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1

Ultrasonic wave attenuation measurement for nondestructive evaluation of concrete  

NASA Astrophysics Data System (ADS)

Various nondestructive evaluation methods using the propagating velocity and attenuation of an ultrasonic wave have been studied. The ultrasonic wave attenuation is more sensitive on evaluating to damage assessment in the medium than the ultrasonic wave velocity method. In this paper, the nondestructive evaluation technique using self-compensating frequency response function is proposed to measure the quantitative ultrasonic wave attenuation on cement-based materials. The proposed technique is able to measure inherent attenuation of material, not its relative attenuation. In advance, the reproducibility and relevancy of proposed technique are validated by an experimental comparison of conventional measurement and proposed ultrasonic wave attenuation measurement on cement-based material. In addition, the ultrasonic attenuation measurements are able to characterize the size distribution and volume fraction of entrained air voids in cement-based materials.

Yim, Hong Jae; Kim, Jae Hong; Kwak, Hyo-Gyoung

2010-03-01

2

Technique of Measurements of Elastic Wave Attenuation Parameters  

Microsoft Academic Search

Certain methodical aspects of using one of the active methods of acoustic testing of materials and products, namely, measurements of the frequency dependence of the attenuation coefficient are considered when the dependence of recorded results on the physical differences between the measurement channels is eliminated. The attenuation coefficients of transverse and longitudinal ultrasonic waves are estimated under the laboratory conditions

S. B. Teodorovich

2003-01-01

3

Measurements of Wave Attenuation Through Model and Live Vegetation in a Wave Tank  

NASA Astrophysics Data System (ADS)

It is well accepted that wetlands have an important role in shoreline protection against wave damage. However, there is still a lack of knowledge on primary mechanisms of wave attenuation though wetland vegetation. The purpose of this study was to understand these mechanisms and quantify the impact of vegetation on the waves through a series of laboratory experiments. Experiments were conducted in a wave tank at the USDA-ARS-National Sedimentation Laboratory to measure the rate of wave attenuation through emergent and submerged rigid and flexible cylindrical stems, and live vegetation. Dormant and healthy Spartina alterniflora and healthy Juncus romerianus, two common plant species in coastal areas, were used during the tests. The time series water surface elevation at five locations was recorded by wave probes and the water surface profile through the vegetation field was recorded using a digital video camera. The recorded data were analyzed with imaging techniques to identify the wave attenuation characteristic of wetland vegetation and drag coefficients.

Ozeren, Y.; Wren, D. G.

2010-12-01

4

Wave attenuation as a measure of muscle quality as measured by magnetic resonance elastography: Initial results  

Microsoft Academic Search

Advances in imaging technologies such as magnetic resonance elastography (MRE) have allowed researchers to gain insights into muscle function in vivo. MRE has been used to examine healthy and diseased muscle by calculating shear modulus. However, additional information can be measured from visualizing a mechanical wave as it passes through a tissue. One such measurable quantity is wave attenuation. The

Zachary J. Domire; Matthew B. McCullough; Qingshan Chen; Kai-Nan An

2009-01-01

5

Wave Attenuation by Artificial Seaweed.  

National Technical Information Service (NTIS)

A series of wave tank tests was conducted at this Center (CERC) to determine the ability of a field of low specific gravity artificial seaweed to attenuate wave action. Wave gages were located on both sides of the seaweed field to measure wave attenuation...

J. P. Ahrens

1976-01-01

6

Measurement of speed and attenuation of longitudinal elastic waves in optical fibers  

Microsoft Academic Search

A longitudinal elastic pulse is generated in a segment of optical fiber. A laser Doppler vibrometer is used to make noncontact measurements of the axial surface velocity at several locations along the optical fiber segment. The measured temporal phase shift and amplitude attenuation of the elastic pulse as it propagates between measurement locations are used to deduce the elastic wave

Brad M. Beadle; Jacek Jarzynski

2001-01-01

7

Measurement of the intrinsic attenuation of longitudinal waves in anisotropic material from uncorrected raw data.  

PubMed

Among the physical parameters characterising the interaction of the ultrasonic beam with its supporting medium, ultrasonic attenuation is an important input parameter to simulate wave propagation and defect-beam phenomena. The measurement of the intrinsic attenuation in anisotropic material however is a difficult task. The paper presents an approach to determine intrinsic attenuation in anisotropic materials such as austenitic stainless steel welds and cladding. It deals with improvements on the initial device, based on measurements on two samples with different thicknesses (10mm and 20mm). A previous paper presented preliminary results with this new approach for isotropic materials. PMID:23601966

Seldis, Thomas

2013-09-01

8

Measurements and mechanisms investigation of seismic wave attenuation for frequencies between 1 and 100 Hz  

NASA Astrophysics Data System (ADS)

Seismic wave attenuation at low frequencies in the earth crust has been explained by partial saturation as well as permeability models. We present results obtained by the Broad Band Attenuation Vessel (BBAV) which measures seismic wave attenuation using the sub-resonance method in the frequency range 0.01 - 100 Hz. The apparatus also allows the investigation of attenuation mechanisms related to fluid flow by means of five pore pressure sensors placed in the specimen. This allows continuous local measurements of pore pressure changes generated by stress field changes. Measurements were performed on 76 mm diameter, 250 mm long, 20% porosity, and ~500 mD permeability Berea sandstone samples. The confining pressure was varied between 0 and 20 MPa, and the specimens were saturated with water between 0% and 90%. Attenuation measurements show dependence with saturation. For instance, when samples are at dry conditions they exhibit attenuation values around 0.01, the same sample saturated with 90% water shows attenuation values between 0.018 and 0.028 across the entire frequency range. Attenuation is also confining pressure dependent. For instance, variations of confining pressure ranging between 0 and 8 MPa lead to quality factors between 40 and 10 at 60 Hz and 60% water saturation. Best fits on these measurements reveal that the corner frequency of the attenuation mechanism decreases from ~800 to ~200 Hz with increasing confining pressure. Using calibration measurements with Aluminum the possibility of apparatus resonances can be ruled out. Local pore pressure measurements corroborate this observation showing pore pressure evolution as a function of saturation. The results are discussed and interpreted in light of known attenuation mechanisms for partially saturated rocks (patchy saturation and squirt flow). We rule out the possibility of patchy saturation occurrence, but squirt flow would offer an explanation. The confining pressure dependence could be the result of crack closure which produces the corner frequency shift. Crack closure in similar samples and conditions (i.e. Berea sandstone at confining pressure less than 20 MPa) was also observed using ultrasonic tests.

Tisato, N.; Madonna, C.; Saenger, E. H.

2012-04-01

9

A theoretical approach to local attenuation measurements of shear waves by MRE. Preliminary experimental results  

NASA Astrophysics Data System (ADS)

An essential highlight of the presented method is the employment of Magnetic Resonance Elastography (MRE) for local measurements of the attenuation of elastic shear waves introduced into a biological sample. Such a measurement can be accomplished by combining the MRE method with those methods, in which collective displacement of spins is induced by external physical factors, such as variable electric field, strong magnetic field gradient or longitudinal elastic wave. A theoretical basis of the method involving external factors and results of preliminary experiments have been presented in this paper.

Klinkosz, Tomasz; Lewa, Czes?aw J.; Madelin, Guillaume; Thiaudiere, Eric

2005-09-01

10

Shear wave velocity and attenuation in the upper layer of ocean bottoms from long-range acoustic field measurements.  

PubMed

Several physics-based seabed geoacoustic models (including the Biot theory) predict that compressional wave attenuation ?(2) in sandy marine sediments approximately follows quadratic frequency dependence at low frequencies, i.e., ?(2)?kf(n) (dB/m), n=2. A recent paper on broadband geoacoustic inversions from low frequency (LF) field measurements, made at 20 locations around the world, has indicated that the frequency exponent of the effective sound attenuation n?1.80 in a frequency band of 50-1000 Hz [Zhou et al., J. Acoust. Soc. Am. 125, 2847-2866 (2009)]. Carey and Pierce hypothesize that the discrepancy is due to the inversion models' neglect of shear wave effects [J. Acoust. Soc. Am. 124, EL271-EL277 (2008)]. The broadband geoacoustic inversions assume that the seabottom is an equivalent fluid and sound waves interact with the bottom at small grazing angles. The shear wave velocity and attenuation in the upper layer of ocean bottoms are estimated from the LF field-inverted effective bottom attenuations using a near-grazing bottom reflection expression for the equivalent fluid model, derived by Zhang and Tindle [J. Acoust. Soc. Am. 98, 3391-3396 (1995)]. The resultant shear wave velocity and attenuation are consistent with the SAX99 measurement at 25 Hz and 1000 Hz. The results are helpful for the analysis of shear wave effects on long-range sound propagation in shallow water. PMID:23231101

Zhou, Ji-Xun; Zhang, Xue-Zhen

2012-12-01

11

Measurement of Attenuation Length for Radio Wave in Natural Rock Salt Samples Concerning Ultra High Energy Neutrino Detection  

NASA Astrophysics Data System (ADS)

Ultra high energy (UHE) neutrinos with the energy larger than 1015 eV, surely arrive at the earth with Greisen, Zatsepin, Kuz'min (GZK) effect, though the rate is very few. The rare call requires us to utilize a large mass (>10 Gton) of detection medium. UHE neutrino generates a huge number of unpaired electrons in rock salt. They would emit sensible radio wave by coherent Cherenkov (Askar'yan) effect. The longer attenuation length of radio wave in rock salt reduces the number of antennas required. Several rock salt samples including synthesized one are measured in attenuation length for radio wave transmission at 0.3 and 1.0 GHz. Some show attenuation length larger than 300 m, which indicate a possibility for constructing a salt neutrino detector.

Chiba, Masami; Watanabe, Yusuke; Yasuda, Osamu; Kamijo, Toshio; Chikashige, Yuichi; Kon, Tadashi; Amano, Akio; Takeoka, Yosito; Shimizu, Yutaka; Mori, Satoshi; Ninomiya, Sosuke

12

Propagation Velocity and Attenuation of a Shear Wave Pulse Measured by Ultrasound Detection in Agarose and Polyacrylamide Gels  

Microsoft Academic Search

The aim of our research was to measure and analyze phase velocity and pulse attenuation of a shear wave in two media: well-known agarose-gelatin gel and seldom-used polyacrylamide gel. These quantities were determined at three temperatures by the method of transmission sonoelastography described by Catheline et al. (1999). The shear wave was generated with a shaker stimulated by an electric

Tomasz Klinkosz; Czeslaw J. Lewa; Jacek Paczkowski

2008-01-01

13

Measurements of seismic wave attenuation for frequencies between 0.1 and 100 Hz in a Paterson Rig  

NASA Astrophysics Data System (ADS)

The study of wave attenuation in partially saturated porous rocks over a broad frequency range provides valuable information about reservoir fluid systems, which are inherently composed of multiple phase fluid. Following an original idea initiated by Luigi, we designed and set up a specific instrument, the Seismic Wave Attenuation Module (SWAM), to experimentally measure the bulk attenuation on partially saturated rocks at frequencies between 0.01 and 100 Hz, using natural rock samples under in situ conditions. We present its bench-top calibration, a series of data collected from different kind of rocks at different confing pressure and the numerical simulations, supporting the obtained results. We employ the sub-resonance test. Assuming that the rock behaves as a linear time invariant (LTI) system, the attenuation factor 1/Q (Q is the quality factor) is equal to the tangent of the phase shift between the stress and the strain signal. The new attenuation measurement equipment is calibrated in a gas apparatus (Paterson rig) using aluminum as elastic standard and Plexiglas as a viscoelastic standard. Measurements were performed on 25.4 mm diameter, 60 mm long samples. Berea sandstone samples with 20% porosity, and ~500 mD permeability have been measured at different saturation conditions. Attenuation measurements show dependence upon saturation. Moreover, measurements on two well-characterized shale samples have been performed. The two shales have significantly different quality factors; which result to be dependent on both the saturation state of the samples and the propagation direction of the oscillatory signal with respect to the sedimentary bedding. The attenuation coefficient parallel to bedding is less than that vertical to bedding. Thanks to Luigi's initiative and inspiration two generations of his Ph.D. students are now able to jointly present these new challenging experimental results.

Madonna, C.; Tisato, N.; Delle Piane, C.; Saenger, E. H.

2012-04-01

14

FRACTIONAL WAVE EQUATIONS WITH ATTENUATION  

PubMed Central

Fractional wave equations with attenuation have been proposed by Caputo [5], Szabo [27], Chen and Holm [7], and Kelly et al. [11]. These equations capture the power-law attenuation with frequency observed in many experimental settings when sound waves travel through inhomogeneous media. In particular, these models are useful for medical ultrasound. This paper develops stochastic solutions and weak solutions to the power law wave equation of Kelly et al. [11].

Straka, Peter; Meerschaert, Mark M.; McGough, Robert J.; Zhou, Yuzhen

2013-01-01

15

Measurement of alkali–silica reaction progression by ultrasonic waves attenuation  

Microsoft Academic Search

Development of non-destructive methods, developed specifically for assessing the damage induced by alkali–silica reaction (ASR) in concrete structures, is needed in order to carry out a systematic evaluation of the concrete condition. The aim of this study is to monitor the evolution of the ASR-damage in laboratory with concrete samples with ultrasonic pulse velocity and attenuation of ultrasonic waves methods.

François Saint-Pierre; Patrice. Rivard; Gérard Ballivy

2007-01-01

16

Feasibility Study of Grain Size Estimation of S45C by Attenuation Measurement of 40 MHz Surface Acoustic Wave Generated by Phase Velocity Scanning of Laser Interference Fringes  

Microsoft Academic Search

Structural change in 0.45 mass % carbon steel during tempering was measured nondestructively as a change in the attenuation coefficient of 40 MHz surface acoustic waves (SAW) generated by scanning interference fringes (SIF). The SIF selectively generate the SAW at an adequate center frequency, which is useful to distinguish the attenuation coefficients between slightly different structures. The attenuation coefficient at

Hideo Nishino; Tsutomu Furukawa; Sunao Takashina; Mikio Takemoto

2000-01-01

17

Through Transmission Technique for Ultrasonic Attenuation Measurement Using Broadband, Plane Wave Pulses  

Microsoft Academic Search

One problem with present pulse-echo or through transmission, phase sensitive methods for measuring ultrasonic attenuation coefficients is that d iffraction corrections are necessary because of the finite size o f the source. Another difficulty common to spectral subtraction methods lies in generating an acoustic pulse with sufficient energy over the frequency range of interest. These problems can be ameliorated by

Gerald K. Harris; Bruce A. Herman; Stephen W. Smith; William J. Bodine

1983-01-01

18

Measurement of Attenuation Length in Rock Salt and Limestone in Radio Wave for Ultra-High Energy Neutrino Detector  

NASA Astrophysics Data System (ADS)

Rock salt and limestone are studied to determine their suitability for use as a radio wave transmission medium in an ultra high energy (UHE) cosmic neutrino detector. The detector would detect radio wave generated by the Askar'yan effect (coherent Cherenkov from negative excess charges in an electromagnetic shower) in the interaction of the UHE neutrinos with the high-density medium. We have measured the radio wave attenuation lengths of the rock salt samples from the Asse mine in Germany at 9.4 GHz and found it to be longer than 3.3 m and then whereas under the assumption of constant tan? with respect to frequency, we estimate it by extrapolation to be longer than 330 m at 94 MHz.

Chiba, Masami; Kawaki, Miho; Inuzuka, Masahide; Kamijo, Toshio; Athar, H.

2002-09-01

19

Midperiod Rayleigh wave attenuation model for Asia  

NASA Astrophysics Data System (ADS)

We present an attenuation model for midperiod Rayleigh waves in Central Asia and surrounding regions. This model is defined by maps of attenuation coefficient across the region of study in the period band 14-24 s. The model is constructed to characterize the regional variations in attenuation of seismic waves in the crust, which are related to the tectonic history of the studied territory, to calibrate the regional surface-wave magnitude scale, and to extend the teleseismic 'surface-wave magnitude - body wave magnitude' (Ms-mb) discriminant to regional distances. The construction of the model proceeds in three stages. The first stage in model construction is the measurement of Rayleigh wave spectral amplitudes. We collected and processed waveform data for 200 earthquakes occurring from 2003 to 2006 inside and around Eurasia, and used records of about 135 broadband permanent and temporary stations. This data set provided a sufficient number of spectral amplitude measurements between 14 and 24 s periods for the construction of two-dimensional tomographic maps of attenuation coefficients. At the second stage of the work, the integral of attenuation coefficients along given paths is estimated using both inter-station measurements and single-station measurements corrected for source and receiver terms. The third stage includes the refining of source parameters, recalculation of attenuation coefficient integrals after this refinement, grooming of resulting coefficients, and multistage tomographic inversion of the data. Tomographic maps for the set of periods from 14 to 24 s, which exhibit clear correlation with geology and tectonics of the territory under study, were obtained. Validation of these maps using the inter-station measurements confirms their accuracy in predicting the observations.

Levshin, Anatoli L.; Yang, Xiaoning; Barmin, Mikhail P.; Ritzwoller, Michael H.

2010-08-01

20

Attenuation of Shock Waves in Solids.  

National Technical Information Service (NTIS)

Attenuation of shock waves was studied in annealed 1060 aluminum, 2024-T351 aluminum, and Teflon by impacting samples with explosively driven aluminum plates. Free-surface velocities were measured as a function of target thickness by recording the time of...

A. B. Christensen G. R. Fowles J. O. Erkman

1966-01-01

21

Ultrasonic measurements of Young's modulus and extensional wave attenuation in refractory metal wires at elevated temperatures with application to ultrasonic thermometry  

Microsoft Academic Search

Ultrasonic velocity and attenuation measurements have been made by traveling-wave methods on several refractory metals and their alloys. Broad-band pulses centered around 120 kHz were used for extensional waves (and some torsional waves) in wire specimens. Elastic moduli calculated from the velocities decrease with increasing temperature; the slope increases in magnitude at about half the absolute melting point. At the

E. P. Papadakis; K. A. Fowler; L. C. Lynnworth; A. Robertson; E. D. Zysk

1974-01-01

22

Measuring sea ice permeability as a function of the attenuation and phase velocity shift of an acoustic wave  

NASA Astrophysics Data System (ADS)

Sea ice is a two-phase porous medium consisting of a solid matrix of pure ice and a salty liquid phase. At spring when ice permeability increases, it has been observed that pressure gradients induced at the ice-water interface upstream and downstream of pressure ridge keels can cause sea water and brine to be forced through the ice water boundary. It suggests that salt and heat fluxes through the bottom ice layers may be a major factor controlling the decay of an ice sheet. Knowing how water flows through the ice matrix is fundamental to a modeling of ocean-ice heat exchanges integrating the advective import/export of latent heat that result from melting/freezing within the ice. Permeability is the measurement of the ease with which fluids flow through a porous medium, however one of the most tricky to measure without altering the porosity of the sampled medium. To further complicate the challenge, horizontal and vertical permeability of the ice, referred as ice anisotropy, is significant. Acoustic wave propagation through porous media have been theorized to relate the acoustic velocity and attenuation to the physical properties of the tested material. It is a non-invasive technique, and as such could provide more reliable measurements of sea ice permeability than anything presently used. Simulations combining the Biot's and squirt flow mechanisms are performed to investigate the effect of permeability on the attenuation and phase velocity as a function of frequency. We first present the attenuation dispersion curves for an isotropic sea ice, then low-frequency and high-frequency limits are determined. Optimal frequency range and resolution requirements are evaluated for testing.

Hudier, E. J.; Bahoura, M.

2012-12-01

23

Measurement of Attenuation Length for UHF Radio Wave in Natural Rock Salt Samples Concerning Ultra High Energy Neutrino Detection  

NASA Astrophysics Data System (ADS)

Ultra high energy (UHE ) neutrinos (E > 1015 eV) exist at any rate due to presence of the cosmic microwave background and UHE cosmic rays implied by Greisen, Zatsepin and Kuz'min (GZK). The low rate of GZK neutrinos requires us to utilize a large mass (> 50 Gton) of detection medium. The UHE neutrino generates a huge number of unpaired electrons in rock salt. They would emit sensible radio wave by coherent Cherenkov effect (Askar'yan effect). Attenuation lengths of natural rock salt samples including synthesized one at 0.3 and 1.0 GHz were measured to find a suitable site constructing a salt neutrino detector. The result indicates a possibility for constructing the salt neutrino detector with economical antenna spacing.

Chiba, Masami; Watanabe, Yusuke; Takayama, Yasuhiro; Fujii, Masatoshi; Yasuda, Osamu; Yabuki, Fumiaki; Shibasaki, Yuji; Kamijo, Toshio; Chikashige, Yuichi; Kon, Tadashi; Amano, Akio; Takeoka, Yoshito; Shimizu, Yutaka; Mori, Satoshi; Ninomiya, Sosuke; Utsumi, Michiaki

2007-03-01

24

Feasibility Study of Grain Size Estimation of S45C by Attenuation Measurement of 40 MHz Surface Acoustic Wave Generated by Phase Velocity Scanning of Laser Interference Fringes  

NASA Astrophysics Data System (ADS)

Structural change in 0.45 mass % carbon steel during tempering was measured nondestructively as a change in the attenuation coefficient of 40 MHz surface acoustic waves (SAW) generated by scanning interference fringes (SIF). The SIF selectively generate the SAW at an adequate center frequency, which is useful to distinguish the attenuation coefficients between slightly different structures. The attenuation coefficient at 40 MHz increased linearly with heating time (30, 60 and 90 min) at 750°C, representing a minute change in the structure of ferrite and pearlite grains. The method revealed a minute structural change in the ferrite-pearlite ratio and in grain size growth due to the heat treatment.

Nishino, Hideo; Furukawa, Tsutomu; Takashina, Sunao; Takemoto, Mikio

2000-05-01

25

Measurement of the speed and attenuation of the Biot slow wave using a large ultrasonic transmitter  

Microsoft Academic Search

Two compressional wave modes, a fast P1 and a slow P2, propagate through fluid-saturated porous and permeable media. This contribution focuses on new experimental tests of existing theories describing wave propagation in such media. Updated observations of this P2 mode are obtained through a water-loaded, porous sintered glass bead plate with a novel pair of ultrasonic transducers consisting of a

Youcef Bouzidi; Douglas R. Schmitt

2009-01-01

26

Broadband Attenuation Measurement for an Absorbing Plate  

SciTech Connect

This research demonstrates the effectiveness of combining laser ultrasonic and appropriate time-frequency signal analysis techniques for attenuation measurements of leaky Lamb waves. Laser ultrasonic techniques provide a non-contact, high-fidelity system of generating and detecting Lamb waves, which is critical for amplitude measurements. Time-frequency signal analysis techniques are used to study the dispersive behavior of Lamb waves and interpret broadband, transient signals. With a series of narrowband, bandpass filtering of time-domain signals from more than two positions, attenuation for each mode at specific frequencies can be calculated. This combined technique is tested with an aluminum plate with water half-space on one side. The experimental results show that the proposed technique captures changes in multi-mode attenuation over a broad frequency range, and the attenuation values are in good agreement with the results predicted by an analytical model where Lamb wave modes are well separated in the time-frequency domain.

Luangvilai, K. [School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0355 (United States); Jacobs, L.J. [School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0355 (United States); G.W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0405 (United States); Wilcox, P.D. [Department of Mechanical Engineering, University of Bristol, Bristol, BS8 1TR (United Kingdom); Lowe, M.J.S. [Department of Mechanical Engineering, Imperial College, London, SW7 2AZ (United Kingdom); Qu, J. [G.W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0405 (United States)

2005-04-09

27

Anomalous attenuation of extraordinary waves in ionosphere heating experiments  

NASA Astrophysics Data System (ADS)

Multiple scattering from artificial irregularities, HF-induced in the ionospheric F region, may cause significant attenuation of both ordinary and extraordinary radio waves in addition to the anomalous absorption of ordinary waves by their conversion into plasma waves. We have confirmed the existence and detailed features of this effect at the Sura heating facility by measurements of the attenuation of the powerful pump wave and weak probing waves of extraordinary polarization. Extraordinary waves are attenuated during heating, 1.5-12 dB below a background (nonheating) attenuation value caused by scattering from natural irregularities. Irregularities involved into the multiple scattering process have geomagnetic field-transverse scales of l? ˜ 0.1-1 km. To determine characteristics of these irregularities, a simple inverse problem solution procedure is implemented.

Zabotin, N. A.; Bronin, A. G.; Zhbankov, G. A.; Frolov, V. L.; Komrakov, G. P.; Mityakov, N. A.; Sergeev, E. N.

2002-12-01

28

Attenuation of ultrasonic waves in rolled metals  

Microsoft Academic Search

Scattering of ultrasonic waves in polycrystals with texture is studied in this article. The attenuations of the three wave modes are determined as a function of dimensionless frequency and propagation direction, respectively, for given orientation distribution coefficients (ODCs). The calculation is done in the case of a statistically orthorhombic sample made up of cubic crystallites. The wave propagation and scattering

Liyong Yang; Joseph A. Turner

2004-01-01

29

Surface Wave Dispersion and Attenuation Model for the Middle East  

NASA Astrophysics Data System (ADS)

LLNL has been developing a surface wave model of the Middle East. In conjunction with collaborators in Saudi Arabia, we have obtained new waveform data from stations in the region and have made thousands of additional surface wave dispersion measurements. These measurements are used to create updated Rayleigh and Love wave group velocity maps which have high-resolution over a wide period band. We have also recently completed the development of the Surface Wave Amplitude Processor (SWAP) tool for making high quality measurements of surface wave amplitudes. The amplitude measurements can be used in a tomography for surface wave attenuation. In general, surface wave amplitude measurements are more difficult to make than group velocity dispersion measurements because information about the source amplitude is needed, requiring a moment tensor solution. Having a focal mechanism is also needed to avoid making measurements at radiation nodes, where amplitudes can be contaminated by multi-pathing. Fortunately, dozens of moment tensor solutions have been determined using regional waveform methods, complementing the large number of Global CMT solutions in the region. We will be presenting preliminary surface wave attenuation maps based on the path measurements from stations in Saudi Arabia and nearby countries. The attenuation maps will be compared and contrasted with our dispersion maps and analyzed for information about the attenuation properties of the sediments, crystalline crust, and upper mantle of the Arabian Peninsula.

Pasyanos, M. E.; Dodge, D. A.; Al-Amri, A. M.

2011-12-01

30

UHF Radio Wave Attenuation Factor Database  

NASA Astrophysics Data System (ADS)

As is known each sea-going vessel is equipped with navigation, communication and other radio engineering facilities that serve to secure the safety of navigation and are chiefly operated at UHF-wave band. In developing these systems and calculating the energy potential for a necessary coverage range one should be well aware of the radio signal attenuation processes on a propagation path. The key parameter of this path is the (radio) wave attenuation factor V and its distance dependence V(R). A diversity of factors influencing the radio signal attenuation over the oceanic expanses, especially well pronounced and quite stable tropospheric ducts, and the lack of experimental data were the compelling reasons why the researchers of the Institute for Radiophysics and Electronics, NASU, had spent many years on comprehensive radiophysical investigations carried out in different regions of the Atlantic, Indian, Arctic and Pacific Oceans. The experimental data obtained allow creating the database of radio wave attenuation factor V.

Khomenko, S. I.; Kostina, V. L.; Mytsenko, I. M.; Roenko, A. N.

2007-07-01

31

Experimental Investigation of Wave Attenuation Through Vegetation  

NASA Astrophysics Data System (ADS)

Wetlands and coastal vegetation can reduce the surge and wave impact on coastal areas. Yet, the primary mechanisms of wave mitigation by vegetation are still unclear. The objective of this study was to investigate and quantify the attenuation of waves through vegetation using laboratory experiments. The wave attenuation properties of artificial vegetation and live and dormant S. alterniflora and J. roemerianus were investigated under monochromatic and irregular wave conditions at full scale in a wave tank facility at the USDA-ARS-National Sedimentation Laboratory in Oxford, Mississippi. Water level sensors and a video camera were used to record water level data. Drag coefficients were estimated for artificial and natural plants and regression equations were derived for the drag coefficients as functions of both Reynolds and Keulegan-Carpenter number. It was observed that vertical variation of vegetation density had an important effect on the drag coefficient.

Ozeren, Y.; Wren, D. G.

2011-12-01

32

Precise measurements of bulk-wave ultrasonic velocity dispersion and attenuation in solid materials in the VHF range.  

PubMed

A general method was established for precisely measuring velocity dispersion and attenuation in solid specimens with acoustic losses in the very high frequency (VHF) range, using the complex-mode measurement method and the diffraction correction method. Experimental procedures were presented for implementing such a method and demonstrated this measurement method in the frequency range of 50-230 MHz, using borosilicate glass (C-7740) as a dispersive specimen and synthetic silica glass (C-7980) as a nondispersive standard specimen. C-7980 exhibited no velocity dispersion; velocity was constant at 5929.14 +/- 0.03 m/s. C-7740 exhibited velocity dispersion, from 5542.27 m/s at 50 MHz to 5544.47 m/s at 230 MHz with an increase of about 2 m/s in the measured frequency range. When frequency dependence of attenuation was expressed as alpha = alpha(0)f(beta), the results were as follows: alpha0 = 1.07 x 10(-16) s2/m and beta = 2 for C-7980 and alpha0 = 5.16 x 10(-9) s(1.25)/m and beta = 1.25 for C-7740. PMID:12822789

Kushibiki, Jun-ichi; Okabe, Ryoichi; Arakawa, Mototaka

2003-06-01

33

Precise measurements of bulk-wave ultrasonic velocity dispersion and attenuation in solid materials in the VHF range  

NASA Astrophysics Data System (ADS)

A general method was established for precisely measuring velocity dispersion and attenuation in solid specimens with acoustic losses in the very high frequency (VHF) range, using the complex-mode measurement method and the diffraction correction method. Experimental procedures were presented for implementing such a method and demonstrated this measurement method in the frequency range of 50-230 MHz, using borosilicate glass (C-7740) as a dispersive specimen and synthetic silica glass (C-7980) as a nondispersive standard specimen. C-7980 exhibited no velocity dispersion; velocity was constant at 5929.14+/-0.03 m/s. C-7740 exhibited velocity dispersion, from 5542.27 m/s at 50 MHz to 5544.47 m/s at 230 MHz with an increase of about 2 m/s in the measured frequency range. When frequency dependence of attenuation was expressed as ?=?0f?, the results were as follows: ?0=1.07×10-16 s2/m and ?=2 for C-7980 and ?0=5.16×10-9 s1.25/m and ?=1.25 for C-7740.

Kushibiki, Jun-Ichi; Okabe, Ryoichi; Arakawa, Mototaka

2003-06-01

34

Ultrasonic Attenuation Measurement by Spectral Ratios Utilizing Signal Processing Techniques  

Microsoft Academic Search

A new approach using signal averaging and signal processing is described for measuring ultrasonic attenuation of compressional (P) and shear (S) waves in highly attenuative (low Q) materials. Broadband ultrasonic pulses in the frequency range of 0.7-1.1 MHz are transmitted through a specimen to be characterized for comparison to a reference with low dissipation. Attenuation is calculated from the ratio

Frederick M. Sears; Brian P. Bonner

1981-01-01

35

Improved CW Technique for Measurement of Ultrasonic Attenuation.  

National Technical Information Service (NTIS)

A technique is described for measuring ultrasonic attenuation by determining the inflectional points of ultrasonic standing wave resonances. Measurements on tantalum are reported. Results obtained by this technique agree with those obtained by the pulse e...

R. G. Leisure

1972-01-01

36

Stress wave attenuation in shock-damaged rock  

NASA Astrophysics Data System (ADS)

The velocity and attenuation of ultrasonic stress waves in gabbroic rock samples (San Marcos, California) subjected to shock loading in the 2 GPa range were studied. Prom P wave velocity measurements we determined the damage parameter Dp and crack density ? of the samples and related these to the attenuation coefficient (quality factor) under dynamic strains of 2×10-7 and at a frequency of 2 MHz using the ultrasonic pulse-echo method. A fit to the data yields the P wave spatial attenuation coefficient at a frequency of 2 MHz, ?p(Dp) = 1.1 + 28.2DP (decibels per centimeter). From the relation between the attenuation coefficient and quality factor, the quality factor Q is given by Q-1 = 0.011(1 + 25.6Dp)(1 - Dp)½. Using O'Connell-Budiansky theory relating crack density to velocity, the parameter in Walsh's theory was determined based on experimental data. An approximate method is also proposed to estimate the average half-length of cracks based on the attenuation measurements.

Liu, Cangli; Ahrens, Thomas J.

1997-03-01

37

Review of methods to attenuate shock/blast waves  

NASA Astrophysics Data System (ADS)

Quick and reliable shock wave attenuation is the goal of every protection facility and therefore it is not surprising that achieving this has drawn much attention during the past hundred years. Different options have been suggested; their usefulness varying from a reasonable protection to the opposite, a shock enhancement. An example for a suggestion for shock mitigation that turned out to be an enhancement of the impinging shock wave was the idea to cover a protected object with a foam layer. While the pressure behind the reflected shock wave from the foam frontal surface was smaller than that recorded in a similar reflection from a rigid wall [25], the pressure on the “protected” surface, attached to the foam's rear-surface, was significantly higher than that recorded in a similar reflection from a bare, rigid wall [11]. In protecting humans and installations from destructive shock and/or blast waves the prime goal is to reduce the wave amplitude and the rate of pressure increase across the wave front. Both measures result in reducing the wave harmful effects. During the past six decades several approaches for achieving the desired protection have been offered in the open literature. We point out in this review that while some of the suggestions offered are practical, others are impractical. In our discussion we focus on recent schemes for shock/blast wave attenuation, characterized by the availability of reliable measurements (notably pressure and optical diagnostics) as well as high-resolution numerical simulations.

Igra, O.; Falcovitz, J.; Houas, L.; Jourdan, G.

2013-04-01

38

Fault-zone attenuation of high-frequency seismic waves  

NASA Astrophysics Data System (ADS)

We have developed a technique to measure seismic attenuation within an active fault-zone at seismogenic depths. Utilizing a pair of stations and pairs of earthquakes, spectral ratios are performed to isolate attenuation produced by wave-propagation within the fault-zone. This empirical approach eliminates common source, propagation, instrument and near-surface site effects. The technique was applied to a cluster of 19 earthquakes recorded by a pair of downhole instruments located within the San Andreas fault-zone, at Parkfield California. Over the 1-40 Hz bandwidth used in this analysis, amplitudes are found to decrease exponentially with frequency. Furthermore, the fault-zone propagation distance correlates with the severity of attenuation. Assuming a constant Q attenuation operator, the S-wave quality factor within the fault-zone at a depth of 5-6 kilometers is 31 (+7,-5). If fault-zones are low-Q environments, then near-source attenuation of high-frequency seismic waves may help to explain phenomenon such as fmax. Fault-zone Q may prove to be a valuable indicator of the mechanical behavior and rheology of fault-zones. Specific asperities can be monitored for precursory changes associated with the evolving stress-field within the fault-zone. The spatial and temporal resolution of the technique is fundamentally limited by the uncertainty in earthquake location and the interval time between earthquakes.

Blakeslee, Sam; Malin, Peter; Alvarez, Marcos

1989-11-01

39

Laboratory experiments on ultrasonic wave attenuation in partially frozen brines  

NASA Astrophysics Data System (ADS)

In order to estimate the amount of methane hydrates (MHs) which form in marine sediments at water depths greater than a few hundred meters, using not only velocity information but also attenuation information can provide much more information about MH-bearing sediments. While the presence of MH increases seismic velocity in the host sediment, recent works on sonic logging data show that sonic waveforms are also significantly affected by the presence of MH. However, the increase of attenuation with increasing velocity is somewhat unintuitive. Thus, it is important to validate these phenomena by experimental study and elucidate the rock physical mechanism responsible for these phenomena. In this study, we conducted laboratory measurements to explain partially the reason for the physically unrealizable phenomenon. The ice generated from brine was assumed to be methane hydrate, namely, partially frozen brine was considered to be as an analogue for a mixture of methane hydrate and water present in the pore space of hydrate bearing sediments. We observed the variations of a transmitted wave with frequency content of 150-1000 kHz through a liquid system to a solid-liquid coexistence system, changing its temperature from 20 to -15 C. The centroid frequency shift technique is adapted to the determination of P-wave attenuation. As a result, P-wave velocity increases up to about 3500 m/s with changing in a solid-liquid coexistence system from a liquid system, while P-wave attenuation increases with changing in a solid-liquid coexistence system from a liquid. Especially in a solid-liquid coexistence system, P-wave attenuation decreases with decreasing unfrozen brine. Our observations indicate that the interaction in a micro scale of the solid and liquid causes the dissipation of transmitted wave energy.

Matsushima, J.; Suzuki, M.; Kato, Y.; Rokugawa, S.

2006-12-01

40

Sonic well logging tool longitudinal wave attenuator  

SciTech Connect

This patent describes an attenuator for use with a well logging tool in attenuating a wave propagating longitudinally along the tool when the tool is disposed in a borehole of an oil well. It comprises: a plurality of layers of a first material. The first material including metal washers; a plurality of layers of a second material interleaved with the plurality of layers of the first material. The second material including rubber-like washers; and an inner member. The interleaved rubber-like washers and metal washers being wrapped around the inner member. The inner member including an outwardly directed flange on which one end of the interleaved rubber-like washers and metal washers rest.

Wignall, A.H.; Hoyle, D.C.

1989-10-10

41

Experimental Study of Atmospheric Visibility and Optical Wave Attenuation for Free Space Optics Communications  

Microsoft Academic Search

Optical wave attenuation due to low atmospheric visibility conditions causes a performance degradation of free- space optical (FSO) communication systems. Both visibility and attenuation are measured on a 100-meter long experimental free space optical link operating with a wavelength of 830 nm. Meteorological conditions causing particular attenuation events are identified. Available models of the relation between atmospheric visibility and optical

Martin Grabner; Vaclav Kvicera

42

Effects of pore pressure on compressional wave attenuation in a young oceanic basalt  

Microsoft Academic Search

Laboratory data are reported for ultrasonic compressional wave attenuation (alphap) as a function of pore pressure in a Juan de Fuca Ridge dredge basalt. Four experiments have been made to determine the relationships between attenuation and quality factor (Qp) and confining and pore pressures in the shallow ocean crust. Attenuation was measured at 1) a constant differential pressure of 40

Michael J. Tompkins; Nikolas I. Christensen

1999-01-01

43

Attenuation of ultrasonic interface waves on metal-polymer-metal boundaries  

NASA Technical Reports Server (NTRS)

The measured sensitivity of interface wave attenuation to defects near the bondline and to variations in the viscosity of the adhesive layer was compared with theoretical changes predicted by the Rokhin model. Differential interferometric optical measurements of interface wave attenuation due to defects near glass polymer metal boundaries are discussed. Pitch catch and pulse echo methods which use variable angle wedge transducers to generate and receive modified interface waves and to measure large bondline defects and adhesive viscosity are described.

Claus, R. O.

1981-01-01

44

State of the art of SWAM: Seismic Wave Attenuation Module  

NASA Astrophysics Data System (ADS)

The study of wave attenuation in partially saturated porous rock over a broad frequency range provides valuable information about the fluid system in reservoirs, which is inherently a multiple phase fluid system. Until now, few laboratory data have been collected in the seismically relevant low frequency range. Therefore, actual data on partially saturated rock are very limited. The main goal of our work is to accurately measure the bulk seismic attenuation at in situ conditions in laboratory. Bench top results show consistency with the few reported experimental data of dry, partially and fully saturated rocks. We report the new apparatus setup to measure seismic wave attenuation at room pressure and temperature on a rock sample of 60mm length and 25.4mm diameter. Our method uses bulk strain measurements, accomplished by measuring the strain across the whole sample with micro-linear variable differential transformers. We can cover the frequency range from 0.1-100 Hz. The results on a sample of Berea Sandstone, with different degrees of saturation, and the calibration data obtained with a standard aluminum sample are described. The acquisition software and the hardware are presented, together with the final goal: the implementation of the attenuation module within a Paterson gas-medium apparatus. This adaptation will allow conducting experiments at confining pressure and depth-temperatures.

Madonna, C.; Tisato, N.; Boutareaud, S.; Burg, J.

2010-12-01

45

Laboratory velocities and attenuation of P-waves in limestones during freeze-thaw cycles  

Microsoft Academic Search

The velocity and the attenuation of compressional P-waves, measured in the laboratory at ultrasonic frequencies during a series of freezing and thawing cycles, are used as a method for predicting frost damage in a bedded limestone. Pulse transmission and spectral ratio techniques are used to determine the P-wave velocities and the attenuation values relative to an aluminum reference samples with

Jean-Michel Remy; M. Bellanger; F. Homand-Etienne

1994-01-01

46

Lateral variations of coda wave attenuation in the Alps  

NASA Astrophysics Data System (ADS)

We explore lateral variations of coda wave attenuation in the French Alps and surrounding regions. The area of investigation extends from the Rhine Graben in the north, to the northern Apennine Range in the south, and includes the Eastern and Western Alps. Following the classical work of Aki and Chouet (1975), coda wave attenuation has been characterized by measuring the coda quality factor of short-period S waves (Qc). We have selected about 2000 weak to moderate earthquakes, with magnitudes ranging from 3 to 5. Waveform data recorded by permanent seismic networks have been collected at the ORFEUS data center through the ArcLink protocol. Qc has been measured in five frequency bands [1-2], [2-4], [4-8], [8-16], [16-32] Hz, by applying a simple linear regression to the smooth energy envelopes of seismograms in the time domain. Various choices of coda window length (Lw), and coda onset time (tw, as measured from the origin time) have been tested to ensure that our measurements are free from any systematic effects of lapse-time dependence in the range of epicentral distance considered. The optimal choice, which simultaneously maximizes the geographical coverage and minimizes the measurement biases, is obtained for Lw=50s and tw=70s, for epicentral distances smaller than 180 km. The map of Qc is obtained by discretizing the Alpine region into pixels of dimension (20km x 20km). For each source/receiver pair, the estimated value of Qc is distributed along the direct ray path. An average over all paths that cross an individual pixel is performed to obtain the local value of Qc. A spatial smoothing over an area covering a square of 9 pixels is subsequently applied. The maps of Qc display strong lateral variations of attenuation in the Alpine area. At all frequencies, the ratio between the lowest and largest value of Qc is typically larger than 2. The attenuation pattern is complex but relatively independent of frequency. A notable exception is a low attenuation region located between Torino and Geneva, which is clearly visible in the 1-2 Hz frequency band and disappears at higher frequencies. Some geological formations such as the Upper Rhine Graben and the eastern Alps show up clearly on the maps and systematically exhibit lower attenuation than the Po Valley and the Apennines. The French Alps are characterized by an attenuation gradient increasing from the north-west to the south-east. The typical scale of the spatial variations of the coda quality factor is of the order of 100km, which suggests rapid lateral variation of attenuation properties in the crust.

Mayor, Jessie; Calvet, Marie; Margerin, Ludovic; Traversa, Paola

2014-05-01

47

Millimeter wave attenuation prediction using a piecewise uniform rain rate model  

NASA Technical Reports Server (NTRS)

A piecewise uniform rain rate distribution model is introduced as a quasi-physical model of real rain along earth-space millimeter wave propagation paths. It permits calculation of the total attenuation from specific attenuation in a simple fashion. The model predications are verified by comparison with direct attenuation measurements for several frequencies, elevation angles, and locations. Also, coupled with the Rice-Holmberg rain rate model, attenuation statistics are predicated from rainfall accumulation data.

Persinger, R. R.; Stutzman, W. L.; Bostian, C. W.; Castle, R. E., Jr.

1980-01-01

48

Seismic attenuation: Laboratory measurements in fluid saturated rocks  

NASA Astrophysics Data System (ADS)

Seismic wave attenuation could be used as an indicator of reservoir fluids due to its dependence on rock and fluid properties. Over the past 30 years, many laboratory methodologies to study attenuation in rocks have been employed, such as ultrasonic (MHz), resonant bar (kHz) and forced oscillation methods in the low frequency range (0.01-100Hz) (Tisato & Madonna 2012; Madonna & Tisato 2013). Forced oscillation methods have gained prominence over time as the frequency range of measurements correspond to that of field seismic data acquired for oil/gas exploration. These experiments measure attenuation as the phase shift between the applied stress (sinusoidal) and measured strain. Since the magnitudes of measured phase shifts are quite low (Q-1 ~0.01-0.1) and the amplitudes of strain applied to the rock samples are of the order ~10-6 (i.e., similar orders of magnitude to seismic waves), it is challenging. A comparison of such forced oscillation setups will be presented to provide an overview of the various possibilities of design and implementation for future setups. In general, there is a lack of laboratory data and most of the published data are for sandstones. Currently, attenuation measurements are being carried out on carbonate and sandstone samples. We employ the Seismic Wave Attenuation Module (SWAM, Madonna & Tisato 2013) to measure seismic attenuation in these samples for different saturation degrees (90% and 100% water) and under three different confining pressures (5, 10 and 15MPa). Preliminary results from these investigations will be discussed. REFERENCES Madonna, C. & Tisato, N. 2013: A new seismic wave attenuation module to experimentally measure low-frequency attenuation in extensional mode. Geophysical Prospecting, doi: 10.1111/1365-2478.12015. Tisato, N. & Madonna, C. 2012: Attenuation at low seismic frequencies in partially saturated rocks: Measurements and description of a new apparatus. Journal of Applied Geophysics, 86, 44-53.

Subramaniyan, Shankar; Madonna, Claudio; Tisato, Nicola; Saenger, Erik; Quintal, Beatriz

2014-05-01

49

A heterogeneous nonlinear attenuating full-wave model of ultrasound.  

PubMed

A full-wave equation that describes nonlinear propagation in a heterogeneous attenuating medium is solved numerically with finite differences in the time domain (FDTD). Three-dimensional solutions of the equation are verified with water tank measurements of a commercial diagnostic ultrasound transducer and are shown to be in excellent agreement in terms of the fundamental and harmonic acoustic fields and the power spectrum at the focus. The linear and nonlinear components of the algorithm are also verified independently. In the linear nonattenuating regime solutions match results from Field II, a well established software package used in transducer modeling, to within 0.3 dB. Nonlinear plane wave propagation is shown to closely match results from the Galerkin method up to 4 times the fundamental frequency. In addition to thermoviscous attenuation we present a numerical solution of the relaxation attenuation laws that allows modeling of arbitrary frequency dependent attenuation, such as that observed in tissue. A perfectly matched layer (PML) is implemented at the boundaries with a numerical implementation that allows the PML to be used with high-order discretizations. A -78 dB reduction in the reflected amplitude is demonstrated. The numerical algorithm is used to simulate a diagnostic ultrasound pulse propagating through a histologically measured representation of human abdominal wall with spatial variation in the speed of sound, attenuation, nonlinearity, and density. An ultrasound image is created in silico using the same physical and algorithmic process used in an ultrasound scanner: a series of pulses are transmitted through heterogeneous scattering tissue and the received echoes are used in a delay-and-sum beam-forming algorithm to generate a images. The resulting harmonic image exhibits characteristic improvement in lesion boundary definition and contrast when compared with the fundamental image. We demonstrate a mechanism of harmonic image quality improvement by showing that the harmonic point spread function is less sensitive to reverberation clutter. PMID:19411208

Pinton, Gianmarco F; Dahl, Jeremy; Rosenzweig, Stephen; Trahey, Gregg E

2009-03-01

50

Measurement and implications of frequency dependence of attenuation  

NASA Astrophysics Data System (ADS)

Constraining the frequency dependence of intrinsic seismic attenuation in the Earth is crucial for: 1. correcting for velocity dispersion due to attenuation; 2. constructing attenuation and velocity models of the interior using datasets with different frequency contents; and, 3. interpreting lateral variations of velocity and attenuation in terms of temperature and composition. Frequency dependence of attenuation q can be represented by a power law q ? q0? - ?. Despite its importance, efforts at determining ? from surface wave and free oscillation data have been thwarted by the strong tradeoffs between the depth- and frequency dependence of attenuation. We develop and validate a new method that eliminates this tradeoff, allowing a direct estimation of effective frequency dependence of attenuation without having to construct a new depth-dependent model of attenuation. Using normal mode and surface wave attenuation measurements between 80 and 3000 s, we find that ? varies with frequency within the absorption band. It is 0.3 at periods shorter than 200 s, it decreases to 0.1 between 300 and 800 s, and becomes negative at periods longer than 1000 s.

Leki?, Ved; Matas, Jan; Panning, Mark; Romanowicz, Barbara

2009-05-01

51

Extensional wave attenuation and velocity in partially-saturated sand in the sonic frequency range  

SciTech Connect

Extensional wave attenuation and velocity measurements on a high permeability Monterey sand were performed over a range of gas saturations for imbibition and degassing conditions. These measurements were conducted using extensional wave pulse propagation and resonance over a 1 - 9 kHz frequency range for a hydrostatic confining pressure of 8.3 MPa. Analysis of the extensional wave data and the corresponding X-ray CT images of the gas saturation show strong attenuation resulting from the presence of the gas (QE dropped from 300 for the dry sand to 30 for the partially-saturated sand), with larger attenuation at a given saturation resulting from heterogeneous gas distributions. The extensional wave velocities are in agreement with Gassmann theory for the test with near-homogeneous gas saturation and with a patchy saturation model for the test with heterogeneous gas saturation. These results show that partially-saturated sands under moderate confining pressure can produce strong intrinsic attenuation for extensional waves.

Liu, Z.; Rector, J.W.; Nihei, K.T.; Tomutsa, L.; Myer, L.R.; Nakagawa, S.

2002-06-17

52

Smart structures for shock wave attenuation using ER inserts  

NASA Astrophysics Data System (ADS)

This Paper demonstrates the possibility of shock wave attenuation propagating through a smart structure that incorporates ER insert. The wave transmission of ER inserted beam is theoretically derived using Mead & Markus model and the theoretical results are compared with the finite element analysis results. To experimentally verify the shock wave attenuation, ER insert in an aluminum plate is made and two piezoceramic disks are used as transmitter and receiver of the wave. The transmitter sends a sine pulse signal such that a component of shock wave travels through the plate structure and the receiver gets the transmitted wave signal. Wave propagation of the ER insert can be adjusted by changing the applied electric field on the ER insert. Details of the experiment are addressed and the possibility of shock wave attenuation is experimentally verified. This kind of smart structure can be used for warship and submarine hull structures to protect fragile and important equipment.

Kim, Jaehwan; Kim, Jung-Yup; Choi, Seung-Bok; Kim, Kyung-Su

2001-08-01

53

The attenuation coefficient of an acoustic wave propagating in a turbulent flow in a long pipeline  

NASA Astrophysics Data System (ADS)

Results of experiments on measuring the attenuation coefficient for acoustic waves propagating in long oil and petroleum product pipelines are presented. A comparison of experimental results with theory is performed. An approximate dependence of the attenuation coefficient on the dimensionless parameter of the flow is proposed.

Barabanov, S. A.; Glikman, B. F.

2009-03-01

54

Theoretical study of different attenuation measurement by acoustic microscopy  

NASA Astrophysics Data System (ADS)

Many works are devoted to study the attenuation of surface waves in media, particularly, leaky surface acoustic waves (LSAW). In this work, a big part of the study is based on the intensity of the output signal, i.e., acoustic signature, V(z). The latter is obtained by the use of quantitative mode of acoustic microscopy in order to measure the velocity and the attenuation of those excited waves at the limit between the specimen and the coupling liquid. Our aim is to compare the attenuation values of the LSAW propagation in porous silicon obtained with three different methods. The first is obtained by resolving Viktorov equation. The second method is the spectral analysis acoustical signature V(z) curves. The third method uses the dark field. The obtained results are in a good agreement with those experiments.

Hamdi, F.; Bouhedja, S.; Amrani, H.

2013-10-01

55

Detection of gas and water using HHT by analyzing P- and S-wave attenuation in tight sandstone gas reservoirs  

NASA Astrophysics Data System (ADS)

A direct detection of hydrocarbons is used by connecting increased attenuation of seismic waves with oil and gas fields. This study analyzes the seismic attenuation of P- and S-waves in one tight sandstone gas reservoir and attempts to give the quantitative distinguishing results of gas and water by the characteristics of the seismic attenuation of P- and S-waves. The Hilbert-Huang Transform (HHT) is used to better measure attenuation associated with gas saturation. A formation absorption section is defined to compute the values of attenuation using the common frequency sections obtained by the HHT method. Values of attenuation have been extracted from three seismic sections intersecting three different wells: one gas-saturated well, one fully water-saturated well, and one gas- and water- saturated well. For the seismic data from the Sulige gas field located in northwest Ordos Basin, China, we observed that in the gas-saturated media the S-wave attenuation was very low and much lower than the P-wave attenuation. In the fully water-saturated media the S-wave attenuation was higher than the P-wave attenuation. We suggest that the joint application of P- and S-wave attenuation can improve the direct detection between gas and water in seismic sections. This study is hoped to be useful in seismic exploration as an aid for distinguishing gas and water from gas- and water-bearing formations.

Xue, Ya-juan; Cao, Jun-xing; Wang, Da-xing; Tian, Ren-fei; Shu, Ya-xiang

2013-11-01

56

Wave attenuation in the marginal ice zone during LIMEX  

NASA Technical Reports Server (NTRS)

During LIMEX'87 and '89, the CCRS CV-580 aircraft collected SAR (synthetic aperture radar) data over the marginal ice zone off the coast of Newfoundland. Based upon the wavenumber spectra from SAR data, the wave attenuation rate is estimated and compared with a model. The model-data comparisons are reasonably good for the ice conditions during LIMEX (Labrador Ice Margin Experiment). Both model and SAR-derived wave attenuation rates show a roll-over at high wavenumbers.

Liu, Antony K.; Peng, Chih Y.; Vachon, Paris W.

1991-01-01

57

Attenuation of electromagnetic wave propagation in sandstorms incorporating charged sand particles  

NASA Astrophysics Data System (ADS)

A theoretical approach for predicting the attenuation of microwave propagation in sandstorms is presented, with electric charges generated on the sand grains taken into account. It is found that the effect of electric charges distributed partially on the sand surface is notable. The calculated attenuation is in good agreement with that measured in certain conditions. The distribution of electric charges on the surface of sand grains, which is not easy to measure, can be approximately determined by measuring the attenuation value of electromagnetic waves. Some effects of sand radius, dielectric permittivity, frequency of electromagnetic wave, and visibility of sandstorms on the attenuation are also discussed quantitatively. Finally, a new electric parameter is introduced to describe the roles of scattering, absorption and effect of charges in attenuation.

Zhou, You-He; Shu He, Qin; Zheng, Xiao Jing

2005-06-01

58

Measuring cast iron graphite size by ultrasonic attenuation  

Microsoft Academic Search

Precipitated graphite geometry is one of the main microstructural parameters that contribute to cast iron mechanical properties. In this paper we address the measurement of the graphite size by ultrasonic attenuation. Samples of different cast iron microstructures were characterized by quantitative metallographic techniques and further correlated with ultrasonic parameters. Longitudinal ultrasonic waves were generated and detected by commercial broadband piezoelectric

S. E. Kruger; J. M. A. Rebello; J. Charlier

2002-01-01

59

Attenuation of Seismic Waves by Grain Boundary Relaxation  

PubMed Central

Experimental observations of the attenuation of elastic waves in polycrystalline ceramics and rocks reveal an attenuation mechanism, called grain boundary relaxation, which is likely to be predominant cause of seismic attenuation in the earth's mantle. For this mechanism, the internal friction (the reciprocal of the “intrinsic Q” of the material) depends strongly upon frequency and is in good agreement with Walsh's theory of attenuation (J. Geophys. Res., 74, 4333, 1969) in partially melted rock. When Walsh's theory is extended to provide a model of the anelasticity of the earth, using the experimental values of physical parameters reported here, the results are in excellent agreement with seismic observations.

Jackson, David D.

1971-01-01

60

Seismic attenuation due to wave-induced flow  

SciTech Connect

Analytical expressions for three P-wave attenuation mechanisms in sedimentary rocks are given a unified theoretical framework. Two of the models concern wave-induced flow due to heterogeneity in the elastic moduli at mesoscopic scales (scales greater than grain sizes but smaller than wavelengths). In the first model, the heterogeneity is due to lithological variations (e.g., mixtures of sands and clays) with a single fluid saturating all the pores. In the second model, a single uniform lithology is saturated in mesoscopic ''patches'' by two immiscible fluids (e.g., air and water). In the third model, the heterogeneity is at ''microscopic'' grain scales (broken grain contacts and/or micro-cracks in the grains) and the associated fluid response corresponds to ''squirt flow''. The model of squirt flow derived here reduces to proper limits as any of the fluid bulk modulus, crack porosity, and/or frequency is reduced to zero. It is shown that squirt flow is incapable of explaining the measured level of loss (10{sup -2} < Q{sup -1} < 10{sup -1}) within the seismic band of frequencies (1 to 10{sup 4} Hz); however, either of the two mesoscopic scale models easily produce enough attenuation to explain the field data.

Pride, S.R.; Berryman, J.G.; Harris, J.M.

2003-10-09

61

Seismic attenuation due to wave-induced flow  

Microsoft Academic Search

Three P wave attenuation models for sedimentary rocks are given a unified theoretical treatment. Two of the models concern wave-induced flow due to heterogeneity in the elastic moduli at “mesoscopic” scales (scales greater than grain sizes but smaller than wavelengths). In the first model, the heterogeneity is due to lithological variations (e.g., mixtures of sands and clays) with a single

S. R. Pride; J. G. Berryman; J. M. Harris

2004-01-01

62

Wave velocity dispersion and attenuation in media exhibiting internal oscillations  

NASA Astrophysics Data System (ADS)

Understanding the dynamical and acoustical behavior of porous and heterogeneous rocks is of great importance in geophysics, e.g. earthquakes, and for various seismic engineering applications, e.g. hydrocarbon exploration. Within a heterogeneous medium oscillations with a characteristic resonance frequency, depending on the mass and internal length of the heterogeneity, can occur. When excited, heterogeneities can self-oscillate with their natural frequency. Another example of internal oscillations is the dynamical behavior of non-wetting fluid blobs or fluid patches in residually saturated pore spaces. Surface tension forces or capillary forces act as the restoring force that drives the oscillation. Whatever mechanism is involved, an oscillatory phenomena within a heterogeneous medium will have an effect on acoustic or seismic waves propagating through such a medium, i.e. wave velocity dispersion and frequency-dependent attenuation. We present two models for media exhibiting internal oscillations and discuss the frequency-dependent wave propagation mechanism. Both models give similar results: (1) The low-frequency (i.e. quasi-static) limit for the phase velocity is identical with the Gassmann-Wood limit and the high-frequency limit is larger than this value and (2) Around the resonance frequency a very strong phase velocity change and the largest attenuation occurs. (1) Model for a homogeneous medium exhibiting internal oscillations We present a continuum model for an acoustic medium exhibiting internal damped oscillations. The obvious application of this model is water containing oscillating gas bubbles, providing the material and model parameters for this study. Two physically based momentum interaction terms between the two inherent constituents are used: (1) A purely elastic term of oscillatory nature that scales with the volume of the bubbles and (2) A viscous term that scales with the specific surface of the bubble. The model is capable of taking into account an arbitrary number of oscillators with different resonance frequencies. Exemplarily, we show a log-normal distribution of resonance frequencies. Such a distribution changes the acoustic properties significantly compared to the case with only one resonance frequency. The dispersion and attenuation resulting from our model agree well with the dispersion and attenuation (1) derived with a more exact mathematical treatment and (2) measured in laboratory experiments. (2) Three-phase model for residually saturated porous media We present a three-phase model describing wave propagation phenomena in residually saturated porous media. The model consists of a continuous non-wetting phase and a discontinuous wetting phase and is an extension of classical biphasic (Biot-type) models. The model includes resonance effects of single liquid bridges or liquid clusters with miscellaneous eigenfrequencies taking into account a visco-elastic restoring force (pinned oscillations and/or sliding motion of the contact line). In the present investigation, our aim is to study attenuation due to fluid oscillations and due to wave-induced flow with a macroscopic three-phase continuum model, i.e. a mixture consisting of one solid constituent building the elastic skeleton and two immiscible fluid constituents. Furthermore, we study monochromatic waves in transversal and longitudinal direction and discuss the resulting dispersion relations for a typical reservoir sandstone equivalent (Berea sandstone).

Frehner, Marcel; Steeb, Holger; Schmalholz, Stefan M.

2010-05-01

63

Determining attenuation properties of interfering fast and slow ultrasonic waves in cancellous bone  

PubMed Central

Previous studies have shown that interference between fast waves and slow waves can lead to observed negative dispersion in cancellous bone. In this study, the effects of overlapping fast and slow waves on measurements of the apparent attenuation as a function of propagation distance are investigated along with methods of analysis used to determine the attenuation properties. Two methods are applied to simulated data that were generated based on experimentally acquired signals taken from a bovine specimen. The first method uses a time-domain approach that was dictated by constraints imposed by the partial overlap of fast and slow waves. The second method uses a frequency-domain log-spectral subtraction technique on the separated fast and slow waves. Applying the time-domain analysis to the broadband data yields apparent attenuation behavior that is larger in the early stages of propagation and decreases as the wave travels deeper. In contrast, performing frequency-domain analysis on the separated fast waves and slow waves results in attenuation coefficients that are independent of propagation distance. Results suggest that features arising from the analysis of overlapping two-mode data may represent an alternate explanation for the previously reported apparent dependence on propagation distance of the attenuation coefficient of cancellous bone.

Nelson, Amber M.; Hoffman, Joseph J.; Anderson, Christian C.; Holland, Mark R.; Nagatani, Yoshiki; Mizuno, Katsunori; Matsukawa, Mami; Miller, James G.

2011-01-01

64

Relation of sound absorption and shallow water modal attenuation to plane wave attenuation.  

PubMed

Prediction of attenuation of acoustic fields in weakly absorbing media often uses the substitution of (omega/c)-->(omega/c)+ialpha(pw) into the idealized equations for constant frequency, with alpha(pw) representing the local plane wave attenuation coefficient. This assumption is flawed whenever the local absorption of sound is proportional to the square of the gradient of the acoustic pressure, as is the case when the absorption is caused by fluid velocity relaxation. A realistic analysis yields an improved weighting function over depth for determination of guided mode attenuation coefficients. PMID:19894791

Pierce, Allan D

2009-11-01

65

Reflection, radiation and attenuation of Stoneley guided waves in fluid-filled finite cracks  

Microsoft Academic Search

Understanding wave propagation in fractured fluid-rock systems is important for estimating, for example, fluid properties or fracture densities from geophysical measurements such as ground motion. In this study, the reflection, radiation and attenuation of Stoneley guided waves in fluid-filled cracks is studied numerically. Stoneley guided waves have been used, for example, to explain long-period volcanic tremor signals or to propose

M. Frehner; S. M. Schmalholz

2009-01-01

66

Imaging Rayleigh wave attenuation and phase velocity in the western and central United States  

NASA Astrophysics Data System (ADS)

The EarthScope USArray provides an opportunity to obtain detailed images of the continental upper mantle at an unprecedented scale. The majority of mantle models derived from USArray data to date contain spatial variations in seismic-wave speed; however, little is known about the attenuation structure of the North American upper mantle. Joint interpretation of seismic attenuation and velocity models can improve upon the interpretations based only on velocity, and provide important constraints on the temperature, composition, melt content, and volatile content of the mantle. We jointly invert Rayleigh wave phase and amplitude observations for phase velocity and attenuation maps for the western and central United States using USArray data. This approach exploits the amplitudes' sensitivity to velocity and the phase delays' sensitivity to attenuation. The phase and amplitude data are measured in the period range 20--100 s using a new interstation cross-correlation approach, based on the Generalized Seismological Data Functional algorithm, that takes advantage of waveform similarity at nearby stations. The Rayleigh waves are generated from 670 large teleseismic earthquakes that occurred between 2006 and 2012, and measured from all available Transportable Array stations. We consider two separate and complementary approaches for imaging attenuation variations: (1) the Helmholtz tomography (Lin et al., 2012) and (2) two-station path tomography. Results obtained from the two methods are contrasted. We provide a preliminary interpretation based on the observed relationship between Rayleigh wave attenuation and phase velocity.

Bao, X.; Dalton, C. A.; Jin, G.; Gaherty, J. B.

2013-12-01

67

Grain-size dependence of shear wave speed dispersion and attenuation in granular marine sediments.  

PubMed

The author has shown that measured shear wave speed dispersion and attenuation in water-saturated silica sand can be predicted by using a gap stiffness model incorporated into the Biot model (the BIMGS model) [Kimura, J. Acoust. Soc. Am. 134, 144-155 (2013)]. In this study, the grain-size dependence of shear wave speed dispersion and attenuation in four kinds of water-saturated silica sands with different grain sizes is measured and calculated. As a result, the grain-size dependence of the aspect ratio in the BIMGS model can be validated and the effects of multiple scattering for larger grain sizes are demonstrated. PMID:24993238

Kimura, Masao

2014-07-01

68

Attenuation of body waves in Southeastern Sicily (Italy)  

Microsoft Academic Search

The attenuation of P- and S-waves in Southeastern Sicily was estimated by applying two different methods in time and frequency domains. We analyzed waveforms from about 290 local events (0.6?ML?4.6) recorded at a three-component digital network.By applying the pulse broadening method to the first P-wave pulse, we found an average Qp value of ca. 140. The application of the frequency

E. Giampiccolo; S. Gresta; G. Ganci

2003-01-01

69

Attenuation of weak shock waves along pseudo-perforated walls  

Microsoft Academic Search

.   In order to attenuate weak shock waves in ducts, effects of pseudo-perforated walls were investigated. Pseudo-perforated\\u000a walls are defined as wall perforations having a closed cavity behind it. Shock wave diffraction and reflection created by\\u000a these perforations were visualized in a shock tube by using holographic interferometer, and also by numerical simulation.\\u000a Along the pseudo-perforated wall, an incident shock

A. Sasoh; K. Matsuoka; K. Nakashio; E. Timofeev; K. Takayama; P. Voinovich; T. Saito; S. Hirano; S. Ono; Y. Makino

1998-01-01

70

Pressure wave attenuation and dispersion in two-phase flow  

SciTech Connect

The pressure shock wave propagation behavior in three vapor-liquid systems, steam-water, ethanol-ethanol, and Freon-Freon, has been investigated over a void fraction, ..cap alpha.., range from zero to 30%. Attenuation and dispersion behavior seems relatively insensitive (no order-of-magnitude deviations) to differences in system physical properties. The attenuation coefficient of water, BETA/sub H/2/sub O/ ranged from 0.021 cm/sup -1/ at 5% void to 0.072 cm/sup -1/ at 30% void fraction. BETA/sub F113/ was as much as 40% lower than BETA/sub ETOH/ or BETA/sub H/2/sub O/ for void fractions less than 20% where the initial wave amplitude, ..delta..P/sub o/ was 2.90 bar. Larger amplitude waves (4.14 bar) demonstrated a greater rate of attenuation throughout the void fraction range, more pronounced in the lower regions: 80% greater for 5% steam-water and 120% greater for 5% Freon-113. The attenuation data from the present investigation tend to lie between one- and two-component acoustic attenuation theories and data. However, near the resonant bubble frequency, the two component results approach the one-component region. As the void fraction is decreased, the one- and two-component acoustic theories and data (small and finite amplitude, including the present experimentation) smoothly converge.

Kovarik, F.S.; Bankoff, S.G.

1987-01-01

71

Attenuation of coda waves in Western Anatolia  

Microsoft Academic Search

By analyzing the decay of coda wave amplitude, we have determined coda Q,Qc, in Western Anatolia (Turkey). Using the single isotropic scattering model, we analyzed 116 earthquakes which registered at the Gebze station by using five narrow frequency bands centered at 1.5, 3, 6, 8 and 10 Hz. Coda Q values were obtained using different lapse times, between 30 and

A. Akinci; A. G. Taktak; S. Ergintav

1994-01-01

72

Radiation and attenuation of waves in a random medium  

NASA Technical Reports Server (NTRS)

The physical mechanisms of excess attenuation are analyzed on the basis of a one-dimensional time-independent model of propagation in a random medium. Attenuation is regarded as the rate of decrease in the mean intensity and the mean energy flux within a propagation range. A source function is assumed to be determinate, appropriate statistical properties are chosen for the sound speed, and specified statistical properties are found for the wave functions, i.e., the mean intensity and the mean energy flux. The medium is considered to be weakly homogeneous, and expansions are developed for the intensity and mean energy flux, along with an attenuation coefficient in two parts, the second of which defines the excess attenuation. The mean radiated power is defined, and backscattering by the random inhomogeneities in the medium is modeled as redistributing the mean intensity and energy flux, with a resultant decay which occurs more quickly than with randomness.

Wenzel, A. R.

1982-01-01

73

Broadband ultrasonic attenuation: are current measurement techniques inherently inaccurate?  

PubMed

Measurements of broadband ultrasonic attenuation (BUA) are currently made using large aperture, piezoelectric transducers. The use of such a receiver is known to lead to the possibility of an overestimate of ultrasonic attenuation due to phase cancellation and it is shown theoretically that this same effect can also lead to an overestimate of BUA. Using a new scanning approach, BUA was measured using two methods, one sensitive to the phase of the acoustic wave, the other not. The phase sensitive BUA measurements were found to be of significantly higher value (p < 0.0001) than the phase insensitive measurements with a mean difference of 31.2 dB MHz-1. These findings are compatible with the hypothesis that BUA measurement systems with large aperture, piezo-electric receivers are inherently inaccurate. PMID:8542228

Petley, G W; Robins, P A; Aindow, J D

1995-11-01

74

Simultaneous measurement of local longitudinal and transverse wave velocities, attenuation, density, and thickness of films by using point-focus ultrasonic spectroscopy  

NASA Astrophysics Data System (ADS)

This paper presents an ultrasonic technique for simultaneous determination of the complete set of acoustical and geometrical properties of a film or a thin layer in a stratified material embedded between two known materials using point-focus ultrasonic spectroscopy, which provides a high lateral resolution. The theoretical model of the two-dimensional spectrum Rt(?,?) of the stratified material is calculated as a function of six parameters of the unknown layer: longitudinal and transverse velocities cl, ct, attenuation ?l, ?t, density ?, and thickness h, which fully determined the properties of the film. The experimental spectrum Re(?,?) can be measured by V(z,t) technique. A two-step algorithm is presented to decompose the searching process of parameters from one six-dimensional to two three-dimensional spaces. The sensitivity of the two-dimensional spectrum to individual properties and its stability against experimental noise are studied. The full set properties of a 250 ?m thick stainless steel film and a 930 ?m thick SiO2 thin layer of a three layered stratified material immersed in water are determined. The proposed technique used a point-focus transducer, which makes the setup simple and reliable. It allows measurement of the local properties of the film and enables precision material characterization.

Ju, Bing-Feng; Bai, Xiaolong; Chen, Jian

2012-10-01

75

Bulk shear wave propagation in an epoxy: attenuation and phase velocity over five decades of frequency.  

PubMed

Proportionality between the ultrasonic wave attenuation coefficient in epoxies and other polymers and frequency is a commonly observed but little understood phenomenon. How it is ultimately explained will depend on the breadth of the frequency range over which it is significant. This paper presents results of experiments to measure loss in a single epoxy material over 5 decades of frequency using 4 complementary techniques--dynamic mechanical analysis, microwave excited low-frequency resonances, a novel guidedwave technique based on a metal-epoxy-metal sandwich, and a conventional pulse mode ultrasonic spectrometer. The results are confined to bulk shear waves in the epoxy. They confirm the linear relationship between attenuation and frequency, and it is shown that the broadband behavior of the attenuation and shear wave phase velocity is consistent with the Kramers- Kronig relationships. PMID:19942536

Wang, Yujie; Challis, Richard E; Phang, Albert P-Y; Unwin, Marion E

2009-11-01

76

Determination of seismic attenuation from surface and downhole measurements  

NASA Astrophysics Data System (ADS)

Attenuation is a potentially very important seismic attribute for seismic exploration and reservoir characterization. In order for attenuation to be utilized successfully as an attribute, it must first be reliably extracted from the seismic data and separated from scattering effects. Existing methods meet fatal difficulties in measuring attenuation from both surface seismic data and vertical seismic profile (VSP) data. Intrinsic attenuation measurement from VSP using spectral ratios is seriously affected by scattering, coupling variations, and difficulties in first-arrival isolation. An algorithm to estimate intrinsic attenuation from VSP data where reliable seismic impedance logs are available effectively handles these problems. Using the available impedance profile calculated from well logs, VSP synthetics including up-going and down-going waves, multiples and attenuation are calculated. The scattering effect is removed iteratively by matching real spectral ratios with synthetic spectral ratios. Numerical modeling of infinite bandwidth and band limited cases shows that this method is accurate, effective and robust providing coupling variations are frequency-independent over the seismic bandwidth. Application to real VSP data from offshore Gulf of Mexico block Eugene island 354 shows high attenuation associated with potential gas pay. Existing methods of attenuation estimation from surface seismic data suffer from wavelet extraction and scattering removal. An inversion method is developed to solve these problems. Instead of trying to extract the wavelet directly from the seismic trace and subsequently separate scattering effects, a full waveform forward modeling and damped generalized linear inversion (GLI) algorithm to invert Q from the surface seismic trace are employed. The forward theory includes all the multiples and attenuation in the synthetic, thus allowing direct separation of the intrinsic Q from scattering effects. The employed forward inelastic wave theory also allows dispersion effects to be accounted for and does not require a constant Q model. Employment of the robust damped GLI algorithm produces a stable and accurate inversion result. Numerical modeling studies show that the Q profile can be recovered even if the initial model is not near the correct answer.

Sun, Shengjie

77

Extensional wave attenuation and velocity in partially saturated sand in the sonic frequency range  

SciTech Connect

Extensional wave attenuation and velocity measurements on a high permeability Monterey sand were performed over a range of gas saturations for imbibition and degassing conditions. These measurements were conducted using extensional wave pulse propagation and resonance over a 1-9 kHz frequency range for a hydrostatic confining pressure of 8.3 MPa. Analysis of the extensional wave data and the corresponding X-ray CT images of the gas saturation show strong attenuation resulting from the presence of the gas (Q{sub E} dropped from 300 for the dry sand to 30 for the partially-saturated sand), with larger attenuation at a given saturation resulting from heterogeneous gas distributions. The extensional wave velocities are in agreement with Gassmann theory for the test with near-homogeneous gas saturation and with a patchy saturation model for the test with heterogeneous gas saturation. These results show that partially-saturated sands under moderate confining pressure can produce strong intrinsic attenuation for extensional waves.

Liu, Z.; Rector, J.W.; Nihei, K.T.; Tomutsa, L.; Myer, L.R.; Nakagawa, S.

2001-08-10

78

Bulk shear wave propagation in an epoxy: attenuation and phase velocity over five decades of frequency  

Microsoft Academic Search

Proportionality between the ultrasonic wave attenuation coefficient in epoxies and other polymers and frequency is a commonly observed but little understood phenomenon. How it is ultimately explained will depend on the breadth of the frequency range over which it is significant. This paper presents results of experiments to measure loss in a single epoxy material over 5 decades of frequency

Y. Wang; R. E. Challis; A. P.-Y. Phang; M. E. Unwin

2009-01-01

79

Attenuation of seismic waves obtained by coda waves analysis in the West Bohemia earthquake swarm region  

NASA Astrophysics Data System (ADS)

Seismic waves are attenuated by number of factors, including geometrical spreading, scattering on heterogeneities and intrinsic loss due the anelasticity of medium. Contribution of the latter two processes can be derived from the tail part of the seismogram - coda (strictly speaking S-wave coda), as these factors influence the shape and amplitudes of coda. Numerous methods have been developed for estimation of attenuation properties from the decay rate of coda amplitudes. Most of them work with the S-wave coda, some are designed for the P-wave coda (only on teleseismic distances) or for the whole waveforms. We used methods to estimate the 1/Qc - attenuation of coda waves, methods to separate scattering and intrinsic loss - 1/Qsc, Qi and methods to estimate attenuation of direct P and S wave - 1/Qp, 1/Qs. In this study, we analyzed the S-wave coda of local earthquake data recorded in the West Bohemia/Vogtland area. This region is well known thanks to the repeated occurrence of earthquake swarms. We worked with data from the 2011 earthquake swarm, which started late August and lasted with decreasing intensity for another 4 months. During the first week of swarm thousands of events were detected with maximum magnitudes ML = 3.6. Amount of high quality data (including continuous datasets and catalogues with an abundance of well-located events) is available due to installation of WEBNET seismic network (13 permanent and 9 temporary stations) monitoring seismic activity in the area. Results of the single-scattering model show seismic attenuations decreasing with frequency, what is in agreement with observations worldwide. We also found decrease of attenuation with increasing hypocentral distance and increasing lapse time, which was interpreted as a decrease of attenuation with depth (coda waves on later lapse times are generated in bigger depths - in our case in upper lithosphere, where attenuations are small). We also noticed a decrease of frequency dependence of 1/Qc with depth, where 1/Qc seems to be frequency independent in depth range of upper lithosphere. Lateral changes of 1/Qc were also reported - it decreases in the south-west direction from the Novy Kostel focal zone, where the attenuation is the highest. Results from more advanced methods that allow for separation of scattering and intrinsic loss show that intrinsic loss is a dominant factor for attenuating of seismic waves in the region. Determination of attenuation due to scattering appears ambiguous due to small hypocentral distances available for the analysis, where the effects of scattering in frequency range from 1 to 24 Hz are not significant.

Bachura, Martin; Fischer, Tomas

2014-05-01

80

High-power microwave attenuator employing slow wave structure  

NASA Astrophysics Data System (ADS)

Using present pulsed microwave amplifier, we can obtain RF peak power beyond one hundred MW. However, it is not easy to test such a high-power RF. To overcome this difficulty we developed a high-power microwave attenuator employing a slow wave structure. For example, the output power of RF pulse compressor for present electron linear accelerator reaches a few hundreds MW RF power, but the existing dummy loads can absorb only a few tens MW of RF power. The attenuator we developed has a kind of periodic structure and is made of metal only. We operated this attenuator using a high-power RF source, and found that it could be operated fewer than 50 pps RF output at 40 MW, 2.5 ?s or 100 MW, 0.5 ?s.

Yoshida, Mitsuhiro; Matsumoto, Hiroshi; Shintake, Tsumoru; Nishiyama, Koji; Miura, Sadao

2012-11-01

81

Laboratory velocities and attenuation of p-waves in limestones during freeze-thaw cycles  

SciTech Connect

The velocity and the attenuation of compressional P-waves, measured in the laboratory at ultrasonic frequencies during a series of freezing and thawing cycles, are used as a method for predicting frost damage in a bedded limestone. Pulse transmission and spectral ratio techniques are used to determine the P-wave velocities and the attenuation values relative to an aluminum reference samples with very low attenuation. Limestone samples were water saturated under vacuum conditions, jacketed with rubber sleeves, and immersed in an antifreeze bath (50 percent methanol solution). They were submitted to repeated 24-hour freezing and thawing cycles simulating natural environment conditions. During the freeze/thaw cycles, P-wave velocities and quality factor Q diminished rapidly in thawed rock samples, indicating modification of the pore space. Measurements of crack porosity were conducted by hydrostatic compression tests on cubic rock samples that had been submitted to these freeze/thaw cycles. These measurements are used as an index of crack formation. The hydrostatic compression tests confirmed the phases of rock damage that were shown by changes in the value of Q. Furthermore, comparison between Q values and crack porosity demonstrate that the variations of P-wave attenuation are caused by the creation of new cracks and not by the enlargement of pre-existing cracks.

Remy, J.M.; Bellanger, M.; Homand-Etienne, F. (Lab. de Geomecanique de Nancy, Vandoeuvre-les-Nancy (France))

1994-02-01

82

Measuring Acoustic Nonlinearity by Collinear Mixing Waves  

NASA Astrophysics Data System (ADS)

It is well known that the acoustic nonlinearity parameter ? is correlated to fatigue damage in metallic materials. Various methods have been developed to measure ?. One of the most often used methods is the harmonic generation technique, in which ? is obtained by measuring the magnitude of the second order harmonic waves. An inherent weakness of this method is the difficulty in distinguishing material nonlinearity from the nonlinearity of the measurement system. In this paper, we demonstrate the possibility of using collinear mixing waves to measure ?. The wave mixing method is based on the interaction between two incident waves in a nonlinear medium. Under certain conditions, such interactions generate a third wave of different frequency. This generated third wave is also called resonant wave, because its amplitude is unbounded if the medium has no attenuation. Such resonant waves are less sensitive to the nonlinearity of the measurement system, and have the potential to identify the source location of the nonlinearity. In this work, we used a longitudinal wave and a shear wave as the incident waves. The resonant shear wave is measured experimentally on samples made of aluminum and steel, respectively. Numerical simulations of the tests were also performed using a finite difference method.

Liu, M.; Tang, G.; Jacobs, L. J.; Qu, J.

2011-06-01

83

Developing a Short-Period, Fundamental-Mode Rayleigh-Wave Attenuation Model for Asia  

NASA Astrophysics Data System (ADS)

We are developing a 2D, short-period (12 - 22 s), fundamental-mode Rayleigh-wave attenuation model for Asia. This model can be used to invert for a 3D attenuation model of the Earth's crust and upper mantle as well as to implement more accurate path corrections in regional surface-wave magnitude calculations. The prerequisite for developing a reliable Rayleigh-wave attenuation model is the availability of accurate fundamental-mode Rayleigh-wave amplitude measurements. Fundamental-mode Rayleigh-wave amplitudes could be contaminated by a variety of sources such as multipathing, focusing and defocusing, body wave, higher-mode surface wave, and other noise sources. These contaminations must be reduced to the largest extent possible. To achieve this, we designed a procedure by taking advantage of certain Rayleigh-wave characteristics, such as dispersion and elliptical particle motion, for accurate amplitude measurements. We first analyze the dispersion of the surface-wave data using a spectrogram. Based on the characteristics of the data dispersion, we design a phase-matched filter by using either a manually picked dispersion curve, or a group-velocity-model predicted dispersion curve, or the dispersion of the data, and apply the filter to the seismogram. Intelligent filtering of the seismogram and windowing of the resulting cross-correlation based on the spectrogram analysis and the comparison between the phase-match filtered data spectrum, the raw-data spectrum and the theoretical source spectrum effectively reduces amplitude contaminations and results in reliable amplitude measurements in many cases. We implemented these measuring techniques in a graphic-user-interface tool called Surface Wave Amplitude Measurement Tool (SWAMTOOL). Using the tool, we collected and processed waveform data for 200 earthquakes occurring throughout 2003-2006 inside and around Eurasia. The records from 135 broadband stations were used. After obtaining the Rayleigh-wave amplitude measurements, we analyzed the attenuation behavior of the amplitudes using source- and receiver-specific terms calculated from a 3D velocity model of the region. Based on the results, we removed amplitudes that yielded negative average attenuation coefficients, and included an additional parameter in the inversion to account for the possible bias of the CMT moments. Using the high-quality amplitude measurements in a tomographic inversion, we obtained a fundamental-mode Rayleigh-wave attenuation- coefficient model for periods between 12 and 22 s for Asia and surrounding regions. The inverted attenuation model is consistent with the geological features of Asia. We observe low attenuation in stable regions such as eastern Europe, the Siberian platforms, the Indian shield, the Arabian platform, the Yangtze craton, and others. High attenuation is observed in tectonically active regions such as the Himalayas, the Tian Shan, Pamir and Zagros mountains.

Yang, X.; Levshin, A. L.; Barmin, M. P.; Ritzwoller, M. H.

2008-12-01

84

Attenuation Measurements in Solutions of Some Carbohydrates  

SciTech Connect

The linear attenuation coefficients in aqueous solutions of three carbohydrates, glucose (C{sub 6}H{sub 12}O{sub 6}), maltose monohydrate (C{sub 12}H{sub 22}O{sub 11}.H{sub 2}O), and sucrose (C{sub 12}H{sub 22}O{sub 11}), were determined at 81, 356, 511, 662, 1173, and 1332 keV by the gamma-ray transmission method in a good geometry setup. From the precisely measured densities of these solutions, mass attenuation coefficients were then obtained that varied systematically with the corresponding changes in the concentrations (g/cm{sup 3}) of these solutions. The experimental results were used in terms of effective atomic numbers and electron densities. A comparison between experimental and theoretical values of attenuation coefficients has proven that the study has a potential application for the determination of attenuation coefficients of solid solutes from their solutions without obtaining them in pure crystalline form.

Gagandeep [Guru Nanak Dev University (India); Singh, Kulwant [Guru Nanak Dev University (India); Lark, B.S. [Guru Nanak Dev University (India); Sahota, H.S. [Punjabi University (India)

2000-02-15

85

Wave Height Attenuation in Heterogeneous Vegetation using Laboratory Observation and Numerical Simulations  

NASA Astrophysics Data System (ADS)

Coastal vegetation is commonly accepted as a means of wave damping, but existing methodologies for predicting the wave height attenuation focus on homogeneous vegetation, primarily in periodic waves. In this project, quarter scale experiments were performed in conjunction with numerical modeling in FUNWAVE to evaluate random wave attenuation through two types of synthetic vegetation. The experiment was performed with two peak periods, three water depths, and two stem densities. For each combination of parameters, free surface time series were collected at 7 locations throughout the vegetation field and 1 location seaward of the vegetation. Each combination of wave conditions was evaluated for four different cases: Case 1 with no vegetation, Case 2 and 3 with short and long specimens, respectively, and Case 4 with mixed vegetation. The decay of the spectral wave heights were fit with the Dalrymple et al. (1984) and Kobayashi et al. (1993) equations. The decay equations provided reasonable predictions, with an average mean square error of 1.3%. We found that adding the coefficients obtained for the cases of the individual plants provided a reasonable prediction of the coefficient for the cases of the combined, heterogeneous vegetation. Use of a reduction factor on the sum of the two coefficients improved the predictions, giving an average mean square error of 2.1% between the predictions and the measured values. A phase resolved numerical model (FUNWAVE) was used to model wave attenuation for these tests using a bottom drag coefficient calibrated for each run. The numerical attenuation followed the same trends as the measured data, with an average mean square error of 1.7% when considering all of the observation locations throughout the vegetation field. Similar to the physical model study, we found that adding the calibrated model drag coefficients for the cases of the individual plants reasonably predicted the wave height attenuation for the cases of the combined vegetation with an average mean square error of 3.2%. References: Dalrymple, R.A., Kirby, J.T., Hwang, P.A., 1984. Wave refraction due to areas of energy dissipation. J. Waterw., Port Coast. Ocean Eng. 110 (1), 67-79. Kobayashi, N., Raichlen, A.W., Asano, T., 1993. Wave attenuation by vegetation. J. Waterw., Port Coast. Ocean Eng. 199 (1), 30-48.

Blackmar, P.; Wu, W.; Cox, D. T.

2012-12-01

86

Attenuation of shock waves in copper and stainless steel  

SciTech Connect

By using shock pins, data were gathered on the trajectories of shock waves in stainless steel (SS-304L) and oxygen-free-high-conductivity copper (OFHC-Cu). Shock pressures were generated in these materials by impacting the appropriate target with thin (approx.1.5 mm) flying plates. The flying plates in these experiments were accelerated to high velocities (approx.4 km/s) by high explosives. Six experiments were conducted, three using SS-304L as the target material and three experiments using OFHC-Cu as the target material. Peak shock pressures generated in the steel experiments were approximately 109, 130, and 147 GPa and in the copper experiments, the peak shock pressures were approximately 111, 132, and 143 GPa. In each experiment, an attenuation of the shock wave by a following release wave was clearly observed. An extensive effort using two characteristic codes (described in this work) to theoretically calculate the attenuation of the shock waves was made. The efficacy of several different constitutive equations to successfully model the experiments was studied by comparing the calculated shock trajectories to the experimental data. Based on such comparisons, the conclusion can be drawn that OFHC-Cu enters a melt phase at about 130 GPa on the principal Hugoniot. There was no sign of phase changes in the stainless-steel experiments. In order to match the observed attenuation of the shock waves in the SS-304L experiments, it was necessary to include strength effects in the calculations. It was found that the values for the parameters in the strength equations were dependent on the equation of state used in the modeling of the experiments. 66 refs., 194 figs., 77 tabs.

Harvey, W.B.

1986-06-01

87

Water saturation effects on elastic wave attenuation in porous rocks with aligned fractures  

NASA Astrophysics Data System (ADS)

Elastic wave attenuation anisotropy in porous rocks with aligned fractures is of interest to seismic remote sensing of the Earth's structure and to hydrocarbon reservoir characterization in particular. We investigated the effect of partial water saturation on attenuation in fractured rocks in the laboratory by conducting ultrasonic pulse-echo measurements on synthetic, silica-cemented, sandstones with aligned penny-shaped voids (fracture density of 0.0298 ± 0.0077), chosen to simulate the effect of natural fractures in the Earth according to theoretical models. Our results show, for the first time, contrasting variations in the attenuation (Q-1) of P and S waves with water saturation in samples with and without fractures. The observed Qs/Qp ratios are indicative of saturation state and the presence or absence of fractures, offering an important new possibility for remote fluid detection and characterization.

Amalokwu, Kelvin; Best, Angus I.; Sothcott, Jeremy; Chapman, Mark; Minshull, Tim; Li, Xiang-Yang

2014-05-01

88

Unsteady plane smooth wave fronts of combined growing-attenuating type  

Microsoft Academic Search

Unsteady plane smooth wave fronts of a combined growing-attenuating type, where the peak of each strain wave is growing, are derived by a qualitative analysis. There are three different modes in this combined type: In mode I, the peak of a particle velocity wave is growing, but that of a stress wave is attenuating; in mode II, the former is

Yukio Sano; Isamu Miyamoto; Peter Arathoon

1997-01-01

89

Study of transmission line attenuation in broad band millimeter wave frequency range.  

PubMed

Broad band millimeter wave transmission lines are used in fusion plasma diagnostics such as electron cyclotron emission (ECE), electron cyclotron absorption, reflectometry and interferometry systems. In particular, the ECE diagnostic for ITER will require efficient transmission over an ultra wide band, 100 to 1000 GHz. A circular corrugated waveguide transmission line is a prospective candidate to transmit such wide band with low attenuation. To evaluate this system, experiments of transmission line attenuation were performed and compared with theoretical loss calculations. A millimeter wave Michelson interferometer and a liquid nitrogen black body source are used to perform all the experiments. Atmospheric water vapor lines and continuum absorption within this band are reported. Ohmic attenuation in corrugated waveguide is very low; however, there is Bragg scattering and higher order mode conversion that can cause significant attenuation in this transmission line. The attenuation due to miter bends, gaps, joints, and curvature are estimated. The measured attenuation of 15 m length with seven miter bends and eighteen joints is 1 dB at low frequency (300 GHz) and 10 dB at high frequency (900 GHz), respectively. PMID:24182108

Pandya, Hitesh Kumar B; Austin, M E; Ellis, R F

2013-10-01

90

Study of transmission line attenuation in broad band millimeter wave frequency range  

SciTech Connect

Broad band millimeter wave transmission lines are used in fusion plasma diagnostics such as electron cyclotron emission (ECE), electron cyclotron absorption, reflectometry and interferometry systems. In particular, the ECE diagnostic for ITER will require efficient transmission over an ultra wide band, 100 to 1000 GHz. A circular corrugated waveguide transmission line is a prospective candidate to transmit such wide band with low attenuation. To evaluate this system, experiments of transmission line attenuation were performed and compared with theoretical loss calculations. A millimeter wave Michelson interferometer and a liquid nitrogen black body source are used to perform all the experiments. Atmospheric water vapor lines and continuum absorption within this band are reported. Ohmic attenuation in corrugated waveguide is very low; however, there is Bragg scattering and higher order mode conversion that can cause significant attenuation in this transmission line. The attenuation due to miter bends, gaps, joints, and curvature are estimated. The measured attenuation of 15 m length with seven miter bends and eighteen joints is 1 dB at low frequency (300 GHz) and 10 dB at high frequency (900 GHz), respectively.

Pandya, Hitesh Kumar B. [ITER-India, IPR, Gandhinagar, Gujarat (India)] [ITER-India, IPR, Gandhinagar, Gujarat (India); Austin, M. E. [Institute for Fusion Studies, the University of Texas at Austin, Austin, Texas (United States)] [Institute for Fusion Studies, the University of Texas at Austin, Austin, Texas (United States); Ellis, R. F. [Laboratory for Plasma and Fusion Energy Studies, University of Maryland, College Park, Maryland 20742 (United States)] [Laboratory for Plasma and Fusion Energy Studies, University of Maryland, College Park, Maryland 20742 (United States)

2013-10-15

91

Surface Wave Constraints on Q in the Upper Mantle: Isolating the Signal of Attenuation  

NASA Astrophysics Data System (ADS)

We use more than 60,000 surface wave amplitude measurements in the period range 150-300 seconds (Ekström et al., 1997) to construct maps of attenuation, or 1/Q, in the upper mantle. We initially calculate Q by constructing a datum that uses four consecutive wave trains to desensitize the amplitudes to effects from the source, instrument, and elastic structure. These Q measurements are inverted for maps of even-degree attenuation structure, and the results show variations of approximately 50% from PREM. When the Q measurements are averaged for nearly coincident great-circle paths, the resulting attenuation maps are nearly identical to the original ones, confirming that, despite extraneous effects, there is a robust signal in the amplitudes. Using the method of Selby and Woodhouse (2002), we invert minor- and major-arc Rayleigh and Love wave amplitudes for even- and odd-degree Q structure. When we assume that the amplitude anomaly is due entirely to intrinsic attenuation, the ability of the models obtained through this process to fit the data is poor. We next include terms in the inversion that allow the source moment and instrument gain to be corrected. These corrections greatly improve the fit of the data by the models. The path integral approximation to the amplitude anomaly (Woodhouse and Wong, 1986) is used both to predict the effect of focusing from existing phase velocity maps and to jointly invert for attenuation and phase velocity. We also perform a pure-path regionalized inversion using a six-tectonic-region model of the Earth, GTR1 (Jordan, 1981). On the most simplistic level, the results show that oceans are more strongly attenuating than continents at all periods, and that the surface wave attenuation values of PREM fall in between those of continents and oceans. The results using the great-circle Q measurements show many familiar patterns, in particular that young oceans are more highly attenuating than older oceans. Although the data set of minor- and major-arc amplitudes is somewhat noisy, its ability to match the results of the great-circle Q regionalization is a good measure of the usefulness of the amplitude corrections described above.

Dalton, C.; Ekström, G.

2003-12-01

92

The attenuation of Love waves and toroidal oscillations of the earth.  

NASA Technical Reports Server (NTRS)

An attempt has been made to invert a large set of attenuation data for Love waves and toroidal oscillations in the earth, using a recent method by Backus and Gilbert. The difficulty in finding an acceptable model of internal friction which explains the data, under the assumption that the internal friction is independent of frequency, casts doubt on the validity of this assumption. A frequency-dependent model of internal friction is presented which is in good agreement with the seismic data and with recent experimental measurements of attenuation in rocks.

Jackson, D. D.

1971-01-01

93

Measurement of Broadband Temperature-Dependent Ultrasonic Attenuation and Dispersion Using Photoacoustics  

Microsoft Academic Search

The broadband ultrasonic characterization of biological fluids and tissues is important for the continued development and application of high-resolution ultrasound imaging modalities. Here, a photoacoustic technique for the transmission measurement of temperature-dependent ultrasonic attenuation and dispersion is described. The system uses a photoacoustic plane wave source constructed from a polymethylmethacrylate substrate with a thin optically absorbent layer. Broadband ultrasonic waves

Bradley E. Treeby; Benjamin Cox; Edward Zhang; Sarah Patch; Paul Beard

2009-01-01

94

Elastic Moduli and Seismic Wave Attenuation in Dry and Saturated Rock. Volume 2. Modulus Dispersion and Attenuation.  

National Technical Information Service (NTIS)

Four different laboratory techniques were used to determine Young's modulus and extensional wave attenuation as a function of frequency for the same rock specimen while minimizing variations in other important parameters. The data were then pieced togethe...

R. J. Martin R. W. Haupt W. Dupree X. M. Tang

1992-01-01

95

Experimental Study of a Method to Attenuate Surface Waves Using Artificially Generated Surface Currents.  

National Technical Information Service (NTIS)

Previous studies showed the effectiveness of laterally-sheared wakes of towed rigid grids in achieving substantial attenuation of following regular wave trains by refraction. Significant attenuation could be obtained in wakes with widths comparable to the...

R. I. Hires

1983-01-01

96

Effect of attenuation on backward-wave oscillation start oscillation condition  

Microsoft Academic Search

In a practical helix traveling-wave tube (TWT), there is always attenuator\\/sever for suppressing the oscillations, including backward-wave oscillation (BWO). The factors of the influencing BWO include start position of the attenuator, its length, and attenuation quantity. In the event that the attenuator\\/sever and nonuniformities in the phase velocity and beam potential were considered, a linear theory is employed to analyze

Zhaoyun Duan; Yubin Gong; Wenxiang Wang; Yanyu Wei; Minzhi Huang

2004-01-01

97

Phase velocities and attenuations of shear, Lamb, and Rayleigh waves in plate-like tissues submerged in a fluid (L).  

PubMed

In the past several decades, the fields of ultrasound and magnetic resonance elastography have shown promising results in noninvasive estimates of mechanical properties of soft tissues. These techniques often rely on measuring shear wave velocity due to an external or internal source of force and relating the velocity to viscoelasticity of the tissue. The mathematical relationship between the measured velocity and material properties of the myocardial wall, arteries, and other organs with non-negligible boundary conditions is often complicated and computationally expensive. A simple relationship between the Lamb-Rayleigh dispersion and the shear wave dispersion is derived for both the velocity and attenuation. The relationship shows that the shear wave velocity is around 20% higher than the Lamb-Rayleigh velocity and that the shear wave attenuation is about 20% lower than the Lamb-Rayleigh attenuation. Results of numerical simulations in the frequency range 0-500 Hz are presented. PMID:22225009

Nenadic, Ivan Z; Urban, Matthew W; Bernal, Miguel; Greenleaf, James F

2011-12-01

98

Temporal change in coda wave attenuation observed during an eruption of Mount St. Helens  

SciTech Connect

During the past few years there have been numerous reports of changes in coda wave attenuation occurring before major earthquakes. These observations are important because they may provide insight into stress-related structural changes taking place in the focal region prior to the occurrence of large earthquakes. The results of these studies led us to suspect that temporal changes in coda wave attenuation might also accompany volcanic eruptions. By measuring power decay envelopes for earthquakes at Mount St. Helens recorded before, during, and after an eruption that took place during September 3--6, 1981, we found that coda Q/sup -1/ for frequencies between 6 and 30 Hz was 20--30% higher before the eruption than after. The change is attributed to an increase in the density of open microcracks in the rock associated with inflation of the volcano prior to the eruption. Q/sup -1/ was found to be only weakly dependent on frequency and displayed a slight peak near 10 Hz. The weak frequency dependence is attributed to the dominance of intrinsic attenuation over scattering attenuation, since it is generally accepted that intrinsic attenuation is constant with frequency, whereas scattering attenuation decreases strongly at higher frequencies. The weak frequency dependence of Q/sup -1/ at Mount St. Helens contrasts with results reported for studies in nonvolcanic regions. The peak in Q/sup -1/ near 10 Hz at Mount St. Helens is attributed to the scale length of heterogeneity responsible for generating backscattered waves. Results for nonvolcanic regions have shown this peak to occur near 0.5 Hz. Thus a smaller scale length of heterogeneity is required to explain the 10-Hz peak at Mount St. Helens. copyright American Geophysical Union 1988

Fehler, M.; Roberts, P.; Fairbanks, T.

1988-05-10

99

Attenuation of High-Frequency Seismic Waves in Eastern Iran  

NASA Astrophysics Data System (ADS)

We investigated the frequency-dependent attenuation of the crust in Eastern Iran by analysis data from 132 local earthquakes having focal depths in the range of 5-25 km. We estimated the quality factor of coda waves (Q c) and body waves (Q p and Q s) in the frequency band of 1.5-24 Hz by applying the single backscattering theory of S-coda envelopes and the extended coda-normalization method, respectively. Considering records from recent earthquakes (Rigan M w 6.5, 2010/12/20, Goharan M w 6.2, 2013/5/11 and Sirch M w 5.5, 2013/1/21), the estimated values of Q c, Q p and Q s vary from 151 ± 49, 63 ± 6, and 93 ± 14 at 1.5 Hz to 1,994 ± 124, 945 ± 84 and 1,520 ± 123 at 24 Hz, respectively. The average frequency-dependent relationships (Q = Q o f n ) estimated for the region are Q c = (108 ± 10)f (0.96±0.01), Q p = (50 ± 5)f (1.01±0.04), and Q s = (75 ± 6)f (1.03±0.06). These results evidenced a frequency dependence of the quality factors Q c, Q p, and Q s, as commonly observed in tectonically active zones characterized by a high degree of heterogeneity, and the low value of Q indicated an attenuative crust beneath the entire region.

Mahood, M.

2014-03-01

100

PIC-MCC simulation of electromagnetic wave attenuation in partially ionized plasmas  

NASA Astrophysics Data System (ADS)

With the use of measured electron-neutral cross sections, the transmission properties of an electromagnetic (EM) wave in a nitrogen (N2) plasma and a helium (He) plasma are studied by means of PIC-MCC (the particle-in-cell method with collision modeling by the Monte Carlo method) simulation. The plasmas are assumed to be uniform, collisional and non-magnetized. Each type of species presented in the plasmas is treated by the PIC method and the electron-neutral collisions are treated by direct Monte Carlo simulation of particle trajectories. And then the dependence of power attenuation of the EM wave on plasma parameters and wave parameters is obtained and discussed. It is found that power attenuation of the EM wave is strongly affected by the plasma density, species of neutral gas, density of neutral gas and the frequency of the EM wave. Moreover, it is also found that the stopband (passband) of EM wave propagation turns out to be narrower (wider) in collisional plasmas both numerically and analytically.

Xu, Yanxia; Qi, Xin; Yang, Xue; Li, Chao; Zhao, Xiaoying; Duan, Wenshan; Yang, Lei

2014-02-01

101

Ultrasonic attenuation measurements in jet-engine nickel alloys  

Microsoft Academic Search

Ultrasonic attenuation plays a role in the inspection of metals, and accurate attenuation values are needed when making probability of detection estimates for internal defects in components. In this work we assess four broadband, pulse\\/echo, immersion methods for measuring attenuation by applying them to coupons of jet-engine nickel alloy. The different methods generally yield very similar results when care is

P. Haldipur; F. J. Margetan; Linxiao Yu; R. B. Thompson; Joseph A. Turner

2001-01-01

102

Lg waves attenuation studies over the Iranian Plateau and Zagros  

NASA Astrophysics Data System (ADS)

Waveforms from regional events collected over the last 15 years by the permanent seismological networks and temporary deployments deployed within the Iranian plateau provide a unique and unprecedented opportunity to investigate the crustal and mantle attenuation characteristics by analysis of the regional phases including Lg and Pg waves. We have investigated the crustal attenuation using Lg waveforms available from 305 stations consisting of 101 permanent and 204 temporary stations. This study is performed within the framework of a larger project aimed at developing high-resolution seismic attenuation models for the Iranian plateau and the Zagros mountains using different data and approaches. We have combined the Iranian data set with data from numerous networks across Turkey, Georgia, Azerbaijan, Syria, Jordan, and Saudi Arabia. This combination provides us with waveforms from over 550 stations spanning most of the Northern Middle East. Simultaneous inversion of the Lg Q values calculated using two-station paths gives us a model of Lg Q that extends from the western Anatolian plate to the eastern edge of the Iranian plateau. Prior studies have suggested strong complexity in the crustal and uppermost mantle attenuation structure beneath much of the Iranian plateau and the surrounding regions. Lg waves propagating over different paths in this region show strong variations in amplitude and frequency content due to this very complex structure. We have created a frequency dependent Lg Q model that covers most of the Iranian plateau using instrument corrected two station method that eliminates the contributions from the source. Our model maps Lg Q around 200 for most part of the central Iranian plateau and Alborz mountains whereas it is lower than 150 for the western Anatolian plateau. Relatively high Q values (>300) are observed in the Zagros belt that abruptly changes across the Zagros suture. We have also found unexpected results, including a high Q zone that surrounds the Caspian Sea. We argue that it originates from energy that is bending around the south Caspian Sea oceanic crust as well as efficient Lg propagation through the Alborz mountain crust.

Kaviani, A.; Sandvol, E. A.; Rumpker, G.; Ku, W.; Gok, R.

2012-12-01

103

Nonlinear attenuation of S-waves and Love waves within ambient rock  

NASA Astrophysics Data System (ADS)

obtain scaling relationships for nonlinear attenuation of S-waves and Love waves within sedimentary basins to assist numerical modeling. These relationships constrain the past peak ground velocity (PGV) of strong 3-4 s Love waves from San Andreas events within Greater Los Angeles, as well as the maximum PGV of future waves that can propagate without strong nonlinear attenuation. During each event, the shaking episode cracks the stiff, shallow rock. Over multiple events, this repeated damage in the upper few hundred meters leads to self-organization of the shear modulus. Dynamic strain is PGV divided by phase velocity, and dynamic stress is strain times the shear modulus. The frictional yield stress is proportional to depth times the effective coefficient of friction. At the eventual quasi-steady self-organized state, the shear modulus increases linearly with depth allowing inference of past typical PGV where rock over the damaged depth range barely reaches frictional failure. Still greater future PGV would cause frictional failure throughout the damaged zone, nonlinearly attenuating the wave. Assuming self-organization has taken place, estimated maximum past PGV within Greater Los Angeles Basins is 0.4-2.6 m s-1. The upper part of this range includes regions of accumulating sediments with low S-wave velocity that may have not yet compacted, rather than having been damaged by strong shaking. Published numerical models indicate that strong Love waves from the San Andreas Fault pass through Whittier Narrows. Within this corridor, deep drawdown of the water table from its currently shallow and preindustrial levels would nearly double PGV of Love waves reaching Downtown Los Angeles.

Sleep, Norman H.; Erickson, Brittany A.

2014-04-01

104

Attenuation of seismic waves in the Trinidad and Tobago area  

NASA Astrophysics Data System (ADS)

The attenuation of seismic waves from earthquakes located within the area bounded by 9-12°N and 60-63°W was estimated from short-period seismograms. Coda- Q, Qc, determinations were made for each of the six seismograph stations within the area, while spectral Q values from P-phases, Q?, were estimated for station TRN. The S-S single-scattering model was assumed for coda generation, and the ?-2 source model was assumed for the spectral Q determinations. The Qc values show a strong frequency dependence in the frequency range 1.5-12 Hz. The value of Q at 1 Hz, Qo, was found to lie within the range 107-132, while the rate of frequency dependence, n, extends from 0.80 to 1.06 for shallow events. For intermediate-depth events, Qo varies from 101 to 173 and n from 0.80 to 1.02. The Q? values obtained show a spatial variation within the region, the highest attenuation was obtained on land Trinidad.

Latchman, Joan L.; Ambeh, William B.; Lynch, Lloyd L.

1996-03-01

105

Imaging the attenuation structure beneath the northwestern margin of Colorado Plateau: Integrating seismic body-wave observations and forward modeling  

NASA Astrophysics Data System (ADS)

The upper mantle beneath the Colorado Plateau (CP) is characterized by high seismic velocities in the plateau interior and lower seismic velocities beneath the plateau margins, below the Basin and Range to the west and the Rio Grande Rift to the east. The seismic velocity contrast across the margins has been interpreted as a thermal- mechanical modification of the sub-CP lithospheric keel, by various mechanisms. Using teleseismic P- and S-wave spectra from the La Ristra 1.5 Array and EarthScope USArray Transportable Array (TA), we measure t*, the seismic parameter representing integrated attenuation along a ray path, across the western margin of the CP. For wave fields from two sets of earthquakes to the Northwest and Southeast of the CP, we measured the spectra of P- and S-waves at each station, relative to the spectra of the reference stations and extracted the differential attenuation factor (dt*) across the frequency band 0.2-4 Hz for P waves and 0.1-1.5 Hz for S waves for each event-station pair. To first order, both tp* and ts* varies from higher in the Basin and Range to lower on the CP, which suggests that coherent variations in attenuation are present across the Northwestern margin of the CP. However, the gradients of dt* for the two sets of NW and SE wave fields are significantly different, with a sharper gradient observed for the NW set. One of our primary questions concerns the origin of these variations: to what extent do they reflect the spatial distribution of intrinsic attenuation structure or wave propagation effects such as focusing and defocusing. To address these questions, our approach is to first build 1- and 2-D models for hypothetical spatial variations in state and compositional variables (T, water and melt content), and then calculate attenuation structures based on experimentally derived power-law frequency-dependent anelastic models. These structures are transferred into our anelastic finite difference wave propagation code, from which we measure t*. From 1D forward models of viscoelastic wave propagation, we show that teleseismic t* measurements are very sensitive to intrinsic attenuation structure at the lithosphere scale (upper 400 km) beneath the array. From 2D models that represent hypothetical structures of the western margin of the CP, wave propagation effects can also be explored. Comparison of 1D and 2D models will help us understand trade-offs between wave propagation effects and intrinsic attenuation on the measured t* variations across the CP.

Bellis, C.; Lin, P.; Holtzman, B. K.; Gaherty, J. B.; Roy, M.

2013-12-01

106

Experimental study of P-wave attenuation in partially frozen brine  

NASA Astrophysics Data System (ADS)

In order to estimate the amount of methane hydrates (MHs) which form in marine sediments at water depths greater than a few hundred meters, using not only velocity information but also attenuation information can provide much more information about MH-bearing sediments. While the presence of MH increases seismic velocity in the host sediment, recent works on sonic logging data show that sonic waveforms are also significantly affected by the presence of MH. These studies also showed a strong correlation of attenuation with velocity in the MH-bearing sediments. However, the increase of attenuation with increasing velocity is somewhat unintuitive. Thus, it is important elucidate the rock physical mechanism responsible for these phenomena. In this study, we conducted laboratory measurements to explain partially the reason for the physically unrealizable phenomenon. The ice generated from brine was assumed to be methane hydrate, namely, partially frozen brine was considered to be as an analogue for a mixture of methane hydrate and water present in the pore space of hydrate bearing sediments. We observed the variations of a transmitted wave with frequency content of 150-V1000 kHz through a liquid system to a solid-liquid coexistence system, changing its temperature from 20 ,aC to -20 ,aC. As a result, P-wave speed increases with changing in a solid-liquid coexistence system from a liquid system, while P-wave attenuation increases with changing in a solid-liquid coexistence system from a liquid system. Our observations indicate that the interaction in a micro scale of the solid and liquid causes the dissipation of transmitted wave energy.

Suzuki, M.; Matsushima, J.; Kato, Y.; Rokugawa, S.

2005-12-01

107

Extracting surface wave attenuation from seismic noise using correlation of the coda of correlation  

NASA Astrophysics Data System (ADS)

surface wave travel time information from the cross-correlation (CC) of seismic ambient noise has been a great success and remains fast growing. However, it is still challenging to exploit the amplitude content of the noise CC. Although spatial average is able to constrain somewhat meaningful attenuation using noise CC amplitudes, clear bias is observed when spatially varying attenuation is estimated with the traditional noise CC calculation methods. Perhaps the key lies in the development of novel techniques that can mitigate the effect of the uneven distribution of natural noise sources. In this paper, we propose a new method to use the correlation of the coda of correlation of noise (C3) for amplitude measurement. We examine the ability of the method to retrieve surface wave attenuation using data from selected line array stations of the USArray. By comparing C3-derived attenuation coefficients with those estimated from earthquake data, we demonstrate that C3 effectively reduces bias and allows for more reliable attenuation estimates from noise. This is probably because of the fact that the coda of noise correlation contains more diffused noise energy, and thus, the C3 processing effectively makes the noise source distribution more homogeneous. When selecting auxiliary stations for C3 calculation, we find that stations closer to noise sources (near the coast) tend to yield better signal-to-noise ratios. We suggest to preprocess noise data using a transient removal and temporal flattening method, to mitigate the effect of temporal fluctuation of the noise source intensity, and to retain relative amplitudes. In this study, we focus our analysis on 18 s measurements.

Zhang, Jian; Yang, Xiaoning

2013-05-01

108

Assessment of broadband ultrasonic attenuation measurements in inhomogeneous media  

Microsoft Academic Search

In this paper, we address the problem of evaluating the acoustic attenuation of “difficult” media, i.e. highly attenuating and scattering media. In a broadband, through transmission setup, the signals acquired from such media are characterized by a poor signal-to-noise ratio. Therefore, an accurate estimate of attenuation cannot be obtained from a single measurement, but multiple measurements must be combined. Two

M. Goueygou; B. Piwakowski; S. Ould Naffa; F. Buyle-Bodin

2002-01-01

109

Attenuation characteristics of coda waves in Mainland Gujarat (India)  

NASA Astrophysics Data System (ADS)

The attenuation characteristics based on coda waves of Mainland Gujarat (India) have been investigated in the present study. The broadband waveforms of 53 local earthquakes (Mw 1.1-3.3) having focal depths in the 6.0-33.6 km range recorded at five stations of Mainland Gujarat region has been used for the analysis. The frequency-dependent relationships (Q = Q0fn) for coda-Q (Qc) and dependency of coda-Q on lapse time windows have been determined for the said region. The average lapse time dependent coda-Q relations estimated for the region are: Qc = (87 ± 13)f(1.01 ± 0.06) (lapse time: 30 s), Qc = (112 ± 20)f(0.94 ± 0.08) (lapse time: 40 s) and Qc = (120 ± 22)f(0.76 ± 0.07) (lapse time: 50 s). The increase in Qc values with lapse time shows the depth dependence of Qc as longer lapse time windows will sample larger area. The observed quality factor is strongly dependent on frequency and lapse time, which indicates that the upper lithosphere, is more heterogeneous and seismotectonically active, while the lower lithosphere is homogeneous and relatively less active. A comparison of the coda-Q estimated for Mainland Gujarat region with those of nearby Kachchh and Saurashtra regions shows that Mainland Gujarat region is more heterogeneous. The rate of decay of attenuation (Q-1) with frequency for the relations obtained here is found to be comparable with those of other regions of the world though the absolute values differ. The obtained relations are expected to be useful for the estimation of source parameters of the earthquakes in the Mainland Gujarat region where no such relations were available earlier. These relations are also important for the simulation of earthquake strong ground motions in the region.

Gupta, Arun K.; Sutar, Anup K.; Chopra, Sumer; Kumar, Santosh; Rastogi, B. K.

2012-03-01

110

On the mechanisms of low-frequency wave attenuation by muddy seabeds  

NASA Astrophysics Data System (ADS)

Low-frequency (LF) wave energy increases as the waves shoal into shallow waters. However, recent field observations reported an unexpected near-shore LF wave energy dissipation on muddy seabeds, which cannot be explained by the classic two-layer formulation. Therefore, this phenomenon has been ascribed to either direct dissipation or nonlinear energy transfer. We investigate, by means of a two-layer nonlinear model, the role of the wave nonlinearity and mud viscosity in controlling these two competing mechanisms of mud-induced LF wave attenuation. Bispectral analysis of the simulated cases reveals the existence of three distinct LF wave attenuation regimes, which determine if the LF wave energy losses are owing to either nonlinear energy transfer or direct dissipation. These regimes can be predicted based on the Ursell number, whereas the mud viscosity controls the amount of energy transfer. The present findings clarify apparent inconsistencies in the literature regarding the mechanisms of LF wave attenuation by mud.

Torres-Freyermuth, Alec; Hsu, Tian-Jian

2014-04-01

111

Attenuation of Coda Waves in the Saurashtra Region, Gujarat (India)  

NASA Astrophysics Data System (ADS)

The attenuation characteristics based on coda waves of two areas—Jamnagar and Junagarh of Saurashtra, Gujarat (India)—have been investigated in the present study. The frequency dependent relationships have been developed for both the areas using single back scattering model. The broadband waveforms of the vertical components of 33 earthquakes (Mw 1.5-3.5) recorded at six stations of the Jamnagar area, and broadband waveforms of 68 earthquakes (Mw 1.6-5) recorded at five stations of the Junagarh area have been used for the analysis. The estimated relations for the Junagarh area are: Q c = (158 ± 5)f(0.99±0.04) (lapse time : 20 s), Q c = (170 ± 4.4)f(0.97±0.02) (lapse time : 30 s) and Q c = (229 ± 6.6)f(0.94±0.03) (lapse time : 40 s) and for the Jamnagar area are: Q c = (178 ± 3)f(0.95±0.05) (lapse time : 20 s), Q c = (224 ± 6)f(0.98±0.06) (lapse time : 30 s) and Q c = (282 ± 7)f(0.91±0.03) (lapse time : 40 s). These are the first estimates for the areas under consideration. The Junagarh area appears to be more attenuative as compared to the Jamnagar area. The increase in Q c values with lapse time found here for both the areas show the depth dependence of Q c as longer lapse time windows will sample larger area. The rate of decay of attenuation ( Q -1) with frequency for the relations obtained here is found to be comparable with those of other regions of the world though the absolute values differ. A comparison of the coda-Q estimated for the Saurashtra region with those of the nearby Kachchh region shows that the Saurashtra region is less heterogeneous. The obtained relations are expected to be useful for the estimation of source parameters of the earthquakes in the Saurashtra region of Gujarat where no such relations were available earlier. These relations are also important for the simulation of earthquake strong ground motions in the region.

Sharma, Babita; Kumar, Dinesh; Teotia, S. S.; Rastogi, B. K.; Gupta, Arun K.; Prajapati, Srichand

2012-01-01

112

Transmission, attenuation and reflection of shear waves in the human brain.  

PubMed

Traumatic brain injuries (TBIs) are caused by acceleration of the skull or exposure to explosive blast, but the processes by which mechanical loads lead to neurological injury remain poorly understood. We adapted motion-sensitive magnetic resonance imaging methods to measure the motion of the human brain in vivo as the skull was exposed to harmonic pressure excitation (45, 60 and 80 Hz). We analysed displacement fields to quantify the transmission, attenuation and reflection of distortional (shear) waves as well as viscoelastic material properties. Results suggest that internal membranes, such as the falx cerebri and the tentorium cerebelli, play a key role in reflecting and focusing shear waves within the brain. The skull acts as a low-pass filter over the range of frequencies studied. Transmissibility of pressure waves through the skull decreases and shear wave attenuation increases with increasing frequency. The skull and brain function mechanically as an integral structure that insulates internal anatomic features; these results are valuable for building and validating mathematical models of this complex and important structural system. PMID:22675163

Clayton, Erik H; Genin, Guy M; Bayly, Philip V

2012-11-01

113

Transmission, attenuation and reflection of shear waves in the human brain  

PubMed Central

Traumatic brain injuries (TBIs) are caused by acceleration of the skull or exposure to explosive blast, but the processes by which mechanical loads lead to neurological injury remain poorly understood. We adapted motion-sensitive magnetic resonance imaging methods to measure the motion of the human brain in vivo as the skull was exposed to harmonic pressure excitation (45, 60 and 80 Hz). We analysed displacement fields to quantify the transmission, attenuation and reflection of distortional (shear) waves as well as viscoelastic material properties. Results suggest that internal membranes, such as the falx cerebri and the tentorium cerebelli, play a key role in reflecting and focusing shear waves within the brain. The skull acts as a low-pass filter over the range of frequencies studied. Transmissibility of pressure waves through the skull decreases and shear wave attenuation increases with increasing frequency. The skull and brain function mechanically as an integral structure that insulates internal anatomic features; these results are valuable for building and validating mathematical models of this complex and important structural system.

Clayton, Erik H.; Genin, Guy M.; Bayly, Philip V.

2012-01-01

114

Measuring Distance with Sound Waves  

NSDL National Science Digital Library

Students learn about sound waves and use them to measure distances between objects. They explore how engineers incorporate ultrasound waves into medical sonogram devices and ocean sonar equipment. Students learn about properties, sources and applications of three types of sound waves, known as the infra-, audible- and ultra-sound frequency ranges. They use ultrasound waves to measure distances and understand how ultrasonic sensors are engineered.

Applying Mechatronics to Promote Science (AMPS) Program GK-12,

115

Shear-wave attenuation and velocity studies in southeastern Asia  

NASA Astrophysics Data System (ADS)

Models of shear-wave Q (Qmu) have been obtained for southeastern Asia using two methods. The first method inverts attenuation coefficients of the fundamental Rayleigh mode obtained using a standard two-station technique. The second method matches theoretical amplitude spectra for the fundamental and higher-mode Rayleigh waves computed for previously obtained velocity and assumed Qmu models, and earthquakes with known source depths and focal mechanisms, to observed spectra. The latter method provides much better regional coverage than the first and allows us to map lateral variations of Qmu at various levels in the crust and uppermost mantle. For the single-station, multi-mode method, I assumed an Earth model consisting of three layers, layer 1 being 10 km, layer 2 being 20 km, and layer 3 being 30 km in thickness. Qmu in layer 1 achieves lowest values (about 40) in the southern part of the Tibetan Plateau and in the Tarim basin and is highest (about 250) in southeastern China. The Qmu map of layer 2 indicates that the highest Qmu values (about 150) he in the central part of China and in parts of the Sino-Korean platform. The lowest Q mu value (about 50) occurs in Tibet and the Pamir thrust system. Layer 2 exhibits an overall increase in Qmu going from south to north. For layer 3 the resolution of crustal variations in Qmu, is poorer than layers 1 and 2. Available results, however, indicate that Qmu, is highest (about 180) under southern Mongolia and the Tarim basin, somewhat lower (100) beneath the southern portion of the Baikal Rift, and lowest (80) under the Pamir thrust system.

Jemberie, Alemayehu Lakew

116

Effects of permeability barriers and pore fluids on S-wave attenuation  

NASA Astrophysics Data System (ADS)

We study seismic attenuation of P- and S-waves caused by the physical mechanism of wave-induced fluid flow at the mesoscopic scale. Stress relaxation experiments are numerically simulated by solving Biot's equations for consolidation of two-dimensional poroelastic media with finite-element modeling. The experiments yield time-dependent stress-strain relations that are used to calculate the complex moduli from which frequency-dependent attenuation is determined. Our model consists of periodically distributed circular or elliptical heterogeneities with much lower porosity and permeability than the background medium, which contains 80% of the total pore space of the medium. This model can represent a hydrocarbon reservoir, where the porous background is either fully saturated with oil or gas, and the low porosity regions are always saturated with water. Three different saturation scenarios were considered: oil-saturated (80% oil, 20% water), gas-saturated (80% gas, 20% water), and fully water-saturated medium. Varying the dry bulk and shear moduli in the background and in the heterogeneities, a consistent tendency is observed in the relative behavior of the S-wave attenuation among the different saturation scenarios. First, in the gas-saturated media the S-wave attenuation is very low and much lower than in the oil-saturated or in the fully water-saturated media. Second, at low frequencies the S-wave attenuation is significantly higher in the oil-saturated media than in the fully water-saturated media. The P-wave attenuation exhibits a more variable relative behavior among the different saturation degrees, but one tendency is observed: At low frequencies the P-wave attenuation is higher in the oil-saturated media than in the fully water-saturated media. Based on the mechanism of wave-induced fluid flow and on our numerical results we suggest that the S-wave attenuation could be used as an indicator of fluid content in a reservoir, in addition to the P-wave attenuation. We also studied the influence of impermeable barriers in the medium. No effect is expected for P-wave attenuation. However, the impermeable barriers cause a significant increase in S-wave attenuation. This suggests that S-wave attenuation could be an indicator of permeability changes in, for example, fracturing operations.

Quintal, B.; Frehner, M.

2012-04-01

117

Compressional wave velocity and attenuation at ultrasonic and sonic frequencies in near-surface sedimentary rocks  

SciTech Connect

Laboratory ultrasonic measurements of compressional wave velocity and attenuation were made as a function of effective pressure on samples of limestone, sandstone and siltstone taken from a shallow borehole test site. The results indicate that the sandstones are pervaded by grain contact microcracks which dramatically affect their compressional wave attenuations. Clean sandstone shows a compressional wave quality factor (Q{sub p}) of 24 {+-} 2 at 5 MPa effective pressure (close to the estimated in situ burial pressure) and a Q{sub p} of 83 {+-} 29 at 60 MPa. The Q{sub p} of limestones and siltstones at the site show negligible and small increases with pressure in the laboratory, respectively. The strong pressure dependence of Q{sub p} in clean sandstone was used to infer the presence of in situ microcracks. Sediment velocities measured in the laboratory at about 1 MHz were compared with those from the full waveform sonic log at about 10 kHz implies that they must also be highly attenuating over a significant part of the frequency range 10 kHz to 1 MHz, to account for the magnitude of the observed velocity dispersion. Assuming the laboratory Q{sub p} values measured at 5 MPa remain constant down to 10 kHz predicts the observed dispersion quite well. Furthermore, the sonic log velocities of sandstones, limestones and siltstones (after normalizing each lithology for porosity and clay content) were found to reflect the same pressure (depth) trends observed in the laboratory. The results provide evidence for the existence of in situ microcracks in near-surface sediments.

Best, A.I. [Univ. of Reading (United Kingdom). Postgraduate Research Inst. for Sedimentology] [Univ. of Reading (United Kingdom). Postgraduate Research Inst. for Sedimentology; Sams, M.S. [Imperial College of Science, Technology and Medicine, London (United Kingdom). Dept. of Geology] [Imperial College of Science, Technology and Medicine, London (United Kingdom). Dept. of Geology

1997-03-01

118

The Self Attenuation Correction for Holdup Measurements, a Historical Perspective  

SciTech Connect

Self attenuation has historically caused both conceptual as well as measurement problems. The purpose of this paper is to eliminate some of the historical confusion by reviewing the mathematical basis and by comparing several methods of correcting for self attenuation focusing on transmission as a central concept.

Oberer, R. B.; Gunn, C. A.; Chiang, L. G.

2006-07-11

119

Assessment of broadband ultrasonic attenuation measurements in inhomogeneous media.  

PubMed

In this paper, we address the problem of evaluating the acoustic attenuation of "difficult" media, i.e. highly attenuating and scattering media. In a broadband, through transmission setup, the signals acquired from such media are characterized by a poor signal-to-noise ratio. Therefore, an accurate estimate of attenuation cannot be obtained from a single measurement, but multiple measurements must be combined. Two methods are considered to yield a single estimate of attenuation from multiple measurements. The first one, the "average attenuation" (AA) method, consists in a simple average of individual attenuation estimates. The second one, the "cross spectrum" (CS) method, is based on a system identification approach. In order to evaluate the estimation errors for these methods, ultrasonic signals transmitted through a material of known attenuation were simulated and mixed with both coherent and incoherent noise. In all tests performed, the "CS" method was found to yield the most accurate estimate. This method, combined time delay compensation, is then applied to real signals measured from a concrete slab. A valid frequency band for the attenuation estimate can be defined based on the coherence function. Results from this research are being applied to characterize the degradation of concrete structures using high-frequency ultrasound. PMID:12160042

Goueygou, M; Piwakowski, B; Ould Naffa, S; Buyle-Bodin, F

2002-05-01

120

Subduction zone guided waves: 3D modelling and attenuation effects  

NASA Astrophysics Data System (ADS)

Waveform modelling is an important tool for understanding complex seismic structures such as subduction zone waveguides. These structures are often simplified to 2D structures for modelling purposes to reduce computational costs. In the case of subduction zone waveguide affects, 2D models have shown that dispersed arrivals are caused by a low velocity waveguide, inferred to be subducted oceanic crust and/or hydrated outer rise normal faults. However, due to the 2D modelling limitations the inferred seismic properties such as velocity contrast and waveguide thickness are still debated. Here we test these limitations with full 3D waveform modelling. For waveguide effects to be observable the waveform must be accurately modelled to relatively high frequencies (> 2 Hz). This requires a small grid spacing due to the high seismic velocities present in subduction zones. A large area must be modelled as well due to the long propagation distances (400 - 600 km) of waves interacting with subduction zone waveguides. The combination of the large model area and small grid spacing required means that these simulations require a large amount of computational resources, only available at high performance computational centres like the UK National super computer HECTOR (used in this study). To minimize the cost of modelling for such a large area, the width of the model area perpendicular to the subduction trench (the y-direction) is made as small as possible. This reduces the overall volume of the 3D model domain. Therefore the wave field is simulated in a model ';corridor' of the subduction zone velocity structure. This introduces new potential sources of error particularly from grazing wave side reflections in the y-direction. Various dampening methods are explored to reduce these grazing side reflections, including perfectly matched layers (PML) and more traditional exponential dampening layers. Defining a corridor model allows waveguide affects to be modelled up to at least 2 Hz (needed for dispersion analysis) for the large model area that is considered. Simulations with a variety of quality factors (Q) at different parts of the subduction zone have been run to investigate how seismic attenuation affects the observed dispersed waveforms. We show that the low Q in the mantle wedge can improve the fit of the dispersed waveforms. A low Q in the low velocity waveguide structure however means that the delayed high frequency energy has very low amplitude, and so is not seen clearly at the surface. The Q of the low velocity crustal waveguide must therefore be greater than 250, suggesting that melting does not occur in the subducted oceanic crust at depths of 220 km or less. The velocity contrast seen at these depths must therefore be due to compositional variations. Benchmarking 2D elastic models with the 3D case shows that 2D models give a good approximation of 3D subduction zone waveguide structure. Visco-elastic simulations show that attenuation in the mantle wedge affects the observed dispersion, but the low velocity waveguide itself does not have significantly reduced Q. This work is an example of how the increasing computing power coupled with well-defined model boundaries can allow high resolution 3D modelling to be applied to specific structures of interest.

Garth, T.; Rietbrock, A.

2013-12-01

121

Stress Wave attenuation in SiC3D/Al Composite  

NASA Astrophysics Data System (ADS)

SiC3D/Al composite is a kind of special composite with interpenetrating network microstructure. The attenuation properties of stress wave propagation along the SiC3D/Al composite are studied by a Split Hopkinson Pressure Bar system & FEM simulations, and the attenuation mechanism is discussed in this paper. Results show that the attenuation rate of the stress wave in the composite is up to 1.73MPa·mm-1. The reduction of the amplitude of waves is caused by that plenty of interfaces between SiC and Al within the composite acting with stress waves. When the incident plane wave reaches the SiC3D/Al interface, reflection wave and transmission wave propagates in different directions along the irregular interface between SiC phase and aluminium phase due to the impedance mismatch of them, which leads to the divergence of stress wave. At the same time, some stress micro-focuses occurs in the aluminium phase for the complex wave superimposition, and some plastic deformation may take place within such micro-regions, which results in the consumption of stress wave energy. In conclusion, the stress wave attenuation is derived from divergence and consumption of stress wave.

Chunyuan, Yuan; Yangwei, Wang; Guoju, Li; Xu, Zhang; Jubin, Gao

2013-03-01

122

Estimation of seismic wave attenuation using sonic logging data -Comparison of estimating methods-  

NASA Astrophysics Data System (ADS)

Methane hydrates (MHs) that form in marine sediments at water depths greater than a few hundred meters are naturally occurring ice-like crystalline solids composed of methane molecules surrounded by water molecules. Several authors have estimated the amount of MH from seismic velocity data, as MH within sediment pore space stiffens the sediment and results in an increase in seismic velocity. Although seismic velocity is potentially a useful indicator of MH concentration, seismic velocity is also strongly controlled by the microscale MH distribution in pore spaces. While the presence of MH increases the seismic velocity of the host sediment, recent work on sonic logging data shows that sonic waveforms are also significantly attenuated by the presence of MH. The combined use of velocity and attenuation data provides greater insight into the MH-bearing sediments. Seismic attenuation can be conveniently separated into intrinsic attenuation and scattering attenuation. Scattering attenuation is the diminution in the amplitude of a seismic wave caused by the scattering of energy from a propagating pulse by heterogeneities in the medium of propagation. In scattering attenuation, energy is only redistributed to other parts of the wavefield. Scattering attenuation needs to be separated from total attenuation for precise estimation of attenuation value. Although there are many methods exist for estimating attenuation, it is not easy to determine which method is the best. The purpose of this study is to compare two methods for estimating attenuation. The method to be applied for estimating attenuation in this study was the median frequency shift method and spectral ratio method. Firstly, we estimated attenuation at Nankai Trough area. Secondly, we calculated scattering attenuation results by an inversion method, assuming the total attenuation factors to be linear combinations of the scattering and intrinsic attenuation factors. After introducing some assumptions to these relationships, we can estimate the scattering attenuation and isolate the intrinsic attenuation. Our results suggested that most part of total attenuation is scattering attenuation. Additionally, in order to validate our results we calculated scattering attenuation using synthetic data generated by the frequency-wavenumber integration method. To calculate synthetic data, we use a complex velocity with various enhancements such as causal attenuation, complex frequencies, and Filon integration. We estimated scattering attenuation from these synthetic data using two methods (inversion method and frequency-wavenumber integration method). Then we compared two methods (median frequency shift method and spectral ratio method) using these estimated scattering attenuation.

Suzuki, H.; Matsushima, J.

2010-12-01

123

A comparison of rain attenuation and drop size distributions measured in Chilbolton and Singapore  

NASA Astrophysics Data System (ADS)

Attenuation of radio waves caused by precipitation, especially in the form of rain, is considered to be the limiting factor for new communication systems that will exploit the radio wave spectrum at frequencies higher than about 30 GHz. Over the last 40 years, much effort has gone into theoretical studies characterizing rain in terms of statistical drop size distributions (DSDs), the shapes and velocity dependence of raindrops, and the calculation of raindrop extinction cross sections. This paper focuses on specific data sets and data processing and different ways of viewing DSDs that may help in quantifying some of the important parameters in radio wave propagation from experimental data. Values for the coefficients k and ? in the relationship for specific rain attenuation ? = kR? are presented, together with rain-rate-dependent parameters for fits of DSDs to standard statistical distributions. These are based on data from Chilbolton, England, and from Singapore. The distributions measured at Chilbolton and Singapore are very different, which strongly suggests that drop size distributions differ under different climatic conditions. Comparisons are also presented of attenuations calculated with values of k and ? determined from the DSDs and values found from logarithmic regression between simultaneous rain rate and attenuation measurements at 57, 97, 135, and 210 GHz at Chilbolton. This paper gives a strong indication that the International Telecommunication Union Radiocommunication Sector model for specific rain attenuation is inadequate at frequencies higher than about 70 GHz.

Åsen, Walther; Gibbins, Chris J.

2002-05-01

124

Attenuation of an electromagnetic wave by charged dust particles in a sandstorm.  

PubMed

We calculate the light scattering properties of the partially charged dust particles with the Mie theory for electromagnetic waves with different frequencies, and the attenuation coefficients of an electromagnetic wave propagating in a sandstorm are also calculated. The results show that the electric charges distributed on the sand surface have a significant effect on the attenuation of the electromagnetic wave, especially for a frequency lower than 40 GHz, and attenuation coefficients increase with the magnitude of charges carried by the dust particles (expressed by the charge-to-mass ratio in this paper). For the higher frequency electromagnetic wave, such as visible light, the effect of charges carried by sand particles on its attenuation is very little, which can be ignored. PMID:21151232

Xie, Li; Li, Xingcai; Zheng, Xiaojing

2010-12-10

125

BROADBAND ATTENUATION MEASUREMENTS OF PHOSPHOLIPID-SHELLED ULTRASOUND CONTRAST AGENTS  

PubMed Central

The aim of this study was to characterize the frequency-dependent acoustic attenuation of three phospholipid-shelled ultrasound contrast agents (UCAs): Definity, MicroMarker and echogenic liposomes. A broadband through-transmission technique allowed for measurement over 2 to 25 MHz with a single pair of transducers. Viscoelastic shell parameters of the UCAs were estimated using a linearized model developed by N. de Jong, L. Hoff, T. Skotland and N. Bom (Ultrasonics 1992; 30:95–103). The effect of diluent on the attenuation of these UCA suspensions was evaluated by performing attenuation measurements in 0.5% (w/v) bovine serum albumin and whole blood. Changes in attenuation and shell parameters of the UCAs were investigated at room temperature (25°C) and physiologic temperature (37°C). The attenuation of the UCAs diluted in 0.5% (w/v) bovine serum albumin was found to be identical to the attenuation of UCAs in whole blood. For each UCA, attenuation was higher at 37°C than at 25°C, underscoring the importance of conducting characterization studies at physiologic temperature. Echogenic liposomes exhibited a larger increase in attenuation at 37°C versus 25°C than either Definity or MicroMarker.

Raymond, Jason L.; Haworth, Kevin J.; Bader, Kenneth B.; Radhakrishnan, Kirthi; Griffin, Joseph K.; Huang, Shao-Ling; McPherson, David D.; Holland, Christy K.

2014-01-01

126

Nocturnal pulse wave attenuation is associated with office blood pressure in a population based cohort  

Microsoft Academic Search

Objective and BackgroundPulse wave amplitude (PWA) derived from the digital vascular bed has been used in sleep studies. The nocturnal attenuation of PWA has been shown to reflect sympathetic activation during sleep. We assessed the relationship between nocturnal PWA attenuation and office blood pressure (BP).

Ding Zou; Ludger Grote; Jakub Radlinski; Derek N. Eder; Ulf Lindblad; Jan Hedner

2009-01-01

127

Coplanar waveguides in silicon with low attenuation and slow wave reduction  

Microsoft Academic Search

This paper presents coplanar waveguide structures with low attenuation and slow-wave reduction implemented in standard silicon technologies and suitable for frequencies of up to 40 GHz. Optimization and modelling of slow-wave coplanar waveguides (SW-CPW) is provided here and compared to standard CPW models. An on-chip SW-CPW attenuation of 0.25 dB\\/mm at 40 GHz is obtained, compared with 2.8 dB\\/mm for

Rony E. Amaya; Ming Li; Robert G. Harrison; N. Garry Tarr

2007-01-01

128

Measurement of broadband temperature-dependent ultrasonic attenuation and dispersion using photoacoustics.  

PubMed

The broadband ultrasonic characterization of biological fluids and tissues is important for the continued development and application of high-resolution ultrasound imaging modalities. Here, a photoacoustic technique for the transmission measurement of temperature-dependent ultrasonic attenuation and dispersion is described. The system uses a photoacoustic plane wave source constructed from a polymethylmethacrylate substrate with a thin optically absorbent layer. Broadband ultrasonic waves are generated by illuminating the absorbent layer with nanosecond pulses of laser light. The transmitted ultrasound waves are detected by a planar 7-microm high-finesse Fabry-Perot interferometer. Temperature-induced thickness changes in the Fabry-Perot interferometer are tracked to monitor the sample temperature and maintain the sensor sensitivity. The measured -6 dB bandwidth for the combined source and sensor is 1 to 35 MHz, with an attenuation corrected signal level at 100 MHz of -10 dB. The system is demonstrated through temperature-dependent ultrasound measurements in castor oil and olive oil. Power law attenuation parameters are extracted by fitting the experimental attenuation data to a frequency power law while simultaneously fitting the dispersion data to the corresponding Kramers-Krönig relation. The extracted parameters are compared with other calibration measurements previously reported in the literature. PMID:19686982

Treeby, Bradley E; Cox, Benjamin T; Zhang, Edward Z; Patch, Sarah K; Beard, Paul C

2009-08-01

129

Spatial variation of Lg-wave attenuation in the Iberian Peninsula  

NASA Astrophysics Data System (ADS)

Within a global context, the Iberian Peninsula is a region where low to moderate (Mw < 5.5) earthquakes occur, most of them at shallow depths (h < 40 km). Seismicity concentrates mainly around the Pyrenean Range, the northwestern part of the peninsula, and the southern deformation zone that includes the Betics, the Alborán Sea and the Gulf of Cádiz. In recent years, considerable improvements in seismic data quality and geographic coverage have been made by the deployment of new permanent and portable broadband seismic stations in the Iberian Peninsula. The dense accumulation of seismic data has allowed us to investigate lateral variation of crustal seismic attenuation to develop the first regional 2D Lg-wave attenuation model for the entire Iberian Peninsula and its frequency dependence. Seismic data used consist of 71 events with magnitudes 3 ? mbLg ? 5.4 focal depths less than 30 km and epicentral distances from 100 to 1000 km which were recorded by 343 seismic stations between January 2008 and October 2013. To avoid confusion with fundamental-mode Love-wave energy on the transverse components, we only analyzed vertical component recordings. Among all the methods proposed to measure Lg attenuation, we considered the reliable Two-Station Method that allows removing the common source term by taking the ratio of Lg amplitudes recorded at two different stations along the same great-circle path from the same event. It requires, however, strict source-station configuration and dense event and station coverage. The spectral ratios collected over high-quality interstation paths were used to determine 1 Hz Lg Q (Q0) and its frequency dependence ?. Then, the lateral variations of the attenuation parameters were mapped using inversion. Lg-wave propagation was found to be inefficient or blocked for most of the paths crossing the Mediterranean Sea, the western Alborán Sea and the Strait of Gibraltar. Our results reflect large variations in Q0 values across the Iberian Peninsula which is in accordance with the different geotectonic characteristics present in the region. Low Lg Q0 values (high attenuation) were found in the Pyrenean Range and in the southern area whereas the most stable western part of Iberia showed high Lg Q0. The obtained Lg ? spatial variation map show that intermediate ? values characterize most of the analyzed region.

Noriega, Raquel; Ugalde, Arantza; Villaseñor, Antonio; José Jurado, María

2014-05-01

130

Effect of finite absorber dimensions on. gamma. -ray attenuation measurements  

SciTech Connect

Using /sup 137/Cs ..gamma.. rays, the effect of finite absorber dimensions on attenuation measurements has been studied. Copper and mercury targets were used. Absorber dimensions up to five mean free paths were used. A correlated effect was observed in the measurements due to absorber thickness and its dimensions in the transverse directions. The values of the attenuation coefficients for copper and mercury have also been determined.

Varier, K.M.; Kunju, S.N.; Madhusudanan, K.

1986-04-01

131

The Velocity and Attenuation of Acoustic Emission Waves in SiC/SiC Composites Loaded in Tension  

NASA Technical Reports Server (NTRS)

The behavior of acoustic waves produced by microfracture events and from pencil lead breaks was studied for two different silicon carbide fiber-reinforced silicon carbide matrix composites. The two composite systems both consisted of Hi-Nicalon (trademark) fibers and carbon interfaces but had different matrix compositions that led to considerable differences in damage accumulation and acoustic response. This behavior was primarily due to an order of magnitude difference in the interfacial shear stress for the two composite systems. Load/unload/reload tensile tests were performed and measurements were made over the entire stress range in order to determine the stress-dependence of acoustic activity for increasing damage states. It was found that using the extensional wave velocities from acoustic emission (AE) events produced from pencil lead breaks performed outside of the transducers enabled accurate measurements of the stiffness of the composite. The extensional wave velocities changed as a function of the damage state and the stress where the measurement was taken. Attenuation for AE waveforms from the pencil lead breaks occurred only for the composite possessing the lower interfacial shear stress and only at significantly high stresses. At zero stress after unloading from a peak stress, no attenuation occurred for this composite because of crack closure. For the high interfacial stress composite no attenuation was discernable at peak or zero stress over the entire stress-range of the composite. From these observations, it is believed that attenuation of AE waveforms is dependent on the magnitude of matrix crack opening.

Morscher, Gregory N.; Gyekenyesi, Andrew L.; Gray, Hugh R. (Technical Monitor)

2002-01-01

132

Attenuation and distortion of compression waves propagating in very long tube  

NASA Astrophysics Data System (ADS)

A lot of phenomena related to propagating various waves are seen when the high-speed train goes through the tunnel, the gas pipeline is broken due to an accident or the air brake of the wagon operates. For instance, a compression wave generated ahead of a high-speed train entering a tunnel propagates to the tunnel exit and spouts as a micro pressure wave, which causes an exploding sound. In order to estimate the magnitude correctly, the mechanism of the attenuation and distortion of a compression wave propagating along a very long tunnel must be understood and the experimental information on these phenomena is required. An experimental investigation is carried out to clarify the attenuation and distortion of the propagating compression wave in a very long tube. Experimental results show that the strength of a compression wave decreases with distance. The attenuation and distortion of compression waves are affected by the initial waveform of the compression wave and by the unsteady boundary layer induced by the propagating wave. The shape of a compression wave becomes different with the propagating distance; that is, a shock wave appears just head of a wavefront and an overshoot on pressure distribution is observed behind a shock wave due to the transition of the unsteady boundary layer.

Nakamura, Shinya; Sasa, Daisuke; Aoki, Toshiyuki

2011-03-01

133

Attenuation Measurements of Cell Pellets Using Through Transmission  

NASA Astrophysics Data System (ADS)

A better understanding of differences in ultrasound tissue characteristics (such as speed of sound, attenuation, and backscatter coefficients) of benign compared to malignant cells could lead to improved cancer detection and diagnosis. A narrow band technique for measuring ultrasonic speed of sound and attenuation of small biological materials was developed and tested. Several mechanical improvements were made to the system to drastically improve alignment, allowing for accurate measurements of small cell pellets. Narrow band attenuation measurements were made first with tissue-mimicking phantoms and then with three different types of cell pellets: Chinese hamster ovary cells, healthy human prostate cells, and cancerous human prostate cells. Attenuation and speed of sound results for all three cell types, as well as the culture medium and tissue mimicking phantoms, are presented for a frequency range of 5 to 25 MHz.

Vadas, Justin; Greene, Claudia; Grygotis, Emma; Kuhn, Stephen; Mahlalela, Sanele; Newland, Tinisha; Ovutmen, Idil; Herd, Maria-Teresa

2011-10-01

134

Attenuation of Lamb waves in the vicinity of a forbidden band in a phononic crystal.  

PubMed

When a Lamb wave propagates on a plate engraved by a periodic grating, it may exhibit attenuation. This attenuation is related to a coupling of this incident mode with other propagating modes. As the propagation takes place in a periodic medium, the dispersion curves of the modes are of interest because they exhibit passbands and stopbands related to the geometry of the waveguide. The goal of this work is to quantitatively establish the relation between the value of the attenuation of the propagating waves and the width of the forbidden bands appearing inside the Brillouin zone. This study is performed by using a finite element method (ATILA code). PMID:19811999

Bavencoffe, Maxime; Hladky-Hennion, Anne-Christine; Morvan, Bruno; Izbicki, Jean-Louis

2009-09-01

135

Ultrasonic attenuation measurements determine onset, degree, and completion of recrystallization  

NASA Technical Reports Server (NTRS)

Ultrasonic attenuation was measured for cold worked Nickel 200 samples annealed at increasing temperatures. Localized dislocation density variations, crystalline order and volume percent of recrystallized phase were determined over the anneal temperature range using transmission electron microscopy, X-ray diffraction, and metallurgy. The exponent of the frequency dependence of the attenuation was found to be a key variable relating ultrasonic attenuation to the thermal kinetics of the recrystallization process. Identification of this key variable allows for the ultrasonic determination of onset, degree, and completion of recrystallization.

Generazio, E. R.

1988-01-01

136

Reflective attenuator for high-energy laser measurements  

SciTech Connect

A high-energy laser attenuator in the range of 250 mJ (20 ns pulse width, 10 Hz repetition rate, 1064 nm wavelength) is described. The optical elements that constitute the attenuator are mirrors with relatively low reflectance, oriented at a 45 deg. angle of incidence. By combining three pairs of mirrors, the incoming radiation is collinear and has the same polarization orientation as the exit. We present damage testing and polarization-dependent reflectance measurements for 1064 nm laser light at 45 deg. angle of incidence for molybdenum, silicon carbide, and copper mirrors. A six element, 74 times (18 dB) attenuator is presented as an example.

Lehman, John H.; Livigni, David; Li Xiaoyu; Cromer, Christopher L.; Dowell, Marla L

2008-06-20

137

Effects of Pressure on Attenuation of Seismic Waves Through Sedimentary Rocks  

NASA Astrophysics Data System (ADS)

The research focuses on the effects of pressure on the Attenuation of Seismic waves propagating three different rock samples from the upper crust. The frequency used ranges from 1Hz to 1000Hz while the pressure was varied from atmospheric to 27,960 Nm -1. The research was carried out in Year 1 Laboratory of the Department of Physics of the Lagos State University Ojo, Nigeria. The Continuous wave Transmission and spectral Amplitude wave ratio technique was employed to determine the Attenuation Coefficient K for each rock sample. Attenuation Coefficients were plotted against frequency on scatter diagram and bar charts were constructed. Result shows sandstone attenuated most of the three rock types used.

Olorode, D. O.; Aregbede, O. S.; Olorode, G. T.

2009-05-01

138

Measurements of earth-space attenuation at 230 GHz  

NASA Technical Reports Server (NTRS)

Measurements of attenuation at 230 GHz through the total atmosphere due to the presence of oxygen and water vapor molecules, clouds, and rain are presented. The measurements were carried out using a specially designed superheterodyne receiver mounted on a sun tracker. Simultaneous measurements were also carried out at 13 GHz. For a measuring site close to sea level at Holmdel, NJ, the 'clear-sky' zenith attenuation was found as a function of the measured ground water vapor density. When the ground temperature was below about 7 C, most cloud and overcast gave less than 0.5-dB attenuation, whereas with a ground temperature greater than 13 C, cloud attenuation was 8-10 times greater. Calculations of zenith attenuation in the 230-GHz atmospheric window were also made using the Gross analytic line shape, Schulze-Tolbert empirical line shape, and an empirically modified Gross line shape. These calculations were based on determinations of water vapor density and temperature made at the measurement site, and on radiosonde measurements made at a distance of 80 km away.

Wrixon, G. T.; Mcmillan, R. W.

1978-01-01

139

Determination of particle size distributions from acoustic wave propagation measurements  

SciTech Connect

The wave equations for the interior and exterior of the particles are ensemble averaged and combined with an analysis by Allegra and Hawley [J. Acoust. Soc. Am. {bold 51}, 1545 (1972)] for the interaction of a single particle with the incident wave to determine the phase speed and attenuation of sound waves propagating through dilute slurries. The theory is shown to compare very well with the measured attenuation. The inverse problem, i.e., the problem of determining the particle size distribution given the attenuation as a function of frequency, is examined using regularization techniques that have been successful for bubbly liquids. It is shown that, unlike the bubbly liquids, the success of solving the inverse problem is limited since it depends strongly on the nature of particles and the frequency range used in inverse calculations. {copyright} {ital 1999 American Institute of Physics.}

Spelt, P.D.; Norato, M.A.; Sangani, A.S.; Tavlarides, L.L. [Department of Chemical Engineering and Materials Science, Syracuse University, Syracuse, New York 13244 (United States)] [Department of Chemical Engineering and Materials Science, Syracuse University, Syracuse, New York 13244 (United States)

1999-05-01

140

Crosswell seismic studies in gas hydrate-bearing sediments: P wave velocity and attenuation tomography  

NASA Astrophysics Data System (ADS)

We present crosswell seismic data from the Mallik 2002 Production Research Well Program, an international research project on Gas Hydrates in the Northwest Territories of Canada. The program participants include 8 partners; The Geological Survey of Canada (GSC), The Japan National Oil Corporation (JNOC), GeoForschungsZentrum Potsdam (GFZ), United States Geological Survey (USGS), United States Department of the Energy (USDOE), India Ministry of Petroleum and Natural Gas (MOPNG)/Gas Authority of India (GAIL) and the Chevron-BP-Burlington joint venture group. The crosswell seismic measurements were carried out by making use of two 1160 m deep observation wells (Mallik 3L-38 and 4L-38) both 45 m from and co-planar with the 1188 m deep production research well (5L-38). A high power piezo-ceramic source was used to generate sweeped signals with frequencies between 100 and 2000 Hz recorded with arrays of 8 hydrophones per depth level. A depth range between 800 and 1150 m was covered, with shot and receiver spacings of 0.75 m. High quality data could be collected during the survey which allow for application of a wide range of crosswell seismic methods. The initial data analysis included suppression of tube wave energy and picking of first arrivals. A damped least-squares algorithm was used to derive P-wave velocities from the travel time data. Next, t* values were derived from the decay of the amplitude spectra, which served as input parameters for a damped least-squares attenuation tomography. The initial results of the P-wave velocity and attenuation tomography reveal significant features reflecting the stratigraphic environment and allow for detection and eventually quantification of gas hydrate bearing sediments. A prominent correlation between P velocity and attenuation was found for the gas hydrate layers. This contradicts to the apparently more meaningful inverse correlation as it was determined for the gas hydrates at the Blake Ridge but supports the results from the Mallik 2L-38 sonic log data. The P velocities and attenuation values, if combined with other information can be important for the quantitative evaluation of the gas hydrate saturation, and may further constrain petrophysical models of the hydrate bearing sediment formation.

Bauer, K.; Haberland, Ch.; Pratt, R. G.; Ryberg, T.; Weber, M. H.; Mallik Working Group

2003-04-01

141

Fast compressional wave attenuation and dispersion due to conversion scattering into slow shear waves in randomly heterogeneous porous media.  

PubMed

Within the viscosity-extended Biot framework of wave propagation in porous media, the existence of a slow shear wave mode with non-vanishing velocity is predicted. It is a highly diffusive shear mode wherein the two constituent phases essentially undergo out-of-phase shear motions (slow shear wave). In order to elucidate the interaction of this wave mode with propagating wave fields in an inhomogeneous medium the process of conversion scattering from fast compressional waves into slow shear waves is analyzed using the method of statistical smoothing in randomly heterogeneous poroelastic media. The result is a complex wave number of a coherent plane compressional wave propagating in a dynamic-equivalent homogeneous medium. Analysis of the results shows that the conversion scattering process draws energy from the propagating wave and therefore leads to attenuation and phase velocity dispersion. Attenuation and dispersion characteristics are typical for a relaxation process, in this case shear stress relaxation. The mechanism of conversion scattering into the slow shear wave is associated with the development of viscous boundary layers in the transition from the viscosity-dominated to inertial regime in a macroscopically homogeneous poroelastic solid. PMID:21568383

Müller, Tobias M; Sahay, Pratap N

2011-05-01

142

Rain attenuation measurements: Variability and data quality assessment  

NASA Technical Reports Server (NTRS)

Year to year variations in the cumulative distributions of rain rate or rain attenuation are evident in any of the published measurements for a single propagation path that span a period of several years of observation. These variations must be described by models for the prediction of rain attenuation statistics. Now that a large measurement data base has been assembled by the International Radio Consultative Committee, the information needed to assess variability is available. On the basis of 252 sample cumulative distribution functions for the occurrence of attenuation by rain, the expected year to year variation in attenuation at a fixed probability level in the 0.1 to 0.001 percent of a year range is estimated to be 27 percent. The expected deviation from an attenuation model prediction for a single year of observations is estimated to exceed 33 percent when any of the available global rain climate model are employed to estimate the rain rate statistics. The probability distribution for the variation in attenuation or rain rate at a fixed fraction of a year is lognormal. The lognormal behavior of the variate was used to compile the statistics for variability.

Crane, Robert K.

1989-01-01

143

Anisotropic dispersion and attenuation due to wave-induced fluid flow: Quasi-static finite element modeling in poroelastic solids  

Microsoft Academic Search

Heterogeneous porous media such as hydrocarbon reservoir rocks are effectively described as anisotropic viscoelastic solids. They show characteristic velocity dispersion and attenuation of seismic waves within a broad frequency band, and an explanation for this observation is the mechanism of wave-induced pore fluid flow. Various theoretical models quantify dispersion and attenuation of normal incident compressional waves in finely layered porous

F. Wenzlau; J. B. Altmann; T. M. Müller

2010-01-01

144

Effect of soil texture on the propagation and attenuation of acoustic wave at unsaturated conditions  

NASA Astrophysics Data System (ADS)

SummaryA central issue in the successful application of acoustic wave method to detect subsurface hydrological properties is a better understanding of the influence of soil texture on the propagation and attenuation of acoustic wave as moisture content is varied, which was numerically investigated in the present study. Our earlier studies have demonstrated the existence of three different modes of acoustic wave in an elastic porous medium containing two immiscible, viscous, compressible fluids. Based on the dispersion equation obtained in the Lo-Sposito-Majer (LSM) model, the phase velocity and attenuation coefficient of the P1 and P2 waves which respectively propagate the fastest and second fastest were determined as a function of water saturation for 11 soil texture classes. The slowest wave (P3) was not characterized in this study since it does not travel far, due to very high attenuation. To provide a more general result, the calculated phase velocity and attenuation coefficient for different soil textures were normalized by those computed for sand. The normalization leads the resulting dimensionless parameters to be frequency independent throughout the whole range (up to 500 Hz) with Darcy's law remaining valid for the description of each fluid flow under wave excitation. The normalized phase velocity of the P1 wave was shown to have a substantially constant value at higher water saturations, but in the lower saturation range it first increases to reach a certain maximum value for different soil types and then decreases. The physical parameter controlling this phenomenon is the ratio of two effective non-wetting fluid storativity factors. Numerical results reveal that the normalized attenuation coefficient of the P1 wave is sensitive to soil texture and water saturation. Sand and loamy sand have the highest and second highest attenuation coefficients for the P1 wave, respectively. The magnitude of the normalized phase velocity of the P2 wave is found to be, with very few exceptions at nearly full saturations, linearly associated with the intrinsic permeability, while relating to the normalized attenuation coefficient of the P2 wave in an opposite manner. These results provide a quantitative clue for acoustic wave method to explore the physical properties in the shallow subsurface.

Lo, Wei-Cheng; Yeh, Chao-Lung; Tsai, Chang-Tai

2007-05-01

145

The Measurement of Broadband Ultrasonic Attenuation in Cancellous Bone  

Microsoft Academic Search

We have carried out measurements of the frequency dependence of ultrasonic attenuation in the range 0.2–1 MHz in in vitro samples of bovine cancellous bone and in vivo os calcis heel bones. A comparison of the results allows us to infer that the in vivo measurements are dependent on the bone mineral content of the os calcis. The bone mineral

C M Langton; S B Palmer; R W Porter

1984-01-01

146

Uncertainty calculation for noise attenuation measurements of hearing protectors  

NASA Astrophysics Data System (ADS)

The objective of this paper is to present a metrology study necessary for accreditation of the Industrial Noise Laboratory (LARI) at The Federal University of Santa Catarina-Brazil for hearing protector noise attenuation procedures using the Real Ear Attenuation at Threshold (REAT) method of the Brazilian National Institute of Metrology Standardization and Industrial Quality-INMETRO. A model for the calculation of measurement uncertainty was developed. The uncertainty calculation was based on the document, ``Guide to expression of uncertainty in measurement,'' by the International Organization for Standardization, first edition, corrected and reprinted in 1995, Geneva, Switzerland. The uncertainty of each source of error was estimated. The overall uncertainty of the noise attenuation measurement of hearing protectors was calculated for each 1/1 octave band frequency test and the results applied in the single number (NRRSF-noise reduction rating for subject fit) uncertainty calculation. It was concluded that the largest uncertainty is due to the determination of the subject's hearing thresholds.

Lima, Fabiano R.; Gerges, Samir N. Y.; Zmijevski, Thiago R. L.

2005-09-01

147

Attenuation zones of periodic pile barriers and its application in vibration reduction for plane waves  

NASA Astrophysics Data System (ADS)

The periodic theory of solid-state physics is introduced to study the reduction characteristics of periodic pile barriers. The attenuation zones of a two-dimensional infinite periodic pile barrier subjected to plane waves are analyzed by plane wave expansion method. Influences of soil parameters and pile configurations on the first no-directional attenuation zone are discussed. The screening effectiveness of finite periodic pile barriers is simulated by the finite element method. The present theoretical results are in well agreement with experimental data, which validates the existence of attenuation zones in the periodic structures. The results show that vibrations with frequencies in the attenuation zones can be reduced significantly. The present investigation provides a new concept for designing pile barriers to block mid-frequency vibration.

Huang, Jiankun; Shi, Zhifei

2013-09-01

148

Determination of ultrasonic parameters based on attenuation and dispersion measurements.  

PubMed

In the measurement of acoustic attenuation that obeys a power-low alpha = beta f, the traditional through-transmission method uses only the amplitude information of the recorded pulses to determine the two parameters, beta and n. In this paper, we propose a new method that utilizes both the amplitude and phase information of the pulses to determine the two parameters. According to this method, the two parameters are estimated by simultaneously performing a least squares fit to the attenuation data that are derived from the amplitude spectra of the pulses, and to the dispersion data that are derived from the phase spectra of the pulses. By fully utilizing the information contained in the recorded pulses and imposing additional constraints on the two parameters, the estimation uncertainty can be reduced. Experimental results from two specimens, one having a linear attenuation and one having a nonlinear attenuation, demonstrate that the new method produces a moderate variance reduction in the case of linear attenuation, and a significant variance reduction in the case of nonlinear attenuation. PMID:10197348

He, P

1998-10-01

149

Regional Body-Wave Attenuation Using a Coda Source Normalization Method: Application to MEDNET Records of Earthquakes in Italy  

SciTech Connect

We develop a new methodology to determine apparent attenuation for the regional seismic phases Pn, Pg, Sn, and Lg using coda-derived source spectra. The local-to-regional coda methodology (Mayeda, 1993; Mayeda and Walter, 1996; Mayeda et al., 2003) is a very stable way to obtain source spectra from sparse networks using as few as one station, even if direct waves are clipped. We develop a two-step process to isolate the frequency-dependent Q. First, we correct the observed direct wave amplitudes for an assumed geometrical spreading. Next, an apparent Q, combining path and site attenuation, is determined from the difference between the spreading-corrected amplitude and the independently determined source spectra derived from the coda methodology. We apply the technique to 50 earthquakes with magnitudes greater than 4.0 in central Italy as recorded by MEDNET broadband stations around the Mediterranean at local-to-regional distances. This is an ideal test region due to its high attenuation, complex propagation, and availability of many moderate sized earthquakes. We find that a power law attenuation of the form Q(f) = Q{sub 0}f{sup Y} fit all the phases quite well over the 0.5 to 8 Hz band. At most stations, the measured apparent Q values are quite repeatable from event to event. Finding the attenuation function in this manner guarantees a close match between inferred source spectra from direct waves and coda techniques. This is important if coda and direct wave amplitudes are to produce consistent seismic results.

Walter, W R; Mayeda, K; Malagnini, L; Scognamiglio, L

2007-02-01

150

Scattering versus intrinsic attenuation in the near surface: Measurements from permanent down-hole geophones  

NASA Astrophysics Data System (ADS)

The study of attenuation, equivalently of the quality (Q) factor, in the near-surface has three main applications. Firstly, low Q values, which are fairly common in near-surface materials, aside from decreasing seismic energy, also distort the waveforms; treatment of this disturbance effect with inverse-Q filters requires reliable Q estimates. Secondly, attenuation is a seismic parameter which improves interpretation of seismograms, as it is correlated with lithological properties. Thirdly, establishing near-surface Q is important in assessing site effects on strong ground motion events in applications of earthquake modeling and seismic engineering design. In view of these applications, theoretical treatments of attenuation, as well as laboratory and field tests, aim at estimating Q as a function of frequency and strain level. To determine the applicability of using different types of Q measurements, laboratory vs. in-situ measurements, to predict Q behavior across the different frequency bands and strain-levels of interest, it is necessary to model and separate the attenuation mechanisms into scattering (heterogeneity of elastic properties causing energy to be redistributed in space) and intrinsic (energy absorption due to conversion to heat) components. The objective of the presented study was to separate scattering versus intrinsic attenuation in the near-surface from a shallow VSP experiment conducted in the Lawrence Livermore National Laboratory (LLNL) facility using permanent down-hole geophones and a vertical impact source. Given that the VSP array was above the watertable, the Q characterization lies within the vadose zone. The first arrival of the vertically-incident transmitted P-wave was used to estimate the P-wave attenuation in the field data. Scattering attenuation estimates were established for a selected range of elastic models, which addressed both the effect of the variance of the elastic properties (density and velocity), as well as the effect of the structure of the variation, i.e. 1D versus 3D heterogeneity, on scattering. The elastic profiles were constructed from a superposition of interval values determined from log information (for the density profile) and first-break arrivals (for the velocity profile) and a high-frequency random component with variance range typical of sedimentary basins. The results for the scattering Q estimates related to one-way transmission and multiple reflections are in the order of 20 to 100, as obtained from 1D analytical and elastic finite-difference models. Given the short propagation pathlengths in the experiment, the results show that attenuation due to lateral heterogeneity is non-significant. In addition, given the experimental geometry of shallow VSP studies, it is shown that the scattering estimates are affected from the presence of the near-field, local impedance, and interference effects, which are termed 'pseudo-Q' factors. The pseudo-Q factors result in a biased estimate for scattering Q derived from both time-domain and frequency-domain methods. Hence, to accurately model the scattering vs. intrinsic components of attenuation, the bias due to the pseudo-Q factors was accounted for. The intrinsic attenuation was deduced from comparison of the field data Q estimates, which contain scattering attenuation, intrinsic attenuation and effects from pseudo-Q factors with the elastic synthetic Q estimates. Results yield very low intrinsic Q values, in the order of 4 to 15, for the low and high scattering attenuation estimates respectively. The intrinsic attenuation is attributed to the interaction of the free gas present in the vadose zone with the compressional wave, which is the only known mechanism that can lead to absorption at seismic frequencies (White, 1975; Dutta and Seriff, 1979). Visco-elastic modeling shows that aside from amplitude decay, an intrinsic attenuation mechanism is required to produce the pulse broadening observed in the field data. For a typical set of conditions in the vadose zone, analytical modeling shows that it is possible for the effect

Mangriotis, Maria-Daphne

151

Near-field measurement of infrared coplanar strip transmission line attenuation and propagation constants.  

PubMed

Impedance matched and low loss transmission lines are essential for optimal energy delivery through an integrated optical or plasmonic nanocircuit. A novel method for the measurement of the attenuation and propagation constants of an antenna-coupled coplanar strip (CPS) transmission line is demonstrated at 28.3 THz using scattering-type scanning near-field optical microscopy. Reflection of the propagating optical wave upon an open-circuit or short-circuit load at the terminal of the CPS provides a standing voltage wave, which is mapped through the associated surface-normal E(z) electric near-field component at the metal-air interface. By fitting the analytical standing wave expression to the near-field data, the transmission line properties are determined. Full-wave models and measured results are presented and are in excellent agreement. PMID:20941067

Krenz, Peter M; Olmon, Robert L; Lail, Brian A; Raschke, Markus B; Boreman, Glenn D

2010-10-11

152

Plasma parameter measurements using neutral-particle-beam attenuation  

NASA Astrophysics Data System (ADS)

Intense and energetic neutral particle beam injection used for fueling or heating magnetically confined, controlled fusion experimental plasmas which make diagnostic measurements of the plasmas are discussed. The attenuation of an atomic beam when passing through a plasma gives the plasma line density. Orthogonal arrays of highly collimated detectors of the secondary electron emission type are used in magnetic mirror experiments to measure neutral beam attenuation along chords through the plasma volume at different radial and axial positions. The radial array is used to infer the radial plasma density profile; the axial array, to infer the axial plasma density profile and the ion angular distribution at the plasma midplane.

Foote, J. H.; Molvik, A. W.; Turner, W. C.

1982-07-01

153

Effects of fracture contact areas on seismic attenuation due to wave-induced fluid flow  

NASA Astrophysics Data System (ADS)

Wave-induced fluid flow (WIFF) between fractures and the embedding matrix is considered to be a predominant seismic attenuation mechanism in fractured rocks. That is, due to the strong compressibility contrast between fractures and embedding matrix, seismic waves induce strong fluid pressure gradients, followed by local fluid flow between such regions, which in turn produces significant energy dissipation. Natural fractures can be conceptualized as two surfaces in partial contact, containing very soft and highly permeable material in the inner region. It is known that the characteristics of the fracture contact areas control the mechanical properties of the rock sample, since as the contact area increases, the fracture becomes stiffer. Correspondingly, the detailed characteristics of the contact area of fractures are expected to play a major role in WIFF-related attenuation. To study this topic, we consider a simple model consisting of a horizontal fracture located at the center of a porous rock sample and represented by a number of rectangular cracks of constant height separated by contact areas. The cracks are modelled as highly compliant, porous, and permeable heterogeneities, which are hydraulically connected to the background material. We include a number of rectangular regions of background material separating the cracks, which represent the presence of contact areas of the fracture. In order to estimate the WIFF effects, we apply numerical oscillatory relaxation tests based on the quasi-static poro-elastic equations. The equivalent undrained, complex plane-wave modulus, which allows to estimate seismic attenuation and velocity dispersion for the vertical direction of propagation, is expressed in terms of the imposed displacement and the resulting average vertical stress at the top boundary. In order to explore the effects of the presence of fracture contact areas on WIFF effects, we perform an exhaustive sensitivity analysis considering different characteristics for the regions of contact. This study enabled us to observe that in the case of regular distributions of contact areas seismic attenuation and dispersion levels increase with decreasing size or increasing separation of the contact areas. In addition, we corroborated that for the same fraction of contact area, seismic attenuation and dispersion are weaker for regular distributions of contact areas and stronger when they are located within a narrow cluster. Our numerical approach also allowed us to explore the vertical solid displacement gap across fractures. We found that this parameter is strongly affected by the geometrical details of the fracture contact areas and turned out to be complex-valued and frequency-dependent due to WIFF effects. Finally, using laboratory measurements of changes in fracture contact area as a function of the applied stress, we proposed a model illustrating the effects related to the evolution of the contact area with increasing stress. The corresponding results suggest that seismic attenuation and phase velocity may constitute useful attributes to extract information on the prevailing effective stress of fractured media.

Germán Rubino, J.; Müller, Tobias M.; Milani, Marco; Holliger, Klaus

2014-05-01

154

Laboratory measurements of seismic attenuation in partially saturated rocks  

NASA Astrophysics Data System (ADS)

Laboratory measurements of seismic attenuation and transient pore fluid pressure are performed on partially saturated Berea sandstone and synthetic borosilicate samples. Various degrees of water (liquid) and nitrogen (gas) saturation are considered. These measurements are carried out at room temperature and under confining pressures varying from ambient conditions up to 25 MPa. The cylindrical samples are 25 cm long and have a diameter of 7.6 cm. In the context of the experimental setup, the solid frames of both the Berea sandstone and the borosilicate samples can be considered homogenous, which in turn allows for isolating and exploring the effects of partial saturation on seismic attenuation. We employ the sub-resonance method, which is based on the application of a time-harmonic vertical stress to the top of the sample and the measurement of the thus resulting strain. For any given frequency, the attenuation is then inferred as the tangent of the phase shift between the applied stress and the observed strain. Using five equally spaced sensors along the central axis of the cylindrical sample, we measure the transient fluid pressure induced by the application of a step-function-type vertical stress to the top of the sample. Both the sensors and the sample are sealed off with the regard to the confining environment. Together with the numerical results from corresponding compressibility tests based on the quasi-static poroelastic equations, these transient fluid pressure measurements are then used to assist the interpretation of the seismic attenuation measurements.

Chapman, Samuel; Tisato, Nicola; Quintal, Beatriz; Holliger, Klaus

2014-05-01

155

Evaluation of laminated composite structures using ultrasonic attenuation measurement  

NASA Astrophysics Data System (ADS)

The existence of delamination and porosity in laminated composite structures will degrade the strength of the structures. The detection of delamination can be easily obtained using ultrasonic C-scan or A-scan methods. But, the detection of porosity in laminated structures has been a difficult task for years, especially in production condition. This paper will analytically evaluate the current techniques used in industry, and develop accurate attenuation measurement methods for the evaluation of porosity. The test samples, which are used in the laminated structures of the German airbus by Textron Aerostructures, Inc, will be tested using ultrasonic C-scan and grid-based A-scan methods. The digitized waveforms are stored and analyzed using different attenuation measurement algorithms. The volume of porosity is calculated using digital imaging analysis. Finally, the correlation between ultrasonic attenuation and the volume fraction of porosity are calculated and analyzed.

Shen, Peitao; Houghton, J. R.

156

Resistivity Measurement of Semiconducting Epitaxial Layers by the Reflection of a Hyperfrequency Electromagnetic Wave  

Microsoft Academic Search

The aim of this work is to measure nondestructively the resistivity of a semiconductor in the form of an epitaxial layer. The method involves the measurements of the attenuation suffered by an electromagnetic wave reflected by a semiconducting surface. A mathematical discussion leads in the first instance to the establishment of a theoretical curve of attenuation vs. resistivity for homogeneous

M. R. E. Bichara; J. P. R. Poitevin

1964-01-01

157

Shear wave attenuation and micro-fluidics in water-saturated sand and glass beads.  

PubMed

An improvement in the modeling of shear wave attenuation and speed in water-saturated sand and glass beads is introduced. Some dry and water-saturated materials are known to follow a constant-Q model in which the attenuation, expressed as Q(-1), is independent of frequency. The associated loss mechanism is thought to lie within the solid frame. A second loss mechanism in fluid-saturated porous materials is the viscous loss due to relative motion between pore fluid and solid frame predicted by the Biot-Stoll model. It contains a relaxation process that makes the Q(-1) change with frequency, reaching a peak at a characteristic frequency. Examination of the published measurements above 1?kHz, particularly those of Brunson (Ph.D. thesis, Oregon State University, Corvalis, 1983), shows another peak, which is explained in terms of a relaxation process associated with the squirt flow process at the grain-grain contact. In the process of deriving a model for this phenomenon, it is necessary to consider the micro-fluidic effects associated with the flow within a thin film of water confined in the gap at the grain-grain contact and the resulting increase in the effective viscosity of water. The result is an extended Biot model that is applicable over a broad band of frequencies. PMID:24907791

Chotiros, Nicholas P; Isakson, Marcia J

2014-06-01

158

Dynamic aspects of apparent attenuation and wave localization in layered media  

USGS Publications Warehouse

We present a theory for multiply-scattered waves in layered media which takes into account wave interference. The inclusion of interference in the theory leads to a new description of the phenomenon of wave localization and its impact on the apparent attenuation of seismic waves. We use the theory to estimate the localization length at a CO2 sequestration site in New Mexico at sonic frequencies (2 kHz) by performing numerical simulations with a model taken from well logs. Near this frequency, we find a localization length of roughly 180 m, leading to a localization-induced quality factor Q of 360.

Haney, M. M.; van, Wijk, K.

2008-01-01

159

Measurement of Acoustic Attenuation and Absorption Coefficients using Thermometry  

Microsoft Academic Search

Accurate knowledge of both the attenuation and the absorption coefficient of tissue are required when planning an optimal high intensity focused ultrasound treatment. A novel technique for simple measurement of this parameters has been developed in which a thin-film thermocouple (TFT) is placed between two layers of tissue of different thicknesses. The sample can be rotated about an axis through

Hugh Morris; Ian Rivens; Adam Shaw; Gail Ter Haar

2007-01-01

160

Measurement of acoustic attenuation in South Pole ice  

Microsoft Academic Search

Using the South Pole Acoustic Test Setup (SPATS) and a retrievable transmitter deployed in holes drilled for the IceCube experiment, we have measured the attenuation of acoustic signals by South Pole ice at depths between 190m and 500m. Three data sets, using different acoustic sources, have been analyzed and give consistent results. The method with the smallest systematic uncertainties yields

R. Abbasi; Y. Abdou; T. Abu-Zayyad; J. Adams; J. A. Aguilar; M. Ahlers; K. Andeen; J. Auffenberg; X. Bai; M. Baker; S. W. Barwick; R. Bay; J. L. Bazo Alba; K. Beattie; J. J. Beatty; S. Bechet; J. K. Becker; M. L. Benabderrahmane; J. Berdermann; P. Berghaus; D. Berley; E. Bernardini; D. Bertrand; M. Bissok; E. Blaufuss; D. J. Boersma; C. Bohm; S. Böser; O. Botner; L. Bradley; J. Braun; S. Buitink; M. Carson; D. Chirkin; B. Christy; J. Clem; F. Clevermann; S. Cohen; C. Colnard; D. F. Cowen; M. V. D’Agostino; C. De Clercq; L. Demirörs; O. Depaepe; F. Descamps; P. Desiati; G. de Vries-Uiterweerd; T. DeYoung; J. C. Díaz-Vélez; J. Dreyer; M. R. Duvoort; R. Ehrlich; J. Eisch; R. W. Ellsworth; O. Engdegård; S. Euler; P. A. Evenson; O. Fadiran; A. R. Fazely; T. Feusels; K. Filimonov; C. Finley; M. M. Foerster; B. D. Fox; A. Franckowiak; R. Franke; T. K. Gaisser; J. Gallagher; R. Ganugapati; M. Geisler; L. Gerhardt; L. Gladstone; T. Glüsenkamp; A. Goldschmidt; J. A. Goodman; D. Grant; T. Griesel; A. Gross; S. Grullon; R. M. Gunasingha; L. Gustafsson; C. Ha; A. Hallgren; F. Halzen; K. Han; K. Hanson; K. Helbing; P. Herquet; S. Hickford; G. C. Hill; K. D. Hoffman; A. Homeier; K. Hoshina; D. Hubert; W. Huelsnitz; J.-P. Hülß; K. Hultqvist; S. Hussain; R. L. Imlay; A. Ishihara; J. Jacobsen; G. S. Japaridze; H. Johansson; J. M. Joseph; K.-H. Kampert; A. Kappes; T. Karg; A. Karle; J. L. Kelley; N. Kemming; P. Kenny; J. Kiryluk; F. Kislat; S. R. Klein; S. Knops; J.-H. Köhne; G. Kohnen; H. Kolanoski; L. Köpke; D. J. Koskinen; M. Kowalski; T. Kowarik; M. Krasberg; T. Krings; G. Kroll; K. Kuehn; T. Kuwabara; M. Labare; S. Lafebre; K. Laihem; H. Landsman; R. Lauer; R. Lehmann; D. Lennarz; J. Lünemann; J. Madsen; P. Majumdar; R. Maruyama; K. Mase; H. S. Matis; M. Matusik; K. Meagher; M. Merck; P. Mészáros; T. Meures; E. Middell; N. Milke; T. Montaruli; R. Morse; S. M. Movit; R. Nahnhauer; J. W. Nam; U. Naumann; P. Nießen; D. R. Nygren; S. Odrowski; A. Olivas; M. Olivo; S. Panknin; L. Paul; C. Pérez de los Heros; J. Petrovic; A. Piegsa; D. Pieloth; R. Porrata; J. Posselt; P. B. Price; M. Prikockis; G. T. Przybylski; K. Rawlins; P. Redl; E. Resconi; W. Rhode; M. Ribordy; A. Rizzo; J. P. Rodrigues; F. Rothmaier; C. Rott; C. Roucelle; T. Ruhe; D. Rutledge; B. Ruzybayev; D. Ryckbosch; H.-G. Sander; S. Sarkar; K. Schatto; S. Schlenstedt; T. Schmidt; D. Schneider; A. Schukraft; O. Schulz; M. Schunck; D. Seckel; B. Semburg; S. H. Seo; Y. Sestayo; S. Seunarine; A. Silvestri; G. M. Spiczak; C. Spiering; M. Stamatikos; T. Stanev; G. Stephens; T. Stezelberger; R. G. Stokstad; S. Stoyanov; E. A. Strahler; T. Straszheim; G. W. Sullivan; Q. Swillens; I. Taboada; A. Tamburro; O. Tarasova; A. Tepe; S. Ter-Antonyan; P. A. Toale; D. Tosi; D. Tur?an; N. van Eijndhoven; J. Vandenbroucke; A. Van Overloop; J. van Santen; B. Voigt; C. Walck; T. Waldenmaier; M. Wallraff; C. Wendt; S. Westerhoff; N. Whitehorn; K. Wiebe; C. H. Wiebusch; G. Wikström; D. R. Williams; R. Wischnewski; H. Wissing; K. Woschnagg; C. Xu; X. W. Xu; J. P. Yanez; G. Yodh; S. Yoshida; P. Zarzhitsky

2011-01-01

161

Plasma parameter measurements using neutral-particle-beam attenuation  

Microsoft Academic Search

Intense and energetic neutral particle beam injection used for fueling or heating magnetically confined, controlled fusion experimental plasmas which make diagnostic measurements of the plasmas are discussed. The attenuation of an atomic beam when passing through a plasma gives the plasma line density. Orthogonal arrays of highly collimated detectors of the secondary electron emission type are used in magnetic mirror

J. H. Foote; A. W. Molvik; W. C. Turner

1982-01-01

162

Measurement of acoustic attenuation in South Pole ice  

NASA Astrophysics Data System (ADS)

Using the South Pole Acoustic Test Setup (SPATS) and a retrievable transmitter deployed in holes drilled for the IceCube experiment, we have measured the attenuation of acoustic signals by South Pole ice at depths between 190 m and 500 m. Three data sets, using different acoustic sources, have been analyzed and give consistent results. The method with the smallest systematic uncertainties yields an amplitude attenuation coefficient ? = 3.20 ± 0.57 km-1 between 10 and 30 kHz, considerably larger than previous theoretical estimates. Expressed as an attenuation length, the analyses give a consistent result for ? ? 1/? of ˜300 m with 20% uncertainty. No significant depth or frequency dependence has been found.

IceCube Collaboration; Abbasi, R.; Abdou, Y.; Abu-Zayyad, T.; Adams, J.; Aguilar, J. A.; Ahlers, M.; Andeen, K.; Auffenberg, J.; Bai, X.; Baker, M.; Barwick, S. W.; Bay, R.; Bazo Alba, J. L.; Beattie, K.; Beatty, J. J.; Bechet, S.; Becker, J. K.; Becker, K.-H.; Benabderrahmane, M. L.; Berdermann, J.; Berghaus, P.; Berley, D.; Bernardini, E.; Bertrand, D.; Besson, D. Z.; Bissok, M.; Blaufuss, E.; Boersma, D. J.; Bohm, C.; Böser, S.; Botner, O.; Bradley, L.; Braun, J.; Buitink, S.; Carson, M.; Chirkin, D.; Christy, B.; Clem, J.; Clevermann, F.; Cohen, S.; Colnard, C.; Cowen, D. F.; D'Agostino, M. V.; Danninger, M.; de Clercq, C.; Demirörs, L.; Depaepe, O.; Descamps, F.; Desiati, P.; de Vries-Uiterweerd, G.; Deyoung, T.; Díaz-Vélez, J. C.; Dreyer, J.; Dumm, J. P.; Duvoort, M. R.; Ehrlich, R.; Eisch, J.; Ellsworth, R. W.; Engdegård, O.; Euler, S.; Evenson, P. A.; Fadiran, O.; Fazely, A. R.; Feusels, T.; Filimonov, K.; Finley, C.; Foerster, M. M.; Fox, B. D.; Franckowiak, A.; Franke, R.; Gaisser, T. K.; Gallagher, J.; Ganugapati, R.; Geisler, M.; Gerhardt, L.; Gladstone, L.; Glüsenkamp, T.; Goldschmidt, A.; Goodman, J. A.; Grant, D.; Griesel, T.; Groß, A.; Grullon, S.; Gunasingha, R. M.; Gurtner, M.; Gustafsson, L.; Ha, C.; Hallgren, A.; Halzen, F.; Han, K.; Hanson, K.; Helbing, K.; Herquet, P.; Hickford, S.; Hill, G. C.; Hoffman, K. D.; Homeier, A.; Hoshina, K.; Hubert, D.; Huelsnitz, W.; Hülß, J.-P.; Hulth, P. O.; Hultqvist, K.; Hussain, S.; Imlay, R. L.; Ishihara, A.; Jacobsen, J.; Japaridze, G. S.; Johansson, H.; Joseph, J. M.; Kampert, K.-H.; Kappes, A.; Karg, T.; Karle, A.; Kelley, J. L.; Kemming, N.; Kenny, P.; Kiryluk, J.; Kislat, F.; Klein, S. R.; Knops, S.; Köhne, J.-H.; Kohnen, G.; Kolanoski, H.; Köpke, L.; Koskinen, D. J.; Kowalski, M.; Kowarik, T.; Krasberg, M.; Krings, T.; Kroll, G.; Kuehn, K.; Kuwabara, T.; Labare, M.; Lafebre, S.; Laihem, K.; Landsman, H.; Lauer, R.; Lehmann, R.; Lennarz, D.; Lünemann, J.; Madsen, J.; Majumdar, P.; Maruyama, R.; Mase, K.; Matis, H. S.; Matusik, M.; Meagher, K.; Merck, M.; Mészáros, P.; Meures, T.; Middell, E.; Milke, N.; Montaruli, T.; Morse, R.; Movit, S. M.; Nahnhauer, R.; Nam, J. W.; Naumann, U.; Nießen, P.; Nygren, D. R.; Odrowski, S.; Olivas, A.; Olivo, M.; Ono, M.; Panknin, S.; Paul, L.; Pérez de Los Heros, C.; Petrovic, J.; Piegsa, A.; Pieloth, D.; Porrata, R.; Posselt, J.; Price, P. B.; Prikockis, M.; Przybylski, G. T.; Rawlins, K.; Redl, P.; Resconi, E.; Rhode, W.; Ribordy, M.; Rizzo, A.; Rodrigues, J. P.; Roth, P.; Rothmaier, F.; Rott, C.; Roucelle, C.; Ruhe, T.; Rutledge, D.; Ruzybayev, B.; Ryckbosch, D.; Sander, H.-G.; Sarkar, S.; Schatto, K.; Schlenstedt, S.; Schmidt, T.; Schneider, D.; Schukraft, A.; Schultes, A.; Schulz, O.; Schunck, M.; Seckel, D.; Semburg, B.; Seo, S. H.; Sestayo, Y.; Seunarine, S.; Silvestri, A.; Slipak, A.; Spiczak, G. M.; Spiering, C.; Stamatikos, M.; Stanev, T.; Stephens, G.; Stezelberger, T.; Stokstad, R. G.; Stoyanov, S.; Strahler, E. A.; Straszheim, T.; Sullivan, G. W.; Swillens, Q.; Taboada, I.; Tamburro, A.; Tarasova, O.; Tepe, A.; Ter-Antonyan, S.; Tilav, S.; Toale, P. A.; Tosi, D.; Tur?an, D.; van Eijndhoven, N.; Vandenbroucke, J.; van Overloop, A.; van Santen, J.; Voigt, B.; Walck, C.; Waldenmaier, T.; Wallraff, M.; Walter, M.; Wendt, C.; Westerhoff, S.; Whitehorn, N.; Wiebe, K.; Wiebusch, C. H.; Wikström, G.; Williams, D. R.; Wischnewski, R.; Wissing, H.; Woschnagg, K.; Xu, C.; Xu, X. W.; Yanez, J. P.; Yodh, G.; Yoshida, S.; Zarzhitsky, P.; IceCube Collaboration

2011-01-01

163

A contrast source method for nonlinear acoustic wave fields in media with spatially inhomogeneous attenuation.  

PubMed

Experimental data reveals that attenuation is an important phenomenon in medical ultrasound. Attenuation is particularly important for medical applications based on nonlinear acoustics, since higher harmonics experience higher attenuation than the fundamental. Here, a method is presented to accurately solve the wave equation for nonlinear acoustic media with spatially inhomogeneous attenuation. Losses are modeled by a spatially dependent compliance relaxation function, which is included in the Westervelt equation. Introduction of absorption in the form of a causal relaxation function automatically results in the appearance of dispersion. The appearance of inhomogeneities implies the presence of a spatially inhomogeneous contrast source in the presented full-wave method leading to inclusion of forward and backward scattering. The contrast source problem is solved iteratively using a Neumann scheme, similar to the iterative nonlinear contrast source (INCS) method. The presented method is directionally independent and capable of dealing with weakly to moderately nonlinear, large scale, three-dimensional wave fields occurring in diagnostic ultrasound. Convergence of the method has been investigated and results for homogeneous, lossy, linear media show full agreement with the exact results. Moreover, the performance of the method is demonstrated through simulations involving steered and unsteered beams in nonlinear media with spatially homogeneous and inhomogeneous attenuation. PMID:21428485

Demi, L; van Dongen, K W A; Verweij, M D

2011-03-01

164

THE ATTENUATION OF HYDROMAGNETIC WAVES IN THE IONOSPHERE  

Microsoft Academic Search

A numerical integration of the hydromagnetic wave equations in the ; ionosphere has been carried out for four model atmospheres corresponding to day ; and night conditions at sunspot maximum and sunspot minimum. The behavior of the ; solutions is discussed in terms of the steady state stored energy, the energy ; flux, and the power dissipation density for monochromatic,

R. Karplus; W. E. Francis; A. J. Dragt

1962-01-01

165

Propagation and Attenuation of Lg Waves in South America.  

National Technical Information Service (NTIS)

Characteristics of Lg waves in La Paz station LPB are analyzed. After realizing that earthquakes with oceanic path and those deep do not produce Lg, they were discarded. Remaining 486 earthquakes, occurred from 1974 to 1986, are considered, looking for Lg...

E. R. Minaya I. J. Alcocer R. R. Ayala R. R. Cabre

1989-01-01

166

Millimeter wave electromagnetic measurement techniques  

Microsoft Academic Search

This report presents the results of studies to develop the rationale for electromagnetic measurement techniques for use in the EMC evaluation of millimeter wave (MMW) communication-electronic equipment and systems. In the development of this rationale, seven basic tasks were performed. Under the first task, the EMC\\/EMI data requirements for MMW equipments and systems were established to provide a clear definition

E. E. Donaldson; J. C. Mantovani; G. B. Melson; D. W. Acree

1982-01-01

167

A Noise-Temperature Measurement System Using a Cryogenic Attenuator  

Microsoft Academic Search

This article describes a method to obtain accurate and repeatable input noise- temperature measurements of cryogenically cooled low-noise ampliflers using a com- mercial noise-flgure meter in conjunction with a cryogenic attenuator co-located with the amplifler under test. The calibration techniques used also are discussed. I. Introduction Accurate and rapid noise-temperature measurements are critical to the modeling and development of high

J. E. Fernandez

168

Measurment and Interpretation of Seismic Attenuation for Hydrocarbon Exploration  

SciTech Connect

This research project is the combined effort of several leading research groups. Advanced theoretical work is being conducted at the Lawrence Berkeley National Laboratory. Here, the fundamental controls on loss mechanisms are being examined, primarily by use of numerical models of heterogeneous porous media. At the University of California, Berkeley, forward modeling is combined with direct measurement of attenuation. This forward modeling provides an estimate of the influence of 1/Q on the observed seismic signature. Direct measures of losses in Vertical Seismic Profiles (VSPs) indicate mechanisms to separate scattering versus intrinsic losses. At the Colorado School of Mines, low frequency attenuation measurements are combined with geologic models of deep water sands. ChevronTexaco is our corporate cosponsor and research partner. This corporation is providing field data over the Genesis Field, Gulf of Mexico. In addition, ChevronTexaco has rebuilt and improved their low frequency measurement system. Soft samples representative of the Genesis Field can now be measured for velocities and attenuations under reservoir conditions. Throughout this project we have: Assessed the contribution of mechanical compaction on time-lapse monitoring; Developed and tested finite difference code to model dispersion and attenuation; Heterogeneous porous materials were modeled and 1/Q calculated vs. frequency; 'Self-affine' heterogeneous materials with differing Hurst exponent modeled; Laboratory confirmation was made of meso-scale fluid motion influence on 1/Q; Confirmed theory and magnitude of layer-based scattering attenuation at Genesis and at a shallow site in California; Scattering Q's of between 40 and 80 were obtained; Measured very low intrinsic Q's (2-20) in a partially saturated vadose zone VSP; First field study to separate scattering and intrinsic attenuation in real data set; Revitalized low frequency device at ChevronTexaco's Richmond lab completed; First complete frequency dependent measurements on Berea sandstones from dry to various saturations (brine and decane); Frequency dependent forward modeling code is running, and tested on a couple of Cases--derives frequency dependent reflectivity from porosity based logs; Genesis seismic data obtained but is on hold until forward modeling is complete; Boundary and end effects modeled for soft material measurements at CSM; and Numerous papers published or submitted and presentations made.

Michael Batzle; Luca Duranti; James Rector; Steve Pride

2007-12-31

169

High-gain observer approach to disturbance attenuation using measurement feedback  

Microsoft Academic Search

A procedure is developed for disturbance attenuation in a linear system via the use of measurement feedback. A high-gain observer is used to recover the disturbance attenuation properties asymptotically, which can be achieved using full state feedback. It is thus shown that the problem of disturbance attenuation via measurement feedback can be decomposed into two problems of disturbance attenuation via

IAN R. PETERSEN; CHRISTOPHER V. HOLLOT

1988-01-01

170

A temporal change in coda wave attenuation observed during an eruption of Mount St. Helens  

Microsoft Academic Search

During the past few years there have been numerous reports of changes in coda wave attenuation occurring before major earthquakes. These observations are important because they may provide insight into stress-related structural changes taking place in the focal region prior to the occurrence of large earthquakes. The results of these studies led us to suspect that temporal changes in coda

Michael Fehler; Peter Roberts; Tom Fairbanks

1988-01-01

171

Magnesium oxide doping reduces acoustic wave attenuation in lithium metatantalate and lithium metaniobate crystals  

NASA Technical Reports Server (NTRS)

Single crystals of lithium metatantalate and lithium metaniobate, grown from melts having different stoichiometries and different amounts of magnesium oxide, show that doping lowers temperature-independent portion of attenuation of acoustic waves. Doped crystals possess optical properties well suited for electro-optical and photoelastic applications.

Croft, W.; Damon, R.; Kedzie, R.; Kestigian, M.; Smith, A.; Worley, J.

1970-01-01

172

Attenuation of coda waves in the Aswan Reservoir area, Egypt  

NASA Astrophysics Data System (ADS)

Coda attenuation characteristics of Aswan Reservoir area of Egypt were analyzed using data recorded by a local earthquake network operated around the reservoir. 330 waveforms obtained from 28 earthquakes recorded by a network of 13 stations were used for this analysis. Magnitude of these earthquakes varied between 1.4 and 2.5. The maximum epicentral distance and depth of focus of these earthquakes were 45 km and 16 km respectively. Single back-scattering method was used for estimation of coda Q ( Qc). The Q0 values ( Qc at 1 Hz) vary between 54 and 100 and frequency dependence parameter " n" values vary between 1 and 1.2 for lapse time varying between 15 s and 60 s. It is observed that coda Q ( Qc) and related parameters are similar at similar lapse times to those observed for those for Koyna, India, where reservoir induced seismicity is also observed. For both regions these parameters are also similar to those observed for tectonically active regions of the world, although Aswan is located in a moderately active region and Koyna is located in a tectonically stable region. However, Qc does not increase uniformly with increasing lapse time, as is observed for several parts of the world. Converting lapse time to depth/distance it is observed that Qc becomes lower or remains almost constant at around 70 to 90 km and 120 km depth/distance. This indicates presence of more attenuative material at those depth levels or distances compared to their immediate surroundings. It is proposed that this variation indicates presence of fluid filled fractures and/or partial melts at some depths/distance from the area of study. The Qc values are higher than those obtained for the Gulf of Suez and Al Dabbab region of Egypt at distances greater than 300 km from the study area by other workers. The turbidity decreases with depth in the study area.

Mohamed, H. H.; Mukhopadhyay, S.; Sharma, J.

2010-09-01

173

2-D Coda and Direct Wave Attenuation Tomography in Northern Italy  

SciTech Connect

A 1-D coda method was proposed by Mayeda et al. (2003) in order to obtain stable seismic source moment-rate spectra using narrowband coda envelope measurements. That study took advantage of the averaging nature of coda waves to derive stable amplitude measurements taking into account all propagation, site, and Sto-coda transfer function effects. Recently this methodology was applied to micro earthquake data sets from three sub-regions of northern Italy (i.e., western Alps, northern Apennines and eastern Alps). Since the study regions were small, ranging between local-to-near-regional distances, the simple 1-D path assumptions used in the coda method worked very well. The lateral complexity of this region would suggest, however, that a 2-D path correction might provide even better results if the datasets were combined, especially when paths traverse larger distances and complicated regions. The structural heterogeneity of northern Italy makes the region ideal to test the extent to which coda variance can be reduced further by using a 2-D Q tomography technique. The approach we use has been developed by Phillips et al. (2005) and is an extension of previous amplitude ratio techniques to remove source effects from the inversion. The method requires some assumptions such as isotropic source radiation which is generally true for coda waves. Our results are compared against direct Swave inversions for 1/Q and results from both share very similar attenuation features that coincide with known geologic structures. We compare our results with those derived from direct waves as well as some recent results from northern California obtained by Mayeda et al. (2005) which tested the same tomographic methodology applied in this study to invert for 1/Q. We find that 2-D coda path corrections for this region significantly improve upon the 1-D corrections, in contrast to California where only a marginal improvement was observed. We attribute this difference to stronger lateral variations in Q for northern Italy relative to California.

Morasca, P; Mayeda, K; Gok, R; Phillips, W S; Malagnini, L

2007-10-17

174

Attenuation of coda waves in the Garhwal Himalaya, India  

Microsoft Academic Search

Qc estimates have been obtained by analysing coda waves of seven local earthquakes recorded in the Garhwal Himalaya. The earthquakes have their epicentral distances within 100 km, focal depths up to 20 km with 2.4 ? ML ? 4.9. Qc values have been computed at central frequencies of 1.5, 3.0, 6.0, 12.0 and 18.0 Hz for different earthquake stations falling

S. C. Gupta; V. N. Singh; Ashwani Kumar

1995-01-01

175

Plasma-parameter measurements using neutral-particle-beam attenuation  

SciTech Connect

Intense and energetic neutral-particle-beam injection used for fueling or heating magnetically confined, controlled-fusion experimental plasmas can also provide diagnostic measurements of the plasmas. The attenuation of an atomic beam (mainly from charge-exchange and ionization interactions) when passing through a plasma gives the plasma line density. Orthogonal arrays of highly collimated detectors of the secondary-electron-emission type have been used in magnetic-mirror experiments to measure neutral-beam attenuation along chords through the plasma volume at different radial and axial positions. The radial array is used to infer the radial plasma-density profile; the axial array, to infer the axial plasma-density profile and the ion angular distribution at the plasma midplane.

Foote, J.H.; Molvik, A.W.; Turner, W.C.

1982-07-07

176

A multiscale poromicromechanical approach to wave propagation and attenuation in bone.  

PubMed

Ultrasonics is an important diagnostic tool for bone diseases, as it allows for non-invasive assessment of bone tissue quality through mass density-elasticity relationships. The latter are, however, quite complex for fluid-filled porous media, which motivates us to develop a rigorous multiscale poromicrodynamics approach valid across the great variety of different bone tissues. Multiscale momentum and mass balance, as well as kinematics of a hierarchical double porous medium, together with Darcy's law for fluid flow and micro-poro-elasticity for the solid phase of bone, give access to the so-called dispersion relation, linking the complex wave numbers to corresponding wave frequencies. Experimentally validated results show that 2.25 MHz acoustical signals transmit healthy cortical bone (exhibiting a low vascular porosity) only in the form of fast waves, agreeing very well with experimental data, while both fast and slow waves transmit highly osteoporotic as well as trabecular bone (exhibiting a large vascular porosity). While velocities and wavelengths of both fast and slow waves, as well as attenuation lengths of slow waves, are always monotonously increasing with the permeability of the bone sample, the attenuation length of fast waves shows a minimum when considered as function of the permeability. PMID:24457030

Morin, Claire; Hellmich, Christian

2014-07-01

177

Broadband ultrasonic attenuation measurements using coded sweep excitations  

Microsoft Academic Search

An experimental method to measure ultrasound attenuation was developed in which the frequency spectrum (FS) of a system consisting of a transmit\\/receive pair of ultrasonic transducers was broadened from 1.79 MHz to 4.57 MHz. A nonlinear specially designed sweep was employed, which was coded based on the FS of the ultrasonic system. Both coded and linear sweeps were used with

R. P. B. da Costa-Felix; J. C. Machado

2004-01-01

178

SITE DIVERSITY GAIN MODEL BASED ON RAIN ATTENUATION MEASUREMENT  

Microsoft Academic Search

The mobile operators often use point-to-point microwave connections for feeder links in their access network. Applying appropriate diversity techniques we can overcome on the problem of high outage percentage of the feeder links. Diversity gain model based on angular correlation analysis of measured rain attenuation data will be introduced. In the telecommunication industry mobile operators often use terrestrial point-to-point microwave

Balázs Héder; Róbert Singliar; János Bitó

179

Impact of attenuation on guided mode wavenumber measurement in axial transmission on bone mimicking plates.  

PubMed

Robust signal processing methods adapted to clinical measurements of guided modes are required to assess bone properties such as cortical thickness and porosity. Recently, an approach based on the singular value decomposition (SVD) of multidimensional signals recorded with an axial transmission array of emitters and receivers has been proposed for materials with negligible absorption, see Minonzio et al. [J. Acoust. Soc. Am. 127, 2913-2919 (2010)]. In presence of absorption, the ability to extract guided mode degrades. The objective of the present study is to extend the method to the case of absorbing media, considering attenuated plane waves (complex wavenumber). The guided mode wavenumber extraction is enhanced and the order of magnitude of the attenuation of the guided mode is estimated. Experiments have been carried out on 2 mm thick plates in the 0.2-2 MHz bandwidth. Two materials are inspected: polymethylacrylate (PMMA) (isotropic with absorption) and artificial composite bones (Sawbones, Pacific Research Laboratory Inc, Vashon, WA) which is a transverse isotropic absorbing medium. Bulk wave velocities and bulk attenuation have been evaluated from transmission measurements. These values were used to compute theoretical Lamb mode wavenumbers which are consistent with the experimental ones obtained with the SVD-based approach. PMID:22225014

Minonzio, Jean-Gabriel; Foiret, Josquin; Talmant, Maryline; Laugier, Pascal

2011-12-01

180

Laboratory Measurement of Guided Wave (Krauklis Wave) Propagation Within a Fluid-Saturated Fracture  

NASA Astrophysics Data System (ADS)

A fluid-saturated flat channel between two solid half-spaces (i.e. a fracture) is known to support a guided wave called the Krauklis wave. In the field, this wave can potentially be used to examine the size and connectivity of natural and hydraulically induced fractures from a borehole. Krauklis waves propagate primarily within the fluid part of a fracture, can have very low velocity and large attenuation, and are very dispersive at low frequencies. We conducted laboratory measurements of the velocity of Krauklis waves using analogue fracture models at frequencies below 1 kHz. The models consisted of (1) two concentric aluminum cylinders with a water-filled gap and (2) a pair of rectangular aluminum plates containing a thin water-filled gap (tri-layer mode). In the latter, the water was contained by an o-ring along the edge of the plates. The velocity of the waves propagating within the models was determined both from waveforms in the time domain measured along the wave path and from acoustic resonances in the system. The results indicated that the waves measured from the cylindrical model were not dispersive at frequencies below 400 Hz, with a phase velocity of ~250 m/s. In contrast, the tri-layer model exhibited strongly dispersive velocity at measured frequencies of 7.5 Hz-500 Hz, with the lowest phase velocity being ~14 m/s at 7.5 Hz. These measurements agree well with our theoretical model predictions.

Nakagawa, S.; Korneev, V. A.

2013-12-01

181

Study of wind speed attenuation at Kavaratti Island using land-based, offshore, and satellite measurements  

NASA Astrophysics Data System (ADS)

The role of dense coconut palms in attenuating the wind speed at Kavaratti Island, which is located in the southeastern Arabian Sea, is examined based on land-based and offshore wind measurements (U10) using anchored-buoy-mounted and satellite-borne sensors (QuikSCAT scatterometer and TMI microwave imager) during an 8-year period (2000-2007). It is found that round the year monthly-mean wind speed measurements from the Port Control Tower (PCT) located within the coconut palm farm at the Kavaratti Island are weaker by 15-61% relative to those made from the nearby offshore region. Whereas wind speed attenuation at the island is ~15-40% in the mid-June to mid-October south-west monsoon period, it is ~41-61% during the rest of the year. Wind direction measurements from all the devices overlapped, except in March-April during which the buoy measurements deviated from the other measurements by ~20°. U10 wind speed measurements from PCT during the November 2009 tropical cyclone "Phyan" indicated approximately 50-80% attenuation relative to those from the seaward boundary of the island's lagoon (and therefore least influenced by the coconut palms). The observed wind speed attenuation can be understood through the theory of free turbulent flow jets embodied in the boundary-layer fluid dynamics, according to which both the axial and transverse components of the efflux of flows discharged through the inter-leaves porosity (orifice) undergo increasing attenuation in the downstream direction with increasing distance from the orifice. Thus, the observed wind speed attenuation at Kavaratti Island is attributable to the decline in wind energy transmission from the seaward boundary of the coconut palm farm with distance into the farm. Just like mangrove forests function as bio-shields against forces from oceanic waves and stormsurges through their large above-ground aerial root systems and standing crop, and thereby playing a distinctive role in ameliorating the effects of catastrophies such as hurricanes, tidal bores, cyclones, and tsunamis, the present study provides an indication that densely populated coconut palms and other tall tree vegetation would function as bio-shields against the damaging effects of storms through attenuation of wind speed.

Joseph, Antony; Rivonkar, Pradhan; Balakrishnan Nair, T. M.

2012-05-01

182

Attenuation of shock waves propagating through nano-structured porous materials  

NASA Astrophysics Data System (ADS)

Porous materials have long been known to be effective in energy absorption and shock wave attenuation. These properties make them attractive in blast mitigation strategies. Nano-structured materials have an even greater potential for blast mitigation because of their high surface-to-volume ratio, a geometric parameter which substantially attenuates shock wave propagation. A molecular dynamics approach was used to explore the effects of this remarkable property on the behavior of traveling shocks impacting on solid materials. The computational setup included a moving piston, a gas region and a target solid wall with and without a porous structure. The gas and porous solid were modeled by Lennard-Jones-like and effective atom potentials, respectively. The shock wave is resolved in space and time and its reflection from a solid wall is gradual, due to the wave's finite thickness, and entails a self-interaction as the reflected wave travels through the incoming incident wave. Cases investigated include a free standing porous structure, a porous structure attached to a wall and porous structures with graded porosity. The effects of pore shape and orientation have been also documented. The results indicate that placing a nano-porous material layer in front of the target wall reduced the stress magnitude and the energy deposited inside the solid by about 30 percent, while at the same time substantially decreasing the loading rate.

Al-Qananwah, Ahmad K.; Koplik, Joel; Andreopoulos, Yiannis

2013-07-01

183

Radio Frequency (RF) Attenuation Measurements of the Space Shuttle Vehicle  

NASA Technical Reports Server (NTRS)

Following the loss of Columbia, the Columbia Accident Investigation Board (CAIB) provided recommendations to be addressed prior to Return To Flight (RTF). As a part of CAIB Recommendation 3.4.1 - Ground Based Imagery, new C-band and X-band radars were added to the array of ground-based radars and cameras already in-situ at Kennedy Space Center. Because of higher power density considerations and new operating frequencies, the team of Subject Matter Experts (SMEs) assembled to investigate the technical details of introducing the new radars recommended a series of radio frequency (RF) attenuation tests be performed on the Space Shuttle vehicle to establish the attenuation of the vehicle outer mold line structure with respect to its external RF environment. Because of time and complex logistical constraints, it was decided to split the test into two separate efforts. The first of these would be accomplished with the assistance of the Air Force Research Laboratory (AFRL), performing RF attenuation measurements on the aft section of OV-103 (Discovery) while in-situ in Orbiter Processing Facility (OPF) 3, located at Kennedy Space Center. The second would be accomplished with the assistance of the National Institute of Standards and Technology (NIST) and the electromagnetic interference (EMI) laboratory out of the Naval Air Warfare Center, Patuxent River, Maryland (PAX River), performing RF attenuation measurements on OV-105 (Endeavour) in-situ inside the Space Shuttle Landing Facility (SLF) hangar, also located at Kennedy Space Center. This paper provides a summary description of these efforts and their results.

Scully, R. C.; Kent, B. M.; Kempf, D. R.; Johnk, R. T.

2006-01-01

184

Teleseismic P wave attenuation and nuclear explosion source functions inferred from Yellowknife Array data  

NASA Astrophysics Data System (ADS)

We report here the results of a comprehensive seismic attenuation investigation along the paths connecting Canada's Yellowknife seismic array (YKA) with seven active nuclear explosion testing areas. The data consist of more than 600 explosion-generated teleseismic P wave records. A dual time-frequency averaging technique is used to take advantage of the array recording characteristics without the drawback of the conventional beam-forming, excessive annihilation of high-frequency signal energies. The dual averaging technique, deployed in conjunction with a multiwindow spectral analysis method, yields smooth amplitude spectra whose falloff at high frequencies suffers little from spectral leakage due to the familiar presence of a prominent low-frequency plateau. Measured in terms of t*, the highest attenuation (0.66 s) is found along the path which originates from the Tuamotu test area; somewhat less attenuating are the two paths which depart from the Pahute Mesa (0.59 s) and Yucca Flat (0.50 s) nuclear test areas, both located within the U.S. Nevada Test Site. We find t* for these three paths to be substantially (up to 0.21 s) higher than recently published estimates (e.g., Der et al., 1985). We attribute these disparities largely to differences in spectral leakage control capability between the conventional single window and the improved multiwindow spectral analysis methods. The least attenuating paths all originate from the Soviet test areas: Novaya Zemlya (NZ), west Kazakhstan, Degelen Mountain (DM), and Shagan River (SR). The last two of these test areas, DM and SR, are both located in east Kazakhstan. The P wave signatures of the Soviet explosions are rich in high-frequency (>4.5 Hz) energies, and the YKA data (0.5-8.0 Hz) support a frequency-dependent t* whose value at high frequencies (>4.5 Hz) is as small as 0.17 s. To gain a grasp of the ramifications of the t* disparity between the multiple-window and the single-window results, we have compared explosion source time functions obtained by the multichannel deconvolution technique of Shumway and Der (1985) in order to assess their sensitivity to the input t* value. In our example involving the deconvolved source functions of five French Tuamotu explosions, we find that a 0.1-s t* difference is large enough to cause clearly discernible signature differences, in terms of the signal frequency content as well as the extractability of a secondary arrival some 0.4 s behind the first P arrival. This secondary arrival is believed to be the depth phase pP, a seismic signature of importance in both yield estimation and earthquake/explosion source discrimination. The absorption band modeling (Minster, 1978a, b) of the French Tuamotu explosion data yields 1.08±0.05 and 0.079±0.008 s for t*0 and ?m, respectively. The corresponding parameter estimates derived from the U.S. explosion data are somewhat smaller. The t*0 and ?m estimates are the smallest along the paths which depart from the four Soviet test areas. For the NZ-YKA path the t*0 and ?m estimates are 0.56±0.08 and 0.061±0.013 s, respectively. Plagued by a strong trade-off between the two model parameters, these estimates are not tightly constrained, however.

Chun, Kin-Yip; Zhu, Tianfei; West, Gordon F.

1991-07-01

185

ULTRASONIC MEASUREMENT MODELS FOR SURFACE WAVE AND PLATE WAVE INSPECTIONS  

SciTech Connect

A complete ultrasonic measurement model for surface and plate wave inspections is obtained, where all the electrical, electromechanical, and acoustic/elastic elements are explicitly described. Reciprocity principles are used to describe the acoustic/elastic elements specifically in terms of an integral of the incident and scattered wave fields over the surface of the flaw. As with the case of bulk waves, if one assumes the incident surface waves or plate waves are locally planar at the flaw surface, the overall measurement model reduces to a very modular form where the far-field scattering amplitude of the flaw appears explicitly.

Schmerr, Lester W. Jr. [Center for NDE, Iowa State University, Ames, IA, 50011 (United States); Dept. of Aerospace Eng., Iowa State University, Ames, IA, 50011 (United States); Sedov, Alexander [Dept of Mech. Eng., Lakehead University, Thunder Bay, ON, P7B 5E1 (Canada)

2010-02-22

186

Dislocation Damping and Anisotropic Seismic Wave Attenuation in Earth's Upper Mantle  

NASA Astrophysics Data System (ADS)

Crystal defects form during tectonic deformation and are reactivated by the shear stress associated with passing seismic waves. Although these defects, known as dislocations, potentially contribute to the attenuation of seismic waves in Earth’s upper mantle, evidence for dislocation damping from laboratory studies has been circumstantial. We experimentally determined the shear modulus and associated strain-energy dissipation in pre-deformed synthetic olivine aggregates under high pressures and temperatures. Enhanced high-temperature background dissipation occurred in specimens pre-deformed by dislocation creep in either compression or torsion, the enhancement being greater for prior deformation in torsion. These observations suggest the possibility of anisotropic attenuation in relatively coarse-grained rocks where olivine is or was deformed at relatively high stress by dislocation creep in Earth’s upper mantle.

Farla, Robert J. M.; Jackson, Ian; Fitz Gerald, John D.; Faul, Ulrich H.; Zimmerman, Mark E.

2012-04-01

187

SHEAR WAVE DISPERSION MEASURES LIVER STEATOSIS  

PubMed Central

Crawling waves, which are interfering shear wave patterns, can be generated in liver tissue over a range of frequencies. Some important biomechanical properties of the liver can be determined by imaging the crawling waves using Doppler techniques and analyzing the patterns. We report that the dispersion of shear wave velocity and attenuation, that is, the frequency dependence of these parameters, are strongly correlated with the degree of steatosis in a mouse liver model, ex vivo. The results demonstrate the possibility of assessing liver steatosis using noninvasive imaging methods that are compatible with color Doppler scanners and, furthermore, suggest that liver steatosis can be separated from fibrosis by assessing the dispersion or frequency dependence of shear wave propagations.

Barry, Christopher T.; Mills, Bradley; Hah, Zaegyoo; Mooney, Robert A.; Ryan, Charlotte K.; Rubens, Deborah J.; Parker, Kevin J.

2012-01-01

188

Variation between os calces as measured by broadband ultrasound attenuation.  

PubMed

We compared broadband ultrasonic attenuation (BUA) values of right with left os calcis in 65 women. All subjects were right handed, and they were divided into two groups: Group 1 consisted of 32 normal volunteers and Group 2 of 33 osteoporotic subjects. Both groups had mean absolute differences in BUA between the two os calces greater than the coefficient of variation (p < 0.001). This difference is not related to stated handedness of the individuals. Osteoporosis affects both os calces similarly. BUA measurements should always be performed in the same site in longitudinal studies, otherwise false comparisons will result. PMID:8061997

Dretakis, E; Damilakis, J; Kontakis, G; Gourtsoyiannis, N

1994-07-01

189

Consideration on frequency dependences of near-surface attenuation of S-waves based on vertical array records  

NASA Astrophysics Data System (ADS)

Frequency dependences of near-surface attenuation of S-waves based on the vertical array records were examined to clarify their physical mechanisms using the data collected at the KiK-net Narita observatory site. The attenuation was estimated as a function of frequency by matching the SH-wave transfer function to the observed spectral ratio using the subsurface velocity structure derived from the PS logging profile. In addition to these examinations, numerical experiments with synthetic pseudo spectral ratio, which was calculated by use of the subsurface model constructed from the velocity and attenuation structure estimated at the Narita observatory, were performed to make clear the cause of frequency dependences of S-wave attenuation from an analytical point of view. The estimated S-wave attenuation of the sedimentary layer-basement system at the Narita observatory has a constant value of about 0.004 - 0.005 (h=0.4 - 0.5%) with its lower limit at frequencies higher than 4 - 5Hz. On the other hand, the attenuation strongly increases with decreasing frequency below around 2 - 3Hz. It is quite likely that selection of the time window for picking out the S-waves portion may lead to artificial frequency dependence of attenuation at these lower frequency ranges. The attenuation value and its frequency dependence tend to decrease as the length of time window increases. In other words, the S-wave attenuation evaluated from the vertical array records seems to have some artificial frequency dependences, especially at lower frequencies. It is therefore important to carefully check errors in estimating attenuation.

Kobayashi, Genyuu; Mamada, Yutaka; Tsutsumi, Hideaki

190

Representative Elementary Length to Measure Soil Mass Attenuation Coefficient  

PubMed Central

With increasing demand for better yield in agricultural areas, soil physical property representative measurements are more and more essential. Nuclear techniques such as computerized tomography (CT) and gamma-ray attenuation (GAT) have been widely employed with this purpose. The soil mass attenuation coefficient (?s) is an important parameter for CT and GAT analysis. When experimentally determined (?es), the use of suitable sized samples enable to evaluate it precisely, as well as to reduce measurement time and costs. This study investigated the representative elementary length (REL) of sandy and clayey soils for ?es measurements. Two radioactive sources were employed (241Am and 137Cs), three collimators (2–4?mm diameters), and 14 thickness (x) samples (2–15?cm). Results indicated ideal thickness intervals of 12–15 and 2–4?cm for the sources 137Cs and 241Am, respectively. The application of such results in representative elementary area (REA) evaluations in clayey soil clods via CT indicated that ?es average values obtained for x?>?4?cm and source 241Am might induce to the use of samples which are not large enough for soil bulk density evaluations (?s). As a consequence, ?s might be under- or overestimated, generating inaccurate conclusions about the physical quality of the soil under study.

Borges, J. A. R.; Pires, L. F.; Costa, J. C.

2014-01-01

191

Measurement of directional wave spectrum with a modular acoustic velocity sensor  

Microsoft Academic Search

Directional wave spectra, valuable to describe the sea-state, can be computed as the correlation of horizontal velocity with pressure measured at a single point. Pressure was used instead of the vertical component of velocity for the correlation since the deployment height of 70 cm above the bottom attenuated the vertical wave velocity component. A Modular Acoustic Velocity Sensor (MAVS) with

Albert J. Williams; Eugene A. Terray

2000-01-01

192

Point-to-point measurement of radio frequency attenuation in South Polar ice  

NASA Astrophysics Data System (ADS)

For ultra high energy (UHE) electromagnetic showers in a dense medium, radio frequency Cherenkov emission is enhanced due to the Askaryan effect. Present and future detectors such as RICE, ANITA, ARIANNA and the Askaryan Radio Array (ARA) exploit this effect to detect UHE neutrinos interacting with Antarctic ice. The radio frequency electromagnetic wave attenuation length (the distance over which signal amplitude diminishes by a factor of 1/e due to absorption or scattering) is of tantamount importance as it determines the size scale and effective volume of these detectors. Previous attenuation measurements rely on reflections off the bedrock of signals from a surface-mounted transmitter. Using RICE in-ice transmitters and IceCube Radio Extension in-ice receivers, we are conducting a point-to-point attenuation measurement in the upper 1500 meters of South Polar ice, the region of interest for planned near-surface detectors such as ARA. We will present the analysis method as well as preliminary results.

Richman, Michael; Hoffman, Kara

2011-04-01

193

INDIRECT MEASUREMENT OF BIOLOGICAL ACTIVITY TO MONITOR NATURAL ATTENUATION  

EPA Science Inventory

The remediation of ground water contamination by natural attenuation, specifically biodegradation, requires continual monitoring. This research is aimed at improving methods for evaluating the long-term performance of Monitored Natural Attenuation (MNA), specifically changes in ...

194

The Use of Ultrasonic Seismic Wave Attenuation (Q) for Better Subsurface Imaging, Energy Exploration, and Tracking of Sequestrated Carbon Dioxide  

NASA Astrophysics Data System (ADS)

Parameters related to seismic and ultrasonic elastic waves traveling through a porous rock material with compliant pores, cracks and isometric pores are subject to variations which are dependent on the physical properties of the rock such as density, porosity, permeability, frame work moduli, fluid moduli, micro structural variation, and effective pressure. Our goal is to understand these variations through experiments completed using Berea sandstone, rhyolites, coal, and carbonate samples. Understanding these lithologies are relevant to enhanced oil recovery, enhanced geothermal, and CO2 storage activities. Working in the COREFLOW laboratory at the National Energy Technology Laboratory (NETL) of the United States Department of Energy (DOE) we performed several experiments on these rock types with various different pore filling fluids, effective pressures, and temperatures. We measured P, S1 and S2 ultrasonic velocities using an New England Research (NER) Autolab 1500 device and calculated the lame parameters (Bulk modulus (K), Young's modulus (E), Lamè's first parameter (?), Shear modulus (G), Poisson's ratio ( ), P-wave modulus (M)). Using an aluminum reference core and the P, S1, and S2 ultrasonic waveform data collected, we employed the spectral ratio method to estimate Q. This method uses the ratio of the amplitude-frequency spectrum (obtained via fast Fourier Transform and processed using Matlab) of the rock core compared with the amplitude-frequency spectrum of the aluminum reference core to calculate the quality factor (Q). The quality factor is a dimensionless value that represents the attenuation of a seismic wave as it travels through a rock. Seismic attenuation is dependent on wave velocity, the path length or time the wave is in the rock, and of course the physical properties of the rock through which the wave travels. Effective pressures used in our experiments varied between 0.01 MPa and 50 MPa and temperatures varied between 21 C to 80 C which allowed us to more accurately represent subsurface conditions. Pore filling fluids consisted of deionized water, oil, gas, and supercritical CO2. We have found that Q for the P, S1, and S2 seismic waves is strongly dependent on and proportional to the effective pressure of the rock. Also our experiments indicate that the presence of different pore filling fluids such as water, oil, and CO2 alter the value of Q. Carbonate samples were tested dry (atmospheric gas as pore fluid) and with deionized water, oil, and CO2. With the substitution of each of these fluids into the dry rock core sample, we see the value of Q shift as much as 20% lower for the P, S1, and S2 seismic waves. Our experiments indicate that the presence of oil, water, or CO2 lowers the value of Q of a rock. For all effective pressures we see this shift in the value of Q, it would seem that with the introduction of these pore-filling fluids the quality factor value is typically lowered, however at higher effective pressures (about 40 MPa) the shift in Q is less. By understanding how seismic waves attenuate we can better understand what collected seismic signals traveled through. This knowledge and understanding of seismic wave attenuation could prove to be a powerful tool for better subsurface imaging, tracking of sequestrated CO2, and energy exploration.

Delaney, D.; Purcell, C. C.; Mur, A. J.; Haljasmaa, I.; Soong, Y.; Harbert, W.

2012-12-01

195

A Split of Direction of Propagation and Attenuation of P Waves in the Po Valley  

NASA Astrophysics Data System (ADS)

On July 17, 2011 a ML 4.8 earthquake occurred in the PO valley at a 48 km epicentral distance from a seismic station located at Palazzo Te (Mantova). The station is situated on deep quaternary sediments: the uppermost layers are mainly composed of clay and silty clay with interbedded sands; the Robertson index is 1.4wave particle motion, that appears rather difficult to explain if we assume the homogeneity of the P waves (that means attenuation is scalar). Note that the degree of nonlinearity is very low given that the maximum strain can be roughly estimated as 10-5 on the basis of maximum ground velocity of the P wave train considered and the Vp. On the contrary we show that P wave particle motion can be fully (and easily) described by a Homogeneous Isotropic Linear Viscoelastic model (HILV). HILV, as in the 2009 Borcherdt formulation adopted here, allows two different directions of propagation and attenuation; in other words attenuation becomes a vector that is not necessarily parallel to the propagation vector. The results evidence that the incidence angle and the inhomogeneity angle (it is the angle between propagation and attenuation vectors and it is closely related to Q factor) are in good agreement with the geological conditions of the site. Finally, we observed that these results are very similar to the ones obtained when we analyzed two explosions recorded by a seismic station in Milano, also situated in the Po valley at some 140 km from Mantova (Marcellini & Tento, 2011). Borcherdt, R.D. (2009) 'Viscoelastic Waves in Layered Media', Cambridge University Press, Cambridge, United Kingdom, 305 pp. Marcellini, A. and A. Tento (2011) ' Explosive Sources Prove the Validity of Homogeneous Isotropic Linear Viscoelastic Models', BSSA, Vol. 101, No. 4, pp. 1576-1583.

Daminelli, R.; Tento, A.; Marcellini, A.

2013-12-01

196

Cloud Attenuation in Millimeter Wave and Microwave Frequencies for Satellite Applications over Equatorial Climate  

NASA Astrophysics Data System (ADS)

A propagation experiment has been carried out at Penang using the SUPERBIRD-C satellite beacon. Cloud occurrences were observed during different months and it is seen that the low cloud occurrences over Penang is very significant from October to January. The cloud attenuation results that are presented, which include the testing of models, have been obtained from the data gathered over five years. The specific attenuation of radio wave due to clouds at various frequencies 12 GHz, 20 GHz, 75 GHz, 50 GHz and 100 GHz has been estimated whereby the values varies from 0.14 dB/km at 12 GHz to 10.1 dB/km at 100 GHz.

Mandeep, J. S.; Hassan, S. I. S.

2008-02-01

197

Attenuation characteristics of the guided THz wave in parallel-plate ferroelectric-graphene waveguides  

NASA Astrophysics Data System (ADS)

Guided THz wave characteristics in a parallel-plate waveguide (PPWG) consisting of ferroelectric film (LiNbO3 and LiTaO3) and multilayer graphene (MLG) is studied in this paper, with their low and tunable attenuation valley predicted. The electrical conductivity of MLG is calculated by a set of closed-form equations with the coupling effect between the bottom graphene layer (BGL) and its substrate taken into account carefully, while the dispersive behavior of ferroelectric film itself is described by the Lorentz model over an ultra-wide THz band. It is shown that the guided TM-mode propagation can be adjusted effectively by changing temperature, frequency, optical pumping intensity, MLG layer number, film thickness and its transverse optical-phonon frequency. Moreover, one low attenuation valley of TM-mode in such ferroelectric-graphene waveguide is captured, which can be exploited for developing some THz planar tunable waveguides with ultra-low loss.

Gu, Xiao-Qiang; Yin, Wen-Yan; Zheng, Ting

2014-11-01

198

Measurements of seismic attenuation and transient fluid pressure in partially saturated Berea sandstone: evidence of fluid flow on the mesoscopic scale  

NASA Astrophysics Data System (ADS)

A novel laboratory technique is proposed to investigate wave-induced fluid flow on the mesoscopic scale as a mechanism for seismic attenuation in partially saturated rocks. This technique combines measurements of seismic attenuation in the frequency range from 1 to 100 Hz with measurements of transient fluid pressure as a response of a step stress applied on top of the sample. We used a Berea sandstone sample partially saturated with water. The laboratory results suggest that wave-induced fluid flow on the mesoscopic scale is dominant in partially saturated samples. A 3-D numerical model representing the sample was used to verify the experimental results. Biot's equations of consolidation were solved with the finite-element method. Wave-induced fluid flow on the mesoscopic scale was the only attenuation mechanism accounted for in the numerical solution. The numerically calculated transient fluid pressure reproduced the laboratory data. Moreover, the numerically calculated attenuation, superposed to the frequency-independent matrix anelasticity, reproduced the attenuation measured in the laboratory in the partially saturated sample. This experimental-numerical fit demonstrates that wave-induced fluid flow on the mesoscopic scale and matrix anelasticity are the dominant mechanisms for seismic attenuation in partially saturated Berea sandstone.

Tisato, Nicola; Quintal, Beatriz

2013-10-01

199

Dislocation Damping and Anisotropic Seismic-wave Attenuation in the Earth's Upper Mantle  

NASA Astrophysics Data System (ADS)

Seismic anisotropy, attributed to olivine lattice preferred orientation, suggests that tectonic deformation in the Earth's shallow upper mantle involves dislocation creep. Reversible glide of dislocations, generated by the prevailing/fossil tectonic stress, may result in anelastic relaxation that contributes to the reduction of seismic wave speeds and associated attenuation. To test this hypothesis, pure polycrystalline olivine specimens were synthesised by isostatic hot-pressing of synthetic powders of Fo90 composition. The hot-pressed material is dense (< 1% porosity), fine-grained, essentially dry and melt-free olivine. Other, more coarse-grained material was prepared in the same way from crushed natural (San Carlos) olivine. These contrasting materials provided the opportunity to distinguish between the influences of grain size, dislocation density and minor impurities. Selected specimens were deformed by dislocation creep either in compression or torsion and characterised for dislocation density via oxidative decoration and backscattered electron imaging. The shear modulus and associated strain-energy dissipation in both hot-pressed and pre-deformed specimens were measured at seismic frequencies and low strain amplitudes under conditions of simultaneous high pressure and temperature with torsional forced-oscillation methods. On the basis of a prior study of dislocation recovery, a maximum temperature of 1100C was chosen to allow sustained forced-oscillation testing under conditions of relatively stable dislocation microstructure. The high-temperature dissipation background, attributed in undeformed fine-grained materials to grain-boundary sliding, and the associated partial relaxation of the shear modulus, are systematically enhanced in the pre-deformed materials - suggesting a role for the dislocations introduced during the prior deformation. The enhancement is systematically greater for prior torsional deformation than for prior deformation in compression. This observation is consistent with the prediction from a simple model of resolved shear stress that dislocations generated by prior torsional deformation are more favourably oriented for glide during the subsequent torsional oscillation measurements. Such dislocation damping is expected to become more significant relative to grainsize-sensitive effects for the larger grain sizes of the Earth's mantle. Moreover, it is predicted that dislocation damping in the Earth's mantle will be anisotropic - being greatest for those shear-wave propagation directions and polarisations with shear stress aligned with the prevailing/fossil tectonic stress.

Farla, R. J. M.; Jackson, I.; Fitz Gerald, J. D.; Faul, U. H.; Zimmerman, M. E.

2012-04-01

200

Attenuation and localization of wave propagation in rods with periodic shunted piezoelectric patches  

NASA Astrophysics Data System (ADS)

Shunted piezoelectric patches are periodically placed along rods to control the longitudinal wave propagation in these rods. The resulting periodic structure is capable of filtering the propagation of waves over specified frequency bands called stop bands. The location and width of the stop bands can be tuned, using the shunting capabilities of the piezoelectric materials, in response to external excitations and to compensate for any structural uncertainty. A mathematical model is developed to predict the response of a rod with periodic shunted piezoelectric patches and to identify its stop band characteristics. The model accounts for the aperiodicity, introduced by proper tuning of the shunted electrical impedance distribution along the rod. Disorder in the periodicity typically extends the stop-bands into adjacent propagation zones and more importantly, produces the localization of the vibration energy near the excitation source. The conditions for achieving localized vibration are established and the localization factors are evaluated for different levels of disorder on the shunting parameters. The numerical predictions demonstrated the effectiveness and potentials of the proposed treatment that requires no control energy and combines the damping characteristics of shunted piezoelectric films, the attenuation potentials of periodic structures, and the localization capabilities of aperiodic structures. The theoretical investigations presented in this work provide the guidelines for designing tunable periodic structures with high control flexibility where propagating waves can be attenuated and localized.

Thorp, Owen G.; Ruzzene, Massimo; Baz, Amr M.

2001-07-01

201

Producing acoustic 'Frozen Waves': simulated experiments with diffraction/attenuation resistant beams in lossy media.  

PubMed

The so-called Localized Waves (LW), and the "Frozen Waves" (FW), have raised significant attention in the areas of Optics and Ultrasound, because of their surprising energy localization properties. The LWs resist the effects of diffraction for large distances, and possess an interesting self-reconstruction -self-healing- property (after obstacles with size smaller than the antenna's); while the FWs, a sub-class of LWs, offer the possibility of arbitrarily modeling the longitudinal field intensity pattern inside a prefixed interval, for instance 0?z?L, of the wave propagation axis. More specifically, the FWs are localized fields "at rest", that is, with a static envelope (within which only the carrier wave propagates), and can be endowed moreover with a high transverse localization. In this paper we investigate, by simulated experiments, various cases of generation of ultrasonic FW fields, with the frequency of f0=1 MHz in a water-like medium, taking account of the effects of attenuation. We present results of FWs for distances up to L=80 mm, in attenuating media with absorption coefficient ? in the range 70???170 dB/m. Such simulated FW fields are constructed by using a procedure developed by us, via appropriate finite superpositions of monochromatic ultrasonic Bessel beams. We pay due attention to the selection of the FW parameters, constrained by the rather tight restrictions imposed by experimental Acoustics, as well as to some practical implications of the transducer design. The energy localization properties of the Frozen Waves can find application even in many medical apparatus, such as bistouries or acoustic tweezers, as well as for treatment of diseased tissues (in particular, for the destruction of tumor cells, without affecting the surrounding tissues; also for kidney stone shuttering, etc.). PMID:24709072

Prego-Borges, José L; Zamboni-Rached, Michel; Recami, Erasmo; Costa, Eduardo Tavares

2014-08-01

202

Assessing the P-wave attenuation and phase velocity characteristics of fractured media based on creep and relaxation tests  

NASA Astrophysics Data System (ADS)

Fractures are present in most geological formations and they tend to dominate not only their mechanical but also, and in particular, their hydraulic properties. For these reasons, the detection and characterization of fractures are of great interest in several fields of Earth sciences. Seismic attenuation has been recognized as a key attribute for this purpose, as both laboratory and field experiments indicate that the presence of fractures typically produces significant energy dissipation and that this attribute tends to increase with increasing fracture density. This energy loss is generally considered to be primarily due to wave-induced pressure diffusion between the fractures and the embedding porous matrix. That is, due to the strong compressibility contrast between these two domains, the propagation of seismic waves can generate a strong fluid pressure gradient and associated pressure diffusion, which leads to fluid flow and in turn results in frictional energy dissipation. Numerical simulations based on Biot's poroelastic wave equations are computationally very expensive. Alternative approaches consist in performing numerical relaxation or creep tests on representative elementary volumes (REV) of the considered medium. These tests are typically based on Biot's consolidation equations. Assuming that the heterogeneous poroelastic medium can be replaced by an effective, homogeneous viscoelastic solid, these numerical creep and relaxation tests allow for computing the equivalent seismic P-wave attenuation and phase velocity. From a practical point of view, an REV is typically characterized by the smallest volume for which rock physical properties are statistically stationary and representative of the probed medium in its entirety. A more general definition in the context of wavefield attributes is to consider an REV as the smallest volume over which the P-wave attenuation and phase velocity dispersion are independent of the applied boundary conditions. That is, the corresponding results obtained from creep and relaxation tests must be equivalent. For most analyses of media characterized by patchy saturation or double-porosity-type structures these two definitions are equivalent. It is, however, not clear whether this equivalence remains true in the presence of strong material contrasts as those prevailing in fractured rocks. In this work, we explore this question for periodically fractured media. To this end, we build a medium composed of infinite replicas of a unit volume containing one fracture. This unit volume coincides with the smallest possible volume that is statistically representative of the whole. Then, we perform several creep and relaxation tests on samples composed of an increasing number of these unit volumes. We find that the wave field signatures determined from relaxation tests are independent from the number of unit volumes. Conversely, the P-wave attenuation and phase velocity characteristics inferred from creep tests are different and vary with the number of unit volumes considered. Quite interestingly, the creep test results converge with those of the relaxation tests as the number of unit volumes increases. These findings are expected to have direct implications for corresponding laboratory measurements as well as for our understanding of seismic wave propagation in fractured media.

Milani, Marco; Germán Rubino, J.; Müller, Tobias M.; Quintal, Beatriz; Holliger, Klaus

2014-05-01

203

The effect of in-stream structures on flood wave attenuation in Western Carpathians of Slovakia  

NASA Astrophysics Data System (ADS)

In-stream structures were built as a part of the erosion and sediment flux control on mountainous streams in Slovakia. These structures, steps, drop structures, and check dams, affect the flow regime and flood wave attenuation. Flood magnitude for ten and hundred-year flood events decreased by 0.21-29% depending on the flow and type of structures used. The largest decrease in flood duration was 39%. Relative change in flow depth and velocity, representing local stream conditions, ranged from 16 to 52%, and 12 to 106% respectively. These changes were modeled with 1D model, HEC-RAS, version 4.0, using unsteady flow simulations. Observed water surface was used for the calibration. Roughness was calculated using Chow and Cowan equations which were based on field observations. The flood events were modeled on Breznicky Creek, Sutovsky Creek, and Ilanovsky Creek in Kremnica Mountains, Little Fatra and Low Tatras as part of the Western Carpathian Mountains. Two scenarios were analyzed for ten and hundred-year flood events: 1) streams in their natural state, and 2) streams which have been altered by different in-stream structures. The results of this study are consistent with practice of torrent control for steps, small in-stream structures, and results from stream study in Czech Republic. The steps, used for local erosion control and habitat improvement, did not change the flood wave attenuation significantly. For drop structures and check dams, actual available water storage created by structures influenced the overall flood wave attenuation change. Quantification of flood magnitude and time duration under different flow regimes with different types of in-stream structures provides necessary information for flood risk management.

Majerova, M.

2010-12-01

204

Attenuation of High Frequency P and S Waves in the Gujarat Region, India  

NASA Astrophysics Data System (ADS)

The local earthquake waveforms recorded on broadband seismograph network of Institute of Seismological Research in Gujarat, India have been analyzed to understand the attenuation of high frequency (2-25 Hz) P and S waves in the region. The frequency dependent relationships for quality factors for P ( Q P) and S ( Q S) waves have been obtained using the spectral ratio method for three regions namely, Kachchh, Saurashtra and Mainland Gujarat. The earthquakes recorded at nine stations of Kachchh, five stations of Saurashtra and one station in mainland Gujarat have been used for this analysis. The estimated relations for average Q P and Q S are: Q P = (105 ± 2) f 0.82 ± 0.01, Q S = (74 ± 2) f 1.06 ± 0.01 for Kachchh region; Q P = (148 ± 2) f 0.92 ± 0.01, Q S = (149 ± 14) f 1.43 ± 0.05 for Saurashtra region and Q P = (163 ± 7) f 0.77 ± 0.03, Q S = (118 ± 34) f 0.65 ± 0.14 for mainland Gujarat region. The low Q (<200) and high exponent of f (>0.5) as obtained from present analysis indicate the predominant seismic activities in the region. The lowest Q values obtained for the Kachchh region implies that the area is relatively more attenuative and heterogeneous than other two regions. A comparison between Q S estimated in this study and coda Q ( Qc) previously reported by others for Kachchh region shows that Q C > Q S for the frequency range of interest showing the enrichment of coda waves and the importance of scattering attenuation to the attenuation of S waves in the Kachchh region infested with faults and fractures. The Q S/ Q P ratio is found to be less than 1 for Kachchh and Mainland Gujarat regions and close to unity for Saurashtra region. This reflects the difference in the geological composition of rocks in the regions. The frequency dependent relations developed in this study could be used for the estimation of earthquake source parameters as well as for simulating the strong earthquake ground motions in the region.

Chopra, Sumer; Kumar, Dinesh; Rastogi, B. K.

2011-05-01

205

Coda wave attenuation in the Parecis Basin, Amazon Craton, Brazil: sensitivity to basement depth  

NASA Astrophysics Data System (ADS)

Small local earthquakes from two aftershock sequences in Porto dos Gaúchos, Amazon craton—Brazil, were used to estimate the coda wave attenuation in the frequency band of 1 to 24 Hz. The time-domain coda-decay method of a single backscattering model is employed to estimate frequency dependence of the quality factor ( Q c) of coda waves modeled using Q_c =Q_0 f^? , where Q 0 is the coda quality factor at frequency of 1 Hz and ? is the frequency parameter. We also used the independent frequency model approach (Morozov, Geophys J Int, 175:239-252, 2008), based in the temporal attenuation coefficient, ?( f) instead of Q( f), given by the equation ? (f) = ? + ? f/Q_e , for the calculation of the geometrical attenuation ( ?) and effective attenuation (Q_e^{-1} ). Q c values have been computed at central frequencies (and band) of 1.5 (1-2), 3.0 (2-4), 6.0 (4-8), 9.0 (6-12), 12 (8-16), and 18 (12-24) Hz for five different datasets selected according to the geotectonic environment as well as the ability to sample shallow or deeper structures, particularly the sediments of the Parecis basin and the crystalline basement of the Amazon craton. For the Parecis basin Q_c =(98± 12)f^{(1.14± 0.08)}, for the surrounding shield Q_c =(167± 46)f^{(1.03± 0.04)}, and for the whole region of Porto dos Gaúchos Q_c =(99± 19)f^{(1.17± 0.02)}. Using the independent frequency model, we found: for the cratonic zone, ? = 0.014 s - 1, Q_e^{-1} =0.0001, ? ? 1.12; for the basin zone with sediments of 500 m, ? = 0.031 s - 1, Q_e^{-1} =0.0003, ? ? 1.27; and for the Parecis basin with sediments of 1,000 m, ? = 0.047 s - 1, Q_e^{-1} =0.0005, ? ? 1.42. Analysis of the attenuation factor ( Q c) for different values of the geometrical spreading parameter ( ?) indicated that an increase of ? generally causes an increase in Q c, both in the basin as well as in the craton. But the differences in the attenuation between different geological environments are maintained for different models of geometrical spreading. It was shown that the energy of coda waves is attenuated more strongly in the sediments, Q_c =(78± 23)f^{(1.17± 0.14)} (in the deepest part of the basin), than in the basement, Q_c =(167± 46)f^{(1.03± 0.04)} (in the craton). Thus, the coda wave analysis can contribute to studies of geological structures in the upper crust, as the average coda quality factor is dependent on the thickness of sedimentary layer.

Vieira Barros, Lucas; Assumpção, Marcelo; Quintero, Ronnie; Ferreira, Vinicius Martins

2011-04-01

206

Electrocardiogram voltage attenuation and shortening of the duration of P-waves, QRS complexes, and QT intervals  

PubMed Central

Multiple pathologies in concert may lead to attenuation of the electrocardiogram (ECG) voltage. A case of a patient illustrating the above is presented, who showed marked attenuation of the ECG voltage. Automated values of the amplitude of the ECG QRS complexes, P-waves, and T-waves (in mm), duration of the QRS complexes, P-waves, and QT intervals (in ms), in 2 ECGs were compared. The patient was a 64-year-old woman who developed in the setting of a fatal illness, pleural and pericardial effusions, pneumomediastinum, pneumoperitoneum, subcutaneous emphysema in the neck and chest, peripheral edema with weight gain of 43.4 lbs, marked hypoalbuminemia, abnormal liver tests, and renal failure. All the above pathologies led to a marked attenuation of the ECG voltage, and shortening of the mean P-wave, QRS complexes, and QTc interval durations. The postulated mechanism of the observed ECG phenomena is discussed.

Madias, John E.

2013-01-01

207

CW Measurement of the Upward-Going Temperature Wave in the Helium-4 Self-Organized Critical State  

SciTech Connect

We describe the first continuous-wave (CW) measurements of the upward-going temperature wave in the self-organized-critical (SOC) state which forms in 4He under conditions of downward heat flow near T{lambda} under gravity. The CW technique permits measurements with extremely low (<1 nK) excitation amplitudes, allows continuous measurement of the wave velocity as the SOC state grows, and has yielded the first quantitative measurements of the attenuation. The CW measurements appear to support predictions for the velocity but disagree with predictions for the attenuation. This new technique may help us understand the underlying mechanism of the SOC state.

Boyd, S. T. P.; Sergatskov, D. A.; Duncan, R. V. [Department of Physics and Astronomy, University of New Mexico, Albuquerque NM 87131 (United States)

2006-09-07

208

Measurement of Neutral Beam Attenuation from Beam Emission  

NASA Astrophysics Data System (ADS)

CXRS measurements of impurities in fusion plasmas are dependent upon local neutral beam densities. These local values can be found from complex penetration codes that depend upon plasma parameters, but they can also be derived directly from beam emission data from the multi-channel MSE diagnostic. Deriving beam densities in this fashion also provides the opportunity to benchmark the penetration codes. Before beam density can be derived from MSE data a channel-to-channel calibration of the MSE system is needed. This can be achieved by analysis of MSE data taken from beam-into-gas shots at a variety of pressures. The pressure variation allows in-situ measurement of the cross-section for beam attenuation, which is then used to acquire the channel-to-channel calibration constants. We will compare these empirical cross-sections with previous measurements. In some cases the atomic beam stopping cross-sections derived with these calibration constants show good agreement with predictions.( Janev, Boley, Post, D.E. (1989) NUCLEAR FUSION, 29 )12, 2125-39

McDermott, R. M.; Yuh, H.; Rowan, W. L.; Scott, S. D.

2004-11-01

209

Ultrasonic wave propagation in thermoviscous moving fluid confined by heating pipeline and flow measurement performance.  

PubMed

Ultrasonic wave propagation in thermoviscous fluid with pipeline shear mean flow in the presence of a temperature gradient is investigated. On the assumption of irrotational and axisymmetric wave propagation, a mathematical formulation of the convected wave equation is proposed without simplification in the manner of Zwikker and Kosten. A method based on the Fourier-Bessel theory, which is complete and orthogonal in Lebesgue space, is introduced to convert the wave equations into homogeneous algebraic equations. Then numerical calculation of the axial wavenumber is presented. In the end, wave attenuation in laminar and turbulent flow is numerically studied. Meanwhile measurement performance of an ultrasonic flow meter is parametrically analyzed. PMID:23967920

Chen, Yong; Huang, Yiyong; Chen, Xiaoqian

2013-09-01

210

Estimation of Coda Wave Attenuation for the National Capital Region, Delhi, India Using Local Earthquakes  

NASA Astrophysics Data System (ADS)

Attenuation of seismic waves is very essential for the study of earthquake source parameters and also for ground-motion simulations, and this is important for the seismic hazard estimation of a region. The digital data acquired by 16 short-period seismic stations of the Delhi Telemetric Network for 55 earthquakes of magnitude 1.5 to 4.2, which occurred within an epicentral distance of 100 km in an area around Delhi, have been used to estimate the coda attenuation Q c . Using the Single Backscattering Model, the seismograms have been analyzed at 10 central frequencies. The frequency dependence average attenuation relationship Q c = 142 f 1.04 has been attained. Four Lapse-Time windows from 20 to 50 seconds duration with a difference of 10 seconds have been analyzed to study the lapse time dependence of Q c . The Q c values show that frequency dependence (exponent n) remains similar at all the lapse time window lengths. While the change in Q 0 values is significant, change in Q 0 with larger lapsetime reflects the rate of homogeneity at the depth. The variation of Q c indicates a definitive trend from west to east in accordance with the geology of the region.

Mohanty, William K.; Prakash, Rajesh; Suresh, G.; Shukla, A. K.; Yanger Walling, M.; Srivastava, J. P.

2009-03-01

211

Measurement of elastic wave dispersion on human femur tissue  

NASA Astrophysics Data System (ADS)

Cortical bone is one of the most complex heterogeneous media exhibiting strong wave dispersion. In such media when a burst of energy goes into the formation of elastic waves the different modes tend to separate according to the velocities of the frequency components as usually occurs in waveguides. In this study human femur specimens were subjected to elastic wave measurements. The main objective of the study is using broadband acoustic emission sensors to measure parameters like wave velocity dispersion and attenuation. Additionally, waveform parameters like the duration, rise time and average frequency, are also examined relatively to the propagation distance as a preparation for acoustic emission monitoring during fracture. To do so, four sensors were placed at adjacent positions on the surface of the cortical bone in order to record the transient response after pencil lead break excitation. The results are compared to similar measurements on a bulk metal piece which does not exhibit heterogeneity at the scale of the propagating wave lengths. It is shown that the microstructure of the tissue imposes a dispersive behavior for frequencies below 1 MHz and care should be taken for interpretation of the signals.

Strantza, M.; Louis, O.; Polyzos, D.; Boulpaep, F.; Van Hemelrijck, D.; Aggelis, D. G.

2014-03-01

212

Measurements of ultrasound velocity and attenuation in numerical anisotropic porous media compared to Biot's and multiple scattering models.  

PubMed

This article quantitatively investigates ultrasound propagation in numerical anisotropic porous media with finite-difference simulations in 3D. The propagation media consist of clusters of ellipsoidal scatterers randomly distributed in water, mimicking the anisotropic structure of cancellous bone. Velocities and attenuation coefficients of the ensemble-averaged transmitted wave (also known as the coherent wave) are measured in various configurations. As in real cancellous bone, one or two longitudinal modes emerge, depending on the micro-structure. The results are confronted with two standard theoretical approaches: Biot's theory, usually invoked in porous media, and the Independent Scattering Approximation (ISA), a classical first-order approach of multiple scattering theory. On the one hand, when only one longitudinal wave is observed, it is found that at porosities higher than 90% the ISA successfully predicts the attenuation coefficient (unlike Biot's theory), as well as the existence of negative dispersion. On the other hand, the ISA is not well suited to study two-wave propagation, unlike Biot's model, at least as far as wave speeds are concerned. No free fitting parameters were used for the application of Biot's theory. Finally we investigate the phase-shift between waves in the fluid and the solid structure, and compare them to Biot's predictions of in-phase and out-of-phase motions. PMID:24125533

Mézière, Fabien; Muller, Marie; Bossy, Emmanuel; Derode, Arnaud

2014-07-01

213

Characteristics of the near-bottom suspended sediment field over the continental shelf off northern California based on optical attenuation measurements during STRESS and SMILE  

USGS Publications Warehouse

Time-series measurements of current velocity, optical attenuation and surface wave intensity obtained during the Sediment Transport Events on Shelves and Slopes (STRESS) experiments, combined with shipboard measurements of conductivity, temperature and optical attenuation obtained during the Shelf Mixed Layer Experiment (SMILE), provide a description of the sediment concentration field over the central and outer shelf off northern California. The questions addressed are: (1) existence and characteristics of bottom nepheloid layers and their relationship to bottom mixed layers; (2) characteristics of temporal fluctuations in sediment concentration and their relationship to waves and currents; (3) spatial scales over which suspended sediment concentrations vary horizontally; and (4) vertical distribution of suspended sediment. ?? 1994.

Trowbridge, J. H.; Butman, B.; Limeburner, R.

1994-01-01

214

Physical Models of Seismic-Attenuation Measurements on Lab Samples  

NASA Astrophysics Data System (ADS)

Seismic attenuation in Earth materials is often measured in the lab by using low-frequency forced oscillations or static creep experiments. The usual assumption in interpreting and even designing such experiments is the "viscoelastic" behavior of materials, i.e., their description by the notions of a Q-factor and material memory. However, this is not the only theoretical approach to internal friction, and it also involves several contradictions with conventional mechanics. From the viewpoint of mechanics, the frequency-dependent Q becomes a particularly enigmatic property attributed to the material. At the same time, the behavior of rock samples in seismic-attenuation experiments can be explained by a strictly mechanical approach. We use this approach to simulate such experiments analytically and numerically for a system of two cylinders consisting of a rock sample and elastic standard undergoing forced oscillations, and also for a single rock sample cylinder undergoing static creep. The system is subject to oscillatory compression or torsion, and the phase-lag between the sample and standard is measured. Unlike in the viscoelastic approach, a full Lagrangian formulation is considered, in which material anelasticity is described by parameters of "solid viscosity" and a dissipation function from which the constitutive equation is derived. Results show that this physical model of anelasticity predicts creep results very close to those obtained by using empirical Burger's bodies or Andrade laws. With nonlinear (non-Newtonian) solid viscosity, the system shows an almost instantaneous initial deformation followed by slow creep towards an equilibrium. For Aheim Dunite, the "rheologic" parameters of nonlinear viscosity are ?=0.79 and ?=2.4 GPa-s. Phase-lag results for nonlinear viscosity show Q's slowly decreasing with frequency. To explain a Q increasing with frequency (which is often observed in the lab and in the field), one has to consider nonlinear viscosity with ? < 0.5 and/or include thermoelastic effects. The model also shows how the Q values measured on the samples depend on the shapes and dimensions of the elements of the experimental system.; Non-linear creep approximating the anelastic part of Burgers' model for Aheim dunite (Chopra, 1997). Non-linear model parameters are ?=0.79, ?=2.4 GPa-s, and the Burger's model parameters are: ?=15.75 GPa and viscosity ?=2040 GPa-s.

Coulman, T. J.; Morozov, I. B.

2012-12-01

215

Lg Wave Attenuation in the Isparta Angle and Anatolian Plateau (Turkey)  

NASA Astrophysics Data System (ADS)

We estimate Lg wave attenuation using local and regional seismic phases in the Isparta Angle and the Anatolian Plateau (Turkey). The Isparta Angle (IA) is a tectonically active zone forming the boundary between the African Plate and the Anatolian Plateau, and is currently undergoing N-S extensional deformation. The Anatolian Plateau contains many intra-continental faults including the North Anatolian Fault Zone and the East Anatolian Fault Zone as well as the Menderes Massif. A large waveform data set was compiled from a variety of local and regional seismic networks including 121 digital seismic stations (broad-band and short period) between 1999 and 2008 spanning the IA, the Anatolian Plateau and Azerbaijan. The data set was used to determine the nature of Lg wave propagation and characterize the nature of seismic attenuation within the crust of these regions. Lg waveforms were used to calculate the frequency-dependent Lg- Q o and Lg- ? . A wide range of Lg- Q o values was obtained between ~52 ± 6 and 524 ± 227. Low Lg- Q o values (~90-155) are calculated towards the north of IA, Iskenderun Gulf and its vicinity, Bingöl-Karl?ova, Izmit and its vicinity. Lg- Q o values are especially low (<90) along the Menderes Massif and the Aksehir-Simav Fault Zones. This may be due to intrinsic attenuation of Lg associated with the partially molten crust and young volcanism. The high Lg- Q o values (~350) are probably caused by the crust not being subject to large amounts of extensional deformation like the Antalya Gulf and apparently being thick enough to support Lg propagation. Relatively higher values along the border of this subduction zone and plate boundary might be related to the Taurus Mountain belts and Bitlis-Zagros Suture Zone. The lateral frequency dependency Lg- ? is also consistent with high tectonic activity in this region.

Sahin, Sakir; Bao, Xueyang; Turkelli, Niyazi; Sandvol, Eric; Teoman, Ugur; Kahraman, Metin

2013-03-01

216

Temporal changes in attenuation of S waves through a fault zone in a South African gold mine  

NASA Astrophysics Data System (ADS)

We investigated the temporal changes in the seismic attenuation of a fault zone using near-source recordings of S waves from repeating microearthquakes that occurred both before and after M ˜ 2 earthquakes in the Bambanani gold mine, South Africa. Because the source locations and the mechanisms of repeating earthquakes can be regarded as identical, the attenuation change can be estimated using the spectral ratios for repeating earthquake pairs. We found an increase in the S-wave attenuation parameter ? on the vertical component which is positively correlated with frequency, corresponding to times before and after the M ˜ 2 earthquakes. This increase can be explained by scattering attenuation, with a typical scale of damage in the fault zone of ˜3 m.

Yoshimitsu, Nana; Kawakata, Hironori; Yamamoto, Akihito; Ogasawara, Hiroshi; Iio, Yoshihisa

2012-12-01

217

Parameterization of a Composite Attenuation Relation for the Dead Sea Area Based on 3-D Modeling of Elastic Wave Propagation  

Microsoft Academic Search

3-D simulations of elastic wave propagation generated by earthquakes with magnitudes between 5.5 and 7.0 are used to parameterize\\u000a strong ground motion attenuation relations for the Dead Sea Rift (DSR) graben structure. The results show that standard attenuation\\u000a relations with an isotropic distance parameter are inadequate for a graben structure with a deep sedimentary trough. A new\\u000a strategy is devised

Adrien Oth; Friedemann Wenzel; Hillel Wust-Bloch; Ellen Gottschämmer; Zvi Ben-Avraham

2007-01-01

218

Reconstruction of Elasticity and Attenuation Maps in Shear Wave Imaging: An Inverse Approach  

Microsoft Academic Search

Acoustic shear waves of low frequency can be detected and measured using a phase contrast based magnetic resonance imaging\\u000a technique called MR Elastography or phase measurement based ultrasound techniques. Spatio-temporal variations of displacements\\u000a caused by the propagating waves can be used to estimate local values of the elasticity of the object being imaged. The currently\\u000a employed technique for estimating the

Armando Manduca; Vinayak Dutt; David T. Borup; Raja Muthupillai; Richard L. Ehman; James F. Greenleaf

1998-01-01

219

A simple model of ultrasound propagation in a cavitating liquid. Part I: Theory, nonlinear attenuation and traveling wave generation.  

PubMed

The bubbles involved in sonochemistry and other applications of cavitation oscillate inertially. A correct estimation of the wave attenuation in such bubbly media requires a realistic estimation of the power dissipated by the oscillation of each bubble, by thermal diffusion in the gas and viscous friction in the liquid. Both quantities and calculated numerically for a single inertial bubble driven at 20 kHz, and are found to be several orders of magnitude larger than the linear prediction. Viscous dissipation is found to be the predominant cause of energy loss for bubbles small enough. Then, the classical nonlinear Caflish equations describing the propagation of acoustic waves in a bubbly liquid are recast and simplified conveniently. The main harmonic part of the sound field is found to fulfill a nonlinear Helmholtz equation, where the imaginary part of the squared wave number is directly correlated with the energy lost by a single bubble. For low acoustic driving, linear theory is recovered, but for larger drivings, namely above the Blake threshold, the attenuation coefficient is found to be more than 3 orders of magnitude larger then the linear prediction. A huge attenuation of the wave is thus expected in regions where inertial bubbles are present, which is confirmed by numerical simulations of the nonlinear Helmholtz equation in a 1D standing wave configuration. The expected strong attenuation is not only observed but furthermore, the examination of the phase between the pressure field and its gradient clearly demonstrates that a traveling wave appears in the medium. PMID:21764348

Louisnard, O

2012-01-01

220

Experimental measurements of seismic attenuation in microfracture sedimentary rock  

SciTech Connect

In a previous paper (Peacock et al., 1994), the authors related ultrasonic velocities in water-saturated Carrara Marble to crack densities in polished sections to verify Hudson's (1980, 1981, 1986) theory for velocities in cracked rock. They describe the empirical relationships between attenuation and crack density that they established during these experiments in the hope of clarifying the mechanism of attenuation in rocks with fluid-filled cracks. Relating seismic velocity and attenuation to crack density is important in predicting the productivity of fractured petroleum reservoirs such as the North Sea Brent Field. It also allows cracks to be used as stress indicators throughout the shallow crust (Crampin and Lovell, 1991).

Peacock, S.; McCann, C.; Sothcott, J.; Astin, T.R. (Univ. of Reading (United Kingdom). Research Inst. for Sedimentology)

1994-09-01

221

High-resolution 3-D P wave attenuation structure of the New Madrid Seismic Zone using local earthquake tomography  

NASA Astrophysics Data System (ADS)

three-dimensional (3-D), high-resolution P wave seismic attenuation model for the New Madrid Seismic Zone (NMSZ) is determined using P wave path attenuation (t*) values of small-magnitude earthquakes (MD < 3.9). Events were recorded at 89 broadband and short-period seismometers of the Cooperative New Madrid Seismic Zone Network and 40 short-period seismometers of the Portable Array for Numerical Data Acquisition experiment. The amplitude spectra of all the earthquakes are simultaneously inverted for source, path (t*), and site parameters. The t* values are inverted for QP using local earthquake tomography methods and a known 3-D P wave velocity model for the region. The four major seismicity arms of the NMSZ exhibit reduced QP (higher attenuation) than the surrounding crust. The highest attenuation anomalies coincide with areas of previously reported high swarm activity attributed to fluid-rich fractures along the southeast extension of the Reelfoot fault. The QP results are consistent with previous attenuation studies in the region, which showed that active fault zones and fractured crust in the NMSZ are highly attenuating.

Bisrat, Shishay T.; DeShon, Heather R.; Pesicek, Jeremy; Thurber, Clifford

2014-01-01

222

Quantum nondemolition measurements. [by gravitational wave antennas  

NASA Technical Reports Server (NTRS)

The article describes new electronic techniques required for quantum nondemolition measurements and the theory underlying them. Consideration is given to resonant-bar gravitational-wave antennas. Position measurements are discussed along with energy measurements and back-action-evading measurements. Thermal noise in oscillators and amplifiers is outlined. Prospects for stroboscopic measurements are emphasized.

Braginskii, V. B.; Vorontsov, Iu. I.; Thorne, K. S.

1980-01-01

223

Measurements for the JASPER Program radial shield attenuation experiment  

SciTech Connect

The Radial Shield Attenuation Experiment was conducted at the Oak Ridge National Laboratory Tower Shielding Facility during FY 1986 to: provide data for calculating the shielding effectiveness of combinations of stainless steel, graphite, and boron carbide shield designs; verify the accuracy of related radiation transport methods and nuclear data; and substantiate the effectiveness of shield designs currently proposed by advanced Liquid Metal Reactor (LMR) designers in Japan and the United States. The Tower Shielding Reactor source was modified to represent neutron spectra at a specified location near the core and in the sodium pool of a typical liquid-metal-cooled reactor. The experimental configurations resulted from successive additions of the various layers of material as specified in the program plan. Integral neutron fluxes were measured behind each of the configurations at specified locations, and neutron spectra were obtained for selected mockups. The experimental data are presented in both tabular and graphical form. This experiment is the first in a series of six experiments to be performed as part of a cooperative effort between the United States Department of Energy and the Japan Power Reactor and Nuclear Fuel Development Corporation. The research program is intended to provide support for the development of advanced sodium-cooled reactors.

Mukenthaler, F.J.

1987-05-01

224

Slant path attenuation and cross-polarization prediction. [radar measurements  

NASA Technical Reports Server (NTRS)

The accuracy with which slant-path attenuation and cross-polarization are predicted using differential reflectivity (ZDR) radar data is discussed. Consideration is given to the use of generalized relationships between radar reflectivity (Z), ZDR, and rainfall rate (R); and between R, attenuation, and cross-polarization (XPD) on a slant path. The forward-scatter matrix which is used to calculate the slant path attenuation and XPD is described. It is shown that the use of a double exponential drop size distribution and forward-scatter matrices improves the accuracy of the prediction of slant-path attenuation and XPD. Data obtained with the VPI & SU S-band radar, using slow switching between orthorzonal polarizations is presented. The results are illustrated in graphs.

Pratt, T.; Marshall, R. E.; Ozbay, C.

1983-01-01

225

Measurement of Elastic Properties of Tissue by Shear Wave Propagation Generated by Acoustic Radiation Force  

NASA Astrophysics Data System (ADS)

Acoustic radiation force (ARF) imaging has been developed as a novel elastography technology to diagnose hepatic disease and breast cancer. The accuracy of shear wave speed estimation, which is one of the applications of ARF elastography, is studied. The Young’s moduli of pig liver and foie gras samples estimated from the shear wave speed were compared with those measured the static Young’s modulus measurement. The difference in the two methods was 8%. Distance attenuation characteristics of the shear wave were also studied using finite element method (FEM) analysis. We found that the differences in the axial and lateral beam widths in pressure and ARF are 16 and 9% at F-number=0.9. We studied the relationship between two branch points in distance attenuation characteristics and the shape of ARF. We found that the maximum measurable length to estimate shear wave speed for one ARF excitation was 8 mm.

Marie Tabaru,; Takashi Azuma,; Kunio Hashiba,

2010-07-01

226

Long term attenuation measurements on optical ground wires  

Microsoft Academic Search

The attenuation stability of optical fibres integrated in optical ground wire (OPGW) cables over temperature and time is of paramount importance in the planning of long distance links. We report here a mean thermal attenuation dependence of 5.5·10-5 dB\\/(km·°C) at 1550 nm, on a 220 km span of dispersion shifted (DS) fibres of an installed OPGW cable. This optical link

Louis Lamarche; Daniel Gagnon; Michel Miron

1996-01-01

227

High-power gyrotron traveling-wave amplifier with distributed wall losses and attenuating severs  

SciTech Connect

Distributed-loss gyrotron traveling-wave amplifiers (gyro-TWTs) with high-gain, broadband, and millimeter-wave capabilities have been demonstrated. Most structures with distributed wall losses are stabilized in gyro-TWTs that operate at low beam currents. Attenuating severs are added to the interaction circuit of a distributed-loss gyro-TWT to prevent high beam currents that result in mode competition. Simulation results show that gyrotron backward-wave oscillations (gyro-BWOs) are not effectively suppressed by the lossy section; in contrast, the severed sections can effectively enhance the start-oscillation threshold of gyro-BWOs in the proposed gyro-TWT. Meanwhile, localized reflective oscillations seem not to occur in the gyro-TWT unless it operates at a high magnetic field or with a high interaction length. The stable gyro-TWT, operating in the low-loss TE{sub 01} mode, is predicted to yield a peak output power of 405 kW at 33 GHz with an efficiency of 20%, a saturated gain of 77 dB and a 3 dB bandwidth of 2.5 GHz for a 100 kV, 20 A electron beam with an axial velocity spread of {delta}v{sub z}/v{sub z}=5%.

Yeh, Y.S.; Shin, Y.Y.; You, Y.C.; Chen, L.K. [Department of Electrical Engineering, Southern Taiwan University of Technology, Tainan, Taiwan (China)

2005-04-15

228

Quasiparticles at the Mott transition in V2O3: wave vector dependence and surface attenuation.  

PubMed

We present an angle resolved photoemission study of V2O3, a prototype system for the observation of Mott transitions in correlated materials. We show that the spectral features corresponding to the quasiparticle peak in the metallic phase present a marked wave vector dependence, with a stronger intensity along the GammaZ direction. The analysis of their intensity for different probing depths shows the existence of a characteristic length scale for the attenuation of coherent electronic excitations at the surface. This length scale, which is larger than the thickness of the surface region as normally defined for noncorrelated electronic states, is found to increase when approaching the Mott transition. These results are in agreement with the behavior of quasiparticles at surfaces as predicted by Borghi et al. PMID:19257621

Rodolakis, F; Mansart, B; Papalazarou, E; Gorovikov, S; Vilmercati, P; Petaccia, L; Goldoni, A; Rueff, J P; Lupi, S; Metcalf, P; Marsi, M

2009-02-13

229

The Attenuation of a Detonation Wave by an Aircraft Engine Axial Turbine Stage  

NASA Technical Reports Server (NTRS)

A Constant Volume Combustion Cycle Engine concept consisting of a Pulse Detonation Combustor (PDC) followed by a conventional axial turbine was simulated numerically to determine the attenuation and reflection of a notional PDC pulse by the turbine. The multi-stage, time-accurate, turbomachinery solver TURBO was used to perform the calculation. The solution domain consisted of one notional detonation tube coupled to 5 vane passages and 8 rotor passages representing 1/8th of the annulus. The detonation tube was implemented as an initial value problem with the thermodynamic state of the tube contents, when the detonation wave is about to exit, provided by a 1D code. Pressure time history data from the numerical simulation was compared to experimental data from a similar configuration to verify that the simulation is giving reasonable results. Analysis of the pressure data showed a spectrally averaged attenuation of about 15 dB across the turbine stage. An evaluation of turbine performance is also presented.

VanZante, Dale; Envia, Edmane; Turner, Mark G.

2007-01-01

230

Probe for electrostatic wave measurements in plasmas  

Microsoft Academic Search

We present a probe arrangement for electrostatic wave measurements in plasmas. The probe picks up potential perturbation by capacitive coupling to a copper sensor. It has the advantages of high resolution (within 5 mm) and easy construction.

K. L. Wong; H. Akiyama

1988-01-01

231

Probe for electrostatic wave measurements in plasmas  

SciTech Connect

We present a probe arrangement for electrostatic wave measurements in plasmas. The probe picks up potential perturbation by capacitive coupling to a copper sensor. It has the advantages of high resolution (within 5 mm) and easy construction.

Wong, K.L.; Akiyama, H.

1988-09-01

232

Beamwidth measurement of individual lithotripter shock waves  

PubMed Central

New lithotripters with narrower foci and higher peak pressures than the original Dornier HM3 electrohydraulic lithotripter have proven to be less effective and less safe. Hence, accurate measurements of the focal characteristics of lithotripter shock waves are important. The current technique for measuring beamwidth requires a collection of single-point measurements over multiple shock waves, thereby introducing error as a result of any shock-to-shock variability. This work reports on the construction of a hydrophone array sensor and on array measurements of individual lithotripter shock waves. Beamwidths for an electrohydraulic lithotripter with a broad-focus HM3-style reflector and a narrow-focus modified reflector were measured using both new and worn electrodes as well as two different electrical charging potentials. The array measured the waveform, beamwidth, and focal location of individual shock waves. The HM3-style reflector produced repeatable focal waveforms and beam profiles at an 18 kV charging potential with new and worn electrodes. Corresponding measurements suggest a narrower beamwidth than reported previously from averaged point measurements acquired under the same conditions. In addition, a lack of consistency in the measured beam profiles at 23 kV underscores the value of measuring individual shock waves.

Kreider, Wayne; Bailey, Michael R.; Ketterling, Jeffrey A.

2009-01-01

233

Long term attenuation measurements on optical ground wires  

SciTech Connect

The attenuation stability of optical fibers integrated in optical ground wires (OPGW) cables over temperature and time is of paramount importance in the planning of long distance links. The authors report here a mean thermal attenuation dependence of 5.5{center_dot}10{sup {minus}5} dB/(km{center_dot}C) at 1,550 nm, on a 220 km span of dispersion shifted (DS) fibers of an installed OPGW cable. This optical link is installed in the James Bay region over a 735 kV power line where temperature varies from {minus}40 C to +30 C annually. The data sample presented covers 1.5 year starting December 1993. The data sample presented covers 1.5 year starting December 1993. During that period, the authors also observed a temporal evolution of the attenuation described by the empirical relation A = A{sub 0} (t{minus}t{sub 0}){sup 0.00394}.

Lamarche, L.; Gagnon, D.; Miron, M. [Hydro-Quebec, Varennes, Quebec1 (Canada)] [Hydro-Quebec, Varennes, Quebec1 (Canada)

1996-11-01

234

S-waves attenuation and separation of scattering and intrinsic absorption of seismic energy in southeastern Sicily (Italy)  

Microsoft Academic Search

Seismic wave attenuation in southeastern Sicily was investigated by using a data set of about 180 local earthquakes (1.5 <=ML<= 4.6) recorded in the period 1994-2003. We first estimated the quality factor of S waves (QS) and clarified its frequency dependence by means of the coda-normalization method, applied in the frequency range 1.5-15 Hz. The average QS as function of

E. Giampiccolo; T. Tuvè; S. Gresta; D. Patanè

2006-01-01

235

Heterogeneities in the field of short period seismic wave attenuation in the lithosphere of central Tien Shan  

Microsoft Academic Search

Records of deep-focus Hindu Kush earthquakes in the depth ranges 70–110 and 190–230 km made by 45 digital and analogue seismic\\u000a stations were analyzed to study the attenuation field of short period seismic waves in the lithosphere of central Tien Shan.\\u000a The dynamic characteristics studied include the ratio of peak amplitudes in S and P waves (S\\/P) and the ratio

Yu. F. Kopnichev; I. N. Sokolova

2007-01-01

236

Anisotropic physical properties of myocardium characterized by ultrasonic measurements of backscatter, attenuation, and velocity  

NASA Astrophysics Data System (ADS)

The goal of elucidating the physical mechanisms underlying the propagation of ultrasonic waves in anisotropic soft tissue such as myocardium has posed an interesting and largely unsolved problem in the field of physics for the past 30 years. In part because of the vast complexity of the system being studied, progress towards understanding and modeling the mechanisms that underlie observed acoustic parameters may first require the guidance of careful experiment. Knowledge of the causes of observed ultrasonic properties in soft tissue including attenuation, speed of sound, and backscatter, and how those properties are altered with specific pathophysiologies, may lead to new noninvasive approaches to the diagnosis of disease. The primary aim of this Dissertation is to contribute to an understanding of the physics that underlies the mechanisms responsible for the observed interaction of ultrasound with myocardium. To this end, through-transmission and backscatter measurements were performed by varying acoustic properties as a function of angle of insonification relative to the predominant myofiber direction and by altering the material properties of myocardium by increased protein cross-linking induced by chemical fixation as an extreme form of changes that may occur in certain pathologies such as diabetes. Techniques to estimate acoustic parameters from backscatter were broadened and challenges to implementing these techniques in vivo were addressed. Provided that specific challenges identified in this Dissertation can be overcome, techniques to estimate attenuation from ultrasonic backscatter show promise as a means to investigate the physical interaction of ultrasound with anisotropic biological media in vivo. This Dissertation represents a step towards understanding the physics of the interaction of ultrasonic waves with anisotropic biological media.

Baldwin, Steven L.

237

Clutter measurements by millimeter-wave radars  

Microsoft Academic Search

An extensive radar clutter database was generated by the University of Michigan's millimeter-wave mobile polarimetric radar system. The database includes millimeter-wave observations of snow, trees, vegetation, and soil and road surfaces at 35, 94, 140, and 215 GHz. The radar measurements were often augmented with close-up observations of the targets including such measurements as water content and surface roughness when

Y. Kuga; A. Nashashibi; F. T. Ulaby

1991-01-01

238

Spatial attenuation rates of interfacial waves: Field and numerical tests of Sommerfeld theory using ground-penetrating radar pulses  

NASA Astrophysics Data System (ADS)

We tested the geometric amplitude attenuation rates predicted by classic Sommerfeld theory for horizontally polarized interfacial waves propagating over dielectric ground. We used ground-penetrating radar pulses, the brief time duration of which allowed different interfacial wave modes to separate. We tested rates in the intermediate range of tens of wavelengths, and for azimuthal and radial polarizations. For azimuthal polarization, a closed form solution predicts inverse range-squared rates, and for radial polarization, calculations suggest an inverse range exponent between 1 and 2. Over low loss frozen ground having a dielectric constant of 6.8 azimuthally polarized air waves centered at 46 MHz attenuated nearly in proportion to the square of range, as predicted, while the radial rate at 37 MHz was close to the 1.6 power of range, as generally expected. At 360-390 MHz, air wave rates were higher than expected and likely caused by scattering losses. Three D time domain modeling at 37 MHz confirmed the rate for azimuthal polarization and the qualitative difference in rates between the two polarizations, but the exponent may be about 26% too high for the radial case. Not readily extractable from Sommerfeld theory are rates for subsurface direct waves, for which our models show that both polarizations attenuate in proportion to the square of range after about 5 subsurface wavelengths. This suggests that geometric rates for all horizontally polarized subsurface interfacial waves spatially attenuate in proportion to range-squared in both intermediate and far field ranges, and so could be subtracted from actual rates to determine loss rates caused by intrinsic attenuation and scattering.

Arcone, Steven; Liu, Lanbo

2012-06-01

239

Quasi-cylindrical 2.5-D wave modeling with a moment-tensor point source and the anelastic attenuation  

NASA Astrophysics Data System (ADS)

An accurate and efficient modeling of regional seismic wave propagation can be achieved by the axisymmetric modeling using the cylindrical coordinates (r, ? , z). It assumes the structural model as rotationally symmetric along the vertical axis (z) including a seismic source, and then solves the 3-D wave equation in cylindrical coordinates only on a 2-D structural cross section. Therefore, this method, a kind of the 2.5-D modeling, can correctly model 3-D geometrical spreading effects and the pulse shape, with computation time and memory comparable to 2-D modeling. On the other hand, application of the conventional purely axisymmetric approximation is difficult in practice because the structure along the measurement line of the seismic survey is rarely symmetric with respect to the source location. To overcome this difficulty, Takenaka et al. (2003, GRL) proposed a 'quasi-cylindrical approach'. It solves the wave equation not in the usual cylindrical domain (0 ? r < ? , -? ? ? ? ? , 0 ? z < ? ), but instead in a newly defined ``quasi-cylindrical domain'' (-? < r < ? , -? /2 ? ? ? ? /2, 0 ? z < ? ). They developed a numerical scheme with the finite-difference method (FDM). The quasi-cylindrical FDM enables modeling of regional seismic wave propagation in a 2-D slice of a structural model of arbitrary lateral heterogeneity, with full consideration of the 3-D geometrical spreading effects. Since the quasi-cylindrical approach was developed for seismic exploration, the FDM code has only treated axisymmetric source mechanisms. In this work we have improved this scheme to include an arbitrary moment-tensor point source and the anelastic attenuation for further realistic modeling. The moment-tensor source can be treated by the Fourier expansion of all wavefield variables in ? direction considering source radiation patterns. This process corresponds to decomposing an arbitrary source mechanism into five moment-tensor elements. Synthesizing all contributions enables us to model wavefields by the asymetric excitation. The anelastic attenuation is also adopted by the so-called memory variables (e.g., Emmerich & Korn, 1987, Geophysics). In the presentation, we will show realistic numerical examples using tomography models of plate subduction zone and shear dislocation sources.

Toyokuni, G.; Takenaka, H.; Okamoto, T.; Zhao, D.

2013-12-01

240

Measurement of Multimode Optical Fiber Attenuation: An NBS (National Bureau of Standards) Special Test Service.  

National Technical Information Service (NTIS)

This document is one of a series that describes optical fiber measurement procedures and capabilities at the National Bureau of Standards (NBS). The authors concentrate here on the measurement of attenuation of multimode, telecommunication-grade fibers fo...

R. L. Gallawa G. E. Chamberlain G. W. Day D. L. Franzen M. Young

1984-01-01

241

Viscosity measurement based on shear-wave laser speckle contrast analysis.  

PubMed

Tissue viscosity is correlated with tissue pathological changes and provides information for tissue characterization. In this study, we report an optical method to track continuous shear-wave propagation at centimeter depths in an optically turbid medium. Shear-wave attenuation coefficients were measured at multiple frequencies using shear-wave laser speckle contrast analysis (SW-LASCA) to quantitatively estimate tissue viscosity using the Voigt model. Shear waves were generated within tissue-mimicking phantoms by an amplitude-modulated ultrasound (modulation frequency: 100 to 600 Hz) and tracked by time-resolved laser speckle contrast difference received on a charged-coupled device camera. Averaged contrast difference over a selected time window was related to shear-wave amplitude and used to calculate the shear-wave attenuation coefficient. Phantoms of varying viscosities (0.1 and 0.3 Pa s) were studied. Attenuation coefficients for different shear-wave frequencies (100 to 600 Hz) were calculated. Derived viscosity values had a maximum standard deviation of 9%, and these values were consistent with the independent measurements reported in a previous study using nonoptical methods. PMID:24357548

Cheng, Yi; Li, Sinan; Eckersley, Robert J; Elson, Daniel S; Tang, Meng-Xing

2013-12-01

242

Attenuation of stress waves in single and multi-layered structures. [mitigation of elastic and plastic stress waves during spacecraft landing  

NASA Technical Reports Server (NTRS)

Analytical and experimental studies were made of the attenuation of the stress waves during passage through single and multilayer structures. The investigation included studies on elastic and plastic stress wave propagation in the composites and those on shock mitigating material characteristics such as dynamic stress-strain relations and energy absorbing properties. The results of the studies are applied to methods for reducing the stresses imposed on a spacecraft during planetary or ocean landings.

Yang, J. C. S.; Tsui, C. Y.

1972-01-01

243

Imaging Lower Mantle Heterogeniety With Differential Dispersion and Attenuation of Core- Diffracted Waves  

NASA Astrophysics Data System (ADS)

We investigate global differential travel-time dispersion and attenuation of core-diffracted phases from large, deep earthquakes. This technique aids in constraining radial velocity structure at the core-mantle interface in a manner analogous to surface wave observables constraining upper mantle structure. We confirm that there is noticeable differential dispersion and attenuation caused by diffraction on a global basis for both Pdiff and Sdiff. Variations in differential dispersion and attenuation are observed with both geographic location and between Pdiff and Sdiff along the same azimuth suggesting lateral variations in Vp, Vs and Vp/Vs ratio in the lowermost mantle. We attempt to utilize dispersion and attenuation characteristics to put bounds on the magnitude and distribution of large-scale velocity perturbations in the lowermost mantle and draw comparisons to variations found in several 3D whole-mantle models. Our dataset consists of broadband records available from the IRIS DMC for deep (>180 km), large (>5.6 mb) teleseismic events. Preprocessing of the records includes deconvolution of the instrument response, rotation of horizontal components, filtering using a set of bandpass filters, and sample-rate decimation (5 sps). Relative arrival times and amplitudes are found by computing cross correlegrams in the frequency domain, detecting and removing poor recordings with cluster analysis, and iteratively converging on a stable low-variance solution with a weighted least-squares inversion while automatically remediating phase-skips utilizing a database of potential relative arrivals. Raypath-approximated corrections for reciever-side differences in ellipticity, mantle, and crust are applied for the derivation of phase velocites in the lowermost mantle as a function of azimuth and frequency. Following previous studies of diffracted signals, we limit our analysis to station pairs located in narrow azimuthal windows spread over a considerable distance while attempting to quantify the acceptable range of aspect ratios. This method has the advantage of removing source-side effects, averaging out minor timing errors, and, for our analysis, averaging out receiver-side frequency-dependent upper mantle and crustal biasing. Comparison with 1D reflectivity and 3D SEM synthetics facilitates our quantitative analysis of the lateral and vertical variations in the seismic velocity structure near the core-mantle boundary region.

Euler, G. G.; Wysession, M. E.; Huhmann, B.

2007-12-01

244

A Simultaneous Multi-phase Approach to Determine P-wave and S-wave Attenuation of the Crust and Upper Mantle  

SciTech Connect

We have generalized the methodology of our regional amplitude tomography from the Lg phase to the four primary regional phases (Pn, Pg, Sn, Lg). Differences in the geometrical spreading, source term, site term, and travel paths are accounted for, while event source parameters such as seismic moment are consistent among phases. In the process, we have developed the first regional attenuation model that uses the amplitudes of four regional phases to determine a comprehensive P-wave and S-wave attenuation model of the crust and upper mantle. When applied to an area encompassing the Middle East, eastern Europe, western Asia, south Asia, and northeast Africa for the 1-2 Hz passband, we find large differences in the attenuation of the lithosphere across the region. The tectonic Tethys collision zone has high attenuation, while stable outlying regions have low attenuation. While crust and mantle Q variations are often consistent, we do find several notable areas where they differ considerably, but are appropriate given the region's tectonic history. Lastly, the relative values of Qp and Qs indicate that scattering Q is likely the dominant source of attenuation in the crust at these frequencies.

Pasyanos, M E; Walter, W R; Matzel, E M

2009-02-26

245

SUPPLEMENTING GROUND TRUTH DATA WITH SHEAR WAVE VELOCITY, SEISMIC ATTENUATION, AND THERMAL STRUCTURE OF THE CONTINENTAL LITHOSPHERE  

Microsoft Academic Search

Ground truth data provide the opportunity to calibrate regional seismic velocity and Q (inverse attenuation) models. However, in many cases, available wave propagation data are too sparse to characterize seismic velocities and Q everywhere. It is therefore of interest to examine on a global basis the relationship between regional geology and heat flow versus the seismic properties (Vs and Qs)

Walter D. Mooney; Irina Artemieva; Shane T. Detweiler; Magali Billien; Jean-Jacques Leveque

246

An improvement in the VIRGO Super Attenuator for interferometric detection of gravitational waves: The use of a magnetic antispring  

SciTech Connect

We present a method of lowering below 2.5 Hz the vertical normal mode frequencies of the Pisa Super Attenuator by using permanent magnets which provide an antispring force. This method allows a more efficient suppression of the seismic noise decreasing the lower limit of the frequency region devoted to gravitational wave detection.

Braccini, S.; Bradaschia, C.; Cobal, M.; Del Fabbro, R.; Di Virgilio, A.; Flaminio, R.; Giazotto, A.; Kautzky, H.; Morganti, M.; Passuello, D. (INFN, Sezione di Pisa and Dipartimento di Fisica, Universita di Pisa, Pisa (Italy)); Calloni, E.; Di Fiore, L. (INFN, Sezione di Napoli, Naples (Italy)); Holloway, L.E. (Physics Department, University of Illinois, Urbana, Illinois 61801 (United States)); Montelatici, V. (Laboratorio ENEA, Frascati (Italy))

1993-02-01

247

Continent-Wide Maps of Lg Coda Q Variation and Rayleigh-wave Attenuation Variation for Eurasia.  

National Technical Information Service (NTIS)

We present new maps of Lg coda Q and its frequency dependence at 1 Hz (Qo and eta, respectively) as well as Rayleigh-wave attenuation coefficients at 5, 10, 20 and 50 s across virtually all of Eurasia. Qo is relatively high, 700 or more, in most cratonic ...

B. J. Mitchell L. Cong

2007-01-01

248

Wave measurements using GPS velocity signals.  

PubMed

This study presents the idea of using GPS-output velocity signals to obtain wave measurement data. The application of the transformation from a velocity spectrum to a displacement spectrum in conjunction with the directional wave spectral theory are the core concepts in this study. Laboratory experiments were conducted to verify the accuracy of the inversed displacement of the surface of the sea. A GPS device was installed on a moored accelerometer buoy to verify the GPS-derived wave parameters. It was determined that loss or drifting of the GPS signal, as well as energy spikes occurring in the low frequency band led to erroneous measurements. Through the application of moving average skill and a process of frequency cut-off to the GPS output velocity, correlations between GPS-derived, and accelerometer buoy-measured significant wave heights and periods were both improved to 0.95. The GPS-derived one-dimensional and directional wave spectra were in agreement with the measurements. Despite the direction verification showing a 10° bias, this exercise still provided useful information with sufficient accuracy for a number of specific purposes. The results presented in this study indicate that using GPS output velocity is a reasonable alternative for the measurement of ocean waves. PMID:22346618

Doong, Dong-Jiing; Lee, Beng-Chun; Kao, Chia Chuen

2011-01-01

249

Application of the Kramers-Kronig relations to measurements of attenuation and dispersion in  

Microsoft Academic Search

* Official contribution of the National Institute of Standards and Technology; not subject to copyright in the United States. Abstract—Ultrasonic (US) assessment of fracture risk in osteoporotic patients is based on measurements of broadband ultrasonic attenuation and speed of sound (SOS) of cancellous bone. Discrepancies in estimates of SOS can result from dispersion and frequency-dependent attenuation. An improved understanding of

B. K. Hoffmeister; J. A. Javarone

250

Effect of collimator size and absorber thickness on gamma ray attenuation measurements for bakelite and perspex  

Microsoft Academic Search

The mass attenuation coefficient (m m ) of 662 keV gamma rays have been measured in the extended media of bakelite and perspex under different collimation conditions. The increase in attenuation coefficient is seen with increase in sample thickness as well as with collimator size due to the contribution of multiple scattered photons in the uncollided beam of 662 keV

Gurdeep S. Sidhu; Karamjit Singh; Parjit S. Singh; Gurmel S. Mudahar

1999-01-01

251

Three-dimensional compressional wave attenuation tomography for the crust and uppermost mantle of Northern and central California  

NASA Astrophysics Data System (ADS)

I present a frequency-independent three-dimensional (3-D) compressional wave attenuation model (indicated by quality factor Qp) for the crust and uppermost mantle of Northern and central California. The tomographic inversion used t? values measured from amplitude spectra of 80,988 P wave arrivals of 3247 events recorded by 463 network stations through a 3-D seismic velocity model. The model has a uniform horizontal grid spacing of 15 km, and the vertical node intervals range between 2 and 10 km down to 45 km depth. In general, the resulting Qp values increase with depth and agree with the surface geology at shallow depth layers. The most significant features observed in the Qp model are the high Qp values in the Sierra Nevada mountains and low Qp anomalies in the western fault zones. Low Qp values are also imaged in Owens Valley and Long Valley at shallow depths and the Cape Mendocino region in the lower crust (˜25 km depth). An overall contrast of Qp values across the fault is observed in the creeping, Parkfield and Cholame-Carrizo sections of the San Andreas Fault. The new 3-D Qp model provides an important complement to the existing regional-scale velocity models for interpreting structural heterogeneity and fluid saturation of rocks in the study area.

Lin, Guoqing

2014-04-01

252

Three-dimensional compressional wave attenuation tomography for the crust and uppermost mantle of northern and central California  

NASA Astrophysics Data System (ADS)

I present a frequency-independent three-dimensional (3D) compressional wave attenuation model (indicated by quality factor Qp) for the crust and uppermost mantle of northern and central California. The tomographic inversion used t* values measured from amplitude spectra of 80,988 P-wave arrivals of 3247 events recorded by 463 network stations through a 3D seismic velocity model. The model has a uniform horizontal grid spacing of 15 km and the vertical node intervals range between 2 and 10 km down to 45 km depth. The resulting Qp model provides an important complement to the existing regional-scale velocity models for interpreting structural heterogeneity and fluid saturation of rocks in the study area. In general, the Qp values increase with depth and agree with the surface geology at shallow depth layers. The most significant features observed in the Qp model are the high Qp values in the Sierra Nevada mountains and low Qp anomalies in the western fault zones. Low Qp values are also imaged in Owens Valley and Long Valley at shallow depths and the Mendocino fault zones in the lower crust. An overall contrast of Qp values across the fault is observed in the creeping, Parkfield and Cholame-Carrizo sections of the San Andreas Fault. Very high Qp anomalies are seen near and below the seismogenic zones at depths in several faults. A nice correlation between shallow Qp values and hear flow is also shown.

Lin, G.

2013-12-01

253

Closing the Gap on Measuring Heat Waves  

NASA Astrophysics Data System (ADS)

Since the 4th IPCC assessment report, the scientific literature has established that anthropogenic climate change encompasses adverse changes in both mean climate conditions and extreme events, such as heat waves. Indeed, the affects of heat waves are felt across many different sectors, and have high economic, human, and physical impacts over many global regions. The spatial and monetary scale of heat wave impacts emphasizes the necessity of measuring and studying such events in an informative manner, which gives justice to the geographical region affected, the communities impacted, and the climatic fields involved. However, due to such wide interest in heat waves, their definition remains broad in describing a period of consecutive days where conditions are excessively hotter than normal. This has allowed for the employment of a plethora of metrics, which are usually unique to a given sector, or do not appropriately describe some of the important features of heat wave events. As such, it is difficult to ascertain a clear message regarding changes in heat waves, both in the observed record and in projections of future climate. This study addresses this issue by developing a multi-index, multi-aspect framework in which to measure heat waves. The methodology was constructed by assessing a wide range of heat wave and heat wave-related indices, both proposed and employed in the scientific literature. The broad implications of the occurrences, frequency and duration of heat waves and respective changes were also highly considered. The resulting indices measure three or more consecutive days where 1) maximum temperature exceeds the 90th percentile (TX90pct); 2) minimum temperature exceeds the 90th percentile (TN90pct); and 3) daily average temperature has a positive excess heat factor (EHF). The 90th percentiles from which TX90pct and TN90pct are calculated are based on 15-day windows for each calendar day, whereas the EHF is based upon two pre-calculated indices that compare the temperature of a three-day window to the previous 30 days and the climatological 95th percentile (see Nairn and Fawcett, 2012, CAWCR Technical Report). Based on a previously defined methodology (Fischer and Shar, 2010, Nature Geoscience), each index is analysed with respect to five properties - heat wave number (HWN) and length (HWD), the number of participating days (HWF), the amplitude or peak of the hottest day (HWA), and mean heat wave magnitude (HWM), thereby assessing the occurrence, intensity and duration of heat waves for each index. The methodology is demonstrated for characterizing changes in observed heat waves at the global scale and regionally over Australia for the latter half of the 20th Century. Overall, general increases in heat wave intensity and duration occur, although the magnitude and significance of this trend shows variation both regionally and among the indices. Trend magnitudes also differ for "warm-spell" (year-round) and summer only events. This framework therefore allows for the broad examination of heat waves, such that the results presented are informative to multiple sectors affected by such events. Indeed, it "closes the gap" on heat wave measurement by reducing the number of indices employed, yet realizing that heat wave measurement cannot be a one size fits all approach, and that there is more than one feature of heat waves that causes adverse impacts.

Perkins, S. E.; Alexander, L.

2012-12-01

254

Using Kinect to Measure Wave Spectrum  

NASA Astrophysics Data System (ADS)

Gas exchange at the air-sea interface is enhanced by aqueous turbulence generated by capillary-gravity waves, affecting the absorption of atmospheric carbon dioxide by the ocean. The mean squared wave slope of these waves correlates strongly with the gas transfer velocity. To measure the energy in capillary-gravity waves, this project aims to use the Microsoft Xbox Kinect to measure the short period wave spectrum. Kinect is an input device for the Xbox 360 with an infrared laser and camera that can be used to map objects at high frequency and spatial resolution, similar to a LiDAR sensor. For air-sea gas exchange, we are interested in the short period gravity waves with a wavenumber of 40 to 100 radians per meter. We have successfully recorded data from Kinect at a sample rate of 30 Hz with 640x480 pixel resolution, consistent with the manufacturer specifications for its scanning capabilities. At 0.5 m distance from the surface, this yields a nominal resolution of approximately 0.7 mm with a theoretical vertical precision of 0.24 mm and a practical 1 ? noise level of 0.91 mm. We have found that Kinect has some limitations in its ability to detect the air-water interface. Clean water proved to be a weaker reflector for the Kinect IR source, whereas a relatively strong signal can be received for liquids with a high concentration of suspended solids. Colloids such as milk and Ca(OH)2 in water proved more suitable media from which height and wave spectra were detectable. Moreover, we will show results from monochromatic as well as wind-wave laboratory studies. With the wave field measurements from Kinect, gas transfer velocities at the air-sea interface can be determined.

Fong, J.; Loose, B.; Lovely, A.

2012-12-01

255

High Resolution of Crustal Seismic Wave Attenuation Tomography in Eastern Tibetan Plateau  

NASA Astrophysics Data System (ADS)

We investigate the frequency dependent attenuation tomography of regional seismic phases Lg and Pg. The intrinsic attenuation of Lg and Pg is employed as an approximation of Qs and Qp in the crust and used as a constraint in interpretation of crustal geothermy, rheology and tectonics. We have generated tomographic images with the best resolution to observe structures as small as 100km2. We applied waveform data from 769 regional events and 222 stations of permanent or temporary networks including CDSN, INDEPTH-IV-ASCENT, NETS, Namche Barwa, and MIT-China within this region. We used a Reverse Two-station/event Method (RTM) to measure inter-station Q; this method theoretically eliminates any contributions from source excitation and site amplification from the estimation of path-based Q. The tomographic images with significant lateral variations in Q suggest a strong lateral variation in the geothermal and rheological properties of the Tibetan crust. The disadvantage of the Two-Station Method (TSM) is that the measurements is contaminated by site amplification terms, thus the RTM is a significant improvement in the methodology of measuring Q. Large-scale scattering is a significant contributor to Lg and Pg attenuation however, we suggest the patterns in our tomographic images suggest that the intrinsic attenuation is the dominant factor causing the observed Q anomalies. The most remarkable results in this study include that (1) a high Q zone bands around the eastern Himalayan syntaxis and even spreads to the entire three-river zone tectonically between the Indus-Yalu suture and the Bangong-Nujiang suture in the southeastern TP; (2) the TP has widespread low to middle Q values, except the mid-eastern Qiangtang terrane, east of the INDEPTH-III profile, with relatively middle to high Q values; (3) approximately along the Kunlun Fault system there is a nearly 1000km E-W very low Q band; (4) high Q values are observed widely in the Qaidam Basin, Tarim Basin, Sichuan Basin, and Ordos Block; (5) the Qilian Shan-Nan Shan thrust belt has low to middle Q values, lower than all of its surrounding areas; and (6) a nearly 400km very low Q zone is exactly consistent with the western Longmenshan thrust belt. Based on the estimation of Qs, Qp, their frequency dependence ?, and Qp/Qs in this study, we deduce various possible interpretations on these anomalies. For example, most of the low Q zones are probably due to fluid content within active fault systems or high temperatures in middle to lower crust, and the high Q anomalies seem to correlate well with tectonically stable and aseismic regions within TP and surrounding area.

Bao, X.; Sandvol, E. A.; Ni, J. F.; Hearn, T. M.; Chen, Y. J.; Shen, Y.

2010-12-01

256

Influence of Forward and Multiple Light Scatter on the Measurement of Beam Attenuation in Highly Scattering Marine Environments  

NASA Astrophysics Data System (ADS)

Using three-dimensional Monte Carlo radiative transfer simulations, we examine the effect of beam transmissometer geometry on the relative error in the measurement of the beam-attenuation coefficient in an aquatic environment characterized by intense light scattering, especially within submerged bubble clouds entrained by surface-wave breaking. We discuss the forward-scattering error associated with the detection of photons scattered at small angles (< 1°) and the multiple-scattering error associated with the detection of photons scattered more than once along the path length of the instrument. Several scattering phase functions describing bubble clouds at different bubble void fractions in the water are considered. Owing to forward-scattering error, a beam-attenuation meter (beam transmissometer) with a half-angle of receiver acceptance of 1.0° and a path length of 0.1 m can underestimate the true beam attenuation within the bubble cloud by more than 50%. For bubble clouds with a beam attenuation of as much as 100 m^-1, the multiple-scattering error is no more than a few percent. These results are compared with simulations for some example phase functions that are representative of other scattering regimes found in natural waters. The forward-scattering error for the Petzold phase function of turbid waters is 16% for a typical instrument geometry, whereas for the Henyey-Greenstein phase function with the asymmetry parameter of 0.7 and 0.9 the error range is 8-28%.

Piskozub, Jacek; Stramski, Dariusz; Terrill, Eric; Melville, W. Kendall

2004-08-01

257

Measuring Acoustic Nonlinearity by Collinear Mixing Waves  

Microsoft Academic Search

It is well known that the acoustic nonlinearity parameter beta is correlated to fatigue damage in metallic materials. Various methods have been developed to measure beta. One of the most often used methods is the harmonic generation technique, in which beta is obtained by measuring the magnitude of the second order harmonic waves. An inherent weakness of this method is

M. Liu; G. Tang; L. J. Jacobs; J. Qu

2011-01-01

258

New constraints on the properties of the Yellowstone mantle plume from P and S wave attenuation tomography  

NASA Astrophysics Data System (ADS)

We estimate attenuation (t*) for teleseismic P and S arrivals to seismometers in the Yellowstone Intermountain Seismic Array; tomographically invert these data for upper mantle Qp-1 and Qs-1 structure; and, with the aid of the upper mantle velocity model of Waite et al. (2006), interpret the results for mantle temperature, partial melt, and water content. Because attenuation analysis is susceptible to contamination by noise, we employ time- and frequency-domain analyses and a careful assessment of the uncertainty associated with each estimate by using the misfit between actual and predicted traces or spectra. The greatest noise source is signal-generated noise, which affects S wave results more than P wave results. S waves also appear more susceptible to the effects of plume focusing. We find the upper mantle to be highly attenuative, but that above 200-250 km the low-velocity plume is progressively less attenuative than the adjacent mantle with decreasing depth. We conclude that water dissolved in mantle minerals causes the upper mantle to be highly attenuative, that the Yellowstone plume is only ~50°C warmer than the surrounding mantle below the North America lithosphere, and that melting within this plume begins at depths of 200-250 km. We attribute the lower attenuation in the partially molten plume to the dehydration of the solid matrix as water partitions into the melt. The source of the upper mantle hydration is attributed to subduction, including water flux from a hydrated transition zone and Laramide-age shallow subduction and direct hydration of North America lithosphere.

Adams, David C.; Humphreys, Eugene D.

2010-12-01

259

Analysis of the Attenuation Characteristics of an Elastic Wave Due to the Wave-Induced Fluid Flow in Fractured Porous Media  

NASA Astrophysics Data System (ADS)

A theoretical model is presented to describe the elastic wave propagation characteristics in porous media of periodically arranged fractures. The effects of fracture geometric parameters on a compressional wave (p-wave) are considered through analysis of the wave induced fluid flow (WIFF) process between the fractures and the background media. The diffusion equation in porous media is used to reveal how the entire diffusion process affects the wave propagation. When the thickness proportion of fractures tends to 0 and 1, the WIFF does not take place almost between fractures and background matrix porosity, and therefore the media elasticity modulus is perfectly elastic. When the fracture thickness fraction achieves a certain value, the peak of the attenuation curve reaches the maximum value at a particular frequency, which is controlled by the fluid mass conservation and stress continuity conditions on each fracture boundary. That is, the inter-coupling of fluid diffusion between the adjacent layers is important for waves attenuation. Physically speaking, the dissipation of a wave is associated with the fluid flux essentially.

Wang, Ding; Wang, Li-Ji; Zhang, Mei-Gen

2014-04-01

260

Effective x-ray attenuation measurements with full field digital mammography  

SciTech Connect

This work shows that effective x-ray attenuation coefficients may be estimated by applying Beer's Law to phantom image data acquired with the General Electric Senographe 2000D full field digital mammography system. Theoretical developments are provided indicating that an approximate form of the Beer's relation holds for polychromatic x-ray beams. The theoretical values were compared with experimentally determined measured values, which were estimated at various detector locations. The measured effective attenuation coefficients are in agreement with those estimated with theoretical developments and numerical integration. The work shows that the measured quantities show little spatial variation. The main ideas are demonstrated with polymethylmethacrylate and breast tissue equivalent phantom imaging experiments. The work suggests that the effective attenuation coefficients may be used as known values for radiometric standardization applications that compensate for the image acquisition influences. The work indicates that it is possible to make quantitative attenuation coefficient measurements from a system designed for clinical purposes.

Heine, John J.; Behera, Madhusmita [The H. Lee Moffitt Cancer Center and Research Institute, 12902 Magnolia Drive, Tampa, Florida 33612-4799 (United States)

2006-11-15

261

Beyond group velocity - Wave velocity and signal velocity. I The group-velocity operator in the absence of attenuation  

NASA Astrophysics Data System (ADS)

Radiation-field propagation in a dispersive medium is investigated theoretically, considering the heuristic case of negligeable attenuation. The wave-packet and wave-front approaches to the metrology of group velocity are reviewed, and a new approach based on a realistic and accesible criterion and free from limiting assumptions about the form of the emitted signal or its spectrum is developed, expanding the analysis of wave moments (Baird, 1972; Bradford, 1976) to encompass field source, medium, and detector. The formalism and methodology of the theory of the spatiotemporal signal and its representations is employed, defining a wave center and a signal center as the spatial and temporal markers of the field, respectively, and characterizing their motions by a wave velocity, and a signal velocity, both dependent on emitted-signal form and medium properties. The nonattenuation case is examined in detail.

Bonnet, G.

1983-10-01

262

Computer signal processing for ultrasonic attenuation and velocity measurements for material property characterizations  

NASA Technical Reports Server (NTRS)

This report deals with instrumentation and computer programming concepts that have been developed for ultrasonic materials characterization. Methods that facilitate velocity and attenuation measurements are described. The apparatus described is based on a broadband, buffered contact probe using a pulse-echo approach for simultaneously measuring velocity and attenuation. Instrumentation, specimen condition, and signal acquisition and acceptance criteria are discussed. Typical results with some representative materials are presented.

Vary, A.

1979-01-01

263

Dependence of CT attenuation values on scanner type using in vivo measurements  

NASA Astrophysics Data System (ADS)

One of the key measures of response to treatment for patients in multicenter clinical trials is the lung density measured in Hounsfield Units (HU) from Computer Tomography (CT) scans. The purpose of this work is to determine the dependence of CT attenuation values on scanner type by using in vivo measurements made from homogeneous anatomic areas. In vivo measurements were made in areas within the trachea, aorta, fat and muscle regions of CT scans obtained from subjects scanned as part of a multicenter treatment trial. Scans were selected so that exams from all four major manufacturers were included in the study. For each anatomic region of interest, the mean and standard deviation values were computed to investigate attenuation dependence on scanners. For example, trachea mean (standard deviation) measurements for exams from GE, Siemens, Philips and Toshiba scanners were -986 HU(+/-15), - 993 HU(+/-9), -988HU(+/-8), -1046(+/-10) respectively. Inter-scanner variability was observed for each scanner showing significant differences (all p-values <0.005). Previous work in examining attenuation dependence on scanners has been performed using anthropomorphic phantoms. The novelty of this work is the use of in vivo measurements from homogeneous regions in order to examine scanner effects on CT attenuation values. Our results show that CT attenuation values for the anatomic regions vary between scanners and hence, dependence of CT attenuation values on scanners is observed.

Prasad, Mithun; Meza, Alicia; Kim, Hyun J.; Brown, Matthew S.; Abtin, Fereidoun; Goldin, Jonathan G.; McNitt-Gray, Michael F.

2008-04-01

264

Wave dispersion and attenuation in viscoelastic isotropic media containing multiphase flow and its application  

NASA Astrophysics Data System (ADS)

In this paper, we introduce the complex modulus to express the viscoelasticity of a medium. According to the correspondence principle, the Biot-Squirt (BISQ) equations in the steady-state case are presented for the space-frequency domain described by solid displacements and fluid pressure in a homogeneous viscoelastic medium. The effective bulk modulus of a multiphase flow is computed by the Voigt formula, and the characteristic squirt-flow length is revised for the gas-included case. We then build a viscoelastic BISQ model containing a multiphase flow. Through using this model, wave dispersion and attenuation are studied in a medium with low porosity and low permeability. Furthermore, this model is applied to observed interwell seismic data. Analysis of these data reveals that the viscoelastic parameter tan ? is not a constant. Thus, we present a linear frequency-dependent function in the interwell seismic frequency range to express tan ?. This improves the fit between the observed data and theoretical results.

Yang, Lei; Yang, DingHui; Nie, JianXin

2014-06-01

265

Wave dispersion and attenuation in viscoelastic isotropic media containing multiphase flow and its application  

NASA Astrophysics Data System (ADS)

In this paper, we introduce the complex modulus to express the viscoelasticity of a medium. According to the correspondence principle, the Biot-Squirt (BISQ) equations in the steady-state case are presented for the space-frequency domain described by solid displacements and fluid pressure in a homogeneous viscoelastic medium. The effective bulk modulus of a multiphase flow is computed by the Voigt formula, and the characteristic squirt-flow length is revised for the gas-included case. We then build a viscoelastic BISQ model containing a multiphase flow. Through using this model, wave dispersion and attenuation are studied in a medium with low porosity and low permeability. Furthermore, this model is applied to observed interwell seismic data. Analysis of these data reveals that the viscoelastic parameter tan ? is not a constant. Thus, we present a linear frequency-dependent function in the interwell seismic frequency range to express tan ?. This improves the fit between the observed data and theoretical results.

Yang, Lei; Yang, DingHui; Nie, JianXin

2014-04-01

266

Polarimetric X-band weather radar measurements in the tropics: radome and rain attenuation correction  

NASA Astrophysics Data System (ADS)

A polarimetric X-band radar has been deployed during one month (April 2011) for a field campaign in Fortaleza, Brazil, together with three additional laser disdrometers. The disdrometers are capable of measuring the raindrop size distributions (DSDs), hence making it possible to forward-model theoretical polarimetric X-band radar observables at the point where the instruments are located. This set-up allows to thoroughly test the accuracy of the X-band radar measurements as well as the algorithms that are used to correct the radar data for radome and rain attenuation. For the campaign in Fortaleza it was found that radome attenuation dominantly affects the measurements. With an algorithm that is based on the self-consistency of the polarimetric observables, the radome induced reflectivity offset was estimated. Offset corrected measurements were then further corrected for rain attenuation with two different schemes. The performance of the post-processing steps was analyzed by comparing the data with disdrometer-inferred polarimetric variables that were measured at a distance of 20 km from the radar. Radome attenuation reached values up to 14 dB which was found to be consistent with an empirical radome attenuation vs. rain intensity relation that was previously developed for the same radar type. In contrast to previous work, our results suggest that radome attenuation should be estimated individually for every view direction of the radar in order to obtain homogenous reflectivity fields.

Schneebeli, M.; Sakuragi, J.; Biscaro, T.; Angelis, C. F.; Carvalho da Costa, I.; Morales, C.; Baldini, L.; Machado, L. A. T.

2012-09-01

267

Measurement of the seismic attenuation performance of the VIRGO Superattenuator  

Microsoft Academic Search

The gravitational wave detector VIRGO aims at extending the detection band down to a few Hertz by isolating the mirrors of the interferometer from seismic noise. This result is achieved by hanging each mirror through an elastic suspension (Superattenuator), designed to filter mechanical vibrations in all the degrees of freedom. An experimental upper limit of the mirror residual seismic noise

S. Braccini; L. Barsotti; C. Bradaschia; G. Cella; A. Di Virgilio; I. Ferrante; F. Fidecaro; I. Fiori; F. Frasconi; A. Gennai; A. Giazotto; F. Paoletti; R. Passaquieti; D. Passuello; R. Poggiani; E. Campagna; G. Guidi; G. Losurdo; F. Martelli; M. Mazzoni; B. Perniola; F. Piergiovanni; R. Stanga; F. Vetrano; A. Viceré; L. Brocco; S. Frasca; E. Majorana; A. Pai; C. Palomba; P. Puppo; P. Rapagnani; F. Ricci; G. Ballardin; R. Barillé; R. Cavalieri; E. Cuoco; V. Dattilo; D. Enard; R. Flaminio; A. Freise; S. Hebri; L. Holloway; P. La Penna; M. Loupias; J. Marque; C. Moins; A. Pasqualetti; P. Ruggi; R. Taddei; Z. Zhang; F. Acernese; S. Avino; F. Barone; E. Calloni; R. De Rosa; L. Di Fiore; A. Eleuteri; L. Giordano; L. Milano; S. Pardi; K. Qipiani; I. Ricciardi; G. Russo; S. Solimeno; D. Babusci; G. Giordano; P. Amico; L. Bosi; L. Gammaitoni; F. Marchesoni; M. Punturo; F. Travasso; H. Vocca; C. Boccara; J. Moreau; V. Loriette; V. Reita; J. M. Mackowski; N. Morgado; L. Pinard; A. Remillieux; M. Barsuglia; M. A. Bizouard; V. Brisson; F. Cavalier; A. C. Clapson; M. Davier; P. Hello; S. Krecklbergh; F. Beauville; D. Buskulic; R. Gouaty; D. Grosjean; F. Marion; A. Masserot; B. Mours; E. Tournefier; D. Tombolato; D. Verkindt; M. Yvert; S. Aoudia; F. Bondu; A. Brillet; E. Chassande-Mottin; F. Cleva; J. P. Coulon; B. Dujardin; J. D. Fournier; H. Heitmann; C. N. Man; A. Spallicci; J. Y. Vinet

2005-01-01

268

Numerical simulation of effective phase velocity and attenuation of shear elastic wave propagation in unidirectional composite materials.  

PubMed

In this paper, a simple simulation approach is presented for calculating the effective phase velocity and attenuation coefficient of elastic shear waves propagating in composite materials with randomly distributed unidirectional inclusions. As an application of the developed numerical approach, the phase velocities and attenuation coefficients of the coherent waves in four different types of composite material are simulated for various incident frequencies up to ?. Numerical results are compared with theoretical predictions obtained from three representative theoretical models. While all theoretical results agree very well with numerical values at low incident frequencies, the discrepancies increase with the increased incident frequency and volume fraction of inclusions. It has been found that within the frequency and volume fraction ranges considered in this work, the generalized self-consistent model by Kanaun and Levin [18] seems to provide the most accurate estimations. PMID:23582239

Zhang, Jun; Ye, Wenjing; Yu, T X

2013-08-01

269

In situ acoustic and laboratory ultrasonic sound speed and attenuation measured in heterogeneous soft seabed sediments: Eel River shelf, California  

USGS Publications Warehouse

We compared in situ and laboratory velocity and attenuation values measured in seafloor sediments from the shallow water delta of the Eel River, California. This region receives a substantial volume of fluvial sediment that is discharged annually onto the shelf. Additionally, a high input of fluvial sediments during storms generates flood deposits that are characterized by thin beds of variable grain-sizes between the 40- and 90-m isobaths. The main objectives of this study were (1) to investigate signatures of seafloor processes on geoacoustic and physical properties, and (2) to evaluate differences between geoacoustic parameters measured in situ at acoustic (7.5 kHz) and in the laboratory at ultrasonic (400 kHz) frequencies. The in situ acoustic measurements were conducted between 60 and 100 m of water depth. Wet-bulk density and porosity profiles were obtained to 1.15 m below seafloor (m bsf) using gravity cores of the mostly cohesive fine-grained sediments across- and along-shelf. Physical and geoacoustic properties from six selected sites obtained on the Eel margin revealed the following. (1) Sound speed and wet-bulk density strongly correlated in most cases. (2) Sediment compaction with depth generally led to increased sound speed and density, while porosity and in situ attenuation values decreased. (3) Sound speed was higher in coarser- than in finer-grained sediments, on a maximum average by 80 m s-1. (4) In coarse-grained sediments sound speed was higher in the laboratory (1560 m s-1) than in situ (1520 m s-1). In contrast, average ultrasonic and in situ sound speed in fine-grained sediments showed only little differences (both approximately 1480 m s-1). (5) Greater attenuation was commonly measured in the laboratory (0.4 and 0.8 dB m-1 kHz-1) than in situ (0.02 and 0.65 dB m-1 kHz-1), and remained almost constant below 0.4 m bsf. We attributed discrepancies between laboratory ultrasonic and in situ acoustic measurements to a frequency dependence of velocity and attenuation. In addition, laboratory attenuation was most likely enhanced due to scattering of sound waves at heterogeneities that were on the scale of ultrasonic wavelengths. In contrast, high in situ attenuation values were linked to stratigraphic scattering at thin-bed layers that form along with flood deposits. ?? 2002 Published by Elsevier Science B.V.

Gorgas, T. J.; Wilkens, R. H.; Fu, S. S.; Neil, Frazer, L.; Richardson, M. D.; Briggs, K. B.; Lee, H.

2002-01-01

270

Concurrent measurements of the directional spectra of microseismic energy and surface gravity waves  

NASA Astrophysics Data System (ADS)

This paper presents concurrent measurements of surface wave directional spectra and double-frequency, long-wave microseisms. Long-wave energy rapidly develops during periods of shifting winds which create bidirectional sea states. Theoretically, nonlinear sum interactions of opposing wavenumber vectors of approximately the same frequency create long-wave energy at twice the frequency, which is only slightly attenuated in shallow water. Bidirectional sea states have been found using a buried ocean bottom seismometer measuring system from which the long wave energy has been measured at double frequencies. This system was incorporated into the Office of Naval Research sponsored Sources of Ambient Microseismic Ocean Noise (SAMSON) experiment for 3 months off the Army Corps of Engineers' Field Research Facility near Duck, North Carolina in the fall of 1990. Four working sensors produced directional spectra results from nearly 22 gigabytes of recorded data, which was collected 2 km offshore of the FRF under 12-13 m of water and approximately 1 m of sediment. Because of the insignificant attenuation the measured energy levels of the double frequency microseisms at the seafloor are of the same order of magnitude as the single-frequency, surface wave energy induced seafloor motion. Various data sets were analyzed that confirmed Longuet-Higgins' theory, which proposes that the propagation direction of double-frequency microseisms occurs in the direction of the vector sum of the opposing single-frequency seas.

Nye, T.; Yamamoto, T.

1994-07-01

271

Spectroscopic measurement of an atomic wave function  

SciTech Connect

We present a simple spectroscopic method based on Autler-Townes spectroscopy to determine the center-of-mass atomic wave function. The detection of spontaneously emitted photons from a three-level atom, in which two upper levels are driven by a classical standing light, yields information about the position and momentum distribution of the atom [A. M. Herkommer, W. P. Schleich, and M. S. Zubairy, J. Mod. Opt. 44, 2507 (1997)]. In this paper, we show that both the amplitude and phase information of the center-of-mass atomic wave function can be obtained from these distributions after a series of conditional measurements on the atom and the emitted photon.

Kapale, Kishore T. [Institute for Quantum Studies, and Department of Physics, Texas A and M University, College Station, Texas 77843-4242 (United States); Qamar, Shahid [Institute for Quantum Studies, and Department of Physics, Texas A and M University, College Station, Texas 77843-4242 (United States); Department of Physics and Applied Mathematics, Pakistan Institute of Engineering and Applied Science, Nilore, Islamabad (Pakistan); Zubairy, M. Suhail [Institute for Quantum Studies, and Department of Physics, Texas A and M University, College Station, Texas 77843-4242 (United States); Department of Electronics, Quaid-i-Azam University, Islamabad (Pakistan)

2003-02-01

272

Effect of collimator size and absorber thickness on gamma ray attenuation measurements for bakelite and perspex  

Microsoft Academic Search

The mass attenuation coefficient (?\\u000a m) of 662 keV gamma rays have been measured in the extended media of bakelite and perspex under different collimation conditions.\\u000a The increase in attenuation coefficient is seen with increase in sample thickness as well as with collimator size due to the\\u000a contribution of multiple scattered photons in the uncollided beam of 662 keV gamma

Gurdeep S Sidhu; Karamjit Singh; Parjit S Singh; Gurmel S Mudahar

1999-01-01

273

MODELING OF SITE ATTENUATION IN A SEMI-ANECHOIC CHAMBER FOR EMC MEASUREMENTS  

Microsoft Academic Search

In this paper, a site attenuation model for semi-anechoic chambers using ray-tracing technique is developed. The proposed model considers multi-re?ection rays, and allows the true radiation pattern of difierent antennas to be included. Thus, this model can be used in the site attenuation measurement prediction performed for all types of electromagnetic compatibility (EMC) antennas in various chambers. The efiect of

KAZI M. AHMED; XU LIN

274

The Characteristics Of Intrinsic And Attenuative Dispersion Of Direct P-waves: Application In The Study Of Earthquake Precursory  

NASA Astrophysics Data System (ADS)

The Morlet wavelet multiple-filter method is applied to measure relative group delays from first cycle P waves, from eight CWBSN stations located near the source of the 1999 Chi Chi, and Chia-Yi, Taiwan earthquakes. The data used in this study is from the year between 1998 and 2000. The epicentral distance is less than 30 km with depth less than 25 km and ML?3.0. Using continuous relaxation model, we can relates intrinsic dispersion to attenuation and by applying the genetic algorithm (GA), we are able to determine Qp, which allows us to investigate the temporal variations of Qp before and after the occurrence of a large earthquake. Our results indicate that the Qp is highly sensitive to crack density. Before the occurrence of a large earthquake, Qp increases significantly, which indicates that the pre-seismic stress accumulation may associate with fluid-filled higher density fractured rock in the source area and causes crack density to increase. One interesting phenomena that we find is that Qp decreases right before the occurrence of a large earthquake, not after the occurrence of an earthquake. This observation implies that t the temporal variation pattern of Qp can serve as an important indicator for stress level change before an earthquake occurs, which also provides another perspective to understand the siemogeneric process in the source area.

Chen, C.; Weng, C.; Chang, W.

2007-12-01

275

Measurement of ultrasonic attenuation in diabetic neuropathic sciatic nerves for diagnostic and therapeutic applications.  

PubMed

Measurements of ultrasonic attenuation in the sciatic nerves of rats were performed to verify the feasibility of ultrasound diagnosis of peripheral neuropathy and to avoid damage to the nerves caused by overheating in pain management applications. A rat model of diabetic peripheral neuropathy was established. The proximal-segment and middle-segment sciatic nerves of control and neuropathic rats were dissected for the attenuation measurement. Two commercial ultrasound transducers and a self-developed experimental platform were used in the measurements. Using H&E staining and transmission electron (TE) microscopy, morphological analysis of the control and neuropathic nerves was performed to determine the relationship between attenuation and the histology of the nerves. The experimental results showed that the attenuation coefficients of the control, second-week, fourth-week, and eighth-week neuropathic nerves were -6.68 ± 0.50, -5.61 ± 0.34, -6.27 ± 0.40, and -7.10 ± 0.35 dB/cm at 2.68 MHz, respectively. The respective values at 7.50 MHz were -14.96 ± 0.79, -12.65 ± 0.28, -13.98 ± 1.07, and -16.00 ± 0.54 dB/cm. The changes in the attenuation coefficients were significantly different among the second-week, fourth-week, and eighth-week DN nerves. Additionally, the ultrasonic attenuation coefficient of the rat sciatic nerve was fourfold that of the cat brain and cow liver and twofold that of human muscle. PMID:24566928

Chen, Gin-Shin; Lee, Yee-Fun; Cheng, Jung-Sung

2014-08-01

276

Principles of local sound velocity and attenuation measurements using transmission acoustic microscope  

Microsoft Academic Search

Fundamentals of transmission acoustic microscopy as applied to measurements of sound velocities and attenuation in thin specimens and films are discussed. The method is based on measuring the output signal A as a function of a distance z between the radiating and the receiving lenses in the two-lens focusing system of the transmission microscope. It is proposed to measure the

Roman G. Maev; Vadim M. Levin

1997-01-01

277

Measurement of Light attenuation in dense fog conditions for FSO applications  

NASA Astrophysics Data System (ADS)

Free Space Optics (FSO) has gained considerable importance in this decade of demand for high bandwidth transmission capabilities. FSO can provide the last mile solution, but the availability and reliability issues concerned with it have acquired more attention, and a need for thorough investigations. In this work, we present our results about fog attenuation at the 950 and 850 nm wavelengths in heavy maritime fog with peak values up to 500 dB/km. For the attenuation measurement, optical wavelengths are transmitted over the same path of fog in free air to a receiver, measuring the power of every wavelength. The RF marker technology employed takes advantage of modulating every optical wavelength with an individual carrier frequency, allowing to use one optical front end for the receiver and to separate individual wavelengths by electrical signal filters. The measurement of fog attenuation at different wavelengths was performed at the France Telecom R & D test facility at La Turbie. Maritime or advection fog, which caused the light attenuation consists of water droplets of larger diameter in the order of 20 ?m and can cause visibilities as low as 30 meters. The visibility was measured using a transmissiometer at 550 nm. We compare our measurement data with the commonly used light attenuation models of Kruse and Kim, and present some interesting insights. The practical measurements described try to validate the models and therefore should lead to a more accurate availability prediction for FSO links.

Gebhart, M.; Leitgeb, E.; Sheikh Muhammad, S.; Flecker, B.; Chlestil, C.; Al Naboulsi, M.; de Fornel, F.; Sizun, H.

2005-08-01

278

Accurate and efficient modeling of global seismic wave propagation for an attenuative Earth model including the center  

NASA Astrophysics Data System (ADS)

We propose a method for modeling global seismic wave propagation through an attenuative Earth model including the center. This method enables accurate and efficient computations since it is based on the 2.5-D approach, which solves wave equations only on a 2-D cross section of the whole Earth and can correctly model 3-D geometrical spreading. We extend a numerical scheme for the elastic waves in spherical coordinates using the finite-difference method (FDM), to solve the viscoelastodynamic equation. For computation of realistic seismic wave propagation, incorporation of anelastic attenuation is crucial. Since the nature of Earth material is both elastic solid and viscous fluid, we should solve stress-strain relations of viscoelastic material, including attenuative structures. These relations represent the stress as a convolution integral in time, which has had difficulty treating viscoelasticity in time-domain computation such as the FDM. However, we now have a method using so-called memory variables, invented in the 1980s, followed by improvements in Cartesian coordinates. Arbitrary values of the quality factor (Q) can be incorporated into the wave equation via an array of Zener bodies. We also introduce the multi-domain, an FD grid of several layers with different grid spacings, into our FDM scheme. This allows wider lateral grid spacings with depth, so as not to perturb the FD stability criterion around the Earth center. In addition, we propose a technique to avoid the singularity problem of the wave equation in spherical coordinates at the Earth center. We develop a scheme to calculate wavefield variables on this point, based on linear interpolation for the velocity-stress, staggered-grid FDM. This scheme is validated through a comparison of synthetic seismograms with those obtained by the Direct Solution Method for a spherically symmetric Earth model, showing excellent accuracy for our FDM scheme. As a numerical example, we apply the method to simulate seismic waves affected by hemispherical variations of P-wavespeed and attenuation in the top 300 km of the inner core.

Toyokuni, Genti; Takenaka, Hiroshi

2012-06-01

279

Estimation of coda wave attenuation for NW Himalayan region using local earthquakes  

NASA Astrophysics Data System (ADS)

The attenuation of seismic wave energy in NW Himalayas has been estimated using local earthquakes. Most of the analyzed events are from the vicinity of the Main Boundary Thrust (MBT) and the Main Central Thrust (MCT), which are well-defined tectonic discontinuities in the Himalayas. The time-domain coda-decay method of a single back-scattering model is employed to calculate frequency dependent values of Coda Q (Qc). A total of 36 local earthquakes of magnitude range 2.1-4.8 have been used for Qc estimation at central frequencies 1.5, 3.0, 6.0, 9.0, 12.0 and 18.0 Hz through eight lapse time windows from 25 to 60 s starting at double the time of the primary S-wave from the origin time. The estimated average frequency dependence quality factor gives the relation, Qc = 158 f1.05, while the average Qc values vary from 210 at 1.5 Hz to 2861 at 18 Hz central frequencies. The observed coda quality factor is strongly dependent on frequency, which indicates that the region is seismic and tectonically active with high heterogeneities. The variation of the quality factor Qc has been estimated at different lapse times to observe its effect with depth. The estimated average frequency dependent relations of Qc vary from 85 f1.16 to 216 f0.91 at 25 to 60 s lapse window length respectively. For 25 s lapse time window, the average Qc value of the region varies from 131 ± 36 at 1.5 Hz to 2298 ± 397 at 18 Hz, while for 60 s lapse time window its variation is from 285 ± 95 at 1.5 Hz to 2868 ± 336 at 18 Hz of central frequency. The variation of Qc with frequency and lapse time shows that the upper crustal layers are seismically more active compared to the lower lithosphere. The decreasing value of the frequency parameter with increasing lapse time shows that the lithosphere acquires homogeneity with depth.

Kumar, Naresh; Parvez, Imtiyaz A.; Virk, H. S.

2005-08-01

280

Change in Seismic Attenuation of the Nojima Fault Zone Measured Using Spectral Ratios from Borehole Seismometers  

NASA Astrophysics Data System (ADS)

We measured the seismic attenuation of the rock mass surrounding the Nojima fault, Japan, by estimating the P-wave quality factor, Qp, using spectral ratios derived from a multi-depth (800 m and 1800 m) seismometer array. We detected an increase of Qp in 2003-2006 compared to 1999-2000. Following the 1995 Kobe earthquake, the project "Fault Zone Probe" drilled three boreholes to depths of 500 m, 800 m, 1800 m, in Toshima, along the southern part of the Nojima fault. The 1800-m borehole was reported to reach the fault surface. One seismometer (TOS1) was installed at the bottom of the 800-m borehole in 1996 and another (TOS2) at the bottom of 1800-m borehole in 1997. The sampling rate of the seismometers is 100 Hz. The slope of the spectral ratios for the two stations plotted on a linear-log plot is -? t^{*}, where t^{*} is the travel time divided by the Qp for the path difference between the stations. For the estimation of Qp, we used events recorded by both TOS1 and TOS2 for periods of 1999-2000 and 2003-2006. To improve the signal-to-noise ratio of the spectral ratios, we first calculated spectra ratios between TOS1 and TOS2 for each event and averaged the values over the earthquakes for each period. We used the events that occurred within 10 km from TOS2, and the numbers of events are 74 for 1999-2000 and 105 for 2003-2006. Magnitudes of the events range from M0.5 to M3.1. The average value of Qp for 1999-2000 increased significantly compared to 2003-2006. The attenuation of rock mass surrounding the fault in 2003-2006 is smaller than that in 1999-2000, which suggests that the fault zone became stiffer after the earthquake. At the Nojima fault, permeability measured by repeated pumping tests decreased with time from the Kobe earthquake, infering the closure of cracks and a fault healing process occurred The increase of Qp is another piece of evidence for the healing process of the Nojima fault zone. u.ac.jp/~kano/

Kano, Y.; Tadokoro, K.; Nishigami, K.; Mori, J.

2006-12-01

281

Design of a Composite Attenuation Relation for the Dead Sea Area Based on 3D Modeling of Elastic Wave Propagation  

NASA Astrophysics Data System (ADS)

Attenuation relations are a crucial component in the prediction of ground motion generated by strong earthquakes. Even though the relations from different authors (e.g. Boore et al., 1997; Abrahamson and Silva, 1997) vary in their form, they all have in common that some engineering ground motion parameter, such as peak ground acceleration (PGA) or peak spectral acceleration (PSA), is determined by the magnitude, distance to the earthquake source, site conditions and possibly source mechanism. In general, attenuation relations parameterize distance in a way that does not take into account a change in geologic features in the region of interest. Sedimentary basins or grabens, however, may strongly influence attenuation, due to both site and basin effects. By engineering seismology practice, site effects are generally taken into account by considering the shear wave velocity structure of the top 30 meters. Basins effects, on the other hand, are caused by deep geologic structures and much harder to quantify, as this requires the consideration of a two-- or three--dimensional wave propagation model. The Dead Sea Basin (DSB) is a 15 km by 100 km, N--S elongated structure around which basin effects have been observed in damage patterns of past earthquakes (Wust--Bloch, 2002). In addition, Gottschämmer et al. (2002) showed through 3D simulation of the 1927 Jericho earthquake (M=6.2) that wave focusing effects in the DSB are indeed significant. The results of this research show that the standard attenuation relation utilized in the area is inadequate to assess the basin--related effect of the DSB. A new strategy for the parametrization of attenuation relations in graben structures is developed by looking at the statistical properties of 53 3D finite--difference simulations (Olsen, 1994) of earthquakes with magnitudes ranging from 5.5 to 7.0 at the boundary fault of the DSB. The frequency range of these simulations is restricted to frequencies lower than about 1.5 Hz. An attenuation relation is designed for the 1 Hz spectral acceleration, modifying the Joyner--Boore relations by adding coefficients suited for three different source--to--site configurations: within the DSB, beyond the DSB and path unaffected by the graben structure.

Oth, A.; Wenzel, F.; Wust-Bloch, H.; Gottschaemmer, E.; Ben-Avraham, Z.

2005-12-01

282

Measurement of silicon dioxide surface phonon-polariton propagation length by attenuated total reflection  

NASA Astrophysics Data System (ADS)

The authors present an experimental measurement of the propagation length of surface phonon-polaritons on amorphous silicon dioxide using the method of attenuated total reflection. The measurements yield a propagation length of 10.8+/-1.3 ?m for the silicon dioxide surface phonon-polariton resonance at 9 ?m, which is in good agreement with the calculated value.

Chen, Dye-Zone A.; Chen, Gang

2007-09-01

283

Retrieval of atmospheric attenuation using combined ground-based and airborne 95-GHz cloud radar measurements  

NASA Technical Reports Server (NTRS)

This paper discusses cloud radar calibration and intercomparison of airborne and ground-based radar measurements and presents a unique algorithm for attenuation retrieval. This algorithm is based on dual 95-GHz radar measurements of the same cloud and precipitation volumes collected from opposing viewing angles.

Li, L.; Sekelsky, S.; Reising, S.; Swift, C.; Durden, S.; Sadowy, G.; Dinardo, S.; Li, F.; Huffman, A.; Stephens, G.; Babb, D.; Rosenberger, H.

2001-01-01

284

Accurate measurement of total attenuation coefficient of thin tissue with optical coherence tomography  

Microsoft Academic Search

Noninvasive accurate measurements of tissue optical properties are needed for many diagnostic and therapeutic applications. Optical coherence tomography (OCT) recently proposed for high-resolution imaging in tissue can potentially be applied for accurate, noninvasive, and high-resolution measurement of tissue total attenuation coefficient. However, confocal function (dependence of OCT sensitivity on the distance of probed site from the focal plane of the

Alexander I. Kholodnykh; Irina Y. Petrova; Massoud Motamedi; Rinat O. Esenaliev

2003-01-01

285

Bottom Boundary Layer Wave Measurements for Particle Studies  

Microsoft Academic Search

Suspended particles, which attenuate light and restrict visibility in moderate depths of the ocean, are commonly resuspended from the bottom by waves. This turbid layer initially consists of fine particles with settling rates of 0.01 mm\\/s that require weeks to settle out. However, the relaxation of the turbid conditions is often only a day or less implying particle settling rates

A. J. Williams

2006-01-01

286

Wave reflection in a reaction-diffusion system: Breathing patterns and attenuation of the echo  

NASA Astrophysics Data System (ADS)

Formation and interaction of the one-dimensional excitation waves in a reaction-diffusion system with the piecewise linear reaction functions of the Tonnelier-Gerstner type are studied. We show that there exists a parameter region where the established regime of wave propagation depends on initial conditions. Wave phenomena with a complex behavior are found: (i) the reflection of waves at a growing distance (the remote reflection) upon their collision with each other or with no-flux boundaries and (ii) the periodic transformation of waves with the jumping from one regime of wave propagation to another (the periodic trigger wave).

Tsyganov, M. A.; Ivanitsky, G. R.; Zemskov, E. P.

2014-05-01

287

Role of vegetation on the attenuation of forces on structures due to cnoidal waves  

NASA Astrophysics Data System (ADS)

The evaluation of forces on structures in the marine environment due to ocean waves is absolutely essential in the planning and development of mitigation measures against natural coastal hazards and dictates their design. Further, studies on the forces on coastal structures due to regular and random waves are well entrenched in literature, whereas, that due to shallow water waves are rather scanty. The recent tsunami has added a new dimension on the role of vegetation on the forces on structures. Due the propagation of tsunami, a number of signature studies have revealed that structures fronted by vegetation have suffered minimum damage compared to that in its absence and as also reported by Yanagisawa (2008). In the present paper, the results from an experimental study to investigate the effect of vegetation on a typical structure located onshore over a slope of 1:30 are reported. The tests were carried out in a wave flume of length 72m, width 2m and 2.7m depth. The water depth at the toe of the slope was 1m. Slender flexible cylindrical members that represent plantation along the coast have been adopted for the tests. Experiments were carried out for different G/B ratios of 0, 0.5,1 and 1.5. (Where G is the distance between front face of vegetation/ green belt and the rear face of the building and B is width of the building). Experiments were repeated for three widths of Green belts (BG) and for each of the green belt, two different diameters of the cylinders of 10mm and 3.0mm were used. The forces on structure were measured with load cells in the presence and absence of the green belt. The Cnoidal waves covering a range of Ursell parameter between 18 and 700 were employed for the experiments. The different vegetal and flow parameters in a non-dimensional form have been identified. The variation of non-dimensionalised force over the slope in the presence and absence of vegetation as a function of the Ursell parameter, Relative rigidity and Reduced velocity for different dimensionless SP/D of the green belt (where SP is the spacing between plantation/diameter of plantation) clearly indicates that there is a significant reduction in the force due to the presence of vegetation. Prior to the experiments with the green belt, for the purpose of validation tests were carried out on the force measurements of waves over a plane slope, the results of which compared with existing results exhibited a good agreement. The details of the experimental set-up, procedure and analysis and discussion of the results are reported in this paper. It has been found that, • The non-dimensional Forces on the structure increases by about 80 %, when the distance between the structure and the Green Belt is in the range of 0.5B to 1.5B. • The most favorable location for the Structure is adjacent to the Green Belt or away from the Green Belt by more than twice the width of the structure. For this configuration, the forces were found to reduce to an extent ranging between 50% and 90%. References Yanagisawa,H., Koshimsura,S., Got,K., Miyagi,T., Imamura, F., Ruangrassamee, A. and Tanavud, C. "The reduction effects of Mangrove forest on a tsunami based on field surveys at Pakarang Cape, Thailan and Numerical Analysis" Estuarine, Coastal and shelf Science, Oct 2008, pp 1-11.

2009-04-01

288

Role of vegetation on the attenuation of forces on structures due to Cnoidal waves  

NASA Astrophysics Data System (ADS)

The evaluation of forces on structures in the marine environment due to ocean waves is absolutely essential in the planning and development of mitigation measures against natural coastal hazards and dictates their design. Further, studies on the forces on coastal structures due to regular and random waves are well entrenched in literature, whereas, that due to shallow water waves are rather scanty. The recent tsunami has added a new dimension on the role of vegetation on the forces on structures. Due the propagation of tsunami, a number of signature studies have revealed that structures fronted by vegetation have suffered minimum damage compared to that in its absence and as also reported by Yanagisawa (2008). In the present paper, the results from an experimental study to investigate the effect of vegetation on a typical structure located onshore over a slope of 1:30 are reported. The tests were carried out in a wave flume of length 72m, width 2m and 2.7m depth. The water depth at the toe of the slope was 1m. Slender flexible cylindrical members that represent plantation along the coast have been adopted for the tests. Experiments were carried out for different G/B ratios of 0, 0.5,1 and 1.5. (Where G is the distance between front face of vegetation/ green belt and the rear face of the building and B is width of the building). Experiments were repeated for three widths of Green belts (BG) and for each of the green belt, two different diameters of the cylinders of 10mm and 3.0mm were used. The forces on structure were measured with load cells in the presence and absence of the green belt. The Cnoidal waves covering a range of Ursell parameter between 18 and 700 were employed for the experiments. The different vegetal and flow parameters in a non-dimensional form have been identified. The variation of non-dimensionalised force over the slope in the presence and absence of vegetation as a function of the Ursell parameter, Relative rigidity and Reduced velocity for different dimensionless SP/D of the green belt (where SP is the spacing between plantation/diameter of plantation) clearly indicates that there is a significant reduction in the force due to the presence of vegetation. Prior to the experiments with the green belt, for the purpose of validation tests were carried out on the force measurements of waves over a plane slope, the results of which compared with existing results exhibited a good agreement. The details of the experimental set-up, procedure and analysis and discussion of the results are reported in this paper. It has been found that, The non-dimensional Forces on the structure increases by about 80 %, when the distance between the structure and the Green Belt is in the range of 0.5B to 1.5B. The most favorable location for the Structure is adjacent to the Green Belt or away from the Green Belt by more than twice the width of the structure. For this configuration, the forces were found to reduce to an extent ranging between 50% and 90%. References Yanagisawa,H., Koshimsura,S., Got,K., Miyagi,T., Imamura, F., Ruangrassamee, A. and Tanavud, C. "The reduction effects of Mangrove forest on a tsunami based on field surveys at Pakarang Cape, Thailan and Numerical Analysis" Estuarine, Coastal and shelf Science, Oct 2008, pp 1-11.

Sundar, V.; Norayanan, L.; Murali, K.

2009-04-01

289

An investigation of the measurement of broadband ultrasonic attenuation in trabecular bone.  

PubMed

Commercial devices for the ultrasonic characterisation of bone normally report the broadband ultrasonic attenuation (BUA). This is the slope of the attenuation against frequency in some part of the frequency range 200-1000 kHz. The assumption is that the relationship is linear and hence independent of the frequency range selected. In this study the ultrasonic attenuation in the frequency range 200 to 800 kHz was measured with a variety of transducers in ten trabecular heel bone samples from elderly cadavers, assumed to be osteoporotic. The results indicate that the attenuation fits better to a second order polynomial function of frequency, than to the linear fit. The use of a straight line fit is only satisfactory in the higher frequency ranges (above 400 kHz). The use of lower frequencies results in a significant measurement error caused by the combination of a poor signal to noise ratio and the departure from linearity and this is greatest for samples with low attenuation. In the worst cases this can amount to a 30% discrepancy between the BUA values measured over different frequency ranges. PMID:9010461

Strelitzki, R; Evans, J A

1996-12-01

290

Measurement of the linear attenuation coefficients of breast tissues by synchrotron radiation computed tomography  

NASA Astrophysics Data System (ADS)

The measurement of the linear attenuation coefficients of breast tissues is of fundamental importance in the field of breast x-ray diagnostic imaging. Different groups have evaluated the linear attenuation coefficients of breast tissues by carrying out direct attenuation measurements in which the specimens were thin and selected as homogeneous as possible. Here, we use monochromatic and high-intensity synchrotron radiation computed tomography (SR CT) to evaluate the linear attenuation coefficients of surgical breast tissues in the energy range from 15 to 26.5 keV. X-ray detection is performed by a custom digital silicon micro-strip device, developed in the framework of the PICASSO INFN experiment. Twenty-three human surgical breast samples were selected for SR CT and histological study. Six of them underwent CT, both as fresh tissue and after formalin fixation, while the remaining 17 were imaged only as formalin-fixed tissues. Our results for fat and fibrous tissues are in good agreement with the published values. However, in contrast to the published data, our measurements show no significant differences between fibrous and tumor tissues. Moreover, our results for fresh and formalin-fixed tissues demonstrate a reduction of the linear attenuation coefficient for fibrous and tumor tissues after fixation.

Chen, R. C.; Longo, R.; Rigon, L.; Zanconati, F.; De Pellegrin, A.; Arfelli, F.; Dreossi, D.; Menk, R.-H.; Vallazza, E.; Xiao, T. Q.; Castelli, E.

2010-09-01

291

On the excess attenuation of sound in the atmosphere  

NASA Technical Reports Server (NTRS)

The attenuation suffered by an acoustic plane wave propagating from an elevated source to the ground, in excess of absorption losses, was studied. Reported discrepancies between attenuation measurements made in the field and theories which only account for absorption losses are discussed. It was concluded that the scattering of sound by turbulence results in a nonnegligible contribution to the total attenuation.

Deloach, R.

1975-01-01

292

Photogrammetric Measurements of CEV Airbag Landing Attenuation Systems  

NASA Technical Reports Server (NTRS)

High-speed photogrammetric measurements are being used to assess the impact dynamics of the Orion Crew Exploration Vehicle (CEV) for ground landing contingency upon return to earth. Test articles representative of the Orion capsule are dropped at the NASA Langley Landing and Impact Research (LandIR) Facility onto a sand/clay mixture representative of a dry lakebed from elevations as high as 62 feet (18.9 meters). Two different types of test articles have been evaluated: (1) half-scale metal shell models utilized to establish baseline impact dynamics and soil characterization, and (2) geometric full-scale drop models with shock-absorbing airbags which are being evaluated for their ability to cushion the impact of the Orion CEV with the earth s surface. This paper describes the application of the photogrammetric measurement technique and provides drop model trajectory and impact data that indicate the performance of the photogrammetric measurement system.

Barrows, Danny A.; Burner, Alpheus W.; Berry, Felecia C.; Dismond, Harriett R.; Cate, Kenneth H.

2008-01-01

293

Seismic-Wave Attenuation and Partial Melting in the Upper Mantle of North America  

Microsoft Academic Search

A model of Q-X based on Walsh's theory for attenuation in partially melted rock is proposed for the upper mantle of western North America. The asthenosphere (or low-Q zone), in which attenuation is attributed to a superposition of thermally activated relaxation processes, is 300 km thick in the model and must be vertically inhomogeneous. The lithosphere (or high-Q lid) is

Sean C. Solomon

1972-01-01

294

The contribution of activated processes to Q. [stress corrosion cracking in seismic wave attenuation  

NASA Technical Reports Server (NTRS)

The possible role of activated processes in seismic attenuation is investigated. In this study, a solid is modeled by a parallel and series configuration of dashpots and springs. The contribution of stress and temperature activated processes to the long term dissipative behavior of this system is analyzed. Data from brittle rock deformation experiments suggest that one such process, stress corrosion cracking, may make a significant contribution to the attenuation factor, Q, especially for long period oscillations under significant tectonic stress.

Spetzler, H. A.; Getting, I. C.; Swanson, P. L.

1980-01-01

295

Measurement of filter attenuation in the 10-um region  

NASA Astrophysics Data System (ADS)

IR imaging sensors are generally designed to be as sensitive as possible. This makes them vulnerable to dazzle and damage by attack from in-band lasers. An obvious method of protecting these sensors is to include rejection filters in the optical system. The required rejection ratio may be many orders of magnitude. Of particular interest is the possible application of rejection filters to protect thermal imagers. Some difficulties have been experienced in the laboratory measurement of the rejection ratio of such filters. These problems are explained and methods to overcome them are discussed so leading to a reliable method of measurement.

Kent, Malcolm J.

1999-12-01

296

Additional attenuation of natural VLF electromagnetic waves observed by the DEMETER spacecraft resulting from preseismic activity  

NASA Astrophysics Data System (ADS)

We use VLF electromagnetic wave data measured by the DEMETER (Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions) satellite at an altitude of about 700 km to check for the presence of statistically significant changes of natural wave intensity (due to signals from lightning) related to preseismic activity. All the relevant data acquired by DEMETER during almost 6.5 years of the mission have been analyzed using a robust two-step data-processing schema. This enables us to compare data from the vicinity of about 8400 earthquakes with an unperturbed background distribution based on data collected during the whole DEMETER mission and to evaluate the statistical significance of the observed effects. We confirm previously reported results of a small but statistically significant decrease of the wave intensity (by ˜2 dB) at frequencies of about 1.7 kHz. The effect is observed for a few hours before the times of the main shocks; it occurs during the night. The effect is stronger between March and August, at higher latitudes and for the positions of hypocenters below the sea. We suggest an explanation based on changed properties of the lower boundary of the ionosphere, which leads to a decrease of the intensity of lightning-generated whistlers observed at the spacecraft altitude. This effect might result from a lowering of the ionosphere associated with an increase in the electrical conductivity of the lower troposphere due to an additional ionization of air molecules at the Earth's surface prior to earthquakes.

PíšA, David; N?Mec, FrantišEk; SantolíK, Ond?Ej; Parrot, Michel; Rycroft, Michael

2013-08-01

297

Thermoreflectance temperature measurement with millimeter wave.  

PubMed

GigaHertz (GHz) thermoreflectance technique is developed to measure the transient temperature of metal and semiconductor materials located behind an opaque surface. The principle is based on the synchronous detection, using a commercial THz pyrometer, of a modulated millimeter wave (at 110 GHz) reflected by the sample hidden behind a shield layer. Measurements were performed on aluminum, copper, and silicon bulks hidden by a 5 cm thick Teflon plate. We report the first measurement of the thermoreflectance coefficient which exhibits a value 100 times higher at 2.8 mm radiation than those measured at visible wavelengths for both metallic and semiconductor materials. This giant thermoreflectance coefficient ?, close to 10(-3) K(-1) versus 10(-5) K(-1) for the visible domain, is very promising for future thermoreflectance applications. PMID:24985839

Pradere, C; Caumes, J-P; BenKhemis, S; Pernot, G; Palomo, E; Dilhaire, S; Batsale, J-C

2014-06-01

298

Microwave radar measurements of ocean wave propagation - Initial results  

SciTech Connect

A microwave radar has been developed to measure the surface orbital velocities of ocean waves, and hence estimate the wave height spectra. The Doppler radar exploits the frequency modulated continuous wave (FMCW) technique to provide good spatial resolution (much less than the ocean wavelengths of interest) making it suitable for ocean wave propagation studies. The authors present initial data demonstrating the radar's capabilities to deduce near-shore ocean wave properties. The spatial and temporal variations of the orbital velocities reveal the wave propagation, and the deduced wave height spectra show wave growth as they approach the shore.

Poulter, E.M.; Smith, M.J.; McGregor, J.A.

1990-11-01

299

Review of underground salt attenuation measurements for SalSA  

NASA Astrophysics Data System (ADS)

We report on the status of the Salt Sensor Array (SalSA), a proposed experiment for detecting ultra-high energy neutrinos through the radio Cherenkov technique with an array of radio-microwave antennas embedded in a large, naturally occurring salt formation. We review the measurements to date aimed at assessing SalSA's feasibility, including a return visit of the Hockley Salt Mine in Hockley, Texas, and discuss the current status of the project.

Connolly, Amy; SalSA Collaboration

2012-01-01

300

Active high-resolution seismic tomography of compressional wave velocity and attenuation structure at Medicine Lake volcano, northern California Cascade Range  

Microsoft Academic Search

We determine compressional wave velocity and attenuation structures for the upper crust beneath Medicine Lake volcano in northeast California using a high-resolution active source seismic tomography method. Medicine Lake volcano is a basalt through rhyolite shield volcano of the Cascade Range, lying east of the range axis. The Pg wave from eight explosive sources which has traveled upward through the

John R. Evans; John J. Zucca

1988-01-01

301

Surface-Wave Attenuation and Crustal Anelasticity in Central North America.  

National Technical Information Service (NTIS)

The southeastern Missouri earthquake of October 21, 1965 generated fundamental- and higher-mode Love and Rayleigh waves which were recorded at numerous North American stations. Love-wave amplitude radiation patterns were determined and found to be consist...

B. J. Mitchell

1972-01-01

302

Interpretation of laser attenuation measurements in sooty fires  

SciTech Connect

This paper presents a sensitivity analysis to determine the impact of particle size, and thus scattering, on the interpretation of the measurements from fiber optic soot probes of two different designs. The single-pass fiber optic probe is found to accurately estimate the monochromatic absorption coefficient in flames with soot size parameters up to 0.5. For larger-diameter soot particles, Beer's law yields values between the true absorption and extinction coefficients. If the probe is properly designed it can give reliable extinction coefficients for size parameters in excess of 10 for both lightly and heavily sooting flames.

Grosshandler, W.L. (Washington State Univ., Pullman, WA (USA). Dept. of Mechanical Engineering)

1989-12-01

303

12C-2 Improved Accuracy of Broadband Ultrasound Attenuation Measurement Using Phase Insensitive Detection: Results in 73 Women  

Microsoft Academic Search

Broadband ultrasonic attenuation (BUA) is a clinically-accepted measurement for diagnosis of osteoporosis. Typical clinical BUA measurements are performed with phase sensitive receivers and therefore can be affected by phase cancellation. In order to separate the effects of conventional attenuation (absorption plus scattering) from phase cancellation, BUA was measured on phantoms with acrylic wedge phase aberrators and on 73 women using

Keith A. Wear

2007-01-01

304

Strain-energy compatible partition of Hooke's law --- Applicationto the modeling of intrinsic attenuation in wave propagation  

Microsoft Academic Search

We have previously reported on a memory-efficient displacement-based\\u000a\\u0009rheological model for incorporating intrinsic attenuation in solids\\u000a\\u0009for wave propagation problems, which we denoted as the BKT model.\\u000a\\u0009This model consists of a set of two parallel Maxwell elements and\\u000a\\u0009a Kelvin-Voigt element in parallel. It exhibits an almost constant\\u000a\\u0009quality factor (Q), with a maximum error of five percent with

H. Karaoglu; R. Taborda; J. Bielak

2011-01-01

305

Attenuation and Shock Waves in Linear Hereditary Viscoelastic Media; Strick-Mainardi, Jeffreys-Lomnitz-Strick and Andrade Creep Compliances  

NASA Astrophysics Data System (ADS)

Dispersion, attenuation and wavefronts in a class of linear viscoelastic media proposed by uc(Strick ) and uc(Mainardi) (Geophys J R Astr Soc 69:415-429, 1982) and a related class of models due to Lomnitz, Jeffreys and Strick are studied by a new method due to the author. Unlike the previously studied explicit models of relaxation modulus or creep compliance, these two classes support propagation of discontinuities. Due to an extension made by Strick, either of these two classes of models comprise both viscoelastic solids and fluids. We also discuss the Andrade viscoelastic media. The Andrade media do not support discontinuity waves and exhibit the pedestal effect.

Hanyga, Andrzej

2014-03-01

306

Blood glucose measurement by using hollow optical fiber-based attenuated total reflection probe.  

PubMed

A noninvasive glucose monitoring system based on mid-infrared, attenuated total reflection spectroscopy using a hollow optical fiber probe is developed. Owing to the flexible fiber probe, measurement of oral mucosa, where blood capillaries are near the skin surface, is possible. Blood glucose levels are measured by detecting the peak intensity of glucose absorption bands, and the experimental results showed that the reproducibility of the measurement is high enough for monitoring blood glucose. PMID:24849387

Kino, Saiko; Tanaka, Yuki; Matsuura, Yuji

2014-05-01

307

Blood glucose measurement by using hollow optical fiber-based attenuated total reflection probe  

NASA Astrophysics Data System (ADS)

A noninvasive glucose monitoring system based on mid-infrared, attenuated total reflection spectroscopy using a hollow optical fiber probe is developed. Owing to the flexible fiber probe, measurement of oral mucosa, where blood capillaries are near the skin surface, is possible. Blood glucose levels are measured by detecting the peak intensity of glucose absorption bands, and the experimental results showed that the reproducibility of the measurement is high enough for monitoring blood glucose.

Kino, Saiko; Tanaka, Yuki; Matsuura, Yuji

2014-05-01

308

Attenuation of seismic waves at regional distances. Final technical report, 1 October 1982-30 September 1984  

SciTech Connect

The coda-Q method was applied to determine the anelastic attenuation of 1-sec period Lg waves at NTS(Nevada Test Site), East Kazakh, the Indian subcontinent, and the South American continent. Mb(Lg) m sub b (Lg) versus explosion yield calibration curves are given for NTS explosions in hard rock and in alluvium. The NTS hard-rock calibration curve, when applied to explosions in other regions of the United States and in the French Sahara, gives realistic yield estimates. The technique also is applied to selected Soviet explosions in East Kazakh. M sub b (Lg) and M sub b (P) values were used to estimate the M sub b (P) bias between NTS and eastern North America. Assuming that explosions and earthquakes of the same M sub b (P) value excite Lg waves of equal amplitude, the P-wave magnitude bias between NTS and eastern North America. Assuming that explosions and earthquakes of the same M sub b (P) value excite Lg waves of equal amplitude, the P-wave magnitude bias between NTS and eastern North America is 0.31 magnitude units. A tentative value for the bias between NTS and Shagan River is 0.41 magnitude units, but this value may be changed. Frequency-dependence of crustal Q seems significant in regions of high Q, but are small or non-existent in regions of low Q values.

Nuttli, O.W.; Mitchell, B.J.

1984-11-27

309

Technique for Measuring Ultrasonic Velocity and Attenuation Spectra in Rocks Under Pressure  

Microsoft Academic Search

An ultrasonic pulse technique has been developed for measuring phase velocity and attenuation spectra in rocks inside a pressure vessel. This technique has been adapted from those used in the nondestructive evaluation field. In essence, a broadband acoustic pulse is directed into a lucite buffer, which is followed by the rock sample and another lucite buffer. The pulse partially reflects

K. W. Winkler; T. J. Plona

1982-01-01

310

Measurements of broadband ultrasonic attenuation in the calcaneus in premenopausal and postmenopausal women  

Microsoft Academic Search

We report a study of broadband ultrasonic attenuation (BUA) in the calcaneus in 248 women. Measurements were performed with a Walker-Sonix UBA-575 ultrasonic bone analyser. The populations studied were 15 healthy young volunteers (group 1, mean age 26 years), 200 healthy pre- and postmenopausal women (group 2, mean age 53 years) and 33 osteoporotic women with vertebral crush fractures (group

R. J. M. Herd; T. Ramalingham; P. J. Ryan; I. Fogelman; G. M. Blake

1992-01-01

311

Technique for measuring ultrasonic velocity and attenuation spectra in rocks under pressure  

Microsoft Academic Search

An ultrasonic pulse technique has been developed for measuring phase velocity and attenuation spectra in rocks inside a pressure vessel. This technique has been adapted from those used in the nondestructive evaluation field. In essence, a broadband acoustic pulse is directed into a lucite buffer, which is followed by the rock sample and another lucite buffer. The pulse partially reflects

K. W. Winkler; T. J. Plona

1982-01-01

312

The feasibility of ranking material fracture toughness by ultrasonic attenuation measurements  

NASA Technical Reports Server (NTRS)

A preliminary study was conducted to assess the feasibility of ultrasonically ranking material fracture toughness. Specimens of two grades of maraging steel for which fracture toughness values were measured were subjected to ultrasonic probing. The slope of the attenuation coefficient versus frequency curve was empirically correlated with the plane strain fracture toughness value for each grade of steel.

Vary, A.

1975-01-01

313

Eplerenone Attenuates Pulse Wave Reflection in Chronic Kidney Disease Stage 3-4 - A Randomized Controlled Study  

PubMed Central

Background Patients with chronic kidney disease (CKD) have high cardiovascular mortality and morbidity associated with increased arterial stiffness. Plasma aldosterone levels are increased in CKD, and aldosterone has been found to increase vascular inflammation and fibrosis. It was hypothesized that aldosterone receptor inhibition with eplerenone could reduce arterial stiffness in CKD stage 3–4. Study Design The design was randomized, open, parallel group. Measurements of arterial stiffness markers were undertaken at weeks 1 and 24. Intervention 24 weeks of add-on treatment with 25–50 mg eplerenone or standard medication. Outcomes Primary outcome parameter was carotid-femoral pulse wave velocity (cfPWV). Secondary outcomes were augmentation index (AIx), ambulatory arterial stiffness index (AASI) and urinary albumin excretion. Results Fifty-four CKD patients (mean eGFR 36 mL/min/1.73 m2, SD 11) were randomized. Forty-six patients completed the trial. The mean difference in cfPWV changes between groups was 0.1 m/s (95%CI: ?1.0, 1.3), P?=?0.8. The mean difference in AIx changes between groups was 4.4% (0.1, 8.6), P?=?0.04. AASI was unchanged in both groups. The ratio of change in urinary albumin excretion in the eplerenone group compared to the control was 0.61 (0.37, 1.01), P?=?0.05. Four patients were withdrawn from the eplerenone group including three because of possible side effects; one was withdrawn from the control group. Mild hyperkalemia was seen on three occasions and was easily managed. Limitations The full planned number of patients was not attained. The duration of the trial may have been too short to obtain full effect of eplerenone on the arteries. Conclusions Add-on treatment with eplerenone in CKD stage 3–4 did not significantly reduce cfPWV. There may be beneficial vascular effects leading to attenuated pulse wave reflection. Treatment was well-tolerated. Trial Registration ClinicalTrials.gov NCT01100203

Boesby, Lene; Elung-Jensen, Thomas; Strandgaard, Svend; Kamper, Anne-Lise

2013-01-01

314

Wave breaking characteristics estimated from wave staff measurements  

Microsoft Academic Search

Radar signals are scattered by short scale roughness elements of the sea surface. These features depend on wind, sea state and other parameters. The dynamical behaviour of this roughness provides the basis of oceanographic radar remote sensing. Sonar signals are also scattered by short waves causing reverberation. Wave breaking and bubble production give rise to transmission loss, reverberation, and ambient

Siegfried Stolte

1994-01-01

315

Acoustic velocity and attenuation measurements in thin rods with application to temperature profiling in coal gasification systems  

SciTech Connect

This paper is concerned with the application of ultrasonic thermometry for temperature profiling in the reactors of coal gasification plants. A temperature profiling sensor typically uses a thin rod with several notches to segregate the sensor length into various zones. An acoustic pulse transmitted through the multizone sensor is partially reflected back at each notch, and measurement of the time interval between each pair of the reflected signals provides an indication of the average temperature in the corresponding zone. The main contributions of this paper are (1) delineation of the reflection and transmission phenomenon of sound waves at a notch, (2) development of an improved method of attenuation measurement in single-zone and multizone sensors employing notches, and 3) determination of the acoustic properties, namely, velocity and attenuation of six candidate materials suitable to the gasifier environment in the temperature range from ambient to 1093/sup 0/C. Computer simulation was employed to analyze the reflected signals from the notches, and the simulation results were corroborated at each stage by experiments. 19 references, 6 figures, 2 tables.

Gopalsami, N.; Raptis, A.C.

1984-01-01

316

MEASURING WAVE INDUCED TURBULENCE NEAR STRUCTURES  

Microsoft Academic Search

For many applications in coastal and offshore engineering it is necessary to know the dy- namics underneath propagating gravity waves. The orbital velocities below undisturbed, monochromatic waves can be calculated by wave theories. The laminar orbital motion beneath progressing waves turns to a turbulent, periodic motion when a semi-submerged breakwater interacts with the flow. In this case the dynamics of

Joachim Lengricht; Hans Kaldenhoff; Kai-Uwe Graw

317

Torsional ultrasonic wave based level measurement system  

DOEpatents

A level measurement system suitable for use in a high temperature and pressure environment to measure the level of coolant fluid within the environment, the system including a volume of coolant fluid located in a coolant region of the high temperature and pressure environment and having a level therein; an ultrasonic waveguide blade that is positioned within the desired coolant region of the high temperature and pressure environment; a magnetostrictive electrical assembly located within the high temperature and pressure environment and configured to operate in the environment and cooperate with the waveguide blade to launch and receive ultrasonic waves; and an external signal processing system located outside of the high temperature and pressure environment and configured for communicating with the electrical assembly located within the high temperature and pressure environment.

Holcomb, David E. (Oak Ridge, TN); Kisner, Roger A. (Knoxville, TN)

2012-07-10

318

Estimation of effective x-ray tissue attenuation differences for volumetric breast density measurement  

NASA Astrophysics Data System (ADS)

Breast density has been identified to be a risk factor of developing breast cancer and an indicator of lesion diagnostic obstruction due to masking effect. Volumetric density measurement evaluates fibro-glandular volume, breast volume, and breast volume density measures that have potential advantages over area density measurement in risk assessment. One class of volume density computing methods is based on the finding of the relative fibro-glandular tissue attenuation with regards to the reference fat tissue, and the estimation of the effective x-ray tissue attenuation differences between the fibro-glandular and fat tissue is key to volumetric breast density computing. We have modeled the effective attenuation difference as a function of actual x-ray skin entrance spectrum, breast thickness, fibro-glandular tissue thickness distribution, and detector efficiency. Compared to other approaches, our method has threefold advantages: (1) avoids the system calibration-based creation of effective attenuation differences which may introduce tedious calibrations for each imaging system and may not reflect the spectrum change and scatter induced overestimation or underestimation of breast density; (2) obtains the system specific separate and differential attenuation values of fibroglandular and fat for each mammographic image; and (3) further reduces the impact of breast thickness accuracy to volumetric breast density. A quantitative breast volume phantom with a set of equivalent fibro-glandular thicknesses has been used to evaluate the volume breast density measurement with the proposed method. The experimental results have shown that the method has significantly improved the accuracy of estimating breast density.

Chen, Biao; Ruth, Chris; Jing, Zhenxue; Ren, Baorui; Smith, Andrew; Kshirsagar, Ashwini

2014-03-01

319

A preliminary evaluation of wave attenuation by four species of seagrass  

NASA Astrophysics Data System (ADS)

Seagrasses are able to modify current flow and sediment composition, yet little information exists describing their effect on waves. Four species of seagrass, Halodule wrightii, Syringodium filiforme, Thalassia testudinum and Zostera marina were evaluated for their ability to reduce wave energy under various combinations of shoot density and water depths over a 1 m test section in a wave tank. Percent wave energy reduction per meter of seagrass bed equaled 40% when the length of these seagrasses was similar to the water depth. Seagrasses are approximately equal to saltmarshes in reducing wave energy on a unit distance basis, but only when water depth is scaled to plant size. When seagrass beds occur as broad, shallow meadows, the influence of seagrasses on wave energy will be substantial.

Fonseca, Mark S.; Cahalan, Jennifer A.

1992-12-01

320

The influence of cortical end-plate on broadband ultrasound attenuation measurements at the human calcaneus using scanning confocal ultrasound  

NASA Astrophysics Data System (ADS)

Quantitative ultrasound (QUS) assessment, including broadband ultrasound attenuation (BUA), is an efficient technique for assessing bone quality in various statuses, e.g., osteoporosis. While assessing trabecular bone loss is essential to bone quality, the existence of cortical bone can substantially reduce the accuracy of BUA measurement. In this study, we developed an approach to quantify the influence of the cortical end-plate in the QUS on 18 cadaver calcanei using both analytical and experimental analyses. A simplified cortical-trabecular-cortical sandwich model has been developed for simulation of wave propagations. Results show that the cortical end-plate has a significant effect on BUA (yielding 8.5+/-3.6 dB/MHz in cortical bone alone), approximately 15% of the BUA value over the whole bone BUA measurement (54.1+/-20.1 dB/MHz). The phenomenon has been predicted by the developed analytical model with a high correlation (r2=0.63,p<0.0001). The data have suggested that the mechanism of the BUA attributed to the cortical end-plate is primarily due to the ultrasonic wave transmission and reflection within the cortical layers. Therefore, the influence of the cortical end-plate in BUA can be quantified and incorporated into the QUS assessment for bone quality, which may provide insight into BUA measurement for accurate diagnosis of bone diseases.

Xia, Yi; Lin, Wei; Qin, Yi-Xian

2005-09-01

321

High-Frequency Seismic Attenuation of Oceanic P and S Waves in the Western Pacific,  

National Technical Information Service (NTIS)

Analyses of oceanic P and S data from an earthquake in the Kuril Islands which occurred along the trend of a 1500-km-long ocean bottom hydrophone array deployment near Wake Island have yielded constraints on high-frequency seismic attenuation in the weste...

R. Butler C. S. McCreery L. N. Frazer D. A. Walker

1987-01-01

322

On the measurement of frequency-dependent ultrasonic attenuation in strongly heterogeneous materials  

Microsoft Academic Search

This paper deals with the measurement of frequency-dependent ultrasonic attenuation in strongly heterogeneous materials, such as cementitious materials. To improve the measurement of this parameter on this kind of materials, a linear swept–frequency signal is used to drive an emitter transducer to conduct a through-transmission inspection in immersion. To filter out undesirable frequency content, time–frequency filtering and detection process are

M. Molero; I. Segura; S. Aparicio; M. G. Hernández; M. A. G. Izquierdo

2010-01-01

323

Temperature Measurements and Internal Waves in Seneca Lake, New York.  

National Technical Information Service (NTIS)

Temperatures were measured near the center of Seneca Lake with thermistors and bathythermographs during four different years. Thermistor chains with probes at five depths revealed large amplitude internal waves. Wave amplitudes of 25 feet were commonly se...

M. H. Fliegel

1973-01-01

324

Seismic-wave attenuation and yield determination at regional distances. Final report, 1 May 1987-30 April 1989  

SciTech Connect

Work was completed on yield determination at the Soviet test site on Novaya Zemlya. Magnitudes and yields, determined for 30 explosions using Lg amplitudes recorded in northwestern Europe, ranged between 2.5 and 4900 kt, the largest since April 1976 being about 145 kt. Studies were completed on seismic wave attenuation of surface waves at intermediate periods and of Lg waves at 1 Hz in several regions of the world. Limits were determined for the degree of frequency dependence of Q (sub beta) which can occur in the crust in stable and tectonically active regions. A stochastic convolution model was proposed for Lg coda at distances > 200 km which considers the effects of dispersion scattering and mode conversions at those distances. A back-projection tomographic method was developed to regionalize large-scale lateral variations of coda Q for Lg waves which traverse long continental paths. A seismically active region in the New Madrid seismic zone was found to be characterized by lower than normal Q values. In the western United States, Q values in the upper mantle vary laterally, becoming smaller from east to west. Crust of the Basin and Range province has a low-Q upper crust overlying a lower crust with higher Q values.

Mitchell, B.J.; Nuttli, O.W.; Xie, J.K.; Al-Shukri, H.; Correig, A.

1989-05-25

325

Determination of rain rate from a spaceborne radar using measurements of total attenuation  

NASA Technical Reports Server (NTRS)

Studies shows that path-integrated rain rates can be determined by means of a direct measurement of attenuation. For ground based radars this is done by measuring the backscattering cross section of a fixed target in the presence and absence of rain along the radar beam. A ratio of the two measurements yields a factor proportional to the attenuation from which the average rain rate is deduced. The technique is extended to spaceborne radars by choosing the ground as reference target. The technique is also generalized so that both the average and range-profiled rain rates are determined. The accuracies of the resulting estimates are evaluated for a narrow beam radar located on a low earth orbiting satellite.

Meneghini, R.; Eckerman, J.; Atlas, D.

1981-01-01

326

Snowpack snow water equivalent measurement using the attenuation of cosmic gamma radiation  

SciTech Connect

Incoming, background cosmic radiation constantly fluxes through the earth`s atmosphere. The high energy gamma portion of this radiation penetrates many terrestrial objects, including the winter snowpack. The attenuation of this radiation is exponentially related to the mass of the medium through which it penetrates. For the past three winters, a device measuring cosmic gamma radiation--and its attenuation through snow--has been installed at the Central Sierra Snow Laboratory, near Donner Pass, California. This gamma sensor, measuring energy levels between 5 and 15 MeV, has proved to be an accurate, reliable, non-invasive, non-mechanical instrument with which to measure the total snow water equivalent of a snowpack. This paper analyzes three winters` worth of data and discusses the physics and practical application of the sensor for the collection of snow water equivalent data from a remote location.

Osterhuber, R. [Univ. of California, Soda Springs, CA (United States). Central Sierra Snow Lab.; Fehrke, F. [California Dept. of Water Resources, Sacramento, CA (United States); Condreva, K. [Sandia National Labs., Livermore, CA (United States)

1998-05-01

327

Full wave modeling of therapeutic ultrasound: Efficient time-domain implementation of the frequency power-law attenuation  

NASA Astrophysics Data System (ADS)

For the simulation of therapeutic ultrasound applications, a method including frequency-dependent attenuation effects directly in the time domain is highly desirable. This paper describes an efficient numerical time-domain implementation of the power-law attenuation model presented by Szabo [Szabo, J. Acoust. Soc. Am. 96, 491-500 (1994)]. Simulations of therapeutic ultrasound applications are feasible in conjunction with a previously presented finite differences time-domain (FDTD) algorithm for nonlinear ultrasound propagation [Ginter et al., J. Acoust. Soc. Am. 111, 2049-2059 (2002)]. Szabo implemented the empirical frequency power-law attenuation using a causal convolutional operator directly in the time-domain equation. Though a variety of time-domain models has been published in recent years, no efficient numerical implementation has been presented so far for frequency power-law attenuation models. Solving a convolutional integral with standard time-domain techniques requires enormous computational effort and therefore often limits the application of such models to 1D problems. In contrast, the presented method is based on a recursive algorithm and requires only three time levels and a few auxiliary data to approximate the convolutional integral with high accuracy. The simulation results are validated by comparison with analytical solutions and measurements. .

Liebler, Marko; Ginter, Siegfried; Dreyer, Thomas; Riedlinger, Rainer E.

2004-11-01

328

Measurement of shear waves in tissue  

Microsoft Academic Search

The wavelength of a propagating pulse of shear wave within tissue is related to the local shear modulus and density through the speed of propagation. If the pulse does not produce standing waves, then the wavelength is a function of the tissue properties and not boundary conditions. Methods for imaging such waves using ultrasound and magnetic resonance imaging have recently

J. F. Greenleaf; V. Dutt; R. Muthupillai; A. Manduca; R. L. Ehman

1996-01-01

329

Reliability of computed tomography measurements in assessment of thigh muscle cross-sectional area and attenuation  

PubMed Central

Background Advancement in technology of computer tomography (CT) and introduction of new medical imaging softwares enables easy and rapid assessment of muscle cross-sectional area (CSA) and attenuation. Before using these techniques in clinical studies there is a need for evaluation of the reliability of the measurements. The purpose of the study was to evaluate the inter- and intra-observer reliability of ImageJ in measuring thigh muscles CSA and attenuation in patients with anterior cruciate ligament (ACL) injury by computer tomography. Methods 31 patients from an ongoing study of rehabilitation and muscle atrophy after ACL reconstruction were included in the study. Axial CT images with slice thickness of 10 mm at the level of 150 mm above the knee joint were analyzed by two investigators independently at two times with a minimum of 3 weeks between the two readings using NIH ImageJ. CSA and the mean attenuation of individual thigh muscles were analyzed for both legs. Results Mean CSA and mean attenuation values were in good agreement both when comparing the two observers and the two replicates. The inter- and intraclass correlation (ICC) was generally very high with values from 0.98 to 1.00 for all comparisons except for the area of semimembranosus. All the ICC values were significant (p < 0,001). Pearson correlation coefficients were also generally very high with values from 0.98 to 1.00 for all comparisons except for the area of semimembranosus (0.95 for intraobserver and 0.92 for interobserver). Conclusion This study has presented ImageJ as a method to monitor and evaluate CSA and attenuation of different muscles in the thigh using CT-imaging. The method shows an overall excellent reliability with respect to both observer and replicate.

2010-01-01

330

Filter Paper: Solution to High Self-Attenuation Corrections in HEPA Filter Measurements  

SciTech Connect

An 8 by 8 by 6 inch High Efficiency Particulate Air (HEPA) filter was measured as part of a uranium holdup survey in June of 2005 as it has been routinely measured every two months since 1998. Although the survey relies on gross gamma count measurements, this was one of a few measurements that had been converted to a quantitative measurement in 1998. The measurement was analyzed using the traditional Generalized Geometry Holdup (GGH) approach, using HMS3 software, with an area calibration and self-attenuation corrected with an empirical correction factor of 1.06. A result of 172 grams of {sup 235}U was reported. The actual quantity of {sup 235}U in the filter was approximately 1700g. Because of this unusually large discrepancy, the measurement of HEPA filters will be discussed. Various techniques for measuring HEPA filters will be described using the measurement of a 24 by 24 by 12 inch HEPA filter as an example. A new method to correct for self attenuation will be proposed for this measurement Following the discussion of the 24 by 24 by 12 inch HEPA filter, the measurement of the 8 by 8 by 6 inch will be discussed in detail.

Oberer, R.B.; Harold, N.B.; Gunn, C.A.; Brummett, M.; Chaing, L.G.

2005-10-01

331

A tunable coherent CO2 lidar for measurements of atmospheric aerosol backscatter and attenuation  

NASA Technical Reports Server (NTRS)

A coherent laser radar system using a grating-tunable, injection-locked TEA-CO2 transmitter is being used to measure the altitude dependence of atmospheric aerosol backscatter and attenuation at a variety of CO2 laser wavelengths in the 9-11 micron region. Injection control of the TEA-CO2 laser allows one to obtain Single-Longitudinal-Mode (SLM) pulses which will follow the frequency of the injected radiation if the TEA laser cavity length is adjusted so that a cavity resonance is in proximity with the injected signal frequency, and if various additional conditions are satisfied. Requirements for generation of SLM pulses in this manner from a TEA CO2 laser with an unstable resonator cavity will be discussed. Procedures used for quantitative range-gated measurements of aerosol backscatter and attenuation will also be discussed.

Menzies, R. T.

1983-01-01

332

The relationship between shear wave velocity, temperature, attenuation and viscosity in the shallow part of the mantle  

NASA Astrophysics Data System (ADS)

Surface wave tomography, using the fundamental Rayleigh wave velocities and those of higher modes between 1 and 4 and periods between 50 and 160 s, is used to image structures with a horizontal resolution of ˜250 km and a vertical resolution of ˜50 km to depths of ˜300 km in the mantle. A new model, PM_v2_2012, obtained from 3×106 seismograms, agrees well with earlier lower resolution models. It is combined with temperature estimates from oceanic plate models and with pressure and temperature estimates from the mineral compositions of garnet peridotite nodules to generate a number of estimates of SV(P,T) based on geophysical and petrological observations alone. These are then used to estimate the unrelaxed shear modulus and its derivatives with respect to pressure and temperature, which agree reasonably with values from laboratory experiments. At high temperatures relaxation occurs, causing the shear wave velocity to depend on frequency. This behaviour is parameterised using a viscosity to obtain a Maxwell relaxation time. The relaxation behaviour is described using a dimensionless frequency, which depends on an activation energy E and volume Va. The values of E and Va obtained from the geophysical models agree with those from laboratory experiments on high temperature creep. The resulting expressions are then used to determine the lithospheric thickness from the shear wave velocity variations. The resolution is improved by about a factor of two with respect to earlier models, and clearly resolves the thick lithosphere beneath active intracontinental belts that are now being shortened. The same expressions allow the three dimensional variations of the shear wave attenuation and viscosity to be estimated.

Priestley, Keith; McKenzie, Dan

2013-11-01

333

Contributions to numerical developments in shock waves attenuation in porous filters  

Microsoft Academic Search

The paper deals with the numerical method of the compressible gas flow through a porous filter emphasizing the treatment of\\u000a the interface between a pure gaseous phase and a solid phase. An incident shock wave is initiated in the gaseous phase interacting\\u000a with a porous filter inducing a transmitted and a reflected wave. To take into account the discontinuity jump

D. Rochette

2007-01-01

334

The Attenuation of Seismic Shear Waves in Quaternary Alluvium in Santa Clara Valley, California  

Microsoft Academic Search

We used shear waves, generated by an air-powered source at the ground surface and recorded in a borehole, to estimate the shear-wave quality factor at strong-motion station Gilroy no. 2. We find similar values of Q using both the decay of the spectra with depth and the slope of the spectral ratio at two depths; we find no evidence of

James F. Gibbs; David M. Boore; William B. Joyner; Thomas E. Fumal

1994-01-01

335

Slant path rain attenuation distribution at frequencies above 10 GHz: Correlation between some propagation models and results of long-term measurements in the Intercosmos Programme  

NASA Astrophysics Data System (ADS)

The development of telecommunications strongly depend on the enhanced use of the frequency range above 10 GHz by satellite systems. The complexity of the parameters of wave propagation is the reason for the still unsatisfactory situation in working out planning methods for satellite systems in this frequency range. In this paper, several models are described and compared. The correlation between the rain attenuation at a space path and terrestrial test path at different frequencies derived from measurements in the frame of the Intercosmos Programme makes possible an approximate conversion of the terrestrially measured values to the space path.

Alexandrova, E.; Bauer, W.; Liebsch, W.; Trommer, H.; Bykov, V.; Svjatogor, V.; Fisher, O.; Kavetzki, A.

336

Symphony orchestra musicians' use of hearing protection and attenuation of custom-made hearing protectors as measured with two different real-ear attenuation at threshold methods.  

PubMed

Despite a high level of sound exposure and a fairly large selection of earplugs available, musicians have often been reported to use personal hearing protectors only seldom. For better hearing conservation, it is important to identify and eliminate the causes for the low motivation to use hearing protection. We explored the usage rate of custom-molded musician's earplugs (ER-15) among 15 symphony orchestra musicians with a questionnaire, and measured the attenuation properties of their earplugs with a Real-Ear Attenuation at Threshold (REAT) procedure in a sound field. Earplug use was found to be low, and the musicians reported that earplugs hampered listening to their own and their colleagues' playing; earplugs affected either timbre or dynamics, or both. Additionally, several reasons related to discomfort of use were itemized, but the musicians who consistently used their earplugs did so in spite of problems with use. The REAT values obtained in sound field were relatively close to the manufacturer's nominal specifications, being 13.7 dB, on average. In the frequency range studied (0.125-8 kHz), individual variation in REAT was, however, up to 15 dB across the measured frequencies. Fluctuation in attenuation might be related to low use of hearing protectors, and REAT measured at fixed center frequencies may be too robust a method to uncover it. We therefore tested 10 additional subjects to find out whether a sweeping signal used in B?k?sy audiometry would bring more detailed information on earplug attenuation. Mean attenuation was found to be somewhat closer to the nominal attenuation of the ER-9 and ER-15 earplugs up to about 1 kHz, whereas REAT measurements in sound field revealed more even attenuation at frequencies between 1 and 6 kHz. No significant association was found between earplug attenuation properties and earplug use. It was concluded that support and determination to get accustomed to hearing protector use are important factors in hearing conservation. PMID:21368443

Huttunen, K H; Sivonen, V P; Poykko, V T

2011-01-01

337

An instrument for measuring high-power laser beam profiles and beam attenuation  

Microsoft Academic Search

An instrument has been developed for measuring high-power laser beam profiles and the amount of beam attenuation during radiative ignition of solid propellants. The detector houses a 1.0 mm square PZT (lead-zirconate-titanate) sensing element that responds to changes in incident laser beam intensity. A chopper wheel with three slots was employed to produce the changes in beam intensity required by

B. L. Fetherolf; T. A. Litzinger; K. K. Kuo

1990-01-01

338

An instrument for measuring high-power laser beam profiles and beam attenuation  

Microsoft Academic Search

This paper describes an instrument for measuring high-power laser beam profiles and the amount of beam attenuation during radiative ignition of solid propellants and solid fuels. The instrument uses a PZT detector element as the high-energy beam sensor that responds to changes in incident laser-beam intensity; the incoming beam is regulated by a slotted chopper wheel that provides three intensity

B. L. Fetherolf; T. A. Litzinger; K. K. Kuo

1990-01-01

339

CTS attenuation and cross-polarization measurements at 11.7 GHz  

NASA Technical Reports Server (NTRS)

The results of data obtained 80 days preceding the solar eclipse shutdown of the CTS 11.7 GHz righthand circularly polarized beacon transmitter are presented. Attenuation and cross polarization isolation were measured. It was determined that depolarization presents a serious limitation to satellite system reliability when frequency reuse by polarization diversity is employed. A 27 db isolation margin would reduce reliability below 99.95%. For the same percentage the required fade margin was below 3 db.

Vogel, W. J.; Straiton, A. W.

1977-01-01

340

Attenuation predictions at extremely low frequencies for measurement-while-drilling electromagnetic telemetry system  

Microsoft Academic Search

Extremely low frequencies (ELFs) are employed to transmit data from underground to the ground surface in the measurement-while-drilling electromagnetic (MWD-EM) telemetry system. Based on electromagnetic field theory, the present work is aimed at predicting the receivability of the signals at the surface. A unified analytic method that is suitable for vertical, directional, or horizontal wells is presented. Attenuation properties are

M. Y. Xia; Z. Y. Chen

1993-01-01

341

Prediction of attenuation of the 28 GHz COMSTAR beacon signal using radar and measured rain drop spectra  

NASA Technical Reports Server (NTRS)

Disdrometer measurements and radar reflectivity measurements were injected into a computer program to estimate the path attenuation of the signal. Predicted attenuations when compared with the directly measured ones showed generally good correlation on a case by case basis and very good agreement statistically. The utility of using radar in conjunction with disdrometer measurements for predicting fade events and long term fade distributions associated with earth-satellite telecommunications is demonstrated.

Goldhirsh, J.

1977-01-01

342

Communication: Singularity-free hybrid functional with a Gaussian-attenuating exact exchange in a plane-wave basis.  

PubMed

Integrable singularity in the exact exchange calculations in hybrid functionals is an old and well-known problem in plane-wave basis. Recently, we developed a hybrid functional named Gaussian-attenuating Perdew-Burke-Ernzerhof (Gau-PBE), which uses a Gaussian function as a modified Coulomb potential for the exact exchange. We found that the modified Coulomb potential of Gaussian function enables the exact exchange calculation in plane-wave basis to be singularity-free and, as a result, the Gau-PBE functional shows faster energy convergence on k and q grids for the exact exchange calculations. Also, a tight comparison (same k and q meshes) between Gau-PBE and two other hybrid functionals, i.e., PBE0 and HSE06, indicates Gau-PBE functional as the least computational time consuming. The Gau-PBE functional employed in conjunction with a plane wave basis provides bandgaps with higher accuracy than the PBE0 and HSE06 in agreement with bandgaps previously calculated using Gaussian-type-orbitals. PMID:23822220

Song, Jong-Won; Giorgi, Giacomo; Yamashita, Koichi; Hirao, Kimihiko

2013-06-28

343

Accuracy of Satellite-Measured Wave Heights in the Australian Region for Wave Power Applications  

ERIC Educational Resources Information Center

This article focuses on the accuracy of satellite data, which may then be used in wave power applications. The satellite data are compared to data from wave buoys, which are currently considered to be the most accurate of the devices available for measuring wave characteristics. This article presents an analysis of satellite- (Topex/Poseidon) and…

Meath, Sian E.; Aye, Lu; Haritos, Nicholas

2008-01-01

344

Void fraction measurements beneath plunging and spilling breaking waves  

Microsoft Academic Search

The temporal and spatial variations of the void fraction fields beneath deepwater breaking waves were investigated in the laboratory. There were a total of 13 measurement positions along the plunging wave; the peak void fractions measured varied from 0.024 to 0.96 and the time-averaged void fractions varied from 0.012 to 0.37. For the spilling wave, there were four measurement positions,

G. Rojas; M. R. Loewen

2010-01-01

345

Shock propagation and attenuation in Green River oil shale  

NASA Astrophysics Data System (ADS)

Shock waves produced by planar impact of thin plates onto samples of oil shale are monitored with time-resolved velocity interferometer diagnostics. Peak shock stresses are below the Hugoniot elastic limit. Stress wave measurements at successive sample thickness are analysed to determine the experimental shock energy attenuation with propagation distance. Shock attenuation is attributed to stress wave scattering at planes of oil shale kerogen within the shale matrix. Wave scattering from planar defects are evaluated from a shock physics perspective and a scattering model is constructed that sensibly reproduces the experimental observation of shock energy attenuation.

Grady, D. E.

2014-05-01

346

Measurements of wave speed and reflected waves in elastic tubes and bifurcations.  

PubMed

Wave intensity analysis is a time domain method for studying waves in elastic tubes. Testing the ability of the method to extract information from complex pressure and velocity waveforms such as those generated by a wave passing through a mismatched elastic bifurcation is the primary aim of this research. The analysis provides a means for separating forward and backward waves, but the separation requires knowledge of the wave speed. The PU-loop method is a technique for determining the wave speed from measurements of pressure and velocity, and investigating the relative accuracy of this method is another aim of this research. We generated a single semi-sinusoidal wave in long elastic tubes and measured pressure and velocity at the inlet, and pressure at the exit of the tubes. In our experiments, the results of the PU-loop and the traditional foot-to-foot methods for determining the wave speed are comparable and the difference is on the order of 2.9+/-0.8%. A single semi-sinusoidal wave running through a mismatched elastic bifurcation generated complicated pressure and velocity waveforms. By using wave intensity analysis we have decomposed the complex waveforms into simple information of the times and magnitudes of waves passing by the observation site. We conclude that wave intensity analysis and the PU-loop method combined, provide a convenient, time-based technique for analysing waves in elastic tubes. PMID:12020997

Khir, A W; Parker, K H

2002-06-01

347

Measurement of viscosity and shear wave velocity of a liquid or slurry for on-line process control  

SciTech Connect

An on-line sensor to measure the density of a liquid or slurry, based on longitudinal wave reflection at the solid-fluid interface, has been developed by staff at Pacific Northwest National Laboratory. The objective of this research is to employ shear-wave reflection at the solid-fluid interface to provide an on-line measurement of viscosity as well. Both measurements are of great interest for process control in many industries. Shear wave reflection measurements were carried out for a variety of liquids. By analyzing multiple reflections within the solid (only 0.63 cm thick - similar to pipe-wall thickness) we increased the sensitivity of the measurement. At the 6th echo, sensitivity was increased sufficiently and this echo was used for fluid interrogation. Shear wave propagation of ultrasound in liquids is dependent upon the viscosity and the shear modulus. The data are analyzed using the theory for light liquids (such as water and sugar water solutions) and also using the theory for highly viscous liquids (such as silica oils). The results show that for light liquids, the shear wave reflection measurements interrogate the viscosity. However, for highly viscous liquids, it is the shear wave modulus that dominates the shear wave reflection. Since the density is known, the shear wave velocity in the liquid can be determined from the shear wave modulus. The results show that shear wave velocities in silica oils are very small and range from 315 cm/s to 2389 cm/s. Shear wave reflection measurements are perhaps the only way that shear wave velocity in liquids can be determined, because the shear waves in liquids are highly attenuated.

Greenwood, Margaret S. (BATTELLE (PACIFIC NW LAB)); Bamberger, Judith A. (BATTELLE (PACIFIC NW LAB))

2001-12-01

348

Spinal axis irradiation with electrons: Measurements of attenuation by the spinal processes  

SciTech Connect

Electrons may be used beneficially for spinal axis irradiation in medulloblastoma children to avoid some of the long-term sequelae induced by megavoltage photons. However, the attenuation by the intervening bone ought to be considered. Three-dimensional computer treatment planning with inhomogeneity correction for electron beams is not yet generally available, and alternate methods are needed to evaluate the attenuation by the complex bony structure of the spine. Here, we present our experimental data showing the alteration in the electron isodoses due to the intervening spinous processes. Film dosimetric measurements were made in the vertebral columns obtained from autopsies of a goat, a dog, and a child. Our results show that electron beam therapy for the spinal axis is a viable option.

Muller-Runkel, R.; Vijayakumar, S.

1986-07-01

349

Altimeter height measurement error introduced by the presence of variable cloud and rain attenuation  

NASA Technical Reports Server (NTRS)

It has recently been recognized that spatially inhomogeneous clouds and rain can substantially affect the height precision obtainable from a spaceborne radar altimeter system. Through computer simulation, it has been found that typical levels of cloud and rain intensities and associated spatial variabilities may degrade altimeter precision at 13.5 GHz and, in particular, cause severe degradation at 35 GHz. This degradation in precision is a result of radar signature distortion caused by variable attenuation over the beam limited altimeter footprint. Because attenuation effects increase with frequency, imprecision caused by them will significantly impact on the frequency selection of future altimeters. In this paper the degradation of altimeter precision introduced by idealized cloud and rain configurations as well as for a realistic rain configuration as measured with a ground based radar is examined.

Monaldo, F. M.; Goldhirsh, J.; Walsh, E. J.

1986-01-01

350

Experimental measurements of ultrasonic propagation velocity and attenuation in a magnetic fluid  

NASA Astrophysics Data System (ADS)

The ultrasonic propagation velocity and attenuation in a magnetic fluid subjected to magnetic field are measured precisely. Various characteristic properties of ultrasonic propagation in magnetic fluid such as hysteresis and anisotropy are observed. These results show that the ultrasonic propagation velocity and attenuation are dependent upon the intensity and the length of time for which the magnetic field is applied. When the magnetic field is applied, some of the magnetic particles in the magnetic fluid form clustering structures that influence ultrasonic propagation in a magnetic fluid. Our results indicate that the inner structure of a magnetic fluid can be analysed experimentally and we discuss the application of this non-contact inspection of the clustering structures in a magnetic fluid by ultrasonic techniques.

Motozawa, M.; Iizuka, Y.; Sawada, T.

2008-05-01

351

Use of Electromagnetic Acoustic Resonance Method to Detect Micro-Voids Via Evaluation of Ultrasonic Wave Attenuation Coefficient of SUS304 Steel Fabricated by Hot Isostatic Press  

NASA Astrophysics Data System (ADS)

Creep damage in SUS304 steel samples fabricated by a hot isostatic press (HIP) at 1050°C was evaluated using the electromagnetic acoustic resonance (EMAR), noise energy and ultrasonic spectroscopy (first moment) methods. The coefficients of attenuation of 1.1 to 5.4 MHz electromagnetically excited acoustic waves in the samples were investigated. By reducing diffraction loss and the loss to the electromagnetic acoustic transducer due to transmission of the ultrasonic waves via mechanical contacts, it was possible to detect shear wave attenuation coefficients as low as 2.5×10-4/microsecond at 1.1 MHz. With specimens fabricated at pressure of 170MPa, the attenuation coefficient increased in proportion to frequency up to 5.4 MHz, whereas with specimens fabricated at pressure lower than 80 MPa the attenuation coefficient increased rapidly above 4 MHz. The void fraction was found to be greater in specimens fabricated under lower pressure, which may be responsible for the markedly higher ultrasonic attenuation in the specimens fabricated at pressure lower than 80MPa. It was apparent from the experiments that the EMAR method detects creep voids with greater sensitivity than the other methods. Accordingly we hope it will be possible for the EMAR method to be used on real facilities in the future.

Nishida, Hidetaka; Yamaguchi, Hiroshi; Yoshida, Masashi

352

An Study of S-wave Attenuation using records from the 20 May, 2012 Emilia Earthquake, Italy and the Main Aftershocks  

NASA Astrophysics Data System (ADS)

We analyze the S-wave spectral amplitude decay with distance using strong-motion records from the 20 May 2012 Emilia-Romagna earthquake (Mw6.1) and five aftershocks with magnitudes ranging between 4.9 and 5.9. The data set consist of 6 earthquakes, 44 stations and 248 records with hypocentral distances in the range 10 < r < 100 km. We rotated the accelerograms to calculate transversal and radial components of the acceleration spectrum. We found nonparametric attenuation functions that describe the spectral amplitude decay of SH and SV waves with distance at 60 different frequencies between 0.1 and 40 Hz. These attenuation functions provide an estimate of the quality factor Q at each frequency analyzed. Assuming that geometrical spreading is 1-r for r ˜ rx and 1/(rxr)0.5 for r>rx with rx= 60 km and normalizing at 15 km (the recording distance where the attenuation functions start to decay), we find that the average Q for SH waves can be approximated by QSH = 82f1.2 and by QSV = 79f1.2 for SV waves in the frequency range 0.10 ˜ f ˜ 10.7 Hz. At higher frequencies, 11.8 ˜ f ˜ 40 Hz, the frequency dependence of Q weakens and is approximated by QSH = 301f0.36 and QSV = 384f0.28. These results indicate that the S-wave attenuation is isotropic at local distances in the epicenter area. The estimates of total Q obtained (intrinsic and scattering attenuation) coincide with the estimates of total Q determined by Del Pezzo et al. (2011) in north central Italy using coda waves and Multiple Lapse Time Window Analysis (MLTWA).

Castro, Raul; Pacor, Francesca; Puglia, Rodolfo; Ameri, Gabriele; Letort, Jean; Massa, Marco; Luzi, Lucia; Augliera, Paolo

2013-04-01

353

Attenuation of Longitudinal Sound Waves in Potasium in an Oblique Magnetic Field.  

National Technical Information Service (NTIS)

The absorption edge for Doppler shifted cyclotron resonance of longitudinal sound waves in potassium is found to agree with the prediction of the free electron model, demonstrating that the ground state of this material does not possess a spin density wav...

M. Greene A. Hoffman G. Seidel A. Houghton R. Peverly

1966-01-01

354

Shock Wave Therapy Effectively Attenuates Inflammation in Rat Carotid Artery following Endothelial Denudation by Balloon Catheter  

Microsoft Academic Search

Background: This study investigates the effectiveness of extracorporeal shock wave (ECSW) in ameliorating inflammatory mediator expression and neointimal formation in a rat model of vascular injury. Methods and Results: Male Sprague-Dawley rats with left carotid artery (LCA) injury induced by balloon dilatation (BD; group 1) were compared with group 2 [LCA injury plus ECSW-181 (defined as 181 total shocks given

Pei-Lin Shao; Chaw-Chi Chiu; Chun-Man Yuen; Sarah Chua; Li-Teh Chang; Jiunn-Jye Sheu; Cheuk-Kwan Sun; Chiung-Jen Wu; Ching-Jen Wang; Hon-Kan Yip

2010-01-01

355

Sound velocity and attenuation in bubbly gels measured by transmission experiments.  

PubMed

Measurements of the phase velocity and attenuation of sound in concentrated samples of bubbly gels are presented. Hair gel was used as a matrix material to obtain well characterized distributions of bubbles. Ultrasonic measurements were conducted over a large range of frequencies, including the resonance frequencies of the bubbles. Surprisingly good agreement with Foldy's prediction was found, even for monodisperse samples at resonance frequencies, up to volume fraction of 1%. Beyond this concentration, the effects of high-order multiple scattering were observed. These results support the feasability of ultrasonic techniques to investigate the size distribution of bubbles in a weak gel or liquid. PMID:18397001

Leroy, Valentin; Strybulevych, Anatoliy; Page, John H; Scanlon, Martin G

2008-04-01

356

The moon and Q. [lunar basalt acoustic attenuation measurement by resonance method  

NASA Technical Reports Server (NTRS)

The acoustic attenuation of a sample of lunar basalt 70215 was measured by the method of sphere resonance. A Q of 1185 was achieved under a vacuum of 7 millionths torr after heating the sample. He and CO2 gas caused a small decrease of Q. H2O vapor, however, resulted in a major decrease in Q. The Q of lunar material when measured on earth is low because of adsorbed gases. However, it is not clear that this effect explains completely the observed high lunar Q.

Schreiber, E.

1977-01-01

357

Ultrasonic database development for the acoustic inspection device: the velocity-attenuation measurement system (VAMS)  

NASA Astrophysics Data System (ADS)

The inspection of sealed containers is a critical task for personnel charged with enforcing government policies, maintaining public safety, and ensuring national security. The Pacific Northwest National Laboratory (PNNL) has developed a portable, handheld acoustic inspection device (AID) that provides non-invasive container interrogation and material identification capabilities. The AID technology has been deployed worldwide and user"s are providing feedback and requesting additional capabilities and functionality. Recently, PNNL has developed a laboratory-based system for automated, ultrasonic characterization of fluids to support database development for the AID. Using pulse-echo ultrasound, ultrasonic pulses are launched into a container or bulk-solid commodity. The return echoes from these pulses are analyzed in terms of time-of-flight and frequency content (as a function of temperature) to extract physical property measurements (acoustic velocity and attenuation) of the material under test. These measured values are then compared to a tailored database of materials and fluids property data acquired using the Velocity-Attenuation Measurement System (VAMS). This bench-top platform acquires key ultrasonic property measurements as a function of temperature and frequency. This paper describes the technical basis for operation of the VAMS, recent enhancements to the measurement algorithms for both the VAMS and AID technologies, and new measurement data from laboratory testing and performance demonstration activities. Applications for homeland security and counterterrorism, law enforcement, drug-interdiction and fuel transportation compliance activities will be discussed.

Diaz, Aaron A.; Burghard, Brion J.; Valencia, Juan D.; Samuel, Todd J.

2004-07-01

358

Ultrasonic database development for the acoustic inspection device: the velocity-attenuation measurement system (VAMS)  

SciTech Connect

The inspection of sealed containers is a critical task for personnel charged with enforcing government policies, maintaining public safety, and ensuring national security. The Pacific Northwest National Laboratory (PNNL) has developed a portable, handheld acoustic inspection device (AID) that provides non-invasive container interrogation and material identification capabilities. The AID technology has been deployed worldwide and user's are providing feedback and requesting additional capabilities and functionality. Recently, PNNL has developed a laboratory-based system for automated, ultrasonic characterization of fluids to support database development for the AID. Using pulse-echo ultrasound, ultrasonic pulses are launched into a container or bulk-solid commodity. The return echoes from these pulses are analyzed in terms of time-of-flight and frequency content (as a function of temperature) to extract physical property measurements (acoustic velocity and attenuation) of the material under test. These measured values are then compared to a tailored database of materials and fluids property data acquired using the Velocity-Attenuation Measurement System (VAMS). This bench-top platform acquires key ultrasonic property measurements as a function of temperature and frequency. This paper describes the technical basis for operation of the VAMS, recent enhancements to the measurement algorithms for both the VAMS and AID technologies, and new measurement data from laboratory testing and performance demonstration activities. Applications for homeland security and counter terrorism, law enforcement, drug-interdiction and fuel transportation compliance activities will be discussed.

Diaz, Aaron A.; Burghard, Brion J.; Valencia, Juan D.; Samuel, Todd J.; Doctor, S. R.

2004-08-01

359

Wavelength dependent measurements of optical fiber transit time, material dispersion, and attenuation  

SciTech Connect

A new method for measuring the wavelength dependence of the transit time, material dispersion, and attenuation of an optical fiber is described. The authors inject light from a 4-ns risetime pulsed broad-band flashlamp into various length fibers and record the transmitted signals with a time-resolved spectrograph. Segments of data spanning an approximately 3,000 {angstrom} range are recorded from a single flashlamp pulse. Comparison of data acquired with short and long fibers enables the determination of the transit time and the material dispersion as functions of wavelength dependence for the entire recorded spectrum simultaneously. The wavelength dependent attenuation is also determined from the signal intensities. The method is demonstrated with experiments using a step index 200-{micro}m-diameter SiO{sub 2} fiber. The results agree with the transit time determined from the bulk glass refractive index to within {+-} 0.035% for the visible (4,000--7,200 {angstrom}) spectrum and 0.12% for the ultraviolet (2,650--4,000 {angstrom}) spectrum, and with the attenuation specified by the fiber manufacturer to within {+-} 10%.

COCHRANE,KYLE ROBERT; BAILEY,JAMES E.; LAKE,PATRICK WAYNE; CARLSON,ALAN L.

2000-04-18

360

Attenuation of an intense electromagnetic wave in an inhomogeneous plasma and 'ultrastrong' plasma turbulence  

NASA Astrophysics Data System (ADS)

A theoretical analysis of plasma turbulence excited by an electromagnetic wave (e.g., laser or microwave radiation) near the critical point of a plasma target is presented. Conditions of 'ultrastrong' plasma turbulence are investigated where there is no inertial interval and plasma oscillations caused by modulational instability arise in the absorption region. The analysis is based on the theory of strong plasma turbulence of Galeev et al. (1977) and Zakharov's theory of Langmuir collapse (1972).

Sagdeev, R. Z.; Shapiro, V. D.; Shevchenko, V. I.

1980-03-01

361

Compressional Wave Q in the Uppermost Mantle Beneath the Tibetan Plateau Measured Using Pn Wave Spectra  

NASA Astrophysics Data System (ADS)

Pn waves from three near-colocated seismic events in the eastern Tarim Basin are well-recorded by the INDEPTH III and II arrays, which are deployed from northern to southern Tibet with a small east-west spread (between ˜88 and 91° E). The paths run southward and sample the Tibetan mantle with epicentral distances increasing from 870 to 1540 km. These waves have spectral contents that are distinctly different from those collected from the Kyrghistan network (KNET), to which the paths traverse westward through the eastern Tienshan. Pn Q beneath Tibet and Tienshan must therefore be different. Xie and Patton (1999,JGR, 104, 941-954) have simultaneously estimated source spectra of the co-located events, and path-averaged Pn Q to the KNET stations. Under a simplified geometrical spreading of ? -1.3, they have estimated Q0 and ? (Pn Q at 1 Hz and its frequency dependence) to KNET to be about 360 and 0.5, respectively. Using those estimates as a priori knowledge, we estimate that Q0 and ? are ~180 and 0.3 along paths to northern Tibet, and ˜260 and 0.0 along paths to southern Tibet. The southward increase of Q0 correlates well with a similar increase in Pn velocity contained in previous tomographic images. Additionally, we measured Pn Q using a two-station method along two profiles (from station SANG to TUNL, and GANZ to MAQI) deployed during the 1991-1992 Sino-US Tibetan Plateau experiment. Both profiles are located to the east of 92° E. Along profile SANG-TUNL, we estimate Q0 and ? to be ˜270 and 0.0, respectively. The Q0 value is rather high, but correlates well with the high Pn velocities of > 8.1 km/s re-measured in this study. Our results suggest that the zone of low Pn Q0 and velocity in northern Tibet, which is likely caused by high mantle temperature and partial melting, is confined to the west of 92° E. This is so despite that the zone of high Sn attenuation extends to further east.

Xie, J.

2003-12-01

362

High-frequency attenuation and backscatter measurements of rat blood between 30 and 60 MHz  

NASA Astrophysics Data System (ADS)

There has recently been a great deal of interest in noninvasive high-frequency ultrasound imaging of small animals such as rats due to their being the preferred animal model for gene therapy and cancer research. Improving the interpretation of the obtained images and furthering the development of the imaging devices require a detailed knowledge of the ultrasound attenuation and backscattering of biological tissue (e.g. blood) at high frequencies. In the present study, the attenuation and backscattering coefficients of the rat red blood cell (RBC) suspensions and whole blood with hematocrits ranging from 6% to 40% were measured between 30 and 60 MHz using a modified substitution approach. The acoustic parameters of porcine blood under the same conditions were also measured in order to compare differences in the blood properties between these two animals. For porcine blood, both whole blood and RBC suspension were stirred at a rotation speed of 200 rpm. Three different rotation speeds of 100, 200 and 300 rpm were carried out for rat blood experiments. The attenuation coefficients of both rat and porcine blood were found to increase linearly with frequency and hematocrit (the values of coefficients of determination (r2) are around 0.82-0.97 for all cases). The average attenuation coefficient of rat whole blood with a hematocrit of 40% increased from 0.26 Nepers mm-1 at 30 MHz to 0.47 Nepers mm-1 at 60 MHz. The maximum backscattering coefficients of both rat and porcine RBC suspensions were between 10% and 15% hematocrits at all frequencies. The fourth-power dependence of backscatter on frequency was approximately valid for rat RBC suspensions with hematocrits between 6% and 40%. However, the frequency dependence of the backscatter estimate deviates from a fourth-power law for porcine RBC suspension with hematocrit higher than 20%. The backscattering coefficient plateaued for hematocrits higher than 15% in porcine blood, but for rat blood it was maximal around a hematocrit of 20% at the same rotation speed, and shifted to a hematocrit of 10% at a higher speed. The backscattering properties of rat RBCs in plasma are similar to those of RBCs in saline at a higher rotation speed. The differences in attenuation and backscattering between rat and porcine blood may be attributed to RBCs' being smaller and the RBC aggregation level being lower for rat blood than for porcine blood.

Huang, Chih-Chung

2010-10-01

363

Effect of decay on ultrasonic velocity and attenuation measurements in wood  

NASA Astrophysics Data System (ADS)

Loblolly pine (Pinus taeda) wood cube specimens were exposed to Gloeophyllum fungus (Gloeophyllum trabeum) for increasing periods of time ranging from one week to twelve weeks. The corresponding mass of each of these specimens was recorded before and after they were subjected to the controlled decay. Using X-ray computed tomography (CT) the specimens' corresponding mass loss due to decay and corresponding densities were calculated. For each of the three principal material directions of these specimens with controlled decay, ultrasonic longitudinal and (polarized) shear velocity measurements along with the corresponding attenuation measurements are presented. The measurements were carried out using longitudinal and shear ultrasonic transducers with a center frequency of 100 kHz. A steel delay line was used because of the relative small size of the wooden specimens relative to the used wavelengths. Waveform averaging was used along with the phase-slope method to measure velocities. It was observed that the velocities increase with increasing frequency and decrease with increasing amount of decay, while the corresponding attenuations increase with increasing frequency and with amount of decay.

McGovern, Megan; Senalik, Adam; Chen, George; Beall, Frank C.; Reis, Henrique

2011-03-01

364

In vitro measurement of attenuation and nonlinear scattering from Echogenic liposomes  

PubMed Central

Echogenic liposomes (ELIP) are an excellent candidate for concurrent imaging and drug delivery applications. They combine the advantages of liposomes—biocompatibility and ability to encapsulate both hydrophobic and hydrophilic drugs—with strong reflections of ultrasound. The objective of this study is to perform a detailed in vitro acoustic characterization—including nonlinear scattering that has not been studied before—along with an investigation of the primary mechanism of echogenicity. Both components are critical for developing viable clinical applications of ELIP. Mannitol, a cryoprotectant, added during the preparation of ELIP is commonly believed to be critical in making them echogenic. Accordingly, here ELIP prepared with varying amount of mannitol concentration are investigated for their pressure dependent linear and non-linear scattered responses. The average diameter of these liposomes is measured to be 125–185 nm. But they have a broad size distribution including liposomes with diameters over a micro-meter as observed by TEM and AEM. These larger liposomes are critical for the overall echogenicity. Attenuation through liposomal solution is measured with four different transducers (central frequencies 2.25, 3.5, 5, 10 MHz). Measured attenuation increases linearly with liposome concentration indicating absence of acoustic interactions between liposomes. Due to the broad size distribution, the attenuation shows a flat response without a distinct peak in the range of frequencies (1–12 MHz) investigated. A 15–20 dB enhancement is observed both for the scattered fundamental and the second harmonic responses at 3.5 MHz excitation frequency and 50–800 kPa amplitude. It demonstrates the efficacy of ELIP for fundamental as well as harmonic ultrasound imaging. The scattered response however does not show any distinct subharmonic peak for the acoustic excitation parameters studied. Small amount of mannitol proves critical for echogenicity. However, mannitol variation above 100 mM shows no effect.

Paul, Shirshendu; Russakow, Daniel; Nahire, Rahul; Nandy, Tapas; Ambre, Avinash H.; Katti, Kalpana; Mallik, Sanku; Sarkar, Kausik

2013-01-01

365

Terahertz reflection response measurement using a phonon polariton wave  

NASA Astrophysics Data System (ADS)

We developed a new technique for the measurement of terahertz reflection responses utilizing a propagating phonon polariton wave. Frequency tunable phonon polariton waves were generated by the recently developed continuously variable spatial frequency transient grating method [K. Katayama, H. Inoue, H. Sugiya, Q. Shen, T. Taro, and K. A. Nelson, Appl. Phys. Lett. 92, 031906 (2008)]. The phonon polariton wave traveled in a ferroelectric crystal in an in-plane direction with an inclined angle of 26°, and the wave reflected at the crystal edge where a sample was positioned. The reflected polariton wave was detected by the same method as that used for the generation of the polariton waves. By comparing the reflection intensities in the presence and absence of the sample, reflectivity of the polariton wave was calculated, and the refractive index and absorption in the terahertz region were obtained.

Inoue, Hayato; Katayama, Kenji; Shen, Qing; Toyoda, Taro; Nelson, Keith A.

2009-03-01

366

Temporal change in scattering and attenuation associated with the earthquake occurrence—A review of recent studies on coda waves  

Microsoft Academic Search

The study of coda waves has recently attracted increasing attention from seismologists. This is due to the fact that it is viewed as a new means by which the stress accumulation stage preceding a large earthquake can be measured, since the scattering paths nearly uniformly cover a fairly large region around the focus and observation stations, compared with the direct

Haruo Sato

1988-01-01

367

Intensified and attenuated waves in a microbubble Taylor-Couette flow  

NASA Astrophysics Data System (ADS)

The effect of the presence of microbubbles on a flow state is experimentally investigated in a Taylor-Couette flow with azimuthal waves, in order to examine the interaction mechanism of bubbles and flows that result in drag reduction. The average diameter of the bubbles is 60 ?m, which is smaller than the Kolmogorov length scale, and the maximum void fraction is 1.2 × 10-4 at the maximum case. The modifications of the fluid properties, bulk density, effective viscosity, and the extra energy input caused by the addition of microbubbles are expected to have a small effect on modifying flow states. The power of the basic wave propagating in the azimuthal direction is enhanced; its modulation, however, is decreased by adding microbubbles in the flow regime corresponding to modulated Taylor vortex flow. Moreover, the gradient of the azimuthal velocity near the walls, source of the wall shear stress, decreases by 10%. The modified velocity distribution by adding microbubbles is comparable to that obtained with a 20% lower Reynolds number. Microbubbles in the coherent structure of the wavy Taylor vortices are visualized and exhibit a preferential distribution and motion at the crests and troughs of the waviness. The roles of the inhomogeneously distributed microbubbles in wavy vortical structures are discussed in view of our findings.

Watamura, T.; Tasaka, Y.; Murai, Y.

2013-05-01

368

Q-structure beneath the north and central Indian Ocean from the inversion of observed Love and Rayleigh wave attenuation data  

NASA Astrophysics Data System (ADS)

The fundamental-mode Love and Rayleigh waves generated by 57 earthquakes which occurred in the north and central Indian Ocean (extending to 40°S) and recorded at Indian seismograph and other WWSSN stations such as HOW, SHL, VIS, MDR, HYB, KOD, CHG, TRD, POO, BOM, GOA, NDI, NIL and QUE are analysed. Love and Rayleigh wave attenuation coefficients are estimated at periods of 15-100 s using the spectral amplitude of these waves for 98 different paths across the Bay of Bengal Fan, the Arabian Fan, and the north and central Indian Ocean. The large standard deviations observed in the surface wave attenuation coefficients may be a result of regional variation of the attenuative properties of the crust and upper mantle beneath these regions. Love wave attenuation coefficients are found to vary from 0.000 03 to 0.000 45 km -1 for the Bay of Bengal Fan; from 0.000 03 to 0.000 85 km -1 for the Arabian Fan; and from 0.000 03 to 0.000 35 km -1 for the north and central Indian Ocean. Similarly, Rayleigh wave attenuation coefficients vary from 0.000 03 to 0.0004 km -1 for the Bay of Bengal Fan; from 0.000 06 to 0.0007 km -1 for the Arabian Fan; and from 0.000 03 to 0.0007 km -1 for the north and central Indian Ocean. Backus and Gilbert inversion theory is applied to these surface wave attenuation data to obtain average Q-1 models for the crust and upper mantle beneath the Bay of Bengal, the Arabian Fan, and the north and central Indian Ocean. Inversion of Love and Rayleigh wave attenuation data shows a high-attenuation zone centred at a depth of > 120 km ( Q? ? 125) for the Bay of Bengal Fan. Similarly, a high-attenuation zone ( Q? ? 40-70) occurs at a depth of 60-160 km for the Arabian Fan at 100-160 km ( Q? ? 115) for the Indian Ocean off Ninetyeast Ridge, and at 80-160 km ( Q? ? 80) for the Indian Ocean across the Ninetyeast Ridge. The Q?-1 models show a lithosphere thickness of 120 km beneath the Bay of Bengal Fan. Similarly, lithosphere thickness of 70, 100 and 80 km is estimated beneath the Arabian Fan, and the Indian Ocean off Ninetyeast Ridge and across Ninetyeast Ridge, respectively. The base of the lithosphere is identified as the depth at which there is a significant increase in the Q?-1 value, which attains its maximum value in the asthenosphere. The thinning of Indian lithosphere beneath the Arabian Fan suggests high temperature below Moho depth (60 km from surface) which has caused a high-attenuation zone at this shallow depth.

Singh, D. D.

369

Delamination of southern Puna lithosphere revealed by body wave attenuation tomography  

NASA Astrophysics Data System (ADS)

southern Puna Plateau has been proposed to result from a major Pliocene delamination event that has previously been inferred from geochemical, geological, and some preliminary geophysical data. Seventy-five seismic stations were deployed across the southern Puna Plateau in 2007-2009 by scientists from the U.S., Germany, Chile, and Argentina to test the delamination model for the region. The Puna passive seismic stations were located between 25 and 28°S. Using the seismic waveform data collected from the PUNA experiment, we employ attenuation tomography methods to resolve both compressional and shear quality factors (Qp and Qs, respectively) in the crust and uppermost mantle. The images clearly show a high-Q Nazca slab subducting eastward beneath the Puna plateau and another high-Q block with a westward dip beneath the Eastern Cordillera. We suggest that the latter is a piece of delaminated South American lithosphere. A significant low-Q zone lies between the Nazca slab and the South American lithosphere and extends southward from the northern margin of the seismic array at 25°S before vanishing around 27.5°S. This low-Q zone extends farther west in the crust and uppermost mantle at the southern end of the seismic array. The low-Q zone reaches ~100 km depth beneath the northern part of the array but only ~50 km depth in the south. Lateral variations of the low-Q zone reflect the possible mechanism conversion between mantle upwelling related to delamination and dehydration. The depth of the Nazca slab as defined by Q images decreases from north to south beneath the plateau, which is consistent with the steep-flat transition of the angle of the subducting slab as defined by previous earthquake studies.

Liang, Xiaofeng; Sandvol, Eric; Kay, Suzanne; Heit, Benjamin; Yuan, Xiaohui; Mulcahy, Patrick; Chen, Chen; Brown, Larry; Comte, Diana; Alvarado, Patricia

2014-01-01

370

Sea Wave Measurements Using a Ship's Radar.  

National Technical Information Service (NTIS)

The capabilities of a shore based ship radar as an ocean wave sensor for short ranges up to 5 km were assessed. Radar data was recorded from a number of fixed points at the sea surface along the line of sight, during a certain time, giving a two dimension...

P. Hoogeboom J. C. M. Kleijweg D. Vanhalsema

1986-01-01

371

Millimeter-wave ground based synthetic aperture radar measurements  

Microsoft Academic Search

In this study, applications of millimeter wave ground based synthetic aperture radar (GB-SAR) experiments are studied. GB-SAR data collection setup is constructed and GB-SAR measurements of different objects are carried out in the semi-anechoic chamber room. Measurements from an aluminum target and metal pipe targets at the millimeter wave regions are collected by the newly constructed measurement setup. Also, real

Enes Yigit; Atilla Unal; Adem Kaya; Sevket Demirci; Harun Cetinkaya; Caner Ozdemir; Alexey Vertiy

2011-01-01

372

Broadband optoacoustic measurements of ultrasound attenuation in severely plastically deformed nickel  

NASA Astrophysics Data System (ADS)

Laser optoacoustics and immersion techniques allowed a broadband ultrasound spectroscopy which was used for measuring the attenuation of severely plastically deformed nickel. A disk shaped specimen of nickel of about 33 mm diameter and 2.5 mm thickness was prepared by the high pressure torsion method. The produced equivalent shear strain linearly increased from a minimum at the center up to 1000% at the edge, gradually refining the grain size distribution down to 200 nm. The metal water interface was illuminated by 5 ns laser pulses, generating longitudinal ultrasound pulses with a pronounced compression phase and a smooth spectrum covering the range from 0.1 up to 150 MHz. The laser beam spot diameter was 6 mm, yielding a maximum power density below 15 MW/cm2. The ultrasound passed through the sample thickness and a 2 mm layer of coupling water. The pulse was detected by a 25 ?m thick piezoelectric foil transducer with a diameter of the sensitive area of 2 mm. The transient signals were locally measured at different radii of the specimen. The attenuation almost linearly increases with frequency while its absolute value decreases from the center to the edge of the specimen.

Kozhushko, Victor V.; Paltauf, Günther; Krenn, Heinz; Scheriau, Stephan; Pippan, Reinhard

2010-05-01

373

Attenuation measurements of passive linear and nonlinear hearing protectors for impulse noise  

NASA Astrophysics Data System (ADS)

As a part of a NIOSH Health Hazard Evaluation of law-enforcement personnel, the attenuation of several types of earplugs were measured in response to impulse noise produced by small-arms gunfire. The earplugs were primarily flanged premolded plugs produced by EAR/Aearo and Bilsom/Baccou-Dalloz. Measurements for the North Sonic Ear Valve, EAR Classic earplugs, and EAR Ultra 9000 passive nonlinear ear muff were conducted. The EAR premolded earplugs were the Combat Arms passive linear and nonlinear, HiFi and Ultratech earplugs. The Bilsom devices were the 555, 655 NST, and 655 ISL earplugs. The Combat Arms and 655 ISL earplugs both utilize a cartridge developed by the French German Research Institute de Saint Louis that provides nonlinear attenuation. The peak reduction of these devices ranged between 10 and 28 dB. The slope of peak reduction with peak level for the Ultra9000 device was about 0.5 dB/dB, while the slopes for most earplugs were about 0.1 to 0.3 dB/dB for weapons impulses between 159- and 170-dB peak level. The peak reductions ranged from 6 dB for the North Ear valve to 30 dB for the EAR Classic foam earplug.

Murphy, William J.; Kardous, Chucri A.

2003-04-01

374

Sea Ice Thickness Measurements Using Shear Wave Reflections.  

National Technical Information Service (NTIS)

Because of the lack of success in measuring sea ice thickness with normal acoustic means, a method utilizing shear waves or 'S' waves was tried during the summer of 1971 off Point Barrow, Alaska. A 551A*Textronic oscilloscope and polaroid camera were used...

G. P. Vance D. D. Benefield D. M. Egan

1971-01-01

375

Measurement of ultrashort pulse with fundamental wave by computer  

Microsoft Academic Search

A new technique of measuring light pulse with fundamental wave information is presented in order to surmount the difficulty of phase matching of tunable laser in second- harmonic wave method. The expressions of upper-envelope of interference correlation function of fundamental pulse are derived for Gaussian and hyperbolic secant pulse shapes. It is pointed out that the width of the envelope

Zhenglie Gong; Zhengyi Huang; Xiaoman Cheng; Xiulan Xia; Zhenping Jiang; Zhifeng Liu; Yangqin Zhan

1996-01-01

376

Pulsar timing measurements and the search for gravitational waves  

Microsoft Academic Search

Pulse arrival time measurements of pulsars may be used to search for gravitational waves with periods on the order of 1 to 10 years and dimensionless amplitudes of approximately 10 to the -11th power. The analysis of published data on pulsar regularity sets an upper limit to the energy density of a stochastic background of gravitational waves, with periods of

S. Detweiler

1979-01-01

377

Extraction of wave information from NOAA's water level measurement network  

Microsoft Academic Search

Long-term coastal wave data are useful information for public safety, coastal erosion studies, coastal flood planning, and coastal engineering projects because of great spatial variability along the coast lines. The collection of such data, however, is quite difficult and expensive. This paper demonstrates the feasibility of obtaining surface wave information from existing NOAA Next Generation Water Level Measurement Systems (NGWLMS)

H. H. Shih; M. A. Basileo

1996-01-01

378

Visualisation and Measurement of Internal Waves by Synthetic Schlieren\\  

Microsoft Academic Search

We present measurements of the density and velocity fields produced when an oscillating circular cylinder... In this paper we examine the structure and amplitude of internal gravity waves generated by a cylinder oscillating vertically at different frequencies and amplitudes, paying particular attention to the role of viscosity in determining the evolution of the waves. In qualitative agreement with theory, it

Bruce R. Sutherland; Stuart B. Dalziel; Graham O. Hughes; P. F. Linden

1999-01-01

379

Measurements of Wave Induced Drift in a Shallow Basin  

Microsoft Academic Search

We have studied rotationally polarized waves driven in a shallow cylindrical basin of ethyl ether. Both the wave motion and the resulting circularly induced drift are observed by tracking a small floating particle with video techniques. Careful attention has been paid to both transient currents and thermally induced convection. The measured induced drift at the free surface is in general

F. M. Ellis; A. K. Shah; A. D. Corwin

1996-01-01

380

Relaxation, dispersion, attenuation, and finite propagation speed in viscoelastic media  

NASA Astrophysics Data System (ADS)

Dispersion and attenuation functions in a linear viscoelastic medium with a positive relaxation spectrum are given by integral representations in terms of a positive Radon measure satisfying a growth condition. Kramers-Kronig dispersion relations with one subtraction can be derived from the integral representations of the dispersion and attenuation functions. The dispersion and attenuation functions have sublinear growth in the high frequency range. The wave number vector can have a linear component in addition to the dispersion function. In this case the viscoelastic waves propagate with a bounded speed. In the other cases viscoelastic wave propagation has a diffusion-like character.

Seredy?ska, M.; Hanyga, Andrzej

2010-09-01

381

Measurement of ocean wave spectra using polarimetric AIRSAR data  

NASA Technical Reports Server (NTRS)

A polarimetric technique for improving the visibility of waves, whose propagation direction has an azimuthal component, in RAR (real aperture radar) or SAR (synthetic aperture radar) images has been investigated. The technique shows promise as a means of producing more accurate 2-D polarimetric RAR ocean wave spectra. For SAR applications domination by velocity-bunching effects may limit its usefulness to long ocean swell. A modification of this technique involving measurement of polarization signature modulations in the image is useful for detecting waves in SAR images and, potentially, estimating RMS wave slopes.

Schuler, D. L.

1993-01-01

382

High frequency measurement of P- and S-wave velocities on crystalline rock massif surface - methodology of measurement  

NASA Astrophysics Data System (ADS)

For the purpose of non-destructive monitoring of rock properties in the underground excavation it is possible to perform repeated high-accuracy P- and S-wave velocity measurements. This contribution deals with preliminary results gained during the preparation of micro-seismic long-term monitoring system. The field velocity measurements were made by pulse-transmission technique directly on the rock outcrop (granite) in Bedrichov gallery (northern Bohemia). The gallery at the experimental site was excavated using TBM (Tunnel Boring Machine) and it is used for drinking water supply, which is conveyed in a pipe. The stable measuring system and its automatic operation lead to the use of piezoceramic transducers both as a seismic source and as a receiver. The length of measuring base at gallery wall was from 0.5 to 3 meters. Different transducer coupling possibilities were tested namely with regard of repeatability of velocity determination. The arrangement of measuring system on the surface of the rock massif causes better sensitivity of S-transducers for P-wave measurement compared with the P-transducers. Similarly P-transducers were found more suitable for S-wave velocity determination then P-transducers. The frequency dependent attenuation of fresh rock massif results in limited frequency content of registered seismic signals. It was found that at the distance between the seismic source and receiver from 0.5 m the frequency components above 40 kHz are significantly attenuated. Therefore for the excitation of seismic wave 100 kHz transducers are most suitable. The limited frequency range should be also taken into account for the shape of electric impulse used for exciting of piezoceramic transducer. The spike pulse generates broad-band seismic signal, short in the time domain. However its energy after low-pass filtration in the rock is significantly lower than the energy of seismic signal generated by square wave pulse. Acknowledgments: This work was partially supported by the Technology Agency of the Czech Republic, project No. TA 0302408

Vilhelm, Jan; Slavík, Lubomír

2014-05-01

383

Volumetric measurements of a spatially growing dust acoustic wave  

SciTech Connect

In this study, tomographic particle image velocimetry (tomo-PIV) techniques are used to make volumetric measurements of the dust acoustic wave (DAW) in a weakly coupled dusty plasma system in an argon, dc glow discharge plasma. These tomo-PIV measurements provide the first instantaneous volumetric measurement of a naturally occurring propagating DAW. These measurements reveal over the measured volume that the measured wave mode propagates in all three spatial dimensional and exhibits the same spatial growth rate and wavelength in each spatial direction.

Williams, Jeremiah D. [Physics Department, Wittenberg University, Springfield, Ohio 45504 (United States)

2012-11-15

384

Direct Measurement of Wave Kernels in Time-Distance Helioseismology  

NASA Technical Reports Server (NTRS)

Solar f-mode waves are surface-gravity waves which propagate horizontally in a thin layer near the photosphere with a dispersion relation approximately that of deep water waves. At the power maximum near 3 mHz, the wavelength of 5 Mm is large enough for various wave scattering properties to be observable. Gizon and Birch (2002,ApJ,571,966)h ave calculated kernels, in the Born approximation, for the sensitivity of wave travel times to local changes in damping rate and source strength. In this work, using isolated small magnetic features as approximate point-sourc'e scatterers, such a kernel has been measured. The observed kernel contains similar features to a theoretical damping kernel but not for a source kernel. A full understanding of the effect of small magnetic features on the waves will require more detailed modeling.

Duvall, T. L., Jr.

2006-01-01

385

Use of accelerometer for wave measurements  

NASA Astrophysics Data System (ADS)

With the fast development of microelectromechanical systems (MEMS) over the past decades, accelerometers have become very reliable and cost efficient. As such, accelerometers are finding their way into all types of hydrological applications. Here, we investigate the usefulness of an accelerometer for recording waves. We use the "USB-Accelerometer 3-axis Self Recording Accelerometer X16-1C" (Gulf Coast Data Concepts LLC) in this experiment. The X16-1C costs less than 100. This instrument records with a frequency of up to 200 Hz acceleration along three dimensions. By fixing the instrument in a float, waves can readily be recorded. Here, we present the first results of field trials.

van de Giesen, N.; de Boer, G.

2012-04-01

386

An investigation of the measurement of broadband ultrasonic attenuation in trabecular bone  

Microsoft Academic Search

Commercial devices for the ultrasonic characterisation of bone normally report the broadband ultrasonic attenuation (BUA). This is the slope of the attenuation against frequency in some part of the frequency range 200–1000 kHz. The assumption is that the relationship is linear and hence independent of the frequency range selected. In this study the ultrasonic attenuation in the frequency range 200

R. Strelitzki; J. A. Evans

1996-01-01

387

Millimeter wave radar with clutter measurements  

Microsoft Academic Search

A portable millimeter wave test radar system, also suitable for battery operation, gives interesting possibilities for clutter recordings at hard-to-reach sites. The designed system covers all common radar frequencies from the Ka- to V-bands and enables spatial detection of targets or clutter elements within an adjustable time gate, whereby spatial clutter profiles of rain can be analyzed. The construction allows

Jukka Ruoskanen; Pekka Eskelinen; Heikki Heikkila

2003-01-01

388

Radiographic least-squares fitting technique accurately measures dimensions and x-ray attenuation  

SciTech Connect

In support of stockpile stewardship and other important nondestructive test (NDT) applications, the authors seek improved methods for rapid evaluation of materials to detect degradation, warping, and shrinkage. Typically, such tests involve manual measurements of dimensions on radiographs. The authors seek to speed the process and reduce the costs of performing NDT by analyzing radiographic data using a least-squares fitting technique for rapid evaluation of industrial parts. In 1985, Whitman, Hanson, and Mueller demonstrated a least-squares fitting technique that very accurately locates the edges of cylindrically symmetrical objects in radiographs. To test the feasibility of applying this technique to a large number of parts, the authors examine whether an automated least squares algorithm can be routinely used for measuring the dimensions and attenuations of materials in two nested cylinders. The proposed technique involves making digital radiographs of the cylinders and analyzing the images. In the authors` preliminary study, however, they use computer simulations of radiographs.

Kelley, T.A.; Stupin, D.M.

1997-10-01

389

Precision of Raman depolarization and optical attenuation measurements of sound tooth enamel.  

PubMed

The demineralization of enamel that is associated with early caries formation affects the optical properties of the enamel. Polarized Raman spectroscopy and optical coherence tomography have been used to detect these changes and potentially offer a means to detect and monitor early caries development. The total optical attenuation coefficient as measured by optical coherence tomography and the polarization anisotropy of the Raman peak arising from the symmetric nu(1) vibration of PO4(3-) at approximately 959 cm(-1) have been demonstrated as being sensitive markers of early caries. This ex vivo study on extracted human teeth demonstrates that these measurements can be made with reasonable precision with concomitantly good repeatability and reproducibility in sound enamel. Such reliability is crucial for these techniques to have a practical clinical value. PMID:17082878

Sowa, Michael G; Popescu, Dan P; Werner, Jeffrey; Hewko, Mark; Ko, Alex C-T; Payette, Jeri; Dong, Cecilia C S; Cleghorn, Blaine; Choo-Smith, Lin-P'ing

2007-03-01

390

Measurements of CO Relaxation in an Unsteady Expansion Wave  

Microsoft Academic Search

Vibrational relaxation of various CO&sngbnd;Ar mixtures in an unsteady expansion wave was measured using an infrared technique. Results indicated no deviations from values predicted using the Landau—Teller model.

T. Just; P. Roth

1971-01-01

391

Possible applications of surface electromagnetic waves to measure absorption coefficients  

Microsoft Academic Search

We show that surface electromagnetic waves can probably be used to measure the absorption coefficients of materials overlaying metals. The proposed experimental method is illustrated in the infrared frequency range using water, Teflon, and polyethylene as sample materials.

R. W. Alexand