• Title/Summary/Keyword: Local domain-inversion

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Extraction of Cole-Cole Parameters from Time-domain Induced Polarization Data (시간영역 유도분극 자료로부터 Cole-Cole 변수 산출)

  • Kim, Yeon-Jung;Cho, In-Ky
    • Geophysics and Geophysical Exploration
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    • v.24 no.4
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    • pp.164-170
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    • 2021
  • Frequency-domain and time-domain induced polarization methods can provide spectral information about subsurface media. Analysis of spectral characteristics has been studied mainly in the frequency-domain, however, time-domain induced polarization research has recently become popular. In this study, assuming a homogeneous half-space model, an inversion method was developed to extract Cole-Cole parameters from the measured secondary potential or electrical resistivity. Since the Cole-Cole parameters of chargeability, time constant, and frequency index are not independent of each other, various problems, such as slow convergence rate, initial model problem, local minimum problem, and divergence, frequently occur when conventional nonlinear inversion is applied. In this study, we developed an effective inversion method using the initial model close to the true model by introducing a grid search method. Finally, the validity of the developed inversion method was verified using inversion experiments.

PROBLEMS IN INVERSE SCATTERING-ILLPOSEDNESS, RESOLUTION, LOCAL MINIMA, AND UNIQUENESSE

  • Ra, Jung-Woong
    • Communications of the Korean Mathematical Society
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    • v.16 no.3
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    • pp.445-458
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    • 2001
  • The shape and the distribution of material construction of the scatterer may be obtained from its scattered fields by the iterative inversion in the spectral domain. The illposedness, the resolution, and the uniqueness of the inversion are the key problems in the inversion and inter-related. The illposedness is shown to be caused by the evanescent modes which carries and amplifies exponentially the measurement errors in the back-propagation of the measured scattered fields. By filtering out all the evanescent modes in the cost functional defined as the squared difference between the measured and the calculated spatial spectrum of the scattered fields from the iteratively chosen medium parameters of the scatterer, one may regularize the illposedness of the inversion in the expense of the resolution. There exist many local minima of the cost functional for the inversion of the large and the high-contrast scatterer and the hybrid algorithm combining the genetic algorithm and the Levenberg-Marquardt algorithm is shown to find efficiently its global minimum. The resolution of reconstruction obtained by keeping all the propating modes and filtering out the evanescent modes for the regularization becomes 0.5 wavelength. The super resolution may be obtained by keeping the evanescent modes when the measurement error and instance, respectively, are small and near.

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Thermomechanical interactions in a non local thermoelastic model with two temperature and memory dependent derivatives

  • Lata, Parveen;Singh, Sukhveer
    • Coupled systems mechanics
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    • v.9 no.5
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    • pp.397-410
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    • 2020
  • The present investigation is concerned with two-dimensional deformation in a homogeneous isotropic non local thermoelastic solid with two temperatures due to thermomechanical sources. The theory of memory dependent derivatives has been used for the study. The bounding surface is subjected to concentrated and distributed sources (mechanical and thermal sources). The Laplace and Fourier transforms have been used for obtaining the solution to the problem in the transformed domain. The analytical expressions for displacement components, stress components and conductive temperature are obtained in the transformed domain. For obtaining the results in the physical domain, numerical inversion technique has been applied. Numerical simulated results have been depicted graphically for explaining the effects of nonlocal parameter on the components of displacements, stresses and conductive temperature. Some special cases have also been deduced from the present study. The results obtained in the investigation should be useful for new material designers, researchers and physicists working in the field of nonlocal material sciences.

Time harmonic interactions in non local thermoelastic solid with two temperatures

  • Lata, Parveen;Singh, Sukhveer
    • Structural Engineering and Mechanics
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    • v.74 no.3
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    • pp.341-350
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    • 2020
  • The present investigation is concerned with two dimensional deformation in a non local thermoelastic solid with two temperatures due to time harmonic sources. The nonlocal thermoelastic solid is homogeneous with the effect of two temperature parameters. Fourier transforms are used to solve the problem. The bounding surface is subjected to concentrated and distributed sources. The analytical expressions of displacement, stress components and conductive temperature are obtained in the transformed domain. Numerical inversion technique has been applied to obtain the results in the physical domain. Numerical simulated results are depicted graphically to show the effect of nonlocal parameter and frequency on the components of displacements, stresses and conductive temperature. Some special cases are also deduced from the present investigation.

Design and Fabrication of 5.5GHZ SSB optical modulator with polarization reversed structure (LiINbO3 기판의 분극반전을 이용한 5.5 GHz 대역 SSB 광변조기의 설계 및 제작)

  • Jeong, W.J.;Kim, W.K.;Yang, W.S.;Lee, H.M.;Lee, H.Y.;Kwon, S.W.
    • Korean Journal of Optics and Photonics
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    • v.17 no.2
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    • pp.175-180
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    • 2006
  • A single sideband(SSB) modulator operating at 5.5 GHz was fabricated by polarization inversion techniques. The dimension of domain inversion in a $LiINbO_3$ Mach-Zehnder structure was precisely controlled so that the RF signal applied on two Mach-Zehnder arms gives rise to $90^{\circ}$ effective phase difference. The single sideband suppression was maximized by optimization of the polarization status of the optical input and by the DC bias value. The fabricated device showed the center frequency of 5.8 GHz and the maximum sideband suppression of 33dB, where the bandwidth of 15 dB sideband suppression ranged over a 2.5 GHz span. The optical phase delay could be regulated by the DC bias voltage, fur example, the enhanced optical modulation sideband was distinctively switched from the upper sideband to the lower sideband by changing the DC bias voltage from 1.9 V to -10.6 V.

Microwave Imaging of a Perfectly Conducting Cylinder by Using Modified Newton's Algorithm in the Angular Spectral Domain (각 스펙트럼 영역에서 개선된 Newton 알고리듬을 이용한 완전도체의 역산란 방법)

  • 박선규;박정석;라정웅
    • Journal of the Korean Institute of Telematics and Electronics A
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    • v.31A no.6
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    • pp.34-44
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    • 1994
  • In this paper, an iterative inversion method in angular spectral domain is presented for microwave imaging of a perfectly conducting cylinder. Angular spectra are calculated from measured far-field scattered fields. And then both the propagating modes and the evanescent modes are defined. The center and initial shape of an unknown conductor may be obtained by the characteristics of angular spectra and the total scattering cross section (TSCS). Finally, the orignal shape is reconstructed by the modified Newton algorithm. By using well estimated initial shape the local minima can be avoided, which might appear when the nonlinear equation is solved with Newton algorithm. It is shown to be robust to noise in scattered fields via numerical examples by keeping only the propagating modes and filtering out the evanescent modes.

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Close-contact melting of ice in a horizontal cylinder (수평원관내 얼음의 접촉융해과정)

  • ;;Ro, Sung Tack
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.19 no.10
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    • pp.2595-2606
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    • 1995
  • Buoyancy-assisted melting of an unconstrained ice in an isothermally heated horizontal enclosure was numerically analyzed in a range of wall temperatures encompassing the density inversion point. The problem as posed here involves two physically distinct domains each of which has its own scales and respective heat transfer mode. These two domains join at the junction where the liquid squeezed out of the film region flushes into the lower melt pool. Both of these domains have been treated separately in the literature by a patching technique which invokes several, otherwise unnecessary, assumptions. The present study eliminates successfully such a superfluous procedure by treating the film and lower melt pool regions as a single domain. As a result of this efficient solution procedure, the interaction of the water stream ejected at the junction and the natural convection in the melt pool could be clarified for different wall temperatures. Though limited by two-dimensionality, the present results conformed indirectly the earlier reported transition of the flow pattern, as the wall temperature was increased over the density inversion point. The transient evolution of the melting surface, the time rate of change in melt volume fraction, the local and temporal variation of the heat transfer coefficients are analyzed and presented.

A Study on Field Seismic Data Processing using Migration Velocity Analysis (MVA) for Depth-domain Velocity Model Building (심도영역 속도모델 구축을 위한 구조보정 속도분석(MVA) 기술의 탄성파 현장자료 적용성 연구)

  • Son, Woohyun;Kim, Byoung-yeop
    • Geophysics and Geophysical Exploration
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    • v.22 no.4
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    • pp.225-238
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    • 2019
  • Migration velocity analysis (MVA) for creating optimum depth-domain velocities in seismic imaging was applied to marine long-offset multi-channel data, and the effectiveness of the MVA approach was demonstrated by the combinations of conventional data processing procedures. The time-domain images generated by conventional time-processing scheme has been considered to be sufficient so far for the seismic stratigraphic interpretation. However, when the purpose of the seismic imaging moves to the hydrocarbon exploration, especially in the geologic modeling of the oil and gas play or lead area, drilling prognosis, in-place hydrocarbon volume estimation, the seismic images should be converted into depth domain or depth processing should be applied in the processing phase. CMP-based velocity analysis, which is mainly based on several approximations in the data domain, inherently contains errors and thus has high uncertainties. On the other hand, the MVA provides efficient and somewhat real-scale (in depth) images even if there are no logging data available. In this study, marine long-offset multi-channel seismic data were optimally processed in time domain to establish the most qualified dataset for the usage of the iterative MVA. Then, the depth-domain velocity profile was updated several times and the final velocity-in-depth was used for generating depth images (CRP gather and stack) and compared with the images obtained from the velocity-in-time. From the results, we were able to confirm the depth-domain results are more reasonable than the time-domain results. The spurious local minima, which can be occurred during the implementation of full waveform inversion, can be reduced when the result of MVA is used as an initial velocity model.

A novel model of a rotating nonlocal micropolar thermoelastic medium with temperature-dependent properties

  • Samia M. Said;Elsayed M. Abd-Elaziz;Mohamed I.A. Othman
    • Structural Engineering and Mechanics
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    • v.90 no.4
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    • pp.429-434
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    • 2024
  • In the current work, the effect of rotation and mechanical force on a nonlocal micropolar thermoelastic solid with temperature-dependent properties was discussed using Erigen's nonlocal thermoelasticity theory. The problem is resolved using Laplace transforms and Fourier series. For the nonlocal and local parameters, the physical fields have been illustrated. The numerical inversion approach is used to acquire the resulting fields in the physical domain. Based on numerical analysis, the effects of rotation, the modulus of elasticity's dependency on temperature, and nonlocal, mechanical force are examined on the physical fields.

Growth and characterization of periodically polarity-inverted ZnO structures grown on Cr-compound buffer layers

  • Park, J.S.;Goto, T.;Hong, S.K.;Chang, J.H.;Yoon, E.;Yao, T.
    • Proceedings of the Korean Vacuum Society Conference
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    • 2010.08a
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    • pp.259-259
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    • 2010
  • Periodically polarity inverted (PPI) ZnO structures on (0001) Al2O3 substrates are demonstrated by plasmas assisted molecular beam epitaxy. The patterning and re-growth methods are used to realize the PPI ZnO by employing the polarity controlling method. For the in-situ polarity controlling of ZnO films, Cr-compound buffer layers are used.[1, 2] The region with the CrN intermediate layer and the region with the Cr2O3 and Al2O3 substrate were used to grow the Zn- and O-polar ZnO films, respectively. The growth behaviors with anisotropic properties of PPI ZnO heterostructures are investigated. The periodical polarity inversion is evaluated by contrast images of piezo-response microscopy. Structural and optical interface properties of PPI ZnO are investigated by the transmission electron microcopy (TEM) and micro photoluminescence ($\mu$-PL). The inversion domain boundaries (IDBs) between the Zn and the O-polar ZnO regions were clearly observed by TEM. Moreover, the investigation of spatially resolved local photoluminescence characteristics of PPI ZnO revealed stronger excitonic emission at the interfacial region with the IDBs compared to the Zn-polar or the O-polar ZnO region. The possible mechanisms will be discussed with the consideration of the atomic configuration, carrier life time, and geometrical effects. The successful realization of PPI structures with nanometer scale period indicates the possibility for the application to the photonic band-gap structures or waveguide fabrication. The details of application and results will be discussed.

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