While these samples are representative of the content of Science.gov,

they are not comprehensive nor are they the most current set.

We encourage you to perform a real-time search of Science.gov

to obtain the most current and comprehensive results.

Last update: November 12, 2013.

1

Attenuation coefficients of Rayleigh and Lg waves

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

2

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

3

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

4

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

5

Wave Attenuation by Artificial Seaweed.

National Technical Information Service (NTIS)

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

J. P. Ahrens

1976-01-01

6

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

7

Investigation of photon attenuation coefficients for marble.

The total linear attenuation coefficients micro (cm(-1)) have been obtained using the XCOM program at photon energies of 1 keV to 1 GeV for six different natural marbles produced in different places in Turkey. The individual contribution of photon interaction processes to the total linear attenuation coefficients for marble has been investigated. The calculated results were also compared with the measurements. The results obtained for marble were also compared with concrete. PMID:15942062

Basyigit, C; Akkurt, I; Kilincarslan, S; Akkurt, A

2005-06-07

8

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

9

Temporal variations of coda Q: An attenuation-coefficient view

NASA Astrophysics Data System (ADS)

Spatial and temporal variations of coda wave attenuation were identified in many studies, and particularly in relation to major earthquakes and volcanic eruptions. Both the coda quality factor, Qc, and its frequency dependence often change following such events, which is often attributed to variations in the properties of large volumes of the subsurface. However, Qc is also strongly sensitive to the assumed theoretical models, which are usually insufficiently accurate for constraining the actual relationships between the geometrical spreading, anelastic dissipation, and scattering. This inaccuracy often leads to significant exaggeration of attenuation effects and complicates the interpretation of temporal variations. To resolve this problem, this study uses a phenomenological approach based on the temporal attenuation coefficient ? instead of Qc. The attenuation coefficient often linearly depends on frequency f, with intercept ?=?(0) related to the geometrical spreading and slope giving the "effective quality" factor Qe as d?/df=?Qe-1. Two published examples of temporal variations of local-earthquake coda are revisited: a non-volcanic (Stone Canyon in central California) and volcanic area (Mount St. Helens, Washington). In both cases, linear ?(f) patterns are found, with the effects of ? on coda decay rates being significantly stronger than those of Qe-1. At Stone Canyon, ? ranged from 0.035 to 0.06 s -1 and Qe varied from 3000 to 10,000, with ? increasing and Qe decreasing during the winter season. At Mount St. Helens, ? remained constant at ˜0.18 s -1, and Qe changed from 400 before the eruption to 750 after it. The observed temporal variations are explained by the near-surface changes caused by seasonal variations in the non-volcanic case and gas-, magma-, and geothermal-system related in the volcanic case. Scattering attenuation does not appear to be a significant factor in these areas, or otherwise it may be indistinguishable due to its fundamental trade-off with the background structure and anelastic attenuation in the data.

Morozov, Igor B.

2011-07-01

10

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

11

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

12

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

13

Symmetries and Interaction Coefficients of Kelvin Waves

NASA Astrophysics Data System (ADS)

We considered symmetry restriction on the interaction coefficients of Kelvin waves and demonstrated that linear in small wave vector asymptotic, obtained analytically, is not forbidden, as one can expect by naive reasoning. Therefore now we have no reason to doubt in this asymptote, that results in the L’vov-Nazarenko energy spectrum of Kelvin waves.

Lebedev, Vladimir V.; L'Vov, Victor S.

2010-12-01

14

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

15

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

16

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

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

17

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

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

18

A model for the diffuse attenuation coefficient of downwelling irradiance

The diffuse attenuation coefficient for downwelling irradiance (Kd) is an important parameter for ocean studies. For the vast ocean the only feasible means to get fine-scale measurements of Kd is by ocean color remote sensing. At present, values of Kd from remote sensing are estimated using empirical algorithms. Such an approach is insufficient to provide an understanding regarding the variation

Zhong-Ping Lee; Ke-Ping Du; Robert Arnone

2005-01-01

19

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

20

Gamma-ray attenuation coefficients in bismuth borate glasses

NASA Astrophysics Data System (ADS)

Mass attenuation coefficients of glasses in the system: xBi2O3(1-x)B2O3 (x=0.30, 0.35, 0.40, 0.45 and 0.55) were determined at 356, 662, 1173 and 1332 keV photon energies using a narrow beam transmission method. Appreciable variations were observed in these coefficients due to changes in the chemical composition of glasses. These coefficients were then used to determine effective atomic numbers of glass samples, which were found to be constant with bismuth concentration and energy.

Singh, Kulwant; Singh, Harvinder; Sharma, Vishal; Nathuram, Rohila; Khanna, Atul; Kumar, Rajesh; Singh Bhatti, Surjit; Singh Sahota, Hari

2002-07-01

21

Attenuation of an air shock wave by perforated baffles

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

22

Gamma ray attenuation coefficient measurement for neutron-absorbent materials

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

23

Surface wave path corrections, deterministic discrimination and body wave attenuation

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

24

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

25

Attenuation Coefficient of Single-Mode Periodic Waveguides

NASA Astrophysics Data System (ADS)

It is widely accepted that, on ensemble average, the transmission T of guided modes decays exponentially with the waveguide length L due to small imperfections, leading to the important figure of merit defined as the attenuation-rate coefficient ?=-?ln?(T)?/L. In this Letter, we evidence that the exponential-damping law is not valid in general for periodic monomode waveguides, especially as the group velocity decreases. This result, that contradicts common beliefs and experimental practices aiming at measuring ?, is supported by a theoretical study of light transport in the limit of very small imperfections, and by numerical results obtained for two waveguide geometries that offer contrasted damping behaviors.

Baron, A.; Mazoyer, S.; Smigaj, W.; Lalanne, P.

2011-10-01

26

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

27

Apparent Linear Attenuation Coefficients in Phase Contrast X-Ray Tomography

In the inline phase contrast x-ray tomography the reconstructed apparent linear attenuation coefficient values may be greatly larger than sample’s linear attenuation coefficients or even be negative. In this work we present a general formula to quantitatively relate the apparent linear attenuation coefficient values in cone-beam phase contrast tomography to sample’s linear attenuation coefficients and refractive indices. This formula overcomes the gross inaccuracy of the existing formula in the literature in analyzing high-resolution phase contrast tomography, and it will be useful for correctly interpreting and quantifying the apparent linear attenuation coefficients in cone-beam x-ray phase contrast tomography.

Yan, Aimin; Wu, Xizeng

2011-01-01

28

Vertical profiles of beam attenuation coefficients in East China Sea

NASA Astrophysics Data System (ADS)

The vertical profiles of beam attenuation coefficient (c) can provide information about the distribution and variability of suspended particles in the water column. Vertical profiles of particulate beam attenuation coefficient at 660 nm (cp(660)), Chlorophyll a (chla) and Particulate Organic Carbon(POC) were analyzed to examine patterns and controlling factors of vertical distributions in the East China Sea (ECS), based on two cruises in summer and late autumn. In late autumn, the cp(660) profiles showed uniform distribution with depth in most of shelf regions, and high value of cp(660) was observed in some inshore stations caused by strong resuspension. In summer, cp(660) exhibited weak subsurface maxima phenomenon in outer shelf, while with the well vertical mixed structures in the northern coast areas of ECS. The variability of cp(660) between summer and autumn were mainly influenced by the changes of thermocline distribution in the ECS. In the late autumn, water potential density were characterized as fully vertical mixed, on the contrary, the strong stratifications of water column were observed in summer. Except for several inshore stations with highly influenced by terrestrial input, significant relationships between POC and cP(660) were observed in both late autumn and summer. The close relationship between POC and cp(660) could be an potential application to retrieve the POC profiles from in situ cP(660) measurements, and be applied to the surface POC estimated from space.

Liu, Qiong; Pan, Delu; Bai, Yan; Zhang, Xuan; Zhang, Lin; Zhu, Qiankun

2012-09-01

29

The CT data acquired in combined PET\\/CT studies provide a fast and essentially noiseless source for the correction of photon attenuation in PET emission data. To this end, the CT values relating to attenuation of photons in the range of 40-140 keV must be transformed into linear attenuation coefficients at the PET energy of 511 keV. As attenuation depends on

C. Burger; G. Goerres; S. Schoenes; A. Buck; A. Lonn; G. von Schulthess

2002-01-01

30

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

31

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

32

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

33

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

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

34

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

35

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

36

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

37

Can the Lambert-Beer law be applied to the diffuse attenuation coefficient of ocean water?

Radiative transfer theory is combined with a bio-optical model of Case 1 waters and an optical model of the atmosphere to simulate the transport of radiation in the ocean-atmosphere system. The results are treated as experimental data to study the downwelling irradiance attenuation coefficient. It is shown that the downwelling irradiance attenuation coefficient just beneath the surface and the mean

HOWARD R. GORDON

1989-01-01

38

Determination of the attenuation coefficients by visible and ultraviolet radiation in heavy water

A long-path-length transmission cell has been used to measure the attenuation coefficients of purified HâO and DâO at various wavelengths between 250 and 580 nm. The principles governing the procedures and corrections for various sources of light attenuation in the transmission cell components are discussed. Detailed chemical histories of the HâO and DâO samples are given. The measured attenuation coefficients

L. P. Boivin; W. F. Davidson; R. S. Storey; D. Sinclair; E. D. Earle

1986-01-01

39

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

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

40

Attenuation of Body Waves and the Q Structure of the Mantle

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

41

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

42

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

43

National Technical Information Service (NTIS)

This work reports an alternative methodology for the linear attenuation coefficient determination ((mu) (rho)) of irregular form samples, in such a way that is not necessary to consider the sample thickness. With this methodology, indigenous archaeologica...

R. M. C. Silva

1997-01-01

44

Correlation equation for the marine drag coefficient and wave steepness

NASA Astrophysics Data System (ADS)

This work questions, starting from dimensional considerations, the generality of the belief that the marine drag coefficient levels off with increasing wind speed. Dimensional analysis shows that the drag coefficient scales with the wave steepness as opposed to a wave-age scaling. A correlation equation is employed here that uses wave steepness scaling at low aspect ratios (inverse wave steepnesses) and a constant drag coefficient at high aspect ratios. Invoked in support of the correlation are measurements sourced from the literature and at the FINO1 platform in the North Sea. The correlation equation is then applied to measurements recorded from buoys during the passage of hurricanes Rita, Katrina (2005) and Ike (2008). Results show that the correlation equation anticipates the expected levelling off in deeper water, but a drag coefficient more consistent with a Charnock type relation is also possible in more shallower water. Some suggestions are made for proceeding with a higher-order analysis than that conducted here.

Foreman, Richard J.; Emeis, Stefan

2012-09-01

45

Measurement of atomic number and mass attenuation coefficient in magnesium ferrite

Pure magnesium ferrite sample was prepared by standard ceramic technique and characterized by X-ray diffraction method. XRD pattern revealed that the sample possess single-phase cubic spinel structure. The linear attenuation coefficient (mu), mass attenuation coefficient (mu\\/rho), total atomic cross-section (sigma_{tot}), total electronic cross-section (sigma_{ele}) and the effective atomic number (Z_{eff}) were calculated for pure magnesium ferrite (MgFe_{2}O_{4}). The values of

R. H. Kadam; S. T. Alone; G. K. Bichile; K. M. Jadhav

2007-01-01

46

Study on Z dependence of partial and total mass attenuation coefficients

NASA Astrophysics Data System (ADS)

The partial and total mass attenuation coefficients ?/?(cmg) of photons at energy of 1 keV 100 GeV have been calculated as a function of atomic number and photon energies using the XCOM program (version 3.1) and data base and the calculated results were compared with the measurement. The results show that the mass attenuation coefficients (?/?) depend on incoming photon energies and Z numbers of the target nuclei.

Akkurt, I.; Mavi, B.; Akkurt, A.; Basyigit, C.; Kilincarslan, S.; Yalim, H. A.

2005-09-01

47

Recent experimental values of X-ray mass attenuation coefficients for the elements zota = 6 to zota = 18 in the energy range from 4 to 25 keV suggest improvements to the data set presented in the ICRU Report 17. The results are, however, in excellent agreement with the theoretical data of Storm and Israel (1970). Values of mass attenuation coefficient for these elements and for a selection of materials of medical and biological importance are presented. PMID:1202514

Millar, R H

1975-11-01

48

Ultrasonic computed tomography reconstruction of the attenuation coefficient using a linear array.

The attenuation coefficient distribution and sound velocity distribution in the breast can be used to complement B-mode ultrasound imaging in the detection of breast cancer. This study investigated an approach for reconstructing the attenuation coefficient distribution in the breast using a linear array. The imaging setup was identical to that for conventional B-mode breast imaging, and the same setup has been used for reconstruction of sound velocity distributions in previous studies. In this study, we further developed a reconstruction method for the attenuation coefficient distribution. In particular, the proposed method incorporates the segmentation information from B-mode images and uses the sound velocity distribution to compensate for refraction effects. Experiments were conducted with a setup consisting of a 5-MHz, 128-channel linear array, a programmable digital array system, a phantom, and a computer. The constructed phantom contained materials mimicking the following breast tissues: glandular tissue, fat, cysts, high-attenuation tumors, and irregular tumors. Application of the proposed technique resulted in all the cysts and tumors (including high-attenuation and irregular tumors) being distinguished by thresholding the reconstructed attenuation coefficients. We have demonstrated that it is possible to use the same imaging setup to acquire data for B-mode image, sound velocity distribution, and attenuation coefficient distribution simultaneously. Moreover, the experimental data indicate its potential in improving the detection of breast cancer. PMID:16422413

Huang, Sheng-Wen; Li, Pai-Chi

2005-11-01

49

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

50

Stochastic solution to a time-fractional attenuated wave equation

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

51

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

52

NASA Astrophysics Data System (ADS)

The goal of this work is to verify different spectral models of the diffuse attenuation and absorption coefficients of sea water and to work out a recommendation for their use. It is shown that the spectral models of the diffuse attenuation coefficient Kd((lambda) ) developed by Austin, Petzold, 1984 and by Volynsky, Sud'bin, 1992 correspond with each other, as well the models of Ivanov, Shemshura, 1973 and of Kopelevich, Shemshura, 1988 for calculation of the spectral absorption coefficient a((lambda) ) on the values of Kd((lambda) ). Theoretical foundation of the relation between a((lambda) ) and Kd((lambda) ) is given. The up-to-date physical model of the sea water light absorption is considered and checked by means of comparison with measured values of the attenuation coefficient at the ultraviolet and visible spectral ranges.

Kopelevich, Oleg V.; Filippov, Yury V.

1994-10-01

53

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

54

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

55

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

56

The results from studies of wave propagation in large arteries carried out over the last 25 years have shown that there is a good agreement among values of the imaginary part of the complex propagation coefficient, as expressed by pressure or flow-rate wave propagation velocity. However, there is considerable disparity among estimations of the degree of wave attenuation, the real

C. D. Bertram; B. S. Gow; S. E. Greenwald

1997-01-01

57

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

58

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

59

Measurement of atomic number and mass attenuation coefficient in magnesium ferrite

NASA Astrophysics Data System (ADS)

Pure magnesium ferrite sample was prepared by standard ceramic technique and characterized by X-ray diffraction method. XRD pattern revealed that the sample possess single-phase cubic spinel structure. The linear attenuation coefficient (?), mass attenuation coefficient (?/?), total atomic cross-section (?_{tot}), total electronic cross-section (?_{ele}) and the effective atomic number (Z_{eff}) were calculated for pure magnesium ferrite (MgFe_{2}O_{4}). The values of ?-ray mass attenuation coefficient were obtained using a NaI energy selective scintillation counter with radioactive ?-ray sources having energy 0.36, 0.511, 0.662, 1.17 and 1.28 MeV. The experimentally obtained values of ?/? and Z_{eff} agreed fairly well with those obtained theoretically.

Kadam, R. H.; Alone, S. T.; Bichile, G. K.; Jadhav, K. M.

2007-05-01

60

Trends in attenuation coefficients in Athens, Greece, from 1954 to 1991

Unsworth and Monteith`s attenuation coefficient T{sub UM} was calculated from midday cloudless sky data in Athens, Greece, for the period 1954 to 1991. An interdependence between T{sub UM} and the Linke factor T{sub L} was found and is expressed as a mathematical function. It was also shown that the minimum turbidity levels occur during the winter and maximum levels occur during summer. An analysis of the long-term variation of the attenuation coefficients depicts the deterioration of air quality during the same period. The dependence of the ratio of diffuse to global radiation on the attenuation coefficient T{sub UM}, is also presented. 26 refs., 4 figs., 1 tab.

Jacovides, C.P.; Kaltsounides, N.A.; Giannourakos, G.P.; Kallos, G.B. [Univ. of Athens (Greece)

1995-06-01

61

The diffuse attenuation coefficient, K (m–1), is a measure of the effective attenuation of light in the water column. It characterizes water clarity and is used as a\\u000a proxy for water quality. Mapping of shallow water benthic habitats using optical means, including daytime visible satellite\\u000a imagery, requires knowledge of K to correct for water column effects such as light absorption

D. Palandro; C. Hu; S. Andréfouët; F. E. Muller-Karger

62

Miniaturised ultrasonic-wave velocity and attenuation sensors for liquid

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

63

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

64

Fault-zone attenuation of high-frequency seismic waves

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

65

Measurement of atomic number and mass attenuation coefficient in magnesium ferrite

Pure magnesium ferrite sample was prepared by standard ceramic technique and characterized by X-ray diffraction method. XRD\\u000a pattern revealed that the sample possess single-phase cubic spinel structure. The linear attenuation coefficient (µ), mass attenuation coefficient (µ\\/?), total atomic cross-section (?\\u000a tot), total electronic cross-section (?\\u000a ele) and the effective atomic number (Z\\u000a eff) were calculated for pure magnesium ferrite (MgFe2O4).

R H Kadam; S T Alone; G K Bichile; K M Jadhav

2007-01-01

66

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

67

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

68

The Attenuation vs Frequency Characteristics of VLF Radio Waves

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

69

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

70

Some building materials, regularly used in Turkey, such as sand, cement, gas concrete (lightweight, aerated concrete), tile and brick, have been investigated in terms of mass attenuation coefficient (?/?), effective atomic, numbers (Z(eff)), effective electron densities (N(e)) and photon interaction cross section (?(a)) at 14 different energies from 81- to 1332-keV gamma-ray energies. The gamma rays were detected by using gamma-ray spectroscopy, a High Purity Germanium (HPGe) detector. The elemental compositions of samples were analysed using an energy dispersive X-ray fluorescence spectrometer. Mass attenuation coefficients of these samples have been compared with tabulations based upon the results of WinXcom. The theoretical mass attenuation coefficients were estimated using the mixture rule and the experimental values of investigated parameters were compared with the calculated values. The agreement of measured values of mass attenuation coefficient, effective atomic numbers, effective electron densities and photon interaction cross section with the theory has been found to be quite satisfactory. PMID:22128356

Damla, N; Baltas, H; Celik, A; Kiris, E; Cevik, U

2011-11-28

71

Comparison of attenuation coefficients for VVER-440 and VVER-1000 pressure vessels

The paper summarizes the attenuation coefficient of the neutron fluence with E > 0.5 MeV through a reactor pressure vessel for vodo-vodyanoi energetichesky reactor (VVER) reactor types measured and/or calculated for mock-up experiments, as well as for operated nuclear power plant (NPP) units. The attenuation coefficient is possible to evaluate directly only by using the retro-dosimetry, based on a combination of the measured activities from the weld sample and concurrent ex-vessel measurement. The available neutron fluence attenuation coefficients (E > 0.5 MeV), calculated and measured at a mock-up experiment simulating the VVER-440-unit conditions, vary from 3.5 to 6.15. A similar situation is used for the calculations and mock-up experiment measurements for the VVER-1000 RPV, where the attenuation coefficient of the neutron fluence varies from 5.99 to 8.85. Because of the difference in calculations for the real units and the mock-up experiments, the necessity to design and perform calculation benchmarks both for VVER-440 and VVER-1000 would be meaningful if the calculation model is designed adequately to a given unit. (authors)

Marek, M.; Rataj, J.; Vandlik, S. [Reactor Physics Dept., Research Centre Rez, Husinec 130, 25068 (Czech Republic)

2011-07-01

72

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

73

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

74

Correction for scattered and attenuated photons is necessary for accurate quantification in dedicated breast SPECT. An implemented dual energy window (DEW) scatter correction method along with attenuation correction has been shown to be accurate to within 10% of true values; however, the DEW method requires multiple processing steps, and thus more time, than an effective attenuation coefficient (EAC) method. This

Steve Mann; Kristy Perez; Martin Tornai

2011-01-01

75

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

76

Quantitative RNFL attenuation coefficient measurements by RPE-normalized OCT data

NASA Astrophysics Data System (ADS)

We demonstrate significantly different scattering coefficients of the retinal nerve fiber layer (RNFL) between normal and glaucoma subjects. In clinical care, SD-OCT is routinely used to assess the RNFL thickness for glaucoma management. In this way, the full OCT data set is conveniently reduced to an easy to interpret output, matching results from older (non- OCT) instruments. However, OCT provides more data, such as the signal strength itself, which is due to backscattering in the retinal layers. For quantitative analysis, this signal should be normalized to adjust for local differences in the intensity of the beam that reaches the retina. In this paper, we introduce a model that relates the OCT signal to the attenuation coefficient of the tissue. The average RNFL signal (within an A-line) was then normalized based on the observed RPE signal, resulting in normalized RNFL attenuation coefficient maps. These maps showed local defects matching those found in thickness data. The average (normalized) RNFL attenuation coefficient of a fixed band around the optic nerve head was significantly lower in glaucomatous eyes than in normal eyes (3.0mm-1 vs. 4.9mm-1, P<0.01, Mann-Whitney test).

Vermeer, K. A.; van der Schoot, J.; Lemij, H. G.; de Boer, J. F.

2012-02-01

77

We report the use of optical coherence tomography (OCT) to determine spatially localized optical attenuation coefficients of human axillary lymph nodes and their use to generate parametric images of lymphoid tissue. 3D-OCT images were obtained from excised lymph nodes and optical attenuation coefficients were extracted assuming a single scattering model of OCT. We present the measured attenuation coefficients for several tissue regions in benign and reactive lymph nodes, as identified by histopathology. We show parametric images of the measured attenuation coefficients as well as segmented images of tissue type based on thresholding of the attenuation coefficient values. Comparison to histology demonstrates the enhancement of contrast in parametric images relative to OCT images. This enhancement is a step towards the use of OCT for in situ assessment of lymph nodes.

Scolaro, Loretta; McLaughlin, Robert A.; Klyen, Blake R.; Wood, Benjamin A.; Robbins, Peter D.; Saunders, Christobel M.; Jacques, Steven L.; Sampson, David D.

2012-01-01

78

Measurements have been made of the total attenuation coefficient sigma t and the scattering phase function, S(theta), of 632.8 nm of light for a number of animal model tissues, blood, and inert scattering and absorbing media. Polystyrene microspheres of known size and refractive index, for which sigma t and S(theta) can be calculated by Mie theory, were used to test the experimental methods. The purpose of the study was to define typical ranges for these optical properties of tissues, as a contribution to the development of experimental and theoretical methods of light dosimetry in tissue, particularly related to photodynamic therapy of solid tumors. The results demonstrate that, for the representative tissues studied, the total attenuation coefficients are of the order of 10-100 mm-1, and that the scattering is highly forward peaked, with average cosine of scatter in the range 0.6-0.97.

Flock, S.T.; Wilson, B.C.; Patterson, M.S.

1987-09-01

79

NASA Astrophysics Data System (ADS)

To study the doses received by patient submitted to ionizing radiation, several materials are used to simulate the human tissue and organs. The total mass attenuation coefficient is a reasonable way for evaluating the usage in dosimetry of these materials. The total mass attenuation coefficient is determined by photon energy and constituent elements of the material. Currently, the human phantoms are composed by a unique material that presents characteristics similar to the mean proprieties of the different tissues within the region. Therefore, the phantoms are usually homogeneous and filled with a material similar to soft tissue. We studied ten materials used as soft tissue-simulating. These materials were named: bolus, nylon®, orange articulation wax, red articulation wax, PMMA, modelling clay, bee wax, paraffin 1, paraffin 2 and pitch. The objective of this study was to verify the best material to simulate the human cerebral tissue. We determined the elementary composition, mass density and, therefore, calculated the total mass attenuation coefficient of each material. The results were compared to the values established by the International Commission on Radiation Units and Measurements - ICRU, report n° 44, and by the International Commission on Radiation Protection - ICRP, report n° 89, to determine the best material for this energy interval. These results indicate that new head phantoms can be constructed with nylon®.

Ferreira, C. C.; Ximenes, R. E.; Garcia, C. A. B.; Vieira, J. W.; Maia, A. F.

2010-11-01

80

Results of a monte carlo investigation of the diffuse attenuation coefficient.

There has been a large effort to relate the apparent optical properties of ocean water to the inherent optical properties, which are the absorption coefficient a, the scattering coefficient b, and the scattering phase function rho(theta). The diffuse attenuation coefficient kdiff' has most often been considered an apparent optical property. However, kdiff' can be considered a quasi-inherent property kdiff' when defined as a steady-state light distribution attenuation coefficient. The Honey-Wilson research empirically relates kdiff' to a and b. The Honey-Wilson relation most likely applies to a limited range of water types because it does not include dependence on rho(theta). A series of Monte Carlo simulations were initiated to calculate kdiff' in an unstratified water column. The calculations, which reflected open ocean water types, used ranges of the single-scattering albedo omega(0) and the mean forward-scattering angle theta(m) for two analytic phase functions with different shapes. It was found that kdiff' is nearly independent of the shape of rho(theta) and can be easily parameterized in terms of a, b, and theta(m) for 0.11

Concannon, B M; Davis, J P

1999-08-20

81

Shear Wave Attenuation and Melting beneath the Mid-Atlantic Ridge

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

82

Connection coefficients for cold plasma wave propagation near metallic surfaces

NASA Astrophysics Data System (ADS)

Sheaths tend to form when immersing metallic objects in plasmas. As it avoids the need to capture the sheath details, which occur on the Debye length scale while antennas are typically various orders of magnitude larger, the sheath boundary condition due to D'Ippolito and Myra (2006 Phys. Plasmas 13 102508, 2008 Phys. Plasmas 15 102501) offers antenna designers a major reduction in the numerical problem size they face. The sheath boundary condition was derived by making a number of simplifying assumptions to enable finding an analytical approximation of the conditions rapidly oscillating waves have to satisfy beyond the sheath that forms close to such objects. This paper discusses the solution of the cold plasma wave equation for sheath relevant density profiles, e.g. highlighting the role of the orientation of the static magnetic field and of oblique incidence, and underlining the impact the density profile has on the wave physics. It illustrates that the cross-talk between the waves impinging on and those excited at the wall and in the sheath sensitively depends on a number of parameters. The 2 × 2 connection coefficient matrix that is numerically obtained captures the sheath region fast time scale wave physics for a given density profile. When supplemented with a satisfactory model for the slow time scale variation it is a numerical tool that permits upgrading the realism of the fast time scale wave physics contained in the sheath boundary condition and that can help delimiting the range of applicability of simplified models, and assessing if a sufficiently general set of boundary conditions to describe the effect of the sheath can at all be constructed.

Van Eester, Dirk; Crombé, Kristel; Kyrytsya, Volodymyr

2013-05-01

83

NASA Astrophysics Data System (ADS)

Total mass attenuation coefficients, effective atomic numbers, effective electron numbers and kerma values for Earth and Martian soils are calculated in the energy range from 1 keV to 100 GeV. The values of mass attenuation and absorption coefficients used in calculations are taken from the WinXCOM program and correct data base. Contributions of different scatterings on the total mass attenuation coefficients of the soils are presented. In addition, the obtained results for Martian soils are compared with the results for Earth soils. The similarities of Earth and Martian soils are also investigated.

Un, A.; Sahin, Y.

2012-10-01

84

P-Wave to Rayleigh-wave conversion coefficients for wedge corners; model experiments

An analytic solution is not available for the diffraction of elastic waves by wedges; however, numerical solutions of finite-difference type are available for selected wedge angles. The P- to Rayleigh-wave conversion coefficients at wedge tips have been measured on two-dimensional seismic models for stress-free wedges with wedge angles, ??0, of 10, 30, 60, 90 and 120??. The conversion coefficients show two broad peaks and a minimum as a function of the angle between the wedge face and the direction of the incident P-wave. The minimum occurs for the P wave incident parallel to the wedge face and one maximum is near an incidence angle of 90?? to the wedge face. The amplitude of this maximum, relative to the other, decreases as the wedge angle increases. The asymmetry of the conversion coefficients, CPR(??; ??0), relative to parallel incidence (?? = 0) increases as the wedge angle increases. The locations of the maxima and the minimum as well as the asymmetry can be explained qualitatively. The conversion coefficients are measured with an accuracy of ??5% in those regions where there are no interfering waves. A comparison of the data for the 10?? wedge with the theoretical results for a half plane (0?? wedge) shows good correlation. ?? 1978.

Gangi, A. F.; Wesson, R. L.

1978-01-01

85

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

86

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

87

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

88

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

89

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

90

Seismic attenuation due to wave-induced flow

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

91

Seismic attenuation due to wave-induced flow

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

92

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

93

NASA Astrophysics Data System (ADS)

Mass attenuation coefficient, ?m , effective atomic number, Zeff, and effective electron density, Nel, were determined experimentally and theoretically for some thermoluminescent dosimetric (TLD) compounds such as MgSO4, CdSO4, Al2O3, Mg2SiO4, ZnSO4, CaSO4, CaF2, NaSO4, Na4P2O7, Ca5F(PO4)3, SiO2, CaCO3 and BaSO4 at 8.04, 8.91, 13.37, 14.97, 17.44, 19.63, 22.10, 24.90, 30.82, 32.06, 35.40, 36.39, 37.26, 43.74, 44.48, 50.38, 51.70, 53.16, 80.99, 276.40, 302.85, 356.01, 383.85 and 661.66 keV photon energies by using an HPGe detector with a resolution of 182 eV at 5.9 keV. The theoretical mass attenuation coefficients were estimated using mixture rule. The calculated values were compared with the experimental values for all compounds. Good agreement has been observed between experimental and theoretical values within experimental uncertainties.

Önder, P.; Tur?ucu, A.; Demir, D.; Gürol, A.

2012-12-01

94

Measurements of reflection coefficient of ion waves in an ion beam-plasma system

NASA Astrophysics Data System (ADS)

The reflection coefficient of ion waves in an ion beam-plasma system is studied using a bipolar electrode as a reflector. It is found that the reflection coefficient of the beam mode is independent of the pulse widths of incident waves, while that of ion-acoustic waves is a decreasing function of frequency.

Noda, Shunichi; Nakamura, Yoshiharu; Kawai, Yoshinobu; Akazaki, Masanori

1988-12-01

95

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

96

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

97

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

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

98

Attenuation anisotropy and the relative frequency content of split shear waves

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

99

Attenuation anisotropy and the relative frequency content of split shear waves

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

100

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

101

Relationships between the satellite-derived diffuse attenuation coefficient of downwelling irradiance (K(d)) and airborne-based vertical attenuation of lidar volume backscattering (?) were examined in two coastal environments. At 1.1 km resolution and a wavelength of 532 nm, we found a greater connection between ? and K(d) when ? was computed below 2 m depth (Spearman rank correlation coefficient up to 0.96), and a larger contribution of K(d) to ? with respect to the beam attenuation coefficient as estimated from lidar measurements and K(d) models. Our results suggest that concurrent passive and active optical measurements can be used to estimate total scattering coefficient and backscattering efficiency in waters without optical vertical structure. PMID:21691366

Montes, Martin A; Churnside, James; Lee, Zhongping; Gould, Richard; Arnone, Robert; Weidemann, Alan

2011-06-20

102

Experimental Studies on Attenuation of Pressure Waves Induced by Thermal Shocks

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

103

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

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

104

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

105

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

106

Effective atomic numbers for total gamma-ray interaction with some selected thermoluminescent dosimetric compounds such as barium acetate, barium sulfate, calcium carbonate, calcium sulfate, calcium sulfate dihydrate, cadmium sulfate (anhydrous), cadmium sulfate, strontium sulfate, and lithium fluoride have been calculated in the 1-keV to 20-MeV energy region. Experimental mass attenuation coefficients and effective atomic numbers for these compounds at selected photon energies of 26.3, 33.2, 59.54, and 661.6 keV have been obtained from good geometry transmission measurements and compared with theoretical values. The effect of absorption edge on effective atomic numbers and its variation with energy, and nonvalidity of the Bragg`s mixture rule at incident photon energies closer to the absorption edges of constituent elements of compounds are discussed.

Shivaramu; Amutha, R.; Ramprasath, V. [Indira Gandhi Centre for Atomic Research, Kalpakkam (India). Safety Research and Health Physics Group

1999-05-01

107

NASA Astrophysics Data System (ADS)

According to the 'European protocol for the quality control of the physical and technical aspects of mammography screening' (EPQC) image quality digital mammography units has to be evaluated at different breast thicknesses. At the standard thickness of 50 mm polymethyl methacrylate (PMMA) image quality is determined by the analysis of CDMAM contrast detail phantom images where threshold contrasts are calculated for different gold disc diameters. To extend these results to other breast thicknesses contrast-to-noise ratios (CNR) and threshold contrast (TC) visibilities have to be calculated for all required thicknesses. To calculate the latter the mass attenuation coefficient (MAC) of gold has to be known for all possible beam qualities in the tube voltage range between 26 and 32 kV. In this paper we first determined the threshold contrast visibility using the CDMAM phantom with the same beam quality at different current-time products (mAs). We can derive from Rose theory that CNR • CT • ? = const, where ? is the diameter of the gold cylinder. From this the corresponding attenuation coefficients can be calculated. This procedure was repeated for four different beam qualities (Mo/Mo 27kV, Rh/Rh 29kV, Rh/Rh 31 kV, and W/Rh 29 kV)). Next, we measured the aluminium half value layer (HVL) of all x-ray spectra relevant for mammography. Using a first order Taylor expansion of MAC as a function of HVL, all other desired MAC can be calculated. The MAC as a function of the HVL was derived to MAChvl = -286.97 * hvl+186.03 with R2 = 0.997, where MAChvl indicates the MAC for all specific x-ray spectrum defined by its aluminium half value layer. Based on this function all necessary MACs needed for quality assurance (QA) were calculated. The results were in good agreement with the data found in the protocol.

Hummel, Johann; Semturs, Friedrich; Menhart, Susanne; Figl, Michael

2010-03-01

108

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

109

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

110

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

111

One hertz seismic attenuation for low frequency gravitational waves interferometers

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

112

Attenuation coefficients of different varieties of gamma irradiated potato (Kufri Chandramukhi, Kufri Jyoti, and Kufri Sindhuri), mango (Himsagar, Langra, Dashehri and Fazli) and prawn (Tiger prawn and Fresh water prawn) of different storage time and physiological stages were determined. After six months storage attenuation coefficient of Kufri Chandramukhi was decreased by 30.8% with decrease of density and moisture content. Decreasing trend of attenuation coefficient during storage was more prominent (almost 50%) in other two varieties of potato. On the other hand in all four varieties, unripe mango consisted of significantly less (p?0.05) attenuation coefficient (around 11-14%) than the ripe one due to changes in physiological properties and density. Different varieties of prawn had different attenuation coefficients due to subtle differences in their proximate composition. Due to having different attenuation coefficients, different food components, even different varieties of same food component absorbed different gamma radiation energy though exposed to same radiation dose. PMID:24128533

Ghosh, Sayanti; Das, M K

2013-09-04

113

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

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

114

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

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

115

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

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

116

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

117

Attenuation of P-Waves by Wave-Induced Fluid Flow

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

118

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

119

The amplification of reversed and nonreversed waves in stimulated light scattering has been compared experimentally using carbon disulfide as a scattering medium. It is found that the amplification coefficient for the conjugate wave is two times greater than for the nonconjugate wave, implying that the number of modes excited is approximately equal to the square root of Nm, where Nm

N. F. Pilipetskii; V. I. Popovichev; V. V. Ragulskii

1981-01-01

120

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

121

The results from studies of wave propagation in large arteries carried out over the last 25 years have shown that there is a good agreement among values of the imaginary part of the complex propagation coefficient, as expressed by pressure or flow-rate wave propagation velocity. However, there is considerable disparity among estimations of the degree of wave attenuation, the real part of the propagation coefficient. In order to determine whether this disparity is due to differences inherent in the various methods used to measure true wave propagation coefficients or whether it is caused by differences in experimental conditions, we have compared three techniques for determining true pulse wave propagation coefficients the three-point method, the occlusion method and a recently described iterative procedure. In addition, the results were compared to apparent propagation coefficients calculated without accounting for reflections. Measurements were carried out using each method in turn on a rubber tube of known transmission characteristics in which the magnitude of reflections was small. The iterative procedure and the three-point method were also compared under conditions of strong reflection. In the tube, the values of propagation velocity and attenuation coefficient determined by each method were similar. Although some discrepancies were noted, they did not amount to a systematic trend. The iterative procedure and the occlusion method were also used to analyse measurements on the thoracic aorta of three anaesthetized greyhounds. In the animal experiments, in spite of increased scatter, partly due to the variation between dogs, the two methods for determining true pulse-wave propagation yielded similar results. Since the differences between our estimates of propagation coefficients obtained by the methods tested are small with respect to those found when comparing the results from several reports in the literature, we conclude that any discrepancies between studies cannot be due to problems associated with the methods themselves but must have been caused by variations in experimental conditions or by other unknown artefacts. PMID:9239640

Bertram, C D; Gow, B S; Greenwald, S E

1997-04-01

122

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

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

123

In this study, the total mass attenuation coefficients (?(m)) for some homo- and hetero-chain polymers, namely polyamide-6 (PA-6), poly-methyl methacrylate (PMMA), low-density polyethylene (LDPE), polypropylene (PP) and polystyrene (PS) were measured at 59.5, 511, 661.6, 1173.2, 1274.5 and 1332.5 keV photon energies. The samples were separately irradiated with (241)Am, (22)Na, (137)Cs and (60)Co (638 kBq) radioactive gamma sources. The measurements were made by performing transmission experiments with a 2?×2? NaI(Tl) scintillation detector having an energy resolution of 7 % at 662 keV gamma ray from the decay of (137)Cs. The effective atomic numbers (Z(eff)) and the effective electron densities (N(eff)) were determined experimentally and theoretically using the obtained ?(m) values for the investigated samples. Furthermore, Z(eff) and N(eff) of each polymer were computed for total photon interaction cross-sections using theoretical data over a wide energy region from 1 keV to 10 MeV. The experimental values of the selected polymers were found to be in good agreement with the theoretical values. PMID:22645382

Kucuk, Nil; Cakir, Merve; Isitman, Nihat Ali

2012-05-29

124

Radiation dose estimation and mass attenuation coefficients of cement samples used in Turkey.

Different cement samples commonly used in building construction in Turkey have been analyzed for natural radioactivity using gamma-ray spectrometry. The mean activity concentrations observed in the cement samples were 52, 40 and 324 Bq kg(-1) for (226)Ra, (232)Th and (40)K, respectively. The measured activity concentrations for these radionuclides were compared with the reported data of other countries and world average limits. The radiological hazard parameters such as radium equivalent activities (Ra(eq)), gamma index (I(gamma)) and alpha index (I(alpha)) indices as well as terrestrial absorbed dose and annual effective dose rate were calculated and compared with the international data. The Ra(eq) values of cement are lower than the limit of 370 Bq kg(-1), equivalent to a gamma dose of 1.5 mSv y(-1). Moreover, the mass attenuation coefficients were determined experimentally and calculated theoretically using XCOM in some cement samples. Also, chemical compositions analyses of the cement samples were investigated. PMID:20018450

Damla, N; Cevik, U; Kobya, A I; Celik, A; Celik, N; Van Grieken, R

2009-12-16

125

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

126

Rain induced attenuation of millimeter waves radio link in Indian continent

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

127

Coplanar waveguides in silicon with low attenuation and slow wave reduction

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

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

2007-01-01

128

NASA Astrophysics Data System (ADS)

Many oscillatory biological systems show periodic travelling waves. These are often modelled using coupled reaction diffusion equations. However, the effects of different movement rates (diffusion coefficients) of the interacting components on the predictions of these equations are largely unknown. Here we investigate the ways in which varying the diffusion coefficients in such equations alters the wave speed, time period, wavelength, amplitude and stability of periodic wave solutions. We focus on two sets of kinetics that are commonly used in ecological applications: lambda omega equations, which are the normal form of an oscillatory coupled reaction diffusion system close to a supercritical Hopf bifurcation, and a standard predator prey model. Our results show that changing the ratio of the diffusion coefficients can significantly alter the shape of the one-parameter family of periodic travelling wave solutions. The position of the boundary between stable and unstable waves also depends on the ratio of the diffusion coefficients: in all cases, stability changes through an Eckhaus (‘sideband’) instability. These effects are always symmetrical in the two diffusion coefficients for the lambda omega equations, but are asymmetric in the predator prey equations, especially when the limit cycle of the kinetics is of large amplitude. In particular, there are two separate regions of stable waves in the travelling wave family for some parameter values in the predator prey scenario. Our results also show the existence of a one-parameter family of travelling waves, but not necessarily a Hopf bifurcation, for all values of the diffusion coefficients. Simulations of the full partial differential equations reveals that varying the ratio of the diffusion coefficients can significantly change the properties of periodic travelling waves that arise from particular wave generation mechanisms, and our analysis of the travelling wave families assists in the understanding of these effects.

Smith, Matthew J.; Sherratt, Jonathan A.

2007-12-01

129

NASA Astrophysics Data System (ADS)

With advances in 3D in vivo imaging technology, non-invasive procedures can be used to characterize tissues to identify tumors and monitor changes over time. Using a dedicated breast CT system with a quasi-monochromatic cone-beam x-ray source and flat-panel digital detector, this study was performed in an effort to directly characterize different materials in vivo based on their absolute attenuation coefficients. CT acquisitions were first acquired using a multi-material rod phantom with acrylic, delrin, polyethylene, fat-equivalent, and glandular-equivalent plastic rods, and also with a human cadaver breast. Projections were collected with and without a beam stop array for scatter correction. For each projection, the 2D scatter was estimated with cubic spline interpolation of the average values behind the shadow of each beam stop overlapping the object. Scatter-corrected projections were subsequently calculated by subtracting the scatter images containing only the region of the object from corresponding projections (consisting of primary and scatter x-rays) without the beam stop array. Iterative OSTR was used to reconstruct the data and estimate the non-uniform attenuation distribution. Preliminary results show that with reduced beam hardening from the x-ray beam, scatter correction further reduces the cupping artifact, improves image contrast, and yields attenuation coefficients < 8% of narrow-beam values of the known materials (range 1.2 - 7.8%). Peaks in the histogram showed clear separation between the different material attenuation coefficients. These findings indicate that minimizing beam hardening and applying scatter correction make it practical to directly characterize different tissues in vivo using absolute attenuation coefficients.

Madhav, Priti; Li, Christina M.; Tornai, Martin P.

2010-03-01

130

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

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

131

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

132

The amount of photosynthetically active radiation (PAR) in the water column is of fundamental importance in determining the\\u000a growth of aquatic plant and aquatic primary production. Light attenuation in aquatic ecosystems has important ecological implication\\u000a and water quality applications. In the present study, the light attenuation through the water column in the Shihmen Reservoir,\\u000a Taiwan was measured. A light attenuation

Wen-Cheng Liu; Ray-Shyan Wu; Edward Ming-Yang Wu; Yu-Pei Chang; Wei-Bo Chen

2010-01-01

133

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

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

134

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

135

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

136

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

137

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

138

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

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

139

STRICHARTZ ESTIMATES FOR OPERATORS WITH NONSMOOTH COEFFICIENTS AND THE NONLINEAR WAVE EQUATION

The aim of this article is threefold. First, we use the FBI transform to set up a calculus for partial differential operators with nonsmooth coefficients. Next, this calculus allows us to prove Strichartz type estimates for the wave equation with nonsmooth coefficients. Finally, we use these Strichartz estimates to improve the local theory for second order nonlinear hyperbolic equations. 1.

DANIEL TATARU

140

Sound absorption coefficient measurements by phase-conjugate ultrasonic waves

NASA Astrophysics Data System (ADS)

Measurements of the sound absorption coefficient in test objects containing solid microparticles randomly distributed over the object volumes are carried out. Two methods are used for this purpose: the standard echo-pulse insert-substitution method and a modified method using phase conjugation of ultrasound. The test objects are made from gelatin, and the size of the particles introduced in it is chosen to allow measurements in both the long- and medium-wavelength scattering modes of the probing beam. It is shown that, in the first scattering mode, in which the presence of particles causes additional viscous and temperature losses, the two aforementioned methods give identical results. In the second scattering mode, in which the dominant mechanism of additional loss is elastic scattering, the use of phase conjugation allows an almost complete reconstruction of the scattered field and, hence, a more reliable upper estimate for the coefficient of ultrasonic absorption in the test objects.

Smagin, N. V.; Krutyansky, L. M.; Brysev, A. P.

2013-03-01

141

We present initial aerosol validation results of the space-borne lidar CALIOP -onboard the CALIPSO satellite- Level 1 attenuated backscatter coefficient profiles, using coincident observations performed with a ground-based lidar in Athens, Greece (37.9° N, 23.6° E). A multi-wavelength ground-based backscatter\\/Raman lidar system is operating since 2000 at the National Technical University of Athens (NTUA) in the framework of the European

R. E. Mamouri; V. Amiridis; A. Papayannis; E. Giannakaki; G. Tsaknakis; D. S. Balis

2009-01-01

142

Parametrization of the total photon mass attenuation coefficients in the energy range 0.1-1000 keV

NASA Astrophysics Data System (ADS)

It is convenient to generate mass attenuation coefficients using semi-empirical schemes. The validity of most of the existing schemes is limited to a relatively narrow energy interval (1-40 keV) and their accuracies are poor in some energy regions. In this work, a semi-empirical scheme flexible enough to give a good fit to data in a very wide photon energy range (0.1-1000 keV) was employed. Fitting coefficients for the entire range were obtained by utilizing mass attenuation data from two sources: (1) semi-empirical data of Henke et al. in the low photon energy region, and (2) theoretical values generated with the XCOM code for fitting in the high energy region. The root mean square of the fit is generally less than 0.2% except for energies below 1 keV where the available data are scattered. A computer code for generating mass attenuation coefficients based on the proposed scheme has been developed.

Orlic, I.; Loh, K. K.; Sow, C. H.; Tang, S. M.; Thong, P.

1993-05-01

143

Control of the Wave Equation by Time-Dependent Coefficient

We study an initial boundary-value problem for a wave equation with time-dependent sound speed. In the control problem, we wish to determine a sound-speed function which damps the vibration of the system. We consider the case where the sound speed can take on only two values, and propose a simple control law. We show that if the number of modes

Antonin Chambolle; Fadil Santosa

2002-01-01

144

Attenuating the ice flexural wave on arctic seismic data

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

145

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

146

Far infrared and submillimeter wave attenuation by clouds and rain

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

147

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

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

148

Measurement of alkali-silica reaction progression by ultrasonic waves attenuation

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

149

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

150

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

151

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

152

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

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

153

Ultrasonic attenuation measurements in Egyptian dry compact rocks

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

154

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

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

155

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

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

156

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

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

157

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

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

158

Deriving attenuation coefficients from 3D CT data for SPECT Monte Carlo simulations

Quantitation of nuclear medicine data is a major goal in medical imaging. It implies that photon attenuation, scatter and depth dependent spatial resolution be corrected for. Realistic, anthropomorphic numerical phantoms are needed to understand how these phenomena degrade nuclear medicine images, and to validate correction methods. We developed a Monte Carlo simulator which simulates photon transport in an anthropomorphic phantom.

Veronique Baccarne; A. Turzo; Y. Bizais; M. Farine

1997-01-01

159

Pitch-angle diffusion coefficients have been calculated for resonant interaction with electrostatic electron cyclotron harmonic (ECH) waves using quasilinear diffusion theory. Unlike previous calculations, the parallel group velocity has been included in this study. Further, ECH wave intensity is expressed as a function of wave frequency and wave normal angle with respect to ambient magnetic field. It is found that observed wave electric field amplitudes in Earth's magnetosphere are sufficient to set electrons on strong diffusion in the energy ranges of a few hundred eV. However, the required amplitudes are larger than the observed values for keV electrons and higher by about a factor of 3 compared to past calculations. Required electric field amplitudes are smaller at larger radial distances. It is concluded that ECH waves are responsible for diffuse auroral precipitation of electrons with energies less than about 500 eV.

Tripathi, A. K.; Singhal, R. P. [Department of Applied Physics, Institute of Technology, Banaras Hindu University, Varanasi U.P. 221005 (India)

2009-11-15

160

Rogue wave solutions to the generalized nonlinear Schrödinger equation with variable coefficients.

A similarity transformation is utilized to reduce the generalized nonlinear Schrödinger (NLS) equation with variable coefficients to the standard NLS equation with constant coefficients, whose rogue wave solutions are then transformed back into the solutions of the original equation. In this way, Ma breathers, the first- and second-order rogue wave solutions of the generalized equation, are constructed. Properties of a few specific solutions and controllability of their characteristics are discussed. The results obtained may raise the possibility of performing relevant experiments and achieving potential applications. PMID:23848816

Zhong, Wei-Ping; Beli?, Milivoj R; Huang, Tingwen

2013-06-07

161

A cataract is a clouding of the lens in the eye that affects vision. Phacoemulsification is the mostly common surgical method for treating cataracts, and determining that the optimal phacoemulsification energy is dependent on measuring the hardness of the lens. This study explored the use of an ultrasound needle transducer for invasive measurements of ultrasound attenuation coefficient to evaluate the hardness of the cataract lens. A 47 MHz high-frequency needle transducer with a diameter of 0.9 mm was fabricated by a polarized PMN-33%PT single crystal in the present study. The attenuation coefficients at different stages of an artificial porcine cataract lens were measured using the spectral shift approach. The hardness of the cataract lens was also evaluated by mechanical measurement of its elastic properties. The results demonstrated that the ultrasonic attenuation coefficient was increased from 0.048 ± 0.02 to 0.520 ± 0.06 dB mm?1 MHz?1 corresponding to an increase in Young’s modulus from 6 ± 0.4 to 96 ± 6.2 kPa as the cataract further developed. In order to evaluate the feasibility of combining needle transducer and phacoemulsification probe for real-time measurement during cataract surgery, the needle transducer was mounted on the phacoemulsification probe for a vibration test. The results indicated that there was no apparent damage to the tip of the needle transducer and the pulse–echo test showed that a good performance in sensitivity was maintained after the vibration test.

Chen, Ruimin; Tsui, Po-Hsiang; Zhou, Qifa; Humayun, Mark S; Shung, K Kirk

2010-01-01

162

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

163

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

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

2011-03-01

164

The 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

165

Bibliography of photon total cross section (attenuation coefficient) measurements 10 eV to 13. 5 Gev

The authors present a bibliography of papers reporting absolute measurements of photon (XUV, x-ray, gamma-ray, bremsstrahlung) total interaction cross sections or attenuation coefficients for the elements and some compounds. The energy range covered is from 10 eV to above 10 GeV. The papers are part of the reference collection of the National Bureau of Standards Photon and Charged Particle Data Center. They cover the period from 1907 to March 1986. Included with each reference are annotations specifying the substances studied and the duplicative references to a total of about 20,000 data points. All these data are available in machine-readable form.

Hubbell, J.H.; Gerstenberg, H.M.; Saloman, E.B.

1986-10-01

166

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

167

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

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

168

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

169

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

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

170

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

171

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

172

NASA Astrophysics Data System (ADS)

A simple expression is presented to quickly estimate specific attenuation coefficient due to fog within the ranges of 100~300GHz and -8~20°C based on the Rayleigh approximation which is not very convenient. To evaluate the expression's estimation performance, the Pearson correlation coefficient (PCC) and maximal absolute value of the relative errors (MAVRE) are calculated. The maximum value of PCC is 1 and it reflects the fitting performance of an empirical expression. MAVRE denotes the largest deviation between a set of estimated values and corresponding theoretical values. Calculations show the PCC and MAVRE of the proposed expression are 0.99985 and 4.162%, respectively. Furthermore, a comparison analysis shows that the new expression has much better estimation performance than other two empirical expressions: the modified Mao expression and the Zhao expression.

Liu, Yun-Long; Hu, Meng-Hao

2013-08-01

173

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

174

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

175

Exact solutions for heat-like and wave-like equations with variable coefficients

In this paper, Adomian decomposition method is presented for solving heat-like and wave-like models with variable coefficients. The method is demonstrated for a variety of problems in one and higher dimensional spaces where exact solutions are obtained. The results obtained in all cases show the reliability and the efficiency of this method.

Abdul-Majid Wazwaz; Alice Gorguis

2004-01-01

176

NASA Astrophysics Data System (ADS)

The optical classification of the different water types provides vital input for studies related to primary productivity, water clarity and determination of euphotic depth. Image data of the IRSP3 MOS-B, for Path 90 of 27th February, 1998 was used for deriving vertical diffuse attenuation coefficient (Kd) and an optical classification based on K d values was performed. An atmospheric correction scheme was used for retrieving water leaving radiances in blue and green channels of 412, 443, 490 and 550 nm. The upwelling radiances from 443 nm and 550 nm spectral channels were used for computation of vertical diffuse attenuation coefficient K d at 490 nm. The waters off the Gujarat coast were classified into different water types based on Jerlov classification scheme. The oceanic water type IA ( K d range 0.035-0.040m-1), type IB (0.042-0.065 m-1), type II (0.07-0.1m-1) and type III (0.115-0.14m-1) were identified. For the coastal waters along Gujarat coast and Gulf of Kachchh, Kd( 490) values ranged between 0.15 m-1 and 0.35 m-1. The depth of 1% of surface light for water type IA, IB, II and III corresponds to 88, 68, 58 and 34 meters respectively. Classification of oceanic and coastal waters based on K d is useful in understanding the light transmission characteristics for sub-marine navigation and under-water imaging.

Sarangi, R. K.; Chauhan, Prakash; Nayak, S. R.

2002-09-01

177

The radiotherapy-related types of nasopharyngeal carcinoma (NPC) have been established, which give the most effective treatment for NPC patients using the individual therapy. To diagnose the types of NPC, we assess the general NPC cell lines CNE1, CNE2 and normal nasopharyngeal cell line NP69 using optical coherence tomography (OCT) in two steps: firstly, the OCT images of the three different types of cell pellets are captured. Secondly, by fitting Beer's law to the averaged A-scans in these OCT datasets, the attenuation coefficients (? t ) of the cells can be extracted. The median attenuation coefficients (interquartile range) of CNE1, CNE2, and NP69 are 5.58 mm(-1) (IQR 5.55 to 5.65 mm(-1)), 5.91 mm(-1) (IQR 5.82 to 5.88 mm(-1)), and 8.96 mm(-1) (IQR 8.80 to 9.47 mm(-1)), respectively. The distinguishable quantitative OCT analysis (by ? t ) shows that the types of NPC could potentially be differentiated in real time and noninvasive. PMID:22618158

Li, Jianghua; Tu, Ziwei; Shen, Zhiyuan; Xia, Yunfei; He, Yonghong; Liu, Songhao; Chen, Changshui

2012-05-22

178

The mass attenuation coefficients (mu/rho) of Rhizophora spp. were determined for photons in the energy range of 15.77-25.27 keV. This was carried out by studying the attenuation of X-ray fluorescent photons from zirconium, molybdenum, palladium, silver, indium and tin targets. The results were compared with theoretical values for average breast tissues in young-age, middle-age and old-age groups calculated using photon cross section database (XCOM), the well-known code for calculating attenuation coefficients and interaction cross-sections. The measured mass attenuation coefficients were found to be very close to the calculated XCOM values in breasts of young-age group. PMID:19482883

Shakhreet, B Z; Bauk, S; Tajuddin, A A; Shukri, A

2009-05-29

179

Absorption coefficients of all elements may be calculated, from short wave-lengths up to the K critical absorption wave-length by the expression: ??&rgr;=??3Z2(2Z?A)???4Z5(2Z?A)+?eN0(Z?A). This formula holds for all elements when suitable values for ? and ? are chosen. Factors ? and ? are related to the atomic number, Z, by the expressions ?=(aZ2+bZ?c), and ?=(dZ2?eZ+f). Different values of the constants a,

John A. Victoreen

1943-01-01

180

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

181

Long-Term Measurements of Drag Coefficients and Waves in High Winds

NASA Astrophysics Data System (ADS)

The WaveWatch III model over-predicts wave heights at high winds speeds. One potential reason is that the momentum flux to the waves is overestimated within the model. Recent results indicate that the momentum flux at wind speeds above 30-40 m s-1 plateaus [Powell et al., 2003] and may lead to a reduction in the drag coefficient. Here we describe the physical relationships between wind history, wave field development, and atmospheric drag during high wind speed events, through the determination of wind speed and stability dependence of drag coefficients from long-term measurements at the US Army Corps of Engineers Field Research Facility (FRF) in Duck, NC. Our approach is to develop a long-term robust measurement suite to capture the conditions during tropical storms and nor'easters. Accurate measurements of 3-D turbulent wind speed components and turbulent water vapour concentration fluctuations are measured at 2 different heights simultaneously with wave height measurements to determine the friction velocity and drag coefficients as a function of wind, waves, and atmospheric boundary layer stability during high wind speeds. Initial results from micrometeorological measurements show that in onshore winds the conditions are representative for open ocean conditions (comparison with TOGA-COARE). However, wind speeds in these experiments were only up to 20 m s-1, whereas for the long-term deployment we are aiming for extreme wind speeds up to at least 40-50 m s-1 that may occur at FRF during winter storms and hurricane conditions. The long-term objective is wave model prediction at high wind speed using improved parameterization of atmospheric inputs.

Zappa, C. J.; McGillis, W. R.; de Leeuw, G.; Moerman, M.; Hanson, J. L.; Friebel, H. C.

2006-12-01

182

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

183

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

184

Bounce-averaged diffusion coefficients in non-dipole field for field-aligned chorus waves

NASA Astrophysics Data System (ADS)

Scattering rates calculated in a dipole field are used in radiation belt codes. We present the results of calculations of the bounce-averaged quasi-linear diffusion coefficients in momentum Dpp, pitch-angle D?? and mixed pitch angle-momentum D?p for field lines (at different distances and MLT) in two non-dipole fields: the Dungey field and the Tsyganenko 89 (T89c) magnetic field. In the T89c field the coefficients were computed for quiet conditions (Kp=2) and storm-time conditions (Kp=6). To calculate diffusion coefficients, we assume that electrons are scattered by the field aligned chorus waves (of Gaussian spectrum) outside the plasmasphere. These waves are observed for MLT between approximately 0 and 12. We also take into consideration the maximum latitude where waves are assumed to be present. We compare calculations of bounce-averaged diffusion coefficients in non-dipole fields with those in the dipole field and discuss the differences. We demonstrate that the effect of bounce averaging in a non-dipole field is negligible at L-shells less than 4, at higher L-shells changes in the field may dramatically alter the scattering rates.

Orlova, K.; Shprits, Y.

2009-12-01

185

Nonlinear inversion of the P-wave P-wave reflection coefficient data

Surface seismic data are used to estimate lithologic parameters at an interface. The four unknown independent parameters at an interface are the ratio of the P-wave velocities and the ratio of the densities of upper and lower media, and the P-wave/S-wave velocity ratios in the upper and lower media respectively. The forward problem is solved by a reparameterized form of the full Zoeppritz equation for PP reflections. The inversion model is fitted to the data using a two part inversion scheme. The near offset (near normal incidence) data is initially inverted using a linearized Zoeppritz normal incidence equation to obtain estimates of the P-wave ratio and density ratio. The estimates of these two parameters are then used as initial guesses in a nonlinear full Zoeppritz inversion by a Levenberg Marquardt procedure. Partial derivatives of the reparameterized Zoeppritz equation for the Jacobian matrix are calculated analytically at each iteration. All parameters are successfully estimated from synthetic data. Poisson`s ratio of the upper and lower media can be calculated from inversion estimates of P-wave/S-wave velocity ratio. Lithologic parameters are estimated for several CDP gathers from a 3D survey of the Rabbit Hills Field in North Central Montana. A sensitivity analysis for the different parameters is performed.

Pate, A.J. [Univ. of Montana, Butte, MT (United States)

1996-06-01

186

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

187

Bounce-averaged diffusion coefficients in the Tsyganenko field model for oblique chorus waves

NASA Astrophysics Data System (ADS)

The assessment of the importance of various acceleration and loss mechanisms of relativistic electrons is crucially important for predicting and understanding the dynamics of the radiation belts. It is commonly accepted that resonant wave-particle interactions play a major role in these processes. Bounce-averaged momentum, pitch-angle, and mixed diffusion coefficients, calculated using various models of spectral properties of waves and spatial distributions of plasma waves, are used in modern radiation belt codes as inputs. The diffusion coefficients for radiation belt models are usually computed using the quasi-linear theory and are bounce-averaged in the dipole magnetic field. During magnetic storms, however, the configuration and the value of the magnetic field are significantly changed, which may potentially influence the scattering rates. The purpose of this work is to estimate the role of a realistic magnetic field model on the bounce-averaged diffusion coefficients. We present the results of computations of bounce-averaged quasi-linear momentum Dpp, pitch-angle D?? and mixed pitch angle-momentum D?p diffusion coefficients in the Tsyganenko magnetic field model. We assume that electrons are scattered by oblique whistler mode chorus waves of Gaussian spread of wave power spectral density and wave normal angle outside the plasmasphere. The scattering rates are computed using the full electromagnetic dispersion relation and up to ±5-order resonance condition including Landau resonance. The diffusion coefficients are calculated for quiet conditions (Kp=2) and storm-time conditions (Kp=6) for the day and night sides. We compare scattering rates bounce-averaged in the Tsyganenko field model with those in the dipole field and discuss the differences. The results are followed by a physical explanation of how the magnetic field model can change the bounce-averaged scattering rates. The calculations show that, during active conditions, the pitch-angle scattering by chorus waves in the realistic magnetic field can diffuse relativistic electrons to the loss cone not only on the day side, as was previously shown, but also on the night side. This explains the often observed microburst precipitation on the night side. Our study shows that while there are still a number of unknown parameters that determine scattering rates, inclusion of bounce-averaging in the realistic field will be crucially important for future radiation belt modeling.

Orlova, Ksenia; Shprits, Yuri

2010-05-01

188

Comparison of photon attenuation coefficients (2-150 KeV) for diagnostic imaging simulations

NASA Astrophysics Data System (ADS)

The Radiology Research Laboratory at the Henry Ford Hospital has been involved in modeling x-ray units in order to predict image quality. A critical part of that modeling process is the accurate choice of interaction coefficients. This paper serves as a review and comparison of existing interaction models. Our objective was to obtain accurate and easily calculated interaction coefficients, at diagnostically relevant energies. We obtained data from: McMaster, Lawrence Berkeley Lab data (LBL), XCOM and FFAST Data from NIST, and the EPDL-97 database via LLNL. Our studies involve low energy photons; therefore, comparisons were limited to Coherent (Rayleigh), Incoherent (Compton) and Photoelectric effects, which were summed to determine a total interaction cross section. Without measured data, it becomes difficult to definitively choose the most accurate method. However, known limitations in the McMaster data and smoothing of photo-edge transitions can be used as a guide to establish more valid approaches. Each method was compared to one another graphically and at individual points. We found that agreement between all methods was excellent when away from photo-edges. Near photo-edges and at low energies, most methods were less accurate. Only the Chanter (FFAST) data seems to have consistently and accurately predicted the placement of edges (through M-shell), while minimizing smoothing errors. The EPDL-97 data by LLNL was the best over method in predicting coherent and incoherent cross sections.

Dodge, Charles W., III; Flynn, Michael J.

2004-05-01

189

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

190

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

191

Two approaches to the solution of coefficient inverse problems for wave equations

NASA Astrophysics Data System (ADS)

Two approaches to solving coefficient inverse problems for wave equations are compared. One approach is based on integral representations obtained with the help of the Green's function for the wave equation. In the other approach, the gradient of the error functional is directly computed in terms of the solution of the adjoint problem for a partial differential equation. The methods developed are intended for finding inhomogeneities in homogeneous media and can be applied in medicine diagnostics, acoustic and seismic near surface exploration, engineering seismics, etc.

Goncharskii, A. V.; Romanov, S. Yu.

2012-02-01

192

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

193

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

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

194

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

195

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

196

Phase of the transmission coefficient of waves in one-dimensional random media

NASA Astrophysics Data System (ADS)

We study the behavior of the phase of the transmission coefficient t in random media by using the invariant imbedding method of wave propagation. We calculate the disorder average of t/t* for waves propagating in one-dimensional random media with uncorrelated Gaussian disorder in a numerically exact manner. We find that the analytical formula derived by Mello et al. [Phys. Rev. Lett. 67, 342 (1991)] is valid only after a major modification and only in the limit where the so-called random phase approximation is valid. We find that the disorder average of t/t* converges to a finite complex number in the large-size limit. We discuss the implications of our results for the probability distribution of the phase of the transmission coefficient.

Lee, Kwang Jin; Kim, Kihong

2012-04-01

197

Finite-floe wave reflection and transmission coefficients from a semi-infinite model

NASA Astrophysics Data System (ADS)

A model to describe the reflection and transmission of ocean waves by a single ice floe is developed from the semi-infinite model of Fox and Squire (1990, 1991). This is done by considering the coefficients for the transition from ice to water in the semi-infinite case in terms of those from water to ice. Finite-floe reflection and transmission coefficients, R and T, respectively, are then found as the solution of a set of four simple simultaneous equations. The properties of R and T are investigated, and examples of their absolute values are given for several geometries. |R| compares well with the predictions of a precise model in the case of deep water. These results suggest that the analytical model described has applications to defining the sea state within marginal ice zones, given the floe size and ice thickness distributions and the incoming sea wave spectrum.

Meylan, Michael; Squire, Vernon A.

1993-07-01

198

An extension of the X-ray extended-range technique is described for measuring X-ray mass attenuation coefficients by introducing absolute measurement of a number of foils - the multiple independent foil technique. Illustrating the technique with the results of measurements for gold in the 38-50 keV energy range, it is shown that its use enables selection of the most uniform and well defined of available foils, leading to more accurate measurements; it allows one to test the consistency of independently measured absolute values of the mass attenuation coefficient with those obtained by the thickness transfer method; and it tests the linearity of the response of the counter and counting chain throughout the range of X-ray intensities encountered in a given experiment. In light of the results for gold, the strategy to be ideally employed in measuring absolute X-ray mass attenuation coefficients, X-ray absorption fine structure and related quantities is discussed.

Chantler, C.T.; Islam, M.T.; Rae, N.A.; Tran, C.Q.; Glover, J.L.; Barnea, Z. (La Trobe); (Melbourne)

2012-09-25

199

The compounds, NaBO, HBO, CdCl and NaCl and their solutions, attenuate gamma rays in addition to neutron absorption. These compounds are widely used in shielding of neutron sources, reactor control and neutron converters. Mass attenuation coefficients of gamma related to saturated solutions of the above four compounds, in energies 1172 keV and 1332 keV have been measured by NaI detector

Jalali; Majid

2006-01-01

200

NASA Astrophysics Data System (ADS)

In the frame of ocean dynamical system, considering the nonlinearity and isotropy of the sub-small scale turbulence the paper derived the second order moment closure equations and according to the statistical theory of breaking waves gave the boundary conditions for the kinetic energy input and the mixing length on the sea surface first, which are the physic-mathematical description of the turbulence generated by sea waves. Considering the observation effect that the dissipation rate of the turbulence kinetic energy has power vertical distribution of sea waves, we derived the balanced solution of the variation equations for the turbulence characteristics and gave the analytical expressions of the kinetic energy and the dissipation rate , and then the analytic expressions of the mixing coefficients in the upper ocean according to the closure technique with high determinacy.The theoretical coefficients were applied to the numerical modeling of ocean circulation and then the substantive progress in qualitative and quantitative modeling was gained on the premise of no any coefficient tune-up.

Yuan, Yeli

2013-04-01

201

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

202

NASA Astrophysics Data System (ADS)

Dual energy computed tomography (DECT) can provide simultaneous estimation of relative electron density ?e and effective atomic number Zeff. The ability to obtain these quantities (?e, Zeff) has been shown to benefit selected radiotherapy applications where tissue characterization is required. The conventional analysis method (spectral method) relies on knowledge of the CT scanner photon spectra which may be difficult to obtain accurately. Furthermore an approximate empirical attenuation correction of the photon spectrum through the patient is necessary. We present an alternative approach based on a parameterization of the measured ratio of low and high kVp linear attenuation coefficients for deriving Zeff which does not require the estimation of the CT scanner spectra. In a first approach, the tissue substitute method (TSM), the Rutherford parameterization of the linear attenuation coefficients was employed to derive a relation between Zeff and the ratio of the linear attenuation coefficients measured at the low and high kVp of the CT scanner. A phantom containing 16 tissue mimicking inserts was scanned with a dual source DECT scanner at 80 and 140 kVp. The data from the 16 inserts phantom was used to obtain model parameters for the relation between Zeff and \\mu \\big|_{140kVp}^{80kVp}. The accuracy of the method was evaluated with a second phantom containing 4 tissue mimicking inserts. The TSM was compared to a more complex approach, the reference tissue method (RTM), which requires the derivation of stoichiometric fit parameters. These were derived from the 16 inserts phantom scans and used to calculate CT numbers at 80 and 140 kVp for a set of tabulated reference human tissues. Model parameters for the parameterization of \\mu \\big|_{140\\;kVp}^{80\\;kVp} were estimated for this reference tissue dataset and compared to the results of the TSM. Residuals on Zeff for the reference tissue dataset for both TSM and RTM were compared to those obtained from the spectral method. The tissue substitutes were well fitted by the TSM with R2 = 0.9930. Residuals on Zeff for the phantoms were similar between the TSM and spectral methods for Zeff < 8 while they were improved by the TSM for higher Zeff. The RTM fitted the reference tissue dataset well with R2 = 0.9999. Comparing the Zeff extracted from TSM and the more complex RTM to the known values from the reference tissue dataset yielded errors of up to 0.3 and 0.15 units of Zeff respectively. The parameterization approach yielded standard deviations which were up to 0.3 units of Zeff higher than those observed with the spectral method for Zeff around 7.5. Procedures for the DECT estimation of Zeff removing the need for estimates of the CT scanner spectra have been presented. Both the TSM and the more complex RTM performed better than the spectral method. The RTM yielded the best results for the reference human tissue dataset reducing errors from up to 0.3 to 0.15 units of Zeff compared to the simpler TSM. Both TSM and RTM are simpler to implement than the spectral method which requires estimates of the CT scanner spectra.

Landry, Guillaume; Seco, Joao; Gaudreault, Mathieu; Verhaegen, Frank

2013-10-01

203

Dual energy computed tomography (DECT) can provide simultaneous estimation of relative electron density ?e and effective atomic number Zeff. The ability to obtain these quantities (?e, Zeff) has been shown to benefit selected radiotherapy applications where tissue characterization is required. The conventional analysis method (spectral method) relies on knowledge of the CT scanner photon spectra which may be difficult to obtain accurately. Furthermore an approximate empirical attenuation correction of the photon spectrum through the patient is necessary. We present an alternative approach based on a parameterization of the measured ratio of low and high kVp linear attenuation coefficients for deriving Zeff which does not require the estimation of the CT scanner spectra. In a first approach, the tissue substitute method (TSM), the Rutherford parameterization of the linear attenuation coefficients was employed to derive a relation between Zeff and the ratio of the linear attenuation coefficients measured at the low and high kVp of the CT scanner. A phantom containing 16 tissue mimicking inserts was scanned with a dual source DECT scanner at 80 and 140 kVp. The data from the 16 inserts phantom was used to obtain model parameters for the relation between Zeff and [Formula: see text]. The accuracy of the method was evaluated with a second phantom containing 4 tissue mimicking inserts. The TSM was compared to a more complex approach, the reference tissue method (RTM), which requires the derivation of stoichiometric fit parameters. These were derived from the 16 inserts phantom scans and used to calculate CT numbers at 80 and 140 kVp for a set of tabulated reference human tissues. Model parameters for the parameterization of [Formula: see text] were estimated for this reference tissue dataset and compared to the results of the TSM. Residuals on Zeff for the reference tissue dataset for both TSM and RTM were compared to those obtained from the spectral method. The tissue substitutes were well fitted by the TSM with R(2) = 0.9930. Residuals on Zeff for the phantoms were similar between the TSM and spectral methods for Zeff < 8 while they were improved by the TSM for higher Zeff. The RTM fitted the reference tissue dataset well with R(2) = 0.9999. Comparing the Zeff extracted from TSM and the more complex RTM to the known values from the reference tissue dataset yielded errors of up to 0.3 and 0.15 units of Zeff respectively. The parameterization approach yielded standard deviations which were up to 0.3 units of Zeff higher than those observed with the spectral method for Zeff around 7.5. Procedures for the DECT estimation of Zeff removing the need for estimates of the CT scanner spectra have been presented. Both the TSM and the more complex RTM performed better than the spectral method. The RTM yielded the best results for the reference human tissue dataset reducing errors from up to 0.3 to 0.15 units of Zeff compared to the simpler TSM. Both TSM and RTM are simpler to implement than the spectral method which requires estimates of the CT scanner spectra. PMID:24025623

Landry, Guillaume; Seco, Joao; Gaudreault, Mathieu; Verhaegen, Frank

2013-09-11

204

Bounce-averaged diffusion coefficients in the Tsyganenko field model for oblique chorus waves

NASA Astrophysics Data System (ADS)

We present the results of computations of bounce-averaged quasi-linear momentum Dpp, pitch-angle D?? and mixed D?p diffusion coefficients in the Tsyganenko magnetic field model. We assume that electrons are scattered by oblique whistler mode chorus waves of Gaussian spread of wave power spectral density and wave normal angle outside the plasmasphere. The scat-tering rates are computed using the full electromagnetic dispersion relation and up to 5-order resonance condition including Landau resonance. The diffusion coefficients are calculated for quiet conditions and storm-time conditions for the day and night sides. We compare scattering rates bounce-averaged in the Tsyganenko field model with those in the dipole field and discuss the differences. The results are followed by a physical explanation of how the magnetic field model can change the bounce-averaged scattering rates. The calculations show that, during active conditions, the pitch-angle scattering by chorus waves in the realistic magnetic field can diffuse relativistic electrons to the loss cone not only on the day side, but also on the night side. Our study shows that while there are still a number of unknown parameters that determine scattering rates, inclusion of bounce-averaging in the realistic field will be crucially important for future radiation belt modeling.

Orlova, Ksenia; Shprits, Yuri

205

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

206

NASA Astrophysics Data System (ADS)

The total mass attenuation coefficients, ?m, for PbO, barite, colemanite, tincal and ulexite were determined at 80.1, 302.9, 356.0, 661.7 and 1250.0 keV photon energies by using NaI (Tl) scintillation detector. Effective atomic number, Zeff, effective electron number, Neff, total atomic cross-section, ?t, total electronic cross-section, ?e, mean free path, mfp, and kerma relative to air were determined experimentally and theoretically. The theoretical mass attenuation coefficients were estimated using mixture rule. The calculated values were compared with the experimental values for all samples.

Un, A.; Sahin, Y.

2011-07-01

207

NASA Astrophysics Data System (ADS)

The Buchdahl-Rimmer third- and fifth-order geometric aberration coefficients are converted or renormalized to a RMS value of the wave aberration function. The purpose of this is to make it possible to compare different aberration coefficients directly since any aberrations which have the same renormalized coefficients will have the same effect on the image quality in terms of the Strehl intensity ratio. This is an advantage which, until now, has only been obtained using the renormalized Zernike coefficients.

Rosete-Aguilar, M.; Rayces, J.

1995-12-01

208

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

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

209

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

210

Bounce-averaged diffusion coefficients in a realistic field model for oblique chorus waves

NASA Astrophysics Data System (ADS)

We present the results of computations of bounce-averaged quasi-linear momentum

Orlova, K.; Shprits, Y.; Ni, B.

2010-12-01

211

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

212

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

213

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

214

A double beam laser method for measuring attenuation coefficients of sea-water throughout the 414-662 nm wavelength region is presented. The radiant source is a pulsed wavelength-tunable dye laser, with a spectral width of 0.01 nm. A test with de-ionised filtered distilled water is described.

H. Mercier; F. Gaillard; J. Cariou; J. Lotrian

1982-01-01

215

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

216

Measurement of the x-ray mass attenuation coefficients of gold in the 38?50-keV energy range

We used synchrotron x rays to measure the x-ray mass attenuation coefficients of gold at nine energies from 38 to 50 keV with accuracies of 0.1%. Our results are much more accurate than previous measurements in this energy range. A comparison of our measurements with calculated mass attenuation coefficients shows that our measurements fall almost exactly midway between the XCOM and FFAST calculated theoretical values, which differ from one another in this energy region by about 4%, even though the range includes no absorption edge. The consistency and accuracy of these measurements open the way to investigations of the x-ray attenuation in the region of the L absorption edge of gold.

Islam, M.T.; Rae, N.A.; Glover, J.L.; Barnea, Z.; de Jonge, M.D.; Tran, C.Q.; Wang, J.; Chantler, C.T. (Melbourne)

2010-11-12

217

Measurement of the x-ray mass attenuation coefficients of gold in the 38-50-keV energy range

NASA Astrophysics Data System (ADS)

We used synchrotron x rays to measure the x-ray mass attenuation coefficients of gold at nine energies from 38 to 50 keV with accuracies of 0.1%. Our results are much more accurate than previous measurements in this energy range. A comparison of our measurements with calculated mass attenuation coefficients shows that our measurements fall almost exactly midway between the XCOM and FFAST calculated theoretical values, which differ from one another in this energy region by about 4%, even though the range includes no absorption edge. The consistency and accuracy of these measurements open the way to investigations of the x-ray attenuation in the region of the L absorption edge of gold.

Islam, M. T.; Rae, N. A.; Glover, J. L.; Barnea, Z.; de Jonge, M. D.; Tran, C. Q.; Wang, J.; Chantler, C. T.

2010-02-01

218

The compounds, Na{sub 2}B{sub 4}O{sub 7}, H{sub 3}BO{sub 3}, CdCl{sub 2} and NaCl and their solutions, attenuate gamma rays in addition to neutron absorption. These compounds are widely used in shielding of neutron sources, reactor control and neutron converters. Mass attenuation coefficients of gamma related to saturated solutions of the above four compounds, in energies 1172 keV and 1332 keV have been measured by NaI detector and agree very well with the results obtained by Xcom code. Experiment and computation show that, H{sub 3}BO{sub 3} has the highest gamma ray attenuation coefficient among the aforementioned compounds. (author)

Jalali, Majid [Esfahan Nuclear Technology Center - ENTC (Iran, Islamic Republic of)

2006-07-01

219

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

220

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

221

Global existence of critical nonlinear wave equation with time dependent variable coefficients

In this paper, we establish global existence of smooth solutions for the Cauchy problem of the critical nonlinear wave equation with time dependent variable coefficients in three space dimensions {equation}\\\\partial_{tt}\\\\phi-\\\\partial_{x_i}\\\\big(g^{ij}(t,x)\\\\partial_{x_j}\\\\phi\\\\big)+\\\\phi^5=0, mathbb{R}_t \\\\times \\\\mathbb{R}_x^3,{equation} where $\\\\big(g_{ij}(t,x)\\\\big)$ is a regular function valued in the spacetime of $3\\\\times3$ positive definite matrix and $\\\\big(g^{ij}(t,x)\\\\big)$ its inverse matrix. Here and in the sequence, a repeated

Yi Zhou; Ning-An Lai

2010-01-01

222

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

223

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

224

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

225

NASA Astrophysics Data System (ADS)

The finite element method is used to solve Biot's equations of consolidation in the displacement-pressure (u - p) formulation. We compute one-dimensional (1-D) and two-dimensional (2-D) numerical quasi-static creep tests with poroelastic media exhibiting mesoscopic-scale heterogeneities to calculate the complex and frequency-dependent P wave moduli from the modeled stress-strain relations. The P wave modulus is used to calculate the frequency-dependent attenuation (i.e., inverse of quality factor) and phase velocity of the medium. Attenuation and velocity dispersion are due to fluid flow induced by pressure differences between regions of different compressibilities, e.g., regions (or patches) saturated with different fluids (i.e., so-called patchy saturation). Comparison of our numerical results with analytical solutions demonstrates the accuracy and stability of the algorithm for a wide range of frequencies (six orders of magnitude). The algorithm employs variable time stepping and an unstructured mesh which make it efficient and accurate for 2-D simulations in media with heterogeneities of arbitrary geometries (e.g., curved shapes). We further numerically calculate the quality factor and phase velocity for 1-D layered patchy saturated porous media exhibiting random distributions of patch sizes. We show that the numerical results for the random distributions can be approximated using a volume average of White's analytical solution and the proposed averaging method is, therefore, suitable for a fast and transparent prediction of both quality factor and phase velocity. Application of our results to frequency-dependent reflection coefficients of hydrocarbon reservoirs indicates that attenuation due to wave-induced flow can increase the reflection coefficient at low frequencies, as is observed at some reservoirs.

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

2011-01-01

226

We used the x-ray extended-range technique to measure the x-ray mass attenuation coefficients of silicon with an accuracy between 0.27% and 0.5% in the 5 keV-20 keV energy range. Subtraction of the x-ray scattering contribution enabled us to derive the corresponding x-ray photoelectric absorption coefficients and determine the absolute value of the imaginary part of the atomic form factor of silicon. Discrepancies between the experimental values of the mass attenuation coefficients and theoretically calculated values are discussed. New approaches to the theoretical calculation will be required to match the precision and accuracy of the experimental results.

Tran, C.Q.; Chantler, C.T.; Barnea, Z.; Paterson, D.; Cookson, D.J. [School of Physics, University of Melbourne, Victoria 3010 (Australia); SRI-CAT, APS, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439 (United States); ANSTO, Private Mail Bag 1, Menai, New South Wales 2234 (Australia); Chem-Mat-CARS-CAT (Sector 15, Building 434D), Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 6043 (United States)

2003-04-01

227

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

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

228

The available results of experimental and prediction studies of the damping coefficient and phase propagation velocity of waves under conditions of pulsating turbulent flow in a narrow channel are reviewed and analyzed. It is demonstrated that the concept of complex damping coefficient may be introduced strictly on condition of certain restrictions imposed on an oscillating and time average flow. The

E. P. Valueva; A. A. Kulik

2003-01-01

229

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

230

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

231

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

232

Real-time viscosity measurement remains a necessity for highly automated industry. To resolve this problem, many studies have been carried out using an ultrasonic shear wave reflectance method. This method is based on the determination of the complex reflection coefficient's magnitude and phase at the solid-liquid interface. Although magnitude is a stable quantity and its measurement is relatively simple and precise, phase measurement is a difficult task because of strong temperature dependence. A simplified method that uses only the magnitude of the reflection coefficient and that is valid under the Newtonian regimen has been proposed by some authors, but the obtained viscosity values do not match conventional viscometry measurements. In this work, a mode conversion measurement cell was used to measure glycerin viscosity as a function of temperature (15 to 25 degrees C) and corn syrup-water mixtures as a function of concentration (70 to 100 wt% of corn syrup). Tests were carried out at 1 MHz. A novel signal processing technique that calculates the reflection coefficient magnitude in a frequency band, instead of a single frequency, was studied. The effects of the bandwidth on magnitude and viscosity were analyzed and the results were compared with the values predicted by the Newtonian liquid model. The frequency band technique improved the magnitude results. The obtained viscosity values came close to those measured by the rotational viscometer with percentage errors up to 14%, whereas errors up to 96% were found for the single frequency method. PMID:20442023

Franco, Ediguer E; Adamowski, Julio C; Buiochi, Flávio

2010-05-01

233

NASA Astrophysics Data System (ADS)

Real-time grading of bladder urothelial carcinoma (UC) is clinically important, but the current standard for grading (histopathology) cannot provide this information. Based on optical coherence tomography (OCT)-measured optical attenuation (?t), the grade of bladder UC could potentially be assessed in real time. We evaluate ex vivo whether ?t differs between different grades of UC and benign bladder tissue. Human bladder tissue specimens are examined ex vivo by 850-nm OCT using dynamic focusing. Three observers independently determine the ?t from the OCT images, and three pathologists independently review the corresponding histology slides. For both methods, a consensus diagnosis is made. We include 76 OCT scans from 54 bladder samples obtained in 20 procedures on 18 patients. The median (interquartile range) ?t of benign tissue is 5.75 mm-1 (4.77 to 6.14) versus 5.52 mm-1 (3.47 to 5.90), 4.85 mm-1 (4.25 to 6.50), and 5.62 mm-1 (5.01 to 6.29) for grade 1, 2, and 3 UC, respectively (p = 0.732). Interobserver agreement of histopathology is ``substantial'' [Kappa 0.62, 95% confidence interval (IC) 0.54 to 0.70] compared to ``almost perfect'' [interclass correlation coefficient (ICC) 0.87, 95% CI 0.80 to 0.92] for OCT. Quantitative OCT analysis (by ?t) does not detect morphological UC changes. This may be due to factors typical for an ex-vivo experimental setting.

Cauberg, Evelyne C. C.; de Bruin, Daniël M.; Faber, Dirk J.; de Reijke, Theo M.; Visser, Mike; de La Rosette, Jean J. M. C. H.; van Leeuwen, Ton G.

2010-11-01

234

NASA Astrophysics Data System (ADS)

The diffuse attenuation coefficient, Kd(?) is a fundamental radiometric parameter that is used to assess the light availability in the water column. A neural network approach is developed to assess Kd(?) at any visible wavelengths from the remote sensing reflectances as measured by the SeaWiFS satellite sensor. The neural network (NN) inversion is trained using a combination of simulated and in-situ data sets covering a broad range ofKd(?), between 0.0073 m-1 at 412 nm and 12.41 m-1at 510 nm. The performance of the retrieval is evaluated against two data sets, one consisting of mainly synthetic data while the other one contains in-situ data only and is compared to those obtained with previous published empirical (NASA, Morel and Maritorena (2001) and Zhang and Fell (2007)) and semi-analytical (Lee et al., 2005b) algorithms. On the in-situ data set from the COASTLOOC campaign, the retrieval accuracy of the present algorithm is quite similar to published algorithms for oligotrophic and mesotrophic ocean waters. But for Kd(490) > 0.25 m-1, the NN approach allows to retrieve Kd(490) with a much better accuracy than the four other methods. The results are consistent when compared with other SeaWiFS wavelengths. This new inversion is as suitable in the open ocean waters as in the turbid waters. The work here is straightforwardly applicable to the MERIS sensor and with few changes to the MODIS-AQUA sensor. The algorithm in matlab and C code is provided as auxiliary material.

Jamet, C.; Loisel, H.; Dessailly, D.

2012-10-01

235

NASA Astrophysics Data System (ADS)

The first geostationary ocean color sensor, Geostationary Ocean Color Imager (GOCI), on board the Korean Communication Ocean and Meteorological Satellite (COMS), was successfully launched on June 26 of 2010. GOCI includes 8 spectral bands in visible and near-infrared wavelengths with a coverage area of 2,500×2,500 km2 centered at 36°N and 130°E over the Korean seas. GOCI will provide an important capability to monitor ocean phenomenon with one hour temporal and 500 m spatial resolutions for a better understanding of biogeochemical processes in the Korean seas. However, there are uncertainties in estimating bio-optical properties since water properties in large areas of Koreans are optically characterized as Case-2 waters due to strong tidal mixing and large amount of river discharges. The newly-developed semi-analytical algorithm of diffusion attenuation coefficient at the wavelength of 490 nm, Kd(490), for the turbid coastal waters was assessed using in situ radiometric and Kd(490) measurement obtained from clear and turbid waters over the global ocean. Results of the Kd(490) data using the new model is well correlated with the in situ Kd(490) measurements. Synoptic maps of Kd(490) data from the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard the Aqua satellite using the new model were derived in the Yellow Sea and East China Sea. The MODIS-derived Kd(490) data show significant increased values along the turbid coastal waters including the Bohai Sea and the Yangtze River Estuary. In general, the highest Kd(490) appeared in winter and the lowest Kd(490) are presented in summer over the all area. Interannual variability of Kd(490) in timing and magnitude is apparent, but there is no consistent trend of interannual variability across all areas.

Son, Seunghyun; Wang, Menghua

2010-10-01

236

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.

237

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.

238

NASA Astrophysics Data System (ADS)

The total mass attenuation coefficients of some amino acids, such as Glycine (C2H5NO2), DL-Alanine (C3H7NO2), Proline (C5H9NO2), L-Leucine (C6H13NO2 ), L-Arginine (C6H14N4O2) and L-Arginine Monohydrochloride (C6H15ClN4O2), were measured at 122, 356, 511, 662, 1170, 1275 and 1330 keV photon energies using a well-collimated narrow beam good geometry set-up. The gamma rays were detected using NaI (Tl) scintillation detection system with a resolution of 10.2% at 662 keV. The attenuation coefficient data were then used to obtain the effective atomic numbers (Zeff) and effective electron densities (Neff) of amino acids. It was observed that the effective atomic number (Zeff) and effective electron densities (Neff) tend to be almost constant as a function of gamma-ray energy. The results show that, the experimental values of mass attenuation coefficients, effective atomic numbers and effective electron densities are in good agreement with the theoretical values with less than 1% error.

Pawar, Pravina P.; Bichile, Govind K.

2013-11-01

239

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

240

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

241

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

242

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

243

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

244

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

245

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

246

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

247

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

248

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

249

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

250

NASA Astrophysics Data System (ADS)

The up-down interaction between two-level systems in dielectric glasses leads to arising of space-delocalized low-energy excitations subsystem. In the case of ultra low temperatures when the phonons are significantly frozen out the relaxation processes will be defined by the excitations of that subsystem. The low-frequency sound attenuation is studied. It is shown that the attenuation coefficient demonstrates crossover from the known phonon-induced behaviour ? ~ T3 to ? ~ T at sufficiently low temperature. This behaviour was recently discovered in amorphous SiO2 [1].

Burin, A. L.; Kagan, Yu.

1994-02-01

251

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

252

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

253

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

254

Measurements have been made to determine ?-rays attenuation coefficients very accurately by using an extremely narrow-collimated-beam transmission method. The effect of the sample thickness on the measured values of the mass attenuation coefficients (?\\/?)cm2\\/g of perspex, bakelite, paraffin, Al, Cu, Pb and Hg have been investigated at three different ?-ray energies (59.54, 661.6 and 1332.5 keV). It is seen that

M. A Abdel-Rahman; E. A Badawi; Y. L Abdel-Hady; N Kamel

2000-01-01

255

Mass attenuation coefficient of the Earth, Moon and Mars samples over 1keV-100GeV energy range.

This work presents the calculation of the mass attenuation coefficient (micro) of lunar, Martian and terrestrial samples in function of the energy. WinXCOM software was employed to determine the micro values for the samples in the range from 1 keV to 100 GeV. The obtained values were practically the same for energies larger than 100 keV, but marked differences among the samples were observed for energies below 25 keV, which is the energy range of interest for the XRF system used in space probes. PMID:16725330

Camargo Moreira, Anderson; Roberto Appoloni, Carlos

2006-05-24

256

Mass attenuation coefficients of some boron compounds (H3BO3,Na2B4O7 and B3Al2O3) and the trommel sieve waste (TSW) have been measured by using an extremely narrow collimated-beam transmission method in the energy range 15.746–40.930keV. The characteristic K? and K? X-rays of Zr, Mo, Ag, In, Sb, Ba and Pr passed through H3BO3,Na2B4O7, B3Al2O3 and TSW were detected with a high-resolution Si(Li) detector.

Orhan ?çelli; Salih Erzeneo?lu; Recep Boncukçuo?lu

2003-01-01

257

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.

258

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

259

We determined the overall external counting efficiency of radiolabeled particles deposited in the sheep lung. This efficiency permits the noninvasive calculation of the number of particles and microcuries (?Ci) from gamma?scintillation lung images of the live sheep. Additionally, we have calculated the attenuation of gamma radiation (120 keV) by the posterior chest wall and the gamma?scintillation camera collection efficiency of

E. G. Langenback; W. M. Foster; E. H. Bergofsky

1989-01-01

260

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

261

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

262

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

263

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

264

The mass attenuation coefficients for 22 high purity elemental materials (C, Al, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Rh, Pd, Ag, Cd, In, Ta, Pt, Au, Pb) were measured in the X-ray energy range from 13 up to 50 keV using a high purity germanium detector with thin (50 microm) Be window and a variable-energy X-ray source. The measured values are compared with the theoretical ones obtained using the XCOM code and data base, as well as with other experimental data showing a general agreement within +/- 5%. The mass attenuation cross-sections were thus derived and compared with other experimental data available on the 1988 NBS database of X-ray attenuation cross-sections. The agreement is always within +/- 8%, but for a few points the discrepancies are up to +/- 18%. The data analysis has also shown that some measurements performed at 50.65 keV as well as at 36.65 keV are to be considered as new data for most of the measured materials. PMID:11545503

Angelone, M; Bubba, T; Esposito, A

2001-10-01

265

NASA Astrophysics Data System (ADS)

Oncogenesis and metastasis of tumor are difficult to detect during the clinic therapy. To explore the optical properties of tumorigenesis and metastasis in nasopharyngeal carcinoma (NPC), we assessed the NPC cell lines 5-8F and 6-10B by optical coherence tomography (OCT): first, the OCT images of the two different types of cell pellets were captured. Second, by fitting Beer's law to the averaged A-scans in these OCT datasets, the attenuation coefficients (?t) of the cells were extracted. The median attenuation coefficients (interquartile range (IQR)) of 5-8F and 6-10B were 6.79 mm-1 (IQR 6.52 to 7.23 mm-1) versus 8.06 mm-1 (IQR 7.65 to 8.40 mm-1), respectively (p < 0.01, df = 39). Subsequently, the results were compared with those obtained by polarization sensitive OCT, which further confirmed that the quantitative OCT analysis (by ?t) could differentiate the oncogenesis and metastasis NPC cell lines in real time non-invasively.

Li, Jianghua; Shen, Zhiyuan; He, Yonghong; Tu, Ziwei; Xia, Yunfei; Chen, Changshui; Liu, Songhao

2012-10-01

266

NASA Astrophysics Data System (ADS)

The effects of wind input parameterizations on wave estimations under hurricane conditions are examined using the unstructured grid, third-generation wave model, Simulating WAves Nearshore (SWAN). Experiments using Hurricane Ike wind forcing, which impacted the Gulf of Mexico in 2008, illustrate that the default and recommended setting for the wind input parameterization tends to overestimate the maximum significant wave heights in the deep Gulf of Mexico by about 2 m when comparing with observations. The overestimation can be remedied either by adjusting the maximum value of the surface drag coefficient or by substituting a high wind speed formula for the default low to moderate wind speed. Because of added dissipative effects in the shallow coastal areas, the overestimations found in deep water have limited effect on the waves in the near shore shallower waters. Thus, previous wave model results using a low to moderate wind speed bulk formula may still be reliable in waters shallower than about 20-30 m even while overestimating significant wave heights in deeper waters under hurricane conditions.

Huang, Yong; Weisberg, Robert H.; Zheng, Lianyuan; Zijlema, Marcel

2013-08-01

267

A Theory of Gravity Wave Absorption by a Boundary Layer

A one-layer model of the atmospheric boundary layer (BL) is proposed to explain the nature of lee-wave attenuation and gravity wave absorption seen in numerical simulations. Two complex coefficients are defined: the compliance coefficient and the wave reflection coefficient. A real-valued ratio of reflected to incident wave energy is also useful. The key result is that, due to horizontal friction,

Ronald B. Smith; Qingfang Jiang; James D. Doyle

2006-01-01

268

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

269

The effect of harmonic modulation of the coupling coefficients of counterpropagating waves on the type of generation of a solid-state Nd:YAG laser is studied. It is shown that, as the modulation depth is increased, transient generation regimes appear in the laser, which are accompanied by considerable frequency nonreciprocity. The boundaries of the regions of existence of different lasing regimes are found. (lasers)

Kravtsov, Nikolai V; Gavrilov, A G [D.V. Skobel'tsyn Institute of Nuclear Physics, M.V. Lomonosov Moscow State University, Moscow (Russian Federation)

2005-08-31

270

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

271

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

272

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

273

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

274

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

275

WaveStat-cluster analysis of image data and wavelet coefficients

The Wavestat project deals with the application of different clustering methods on wavelet coefficients of image data to approach the reconstruction of the image from the clustered and averaged wavelet coefficients. The quality of the reconstruction depends on the used wavelet-transform, the kind of applied cluster analysis and the number of iterations when performing the inverse wavelet transform

Ute Simon; Manfred Berndtgen

1998-01-01

276

NASA Astrophysics Data System (ADS)

Often structures comprise waveguides connected by joints. The knowledge of the reflection and transmission properties of these joints is important for many applications. This paper presents a hybrid approach, combining a finite element (FE) and a wave and finite element (WFE) model, for calculating the reflection and transmission coefficients of a joint. First, the joint is modelled using standard FE. Then, the waveguide is modelled using the WFE method, where the FE model of a small segment of the waveguide, whose cross-section could be arbitrarily complex, is post-processed to yield the wave properties of the whole waveguide. The two models are coupled to find the reflection and transmission matrices of the joint. This hybrid approach allows for developing a model of the structure where the basis functions are the waves travelling through the structure's various waveguides. Numerical examples are presented.

Renno, Jamil M.; Mace, Brian R.

2013-04-01

277

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

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

278

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

279

NASA Astrophysics Data System (ADS)

The X-ray linear attenuation coefficient was measured for materials containing elements hydrogen to calcium. Characteristic X-rays with energies 32-66keV were produced by X-ray fluorescence using a secondary target system, and 140keV gamma rays were obtained from an unsealed 99mTc source. The photon beams were highly collimated and recorded using energy dispersive detection. A high-purity germanium detector was utilised to distinguish between measurements with K? and K? characteristic X-rays, and the gamma ray measurements used a sodium iodide detector. Samples were selected on the basis of having known composition and mass densities were measured using a pycnometer. The samples comprised six plastics, seven crystalline materials, three tissue substitute materials, three liquids and six salt solutions. Our results have an uncertainty of less than 2% and are a few percent lower than values predicted by the tabulations.

Midgley, S. M.

2005-03-01

280

NASA Astrophysics Data System (ADS)

The K-shell absorption jump factors and jump ratios were derived from new mass attenuation coefficients measured using an energy dispersive X-ray fluorescence (EDXRF) spectrometer for Tm, Yb elements being Tm2O3, Yb2O3 compounds and pure Lu, Hf, Ta, W, Re and Os. The measurements, in the region 56 77 keV, were done in a transmission geometry utilizing the K?1, K?2, K?1 and K?2 X- rays from different secondary source targets (Yb, Ta, Os, W, Re and Ir, etc.) excited by the 123.6 keV ?-photons from an 57Co annular source and detected by an Ultra-LEGe solid state detector with a resolution of 150 eV at 5.9 keV. Experimental results have been compared with theoretically calculated values. The measured values of Tm, Yb, Lu, Hf, Ta, W, Re and Os are reported here for the first time.

Kaya, Necati; T?ra?o?lu, Engin; Apayd?n, Gökhan; Ayl?kc?, Volkan; Cengiz, Erhan

2007-08-01

281

A bibliography is presented of papers reporting absolute measurements of photon (XUV, x-ray, gamma-ray, bremsstrahlung) total interaction cross sections or attenuation coefficients for the elements and some compounds. The energy range covered is from 10 eV to above 10 GeV. These papers are part of the reference collection of the National Institute of Standards and Technology Photon and Charged Particle Data Center. They cover the period from 1907 through 1993 and into 1994. Thus this report is an update of the 1986 earlier report NBSIR 86-3461 (PB87-116141), and also includes additional papers dating back as far as 1966 which have since been found or brought to the attention of the author. Included with each reference are annotations specifying the energy range covered and the substances studied. This updated bibliography now includes 573 non-duplicative references to available measured data, plus 42 references to critical evaluations and review articles.

Hubbell, J.H.

1994-05-01

282

NASA Astrophysics Data System (ADS)

Each year spatial patterns of ocean color in the Baltic Sea differ in temporal evolution and magnitude. We have investigated the interannual variability of the spatially averaged vertical diffuse attenuation coefficient at 490 nm, Kd(490), in response to atmospheric forcing and river discharge. Our results indicate that atmospheric forcing does not have a significant influence on the interannual anomalies of Kd(490) in the Baltic Sea. This is in contrast to the North Atlantic site located at similar latitudes, were interannual variability of phytoplankton blooms (and ocean color) is to a large degree controlled by a local weather. Instead, in the Baltic Sea, the interannual variability of Kd(490) is significantly influenced by the river runoff. Higher values of Kd(490) are observed in years with larger inflow of water from rivers. Without an access to more detailed information about the concentrations of various optically significant water components, we can only speculate about the possible reasons for this correlation, but it is most likely a combination of several factors. These include: development of more intense phytoplankton blooms associated with larger supply of nutrients delivered by rivers, advection of optically important material with river water, as well as different physical condition for phytoplankton growth due to more stable water stratification. The diffuse attenuation coefficient plays a critical role in many oceanographic processes. For example, Kd is essential for quantification of radiative heating of the ocean, in models of primary production and other photoprocesses, and in studies discussing water turbidity and water quality. Better understanding of the variability of Kd in the Baltic Sea can impove our knowledge of this marine environment.

Stramska, Malgorzata

2013-04-01

283

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

284

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

285

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

286

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

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

287

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

288

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

289

NASA Astrophysics Data System (ADS)

Ambient particulate matter (PM) samples were collected on quartz filters at a rural site in central Ontario during an intensive study in 2007. The concentrations of organic carbon (OC), pyrolysis organic carbon (POC), and elemental carbon (EC) were determined by thermal analysis. The concentrations are compared to the organic aerosol mass concentration (OM) measured with an Aerodyne C-ToF Aerosol Mass Spectrometer (AMS) and to the particle absorption coefficient (basp) obtained from a Radiance Research Particle Soot Absorption Photometer (PSAP). The total organic mass to organic carbon ratios (OM/OC) and specific attenuation coefficients (SAC=basp/EC) are derived. Proportionality of the POC mass with the oxygen mass in the aerosols estimated from the AMS offers a potential means to estimate OM/OC from thermal measurements only. The mean SAC for the study is 3.8±0.3 m2 g-1. It is found that the SAC is independent of or decrease with increasing particle mass loading, depending on whether or not the data are separated between aerosols dominated by more recent anthropogenic input and aerosols dominated by longer residence time or biogenic components. There is no evidence to support an enhancement of light absorption by the condensation of secondary material to particles, suggesting that present model simulations built on such an assumption may overestimate atmospheric warming by BC.

Chan, T. W.; Huang, L.; Leaitch, W. R.; Sharma, S.; Brook, J. R.; Slowik, J. G.; Abbatt, J. P. D.; Brickell, P. C.; Liggio, J.; Li, S.-M.; Moosmüller, H.

2010-03-01

290

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

291

NASA Astrophysics Data System (ADS)

In this paper, a similarity transformation is presented to reduce the generalized (3 + 1)-dimensional cubic-quintic nonlinear Schrödinger equation with distributed coefficients to the related constant-coefficients one. Then a number of spatiotemporal self-similar wave solutions are constructed. Under the specific choice of the dispersion, cubic and quintic nonlinearities, phase modulation and the gain/loss, we investigate the dynamical behaviors of those spatiotemporal self-similar waves in an inhomogeneous optical fiber media.

Liu, Xiao-Bei; Zhang, Xiao-Fei; Li, Biao

2012-03-01

292

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

293

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

294

Neural classification of Lamb wave ultrasonic weld testing signals using wavelet coefficients

This paper presents an ultrasonic nondestructive weld testing method based on the wavelet transform (WT) of inspection signals and their classification by a neural network (NN). The use of Lamb waves generated by an electromagnetic acoustic transducer (EMAT) as a probe allows us to test metallic welds. In this work, the case of an aluminum weld is treated. The feature

Sylvie Legendre; Daniel Massicotte; Jacques Goyette; Tapan K. Bose

2001-01-01

295

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

296

Behavior of the Mean Wind, the Drag Coefficient, and the Wave Field in the Open Ocean

To specify the large-scale dynamics of the ocean, fluxes of momentum, heat, and moisture across the air-sea interface may be estimated from bulk aerodynamic formulas [Jacobs, 1951] specifying these fluxes. in terms of routinely available mean wind speed and the air-sea temperature and humidity differences. Such formulas require well-founded constants or adjustable coefficients that depend on stability, which in turn

K. L. Denman; M. Miyake

1973-01-01

297

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

298

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

299

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

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

300

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

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

301

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

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

302

This paper studies a low-frequency asymptotic expansion for a unique strong solution to an initial-boundary value problem of a semilinear wave equation. This equation admits space-time dependent coefficients and a memory boundarylike antiperiodic condition. For some small parameters from coefficients of this semilinear wave equation and of boundary conditions, we approximate a unique strong solution to this problem by a polynomial of these parameters, and coefficients of this polynomial are strong solutions of a sequence of well-defined linear initial-boundary value problems.

Le, Ut V. [Department of Mathematical Sciences, University of Oulu, P.O. Box 3000, FIN-90014 (Finland)

2011-02-15

303

Pressure diffusion waves in porous media

Pressure diffusion wave in porous rocks are under consideration. The pressure diffusion mechanism can provide an explanation of the high attenuation of low-frequency signals in fluid-saturated rocks. Both single and dual porosity models are considered. In either case, the attenuation coefficient is a function of the frequency.

Silin, Dmitry; Korneev, Valeri; Goloshubin, Gennady

2003-04-08

304

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

305

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

306

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

307

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

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

308

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

309

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

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

310

As different types of radionuclides (e.g., {sup 131}Cs source) are introduced for clinical use in brachytherapy, the question is raised regarding whether a relatively simple method exists for the derivation of values of the half value layer (HVL) or the tenth value layer (TVL). For the radionuclide that has been clinically used for years, such as {sup 125}I and {sup 103}Pd, the sources have been manufactured and marketed by several vendors with different designs and structures. Because of the nature of emission of low energy photons for these radionuclides, energy spectra of the sources are very dependent on their individual designs. Though values of the HVL or the TVL in certain commonly used shielding materials are relatively small for these low energy photon emitting sources, the question remains how the variations in energy spectra affect the HVL (or TVL) values and whether these values can be calculated with a relatively simple method. A more fundamental question is whether a method can be established to derive the HVL (TVL) values for any brachytherapy sources and for different materials in a relatively straightforward fashion. This study was undertaken to answer these questions. Based on energy spectra, a well established semiempirical mass attenuation coefficient computing scheme was utilized to derive the HVL (TVL) values of different materials for different types of brachytherapy sources. The method presented in this study may be useful to estimate HVL (TVL) values of different materials for brachytherapy sources of different designs and containing different radionuclides.

Yue, Ning J. [Department of Radiation Oncology, Cancer Institute of New Jersey, UMDNJ-Robert Wood Johnson Medical School, New Brunswick, New Jersey 08903 (United States)

2008-06-15

311

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

312

NASA Astrophysics Data System (ADS)

Carbonaceous species (organic carbon (OC) and elemental carbon (EC)) contribute a large portion of atmospheric fine particle mass and influence air quality, human health, and climate forcing. However, their emission sources and atmospheric aging processes are not well understood. The OM/OC ratio, defined as the organic mass per unit OC mass, is useful to understand the degree of oxidation of aerosol particles in atmospheric processes. We define the modified BC/EC (mod BC/EC) ratio as the ratio of the non-scattering corrected absorption coefficient per unit mass of EC. The mod BC/EC ratio has a similar meaning as the site specific attenuation coefficient, which is an important parameter used to convert light absorption measurements to black carbon mass. The mod BC/EC ratio can vary due to light scattering effect on absorption measurements, in which the oxygenated organics may play a role. The pyrolysis organic carbon (POC) is defined as the carbon mass fraction obtained at T= 870°C under a pure helium environment using the thermal separation method [Huang et al., 2006]. Since POC mass is generally proportional to the amount of oxygenated OC, studying the relationships among OC, EC, POC, as well as OM/OC and mod BC/EC ratios may help us understand the mechanisms of aerosol aging from different emission sources. Two 1-month field studies were conducted at a rural site in southern Ontario (NW of Toronto) during fall 2005 and spring 2007. Quartz filter samples were collected and analyzed for OC, POC, and EC concentrations using a thermal/optical method [Huang et al., 2006]. Together with the total organic matter measured by an Aerodyne Aerosol Mass Spectrometer (AMS) and the absorption coefficient obtained from a Particle Soot Absorption Photometer (PSAP), the OM/OC and mod BC/EC ratios for ambient aerosols were obtained. Our results show that when air mass was mainly from south, OC, POC, and EC were relatively high, with average ratios of OC/EC, OM/OC, and POC/EC as 1.94, 1.41, and 0.52, respectively; this indicates significant anthropogenic impacts and relatively large portion of oxygenated OC, which might be due to either primary emissions or photo-chemical reactions occurred in a short period of time. When air mass was mainly from north, OC, POC, and EC were much lower, with average ratios of OC/EC, OM/OC, and POC/EC as 3.10, 1.20, and 0.79, respectively; this suggests less influence from anthropogenic emissions and relatively aged air mass from biogenic-source dominated clean air. Using POC, we estimate the specific attenuation at the site to be 5.8 m2 g-1 independent of the air mass origin. The relationships among OM/OC, mod BC/EC, and POC will be further discussed. References: Huang, L., Brook, J.R., Zhang, W., Li, S.M., Graham, L., Ernst, D., Chivulescu, A., and Lu, G. (2006) Stable isotope measurements of carbon fractions (OC/EC) in airborne particulate: a new dimension for source characterization and apportionment, Atmospheric Environment, 40, 2690-2705.

Chan, T. W.; Huang, L.; Leaitch, R.; Sharma, S.; Brook, J.; Slowik, J.; Abbatt, J.

2008-05-01

313

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

314

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

315

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

316

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

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

317

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

318

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

319

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

320

Diffraction effects on bulk-wave ultrasonic velocity and attenuation measurements

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

321

The electrical parameters of sandy and loamy soil in the centimeter, decimeter and meter wave ranges

The electrical parameters of sandy and loamy soil in the 0.8 to 266 cm range were measured by the short-circuit method using measuring waveguides. The dependence of electrical permeability and attenuation of radio waves on the soil moisture and the frequency of radio oscillations was studied. It was shown that in all of the investigated wave lengths, the attenuation coefficient

Y. I. Leshchanskiy; G. N. Lebedeva; V. D. Shumilin

1975-01-01

322

NASA Astrophysics Data System (ADS)

At millimeter wavelengths, normalized fog attenuation (NFA) in units of (dB/km)/ (g/m3) is generally calculated by the Rayleigh approximation when working wavelengths are much larger than the average diameter of fog droplets. The calculations of the Rayleigh approximation are much less than those of Mie scattering theory, but still complex and heavy. To solve the above problem and facilitate the engineering applications of the Rayleigh approximation, a new empirical formula is discussed to estimate NFA in the frequency range 30 ~ 100 GHz and the fog common temperature range -8 ~ 20 °C. The simulation results of the new formula are compared with those got by other three empirical formulae: the Altshuler empirical formula, the Liebe empirical formula and the Zhao empirical formula. Maximal absolute value of the relative errors (MAVRE) and Pearson correlation coefficient (PCC) indicate the largest deviation of estimated results and the fitting performance of an empirical formula, respectively. Comparisons show that the MAVRE of the new formula is only 4.482 %, which is much smaller than those of the other three formulae. The mean value of the Pearson correlation coefficients (PCCs) of the proposed formula is 0.999943, larger than those of other methods. Additionally, relative error (RE) curves of the four empirical formulae are given at four certain temperatures -8 °C, 0 °C, 10 °C and 20 °C.

Mao, Xia; Liu, Yun-Long; Chen, Li-Jiang; Xue, Yu-Li

2013-04-01

323

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

324

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

325

Intensity-modulated radiation therapy (IMRT) can be performed by using compensators. To make a compensator for an IMRT practice, it is required to calculate the effective attenuation coefficient (?(eff)) of its material, which is affected by various factors. We studied the effect of the variation of the most important factors on the calculation of the ?(eff) of the cerrobend compensator for 6-MV photon beams, including the field size, compensator thickness, and off-axis distance. Experimental measurements were carried out at 100 cm source-to-surface distance and 10 cm depth for the 6-MV photon beams of an Elekta linac using various field size, compensator thickness, and off-axis settings. The field sizes investigated ranged from 4 × 4 to 25 × 25 cm² and the cerrobend compensator thicknesses from 0.5-6 cm. For a fixed compensator thickness, variation of the ?(eff) with the field size ranged from 3.7-6.8%, with the highest value attributed to the largest compensator thickness. At the reference field size of 10 × 10 cm², the ?(eff) varied by 16.5% when the compensator thickness was increased from 0.5-6 cm. However, the variation of the ?(eff) with the off-axis distance was only 0.99% at this field size, whereas for the largest field size, it was more significant. Our results indicated that the compensator thickness and field size have the most significant effect on the calculation of the compensator ?(eff) for the 6-MV photon beam. Therefore, it is recommended to consider these parameters when calculating the compensator thickness for an IMRT practice designed for these beams. The off-axis distance had a significant effect on the calculation of the ?(eff) only for the largest field size. Hence, it is recommended to consider the effect of this parameter only for field sizes larger than 25 × 25 cm². PMID:22835650

Haghparast, Abbas; Hashemi, Bijan; Eivazi, Mohammad Taghi

2012-07-25

326

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

327

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

328

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

329

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

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

330

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

331

The mass attenuation coefficients, {mu}/{rho}, for Clear-Pb{reg_sign} for photon energies ranging from 10 keV to 10 MeV were determined using Monte Carlo methods and simple equations used to manipulate elemental mass attenuation coefficients. It was determined that the effectiveness of Clear-Pb{reg_sign} as a radiation shielding material was greater than plain acrylic for all photon energies, especially those less than 150 keV, and for deep penetration problems where the differences in {mu}/{rho} between Clear-Pb{reg_sign} as a shielding material when compared with acrylic was determined for the following commonly used radionuclides: {sup 125}I, {sup 103}Pd, {sup 99m}Tc, {sup 192}Ir, {sup 137}Cs, and {sup 60}Co.

Rivard, M.J. [Tufts Univ. School of Medicine, Boston, MA (United States). Dept. of Radiation Oncology; Waid, D.S. [Hackley Hospital, Muskegon, MI (United States). Radiation Oncology Dept.; Wierzbicki, J.G. [St. Mary`s Medical Center, Saginaw, MI (United States). Cancer Treatment Center

1999-11-01

332

The mass attenuation coefficients, [mu]/[rho], for Clear-Pb[reg sign] for photon energies ranging from 10 keV to 10 MeV were determined using Monte Carlo methods and simple equations used to manipulate elemental mass attenuation coefficients. It was determined that the effectiveness of Clear-Pb[reg sign] as a radiation shielding material was greater than plain acrylic for all photon energies, especially those less than 150 keV, and for deep penetration problems where the differences in [mu]/[rho] between Clear-Pb[reg sign] as a shielding material when compared with acrylic was determined for the following commonly used radionuclides: [sup 125]I, [sup 103]Pd, [sup 99m]Tc, [sup 192]Ir, [sup 137]Cs, and [sup 60]Co.

Rivard, M.J. (Tufts Univ. School of Medicine, Boston, MA (United States). Dept. of Radiation Oncology); Waid, D.S. (Hackley Hospital, Muskegon, MI (United States). Radiation Oncology Dept.); Wierzbicki, J.G. (St. Mary's Medical Center, Saginaw, MI (United States). Cancer Treatment Center)

1999-11-01

333

NASA Astrophysics Data System (ADS)

The mass attenuation coefficients of InSe and InSe having different holmium concentrations were measured in the energy region 15.746 40.930 keV using a Si(Li) detector. InSe and InSe:holmium(0.0025), InSe:holmium(0.0050), InSe:holmium(0.025) and InSe:holmium(0.05) crystals were grown by the Bridgman Stocbarger method. The measured values are compared with the theoretical ones obtained using WinXcom which is a Windows version of XCOM. The measurement of mass attenuation coefficients of ternary semiconductors is very important because of its use in technology.

Erzeneo?lu, S.; Içelli, O.; Gürbulak, B.; Ate?, A.

2006-12-01

334

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

335

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

336

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

337

Using the solution of general Korteweg-de Vries (KdV) equation, the solutions of the generalized variable coefficient Kadomtsev-Petviashvili (KP) equation are constructed, and then its new solitary wave-like solution and Jacobi elliptic function solution are obtained.

Jie-Jian Mao; Jian-Rong Yang

2006-01-01

338

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

339

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 attenuation of radio waves in the frequency range 40 c\\/s-10 kc\\/s to be calculated. Observations were made

R. A. Challinor

1967-01-01

340

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

341

NASA Astrophysics Data System (ADS)

We used strong-motion records from the 2012 May 20 and 29 Emilia-Romagna earthquakes (Mw 6.1 and 5.9, respectively) and four aftershocks with magnitudes ranging between 4.9 and 5.5 to analyse the S-wave spectral amplitude decay with distance and estimate acceleration source functions and site effects. The data set consists of six earthquakes, 44 stations and 248 records with hypocentral distances in the range 10 < r < 100 km. We rotated the accelerograms to calculate transverse and radial components of the acceleration spectrum. We found non-parametric attenuation functions that describe the spectral amplitude decay of SH and SV waves with distance at 60 different frequencies between 0.1 and 40 Hz. These attenuation functions provide an estimate of the quality factor Q at each frequency analysed. Assuming that geometrical spreading is 1/r for r ? rx and 1/(rx r)0.5 for r > rx with rx = 60 km and normalizing at 15 km (the recording distance where the attenuation functions start to decay), we find that the average Q for SH waves can be approximated by QSH = 82 ± 1 f 1.2±0.02 and by QSV = 79 ± 1 f 1.24±0.03 for SV waves in the frequency range 0.10 ? f ? 10.7 Hz. At higher frequencies, 11.8 ? f ? 40 Hz, the frequency dependence of Q weakens and is approximated by QSH = 301 ± 1 f 0.36±0.04 and QSV = 384 ± 1 f 0.28±0.04. These results indicate that the S-wave attenuation is radially isotropic at local distances in the epicentral area. Nevertheless, we used these attenuation parameters separately to correct the radial (with QSV) and transverse (with QSH) components of the acceleration spectra and to separate source and site effects using a non-parametric spectral inversion scheme. We found that the source function of the main event and the bigger aftershocks show enhanced low frequency radiation between 0.4 and 3.0 Hz. We converted the source functions into far-field source acceleration spectra and interpreted the resulting source spectra in terms of Brune's model. The stress drops obtained range between approximately 0.9 and 2.9 MPa. Although all the recording stations used are located in the Po Plain, the site functions obtained from the spectral inversion show important amplification variability between the sites. We compared these site functions with the average horizontal to vertical spectral ratios calculated for each station, and we found consistent results for most stations.

Castro, Raúl R.; Pacor, Francesca; Puglia, Rodolfo; Ameri, Gabriele; Letort, Jean; Massa, Marco; Luzi, Lucia

2013-10-01

342

The attenuation of microwave radiation by fog and rain

NASA Astrophysics Data System (ADS)

In this report, the equations which describe the attenuation of long-wavelength electromagnetic radiation by water fogs and rain are briefly reviewed and explained under the assumption that the aerosol droplets are spherical and that the irradiance of the beam is in the 'linear' regime. Calculations of water fog attenuation coefficients are made using the Rayleigh approximation, and an approximate error analysis of this approximation is made by comparing Rayleigh approximation calculations of absorption efficiency with exact Mie theory calculations of extinction efficiency. Numerical integration of the Mie extinction efficiency is used to compute the attenuation coefficient for rain with a Marshall-Palmer drop size distribution for various rain rates and temperatures. These results are compared with those given by a power law relationship with coefficients given by Olsen, Rogers, and Hodge which was used in the Near Milimeter Wave (NMMW) Module of the Electro- Optical Systems Atmospheric Effects Library (EOSAEL).

Pendleton, J. D.; Niles, Stanley

1994-08-01

343

We estimate attenuation (t*) for teleseismic P and S arrivals to seismometers in the Yellowstone Intermountain Seismic Array; tomographically invert these data for upper mantle Qp-1 and Qs-1 structure; and, with the aid of the upper mantle velocity model of Waite et al. (2006), interpret the results for mantle temperature, partial melt, and water content. Because attenuation analysis is susceptible

David C. Adams; Eugene D. Humphreys

2010-01-01

344

NASA Astrophysics Data System (ADS)

A variable-coefficient variant Boussinesq (VCVB) model describes the propagation of long waves in shallow water, the nonlinear lattice waves, the ion sound waves in plasmas, and the vibrations in a nonlinear string. With the help of symbolic computation, a VCVB model is investigated for its integrability through the Painlevé analysis. Then, by truncating the Painlevé expansion at the constant level term with two singular manifolds, the dependent variable transformations are obtained through which the VCVB model is bilinearized. Furthermore, the corresponding N-solitonic solutions with graphic analysis are given by the Hirota method and Wronskian technique. Additionally, a bilinear Bäcklund transformation is constructed for the VCVB model, by which a sample one-solitonic solution is presented.

Wang, Ming-Zhen; Gao, Yi-Tian; Zhang, Cheng; Meng, Xiang-Hua; Yu, Xin; Xu, Tao; Feng, Qian

345

Effects of shock-induced cracks on the ultrasonic velocity and attenuation in granite

NASA Astrophysics Data System (ADS)

Measurements of the compressional wave velocity and the attenuation coefficients of 1-cm cubes were conducted. Samples were taken at various radii and depths beneath a 20 × 20 × 15 cm San Marcos granite block, impacted by a lead bullet at a velocity of 1200 m/s. The damage parameters of the cubes are calculated from the measured preimpact and postimpact P wave velocities, Vp0 and Vp, and the crack density is inverted from the measured P wave velocities. The anisotropic orientation of cracks is more obvious from the attenuation than crack density and damage parameters calculated from the ultrasonic velocity. P wave velocity and the normalized distance from the impact point follow an exponential decay relation. Other properties, such as the damage parameter, crack density, and attenuation coefficient, are expressed by a power law decay with distance. The damage parameter and attenuation coefficients are approximately linearly related. The slope of the linear fitting results in directions normal to the crack orientation is about twice the value in direction along the crack orientation. The attenuation coefficient is found to be a more useful parameter than elastic velocity in describing the anisotropic orientation of cracks.

Ai, Huirong A.; Ahrens, Thomas J.

2007-01-01

346

Submersed aquatic vegetation (SAV) is an important component of shallow water estuarine systems that has declined drastically\\u000a in recent decades. SAV has particularly high light requirements, and losses of SAV have, in many cases, been attributed to\\u000a increased light attenuation in the water column, frequently due to coastal eutrophication. The desire to restore these valuable\\u000a habitats to their historical levels

Charles L. Gallegos

2001-01-01

347

Dark optical solitons in power law media with time-dependent coefficients

This Letter talks about the dynamics of dark optical solitons that are governed by the nonlinear Schrödinger's equation with power law nonlinearity. The solitons are considered in presence of linear attenuation, third order dispersion and self-steepening terms, all with time-dependent coefficients. The solitary wave ansatz is used to carry out the integration and an exact soliton solution is obtained. It

Manirupa Saha; Amarendra K. Sarma; Anjan Biswas

2009-01-01

348

NASA Astrophysics Data System (ADS)

A better understanding of the influences of different surface fluid drainage conditions on the propagation and attenuation of surface waves as the stipulated frequency is varied is a key issue to apply surface wave method to detect subsurface hydrological properties. Our study develops three-dimensional dynamical Green's functions in poroelastic media for Rayleigh waves of possible free surface conditions: permeable - "open pore," impermeable - "closed pore," and partially permeable boundaries. The full transient response of wave fields and spectra due to a stress impulse wavelet on the surface are investigated in the exploration seismic frequency band for typical surface drainage conditions, viscous coupling-damping, solid frame properties and porous fluid flowing configuration. Our numerical results show that, due to the slow dilatational wave - P2 wave, two types of Rayleigh waves, designated as R1 and R2 waves, exist along the surface. R1 wave possesses high energy as classic Rayleigh waves in pure elastic media for each porous materials. A surface fluid drainage condition is a significant factor to influence dispersion and attenuation, especially attenuation of R1 waves. R2 wave for closed pore and partially permeable surfaces is only observed for a low coupling-damping coefficient. The non-physical wave for partially surface conditions causes the R1 wave radiates into the R2 wave in the negative attenuation frequency range. It makes weaker R1 wave and stronger R2 wave to closed pore surface. Moreover, it is observed that wave fields and spectra of R1 wave are sensitive to frame elastic moduli change for an open pore surface, and to pore fluid flow condition change for closed pore and partially permeable surface.

Zhang, Yu; Xu, Yixian; Xia, Jianghai

2012-12-01

349

NASA Astrophysics Data System (ADS)

The resonance regions for resonant interactions of radiation belt electrons with obliquely propagating whistler-mode chorus waves are investigated in detail in the Dungey magnetic fields that are parameterized by the intensity of uniform southward interplanetary magnetic field (IMF) Bz or, equivalently, by the values of D=(M/Bz,0)1/3 (where M is the magnetic moment of the dipole and Bz,0 is the uniform southward IMF normal to the dipole's equatorial plane). Adoption of background magnetic field model can considerably modify the determination of resonance regions. Compared to the results for the case of D = 50 (very close to the dipole field), the latitudinal coverage of resonance regions for 200 keV electrons interacting with chorus waves tends to become narrower for smaller D-values, regardless of equatorial pitch angle, resonance harmonics, and wave normal angle. In contrast, resonance regions for 1 MeV electrons tend to have very similar spatial lengths along the field line for various Dungey magnetic field models but cover different magnetic field intervals, indicative of a strong dependence on electron energy. For any given magnetic field line, the resonance regions where chorus-electron resonant interactions can take place rely closely on equatorial pitch angle, resonance harmonics, and kinetic energy. The resonance regions tend to cover broader latitudinal ranges for smaller equatorial pitch angles, higher resonance harmonics, and lower electron energies, consistent with the results in Ni and Summers [Phys. Plasmas 17, 042902, 042903 (2010)]. Calculations of quasi-linear bounce-averaged diffusion coefficients for radiation belt electrons due to nightside chorus waves indicate that the resultant scattering rates differ from using different Dungey magnetic field models, demonstrating a strong dependence of wave-induced electron scattering effect on the adoption of magnetic field model. Our results suggest that resonant wave-particle interaction processes should be implemented into a sophisticated, accurate global magnetic field model to pursue comprehensive and complete models of radiation belt electron dynamics.

Shi, Run; Ni, Binbin; Gu, Xudong; Zhao, Zhengyu; Zhou, Chen

2012-07-01

350

Recently Adomian method was used to solve various kinds of heat-like and wave-like equations. In this Letter, an alternative approach called the variational iteration method is presented to overcome the demerit of complex calculation of Adomian polynomial. Some examples are given to show the reliability and the efficiency of the variational iteration method.

Da-Hua Shou; Ji-Huan He

2008-01-01

351

The offshore platforms are generally designed with sufficient vertical clearance from the maximum predicted wave crest elevations. This vertical clearance is termed as ‘air gap’. However, due to compelling reasons of hydrocarbon processes and also due to the increase in water levels due to climatic changes or seabed subsidence due to reservoir subsidence, the lower decks may become vulnerable to

Gopu R. Sekhar; S. Nallayarasu

2012-01-01

352

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

353

It has been accepted that rain attenuation (in an environment in which the rainfall rate is assumed uniform along the whole length of the radio link) is linear with respect to path length. It is shown here that for nonspherical raindrops this is not generally the case. Results over the frequency band 3-30 GHz are presented. These demonstrate that, in

S. A. J. Upton; B. G. Evans; A. R. Holt

1982-01-01

354

NASA Astrophysics Data System (ADS)

Using data from regional earthquakes recorded by the Hi-CLIMB array in Tibet, we utilize seismic attributes from crustal and Pn arrivals to constrain the velocity and attenuation structure in the crust and the upper mantle in central and western Tibet. The seismic attributes considered include arrival times, Hilbert envelope amplitudes, and instantaneous as well as spectral frequencies. We have constructed more than 30 high-quality regional seismic profiles, and of these, 10 events have been selected with excellent crustal and Pn arrivals for further analysis. Travel-times recorded by the Hi-CLIMB array are used to estimate the large-scale velocity structure in the region, with four near regional events to the array used to constrain the crustal structure. The travel times from the far regional events indicate that the Moho beneath the southern Lhasa terrane is up to 75 km thick, with Pn velocities greater than 8 km/s. In contrast, the data sampling the Qiangtang terrane north of the Bangong-Nujiang (BNS) suture shows thinner crust with Pn velocities less than 8 km/s. Seismic amplitude and frequency attributes have been extracted from the crustal and Pn wave trains, and these data are compared with numerical results for models with upper-mantle velocity gradients and attenuation, which can strongly affect Pn amplitudes and pulse frequencies. The numerical modeling is performed using the complete spectral element method (SEM), where the results from the SEM method are in good agreement with analytical and reflectivity results for different models with upper-mantle velocity gradients. The results for the attenuation modeling in Tibet imply lower upper mantle Q values in the Qiangtang terrane to the north of the BNS compared to the less attenuative upper mantle beneath the Lhasa terrane to the south of the BNS.

Nowack, R. L.; Bakir, A. C.; Griffin, J.; Chen, W.; Tseng, T.

2010-12-01

355

Ultrasonic Attenuation in Zircaloy4

In this work the relationship between Zircaloy-4 grain size and ultrasonic attenuation behavior was studied for longitudinal waves in the frequency range of 10–90 MHz. The attenuation was analyzed as a function of frequency for samples with different mechanical and heat treatments having recrystallized and Widmanstatten structures with different grain size. The attenuation behavior was analyzed by different scattering models,

M. P. Go´mez; A. D. Banchik; M. I. Lo´pez Pumarega; J. E. Ruzzante

2005-01-01

356

Ultrasonic Attenuation in Zircaloy4

In this work the relationship between Zircaloy-4 grain size and ultrasonic attenuation behavior was studied for longitudinal waves in the frequency range of 10-90 MHz. The attenuation was analyzed as a function of frequency for samples with different mechanical and heat treatments having recrystallized and Widmanstatten structures with different grain size. The attenuation behavior was analyzed by different scattering models,

M. P. Gómez; A. D. Banchik; M. I. López Pumarega; J. E. Ruzzante

2005-01-01

357

The bromine atom recombination rate constants, kr,fl's, obtained in flash photolysis experiments between 300 and 1300°K (preceding paper) were compared with the dissociation rate constants of Br2, kd,sh's, obtained in shock-wave experiments between 1250 and 2300°K. It was found that the phenomenological equation kd,sh ? kr,fl = K, where K is the equilibrium constant, is not obeyed if the kd,sh

J. K. K. Ip; George Burns

1969-01-01

358

The lower hybrid current drive (LHCD) is one of the promising methods not only for driving the non-inductive current required for steady-state tokamak operation, but also for controlling the plasma current profile to improve confinement in tokamak experiments. A direct consequence of experimental imperfection is difficult to obtain reliable estimate of the radial diffusion coefficient (D{sub st}) of the lower hybrid driven current. In this paper, the radial profile of D{sub st} is estimated to investigate its effect on the current driven by lower hybrid wave (LHW) in Experimental Advanced Superconducting Tokamak. Compared with the case of the constant radial diffusion coefficient, the efficiency of LHW driven current with the radial dependent diffusion coefficient D{sub st} ({rho}) becomes either higher or lower with respect to the plasma parameters, such as the density and the magnetic fluctuation. It is also found that the profiles of the LHW driven current are different. Therefore, it is necessary to consider the radial dependence of D{sub st} in order to get an accurate and reliable result in the numerical simulation of LHCD.

Zhang Xianmei; Wang Yanhui; Yu Limin; Shen Xin; Wang Jianbin [Department of Physics, East China University of Science and Technology, P.O. Box 385, Shanghai 200237 (China)

2012-07-15

359

Chromatic aberration coefficients

NASA Astrophysics Data System (ADS)

Our work deals with the influence of the wavelength of light on values of wave aberration coefficients. It is proposed a technique for calculation of the dependence of aberration coefficients on the wavelength, their interpretation and the connection to chromatic aberrations. It is also shown the calculation of the Strehl definition using chromatic aberration coefficients and the tolerance limits are given. The proposed method for calculation of chromatic aberration coefficients is shown for the case of the imaging of axial point by the rotationally symmetrical optical system. Relations that enable calculation of chromatic aberration coefficients up to fifth order are carried out. These relations are accurate enough for most optical systems in practice.

Miks, Antonin; Novak, Jiri; Novak, Pavel

2007-05-01

360

We propose a 3-D crust–upper mantle seismic attenuation (QP) model of the southern Apennines–Calabrian Arc subduction zone together with a 3-D velocity (VP) model. The QP model is calculated from relative t* using the spectral ratio method and the VP from traveltime data. The final data set used for the inversion of the VP model consists of 2400 traveltime arrivals

Stephen Monna; Torsten Dahm

2009-01-01

361

The lithosphere beneath a continental rift should be significantly modified due to extension. To image the lithosphere beneath the Rio Grande rift (RGR), we analyzed teleseismic travel time delays of both P and S wave arrivals and solved for the attenuation of P and S waves for four seismic experiments spanning the Rio Grande rift. Two tomographic inversions of the P wave travel time data are given: an Aki-Christofferson-Husebye (ACH) block model inversion and a downward projection inversion. The tomographic inversions reveal a NE-SW to NNE-SSW trending feature at depths of 35 to 145 km with a velocity reduction of 7 to 8% relative to mantle velocities beneath the Great Plains. This region correlates with the transition zone between the Colorado Plateau and the Rio Grande rift and is bounded on the NW by the Jemez lineament, a N52??E trending zone of late Miocene to Holocene volcanism. S wave delays plotted against P wave delays are fit with a straight line giving a slope of 3.0??0.4. This correlation and the absolute velocity reduction imply that temperatures in the lithosphere are close to the solidus, consistent with, but not requiring, the presence of partial melt in the mantle beneath the Rio Grande rift. The attenuation data could imply the presence of partial melt. We compare our results with other geophysical and geologic data. We propose that any north-south trending thermal (velocity) anomaly that may have existed in the upper mantle during earlier (Oligocene to late Miocene) phases of rifting and that may have correlated with the axis of the rift has diminished with time and has been overprinted with more recent structure. The anomalously low-velocity body presently underlying the transition zone between the core of the Colorado Plateau and the rift may reflect processes resulting from the modern (Pliocene to present) regional stress field (oriented WNW-ESE), possibly heralding future extension across the Jemez lineament and transition zone.

Slack, P. D.; Davis, P. M.; Baldridge, W. S.; Olsen, K. H.; Glahn, A.; Achauer, U.; Spence, W.

1996-01-01

362

NASA Astrophysics Data System (ADS)

During magma emplacement in the shallow crust, transient variations of physical properties underneath active volcanoes are expected and in a few cases observed. The predictability of such changes strongly depends on how fast this process is, compared to our ability to handle geophysical data and consistently resolve transient anomalies in the physical properties of the medium. The velocity of the magma upwelling depends on the local conditions of the volcanic conduit and rheology of the magma. Mt Etna is a perfect natural laboratory to investigate such issues, due to the almost continuous magmatic activity and the high quality of seismologic and geodetic data. Our experience with the most recent eruptive activity at Etna volcano (1989, 1991-1993, 1999, 2001, 2002-2003, 2004, 2006-2007, 2008-2009) has indicated that most of these eruptions were preceded by changes in several geophysical parameters, the most evident being: i) increase of seismicity; ii) deformation and iii) stress field variations. Changes in seismic attenuation properties in the region of magma intrusion can be also detected, and the 3D tomography by using a set of earthquakes recorded just before an eruption provides an image of such changes. Thus, to recognize if any change in the attenuation parameters, QP and/or QS, was produced by intrusive processes at Mt Etna, we analyzed the seismicity occurred in two different periods (2001-2003 and 2007-2008) during which three eruptive episodes occurred. Here we show that seismic attenuation of local earthquakes strongly increases due to the emplacement of magma within the crust, forecasting eruptions.

Giampiccolo, E.; De Gori, P.; Chiarabba, C.; Cocina, O.; Patanè, D.

2012-04-01

363

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

364

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

365

NASA Astrophysics Data System (ADS)

We present the results of calculations of the bounce-averaged pitch angle, mixed, and momentum diffusion coefficients in a dipole and two realistic field models (the T01s model for quiet and storm conditions). We consider resonant interactions of the outer radiation belt electrons with oblique chorus waves. We demonstrate that on the dayside, the use of a realistic magnetic field versus a dipole field only makes a significant difference for small equatorial pitch angles at energies larger than E = 1 MeV. On the nightside, the differences between the scattering rates calculated in the Tsyganenko and dipole models can reach several orders of magnitude at various equatorial pitch angles for electrons with E ? 0.5 MeV. The most significant changes in the scattering rates computed in the realistic and dipole magnetic fields occur during the geomagnetically active conditions. On the nightside, for E ? 0.5 MeV, the diffusion coefficients calculated in the Tsyganenko field show significant scattering near the edge of the loss cone that can produce loss of electrons to the atmosphere, while in the dipole model there is no scattering at small equatorial pitch angles. Our computations in the realistic field show that resonant interactions between electrons with E ? 1 MeV and chorus waves can be an effective net loss mechanism on both the dayside and the nightside. To explain the differences in the scattering rates associated with a change in the magnetic field model, we present the contribution of various resonant harmonics to the diffusion and examine the changes in the resonance condition.

Orlova, Ksenia G.; Shprits, Yuri Y.; Ni, Binbin

2012-07-01

366

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

367

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

368

NASA Astrophysics Data System (ADS)

Multiparameter full waveform inversion (FWI) is a challenging quantitative seismic imaging method for lithological characterization and reservoir monitoring. The difficulties in multiparameter FWI arise from the variable influence of the different parameter classes on the phase and amplitude of the data, and the trade-off between these. In this framework, choosing a suitable parametrization of the subsurface and designing the suitable FWI workflow are two key methodological issues in non-linear waveform inversion. We assess frequency-domain visco-acoustic FWI to reconstruct the compressive velocity (VP), the density (?) or the impedance (IP) and the quality factor (QP), from the hydrophone component, using a synthetic data set that is representative of the Valhall oil field in the North Sea. We first assess which of the (VP, ?) and (VP, IP) parametrizations provides the most reliable FWI results when dealing with wide-aperture data. Contrary to widely accepted ideas, we show that the (VP, ?) parametrization allows a better reconstruction of both the VP, ? and IP parameters, first because it favours the broad-band reconstruction of the dominant VP parameter, and secondly because the trade-off effects between velocity and density at short-to-intermediate scattering angles can be removed by multiplication, to build an impedance model. This allows for the matching of the reflection amplitudes, while the broad-band velocity model accurately describes the kinematic attributes of both the diving waves and reflections. Then, we assess different inversion strategies to recover the quality factor QP, in addition to parameters VP and ?. A difficulty related to attenuation estimation arises because, on the one hand the values of QP are on average one order of magnitude smaller than those of VP and ?, and on the other hands model perturbations relative to the starting models can be much higher for QP than for VP and ? during FWI. In this framework, we show that an empirical tuning of the FWI regularization, which is adapted to each parameter class, is a key issue to correctly account for the attenuation in the inversion. We promote a hierarchical approach where the dominant parameter VP is reconstructed first from the full data set (i.e. without any data preconditioning) to build a velocity model as kinematically accurate as possible before performing the joint update of the three parameter classes during a second step. This hierarchical imaging of compressive wave speed, density and attenuation is applied to a real wide-aperture ocean-bottom-cable data set from the Valhall oil field. Several geological features, such as accumulation of gas below barriers of claystone and soft quaternary sediment are interpreted in the FWI models of density and attenuation. The models of VP, ? and QP that have been developed by visco-acoustic FWI of the hydrophone data can be used as initial models to perform visco-elastic FWI of the geophone data for the joint update of the compressive and shear wave speeds.

Prieux, Vincent; Brossier, Romain; Operto, Stéphane; Virieux, Jean

2013-09-01

369

This paper extends a previous study of the harmonic (or AC) flow of a compressible fluid through a single, elastic, thick-wall pipe. The model previously developed is used to investigate propagation of pore-scale Biot slow waves through heterogeneous one-, two- and three-dimensional networks of pipes. A novel method is applied to the results of the network simulations to numerically determine

Y. Bernabé

2009-01-01

370

NASA Astrophysics Data System (ADS)

Continuous recordings of 17 broadband and short-period digital seismic stations from a newly established seismological network in Saudi Arabia, along with digital recordings from the broadband stations of the GSN, MEDNET, GEOFON, a temporary array in Saudi Arabia, and temporary short period stations in Oman, were analysed to study the lithospheric structure of the Arabian Plate and surrounding regions. The Arabian Plate is surrounded by a variety of types of plate boundaries: continental collision (Zagros Belt and Bitlis Suture), continental transform (Dead Sea fault system), young seafloor spreading (Red Sea and the Gulf of Aden) and oceanic transform (Owen fracture zone). Also, there are many intraplate Cenozoic processes such as volcanic eruptions, faulting and folding that are taking place. We used this massive waveform database of more than 6200 regional seismograms to map zones of blockage, inefficient and efficient propagation of the Lg and Sn phases in the Middle East and East Africa. We observed Lg blockage across the Bitlis Suture and the Zagros fold and thrust belt, corresponding to the boundary between the Arabian and Eurasian plates. This is probably due to a major lateral change in the Lg crustal waveguide. We also observed inefficient Lg propagation along the Oman mountains. Blockage and inefficient Sn propagation is observed along and for a considerable distance to the east of the Dead Sea fault system and in the northern portion of the Arabian Plate (south of the Bitlis Suture). These mapped zones of high Sn attenuation, moreover, closely coincide with extensive Neogene and Quaternary volcanic activity. We have also carefully mapped the boundaries of the Sn blockage within the Turkish and Iranian plateaus. Furthermore, we observed Sn blockage across the Owen fracture zone and across some segments of the Red Sea. These regions of high Sn attenuation most probably have anomalously hot and possibly thin lithospheric mantle (i.e. mantle lid). A surprising result is the efficient propagation of Sn across a segment of the Red Sea, an indication that active seafloor spreading is not continuous along the axis of the Red Sea. We also investigated the attenuation of Pn phase (QPn) for 1-2 Hz along the Red Sea, the Dead Sea fault system, within the Arabian Shield and in the Arabian Platform. Consistent with the Sn attenuation, we observed low QPn values of 22 and 15 along the western coast of the Arabian Plate and along the Dead Sea fault system, respectively, for a frequency of 1.5 Hz. Higher QPn values of the order of 400 were observed within the Arabian Shield and Platform for the same frequency. Our results based on Sn and Pn observations along the western and northern portions of the Arabian Plate imply the presence of a major anomalously hot and thinned lithosphere in these regions that may be caused by the extensive upper mantle anomaly that appears to span most of East Africa and western Arabia.

Al-Damegh, Khaled; Sandvol, Eric; Al-Lazki, Ali; Barazangi, Muawia

2004-05-01

371

Attenuation of shear-waves in the lithosphere for frequencies from 0.05 to 25 Hz

Q for shear-waves in the crust and upper mantle was determined as a function of frequency in the range 1-25 Hz, using band-pass filtered records of about 900 earthquakes occurring in the central Japan area with focal depths from 0 to 150 km. The data were supplied from two stations in the Kanto region, operated by the Earthquake Research Institute,

Keiiti Aki

1980-01-01

372

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

373

A high peak power level r-f attenuator that is readily and easily insertable along a coaxial cable having an inner conductor and an outer annular conductor without breaking the ends thereof is presented. Spaced first and second flares in the outer conductor face each other with a slidable cylindrical outer conductor portion therebetween. Dielectric means, such as water, contact the cable between the flares to attenuate the radio-frequency energy received thereby. The cylindrical outer conductor portion is slidable to adjust the voltage standing wave ratio to a low level, and one of the flares is slidable to adjust the attenuation level. An integral dielectric container is also provided. (AFC)

Giordano, S.

1963-11-12

374

Potential Advantages for Millimeter-Wave Heating of Powdered Metals

Based on electromagnetic induction heating, an interaction model of microwaves with powdered metal has been established. The formulae of attenuation coefficient, heating rate and heating conversion efficiency are obtained and analyzed. The results of calculations show that millimeter waves may be able to overcome the obstacle caused by smaller skin depth and have strong advantages for the microwave heating of

Jirun Luo; Christian Hunyar; Lambert Feher; Guido Link; Manfred Thumm; Paola Pozzo

2004-01-01

375

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

376

Ultrasonic Attenuation in Zircaloy-4

NASA Astrophysics Data System (ADS)

In this work the relationship between Zircaloy-4 grain size and ultrasonic attenuation behavior was studied for longitudinal waves in the frequency range of 10-90 MHz. The attenuation was analyzed as a function of frequency for samples with different mechanical and heat treatments having recrystallized and Widmanstatten structures with different grain size. The attenuation behavior was analyzed by different scattering models, depending on grain size, wavelength and frequency.

Gómez, M. P.; Banchik, A. D.; López Pumarega, M. I.; Ruzzante, J. E.

2005-04-01

377

NASA Astrophysics Data System (ADS)

Five melt-bearing polycrystalline olivine aggregates have been newly prepared by hot isostatic pressing and tested at high temperature and pressure with torsional forced-oscillation and microcreep methods. Cylindrical specimens, varying in average grain size from 7 to 52 ?m, were annealed and then tested during slow staged cooling under 200 MPa pressure from maximum temperatures of 1240-1300°C where they contained basaltic melt fractions ranging from ˜0.0001 to 0.037. For temperatures ?1000°C, pronounced departures from elastic behavior are evident in strain energy dissipation Q-1 and associated dispersion of the shear modulus G. In marked contrast with the high-temperature viscoelastic behavior of melt-free materials, a broad dissipation peak is observed for each of the melt-bearing specimens - superimposed upon a melt-enhanced level of monotonically frequency- and temperature-dependent "background" dissipation. The oscillation period at which the peak is centered decreases systematically with increasing temperature. A "global" model comprising an Andrade-pseudoperiod background plus Gaussian peak accounts adequately for the variation of Q-1 with frequency, temperature, average grain size and melt fraction. In the following paper (Part II) a microstructural explanation for the observed viscoelastic behavior is sought and the global model is used to extrapolate the experimental data to the conditions of teleseismic wave propagation in the Earth's upper mantle.

Jackson, Ian; Faul, Ulrich H.; Fitz Gerald, John D.; Tan, Ben H.

2004-06-01

378

NASA Astrophysics Data System (ADS)

Ambient particulate matter (PM) samples were collected on quartz filters at a rural site in southern Ontario during intensive studies in 2005 and 2007. The concentrations of organic carbon (OC), pyrolysis organic carbon (POC), and elemental carbon (EC) were determined by thermal analysis. These results were compared to the organic aerosol mass concentration (OM) measured by an Aerodyne Aerosol Mass Spectrometer (AMS) and to the particle absorption coefficient (b_asp) obtained from a Radiance Research Particle Soot Absorption Photometer (PSAP). The total organic mass to organic carbon ratios (OM/OC) and specific attenuation coefficients (SAC) were also derived. According to the results, the POC mass is proportional to the approximated oxygen mass in the aerosols and OM/OC ratios can be estimated directly from thermal measurements. The study also suggests that the air masses from the south, with relatively low OC/EC ratios, high EC, sulphate contents and OM/OC ratios, were originated from urban and industrial emissions and subsequently experienced photo-oxidations in the atmosphere, implying that the oxygenated organics could come from both primary and secondary sources. Whereas the air masses from the north, with relatively high OC/EC ratios, low EC, sulphate contents and OM/OC ratios, were dominant by the background clean air with relatively larger contributions from biogenic emissions. The mean SAC derived from the 2005 and 2007 studies are 4.9 m2 g-1 and 3.8 m2 g-1, respectively. When POC mass approaching zero (i.e. the impact of atmospheric aging is minimized), the SAC for primary emitted soot is estimated to be 5.8 m2 g-1 and 6.3 m2 g-1 for the northern and southern air masses, respectively, supported by the corresponding values when particulate sulphate concentration approaches zero. A decreasing trend in the SAC value with atmospheric aging of the aerosol was observed at the site, suggesting that during the study, the light absorption enhancement due to the presence of coating on particles was likely to be offset by the decrease in light absorption caused by increasing soot particle diameter and collapsing of soot particle structure. This result may imply that model simulations of atmospheric warming by BC could be 50% too high.

Chan, T. W.; Huang, L.; Leaitch, W. R.; Sharma, S.; Brook, J. R.; Slowik, J. G.; Abbatt, J. P. D.; Brickell, P. C.; Liggio, J.; Li, S.-M.; Moosmüller, H.

2009-07-01

379

Viscothermal Coupling Effects on Sound Attenuation in Concentrated Colloidal Dispersions.

NASA Astrophysics Data System (ADS)

This thesis describes a Unified Coupled Phase Continuum (UCPC) model to analyze sound propagation through aerosols, emulsions and suspensions in terms of frequency dependent attenuation coefficient and sound speed. Expressions for the viscous and thermal coupling coefficients explicitly account for the effects of particle size, shape factor, orientation as well as concentration and the sound frequency. The UCPC model also takes into account the intrinsic acoustic absorption within the fluid medium due to its viscosity and heat conductivity. The effective complex wave number as a function of frequency is derived. A frequency- and concentration-dependent complex Nusselt number for the interfacial thermal coupling coefficient is derived using an approximate similarity between the 'viscous skin drag' and 'heat conduction flux' associated with the discontinuous suspended phase, on the basis of a cell model. The theoretical predictions of attenuation spectra provide satisfactory agreement with reported experimental data on two concentrated suspensions (polystyrene latex and kaolin pigment), two concentrated emulsions (toluene -in-water, n-hexadecane-in-water), and two aerosols (oleic acid droplets-in-nitrogen, alumina-in-air), covering a wide range of relative magnitudes (from 10^ {-3} to 10^{3}) of thermal versus viscous contributions, for dispersed phase volume fractions as high as 50%. The relative differences between the additive result of separate viscous and thermal loss estimates and combined viscothermal absorption results are also presented. Effects of particle shape on viscous attenuation of sound in concentrated suspensions of non-spherical clay particles are studied. Attenuation spectra for 18 frequencies from 3 to 100 MHz are measured and analyzed for eleven kaolin clay slurries with solid concentrations ranging from 0.6% to 35% (w/w). A modified viscous drag coefficient that considers frequency, concentration, particle size, shape and orientation of spheroids, is developed and applied to estimate the viscous attenuation coefficients. With incorporation of particle size and shape distributions (PSSD), predictions agree quantitatively with observed attenuation coefficients. The effects of particle aspect ratio and orientation become more evident as particle concentrations and frequencies are increased. The UCPC model combined with the ultrasonic spectroscopy techniques can provide for theoretical and experimental frameworks in characterization of concentrated colloidal dispersions.

Han, Wei

380

Homomorphic processing of the tube wave generated during acoustic logging

The authors have developed a new method to process the tube wave, which is generated during acoustic logging, to obtain estimates for its wavenumber, attenuation coefficient, amplitude, and phase at every frequency. To improve the accuracy of the estimates, the method can use data from multiple sources and data collected at successive depths in the borehole. This new method has several advantages over other methods that are currently used to process acoustic logging data: the new method can obtain accurate estimates of the wavenumber and amplitude from only a few receivers; the receivers can be irregularly spaced; and no spurious estimates are generated. Nonetheless, this new method has one disadvantage compared to others: it can only estimate the parameters for one, high-amplitude wave like the tube wave. Also, like all other existing methods, the new method obtains only reasonable estimates for the attenuation coefficient when data from many receivers are processed.

Ellefsen, K.J. (New England Research Inc., Quincy, MA (United States)); Cheng, C.H. (Massachusetts Inst. of Tech., Cambridge, MA (United States). Dept. of Earth, Atmospheric, and Planetary Sciences); Burns, D.R.

1993-10-01

381

Full-wave description of the lower hybrid reflection of whistler waves

NASA Astrophysics Data System (ADS)

A quasi-electrostatic whistler wave propagating in the direction of increasing lower hybrid resonance (LHR) frequency experiences reflection from the region in which its frequency becomes lower than the LHR frequency. This phenomenon is usually described in the framework of geometrical optics. For a wave propagating along a magnetospheric trajectory, the LHR reflection frequently takes place in the ionospheric region in which electron-neutral collisions are essential and lead to wave attenuation. In this case, the wave approach to the description of the LHR reflection is most consistent. This work is aimed at developing such an approach. The coefficients of the wave reflection are calculated for different plasma parameters. The relation between the problem under consideration and the problem of exit of whistler-mode waves to the ground is considered.

Kuzichev, I. V.; Shklyar, D. R.

2013-10-01

382

Short surface waves in the Canadian Arctic in 2007 and 2008

NASA Astrophysics Data System (ADS)

We have collected time series data of short oceanic waves as a part of the International Polar Year (IPY) 2007-2008. Using a shipboard laser wave slope (LAWAS) system operating at 900 nm, we have obtained wave slopes measurements up to 60 rad m-1 wave number. We have compared our in situ wave slopes with collocated and concurrent high-resolution upwind Normalized Radar Cross Sections (NRCS) collected by QuikSCAT. The LAWAS measured wave slope spectra were consistent with local wind speeds and QuikSCAT measured NRCS. Our measured short wave mean slopes indicate their enhancement by long waves (0-1 rad m-1) at small values of long-wave slope. Concurrent with wave slope measurements, the strength of the reflected LAWAS light beam was analyzed in terms of the light attenuation coefficient at 900 nm. We have observed a correlation between surface elevation and light attenuation. The mechanism of wave modulated beam attenuation was found to be related to the instantaneous long wave skewness.

Bogucki, D. J.; Drennan, W. M.; Woods, S.; Gremes-Cordero, S.; Long, D. G.; Mitchell, C.

2013-07-01

383

The analysis of the ultrasonic frequency-dependent backscatter coefficient of aggregating red blood cells reveals information about blood structural properties. The difficulty in applying this technique in vivo is due to the frequency-dependent attenuation caused by intervening tissue layers that distorts the spectral content of signals backscattered by blood. An optimization method is proposed to simultaneously estimate tissue attenuation and blood structure properties, and was termed the structure factor size and attenuation estimator (SFSAE). An ultrasound scanner equipped with a wide-band 25 MHz probe was used to insonify porcine blood sheared in both Couette and tubular flow devices. Since skin is one of the most attenuating tissue layers during in vivo scanning, four skin-mimicking phantoms with different attenuation coefficients were introduced between the transducer and the blood flow. The SFSAE gave estimates with relative errors below 25% for attenuations between 0.115 and 0.411 dB?MHz and kR<2.08 (k being the wave number and R the aggregate radius). The SFSAE can be useful to examine in vivo and in situ abnormal blood conditions suspected to promote pathophysiological cardiovascular consequences.

Franceschini, Emilie; Yu, Francois T.H.; Destrempes, Francois; Cloutier, Guy

2010-01-01

384

Rayleigh Waves Traveling Along the Impermeable Surface of an Unsaturated Poroelastic Half-space

NASA Astrophysics Data System (ADS)

This study presents an analytical model of Rayleigh waves propagating along the impermeable surface of an unsaturated poroelastic half-space. The developed equation reveals that there are three modes of Rayleigh waves, based on the poroelastic equations in a porous medium containing two immiscible viscous compressible fluids formulated by Lo et al.[Wave propagation through elastic porous media containing two immiscible fluids. Water Resour Res 2005;41:W02025]. These three Rayleigh waves induced by three modes, corresponding to three dilatational waves in a medium saturated by two fluids, can be expressed as the R1, R2, and R3 waves in the descending order of magnitude, respectively. As an excitation frequency is given, the dispersion equation of a cubic polynomial will be solved numerically to derive the three phase speeds and the attenuation coefficients of the R1, R2, and R3 waves in Columbia fine sandy loam penetrated by air and water fluids. The numerical results show that the phase speed of the R1 wave is frequency independent, approximately 93 % to 95 % of the shear wave speed, and nearly 28 % to 49 % of the first dilatational wave speed at the frequencies of 1 Hz, 10 Hz, and 100Hz related to relative water saturation ranges (0.01-0.99). Nevertheless, the R2 and R3 waves are dispersive. In the same frequency ranges, we also find the two ratios of the phase speeds of the R2 and R3 waves to the second and third dilatational wave speeds are both around 56 % to 90 %. In addition, the R1 wave attenuates least while the R3 wave has the highest attenuation coefficient along the impermeable surface. Lastly, all the three modes of Rayleigh wave satisfy the condition of decaying exponentially with the distance far away from the surface of a porous medium.

Chen, Y.; Lo, W.; Leu, J.; Cheng, A. H.

2009-05-01

385

Optimising HIFU Lesion Formation with Backscatter Attenuation Estimation (BAE)

Ultrasound attenuation is an important dosimetric factor for HIFU treatments of soft tissue tumours. During clinical HIFU treatments ultrasound attenuation in the tissue overlying the focal volume leads to a loss in intensity. In clinical treatments at the Royal Marsden Hospital (UK), ultrasound attenuation is currently estimated using published tissue attenuation coefficients and the thickness of tissue layers determined from

John Civale; Jeff Bamber; Ian Rivens; Gail Ter Haar

2006-01-01

386

ERIC Educational Resources Information Center

|Discusses and provides an example of reflectivity approximation to determine whether reflection will occur. Provides a method to show thin-film interference on a projection screen. Also applies the reflectivity concepts to electromagnetic wave systems. (MVL)|

Greenslade, Thomas B., Jr.

1994-01-01

387

NASA Astrophysics Data System (ADS)

Photoacoustic Imaging (also known as thermoacoustic or optoacoustic imaging) is a novel imaging method which combines the advantages of Diffuse Optical Imaging (high contrast) and Ultrasonic Imaging (high spatial resolution). A short laser pulse excites the sample. The absorbed energy causes a thermoelastic expansion and thereby launches a broadband ultrasonic wave (photoacoustic signal). This way one can measure the optical contrast of a sample with ultrasonic resolution. For collecting photoacoustic signals our group introduced so called integrating detectors a few years ago. Such integrating detectors integrate the pressure in one or two dimensions -a line or a plane detector, respectively. Thereby the three dimensional imaging problem is reduced to a two or a one dimensional problem for the projections and a two or three dimensional inverse radon transform as a second step to get the three dimensional initial pressure distribution. The integrating detectors are mainly optical detectors and thus can provide a high bandwidth up to several 100 MHz. Using these detectors the resolution is often limited by the acoustic attenuation in the sample itself, because attenuation increases with higher frequencies. Stoke's equation describes the attenuation of photoacoustic generated waves in liquids very well, which results in an increase of the acoustic attenuation with the square of the frequency. For fat tissue an absorption coefficient which is approximately linear proportional to frequency is reported. Presented measurements give an exponential power law dependency with an exponent between 1.31 and 1.36 in fat tissue near the skin of a pig. These equations describing frequency dependent acoustic attenuation have been solved in the past by decomposing the pressure wave into plane waves damped in space, described by the complex part of the wave number equal to the attenuation coefficient. One main result of this paper is that for Photoacoustic Tomography another description seems to be very useful: like for a standing wave in a resonator the wave number is real but the frequency is complex. The complex part of the frequency is the damping in time. Both descriptions are equivalent, but with the complex frequency description acoustic attenuation can be included in all "k-space" methods well known in Photoacoustic Tomography just by introducing a factor describing the exponential decay in time.

Burgholzer, P.; Roitner, H.; Bauer-Marschallinger, J.; Paltauf, G.

2010-02-01

388

Acoustic wave properties and device characterization of 55°-rotated y-cut quartz

NASA Astrophysics Data System (ADS)

The properties of the acoustic wave propagation on or near the surface on the 55°-rotated y-cut in quartz are experimentally studied to determine the suitability of this cut in device applications. The wave is shown to be a combination of a surface-skimming bulk wave (SSBW) and a Bleustein-Guylaev wave. The velocity, temperature coefficient of delay, and attenuation associated with the wave have been measured. The measured attenuation was found to be significantly lower than previously investigated pure SSBW orientations. Using this wave, various bandpass filters were designed, fabricated, and tested. An aluminum layer deposited between the input and output electrodes was found to lower the insertion loss. The results are described and compared to the more commonly used SSBW orientations in quartz.

Josse, F.; Vetelino, J. F.

1980-12-01

389

Shear waves in vegetal tissues at ultrasonic frequencies

NASA Astrophysics Data System (ADS)

Shear waves are investigated in leaves of two plant species using air-coupled ultrasound. Magnitude and phase spectra of the transmission coefficient around the first two orders of the thickness resonances (normal and oblique incidence) have been measured. A bilayer acoustic model for plant leaves (comprising the palisade parenchyma and the spongy mesophyll) is proposed to extract, from measured spectra, properties of these tissues like: velocity and attenuation of longitudinal and shear waves and hence Young modulus, rigidity modulus, and Poisson's ratio. Elastic moduli values are typical of cellular solids and both, shear and longitudinal waves exhibit classical viscoelastic losses. Influence of leaf water content is also analyzed.

Fariñas, M. D.; Sancho-Knapik, D.; Peguero-Pina, J. J.; Gil-Pelegrín, E.; Gómez Álvarez-Arenas, T. E.

2013-03-01

390

Reflection of nonlinear waves from a domain boundary

Boundaries between domains of traveling waves are studied in convection in an 8{percent} mixture of ethanol and water. A configuration is described in which rolls move in opposite directions on either side of a domain wall. Demodulation techniques are used to measure the interaction of waves across the boundary. It is found that rolls approaching the boundary with an oblique angle of incidence are reflected from the boundary. The reflection coefficient and the attenuation of the reflected wave are measured. {copyright} {ital 1997} {ital The American Physical Society}

La Porta, A.; Surko, C.M. [Department of Physics, University of California, San Diego, La Jolla, California 92093 (United States)

1997-06-01

391

Global Attenuation Tomography and Implications for Upper-Mantle Thermal Structure

NASA Astrophysics Data System (ADS)

Observation of seismic-wave attenuation provides a direct measure of the Earth's anelasticity. The sensitivity of attenuation to temperature, composition, partial melt, and water content is different from that of seismic velocity, and joint interpretation of elastic and anelastic models may be used to improve constraints on these properties throughout the Earth. Historically, the development of attenuation models has lagged behind velocity models. However, the availability of large seismic datasets and improved techniques to treat these data have recently led to better and higher-resolution attenuation models. We have developed a new 3-D global model of shear attenuation in the upper mantle. This new model, QRFSI12, is derived from > 30,000 fundamental-mode Rayleigh wave amplitude measurements at each period (period range 50-250 s). The amplitudes are inverted simultaneously for the coefficients of the 3-D model as well as frequency-dependent amplitude correction factors for each source and receiver. We have found that focusing by elastic heterogeneity can significantly influence surface-wave amplitudes and that this effect can be modeled at long periods using ray-theoretical approximations. We therefore subtract focusing effects from the data prior to inversion by using phase-velocity maps determined from jointly inverting amplitude and phase-delay datasets. In the shallow mantle, QRFSI12 exhibits a strong correlation with tectonic features, and different tectonic provinces are characterized by distinct attenuative properties. At depths > 250 km, the model is dominated by high attenuation beneath the southeastern Pacific and eastern Africa and low attenuation associated with subduction zones in the western Pacific. Comparison of QRFSI12 with global shear-velocity models shows a strong anti-correlation throughout the upper mantle. At 100-km depth, a clear trend of increasing velocity and decreasing attenuation with increasing age of the seafloor is apparent, and tectonically active continental areas are associated with slower velocities and higher attenuation than stable continental interiors. At depths of 150 and 200 km, oceanic regions exhibit a larger decrease in attenuation per fractional increase in velocity than stable continental regions do, suggesting differences in the mechanisms that influence the seismic properties within these two regions. Comparison with recent laboratory measurements (Faul and Jackson, 2005) of attenuation and velocity for olivine helps to quantify the extent to which temperature alone can explain the observed variability. We find that the mineral-physics predictions agree well with the global seismic models for the oceanic regions between 150- and 250-km depth, but that the cratonic areas cannot be fit.

Dalton, C. A.; Ekström, G.; Dziewonski, A. M.

2007-12-01

392

NASA Astrophysics Data System (ADS)

To find variations in the dynamics of the surface M 2 tide in the White Sea induced by the spatially inhomogeneity of the resistance coefficient, we use a modified version of the QUODDY-4 three-dimensional finite-element hydrostatic model. This version differs from the original version in that it has a module introduced to calculate the resistance coefficient in the bottom boundary layer (BBL). The resistance coefficient is found from resistance laws for an oscillating rotating turbulent BBL over hydrodynamically rough and partially rough (smoothly rough) underlying surfaces describing the dependence of the resistance coefficient and other integral characteristics of resistance on dimensionless similarity parameters: the sea-bottom Rossby number Ro, the streaming Reynolds number Re, and the relative (normalized to tidal frequency) inertial frequency f/?. The use of spatial inhomogeneity of the resistance coefficient was shown not to lead to considerable changes in tidal characteristics. The values of these characteristics are several times larger than the instrumental measurement errors for the level and velocity but less than the errors in their calculation.

Kagan, B. A.; Timofeev, A. A.; Rashidi, E. H. A.

2012-07-01

393

Body waves in poroelastic media saturated by two immiscible fluids

NASA Astrophysics Data System (ADS)

A study of body waves in elastic porous media saturated by two immiscible Newtonian fluids is presented. We analytically show the existence of three compressional waves and one rotational wave in an infinite porous medium. The first and second compressional waves are analogous to the fast and slow compressional waves in Biot's theory. The third compressional wave is associated with the pressure difference between the fluid phases and dependent on the slope of capillary pressure-saturation relation. Effect of a second fluid phase on the fast and slow waves is numerically investigated for Massillon sandstone saturated by air and water phases. A peak in the attenuation of the first and second compressional waves is observed at high water saturations. Both the first and second compressional waves exhibit a drop in the phase velocity in the presence of air. The results are compared with the experimental data available in the literature. Although the phase velocity of the first compressional and rotational waves are well predicted by the theory, there is a discrepancy between the experimental and theoretical values of attenuation coefficients. The causes of discrepancy are explained based on experimental observations of other researchers.

Tuncay, Kagan; Yavuz Corapcioglu, M.

1996-11-01

394

Prediction of spectral acceleration response ordinates based on PGA attenuation

Developed herein is a new peak ground acceleration (PGA)-based predictive model for 5% damped pseudospectral acceleration (SA) ordinates of free-field horizontal component of ground motion from shallow-crustal earthquakes. The predictive model of ground motion spectral shape (i.e., normalized spectrum) is generated as a continuous function of few parameters. The proposed model eliminates the classical exhausted matrix of estimator coefficients, and provides significant ease in its implementation. It is structured on the Next Generation Attenuation (NGA) database with a number of additions from recent Californian events including 2003 San Simeon and 2004 Parkfield earthquakes. A unique feature of the model is its new functional form explicitly integrating PGA as a scaling factor. The spectral shape model is parameterized within an approximation function using moment magnitude, closest distance to the fault (fault distance) and VS30 (average shear-wave velocity in the upper 30 m) as independent variables. Mean values of its estimator coefficients were computed by fitting an approximation function to spectral shape of each record using robust nonlinear optimization. Proposed spectral shape model is independent of the PGA attenuation, allowing utilization of various PGA attenuation relations to estimate the response spectrum of earthquake recordings.

Graizer, V.; Kalkan, E.

2009-01-01

395

Estimating total ultrasound attenuation from backscatter data is essential in the field of quantitative ultrasound (QUS) because of the need to compensate for attenuation when estimating the backscatter coefficient and QUS parameters. This work uses a reference phantom method of attenuation estimation to create a spatial map of attenuation slope (AS) from backscatter radio-frequency (RF) data of three phantoms and a rat mammary adenocarcinoma tumor (MAT). The attenuation maps show changes in attenuation between different regions of the phantoms and the MAT tumor. Analyses of the attenuation maps of the phantoms suggest that the AS estimates are in good quantitative agreement with the known values for the phantoms. Furthermore, estimates of total attenuation from the attenuation maps are likewise in good quantitative agreement with known values.

Pawlicki, Alexander D.; O'Brien, William D.

2013-01-01

396

Estimating total ultrasound attenuation from backscatter data is essential in the field of quantitative ultrasound (QUS) because of the need to compensate for attenuation when estimating the backscatter coefficient and QUS parameters. This work uses a reference phantom method of attenuation estimation to create a spatial map of attenuation slope (AS) from backscatter radio-frequency (RF) data of three phantoms and a rat mammary adenocarcinoma tumor (MAT). The attenuation maps show changes in attenuation between different regions of the phantoms and the MAT tumor. Analyses of the attenuation maps of the phantoms suggest that the AS estimates are in good quantitative agreement with the known values for the phantoms. Furthermore, estimates of total attenuation from the attenuation maps are likewise in good quantitative agreement with known values. PMID:23493614

Pawlicki, Alexander D; O'Brien, William D

2013-04-01