Journal articles on the topic 'Method of imaginary sources'
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1
Sun, Chao, and Yuechan Liu. "Spherical Reverse Beamforming for Sound Source Localization Based on the Inverse Method." Sensors 19, no. 11 (June 9, 2019): 2618. http://dx.doi.org/10.3390/s19112618.
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A spherical array is not limited to providing an acoustic map in all directions by the azimuth of the array. In this paper, spherical reverse beamforming for sound source localization based on spherical harmonic beamforming and the principle of sound field reconstruction is proposed in order to output a sharper scanning beam. It is assumed that there is an imaginary sound source at each scan point, and the acoustic map of a spherical array to the actual sound source is regarded as the combination of all of the imaginary sound sources. Sound source localization can be realized by calculating the contribution of each imaginary sound source to the sound field. Also in this work, the non-convex constrained optimization problem is established using p-norm. Combined with the norm method, the sparse solution of the imaginary sources is obtained through iterative weighted techniques, and the resolution of sound source localization is improved significantly. The performance of this method is investigated in comparison to conventional spherical beamforming. The numerical results show that the proposed method can achieve higher resolution for the localization of sound sources without being limited by the frequency and array aperture, and has a stronger ability to suppress fluctuations in background noise.
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Shahbazi Avarvand, Forooz, Arne Ewald, and Guido Nolte. "Localizing True Brain Interactions from EEG and MEG Data with Subspace Methods and Modified Beamformers." Computational and Mathematical Methods in Medicine 2012 (2012): 1–11. http://dx.doi.org/10.1155/2012/402341.
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To address the problem of mixing in EEG or MEG connectivity analysis we exploit that noninteracting brain sources do not contribute systematically to the imaginary part of the cross-spectrum. Firstly, we propose to apply the existing subspace method “RAP-MUSIC” to the subspace found from the dominant singular vectors of the imaginary part of the cross-spectrum rather than to the conventionally used covariance matrix. Secondly, to estimate the specific sources interacting with each other, we use a modified LCMV-beamformer approach in which the source direction for each voxel was determined by maximizing the imaginary coherence with respect to a given reference. These two methods are applicable in this form only if the number of interacting sources is even, because odd-dimensional subspaces collapse to even-dimensional ones. Simulations show that (a) RAP-MUSIC based on the imaginary part of the cross-spectrum accurately finds the correct source locations, that (b) conventional RAP-MUSIC fails to do so since it is highly influenced by noninteracting sources, and that (c) the second method correctly identifies those sources which are interacting with the reference. The methods are also applied to real data for a motor paradigm, resulting in the localization of four interacting sources presumably in sensory-motor areas.
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Petrov, Yu V., S. I. Bakaras, and S. A. Yukhno. "DETERMINATION OF RADIO SOURCES LOCATION BY THE METHOD OF "IMAGINARY BASE" WHEN USING THE LINEAR MODEL." Issues of radio electronics, no. 7 (July 20, 2018): 124–30. http://dx.doi.org/10.21778/2218-5453-2018-7-124-130.
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This article presents the expressions which allow evaluating the potential accuracy of radio source location by the method of «imaginary base» when using the linear model of changing the bearing on it. The concept of the method of «imaginary base» is to be used in solving the triangulation problem not only of measuring bearing, but also their extrapolated values at a certain time interval. Potential characteristics is determined by accuracy, dynamic and geometrical factors, bearing measurement and extrapolation times. The article shows that when using a linear model, there are limitations both on the time of measuring bearing and on the time of extrapolation. It will be because of the increase in the variance of the error of estimating the distance. Limiting of series decomposition members number of non-linear bearing change dependence from time there are. It depends on the speed of changing bearing (depends on the range and speed) and the initial bearing (depends on the track angle). Extrapolation over long time intervals is possible only at long distances and at relatively low speeds.
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Pereira da Silva, Valéria Cristina. "Venise des deux côtés du miroir : Imaginaire et identité entre l’amour et la mort." Caietele Echinox 40 (June 28, 2021): 269–83. http://dx.doi.org/10.24193/cechinox.2021.40.21.
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"Venice, deeply imaginary and symbolic, is in various cultural documents, like books, paintings, cinema, music, photography and other arts. In this research, we use the literary and the poetic narrative as privileged sources for understanding the imaginary and the identity of this city, closely connected with love and with death too. This investigation uses as a method Gaston Bachelard’s phenomenology defined in The Poetics of Space and the symbolical imaginary described in relation to the material imagination in Water and Dreams. Venice is a city on water and its identity is closely associated with love, as one mirror side, and with death or even hell, as the other mirror side."
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Kleschev, A. "Sound diffraction on an elastic spheroidal shell." Transactions of the Krylov State Research Centre 3, no. 397 (August 6, 2021): 97–114. http://dx.doi.org/10.24937/2542-2324-2021-3-397-97-114.
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Object and purpose of research. This paper obtains solutions and performs estimations of characteristics of sound reflection and scattering by ideal and elastic bodies of various shapes (analytical and non-analytical) near media interface, or underwater sonic channel, or in a planar waveguide with a solid elastic bottom. Materials and methods. The harmonic signals are investigated with the method of normal waves based on the phase velocity of signal propagation, and impulse signals related to the energy transfer are studied using the method of real and imaginary sources and scatterers based on the group velocity of propagation. Main results. The scattered sound field is calculated for ideal spheroids (elongated and compressed) at fluid – ideal medium interface. The spectrum of a scattered impulse signal is calculated for a body placed in a sonic channel. First reflected impulses are found for an ideal spheroid in a planar waveguide with anisotropic bottom. Conclusion. In the studies of diffraction characteristics of bodies at media interfaces it was found that the main contribution to scattered field is given by interference of scattered fields rather than interaction of scatterers (real or imaginary). It is shown that at long distances the spectral characteristics of the channel itself have a prevalent role. When impulse sound signals in the planar waveguide are used, it is necessary to apply the method of real and imaginary sources and scatterers based on the group velocity of sound propagation.
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Kleshchev, Alexander. "Diffraction of Pulsed Sound Signals by Elastic Bodies of Analytical and Non-analytical Forms, Put in Plane Waveguide." Zeitschrift für Naturforschung A 70, no. 6 (June 1, 2015): 419–27. http://dx.doi.org/10.1515/zna-2015-0062.
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AbstractWith the help of the Fourier transform and imaginary sources and scatterers method the problem of the pulse sound signal scattering by the elastic spheroidal bodies put in the plane waveguide is solved. Based on the integral method equations the problem of the pulse sound signal diffraction at elastic body of the nonanalytical form in the plane waveguide is solved.
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Weaver, R. L., W. Sachse, and Kwang Yul Kim. "Transient Elastic Waves in a Transversely Isotropic Plate." Journal of Applied Mechanics 63, no. 2 (June 1, 1996): 337–46. http://dx.doi.org/10.1115/1.2788870.
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The elastodynamic response of a thick plate, with the axis of transverse isotropy normal to the plate surface, is calculated by double numerical inverse transforms, a method particularly well-suited for calculations of responses in the near field of layered structures. Applications of these calculations include point-source/point-receiver ultrasonics, quantitative acoustic emission measurements, and seismology. The singularities of the integrand are eliminated by the introduction of a small, but nonzero, imaginary part to the frequency. We discuss issues of numerical efficiency and accuracy in the evaluation of the resulting integrals. The method can be generalized to calculate the responses in materials of more general symmetry, in viscoelastic materials and to include the effects of finite aperture sources and receivers. The calculated responses are compared to those measured in a single crystal specimen of zinc.
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Rejer, Izabela. "EEG Feature Selection for BCI Based on Motor Imaginary Task." Foundations of Computing and Decision Sciences 37, no. 4 (December 1, 2012): 283–92. http://dx.doi.org/10.2478/v10209-011-0016-7.
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AbstractThe greatest problem met when a Brain Computer Interface (BCI) based on electroencephalographic (EEG) signals is to be created is a huge dimensionality of EEG feature space and at the same time very limited number of possible observations. The first is a result of a huge amount of data which can be recorded during the single trial, the latter - the result of individuality of EEG signals, which can significantly differ in different frequency bands determined for different subjects. These two reasons force the brain researches to reduce the huge EEG feature space to only some features, those which allow to build a BCI of a satisfactory accuracy. The paper presents the comparison of two methods of feature selection - blind source separation (BSS) method and method using interpretable features. The comparison was carried out with the data set recorded during EEG session with a subject whose task was to imagine movements of right and left hand.
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Song, Zhong‐Min, and Paul R. Williamson. "Frequency‐domain acoustic‐wave modeling and inversion of crosshole data: Part I—2.5-D modeling method." GEOPHYSICS 60, no. 3 (May 1995): 784–95. http://dx.doi.org/10.1190/1.1443817.
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Crosshole experiments usually have sources and receivers confined to a plane, and it is assumed that there is negligible variation in the properties of the medium normal to this plane. Therefore, the problem appears two‐dimensional, except for the sources which are 3-D points rather than lines. This configuration is denoted as two‐and‐one‐half‐dimensional. We present a frequency‐domain approach to modeling acoustic wave propagation in such situations which allows correct treatment of point sources but takes advantage of the assumed 2-D nature of the medium to avoid full 3-D simulations. The approach uses a Fourier transform with respect to the out‐of‐plane coordinate to reduce the problem of modeling in 3-D to repeatedly solving a 2-D equation, which we accomplish using finite differences. The discrete inverse Fourier transform from the out‐of‐plane wavenumber implies the existence of an infinite number of spurious “ghost sources” spaced periodically in the out‐of‐plane direction. These sources generate significant artifacts on the time‐domain traces, even when their spatial period is much greater than the (in‐plane) dimensions of the survey area, because of time‐wrapping in the transform from the frequency domain. We describe two methods for reducing these artefacts, the more effective of which entails exponential damping by adding a positive imaginary part to the frequency, compensated by ramping of the wrapped time domain records. We check the modeling scheme by analysis of direct and scattered arrivals from simple models. The observed seismograms agree well with those calculated using Born theory, and so confirm the potential of this modeling method for use in inversion.
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Chen, Hanbo, Bin Xiong, Yang Yang, Yu Han, and Ziyu Cheng. "3D marine controlled-source electromagnetic modeling using an edge-based finite element method with a block Krylov iterative solver." Open Geosciences 14, no. 1 (January 1, 2022): 341–53. http://dx.doi.org/10.1515/geo-2022-0366.
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Abstract An edge-based finite element method for the numerical modeling of electromagnetic fields in complex media is presented. We used the analytical solution on an electric field in a homogeneous half space to develop a source correct factor to reduce the influence of source singularity and boundary conditions on the numerical accuracy, so that we can minimize the time required to construct the field source term in the scattered field formula. The modeling domain was discretized using an unstructured tetrahedral mesh. We transformed the complex equations of the electrical field into two real-valued equations by decomposing the field into real and imaginary components. Thereafter, we adopted a block conjugate orthogonal conjugate gradient (BL_COCR) iterative solver with an incomplete LU decomposition preconditioner, which was robust for ill-conditioned systems and efficient for multiple source electromagnetic modeling to solve the real-valued equation systems. Using the analytical solution on an electric field in a homogeneous layer model, we evaluated the accuracy of our numerical forward solution and the results showed that the source correct factor can reduce forward modeling errors associated with boundary effects and source singularities. We also applied the developed algorithm to compute the CSEM responses for typical 3D marine geo-electric models with different number of sources and compared with different iterative solvers, and the results showed that the BL_COCR solver has high computational efficiency when solving multiple right-hand term problems.
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Medeiros, Walter E., and João B. C. Silva. "Gravity source moment inversion: A versatile approach to characterize position and 3-D orientation of anomalous bodies." GEOPHYSICS 60, no. 5 (September 1995): 1342–53. http://dx.doi.org/10.1190/1.1443870.
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We present a 3-D gravity interpretation method based on the inversion of source moments employing the series derived from the gravity anomaly expansion in multipoles and retaining moments up to second order only. It presents the advantages of being essentially linear and allowing a straightforward computer implementation. The method requires neither an explicit assumption about the source geometry nor a priori knowledge about the density contrast distribution, which may even be nonuniform. The method assumes implicitly: (1) that the source fits in the interior of an imaginary sphere whose center coincides with the source center of mass and whose radius is smaller than the depth to the source center of mass relative to the measuring plane, and (2) that the spatial density distribution presents three ortogonal planes of symmetry intersecting at the source center of mass. The first assumption can be met by upward continuing the observed anomaly. When both assumptions are met, the method produces reliable and stable estimates of the total anomalous mass, the coordinates of the center of mass, the three principal axes directions of the anomalous body, and the relative importance among the axes. The method is particularly suited for interpreting compact, isolated or disjoint, but spatially correlated sources. The method is sensitive to an incomplete removal of the regional field (presumably superimposed on the residual anomaly of interest) because the unremoved part of the regional field may strongly affect the estimates of the residual source moments.
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Yin, Changchun, Bo Zhang, Yunhe Liu, and Jing Cai. "A goal-oriented adaptive finite-element method for 3D scattered airborne electromagnetic method modeling." GEOPHYSICS 81, no. 5 (September 2016): E337—E346. http://dx.doi.org/10.1190/geo2015-0580.1.
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We have developed a goal-oriented adaptive unstructured finite-element method based on the scattered field for 3D frequency-domain airborne electromagnetic (AEM) modeling. To guarantee the EM field divergence free within each element and the continuity conditions at electrical material interfaces, we have used the edge-based shape functions to approximate the electrical field. The posterior error for finite-element adaptive meshing procedure is estimated from the continuity of the normal component of the current density, whereas the influence functions are estimated by solving a dual forward problem. Because the imaginary part of the scattered current is discontinuous and the real part is continuous, we use the latter to estimate the posterior error. For the multisources and multifrequencies problem in AEM, we calculate the weighted posterior error for each element by considering only those transmitter-receiver pairs that do not adhere to our convergence criteria. Finally, we add a minimum volume constraint to improve the stability of the adaptive procedure. To check the accuracy, we compared our adaptive results with the semianalytical solutions for AEM systems over a half-space model. To test the effectiveness of our algorithm for multiple sources and multiple frequencies of AEM, we analyzed meshes for separate frequencies and for combined frequencies. Finally, we calculated the AEM responses over a hill model with and without embedded abnormal bodies to prove the feasibility of our algorithm for AEM variable topography modeling.
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Demazière, C., A. Tatidis, and P. Vinai. "MONTE CARLO-BASED DYNAMIC CALCULATIONS OF STATIONARY PERTURBATIONS." EPJ Web of Conferences 247 (2021): 21003. http://dx.doi.org/10.1051/epjconf/202124721003.
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Capitalizing on some earlier work, this paper presents a novel Monte Carlo-based approach that allows estimating the neutron noise induced by stationary perturbations of macroscopic cross-sections in the frequency domain. This method relies on the prior computation using Monte Carlo of modified Green’s functions associated to the real part of the dynamic macroscopic cross-sections, mimicking equivalent subcritical problems driven by external neutron sources. Once such modified Green’s functions are estimated, the neutron noise induced by any type of perturbations can be recovered, by solving a linear algebra problem accounting for the interdependence between the real and imaginary parts of the governing balance equations. The newly derived method was demonstrated on a large homogeneous test system and on a small heterogeneous test system to provide results comparable to a diffusion-based solver specifically developed for neutron noise applications. The new method requires the specification by the user of the real part of the Fourier transform of the macroscopic cross-sections. This is accomplished using ACE-formatted cross-section files defined by the user. Beyond this input data preparation, no change to the Monte Carlo source code is necessary. This represents the main advantage of the proposed method as compared to similar efforts requiring extensive modifications to the Monte Carlo source code.
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Gao, Feng, and Wei Sun. "Free vibration analysis of the hard-coating splitter blisk using the energy-based finite element method." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 233, no. 13 (February 21, 2019): 4577–89. http://dx.doi.org/10.1177/0954406219832228.
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This paper presents the free vibration analysis of the hard-coating splitter blisk (known as the splitter blisk deposited hard coating) and the damping-improved performance of the hard coating for vibration suppression of the splitter blisk. Based on the proposed energy-based finite element method by the energy considerations, complex modulus theory and composite Mindlin plate theory, the equations of motion of hard-coating splitter blisk are formulated. And, the complex solutions for free vibration problem are then solved, whose real and imaginary parts are closely related to natural frequencies and loss factors. Considering the academic splitter blisk deposited NiCoCrAlY+YSZ hard coating as the benchmark, the comparisons for vibration characteristics of hard-coating splitter blisk originating from different sources are performed for model validation, and the influence of hard coating on the dynamics of splitter blisk are also investigated. The numerical results reveal that the vibration amplitudes of splitter blisk are suppressed remarkably by the hard coating without altering natural frequencies significantly.
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Xie, Jian, Qiuping Wang, Yuexian Wang, and Xin Yang. "Efficient Two-Dimensional Direction Finding Algorithm for Rectilinear Sources Under Unknown Mutual Coupling." Sensors 20, no. 7 (March 30, 2020): 1914. http://dx.doi.org/10.3390/s20071914.
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Digital communication signals in wireless systems may possess noncircularity, which can be used to enhance the degrees of freedom for direction-of-arrival (DOA) estimation in sensor array signal processing. On the other hand, the electromagnetic characteristics between sensors in uniform rectangular arrays (URAs), such as mutual coupling, may significantly deteriorate the estimation performance. To deal with this problem, a robust real-valued estimator for rectilinear sources was developed to alleviate unknown mutual coupling in URAs. An augmented covariance matrix was built up by extracting the real and imaginary parts of observations containing the circularity and noncircularity of signals. Then, the actual steering vector considering mutual coupling was reparameterized to make the rank reduction (RARE) property available. To reduce the computational complexity of two-dimensional (2D) spectral search, we individually estimated y-axis and x-axis direction-cosines in two stages following the principle of RARE. Finally, azimuth and elevation angle estimates were determined from the corresponding direction-cosines respectively. Compared with existing solutions, the proposed method is more computationally efficient, involving real-valued operations and decoupled 2D spectral searches into twice those of one-dimensional searches. Simulation results verified that the proposed method provides satisfactory estimation performance that is robust to unknown mutual coupling and close to the counterparts based on 2D spectral searches, but at the cost of much fewer calculations.
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CHEN, I. L., Y. T. LEE, P. S. KUO, and J. T. CHEN. "ON THE TRUE AND SPURIOUS EIGENVALUES BY USING THE REAL OR THE IMAGINARY-PART OF THE METHOD OF FUNDAMENTAL SOLUTIONS." International Journal of Computational Methods 10, no. 02 (March 2013): 1341003. http://dx.doi.org/10.1142/s021987621341003x.
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In this paper, the method of fundamental solutions (MFS) of real-part or imaginary-part kernels is employed to solve two-dimensional eigenproblems. The occurring mechanism of spurious eigenvalues for circular and elliptical membranes is examined. It is found that the spurious eigensolution using the MFS depends on the location of the fictitious boundary where the sources are distributed. By employing the singular value decomposition technique, the common left unitary vectors of the true eigenvalue for the single- and double-layer potential approaches are found while the common right unitary vectors of the spurious eigenvalue are obtained. Dirichlet and Neumann eigenproblems are both considered. True eigenvalues are dependent on the boundary condition while spurious eigenvalues are different in the different approach, single-layer or double-layer potential MFS. Two examples of circular and elliptical membranes are numerically demonstrated to see the validity of the present method and the results are compared well with the theoretical prediction.
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Wang, Yu Qing. "Local Variance Based Color Image Quality Assessment Method." Advanced Materials Research 301-303 (July 2011): 1254–59. http://dx.doi.org/10.4028/www.scientific.net/amr.301-303.1254.
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In this paper, local variance is used to describe the structural information of a color image in order to assess its quality. The representation method is different from conventional models in that some information that is sensitive to human eyes is enhanced by using local variance distribution. It encodes the local variance distribution of different channels of a color image into the three imaginary parts of a quaternion. The distance between the singular value feature vectors of the source image block and the distorted image block which are described by quaternion matrices is calculated. The experimental results show that the assessment results of the proposed assessment method are more consistent with the Human Visual System than those of the conventional assessment methods.
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Zhang, Yong-Bin, Qi Yao, Lei Xiao, Xiao-Zheng Zhang, Chang-Jun Zheng, and Chuan-Xing Bi. "On the Resonance of a Lined Tire Cavity." Acta Acustica united with Acustica 105, no. 6 (November 1, 2019): 1237–42. http://dx.doi.org/10.3813/aaa.919400.
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Cavity resonance is one of the important sources of tire noise. The measures commonly used for suppressing the cavity resonance is to paste sound absorbing material on the inner surface of the tire, which has been proved to be very effective by many experimental studies. But so far there is a lack of methods to assess the influence of absorbing material on the cavity resonance and help determine the optimal sound absorbing material for a tire. To resolve this problem, a method based on the eigenvalue analysis is proposed. In the method, the resonance of a tire cavity lined with sound absorbing material is turned into a complex eigenvalue problem of a closed cavity with prescribed boundary conditions. The real and imaginary parts of the complex eigenvalue can then be used to represent the influence of sound absorbing material on the cavity resonance. Experiments were conducted on a tire lined with polyurethane foams of different thickness and flow resistivity to validate the results obtained by the proposed method, and a good agreement between their results is achieved.
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Petrenko, E. M., and V. A. Semenova. "Residual Capacitance Estimation in Lithium-Thionyl-Chloride Chemical Current Sources using Impedance Spectroscopy." Herald of the Bauman Moscow State Technical University. Series Natural Sciences, no. 1 (94) (February 2021): 116–25. http://dx.doi.org/10.18698/1812-3368-2021-1-116-125.
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Purpose of this work is to elaborate operational and reliable method for ensuring non-destructive control over primary lithium-thionyl-chloride chemical current sources (LCCS) using the impedance spectroscopy. Results and conclusions presented in this work are based on a series of experimental studies. Result reliability was experimentally proven on models and samples with known characteristics. Mathematical apparatus used in processing experimental data using the Fourier transforms allows obtaining information on impedance in a wide frequency range based on results of a single experiment and prompt calculating its main parameters (impedance imaginary value at the hodograph extreme point, its frequency, high-frequency resistance and phase). Ways to reduce the passive film influence, which is appearing on the lithium electrode during storage and operation, on the impedance characteristics are shown. Based on the electrochemical impedance spectra analysis, most informative frequency ranges were determined, and correlates were found connecting the impedance characteristics with the investigated current source state. It is proposed to use the phase angle value measured at the impedance hodograph extreme point as a correlate allowing to estimate the LCCS residual capacitance. It was determined that in assessing the LCCS discharge degree in the range of 0--70 % residual capacity, results of impedance spectroscopy are being quite informative
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Li, Zhang Yong, Fei Ba Chang, Xiao Bo Chen, Rui Leng, and Wei Wang. "A Design Based on Bioimpedance Spectroscopy Method in Human Abdominal Adipose Measurement System." Applied Mechanics and Materials 263-266 (December 2012): 241–45. http://dx.doi.org/10.4028/www.scientific.net/amm.263-266.241.
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This article describes a measurement of human abdominal fat device designed based on BIS (bioimpedance spectroscopy), the device adopts four electrodes multi-frequency bioelectrical impedance measurement system, including the programmable signal generator module and the amplitude and phase detection module. Program controlled signal generator module can generate the high output impedance of the constant current source in the eight frequency points constant current source between 5KHz and1MHz; amplitude phase detecting module can detect the human body electrical impedance real part and imaginary part information. Therefore, the device can be accurate measurement of human abdominal impedance information in the whole frequency range. Meanwhile, according to the selected electrode fixed position and the appropriate measurement scheme, can calculate the corresponding depth of abdominal fat content.
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Chen, Bo, and Xiaofeng Jia. "Staining algorithm for seismic modeling and migration." GEOPHYSICS 79, no. 4 (July 1, 2014): S121—S129. http://dx.doi.org/10.1190/geo2013-0262.1.
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In seismic migration, some structures such as those in subsalt shadow zones are not imaged well. The signal in these areas may be even weaker than the artifacts elsewhere. We evaluated a method to significantly improve the signal-to-noise ratio (S/N) in poorly illuminated areas of the model. We constructed a “phantom” wavefield: an extension of the wavefield to the complex domain. The imaginary wavefield was synchronized with the real wavefield, but it contained only the events relevant to a target region of the model, which was specified using a staining algorithm. The real wavefield interacted with the entire model. However, all structures except for the target were transparent to the imaginary wavefield, which is excited only when the real wavefront arrives at the target structure. The real and the imaginary source wavefields were crosscorrelated with the regular receiver wavefield. The results were revealed in two images: the conventional reverse time migration image and an image of the target region only. Synthetic experiments showed that the S/N of the target structures was improved significantly, with other structures effectively muted.
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Wickert, J. A., and C. D. Mote. "Response and Discretization Methods for Axially Moving Materials." Applied Mechanics Reviews 44, no. 11S (November 1, 1991): S279—S284. http://dx.doi.org/10.1115/1.3121365.
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Through a convective acceleration component, the equations of motion for axially-moving materials are skew-symmetric in the state space formulation, so that the response problem is best analyzed within the broader context of continuous gyroscopic systems. With particular application to the prototypical traveling string and beam models, a modal analysis that associates degrees of freedom with the complex state eigenfunctions and their conjugates is presented. This procedure is well-suited for harmonic excitation sources, and in some instances, it is more convenient than previous methods which decompose the modal coordinates, eigenfunctions, and generalized forces into real and imaginary components. Also from the state space perspective, Rayleigh’s quotient for gyroscopic systems provides a variational method for determining the eigensolutions of axially-moving materials. Ritz discretization of the quotient can make effective use of the speed-adapting modes of the traveling string and beam models as they are rich in phase, as well as amplitude, content.
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Khramtsova, N. I., Yu Yu Zayakin, S. A. Plaksin, and V. А. Kurkina. "Body dysmorphic disorder (dysmorphophobia / dysmorphomania): literature review." Perm Medical Journal 37, no. 2 (June 1, 2020): 15–23. http://dx.doi.org/10.17816/pmj37215-23.
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A literature review regarding body dysmorphic disorder. Analysis of Russian and foreign bibliographic sources. Dysmorphophobia (body dysmorphic disorder, dysmorphomania) is a psychopathological disorder with ideas of imaginary or exaggerated personal physical inferiority. In the general population it occurs in more than 2 %. Criteria for dysmorphophobia diagnosis are the following: excessive preoccupation with any imaginary or insignificant defect in appearance; preoccupation with a clinically significant disorder or impairment in social, occupational or other important areas of functioning; the clinical picture is not explained by another mental disorder. A unique approach to the diagnosis of dysmorphophobia has not been developed yet; clinical, pathopsychological and anamnestic methods are used as well as special questionnaires. Treatment includes drug and psychotherapeutic approaches. The disease is usually chronic, only 9 % of patients manage to achieve stable remission and only 21 % partial. Narrow specialists are not always acquainted with dysmorphophobia; it leads to an incorrect diagnosis and treatment. It is necessary to improve methods for the timely detection and correction of this form of mental pathology in order to prevent severe personal and social consequences of the disease.
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Sapuan, Imam, Moh Yasin, Khusnul Ain, and Retna Apsari. "Anomaly Detection Using Electric Impedance Tomography Based on Real and Imaginary Images." Sensors 20, no. 7 (March 30, 2020): 1907. http://dx.doi.org/10.3390/s20071907.
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This research offers a method for separating the components of tissue impedance, namely resistance and capacitive reactance. Two objects that have similar impedance or low contrast can be improved through separating the real and imaginary images. This method requires an Electrical Impedance Tomography (EIT) device. EIT can obtain potential data and the phase angle between the current and the potential measured. In the future, the device is very suitable for imaging organs in the thorax and abdomen that have the same impedance but different resistance and capacitive reactance. This device consists of programmable generators, Voltage Controlled Current Source (VCCS), mulptiplexer-demultiplexer potential meters, and phase meters. Data collecting was done by employing neighboring, while reconstruction was used the linear back-projection method from two different data frequencies, namely 10 kHz and 100 kHz. Phantom used in this experiment consists of distillated water and a carrot as an anomaly. Potential and phase data from the device is reconstructed to produce impedance, real, and imaginary images. Image analysis is performed by comparing the three images to the phantom. The experimental results show that the device is reliable.
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Gajewski, Dirk, and Ivan Pšenčík. "Vector wavefields for weakly attenuating anisotropic media by the ray method." GEOPHYSICS 57, no. 1 (January 1992): 27–38. http://dx.doi.org/10.1190/1.1443186.
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The ray method is used to compute high‐frequency seismic vector wavefields in weakly attenuating layered anisotropic structures. The attenuating effects are introduced by substituting the real elastic parameters for perfectly elastic media by complex frequency dependent elastic parameters with small imaginary parts. The imaginary parts are formally considered to be of the order of [Formula: see text] for [Formula: see text]. Under this assumption, it is possible to work with real rays, only the eikonal is complex. The approximate computations based on this algorithm are only a few percent slower than those for perfectly elastic anisotropic media. The range of applicability of the weak attenuation concept is investigated by comparison of ray computations with results of the reflectivity method for an isotropic, constant gradient model. The study indicates that the region of applicability of the weak attenuation concept may be broader than expected. The combined effects of anisotropy and attenuation on the propagation of seismic waves in a three‐dimensional model of the uppermost crust with an anisotropic attenuating layer are then studied. The anisotropy as well as the attenuation are supposed to be caused by aligned partially liquid‐filled cracks. Hudson’s formulas to compute complex effective elastic parameters are used. Frequency responses and VSP synthetic seismograms for different degrees of viscosity of the liquid, and, thus, different degree of attenuation, show the effects of attenuation on the propagating waves. Nine‐component VSP vector wavefields are computed for two different source‐borehole directions along the strike of the cracks and 45 degrees off the strike of the cracks. The seismograms for the attenuating model are compared with seismograms for the corresponding perfectly elastic model.
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Burdovitsin, V. A., A. V. Tyunkov, Y. G. Yushkov, and D. B. Zolotukhin. "Two-stage PVD method for protective coating formation." Journal of Physics: Conference Series 2064, no. 1 (November 1, 2021): 012074. http://dx.doi.org/10.1088/1742-6596/2064/1/012074.
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Abstract The CVD methods are typically used for the formation of aluminum oxide coatings since aluminum oxide is a dielectric. The adhesion between the protective coating and the substrate material is normally improved by growing thin intermediate layers based on titanium oxides and nitrides. These intermediate layers are mainly formed using the PVD methods. In this paper, we propose a two-stage PVD method for forming a layered structure on the titanium substrate. The formation of intermediate layers was carried out by the magnetron method (first stage), and the main protective layer was deposited at the second stage using a fore-vacuum electron source. The dense beam plasma generated during the electron beam transport in a fore-vacuum gas medium compensates for the negative electrical charge accumulating on the surface of the aluminum oxide target and facilitates its effective evaporation. The electrical properties of the intermediate layers and the resulting layered coatings have been investigated, including the tangent of dielectric loss angle, the real and imaginary parts of the conductivity and the dielectric constant dependencies on frequency.
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Salman, Sabah A., Ziad T. Khodair, and Sahar J. Abed. "Study the Effect of Substrate Temperature on the Optical Properties of CoFe2O4 Films Prepared by Chemical Spray Pyrolysis Method." International Letters of Chemistry, Physics and Astronomy 61 (November 2015): 118–27. http://dx.doi.org/10.18052/www.scipress.com/ilcpa.61.118.
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Cobalt Ferrite CoFe2O4 thin films have been deposited by chemical spray pyrolysis method (CSP) on glass substrates at different substrate temperatures (300, 350, 400 and 450°C) with an interval of (50°C) using Cobalt Nitrate and Ferric Nitrate as Cobalt and Iron sources respectively, at thickness (400±20) nm. The effect of substrate temperatures change on the optical properties for all prepared films was studied. The optical properties for all the films were studied by recording the transmittance and absorbance spectrum in the range of (300-900) nm. The results showed decreases in transmittance and increases in absorbance with increasing the substrate temperatures. the optical energy gap for allowed direct electronic transition was calculated and it was found that decreases with increasesing the substrate temperatures (2.40-2.22 eV), the Urbach energy increases with increasesing the substrate temperatures and it is values range between (634.6-700.5) meV. The optical constants (absorption coefficient, refractive index, extinction coefficient, real and imaginary parts of dielectric constant and optical conductivity) as a function of photon energy for all prepared films were calculated.
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Geremew, Temesgen, and Tizazu Abza. "Microstructural and Optical Characterization of Heterostructures of ZnS/CdS and CdS/ZnS Synthesized by Chemical Bath Deposition Method." Advances in Materials Science and Engineering 2020 (November 20, 2020): 1–11. http://dx.doi.org/10.1155/2020/1401689.
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ZnS/glass and CdS/glass single layers and ZnS/CdS and CdS/ZnS heterojunction thin films were deposited by the chemical bath deposition method using zinc acetate and cadmium acetate as the metal ion sources and thioacetamide as a nonmetallic ion source in acidic medium. Na2EDTA was used as a complexing agent to control the free cation concentration. The single layer and heterojunction thin films were characterized with X-ray diffraction (XRD), a scanning electron microscope (SEM), energy dispersive X-ray (EDX), and a UV-VIS spectrometer. The XRD patterns of the CdS/glass thin film deposited on the soda lime glass substrate crystalized in the cubic structure with a single peak along the (111) plane. The ZnS/CdS heterojunction and ZnS/glass single layer thin films were crystalized in the hexagonal ZnS structure. The CdS/ZnS heterojunction thin film is nearly amorphous. The optical analysis results confirmed single band gap values of 2.75 eV and 2.5 eV for ZnS/CdS and CdS/ZnS heterojunction thin films, respectively. The CdS/glass and CdS/ZnS thin films have more imaginary dielectric components than the real part. The optical conductivity of the single layer and heterojunction films is in the order of 10 15 1/s. The optical study also confirmed refractive index values between 2 and 2.7 for ZnS/glass, ZnS/CdS, and CdS/ZnS thin films for incident photon energies between 1.2 eV and 3.8 eV. The surface morphology studies revealed compacted spherical grains covering the substrate surfaces with few cracks on ZnS/glass, ZnS/CdS, and CdS/glass and voids on CdS/ZnS thin films. The EDX result confirmed nearly 1 : 1 metallic to nonmetallic ion ratio in the single-layered thin films and the dominance of Zn ion over Cd ion in both ZnS/CdS and CdS/ZnS heterojunction thin films.
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Hao, Qi, and Tariq Alkhalifah. "An acoustic eikonal equation for attenuating orthorhombic media." GEOPHYSICS 82, no. 4 (July 1, 2017): WA67—WA81. http://dx.doi.org/10.1190/geo2016-0632.1.
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Attenuating orthorhombic models are often used to describe the azimuthal variation of the seismic wave velocity and attenuation in finely layered hydrocarbon reservoirs with vertical fractures. In addition to the P-wave related medium parameters, S-wave parameters are also present in the complex eikonal equation needed to describe the P-wave complex-valued traveltime in an attenuating orthorhombic medium, which increases the complexity of using the P-wave traveltime to invert for the medium parameters in practice. We have used the acoustic assumption to derive an acoustic eikonal equation that approximately governs the complex-valued traveltime of P-waves in an attenuating orthorhombic medium. For a homogeneous attenuating orthorhombic media, we solve the eikonal equation using a combination of the perturbation method and Shanks transform. For a horizontal attenuating orthorhombic layer, the real and imaginary parts of the complex-valued reflection traveltime have nonhyperbolic behaviors in terms of the source-receiver offset. Similar to the roles of normal moveout (NMO) velocity and anellipticity, the attenuation NMO velocity and the attenuation anellipticity characterize the variation of the imaginary part of the complex-valued reflection traveltime around zero source-receiver offset.
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HAGEN, C. K., P. C. DIEMOZ, M. ENDRIZZI, P. R. T. MUNRO, M. B. SZAFRANIEC, T. P. MILLARD, R. SPELLER, and D. A. OLIVO. "A LABORATORY-BASED X-RAY PHASE CONTRAST IMAGING SCANNER WITH APPLICATIONS IN BIOMEDICAL AND NON-MEDICAL DISCIPLINES." International Journal of Modern Physics: Conference Series 27 (January 2014): 1460150. http://dx.doi.org/10.1142/s2010194514601501.
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X-ray phase contrast imaging (XPCi) provides a much higher visibility of low-absorbing details than conventional, attenuation-based radiography. This is due to the fact that image contrast is determined by the unit decrement of the real part of the complex refractive index of an object rather than by its imaginary part (the absorption coefficient), which can be up to 1000 times larger for energies in the X-ray regime. This finds applications in many areas, including medicine, biology, material testing, and homeland security. Until lately, XPCi has been restricted to synchrotron facilities due to its demanding coherence requirements on the radiation source. However, edge illumination XPCi, first developed by one of the authors at the ELETTRA Synchrotron in Italy, substantially relaxes these requirements and therefore provides options to overcome this problem. Our group has built a prototype scanner that adapts the edge-illumination concept to standard laboratory conditions and extends it to large fields of view. This is based on X-ray sources and detectors available off the shelf, and its use has led to impressive results in mammography, cartilage imaging, testing of composite materials and security inspection. This article presents the method and the scanner prototype, and reviews its applications in selected biomedical and non-medical disciplines.
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Xu, Shi‐zhe, Chieh‐Hou Yang, Shikun Dai, and Dahai Zhang. "A new method for continuation of 3D potential fields to a horizontal plane." GEOPHYSICS 68, no. 6 (November 2003): 1917–21. http://dx.doi.org/10.1190/1.1635045.
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A 3D potential on a 3D topography is approximately regarded as a potential on an imaginary horizontal plane. A fast Fourier transform (FFT) is applied to calculate the outward normal derivative of the potential on the horizontal plane. An approximation can be made such that the calculated derivative is used as the outward normal derivative of the potential on the 3D topographic surface. Based on the potential and the approximated normal derivative on the topography, Green's formula is used to obtain the potential at an arbitrary point above the topography. When the potential at a flat level above the topography is obtained, an FFT is used again to determine the potential at other levels above the source of the potential. A model test shows that the results from this method compare well with analytic solutions. The method has high computation speed and can be used for continuation of 3D potential fields for large data sets, e.g., aeromagnetic data.
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Zeru, Allelign, and Gerhard Schäfer. "Volume-based inverse model (VINMOD): innovative approach to quantify groundwater pollution in heterogeneous aquifers." Journal of Hydroinformatics 10, no. 3 (May 1, 2008): 215–26. http://dx.doi.org/10.2166/hydro.2008.020.
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The inversion method of pumped concentration can be used as an alternative or complementary method to the conventional methods for groundwater pollution evaluation and quantification. This method is useful even when the monitoring wells are few and also when the contamination source is unknown. In a homogeneous-isotropic case, with radially dominated groundwater flow field, this method of inversion can be performed analytically. However, in many cases, the real aquifer systems are heterogeneous. A novel volume-based inverse model (VINMOD) is developed for numerical inversion of pumped concentration under heterogeneous conditions. VINMOD helps us to determine the mean concentration and mass flow rate of an “undisturbed” contaminant plume at a predefined imaginary control plane (ICP). Model verification and preliminary tests are presented using a hypothetical single-layer aquifer. It is noticed that VINMOD is highly sensitive to the groundwater flow velocity and the well capture zone geometry, which in fact influences the determination of total mass flow rate of a pollutant in the groundwater.
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Davydycheva, Sofia, Nikolai Rykhlinski, and Peter Legeido. "Electrical-prospecting method for hydrocarbon search using the induced-polarization effect." GEOPHYSICS 71, no. 4 (July 2006): G179—G189. http://dx.doi.org/10.1190/1.2217367.
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We propose a method of surface and marine electrical prospecting using controlled-source excitation. The method is designed to detect hydrocarbon deposits at depths of a few kilometers and to map their boundaries. The technique is based on imaging the induced-polarization (IP) parameters of the geologic formation. We use the fact that, because of the imaginary part of the electric conductivity, polarized media support wave propagation processes whose nature is similar to displacement currents induced by the dielectric permittivity. However, unlike displacement currents, these processes reveal themselves at much lower frequencies and, therefore, at greater depths. It is established that the ratio of the second and the first differences of the electric potential does not decay after the current turn-off in polarized media, whereas it decays quickly if the IP effect is absent. Thus, the IP response can be observed directly and separated from the electromagnetic (EM) response. We use a vertical focusing of the electric current to decrease the effect of laterally adjacent formations to apply a 1D layered model in a 3D environment. This method obtained promising results in several regions of Russia.
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Cheng, Xue, and Yingmin Wang. "Noise Suppression for Direction of Arrival Estimation in Co-located MIMO Sonar." Sensors 19, no. 6 (March 16, 2019): 1325. http://dx.doi.org/10.3390/s19061325.
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Noise suppression capacity in multiple-input multiple-output (MIMO) sonar signal processing is derived under the assumption of white Gaussian noise. However, underwater noise mainly includes white Gaussian noise and colored noise. There exists a certain correlation between the noise signals received by each MIMO sonar array element. The performance of traditional direction-of-arrival (DOA) estimation methods decreases obviously in complex marine noise. In this paper, we propose a marine environment noise suppression method for MIMO applied to multiple targets’ DOA estimation. The noise field can be decomposed into a symmetric noise component and an asymmetric noise component. We use the covariance matrix imaginary component to pre-estimate the signal sources, then use the dimension reduction transformation to reconstruct the real component of the covariance matrix. The Toeplitz technique is utilized to reduce the correlation of the reconstructed covariance matrix. Thus, the subspace decomposition-based techniques such as multiple signal classification (MUSIC) can be used for multiple targets’ DOA estimation. To reduce the computational complexity of the methods, search-free direction-finding techniques such as the estimation of signal parameters via rotational invariance techniques (ESPRIT) can be utilized. As a result, the proposed methods can achieve better direction-finding performance in the condition of limited snapshots with lower computational cost. The corresponding Cramer-Rao bound (CRB) is deduced and the signal-to-noise ratio (SNR) gain obtained by dimension reduction processing is discussed. Simulation results also show the superiority of the proposed method over the existing methods.
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Mogilnikov, A. V., and Yu P. Akulinichev. "Limiting accuracy of two-dimensional parabolic equation solution using split-step Fourier transform method." Izvestiya vysshikh uchebnykh zavedenii. Fizika 64, no. 1 (2021): 43–49. http://dx.doi.org/10.17223/00213411/64/1/43.
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Numerical solution of the wave parabolic equation on a rectangular grid is analyzed, when the method of discrete split-step Fourier transform (FT) is used to calculate the values of the field in an inhomogeneous medium at the next step in the range. The goal was to identify the limiting possibilities of the FT method itself, so studies were carried out for the case of radio wave propagation in free space. Two related problems were solved: what is the minimum value of the root-mean-square error (RMSE) of the field calculation and what should be the values of the transfer coefficients of the Fourier series harmonics and the values of the coefficients of the artificial absorbing layer (AL) both depending on the parameters of the computational scheme. It is shown that the dependence of the RMSE on the distance to the source always has the maximum. The forms of the optimal AL differ from those traditionally used primarily due to the presence of a significant imaginary component.
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Picornell, Mercè. "The back side of the postcard: Subversion of the island tourist gaze in the contemporary Mallorcan imaginary." Island Studies Journal 15, no. 2 (2020): 291–314. http://dx.doi.org/10.24043/isj.109.
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This article analyses the manner in which certain artists and activists in Mallorca have recently generated a counter-image of the traditional postcard, which essentially symbolises the tourist gaze. Taking examples from diverse sources, such as artistic pieces, memes, protest posters and underground comics, I analyse the mechanisms used to subvert the conventional tourist perspective of the island space. More specifically, I identify two strategies associated with the limitation of the space and time portrayed in the postcard. The confines of the space are manifest in the display of the off-camera and the critical anchorage of the image, while the limits of temporality are presented in a dystopic revision of the island map. To support the findings of this study, I have drawn on the ideas, theories and methods of island studies, tourism studies, postcolonial criticism and the rhetoric of images. The conclusions of this article aim to provide an interpretation of the complex emergence of a resistant social agency capable of creating its own portrayals of the island.
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Huang, Xingguo, Hui Sun, Zhangqing Sun, and Nuno Vieira da Silva. "A complex point-source solution of the acoustic eikonal equation for Gaussian beams in transversely isotropic media." GEOPHYSICS 85, no. 3 (April 14, 2020): T191—T207. http://dx.doi.org/10.1190/geo2019-0264.1.
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The complex traveltime solutions of the complex eikonal equation are the basis of inhomogeneous plane-wave seismic imaging methods, such as Gaussian beam migration and tomography. We have developed analytic approximations for the complex traveltime in transversely isotropic media with a titled symmetry axis, which is defined by a Taylor series expansion over the anisotropy parameters. The formulation for the complex traveltime is developed using perturbation theory and the complex point-source method. The real part of the complex traveltime describes the wavefront, and the imaginary part of the complex traveltime describes the decay of the amplitude of waves away from the central ray. We derive the linearized ordinary differential equations for the coefficients of the Taylor-series expansion using perturbation theory. The analytical solutions for the complex traveltimes are determined by applying the complex point-source method to the background traveltime formula and subsequently obtaining the coefficients from the linearized ordinary differential equations. We investigate the influence of the anisotropy parameters and of the initial width of the ray tube on the accuracy of the computed traveltimes. The analytical formulas, as outlined, are efficient methods for the computation of complex traveltimes from the complex eikonal equation. In addition, those formulas are also effective methods for benchmarking approximated solutions.
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Castangia, P., G. Surcis, A. Tarchi, A. Caccianiga, P. Severgnini, and R. Della Ceca. "Water masers in Compton-thick AGN." Astronomy & Astrophysics 629 (August 29, 2019): A25. http://dx.doi.org/10.1051/0004-6361/201935421.
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Aims. Investigations of H2O maser galaxies at X-ray energies reveal that most active galactic nuclei (AGN) associated with water masers are characterized by high levels of absorption. With the aim of finding new maser sources for possible interferometric follow-ups, we have searched for water maser emission in a well-defined sample of heavily absorbed AGN (NH > 1023 cm−2), including Compton-thick (CT) sources. Methods. Previous surveys already searched for 22 GHz water maser emission in all the galaxies in this sample. With the goal of providing a detection or a stringent upper limit on the H2O luminosity, we reobserved some of the non-detected sources with the Green Bank Telescope. A new luminous H2O maser (LH2O ∼ 200 L⊙) was detected in the mid-IR-bright Seyfert 2 galaxy IRAS 15480−0344 and then followed-up with the Very Long Baseline Array. In order to shed light on the origin of the maser (jet, outflow, or disk), we recently observed the radio continuum emission in IRAS 15480-0344 with the European VLBI network (EVN) at 1.7 and 5.0 GHz. Results. With the newly discovered megamaser in IRAS 15480−0344 revealing a narrow (∼0.6 km s−1) and a broad (∼90 km s−1) component, the maser detection rate of the CT AGN sample is 50% (18/36), which is one of the highest ever found in maser surveys. The EVN maps show two bright sources (labeled SW and NE) in the nuclear region of IRAS 15480−0344, which we interpret as jet knots tracing regions where the radio plasma impacts dense molecular clouds. The narrow maser feature is approximately at the center of the imaginary line connecting the two continuum sources, likely pinpointing the core, and might be associated with the accretion disk or a nuclear outflow. The location of the broad maser feature, instead, coincides with source NE, suggesting that the maser emission might be produced by a jet-cloud interaction, as it was proposed for NGC 1068 and Mrk 348.
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Крыгин, Сергей Сергеевич, and Юрий Иванович Торба. "Измерение напряженно-деформированного состояния деталей АГТД методом тензометрии." Aerospace technic and technology, no. 4sup2 (August 27, 2021): 44–51. http://dx.doi.org/10.32620/aktt.2021.4sup2.06.
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The subject of study in the article is various methods of measuring the stress-strain state of AGTE parts by the tensometry method. Differences were revealed when measuring the stress-strain state of rotor and stator parts, in different frequency ranges (study of static, static-dynamic and dynamic deformations). Methods for compensating or reducing the influence of external factors on the measurement results, such as temperature changes and electromagnetic interference, are indicated. The aim is to develop recommendations for research of AGTE parts in a test bench in a gradient of varying temperatures and in a complex electromagnetic environment of the engine. A review of the sources of inaccuracies, errors and interference arising during preparation for testing and directly during the measurement of the SDS of AGTE parts is performed. The effects of wiring, cabling, grounding and shielding can not only increase the level of errors, but can also negate the advantages of an expensive and extremely reliable electronic part of the system. The advantages and disadvantages of the most common schemes for connecting strain gages, as well as their areas of application are presented. Possible ways to compensate for imaginary deformations at temperatures outside the range of thermal compensation of primary converters. A list of common strain gauge systems with their advantages and disadvantages is given for each type of parts and frequency ranges of measurements. When strain measurement rotary parts to output the signal from the strain gauge to recording equipment used various current collector. The possibility of using wireless interfaces for communication between the primary converter and the recording equipment is also indicated. The described methods are: ways to compensate for imaginary deformations caused by changes in the temperature of the investigated part and connecting wires. Elimination or minimization of electromagnetic interference on the measuring channel. An estimate is given of the total error in measuring the deformation for a particular object under study for the final loading cycle, the specificity of the bench strain gauge path, the errors of the current collector in bench conditions, and others in the process of static strain gauging.
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Abbas, Bassam, and Mohammad Alshikh Khalil. "Third-order optical nonlinearity of DSR13/THF solutions under CW He–Ne laser irradiation using Z-scan method." Canadian Journal of Physics 100, no. 1 (January 2022): 53–59. http://dx.doi.org/10.1139/cjp-2018-0991.
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The Z-scan technique was employed to explore the third-order nonlinear optical properties of disperse red 13 organic chromophore solutions in tetrahydrofuran. A continuous-wave He–Ne laser (632.8 nm) was used as a source of irradiation. The nonlinear absorption and nonlinear refractive index coefficients of this dye were investigated. The results showed that this dye has a good nonlinear response with its real and imaginary quantities of third-order susceptibility. The solutions showed negative nonlinear refraction. The best obtained value of the third-order susceptibility was 6.37 × 10–3 esu at a dye concentration of 3.15 × 10–4 mol/L. Moreover, the nonlinear optical properties were enhanced with higher dye concentrations, and an elevated trend in nonlinear absorption and nonlinear refractive index coefficients was observed. Also, it was found that the reverse saturable absorption was the main mechanism responsible for the two-photon absorption effect in DSR13/THF samples.
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Dastas, Mark Brian, and Hwachang Song. "Renewable Energy Generation Assessment in Terms of Small-Signal Stability." Sustainability 11, no. 24 (December 11, 2019): 7079. http://dx.doi.org/10.3390/su11247079.
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The popularity and role of renewable energy in the power grid are increasing nowadays as countries are shifting to cleaner forms of energy. This brings new challenges in maintaining a secure and stable power system, as renewable energy is known to be intermittent in nature and may introduce stability issues to the grid. In this paper, a screening framework of renewable energy generation scenarios is proposed to determine which power system conditions and scenarios will make the system unstable. The scenario screening framework is based on a sensitivity analysis of the system eigenvalues with respect to the renewable energy penetration to the system. The average scheduled renewable energy output, forecasting error standard deviation, average forecasting error, and bus location of the renewable energy source were used to define a renewable energy generation scenario. Depending on the amount and variability of renewable energy, there is a possibility for a critical eigenvalue to cross the imaginary axis. The estimated eigenvalue location resulting from the penetration of variable renewable energy is computed by adding the computed eigenvalue sensitivity to the initial operating point. If any of the estimated system eigenvalues cross the imaginary axis, the power system might be unstable in this scenario, so it requires more detailed simulations and countermeasures. Renewable energy forecasting was done using the long short-term memory model, and the proposed method was simulated using the IEEE 39-bus New England test system. The results of the proposed method were verified by comparing the simulation results to the eigenanalysis solution. The obtained results have shown that the proposed method can determine whether the renewable energy generation scenario is critical in power system operation.
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Asten, Michael W. "On bias and noise in passive seismic data from finite circular array data processed using SPAC methods." GEOPHYSICS 71, no. 6 (November 2006): V153—V162. http://dx.doi.org/10.1190/1.2345054.
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The finite nature of typical small seismic arrays used in conjunction with spatial autocorrelation (SPAC) processing for observing the microtremor wavefield causes predictable perturbations of the SPAC spectrum when sources of seismic noise are confined to a restricted range of azimuths. Such perturbations are especially evident at higher frequencies where wavelengths are on the order of the array radius. The effects are readily modeled and show that the triangular array geometries commonly used for microtremor studies require azimuthal distributions of wave energy on the order of [Formula: see text] or greater to have a high probability of being free of such perturbations. The imaginary component of the SPAC spectrum, which is ideally zero for a sufficiently dense circular array and/or a sufficiently isotropic wavefield, is in practice often nonzero and provides three quality-control indicators: (1) an indication of insufficient spatial averaging, (2) an empirical measure of the level of statistical uncertainty in SPAC spectral estimates, and (3) an indication of departures from plane-wave stationarity of the seismic noise wavefield.
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McConnell, C. L., P. Formenti, E. J. Highwood, and M. A. J. Harrison. "Using aircraft measurements to determine the refractive index of Saharan dust during the DODO experiments." Atmospheric Chemistry and Physics Discussions 9, no. 6 (November 5, 2009): 23505–46. http://dx.doi.org/10.5194/acpd-9-23505-2009.
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Abstract. Much uncertainty in the value of the imaginary part of the refractive index of mineral dust contributes to uncertainty in the radiative effect of mineral dust in the atmosphere. A synthesis of optical, chemical and physical in-situ aircraft measurements from the DODO experiments during February and August 2006 are used to calculate the refractive index mineral dust encountered over West Africa. Radiative transfer modeling and measurements of broadband shortwave irradiance at a range of altitudes are used to test and validate these calculations for a specific dust event on 23 August 2006 over Mauritania. Two techniques are used to determine the refractive index: firstly a method combining measurements of scattering, absorption, size distributions and Mie code simulations, and secondly a method using composition measured on filter samples to apportion the content of externally mixed quartz, calcite and iron oxide-clay aggregates, where the iron oxide is represented by either hematite or goethite and clay by either illite or kaolinite. The imaginary part of the refractive index at 550 nm (ni550) is found to range between 0.0001i to 0.0046i, and where filter samples are available, agreement between methods is found depending on mineral combination assumed. The refractive indices are also found to agree well with AERONET data where comparisons are possible. ni550 is found to vary with dust source, which is investigated with the NAME model for each case. The relationship between both size distribution and ni550 on the accumulation mode single scattering albedo at 550nm (ω0550) are examined and size distribution is found to have no correlation to ω0550, while ni550 shows a strong linear relationship with ω0550. Radiative transfer modeling indicates that Mie-derived values of ni550 and the goethite-kaolinite combination resulted in the best agreement with irradiance measurements, for the particular dust event examined. The radiative effect of the dust is found to be very sensitive to the mineral combination (and hence refractive index) assumed.
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Bimberekov, Pavel. "Graphical analysis of free-surface wave fields from moving two consecutive posts connected by thin plate." Vestnik of Astrakhan State Technical University. Series: Marine engineering and technologies 2020, no. 1 (February 17, 2020): 45–53. http://dx.doi.org/10.24143/2073-1574-2020-1-45-53.
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The article presents photographic materials of wave pictures from two consecutive posts of teardrop cross-section and the same posts with a thin plate installed between them, which introduces into consideration not only separate sequentially moving sources, but also reunites them into a single object, interacting along its entire length with the system of waves from the first source. The regularities of the wave field of consecutive posts with a plate in-stalled between them by means of graphic processing are considered. The possibility of finding the front imaginary source of the Kelvin wave pattern forming the ship's wave system at the position of both one and two wave-lengths in front of the top of the bow retaining wave is estimated. A method is proposed for determining the position of the fictitious location of the aft Kelvin wave system of the ship's wave system based on the results of the analysis of the wave field at the characteristic speeds
of movement, leading to the most successfully fixed inter-location of the wave pattern from the bow and aft extremities. There are shown the pictures of moving forward a pair of posts with
a blunt end of a horizontal section at the same speed and photo fixation from a close angle, pictures of moving forward the posts with a plate between them with a blunt end of a teardrop-shaped cross section at a low speed, moving forward posts with a plate at the side with a sharp end of a teardrop-shaped cross section, etc. All presented photographs were taken in the experimental pool of the Siberian state University of water transport (Novosibirsk state Academy of water transport) in 2006.
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Zhao, Dong Lin, Wei Dong Chi, and Zeng Min Shen. "Preparation of Carbon Nanotube Reinforced Epoxy Resin Coating and its Microwave Characteristics." Key Engineering Materials 334-335 (March 2007): 677–80. http://dx.doi.org/10.4028/www.scientific.net/kem.334-335.677.
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The carbon nanotubes were prepared by catalytic decompose of benzene using floating transition method at 1100~1200°C. Benzene was used as carbon source and iron as catalyst with sulfur. The carbon nanotubes are straight with diameter 30~80nm, internal diameter 10~50nm and length 50~100μm. The carbon nanotubes and epoxy resin were sufficiently mixed. The mixture was smeared on to a pure aluminum plate layer by layer until the thickness of the composite layer reached 1.0 mm. The coating resin was cured by heating under infrared radiation. Complex permittivity, permeability and microwave reflectivity of carbon nanotubes reinforced epoxy resin coating had been investigated at the frequency ranges of 8.2~12.4GHz and 2~18GHz respectively. The real part (ε′) of complex permittivity of this coating ranges from 14.87 to 13.86, and the imaginary part (ε″), from 6.42 to 5.87, the loss tangent tgδε (ε″/ε′), from 0.42 to 0.45. The real part (μ′) of complex permeability of this coating ranges from 1.02 to 1.14, and the imaginary part (μ″), from 0.08 to 0.11, the loss tangent tgδμ (μ″/μ′), from 0.06 to 0.11. The maximum absorbing peak of the carbon nanotube reinforced epoxy resin coating is 22.89 dB at 11.40GHz. The band width (R<-10dB) of this coating with thickness of 1.0 mm is 3.0GHz, band width (R<-5dB) is 4.7GHz at the frequency range of 8~18GHz. This carbon nanotube reinforced epoxy resin coating would be a good candidate for microwave absorbing material.
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Nurhandoko, Bagus E. B., Fajril Ambia, Kaswandhi Triyoso, M. Thurisina Choliq, Mahatman L. Budi, Asep Suhendi, and Wahyu E. Abdianto. "Marine Seismic Tomography for Detecting Fracture and Void of Subsurface Seabed : a Theoretical Framework Development and Application of Wide-Band Fresnel Tomography." Indonesian Journal of Physics 19, no. 4 (November 3, 2016): 103–6. http://dx.doi.org/10.5614/itb.ijp.2008.19.4.2.
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Fracture as well as void can generate unstable structure in offshore building. We use seismic tomography based on scattering wave instead of conventional raypath seismic tomography. Conventional raypath tomography usually needs dense source-receiver configuration as well as wide-angle measurement. Therefore, it will be high cost in field data acquisition. We propose scattering wavepath tomography by means of Fresnel interpolated wavepath (FIW) wide-band inversion. FIW is an interpolation between imaginary part of Rhytov scattering wavepath and raypath. Then, FIW is combined with wide band inversion procedure to handle sparseness configuration of measurement. By this method, smooth constraint is implemented more naturally by based on wave's spectrum. In this paper, we showed some applications of Wide-band inversion of FIW tomography in imaging fracture and void in marine carbonate sea bed.
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Бойков, Алексей, and Aleksey Boykov. "About Building of Models for Objects in Space of Four and More Dimensions in Educational Process." Geometry & Graphics 6, no. 4 (January 29, 2019): 54–71. http://dx.doi.org/10.12737/article_5c21f96dce5de8.36096061.
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In this paper the visibility concept in the context of modeling of multidimensional spaces’ objects is clarified. It is concluded that such model’s visibility should be defined as unambiguity and completeness of information presented in this model and consistent with the student’s experience in the area of modeling a space of higher dimension (3D) by elements of spaces of lower dimension (2D). Such possibilities are presented by the generalized complex drawing. Examples for objects 4D-modeling using two 3D or three 2D flat projections are presented, some properties of the 4D generalized drawing are listed. The solution of problems with 4D-objects is considered on the example of 4D-pyramid section construction, and deploying its lateral surface. It is shown that to simplify the solution of these problems is required a system allowing automatically perform repetitive sequences of constructions. A list of elementary constructions is presented, and a method for recording of composite constructions and based on them algorithms for problems solving is shown. It is demonstrated that a 3D-scan of 4D-pyramid’s lateral surface, constructed with 2D drawing, can be imported into CAD as a 3D-model. The deploying of the 4D-cone’s lateral surface is considered. The resulting scan’s surface 3D-model imported into CAD is shown. Cases are indicated when a multidimensional space’s object 3D-model may be more visual than a flat one. As an example, 2D-models for imaginary continuations of lines and circles of the complex plane (simulated by Euclidean 4D-space) are presented. Two 3D-projections for imaginary continuations of a circle with a real radius as 3D-space surfaces are shown. It is noted that in order to combine in an educational course the multidimensional space’s objects modeling and work in CAD the tasks on designing of complex technical surfaces by means of output in multidimensional space are suitable. A brief review of sources is given, in which theoretical foundations and the use of key geometrical methods for surfaces construction are considered; an example of a surface constructed by a progressive key method and imported into CAD is shown. The concept of a product’s electronic model (PEM) is described, in which the modeled object’s 3D-simulator as its visual representation is combined with numerous 2D-layers, which elements automatically perform geometrical and graphical calculations in spaces of any dimensions, and control 3D-model’s dimensions and shape through constructive and parametric links. Conclusions are drawn about the possibility of visual multidimensional modeling in the educational process, the advantages of using a complex drawing for solving of problems with multidimensional objects, the need to use special systems of constructive geometric modeling that automate repetitive sequences of constructions. It is also concluded that multidimensional objects’ 2D-models can and should be directly involved in the PEM formation.
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McConnell, C. L., P. Formenti, E. J. Highwood, and M. A. J. Harrison. "Using aircraft measurements to determine the refractive index of Saharan dust during the DODO Experiments." Atmospheric Chemistry and Physics 10, no. 6 (March 31, 2010): 3081–98. http://dx.doi.org/10.5194/acp-10-3081-2010.
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Abstract. Much uncertainty in the value of the imaginary part of the refractive index of mineral dust contributes to uncertainty in the radiative effect of mineral dust in the atmosphere. A synthesis of optical, chemical and physical in-situ aircraft measurements from the DODO experiments during February and August 2006 are used to calculate the refractive index mineral dust encountered over West Africa. Radiative transfer modeling and measurements of broadband shortwave irradiance at a range of altitudes are used to test and validate these calculations for a specific dust event on 23 August 2006 over Mauritania. Two techniques are used to determine the refractive index: firstly a method combining measurements of scattering, absorption, size distributions and Mie code simulations, and secondly a method using composition measured on filter samples to apportion the content of internally mixed quartz, calcite and iron oxide-clay aggregates, where the iron oxide is represented by either hematite or goethite and clay by either illite or kaolinite. The imaginary part of the refractive index at 550 nm (ni550) is found to range between 0.0001 i to 0.0046 i, and where filter samples are available, agreement between methods is found depending on mineral combination assumed. The refractive indices are also found to agree well with AERONET data where comparisons are possible. ni550 is found to vary with dust source, which is investigated with the NAME model for each case. The relationship between both size distribution and ni550 on the accumulation mode single scattering albedo at 550 nm (ω0550) are examined and size distribution is found to have no correlation to ω0550, while ni550 shows a strong linear relationship with ω0550. Radiative transfer modeling was performed with different models (Mie-derived refractive indices, but also filter sampling composition assuming both internal and external mixing). Our calculations indicate that Mie-derived values of ni550 and the externally mixed dust where the iron oxide-clay aggregate corresponds to the goethite-kaolinite combination result in the best agreement with irradiance measurements. The radiative effect of the dust is found to be very sensitive to the mineral combination (and hence refractive index) assumed, and to whether the dust is assumed to be internally or externally mixed.
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Saijo, Tatsuyoshi. "Future Design: Bequeathing Sustainable Natural Environments and Sustainable Societies to Future Generations." Sustainability 12, no. 16 (August 11, 2020): 6467. http://dx.doi.org/10.3390/su12166467.
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“Future Design,” a new movement among Japanese researchers and stakeholders, asks the following question: What types of social systems are necessary if we are to leave future generations sustainable environments and societies? Looking at the human activity impact on the global environment and society, I ask: Why is this society we live in generating a series of future failures that will cost future generations so much? I then argue that the source of such a society could be liberalism and that the market and democracy derived from it will not help avoid these future failures. To achieve this, one must design social systems that activate a human trait called futurability, where people experience an increase in happiness because of deciding and acting toward foregoing current benefits to enrich future generations. One method to study these is by employing “imaginary future generations”. Here, I present an overview of the theoretical background of this method, the results of relevant laboratory and field experiments, and the nature of relevant practical applications implemented in cooperation with several local governments.
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Glukhova, Natalia N. "Types of space in Mari verbal charms." Finno-Ugric World 10, no. 4 (December 24, 2018): 34–46. http://dx.doi.org/10.15507/2076-2577.010.2018.04.034-046.
Full textAbstract:
The object of the research is the Mari verbal charms; the subject is their lexical level. The aim of this article is to reveal, describe and classify types of space constituting a system of spatial images and symbols. The significance of the verbal charms as a source of information is beyond doubt and lies in the fact that verbal magic formulas are original, statistically undoubted material that has been created and used for centuries on the territories inhabited by the ethnic group. The methodological basis of the research includes the use of a number of provisions of the theory of system analysis (text is a systemic, a hierarchically structured unit, consisting of a number of elements), which is supplemented by the use of factor (types of space) and statistical types of analysis. They are combined with linguistic methods of semantic research: method of vocabulary analysis, componential and contextual analysis. Imaginary and real actions necessary to achieve the goals of verbal formulas occur in the space-time continuum. In the folklore reflection of reality, the space is used as a background for the events. It is characterized by geographical and climatic features. The article identifies and analyzes the elements of the terrain and geographical objects defined by the term “types of space”. The algorithm of the research includes a number of following steps. First, the lexical composition of 428 texts from various sources is analyzed. Then, using the definitional and component types of analysis, individual lexemes are defined, denoting the types of space. After this step, the frequency of their use is calculated. The ranking of factors contributes to the allocation of four groups of space types, combining eighteen items. The obtained results make it possible to determine the symbols and archetypes of the space of the Mari folklore genres. The most common types of space in the analyzed texts consist of 55,7 % of geographical objects and are marked by the following lexemes: ponds and their parts, housing, earth, sky. They have symbolic meanings containing Mari ethnic religious and mythological view of the universe.