These are representative sample records from Science.gov related to your search topic.
For comprehensive and current results, perform a real-time search at Science.gov.
1

Attenuation coefficients of Rayleigh and Lg waves  

Microsoft Academic Search

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

Igor B. Morozov

2010-01-01

2

Simultaneous estimation of ultrasonic wave speed, sample thickness, attenuation coefficient, and reflection coefficient  

NASA Astrophysics Data System (ADS)

Acoustic wave speed, sample thickness, acoustic attenuation coefficient, and acoustic reflection coefficient are routinely estimated for materials characterization and flaw detection. Previous work at MU yielded a new technique to estimate the wave speed and sample thickness simultaneously. Prior work at MU has also lead to a new approach for simultaneous estimation of attenuation and reflection coefficients given prior knowledge of the sample wave speed and thickness. The research reported in this thesis shows that the simultaneous wave speed and sample thickness estimation technique can be combined with the simultaneous attenuation and reflection coefficient estimation approach. Once the wave speed and Reflection coefficient are estimated the material density can also be estimated. This study shows that without prior knowledge of a sample's properties, it is possible to estimate thickness, acoustic wave speed, acoustic attenuation coefficient, and acoustic reflection coefficient. This is shown theoretically and demonstrated experimentally. The models used are for an isotropic material with a sample of plate type geometry. This is a single sided approach using pulse-echo ultrasonic techniques. The technique utilizes axial scans to find equal diffraction points of interface reflections. The knowledge of the location in the water path length of the equal diffraction points of the interface reflections allows for the estimation of the wave speed and thickness of the sample. Data at the equal diffraction points is then used to calculate the attenuation and reflection coefficients simultaneously. Validity of the combined approach is demonstrated experimentally. Measurement procedures and data processing methods are detailed. Results are given for plastic, copper, and quartz samples. These results are shown with different broadband focused transducers with nominal center frequencies of 5, 10, and 15MHz.

Kinzie, Aaron Wagner

3

Midperiod Rayleigh wave attenuation model for Asia  

Microsoft Academic Search

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

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

2010-01-01

4

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

Microsoft Academic Search

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

Hidetaka Nishida; Hiroshi Yamaguchi; Masashi Yoshida

2001-01-01

5

Measurements of Gamma-Ray Attenuation Coefficients  

Microsoft Academic Search

Measurements have been made to determine gamma-ray attenuation coefficients very accurately by using an extremely-narrow-collimated-beam transmission method which effectively excluded corrections due to small-angle and multiple scattering of photons. The measured mass attenuation coefficients with maximum errors less than 3% for 34 elements in the range from hydrogen to lead are given.

B. Goswami; N. Chaudhuri

1973-01-01

6

Gamma-Ray Attenuation Coefficient Measurements  

Microsoft Academic Search

In an earlier paper, published by the authors elsewhere, it was shown that for 661.6-keV gamma rays the measurements of gamma-ray attenuation coefficients would greatly improve if one uses the counting sequence of Conner et al. together with a new criterion mut<1, where mu is the gamma-ray attenuation coefficient and t is the thickness of the sample. In this paper

S. Gopal; B. Sanjeevaiah

1973-01-01

7

Optical attenuation coefficient in individual ZnO nanowires.  

PubMed

Attenuation coefficient measurements for the propagation of bandedge luminescence are made on individual ZnO nanowires by combining the localized excitation capability of a scanning electron microscope (SEM) with near-field scanning optical microscopy (NSOM) to record the distribution and intensity of wave-guided emission. Measurements were made for individual nanostructures with triangular cross-sections ranging in diameter from 680 to 2300 nm. The effective attenuation coefficient shows an inverse dependence on nanowire diameter (d(-1)), indicating scattering losses due to non-ideal waveguiding behavior. PMID:23482201

Little, Anree; Hoffman, Abigail; Haegel, Nancy M

2013-03-11

8

Measurement of $gamma$-ray attenuation coefficients  

Microsoft Academic Search

Gamma-ray attenuation coefficients have been determined for aluminum, ; copper, tin, platinum and lead (elements with Z between 13 and 82) using gamma -; rays with energies between 295 and 2440 keV from a sealed Ra-226 source. A ; lithium-drifted germanium detector was employed without collimation or shielding. ; The average standard error of the experimental results was 1%. (auth)

Christmas

1974-01-01

9

Unbiased Estimation of Atmosphere Attenuation Coefficient  

Microsoft Academic Search

According to the passive sensors’ nature, only the azimuth and elevation angles are used for the target state estimation.\\u000a In some scenarios, additional information like the irradiances generated by the passive sensors must be introduced to improve\\u000a the estimation process. On the other hand, irradiances are strongly dependent on the atmosphere properties that may be described\\u000a by attenuation coefficient. An

G. D. Dikic; Z. M. Djurovic

2007-01-01

10

Linear attenuation coefficients for compensator based imrt  

Microsoft Academic Search

With rapid technological improvements in computer driven 3-D radiotherapy treatment planning systems (RTPS) the use of compensating\\u000a filters for intensity modulated radiation therapy (IMRT) will dramatically increase the ease of treatment. The procedure for\\u000a commissioning .decimal™ (Sanford, Florida) compensators involved the measurement of the effective linear attenuation coefficients\\u000a for aluminium and brass. Field sizes to be measured vary from small

T. Bartrum; M. Bailey; V. Nelson; M. Grace

2007-01-01

11

Gamma-Ray Attenuation-Coefficient Measurements  

Microsoft Academic Search

Total gamma-ray attenuation coefficients have been measured at nine energies in the range of 88 keV to 2.75 MeV for the following elements: Be, C, Mg, Al, S, Ti, Fe, Ni, Cu, Zn, Zr, Nb, Mo, Ag, Sn, La, Gd, Hf, W, Au, Pb, Th, U, and Pu. Radioactive isotopes were used as sources of monoenergetic gamma radiation in a

A. L. Conner; H. F. Atwater; Elizabeth H. Plassmann; J. H. McCrary

1970-01-01

12

Gamma-ray attenuation coefficients for human tissues  

Microsoft Academic Search

The diagnosis of soft tissue disease such as cancer by radiographic means depends to some extent on the difference in the attenuation of gamma -rays in healthy and diseased tissues. Since devices for imaging very small changes in attenuation are now being introduced, a more exact knowledge of such attenuation coefficients in various tissues would be of help in the

P S Rao; E C Gregg

1974-01-01

13

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

14

Gamma Ray Attenuation Coefficient of Microalloyed Stainless Steel  

Microsoft Academic Search

Gamma ray attenuation coefficients of microalloyed steel have been investigated. For this purposes the linear attenuation\\u000a coefficients of steel have been measured at the photon energy of 0.662, 1.173 and 1.332 MeV and the results were compared\\u000a with the calculation at the photon energy of 1–105 MeV obtained using XCOM.

I. Akkurt; H. Aky?ld?r?m; A. Calik; O. B. Aytar; N. Uçar

2011-01-01

15

Plane-wave attenuation anisotropy in orthorhombic media  

Microsoft Academic Search

Orthorhombic models are often used in the interpretation of azimuthally varying seismic signatures recorded over fractured reservoirs. Here, we develop an analytic framework for describ- ing the attenuation coefficients in orthorhombic media with orthorhombic attenuationi.e., the symmetry of both the real and imaginary parts of the stiffness tensor is identical under the as- sumption of homogeneous wave propagation. The analogous

Yaping Zhu; Ilya Tsvankin

2007-01-01

16

Measurement of Acoustic Attenuation and Absorption Coefficients using Thermometry  

Microsoft Academic Search

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

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

2007-01-01

17

Anisotropy of intrinsic attenuation in the Earth's inner core: quantitative models from normal mode splitting function coefficients  

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

18

Wave attenuation due to Posidonia oceanica meadows  

Microsoft Academic Search

An experimental study carried out in a flume to a scale of 1\\/20 is presented to assess the wave height attenuation induced by submerged meadows of Posidonia oceanica. After examination of the appropriate scaling laws and selection of the model material, an extensive test programme included both regular and random waves. A semi-empirical formulation for estimating the wave height transformation

José Francisco Sánchez-González; Virginia Sánchez-Rojas; Constantine Demetrius Memos

2011-01-01

19

Gamma-ray attenuation coefficients in bismuth borate glasses  

Microsoft Academic Search

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

20

SEISMIC WAVE ATTENUATION IN FLUIDSATURATED POROUS MEDIA  

E-print Network

SEISMIC WAVE ATTENUATION IN FLUID­SATURATED POROUS MEDIA James G. Berryman Lawrence Livermore, seismic attenuation in Biot's theory of fluid­saturated porous media is due to viscous damping of local (not global) pore­ fluid motion. Since substantial inhomogeneities in fluid permeability of porous

21

Gamma ray attenuation coefficient measurement for neutron-absorbent materials  

Microsoft Academic Search

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

Majid Jalali; Ali Mohammadi

2008-01-01

22

Wave Attenuation in Mangrove Forests Numerical modelling of wave attenuation by implementation of a physical description of vegetation in SWAN  

E-print Network

Wave Attenuation in Mangrove Forests Numerical modelling of wave attenuation by implementation. H.J. Verhagen Drs. M. de Vries Dr. ir. M. Zijlema H.J. Opdam #12;Wave Attenuation in Mangrove of interest in this thesis is wave attenuation in vegetation and in particular in mangrove forests

Langendoen, Koen

23

Investigations of the attenuation coefficient of a narrow-bandwidth pulsed laser beam in water  

Microsoft Academic Search

The attenuation coefficient of a pulsed laser beam in water is investigated experimentally. It is found that the attenuation coefficient is dependent on the pulse energy and the linewidth of the laser, rather than a constant. The attenuation coefficient for a narrow linewidth laser can exceed that of a broad linewidth laser due to stimulated Brillouin scattering when the laser

Jianhui Bai; Juan Liu; Yi Huang; Yinan Liu; Lu Sun; Dahe Liu; E. S. Fry

2007-01-01

24

Apparent Linear Attenuation Coefficients in Phase Contrast X-Ray Tomography  

PubMed Central

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. PMID:21691420

Yan, Aimin; Wu, Xizeng

2011-01-01

25

TOWARD A RAYLEIGH WAVE ATTENUATION MODEL FOR ASIA AND SURROUNDING REGIONS  

Microsoft Academic Search

We report on the progress toward the development of attenuation models for short-period (12-22 sec) Rayleigh waves in Asia and surrounding regions. This model is defined by maps of attenuation coefficients across the region of study in the specified period band. The model is designed to calibrate the regional surface-wave magnitude scale and to extend the teleseismic 'surface-wave magnitude -

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

26

Measurement of Acoustic Attenuation and Absorption Coefficients using Thermometry  

NASA Astrophysics Data System (ADS)

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 the junction of the TFT so that it can be insonated from either side leaving the tissue adjacent to the junction unchanged, but changing the overlying thickness. The attenuation and absorption coefficients can be calculated from the heating curves measured in the two orientations. Experiments have been carried out in both tissue mimicking material (TMM) and in ex vivo liver tissue. Weakly focused transducers, resonant at 1.05 MHz, 2.4 MHz and 3.55 MHz were used at free-field spatial peak intensities of 9-14 W/cm2. The temperature rise was measured as a function of time using a TFT. These thermocouples are not subject to the viscous heating artefact that is common to other thermocouple devices and so are advantageous for this purpose. Alignment was achieved with a 3D automated gantry system, which was controlled with specialised software. Timing and data acquisition were also controlled with this software. All experiments were carried out in degassed water. Results for TMM and degassed excised bovine liver are presented.

Morris, Hugh; Rivens, Ian; Shaw, Adam; ter Haar, Gail

2007-05-01

27

PET attenuation coefficients from CT images: experimental evaluation of the transformation of CT into PET 511keV attenuation coefficients  

Microsoft Academic Search

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

28

Uranium soft x-ray total attenuation coefficients  

SciTech Connect

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 accuracy was 3%. Prominent structure was measured within 20 eV of the M/sub 5/ (3.552 keV) and M/sub 4/ (3.728 keV) edges. Jump ratios were determined from log-log polynomial fits to data at energies apart from the near-edge regions. These data were compared with calculations based on a relativistic HFS central potential model and with previously tabulated data.

Del Grande, N.K.; Oliver, A.J.

1981-01-01

29

Representative Elementary Length to Measure Soil Mass Attenuation Coefficient  

PubMed Central

With increasing demand for better yield in agricultural areas, soil physical property representative measurements are more and more essential. Nuclear techniques such as computerized tomography (CT) and gamma-ray attenuation (GAT) have been widely employed with this purpose. The soil mass attenuation coefficient (?s) is an important parameter for CT and GAT analysis. When experimentally determined (?es), the use of suitable sized samples enable to evaluate it precisely, as well as to reduce measurement time and costs. This study investigated the representative elementary length (REL) of sandy and clayey soils for ?es measurements. Two radioactive sources were employed (241Am and 137Cs), three collimators (2–4?mm diameters), and 14 thickness (x) samples (2–15?cm). Results indicated ideal thickness intervals of 12–15 and 2–4?cm for the sources 137Cs and 241Am, respectively. The application of such results in representative elementary area (REA) evaluations in clayey soil clods via CT indicated that ?es average values obtained for x?>?4?cm and source 241Am might induce to the use of samples which are not large enough for soil bulk density evaluations (?s). As a consequence, ?s might be under- or overestimated, generating inaccurate conclusions about the physical quality of the soil under study. PMID:24672338

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

2014-01-01

30

Representative elementary length to measure soil mass attenuation coefficient.  

PubMed

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 ((241)Am and (137)Cs), 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 (137)Cs and (241)Am, 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 (241)Am 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. PMID:24672338

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

2014-01-01

31

The attenuation of strong shock waves  

E-print Network

the shock fzontl revealed that this region lags the shock front by an amount which increases as the shock velocity decreases. However, the magnitude of this lag was tound to depend upon the gain of the photo-detecting circuit employed, so... that with sufficient amplification of the detection signal, its rise approaches coincidence with the shock front arrival. The analysis of the attenuation of strong shock waves presented here represents a preliminary approach to the problem, the theory being over...

Kirkpatrick, Ronald Crecelius

1963-01-01

32

Pressure wave attenuating main steam line apparatus  

SciTech Connect

A main steam line apparatus of a boiling water nuclear reactor plant is claimed including piping for introducing a steam produced in a pressure vessel into a turbine, a main steam valve for rapidly stopping the steam being supplied to the turbine through the piping, and a header. The header is located in the piping between the pressure vessel and the main steam valve. The header causes the pressure wave which occurs when the main steam valve is rapidly closed to be attenuated and an increase in pressure vessel pressure to be suppressed.

Arinobu, M.; Suzuki, I.

1984-05-15

33

Attenuation of a Stoneley wave and higher Lamb modes due to the scattering by two-dimensional irregularities of the walls of a fluid-filled borehole  

Microsoft Academic Search

Attenuation of Stoneley waves and higher Lamb modes propagating along an irregular surface of a fluid-filled borehole is investigated. This problem generalizes the problem on the attenuation of Rayleigh waves by an irregular surface of an empty borehole [10]. The technique used to evaluate the attenuation coefficient is based on the perturbation method (surface irregularity heights are considered to be

G. A. Maximov; E. Ortega; E. V. Pod Yachev

2007-01-01

34

Influences of obstacle geometries on shock wave attenuation  

NASA Astrophysics Data System (ADS)

The interactions of planar shock waves with obstacles of different geometries were investigated numerically using large eddy simulation and a high-order numerical scheme. The immersed boundary method was also employed to handle complex boundary geometries. The development and variations of shock wave structures during the interaction processes were discussed. The influences of the upper side, windward and leeward geometries of the obstacles on shock wave attenuation were also examined. Our numerical results showed that the shock wave attenuation is inversely related to the width of the upper side of the obstacles. For the windward sides of the obstacles, negative slopes have better effects on shock wave attenuation than do other values. In addition, the influence of the leeward slope on shock wave attenuation is weaker than that of the upside and windward slopes. Finally, obstacle shapes with a high efficiency for shock wave attenuation have been obtained and validated.

Sha, S.; Chen, Z.; Jiang, X.

2014-11-01

35

EVALUATION OF SATELLITE DERIVED SPECTRAL DIFFUSE ATTENUATION COEFFICIENTS  

Microsoft Academic Search

Spectral diffuse attenuation Kd(?) is an important apparent optical property that provide information about the attenuation of the spectral downwelling solar irradiance with depth in water. Here we have compared the spectral Kd(?) at ?= 412, 443, 490, 510, 555 and 670 nm derived from the ocean color satellite sensor, SeaWiFS with the in-situ measured values from the Arabian Sea.

T. Suresh; Madhubala Talaulikar; Elgar Desa; Antonio Mascaranhas; S. G. Prabhu

2007-01-01

36

Torsional guided-wave attenuation in coal-tar-enamel-coated, buried piping  

Microsoft Academic Search

Attenuation of the fundamental torsional guided waves in a coal-tar-enamel-coated pipe was investigated experimentally over a 5–30-kHz frequency range and up to a 1.7-m soil cover. The attenuation coefficients in the coated pipe above the ground were an order of magnitude greater than in bare pipe and, over the frequency range studied, it increased approximately linearly with frequency. Soil cover

H Kwun; S. Y Kim; M. S Choi; S. M Walker

2004-01-01

37

Eddy Diffusion Coefficients due to Instabilities in Internal Gravity Waves  

Microsoft Academic Search

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

38

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

39

Monitoring changes of optical attenuation coefficients of acupuncture points during laser acupuncture by optical coherence tomography  

NASA Astrophysics Data System (ADS)

The physical properties of acupuncture point were important to discover the mechanism of acupuncture meridian. In this paper, we used an optical coherence tomography to monitor in vivo the changes of optical attenuation coefficients of Hegu acupuncture point and non-acupuncture point during laser irradiation on Yangxi acupuncture point. The optical attenuation coefficients of Hegu acupuncture point and non-acupuncture point were obtained by fitting the raw data according to the Beer-Lambert's law. The experimental results showed that the optical attenuation coefficient of Hegu acupuncture point decreased during the laser acupuncture, in contrast to a barely changed result in that of non-acupuncture point. The significant change of optical attenuation coefficient of Hegu acupuncture point indicated that there was a correlation between Hegu and Yangxi acupuncture points to some extent.

Huang, Yimei; Yang, Hongqin; Wang, Yuhua; Zheng, Liqin; Xie, Shusen

2010-11-01

40

NXcom – A program for calculating attenuation coefficients of fast neutrons and gamma-rays  

Microsoft Academic Search

This work is concerned with a construction and use of NXcom computer program for calculating the removal and attenuation coefficients of transmitted fast neutrons and ?-rays, respectively, through mixtures, composites, concretes and compounds. The program uses only one input data file for neutrons and ?-rays calculations. For ?-ray attenuation, the program predictions were tested by comparing them with the well-known

A. M. El-Khayatt

2011-01-01

41

Measurement of atomic number and mass attenuation coefficient in magnesium ferrite  

Microsoft Academic Search

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

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

2007-01-01

42

A Precision Measurement of some Attenuation Coefficients for 1.33 MeV Gamma Rays  

Microsoft Academic Search

Measurements of some mass attenuation coefficients for 1.33 MeV ? radiation of 60Co have been performed in excellent narrow beam collimated geometry. The mass attenuation coefficient of aluminum was determined from the experimental transmission curve with a good accuracy (less than 2 × 10-3) and the value obtained was then used as a reference for other elements or compounds: copper,

A-M Roux

1976-01-01

43

A method to determine the gamma-ray linear attenuation coefficient  

Microsoft Academic Search

In this work, gamma-ray linear attenuation coefficients of the materials such as Pb, Fe, Cu and Al were determined by means of traditional energy method and the developed timing detection technique. 1.33MeV-energy radiation emitted from 60Co radioisotope was used in the experiments. The gamma-ray linear attenuation coefficient values of the materials were calculated by using Xcom code, and the experimental

C. Celiktas

2011-01-01

44

A Precision Measurement of some Attenuation Coefficients for 1.33 MeV Gamma Rays  

Microsoft Academic Search

Measurements of some mass attenuation coefficients for 1.33 MeV gamma radiation of 60Co have been performed in excellent narrow beam collimated geometry. The mass attenuation coefficient of aluminum was determined from the experimental transmission curve with a good accuracy (less than 2 × 10-3) and the value obtained was then used as a reference for other elements or compounds: copper,

A.-M. Roux

1976-01-01

45

Study of effective atomic numbers and mass attenuation coefficients in some compounds  

Microsoft Academic Search

The effective atomic numbers and mass attenuation coefficients of some different compounds for total and partial photon interactions have been calculated in the energy range 10?2–105 MeV. The effective atomic numbers and mass attenuation coefficients have also been determined experimentally in the energy range 123–1132 keV by a transmission method. Experimental and theoretical values are in good agreement. The values

K. Singh; Rajinderjit Kaur; Vandana Kumar; Vijay Kumar

1996-01-01

46

ATTENUATION COEFFICIENTS FOR GAMMA RAYS FROM Co⁶°  

Microsoft Academic Search

Attention coefficients in seven different alloys and in Perspex for the ; 1.1715 and 1.3316 Mev gamma radiations from a 17 mc Co⁶° source have been ; estimated by the method of least squares, employing the narrow beam geometry of ; Davisson and Evans with provision for accurate collimation. The experimental ; values for the coefficients and the theoretical values,

S. S. R. Sastry; S. Jnanananda

1958-01-01

47

FREQUENCY DEPENDENT ULTRASONIC ATTENUATION COEFFICIENT ASSESSMENT IN FRESH  

E-print Network

states that the Langevin radiation pressure on a perfectly absorbing target in an open vessel is 2-PL the speed of sound in the medium (1). Multiplying Langevin radiation pressure by the area of the sound beam. Multiplying that force by the speed of sound yields total acoustic power. Attenuation measurements can be made

Illinois at Urbana-Champaign, University of

48

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

49

Mathematical approach to determine the linear attenuation coefficient without collimator in gamma-ray spectrometry.  

PubMed

The linear attenuation coefficient is an important factor in the correction of self-attenuation. In this study, a cone beam from a source of ?1 ?Ci was utilised, not equipped with the collimator, and a complete geometric configuration was mathematically modelled. Samples of NaCl, Na2CO3 and (NH4)2SO4 were used to verify the mathematical model. The linear attenuation coefficient can be calculated within ?4 % of difference in the cylindrical sample at energies of 59.5, 121.8, 244.7, 344.2 and 444.0 keV. PMID:23230217

Kim, Chang-Jong; Cho, Yoon-Hae; Byun, Jong-In; Yun, Ju-Yong

2013-07-01

50

TOTAL ATTENUATION COEFFICIENTS OF 5-11 Mev GAMMA RAYS  

Microsoft Academic Search

The attenuation of neutron-capture gamma rays in Be, Al, Cu, Sn, and ; Pb was measured at energies of 5.44, 6.40, 7.73, and 10.83 Mev. Absorption of ; thermal neutrons frora a reactor by different elements, with the subsequent ; emission of photons, provided the monoenergetic gamma -ray source. An intense ; well-collimated photon beam allowed uncertainties to be held

Barlett

1963-01-01

51

Wave attenuation characteristics of a tethered float system  

Microsoft Academic Search

Wave attenuation characteristics of a tethered float system have been investigated for various wave heights, wave periods, water depths, depths of submergence of floats and float sizes. As the floats are similar in size and shape, only a single tethered spherical float is considered for the theoretical analysis. Float motion is determined through the dynamical equation of motion, developed for

P. Vethamony

1995-01-01

52

Modeling spectral diffuse attenuation, absorption, and scattering coefficients in a turbid estuary  

Microsoft Academic Search

Spectral diffuse attenuation coefficients were measured in the Rhode River and Chesapeake Bay, Maryland, on 28 occasions in 1988 and 1989. The model of Kirk was used to extract scattering and absorption coefficients from the measurements in waters considerably more turbid than those in which the model was previously applied. Estimated scattering coefftcients were linearly related to mineral suspended solids.

CHARLES L. GALLEGOS; DAVID L. CORRELL; J. W. PIERCE

1990-01-01

53

Research on the Submillimeter Wave Hydrometeors Attenuation Characteristic  

Microsoft Academic Search

In the sub-millimeter wave propagation process, attenuation is mainly due to the effects of atmospheric particles, such as\\u000a water vapor. It’s also caused by absorption and scattering by hydrometeors. This paper focuses on the effects of hydrometeors\\u000a on sub-millimeter wave propagation. The formula for calculating the attenuation cross-section of raindrops is given, as well\\u000a as the distance formula of sub-millimeter

Bing Gong; Guowei Lou; Xingguo Li

2009-01-01

54

Stress-associated scattering attenuation and intrinsic attenuation of laboratory ultrasonic waves  

NASA Astrophysics Data System (ADS)

In comparison with seismic velocity and static moduli connected with the large-scale heterogeneous structure, seismic coda attenuation, in response to the small-scale random heterogeneities, has proved to be more sensitive to stress changes. Thus, it has a better chance to become one of the critical values for examining the state of stress changes in rocks. We perform an experiment on ultrasonic scattering using a cylindrical rock sample associated with intra-grain pores and fractures to study the effect of pore-pressure induced stress changes on coda attenuation as a combination of intrinsic attenuation and scattering attenuation. The main problem is to handle multiple side-reflected waves from the rock sample boundaries that may contaminate the ultrasonic coda waves. We analyze the ultrasonic coda data by employing a strongly scattering cylindrical model with two types of extreme boundary conditions. The study confirms that the induced heterogeneous cracks in cylindrical rock make a great impact on estimate of scattering parameters and lead to different stress or frequency dependence of coda attenuation. Comparisons of scattering attenuation and intrinsic attenuation indicate the ultrasonic coda attenuation is mainly contributed by scattering attenuation especially at high frequencies or high stresses.

Wei, W.; Fu, L.

2012-12-01

55

Beam hardening: Analytical considerations of the effective attenuation coefficient of x-ray tomography  

SciTech Connect

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

56

Reconstruction of Ultrasonic Sound Velocity and Attenuation Coefficient Using Linear Arrays: Clinical Assessment  

Microsoft Academic Search

The aim of this study was to determine the efficacy of using sound velocity and tissue attenuation to clinically discriminate breast cancer from healthy tissues. The methods for reconstructing the sound-velocity and attenuation-coefficient distributions were previously proposed and tested on tissue-mimicking phantoms. The methods require only raw channel data acquired by a linear transducer array and can therefore be implemented

Chen-Han Chang; Sheng-Wen Huang; Hsin-Chia Yang; Yi-Hong Chou; Pai-Chi Li

2007-01-01

57

X-Ray Attenuation Coefficients from 13 to 80 Mev for Hydrogen, Carbon, Water, and Aluminum  

Microsoft Academic Search

The x-ray attenuation coefficients for hydrogen, carbon, water, and aluminum have been measured in the energy range from 13 to 80 Mev by placing varying lengths of attenuators in a 90-Mev bremsstrahlung beam in a good geometry experiment using a large sodium-iodide total-absorption spectrometer as the detector. In the hydrogen case, a difference method employing cyclohexane (C6H12) and graphite was

J. M. Wyckoff; H. W. Koch

1960-01-01

58

Linear attenuation coefficient and build up factor of MCP-96 alloy for radiation shielding and protection  

Microsoft Academic Search

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 gamma-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

Deidre Hopkins; Muhammad Maqbool; Mohammed Islam

2009-01-01

59

IEEE TRANSACTIONSON SONICS ANDULTRASONICS, VOL. SU-32,NO. 2, MARCH 1985 259 Attenuation Coefficient Measurement Technique at  

E-print Network

is the ultrasonic attenuation coefficient, which is the de- crease in energy of the sound wavewhenit propagates throughamaterial. The attenuation includes absorption and scattering.Absorption represents the loss of energy

Illinois at Urbana-Champaign, University of

60

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

NASA Astrophysics Data System (ADS)

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

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

2010-09-01

61

Wave attenuation in thick graphite\\/epoxy composites  

Microsoft Academic Search

The mechanics of wave attenuation in thick graphite\\/epoxy composites is examined in order to facilitate interpretation of the wave amplitudes recorded in ultrasonic experiments. The values of a small number of parameters are determined through comparison between calculated and measured waveforms for four specimens. The agreement between the measured and calculated waveforms are shown to be excellent in all four

A. K. Mal; Y. Bar-Cohen

1992-01-01

62

Wave attenuation in thick graphite/epoxy composites  

NASA Technical Reports Server (NTRS)

The mechanics of wave attenuation in thick graphite/epoxy composites is examined in order to facilitate interpretation of the wave amplitudes recorded in ultrasonic experiments. The values of a small number of parameters are determined through comparison between calculated and measured waveforms for four specimens. The agreement between the measured and calculated waveforms are shown to be excellent in all four cases.

Mal, A. K.; Bar-Cohen, Y.

1992-01-01

63

Measurement of atomic number and mass attenuation coefficient in magnesium ferrite  

Microsoft Academic Search

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

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

2007-01-01

64

Remote sensing algorithm of particle attenuation coefficient in East China Sea  

NASA Astrophysics Data System (ADS)

China coastal sea is characteristic of the high concentration of suspended matter which has complex components of mineral particles, organic detritus and phytoplankton, etc. The similarity of spectrum characters of mineral particles and organic particles in backscattering coefficient, and the organic detritus and color dissolve organic matters (CDOM) in absorption coefficient makes the information inverse of coastal ocean color become a very difficult work. In this paper, based on the in situ data of optical investigation in East China Sea in the spring of 2003, including the absorption coefficients of CDOM and de-pigment particles from laboratory spectrophotometer measurement, and the field measurement with ac-9 (WET labs, Inc.), the optical properties of suspended particles were studied. And then, a semi-analysis algorithm of particle attenuation coefficient (Cp) in ECS was developed. There are two key steps in this algorithm, one is the estimation of the ratio of particle backscattering coefficient to the total scattering coefficient; and the other is the retrieval of absorption coefficient of CDOM. With this inversion algorithm of Cp and the input of remote sensing reflectance obtained from the underwater profiler radiometer (Satlantic. Inc.), the particle attenuation coefficient was inversed, which was consistent well with the in situ data of Cp . In the high turbid water, the scattering signal is dominant in the Cp values, so the modeled-Cp was less than the in situ data due to the underestimation of backscattering coefficient in IOPs semi-analysis algorithms. The modeled -Cp at 660nm wavelength has the R2 of 0.84 and RMSE=0.22 compared with the attenuation coefficient at 650nm measured by the ac-9, in which the absorption coefficient of CDOM is neglect. The semi-analysis algorithms of Cp developed in this paper showed a good potential to estimate the biogeochemical parameters, like POC, but the further study should be focused on the distinguish of the sub-division materials with more in situ data set.

Bai, Yan; He, Xianqiang; Pan, Delu; Hao, Zengzhou; Song, Qingjun; Lei, Hui

2008-10-01

65

Angular correlation function and scattering coefficient of electromagnetic waves  

E-print Network

Angular correlation function and scattering coefficient of electromagnetic waves scattered We study three-dimensional (3-D) electromagnetic wave scattering from a buried object under a two-3232(98)00412-8] OCIS codes: 290.0290, 290.5880. 1. INTRODUCTION The study of electromagnetic wave scattering

Zhang, Guifu

66

Analysis of dispersion and attenuation of surface waves in poroelastic media in the exploration-seismic frequency band  

USGS Publications Warehouse

We analyse dispersion and attenuation of surface waves at free surfaces of possible vacuum/poroelastic media: permeable-'open pore', impermeable-'closed pore' and partially permeable boundaries, which have not been previously reported in detail by researchers, under different surface-permeable, viscous-damping, elastic and fluid-flowing conditions. Our discussion is focused on their characteristics in the exploration-seismic frequency band (a few through 200 Hz) for near-surface applications. We find two surface-wave modes exist, R1 waves for all conditions, and R2 waves for closed-pore and partially permeable conditions. For R1 waves, velocities disperse most under partially permeable conditions and least under the open-pore condition. High-coupling damping coefficients move the main dispersion frequency range to high frequencies. There is an f1 frequency dependence as a constant-Q model for attenuation at high frequencies. R1 waves for the open pore are most sensitive to elastic modulus variation, but least sensitive to tortuosities variation. R1 waves for partially permeable surface radiate as non-physical waves (Im(k) < 0) at low frequencies. For R2 waves, velocities are slightly lower than the bulk slow P2 waves. At low frequencies, both velocity and attenuation are diffusive of f1/2 frequency dependence, as P2 waves. It is found that for partially permeable surfaces, the attenuation displays -f1 frequency dependence as frequency increasing. High surface permeability, low-coupling damping coefficients, low Poisson's ratios, and low tortuosities increase the slope of the -f1 dependence. When the attenuation coefficients reach 0, R2 waves for partially permeable surface begin to radiate as non-physical waves. ?? 2011 The Authors Geophysical Journal International ?? 2011 RAS.

Zhang, Y.; Xu, Y.; Xia, J.

2011-01-01

67

Dispersion and attenuation of acoustic waves in randomly heterogeneous media  

NASA Astrophysics Data System (ADS)

We derive the effective displacement relation for acoustic waves in a spatially random heterogeneous one-dimensional medium. This relationship is expressed in terms of parameters ?R and ?A which represent the standard deviations of the randomly varying density ?( x) and the randomly varying Young's modulus ?( x), of the medium. In this way, we build the contributions into the total displacement relationship for the spatially random heterogeneous medium and apply this result to determine the dispersion and attenuation of acoustic waves propagating in the random heterogeneous medium. Attenuation and dispersion of waves propagating in media with randomly varying properties has been the subject of much study. Most of this work has neglected the effects of intrinsic dispersion and attenuation in order to concentrate on the effects of the medium inhomogeneities. We demonstrate how intrinsic attenuation may be easily included in the theoretical development, and explore the combined effects of scattering-based and intrinsic attenuation and dispersion on wave propagation. We apply the solution to model interwell acoustic waves propagating in the Kankakee formation at the Buckhorn Test Site, IL. The modeling results show that the strong dispersion in the frequency range of 500-2000 Hz is due to the reservoir heterogeneity. Alternatively, the velocity dispersion for frequencies greater than 2000 Hz corresponds to the intrinsic properties of the reservoir.

Parra, J. O.; Hackert, C. L.; Ababou, R.; Sablik, M. J.

1999-10-01

68

Attenuation of a Stoneley wave and higher Lamb modes due to the scattering by two-dimensional irregularities of the walls of a fluid-filled borehole  

Microsoft Academic Search

Attenuation of Stoneley waves and higher Lamb modes propagating along an irregular surface of a fluid-filled borehole is investigated.\\u000a This problem generalizes the problem on the attenuation of Rayleigh waves by an irregular surface of an empty borehole [10].\\u000a The technique used to evaluate the attenuation coefficient is based on the perturbation method (surface irregularity heights\\u000a are considered to be

G. A. Maximov; E. Ortega; E. V. Pod”yachev

2007-01-01

69

ELASTIC WAVE ATTENUATION IN ROCKS CONTAINING FLUIDS  

E-print Network

, 17\\Gamma19 (3) macroscopic flow between regions of liquid saturation and regions of gas saturation widely in magnitude. A simple calculation of the overall behavior of a layered porous material using local­flow Biot theory shows that the effective permeability for attenuation is the mean

70

Linear attenuation coefficient and build up factor of MCP-96 alloy for radiation shielding and protection  

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

71

Frequency dispersion of ultrasonic velocity and attenuation of longitudinal waves propagating in 0.68Pb,,Mg1/3Nb2/3...O30.32PbTiO3 single crystals  

E-print Network

Frequency dispersion of ultrasonic velocity and attenuation of longitudinal waves propagating in 0 ultrasonic spectroscopy, the frequency dispersion of ultrasonic velocity and attenuation in the frequency coefficient and higher attenuation of ultrasonic waves in multiple-domain 1-x Pb Mg1/3Nb2/3 O3­xPbTiO3 single

Cao, Wenwu

72

Gamma ray attenuation coefficient measurements at 1115, 1173, and 1332 keV  

Microsoft Academic Search

Gamma ray attenuation coefficients in C, Al, Cu, Zr, Sn and Pb were measured for gamma ray energies 1115, 1173 and 1330 keV using the technique employed earlier by the authors for similar measurements at lower energies. The results will be presented here and discussed.

S. Gopal; B. Sanjeevaiah

1977-01-01

73

Two media method for gamma ray attenuation coefficient measurement of archaeological ceramic samples  

Microsoft Academic Search

This work reports the application of an alternative methodology for the linear attenuation coefficient determination of irregular shape samples, in such a way that it is not necessary to know the sample thickness. Based on this method, indigenous archaeological ceramic fragments from the region of Londrina, north of Parana State in Brazil, were studied. On the other hand, theoretical mass

R. M Cunha e Silva; C. R Appoloni; P. S Parreira; F. R Espinoza-Quiñones; M. M Coimbra; P. H. A Aragão

2000-01-01

74

Improvements in the two media method for measurements of gamma-ray linear attenuation coefficients  

Microsoft Academic Search

The two media method has been previously presented as a solution to the problem of measuring gamma-ray attenuation coefficients of odd-shaped samples. We propose that air is chosen as one of the two media. We theoretically demonstrate that this choice simplifies the equation used, as well as the laboratory work, and also reduces some of the terms associated with experimental

Elimoel A. Elias

2003-01-01

75

Modeling the vertical distributions of downwelling plane irradiance and diffuse attenuation coefficient in optically deep waters  

Microsoft Academic Search

The diffuse attenuation coefficient (Kd) is critical to understand the vertical distribution of underwater downwelling irradiance (Ed). Theoretically Ed is composed of the direct solar beam and the diffuse sky irradiance. Applying the statistical results from Hydrolight radiative transfer simulations, Kd is expressed into a mathematical equation (named as PZ06) integrated from the contribution of direct solar beam and diffuse

Xiaoju Pan; Richard C. Zimmerman

2010-01-01

76

Total photon attenuation coefficients in some rare earth elements using selective excitation method  

NASA Astrophysics Data System (ADS)

The total mass attenuation coefficients were measured in the elements La, Nd, Sm, Gd and Dy belonging to rare earth region in the energy range 30-55 keV by employing the selective excitation method. This method facilitates selection of excitation energies near the K edge. The present experimental results were compared with the theoretical values due to Chantler and XCOM.

SitaMahalakshmi, N. V.; Kareem, M. A.; Premachand, K.

2015-01-01

77

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

78

Attenuation of acoustic waves in glacial ice and salt domes  

E-print Network

Two classes of natural solid media (glacial ice and salt domes) are under consideration as media in which to deploy instruments for detection of neutrinos with energy >1e18 eV. Though insensitive to 1e11 to 1e16 eV neutrinos for which observatories (e.g., AMANDA and IceCube) that utilize optical Cherenkov radiation detectors are designed, radio and acoustic methods are suited for searches for the very low fluxes of neutrinos with energies >1017 eV. This is because, due to the very long attenuation lengths of radio and acoustic waves in ice and salt, detection modules can be spaced very far apart. In this paper, I calculate the absorption and scattering coefficients as a function of frequency and grain size for acoustic waves in glacial ice and salt domes and show that experimental measurements on laboratory samples and in glacial ice and salt domes are consistent with theory. For South Pole ice with grain size 0.2 cm at -51 degrees C, scattering lengths are calculated to be 2000 km and 25 km at 10 kHz and 30 kHz, respectively, and the absorption length is calculated to be 9 km at frequencies above 100 Hz. For NaCl (rock salt) with grain size 0.75 cm, scattering lengths are calculated to be 120 km and 1.4 km at 10 kHz and 30 kHz, and absorption lengths are calculated to be 30,000 km and 3300 km at 10 kHz and 30 kHz. Existing measurements are consistent with theory. For ice, absorption is the limiting factor; for salt, scattering is the limiting factor.

P. B. Price

2005-06-27

79

Estimate of attenuation coefficient for ultrasonic tissue characterization using time-varying state-space model.  

PubMed

The images generated from ultrasound pulse-echo signals have long been used to aid clinical diagnosis. Recently, there has been a growing interest in quantitatively determining the acoustic parameters of the tissue as a means of classification and diagnosis. For example, the frequency-dependent attenuation is known to be correlated with different diseases in the liver. In this paper we introduce a new technique for estimating the attenuation coefficient. The effect of attenuation on an interrogating signal with a gaussian-shaped spectrum can be obtained by studying the Wigner distribution of reflected rf data based on a one-dimensional signal model. We show that under the condition that the attenuation varies linearly with frequency, the spectral mean of the reflected signal decreases linearly with time. The estimation algorithm models the pulse-echo signal as the output of a second-order time-varying state-space innovations model driven by white noise. The state coupling matrix A and the output coupling vector C vary with time in a known fashion; moreover, they are also functions of an unknown constant parameter theta. The attenuation coefficient, which is one of the elements of theta, can be estimated directly using a recursive system identification algorithm. The algorithm was verified using both computer-generated synthetic data and in-vivo liver data of known diagnosis. The results show correlation between the estimated parameter and the pathological state of the tissue. PMID:3057715

Shih, L Y; Barnes, C W; Ferrari, L A

1988-04-01

80

Determination of attenuation coefficient for self-absorption correction in routine gamma ray spectrometry of environmental bulk sample  

Microsoft Academic Search

A simple method to determine -ray attenuation coefficients using Ba-133 -rays has been developed and applied to self-absorption correction in routine -ray spectrometry for environmental samples composed of unknown matrix elements. Experimental values of the mass attenuation coefficient obtained by the method agree well with calculated values for samples of known elemental composition which was determined by means of chemical

K. Satoh; N. Ohashi; H. Higuchi; M. Noguchi

1984-01-01

81

Attenuation of electromagnetic waves in onion-like carbon composites  

Microsoft Academic Search

We report the first results on measurements of electromagnetic wave attenuation of onion-like carbon (OLC) powders and OLC-based polymer films on a substrate. The measurements cover a wide frequency range 2–38 GHz and demonstrate promising high potential of OLC-based composites as basic components for wideband electromagnetic wave absorbing materials. A description of the measurement technique is presented. Possibility and mechanisms of

S. A. Maksimenko; V. N. Rodionova; G. Ya. Slepyan; V. A. Karpovich; O. Shenderova; J. Walsh; V. L. Kuznetsov; I. N. Mazov; S. I. Moseenkov; A. V. Okotrub; Ph. Lambin

2007-01-01

82

A generalized method of converting CT image to PET linear attenuation coefficient distribution in PET/CT imaging  

NASA Astrophysics Data System (ADS)

The accuracy of attenuation correction in positron emission tomography scanners depends mainly on deriving the reliable 511-keV linear attenuation coefficient distribution in the scanned objects. In the PET/CT system, the linear attenuation distribution is usually obtained from the intensities of the CT image. However, the intensities of the CT image relate to the attenuation of photons in an energy range of 40 keV-140 keV. Before implementing PET attenuation correction, the intensities of CT images must be transformed into the PET 511-keV linear attenuation coefficients. However, the CT scan parameters can affect the effective energy of CT X-ray photons and thus affect the intensities of the CT image. Therefore, for PET/CT attenuation correction, it is crucial to determine the conversion curve with a given set of CT scan parameters and convert the CT image into a PET linear attenuation coefficient distribution. A generalized method is proposed for converting a CT image into a PET linear attenuation coefficient distribution. Instead of some parameter-dependent phantom calibration experiments, the conversion curve is calculated directly by employing the consistency conditions to yield the most consistent attenuation map with the measured PET data. The method is evaluated with phantom experiments and small animal experiments. In phantom studies, the estimated conversion curve fits the true attenuation coefficients accurately, and accurate PET attenuation maps are obtained by the estimated conversion curves and provide nearly the same correction results as the true attenuation map. In small animal studies, a more complicated attenuation distribution of the mouse is obtained successfully to remove the attenuation artifact and improve the PET image contrast efficiently.

Wang, Lu; Wu, Li-Wei; Wei, Le; Gao, Juan; Sun, Cui-Li; Chai, Pei; Li, Dao-Wu

2014-02-01

83

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.

2012-03-01

84

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

85

Attenuation of sound waves in drill strings  

Microsoft Academic Search

During drilling of deep wells, digital data are often transmitted from sensors located near the drill bit to the surface. Development of a new communication system with increased data capacity is of paramount importance to the drilling industry. Since steel drill strings are used, transmission of these data by elastic carrier waves traveling within the drill pipe is possible, but

Douglas S. Drumheller

1993-01-01

86

Attenuation of coda waves in Western Anatolia  

Microsoft Academic Search

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

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

1994-01-01

87

Spectral wave flow attenuation within submerged canopies: Implications for wave energy dissipation  

Microsoft Academic Search

Communities of benthic organisms can form very rough surfaces (canopies) on the seafloor. Previous studies have shown that an oscillatory flow induced by monochromatic surface waves will drive more flow inside a canopy than a comparable unidirectional current. This paper builds on these previous studies by investigating how wave energy is attenuated within canopies under spectral wave conditions, or random

Ryan J. Lowe; James L. Falter; Jeffrey R. Koseff; Stephen G. Monismith; Marlin J. Atkinson

2007-01-01

88

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

Microsoft Academic Search

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

Y. Ozeren; D. G. Wren

2010-01-01

89

Total attenuation coefficient of intralipid dilutions for discrete laser wavelengths between 405 and 1315 nm  

NASA Astrophysics Data System (ADS)

The experimental investigations on different aspects of optical tomography require the knowledge of the optical parameters of tissues and tissue-like phantoms in order to unambiguously interpret the experimental data and specify characteristic inhomogeneities in tissue diagnostics. The main optical parameters of interest are the absorption coefficient, the scattering, backscattering, and reduced-scattering coefficients, the total attenuation (extinction) coefficient and the anisotropy factor. In this work, we extend our investigations of the optical properties of tissuemimicking phantoms, such as Intralipid-20% fat emulsion, using an approach we have developed recently based on the peculiarities of laser radiation beams propagating through semi-infinite turbid media. The dependence of the total attenuation coefficient on the Intralipid concentration, for laser radiation wavelengths ?=405, 672, 850, and 1314 nm, is studied, by using a set of phantoms consisting of different dilutions of Intralipid in distilled water. The experimental results for the extinction are in agreement with our previous results and with empiric formulae found by other authors concerning the wavelength dependence of the scattering coefficient of Intralipid -10% and Intralipid - 20%. They are also in agreement with known data of the water absorptance. As a whole, the results obtained in this work confirm the consideration of the experimental phantoms as semi-infinite media. They also confirm and extend theoretical and experimental results obtained previously, and reveal advantages of using longer wavelengths for deeper diagnostics of tissues and mimic turbid media.

Dreischuh, Tanja N.; Gurdev, Ljuan L.; Vankov, Orlin I.; Avramov, Lachezar A.; Stoyanov, Dimitar V.

2015-01-01

90

Measurement of photon mass attenuation coefficients of plutonium from 60 to 2615 keV  

Microsoft Academic Search

Measurements have been made to determine plutonium photon mass attenuation coefficients by using a collimated-beam transmission method in the energy range from 60 to 2615keV. These experimental results were compared with previous experimental and theoretical data. Good agreements are observed in the 240–800keV energy range, whereas differences up to maximum 10% are observed out of these limits.

M. Rettschlag; R. Berndt; P. Mortreau

2007-01-01

91

Measurement of mass attenuation coefficients of biological materials by energy dispersive X-ray fluorescence spectrometry  

Microsoft Academic Search

The mass attenuation coefficients for cornea taken from keratitis patient and soft contact lens (-1.75, -3.75, -4 dioptres), leiomyomata uteri and uterus were measured in the X-ray energy (5.9keV) using a SiLi detector and Fe55 annular source. Full details of the experimental method, experimental set up, the procedure of sample preparation and the results within estimated error are presented. Energy

N. Ekinci; N. Astam

2007-01-01

92

Comparison of measured and satellite-derived spectral diffuse attenuation coefficients for the Arabian Sea  

Microsoft Academic Search

We present here the results of our study comparing the spectral diffuse attenuation coefficients Kd(?) measured in the Arabian Sea with those derived from the Sea-Viewing Wide Field-of-View Sensor (SeaWiFS) using three algorithms, of which two are empirical-data-driven and one is semi-analytical. The measurements were carried out in all water types and the mean values of the measured spectral Kd(?)

Suresh Thayapurath; Madhubala Talaulikar; Elgar Desa; S. G. P. Matondkar; Antonio Mascarenhas

2011-01-01

93

Gamma-ray attenuation coefficients of some building materials available in Egypt  

Microsoft Academic Search

Mass attenuation coefficients of various types of building materials were measured using a high-resolution HPGe spectrometer detector. Samples were irradiated by gamma-rays emitted from point sources of 241Am, 133Ba, 60Co and 137Cs. The results are in good agreement with the theoretical calculations of XCOM code. The effectiveness of building materials in shielding were determined over the range 50–3000keV. Finally, the

M. E. Medhat

2009-01-01

94

Determination of attenuation coefficients, thicknesses and effective atomic numbers for CuInSe 2 semiconductor  

Microsoft Academic Search

The X-rays attenuation coefficients for Cu, In and Se in elemental state and the semiconductor CuInSe2 were measured at 15 different energies from 11.9 to 37.3keV by using the secondary excitation method. Monochromatic photons were obtained using the following secondary targets: Br, Sr, Mo, Cd, Te and Ba. 59.5keV gamma rays emitted from an annular 241Am radioactive source were used

Hasan Baltas; Ahmet Çelik; Emin Bacaksiz

2006-01-01

95

Diffuse attenuation coefficient of downwelling irradiance: An evaluation of remote sensing methods  

Microsoft Academic Search

The propagation of downwelling irradiance at wavelength ? from surface to a depth (z) in the ocean is governed by the diffuse attenuation coefficient, $\\\\bar{K}_{d}$(?). There are two standard methods for the derivation of $\\\\bar{K}_{d}$(?) 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 $\\\\bar{K}_{d}$(?) from

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

2005-01-01

96

Body Wave Crustal Attenuation Characteristics in the Garhwal Himalaya, India  

NASA Astrophysics Data System (ADS)

We estimate frequency-dependent attenuation of P and S waves in Garhwal Himalaya using the extended coda normalization method for the central frequencies 1.5, 2, 3, 4, 6, 8, 10, 12, and 16 Hz, with earthquake hypocentral distance ranging from 27 to 200 km. Forty well-located local earthquake waveforms were used to study the seismic attenuation characteristics of the Garhwal Himalaya, India, as recorded by eight stations operated by Wadia Institute of Himalayan Geology, Dehradun, India, from 2007 to 2012. We find frequency-dependent P and S wave quality factors as defined by the relations Q P = 56 ± 8f 0.91±0.002 and Q S = 151 ± 8f 0.84±0.002 by fitting a power-law frequency dependence model for the estimated values over the whole region. Both the Q P and Q S values indicate strong attenuation in the crust of Garhwal Himalaya. The ratio of Q S/Q P > 1 obtained for the entire analyzed frequency range suggests that the scattering loss is due to a random and high degree of heterogeneities in the earth medium, playing an important role in seismic wave attenuation in the Himalayan crust.

Negi, Sanjay S.; Paul, Ajay; Joshi, Anand; Kamal

2014-11-01

97

Periodic solutions to nonlinear wave equations with spatially dependent coefficients  

NASA Astrophysics Data System (ADS)

This paper investigates the existence and uniqueness of weak solutions to a periodic boundary value problem for a system of nonlinear wave equations with spatially dependent coefficients. Priori estimates of weak solutions are also established for the periodic boundary value problem. The arguments rely on spectral properties of the corresponding wave operator and a global inverse function theorem. The results presented in this paper extend the ones known in the literature in that eigenvalues of nonlinear perturbing terms appeared in the system of nonlinear wave equations can be chosen from the spectrum of the underlying wave operator.

Chen, Jinhai

2015-01-01

98

Observations of the vertical structure of the diffuse attenuation coefficient spectrum  

NASA Astrophysics Data System (ADS)

Profiles of the diffuse attenuation coefficient spectrum for downwelling spectral irradiance ( Kd( z, ?)) were determined using data taken during the autumn of 1982 in the eastern North Pacific Ocean as part of the Optical Dynamics Experiment (ODEX). The near-surface Kd(5 m, ?) was consistent with Jerlov water types IA or IB and did not show any significant variations with sun altitude angle or cloud amount, supporting the notion that Kd( z, ?) is a "quasi-inherent" optical property. Vertical profiles of Kd( z, ?) showed significant structures with amplitudes that decrease with increasing wavelength. The observed depth-wavelength distribution may be divided into a blue-green group (400-500 nm) with a vertical structure similar to the vertical distribution of chlorophyll pigments and a green-yellow group (500-575 nm) with little vertical variation. For wavelengths >575 nm, the values of Kd( z, ?) decreased with depth apparently because of limitations of the irradiance sensors. The mean vertical distribution of Kd( z, ?) for the blue-green group was well-correlated with the mean in situ fluorescence (correlation coefficient r ˜ 0.94-0.99) and with the mean total pigment concentration ( r ˜ 0.90-0.95). The correlation coefficients relating Kd( z, ?) with the phaeopigment concentration ( r ˜ 0.84-0.92) were higher than those relating the chlorophyll a concentration ( r ˜ 0.63-0.90), indicating the contributions of detrital materials. The mean beam attenuation coefficient at 660 nm was not significantly correlated with Kd( z, ?). The total pigment specific diffuse attenuation coefficient spectrum was similar to spectra determined from previous studies, with departures only in the blue region of the spectrum ( ? < 440 nm). The differences may be attributed to detrital effects.

Siegel, D. A.; Dickey, T. D.

1987-04-01

99

Frequency-Dependent Attenuation of Coda Waves in the Crust in Southwest Anatolia (Turkey)  

NASA Astrophysics Data System (ADS)

The attenuation of coda waves in the earth's crust in southwest (SW) Anatolia is estimated by using the coda wave method, which is based on the decrease of coda wave amplitude in time and distance. A total of 159 earthquakes were recorded between 1997 and 2010 by 11 stations belonging to the KOERI array. The coda quality factor Q c is determined from the properties of scattered coda waves in a heterogeneous medium. Firstly, the quality factor Q 0 (the value of Q c at 1 Hz.) and its frequency dependency ? are determined from this method depending on the attenuation properties of scattered coda waves for frequencies of 1.5, 3.0, 6.0, 8.0, 12 and 20 Hz. Secondly, the attenuation coefficients ( ?) are estimated. The shape of the curve is controlled by the scattering and attenuation in the crustal volume sampled by the coda waves. The average Q c values vary from 110 ± 15 to 1,436 ± 202 for the frequencies above. The Q 0 and ? values vary from 63 ± 7 to 95 ± 10 and from 0.87 ± 0.03 to 1.04 ± 0.09, respectively, for SW Anatolia. In this region, the average coda Q- f relation is described by Q c = (78 ± 9) f 0.98±0.07 and ? = 0.012 km-1. The low Q 0 and high ? are consistent with a region characterized by high tectonic activity. The Q c values were correlated with the tectonic pattern in SW Anatolia.

?ahin, ?akir; Çinar, Mutlu

2014-07-01

100

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

Microsoft Academic Search

The linear attenuation coefficient (mu) and mass attenuation coefficients (mu\\/rho) 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. A comparison of shielding properties of these glasses

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

1996-01-01

101

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

Microsoft Academic Search

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

102

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

103

Spatial variation of coda wave attenuation in northwestern Colombia  

NASA Astrophysics Data System (ADS)

One thousand seven hundred and eighty-six vertical-component, short-period observations of microearthquake codas from regional earthquakes recorded by 17 stations belonging to the National Seismological Network of Colombia were used to estimate seismic wave attenuation in Colombia. Local magnitudes range from 2.9 to 6.0 and only events occurring at hypocentral distances up to 255 km were considered for the analysis. The frequencies of interest lay between 1 and 19 Hz and the analysis was performed for each seismic station separately. Coda-wave attenuation (Q-1c) was estimated by means of a single-scattering method whereas the separation of intrinsic absorption (Q-1i) and scattering attenuation (Q-1s) from total attenuation (Q-1t) was performed using a multiple lapse time-window analysis based on the hypothesis of multiple isotropic scattering and uniform distribution of scatterers. A regionalization of the estimated Q0 (Qc at 1 Hz) values was performed and a contour map of seismic coda attenuation in Colombia is presented, where four zones with significant variations of attenuation related to different geological and tectonic characteristics can be observed. The highest attenuation is linked to the central and western regions (Q0 around 50 and 56) whereas a lower attenuation (Q0 around 69 and 67) is assigned to the northern and eastern regions. Results show that the Q-1 values are frequency dependent in the considered frequency range, and are approximated by a least-square fit to the power law Q-1(f) =Q-10(f/f0)-?. The exponents of the frequency dependence law ranged from ?= 0.65 to 1.01 for Q-1c, ?= 0.62 to 1.78 for Q-1i, ?= 0.28 to 1.49 for Q-1s, and ?= 0.53 to 1.67 for Q-1t. On the other hand, intrinsic absorption is found to dominate over scattering in the attenuation process for most of the stations and frequency bands analysed. Some discrepancies have been observed between the theoretical model and the observations for some frequency bands which indicate that it would be necessary to consider models for depth-dependent velocity structure and/or non-isotropic scattering patterns.

Vargas, Carlos A.; Ugalde, Arantza; Pujades, Lluís G.; Canas, José A.

2004-08-01

104

Simultaneous reconstruction of emission activity and attenuation coefficient distribution from TOF data, acquired with external transmission source  

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

105

Wave attenuation over coastal salt marshes under storm surge conditions  

NASA Astrophysics Data System (ADS)

Coastal communities around the world face an increasing risk from flooding as a result of rising sea level, increasing storminess and land subsidence. Salt marshes can act as natural buffer zones, providing protection from waves during storms. However, the effectiveness of marshes in protecting the coastline during extreme events when water levels are at a maximum and waves are highest is poorly understood. Here we experimentally assess wave dissipation under storm surge conditions in a 300-metre-long wave flume tank that contains a transplanted section of natural salt marsh. We find that the presence of marsh vegetation causes considerable wave attenuation, even when water levels and waves are highest. From a comparison with experiments without vegetation, we estimate that up to 60% of observed wave reduction is attributed to vegetation. We also find that although waves progressively flatten and break vegetation stems and thereby reduce dissipation, the marsh substrate remained stable and resistant to surface erosion under all conditions. The effectiveness of storm wave dissipation and the resilience of tidal marshes even at extreme conditions suggest that salt marsh ecosystems can be a valuable component of coastal protection schemes.

Möller, Iris; Kudella, Matthias; Rupprecht, Franziska; Spencer, Tom; Paul, Maike; van Wesenbeeck, Bregje K.; Wolters, Guido; Jensen, Kai; Bouma, Tjeerd J.; Miranda-Lange, Martin; Schimmels, Stefan

2014-10-01

106

Seismic wave attenuation and dispersion in thin layer sequences  

E-print Network

, is considered a linear function of frequency. This suggests another method for separating the contri- butions of absorption and dispersion. The fine structure of the spectra are due to resonances in individual layers or groupings of layers. An average...SEISMIC WAVE ATTENUATION AND DISPERSION IN THIN LAYER SEQUENCES A Thesis by CLIFFORD MURRAY EDWARDS Submitted to the Graduate College of Texas A&M University in partial fulfillment of the requirement for the degree of MASTER OF SCIENCE...

Edwards, Clifford Murray

1975-01-01

107

Determination of Mass Attenuation Coefficients for CuInSe2 and CuGaSe2 Semiconductors  

Microsoft Academic Search

This work presents mass attenuation coefficients values of CuInSe2 and CuGaSe2 semiconductor thin films commonly used in photovoltaic devices. The mass attenuation coefficients were measured at different energies from 11.9 to 37.3 keV by using the secondary excitation method. Monochromatic photons were obtained using the Br, Sr, Mo, Cd, Te, Ba and Nd secondary targets. 59.5 keV gamma rays emitted

Emin Bacaksiz

2007-01-01

108

Retrieval of diffuse attenuation coefficient in the Chesapeake Bay and turbid ocean regions for satellite ocean color applications  

Microsoft Academic Search

There are several empirical and semianalytical models for the satellite-based estimation of the diffuse attenuation coefficient for the downwelling spectral irradiance at the wavelength 490 nm, Kd(490), or the diffuse attenuation coefficient for the downwelling photosynthetically available radiation (PAR), Kd(PAR). An empirical algorithm has been used to routinely produce NASA standard Kd(490) product from the Moderate Resolution Imaging Spectroradiometer (MODIS).

Menghua Wang; SeungHyun Son; Lawrence W. Harding Jr

2009-01-01

109

Measurement of mass attenuation coefficients and effective atomic numbers for MgB 2 superconductor using X-ray energies  

Microsoft Academic Search

The powder and bulk MgB2 superconductors sintered in different Ar gas pressures were investigated using X-ray diffraction patterns, mass density and mass attenuation coefficient measurements. During the sintering process, 2, 4, 6, 8 and 10bar argon pressures were used to minimize the evaporation of Mg from the compound. Mass attenuation coefficients (?\\/?) of powder and bulk samples were determined by

H. Balta?; ?. Çelik; U. Çevik; E. Yanmaz

2007-01-01

110

Evaluation of Compton scattering and self-attenuation coefficient after ? -ray analysis of naturally occurring radioactive elements in environmental samples  

Microsoft Academic Search

Comparison of Compton scattering and Compton scattering cross section with self-attenuation coefficient were explained based\\u000a on the kinematic equation and Klein-Nishina formula. Naturally occurring elements, 238U (226Ra), 40K, 232Th (228Ra) and 137Cs were determined in sediments and water from Ismailia canal in Egypt which were found in the range of permissible level.\\u000a Self-attenuation coefficients, K, the ratio between photopeak detection

A. A. El-Sayed

2007-01-01

111

Attenuation of shock waves in copper and stainless steel  

SciTech Connect

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

Harvey, W.B.

1986-06-01

112

Dynamic changes of integrated backscatter, attenuation coefficient and bubble activities during high-intensity focused ultrasound (HIFU) treatment.  

PubMed

This paper simultaneously investigated the transient characteristics of integrated backscatter (IBS), attenuation coefficient and bubble activities as time traces before, during and after HIFU treatment, with different HIFU parameters (acoustic power and duty cycle) in both transparent tissue-mimicking phantoms and freshly excised bovine livers. These dynamic changes of acoustic parameters and bubble activities were correlated with the visualization of lesion development selected from photos, conventional B-mode ultrasound images and differential IBS images over the whole procedure of HIFU treatment. Two-dimensional radiofrequency (RF) data were acquired by a modified diagnostic ultrasound scanner to estimate the changes of mean IBS and attenuation coefficient averaged in the lesion region, and to construct the differential IBS images and B-mode ultrasound images simultaneously. Bubble activities over the whole procedure of HIFU treatment were investigated by the passive cavitation detection (PCD) method and the changes in subharmonic and broadband noise were correlated with the transient characteristics of IBS and attenuation coefficient. When HIFU was switched on, IBS and attenuation coefficient increased with the appearance of bubble clouds in the B-mode and differential IBS image. At the same time, the level of subharmonic and broadband noise rose abruptly. Then, there was an initial decrease in the attenuation coefficient, followed by an increase when at lower HIFU power. As the lesion appeared, IBS and attenuation coefficient both increased rapidly to a value twice that of normal. Then the changes in IBS and attenuation coefficient showed more complex patterns, but still showed a slower trend of increases with lesion development. Violent bubble activities were visible in the gel and were evident as strongly echogenic regions in the differential IBS images and B-mode images simultaneously. This was detected by a dramatic high level of subharmonic and broadband noise at the same time. These bubble activities caused fluctuations in IBS and attenuation coefficient during HIFU treatment. After HIFU, IBS and attenuation coefficient decreased gradually accompanied by the fadeout of bright hyperechoic spot in the B-mode and differential IBS image, but were still higher than normal when they were stable. The increases of IBS and attenuation coefficient were greater when using higher acoustic power or a higher duty cycle of the therapeutic emission. These experiments indicated that the bubble activities had the dominant effects on the transient characteristics of IBS and attenuation. This should be taken into consideration when using the dynamic acoustic-property changes for the potentially real-time monitoring imaging of HIFU treatment. PMID:19716225

Zhang, Siyuan; Wan, Mingxi; Zhong, Hui; Xu, Cheng; Liao, Zhenzhong; Liu, Huanqing; Wang, Supin

2009-11-01

113

Estimating dynamic changes of tissue attenuation coefficient during high-intensity focused ultrasound treatment  

PubMed Central

Background This study investigated the dynamic changes of tissue attenuation coefficients before, during, and after high-intensity focused ultrasound (HIFU) treatment at different total acoustic powers (TAP) in ex vivo porcine muscle tissue. It further assessed the reliability of employing changes in tissue attenuation coefficient parameters as potential indicators of tissue thermal damage. Methods Two-dimensional pulse-echo radio frequency (RF) data were acquired before, during, and after HIFU exposure to estimate changes in least squares attenuation coefficient slope (??) and attenuation coefficient intercept (??0). Using the acquired RF data, ?? and ??0 images, along with conventional B-mode ultrasound images, were constructed. The dynamic changes of ?? and ??0, averaged in the region of interest, were correlated with B-mode images obtained during the HIFU treatment process. Results At a HIFU exposure duration of 40 s and various HIFU intensities (737–1,068 W/cm2), ?? and ??0 increased rapidly to values in the ranges 1.5–2.5 dB/(MHz.cm) and 4–5 dB/cm, respectively. This rapid increase was accompanied with the appearance of bubble clouds in the B-mode images. Bubble activities appeared as strong hyperechoic regions in the B-mode images and caused fluctuations in the estimated ?? and ??0 values. After the treatment, ?? and ??0 values gradually decreased, accompanied by fade-out of hyperechoic spots in the B-mode images. At 10 min after the treatment, they reached values in ranges 0.75–1 dB/(MHz.cm) and 1–1.5 dB/cm, respectively, and remained stable within those ranges. At a long HIFU exposure duration of around 10 min and low HIFU intensity (117 W/cm2), ?? and ??0 gradually increased to values of 2.2 dB/(MHz.cm) and 2.2 dB/cm, respectively. This increase was not accompanied with the appearance of bubble clouds in the B-mode images. After HIFU treatment, ?? and ??0 gradually decreased to values of 1.8 dB/(MHz.cm) and 1.5 dB/cm, respectively, and remained stable at those values. Conclusions ?? and ??0 estimations were both potentially reliable indicators of tissue thermal damage. In addition, ?? and ??0 images both had significantly higher contrast-to-speckle ratios compared to the conventional B-mode images and outperformed the B-mode images in detecting HIFU thermal lesions at all investigated TAPs and exposure durations. PMID:25516802

2013-01-01

114

Dispersion and attenuation for an acoustic wave equation consistent with viscoelasticity  

E-print Network

An acoustic wave equation for pressure accounting for viscoelastic attenuation is derived from viscoelastic equations of motion. It differs significantly from the equations proposed by Szabo. Dispersion and attenuation associated with the viscoelastic wave equation is examined. The theory is applied to three classes of viscoelastic models and to the linear attenuation model.

Andrzej Hanyga

2014-01-30

115

Reflection and Transmission Coefficients for an Incident Plane Shear Wave at an Interface Separating Two Dissimilar Poroelastic Solids  

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

2014-09-01

116

An experimental model of ice floe induced attenuation of ocean waves  

E-print Network

An experimental model of ocean wave attenuation due to interactions with an ice floe is presented. Evolution of mechanically-generated, regular waves is monitored in front and in the lee of a solitary, square floe, made of a synthetic material. Results confirm dependence of attenuation on the period of the incident wave. Results also indicate dependence of attenuation on the depth of wave overwash on the floe.

Toffoli, Alessandro; Bennetts, Luke G; Meylan, Michael H; Cavaliere, Claudio; Babanin, Alexandr

2014-01-01

117

Attenuation of whistler waves through conversion to lower hybrid waves in the low-altitude ionosphere  

NASA Astrophysics Data System (ADS)

VLF waves excited by powerful ground-based transmitters propagate in the Earth-ionosphere waveguide and leak through the ionosphere to the magnetosphere, where they are often recorded by satellites. Simulations of the propagation of whistler waves using coupled transionospheric VLF propagation and three-dimensional ray-tracing models have shown systematic overestimates of the VLF wavefield strength near 20 kHz in the magnetosphere by about 20 dB in the night and 10 dB during the day. The paper presents numerical simulations of the conversion between whistler and lower hybrid waves interactions in the presence of short-scale field-aligned density irregularities (striations) in Earth's lower ionosphere. The simulations, which incorporate a realistic ionospheric density profile, show that the mode conversion of whistler waves to lower hybrid waves leads to significant attenuation of whistler waves at altitudes between 90 and 150 km. The striation width plays an important role in the conversion efficiency between whistler and lower hybrid wave. Uniformly distributed striations with 8 m transverse size result in 15 dB attenuation in the 90-150 km propagation range, while a spectrum from 2 to 10 m results in 9 dB attenuation. It is argued that the attenuation of whistler waves in the presence of short-scale density striations in Earth's ionosphere can account for most of the observed ˜20 dB loss in VLF intensity. Furthermore, it predicts that VLF/ELF waves with frequencies below 5 kHz will not suffer similar attenuation.

Shao, X.; Eliasson, B.; Sharma, A. S.; Milikh, G.; Papadopoulos, K.

2012-04-01

118

Linear attenuation coefficients of tissues from 1 keV to 150 keV  

NASA Astrophysics Data System (ADS)

The linear attenuation coefficients and three interaction processes have been computed for liver, kidney, muscle, fat and for a range of x-ray energies from 1 keV to 150 keV. Molecular photoelectric absorption cross sections were calculated from atomic cross section data. Total coherent (Rayleigh) and incoherent (Compton) scattering cross sections were obtained by numerical integration over combinations of F2m(x) with the Thomson formula and Sm(x) with the Klein-Nishina formula, respectively. For the coherent (Rayleigh) scattering cross section calculations, molecular form factors were obtained from recent experimental data in the literature for values of x<1 Å-1 and from the relativistic modified atomic form factors for values of x?1 Å-1. With the inclusion of molecular interference effects in the coherent (Rayleigh) scattering, more accurate knowledge of the scatter from these tissues will be provided. The number of elements involved in tissue composition is 5 for liver, 47 for kidney, 44 for muscle and 3 for fat. The results are compared with previously published experimental and theoretical linear attenuation coefficients. In general, good agreement is obtained. The molecular form factors and scattering functions and cross sections are incorporated into a Monte Carlo program. The energy distributions of x-ray photons scattered from tissues have been simulated and the results are presented.

Böke, Aysun

2014-09-01

119

Influence Of Scattering On The Diffuse Attenuation Coefficient In The Asymptotic Region  

NASA Astrophysics Data System (ADS)

In a homogeneous ocean that both scatters and absorbs the radiance decreases with depth and the angular dependence of the radiance becomes independent of depth and of the incident distribution at the surface. In the diffusion region the asymptotic radiance distribution is only dependent on the inherent properties of the medium including the scattering phase function. Under these conditions an exact integral equation can be derived for the asymptotic radiance. A numerical calculation of the asymptotic radiance was made with Lobatto quadrature resulting in a precise estimate of the diffuse attenuation coefficient for selected values of the single scattering albedo. Calculations were made using estimated single scattering phase functions derived from scattering measurements made for a wide variety of marine and freshwater water types. A two parameter empirical expression was derived from these model calculations relating the diffuse attenuation coefficient and the single scattering albedo. Predictions are made over the entire range of single scattering albedos and are compared to those given by other investigators. The predictability of this relationship and the influence of the scattering phase function are evaluated for each of the scattering phase functions examined. Individual derived relationships are able to predict the diffusion exponent with RMS errors of less than one percent. The overall variation in determining the two parameters is approximately 3 and 18 percent using samples which varied optically from very clear waters of Sargasso Sea to the turbid waters of Lake Erie.

Tanis, Fred J.; Kattawar, George W.; Hickman, G. Daniel

1986-08-01

120

Impact of attenuator models on computed traveling wave tube performances  

NASA Astrophysics Data System (ADS)

Radio frequency characteristics of helix traveling wave tubes are analyzed with a one-dimensional numerical model that includes a new, more rigorous, self-consistent attenuator model. The nonlinear properties of the beam-wave interaction, including gain, phase distortion, and intermodulation distortion, are analyzed and compared with simulations using a conventional one-dimensional model of the attenuator. The comparative results show that the small signal gain is about 2-5dB smaller with the new model than with the conventional and wave phase has a difference of 2°-6° between the new and conventional models in the intermediate and large signal regions. The amplitude modulation/phase modulation (AM/PM) conversion from the new model shows a slower reach to maximum than that from the conventional, and when the large input signal is applied, the conventional model's AM/PM conversion oscillates more quickly compared to the new. Under two-frequency excitation, the fundamental tones are about 5-7dB smaller with the new model than the conventional, while the intermodulation products are approximately 10dB smaller relative to the conventional model.

Duan, Zhaoyun; Gong, Yubin; Wei, Yanyu; Wang, Wenxiang

2007-09-01

121

Active high-resolution compressional wave attenuation tomography at Newberry Volcano, Central Cascade Range  

NASA Astrophysics Data System (ADS)

The 3D compressional wave-attenuation structure of the Newberry Volcano is determined by analyzing seismic data from 120 seismic stations. Spectral ratios are used to compute the delta(t)* values and subsequently the attenuation in the manner of Evans and Zucca (1988). Regions of two-phase pore fluid are shown to correlate spatially with regions of high attenuation, and two-phase geothermal reservoirs are identified and located based on compressional wave velocity and attenuation images.

Zucca, John J.; Evans, John R.

1992-07-01

122

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

NASA Astrophysics Data System (ADS)

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

Gibson, Alex; Gallo, Gonzalo E.

2004-02-01

123

Relative velocity of seagrass blades: Implications for wave attenuation in low-energy environments  

Microsoft Academic Search

While the ability of subaquatic vegetation to attenuate wave energy is well recognized in general, there is a paucity of data from the field to describe the rate and mechanisms of wave decay, particularly with respect to the relative motion of the vegetation. The purpose of this study was to quantify the attenuation of incident wave height through a seagrass

Kevin Bradley; Chris Houser

2009-01-01

124

Wave dispersion and attenuation on human femur tissue.  

PubMed

Cortical bone is a highly heterogeneous material at the microscale and has one of the most complex structures among materials. Application of elastic wave techniques to this material is thus very challenging. In such media the initial excitation energy goes into the formation of elastic waves of different modes. Due to "dispersion", these modes tend to separate according to the velocities of the frequency components. This work demonstrates elastic wave measurements on human femur specimens. The aim of the study is to measure parameters like wave velocity, dispersion and attenuation by using broadband acoustic emission sensors. First, four sensors were placed at small intervals on the surface of the bone to record the response after pencil lead break excitations. Next, the results were compared to measurements on a bulk steel block which does not exhibit heterogeneity at the same wave lengths. It can be concluded that the microstructure of the tissue imposes a dispersive behavior for frequencies below 1 MHz and care should be taken for interpretation of the signals. Of particular interest are waveform parameters like the duration, rise time and average frequency, since in the next stage of research the bone specimens will be fractured with concurrent monitoring of acoustic emission. PMID:25196011

Strantza, Maria; Louis, Olivia; Polyzos, Demosthenes; Boulpaep, Frans; van Hemelrijck, Danny; Aggelis, Dimitrios G

2014-01-01

125

Seismic attenuation due to wave-induced flow  

SciTech Connect

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

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

2003-10-09

126

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

NASA Astrophysics Data System (ADS)

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

Houser, C.; Hill, P. R.

2010-12-01

127

Determination of mass attenuation coefficients for threshold contrast evaluation in digital mammography  

NASA Astrophysics Data System (ADS)

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

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

2010-04-01

128

Dependence of optical attenuation coefficient and mechanical tension of irradiated human cartilage measured by optical coherence tomography.  

PubMed

As banked human tissues are not widely available, the development of new non-destructive and contactless techniques to evaluate the quality of allografts before distribution for transplantation is very important. Also, tissues will be processed accordingly to standard procedures and to minimize disease transmission most tissue banks will include a decontamination or sterilization step such as ionizing radiation. In this work, we present a new method to evaluate the internal structure of frozen or glycerol-processed human cartilages, submitted to various dosis of irradiation, using the total optical attenuation coefficient retrieved from optical coherence tomography (OCT) images. Our results show a close relationship between tensile properties and the total optical attenuation coefficient of cartilages. Therefore, OCT associated with the total optical attenuation coefficient open a new window to evaluate quantitatively biological changes in processed tissues. PMID:24322969

Martinho Junior, A C; Freitas, A Z; Raele, M P; Santin, S P; Soares, F A N; Herson, M R; Mathor, M B

2015-03-01

129

Noninvasive monitoring of photodynamic therapy on skin neoplastic lesions using the optical attenuation coefficient measured by optical coherence tomography.  

PubMed

Photodynamic therapy (PDT) has become a promising alternative for treatment of skin lesions such as squamous cell carcinoma. We propose a method to monitor the effects of PDT in a noninvasive way by using the optical attenuation coefficient (OAC) calculated from optical coherence tomography (OCT) images. We conducted a study on mice with chemically induced neoplastic lesions and performed PDT on these lesions using homemade photosensitizers. The response of neoplastic lesions to therapy was monitored using, at the same time, macroscopic clinical visualization, histopathological analysis, OCT imaging, and OCT-based attenuation coefficient measurement. Results with all four modalities demonstrated a positive response to treatment. The attenuation coefficient was found to be 1.4 higher in skin lesions than in healthy tissue and it decreased after therapy. This study shows that the OAC is a potential tool to noninvasively assess the evolution of skin neoplastic lesions with time after treatment. PMID:25415566

Goulart, Viviane P; dos Santos, Moisés O; Latrive, Anne; Freitas, Anderson Z; Correa, Luciana; Zezell, Denise M

2015-05-01

130

Determination of the mass attenuation coefficients for X-ray fluorescence measurements correction by the Rayleigh to Compton scattering ratio  

NASA Astrophysics Data System (ADS)

X-ray fluorescence technique plays an important role in nondestructive analysis nowadays. The development of equipment, including portable ones, enables a wide assortment of possibilities for analysis of stable elements, even in trace concentrations. Nevertheless, despite of the advantages, one important drawback is radiation self-attenuation in the sample being measured, which needs to be considered in the calculation for the proper determination of elemental concentration. The mass attenuation coefficient can be determined by transmission measurement, but, in this case, the sample must be in slab shape geometry and demands two different setups and measurements. The Rayleigh to Compton scattering ratio, determined from the X-ray fluorescence spectrum, provides a link to the mass attenuation coefficient by means of a polynomial type equation. This work presents a way to construct a Rayleigh to Compton scattering ratio versus mass attenuation coefficient curve by using the MCNP5 Monte Carlo computer code. The comparison between the calculated and literature values of the mass attenuation coefficient for some known samples showed to be within 15%. This calculation procedure is available on-line at www.macx.net.br.

Conti, C. C.; Anjos, M. J.; Salgado, C. M.

2014-09-01

131

A theory of the attenuator-coated helical slow-wave structure of a traveling-wave tube  

Microsoft Academic Search

A theory of the attenuator-coated helical slow-wave structure of a traveling-wave tube has been developed by considering the helix turns to be effectively shorted by a resistive coating. Power propagating down the structure is interpreted for the interaction impedance in the presence of the attenuator-coating losses. The dependence of the attenuation and phase propagation constants as well as the interaction

P. K. Jain; B. N. Basu

1988-01-01

132

Seismic waves attenuation in the lithosphere of the northern Basin and Range Province  

NASA Astrophysics Data System (ADS)

The seismic quality factor of the direct body waves (P- and S-waves) and coda and their frequency dependence (n) were estimated for the northern Basin and Range Province using traces of 66 local earthquakes and explosions recorded during 1988-1989 PASSCAL Basin and Range Passive Seismic Experiment. For calculation of Q-coda the single backscattering model by Aki was used. Q-coda values were estimated for six central frequencies (f): 0.3±0.1, 0.75±0.25, 1.5±0.5, 3.0±1.0, 6.0±2.0 and 12.0±4.0 Hz and for 18 lapse time windows (W) - from 10 to 95 sec with a step 5 sec. The Qp and Qs values were obtained by the method of the maximum amplitudes for the frequency bands 0.5-1.0, 1.0-2.0, 2.0-4.0 ? 4.0-8.0 Hz. Also we tired to evaluate the part of the intrinsic and scattering attenuation (Qi and Qsc respectively) in the total attenuation using Wennerberg's method. The Q-coda increases and the frequency parameter n and the attenuation coefficient ? decrease with increasing of frequency and lapse time windows. This fact shows that the upper part of the lithosphere is more heterogeneous compared to its lower layers. The deep variations of the frequency parameter n and the attenuation coefficient ? show the sharp change at the depth about 150 km - at the same depth the boundary of the low velocity anomaly is observed (Bensen et al., 2009; Wagner et al., 2012; Shen et al., 2012). The Qs and Qp values also increase with frequency: Qs varies from 42 (0.84 Hz) to 298 (5.52 Hz) and Qp - from 60 (0.84 Hz) to 279 (6.05 Hz). The following empirical relations of Q vs. f are deduced for P- and S-waves respectively: Qp(f)=69*f0.78 and Qs(f)=53*f1.08. The Q-values, describing the intrinsic and scattering attenuation, also show a significant dependence on frequency and lapse time windows: the empirical relations of Q vs. f are: Qi(f)=8*f1.2 and Qsc(f)=13*f1.1 (for W=10 sec) and Qi(f)=5*f1.2 and Qsc(f)=102*f1.0 (for W=95 sec) respectively. The comparison of the intrinsic and scattering attenuation shows that the intrinsic attenuation is dominant over scattering attenuation in the frequency range analyzed for all deep levels. The reported study was supported by RFBR, research project No. 12-05-31038.

Dobrynina, Anna

2013-04-01

133

Pulse-echo method can't measure wave attenuation accurately  

E-print Network

A number of techniques with different degrees of accuracies have been devised for the measurement of acoustic wave attenuation in solids and liquids. Still, a wide variation is observed in the attenuation values in different materials reported in the literature. Present numerical study based on a 'propagating wave' model analysis clearly shows that the attenuation constant obtained from exponential fitting of the echo heights in pulse-echo method differs from the exact value of intrinsic attenuation in the medium, even in the ideal situation of plane wave propagation without diffraction, dispersion or scattering.

Pal, Barnana

2014-01-01

134

Comparison of Chang's with Sorenson's Attenuation Correction Method by Varying Linear Attenuation Coefficient Values in Tc99m SPECT Imaging  

Microsoft Academic Search

Attenuation (scattering and absorption) of gamma photons in the patient’s body is one of the major limitations among the others\\u000a in single photon emission computed tomography (SPECT). It reduces quantitative accuracy of measured radioactivity concentration\\u000a and causes hot rim artifacts in reconstructed images if not corrected for. A variety of approximate attenuation correction\\u000a methods has been developed or proposed by

Inayatullah Shah Sayed; Ahmed Zakaria; Norhafiza Nik

2007-01-01

135

Connection coefficients for cold plasma wave propagation near metallic surfaces  

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

136

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

137

Application of sound-absorbent plastic to weak-shock-wave attenuators  

Microsoft Academic Search

A device for attenuating weak shock waves propagating in a duct has been developed utilizing sound-absorbent plastic which is usually used for attenuating sound waves. The device has a tube made of the sound-absorbent plastic installed coaxially to a surrounding metal tube with a clearance between them. The clearance acts as an air layer to enhance the performance of the

Katsuhisa Ootsuta; Kei Matsuoka; Akihiro Sasoh; Kazuyoshi Takayama

1998-01-01

138

Parameters Affecting Water Hammer Wave Attenuation, Shape by Anton Bergant1  

E-print Network

Parameters Affecting Water Hammer Wave Attenuation, Shape and Timing by Anton Bergant1 and Arris.s.tijsseling@TUE.nl This paper investigates parameters that may affect water hammer wave attenuation, shape and timing. Possible friction, cavitation, and a number of fluid-structure interaction (FSI) effects. The discrepancies

Eindhoven, Technische Universiteit

139

Shear wave speed and attenuation in water-saturated glass beads and sand  

E-print Network

Shear wave speed and attenuation in water-saturated glass beads and sand N. P. Chotiros and M. J dependence of shear wave attenuation in water-saturated glass beads and sand contains distinguishable, in the frequency band from 200 Hz to 2 kHz, indicated that the constant-Q model may be applicable to dry sand

Paris-Sud XI, Université de

140

Linear attenuation coefficient and buildup factor of MCP-96 alloy for dose accuracy, beam collimation, and radiation protection.  

PubMed

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

141

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

142

Prediction of the light attenuation coefficient through the Secchi disk depth: empirical modeling in two large Neotropical ecosystems  

Microsoft Academic Search

The easiest way to evaluate water transparency is from the Secchi disk depth (SD). The behavior of radiation passing through\\u000a water can also be quantified by the light attenuation coefficient (k) of photosynthetically active radiation (PAR), measured using quanta meters. Due to the high costs of quanta meters, k is usually predicted from SD. This prediction can be made using

André Andrian Padial; Sidinei Magela Thomaz

2008-01-01

143

Precise measurement of attenuation coefficients of gamma rays in the 7.5 MeV region  

Microsoft Academic Search

A new technique utilising nuclear resonance scattering of gamma rays was used for measuring total attenuation coefficients of 15 elements between Be and U. The gamma-ray energies were 7.279 and 7.646 MeV, and the results were found to be generally higher than the calculated values.

R. Moreh; D. Salzmann; Y. Wand

1969-01-01

144

Evaluation of moisture-related attenuation coefficient and water diffusion velocity in human skin using optical coherence tomography.  

PubMed

In this study, time-resolved optical coherence tomography (OCT) scanning images of the process of water diffusion in the skin that illustrate the enhancement in the backscattered intensities due to the increased water concentration are presented. In our experiments, the water concentration in the skin was increased by soaking the hand in water, and the same region of the skin was scanned and measured with the OCT system and a commercial moisture monitor every three minutes. To quantitatively analyze the moisture-related optical properties and the velocity of water diffusion in human skin, the attenuation coefficients of the skin, including the epidermis and dermis layers, were evaluated. Furthermore, the evaluated attenuation coefficients were compared with the measurements made using the commercial moisture monitor. The results demonstrate that the attenuation coefficient increases as the water concentration increases. Furthermore, by evaluating the positions of center-of mass of the backscattered intensities from OCT images, the diffusion velocity can be estimated. In contrast to the commercial moisture monitor, OCT can provide three-dimensional structural images of the skin and characterize its optical property, which together can be used to observe morphological changes and quantitatively evaluate the moisture-related attenuation coefficients in different skin layers. PMID:23529149

Lee, Cheng-Kuang; Tsai, Meng-Tsan; Chang, Feng-Yu; Yang, Chih-Hsun; Shen, Su-Chin; Yuan, Ouyang; Yang, Chih-He

2013-01-01

145

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

USGS Publications Warehouse

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

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

1978-01-01

146

Viscoacoustic wave propagation in 2-D random media and separation of absorption and scattering attenuation  

Microsoft Academic Search

Wave theoretical analysis of scalar, time-harmonic waves propagating in a constant density medium with isotropic, random velocity fluctuations and being scattered mainly in the forward direction yields a simple and robust procedure that combines the logarithm of the mean wave amplitude with the mean logarithm of the wave amplitude to perform a separation of scattering attenuation and absorption effects. Finite-difference

Guido Kneib; S. A. Shapiro

1995-01-01

147

Investigation of the Attenuation of Plane Shock Waves Moving over very Rough Surfaces  

NASA Technical Reports Server (NTRS)

Experimental measurements of the attenuation of plane shock waves moving over rough walls have been made in a shock tube. Measurements of the boundary-layer characteristics, including thickness and velocity distribution behind the shock, have also been made with the aid of new cal techniques which provide direct information on the local boundary-layer conditions at the rough walls. Measurements of shock speed and shock pressure ratio are presented for both smooth-wall and rough-wall flow over lengths of machined-smooth and rough strips which lined all four walls of the shock tube. A simplified theory based on Von Karman's expression for skin-friction coefficient for flow over rough walls, along with a wave-model concept and extensions to include time effects, is presented. In this theory, the shock-tube flow is assumed to be one-dimensional at all times and the wave-model concept is used to relate the local layer growth to decreases in shock strength. This concept assumes that local boundary-layer growths act as local mass-flow sinks, which give rise to expansion waves which, in turn, overtake the shock and lower its mass flow accordingly.

Huber, Paul W.; McFarland, Donald R.; Levine, Philip

1953-01-01

148

Broadband attenuation of Lamb waves through a periodic array of thin rectangular junctions  

NASA Astrophysics Data System (ADS)

We study theoretically subwavelength physical phenomena, such as resonant transmission and broadband sound shielding for Lamb waves propagating in an acoustic metamaterial made of a thin plate drilled with one or two row(s) of rectangular holes. The resonances and antiresonances of periodically arranged rectangular junctions separated by holes are investigated as a function of the geometrical parameters of the junctions. With one and two row(s) of holes, high frequency specific features in the transmission coefficient are explained in terms of a coupling of incident waves with both Fabry-Perot oscillations inside the junctions and induced surface acoustic waves between the homogeneous part of the plate and the row of holes. With two rows of holes, low frequency peaks and dips appear in the transmission spectrum. The choice of the distance between the two rows of holes allows the realization of a broadband low frequency acoustic shielding with attenuation over 99% for symmetric waves in a wide low frequency range and over 90% for antisymmetric ones. The origin of the transmission gap is discussed in terms of localized modes of the "H" element made by the junctions, connecting the two homogeneous parts of the plate.

Moiseyenko, Rayisa P.; Pennec, Yan; Marchal, Rémi; Bonello, Bernard; Djafari-Rouhani, Bahram

2014-10-01

149

Asymptotic laws for the attenuation of weak continuous and shock waves in a dusty gas  

NASA Astrophysics Data System (ADS)

Asymptotic laws are obtained for the attenuation of plane, cylindrical, and spherical shock and continuous waves whose amplitude and width are such that particle acceleration and changes in the particle temperature can be neglected. It is assumed that heat transfer between the phases is proportional to the temperature difference and that momentum exchange between the phases due to friction forces is proportional to the velocity difference. The attenuation laws obtained for plane waves are found to be identical with the laws governing the attenuation of magnetohydrodynamic waves in a medium of finite conductivity. In this case, Joule disipation and an additional ponderomotive force in a traveling wave or in a gas flow behind a shock wave lead to an exponential amplitude attenuation of the wave amplitude.

Kulikovskii, V. A.

1983-06-01

150

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

PubMed

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

151

Attenuation of intense sinusoidal waves in air-saturated, bulk porous materials  

NASA Technical Reports Server (NTRS)

As intense, initially sinusoidal waves propagate in fluids, shocks form and excess attenuation of the wave occurs. Data are presented indicating that shock formation is not necessary for the occurrence of excess attenuation in nonlinear, lossy media, i.e., air-saturated, porous materials. An empirical equation is used to describe the excess attenuation of intense sinusoids in porous materials. The acoustic nonlinearity of and the excess attenuation in porous materials may be predicted directly from dc flow resistivity data. An empirical relationship is used to relate an acoustic nonlinearity parameter to the fundamental frequency and relative dc nonlinearity of two structurally different materials.

Kuntz, Herbert L.; Blackstock, David T.

1987-01-01

152

Single-experiment simultaneous-measurement of elemental mass-attenuation coefficients of hydrogen, carbon and oxygen for 0.123–1.33 MeV gamma rays  

Microsoft Academic Search

As it is inconvenient to use elements like hydrogen, carbon and oxygen in pure forms for measurement of their gamma mass-attenuation coefficients, the measurements are to be done indirectly, by using compounds of the elements or a mixture of them. We give here a simple method of measuring the total mass-attenuation coefficients ?\\/? of the elements in a compound simultaneously

M. T. Teli; R. Nathuram; C. S. Mahajan

2000-01-01

153

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

154

The precise measurement of the attenuation coefficients of various IR optical materials applicable to immersion grating  

NASA Astrophysics Data System (ADS)

Immersion grating is a next-generation diffraction grating which has the immersed the diffraction surface in an optical material with high refractive index of n > 2, and can provide higher spectral resolution than a classical reflective grating. Our group is developing various immersion gratings from the near- to mid-infrared region (Ikeda et al.1, 2, 3, 4, Sarugaku et al.5, and Sukegawa et al.6). The internal attenuation ?att of the candidate materials is especially very important to achieve the high efficiency immersion gratings used for astronomical applications. Nevertheless, because there are few available data as ?att < 0.01cm-1 in the infrared region, except for measurements of CVD-ZnSe, CVD-ZnS, and single-crystal Si in the short near-infrared region reported by Ikeda et al.7, we cannot select suitable materials as an immersion grating in an aimed wavelength range. Therefore, we measure the attenuation coefficients of CdTe, CdZnTe, Ge, Si, ZnSe, and ZnS that could be applicable to immersion gratings. We used an originally developed optical unit attached to a commercial FTIR which covers the wide wavelength range from 1.3?m to 28?m. This measurement system achieves the high accuracy of (triangle)?att ~ 0.01cm-1. As a result, high-resistivity single-crystal CdZnTe, single-crystal Ge, single-crystal Si, CVD-ZnSe, and CVD-ZnS show ?att < 0.01cm-1 at the wavelength range of 5.5 - 19.0?m, 2.0 - 10.5?m, 1.3 - 5.4?m, 1.7 - 13.2?m, and 1.9 - 9.2?m, respectively. This indicates that these materials are good candidates for high efficiency immersion grating covering those wavelength ranges. We plan to make similar measurement under the cryogenic condition as T <= 10K for the infrared, especially mid-infrared applications.

Kaji, Sayumi; Sarugaku, Yuki; Ikeda, Yuji; Kobayashi, Naoto; Nakanishi, Kenshi; Kondo, Sohei; Yasui, Chikako; Kawakita, Hideyo

2014-07-01

155

Surface acoustic wave attenuation in epitaxial films of rare earth metal ferrite-garnets  

NASA Astrophysics Data System (ADS)

Surface acoustic wave attenuation in a 6.4-micron-thick (111)-oriented epitaxial ferrite-garnet film of the composition (Y1Sm0.25Tm1Ca0.75)(Fe4.1Ge0.9)012 is investigated experimentally as a function of the intensity and direction of the external magnetic field. An analysis of the results obtained indicates that surface acoustic wave attenuation in the ferrite-garnet film is associated with relaxation processes and determined by the presence of a domain structure. Maximum SAW attenuation is observed when the wave vector is parallel to the magnetic field in the film plane.

Tikhonov, S. K.; Bokov, V. A.; Leonov, E. I.; Orlov, V. M.; Sherman, A. B.

1987-06-01

156

Using water quality variables to predict light attenuation coefficient: case study in Shihmen Reservoir  

Microsoft Academic Search

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

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

2010-01-01

157

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

158

Millimeter wave attenuation prediction using a piecewise uniform rain rate model  

Microsoft Academic Search

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

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

1980-01-01

159

Calibration of a turbidity meter for making estimates of total suspended solids concentrations and beam attenuation coefficients in field experiments  

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

160

Plastic yielding as a frequency and amplitude independent mechanism of seismic wave attenuation  

E-print Network

Plastic yielding as a frequency and amplitude independent mechanism of seismic wave attenuation processes: irreversible plastic yielding and formation of radial microfractures around microscopic cavities to frequency-independent attenuation due to rate-inde- pendence of plasticity formulation. Quality factor Q

Podladchikov, Yuri

161

Estimation of compressional seismic wave attenuation of carbonate rocks in Abu Dhabi, United Arab Emirates  

NASA Astrophysics Data System (ADS)

The subsurface geology of Abu Dhabi in the United Arab Emirates is primarily composed of carbonate rocks. Such media are known to be highly heterogeneous. Very few studies have attempted to estimate attenuation in carbonate rocks. In Abu Dhabi no attenuation profile has been published. This study provides the first seismic wave attenuation profiles in Abu Dhabi using dense array of VSP data. We estimated three attenuation profiles: the apparent, the scattering, and the intrinsic attenuations. The apparent attenuation profile was computed using amplitude decay and spectral-ratio methods. The scattering attenuation profile was estimated using a generalized reflection-transmission matrix forward model. It is usually estimated from the sonic log, but to be more consistent with the apparent attenuation, we succeeded in this paper to estimate it from the VSP data. We subtracted the scattering attenuation from the apparent attenuation to deduce the intrinsic attenuation. The results of the study indicate that the scattering attenuation is significant compared to the published studies that are mainly based on clastic rocks. The high scattering attenuation can reach up to 0.02. It can be explained by the strong heterogeneity of the carbonate rocks. This study demonstrates that the Simsima and Rus Formations have considerable scattering and intrinsic attenuations. These formations are considered aquifers in Abu Dhabi; we therefore interpreted this high intrinsic attenuation zones to be due to the heterogeneity and to the fluids contained in these formations. The Umm-Er-Radhuma Formation is a more homogenous formation with limited aquifer potential. Hence, scattering and intrinsic attenuations of the Umm-Er-Radhuma Formation are low.

Bouchaala, Fateh; Ali, Mohammed Y.; Farid, Asam

2014-07-01

162

Derivation of total diffuse attenuation coefficient from water column temperature data and meteorological water surface fluxes: A simple management tool  

Microsoft Academic Search

The total diffuse attenuation coefficient of Photosynthetically Available Radiation (Kd(PAR)) is derived by optimising the solution of a surface layer model to match temperature profiles measured with a precision thermistor chain; a non?linear least?squares Levenberg?Marquardt scheme is applied to optimize Kd(PAR). The method was validated in Lake Kinneret (Israel) over 10 days in summer to early winter 2001, Valle de

Sri Adiyanti; Jörg Imberger

2007-01-01

163

Measurement of the mass attenuation coefficients of Ge and BGO for high-energy gamma-rays  

Microsoft Academic Search

The gamma-ray mass attenuation coefficients of important materials for gamma-ray detection have been measured using the laser-Compton backscattering gamma-rays (LCS gamma-rays) and the high-resolution high-energy photon spectrometer (HHS). The preliminary results performed for materials (Ge and BGO) are presented for gamma-ray energy of 5.1 MeV. The measured data are compared with tabulated theoretical calculations.

Hideo Harada; Fumito Kitatani; Kaoru Y. Hara; Hiroyuki Toyokawa; Takeshi Kaihori; Hiroaki Utsunomiya

2007-01-01

164

Determination of mass attenuation coefficients of some boron ores at 59.54keV by using scintillation detector.  

PubMed

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

165

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

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

166

Near-surface seismic attenuation of P-waves in West Texas  

E-print Network

(Member) Robert R. Berg (Member) el S. Watkins (Head of Department) August 1992 ABSTRACT Near-surface Seismic Attenuation of P-Waves in West Texas. (August 1992) Said Awdhah AI-Zahrani, B. S, University of Petroleum and Minerals, Dhahran, Saudi... Arabia Chair of Advisory Committee: Dr. Steven H. Harder Field experiments were conducted near Monahans, Texas, to measure the seismic P-wave attenuation of near-surface sediments. The field measurements consisted of recording two dynamite shots at a...

Al-Zahrani, Said Awdhah

1992-01-01

167

Improved Algorithms for Accurate Retrieval of UV - Visible Diffuse Attenuation Coefficients in Optically Complex, Inshore Waters  

NASA Technical Reports Server (NTRS)

Photochemical processes driven by high-energy ultraviolet radiation (UVR) in inshore, estuarine, and coastal waters play an important role in global bio geochemical cycles and biological systems. A key to modeling photochemical processes in these optically complex waters is an accurate description of the vertical distribution of UVR in the water column which can be obtained using the diffuse attenuation coefficients of down welling irradiance (Kd()). The Sea UV Sea UVc algorithms (Fichot et al., 2008) can accurately retrieve Kd ( 320, 340, 380,412, 443 and 490 nm) in oceanic and coastal waters using multispectral remote sensing reflectances (Rrs(), Sea WiFS bands). However, SeaUVSeaUVc algorithms are currently not optimized for use in optically complex, inshore waters, where they tend to severely underestimate Kd(). Here, a new training data set of optical properties collected in optically complex, inshore waters was used to re-parameterize the published SeaUVSeaUVc algorithms, resulting in improved Kd() retrievals for turbid, estuarine waters. Although the updated SeaUVSeaUVc algorithms perform best in optically complex waters, the published SeaUVSeaUVc models still perform well in most coastal and oceanic waters. Therefore, we propose a composite set of SeaUVSeaUVc algorithms, optimized for Kd() retrieval in almost all marine systems, ranging from oceanic to inshore waters. The composite algorithm set can retrieve Kd from ocean color with good accuracy across this wide range of water types (e.g., within 13 mean relative error for Kd(340)). A validation step using three independent, in situ data sets indicates that the composite SeaUVSeaUVc can generate accurate Kd values from 320 490 nm using satellite imagery on a global scale. Taking advantage of the inherent benefits of our statistical methods, we pooled the validation data with the training set, obtaining an optimized composite model for estimating Kd() in UV wavelengths for almost all marine waters. This optimized composite set of SeaUVSeaUVc algorithms will provide the optical community with improved ability to quantify the role of solar UV radiation in photochemical and photobiological processes in the ocean.

Cao, Fang; Fichot, Cedric G.; Hooker, Stanford B.; Miller, William L.

2014-01-01

168

Wave attenuation and mode dispersion in a waveguide coated with lossy dielectric material  

NASA Technical Reports Server (NTRS)

The modal attenuation constants in a cylindrical waveguide coated with a lossy dielectric material are studied as functions of frequency, dielectric constant, and thickness of the dielectric layer. A dielectric material best suited for a large attenuation is suggested. Using Kirchhoff's approximation, the field attenuation in a coated waveguide which is illuminated by a normally incident plane wave is also studied. For a circular guide which has a diameter of two wavelengths and is coated with a thin lossy dielectric layer (omega sub r = 9.1 - j2.3, thickness = 3% of the radius), a 3 dB attenuation is achieved within 16 diameters.

Lee, C. S.; Chuang, S. L.; Lee, S. W.; Lo, Y. T.

1984-01-01

169

Frequency-dependent attenuation of S and coda waves in Erzincan region (Turkey)  

Microsoft Academic Search

The attenuation structure of the Erzincan region is studied using the single scattering model of the coda wave generation and coda normalization method for S waves. We have determined the seismic quality factors Qs(f) (for S waves) and Qc(f) (for coda waves) as a function of frequency for the frequency range 1.5–24 Hz. The quality factors were derived for 161

Aybige Akinci; Haluk Eyido?an

1996-01-01

170

Measurement of X-ray mass attenuation coefficients in biological and geological samples in the energy range of 7-12keV.  

PubMed

Information about X-ray mass attenuation coefficients in different materials is necessary for accurate X-ray fluorescent analysis. The X-ray mass attenuation coefficients for energy of 7-12keV were measured in biological (Mussel and Oyster tissues, blood, hair, liver, and Cabbage leaves) and geological (Baikal sludge, soil, and Alaskite granite) samples. The measurements were carried out at the EXAFS Station of Siberian Synchrotron Radiation Center (VEPP-3). Obtained experimental mass attenuation coefficients were compared with theoretical values calculated for some samples. PMID:25464176

Trunova, Valentina; Sidorina, Anna; Kriventsov, Vladimir

2014-10-17

171

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

USGS Publications Warehouse

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

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

1988-01-01

172

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

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

173

Anisotropic changes in P-wave velocity and attenuation during deformation and fluid infiltration of granite  

USGS Publications Warehouse

Fluid infiltration and pore fluid pressure changes are known to have a significant effect on the occurrence of earthquakes. Yet, for most damaging earthquakes, with nucleation zones below a few kilometers depth, direct measurements of fluid pressure variations are not available. Instead, pore fluid pressures are inferred primarily from seismic-wave propagation characteristics such as Vp/Vs ratio, attenuation, and reflectivity contacts. We present laboratory measurements of changes in P-wave velocity and attenuation during the injection of water into a granite sample as it was loaded to failure. A cylindrical sample of Westerly granite was deformed at constant confining and pore pressures of 50 and 1 MPa, respectively. Axial load was increased in discrete steps by controlling axial displacement. Anisotropic P-wave velocity and attenuation fields were determined during the experiment using an array of 13 piezoelectric transducers. At the final loading steps (86% and 95% of peak stress), both spatial and temporal changes in P-wave velocity and peak-to-peak amplitudes of P and S waves were observed. P-wave velocity anisotropy reached a maximum of 26%. Transient increases in attenuation of up to 483 dB/m were also observed and were associated with diffusion of water into the sample. We show that velocity and attenuation of P waves are sensitive to the process of opening of microcracks and the subsequent resaturation of these cracks as water diffuses in from the surrounding region. Symmetry of the orientation of newly formed microcracks results in anisotropic velocity and attenuation fields that systematically evolve in response to changes in stress and influx of water. With proper scaling, these measurements provide constraints on the magnitude and duration of velocity and attenuation transients that can be expected to accompany the nucleation of earthquakes in the Earth's crust.

Stanchits, S.A.; Lockner, D.A.; Ponomarev, A.V.

2003-01-01

174

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

Microsoft Academic Search

Summary A central issue in the successful application of acoustic wave method to detect subsurface hydrological properties is a better understanding of the influence of soil tex- ture 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 demon- strated the existence of three different

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

2007-01-01

175

Solution of coupled acousticelastic wave propagation problems with anelastic attenuation using automatic hp-adaptivity  

E-print Network

with a multipole acoustic excitation was presented by Randall et al. [7]. In [8], Leslie and Randall applied a 2Solution of coupled acoustic­elastic wave propagation problems with anelastic attenuation using Keywords: Borehole acoustic logging Wave propagation Linear elasticity Coupled problems Hp-adaptive finite

Torres-Verdín, Carlos

176

Photon attenuation coefficients of Heavy-Metal Oxide glasses by MCNP code, XCOM program and experimental data: A comparison study  

NASA Astrophysics Data System (ADS)

The mass attenuation coefficients, ?/?, total interaction cross-section, ?t, and mean free path (MFP) of some Heavy Metal Oxides (HMO) glasses, with potential applications as gamma ray shielding materials, have been investigated using the MCNP-4C code. Appreciable variations are noted for all parameters by changing the photon energy and the chemical composition of HMO glasses. The numerical simulations parameters are compared with experimental data wherever possible. Comparisons are also made with predictions from the XCOM program in the energy region from 1 keV to 100 MeV. Good agreement noticed indicates that the chosen Monte Carlo method may be employed to make additional calculations on the photon attenuation characteristics of different glass systems, a capability particularly useful in cases where no analogous experimental data exist.

El-Khayatt, A. M.; Ali, A. M.; Singh, Vishwanath P.

2014-01-01

177

A theory of the attenuator-coated helical slow-wave structure of a traveling-wave tube  

NASA Astrophysics Data System (ADS)

A theory of the attenuator-coated helical slow-wave structure of a traveling-wave tube has been developed by considering the helix turns to be effectively shorted by a resistive coating. Power propagating down the structure is interpreted for the interaction impedance in the presence of the attenuator-coating losses. The dependence of the attenuation and phase propagation constants as well as the interaction impedance on the surface resistivity of the coating, the operating frequency, the thickness/proximity of the envelope, the permittivity of the dielectric, and the pitch of the helix have been studied for two situations in which the attenuator coating is applied (1) inside a dielectric tube that the helix fits into, the whole enclosed in a metal envelope, and (2) over a dielectric tube enclosure for the helix.

Jain, P. K.; Basu, B. N.

1988-10-01

178

Measurements of the thermal coefficient of optical attenuation at different depth regions of in vivo human skins using optical coherence tomography: a pilot study  

PubMed Central

We present detailed measurement results of optical attenuation’s thermal coefficients (referenced to the temperature of the skin surface) in different depth regions of in vivo human forearm skins using optical coherence tomography (OCT). We first design a temperature control module with an integrated optical probe to precisely control the surface temperature of a section of human skin. We propose a method of using the correlation map to identify regions in the skin having strong correlations with the surface temperature of the skin and find that the attenuation coefficient in these regions closely follows the variation of the surface temperature without any hysteresis. We observe a negative thermal coefficient of attenuation in the epidermis. While in dermis, the slope signs of the thermal coefficient of attenuation are different at different depth regions for a particular subject, however, the depth regions with a positive (or negative) slope are different in different subjects. We further find that the magnitude of the thermal coefficient of attenuation coefficient is greater in epidermis than in dermis. We believe the knowledge of such thermal properties of skins is important for several noninvasive diagnostic applications, such as OCT glucose monitoring, and the method demonstrated in this paper is effective in studying the optical and biological properties in different regions of skin. PMID:25780740

Su, Ya; Yao, X. Steve; Li, Zhihong; Meng, Zhuo; Liu, Tiegen; Wang, Longzhi

2015-01-01

179

EE334 -Reflection Coefficient & Standing Waves 4 Lecture: pp 53-61 2-5  

E-print Network

4-1 EE334 - Reflection Coefficient & Standing Waves 4 Lecture: pp 53-61 2-5 The voltage at the load amplitude and phase These interfere to create a standing wave What is the voltage as a function of position a wavelength. No standing wave without some reflected signal (impedance matched) #12;4-6 Our book uses

Kaiser, Todd J.

180

Laboratory measurements of wave attenuation through model and live vegetation  

Technology Transfer Automated Retrieval System (TEKTRAN)

Surge and waves generated by hurricanes and tropical storms often cause severe damage and loss of life in coastal areas. It is widely recognized that wetlands along coastal fringes reduce storm surge and waves. Yet, the potential role and primary mechanisms of wave mitigation by wetland vegetation a...

181

The large-scale influence of the Great Barrier Reef matrix on wave attenuation  

NASA Astrophysics Data System (ADS)

Offshore reef systems consist of individual reefs, with spaces in between, which together constitute the reef matrix. This is the first comprehensive, large-scale study, of the influence of an offshore reef system on wave climate and wave transmission. The focus was on the Great Barrier Reef (GBR), Australia, utilizing a 16-yr record of wave height from seven satellite altimeters. Within the GBR matrix, the wave climate is not strongly dependent on reef matrix submergence. This suggests that after initial wave breaking at the seaward edge of the reef matrix, wave energy that penetrates the matrix has little depth modulation. There is no clear evidence to suggest that as reef matrix porosity (ratio of spaces between individual reefs to reef area) decreases, wave attenuation increases. This is because individual reefs cast a wave shadow much larger than the reef itself; thus, a matrix of isolated reefs is remarkably effective at attenuating wave energy. This weak dependence of transmitted wave energy on depth of reef submergence, and reef matrix porosity, is also evident in the lee of the GBR matrix. Here, wave conditions appear to be dependent largely on local wind speed, rather than wave conditions either seaward, or within the reef matrix. This is because the GBR matrix is a very effective wave absorber, irrespective of water depth and reef matrix porosity.

Gallop, Shari L.; Young, Ian R.; Ranasinghe, Roshanka; Durrant, Tom H.; Haigh, Ivan D.

2014-12-01

182

Shear wave anisotropy from aligned inclusions: ultrasonic frequency dependence of velocity and attenuation  

NASA Astrophysics Data System (ADS)

To understand their influence on elastic wave propagation, anisotropic cracked media have been widely investigated in many theoretical and experimental studies. In this work, we report on laboratory ultrasound measurements carried out to investigate the effect of source frequency on the elastic parameters (wave velocities and the Thomsen parameter ?) and shear wave attenuation) of fractured anisotropic media. Under controlled conditions, we prepared anisotropic model samples containing penny-shaped rubber inclusions in a solid epoxy resin matrix with crack densities ranging from 0 to 6.2 per cent. Two of the three cracked samples have 10 layers and one has 17 layers. The number of uniform rubber inclusions per layer ranges from 0 to 100. S-wave splitting measurements have shown that scattering effects are more prominent in samples where the seismic wavelength to crack aperture ratio ranges from 1.6 to 1.64 than in others where the ratio varied from 2.72 to 2.85. The sample with the largest cracks showed a magnitude of scattering attenuation three times higher compared with another sample that had small inclusions. Our S-wave ultrasound results demonstrate that elastic scattering, scattering and anelastic attenuation, velocity dispersion and crack size interfere directly in shear wave splitting in a source-frequency dependent manner, resulting in an increase of scattering attenuation and a reduction of shear wave anisotropy with increasing frequency.

de Figueiredo, J. J. S.; Schleicher, J.; Stewart, R. R.; Dayur, N.; Omoboya, B.; Wiley, R.; William, A.

2013-04-01

183

Simultaneous measurement and inversion of surface wave dispersion and attenuation curves  

Microsoft Academic Search

Surface wave tests are non-invasive seismic techniques that have traditionally been used to determine the shear wave velocity (i.e. shear modulus) profile of soil deposits and pavement systems. Recently, Rix et al. [J. Geotech. Geoenviron. Engng 126 (2000) 472] developed a procedure to obtain near-surface values of material damping ratio from measurements of the spatial attenuation of Rayleigh waves. To

Carlo G. Lai; Glenn J. Rix; Sebastiano Foti; Vitantonio Roma

2002-01-01

184

Multi-frequency characterization of the speed of sound and attenuation coefficient for longitudinal transmission of freshly excised human skulls  

PubMed Central

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. PMID:21149950

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

2011-01-01

185

Multi-frequency characterization of the speed of sound and attenuation coefficient for longitudinal transmission of freshly excised human skulls  

NASA Astrophysics Data System (ADS)

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 µg 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

186

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

PubMed

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

Seldis, Thomas

2013-09-01

187

Characterization of the ultrasonic attenuation coefficient and its frequency dependence in a polymer gel dosimeter  

Microsoft Academic Search

Research on polymer-gel dosimetry has been driven by the need for three-dimensional dosimetry, and because alternative dosimeters are unsatisfactory or too slow for that task. Magnetic resonance tomography is currently the most well-developed technique for determining radiation-induced changes in polymer structure, but quick low-cost alternatives remain of significant interest. In previous work, ultrasound attenuation and speed of sound were found

Remo A. Crescenti; Jeffrey C. Bamber; Mike Partridge; Nigel L. Bush; Steve Webb

2007-01-01

188

The effect of frequency on Young`s modulus and seismic wave attenuation  

SciTech Connect

Laboratory experiments were performed to measure the effect of frequency, water-saturation, and strain amplitude on Young`s modulus and seismic wave attenuation on rock cores recovered on or near the site of a potential nuclear waste repository at Yucca Mountain, Nevada. The purpose of this investigation is to perform the measurements using four techniques: cyclic loading, waveform inversion, resonant bar, and ultrasonic velocity. The measurements ranged in frequency between 10{sup {minus}2} and 10{sup 6} Hz. For the dry specimens Young`s modulus and attenuation were independent of frequency; that is, all four techniques yielded nearly the same values for modulus and attenuation. For saturated specimens, a frequency dependence for both Young`s modulus and attenuation was observed. In general, saturation reduced Young`s modulus and increased seismic wave attenuation. The effect of strain amplitude on Young`s modulus and attenuation was measured using the cyclic loading technique at a frequency of 10{sup {minus}1} Hz. The effect of strain amplitude in all cases was small. For some rocks, such as the potential repository horizon of the Topopah Spring Member tuff (TSw2), the effect of strain amplitude on both attenuation and modulus was minimal.

Price, R.H. [Sandia National Labs., Albuquerque, NM (United States). YMP Performance Assessment Applications Dept.; Martin, R.J. III; Haupt, R.W. [New England Research, Inc., White River Junction, VT (United States)

1994-07-01

189

Measurement of alkali-silica reaction progression by ultrasonic waves attenuation  

SciTech Connect

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

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

2007-06-15

190

Study on energy attenuation of ultrasonic guided waves going through girth welds.  

PubMed

Ultrasonic guided wave is introduced as a new non-destructive long range pipe inspection method. It can be used to inspect pipe which is inaccessible to other conventional NDT methods, and rapid, long distance inspection can be achieved. An investigation of the guided ultrasonic waves traveling along pipe with special geometry characteristics, such as elbow, several girth welds, and some artificial defects is described. In this paper, factors that may cause attenuation of ultrasonic guided waves are discussed and energy attenuation of longitudinal and torsional guided waves is studied on an experimental pipe having seven girth welds. Good agreement has been obtained between the experiments and the predictions. In the end, the detection sensitivity and locating precision of two guided waves, namely longitudinal and torsional, were compared on defects, such as notch, burr and branch. PMID:17070566

Yibo, Li; Liying, Sun; Zhidong, Song; Yuankai, Zhang

2006-12-22

191

Experimental investigation of wave attenuation through model and live vegetation  

Technology Transfer Automated Retrieval System (TEKTRAN)

Hurricanes and tropical storms often cause severe damage and loss of life in coastal areas. It is widely recognized that wetlands along coastal fringes reduce storm surge and waves. Yet, the potential role and primary mechanisms of wave mitigation by wetland vegetation are not fully understood. K...

192

Determination of surface tension coefficient of liquids by diffraction of light on capillary waves  

NASA Astrophysics Data System (ADS)

This paper describes a simple technique for determining the coefficient of the surface tension of liquids, based on laser light diffraction on capillary waves. Capillary waves of given frequency are created by an exciter needle acting on the surface of liquid and represent a reflective diffraction grating, the constant of which (the wavelength of capillary waves) can be determined based on a known incidence angle of light (grazing angle). We obtain the coefficient of the surface tension of liquids by applying the dispersion relation for capillary waves and analyze the difficulties that arise when setting up and conducting the experiment in detail.

Nikoli?, D.; Neši?, Lj

2012-11-01

193

Surface acoustic wave attenuation in epitaxial films of rare earth metal ferrite-garnets  

Microsoft Academic Search

Surface acoustic wave attenuation in a 6.4-micron-thick (111)-oriented epitaxial ferrite-garnet film of the composition (Y1Sm0.25Tm1Ca0.75)(Fe4.1Ge0.9)012 is investigated experimentally as a function of the intensity and direction of the external magnetic field. An analysis of the results obtained indicates that surface acoustic wave attenuation in the ferrite-garnet film is associated with relaxation processes and determined by the presence of a domain

S. K. Tikhonov; V. A. Bokov; E. I. Leonov; V. M. Orlov; A. B. Sherman

1987-01-01

194

Comparison of fractional wave equations for power law attenuation in ultrasound and elastography.  

PubMed

A set of wave equations with fractional loss operators in time and space are analyzed. The fractional Szabo equation, the power law wave equation and the causal fractional Laplacian wave equation are all found to be low-frequency approximations of the fractional Kelvin-Voigt wave equation and the more general fractional Zener wave equation. The latter two equations are based on fractional constitutive equations, whereas the former wave equations have been derived from the desire to model power law attenuation in applications like medical ultrasound. This has consequences for use in modeling and simulation, especially for applications that do not satisfy the low-frequency approximation, such as shear wave elastography. In such applications, the wave equations based on constitutive equations are the viable ones. PMID:24433745

Holm, Sverre; Näsholm, Sven Peter

2014-04-01

195

Spectral modification of Beer's law and relation to the humidity attenuation coefficient in atmospheric maritime mist  

NASA Astrophysics Data System (ADS)

Similarity theory and dimensional analysis are applied to the construction of a relationship for the spectral aerosol extinction coefficient in the visible atmospheric window 0.48 (DOT) 10-4 cm < (lambda) < 0.76 (DOT) 10-4 cm. For maritime mist the results allow one to compare the dependence of the spectral extinction coefficient on humidity as determined in situ with known laboratory observations on the variation in the radius of aerosol particle in moist air. Raoult's modified law is used to show that the variation in the optical properties of soluble aerosol is entirely determined by the variation in the average radius of particles depending on humidity.

Vul'fson, A. N.

2000-12-01

196

Dynamic aspects of apparent attenuation and wave localization in layered media  

USGS Publications Warehouse

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

Haney, M.M.; Van Wijk, K.

2008-01-01

197

Wave attenuation over coastal salt marshes under storm surge conditions  

E-print Network

Coastal communities around the world face increasing risk from flooding as a result of rising sea level, increasing storminess, and land subsidence1–2. Salt marshes can act as natural buffer zones, providing protection from waves during storms3...

Möller, Iris; Kudella, Matthias; Rupprecht, Franziska; Spencer, Tom; Paul, Maike; van Wesenbeeck, Bregje K.; Wolters, Guido; Jensen, Kai; Bouma, Tjeerd J.; Miranda-Lange, Martin; Schimmels, Stefan

2014-09-29

198

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

PubMed

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

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

2013-10-01

199

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

NASA Astrophysics Data System (ADS)

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.; Austin, M. E.; Ellis, R. F.

2013-10-01

200

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

SciTech Connect

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

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

2013-10-15

201

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

NASA Astrophysics Data System (ADS)

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 media. Similar models of shear wave attenuation are not known, nor do general theories exist to predict wave-induced fluid flow effects in media with a more complex distribution of medium heterogeneities. By using finite element simulations of poroelastic relaxation, the total frequency-dependent complex stiffness tensor can be computed for a porous medium with arbitrary internal heterogeneity. From the stiffness tensor, velocity dispersion and frequency-dependent attenuation are derived for compressional and shear waves as a function of the angle of incidence. We apply our approach to the case of layered media and to that of an ellipsoidal poroelastic inclusion. In the case of the ellipsoidal inclusion, compressional and shear wave modes show significant attenuation, and the characteristic frequency dependence of the effect is governed by the spatiotemporal scale of the pore fluid pressure relaxation. In our anisotropic examples, the angle dependence of the attenuation is stronger than that of the velocity dispersion. It becomes clear that the spatial attenuation patterns show specific characteristics of wave-induced fluid flow, implying that anisotropic attenuation measurements may contribute to the inversion of fluid transport properties in heterogeneous porous media.

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

2010-07-01

202

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

Microsoft Academic Search

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

O. F. Tyrnov

1974-01-01

203

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

204

An elastic plate model for wave attenuation and ice floe breaking in the marginal ice zone  

Microsoft Academic Search

We present a model for wave attenuation in the marginal ice zone (MIZ) based on a two-dimensional (one horizontal and one vertical dimension) multiple floating elastic plate solution in the frequency domain, which is solved exactly using a matched eigenfunction expansion. The only physical parameters that enter the model are length, mass, and elastic stiffness (of which, the latter two

A. L. Kohout; M. H. Meylan

2008-01-01

205

Shear wave attenuation and dispersion in melt-bearing olivine polycrystals  

E-print Network

Shear wave attenuation and dispersion in melt-bearing olivine polycrystals: 1. Specimen fabrication and associated dispersion of the shear modulus G. In marked contrast with the high-temperature viscoelastic with increasing temperature. A ``global'' model comprising an Andrade-pseudoperiod background plus Gaussian peak

206

Attenuation, transport and diffusion of scalar waves in textured random media  

Microsoft Academic Search

Most theoretical investigations of seismic wave scattering rely on the assumption that the underlying medium is statistically isotropic. However, deep seismic soundings of the crust as well as geological observations often reveal the existence of elongated or preferentially oriented scattering structures. In this paper, we develop mean field and radiative transfer theories to describe the attenuation and multiple scattering of

L. Margerin

2006-01-01

207

Shear wave attenuation and dispersion in melt-bearing olivine polycrystals  

E-print Network

Shear wave attenuation and dispersion in melt-bearing olivine polycrystals: 2. Microstructural forced oscillation tests of melt-bearing olivine aggregates reported by Jackson et al. [2004. While the nanometer scale grain boundary structure in the melt-bearing aggregates is essentially

208

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

NASA Technical Reports Server (NTRS)

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

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

1970-01-01

209

WAVELET BASED CHARACTERIZATION OF ACOUSTIC ATTENUATION IN POLYMERS USING LAMB WAVE MODES  

E-print Network

Ultrasonic non-destructive testing (NDT) has been practiced for the last several decades. NDT ultrasonic. In industrial applications, ultrasonic testing is commonly used on metals, plastics, composites, and ceramics. Acoustical properties like attenuation of propagating ultrasonic waves through polymers vary in a broad

Boyer, Edmond

210

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

Microsoft Academic Search

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

Michael Fehler; Peter Roberts; Tom Fairbanks

1988-01-01

211

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

NASA Astrophysics Data System (ADS)

There is evidence that spiral waves and their breakup underlie mechanisms related to a wide spectrum of phenomena ranging from spatially extended chemical reactions to fatal cardiac arrhythmias [A. T. Winfree, The Geometry of Biological Time (Springer-Verlag, New York, 2001); J. Schutze, O. Steinbock, and S. C. Muller, Nature 356, 45 (1992); S. Sawai, P. A. Thomason, and E. C. Cox, Nature 433, 323 (2005); L. Glass and M. C. Mackey, From Clocks to Chaos: The Rhythms of Life (Princeton University Press, Princeton, 1988); R. A. Gray et al., Science 270, 1222 (1995); F. X. Witkowski et al., Nature 392, 78 (1998)]. Once initiated, spiral waves cannot be suppressed by periodic planar fronts, since the domains of the spiral waves grow at the expense of the fronts [A. N. Zaikin and A. M. Zhabotinsky, Nature 225, 535 (1970); A. T. Stamp, G. V. Osipov, and J. J. Collins, Chaos 12, 931 (2002); I. Aranson, H. Levine, and L. Tsimring, Phys. Rev. Lett. 76, 1170 (1996); K. J. Lee, Phys. Rev. Lett. 79, 2907 (1997); F. Xie, Z. Qu, J. N. Weiss, and A. Garfinkel, Phys. Rev. E 59, 2203 (1999)]. Here, we show that introducing periodic planar waves with long excitation duration and a period longer than the rotational period of the spiral can lead to spiral attenuation. The attenuation is not due to spiral drift and occurs periodically over cycles of several fronts, forming a variety of complex spatiotemporal patterns, which fall into two distinct general classes. Further, we find that these attenuation patterns only occur at specific phases of the descending fronts relative to the rotational phase of the spiral. We demonstrate these dynamics of phase-dependent spiral attenuation by performing numerical simulations of wave propagation in the excitable medium of myocardial cells. The effect of phase-dependent spiral attenuation we observe can lead to a general approach to spiral control in physical and biological systems with relevance for medical applications.

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

2007-03-01

212

Gamma Ray Attenuation Coefficient Measurement in Energies 1172 keV and 1332 keV for Neutron Absorbent Saturated Solutions  

Microsoft Academic Search

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

Jalali; Majid

2006-01-01

213

Determination of photon attenuation coefficient, porosity and field capacity of soil by gamma-ray transmission for 60, 356 and 662 keV gamma rays  

Microsoft Academic Search

Gamma-ray transmission methods have been used accurately for the study of the properties of soil in the agricultural purposes. In this study, photon attenuation coefficient, porosity and field capacity of soil are determined by using gamma-ray transmission method. To this end, the soil sample was collected from Erzurum and a 2×2 in NaI (Tl) scintillation detector measured the attenuation of

D. Demir; A. Ün; M. Özgül; Y. ?ahin

2008-01-01

214

New consistency tests for high-accuracy measurements of X-ray mass attenuation coefficients by the X-ray extended-range technique  

SciTech Connect

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

215

Wave energy attenuation and shoreline alteration characteristics of submerged breakwaters  

E-print Network

OF CONTENTS Page ABSTRACT ACKNOWLEDGEMENTS TABLE OF CONTENTS LIST OF FIGURES LIST OF TABLES NOMENCLATURE CHAPTER I INTRODUCTION 1. 1 General 1. 2 Objective II LITERATURE REVIEW . III EXPERIMENTAL SETUP AND PROCEDURE 3. I General 3. 2 Data... Acquisition and Instrumentation 3. 3 Experimental Parameters . . . . . 3. 4 Breakwater Construction 3. 5 Procedure IV ANALYSIS METHODS 4. I Shoreline Analysis 4. 2 Wave Response Analysis V RESULTS 5. 1 Development of the Nearshore Zone...

Krafft, Katherine Margaret

1993-01-01

216

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

SciTech Connect

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

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

1988-05-10

217

Functional relations between total scattering and backscattering for retrieving the profile of the attenuation coefficient in the atmosphere from lidar-sensing data  

SciTech Connect

The possibility of using a variable along a sensing path backscattering phase function in lidar data processing with the goal of increasing the accuracy of retrieving the profile of the attenuation coefficient in the inhomogeneous atmosphere is analyzed. Approximated dependences of the total aerosol scattering an aerosol backscattering are given based on the published experimental data. By way of example, the model profiles of the attenuation coefficient are given retrieved with the use of the scattering phase functions being constant and variable along the sensing path. 12 refs., 5 figs.

Kovalev, V.A. (A.I. Voeikov Main Geophysical Observatory, St. Petersburg (Russian Federation))

1992-05-01

218

Numerical investigation of wave attenuation by vegetation using a 3D RANS model  

NASA Astrophysics Data System (ADS)

Vegetation has been recognized as an important natural shoreline protection against storm surges and waves. Understanding of wave-vegetation interaction is essential for assessing the ability of vegetation patches, such as wetlands, to mitigate storm damages. In this study the wave attenuation by vegetation is investigated numerically using a 3-D model which solves the Reynolds-Averaged Navier-Stokes equations (RANS) by means of a finite-volume method based on collocated hexahedron mesh. A mixing length model is used for turbulence closure of the RANS equations. The water surface boundary is tracked using the Volume-of-Fluid (VOF) method with the Compressive Interface Capturing Scheme for Arbitrary Meshes (CICSAM) to solve the VOF advection equation. The presence of vegetation is taken into account by adding the vegetation drag and inertia forces to the momentum equations. The model is validated by several laboratory experiments of short wave propagation through vegetation over flat and sloping beds. The comparisons show good agreement between the measured data and calculated results, but the swaying motion of flexible vegetation which is neglected in this study can influence the accuracy of the wave height predictions. The model is then applied to one of the validation tests with different vegetation properties, revealing that the wave height attenuation by vegetation depends not only on the wave conditions, but also the vegetation characteristics such as vegetation height and density.

Marsooli, Reza; Wu, Weiming

2014-12-01

219

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

PubMed

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

Morin, Claire; Hellmich, Christian

2014-07-01

220

Tables of X-ray mass attenuation coefficients and mass energy-absorption coefficients 1 keV to 20 MeV for elements Z=1 to 92 and 48 additional substances of dosimetric interest  

Microsoft Academic Search

Tables and graphs of the photon mass attenuation coefficient mu\\/rho and the mass energy-absorption coefficient mu(en)\\/rho are presented for all of the elements Z=1 to 92, and for 48 compounds and mixtures of radiological interest. The tables cover energies of the photon (x ray, gamma ray, bremsstrahlung) from 1 keV to 20 MeV. The mu\\/rho values are taken from the

J. H. Hubbell; Stephen M Seltzer

1995-01-01

221

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

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

222

Analysis of coherent surface wave dispersion and attenuation for non-destructive testing of concrete.  

PubMed

Rayleigh waves measurements are used to characterise cover concrete and mortar in the frequency range 60-180 kHz. At these frequencies, the wavelength is comparable to the size of the aggregates, and waves propagate in a multiple scattering regime. Acquired signals are then difficult to interpret due to an important incoherent part. The method proposed here is the study of the coherent waves, obtained by averaging signals over several configurations of disorder. Coherent waves give information on an equivalent homogeneous medium. To acquire a large amount of measurements with accuracy, an optimised piezoelectric source is used with a laser interferometer for reception. Adapted signal processing technique are presented to evaluate the coherent phase and group velocities and also the coherent attenuation parameter. The sensitivity of these three parameters with the properties of concrete is discussed, as well as the necessity to use coherent waves to obtain accurate results. PMID:19545883

Chekroun, M; Le Marrec, L; Abraham, O; Durand, O; Villain, G

2009-12-01

223

Simple Formulas for Stopband Attenuation Characteristics of Asymmetric Helical Slow-Wave Structures of Traveling-Wave Tubes  

Microsoft Academic Search

Simple closed-form formulas for the estimation of the ?-mode stopband and the stopband attenuation in an azimuthally asymmetric helical slow-wave structure (SWS) are developed, following the coupled-mode analysis of multiple reflections. The formulas are simple and amenable to easy computation, and also allow the use of the dispersion characteristics of the structure obtainable from any standard electromagnetic modeling, thereby accruing

Subrata Kumar Datta; Vemula Bhanu Naidu; P. Raja Ramana Rao; Lalit Kumar; Baidyanath Basu

2010-01-01

224

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

225

Seismic?wave attenuation determined from tectonic tremor in multiple subduction zones  

USGS Publications Warehouse

Tectonic tremor provides a new source of observations that can be used to constrain the seismic attenuation parameter for ground?motion prediction and hazard mapping. Traditionally, recorded earthquakes of magnitude ?3–8 are used to develop ground?motion prediction equations; however, typical earthquake records may be sparse in areas of high hazard. In this study, we constrain the distance decay of seismic waves using measurements of the amplitude decay of tectonic tremor, which is plentiful in some regions. Tectonic tremor occurs in the frequency band of interest for ground?motion prediction (i.e., ?2–8??Hz) and is located on the subducting plate interface, at the lower boundary of where future large earthquakes are expected. We empirically fit the distance decay of peak ground velocity from tremor to determine the attenuation parameter in four subduction zones: Nankai, Japan; Cascadia, United States–Canada; Jalisco, Mexico; and southern Chile. With the large amount of data available from tremor, we show that in the upper plate, the lower crust is less attenuating than the upper crust. We apply the same analysis to intraslab events in Nankai and show the possibility that waves traveling from deeper intraslab events experience more attenuation than those from the shallower tremor due to ray paths that pass through the subducting and highly attenuating oceanic crust. This suggests that high pore?fluid pressure is present in the tremor source region. These differences imply that the attenuation parameter determined from intraslab earthquakes may underestimate ground motion for future large earthquakes on the plate interface.

Yabe, Suguru; Baltay, Annemarie S.; Ide, Satoshi; Beroza, Gregory C.

2014-01-01

226

Numerical Analysis of Pulsed Pressure Waves in Attenuative and Dispersive Media.  

NASA Astrophysics Data System (ADS)

This thesis examines the behavior of pulsed pressure waves as they propagate through dissipative fluids whose attenuation is characterized by a frequency power law. This means that the degree of attenuation increases as the frequency of a sinusoidal input signal increases where the rate of change is a physical property of the substance. Previously published experimental data indicates that this form of attenuation is typical of many viscous materials including biological tissues and fluids, adhesive glues, etc. The model developed to describe this behavior is based on the assumption that the pulsed waves have finite amplitude and can therefore be uniquely represented in the Fourier frequency domain in which the attenuation is equal to the imaginary part of the complex wavenumber. To ensure causality of the system impulse response, it is shown that the real part of the wavenumber must be nonlinearly dependent on frequency. This means that the physical system must be dispersive as well as attenuative and consequently pulsed waves are distorted as they propagate. Based on the complex wavenumber, a dispersive version of the wave equation which satisfies continuity conditions at material interfaces is derived. A spatial and temporal discretization of this equation allows for the analysis of realistic imaging regions. Due to noninteger powers of frequency in the wavenumber a continuous time version of the wave equation is not easily obtained making traditional finite difference time domain operators inapplicable. The interdependence of imaginary and real parts of the wavenumber, however, makes it possible to combine the corresponding terms in the wave equation into a single factor. This factor can then be mapped into discrete time frequency. In this domain noninteger exponents can be eliminated via a power series expansion and the resulting equations transform naturally to discrete time operators. The validity of this method is verified by comparing the results with those obtained through a numerical frequency domain implementation. The algorithm is demonstrated in two dimensions by simulating pulsed pressure waves radiating from a finite aperture through an adhesive bond layer in which case a thin dispersive layer is sandwiched between two lossless fluids.

Wismer, Margaret Gertrude

227

Attenuation of coda waves in the Garhwal Lesser Himalaya, India  

NASA Astrophysics Data System (ADS)

Qc estimates for the Uttarkashi and the Chamoli regions of the Garhwal Lesser Himalaya have been obtained by analyzing the coda waves of 159 local earthquakes recorded during 2008 and 2009 employing a 12-station seismological network. Earthquakes around the Uttarkashi region are located in the epicentral distance range of 5.0 to 93.9 km, focal depth range of 1.63 to 42.13 km, and coda magnitude range of 0.2 to 2.9, whereas earthquakes around Chamoli region are located in the epicentral distance range of 19.8-109.2 km, focal depth range of 1.36 to 40.72 km, and coda magnitude range of 1.0 to 3.0. The coda waves of 30 s duration, recorded on 982 seismograms, have been analyzed in seven frequencies range centered at 1.5, 3.0, 6.0, 9.0, 12.0, 18.0, and 24.0 Hz for four to five lapse time windows (LTW) using the single backscattering model given by Aki and Chouet (J Geophys Res 80:3322-3342, 1975). Mean value of Qc estimates vary from 76 at 1.5 Hz to 2201 at 24.0 Hz for LTW range of 10-40 s and from 216 at 1.5 Hz to 3243 at 24.0 Hz for LTW range of 50-80 s (for the Uttarkashi region) and from 147 at 1.5 Hz to 2273 at 24.0 Hz for LTW range of 20-50 s and from 188 at 1.5 Hz to 2826 at 24.0 Hz for LTW range of 50-80 s (for Chamoli region). The Qc values thus obtained showed a clear dependence on frequency and LTW and frequency dependence Qc relationships, Qc = Q0f?, for LTWs that have been obtained as Qc = 57f1.20 (10-40 s), Qc = 97f1.07 (20-50 s), Qc = 116f1.03 (30-60 s), Qc = 130f1.03 (40-70 s), and Qc = 162f0.95 (50-80 s) for Uttarkashi region and Qc = 107f0.95 (20-50 s), Qc = 115f0.96 (30-60 s), Qc = 128f0.95 (40-70 s), and Qc = 145f0.95 (50-80 s) for Chamoli region.

Jain, S. K.; Gupta, S. C.; Kumar, Ashwani

2015-04-01

228

An observation related to directional attenuation of SKS waves propagating in anisotropic media  

NASA Astrophysics Data System (ADS)

Azimuthal anisotropy of attenuation is a physical phenomenon related to the directional change of attenuation. This study examines the frequency properties and directional attenuation of SKS waves. The directional frequency-dependent characteristics of SKS waves are investigated in the frequency band of 0.02-0.5 Hz using data from 53 permanent seismic stations located throughout the northern Yangtze Craton, the southern North China Craton and adjacent areas. In addition to normal splitting behavior, the analysis reveals that many SKS splitting measurements exhibit a lemniscate shape, reflecting frequency differences along fast and slow polarization directions. Frequency analysis shows that spectral ratios between fast/slow components of the lemniscate-type splitting results fluctuate strongly in a higher frequency band of 0.2-0.5 Hz, and fluctuate less within the main frequency band of 0.02-0.2 Hz. For each station, the ratio of the peak amplitude of the fast/slow components can be represented as a cotangential function of event backazimuth multiplying with a constant = 0.42 ± 0.10. This transformation shows that the regional average angles consistently fall within the relatively narrow range of -46.5 ± 3° with respect to the north, suggesting that a regional tectonic controlling factor dictates the relatively uniform directional attenuation of SKS waves within the frequency band of 0.02-0.2 Hz. Further analysis is performed by projecting the SKS waves onto the components along and perpendicular to the regional average angles. The calculation also shows that, in the 0.02-0.2 Hz band, the relationship between amplitude ratio and event backazimuth matches a cotangential functions with the same best matching angles and constant a < 1. Synthetic calculations demonstrate that although different filters influence the splitting parameters, attenuation anisotropy cannot be explained by elastic anisotropic media, including multilayer anisotropy and anisotropy with a tilting symmetrical axis. This observed behavior of the SKS wave may arise from the combined effects of frequency-dependent attenuation anisotropy and small-scale heterogeneities in the crust and the upper mantle.

Zhao, Liang; Xue, Mei

2015-04-01

229

Retrieval of phytoplankton biomass from simultaneous inversion of reflectance, the diffuse attenuation coefficient, and Sun-induced fluorescence in coastal waters  

Microsoft Academic Search

A model has been developed to retrieve phytoplankton absorption, a proxy for phytoplankton biomass, from observations of reflectance (R) and the diffuse attenuation coefficient (K d) collected by moored radiometers in coastal waters, where high concentrations of chromophoric dissolved organic matter (CDOM) confound conventional ocean color algorithms. The inversion uses simultaneously two forward models: (1) a look-up table (LUT) that

Yannick Huot; Catherine A. Brown; John J. Cullen

2007-01-01

230

Retrieval of phytoplankton biomass from simultaneous inversion of reflectance, the diffuse attenuation coefficient, and Sun-induced fluorescence in coastal waters  

Microsoft Academic Search

A model has been developed to retrieve phytoplankton absorption, a proxy for phytoplankton biomass, from observations of reflectance (R) and the diffuse attenuation coefficient (Kd) collected by moored radiometers in coastal waters, where high concentrations of chromophoric dissolved organic matter (CDOM) confound conventional ocean color algorithms. The inversion uses simultaneously two forward models: (1) a look-up table (LUT) that accounts

Yannick Huot; Catherine A. Brown; John J. Cullen

2007-01-01

231

Seasonal variability in the vertical attenuation coefficient at 490 nm (K490) in waters around Puerto Rico and US Virgin Islands  

Microsoft Academic Search

Satellite sensors provide a valuable tool in understanding the seasonal variability of ocean color properties. The vertical diffuse attenuation coefficient (Kd) was evaluated for the waters around Puerto Rico and the US Virgin Islands. The MODIS K490 of Band 3 Level82 daily images were processed with a resolution of 1 kilometer for the year 2008. The images were projected to

William J. Hernandez; Fernando Gilbes

232

Study of variance and covariance terms in linear attenuation coefficient measurements of irregular samples through the two media method by gamma-ray transmission  

Microsoft Academic Search

The two media method permits the application of Beer's law (Thesis (Master Degree), Universidade Estadual de Londrina, PR, Brazil, pp. 23) for the linear attenuation coefficient determination of irregular thickness samples by gamma-ray transmission. However, the use of this methodology introduces experimental complexity due to the great number of variables to be measured. As consequence of this complexity, the uncertainties

Renato Yoichi Ribeiro Kuramoto; Carlos Roberto Appoloni

2002-01-01

233

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

SciTech Connect

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

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

2010-11-12

234

The propagation and attenuation of complex acoustic waves in treated circular and annular ducts  

NASA Technical Reports Server (NTRS)

The propagation of plane waves and higher order acoustic modes in a circular multisectioned duct was studied. A unique source array consisting of two concentric rings of sources, providing phase and amplitude control in the radial, as well as circumferential direction, was developed to generate plane waves and both spinning and nonspinning higher order modes. Measurements of attenuation and radial mode shapes were taken with finite length liners between the hard wall sections of an anechoically terminated duct. Materials tested as liners included a glass fiber material and both sintered fiber metals and perforated sheet metals with a honeycomb backing. The fundamental acoustic properties of these materials were studied with emphasis on the attenuation of sound by the liners and the determination of local versus extended reaction behavior for the boundary condition. The experimental results were compared with a mathematical model for the multisectioned duct.

Reethof, G.

1976-01-01

235

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

NASA Astrophysics Data System (ADS)

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

Birger, B. I.

2006-11-01

236

Diffusion coefficients from resonant interactions with electrostatic electron cyclotron harmonic waves  

SciTech Connect

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

237

Accurate tape analysis of the attenuator-coated helical slow-wave structure  

Microsoft Academic Search

The tape-helix model is used to analyze the helical slow-wave structure considering the helix turns to be effectively shorted by the resistive attenuator coating on dielectric helix-support rods. An effective surface resistivity is calculated based on the resistive coating on discrete support rods. The results of the analysis are validated against reported experimental results in the special case of no

Zhaoyun Duan; Yubin Gong; Wenxiang Wang; B. N. Basu; Yanyu Wei

2006-01-01

238

Ultrasonic attenuation in pearlitic steel.  

PubMed

Expressions for the attenuation coefficients of longitudinal and transverse ultrasonic waves are developed for steel with pearlitic microstructure. This type of lamellar duplex microstructure influences attenuation because of the lamellar spacing. In addition, longitudinal attenuation measurements were conducted using an unfocused transducer with 10 MHz central frequency on the cross section of a quenched railroad wheel sample. The dependence of longitudinal attenuation on the pearlite microstructure is observed from the changes of longitudinal attenuation from the quenched tread surface to deeper locations. The results show that the attenuation value is lowest and relatively constant within the quench depth, then increases linearly. The experimental results demonstrate a reasonable agreement with results from the theoretical model. Ultrasonic attenuation provides an important non-destructive method to evaluate duplex microstructure within grains which can be implemented for quality control in conjunction with other manufacturing processes. PMID:24268679

Du, Hualong; Turner, Joseph A

2014-03-01

239

Electric field analysis in the earth considering attenuation of electromagnetic waves propagated in lossy media  

SciTech Connect

In the field of oil well drilling. EM-MWD (Electromagnetic Measurement While Drilling) offers many advantages. The EM-MWD system can transmit measured data from the well bottom to the surface with high speed using electromagnetic waves. Developing the EM-MWD technology requires analysis of the electric field around a drill string. A new computer simulation method has been developed. The method considers attenuation of electromagnetic waves propagated in lossy media, the earth, using features of analysis models. This paper reports that the simulation method can be applied to waveform simulation. This method has been verified by field experiment using a borehole of 500m depth.

Mackawa, T.; Shimada, T.; Inoue, S.; Jitsumori, A. (Mitsubishi Electric Corp., 8-1-1 Tsukaguchi-honmachi, Amagasaki, Hyogo 661 (JP)); Okumura, N. (Japan National Oil Corp., 1-1-2 Hamada, Chiba 260 (JP)); Akizuki, K. (Waseda Univ., 3-4-1 Okubo, Shinjuku-ku, Tokyo 160 (JP))

1992-03-01

240

MODIS-based retrieval of suspended sediment concentration and diffuse attenuation coefficient in Chinese estuarine and coastal waters  

NASA Astrophysics Data System (ADS)

Radiative transfer modelling in atmosphere, water, and on the air-water surface was used to create an algorithm and computer code for satellite monitoring Chinese estuarine and coastal waters. The atmospheric part of the algorithm is based on the Reference Evaluation of Solar Transmittance (REST) model for calculation of optical properties of the atmosphere from the top of the atmosphere to the target; for modelling optical properties from target towards satellite's sensor, an optical reciprocity principle has been used. An algorithm uses estimates derived from three different sources: 1) the MODIS-based software; 2) radiative transfer equations, and 3) well-known empirical relationships between measured parameters and optical depths and transmittances for such atmospheric components as molecules, aerosols, ozone, nitrogen dioxide, precipitable water vapor and uniformly mixed gases. Using this model allowed us to derive a reliable relationship relating an important parameter, the diffuse-to-global solar incoming irradiance ratio, to the aerosol optical thickness, solar zenith angle and wavelength. The surface and underwater parts of the algorithm contained theoretical and semi-empirical relationships between inherent (such as absorption, scattering and backscattering coefficients) and apparent (remote-sensing reflectance and diffuse attenuation coefficient, Kd) optical properties, and suspended sediment concentration (SSC) measured in the Yangtze River Estuary and its adjacent coastal area. The first false colour maps of SSC and Kd demonstrated a well accordance with the multi-year field observations in the region, and suggest promise for use of this algorithm for the regular monitoring of Chinese and worldwide natural waters.

Sokoletsky, Leonid; Yang, Xianping; Shen, Fang

2014-11-01

241

The wave equation with viscoelastic attenuation and its application in problems of shallow-sea acoustics  

NASA Astrophysics Data System (ADS)

A suitable tool for the simulation of low frequency acoustic pulse signals propagating in a shallow sea is the numerical integration of the nonstationary wave equation. The main feature of such simulation problems is that in this case the sound waves propagate in the geoacoustic waveguide formed by the upper layers of the bottom and the water column. By this reason, the correct dependence of the attenuation of sound waves in the bottom on their frequency must be taken into account. In this paper we obtain an integro-differential equation for the sound waves in the viscoelastic fluid, which allows to simulate the arbitrary dependence of acoustic wave attenuation on frequency in the time domain computations. The procedure of numerical solution of this equation based on its approximation by a system of differential equations is then considered and the methods of artificial limitation of computational domain are described. We also construct a simple finite-difference scheme for the proposed equation suitable for the numerical solution of nonstationary problems arising in the shallow-sea acoustics.

Petrov, P. S.; Zakharenko, A. D.; Trofimov, M. Yu.

2012-11-01

242

Inverse bremsstrahlung absorption coefficient and initiation of laser- supported detonation waves in air  

Microsoft Academic Search

The inverse bremsstrahlung absorption coefficient in LASNEX was modified ; for application to laser effects calculations at temperatures below 10 eV. These ; modifications are described and the initiation condition for a laser-supported ; detonation (LSD) wave is crudely estimated for air in the vicinity of a solid ; target. (auth)

Winslow

1973-01-01

243

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

Microsoft Academic Search

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

244

Attenuation and velocity structure from diffuse coda waves: Constraints from underground array data  

NASA Astrophysics Data System (ADS)

An analysis of coda waves excited in the 0.2-20 Hz frequency band and recorded by the underground array Underseis (central Italy) has been performed to constrain both seismic attenuation at regional scale and velocity structure in the Mount Gran Sasso area. Attenuation was estimated with the MLTWA method, and shows a predominance of scattering phenomena over intrinsic absorption. The values of Qi and Qs are compatible with other estimates obtained in similar tectonic environments. Array methods allowed for a detailed study of the propagation characteristics, demonstrating that earthquake coda at frequencies greater than about 6 Hz is composed of only body waves. Coherence and spectral characteristics of seismic waves measured along the coda of local and regional earthquakes indicate that the wavefield becomes fully diffuse only in the late coda. The frequency-dependent energy partitioning between horizontal and vertical components has been also estimated and compared with synthetic values computed in a layered half-space under the diffuse field assumption. This comparison confirms that, for frequencies higher than 6 Hz, the coda appears as a sum of body waves coming from all directions while, in the low frequency range (0.2-2 Hz), the observations can be well explained by a coda wavefield composed of an equipartition mixture of surface and body waves traveling in a multiple-layered medium. A Monte-Carlo inversion has been performed to obtain a set of acceptable velocity models of the upper crust. The present results show that a broadband coda wavefield recorded in an underground environment is useful to constrain both the regional attenuation and the velocity structure of the target area, thereby complementing the results of classical array analysis of the wavefield.

Galluzzo, Danilo; La Rocca, Mario; Margerin, Ludovic; Del Pezzo, Edoardo; Scarpa, Roberto

2015-03-01

245

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

PubMed

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

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

2012-11-01

246

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

PubMed Central

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

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

2012-01-01

247

Estimation of the intrinsic absorption and scattering attenuation in Northeastern Venezuela (Southeastern Caribbean) using coda waves  

USGS Publications Warehouse

Northeastern Venezuela has been studied in terms of coda wave attenuation using seismograms from local earthquakes recorded by a temporary short-period seismic network. The studied area has been separated into two subregions in order to investigate lateral variations in the attenuation parameters. Coda-Q-1 (Q(c)-1) has been obtained using the single-scattering theory. The contribution of the intrinsic absorption (Q(i)-1) and scattering (Q(s)-1) to total attenuation (Q(t)-1) has been estimated by means of a multiple lapse time window method, based on the hypothesis of multiple isotropic scattering with uniform distribution of scatterers. Results show significant spatial variations of attenuation: the estimates for intermediate depth events and for shallow events present major differences. This fact may be related to different tectonic characteristics that may be due to the presence of the Lesser Antilles subduction zone, because the intermediate depth seismic zone may be coincident with the southern continuation of the subducting slab under the arc.

Ugalde, A.; Pujades, L.G.; Canas, J.A.; Villasenor, A.

1998-01-01

248

Viscoelastic characteristics of low-frequency seismic wave attenuation in porous media  

NASA Astrophysics Data System (ADS)

Mesoscopic fluid flow is the major cause of wave attenuation and velocity dispersion at seismic frequencies in porous rocks. The Johnson model provides solutions for the frequency-dependent quality factor and phase velocity in partially saturated porous media with pore patches of arbitrary shapes. We use the Johnson model to derive approximations for the quality factor Q at the high and low frequency limit, and obtain the approximate equation for Q min based on geophysical and geometric parameters. A more accurate equation for Q min is obtained after correcting for the linear errors between the exact and approximate Q values. The complexity of the pore patch shape affects the maximum attenuation of Q min and the transition frequency ftr; furthermore, the effect on f tr is stronger than that on Q min . Numerical solutions to Biot's equation are computationally intensive; thus, we build an equivalent viscoelastic model on the basis of the Zener model, which well approximates the wave attenuation and dispersion in porous rocks in the seismic band.

Ling, Yun; Han, Li-Guo; Zhang, Yi-Ming

2014-12-01

249

Velocity Dispersion and Attenuation of Acoustic Waves in Granular Sedimentary Media.  

NASA Astrophysics Data System (ADS)

An experimental and theoretical investigation of the effects of stress, frequency, and clay content on compressional and shear wave velocities and attenuations has been conducted using tight gas sandstone samples. The ultrasonic pulse transmission technique (~ 1 MHz) was used to measure velocities and attenuations and calculate dynamic moduli of fully brine saturated samples with porosities from 3 to 11.9 percent and clay contents from 1 to 38 percent. Simultaneous measurements were carried out to record axial and radial deformation under a biaxial stress state in order to calculate the static elastic moduli. The static moduli were found to be 1 to 6 times smaller than the dynamic moduli under the stress state. The velocities measured at ultrasonic frequency were also compared to the sonic log velocities (~20 KHz) in order to investigate dispersion effects. The trend observed in P and S wave velocities in homogeneous intervals shows that clean sandstone velocities measured in the ultrasonic frequency range deviate systematically from the log derived velocities. Compressional and shear wave amplitude data exhibited a shift in peak frequency toward lower frequencies for clay rich samples as compared to clean samples showing the important role clays play in the dissipative behavior of sandstones. The deviations from the log derived velocities are correlatable in most cases to the clay content and dispersion. The presence of clay softens the rock grain contacts and causes larger contact area values compared to the values for nearly clean rock under the same applied load. The frame moduli of sedimentary rocks are strongly influenced by the properties of the grain contacts. A modified Hertz contact theory is presented for the self consistent calculation of contact deformation, equilibrium separation distance (film thickness) and contact area for two spherical asperities in contact and subjected to an external load. It is shown that surface forces, i.e. electrostatic repulsion, Born, structural, and Van der Waals forces can be incorporated into the contact deformation problem. These forces play an important role in determining seismic wave velocities and attenuations at low confining stresses. The computed equilibrium separation distances and contact radii were used to calculate velocities and attenuations as a function of frequency and compared with measured values for glass beads, Navajo, Berea, Obernkirchner and Fort Union sandstones. The velocities and attenuations calculated as functions of stress, frequency, fluid type and saturation are all in good agreement with reported experimental data.

Tutuncu, Azra Nur

250

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

251

Technological cost-reduction pathways for attenuator wave energy converters in the marine hydrokinetic environment.  

SciTech Connect

This report considers and prioritizes the primary potential technical costreduction pathways for offshore wave activated body attenuators designed for ocean resources. This report focuses on technical research and development costreduction pathways related to the device technology rather than environmental monitoring or permitting opportunities. Three sources of information were used to understand current cost drivers and develop a prioritized list of potential costreduction pathways: a literature review of technical work related to attenuators, a reference device compiled from literature sources, and a webinar with each of three industry device developers. Data from these information sources were aggregated and prioritized with respect to the potential impact on the lifetime levelized cost of energy, the potential for progress, the potential for success, and the confidence in success. Results indicate the five most promising costreduction pathways include advanced controls, an optimized structural design, improved power conversion, planned maintenance scheduling, and an optimized device profile.

Bull, Diana L; Ochs, Margaret Ellen

2013-09-01

252

Seismic attenuation: effects of interfacial impedance on wave-induced pressure diffusion  

NASA Astrophysics Data System (ADS)

Seismic attenuation and dispersion in layered sedimentary structures are often interpreted in terms of the classical White model for wave-induced pressure diffusion across the layers. However, this interlayer flow is severely dependent on the properties of the interface separating two layers. This interface behaviour can be described by a pressure jump boundary condition involving a non-vanishing interfacial impedance. In this paper, we incorporate the interfacial impedance into the White model by solving a boundary value problem in the framework of quasi-static poroelasticity. We show that the White model predictions for attenuation and dispersion substantially change. These changes can be attributed to petrophysically plausible scenarios such as imperfect hydraulic contacts or the presence of capillarity.

Qi, Qiaomu; Müller, Tobias M.; Rubino, J. Germán

2014-12-01

253

Shape effect of elongated grains on ultrasonic attenuation in polycrystalline materials  

Microsoft Academic Search

Longitudinal and transverse wave attenuation coefficients are obtained in a simple integral form for ultrasonic waves in cubic polycrystalline materials with elongated grains. Dependences of attenuation on frequency and grain shape are described in detail. The explicit analytical solutions for ellipsoidal grains in the Rayleigh and stochastic frequency limits are given for a wave propagating in an arbitrary direction relative

L. Yang; O. I. Lobkis; S. I. Rokhlin

2011-01-01

254

Air-ground interface: Surface waves, surface impedance and acoustic-to-seismic coupling coefficient  

NASA Technical Reports Server (NTRS)

In atmospheric acoustics, the subject of surface waves has been an area of discussion for many years. The existence of an acoustic surface wave is now well established theoretically. The mathematical solution for spherical wave propagation above an impedance boundary includes the possibility of a contribution that possesses all the standard properties for a surface wave. Surface waves exist when the surface is sufficiently porous, relative to its acoustical resistance, that it can influence the airborne particle velocity near the surface and reduce the phase velocity of sound waves in air at the surface. This traps some of the sound energy in the air to remain near the surface as it propagates. Above porous grounds, the existence of surface waves has eluded direct experimental confirmation (pulse experiments have failed to show a separate arrival expected from the reduced phase speed) and indirect evidence for its existence has appeared contradictory. The experimental evidence for the existence of an acoustical surface wave above porous boundaries is reviewed. Recent measurements including pulse experiments are also described. A few years ago the acoustic impedance of a grass-covered surface was measured in the frequency range 30 to 300 Hz. Here, further measurements on the same site are discussed. These measurements include core samples, a shallow refractive survey to determine the seismic velocities, and measurements of the acoustic-to-seismic coupling coefficient.

Daigle, Gilles; Embleton, Tony

1990-01-01

255

S wave attenuation and site effects in the region of Friuli, Italy  

NASA Astrophysics Data System (ADS)

We used strong motion records from the 1976 Friuli earthquake (M 6.4) and 10 of the biggest aftershocks recorded by the National Accelerograph Network of the Electrical Power Company of Italy to estimate the quality factor Q of S waves in this region. The wide distance range of the recordings (10 < r < 190 km) permits us to analyze the spectral amplitude decay of the records using a nonparametric approach [e.g., Anderson and Quaas, 1988; Castro et al., 1990; Anderson, 1991]. We obtained attenuation functions for a set of 18 frequencies ranging between 0.4 and 25.0 Hz. The values of Q retrieved from the attenuation functions obtained follow the frequency-dependent relation Q = 20.4f. A test of the method was made using a second data set consisting of digital seismograms from the Friuli-Venezia Giulia Seismograph Network. In spite of the different size of the volume sampled by these data (10 < r < 131 km), the frequency dependence of Q obtained (Q = 16.1f0.92) is similar to that obtained with the strong motion data set. The near-surface attenuation was also estimated using the model proposed by Anderson and Hough [1984] and Anderson [1991]. We found that ?0 is smaller for the strong motion stations located on rock compared to stations located on either shallow or soft sediments. To estimate the site response of the strong motion stations, we corrected the spectral records for the attenuation effect and then inverted the corrected records to separate source and site effects using the inversion scheme proposed by Andrews [1986]. To verify the site amplification estimates obtained, we also calculated the transfer function of each site using Nakamura's [1989] method for S wave [e.g., Lermo and Chavez-García, 1993]. In general, the shapes of the site functions obtained with the inversion are consistent with the transfer functions obtained calculating the horizontal to vertical component ratio.

Castro, Raúl R.; Pacor, Francesca; Sala, Alfio; Petrungaro, Carmine

1996-10-01

256

Study of Spectral Attenuation Laws of Seismic Waves for Michoacán state, México  

NASA Astrophysics Data System (ADS)

Several attenuation relationships have been developed for Mexico, mostly after the earthquake of September 19, 1985, an event that gave great impetus to the development of engineering seismology in Mexico. Since 1985, the number of seismic stations in the country has increased significantly, especially between the Coast of Guerrero and Mexico City. This is due to the infamous large amplifications observed in the lake area of Mexico City with respect to hard ground sites. Some studies have analyzed how seismic waves are attenuated or amplified from the Pacific Coast toward the inland. The attenuation relationship used for seismic hazard assessment in Mexico is that of Ordaz (1989), which uses data from the Guerrero acceleration network. Another recent study is that of García et al. (2005), which uses more recent data from intraplate earthquakes recorded at the Guerrero acceleration network. It is important to note that, since these relations were derived for only part of the Mexican subduction zone and for certain types of seismic sources, caution should be exercised when using them for earthquake risk studies in other regions of Mexico. In the present work, we study the state of Michoacán, one of the most important seimogenic zones in Mexico. Three kinds of sources exist in the state, producing tectonic earthquakes, volcanic earthquakes, and events due to local faults in the region. For this reason, it is of vital importance to study the propagation of seismic waves within Michoacán state, and in this paper in particular we study their attenuation. We installed a temporary network consisting of 7 accelerograph stations across the state, at the following locations: Faro de Brucerías, Aguililla, Apatzingán, Taretán, Pátzcuaro, Morelia, and Maravatío. The stations form a line that is perpendicular to the coastline and has a total length of 366 km, while the distance between neighboring stations varies from 60 to 80 km. Among all the seismic events recorded at this temporary network, we select 8 events that originated along the coastline of Michoacán, with moment magnitudes ranging from 4.3 to 5.1 Mw. Using these records, we calculate Q values for frequencies between 0.1 and 10 Hz, which is the frequency range of interest for Earthquake Engineering. According to our preliminary results, the attenuation estimated is significantly larger than what the attenuation laws predict for the states of Guerrero and Colima. One limitation of this study is that we used relatively small-magnitude earthquakes. This was a consequence of the relatively short operation period of the temporary network, which had to be limited to 3 months.

Vazquez Rosas, R.; Aguirre, J.; Mijares Arellano, H.

2009-12-01

257

On the scaling of streamwise streaks and their efficiency to attenuate Tollmien-Schlichting waves  

NASA Astrophysics Data System (ADS)

Streaky boundary layers generated by an array of miniature vortex generators (MVGs) mounted on a flat plate have recently shown to have a stabilizing effect on both two- and three-dimensional disturbances. An experimental study on the effect of the geometrical parameters of MVGs on the generated streamwise streaks in the flat plate boundary layer is carried out, and the corresponding stabilizing effect on Tollmien-Schlichting (TS) wave disturbances is quantified. The new experimental configurations have led to an improved empirical scaling law, which includes additional geometrical parameters of the MVGs compared to the previously reported relation. It is found that the MVG configuration can be optimized with respect to the attenuation of disturbances. In addition, the streamwise location of branch I of the neutral stability curve, with regard to the location of the MVG array, is found to be correlated with the initial receptivity of TS waves on the MVG array and the attenuation of the TS wave amplitude in the unstable region.

Sattarzadeh, Sohrab S.; Fransson, Jens H. M.

2015-03-01

258

Quasi-static finite element modeling of seismic attenuation and dispersion due to wave-induced fluid flow in poroelastic media  

NASA Astrophysics Data System (ADS)

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

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

2011-01-01

259

K-shell absorption jump factors and jump ratios in elements between Tm ( Z = 69) and Os ( Z = 76) derived from new mass attenuation coefficient measurements  

Microsoft Academic Search

The K-shell absorption jump factors and jump ratios were derived from new mass attenuation coefficients measured using an energy dispersive X-ray fluorescence (EDXRF) spectrometer for Tm, Yb elements being Tm2O3, Yb2O3 compounds and pure Lu, Hf, Ta, W, Re and Os. The measurements, in the region 56–77keV, were done in a transmission geometry utilizing the K?1, K?2, K?1 and K?2

Necati Kaya; Engin Tirasoglu; Gökhan Apaydin; Volkan Aylikci; Erhan Cengiz

2007-01-01

260

Measurements of the X-ray linear attenuation coefficient for low atomic number materials at energies 32–66 and 140 keV  

Microsoft Academic Search

The X-ray linear attenuation coefficient was measured for materials containing elements hydrogen to calcium. Characteristic X-rays with energies 32–66keV were produced by X-ray fluorescence using a secondary target system, and 140keV gamma rays were obtained from an unsealed 99mTc source. The photon beams were highly collimated and recorded using energy dispersive detection. A high-purity germanium detector was utilised to distinguish

S. M. Midgley

2005-01-01

261

Changes in the linear attenuation coefficient of canine appendicular bone following intravenous infusion of strontium lactate, measured using gamma-ray computed tomography  

Microsoft Academic Search

Changes in the average linear attenuation coefficient (LAC) within a fixed measurement volume in the proximal end of the dog tibia, which contains trabecular bone and associated soft tissues (the trabecular bone “space”), were monitored continuously using gamma-ray computed tomography (?-CT) prior to, during, and following intravenous infusion of strontium (Sr) lactate. An infusion of 1.3–4.7 g of Sr over

Thomas R. Overton; Richard E. Snyder; Thomas N. Hangartner; Safwat Girgis; Robert J. Audette; David C. Secord

1992-01-01

262

Measurement of attenuation coefficients for bone, muscle, fat and water at 140, 364 and 662 keV gamma-ray energies  

Microsoft Academic Search

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 gamma-ray energies by using the ATOMLABTM-930 medical spectrometer. The gamma-rays were obtained from 99mTc, 131I and 137Cs gamma-ray point sources. Also theoretical calculations have been performed in order to obtain the half-value thicknesses

A. Akar; H. Baltas; U. Çevik; F. Korkmaz; N. T. Okumusoglu

2006-01-01

263

Measurement of x-ray attenuation coefficients for elements in the range 79 less than or equal to Z less than or equal to 92  

Microsoft Academic Search

A method for measuring the X-ray attenuation coefficients for elements with 79 less than or equal to Z less than or equal to 92 at the excitation energy of 121.9 keV (Gamma-rays emitted by Co-57 radioisotope source) is described. The accuracy is greatly improved by intensity ratio measurements of infinitely thin and thick targets; thus the uncertainties in the fundamental

N. S. Saleh; M. A. Sharif; K. A. Al-Saleh

2009-01-01

264

Measurements of the X-ray linear attenuation coefficient for low atomic number materials at energies 32-66 and 140keV  

Microsoft Academic Search

The X-ray linear attenuation coefficient was measured for materials containing elements hydrogen to calcium. Characteristic X-rays with energies 32-66keV were produced by X-ray fluorescence using a secondary target system, and 140keV gamma rays were obtained from an unsealed 99mTc source. The photon beams were highly collimated and recorded using energy dispersive detection. A high-purity germanium detector was utilised to distinguish

S. M. Midgley

2005-01-01

265

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

266

Wave Attenuation at a Salt Marsh Margin: A Case Study of an Exposed Coast on the Yangtze Estuary  

Microsoft Academic Search

To quantify wave attenuation by (introduced) Spartina alterniflora vegetation at an exposed macrotidal coast in the Yangtze Estuary, China, wave parameters and water depth were measured during\\u000a 13 consecutive tides at nine locations ranging from 10 m seaward to 50 m landward of the low marsh edge. During this period,\\u000a the incident wave height ranged from <0.1 to 1.5 m, the maximum of

S. L. Yang; B. W. Shi; T. J. Bouma; T. Ysebaert; X. X. Luo

2012-01-01

267

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

268

Stable harmonic multiplying gyrotron traveling-wave amplifier with distributed wall losses and attenuating severs  

NASA Astrophysics Data System (ADS)

Harmonic multiplying gyrotron traveling-wave amplifiers (gyro-TWTs) provide magnetic field reduction and frequency multiplication. However, spurious oscillations may reduce the amplification of the gyro-TWT. Most distributed-loss structures 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. This study proposes a Ka-band harmonic multiplying gyro-TWT, using distributed wall losses and attenuating severs, to improve the stability of the amplification and the performance of the amplifier. Simulation results reveal that the absolute instabilities are effectively suppressed by wall losses of the lossy and severed sections, especially in the low-kz and high-order modes. Meanwhile, the severed section, dividing an interaction circuit into several short sections, reduces the effective interaction lengths of the absolute instabilities. The stable harmonic multiplying gyro-TWT is predicted to yield a peak output power of 230kW at 33.65GHz with an efficiency of 30%, a saturated gain of 40dB, and a 3dB bandwidth of 0.8GHz for a 60kV, 13A electron beam with an axial velocity spread of ?vz/vz=8%. The power/gain scaling and phase relation between the drive and the output waves are elucidated.

Yeh, Y. S.; Cheng, J. H.; Chen, L. K.; Hung, C. W.; Lo, C. Y.; Liao, C. W.

2008-02-01

269

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

270

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

E-print Network

The so-called Localized Waves (LW), and the "Frozen Waves" (FW), have arisen 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 theirs, offer the possibility of arbitrarily modeling the field longitudinal 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 frequency f_o = 1 MHz in a water-like medium, taking account of the effects of attenuation. We present res...

Prego-Borges, Jose' L; Recami, Erasmo; Tavares-Costa, Eduardo

2013-01-01

271

Analysis of P-wave attenuation in hydrate-bearing sediments in the Shenhu area, South China Sea  

NASA Astrophysics Data System (ADS)

In order to analyze the wave attenuation characteristics in hydrate-bearing sediments, the Biot-Squirt (BISQ) porous medium model was implemented in the Shenhu area, South China Sea. Theoretical studies indicated that decrease of P-wave attenuation at seismic frequency range is observed with the increasing hydrate saturation. In the case studies in the Shenhu area, we estimated the quality factor from seismic reflection data after spectral correction by using the centroid-frequency method. The quality factor in the hydrate-bearing sediments is greater than 30, and with the hydrate saturation increasing to 40 % the quality factor increases from 30 to 50. This shows good agreement with the theoretical results based on the BISQ model. The field data example indicated that seismic wave attenuation is an effective attribute to identify the distribution of gas hydrates.

Li, Chuanhui; Feng, Kai; Liu, Xuewei

2014-11-01

272

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

273

S wave attenuation structure on the western side of the Nankai subduction zone: Implications for fluid distribution and dynamics  

NASA Astrophysics Data System (ADS)

We estimated the S wave attenuation structure in southwestern Japan and the western Nankai Trough by analyzing maximum S wave amplitudes at 4-8, 8-16, and 16-32 Hz with a correction term for apparent amplitude attenuation due to multiple forward scattering. Because the estimated attenuation (Q-1) in our tomographic study was much larger than Q-1 due to wide-angle scattering, our estimated Q-1 was composed mainly of intrinsic attenuation. High-attenuation areas (Q-1 > 1/300 at 4-8 Hz) were imaged beneath Quaternary volcanoes and south off Shikoku. Low (<1/1500 at 4-8 Hz) or moderate Q-1 (1/500-1/1000 at 4-8 Hz) was imaged beneath Shikoku and nonvolcanic areas of Chugoku. High and moderate Q-1 in and around Shikoku are located near the top of subducting Philippine Sea Plate. This correspondence implies that these high and moderate Q-1 reflect fluid in the subducting slab. By applying a theoretical model of attenuation in water-saturated porous random media, we examined wave-induced fluid flow induced by lower frequency (<1 Hz) seismic waves that may be related with triggering of nonvolcanic tremor by surface waves. Even though Q-1 structure in this study cannot fully explain the tremor triggering by wave-induced fluid flow, large uncertainties of Q-1 in tremor zone suggest that high resolution imaging of Q-1 and random inhomogeneities would give some constraints for the spatial variation of permeability and other medium properties.

Takahashi, Tsutomu; Obana, Koichiro; Yamamoto, Yojiro; Nakanishi, Ayako; Kodaira, Shuichi; Kaneda, Yoshiyuki

2014-10-01

274

Excitation of surface electromagnetic waves at an anisotropically conducting vacuum-metamaterial interface by the attenuated total internal reflection method  

NASA Astrophysics Data System (ADS)

The excitation of well-localized oblique surface waves above the surface of a dielectric with a one-dimensional array of perfectly conducting wires is studied theoretically using the attenuated total internal reflection method. It is assumed that the distance between the wires and their diameter are much smaller than the surface wavelength. The frequencies of excited surface waves are much lower than the plasma frequency of the metal, and their electric field is orthogonal to the wires. It is shown that such surface waves can be excited with the help of a homogeneous TM wave as well as with the help of a homogeneous wave with an electric field polarized perpendicularly to the wires. It is found that in the course of excitation of oblique waves, the incident TM wave is partly polarized into a wave of the TE type.

Averkov, Yu. O.; Yakovenko, V. M.

2011-04-01

275

Theory and applications of quarter-wave resonators: A prelude to their use for attenuating noise entering buildings through ventilation openings  

Microsoft Academic Search

This paper concerns the use of quarter-wave resonators to attenuate noise. Qualitative and quantitative derivations of the relationship between cavity length and wavelength of sound to be attenuated are presented. The mechanism by which resonators can be used to attenuate noise is developed in terms of the optimum scattering and absorption conditions at resonance. The aim is not to present

C. D. Field; F. R. Fricke

1998-01-01

276

Seismic modelling study of P-wave attenuation and velocity dispersion in patchy-saturated porous media  

NASA Astrophysics Data System (ADS)

Seismic wave propagation in patchy-saturated porous media is studied by numerical simulation in time domain at the seismic frequency band (1–1000?Hz). The models consist of hundreds of representative elementary volumes (REVs), where the REV is partially saturated with water and gas pockets. Seismic modelling experiments are implemented in a traditional way, with ‘periodic’ boundary conditions applied to get rid of undrained boundary conditions at the outer edges of the REVs. The characteristics of confining pressure, induced pore pressure, solid particle velocities and Darcy filtration velocities are analysed. The snapshots show that strong pore pressure gradients are generated across the interface between gas and water phases, and significant fluid flow occurs. The conversion of a fast P-wave into a dissipating slow P-wave takes place at seismic frequencies, and the converted slow P-wave diffuses strongly in both gas- and water-saturated phases. These numerical results can help us to understand the loss mechanism at seismic frequencies. Then, P-wave attenuation and velocity dispersion of a heterogeneous REV are calculated during traditional seismic modelling at seismic frequencies. The numerical results show good agreement with theoretical predictions obtained from patchy saturation theory. Furthermore, the effects of different fluid distributions on P-wave attenuation and velocity dispersion are analysed numerically. A series of experiments are implemented by considering large, small and random gas-patchy inclusions. The decrease of gas pocket size makes the peak frequency move towards high frequencies. Random distribution of gas patches may affect both the peak attenuation and peak frequencies. Seismic attenuation caused by Biot global flow, elastic scattering and wave-induced fluid flow (WIFF) associated with patchy saturation are computed numerically. The results show that the contribution of Biot’s global flow and scattering to the overall attenuation are negligible. Mesoscopic WIFF may dominate the loss mechanism in patchy-saturated media at seismic frequencies (1–1000?Hz).

Li, Xiaobo; Dong, Liangguo; Zhao, Qun

2014-12-01

277

Experimental Studies on Role of Scattering Centers on Wave Energy Attenuation  

SciTech Connect

In accelerator-driven neutron sources such as the Spallation Neutron Source (SNS) with powers in the 2 MW range (time-averaged), the interaction of the energetic proton beam with the mercury target can lead to very high heating rates in the target. Although the resulting temperature rise is relatively small (a few C), the rate of temperature rise is enormous (ca.10{sup 7} C/s) during the very brief beam pulse (-0.58 ps). The resulting thermal-shock induced compression of the mercury leads to the production of large amplitude pressure waves in the mercury that interact with the walls of the mercury target and the bulk flow field. Understanding and predicting propagation of pressure pulses in the target are considered critical for establishing the feasibility of constructing and safely operating such devices. Safety-related operational concerns exist in two main areas, viz., (1) possible target enclosure failure from impact of thermal shocks on the wall due to its direct heating from the proton beam and the loads transferred from the mercury compression waves, and (2) impact of the compression-cumrarefaction wave-induced effects such as cavitation bubble emanation and fluid surging. Preliminary stress evaluations indicate stress levels approaching yielding conditions and beyond in selected regions of the target. Also, the induction of cavitation (that could assist in attenuation) can also release gases that may accumulate at undesirable locations and impair heat transfer.

Kim, S.H.; Knaff, C.L.; Taleyarkhan, R.P.

2000-06-18

278

Effect of sample thickness on the measured mass attenuation coefficients of some compounds and elements for 59.54, 661.6 and 1332.5 keV \\/gamma-rays  

Microsoft Academic Search

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

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

2000-01-01

279

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

280

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

NASA Astrophysics Data System (ADS)

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

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

281

Nonlinear viscoelastic wave propagation: an extension of Nearly Constant Attenuation (NCQ) models  

E-print Network

Hysteretic damping is often modeled by means of linear viscoelastic approaches such as ?nearly constant Attenuation (NCQ)? models. These models do not take into account nonlinear effects either on the stiffness or on the damping, which are well known features of soil dynamic behavior. The aim of this paper is to propose a mechanical model involving nonlinear viscoelastic behavior for isotropic materials. This model simultaneously takes into account nonlinear elasticity and nonlinear damping. On the one hand, the shear modulus is a function of the excitation level; on the other, the description of viscosity is based on a generalized Maxwell body involving non-linearity. This formulation is implemented into a 1D finite element approach for a dry soil. The validation of the model shows its ability to retrieve low amplitude ground motion response. For larger excitation levels, the analysis of seismic wave propagation in a nonlinear soil layer over an elastic bedrock leads to results which are physically satisfact...

Delépine, Nicolas; Bonnet, Guy; Semblat, Jean-François

2009-01-01

282

Study of the absorption coefficient of alpha particles to lower hybrid waves in tokamak  

SciTech Connect

Part of the energy of the Lower Hybrid (LH) waves may be absorbed by the ? particles via the so-called perpendicular landau damping mechanism, which depends on various parameters of fusion reactors and the LH waves. In this article, we calculate the absorption coefficient ?{sub ?} of LH waves due to ? particles. Results show that, the ?{sub ?} increases with the parallel refraction index n{sub ?} while deceases with increasing the frequency of LH waves ?{sub LH} over a wide range. Higher background plasma temperature and toroidal magnetic field will increase the absorption, and there is a peak value of ?{sub ?} when n{sub e}?8×10{sup 19}m{sup ?3} for ITER-like scenario. The thermal corrections to the cold plasma dispersion relation will change the damping rate to a certain extent under some specific conditions. We have also evaluated the fraction of LH power absorbed by the alpha particles, ? ? 0.47% and 4.1% for an LH frequency of 5 GHz and 3.7 GHz respectively for ITER-like scenario. This work gives the effective reference for the choice of parameters of future fusion reactors.

Wang, Jianbing, E-mail: zhangxm@ecust.edu.cn; Zhang, Xianmei, E-mail: zhangxm@ecust.edu.cn; Yu, Limin, E-mail: zhangxm@ecust.edu.cn; Zhao, Xiang, E-mail: zhangxm@ecust.edu.cn [Department of Physics, East China University of Science and Technology, P.O. Box 385, Shanghai 200237 (China)

2014-02-12

283

Measurement of the mass attenuation coefficients and electron densities for BiPbSrCaCuO superconductor at different energies  

Microsoft Academic Search

The mass attenuation coefficients for Bi, Pb, Sr, Ca, Cu metals, Bi2O3, PbO, SrCO3, CaO, CuO compounds and solid-state forms of Bi1.7Pb0.3Sr2Ca2Cu3O10 superconductor were determined at 57.5, 65.2, 77.1, 87.3, 94.6, 122 and 136keV energies. The samples were irradiated using a 57Co point source emitted 122 and 136keV ?-ray energies. The X-ray energies were obtained using secondary targets such as

U. Çevik; H. Baltas

2007-01-01

284

X-ray attenuation coefficients of Fe compounds in the Kedge region at different energies and the validity of the mixture rule  

Microsoft Academic Search

The total mass attenuation coefficients for element Fe and compounds FeF3, Fe2O3, FeCl2·4H2O, FeCl32NH4Cl·H2O were measured at different energies between 4.508–17.443keV range by using secondary excitation method. Ti, V, Cr, Ni, Cu, Zn, As, Se, Br, Rb, Sr, Y, Zr, Nb, Mo were chosen as secondary exciter. 59.5keV gamma rays emitted from an 241Am annular source were used to excite

U. Turgut; E. Buyukkasap; O. ?im?ek; M. Ertugrul

2005-01-01

285

Simultaneous evaluation of the linear and quadratic electro-optic coefficients of the nonlinear optical polymer by attenuated-total-reflection technique  

NASA Astrophysics Data System (ADS)

A method of simultaneously evaluating the linear electro-optic and quadratic electro-optic coefficients of the nonlinear polymer poly (9,9-dioctyl-2,7-fluorene-co-benzo[c][1,2,5]thiadiazole-co-9-hexyl-3, 6-carbazole) (PF8-BT-CZ) was proposed based on the attenuated-total-reflection (ATR) technique. The measurement was sensitively carried out without the lock-in amplifier due to the prism-waveguide configuration of the sample and only one single optical path was applied, which simplified the experimental setup.

Zhu, Xiaohui; Deng, Xiaoxu; Li, Honggen; Cao, Zhuangqi; Shen, Qishun; Wei, Wei; Liu, Feng

2011-05-01

286

Measurement of mass attenuation coefficients of some boron compounds and the trommel sieve waste in the energy range 15.746– 40.930 keV  

Microsoft Academic Search

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

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

2003-01-01

287

Seismic wave attenuation and dispersion due to wave-induced fluid flow in rocks with strong permeability fluctuations.  

PubMed

Oscillatory fluid movements in heterogeneous porous rocks induced by seismic waves cause dissipation of wave field energy. The resulting seismic signature depends not only on the rock compressibility distribution, but also on a statistically averaged permeability. This so-called equivalent seismic permeability does not, however, coincide with the respective equivalent flow permeability. While this issue has been analyzed for one-dimensional (1D) media, the corresponding two-dimensional (2D) and three-dimensional (3D) cases remain unexplored. In this work, this topic is analyzed for 2D random medium realizations having strong permeability fluctuations. With this objective, oscillatory compressibility simulations based on the quasi-static poroelasticity equations are performed. Numerical analysis shows that strong permeability fluctuations diminish the magnitude of attenuation and velocity dispersion due to fluid flow, while the frequency range where these effects are significant gets broader. By comparing the acoustic responses obtained using different permeability averages, it is also shown that at very low frequencies the equivalent seismic permeability is similar to the equivalent flow permeability, while for very high frequencies this parameter approaches the arithmetic average of the permeability field. These seemingly generic findings have potentially important implications with regard to the estimation of equivalent flow permeability from seismic data. PMID:25669286

Germán Rubino, J; Monachesi, Leonardo B; Müller, Tobias M; Guarracino, Luis; Holliger, Klaus

2013-12-01

288

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

SciTech Connect

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

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

2009-02-26

289

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

NASA Technical Reports Server (NTRS)

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

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

1972-01-01

290

Transmission and Reflection Coefficients for Longitudinal Waves Obtained by a Combination of Refined Rod Theory and FEM  

NASA Astrophysics Data System (ADS)

The complex coefficients of reflection and transmission of elastic waves in rods at the location of a sudden change in cross-section are examined. Knowledge of them is useful, for example, in insulation against structure-borne sound. The values given in the literature for these coefficients are usually determined by using elementary rod and beam theory, in which the cross-sections are assumed to remain planar. In the present paper, the attention is restricted to longitudinal waves in rods. The vibrations are described by a one-dimensional linear wave equation for which the transition relations are formulated at the point of discontinuity of the cross-section. While in a previous paper simple rod theory was applied, in the present paper for small wavelengths Love's theory is used, which takes into account the kinetic energy due to transverse contraction. Although the corresponding one-dimensional wave equation can give an excellent approximation to waves obtained from the theory of three-dimensional elasticity, this is certainly not true in the immediate neighborhood of a sudden change of cross-section. The coefficients of reflection and transmission computed in this manner are therefore of questionable value. It is shown here how the coefficients of reflection and transmission can be computed by using standard finite element codes designed for the solution of eigenvalue rather than wave propagation problems. The values of the coefficients computed by using the three-dimensional theory of elasticity are then compared to the values obtained via rod theory.

Seemann, W.

1996-12-01

291

Diffraction, attenuation, and source corrections for nonlinear Rayleigh wave ultrasonic measurements.  

PubMed

This research considers the effects of diffraction, attenuation, and the nonlinearity of generating sources on measurements of nonlinear ultrasonic Rayleigh wave propagation. A new theoretical framework for correcting measurements made with air-coupled and contact piezoelectric receivers for the aforementioned effects is provided based on analytical models and experimental considerations. A method for extracting the nonlinearity parameter ?11 is proposed based on a nonlinear least squares curve-fitting algorithm that is tailored for Rayleigh wave measurements. Quantitative experiments are conducted to confirm the predictions for the nonlinearity of the piezoelectric source and to demonstrate the effectiveness of the curve-fitting procedure. These experiments are conducted on aluminum 2024 and 7075 specimens and a ?11(7075)/?11(2024) measure of 1.363 agrees well with previous literature and earlier work. The proposed work is also applied to a set of 2205 duplex stainless steel specimens that underwent various degrees of heat-treatment over 24h, and the results improve upon conclusions drawn from previous analysis. PMID:25287976

Torello, David; Thiele, Sebastian; Matlack, Kathryn H; Kim, Jin-Yeon; Qu, Jianmin; Jacobs, Laurence J

2015-02-01

292

Attenuation of standing waves in a large water tank using arrays of large tethered encapsulated bubbles.  

PubMed

The use of bubble resonance effects to attenuate low-frequency underwater sound was investigated experimentally in a large water tank. A compact electromechanical sound source was used to excite standing wave fields at frequencies ranging between 50 and 200 Hz in the tank. The source was then surrounded by a stationary array of tethered encapsulated air bubbles, and reduction in standing wave amplitude by as much as 26?dB was observed. The bubbles consisted of either thin-shelled latex balloons with approximately 5?cm radii or thicker-shelled vinyl boat fenders with 6.9?cm radii. The effects of changing the material and thickness of the bubble shells were found to be in qualitative agreement with predictions from Church's model for sound propagation in a liquid containing encapsulated bubbles [J. Acoust. Soc. Am. 97, 1510-1521 (1995)]. Although demonstrated here for low frequency noise abatement within a tank, which is useful for quieting acoustic test facilities and large tanks used for marine life husbandry, the eventual aim of this work is to use stationary arrays of large tethered encapsulated bubbles to abate low frequency underwater noise from anthropogenic sources in the marine environment. PMID:25234970

Lee, Kevin M; Wilson, Preston S; Wochner, Mark S

2014-04-01

293

Quantitative measurement on optical attenuation coefficient of cell lines 5-8F and 6-10B using optical coherence tomography  

NASA Astrophysics Data System (ADS)

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

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

2012-10-01

294

Ex vivo determination of glucose permeability and optical attenuation coefficient in normal and adenomatous human colon tissues using spectral domain optical coherence tomography  

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

295

Chemical effects on K?/K? X-ray intensity ratios of Mo, Ag, Cd, Ba, La, Ce compounds and total mass attenuation coefficients of Fe and Cu  

NASA Astrophysics Data System (ADS)

The K?/K? intensity ratios for pure Mo, Ag, Cd, Ba, La and Ce elements and for some of their compounds were investigated. The vacancies in the K shell were created by 59.5-keV ?-rays from a heavily filtered 241Am radioactive source. K X-rays were measured using a Si(Li) detector with a resolution of 155 eV at 5.9 keV. We observed chemical effects on K?/K? intensity ratios of Mo, Ag, Cd, Ba, La and Ce compounds. Detailed interpretation of data obtained from X-ray transmission measurements usually depends on the assumption that the contribution of each element is additive. This assumption yields the mixture rule for X-ray attenuation coefficients which is valid if molecular and chemical effects are negligible. We measured the total mass attenuation coefficients of Fe and Cu in various compounds. Self-absorption corrections were carried out on data for ligands in the different compounds. Our values were compared with the theoretical values for pure elements.

Sögüt, Ö.; Seven, S.; Baydas, E.; Büyükkasap, E.; Küçükönder, A.

2001-08-01

296

Wave propagation through a random array of pinned dislocations: Velocity change and attenuation in a generalized Granato and Luecke theory  

SciTech Connect

A quantitative theory of the elastic wave damping and velocity change due to interaction with dislocations is presented. It provides a firm theoretical basis and a generalization of the Granato and Luecke model [J. Appl. Phys. 27, 583 (1956)]. This is done considering the interaction of transverse (T) and longitudinal (L) elastic waves with an ensemble of dislocation segments randomly placed and randomly oriented in an elastic solid. In order to characterize the coherent wave propagation using multiple scattering theory, a perturbation approach is used, which is based on a wave equation that takes into account the dislocation motion when forced by an external stress. In our calculations, the effective velocities of the coherent waves appear at first order in perturbation theory while the attenuations have a part at first order due to the internal viscosity and a part at second order due to the energy that is taken away from the incident direction. This leads to a frequency dependence law for longitudinal and transverse attenuations that is a combination of quadratic and quartic terms instead of the usual quadratic term alone. Comparison with resonant ultrasound spectroscopy (RUS) and electromagnetic acoustic resonance (EMAR) experiments is proposed. The present theory explains the difference experimentally observed between longitudinal and transverse attenuations [Ledbetter, J. Mater. Res. 10, 1352 (1995)].

Maurel, Agnes [Laboratoire Ondes et Acoustique, UMR CNRS 7587, Ecole Superieure de Physique et de Chimie Industrielles, 10 rue Vauquelin, 75005 Paris (France); Pagneux, Vincent [Laboratoire d'Acoustique de l'Universite du Maine, UMR CNRS 6613 Avenue Olivier Messiaen, 72085 Le Mans Cedex 9 (France); Barra, Felipe [Departamento de Fisica, Facultad de Ciencias Fisicas y Matematicas, Universidad de Chile, Casilla 487-3, Santiago (Chile); Lund, Fernando [Departamento de Fisica, Facultad de Ciencias Fisicas y Matematicas, Universidad de Chile, Casilla 487-3, Santiago (Chile); Centro para la Investigacion Interdisciplinaria Avanzada en Ciencias de los Materiales (CIMAT), Santiago (Chile)

2005-11-01

297

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

SciTech Connect

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

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

2007-10-17

298

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

299

Three-dimensional attenuation structure of intrinsic absorption and wide-angle scattering of S waves in northeastern Japan  

NASA Astrophysics Data System (ADS)

Intrinsic absorption and random velocity inhomogeneities are important medium properties for studies on wave propagation at high frequency (>1 Hz) in the lithosphere. Recent studies have shown that the spatial distribution of random velocity inhomogeneities can be estimated by an inversion analysis of peak delay times, where the peak delay time is the time lag between direct wave onset and its maximal amplitude arrival. This study estimates the 3-D structure of the S-wave attenuation quality factor Q-1, after we corrected the maximal amplitude attenuation due to multiple forward scattering on the basis of the Markov approximation for parabolic wave equation. Even though this estimate of Q-1 includes both intrinsic absorption and wide-angle scattering, the contribution of wide-angle scattering can be identified by taking into account random inhomogeneities estimated in the peak delay time analysis. The estimated Q-1 structure in northeastern Japan shows weak attenuation (Q-1(f) ˜ 10-2.5f-0.5) on the forearc side of the volcanic front, and strong attenuation (Q-1(f) ˜ 10-2.3f-0.3) beneath the Quaternary volcanoes and near the collision zone between the Honshu and Kuril arcs. According to the Born approximation, the estimated Q-1 at 0-40 km depth consists mainly of the intrinsic absorption if the characteristic scale of random inhomogeneities is 5 km or longer. Beneath the Quaternary volcanoes of northeastern Japan, Q-1(f) shows weak frequency dependence and the power spectral density functions of random velocity inhomogeneities are characterized by a weak spectral gradient that means rich in small-scale inhomogeneities. These results demonstrate the importance of the frequency dependence of wave propagation in the lithosphere. That is, the scale dependence of velocity fluctuation or small-scale inhomogeneities is an important property of the lithosphere underlying Quaternary volcanoes.

Takahashi, Tsutomu

2012-06-01

300

Optical rogue waves in the generalized inhomogeneous higher-order nonlinear Schrodinger equation with modulating coefficients  

E-print Network

The higher-order dispersive and nonlinear effects (alias {\\it the perturbation terms}) like the third-order dispersion, the self-steepening, and the self-frequency shift play important roles in the study of the ultra-short optical pulse propagation. We consider optical rogue wave solutions and interactions for the generalized higher-order nonlinear Schr\\"odinger (NLS) equation with space- and time-modulated parameters. A proper transformation is presented to reduce the generalized higher-order NLS equation to the integrable Hirota equation with constant coefficients. This transformation allows us to relate certain class of exact solutions of the generalized higher-order NLS equation to the variety of solutions of the integrable Hirota equation. In particular, we illustrate the approach in terms of two lowest-order rational solutions of the Hirota equation as seeding functions to generate rogue wave solutions localized in time that have complicated evolution in space with or without the differential gain or lo...

Yan, Zhenya

2013-01-01

301

Improvement of the seismic noise attenuation performance of the Monolithic Geometric Anti-Spring filters for gravitational wave interferometric detectors  

NASA Astrophysics Data System (ADS)

The Monolithic Geometric Anti-Spring (GAS) filter is one of the most efficient vertical seismic isolation devices for Gravitational Wave (GW) interferometers. However, the attenuation of this filter was previously limited to around 60 dB due to the high frequency saturation associated with the filter's distributed mass—a problem typical of passive mechanical filters. We show that it is possible to circumvent this limit using a compensation wand based on the Center Of Percussion (COP) effect. When this device is mounted in parallel with the blade springs of a GAS filter, attenuation improves to 80 dB in the region above 10 Hz. Using this device it is therefore possible to design simpler attenuation chains consisting of fewer stages.

Stochino, Alberto; DeSalvo, Riccardo; Huang, Yumei; Sannibale, Virginio

2007-10-01

302

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

303

Element analysis and calculation of the attenuation coefficients for gold, bronze and water matrixes using MCNP, WinXCom and experimental data  

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

304

Measurement of mass attenuation coefficients in some Cr, Co and Fe compounds around the absorption edge and the validity of the mixture rule  

Microsoft Academic Search

The total mass attenuation coefficients for elements Cr, Co and Fe and compounds CrCl2, CrCl3, Cr2(SO4)3K2SO4·24H2O, CoO, CoCl2, Co(CH3COO)2, FePO4, FeCl3·6H2O, Fe(SO4)2NH4·12H2O were measured at different energies between 4.508 and 14.142 keV using secondary excitation method. Ti, V, Cr, Mn, Fe, Co,\\u000a Ni, Cu, Zn, As, Se, Br, Rb, Sr were chosen as secondary exciters. 59.5 keV ?-rays emitted from

U. Turgut; O. ?im?ek; E. Büyükkasap

2007-01-01

305

X-Ray attenuation coefficients at different energies and the validity of the mixture rule for compounds around the absorption edge  

Microsoft Academic Search

The total mass attenuation coefficients for the elements Co, Mn and Co2O3, compounds CoCl2.6H2O, CoSO4, CoSO4.7H2O, MnCO3, KMnO4, MnCl2.2H2O, and MnCl2.4H2O were measured at different energies between 4.508 and 11.210 keV using a secondary excitation method. Ti, Co, Ni, Cu, Zn, As, Se were chosen as secondary exciter. Gamma rays (59.5 keV) emitted from an 241Am annular source were used

Ü. Turgut; Ö ?im?ek; E. Büyükkasap; M. Ertu?rul

2002-01-01

306

Absorption and Attenuation Coefficients Using the WET Labs ac-s in the Mid-Atlantic Bight: Field Measurements and Data Analysis  

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

307

Electromagnetic Waves Attenuation due to Rain: A Prediction Model for Terrestrial or L.O.S SHF and EHF Radio Communication Links  

Microsoft Academic Search

Because of the interest raised for SHF and EHF radio communications, the attenuation of electromagnetic waves by rain will\\u000a always constitute a major concern for telecommunication engineers and scientists. The rain attenuation prediction models exposed\\u000a in literature calculate the attenuation related to a given rain rate or else to a given percentage of time. The new model\\u000a proposed in this

Fidèle Moupfouma

2009-01-01

308

Wave-induced fluid flow in random porous media: Attenuation and ...  

E-print Network

At high frequencies the attenuation .... high-frequency asymptotic behavior of both velocity and at- .... tion spectrum power spectrum, that is, the spatial Fourier ... where h(L, ) is the impulse response and s is the source ... such as x-ray images of rock samples. ..... Typically in the seismic frequency band attenuation is of.

2005-04-20

309

Suppression of reflection coefficients of surface acoustic wave filters using quadrature hybrids.  

PubMed

This paper proposes a simple technique to suppress the reflection coefficients S11 and S22 of surface acoustic wave (SAW) filters. Two identical SAW filters are sandwiched in between two quadrature hybrids, where their two ports are used as input and output, and others are terminated by matched loads. First, it is shown by simulation that both [S11] and [S22] are suppressed to be less than -20 dB without deteriorating the transmission characteristics. Next, two hybrids using microstrip lines were fabricated, and two RF SAW filters for GSM850 were sandwiched in between them. The result showed that the maximum [S11] within the passband was improved from -12.5 dB to -21.7 dB, i.e., 9.2 dB suppression of [S11] was achieved by sacrificing only the insertion loss of less than 0.6 dB. We also attempted to replace the microstrip lines with lumped elements. In this case, the maximum [S11] within the passband was improved more than 7.5 dB with the increased insertion loss of less than 1.5 dB. Finally, simple discussion is given on the inclusion of the transformer function in the quadrature hybrid. PMID:17036800

Wen, Jiguo; Hashimoto, Ken-Ya; Omori, Tatsuya; Yamaguchi, Masatsune; Kawachi, Osamu; Ueda, Masanori

2006-10-01

310

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

E-print Network

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 ...

Louisnard, Olivier

2013-01-01

311

Estimation of Coda Wave Attenuation in the East Anatolia Fault Zone, Turkey  

NASA Astrophysics Data System (ADS)

In this study, the attenuation of coda waves Q c( f) has been estimated for different lapse times and frequencies in the East Anatolian Fault Zone (EAFZ) in Turkey using a single back-scattering model of S-coda envelopes. The data include 255 earthquakes recorded by ten stations. The frequency-dependent Q c values are estimated at central frequencies of 1.5, 3, 6, 8, 12, and 18 Hz using 20-30-40 s lapse time windows. Along this fault zone, the frequency-dependent Q c obtained for all data and lapse time is Q c = 57.5 f 0.82. The entire study area is divided into six subregions according to the magnitude of the earthquakes and the location of the fault segments. The estimated average frequency-dependent relation for all lapse times are; Q_{{{{c}}_{{( {{I}} )}} }} = 3 4. 3f^{0. 9 3} for Bingöl-Karliova-Erzincan triple junction; Q_{{{{c}}_{{( {{II}} )}} }} = 56.3f^{0.71} for Bingol-Lake Hazar segment; Q_{{{{c}}_{{( {{III}} )}} }} = 68.5f^{0.75} for Lake Hazar-Sincik segment; Q_{{{{c}}_{{( {{IV}} )}} }} = 72.5f^{0.78} Hazar-Sincik and Çelikhan-Gölba?? faults; Q_{{{{c}}_{{( {{V}} )}} }} = 59.7f^{0.87} for Kahramanmaras triple junction and Q_{{{{c}}_{{( {{VI}} )}} }} = 67.4f^{0.94} for Amanos Range and Karasu Basin. The lowest Q c is determined between Bingol and Malatya. The highest Q c value is along Amanos Range. In addition, Q c values are calculated for each regions at different lapse times. The average Q c value of the study region varies from 53 ± 11 at 1.5 Hz to 498 ± 41 at 18 Hz for 20 s lapse time window, as its variation is from 116 ± 11 at 1.5 Hz to 749 ± 75 at 18 Hz of central frequency for 40 s lapse time window. The increase of Q c with lapse times changes from one subregion to another along the fault zone. The rate of increment is significantly higher in Bingöl-Karliova-Erzincan triple junction than in the other subregions. This rapid increase of low Q c values in the junction reaches the general attenuation characteristics of the fault at 40 s lapse time. Finally, the low Q 0 and high n values can be attributed to the energy loss as a result of the heterogeneity and activity along the fault zone. The increase of Q c with frequency, lapse time may be related to heterogeneity decreases with depth. The rapid increase of Q c with depth in Bingöl-Karliova-Erzincan triple junction may be interpreted that the effect of the Northern Anatolian Fault Zone is effective in the upper crust is not so deep compared to EAFZ.

Sertçelik, Fadime

2012-07-01

312

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

Microsoft Academic Search

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

Sean C. Solomon

1972-01-01

313

Modulational instability, nonautonomous breathers and rogue waves for a variable-coefficient derivative nonlinear Schrödinger equation in the inhomogeneous plasmas  

NASA Astrophysics Data System (ADS)

Under investigation in this paper is a variable-coefficient derivative nonlinear Schrödinger (vc-DNLS) equation modeling the nonlinear Alfvén waves in the inhomogeneous plasmas. The modulation instability is examined for this inhomogeneous nonlinear model. The nonautonomous breather and rogue wave solutions of the vc-DNLS equation are obtained via the modified Darboux transformation. It is found that the velocity and amplitude of the breather can be controlled by the inhomogeneous magnetic field and nonuniform density. Such novel phenomena as breather amplification and nonlinear Talbot effect-like property are demonstrated with the proper choices of the inhomogeneous parameters. Furthermore, dynamics of the fundamental rogue wave, periodical rogue wave, and composite rogue wave are graphically discussed. The trajectories and amplitudes of the rogue waves can be manipulated by the inhomogeneous magnetic field and nonuniform density. In addition, the nonlinear tunneling of the rogue waves and breathers is studied. As an application, a sample model is treated with our results, and the graphical illustrations exhibit the compressing, expanding, and fluctuating phenomena of the Alfvén rogue waves.

Wang, Lei; Li, Min; Qi, Feng-Hua; Xu, Tao

2015-03-01

314

Impact of Basset force on threshold values of particle drag coefficient and density parameter in standing sinusoidal wave  

NASA Astrophysics Data System (ADS)

A one-dimensional drift of spherical particle in standing sinusoidal wave is studied numerically. The impact of stationary and non-stationary forces of viscous drag, as well as Archimedes, added masses and Basset forces on particle drift direction is investigated. For various Reynolds and Strouhal numbers the dependencies of the threshold particle drag coefficient on density parameter have been found. These dependencies show that with increasing Reynolds and Strouhal numbers the threshold value of the squared drag coefficient decreases markedly. Impact of Basset force on threshold values is especially strong for low- density particles.

Gubaidullin, D. A.; Osipov, P. P.; Zakirov, A. N.

2014-11-01

315

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

316

Attenuation of electromagnetic waves at the frequency ~1.7 kHz in the vicinity of earthquakes observed in the upper ionosphere by the DEMETER satellite  

E-print Network

1 Attenuation of electromagnetic waves at the frequency ~1.7 kHz in the vicinity of earthquakes of VLF electromagnetic waves observed in the upper ionosphere. A robust two-step data processing has been is the first satellite specially dedicated to observe the electromagnetic10 phenomena connected

Santolik, Ondrej

317

Attenuation of electromagnetic waves at the frequency ~1.7 kHz in the upper ionosphere observed by the DEMETER satellite in the vicinity of  

E-print Network

Attenuation of electromagnetic waves at the frequency ~1.7 kHz in the upper ionosphere observed frequency electromagnetic waves recorded in the upper ionosphere. Robust two-step data processing has been was the first satellite specifically dedicated to the recording of electromagnetic phenomena connected

Santolik, Ondrej

318

Elastic coefficients of aluminum as functions of the degree of compression in a shock wave  

Microsoft Academic Search

The velocities of elastic relief waves in commercial aluminum (AD1) and aluminum alloy (D16) samples compressed by a shock wave were measured by the most direct method. Using these results together with the relationship for the three-dimensional velocity of sound as a function of the intensity of the sound wave (derived on the assumption that the shock adiabat and the

A. A. Vorob'ev; A. N. Dremin; G. I. Kanel

1974-01-01

319

Experimental study on the determination of the shear-wave reflection coefficient at the solid-liquid interface  

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

320

Determination of the acoustoelastic coefficient for surface acoustic waves using dynamic acoustoelastography: an alternative to static strain.  

PubMed

The third-order elastic constants of a material are believed to be sensitive to residual stress, fatigue, and creep damage. The acoustoelastic coefficient is directly related to these third-order elastic constants. Several techniques have been developed to monitor the acoustoelastic coefficient using ultrasound. In this article, two techniques to impose stress on a sample are compared, one using the classical method of applying a static strain using a bending jig and the other applying a dynamic stress due to the presence of an acoustic wave. Results on aluminum samples are compared. Both techniques are found to produce similar values for the acoustoelastic coefficient. The dynamic strain technique however has the advantages that it can be applied to large, real world components, in situ, while ensuring the measurement takes place in the nondestructive, elastic regime. PMID:24606250

Ellwood, R; Stratoudaki, T; Sharples, S D; Clark, M; Somekh, M G

2014-03-01

321

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

SciTech Connect

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

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

1984-11-27

322

Shallow S wave attenuation and actively degassing magma beneath Taal Volcano, Philippines  

NASA Astrophysics Data System (ADS)

Taal Volcano, Philippines, is one of the world's most dangerous volcanoes given its history of explosive eruptions and its close proximity to populated areas. A real-time broadband seismic network was recently deployed and has detected volcano-tectonic events beneath Taal. Our source location analysis of these volcano-tectonic events, using onset arrival times and high-frequency seismic amplitudes, points to the existence of a region of strong attenuation near the ground surface beneath the east flank of Volcano Island in Taal Lake. This region is beneath the active fumarolic area and above sources of pressure contributing inflation and deflation, and it coincides with a region of high electrical conductivity. The high-attenuation region matches that inferred from an active-seismic survey conducted at Taal in 1993. These features strongly suggest that the high-attenuation region represents an actively degassing magma body near the surface that has existed for more than 20 years.

Kumagai, Hiroyuki; Lacson, Rudy; Maeda, Yuta; Figueroa, Melquiades S.; Yamashina, Tadashi

2014-10-01

323

Determination of Shear Wave Velocity and Attenuation From Waveforms in Low Velocity Formations  

E-print Network

In boreholes where formation shear velocity is lower than borehole fluid velocity neither refracted shear waves nor pseudo-Rayleigh waves can propagate. When frequency response of the sonde does not extend to low frequencies ...

Toksoz, M. Nafi

1984-01-01

324

Influence of plasma parameters on the absorption coefficient of alpha particles to lower hybrid waves in tokamaks  

SciTech Connect

In tokamaks, fusion generated ? particles may absorb lower hybrid (LH) wave energy, thus reducing the LH current drive efficiency. The absorption coefficient ?{sub ?} of LH waves due to ? particles changing with some typical parameters is calculated in this paper. Results show that ?{sub ?} increases with the parallel refraction index n{sub ?}, while decreases with the frequency of LH waves ? over a wide range. Higher background plasma temperature and toroidal magnetic field will increase the absorption. The absorption coefficient ?{sub ?} increases with n{sub e} when n{sub e} ? 8 × 10{sup 19} m{sup ?3}, while decreases with n{sub e} when n{sub e} becomes larger, and there is a peak value of ?{sub ?} when n{sub e} ? 8 × 10{sup 19} m{sup ?1} for the ITER-like scenario. The influence of spectral broadening in parametric decay instabilities on the absorption coefficient is evaluated. The value of ?{sub ?} with n{sub ?} being 2.5 is almost two times larger than that with n{sub ?} being 2.0 and is even lager in the case of 2.9, which will obviously increase the absorption of the LH power by alpha particles.

Wang, J.; Zhang, X., E-mail: zhangxm@ecust.edu.cn; Yu, L.; Zhao, X. [East China University of Science and Technology, Department of Physics (China)

2014-12-15

325

Influence of plasma parameters on the absorption coefficient of alpha particles to lower hybrid waves in tokamaks  

NASA Astrophysics Data System (ADS)

In tokamaks, fusion generated ? particles may absorb lower hybrid (LH) wave energy, thus reducing the LH current drive efficiency. The absorption coefficient ?? of LH waves due to ? particles changing with some typical parameters is calculated in this paper. Results show that ?? increases with the parallel refraction index n ?, while decreases with the frequency of LH waves ? over a wide range. Higher background plasma temperature and toroidal magnetic field will increase the absorption. The absorption coefficient ?? increases with n e when n e ? 8 × 1019 m-3, while decreases with n e when n e becomes larger, and there is a peak value of ?? when n e ? 8 × 1019 m-1 for the ITER-like scenario. The influence of spectral broadening in parametric decay instabilities on the absorption coefficient is evaluated. The value of ?? with n ? being 2.5 is almost two times larger than that with n ? being 2.0 and is even lager in the case of 2.9, which will obviously increase the absorption of the LH power by alpha particles.

Wang, J.; Zhang, X.; Yu, L.; Zhao, X.

2014-12-01

326

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

327

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

NASA Technical Reports Server (NTRS)

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

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

1995-01-01

328

Wave simulation in 2D heterogeneous transversely isotropic porous media with fractional attenuation: a Cartesian grid approach  

E-print Network

A time-domain numerical modeling of transversely isotropic Biot poroelastic waves is proposed in two dimensions. The viscous dissipation occurring in the pores is described using the dynamic permeability model developed by Johnson-Koplik-Dashen (JKD). Some of the coefficients in the Biot-JKD model are proportional to the square root of the frequency. In the time-domain, these coefficients introduce shifted fractional derivatives of order 1/2, involving a convolution product. Based on a diffusive representation, the convolution kernel is replaced by a finite number of memory variables that satisfy local-in-time ordinary differential equations, resulting in the Biot-DA (diffusive approximation) model. The properties of both the Biot-JKD and the Biot-DA model are analyzed: hyperbolicity, decrease of energy, dispersion. To determine the coefficients of the diffusive approximation, two approaches are analyzed: Gaussian quadratures and optimization methods in the frequency range of interest. The nonlinear optimizat...

Blanc, Emilie; Lombard, Bruno

2015-01-01

329

Impact of diffusion coefficient averaging on solution accuracy of the 2D nonlinear diffusive wave equation for floodplain inundation  

NASA Astrophysics Data System (ADS)

In the study, the averaging technique of diffusion coefficients in the two-dimensional nonlinear diffusive wave equation applied to the floodplain inundation is presented. As a method of solution, the splitting technique and the modified finite element method with linear shape functions are used. On the stage of spatial integration, it is often assumed that diffusion coefficient is constant over element and equal to its average value. However, the numerical experiments indicate that in the case of the flow over the dry floodplain with sudden changes in depths an inadequate averaging of these coefficients can lead to a non-physical solution or even to its instability. In the paper, the averaging techniques for estimation of diffusion coefficients were examined using the arithmetic, geometric, harmonic and the direction dependent means. The numerical tests were carried out for the flows over initially dry floodplain with varied elevation of bottom. It was shown that the averaging method based on the arithmetic mean with respect to the diffusion coefficients provides the satisfactory results in comparison to other techniques.

G?siorowski, Dariusz

2014-09-01

330

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

SciTech Connect

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

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

1989-05-25

331

Laboratory experiments and numerical modeling of wave attenuation through artificial vegetation  

E-print Network

friction factor approach, have been successfully applied to determine bottom friction coefficients for flows in the presence of vegetation. There have been numerous relationships derived relating the friction factor to different flow regime boundary layers...

Augustin, Lauren Nicole

2009-05-15

332

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

NASA Astrophysics Data System (ADS)

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

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

2008-03-01

333

Brillouin scattering measurements of the velocity and attenuation of high frequency sound waves in superfluid helium  

Microsoft Academic Search

We have measured, from the Brillouin spectrum of scattered laser light, the velocity and attenuation of thermally driven high frequency first sound in liquid helium under its saturated vapor pressure between 1.25°K and the lambda point. The sound wavevector was fixed at 2.0339 × 105 cm-1; the frequency varied from 768 MHz at our lowest temperature to 709 MHz near

R. L. St. Peters; T. J. Greytak; G. B. Benedek

1970-01-01

334

Accurate and Fast Finite-Element Modeling of Attenuation in Slow-Wave Structures for Traveling-Wave Tubes  

Microsoft Academic Search

This paper presents a novel 3-D finite-element modeling technique for the arbitrary lossy slow-wave structure (SWS) of a traveling-wave tube (TWT). By using this technique, we can accurately and quickly calculate not only dielectric losses but also conductivity losses of the SWS. In this modeling technique, a new frequency-specified eigenmode analysis (FSEA) for SWSs is proposed and utilized. Unlike the

Li Xu; Zhong-Hai Yang; Jian-Qing Li; Bin Li

2012-01-01

335

Effect of Surface Waves on Air Sea Momentum Exchange. Part II: Behavior of Drag Coefficient under Tropical Cyclones.  

NASA Astrophysics Data System (ADS)

Present parameterizations of air sea momentum flux at high wind speed, including hurricane wind forcing, are based on extrapolation from field measurements in much weaker wind regimes. They predict monotonic increase of drag coefficient (Cd) with wind speed. Under hurricane wind forcing, the present numerical experiments using a coupled ocean wave and wave boundary layer model show that Cd at extreme wind speeds strongly depends on the wave field. Higher, longer, and more developed waves in the right-front quadrant of the storm produce higher sea drag; lower, shorter, and younger waves in the rear-left quadrant produce lower sea drag. Hurricane intensity, translation speed, as well as the asymmetry of wind forcing are major factors that determine the spatial distribution of Cd. At high winds above 30 m s-1, the present model predicts a significant reduction of Cd and an overall tendency to level off and even decrease with wind speed. This tendency is consistent with recent observational, experimental, and theoretical results at very high wind speeds.


Moon, Il-Ju; Ginis, Isaac; Hara, Tetsu

2004-10-01

336

Pressure diffusion waves in porous media  

SciTech Connect

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

Silin, Dmitry; Korneev, Valeri; Goloshubin, Gennady

2003-04-08

337

X-ray attenuation coefficient measurements for photon energies 4.508–13.375 keV in Cu, Cr and their compounds and the validity of the mixture rule  

Microsoft Academic Search

To investigate the validity of the mixture rule which is used to compute the mass attenuation coefficients in compounds, the total mass attenuation coefficients for Cu, Cr elements and Cu2O, CuC2O4, CuCl2·2H2O, Cu(C2H3O2)2·H2O, Cr2O3, Cr(NO3)3, Cr2(SO4)3·H2O, Cr3(CH3CO7)(OH)2 compounds were measured at photon energies between 4.508 and 13.375keV by using the secondary excitation method. Ti, Mn, Fe, Ni, Zn, Ge, As,

Ü Turgut; Ö ?im?ek; E Büyükkasap; M Ertu?rul

2004-01-01

338

Invariance of Hypersonic Normal Force Coefficients with Reynolds Number and Determination of Inviscid Wave Drag from Laminar Experimental Results  

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

339

Measurement of the x-ray mass attenuation coefficient and determination of the imaginary component of the atomic form factor of tin over the energy range of 29-60 keV  

Microsoft Academic Search

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

Martin D. de Jonge; Chanh Q. Tran; Christopher T. Chantler; Zwi Barnea; Bipin B. Dhal; David Paterson; Elliot P. Kanter; Stephen H. Southworth; Linda Young; Mark A. Beno; Jennifer A. Linton; Guy Jennings

2007-01-01

340

Measurement of the x-ray mass attenuation coefficient and determination of the imaginary component of the atomic form factor of tin over the energy range of 29-60keV  

Microsoft Academic Search

We use the x-ray extended-range technique (XERT) [C. T. Chantler , Phys. Rev. A 64, 062506 (2001)] to measure the mass attenuation coefficients of tin in the x-ray energy range of 29-60keV 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

Martin D. de Jonge; Chanh Q. Tran; Christopher T. Chantler; Zwi Barnea; Bipin B. Dhal; David Paterson; Elliot P. Kanter; Stephen H. Southworth; Linda Young; Mark A. Beno; Jennifer A. Linton; Guy Jennings

2007-01-01

341

Measurement of the x-ray mass attenuation coefficient and determination of the imaginary component of the atomic form-factor of tin over the energy range of 29 keV-60 keV.  

SciTech Connect

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

342

Measurement of the x-ray mass attenuation coefficient and determination of the imaginary component of the atomic form factor of tin over the energy range of 29-60 keV  

SciTech Connect

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

343

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

NASA Astrophysics Data System (ADS)

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.

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

2013-06-01

344

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

NASA Astrophysics Data System (ADS)

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

Hudier, E. J.; Bahoura, M.

2012-12-01

345

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

Microsoft Academic Search

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

Yong Keun Hwang; Jeroen Ritsema; Saskia Goes

2009-01-01

346

High-frequency Po/So guided waves in the oceanic lithosphere: II-heterogeneity and attenuation  

NASA Astrophysics Data System (ADS)

In the western Pacific, high-frequency seismic energy is carried to very great distances from the source. The Po and So phases with observed seismic velocities characteristic of the mantle lithosphere have complex and elongated waveforms that are well explained by a model of stochastic heterogeneity. However, in the eastern part of the Pacific Basin equivalent paths show muted Po and weak, or missing, So. Once established, it is hard to eliminate such guided Po and So energy in the mantle lithosphere by purely structural effects. Even sharp changes in lithospheric thickness or complex transitions at fracture zones only weaken the mantle ducted wave trains, but Po and So remain distinct. In contrast, the effect of attenuation is much more severe and can lead to suppression of the So phase to below the noise level after passage of a few hundred kilometres. The differing characteristics of Po and So across the Pacific can therefore be related directly to the thermal state via the enhanced attenuation in hotter regions, such as the spreading ridges and backarc regions.

Kennett, B. L. N.; Furumura, T.; Zhao, Y.

2014-10-01

347

Radiometric observations of atmospheric attenuation at 20.6 and 31.65 GHz: The Wave Propagation Laboratory data base  

NASA Technical Reports Server (NTRS)

The National Oceanic and Atmospheric Administration (NOAA) Wave Propagation Laboratory (WPL) presently operates five dual-channel microwave radiometers, one triple-channel microwave radiometer, and one six-channel microwave radiometer. The dual-channel radiometers operate at frequencies of 20.6 or 23.87 GHz and 31.4 or 31.65 GHz. The triple-channel radiometer operates at 20.6, 31.65, and 90.0 GHz. The six-channel radiometer operates at frequencies of 20.6, 31.65, 52.85, 53.85, 55.45, and 58.8 GHz. Recent brightness temperature measurements and attenuation values from some of the above radiometers are presented. These radiometric measurements, taken in different locations throughout the world, have given WPL a diverse set of measurements under a variety of atmospheric conditions. We propose to do a more complete attenuation analysis on these measurements in the future. In addition, a new spinning reflector was installed recently for the dual-channel radiometer at the Platteville, Colorado site. This reflector will extend our measurement capabilities during precipating conditions. Locating the three-channel and portable dual-channel radiometers at or near Greeley, Colorado to support the Advanced Communications Technology Satellite (ACTS) program is discussed.

Jacobson, Mark D.; Snider, J. B.; Westwater, E. R.

1993-01-01

348

Intense surface acoustic waves in electron plasma of a quantum well: classical and quantum effects in the nonlinear sound attenuation  

NASA Astrophysics Data System (ADS)

We study theoretically and experimentally the nonlinear interaction of intense surface acoustic waves (SAW) and electrons in a semiconductor quantum well [1]. The experiments performed on hybrid semiconductor-piezoelectric structures exhibit strongly nonlinear effects due to the formation of moving electron wires. To describe the experiments, we develop a coupled-amplitude nonlinear theory for the two-dimensional plasma in the classical and quantum regimes. At low temperatures, the calculated attenuation of sound exhibits quantum oscillations caused by the discrete level spectrum and the density of states in moving quantum wires. [1] M. Rotter et al., Phys. Rev. Lett. 82, 2171 (1999); A. O. Govorov et al., Phys. Rev. B 62, 2659 (2000).

Govorov, Alexander O.; Wixforth, Achim; Kalameitsev, Alexander V.

2001-03-01

349

Surface-wave amplitude analysis for array data with non-linear waveform fitting: Toward high-resolution attenuation models of the upper mantle  

NASA Astrophysics Data System (ADS)

Anelastic attenuation of seismic waves provides us with valuable information on temperature and water content in the Earth's mantle. While seismic velocity models have been investigated by many researchers, anelastic attenuation (or Q) models have yet to be investigated in detail mainly due to the intrinsic difficulties and uncertainties in the amplitude analysis of observed seismic waveforms. To increase the horizontal resolution of surface wave attenuation models on a regional scale, we have developed a new method of fully non-linear waveform fitting to measure inter-station phase velocities and amplitude ratios simultaneously, using the Neighborhood Algorithm (NA) as a global optimizer. Model parameter space (perturbations of phase speed and amplitude ratio) is explored to fit two observed waveforms on a common great-circle path by perturbing both phase and amplitude of the fundamental-mode surface waves. This method has been applied to observed waveform data of the USArray from 2007 to 2008, and a large-number of inter-station amplitude and phase speed data are corrected in a period range from 20 to 200 seconds. We have constructed preliminary phase speed and attenuation models using the observed phase and amplitude data, with careful considerations of the effects of elastic focusing and station correction factors for amplitude data. The phase velocity models indicate good correlation with the conventional tomographic results in North America on a large-scale; e.g., significant slow velocity anomaly in volcanic regions in the western United States. The preliminary results of surface-wave attenuation achieved a better variance reduction when the amplitude data are inverted for attenuation models in conjunction with corrections for receiver factors. We have also taken into account the amplitude correction for elastic focusing based on a geometrical ray theory, but its effects on the final model is somewhat limited and our attenuation model show anti-correlation with the phase velocity models; i.e., lower attenuation is found in slower velocity areas that cannot readily be explained by the temperature effects alone. Some former global scale studies (e.g., Dalton et al., JGR, 2006) indicated that the ray-theoretical focusing corrections on amplitude data tend to eliminate such anti-correlation of phase speed and attenuation, but this seems not to work sufficiently well for our regional scale model, which is affected by stronger velocity gradient relative to global-scale models. Thus, the estimated elastic focusing effects based on ray theory may be underestimated in our regional-scale studies. More rigorous ways to estimate the focusing corrections as well as data selection criteria for amplitude measurements are required to achieve a high-resolution attenuation models on regional scales in the future.

Hamada, K.; Yoshizawa, K.

2013-12-01

350

Microscopic Observation of Mechanism for Shear Wave Attenuation in Nylon-66  

NASA Astrophysics Data System (ADS)

Gupta[1] found rapid shear attenuation near the impact surface for PMMA target. However, the physical mechanism remains unknown. In this article, nylon-66 was chosen for experimental investigation by using a keyed gas gun and EMV method, since nylon-66 has the spherical grain structure, which can be observed under a polarized microscope. The similar rapid shear attenuation occurs in the present study when the impact velocity and inclination angle reach a critical value. The polarized micro-observation of recovered samples shows that near the impact surface there is a melting layer of thickness about 6-8?m, which causes the decay of the shear component propagating into the sample. The interesting thing is that there is a discontinuous crystalline layer about 2-3?m thick above the melting layer, which indicates the melting may not directly caused by the friction on the impact surface and the heat produces inside of the sample and near the surface. Further observation discloses an adiabatic shear band near the surface to cause the material failure. [1]Gupta Y M, J. Appl. Phys. 51(1980), 5352.

Li, Ting

2005-07-01

351

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

Microsoft Academic Search

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

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

2001-01-01

352

Extended Capillary Waves and the Negative Rigidity Coefficient in the d=2 SOS model  

E-print Network

The solid-on-solid (SOS) model of an interface separating two phases is exactly soluble in two dimensions (d=2) when the interface becomes a one-dimensional string. The exact solution in terms of the transfer matrix is recalled and the density-density correlation function $H(z_1,z_2;\\Delta x)$ together with its projections, is computed. It is demonstrated that the shape fluctuations follow the (extended) capillary-wave theory expression $S(q)=kT/(D+\\gamma q^2 +\\kappa q^4) $ for sufficiently small wave vectors $q$. We find $\\kappa$ {\\it negative}, $\\kappa <0$ . At $q=2\\pi$ there is a strong nearest-neighbor peak. Both these results confirm the earlier findings as established in simulations in d=3 and in continuous space, but now in an exactly soluble lattice model.

J. Stecki

2006-02-15

353

Quality-factor and reflection-coefficient estimation using surface-wave ghost reflections from subvertical structures  

NASA Astrophysics Data System (ADS)

Seismic interferometry can retrieve the Green's function between receivers from the cross-correlation and summation of recordings from a boundary of surrounding sources. Having the sources only along a boundary is sufficient if the medium is lossless. If the medium is dissipative, the retrieved result using cross-correlation contains non-physical (ghost) arrivals. When using receivers at the surface and transient sources in the subsurface for the retrieval of the reflection response in a dissipative medium, it has been shown that the retrieved ghost reflections are characteristic of the quality factor of the subsurface. The ghost reflections are caused by internal reflections inside subsurface layers. It has been shown with numerical examples for recordings in a borehole from a surface source that a ghost reflection can be discriminated from physical reflections and tied to a specific subsurface layer. After connecting the ghost reflection to a specific layer, the quality factor of the medium above this layer and the reflection coefficient at the layer interface can be estimated. In this article, we show how the above principles can be adapted and applied for surface waves. Due to intrinsic losses in the medium, surface-wave ghost reflections are retrieved from internal scattering between subvertical boundaries. We demonstrate the method on an ultrasonic dataset recorded on a sample composed of a PVC block and an aluminum block. The aluminum block has a groove parallel to the PVC/aluminum interface. Using a surface-wave ghost reflection between the groove and the PVC/aluminum interface, we estimate the quality factor of the PVC and the reflection coefficient at the PVC/aluminum interface. We also show that the ghost reflection can be identified and tied to the layer between the groove and the PVC/aluminum interface, thus confirming previous numerical findings.

Draganov, Deyan; Ruigrok, Elmer; Ghose, Ranajit; Mikesell, Dylan; van Wijk, Kasper

2015-01-01

354

Relationship between P-wave attenuation and water saturation in an homogeneous unconsolidated and partially saturated porous media : An experimental study  

NASA Astrophysics Data System (ADS)

Nowadays, it is well known that hydrogeological properties of the porous media (porosity, fluid saturation and permeability) can influence seismic properties. The major theory which links hydrogeological and seismic parameters is poroelasticity proposed by Biot (1956) for saturated porous media in a wetting phase fluid. However the Biot relaxation process can't explain the level of attenuation of seismic waves generally measured on field from seismic to sonic frequency range in the case of partially saturated media. Laboratory experiments are necessary to better understand the effects of fluids on the attenuation of waves but few ones are done in the low frequency range (1Hz to 10 kHz) where the wavelength is greater than heterogeneities size. We propose an experimental study to determine the attenuation of propagative P-wave in the sonic frequency range on unconsolidated and partially saturated porous media, typical of near surface hydrogeological media. 10 accelerometers (0.0001-17kHz) and 6 capacitance probes (soil moisture sensors) are placed in a container (107 cm x 34 cm x 35cm) full of homogeneous sand (99% silica). An acoustic source (0 - 20 kHz) generate seismic waves which are recorded by the accelerometers during three cycles of imbibition-drainage (corresponding to a water saturation range from 0% to 95%). Values of attenuation (quality factor Q) versus water saturation and frequency are calculated with the well-known spectral ratio method. The spectrum of each recorded P-wave is obtained by a continuous wavelet transform, more adapted than Fourier transform for a non-stationary signal, such as seismic signal, whose frequency content varies with time. The first analyses show a strong dependence of the quality factor with frequency and water saturation, notably at high water saturation (above 60 %) where the attenuation is maximum. Knowing some important parameters of the studied media such as porosity and permeability, we interpret physically our results in accordance with some recent poroelastic models.

Barrière, J.; Sénéchal, P.; Bordes, C.; Perroud, H.

2010-12-01

355

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

NASA Astrophysics Data System (ADS)

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

Lin, Guoqing

2014-04-01

356

Wave simulation in 2D heterogeneous transversely isotropic porous media with fractional attenuation: A Cartesian grid approach  

NASA Astrophysics Data System (ADS)

A time-domain numerical modeling of transversely isotropic Biot poroelastic waves is proposed in two dimensions. The viscous dissipation occurring in the pores is described using the dynamic permeability model developed by Johnson-Koplik-Dashen (JKD). Some of the coefficients in the Biot-JKD model are proportional to the square root of the frequency. In the time-domain, these coefficients introduce shifted fractional derivatives of order 1/2, involving a convolution product. Based on a diffusive representation, the convolution kernel is replaced by a finite number of memory variables that satisfy local-in-time ordinary differential equations, resulting in the Biot-DA (diffusive approximation) model. The properties of both the Biot-JKD and the Biot-DA models are analyzed: hyperbolicity, decrease of energy, dispersion. To determine the coefficients of the diffusive approximation, two approaches are analyzed: Gaussian quadratures and optimization methods in the frequency range of interest. The nonlinear optimization is shown to be the better way of determination. A splitting strategy is then applied to approximate numerically the Biot-DA equations. The propagative part is discretized using a fourth-order ADER scheme on a Cartesian grid, whereas the diffusive part is solved exactly. An immersed interface method is implemented to take into account heterogeneous media on a Cartesian grid and to discretize the jump conditions at interfaces. Numerical experiments are presented. Comparisons with analytical solutions show the efficiency and the accuracy of the approach, and some numerical experiments are performed to investigate wave phenomena in complex media, such as multiple scattering across a set of random scatterers.

Blanc, Emilie; Chiavassa, Guillaume; Lombard, Bruno

2014-10-01

357

Sea ice floes dissipate the energy of steep ocean waves  

E-print Network

Wave attenuation by ice floes is an important parameter for modelling the Arctic Oceans. At present, attenuation coefficients are extracted from linear models as a function of the incident wave period and floe thickness. Recent explorations in the Antarctic Mixed Ice Zone (MIZ) revealed a further dependence on wave amplitude, suggesting that nonlinear contributions are non-negligible. An experimental model for wave attenuation by a single ice floe in a wave flume is here presented. Observations are compared with linear predictions based on wave scattering. Results indicate that linear models perform well under the effect of gently sloping waves. For more energetic wave fields, however, transmitted wave height is normally over predicted. Deviations from linearity appear to be related to an enhancement of wave dissipation induced by unaccounted wave-ice interaction processes, including the floe over wash.

Toffoli, Alessandro; Meylan, Michael H; Cavaliere, Claudio; Alberello, Alberto; Elsnab, John; Monty, Jason P

2015-01-01

358

Attenuation of vertical S-wave amplitude from Wadati-Benioff earthquakes in Washington  

Microsoft Academic Search

Regression of 842 vertical S-wave seismograms from 45 microearthquakes sampling the Wadati-Benioff source zone beneath western Washington suggests a regional control of ground amplitude at 7 to 10 Hz frequency. Mean station amplitude residuals fall in two distinct populations that are geographically coincident with the tectonic regions of the Coast Range-Puget Lowlands to the west (yielding smaller amplitudes) and the

B. P. Cohee

1991-01-01

359

Electric field analysis in the Earth considering attenuation of electromagnetic waves propagated in lossy media  

Microsoft Academic Search

It is pointed out that, in the field of oil well drilling, EM-MWD (electromagnetic measurement while drilling) offers many advantages. The EM-MWD system can transmit measured data from the well bottom to the surface at high speed using electromagnetic waves. Developing the EM-MWD technology requires analysis of the electric field around a drill string. A novel computer simulation method has

T. Maekawa; T. Shimada; S. Inoue; A. Jitsumori; N. Okumura; K. Akizuki

1992-01-01

360

Localized suppression of cortical growth hormone releasing hormone receptors state-specifically attenuates EEG delta waves  

PubMed Central

Growth hormone releasing hormone (GHRH) promotes non-rapid eye movement sleep (NREMS), in part via a well-characterized hypothalamic sleep-promoting site. However, GHRH may also act in the cortex to influence sleep. Application of GHRH to the surface of the cortex changes electroencephalographic (EEG) delta power. GHRH and the GHRH receptor (GHRHR) mRNAs are detectable in the rat cortex and the expression of cortical GHRHR is activity-dependent. Here we microinjected a GHRH antagonist or GHRHR siRNA (siGHRHR) onto the somatosensory cortex surface in rats. The unilateral application of the GHRH antagonist ipsilaterally decreased EEG delta wave power during NREMS, but not wakefulness, during the initial 40 min after injection. Similarly, the injection of siGHRHR reduced cortical expression of GHRHR and suppressed NREMS EEG delta wave power during 20- to 24-h post-injection. Using the Fura-2 calcium imaging technique, cultured cortical cells responded to GHRH by increasing intracellular calcium. Approximately 18% of the GHRH-responsive cells were GABAergic as illustrated by GAD67 immunostaining. Double labeling for GAD67 and GHRHR in vitro and in vivo indicated that only a minorityof cortical GHRHR-containing cells were GABAergic. Our data suggest that endogenous cortical GHRH activates local cortical cells to affect EEG delta wave power state-specifically. Results are also consistent with the hypothesis that GHRH contributes to local network state regulation. PMID:20237285

Liao, Fan; Taishi, Ping; Churchill, Lynn; Urza, Marcus J.; Krueger, James M.

2010-01-01

361

Delamination of southern Puna lithosphere revealed by body wave attenuation tomography  

NASA Astrophysics Data System (ADS)

The 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

362

Prospects for in vivo estimation of photon linear attenuation coefficients using postprocessing dual-energy CT imaging on a commercial scanner: Comparison of analytic and polyenergetic statistical reconstruction algorithms  

SciTech Connect

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

363

Prospects for in vivo estimation of photon linear attenuation coefficients using postprocessing dual-energy CT imaging on a commercial scanner: Comparison of analytic and polyenergetic statistical reconstruction algorithms  

PubMed Central

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 noninvasive in 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 mm3 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. PMID:24320525

Evans, Joshua D.; Whiting, Bruce R.; O’Sullivan, Joseph A.; Politte, David G.; Klahr, Paul H.; Yu, Yaduo; Williamson, Jeffrey F.

2013-01-01

364

Simulation of stress waves in attenuating drill strings, including piezoelectric sources and sensors  

PubMed

A key element in drill steering and prediction of lithology ahead-of-the-bit is the transmission of while-drilling information from the bottom of the well to the rig operator and the geophysicists. Mud-pulse telemetry, based on pressure pulses along the drilling mud and extensional waves through the drill string, is the most used technique. The last method, properly designed, could transmit data rates up to 100 bits per second, against the 1 or 2 bits per second achieved with pressure pulses. In this work, a time-domain algorithm is developed for the propagation of one-dimensional axial, torsional, and flexural stress waves, including transducer sources and sensors. In addition, the equations include relaxation mechanisms simulating the viscoelastic behavior of the steel, dielectric losses, and any other losses, such as those produced by the presence of the drilling mud, the casing, and the formation. Moreover, the algorithm simulates the passbands and stopbands due to the presence of the coupling joints and pulse distortion and delay due to nonuniform cross-section areas. Acoustic and electric pulses, generated at one location in the string, can be propagated and detected at any other location by piezoelectric and acoustic sensors, such as PCB accelerometers, clamp-on ammeters, force, and strain transducers. PMID:10923870

Carcione; Poletto

2000-07-01

365

Pulse echo and combined resonance techniques: a full set of LGT acoustic wave constants and temperature coefficients.  

PubMed

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

366

Using the pressure transmission coefficient of a transmitted wave to evaluate some of the mechanical properties of refractory metals.  

PubMed

Refractory metals have attracted increasing interest in recent years because of their use in many high-temperature applications. However, the characteristics of these metals calculated using loaded tests (such as tensile strength tests) differ considerably from those calculated using one of the most famous methods in NDT which is called time of flying of the wave (TOF).The present study presents two solutions based on calculating the pressure transmission coefficient (PTC) of the transmitted wave between the test sample and magnesium metal. The first is based on the development of a highly accurate algorithm that lowers the cost by determining the acoustic impedance of the test specimen to calculating mechanical properties. Up to 26 theoretical tests were done (10 of these tests for refractory materials) according to their known mechanical properties to verify the accuracy of the algorithm. The convergence in results ranged from 92% to 99%. The second solution was designed to solve the same problem for specimens with a thickness of less than 1mm. Eight experimental tests were done (five using refractory materials) to verify the accuracy of the second solution, with the convergence in the results ranging from 94% to 97%. The relationships of the Vrms measured from the oscilloscope with the PTC and with the Fourier transform spectrum were derived. The results of this research were closer to the standard mechanical properties for refractory metals compared with several recent acoustic tests. PMID:25096851

Mohammed, Arshed Abdulhamed; Haris, Sallehuddin Mohamed; Nuawi, Mohd Zaki

2015-01-01

367

Anisotropy of Earth's inner core intrinsic attenuation from seismic normal mode models  

NASA Astrophysics Data System (ADS)

The Earth's inner core, the slowly growing sphere of solid iron alloy at the centre of our planet, is known to exhibit seismic anisotropy. Both normal mode and body wave studies have established that, when the global average is taken, compressional waves propagate faster in the North-South direction than in the equatorial plane. Recent body wave studies also indicate that this fast direction may be more attenuating, and interpret this anisotropic attenuation in terms of anisotropic scattering due to inner core texturing. Here we use the Earth's normal modes to study the attenuation anisotropy of both compressional and shear waves in the inner core. As normal modes have wavelengths several orders of magnitude longer than estimates of inner core grain size, any attenuation anisotropy quantified using normal modes must reflect the anisotropy of intrinsic (viscoelastic) attenuation of the crystalline inner core alloy. By inverting zonal anelastic and elastic normal mode splitting function coefficients of twenty inner core sensitive modes, we construct models of inner core intrinsic attenuation and velocity anisotropy. We find that, for compressional waves, the North-South direction is both fast and more strongly attenuating. The existence of intrinsic inner core attenuation anisotropy can be interpreted in terms of anisotropic Zener relaxation in the metallic alloy comprising the inner core. Such anisotropic Zener relaxation has only been observed in the presence of solute atoms, and is thus entirely consistent with the presence of a few atomic per cent of light elements in the Earth's inner core.

Mäkinen, Anna M.; Deuss, Arwen; Redfern, Simon A. T.

2014-10-01

368

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

369

Changes in clot lysis levels of reteplase and streptokinase following continuous wave ultrasound exposure, at ultrasound intensities following attenuation from the skull bone  

Microsoft Academic Search

BACKGROUND: Ultrasound (US) has been used to enhance thrombolytic therapy in the treatment of stroke. Considerable attenuation of US intensity is however noted if US is applied over the temporal bone. The aim of this study was therefore to explore possible changes in the effect of thrombolytic drugs during low-intensity, high-frequency continuous-wave ultrasound (CW-US) exposure. METHODS: Clots were made from

Bjarne Madsen Härdig; Jonas Carlson; Anders Roijer

2008-01-01

370

Theoretical prediction of the source-detector separation distance suited to the application of the spatially resolved spectroscopy from the near-infrared attenuation data cube of tissues  

E-print Network

The modified Beer-Lambert law (MBL) and the spatially resolved spectroscopy are used to measure the tissue oxidation in muscles and brains by the continuous wave near-infrared spectroscopy. The spatially resolved spectroscopy predicts the change in the concentration of the absorber by measuring the slope of attenuation data according to the separation and calculating the absorption coefficients of tissue on the basis of the slop in attenuation at the separation distance satisfying the linearity of this slop. This study analyzed the appropriate source-detector separation distance by using the diffuse approximation resolution for photon migration when predicting the absorption coefficient by the spatially resolved spectroscopy on the basis of the reflective image of the tissue. We imagine the 3 dimensional attenuation image with the absorption coefficient, reduced scattering coefficient and separation distance as its axes and obtained the attenuation data cube by calculating the attenuation on a certain interva...

Ri, Yong-Wu; Im, Song-Jin

2014-01-01

371

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

Microsoft Academic Search

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

David C. Adams; Eugene D. Humphreys

2010-01-01

372

Circumferentially segmented duct lines optimized for axisymmetric and standing wave sources. [reducing noise from turbofan engines galerkin method acoustic attenuation  

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

373

Influence of attenuation on acoustic emission signals in carbon fiber reinforced polymer panels.  

PubMed

Influence of attenuation on acoustic emission (AE) signals in Carbon Fiber Reinforced Polymer (CFRP) crossply and quasi-isotropic panels is examined in this paper. Attenuation coefficients of the fundamental antisymmetric (A0) and symmetric (S0) wave modes were determined experimentally along different directions for the two types of CFRP panels. In the frequency range from 100kHz to 500kHz, the A0 mode undergoes significantly greater changes due to material related attenuation compared to the S0 mode. Moderate to strong changes in the attenuation levels were noted with propagation directions. Such mode and frequency dependent attenuation introduces major changes in the characteristics of AE signals depending on the position of the AE sensor relative to the source. Results from finite element simulations of a microscopic damage event in the composite laminates are used to illustrate attenuation related changes in modal and frequency components of AE signals. PMID:25682294

Asamene, Kassahun; Hudson, Larry; Sundaresan, Mannur

2015-05-01

374

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

Microsoft Academic Search

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

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

2004-01-01

375

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

Microsoft Academic Search

(1) 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

Huirong A. Ai; Thomas J. Ahrens

2007-01-01

376

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

Microsoft Academic Search

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

Huirong A. Ai; Thomas J. Ahrens

2007-01-01

377

Second-order rogue wave breathers in the nonlinear Schrödinger equation with quadratic potential modulated by a spatially-varying diffraction coefficient.  

PubMed

Nonlinear Schrödinger equation with simple quadratic potential modulated by a spatially-varying diffraction coefficient is investigated theoretically. Second-order rogue wave breather solutions of the model are constructed by using the similarity transformation. A modal quantum number is introduced, useful for classifying and controlling the solutions. From the solutions obtained, the behavior of second order Kuznetsov-Ma breathers (KMBs), Akhmediev breathers (ABs), and Peregrine solitons is analyzed in particular, by selecting different modulation frequencies and quantum modal parameter. We show how to generate interesting second order breathers and related hybrid rogue waves. The emergence of true rogue waves - single giant waves that are generated in the interaction of KMBs, ABs, and Peregrine solitons - is explicitly displayed in our analytical solutions. PMID:25836223

Zhong, Wei-Ping; Beli?, Milivoj; Zhang, Yiqi

2015-02-01

378

Inhomogeneous waves in lossy metamaterials and negative refraction  

E-print Network

We study the formation of inhomogeneous waves at the interface of a lossy metamaterial. We show that negative refraction can be interpreted as the formation of an inhomogeneous wave with the obtuse angle between equiamplitude and equiphase planes. Additionally we show that the refractive index and attenuation coefficient of a lossy metamaterial depend on an incident angle even if this metamaterial is isotropic.

Fedorov, Vladimir Yu

2013-01-01

379

Cryogenic measurement of the optical absorption coefficient in sapphire crystals at 1.064(micro)m for the Large-scale Cryogenic Gravitational wave Telescope  

E-print Network

We have applied laser calorimetry to the measurement of optical absorption in mono-crystalline sapphire at cryogenic temperatures. Sapphire is a promising candidate for the mirror substrates of the Large-scale Cryogenic Gravitational wave Telescope. The optical absorption coefficients of different sapphire samples at a wavelength of 1.064(micro)m at 5K were found to average 90ppm/cm.

Takayuki Tomaru; Takashi Uchiyama; Daisuke Tatsumi; Shinji Miyoki; Masatake Ohashi; Kazuaki Kuroda; Toshikazu Suzuki; Akira Yamamoto; Takakazu Shintomi

2001-03-08

380

Studying the possibility of extracting material parameters from reflection and transmission coefficients of plane wave for multilayer metamaterials based on metal nanogrids  

Microsoft Academic Search

To more adequately extract the effective refractive index and other so-called metamaterial parameters from the reflection and transmission coefficients of a wave for multilayer grid nanostructures in the near-IR spectral range, the Nicholson-Ross-Weir method was modified. The rate of convergence of each extracted metamaterial parameter to a certain limit is studied with increasing number of layers of the structure. For

P. A. Belov; E. A. Yankovskaya; I. V. Melchakova; C. R. Simovski

2010-01-01

381

Studying the possibility of extracting material parameters from reflection and transmission coefficients of plane wave for multilayer metamaterials based on metal nanogrids  

Microsoft Academic Search

To more adequately extract the effective refractive index and other so-called metamaterial parameters from the reflection\\u000a and transmission coefficients of a wave for multilayer grid nanostructures in the near-IR spectral range, the Nicholson-Ross-Weir\\u000a method was modified. The rate of convergence of each extracted metamaterial parameter to a certain limit is studied with increasing\\u000a number of layers of the structure. For

P. A. Belov; E. A. Yankovskaya; I. V. Melchakova; C. R. Simovski

2010-01-01

382

Attenuated direct and scattered wave propagation on simulated land mobile satellite service paths in the presence of trees  

NASA Technical Reports Server (NTRS)

Measurements were made of direct path with no trees, attenuated direct, and tree scattered signal levels at 1.3 GHz. Signals were received in two small groves of mixed hardwood trees. In the groves studied, average total signal levels were about 13 dB below adjacent no-trees locations, with attenuated direct signal levels about 14.6 dB below the no-trees case and scattered signals about 17.3 dB below the no-trees case. A simple model for land mobile satellite service (LMSS) propagation in groves of trees is proposed. The model assumes a constant scattered signal contribution at 17 dB below no-trees levels added to an attenuated direct signal which varies, depending on the number and density of trees in the direct path. When total signal levels are strong, the attenuated direct signal dominates. When total signal levels are more than 15 dB below no-trees levels, the scattered signals dominate.

Campbell, Richard L.; Estus, Robert

1988-01-01

383

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

NASA Astrophysics Data System (ADS)

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

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

2004-11-01

384

Multi-resolution S- and P-wave attenuation images of Campi Flegrei: application of novel methods and verification of the tomographic results.  

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

385

Calculation of reflection and transmission coefficients for qP waves incident on a planar interface between isotropic and triclinic media  

NASA Astrophysics Data System (ADS)

In the paper by Chattopadhyay and Rajneesh (2006, “Reflection and refraction of waves at the interface of an isotropic medium over a highly anisotropic medium’, Acta Geophysica, vol. 54, no. 3, pp. 239 249), the authors proposed a process to calculate R/T (reflection and transmission) coefficients at the interface between isotropic and triclinic half-spaces, with incident qP waves in triclinic media. Unfortunately, besides several misprints, the authors made a fatal assumption that there is no transmitted SH wave generated in isotropic media, which led the successive analytical derivations and numerical calculations thoroughly wrong. In this paper, the errors are analyzed at length and corrections are given. Then an alternative approach to solve the problem is proposed and numerical results are shown and discussed.

Li, Lei

2008-06-01

386

Measurement of heat-transfer coefficients in shock wave-turbulent boundary layer interaction regions with a multi-layered thin film heat transfer gauge  

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

387

1D model of seismic wave attenuation in the crust and upper mantle in the north-eastern flanc of the Baikal rift system  

NASA Astrophysics Data System (ADS)

The deep profiles of quality factor were obtained using coda-waves of local strong and moderate earthquakes (epicentral distances up to 50 km) occurred within north-eastern flanc of the Baikal rift system during 2002-2009. We used two methods: 1 - the coda envelope method [Experimental.., 1981; Kopnichev, 1991] and 2 - the sliding window method (lapse time window 10-15 sec with a step of 5 sec). Depth of coda-wave penetration was determined according to Pulli's formulae [1984], the velocity of coda-wave is 3.55 km/s (equal to shear wave velocity). For analysis we used the Q values at frequency 1 Hz since for this frequency the attenuation field heterogeneity is most evident [Aptikaeva and Kopnichev, 1991]. In result Q-profiles for eleven local areas were obtained. The Q-values vary from 50 to 170 for different profiles and depths. Herewith quality factor changes nonuniformly - the alternation of layers with high and low Q-values is observed. This phenomenon can be explained by existing velocity discontinuity. In particular for all profiles this alternation is confined to the depth about 100 km. Analysis VP-anomalies obtained in result of 2D teleseismic tomography along Baikal rift system [Mordvinova, 2009] shows the existence discontinuity on depth about 100 km under most of Baikal rift system structures. Analysis of 1D profiles of shear wave velocities in the crust and upper mantle after inversion of receiver functions [Anan'in et al., 2009] also shows presence of these discontinuity dividing high and low velocity layers. The comparison of Q-values and shear wave velocities [Anan'in et al., 2009] shown that in high velocity layers quality factor is higher too and vice versa. Multilayer quality factor model for the lithosphere in north-eastern flanc of the Baikal rift system with the alternation of layers with high and low attenuation determined by us together with analogous data obtained by Yu.F. Kopnichev [1992] for south-western flanc of the rift system can be one of inferential evidences of passive rifting mechanism in studied area. The reported study was supported by RFBR (research project N12-05-31038-mol_a) and by grant of President of Russian Federation (research project N MK-1171.2014.5).

Dobrynina, Anna; Sankov, Vladimir; Chechelnitsky, Vladimir

2014-05-01

388

Shear wave attenuation and dispersion in melt-bearing olivine polycrystals: 2. Microstructural interpretation and seismological implications  

Microsoft Academic Search

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

389

SEISMIC ATTENUATION FOR RESERVOIR CHARACTERIZATION  

SciTech Connect

Wave-induced variations of pore pressure in a partially-saturated reservoir result in oscillatory liquid flow. The viscous losses during this flow are responsible for wave attenuation. The same viscous effects determine the changes in the dynamic bulk modulus of the system versus frequency. These changes are necessarily linked to attenuation via the causality condition. We analytically quantify the frequency dependence of the bulk modulus of a partially saturated rock by assuming that saturation is patchy and then link these changes to the inverse quality factor. As a result, the P-wave attenuation is quantitatively linked to saturation and thus can serve as a saturation indicator.

Joel Walls; M.T. Taner; Gary Mavko; Jack Dvorkin

2002-04-01

390

The upper mantle structure of the central Rio Grande rift region from teleseismic P and S wave travel time delays and attenuation  

USGS Publications Warehouse

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

391

Fermi-surface reconstruction and transport coefficients from a mean-field bidirectional charge-density wave state in the high-Tc cuprates  

NASA Astrophysics Data System (ADS)

The recent discovery of an incipient charge-density wave (CDW) instability competing with superconductivity in a class of high-temperature cuprate superconductors has brought the role of charge order in the phase diagram of the cuprates under renewed focus. Here, we take a mean field Q1=(2 ? /3 ,0 ) and Q2=(0 ,2 ? /3 ) biaxial CDW state and calculate the Fermi-surface topology and the resulting Hall and Seebeck coefficients as a function of temperature and hole doping. We establish that, in the appropriate doping ranges where the low-temperature state (in the absence of superconductivity) is a CDW, the Fermi surface consists of electron pockets, resulting in the Hall and Seebeck coefficients becoming negative at low temperatures, as seen in experiments.

Seo, Kangjun; Tewari, Sumanta

2014-11-01

392

Attenuation Distance of Low Frequency Waves Upstream of the Pre-Dawn Bow Shock: GEOTAIL snd ISEE-3 Comparison  

NASA Technical Reports Server (NTRS)

This paper presents a statistical study of the spatial distribution of low frequency waves in the region upstream of the pre-dawn to dawn side bow shock using both GEOTAIL and ISEE-3 magnetometer data.

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

1994-01-01

393

Ultrasonic Attenuation in Zircaloy-4  

SciTech Connect

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

Gomez, M.P. [Departamento de Ingenieria Electrica, Facultad Regional Buenos Aires, Universidad Tecnologica Nacional, Medrano 951 (C1179AAQ), Buenos Aires (Argentina); Banchik, A.D. [Grupo LMFAE, CAE, Comision Nacional de Energia Atomica, Presbitero Luis Gonzalez y Aragon 15 (B1802AYA), Ezeiza, Buenos Aires (Argentina); Lopez Pumarega, M.I. [Grupo de Ondas Elasticas, UA ENDE, CAC, Comision Nacional de Energia Atomica, Av. General Paz 1499 (1650) San Martin, Buenos Aires (Argentina); Ruzzante, J.E. [Departamento de Ingenieria Electrica, Facultad Regional Buenos Aires, Universidad Tecnologica Nacional, Medrano 951 (C1179AAQ), Buenos Aires (Argentina); Grupo de Ondas Elasticas, UA ENDE, CAC, Comision Nacional de Energia Atomica, Av. General Paz 1499 (1650) San Martin, Buenos Aires (Argentina)

2005-04-09

394

Broadband time-domain reflectometry measurement of attenuation and phase velocity in highly attenuating suspensions with application to the ultrasound contrast medium Albunex.  

PubMed

We describe a technique for broadband measurements of the attenuation coefficient and phase velocity of highly attenuating liquid suspensions. To validate the technique we apply it to the ultrasound contrast agent Albunex at concentrations ranging from 0.69 x 10(6) particles/mL to 364 x 10(6) particles/mL. These longitudinal wave measurements were performed on Albunex suspensions maintained at 37 degrees C in a special time-domain reflectometer designed and constructed in our laboratory. The frequency-dependent attenuation coefficients and phase velocities obtained in the reflectometer are compared to broadband through-transmission measurements of these same quantities, which were also performed in our laboratory. Although comparison data between the two techniques are only available at lower concentrations, the agreement is quite good and serves to validate the methods described in this paper. PMID:10955648

Hughes, M S; Klibanov, A L; Marsh, J N; Miller, J G; Brandenburger, G H

2000-08-01

395

Emission of surface light waves from a corrugated part of a thin-film waveguide  

Microsoft Academic Search

A theoretical analysis is made of the influence of interference on the emission of surface light waves from a corrugated part of a thin-film waveguide. It is shown that the interference effects are strongest when the film is corrugated on the substrate side. A strong dependence of the attenuation coefficient of a wave on the film thickness and its modulation

A. A. Zlenko; V. A. Kiselev; A. M. Prokhorov; A. A. Spikhal'skii; V. A. Sychugov

1975-01-01

396

About homotopy perturbation method for solving heat-like and wave-like equations with variable coefficients  

E-print Network

We analyze a recent application of homotopy perturbation method to some heat-like and wave-like models and show that its main results are merely the Taylor expansions of exponential and hyperbolic functions. Besides, the authors require more boundary conditions than those already necessary for the solution of the problem by means of power series.

Francisco M. Fernandez

2008-11-17

397

Beyond Adomian method: The variational iteration method for solving heat-like and wave-like equations with variable coefficients  

Microsoft Academic Search

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

398

Effects of the radial dependence of the fast electron diffusion coefficient on the current driven by lower-hybrid waves in tokamak  

SciTech Connect

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

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

2012-07-15

399

Effects of atmospheric turbulence on microwave and millimeter wave satellite communications systems. [attenuation statistics and antenna design  

NASA Technical Reports Server (NTRS)

A model of the microwave and millimeter wave link in the presence of atmospheric turbulence is presented with emphasis on satellite communications systems. The analysis is based on standard methods of statistical theory. The results are directly usable by the design engineer.

Devasirvatham, D. M. J.; Hodge, D. B.

1981-01-01

400

Diffracted and head waves associated with waves on nonseparable surfaces  

NASA Technical Reports Server (NTRS)

A theory is presented for computing waves radiated from waves on a smooth surface. With the assumption that attention of the surface wave is due only to radiation and not to dissipation in the surface material, the radiation coefficient is derived in terms of the attenuation factor. The excitation coefficient is determined by the reciprocity condition. Formulas for the shape and the spreading of the radiated wave are derived, and some sample calculations are presented. An investigation of resonant phase matching for nonseparable surfaces is presented with a sample calculation. A discussion of how such calculations might be related to resonant frequencies of nonseparable thin shell structures is included. A description is given of nonseparable surfaces that can be modeled in the vector that facilitates use of the appropriate formulas of differential geometry.

Barger, Raymond L.

1992-01-01

401

Waves  

NSDL National Science Digital Library

We will review some basic properties of waves and then further explore sound and light. For a quick overview of some properties of all waves, click on this first site. Make sure you fill out your hand out as you work! Waves and Wave Motion : Describing Waves Practice what you've already learned about waves with this site: Waves This site will let you play around some more with transverse waves: Wave on a String Sound waves are mechanical waves, ...

Mrs. Petersen

2014-05-27

402

Inverse problems of ultrasound tomography in models with attenuation  

NASA Astrophysics Data System (ADS)

We develop efficient methods for solving inverse problems of ultrasound tomography in models with attenuation. We treat the inverse problem as a coefficient inverse problem for unknown coordinate-dependent functions that characterize both the speed cross section and the coefficients of the wave equation describing attenuation in the diagnosed region. We derive exact formulas for the gradient of the residual functional in models with attenuation, and develop efficient algorithms for minimizing the gradient of the residual by solving the conjugate problem. These algorithms are easy to parallelize when implemented on supercomputers, allowing the computation time to be reduced by a factor of several hundred compared to a PC. The numerical analysis of model problems shows that it is possible to reconstruct not only the speed cross section, but also the properties of the attenuating medium. We investigate the choice of the initial approximation for iterative algorithms used to solve inverse problems. The algorithms considered are primarily meant for the development of ultrasound tomographs for differential diagnosis of breast cancer.

Goncharsky, Alexander V.; Romanov, Sergey Y.

2014-04-01

403

Resonance zones and quasi-linear diffusion coefficients for radiation belt energetic electron interaction with oblique chorus waves in the Dungey magnetosphere  

SciTech Connect

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

Shi Run [Polar Research Institute of China, Shanghai (China); Ni, Binbin [Department of Atmospheric and Oceanic Sciences, UCLA, Los Angeles, California 90095-1565 (United States); Gu Xudong [Institute of Geophysics and Planetary Physics, UCLA, Los Angeles, California 90095-1567 (United States); Zhao Zhengyu; Zhou Chen [Department of Space Physics, Wuhan University, Wuhan, Hubei (China)

2012-07-15

404

A numerical upscaling procedure to estimate effective plane wave ...  

E-print Network

Feb 15, 2009 ... resent these mesoscopic heterogeneities and their attenuation effects on the fast waves. An alternative .... The coefficient l is the shear modulus of the bulk material, consid- ered to be equal to ...... 62 (2007) 193–203. [20] J.E. ...

"Juan E. Santos; J. Germ?n Rubino; Claudia L. Ravazzoli"

2009-04-16

405

X-Ray Form Factor, Attenuation and Scattering Tables  

National Institute of Standards and Technology Data Gateway

SRD 66 X-Ray Form Factor, Attenuation and Scattering Tables (Web, free access)   This database collects tables and graphs of the form factors, the photoabsorption cross section, and the total attenuation coefficient for any element (Z <= 92).

406

In vivo ketogenic diet treatment attenuates pathologic sharp waves and high frequency oscillations in in vitro hippocampal slices from epileptic Kv 1.1? knockout mice.  

PubMed

The ketogenic diet (KD) is an effective therapy for pediatric refractory epilepsies; however, whether the KD changes the pathologic network oscillations generated by an epileptic brain remains unknown. We have reported that hippocampal CA3 regions of epileptic Kv1.1? knockout (KO) mice generate pathologic sharp waves (SPWs) and high-frequency oscillations (HFOs) that have higher incidence, longer duration, and fast ripples compared to wild-type (WT). Synaptic activity of hyperexcitable KO mossy fibers significantly decreased CA3 principal cell spike-timing reliability, which contributed to this network pathology. In addition, we have demonstrated that the KD reduces seizures by 75% in KO mice. Here, we determined whether 10- to 14-day in vivo KD treatment exerts disease-modifying effects that alter the spontaneous SPW-HFO complexes generated by the hippocampal CA3 region of KO mice in vitro using extracellular multielectrode array recordings. We found that KD treatment significantly attenuated the pathologic features of KO SPWs and ripples and reduced the incidence of fast ripples. The KD also improved spike-timing reliability of KO CA3 principal cells, decreased mossy fiber excitability, increased mossy fiber-CA3 paired-pulse ratios, and reduced coupling of field excitatory postsynaptic potentials and population spikes in the CA3 region. Collectively, these data indicate that KD treatment modulates CA3-generated pathologic oscillations by dampening hyperactive mossy fiber synapses. PMID:24702645

Simeone, Timothy A; Samson, Kaeli K; Matthews, Stephanie A; Simeone, Kristina A

2014-05-01

407

Propagation properties of guided wave in the anchorage structure of rock bolts  

NASA Astrophysics Data System (ADS)

We investigated the properties of guided wave propagating in grouted rock bolts and the formation of the interface wave through theoretical analysis along with experimental and numerical simulations. Experimental and numerical simulations reveal that the wave propagating in anchorage structure is related to boundary conditions within the range of excitation wave frequencies. Waves with different frequencies have different propagation velocities and attenuation characteristics. The optimal excitation wave occurs in grouted rock bolts with minimized attenuation and maximized propagation distance, and the end reflection of grouted rock bolts can be observed clearly. Longitudinal wave propagating in rock bolts is very sensitive to anchorage strength. With the increase of anchorage strength, longitudinal wave gradually attenuates and eventually disappears. Subsequently, interface wave appears and the velocity of wave propagating in the grouted part becomes that of the interface wave. Based on these studies, ultrasonic guided wave was used to study the end reflection of embedded rock bolts with different anchorage strengths and bonding lengths. The relationships among anchorage strength, bonding length and attenuation coefficient K, as well as the means to inspect the bonding quality of the embedded rock bolts were also evaluated.

Wang, Cheng; He, Wen; Ning, Jianguo; Zhang, Changsuo

2009-12-01

408

Three-Dimensional Attenuation Structure of the Kumaon Himalayas, India, Based on Inversion of Strong Motion Data  

NASA Astrophysics Data System (ADS)

Three-dimensional attenuation structure based on frequency-dependent shear wave quality factor, Q ? ( f), has been determined for the Kumaon region of the Himalayas. An algorithm based on inversion of strong motion data developed by J oshi (Curr Sci 90:581-585, 2006a) and later modified by K umar et al. (Pure Appl Geophys, doi: 10.1007/s00024-013-0658-x, 2013) was used for determination of three-dimensional attenuation coefficients. The input of this algorithm is the spectral acceleration of the S phase of the accelerogram and the outcome is the attenuation coefficient and the source acceleration spectra. A dense network monitoring strong ground motion in the Kumaon region of the Uttarakhand Himalayas has been operating since 2006. This network recorded 287 earthquakes up to July, 2013, of which 18 were used for this work. Shear-wave quality-factors were estimated for frequencies of 1.0, 5.0, and 10.0 Hz for two rectangular blocks of surface of dimensions 85 × 55 and 90 × 30 km2 in the Kumaon region of the Himalayas. Both blocks were divided into 25 three-dimensional blocks of uniform thickness with different Q ? ( f) values. The spatial distribution of frequency-dependent shear-wave quality factors in two different blocks reveal the attenuation properties of the region. The profiles of the contours of shear-wave quality factors observed were comparable with those of major tectonic units present in the region.

Kumar, Parveen; Joshi, A.; Sandeep; Kumar, Ashvini

2015-02-01

409

The influence of porosity on ultrasound attenuation in carbon fiber reinforced plastic composites using the laser-ultrasound spectroscopy  

NASA Astrophysics Data System (ADS)

Wideband acoustic spectroscopy with a laser ultrasound source for quantitative analysis of the effect of porosity on the attenuation coefficient of longitudinal acoustic waves in carbon fiber reinforced plastic (CFRP) composite materials was experimentally implemented. The samples under study had different bulk-porosity levels (up to 10%), which were determined using X-ray computer tomography. A resonance ultrasound attenuation peak associated with the one-dimensional periodicity of the layered composite structure was observed for all samples. The absolute value of the resonance-peak maximum and its width depend on the local concentration of microscopic isolated pores and extended delaminations in the sample structure. The obtained empirical relationships between these parameters of the frequency dependence of the ultrasound attenuation coefficient and the type of inhomogeneities and their volume concentration can be used for rapid evaluation of the structural quality of CFRP composites.

Karabutov, A. A.; Podymova, N. B.; Belyaev, I. O.

2013-11-01

410

Attenuation of high-frequency radio waves in the low ionosphere at high latitudes when the ionosphere is artificially perturbed by powerful radio emission  

Microsoft Academic Search

We have discovered a significant (up to 60% and more) attenuation of the intensity of high frequency probe signals received from the low nighttime ionosphere at high altitudes. The reason for the attenuation is that the ionosphere is being influenced by powerful shortwave radio emission. The Polar Geophysical Institute (PGI) was set up so that powerful shortwave radiation could artificially

S. I. Martynenko; V. A. Misyura; V. G. Simov; L. F. Chernogor; A. S. Shemet

1983-01-01

411

Reduced-dimensionality quantum calculations of the thermal rate coefficient for the Cl+HCl --> ClH+Cl reaction: Comparison with centrifugal-sudden distorted wave, coupled channel hyperspherical, and experimental results  

NASA Astrophysics Data System (ADS)

Reduced dimensionality (RD) cumulative reaction probabilities (CRPs) are reported for the Cl+HCl?ClH+Cl reaction using two semiempirical extended London-Eyring-Polanyi-Sato potential energy surfaces. Comparison is made with CRPs from centrifugal-sudden distorted wave (CSDW) calculations, and with accurate coupled channel hyperspherical (CCH) CRPs for total angular momentum quantum number J=0. Rotational and bending energy-shift approximations are applied to the CCH CRPs for J=0 to obtain approximate CRPs for J>0. A test of this approximation is made using CSDW partial wave CRPs. New expressions for the thermal rate coefficient are derived using these approximations. The rate coefficients calculated from RD and energy-shifted CCH CRPs are in excellent agreement with each other. They also agree well with the CSDW and experimental rate coefficients.

Sun, Qiyan; Bowman, Joel M.; Schatz, George C.; Sharp, J. R.; Connor, J. N. L.

1990-02-01

412

Light attenuation on unicellular marine phytoplankton  

Microsoft Academic Search

Sea phytoplankton plays a considerable role in the interactive processes between light and the sea. Its species composition and the physiological development phase influence the spectrum of the light attenuation coefficient in the sea. Laboratory measurements of light attenuation spectrum were carried out on three different phytoplankton monocultures of the unicellular green algae Chlorella vulgaris and the larger Chlorella kesleri

Tadeusz Krol; Maria Lotocka

1994-01-01

413

Prediction of spectral acceleration response ordinates based on PGA attenuation  

USGS Publications Warehouse

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

Graizer, V.; Kalkan, E.

2009-01-01

414

Acoustic waves in polydispersed bubbly liquids  

NASA Astrophysics Data System (ADS)

The propagation of acoustic waves in polydispersed mixtures of liquid with two sorts of gas bubbles each of which has its own bubble size distribution function is studied. The system of the differential equations of the perturbed motion of a mixture is presented, the dispersion relation is obtained. Equilibrium speed of sound, low-frequency and high-frequency asymptotes of the attenuation coefficient are found. Comparison of the developed theory with known experimental data is presented.

Gubaidullin, D. A.; Gubaidullina, D. D.; Fedorov, Yu V.

2014-11-01

415

Acoustic waves of zero order in piezoelectric cylinders and tubes bordered with non-conducting viscous liquid  

NASA Astrophysics Data System (ADS)

A theoretical study of cylindrical acoustic waves of zero order propagating in cylindrical waveguide in contact with nonconducting viscous liquid was carried out. Waveguides considered in this paper are represented by circular rod of piezoelectric ceramics, surrounded by a viscous liquid or thick-walled piezoelectric tube filled with liquid. The orientation of the piezoceramic was chosen in this way that the polarization vector coincided with the cylinder axis. In this case due to the isotropy in the plane which is perpendicular to the cylinder axis one can use the mathematic methods based on the cylindrical functions expansion of the wave potentials. As a result we found the phase and group velocities of the waves under study and also their electromechanical coupling coefficient and attenuation coefficient. It has been shown that compressional wave of zero order c0 has a high electromechanical coupling coefficient and low attenuation. The obtained results may be used for development of the sensors operating in hostile environment.

Teplykh, A. A.; Zaitsev, B. D.; Kuznetsova, I. E.

2012-05-01

416

Seismic Attenuation Inversion with t* Using tstarTomog.  

SciTech Connect

Seismic attenuation is defined as the loss of the seismic wave amplitude as the wave propagates excluding losses strictly due to geometric spreading. Information gleaned from seismic waves can be utilized to solve for the attenuation properties of the earth. One method of solving for earth attenuation properties is called t*. This report will start by introducing the basic theory behind t* and delve into inverse theory as it pertains to how the algorithm called tstarTomog inverts for attenuation properties using t* observations. This report also describes how to use the tstarTomog package to go from observed data to a 3-D model of attenuation structure in the earth.

Preston, Leiph

2014-09-01

417

Measurement of ultrasonic scattering attenuation in austenitic stainless steel welds: realistic input data for NDT numerical modeling.  

PubMed

Multipass welds made of 316L stainless steel are specific welds of the primary circuit of pressurized water reactors in nuclear power plants. Because of their strong heterogeneous and anisotropic nature due to grain growth during solidification, ultrasonic waves may be greatly deviated, split and attenuated. Thus, ultrasonic assessment of the structural integrity of such welds is quite complicated. Numerical codes exist that simulate ultrasonic propagation through such structures, but they require precise and realistic input data, as attenuation coefficients. This paper presents rigorous measurements of attenuation in austenitic weld as a function of grain orientation. In fact attenuation is here mainly caused by grain scattering. Measurements are based on the decomposition of experimental beams into plane-wave angular spectra and on the modeling of the ultrasonic propagation through the material. For this, the transmission coefficients are calculated for any incident plane wave on an anisotropic plate. Two different hypotheses on the welded material are tested: first it is considered as monoclinic, and then as triclinic. Results are analyzed, and validated through comparison to theoretical predictions of related literature. They underline the great importance of well-describing the anisotropic structure of austenitic welds for UT modeling issues. PMID:24759567

Ploix, Marie-Aude; Guy, Philippe; Chassignole, Bertrand; Moysan, Joseph; Corneloup, Gilles; El Guerjouma, Rachid

2014-09-01

418

A linear model approach for ultrasonic inverse problems with attenuation and dispersion.  

PubMed

Ultrasonic inverse problems such as spike train deconvolution, synthetic aperture focusing, or tomography attempt to reconstruct spatial properties of an object (discontinuities, delaminations, flaws, etc.) from noisy and incomplete measurements. They require an accurate description of the data acquisition process. Dealing with frequency-dependent attenuation and dispersion is therefore crucial because both phenomena modify the wave shape as the travel distance increases. In an inversion context, this paper proposes to exploit a linear model of ultrasonic data taking into account attenuation and dispersion. The propagation distance is discretized to build a finite set of radiation impulse responses. Attenuation is modeled with a frequency power law and then dispersion is computed to yield physically consistent responses. Using experimental data acquired from attenuative materials, this model outperforms the standard attenuation-free model and other models of the literature. Because of model linearity, robust estimation methods can be implemented. When matched filtering is employed for single echo detection, the model that we propose yields precise estimation of the attenuation coefficient and of the sound velocity. A thickness estimation problem is also addressed through spike deconvolution, for which the proposed model also achieves accurate results. PMID:24960708

Carcreff, Ewen; Bourguignon, Sébastien; Idier, Jérôme; Simon, Laurent

2014-07-01

419

Seismic attenuation in fractured media  

NASA Astrophysics Data System (ADS)

The prime objective of this paper is to quantitatively estimate seismic attenuation caused by fractures with different physical parameters. In seismic wave simulation, the fractured media are treated as the anisotropic media and fractures are represented by frequency-dependent elastic constants. Based on numerical experiments with three different parameters, namely viscosity, porosity and the Lamé parameters, this paper has the following observations. First, seismic attenuation is not affected by the viscosity within fractures, although it increases with the increase of porosity and decreases with the increase of the Lamé parameters within fractures. Among the latter two parameters, seismic attenuation is more sensitive to the Lamé parameters than to the porosity. Second, for the attenuation anisotropy, low frequencies have more anisotropic effect than high frequencies. For example, a 50?Hz wavefield has the strongest anisotropy effect if compared to 100 and 150?Hz wavefields. The attenuation anisotropy for low frequency (say 50?Hz) is more sensitive to the viscosity than the porosity and the Lamé parameters have the weakest effect among these three parameters. These observations suggest that low-frequency seismic attenuation, and especially the attenuation anisotropy in low frequency, would have great potential for fluid discrimination within fractured media.

Rao, Ying; Wang, Yanghua

2015-02-01

420

Reflection Coefficients.  

ERIC Educational Resources Information Center

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

Greenslade, Thomas B., Jr.

1994-01-01

421

Modeling of the Infrasound Propagation in the Atmosphere: With Gravitational Effect and Attenuation Considered  

NASA Astrophysics Data System (ADS)

For modeling the propagation of infrasound below 5 Hz, the high frequency approximation is no longer valid and the effect of gravity needs to be taken into account. Damping of infrasound in the realistic atmosphere is another important ingredient. With the impacts of gravitational field and realistic atmospheric attenuation considered, an acoustic ray tracing model and a Finite Difference Time Domain (FDTD) model are developed. The ray tracing equations are deduced from the real part of the dissipative dispersion relation of acoustic wave, while the acoustic attenuation coefficient and growth rate in a stratified moving atmosphere are deduced from the imaginary part of the dispersion relation.The buoyancy frequency and the cut-off frequency of acoustic wave are set to be the values in a nonisothermal atmosphere, and the attenuation coefficient is corrected by the realistic absorption. In the FDTD model, the governing equations of acoustic wave in a dissipative gravitational-stratified atmosphere is solved by combing a dispersion relation preserving scheme in space and a Runge-Kutta scheme in time. The results show that the ray trajectory obtained by the ray tracing model agrees well with that simulated by the FDTD model. The simulation of the ray tracing model illustrate that the gravitational effect plays a dominant role in the stratospheric ducting and the attenuation effect could be neglected. However, the contribution of the absorption becomes more important and can't be ignored in the thermospheric ducting. By taking the gravity into consideration, the acoustic frequency in our models is no longer constrained by the high frequency approximation. Consideration of the dissipation effect can also improve the computation accuracy of ray trajectories and the efficiency of wave amplitude evaluation.

Song, Yang

2014-05-01

422

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

SciTech Connect

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

Kuzichev, I. V., E-mail: mar-cuss@yandex.ru; Shklyar, D. R. [Russian Academy of Sciences, Space Research Institute (Russian Federation)] [Russian Academy of Sciences, Space Research Institute (Russian Federation)

2013-10-15

423

Ultrasound fields in attenuating media.  

PubMed

For medical ultrasonic imaging and for nondestructive testing, the attenuation of pressure waves and the resulting shift in wave velocity are important features in commonly used transmission media such as biological tissue. An algorithm for the numerical evaluation of pressure field distributions generated by ultrasonic transducers is presented. The attenuation and dispersion of the sound transmission medium are taken into consideration. The sound fields are computed numerically for continuous wave as well as pulse excitation. The transducer has plane or gently curved geometry and is embedded in a plane rigid baffle. The numerically determined pressure fields are presented as 3D plots, as gray-scale images for a fixed time stamp (like a snapshot), or as isobars regarding the maximum values over time for each local point in the area under investigation. The algorithm described here can be utilized as a tool for design of ultrasound transducers, especially array antennas. PMID:3771930

Lerch, R; Friedrich, W

1986-10-01

424

Experimental investigation of ?-ray attenuation in Jordanian building materials using HPGe-spectrometer  

Microsoft Academic Search

The capabilities of some building materials used in Jordan to attenuate gamma radiation were tested. Measurements of the attenuation coefficients of limestone, bricks and concrete have been carried out using a HPGe-spectrometer. Narrow beam technique was used, with a multiple gamma radiation source of different energy lines. Results indicate that variations in the attenuation coefficient for all limestone samples, at

Mohammad I. Awadallah; Mousa M. A. Imran

2007-01-01

425

On the excess attenuation of sound in the atmosphere  

NASA Technical Reports Server (NTRS)

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

Deloach, R.

1975-01-01

426

Thrust-augmented vortex attenuation  

NASA Technical Reports Server (NTRS)

An experimental investigation was conducted to determine the vortex attenuating effect of engine thrust. Tests were made using a 0.03-scale model of the Boeing 747 transport aircraft as a vortex generating model. A Learjet-class probe model was used to measure the vortex induced rolling moment at a scale separation distance of 1.63 km. These tests were conducted at a lift coefficient of 1.4 at a model velocity of 30.48 m/s. The data presented indicate that engine thrust is effective as a vortex attenuating device when the engines are operated at high thrust levels and are positioned to direct the high energy engine wake into the core of the vortex. The greatest thrust vortex attenuation was obtained by operating the inboard engine thrust reversers at one-quarter thrust and the outboard engines at maximum forward thrust.

Patterson, J. C., Jr.; Jordan, F. L., Jr.

1977-01-01

427

The Physics of the Gas Attenuator for the Linac Coherent Light Source (LCLS)  

SciTech Connect

A systematic assessment of a variety of physics issues affecting the performance of the LCLS X-ray beam attenuator is presented. Detailed analysis of the gas flow in the gas attenuator and in the apertures is performed. A lot of attention is directed towards the gas ionization and heating by intense X-ray pulses. The role of these phenomena in possible deviations of the attenuation coefficient from its 'dialed in' value is evaluated and found small in most cases. Other sources of systematic and statistical errors are also discussed. The regimes where the errors may reach a few percent correspond to the lower X-ray energies (less than 2 keV) and highest beam intensities. Other effects discussed include chemical interaction of the gas with apertures, shock formation in the transonic flow in the apertures of the attenuator, generation of electromagnetic wakes in the gas, and head-to-tail variation of the attenuation caused by the ionization of gas or solid. Possible experimental tests of the consistency of the physics assumptions used in the concept of the gas attenuator are discussed. Interaction of X-rays with the solid attenuator (that will be used at higher X-ray energies, from 2.5 to 8 keV) is considered and thermo-mechanical effects caused by the beam heating are evaluated. Wave-front distortions induced by non-uniform heating of both the solid and the gas are found to be small. An overall conclusion drawn from the analysis presented is that the attenuator will be a reliable and highly versatile device, provided that some caution is exercised in its use for highest beam intensities at lowest X-ray energies.

Ryutov, D.D.; Bionta, R.M.; Hau-Riege, S.P.; Kishiyama, K.I.; McMahon, D.; Roeben, M.D.; Shen, S.; /LLNL, Livermore; Stefan, P.M.; /SLAC; ,

2011-02-07

428

Shear waves in vegetal tissues at ultrasonic frequencies  

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

429