An analysis of the magnetotelluric impedance for three‐dimensional conductivity structures

Geophysics ◽  
1986 ◽  
Vol 51 (9) ◽  
pp. 1819-1829 ◽  
Author(s):  
G. A. LaTorraca ◽  
T. R. Madden ◽  
J. Korringa
Keyword(s):  
Electric Fields ◽  
Principal Axis ◽  
Current System ◽  
A Priori ◽  
Three Dimensional ◽  
Singular Values ◽  
Skew Angle ◽  
Characteristic Values ◽  
Two Phases ◽  
Value Decomposition

The eigenstate analysis of Lanczos, also known as singular value decomposition (SVD), is used to define eight parameters which uniquely describe the magnetotelluric impedance Z. These parameters are independent of a priori assumptions about Z and can be interpreted in terms of three‐dimensional conductivity structures. Through SVD, the impedance is represented by two characteristic states. These states consist of two pairs (E and H) of complex vectors and two corresponding, real, singular values which together describe the extremal properties of Z. The singular values are the maximum and minimum |E|/|H| ratios possible at the observation site and therefore yield the true maximum and minimum apparent resistivities. We use a variation of SVD analysis by incorporating phases in the singular values, which are then called characteristic values. These phases reflect the delay (caused by the earth’s conductivity) of the electric fields relative to their associated magnetic fields. In this analysis of Z, the characteristic values contain four parameters, two singular values and two phases. The characteristic vectors contain the remaining four parameters, two principal axis directions and two ellipticities. The principal axis directions for the E and H vectors need not be at right angles as in biorthogonal analysis. The deviation of these axes from orthogonality is called the “skew angle” S. From a model by Park, we have found S to be closely related to distortions in the telluric current system caused by current gathering due to a good conductor. From the same model, we have found the ellipticity parameters to be the largest in regions of high current distortion and at the shorter periods. Consequently, we speculate that the ellipticity parameters are associated with local induction.

scholarly journals Transient production of F-region irregularities associated with TCV passage

2003 ◽  
Vol 21 (7) ◽  
pp. 1531-1541 ◽  
Author(s):  
R. Kataoka ◽  
H. Fukunishi ◽  
K. Hosokawa ◽  
H. Fujiwara ◽  
A. S. Yukimatu ◽  
...  
Keyword(s):  
Electric Fields ◽  
Current System ◽  
Rapid Evolution ◽  
Three Dimensional ◽  
Leading Edge ◽  
Spectral Width ◽  
Plasma Convection ◽  
Plasma Irregularities ◽  
F Region ◽  
Field Aligned Current

Abstract. Transient production of F-region plasma irregularities due to traveling convection vortices (TCVs) was investigated using the Super Dual Auroral Radar Network (SuperDARN) combined with ground magnetometer networks and the POLAR ultraviolet imager. We selected two large-amplitude (100–200 nT) TCV events that occurred on 22 May 1996 and 24 July 1996. It is found that the TCV-associated HF backscatter arises in blobs with spatial scale of a few hundreds km. They traveled following tailward bulk motion of the TCV across the three fields-of-view of the SuperDARN HF radars in the prenoon sector. The spectra in the blobs showed unidirectional Doppler velocities of typically 400–600 m/s, with flow directions away from the radar. These unidirectional velocities correspond to the poleward and/or eastward convective flow near the leading edge of upward field-aligned current. The backscatter blobs overlapped the poleward and westward part of the TCV-related transient aurora. It is likely that the transient backscatter blobs are produced by the three-dimensional gradient drift instabilities in the three-dimensional current system of the TCV. In this case, nonlinear rapid evolution of irregularities would occur in the upward field-aligned current region. The spectral width of the backscatter blob is typically distributed between 50 and 300 m/s, but sometimes it is over 400 m/s. This suggests that the temporal broad spectra over 400 m/s are produced by Pc1–2 bursts, while the background spectral width of 50–300 m/s are produced by the velocity gradient structure of convection vortices themselves.Key words. Ionosphere (Electric fields and currents; Ionospheric irregularities; Plasma convection)

A SVD and Modified Firefly Optimization Based Robust Digital Image Watermarking Technique

2017 ◽  
Vol 7 (7) ◽  
pp. 268
Author(s):  
Chauhan Usha ◽  
Singh Rajeev Kumar
Keyword(s):  
Digital Media ◽  
Firefly Algorithm ◽  
Image Watermarking ◽  
Singular Values ◽  
Robust Watermarking ◽  
Scaling Factors ◽  
Geometric Attacks ◽  
Host Image ◽  
Firefly Optimization ◽  
Value Decomposition

Digital Watermarking is a technology, to facilitate the authentication, copyright protection and Security of digital media. The objective of developing a robust watermarking technique is to incorporate the maximum possible robustness without compromising with the transparency. Singular Value Decomposition (SVD) using Firefly Algorithm provides this objective of an optimal robust watermarking technique. Multiple scaling factors are used to embed the watermark image into the host by multiplying these scaling factors with the Singular Values (SV) of the host image. Firefly Algorithm is used to optimize the modified host image to achieve the highest possible robustness and transparency. This approach can significantly increase the quality of watermarked image and provide more robustness to the embedded watermark against various attacks such as noise, geometric attacks, filtering attacks etc.

Controllable Electrochemical Synthesis of Ag Hierarchical Micro/Nanostructures with High SERS-Activity

NANO ◽  
2020 ◽  
Vol 15 (04) ◽  
pp. 2050043
Author(s):  
Huayu Zhou ◽  
Jingjing Wang ◽  
Qiong Yang ◽  
Menglei Chen ◽  
Changsheng Song ◽  
...  
Keyword(s):  
Indium Tin Oxide ◽  
Current System ◽  
Three Dimensional ◽  
Constant Current ◽  
Localized Surface Plasmon ◽  
Excitation Wavelength ◽  
Raman Signal ◽  
Mixed Solution ◽  
Raman Enhancement ◽  
One Step

We report a one-step electrochemical deposition technique to prepare three-dimensional (3D) Ag hierarchical micro/nanostructured film consisting of well-crystallized Ag nanosheets grown on an indium tin oxide (ITO) conductive substrate. The Ag hierarchical micro/nanostructures were fabricated in the mixed solution of AgNO3 and sodium citrate in a constant current system at room temperature. Through reduction of Ag[Formula: see text] electrodeposited on the surface of ITO substrate, nanoparticles were grown to form nanosheets which further combined into 3D sphere-like microstructures. The 3D Ag micro/nanostructures have many sharp edges and nanoscale gaps which can give rise to good Raman-enhanced effect. Due to localized surface plasmon resonance (LSPR) effects, these special Ag micro/nanostructures exhibited good Raman-enhanced performance. Using Rhodamine 6G (R6G) molecules as probe molecule, we studied the influence of excitation wavelength on Raman enhancement. The results showed that the 532[Formula: see text]nm excitation wavelength is the best to obtain the strongest Raman signal and to reduce the influence of other impurity peaks. Using the as-synthesized Ag hierarchical micro/nanostructures, we can detect the 10[Formula: see text][Formula: see text]mol/L R6G aqueous solution, exhibiting great Raman-enhanced effect.

scholarly journals A Three-Phase Fundamental Diagram from Three-Dimensional Traffic Data

Axioms ◽  
2021 ◽  
Vol 10 (1) ◽  
pp. 17
Author(s):  
Maria Laura Delle Delle Monache ◽  
Karen Chi ◽  
Yong Chen ◽  
Paola Goatin ◽  
Ke Han ◽  
...  
Keyword(s):  
Dimensional Space ◽  
Three Dimensional ◽  
Time Estimation ◽  
Travel Time Estimation ◽  
Traffic Data ◽  
Fundamental Diagram ◽  
Model Based Clustering ◽  
Three Phase ◽  
Characterization Of Solutions ◽  
Two Phases

This paper uses empirical traffic data collected from three locations in Europe and the US to reveal a three-phase fundamental diagram with two phases located in the uncongested regime. Model-based clustering, hypothesis testing and regression analyses are applied to the speed–flow–occupancy relationship represented in the three-dimensional space to rigorously validate the three phases and identify their gaps. The finding is consistent across the aforementioned different geographical locations. Accordingly, we propose a three-phase macroscopic traffic flow model and a characterization of solutions to the Riemann problems. This work identifies critical structures in the fundamental diagram that are typically ignored in first- and higher-order models and could significantly impact travel time estimation on highways.

scholarly journals Partial aperture imaging system based on sparse point spread holograms and nonlinear cross-correlations

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Angika Bulbul ◽  
Joseph Rosen
Keyword(s):  
Structural Changes ◽  
Imaging System ◽  
Current System ◽  
Three Dimensional ◽  
Phase Mask ◽  
Coded Aperture ◽  
Space Telescopes ◽  
Reconstruction Process ◽  
Cross Correlations ◽  
Equivalent Systems

AbstractPartial aperture imaging system (PAIS) is a recently developed concept in which the traditional disc-shaped aperture is replaced by an aperture with a much smaller area and yet its imaging capabilities are comparable to the full aperture systems. Recently PAIS was demonstrated as an indirect incoherent digital three-dimensional imaging technique. Later it was successfully implemented in the study of the synthetic marginal aperture with revolving telescopes (SMART) to provide superresolution with subaperture area that was less than one percent of the area of the full synthetic disc-shaped aperture. In the study of SMART, the concept of PAIS was tested by placing eight coded phase reflectors along the boundary of the full synthetic aperture. In the current study, various improvements of PAIS are tested and its performance is compared with the other equivalent systems. Among the structural changes, we test ring-shaped eight coded phase subapertures with the same area as of the previous circular subapertures, distributed along the boundary of the full disc-shaped aperture. Another change in the current system is the use of coded phase mask with a point response of a sparse dot pattern. The third change is in the reconstruction process in which a nonlinear correlation with optimal parameters is implemented. With the improved image quality, the modified-PAIS can save weight and cost of imaging devices in general and of space telescopes in particular. Experimental results with reflective objects show that the concept of coded aperture extends the limits of classical imaging.

Applications of 3D printing in critical care medicine: A scoping review

2021 ◽  
pp. 0310057X2097665
Author(s):  
Natasha Abeysekera ◽  
Kirsty A Whitmore ◽  
Ashvini Abeysekera ◽  
George Pang ◽  
Kevin B Laupland
Keyword(s):  
Critical Care ◽  
Scoping Review ◽  
A Priori ◽  
Three Dimensional ◽  
Critical Care Medicine ◽  
Future Research ◽  
Care Practice ◽  
Three Dimensional Printing ◽  
Wide Range ◽  
Dimensional Printing

Although a wide range of medical applications for three-dimensional printing technology have been recognised, little has been described about its utility in critical care medicine. The aim of this review was to identify three-dimensional printing applications related to critical care practice. A scoping review of the literature was conducted via a systematic search of three databases. A priori specified themes included airway management, procedural support, and simulation and medical education. The search identified 1544 articles, of which 65 were included. Ranging across many applications, most were published since 2016 in non – critical care discipline-specific journals. Most studies related to the application of three-dimensional printed models of simulation and reported good fidelity; however, several studies reported that the models poorly represented human tissue characteristics. Randomised controlled trials found some models were equivalent to commercial airway-related skills trainers. Several studies relating to the use of three-dimensional printing model simulations for spinal and neuraxial procedures reported a high degree of realism, including ultrasonography applications three-dimensional printing technologies. This scoping review identified several novel applications for three-dimensional printing in critical care medicine. Three-dimensional printing technologies have been under-utilised in critical care and provide opportunities for future research.

Combined Radar and Radiometer Analysis of Precipitation Profiles for a Parametric Retrieval Algorithm

2005 ◽  
Vol 22 (7) ◽  
pp. 909-929 ◽  
Author(s):  
Hirohiko Masunaga ◽  
Christian D. Kummerow
Keyword(s):  
A Priori ◽  
Three Dimensional ◽  
Tropical Rainfall Measuring Mission ◽  
Dimensional Structure ◽  
Retrieval Algorithm ◽  
Brightness Temperatures ◽  
Precipitation Measurement ◽  
Microwave Imager ◽  
Trmm Microwave Imager ◽  
Global Precipitation

Abstract A methodology to analyze precipitation profiles using the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) and precipitation radar (PR) is proposed. Rainfall profiles are retrieved from PR measurements, defined as the best-fit solution selected from precalculated profiles by cloud-resolving models (CRMs), under explicitly defined assumptions of drop size distribution (DSD) and ice hydrometeor models. The PR path-integrated attenuation (PIA), where available, is further used to adjust DSD in a manner that is similar to the PR operational algorithm. Combined with the TMI-retrieved nonraining geophysical parameters, the three-dimensional structure of the geophysical parameters is obtained across the satellite-observed domains. Microwave brightness temperatures are then computed for a comparison with TMI observations to examine if the radar-retrieved rainfall is consistent in the radiometric measurement space. The inconsistency in microwave brightness temperatures is reduced by iterating the retrieval procedure with updated assumptions of the DSD and ice-density models. The proposed methodology is expected to refine the a priori rain profile database and error models for use by parametric passive microwave algorithms, aimed at the Global Precipitation Measurement (GPM) mission, as well as a future TRMM algorithms.

Three-Dimensional Hopf Bifurcation for a Class of Cubic Kolmogorov Model

2014 ◽  
Vol 24 (03) ◽  
pp. 1450036 ◽  
Author(s):  
Chaoxiong Du ◽  
Qinlong Wang ◽  
Wentao Huang
Keyword(s):  
Hopf Bifurcation ◽  
Singular Point ◽  
Three Dimensional ◽  
Singular Values ◽  
Bifurcation Problem ◽  
Disturbed Condition ◽  
Differential Systems ◽  
Kolmogorov Model ◽  
Polynomial Differential Systems ◽  
Fine Focus

We study the Hopf bifurcation for a class of three-dimensional cubic Kolmogorov model by making use of our method (i.e. singular values method). We show that the positive singular point (1, 1, 1) of an investigated model can become a fine focus of 5 order, and moreover, it can bifurcate five small limit cycles under certain coefficients with disturbed condition. In terms of three-dimensional cubic Kolmogorov model, published references can hardly be seen, and our results are new. At the same time, it is worth pointing out that our method is valid to study the Hopf bifurcation problem for other three-dimensional polynomial differential systems.

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