SOME ASPECTS OF ELASTIC WAVE PROPAGATION IN FLUID‐SATURATED POROUS SOLIDS

Geophysics ◽  
1961 ◽  
Vol 26 (2) ◽  
pp. 169-181 ◽  
Author(s):  
J. Geertsma ◽  
D. C. Smit
Keyword(s):  
Wave Propagation ◽  
Low Frequency ◽  
Normal Incidence ◽  
Approximate Solutions ◽  
Porous Solids ◽  
Geophysical Research ◽  
Weak Points ◽  
Biot’S Equations ◽  
Second Wave ◽  
The Waves

Biot’s equations for the propagation of dilatational waves in fluid‐saturated porous solids in the low‐frequency range are analyzed for the purpose of application in geophysical research. The deformation constants of the system are unraveled in terms of compressibilities and porosity, and suitable approximate solutions for wave velocity and attenuation of the waves of both the first and the second kind are obtained. A saturated elastic porous solid is found to behave, as far as the wave of the first kind is concerned, approximately as a standard element. The wave of the second kind rapidly dies out with increasing distance from the source and consequently one might infer that in seismic studies only the wave of the first kind needs consideration. It is shown, however, that its presence has an effect upon the reflection and absorption at any interface between two different fluid‐saturated porous solids. At such an interface a wave of the second kind is again generated. General formulae for the reflection and absorption for normal incidence at the interface are obtained, which include the effect of second‐wave generation. Additional results of the investigation are the following: A rather simple formula for the speed of sound in sedimentary rocks (the wave of the first kind) is obtained, which has to replace the so‐called “time‐average relation” now sometimes used. A comparison between the results obtained here and published results on wave propagation in simpler fluid‐solid systems, such as, for instance, suspensions, showed some weak points in the older theories. Suggestions for possible improvements are given.

scholarly journals Anomalous Anderson localization behavior in gain-loss balanced non-Hermitian systems

Nanophotonics ◽  
2020 ◽  
Vol 10 (1) ◽  
pp. 443-452
Author(s):  
Tianshu Jiang ◽  
Anan Fang ◽  
Zhao-Qing Zhang ◽  
Che Ting Chan
Keyword(s):  
Wave Propagation ◽  
Electromagnetic Waves ◽  
Anderson Localization ◽  
Random Media ◽  
Normal Incidence ◽  
Disordered Media ◽  
One Dimensional ◽  
Gain Loss ◽  
The Waves ◽  
Localization Behavior

AbstractIt has been shown recently that the backscattering of wave propagation in one-dimensional disordered media can be entirely suppressed for normal incidence by adding sample-specific gain and loss components to the medium. Here, we study the Anderson localization behaviors of electromagnetic waves in such gain-loss balanced random non-Hermitian systems when the waves are obliquely incident on the random media. We also study the case of normal incidence when the sample-specific gain-loss profile is slightly altered so that the Anderson localization occurs. Our results show that the Anderson localization in the non-Hermitian system behaves differently from random Hermitian systems in which the backscattering is suppressed.

The low-frequency scattering by a perfectly conducting strip

1961 ◽  
Vol 57 (2) ◽  
pp. 364-366 ◽  
Author(s):  
D. S. Jones ◽  
B. Noble
Keyword(s):  
Power Series ◽  
Plane Wave ◽  
Low Frequency ◽  
Normal Incidence ◽  
Approximate Solutions ◽  
Wave Number ◽  
Expansion Parameter ◽  
Higher Order Terms ◽  
Image Position ◽  
Conducting Strip

Various authors, e.g. Sommerfeld (8), Bouwkamp(i), Groschwitz and Hönl(2), Müller and Westpfahl(7), have considered approximate solutions to the problem of the diffraction of a plane wave by a narrow perfectly conducting strip. If the electric vector is polarized parallel to the strip they find that the scattering coefficient, for normal incidence, is given by, where k is the wave number, 2b the width of the strip and γ(= 0·5572…) being Euler's constant. Any attempt to discuss the convergence of such a pseudo-power series requires a knowledge of the higher order terms and naturally leads to the question of what is the proper expansion parameter.

scholarly journals Airglow Measurements of Gravity Wave Propagation and Damping over Kolhapur (16.5°N, 74.2°E)

2014 ◽  
Vol 2014 ◽  
pp. 1-9 ◽  
Author(s):  
R. N. Ghodpage ◽  
A. Taori ◽  
P. T. Patil ◽  
S. Gurubaran ◽  
A. K. Sharma ◽  
...  
Keyword(s):  
Wave Propagation ◽  
Gravity Wave ◽  
Meridional Wind ◽  
Vertical Wavelength ◽  
Emission Layer ◽  
Positive Correlation ◽  
Intensity Measurements ◽  
Wind Shears ◽  
The Waves ◽  
Airglow Intensity

Simultaneous mesospheric OH and O  (1S) night airglow intensity measurements from Kolhapur (16.8°N, 74.2°E) reveal unambiguous gravity wave signatures with periods varying from 01 hr to 9 hr with upward propagation. The amplitudes growth of these waves is found to vary from 0.4 to 2.2 while propagating from the OH layer (~87 km) to the O (1S) layer (~97 km). We find that vertical wavelength of the observed waves increases with the wave period. The damping factors calculated for the observed waves show large variations and that most of these waves were damped while traveling from the OH emission layer to the O (1S) emission layer. The damping factors for the waves show a positive correlation at vertical wavelengths shorter than 40 km, while a negative correlation at higher vertical wavelengths. We note that the damping factors have stronger positive correlation with meridional wind shears compared to the zonal wind shears.

The role of the Pacific Decadal Oscillation and ocean-atmosphere interactions in driving United States heatwaves

2021 ◽  
Author(s):  
Sem Vijverberg ◽  
Dim Coumou
Keyword(s):  
Rossby Wave ◽  
Rossby Waves ◽  
Low Frequency ◽  
Causal Link ◽  
Causal Mechanism ◽  
Temperature Forecast ◽  
The Pacific ◽  
Ocean Atmosphere ◽  
The Waves

<p>Heatwaves can have devastating impact on society and reliable early warnings at several weeks lead time are needed. Heatwaves are often associated with quasi-stationary Rossby waves, which interact with sea surface temperature (SST). Previous studies showed that north-Pacific SST can provide long-lead predictability for eastern U.S. temperature, moderated by an atmospheric Rossby wave. The exact mechanisms, however, are not well understood. Here we analyze Rossby waves associated with heatwaves in western and eastern US. Causal inference analyses reveal that both waves are characterized by positive ocean-atmosphere feedbacks at synoptic timescales, amplifying the waves. However, this positive feedback on short timescales is not the causal mechanism that leads to a long-lead SST signal. Only the eastern US shows a long-lead causal link from SSTs to the Rossby wave. We show that the long-lead SST signal derives from low-frequency PDO variability, providing the source of eastern US temperature predictability. We use this improved physical understanding to identify more reliable long-lead predictions. When, at the onset of summer, the Pacific is in a pronounced PDO phase, the SST signal is expected to persist throughout summer. These summers are characterized by a stronger ocean-boundary forcing, thereby more than doubling the eastern US temperature forecast skill, providing a temporary window of enhanced predictability.</p>

Numerical Simulation of the Buried Object Detection Based on Underwater Plasma Acoustic Source

2011 ◽  
Vol 105-107 ◽  
pp. 80-83
Author(s):  
Jun Zhang ◽  
Xin Wu Zeng ◽  
Yi Bo Wang ◽  
Zhen Fu Zhang ◽  
Dan Chen
Keyword(s):  
Wave Propagation ◽  
Object Detection ◽  
Pulse Length ◽  
Low Frequency ◽  
Basic Mechanism ◽  
Propagation Model ◽  
Staggered Grid ◽  
Acoustic Source ◽  
Buried Objects ◽  
Buried Object

Detection and classification of buried objects is of great importance in underwater counterterrorism and archaeology. To penetrate the sediment, a low frequency intensive acoustic source is needed. Underwater plasma acoustic source (UPAS) with high voltage discharge has the advantage of adjustable pulse length, high source level output and no pollution to the environment, which can satisfy these needs. In this paper, we introduced the UPAS, including its basic mechanism, structure and pressure output. Then we build up an elastic wave propagation model, solved it with finite difference and staggered grid methods, and combined with certain source and boundary condition, we simulated and analyzed the pressure wave propagation in time domain with an aluminum cylinder buried in sediment, from the results we validated the effectiveness of UPAS in the application of buried object detection.

scholarly journals Women Serial Killers in a Climate of Changing Gender Norms

2018 ◽  
Author(s):  
Elizabeth Benkart
Keyword(s):  
Multivariate Regression ◽  
Gulf Coast ◽  
Gender Norms ◽  
Serial Killer ◽  
Serial Killers ◽  
Florida Gulf Coast ◽  
Time Period ◽  
American Society ◽  
Second Wave ◽  
The Waves

Existing research suggests that patterns of both men and women serial killers are hyper-gendered. In American society, however, gender norms for women have dramatically changed over time. This study proposes that the patterns of women serial killers reflect the femininity ideals of the time period in which they operated in. The shifts in gender norms are operationalized by three time periods representative of the waves of feminism. The Radford/Florida Gulf Coast University’s serial killer database is used to establish a sample of 1,321 serial killers. Using multivariate regression analyses and controlling for age of last kill, which could potentially alter the kill method but be unrelated to gender, women serial killers do appear to be impacted by the femininity ideals of their time period but not as clearly as initially anticipated. Men serial killers were also found to be affected by changes in femininity ideals. Both women and men serial killers had more feminine kill patterns during the first wave of feminism, but men serial killers had a very violent, hyper-masculine peak during the second wave of feminism that women serial killers did not have.

scholarly journals CLUSTER–STAFF search coil magnetometer calibration – comparisons with FGM

2014 ◽  
Vol 3 (2) ◽  
pp. 153-177 ◽  
Author(s):  
P. Robert ◽  
N. Cornilleau-Wehrlin ◽  
R. Piberne ◽  
Y. de Conchy ◽  
C. Lacombe ◽  
...  
Keyword(s):  
Transfer Functions ◽  
Low Frequency ◽  
Temporal Analysis ◽  
Fluxgate Magnetometer ◽  
Data Sets ◽  
Spectral Matrix ◽  
Spatio Temporal ◽  
Cross Calibration ◽  
The Waves ◽  
The Way

Abstract. The main part of the Cluster Spatio-Temporal Analysis of Field Fluctuations (STAFF) experiment consists of triaxial search coils allowing the measurements of the three magnetic components of the waves from 0.1 Hz up to 4 kHz. Two sets of data are produced, one by a module to filter and transmit the corresponding waveform up to either 10 or 180 Hz (STAFF-SC), and the second by the onboard Spectrum Analyser (STAFF-SA) to compute the elements of the spectral matrix for five components of the waves, 3 × B and 2 × E (from the EFW experiment), in the frequency range 8 Hz to 4 kHz. In order to understand the way the output signals of the search coils are calibrated, the transfer functions of the different parts of the instrument are described as well as the way to transform telemetry data into physical units across various coordinate systems from the spinning sensors to a fixed and known frame. The instrument sensitivity is discussed. Cross-calibration inside STAFF (SC and SA) is presented. Results of cross-calibration between the STAFF search coils and the Cluster Fluxgate Magnetometer (FGM) data are discussed. It is shown that these cross-calibrations lead to an agreement between both data sets at low frequency within a 2% error. By means of statistics done over 10 yr, it is shown that the functionalities and characteristics of both instruments have not changed during this period.

Low-frequency noise control using layered granular aerogel and limp porous media

2021 ◽  
Vol 263 (4) ◽  
pp. 2724-2729
Author(s):  
Yutong Xue ◽  
Amrutha Dasyam ◽  
J. Stuart Bolton ◽  
Bhisham Sharma
Keyword(s):  
Noise Control ◽  
Glass Fibers ◽  
Low Frequency ◽  
Normal Incidence ◽  
Frequency Noise ◽  
Fibrous Materials ◽  
Low Frequency Noise ◽  
Frequency Range ◽  
Fibrous Media ◽  
Impedance Tube Method

The acoustic absorption of granular aerogel layers with a granule sizes in the range of 2 to 40 μm is dominated by narrow-banded, high absorption regions in the low-frequency range and by reduced absorption values at higher frequencies. In this paper, we investigate the possibility of developing new, low-frequency noise reduction materials by layering granular aerogels with traditional porous sound absorbing materials such as glass fibers. The acoustic behavior of the layered configurations is predicted using the arbitrary coefficient method, wherein the granular aerogel layers are modeled as an equivalent poro-elastic material while the fibrous media and membrane are modeled as limp media. The analytical predictions are verified using experimental measurements conducted using the normal incidence, two-microphone impedance tube method. Our results show that layered configurations including granular aerogels, fibrous materials, and limp membranes provide enhanced sound absorption properties that can be tuned for specific noise control applications over a broad frequency range.

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