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: August 15, 2014.

1

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

NASA Astrophysics Data System (ADS)

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

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

2009-03-01

2

NASA Astrophysics Data System (ADS)

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

Nishida, Hidetaka; Yamaguchi, Hiroshi; Yoshida, Masashi

3

Attenuation of ultrasonic waves in rolled metals

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

Liyong Yang; Joseph A. Turner

2004-01-01

4

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

5

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

6

Determination of Dimensionless Attenuation Coefficient in Shaped Resonators

NASA Technical Reports Server (NTRS)

The value of dimensionless attenuation coefficient is an important factor when numerically predicting high-amplitude acoustic waves in shaped resonators. Both the magnitude of the pressure waveform and the quality factor rely heavily on this dimensionless parameter. Previous authors have stated the values used, but have not completely explained their methods. This work fully describes the methodology used to determine this important parameter. Over a range of frequencies encompassing the fundamental resonance, the pressure waves were experimentally measured at each end of the shaped resonators. At the corresponding dimensionless acceleration, the numerical code modeled the acoustic waveforms generated in the resonator using various dimensionless attenuation coefficients. The dimensionless attenuation coefficient that most closely matched the pressure amplitudes and quality factors of the experimental and numerical results was determined to be the value to be used in subsequent studies.

Daniels, C.; Steinetz, B.; Finkbeiner, J.; Raman, G.; Li, X.

2003-01-01

7

Midperiod Rayleigh wave attenuation model for Asia

NASA Astrophysics Data System (ADS)

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

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

2010-08-01

8

Attenuation coefficients for water quality trading.

Water quality trading has been proposed as a cost-effective approach for reducing nutrient loads through credit generation from agricultural or point source reductions sold to buyers facing costly options. We present a systematic approach to determine attenuation coefficients and their uncertainty. Using a process-based model, we determine attenuation with safety margins at many watersheds for total nitrogen (TN) and total phosphorus (TP) loads as they transport from point of load reduction to the credit buyer. TN and TP in-stream attenuation generally increases with decreasing mean river flow; smaller rivers in the modeled region of the Ohio River Basin had TN attenuation factors per km, including safety margins, of 0.19-1.6%, medium rivers of 0.14-1.2%, large rivers of 0.13-1.1%, and very large rivers of 0.04-0.42%. Attenuation in ditches transporting nutrients from farms to receiving rivers is 0.4%/km for TN, while for TP attenuation in ditches can be up to 2%/km. A 95 percentile safety margin of 30-40% for TN and 6-10% for TP, applied to the attenuation per km factors, was determined from the in-stream sensitivity of load reductions to watershed model parameters. For perspective, over 50 km a 1% per km factor would result in 50% attenuation = 2:1 trading ratio. PMID:24866482

Keller, Arturo A; Chen, Xiaoli; Fox, Jessica; Fulda, Matt; Dorsey, Rebecca; Seapy, Briana; Glenday, Julia; Bray, Erin

2014-06-17

9

FRACTIONAL WAVE EQUATIONS WITH ATTENUATION

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

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

2013-01-01

10

The photon attenuation coefficients of barite, marble and limra

The linear attenuation coefficients ? (cm?1) and total mass attenuation coefficients ?? (cm2 g?1) of ?-rays for barite, marble and limra have been calculated using the XCOM program (Version 3.1) at energies from 1 keV to 300 MeV. The calculated results were compared with the estimation coefficients ?? based on the measured total linear attenuation coefficients (?).

I. Akkurt; S. Kilincarslan; C. Basyigit

2004-01-01

11

Technique of Measurements of Elastic Wave Attenuation Parameters

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

S. B. Teodorovich

2003-01-01

12

Temporal Variations of Seismic Coda: Attenuation-Coefficient View

NASA Astrophysics Data System (ADS)

When monitoring spatial or temporal variations of the subsurface, it is important to use properties that objectively exist and are insensitive to observational uncertainties. Although the frequency-dependent seismic coda quality factor, Qc is often found to change prior and following relation to major earthquakes and volcanic eruptions, it does not represent such a property. Qc is strongly dependent on the assumed theoretical models, which are usually insufficiently accurate for constraining the actual relationships between the geometrical spreading, anelastic dissipation, and scattering of seismic waves. This inaccuracy often leads to significant exaggeration of attenuation effects, and particularly to interpretations of temporal variations in Qc as related to changes in lithospheric scattering. To overcome this bias, we use an approach based on the temporal attenuation-coefficient, ?(f), instead of Q(f) for describing coda attenuation. Several attenuation case studies suggest that ?(f) typically linearly depends on f, with both the intercept ? = ?(0) and slope d?(f)/df = ?Qe-1 being sensitive to the physical state of the subsurface. Two published examples of temporal variations of local-earthquake coda Q are revisited: non-volcanic (near Stone Canyon in central California) and volcanic (Mt. St. Helens, Washington). In both cases, linear ?(f) patterns are found, with the effects of geometrical spreading (?) on coda attenuation being significantly stronger than those of Qe-1. At Stone Canyon, ? values ranged from 0.035 to 0.06 s-1 and Qe varies from 3000 to 10000, with ? increasing and Qe decreasing during the winter season. At Mt. St. Helens, ? ? 0.18 s-1, and Qe changed from 400 before the eruption to 750 after it. The observed temporal variations are explained by near-surface effects (seasonal variations in the non-volcanic case and gas-, magma-, and geothermal-system related in the volcanic case),which mostly affect the geometrical spreading and anelastic attenuation. Scattering does not appear to be a significant attenuation factor in these areas, or otherwise it may be indistinguishable from the intrinsic attenuation in the data.

Morozov, I. B.

2010-12-01

13

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

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

Pierce, Allan D

2009-11-01

14

Attenuation coefficients of body tissues using principal-components analysis

Principal-components analysis is used to obtain a set of parameters for dual-energy radiography that completely describes the attenuation coefficient of any tissue over a given energy range. These parameters are the weighted averages of the densities of the elements present in a substance. Principal-components (PC) parameters are calculated for several soft tissues from measured attenuation coefficients published by Phelps et

J. B. Weaver; A. L. Huddleston

2009-01-01

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

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

17

UHF Radio Wave Attenuation Factor Database

NASA Astrophysics Data System (ADS)

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

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

2007-07-01

18

NASA Astrophysics Data System (ADS)

Seismic normal mode and body wave studies find that the Earth's inner core is characterized by strong, large-scale average, cylindrically symmetric velocity anisotropy: compressional waves traversing the inner core in the North-South (polar) direction propagate faster than those travelling in the equatorial plane. Compressional body wave studies also suggest that the inner core exhibit anisotropy of attenuation, finding that compressional waves are also more strongly attenuated in the fast direction. This relationship between anisotropy of velocity and attenuation in the metallic inner core is the reverse of that observed in the silicate mantle; thus far, the existing body wave observations of anisotropic attenuation have been interpreted almost exclusively in terms of anisotropic scattering attenuation. However, body waves cannot distinguish between attenuation by intrinsic (anelastic) mechanisms and by scattering, which prevents us from understanding the physical origin of the attenuation anisotropy. Here, we elucidate attenuation anisotropy using normal modes, the low-frequency free oscillations of the planet as a whole. Due to their very long wavelengths, normal modes are transparent to scattering from small-scale heterogeneities; this makes them a particularly valuable tool for probing the intrinsic component of attenuation, and its possible anisotropy. They are also simultaneously sensitive to both compressional and shear wave properties of the inner core, unlike the various inner core body wave phases. Here, we invert our recently measured anelastic normal mode splitting function coefficients of inner core sensitive normal modes and present a new model of attenuation anisotropy of the Earth's inner core. Our model reveals that the intrinsic attenuation is anisotropic, and confirms that for compressional waves, attenuation anisotropy is indeed correlated with velocity anisotropy, with the fast direction being also more attenuating. Such anisotropy of intrinsic attenuation has the characteristics of anisotropic Zener-like relaxations within single iron crystals due to the reorientation of pairs of solute atoms, and confirms the necessity of incorporating a few per cent of light elements into the solid inner core.

Makinen, A.; Deuss, A. F.; Redfern, S. A.

2013-12-01

19

Measurement of Acoustic Attenuation and Absorption Coefficients using Thermometry

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

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

2007-01-01

20

Uranium Soft X-Ray Total Attenuation Coefficients.

National Technical Information Service (NTIS)

Uranium total attenuation coefficients were measured continuously from 0.84 to 6.0 keV and at selected higher energies using a vacuum single crystal diffractometer and flow-proportional counter. Statistical fluctuations ranged from 0.5% to 2%. The overall...

N. K. Del Grande A. J. Oliver

1981-01-01

21

Inferential Procedures for Correlation Coefficients Corrected for Attenuation.

ERIC Educational Resources Information Center

A model and computation procedure based on classical test score theory are presented for determination of a correlation coefficient corrected for attenuation due to unreliability. Delta and Monte Carlo method applications are discussed. A power analysis revealed no serious loss in efficiency resulting from correction for attentuation. (TJH)

Hakstian, A. Ralph; And Others

1988-01-01

22

Gamma-ray attenuation coefficients in bismuth borate glasses

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

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

2002-01-01

23

Radiation and attenuation of waves in a random medium

NASA Technical Reports Server (NTRS)

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

Wenzel, A. R.

1982-01-01

24

Pressure wave attenuation and dispersion in two-phase flow

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

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

1987-01-01

25

Attenuation of Shock Waves in Solids.

National Technical Information Service (NTIS)

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

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

1966-01-01

26

Apparent linear attenuation coefficients in phase contrast X-ray tomography

NASA Astrophysics Data System (ADS)

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

2011-08-01

27

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

Hideo Nishino; Tsutomu Furukawa; Sunao Takashina; Mikio Takemoto

2000-01-01

28

A novel parameterization of x-ray interaction cross-sections is developed, and employed to describe the x-ray linear attenuation coefficient and mass energy absorption coefficient for both elements and mixtures. The new parameterization scheme addresses the Z-dependence of elemental cross-sections (per electron) using a simple function of atomic number, Z. This obviates the need for a complicated mathematical formalism. Energy dependent coefficients describe the Z-direction curvature of the cross-sections. The composition dependent quantities are the electron density and statistical moments describing the elemental distribution. We show that it is possible to describe elemental cross-sections for the entire periodic table and at energies above the K-edge (from 6 keV to 125 MeV), with an accuracy of better than 2% using a parameterization containing not more than five coefficients. For the biologically important elements 1 < or = Z < or = 20, and the energy range 30-150 keV, the parameterization utilizes four coefficients. At higher energies, the parameterization uses fewer coefficients with only two coefficients needed at megavoltage energies. PMID:15083673

Midgley, S M

2004-01-21

29

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

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

Xie, Li; Li, Xingcai; Zheng, Xiaojing

2010-12-10

30

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

31

Sonic well logging tool longitudinal wave attenuator

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

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

1989-10-10

32

Representative Elementary Length to Measure Soil Mass Attenuation Coefficient

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

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

2014-01-01

33

Ultrasonic wave attenuation measurement for nondestructive evaluation of concrete

NASA Astrophysics Data System (ADS)

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

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

2010-03-01

34

Effects of Pressure on Attenuation of Seismic Waves Through Sedimentary Rocks

NASA Astrophysics Data System (ADS)

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

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

2009-05-01

35

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

36

Eddy Diffusion Coefficients due to Instabilities in Internal Gravity Waves

Internal gravity waves in the upper atmosphere tend to grow in amplitude with increasing height to maintain continuous vertical transport of wave energy. The growth of amplitude of a wave is limited by convective instabilities that must form at the heighwhere the tem- perature oscillation becomes great enough to include a superadiabatic region. This turbulence attenuates the wave by eddy

R. R. Hodges Jr.; R. R. Jr

1969-01-01

37

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

NASA Astrophysics Data System (ADS)

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

Sleep, Norman H.; Erickson, Brittany A.

2014-04-01

38

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

39

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

NASA Astrophysics Data System (ADS)

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

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

2007-05-01

40

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

41

Anomalous attenuation of extraordinary waves in ionosphere heating experiments

NASA Astrophysics Data System (ADS)

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

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

2002-12-01

42

Smart structures for shock wave attenuation using ER inserts

NASA Astrophysics Data System (ADS)

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

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

2001-08-01

43

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

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

2009-01-01

44

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

45

Factors That Attenuate the Correlation Coefficient and Its Analogs.

ERIC Educational Resources Information Center

The correlation coefficient is an integral part of many other statistical techniques (analysis of variance, t-tests, etc.), since all analytic methods are actually correlational (G. V. Glass and K. D. Hopkins, 1984). The correlation coefficient is a statistical summary that represents the degree and direction of relationship between two variables.…

Dolenz, Beverly

46

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

47

Wave attenuation in the marginal ice zone during LIMEX

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

48

The ultrasonic attenuation and kinetic coefficients in pure and random uniaxial ferromagnets with both short range exchange and long range dipolar interactions are calculated near the critical point using renormalization group theory. The dispersion and temperature dependences found differ logarithmically from classical theory and suggest new experiments. In the pure system a recent phenomenological calculation of the ultrasonic attenuation in

B. Schaub; H. G. Schuster

1978-01-01

49

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

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

2009-11-01

50

Attenuation of Seismic Waves by Grain Boundary Relaxation

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

Jackson, David D.

1971-01-01

51

Comparison of RNFL thickness and RPE-normalized RNFL attenuation coefficient for glaucoma diagnosis

NASA Astrophysics Data System (ADS)

Recently, a method to determine the retinal nerve fiber layer (RNFL) attenuation coefficient, based on normalization on the retinal pigment epithelium, was introduced. In contrast to conventional RNFL thickness measures, this novel measure represents a scattering property of the RNFL tissue. In this paper, we compare the RNFL thickness and the RNFL attenuation coefficient on 10 normal and 8 glaucomatous eyes by analyzing the correlation coefficient and the receiver operator curves (ROCs). The thickness and attenuation coefficient showed moderate correlation (r=0.82). Smaller correlation coefficients were found within normal (r=0.55) and glaucomatous (r=0.48) eyes. The full separation between normal and glaucomatous eyes based on the RNFL attenuation coefficient yielded an area under the ROC (AROC) of 1.0. The AROC for the RNFL thickness was 0.9875. No statistically significant difference between the two measures was found by comparing the AROC. RNFL attenuation coefficients may thus replace current RNFL thickness measurements or be combined with it to improve glaucoma diagnosis.

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

2013-03-01

52

Nuclear medicine tracers using {sup 111}In as a radiolabel are increasing in their use, especially in the domain of oncologic imaging. In these applications, it often is critical to have the capability of quantifying radionuclide uptake and being able to relate it to the biological properties of the tumor. However, images from single photon emission computed tomography (SPECT) can be degraded by photon attenuation, photon scattering, and collimator blurring; without compensation for these effects, image quality can be degraded, and accurate and precise quantification is impossible. Although attenuation correction for SPECT is becoming more common, most implementations can only model single energy radionuclides such as {sup 99m}Tc and {sup 123}I. Thus, attenuation correction for {sup 111}In is challenging because it emits two photons (171 and 245 keV) at nearly equal rates (90.2% and 94% emission probabilities). In this paper, we present a method of calculating a single 'effective' attenuation coefficient for the dual-energy emissions of {sup 111}In, and that can be used to correct for photon attenuation in radionuclide images acquired with this radionuclide. Using this methodology, we can derive an effective linear attenuation coefficient {mu}{sub eff} and an effective photon energy E{sub eff} based on the emission probabilities and linear attenuation coefficients of the {sup 111}In photons. This approach allows us to treat the emissions from {sup 111}In as a single photon with an effective energy of 210 keV. We obtained emission projection data from a tank filled with a uniform solution of {sup 111}In. The projection data were reconstructed using an iterative maximum-likelihood algorithm with no attenuation correction, and with attenuation correction assuming photon energies of 171, 245, and 210 keV (the derived E{sub eff}). The reconstructed tomographic images demonstrate that the use of no attenuation correction, or correction assuming photon energies of 171 or 245 keV introduces inaccuracies into the reconstructed radioactivity distribution when compared against the effective energy method. In summary, this work provides both a theoretical framework and experimental methodology of attenuation correction for the dual-energy emissions from {sup 111}In. Although these results are specific to {sup 111}In, the foundation could easily be extended to other multiple-energy isotopes.

Seo, Youngho; Wong, Kenneth H.; Hasegawa, Bruce H. [Physics Research Laboratory, Department of Radiology, University of California, San Francisco, California 94143 (United States); Physics Research Laboratory, Department of Radiology, University of California, San Francisco, California 94143 and Joint Graduate Group in Bioengineering, University of California, San Francisco and Berkeley, California 94143 (United States); Physics Research Laboratory, Department of Radiology, University of California, San Francisco, California 94143, Department of Nuclear Engineering, University of California, Berkeley, California 94720 (United States) and Joint Graduate Group in Bioengineering, University of California, San Francisco and Berkeley, California 94143 (United States)

2005-12-15

53

Seismic attenuation due to wave-induced flow

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

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

2004-01-01

54

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

55

FXG mass attenuation coefficient evaluation for radiotherapy routine

The knowledge of a radioactive beam energy or quality is important in radiotherapy once it is correlated with the type, size, and localization of the tumor. One indicative of the radiation quality is the half-value-layer (HVL), the material thickness which reduces the beam intensity to half. The analysis of a treatment beam spectrum can be inferred through its homogeneity coefficient

M. V. Moreira; A. de Almeida; R. T. Costa; L. A. Perles

2004-01-01

56

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, Yuri V.

1994-10-01

57

FXG mass attenuation coefficient evaluation for radiotherapy routine

NASA Astrophysics Data System (ADS)

The knowledge of a radioactive beam energy or quality is important in radiotherapy once it is correlated with the type, size, and localization of the tumor. One indicative of the radiation quality is the half-value-layer (HVL), the material thickness which reduces the beam intensity to half. The analysis of a treatment beam spectrum can be inferred through its homogeneity coefficient (HC, ratio between the first and the second HVL) that for values >= 0.7 has the indication to be adequate for treatments. Another important indicator of radiation quality is the mass absorption coefficient (cm2/g), related to the photons energies absorbed in a particular exposed material. Once that several materials can be used as radiation detectors for X and ? dosimetry, this work has the purpose to verify the ferrous Xylenol gelatin (FXG) material performance, through its ?/? behavior and compare it with the ?/? behavior for soft tissue. The X and ? energies where selected, in the energies normally used in radiotherapy and their spectra were evaluated using the HC coefficient. The ?/?, for the FXG material, were obtained experimentally and from simulation with X-COM and a developed routine using the GEANT4 Library. From the results from all ?/? values obtained for the FXG material, when compared to those from water, one can see similar behaviors, when one considers measurements for energies greater than 78.0 keV. These results indicate that, once the human body is composed with +/-80 % of water, the FXG for the energies used, could also be used as soft tissue simulator.

Moreira, M. V.; de Almeida, A.; Costa, R. T.; Perles, L. A.

2004-01-01

58

Polychromatic x-ray beams traveling though material are prone to beam hardening, i.e., the high energy part of the incident spectrum gets over represented when traveling farther into the material. This study discusses the concept of a mean attenuation coefficient in a formal way. The total energy fluence is one-to-one related to the traveled distance in case of a polychromatic beam moving through a given, inhomogeneous material. On the basis of this one-to-one relation, it is useful to define a mean attenuation coefficient and study its decrease with depth. Our results are based on a novel parametrization of the energy dependence of the attenuation coefficient that allows for closed form evaluation of certain spectral integrals. This approach underpins the ad hoc semianalytical expressions given in the literature. An analytical model for the average attenuation coefficient is proposed that uses a simple fit of the attenuation coefficient as a function of the photon energy as input. It is shown that a simple extension of this model gives a rather good description of beam hardening for x-rays traveling through water.

Alles, J.; Mudde, R. F. [Kramers Laboratorium voor Fysische Technology, Department of Multi-Scale Physics, Delft University of Technology, Pr. Bernhardlaan 6, 2628 Delft (Netherlands)

2007-07-15

59

Possible applications of surface electromagnetic waves to measure absorption coefficients

We show that surface electromagnetic waves can probably be used to measure the absorption coefficients of materials overlaying metals. The proposed experimental method is illustrated in the infrared frequency range using water, Teflon, and polyethylene as sample materials.

R. W. Alexander; R. J. Bell; C. A. Ward; J. H. Weaver; I. L. Tyler; B. Fischer

1973-01-01

60

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

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

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

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

2004-01-01

63

NASA Astrophysics Data System (ADS)

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

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

2010-09-01

64

Shear-wave attenuation and velocity studies in southeastern Asia

NASA Astrophysics Data System (ADS)

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

Jemberie, Alemayehu Lakew

65

NASA Astrophysics Data System (ADS)

An alternative approach is used to measure normalized mass attenuation coefficients (µ/?) of materials with unknown thickness and density. The adopted procedure is based on the use of simultaneous emission of K? and K? X-ray lines as well as gamma peaks from radioactive sources in transmission geometry. 109Cd and 60Co radioactive sources were used for the purpose of the investigation. It has been observed that using the simultaneous X- and/or gamma rays of different energy allows accurate determination of relative mass attenuation coefficients by eliminating the dependence of µ/? on thickness and density of the material.

Kurudirek, M.; Medhat, M. E.

2014-07-01

66

The paper presents a Fourier transform-based signal processing procedure for quantifying the reflection and transmission coefficients and mode conversion of guided waves diffracted by defects in plates made of viscoelastic materials. The case of the S(0) Lamb wave mode incident on a notch in a Perspex plate is considered. The procedure is applied to numerical data produced by a finite element code that simulates the propagation of attenuated guided modes and their diffraction by the notch, including mode conversion. Its validity and precision are checked by the way of the energy balance computation and by comparison with results obtained using an orthogonality relation-based processing method. PMID:17552692

Hosten, Bernard; Moreau, Ludovic; Castaings, Michel

2007-06-01

67

Attenuation of body waves in Southeastern Sicily (Italy)

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

E. Giampiccolo; S. Gresta; G. Ganci

2003-01-01

68

Attenuation of weak shock waves along pseudo-perforated walls

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

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

1998-01-01

69

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

70

Laboratory experiments on ultrasonic wave attenuation in partially frozen brines

NASA Astrophysics Data System (ADS)

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

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

2006-12-01

71

Attenuation of coda waves in Western Anatolia

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

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

1994-01-01

72

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

73

NASA Astrophysics Data System (ADS)

Build-up factors and linear attenuation coefficients of MCP-96 alloy are determined for radiation shielding and protection, using ^60Co and ^137Cs gamma emitters. A narrow collimated beam of ?-rays is passed through various thicknesses of MCP-96 alloy and the attenuation in the intensity of the beam is determined. The thickness of the 4 x 4 cm^2 blocks varies from 0.5 cm to 6 cm. Plotting the thickness of the alloy and the corresponding intensity of the beam allowed us to determine its linear attenuation coefficient. The narrow beam geometry is then replaced by broad beam geometry by removing the collimator and the radiation beam is able to interact with the MCP-96 alloy at all possible positions facing the radiation source. Additional radiations obtained by the detector as a result from the scattering of radiation develops the build-up factor. The buildup factor is then calculated using the attenuated beam received by the detector in the broad beam geometry and in the narrow beam geometry. The buildup factor is found to be dependent on the thickness of the MCP-96 attenuator, the beam energy and the source to attenuator distance. These values are providing ways for dose correction in radiation oncology and radiation shielding and protection when MCP-96 is used as tissue compensator or for radiation protection purposes.

Hopkins, Deidre; Maqbool, Muhammad; Islam, Mohammed

2009-10-01

74

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

2012-07-01

75

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

76

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

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

2003-01-01

77

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

78

Reduction of TGS image reconstruction times using separable attenuation coefficient models

The tomographic gamma scanner (TGS) method for assaying transuranic and low-level waste produces low-resolution {open_quotes}density{close_quotes} images of 208-l waste drums at two or more transmission gamma-ray energies and uses these to make detailed attenuation corrections at neighboring emission gamma-ray energies. For example, we have used the 136-, 285-, and 401-keV lines from a {sup 75}Se transmission source to correct for attenuation of the 129-, 203-, 345-, and 414-keV lines in {sup 239}Pu assays. The list can expand to 20 or more emission energies when performing multiple-isotope assays. Methods for projecting attenuation images from transmission to emission energies were recently discussed with emphasis on the problems encountered when the opacity of a sample leads to poor counting statistics. This report focuses on increases in computational speed that can be attained by using separable attenuation coefficient models.

Estep, R.J.; Prettyman, T.H.; Sheppard, G.A. [Los Alamos National Lab., Livermore, CA (United States)

1995-12-31

79

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

National Technical Information Service (NTIS)

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

B. J. Mitchell L. Cong

2007-01-01

80

Substrates for zero temperature coefficient Love wave sensors.

Microacoustic Love wave delay lines show high sensitivity to perturbations such as mass depositions on the wave-guide surface. Furthermore, because of their shear polarization, Love waves are ideally suited for liquid sensing applications. Using a Love wave delay line as feedback element in an oscillator allows the realization of viscosity sensors, and, using a chemical interface, chemical sensors, where the output signal is the oscillation frequency. To achieve a high effective sensitivity, the cross-sensitivity to temperature has to be kept low. We outline the proper choice of a material and especially focus on the influence of crystal cut and the major device design parameters (mass sensitivity and coupling coefficient) on the temperature coefficient of the sensor. PMID:18238599

Jakoby, B; Vellekoop, M J

2000-01-01

81

NASA Astrophysics Data System (ADS)

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

Bachura, Martin; Fischer, Tomas

2014-05-01

82

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

83

High-power microwave attenuator employing slow wave structure

NASA Astrophysics Data System (ADS)

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

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

2012-11-01

84

Lateral variations of coda wave attenuation in the Alps

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

85

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

86

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

87

The Sound Wave Method for Measurement of Evaporation Coefficient

NASA Astrophysics Data System (ADS)

A new method for measurement of evaporation coefficient using sound resonance experiment is proposed on the basis of a theory of molecular gas dynamics, by which the evaporation coefficient is expressed as a function of the amplitude of standing sound wave between a planar sound source and a vapor-liquid interface facing against it. To demonstrate the applicability of this method, we carried out test experiments under the condition of neither evaporation nor condensation for several initial pressures, 30, 50, 80 and 101 kPa, at room temperature. In the experiments, we measure the amplitude of standing wave with a resonant frequency generated in a cylindrical space filled with air and closed by liquid water. We utilize the second harmonics component excited by the nonlinearity of sound to determine the evaporation coefficient, thereby eliminating the electromagnetic noises from measured signals. We find that the amplitude of the second harmonics at sound resonance decreases with the decrease in the initial pressure.

Nakamura, Shigeto; Yano, Takeru; Watanabe, Masao; Fujikawa, Shigeo

88

NASA Astrophysics Data System (ADS)

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

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

2000-05-01

89

Attenuation of shock waves in copper and stainless steel

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

Harvey, W.B.

1986-06-01

90

Unsteady plane smooth wave fronts of combined growing-attenuating type

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

Yukio Sano; Isamu Miyamoto; Peter Arathoon

1997-01-01

91

A heterogeneous nonlinear attenuating full-wave model of ultrasound.

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

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

2009-03-01

92

NASA Astrophysics Data System (ADS)

Using Biot's poroelasticity theory, we derive expressions for the reflection and transmission coefficients for a plane shear wave incident on an interface separating two different poroelastic solids. The coefficients are formulated as a function of the wave incidence angle, frequency and rock properties. Specific cases calculated include the boundary between water-saturated sand and water-saturated sandstone and the gas-water interface in sand. The results show a very different interface response to that of an incident P wave. Plane SV wave incidence does not significantly excite the Biot slow P wave if the frequency of the wave is below the transition frequency. Above this frequency, an incident plane SV wave can generate a mode-converted slow Biot P wave which is actually a normal propagating wave and not highly attenuating as in the usual (diffusive) case. For an incident SV wave onto a gas-water interface, even at very high frequency, there is no significant Biot second P wave produced. For small incident angles, the gas-water interface is essentially transparent. With increasing angles, there can arise an unusual "definitive angle" in the reflection/transmission coefficient curves which is related to the change of fluid viscosity on both sides of the interface and provides a possible new means for underground fluid assessment.

Liu, Xu; Greenhalgh, Stewart

2014-04-01

93

Local energy decay for linear wave equations with variable coefficients

NASA Astrophysics Data System (ADS)

A uniform local energy decay result is derived to the linear wave equation with spatial variable coefficients. We deal with this equation in an exterior domain with a star-shaped complement. Our advantage is that we do not assume any compactness of the support on the initial data, and its proof is quite simple. This generalizes a previous famous result due to Morawetz [The decay of solutions of the exterior initial-boundary value problem for the wave equation, Comm. Pure Appl. Math. 14 (1961) 561-568]. In order to prove local energy decay, we mainly apply two types of ideas due to Ikehata-Matsuyama [L2-behaviour of solutions to the linear heat and wave equations in exterior domains, Sci. Math. Japon. 55 (2002) 33-42] and Todorova-Yordanov [Critical exponent for a nonlinear wave equation with damping, J. Differential Equations 174 (2001) 464-489].

Ikehata, Ryo

2005-06-01

94

Gamma-ray attenuation coefficients in some heavy metal oxide borate glasses at 662 keV

The linear attenuation coefficient (?) and mass attenuation coefficients (??) of glasses in three systems: xPbO(1 ? x)B2O3, 0.25PbO · xCdO(0.75 ? x)B2O3 and xBi2O3(1 ? x)B2O3 were measured at 662 keV. Appreciable variations were noted in the attenuation coefficients due to changes in the chemical composition of glasses. In addition to this, absorption cross-sections per atom were also calculated.

Atul Khanna; S. S. Bhatti; K. J. Singh; K. S. Thind

1996-01-01

95

The simultaneous PET data reconstruction of emission activity and attenuation coefficient distribution is presented, where the attenuation image is constrained by exploiting an external transmission source. Data are acquired in time-of-flight (TOF) mode, allowing in principle for separation of emission and transmission data. Nevertheless, here all data are reconstructed at once, eliminating the need to trace the position of the transmission source in sinogram space. Contamination of emission data by the transmission source and vice versa is naturally modeled. Attenuated emission activity data also provide additional information about object attenuation coefficient values. The algorithm alternates between attenuation and emission activity image updates. We also proposed a method of estimation of spatial scatter distribution from the transmission source by incorporating knowledge about the expected range of attenuation map values. The reconstruction of experimental data from the Siemens mCT scanner suggests that simultaneous reconstruction improves attenuation map image quality, as compared to when data are separated. In the presented example, the attenuation map image noise was reduced and non-uniformity artifacts that occurred due to scatter estimation were suppressed. On the other hand, the use of transmission data stabilizes attenuation coefficient distribution reconstruction from TOF emission data alone. The example of improving emission images by refining a CT-based patient attenuation map is presented, revealing potential benefits of simultaneous CT and PET data reconstruction. PMID:23648397

Panin, V Y; Aykac, M; Casey, M E

2013-06-01

96

NASA Astrophysics Data System (ADS)

The simultaneous PET data reconstruction of emission activity and attenuation coefficient distribution is presented, where the attenuation image is constrained by exploiting an external transmission source. Data are acquired in time-of-flight (TOF) mode, allowing in principle for separation of emission and transmission data. Nevertheless, here all data are reconstructed at once, eliminating the need to trace the position of the transmission source in sinogram space. Contamination of emission data by the transmission source and vice versa is naturally modeled. Attenuated emission activity data also provide additional information about object attenuation coefficient values. The algorithm alternates between attenuation and emission activity image updates. We also proposed a method of estimation of spatial scatter distribution from the transmission source by incorporating knowledge about the expected range of attenuation map values. The reconstruction of experimental data from the Siemens mCT scanner suggests that simultaneous reconstruction improves attenuation map image quality, as compared to when data are separated. In the presented example, the attenuation map image noise was reduced and non-uniformity artifacts that occurred due to scatter estimation were suppressed. On the other hand, the use of transmission data stabilizes attenuation coefficient distribution reconstruction from TOF emission data alone. The example of improving emission images by refining a CT-based patient attenuation map is presented, revealing potential benefits of simultaneous CT and PET data reconstruction.

Panin, V. Y.; Aykac, M.; Casey, M. E.

2013-06-01

97

National Technical Information Service (NTIS)

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

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

1992-01-01

98

National Technical Information Service (NTIS)

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

R. I. Hires

1983-01-01

99

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

Louisnard, O

2012-01-01

100

Effect of attenuation on backward-wave oscillation start oscillation condition

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

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

2004-01-01

101

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

NASA Astrophysics Data System (ADS)

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

Zhang, Jian; Yang, Xiaoning

2013-05-01

102

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

103

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

104

Attenuation of High-Frequency Seismic Waves in Eastern Iran

NASA Astrophysics Data System (ADS)

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

Mahood, M.

2014-03-01

105

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

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

2013-08-01

106

Remote sensing of the diffuse attenuation coefficient of ocean water. [coastal zone color scanner

NASA Technical Reports Server (NTRS)

A technique was devised which uses remotely sensed spectral radiances from the sea to assess the optical diffuse attenuation coefficient, K (lambda) of near-surface ocean water. With spectral image data from a sensor such as the coastal zone color scanner (CZCS) carried on NIMBUS-7, it is possible to rapidly compute the K (lambda) fields for large ocean areas and obtain K "images" which show synoptic, spatial distribution of this attenuation coefficient. The technique utilizes a relationship that has been determined between the value of K and the ratio of the upwelling radiances leaving the sea surface at two wavelengths. The relationship was developed to provide an algorithm for inferring K from the radiance images obtained by the CZCS, thus the wavelengths were selected from those used by this sensor, viz., 443, 520, 550 and 670 nm. The majority of the radiance arriving at the spacecraft is the result of scattering in the atmospheric and is unrelated to the radiance signal generated by the water. A necessary step in the processing of the data received by the sensor is, therefore, the effective removal of these atmospheric path radiance signals before the K algorithm is applied. Examples of the efficacy of these removal techniques are given together with examples of the spatial distributions of K in several ocean areas.

Austin, R. W.

1981-01-01

107

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

108

NASA Astrophysics Data System (ADS)

The mass attenuation coefficients of some amino acids, such as DL-aspartic acid-LR(C4H7NO4), L-glutamine (C4H10N2O3), creatine monohydrate LR(C4H9N3O2H2O), creatinine hydrochloride (C4H7N3O·HCl) L-asparagine monohydrate(C4H9N3O2H2O), L-methionine LR(C5H11NO2S), 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 0.101785 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) initially decrease and tend to be almost constant as a function of gamma-ray energy. Zeff and Neff experimental values showed good agreement with the theoretical values with less than 1% error for amino acids.

Kore, Prashant S.; Pawar, Pravina P.

2014-05-01

109

Lg waves attenuation studies over the Iranian Plateau and Zagros

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

110

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

Martin Grabner; Vaclav Kvicera

111

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

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

Michael J. Tompkins; Nikolas I. Christensen

1999-01-01

112

Attenuation of seismic waves in the Trinidad and Tobago area

NASA Astrophysics Data System (ADS)

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

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

1996-03-01

113

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

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

2014-08-01

114

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

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

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

1994-01-01

115

NASA Astrophysics Data System (ADS)

The total mass attenuation coefficients ( ? m) for SiO 2 {Quartz (1 1 0 1), Quartz (1 1 0 0) and Quartz (0 0 0 1)}, KAlSi 3O 8 {Orthoclase (0 1 0), Orthoclase (1 0 0)}, CaSO 4·2H 2O (gypsum), FeS 2 (pyrite) and Mg 2Si 2O 6 (pyroxene) natural minerals were measured at 22.1, 25.0, 59.5 and 88.0 keV photon energies. The ?- and X-rays were counted by a Si(Li) detector with a resolution of 160 eV at 5.9 keV. Atomic and electronic cross sections ( ? t and ? e), the effective atomic and electron numbers or electron densities ( Z eff and N eff) were determined using the obtained ? m values for investigated samples.

Han, I.; Demir, L.; ?ahin, M.

2009-09-01

116

Calculation of solar attenuation coefficient using ACCOS V along a critical scattering path

NASA Technical Reports Server (NTRS)

An appraisal of the optical properties of the AVHRR is made for a proposed orbital trajectory which results in an unexpected solar stray-light path; i.e., bypassing the external scan mirror and Cassegrain telescope and proceeding directly to the inner conical baffle. This stray-light path is directed onto an internal beamsplitter which, in turn, is directly observed by the detectors. Stray-light analysis, as a goal, seeks to remove or minimize the influence of such critical scattering paths. The AVHRR path is evaluated using a standard optical ray-tracing program, ACCOS V. To determine the expected sensor degradation, a calculation of the expected attenuation coefficient of scattered sunlight in the AVHRR sensor is estimated based on this important critical scattering path.

Ames, Alan J.

1989-01-01

117

Millimeter wave attenuation prediction using a piecewise uniform rain rate model

NASA Technical Reports Server (NTRS)

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

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

1980-01-01

118

Photostimulated attenuation of hypersound in superlattice.

National Technical Information Service (NTIS)

Photostimulated attenuation of hypersound in semiconductor superlattice has been investigated. It is shown that the attenuation coefficient depends on the phonon wave vector q in an oscillatory manner and that from this oscillation the band width (Delta) ...

S. Y. Mensah, F. K. Allotey, S. K. Adjepong

1992-01-01

119

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

120

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

NASA Astrophysics Data System (ADS)

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

Torres-Freyermuth, Alec; Hsu, Tian-Jian

2014-04-01

121

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

122

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

NASA Technical Reports Server (NTRS)

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

Claus, R. O.

1981-01-01

123

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

NASA Astrophysics Data System (ADS)

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

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

2011-04-01

124

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

NASA Astrophysics Data System (ADS)

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

Quintal, B.; Frehner, M.

2012-04-01

125

Diffuse Attenuation Coefficient of Downwelling Irradiance: An Evaluation of Remote Sensing Methods

NASA Technical Reports Server (NTRS)

The propagation of downwelling irradiance at wavelength lambda from surface to a depth (z) in the ocean is governed by the diffuse attenuation coefficient, K(sup -)(sub d)(lambda). There are two standard methods for the derivation of K(sup -)(sub d)(lambda) in remote sensing, which both are based on empirical relationships involving the blue-to-green ratio of ocean color. Recently, a semianalytical method to derive K(sup -)(sub d)(lambda) from reflectance has also been developed. In this study, using K(sup -)(sub d)(490) and K(sup -)(sub d)(443) as examples, we compare the K(sup -)(sub d)(lambda) values derived from the three methods using data collected in three different regions that cover oceanic and coastal waters, with K(sup -)(sub d)(490) ranging from approximately 0.04 to 4.0 per meter. The derived values are compared with the data calculated from in situ measurements of the vertical profiles of downwelling irradiance. The comparisons show that the two standard methods produced satisfactory estimates of K(sup -)(sub d)(lambda) in oceanic waters where attenuation is relatively low but resulted in significant errors in coastal waters. The newly developed semianalytical method appears to have no such limitation as it performed well for both oceanic and coastal waters. For all data in this study the average of absolute percentage difference between the in situ measured and the semianalytically derived K(sup -)(sub d) is approximately 14% for lambda = 490 nm and approximately 11% for lambda = 443 nm.

Lee, Zhong-Ping; Darecki, Miroslaw; Carder, Kendall L.; Davis, Curtiss O.; Stramski, Dariusz; Rhea, W. Joseph

2005-01-01

126

The linear attenuation coefficients and buildup factor of MCP-96 alloy were determined for (60)Co, (54)Mn, and (137)Cs gamma emitters and a NaI detector. The thickness of the MCP-96 attenuator was varied from 1 to 4 cm. A collimated beam of gamma rays was allowed to pass through various thicknesses of the MCP-96 alloy. The attenuated beam was detected by a NaI detector, and data were recorded by a multichannel analyzer. The run was repeated without the collimator for broad-beam geometry. For each run, the attenuated beam intensity was normalized by the intensity of the unattenuated incident beam obtained by removing the attenuators. Linear attenuation coefficients were determined by plotting of the intensity of the collimated beam against the attenuator thickness. For every thickness of the alloy, the ratio of the attenuated to the unattenuated beam was found to be higher in broad-beam geometry as compared to the same ratio in narrow-beam geometry. We used the difference in these ratios in broad and narrow-beam geometries to calculate the buildup factor. The buildup factor was found to increase with beam energy and attenuator thickness. Variation in the source-to-detector distance gave a lower value of the buildup factor for a small and a large distance and a higher value for an intermediate distance. The buildup factor was found to be greater than 1 in all cases. We conclude that the buildup factor must be calculated and incorporated for dose correction and precision when the MCP-96 alloy is used for tissue compensation or radiation shielding and protection purposes. PMID:22585280

Hopkins, Deidre N; Maqbool, Muhammad; Islam, Mohammed S

2012-07-01

127

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

128

Ultrasonic Attenuation in Lanthanum Monochalcogenides

Ultrasonic attenuation due to phonon-phonon interaction and thermoelastic relaxation are studied in Lanthanum Monochalcogenides in direction at different higher temperatures. For evaluation of ultrasonic absorption coefficients the second and third order elastic constants (SOEC) and (TOEC) are also calculated. Shear wave attenuation shows maximum along propagation direction with polarized along and the attenuation increases at higher temperatures. Thermo-elastic loss is

Raja Ram Yadav; Devraj Singh

2001-01-01

129

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

130

Subduction zone guided waves: 3D modelling and attenuation effects

NASA Astrophysics Data System (ADS)

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

Garth, T.; Rietbrock, A.

2013-12-01

131

The limiting uncertainty in recent high accuracy measurements of the mass attenuation coefficient is the measurement of the integrated column density. An improvement in the design of the absorption foil holder is described which reduces the integrated column density uncertainty. The new design allows the edges of the foil to be more accurately mapped by the X-ray beam by reducing

Nicholas A. Rae; Jack L. Glover; Christopher T. Chantler

2010-01-01

132

Stress Wave attenuation in SiC3D/Al Composite

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

133

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

NASA Astrophysics Data System (ADS)

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

Suzuki, H.; Matsushima, J.

2010-12-01

134

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

2010-04-15

135

NASA Astrophysics Data System (ADS)

We proposed a method of quantifying the effective attenuation coefficients of optical absorbers which uses the continuous wavelet transform to calculate the time-resolved frequency spectra of photoacoustic (PA) signals. In order to apply the method to blood oxygenation monitoring of blood vessels, this study discusses how to reduce the effects of blood vessel diameters, which influences on the time resolved frequency spectra of PA signals. Numerical simulations which calculate the PA signals produced from blood vessel phantoms with various diameters were performed. The simulations revealed that the frequency of PA signal became independent from the vessel diameters by measuring the PA signal from small area. The frequencies of simulated PA signals were proportional to the effective attenuation coefficients with a correlation coefficient of 0.99, and a slope of 0.035 MHz/cm-1 under condition that the measurement area was 4.0 mm at a frequency of 1.5 MHz. Thus we used the focused acoustic sensor of which focusing the foregoing measurement area. It consisted of a P(VDF-TrFE) film, which was characterized by broad frequency band. As results of experiments using the focused acoustic sensor, the frequencies of PA signals produced from blood vessel phantoms were proportional to the effective attenuation coefficients with correlation coefficient of 0.96 although the frequencies were suffered from deviations of 0.135 MHz, which corresponded to the effective attenuation coefficient of 3.46 cm-1. Since the large deviations were caused by experimental factors such as sensor alignment, it is required to improve robustness to the experimental factors.

Hirasawa, T.; Okawa, S.; Fujita, M.; Kushibiki, T.; Ishihara, M.

2014-03-01

136

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

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

2009-01-01

137

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

138

National Technical Information Service (NTIS)

The document contains the following two papers: X-ray attenuation coefficient and photoelectric cross sections of Sn for the Energy Range 3.3 KeV to 29.1 KeV - by Wang Dachun, Yang Hua and Luo Pingan. X-ray attenuation coefficients and photoelectric cross...

Wang Dachun Yang Hua Luo Pingan Ding Xunliang Wang Xinfu

1991-01-01

139

Attenuation and distortion of compression waves propagating in very long tube

NASA Astrophysics Data System (ADS)

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

Nakamura, Shinya; Sasa, Daisuke; Aoki, Toshiyuki

2011-03-01

140

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

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

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

2009-09-01

141

Attenuation of electromagnetic wave propagation in sandstorms incorporating charged sand particles

NASA Astrophysics Data System (ADS)

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

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

2005-06-01

142

NASA Astrophysics Data System (ADS)

The half-value thicknesses, linear and mass attenuation coefficients of biological samples such as bone, muscle, fat and water have been measured at 140, 364 and 662 keV ?-ray energies by using the ATOMLABTM-930 medical spectrometer. The ?-rays were obtained from 99mTc, 131I and 137Cs ?-ray point sources. Also theoretical calculations have been performed in order to obtain the half-value thicknesses and, mass and linear attenuation coefficients at photon energies 0.001 keV 20 MeV for bone, muscle and water samples. The calculated value and the experimental results of this work and the other results in literature are found to be in good agreement.

Akar, A.; Balta?, H.; Çevik, U.; Korkmaz, F.; Okumu?o?lu, N. T.

2006-11-01

143

NASA Technical Reports Server (NTRS)

Management of water resources such as a reservoir requires using analytical models which describe such parameters as the suspended sediment field. To select or develop an appropriate model requires making many measurements to describe the distribution of this parameter in the water column. One potential method for making those measurements expeditiously is to measure light transmission or turbidity and relate that parameter to total suspended solids concentrations. An instrument which may be used for this purpose was calibrated by generating curves of transmission measurements plotted against measured values of total suspended solids concentrations and beam attenuation coefficients. Results of these experiments indicate that field measurements made with this instrument using curves generated in this study should correlate with total suspended solids concentrations and beam attenuation coefficients in the water column within 20 percent.

Usry, J. W.; Whitlock, C. H.

1981-01-01

144

This paper reports a method for measuring the specific acoustic impedance or absorption coefficient of acoustic material using a standing wave tube without a microphone. The method was validated by tests conducted in a normal standing wave or impedance tube—a straight solid-wall tube with a speaker and a material specimen perpendicularly mounted at each end, respectively. Assuming that sound waves

Dewei Peng; Shih-Fu Ling

2005-01-01

145

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

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

2009-01-01

146

Attenuation of terahertz transmission through rain

NASA Astrophysics Data System (ADS)

Based on the Marshall-Palmer, Weibull raindrop size distribution and Mie electromagnetic scattering model, the relationships of attenuation coefficient of terahertz (THz) atmospheric window waves with precipitation rate and temperature are studied. Furthermore, combined with the loss of electromagnetic wave transmission in free space, the attenuation of THz communication and the transmission of current mobile communication signals through rain are compared and analyzed. The results show that the attenuation coefficient of THz transmission is increased with increasing precipitation rate, the difference of attenuation coefficient at different THz window waves is small, and the maximum difference is about 3 dB. The rain attenuation of THz wave is first decreased and then increased with increasing temperature, but the temperature has little effect on it. The attenuation of THz wave through rain is much larger than that of mobile communication signal.

Luo, Yi; Huang, Wan-xia; Luo, Zi-yi

2012-07-01

147

The mass attenuation coefficients of the 59.54keV radiation of (241)Am point source in boron ores such as tincal, ulexite and colemanite were determined experimentally by a scintillation detector and theoretically. Since boron ores contain boron, hydrogen, and a lot of elements, they may be used as shielding against neutrons and gammas simultaneously, e.g. for shielding (241)Am/Be neutron sources, as they emit both gammas and neutrons. PMID:19800806

Demir, Faruk

2010-01-01

148

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

149

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

150

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

151

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

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

2010-01-01

152

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

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

M. Frehner; S. M. Schmalholz

2009-01-01

153

NASA Technical Reports Server (NTRS)

The linearized attenuation theory of NACA Technical Note 3375 is modified in the following manner: (a) an unsteady compressible local skin-friction coefficient is employed rather than the equivalent steady-flow incompressible coefficient; (b) a nonlinear approach is used to permit application of the theory to large attenuations; and (c) transition effects are considered. Curves are presented for predicting attenuation for a shock pressure ratio up to 20 and a range of shock-tube Reynolds numbers. Comparison of theory and experimental data for shock-wave strengths between 1.5 and 10 over a wide range of Reynolds numbers shows good agreement with the nonlinear theory evaluated for a transition Reynolds number of 2.5 X 10(exp 5).

Trimpi, Robert L.; Cohen, Nathaniel B.

1961-01-01

154

NASA Astrophysics Data System (ADS)

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

Huang, Jiankun; Shi, Zhifei

2013-09-01

155

Velocity-Space Diffusion Coefficients Due to Full-Wave ICRF Fields in Toroidal Geometry

Jaeger et al. have calculated bounce-averaged QL diffusion coefficients from AORSA full-wave fields, based on non-Maxwellian distributions from CQL3D Fokker-Planck code. A zero banana-width approximation is employed. Complementing this calculation, a fully numerical calculation of ion velocity diffusion coefficients using the full-wave fields in numerical tokamak equilibria has been implemented to determine the finite orbit width effects. The un-approximated Lorentz equation of motion is integrated to obtain the change in velocity after one complete poloidal transit of the tokamak. Averaging velocity changes over initial starting gyro-phase and toroidal angle gives bounce-averaged diffusion coefficients. The coefficients from the full-wave and Lorentz orbit methods are compared for an ITER DT second harmonic tritium ICRF heating case: the diffusion coefficients are similar in magnitude but reveal substantial finite orbit effects.

Harvey, R.W. [CompX, P.O. Box 2672, Del Mar, CA 92014-5672 (United States); Jaeger, F.; Berry, L.A.; Batchelor, D.B.; D'Azevedo, E.; Carter, M.D. [ORNL, Oak Ridge, TN (United States); Ershov, N.M.; Smirnov, A.P. [Moscow State Univ. (Russian Federation); Bonoli, P.; Wright, J.C. [PSFC, MIT, Boston, MA (United States); Smithe, D.N. [ATK-Mission Research (United States)

2005-09-26

156

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

Seldis, Thomas

2013-09-01

157

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

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

Kimura, Masao

2014-07-01

158

NASA Astrophysics Data System (ADS)

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

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

2005-12-01

159

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

160

National Technical Information Service (NTIS)

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 e...

J. H. Hubbell

1994-01-01

161

Dynamic aspects of apparent attenuation and wave localization in layered media

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

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

2008-01-01

162

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

163

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

164

Accurate measurements have been made to determine radiation transmission of concretes produced with barite, colemanite and normal aggregate by using beam transmission method for 0.663MeV ?-rays energy of 137Cs radioactive isotopes by using NaI(Tl) scintillation detector. Linear and mass attenuation coefficients of thirteen heavy- and four normal-weight concretes were calculated. It was determined that the linear attenuation coefficient (?, cm?1)

F. Demir; G. Budak; R. Sahin; A. Karabulut; M. Oltulu; A. Un

2011-01-01

165

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

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

1983-01-01

166

We report on the investigation of magnetic field induced charge density waves and Hall coefficient sign reversal in a quasi-two-dimensional electronic system of highly oriented pyrolytic graphite under very strong magnetic field. The change of Hall sign coefficient from negative to positive occurs at low temperature and high magnetic field just after the charge density wave transition, suggesting the role of hole-like quasi-particles in this effect. Angular dependent measurements show that the charge density wave transition and Hall sign reversal fields follow the magnetic field component along the c-axis of graphite. PMID:21403339

Kumar, Amit; Poumirol, Jean-Marie; Escoffier, Walter; Goiran, Michel; Raquet, Bertrand; Claude Pivin, Jean

2010-11-01

167

For medical applications of ultrasound inside the brain, it is necessary to understand the relationship between the apparent density of skull bone and its corresponding speed of sound and attenuation coefficient. Although there have been previous studies exploring this phenomenon, there is still a need to extend the measurements to cover more of the clinically relevant frequency range. The results of measurements of the longitudinal speed of sound and attenuation coefficient are presented for specimens of human calvaria. The study was performed for the frequencies of 0.27, 0.836, 1.402, 1.965 and 2.525 MHz. Specimens were obtained from fresh cadavers through a protocol with the Division of Anatomy of the University of Toronto. The protocol was approved by the Research Ethics Board of Sunnybrook Health Sciences Centre. The specimens were mounted in polycarbonate supports that were marked for stereoscopic positioning. Computer tomography (CT) scans of the skulls mounted on their supports were performed, and a three-dimensional skull surface was reconstructed. This surface was used to guide a positioning system to ensure the normal sound incidence of an acoustic signal. This signal was produced by a focused device with a diameter of 5 cm and a focal length of 10 cm. Measurements of delay in time of flight were carried out using a needle hydrophone. Measurements of effective transmitted energy were carried out using a radiation force method with a 10 ?g resolution scale. Preliminary functions of speed of sound and attenuation coefficient, both of which are related to apparent density, were established using a multi-layer propagation model that takes into account speed of sound, density and thickness of the layer. An optimization process was executed from a large set of random functions and the best functions were chosen for those ones that closest reproduced the experimental observations. The final functions were obtained after a second pass of the optimization process was executed, but this time using a finite-difference time-difference solution of the Westervelt equation, which is more precise than the multi-layer model but much more time consuming for computation. For six of seven specimens, measurements were carried out on five locations on the calvaria, and for the other specimen three measurements were made. In total, measurements were carried out on 33 locations. Results indicated the presence of dispersion effects and that these effects are different according to the type of bone in the skull (cortical and trabecular). Additionally, both the speed of sound and attenuation showed dependence on the skull density that varied with the frequency. Using the optimal functions and the information of density from the CT scans, the average values (±s.d.) of the speed of sound for cortical bone were estimated to be 2384(±130), 2471(±90), 2504(±120), 2327(±90) and 2053(±40) m s?1 for the frequencies of 270, 836, 1402, 1965 and 2526 kHz, respectively. For trabecular bone, and in the same order of frequency values, the speeds of sound were 2140(±130), 2300(±100), 2219(±200), 2133(±130) and 1937(±40) m s?1, respectively. The average values of the attenuation coefficient for cortical bone were 33(±9), 240(±9) and 307(±30) Np m?1 for the frequencies of 270, 836, and 1402, respectively. For trabecular bone, and in the same order of frequency values, the average values of the attenuation coefficient were 34(±13), 216(±16) and 375(±30) Np m?1, respectively. For frequencies of 1.965 and 2.525 MHz, no measurable radiation force was detected with the setup used.

Pichardo, Samuel; Sin, Vivian W; Hynynen, Kullervo

2011-01-01

168

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

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

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

2013-10-01

169

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

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

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

2013-10-15

170

NASA Astrophysics Data System (ADS)

The fundamental-mode Love and Rayleigh waves generated by 57 earthquakes which occurred in the north and central Indian Ocean (extending to 40°S) and recorded at Indian seismograph and other WWSSN stations such as HOW, SHL, VIS, MDR, HYB, KOD, CHG, TRD, POO, BOM, GOA, NDI, NIL and QUE are analysed. Love and Rayleigh wave attenuation coefficients are estimated at periods of 15-100 s using the spectral amplitude of these waves for 98 different paths across the Bay of Bengal Fan, the Arabian Fan, and the north and central Indian Ocean. The large standard deviations observed in the surface wave attenuation coefficients may be a result of regional variation of the attenuative properties of the crust and upper mantle beneath these regions. Love wave attenuation coefficients are found to vary from 0.000 03 to 0.000 45 km -1 for the Bay of Bengal Fan; from 0.000 03 to 0.000 85 km -1 for the Arabian Fan; and from 0.000 03 to 0.000 35 km -1 for the north and central Indian Ocean. Similarly, Rayleigh wave attenuation coefficients vary from 0.000 03 to 0.0004 km -1 for the Bay of Bengal Fan; from 0.000 06 to 0.0007 km -1 for the Arabian Fan; and from 0.000 03 to 0.0007 km -1 for the north and central Indian Ocean. Backus and Gilbert inversion theory is applied to these surface wave attenuation data to obtain average Q-1 models for the crust and upper mantle beneath the Bay of Bengal, the Arabian Fan, and the north and central Indian Ocean. Inversion of Love and Rayleigh wave attenuation data shows a high-attenuation zone centred at a depth of > 120 km ( Q? ? 125) for the Bay of Bengal Fan. Similarly, a high-attenuation zone ( Q? ? 40-70) occurs at a depth of 60-160 km for the Arabian Fan at 100-160 km ( Q? ? 115) for the Indian Ocean off Ninetyeast Ridge, and at 80-160 km ( Q? ? 80) for the Indian Ocean across the Ninetyeast Ridge. The Q?-1 models show a lithosphere thickness of 120 km beneath the Bay of Bengal Fan. Similarly, lithosphere thickness of 70, 100 and 80 km is estimated beneath the Arabian Fan, and the Indian Ocean off Ninetyeast Ridge and across Ninetyeast Ridge, respectively. The base of the lithosphere is identified as the depth at which there is a significant increase in the Q?-1 value, which attains its maximum value in the asthenosphere. The thinning of Indian lithosphere beneath the Arabian Fan suggests high temperature below Moho depth (60 km from surface) which has caused a high-attenuation zone at this shallow depth.

Singh, D. D.

171

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

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

THE ATTENUATION OF HYDROMAGNETIC WAVES IN THE IONOSPHERE

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

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

1962-01-01

174

Propagation and Attenuation of Lg Waves in South America.

National Technical Information Service (NTIS)

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

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

1989-01-01

175

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

176

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

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

Brad M. Beadle; Jacek Jarzynski

2001-01-01

177

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

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

Michael Fehler; Peter Roberts; Tom Fairbanks

1988-01-01

178

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

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

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

1994-02-01

179

NASA Technical Reports Server (NTRS)

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

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

1970-01-01

180

Attenuation of coda waves in the Aswan Reservoir area, Egypt

NASA Astrophysics Data System (ADS)

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

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

2010-09-01

181

Measurements of the semi-diurnal drag coefficient over sand waves

NASA Astrophysics Data System (ADS)

Simultaneous measurements of tidal flow and pressure gradient over a 10 km distance have been used to estimate the frictional drag coefficient over sand waves in the southern North Sea. The measurements were made over a 27-day period in October-November 1988 at 52°10'N, 3°46'E, within a field of essentially two-dimensional sand waves approximately 3 m high and of wavelength 250 m. The M 2 drag coefficient for depth-averaged flow normal to sand wave crests is found to be 2.95 × 10 -3, in good agreement with values used in numerical models of the region. The uncertainty in this value is estimated to be of the order of 10%, primarily due to possible errors in the phase of the flow relative to the pressure gradient. The time series of daily-averaged semi-diurnal ( Z 2) drag coefficients over the 27-day period shows surprisingly little correlation with nearbed wave orbital velocities. The time of highest waves is associated with a decrease in drag coefficient rather than the increase predicted by most wave-current interaction theories and some previous observations. It is suggested that this behaviour is caused by stratification near the bed due to sediment resuspension under high waves. Predictions using the GLENN and GRANT (1987, Journal of Geophysical Research, 92, 8244-8264) theory provide qualitative support for this hypothesis, though the magnitude of the predicted effect is smaller than observed. The relative insensitivity of the drag coefficient to wave conditions suggests that incorporating simple wave-current algorithms into numerical models may be misleading.

Huntley, David A.; Nicholls, Robert J.; Liu, Chunlei; Dyer, Keith R.

1994-04-01

182

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

2013-02-01

183

The activity concentrations of 226Ra, 232Th, and 40K in lime and gypsum samples used as building materials in Turkey were measured using gamma spectrometry. The mean activity concentrations of 226Ra, 232Th, and 40K were found to be 38±16, 20±9, and 156±54 Bq kg(-1) for lime and found to be 17±6, 13±5, and 429±24 Bq kg(-1) for gypsum, respectively. The radiological hazards due to the natural radioactivity in the samples were inferred from calculations of radium equivalent activities (Raeq), indoor absorbed dose rate in the air, the annual effective dose, and gamma and alpha indices. These radiological parameters were evaluated and compared with the internationally recommended limits. The experimental mass attenuation coefficients (?/?) of the samples were determined in the energy range 81-1,332 keV. The experimental mass attenuation coefficients were compared with theoretical values obtained using XCOM. It is found that the calculated values and the experimental results are in good agreement. PMID:19921450

Damla, Nevzat; Cevik, U?ur; Kobya, Ali Ihsan; Celik, Ahmet; Celik, Necati

2010-11-01

184

Attenuation of coda waves in the Garhwal Himalaya, India

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

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

1995-01-01

185

Periodic Semifolded Solitary Waves for (2+1)-Dimensional Variable Coefficient Broer Kaup System

NASA Astrophysics Data System (ADS)

Applying the extended mapping method via Riccati equation, many exact variable separation solutions for the (2+1)-dimensional variable coefficient Broer Kaup equation are obtained. Introducing multiple valued function and Jacobi elliptic function in the seed solution, special types of periodic semifolded solitary waves are derived. In the long wave limit these periodic semifolded solitary wave excitations may degenerate into single semifolded localized soliton structures. The interactions of the periodic semifolded solitary waves and their degenerated single semifolded soliton structures are investigated graphically and found to be completely elastic.

Huang, Wen-Hua

2008-06-01

186

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

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

Morin, Claire; Hellmich, Christian

2014-07-01

187

NASA Astrophysics Data System (ADS)

Low attenuation of Sezawa modes operating at GHz frequencies in ZnO/GaAs systems immersed in liquid helium has been observed. This unexpected behaviour for Rayleigh-like surface acoustic waves (SAWs) is explained in terms of the calculated depth profiles of their acoustic Poynting vectors. This analysis allows reproduction of the experimental dispersion of the attenuation coefficient. In addition, the high attenuation of the Rayleigh mode is compensated by the strengthening provided by the ZnO layer. The introduction of the ZnO film will enable the operation of SAW-driven single-photon sources in GaAs-based systems with the best thermal stability provided by the liquid helium bath.

Pedrós, J.; García-Gancedo, L.; Ford, C. J. B.; Griffiths, J. P.; Jones, G. A. C.; Flewitt, A. J.

2013-01-01

188

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

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

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

1988-05-10

189

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

NASA Technical Reports Server (NTRS)

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

Jackson, D. D.

1971-01-01

190

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

191

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

2013-06-01

192

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

193

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

194

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

NASA Astrophysics Data System (ADS)

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

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

2014-02-01

195

Attenuation of shock waves propagating through nano-structured porous materials

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

196

Estimation of shear wave velocity profiles by the inversion of spatial autocorrelation coefficients

NASA Astrophysics Data System (ADS)

The subsurface shear-wave velocity (Vs) is considered to be a key parameter for site characterization and assessment of earthquake hazard because of its great influence on local ground-motion amplification. Array microtremor measurements are widely used for the estimation of shear-wave velocities. Compared to other methods such as frequency-wavenumber (f-k) methods, the spatial autocorrelation (SPAC) method requires fewer sensors and thus is relatively easier to implement and gives robust estimations of shear-wave velocity profiles for depths down to a few hundred meters. The quantity derived from observed data is the SPAC coefficient, which is a function of correlation distance, frequency and phase velocity. Generally, estimation of Vs profiles is a two stage process: Estimation of the dispersion data from the SPAC coefficients and inversion of the dispersion data for shear-wave velocity structure. In this study, instead of inverting dispersion curves, a more practical approach is used; that is, observed SPAC coefficients are directly inverted for the S-wave velocities. A synthetic case and a field data application are presented to test the potential of the inversion algorithm. We obtain an iterative damped least-squares solution with differential smoothing. The differential smoothing approach constrains the change in shear-wave velocities of the adjacent layers and thus stabilizes the inversion.

Kocao?lu, Argun H.; F?rtana, Karolin

2011-10-01

197

Physics-based ULF Wave Radial Diffusion Coefficients in the Van Allen Belts

NASA Astrophysics Data System (ADS)

Power in the Pc5 ULF wave band is believed to have strong impact on the acceleration and transport of MeV energy electrons in the outer radiation belt. Typically, radial belt diffusion coefficients are defined from empirical approaches, based on observed flux variations and param-eterised by geomagnetic indices. We report the results of new ULF wave diffusion coefficients derived from statistical analyses of ULF wave power from ground-based magnetometers from the CARISMA chain, as well as from in-situ data from GOES and THEMIS. These results are compared to previous empirical results, and the dependence of the wave-driven coefficients on energy and solar wind speed presented. The ULF wave physics model illustrates the importance of global measurements for identifying dominant or active acceleration mechanisms. Future in-situ radiation belt missions such as the Canadian Space Agency Outer Radiation Belt Injec-tion, Transport, Acceleration and Loss Satellite (ORBITALS) will enable these physics-based models to be tested and the relative importance of various ULF and VLF wave acceleration and loss processes established. In combination with the approved NASA LWS RBSP mission, and the proposed Japanese ERG satellite, the ORBITALS-RBSP-ERG three petal constella-tion together with supporting ground-based and geosynchronous measurements will resolve the spatio-temporal ambiguities and global dynamics and morphology of the Earths radiation belts.

Mann, Ian; Rae, Jonathan; Murphy, Kyle; Ozeke, Louis; Milling, David; Chan, Anthony; Elkington, Scot; Angelopoulos, Vassilis

198

Dual-energy x-ray computed tomography (DECT) has the capability to decompose attenuation coefficients using two basis functions and has proved its potential in reducing beam-hardening artifacts from reconstructed images. The method typically involves two successive scans with different x-ray tube voltage settings. This work proposes an approach to dual-energy imaging through x-ray beam filtration that requires only one scan and a single tube voltage setting. It has been implemented in a preclinical microCT tomograph with minor modifications. Retrofitting of the microCT scanner involved the addition of an automated filter wheel and modifications to the acquisition and reconstruction software. Results show that beam-hardening artifacts are reduced to noise level. Acquisition of a ?-Compton image is well suited for attenuation-correction of PET images while dynamic energy selection (4D viewing) offers flexibility in image viewing by adjusting contrast and noise levels to suit the task at hand. All dual-energy and single energy reference scans were acquired at the same soft tissue dose level of 50 mGy.

Taschereau, R; Silverman, R W; Chatziioannou, A F

2010-01-01

199

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

200

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

201

Determination of the optical absorption coefficient via analysis of laser-generated plate waves

A technique has been demonstrated which measures the optical absorption coefficient in weakly to moderately absorbing homogeneous isotropic elastic plates. This technique involves generating plate waves with a pulsed Nd:YAG laser and then detecting the disturbances in the acoustic far field where the majority of the acoustic energy has been coupled into the first symmetric, so, and antisymmetric, a o,

David H. Hurley; James B. Spicer; R. Jay Conant; Ken L. Telschow

1997-01-01

202

Inverse problem for a class of one-dimensional wave equations with piecewise constant coefficients

We consider the problem of reconstructing the piecewise constant coefficient of a one-dimensional wave equation on the halfline from the knowledge of the displacement on the boundary caused by an impulse at time zero. This problem is formulated as a nonlinear optimization problem. The objective function of this optimization problem has several special features that have been exploited in building

A. Bartoloni; C. Lodovici; F. Zirilli

1993-01-01

203

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

204

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,

Ediguer E. Franco; Julio Adamowski; Flavio Buiochi

2010-01-01

205

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.

François Saint-Pierre; Patrice. Rivard; Gérard Ballivy

2007-01-01

206

Experimental study of P-wave attenuation in partially frozen brine

NASA Astrophysics Data System (ADS)

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

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

2005-12-01

207

NASA Astrophysics Data System (ADS)

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

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

2005-09-01

208

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, Z eff, effective electron number, N eff, 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

209

NASA Astrophysics Data System (ADS)

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

Kobayashi, Genyuu; Mamada, Yutaka; Tsutsumi, Hideaki

210

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

211

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

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

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

2012-11-01

212

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

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

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

2012-01-01

213

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 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 radiation emitted from the lung. Four methods were employed in our experiments: (1) by light microscopic counting of discrete carbonized polystyrene particles with a count median diameter (CMD) of 2.85 microns and tagged with cobalt-57, we delineated a linear relationship between the number of particles and the emitted counts per minute (cpm) detected by well scintillation counting; (2) from this conversion relationship we determined the number of particles inhaled and deposited in the lungs by scintillation counting fragments of dissected lung at autopsy; (3) we defined a linear association between the number of particles or microcuries contained in the lung and the emitted radiation as cpm detected by a gamma scintillation camera in the live sheep prior to autopsy; and (4) we compared the emitted radiation from the lungs of the live sheep to that of whole excised lungs in order to calculate the attenuation coefficient (ac) of the chest wall. The mean external counting efficiency was 4.00 X 10(4) particles/cpm (5.1 X 10(-3) microCi/cpm), the camera collection efficiency was 1 cpm/10(4) disintegrations per minute (dpm), and the ac had a mean of 0.178/cm. The external counting efficiency remained relatively constant over a range of particles and microcuries, permitting a more general use of this ratio to estimate number of particles or microcuries depositing after inhalation in a large mammalian lung if a similarly collimated gamma camera system is used.

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

1989-01-01

214

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

215

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

216

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

NASA Astrophysics Data System (ADS)

On July 17, 2011 a ML 4.8 earthquake occurred in the PO valley at a 48 km epicentral distance from a seismic station located at Palazzo Te (Mantova). The station is situated on deep quaternary sediments: the uppermost layers are mainly composed of clay and silty clay with interbedded sands; the Robertson index is 1.4

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

2013-12-01

217

NASA Astrophysics Data System (ADS)

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

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

2008-02-01

218

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

219

We describe a new approach to recover an absolute optical absorption coefficient from measured photoacoustic signals based on an exact solution of the wave equation. We present a numerical model to describe the detection of photoacoustic waves by introducing a point spread function of a photoacoustic measuring system. This model is employed in an iterative fitting procedure in order to recover an absolute optical absorption coefficient. In addition, the fitting procedure utilizes the ratios of the amplitudes of the characteristic peaks of photoacoustic signals as the input, as opposed to using the total measured photoacoustic data. Such an arrangement increases computational speed and reduces the influence of signals from neighboring objects. The proposed method is then verified both numerically and experimentally on the gel samples, from which the accuracy is found to be in the range -5.2% to 4.8%. PMID:18854608

Wang, Yi; Wang, Ruikang

2008-11-01

220

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

221

The characterization of stress states in materials is often necessary in some industrial application. The ultrasonic methods can be potentially convenient since stress states inside materials can be obtained even if materials are opaque. Nevertheless, the knowledge of acousto-elastic coefficients is generally necessary to estimate residual stresses by ultrasonic methods, but the experimental determination of these acousto-elastic coefficients can be difficult in some cases. In this paper, Rayleigh wave (RW) acousto-elastic coefficients of an orthotropic material are theoretically determined according to its characteristics, i.e. the density and the secondand third-order elastic constants. Then, these RW acousto-elastic coefficients are directly measured during an experimental stage and a comparison between calculated and measured coefficients is realized. This study allows on the one hand to check the theoretical development and on the other hand to show that it is possible to calculate acousto-elastic coefficients theoretically from intrinsic characteristics of the material rather than measuring them directly during a calibration phase which is sometimes long and difficult to realize. PMID:12109548

Duquennoy, Marc; Ouaftouh, Mohammadi; Ourak, Mohamed; Jenot, Frédéric

2002-06-01

222

Measurement of acoustic absorption coefficient with phase-conjugate ultrasonic waves

Experimental results on measurements of the acoustic absorption coefficient in test objects that were obtained with two methods, i.e., a standard insert-substitution method and a modification thereof using phase-conjugate waves, are given. Samples of gelatin and biological tissue in vitro (porcine muscle fibers) were used as test objects. Gelatin objects were manufactured that were both homogeneous and with inhomogeneities in

N. V. Smagin; L. M. Krutyansky; A. P. Brysev; F. V. Bunkin

2011-01-01

223

Measurement of acoustic absorption coefficient with phase-conjugate ultrasonic waves

Experimental results on measurements of the acoustic absorption coefficient in test objects that were obtained with two methods,\\u000a i.e., a standard insert-substitution method and a modification thereof using phase-conjugate waves, are given. Samples of\\u000a gelatin and biological tissue in vitro (porcine muscle fibers) were used as test objects. Gelatin objects were manufactured\\u000a that were both homogeneous and with inhomogeneities in

N. V. Smagin; L. M. Krutyansky; A. P. Brysev; F. V. Bunkin

2011-01-01

224

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

NASA Astrophysics Data System (ADS)

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

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

2001-07-01

225

Correlation Between Drag Coefficient and Wave Slope at Extremely High Wind Speeds

NASA Astrophysics Data System (ADS)

Reliable predictions of the intensity of a tropical cyclone need accurate estimates of momentum and heat transfer rates across the sea surface. For the momentum transfer across the sea surface, it is well known that that drag coefficient (CD) monotonically increases with increasing the wind speed U10 at normal wind speeds. On the other hands, at extremely high wind speeds, recent field measurements [Powell et al., Nature, 2003] in a tropical cyclone showed that CD decreases with increasing U10, and recent laboratory data showed almost constant values of CD. Such dependence of CD on U10 is possibly changed by difference between ocean surface conditions at normal (U10 < 35 m/s) and extremely high (U10 > 35 m/s) wind speeds. Therefore, we aim to investigate how the dependence of wind wave parameters on wind speeds is different between normal and extremely high wind speeds, by using high-speed wind-wave tank [Takagaki et al., GRL, 2012]. Figure 1 shows the power spectrum of water-level fluctuation at U10 = 68 m/s. Although the spectral slope at high frequency region is known to be -5 at normal wind speeds of U10 < 35m/s, the present slope shows -3 at the extremely high wind speed. This means that the wind waves are broken by high wind shear and the power spectrum at the significant wave frequency is damped. Figure 2 shows the relationship between the wave slope and U10. At normal wind speeds, the wave slope increases with increasing U10, but it saturates at U10 ~ 20 m/s. Then, the wave slope gradually decreases at extremely high wind speeds. The results suggest that the wave slope is damped by wave breaking due to high wind shear and then the damping of the wave slope at extremely high wind speeds causes the trend of drag coefficient against U10 (see Figure 1a of Takagaki et al. [2012, GRL]). Figure 1. Spectrum of water-level fluctuation at U10 = 68m/s. Figure 2. Wave slope HS/LS against U10.

Takagaki, N.; Iwano, K.; Komori, S.

2013-12-01

226

Photostimulated attenuation of hypersound in superlattices

NASA Astrophysics Data System (ADS)

Photostimulated attenuation of hypersound in semiconductor superlattices has been investigated theoretically. It is shown that the attenuation coefficient depends on the phonon wave vector qin an oscillatory manner and that from this oscillation the band width ? of the superlattice can be found.

Mensah, S. Y.; Allotey, F. K.; Adjepong, S. K.; Mensah, N. G.

1997-12-01

227

Photostimulated attenuation of hypersound in superlattice

NASA Astrophysics Data System (ADS)

Photostimulated attenuation of hypersound in a semiconductor superlattice has been investigated. It is shown that the attenuation coefficient depends on the phonon wave vector q in an oscillatory manner and that from this oscillation the band width of superlattice can be found.

Mensah, S. Y.; Allotey, F. K.; Adjepong, S. K.

1992-10-01

228

The authors apply optimal control techniques to find approximate solutions to an inverse problem for the acoustic wave equation. The inverse problem (assumed here to have a solution) is to determine the boundary reflection coefficient from partial measurements of the acoustic signal. The sought reflection coefficient is treated as a control and the goal--quantified by an approximate functional--is to drive the model solution close to the experimental data by adjusting this coefficient. The problem is solved by finding the optimal control that minimizes the approximate functional. Then by driving the cost of the control to zero one proves that the corresponding sequence of optimal controls represents a converging sequence of estimates for the solution of the inverse problem. Compared to classical regularization methods (e.g., Tikhonov coupled with optimization schemes), their approach yields: (1) a systematic procedure to solve inverse problems of identification type and (ii) an explicit expression for the approximations of the solution.

Lenhart, S. [Univ. of Tennessee, Knoxville, TN (United States). Mathematics Dept.]|[Oak Ridge National Lab., TN (United States). Computer Science and Mathematics Div.; Protopopescu, V. [Oak Ridge National Lab., TN (United States). Computer Science and Mathematics Div.; Yong, J. [Fudan Univ., Shanghai (China). Dept. of Mathematics

1997-12-31

229

Spatial variation of Lg-wave attenuation in the Iberian Peninsula

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

230

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

231

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

NASA Astrophysics Data System (ADS)

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

Majerova, M.

2010-12-01

232

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

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

1997-03-01

233

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

234

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

235

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

236

NASA Astrophysics Data System (ADS)

Much current research in magnetospheric physics is directed toward understanding the dramatic variations in relativistic (>1 MeV) electron fluxes that can take place in the Earth's outer zone during magnetic storms. The behavior of outer-zone energetic electrons is partly controlled by the competing mechanisms of acceleration and loss that result from wave-particle interactions, in particular electron gyroresonance with ELF, VLF, and electromagnetic ion cyclotron (EMIC) waves. Powerful techniques for treating gyroresonant wave-particle interactions are provided by quasi-linear diffusion theory. In this paper, we derive formulae for the quasi-linear (momentum, mixed, and pitch-angle) diffusion coefficients for cyclotron resonance with field-aligned electromagnetic waves of any mode and general spectral density. The formulae are fully exact, expressed in closed analytical form, and easily computable. Our results can therefore be readily used to determine accurate diffusion rates for many forms of wave-particle interaction in the magnetosphere and other space plasmas. We find that momentum diffusion rates for MeV electrons in gyroresonance with VLF chorus can be less than a day in the lower-density regions outside the plasmasphere. The mechanism of stochastic acceleration by VLF chorus could therefore be instrumental in generating relativistic electrons during the recovery phase of a magnetic storm. Pitch-angle diffusion rates of MeV electrons scattered by EMIC waves along the plasmapause can approach the limit of strong diffusion. EMIC wave scattering could hence contribute significantly to electron precipitation loss over the course of a storm. Codes designed to model electron dynamics in the radiation belts need to incorporate, in addition to radial (cross-L) diffusion, resonant diffusion due to electron gyroresonance with ELF, VLF, and EMIC waves. In order to determine the quasi-linear diffusion coefficients for such codes, observational data are required on the power spectral density, spatial distribution, and temporal variation of these wave modes. Currently, only limited wave data sets are available. In addition, problems of numerical instability associated with diffusion codes need to be solved. The development of fully comprehensive models of radiation belt electron dynamics remains a considerable scientific challenge.

Summers, Danny

2005-08-01

237

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

Madias, John E.

2013-01-01

238

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

239

NASA Astrophysics Data System (ADS)

The roots of Eremurus spp. were used as a bio-adhesive in the fabrication of Rhizophora spp. particleboards. The mass attenuation coefficients of Eremurus-Rhizophora spp. particleboard of six samples with two different weight percentages of the Eremurus spp. root (6% and 12%) and three various Rhizophora spp. particle sizes (?149 ?m, 149-500 ?m and 500-1000 ?m) were determined by using X-ray fluorescence (XRF) photons in 16.63 keV and 25.30 keV of the photon energy range. The results were compared with theoretically calculated mass attenuations using the XCOM computer program for younger-age (breast 1: 75% muscle+25% fat), middle-age (breast 2: 50% muscle+50% fat), and old-age (breast 3: 25% muscle+75% fat) breasts. The results indicated that Eremurus-Rhizophora spp. particleboard is the appropriate suitable phantom in the diagnostic energy region. The mass attenuation coefficient in the low weight percentage of the bio-adhesive and the large Rhizophora spp. particle size were found very close to breast 1. Moreover the mass attenuation coefficient of the sample with high weight percentage of the bio-adhesive and small Rhizophora spp. particle size was found very close to water as a standard material phantom. In addition, the viscosity of dissolved Eremurus spp. root in water could be considerably higher than that of formaldehyde-based adhesives, which affects on some properties such as high strength and high binding.

Tousi, E. T.; Bauk, S.; Hashim, R.; Jaafar, M. S.; Abuarra, A.; Aldroobi, K. S. A.; Al-Jarrah, A. M.

2014-10-01

240

NASA Astrophysics Data System (ADS)

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

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

2009-03-01

241

NASA Astrophysics Data System (ADS)

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

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

2003-04-01

242

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

243

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. PMID:21198187

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

2010-01-01

244

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

245

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

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

246

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

247

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

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

2007-01-01

248

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

249

NASA Astrophysics Data System (ADS)

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

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

250

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

251

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

252

Long-Time Dynamics of Variable Coefficient mKdV Solitary Waves

We study the Korteweg-de Vries-type equation dt u=-dx(dx^2 u+f(u)-B(t,x)u),\\u000awhere B is a small and bounded, slowly varying function and f is a\\u000anonlinearity. Many variable coefficient KdV-type equations can be rescaled into\\u000athis equation. We study the long time behaviour of solutions with initial\\u000aconditions close to a stable, B=0 solitary wave. We prove that for long time\\u000aintervals,

S. I. Dejak; B. L. G. Jonsson

2005-01-01

253

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. PMID:22338654

Chantler, C T; Islam, M T; Rae, N A; Tran, C Q; Glover, J L; Barnea, Z

2012-03-01

254

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

255

NASA Astrophysics Data System (ADS)

In this work, the mass attenuation coefficients, partial interactions and the effective atomic numbers ( Zeff) of Bi 2O 3, PbO and BaO in xR mO n:(100- x)P 2O 5 (where x=30? x?70 (% by weight)) glass system have been investigated on the basis of the mixture rule at 662 keV. The total and partial interactions were calculated by WinXCom software. It has been found that the total mass attenuation coefficients of glasses increase with increasing Bi 2O 3 and PbO concentrations, due to the increasing photoelectric absorption in glass samples. However, Compton scattering gives dominant contribution to the total mass attenuation coefficients for the studied glass samples. The Zeff increases with increase in Bi 2O 3, PbO and BaO concentrations. For comparison, the Zeff of PbO glasses are comparable to that of Bi 2O 3 glasses and Zeff of both glasses are greater than BaO glasses. These results are very useful for designing radiation shielding glass and reflecting the influence of bismuth, barium, and lead content in radiation shielding phosphate glass. Besides the mentioned usefulness of the new materials, development of lead-free radiation protecting glass also leaves non-toxic impact on our environment.

Kaewkhao, J.; Limsuwan, P.

2010-07-01

256

The mass attenuation and energy-absorption coefficients (radiation interaction data), which are widely used in the shielding and dosimetry of X-rays used for medical diagnostic and orthovoltage therapeutic procedures, are strongly dependent on the energy of photons, elements and percentage by weight of elements in body tissues and substitutes. Significant disparities exist in the values of percentage by weight of elements reported in literature for body tissues and substitutes for individuals of different ages, genders and states of health. Often, interested parties are in need of these radiation interaction data for body tissues or substitutes with percentage by weight of elements and intermediate energies that are not tabulated in literature. To provide for the use of more precise values of these radiation interaction data, parameters and computer programs, MUA_T and MUEN_T are presented for the computation of mass attenuation and energy-absorption coefficients for body tissues and substitutes of arbitrary percentage-by-weight elemental composition and photon energy ranging between 1 keV (or k-edge) and 400 keV. Results are presented, which show that the values of mass attenuation and energy-absorption coefficients obtained from computer programs are in good agreement with those reported in literature.

Okunade, Akintunde A.

2007-01-01

257

The mass attenuation and energy-absorption coefficients (radiation interaction data), which are widely used in the shielding and dosimetry of X-rays used for medical diagnostic and orthovoltage therapeutic procedures, are strongly dependent on the energy of photons, elements and percentage by weight of elements in body tissues and substitutes. Significant disparities exist in the values of percentage by weight of elements reported in literature for body tissues and substitutes for individuals of different ages, genders and states of health. Often, interested parties are in need of these radiation interaction data for body tissues or substitutes with percentage by weight of elements and intermediate energies that are not tabulated in literature. To provide for the use of more precise values of these radiation interaction data, parameters and computer programs, MUA_T and MUEN_T are presented for the computation of mass attenuation and energy-absorption coefficients for body tissues and substitutes of arbitrary percentage-by-weight elemental composition and photon energy ranging between 1 keV (or k-edge) and 400 keV. Results are presented, which show that the values of mass attenuation and energy-absorption coefficients obtained from computer programs are in good agreement with those reported in literature. PMID:21157532

Okunade, Akintunde A

2007-07-01

258

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

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

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

2005-04-15

259

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

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

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

2009-02-13

260

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

NASA Technical Reports Server (NTRS)

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

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

2007-01-01

261

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

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

Chotiros, Nicholas P; Isakson, Marcia J

2014-06-01

262

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

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

2006-01-01

263

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

Yu. F. Kopnichev; I. N. Sokolova

2007-01-01

264

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

Tomasz Klinkosz; Czeslaw J. Lewa; Jacek Paczkowski

2008-01-01

265

NASA Astrophysics Data System (ADS)

The study is based on a 1 year record ( n=46) of the diffuse attenuation coefficient— Kd(PAR) (m -1)—in combination with CTD-casts at one position in Århus Bay, Kattegat, the North Sea-Baltic Sea estuarine transition. Water samples were collected occasionally for determination of suspended particulate matter (SPM) and chromomorphic dissolved organic matter (CDOM). The Kd(PAR) varied between 0.152 and 0.557 (m -1) with an average of 0.293 (m -1). The depth of the photic zone (1% light level) varied between 8.3 and 15.7 m at maximum and average Kd(PAR). Maximum Kd(PAR) values occurred in periods of high chl-a concentrations. The average CDOM absorption coefficient was 0.232 (m -1) whereas the average chl-a and inorganic SPM concentrations equalled 3.3 (mg m -3) and 4.5 (g m -3). Light attenuation partitioning in percent was: water (9), CDOM (17), SPM (42), and phytoplankton (32) at average conditions. Attenuation by phytoplankton reached up to 74% at high chl-a concentrations whereas SPM light attenuation reached 45% at high SPM concentrations. Results show that light attenuation in the bay is governed by phytoplankton and SPM concentrations whereas CDOM is of less significance. Light absorption in the PAR range— a(PAR)—ranged between 0.262 (m -1) at average conditions and 0.49 (m -1) at maximum phytoplankton concentrations. Scattering was governed by SPM at average conditions whereas phytoplankton scattering was higher than SPM scattering at chl-a concentrations >4.5 (mg m -3).

Lund-Hansen, Lars Chresten

2004-10-01

266

NASA Astrophysics Data System (ADS)

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

Arcone, Steven; Liu, Lanbo

2012-06-01

267

NASA Technical Reports Server (NTRS)

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

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

1972-01-01

268

NASA Astrophysics Data System (ADS)

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

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

2007-12-01

269

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

270

Ultrasonic Attenuation in Lanthanum Monochalcogenides

NASA Astrophysics Data System (ADS)

Ultrasonic attenuation due to phonon-phonon interaction and thermoelastic relaxation are studied in Lanthanum Monochalcogenides in <110> direction at different higher temperatures. For evaluation of ultrasonic absorption coefficients the second and third order elastic constants (SOEC) and (TOEC) are also calculated. Shear wave attenuation shows maximum along <110> propagation direction with polarized along <110> and the attenuation increases at higher temperatures. Thermo-elastic loss is very small compared to phonon-viscosity loss. Behavior of temperature dependence of the absorption is the same as in case of pure metals and dielectric crystals.

Yadav, Raja; Singh, Devraj

2001-06-01

271

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

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

272

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

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

1993-02-01

273

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

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

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

2007-10-17

274

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

275

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

NASA Technical Reports Server (NTRS)

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

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

2002-01-01

276

NASA Astrophysics Data System (ADS)

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

Adams, David C.; Humphreys, Eugene D.

2010-12-01

277

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

278

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

279

NASA Astrophysics Data System (ADS)

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

Bonnet, G.

1983-10-01

280

Influence of the surface drag coefficient (young waves) on the current structure of the Berre lagoon

NASA Astrophysics Data System (ADS)

Due to the shallowness, currents and hydrodynamics of Berre lagoon (South of France) are closely conditioned by the bottom topography, and wind affects the entire water column, as for many other Mediterranean lagoons (Perez-Ruzafa, 2011). Wind stress, which is caused by moving atmospheric disturbance, is known to have a major influence in lagoon water circulation. According to the numerical simulation for the main directions of the wind: N-NW, S-SE and W (wind speed of 80 km/h) it is observed that the current is maximal alongshore in the wind direction; the bottom nearshore current being larger in shallower area. This fact is coherent with fundamental principle of wind-driven flows in closed or partially closed basins which states that in shallow water the dominant force balance is between surface wind stress and bottom friction, yielding a current in the direction of the wind (Mathieu et al, 2002, Hunter and Hearn, 1987; Hearn and Hunter,1990). A uniform wind stress applied at the surface of a basin of variable depth sets up a circulation pattern characterized by relatively strong barotropic coastal currents in the direction of the wind, with return flow occurring over the deeper regions (Csanady, 1967; Csanady, 1971). One of the key parameters characterizing the wind stress formulation is a surface drag coefficient (Cds). Thus, an effect of a surface drag coefficient, in the range 0.0016 - 0.0032, will be analyzed in this work. The value of surface drag coefficient Cds = 0.0016 used in our previous studies (Alekseenko et al., 2012), would correspond to mature waves (open sea). But, in the case of semi-closed lagoonal ecosystem, it would be more appropriate to consider "young waves" mechanism. A dependency of this coefficient in terms of the wind speed is given by Young (1999) in both cases of mature waves and young waves. For "young waves" generated at a wind speed of 80 km/h, Cds = 0.0032. So, the influence of Cds on the vertical profile of the velocity in the water column is analyzed in the range 0.0016 - 0.0032. For the three main wind directions considered in this work, for a wind speed of 80 km/h, the complex current structure of the Berre lagoon is analysed. In the nearshore zones, strong alongshore downwind currents are generated, reaching values of the order of 1m/s (up to 1.5 m/s) at the free surface, and 0.5 - 0.6 m/s at the bottom. References Alekseenko E., B. Roux, A. Sukhinov, R. Kotarba, D. Fougere. Coastal hydrodynamics in a windy lagoon; submitted to Computers and Fluids, oct. 2012 Csanady G. T.: Large-scale motion in the Great Lakes, Journal of Geophysical Research, 72(16), 4151-4161, 1967. Csanady G. T. : Baroclinic boundary currents and long edge-waves in basins with sloping shores. J. Physical Oceanography 1(2):92-104, 1971. Hunter, J.R. and Hearn, C.J.: Lateral and vertical variations in the wind-driven circulations in long, shallow lakes, Journal of Geophysical Research, 92 (C12), 1987. Hearn, C.J. and Hunter, J.R.: A note on the equivalence of some two- and three-dimensional models of wind-driven barotropic flow in shallow seas, Applied Mathematical Modelling, 14, 553-556, 1990. Mathieu P.P., Deleersnijder E., Cushman-Roisin B., Beckers J.M. and Bolding K.: The role of topography in small well-mixed bays, with application to the lagoon of Mururoa. Continental Shelf research, 22(9), 1379-1395, 2002. A. Pérez-Ruzafa, C. Marcos, I.M. Pérez-Ruzafa (2011). Mediterranean coastal lagoons in an ecosystem and aquatic resources management context//Physics and Chemistry of the Earth, Parts A/B/C, Volume 36, Issues 5-6, 2011, Pages 160-166 Young I.R., Wind generated ocean waves. Ocean Engineering Series Editors. Elsevier, 1999, ISBN: 0-08-043317-0.

Alekseenko, Elena; Roux, Bernard; Kharif, Christian; Sukhinov, Alexander; Kotarba, Richard; Fougere, Dominique; Chen, Paul Gang

2013-04-01

281

Traveling wave solutions for fifth-order KdV type equations with time-dependent coefficients

NASA Astrophysics Data System (ADS)

We investigate two families of fifth-order KdV equations with time-dependent coefficients and linear damping term. These models apply to the description of envelope wave dynamics in inhomogeneous systems modeled by KdV-type equation. The modified sine-cosine method is used to construct exact periodic solutions and solitons solutions for the wave equations. The conditions of existence and uniqueness of exact solutions are also presented. The obtained results show that the sine-cosine.method provides a powerful mathematical tool for solving nonlinear equations with variable coefficients.

Triki, Houria; Wazwaz, Abdul-Majid

2014-03-01

282

NASA Astrophysics Data System (ADS)

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

Yang, Lei; Yang, DingHui; Nie, JianXin

2014-06-01

283

NASA Astrophysics Data System (ADS)

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

Yang, Lei; Yang, DingHui; Nie, JianXin

2014-04-01

284

NASA Astrophysics Data System (ADS)

Recent reports have suggested that spectral domain optical coherence tomography (SD-OCT) is a useful tool for quantifying the permeability of hyperosmotic agents in various tissues. We report our preliminary results on quantification of glucose diffusion and assessment of the optical attenuation change due to the diffusion of glucose in normal and adenomatous human colon tissues in vitro by using a SD-OCT and then calculated the permeability coefficients (PC) and optical attenuation coefficients (AC). The PC of a 30% aqueous solution of glucose was 3.37±0.23×10-6 cm/s in normal tissue and 5.65±0.16×10-6 cm/s in cancerous colon tissue. Optical AC in a normal colon ranged from 3.48±0.37 to 2.68±0.82 mm-1 and was significantly lower than those seen in the cancerous tissue (8.48±0.95 to 3.16±0.69 mm-1, p<0.05). The results suggest that quantitative measurements of using PC and AC from OCT images could be a potentially powerful method for colon cancer detection.

Zhao, Qingliang; Zhou, Chuanqing; Wei, Huajiang; He, Yonghong; Chai, Xinyu; Ren, Qiushi

2012-10-01

285

National Technical Information Service (NTIS)

A method for calculating spring and damping coefficients for the tilting pad journal bearing is presented. The analysis includes the effect of pad inertia. Numerical results are given in form of design curves for the centrally pivoted 4 shoe, 5 shoe, 6 sh...

J. Lund

1964-01-01

286

The deduction of Zernike coefficients is usually influenced by the finite number of sampling dots on interferogram and their inherited measurement errors. In this paper, a simplified Gram–Schmidt method for solving the Zernike polynomial with the higher fitting precision is presented and used to analyze the wave front aberrations for the circle interference fringe of the fine polished aluminum disk

Xuelian Yu; Yong Yao; Yunxu Sun; Jiajun Tian

2011-01-01

287

NASA Astrophysics Data System (ADS)

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

Toyokuni, Genti; Takenaka, Hiroshi

2012-06-01

288

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

NASA Astrophysics Data System (ADS)

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

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

2005-08-01

289

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

290

NASA Astrophysics Data System (ADS)

In this study, element analysis and the mass attenuation coefficient for matrixes of gold, bronze and water with various impurities and the concentrations of heavy metals (Cu, Mn, Pb and Zn) are evaluated and calculated by the MCNP simulation code for photons emitted from Barium-133, Americium-241 and sources with energies between 1 and 100 keV. The MCNP data are compared with the experimental data and WinXCom code simulated results by Medhat. The results showed that the obtained results of bronze and gold matrix are in good agreement with the other methods for energies above 40 and 60 keV, respectively. However for water matrixes with various impurities, there is a good agreement between the three methods MCNP, WinXCom and the experimental one in low and high energies.

Esfandiari, M.; Shirmardi, S. P.; Medhat, M. E.

2014-06-01

291

NASA Astrophysics Data System (ADS)

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

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

2002-09-01

292

NASA Technical Reports Server (NTRS)

Ocean color algorithms are based on the parameterization of apparent optical properties as a function of inherent optical properties. WET Labs underwater absorption and attenuation meters (ac-9 and ac-s) measure both the spectral beam attenuation [c (lambda)] and absorption coefficient [a (lambda)]. The ac-s reports in a continuous range of 390-750 nm with a band pass of 4 nm, totaling approximately 83 distinct wavelengths, while the ac-9 reports at 9 wavelengths. We performed the ac-s field measurements at nine stations in the Mid-Atlantic Bight from water calibrations to data analysis. Onboard the ship, the ac-s was calibrated daily using Milli Q-water. Corrections for the in situ temperature and salinity effects on optical properties of water were applied. Corrections for incomplete recovery of the scattered light in the ac-s absorption tube were performed. The fine scale of spectral and vertical distributions of c (lambda) and a (lambda) were described from the ac-s. The significant relationships between a (674) and that of spectrophotometric analysis and chlorophyll a concentration of discrete water samples were observed.

Ohi, Nobuaki; Makinen, Carla P.; Mitchell, Richard; Moisan, Tiffany A.

2008-01-01

293

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

294

National Technical Information Service (NTIS)

It is no longer necessary to use extrapolated microwave dielectric values when designing millimeter wave components and systems. Our recent highly accurate broadband millimeter wave data on complex refractive index, complex refractive index, complex diele...

M. N. Afsar K. J. Button

1983-01-01

295

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

296

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

NASA Technical Reports Server (NTRS)

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

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

1980-01-01

297

NASA Astrophysics Data System (ADS)

By considering the energy dispersion of the conduction subband, we found the corrected Rashba coefficient (?') in AlGaN/GaN quantum wells (QWs) decreases with the in-plane wave vector k//, and the corrected Rashba spin splitting (?E') increases nonlinearly as a function of k//. Moreover, the correction to the Rashba spin splitting also increases with k//, since the ratio of the kinetic energy in the effective band gap increases. The effect of energy dispersion on the correction to the Rashba spin splitting will be greater for large in-plane wave vectors and materials with narrow band gap. Although the band gap of the barrier increases with Al content (x), we found the corrections to the Rashba coefficient and Rashba spin splitting at the Fermi level in AlxGa1-xN/GaN QWs increase with x, since the expansion region of the envelope functions decrease, and the polarized electric field in the well increases rapidly.

Li, M.; Zhang, Y. M.; Fan, L. B.

2014-08-01

298

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

299

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

300

NASA Astrophysics Data System (ADS)

This work implements the ultrasonic shear-wave reflectance method for viscosity measurements. A modeconversion device was used for the dynamic viscosity measurement of mineral oil, SAE 40 automotive oil and glycerin samples at room temperature and 1 MHz. A novel signals processing technique that calculates the reflection coefficient magnitude in a frequency band, instead of a single frequency, was employed, showing an important improvement on the measurement accuracy.

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

2012-05-01

301

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

302

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

National Technical Information Service (NTIS)

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

B. J. Mitchell

1972-01-01

303

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

H. Karaoglu; R. Taborda; J. Bielak

2011-01-01

304

NASA Astrophysics Data System (ADS)

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

Hanyga, Andrzej

2014-03-01

305

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

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

1984-11-27

306

NASA Astrophysics Data System (ADS)

We developed a method that combines a similarity transformation with a mapping that solves a generalized nonautonomous nonlinear Schrödinger (NLS) equation containing cubic, quintic and higher order terms in the conjunction with spatially and temporary varying dispersion, containing higher nonlinearities, and external potential. We have studied various classes of solutions in closed form representing front, bright and dark solitary-like waves. We introduced a transformation that solves the related transformed NLS in the constant coefficients. As an application of this technique, we have analyzed the dynamical behavior of several specific classes of solutions such as moving, breathing, resonant both for periodic and quasi-periodic solitary-like waves. The stability of the obtained solitary-like waves is examined using analytical and numerical methods.

Zakeri, Gholam-Ali; Yomba, Emmanuel

2013-10-01

307

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

308

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

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

1974-01-01

309

A preliminary evaluation of wave attenuation by four species of seagrass

NASA Astrophysics Data System (ADS)

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

Fonseca, Mark S.; Cahalan, Jennifer A.

1992-12-01

310

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

National Technical Information Service (NTIS)

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

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

1987-01-01

311

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

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

1989-05-25

312

The x-ray mass attenuation coefficients of zinc are measured in a high-accuracy experiment between 7.2 and 15.2 keV with an absolute accuracy of 0.044% and 0.197%. This is the most accurate determination of any attenuation coefficient on a bending-magnet beamline and reduces the absolute uncertainty by a factor of 3 compared to earlier work by advances in integrated column density determination and the full-foil mapping technique described herein. We define a relative accuracy of 0.006%, which is not the same as either the precision or the absolute accuracy. Relative accuracy is the appropriate parameter for standard implementation of analysis of near-edge spectra. Values of the imaginary components f'' of the x-ray form factor of zinc are derived. Observed differences between the measured mass attenuation coefficients and various theoretical calculations reach a maximum of about 5% at the absorption edge and up to 2% further than 1 keV away from the edge. The measurements invite improvements in the theoretical calculations of mass attenuation coefficients of zinc.

Rae, Nicholas A.; Chantler, Christopher T.; Barnea, Zwi; Jonge, Martin D. de; Tran, Chanh Q.; Hester, James R. [School of Physics, University of Melbourne, Victoria 3010 (Australia); Australian Synchrotron, Victoria 3168 (Australia); La Trobe University, Victoria 3086 (Australia); Australian Nuclear Science and Technology Organisation, New South Wales 2234 (Australia)

2010-02-15

313

The effect of structural disorder on anomalous critical attenuation of ultrasound by solids

NASA Astrophysics Data System (ADS)

A field-theory description of dynamic effects of acoustic wave propagation in solids under phase transition is performed. The effects of structure defects on critical attenuation of ultrasound in Ising-like three-dimensional systems is discussed. Calculations of the attenuation coefficient and scaling function are carried out in a two-loop approximation for regular and disordered systems.

Prudnikov, P. V.; Prudnikov, V. V.

2007-05-01

314

Elastic wave propagation and attenuation in a double-porosity dual-permeability medium

To account for large-volume low-permeability storage porosity and low-volume high-permeability fracture\\/crack porosity in oil and gas reservoirs, phenomenological equations for the poroelastic behavior of a double porosity medium have been formulated and the coefficients in these linear equations identified. This generalization from a single porosity model increases the number of independent inertial coefficients from three to six, the number of

J. G. Berryman; H. F. Wang

2000-01-01

315

NASA Technical Reports Server (NTRS)

Observations have been made and reported that the experimental normal force coefficients at a constant angle of attack were constant with a variation of more than 2 orders of magnitude of Reynolds number at a free-stream Mach number M(sub infinity) of 8.00 and more than 1 order of magnitude variation at M(sub infinity) = 6.00 on the same body-wing hypersonic cruise configuration. These data were recorded under laminar, transitional, and turbulent boundary layer conditions with both hot-wall and cold-wall models. This report presents experimental data on 25 configurations of 17 models of both simple and complex geometry taken at M(sub infinity) = 6.00, 6.86, and 8.00 in 4 different hypersonic facilities. Aerodynamic calculations were made by computational fluid dynamics (CID) and engineering methods to analyze these data. The conclusions were that the normal force coefficients at a given altitude are constant with Reynolds numbers at hypersonic speeds and that the axial force coefficients recorded under laminar boundary-layer conditions at several Reynolds numbers may be plotted against the laminar parameter (the reciprocal of the Reynolds number to the one-half power) and extrapolated to the ordinate axis to determine the inviscid-wave-drag coefficient at the intercept.

Hawkins, Richard; Penland, Jim A.

1997-01-01

316

NASA Astrophysics Data System (ADS)

Many models using electromagnetic sounding techniques have been formulated for use in exploration activities. In deriving the governing equations for the models, Maxwell's equations are used and the earth is taken as a layered medium. Using these boundary conditions, the Sommerfeld integrals are obtained for several models. However, the difficulties and limitations posed by the iterations of the functions, especially the strong oscillations and slow convergence of the Bessel function, call for a search for new methods. This work aims to formulate models, with the advantage of bypassing the problems highlighted above, and to discover new response parameters not considered by the older models due to the limitations of time. Three measurable field parameters, (1) amplitude of the correction factor to the wave tilt, (2) phase of the amplitude of the correction factor to the wave tilt and (3) reflection coefficient, were calculated from this model with various conductivity contrasts over a two-layered earth. Two cases of a top layer overlying a more conductive basement and a more conductive top layer overlying a resistive basement were considered with a radio frequency of 125 kHz and a low frequency of 10 Hz. The model was tested using data from existing models and was then applied to a homogeneous and a layered earth. Results revealed that the phase of the amplitude of the correction to the wave tilt was found to be most diagnostic of the changes in layer parameters. Also, depths of 20 m and 2000 m were achieved with the two respective frequency values. The reflection coefficient was discovered to be an important parameter for detecting layered earth structures, in addition to other parameters. Furthermore, an inverse relationship between the transverse electric and transverse magnetic modes of the reflection coefficient is established.

Olowofela, J. A.; Ozebo, V. C.

2006-06-01

317

The inverse scattering problem for the one-dimensional Schrödinger equation is considered when the potential is real valued and integrable and has a finite first-moment and no bound states. Corresponding to such potentials, for rational reflection coefficients with only simple poles in the upper half complex plane, a method is presented to recover the potential and the scattering solutions explicitly. A

Tuncay Aktosun; Michael H. Borkowski; Alyssa J. Cramer; Lance Pittman

318

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

319

NASA Astrophysics Data System (ADS)

In this paper, a new auxiliary equation method is presented of constructing more new non-travelling wave solutions of nonlinear differential equations in mathematical physics, which is direct and more powerful than projective Riccati equation method. In order to illustrate the validity and the advantages of the method, (2+1)-dimensional asymmetric Nizhnik-Novikov-Vesselov equation is employed and many new double periodic non-travelling wave solutions are obtained. This algorithm can also be applied to other nonlinear differential equations.

Lu, Bin; Zhang, Hong-Qing

2008-11-01

320

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

321

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

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

Youcef Bouzidi; Douglas R. Schmitt

2009-01-01

322

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

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

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

1998-01-01

323

Contributions to numerical developments in shock waves attenuation in porous filters

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

D. Rochette

2007-01-01

324

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

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

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

1994-01-01

325

NASA Astrophysics Data System (ADS)

The effect of absorption on the diffusion constant of classical waves propagating in media with randomly positioned Mie scatterers is studied. Profound changes including a significant increase in the diffusion constant are found and attributed to the growth of the transport mean free path in the vicinity of Mie resonances. Copyright (c) 1995 Optical Society of America

Livdan, D.; Lisyansky, A. A.

1995-12-01

326

Some Calculations of Ionospheric Reflection Coefficients for Low Frequency Radio Waves.

National Technical Information Service (NTIS)

Results are presented of the computation of the reflective properties of a sharply bounded ionosphere for low frequency radio waves. The method of Barber and Crombie has been adopted. It is shown that for this model of ionosphere the phase of the reflecti...

B. Burgess G. C. A. Sunderland

1966-01-01

327

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

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

2013-06-28

328

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

329

NASA Astrophysics Data System (ADS)

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

Hudier, E. J.; Bahoura, M.

2012-12-01

330

NASA Astrophysics Data System (ADS)

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

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

2007-03-01

331

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

332

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

2013-01-01

333

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

334

NASA Astrophysics Data System (ADS)

The aim of this paper is to present solitary wave solution of two different forms of regularized long-wave equation with time-dependent coefficients that models shallow-water waves in fluid dynamics and some phenomena in elastic media, optic fibres and plasma physics. The simplest equation method is applied to solve the governing equations and then exact 1-soliton solutions are obtained. It is shown that this method provides us with a powerful mathematical tool for solving nonlinear evolution equations with time-dependent coefficients in mathematical physics.

Eslami, M.; Mirzazadeh, M.

2014-02-01

335

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

National Technical Information Service (NTIS)

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

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

1966-01-01

336

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

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

2010-01-01

337

Transport coefficients of the superfluid Fermi gas in p-wave state at low temperatures

NASA Astrophysics Data System (ADS)

In this paper, we obtain the shear viscosity and diffusive thermal conductivity of the superfluid p-wave Fermi gas with weak interaction by using the quasi-particle relaxation rate ?P-1, and the Boltzmann equation approach at low temperatures. We show that ?P-1 is proportional to T4. The shear viscosity components, ?xx, ?yy, ?xy are proportional to T-2, whereas ?xz, ?yz and ?zz are proportional to T-4 and T-6, respectively. The components of the diffusive thermal conductivity Kxx and Kyy are proportional to T-1, whereas Kzz is proportional to T-3.

Nasirimoghadam, S.; Nabipoor, F.; Khademi-Dehkordi, M.; Shahzamanian, M. A.

2012-12-01

338

NASA Astrophysics Data System (ADS)

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

Lin, Guoqing

2014-04-01

339

NASA Astrophysics Data System (ADS)

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

Lin, G.

2013-12-01

340

NASA Astrophysics Data System (ADS)

A theoretical analysis of plasma turbulence excited by an electromagnetic wave (e.g., laser or microwave radiation) near the critical point of a plasma target is presented. Conditions of 'ultrastrong' plasma turbulence are investigated where there is no inertial interval and plasma oscillations caused by modulational instability arise in the absorption region. The analysis is based on the theory of strong plasma turbulence of Galeev et al. (1977) and Zakharov's theory of Langmuir collapse (1972).

Sagdeev, R. Z.; Shapiro, V. D.; Shevchenko, V. I.

1980-03-01

341

We use the x-ray extended-range technique (XERT) [C. T. Chantler et al., Phys. Rev. A 64, 062506 (2001)] to measure the mass attenuation coefficients of tin in the x-ray energy range of 29-60 keV to 0.04-3 % accuracy, and typically in the range 0.1-0.2 %. Measurements made over an extended range of the measurement parameter space are critically examined to identify, quantify, and correct a number of potential experimental systematic errors. These results represent the most extensive experimental data set for tin and include absolute mass attenuation coefficients in the regions of x-ray absorption fine structure, extended x-ray absorption fine structure, and x-ray absorption near-edge structure. The imaginary component of the atomic form factor f{sub 2} is derived from the photoelectric absorption after subtracting calculated Rayleigh and Compton scattering cross sections from the total attenuation. Comparison of the result with tabulations of calculated photoelectric absorption coefficients indicates that differences of 1-2 % persist between calculated and observed values.

Jonge, Martin D. de; Tran, Chanh Q.; Chantler, Christopher T.; Barnea, Zwi; Dhal, Bipin B.; Paterson, David; Kanter, Elliot P.; Southworth, Stephen H.; Young, Linda; Beno, Mark A.; Linton, Jennifer A.; Jennings, Guy [X-Ray Operations and Research, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439 (United States); School of Physics, University of Melbourne, Victoria 3010 (Australia); Australian Synchrotron Project, Major Projects Victoria, 800 Blackburn Road, Clayton, Victoria 3168 (Australia); Chemistry Division, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439 (United States); BESSRC-CAT, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439 (United States)

2007-03-15

342

We use the x-ray extended-range technique (XERT) [C. T. Chantler et al., Phys. Rev. A 64, 062506 (2001)] to measure the mass attenuation coefficients of tin in the x-ray energy range of 29-60 keV to 0.04-3 % accuracy, and typically in the range 0.1-0.2 %. Measurements made over an extended range of the measurement parameter space are critically examined to identify, quantify, and correct a number of potential experimental systematic errors. These results represent the most extensive experimental data set for tin and include absolute mass attenuation coefficients in the regions of x-ray absorption fine structure, extended x-ray absorption fine structure, and x-ray absorption near-edge structure. The imaginary component of the atomic form factor f{sub 2} is derived from the photoelectric absorption after subtracting calculated Rayleigh and Compton scattering cross sections from the total attenuation. Comparison of the result with tabulations of calculated photoelectric absorption coefficients indicates that differences of 1-2 % persist between calculated and observed values.

de Jonge, M. D.; Tran, C. Q.; Chantler, C. T.; Barnea, Z.; Dhal, B. P.; Paterson, D.; Kanter, E. P.; Southworth, S. H.; Young, L.; Beno, M. A.; Linton, J. A.; Jennings, G.; Univ. of Melbourne; Australian Synchrotron Project

2007-01-01

343

We use the x-ray extended-range technique (XERT) [Chantler et al., Phys. Rev. A 64, 062506 (2001)] to measure the mass attenuation coefficients of molybdenum in the x-ray energy range of 13.5-41.5 keV to 0.02-0.15 % accuracy. Measurements made over an extended range of the measurement parameter space are critically examined to identify, quantify, and correct where necessary a number of experimental systematic errors. These results represent the most extensive experimental data set for molybdenum and include absolute mass attenuation coefficients in the regions of the x-ray absorption fine structure (XAFS) and x-ray-absorption near-edge structure (XANES). The imaginary component of the atomic form-factor f{sub 2} is derived from the photoelectric absorption after subtracting calculated Rayleigh and Compton scattering cross sections from the total attenuation. Comparison of the result with tabulations of calculated photoelectric absorption coefficients indicates that differences of 1-15 % persist between the calculated and observed values.

Jonge, Martin D. de; Tran, Chanh Q.; Chantler, Christopher T.; Barnea, Zwi; Dhal, Bipin B.; Cookson, David J.; Lee, Wah-Keat; Mashayekhi, Ali [School of Physics, University of Melbourne, Melbourne, Victoria 3010 (Australia); Chem-Mat-CARS, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439 (United States); XOR 1-ID, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439 (United States)

2005-03-01

344

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

NASA Astrophysics Data System (ADS)

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

2009-04-01

345

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

NASA Astrophysics Data System (ADS)

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

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

2009-04-01

346

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

347

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

348

This work reports on the determination of langatate elastic and piezoelectric constants and their associated temperature coefficients employing 2 independent methods, the pulse echo overlap (PEO) and a combined resonance technique (CRT) to measure bulk acoustic wave (BAW) phase velocities. Details on the measurement techniques are provided and discussed, including the analysis of the couplant material in the PEO technique used to couple signal to the sample, which showed to be an order of magnitude more relevant than the experimental errors involved in the data extraction. At room temperature, elastic and piezoelectric constants were extracted by the PEO and the CRT methods and showed results consistent to within a few percent for the elastic constants. Both raw acquired data and optimized constants, based on minimization routines applied to all the modes involved in the measurements, are provided and discussed. Comparison between the elastic constants and their temperature behavior with the literature reveals the recent efforts toward the consistent growth and characterization of LGT, in spite of significant variations (between 1 and 30%) among the constants extracted by different groups at room temperature. The density, dielectric permittivity constants, and respective temperature coefficients used in this work have also been independently determined based on samples from the same crystal boule. The temperature behavior of the BAW modes was extracted using the CRT technique, which has the advantage of not relying on temperature dependent acoustic couplants. Finally, the extracted temperature coefficients for the elastic and piezoelectric constants between room temperature and 120 degrees C are reported and discussed in this work. PMID:19406707

Sturtevant, Blake T; Davulis, Peter M; da Cunha, Mauricio Pereira

2009-04-01

349

Delamination of southern Puna lithosphere revealed by body wave attenuation tomography

NASA Astrophysics Data System (ADS)

southern Puna Plateau has been proposed to result from a major Pliocene delamination event that has previously been inferred from geochemical, geological, and some preliminary geophysical data. Seventy-five seismic stations were deployed across the southern Puna Plateau in 2007-2009 by scientists from the U.S., Germany, Chile, and Argentina to test the delamination model for the region. The Puna passive seismic stations were located between 25 and 28°S. Using the seismic waveform data collected from the PUNA experiment, we employ attenuation tomography methods to resolve both compressional and shear quality factors (Qp and Qs, respectively) in the crust and uppermost mantle. The images clearly show a high-Q Nazca slab subducting eastward beneath the Puna plateau and another high-Q block with a westward dip beneath the Eastern Cordillera. We suggest that the latter is a piece of delaminated South American lithosphere. A significant low-Q zone lies between the Nazca slab and the South American lithosphere and extends southward from the northern margin of the seismic array at 25°S before vanishing around 27.5°S. This low-Q zone extends farther west in the crust and uppermost mantle at the southern end of the seismic array. The low-Q zone reaches ~100 km depth beneath the northern part of the array but only ~50 km depth in the south. Lateral variations of the low-Q zone reflect the possible mechanism conversion between mantle upwelling related to delamination and dehydration. The depth of the Nazca slab as defined by Q images decreases from north to south beneath the plateau, which is consistent with the steep-flat transition of the angle of the subducting slab as defined by previous earthquake studies.

Liang, Xiaofeng; Sandvol, Eric; Kay, Suzanne; Heit, Benjamin; Yuan, Xiaohui; Mulcahy, Patrick; Chen, Chen; Brown, Larry; Comte, Diana; Alvarado, Patricia

2014-01-01

350

NASA Astrophysics Data System (ADS)

A method is proposed by extending the linear traveling wave transformation into the nonlinear transformation with the ( G'/ G)-expansion method. The non-traveling wave solutions with variable separation can be constructed for the (2 + 1)-dimensional Broer-Kaup equations with variable coefficients via the method. A novel class of fractal soliton, namely, the cross-like fractal soliton is observed by selecting appropriately the arbitrary functions in the solutions.

Li, Bangqing; Ma, Yulan

2011-01-01

351

NASA Astrophysics Data System (ADS)

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

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

2007-12-01

352

Generalized Green's Function Surface Integral Equation Method (G-GFSIEM) is used to study propagation of surface plasmon polariton waves at interface of two semi-infinite metal-dielectric waveguides. Reflection, transmission, and scattering coefficients for structures with different dielectric constants are calculated by using this method and by using energy conservation law. Conditions where scattering coefficient is maximized or minimized are studied. It is found that by using appropriate materials with specified dielectric constants, structures with required reflection, transmission, and scattering coefficients can be designed. PMID:20588702

Zavareian, Nafiseh; Massudi, Reza

2010-04-12

353

The mass attenuation coefficients of Rhizophora spp. binderless particleboard with four different particle sizes (samples A, B, C and D) and natural raw Rhizophora spp. wood (sample E) were determined using single-beam photon transmission in the energy range between 16.59 and 25.26 keV. This was done by determining the attenuation of K(?1) X-ray fluorescent (XRF) photons from niobium, molybdenum, palladium, silver and tin targets. The results were compared with theoretical values of young-age breast (Breast 1) and water calculated using a XCOM computer program. It was found that the mass attenuation coefficient of Rhizophora spp. binderless particleboards to be close to the calculated XCOM values in water than natural Rhizophora spp. wood. Computed tomography (CT) scans were then used to determine the density profile of the samples. The CT scan results showed that the Rhizophora spp. binderless particleboard has uniform density compared to natural Rhizophora spp. wood. In general, the differences in the variability of the profile density decrease as the particle size of the pellet samples decreases. PMID:22304963

Marashdeh, M W; Bauk, S; Tajuddin, A A; Hashim, R

2012-04-01

354

NASA Astrophysics Data System (ADS)

Self attenuation of TL and relative TL efficiency of polytetra fluoro ethylene (PTFE) embedded CaSO 4:Dy disc, LiF:Mg,Ti (MTS) disc and LiF:Mg,Cu,P (MCP-N) chip were determined in the present study for photons of energy 10-34 keV. The relative TL efficiency was determined using an alternative approach in which ratio of experimental response and corrected theoretical response was used instead of measuring the absolute TL emission in photon counting mode. For CaSO 4:Dy disc, it was found that with increasing the proportion of CaSO 4:Dy phosphor in the disc, the light attenuation coefficient increases. The light attenuation coefficient of MTS disc and MCP-N chip was found to be 23.4 and 45.5 cm -1, respectively. The relative TL efficiency in the photon energy range of 10-34 keV for MTS discs and MCP-N chips, evaluated in the present study matches well with the reported values in the literature.

Bakshi, A. K.; Chatterjee, S.; Palani Selvam, T.; Joshi, V. J.; Chougaonkar, M. P.

2011-10-01

355

NASA Astrophysics Data System (ADS)

The estimation of shear wave velocity and attenuation in near-surface geology is of primary importance in engineering seismology. In fact, their knowledge is essential for site response studies when preparing improved seismic hazard scenarios. In this study, we propose two approaches for estimating the average shear wave quality factor Qs by using recordings of a vertical array of accelerometers. The methods are mainly based on the deconvolution of the wavefield recorded in a borehole with that recorded at the surface. The first method requires the Fourier transform of the deconvolved wavefield to be fitted with a theoretical transfer function valid for the vertical or nearly vertical (in the case at hand up to 30° incidence angle) propagation of S waves. The second method is based on the spectral fitting of the Fourier transform of only the acausal part of the deconvolved wavefield with a theoretical transfer function. Both methods can be applied without any prior knowledge of the subsoil structure (since they are based on empirical data analysis) and do not require a precise knowledge of the azimuthal orientation of the sensors in the boreholes (which is seldom available). First, we describe the theoretical framework of the proposed methodologies for Qs estimation, which are based on the assumption that the structure in the borehole is weakly heterogeneous in the vertical direction (i.e. no large impedance contrast exists between the borehole sensor and the surface). Second, by using synthetic accelerograms, we verify that in a realistic subsoil structure, the assumption of vertical homogeneity can hold and we investigate the robustness and the suitability of the proposed methods. Finally, only the method that was shown to provide the more stable results, based on fitting the borehole-to-surface spectral ratio with a theoretical function, is applied to earthquakes signals recorded by a vertical array of accelerometers installed in Ataköy (western Istanbul). Results show that using borehole data provides a fair and robust estimate of an average Qs (of about 30, 46 and 99 for the 0-50, 0-70, 0-140 m depth ranges, respectively) that can be used for numerical simulations of ground motion.

Parolai, S.; Bindi, D.; Ansal, A.; Kurtulus, A.; Strollo, A.; Zschau, J.

2010-05-01

356

National Technical Information Service (NTIS)

The physical models of electromagnetic wave diffusion for spherical and ellipsoidal rain drops are used to determine attenuation coefficients and phase shift in the range frequency between 10 and 100 GHz for several polarization conditions. The results ar...

D. Maggiori

1978-01-01

357

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

358

The nonlinear absorption coefficient (NAC) of a strong electromagnetic wave (EMW) by confined electrons in quantum wells under the influences of confined phonons is theoretically studied by using the quantum transport equation for electrons. In comparison with the case of unconfined phonons, the dependence of the NAC on the energy (??), the amplitude (Eo) of external strong EMW, the width

N. Q. Bau; L. T. Hung; N. D. Nam

2010-01-01

359

Purpose: Accurate patient-specific photon cross-section information is needed to support more accurate model-based dose calculation for low energy photon-emitting modalities in medicine such as brachytherapy and kilovoltage x-ray imaging procedures. A postprocessing dual-energy CT (pDECT) technique for noninvasivein vivo estimation of photon linear attenuation coefficients has been experimentally implemented on a commercial CT scanner and its accuracy assessed in idealized phantom geometries. Methods: Eight test materials of known composition and density were used to compare pDECT-estimated linear attenuation coefficients to NIST reference values over an energy range from 10 keV to 1 MeV. As statistical image reconstruction (SIR) has been shown to reconstruct images with less random and systematic error than conventional filtered backprojection (FBP), the pDECT technique was implemented with both an in-house polyenergetic SIR algorithm, alternating minimization (AM), as well as a conventional FBP reconstruction algorithm. Improvement from increased spectral separation was also investigated by filtering the high-energy beam with an additional 0.5 mm of tin. The law of propagated uncertainty was employed to assess the sensitivity of the pDECT process to errors in reconstructed images. Results: Mean pDECT-estimated linear attenuation coefficients for the eight test materials agreed within 1% of NIST reference values for energies from 1 MeV down to 30 keV, with mean errors rising to between 3% and 6% at 10 keV, indicating that the method is unbiased when measurement and calibration phantom geometries are matched. Reconstruction with FBP and AM algorithms conferred similar mean pDECT accuracy. However, single-voxel pDECT estimates reconstructed on a 1 × 1 × 3 mm{sup 3} grid are shown to be highly sensitive to reconstructed image uncertainty; in some cases pDECT attenuation coefficient estimates exhibited standard deviations on the order of 20% around the mean. Reconstruction with the statistical AM algorithm led to standard deviations roughly 40% to 60% less than FBP reconstruction. Additional tin filtration of the high energy beam exhibits similar pDECT estimation accuracy as the unfiltered beam, even when scanning with only 25% of the dose. Using the law of propagated uncertainty, low Z materials are found to be more sensitive to image reconstruction errors than high Z materials. Furthermore, it is estimated that reconstructed CT image uncertainty must be limited to less than 0.25% to achieve a target linear-attenuation coefficient estimation uncertainty of 3% at 28 keV. Conclusions: That pDECT supports mean linear attenuation coefficient measurement accuracies of 1% of reference values for energies greater than 30 keV is encouraging. However, the sensitivity of the pDECT measurements to noise and systematic errors in reconstructed CT images warrants further investigation in more complex phantom geometries. The investigated statistical reconstruction algorithm, AM, reduced random measurement uncertainty relative to FBP owing to improved noise performance. These early results also support efforts to increase DE spectral separation, which can further reduce the pDECT sensitivity to measurement uncertainty.

Evans, Joshua D., E-mail: jevans2@mcvh-vcu.edu; Yu, Yaduo; Williamson, Jeffrey F. [Department of Radiation Oncology, Virginia Commonwealth University, Richmond, Virginia 23298 (United States)] [Department of Radiation Oncology, Virginia Commonwealth University, Richmond, Virginia 23298 (United States); Whiting, Bruce R. [Department of Radiology, University of Pittsburgh, Pittsburgh, Pennsylvania 15213 (United States)] [Department of Radiology, University of Pittsburgh, Pittsburgh, Pennsylvania 15213 (United States); O’Sullivan, Joseph A. [Department of Electrical and Systems Engineering, Washington University, St. Louis, Missouri 63130 (United States)] [Department of Electrical and Systems Engineering, Washington University, St. Louis, Missouri 63130 (United States); Politte, David G. [Mallinckrodt Institute of Radiology, Washington University, St. Louis, Missouri 63110 (United States)] [Mallinckrodt Institute of Radiology, Washington University, St. Louis, Missouri 63110 (United States); Klahr, Paul H. [Philips Healthcare, 595 Miner Rd., Highland Hts., Ohio 44143 (United States)] [Philips Healthcare, 595 Miner Rd., Highland Hts., Ohio 44143 (United States)

2013-12-15

360

NASA Astrophysics Data System (ADS)

We investigate the self-intermediate scattering function (SISF) in a three-dimensional (3D) cubic lattice fluid (interacting lattice gas) with attractive nearest-neighbor interparticle interactions at a temperature slightly above the critical one by means of Monte Carlo simulations. A special representation of SISF as an exponent of the mean tracer diffusion coefficient multiplied by the geometrical factor and time is considered to highlight memory effects that are included in time and wave-vector dependence of the diffusion coefficient. An analytical expression for the diffusion coefficient is suggested to reproduce the simulation data. It is shown that the particles' mean-square displacement is equal to the time integral of the diffusion coefficient. We make a comparison with the previously considered 2D system on a square lattice. The main difference with the two-dimensional case is that the time dependence of particular characteristics of the tracer diffusion coefficient in the 3D case cannot be described by exponentially decreasing functions, but requires using stretched exponentials with rather small values of exponents, of the order of 0.2. The hydrodynamic values of the tracer diffusion coefficient (in the limit of large times and small wave vectors) defined through SIFS simulation results agree well with the results of its direct determination by the mean-square displacement of the particles in the entire range of concentrations and temperatures.

Skarpalezos, Loukas; Argyrakis, Panos; Vikhrenko, Vyacheslav S.

2014-05-01

361

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

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

2013-01-01

362

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

363

Second coefficient of viscosity in air

NASA Technical Reports Server (NTRS)

Acoustic attenuation measurements in air were analyzed in order to estimate the second coefficient of viscosity. Data over a temperature range of 11 C to 50 C and at relative humidities between 6 percent and 91 percent were used. This analysis showed that the second coefficient of viscosity varied between 1900 and 20,000 times larger than the dynamic or first coefficient of viscosity over the temperature and humidity range of the data. In addition, the data showed that the molecular relaxation effects, which are responsible for the magnitude of the second coefficient of viscosity, place severe limits on the use of time-independent, thermodynamic equations of state. Compressible flows containing large streamwise velocity gradients, like shock waves, which cause significant changes in particle properties to occur during time intervals shorter than hundredths of seconds, must be modeled using dynamic equations of state. The dynamic model approach is described briefly.

Ash, Robert L.; Zuckerwar, Allan J.; Zheng, Zhonquan

1991-01-01

364

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

365

NASA Technical Reports Server (NTRS)

Optimum and off-optimum properties of circumferentially segmented duct liners are compared with those of uniform liners to identify any potential benefits of circumferentially segmented liners. High- and low-order spinning-mode sources are considered in the study. The solution for the segmented liner is obtained by a multimodal expansion of the segmented-liner eigenmodes in terms of a series of hardwall duct models. The coefficients in the hard-wall series are obtained by using Galerkin's method. Results show that for some frequencies and duct lengths, circumferentially segmented liners scatter energy equally between a higher and lower order circumferential wave number. Studies for higher order spinning-mode sources show that an optimized segmented liner with a hard-wall/soft-wal admittance variation representing an optimum configuration gives better performance than an optimized uniform liner. Overall, the greatest benefit of the segmented liner over the uniform liner occurs under off-optimum conditions. The optimized segmented liner gives more effective broadband performance than the optimized uniform liner.

Watson, W. R.

1982-01-01

366

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

367

Modeling, evaluation, and asymptotic analysis of attenuation anisotropy

NASA Astrophysics Data System (ADS)

Seismic attenuation is sensitive to the physical properties of the subsurface, which makes attenuation analysis a useful tool for reservoir characterization. In this thesis, I present algorithms for estimating directionally dependent attenuation coefficients and perform asymptotic and numerical analysis of wave propagation in attenuative anisotropic media. First, I introduce a methodology to estimate the S-wave interval attenuation coefficient by extending the layer-stripping method of Behura and Tsvankin (2009) to mode-converted (PS) waves. Kinematic reconstruction of pure shear (SS) events in the target layer and the overburden is performed by combining velocity-independent layer stripping with the PP+PS=SS method. Then, application of the spectral-ratio method and the dynamic version of velocity-independent layer stripping to the constructed SS reflections yields the S-wave interval attenuation coefficient in the target layer. The attenuation coefficient estimated for a range of source-receiver offsets can be inverted for the interval attenuation-anisotropy parameters. The method is tested on synthetic data generated with the anisotropic reflectivity method for layered VTI (transversely isotropic with a vertical symmetry axis) media and vertical symmetry planes of orthorhombic media. Then, I analyze a cross-hole data set generated by perforation shots set off in a horizontal borehole to induce hydraulic fracturing in a tight gas reservoir. The spectral-ratio method is applied to pairs of traces to set up a system of equations for directionally-dependent effective attenuation. Although the inversion provides clear evidence of attenuation anisotropy, the narrow range of propagation directions impairs the accuracy of anisotropy analysis. The observed variations of the attenuation coefficient between different perforation stages appear to be related to changes in the medium due to hydraulic fracturing and stimulation. Important insights into point-source radiation in attenuative anisotropic media can be gained by applying asymptotic methods. I derive the asymptotic Green's function in homogeneous, attenuative, arbitrarily anisotropic media using the steepest-descent method. The saddle-point condition helps describe the behavior of the far field slowness and group-velocity vectors and evaluate the inhomogeneity angle (the angle between the real and imaginary parts of the slowness vector). The results from the asymptotic analysis are compared with those from the ray-perturbation method for P-waves in TI media. Finally, I address the problem of efficient viscoelastic modeling in heterogeneous anisotropic media. The Kirchhoff scattering integral is employed to generate reflected P-waves, with the required Green's functions computed by summation of Gaussian beams. The influence of attenuation on the Gaussian beams is incorporated using ray-perturbation theory. The method is applied to generate synthetic data from a highly attenuative VTI medium above a horizontal reflector and a structurally complex acoustic model with a salt body.

Shekar, Bharath Chandra

368

Wave propagation through saturated porous media.

The homogenization procedure is applied to the problem of wave propagation in the biphasic mode in porous media saturated with a Newtonian fluid. The local problems corresponding to the solid and fluid phases have been solved separately for complex three-dimensional media. The effective rigidity tensor, some effective coefficients, the dynamic permeability, the celerities, and the attenuation of the three waves are systematically determined. The characteristic length Lambda was successfully used to gather results for the dynamic permeability as well as for the attenuation coefficients for all media. PMID:18643366

Malinouskaya, I; Mourzenko, V V; Thovert, J-F; Adler, P M

2008-06-01

369

Love wave propagation in piezoelectric layered structure with dissipation.

We investigate analytically the effect of the viscous dissipation of piezoelectric material on the dispersive and attenuated characteristics of Love wave propagation in a layered structure, which involves a thin piezoelectric layer bonded perfectly to an unbounded elastic substrate. The effects of the viscous coefficient on the phase velocity of Love waves and attenuation are presented and discussed in detail. The analytical method and the results can be useful for the design of the resonators and sensors. PMID:19022465

Du, Jianke; Xian, Kai; Wang, Ji; Yong, Yook-Kong

2009-02-01

370

Cardiac Shock Wave Therapy Attenuates H9c2 Myoblast Apoptosis by Activating the AKT Signal Pathway.

Background: Previous studies have demonstrated that Cardiac Shock Wave Therapy (CSWT) improves myocardial perfusion and cardiac function in a porcine model of chronic myocardial ischemia and also ameliorates myocardial ischemia in patients with severe coronary artery disease (CAD). Apoptosis plays a key role in ischemic myocardial pathogenesis. However, it remains unclear whether CSWT is beneficial for ischemia/hypoxia (I/H)-induced myocardial cell apoptosis and by which mechanism CSWT could improve heart function. We put forward the hypothesis that CSWT might protect heart function during ischemia/hypoxia by decreasing apoptosis. Methods: We generated ischemia/hypoxia (I/H)-induced apoptosis in the H9c2 myoblast cell line to examine the CSWT function and possible mechanisms. H9c2 cells were treated under hypoxic serum-starved conditions for 24 h and then treated with or without CSWT (500 shots, 0.06, 0.09, 0.12mJ/mm(2)). The apoptotic cell rate was determined by flow cytometry assay, cell viability was examined by the MTT assay, nuclear fragmentation was detected by Hoechst 33342 staining, and the mitochondrial-mediated intrinsic pathway of apoptosis was assessed by the expression of Bax and Bcl-2 protein and Caspase3 activation. Results: First, apoptosis could be induced by ischemia/hypoxia in H9c2 cells. Second, CSWT attenuates the cell death and decreases the H9c2 cell apoptosis rate induced by ischemia and hypoxia. Third, CSWT suppresses the expression of apoptosis molecules that regulate the intrinsic pathway of apoptosis in H9c2 cells. Fourth, CSWT increases the phosphorylation of AKT, which indicates the activation of the PI3K-AKT pathway. Conclusions: These results indicate that CSWT exerts a protective effect against I/H-induced cell death, potentially by preventing the activation of components of the mitochondrial-dependent intrinsic apoptotic pathway. We also demonstrate that the PI3K-Akt pathway may be involved in the CSWT effects on apoptosis. © 2014 S. Karger AG, Basel. PMID:24802592

Yu, Weiwei; Shen, Tao; Liu, Baoyi; Wang, Shu; Li, Jian; Dai, Dapeng; Cai, Jianping; He, Qing

2014-01-01

371

The attenuation of P waves, the site responses, and the source parameters (seismic moment, corner frequency, source dimension) of 490 seismic events that occurred during the 1997 Colfiorito, Umbria-Marche seismic sequence have been inferred from the inversion of P wave velocity spectra. The Boatwright source model has been assumed to model the source spectra. A global nonlinear inversion scheme was

Salvatore de Lorenzo; Aldo Zollo; Giammaria Zito

2010-01-01

372

National Technical Information Service (NTIS)

An experimental investigation of the refraction of surface gravity waves by relatively narrow (of the order of or less than one wave length) and shallow, laterally sheared, surface currents was undertaken to determine the feasibility of employing artifici...

R. I. Hires

1978-01-01

373

On the apparent attenuation in the spatial coherence estimated from seismic arrays

NASA Astrophysics Data System (ADS)

Several recent studies have used the coherence of seismic noise between stations to retrieve the phase slowness and attenuation. However, there is considerable debate on the feasibility of attenuation retrieval, its interpretation, and its dependence on the noise directionality and has been the subject of several analytical and numerical studies. In this article, we perform a detailed analysis of the various factors that play a role in the estimation of spatial coherence and attenuation from seismic arrays using data from the Southern California Seismic Network. For instance, certain common preprocessing steps such as averaging neighboring frequencies to improve the estimate are sufficient to introduce attenuation-like effects. The presence of first-mode surface Rayleigh wave and P waves in addition to the fundamental mode in Southern California (at frequencies 0.05-0.2 Hz) suggests that the underlying spatial coherence is better modeled as a linear combination of the above wave types. Although this describes the observed coherence better than a simple zeroth-order Bessel function, the resulting phase cancelations due to the multiple seismic waves can be misconstrued as attenuation if not taken into consideration. Using simulations, we show that due to the slowness inhomogeneity, azimuthally averaging the coherence is not equivalent to homogenizing the medium and instead introduces apparent attenuation in the coherence due to interference. Trying to fit an exponential decay model to this apparent attenuation results in an attenuation coefficient which is similar to previously published results.

Menon, Ravishankar; Gerstoft, Peter; Hodgkiss, William S.

2014-04-01

374

We study the effects of frequency-dependent squeeze-amplitude attenuation and squeeze-angle rotation by electromagnetically induced transparency (EIT) on gravitational-wave (GW) interferometers. We propose the use of low-pass, bandpass, and high-pass EIT filters, an S-shaped EIT filter, and an intracavity EIT filter to generate frequency-dependent squeezing for injection into the antisymmetric port of GW interferometers. We find that the EIT filters have several advantages over the previous filter designs with regard to optical losses, compactness, and the tunability of the filter linewidth.

Mikhailov, Eugeniy E.; Goda, Keisuke; Corbitt, Thomas; Mavalvala, Nergis [LIGO Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)

2006-05-15

375

Feasibility of determining Q of near-surface materials from Love waves

NASA Astrophysics Data System (ADS)

High-frequency (? 2 Hz) Multi-channel Analysis of Love Waves (MALW) provides a practical way to determine velocity of horizontally polarized shear (SH) waves for a layered earth model up to 30 m below the ground surface in many geological settings. The information used in the MALW method is phase of Love waves. Information on amplitude of Love waves is not utilized in the MALW method. In this paper we present a method that uses information on amplitude of high-frequency Love waves to estimate quality factors (Qs) of near-surface materials. Unlike Rayleigh waves, attenuation coefficients (amplitude) of Love waves are independent of quality factors for P waves and are function of quality factors of Love waves. In theory, a fewer parameters make the inversion of attenuation coefficients of Love waves more stable and reduce the degree of nonuniqueness. We discussed sensitivity of an inversion system based on a linear relationship between attenuation coefficients and dissipation factors (1/Qs). The sensitivity analysis suggested that damping and constraints to an inversion system are necessary to obtain a smooth and meaningful quality factor model when no other information is available. We used synthetic and real-world data to demonstrate feasibility of inversion of attenuation coefficients of high-frequency Love-wave data acquired with the MALW method for quality factors with a linear, damped and constrained system.

Xia, Jianghai; Yin, Xiaofei; Xu, Yixian

2013-08-01

376

NASA Technical Reports Server (NTRS)

A thin film heat transfer gauge is applied to the measurement of heat transfer coefficients in the interaction regions of incident shock waves and fully developed turbulent boundary layers. It was developed to measure heat flux with high spatial resolution and fast response for wind tunnels with long flow duration. To measure the heat transfer coefficients in the interaction region in detail, experiments were performed under the conditions of Mach number = 4, total pressure = 1.2 MPa, 0.59 to approximately 0.65. Reynolds number = 1.3 to approximately 1.5 x 10 to the 7th power and incident shock angles from 17.8 to 22.8 degrees. The results show that the heat transfer coefficient changes complicatedly in the interaction region. At the beginning the interaction region, the heat transfer coefficient decreases at first, reaches its minimum value at the point where the pressure begins to increase, and then increases sharply. When the boundary layer begins to separate, even a small separation bubble causes significant changes in the heat transfer coefficient, while the pressure does not show any changes which suggests that the boundary layer begins to separate.

Hayashi, M.; Sakurai, A.; Aso, S.

1986-01-01

377

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

378

NASA Astrophysics Data System (ADS)

Passive, high resolution attenuation tomography is used to image the geological structure in the first upper 5 km of shallow crust beneath the Campi Flegrei caldera, Southern Italy. The data set used is composed by 246 local, small magnitude earthquakes recorded at a maximum number of 15 three component, high dynamical range, digital seismic stations. Relocations of the earthquake sources were obtained on the base of the tomography deduced P- and S- velocity model of Battaglia et al. (2008). Single-path inverse-Q for S direct waves was estimated for each source-receiver path using a novel application of coda-normalization method; a modified slope decay method was used instead for direct P-waves. Inversion was carried out using a multi-resolution method, which ensures a minimum cell size resolution of 500 meters in the zones with sufficient ray coverage, and 1000 meters outside these zones. Robustness, stability and checkerboard tests guarantee an optimal reproduction of the synthetic input in a wide area located in the center of the Campi Flegrei caldera, in the depth range between the surface and about 3000 m. The attenuation images are compared with the velocity images obtained by Battaglia et al. (2008) showing high attenuation vertical structures extending between the surface and a depth of about 3000 m below sea level. These structures are interpreted as corresponding to gas reservoirs beneath Solfatara and San Vito, and to intense fluid circulation beneath Mofete, Mt. Nuovo and Astroni-Agnano.The method is also able to image the upper part of the conduit connecting the deep (7 km) magma reservoir to the hydrothermal basins and gas reservoirs under Pozzuoli-Solfatara.

de Siena, L.; Del Pezzo, E.; Bianco, F.

2009-04-01

379

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

380

Quantitative diffusive wave spectroscopy in tissues

High frequency, intensity-modulated light waves are attenuated and phase-shifted by the absorption and scattering properties of highly scattering media, such as tissue. The simultaneous measurement of the average light intensity, modulation amplitude, and phase- shift at a fixed distance from a sinusoidally modulated light source, permits a quantitative determination of the absolute values of the absorption and scattering coefficients from

William W. Mantulin; Joshua B. Fishkin; Peter T. So; Enrico Gratton; John S. Maier

1993-01-01

381

The torsional forced oscillation tests of melt-bearing olivine aggregates reported by Jackson et al. [2004] consistently show a peak in attenuation that is absent from melt-free aggregates tested under similar conditions and grain sizes. Characterization by SEM shows that the melt resides in triple junction tubules and larger pockets as previously described. TEM imaging and EDS analysis reveals that olivine-olivine

Ulrich H. Faul; John D. Fitz Gerald; Ian Jackson

2004-01-01

382

NASA Astrophysics Data System (ADS)

A new type of thin-film heat transfer gauge is applied to the measurement of heat-transfer coefficients in the interaction regions of oblique shock waves and fully developed turbulent boundary layers, for wind tunnels with long flow duration. Experiments have been performed under the conditions of Mach number = 4, total pressure = 1.2 MPa, T(w)/T(o) = 0.59-0.65, Reynolds number = 13-15 million, and incident shock angles from 17.8 to 22.8 deg. Flow fields are visualized by the schlieren technique. Both distributions of surface pressure and heat-transfer coefficient are measured throughout the interaction regions by scanning the shock generator parallel to the free stream. Owing to the high spatial resolution of the new sensor, complicated features of the aerodynamic heating in the interaction regions are revealed.

Hayashi, Masanori; Sakurai, Akira; Aso, Shigeru

383

NASA Astrophysics Data System (ADS)

The Northeast China is an important region of the occurrence of deep earthquakes. In our work we have selected lots of ML amplitudes and travel times of Pn arrivals as reported in the Annual Bulletin of Chinese Earthquakes and regional seismic network of Northeast China. A two-dimensional tomography method is employed to find regional variation of crustal attenuation, Pn velocity and anisotropy in the uppermost mantle in Northeast China and its adjacent regions. Regions with the highest attenuation are beneath Bohai Basin, and Songliao Plain and Hailaer Basin also have low Q0 values, as these areas have thick sedimentary and strong tectonic activity. The entire Northeast region shows distribution of alternating high and low attenuation. And Pn velocity structure is close to the regional tectonic structure and shows distribution of alternating high and low Pn velocity in the direction of NE-NNE. Quantitative analysis result indicates that Pn velocity is positively correlated with crust thickness and negatively correlated with Earth's heatflow. The Pn velocities in the Changbai volcano and Jingpohu volcano activities are obviously low. In addition, the overall performance of Pn anisotropy is weak. This study was supported by the international cooperation project of the Ministry of Science and Technology of China (NO.2011DFB20210) and NSFC (Grant No.41004034).

Sun, Lian; Wu, Qingju

2014-05-01

384

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

385

Flood wave attenuation by a wetland following a beaver dam failure on a second order boreal stream

On June 8 1994, a beaver dam on Rocky Creek, a small stream in central Alberta, failed and released about 7500 m3 of water. The estimated peak of the resulting flood wave was 15 m3 s?1, which is 3.5 times the maximum discharge recorded for the creek over 23 years. The flood wave destroyed five hydrometric\\u000a stations, scoured some channel

Graham R. Hillman

1998-01-01

386

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

387

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

388

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

389

The study of coda waves has recently attracted increasing attention from seismologists. This is due to the fact that it is viewed as a new means by which the stress accumulation stage preceding a large earthquake can be measured, since the scattering paths nearly uniformly cover a fairly large region around the focus and observation stations, compared with the direct

Haruo Sato

1988-01-01