaded with O-DGS unit, has good selectivity and wide upper pass band performance with good rejection based on defected ground structure (DGS) integrating a circular ring resonator to suppress undesired spurious bands frequency or harmonics in radio frequency and microwave circuits is proposed. An equivalent circuit model has been derived for the both structures of circular DGS and circular DGS loaded. The presented filter has a compact size because the circular ring resonator is integrated in DGS, the both of them are etching in the ground plane. The proposed filter presents an optimization method for generating multi-band characteristics without using a periodic cells or other complicate topology. The simulated results by ADS Agilent are presented and compared with the results simulated by two others software: CST and HFSS. Good agreement between the three simulated results is observed.</p>

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Kristiansen, T., et O. M. Faltinsen. « Higher harmonic wave loads on a vertical cylinder in finite water depth ». Journal of Fluid Mechanics 833 (14 novembre 2017) : 773–805. http://dx.doi.org/10.1017/jfm.2017.702.

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The theory of Faltinsen et al. (J. Fluid Mech., vol. 289, 1995, pp. 179–198; FNV) for calculation of higher-order wave loads in deep water on a vertical free-surface-piercing circular bottom-mounted non-moving cylinder, based on potential flow of an incompressible fluid, is generalized to finite water depth. Systematic regular wave experiments are carried out, and the harmonics of the horizontal wave loads are compared with the generalized FNV theory. The horizontal force and mudline overturning moment are studied. The main focus is on the third harmonic of the loads, although all harmonics from one to five are considered. The theoretically predicted third harmonic loads are shown to agree well with the experiments for small to medium wave steepnesses, up to a rather distinct limiting wave steepness. Above this limit, the theory overpredicts, and the discrepancy in general increases monotonically with increasing wave steepness. The local Keulegan–Carpenter ($KC$) number along the axis of the cylinder indicates that flow separation will occur for the wave conditions where there are discrepancies. The assumption of $KC$-dependent added mass coefficients and the addition of a drag term in the FNV model, as is done in Morison’s equation, do not explain the discrepancies. A distinct run-up at the rear of the cylinder is observed in the experiments. A 2D Navier–Stokes simulation is carried out, and the resulting pressure, due to flow separation, is shown to qualitatively explain the local rear run-up.

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Uruba, Václav, et Pavel Procházka. « POD Spectrum of the Wake behind a Circular Cylinder ». MATEC Web of Conferences 328 (2020) : 05006. http://dx.doi.org/10.1051/matecconf/202032805006.

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The wake dynamics behind a long circular cylinder in cross-flow was studied using the POD method. The temporal parts of POD modes, Chronoses, are subjected to frequency analysis. Five groups of modes are distinguished according to the frequency contents. The low order high energy modes contain the vortex shedding frequency or its harmonics up to 3rd order plus Kolmogorov spectrum. The higher order modes are characterized by combination of Kolmogorov spectrum with the white noise spectrum, its importance grows with the mode order. The very high order modes are characterised by the white noise spectrum only.

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Uruba, Václav, et Pavel Procházka. « On Vorticity Dynamics in Turbulent Wake behind Circular Cylinder ». MATEC Web of Conferences 369 (2022) : 05001. http://dx.doi.org/10.1051/matecconf/202236905001.

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The circular cylinder turbulent wake is studied experimentally using Particle Image Velocimetry (PIV) method. The vorticity component parallel to the cylinder axis is evaluated from measured velocity field. Dynamics of the vorticity field is analysed using the Oscillation Pattern Decomposition (OPD) method. The 3 dominant modes corresponding to the 1st, 2nd and 3rd harmonics of Strouhal frequency are detected and presented. The corresponding topologies are characterized by waves of vortical systems. The results are similar to the dynamics of velocity field, however the procedure is much easier to implement, as only half number of degrees of freedom are active.

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Kim, Yoon Young, et Charles R. Steele. « End Effects and Time-Harmonic Longitudinal Wave Propagation in a Semi-Infinite Solid Cylinder ». Journal of Applied Mechanics 56, n^o 2 (1 juin 1989) : 334–46. http://dx.doi.org/10.1115/1.3176088.

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Axisymmetric end problems of longitudinal wave propagation are studied in a semi-infinite isotropic solid circular cylinder which is free of traction on its cylindrical surface. An accurate and computationally efficient method of solution is presented which can exploit the asymptotic behavior for high harmonics in the radial direction. The stresses and displacements are expanded in terms of the eigenfunctions of the case of a lubricated-rigid cylindrical surface condition. The expansions are used to construct a stiffness matrix relating the harmonics of stress and displacement for the traction-free case, which is shown to approach asymptotically that of the case of the mixed condition. Unlike other approaches such as finite element or boundary integral methods, which typically require the solution of large systems of equations for rapidly varying end conditions, the present formulation can lead to a coupled system of equations for lower spatial harmonics and a weakly coupled system for higher spatial harmonics. Due to the small number of equations in the coupled system, the present approach is very effective in handling general boundary conditions, and is particularly efficient for end conditions with rapid spatial variation.

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Dina, Lorenzo, Fabio Mangini et Fabrizio Frezza. « Electromagnetic Scattering of Inhomogeneous Plane Wave by Ensemble of Cylinders ». Journal of Telecommunications and Information Technology 3 (30 septembre 2020) : 1–7. http://dx.doi.org/10.26636/jtit.2020.138519.

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The interaction between an ensemble of cylinders and an inhomogeneous plane wave is introduced and is determined, in the present paper, through a rigorous theoretical approach. Scattered electromagnetic ﬁeld generated by an indeﬁnite number of inﬁnite circular cylinders is analyzed by the application of the generalized vector cylinder harmonics (VCH) expansion. The exact mathematical model relied upon to represent this scenario considers the so-called complex-angle formalism reaching a superposition of vectorial cylindrical-harmonics and Foldy-Lax Multiple scattering equations (FLMSE) to account for the multiscattering process between the cylinders. The method was validated by comparing the numerical results obtained with the use of the ﬁnite element method and a homemade Matlab code

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Pang, Zeyue, Zhe Wang, Fengbei Shen et Weiyi Hong. « Phase-matching control of high-order harmonics with circular Airy-Gaussian beams ». Optics Express 29, n^o 18 (26 août 2021) : 29308. http://dx.doi.org/10.1364/oe.436029.

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Chih-Sheng Chang et Hung-Chun Chang. « Theory of the circular harmonics expansion method for multiple-optical-fiber system ». Journal of Lightwave Technology 12, n^o 3 (mars 1994) : 415–17. http://dx.doi.org/10.1109/50.285344.

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Fan, Jun, Jiangchuan Lin, Feng Qin, Jinliang Cai et Mingxu Kan. « Ultrawideband Harmonic Suppression in Microstrip Patch Antenna Using Novel Defected Ground Structures ». International Journal of Antennas and Propagation 2020 (14 octobre 2020) : 1–8. http://dx.doi.org/10.1155/2020/9602841.

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Suppressing higher-order modes up to sixth harmonics of the fundamental working frequency in a single-layer microstrip line-fed patch antenna has been successfully demonstrated. Higher-order modes of the antenna are suppressed by simultaneously employing a circular head open stub connected to the feed line and a novel defected ground structure (DGS) beneath the feed line. The filtering property of the antenna has been improved by the novel DGS significantly. The role played by the novel DGS is carefully analyzed, and the effect of some key parameters of DGS is further discussed. A microstrip patch antenna with the working frequency 3.13 GHz (fc) is designed and manufactured. The designed antenna possesses an ultrawideband harmonic suppression capability ranging from 2fc to 6fc. More importantly, the area occupied by the novel DGS is decreased by 41% compared to the earlier design.

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Penoyre, Zephyr, et Emily Sandford. « Higher order harmonics in the light curves of eccentric planetary systems ». Monthly Notices of the Royal Astronomical Society 488, n^o 3 (25 juillet 2019) : 4181–94. http://dx.doi.org/10.1093/mnras/stz1941.

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ABSTRACTAs a planet orbits, it causes periodic modulations in the light curve of its host star. Due to the combined effects of the planet raising tides on the host star, relativistic beaming of the starlight, and reflection of light off the planet’s surface, these modulations occur at the planet’s orbital frequency, as well as integer multiples of this frequency. In particular, planets on eccentric orbits induce third and higher order harmonics in the stellar light curve which cannot be explained by circular-orbit models. Even at moderate eccentricities, such as those typical of Solar system planets, these harmonics are detectable in current and future photometric data. We present an analysis of the harmonics caused by tides, beaming, and reflection in eccentric planetary systems. We explore the dependence of these signals on the parameters of the system, and we discuss prospects for current and future observations of these signals, particularly by the NASA TESS mission. Finally, we present publicly available code for computation of light curves with tidal, beaming, and reflection signals, oot.

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Lokesh Reddy, B., et Anith Nelleri. « Single-Pixel Compressive Digital Holographic Encryption System Based on Circular Harmonic Key and Parallel Phase Shifting Digital Holography ». International Journal of Optics 2022 (14 juillet 2022) : 1–20. http://dx.doi.org/10.1155/2022/6298010.

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An encryption system that combines compressive sensing (CS) and two-step parallel phase shifting digital holography (PPSDH) using double random phase encoding (DRPE) is presented in this paper. The two-step PPSDH is a linear inline holographic scheme and is much suitable for encrypting the 2D/3D information in a single exposure. The distribution of random phase mask (RPM) in the DRPE is implemented using circular harmonic key which increases the security of the encryption process. In this system, the keys used to encrypt are spatial positions of the planes, wavelength, and rotation of the circular harmonics in RPMs, and CS acts as an additional key that makes the system more secure than the conventional optical encryption methods. At the transmission end, two-step PPSDH is applied to encrypt the object information in single hologram. The digital mirror device (DMD) is placed between the object and a single-pixel detector for acquiring fewer hologram measurements. At the receiver end, the single digital hologram is numerically recovered by using a CS optimization problem. The original complex object field is decrypted from the CS recovered holograms by the inversion of two-step PPSDH process with the help of the correct keys. The numerical simulations are presented for complex 2D and 3D objects to test the feasibility of the proposed encryption and decryption system. The proposed method carried out intensity and phase reconstruction of the original object field using single-pixel compressive imaging. The computer simulation results demonstrated that the encrypted information is highly secured with the rotation of the circular harmonic key. The sensitivity of the decrypted intensity and phase images is also studied with variations of the encrypted keys. The obtained results show that the proposed encryption scheme is feasible and has better security performance and robustness.

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Hamdan, Sinin, Ahmad Faudzi Musib, Khairul Anwar Mohamad Said, Saiful Hairi Othman et Marini Sawawi. « Investigation of Acoustic and Vibrational Properties Using Laser Doppler Vibrometry (LDV) and Electronic Speckle Pattern Interferometry (ESPI) of the Kulintangan Instruments ». Pertanika Journal of Science and Technology 31, n^o 2 (20 mars 2023) : 1105–20. http://dx.doi.org/10.47836/pjst.31.2.24.

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This study visualises the mode of the vibration of kulintangan using Electronic Speckle Pattern Interferometry (ESPI) to reveal the modes. It was found that the production of sound by the kulintangan was dominated by a particular mode which may be the (0,1), (1,1), (2,2), (3,2), and (4,2) of free edge circular gong. The spectrum distribution from the strike on the kulintangan showed it. The small gong A-H has an approximately harmonic spectrum with a fundamental frequency of 1240, 1055, 934, 792, 705, 624, 474, and 422 Hz. The gong does not display a similar occurrence of harmonics due to the ruggedness of the surface texture of the gong. This finding can be of great importance to facilitate a better understanding of the mechanisms involved in the sound production of musical instruments. Our research is visualising the sound sonically through PicoScope oscilloscopes and ESPI.

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Maslova, A. I., A. V. Pirozhenko et V. V. Vasylіev. « Minimum altitude variation orbits. Analysis of characteristics and stability ». Technical mechanics 2021, n^o 4 (7 décembre 2021) : 44–55. http://dx.doi.org/10.15407/itm2021.04.044.

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The article discusses the regularities of satellite motion in almost circular orbits under the influence of the second zonal harmonic of the geopotential. The aim of the research is to determine the parameters of orbits with a minimum change in radius and to study the properties of these orbits. It is shown that the problem of determining the parameters of orbits with a minimum change in radius is of theoretical and practical interest. These orbits are the closest to Keplerian circular orbits. The practical interest in such orbits is determined by the possibility of using them for scientific research and Earth observation systems. Based on the analysis of the literature, it was concluded that the solution of the problem under consideration is not complete by now: the algorithm for determining the parameters of the orbits are not well founded and unnecessarily complicated; there is no analytical analysis of the stability of the orbits of the minimum change in radius. The efficiency of application of the previously developed theory of describing the motion of satellites in almost circular orbits for determining the parameters of orbits with a minimum change in radius is shown. For this purpose, the solutions of the first approximation of the motion of satellites in almost circular orbits under the influence of the second zonal harmonic of the geopotential have been improved. These solutions make it easy to determine the parameters of the orbits of the minimum change in radius. The averaged equations of the second approximation of the influence of the second zonal harmonic on the satellite motion are constructed and, on their basis, the stability of the orbits with a minimum change in radius is proved. It is shown that the second approximation in small parameters completely describes the main regularities of the long-period satellite motion under the influence of the second zonal harmonic of the geopotential. With the help of numerical studies, the instability of orbits with a minimum change in radius is shown with allowance for the effect of higher order harmonics of the geopotential. Analysis of the area of possible application of orbits with a minimum change in radius showed that such orbits can be of practical importance for very low and ultra low orbits, where the control action on the satellite movement is carried out at least once every two days.

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Garcia-Martinez, Pascuala, Henri H. Arsenault et Carlos Ferreira. « Improved rotation invariant pattern recognition using circular harmonics of binary gray level slices ». Optics Communications 185, n^o 1-3 (novembre 2000) : 41–48. http://dx.doi.org/10.1016/s0030-4018(00)00979-2.

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Douglas, D. J., T. A. Glebova, N. V. Konenkov et M. Yu Sudakov. « Spatial harmonics of the field in a quadrupole mass filter with circular electrodes ». Technical Physics 44, n^o 10 (octobre 1999) : 1215–19. http://dx.doi.org/10.1134/1.1259497.

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Bauer, Svetlana M., et Eva B. Voronkova. « On non-axisymmetric buckling modes of inhomogeneous circular plates ». Vestnik of Saint Petersburg University. Mathematics. Mechanics. Astronomy 8, n^o 2 (2021) : 204–11. http://dx.doi.org/10.21638/spbu01.2021.201.

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Unsymmetrical buckling of nonuniform circular plates with elastically restrained edge and subjected to normal pressure is studied in this paper. The asymmetric part of the solution is sought in terms of multiples of the harmonics of the angular coordinate. A numerical method is employed to obtain the lowest load value at which waves in the circumferential direction can appear. The effect of material heterogeneity and boundary on the buckling load is examined. For a plate with elastically restrained edge, the buckling pressure and mode number increase with a rise of spring stiffness. Increasing of the elasticity modulus to the plate edge leads to increasing of the buckling pressure, but the mode number does not change. If the translational flexibility coefficient is small, decreasing of the elasticity modulus to the shell (plate) edge leads to sufficient lowering of the buckling pressure.

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Jia, Maoshen, Wenbei Wang et Ziyu Yang. « 2.5D Sound Field Reproduction Using Higher Order Loudspeakers ». Cybernetics and Information Technologies 15, n^o 6 (1 décembre 2015) : 5–15. http://dx.doi.org/10.1515/cait-2015-0063.

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Abstract Using 3-Dimensional (3D) sound sources as secondary sources to 2-Dimensional (2D) sound field reproduction, it is termed 2.5-Dimensional (2.5D) sound field reproduction which is currently drawing broad interest in acoustic signal processing. In this paper we propose a method to reproduce a 2D sound field, using a circular array of 3D High Order (HO) loudspeakers, which provides a mode matching solution based on 3D wave field translation. Using the spherical addition theorem, we first obtain a spherical harmonics representation of a 2D sound field reproduced by an array of HO loudspeakers. Then, the corresponding relationship between the reproduced sound field and the desired sound field is established by spherical/cylindrical harmonic expansions. Finally, the modal weights of HO loudspeakers are designed by using a least squares method. Simulation results show that the proposed method extends the reproduction region and significantly reduces the required minimum number of loudspeakers over the other referenced methods.

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Kumar, Deepak, et Kalpana Chaudhary. « Design of a Circular Polarized Printed Rectenna for Satellite Solar Power Station Array Construction ». International Journal of Engineering & ; Technology 7, n^o 4.5 (22 septembre 2018) : 254. http://dx.doi.org/10.14419/ijet.v7i4.5.20081.

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A circularly polarized single feed microstrip patch antenna with voltage doubler rectification is designed at 2.45 GHz for satellite solar wireless power transfer application. A bandpass filter is also designed and combined with an antenna that will efficiently eliminate signal harmonics up to third order. An HSMS-8202 microwave zero-bias Schottky barrier diodes accessible in SOT 23 package as the series pair is utilized in the proposed rectenna design. The rectenna has a high conversion efficiency of 70%. The printed rectenna can be interconnected to construct the rectenna arrays.

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Liu, Runzhi, Yanlin Shao, Jikang Chen et Hui Liang. « Nonlinear liquid sloshing in an upright circular container : Modal responses and higher-order harmonics ». Physics of Fluids 34, n^o 1 (janvier 2022) : 012116. http://dx.doi.org/10.1063/5.0077206.

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Silin, V. P., et P. V. Silin. « Phenomenon of bifurcation of the circular polarization of the bremsstrahlung-generated pump field harmonics ». Plasma Physics Reports 32, n^o 8 (août 2006) : 695–702. http://dx.doi.org/10.1134/s1063780x0608006x.

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Zeng, Gengsheng L., et Grant T. Gullberg. « Cone-beam and fan-beam image reconstruction algorithms based on spherical and circular harmonics ». Physics in Medicine and Biology 49, n^o 11 (20 mai 2004) : 2239–56. http://dx.doi.org/10.1088/0031-9155/49/11/009.

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Chang, Chi-Ching, Hon-Fai Yau, Yuh-Ping Tong et Nen-Wen Puh. « Rotational invariant pattern recognition with the method of circular harmonics using a BaTiO3 crystal ». Optics Communications 87, n^o 5-6 (février 1992) : 219–22. http://dx.doi.org/10.1016/0030-4018(92)90462-z.

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Slyozkin, Vitaly, et Mikhail Nevedrov. « Parameter optimization for the three-frequency feed for the mirror antenna of the non-linear radar ». ITM Web of Conferences 30 (2019) : 05018. http://dx.doi.org/10.1051/itmconf/20193005018.

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Analyzed below is a radiating structure represented by a flat self-complementary three-sector structure fed by three segments of the microstrip line and located above the stepped metal screen, and to be used as an exciter for the non-linear radar antenna. When proper matching with the feeding coaxial cable is achieved, results of the numerical simulation proved that the antenna can provide near-circular polarization of radiation at the probing signal frequency, and linear polarization at the second and third harmonics of this signal.

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Senf, F., K. J. S. Sawhney, R. Follath, M. Scheer, F. Schäfers, J. Bahrdt, A. Gaupp et W. Gudat. « A plane-grating monochromator for circularly polarized undulator radiation at BESSY II ». Journal of Synchrotron Radiation 5, n^o 3 (1 mai 1998) : 747–49. http://dx.doi.org/10.1107/s0909049597019869.

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At BESSY II, a third-generation 1.7 GeV storage ring is under construction. A planar elliptical undulator will be installed as a source of X-rays that have a high degree of circular polarization. Radiation in the first, third and fifth harmonics will cover the energy range 87–1330 eV. The beamline will essentially consist of a plane-grating monochromator working with collimated light in the dispersion plane. A single set of optical elements can be used to handle the two angularly separated beams of opposite helicity from the double undulator. The degree of circular polarization ranges from 73 to 100%, and a flux of up to 5 × 1013 photons s−1 (100 mA)−1 can be achieved. A maximum spectral resolution of about 13 000 will be possible at 100 eV using a 20 µm slit.

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KUNKA, M. D., et M. R. FOSTER. « Oscillatory flow past a circular cylinder in a rotating frame ». Journal of Fluid Mechanics 345 (25 août 1997) : 101–31. http://dx.doi.org/10.1017/s0022112097006204.

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Because of the importance of oscillatory components in the oncoming flow at certain oceanic topographic features, we investigate the oscillatory flow past a circular cylinder in an homogeneous rotating fluid. When the oncoming flow is non-reversing, and for relatively low-frequency oscillations, the modifications to the equivalent steady flow arise principally in the ‘quarter layer’ on the surface of the cylinder. An incipient-separation criterion is found as a limitation on the magnitude of the Rossby number, as in the steady-flow case. We present exact solutions for a number of asymptotic cases, at both large frequency and small nonlinearity. We also report numerical solutions of the nonlinear quarter-layer equation for a range of parameters, obtained by a temporal integration. Near the rear stagnation point of the cylinder, we find a generalized velocity ‘plateau’ similar to that of the steady-flow problem, in which all harmonics of the free-stream oscillation may be present. Further, we determine that, for certain initial conditions, the boundary-layer flow develops a finite-time singularity in the neighbourhood of the rear stagnation point.

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Riley, Thomas L. « Measurement of harmonics generated by finite amplitude sound radiated by a circular piston in water ». Journal of the Acoustical Society of America 77, S1 (avril 1985) : S46. http://dx.doi.org/10.1121/1.2022351.

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