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1

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

2

Measurement of velocity and attenuation of shear waves in bovine compact bone using ultrasonic spectroscopy  

Microsoft Academic Search

The ultrasonic spectroscopy (broadband pulse) technique was applied to simultaneously measure phase velocity and attenuation coefficient of shear waves in bovine compact bone at frequencies ranging from 4.0–10.0 MHz. It was found that the ratio of attenuation coefficient of shear waves to that of longitudinal waves at a particular frequency for bovine compact bone was smaller than that of other

Junru Wu; Frances Cubberley

1997-01-01

3

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

4

Laboratory measurement of seismic wave dispersion and attenuation: Recent progress  

NASA Astrophysics Data System (ADS)

Progress in the laboratory study of seismic wave dispersion and attenuation is reviewed, with particular emphasis on exploitation of the complementarity of forced oscillation and microcreep tests. Relatively fine-grained synthetic materials, which have the twin advantages of controlled microstructure and resistance to thermal cracking, have been the focus of much of the recent experimental work. Results representative of the low-strain-amplitude linear regime for low-carbon iron alloys and FO90 olivine and CaTiO3 perovskite polycrystals indicate that dissipation and associated shear modulus dispersion both increase monotonically with increasing temperature and decreasing frequency. The extent of the departure from elastic behaviour in these generally fine-grained materials appears to be sensitive to both grainsize and impurity content. The viscous behaviour is apparently dominated by grain-boundary sliding accommodated by grain-scale diffusion; diffusion over more restricted spatial scales probably facilitates anelastic relaxation involving the reversible (normal) migration and elastically accommodated sliding of grain-boundary segments. Difficulties in explaining the behaviour of relatively coarse-grained fcc iron with such a model suggest that linear dislocation migration processes may be responsible for its viscoelasticity. A tentative extrapolation in grainsize of the Andrade rheology determined from forced oscillation and microcreep experiments on fine-grained FO90 olivine somewhat underestimates the levels of attenuation typical of the Earth's upper mantle, increasing the likelihood that other (dislocation-related) mechanisms dominate the viscoelastic behaviour at mantle grainsizes.

Jackson, Ian

5

Measurements of rain drop size distributions and estimation of radio-wave attenuation coefficients  

NASA Astrophysics Data System (ADS)

Results of photoelectron-detector measurements of rain drop size distributions carried out near Dubna, USSR during May-September, 1987 are presented. It is shown that, for large and small drop diameters, these distributions differ from the Marshall-Palmer ones. Radio-wave attenuation coefficients are evaluated for such distributions.

Zakharian, M. V.; Kornilov, L. N.; Pozhidaev, V. N.

1989-10-01

6

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

7

Regional dependence of very low-frequency sound attenuation in the deep sound channel: Correlation with internal wave measurements  

NASA Astrophysics Data System (ADS)

The most promising mechanism for the very low-frequency sound attenuation observed in the deep sound channel is diffusive scattering by internal waves, Mellen, et al. (1976) have obtained estimates for the extra attenuation using the Garrett-Munk internal wave model and found consistency with the lower experimental values reported. Kibblewhite, et al, (1978) have shown a definite regional dependence in the Pacific. This paper compares regional oceanographic measurements with the Garrett-Munk internal wave model and also correlate local acoustic measurements with estimates of the extra attenuation.

Browning, D. G.; Fecher, M. J.; Mellen, R. H.

1981-09-01

8

A comparison of theory and laboratory measurements of wave propagation and attenuation in grease ice  

Microsoft Academic Search

In an experimental study using a wave tank in a laboratory cold room we determine the dispersion relation and amplitude attenuation for surface waves propagating through different thicknesses of grease ice. We compare our results to two ice rheology models: the mass-loading model, which predicts a wavelength decrease relative to open water, and an infinite depth viscous fluid model, which

Karl Newyear; Seelye Martin

1997-01-01

9

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

10

Measurement of alkali-silica reaction progression by ultrasonic waves attenuation  

SciTech Connect

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. For this study, results of both methods were compared with expansion and mass variation. One reactive concrete mixture was made with reactive aggregate, and one other mixture, incorporating non-reactive aggregate, was made as a control. Specimens were kept at 38 deg. C in a 1 mol l{sup -1} NaOH solution to accelerate the reaction. Attenuation of transmitted ultrasonic waves appeared to be more appropriate for the evaluation of ASR-damage compared with pulse velocity. The attenuation of accelerated reactive concrete cylinders increased by 90% after 1 year while it increased by 40% for the non-reactive concrete used as a control. Major part of the attenuation increase in the non-reactive concrete is due to liquid absorption. This work suggests that in-situ non-destructive techniques based on ultrasonic wave attenuation, like ultrasonic attenuation tomography, should be developed in order to evaluate the development of ASR in concrete structures. Petrographic examination confirmed that damage to concrete is associated with ASR.

Saint-Pierre, Francois [Centre de Recherche sur les Infrastructures en beton - CRIB, Civil Engineering Department, Universite de Sherbrooke, J1K 2R1 (Canada); Rivard, Patrice [Centre de Recherche sur les Infrastructures en beton - CRIB, Civil Engineering Department, Universite de Sherbrooke, J1K 2R1 (Canada)]. E-mail: Patrice.Rivard@Usherbrooke.ca; Ballivy, Gerard [Centre de Recherche sur les Infrastructures en beton - CRIB, Civil Engineering Department, Universite de Sherbrooke, J1K 2R1 (Canada)

2007-06-15

11

Experimental Measurements Of Seismic Wave Speeds And Attenuation In CO2 Saturated Porous Rocks  

NASA Astrophysics Data System (ADS)

Due to the sensitivity of seismic waves to pore fluid contents, time lapse seismology is regarded as a promising monitoring method for geological CO2 sequestration projects and is employed in all industrial scale projects (Sleipner, Weyburn, In Salah). Therefore, understanding the effect of CO2 as a pore fluid on the overall rock seismic response is critical, and it is particularly interesting as CO2 can be in gas, liquid, or supercritical phases even at the relatively modest pore pressures and temperatures in the uppermost kilometer of the earth's crust. To address this issue, ultrasonic P- and S-wave pulse transmission experiments were carried out on fully CO2 saturated samples of a synthetic porous ceramic, Berea and Fontainebleau sandstones, and carbonates under a variety of temperatures and pressures representative of conditions expected in volcanic edifices and geological sequestration projects. The synthetic sample was chosen because of its lack of microcracks, which can complicate the acoustic behavior of real rocks. Although this sample is extremely porous (58%) and is not reflective of real reservoir rocks, its large porosity allows the overall rock behavior to be more susceptible to the changes in the physical properties of the pore fluid; this could provide an extreme end member understanding on the rock physics involved with CO2 as the pore fluid. Laboratory results show waveform variations (velocity, amplitude, attenuation) in response to CO2's varying phase state. For the ceramic rod, CO2 phase changes (gas to liquid and gas to supercritical fluid) are marked by a drop in velocities of 4-5% likely due to the increased density of the liquid or the supercritical fluid relative to the gas. Wave attenuation increases with pore pressure and with frequency. The measured elastic wave velocities showed good agreement with Biot's model in this highly porous sample. The real sandstones, in contrast, display more complicated behaviour at the point of the phase transition. The abruptness in the velocity change differs significantly between the gas-liquid and gas-supercritical fluid transitions; and the gradual variations seen for the latter suggest that this will be difficult to detect using seismic reflection methods.

Njiekak, G.; Yam, H.; Kofman, R. S.; Chowdhury, M.; Schmitt, D. R.

2011-12-01

12

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

13

Global teleseismic S wave attenuation  

NASA Astrophysics Data System (ADS)

We have measured 140,000 teleseismic S wave spectra from 150 deep (focal depth > 200 km) earthquakes recorded at 890 broadband global and regional network stations up to 0.7 Hz. We have analyzed these data to constrain the (1) epicentral distance and (2) spatial variation of the shear wave attenuation parameter tS*. tS* increases by about 2 s between 30° and 98°. The increase in tS* is consistent (correlation coefficient of 0.9) with global QS profiles (Dziewonski and Anderson, 1981; Durek and Ekström, 1996; Lawrence and Wysession, 2006). However, there are well resolved departures in the distance dependence of tS*. Most notably, tS* is lower than PREM-predicted values between 58°-64°. This indicates a reduction in shear attenuation from the global average at ~1600 km depth beneath Central America, eastern Asia, and Alaska. These regions have previously been identified as downwelling mantle regions on the basis of seismic tomography (Grand et al., 1997), plate reconstructions (Ricard et al., 1993), and waveform analysis (Lay et al., 2004). Stations terms of tS* represent the spatial variation of attenuation in the upper mantle. Using multi-channel cross-correlation and least-squares inversion of differential spectra we resolve high attenuation in the upper mantle beneath western North America, western Europe, and eastern Africa. Attenuation is low beneath eastern North America, the Baltic regions, and central and southern Africa. This variation correlates well with global variations in heat flow (Pollack et al., 1993) and crustal age (Mooney et al., 1995).

Hwang, Y.; Ritsema, J. E.

2009-12-01

14

Radial upper mantle attenuation structure of inactive back arc basins from differential shear wave measurements  

NASA Astrophysics Data System (ADS)

We measure differential attenuation between sS-S and sScS-ScS phase pairs to characterize the variation of attenuation with depth in the upper mantle of five inactive back arc basins: the Kuril Basin, Sea of Japan, Banda Sea, the Celebes and Sulu Seas, and the Shikoku Basin. A spectral radio technique is used to measure the differential attenuation operator of the transversely polarized waveforms over a frequency band of 10 to 83 mHz. Two algorithms are employed to compute the vertically averaged attenuation structure: a spectral stacking procedure and a least squares inversion. In the spectral stacking method, the indiviual spectra are corrected for the elastic structure at the sS or sScS bounce point, and the differential attenuation operator is computed by spectral division. The attenuation operators are then normalized and stacked by source depth to obtain more stable spectra, and an average delta t(*) for sources within a restricted depth range is obtained from the slope of the log-amplitude spectrum. A model for the depth dependent Q structure is then calculated from the delta t(*) measurements assuming Q is frequency independent. Alternatively, delta t(*) measurements for individual phase pairs are made using a similar technique and analyzed by ray tracing and a least squares inversion to obtain the Q(exp -1) estimates. The Q results obtained from the stacking and inversion methods are generally in good agreement. The Q structures for the various back arc regions are similar to each other within the uncertainties of the derived Q models. The most striking feature of this study is the observation of very strong attenuation concentrated at shallow depths (less than 160 km) in the upper mantle beneath these basins.

Flanagan, Megan P.; Wiens, Douglas A.

1994-08-01

15

Thermal structure beneath Tanzania from attenuation measurements using teleseismic P wave spectra  

NASA Astrophysics Data System (ADS)

Using P wave spectral amplitude ratios from deep-focus earthquakes recorded at broadband seismic stations of the Tanzania PASSCAL network, we estimate the regional variation of sublithospheric mantle attenuation beneath the Tanzania craton and the eastern branch of the East African Rift. To constrain the thermal anomaly beneath the eastern rift, we analyze P wave attenuation beneath the Tanzania seismic network and the adjacent rift system in combination with velocity anomalies determined from seismic tomography. We conclude that the observed variation in t* can be explained by variation in Qp in the sublithospheric mantle and obtain values of Qp ˜175 beneath the cratonic lithosphere and Qp ˜80 beneath the rifted lithosphere. By combining the Qp values and a model of P wave velocity perturbations, we estimate that the temperature beneath the rifted lithosphere (100-400km depth) is 140-280K higher than ambient mantle temperatures, consistent with the observation that the 410km discontinuity in this region is depressed by 30-40km.

Ritsema, J.; Venkataraman, A.; Nyblade, A.

2004-12-01

16

The upper mantle degree 2: constraints and inference from global mantle wave attenuation measurements  

Microsoft Academic Search

We present the results of an analysis of global lateral variations in anelasticity of the upper mantle, as measured from very long period Rayleigh waves observed on the GEOSCOPE network. Four consecutive wave trains are used on each record to eliminate uncertainty on the amplitude at the source and to take into account, in a linear manner, focussing effects due

Barbara Romanowicz

1990-01-01

17

Diffraction effects on bulk-wave ultrasonic velocity and attenuation measurements  

PubMed

The loss and phase advance due to diffraction are experimentally observed by measuring the amplitude and phase of radio frequency (rf) tone burst signals in the VHF range, in an ultrasonic transmission line consisting of a buffer rod with an ultrasonic transducer on one end, a couplant of water, and a solid specimen of synthetic silica glass. The measured results agree well with the calculated results from the exact integral expression of diffraction. The diffraction effects on the velocity and attenuation measured in this frequency range and their corrections are investigated to realize more accurate measurements. It is shown that attenuation measurements are influenced by diffraction losses and can be corrected by numerical calculations, and that velocity measurements are affected by the phase advance caused by diffraction. This investigation demonstrates that, in complex-mode velocity measurements, in which the velocity is determined from the measured phase of the signals, the true velocity at each frequency can be obtained by correction using the numerical calculation of diffraction. Based on this result, a new correction method in amplitude-mode velocity measurements is also proposed. In this new method, the velocity is determined from the intervals of interference output obtained by sweeping the ultrasonic frequency for the superposed signals generated by the double-pulse method. Velocity may be measured accurately at frequencies in the Fresnel region, and diffraction correction is essential to obtain highly accurate values with five significant figures or more. PMID:10955621

Kushibiki; Arakawa

2000-08-01

18

Seismic-wave Attenuation in the Asthenosphere  

NASA Astrophysics Data System (ADS)

Seismic-wave attenuation (1/Q) is thought to be highly sensitive to variations in temperature, and joint interpretation of attenuation and velocity models should aid in distinguishing between thermal and chemical heterogeneity in the mantle. However, global attenuation tomography has thus far contributed little to our understanding of Earth structure, and the existing 3-D global Q models show only limited qualitative agreement. The primary reason for this is that factors other than attenuation influence wave amplitude. Principally, amplitudes are affected by focusing and defocusing due to lateral velocity variations, but uncertainties in the calculation of source excitation as well as inaccuracies and problems associated with the instrument response can also obscure the attenuation signal in the data. We have developed a method to remove these extraneous effects and isolate the signal due to attenuation. We invert a large data set of fundamental-mode Rayleigh wave amplitudes in the period range 50--250 seconds simultaneously for maps of attenuation, maps of phase velocity, and amplitude correction factors for each source and receiver in the data set. Measurements of phase delay are included in the inversion as an additional constraint on velocity structure. The maps of attenuation obtained by simultaneous inversion for elastic and anelastic models contain important features that are not robustly imaged when the effect of focusing is ignored. The shallow mantle (~100--300 km) is characterized by high attenuation along western North America and along the East Pacific Rise and other ridge systems, and low attenuation within stable continental interiors. Lateral variations in attenuation are ±60--80% at these depths, with differences most pronounced between the high-Q old continental regions and low-Q mid-ocean ridges. Such large variations require the presence of areas of very low Q, and correspondingly low velocity, in the asthenosphere and underscore the importance of lateral variability in physical dispersion. Our global maps of surface-wave attenuation exhibit a strong correlation with maps of phase velocity corrected for the effect of the crust, particularly for periods < 200 seconds. The correlation suggests that the variability in both Q and velocity in the shallow upper mantle has a common origin, which is most likely thermal. At the greatest depths sampled by our data (400--500 km) a different pattern, consisting of high attenuation in the southeastern Pacific and Red Sea regions and low attenuation along several subduction zones in the Pacific, dominates.

Dalton, C. A.; Ekstrom, G.

2005-12-01

19

Lg wave attenuation in Britain  

NASA Astrophysics Data System (ADS)

The Lg wave quality factor (QLg) in Britain has been modelled using data from the UK Seismic Network, operated by the British Geological Survey. The data set consists of 631 vertical, mostly short-period recordings of Lg waves from 64 earthquakes (2.7-4.7 ML) and 93 stations. We have inverted for both regional average QLg and tomographic images of QLg, and simultaneously a source term for each event and a site term for each station for 22 frequencies in the band 0.9-10.0 Hz. The regional average model is 266f0.53 between 1.0 and 10.0 Hz and indicates that attenuation in Britain is slightly higher than in France, and significantly higher than in eastern North America and Scandinavia. Tomographic inversions at each frequency indicate that QLg varies spatially. Broadly speaking, southeastern England, the Lake District and parts of the East Irish Sea Basin, and a small region between the Highland Boundary Fault and the Southern Uplands Fault are characterized by higher than average attenuation. Southwestern England, eastern central England and northwestern Scotland are regions of relatively low attenuation. To some extent, these regions correlate with what is known about the tectonics and structure of the crust in the UK.

Sargeant, Susanne; Ottemöller, Lars

2009-12-01

20

Attenuation coefficients of Rayleigh and Lg waves  

Microsoft Academic Search

Analysis of the frequency dependence of the attenuation coefficient leads to significant changes in interpretation of seismic\\u000a attenuation data. Here, several published surface-wave attenuation studies are revisited from a uniform viewpoint of the temporal\\u000a attenuation coefficient, denoted by ?. Theoretically, ?( f) is expected to be linear in frequency, with a generally non-zero intercept ??=??(0) related to the variations of

Igor B. Morozov

2010-01-01

21

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

22

Performance characteristics of a wave attenuation for pulsed chemical lasers  

NASA Astrophysics Data System (ADS)

Parametric performance measurements are reported for a pulsed chemical laser wave attenuator. The attenuator utilizes the combined effects of flow channel area expansion, caustic water spray, and flow-through damping screens to suppress and control the pressure disturbances produced by the chemical heat release of the F2 + D2 chain reaction. Experimental results that illustrate the effects of different area expansion geometries, water spray configurations, and damping screen arrangements are presented. Capability to tune the attenuator system to provide short pressure wave clearing times is emphasized. An attenuator configuration is reported which gives a wave clearing time of 2 msec with a corresponding entropy-wave density nonuniformity of 0.001 for a 18.5/6/76.5 F2/O2/diluent gas mixture at a pulse repetition frequency of 100 Hz.

Buonadonna, V.; Weisbach, M. F.; Tong, K.-O.; McClure, J. D.

1981-06-01

23

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

24

Ultrasonic attenuation measurements in Egyptian dry compact rocks  

Microsoft Academic Search

The attenuation of ultrasonic waves in specific dry rocks is measured in laboratory. The pulse echo technique is used to determine attenuation coefficients (?) and quality factor (Q) values of different kinds of rocks in the frequency range of 1-5 MHz. The laboratory measurements showed that, the attenuation coefficients are linearly proportional to frequency (constant Q) in the considered frequency

S. M. El-Sherbiny; A. G. Hassanin; H. A. Nofal; S. M. Abd-Alkader

2003-01-01

25

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

26

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

27

Surface wave path corrections, deterministic discrimination and body wave attenuation  

Microsoft Academic Search

Rayleigh waves from the Eastern Kazakh test site recorded at Seismic research Observatory receivers have been analysed for phase-velocity dispersion, group velocity dispersion and spectral amplitude. Linear inversion theory has been used to interpret these data as arising from waves propagating in plane-layered earth models. This yields the mean shear velocity and attenuation over each path as well as the

W. E. Farrell; J. L. Stevens; J. M. Savino; B. Snkoller; L. B. Bache

1982-01-01

28

Estimates of Shock Wave Attenuation in Snow.  

National Technical Information Service (NTIS)

A simple momentum model, assuming that snow compacts to its final density at negligible stress, is used to estimate shock wave attenuation in snow. Four shock loading situations are examined: a one-dimensional pressure impulse of finite duration and insta...

J. B. Johnson

1990-01-01

29

Shear Wave Attenuation and Melting beneath the Mid-Atlantic Ridge  

Microsoft Academic Search

chanics of the intrusion process. Our approach is to measure the differential attenuation of long-period shear waves, using a spectral ratio technique, from earthquakes on the ridge and to look for variations in attenuation with propagation direction. We correct for propagation distance and, where known, the upper mantle attenuation beneath the receiving stations. The azimuthal dependence of attenuation of S

Sean C. Solomon

1973-01-01

30

Lateral Variations in Upper Mantle Shear Wave Attenuation  

NASA Astrophysics Data System (ADS)

%\\def\\tstar{t^*} %\\def\\tstarbar{\\overline{\\tstar}} %\\def\\deltstarbar{\\delta\\tstarbar} %\\def\\deg{{o\\ }} %\\def\\degn{{o}} We study the lateral variations in shear wave attenuation in the upper mantle by analyzing the spectra from S and SS arrivals from selected seismograms in the IRIS FARM database between 1988 and 1999. We use seismograms from shallow earthquakes (<=50~km depth) at epicentral distances of 40\\deg--80\\deg~ for S waves and 80\\deg--160\\deg~ for SS waves. Each spectrum is the product of source, receiver, and propagation response functions as well as local source- and receiver-side effects. We correct each spectrum for the known instrument response, a source model with an ? -2 falloff at high frequencies, and a one-dimensional Q? model. Since there are multiple receivers for each source and multiple sources for each receiver, we can approximate the source- and receiver-side terms by stacking the appropriate S log spectra. The resulting source-specific response functions include any remaining source spectrum and the effect of near-source attenuation in the upper mantle; the receiver stacks include the site response and near-receiver Q structure. We correct the SS log spectra for the appropriate source- and receiver-side stacks found from the S waves. Since attenuation in the lower mantle is small, the residual SS log spectrum approximates attenuation in the upper mantle near the SS bounce point, and can be used to estimate ? /line{t*} at frequencies between 0.01~and 0.1~Hz. The resulting bounce point ? /line{t*} measurements, which we smooth into caps of 5\\deg radius, show spatially coherent patterns of more and less attenuating regions. We will compare these patterns with our previous results using the same method for higher-frequency P wave attenuation and with other studies of lateral variations in shear wave attenuation.

Warren, L. M.; Shearer, P. M.

2001-12-01

31

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

32

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

33

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

34

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

35

Fault-zone attenuation of high-frequency seismic waves  

SciTech Connect

The authors 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. The 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 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 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,{minus}5). If fault-zones are low-Q environments, then near-source attenuation of high-frequency seismic waves may help to explain phenomenon such as f{sub max}. 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, S.; Malin, P.; Alvarez, M. (Univ. of California, Santa Barbara (USA))

1989-11-01

36

Surface acoustic wave measurements of evaporation rate  

Microsoft Academic Search

Measurements of the surface acoustic wave (SAW) attenuation versus time have been performed in liquids with a relatively high evaporation rate (acetone, ethyl acetate, etc.). The linear dependence of the SAW attenuation versus time has been observed. The possibility of determining the ‘unknown’ molecular mass of the liquid from the SAW attenuation versus time dependence is presented. The special experimental

Pavol Koštial

1996-01-01

37

Attenuation of seismic waves at regional distances  

NASA Astrophysics Data System (ADS)

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.

1984-11-01

38

Attenuation anisotropy and the relative frequency content of split shear waves  

Microsoft Academic Search

The variation of frequency-dependent seismic wave attenuation with direction (attenuation anisotropy) contains additional information to that contained in velocity anisotropy. In particular, it has the potential to distinguish between different mechanisms that can cause velocity anisotropy. For example, aligned fracturing might be expected to cause measurable velocity and attenuation anisotropy, while preferred crystal orientation leads to significant velocity anisotropy but

Andrew J. Carter; J.-Michael Kendall

2006-01-01

39

Attenuation anisotropy and the relative frequency content of split shear waves  

Microsoft Academic Search

SUMMARY The variation of frequency-dependent seismic wave attenuation with direction (attenuation anisotropy) contains additional information to that contained in velocity anisotropy. In par- ticular, it has the potential to distinguish between different mechanisms that can cause ve- locity anisotropy. For example, aligned fracturing might be expected to cause measurable velocity and attenuation anisotropy, while preferred crystal orientation leads to significant

Andrew J. Carter; J.-Michael Kendall

2006-01-01

40

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

41

Experimental Studies on Attenuation of Pressure Waves Induced by Thermal Shocks  

Microsoft Academic Search

High magnitude pressure waves are expected in the mercury-filled Spallation Neutron Source target system. An appropriate measure is needed to protect the target system from such high pressure waves. It has been known that inclusion of devices like scattering centers in the pressure field will attenuate pressure waves by scattering waves between scattering centers. A series of experiments have been

Seokho H. Kim; Rusi P. Taleyarkhan

2001-01-01

42

Millimeter wave attenuation prediction using a piecewise uniform rain rate model  

NASA Astrophysics Data System (ADS)

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.

1980-03-01

43

Evaluation of relative permittivity and conductivity of forest slab from experimentally measured data on lateral wave attenuation constant†  

Microsoft Academic Search

Many experiments have been carried out to study the absorption and scattering properties of forest vegetation on radiowaves but very little has been reported on the measurements of relative permittivity (?r) and conductivity (?) of forest slab. Due to various constraints, the in-situ measurements of ?, and ? were limited to 75 MHz. Inverse methods have reportedly been employed to

R. K. TEWARI; S. SWARUP; M. N. ROY

1986-01-01

44

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

45

Improvement of Velocity Measurement Accuracy of Leaky Surface Acoustic Waves for Materials with Highly Attenuated Waveform of the V(z) curve by the Line-Focus-Beam Ultrasonic Material Characterization System  

NASA Astrophysics Data System (ADS)

Measurement accuracies of leaky surface acoustic wave (LSAW) velocities for materials with highly attenuated waveforms of V(z) curves obtained by the line-focus-beam ultrasonic material characterization (LFB-UMC) system are investigated. Theoretical investigations were carried out and experiments were performed for TiO2-SiO2 glass (C-7972), Li2O-Al2O3-SiO2 glass ceramic (Zerodur\\textregistered), and (111) gadolinium gallium garnet (GGG) single crystal as specimens. Waveform attenuations of V(z) curves for C-7972 and Zerodur\\textregistered are greater than those for the (111) GGG single crystal. Frequency dependences of the waveform attenuations were calculated for each specimen by considering the propagation attenuation of LSAWs. The theoretical results revealed that the waveform attenuation dominantly depends upon the acoustic energy loss due to the water loading effect on the specimen surface, and that the waveform attenuation becomes smaller with decreasing frequency. Significant improvement of the measurement precision of LSAW velocities was demonstrated for each specimen using three LFB ultrasonic devices with different curvature radii R of the cylindrical acoustic lenses: R=2.0 mm at 75 MHz, R=1.5 mm at 110 MHz, and R=1.0 mm at 225 MHz; for C-7972, the precisions were improved from ± 0.0053% at 225 MHz to ± 0.0020% at 75 MHz.

Ohashi, Yuji; Arakawa, Mototaka; Kushibiki, Jun?ichi

2006-05-01

46

Development of an Experimental Set-Up for the Measurement of Acoustic Attenuation in Sea-Water and Studies of the Usefulness of Acoustic Attenuation as a Parameter in Oceanographic Research.  

National Technical Information Service (NTIS)

A senson element is described for the measurement of ultrasound wave attenuation in water. This device has been developed for in-situ measurements of the additional attenuation caused by particles or air bubbles. Results are presented for the attenuation ...

R. Barkmann

1982-01-01

47

Fluid viscosity and the attenuation of surface waves: a derivation based on conservation of energy  

NASA Astrophysics Data System (ADS)

More than a century ago, Stokes (1819-1903) pointed out that the attenuation of surface waves could be exploited to measure viscosity. This paper provides the link between fluid viscosity and the attenuation of surface waves by invoking the conservation of energy. First we calculate the power loss per unit area due to viscous dissipation. Next we calculate the power loss per unit area as manifested in the decay of the wave amplitude. By equating these two quantities, we derive the relationship between the fluid viscosity and the decay coefficient of the surface waves in a transparent way.

Behroozi, F.

2004-01-01

48

Ultrasonic P-wave and S-wave attenuation in partially frozen porous material saturated with brine  

NASA Astrophysics Data System (ADS)

Ultrasonic wave transmission measurements were conducted in order to examine the influence of ice-brine coexisting system grown in porous material on ultrasonic P- and S-waves. We observed the variations of a transmitted wave with a frequency content of 150-1000 kHz through a liquid system to a solid-liquid coexistence system, changing its temperature from 20°C to -15°C. We quantitatively estimated attenuation for porous materials with two different porosities (37.3 and 48.2 %) during the freezing of salty water in porous material by considering different distances between the source and receiver transducers. This paper is concerned with attenuation at ultrasonic frequencies of 500-1000 kHz for P-waves and 100-400 kHz for S-waves. The waveform analyses indicate that the attenuation curves reach their peak at a temperature of -3°C and gradually decrease with decreasing temperature. We found a positive correlation between the attenuation of ultrasonic waves and the existence of unfrozen brine estimated by the pulsed nuclear magnetic resonance (NMR) technique. Thus, the laboratory experiments of the present study demonstrated that ultrasonic waves with such a frequency range are significantly affected by the existence of a solid-liquid coexistence system in the porous material. In terms of a plausible mechanism for attenuation, we must consider the physical interactions between pore fluid and ice, that is, the pore microstructure and permeability in such system is important. Furthermore, We demonstrate a method that derives a more accurate measurement of ultrasonic attenuation by using sweep-type signals than by using impulse-type signals. We obtained spectral amplitude of the sweep signal in frequency-time domain using the continuous wavelet transform (CWT) and estimated attenuation in the time-frequency domain using the spectral-ratio method. The advantage of this method is independent on the effect of windowing. Finally we demonstrated the possibility of sweep signal to estimate attenuation.

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

2010-12-01

49

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

50

Field observations and modeling of wave attenuation over colonized beachrocks  

NASA Astrophysics Data System (ADS)

Beachrocks are common coastal formations, constructed through the lithification of beach sediments by carbonate cements. The objectives of the present contribution were to (a) assess the impacts of beachrock benthic communities on nearshore wave dynamics; (b) present a numerical model, developed to simulate wave propagation over shallow nearshore waters characterized by both loose sediment beds and colonized/non-colonized beachrocks; and (c) discuss the structure and dynamics of beachrock macro-benthic communities in an E. Mediterranean micro-tidal beach (Vatera, Lesbos Island, NE Aegean Sea), as well as their interactions with the wave forcing. Field measurements of wave height and flow velocity were processed to assess shoaling wave energy dissipation due to bottom friction from the colonized beachrock outcrops. The equivalent Nikuradse hydraulic roughness of the beachrock surface, estimated through spectral wave attenuation calculations, was found to be around kN=0.13 m. The corresponding wave friction factors were incorporated into a wave propagation model to obtain estimates of the wave-induced bed shear stress ?w acting on the beachrock benthic communities. Information about the structure and characteristics of the latter was obtained through the collection and analysis of samples from 15 stations along a beach transect, during two months of the year (April and September) and the results showed that benthic communities at the beachrock habitat were very similar to the ones typically found at NE Mediterranean hard substrates. Wave-induced bed shear stress ?w values were able to explain cross-shore variations in population density and biomass, both decreasing significantly above water depths of about h=1.8-2 m. The latter values corresponded, for the studied conditions, to shear stresses of about ?w=2.2 Nt/m2. The present findings clearly show that nearshore wave patterns not only control to a certain extent the spatial structure of the beachrock habitats, but can be also influenced by them. Thus, hydrodynamics and beachrocks habitats constitute a complex system which remains very little understood and demands for further investigation.

Vousdoukas, M. I.; Velegrakis, A. F.; Paul, M.; Dimitriadis, C.; Makrykosta, E.; Koutsoubas, D.

2012-10-01

51

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 field data.

Pride, S; Berryman, J; Harris, J

2003-10-17

52

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

53

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

54

Attenuation anisotropy and the relative frequency content of split shear waves  

NASA Astrophysics Data System (ADS)

The variation of frequency-dependent seismic wave attenuation with direction (attenuation anisotropy) contains additional information to that contained in velocity anisotropy. In particular, it has the potential to distinguish between different mechanisms that can cause velocity anisotropy. For example, aligned fracturing might be expected to cause measurable velocity and attenuation anisotropy, while preferred crystal orientation leads to significant velocity anisotropy but may cause only small amounts of attenuation. Attenuation anisotropy may also contain useful information about pore-fluid content and properties. We present a methodology for analysis of attenuation anisotropy, and apply it to a microseismic data set previously analysed for shear-wave splitting by Teanby et al. (2004). Attenuation anisotropy values obtained show a temporal variation which appears to correlate with the temporal variation in the velocity anisotropy. The comparison of the relative frequency content of fast (S1) and slow (S2) split shear waves is a convenient method for examining seismic attenuation anisotropy. Provided that S1 and S2 initially have the same spectral colouring, that no spectral distortion is introduced by the differences between receiver responses of geophone components, and that spectral distortion due to background noise can be ignored or corrected for, we can attribute any differences in their frequency content to attenuation anisotropy. Attenuation anisotropy, where present, should be detected by the different (approximately orthogonal) polarizations of S1 and S2 as they pass through the anisotropic medium. In the presence of attenuation anisotropy S1 and S2 should experience different levels of frequency-dependent attenuation. We quantify the differential attenuation of S1 and S2 using a scheme based on a spectral ratio method. We present results from a microseismic data set acquired in an abandoned oil well at Valhall, a North Sea oil field. The results are surprising in that sometimes the slower arrival, S2, is richer in high frequencies than the faster, S1. This appears to be contrary to results predicted by theoretical crack models for attenuation anisotropy (e.g. Hudson 1981). The mechanism responsible for these observations is not clear. Our differential attenuation attribute correlates with the angle between the strike of the inferred initial shear-wave source polarization and the fast shear-wave polarization, which suggests that the split shear wave with the larger amplitude is preferentially attenuated. Our attribute also correlates with the event backazimuth, and the minimum percentage anisotropy.

Carter, Andrew J.; Kendall, J.-Michael

2006-06-01

55

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

56

Stochastic solution to a time-fractional attenuated wave equation  

PubMed Central

The power law wave equation uses two different fractional derivative terms to model wave propagation with power law attenuation. This equation averages complex nonlinear dynamics into a convenient, tractable form with an explicit analytical solution. This paper develops a random walk model to explain the appearance and meaning of the fractional derivative terms in that equation, and discusses an application to medical ultrasound. In the process, a new strictly causal solution to this fractional wave equation is developed.

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

2012-01-01

57

Attenuation character of seismic waves in Sikkim Himalaya  

NASA Astrophysics Data System (ADS)

In this study, we investigate the seismic wave attenuation beneath Sikkim Himalaya using P, S and coda waves from 68 local earthquakes registered by eight broad-band stations of the SIKKIM network. The attenuation quality factor (Q) depends on frequency as well as lapse time and depth. The value of Q varies from (i) 141 to 639 for P waves, (ii) 143 to 1108 for S waves and (iii) 274 to 1678 for coda waves, at central frequencies of 1.5 Hz and 9 Hz, respectively. The relations that govern the attenuation versus frequency dependence are Q? = (96 ± 0.9) f (0.94 ± 0.01), Q? = (100 ± 1.4) f (1.16 ± 0.01) and Qc = (189 ± 1.5) f (1.2 ± 0.01) for P, S and coda waves, respectively. The ratio between Q? and Q? is larger than unity, implying larger attenuation of P compared to S waves. Also, the values of Qc are higher than Q?. Estimation of the relative contribution of intrinsic (Qi) and scattering (Qs) attenuation reveals that the former mechanism is dominant in Sikkim Himalaya. We note that the estimates of Qc lie in between Qi and Qs and are very close to Qi at lower frequencies. This is in agreement with the theoretical and laboratory experiments. The strong frequency and depth dependence of the attenuation quality factor suggests a highly heterogeneous crust in the Sikkim Himalaya. Also, the high Q values estimated for this region compared to the other segments of Himalaya can be reconciled in terms of moderate seismic activity, unlike rest of the Himalaya, which is seismically more active.

Hazarika, Pinki; Kumar, M. Ravi; Kumar, Dinesh

2013-10-01

58

[Attenuation of photosynthetically available radiation (PAR) in Meiliang Bay under different winds and waves].  

PubMed

Based on the successive underwater irradiance measurement in situ from Jul. 12 to 17 in 2003, the attenuation of photosynthetically available radiation (PAR) and euphotic depth in Meiliang Bay were analyzed under different winds and waves. The results showed that the downward PAR attenuation coefficients ranged from 2.63 to 4.7 m(-1), with an average of 3.63 +/- 0.47 x m(-1), and the corresponding euphotic depth ranged from 0.98 to 1.75 m, with an average of 1.29 +/- 0.18 m, which demonstrated that phytoplankton and macrophyte could not grow below 1.5 m due to the lack of adequate solar radiation. The total suspended solids resulted from wind and wave increased the attenuation of light, with the downward attenuation coefficients of PAR being 2.63, 3.72 and 4.37 x m(-1) under small, medium and large wind and wave, respectively. Significant linear correlations were found between transparence, PAR attenuation coefficient, euphotic depth and total suspended solid, especially inorganic suspended solid, while chlorophyll a was the most nonsignificant light attenuator. Multiple stepwise linear regressions showed that inorganic suspended solid was the most important light attenuator dominating the light attenuation in wind-exposed Meiliang Bay. PMID:16180769

Zhang, Yunlin; Qin, Boqiang; Chen, Weimin; Hu, Weiping; Gao, Guang; Zhu, Guangwei; Luo, Liancong

2005-06-01

59

Compressional- and shear-wave velocities and attenuation in deep-sea sediment during laboratory compaction  

NASA Astrophysics Data System (ADS)

Velocities and attenuation of compressional (50 kHz) and shear waves (100 kHz) in two deep-sea sediment samples are investigated as a function of effective pressure up to 20 MPa with simultaneous measurement of porosity, density, and permeability. In both samples, the compressional-wave velocities show a strong increase with pressure, ranging from 1683 m/s at 1 MPa to 2128 m/s at 20 MPa in a silty clay and from 1840 m/s to 2462 m/s in a foraminiferal mud. Shear wave propagation is strongly restricted at pressures below 4 and 9 MPa in the respective sample, indicating a structural change in the sediment material at critical porosity values of 0.430 and 0.397, respectively. The compressional-wave attenuation, in terms of 1/QP, varies between 0.03 and 0.08, and 0.04 and 0.07, respectively. A result previously not reported in laboratory studies is a maximum in 1/QP as a function of effective pressure observed in both samples. The shear-wave attenuation is nearly constant as a function of pressure, having average values of about 0.07. The maximum of compressional-wave attenuation occurs at the respective critical porosity for each sample. Velocities and attenuation from this experiment exhibit a systematic pattern in a QP/QS vs (VP/VS)2 representation. .

Leurer, Klaus C.

2004-10-01

60

Formation, Propagation, and Attenuation of Shocks Waves in Jammed Matter  

NASA Astrophysics Data System (ADS)

We study the formation and propagation of fully non-linear waves in jammed granular media. Close to the jamming point, an arbitrary initial distortion of the media will induce the formation of non-linear finite amplitude waves. There are two regimes in the evolution of these waves. At early times non-linear interactions dominate the propagation, leading to a temporal evolution strongly dependent on the initial distortion. At long times the propagation is characterized by a new universal regime, dominated by hydrodynamical attenuation. Here the non-linear waves evolve in a self-similar fashion, characterized by a power law attenuation whose exponent is weakly dependent on the initial pressure of the system.

Gomez, Leopoldo; Vitelli, Vincenzo

2012-02-01

61

Miniaturised ultrasonic-wave velocity and attenuation sensors for liquid  

Microsoft Academic Search

The development of miniaturized ultrasonic-wave velocity and attenuation sensors for liquids is described. The sensors employ ZnO-film\\/Pyrex-glass composite diaphragm transducers. The transducers efficiently launch spurious-free ultrasonic-waves into liquids over a wide bandwidth in VHF\\/UHF ranges. Emphasis is placed on the development of sensors used for online monitoring of industrial production processes. The sensor is made by uniting the transducer with

K.-Y. Hashimoto; Yoshihisa Yamada; Takuya Ienaka; Masatsune Yamaguchi

1992-01-01

62

Attenuation of groundwater pressure due to surface waves.  

NASA Astrophysics Data System (ADS)

For tideless seas, the groundwater flow in shallow water is governed entirely by the surface wave dynamics on the beach. As waves propagate towards the shore, they become steeper owing to the decreasing water depth and at some depth, the waves lose their stability and start to break. When waves break, waves energy is dissipated and the spatial changes of the radiation stress give rise to changes in the mean sea level, known as the set_up. Longuet-Higgins demonstrated that the mean on-shore pressure gradient due to wave set_up driver a groundwater circulation within the beach zone. Water infiltrates into the coastal aquifer on the upper part of the beach near the maximum run_up, and exfiltration occurs on the lower part of the beach face near the breaking point. The velocity of the flow as well as the amount of water circulation within the permeable beach is important for the biological status of the organisms inhabiting the beach sand, transporting organic matter and dissolved oxygen to beach body , influence on sediment transport at shallow waters and stability of engineering structures. The paper is organized in two main parts. The first part of the paper is dedicated to the formulation of the mathematical model for attenuation of pore pressure in shallow water zone when wave breaking is present. Solution of system of nonlinear equations for wave propagation on permeable beach is compared with experimental data. The main purpose of the experimental part of the paper is dealing with the analysis of sets of good quality data on pore pressure data which will serve for comparison with theoretical results. In particular, two set of data are discussed, namely data obtained during measurements in the shallow water at the Coastal Station Lubiatowo (Poland) in Southern Baltic Sea and data from the large scale laboratory experiments in the Grossen Wallenkanal in Hannover (Germany). In the first case, the set of transmittance functions between the surface waves and pore pressure in the soil at various levels and transmittance functions between the pressures recorded at different levels are compared with the developed theory. During the laboratory experiment in Hannover two components of pore pressure were clearly distinguished i.e. in the zone of non-breaking waves only so called phase resolving component induced by surface waves is observed and in the surf zone two types of pore pressure are present : phase resolving and so called phase averaged , induced by set-up phenomena (mean water level rising). The total pressure recorded by the pressure gauges is a summation of the phase-averaged and the phase-resolving components. The pore pressure gradients provide also valuable information on the kinematics of groundwater flow in the beach body. In the experiment we are not able to measure the flow velocity in a straightforward manner, but the flow velocity can be estimated from the recorded pressure gradients using the formulas resulting from the theoretical solution.

Przyborska, Anna

2010-05-01

63

Magnetic Field Dependence of the Ultrasonic Attenuation of Shear Waves in Cesium.  

National Technical Information Service (NTIS)

The magnetic field dependence of the ultrasonic attenuation of shear waves has been measured in high-purity single crystals of cesium. Measurements were made at frequencies between 15 and 87 MHz at 4.2 and 1.3K, corresponding to a range of ql from 1 to 35...

B. Keramidas G. Kaltenbach J. Trivisonno

1972-01-01

64

Attenuation of Ultrasonic Waves in Coal-Water Slurries.  

National Technical Information Service (NTIS)

Attenuation of ultrasonic waves in coal-water slurries was investigated in the frequency range of 200 kHz to 1 MNZ (up to 30% by weight). The coal used in this study was West Kentucky number nine coal with particle size ranging from 90 to 30 mu m. Attenua...

S. H. Sheen A. C. Raptis

1979-01-01

65

The Attenuation vs Frequency Characteristics of VLF Radio Waves  

Microsoft Academic Search

The theoretical dependence on frequency of the attenuation of the wave guide modes in vlf propagation is discussed in some detail. It is indicated that most of the published experimental data between 1 and 30 kc was compatible with the sharply bounded model of the ionosphere with a reflecting height of about 70 km during the day and 90 km

James Wait

1957-01-01

66

Attenuation Anisotropy and the Relative Frequency Content of Split Shear-Waves  

NASA Astrophysics Data System (ADS)

The variation of frequency-dependent seismic wave attenuation with direction (attenuation anisotropy) contains additional information to that contained in velocity anisotropy. In particular it has the potential to distinguish between different mechanisms that can cause velocity anisotropy. For example, aligned fracturing might be expected to cause both velocity and attenuation anisotropy, whilst preferred crystal orientation should lead only to velocity anisotropy. Attenuation anisotropy may also contain useful information about pore-fluid content and properties. We present a methodology for analysis of attenuation anisotropy, and apply it to a microseismic dataset previously analysed for shear-wave splitting by Teanby et al. (2004). The comparison of the relative frequency content of fast (S1) and slow (S2) split shear-waves is a convenient method for examining seismic attenuation anisotropy. Provided that S1 and S2 initially have the same spectral colouring, that no spectral distortion is introduced by the differences between receiver responses of geophone components, and that spectral distortion due to background noise can be ignored or corrected for, we can attribute any differences in their frequency content to attenuation anisotropy. Attenuation anisotropy should be detected by the different (approximately orthogonal) polarisations of S1 and S2 as they pass through the anisotropic medium. In the presence of attenuation anisotropy S1 and S2 should experience different levels of frequency-dependent attenuation. We quantify the differential attenuation of S1 and S2 using a scheme based on the spectral ratio method. We present results from a microseismic dataset acquired in an abandoned oil well at Valhall, a North Sea oil field. The results are surprising in that sometimes the slower arrival, S2, is richer in high frequencies than the faster, S1. This appears to be contrary to results predicted by theoretical crack models for attenuation anisotropy (e.g. Hudson 1981). The mechanism responsible for these observations is not clear. Our differential attenuation measurements correlate with the angles between the initial shear-wave source polarization and the crack normal, the event back azimuths, and the splitting times.

Carter, A. J.; Kendall, J.

2004-12-01

67

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

68

Attenuation and fluctuation of millimeter radio waves  

Microsoft Academic Search

This paper contains a resume of the millimeter propagation measurements conducted by the Electrical Engineering Research Laboratory of The University of Texas. These measurements were made at wavelengths of 8.6 millimeters and 4. 3 millimeters, and more recently and as yet unreported, at a wavelength of 3.35 millimeters. The 8.6 and 4.3 millimeter measurements were made at elevations of 0.25

C. W. Tolbert; A. W. Straiton

1957-01-01

69

Seismic Wave Attenuation in the Greater Cairo Region, Egypt  

NASA Astrophysics Data System (ADS)

In the present study, a digital waveform dataset of 216 local earthquakes recorded by the Egyptian National Seismic Network (ENSN) was used to estimate the attenuation of seismic wave energy in the greater Cairo region. The quality factor and the frequency dependence for Coda waves and S-waves were estimated and clarified. The Coda waves ( Q c) and S-waves ( Q d) quality factor were estimated by applying the single scattering model and Coda Normalization method, respectively, to bandpass-filtered seismograms of frequency bands centering at 1.5, 3, 6, 12, 18 and 24 Hz. Lapse time dependence was also studied for the area, with the Coda waves analyzed through four lapse time windows (10, 20, 30 and 40 s). The average quality factor as function of frequency is found to be Q c = 35 ± 9 f 0.9±0.02 and Q d = 10 ± 2 f 0.9±0.02 for Coda and S-waves, respectively. This behavior is usually correlated with the degree of tectonic complexity and the presence of heterogeneities at several scales. The variation of Q c with frequency and lapse time shows that the lithosphere becomes more homogeneous with depth. In fact, by using the Coda Normalization method we obtained low Q d values as expected for a heterogeneous and active zone. The intrinsic quality factor ( Q {i/-1}) was separated from the scattering quality factor ( Q {s/-1}) by applying the Multiple Lapse Time Domain Window Analysis (MLTWA) method under the assumption of multiple isotropic scattering with uniform distribution of scatters. The obtained results suggest that the contribution of the intrinsic attenuation ( Q {i/-1}) prevails on the scattering attenuation ( Q {s/-1}) at frequencies higher than 3 Hz.

Badawy, Ahmed; Morsy, Mamdouh A.

2012-09-01

70

Attenuation Tomography of Body Waves in Thickness-varying Layered Media  

NASA Astrophysics Data System (ADS)

The intrinsic attenuation of seismic waves, which is quantified as inverse to the quality factor (Q) of a medium, is a well-publicized and yet poorly studied subject. While it is common to deduce Q values from measured dispersion data for surface waves, previous studies on the intrinsic attenuation of body waves have relied on measurements of the waveform of first arrivals or reflections. Better understanding is needed for both solid Earth geophysics and applied seismology to quantify the contributing factors to seismic attenuation and decompose Q from other factors because Q is closely related to rock property and fluid saturation. This study focuses on forward modeling and tomographic inversion for the Q values in thickness-varying layered media. Many of the existing theoretical Q models work in such media. Our work is an extension of the deformable- layer tomography (Zhou, 2004) to dissipative media. In the first phase of this study, we evaluated, through numerical modeling the various factors contributing to the attenuation of body waves. Theoretically, there are intrinsic attenuation, which is related to rock and pore fluid properties, and attenuation due to wave propagation effects, such as geometrical spreading and energy partition across interfaces (transmission and reflection). We made several representative numerical models, and conducted forward modeling using both wave theory and ray theory to quantify the amount of the attenuation of body waves due to different factors. In the second phase, we are integrating the forward modeling with the deformable-layer tomography algorithm to develop means to invert for Q distribution in thickness-varying layer media. While the deformable-layer tomography determines layer velocities and geometry, the current work intends to invert for Q values of the thickness-varying model layers as well as parameters associated with interface energy partition and geometric spreading. In the third phase, we plan to apply the methodology of attenuation tomography to a field dataset. The field data will be chosen based on the applicability gauged from the numerical model studies. The resultant attenuation models will be compared with the lithology and pore fluid information from well logs, so that the effectiveness of this method will be quantified with real data.

Cao, H.; Zhou, H.

2006-12-01

71

Wave-induced fluid flow in random porous media: attenuation and dispersion of elastic waves.  

PubMed

A detailed analysis of the relationship between elastic waves in inhomogeneous, porous media and the effect of wave-induced fluid flow is presented. Based on the results of the poroelastic first-order statistical smoothing approximation applied to Biot's equations of poroelasticity, a model for elastic wave attenuation and dispersion due to wave-induced fluid flow in 3-D randomly inhomogeneous poroelastic media is developed. Attenuation and dispersion depend on linear combinations of the spatial correlations of the fluctuating poroelastic parameters. The observed frequency dependence is typical for a relaxation phenomenon. Further, the analytic properties of attenuation and dispersion are analyzed. It is shown that the low-frequency asymptote of the attenuation coefficient of a plane compressional wave is proportional to the square of frequency. At high frequencies the attenuation coefficient becomes proportional to the square root of frequency. A comparison with the 1-D theory shows that attenuation is of the same order but slightly larger in 3-D random media. Several modeling choices of the approach including the effect of cross correlations between fluid and solid phase properties are demonstrated. The potential application of the results to real porous materials is discussed. PMID:15957744

Müller, Tobias M; Gurevich, Boris

2005-05-01

72

Surface wave path corrections, deterministic discrimination and body wave attenuation. Semiannual technical report  

Microsoft Academic Search

Rayleigh waves from the Eastern Kazakh test site recorded at Seismic research Observatory receivers have been analysed for phase-velocity dispersion, group velocity dispersion and spectral amplitude. Linear inversion theory has been used to interpret these data as arising from waves propagating in plane-layered earth models. This yields the mean shear velocity and attenuation over each path as well as the

W. E. Farrell; J. L. Stevens; J. M. Savino; B. Snkoller; L. B. Bache

1982-01-01

73

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

74

Attenuation of an air shock wave by perforated baffles  

SciTech Connect

One of the ways of attenuating an air shock wave (ASW) is to use a perforated shield; the parameters of the ASW behind a perforated baffle in the form of a steel sheet with holes are determined by the amplitude of the incident ASW and the sheet perforation coefficient. The authors examine the effects of the perforated shield structure on the ASW behind it and examples are given where the results can be used in the design of test chambers.

Klapovskii, V.E.; Grigor'ev, G.S.; Logvenov, A.Y.; Mineev, V.N.; Vershinin, V.Y.

1984-03-01

75

Attenuation of individual seismic wave types using various architectural enclosures for geophones  

NASA Astrophysics Data System (ADS)

A major difficulty in classifying seismic events in the near field is the existence of multiple wave types and their lack of time to separate from one another. During an impulsive seismic event, as the seismic wave components travel through a medium, the difference in their velocities results in a superimposed signal that will look drastically different at varying distances. It would be most beneficial to detect, classify and localize targets creating impulsive events if seismic sensor data could be reduced to a single wave type that has an expected shape and consistent features that do not change as a function of distance. Research was conducted to determine if measuring seismic data from within enclosures of specific architectural design could be used to attenuate specific wave types while maintaining energy of other wave types. The resulting waves produced by these geophone enclosures were then subject to testing using various algorithms to determine their ability to detect, classify, and localize seismic targets.

Schumer, Sean

2011-05-01

76

Shock wave measurements  

SciTech Connect

Much of our knowledge of the properties of matter at high pressures, from the static ruby pressure scale to shock compression at Gbar pressures, rests ultimately on the use of shock waves. Simple conservation relations define the initial and final states, leading to absolute measurements. I will describe some methods for measuring the equation of state of materials under shock loading for a variety of methods of shock production, and also describe the basis for other optical methods used widely in shock physics.

Holmes, N.C.

1995-09-12

77

Frequency-dependent attenuation of S-waves in the Kanto region, Japan  

NASA Astrophysics Data System (ADS)

Apparent, scattering, and intrinsic S-wave attenuations (QS-1, Qscat-1 and Qint-1) of the upper lithosphere in the Kanto region of Japan were measured in the 1- to 32-Hz frequency range using Multiple Lapse Time Window Analysis (MLTWA) for 115 borehole seismograms of local earthquakes. A new set of time windows for MLTWA, in which multiple isotropic scattering is assumed, was proposed and employed to estimate the frequency dependence of S-wave attenuation parameters. Scattering attenuation was found to dominate intrinsic attenuation in the S-wave attenuation mechanism at low frequencies (<2 Hz), whereas the opposite relation was observed at high frequencies. The transition is caused by the different frequency dependences of Qscat-1(? f -1.5) and Qint-1(? f -0.7) at this frequency. Interestingly, Qscat-1 is almost frequency independent at frequencies >8 Hz, which implies the self-similar nature of short-wavelength heterogeneities in the upper lithosphere. In terms of the upper lithosphere of the Kanto region, these results may indicate that the random heterogeneities characterized by the Gaussian autocorrelation function with a fractional fluctuation ? ? 10% and a correlation length a ? 2 km are superimposed on the weak background self-similar heterogeneity.

Yoshimoto, K.; Okada, M.

2009-09-01

78

Crack closure and healing studies in WIPP (Waste Isolation Pilot Plant) salt using compressional wave velocity and attenuation measurements: Test methods and results.  

National Technical Information Service (NTIS)

Compressional wave ultrasonic data were used to qualitatively assess the extent of crack closure during hydrostatic compression of damaged specimens of WIPP salt. Cracks were introduced during constant strain-rate triaxial tests at low confining pressure ...

N. S. Brodsky

1990-01-01

79

New method of spatial superposition of attenuated waves for ultrasound field modelling.  

PubMed

The objective of this work is the contrary issues of ultrasonic diagnostics in medicine when modern requirements for resolution are in conflict with strict safety issues. There is only one way to make progress by starting to take into account the attenuation in biological tissues and the wave diffraction phenomena. The aim of this work is to develop the flexible ultrasound field model implemented in routine algorithms of digital signal processing. The method consists of the calculation of plane wave propagation and the calculation of an ultrasound signal field. On the basis of the spatial impulse response of an aperture for calculation of space-spread ultrasound signals and the spectrum decomposition method for modelling plane wave propagation in lossy media, the modified method of spatial superposition of attenuated waves was developed. Using the method of equidistant line calculation the time and frequency features of the ultrasound signal field caused by the geometry and dynamics of the aperture, the attenuation and velocity dispersion in the medium are determined. The method was successfully applied to the investigation of the system for intracranial media monitoring, where a new measurement channel based on the changes of attenuation and dispersion in intracranial medium has been implemented. PMID:12160052

Jurkonis, R; Lukosevicius, A

2002-05-01

80

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

81

Elastic-wave velocity and attenuation as used to define phases of loading and failure in coal. Rept. of Investigations/1991  

SciTech Connect

The U.S. Bureau of Mines report discusses elastic wave velocity and attenuation behavior as an indicator for changes in load and structural integrity of coal samples. Measuring changes in compressional (P)-wave and shear (S)-wave attenuation and velocity under uniaxial and triaxial compression tests revealed their effectiveness for distinguishing changes in applied load and structural failure of samples. The velocity and attenuation values were used in further calculations such as ratios of P-wave to S-wave values, dynamic elastic constants, normalized velocities, and attenuation coefficients to reveal trends for loading and failure. The behavior of both P-wave and S-wave attenuation and velocity together defines distinct and consistent phases of load change and failure for uniaxial and triaxial tests. The S-wave velocity and attenuation illustrate changing axial load and initial development of microfractures within the sample preceding structural failure more clearly than those of the P-wave. The attenuation and velocity ratios and dynamic elastic constants (except the bulk modulus) respond to closure of small preexisting fractures within the coal sample with initial loading to failure of coal samples. The attenuation coefficients and normalized velocities reveal trends similar to those shown by velocity and attenuation.

Shea-Albin, V.R.; Hanson, D.R.; Gerlick, R.E.

1991-01-01

82

Ultrasound attenuation as a quantitative measure of fracture healing  

NASA Astrophysics Data System (ADS)

The monitoring of fracture healing still relies upon the judgment of callus formation and on the manual assessment of the stiffness of the fracture. A diagnostic tool capable of quantitatively measuring healing progression of a fracture would allow the fine-tuning of the treatment regime. Ultrasound attenuation measurements were adopted as a possible method of assessing the healing process in human long bones. The method involves exciting ultrasonic waves at 200 kHz in the bone and measuring the reradiation along the bone and across the fracture zone. Seven cadaveric femora were tested in vitro in intact form and after creating a transverse fracture by sawing through the cortex. The effects of five different fracture types were investigated. A partial fracture, corresponding to a 50% cut through the cortex, a closed fracture, and fractures of widths varying between 1, 2, and 4 mm were investigated. The introduction of a fracture was found to produce a dramatic effect on the amplitude of the signal. Ultrasound attenuation was found to be sensitive to the presence of a fracture, even when the fracture was well reduced. It would therefore appear feasible to adopt attenuation across a fracture as a quantitative measurement of fracture healing.

Gheduzzi, Sabina; Humphrey, Victor F.; Dodd, Simon P.; Cunningham, James L.; Miles, Anthony W.

2004-10-01

83

Attenuation of high-frequency seismic waves in northeast India  

NASA Astrophysics Data System (ADS)

We studied attenuation of S and coda waves, their frequency and lapse time dependencies in northeast India in the frequency range of 1-24 Hz. We adopted theories of both single and multiple scattering to bandpass-filtered seismograms to fit coda envelopes to estimate Q for coda waves (QC) and Q for S-waves (QS) at five central frequencies of 1.5, 3, 6, 12 and 24 Hz. The selected data set consists of 182 seismograms recorded at ten seismic stations within epicentral distance of 22-300 km in the local magnitude range of 2.5-5.2. We found that with the increase in lapse time window from 40 to 60 s, Q0 (QC at 1 Hz) increases from 213 to 278, while the frequency dependent coefficient n decreases from 0.89 to 0.79. Both QC and QS increase with frequency. The average value of QS obtained by using coda normalization method for NE India has the power law form of (96.8 +/- 21.5)f(1.03+/-0.04) in 1-24 Hz. We adopted energy flux model (EFM) and diffusion model for the multiple scattered wave energy in three-dimensions. The results show that the contribution of multiple scattering dominates for longer lapse time close to or larger than mean free time of about 60 s. The estimates of QC are overestimated at longer lapse time by neglecting the effects of multiple scattering. Some discrepancies have been observed between the theoretical predictions and the observations, the difference could be due to the approximation of the uniform medium especially at large hypocentral distances. Increase in QC with lapse time can be explained as the result of the depth dependent attenuation properties and multiple scattering effect.

Padhy, Simanchal; Subhadra, N.

2010-04-01

84

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

85

An experimental investigation of factors influencing compressional- and shear-wave velocities and attenuations in tight gas sandstones  

SciTech Connect

Results are presented for compressional and shear velocities and attenuations in fully brine-saturated tight gas cores with porosities from 3 to 11.9 percent and clay contents from 1 to 38 percent. The influence of porosity, clay content, frequency, and stress on velocities and attenuations were examined using the amplitude spectra of P- and S-waves in the frequency domain. Attenuations of samples were obtained using the spectral ratio method. For a few selected samples the attenuations were also measured using the length correlation method and these results were compared with the spectral ratio results. In tight gas sandstones, the attenuations obtained were 2 to 5 times greater than the attenuation obtained for Berea sandstone. In general, the presence of clay softens the rock grain contacts causing smaller values of compressional (V{sub P}) and shear (V{sub S}) velocities as the clay content increases. However, the V{sub P}/V{sub S} ratio was found to increase with clay content. Compressional- and shear-wave amplitude spectra exhibited a shift in peak frequency toward lower frequencies for samples with higher clay content when compared to clean samples. Velocities and attenuations were found to be frequency dependent, but the positive slope of both compressional and shear attenuations indicate that scattering starts to dominate at the lower frequency end of the ultrasonic measurements. Both V{sub P} and V{sub S} increased while both compressional and shear attenuations decreased when stress was increased.

Tutuncu, A.N.; Podio, A.L.; Sharma, M.M. [Univ. of Texas, Austin, TX (United States). Petroleum Engineering Dept.

1994-01-01

86

Determining surface wave attenuation by modeling surface wave amplitudes including finite-frequency focusing and defocusing effects  

NASA Astrophysics Data System (ADS)

We have developed a technique that uses cluster analysis method to efficiently measure Rayleigh wave phase and amplitude anomalies. Amplitude anomaly measurements have been made on the vertical components of all permanent stations recording LHZ data from IRIS. We currently consider earthquakes with Ms>5.5 between 1990 and 2004 and correct for source phase and magnitude according to the CMT. This technique leads to a large set of amplitude measurements at 7mHz, 10mHz, 15mHz and 20mHz. We discard data with erroneously large amplitude anomalies (|dlnA|>1) and inconsistent instrument responses and we only use earthquakes recorded by more than 30 stations. Out of about 250000 raw measurements for each frequency, about 140000 measurements are retained for inverting for attenuation structure. Similar to Dalton and Ekstrom (2006), phase and amplitude data are inverted together for phase velocity maps, attenuation maps, and source and receiver terms. However, we use the 2D finite frequency amplitude kernel of Zhou et al, (2004) to model the focusing-defocusing effects. Ray theory, which has been used to date, gives amplitude anomaly predictions which depend strongly on short wavelength structure and so are very sensitive to how phase velocity maps are smoothed. Our resulting attenuation maps show structures correlating well with surface tectonics, with high attenuation in regions of ridges, back-arc basins and western North America, and low attenuation in stable continental shields. The success of getting reasonable attenuation structures demonstrates the feasibility of applying 2D finite frequency amplitude kernel to real data.

Ma, Z.; Masters, G.

2011-12-01

87

Crustal Lg-wave attenuation in and around Tibetan plateau  

NASA Astrophysics Data System (ADS)

Based on regional Lg-wave data, we develop a broadband high-resolution attenuation model for Tibetan Plateau and its surrounding regions. We collect vertical component seismograms recorded at 146 stations form 232 crustal earthquakes to calculate the Lg-wave amplitude spectra. The spectra are sampled at 58 discrete frequencies distributed log evenly between 0.05 and 10.0 Hz. Both dual-station and single-station datasets are constructed for jointly inverting the Lg Q distribution and Lg wave excitation function. The maximum spatial resolution is approximately 0.8°×0.8° in well-covered areas and for frequencies between 0.5 and 2.0 Hz. The Lg Q image reveals the relations between attenuations and geological structures. The average Lg Q0 (1 Hz Q) is 280 for Tibetan Plateau (regions with elevations above 4,000 m ). The Q0 values change from the south to north by first decrease (the Himalaya: 386, Lhasa : 284, Qiangtang: 238, and Songpan-Ganze blocks: 217), and then increase ( East Kunlun: 289, West Kunlun: 330, and Qilianshan blocks: 315). The QLg distributions are consistent with the lower crust material flow around the Eastern Himalayan syntaxis and the rigid Sichuan basin. The regions surrounding the Tibetan plateau are characterized by high Q0 values (Tarim basin: 433, Altyn mountain: 517, Qaidam basin: 385, Alashan uplift: 452, Inner Mongolian platform: 444, Ordos: 395, and Sichuan basins: 456), except for Yungui Plateau which has a relatively low Q0 of 247. A statistical method is used to investigate the regional variations of the Lg Q frequency dependence. The Lg Q generally increases with the increase of frequencies but show complex frequency dependency, indicating the commonly used power-law Q model may not be appropriate within a broad frequency band. The Lg Q frequency dependence also shows regional variations.

Zhao, L.; Xie, X.; Yao, Z.

2011-12-01

88

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,

89

Material hardness and ageing measurement using guided ultrasonic waves.  

PubMed

Elastic properties of materials can be easily determined from the ultrasonic wave velocity measurement. However, material hardness cannot be obtained from the ultrasonic wave speed. Heat treatment and ageing affect the microstructure of many materials changing their hardness and strength. It has been already established that ultrasonic attenuation and dispersion are also affected by the material microstructure. It is investigated in this paper if the attenuation of ultrasonic guided waves can be correlated with the material ageing or duration of heat treatment and material hardness. To this aim six identical aluminum 2024 alloy plate specimens were subjected to different durations of heat treatment at 150°C and were inspected nondestructively propagating Lamb waves through the specimens. Attenuation of the Lamb wave was found to be inversely related to the hardness. Rockwell hardness test was performed to corroborate the ultrasonic observations. In comparison to the Rockwell hardness test the ultrasonic inspection was found to be more sensitive to the heat treatment duration and material ageing. From these results it is concluded that guided wave inspection method is a reliable and probably more desirable alternative for characterizing the hardness and microstructure of heat treated materials. Earlier investigations correlated the bulk wave attenuation with the material ageing while this work is the first attempt to correlate the guided wave attenuation to the material hardness and ageing. PMID:23047018

Korde, Nilesh; Kundu, Tribikram

2012-09-18

90

On attenuation of plane sound waves in turbulent mean flow  

NASA Astrophysics Data System (ADS)

Plane sound waves in a smooth pipe turbulent boundary layer are known to be more strongly damped when the acoustic boundary layer becomes thicker than the viscous sublayer. The attenuation constants that govern this phenomenon are accurately predicted by the mathematical model proposed by M.S. Howe [The damping of sound by wall turbulent shear layers. Journal of the Acoustical Society of America 98(3) (1995) 1725-1730. Also in: Acoustics of Fluid-Structure Interactions, Cambridge University Press, Cambridge, 1998]. This model assumes uniform mean core flow. The present paper proposes a variant of this model which is based on the assumption of parallel sheared mean core flow. Predictions of the two approaches are compared.

Dokumaci, E.

2009-03-01

91

Attenuation Anisotropy and the Relative Frequency Content of Split Shear-Waves  

Microsoft Academic Search

The variation of frequency-dependent seismic wave attenuation with direction (attenuation anisotropy) contains additional information to that contained in velocity anisotropy. In particular it has the potential to distinguish between different mechanisms that can cause velocity anisotropy. For example, aligned fracturing might be expected to cause both velocity and attenuation anisotropy, whilst preferred crystal orientation should lead only to velocity anisotropy.

A. J. Carter; J. Kendall

2004-01-01

92

Wave Attenuation in Effective Models Describing Porous and Fractured Media Saturated by a Fluid  

Microsoft Academic Search

Wave attenuation is introduced in the effective model of media that consists of alternating elastic and fluid layers. This attenuation is due to the friction on the boundaries between elastic and fluid layers and is described by additional terms in equations of the effective model. An investigation of these equations allows one to derive expressions of the attenuation coefficients for

L. A. Molotkov

2005-01-01

93

Laboratory Measurements of Velocity and Attenuation in Sediments  

SciTech Connect

Laboratory measurements are required to establish relationships between the physical properties of unconsolidated sediments and P- and S-wave propagation through them. Previous work has either focused on measurements of compressional wave properties at depths greater than 500 m for oil industry applications or on measurements of dynamic shear properties at pressures corresponding to depths of less than 50 m for geotechnical applications. Therefore, the effects of lithology, fluid saturation, and compaction on impedance and P- and S-wave velocities of shallow soils are largely unknown. We describe two state-of-the-art laboratory experiments. One setup allows us to measure ultrasonic P-wave velocities at very low pressures in unconsolidated sediments (up to 0.1 MPa). The other experiment allows P- and S-wave velocity measurements at low to medium pressures (up to 20 MPa). We summarize the main velocity and attenuation results on sands and sand - clay mixtures under partially saturated and fully saturated conditions in two ranges of pressures (0 - 0.1 MPa and 0.1 - 20 MPa) representative of the top few meters and the top 1 km, respectively. Under hydrostatic pressures of 0.1 to 20 MPa, our measurements demonstrate a P- and S-wave velocity-dependence in dry sands around a fourth root (0.23 -0.26) with the pressure dependence for S-waves being slightly lower. The P- velocity-dependence in wet sands lies around 0.4. The Vp-Vs and the Qp-Qs ratios together can be useful tools to distinguish between different lithologies and between pressure and saturation effects. These experimental velocities at the frequency of measurement (200 kHz) are slightly higher that Gassmann's static result. For low pressures under uniaxial stress, Vp and Vs were a few hundred meters per second with velocities showing a strong dependence on packing, clay content, and microstructure. We provide a typical shallow soil scenario in a clean sand environment and reconstruct the velocity profile of such a sediment packet.

Zimmer, M A; Berge, P A; Bonner, B P; Prasad, M

2004-06-08

94

Shear Wave Velocity, Seismic Attenuation, and Thermal Structure of the Continental Lithosphere  

Microsoft Academic Search

Theoretical models based on laboratory studies of dissipation of energy in the crystalline rocks typical for the Earth's mantle suggest a temperature dependence of attenuation through the activation energy. We therefore compare global maps of the thermal structure of the continental lithosphere with the inverse attenuation of seismic shear waves Qs and seismic velocity Vs as determined from surface wave

M. Billien; I. M. Artemieva; J. Leveque; W. D. Mooney

2002-01-01

95

A Rayleigh-Wave Attenuation Method for Crack Depth Determination in Asphalt Beams  

NASA Astrophysics Data System (ADS)

It has been established through research on concrete structures that the attenuation of surface waves is sensitive to the presence of a surface-breaking obstructing its path. This is the basis for a non-destructive crack depth measurement technique to quantitatively establish the extent of damage on a pavement subject to of top-down cracking. A previously developed self-compensating technique was applied to asphalt concrete beams constructed with a variety of crack and notch configurations. In the study different notch geometries and the effect of crack width, by comparing results from saw-cut notches to those of narrow cracks, were examined. Two types of impact sources were used and the results obtained were compared to each other. The frequency-dependent signal transmission coefficient was measured at 30 and 50 mm spacing for both undamaged and cracked beams. A single relationship between signal attenuation and crack depth can be attained by normalizing the crack depth with respect to the wavelength. Although the frequency response of a beam is different to that of a slab, the viability of Rayleigh wave attenuation measurements in asphalt pavement surfaces was proved if certain corrections are considered. The method may provide a non-destructive means to determine the depth of cracks in asphalt, such as it does in concrete, with the future understanding of certain phenomena encountered in this work.

Gibson, Alex; Gallo, Gonzalo E.

2004-02-01

96

Numerical simulation of ultrasonic wave propagation in anisotropic and attenuative solid materials.  

PubMed

The axisymmetric elastodynamic finite element code developed is capable of predicting quantitatively accurate displacement fields for elastic wave propagation in isotropic and transversely isotropic materials. The numerical algorithm incorporates viscous damping by adding a time-dependent tensor to Hooke's law. Amplitude comparisons are made between the geometric attenuation in the far field and the corresponding finite element predictions to investigate the quality and validity of the code. Through-transmission experimental measurements made with a 1 MHz L-wave transducer attached to an aluminum sample support the code predictions. The algorithm successfully models geometric beam spreading dispersion and energy absorption due to viscous damping. This numerical model is a viable tool for the study of elastic wave propagation in nondestructive testing applications. PMID:18267605

You, Z; Lusk, M; Ludwig, R; Lord, W

1991-01-01

97

State-of-the-Art for Assessing Earthquake Hazards in the United States. Report 10. Attenuation of High-Frequency Seismic Waves in the Central Mississippi Valley.  

National Technical Information Service (NTIS)

This study was concerned with the attenuation of high-frequency earthquake waves in the central Mississippi valley. The data were obtained from seismographs which measured the vertical component of ground motion. Recording was on analog magnetic tape and ...

J. J. Dwyer O. W. Nuttli

1978-01-01

98

Frequency-dependent Attenuation of High-frequency P and S Waves in the Upper Crust in Western Nagano, Japan  

NASA Astrophysics Data System (ADS)

Borehole seismograms from local earthquakes in the aftershock region of the 1984 western Nagano Prefecture, Japan earthquake were analyzed to measure the frequency-dependent characteristics of P- and S-wave attenuation in the upper crust. The records from a three-component velocity seismometer at the depth of 145m exhibit high S/N-ratio in a wide frequency range up to 100 Hz. Extended coda normalization methods were applied to bandpass-filtered seismograms of frequencies from 25 to 102 Hz. For the attenuation of high-frequency P and S waves, our measurements show QP-1 = 0.052ƒ-0.66 and QS-1 = 0.0034ƒ-0.12 respectively. The frequency dependence of the quality factor of S waves is very weak as compared with that of P waves. The ratio of QP-1/QS-1 is larger than unity in the entire analyzed frequency range.

Yoshimoto, K.; Sato, H.; Iio, Y.; Ito, H.; Ohminato, T.; Ohtake, M.

99

Toward improving global attenuation models: Interpreting surface-wave amplitudes with approximate theories  

NASA Astrophysics Data System (ADS)

Surface-wave amplitudes provide the primary constraint on upper-mantle anelastic structure and are also sensitive to small-scale elastic structure through focusing effects. However, the use of amplitudes for seismic imaging presents several challenges. One, amplitudes are affected not only by propagation through anelastic and elastic heterogeneity but also by uncertainty in the source excitation, local receiver structure, and instrument response. Two, accounting for focusing and defocusing effects, which is important if amplitudes are to be used to study anelasticity, depends considerably on the chosen theoretical treatment. Three, multiple scattering of seismic energy by elastic heterogeneity can be mapped into attenuation, especially at high frequencies. With the objective of improving our ability to image mantle seismic attenuation using real amplitude observations, we investigate how approximations in the theoretical treatment of wave excitation and propagation influence the interpretation of amplitudes. We use a spectral-element wave-propagation solver (SPECFEM3D_GLOBE) to generate accurate seismograms for global Earth models containing one-dimensional attenuation structure and three-dimensional variations in seismic velocity. The seismograms are calculated for 42 realistically distributed earthquakes. Fundamental-mode Rayleigh wave amplitudes in the period range 50--200 seconds are measured using the approach of Ekström et al. (1997), for which PREM is the assumed Earth model. We show that using the appropriate local seismic structure at the source and receiver instead of PREM has a non-negligible effect on the amplitudes and improves their interpretation. The amplitudes due to focusing and defocusing effects are predicted for great-circle ray theory, exact ray theory (JWKB theory), and finite-frequency theory. We assess the ability of each theory to predict amplitudes that agree with those measured from the SPECFEM synthetics for an Earth model that contains short-wavelength velocity structure and one that does not. We also evaluate to what extent unmodeled focusing and scattering effects can be mapped into anelastic heterogeneity.

Dalton, C. A.; Hjorleifsdottir, V.; Ekstrom, G.

2011-12-01

100

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

101

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

102

Sediment non-linearity and attenuation of seismic waves: a study of accelerograms from Lefkas, western Greece  

Microsoft Academic Search

We investigate the dependence of the S-wave high-frequency spectral-decay parameter, ? (“kappa”) — a measure of wave attenuation — on ground-motion amplitude. 21 three-component accelerograms from two adjacent sediment sites in the town of Lefkas, western Greece, are used, representing 17 earthquakes with magnitudes Mw 4.7–7.0 and hypocentral distances 12–93km. Recorded peak horizontal ground accelerations (PGA) and velocities (PGV) are

P. Dimitriu; N. Theodulidis; P. Hatzidimitriou; A. Anastasiadis

2001-01-01

103

Modelling Short Duration Shock Wave Attenuation in Explosives.  

National Technical Information Service (NTIS)

The HULL hydrocode is used to predict the shock attenuation within a non-initiating explosive target following thin flyer plate impact. The attenuation relationship between the flyer plate thickness and the initial velocity is investigated. Agreement betw...

J. Waschl R. Kummer

1992-01-01

104

One hertz seismic attenuation for low frequency gravitational waves interferometers  

Microsoft Academic Search

This article describes a mechanical vertical attenuation system capable to provide large attenuation factors above 1Hz. This system is derived from, and improves, the passive Geometric Anti-Spring seismic attenuation filters minimizing their vertical resonant frequency by means of a tunable electromagnetic spring mounted in parallel with the main spring. The tunable spring is also used to compensate thermal drift in

Maddalena Mantovani; Riccardo Desalvo

2005-01-01

105

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; Sams, M.S. [Imperial College of Science, Technology and Medicine, London (United Kingdom). Dept. of Geology

1997-03-01

106

New Hearing Protector Attenuation Measurement Method.  

National Technical Information Service (NTIS)

Bone conduction loudness balance (BCLB), a new method for determining the attenuation of hearing protective devices (HPDs), was evaluated. When using BCLB for earplug testing with headphones, pure tones of equal frequency can be used for both the air cond...

M. J. Ellenbecker T. W. Rimmer

1995-01-01

107

A three-dimensional model of wave attenuation in the marginal ice zone  

Microsoft Academic Search

A three-dimensional model of wave scattering by a large array of floating thin elastic plates is used to predict the rate of ocean wave attenuation in the marginal ice zone in terms of the properties of the ice cover and the incoming wavefield. This is regarded as a small step toward assimilating interactions of ocean waves with areas of sea

L. G. Bennetts; M. A. Peter; V. A. Squire; M. H. Meylan

2010-01-01

108

Extracting the Green's function of attenuating heterogeneous acoustic media from uncorrelated waves  

Microsoft Academic Search

The Green's function of acoustic or elastic wave propagation can, for loss-less media, be retrieved by correlating the wave field that is excited by random sources and is recorded at two locations. Here the generalization of this idea to attenuating acoustic waves in an inhomogeneous medium is addressed, and it is shown that the Green's function can be retrieved from

Roel Snieder

2007-01-01

109

Measurements of the propagation of UHF radio waves on an underground railway train  

Microsoft Academic Search

Measurements of the natural propagation of UHF radio waves on an underground train are reported. Of prime interest are the natural propagation attenuation and the median signal level behavior. The propagation attenuation rates or the median signal level behaviors are found to correlate with the train carriages and frequency. On the front carriage, the propagation attenuation rate is 54 dB\\/100

Y. P. Zhang; Z. R. Jiang; T. S. Ng; J. H. Sheng

2000-01-01

110

Wave attenuation and sediment transport over an intertidal sand flat on the Fraser River Delta (Invited)  

NASA Astrophysics Data System (ADS)

This paper describes the results of two instrument field studies to examine sediment transport processes and wave attenuation across Roberts Bank, a sandy intertidal bank on the Fraser River Delta. The field work was completed as part of a three-year study of the sensitivity of Roberts Bank to sea level rise and changing storminess. It was hypothesized that the response of the mudflats and salt marshes along the landward margin of the delta were dependent on the ability of the fronting sand flat to attenuate wave height and energy. The attenuation of wave height and energy was monitored at four stations along a shore-normal transect between December 23, 2003 and February 10, 2004. The attenuation varied with the relative wave height ratio (Hs h-1) along the seaward margin, with dissipation increasing as water depths decrease and/or incident wave heights increase. Under the most dissipative conditions observed (Hs h-1 ? 0.25), the exponential decay coefficient reached 0.00045. This decay coefficient is an order of magnitude smaller than predicted by a simple wave transformation model due to the relatively large wind fetch over the sand flat. Despite the maintenance of wave energy, the range of wave heights remains constrained in the landward direction, with the frequency of waves capable of entraining sediment on the sand flat decreasing from 11% at the outer flat to 2% at the inner stations. In response, bed elevation change and depth of sediment activation are greatest at the seaward margin and decrease exponentially landward. It is argued that the sand flat provides a natural barrier that defines the extent of mudflat development by limiting the potential for sediment resuspension and morphological change on the mudflat. The ability of the sand flat to provide continued protection to the mudflats and salt marshes depends on how it will respond to change in sea level and storminess. A comparison of the dimensionless, current-induced skin friction with the critical skin friction for the initiation of sediment motion suggests that the currents are only capable of entraining sediment briefly with the ebbing tide or when enhanced by the wind. Since these wind-generated currents are associated with storm waves, which typically exceed the critical skin friction, they have a disproportionately large impact on the direction of the sediment transport. An energetics-based model, driven by locally measured near-bottom currents, is used to characterize the rate and direction of bedload and suspended load transport. The largest transport rates were predicted in response to storm waves and were initially directed onshore with weak oscillatory transport and alongshore by wind-generated currents that turned offshore as the ebbing currents strengthened. The integrated transport (over the duration of the study) was predicted to be weakly offshore, but this is ascribed to the coincidental occurrence of storm activity with the ebbing tide. It is argued that if storm waves were equally distributed between the flood and ebb phases of the tide, the wind-generated currents and oscillatory transport would lead to a partly onshore-directed net transport during storms, which may contribute to sand flat accretion and maintenance of form as it migrates landward in response to sea level rise.

Houser, C.; Hill, P. R.

2010-12-01

111

The local amplification of surface waves: A new observable to constrain elastic velocities, density, and anelastic attenuation  

NASA Astrophysics Data System (ADS)

The deployment of USArray across the continental U.S. has prompted developments within surface wave tomography to exploit this unprecedented data set. Here, we present a method to measure a new surface wave observable: broadband surface wave amplification that provides new and unique constraints on elastic velocities and density within the crust and upper mantle. The method, similar to its phase velocity counterpart referred to as Helmholtz tomography, initiates by constructing phase travel time and amplitude maps across the array for each period and earthquake. Spatial differential operators are then applied to evaluate the amplitude variation, as well as the effect of focusing/defocusing. Based on the 2-D damped wave equation, the amplitude variation corrected for focusing/defocusing is linked directly to both local amplification and intrinsic attenuation, which are separated by examining waves propagating in opposite directions. We apply the method to teleseismic Rayleigh waves observed across USArray between periods of 24 and 100 s and show that the observed amplification maps are strongly correlated with known geological features. Small-scale attenuation measurements are contaminated by wavefield complexities, but larger-scale anelastic attenuation is estimated reliably. The observed amplification maps compare well with predictions based on recent 3-D shear velocity models of the western U.S. that were produced from ambient noise and earthquake data. Notably, predictions based on models with different prescribed density structures demonstrate the potential for using estimates of local amplification to constrain not only 3-D velocity structure but also density.

Lin, Fan-Chi; Tsai, Victor C.; Ritzwoller, Michael H.

2012-06-01

112

Attenuation of P-Waves by Wave-Induced Fluid Flow  

SciTech Connect

Analytical expressions for three P-wave attenuation mechanisms in rocks are given and numerically-compared. The mechanisms are: (1) Biot loss, in which flow occurs at the scale of the wavelength between the peaks and troughs of a P wave; (2) squirt loss, in which flow occurs at the grain scale between microcracks the grains and the adjacent pores; and (3) mesoscopic loss, in which flow occurs at intermediate scales between the various lithological bodies that are present in an averaging volume of earth material. Each mechanism is of importance over different frequency bands. Typically, Biot loss is only important at the highest of ultrasonic frequencies (> 1 MHz), squirt-loss (when it occurs) is important in the range of 10 kHz to 1 MHz, while mesoscale loss dominates at the lower frequencies (<10 kHz) employed in seismology.

Pride, S R; Berryman, J G

2002-03-29

113

Aircraft measurements of wave cloud  

NASA Astrophysics Data System (ADS)

In this paper, aircraft measurements are presented of liquid phase (ice-free) wave clouds made at temperatures greater than -5 °C that formed over Scotland, UK. The horizontal variations of the vertical velocity across wave clouds display a distinct pattern. The maximum updraughts occur at the upshear flanks of the clouds and the strong downdraughts at the downshear flanks. The cloud droplet concentrations were a couple of hundreds per cubic centimetres, and the drops generally had a mean diameter between 15-45 ?m. A small proportion of the drops were drizzle. A new definition of a mountain-wave cloud is given, based on the measurements presented here and previous studies. The results in this paper provide a case for future numerical simulation of wave cloud and the interaction between wave and clouds.

Cui, Z.; Blyth, A. M.; Bower, K. N.; Crosier, J.; Choularton, T.

2012-05-01

114

Aircraft measurements of wave clouds  

NASA Astrophysics Data System (ADS)

In this paper, aircraft measurements are presented of liquid phase (ice-free) wave clouds made at temperatures greater than -5°C that formed over Scotland, UK. The horizontal variations of the vertical velocity across wave clouds display a distinct pattern. The maximum updraughts occur at the upshear flanks of the clouds and the strong downdraughts at the downshear flanks. The cloud droplet concentrations were a couple of hundreds per cubic centimetres, and the drops generally had a mean diameter between 15-45 ?m. A small proportion of the drops were drizzle. The measurements presented here and in previous recent studies suggest a different interaction of dynamics and microphysics in wave clouds from the accepted model. The results in this paper provide a case for future numerical simulation of wave cloud and the interaction between wave and cloud.

Cui, Z.; Blyth, A. M.; Bower, K. N.; Crosier, J.; Choularton, T.

2012-10-01

115

Attenuation in melting snow on microwave- and millimetre-wave terrestrial radio links  

Microsoft Academic Search

The scattering properties of melting snow on microwave and millimeter-wave terrestrial radio links are predicted using a new model for melting which includes coalescence. Attenuation, differential attenuation and differential phase are calculated for a horizontal path, with results at 36.25 GHz presented. Peak specific attenuation in the range 8-13 dB\\/km is expected for underspread rain with 10-15 mm\\/h rain rates.

Y. M. Jain; P. A. Watson

1985-01-01

116

Attenuation of high-frequency seismic waves beneath the central Andean plateau  

NASA Astrophysics Data System (ADS)

A map of lateral variations in upper mantle P and S wave attenuations beneath the plateau was compiled using observations of seismic waveforms from shallow- and intermediate-depth earthquakes recorded by a portable seismic array deployed in Jujuy Province, Argentina. Large differences were found in the amplitudes and frequencies of P and S waves, recorded from earthquakes at various azimuths, depths, and distances, indicating substantial variations in the upper mantle attenuation structure beneath the Altiplano-Puna plateau and adjacent foreland.

Whitman, Dean; Isacks, Bryan L.; Chatelain, Jean-Luc; Chiu, Jer-Ming; Perez, Alejandro

1992-12-01

117

Rain induced attenuation of millimeter waves radio link in Indian continent  

Microsoft Academic Search

The performance and reliability of millimeter wave radio link is degraded mainly by rain. In the present paper the aspect\\u000a of rain induced attenuation with respect to raindrop is described. How the microstructure details of rain are necessary for\\u000a estimating the rain induced attenuation in millimeter wave region are explained on the basis of the rain data for different\\u000a stations

Saxena Poonam; T. K. Bandopadhyaya

1997-01-01

118

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

119

Non-destructive Inspection of Chloride Ion in Concrete Structures Using Attenuated Total Reflection of Millimeter Waves  

NASA Astrophysics Data System (ADS)

The chloride induced corrosion of reinforcing steel bar is one of the major causes of deterioration of concrete structures. Therefore, it is essential to periodically monitor the level of chloride ion (Cl-) concentration in concrete structures. In this work, we developed millimeter wave attenuated total reflection measurement setup in order to determine the Cl- concentration in concrete structures. We prepared concrete samples with different compositions and varying Cl- concentrations and we measured their attenuated total reflectance at 65 GHz. We observed that the reflectance decreases almost linearly with the increase in Cl- concentration indicating that this technique could be used to inspect the Cl- concentration in concrete structures nondestructively.

Tripathi, Saroj R.; Inoue, Hiroo; Hasegawa, Tsuyoshi; Kawase, Kodo

2013-02-01

120

Determination of particle size distributions from acoustic wave propagation measurements  

NASA Astrophysics Data System (ADS)

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. 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.

Spelt, Peter D. M.; Norato, Michael A.; Sangani, Ashok S.; Tavlarides, Lawrence L.

1999-05-01

121

On the reliability of attenuation measurements from ambient noise cross-correlations  

NASA Astrophysics Data System (ADS)

We compare spatially averaged Rayleigh wave attenuation between 10 and 18 sec period observed on the symmetric component of ambient noise cross-correlations with regional seismic event measurements observed by the USArray Transportable Array across the western US. The ambient noise attenuation measurements are shown to be consistent with attenuation observed following an earthquake in Nevada and a mining blast in Wyoming. We demonstrate that common ambient noise data processing procedures such as temporal normalization and spectral whitening can be retained as long as the amplitudes of the cross-correlations are corrected for (1) the duration of the ambient noise cross-correlation, (2) geometrical spreading, and (3) the azimuthal variation in the strength of ambient noise sources. Correction for time-series length can be achieved accurately by dividing the empirical Green's function by the squared root-mean-squared (rms) amplitude of the trailing noise. These results provide strong justification for the ability to constrain seismic attenuation using ambient noise. However, further study of the expected asymmetry in attenuation for waves approaching (incoming) or receding from (outgoing) a central station is needed to understand the effect of uneven noise source distribution prior to estimation of local variations in attenuation.

Lin, Fan-Chi; Ritzwoller, Michael H.; Shen, Weisen

2011-06-01

122

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

123

Tomographic Reconstruction of Rainfall Fields through Microwave Attenuation Measurements  

Microsoft Academic Search

A new method is presented for estimating the space-time rainfall intensity distribution at ground level over a limited area. This is based on a tomographic technique that exploits the relationship between microwave attenuation and rainfall intensity. At each time step, the spatial distribution of rainfall intensity is calculated from a set of path-integrated microwave attenuation measurements, performed over the monitored

D. Giuli; A. Toccafondi; G. Biffi Gentili; A. Freni

1991-01-01

124

Frequency-dependent effects on global S-wave traveltimes: wavefront-healing, scattering and attenuation  

NASA Astrophysics Data System (ADS)

We present a globally distributed data set of ~400000 frequency-dependent SH-wave traveltimes. An automated technique is used to measure teleseismic S, ScS and SS traveltimes at several periods ranging from 10 to 51 s. The targeted seismic phases are first extracted from the observed and synthetic seismograms using an automated time window algorithm. Traveltimes are then measured at several periods, by cross-correlation between the selected observed and synthetic filtered waveforms. Frequency-dependent effects due to crustal reverberations beneath each receiver are handled by incorporating crustal phases into WKBJ synthetic waveforms. After correction for physical dispersion due to intrinsic anelastic processes, we observe a residual traveltime dispersion on the order of 1-2 s in the period range of analysis. This dispersion occurs differently for S, ScS and SS, which is presumably related to their differing paths through the Earth. We find that: (1) Wavefront-healing phenomenon is observed for S and to a lesser extent SS waves having passed through very low velocity anomalies. (2) A preferred sampling of high velocity scatterers located at the CMB may explain our observation that ScS waves travel faster at low-frequency than at high-frequency. (3) A frequency-dependent attenuation q(?) ~ q0 × ?-?, with ? ~ 0.2, is compatible with the globally averaged dispersion observed for S waves.

Zaroli, Christophe; Debayle, Eric; Sambridge, Malcolm

2010-08-01

125

Global Love wave overtone measurements  

NASA Astrophysics Data System (ADS)

Love wave phase velocities for fundamental and higher modes are difficult to measure because the different modes cannot easily be separated. Following Yoshizawa and Kennett (2002), we generate suites of path specific one-dimensional shear wave velocity profiles using the Neighbourhood Algorithm of Sambridge (1999a). From this family of O(104) models both fundamental and higher mode phase velocities with mutually consistent uncertainties are calculated. We have fully automated the method and analysed over forty thousand Love wave seismograms from the GDSN and GEOSCOPE global networks from 1994-2004. Our phase velocity measurements agree remarkably well with previous studies, but we have been able to enlarge the available dataset dramatically. We present global Love wave phase velocity maps (up to the fifth overtone) with unprecedented resolution due to the improved path coverage. Comparing these maps to existing tomographic models, we discern evidence of significant anisotropy in the lower mantle around a depth of 1000 km in the Pacific.

Visser, K.; Lebedev, S.; Trampert, J.; Kennett, B. L. N.

2007-02-01

126

Integrated Measurement of Soil Moisture by Use of Radio Waves.  

National Technical Information Service (NTIS)

An integrated value of soil moisture can be determined by measuring the attenuation of vertically-polarized surface radio waves that are propagated over the ground between a transmitting and receiving antenna. Soil moisture values in the root-zone region ...

D. G. Chadwick

1973-01-01

127

Anomalous shear wave attenuation in the shallow crust beneath the Coso volcanic regionn, California ( USA).  

USGS Publications Warehouse

We use seismograms of local earthquakes to image relative shear wave attenuation structure in the shallow crust beneath the region containing the Coso volcanic-geothermal area of E California. Seismograms of 16 small earthquakes show SV amplitudes which are greatly diminished at some azimuths and takeoff angles, indicating strong lateral variations in S wave attenuation in the area. 3-D images of the relative S wave attenuation structure are obtained from forward modeling and a back projection inversion of the amplitude data. The results indicate regions within a 20 by 30 by 10 km volume of the shallow crust (one shallower than 5 km) that severely attenuate SV waves passing through them. These anomalies lie beneath the Indian Wells Valley, 30 km S of the Coso volcanic field, and are coincident with the epicentral locations of recent earthquake swarms. No anomalous attenuation is seen beneath the Coso volcanic field above about 5 km depth. Geologic relations and the coincidence of anomalously slow P wave velocities suggest that the attenuation anomalies may be related to magmatism along the E Sierra front.-from Authors

Sanders, C.; Ho-Liu, P.; Rinn, D.; Hiroo, Kanamori

1988-01-01

128

Influence of attenuation on the behavior of refracted elastic waves at the interface between anisotropic media  

Microsoft Academic Search

During the ultrasonic non-destructive evaluation of complex materials, like multilayer or composite materials, the behavior of the ultrasonic waves at the interface of samples is strongly dependent upon the anisotropy as well as the attenuation characteristics of the propagation media. In the generally arbitrary case, the incident wave is assumed to be inhomogeneous. Therefore the application of the Snell–Descartes laws

Morched Ben Amor; Bruno Rogé; Mohamed Hédi Ben Ghozlen; Patrick Lanceleur

2002-01-01

129

Biomechanics of Salt Marsh Vegetation Applied to Wave and Surge Attenuation.  

National Technical Information Service (NTIS)

The Northern coast of the Gulf of Mexico is threatened by storm surge and waves from tropical storms. It has been long known that marsh vegetation attenuates storm surge and waves and is vital for sustaining marsh edges. However, little is known about the...

J. Chatagnier

2012-01-01

130

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

131

Sound velocity and sound attenuation measurements by dynamic light scattering  

NASA Astrophysics Data System (ADS)

Dynamic light scattering (photon correlation spectroscopy) has been applied to the determination of sound velocity and sound attenuation from the Brillouin component of the frequency spectrum scattered from a fluid sample transversed by a laser beam. In this paper the time-resolved determination of the Brillouin component is described. The measurement of the linewidth allows an accurate determination of the sound attenuation, while the central frequency is connected to the adiabatic sound velocity. Sound attenuation and sound velocity measurements are presented for the new refrigerant pentafluorethane (R125). The accuracy and possible systematic errors of this technique are discussed and compared to those obtained from other spectroscopic and acoustic techniques.

Kraft, K.; Leipertz, A.

1995-03-01

132

Propagation and attenuation of Rayleigh waves in a semi-infinite unsaturated poroelastic medium  

NASA Astrophysics Data System (ADS)

An analytical model for describing the propagation and attenuation of Rayleigh waves along the free surface of an elastic porous medium containing two immiscible, viscous, compressible fluids is developed in the present study based on the poroelastic equations formulated by Lo et al. [Lo WC, Sposito G, Majer E. Wave propagation through elastic porous media containing two immiscible fluids. Water Resour Res 2005;41:W02025]. The dispersion equation obtained is complex-valued due to viscous dissipation resulting from the relative motion of the solid to the pore fluids. As an excitation frequency is stipulated, the dispersion equation that is a cubic polynomial is numerically solved to determine the phase speed and attenuation coefficient of Rayleigh waves in Columbia fine sandy loam permeated by an air-water mixture. Our numerical results show that, corresponding to three dilatational waves, there is also the existence of three different modes of Rayleigh wave in an unsaturated porous medium, which are designated as the R1, R2, and R3 waves in descending order of phase speed, respectively. The phase speed of the R1 wave is non-dispersive (frequency-independent) in the frequency range we examined (10 Hz-10 kHz) and decreases as water saturation increases, whose magnitude ranges from 20% to 49% of that of the first dilatational wave with respect to water content. However, it is revealed numerically that the R2 and R3 waves are functions of excitation frequency. Given the same water saturation and excitation frequency, the phase speeds of the R2 and R3 waves are found to be approximately 90% of those of the second and third dilatational waves, respectively. The R1 wave has the lowest attenuation coefficient whereas the R3 wave attenuates highest.

Lo, Wei-Cheng

2008-10-01

133

Global study if seismic wave attenuation in the upper mantle behind island arcs using pP waves  

Microsoft Academic Search

Observations of striking and consistent differences in the attenuation of pP produced by mantle earthquakes and recorded by the World-Wide Standard Seismograph Network (WWSSN) provide data for mapping variations in the attenuation of high-frequency (0.5- to 2-Hz) compressional waves in the wedge of mantle above nearly all of the inclined seismic zones on earth. The data reveal several zones of

Muawia Barazangi; Wayne Pennington; Bryan Isacks

1975-01-01

134

Amplitude measurements of Faraday waves.  

PubMed

A light reflection technique is used to measure quantitatively the surface elevation of Faraday waves. The performed measurements cover a wide parameter range of driving frequencies and sample viscosities. In the capillary wave regime the bifurcation diagrams exhibit a frequency independent scaling proportional to the wavelength. We also provide numerical simulations of the full Navier-Stokes equations, which are in quantitative agreement up to supercritical drive amplitudes of epsilon approximately equal 20%. The validity of an existing perturbation analysis is found to be limited to epsilon<2.5%. PMID:11308766

Wernet, A; Wagner, C; Papathanassiou, D; Müller, H W; Knorr, K

2001-02-27

135

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

136

A Crustal Fluid Based Interpretation of the Frequency Dependent Shear Wave Attenuation Observed in the Lithosphere Beneath the Kanto Area, Japan.  

NASA Astrophysics Data System (ADS)

Seismic attenuation measurements in the band 0.01 - 10 Hz have now been reported for a large number of tectonic areas. For tectonically active regions, the measured attenuation appears higher and more frequency-dependent than for passive regions. It has been hypothesised that such an observation reflects the presence of a high density of fluid-saturated fractures along the paths of the seismic waves used to estimate the attenuation. In order to quantitatively test this hypothesis, both a seismic attenuation data set that spans a large band of frequencies and a quantitative seismic absorption model that involves fluids are needed. This hypothesis is tested here using the set of shear-wave attenuation data reported for the Kanto Area, which shows a clear maximum in attenuation near one Hz, and the squeeze-flow mechanism model (i.e. squirt-flow adapted to the field-based fracture-porosity scale and crustal hydraulic attributes), which predicts well-defined attenuation maxima. The modelling results show that the squeezing of fracture-bound saline fluid produces shear-wave Q values that match the magnitude and frequency dependence of the data-inferred shear-wave Qs. In particular, the depth-distribution of squeeze-flow Qs for the sampled area shows a zone of very high absorption and pronounced frequency dependence that correlates well with a zone of impedance contrast imaged via body wave tomographs reported for the same area. Thus, the squeeze-flow mechanism supports the hypothesis that viscous flow of crustal fluids effectively attenuates high-frequency seismic waves in the crust and so suggests a cause for the shear-wave Q versus frequency trend observed in the Kanto area.

Rouleau, P. M.

2004-05-01

137

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

NASA Astrophysics Data System (ADS)

A 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

138

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

NASA Astrophysics Data System (ADS)

A central issue in successfully applying 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 et al. (2005) model, the phase velocity and attenuation coefficient of the P1 and P2 waves which respectively have the greatest and second greatest speeds were determined for eleven soil texture classes as a function of water saturation. The slowest wave (P3) was not characterized since it does not travel far due to very high attenuation. To provide a more general result, the calculated phase velocity and attenuation coefficient were normalized by those of sand. The normalization leads the resulting dimensionless parameters to be frequency-independent in the whole range (up to 500 Hz) where Darcy's law remains valid for describing each fluid flow under wave excitation. The dimensionless 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 increases to reach a certain maximum value for different soil types and then decreases. The physical parameter controlling the phenomenon is the ratio of two effective non-wetting fluid storativity factors. Numerical results reveal that the dimensionless 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. It is also found, with very few exceptions at nearly full saturations, that the magnitude of the dimensionless phase velocity of the P2 wave is linearly associated with the intrinsic permeability, but it relates to the dimensionless attenuation coefficient of the P2 wave in an opposite manner. These results therefore provide a quantitative clue for acoustic wave method to explore the physical properties in the shallow subsurface.

Lo, W.; Yeh, C.; Tsai, C.

2006-12-01

139

Field experiments on the velocity dispersion and attenuation of acoustic waves through sandy sediments in shallow waters  

Microsoft Academic Search

The velocity dispersion and attenuation of acoustic waves though a sandy bottom in a shallow ocean were measured for a broad frequency band of 1-500 kHz using a buried horizontal hydrophone array and several broadband piezoelectric sources. The sands have a fairly uniform grain size of 0.22 mm and a porosity of 0.44. The experimental data were compared with the

Tokuo Yamamoto; Haruhiko Yamaoka; Junichi Sakakibara

2001-01-01

140

Attenuating the ice flexural wave on arctic seismic data  

Microsoft Academic Search

Among the challenges facing seismic explorationists in the arctic environment is a type of source-generated noise practically unique to this setting, the ice flexural wave. One of the strongest known coherent noises, the flexural wave originates in uniform plates of ice floating on liquid water, a situation commonly associated with both river channels and offshore sea ice. In addition to

David C. Henley

2006-01-01

141

Far infrared and submillimeter wave attenuation by clouds and rain  

Microsoft Academic Search

Newly determined optical constants for water at far infrared and submillimeter wavelengths are used to estimate water cloud and rain attenuation over the wavelength range between 12 micrometers and 2cm. For this purpose new analytic dropsize distribution models simulating fog, nimbostratus cloud, and rain corresponding to rainfall rates of 10 and 50 mm per hr. are set up. The corresponding

D. Deirmendjian

1975-01-01

142

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

143

Linking multiple relaxation, power-law attenuation, and fractional wave equations.  

PubMed

The acoustic wave attenuation is described by an experimentally established frequency power law in a variety of complex media, e.g., biological tissue, polymers, rocks, and rubber. Recent papers present a variety of acoustical fractional derivative wave equations that have the ability to model power-law attenuation. On the other hand, a multiple relaxation model is widely recognized as a physically based description of the acoustic loss mechanisms as developed by Nachman et al. [J. Acoust. Soc. Am. 88, 1584-1595 (1990)]. Through assumption of a continuum of relaxation mechanisms, each with an effective compressibility described by a distribution related to the Mittag-Leffler function, this paper shows that the wave equation corresponding to the multiple relaxation approach is identical to a given fractional derivative wave equation. This work therefore provides a physically based motivation for use of fractional wave equations in acoustic modeling. PMID:22087931

Näsholm, Sven Peter; Holm, Sverre

2011-11-01

144

Estimation of surface-wave phase velocities and attenuation coefficients in southern Korea from spatial coherency of the ambient seismic noise  

NASA Astrophysics Data System (ADS)

The measurements of the spatial coherency of the ambient seismic noise as a function of interstation distance produce distribution of surface-wave phase velocities and attenuation coefficients in southern Korea. The coherency pairs from 43 broadband stations are used for the estimation of phase velocity and attenuation coefficient in the period band of 5 - 20 seconds. From these measurements we simultaneously invert 1-D shear wave velocity and Q as a function of depth beneath southern Korea. To investigate localized velocities and attenuations associated with tectonic units, we subdivide the measurements according to the interstation paths. We retrieve lower-wave velocities and lower-quality factors in the Gyeongsang basin, Cretaceous nonmarine basin in the southeastern area.

Cho, H.; Shin, J.

2011-12-01

145

Propagation and attenuation of Lg waves in South America  

NASA Astrophysics Data System (ADS)

Characteristics of Lg waves in La Paz station LPB are analyzed. After realizing that earthquakes with oceanic path and those deep enough do not produce Lg, they were discarded. The remaining 486 earthquakes, occurred from 1974 to 1986, are considered, looking for Lg characteristics, according to origin region. Lg are guided waves SH type, originated in surficial and in subduction intermediate depth earthquakes. Apparent velocity is 3.57 km/s independent of distance, but with some dispersion (beginning often is not clear). Predominant period is 1.1 to 1.3 s. Amplitude in most cases equals P amplitude; it is normalized by dividing Lg/P, with results similar to Bath's normalized wave energy. They are transmitted efficiently through shields, poorly along cordilleran structures; from Peru Lg recording is uneven, meriting a more detailed study; from southern region (Argentina and Chile) waves are weak, but not so much as suggested by a first glance (wave period longer finds lesser recording gain). Recording in several South American stations is considered. Some earthquakes were revised. They confirm previous conclusions and help to identify efficiency of different paths and type of Lg recording, since origin regions and recording stations are at the ends of wave path. Type of recording may unveil hidden cordilleran structure in Andes-plains transition.

Cabre, Ramon Roige; Minaya, Estela Ramos; Alcocer, Ivar John; Ayala, Rene Rodolfo

1989-09-01

146

Influence of Clays and Clay Fluid Interactions on Seismic Wave Attenuation in Reservoir Rocks. Final Report, April 1990-April 1994.  

National Technical Information Service (NTIS)

In order to understand the effects of clays on attenuation of seismic waves in gas reservoir rocks, compressional and shear waves were propagated across thin layers pressed between optically smooth silica disks and through silica beads coated with clay. R...

L. R. Myer N. G. W. Cook R. Suarez-Rivera S. Ita

1994-01-01

147

Poroelastic model to relate seismic wave attenuation and dispersion to permeability anisotropy  

SciTech Connect

A transversely isotropic model with a horizontal axis of symmetry, based on the Biot and squirt-flow mechanisms, predicts seismic waves in poroelastic media. The model estimates velocity dispersion and attenuation of waves propagating in the frequency range of crosswell and high-resolution reverse vertical seismic profiling (VSP) (250--1,250 HZ) for vertical permeability value much greater than horizontal permeability parameters. The model assumes the principal axes of the stiffness constant tensor are aligned with the axes of the permeability and squirt-flow tensors. In addition, the unified Biot and squirt-flow mechanism (BISQ) model is adapted to simulate cracks in permeable media. Under these conditions, the model simulations demonstrate that the preferential direction of fluid flow in a reservoir containing fluid-filled cracks can be determined by analyzing the phase velocity and attenuation of seismic waves propagating at different azimuth and incident angles. As a result, the fast compressional wave can be related to permeability anisotropy in a reservoir. The model results demonstrate that for fast quasi-P-wave propagating perpendicular to fluid-filled cracks, the attenuation is greater than when the wave propagates parallel to the plane of the crack. Theoretical predictions and velocity dispersion of interwell seismic waves in the Kankakee Limestone Formation at the Buckhorn test site (Illinois) demonstrate that the permeable rock matrix surrounding a low-velocity heterogeneity contains vertical cracks.

Parra, J.O.

2000-02-01

148

Measurement and Modeling of Ultrasonic Attenuation in Aluminum Rolled Plate  

SciTech Connect

When fabricating a new set of calibration blocks for Aluminum 7075 plate inspections, it is advantageous that the new blocks have similar ultrasonic attenuation to existing block sets. This allows the new set to qualify under the same ASTM procedures used for older sets. In the course of surveying candidate materials for possible use as calibration blocks, some interesting attenuation results were observed. When a candidate block was cut from a thick section of rolled plate, measured back-wall attenuation values in the rolling or transverse direction were quite sensitive to position in the plate-normal direction. Such variations are presumably tied to microstructural variations within the plate, as revealed by metallography. Some measured attenuation values were found to be in good agreement with predictions of the Stanke-Kino model, while others were not. The measurements and modeling work are reviewed, and additional experiments conducted to clarify certain issues are discussed. Those additional experiments suggest that beam distortion effects, due to microstructure variations within the beam cross-section, are primarily responsible for differences between measured and predicted attenuation values.

Li, Anxiang; Kim, Hak-Joon; Margetan, Frank; Thompson, R. B. [Center for Nondestructive Evaluation, Iowa State University, Ames, IA 50011 (United States)

2006-03-06

149

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

150

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

151

Controls of Seismic Attenuation System (SAS) for the LIGO II Gravitational Wave Detector  

NASA Astrophysics Data System (ADS)

The Seismic Attenuation System (SAS) has to be actively controlled over a frequency band of up to several Hz in order to damp its own rigid body modes (inertial damping), to generate DC local and global positioning, and to reduce residual rms motion to acquire the locking of the interferometer. The control system incorporates signals from local sensors (for displacement and acceleration) and the interferometer and generates adequate feedback signals for various actuators on different levels of the SAS chain. The control system is organized in a hierarchical scheme. With a large dynamic range at higher stages of the SAS, it damps internal modes of the system which minimizes requirements for the suspension control. The control system is a Multiple Input and Multiple Output (MIMO) that can be separated to simple Single Input and Single Output (SISO) feedback loops by using fast DSP boards. SAS controls are limited to a frequency band well below 10 Hz, to avoid noise injection in the gravitational wave band. Above this frequency, the SAS behaves as a completely passive seismic attenuator. According to simulated SAS performance based on measured seismic noise, achievable residual r.m.s. motion of SAS is a few tens of nm above 100 mHz. A similar system for VIRGO has already achieved 50 nm r.m.s. displacement.

Sannibale, Virginio; Bertolini, Alessandro; Cella, Giancarlo; Kovalik, Joseph; Tariq, Hareem; Desalvo, Riccardo; Takamori, Akiteru; Marka, Szabolcz; Viboud, Nicolas

2000-04-01

152

Shallow Seismic Attenuation and Shear Waves Splitting In The Short Period Range of Deception Island Volcano (antarctica)  

NASA Astrophysics Data System (ADS)

The occurrence of a seismic series in Deception Island volcano (Antarctica), com- posed by hundreds of local volcano-tectonic earthquakes, has permitted us to study the seismic attenuation of such a volcanic environment in the short-distance and high- frequency range. This study has been performed using P, S and coda waves and ap- plying different, frequency dependent and independent, techniques. The methods used for this analysis have been: Spectral and Broadening of the Pulse, for direct P and S waves, Coda Normalization for S-waves and Single Back-Scattering model for coda waves. The results show that, in general, Q values are significantly smaller, for all the frequency range used (6-30 Hz), than those found in other volcanic and tectonic areas. The attenuation for P-waves is greater than for S-waves in the frequency in- dependent methods, with a Qb/QP ratio that ranges between 1.9 and 3.2. Comparing the Q factor obtained for S-waves we have observed clear differences as a function of the method used; the Coda Normalization Method has supplied significantly higher Q values (Qd) than the other two methods (Qb). These Qd values are similar to the Q factor for coda waves (Qc). We have interpreted this discrepancy as an effect of the methods: Coda Normalization and Single Back-Scattering methods eliminate the con- tribution of the near surface attenuation in their Q values. Comparing both Qb and Qd we have estimated the near surface attenuation under the recording site, named Qk. On the other hand, we have observed that Qd has an anomalous frequency dependence, with a minimum value at 21 Hz. This pattern is interpreted as an effect of strong scat- tering of the seismic waves in the source area of the earthquakes. Qc values depend clearly with frequency and lapse time, and the lapse time dependence is interpreted as a depth dependence of the seismic attenuation in Deception Island volcano. The de- rived Q values have allowed us to separate the contribution of intrinsic and scattering attenuation, deriving that the scattering attenuation is predominant over the intrinsic effects. Finally, in order to investigate how the heterogeneous medium of the volcanic island could produce other effects, we have measured the splitting of the shear waves of the same data set. The observations reveal that the arrival delay of the shear waves horizontal components varies between 0.02 and 0.14 seconds, a big amount if we take into account the short hypocentral distances (less than 5 km). The study of the polar- 1 ization direction indicates a main E-W direction. All these evidences reveal the strong heterogeneous structure of Deception Island volcano. 2

Martínez-Arévalo, C.; Bianco, F.; Ibáñez, J. M.; del Pezzo, E.

153

Radio-wave attenuation and sulfuric-acid vapor content in the Venus atmosphere  

Microsoft Academic Search

Radio-wave absorption in the Venus atmosphere is investigated using radio probing data on variations of the field strengths of 5-cm and 32-cm signals. It is shown that the most probable cause of cm-wave attenuation at altitudes below 50 km is absorption by sulfuric-acid vapor. Sulfuric-acid vapor contents equal to 15 ppm at 48 km and 19 ppm at 47 km

V. N. Gubenko; O. I. Iakovlev; S. S. Matiugov; A. I. Kucheriavenkov; I. R. Vaganov

1989-01-01

154

Attenuation of centimeter radio waves by two H2O phases in the atmosphere of Venus  

Microsoft Academic Search

Using data obtained by Veneras 4 through 6, the integral radio-wave absorption by the uncondensed H2O phase in the Venusian atmosphere is calculated as a function of the impact parameter for the frequency range between 9300 and 21,000 MHz. The height profile of total radio-wave attenuation by uncondensed water vapor and condensed water in the atmosphere is calculated for the

O. F. Tyrnov

1974-01-01

155

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

Microsoft Academic Search

Small local earthquakes from two aftershock sequences in Porto dos Gaúchos, Amazon craton—Brazil, were used to estimate the\\u000a coda wave attenuation in the frequency band of 1 to 24 Hz. The time-domain coda-decay method of a single backscattering model\\u000a is employed to estimate frequency dependence of the quality factor (Q\\u000a c) of coda waves modeled using , where Q\\u000a 0 is

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

2011-01-01

156

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

157

Calculation of the probability distributions of cm-wave and mm-wave attenuation on communications links, taking various atmospheric phenomena into account  

Microsoft Academic Search

The paper presents a review of the literature on the current status of the problem of calculating radio-wave attenuation on communications links. The calculation of the mean values of probability distributions of radio-wave attenuation due to different factors is considered together with the ranges of possible variations of these distributions with respect to the calculated mean. Particular attention is given

V. N. Pozhidaev

1992-01-01

158

Parameters affecting water-hammer wave attenuation, shape and timing—Part 1: Mathematical tools  

Microsoft Academic Search

This two-part paper investigates key parameters that may affect the pressurewaveform predicted by the classical theory ofwater-hammer. Shortcomings in the prediction of pressure wave attenuation, shape and timing originate from violation of assumptions made in the derivation of the classical waterhammer equations. Possible mechanisms that may significantly affect pressure waveforms include unsteady friction, cavitation (including column separation and trapped air

Anton Bergant; Arris S. Tijsseling; John P. Vítkovský; Dídia I. C. Covas; Angus R. Simpson; Martin F. Lambert

2008-01-01

159

Attenuation of strain waves in core samples of three types of rock  

Microsoft Academic Search

Dynamic photoelasticity was employed to determine the velocity of longitudinal stress waves, dynamic modulus of elasticity and attenuation coefficients in rockcore samples 1 in. (25 mm) in diameter, 18 in. (0.46 m) long. Birefringent strips bonded to the core samples of Salem limestone, Charcoal granite and Berea sandstone provided all the data needed for the dynamic characterization of these rock

W. L. Fourney; J. W. Dally; D. C. Holloway

1976-01-01

160

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

Microsoft Academic Search

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

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

1991-01-01

161

Attenuation of Body Waves and the Q Structure of the Mantle   

Microsoft Academic Search

eliminate the source effect and the effect of the wave front divergence. It is shown that, when instrumental and crustal effects are removed, the logarithm of the spectral ratio is a linear function of frequency. The coefficient of the linear term, called the differential attenuation, is used to invert for a Qdepth structure. Two possible Qa models are presented, both

Seismological Laborat

1968-01-01

162

Three-Wave Mixing with Three Incoming Waves: Signal-Idler Coherent Attenuation and Gain Enhancement in a Parametric Amplifier  

NASA Astrophysics Data System (ADS)

We demonstrate the time-reversed process of nondegenerate three-wave parametric amplification from three distinct sources in the fully nonlinear regime using a Josephson amplifier. In the reverse process, coherent attenuation, signal and idler beams destructively interfere in the presence of a pump to generate additional pump photons. This effect is observed through the symmetric phase-dependent amplification and attenuation of the signal and idler beams and, in the depleted pump regime, through the phase-dependent modulation of the amplifier gain, directly probing the enhancement of the pump. Results are found to be in good agreement with theory.

Schackert, Flavius; Roy, Ananda; Hatridge, Michael; Devoret, Michel H.; Stone, A. Douglas

2013-08-01

163

Angular and Frequency-Dependent Wave Velocity and Attenuation in Fractured Porous Media  

NASA Astrophysics Data System (ADS)

Wave-induced fluid flow generates a dominant attenuation mechanism in porous media. It consists of energy loss due to P-wave conversion to Biot (diffusive) modes at mesoscopic-scale inhomogeneities. Fractured poroelastic media show significant attenuation and velocity dispersion due to this mechanism. The theory has first been developed for the symmetry axis of the equivalent transversely isotropic (TI) medium corresponding to a poroelastic medium containing planar fractures. In this work, we consider the theory for all propagation angles by obtaining the five complex and frequency-dependent stiffnesses of the equivalent TI medium as a function of frequency. We assume that the flow direction is perpendicular to the layering plane and is independent of the loading direction. As a consequence, the behaviour of the medium can be described by a single relaxation function. We first consider the limiting case of an open (highly permeable) fracture of negligible thickness. We then compute the associated wave velocities and quality factors as a function of the propagation direction (phase and ray angles) and frequency. The location of the relaxation peak depends on the distance between fractures (the mesoscopic distance), viscosity, permeability and fractures compliances. The flow induced by wave propagation affects the quasi-shear (qS) wave with levels of attenuation similar to those of the quasi-compressional (qP) wave. On the other hand, a general fracture can be modeled as a sequence of poroelastic layers, where one of the layers is very thin. Modeling fractures of different thickness filled with CO2 embedded in a background medium saturated with a stiffer fluid also shows considerable attenuation and velocity dispersion. If the fracture and background frames are the same, the equivalent medium is isotropic, but strong wave anisotropy occurs in the case of a frameless and highly permeable fracture material, for instance a suspension of solid particles in the fluid.

Carcione, José M.; Gurevich, Boris; Santos, Juan E.; Picotti, Stefano

2013-02-01

164

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

165

Measurment and Interpretation of Seismic Attenuation for Hydrocarbon Exploration  

Microsoft Academic Search

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

Michael Batzle; Luca Duranti; James Rector; Steve Pride

2007-01-01

166

Acoustic Measurement of Suspended Fine Particle Concentrations by Attenuation  

Technology Transfer Automated Retrieval System (TEKTRAN)

Knowledge of sediment concentration is important in the study of streams and rivers. The work presented explores the appropriate frequency and transducer spacing for acoustic measurement of suspended particles in the range of 0.1 – 64 microns. High frequency (20 MHz) acoustic signal attenuation wa...

167

High frequency attenuation of shear waves in the southeastern Alps and northern Dinarides  

NASA Astrophysics Data System (ADS)

We investigated the high frequency attenuation of S waves in the southeastern Alps and northern External Dinarides using waveforms from 331 earthquakes (3.0 < Mw < 6.5). The spectral decay parameter, k, was computed using 1345 three component high quality records, collected by the Italian Strong Motion Network (RAN) and by the Short-Period Seismometric Network of northeastern Italy (NEI) in the period 1976-2007. Weak motion data from 11 stations of the NEI network and strong motion data collected by five accelerometers of the RAN were analysed. The k parameter was estimated in the 0-250 km distance range, in a frequency band extending from the corner frequency of the event up to 25 or 45 Hz, using the amplitude acceleration Fourier spectra of S waves. The observed record-to-record variability of k was modelled by applying a generalized inversion procedure, using both parametric and non-parametric approaches. Our results evidence that k is independent on earthquake size, while it shows both site and distance dependence. Stations of the NEI network present the same increase of k with epicentral distance, RE, and show values of the zero-distance k parameter, k0(S), between 0.017 and 0.053 s. For the whole region, the k increase with distance can be described through a linear model with slope dk/dRE= (1.4 ± 0.1) × 10-4 s km-1. Assuming an average S-wave velocity, ? km s-1 between 5 and 15 km depth, we estimate an average frequency independent quality factor, ?, for the corresponding crustal layer. The non-parametric approach evidences a weak positive concavity of the curve that describes the k increase with RE at about 90 km distance. This result can be approximated through a piecewise linear function with slopes of 1.0 × 10-4 and 1.7 × 10-4 s km-1, in accordance with a three layers model where moving from the intermediate to the bottom layer both ? and ? decrease. Two regional dependences were found: data from earthquakes located westward to the NEI network evidence weaker attenuation properties, probably because of S-wave reflections from different parts of the Moho discontinuity under the eastern Po Plain, at about 25-30 km depth, while earthquakes located eastward (in western Slovenia), where the Moho deepens up to 45-50 km, evidence a higher attenuation. Moreover, the k estimates obtained with data from earthquakes located in the area of the 1998 (Mw= 5.7) and 2004 (Mw= 5.2) Kobarid events are 0.017 s higher than the values predicted for the whole region, probably because of the high level of fracturing that characterizes fault zones. The comparison between measured and theoretical values of k, computed at a few stations with available S-wave velocity profiles, reveals that the major contribution to the total k0(S) is due to the sedimentary column (from surface to 800 m depth). The hard rock section contribution is limited to 0.005 s, in accordance with a maximum contribution of 0.010 s predicted by the non-parametric inversion.

Gentili, Stefania; Franceschina, Gianlorenzo

2011-06-01

168

55-Gallon Drum Attenuation Corrections for Waste Assay Measurements  

SciTech Connect

The present study shows how the percent attenuation for low-level waste (LLW), carbon-steel 55-gallon drums (44 and 46 mil) and for transuranic (TRU) DOT Type 7A 55-gallon drums (approximately 61 mil) changes with gamma energy from 60 keV to 1400 keV. Attenuation for these drums is in the range of 5 to 15 percent at energies from 400 to 1400 keV and from 15 to 35 percent at energies from 120 to 400 keV. At 60 keV, these drums attenuate 70-80 percent of the gamma rays. Correction factors were determined in order to correct for gamma attenuation of a TRU drum if a calibration is performed with a LLW drum. These correction factors increase the activities of the TRU drum by from 10 percent to 2 percent in the energy range of 165 to 1400 keV, with an increase of about 50 percent at 60 keV. Correction factors for TRU drums and for analyses without a drum were used to adjust the percent yield for frequently measured gamma rays, so that the assay libraries could be modified to provide the drum attenuation corrections.

Casella, V.R.

2002-04-03

169

Attenuation of Elastic Waves due to Scattering from Spherical Cavities and Elastic Inclusions.  

NASA Astrophysics Data System (ADS)

The attenuation of elastic waves due to scattering from a spherical inclusion of arbitrary size in an infinitely extended medium is investigated. The spherical scatterer and the exterior medium are isotropic, homogeneous, and linearly elastic, but of arbitrarily differing material parameters, with compressional and shear waves supported in both media. Exact expressions for scattered and transmitted fields caused by an incident plane compressional or shear wave of unit amplitude are calculated analytically and general expressions for extinction and scattering cross -sections are derived for both lossy and lossless scattering. Application to ultrasonic determination of porosity in cast aluminum is investigated.

Hinders, Mark Karl

1990-01-01

170

Shear wave velocity, seismic attenuation, and thermal structure of the continental upper mantle  

USGS Publications Warehouse

Seismic velocity and attenuation anomalies in the mantle are commonly interpreted in terms of temperature variations on the basis of laboratory studies of elastic and anelastic properties of rocks. In order to evaluate the relative contributions of thermal and non-thermal effects on anomalies of attenuation of seismic shear waves, QS-1, and seismic velocity, VS, we compare global maps of the thermal structure of the continental upper mantle with global QS-1 and Vs maps as determined from Rayleigh waves at periods between 40 and 150 S. We limit the comparison to three continental mantle depths (50, 100 and 150 km), where model resolution is relatively high. The available data set does not indicate that, at a global scale, seismic anomalies in the upper mantle are controlled solely by temperature variations. Continental maps have correlation coefficients of <0.56 between VS and T and of <0.47 between QS and T at any depth. Such low correlation coefficients can partially be attributed to modelling arrefacts; however, they also suggest that not all of the VS and QS anomalies in the continental upper mantle can be explained by T variations. Global maps show that, by the sign of the anomaly, VS and QS usually inversely correlate with lithospheric temperatures: most cratonic regions show high VS and QS and low T, while most active regions have seismic and thermal anomalies of the opposite sign. The strongest inverse correlation is found at a depth of 100 km, where the attenuation model is best resolved. Significantly, at this depth, the contours of near-zero QS anomalies approximately correspond to the 1000 ??C isotherm, in agreement with laboratory measurements that show a pronounced increase in seismic attenuation in upper mantle rocks at 1000-1100 ??C. East-west profiles of VS, QS and T where continental data coverage is best (50??N latitude for North America and 60??N latitude for Eurasia) further demonstrate that temperature plays a dominant, but non-unique, role in determining the value of lithospheric VS and QS. At 100 km depth, where the resolution of seismic models is the highest, we compare observed seismic VS and QS with theoretical VST and QST values, respectively, that are calculated solely from temperature anomalies and constrained by experimental data on temperature dependencies of velocity and attenuation. This comparison shows that temperature variations alone are sufficient to explain seismic VS and QS in ca 50 per cent of continental regions. We hypothesize that compositional anomalies resulting from Fe depletion can explain the misfit between seismic and theoretical VS in cratonic lithosphere. In regions of active tectonics, temperature effects alone cannot explain seismic VS and QS in the lithosphere. It is likely that partial melts and/or fluids may affect seismic parameters in these regions. This study demonstrates that lithospheric temperature plays the dominant role in controlling VS and QS anomalies, but other physical parameters, such as compositional variations, fluids, partial melting and scattering, may also play a significant role in determining VS and QS variations in the continental mantle. ?? 2004 RAS.

Artemieva, I. M.; Billien, M.; Leveque, J. -J.; Mooney, W. D.

2004-01-01

171

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

172

Acoustic shear wave displacement measurement using ultrasound  

Microsoft Academic Search

Echo ultrasound can be used to detect and measure acoustic shear waves. Earlier it has been shown that a phase contrast based magnetic resonance imaging technique can be used for cyclic shear wave displacement measurement. Echo ultrasound presents an alternate method for imaging of such shear waves. The ultrasound based method uses the phase of quadrature echo signals to estimate

Vinayak Dutt; Randall R. Kinnick; James F. Greenleaf

1996-01-01

173

Upper mantle attenuation structure beneath East Africa from relative t* measurements  

NASA Astrophysics Data System (ADS)

We are studying the attenuation structure of the upper mantle beneath east Africa using body waves recorded by a PASSCAL array that was deployed in Tanzania between 1994-1995. The array runs along two profiles (EW and NE-SW) that traverse the Tanzania craton and the surrounding rifted mobile belts. Studying this region may provide important clues on the initiation of Cenozoic rifting in east Africa and hence, give us insights into the tectonic and geodynamic processes that occur during the initial stages of rift development. The same dataset has been used to obtain tomographic velocity models, so we can compare the velocity structure to the attenuation structure. We determined the P wave spectral amplitude ratios of data from the same earthquake recorded at different stations (thereby eliminating the source effect), and computed relative t* (path integrated attenuation) from the slopes of these ratios. We then used a least-squares inversion to determine the t* at each station relative to the average t* of the array. We applied the same procedure to determine relative t* for S waves from the transverse components of the data (i.e., SH only). To simplify the problem, we selected events that have azimuths along the two profiles, and we have initially focused on events along the EW profile. On comparing the estimates of t* to the residual travel times estimated by Ritsema et. al., (1998), we observe that the t* values and residual travel times are not always correlated. Also, the observed t* values from P wave data are anti-correlated to the observed S wave data for stations within the craton. We are planning to compute forward models in order to isolate elastic from anelastic effects on our t* measurements, and to place constraints on upper mantle Q values.

Nyblade, A. A.; Venkataraman, A.; Ritsema, J.

2003-12-01

174

Mantle Attenuation Estimated from Regional and Teleseismic P-waves of Deep Earthquakes and Surface Explosions  

NASA Astrophysics Data System (ADS)

We estimated the network-averaged mantle attenuation t*(total) of 0.5 s beneath the North Korea test site (NKTS) by use of P-wave spectra and normalized spectral stacks from the 25 May 2009 declared nuclear test (mb 4.5; IDC). This value was checked using P-waves from seven deep (580-600 km) earthquakes (4.8 < M w < 5.5) in the Jilin-Heilongjiang, China region that borders with Russia and North Korea. These earthquakes are 200-300 km from the NKTS, within 200 km of the Global Seismic Network seismic station in Mudanjiang, China (MDJ) and the International Monitoring System primary arrays at Ussuriysk, Russia (USRK) and Wonju, Republic of Korea (KSRS). With the deep earthquakes, we split the t*(total) ray path into two segments: a t*(u), that represents the attenuation of the up-going ray from the deep hypocenters to the local-regional receivers, and t*(d), that represents the attenuation along the down-going ray to teleseismic receivers. The sum of t*(u) and t*(d) should be equal to t*(total), because they both share coincident ray paths. We estimated the upper-mantle attenuation t*(u) of 0.1 s at stations MDJ, USRK, and KSRS from individual and stacks of normalized P-wave spectra. We then estimated the average lower-mantle attenuation t*(d) of 0.4 s using stacked teleseismic P-wave spectra. We finally estimated a network average t*(total) of 0.5 s from the stacked teleseismic P-wave spectra from the 2009 nuclear test, which confirms the equality with the sum of t*(u) and t*(d). We included constraints on seismic moment, depth, and radiation pattern by using results from a moment tensor analysis and corner frequencies from modeling of P-wave spectra recorded at local distances. We also avoided finite-faulting effects by excluding earthquakes with complex source time functions. We assumed ?2 source models for earthquakes and explosions. The mantle attenuation beneath the NKTS is clearly different when compared with the network-averaged t* of 0.75 s for the western US and is similar to values of approximately 0.5 s for the Semipalatinsk test site within the 0.5-2 Hz range.

Ichinose, G.; Woods, M.; Dwyer, J.

2013-01-01

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

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

177

Rheological anisotropy of the Earth's mantle and attenuation of seismic waves  

NASA Astrophysics Data System (ADS)

The nonlinear integral (having memory) model previously proposed by the author for the description of the dislocation rheology of mantle rocks is generalized to the case of crystals with anisotropic rheology. The latter is caused by a large difference between the effective viscosities associated with dislocation glide and dislocation climb (in the crystallographic coordinate system, the dislocation glide governs simple shear, whereas the dislocation climb governs pure shear). Since the mantle is polycrystalline and crystal grains an order of a millimeter in size are oriented chaotically, anisotropy vanishes with volume averaging. However, convective flows in the mantle produce large strains and lead to a preferred orientation of grains and, thereby, anisotropy of the upper mantle. The lower mantle is dominated by diffusion rheology, which cannot cause anisotropy. The mantle rheological anisotropy gives rise to anisotropic attenuation of seismic waves. It is shown that the attenuation depends on the polarization and direction of seismic waves and on the parameters of the rheological model.

Birger, B. I.

2006-11-01

178

Attenuation and localization of bending waves in a periodic/disordered fourfold composite beam  

NASA Astrophysics Data System (ADS)

By using the transfer matrix method this paper presents a study of the complex band structure, attenuation spectra and localization of bending waves in a periodic/disordered fourfold composite beam constructed by inserting thin piezoelectric or soft rubber layer at each interface of original elastic composite structures. Numerical examples are presented and the accuracy is validated by the wavelet method. The results show that the piezoelectricity can adjust the band gaps and the soft rubber can enlarge the degree of the localization and the frequency ranges of the complex band gaps. The localization factor resembles the shape of the attenuation curve in the complex band gaps. Subtle differences between the random disorder and the deterministic disorder are observed, except at lower frequencies. The behavior of the wave propagation and localization in random disordered beams can be altered by tuning different inserting position. The existence of piezoelectricity and/or soft rubber layers lends new insight into the vibration control of composite beams.

Yan, Zhi-Zhong; Zhang, Chuanzeng; Wang, Yue-Sheng

2009-10-01

179

Parameters affecting water-hammer wave attenuation, shape and timing—Part 2: Case studies  

Microsoft Academic Search

This two-part paper investigates parameters that may significantly affect water-hammer wave attenuation, shape and timing. Possible sources that may affect the waveform predicted by classical water-hammer theory include unsteady friction, cavitation (including column separation and trapped air pockets), a number of fluid–structure interaction effects, viscoelastic behaviour of the pipe-wall material, leakages and blockages. Part 1 of this two-part paper presents

Anton Bergant; Arris S. Tijsseling; John P. Vítkovský; Dídia I. C. Covas; Angus R. Simpson; Martin F. Lambert

2008-01-01

180

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

Microsoft Academic Search

Attenuation of seismic waves is very essential for the study of earthquake source parameters and also for ground-motion simulations,\\u000a and this is important for the seismic hazard estimation of a region. The digital data acquired by 16 short-period seismic\\u000a stations of the Delhi Telemetric Network for 55 earthquakes of magnitude 1.5 to 4.2, which occurred within an epicentral distance\\u000a of

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

2009-01-01

181

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

Microsoft Academic Search

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

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

2009-01-01

182

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

183

Detection of Alpher-Rubin attenuation and a search for nuclear acoustic resonance of surface waves in tantalum films  

NASA Astrophysics Data System (ADS)

The first observation of Alpher-Rubin attenuation of surface acoustic waves is reported. The surface waves were propagated on an ST-cut quartz substrate, and absorption occurred in a 10-?m tantalum film due to the surface-wave-driven oscillation of conduction electrons in an external 24-kG magnetic field. A scaling law is derived that relates attenuation coefficients of bulk and surface waves. Unsuccessful searches were made for nuclear acoustic resonance (NAR) of surface waves due to electric quadrupole transitions of 181Ta and magnetic dipole transitions of 1H. Theoretical estimates of the attenuation of surface waves agree with the observed Alpher-Rubin effect and indicate that the NAR signal was less than the noise.

Spulak, Robert G., Jr.

1989-09-01

184

Acoustic measurements of air entrainment by breaking waves  

NASA Astrophysics Data System (ADS)

Wave breaking at the surface of the ocean plays an important role in air-sea interaction processes. Bubbles entrained by breaking waves not only enhance the transfer of atmospheric gases to the ocean, but also modify the phase speed and attenuation of acoustic waves propagating through the bubbly medium. The development of acoustic instruments to measure bubbles and the results obtained from a number of field and laboratory experiments are presented. The first part of this dissertation addresses sound speed measurements made in the North Atlantic as part of the Acoustic Surface Reverberation Experiment (ASREX). An autonomous buoy system that directly measures the sound speed in the surface wave layer was developed. Data obtained with the instrument spanned several storm cycles with wind speeds and significant wave heights reaching 20 m/s and 8 m, respectively. The use of Wood's relation (1946) allows the calculation of the void fraction of air based on the low-frequency sound speed measurements. The highly variable near-surface sound speed/void fraction field is analyzed with respect to wind and surface wave- breaking parameters. The second part of this dissertation presents the development of a broadband acoustic technique which simultaneously measures the phase speed and attenuation at acoustic frequencies ranging from 4-100 kHz. The acoustic data is inverted for the size distribution of bubbles using algorithms that are based upon the physics of sound propagation through a bubbly mixture. This acoustic technique was evaluated in the large wave channel at the Hydraulics Laboratory, Scripps Institution of Oceanography, using mechanically generated breaking waves in seawater. Field measurements of bubble concentrations that result from wave breaking were made in both shallow water off Scripps Pier, California and in deep water near Point Conception, California using the broadband technique. Significant variability is observed in the bubble field, characterized by number densities of bubbles changing several orders of magnitude over short time periods. Analysis of the data with supporting environmental measurements reveal that features in the observed bubble size distributions correlate with mixing and transport processes.

Terrill, Eric James

1998-11-01

185

A coronary pulse wave velocity measurement system.  

PubMed

Pulse wave velocity (PWV) is a basic parameter in the dynamics of pressure and flow wave traveling in arteries. But it is difficult to measure the pulse wave transmission time between coronary arterial proximal and distal point by manual method using the graph on which pulse wave and ECG are recorded. The system that can measure PWV in real time was developed and clinical experiment was carried out for patients to validate the accuracy of the measured coronary arterial PWV. The average value of the measured coronary arterial PWV was 934.764+/-104.606 cm/sec. PMID:18002122

Nam, Taewoo; Cho, Jongman; Choi, Junghyeon; Park, Junho; Cho, Wookhyun

2007-01-01

186

Reference Materials for the Measurement of Acoustic Attenuation Coefficients  

NASA Astrophysics Data System (ADS)

In this work, we present a reference material for measuring the acoustic attenuation coefficient of biological tissues or tissue-mimicking materials by a transmission method. Accurate measurements by the method require a reference material that has the same acoustic velocity and density as the biological tissue. The newly developed reference material was prepared from NaCl and MgSO4 aqueous solutions. The inorganic material is stable through time. To formulate materials with the desired acoustic velocity and density, the ratio of three constituents (i.e., water, NaCl, and MgSO4) can be determined depending on the method of experiments with mixtures by Scheffe.

Yoshida, Tomoji; Gotow, Akari; Tanaka, Kouhei; Kondo, Toshio

2011-07-01

187

Seismic attenuation in the eastern Australian and Antarctic plates, from multiple ScS waves  

NASA Astrophysics Data System (ADS)

The attenuation of seismic shear waves in the mantle beneath the eastern Australian and Antarctic plates is analysed using a large data set of multiple ScSn waves, reflected n times at the core-mantle boundary and (n-1) times at the surface. The data are the transverse components of deep earthquakes from the subduction zones north and east of Australia, recorded at stations in Antarctica, Australia, Indonesia, New Caledonia and New Zealand. The data are filtered with narrow bandpass filters at five frequencies in the range 0.013-0.040 Hz. The ScSn+1/ScSn amplitude ratios of successive ScS phases are compared to the ratios computed for synthetic seismograms for the same paths and same focal mechanisms, to eliminate the effects of source radiation and geometric attenuation. The synthetic seismograms are computed from a summation of toroidal modes for the 1-D reference model PREM. The observed to computed spectral ratios appear consistent for similar paths. They reveal that the attenuation is not frequency dependent, that the contribution of scattering to attenuation is low, and that the PREM model is a valuable reference model for the study region at the considered frequencies. An inversion of the data at 0.026 Hz is performed to retrieve the quality factor Q in the upper mantle, in regions defined using a priori constraints inferred from seismic shear velocities. Q-values close to those of PREM are found beneath the Australian and Antarctic cratons, lower values beneath the Eastern Australian Phanerozoic margin, and very low values beneath the oceanic region between Australia and Antarctica, where ridges and a triple junction are present. The Australian-Antarctic Discordance along the South-Indian ridge appears as an exception with a Q-value close to those of stable continents. The highest Q-values are found beneath the subduction zones, a feature which is not apparent in global attenuation models possibly because of its narrow lateral extension, and because it extends at depths larger than those sampled by surface waves. Despite limitations due to the uneven distribution of the ScSn bounce points at the surface and to the difficulty of collecting a large number of high quality data, our approach appears very promising. It is complementary to the more widely used determination of seismic attenuation using surface waves because it provides increased depth coverage, and a broader spectral coverage. It therefore has a considerable potential in future investigations of mantle structure and dynamics.

Souriau, Annie; Rivera, Luis; Maggi, Alessia; Lévêque, Jean-Jacques

2012-07-01

188

Turbulent current measurements in a wind-wave tank  

NASA Astrophysics Data System (ADS)

Laboratory experiments were conducted in a wind-wave tank to study the turbulence characteristics in the air and wave boundary layers generated by wind and waves. The turbulent air boundary layer over the water surface was surveyed using two hot-wire probes. It was found to be a good simulation of an atmospheric boundary layer over a body of water. Capacitance probes were used to record the wave height. Spectra, wave phase velocity, dominant wavelength and frequency, and other statistics of the wind waves were computed. The water boundary layer below the water surface was surveyed using an array of 10 cross-element hot-film probes to measure the stream wise and vertical components of velocity. Various turbulence statistics including mean velocity, root-mean-square velocity fluctuations, Reynolds stress, dissipation rate, spectra, and higher-order statistics were computed. Similarity profiles were found for the mean subsurface current and the rms turbulent fluctuations in the streamwise and vertical directions. The velocity spectra indicated the relative importance of the wave-induced motion, which attenuated ex-pontentially with depth.

Lin, Jung-Tai; Gad-El-Hak, Mohamed

1984-01-01

189

Attenuation and phase variation of millimeter and centimeter radio waves in a medium consisting of dry and wet dust particles  

Microsoft Academic Search

The attenuating and refracting properties of wet dust particles with sand and loam nuclei at wavelengths of about 0.1–10 cm are considered. Quantitative characteristics of radio-wave attenuation obtained for various models of homogeneous particles with effective permittivity are compared with an exact solution of the electrodynamic problem for two-layer particles (“sphere in envelope”). Radio-wave phase variations caused by the presence

E. N. Vinyaikin; M. B. Zinicheva; A. P. Naumov

1994-01-01

190

Stone Attenuation Value and Cross-Sectional Area on Computed Tomography Predict the Success of Shock Wave Lithotripsy  

PubMed Central

Purpose To identify the parameters on noncontrast computed tomography (NCCT) that best predict the success of shock wave lithotripsy (SWL). Materials and Methods We reviewed the records of 75 patients who underwent SWL for urinary calculi measuring 5 to 20 mm. Using NCCT images, we estimated the largest stone cross-sectional area and contoured the inner edge of the stone. Clinical outcome was classified as successful (stone-free or <4 mm in diameter) or failed (stone fragments, ?4 mm). The impact of preoperative parameters was evaluated by univariate and multivariate analysis. Results The overall success rate was 73.3%. Average stone attenuation value, stone length, and stone cross-sectional area in the success and failure groups were 627.4±166.5 HU (Hounsfield unit) vs. 788.1±233.9 HU (p=0.002), 11.7±3.8 mm vs. 14.2±3.6 mm (p=0.015), and 0.31±0.17 cm2 vs. 0.57±0.41 cm2 (p<0.001), respectively. In the multivariate analysis, stone attenuation value was the only independent predictor of SWL success (p=0.023), although stone cross-sectional area had a tendency to be associated with SWL success (p=0.053). Patients were then classified into four groups by using cutoff values of 780 HU for stone attenuation value and 0.4 cm2 for cross-sectional area. By use of these cutoff values, the group with a low stone attenuation value and a low cross-sectional area was more than 11.6 times as likely to have a successful result on SWL as were all other groups (odds ratio, 11.6; 95% confidence interval, 3.9 to 54.7; p<0.001). Conclusions Stone attenuation value and stone cross-sectional area are good predictors of extracorporeal SWL outcome.

Yokota, Eisuke; Toyonaga, Yoichiro; Shimizu, Fumitaka; Ishii, Yoshiyuki; Fujime, Makoto; Horie, Shigeo

2013-01-01

191

Understanding and Quantifying the Importance of Noise Distributions on Ambient Noise Attenuation Measurements  

NASA Astrophysics Data System (ADS)

Cross correlations of ambient seismic noise have been used to produce both travel time and attenuation maps. However, while there is currently good understanding of what affects the travel times of noise correlation measurements, theory to understand the amplitudes has just begun to be worked out. Here, using a ray-theory framework that accounts for attenuation and the spatial distribution of noise sources (Tsai, JGR, 2011, in press), we evaluate the effect of various noise source distributions on the decay of amplitudes with station-station distance. For relatively simple and symmetric noise distributions, analytic solutions for both the raw cross correlation and the coherency are possible. For example, solutions for an arbitrary far-field distribution of sources placed symmetrically about the station pair can be expressed in terms of Bessel and modified Bessel functions. Cross correlations for more complicated noise distributions cannot be solved analytically but a few representative numerical computations are provided. In all cases except for the fully homogeneous distribution of noise sources, the decay of amplitudes does not match the exponential decay expected of the Green's function for the damped wave equation. One important consequence is that there are cases for which the cross correlation phases are consistent with the Green's function but the cross correlation amplitudes are not (e.g. when the noise distribution is azimuthally uniform but not uniform with distance). In general, cross correlation amplitudes are observed to be more sensitive to noise distributions than cross correlation phases. Despite this increased sensitivity, certain somewhat realistic noise distributions yield attenuation coefficient biases of less than an order of magnitude. This suggests that attenuation tomography may be feasible if researchers are careful in selecting data and performing the attenuation measurement.

Tsai, V. C.

2011-12-01

192

Atmospheric Gravity Wave Processes from Aqua Measurements  

NASA Astrophysics Data System (ADS)

Although not originally designed for this purpose, the high spatial resolution of AIRS and AMSU measurements have revealed new details of small-scale atmospheric gravity waves and their many effects on climate processes during the last decade. Gravity waves themselves drive localized temperature fluctuations with important impacts on clouds, precipitation, and atmospheric chemistry. Drag forces associated with gravity wave breaking drive circulation changes in climate models with additional wide-ranging effects. Models used for global weather forecasting now resolve some gravity wave features with scales of several hundred km, but many other gravity waves remain unresolved, while climate models resolve only some of the largest scale gravity waves. Understanding these waves, how they are generated, and how their climate effects can be best parameterized have become important issues both for testing current models and improving next generation climate predictions. Our research focuses both on waves from convection and mountain waves. AIRS radiance measurements provide the highest resolution, and we use these data to quantify wave generation by small mountainous islands and the effects of these waves on the general circulation. We also estimate the relative importance of the smallest-resolvable versus larger-scale mountain waves to the circulation directly from AIRS measurements. Details of wave generation within convective clouds are also examined, where AIRS measurements provide the constraints for simulations of their generation and propagation. These studies allow us to test assumptions employed in current parameterization methods. We will also show how the local-time sampling of Aqua is an important limitation for studies of gravity waves generated by convection.

Alexander, M.; Eckermann, S. D.; Grimsdell, A.; Hoffmann, L.; Teitelbaum, H.

2011-12-01

193

Attenuation of P-waves due to interlayer fluid flow in hydrate-bearing sediments  

NASA Astrophysics Data System (ADS)

Gas hydrates are currently the focus of intense research covering a broad variety of scientific branches. Numerous field studies, laboratory and numerical experiments have revealed some interesting aspects of sediments containing gas hydrates of which some are still under debate. While there exist several models explaining observed increased seismic velocities, the mechanism of formation of gas hydrates and the reasons for strong attenuation are not fully understood. Two rock physical models are controversially debated: one attributes the occurrence of hydrates to the properties of the rock's matrix, the other relates the presence of hydrates to the properties of the pore fluid. In our approach we assume that an occurrence of hydrates affects both the properties of the fluid and the solid phase of the host sediment. This causes the fluctuations in the elastic properties to become large between the layers of sediments. A poroelastic generalization of the O'Doherty-Anstey theory (ODA-theory) indicates that this would result in increased values for attenuation especially in the seismically relevant lower frequency range. Linking seismic attributes such as velocity and attenuation to statistical properties of material heterogeneities caused by the presence of gas hydrates enables us to numerically evaluate seismic signatures of these heterogeneities and identify parameters responsible for attenuation. To work with realistic models of multilayered, poroelastic media and to account for observed strong fluctuations in hydrate-bearing sedimentary layers we investigate exponentially correlated, randomly layered media. Numerical and analytical results for vertically incident plane P-waves confirm that strong correlated fluctuations in properties of the frame, grain and fluid cause significant and realistic attenuation values (QP of 20-30). Results show a significant amount of attenuation taking place in the lower frequency range being caused by interlayer (i.e., mesoscopic) fluid flow. Interlayer flow is promoted by strong heterogeneities in elastic properties between adjacent layers. These heterogeneous layered structures can in a pronounced manner be observed in hydrate-bearing sediments.

Gerner, Andreas; Saenger, Erik H.; Shapiro, Serge A.

2007-12-01

194

Wave Measurements on Truss Model.  

National Technical Information Service (NTIS)

Large space structures (LSS) are large periodic lattice structures being considered for space applications in earth orbit. The vibration and wave propagation characteristics of these structures can affect their performance, integrity and the ability to no...

J. H. Williams H. L. Ou S. S. Lee

1985-01-01

195

Compressional Wave Velocity and Attenuation in Carbonate Sediments of Kaneohe Bay, Oahu  

NASA Astrophysics Data System (ADS)

Measurements of geoacoustic and physical properties were made of near-surface carbonate sediments at one coarse-grained site (Site 1) and one finer-grained site (Site 2) in Kaneohe Bay, Oahu. Velocity dispersion in the measured frequency range (20 - 100 kHz) was observed at both sites, with velocity increasing from 1691 to 1708 m/s at Site 1 and from 1579 to 1585 m/s at Site 2. At both sites, effective attenuation scaled linearly with frequency, increasing from 15 to 75 dB/m at Site 1 and from 22 to 62 dB/m at Site 2. Data were compared to predictions of two common sediment geoacoustic models, namely Biot-Stoll and the Grain Shearing model. In both models, two unknown parameters were varied to find best fits at each site to (1) both attenuation and velocity data, and (2) velocity data only. Both models gave similar fits. In the fits to attenuation and velocity data, both models predicted more velocity dispersion than was measured. In the fits to velocity only, both models predicted attenuation well below measured values. This can be partially attributed to scattering since the models predict intrinsic attenuation only and the abundant shell material at both sites suggests that scattering loss should be significant.

Nosal, E.; Tao, C.; Baffi, S.; Wilkens, R. H.; Fu, S. S.; Richardson, M. D.

2006-12-01

196

Pressure measurements of nonplanar stress waves  

SciTech Connect

A useful gage has been developed for measuring pressure of nonplanar or obliquely incident stress waves. The measurements made with these gages are not as precise as direct strain gage measurements, but are very good considering the conditions under which these gages are used. We feel a need to further develop our ability to measure nonplanar stress waves in the 0 to 10 kbar range. Carbon or ytterbium will probably be chosen for the sensing element.

Carlson, G.H.; Charest, J.A.

1981-02-27

197

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

198

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

199

Prediction of earplug attenuation based on impedance measurements in the ear canal  

Microsoft Academic Search

the inside of the inserted earplug, and to predict the attenuation based on features of the impedance measurement. The impedance has been measured on a number of subjects and with a number of repeated insertions. Simultaneously, the attenuation has been evaluated with a Microphone In Real Ear (MIRE) procedure. A clear correlation can be found between the attenuation and certain

Viggo Henriksen

200

Nonlinear Acoustic Measurements and Rayleigh Waves  

NASA Astrophysics Data System (ADS)

An effective way to evaluate changes in the microstructure of a material or to assess fatigue damage at an early stage in fatigue life is by measuring the acoustic nonlinearity parameter ?. Beta is defined originally for plane harmonic longitudinal waves and depends on the ratio of the amplitudes of the first and second harmonics in the measured signal. This paper extends the concept of the conventional nonlinear parameter to the case of nonlinear Rayleigh surface waves. Surface waves are more efficient in detecting fatigue damage that is usually initiated and more concentrated near the material surface. Based on using an approximate model for nonlinear wave propagation, a nonlinearity parameter ?R for Rayleigh surface waves is proposed. Comparisons and discussions are made on the use of the nonlinearity parameter ?R for Rayleigh surface waves.

Mueller, T. O.; Kim, J.-Y.; Qu, J.; Jacobs, L. J.

2006-03-01

201

Attenuation and localization of wave propagation in periodic rods using shape memory inserts  

NASA Astrophysics Data System (ADS)

The capability of periodic structures to act as filters for traveling waves is used to control the longitudinal wave propagation in rods. Shape memory inserts placed periodically along the rods act as sources of impedance mismatch with tunable characteristics. Such characteristics are attributed to the unique behavior of the shape memory alloy whereby the elastic modulus of the inserts can be varied up to three times as the alloy undergoes a phase transformation. With such controllable capability, the inserts can introduce the proper impedance mismatch necessary to reduce the wave propagation. An analytical model based on the transfer matrix approach is developed to predict the performance of the periodic rods with shape memory inserts. The activation temperatures of the shape memory inserts are controlled using two different strategies. The propagation constants as well as the response of the composite rod are first evaluated when the inserts are all activated at the same temperature. The obtained results show that changing the thermal activation modifies the width and location of the pass and stop bands. The rod can therefore be tuned to attenuate waves propagating at selected frequencies. The tunable characteristics of the shape memory alloy are also used to introduce irregularities in the periodic structure. The source of disorder is the variance in the activation temperature of the inserts. Disorder in the periodicity typically extends the stop-bands into adjacent propagation zones. More importantly, it produces the localization of the vibration energy near the excitation source. The obtained results demonstrate the localization phenomenon and its control through appropriate tuning of the level of disorder in the activation temperatures. The theoretical investigations presented here provide guidelines for the level of disorder in the activation temperatures. The theoretical investigations presented here provide guidelines for designing tunable periodic structures with high control flexibility where propagating waves can be attenuated and localized.

Ruzzene, Massimo; Baz, Amr M.

2000-06-01

202

Shear Wave Velocity, Seismic Attenuation, and Thermal Structure of the Continental Lithosphere  

NASA Astrophysics Data System (ADS)

Theoretical models based on laboratory studies of dissipation of energy in the crystalline rocks typical for the Earth's mantle suggest a temperature dependence of attenuation through the activation energy. We therefore compare global maps of the thermal structure of the continental lithosphere with the inverse attenuation of seismic shear waves Qs and seismic velocity Vs as determined from surface wave dispersion and amplitudes. Our study is based on recently available global databases. We compare the values of Qs, Vs, and temperature T at the depths of 50, 100, and 150 km in the continental lithosphere. We find that qualitatively (by the sign of the anomaly) the maps of Qs closely correlate with lithospheric temperatures. The best correlation is observed for the depth of 100 km, where the resolution of the attenuation model is the highest. At this depth, the contour of zero attenuation anomaly approximately corresponds to the 1000°C contour of lithospheric temperature, in agreement with laboratory data on a sharp change in seismic attenuation and shear velocities in upper mantle rocks at 900-1000°C. The correlation between Vs and two other parameters (T and Qs), though present, is less distinct. We find that most cratonic regions (the Siberian Craton, the East European Platform and the Baltic Shield, the North American Craton, West Africa, western Australia) show high lithospheric Vs, Qs and low T. In contrast, the South African craton has neither high Qs, nor low temperatures. Several prominent low Qs regions correlate with high lithospheric temperatures; this includes the Paleozoic West Siberian Basin, the Cenozoic-Paleozoic structures of the Western Europe, and western North America. We calculate correlation coefficients between Vs, Qs and T and find that at any depth, for any pair of the parameters the correlation is less than 0.42. It implies that even if temperature variations in the lithosphere are the main cause of seismic velocity and attenuation variations, the relation between temperature and seismic properties is non-linear and the concept of the compositionally homogeneous lithospheric roots is not true.

Billien, M.; Artemieva, I. M.; Leveque, J.; Mooney, W. D.

2002-12-01

203

Axisymmetric wave propagation in fluid-filled pipes: wavenumber measurements in in vacuo and buried pipes  

NASA Astrophysics Data System (ADS)

Detection of water leaks in buried distribution pipes using acoustic methods is common practice in many countries. Correlation techniques are widely used in leak detection, but for these to be effective, the propagation wave speeds and wave attenuation must be known. Relatively predictable for metal pipes, these are largely unknown for the newer plastic pipes, being highly dependent on the pipe wall properties and the surrounding medium. In a previous paper a theoretical model of a buried fluid-filled pipe to predict both wavespeed and attenuation was presented; the aim of the work in this paper is to validate this model experimentally. Wavenumber measurements, encompassing both wavespeed and wave attenuation are made on a water-filled pipe in vacuo and on a buried water-filled pipe. In general, the measurements show good agreement with the theoretical predictions.

Muggleton, J. M.; Brennan, M. J.; Linford, P. W.

2004-02-01

204

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

205

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

206

Tracking accelerated aging of composites with ultrasonic attenuation measurements  

SciTech Connect

Composite materials are steadily replacing traditional materials in many industries. For many carbon composite materials, particularly in aerospace applications, durability is a critical design parameter which must be accurately characterized. Lawrence Livermore National Laboratory (LLNL) and Boeing Commercial Airplane Group have established a cooperative research and development agreement (CRADA) to assist in the high speed research program at Boeing. LLNL`s expertise in fiber composites, computer modeling, mechanical testing, chemical analysis and nondestructive evaluation (ND) will contribute to the study of advanced composite materials in commercial aerospace applications. Through thermo-mechanical experiments with periodic chemical analysis and nondestructive evaluation, the aging mechanisms in several continuous fiber polymer composites will be studied. Several measurement techniques are being studied for their correlation with aging. This paper describes through-transmission ultrasonic attenuation measurements of isothermally aged composite materials and their use as a tracking parameter for accelerated aging.

Chinn, D.J.; Durbin, P.F.; Thomas, G.H.; Groves, S.E.

1996-10-01

207

Measurement of frequency dependent Lg attenuation in the Great Basin  

Microsoft Academic Search

Measurement of the spatial decay of spectral amplitudes of the higher-mode seismic surface wave train Lg indicates that in the Great Basin the apparent seismic quality factor, Q, is a function of frequency. Observations along a 300 km profile recording of a nuclear explosion yield the function Q(ƒ)=206ƒ0.68 over the band 0.3 ? ƒ ? 10.0 Hz. Similar analysis using

David E. Chfivez; Keith F. Priestley

1986-01-01

208

Measurement of frequency dependent Lg attenuation in the great basin  

Microsoft Academic Search

Measurement of the spatial decay of spectral amplitudes of the higher-mode seismic surface wave train Lg indicates that in the Great Basin the apparent seismic quality factor, Q, is a function of frequency. Observations along a 300 km profile recording of a nuclear explosion yield the function Q(f)=206f0.68 over the band 0.3<=f<=10.0 Hz. Similar analysis using numerous recordings of earthquakes

David E. Chávez; Keith F. Priestley

1986-01-01

209

Velocity and attenuation of scalar and elastic waves in random media: a spectral function approach.  

PubMed

This paper investigates the scattering of scalar and elastic waves in two-phase materials and single-mineral-cubic, hexagonal, orthorhombic-polycrystalline aggregates with randomly oriented grains. Based on the Dyson equation for the mean field, explicit expressions for the imaginary part of Green's function in the frequency-wavenumber domain (?, p), also known as the spectral function, are derived. This approach allows the identification of propagating modes with their relative contribution, and the computation of both attenuation and phase velocity for each mode. The results should be valid from the Rayleigh (low-frequency) to the geometrical optics (high-frequency) regime. Comparisons with other approaches are presented for both scalar and elastic waves. PMID:22423683

Calvet, Marie; Margerin, Ludovic

2012-03-01

210

Variation of Seismic Coda Wave Attenuation in the Garhwal Region, Northwestern Himalaya  

NASA Astrophysics Data System (ADS)

Seismic coda wave attenuation ( Q_{text{c}}^{ - 1} ) characteristics in the Garhwal region, northwestern Himalaya is studied using 113 short-period, vertical component seismic observations from local events with hypocentral distance less than 250 km and magnitude range between 1.0 to 4.0. They are located mainly in the vicinity of the Main Boundary Thrust (MBT) and the Main Central Thrust (MCT), which are well-defined tectonic discontinuities in the Himalayas. Coda wave attenuation ( Q_{text{c}}^{ - 1} ) is estimated using the single isotropic scattering method at central frequencies 1.5, 3, 5, 7, 9, 12, 16, 20, 24 and 28 Hz using several starting lapse times and coda window lengths for the analysis. Results show that the ( Q_{text{c}}^{ - 1} ) values are frequency dependent in the considered frequency range, and they fit the frequency power law ( Q_{text{c}}^{ - 1} left( f right) = Q0^{ - 1} f^{ - n} ). The Q 0 ( Q c at 1 Hz) estimates vary from about 50 for a 10 s lapse time and 10 s window length, to about 350 for a 60 s lapse time and 60 s window length combination. The exponent of the frequency dependence law, n ranges from 1.2 to 0.7; however, it is greater than 0.8, in general, which correlates well with the values obtained in other seismically and tectonically active and highly heterogeneous regions. The attenuation in the Garhwal region is found to be lower than the Q {c/-1} values obtained for other seismically active regions of the world; however, it is comparable to other regions of India. The spatial variation of coda attenuation indicates that the level of heterogeneity decreases with increasing depth. The variation of coda attenuation has been estimated for different lapse time and window length combinations to observe the effect with depth and it indicates that the upper lithosphere is more active seismically as compared to the lower lithosphere and the heterogeneity decreases with increasing depth.

Tripathi, Jayant N.; Singh, Priyamvada; Sharma, Mukat L.

2012-01-01

211

Velocity and attenuation of seismic waves in random media: A spectral function approach  

NASA Astrophysics Data System (ADS)

This contribution investigates the scattering of scalar and elastic waves in two-phase materials and single-mineral-cubic, hexagonal, orthorhombic-polycrystalline aggregates with randomly oriented grains. Based on the Dyson equation for the mean field, explicit expressions for the imaginary part of Green's function in the frequency-wavenumber domain (?,p), also known as the spectral function, are derived. This approach allows the identification of propagating modes with their relative contribution, and the computation of both attenuation and phase velocity for each mode. The results should be valid from the Rayleigh (low-frequency) to the geometrical optics (high-frequency) regime. Applications of the proposed theory to the structure of the inner core of the Earth will be presented. In particular, it will be shown that our scattering theory can explain the striking correlation between velocity and attenuation and the associated hemispherical variations revealed by PKP waves propagating through the inner core of the Earth. The implications for inner core dynamics will be summarized.

Margerin, Ludovic; Calvet, Marie; Monnereau, Marc; Souriau, Annie

2013-04-01

212

Average attenuation of 0.7-5.0 Hz Lg waves and magnitude scale determination for the region bounding the western branch of the East African Rift  

NASA Astrophysics Data System (ADS)

The investigation of LG attenuation characteristics in the region bounding the western branch of the East African rift system using digital recordings from a seismic network located along the rift between Lake Rukwa and Lake Malawi is reported. A set of 24 recordings of LG waves from 12 regional earthquakes has been used for the determination of anelastic attenuation, QLg , and regional body-wave magnitude, MbLg , scale. The events used have body-wave magnitudes, Mb , between 4.6 and 5.5, which have been determined teleseismically and listed in ISC bulletins. The data were time-domain displacement amplitudes measured at 10 different frequencies (0.7-5.0 Hz). QLg and its frequency dependence, ?, in the region can be represented in the form QLg = (186.2 +/- 6.5)F(0.78+/-0.05). This model is in agreement with models established in other active tectonic regions. The LG-wave-based magnitude formula for the region is given by MbLg = log A + (3.76 +/- 0.38) log D - (5.72 +/- 1.06), where A is a half-peak-to-peak maximum amplitude of the 1 s LG wave amplitude in microns and D is the epicentral distance in kilometres. Magnitude results for the 12 regional earthquakes tested are in good agreement with the ISC body-wave magnitude scale.

Ferdinand, Richard W.

1998-09-01

213

Measuring colloidal forces using evanescent wave scattering  

Microsoft Academic Search

The evanescent wave scattering technique total internal reflection microscopy has enabled the direct measurement of the mean potential energy of interaction between a Brownian particle and a flat surface. With a distance resolution of 1 nm and a force resolution of 10 fN, this technique has successfully measured a variety of colloidal forces. Recent measurements of van der Waals interactions

Stacy G Bike

2000-01-01

214

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

2011-01-18

215

Microwave and Millimeter Wave Characteristics and Attenuation of Clouds over some Malaysian Equatorial Stations  

NASA Astrophysics Data System (ADS)

Based on radar range height indicator (RHI) measurements, cloud characteristics in relation to radiowave propagation over three locations in different geographical region in western Malaysia have been presented. It is seen that low cloud occurrence over these locations are quite significant. Cloud attenuation and noise temperature can result in serious degradation of telecommunication link performances. This paper presents cloud coverage in different months, 0°C isotherm height and cloud attenuation results at 12 GHz, 20 GHz, 36 GHz, 50 GHz, 70 GHz and 100 GHz over measurement site. The low level cloud over the measurement sites has been found to occur for many days and nights and particularly in the months of April to May and October to December. Such results are useful for satellite communication and remote sensing application in Malaysia.

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

2008-03-01

216

Millimeter-wave atmospheric turbulence measurements: Instrumentation, selected results, and system effects  

Microsoft Academic Search

Increasing interest in and greater usage of the millimeter-wave frequency bands has resulted in a need for better characterization\\u000a of atmospheric effects at these frequencies. While attenuation is recognized as the most significant effect, recent measurements\\u000a of fluctuations in intensity and phase caused by atmospheric turbulence have shown that these phenomena will also degrade\\u000a system performance at both millimeter-wave and

R. W. McMillan; R. A. Bohlander; W. J. Baldygo

1997-01-01

217

Numerical simulation of electromagnetic wave attenuation in a nonequilibrium chemically reacting hypervelocity flow  

NASA Astrophysics Data System (ADS)

The effects of various gasdynamic phenomena on the attenuation of an electromagnetic wave propagating through the nonequilibrium chemically reacting air flow field generated by an aerodynamic body travelling at high velocity is investigated. The nonequilibrium flow field is assumed to consist of seven species including nitric oxide ions and free electrons. The ionization of oxygen and nitrogen atoms is ignored. The aerodynamic body considered is a blunt wedge. The nonequilibrium chemically reacting flow field around this body is numerically simulated using a computer code based on computational fluid dynamics. The computer code solves the Navier-Stokes equations including mass diffusion and heat transfer, using a time-marching, explicit Runge-Kutta scheme. A nonequilibrium air kinetics model consisting of seven species and twenty-eight reactions as well as an equilibrium air model consisting of the same seven species are used. The body surface boundaries are considered as adiabatic or isothermal walls, as well as fully-catalytic and non-catalytic surfaces. Both laminar and turbulent flows are considered; wall generated flow turbulence is simulated using an algebraic mixing length model. An electromagnetic wave is considered as originating from an antenna within the body and is effected by the free electrons in the chemically reacting flow. Analysis of the electromagnetics is performed separately from the fluid dynamic analysis using a series solution of Maxwell's equations valid for the propagation of a long-wavelength plane electromagnetic wave through a thin (i.e., in comparison to wavelength) inhomogeneous plasma layer. The plasma layer is the chemically reacting shock layer around the body. The Navier-Stokes equations are uncoupled from Maxwell's equations. The results of this computational study demonstrate for the first time and in a systematic fashion, the importance of several parameters including equilibrium chemistry, nonequilibrium chemical kinetics, the reaction mechanism, flow viscosity, mass diffusion, and wall boundary conditions on modeling wave attenuation resulting from the interaction of an electromagnetic wave with an aerodynamic plasma. Comparison is made with experimental data.

Nusca, Michael Joseph, Jr.

218

Measurement of mean flows of Faraday waves.  

PubMed

We measure the velocities of the mean flows that are driven by curved rolls in a pattern formation system. Curved rolls in Faraday waves are generated in experimental cells consisting of channels with varying widths. The mean flow magnitudes are found to scale linearly with roll curvatures and squares of wave amplitudes, agreeing with the prediction from the analysis of phase dynamics expansion. The effects of the mean flows on reducing roll curvatures are also seen. PMID:15323636

Chen, Peilong

2004-08-04

219

A buoy mounted barometric pressure instrument for wave height measurement  

Microsoft Academic Search

This paper describes the design, operation and testing of an ocean wave height sensor based on the measurement of wave-related barometric pressure variations. The work was done under the auspices of the NOAA Data Buoy Office (NDBO). Wave theory used and design of circuits to convert the continuous analog wave height signal to significant wave height, peak wave height and

John F. Holmes; Ronald T. Miles

1977-01-01

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

Attenuation of seismic waves and the universal rheological model of the Earth's mantle  

NASA Astrophysics Data System (ADS)

Analysis of results of laboratory studies on creep of mantle rocks, data on seismic wave attenuation in the mantle, and rheological micromechanisms shows that the universal, i.e., relevant to all time scales, rheological model of the mantle can be represented as four rheological elements connected in series. These elements account for elasticity, diffusion rheology, high temperature dislocation rheology, and low temperature dislocation rheology. The diffusion rheology element is described in terms of a Newtonian viscous fluid. The high temperature dislocation rheology element is described by the rheological model previously proposed by the author. This model is a combination of a power-law non-Newtonian fluid model for stationary flows and the linear hereditary Andrade model for flows associated with small strains. The low temperature dislocation rheology element is described by the linear hereditary Lomnitz model.

Birger, B. I.

2007-08-01

222

VHF/UHF wave attenuation in a city with regularly spaced buildings  

NASA Astrophysics Data System (ADS)

In this work a theoretical and experimental investigation analyzing VHF/UHF radio wave propagation in a suburban environment with a grid-type street plan is presented for the purpose of personal communication services prediction. A waveguide with randomly distributed gaps (slits) between the sides of buildings is considered as a model of straight streets with two- and three-story buildings. The average field intensity and path loss at the street level, taking into account the reflection from the ground, multireflection, and diffraction from the walls and building edges, are investigated in line-of-sight (LOS) conditions using a new three-dimensional multislit waveguide model. This model gives good agreement with the two-rays model and with an experimentally found law of field intensity attenuation at the street level with high and low building density up to 1-2 km from the source.

Blaunstein, N.; Levin, M.

1996-03-01

223

Attenuation in the Australian-Antarctic region from multiple ScS waves  

NASA Astrophysics Data System (ADS)

The shear attenuation in the mantle beneath the Australian-Antarctic region is analyzed using a large data set of multiple ScSn waves. The data are the transverse components of deep earthquakes from the subduction zones North and East of Australia, recorded at stations in Antarctica, Australia, Indonesia, New Caledonia and New Zealand. The ScS(n+1)/ScSn amplitude ratios of successive ScS phases are compared to the ratios computed for PREM synthetic seismograms for the same paths and same focal mechanisms, in order to eliminate the effects of source radiation and geometric attenuation. A possible Q frequency dependence is investigated using narrow band-pass filters at several frequencies in the range 0.013-0.040 Hz. Assuming that Q heterogeneities are concentrated in the upper mantle, close to the upper bounce points, an inversion of the data at 0.026 Hz is performed to retrieve the quality factor in 5 regions defined using a priori constraints inferred from seismic shear velocities. Most stable results are obtained when restricting the analysis to ScS3/ScS2 and ScS4/ScS3 ratios, for which seismic phases can be properly isolated and whose bounce points sample sufficiently 4 of the 5 regions. Q values close to PREM's one are found beneath the Australian and Antarctic cratons, lower values beneath the Eastern Australian Phanerozoic margin, and very low values beneath the oceanic region between Australia and Antarctica, where ridges and a triple junction are present. The highest Q values are found beneath the subduction zones, a feature which is not apparent in global attenuation models. In the frequency range considered (0.013-0.040 Hz), our data do not require a frequency dependent quality factor. This result is robust and is consistent with previous results based on the decay of ScSn spectral ratios, obtained for various regions of the world.

Souriau, A.; Rivera, L.; Maggi, A.; Lévêque, J.-J.

2012-04-01

224

Phase measurements on terahertz waves.  

PubMed

The change in phase of the free space terahertz (THz) electric field as a sample of material introduced into the THz beampath of a CW THz system is measured and used to calculate the index of refraction of materials at 250 GHz. PMID:24081031

Cordes, A H; Thomas, D H; von der Weid, J P

2013-10-01

225

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

226

Time-domain apparent-attenuation operators for compressional and shear waves: Experiment versus single-scattering theory  

Microsoft Academic Search

We derive time-domain apparent-attenuation operators from both laboratory data and a single-scattering theory. The scattering medium consists of a homogeneous elastic block containing parallel cylindrical voids, with volume fractions in the range from 0.66% to 3.75%. The attenuation operators were computed by first measuring (or theoretically predicting) the attenuation of spectral amplitude and then constructing a casual seismogram using the

Bruce Dubendorff; William Menke

1986-01-01

227

Gamma ray attenuation coefficient measurement for neutron-absorbent materials  

NASA Astrophysics Data System (ADS)

The compounds Na2B4O7, H3BO3, CdCl2 and NaCl and their solutions attenuate gamma rays in addition to neutron absorption. These compounds are widely used in the shielding of neutron sources, reactor control and neutron converters. Mass attenuation coefficients of gamma related to the four compounds aforementioned, in energies 662, 778.9, 867.38, 964.1, 1085.9, 1173, 1212.9, 1299.1,1332 and 1408 keV, have been determined by the ? rays transmission method in a good geometry setup; also, these coefficients were calculated by MCNP code. A comparison between experiments, simulations and Xcom code has shown that the study has potential application for determining the attenuation coefficient of various compound materials. Experiment and computation show that H3BO3 with the lowest average Z has the highest gamma ray attenuation coefficient among the aforementioned compounds.

Jalali, Majid; Mohammadi, Ali

2008-05-01

228

Influence of scattering on seismic waves: Velocity and attenuation of the upper crust in southeast Maine  

NASA Astrophysics Data System (ADS)

Rg and Pg velocities and Rg attenuation have been examined for the Central Merrimack Synclinorium and nearby regions in southeastern Maine using digital records from a seismic refraction experiment. Determination of Rg group velocities and Pg travel times indicates that both lateral variations and azimuthal anisotropy are present in the study area. The axes of the azimuthal velocity anisotropy appear to lie along and perpendicular to the Appalachian structural strike in the region, with Rg group velocities along strike up to 20 percent faster than cross strike velocities. Measurement of Rg attenuation gives Q values of 25 to 80, varying with frequency. Inversion of the Rg group velocity for velocity structure shows that both the compressional and shear velocities increase rapidly with depth in the upper 1 km in the region.

Reister, Edmund; Dainty, Anton M.; Toksoez, M. N.

1988-03-01

229

55Gallon Drum Attenuation Corrections for Waste Assay Measurements  

Microsoft Academic Search

The present study shows how the percent attenuation for low-level waste (LLW), carbon-steel 55-gallon drums (44 and 46 mil) and for transuranic (TRU) DOT Type 7A 55-gallon drums (approximately 61 mil) changes with gamma energy from 60 keV to 1400 keV. Attenuation for these drums is in the range of 5 to 15 percent at energies from 400 to 1400

Casella

2002-01-01

230

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

231

Measurement of frequency dependent Lg attenuation in the Great Basin  

NASA Astrophysics Data System (ADS)

Measurement of the spatial decay of spectral amplitudes of the higher-mode seismic surface wave train Lg indicates that in the Great Basin the apparent seismic quality factor, Q, is a function of frequency. Observations along a 300 km profile recording of a nuclear explosion yield the function Q(ƒ)=206ƒ0.68 over the band 0.3 ? ƒ ? 10.0 Hz. Similar analysis using numerous recordings of earthquakes along paths which provide a good average sampling of the Great Basin crust gives Q(ƒ) = 214(± 15)ƒ0.54(±0.09), for 0.3 ? ƒ ? 5.0 Hz. If the crustal sampling by Lg energy from nuclear explosions (surface sources) is primarily in the shallow crust, as has been suggested, then these results indicate a greater frequency dependence of apparent Q there than at depth.

Chávez, David E.; Priestley, Keith F.

1986-06-01

232

Variations in mutual coupling correction factors for resonant dipoles used in site attenuation measurements  

Microsoft Academic Search

Site attenuation measurements using resonant dipole antennas are commonly used to certify test sites for compliance testing to the Federal Communication Commission Part 15 requirements. Mutual coupling has previously been shown to affect the impedance of resonant dipole antennas. It is pointed out that a correction factor must be added to ANS C63.4 normalized site attenuation for these measurements to

John Berry; Barry Pate; Alan Knight

1990-01-01

233

Measurements of shock-induced guided and surface acoustic waves along boreholes in poroelastic materials  

NASA Astrophysics Data System (ADS)

Acoustic experiments on the propagation of guided waves along water-filled boreholes in water-saturated porous materials are reported. The experiments were conducted using a shock tube technique. An acoustic funnel structure was placed inside the tube just above the sample in order to enhance the excitation of the surface modes. A fast Fourier transform-Prony-spectral ratio method is implemented to transform the data from the time-space domain to the frequency-wave-number domain. Frequency-dependent phase velocities and attenuation coefficients were measured using this technique. The results for a Berea sandstone material show a clear excitation of the fundamental surface mode, the pseudo-Stoneley wave. The comparison of the experimental results with numerical predictions based on Biot's theory of poromechanics [J. Acoust. Soc. Am. 28, 168 (1956)], shows that the oscillating fluid flow at the borehole wall is the dominant loss mechanism governing the pseudo-Stoneley wave and it is properly described by the Biot's model at frequencies below 40 kHz. At higher frequencies, a systematic underestimation of the theoretical predictions is found, which can be attributed to the existence of other losses mechanisms neglected in the Biot formulation. Higher-order guided modes associated with the compressional wave in the porous formation and the cylindrical geometry of the shock tube were excited, and detailed information was obtained on the frequency-dependent phase velocity and attenuation in highly porous and permeable materials. The measured attenuation of the guided wave associated with the compressional wave reveals the presence of regular oscillatory patterns that can be attributed to radial resonances. This oscillatory behavior is also numerically predicted, although the measured attenuation values are one order of magnitude higher than the corresponding theoretical values. The phase velocities of the higher-order modes are generally well predicted by theory.

Chao, Gabriel; Smeulders, D. M. J.; van Dongen, M. E. H.

2006-05-01

234

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.

235

Some Remarks on the Microscopic Physics of Seismic Wave Attenuation and Tidal Dissipation (Invited)  

NASA Astrophysics Data System (ADS)

There are a number of questions on the Q of planetary bodies. They include: (1) Seismic Q of Earth’s interior varies from one region to another. What is the cause for lateral and depth variation of seismic Q? Is it due to the variation in temperature, grain-size, partial melting and/or water content? (2) What is the relationship between seismic Q and long-term rheology? (3) The Moon’s seismic Q is large (>1000) at least for waves passing the shallow part. However, the tidal Q reflecting energy dissipation in the deep part of the Moon is small (~50). If the Moon is a “dry” body, why is tidal Q of the Moon so small? (4) Exo-solar planets are usually found close to their parent stars. But these planets likely have undergone orbital evolution that is controlled by tidal energy dissipation. What controls the magnitude of tidal dissipation in these planets? I will provide a brief review to address some of these questions with a focus on the microscopic physics of anelastic energy dissipation. The most important message from recent lab studies is that solid materials show large energy dissipation (Q of ~100 or less) at modestly high temperatures (T/Tm>0.5, Tm: melting temperature). This implies that the majority of seismic wave attenuation is likely attributed to solid-state processes and energy loss in many of the exo-solar planets might be due to small rocky cores. Some details of solid-state mechanisms of energy dissipation in solids will be reviewed including the influence of frequency, temperature, grain-size, strain amplitude and some impurities such as hydrogen. A common observation among many solids so far studied at high T/Tm is power-law frequency dependence of Q with a modest frequency exponent (~0.3+/-0.1) with a gradual change to the Maxwell body (viscous) behavior at lower frequencies. The transition frequency to the Maxwell body behavior is also dependent on strain amplitude, causing larger energy dissipation at higher strain amplitudes. These observations suggest a close link between seismic wave attenuation (tidal dissipation) and long-term creep.

Karato, S.

2009-12-01

236

CW (Continuous Wave) Measurement System. Operating Manual.  

National Technical Information Service (NTIS)

This document was prepared for the Defense Nuclear Agency under Contract DNA001-80-C-0290 and submitted to satisfy CDRL item 4. This document contains the operating instructions for the Upgraded DNA Continuous Wave (CW) Measurement System. The CW Measurem...

G. A. Gagliano J. Burns J. E. Bridge R. B. Reinman

1982-01-01

237

Anisotropic Changes in P-Wave Velocity and Attenuation during Deformation and Fluid Infiltration of Granite  

Microsoft Academic Search

4 Abstract. Fluid infiltration and pore fluid pressure changes are known to have a significant effect on the occurrence of earthquakes. Yet, for most damaging earthquakes, with nucleation zones below a few kilometers depth, direct measurements of fluid pressure variations are not available. Instead, pore fluid pressures are inferred primarily from seismic wave propagation characteristics such as V p\\/Vs ratio,

Sergei A. Stanchits; David A. Lockner; Alexander V. Ponomarev

2003-01-01

238

Measurements of attenuation and absorption lengths with the KASCADE experiment  

NASA Astrophysics Data System (ADS)

The attenuation of the electron shower size beyond the shower maximum is studied with the KASCADE extensive air shower (EAS) experiment in the primary energy range of about 1014-1016 eV. Attenuation and absorption lengths are determined by applying different approaches, including the method of constant intensity, the decrease of the flux of EASs with increasing zenith angle, and its variation with ground pressure. We observe a significant dependence of the results on the applied method. The determined values of the attenuation length ranges from 175 to 196 g/cm2 and of the absorption length from 100 to 120 g/cm2. The origin of these differences is discussed emphasizing the influence of intrinsic shower fluctuations.

KASCADE Collaboration; Antoni, T.; Apel, W. D.; Badea, A. F.; Bekk, K.; Bercuci, A.; Blümer, H.; Bozdog, H.; Brancus, I. M.; Büttner, C.; Chilingarian, A.; Daumiller, K.; Doll, P.; Engel, R.; Engler, J.; Feßler, F.; Gils, H. J.; Glasstetter, R.; Haeusler, R.; Haungs, A.; Heck, D.; Hörandel, J. R.; Iwan, A.; Kampert, K.-H.; Klages, H. O.; Maier, G.; Mathes, H. J.; Mayer, H. J.; Milke, J.; Müller, M.; Obenland, R.; Oehlschläger, J.; Ostapchenko, S.; Petcu, M.; Rebel, H.; Risse, M.; Roth, M.; Schatz, G.; Schieler, H.; Scholz, J.; Thouw, T.; Ulrich, H.; Vardanyan, A.; Weber, J. H.; Weindl, A.; Wentz, J.; Wochele, J.; Zabierowski, J.

2003-09-01

239

Gamma ray attenuation coefficient measurement for neutron-absorbent materials  

Microsoft Academic Search

The compounds Na2B4O7, H3BO3, CdCl2 and NaCl and their solutions attenuate gamma rays in addition to neutron absorption. These compounds are widely used in the shielding of neutron sources, reactor control and neutron converters. Mass attenuation coefficients of gamma related to the four compounds aforementioned, in energies 662, 778.9, 867.38, 964.1, 1085.9, 1173, 1212.9, 1299.1,1332 and 1408keV, have been determined

Majid Jalali; Ali Mohammadi

2008-01-01

240

Evaluation of Seismic Attenuation Measurements from Vertical Seismic Profile Registered Data.  

National Technical Information Service (NTIS)

This work is aimed at looking for a possibility of attenuation measurement from seismic data, then at the estimation of the basic element perturbing possibly this measurement and consequently limiting it. So principles and interest of vertical seismic pro...

M. J. Petit

1986-01-01

241

Rogue wave early warning through spectral measurements?  

NASA Astrophysics Data System (ADS)

We study the spectra of the Peregrine soliton and higher-order rational solutions of the nonlinear Schrödinger equation (NLSE), which we use as a model of the rogue waves in optics and in the deep ocean. We show that these solutions have specific triangular spectra that are certainly easily measurable in optical systems and which may be amenable to characterisation in ocean environments. As the triangular feature of the solutions appears at an early stage of their evolution, this raises the possibility of early detection and possible localized warning of the appearance of rogue waves. We anticipate that studying the characteristics of "early warning spectra" of rogue waves may become an important future field of research.

Akhmediev, Nail; Ankiewicz, Adrian; Soto-Crespo, J. M.; Dudley, John M.

2011-01-01

242

Upper mantle attenuation structure beneath East Africa from relative t* measurements  

Microsoft Academic Search

We are studying the attenuation structure of the upper mantle beneath east Africa using body waves recorded by a PASSCAL array that was deployed in Tanzania between 1994-1995. The array runs along two profiles (EW and NE-SW) that traverse the Tanzania craton and the surrounding rifted mobile belts. Studying this region may provide important clues on the initiation of Cenozoic

A. A. Nyblade; A. Venkataraman; J. Ritsema

2003-01-01

243

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

244

Correlation Attenuation Due to Measurement Error: A New Approach Using the Bootstrap Procedure  

ERIC Educational Resources Information Center

Issues with correlation attenuation due to measurement error are well documented. More than a century ago, Spearman proposed a correction for attenuation. However, this correction has seen very little use since it can potentially inflate the true correlation beyond one. In addition, very little confidence interval (CI) research has been done for…

Padilla, Miguel A.; Veprinsky, Anna

2012-01-01

245

Correlation Attenuation Due to Measurement Error: A New Approach Using the Bootstrap Procedure  

ERIC Educational Resources Information Center

|Issues with correlation attenuation due to measurement error are well documented. More than a century ago, Spearman proposed a correction for attenuation. However, this correction has seen very little use since it can potentially inflate the true correlation beyond one. In addition, very little confidence interval (CI) research has been done for…

Padilla, Miguel A.; Veprinsky, Anna

2012-01-01

246

Attenuation measurements of ultrasound in a kaolin-water slurry. A linear dependence upon frequency  

SciTech Connect

The attenuation of ultrasound through a kaolin-water slurry was measured for frequencies ranging from 0.5 to 3.0 MHz. The maximum concentration of the slurry was for a weight percentage of 44% (or a volume fraction of 0.24). The goal of these measurements was to assess the feasibility of using ultrasonic attenuation to determine the concentration of a slurry of known composition. The measurements were obtained by consecutively adding kaolin to the slurry and measuring the attenuation at each concentration. After reaching a maximum concentration a dilution technique was used, in which an amount of slurry was removed and water was added, to obtain the attenuation as a function of the concentration. The dilution technique was the more effective method to obtain calibration data. These measurements were carried out using two transducers, having a center frequency of 2.25 MHz, separated by 0.1016m (4.0 in.). The maximum attenuation measured in these experiments was about 100Np/m, but the experimental apparatus has the capability of measuring a larger attenuation if the distance between the two transducers is decreased. For a given frequency, the data show that ln V/V[sub 0] depends linearly upon the volume fraction (V is the received voltage for the slurry and V[sub 0] is that obtained for water). This indicated that each particle acts independently in attenuating ultrasound. 12 refs., 7 figs., 3 tabs.

Greenwood, M.S.; Mai, J.L.; Good, M.S. (Pacific Northwest Lab., Richland, WA (United States))

1993-08-01

247

Effects of Temperature and Saturation on the Velocity and Attenuation of Seismic Waves in Rocks: Applications to Geothermal Reservoir Evaluation  

SciTech Connect

In the evaluation of a geothermal resource it is critical to know the reservoir geometry, temperature, saturation, state of saturants, pore pressure, porosity and permeability. These are the parameters which will determine the production feasibility and cost effectivness of a geothermal prospect. The increasing sophistication of seismic wave data collection and processing and recent exerimental work on factors governing wave propagation in rocks has stimulated increased interest in the use of active seismic techniques to determine the in situ physical state of crustal rocks for engineering applications. In this paper we review experimental work showing how wave velocities in rocks are sensitive to parameters of interest to geothermal exploration; effective pressure, the degree of water saturation of the pores, and the bulk modulus of the pore phase. Seismic attenuation is even more sensitive to the degree of saturation and the microgeometry of the pores. Both velocity and attenuation are strongly temperature dependent and reflect thermal fracturing of the rocks at elevated temperatures. By combining data on attenuation and velocity of compressional and shear waves considerably greater constraints may be placed on the environmental state of the rocks than on the basis of P velocities alone.

Jones, Terry; Murphy, William; Nur, Amos

1980-12-18

248

Setting Time Measurement Using Ultrasonic Wave Reflection  

SciTech Connect

Ultrasonic shear wave reflection was used to investigate setting times of cement pastes by measuring the reflection coefficient at the interface between hydrating cement pastes of varying water-to-cement ratio and an ultrasonic buffer material. Several different buffer materials were employed, and the choice of buffer was seen to strongly affect measurement sensitivity; high impact polystyrene showed the highest sensitivity to setting processes because it had the lowest acoustic impedance value. The results show that ultrasonic shear-wave reflection can be used successfully to monitor early setting processes of cement paste with good sensitivity when such a very low impedance buffer is employed. Criteria are proposed to define set times, and the resulting initial and final set times agreed broadly with those determined using the standard penetration resistance test.

Chung, Chul-Woo; Suraneni, Prannoy; Popovics, John S.; Struble, Leslie J.

2012-01-09

249

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

250

S wave attenuation in the coastal region of Jalisco-Colima, México  

NASA Astrophysics Data System (ADS)

Aftershock data from the October 9, 1995, M=7.6 earthquake, that occurred in the coastal subduction region of Colima-Jalisco, Mexico, are used to obtain estimates of the frequency independent quality factor Qs and spectral decay parameter ?, in the approximate frequency range 3 Hz? f?40 Hz, as functions of hypocentral distance r. A regression analysis results in the relations for S waves: Q s=261.397+3.198r±15.536 ?=0.009651+0.000462r±0.0012.The observed distance dependence of Qs and ? is similar to that reported for the Mexican regions of Oaxaca and Guerrero. Our Qs values agree with those reported for Oaxaca and northern Baja CA for frequencies around 8 Hz, and are somewhat lower (a factor of ˜0.8 to ˜0.5) for higher frequencies around 20 Hz; however, they are significantly lower than all but the lowest values reported for the Guerrero region, attaining factors ˜0.25 and ˜0.13 for frequency ranges around 8 and 20 Hz, respectively. It thus appears that the Guerrero region has an anomalously low attenuation compared with the flanking coastal regions of Oaxaca-Chiapas to the SE and Jalisco-Colima to the NW.

Nava, F. Alejandro; Garc?´a-Arthur, Rosal?´a.; Castro, Raul R.; Suárez, Carlos; Márquez, Bertha; Núñez-Cornú, Francisco; Saavedra, Gustavo; Toscano, Roberto

1999-10-01

251

An iterative effective medium approximation (IEMA) for wave dispersion and attenuation predictions in particulate composites, suspensions and emulsions.  

PubMed

In the present work we deal with the scattering dispersion and attenuation of elastic waves in different types of nonhomogeneous media. The iterative effective medium approximation based on a single scattering consideration, for the estimation of wave dispersion and attenuation, proposed in Tsinopoulos et al., [Adv. Compos. Lett. 9, 193-200 (2000)] is examined herein not only for solid components but for liquid suspensions as well. The iterations are conducted by means of the classical relation of Waterman and Truell, while the self-consistent condition proposed by Kim et al. [J. Acoust. Soc. Am. 97, 1380-1388 (1995)] is used for the convergence of the iterative procedure. The single scattering problem is solved using the Ying and Truell formulation, which with a minor modification can accommodate the solution of scattering on inclusions in liquid. Theoretical results for several different systems of particulates and suspensions are presented being in excellent agreement with experimental data taken from the literature. PMID:15658695

Aggelis, D G; Tsinopoulos, S V; Polyzos, D

2004-12-01

252

An iterative effective medium approximation (IEMA) for wave dispersion and attenuation predictions in particulate composites, suspensions and emulsions  

NASA Astrophysics Data System (ADS)

In the present work we deal with the scattering dispersion and attenuation of elastic waves in different types of nonhomogeneous media. The iterative effective medium approximation based on a single scattering consideration, for the estimation of wave dispersion and attenuation, proposed in Tsinopoulos et al., [Adv. Compos. Lett. 9, 193-200 (2000)] is examined herein not only for solid components but for liquid suspensions as well. The iterations are conducted by means of the classical relation of Waterman and Truell, while the self-consistent condition proposed by Kim et al. [J. Acoust. Soc. Am. 97, 1380-1388 (1995)] is used for the convergence of the iterative procedure. The single scattering problem is solved using the Ying and Truell formulation, which with a minor modification can accommodate the solution of scattering on inclusions in liquid. Theoretical results for several different systems of particulates and suspensions are presented being in excellent agreement with experimental data taken from the literature. .

Aggelis, D. G.; Tsinopoulos, S. V.; Polyzos, D.

2004-12-01

253

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

254

Further possibilities of APR and attenuation studies by means of transverse hypersonic waves at 9.4 GHz  

Microsoft Academic Search

New developments for the study of acoustic paramagnetic resonance (APR) and hypersonic attenuation in solids at 9.4 GHz are presented. Efficient electro-acoustic conversion for the transverse mode was achieved together with the generation of longitudinal waves in a high-quality CdS thin film placed parallel to the electric field in the re-entrant cavity. An electron bombardment set up was used for

C. Laermans; B. Daudin

1978-01-01

255

Non-contact sound velocities and attenuation measurements of several ceramics at elevated temperatures.  

PubMed

Laser ultrasonic technique has been employed to carry out the sound velocities and attenuation measurements as a function of temperature in alumina, two kinds of silicon nitride and partially stabilized zirconia (PSZ) samples. Accuracy of the laser technique used has been checked in terms of the diffraction effect and reproducibility of the results. Results of attenuation at room temperature have been compared with quartz transducer technique. In PSZ, velocity behavior has become non-linear and also, a peak in attenuation has been observed around 500 degrees C. In one of the silicon nitride sample, which uses glassy sintering agent, attenuation has shown a sharp peak around 950 degrees C. Interestingly, when the experiment was repeated from 800 to 1000 degrees C, this anomalous attenuation peak has disappeared, leaving a background increasing towards higher temperatures. PMID:12464408

Singh, K J; Matsuda, Y; Hattori, K; Nakano, H; Nagai, S

2003-01-01

256

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

257

Soundspeed measurements in vapor-liquid mixtures behind shock waves  

Microsoft Academic Search

In the experimental investigation of liquefaction shock waves, it is possible to measure the soundspeed of the two-phase, liquid-vapor mixture behind the shock wave. The expansion wave, produced as the shock wave emerges from the open end of a shock tube, intersects the shockfront at an observable point, allowing a simple Mach construction for the determination of the mixture soundspeed.

G. Chen; Ph. A. Thompson; J. W. Bursik

1986-01-01

258

Using impedance measurements to detect and quantify the effect of air leaks on the attenuation of earplugs.  

PubMed

The impedance of a simple artificial ear occluded with an earplug and bypassed with narrow air leaks was measured along with the attenuation of sound through the air leaks. A lumped element model is suggested for the simple occluded artificial ear with an air leak. The suggested model was adapted to the impedance measurements and the attenuation was predicted from the model. The attenuation predictions were compared to the attenuation measurements and were found to be within [-3.5,+3] dB of the measured attenuation over the frequency range of 50-1000 Hz and an attenuation range of -2-38 dB. The average difference between the measured and predicted attenuation for four different leaks in the frequency range of 50-1000 Hz was -0.7 dB, indicating a very slight underestimation of the attenuation. PMID:18646994

Henriksen, Viggo

2008-07-01

259

10 GHz-Range Surface Acoustic Wave Low Loss Filter Measured at Low Temperature  

Microsoft Academic Search

The 10 GHz-range surface acoustic wave (SAW) is of great importance in the field of physical acoustics and application of SAW devices, for example, in mobile and wireless communications. The temperature dependency of the propagation attenuation at 10 GHz-range is measured using the three-transducer system with an electrode width of less than 0.1 µm, which is fabricated using an electron

Kazuhiko Yamanouchi; Hideyuki Nakagawa; Jamil Ahmad Qureshi; Hiroyuki Odagawa

1999-01-01

260

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 = 158f1.05, 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 85f1.16 to 216f0.91 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

261

The effect of methane hydrate morphology and water saturation on seismic wave attenuation in sand under shallow sub-seafloor conditions  

NASA Astrophysics Data System (ADS)

A better understanding of seismic wave attenuation in hydrate-bearing sediments is needed for the improved geophysical quantification of seafloor methane hydrates, important for climate change, geohazard and economic resource assessment. Hence, we conducted a series of small strain (<10-6), seismic frequency (50-550 Hz), laboratory resonant column experiments on synthetic methane hydrate-bearing sands under excess-water seafloor conditions. The results show a complex dependence of P- and S-wave attenuation on hydrate saturation and morphology. P- and S-wave attenuation in excess-water hydrate-bearing sand is much higher than in excess-gas hydrate-bearing sand and increases with hydrate saturation between 0 and 0.44 (the experimental range). Theoretical modelling suggests that load-bearing hydrate is an important cause of heightened attenuation for both P- and S-waves in gas and water saturated sands, while pore-filling hydrate also contributes significantly to P-wave attenuation in water saturated sands. A squirt flow attenuation mechanism, related to microporous hydrate and low aspect ratio pores at the interface between sand grains and hydrate, is thought to be responsible for the heightened levels of attenuation in hydrate-bearing sands at low hydrate saturations (<0.44).

Best, Angus I.; Priest, Jeffrey A.; Clayton, Christopher R. I.; Rees, Emily V. L.

2013-04-01

262

Ultrasound Attenuation Measurements using a Reference Phantom with a Sound Speed Mismatch  

PubMed Central

Ultrasonic attenuation may be measured accurately with clinical systems and array transducers by using reference phantom methods (RPM) to account for diffraction and other system dependencies on echo signals. Assumptions with the RPM are that the speeds of sound in the sample (csam) and in the reference medium (cref) are the same and that they match the speed assumed in the system beamformer (cbf). This work assesses the accuracy of attenuation measurements by the RPM when these assumptions are not met. Attenuation was measured for two homogeneous phantoms, one with a speed of sound of 1500m/s and the other with a sound speed of 1580m/s. Both have an attenuation coefficient approximately equal to that of the reference, in which the speed of sound is 1540m/s. Echo signals from the samples and the reference were acquired from a Siemens S2000 scanner with a 9L4 linear array transducer. Separate acquisitions were obtained with cbf at its default value of 1540m/s, and when it was set at values matching the speeds of sound of the phantoms. Simulations were also performed using conditions matching those of the experiment. RPM measured attenuation coefficients exhibited spatially-dependent biases when csam differed from cbf and cref. Mean errors of 19% were seen for simulated data, with the maximum errors in attenuation measurements occurring for regions of interest near the transmit focus. Biases were minimized (mean error with simulated data was 5.6%) using cbf that matched csam, and assuring that power spectra used for attenuation computations in the sample are from precisely the same depth as those from the reference. Setting the transmit focus well beyond the depth range used to compute attenuation values minimized the bias.

NAM, KIBO; ROSADO-MENDEZ, IVAN M.; RUBERT, NICHOLAS C.; MADSEN, ERNEST L.; ZAGZEBSKI, JAMES A.; HALL, TIMOTHY J.

2012-01-01

263

FDTD3C—A FORTRAN program to model multi-component seismic waves for vertically heterogeneous attenuative media  

NASA Astrophysics Data System (ADS)

Full-waveform seismic response of horizontally layered media can be calculated by semi-analytical methods. However, for gradient velocity and randomly heterogeneous structures the semi-analytical methods face difficulties. In such cases, numerical methods such as the finite-difference (FD) method have to be used. We develop an efficient numerical scheme to calculate plane-wave response of vertically heterogeneous attenuative media by applying Radon transform to the three-dimensional wave equation. The scheme employs fourth-order FD operator in space and second-order FD operator in time to solve the wave equation. In order to facilitate applicability of the scheme we introduce the FORTRAN code FDTD3C which implements the algorithm and provides multi-component response of the media to oblique incident P-, SV-, and SH-waves incoming from arbitrary azimuth. The calculated components are three particle velocity components in three Cartesian directions, and divergence and rotation of the wavefield. The code is extremely efficient and is capable of incorporating highly fluctuating subsurface velocity and attenuation models. This program is intended for all FD users who are concerned with full-waveform seismic modelling and inversion. Wide range of applicability of the code is demonstrated with a set of numerical examples.

JafarGandomi, Arash; Takenaka, Hiroshi

2013-02-01

264

Geodynamic Environment by Satellite Geodesy, Seismic Attenuation and S-wave Splitting. Example from Vrancea Seismogenic Zone, SE Carpathians  

NASA Astrophysics Data System (ADS)

In the Vrancea seismogenic zone (SE Carpathians), where very strong earthquakes (Mw > 7) are reported several times a century, the seismotectonics is very complex. It develops beneath the contact between the Moldavian East European Platform, the Scythian Platform, and the Moesian Platform, to the east and southeast, and terranes of the Transylvania Basin lying within the Carpathian arc. Several hypothesis have been considered by scientists in order to explain the clustered foci of crustal and intermediate events (as deep as 200 km). However, until now, there is no tectonic scenario which could explain all geological and geophysical observations. We try to integrate long-term permanent and campaign GPS outcomes with contributions from seismic attenuation and S-wave splitting results. GPS contributions mainly refer to determination of velocity vectors. 15 campaigns and seven permanent stations are being used in order to determine the detailed kinematics of an area characterized by very small velocities (1-2 mm/y), bringing the satellite technique to almost its limit. The results suggest a counterclockwise mantle flow around the Vrancea seismogenic zone, which is a high velocity body developed in an almost vertical position, developing deeper than 200 km. This results is also supported by seismic attenuation studies. We found that models like delamination and subduction could be supported by seismic attenuation studies in this zone. The delamination model implies strong upwelling and horizontal inflow of asthenosphere into the gap between the delaminating and remnant lithosphere. The other model implies downwelling and perhaps lateral-horizontal inflow along the slab detachment or tear. The models imply different distributions of density and rheological properties associated with the different lithosphere - asthenosphere structures. We use the ratio of spectral amplitudes of P and S waves from vertical and transverse seismograms to estimate the S to P ratio in the frequency domain, and then we calculate Qs, the relative shear wave attenuation via two complementary techniques: We find that stations located near and above the Vrancea zone and in the Transylvanian Basin, attenuation is high (low Q). Stations situated on the East European, Moesian, and Scythian Platforms are characterized by higher Qs (low attenuation). We interpret the high attenuation in the Vrancea and Transylvanian Basin is the result of shallow hot asthenosphere present in this area. Observations of source-side shear wave splitting clearly show that upper mantle anisotropy is strongly variable in the region of the tightly curved Carpathian Arc: shear waves taking off from Vrancea along paths that sample the East and Southern Carpathians have fast anisotropy axes parallel to these ranges, whereas those leaving the source region to traverse the upper mantle beneath the Transylvanian Basin (i.e., mantle wedge side) trend NE-SW. Shear waves sampling the East European and Scythian Platforms are separable into two groups, one characterized by fast shear trends to the NE-SW, and a second, deeper group, with trends to NW-SE; also, the majority of null splits occur along paths leaving Vrancea in these NE-E azimuths. Deeper fabric with E-W trend marking asthenospheric flow beneath the craton's base. This more complex anisotropy beneath the western edge of the East European Platform would account for both the variability of observed splitting of waves that sample this volume.

Mocanu, Victor; Russo, Raymond; Ambrosius, Boudewijn

2010-05-01

265

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

Microsoft Academic Search

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

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

2010-01-01

266

Pressure measurements of nonplanar stress waves  

SciTech Connect

Measuring the pressure of non-planar stress waves using thin piezo-resistive gages requires correcting for induced strain parallel to the sensing elements. A technique has been developed that permits such measurements, making use of a dual element gage. One element, Manganin, is sensitive to stress both parallel and perpendicular to the sensing element; the other element, Constantan, is primarily sensitive to stress parallel to the sensing element. The change in resistance in the Constantan element is thereby used to correct for the strain effect parallel to the Manganin element axis. Individual and combined Manganin and Constantan elements were subjected to controlled gas gun impact tests in the pressure and strain ranges of 0 to 50 kbar and 0 to 7%, respectively. From planar wave tests, the piezoresistivity of Constantan was found to be positive but negligible in comparison with Manganin. From combined stress and strain environments, the compression and tension strain factors of Constantan were found to be constant and equal to 2.06. The strain factors of Manganin were found to increase from 1.2 to 2.0 asymptotically in the range of 0 to 3% strain. It was experimentally demonstrated that, because of the closeness of their strain factors, the Manganin-Constantan dual element gage could be used in the differential recording mode to yield pressure directly. In this mode the gage is a strain compensating gage. Analytical techniques have also been developed for more accurate strain compensation.

Carlson, G.H.; Charest, J.A.

1981-01-01

267

Characterization of bubble liposomes by measurements of ultrasound attenuation: Effects of shell materials  

Microsoft Academic Search

Two types of gas-encapsulated liposomes (Bubble liposomes) with different shell compositions were evaluated by measurements of pressure-dependent ultrasound attenuation of bubble suspensions and by high-speed observations of bubble behaviors under exposure to pulsed ultrasound. Attenuation peaks were observed at the frequency range of 16-19 MHz, suggesting that the size of Bubble liposomes is around 400 nm. There was a large

Katsuji Sakaguchi; Nobuki Kudo; Katsuyuki Yamamoto; Ryo Suzuki; Kazuo Maruyama

2008-01-01

268

Attenuation corrections for in-cylinder NO LIF measurements in a heavy-duty Diesel engine  

Microsoft Academic Search

Quantification of the nitric oxide (NO) concentration inside the cylinder of a Diesel engine by means of laser-induced fluorescence\\u000a (LIF) measurements requires, amongst others, knowledge of the attenuation of the ultraviolet radiation involved. We present\\u000a a number of laser diagnostic techniques to assess this attenuation, enabling a correction for laser intensity and detection\\u000a efficiency of the raw NO LIF data.

K. Verbiezen; R. J. H. Klein-Douwel; A. P. van Vliet; A. J. Donkerbroek; W. L. Meerts; N. J. Dam; J. J. ter Meulen

2006-01-01

269

Wave buoy measurements at the Antarctic sea ice edge compared with an enhanced ECMWF WAM: Progress towards global waves-in-ice modelling  

NASA Astrophysics Data System (ADS)

The breakup of pack ice in the Weddell Sea is examined with respect to a single wave buoy, frozen into the pack ice six months earlier, and the ECMWF WAM model. The pack ice broke up around the buoy on 14th September 2000 as large amplitude storm waves approached the ice edge at the buoy's location. The WAM model is modified to allow waves to propagate into the ice cover, in contrast to the operational scheme which sets wave energy to zero at ice concentrations over 30%. A simple, lookup-table-based, wave scattering attenuation scheme is then added and is combined with a sea ice drag attenuation parameterisation. WAM results at the location of the buoy are compared to the observations over a two-month period straddling the breakup. The modified WAM scheme generally reproduces the significant wave height, wave period and spectral characteristics measured by the buoy, though the model does not yet have any concept of floe breaking and re-freezing, assuming only that the ice cover is broken if the concentration is less than 80%. The simplistic nature of these modifications is designed to allow operational implementation, to eventually provide a global assessment of the wave-influenced ice zone.

Doble, Martin J.; Bidlot, Jean-Raymond

2013-10-01

270

Direct Measurement of Wave-Induced Bottom Shear Stress Under Irregular Waves  

Microsoft Academic Search

\\u000a Wave-induced bottom shear stress is one of most important parameters in modelling of wave hydrodynamics and coastal sediment\\u000a transport, but has not been accurately estimated so far. A new type of shear plate is developed to measure instantaneous wave\\u000a bottom shear stress under both regular and irregular waves. The shear plate directly measures instantaneous horizontal force\\u000a by applying the Wheatstone

Zaijin You; Baoshu Yin; Guang Huo

271

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

272

VLF wave attenuation in the ionosphere observed by the DEMETER spacecraft in the vicinity of earthquakes  

NASA Astrophysics Data System (ADS)

We present a statistical study of VLF electromagnetic wave perturbations in the upper ionosphere based on almost 6.5 years of DEMETER satellite data. This spacecraft was operating between 2004 and 2010 at an altitude of ~ 660 km. We have processed all available data measured 0-4 hours before the time of the main shocks. we have selected data recorded when the satellite projection on the ground was within 440 km from the epicenters to large earthquakes. Altogether, data related to more than 9000 earthquakes selected from the USGS earthquake catalog with a magnitude larger or equal to 5 and a depth lower than 40 km have been analyzed. We have used a two-step data processing, which allows us to compare these data with an unperturbed background distribution based on data collected during the whole DEMETER mission. We confirm the previously reported results of a significant decrease of the wave intensity at a frequency of about 1.7 kHz. Two statistical tests show that this effect is unlikely to be random. Earthquake parameters needed to observe the phenomenon are discussed.

Píša, D.; N?mec, F.; Parrot, M.; Santolík, O.

2012-04-01

273

Anelastic structure and evolution of the continental crust and upper mantle from seismic surface wave attenuation  

NASA Astrophysics Data System (ADS)

Regional variations of the intrinsic shear wave quality factor Qµ in both the upper crust and upper mantle of continents are large, with values in old, stable cratons exceeding those in tectonically active regions in both depth ranges by as much as an order of magnitude or more. Qµ depends upon frequency, at least near 1 Hz, and that frequency dependence also varies regionally in the upper crust. It is typically low in tectonically active regions and higher in stable regions. Because of the large variations in Qµ from region to region, it is easy to map regional variations of both upper crustal Qµ and Q estimated from the coda of Lg waves (QLgc), even though both measurements may be marked by large uncertainties. Although coda Q of direct body waves may be strongly affected by scattering, QLgc appears to be primarily governed by intrinsic Qµ in the upper crust. Both upper crustal Qµ and QLgc values correlate with the time that has elapsed since the most recent tectonic activity in continental regions. A tomographic image of the variation of QLgc values across Africa shows reduced Q values which correspond to recent tectonic activity in the East African rift system and other regions of Mesozoic or younger age. Reductions of QLgc that correlate with tectonic activity that occurred in the early Paleozoic during the coalescence of the cratons which formed that continent can also be detected. Qµ increases rapidly at midcrustal depths, in a range which appears to coincide with the transition to the plastic lower crust. In the lower crust and upper mantle, Qµ decreases with increasing depth, possibly by progressive unpinning of dislocations with increasing temperature. Observed regional variations in upper mantle Qµ at depths of about 150 km can be explained by differences in temperature alone, but those at crustal depths cannot. Regional variations of Qµ in the upper crust are most easily explained by differences in the density of fluid-filled fractures in which fluids can move during the propagation of seismic waves. Studies of the regional variation of Qµ and QLgc indicate that crack density is greatest during and immediately following tectonic activity in a region and that it decreases with time. Permeability determinations in deep wells show that fluid movements in those cracks may be largely restricted to zones of crustal fracturing. That situation will produce widely differing values of Q in local studies, depending on the location of the study relative to the fractures. The fluid volume in cracks appears to decrease with time by loss to the surface or by retrograde metamorphism, causing a reduction in the number of open cracks and a concomitant increase in Qµ.

Mitchell, Brian J.

1995-11-01

274

Measurement of rainfall path attenuation near nadir: A comparison of radar and radiometer methods at 13.8 GHz  

Microsoft Academic Search

Rain profile retrieval from spaceborne radar is difficult because of the presence of attenuation at the higher frequencies planned for these systems. One way to reduce the ambiguity in the retrieved rainfall profile is to use the path-integrated attenuation as a constraint. Two techniques for measuring the path-integrated attenuation have been proposed: the radar surface reference technique and microwave radiometry.

S. L. Durden; Z. S. Haddad; A. Kitiyakara; F. K. Li; A. B. Tanner

1994-01-01

275

Wave intensity amplification and attenuation in non-linear flow: implications for the calculation of local reflection coefficients.  

PubMed

Local reflection coefficients (R) provide important insights into the influence of wave reflection on vascular haemodynamics. Using the relatively new time-domain method of wave intensity analysis, R has been calculated as the ratio of the peak intensities (R(PI)) or areas (R(CI)) of incident and reflected waves, or as the ratio of the changes in pressure caused by these waves (R(DeltaP)). While these methods have not yet been compared, it is likely that elastic non-linearities present in large arteries will lead to changes in the size of waves as they propagate and thus errors in the calculation of R(PI) and R(CI). To test this proposition, R(PI), R(CI) and R(DeltaP) were calculated in a non-linear computer model of a single vessel with various degrees of elastic non-linearity, determined by wave speed and pulse amplitude (DeltaP(+)), and a terminal admittance to produce reflections. Results obtained from this model demonstrated that under linear flow conditions (i.e. as DeltaP(+)-->0), R(DeltaP) is equivalent to the square-root of R(PI) and R(CI) (denoted by R(PI)(p) and R(CI)(p)). However for non-linear flow, pressure-increasing (compression) waves undergo amplification while pressure-reducing (expansion) waves undergo attenuation as they propagate. Consequently, significant errors related to the degree of elastic non-linearity arise in R(PI) and R(CI), and also R(PI)(p) and R(CI)(p), with greater errors associated with larger reflections. Conversely, R(Delta)(P) is unaffected by the degree of non-linearity and is thus more accurate than R(PI) and R(CI). PMID:19019371

Mynard, Jonathan; Penny, Daniel J; Smolich, Joseph J

2008-11-18

276

Attenuation and dispersion of compressional waves in fluid-filled porous rocks with partial gas saturation (White model). Part II. Results  

Microsoft Academic Search

In this investigation, Biot's (1962) theory for wave propagation in porous solids is applied to study the velocity and attenuation of compressional seismic waves in partially gas-saturated porous rocks. The physical model, proposed by White (1975), is solved rigorously by using Biot's equations which describe the coupled solid-fluid motion of a porous medium in a systematic way. The quantiative results

N. C. Dutta; H. Ode

1979-01-01

277

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

278

Statistical attenuation characteristics of radio waves with frequencies above 10 GHz on surface communication lines  

Microsoft Academic Search

The paper presents results of multiyear experimental studies of the statistical characteristics of microwave attenuation in the absence of rain. Experiments were conducted on a 12.65-km Dubna-Intercosmos link at frequencies of 11.5, 19.3, and 29.3 GHz, and on a 15.4-km link in Poland at a frequency of 18.6 GHz. Significant attenuation, associated with irregularities of the atmospheric refractive index, are

E. Aleksandrova; V. V. Sviatogor; V. N. Pozhidaev; A. Kavetski

1991-01-01

279

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

280

Toward Improved Methods of Estimating Attenuation, Phase and Group velocity of surface waves observed on Shallow Seismic Records  

NASA Astrophysics Data System (ADS)

This contribution is concerned with the estimate of attenuation and dispersion characteristics of surface waves observed on a shallow seismic record. The analysis is based on a initial parameterization of the phase and attenuation functions which are then estimated by minimizing a properly defined merit function. To minimize the effect of random noise on the estimates of dispersion and attenuation we use cross-correlations (in Fourier domain) of preselected traces from some region of interest along the survey line. These cross-correlations are then expressed in terms of the parameterized attenuation and phase functions and the auto-correlation of the so-called source trace or reference trace. Cross-corelation that enter the optimization are selected so as to provide an average estimate of both the attenuation function and the phase (group) velocity of the area under investigation. The advantage of the method over the standard two stations method using Fourier technique is that uncertainties related to the phase unwrapping and the estimate of the number of 2? cycle skip in the phase phase are eliminated. However when mutliple modes arrival are observed, its become merely impossible to obtain reliable estimate the dipsersion curves for the different modes using optimization method alone. To circumvent this limitations we using the presented approach in conjunction with the wavelet propagation operator (Kulesh et al., 2003) which allows the application of band pass filtering in (? -t) domain, to select a particular mode for the minimization. Also by expressing the cost function in the wavelet domain the optimization can be performed either with respect to the phase, the modulus of the transform or a combination of both. This flexibility in the design of the cost function provides an additional mean of constraining the optimization results. Results from the application of this dispersion and attenuation analysis method are shown for both synthetic and real 2D shallow seismic data sets. M. Kulesh, M. Holschneider, M. S. Diallo, Q. Xie and F. Scherbaum, Modeling of Wave Dispersion Using Wavelet Transfrom (Submitted to Pure and Applied Geophysics).

Diallo, M. S.; Holschneider, M.; Kulesh, M.; Scherbaum, F.; Ohrnberger, M.; Lück, E.

2004-05-01

281

Measurement of the Properties of Fluids Inside Pipes Using Guided Longitudinal Waves  

NASA Astrophysics Data System (ADS)

A new technique for measuring the longitudinal bulk velocity and shear viscosity of a fluid contained inside a pipe without a need for extracting a sample from the inside of the pipe is presented. It is based on the measurement of the change of the dispersion properties and attenuation of longitudinal guided waves propagating in the pipe due to the presence of the fluid. The technique to extract longitudinal bulk velocity and shear viscosity is discussed and experimentally demonstrated by measuring both low viscosity (glycerol) and highly viscous (Cannon viscosity standard VP8400) fluids.

Ma, J.; Lowe, M. J. S.; Simonetti, F.

2007-03-01

282

Photogrammetric Measurements of CEV Airbag Landing Attenuation Systems.  

National Technical Information Service (NTIS)

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...

A. W. Burner D. A. Barrows F. C. Berry H. R. Dismond K. H. Cate

2008-01-01

283

Fully automated attenuation measurement and motion correction in FLIP image sequences.  

PubMed

Fluorescence loss in photobleaching (FLIP) is a method to study compartment connectivity in living cells. A FLIP sequence is obtained by alternatively bleaching a spot in a cell and acquiring an image of the complete cell. Connectivity is estimated by comparing fluorescence signal attenuation in different cell parts. The measurements of the fluorescence attenuation are hampered by the low signal to noise ratio of the FLIP sequences, by sudden sample shifts and by sample drift. This paper describes a method that estimates the attenuation by modeling photobleaching as exponentially decaying signals. Sudden motion artifacts are minimized by registering the frames of a FLIP sequence to target frames based on the estimated model and by removing frames that contain deformations. Linear motion (sample drift) is reduced by minimizing the entropy of the estimated attenuation coefficients. Experiments on 16 in vivo FLIP sequences of muscle cells in Drosophila show that the proposed method results in fluorescence attenuations similar to the manually identified gold standard, but with standard deviations of approximately 50 times smaller. As a result of this higher precision, cell compartment edges and details such as cell nuclei become clearly discernible. The main value of this method is that it uses a model of the bleaching process to correct motion and that the model based fluorescence intensity and attenuation estimates can be interpreted easily. The proposed method is fully automatic, and runs in approximately one minute per sequence, making it suitable for unsupervised batch processing of large data series. PMID:21997250

van de Giessen, Martijn; van der Laan, Annelies; Hendriks, Emile A; Vidorreta, Marta; Reiber, Johan H C; Jost, Carolina R; Tanke, Hans J; Lelieveldt, Boudewijn P F

2011-10-13

284

Wind and wave measurements using complex ERS-2 SAR wave mode data  

Microsoft Academic Search

A global dataset of complex synthetic aperture (SAR) images is processed from wave mode raw data acquired by the ERS-2 satellite. Using these data, different algorithms for wind and wave measurements recently developed in view of future ENVISAT ASAR data are analyzed on a statistical basis. Different aspects of complex SAR wave mode processing with the DLR processor BSAR are

Susanne Lehner; Johannes Schulz-Stellenfleth; Birgit Schättler; Helko Breit; Jochen Horstmann

2000-01-01

285

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

286

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

287

Measurement of magnetostatic wave profiles using the interaction with transverse optical guided waves  

Microsoft Academic Search

The profile of magnetostatic forward volume waves along the direction of propagation is measured using the transverse interaction with optical guided modes. The technique is used in regimes of both linear and nonlinear magnetostatic wave excitation. A microwave input power of up to 700 mW in the frequency range of 6-8 GHz was used to excite magnetostatic waves in a

Andrew F. Cash; D. D. Stancil

1996-01-01

288

Excitation and measurement of flexural waves in arterial vessels  

Microsoft Academic Search

Pulse wave velocity in an artery is a very important indicator of the stiffness and disease of the artery. The pulse wave velocity is directly related to the Young's modulus in the circumferential direction of the artery by the well known Moens-Korteweg equation. Pulse wave velocity in an artery is measured with the standard pulse delay technique. However, the precise

Xiaoming Zhang; R. R. Kinnick; M. Fatemi; J. F. Greenleaf

2003-01-01

289

A Method of Usability Testing by Measuring Brain Waves  

Microsoft Academic Search

In this research, we propose a method for evaluating software usability with subject's brain waves. Two phases are conducted in this method. In the former phase, patterns of subject's brain waves are induced and measured, when the subject uses th e reference software for evoking subject's emotions or feelings related to software usability. In the latter phase, subject's brain waves

Jian Hu; Masahiro Nakanishi; Ken-ichi Matsumoto; Hirokazu Tagaito; Katsuro Inoue

290

Attenuation corrections for in-cylinder NO LIF measurements in a heavy-duty Diesel engine  

NASA Astrophysics Data System (ADS)

Quantification of the nitric oxide (NO) concentration inside the cylinder of a Diesel engine by means of laser-induced fluorescence (LIF) measurements requires, amongst others, knowledge of the attenuation of the ultraviolet radiation involved. We present a number of laser diagnostic techniques to assess this attenuation, enabling a correction for laser intensity and detection efficiency of the raw NO LIF data. Methods discussed include overall laser beam transmission, bidirectional laser scattering (bidirectional LIF), spectrally resolved fluorescence imaging, and Raman scattering by N2. A combination of techniques is necessary to obtain the complete attenuation of laser beam and NO fluorescence. The overall laser beam transmission measurements and bidirectional LIF measurements (the latter yielding spatially resolved transmission) provide evidence of a non-uniform attenuation distribution, with predominant attenuation within or near the piston bowl. Fluorescence imaging of multiple vibrational bands through a spectrograph is shown to be a powerful method for obtaining spatially resolved data on the transmission losses of fluorescence. Special attention is paid to the role of CO2 and O2 as UV light absorbers, and the consequences to different excitation-detection schemes for NO.

Verbiezen, K.; Klein-Douwel, R. J. H.; van Vliet, A. P.; Donkerbroek, A. J.; Meerts, W. L.; Dam, N. J.; Ter Meulen, J. J.

2006-04-01

291

Measurement of the attenuation coefficient for Livermore Thoracic Phantom lungs fabricated using contemporary materials.  

PubMed

The University of Cincinnati has reproduced the original formulation for the Livermore Thoracic Phantom lungs using contemporary materials and has adopted the linear attenuation coefficient as the primary quality assurance parameter for evaluating the performance capabilities of these new lung phantoms. The Livermore Thoracic Phantom was originally fabricated in 1978 to intercalibrate detector systems used to measure plutonium and other low-energy, photon emitting radionuclides deposited in the respiratory tract. The linear attenuation coefficient is a critical performance indicator for these phantom lungs since the presence of any material with a high effective atomic number (where Z > or = 20) will make a significant change in the photoelectric cross section, the predominant mode of interaction for plutonium x rays. A set of test lungs was fabricated with KCl to introduce a known quantity of 40K in the phantom and to determine, by measurement and calculations, what change would be made to the attenuation coefficient at photon energies below 100 keV as a result of the modified formulation. The KCl increased the linear attenuation coefficient below 60 keV by more than a factor of two, which would produce a substantial systematic error in any subsequent calibration measurements performed with these modified phantom lungs. These results support use of the attenuation coefficient as an important performance indicator for the Livermore Thoracic Phantom lungs and also suggest that KCl not be added to the lung tissue substitute formulation as a means to incorporate 40K in the phantom for low energy calibrations. PMID:8200800

Spitz, H; Glover, S; Liu, N; Smith, B; Hickman, D; Kruchten, D; Anderson, L

1994-07-01

292

A Computer Controlled Attenuation Measurement System for TE01Mode Circular Waveguide from 32 to 110 GHz  

Microsoft Academic Search

The paper describes a computer controlled attenuation measurement system. This has been developed for the measurement of the attenuation of the British Post Office Research Department field trial TE01-mode circular waveguide route. Measurements must be made at close frequency spacing over the whole waveguide band from 32 to 110 GHz. In order to achieve the high measurement speed which is

R. P. Bomer

1974-01-01

293

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

294

Attenuation distance of low frequency waves upstream of the pre-dawn bow shock: GEOTAIL and ISEE 3 comparison  

NASA Astrophysics Data System (ADS)

We have made a statistical study of the spatial distribution of low frequency waves (approx. 0.01-0.1 Hz) in the region upstream of the pre-dawn to dawn side bow shock (-50 Re less than X less than 15 Re) using both GEOTAIL and international sun earth explorer 3 (ISEE-3) magnetometer data. We have found that the wave amplitude dependence on D and X(sub s), where D is the distance from the bow shock and X(sub s) the x-coordinate position of shock foot point of the IMF, can be described by a functional form of A exp (X(sub s)/L(sub X)-D/L(sub D), with the characteristic attenuation distances, L(sub X) = 62 +/- 12 Re and L(sub D) = 59 +/- 38 Re.

Sugiyama, T.; Terasawa, T.; Kawano, H.; Yamamoto, T.; Kokubun, S.; Frank, L. A.; Ackerson, K.; Tsurutani, B. T.

1995-01-01

295

Ten-element photodetector for optical power and attenuation measurements  

SciTech Connect

The properties of what is, to the best of our knowledge, the first ten-element polarization-dependent transmission trap detector consisting of silicon photodiodes are described. The responsivity and the transmittance of the photodetector were measured at laser wavelengths of 476.2 and 647.1nm. In particular, the effect of the polarization state of the incident radiation on the transmittance was determined. Differences in transmittance of an order of magnitude were observed between s and p polarization. These values were compared with theoretical values calculated using the Fresnel reflection formulas. The difference between the calculated and measured values was less than {+-}3x10{sup -7}. The spatial nonuniformity of the response was measured to be less than {+-}3x10{sup -4}. The transmittance was measured to be spatially uniform across a 5mmx5mm area of the trap detector aperture to within {+-}1.5x10{sup -6} for s-polarized input and within {+-}1.5x10{sup -7} for p-polarized input.

Kuebarsepp, Toomas; White, Malcolm

2010-07-01

296

An indirect method of X-ray spectra measurement by simultaneous attenuations of the scattered beam  

NASA Astrophysics Data System (ADS)

Direct and indirect methods of X-ray spectra determination present obstacles to their practical use since they must position either the collimator-detector assembly or the attenuators-ionization chamber, respectively, along the X-ray beam direction. These arrangements require considerable space and in many instances the detectors promptly saturate. An indirect procedure, which overcomes the aforementioned problems, is developed. It consists of the scattering of the X-ray beam from a carbon disk, which is detected simultaneously by several detectors placed away from the beam. The X-ray flux reaching each of these detectors is attenuated in metal sheets of different thicknesses, thus obtaining simultaneously the attenuation curve values. A set of analytical equations are derived to calculate attenuation curves by taking into account all the absorption and elastic and inelastic scattering processes that a beam of photons undergoes when going from the X-ray tube to the detector. Users, even those who are not well acquainted with computer programming, can easily obtain the X-ray spectrum by a least square fitting of a measured attenuation curve to a previously derived analytical expression. A simulated Monte Carlo program of photon transport from the X-ray tube to the detector provided simulated attenuation curves data. Analytically calculated and simulated attenuation curves for the same input spectrum wholly overlap and furthermore, reconstructed spectra from both sets of curves for different kilovoltages are also in full agreement. Finally, in addition to the importance of having the detectors out of the beam direction, the proposed arrangement features other main advantages, namely, only one X-ray tube shot is needed to obtain the required data, the physical processes involved are very well known, analytical equations are easily interpreted, and the measuring apparatuses can be comparatively simple to assemble and operate.

Mainardi, Raúl T.; Bonzi, Edgardo V.

2008-05-01

297

Depolarization, Scattering, and Attenuation of Circularly Polarized Radio Waves by Spherically Asymmetric Melting Ice Particles  

Microsoft Academic Search

The eccentric spheres model and an extended Mie solution are used to formulate scattering of a plane, electromagnetic wave by a single melting ice particle as well as by a horizontal layer of such particles. The incident wave is left-hand circularly polarized, whereas the scattered wave, as a result of depolarization by the spherically asymmetric particles, comprises left-hand and right-hand

Melina P. Ioannidou; Dimitris P. Chrissoulidis

2007-01-01

298

Digital measurements of LF radio wave absorption in the lower ionosphere and inferred gravity wave activity  

Microsoft Academic Search

Low frequency (LF) radio wave absorption in the lower ionosphere has been measured at Pruhonice (approximately 50 deg N) since 1957. A new digital computer-controlled measuring-recording-processing system was introduced in 1988. The A3 method of radio wave absorption measurement, the measuring equipment used for the digital measurements at 270 kHz, is briefly described. The digital nighttime LF A3 measurements allow

J. Lastovicka; J. Boska; D. Buresova

1993-01-01

299

Shock Wave Propagation Measurements in Glow Discharge Plasmas  

NASA Astrophysics Data System (ADS)

Mach 1.5--2.2 shock waves are produced in argon over a range of pressures 3--15 Torr by a fast capacitor discharge (quarter period ?1/4 = 1.4 ?s). The shock waves are allowed to traverse through a glow discharge plasma inside the shock tube, where the deflections of the laser beams, caused by the density jump at the shock front, are recorded on a fast oscilloscope. An average shock wave velocity in plasma is determined from the time history of the laser deflection signals. Shock wave speeds in plasma are found to be dependent on the plasma discharge current. Shock wave speeds increase by 18% for the plasma at 3.6 Torr over a range of plasma discharge current I = 0--150 mA and by 46% for the plasma at 15 Torr over I = 7--150 mA. In addition, shock wave amplitudes are attenuated in plasma and show linear dependence on the shock wave speed or Mach number.

Podder, Nirmol K.; Tarasova, Anastasia V.; Wilson, Ralph B., IV

2006-10-01

300

Measurements of Impedance and Attenuation at CENELEC Bands for Power Line Communications Systems  

PubMed Central

Power line impedance is a very important parameter on the design of power line communications (PLC) modem architecture. Variations on the impedance of the power line affect the communications circuit performance. In order to determine impedance of the power lines, measurements were carried out in Turkey at frequencies ranging from 10 to 170 kHz, (CENELEC A,B,C,D bands). Measurements were conducted in three categories: rural, urban and the industrial power lines. Experimental results are presented in graphical form. The measured impedances were determined as 3-17 ohms, 1-17 ohms, and 1-21 ohms for rural, urban and the industrial lines, respectively. A set of the formulas between impedance and frequency are developed on the power lines using the regression analysis from the obtained empirical data. Signal attenuations on the power lines in the CENELEC band are also measured for rural, urban and industrial regions. Attenuation measurements are repeated for phase-neutral, phase-ground and the neutral-ground conductors. Signal attenuations are found to be 4-30 dB, for different power lines. To establish validity of obtained results for the design of PLC systems, the results are compared with previous investigations. The effects of some household appliances such as TV, PC, UPS, lighting and cooling systems on the impedances and the attenuations for power line communications systems are observed. Some suggestions and proposals are presented for PLC modem designers.

Cavdar, I. Hakki; Karadeniz, Engin

2008-01-01

301

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

302

Breaking wave measurements with sar depolarized returns  

Microsoft Academic Search

The wind generates a distribution of small slope waves and sporadic steep breaking events. Such double structure of the sea surface is expected to have a strong impact on the radar scattering from the ocean surface. The signature of the double structure is in the wind speed dependence of radar returns: linear for scattering from gentle waves and cubic for

Paul A. Hwang; Biao Zhang; William Perrie

2010-01-01

303

The experimental study of acoustic waves of frequency ? 40GHz  

Microsoft Academic Search

The temperature dependencies of attenuation of: (i) longitudinal and shear waves in lithium niobate, (ii) longitudinal waves in ruby, and (iii) longitudinal and shear waves in magnesium aluminate spinel (spinel) at the frequency 36.5 GHz were measured. For the most crystals and wave types the temperature range was 78- ~150 K, i.e. the strong attenuation did not allow to watch

Boris Zaitsev; Iren Kuznetsova; M. Grigoriev

2009-01-01

304

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

305

Regional Wave Propagation from Mexican Subduction Zone Earthquakes: The Attenuation Functions for Interplate and Inslab Events  

Microsoft Academic Search

The seismic waves from subduction zone earthquakes are significantly affected by the presence of 3D variation in crust and upper-mantle structure around the source area. These heterogeneous structures also profoundly modify the character of seismic waves as they propagate from the source area to regional distances. This is illustrated by studying shallow, interplate earthquakes along the Mexican subduc- tion zone,

T. Furumura; S. K. Singh

2002-01-01

306

Radio-Wave Propagation Into Large Building Structures—Part 1: CW Signal Attenuation and Variability  

Microsoft Academic Search

We report on our investigation into radio communications problems faced by emergency responders in disaster situations. A fundamental challenge to communications into and out of large buildings is the strong attenuation of radio signals caused by losses and scattering in the building materials and structure. Another challenge is the large signal variability that occurs throughout these large structures. We designed

William F. Young; Christopher L. Holloway; Galen Koepke; Dennis Camell; Yann Becquet; Kate A. Remley

2010-01-01

307

Effects of pressure and saturating fluid on wave velocity and attenuation in anisotropic rocks  

Microsoft Academic Search

We obtain the energy velocities and quality factors of anisotropic reservoir rocks as a function of pore pressure, partial saturation and frequency. The model is based on Biot's poroelastic theory for anisotropic media. The directional dependence of attenuation is obtained by generalizing the eigenstiffnesses of the undrained medium to relaxation functions (six at most, depending on the material symmetry). The

J. M. Carcione; K. Helbig; H. B. Helle

2003-01-01

308

Attenuation and reflection of radio waves by a melting layer of precipitation  

Microsoft Academic Search

Attenuation and reflection of a melting layer are calculated using a meteorological model. The model employs (1) a new scheme for calculating the dielectric properties of melting ice particles with densities ranging from those of loose snow to hail and (2) a new scheme for calculating the melting rate. The input parameters are derived from high-resolution Doppler radar data and

W. Klaassen

1990-01-01

309

WATER CONTENT MEASUREMENT WITH 60 keV GAMMA RAY ATTENUATION  

Microsoft Academic Search

The purpose of this paper is to discuss the specific problems dealing with the use of Americium 241 for measuring the water content of soil sample by attenuation of low energy gamma rays. One of the advantages is that the optimum thickness of the soil sample is about 4 to 5 cm. However, one of the difficulties encountered is related

P. H. GROENEVELT; J. G. de SWART; J. CISLER

1969-01-01

310

Measurement of the Gouy phase anomaly for electron waves  

NASA Astrophysics Data System (ADS)

We measure the Gouy phase anomaly for matter waves using in-line holography to retrieve the full complex field of an astigmatic electron wave function. Sequential phase shifts of ?/2 rad are observed for electron trajectories along the optic axis that pass through each line-focus caustic of subnanometer transverse width. Our observations demonstrate that anomalous phase shifts of matter waves in the vicinity of caustics can be robustly measured using phase retrieval, extending the current scope of singular electron optics.

Petersen, T. C.; Paganin, D. M.; Weyland, M.; Simula, T. P.; Eastwood, S. A.; Morgan, M. J.

2013-10-01

311

Seismic wave attenuation from borehole and surface records in the top 2.5 km beneath the city of Basel, Switzerland  

NASA Astrophysics Data System (ADS)

We investigate attenuation (Q-1) of sediments of 2.5-3.5 km thickness underneath the city of Basel, Switzerland. We use recordings of 195 induced events that were obtained during and after the stimulation of a reservoir for a Deep Heat Mining Project in 2006 and 2007. The data set is ideally suited to estimate Q as all events are confined to a small source volume and were recorded by a dense surface network as well as six borehole sensors at various depths. The deepest borehole sensor is positioned at a depth of 2.7 km inside the crystalline basement at a mean hypocentral distance of 1.8 km. This allows us to measure Q for frequencies between 10 and 130 Hz. We apply two different methods to estimate Q. First, we use a standard spectral ratio technique to obtain Q, and as a second measure we estimate Q in the time domain, by convolving signals recorded by the deepest sensor with a Q operator and then comparing the convolved signals to recordings at the shallower stations. Both methods deliver comparable values for Q. We also observe similar attenuation for P- and S- waves (QP˜QS). As expected, Q increases with depth, but with values around 30-50, it is low even for the consolidated Permian and Mesozoic sediments between 500 and 2700 m.

Bethmann, Falko; Deichmann, Nicholas; Mai, P. Martin

2012-08-01

312

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

313

New method to measure the attenuation of hadrons in extensive air showers  

SciTech Connect

Extensive air showers are generated through interactions of high-energy cosmic rays impinging the Earth's atmosphere. A new method is described to infer the attenuation of hadrons in air showers. The numbers of electrons and muons, registered with the scintillator array of the KASCADE experiment, are used to estimate the energy of the shower inducing primary particle. A large hadron calorimeter is used to measure the hadronic energy reaching observation level. The ratio of energy reaching ground level to the energy of the primary particle is used to derive an attenuation length of hadrons in air showers. In the energy range from 10{sup 6} to 3x10{sup 7} GeV the attenuation length obtained increases from 170 to 210 g/cm{sup 2}. The experimental results are compared to predictions of simulations based on contemporary high-energy interaction models.

Apel, W. D.; Badea, F.; Bekk, K.; Bozdog, H.; Daumiller, K.; Doll, P.; Engel, R.; Engler, J.; Finger, M.; Gils, H. J.; Haungs, A.; Heck, D.; Huege, T.; Isar, P. G.; Klages, H. O.; Mathes, H. J.; Mayer, H. J.; Milke, J.; Nehls, S.; Oehlschlaeger, J. [Institut fuer Kernphysik, Forschungszentrum Karlsruhe, 76021 Karlsruhe (Germany)] (and others)

2009-07-15

314

Electron temperature measurements in plasmas with surface wave absorption and wave cutoff frequency  

Microsoft Academic Search

A method for the measurements of electron temperature in the plasma using cutoff frequency and surface wave absorption frequency is described. The cutoff frequency, which gives directly the plasma density, is obtained from the transmission spectrum measured between two antennas exposed to the plasma. The surface wave absorption frequency, which has the information of the sheath determined by the electron

Jung-Hyung Kim; S. J. You; Dae-Jin Seong; Yong-Hyeon Shin

2007-01-01

315

Transducer Instrumentation for Surface Wave Measurement.  

National Technical Information Service (NTIS)

The transducer instrumentation system portion of the surface wave system is described. An accelerometer is vertically stabilized by a gyro. This gyro also drives potentiometers which provide pitch and roll outputs. Heading is obtained by a gyro-stabilized...

H. D. Goldberg M. I. Goldberg

1969-01-01

316

The photon transverse wave function and its measurement  

Microsoft Academic Search

We report on a technique to measure the photon transverse wave function in coordinate space using a photon-counting, parity-inverting Sagnac interferometer. We present measurements of a TEM10 Hermite-Gaussian beam

B. J. Smith; M. G. Raymer; Bryan Killett; K. Banaszek; I. A. Walmsley

2004-01-01

317

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

318

Spatial variations of P wave attenuation in the mantle beneath North America  

Microsoft Academic Search

We estimate the spatial variation of the seismic parameter t* using teleseismic (epicentral distance = 30°–85°) P wave spectra of about 200 deep (focal depths > 200 km) earthquakes recorded by 378 broadband seismometers in the United States and Canada. Relative P wave spectral ratios up to 1 Hz for about 63,000 station pairs with high signal-to-noise ratio and impulsive

Yong Keun Hwang; Jeroen Ritsema; Saskia Goes

2009-01-01

319

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

320

Variation of coda wave attenuation in the Alborz region and central Iran  

NASA Astrophysics Data System (ADS)

More than 340 earthquakes recorded by the Institute of Geophysics, University of Tehran (IGUT) short period stations from 1996 to 2004 were analysed to estimate the S-coda attenuation in the Alborz region, the northern part of the Alpine-Himalayan orogen in western Asia, and in central Iran, which is the foreland of this orogen. The coda quality factor, Qc, was estimated using the single backscattering model in frequency bands of 1-25 Hz. In this research, lateral and depth variation of Qc in the Alborz region and central Iran are studied. It is observed that in the Alborz region there is absence of significant lateral variation in Qc. The average frequency relation for this region is Qc = 79 +/- 2f1.07+/-0.08. Two anomalous high-attenuation areas in central Iran are recognized around the stations LAS and RAZ. The average frequency relation for central Iran excluding the values of these two stations is Qc = 94 +/- 2f0.97+/-0.12. To investigate the attenuation variation with depth, Qc value was calculated for 14 lapse times (25, 30, 35,... 90s) for two data sets having epicentral distance range R < 100 km (data set 1) and 100 < R < 200 km (data set 2) in each area. It is observed that Qc increases with depth. However, the rate of increase of Qc with depth is not uniform in our study area. Beneath central Iran the rate of increase of Qc is greater at depths less than 100 km compared to that at larger depths indicating the existence of a high attenuation anomalous structure under the lithosphere of central Iran. In addition, below ~180 km, the Qc value does not vary much with depth under both study areas, indicating the presence of a transparent mantle under them.

Rahimi, H.; Motaghi, K.; Mukhopadhyay, S.; Hamzehloo, H.

2010-06-01

321

Intrinsic attenuation and scattering of shear waves in the lithosphere of Kamchatka  

Microsoft Academic Search

Records of small local Kamchatka earthquakes were processed using Multiple Lapse Time Window Analysis (MLTWA). The method\\u000a makes use of normalized integrals of 3D seismic energy density in several windows applied to an earthquake record that has\\u000a been put through a bandpass filter. The intrinsic attenuation and scattering properties of the earth were estimated by choosing\\u000a parameters that provide the

V. K. Lemzikov

2007-01-01

322

Measuring acoustic nonlinearity parameter using collinear wave mixing  

NASA Astrophysics Data System (ADS)

This study introduces a new acoustic nonlinearity parameter ?T. It is shown that ?T is associated with the interaction between a longitudinal wave and a shear wave in isotropic elastic solids with quadratic nonlinearity. Experimental measurements are conducted to demonstrate that the collinear wave mixing technique is capable of measuring ?T nondestructively. Further, it is shown that ?T is well-correlated with the plastic deformation in Al-6061 alloys. These results indicate that collinear wave mixing is a promising method for nondestructive assessment of plastic deformation, and possibly, fatigue damage in metallic materials.

Liu, Minghe; Tang, Guangxin; Jacobs, Laurence J.; Qu, Jianmin

2012-07-01

323

Magnetic Wave Field Measurements In The Solar Orbiter Project  

NASA Astrophysics Data System (ADS)

Although the wave activity observed in the solar wind near the terrestrial orbit is rather well understood, many questions remain concerning waves that occur much closer to the Sun. The measurements closest to the Sun have so far been obtained by the Helios 1 and 2 spacecraft at approximately 0.3 AU. Based on these observations, we present the characteristics of the waves that are expected to occur near 0.2 AU and discuss the magnetic field sensors that are required to measure them. The Search Coil Magnetometer (SCM) we propose is the part of the Radio and plasma wave experiment that is described in Maksimovic et al., 2006.

Krasnoselskikh, V.; Pinçon, J.-L. Dudok de Wit, T.; Fergeau, P.; Jannet, G.; Chust, T.; Coillot, C.; Maksimovic, M.

2007-01-01

324

CFHT’s Skyprobe: True Atmospheric Attenuation Measurement in the Telescope Field  

Microsoft Academic Search

Developed at the Canada France Hawaii Telescope (CFHT), SkyProbe is a system that allows the direct measurement of the true\\u000a attenuation by clouds. This measurement is performed approximately once per min, directly on the field viewed by the telescope.\\u000a It has been possible to make this system relatively inexpensively due to low cost CCD cameras available on the amateur market.

Jean-Charles Cuillandre; Eugene A. Magnier; Sidik Isani; Dan Sabin; Wiley Knight; Simon Kras; Kamson Lai

2004-01-01

325

SHEAR-WAVE Q AND ITS FREQUENCY DEPENDENCE IN THE CRUST OF SOUTHEASTERN ASIA FROM SURFACE-WAVE ATTENUATION  

Microsoft Academic Search

Models of shear-wave Q (Qµ) have been obtained for the crust over a broad region of southeastern Asia, including China and portions of surrounding countries, using a single-station multi-mode method. Event and station coverage is sufficient to allow the mapping of Qµ variations for three depth ranges in the crust and, in some sub-regions, the uppermost mantle. In layer 1

Alemayehu L. Jemberie; Brian J. Mitchell

2002-01-01

326

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

327

Techniques for measuring aerosol attenuation using the Central Laser Facility at the Pierre Auger Observatory  

NASA Astrophysics Data System (ADS)

The Pierre Auger Observatory in Malargüe, Argentina, is designed to study the properties of ultra-high energy cosmic rays with energies above 1018eV. It is a hybrid facility that employs a Fluorescence Detector to perform nearly calorimetric measurements of Extensive Air Shower energies. To obtain reliable calorimetric information from the FD, the atmospheric conditions at the observatory need to be continuously monitored during data acquisition. In particular, light attenuation due to aerosols is an important atmospheric correction. The aerosol concentration is highly variable, so that the aerosol attenuation needs to be evaluated hourly. We use light from the Central Laser Facility, located near the center of the observatory site, having an optical signature comparable to that of the highest energy showers detected by the FD. This paper presents two procedures developed to retrieve the aerosol attenuation of fluorescence light from CLF laser shots. Cross checks between the two methods demonstrate that results from both analyses are compatible, and that the uncertainties are well understood. The measurements of the aerosol attenuation provided by the two procedures are currently used at the Pierre Auger Observatory to reconstruct air shower data.

The Pierre Auger Collaboration

2013-04-01

328

Shear wave speed measurement using an unfocused ultrasound beam.  

PubMed

Tissue elasticity is related to pathology and, therefore, has important medical applications. Radiation force from a focused ultrasound beam has been used to produce shear waves in tissues for shear wave speed and tissue elasticity measurements. The feasibility of shear wave speed measurement using radiation force for an unfocused ultrasound beam is demonstrated in this study with a linear and a curved array transducer. Consistent measurement of shear wave speed was achieved over a relatively long axial extent (z = 10-40 mm for the linear array, and z = 15-60 mm for the curved array) in three calibrated phantoms with different shear moduli. In vivo measurements on the biceps of a healthy volunteer show consistent increase of shear wave speed for the biceps under 0, 1, 2 and 3 kg loading. Advantages and limitations of unfocused push are discussed. PMID:22766123

Zhao, Heng; Song, Pengfei; Urban, Matthew W; Greenleaf, James F; Chen, Shigao

2012-07-03

329

Electron temperature measurements in plasmas with surface wave absorption and wave cutoff frequency  

SciTech Connect

A method for the measurements of electron temperature in the plasma using cutoff frequency and surface wave absorption frequency is described. The cutoff frequency, which gives directly the plasma density, is obtained from the transmission spectrum measured between two antennas exposed to the plasma. The surface wave absorption frequency, which has the information of the sheath determined by the electron density and the electron temperature, is obtained from the reflection spectrum measured at radiating antenna. The electron temperature is derived from the dispersion equation of the surface wave with the electron density measured from cutoff frequency.

Kim, Jung-Hyung; You, S. J.; Seong, Dae-Jin; Shin, Yong-Hyeon [Center for Vacuum Technology, Korea Research Institute of Standards and Science, Daejeon 305-306 (Korea, Republic of)

2007-11-12

330

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

331

Ultrafast optical measurements of ultrasound attenuation in amorphous silicon at 50 and 100 GHz  

NASA Astrophysics Data System (ADS)

We present ultrafast optical measurements of the attenuation of 50 -- 100 GHz ultrasound in hydrogenated amorphous silicon (a-Si:H) thin films. The films were grown using a modified very high frequency glow discharge method on steel substrates. The deposition conditions were similar to those used for high efficiency solar cells. The measurements were performed at 300 K using the picosecond ultrasonics technique. Films of varying thickness were measured so that the effect of intrinsic acoustic loss within the a-Si:H could be determined. We find that the ultrasonic attenuation in a-Si:H at 100 GHz is more than an order of magnitude lower than is found in other amorphous materials. Our results may impact theoretical models of thermal transport in amorphous materials, and could provide a new avenue for studying voids in a-Si:H and nanocrystalline Si films.

Daly, Brian; Hondongwa, Donald; Norris, Theodore; Yan, Baojie; Yang, Jeff; Guha, Subhendu

2011-03-01

332

IWA : an analysis program for isentropic wave measurements.  

SciTech Connect

IWA (Isentropic Wave Analysis) is a program for analyzing velocity profiles of isentropic compression experiments. IWA applies incremental impedance matching correction to measured velocity profiles to obtain in-situ particle velocity profiles for Lagrangian wave analysis. From the in-situ velocity profiles, material properties such as wave velocities, stress, strain, strain rate, and strength are calculated. The program can be run in any current version of MATLAB (2008a or later) or as a Windows XP executable.

Ao, Tommy

2009-02-01

333

Stiffness matrix determination of composite materials using lamb wave group velocity measurements  

NASA Astrophysics Data System (ADS)

The use of Lamb waves in Non-Destructive Evaluation (NDE) and Structural Health Monitoring (SHM) is gaining popularity due to their ability to travel long distances without significant attenuation, therefore offering large area inspections with a small number of sensors. The design of a Lamb-wave-based NDE/SHM system for composite materials is more complicated than for metallic materials due to the directional dependence of Lamb wave propagation characteristics such as dispersion and group velocity. Propagation parameters can be theoretically predicted from known material properties, specifically the stiffness matrix and density. However, in practice it is difficult to obtain the stiffness matrix of a particular material or structure with high accuracy, hence introducing errors in theoretical predictions and inaccuracies in the resulting propagation parameters. Measured Lamb wave phase velocities can be used to infer the stiffness matrix, but the measurements are limited to the principal directions due to the steering effect (different propagation directions of phase and corresponding group velocities). This paper proposes determination of the stiffness matrix from the measured group velocities, which can be unambiguously measured in any direction. A highly anisotropic carbon-fibre-reinforced polymer plate is chosen for the study. The influence of different stiffness matrix elements on the directional group velocity profile is investigated. Thermodynamic Simulated Annealing (TSA) is used as a tool for inverse, multi variable inference of the stiffness matrix. A good estimation is achieved for particular matrix elements.

Putkis, O.; Croxford, A. J.

2013-04-01

334

High dynamic range terahertz-wave transmission loss measurement at 330-500 GHz  

NASA Astrophysics Data System (ADS)

Terahertz-wave transmission loss measurement systems at 330-500 GHz using single- and dual-channel superheterodyne receivers are described. It is shown that the phase noise effect in a single-channel system causes significant signal level fluctuation in the lock-in amplifier. The dual-channel system can eliminate the phase noise effect in synchronous detection and achieve a room-temperature noise floor of -170 dBm. The dynamic range of the dual-channel system is estimated to be 140-152 dB. The measurement uncertainty of the system is analyzed. A 0-100 dB WR-2.2 waveguide attenuator can be measured with expanded uncertainties of 0.078-0.24 dB at 480 GHz. The dual-channel system can serve as a national measurement standard for waveguide transmission measurement at 330-500 GHz and provide traceability for measurements made using commercial instruments.

Wu, Thomas Y.

2012-08-01

335

Measurements of radiated elastic wave energy from dynamic tensile cracks  

NASA Astrophysics Data System (ADS)

To determine the conditions under which elastic waves are radiated from crack sources, dynamic tensile cracks were propagated in glass samples in the double cantilever beam geometry. This geometry allows simple calculation of the strain energy release rate G at initiation from measured parameters of crack length, applied crack opening force, and crack opening displacement. Partial control over the strain energy state in the sample at fracture initiation, and hence G at initiation, was achieved by varying the geometry of the notch tip from which the fracture emanates. Elastic wave displacements were monitored with a broadband capacitance transducer with a pointlike probe. A single component of elastic wave displacement (parallel to the crack plane and perpendicular to the crack propagation direction) was measured. Two fracture configurations were investigated: (1) "primary fracture" in glass plates of dimension 305×102 ×12.7 mm and (2) "secondary fracture" in previously fractured glass plates of the same dimensions, bonded intermittently along the fracture plane. Primary fracture experiments afforded a means of investigating elastic wave radiation from mode I cracks in a highly brittle material, such that the strain energy released by the fracture is partitioned into fracture surface energy of the newly formed crack walls and radiated elastic wave energy; negligible energy is expended in ductile or frictional processes. Secondary fracture experiments afforded a means of investigating elastic wave radiation in the case of varying fracture surface energy along the crack path. For primary fracture, measurable elastic waves from the macrofracture were generated in 31% of the 16 dynamic fracture events monitored. The condition for radiation of measurable waves from these fractures appears to be a local abrupt change in the fracture path direction, such as occurs when the fracture intersects a surface flaw. For the five events with measurable elastic waves, the ratio of radiated elastic wave energy in the measured component to the fracture surface energy of the macrocrack was 0.0001-0.001. For secondary fracture, 100% of the 13 events monitored showed measurable elastic waves. The ratio of radiated elastic wave energy in the measured component to fracture surface energy was 0.001-0.01, or 10 times greater than for primary fracture. The observed value of G at crack initiation for both primary and secondary fracture ranged from 3 to 48 J m-2. When the time window for radiated elastic wave energy calculation was restricted to a few microseconds after the first arrival, a weak correlation of radiated elastic wave energy with initiation G value was observed for secondary fractures.

Boler, Frances M.

1990-03-01

336

Spin wave relaxation rate measurement under perpendicular pumping  

Microsoft Academic Search

This paper is concerned with the time variation of the RF magnetization of a ferrite biased to resonance and subject to a first-order spin wave instability. Two methods of a fully experimental measurement of the spin wave relaxation rates are derived from the theoretical results. Experiments are given which were performed in a nonresonant device in order to avoid spurious

BERNARD DESORMIERE; EDOUARD MILOT

1967-01-01

337

Anelastic structure and evolution of the continental crust and upper mantle from seismic surface wave attenuation  

Microsoft Academic Search

Regional variations of the intrinsic shear wave quality factor Qmu in both the upper crust and upper mantle of continents are large, with values in old, stable cratons exceeding those in tectonically active regions in both depth ranges by as much as an order of magnitude or more. Qmu depends upon frequency, at least near 1 Hz, and that frequency

Brian J. Mitchell

1995-01-01

338

Anelastic structure and evolution of the continental crust and upper mantle from seismic surface wave attenuation  

Microsoft Academic Search

Regional variations of the intrinsic shear wave quality factor Qµ in both the upper crust and upper mantle of continents are large, with values in old, stable cratons exceeding those in tectonically active regions in both depth ranges by as much as an order of magnitude or more. Qµ depends upon frequency, at least near 1 Hz, and that frequency

Brian J. Mitchell

1995-01-01

339

Patterns of spiral wave attenuation by low-frequency periodic planar fronts  

Microsoft Academic Search

There is evidence that spiral waves and their breakup underlie mechanisms related to a wide spectrum of phenomena ranging from spatially extended chemical reactions to fatal cardiac arrhythmias [A. T. Winfree, The Geometry of Biological Time (Springer-Verlag, New York, 2001); J. Schutze, O. Steinbock, and S. C. Muller, Nature 356, 45 (1992); S. Sawai, P. A. Thomason, and E. C.

Miguel A. de La Casa; F. Javier de La Rubia; Plamen Ch. Ivanov

2007-01-01

340

Permeability and Elastic Wave Velocity and Attenuation of Tight Porous Rock.  

National Technical Information Service (NTIS)

The study of seismic waves in tight gas sandstones is aimed at determining partial gas saturation in situ from logs. The purpose of the study of the effects of water and its salinity on gas flow in tight gas sandstones is to estimate in situ gas permeabil...

A. Nur

1982-01-01

341

The Ground-Wave Attenuation Function for Propagation over a Highly Inductive Surface.  

National Technical Information Service (NTIS)

Propagation of an electromagnetic ground wave over a plane surface in which the argument of the surface impedance is greater than wavelength/4 but less than wavelength/2 is considered in some detail. The numerical distance, p, over such a surface is chara...

R. J. King G. A. Schlak

1966-01-01

342

Direct measurement of evanescent wave enhancement inside passive metamaterials  

NASA Astrophysics Data System (ADS)

Electric-field measurements inside a negative-permeability-positive-permittivity metamaterial composed of arrays of split-ring resonators directly show that the theoretically predicted enhancement of evanescent waves in passive materials is physically realizable. To circumvent the extreme sensitivity of this phenomenon to the material parameters, we show how the basic phenomenon occurs under relaxed conditions for a single transverse wave number and use this approach in our measurements. Measurements of the spatial distribution of the electric field in a three-slab configuration confirm that the evanescent wave enhancement responsible for the subwavelength focusing effect occurs in an electromagnetic material in a manner in close agreement with theory.

Popa, Bogdan-Ioan; Cummer, Steven A.

2006-01-01

343

Attenuation measurement in low-loss optical glass by polarized radiation.  

PubMed

For the production of fiber waveguides suitable for optical communications cables, glasses with extremelylow attenuation are required. A new method is described for measuring the optical attenuation of bulk glasses in the wavelength range of 0.4-1.1 microm. Using a quartz halogen source with highly stabilized radiation power, a linearly polarized, monochromatic, collimated beam was produced, passing the sample at the Brewster angle. Transmission loss, residual reflection, and surface scattering were measured by low-noise photodiodes and integrating digital voltmeters. A stability of 10(-5) and a resolution of 10(-5) or better were achieved. Results for two different kinds of commercial glasses, fused quartz (Ultrasil) and synthetic vitreous silica (Suprasil W1), are reported and discussed. PMID:20155151

Heitmann, W

1975-12-01

344

Estimation of the source parameters of the Himalaya earthquake of October 19, 1991, average effective shear wave attenuation parameter and local site effects from accelerograms  

Microsoft Academic Search

A simple and rapid methodology based on band-limited strong motion data to obtain estimates of double couple fault plane solution, average effective shear wave attenuation parameter (Qseff) and locate and analyze sub-events of the earthquake process has been presented. This method will be particularly efficient in the study of smaller earthquakes that may have been recorded locally at a small

Dinesh Kumar; Irene Sarkar; V. Sriram; K. N. Khattri

2005-01-01

345

Attenuation and dispersion of compressional waves in fluid-filled porous rocks with partial gas saturation (White model). Part I. Biot theory  

Microsoft Academic Search

An exact theory of attenuation and dispersion of seismic waves in porous rocks containing spherical gas pockets (White model) is presented using the coupled equations of motion given by Biot. Assumptions made are (1) the acoustic wavelength is long with respect to the distance between gas pockets and their size, and (2) the gas pockets do not interact. Thus, the

N. C. Dutta; H. Ode

1979-01-01

346

High frequency ultrasound measurements of the attenuation and backscatter from biological tissues  

NASA Astrophysics Data System (ADS)

There are now diagnostic ultrasonic imaging devices that operate at very high frequencies (VHF) of 20 MHz and beyond for clinical applications in ophthalmology, dermatology, and vascular surgery. To be able to better interpret these images and to further the development of these devices, knowledge of ultrasonic attenuation and scattering of biological tissues in this high frequency range is crucial. Though currently VHF ultrasound is applied mostly to the eye and skin tissue, in this thesis, VHF experiments were performed on porcine red blood cell suspensions and bovine myocardium, liver, and kidney because these tissues are easy to obtain, are similar in structure to their human counterparts and have been used in ultrasound experiments by many investigators but in a lower frequency range. Attenuation and backscatter coefficients of porcine blood and bovine tissues were measured, respectively, using substitution methods. Unfocused and focused transducers were employed in the experiments and corresponding results were compared. This dissertation presents the results of measurements of acoustic attenuation and backscatter from various biological materials (bovine myocardium, liver, and kidney, and porcine blood) in a wide frequency range (10 to 90 MHz) and compares them to previous lower frequency results. Based on the methods used to calculate the acoustic parameters, the frequency limits of the measurements are also defined.

Maruvada, Subha

347

Determination of mineral concentration in dental enamel from X-ray attenuation measurements.  

PubMed

The mineral content of dental enamel is commonly measured by X-ray attenuation experiments. Most studies have used contact microradiography in which intensities are measured with photographic film which is convenient and gives high spatial resolution. However photon counting intensity measurements are to be preferred in many experiments (longitudinal and scanning microradiography, and microtomography), as illustrated here, because they have a larger dynamic range and greater sensitivity to small intensity changes. Additionally, the detector and specimen are well separated which allows the pseudo-continuous study of de- and remineralization. The mineral content is often quoted as 95 wt% or 87 vol% hydroxyapatite for permanent human enamel. This determination from attenuation experiments requires accurate values of elemental mass attenuation coefficients and a number of assumptions. The effects of possible choices of these are considered and it is shown that the most important is the density of enamel mineral used in conversion of wt% to vol%. If the density is taken as 2.99 g cm(-3), as recently suggested (J.C. Elliott, Dental Enamel, Ciba Foundation Symposium 205, Wiley, Chichester, pp. 54-72, 1997), instead of 3.15 g cm(-3) as for hydroxyapatite, the calculated vol% is approximately 93 instead of approximately 87. PMID:11063016

Elliott, J C; Wong, F S; Anderson, P; Davis, G R; Dowker, S E

1998-01-01

348

Volumetric measurements of a spatially growing dust acoustic wave  

NASA Astrophysics Data System (ADS)

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.

2012-11-01

349

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

350

Measuring high-frequency wave propagation in railroad tracks by joint time-frequency analysis  

NASA Astrophysics Data System (ADS)

The behavior of high-frequency elastic waves propagating in railroad tracks is relevant to the field of rail noise generation and long-range rail inspection. While a large amount of theoretical and numerical work exists to predict transient vibrations propagating in rails, obtaining experimental data has been particularly challenging due to the multimode and dispersive behavior of the waves. In this work a joint time-frequency analysis based on the Gabor wavelet transform is employed for characterizing longitudinal, lateral and vertical vibrational modes propagating in rails in the 1000-7000Hz range. The Gabor transform optimizes the time-frequency resolution of the measurements and theoretically requires a single excitation point and a single measurement point. These features make the analysis well-suited for the study of wave propagation in rails. The theory of the wavelet transform is reviewed in the context of dispersive measurements. Accelerometer data were taken from a section of rail subject to impulse dynamic testing in the laboratory. The group (energy) velocity dispersion curves and the frequency-dependent attenuation of the waves were successfully extracted from the wavelet scalograms of the accelerometer signals.

Lanza di Scalea, F.; McNamara, J.

2004-06-01

351

Radiometric measurement of zenith path attenuation due to rain at 19.9 GHz at Amritsar, India  

Microsoft Academic Search

This paper describes the measurement of zenith path attenuation due to rain in winter and monsoon seasons of the year 2001 at Amritsar (31° 38' N 74° 52' E) India, using zenith looking radiometer operating at 19.9 GHz frequency. The effective rain height has been obtained from the analysis of the radiometric data and point rainfall intensity. Specific attenuation for

I. S. Hudiara; Ashok Kumar; Sarita Sharma

2004-01-01

352

Separation of intrinsic and scattering seismic wave attenuation in Northeast India  

NASA Astrophysics Data System (ADS)

We have analysed the local earthquakes (2.0 ? ML ? 5.5) occurred in northeast (NE) India recorded by a temporary seismic network of 10 stations operated by National Geophysical Research Institute (NGRI), Hyderabad to evaluate the relative contributions of scattering loss (Q_{sc}^{ - 1}) and intrinsic absorption (Q_i^{ - 1}) to total attenuation (Q_t^{ - 1}) using the multiple lapse time window analysis assuming multiple isotropic scattering in a medium of uniformly distributed scatterers. The results show that Q_i^{ - 1} is greater than Q_{sc}^{ - 1} at high frequencies (f > 3 Hz), while the opposite is observed at low frequencies (f < 3 Hz). The observed frequency dependence of Q_{sc}^{ - 1} corresponds to the scale length of lithospheric heterogeneity beneath NE India, at least comparable with the wavelength for the lowest frequencies analysed, of about 1 km. The observed Q_{{c}}^{ - 1} for the study region obtained with single scattering theory is close to Q_i^{ - 1} at high frequencies, in agreement with theoretical prediction for an idealized case of uniform distribution of scatterers. However, a discrepancy exists between the two at low frequencies, which can be explained by a depth-dependent velocity and attenuation structure. High value of Q_t^{ - 1} is correlated with the geology and tectonic settings of the region characterized by Himalayan and Burman collision zones with a strong lateral heterogeneity. The Q_i^{ - 1} estimates obtained in this study can be used to infer the average temperature of the lower crust with an upper limit estimate of ˜800 °C assuming a lower crustal gabbroic lithology. small

Padhy, Simanchal; Subhadra, N.

2013-09-01

353

IWA: An Analysis Program for Isentropic Wave Measurements.  

National Technical Information Service (NTIS)

IWA (Isentropic Wave Analysis) is a program for analyzing velocity proles of isentropic compression experiments. IWA applies incremental impedance matching correction to measured velocity proles to obtain in-situ particle velocity proles for Lagrangian wa...

T. Ao

2009-01-01

354

Phase velocity dispersion and attenuation of seismic waves due to trapped fluids in residual-saturated porous media  

NASA Astrophysics Data System (ADS)

Propagation of seismic waves in partially saturated porous media depends on various material properties, e.g. saturation, porosity, elastic properties of the skeleton, viscous properties of the pore fluids and, additionally, capillary pressure and effective permeability. If the wetting fluid is in a discontinuous state, i.e. residual-saturated configuration, phase velocities and frequency-dependent attenuation additionally depend on microscopical (pore-scale) properties such as droplet and/or ganglia size. To model wave propagation in residual-saturated porous media, we developed a three-phase model based on an enriched continuum mixture theory capturing the strong coupling between the micro- and the macroscale. The three-phase model comprises the porous solid skeleton, a continuous fluid part and a discontinuous fluid part. The discontinuous part describes the movement of blobs/clusters of the wetting fluid and is based on an oscillator rheology. On the microscale, the oscillators are determined by their mass, damping and eigenfrequency. Amongst others, these properties depend on the microscopic geometry and surface tension. To embed the microscopic oscillators into a macroscopic poroelastic description of the non-wetting fluid and the skeleton, a scale bridging between both spatial scales is applied conserving density, eigenfrequency and damping. This homogenization approach accounts for the discontinuous character of the wetting fluid. Furthermore, probability density functions are used to describe the size distribution of different kinds of fluid clusters. The discontinuous fluid part is linked to the continuous solid phase by momentum exchange in the form of pinned or sliding oscillators. The non-wetting continuous fluid phase exhibits similar behavior as the poroelastic model introduced by Biot. The final model delivers insight into the behavior of propagating waves on the macroscale, influenced by different properties of the microscopic oscillating fluid clusters. Furthermore, the dispersion relations allow for a comparison with continuous models, such as the Biot model, and for the calculation of characteristic values, which might be helpful for the comparison with experimental studies. We define a dimensionless parameter that determines if the overall motion of the residual fluid is dominated by oscillations (underdamped, resonance) or not (overdamped). Our results show that the residual fluid has a significant impact on the velocity dispersion and attenuation, no matter if it oscillates or not. For long wavelengths, our model coincides with the Biot-Gassmann equations. We show under which conditions and how the classical biphasic models can be used to approximate the dynamic behavior of residual-saturated porous media.

Steeb, H.; Kurzeja, P.; Frehner, M.; Schmalholz, S. M.

2012-04-01

355

Measurement of shock waves in the focus of a lithotripter  

Microsoft Academic Search

For the measurement of ultrasonic shock waves with amplitudes near 40 MPa, two different hydrophones were constructed. The first is a high-bandwidth PVDF membrane hydrophone with a capacitively coupled signal. The second is a small acousto-optic fiber hydrophone which measures the shock-wave-induced variation of the refractive index of a liquid at the front end of the fiber. The properties of

B. Granz; R. Holzapfel; G. Kohler

1989-01-01

356

Schlieren measurements of internal waves in non-Boussinesq fluids  

Microsoft Academic Search

Previous experiments that have examined the generation of internal gravity waves by a monochromatic source have been restricted\\u000a to small amplitude forcing in Boussinesq stratified fluids. Here we present measurements of internal waves generated by a\\u000a circular cylinder oscillating at large amplitude in a non-Boussinesq fluid. The ‘synthetic schlieren’ optical measurement\\u000a technique (Sutherland et al. in J Fluid Mech 390:93–126, 1999)

H. A. Clark; Bruce R. Sutherland

2009-01-01

357

Surface acoustic-wave attenuation by a two-dimensional electron gas in a strong magnetic field  

NASA Astrophysics Data System (ADS)

The propagation of a surface acoustic wave (SAW) on GaAs/AlxGa1-xAs heterostructures is studied in the case where a two-dimensional electron gas (2DEG) is subject to a strong magnetic field and a smooth random potential with correlation length ? and amplitude ?. The electron wave functions are described in a quasiclassical picture using results of percolation theory for two-dimensional systems. In accordance with the experimental situation, ? is assumed to be much smaller than the sound wavelength 2?/q. This restricts the absorption of surface phonons at a filling factor ?¯~=1/2 to electrons occupying extended trajectories of fractal structure. Both piezoelectric and deformation potential interactions of surface acoustic phonons with electrons are considered and the corresponding interaction vertices are derived. These vertices are found to differ from those valid for three-dimensional bulk phonon systems with respect to the phonon wave-vector dependence. We derive the appropriate dielectric function ?(?,q) to describe the effect of screening on the electron-phonon coupling. In the low-temperature, high-frequency regime T<attenuation coefficient ? and ?(?,q) are independent of temperature. The classical percolation indices give ?/2?=3/7. The width of the region where a strong absorption of the SAW occurs is found to be given by the scaling law \\|??¯\\|~=(?q?/vD)?/2?. The dependence of the electron-phonon coupling and the screening due to the 2DEG on the filling factor leads to a double-peak structure for ?(?¯).

Knäbchen, Andreas; Levinson, Yehoshua B.; Entin-Wohlman, Ora

1996-10-01

358

Attenuation and scintillation of radio waves in the Earth's atmosphere from radio occultation experiments on satellite-to-  

Microsoft Academic Search

A theoretical analysis of refractive loss of radio waves by the Earth's atmosphere in radio occultation measurements along the satellite-to-satellite line for various altitude profiles of the refractive index is given. Experimental results for refractive loss on the orbital spacecraft - geostationary satellite link are presented. Theoretical calculations are compared with experimental data, and a conclusion is drawn that the

O. I. Yakovlev; I. A. Vilkov

1995-01-01

359

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

360

Millimeter wave passive components for polarization measurements  

NASA Astrophysics Data System (ADS)

The Stokes parameters of the polarized sky emission are detected by a correlation unit called Hybrid Phase Discriminator (HPD), which uses signals obtained by an Ortho-mode Transducer (OMT). In the millimeter wave range and for rather large bandwidths, heterodyne receivers are not applicable, and the correlation units have to work at the frequency of the radiometer. This contribution deals with a Ka-band prototype of a new configuration of waveguide HPD, which presents a high degree of sensitivity for the detection of linearly polarized radiation. .

Peverini, O. A.; Baralis, M.; Tascone, R.; Trinchero, D.; Olivieri, A.; Carretti, E.; Cortiglioni, S.

2002-03-01

361

S wave attenuation in the coastal region of Jalisco–Colima, México  

Microsoft Academic Search

Aftershock data from the October 9, 1995, M=7.6 earthquake, that occurred in the coastal subduction region of Colima–Jalisco, Mexico, are used to obtain estimates of the frequency independent quality factor Qs and spectral decay parameter ?, in the approximate frequency range 3 Hz?f?40 Hz, as functions of hypocentral distance r. A regression analysis results in the relations for S waves:Qs=261.397+3.198r±15.536?=0.009651+0.000462r±0.0012.The

F. Alejandro Nava; Rosal??a Garc??a-Arthur; Raul R Castro; Carlos Suárez; Bertha Márquez; Francisco Núñez-Cornú; Gustavo Saavedra; Roberto Toscano

1999-01-01

362

Directional wave measurements from three wave sensors during the FETCH experiment  

NASA Astrophysics Data System (ADS)

During the Flux, Etat de la mer et Télédéction en Condition de fetcH variable (FETCH) experiment, directional wave measurements were made by an airborne radar RESSAC and by two moored buoys, an Air-Sea Interaction Spar (ASIS) and a Directional Waverider. In order to define the performance and compatibility of these wave sensors with different measuring principles, a comparison of the directional measurements in a variety of meteorological conditions during the experiment is presented in this paper. It was found that within the limits of their operational ranges, the sensors agreed on the one-dimensional spectrum and the basic parameters derived from it—significant wave height and peak frequency. The sensors reported the directional features of the wave field and the mean direction consistently, but in some cases the two buoys disagreed on the directional width of the spectrum. Most of these cases were associated with a single swell-dominated event.

Pettersson, Heidi; Graber, Hans C.; Hauser, DanièLe; Quentin, CéLine; Kahma, Kimmo K.; Drennan, William M.; Donelan, Mark A.

2003-03-01

363

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

364

Physical measurements of breaking wave impact on a floating wave energy converter  

NASA Astrophysics Data System (ADS)

Marine energy converter must both efficiently extract energy in small to moderate seas and also successfully survive storms and potential collisions. Extreme loads on devices are therefore an important consideration in their design process. X-MED is a SuperGen UKCMER project and is a collaboration between the Universities of Manchester, Edinburgh and Plymouth and the Scottish Association for Marine Sciences. Its objective is to extend the knowledge of extreme loads due to waves, currents, flotsam and mammal impacts. Plymouth Universities contribution to the X-MED project involves measuring the loading and response of a taut moored floating body due to steep and breaking wave impacts, in both long crested and directional sea states. These measurements are then to be reproduced in STAR-CCM+, a commercial volume of fluid CFD solver, so as to develop techniques to predict the wave loading on wave energy converters. The measurements presented here were conducted in Plymouth Universities newly opened COAST laboratories 35m long, 15.5m wide and 3m deep ocean basin. A 0.5m diameter taut moored hemispherical buoy was used to represent a floating wave energy device or support structure. The changes in the buoys 6 degree of freedom motion and mooring loads are presented due to focused breaking wave impacts, with the breaking point of the wave changed relative to the buoy.

Hann, Martyn R.; Greaves, Deborah M.; Raby, Alison

2013-04-01

365

Molecular Velocity Distribution Function Measurements in a Normal Shock Wave  

Microsoft Academic Search

Molecular velocity distribution functions have been measured throughout a normal, M = 1.59 helium shock wave that was formed in a low-density wind tunnel. The measurements were obtained by using the electron beam fluorescence technique. Throughout the shock transition, distributions of random velocities were observed from directions both parallel and perpendicular to the flow. Also, direct measurements were made of

E. P. Muntz; L. N. Harnett

1969-01-01

366

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

367

Mechanical Loss Measurements of Coated Substrates for Gravitational Wave Interferometry  

NASA Astrophysics Data System (ADS)

Gravitational waves from sources such as binary star systems, supernovae explosions and stochastic background radiation have yet to be directly detected by experimental observations. Alongside international collaborators, the Laser Interferometer Gravitational-Wave Observatory (LIGO) is designed to realize direct detection of gravitational waves using interferometric techniques. The second generation of gravitational wave observatories, known as Advanced LIGO, are currently undergoing installation and commissioning at sites in Hanford, Washington and Livingston, Louisiana. The ultimate sensitivity of Advanced LIGO within select spectral bands is limited by thermal noise in the high-reflective coatings of the interferometer optics. The LIGO lab at American University is measuring the mechanical loss of coated substrates to predict thermal noise within these spectral bands. These predictions are used to ensure the ultimate design sensitivity of Advanced LIGO and to study coating and substrate materials for future gravitational wave detectors.

Newport, Jonathan; Belyea, David; Robie, Raymond; Harry, Gregg

2013-03-01

368

Attenuation of the S+Lg+Surface Wave Group out to 600 km in Northeastern North America: A Baseline Study?  

NASA Astrophysics Data System (ADS)

We analyze the S+Lg+surface wave groups radiated out to 600 km by four moderate (4 ? M ? 5) earthquakes in Quebec, New York, and Maine: the 1997 Cap Rouge, 2002 Ausable Forks, 2005 Rivière du Loup, and 2006 Bar Harbor earthquakes. The raypaths predominately sample the Appalacian Province, and the crustal velocity structure is roughly homogeneous across the study area. We compute spectra using 20-60 s windows of the horizontal broadband components. We restrict our analysis to hard-rock (Vs > 1500 m/s) and soft-rock (Vs > 700 m/s) sites, avoiding resonant sedimentary sites; we model site amplification using average 1D impedance functions (Boore and Joyner, 1997). We use ro = 50 km instead of ro = 100 km for the crossover distance in the Street et al. (1975) function for geometrical spreading: this distance adjusts the corrected spectra at 10 s to the moment tensor estimates. This simple correction scheme allows us to regress for Q directly as a function of frequency: the source spectral shape is entirely unconstrained. Fitting a Qo f q function to the Q estimates from 0.2 to 25 Hz yields Q = 410 f 0.5 for a group velocity of 3.5 km/s. This attenuation is stronger than the Lg attenuation of 650 f 0.36 obtained by Erickson et al. (2004). The Q estimates are consistent for individual events. For f > 20 Hz, the Q estimates increase more rapidly than f 0.5: this deviation from the Qo f q form appears characteristic. To gauge how these Q estimates depend on the distance limit, we will rerun the analysis using broadband data out to 1000 km, adding 30% more recordings to the dataset.

Boatwright, J.; Seekins, L. C.

2009-12-01

369

Permeability and Elastic Wave Velocity and Attenuation of Tight Porous Rock.  

National Technical Information Service (NTIS)

A rapid, accurate method for measuring the gas permeability of low permeability sandstones has been developed and tested. The apparatus can measure permeability from .01 microdarcy to several hundred microdarcy with simulated pore pressure and confining p...

A. Nur

1981-01-01

370

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

371

Lidar Measurements of Gravity Wave Spectra from Eureka, Canada  

NASA Astrophysics Data System (ADS)

Compositional variations of critical species such as ozone and water vapour in the polar middle atmosphere are intimately tied to dynamical variations, including perturbations and mixing due to waves. The suite of instruments at the Canadian Network for the Detection of Atmospheric Change's (CANDAC) Polar Environment Atmosphere Research Laboratory (PEARL) in Eureka, Canada (80°N, 86°W) is particularly well instrumented with sensors capable of measuring the chemical and dynamic state of the lower, middle and upper atmosphere. During the intensive Polar Sunrise ACE Validation Campaign of February and March 2009, 19 nights of relative density measurements were made with the CANDAC - Environment Canada DIAL lidar, and the perturbations due to gravity waves in the stratosphere above Eureka were found to have nightly-averaged potential energy per unit mass on the order of 10 J/kg. The variability evident over the course of each night, as well as variations on timescales of days, were similar to previous measurements from this system in the 1990's by Whiteway, Duck and colleagues, who interpreted these spectra as a superposition of many waves. Further analysis of the current measurements using Prony's method will be carried out to determine if only a few waves are present at high latitudes, and whether these waves carry most of the wave energy, similar to what was found in the upper stratosphere at middle latitudes by the University of Western Ontario's Purple Crow Lidar.

McCullough, E. M.; Sica, R. J.; Strawbridge, K. B.; Drummond, J. R.

2009-12-01

372

An Instrument for the Measurement of Spectral Attenuation Coefficient and Narrow Angle Volume Scattering Function of Ocean Waters.  

National Technical Information Service (NTIS)

A new instrument has been developed for the study of those optical properties of ocean water that affect the transmission of image-forming light. The instrument performs simultaneous measurements of the volume attenuation coefficient and the volume scatte...

R. W. Austin T. J. Petzold

1975-01-01

373

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

374

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

375

Ultrasonic Attenuation Measurement in Semi-insulating GaAs with Defects in the EL2 and EL2* States  

Microsoft Academic Search

The longitudinal ultrasonic attenuation in semi-insulating GaAs with grown-in EL2 defects has been measured in the temperature range between 80 K and 140 K. Measurement of the ultrasonic attenuation is based on the phase detection technique. A Matec-8000 system with a single transducer set up was used in this work. The samples that were used in this experiment were all

Fouzi Arammash

2001-01-01

376

Telemetry system for slow wave measurement from the small bowel  

Microsoft Academic Search

A telemetry capsule system was designed and implemented to measure the slow wave activity of the small bowel, which is an\\u000a important parameter for the diagnosis of gastric diseases. The capsule amplified the slow wave signal from the intraluminal\\u000a electrodes, and transmitted the digitally sampled data by means of a radio frequency transmitter. The implemented capsule\\u000a (11 × 21 mm2) was smaller than

S. H. Woo; J. H. Cho

2010-01-01

377

Underwater depth reconstruction by local water wave measurements  

NASA Astrophysics Data System (ADS)

We present an experimental study of underwater depth reconstruction obtained by a method based on the Bessel series expansion of the solutions of the 2D linear water wave equation. This is achieved by measuring capillary-gravity waves using a contactless space-time resolved Fourier Transform Profilometry method. The ability of the method is exemplified for several type of bathymetry in laboratory experiments.

Przadka, A.; Petitjeans, P.; Pagneux, V.; Maurel, A.; Ing, R. K.

2013-09-01

378

Measurements and global models of surface wave propagation  

Microsoft Academic Search

A new technique for making single-station phase velocity measurements is developed and applied to a large number of globally recorded Rayleigh and Love waves in the period range 35-150 s. The method is based on phase-matched filter theory and iteratively suppresses the effect of interfering overtones by minimizing residual dispersion. The model surface wave signal is described by its amplitude

Göran Ekström; Jeroen Tromp; Erik W. F. Larson

1997-01-01

379

Open ocean surface wave measurement using Doppler sonar  

Microsoft Academic Search

In October-November 1983, Doppler sonars mounted on the research platform Flip were used to scatter 75-kHz sound from the underside of the sea surface at low angle, as well as from the interior of the mixed layer. Surface gravity waves were seen in velocity estimates from the surface scattering sonar, even though the wave conditions were unusually calm. Valid measurements

R. Pinkel; J. A. Smith

1987-01-01

380

Measurement of light-cone wave functions by diffractive dissociation  

Microsoft Academic Search

Diffractive dissociation of particles can be used to study their light-cone wave function. Results from Fermilab experiment E791 for diffractive dissociation of 500 GeV\\/c?? mesons into di-jets are presented. The results show that the |qq?? light-cone asymptotic wave function describes the data well for Q2 ? 10 (GeV\\/c)2 or more. Evidence for color transparency comes from a measurement of the

Daniel Ashery; Beverly Sackler

2000-01-01

381

The criteria for measuring average density by x-ray attenuation: The role of spatial resolution  

SciTech Connect

It is well known that the attenuation of X-rays as they pass through a material can be used to quantify the amount of matter in their path. This is the basis for the gamma ray densitometer which can measure the amount of material on a moving conveyor belt. It is also the rationale for using X-rays for medical imaging as the attenuation can discriminate between tissue of different density and composition, yielding images of great diagnostic utility. Spatial resolution is obviously important with regard to detecting small features. However, it is less obvious that it plays an important role in obtaining quantitative information from the X-ray transmission data since the spatial resolution of the instrument can affect the accuracy of those measurements. This problem is particularly severe in the case of computed tomography where the accuracy of the reconstruction is dependent on the accuracy of the initial projection data. It should be noted that spatial resolution is not a concern for the case where the material is uniform. Here uniform is defined by small variations related to either the scale size of the resolution element in the detector, or to the size of a collimated X-ray beam. However, if the material has non-homogeneous composition or changes in density on the scale size of the systems spatial resolution, then there can be effects that will compromise the transmission data before it is acquired and these errors can not be corrected by any subsequent data processing. A method is presented for computing the density measurement error which parameterizes the effect in terms of the actual modulation on the face of the detector and the attenuation in the material. For cases like stacks of lead plates the errors can exceed 80%.

Friedman, W.

1999-07-29

382

Complexity measures of brain wave dynamics.  

PubMed

To understand the nature of brain dynamics as well as to develop novel methods for the diagnosis of brain pathologies, recently, a number of complexity measures from information theory, chaos theory, and random fractal theory have been applied to analyze the EEG data. These measures are crucial in quantifying the key notions of neurodynamics, including determinism, stochasticity, causation, and correlations. Finding and understanding the relations among these complexity measures is thus an important issue. However, this is a difficult task, since the foundations of information theory, chaos theory, and random fractal theory are very different. To gain significant insights into this issue, we carry out a comprehensive comparison study of major complexity measures for EEG signals. We find that the variations of commonly used complexity measures with time are either similar or reciprocal. While many of these relations are difficult to explain intuitively, all of them can be readily understood by relating these measures to the values of a multiscale complexity measure, the scale-dependent Lyapunov exponent, at specific scales. We further discuss how better indicators for epileptic seizures can be constructed. PMID:22654989

Gao, Jianbo; Hu, Jing; Tung, Wen-Wen

2011-02-09

383

High-accuracy wave-number measurements in molecular iodine.  

PubMed

Absolute wave-number measurements, with an accuracy of 2-11 parts in 10(9), are presented for 27 (127)I(2) hyperfine-structure lines in the range 5763-6563 A. Individual components were resolved by saturation spectroscopy and their wave numbers measured by a comparison with wavelength standards made using a temperature-stabilized Fabry-Perot interferometer. Good consistency is found among the four accepted (127)I(2)wavelength standards. The result of a previous measurement at 6563 A, which was used as the basis for a Rydberg-constant determination, is also confirmed. PMID:19718101

Hlousek, L; Fairbank, W M

1983-06-01

384

Precision Ultrasonic Wave Measurements with Simple Equipment.  

National Technical Information Service (NTIS)

The authors describe the design and construction of a relatively simple, inexpensive laser interferometer system for accurate measurements of ultrasonic surface displacement waveforms in reasonable friendly environments. The authors show how analysis of a...

S. E. Fick C. H. Palmer

2001-01-01

385

Measurement of ocean wave heights using the Geos 3 altimeter  

Microsoft Academic Search

Radar altimeter signals transmitted from the low-orbiting satellite Geos 3 were analyzed for two selected orbits over high seas associated with hurricane 'Caroline' in the Gulf of Mexico and a North Atlantic storm. The measured values of significant wave height are in reasonable agreement with surface measurements, provided that the altimeter data are properly edited. The internal consistency of estimated

Clifford L. Rufenach; Werner R. Alpers

1978-01-01

386

Measurement of Ocean Wave Heights Using the Geos 3 Altimeter  

Microsoft Academic Search

Radar altimeter signals transmitted from the low-orbiting satellite Geos 3 were analyzed for two selected orbits over high seas associated with hurricane 'Caroline' in the Gulf of Mexico and a North Atlantic storm. The measured values of significant wave height are in reasonable agreement with surface measurements, provided that the altimeter data are properly edited. The internal consistency of estimated

Clifford L. Rufenach; Werner R. Alpers

1978-01-01

387

A New Dual Channel Pulse Wave Velocity Measurement System  

Microsoft Academic Search

Pulse wave velocity (PWV) is the most popular index to assessment the arterial stiffness. Currently, several non-invasive examination methods with single channel for PWV are announced. This paper proposes a non-invasive digital volume pulse (DVP) measuring system using a dual channel simultaneous measurement method try to meet the demands for home healthcare equipment which is easy to operate. Through synchronal

Yung-kang Chen; Hsien-tsai Wu; Chih-kai Chi; Wei-chuan Tsai; Ju-yi Chen; Ming-chun Wang

2004-01-01

388

On the Use of Radiometric Measurements to Estimate Atmospheric Attenuation at 100 and 300 GHz  

NASA Astrophysics Data System (ADS)

At frequencies of between 100 GHz and 30 THz, propagation conditions are severely affected by the influence of the composition and phenomena of the troposphere. This paper focuses on the use of radiometric measurements to estimate attenuation at 100 and 300 GHz, considering non-scattering scenarios, in which the main contributions are given by atmospheric gases and non-rainy clouds. These techniques allow the estimation of the absorption loss through the entire atmosphere, without the need for a signal source situated in a satellite or a high altitude aircraft. On the basis of well-accepted absorption models, the results of calculating gaseous, cloud, and total attenuation using 3-year meteorological data from Madrid, Spain, are detailed, as well as estimates of the expected values of the sky brightness temperature as measured by the radiometer. Finally, based on the results obtained, a discussion on the use of radiometric measurements at both frequencies is presented, in connection with an experimental campaign currently under preparation.

Siles, Gustavo A.; Riera, José M.; García-Del-Pino, Pedro

2011-04-01

389

Wavenumber prediction and measurement of axisymmetric waves in buried fluid-filled pipes: Inclusion of shear coupling at a lubricated pipe/soil interface  

NASA Astrophysics Data System (ADS)

Acoustic methods have been widely used to detect water leaks in buried fluid-filled pipes, and these technologies also have the potential to locate buried pipes and cables. Relatively predictable for metal pipes, there is considerably more uncertainty with plastic pipes, as the wave propagation behaviour becomes highly coupled between the pipe wall, the contained fluid and surrounding medium. Based on the fully three-dimensional effect of the surrounding soil, pipe equations for n=0 axisymmetric wave motion are derived for a buried, fluid-filled pipe. The characteristics of propagation and attenuation are analysed for two n=0 waves, the s=1 wave and s=2 wave, which correspond to a predominantly fluid-borne wave and a compressional wave predominantly in the shell, respectively. At the pipe/soil interface, two extreme cases may be considered in order to investigate the effects of shear coupling: the "slip" condition representing lubricated contact; and the "no slip" condition representing compact contact. Here, the "slip" case is considered, for which, at low frequencies, analytical expressions can be derived for the two wavenumbers, corresponding to the s=1 and s=2 waves. These are both then compared with the situations in which there is no surrounding soil and in which the pipe is surrounded by fluid only, which cannot support shear. It is found that the predominant effect of shear at the pipe/soil interface is to add stiffness along with damping due to radiation. For the fluid-dominated wave, this causes the wavespeed to increase and increases the wave attenuation. For the shell-dominated wave there is little effect on the wavespeed but a marked increase in wave attenuation. Comparison with experimental measurements confirms the theoretical findings.

Muggleton, J. M.; Yan, J.

2013-03-01

390

Attenuation and scintillation of radio waves in the Earth's atmosphere from radio occultation experiments on satellite-to-satellite links  

Microsoft Academic Search

A theoretical analysis of refractive loss of radio waves by the Earth's atmosphere in radio occultation measurements along the satellite-to-satellite line for various altitude profiles of the refractive index is given. Experimental results for refractive loss on the orbital spacecraft-geostationary satellite link are presented. Theoretical calculations are compared with experimental data, and a conclusion is drawn that the signal amplitude

O. I. Yakovlev; S. S. Matyugov; I. A. Vilkov

1995-01-01

391

Radio wave refractivity deduced from lidar measurements  

NASA Astrophysics Data System (ADS)

A high resolution lidar is used to backscatter light from atmospheric aerosols. The actual relative humidity is measured at altitudes corresponding to those from which the backscattered light occurs. A mathematical relationship between the two is then derived and this is used to predict atmospheric relative humidity from subsequent lidar backscatter's measurements. The predicted relative humidity is used with temperature and pressures derived from standard lapse rates to calculate the radio refractivity of the atmosphere. Radio ray coverage is then determined based upon the calculated radio refractivity.

Paulson, Merle R.; Hughes, Herbert G.

1993-12-01

392

Atmospheric Wave Detection and Parameter Estimation Using Passive Measurements of Thermal Emission Near 118 GHZ.  

NASA Astrophysics Data System (ADS)

Measurements of atmospheric thermal emission near the 118.75-GHz (1^-) oxygen line were made with a scanning multi-channel spectrometer and used to measure thermodynamic effects of buoyancy wave motions in the lower atmosphere. A system model incorporating the physics of radiative transfer with the geometry and timing of the observation process is derived and then interpreted for small perturbations in atmospheric temperature and composition. A set of properties specific to plane wave inputs, which include an altitude-dependent distortion of the planar wavefronts and a viewing-angle-dependent amplitude attenuation, is developed, and the implications of these properties on the mathematical inversion process are investigated. The wave detection and parameter estimation problems are posed in a maximum-likelihood (ML) framework whose structure is similar to that used in the classical bearing estimation problem. The wavefront distortion and attenuation effects are accommodated using a signal model in which individual spatial frequency components are mapped to distinct altitudes in the atmosphere. The strict ML solution and two suboptimal but efficient variants of this method are derived. A complete analytical evaluation of estimator performance and minimum detection thresholds follows. For a typical 8-channel, 10-minute observation segment, assuming a single-spot brightness accuracy of 0.5 K rms, theoretical detection thresholds of ~0.05 K and vertical profile accuracies of 0.1 K (at 4-km resolution) are achieved for a 10-km wavelength disturbance. Three methods for discriminating between the radiometric signatures of atmospheric waves and periodic interference are also developed and evaluated. The detection and parameter estimation methods are applied to an extensive database of 118-GHz imagery gathered from high-altitude aircraft and ground-based platforms. A statistical survey of the aircraft-based database elicits fewer than 14 wave candidates in a 33-hour statistical sample, and no evidence of wave activity above 0.17 K amplitude. Ground -based imagery from the New Hampshire White Mountains region reveals an abundance of ~5-10 K periodic brightness structure which is demonstrated to be consistent with 2-10 km-wavelength modulations in either relative humidity or cloud liquid density. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253-1690.).

Bonanni, Pierino Gianni

393

Estimation of Nonlinear Internal Wave Properties Using Moored ADCP Measurements  

NASA Astrophysics Data System (ADS)

Methods are presented to estimate nonlinear internal wave (NLIW) properties including isopycnal displacement, wave propagation direction and speed, kinetic energy, and potential energy using three sets of bottom-moored ADCP measurements taken on the continental slope in the South China Sea in 2006-2007. The vertical displacement is computed as the time integration of the direct vertical velocity observations. The vertical current of NLIWs displaces the background current and shear by as much as 200 m. The wave current velocity is computed by subtracting the background current velocity following the isopycnal displacements. The propagation direction is estimated as the principal direction of the wave induced horizontal velocity. The propagation speed is estimated as -?t u'/?z w',assuming the wave structure and the propagation velocity remain constant when passing the mooring. The kinetic energy is computed directly from estimates of wave induced velocity. The potential energy is computed using the estimated vertical isopycnal displacements and background stratification. We confirm these methods by comparing estimated properties from mooring measurements with direct shipboard observations. The estimated NLIW amplitudes ranged from 50 to 200 m. NLIWs propagated northwestward to westward, 140°-180° counterclockwise from the east, at a speed of 1-2.5 m s-1. The depth integrated potential energy of NLIWs is 1-6 kJ m-2, which is similar to the depth integrated kinetic energy.

Chang, M.; Lien, R.; Tang, T.

2008-12-01

394

Measuring the quantum mechanical wave function  

Microsoft Academic Search

In the past few years experimenters have learned how to determine the complete quantum state of an ensemble of particles or ® elds which have been prepared according to some unknown procedure. Through these experiments they have answered a question posed by W. Pauli in the 1930s. The methods used involve measuring statistical distributions of a well chosen set of

M. G. RAYMER

1997-01-01

395

Measurements of shoaling internal waves and turbulence in an estuary  

NASA Astrophysics Data System (ADS)

AbstractThe shoaling of horizontally propagating internal <span class="hlt">waves</span> may represent an important source of mixing and transport in estuaries and coastal seas. Including such effects in numerical models demands improvements in the understanding of several aspects of the energetics, especially those relating to turbulence generation, and observations are needed to build this understanding. To address some of these issues in the estuarine context, we undertook an intensive field program for 10 days in the summer of 2008 in the St. Lawrence Estuary. The sampling involved shore-based photogrammetry, ship-based surveys, and an array of moorings in the shoaling region that held both conventional and turbulence-resolving sensors. The <span class="hlt">measurements</span> shed light on many aspects of the <span class="hlt">wave</span> shoaling process. <span class="hlt">Wave</span> arrivals were generally phase-locked with the M2 tide, providing hints about far-field forcing. In the deeper part of the study domain, the <span class="hlt">waves</span> propagated according to the predictions of linear theory. In intermediate-depth waters, the <span class="hlt">waves</span> traversed the field site perpendicularly to isobaths, a pattern that continued as the <span class="hlt">waves</span> transformed nonlinearly. Acoustic Doppler velocimeters permitted inference of the turbulent energetics, and two main features were studied. First, during a period of shoaling internal <span class="hlt">waves</span>, turbulence dissipation rates exceeded values associated with tidal shear by an order of magnitude. Second, the evolving spectral signatures associated with a particular <span class="hlt">wave</span>-shoaling event suggest that the turbulence is at least partly locally generated. Overall, the results of this study suggest that parameterizations of <span class="hlt">wave</span>-induced mixing could employ relatively simple dynamics in deep water, but may have to handle a wide suite of turbulence generation and transport mechanisms in inshore regions.</p> <div class="credits"> <p class="dwt_author">Richards, Clark; Bourgault, Daniel; Galbraith, Peter S.; Hay, Alex; Kelley, Dan E.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">396</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1990PhRvB..42.5842V"> <span id="translatedtitle">Tunneling states in neutron-irradiated quartz: <span class="hlt">Measurements</span> of the ultrasonic <span class="hlt">attenuation</span> and velocity change</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We report the results of a systematic investigation of the tunneling states (TS's) in neutron-irradiated quartz. <span class="hlt">Measurements</span> of the acoustic absorption and the variation of the velocity of sound were carried out as a function of temperature (0.3-300 K) and in the ultrasonic frequency range 200-700 MHz, on quartz specimens exposed to different neutron doses. From numerical fits of the data with the tunneling model, including Raman processes, the density of states P¯ and the coupling parameter ?l were determined independently. A comparison of the TS parameters obtained from both <span class="hlt">attenuation</span> and velocity <span class="hlt">measurements</span> with each other and with our previous ultrasonic-<span class="hlt">attenuation</span> studies and with thermal-conductivity and vibrating-reed experiments shows that the results are qualitatively in agreement with each other, but indicates some shortcomings of the tunneling model, also observed in glasses. TS parameters deduced from experiments which probe TS's of different parts of the distribution function are systematically found to be slightly different. The results are further related to studies of the damage induced by neutron irradiation in quartz. The differences in dose units, used by different authors, are considered more closely, which leads to a consistent picture of the damage-related parameters and allows a more reliable comparison between the TS and the damage.</p> <div class="credits"> <p class="dwt_author">Vanelstraete, A.; Laermans, C.</p> <p class="dwt_publisher"></p> <p class="publishDate">1990-09-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">397</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013JPhD...46R5502D"> <span id="translatedtitle">Ultrasonic metal sheet thickness <span class="hlt">measurement</span> without prior <span class="hlt">wave</span> speed calibration</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Conventional ultrasonic mensuration of sample thickness from one side only requires the bulk <span class="hlt">wave</span> reverberation time and a calibration speed. This speed changes with temperature, stress, and microstructure, limiting thickness <span class="hlt">measurement</span> accuracy. Often, only one side of a sample is accessible, making in situ calibration impossible. Non-contact ultrasound can generate multiple shear horizontal guided <span class="hlt">wave</span> modes on one side of a metal plate. <span class="hlt">Measuring</span> propagation times of each mode at different transducer separations, allows sheet thickness to be calculated to better than 1% accuracy for sheets of at least 1.5 mm thickness, without any calibration.</p> <div class="credits"> <p class="dwt_author">Dixon, S.; Petcher, P. A.; Fan, Y.; Maisey, D.; Nickolds, P.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-11-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">398</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/22068544"> <span id="translatedtitle">Subwavelength position <span class="hlt">measurements</span> with running-<span class="hlt">wave</span> driving fields</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">Subwavelength position <span class="hlt">measurement</span> of quantum particles is discussed. Our setup is based on a closed-loop driving-field configuration, which enforces a sensitivity of the particle dynamics to the phases of the applied fields. Thus, running <span class="hlt">wave</span> fields are sufficient, avoiding limitations associated with standing-<span class="hlt">wave</span>-based localization schemes. Reversing the directions of the driving laser fields switches between different magnification levels for the position determination. This allows us to optimize the localization, and at the same time eliminates the need for additional classical <span class="hlt">measurements</span> common to all previous localization schemes based on spatial periodicity.</p> <div class="credits"> <p class="dwt_author">Evers, Joerg [Max-Planck-Institut fuer Kernphysik, Saupfercheckweg 1, D-69117 Heidelberg (Germany); Qamar, Sajid [Max-Planck-Institut fuer Kernphysik, Saupfercheckweg 1, D-69117 Heidelberg (Germany); Centre for Quantum Physics, COMSATS Institute of Information Technology, Islamabad (Pakistan)</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-08-15</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">399</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/40161069"> <span id="translatedtitle">Dynamic Model of Fracture Normal Behaviour and Application to Prediction of Stress <span class="hlt">Wave</span> <span class="hlt">Attenuation</span> Across Fractures</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Summary.  The purpose of this paper is to establish a dynamic constitutive model of fracture normal behaviour, based on laboratory tests\\u000a of artificial fractures cast by cement mortar. A series of tests are systematically carried out under quasi-static (10?1?MPa\\/s) up to highly dynamic (103 MPa\\/s) monotonic loading conditions. The normal stress-fracture closure response is <span class="hlt">measured</span> at different loading rates.\\u000a Based on</p> <div class="credits"> <p class="dwt_author">J. Zhao; J. G. Cai; X. B. Zhao; H. B. Li</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">400</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/53863356"> <span id="translatedtitle">The phase velocity and <span class="hlt">attenuation</span> of audio-frequency electro-magnetic <span class="hlt">waves</span> from simultaneous observations of atmospherics at two spaced stations</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Radio-atmospherics of known origin were recorded on magnetic tape from two broad-band receivers 285 km apart in the United Kingdom, and, from photographs of the waveforms, the Fourier phase and amplitude spectra of the pulses were computed. This enabled the phase velocity and <span class="hlt">attenuation</span> of radio <span class="hlt">waves</span> in the frequency range 40 c\\/s-10 kc\\/s to be calculated. Observations were made</p> <div class="credits"> <p class="dwt_author">R. A. Challinor</p> <p class="dwt_publisher"></p> <p class="publishDate">1967-01-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_19");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' 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class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_20");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' href="#">4</a> <a onClick='return showDiv("page_5");' href="#">5</a> <a onClick='return showDiv("page_6");' href="#">6</a> <a onClick='return showDiv("page_7");' href="#">7</a> <a onClick='return showDiv("page_8");' href="#">8</a> <a onClick='return showDiv("page_9");' href="#">9</a> <a onClick='return showDiv("page_10");' href="#">10</a> <a onClick='return showDiv("page_11");' href="#">11</a> <a onClick='return 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onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">401</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/56768229"> <span id="translatedtitle">Ultrasonic <span class="hlt">attenuation</span> studies in deuterated and undeuterated chromium potassium alum</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The <span class="hlt">attenuation</span> of 10- and 30-MHz sound <span class="hlt">waves</span> in deuterated and undeuterated chromium potassium alum have been <span class="hlt">measured</span> over the temperature range 300–4.2 K. A very large <span class="hlt">attenuation</span> peak occurs in the temperature range 70–160 K. It is believed that this is associated with phonon-phonon scattering.</p> <div class="credits"> <p class="dwt_author">R. E. Miller; M. H. Norwood; B. J. Marshall</p> <p class="dwt_publisher"></p> <p class="publishDate">1972-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">402</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/22093700"> <span id="translatedtitle"><span class="hlt">Measurements</span> of parallel electron velocity distributions using whistler <span class="hlt">wave</span> absorption</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">We describe a diagnostic to <span class="hlt">measure</span> the parallel electron velocity distribution in a magnetized plasma that is overdense ({omega}{sub pe} > {omega}{sub ce}). This technique utilizes resonant absorption of whistler <span class="hlt">waves</span> by electrons with velocities parallel to a background magnetic field. The whistler <span class="hlt">waves</span> were launched and received by a pair of dipole antennas immersed in a cylindrical discharge plasma at two positions along an axial background magnetic field. The whistler <span class="hlt">wave</span> frequency was swept from somewhat below and up to the electron cyclotron frequency {omega}{sub ce}. As the frequency was swept, the <span class="hlt">wave</span> was resonantly absorbed by the part of the electron phase space density which was Doppler shifted into resonance according to the relation {omega}-k{sub ||v||} = {omega}{sub ce}. The <span class="hlt">measured</span> absorption is directly related to the reduced parallel electron distribution function integrated along the <span class="hlt">wave</span> trajectory. The background theory and initial results from this diagnostic are presented here. Though this diagnostic is best suited to detect tail populations of the parallel electron distribution function, these first results show that this diagnostic is also rather successful in <span class="hlt">measuring</span> the bulk plasma density and temperature both during the plasma discharge and into the afterglow.</p> <div class="credits"> <p class="dwt_author">Thuecks, D. J.; Skiff, F.; Kletzing, C. A. [Department of Physics and Astronomy, University of Iowa, 203 Van Allen Hall, Iowa City, Iowa 52242 (United States)</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-08-15</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">403</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/22938290"> <span id="translatedtitle"><span class="hlt">Measurements</span> of parallel electron velocity distributions using whistler <span class="hlt">wave</span> absorption.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">We describe a diagnostic to <span class="hlt">measure</span> the parallel electron velocity distribution in a magnetized plasma that is overdense (?(pe) > ?(ce)). This technique utilizes resonant absorption of whistler <span class="hlt">waves</span> by electrons with velocities parallel to a background magnetic field. The whistler <span class="hlt">waves</span> were launched and received by a pair of dipole antennas immersed in a cylindrical discharge plasma at two positions along an axial background magnetic field. The whistler <span class="hlt">wave</span> frequency was swept from somewhat below and up to the electron cyclotron frequency ?(ce). As the frequency was swept, the <span class="hlt">wave</span> was resonantly absorbed by the part of the electron phase space density which was Doppler shifted into resonance according to the relation ? - k([parallel])v([parallel]) = ?(ce). The <span class="hlt">measured</span> absorption is directly related to the reduced parallel electron distribution function integrated along the <span class="hlt">wave</span> trajectory. The background theory and initial results from this diagnostic are presented here. Though this diagnostic is best suited to detect tail populations of the parallel electron distribution function, these first results show that this diagnostic is also rather successful in <span class="hlt">measuring</span> the bulk plasma density and temperature both during the plasma discharge and into the afterglow. PMID:22938290</p> <div class="credits"> <p class="dwt_author">Thuecks, D J; Skiff, F; Kletzing, C A</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-08-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">404</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012RScI...83h3503T"> <span id="translatedtitle"><span class="hlt">Measurements</span> of parallel electron velocity distributions using whistler <span class="hlt">wave</span> absorption</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We describe a diagnostic to <span class="hlt">measure</span> the parallel electron velocity distribution in a magnetized plasma that is overdense (?pe > ?ce). This technique utilizes resonant absorption of whistler <span class="hlt">waves</span> by electrons with velocities parallel to a background magnetic field. The whistler <span class="hlt">waves</span> were launched and received by a pair of dipole antennas immersed in a cylindrical discharge plasma at two positions along an axial background magnetic field. The whistler <span class="hlt">wave</span> frequency was swept from somewhat below and up to the electron cyclotron frequency ?ce. As the frequency was swept, the <span class="hlt">wave</span> was resonantly absorbed by the part of the electron phase space density which was Doppler shifted into resonance according to the relation ? - k||v|| = ?ce. The <span class="hlt">measured</span> absorption is directly related to the reduced parallel electron distribution function integrated along the <span class="hlt">wave</span> trajectory. The background theory and initial results from this diagnostic are presented here. Though this diagnostic is best suited to detect tail populations of the parallel electron distribution function, these first results show that this diagnostic is also rather successful in <span class="hlt">measuring</span> the bulk plasma density and temperature both during the plasma discharge and into the afterglow.</p> <div class="credits"> <p class="dwt_author">Thuecks, D. J.; Skiff, F.; Kletzing, C. A.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-08-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">405</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1998JMMM..177..533N"> <span id="translatedtitle"><span class="hlt">Measurement</span> of paramagnetic Meissner effect in s-<span class="hlt">wave</span> superconductor</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We <span class="hlt">measured</span> magnetic moments of various s-<span class="hlt">wave</span> superconductors. The paramagnetic moment was observed in a superconducting Nb disk as reported by another group. But it disappeared in an annealed sample. We <span class="hlt">measured</span> magnetic moment of a Pb disk. In this sample the paramagnetic moment was not observed. We also <span class="hlt">measured</span> the cylindrical superconductors. In this sample a step-like increase of paramagnetic moment was observed at temperatures below Tc. We consider that this behavior is caused by the flux compression.</p> <div class="credits"> <p class="dwt_author">Nakagawa, M.; Utsumi, S.; Hirayama, T.; Sumiyama, A.; Oda, Y.</p> <p class="dwt_publisher"></p> <p class="publishDate">1998-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">406</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/1566188"> <span id="translatedtitle">Laboratory <span class="hlt">measurements</span> of polarization radios of wind <span class="hlt">wave</span> surfaces</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Polarization ratios (sigma_{vv}\\/sigma_{HH}) of wind-generated rough water surfaces are studied experimentally by means of radar backscatter power <span class="hlt">measurements</span>. The <span class="hlt">measurements</span> were made at 9.23 GHz with incidence angles between45degand55degfor wind speeds between 3 m\\/s to 10 m\\/s. Scattering surface statistics at all wind speeds were also <span class="hlt">measured</span> by means of a <span class="hlt">wave</span> height gauge and a laser slope gauge. The</p> <div class="credits"> <p class="dwt_author">PETER H. Y. LEE</p> <p class="dwt_publisher"></p> <p class="publishDate">1978-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">407</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/17082878"> <span id="translatedtitle">Precision of Raman depolarization and optical <span class="hlt">attenuation</span> <span class="hlt">measurements</span> of sound tooth enamel.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">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 <span class="hlt">attenuation</span> coefficient as <span class="hlt">measured</span> by optical coherence tomography and the polarization anisotropy of the Raman peak arising from the symmetric nu(1) vibration of PO4(3-) at a