Time Domain Resolution of Forward and Reflected Waves in the Aorta

1986 ◽  
Vol BME-33 (8) ◽  
pp. 783-785 ◽  
Author(s):  
John. K.-J. Li
Keyword(s):  
Time Domain ◽  
Reflected Waves

scholarly journals Extending the Application of One-Terminal Fault Location Method Available in Actual Time Domain Relay

2020 ◽  
Author(s):  
Gustavo A. Cunha ◽  
Felipe V. Lopes ◽  
Tiago H. Honorato
Keyword(s):  
Transmission Lines ◽  
Time Domain ◽  
Traveling Wave ◽  
Fault Location ◽  
Reflected Waves ◽  
Location Method ◽  
Actual Time ◽  
The One

Traveling wave-based fault location has attracted more and more attention from industries worldwide. This theory allowed the implementation of functions in order to increase the reliability of the obtained fault location results. Among existing functions, the classical one-terminal method requires the detection of the wave reflected from the fault, which is still considered a challenging task. A commercial relay was released with a function able to identify these reflected waves by evaluating patterns and weighted hypotheses, identifying the wavefront most likely to be the one re ected from the fault. However, as this function is embedded into a relay, it is not possible to change the method settings. Thus, this paper presents a validation of this function which is implemented externally to the relay. Besides, its application is extended for transmission lines to which the relay can not be applied, such as huge HVDC lines.

Efficient Guiding of Terahertz Wave by Thin Metal Corrugation on Both Surfaces

2011 ◽  
Vol 687 ◽  
pp. 65-69 ◽  
Author(s):  
Dong Bin Tian ◽  
Huai Wu Zhang ◽  
Qi Ye Wen ◽  
Wei Wei Ling ◽  
Yuan Qiang Song ◽  
...  
Keyword(s):  
Surface Plasmon ◽  
Surface Plasmon Polaritons ◽  
Time Domain ◽  
Terahertz Wave ◽  
Transmission Characteristic ◽  
Low Loss ◽  
Reflected Waves ◽  
Resonance Modes ◽  
Fabry Perot ◽  
Plasmon Polaritons

Thin structured periodic metallic corrugations on both sides of low-loss thin polythene slab are proposed to efficiently guide terahertz (THz) wave based on the surface plasmon polaritons (SPPs). THz time domain spectrometer was used to measure the transmission characteristic. Long-lasting Fabry-Perot resonance modes are demonstrated due to the interferences of the multiple reflected waves.

scholarly journals Lithological Interface Detection Using an Impact Source

2020 ◽  
Vol 2020 ◽  
pp. 1-14
Author(s):  
Xu Jian ◽  
Hongtao Li ◽  
Gao Li ◽  
Pan Fang ◽  
Xu Yang ◽  
...  
Keyword(s):  
Early Detection ◽  
Time Domain ◽  
Distance Measurement ◽  
Coda Waves ◽  
Metal Base ◽  
Reflected Waves ◽  
Measurement Experiment ◽  
Metal Materials ◽  
The Time Domain ◽  
Petroleum Drilling

Early detection of abnormal geological targets during drilling can enhance the safety of petroleum drilling. An impact source equipped with the advantage of long detection distances can recognize lithological interfaces. However, coda waves in the vibration waveform are significant to reflected waves, which are difficult to recognize in the time domain. This paper presents the design of an impact source that includes a hammer, impacted metal, Teflon, and a metal base. With the length and diameter of Teflon kept constant, the effect of the hammer, impacted metal, and metal base on the coda waves was experimentally investigated. According to the preferred metal materials, the effect of the length and diameter of Teflon on coda waves was also experimentally studied. A distance measurement experiment was implemented on 1.2 m sandstone on the basis of the preferred impact source design. The experimental results show that the coda waves are significantly attenuated by the preferred impact source. Moreover, the reflected waves are clearly identified in the time domain. Therefore, the preferred impact source can be used effectively in lithological interface detection.

scholarly journals Time-domain representation of ventricular-arterial coupling as a windkessel and wave system

2003 ◽  
Vol 284 (4) ◽  
pp. H1358-H1368 ◽  
Author(s):  
Jiun-Jr Wang ◽  
Aoife B. O'Brien ◽  
Nigel G. Shrive ◽  
Kim H. Parker ◽  
John V. Tyberg
Keyword(s):  
Time Domain ◽  
Aortic Pressure ◽  
Domain Model ◽  
Wave System ◽  
Reflected Waves ◽  
Arterial Hemodynamics ◽  
Arterial Model ◽  
Anesthetized Dogs ◽  
The Difference ◽  
Flow Waveforms

The differences in shape between central aortic pressure (PAo) and flow waveforms have never been explained satisfactorily in that the assumed explanation (substantial reflected waves during diastole) remains controversial. As an alternative to the widely accepted frequency-domain model of arterial hemodynamics, we propose a functional, time-domain, arterial model that combines a blood conducting system and a reservoir (i.e., Frank's hydraulic integrator, the windkessel). In 15 anesthetized dogs, we measured PAo, flows, and dimensions and calculated windkessel pressure (PWk) and volume (VWk). We found that PWk is proportional to thoracic aortic volume and that the volume of the thoracic aorta comprises 45.1 ± 2.0% (mean ± SE) of the total VWk. When we subtracted PWk from PAo, we found that the difference (excess pressure) was proportional to aortic flow, thus resolving the differences between PAo and flow waveforms and implying that reflected waves were minimal. We suggest that PAo is the instantaneous summation of a time-varying reservoir pressure (i.e., PWk) and the effects of (primarily) forward-traveling waves in this animal model.

A multiscale approach to full-waveform inversion using a sequence of time-domain misfit functions

Geophysics ◽  
2019 ◽  
Vol 84 (4) ◽  
pp. R539-R551
Author(s):  
Renato R. S. Dantas ◽  
Walter E. Medeiros ◽  
Jessé C. Costa
Keyword(s):  
Time Domain ◽  
Waveform Inversion ◽  
Peak Frequency ◽  
Smooth Transition ◽  
Multiscale Approach ◽  
Minor Effect ◽  
Full Waveform Inversion ◽  
Data Set ◽  
Reflected Waves ◽  
Full Waveform

Most of the approaches designed to avoid cycle skipping in full-waveform inversion (FWI) involve calculating a sequence of inversions in a multiscale fashion. We have adopted an alternative strategy, which is inverting a sequence of different misfit functions in the time domain. This is an implicit multiscale approach in the sense that the used misfit functions are sensitive to different wavelengths, but all of the inversion steps use the same modeling algorithm and the same model grid. In the first and third inversion steps, the transmitted (early arrivals) and reflected (late arrivals) components of the wavefield envelopes are respectively fitted. The second step promotes a smooth transition between the first and third steps, by using the envelope of the complete waveform. Because fitting just the envelope of the reflected waves has a minor effect on the misfit function of the whole data set, the phases of the reflected waves are mostly fitted in the fourth step, which is based on the waveform misfit function preserving only the late arrivals. The third and fourth steps are of crucial importance to fit the reflected events. We test the sequential inversion approach with the Marmousi model using data sets with different frequencies, obtaining better estimates of the velocity field than those obtained with the classic FWI. The solutions obtained with classic FWI and sequential inversion approach degrade with a progressively higher peak frequency data set, but the classic FWI solution degrades more rapidly.

Measurement of Sound Absorption Using a Single Fixed Microphone in a Circular Pulse-Tube

2019 ◽  
Vol 105 (6) ◽  
pp. 1228-1236
Author(s):  
Zhengyu Wei ◽  
Hong Hou ◽  
Nansha Gao ◽  
Yunke Huang ◽  
Jianhua Yang
Keyword(s):  
Time Domain ◽  
Sound Absorption ◽  
Normal Incidence ◽  
Pulse Generation ◽  
Pulse Tube ◽  
Reflected Waves ◽  
Generation Technique ◽  
Pulse Separation ◽  
The Time Domain ◽  
Good Agreement

This study presents a method for measuring the normal incidence sound absorption coefficient of acoustical materials by separating the incident and first reflected waves in the time domain using a pulse-tube with only a single microphone whose position is fixed. Based on the pulse generation technique, the effect of the characteristics of tube termination can be eliminated, and the drive signal used for the measurement is obtained. A moveable piston is used to move the sample to a certain position in the tube, which renders the recorded incident and first reflected waves separated. As a validation of the proposed method, two different materials are investigated. Good agreement is found between the proposed method and both the well-established two-microphone transfer function (TMF) method and the verified pulse separation method.

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