PROCESSING AND INTERPRETATION OF MAGNETOTELLURIC SOUNDINGS

Geophysics ◽  
1972 ◽  
Vol 37 (6) ◽  
pp. 1005-1021 ◽  
Author(s):  
G. Kunetz
Keyword(s):  
Transfer Function ◽  
Time Domain ◽  
Transfer Functions ◽  
Seismic Analysis ◽  
Magnetotelluric Soundings ◽  
Automatic Interpretation ◽  
Uniqueness Of The Solution ◽  
Experimental Values ◽  
The Time Domain ◽  
Analytical Expressions

A few methods in the processing and interpretation of magnetotelluric soundings over a stratified earth are investigated, with emphasis on the less commonly used time‐domain procedures. Analytical expressions of the theoretical transfer function between the magnetic‐ and electric‐field variations, both in frequency and time domain, are derived. Their properties are studied, and recursive algorithms are given for their numerical computation. On the other hand, a procedure is outlined which leads directly in the time domain to the experimental values of this transfer function. It is similar to the methods used in seismic analysis for signal determination and makes use of the auto‐ and crosscorrelation functions of the measured field variations. Finally, methods of interpretation, based either on a visual or on an automatic comparison of these theoretical and experimental transfer functions, are proposed. For the case of automatic interpretation, complementary geologic data should be used where possible to take care of the lack of uniqueness of the solution.

scholarly journals Research on improving measurement accuracy of acoustic transfer function of underwater vehicle

2021 ◽  
Vol 336 ◽  
pp. 01006
Author(s):  
Jiangqiao Li ◽  
Li Jiang ◽  
Fujian Yu ◽  
Ye Zhang ◽  
Kun Gao
Keyword(s):  
Transfer Function ◽  
Impulse Response ◽  
Time Domain ◽  
Transfer Functions ◽  
Least Squares Method ◽  
Signal To Noise Ratio ◽  
Random Noise ◽  
Phase Compensation ◽  
Acoustic Transfer Function ◽  
The Time Domain

To address the problem that acoustic transfer functions with underwater platforms cannot be measured accurately, this paper presents a method based on phase compensation to improve the accuracy of acoustic transfer function measurements on underwater platforms. The time-domain impulse response signals with multiple cycles are first collected and intercepted, and then their phase differences are estimated using the least-squares method, and phase compensation is used to align the phases of all the signals, and then the impulse response signals are weighted and averaged over all the impulse response signals to cancel out the random noise. The water pool test proves that this method reduces the measurement random noise while obtaining a high-fidelity time domain transfer function, which effectively improves the signal-to-noise ratio of the measurement. The method adopts only one measurement signal, and without changing the measurement system, the random noise is cancelled out by the in-phase superposition of the multi-cycle impulse response signals to avoid the nonlinear distortion of the measurement results.

Analytical Expressions for Electromagnetic Fields Associated with the Inclined Lightning Channels in the Time Domain

2012 ◽  
Vol 40 (4) ◽  
pp. 414-438 ◽  
Author(s):  
Mahdi Izadi ◽  
Mohd Zainal Ab Kadir ◽  
Chandima Gomes ◽  
Wan Fatin Hamamah Wan Ahmad
Keyword(s):  
Electromagnetic Fields ◽  
Time Domain ◽  
The Time Domain ◽  
Analytical Expressions

scholarly journals STEADY-STATE ANALYSIS OF NONLINEARLY COUPLED CHUA'S CIRCUITS WITH PERIODIC INPUT

2003 ◽  
Vol 13 (11) ◽  
pp. 3395-3407 ◽  
Author(s):  
F. A. SAVACI ◽  
M. E. YALÇIN ◽  
C. GÜZELIŞ
Keyword(s):  
Steady State ◽  
Time Domain ◽  
Transfer Functions ◽  
Piecewise Linear ◽  
Time Domain Analysis ◽  
Steady State Analysis ◽  
Linear Dynamic Systems ◽  
Periodic Input ◽  
The Time Domain ◽  
State Analysis

In this paper, nonlinearly coupled identical Chua's circuits, when driven by sinusoidal signal have been analyzed in the time-domain by using the steady-state analysis techniques of piecewise-linear dynamic systems. With such techniques, it has become possible to obtain analytical expressions for the transfer functions in terms of the circuit parameters. The proposed system under consideration has also been studied by analog simulations of the overall system on a hardware realization using off-the-shelf components as well as by a time-domain analysis of the synchronization error.

scholarly journals Relativistic modeling of atmospheric occultations with time transfer functions

2021 ◽  
Vol 648 ◽  
pp. A46
Author(s):  
A. Bourgoin ◽  
M. Zannoni ◽  
L. Gomez Casajus ◽  
P. Tortora ◽  
P. Teyssandier
Keyword(s):  
Transfer Function ◽  
Transfer Functions ◽  
Integral Form ◽  
Original Method ◽  
Electromagnetic Signal ◽  
Time Transfer ◽  
Spacetime Curvature ◽  
Covariant Description ◽  
Analytical Expressions ◽  
Optical Metric

Context. Occultation experiments represent unique opportunities to remotely probe the physical properties of atmospheres. The data processing involved in modeling the time and frequency transfers of an electromagnetic signal requires that refractivity be properly accounted for. On theoretical grounds, little work has been done concerning the elaboration of a covariant approach for modeling occultation data. Aims. We present an original method allowing fully analytical expressions to be derived up to the appropriate order for the covariant description of time and frequency transfers during an atmospheric occultation experiment. Methods. We make use of two independent powerful relativistic theoretical tools, namely the optical metric and the time transfer functions formalism. The former allows us to consider refractivity as spacetime curvature while the latter is used to determine the time and frequency transfers occurring in a curved spacetime. Results. We provide the integral form of the time transfer function up to any post-Minkowskian order. The discussion focuses on the stationary optical metric describing an occultation by a steadily rotating and spherically symmetric atmosphere. Explicit analytical expressions for the time and frequency transfers are provided at the first post-Minkowskian order and their accuracy is assessed by comparing them to results of a numerical integration of the equations for optical rays. Conclusions. The method accurately describes vertical temperature gradients and properly accounts for the light-dragging effect due to the motion of the optical medium. It can be pushed further in order to derive the explicit form of the time transfer function at higher order and beyond the spherical symmetry assumption.

scholarly journals Selective quantification of the cardiac sympathetic and parasympathetic nervous systems by multisignal analysis of cardiorespiratory variability

2008 ◽  
Vol 294 (1) ◽  
pp. H362-H371 ◽  
Author(s):  
Xiaoxiao Chen ◽  
Ramakrishna Mukkamala
Keyword(s):  
Nervous System ◽  
Transfer Function ◽  
Parasympathetic Nervous System ◽  
Transfer Functions ◽  
Low Frequency ◽  
Sympathetic Blockade ◽  
Nervous Systems ◽  
Autonomic Nervous ◽  
Arterial Blood ◽  
The Time Domain

Heart rate (HR) power spectral indexes are limited as measures of the cardiac autonomic nervous systems (CANS) in that they neither offer an effective marker of the β-sympathetic nervous system (SNS) due to its overlap with the parasympathetic nervous system (PNS) in the low-frequency (LF) band nor afford specific measures of the CANS due to input contributions to HR [e.g., arterial blood pressure (ABP) and instantaneous lung volume (ILV)]. We derived new PNS and SNS indexes by multisignal analysis of cardiorespiratory variability. The basic idea was to identify the autonomically mediated transfer functions relating fluctuations in ILV to HR (ILV→HR) and fluctuations in ABP to HR (ABP→HR) so as to eliminate the input contributions to HR and then separate each estimated transfer function in the time domain into PNS and SNS indexes using physiological knowledge. We evaluated these indexes with respect to selective pharmacological autonomic nervous blockade in 14 humans. Our results showed that the PNS index derived from the ABP→HR transfer function was correctly decreased after vagal and double (vagal + β-sympathetic) blockade ( P < 0.01) and did not change after β-sympathetic blockade, whereas the SNS index derived from the same transfer function was correctly reduced after β-sympathetic blockade in the standing posture and double blockade ( P < 0.05) and remained the same after vagal blockade. However, this SNS index did not significantly decrease after β-sympathetic blockade in the supine posture. Overall, these predictions were better than those provided by the traditional high-frequency (HF) power, LF-to-HF ratio, and normalized LF power of HR variability.

scholarly journals Effect of Wave-Current Interaction on Structural Responses of a Very Long and Side-Anchored Floating Bridge

2020 ◽  
Author(s):  
Jian Dai ◽  
Bjørn Christian Abrahamsen ◽  
Bernt Johan Leira
Keyword(s):  
Time Domain ◽  
Transfer Functions ◽  
Computational Study ◽  
Three Dimensional ◽  
Time Domain Analysis ◽  
Bridge Model ◽  
Structural Responses ◽  
Floating Bridge ◽  
Current Interaction ◽  
The Time Domain

Abstract This paper is concerned with a computational study on the hydroelastic response of a long, straight and side-anchored fjord-crossing floating bridge accounting for the wave-current interaction. The effect of this interaction on a single bridge pontoon is investigated by using the three-dimensional potential solver VERES3D. The frequency-dependent hydrodynamic coefficients and excitation force transfer functions are presented and compared with WAMIT results where the current effect is ignored. Based on the frequency domain results, an approach to account for the wave-current interaction in time domain analysis is proposed. Next, a generic straight and side-anchored floating bridge model is put forward to examine the stochastic structural responses in the time domain. For the purpose of comparison, the bridge responses under waves and current without interaction are also investigated. This study attempts to quantify the wave-current interaction effect on the structural responses of a floating bridge and provide useful recommendations and suggestions to researchers and engineers for their study of similar structures.

Operation of T-Foils and Stern Tabs to Improve Passenger Comfort on High-Speed Ferries

2021 ◽  
pp. 1-20
Author(s):  
Michael R. Davis
Keyword(s):  
Time Domain ◽  
High Speed ◽  
Transfer Functions ◽  
Passenger Comfort ◽  
Strip Theory ◽  
Head Waves ◽  
Similar Range ◽  
Vertical Accelerations ◽  
The Time Domain ◽  
Passenger Discomfort

High-speed ferries of around 100 m length cruising at around 40 knots can cause significant passenger discomfort in head waves. This is due to the frequencies of encountering waves, of maximum hull response to encountered waves and of maximum passenger discomfort all falling within a similar range. In this paper, the benefit obtained by fitting active T-foils and stern tabs to control heave and pitch in head waves is considered. Ship motion responses are computed by numerical integration in the time domain including unsteady control actions using a time domain, high-speed strip theory. This obviates the need to identify transfer functions, the computed time responses including nonlinear hull immersion terms. The largest passenger vertical accelerations occur at forward locations and are best controlled by a forward located T-foil acting in combination with active stern tabs. Various feedback control algorithms have been considered and it is found that pitch damping control gives the greatest improvement in passenger comfort at forward positions. Operation in adaptive and nonlinear modes so that the control deflections are maximized under all conditions give the greatest benefit and can reduce passenger motion sickness incidence (MSI) by up to 25% in a 3-m head sea on the basis of International Organization for Standardization (ISO) recommendations for calculation of MSI for a 90-minute seaway passage.

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