Experimental study of attenuation coefficient of ultrasonic waves in concrete and plaster
A. Abdullah; E. Fallahi Sichani
2009-01-01
This study has been dedicated to the determination and comparison of ultrasound attenuation coefficient in two kinds of frequently\\u000a used masonry, namely concrete and plaster. The results of this investigation can be mainly applied for optimum acoustical\\u000a designing of buildings which are exposed to high-power ultrasonic waves. Another expected benefit of this investigation is\\u000a determining the possibility of using ultrasonic
SEISMIC WAVE ATTENUATION IN FLUIDSATURATED POROUS MEDIA
and measured attenuation of compressional and shear waves in porous earth. One unfortunate consequence that the coefficients for viscous attenuation of shear waves and of the fast compressional wave are proportional compressional wave at ultrasonic frequencies (Plona 1980, Berryman 1980) and has provided accurate estimates
Experimental Investigation of Wave Attenuation Through Vegetation
NASA Astrophysics Data System (ADS)
Ozeren, Y.; Wren, D. G.
2011-12-01
Wetlands and coastal vegetation can reduce the surge and wave impact on coastal areas. Yet, the primary mechanisms of wave mitigation by vegetation are still unclear. The objective of this study was to investigate and quantify the attenuation of waves through vegetation using laboratory experiments. The wave attenuation properties of artificial vegetation and live and dormant S. alterniflora and J. roemerianus were investigated under monochromatic and irregular wave conditions at full scale in a wave tank facility at the USDA-ARS-National Sedimentation Laboratory in Oxford, Mississippi. Water level sensors and a video camera were used to record water level data. Drag coefficients were estimated for artificial and natural plants and regression equations were derived for the drag coefficients as functions of both Reynolds and Keulegan-Carpenter number. It was observed that vertical variation of vegetation density had an important effect on the drag coefficient.
Elastic wave attenuation in composite laminates with cracks
David Miller; Santanu Das; Xu Zhou; Aditi Chattopadhyay
2005-01-01
In structural health monitoring, energy dissipation of wave propagation is a key factor to determine optimal placement of sensors and quantify damage. This paper focuses on the study of wave scattering and attenuation in fiber-reinforced composite laminates with damage. In order to obtain the overall attenuation coefficient, the propagation of elastic shear wave in fiber-matrix medium is investigated starting from
Seismic wave characteristics in anisotropic attenuating media
NASA Astrophysics Data System (ADS)
Sinha, Satish
A synthetic seismogram is a tool to investigate seismic wave characteristics in anisotropic attenuating media. A numerical technique for the computation of synthetic seismograms in a homogeneous, as well as in a multilayered anisotropic medium was developed. Full waveform theory is used to compute the synthetic seismograms. The medium can be elastic or viscoelastic. In the latter case, attenuation is introduced by giving materials complex elastic constants. To ensure that there are no false arrivals in the synthetic seismogram, it is important to carefully control the integration kernel singularity points, especially those due to repeated roots of the associated Green-Christoffel equation. A novel approach is developed to safely track the continuity of the integration kernel and, hence, the polarization vectors in critical and supercritical zones. The reflectivity approach is followed to consider wave propagation in a multilayered medium. A simple and concise implementation of this method is developed. This approach also enables one to investigate frequency dependent reflection coefficients varying with incidence angle and azimuth. The modeling of reflection coefficients in fractured media suggests that amplitude versus offset and azimuth (AVOAz) can be helpful in detecting fractured reservoirs. In a new development, the effect of attenuation on P- and S-wave radiation patterns in viscoelastic anisotropic media is investigated. The understanding of radiation patterns in homogeneous media is applied to interpret various wave types in attenuating multilayered media. Both the amplitude and the frequency content of the synthetic seismograms are affected by attenuation properties of the media. The spectral decomposition technique is found to be useful in our understanding of the attenuation effects. Seismic anisotropy in shales is a complex phenomenon. A number of theoretical shale models are investigated to study the effects of clay orientation, aspect ratio of cracks, porosity and fluid types on the synthetic seismograms.
Calculation of radiation attenuation coefficients for shielding concretes
I. I. Bashter
1997-01-01
Theoretical calculations have been performed in order to obtain the mass attenuation coefficients and the linear attenuation coefficients at photon energies from 10 keV to 1 GeV for ordinary, hematite-serpentine, ilmenite-limonite, basalt-magnetite, ilmenite, steel-scrap and steel-magnetite concretes. The concrete densities ranged from 2.3 to 5.11 g cm?3. The calculated values of linear attenuation coefficients have been compared with those measured
Stokes coefficients and wave resistance
NASA Astrophysics Data System (ADS)
Maklakov, D. V.; Petrov, A. G.
2015-07-01
With the help of the Hamilton variational principle an infinite chain of compactly written quadratic equations with respect to the Stokes coefficients determining the periodic progressive finite-depth waves is constructed. An efficient algorithm of calculation of these coefficients in the form of series in terms of wave-amplitude powers is given. In analytical form, a ten-term expansion in terms of the amplitude for the wave-resistance force arising from motion under the free surface of a two-dimensional body generating the waves is constructed. The obtained expansion is compared with the Kelvin formula, which is single-term in amplitude, and with an accurate numerical solution.
Temporal Variations of Seismic Coda: Attenuation-Coefficient View
NASA Astrophysics Data System (ADS)
Morozov, I. B.
2010-12-01
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.
Boundary attenuation angles for inhomogeneous plane waves
Cerveny, Vlastislav
Boundary attenuation angles for inhomogeneous plane waves in anisotropic dissipative media@ig.cas.cz. Summary Attenuation angles of inhomogeneous plane waves propagating in isotropic or aniso- tropic and on the properties of the plane wave under consideration, mainly on the direction of propagation of the wave
Coherent wave propagation: attenuation and phase shift
Zhang, Guifu
Coherent wave propagation: attenuation and phase shift Â· Coherent scattering exist only in forward direction Â· Modeled as effective medium Â Attenuation: I=I0e-!z Â Phase shift: km'z Â Effective wave number" k nf ( ^ki, ^ki ) = k + 2" k f ( ^ki, ^ki )N(D)dD# #12;Attenuation and phase shift Â· Intensity
NOTE: Investigation of photon attenuation coefficients for marble
C. Basyigit; I. Akkurt; S. Kilincarslan; A. Akkurt
2005-01-01
The total linear attenuation coefficients mu (cm-1) have been obtained using the XCOM program at photon energies of 1 keV to 1 GeV for six different natural marbles produced in different places in Turkey. The individual contribution of photon interaction processes to the total linear attenuation coefficients for marble has been investigated. The calculated results were also compared with the
Surface wave attenuation characteristics at the APS site
Jendrzejczyk, J.A.; Wambsganss, M.W.; Smith, R.K.
1992-05-01
During operation of the Advanced Photon Source (APS) Facility, there will be many potential sources of vibration that may be transmitted through the ground to the storage ring basement and experimental hall. These sources include chillers, pumps, blowers and fans. Some may produce amplitudes of sufficient magnitude to adversely affect the stability of the closed orbit of the beam. Where possible, these vibration sources will be monitored as they become operational, to determine their vibrational characteristics, such as amplitude and frequency, and duty cycle. Vibrations travel through the ground as body [compression (P) and shear (S)] waves and Rayleigh (R) waves, which are surface waves. The amplitudes of these waves decrease with distance from their source as a result of both geometric and material damping. Because the storage ring basement is {open_quotes}on grade{close_quotes}, the authors are primarily interested in waves on the surface. The R-waves, being surface waves, attenuate with distance more slowly than the body waves; for an R-wave, attenuation is proportional to 1/{radical}r, whereas for a body wave at the surface, attenuation is proportional to 1/r{sup 2}, where r is the distance from the source. Because R-waves attenuate more slowly, they are of primary interest relative to the isolation of vibration-sensitive facilities such as the APS. Measurement of surface wave attenuation requires a vibration source that is capable of producing a ground displacement level considerably greater than that of the ambient background. A pile driver that was used to drive steel pilings at the APS vehicle tunnel provided such a source. This study provides a measure of the attenuation of surface waves in the ground by the combination of geometric and material damping. An average coefficient of attenuation of 0.003 was derived from measured responses to vibrations provided by a pile driver.
Physical modeling and analysis of P-wave attenuation anisotropy in transversely isotropic media
Tsvankin, Ilya
Physical modeling and analysis of P-wave attenuation anisotropy in transversely isotropic media analyzes measurements of the P-wave attenuation coeffi- cient in a transversely isotropic sample made coefficient of P-waves transmitted through the sample for a wide range of propagation angles from 0° to 90
Gamma ray attenuation coefficient measurement for neutron-absorbent materials
Majid Jalali; Ali Mohammadi
2008-01-01
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
Compressional head waves in attenuative formations
Liu, Q.H.; Chang, C.
1994-12-31
The attenuation of compressional head waves in a fluid-filled borehole is studied with the branch-cut integration method. The borehole fluid and solid formation are both assumed lossy with quality factors Q{sub f}({omega}) for the fluid, and Q{sub c}({omega}) and Q{sub s}({omega}) for the compressional and shear waves in the solid, respectively. The branch-cut integration method used in this work is an extension of that for a lossless medium. With this branch-cut integration method, the authors can isolate the groups of individual arrivals such as the compressional head waves and shear head waves, and study the attenuation of those particular wavefields in lossy media. This study, coupled with experimental work to be performed, may result in an effective way of measuring compressional head wave attenuation in the field.
Attenuation coefficient estimates of mouse and rat chest wall
Geraldine A. Teotico; Rita J. Miller; Leon A. Frizzell; James F. Zachary; William D. O'Brien
2001-01-01
Attenuation coefficients of intercostal tissues were estimated from chest walls removed postmortem (pm) from 41 6-to-7-week-old female ICR mice and 27 10-to-11-week-old female Sprague-Dawley rats. These values were determined from measurements through the intercostal tissues, from the surface of the skin to the parietal pleura. Mouse chest walls were sealed in plastic wrap and stored at 4\\\\°C until evaluated, and
Attenuation of a shock wave in organoplastic
Bordzilovskii, S.A.; Karakhanov, S.M.; Merzhievskii, L.A.; Resnyanskii, A.D.
1995-09-01
The attenuation of a plane shock wave in organoplastic was experimentally and numerically investigated during its interaction with an overtaking rarefaction wave. Measurements were carried out with manganin gauges. An earlier formulation model of the dynamic deformation of composites was used in calculations. A comparison of calculated and experimental data has shown their good agreement.
Wave-induced fluid flow in random porous media: attenuation and dispersion of elastic waves.
Müller, Tobias M; Gurevich, Boris
2005-05-01
A detailed analysis of the relationship between elastic waves in inhomogeneous, porous media and the effect of wave-induced fluid flow is presented. Based on the results of the poroelastic first-order statistical smoothing approximation applied to Biot's equations of poroelasticity, a model for elastic wave attenuation and dispersion due to wave-induced fluid flow in 3-D randomly inhomogeneous poroelastic media is developed. Attenuation and dispersion depend on linear combinations of the spatial correlations of the fluctuating poroelastic parameters. The observed frequency dependence is typical for a relaxation phenomenon. Further, the analytic properties of attenuation and dispersion are analyzed. It is shown that the low-frequency asymptote of the attenuation coefficient of a plane compressional wave is proportional to the square of frequency. At high frequencies the attenuation coefficient becomes proportional to the square root of frequency. A comparison with the 1-D theory shows that attenuation is of the same order but slightly larger in 3-D random media. Several modeling choices of the approach including the effect of cross correlations between fluid and solid phase properties are demonstrated. The potential application of the results to real porous materials is discussed. PMID:15957744
Modelling of attenuation of Lamb waves using Rayleigh damping: Numerical and experimental studies
C. Ramadas; Krishnan Balasubramaniam; Avinash Hood; Makarand Joshi; C. V. Krishnamurthy
2011-01-01
In this study, the Lamb mode attenuation constants were derived in terms of the attenuation coefficient, group velocity and central frequency of excitation of the Lamb mode, using the Rayleigh damping model. Attenuation of Lamb waves, both fundamental symmetric and anti-symmetric modes, propagating through viscoelastic media (cross-ply glass\\/epoxy laminate) was modelled using the Finite Element Method. Numerically simulated attenuation of
X-Ray Mass Attenuation Coefficient of Silicon: Theory versus Experiment
C. Q. Tran; C. T. Chantler; Z. Barnea
2003-01-01
We compare new experimental x-ray total mass attenuation coefficients of silicon obtained with the x-ray extended-range technique (XERT) from 5 to 20 keV with theoretical calculations and earlier experimental measurements over a 5 to 50 keV energy range. The accuracy of between 0.27% and 0.5% of the XERT data allows us to probe alternate atomic and solid state wave function
Scattering and Attenuation of Seismic Waves in the Lithosphere / 1 ch11Text.doc 12/30/99 6:41 PM
wave propagation in heterogeneous media. Glossaries: Born approximation, coda waves, coda attenuation, envelope broadening, lapse time, parabolic approximation, Q value, radiative transfer theory, random media, Rytov method, scattering, scattering coefficient, seismic albedo, seismic array. I. Attenuation
Pressure wave attenuation and dispersion in two-phase flow
Kovarik, F.S.; Bankoff, S.G.
1987-01-01
The pressure shock wave propagation behavior in three vapor-liquid systems, steam-water, ethanol-ethanol, and Freon-Freon, has been investigated over a void fraction, ..cap alpha.., range from zero to 30%. Attenuation and dispersion behavior seems relatively insensitive (no order-of-magnitude deviations) to differences in system physical properties. The attenuation coefficient of water, BETA/sub H/2/sub O/ ranged from 0.021 cm/sup -1/ at 5% void to 0.072 cm/sup -1/ at 30% void fraction. BETA/sub F113/ was as much as 40% lower than BETA/sub ETOH/ or BETA/sub H/2/sub O/ for void fractions less than 20% where the initial wave amplitude, ..delta..P/sub o/ was 2.90 bar. Larger amplitude waves (4.14 bar) demonstrated a greater rate of attenuation throughout the void fraction range, more pronounced in the lower regions: 80% greater for 5% steam-water and 120% greater for 5% Freon-113. The attenuation data from the present investigation tend to lie between one- and two-component acoustic attenuation theories and data. However, near the resonant bubble frequency, the two component results approach the one-component region. As the void fraction is decreased, the one- and two-component acoustic theories and data (small and finite amplitude, including the present experimentation) smoothly converge.
Burger, C; Goerres, G; Schoenes, S; Buck, A; Lonn, A H R; Von Schulthess, G K
2002-07-01
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 photon energy and the absorbing material, an accurate theoretical relation cannot be devised. The transformation implemented in the Discovery LS PET/CT scanner (GE Medical Systems, Milwaukee, Wis.) uses a bilinear function based on the attenuation of water and cortical bone at the CT and PET energies. The purpose of this study was to compare this transformation with experimental CT values and corresponding PET attenuation coefficients. In 14 patients, quantitative PET attenuation maps were calculated from germanium-68 transmission scans, and resolution-matched CT images were generated. A total of 114 volumes of interest were defined and the average PET attenuation coefficients and CT values measured. From the CT values the predicted PET attenuation coefficients were calculated using the bilinear transformation. When the transformation was based on the narrow-beam attenuation coefficient of water at 511 keV (0.096 cm(-1)), the predicted attenuation coefficients were higher in soft tissue than the measured values. This bias was reduced by replacing 0.096 cm(-1) in the transformation by the linear attenuation coefficient of 0.093 cm(-1) obtained from germanium-68 transmission scans. An analysis of the corrected emission activities shows that the resulting transformation is essentially equivalent to the transmission-based attenuation correction for human tissue. For non-human material, however, it may assign inaccurate attenuation coefficients which will also affect the correction in neighbouring tissue. PMID:12111133
Measurement of Acoustic Attenuation and Absorption Coefficients using Thermometry
NASA Astrophysics Data System (ADS)
Morris, Hugh; Rivens, Ian; Shaw, Adam; ter Haar, Gail
2007-05-01
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.
Hideo Nishino; Tsutomu Furukawa; Sunao Takashina; Mikio Takemoto
2000-01-01
Structural change in 0.45 mass % carbon steel during tempering was measured nondestructively as a change in the attenuation coefficient of 40 MHz surface acoustic waves (SAW) generated by scanning interference fringes (SIF). The SIF selectively generate the SAW at an adequate center frequency, which is useful to distinguish the attenuation coefficients between slightly different structures. The attenuation coefficient at
C. Burger; G. Goerres; S. Schoenes; A. Buck; A. Lonn; G. von Schulthess
2002-01-01
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
Reflection coefficients in attenuative anisotropic media Jyoti Behura1
Tsvankin, Ilya
Such reservoir rocks as tar sands are characterized by signifi- cant attenuation and, in some cases, attenuation for highly attenuative e.g., gas-sand and heavy-oil reservoirs. INTRODUCTION Conventional amplitude
Uranium soft x-ray total attenuation coefficients
Del Grande, N.K.; Oliver, A.J.
1981-01-01
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.
Attenuation of an electromagnetic wave by charged dust particles in a sandstorm.
Xie, Li; Li, Xingcai; Zheng, Xiaojing
2010-12-10
We calculate the light scattering properties of the partially charged dust particles with the Mie theory for electromagnetic waves with different frequencies, and the attenuation coefficients of an electromagnetic wave propagating in a sandstorm are also calculated. The results show that the electric charges distributed on the sand surface have a significant effect on the attenuation of the electromagnetic wave, especially for a frequency lower than 40 GHz, and attenuation coefficients increase with the magnitude of charges carried by the dust particles (expressed by the charge-to-mass ratio in this paper). For the higher frequency electromagnetic wave, such as visible light, the effect of charges carried by sand particles on its attenuation is very little, which can be ignored. PMID:21151232
Jiang, Hangyi
Measurement of x-ray attenuation coefficients of aqueous solutions of indocyanine green report our experimental results of measurements of x-ray attenuation coefficients of aqueous solutions of metastatic tumors in rats using a novel laser immunotherapy these solutions were administered in situ. The x-ray
Vermeer, K. A.; Mo, J.; Weda, J. J. A.; Lemij, H. G.; de Boer, J. F.
2013-01-01
We present a method, based on a single scattering model, to calculate the attenuation coefficient of each pixel in optical coherence tomography (OCT) depth profiles. Numerical simulations were used to determine the model’s response to different depths and attenuation coefficients. Experiments were performed on uniform and layered phantoms with varying attenuation coefficients. They were measured by a 1300 nm OCT system and their attenuation coefficients were evaluated by our proposed method and by fitting the OCT slope as the gold standard. Both methods showed largely consistent results for the uniform phantoms. On the layered phantom, only our proposed method accurately estimated the attenuation coefficients. For all phantoms, the proposed method largely reduced the variability of the estimated attenuation coefficients. The method was illustrated on an in-vivo retinal OCT scan, effectively removing common imaging artifacts such as shadowing. By providing localized, per-pixel attenuation coefficients, this method enables tissue characterization based on attenuation coefficient estimates from OCT data. PMID:24466497
5. SOUND ATTENUATION 5.1 NATURE OF SOUND WAVE
Cambridge, University of
5. SOUND ATTENUATION 5.1 NATURE OF SOUND WAVE Historically, acoustic is the scientific study of sound. Sound can be considered as a wave phenomenon. A sound wave is a longitudinal wave where particles the sound wave, the particles of the medium through which the sound moves is vibrating in a back and forth
Effect of soil texture on the propagation and attenuation of acoustic wave at unsaturated conditions
NASA Astrophysics Data System (ADS)
Lo, Wei-Cheng; Yeh, Chao-Lung; Tsai, Chang-Tai
2007-05-01
SummaryA central issue in the successful application of acoustic wave method to detect subsurface hydrological properties is a better understanding of the influence of soil texture on the propagation and attenuation of acoustic wave as moisture content is varied, which was numerically investigated in the present study. Our earlier studies have demonstrated the existence of three different modes of acoustic wave in an elastic porous medium containing two immiscible, viscous, compressible fluids. Based on the dispersion equation obtained in the Lo-Sposito-Majer (LSM) model, the phase velocity and attenuation coefficient of the P1 and P2 waves which respectively propagate the fastest and second fastest were determined as a function of water saturation for 11 soil texture classes. The slowest wave (P3) was not characterized in this study since it does not travel far, due to very high attenuation. To provide a more general result, the calculated phase velocity and attenuation coefficient for different soil textures were normalized by those computed for sand. The normalization leads the resulting dimensionless parameters to be frequency independent throughout the whole range (up to 500 Hz) with Darcy's law remaining valid for the description of each fluid flow under wave excitation. The normalized phase velocity of the P1 wave was shown to have a substantially constant value at higher water saturations, but in the lower saturation range it first increases to reach a certain maximum value for different soil types and then decreases. The physical parameter controlling this phenomenon is the ratio of two effective non-wetting fluid storativity factors. Numerical results reveal that the normalized attenuation coefficient of the P1 wave is sensitive to soil texture and water saturation. Sand and loamy sand have the highest and second highest attenuation coefficients for the P1 wave, respectively. The magnitude of the normalized phase velocity of the P2 wave is found to be, with very few exceptions at nearly full saturations, linearly associated with the intrinsic permeability, while relating to the normalized attenuation coefficient of the P2 wave in an opposite manner. These results provide a quantitative clue for acoustic wave method to explore the physical properties in the shallow subsurface.
Effect of soil texture on the propagation and attenuation of acoustic wave at unsaturated conditions
NASA Astrophysics Data System (ADS)
Lo, W.; Yeh, C.; Tsai, C.
2006-12-01
A central issue in successfully applying acoustic wave method to detect subsurface hydrological properties is a better understanding of the influence of soil texture on the propagation and attenuation of acoustic wave as moisture content is varied, which was numerically investigated in the present study. Our earlier studies have demonstrated the existence of three different modes of acoustic wave in an elastic porous medium containing two immiscible, viscous, compressible fluids. Based on the dispersion equation obtained in the Lo et al. (2005) model, the phase velocity and attenuation coefficient of the P1 and P2 waves which respectively have the greatest and second greatest speeds were determined for eleven soil texture classes as a function of water saturation. The slowest wave (P3) was not characterized since it does not travel far due to very high attenuation. To provide a more general result, the calculated phase velocity and attenuation coefficient were normalized by those of sand. The normalization leads the resulting dimensionless parameters to be frequency-independent in the whole range (up to 500 Hz) where Darcy's law remains valid for describing each fluid flow under wave excitation. The dimensionless phase velocity of the P1 wave was shown to have a substantially constant value at higher water saturations, but in the lower saturation range it increases to reach a certain maximum value for different soil types and then decreases. The physical parameter controlling the phenomenon is the ratio of two effective non-wetting fluid storativity factors. Numerical results reveal that the dimensionless attenuation coefficient of the P1 wave is sensitive to soil texture and water saturation. Sand and loamy sand have the highest and second highest attenuation coefficients for the P1 wave, respectively. It is also found, with very few exceptions at nearly full saturations, that the magnitude of the dimensionless phase velocity of the P2 wave is linearly associated with the intrinsic permeability, but it relates to the dimensionless attenuation coefficient of the P2 wave in an opposite manner. These results therefore provide a quantitative clue for acoustic wave method to explore the physical properties in the shallow subsurface.
Wave attenuation to clock sojourn times
Colin Benjamin; A. M. Jayannavar
2002-04-01
The subject of time in quantum mechanics is of perennial interest especially because there is no observable for the time taken by a particle to transmit (or reflect) from a particular region. Several methods have been proposed based on scattering phase shifts and using different quantum clocks, where the time taken is clocked by some external input or indirectly from the phase of the scattering amplitudes. In this work we give a general method for calculating conditional sojourn times based on wave attenuation. In this approach clock mechanism does not couple to the Hamiltonian of the system. For simplicity, specific case of a delta dimer is considered in detail. Our analysis re-affirms recent results based on correcting quantum clocks using optical potential methods, albeit in a much simpler way.
Trends in Attenuation Coefficients in Athens, Greece, from 1954 to 1991.
NASA Astrophysics Data System (ADS)
Jacovides, C. P.; Kaltsounides, N. A.; Giannourakos, G. P.; Kallos, G. B.
1995-06-01
Unsworth and Monteith's attenuation coefficient TUM was calculated from midday cloudless sky data in Athens, Greece, for the period 1954 to 1991. An interdependence between TUM and the Linke factor TL was found and is expressed as a mathematical function. It was also shown that the minimum turbidity levels occur during the winter and maximum levels occur during summer. An analysis of the long-term variation of the attenuation coefficients depicts the deterioration of air quality during the same period. The dependence of the ratio of diffuse to global radiation on the attenuation coefficient TUM, is also presented.
NASA Astrophysics Data System (ADS)
Huang, Yimei; Yang, Hongqin; Wang, Yuhua; Zheng, Liqin; Xie, Shusen
2010-11-01
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.
Derivation of linear attenuation coefficients from CT numbers for low-energy photons.
Watanabe, Y
1999-09-01
One can estimate photon attenuation properties from the CT number. In a standard method one assumes that the linear attenuation coefficient is proportional to electron density and ignores its nonlinear dependence on atomic number. When the photon energy is lower than about 50 keV, such as for brachytherapy applications, however, photoelectric absorption and Rayleigh scattering become important. Hence the atomic number must be explicitly considered in estimating the linear attenuation coefficient. In this study we propose a method to more accurately estimate the linear attenuation coefficient of low-energy photons from CT numbers. We formulate an equation that relates the CT number to the electron density and the effective atomic number. We use a CT calibration phantom to determine unknown coefficients in the equation. The equation with a given CT number is then solved for the effective atomic number, which in turn is used to calculate the linear attenuation coefficient for low-energy photons. We use the CT phantom to test the new method. The method significantly improves the standard method in estimating the attenuation coefficient at low photon energies (20 keV < or = E < or = 40 keV) for materials with high atomic numbers. PMID:10495115
Seo, Youngho; Wong, Kenneth H.; Hasegawa, Bruce H. [Physics Research Laboratory, Department of Radiology, University of California, San Francisco, California 94143 (United States); Physics Research Laboratory, Department of Radiology, University of California, San Francisco, California 94143 and Joint Graduate Group in Bioengineering, University of California, San Francisco and Berkeley, California 94143 (United States); Physics Research Laboratory, Department of Radiology, University of California, San Francisco, California 94143, Department of Nuclear Engineering, University of California, Berkeley, California 94720 (United States) and Joint Graduate Group in Bioengineering, University of California, San Francisco and Berkeley, California 94143 (United States)
2005-12-15
Nuclear medicine tracers using {sup 111}In as a radiolabel are increasing in their use, especially in the domain of oncologic imaging. In these applications, it often is critical to have the capability of quantifying radionuclide uptake and being able to relate it to the biological properties of the tumor. However, images from single photon emission computed tomography (SPECT) can be degraded by photon attenuation, photon scattering, and collimator blurring; without compensation for these effects, image quality can be degraded, and accurate and precise quantification is impossible. Although attenuation correction for SPECT is becoming more common, most implementations can only model single energy radionuclides such as {sup 99m}Tc and {sup 123}I. Thus, attenuation correction for {sup 111}In is challenging because it emits two photons (171 and 245 keV) at nearly equal rates (90.2% and 94% emission probabilities). In this paper, we present a method of calculating a single 'effective' attenuation coefficient for the dual-energy emissions of {sup 111}In, and that can be used to correct for photon attenuation in radionuclide images acquired with this radionuclide. Using this methodology, we can derive an effective linear attenuation coefficient {mu}{sub eff} and an effective photon energy E{sub eff} based on the emission probabilities and linear attenuation coefficients of the {sup 111}In photons. This approach allows us to treat the emissions from {sup 111}In as a single photon with an effective energy of 210 keV. We obtained emission projection data from a tank filled with a uniform solution of {sup 111}In. The projection data were reconstructed using an iterative maximum-likelihood algorithm with no attenuation correction, and with attenuation correction assuming photon energies of 171, 245, and 210 keV (the derived E{sub eff}). The reconstructed tomographic images demonstrate that the use of no attenuation correction, or correction assuming photon energies of 171 or 245 keV introduces inaccuracies into the reconstructed radioactivity distribution when compared against the effective energy method. In summary, this work provides both a theoretical framework and experimental methodology of attenuation correction for the dual-energy emissions from {sup 111}In. Although these results are specific to {sup 111}In, the foundation could easily be extended to other multiple-energy isotopes.
Comparison of RNFL thickness and RPE-normalized RNFL attenuation coefficient for glaucoma diagnosis
NASA Astrophysics Data System (ADS)
Vermeer, K. A.; van der Schoot, J.; Lemij, H. G.; de Boer, J. F.
2013-03-01
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.
Seismic Wave Attenuation in the Greater Cairo Region, Egypt
Ahmed Badawy; Mamdouh A. Morsy
2011-01-01
In the present study, a digital waveform dataset of 216 local earthquakes recorded by the Egyptian National Seismic Network\\u000a (ENSN) was used to estimate the attenuation of seismic wave energy in the greater Cairo region. The quality factor and the\\u000a frequency dependence for Coda waves and S-waves were estimated and clarified. The Coda waves (Q\\u000a c) and S-waves (Q\\u000a d)
ERIC Educational Resources Information Center
Wilson, Celia M.
2010-01-01
Research pertaining to the distortion of the squared canonical correlation coefficient has traditionally been limited to the effects of sampling error and associated correction formulas. The purpose of this study was to compare the degree of attenuation of the squared canonical correlation coefficient under varying conditions of score reliability.…
Seismic wave attenuation in carbonates L. Adam,1,2
Boise State University
Seismic wave attenuation in carbonates L. Adam,1,2 M. Batzle,3 K. T. Lewallen,4 and K. van Wijk1100 Hz), attenuation is practically constant for the measured samples. Citation: Adam, L., M. Batzle, K be defined as QÀ1 = Im[M*]/Re[M*], where M* is the complex modulus or velocity; and the imaginary part (Im
NASA Astrophysics Data System (ADS)
Ebru Ermis, Elif; Celiktas, Cuneyt
2015-07-01
Calculations of gamma-ray mass attenuation coefficients of various detector materials (crystals) were carried out by means of FLUKA Monte Carlo (MC) method at different gamma-ray energies. NaI, PVT, GSO, GaAs and CdWO4 detector materials were chosen in the calculations. Calculated coefficients were also compared with the National Institute of Standards and Technology (NIST) values. Obtained results through this method were highly in accordance with those of the NIST values. It was concluded from the study that FLUKA MC method can be an alternative way to calculate the gamma-ray mass attenuation coefficients of the detector materials.
The role of the reflection coefficient in precision measurement of ultrasonic attenuation
NASA Technical Reports Server (NTRS)
Generazio, E. R.
1984-01-01
Ultrasonic attenuation measurements using contact, pulse-echo techniques are sensitive to surface roughness and couplant thickness variations. This can reduce considerable inaccuracies in the measurement of the attenuation coefficient for broadband pulses. Inaccuracies arise from variations in the reflection coefficient at the buffer-couplant-sample interface. The reflection coefficient is examined as a function of the surface roughness and corresponding couplant thickness variations. Interrelations with ultrasonic frequency are illustrated. Reliable attenuation measurements are obtained only when the frequency dependence of the reflection coefficient is incorporated in signal analysis. Data are given for nickel 200 samples and a silicon nitride ceramic bar having surface roughness variations in the 0.3 to 3.0 microns range for signal bandwidths in the 50 to 100 MHz range.
Bubbles cause seismic wave attenuation: Laboratory measurements and numerical simulations
NASA Astrophysics Data System (ADS)
Tisato, Nicola; Quintal, Beatriz; Chapman, Samuel; Podladchikov, Yury; Grasselli, Giovanni; Burg, Jean-Pierre
2015-04-01
Seismic wave attenuation (1/Q) is a key to uncover the saturation and, in general, to improve the monitoring and surveying of subsurface domains. Nevertheless, how fluids that saturate rocks absorb elastic energy (i.e. cause 1/Q) is still poorly understood, studied and incorporated in geophysical methods. One of the invoked mechanisms, wave induced fluid flow (WIFF), is reputed to cause significant attenuation. This mechanism is governed by the flow of viscous fluids into a porous rock, and causes attenuation as a function of the fluid diffusivity [m2/s] and the pressure gradient [Pa/m], which is generated by the propagation of the elastic wave. However, some published, and newly acquired laboratory data-sets reporting 1/Q in almost fully saturated sandstones are difficult to explain with WIFF theories as they are frequency-dependent and have maximum of attenuation at frequencies
Study of photon attenuation coefficients of some multielement materials. [123-1250 keV
Bhandal, G.S. (N.J.S.A. Government Coll., Punjab (India)); Singh, K. (Guru Nanak Dev Univ., Amritsar (India). Dept. of Physics)
1994-03-01
Total photon mass attenuation of six multielement shielding materials (concrete, plaster of paris, quick lime, black cement, white cement, and silica) is measured in the 123- to 1,250-keV energy range. The experimental results are analyzed in terms of cross sections, effective atomic numbers, and electron densities. Considerable sensitivity of the total mass attenuation coefficients and effective atomic numbers to variations in oxygen content are found in these multielement materials.
Investigation of photon attenuation coefficient of some building materials used in Turkey
NASA Astrophysics Data System (ADS)
Dogan, B.; Altinsoy, N.
2015-03-01
In this study, some building materials regularly used in Turkey, such as concrete, gas concrete, pumice and brick have been investigated in terms of mass attenuation coefficient at different gamma-ray energies. Measurements were carried out by gamma spectrometry containing NaI(Tl) detector. Narrow beam gamma-ray transmission geometry was used for the attenuation measurements. The results are in good agreement with the theoretical calculation of XCOM code.
Relative velocity of seagrass blades: Implications for wave attenuation in low-energy environments
NASA Astrophysics Data System (ADS)
Bradley, Kevin; Houser, Chris
2009-03-01
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 meadow and characterize the blade movement under oscillatory flow under the low-energy conditions characteristic of fetch-limited and sheltered environments. The horizontal motion of the seagrass blades and the velocity just above the seagrass canopy were measured using a digital video camera and an acoustic Doppler velicometer (ADV) respectively in order to refine the estimates of the drag coefficient based on the relative velocity. Significant wave heights (Hs) were observed to increase by ˜0.02 m (˜20%) through the first 5 m of the seagrass bed but subsequently decrease exponentially over the remainder of the bed. The exponential decay coefficient varied in response to the Reynolds number calculated using blade width (as the length scale) and the oscillatory velocity measured immediately above the canopy. The ability of the seagrass to attenuate wave energy decreases as incident wave heights increase and conditions become more turbulent. Estimates of the time-averaged canopy height and the calculated hydraulic roughness suggest that, as the oscillatory velocity increases, the seagrass becomes fully extended and leans in the direction of flow for a longer part of the wave cycle. The relationship between the drag coefficient and the Reynolds number further suggests that the vegetation is swaying (going with the flow) at low-energy conditions but becomes increasingly rigid as oscillatory velocities increase over the limited range of the conditions observed (200 < Re < 800). In addition to the changing behavior of the seagrass motion, the attenuation was not uniform with wave frequency, and waves at a secondary frequency of 0.38 Hz (2.6 s) appeared to be unaffected by the seagrass. Cospectral analysis between the oscillatory and blade velocity suggests that the seagrass was moving in phase with the current at the (lower) secondary frequency and out of phase at the (higher) peak frequency. In this respect, seagrass is not only an attenuator of wave energy but also serves as a low-pass filter; higher frequencies in the spectra tend to be more attenuated.
Ex-vivo ultrasound attenuation coefficient for human cervical and uterine tissue from 5 – 10 MHz
Kiss, Miklos Z.; Varghese, Tomy; Kliewer, M.A.
2010-01-01
Attenuation estimation and imaging in the cervix has been utilized to evaluate the onset of cervical ripening during pregnancy. This feature has also been utilized for the acoustic characterization of leiomyomas and myometrial tissue. In this paper, we present direct narrowband substitution measurement values of the variation in the ultrasonic attenuation coefficient in ex vivo human uterine and cervical tissue, in the 5–10 MHz frequency range. At 5 MHz, the attenuation coefficient values are similar for the different orientations of uterine tissue with values of 4.1 – 4.2 dB/cm, 5.1 dB/cm for the leiomyoma, and 6.3 dB/cm for the cervix. As the frequency increases, the attenuation coefficient values increase and are also spread out, with a value of approximately 12.6 dB/cm for the uterus (both parallel and perpendicular), 16.0 for the leiomyoma, and 26.8 dB/cm for the cervix at 10 MHz. The attenuation coefficient measured increases monotonically over the frequency range measured following a power law. PMID:21163508
NASA Astrophysics Data System (ADS)
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
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.
Hirasawa, Takeshi; Fujita, Masanori; Okawa, Shinpei; Kushibiki, Toshihiro; Ishihara, Miya
2013-12-10
A method for quantifying the effective attenuation coefficients of optical absorbers by using the continuous wavelet transform (CWT) to calculate the time-resolved frequency spectra of photoacoustic signals is proposed. Because the coefficients can be quantified according to the relative intensity of the frequency content of the signals, it is unnecessary to determine the fluences. A computational simulation reveals that the time-resolved frequency spectra exhibit better correlation with the coefficients than do power spectra calculated using a Fourier transformation. The CWT-based method was experimentally verified, and the coefficients were quantified with mean square error of 2.0??cm(-1). PMID:24513902
Zhang, Y.; Xu, Y.; Xia, J.
2011-01-01
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.
Stochastic solution to a time-fractional attenuated wave equation
Meerschaert, Mark M.; Straka, Peter; Zhou, Yuzhen; McGough, Robert J.
2012-01-01
The power law wave equation uses two different fractional derivative terms to model wave propagation with power law attenuation. This equation averages complex nonlinear dynamics into a convenient, tractable form with an explicit analytical solution. This paper develops a random walk model to explain the appearance and meaning of the fractional derivative terms in that equation, and discusses an application to medical ultrasound. In the process, a new strictly causal solution to this fractional wave equation is developed. PMID:23258950
Xu, F; Liu, H; Wu, X; Jiang, H; Nordquist, R E; Chen, W R
1999-07-01
We report our experimental results of measurements of x-ray attenuation coefficients of aqueous solutions of a light absorbing dye, indocyanine green, and an immunoadjuvant, glycated chitosan. In the treatment of metastatic tumors in rats using a novel laser immunotherapy these solutions were administered in situ. The x-ray attenuation data of the solutions are essential to development of an x-ray digital imaging system for monitoring the administration of the solution, as well as for the distribution and the diffusion of the solution in tumors and in surrounding tissue. The composition of the solutions, the measurement system configuration, and the technique used to determine the attenuation coefficients are described. The experimental results show that glycated chitosan has a higher attenuation coefficient compared to indocyanine green and water. Our experimental data proved that, even at low concentrations, the x-ray attenuation through these aqueous solutions could be differentiated. Therefore, a digital x-ray imaging technique can be used effectively in monitoring and controlling the intratumor diffusion and distributions of these solutions. PMID:10435540
Pore-Scale Modeling of Pore Structure Effects on P-Wave Scattering Attenuation in Dry Rocks
Li, Tianyang; Qiu, Hao; Wang, Feifei
2015-01-01
Underground rocks usually have complex pore system with a variety of pore types and a wide range of pore size. The effects of pore structure on elastic wave attenuation cannot be neglected. We investigated the pore structure effects on P-wave scattering attenuation in dry rocks by pore-scale modeling based on the wave theory and the similarity principle. Our modeling results indicate that pore size, pore shape (such as aspect ratio), and pore density are important factors influencing P-wave scattering attenuation in porous rocks, and can explain the variation of scattering attenuation at the same porosity. From the perspective of scattering attenuation, porous rocks can safely suit to the long wavelength assumption when the ratio of wavelength to pore size is larger than 15. Under the long wavelength condition, the scattering attenuation coefficient increases as a power function as the pore density increases, and it increases exponentially with the increase in aspect ratio. For a certain porosity, rocks with smaller aspect ratio and/or larger pore size have stronger scattering attenuation. When the pore aspect ratio is larger than 0.5, the variation of scattering attenuation at the same porosity is dominantly caused by pore size and almost independent of the pore aspect ratio. These results lay a foundation for pore structure inversion from elastic wave responses in porous rocks. PMID:25961729
Le, Cheng-Feng; Li, Yun-Mei; Zha, Yong; Sun, De-Yong; Wang, Li-Zhen
2009-02-01
The spectral and chemical analytical data of Taihu Lake water quality in Nov. 8-22, 2007 were used to analyze the spectral characteristics of diffuse attenuation coefficient (Kd) of the water body in autumn and related affecting factors. On the basis of this analysis, the Kd at band 490 nm, Kd (490), was used as a variable to build the relationship between Kd and remote sensing reflectance. The results indicated that within the scope of visible band, the Kd of the water body at most locations of Taihu Lake presented an exponent decreasing trend with the increase of wave length. Due to the higher concentration of phytoplankton in some locations, a peak value of Kd was presented at band 675 nm. Non-organic suspended particles, because of their higher content in suspended sediment, had larger effects on Kd than organic suspended ones. There was a good correlation between Kd and remote sensing reflectance. Taking Rrs (550), Rrs (675) and Rrs (731) as independent variables and doing regression analysis with Kd (490), a good linear relationship was found between Kd (490) and Rrs (731), and multi-variate linear regression analysis using variables Rrs (550), Rrs (675) and Rrs (731) could get better effect (R2 > 0.96) than the regression analysis using variable Rrs (731). PMID:19459373
Guided wave attenuation in pipes buried in sand
NASA Astrophysics Data System (ADS)
Leinov, Eli; Cawley, Peter; Lowe, Michael JS
2015-03-01
Long-range ultrasonic guided wave testing of pipelines is used routinely for detection of corrosion defects in a variety of industries, e.g. petrochemical and energy. When the method is applied to pipelines that are buried in soil, test ranges tend to be significantly compromised compared to those achieved for pipelines above ground because of the attenuation of the guided wave, due to energy leaking into the embedding soil. The attenuation characteristics of guided wave propagation in a pipe buried in sand are investigated using a full scale experimental rig. The apparatus consists of an 8"-diameter, 6-meters long steel pipe embedded over 3 meters in a rectangular container filled with sand and fitted with an air-bladder for the application of overburden pressure. Measurements of the attenuation of the T(0,1) and L(0,2) guided wave modes over a range of sand conditions, including loose, compacted, water saturated and drained, are presented. Attenuation values are found to be in the range of 1-5.5 dB/m. The application of overburden pressure modifies the compaction of the sand and increases the attenuation. The attenuation decreases in the fully water-saturated sand, while it increases in drained sand to values comparable with those obtained for the compacted sand. The attenuation behavior of the torsional guided wave mode is found not to be captured by a uniform soil model; comparison with predictions obtained with the Disperse software suggest that this is likely to be due to a layer of sand adhering to the surface of the pipe.
NASA Astrophysics Data System (ADS)
van der Meer, Freek J.; Perree, Jop; Faber, Dirk J.; Baraznji Bassoon, David M.; Aalders, Maurice C. G.; van Leeuwen, Ton G.
2005-04-01
Imaging of human autopsy samples was performed from the luminal side with a high (3.5 ?m axial and 7 ?m lateral) resolution OCT system (around 800 nm) or a regular (15-20 ?m axial and 20 ?m lateral resolution) OCT system (around 1300 nm). For each sample, dimensions were measured by histomorphometry and OCT and the optical attenuation was measured. Quantitative analysis showed a strong and significant correlation between OCT and histology cap thickness measurements for both OCT systems. For both systems, the measured attenuation coefficients of diffuse intimal thickening and lipid-rich regions differed significantly from media and calcifications. Both the high and regular resolution OCT systems can precisely image the atherosclerotic plaques. Quantitative analysis of the OCT signals allowed in situ determination of the intrinsic optical attenuation coefficient of atherosclerotic tissue components within regions of interest, which can further help to discriminate the plaque and arterial wall components.
Comparison of attenuation coefficients for VVER-440 and VVER-1000 pressure vessels
Marek, M.; Rataj, J.; Vandlik, S. [Reactor Physics Dept., Research Centre Rez, Husinec 130, 25068 (Czech Republic)
2011-07-01
The paper summarizes the attenuation coefficient of the neutron fluence with E > 0.5 MeV through a reactor pressure vessel for vodo-vodyanoi energetichesky reactor (VVER) reactor types measured and/or calculated for mock-up experiments, as well as for operated nuclear power plant (NPP) units. The attenuation coefficient is possible to evaluate directly only by using the retro-dosimetry, based on a combination of the measured activities from the weld sample and concurrent ex-vessel measurement. The available neutron fluence attenuation coefficients (E > 0.5 MeV), calculated and measured at a mock-up experiment simulating the VVER-440-unit conditions, vary from 3.5 to 6.15. A similar situation is used for the calculations and mock-up experiment measurements for the VVER-1000 RPV, where the attenuation coefficient of the neutron fluence varies from 5.99 to 8.85. Because of the difference in calculations for the real units and the mock-up experiments, the necessity to design and perform calculation benchmarks both for VVER-440 and VVER-1000 would be meaningful if the calculation model is designed adequately to a given unit. (authors)
Damla, N; Baltas, H; Celik, A; Kiris, E; Cevik, U
2012-07-01
Some building materials, regularly used in Turkey, such as sand, cement, gas concrete (lightweight, aerated concrete), tile and brick, have been investigated in terms of mass attenuation coefficient (?/?), effective atomic, numbers (Z(eff)), effective electron densities (N(e)) and photon interaction cross section (?(a)) at 14 different energies from 81- to 1332-keV gamma-ray energies. The gamma rays were detected by using gamma-ray spectroscopy, a High Purity Germanium (HPGe) detector. The elemental compositions of samples were analysed using an energy dispersive X-ray fluorescence spectrometer. Mass attenuation coefficients of these samples have been compared with tabulations based upon the results of WinXcom. The theoretical mass attenuation coefficients were estimated using the mixture rule and the experimental values of investigated parameters were compared with the calculated values. The agreement of measured values of mass attenuation coefficient, effective atomic numbers, effective electron densities and photon interaction cross section with the theory has been found to be quite satisfactory. PMID:22128356
NASA Astrophysics Data System (ADS)
Lo, Wei-Cheng; Yeh, Chao-Lung; Jan, Chyan-Deng
2008-08-01
SummaryThe study of the propagation and dissipation of acoustic waves through a fluid-containing porous medium is crucial for the successful application of seismic methods to characterize subsurface hydrological properties. To gain a better understanding of changes in two important acoustic wave characteristics (speed and attenuation) due to the effect of soil texture and excitation frequency, a complex-valued dispersion relation obtained from the Biot theory of poroelasticity was solved numerically for eleven soil texture classes whose pore space is fully saturated by one of two very different fluids, air or water. Two modes of acoustic motion can be demonstrated to exist, known as the Biot fast and slow waves. Five lower excitation frequencies (100-500 Hz) were selected for numerical simulation, below which Darcy's law remains valid for describing porous media flow under wave perturbation. Numerical results show that in the frequency range we examined, the predicted phase speed of the Biot fast wave takes the same value as the Biot reference speed. The variation in speed is not obvious in a water-filled system, but becomes more significant in an air-filled system. When the pore fluid is water, an inverse linear relation exists between the phase speed of the Biot fast wave and porosity. An important physical parameter controlling its attenuation coefficient is intrinsic permeability, which renders a positive impact. A statistical analysis indicates that the attenuation coefficient of the Biot fast wave linearly increases with an increase in intrinsic permeability. In an air-saturated system, the phase speed of the Biot slow wave is found to be quadratically proportional to intrinsic permeability, whereas the attenuation coefficient of the Biot slow wave bears a quadratic relation with the inverse of intrinsic permeability. A study on the influence of pore fluid reveals that the Biot fast wave attenuates more in the water-saturated system than in the air-saturated system; an exception occurs in clay. A reverse trend is observed for the Biot slow wave. As far as the effect of excitation frequency is concerned, the attenuation coefficient of the Biot fast wave is essentially proportional to the square of excitation frequency, whereas the phase speed and attenuation coefficient of the Biot slow wave are both proportional to the square root of excitation frequency. The phase speed of the Biot fast wave is frequency independent.
NASA Astrophysics Data System (ADS)
Richter, Tom; Wegler, Ulrich
2015-04-01
Modeling of peak ground velocity caused by induced earthquakes requires detailed knowledge about seismic attenuation properties of the subsurface. Especially shear wave attenuation is important, because shear waves usually show the largest amplitude in high frequency seismograms. We report intrinsic and scattering attenuation coefficients of shear waves near three geothermal reservoirs in Germany for frequencies between 2 Hz and 50 Hz. The geothermal plants are located in the sedimentary basins of the upper Rhine graben (Insheim and Landau) and the Molasse basin (Unterhaching). The method optimizes the fit between Green's functions for the acoustic, isotropic radiative transfer theory and observed energy densities of induced earthquakes. The inversion allows the determination of scattering and intrinsic attenuation, site corrections, and spectral source energies for the investigated frequency bands. We performed the inversion at the three sites for events with a magnitude between 0.7 and 2. We determined a transport mean free path of 70 km for Unterhaching. For Landau and Insheim the transport mean free path depends on frequency. It ranges from 2 km (at 2 Hz) to 30 km (at 40 Hz) for Landau and from 9 km to 50 km for Insheim. The quality factor for intrinsic attenuation is constant for frequencies smaller than 10 Hz at all three sites. It is around 100 for Unterhaching and 200 for Landau and Insheim with higher values above 10 Hz.
Relating wave attenuation to pancake ice thickness, using field measurements and model results
NASA Astrophysics Data System (ADS)
Doble, Martin J.; De Carolis, Giacomo; Meylan, Michael H.; Bidlot, Jean-Raymond; Wadhams, Peter
2015-06-01
Wave attenuation coefficients (?, m-1) were calculated from in situ data transmitted by custom wave buoys deployed into the advancing pancake ice region of the Weddell Sea. Data cover a 12 day period as the buoy array was first compressed and then dilated under the influence of a passing low-pressure system. Attenuation was found to vary over more than 2 orders of magnitude and to be far higher than that observed in broken-floe marginal ice zones. A clear linear relation between ? and ice thickness was demonstrated, using ice thickness from a novel dynamic/thermodynamic model. A simple expression for ? in terms of wave period and ice thickness was derived, for application in research and operational models. The variation of ? was further investigated with a two-layer viscous model, and a linear relation was found between eddy viscosity in the sub-ice boundary layer and ice thickness.
NASA Astrophysics Data System (ADS)
Cui, Y.; Zou, D. H.
2006-08-01
In this paper, the guided ultrasonic wave propagating in grouted rock bolts was simulated with finite element method. An 800 mm partially grouted cylindrical rock bolt model was created. Dynamic input signals with frequency from 25 to 100 kHz were used to excite ultrasonic wave. The simulated waveform, group velocity and amplitude ratio matched well with the experimental results. This model made it possible to study the behaviour of the guided waves in the grouted bolt along its central axis. Analysis of the simulated results showed that the group velocity in grouted rock bolts is constant along the grouted length, and the boundary effect on the group velocity is negligible. This paper also presents methods to determine the attenuation coefficient from simulation and to determine the boundary effect on attenuation at the bolt ends. The analysis showed that the attenuation of the guided wave propagating inside the grouted bolts is similar to the theoretical solution in steel bar with infinite length. After correction for the boundary effects the grout length of a grouted rock bolt can be determined using the measured attenuation, with sufficient accuracy.
The attenuation of strong shock waves
Kirkpatrick, Ronald Crecelius
1963-01-01
power law of radiation. The convective energy transport appears as turbulence behind the shock front which tends to mix that region so that there is a strong tendency toward equilibrium behind the front. The loss of energy from the shock wave, however... velocity, so that the radiative losses are dependent to a higher degree upon the shock velocity, while the viscous and conduc- tive losses are dependent to a lower degree upon the shock velocity than the energy supporting the shock wave...
Fault-zone attenuation of high-frequency seismic waves
Blakeslee, S.; Malin, P.; Alvarez, M. )
1989-11-01
The authors have developed a technique to measure seismic attenuation within an active fault-zone at seismogenic depths. Utilizing a pair of stations and pairs of earthquakes, spectral ratios are performed to isolate attenuation produced by wave-propagation within the fault-zone. The empirical approach eliminates common source, propagation, instrument and near-surface site effects. The technique was applied to a cluster of 19 earthquakes recorded by a pair of downhole instruments located within the San Andreas fault-zone, at instruments located within the San Andreas fault-zone, at Parkfield, California. Over the 1-40 Hz bandwidth used in this analysis, amplitudes are found to decrease exponentially with frequency. Furthermore, the fault-zone propagation distance correlates with severity of attenuation. Assuming a constant Q attenuation operator, the S-wave quality factor within the fault-zone at a depth of 5-6 kilometers is 31 (+7,{minus}5). If fault-zones are low-Q environments, then near-source attenuation of high-frequency seismic waves may help to explain phenomenon such as f{sub max}. Fault-zone Q may prove to be a valuable indicator of the mechanical behavior and rheology of fault-zones. Specific asperities can be monitored for precursory changes associated with the evolving stress-field within the fault-zone. The spatial and temporal resolution of the technique is fundamentally limited by the uncertainty in earthquake location and the interval time between earthquakes.
Angular correlation function and scattering coefficient of electromagnetic waves
Zhang, Guifu
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
NASA Astrophysics Data System (ADS)
Wang, Lu; Wu, Li-Wei; Wei, Le; Gao, Juan; Sun, Cui-Li; Chai, Pei; Li, Dao-Wu
2014-02-01
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.
NASA Astrophysics Data System (ADS)
Zhang, Shuzeng; Jeong, Hyunjo; Cho, Sungjong; Li, Xiongbing
2015-07-01
A novel method to determine acoustic parameters involved in measuring the nonlinearity parameter of fluids or solids is proposed. The approach is based on the measurement of fundamental and second harmonic pressures with a calibrated receiver, and on a nonlinear least squares data-fitting to multi-Gaussian beam (MGB) equations which explicitly define the attenuation and diffraction effects in the quasilinear regime. Results obtained in water validate the proposed method. The choice of suitable source pressure is discussed with regard to the quasilinear approximation involved. The attenuation coefficients are also acquired in nonlinear regime and their relations are discussed.
Huang, Chang-Chun; Li, Yun-Mei; Sun, De-Yong; Le, Cheng-Feng; Wu, Lan; Wang, Li-Zhen; Wang, Xing
2009-02-15
According to the optical property data measured in Taihu Lake at October and November 2006, the characteristics of the diffuse attenuation coeffcient (Kd), the contribution of each factor effecting on Kd and the effect of Kd on the aquatic ecology environment were analyzed. The results indicate that, the diffuse attenuation coefficient Kd of Taihu Lake has two main trends in the whole visible wavelength range (400-700 nm). The first type is that, Kd decreases with the wavelengths by exponential style in the range of less than 571 nm wavelengths, and the second type is that, Kd is in the form of fluctuations in the range of larger than 571 nm wavelengths. In the range of 400-700 nm wavelength, the absorption coefficient of pigment particles is the first contributors of diffuse attenuation coefficient. Non-pigment particles absorption and scattering coefficients is the second contributor, and the rate of contribution of yellow substance is the smallest. The Kd of Taihu Lake determines the light factor of the Taihu water ecosystem. The "water window" shaped by the Kd provides the light base for different kinds of ecosystem and the appearance of Microcystic aentginosa which is the preponderant algae in the "algal blooms" phenomenon. PMID:19402480
Quantitative RNFL attenuation coefficient measurements by RPE-normalized OCT data
NASA Astrophysics Data System (ADS)
Vermeer, K. A.; van der Schoot, J.; Lemij, H. G.; de Boer, J. F.
2012-03-01
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).
A new instrumentation to measure seismic waves attenuation
NASA Astrophysics Data System (ADS)
Tisato, N.; Madonna, C.; Boutareaud, S.; Burg, J.
2010-12-01
Attenuation of seismic waves is the general expression describing the loss of energy of an elastic perturbation during its propagation in a medium. As a geophysical method, measuring the attenuation of seismic waves is a key to uncover essential information about fluid saturation of buried rocks. Attenuation of seismic waves depends on several mechanisms. In the case of saturated rock, fluids play an important role. Seismic waves create zones of overpressure by mobilizing the fluids in the pores of the rock. Starting from Gassmann-Biot theory (Gassman, 1951), several models (e.g. White, 1975; Mavko and Jizba, 1991) have been formulated to describe the energy absorption by flow of fluids. According to Mavko et al. (1998) for rock with permeability equals or less than 1 D, fluid viscosity between 1 cP and 10 cP and low frequencies seismic wave (< 100 Hz), the most important processes that subtract energy from the seismic waves are squirt flow and patchy saturation. Numerical models like Quintal et al. (2009) calculate how a patchy saturated vertical rock section (25 cm height), after stress steps of several kPa (i.e. 30 kPa) show a dissimilar increase in pore pressure between gas-saturated and liquid-saturated layers. The Rock Deformation Laboratory at ETH-Zürich has designed and set up a new pressure vessel to measure seismic wave attenuation in rocks at frequencies between 0.1 and 100 Hz and to verify the predicted influence of seismic waves on the pore pressure in patchy saturated rocks. We present this pressure vessel which can reach confining pressures of 25 MPa and holds a 250 mm long and 76 mm diameter sample. Dynamic stress is applied at the top of the rock cylinder by a piezoelectric motor that can generate a stress of several kPa (> 100 KPa) in less than 10 ms. The vessel is equipped with 5 pressure sensors buried within the rock sample, a load cell and a strain sensor to measure axial shortening while the motor generates the seismic waves. The sensor conditioning system has been designed and realized by us and the acquisition software has been developed in Matlab. We present the first results, at room pressure and temperature, based on the measurements of pore fluid pressure increase in a sandstone sample with a permeability of 200 to 500 mD and partially saturated with water and air. These preliminary results show the reliability of this new instrumentation to measure seismic wave attenuation at low frequency and to verify the pore fluid flow driven by seismic waves.
Developing a Short-Period, Fundamental-Mode Rayleigh-Wave Attenuation Model for Asia
NASA Astrophysics Data System (ADS)
Yang, X.; Levshin, A. L.; Barmin, M. P.; Ritzwoller, M. H.
2008-12-01
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.
Flock, S.T.; Wilson, B.C.; Patterson, M.S.
1987-09-01
Measurements have been made of the total attenuation coefficient sigma t and the scattering phase function, S(theta), of 632.8 nm of light for a number of animal model tissues, blood, and inert scattering and absorbing media. Polystyrene microspheres of known size and refractive index, for which sigma t and S(theta) can be calculated by Mie theory, were used to test the experimental methods. The purpose of the study was to define typical ranges for these optical properties of tissues, as a contribution to the development of experimental and theoretical methods of light dosimetry in tissue, particularly related to photodynamic therapy of solid tumors. The results demonstrate that, for the representative tissues studied, the total attenuation coefficients are of the order of 10-100 mm-1, and that the scattering is highly forward peaked, with average cosine of scatter in the range 0.6-0.97.
Flock, S T; Wilson, B C; Patterson, M S
1987-01-01
Measurements have been made of the total attenuation coefficient sigma t and the scattering phase function, S(theta), of 632.8 nm of light for a number of animal model tissues, blood, and inert scattering and absorbing media. Polystyrene microspheres of known size and refractive index, for which sigma t and S(theta) can be calculated by Mie theory, were used to test the experimental methods. The purpose of the study was to define typical ranges for these optical properties of tissues, as a contribution to the development of experimental and theoretical methods of light dosimetry in tissue, particularly related to photodynamic therapy of solid tumors. The results demonstrate that, for the representative tissues studied, the total attenuation coefficients are of the order of 10-100 mm-1, and that the scattering is highly forward peaked, with average cosine of scatter in the range 0.6-0.97. PMID:3683313
Mass attenuation coefficients of X-rays in different medicinal plants.
Morabad, R B; Kerur, B R
2010-02-01
The mass attenuation coefficients of specific parts of several plants, (fruits, leaves, stem and seeds) often used as medicines in the Indian herbal system, have been measured employing NaI (TI)) detector. The electronic setup used is a NaI (TI) detector, which is coupled to MCA for analysis of the spectrum. A source of (241)Am is used to get X-rays in the energy range 8-32keV from Cu, Rb, Mo, Ag and Ba targets. In the present study, the measured mass attenuation coefficient of Ocimum sanctum, Catharanthus roseus, Trigonella foenum-graecum, Azadirachta indica, Aegle marmelos, Zingiber officinalis, Emblica officinalis, Anacardium occidentale, Momordica charantia and Syzygium cumini show a linear relation with the energy. PMID:19910203
Sharma, R C; Haridasan, T K
1999-08-01
Total linear attenuation coefficients of three tissue equivalent materials differing in their fat contents were experimentally determined for low energy photons in the range 13-51 keV. It is found that their variations with photon energy for each of these materials are describable by two distinct power functions with the validity ranges being (13-23 keV) and (32-51 keV), respectively. Therefore, to adequately represent the variation of total linear attenuation coefficients over the full photon energy range i.e., 13-51 keV, a sum of two power functions is needed. Least squares fitted equations to the entire experimental data are thus included. For muscle, the experimental data show a reasonably good agreement with the theoretically computed values that are available in literature. PMID:12877342
Bubbles attenuate elastic waves at seismic frequencies: First experimental evidence
NASA Astrophysics Data System (ADS)
Tisato, Nicola; Quintal, Beatriz; Chapman, Samuel; Podladchikov, Yury; Burg, Jean-Pierre
2015-05-01
The migration of gases from deep to shallow reservoirs can cause damageable events. For instance, some gases can pollute the biosphere or trigger explosions and eruptions. Seismic tomography may be employed to map the accumulation of subsurface bubble-bearing fluids to help mitigating such hazards. Nevertheless, how gas bubbles modify seismic waves is still unclear. We show that saturated rocks strongly attenuate seismic waves when gas bubbles occupy part of the pore space. Laboratory measurements of elastic wave attenuation at frequencies <100 Hz are modeled with a dynamic gas dissolution theory demonstrating that the observed frequency-dependent attenuation is caused by wave-induced-gas-exsolution-dissolution (WIGED). This result is incorporated into a numerical model simulating the propagation of seismic waves in a subsurface domain containing CO2-gas bubbles. This simulation shows that WIGED can significantly modify the wavefield and illustrates how accounting for this physical mechanism can potentially improve the monitoring and surveying of gas bubble-bearing fluids in the subsurface.
Correlation equation for the marine drag coefficient and wave steepness
NASA Astrophysics Data System (ADS)
Foreman, Richard J.; Emeis, Stefan
2012-09-01
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.
NASA Astrophysics Data System (ADS)
Dreischuh, Tanja N.; Gurdev, Ljuan L.; Vankov, Orlin I.; Avramov, Lachezar A.; Stoyanov, Dimitar V.
2015-01-01
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.
Mass attenuation coefficients of X-rays in different medicinal plants
R. B. Morabad; B. R. Kerur
2010-01-01
The mass attenuation coefficients of specific parts of several plants, (fruits, leaves, stem and seeds) often used as medicines in the Indian herbal system, have been measured employing NaI (TI)) detector. The electronic setup used is a NaI (TI) detector, which is coupled to MCA for analysis of the spectrum. A source of 241Am is used to get X-rays in
Frequency-Dependent Attenuation of Coda Waves in the Crust in Southwest Anatolia (Turkey)
NASA Astrophysics Data System (ADS)
?ahin, ?akir; Çinar, Mutlu
2014-07-01
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.
Lateral variations of coda wave attenuation in the Alps
NASA Astrophysics Data System (ADS)
Mayor, Jessie; Calvet, Marie; Margerin, Ludovic; Traversa, Paola
2014-05-01
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.
Panin, V Y; Aykac, M; Casey, M E
2013-06-01
The simultaneous PET data reconstruction of emission activity and attenuation coefficient distribution is presented, where the attenuation image is constrained by exploiting an external transmission source. Data are acquired in time-of-flight (TOF) mode, allowing in principle for separation of emission and transmission data. Nevertheless, here all data are reconstructed at once, eliminating the need to trace the position of the transmission source in sinogram space. Contamination of emission data by the transmission source and vice versa is naturally modeled. Attenuated emission activity data also provide additional information about object attenuation coefficient values. The algorithm alternates between attenuation and emission activity image updates. We also proposed a method of estimation of spatial scatter distribution from the transmission source by incorporating knowledge about the expected range of attenuation map values. The reconstruction of experimental data from the Siemens mCT scanner suggests that simultaneous reconstruction improves attenuation map image quality, as compared to when data are separated. In the presented example, the attenuation map image noise was reduced and non-uniformity artifacts that occurred due to scatter estimation were suppressed. On the other hand, the use of transmission data stabilizes attenuation coefficient distribution reconstruction from TOF emission data alone. The example of improving emission images by refining a CT-based patient attenuation map is presented, revealing potential benefits of simultaneous CT and PET data reconstruction. PMID:23648397
Wave attenuation over coastal salt marshes under storm surge conditions
NASA Astrophysics Data System (ADS)
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
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.
Lateral Variations of Coda Wave Attenuation in the Alps
NASA Astrophysics Data System (ADS)
Mayor, J.; Margerin, L.; Calvet, M.; Traversa, P.
2014-12-01
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. 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 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.
Stress wave attenuation in thin structures by ultrasonic through-transmission
NASA Technical Reports Server (NTRS)
Lee, S. S.; Williams, J. H., Jr.
1980-01-01
The steady state amplitude of the output of an ultrasonic through transmission measurement is analyzed and the result is given in closed form. Provided that the product of the input and output transduction ratios; the specimen-transducer reflection coefficient; the specimen-transducer phase shift parameter; and the material phase velocity are known, this analysis gives a means for determining the through-thickness attenuation of an individual thin sample. Multiple stress wave reflections are taken into account and so signal echoes do not represent a difficulty. An example is presented for a graphite fiber epoxy composite (Hercules AS/3501-6). A direct method for continuous or intermittent monitoring of through thickness attenuation of plate structures which may be subject to service structural degradation is provided.
Stress-wave attenuation in thin structures by ultrasonic through-transmission
NASA Technical Reports Server (NTRS)
Lee, S. S.; Williams, J. H., Jr.
1980-01-01
The steady-state amplitude of the output of an ultrasonic through-transmission measurement is analyzed and the result is given in closed form. Provided that the product of the input and output transduction ratios, the specimen-transducer reflection coefficient, the specimen-transducer phase-shift parameter, and the material phase velocity are known, this analysis gives a means for determining the through-thickness attenuation of an individual thin sample. Multiple stress-wave reflections are taken into account, and so signal echoes do not represent a difficulty. An example is presented for a graphite fiber epoxy composite (Hercules AS/3501-6). Thus, the technique provides a direct method for continuous or intermittent monitoring of through-thickness attenuation of plate structures which may be subject to service structural degradation.
NASA Astrophysics Data System (ADS)
Du, Shan; Shehata, Mohamed; Badawy, Wael; Rahman, Choudhury A.
2013-03-01
In this paper, we proposed a discrete cosine transform (DCT)-based attnuation and accentuation method to remove lighting effects on face images for faciliating face recognition task under varying lighting conditions. In the proposed method, logorithm transform is first used to convert a face image into logarithm domain. Then discrete cosine transform is applied to obtain DCT coefficients. The low-frequency DCT coefficients are attenuated since illumination variations mainly concentrate on the low-frequency band. The high-frequency coefficients are accentuated since when under poor illuminations, the high-frequency features become more important in recognition. The reconstructed log image by inverse DCT of the modified coefficients is used for the final recognition. Experiments are conducted on the Yale B database, the combination of Yale B and Extended Yale B databases and the CMU-PIE database. The proposed method does not require modeling and model fitting steps. It can be directly applied to single face image, without any prior information of 3D shape or light sources.
Linear attenuation coefficients of tissues from 1 keV to 150 keV
NASA Astrophysics Data System (ADS)
Böke, Aysun
2014-09-01
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.
Remote sensing of the diffuse attenuation coefficient of ocean water. [coastal zone color scanner
NASA Technical Reports Server (NTRS)
Austin, R. W.
1981-01-01
A technique was devised which uses remotely sensed spectral radiances from the sea to assess the optical diffuse attenuation coefficient, K (lambda) of near-surface ocean water. With spectral image data from a sensor such as the coastal zone color scanner (CZCS) carried on NIMBUS-7, it is possible to rapidly compute the K (lambda) fields for large ocean areas and obtain K "images" which show synoptic, spatial distribution of this attenuation coefficient. The technique utilizes a relationship that has been determined between the value of K and the ratio of the upwelling radiances leaving the sea surface at two wavelengths. The relationship was developed to provide an algorithm for inferring K from the radiance images obtained by the CZCS, thus the wavelengths were selected from those used by this sensor, viz., 443, 520, 550 and 670 nm. The majority of the radiance arriving at the spacecraft is the result of scattering in the atmospheric and is unrelated to the radiance signal generated by the water. A necessary step in the processing of the data received by the sensor is, therefore, the effective removal of these atmospheric path radiance signals before the K algorithm is applied. Examples of the efficacy of these removal techniques are given together with examples of the spatial distributions of K in several ocean areas.
Montes, Martin A; Churnside, James; Lee, Zhongping; Gould, Richard; Arnone, Robert; Weidemann, Alan
2011-06-20
Relationships between the satellite-derived diffuse attenuation coefficient of downwelling irradiance (K(d)) and airborne-based vertical attenuation of lidar volume backscattering (?) were examined in two coastal environments. At 1.1 km resolution and a wavelength of 532 nm, we found a greater connection between ? and K(d) when ? was computed below 2 m depth (Spearman rank correlation coefficient up to 0.96), and a larger contribution of K(d) to ? with respect to the beam attenuation coefficient as estimated from lidar measurements and K(d) models. Our results suggest that concurrent passive and active optical measurements can be used to estimate total scattering coefficient and backscattering efficiency in waters without optical vertical structure. PMID:21691366
Attenuation of wave in a thin plasma layer by finite-difference time-domain analysis
Minghai Liu; Xiwei Hu; Zhonghe Jiang; Shu Zhang; Chaohui Lan
2007-01-01
The attenuation of the electromagnetic wave in a thin plasma layer at high pressure is investigated with finite-difference time-domain method. The effects of the plasma thickness, plasma density distribution function, collision frequency between electron and neutrals, and the frequency of incident wave on the attenuation of the electromagnetic wave are discussed. Numerical results indicate that the phase shift is sensitive
Wave dispersion and attenuation on human femur tissue.
Strantza, Maria; Louis, Olivia; Polyzos, Demosthenes; Boulpaep, Frans; van Hemelrijck, Danny; Aggelis, Dimitrios G
2014-01-01
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
Wave velocity dispersion and attenuation in media exhibiting internal oscillations
NASA Astrophysics Data System (ADS)
Frehner, Marcel; Steeb, Holger; Schmalholz, Stefan M.
2010-05-01
Understanding the dynamical and acoustical behavior of porous and heterogeneous rocks is of great importance in geophysics, e.g. earthquakes, and for various seismic engineering applications, e.g. hydrocarbon exploration. Within a heterogeneous medium oscillations with a characteristic resonance frequency, depending on the mass and internal length of the heterogeneity, can occur. When excited, heterogeneities can self-oscillate with their natural frequency. Another example of internal oscillations is the dynamical behavior of non-wetting fluid blobs or fluid patches in residually saturated pore spaces. Surface tension forces or capillary forces act as the restoring force that drives the oscillation. Whatever mechanism is involved, an oscillatory phenomena within a heterogeneous medium will have an effect on acoustic or seismic waves propagating through such a medium, i.e. wave velocity dispersion and frequency-dependent attenuation. We present two models for media exhibiting internal oscillations and discuss the frequency-dependent wave propagation mechanism. Both models give similar results: (1) The low-frequency (i.e. quasi-static) limit for the phase velocity is identical with the Gassmann-Wood limit and the high-frequency limit is larger than this value and (2) Around the resonance frequency a very strong phase velocity change and the largest attenuation occurs. (1) Model for a homogeneous medium exhibiting internal oscillations We present a continuum model for an acoustic medium exhibiting internal damped oscillations. The obvious application of this model is water containing oscillating gas bubbles, providing the material and model parameters for this study. Two physically based momentum interaction terms between the two inherent constituents are used: (1) A purely elastic term of oscillatory nature that scales with the volume of the bubbles and (2) A viscous term that scales with the specific surface of the bubble. The model is capable of taking into account an arbitrary number of oscillators with different resonance frequencies. Exemplarily, we show a log-normal distribution of resonance frequencies. Such a distribution changes the acoustic properties significantly compared to the case with only one resonance frequency. The dispersion and attenuation resulting from our model agree well with the dispersion and attenuation (1) derived with a more exact mathematical treatment and (2) measured in laboratory experiments. (2) Three-phase model for residually saturated porous media We present a three-phase model describing wave propagation phenomena in residually saturated porous media. The model consists of a continuous non-wetting phase and a discontinuous wetting phase and is an extension of classical biphasic (Biot-type) models. The model includes resonance effects of single liquid bridges or liquid clusters with miscellaneous eigenfrequencies taking into account a visco-elastic restoring force (pinned oscillations and/or sliding motion of the contact line). In the present investigation, our aim is to study attenuation due to fluid oscillations and due to wave-induced flow with a macroscopic three-phase continuum model, i.e. a mixture consisting of one solid constituent building the elastic skeleton and two immiscible fluid constituents. Furthermore, we study monochromatic waves in transversal and longitudinal direction and discuss the resulting dispersion relations for a typical reservoir sandstone equivalent (Berea sandstone).
Seismic attenuation due to wave-induced flow
Pride, S.R.; Berryman, J.G.; Harris, J.M.
2003-10-09
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.
Attenuation of High-Frequency Seismic Waves in Eastern Iran
NASA Astrophysics Data System (ADS)
Mahood, M.
2014-09-01
We investigated the frequency-dependent attenuation of the crust in Eastern Iran by analysis data from 132 local earthquakes having focal depths in the range of 5-25 km. We estimated the quality factor of coda waves ( Q c) and body waves ( Q p and Q s) in the frequency band of 1.5-24 Hz by applying the single backscattering theory of S-coda envelopes and the extended coda-normalization method, respectively. Considering records from recent earthquakes (Rigan M w 6.5, 2010/12/20, Goharan M w 6.2, 2013/5/11 and Sirch M w 5.5, 2013/1/21), the estimated values of Q c, Q p and Q s vary from 151 ± 49, 63 ± 6, and 93 ± 14 at 1.5 Hz to 1,994 ± 124, 945 ± 84 and 1,520 ± 123 at 24 Hz, respectively. The average frequency-dependent relationships ( Q = Q o f n ) estimated for the region are Q c = (108 ± 10) f (0.96±0.01), Q p = (50 ± 5) f (1.01±0.04), and Q s = (75 ± 6) f (1.03±0.06). These results evidenced a frequency dependence of the quality factors Q c, Q p, and Q s, as commonly observed in tectonically active zones characterized by a high degree of heterogeneity, and the low value of Q indicated an attenuative crust beneath the entire region.
NASA Astrophysics Data System (ADS)
Houser, C.; Hill, P. R.
2010-12-01
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.
NASA Astrophysics Data System (ADS)
Hummel, Johann; Semturs, Friedrich; Menhart, Susanne; Figl, Michael
2010-04-01
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.
Lg waves attenuation studies over the Iranian Plateau and Zagros
NASA Astrophysics Data System (ADS)
Kaviani, A.; Sandvol, E. A.; Rumpker, G.; Ku, W.; Gok, R.
2012-12-01
Waveforms from regional events collected over the last 15 years by the permanent seismological networks and temporary deployments deployed within the Iranian plateau provide a unique and unprecedented opportunity to investigate the crustal and mantle attenuation characteristics by analysis of the regional phases including Lg and Pg waves. We have investigated the crustal attenuation using Lg waveforms available from 305 stations consisting of 101 permanent and 204 temporary stations. This study is performed within the framework of a larger project aimed at developing high-resolution seismic attenuation models for the Iranian plateau and the Zagros mountains using different data and approaches. We have combined the Iranian data set with data from numerous networks across Turkey, Georgia, Azerbaijan, Syria, Jordan, and Saudi Arabia. This combination provides us with waveforms from over 550 stations spanning most of the Northern Middle East. Simultaneous inversion of the Lg Q values calculated using two-station paths gives us a model of Lg Q that extends from the western Anatolian plate to the eastern edge of the Iranian plateau. Prior studies have suggested strong complexity in the crustal and uppermost mantle attenuation structure beneath much of the Iranian plateau and the surrounding regions. Lg waves propagating over different paths in this region show strong variations in amplitude and frequency content due to this very complex structure. We have created a frequency dependent Lg Q model that covers most of the Iranian plateau using instrument corrected two station method that eliminates the contributions from the source. Our model maps Lg Q around 200 for most part of the central Iranian plateau and Alborz mountains whereas it is lower than 150 for the western Anatolian plateau. Relatively high Q values (>300) are observed in the Zagros belt that abruptly changes across the Zagros suture. We have also found unexpected results, including a high Q zone that surrounds the Caspian Sea. We argue that it originates from energy that is bending around the south Caspian Sea oceanic crust as well as efficient Lg propagation through the Alborz mountain crust.
NASA Astrophysics Data System (ADS)
Lo, WeiCheng; Lee, JheWei; Lee, ChengHaw
2015-04-01
A central issue in the theoretical treatment of a multiphase system is the proper mathematical description of momentum transfer across fluid-solid and fluid-fluid interfaces. Although recent studies have advanced our knowledge on modeling the coupling behavior between a porous framework and the fluids permeating it, the effect of viscous resistance caused by two-fluid flow on elastic wave behavior in unsaturated porous media still remains unaddressed. In the present study, we generalize the theory of dynamic poroelasticity to incorporate viscous cross coupling arising from the velocity difference between two adjacent fluids for examining the dynamic behavior of fluid flow in deformable porous media related to harmonic wave perturbation. The corresponding dispersion relations that characterize three compressional waves and one shear wave are precisely formulated, with the coefficients featuring all elasticity, inertial coupling, and viscous coupling parameters, for describing how wave number changes as excitation frequency is stipulated. To evaluate quantitatively this as-yet unknown effect, numerical simulations are implemented to solve the dispersion relations for Columbia fine sandy loam bearing an oil-water mixture with respect to three representative wave excitation frequencies. Our results show that the phase speed and attenuation coefficient of the third compressional wave which has the smallest speed is strongly sensitive to the presence of viscous cross coupling, as expected for this wave being attributed primarily to the out-of-phase motion of the two pore fluids. Viscous cross coupling also exerts an impact on the attenuation coefficient of the shear wave and the first compressional wave whose speed is greatest, which exhibits two opposite trends at different ranges of low and high water contents. A sensitivity analysis is further conducted to provide information on the importance of the coupling parameter, revealing that the effect becomes more significant as the coupling is stronger.
Evaluation of coastal wave attenuation due to viscous fluid sediment at Jefferson County, Texas
Tuttle, Meghan I
2000-01-01
between field conditions and model limitations. The model produces wave attenuation in excess of actual beach conditions. An empirical formula is evaluated for this region and shows good correlation. Damping varies with water depth and wave amplitude...
NASA Astrophysics Data System (ADS)
Kheireddine, Malika; Antoine, David
2014-08-01
The diel variability of the particulate beam attenuation coefficient, cp, and of the particulate backscattering coefficient, bbp, were investigated during five seasonal cycles at an oceanic site in the northwestern Mediterranean Sea, covering contrasting physical and trophic situations. We observed a diel cycle in cp and bbp, related to changes in phytoplankton properties (i.e., size and refractive index) induced by the accumulation of carbon within phytoplankton cells associated with photosynthetic processes, during the winter mixing of the water column, the development of the spring phytoplankton bloom, its decline, and during the summer oligotrophy. The relative amplitude of the cp diel variability was much larger during the spring bloom (20-50%) than during other seasons (10-20%), whereas that of bbp is steadily around 20% and does not show significant seasonal variability. The minimal cp and bbp occurred at sunrise and are synchronized, whereas maximum bbp values are often reached 3-6 h before those for cp (except during bloom conditions), which occur near sunset. These different amplitudes and timing are tentatively explained using Mie computations, which allow discerning the respective roles of changes in the particle size distribution and refractive index. The differences observed here in the diel cycles of cp and bbp show that they cannot be used interchangeably to determine the daily increase of the particle pool. This result has implications on the feasibility to determine net community production from the bbp diel changes, when only bbp is measured in situ or available from ocean color observations.
Seismic waves attenuation in the lithosphere of the northern Basin and Range Province
NASA Astrophysics Data System (ADS)
Dobrynina, Anna
2013-04-01
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.
Prego-Borges, José L; Zamboni-Rached, Michel; Recami, Erasmo; Costa, Eduardo Tavares
2014-08-01
The so-called Localized Waves (LW), and the "Frozen Waves" (FW), have raised significant attention in the areas of Optics and Ultrasound, because of their surprising energy localization properties. The LWs resist the effects of diffraction for large distances, and possess an interesting self-reconstruction -self-healing- property (after obstacles with size smaller than the antenna's); while the FWs, a sub-class of LWs, offer the possibility of arbitrarily modeling the longitudinal field intensity pattern inside a prefixed interval, for instance 0?z?L, of the wave propagation axis. More specifically, the FWs are localized fields "at rest", that is, with a static envelope (within which only the carrier wave propagates), and can be endowed moreover with a high transverse localization. In this paper we investigate, by simulated experiments, various cases of generation of ultrasonic FW fields, with the frequency of f0=1 MHz in a water-like medium, taking account of the effects of attenuation. We present results of FWs for distances up to L=80 mm, in attenuating media with absorption coefficient ? in the range 70???170 dB/m. Such simulated FW fields are constructed by using a procedure developed by us, via appropriate finite superpositions of monochromatic ultrasonic Bessel beams. We pay due attention to the selection of the FW parameters, constrained by the rather tight restrictions imposed by experimental Acoustics, as well as to some practical implications of the transducer design. The energy localization properties of the Frozen Waves can find application even in many medical apparatus, such as bistouries or acoustic tweezers, as well as for treatment of diseased tissues (in particular, for the destruction of tumor cells, without affecting the surrounding tissues; also for kidney stone shuttering, etc.). PMID:24709072
FURTHER INVESTIGATION OF PARAMETERS AFFECTING WATER HAMMER WAVE ATTENUATION, SHAPE AND TIMING
Eindhoven, Technische Universiteit
FURTHER INVESTIGATION OF PARAMETERS AFFECTING WATER HAMMER WAVE ATTENUATION, SHAPE AND TIMING PART that may affect water hammer wave attenuation, shape and timing (Bergant and Tijsseling 2001). New sources that may affect the waveform predicted by classical water hammer theory include viscoelastic behaviour
Parameters Affecting Water Hammer Wave Attenuation, Shape by Anton Bergant1
Eindhoven, Technische Universiteit
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 sources that may affect the waveform predicted by the classical water hammer theory include unsteady
Diffuse Attenuation Coefficient of Downwelling Irradiance: An Evaluation of Remote Sensing Methods
NASA Technical Reports Server (NTRS)
Lee, Zhong-Ping; Darecki, Miroslaw; Carder, Kendall L.; Davis, Curtiss O.; Stramski, Dariusz; Rhea, W. Joseph
2005-01-01
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.
Hoge, Frank E
2006-04-01
It is shown that the oceanic beam attenuation coefficient can be retrieved from airborne laser-induced and depth-resolved chromophoric dissolved organic matter (CDOM) fluorescence. The radiative transfer equation (RTE) retrieval methodology does not require a laser beam spread function model since two CDOM fluorescence bands are used in conjunction with a beam attenuation spectral model, is self-normalizing since the CDOM absorption coefficient and laser beam irradiance are common to both fluorescence observational channels, and is enabled by the known isotropic phase function for CDOM fluorescence. Although this RTE analytical inversion theory is exact, the retrieval uncertainty is reduced by configuring the proposed lidar in the multiple-field-of-view beam attenuation mode to significantly diminish observation of multiple scattering. The theory can be applied over wide regions of the ocean's continental margins, estuaries, lakes, and rivers that are known to have sufficient CDOM. PMID:16608003
Lee, Cheng-Kuang; Tsai, Meng-Tsan; Chang, Feng-Yu; Yang, Chih-Hsun; Shen, Su-Chin; Yuan, Ouyang; Yang, Chih-He
2013-01-01
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
Attenuation coefficient of the light in skin of BALB/c and C57BL/6 mice
NASA Astrophysics Data System (ADS)
Silva, C. R.; Camargo, C. F. M.; Aureliano, D. P.; De Pretto, L. R.; Freitas, A. Z.; Ribeiro, M. S.
2015-06-01
Optical properties of the biological tissue play an important role to a correct use of optical techniques for therapy and diagnosis. The mice skin presents morphological differences due to characteristics such as gender, body mass and age. Murine models are frequently used in pre-clinical trials in optical therapy and diagnosis. Therefore, the assessment of the skin tissue in animal models is needed for a proper understanding of how light interacts with skin. Noninvasive techniques such as optical coherence tomography (OCT) have been used to obtain optical information of the tissue, as the attenuation coefficient, with the advantage of obtaining sectional images in real time. In this study, eight female BALB/c albino mice (twenty-four weeks old) and eight male C57BL/6 black mice (eight weeks old) were used to measure the attenuation coefficient of the light in the skin, utilizing the OCT technique, aiming to check for influence of the aging process. Two moments were assessed twenty-two weeks apart from each other. Our data show that the aging process significantly affects the light attenuation coefficient in mice skin. Twenty-two weeks after, statistical significant differences were observed between groups within a same strain. We conclude that light attenuation coefficient of mice skin may be influenced by factors such as disorganization of the dermis. Morphological aspects of skin should be taken into account in studies that involve optical strategies in murine models.
Attenuation of groundwater pressure due to surface waves.
NASA Astrophysics Data System (ADS)
Przyborska, Anna
2010-05-01
For tideless seas, the groundwater flow in shallow water is governed entirely by the surface wave dynamics on the beach. As waves propagate towards the shore, they become steeper owing to the decreasing water depth and at some depth, the waves lose their stability and start to break. When waves break, waves energy is dissipated and the spatial changes of the radiation stress give rise to changes in the mean sea level, known as the set_up. Longuet-Higgins demonstrated that the mean on-shore pressure gradient due to wave set_up driver a groundwater circulation within the beach zone. Water infiltrates into the coastal aquifer on the upper part of the beach near the maximum run_up, and exfiltration occurs on the lower part of the beach face near the breaking point. The velocity of the flow as well as the amount of water circulation within the permeable beach is important for the biological status of the organisms inhabiting the beach sand, transporting organic matter and dissolved oxygen to beach body , influence on sediment transport at shallow waters and stability of engineering structures. The paper is organized in two main parts. The first part of the paper is dedicated to the formulation of the mathematical model for attenuation of pore pressure in shallow water zone when wave breaking is present. Solution of system of nonlinear equations for wave propagation on permeable beach is compared with experimental data. The main purpose of the experimental part of the paper is dealing with the analysis of sets of good quality data on pore pressure data which will serve for comparison with theoretical results. In particular, two set of data are discussed, namely data obtained during measurements in the shallow water at the Coastal Station Lubiatowo (Poland) in Southern Baltic Sea and data from the large scale laboratory experiments in the Grossen Wallenkanal in Hannover (Germany). In the first case, the set of transmittance functions between the surface waves and pore pressure in the soil at various levels and transmittance functions between the pressures recorded at different levels are compared with the developed theory. During the laboratory experiment in Hannover two components of pore pressure were clearly distinguished i.e. in the zone of non-breaking waves only so called phase resolving component induced by surface waves is observed and in the surf zone two types of pore pressure are present : phase resolving and so called phase averaged , induced by set-up phenomena (mean water level rising). The total pressure recorded by the pressure gauges is a summation of the phase-averaged and the phase-resolving components. The pore pressure gradients provide also valuable information on the kinematics of groundwater flow in the beach body. In the experiment we are not able to measure the flow velocity in a straightforward manner, but the flow velocity can be estimated from the recorded pressure gradients using the formulas resulting from the theoretical solution.
NASA Astrophysics Data System (ADS)
Akimov, A. A.; Ivakhnik, V. V.; Nikonov, V. I.
2015-01-01
We have obtained the dependences of the conversion coefficient and the bandwidth of spatial frequencies on the intensity of pump waves for a four-wave converter of radiation for the resonance and thermal nonlinearity in a scheme with concurrent pump waves. The connection between the conversion coefficient and spatial selectivity of a four-wave radiation converter has been found.
Attenuation characteristics of coda waves in Mainland Gujarat (India)
NASA Astrophysics Data System (ADS)
Gupta, Arun K.; Sutar, Anup K.; Chopra, Sumer; Kumar, Santosh; Rastogi, B. K.
2012-03-01
The attenuation characteristics based on coda waves of Mainland Gujarat (India) have been investigated in the present study. The broadband waveforms of 53 local earthquakes (Mw 1.1-3.3) having focal depths in the 6.0-33.6 km range recorded at five stations of Mainland Gujarat region has been used for the analysis. The frequency-dependent relationships (Q = Q0fn) for coda-Q (Qc) and dependency of coda-Q on lapse time windows have been determined for the said region. The average lapse time dependent coda-Q relations estimated for the region are: Qc = (87 ± 13)f(1.01 ± 0.06) (lapse time: 30 s), Qc = (112 ± 20)f(0.94 ± 0.08) (lapse time: 40 s) and Qc = (120 ± 22)f(0.76 ± 0.07) (lapse time: 50 s). The increase in Qc values with lapse time shows the depth dependence of Qc as longer lapse time windows will sample larger area. The observed quality factor is strongly dependent on frequency and lapse time, which indicates that the upper lithosphere, is more heterogeneous and seismotectonically active, while the lower lithosphere is homogeneous and relatively less active. A comparison of the coda-Q estimated for Mainland Gujarat region with those of nearby Kachchh and Saurashtra regions shows that Mainland Gujarat region is more heterogeneous. The rate of decay of attenuation (Q-1) with frequency for the relations obtained here is found to be comparable with those of other regions of the world though the absolute values differ. The obtained relations are expected to be useful for the estimation of source parameters of the earthquakes in the Mainland Gujarat region where no such relations were available earlier. These relations are also important for the simulation of earthquake strong ground motions in the region.
Measurement of mass attenuation coefficients for YBaCuO superconductor at different energies
NASA Astrophysics Data System (ADS)
Çevik, U.; Baltas, H.; Çelik, S.; Karaca, I.; Kopya, I.
2005-01-01
The mass attenuation coefficients for Y2O3, BaCO3, CuO compounds, and solid-state forms of YBa2Cu3O7 superconductor were determined at energies of 57.5, 59.5, 65.2, 74.8, 77.1, 87.3, 94.6, 98.4, 122, and 136 keV. The samples were irradiated using a 241Am point source emitting 59.5 keV photon energies and a 57Co point source emitting 122 and 136 keV photon energies. The other energies were obtained using secondary targets such as Ta, Bi2O3, and (CH3COO)2UO22H2O. The gamma- and x-rays were counted by a Si(Li) detector with a resolution of 160 eV at 5.9 keV. Samples were selected on the basis of known composition and mass densities were measured using a densitometer. The experimental results obtained in this study are compared with theoretical values.
Attenuation of Coda Waves in the Saurashtra Region, Gujarat (India)
NASA Astrophysics Data System (ADS)
Sharma, Babita; Kumar, Dinesh; Teotia, S. S.; Rastogi, B. K.; Gupta, Arun K.; Prajapati, Srichand
2012-01-01
The attenuation characteristics based on coda waves of two areas—Jamnagar and Junagarh of Saurashtra, Gujarat (India)—have been investigated in the present study. The frequency dependent relationships have been developed for both the areas using single back scattering model. The broadband waveforms of the vertical components of 33 earthquakes (Mw 1.5-3.5) recorded at six stations of the Jamnagar area, and broadband waveforms of 68 earthquakes (Mw 1.6-5) recorded at five stations of the Junagarh area have been used for the analysis. The estimated relations for the Junagarh area are: Q c = (158 ± 5)f(0.99±0.04) (lapse time : 20 s), Q c = (170 ± 4.4)f(0.97±0.02) (lapse time : 30 s) and Q c = (229 ± 6.6)f(0.94±0.03) (lapse time : 40 s) and for the Jamnagar area are: Q c = (178 ± 3)f(0.95±0.05) (lapse time : 20 s), Q c = (224 ± 6)f(0.98±0.06) (lapse time : 30 s) and Q c = (282 ± 7)f(0.91±0.03) (lapse time : 40 s). These are the first estimates for the areas under consideration. The Junagarh area appears to be more attenuative as compared to the Jamnagar area. The increase in Q c values with lapse time found here for both the areas show the depth dependence of Q c as longer lapse time windows will sample larger area. The rate of decay of attenuation ( Q -1) with frequency for the relations obtained here is found to be comparable with those of other regions of the world though the absolute values differ. A comparison of the coda-Q estimated for the Saurashtra region with those of the nearby Kachchh region shows that the Saurashtra region is less heterogeneous. The obtained relations are expected to be useful for the estimation of source parameters of the earthquakes in the Saurashtra region of Gujarat where no such relations were available earlier. These relations are also important for the simulation of earthquake strong ground motions in the region.
NASA Astrophysics Data System (ADS)
Hirasawa, T.; Okawa, S.; Fujita, M.; Kushibiki, T.; Ishihara, M.
2014-03-01
We proposed a method of quantifying the effective attenuation coefficients of optical absorbers which uses the continuous wavelet transform to calculate the time-resolved frequency spectra of photoacoustic (PA) signals. In order to apply the method to blood oxygenation monitoring of blood vessels, this study discusses how to reduce the effects of blood vessel diameters, which influences on the time resolved frequency spectra of PA signals. Numerical simulations which calculate the PA signals produced from blood vessel phantoms with various diameters were performed. The simulations revealed that the frequency of PA signal became independent from the vessel diameters by measuring the PA signal from small area. The frequencies of simulated PA signals were proportional to the effective attenuation coefficients with a correlation coefficient of 0.99, and a slope of 0.035 MHz/cm-1 under condition that the measurement area was 4.0 mm at a frequency of 1.5 MHz. Thus we used the focused acoustic sensor of which focusing the foregoing measurement area. It consisted of a P(VDF-TrFE) film, which was characterized by broad frequency band. As results of experiments using the focused acoustic sensor, the frequencies of PA signals produced from blood vessel phantoms were proportional to the effective attenuation coefficients with correlation coefficient of 0.96 although the frequencies were suffered from deviations of 0.135 MHz, which corresponded to the effective attenuation coefficient of 3.46 cm-1. Since the large deviations were caused by experimental factors such as sensor alignment, it is required to improve robustness to the experimental factors.
Coda wave attenuation in the Parecis Basin, Amazon Craton, Brazil: sensitivity to basement depth
NASA Astrophysics Data System (ADS)
Vieira Barros, Lucas; Assumpção, Marcelo; Quintero, Ronnie; Ferreira, Vinicius Martins
2011-04-01
Small local earthquakes from two aftershock sequences in Porto dos Gaúchos, Amazon craton—Brazil, were used to estimate the coda wave attenuation in the frequency band of 1 to 24 Hz. The time-domain coda-decay method of a single backscattering model is employed to estimate frequency dependence of the quality factor ( Q c) of coda waves modeled using Q_c =Q_0 f^? , where Q 0 is the coda quality factor at frequency of 1 Hz and ? is the frequency parameter. We also used the independent frequency model approach (Morozov, Geophys J Int, 175:239-252, 2008), based in the temporal attenuation coefficient, ?( f) instead of Q( f), given by the equation ? (f) = ? + ? f/Q_e , for the calculation of the geometrical attenuation ( ?) and effective attenuation (Q_e^{-1} ). Q c values have been computed at central frequencies (and band) of 1.5 (1-2), 3.0 (2-4), 6.0 (4-8), 9.0 (6-12), 12 (8-16), and 18 (12-24) Hz for five different datasets selected according to the geotectonic environment as well as the ability to sample shallow or deeper structures, particularly the sediments of the Parecis basin and the crystalline basement of the Amazon craton. For the Parecis basin Q_c =(98± 12)f^{(1.14± 0.08)}, for the surrounding shield Q_c =(167± 46)f^{(1.03± 0.04)}, and for the whole region of Porto dos Gaúchos Q_c =(99± 19)f^{(1.17± 0.02)}. Using the independent frequency model, we found: for the cratonic zone, ? = 0.014 s - 1, Q_e^{-1} =0.0001, ? ? 1.12; for the basin zone with sediments of 500 m, ? = 0.031 s - 1, Q_e^{-1} =0.0003, ? ? 1.27; and for the Parecis basin with sediments of 1,000 m, ? = 0.047 s - 1, Q_e^{-1} =0.0005, ? ? 1.42. Analysis of the attenuation factor ( Q c) for different values of the geometrical spreading parameter ( ?) indicated that an increase of ? generally causes an increase in Q c, both in the basin as well as in the craton. But the differences in the attenuation between different geological environments are maintained for different models of geometrical spreading. It was shown that the energy of coda waves is attenuated more strongly in the sediments, Q_c =(78± 23)f^{(1.17± 0.14)} (in the deepest part of the basin), than in the basement, Q_c =(167± 46)f^{(1.03± 0.04)} (in the craton). Thus, the coda wave analysis can contribute to studies of geological structures in the upper crust, as the average coda quality factor is dependent on the thickness of sedimentary layer.
NASA Astrophysics Data System (ADS)
Kaji, Sayumi; Sarugaku, Yuki; Ikeda, Yuji; Kobayashi, Naoto; Nakanishi, Kenshi; Kondo, Sohei; Yasui, Chikako; Kawakita, Hideyo
2014-07-01
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.
Studies on Shock Attenuation in Plastic Materials and Applications in Detonation Wave Shaping
NASA Astrophysics Data System (ADS)
Khurana, Ritu; Gautam, P. C.; Rai, Rajwant; Kumar, Anil; Sharma, A. C.; Singh, Manjit, Dr
2012-07-01
Pressure in plastic materials attenuates due to change of impedance, phase change in the medium and plastic deformation. A lot of theoretical and experimental efforts have been devoted to the attenuation of shock wave produced by the impact of explosive driven flyer plate. However comparatively less work has been done on the attenuation of shock waves due to contact explosive detonation. Present studies deal with the attenuation of explosive driven shock waves in various plastic materials and its applications in design of Hybrid Detonation Wave Generator In present work shock attenuating properties of different polymers such as Perspex, Teflon, nylon, polypropylene and viton has been studied experimentally using rotating mirror streak camera and electrical position pins. High explosive RDX/TNT and OCTOL of diameter 75-100mm and thickness 20 to 50mm were detonated to induce shock wave in the test specimens. From experimental determined shock velocity at different locations the attenuation in shock pressure was calculated. The attenuation of shock velocity with thickness in the material indicates exponential decay according to relation US = UOexp(-ax). In few of the experiments manganin gauge of resistance 50 ohms was used to record stress time profile across shock wave. The shock attenuation data of Viton has successfully been used in the design of hybrid detonation wave generator using Octol as high explosive. While selecting a material it was ensured that the attenuated shock remains strong enough to initiate an acceptor explosive. Theoretical calculation were supported by Autodyne 2D hydro-code simulation which were validated with the experiments conducted using high speed streak photography and electrical shock arrival pins. Shock attenuation data of Perspex was used to establishing card gap test and wedge test in which test items is subjected to known pressure pulse by selecting the thickness of the plastic material.
Measurement of the dispersion and attenuation of cylindrical ultrasonic guided waves in long bone.
Ta, Dean; Wang, Weiqi; Wang, YuanYuan; Le, Lawrence H; Zhou, Yuqing
2009-04-01
Osteoporotic bones are likely to have less cortical bone than healthy bones. The velocities of guided waves propagating in a long cylindrical bone are very sensitive to bone properties and cortical thickness (CTh). This work studies the dispersion and attenuation of ultrasonic guided waves propagating in long cylindrical bone. A hollow cylinder filled with a viscous liquid was used to model the long bone and then to calculate the theoretical phase and group velocities, as well as the attenuation of the waves. The generation and selection of guided wave modes were based on theoretical dispersive curves. The phase velocity and attenuation of cylindrical guided wave modes, such as L(0,1), L(0,2) and L(0,3), were measured in bovine tibia using angled beam transducers at various propagation distances ranging from 75 to 160 mm. The results showed that the phase velocity of the L(0,2) guided wave mode decreased with an increase in CTh. The attenuation of the low cylindrical guided wave modes was a nonlinear function that increased with propagation distance and mode order. The L(0,2) mode had a different attenuation for each CTh. The experimental results were in good agreement with the predicted values. Cylindrical guided waves of low-frequency and low-order have been shown to demonstrate more dispersion and less attenuation and should, therefore, be used to evaluate long bone. PMID:19153000
P-Wave to Rayleigh-wave conversion coefficients for wedge corners; model experiments
Gangi, A.F.; Wesson, R.L.
1978-01-01
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.
NASA Astrophysics Data System (ADS)
Bouchaala, Fateh; Ali, Mohammed Y.; Farid, Asam
2014-07-01
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.
NASA Technical Reports Server (NTRS)
Usry, J. W.; Whitlock, C. H.
1981-01-01
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.
Effects of 3D Attenuation on Seismic Wave Amplitude and Phase Measurements
Komatitsch, Dimitri
Effects of 3D Attenuation on Seismic Wave Amplitude and Phase Measurements by Brian Savage, Dimitri is the laterally varying temperature structure of the mantle, (2) what is the percentage of volatiles and melt
The Attenuation of Electromagnetic Waves By Multiple Knife-Edge Diffraction
L. E. Vogler
1981-01-01
ABSTRACT TABLE OF CONTENTS Page 1 l. INTRODUCTION 2. , NUMERICAL EVALUATION,9 4. EXAMPLE CALCULATIONS,13 5. SUMt1ARY,18 6. ACKNmILEDG~1ENTS,19 7. REFERENCES,19 iii THE ATTENUATION OF ELECTROMAGNETIC WAVES BY
Zhonghe Jiang; Xiwei Hu; Minghai Liu; Chaohui Lan; Shu Zhang; Yong He; Yuan Pan
2007-01-01
Finite-difference-time-domain arithmetic is applied to simulate the propagation of an electromagnetic (EM) wave in a two-dimensional atmospheric pressure plasma (APP) and a metal layer with strong electron-neutral collisions. The dependences of the EM wave attenuation on the parameters of the APP are provided. The two-dimensional numerical results indicate that when the profile of the electron density is given, the attenuation
Wave attenuation and mode dispersion in a waveguide coated with lossy dielectric material
NASA Technical Reports Server (NTRS)
Lee, C. S.; Chuang, S. L.; Lee, S. W.; Lo, Y. T.
1984-01-01
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.
NASA Astrophysics Data System (ADS)
Potel, Catherine; Leduc, Damien; Morvan, Bruno; Depollier, Claude; Hladky-Hennion, Anne-Christine; Izbicki, Jean-Louis; Pareige, Pascal; Bruneau, Michel
2008-10-01
The characterization of bounded roughened surfaces before applying adhesive joint, in order to detect poor cohesive and adhesive properties, remains difficult. Earlier studies based on analysis of surface wave (Rayleigh waves or Scholte waves) are not really adapted to the characterization of such surfaces. Guided acoustic waves, i.e., Lamb waves, turn out to be the best adapted kind of waves to characterize this roughness when plates are bounded together. It is the aim of this paper to provide analytical and experimental approaches to analyze the behavior of Lamb waves propagating inside plates with a rough surface (small perturbations). First, experimental results of the attenuation effects are given on roughened glass plates. Second, the attenuation factor of the Lamb wave in an anisotropic rough solid plate is calculated through a complex analytical model of the dispersion equation which accounts for the effect of the power spectrum density of the rough profile (including the effect of the statistical roughness parameters).
Attenuation of electromagnetic wave propagation in sandstorms incorporating charged sand particles
NASA Astrophysics Data System (ADS)
Zhou, You-He; Shu He, Qin; Zheng, Xiao Jing
2005-06-01
A theoretical approach for predicting the attenuation of microwave propagation in sandstorms is presented, with electric charges generated on the sand grains taken into account. It is found that the effect of electric charges distributed partially on the sand surface is notable. The calculated attenuation is in good agreement with that measured in certain conditions. The distribution of electric charges on the surface of sand grains, which is not easy to measure, can be approximately determined by measuring the attenuation value of electromagnetic waves. Some effects of sand radius, dielectric permittivity, frequency of electromagnetic wave, and visibility of sandstorms on the attenuation are also discussed quantitatively. Finally, a new electric parameter is introduced to describe the roles of scattering, absorption and effect of charges in attenuation.
Trunova, Valentina; Sidorina, Anna; Kriventsov, Vladimir
2014-10-17
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
Seismic attenuation due to wave-induced flow
2004-01-03
Jan 14, 2004 ... patchy saturation model of Johnson [2001] and demon- strate numerically that ...... is the permeability) showing that surface tension effects become more ...... The squirt mechanism produces a great deal of attenuation at the.
Attenuation and distortion of compression waves propagating in very long tube
NASA Astrophysics Data System (ADS)
Nakamura, Shinya; Sasa, Daisuke; Aoki, Toshiyuki
2011-03-01
A lot of phenomena related to propagating various waves are seen when the high-speed train goes through the tunnel, the gas pipeline is broken due to an accident or the air brake of the wagon operates. For instance, a compression wave generated ahead of a high-speed train entering a tunnel propagates to the tunnel exit and spouts as a micro pressure wave, which causes an exploding sound. In order to estimate the magnitude correctly, the mechanism of the attenuation and distortion of a compression wave propagating along a very long tunnel must be understood and the experimental information on these phenomena is required. An experimental investigation is carried out to clarify the attenuation and distortion of the propagating compression wave in a very long tube. Experimental results show that the strength of a compression wave decreases with distance. The attenuation and distortion of compression waves are affected by the initial waveform of the compression wave and by the unsteady boundary layer induced by the propagating wave. The shape of a compression wave becomes different with the propagating distance; that is, a shock wave appears just head of a wavefront and an overshoot on pressure distribution is observed behind a shock wave due to the transition of the unsteady boundary layer.
Attenuation of high-frequency body waves in the crust of the Central External Dinarides
NASA Astrophysics Data System (ADS)
Dasovi?, Iva; Ruš?i?, Marija; Herak, Davorka; Herak, Marijan
2015-05-01
The Central External Dinarides are known as a tectonically complex region of moderate seismicity where several strong earthquakes occurred in the last century. In order to gain insight into the attenuation of seismic waves in the area, the extended coda normalization method was applied to band-pass-filtered seismograms of local earthquakes recorded at seven seismological broadband stations. Obtained results indicate strong attenuation of direct body waves: Q 0,P = Q P(1 Hz) is found between 21 and 120 and Q 0,S = Q S(1 Hz) is between 46 and 113, whereas the exponent n in the power law of frequency dependence of the quality factor is found in the range of 0.63-1.52 and 0.65-0.97 for n P and n S, respectively. P-waves are, on the average, attenuated more than S-waves. The three island stations (Dugi Otok (DUGI), Žirje (ZIRJ), Hvar (HVAR)) are distinguished by the strong low-frequency P-wave attenuation and more pronounced frequency dependence of the Q P factor (Q 0,S/Q 0,P > 1.7, Q 0,P < 60, n P > n S). The remaining four inland stations (Udbina (UDBI), Mori?i (MORI), Kijevo (KIJV), ?a?vina (CACV)) all exhibit similar qualitative attenuation properties for P- and S-waves (n P ? n S ? 1 and Q 0,S ? Q 0,P), although individual values of the Q-factors vary notably within this group. Low-frequency attenuation of direct S-waves in the crust is stronger than mean attenuation of scattered coda waves in the lithosphere, especially for long coda lapse times. The results are also qualitatively in agreement with the thermal regime in the area.
Attenuation of high-frequency body waves in the crust of the Central External Dinarides
NASA Astrophysics Data System (ADS)
Dasovi?, Iva; Ruš?i?, Marija; Herak, Davorka; Herak, Marijan
2015-10-01
The Central External Dinarides are known as a tectonically complex region of moderate seismicity where several strong earthquakes occurred in the last century. In order to gain insight into the attenuation of seismic waves in the area, the extended coda normalization method was applied to band-pass-filtered seismograms of local earthquakes recorded at seven seismological broadband stations. Obtained results indicate strong attenuation of direct body waves: Q 0,P = Q P(1 Hz) is found between 21 and 120 and Q 0,S = Q S(1 Hz) is between 46 and 113, whereas the exponent n in the power law of frequency dependence of the quality factor is found in the range of 0.63-1.52 and 0.65-0.97 for n P and n S, respectively. P-waves are, on the average, attenuated more than S-waves. The three island stations (Dugi Otok (DUGI), Žirje (ZIRJ), Hvar (HVAR)) are distinguished by the strong low-frequency P-wave attenuation and more pronounced frequency dependence of the Q P factor ( Q 0,S/ Q 0,P > 1.7, Q 0,P < 60, n P > n S). The remaining four inland stations (Udbina (UDBI), Mori?i (MORI), Kijevo (KIJV), ?a?vina (CACV)) all exhibit similar qualitative attenuation properties for P- and S-waves ( n P ? n S ? 1 and Q 0,S ? Q 0,P), although individual values of the Q-factors vary notably within this group. Low-frequency attenuation of direct S-waves in the crust is stronger than mean attenuation of scattered coda waves in the lithosphere, especially for long coda lapse times. The results are also qualitatively in agreement with the thermal regime in the area.
Sanders, C.; Ho-Liu, P.; Rinn, D.; Hiroo, Kanamori
1988-01-01
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
Stanchits, S.A.; Lockner, D.A.; Ponomarev, A.V.
2003-01-01
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.
Attenuation of elastic surface waves in thin films of superconducting zinc
W. E. Bailey
1978-01-01
The attenuation of 90 MHz acoustic surface waves in zinc thin films was measured in the temperature region around the superconducting transition temperature. Films of 3000A and 10,000A were evaporated, with the use of an Electron Beam Gun, onto lithium niobate substrates. These acoustic surface waves were generated and detected using interdigital transducers, with a fundamental frequency of 90 MHz,
Electromagnetic wave attenuation measurements in a ring-shaped inductively coupled air plasma
NASA Astrophysics Data System (ADS)
Wei, Xiaolong; Xu, Haojun; Li, Jianhai; Lin, Min; Su; Chen
2015-05-01
An aerocraft with the surface, inlet and radome covered large-area inductive coupled plasma (ICP) can attenuate its radar echo effectively. The shape, thickness, and electron density ( N e ) distribution of ICP are critical to electromagnetic wave attenuation. In the paper, an air all-quartz ICP generator in size of 20 × 20 × 7 cm3 without magnetic confinement is designed. The discharge results show that the ICP is amorphous in E-mode and ring-shaped in H-mode. The structure of ICP stratifies into core region and edge halo in H-mode, and its width and thickness changes from power and pressure. Such phenomena are explained by the distribution of RF magnetic field, the diffusion of negative ions plasma and the variation of skin depth. In addition, the theoretical analysis shows that the N e achieves nearly uniform within the electronegative core and sharply steepens in the edge. The N e of core region is diagnosed by microwave interferometer under varied conditions (pressure in range of 10-50 Pa, power in 300-700 W). Furthermore, the electromagnetic wave attenuation measurements were carried out with the air ICP in the frequencies of 4-5 GHz. The results show that the interspaced ICP is still effective to wave attenuation, and the wave attenuation increases with the power and pressure. The measured attenuation is approximately in accordance with the calculation data of finite-different time-domain simulations.
Experimental and Numerical Investigation of Pressure Wave Attenuation due to Bubbly Layers
NASA Astrophysics Data System (ADS)
Jayaprakash, Arvind; Fourmeau, Tiffany; Hsiao, Chao-Tsung; Chahine, Georges; Dynaflow Inc. Team
2013-03-01
In this work, the effects of dispersed microbubbles on a steep pressure wave and its attenuation are investigated both numerically and experimentally. Numerical simulations were carried out using a compressible Euler equation solver, where the liquid-gas mixture was modeled using direct numerical simulations involving discrete deforming bubbles. To reduce computational costs a 1D configuration is used and the bubbles are assumed distributed in layers and the initial pressure profile is selected similar to that of a one-dimensional shock tube problem. Experimentally, the pressure pulse was generated using a submerged spark electric discharge, which generates a large vapor bubble, while the microbubbles in the bubbly layer are generated using electrolysis. High speed movies were recorded in tandem with high fidelity pressure measurements. The dependence of pressure wave attenuation on the bubble radii, the void fraction, and the bubbly layer thickness were parametrically studied. It has been found that the pressure wave attenuation can be seen as due to waves reflecting and dispersing in the inter-bubble regions, with the energy absorbed by bubble volume oscillations and re-radiation. Layer thickness and small bubble sizes were also seen as having a strong effect on the attenuation with enhanced attenuation as the bubble size is reduced for the same void fraction. In this work, the effects of dispersed microbubbles on a steep pressure wave and its attenuation are investigated both numerically and experimentally. Numerical simulations were carried out using a compressible Euler equation solver, where the liquid-gas mixture was modeled using direct numerical simulations involving discrete deforming bubbles. To reduce computational costs a 1D configuration is used and the bubbles are assumed distributed in layers and the initial pressure profile is selected similar to that of a one-dimensional shock tube problem. Experimentally, the pressure pulse was generated using a submerged spark electric discharge, which generates a large vapor bubble, while the microbubbles in the bubbly layer are generated using electrolysis. High speed movies were recorded in tandem with high fidelity pressure measurements. The dependence of pressure wave attenuation on the bubble radii, the void fraction, and the bubbly layer thickness were parametrically studied. It has been found that the pressure wave attenuation can be seen as due to waves reflecting and dispersing in the inter-bubble regions, with the energy absorbed by bubble volume oscillations and re-radiation. Layer thickness and small bubble sizes were also seen as having a strong effect on the attenuation with enhanced attenuation as the bubble size is reduced for the same void fraction. This study was supported by the Department of Energy, under SBIR Phase II Contract DE-FG02-07ER84839.
Chen, Ruimin; Tsui, Po-Hsiang; Zhou, Qifa; Humayun, Mark S; Shung, K Kirk
2010-01-01
A cataract is a clouding of the lens in the eye that affects vision. Phacoemulsification is the mostly common surgical method for treating cataracts, and determining that the optimal phacoemulsification energy is dependent on measuring the hardness of the lens. This study explored the use of an ultrasound needle transducer for invasive measurements of ultrasound attenuation coefficient to evaluate the hardness of the cataract lens. A 47 MHz high-frequency needle transducer with a diameter of 0.9 mm was fabricated by a polarized PMN-33%PT single crystal in the present study. The attenuation coefficients at different stages of an artificial porcine cataract lens were measured using the spectral shift approach. The hardness of the cataract lens was also evaluated by mechanical measurement of its elastic properties. The results demonstrated that the ultrasonic attenuation coefficient was increased from 0.048 ± 0.02 to 0.520 ± 0.06 dB mm?1 MHz?1 corresponding to an increase in Young’s modulus from 6 ± 0.4 to 96 ± 6.2 kPa as the cataract further developed. In order to evaluate the feasibility of combining needle transducer and phacoemulsification probe for real-time measurement during cataract surgery, the needle transducer was mounted on the phacoemulsification probe for a vibration test. The results indicated that there was no apparent damage to the tip of the needle transducer and the pulse–echo test showed that a good performance in sensitivity was maintained after the vibration test. PMID:19759408
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...
NASA Astrophysics Data System (ADS)
Huang, Jiankun; Shi, Zhifei
2013-09-01
The periodic theory of solid-state physics is introduced to study the reduction characteristics of periodic pile barriers. The attenuation zones of a two-dimensional infinite periodic pile barrier subjected to plane waves are analyzed by plane wave expansion method. Influences of soil parameters and pile configurations on the first no-directional attenuation zone are discussed. The screening effectiveness of finite periodic pile barriers is simulated by the finite element method. The present theoretical results are in well agreement with experimental data, which validates the existence of attenuation zones in the periodic structures. The results show that vibrations with frequencies in the attenuation zones can be reduced significantly. The present investigation provides a new concept for designing pile barriers to block mid-frequency vibration.
The large-scale influence of the Great Barrier Reef matrix on wave attenuation
NASA Astrophysics Data System (ADS)
Gallop, Shari L.; Young, Ian R.; Ranasinghe, Roshanka; Durrant, Tom H.; Haigh, Ivan D.
2014-12-01
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.
NASA Astrophysics Data System (ADS)
Pichardo, Samuel; Sin, Vivian W.; Hynynen, Kullervo
2011-01-01
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.
Müller, Tobias M; Sahay, Pratap N
2011-05-01
Within the viscosity-extended Biot framework of wave propagation in porous media, the existence of a slow shear wave mode with non-vanishing velocity is predicted. It is a highly diffusive shear mode wherein the two constituent phases essentially undergo out-of-phase shear motions (slow shear wave). In order to elucidate the interaction of this wave mode with propagating wave fields in an inhomogeneous medium the process of conversion scattering from fast compressional waves into slow shear waves is analyzed using the method of statistical smoothing in randomly heterogeneous poroelastic media. The result is a complex wave number of a coherent plane compressional wave propagating in a dynamic-equivalent homogeneous medium. Analysis of the results shows that the conversion scattering process draws energy from the propagating wave and therefore leads to attenuation and phase velocity dispersion. Attenuation and dispersion characteristics are typical for a relaxation process, in this case shear stress relaxation. The mechanism of conversion scattering into the slow shear wave is associated with the development of viscous boundary layers in the transition from the viscosity-dominated to inertial regime in a macroscopically homogeneous poroelastic solid. PMID:21568383
Li, Jianghua; Tu, Ziwei; Shen, Zhiyuan; Xia, Yunfei; He, Yonghong; Liu, Songhao; Chen, Changshui
2013-02-01
The radiotherapy-related types of nasopharyngeal carcinoma (NPC) have been established, which give the most effective treatment for NPC patients using the individual therapy. To diagnose the types of NPC, we assess the general NPC cell lines CNE1, CNE2 and normal nasopharyngeal cell line NP69 using optical coherence tomography (OCT) in two steps: firstly, the OCT images of the three different types of cell pellets are captured. Secondly, by fitting Beer's law to the averaged A-scans in these OCT datasets, the attenuation coefficients (? t ) of the cells can be extracted. The median attenuation coefficients (interquartile range) of CNE1, CNE2, and NP69 are 5.58 mm(-1) (IQR 5.55 to 5.65 mm(-1)), 5.91 mm(-1) (IQR 5.82 to 5.88 mm(-1)), and 8.96 mm(-1) (IQR 8.80 to 9.47 mm(-1)), respectively. The distinguishable quantitative OCT analysis (by ? t ) shows that the types of NPC could potentially be differentiated in real time and noninvasive. PMID:22618158
Body-wave Attenuation in the South-Central Region of the Gulf of California, México
NASA Astrophysics Data System (ADS)
Castro, R. R.; Vidales-Basurto, C. A.; Huerta, C. I.; Sumy, D. F.; Gaherty, J. B.; Collins, J. A.
2014-12-01
We present results from a recent study of seismic attenuation of body waves in the south-central region of the Gulf of California (GoC) obtained using records from the Network of Autonomously Recording Seismographs of Baja California (NARS-Baja), from the CICESE's Broadband Seismological Network of the GoC (RESBAN), and from the Ocean Bottom Seismographs (OBS) deployed as part of the Sea of Cortez Ocean Bottom Array experiment (SCOOBA). We examine 27 well-located earthquakes that occurred from October 2005 to October 2006 with magnitudes (Mw) between 3.5 and 4.8. We estimated S-wave site effects by calculating horizontal to vertical spectral ratios and determined attenuation functions with a nonparametric model by inverting the observed spectral amplitudes of 21 frequencies between 0.13 and 12.59 Hz for the SCOOBA (OBS) stations and 19 frequencies between 0.16 and 7.94 Hz for NARS-Baja and RESBAN stations. We calculated the geometrical spreading and the attenuation (1/Q) factors for two distance intervals (10-120 km and 120-220 km, respectively) for each frequency considered. The estimates of Q obtained with the SCOOBA (OBS) records for the interval 10-120 km indicate that the P waves attenuate more than S waves (QP=34 f 0.82, QS=59 f 0.90) for frequencies between 0.6 and 12.6 Hz; while for the 120-220 km interval, where ray-paths travel deeper, S waves attenuate more than P waves (QP=117 f 0.44, QS=51 f 1.12). The estimates of Q obtained using NARS-Baja and RESBAN records, within 10-120 km, indicate that P waves attenuate more than S waves (QP=69 f 0.87, QS=176 f 0.61) at frequencies between 0.3 and 6.3 Hz; while at the 120-220 km distance interval S waves attenuate slightly more than P waves (QP=39 f 0.64, QS=48 f 0.37) at high frequencies (f > 3 Hz). These results, based on a unique OBS dataset, provide an indirect mean to constrain future models of the thermal structure beneth the GoC.
Ladefoged, Claes N; Benoit, Didier; Law, Ian; Holm, Søren; Kjær, Andreas; Højgaard, Liselotte; Hansen, Adam E; Andersen, Flemming L
2015-10-21
The reconstruction of PET brain data in a PET/MR hybrid scanner is challenging in the absence of transmission sources, where MR images are used for MR-based attenuation correction (MR-AC). The main challenge of MR-AC is to separate bone and air, as neither have a signal in traditional MR images, and to assign the correct linear attenuation coefficient to bone. The ultra-short echo time (UTE) MR sequence was proposed as a basis for MR-AC as this sequence shows a small signal in bone. The purpose of this study was to develop a new clinically feasible MR-AC method with patient specific continuous-valued linear attenuation coefficients in bone that provides accurate reconstructed PET image data.A total of 164 [(18)F]FDG PET/MR patients were included in this study, of which 10 were used for training. MR-AC was based on either standard CT (reference), UTE or our method (RESOLUTE). The reconstructed PET images were evaluated in the whole brain, as well as regionally in the brain using a ROI-based analysis. Our method segments air, brain, cerebral spinal fluid, and soft tissue voxels on the unprocessed UTE TE images, and uses a mapping of [Formula: see text] values to CT Hounsfield Units (HU) to measure the density in bone voxels.The average error of our method in the brain was 0.1% and less than 1.2% in any region of the brain. On average 95% of the brain was within??±10% of PETCT, compared to 72% when using UTE.The proposed method is clinically feasible, reducing both the global and local errors on the reconstructed PET images, as well as limiting the number and extent of the outliers. PMID:26422177
A restricted meniscus motion model for wave attenuation in partially fluid-saturated porous rock
NASA Astrophysics Data System (ADS)
Waite, William Frederick
Seismic wave attenuation analysis, the study of how seismic waves lose their energy while they travel, relies on models to transform measured data into descriptions of the subsurface environment. Seismic attenuation in fluid bearing rock is dominated by interactions between the fluid and the rock. Standard attenuation theories model attenuation due to viscous shear within the flowing fluid (local fluid flow), shear between the pore fluid and pore walls (global fluid flow), or fluid-assisted thermal diffusion. All of these models rely solely on physical and geometrical properties of the system to describe the mechanism by which attenuation occurs. These models do not account for attenuative physicochemical interactions between the pore fluid and pore walls. Effects of physicochemical interactions between the pore fluid and pore walls are considered in this work. Physicochemical interactions between the solid crack surface and the fluid meniscus can restrict contact line motion (motion of the three phase boundary) across the solid surface. In partially saturated cracks subjected to seismic deformation, two consequences of restricted contact line motion are crack stiffening and energy loss. Fluid redistribution in a deforming, partially saturated crack occurs via meniscus deformation or contact line motion or both. If there is some resistance to contact line motion, during the initial response to fluid redistribution the contact lines remain stationary while the meniscus deforms. The meniscus deforms because the fluid pressure is changing, and these fluid pressure changes always act against further crack deformation. The fluid pressurization makes the crack more stiff than a dry crack or a crack in which only stiffening due to viscous flow is considered. If crack deformation pressurizes the fluid enough that the force applied by the deforming meniscus on a contact line exceeds the resistive force holding the contact line stationary, contact line motion occurs. Contact line motion against the resistive force requires energy, which is lost from the seismic wave causing the original crack deformation. This friction-like energy loss mechanism is responsible for the attenuation in the restricted meniscus motion model. The restricted meniscus motion model interprets attenuation and stiffness data which can not be described by attenuation theories relying solely on the physical and geometrical parameters (pore fluid viscosity, fluid and solid compressibilities) used in the standard models. The restricted geometry, meniscus motion model, born from attenuation and stiffening observations in an artificial glass crack sample, is itself composed of parameters which can be measured or estimated using experiments which are distinct from the attenuation and stiffness measurements. These independently measured model parameters are in general agreement with the model parameters used to fit attenuation and stiffness results measured on the artificial glass crack samples.
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...
Comparison of fractional wave equations for power law attenuation in ultrasound and elastography.
Holm, Sverre; Näsholm, Sven Peter
2014-04-01
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
NASA Astrophysics Data System (ADS)
Singh, D. D.
The fundamental-mode Love and Rayleigh waves generated by 57 earthquakes which occurred in the north and central Indian Ocean (extending to 40°S) and recorded at Indian seismograph and other WWSSN stations such as HOW, SHL, VIS, MDR, HYB, KOD, CHG, TRD, POO, BOM, GOA, NDI, NIL and QUE are analysed. Love and Rayleigh wave attenuation coefficients are estimated at periods of 15-100 s using the spectral amplitude of these waves for 98 different paths across the Bay of Bengal Fan, the Arabian Fan, and the north and central Indian Ocean. The large standard deviations observed in the surface wave attenuation coefficients may be a result of regional variation of the attenuative properties of the crust and upper mantle beneath these regions. Love wave attenuation coefficients are found to vary from 0.000 03 to 0.000 45 km -1 for the Bay of Bengal Fan; from 0.000 03 to 0.000 85 km -1 for the Arabian Fan; and from 0.000 03 to 0.000 35 km -1 for the north and central Indian Ocean. Similarly, Rayleigh wave attenuation coefficients vary from 0.000 03 to 0.0004 km -1 for the Bay of Bengal Fan; from 0.000 06 to 0.0007 km -1 for the Arabian Fan; and from 0.000 03 to 0.0007 km -1 for the north and central Indian Ocean. Backus and Gilbert inversion theory is applied to these surface wave attenuation data to obtain average Q-1 models for the crust and upper mantle beneath the Bay of Bengal, the Arabian Fan, and the north and central Indian Ocean. Inversion of Love and Rayleigh wave attenuation data shows a high-attenuation zone centred at a depth of > 120 km ( Q? ? 125) for the Bay of Bengal Fan. Similarly, a high-attenuation zone ( Q? ? 40-70) occurs at a depth of 60-160 km for the Arabian Fan at 100-160 km ( Q? ? 115) for the Indian Ocean off Ninetyeast Ridge, and at 80-160 km ( Q? ? 80) for the Indian Ocean across the Ninetyeast Ridge. The Q?-1 models show a lithosphere thickness of 120 km beneath the Bay of Bengal Fan. Similarly, lithosphere thickness of 70, 100 and 80 km is estimated beneath the Arabian Fan, and the Indian Ocean off Ninetyeast Ridge and across Ninetyeast Ridge, respectively. The base of the lithosphere is identified as the depth at which there is a significant increase in the Q?-1 value, which attains its maximum value in the asthenosphere. The thinning of Indian lithosphere beneath the Arabian Fan suggests high temperature below Moho depth (60 km from surface) which has caused a high-attenuation zone at this shallow depth.
Kubo, Kohjiro; Norisuye, Tomohisa; Tran, Thao Nguyen; Shibata, Daisuke; Nakanishi, Hideyuki; Tran-Cong-Miyata, Qui
2015-09-01
Size and elastic properties of micro-particles suspended in liquid can be acoustically determined by ultrasound attenuation and velocity measurements with the aid of elastic scattering theories and a dispersion relation. While quantitative evaluation for hard micron-sized spheres using the theories is available in literature, that for hollow particles is not yet achieved. In this study, we show that the shell thickness and the elastic modulus of hollow particles can be quantitatively evaluated by ultrasound spectroscopy. Several kinds of microparticles including polystyrene rigid particles, polydivinylbenzene rigid particles, borosilicate hollow particles, and phenolic-resin hollow particles were examined as a function of the particle concentration. PMID:26067926
Study of transmission line attenuation in broad band millimeter wave frequency range.
Pandya, Hitesh Kumar B; Austin, M E; Ellis, R F
2013-10-01
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
Study of transmission line attenuation in broad band millimeter wave frequency range
Pandya, Hitesh Kumar B.; Austin, M. E.; Ellis, R. F.
2013-10-15
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.
Dynamic aspects of apparent attenuation and wave localization in layered media
Haney, M.M.; Van Wijk, K.
2008-01-01
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.
NASA Astrophysics Data System (ADS)
Yabe, S.; Baltay, A.; Ide, S.; Beroza, G. C.
2013-12-01
Ground motion prediction is an essential component of earthquake hazard assessment. Seismic wave attenuation with distance is an important, yet difficult to constrain, factor for such estimation. Using the empirical method of ground motion prediction equations (GMPEs), seismic wave attenuation with distance, which includes both the effect of anelastic attenuation and scattering, can be estimated from the distance decay of peak ground velocity (PGV) or peak ground acceleration (PGA) of ordinary earthquakes; however, in some regions where plate-boundary earthquakes are infrequent, such as Cascadia and Nankai, there are fewer data with which to constrain the empirical parameters. In both of those subduction zones, tectonic tremor occurs often. In this study, we use tectonic tremor to estimate the seismic wave attenuation with distance, and in turn use the attenuation results to estimate the radiated seismic energy of tremor. Our primary interest is in the variations among subduction zones. Ground motion attenuation and the distribution of released seismic energy from tremors are two important subduction zone characteristics. Therefore, it is very interesting to see whether there are variations of these parameters in different subduction zones, or regionally within the same subduction zone. It is also useful to estimate how much energy is released by tectonic tremor from accumulated energy to help understand subduction dynamics and the difference between ordinary earthquakes and tremor. We use the tectonic tremor catalog of Ide (2012) in Nankai, Cascadia, Mexico and southern Chile. We measured PGV and PGA of individual tremor bursts at each station. We assume a simple GMPE relationship and estimate seismic attenuation and relative site amplification factors from the data. In the Nankai subduction zone, there are almost no earthquakes on the plate interface, but intra-slab earthquakes occur frequently. Both the seismic wave attenuation with distance and the site response obtained from intra-slab earthquakes is almost the same as that determined from tectonic tremor. This means the attenuation parameter should be well estimated from tremor. Furthermore, we find substantial along-strike variation in the estimated attenuation parameter in the Nankai subduction zone, allowing us to infer with-in region differences in behavior.
Grujicic, Mica
-grained molecular-dynamics simulations in order to assess shock-wave attenuation and dispersion capacity of polyurea these phenomena and processes, meso-scale simulations of the formation of nano- segregated microstructure and its function of the polyurea soft-segment molecular weight. In particular, the ability of release
NASA Astrophysics Data System (ADS)
Wang, Weihua; Hao, Hong; Li, Xibing; Yan, Zhe; Gong, Fengqiang
2015-09-01
Open joints have significantly different effects on stress wave propagation across them as compared to closed and filled joints. In the present study, a theoretical model is developed based on the analysis of interaction process between stress waves and a single open joint. The analytical solutions to the energy transmission coefficient are mathematically derived for stress waves across an open joint. Parametric studies are conducted to evaluate the effects of various parameters on the energy transmission coefficient. It is found that the energy transmission coefficient follows a similar trend for all types of stress waves, but stress waves with different waveforms have different values. The energy transmission coefficient increases with the increase in the wave amplitude and duration, but decreases with the gap width. It also increases at the outset, and then decreases gradually with the increase in the incident angle for rectangle, symmetric triangle and ascending triangle waves, but it decreases with the incident angle for sine and descending triangle waves. Furthermore, different-shaped stress waves have different critical gap widths for wave transmission. The optimal incident angle and the critical gap width increase as the wave duration increases, but the critical stress amplitude decreases.
WAVELET BASED CHARACTERIZATION OF ACOUSTIC ATTENUATION IN POLYMERS USING LAMB WAVE MODES
Boyer, Edmond
WAVELET BASED CHARACTERIZATION OF ACOUSTIC ATTENUATION IN POLYMERS USING LAMB WAVE MODES Rais Ahmad@csun.edu ABSTRACT Polymers have been used in a wide range of applications ranging from fabrication of sophisticated medical equipment to manufacturing aircrafts. The design advantages of using polymers are its high
NASA Astrophysics Data System (ADS)
Wang, Lei; Zhang, Lu Lu; Qi, Feng-Hua
2015-04-01
Under investigation in this paper is an inhomogeneous modified nonlinear Schrödinger (MNLS) equation describing the ultrashort pulse dynamics with the distributed dispersion, self-phase modulation, self-steepening, and linear gain/loss. Nonautonomous rogue waves for the inhomogeneous MNLS equation are constructed via the modified Darboux transformation with the inhomogeneous parameters. The dynamical behaviours and main characteristics of the nonautonomous rogue waves in inhomogeneous fibers are discussed by analysing certain physical quantities. The inhomogeneous effects on the evolution of rogue waves are considered by virtue of the presented rational solutions with distributed coefficients. It is found that the group velocity dispersion (GVD) and linear gain/loss coefficients have effects on the trajectories and amplitudes of the rogue waves, respectively. Additionally, an intriguing composite rogue wave of the inhomogeneous MNLS equation is revealed, owing to the proper choice of the GVD coefficient. Our results could be useful for controlling the rogue waves in the dispersion-managed fiber system.
Seismic wave attenuation and dispersion in thin layer sequences
Edwards, Clifford Murray
1975-01-01
be attributed to wave propagation through cyclic sequences consisting of thin layers with no absorption. iv Multiples tend to disperse the seismogram in the time domain, In frequency bands in which dispersion is pronounced, notches appear in the amplitude... The mathmaatical description of a downgoing plane wave in an in- finite homogeneous medium which exhibits both frequency selective at- tenuation and dispersion is given by Morse (1948): A(f z) 12Hft A (f) -Y(f)Z 12Hf[t ? Z/C(f)] 0 where A(f, Z) is the spectrum...
NASA Astrophysics Data System (ADS)
Golosio, B.; Brunetti, A.; Cesareo, R.; Amendolia, S. R.; Rao, D. V.; Seltzer, S. M.
2001-06-01
Images of soft materials are obtained using image intensifier based X-ray system (Rao et al., Nucl. Instr. and Meth. A 437 (1999) 141). The interior of the soft material is visualized using the novel software in order to know the distribution of attenuation coefficient in terms of density. The novel software is based mainly on graphical library and applicable to several operating systems without any change. It can be applied to several applications starting from biomedical to industries, for example, quality control. The results for walnut and brew tooth are presented as a set of images from the internal parts of the sample. A description of the principal parameters required for tomographic visualization is given and some results based on this technique are reported and discussed.
Akman, F; Durak, R; Turhan, M F; Kaçal, M R
2015-07-01
The effective atomic numbers and electron densities of some samarium compounds were determined using the experimental total mass attenuation coefficient values near the K edge in the X-ray energy range from 36.847 up to 57.142 keV. The measurements, in the region from 36.847 to 57.142 keV, were done in a transmission geometry utilizing the K?2, K?1, K?1 and K?2 X-rays from different secondary source targets excited by the 59.54 keV gamma-photons from an Am-241 annular source. This paper presents the first measurement of the effective atomic numbers and electron densities for some samarium compounds near the K edge. The results of the study showed that the measured values were in good agreement with the theoretically calculated ones. PMID:25880612
Excitation and Attenuation of Hypersonic Waves in Quartz
H. E. Bömmel; K. Dransfeld
1960-01-01
A method for the generation and detection of hypersonic waves, which has only been briefly described earlier, together with some absorption measurements in quartz, is discussed in some detail. Further measurements of the hypersonic absorption in quartz at different crystal orientations and after neutron irradiation are reported. The results are in qualitative agreement with a phonon-phonon relaxation process.
Patterns of spiral wave attenuation by low-frequency periodic planar fronts.
de la Casa, Miguel A; de la Rubia, F Javier; Ivanov, Plamen Ch
2007-03-01
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. PMID:17411266
Patterns of spiral wave attenuation by low-frequency periodic planar fronts
NASA Astrophysics Data System (ADS)
de la Casa, Miguel A.; de la Rubia, F. Javier; Ivanov, Plamen Ch.
2007-03-01
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.
Klyen, Blake R.; Scolaro, Loretta; Shavlakadze, Tea; Grounds, Miranda D.; Sampson, David D.
2014-01-01
We present the assessment of ex vivo mouse muscle tissue by quantitative parametric imaging of the near-infrared attenuation coefficient µt using optical coherence tomography. The resulting values of the local total attenuation coefficient µt (mean ± standard error) from necrotic lesions in the dystrophic skeletal muscle tissue of mdx mice are higher (9.6 ± 0.3 mm?1) than regions from the same tissue containing only necrotic myofibers (7.0 ± 0.6 mm?1), and significantly higher than values from intact myofibers, whether from an adjacent region of the same sample (4.8 ± 0.3 mm?1) or from healthy tissue of the wild-type C57 mouse (3.9 ± 0.2 mm?1) used as a control. Our results suggest that the attenuation coefficient could be used as a quantitative means to identify necrotic lesions and assess skeletal muscle tissue in mouse models of human Duchenne muscular dystrophy. PMID:24761302
Velocity-Space Diffusion Coefficients Due to Full-Wave ICRF Fields in Toroidal Geometry
Harvey, R.W.; Jaeger, F.; Berry, L.A.; Batchelor, D.B.; D'Azevedo, E.; Carter, M.D.; Ershov, N.M.; Smirnov, A.P.; Bonoli, P.; Wright, J.C.; Smithe, D.N.
2005-09-26
Jaeger et al. have calculated bounce-averaged QL diffusion coefficients from AORSA full-wave fields, based on non-Maxwellian distributions from CQL3D Fokker-Planck code. A zero banana-width approximation is employed. Complementing this calculation, a fully numerical calculation of ion velocity diffusion coefficients using the full-wave fields in numerical tokamak equilibria has been implemented to determine the finite orbit width effects. The un-approximated Lorentz equation of motion is integrated to obtain the change in velocity after one complete poloidal transit of the tokamak. Averaging velocity changes over initial starting gyro-phase and toroidal angle gives bounce-averaged diffusion coefficients. The coefficients from the full-wave and Lorentz orbit methods are compared for an ITER DT second harmonic tritium ICRF heating case: the diffusion coefficients are similar in magnitude but reveal substantial finite orbit effects.
Pulse wave attenuation measurement by linear and nonlinear methods in nonlinearly elastic tubes.
Bertram, C D; Pythoud, F; Stergiopulos, N; Meister, J J
1999-04-01
Reasons for the continuing difficulty in making definitive measurements of pulse wave attenuation in elastic tubes and arteries in the presence of reflections are sought. The measurement techniques available were re-examined in elastic tubes mimicking the arterial compliance nonlinearity, under conditions of strong reflection. The pulse was of physiological shape, and two different pulse amplitudes in the physiological range were used. Measurements of pressure, flow-rate and diameter pulsation allowed the deployment of four of the classical linear methods of analysis. In addition, a method of separating the forward- and backward-travelling waves that does not require linearising assumptions was used, and the attenuation in the forward and reverse directions was calculated from the resulting waveforms. Overall, the results obtained here suggest that a fully satisfactory way of measuring arterial attenuation has yet to be devised. The classical linear methods all provided comparable attenuation estimates in terms of average value and degree of scatter across frequency. Increased scatter was generally found at the higher pulse amplitude. When the forward waveforms from the separation were similarly compared in terms of frequency components, the average value at energetic harmonics was similar to both the value indicated by the linear methods and the values predicted from linear theory on the basis of estimated viscous and viscoelastic parameter data. The backward waveforms indicated a physically unreasonable result, attributed as the expression for this technique of the same difficulties that normally manifest in scatter. Data in the literature suggesting that one of the classical methods, the three-point, systematically over-estimates attenuation were not supported, but it was confirmed that this method becomes prone to negative attenuation estimates at low harmonics as pulse amplitude increases. Although the goal of definitive attenuation measurement remains elusive, the task provides a sensitive tool for the examination of the effect of nonlinearities in the arterial system. PMID:10468357
Temporal change in coda wave attenuation observed during an eruption of Mount St. Helens
Fehler, M.; Roberts, P.; Fairbanks, T.
1988-05-10
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
On shallow water waves in a medium with time-dependent dispersion and nonlinearity coefficients.
Abdel-Gawad, Hamdy I; Osman, Mohamed
2015-07-01
In this paper, we studied the progression of shallow water waves relevant to the variable coefficient Korteweg-de Vries (vcKdV) equation. We investigated two kinds of cases: when the dispersion and nonlinearity coefficients are proportional, and when they are not linearly dependent. In the first case, it was shown that the progressive waves have some geometric structures as in the case of KdV equation with constant coefficients but the waves travel with time dependent speed. In the second case, the wave structure is maintained when the nonlinearity balances the dispersion. Otherwise, water waves collapse. The objectives of the study are to find a wide class of exact solutions by using the extended unified method and to present a new algorithm for treating the coupled nonlinear PDE's. PMID:26199750
On shallow water waves in a medium with time-dependent dispersion and nonlinearity coefficients
Abdel-Gawad, Hamdy I.; Osman, Mohamed
2014-01-01
In this paper, we studied the progression of shallow water waves relevant to the variable coefficient Korteweg–de Vries (vcKdV) equation. We investigated two kinds of cases: when the dispersion and nonlinearity coefficients are proportional, and when they are not linearly dependent. In the first case, it was shown that the progressive waves have some geometric structures as in the case of KdV equation with constant coefficients but the waves travel with time dependent speed. In the second case, the wave structure is maintained when the nonlinearity balances the dispersion. Otherwise, water waves collapse. The objectives of the study are to find a wide class of exact solutions by using the extended unified method and to present a new algorithm for treating the coupled nonlinear PDE’s. PMID:26199750
Plane-wave reflection coefficients for gas sands at nonnormal angles of incidence
W. J. Ostrander
1984-01-01
The P-wave reflection coefficient at an interface sep- arating two media is known to vary with angle of inci- dence. The manner in which it varies is strongly affected by the relative values of Poisson's ratio in the two media. For moderate angles of incidence, the relative change in reflection coefficient is particularly significant when Poisson's ratio differs greatly between
Imaging Rayleigh Wave Attenuation and Phase Velocity beneath North America with USArray
NASA Astrophysics Data System (ADS)
Bao, X.; Dalton, C. A.; Jin, G.; Gaherty, J. B.
2014-12-01
The EarthScope USArray provides an opportunity to obtain detailed images of the continental upper mantle of United States at a novel scale. The majority of mantle models derived from USArray data contain spatial variations in velocity; however, little is known about the attenuation structure of the North American upper mantle. Joint interpretation of seismic attenuation and velocity models can improve upon the interpretations based only on velocity, and provide important constraints on the temperature, composition, melt content, and volatile content of the mantle. In this study, Rayleigh wave travel time and amplitude are measured using an interstation cross-correlation version of the Generalized Seismological Data Functional algorithm, which takes advantage of waveform similarity at nearby stations. Our data are from 670 large teleseismic earthquakes that occurred from 2006 to 2014 and were recorded by 1,764 Transportable Array stations. More than 4.8 million measurements at periods between 20 and 100 s are collected into our database. Isolating the signal of attenuation in the amplitude observations is challenging because amplitudes are sensitive to a number of factors in addition to attenuation, such as focusing/defocusing and local site amplification. We generate several Rayleigh wave attenuation maps at each period, using several different approaches to account for source and receiver effects on amplitude. This suite of attenuation maps allows us to distinguish between the robust features in the maps and the features that are sensitive to the treatment of source and receiver effects. We apply Helmholtz surface-wave tomography (Lin et al., 2012) to determine velocity and attenuation maps. A significant contrast in velocity and attenuation is observed in the transition between the western and central United States along the Rocky Mountain front. We find low Q values in the western US, along the eastern coast, and the Gulf plain. These areas are also characterized by low wave speed in the phase-velocity maps. The lateral variations in Q may indicate possible temperature variations in the upper mantle of the continental interior. Our Q maps in the western US show good agreement with those presented by Lin et al. (2012). Both models contain low Q (< 100) beneath the Colorado Plateau and the West Coast for 60 s.
Landry, Guillaume; Seco, Joao; Gaudreault, Mathieu; Verhaegen, Frank
2013-10-01
Dual energy computed tomography (DECT) can provide simultaneous estimation of relative electron density ?e and effective atomic number Zeff. The ability to obtain these quantities (?e, Zeff) has been shown to benefit selected radiotherapy applications where tissue characterization is required. The conventional analysis method (spectral method) relies on knowledge of the CT scanner photon spectra which may be difficult to obtain accurately. Furthermore an approximate empirical attenuation correction of the photon spectrum through the patient is necessary. We present an alternative approach based on a parameterization of the measured ratio of low and high kVp linear attenuation coefficients for deriving Zeff which does not require the estimation of the CT scanner spectra. In a first approach, the tissue substitute method (TSM), the Rutherford parameterization of the linear attenuation coefficients was employed to derive a relation between Zeff and the ratio of the linear attenuation coefficients measured at the low and high kVp of the CT scanner. A phantom containing 16 tissue mimicking inserts was scanned with a dual source DECT scanner at 80 and 140 kVp. The data from the 16 inserts phantom was used to obtain model parameters for the relation between Zeff and [Formula: see text]. The accuracy of the method was evaluated with a second phantom containing 4 tissue mimicking inserts. The TSM was compared to a more complex approach, the reference tissue method (RTM), which requires the derivation of stoichiometric fit parameters. These were derived from the 16 inserts phantom scans and used to calculate CT numbers at 80 and 140 kVp for a set of tabulated reference human tissues. Model parameters for the parameterization of [Formula: see text] were estimated for this reference tissue dataset and compared to the results of the TSM. Residuals on Zeff for the reference tissue dataset for both TSM and RTM were compared to those obtained from the spectral method. The tissue substitutes were well fitted by the TSM with R(2) = 0.9930. Residuals on Zeff for the phantoms were similar between the TSM and spectral methods for Zeff < 8 while they were improved by the TSM for higher Zeff. The RTM fitted the reference tissue dataset well with R(2) = 0.9999. Comparing the Zeff extracted from TSM and the more complex RTM to the known values from the reference tissue dataset yielded errors of up to 0.3 and 0.15 units of Zeff respectively. The parameterization approach yielded standard deviations which were up to 0.3 units of Zeff higher than those observed with the spectral method for Zeff around 7.5. Procedures for the DECT estimation of Zeff removing the need for estimates of the CT scanner spectra have been presented. Both the TSM and the more complex RTM performed better than the spectral method. The RTM yielded the best results for the reference human tissue dataset reducing errors from up to 0.3 to 0.15 units of Zeff compared to the simpler TSM. Both TSM and RTM are simpler to implement than the spectral method which requires estimates of the CT scanner spectra. PMID:24025623
A multiscale poromicromechanical approach to wave propagation and attenuation in bone.
Morin, Claire; Hellmich, Christian
2014-07-01
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
Characteristics of vibrational wave propagation and attenuation in submarine fluid-filled pipelines
NASA Astrophysics Data System (ADS)
Yan, Jin; Zhang, Juan
2015-04-01
As an important part of lifeline engineering in the development and utilization of marine resources, the submarine fluid-filled pipeline is a complex coupling system which is subjected to both internal and external flow fields. By utilizing Kennard's shell equations and combining with Helmholtz equations of flow field, the coupling equations of submarine fluid-filled pipeline for n=0 axisymmetrical wave motion are set up. Analytical expressions of wave speed are obtained for both s=1 and s=2 waves, which correspond to a fluid-dominated wave and an axial shell wave, respectively. The numerical results for wave speed and wave attenuation are obtained and discussed subsequently. It shows that the frequency depends on phase velocity, and the attenuation of this mode depends strongly on material parameters of the pipe and the internal and the external fluid fields. The characteristics of PVC pipe are studied for a comparison. The effects of shell thickness/radius ratio and density of the contained fluid on the model are also discussed. The study provides a theoretical basis and helps to accurately predict the situation of submarine pipelines, which also has practical application prospect in the field of pipeline leakage detection.
Sound absorption coefficient measurements by phase-conjugate ultrasonic waves
NASA Astrophysics Data System (ADS)
Smagin, N. V.; Krutyansky, L. M.; Brysev, A. P.
2013-03-01
Measurements of the sound absorption coefficient in test objects containing solid microparticles randomly distributed over the object volumes are carried out. Two methods are used for this purpose: the standard echo-pulse insert-substitution method and a modified method using phase conjugation of ultrasound. The test objects are made from gelatin, and the size of the particles introduced in it is chosen to allow measurements in both the long- and medium-wavelength scattering modes of the probing beam. It is shown that, in the first scattering mode, in which the presence of particles causes additional viscous and temperature losses, the two aforementioned methods give identical results. In the second scattering mode, in which the dominant mechanism of additional loss is elastic scattering, the use of phase conjugation allows an almost complete reconstruction of the scattered field and, hence, a more reliable upper estimate for the coefficient of ultrasonic absorption in the test objects.
NASA Astrophysics Data System (ADS)
Ichinose, G.; Woods, M.; Dwyer, J.
2014-03-01
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.
NASA Astrophysics Data System (ADS)
Lemein, T.; Cox, D. T.; Albert, D.; Blackmar, P.
2012-12-01
Feedbacks between vegetation, wave climate, and sedimentation create stable ecosystem states within estuaries that provide ecosystem services such as wildlife habitat, erosion control, and pollution filtration. Flume and field studies conducted with cordgrass (Spartina spp.) and sea grasses (Zostera spp., Halodule spp.) have demonstrated that the presence of vegetation reduces wave energy and increases sediment retention. Since the spatial distribution of plant species and the presence of unique plant species differ between estuaries, there is a need to understand how individual plant species, or groups of species with similar morphology, influence wave characteristics and sedimentation. Within Tillamook Bay, Oregon, three species of emergent vascular vegetation species (Carex lyngbyei, Eleocharis sp., Schoenoplectus pungens) and one species of submergent vascular vegetation species (Zostera marina) are present in the high wave energy portion of the estuary at the border of open water and the start of vegetation. These species represent three distinct growth forms (emergent reeds, emergent grasses, submergent grasses) and occur at varying densities relative to each other, as well as within the estuary. Using paired acoustic Doppler velocimeters (ADVs), we quantify the relative attenuation of wave velocity between vegetation types and densities within the estuary and compare these results with published attenuation rates from flume and field studies in different environments. The effect of decreased wave velocity on sediment retention is measured using permanent sediment markers within and outside of vegetation stands and paired with ADV data. Sediment retention is predicted to vary seasonally with seasonal vegetation composition changes and remain constant in unvegetated areas. From this experiment we expect to identify like groups of plant species whose attenuation characteristics are the same, allowing for models of wave-vegetation-sediment interaction to be created with multiple vegetation types.
Seismic?wave attenuation determined from tectonic tremor in multiple subduction zones
Yabe, Suguru; Baltay, Annemarie S.; Ide, Satoshi; Beroza, Gregory C.
2014-01-01
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.
Self-Similar Asymptotic Optical Waves in Quintic Nonlinear Media with Distributed Coefficients
NASA Astrophysics Data System (ADS)
Jin, Hai-Qin
2015-08-01
The self-similar asymptotic optical waves propagating in quintic nonlinear media with distributed coefficients are investigated. These optical waves are predicted to exist in (i) normal dispersion and self-focusing quintic nonlinear media and (ii) anomalous dispersion and self-defocusing quintic nonlinear media. The possibility of controlling the shape of output asymptotic optical waves is demonstrated. The analytical results are confirmed by numerical simulations.
PIC-MCC simulation of electromagnetic wave attenuation in partially ionized plasmas
NASA Astrophysics Data System (ADS)
Xu, Yanxia; Qi, Xin; Yang, Xue; Li, Chao; Zhao, Xiaoying; Duan, Wenshan; Yang, Lei
2014-02-01
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.
Ali, E S M; Spencer, B; McEwen, M R; Rogers, D W O
2015-02-21
In this study, a quantitative estimate is derived for the uncertainty in the XCOM photon mass attenuation coefficients in the energy range of interest to external beam radiation therapy-i.e. 100 keV (orthovoltage) to 25 MeV-using direct comparisons of experimental data against Monte Carlo models and theoretical XCOM data. Two independent datasets are used. The first dataset is from our recent transmission measurements and the corresponding EGSnrc calculations (Ali et al 2012 Med. Phys. 39 5990-6003) for 10-30 MV photon beams from the research linac at the National Research Council Canada. The attenuators are graphite and lead, with a total of 140 data points and an experimental uncertainty of ?0.5% (k = 1). An optimum energy-independent cross section scaling factor that minimizes the discrepancies between measurements and calculations is used to deduce cross section uncertainty. The second dataset is from the aggregate of cross section measurements in the literature for graphite and lead (49 experiments, 288 data points). The dataset is compared to the sum of the XCOM data plus the IAEA photonuclear data. Again, an optimum energy-independent cross section scaling factor is used to deduce the cross section uncertainty. Using the average result from the two datasets, the energy-independent cross section uncertainty estimate is 0.5% (68% confidence) and 0.7% (95% confidence). The potential for energy-dependent errors is discussed. Photon cross section uncertainty is shown to be smaller than the current qualitative 'envelope of uncertainty' of the order of 1-2%, as given by Hubbell (1999 Phys. Med. Biol 44 R1-22). PMID:25622289
Attenuation of coda waves in the Garhwal Lesser Himalaya, India
NASA Astrophysics Data System (ADS)
Jain, S. K.; Gupta, S. C.; Kumar, Ashwani
2015-04-01
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.
Extraction of surface wave attenuation from ambient noise: approaches to simulated and real data
NASA Astrophysics Data System (ADS)
Song, X.; Zhou, L.; Weaver, R. L.
2012-12-01
Attenuation, or its inverse, quality factor (Q), is one of the most fundamental parameters of the Earth's media. Measurement of attenuation at regional distances traditionally uses seismic waves generated by earthquakes, which generally requires either a good knowledge of the source or a special choice of geometries to cancel out source effects. Seismic ambient noise correlation methodology has been demonstrated to be highly effective at extracting seismic velocities. Extracting amplitude information is more challenging. The greatest challenge is that the Earth's ambient noise field is highly anisotropic, non-uniform, and variable with time. Here, we explore the methodologies and procedures for extracting surface wave attenuation from empirical Green functions (EGFs) constructed from seismic ambient noise. Our approaches are to combine sound theoretical understanding and practical considerations with real data. Recent theoretical derivations and numerical simulations show that even in the case of incompletely diffuse noise fields, we can robustly recover not only travel times, but also ray arrival amplitudes, the ambient field's specific intensity, the strength and density of its scatterers if any, site amplification factors, and most importantly attenuation. In applications to the Earth, we propose two approaches with detailed formulations: linear array methods and more general methods for 2D station networks, each to be developed through applications to numerically simulated data, and to real data. In the preprocessing of real data, we explore a temporal "flattening" procedure, which speeds up EGF convergence and, in the mean time, preserves amplitudes.
Measurement of the x-ray mass attenuation coefficients of gold in the 38?50-keV energy range
Islam, M.T.; Rae, N.A.; Glover, J.L.; Barnea, Z.; de Jonge, M.D.; Tran, C.Q.; Wang, J.; Chantler, C.T.
2010-11-12
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.
Jalali, Majid
2006-07-01
The compounds, Na{sub 2}B{sub 4}O{sub 7}, H{sub 3}BO{sub 3}, CdCl{sub 2} and NaCl and their solutions, attenuate gamma rays in addition to neutron absorption. These compounds are widely used in shielding of neutron sources, reactor control and neutron converters. Mass attenuation coefficients of gamma related to saturated solutions of the above four compounds, in energies 1172 keV and 1332 keV have been measured by NaI detector and agree very well with the results obtained by Xcom code. Experiment and computation show that, H{sub 3}BO{sub 3} has the highest gamma ray attenuation coefficient among the aforementioned compounds. (author)
Measurements of the semi-diurnal drag coefficient over sand waves
NASA Astrophysics Data System (ADS)
Huntley, David A.; Nicholls, Robert J.; Liu, Chunlei; Dyer, Keith R.
1994-04-01
Simultaneous measurements of tidal flow and pressure gradient over a 10 km distance have been used to estimate the frictional drag coefficient over sand waves in the southern North Sea. The measurements were made over a 27-day period in October-November 1988 at 52°10'N, 3°46'E, within a field of essentially two-dimensional sand waves approximately 3 m high and of wavelength 250 m. The M 2 drag coefficient for depth-averaged flow normal to sand wave crests is found to be 2.95 × 10 -3, in good agreement with values used in numerical models of the region. The uncertainty in this value is estimated to be of the order of 10%, primarily due to possible errors in the phase of the flow relative to the pressure gradient. The time series of daily-averaged semi-diurnal ( Z 2) drag coefficients over the 27-day period shows surprisingly little correlation with nearbed wave orbital velocities. The time of highest waves is associated with a decrease in drag coefficient rather than the increase predicted by most wave-current interaction theories and some previous observations. It is suggested that this behaviour is caused by stratification near the bed due to sediment resuspension under high waves. Predictions using the GLENN and GRANT (1987, Journal of Geophysical Research, 92, 8244-8264) theory provide qualitative support for this hypothesis, though the magnitude of the predicted effect is smaller than observed. The relative insensitivity of the drag coefficient to wave conditions suggests that incorporating simple wave-current algorithms into numerical models may be misleading.
NASA Astrophysics Data System (ADS)
Sokoletsky, Leonid; Yang, Xianping; Shen, Fang
2014-11-01
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.
Seismic attenuation in the eastern Australian and Antarctic plates, from multiple ScS waves
NASA Astrophysics Data System (ADS)
Souriau, Annie; Rivera, Luis; Maggi, Alessia; Lévêque, Jean-Jacques
2012-07-01
The attenuation of seismic shear waves in the mantle beneath the eastern Australian and Antarctic plates is analysed using a large data set of multiple ScSn waves, reflected n times at the core-mantle boundary and (n-1) times at the surface. The data are the transverse components of deep earthquakes from the subduction zones north and east of Australia, recorded at stations in Antarctica, Australia, Indonesia, New Caledonia and New Zealand. The data are filtered with narrow bandpass filters at five frequencies in the range 0.013-0.040 Hz. The ScSn+1/ScSn amplitude ratios of successive ScS phases are compared to the ratios computed for synthetic seismograms for the same paths and same focal mechanisms, to eliminate the effects of source radiation and geometric attenuation. The synthetic seismograms are computed from a summation of toroidal modes for the 1-D reference model PREM. The observed to computed spectral ratios appear consistent for similar paths. They reveal that the attenuation is not frequency dependent, that the contribution of scattering to attenuation is low, and that the PREM model is a valuable reference model for the study region at the considered frequencies. An inversion of the data at 0.026 Hz is performed to retrieve the quality factor Q in the upper mantle, in regions defined using a priori constraints inferred from seismic shear velocities. Q-values close to those of PREM are found beneath the Australian and Antarctic cratons, lower values beneath the Eastern Australian Phanerozoic margin, and very low values beneath the oceanic region between Australia and Antarctica, where ridges and a triple junction are present. The Australian-Antarctic Discordance along the South-Indian ridge appears as an exception with a Q-value close to those of stable continents. The highest Q-values are found beneath the subduction zones, a feature which is not apparent in global attenuation models possibly because of its narrow lateral extension, and because it extends at depths larger than those sampled by surface waves. Despite limitations due to the uneven distribution of the ScSn bounce points at the surface and to the difficulty of collecting a large number of high quality data, our approach appears very promising. It is complementary to the more widely used determination of seismic attenuation using surface waves because it provides increased depth coverage, and a broader spectral coverage. It therefore has a considerable potential in future investigations of mantle structure and dynamics.
Yang, Lei; Ume, I Charles
2015-12-01
The non-contact feature of the Laser/EMAT ultrasonic (LEU) technique is attractive for its NDT applications. However, it is challenging to apply it in thin structures because of the difficulties in the signal interpretations. In this work, the LEU technique is used to inspect the notch depths in thin steel plates. A Continuous Wavelet Transform (CWT)-based algorithm is developed to calculate the transmission coefficients of laser-generated Lamb waves. The effect of varying notch depths on Lamb waves' transmission coefficients is investigated both numerically and experimentally. The transmission coefficients of laser-generated Lamb waves calculated using CWT have been used successfully to predict the notch depths in thin structures. PMID:26195299
Rhode Island, University of
Effect of surface waves on Charnock coefficient under tropical cyclones Il-Ju Moon, Isaac Ginis waves and tides (1255); 4263 Oceanography: General: Ocean prediction. Citation: Moon, I.-J., I. Ginis, and T. Hara (2004), Effect of surface waves on Charnock coefficient under tropical cyclones, Geophys
Ugalde, A.; Pujades, L.G.; Canas, J.A.; Villasenor, A.
1998-01-01
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.
Estimates of ocean wave heights and attenuation in sea ice using the SAR wave mode on Sentinel-1A
NASA Astrophysics Data System (ADS)
Ardhuin, Fabrice; Collard, Fabrice; Chapron, Bertrand; Girard-Ardhuin, Fanny; Guitton, Gilles; Mouche, Alexis; Stopa, Justin
2015-04-01
Swell evolution from the open ocean into sea ice is poorly understood, in particular the amplitude attenuation expected from scattering and dissipation. New synthetic aperture radar (SAR) data from Sentinel-1 wave mode reveal intriguing patterns of bright oscillating lines shaped like instant noodles. We investigate cases in which the oscillations are in the azimuth direction, around a straight line in the range direction. This observation is interpreted as the distortion by the SAR processing of crests from a first swell, due to the presence of a second swell. As deviations from a straight line should be proportional to the orbital velocity towards the satellite, swell height can be estimated, from 1.5 to 5 m in the present case. This evolution of this 13 s period swell across the ice pack is consistent with an exponential attenuation on a length scale of 200 km.
Estimates of ocean wave heights and attenuation in sea ice using the SAR wave mode on Sentinel-1A
NASA Astrophysics Data System (ADS)
Ardhuin, Fabrice; Collard, Fabrice; Chapron, Bertrand; Girard-Ardhuin, Fanny; Guitton, Gilles; Mouche, Alexis; Stopa, Justin E.
2015-04-01
Swell evolution from the open ocean into sea ice is poorly understood, in particular the amplitude attenuation expected from scattering and dissipation. New synthetic aperture radar (SAR) data from Sentinel-1A wave mode reveal intriguing patterns of bright oscillating lines shaped like instant noodles. We investigate cases in which the oscillations are in the azimuth direction, around a straight line in the range direction. This observation is interpreted as the distortion by the SAR processing of crests from a first swell, due to the presence of a second swell. Since deviations from a straight line should be proportional to the orbital velocity toward the satellite, swell height can be estimated, from 1.5 to 5 m in the present case. The evolution of this 13 s period swell across the ice pack is consistent with an exponential attenuation on a length scale of 200 km.
Velocity Dispersion and Attenuation of Acoustic Waves in Granular Sedimentary Media.
NASA Astrophysics Data System (ADS)
Tutuncu, Azra Nur
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.
NASA Astrophysics Data System (ADS)
Collard, F.; Ardhuin, F.; Guitton, G.; Dumont, D.; Nicot, P.; Accenti, M.; Girard-Ardhuin, F.
2014-12-01
Sentinel-1A launched by the European Space Agency in April 2014 will complete its full calibration and validation phase including Level2 products early in 2015 but image quality is already good enought for scientific exploitation of observed wave modulations. The larger frequency bandwidth and new acquisition modes are providing a much improved capability for imaging ocean waves in the open water and in the ice compared to Envisat. Here we estimate wave spectra in the Arctic assuming a spatially uniform modulation transfer function where the backscatter over ice is homogeneous, matching the wave heights in open ocean and ice at the ice edge. These wave properties are used to estimate attenuation scales for wavelength longer than twice the radar image resolution. These estimated attenuations are compared to model results based on WAVEWATCH III, where attenuation and scattering uses a combination of friction below the ice and scattering adapted from Dumont et al. (2011) and Williams et al. (2013).
NASA Astrophysics Data System (ADS)
Dalton, C. A.; Hjorleifsdottir, V.; Ekstrom, G.
2011-12-01
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.
Numerical simulation of ultrasonic wave propagation in anisotropic and attenuative solid materials.
You, Z; Lusk, M; Ludwig, R; Lord, W
1991-01-01
The axisymmetric elastodynamic finite element code developed is capable of predicting quantitatively accurate displacement fields for elastic wave propagation in isotropic and transversely isotropic materials. The numerical algorithm incorporates viscous damping by adding a time-dependent tensor to Hooke's law. Amplitude comparisons are made between the geometric attenuation in the far field and the corresponding finite element predictions to investigate the quality and validity of the code. Through-transmission experimental measurements made with a 1 MHz L-wave transducer attached to an aluminum sample support the code predictions. The algorithm successfully models geometric beam spreading dispersion and energy absorption due to viscous damping. This numerical model is a viable tool for the study of elastic wave propagation in nondestructive testing applications. PMID:18267605
High precision ultrasonic velocity and attenuation measurements of Lamb waves in anisotropic plates
NASA Astrophysics Data System (ADS)
Reed, R. W.
A technique is described which involves noncontacting electromagnetic acoustic transducers and automated signal processing for measuring the attenuation and velocity of wideband pulses of Lamb waves in thin metal plates. The measurements are made at 0.3-3 MHz with four transducers (two transmitters, two receivers). A numerical expression is developed for the apparent acoustic attenuation to free the calculations from errors caused by transducer coupling efficiency decrements. Gr/Al plates were scanned at 1 cm/sec assembly to test the efficacy of the technique. Sound velocity accelerations at spot welds joining plates to structures were clearly revealed by the technique, as were the locations of precursor wires of different densities embedded within an unwelded plate. Finally, the use of long receiver gage lengths permitted identifying variations in the plate mechanical properties such as the elastic modulus.
NASA Astrophysics Data System (ADS)
Mandeep, J. S.; Hassan, S. I. S.
2008-02-01
A propagation experiment has been carried out at Penang using the SUPERBIRD-C satellite beacon. Cloud occurrences were observed during different months and it is seen that the low cloud occurrences over Penang is very significant from October to January. The cloud attenuation results that are presented, which include the testing of models, have been obtained from the data gathered over five years. The specific attenuation of radio wave due to clouds at various frequencies 12 GHz, 20 GHz, 75 GHz, 50 GHz and 100 GHz has been estimated whereby the values varies from 0.14 dB/km at 12 GHz to 10.1 dB/km at 100 GHz.
NASA Astrophysics Data System (ADS)
Gu, Xiao-Qiang; Yin, Wen-Yan; Zheng, Ting
2014-11-01
Guided THz wave characteristics in a parallel-plate waveguide (PPWG) consisting of ferroelectric film (LiNbO3 and LiTaO3) and multilayer graphene (MLG) is studied in this paper, with their low and tunable attenuation valley predicted. The electrical conductivity of MLG is calculated by a set of closed-form equations with the coupling effect between the bottom graphene layer (BGL) and its substrate taken into account carefully, while the dispersive behavior of ferroelectric film itself is described by the Lorentz model over an ultra-wide THz band. It is shown that the guided TM-mode propagation can be adjusted effectively by changing temperature, frequency, optical pumping intensity, MLG layer number, film thickness and its transverse optical-phonon frequency. Moreover, one low attenuation valley of TM-mode in such ferroelectric-graphene waveguide is captured, which can be exploited for developing some THz planar tunable waveguides with ultra-low loss.
Attenuation Of Current Wave Propagating Along A Perfectly Conducting Wire: Application To Lightning
NASA Astrophysics Data System (ADS)
Baba, Y.; Rakov, V. A.
2003-12-01
In this study, using the finite-difference time-domain (FDTD) method for solving Maxwell_fs equations, we demonstrate that a vertical phased array of current sources above perfectly conducting ground, activated as prescribed by the transmission line (TL) model with return-stroke speed equal to the speed of light (v = c), produces a spherical TEM wave, identical to that analytically derived for the TL model with v = c by Thottappillil et al. [2001]. (This can be viewed as a proof of validity of the FDTD method used here.) Then, we apply the same approach to the case of a lumped current source at the bottom of a vertical perfectly conducting wire above perfectly conducting ground and show that the current wave launched by the current source propagates upward with attenuation and that the resultant field structure is non-TEM, as also follows from other lightning return stroke models based on solving Maxwell_fs equations. The attenuation is stronger for shorter current pulses and for current sources of smaller length. Thus, it appears that the basic assumption of the TL model (no current attenuation with height) is inconsistent with Maxwell_fs equations, unless the lightning channel is viewed as a phased array of current sources. It is inconsistent with the transmission line theory either, since a vertical wire above ground constitutes a non-uniform transmission line, whose characteristic impedance varies with height. We will try to explain the mechanism of current attenuation on a vertical perfectly conducting wire above perfectly conducting ground, usually attributed to radiation losses, on the basis of the electromagnetic field theory. In particular, we will discuss the interaction of the electromagnetic field produced by the source with the vertical conductor and ground and the direction of resultant Poynting vector. Thottappillil, R., J. Schoene, and M. A. Uman, Return stroke transmission line model for stroke speed near and equal that of light, Geophys. Res. Lett, 28(18), 3593-3596, 2001.
Spatial variation of Lg-wave attenuation in the Iberian Peninsula
NASA Astrophysics Data System (ADS)
Noriega, Raquel; Ugalde, Arantza; Villaseñor, Antonio; José Jurado, María
2014-05-01
Within a global context, the Iberian Peninsula is a region where low to moderate (Mw < 5.5) earthquakes occur, most of them at shallow depths (h < 40 km). Seismicity concentrates mainly around the Pyrenean Range, the northwestern part of the peninsula, and the southern deformation zone that includes the Betics, the Alborán Sea and the Gulf of Cádiz. In recent years, considerable improvements in seismic data quality and geographic coverage have been made by the deployment of new permanent and portable broadband seismic stations in the Iberian Peninsula. The dense accumulation of seismic data has allowed us to investigate lateral variation of crustal seismic attenuation to develop the first regional 2D Lg-wave attenuation model for the entire Iberian Peninsula and its frequency dependence. Seismic data used consist of 71 events with magnitudes 3 ? mbLg ? 5.4 focal depths less than 30 km and epicentral distances from 100 to 1000 km which were recorded by 343 seismic stations between January 2008 and October 2013. To avoid confusion with fundamental-mode Love-wave energy on the transverse components, we only analyzed vertical component recordings. Among all the methods proposed to measure Lg attenuation, we considered the reliable Two-Station Method that allows removing the common source term by taking the ratio of Lg amplitudes recorded at two different stations along the same great-circle path from the same event. It requires, however, strict source-station configuration and dense event and station coverage. The spectral ratios collected over high-quality interstation paths were used to determine 1 Hz Lg Q (Q0) and its frequency dependence ?. Then, the lateral variations of the attenuation parameters were mapped using inversion. Lg-wave propagation was found to be inefficient or blocked for most of the paths crossing the Mediterranean Sea, the western Alborán Sea and the Strait of Gibraltar. Our results reflect large variations in Q0 values across the Iberian Peninsula which is in accordance with the different geotectonic characteristics present in the region. Low Lg Q0 values (high attenuation) were found in the Pyrenean Range and in the southern area whereas the most stable western part of Iberia showed high Lg Q0. The obtained Lg ? spatial variation map show that intermediate ? values characterize most of the analyzed region.
Efficient computation of the time-domain TM plane-wave reflection coefficient
E. J. Rothwell; J. W. Thomas
2005-01-01
An efficient method for the calculation of the transient reflection coefficient for TM plane wave reflection from a conducting half space is given. The corrected series form, which is valid for angles of incidence less than the Brewster angle, is shown to converge within a few terms for typical values of material parameters.
NASA Astrophysics Data System (ADS)
Roy, Bunty Rani; Rajput, Parasmani; Jha, S. N.; Nageswara Rao, A. S.
2015-09-01
The work presents the X-ray absorption fine structure (XAFS) technique for measuring the X-ray mass attenuation coefficient of nickel metal foil in the X-ray energy range of 8271.2-8849.4 eV using scanning XAFS beam line (BL-09) at Indus-2 synchrotron radiation source facility, Raja Ramanna Centre for Advanced Technology (RRCAT) at Indore, India. The result represents the X-ray mass attenuation coefficient data for 0.02 mm thick Ni metal foil in the XAFS region of Ni K-edge. However, the results are compared to theoretical values using X-COM. There is a maximum deviation which is found exactly near the K-edge jump and decreases as we move away from the absorption edge. Oscillatory structure appears just above the observed absorption edge i.e., 8348.7 eV and is confined to around 250 eV above the edge.
Rivard, M J; Waid, D S; Wierzbicki, J G
1999-11-01
The mass attenuation coefficients, mu/rho, for Clear-Pb for photon energies ranging from 10 keV to 10 MeV were determined using Monte Carlo methods and simple equations used to manipulate elemental mass attenuation coefficients. It was determined that the effectiveness of Clear-Pb as a radiation shielding material was greater than plain acrylic for all photon energies, especially those less than 150 keV, and for deep penetration problems where the differences in mu/rho between Clear-Pb and acrylic became more significant. Finally, the usefulness of Clear-Pb as a shielding material when compared with acrylic was determined for the following commonly used radionuclides: 125I, 103Pd, 99mTc, 192Ir, 137Cs, and 60Co. PMID:10524511
Zhou, Ji-Xun; Zhang, Xue-Zhen
2012-12-01
Several physics-based seabed geoacoustic models (including the Biot theory) predict that compressional wave attenuation ?(2) in sandy marine sediments approximately follows quadratic frequency dependence at low frequencies, i.e., ?(2)?kf(n) (dB/m), n=2. A recent paper on broadband geoacoustic inversions from low frequency (LF) field measurements, made at 20 locations around the world, has indicated that the frequency exponent of the effective sound attenuation n?1.80 in a frequency band of 50-1000 Hz [Zhou et al., J. Acoust. Soc. Am. 125, 2847-2866 (2009)]. Carey and Pierce hypothesize that the discrepancy is due to the inversion models' neglect of shear wave effects [J. Acoust. Soc. Am. 124, EL271-EL277 (2008)]. The broadband geoacoustic inversions assume that the seabottom is an equivalent fluid and sound waves interact with the bottom at small grazing angles. The shear wave velocity and attenuation in the upper layer of ocean bottoms are estimated from the LF field-inverted effective bottom attenuations using a near-grazing bottom reflection expression for the equivalent fluid model, derived by Zhang and Tindle [J. Acoust. Soc. Am. 98, 3391-3396 (1995)]. The resultant shear wave velocity and attenuation are consistent with the SAX99 measurement at 25 Hz and 1000 Hz. The results are helpful for the analysis of shear wave effects on long-range sound propagation in shallow water. PMID:23231101
NASA Astrophysics Data System (ADS)
Grujicic, Mica; Snipes, J. S.; Ramaswami, S.; Yavari, R.; Ramasubramanian, M. K.
2014-01-01
Over the past several years, considerable research efforts have been made toward investigating polyurea, a segmented thermoplastic elastomer, and particularly its shock-mitigation capacity, i.e., an ability to attenuate and disperse shock-waves. These research efforts have clearly established that the shock-mitigation capacity of polyurea is closely related to its chemistry, processing route, and the resulting microstructure. Polyurea typically possesses a nano-segregated microstructure consisting of (high glass transition temperature, T g) hydrogen-bonded discrete hard domains and a (low T g) contiguous soft matrix. While the effect of polyurea microstructure on its shock-mitigation capacity is well-established, it is not presently clear what microstructure-dependent phenomena and processes control its shock-mitigation capacity. To help identify these phenomena and processes, meso-scale simulations of the formation of nano-segregated microstructure and its interaction with a leading shock-wave and a trailing release-wave is analyzed in the present work. The results obtained revealed that shock-induced hard-domain densification makes an important contribution to the superior shock-mitigation capacity of polyurea, and that the extent of densification is a sensitive function of the polyurea soft-segment molecular weight. In particular, the ability of release-waves to capture and neutralize shock-waves has been found to depend strongly on the extent of shock-induced hard-domain densification and, thus, on the polyurea soft-segment molecular weight.
Attenuation of High Frequency P and S Waves in the Gujarat Region, India
NASA Astrophysics Data System (ADS)
Chopra, Sumer; Kumar, Dinesh; Rastogi, B. K.
2011-05-01
The local earthquake waveforms recorded on broadband seismograph network of Institute of Seismological Research in Gujarat, India have been analyzed to understand the attenuation of high frequency (2-25 Hz) P and S waves in the region. The frequency dependent relationships for quality factors for P ( Q P) and S ( Q S) waves have been obtained using the spectral ratio method for three regions namely, Kachchh, Saurashtra and Mainland Gujarat. The earthquakes recorded at nine stations of Kachchh, five stations of Saurashtra and one station in mainland Gujarat have been used for this analysis. The estimated relations for average Q P and Q S are: Q P = (105 ± 2) f 0.82 ± 0.01, Q S = (74 ± 2) f 1.06 ± 0.01 for Kachchh region; Q P = (148 ± 2) f 0.92 ± 0.01, Q S = (149 ± 14) f 1.43 ± 0.05 for Saurashtra region and Q P = (163 ± 7) f 0.77 ± 0.03, Q S = (118 ± 34) f 0.65 ± 0.14 for mainland Gujarat region. The low Q (<200) and high exponent of f (>0.5) as obtained from present analysis indicate the predominant seismic activities in the region. The lowest Q values obtained for the Kachchh region implies that the area is relatively more attenuative and heterogeneous than other two regions. A comparison between Q S estimated in this study and coda Q ( Qc) previously reported by others for Kachchh region shows that Q C > Q S for the frequency range of interest showing the enrichment of coda waves and the importance of scattering attenuation to the attenuation of S waves in the Kachchh region infested with faults and fractures. The Q S/ Q P ratio is found to be less than 1 for Kachchh and Mainland Gujarat regions and close to unity for Saurashtra region. This reflects the difference in the geological composition of rocks in the regions. The frequency dependent relations developed in this study could be used for the estimation of earthquake source parameters as well as for simulating the strong earthquake ground motions in the region.
NASA Astrophysics Data System (ADS)
Pawar, Pravina P.; Bichile, Govind K.
2013-11-01
The total mass attenuation coefficients of some amino acids, such as Glycine (C2H5NO2), DL-Alanine (C3H7NO2), Proline (C5H9NO2), L-Leucine (C6H13NO2 ), L-Arginine (C6H14N4O2) and L-Arginine Monohydrochloride (C6H15ClN4O2), were measured at 122, 356, 511, 662, 1170, 1275 and 1330 keV photon energies using a well-collimated narrow beam good geometry set-up. The gamma rays were detected using NaI (Tl) scintillation detection system with a resolution of 10.2% at 662 keV. The attenuation coefficient data were then used to obtain the effective atomic numbers (Zeff) and effective electron densities (Neff) of amino acids. It was observed that the effective atomic number (Zeff) and effective electron densities (Neff) tend to be almost constant as a function of gamma-ray energy. The results show that, the experimental values of mass attenuation coefficients, effective atomic numbers and effective electron densities are in good agreement with the theoretical values with less than 1% error.
NASA Astrophysics Data System (ADS)
Kaewkhao, J.; Limsuwan, P.
2010-07-01
In this work, the mass attenuation coefficients, partial interactions and the effective atomic numbers ( Zeff) of Bi 2O 3, PbO and BaO in xR mO n:(100- x)P 2O 5 (where x=30? x?70 (% by weight)) glass system have been investigated on the basis of the mixture rule at 662 keV. The total and partial interactions were calculated by WinXCom software. It has been found that the total mass attenuation coefficients of glasses increase with increasing Bi 2O 3 and PbO concentrations, due to the increasing photoelectric absorption in glass samples. However, Compton scattering gives dominant contribution to the total mass attenuation coefficients for the studied glass samples. The Zeff increases with increase in Bi 2O 3, PbO and BaO concentrations. For comparison, the Zeff of PbO glasses are comparable to that of Bi 2O 3 glasses and Zeff of both glasses are greater than BaO glasses. These results are very useful for designing radiation shielding glass and reflecting the influence of bismuth, barium, and lead content in radiation shielding phosphate glass. Besides the mentioned usefulness of the new materials, development of lead-free radiation protecting glass also leaves non-toxic impact on our environment.
Prego-Borges, Jose' L; Recami, Erasmo; Tavares-Costa, Eduardo
2013-01-01
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 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...
Wave Attenuation at a Salt Marsh Margin: A Case Study of an Exposed Coast on the Yangtze Estuary
S. L. Yang; B. W. Shi; T. J. Bouma; T. Ysebaert; X. X. Luo
2012-01-01
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
NASA Technical Reports Server (NTRS)
Yang, J. C. S.; Tsui, C. Y.
1972-01-01
The propagation of an initialrcidrical pressure pulse through a linear elastic fiber reinforced composite medium is analysed, both experimentally and analytically. In the experiment, tests were performed on plates with single and multiple circular inclusions embedded in a matrix of lower characteristic impedance. Sharp compression pulses were generated at an edge of the plate. Strain gages were mounted on various positions of the plate to determine the attenuation of the transient stress in the fiber reinforced composite. The qualitative analytical treatment is based on the methods of propagating stress discontinuities. Computer programs were written to numerically determine the changes in the shape of the leading wave front and the stresses immediately behind it. Experimental results for the attenuation of stress wave on steel-aluminum and steel-brass fiber-matrix composites compared very well with the computed analytical results when the applied pressure is generated by small explosive charges. The results did not compare well when the applied pressure is generated by projectile impact.
Attenuation Characteristics of Body-Waves for the Bilaspur Region of Himachal Lesser Himalaya
NASA Astrophysics Data System (ADS)
Vandana; Kumar, Ashwani; Gupta, S. C.
2015-06-01
The attenuation characteristics around Bilaspur region of the Himachal Lesser Himalaya have been estimated adopting extended-coda-normalization method, and using a data set of 41 local events (0.5 < M L ? 2.9) that occurred in the region from May 2013 to March 2014. The frequency-dependent relations governing the quality factors of P-waves (Q ? ) and S-waves (Q ? ) in the frequency range from 1.5 to 24 Hz are: (Q ? ) = (43 ± 4) f 1.30±0.04 and Q ? = (79 ± 6) f 1.25±0.02. The average estimates of (Q ? ) and (Q ? ) are found to vary from 71 and 125 at 1.5 Hz to 2901 and 4243 at 24 Hz, respectively. The (Q ? ) and (Q ? ) estimates are compared to the similar estimates obtained for the other seismically active regions of the Himalaya. It is found that for the various Himalayan regions, the (Q ? ) estimates at 1 Hz vary between 22 (for the Kumaon Himalaya) and 97 (for the northwest Himalaya), whereas (Q ? ) estimates range between 63 (for the Garhwal Himalaya) and 127 (for the northwest Himalaya). For the Bilaspur region, the (Q ? )/(Q ? ) ratio is greater than unity and varies between 1.84 and 1.45 in the frequency range from 1 to 24 Hz. The region-specific attenuation relations can be adopted for estimating earthquake source parameters, simulating strong ground motion and assessing seismic hazard for the Bilaspur region of Himachal Lesser Himalaya.
NASA Astrophysics Data System (ADS)
Yeh, Y. S.; Cheng, J. H.; Chen, L. K.; Hung, C. W.; Lo, C. Y.; Liao, C. W.
2008-02-01
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. [Department of Electro-Optical Engineering, Southern Taiwan University, Tainan 710, Taiwan (China)
2008-02-15
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-k{sub z} 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 230 kW at 33.65 GHz with an efficiency of 30%, a saturated gain of 40 dB, and a 3 dB bandwidth of 0.8 GHz for a 60 kV, 13 A electron beam with an axial velocity spread of {delta}v{sub z}/v{sub z}=8%. The power/gain scaling and phase relation between the drive and the output waves are elucidated.
Transmission coefficient of Tollmien-Schlichting waves undergoing small indentation/hump distortion
NASA Astrophysics Data System (ADS)
Xu, Hui; Sherwin, Spencer; Wu, Xuesong
2013-11-01
The influences of short indentation/hump on a flat plate boundary layer are investigated. The aim is to address transmission coefficient of Tollmien.Schlichting (T-S) waves undergoing indentation/hump distortion with different depth (? , or height)/width (\\dcirc) scales and provide insights about the effects of the transmission coefficient on transition. When d =Re 3 / 8 \\dcirc is smaller than or equal to O (1) , because of marching step size restriction, the streamwise marching PSE (parabolized stability equations) are not suitable for addressing the influences of indentation/hump on boundary layers effectively. Hence, the simulations are conducted by linearized Navier-Stokes equations (LNSEs) solved by high-precision spectral element methods. For base flow generation, velocity profiles at flow inlet are set according to solutions of Blasius' equation. For LNSEs, at flow inlet perturbation profiles are set by eigenfunctions of the most unstable discrete mode of Orr-Sommerfeld equation. The transmission coefficients are measured for different ? in terms of T-S waves of flat plate boundary layers. Further, the exponent of ? in transmission coefficient formula is also investigated. The influences of short indentation/hump on a flat plate boundary layer are investigated. The aim is to address transmission coefficient of Tollmien.Schlichting (T-S) waves undergoing indentation/hump distortion with different depth (? , or height)/width (\\dcirc) scales and provide insights about the effects of the transmission coefficient on transition. When d =Re 3 / 8 \\dcirc is smaller than or equal to O (1) , because of marching step size restriction, the streamwise marching PSE (parabolized stability equations) are not suitable for addressing the influences of indentation/hump on boundary layers effectively. Hence, the simulations are conducted by linearized Navier-Stokes equations (LNSEs) solved by high-precision spectral element methods. For base flow generation, velocity profiles at flow inlet are set according to solutions of Blasius' equation. For LNSEs, at flow inlet perturbation profiles are set by eigenfunctions of the most unstable discrete mode of Orr-Sommerfeld equation. The transmission coefficients are measured for different ? in terms of T-S waves of flat plate boundary layers. Further, the exponent of ? in transmission coefficient formula is also investigated. This research was performed in the Laminar Flow Control Centre at Imperial College London. The Centre is supported by EPSRC, Airbus UK and EADS Innovation Works.
Air-ground interface: Surface waves, surface impedance and acoustic-to-seismic coupling coefficient
NASA Technical Reports Server (NTRS)
Daigle, Gilles; Embleton, Tony
1990-01-01
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.
Bounce-averaged diffusion coefficients in the Tsyganenko field model for oblique chorus waves
NASA Astrophysics Data System (ADS)
Orlova, Ksenia; Shprits, Yuri
2010-05-01
The assessment of the importance of various acceleration and loss mechanisms of relativistic electrons is crucially important for predicting and understanding the dynamics of the radiation belts. It is commonly accepted that resonant wave-particle interactions play a major role in these processes. Bounce-averaged momentum, pitch-angle, and mixed diffusion coefficients, calculated using various models of spectral properties of waves and spatial distributions of plasma waves, are used in modern radiation belt codes as inputs. The diffusion coefficients for radiation belt models are usually computed using the quasi-linear theory and are bounce-averaged in the dipole magnetic field. During magnetic storms, however, the configuration and the value of the magnetic field are significantly changed, which may potentially influence the scattering rates. The purpose of this work is to estimate the role of a realistic magnetic field model on the bounce-averaged diffusion coefficients. We present the results of computations of bounce-averaged quasi-linear momentum Dpp, pitch-angle D?? and mixed pitch angle-momentum D?p diffusion coefficients in the Tsyganenko magnetic field model. We assume that electrons are scattered by oblique whistler mode chorus waves of Gaussian spread of wave power spectral density and wave normal angle outside the plasmasphere. The scattering rates are computed using the full electromagnetic dispersion relation and up to ±5-order resonance condition including Landau resonance. The diffusion coefficients are calculated for quiet conditions (Kp=2) and storm-time conditions (Kp=6) for the day and night sides. We compare scattering rates bounce-averaged in the Tsyganenko field model with those in the dipole field and discuss the differences. The results are followed by a physical explanation of how the magnetic field model can change the bounce-averaged scattering rates. The calculations show that, during active conditions, the pitch-angle scattering by chorus waves in the realistic magnetic field can diffuse relativistic electrons to the loss cone not only on the day side, as was previously shown, but also on the night side. This explains the often observed microburst precipitation on the night side. Our study shows that while there are still a number of unknown parameters that determine scattering rates, inclusion of bounce-averaging in the realistic field will be crucially important for future radiation belt modeling.
Effects of fracture contact areas on seismic attenuation due to wave-induced fluid flow
NASA Astrophysics Data System (ADS)
Germán Rubino, J.; Müller, Tobias M.; Milani, Marco; Holliger, Klaus
2014-05-01
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.
Finite-floe wave reflection and transmission coefficients from a semi-infinite model
NASA Astrophysics Data System (ADS)
Meylan, Michael; Squire, Vernon A.
1993-07-01
A model to describe the reflection and transmission of ocean waves by a single ice floe is developed from the semi-infinite model of Fox and Squire (1990, 1991). This is done by considering the coefficients for the transition from ice to water in the semi-infinite case in terms of those from water to ice. Finite-floe reflection and transmission coefficients, R and T, respectively, are then found as the solution of a set of four simple simultaneous equations. The properties of R and T are investigated, and examples of their absolute values are given for several geometries. |R| compares well with the predictions of a precise model in the case of deep water. These results suggest that the analytical model described has applications to defining the sea state within marginal ice zones, given the floe size and ice thickness distributions and the incoming sea wave spectrum.
NASA Astrophysics Data System (ADS)
Lin, F.; Ritzwoller, M. H.
2011-12-01
The deployment of the EarthScope/USArray Transportable Array has promoted new and better ways to utilize the dense array configuration and to resolve higher resolution crustal and upper mantle structures beneath the US. Here, we present a local inversion method for surface wave that utilizes the USArray first to determine the surface wave wavefield empirically and then to directly measure the surface wave propagation characteristics such as isotropic velocity, azimuthal anisotropy, and intrinsic attenuation by solving the 2D Helmholtz wave equation. The method starts with single event analysis, where for each period and earthquake all measurements across the array are aggregated to determine maps of phase travel time and amplitude on a fine spatial grid, which essentially describes the surface wave wavefield. The solution of the 2D wave equation contains real and imaginary parts, which are relevant to velocity and attenuation measurements, respectively. For the real part, directionally dependent phase velocities at each location are estimated from the gradient of phase travel time along with the Laplacian of amplitude. For the imaginary part, on the other hand, intrinsic attenuation at each location is estimated from the dot product of the gradients of phase travel time and amplitude along with the Laplacian of phase travel time. In both cases, the terms that contain the gradient operator are directly related to traditional ray theoretic approaches (e.g., eikonal equation for velocity measurement) whereas the terms involving the Laplacian operator provide corrections for off-ray sensitivity. In principle, by applying the correction terms, finite frequency effects such as wave interference, wavefront healing, and backward scattering are accounted for in phase velocity measurements and focus/defocusing is accounted for in attenuation measurements. We apply the method to Rayleigh wave measurements between 30 and 100 sec period from more than 700 earthquakes and all measurements from single event analysis are statistically summarized to estimate the final maps for isotropic, anisotropic, and attenuation structures and their uncertainties. For velocity tomography, we show that at long period (>50), the method, called Helmholtz tomography, better resolves sub-wavelength velocity structures and unbiased azimuthal anisotropy than its ray theoretic analog, eikonal tomography. For attenuation tomography, we present preliminary attenuation maps for the western US and emphasize the importance of accounting for focusing-defocusing effects in resolving intrinsic attenuation structures.
Piezooptic Coefficients and Acoustic Wave Velocities in Sn2P2S6 Crystals
O. Mys; I. Martynyuk-Lototska; A. Grabar; Yu. Vysochanskii; R. Vlokh
2007-06-28
Piezooptic coefficients of Sn2P2S6 crystals are experimentally determined for l=623.8 nm and T=293 K with the aid of interferometric technique. The components of the elastic stiffness tensor for these crystals are calculated on the basis of studies for the acoustic wave velocities. It is shown that acoustooptic figure of merit can achieve extremely high values for Sn2P2S6 crystals (M2 - 2x10-12s3/kg2).
NASA Astrophysics Data System (ADS)
Yuan, Yeli
2013-04-01
In the frame of ocean dynamical system, considering the nonlinearity and isotropy of the sub-small scale turbulence the paper derived the second order moment closure equations and according to the statistical theory of breaking waves gave the boundary conditions for the kinetic energy input and the mixing length on the sea surface first, which are the physic-mathematical description of the turbulence generated by sea waves. Considering the observation effect that the dissipation rate of the turbulence kinetic energy has power vertical distribution of sea waves, we derived the balanced solution of the variation equations for the turbulence characteristics and gave the analytical expressions of the kinetic energy and the dissipation rate , and then the analytic expressions of the mixing coefficients in the upper ocean according to the closure technique with high determinacy.The theoretical coefficients were applied to the numerical modeling of ocean circulation and then the substantive progress in qualitative and quantitative modeling was gained on the premise of no any coefficient tune-up.
NASA Astrophysics Data System (ADS)
Nusca, Michael Joseph, Jr.
The effects of various gasdynamic phenomena on the attenuation of an electromagnetic wave propagating through the nonequilibrium chemically reacting air flow field generated by an aerodynamic body travelling at high velocity is investigated. The nonequilibrium flow field is assumed to consist of seven species including nitric oxide ions and free electrons. The ionization of oxygen and nitrogen atoms is ignored. The aerodynamic body considered is a blunt wedge. The nonequilibrium chemically reacting flow field around this body is numerically simulated using a computer code based on computational fluid dynamics. The computer code solves the Navier-Stokes equations including mass diffusion and heat transfer, using a time-marching, explicit Runge-Kutta scheme. A nonequilibrium air kinetics model consisting of seven species and twenty-eight reactions as well as an equilibrium air model consisting of the same seven species are used. The body surface boundaries are considered as adiabatic or isothermal walls, as well as fully-catalytic and non-catalytic surfaces. Both laminar and turbulent flows are considered; wall generated flow turbulence is simulated using an algebraic mixing length model. An electromagnetic wave is considered as originating from an antenna within the body and is effected by the free electrons in the chemically reacting flow. Analysis of the electromagnetics is performed separately from the fluid dynamic analysis using a series solution of Maxwell's equations valid for the propagation of a long-wavelength plane electromagnetic wave through a thin (i.e., in comparison to wavelength) inhomogeneous plasma layer. The plasma layer is the chemically reacting shock layer around the body. The Navier-Stokes equations are uncoupled from Maxwell's equations. The results of this computational study demonstrate for the first time and in a systematic fashion, the importance of several parameters including equilibrium chemistry, nonequilibrium chemical kinetics, the reaction mechanism, flow viscosity, mass diffusion, and wall boundary conditions on modeling wave attenuation resulting from the interaction of an electromagnetic wave with an aerodynamic plasma. Comparison is made with experimental data.
Experimental Studies on Role of Scattering Centers on Wave Energy Attenuation
Kim, S.H.; Knaff, C.L.; Taleyarkhan, R.P.
2000-06-18
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.
NASA Astrophysics Data System (ADS)
Blom, M. R.; Beker, M. G.; Bertolini, A.; van den Brand, J. F. J.; Bulten, H. J.; Hennes, E.; Mul, F. A.; Rabeling, D. S.; Schimmel, A.
2013-08-01
In November 2011 a major upgrade of the Virgo gravitational wave detector was started. After these improvements the detector's sensitivity will have increased by an order of magnitude, increasing the expected event rate by 103 compared to its predecessor. Extensive noise studies showed that this improvement can only be accomplished if a number of optical benches, hosting ancillary optics and optical sensors for the alignment of the interferometer, are isolated from seismic ground motion to reduce the amount of beam jitter and control noise they introduce. Here we present the first of these systems: the External Injection Bench Seismic Attenuation System, or EIB-SAS, which is able to reduce seismically induced motion of the external injection bench (last bench before laser beam enters the vacuum system) by more than 40 dB above 10 Hz in 6 degrees of freedom.
VHF/UHF wave attenuation in a city with regularly spaced buildings
NASA Astrophysics Data System (ADS)
Blaunstein, N.; Levin, M.
1996-03-01
In this work a theoretical and experimental investigation analyzing VHF/UHF radio wave propagation in a suburban environment with a grid-type street plan is presented for the purpose of personal communication services prediction. A waveguide with randomly distributed gaps (slits) between the sides of buildings is considered as a model of straight streets with two- and three-story buildings. The average field intensity and path loss at the street level, taking into account the reflection from the ground, multireflection, and diffraction from the walls and building edges, are investigated in line-of-sight (LOS) conditions using a new three-dimensional multislit waveguide model. This model gives good agreement with the two-rays model and with an experimentally found law of field intensity attenuation at the street level with high and low building density up to 1-2 km from the source.
Illinois at Urbana-Champaign, University of
of cervical ripening in human pregnancy Yassin Labyed a,*, Timothy A. Bigelow a , Barbara L. McFarlin b online 19 May 2010 Keywords: Quantitative ultrasound Attenuation estimation Cervical ripening a b s t r to diagnose symptoms prior to uterine contractions. Cervical ripening is a long period that precedes
Illinois at Urbana-Champaign, University of
throughamaterial. The attenuation includes absorption and scattering.Absorption represents the loss of energy into heat within the specimen. Scattering is a redirection of the energy due to the inhomogeneities, the light and dark areasin the acoustic image correspond to areas with low or high ultrasonic at- tenuation
Mass attenuation coefficient of the Earth, Moon and Mars samples over 1keV-100GeV energy range.
Camargo Moreira, Anderson; Roberto Appoloni, Carlos
2006-09-01
This work presents the calculation of the mass attenuation coefficient (micro) of lunar, Martian and terrestrial samples in function of the energy. WinXCOM software was employed to determine the micro values for the samples in the range from 1 keV to 100 GeV. The obtained values were practically the same for energies larger than 100 keV, but marked differences among the samples were observed for energies below 25 keV, which is the energy range of interest for the XRF system used in space probes. PMID:16725330
Orhan ?çelli; Salih Erzeneo?lu; Recep Boncukçuo?lu
2003-01-01
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.
Experimental Measurements Of Seismic Wave Speeds And Attenuation In CO2 Saturated Porous Rocks
NASA Astrophysics Data System (ADS)
Njiekak, G.; Yam, H.; Kofman, R. S.; Chowdhury, M.; Schmitt, D. R.
2011-12-01
Due to the sensitivity of seismic waves to pore fluid contents, time lapse seismology is regarded as a promising monitoring method for geological CO2 sequestration projects and is employed in all industrial scale projects (Sleipner, Weyburn, In Salah). Therefore, understanding the effect of CO2 as a pore fluid on the overall rock seismic response is critical, and it is particularly interesting as CO2 can be in gas, liquid, or supercritical phases even at the relatively modest pore pressures and temperatures in the uppermost kilometer of the earth's crust. To address this issue, ultrasonic P- and S-wave pulse transmission experiments were carried out on fully CO2 saturated samples of a synthetic porous ceramic, Berea and Fontainebleau sandstones, and carbonates under a variety of temperatures and pressures representative of conditions expected in volcanic edifices and geological sequestration projects. The synthetic sample was chosen because of its lack of microcracks, which can complicate the acoustic behavior of real rocks. Although this sample is extremely porous (58%) and is not reflective of real reservoir rocks, its large porosity allows the overall rock behavior to be more susceptible to the changes in the physical properties of the pore fluid; this could provide an extreme end member understanding on the rock physics involved with CO2 as the pore fluid. Laboratory results show waveform variations (velocity, amplitude, attenuation) in response to CO2's varying phase state. For the ceramic rod, CO2 phase changes (gas to liquid and gas to supercritical fluid) are marked by a drop in velocities of 4-5% likely due to the increased density of the liquid or the supercritical fluid relative to the gas. Wave attenuation increases with pore pressure and with frequency. The measured elastic wave velocities showed good agreement with Biot's model in this highly porous sample. The real sandstones, in contrast, display more complicated behaviour at the point of the phase transition. The abruptness in the velocity change differs significantly between the gas-liquid and gas-supercritical fluid transitions; and the gradual variations seen for the latter suggest that this will be difficult to detect using seismic reflection methods.
Pasyanos, M E; Walter, W R; Matzel, E M
2009-02-26
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.
Torello, David; Thiele, Sebastian; Matlack, Kathryn H; Kim, Jin-Yeon; Qu, Jianmin; Jacobs, Laurence J
2015-02-01
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
NASA Technical Reports Server (NTRS)
Yang, J. C. S.; Tsui, C. Y.
1972-01-01
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.
NASA Astrophysics Data System (ADS)
Li, Jianghua; Shen, Zhiyuan; He, Yonghong; Tu, Ziwei; Xia, Yunfei; Chen, Changshui; Liu, Songhao
2012-10-01
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.
NASA Astrophysics Data System (ADS)
Schautz, Friedemann; Fahy, Stephen
2002-03-01
A quantum Monte Carlo method for obtaining multideterminant Jastrow-Slater wave functions for which the energy is stationary with respect to variations of CI coefficients is presented. It is a generalization of a recently developed approach to the optimization of single particle functions [C. Filippi and S. Fahy, J. Chem. Phys. 112, 3523 (2000)]. Using ground state calculations of the atoms Be, C, and Ne and the dimer Si2 as illustrative examples, the method is shown to converge rapidly and to significantly lower the energy in most cases.
Explicit use of the Biot coefficient in predicting shear-wave velocity of water-saturated sediments
Lee, M.W.
2006-01-01
Predicting the shear-wave (S-wave) velocity is important in seismic modelling, amplitude analysis with offset, and other exploration and engineering applications. Under the low-frequency approximation, the classical Biot-Gassmann theory relates the Biot coefficient to the bulk modulus of water-saturated sediments. If the Biot coefficient under in situ conditions can be estimated, the shear modulus or the S-wave velocity can be calculated. The Biot coefficient derived from the compressional-wave (P-wave) velocity of water-saturated sediments often differs from and is less than that estimated from the S-wave velocity, owing to the interactions between the pore fluid and the grain contacts. By correcting the Biot coefficients derived from P-wave velocities of water-saturated sediments measured at various differential pressures, an accurate method of predicting S-wave velocities is proposed. Numerical results indicate that the predicted S-wave velocities for consolidated and unconsolidated sediments agreewell with measured velocities. ?? 2006 European Association of Geoscientists & Engineers.
2-D Coda and Direct Wave Attenuation Tomography in Northern Italy
Morasca, P; Mayeda, K; Gok, R; Phillips, W S; Malagnini, L
2007-10-17
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.
Wave functions of the Q.Q interaction in terms of unitary 9-j coefficients
Larry Zamick; Matthew Harper
2015-03-20
We obtain wave functions for 2 protons and 2 neutrons in the g_{9/2} shell expressed as column vectors with amplitudes D(J_{p},J_{n}). When we use a quadrupole-quadrupole interaction (Q.Q) we get, in many cases, a very strong overlap with wave functions given by a single set of unitary 9j coefficients --U9j= ((jj)^{2j} (jj^{J_{B}} \\ (jj)^{J_{p}} (jj)^{J_{n}})^{I}. Here J_{B}=9 for even I T =0 states. For both even and odd T=1 states we take JB equal to 8 whilst for odd I, T=0 we take JB to be 7. We compare the Q.Q results with those of a more realistic interaction.
NASA Astrophysics Data System (ADS)
Zhou, Wanlu; Wu, You; Zuo, Lei
2015-06-01
Beam or plate metamaterials with periodic piezoelectric arrays have attracted more and more attention in recent years for wave propagation attenuation and the corresponding vibration reduction. Conventional designs use resistive shunt (R-shunt) and resistor-inductor shunt (RL-shunt). An innovative metamaterial with a high-order resonant shunt circuit is proposed and investigated for vibration and wave propagation attenuation in this paper. The proposed high-order resonant shunt circuit can introduce two local resonances in series around the tuning frequency to broaden the attenuation bandwidth, or can create two separate resonances to achieve two separate bandgaps. Finite element modeling of the beam metamaterial with wave propagation and vibration in the transverse direction is established. Simulations have been conducted to compare the vibration attenuation performances among R-shunt, RL-shunt, and the proposed high-order shunt. An impedance-based method has been presented for the parameter design of electrical components in the proposed high-order shunt for bandgaps at two desired frequencies.
The Velocity and Attenuation of Acoustic Emission Waves in SiC/SiC Composites Loaded in Tension
NASA Technical Reports Server (NTRS)
Morscher, Gregory N.; Gyekenyesi, Andrew L.; Gray, Hugh R. (Technical Monitor)
2002-01-01
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.
Walter, W R; Mayeda, K; Malagnini, L; Scognamiglio, L
2007-02-01
We develop a new methodology to determine apparent attenuation for the regional seismic phases Pn, Pg, Sn, and Lg using coda-derived source spectra. The local-to-regional coda methodology (Mayeda, 1993; Mayeda and Walter, 1996; Mayeda et al., 2003) is a very stable way to obtain source spectra from sparse networks using as few as one station, even if direct waves are clipped. We develop a two-step process to isolate the frequency-dependent Q. First, we correct the observed direct wave amplitudes for an assumed geometrical spreading. Next, an apparent Q, combining path and site attenuation, is determined from the difference between the spreading-corrected amplitude and the independently determined source spectra derived from the coda methodology. We apply the technique to 50 earthquakes with magnitudes greater than 4.0 in central Italy as recorded by MEDNET broadband stations around the Mediterranean at local-to-regional distances. This is an ideal test region due to its high attenuation, complex propagation, and availability of many moderate sized earthquakes. We find that a power law attenuation of the form Q(f) = Q{sub 0}f{sup Y} fit all the phases quite well over the 0.5 to 8 Hz band. At most stations, the measured apparent Q values are quite repeatable from event to event. Finding the attenuation function in this manner guarantees a close match between inferred source spectra from direct waves and coda techniques. This is important if coda and direct wave amplitudes are to produce consistent seismic results.
Study of the absorption coefficient of alpha particles to lower hybrid waves in tokamak
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
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.
NASA Astrophysics Data System (ADS)
Preston, L.; Smith, K.
2006-12-01
The UE#25 UZ-16 borehole array at Yucca Mountain, Nevada (designated site for the nation's high-level nuclear waste repository), provides a prime opportunity to investigate near surface effects on seismic waveforms as a function of depth. The borehole 3-component geophone array consists of 96 depth levels of 4.5 Hz sensors from about 30 m to 500 m depth below the surface. Currently we are recording at 18 approximately equally spaced depth levels and the array was recently augmented with three 3-component matching surface sensors (totaling 63 16-bit 200 sps data channels). The time stamped continuous digital data stream is telemetered in real-time to the Nevada Seismological Laboratory where it is visually inspected and event data is subset and integrated with regional network data when necessary; system check calibrations have been performed on all recorded sensors. Therefore, we have high resolution time-depth local and regional earthquake waveform histories from 500 m to the surface within the Yucca Mountain block. Due to the thick cover of Miocene volcanic tuffs at Yucca Mountain, the borehole does not penetrate into the underlying Paleozoic basement but samples tuff horizons of varying thicknesses and properties. Ground motion design criteria for the repository and surface facilities are based, in part, on characterizing the near surface velocities and the amplification, intrinsic attenuation, and scattering of seismic waves from local earthquakes. We present results from several investigations of local earthquake recordings including spectral ratios and attenuation as a function of depth and characterize scattering in the tuff layers. Preliminary results indicate differences in spectral ratios depending on component, with E-W components indicating higher ratios relative to N-S and Z components as compared to the bottom most geophone, most likely due to the structural fabric of Yucca Mountain. Also, most observed amplification from spectral ratios (from about 3 Hz to 15 Hz) appears to occur within the top 60 m of the borehole with the surface geophones demonstrating the largest amplifications, as expected. Preliminary results indicate coda energy amplification, as a function of depth, within the first 5 s after the primary S-wave arrival.
NASA Technical Reports Server (NTRS)
Ohi, Nobuaki; Makinen, Carla P.; Mitchell, Richard; Moisan, Tiffany A.
2008-01-01
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.
NASA Astrophysics Data System (ADS)
Stramska, Malgorzata
2013-04-01
Each year spatial patterns of ocean color in the Baltic Sea differ in temporal evolution and magnitude. We have investigated the interannual variability of the spatially averaged vertical diffuse attenuation coefficient at 490 nm, Kd(490), in response to atmospheric forcing and river discharge. Our results indicate that atmospheric forcing does not have a significant influence on the interannual anomalies of Kd(490) in the Baltic Sea. This is in contrast to the North Atlantic site located at similar latitudes, were interannual variability of phytoplankton blooms (and ocean color) is to a large degree controlled by a local weather. Instead, in the Baltic Sea, the interannual variability of Kd(490) is significantly influenced by the river runoff. Higher values of Kd(490) are observed in years with larger inflow of water from rivers. Without an access to more detailed information about the concentrations of various optically significant water components, we can only speculate about the possible reasons for this correlation, but it is most likely a combination of several factors. These include: development of more intense phytoplankton blooms associated with larger supply of nutrients delivered by rivers, advection of optically important material with river water, as well as different physical condition for phytoplankton growth due to more stable water stratification. The diffuse attenuation coefficient plays a critical role in many oceanographic processes. For example, Kd is essential for quantification of radiative heating of the ocean, in models of primary production and other photoprocesses, and in studies discussing water turbidity and water quality. Better understanding of the variability of Kd in the Baltic Sea can impove our knowledge of this marine environment.
Zhang, Yunlin; Liu, Xiaohan; Yin, Yan; Wang, Mingzhu; Qin, Boqiang
2012-08-27
Accurate estimation of the diffuse attenuation coefficient is critical for our understanding and modelling of key physical, chemical, and biological processes in water bodies. For extremely turbid, shallow, Lake Taihu in China, we synchronously monitored the diffuse attenuation coefficient of photosynthetically active radiation (Kd(PAR)) and the remote sensing reflectance at 134 sites. Kd(PAR)) varied greatly among different sites from 1.62 to 14.68 m(-1) with a mean value of 5.62 ± 2.99 m(-1). A simple optical model from near-infrared remote sensing reflectance of MODIS channels 2 (859 nm) and 15 (748 nm) was calibrated, and validated, to estimate Kd(PAR). With the simple optical model, the root mean square error and mean relative error were 0.95 m(-1) and 17.0% respectively at 748 nm, and 0.98 m(-1) and 17.6% at 859 nm, based on an independent validation data set. Our results showed a good precision of estimation for Kd(PAR) using the new simple optical model, contrasting with the poor estimations derived from existing empirical and semi-analytical models developed in clear, open ocean waters or slightly turbid coastal waters. Although at 748 nm the model had slightly higher precision than at 859 nm, the spatial resolution at 859 nm was four times that at 748 nm. Therefore, we propose a new model based on the MODIS-derived normalized water-leaving radiances at a wavelength of 859 nm, for accurate retrieval of Kd(PAR) in extremely turbid, shallow lakes with Kd(PAR) larger than 1.5 m(-1). PMID:23037096
NASA Astrophysics Data System (ADS)
Milani, Marco; Rubino, J. Germán; Baron, Ludovic; Sidler, Rolf; Holliger, Klaus
2015-10-01
The attenuation and velocity dispersion of sonic waves contain valuable information on the mechanical and hydraulic properties of the probed medium. An inherent complication arising in the interpretation of corresponding measurements is, however, that there are multiple physical mechanisms contributing to the energy dissipation and that the relative importance of the various contributions is difficult to unravel. To address this problem for the practically relevant case of terrestrial alluvial sediments, we analyse the attenuation and velocity dispersion characteristics of broad-band multifrequency sonic logs with dominant source frequencies ranging between 1 and 30 kHz. To adequately compensate for the effects of geometrical spreading, which is critical for reliable attenuation estimates, we simulate our experimental setup using a correspondingly targeted numerical solution of the poroelastic equations. After having applied the thus inferred corrections, the broad-band sonic log data set, in conjunction with a comprehensive suite of complementary logging data, allows for assessing the relative importance of a range of pertinent attenuation mechanisms. In doing so, we focus on the effects of wave-induced fluid flow over a wide range of scales. Our results indicate that the levels of attenuation due to the presence of mesoscopic heterogeneities in unconsolidated clastic sediments fully saturated with water are expected to be largely negligible. Conversely, Monte-Carlo-type inversions indicate that Biot's classical model permits to explain most of the considered data. Refinements with regard to the fitting of the observed attenuation and velocity dispersion characteristics are locally provided by accounting for energy dissipation at the microscopic scale, although the nature of the underlying physical mechanism remains speculative.
NASA Astrophysics Data System (ADS)
Sleep, Norman H.; Nakata, Nori
2015-07-01
Strong seismic waves bring rock into frictional failure at the uppermost few hundred meters. Numerous small fractures slip with the cumulative effect of anelastic strain and nonlinear attenuation; these fractures should not distinguish between remote sources of stress. Still, frictional failure criteria are not evident especially when seismic waves change the normal traction on fractures. We identify three earthquakes as examples where consideration of interaction among dynamic stresses from different wave types and ambient tectonic stress provides theoretical predictions of nonlinear attenuation that are potentially testable with single station seismograms. For example, because Rayleigh waves produce shallow horizontal dynamic tension and compression, frictional failure should preferentially occur on the tensile half-cycle if no shallow tectonic stress is present and on the compressional half-cycle if the tectonic stress is already near thrust-faulting failure. We observed neither effect on records from the 2011 Mw 9.0 Great Tohoku earthquake. However, Rayleigh waves from this event appear to have brought rock beneath MYGH05 station into frictional failure at ˜10 m depth and thus suppressed high-frequency S waves. The tensile half-cycle of high-frequency P waves reduced normal traction on horizontal planes beneath station IWTH25 during the 2008 Mw 6.9 Iwate-Miyagi earthquake, weakening the rock in shear and suppressing high-frequency S waves. The near-field velocity pulse from the 1992 Mw 7.3 Landers earthquake brought the uppermost few hundred meters of granite beneath Lucerne station into frictional failure, suppressing high-frequency S waves. These moderately positive examples support the reality of nonlinear wave interaction, warranting study future strong ground motions.
NASA Astrophysics Data System (ADS)
Le Pommellec, Jean-Yves; Piron, Vianney; Askoura, Mohamed-Lamine; L'Huillier, Jean-Pierre
2015-07-01
The knowledge of the light fluence rate distribution inside a biological tissue irradiated by a Laser (or LED) is fundamental to achieve medical treatments. In this paper, we present a semi-analytical model based on the 2-D Fourier Transform of the diffusion equation. This method can be applied to any irradiation source (cylindrically symmetric or not) at the surface of the tissue. Two particular beam shapes are studied: planar irradiation and flat beam with finite radius. The total fluence rate along the depth in tissues was computed by adding the collimated and the diffuse components. The analytical solution was also used to study the effect of the beam radius on the light attenuation. Measurements were performed using a tank filled with a liquid-simulating medium (Milk), illuminated with a LED array (660 nm, 100mm×100mm). Several circular diaphragms were used to obtain uniform circular beams with well defined radii. An optical fibre (with an isotropic tip) was used to measure the fluence rate inside the medium. Preliminary experimental results are in agreement with theoretical predictions.
NASA Astrophysics Data System (ADS)
Mocanu, Victor; Russo, Raymond; Ambrosius, Boudewijn
2010-05-01
In the Vrancea seismogenic zone (SE Carpathians), where very strong earthquakes (Mw > 7) are reported several times a century, the seismotectonics is very complex. It develops beneath the contact between the Moldavian East European Platform, the Scythian Platform, and the Moesian Platform, to the east and southeast, and terranes of the Transylvania Basin lying within the Carpathian arc. Several hypothesis have been considered by scientists in order to explain the clustered foci of crustal and intermediate events (as deep as 200 km). However, until now, there is no tectonic scenario which could explain all geological and geophysical observations. We try to integrate long-term permanent and campaign GPS outcomes with contributions from seismic attenuation and S-wave splitting results. GPS contributions mainly refer to determination of velocity vectors. 15 campaigns and seven permanent stations are being used in order to determine the detailed kinematics of an area characterized by very small velocities (1-2 mm/y), bringing the satellite technique to almost its limit. The results suggest a counterclockwise mantle flow around the Vrancea seismogenic zone, which is a high velocity body developed in an almost vertical position, developing deeper than 200 km. This results is also supported by seismic attenuation studies. We found that models like delamination and subduction could be supported by seismic attenuation studies in this zone. The delamination model implies strong upwelling and horizontal inflow of asthenosphere into the gap between the delaminating and remnant lithosphere. The other model implies downwelling and perhaps lateral-horizontal inflow along the slab detachment or tear. The models imply different distributions of density and rheological properties associated with the different lithosphere - asthenosphere structures. We use the ratio of spectral amplitudes of P and S waves from vertical and transverse seismograms to estimate the S to P ratio in the frequency domain, and then we calculate Qs, the relative shear wave attenuation via two complementary techniques: We find that stations located near and above the Vrancea zone and in the Transylvanian Basin, attenuation is high (low Q). Stations situated on the East European, Moesian, and Scythian Platforms are characterized by higher Qs (low attenuation). We interpret the high attenuation in the Vrancea and Transylvanian Basin is the result of shallow hot asthenosphere present in this area. Observations of source-side shear wave splitting clearly show that upper mantle anisotropy is strongly variable in the region of the tightly curved Carpathian Arc: shear waves taking off from Vrancea along paths that sample the East and Southern Carpathians have fast anisotropy axes parallel to these ranges, whereas those leaving the source region to traverse the upper mantle beneath the Transylvanian Basin (i.e., mantle wedge side) trend NE-SW. Shear waves sampling the East European and Scythian Platforms are separable into two groups, one characterized by fast shear trends to the NE-SW, and a second, deeper group, with trends to NW-SE; also, the majority of null splits occur along paths leaving Vrancea in these NE-E azimuths. Deeper fabric with E-W trend marking asthenospheric flow beneath the craton's base. This more complex anisotropy beneath the western edge of the East European Platform would account for both the variability of observed splitting of waves that sample this volume.
Influence of the surface drag coefficient (young waves) on the current structure of the Berre lagoon
NASA Astrophysics Data System (ADS)
Alekseenko, Elena; Roux, Bernard; Kharif, Christian; Sukhinov, Alexander; Kotarba, Richard; Fougere, Dominique; Chen, Paul Gang
2013-04-01
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.
Louisnard, Olivier
2013-01-01
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 ...
Lavrentyev, A.I.; Rokhlin, S.I.
1997-06-01
Distinctive features of ultrasonic spectroscopy of adhesive joints of dissimilar materials (including anisotropic) are addressed both in theory and experiment. It is found that for dissimilar joining materials the depth of the reflection spectrum minimum depends nonmonotonically on attenuation in the layer and differs for measurements from opposite sides of the joint. It depends on both the attenuation in the adhesive and on adhesive/substrate impedance mismatches, resulting sometimes in zero reflectivity at nonzero attenuation in the adhesive. The effect is observed at normal and oblique incidence. A technique for measurement of the layer attenuation from amplitude and phase spectra is proposed. Experimental results show good agreement with theoretical predictions. {copyright} {ital 1997 Acoustical Society of America.}
Experimental investigation of millimeter-wave attenuation in a cloudy atmosphere
V. F. Zabolotnii; I. I. Zinchenko; I. A. Iskhakov; A. V. Sokolov; E. V. Sukhnonin; V. I. Chernyshev
1980-01-01
We present the results of a 2-yr investigation of the attenuation of radiation at the wavelengths ), = 4.1, 4.0, 3.5, 2.0, 1.3, 1.25, and 0.73 mm in clouds of various forms by the method of oblique sounding of the atmosphere. We establish that in clouds of the same form the attenuation is significantly greater in the warmer 6 months
Yokota, Eisuke; Toyonaga, Yoichiro; Shimizu, Fumitaka; Ishii, Yoshiyuki; Fujime, Makoto; Horie, Shigeo
2013-01-01
Purpose To identify the parameters on noncontrast computed tomography (NCCT) that best predict the success of shock wave lithotripsy (SWL). Materials and Methods We reviewed the records of 75 patients who underwent SWL for urinary calculi measuring 5 to 20 mm. Using NCCT images, we estimated the largest stone cross-sectional area and contoured the inner edge of the stone. Clinical outcome was classified as successful (stone-free or <4 mm in diameter) or failed (stone fragments, ?4 mm). The impact of preoperative parameters was evaluated by univariate and multivariate analysis. Results The overall success rate was 73.3%. Average stone attenuation value, stone length, and stone cross-sectional area in the success and failure groups were 627.4±166.5 HU (Hounsfield unit) vs. 788.1±233.9 HU (p=0.002), 11.7±3.8 mm vs. 14.2±3.6 mm (p=0.015), and 0.31±0.17 cm2 vs. 0.57±0.41 cm2 (p<0.001), respectively. In the multivariate analysis, stone attenuation value was the only independent predictor of SWL success (p=0.023), although stone cross-sectional area had a tendency to be associated with SWL success (p=0.053). Patients were then classified into four groups by using cutoff values of 780 HU for stone attenuation value and 0.4 cm2 for cross-sectional area. By use of these cutoff values, the group with a low stone attenuation value and a low cross-sectional area was more than 11.6 times as likely to have a successful result on SWL as were all other groups (odds ratio, 11.6; 95% confidence interval, 3.9 to 54.7; p<0.001). Conclusions Stone attenuation value and stone cross-sectional area are good predictors of extracorporeal SWL outcome. PMID:23878688
/T coefficient method Donghong Pei1 , John N. Louie2 , and Satish K. Pullammanappallil3 Authors' affiliations of surface waves have to be calculated for many applications, for example in modeling regional Lg and Rg). Later improvements on the formalism are to overcome these problems, including the delta matrix (Pestel
On the sound attenuation in fluid due to the thermal diffusion and viscous dissipation
NASA Astrophysics Data System (ADS)
Hu, Hanping; Wang, Yandong; Wang, Dongdong
2015-09-01
We review the sound attenuation in fluid due to the thermal diffusion and viscous dissipation and derive the formula of the sound attenuation coefficient in fluid by solving a fully thermally-mechanically coupled equation set. Problem occurring in Stokes-Kirchhoff relation, the well-known and widely used classical formula for sound attenuation coefficient, is therefore found and pointed out. The reason for its generation is analyzed and verified. An improved formula to replace Stokes-Kirchhoff relation is suggested and the typical case for the error in calculating sound pressure level (SPL) of attenuated sound wave in fluid between the two formulas is also given.
Ashoor, Mansour; Asgari, Afrouz; Khorshidi, Abdollah; Rezaei, Ali
2015-01-01
Purpose: Estimation of Compton attenuation and the photoelectric absorption coefficients were explored at various depths. Methods: A new method was proposed for estimating the depth based on the convolution of two exponential functions, namely convolution of scattering and primary functions (CSPF), which the convolved result will conform to the photopeak region of energy spectrum with the variable energy-window widths (EWWs) and a theory on the scattering cross-section. The triple energy-windows (TEW) and extended triple energy-windows scatter correction (ETEW) methods were used to estimate the scattered and primary photons according to the energy spectra at various depths due to a better performance than the other methods in nuclear medicine. For this purpose, the energy spectra were employed, and a distinct phantom along with a technetium-99 m source was simulated by Monte Carlo method. Results: The simulated results indicate that the EWW, used to calculate the scattered and primary counts in terms of the integral operators on the functions, was proportional to the depth as an exponential function. The depth will be calculated by the combination of either TEW or ETEW and proposed method resulting in the distinct energy-window. The EWWs for primary photons were in good agreement with those of scattered photons at the same as depths. The average errors between these windows for both methods TEW, and ETEW were 7.25% and 6.03% at different depths, respectively. The EWW value for functions of scattered and primary photons was reduced by increasing the depth in the CSPF method. Conclusions: This coefficient may be an index for the scattering cross-section. PMID:26170567
NASA Astrophysics Data System (ADS)
Ye, Peng-Cheng; Pan, Guang
2015-06-01
Due to the high speed of underwater vehicles, cavitation is generated inevitably along with the sound attenuation when the sound signal traverses through the cavity region around the underwater vehicle. The linear wave propagation is studied to obtain the influence of bubbly liquid on the acoustic wave propagation in the cavity region. The sound attenuation coefficient and the sound speed formula of the bubbly liquid are presented. Based on the sound attenuation coefficients with various vapor volume fractions, the attenuation of sound intensity is calculated under large cavitation number conditions. The result shows that the sound intensity attenuation is fairly small in a certain condition. Consequently, the intensity attenuation can be neglected in engineering. Project supported by the National Natural Science Foundation of China (Grant Nos. 51279165 and 51479170) and the National Defense Basic Scientific Research Program of China (Grant No. B2720133014).
NASA Astrophysics Data System (ADS)
Hanyga, Andrzej
2014-09-01
Dispersion, attenuation and wavefronts in a class of linear viscoelastic media proposed by Strick and Mainardi (Geophys J R Astr Soc 69:415-429, 1982) and a related class of models due to Lomnitz, Jeffreys and Strick are studied by a new method due to the author. Unlike the previously studied explicit models of relaxation modulus or creep compliance, these two classes support propagation of discontinuities. Due to an extension made by Strick, either of these two classes of models comprise both viscoelastic solids and fluids. We also discuss the Andrade viscoelastic media. The Andrade media do not support discontinuity waves and exhibit the pedestal effect.
NASA Astrophysics Data System (ADS)
Przadka, A.; Cabane, B.; Pagneux, V.; Maurel, A.; Petitjeans, P.
2012-02-01
We present a study of the damping of capillary-gravity waves in water containing pigments. The practical interest comes from a recent profilometry technique (FTP for Fourier Transform Profilometry) using fringe projection onto the liquid-free surface. This experimental technique requires diffusive reflection of light on the liquid surface, which is usually achieved by adding white pigments. It is shown that the use of most paint pigments causes a large enhancement of the damping of the waves. Indeed, these paints contain surfactants which are easily adsorbed at the air-water interface. The resulting surface film changes the attenuation properties because of the resonance-type damping between capillary-gravity waves and Marangoni waves. We study the physicochemical properties of coloring pigments, showing that particles of the anatase (TiO2) pigment make the water surface light diffusive while avoiding any surface film effects. The use of the chosen particles allows to perform space-time resolved FTP measurements on capillary-gravity waves, in a liquid with the damping properties of pure water.
NASA Astrophysics Data System (ADS)
Chan, T. W.; Huang, L.; Leaitch, R.; Sharma, S.; Brook, J.; Slowik, J.; Abbatt, J.
2008-05-01
Carbonaceous species (organic carbon (OC) and elemental carbon (EC)) contribute a large portion of atmospheric fine particle mass and influence air quality, human health, and climate forcing. However, their emission sources and atmospheric aging processes are not well understood. The OM/OC ratio, defined as the organic mass per unit OC mass, is useful to understand the degree of oxidation of aerosol particles in atmospheric processes. We define the modified BC/EC (mod BC/EC) ratio as the ratio of the non-scattering corrected absorption coefficient per unit mass of EC. The mod BC/EC ratio has a similar meaning as the site specific attenuation coefficient, which is an important parameter used to convert light absorption measurements to black carbon mass. The mod BC/EC ratio can vary due to light scattering effect on absorption measurements, in which the oxygenated organics may play a role. The pyrolysis organic carbon (POC) is defined as the carbon mass fraction obtained at T= 870°C under a pure helium environment using the thermal separation method [Huang et al., 2006]. Since POC mass is generally proportional to the amount of oxygenated OC, studying the relationships among OC, EC, POC, as well as OM/OC and mod BC/EC ratios may help us understand the mechanisms of aerosol aging from different emission sources. Two 1-month field studies were conducted at a rural site in southern Ontario (NW of Toronto) during fall 2005 and spring 2007. Quartz filter samples were collected and analyzed for OC, POC, and EC concentrations using a thermal/optical method [Huang et al., 2006]. Together with the total organic matter measured by an Aerodyne Aerosol Mass Spectrometer (AMS) and the absorption coefficient obtained from a Particle Soot Absorption Photometer (PSAP), the OM/OC and mod BC/EC ratios for ambient aerosols were obtained. Our results show that when air mass was mainly from south, OC, POC, and EC were relatively high, with average ratios of OC/EC, OM/OC, and POC/EC as 1.94, 1.41, and 0.52, respectively; this indicates significant anthropogenic impacts and relatively large portion of oxygenated OC, which might be due to either primary emissions or photo-chemical reactions occurred in a short period of time. When air mass was mainly from north, OC, POC, and EC were much lower, with average ratios of OC/EC, OM/OC, and POC/EC as 3.10, 1.20, and 0.79, respectively; this suggests less influence from anthropogenic emissions and relatively aged air mass from biogenic-source dominated clean air. Using POC, we estimate the specific attenuation at the site to be 5.8 m2 g-1 independent of the air mass origin. The relationships among OM/OC, mod BC/EC, and POC will be further discussed. References: Huang, L., Brook, J.R., Zhang, W., Li, S.M., Graham, L., Ernst, D., Chivulescu, A., and Lu, G. (2006) Stable isotope measurements of carbon fractions (OC/EC) in airborne particulate: a new dimension for source characterization and apportionment, Atmospheric Environment, 40, 2690-2705.
Determination of Shear Wave Velocity and Attenuation From Waveforms in Low Velocity Formations
Toksoz, M. Nafi
1984-01-01
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 ...
NASA Technical Reports Server (NTRS)
Sugiyama, T.; Terasawa, T.; Kawano, H.; Yamamoto, T.; Kokubun, S.; Frank, L. A.; Ackerson, K.; Tsurutani, B. T.
1995-01-01
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.
Blanc, Emilie; Lombard, Bruno
2015-01-01
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...
NASA Astrophysics Data System (ADS)
Gubaidullin, D. A.; Osipov, P. P.; Zakirov, A. N.
2014-11-01
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.
Haghparast, Abbas; Hashemi, Bijan; Eivazi, Mohammad Taghi
2013-04-01
Intensity-modulated radiation therapy (IMRT) can be performed by using compensators. To make a compensator for an IMRT practice, it is required to calculate the effective attenuation coefficient (?{sub eff}) of its material, which is affected by various factors. We studied the effect of the variation of the most important factors on the calculation of the ?{sub eff} of the cerrobend compensator for 6-MV photon beams, including the field size, compensator thickness, and off-axis distance. Experimental measurements were carried out at 100 cm source-to-surface distance and 10 cm depth for the 6-MV photon beams of an Elekta linac using various field size, compensator thickness, and off-axis settings. The field sizes investigated ranged from 4 × 4 to 25 × 25 cm{sup 2} and the cerrobend compensator thicknesses from 0.5–6 cm. For a fixed compensator thickness, variation of the ?{sub eff} with the field size ranged from 3.7–6.8%, with the highest value attributed to the largest compensator thickness. At the reference field size of 10 × 10 cm{sup 2}, the ?{sub eff} varied by 16.5% when the compensator thickness was increased from 0.5–6 cm. However, the variation of the ?{sub eff} with the off-axis distance was only 0.99% at this field size, whereas for the largest field size, it was more significant. Our results indicated that the compensator thickness and field size have the most significant effect on the calculation of the compensator ?{sub eff} for the 6-MV photon beam. Therefore, it is recommended to consider these parameters when calculating the compensator thickness for an IMRT practice designed for these beams. The off-axis distance had a significant effect on the calculation of the ?{sub eff} only for the largest field size. Hence, it is recommended to consider the effect of this parameter only for field sizes larger than 25 × 25 cm{sup 2}.
2D optical rogue waves in self-focusing Kerr-type media with spatially modulated coefficients
NASA Astrophysics Data System (ADS)
Yang, Zheng Ping; Zhong, Wei-Ping; Beli?, Milivoj
2015-08-01
A similarity transformation is introduced to reduce the generalized two-dimensional (2D) nonlinear Schrödinger (NLS) equation with modulated spatial coefficients and a special external potential to the standard NLS equation with constant coefficients. The 2D rogue wave solutions are constructed with the help of Whittaker functions in polar coordinates. We present some typical examples of the obtained solutions by selecting the two free parameters: the azimuthal number (the topological charge) and the radial node. With the help of two free parameters, the unique properties of solutions are discussed. Furthermore, we find that the rogue waves display different intensity patterns, such as the circular-pyramid, annular-ring and vortex-ring patterns.
Laboratory experiments and numerical modeling of wave attenuation through artificial vegetation
Augustin, Lauren Nicole
2009-05-15
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...
Change of polarity for periodic waves in the variable-coefficient Korteweg-de Vries equation
term. This change of polarity causes a solitary wave of depression to transform into a train the critical point, but a phase change is generated causing the wave to reverse its polarity. 1. Introduction
NASA Astrophysics Data System (ADS)
Franco, Ediguer E.; Adamowski, Julio C.; Buiochi, Flávio
2012-05-01
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.
Calculating QuasiLinear Pitch Angle Diffusion Coefficients in Terms of the Wave Normal Angle
B. Abel; R. M. Thorne
2005-01-01
Resonant pitch angle diffusion of magnetospherically trapped charged particles is modeled in terms of the wave normal angle. The relativistic, multi-species formulation utilizes the full quasi-linear dispersion relation. The resonant wave angle solution reduces to a quadratic equation, compared to the tenth order polynomial produced when the same relation is solved in terms of the wave frequency. Although it must
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
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.
Fringer, Oliver B.
. Fringer, and Jeffrey R. Koseff Environmental Fluid Mechanics Laboratory, Department of Civil on the following observations. During the portion of the wave period when the fluid velocities are highest fluid velocity over the wave period. The relative contribution to the total turbulence production over
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
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
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.
NASA Astrophysics Data System (ADS)
Huang, Y.; Weisberg, R. H.; Zheng, L.
2012-12-01
Effects of wind input parameterizations to hurricane wave estimation are examined by using an unstructured grid, third generation wave model Simulating WAves Nearshore (SWAN) forced by real Hurricane Ike wind field impacting the Gulf of Mexico in 2008. Experiments illustrate the default and recommended setting of wind input parameterization tend to overestimate the maximum significant wave heights about 2m in the middle of Gulf of Mexico when comparing with mooring observed data. The overestimation can be relieved by adjusting the cap value of drag coefficient or by substituting the high-wind-speed bulk formula for default low-to-moderate one. Since the significant cushion effects of coastal areas with 20m ~ 30m water depth, the overestimated waves have limited negative effects to shallower waters along beach line. Thus previous wave model results depends on low-to-moderate wind speed bulk formulas maybe still reliable in water areas shallower than 20m, but tend to overestimation in deeper waters for high wind speed conditions like hurricanes.
NASA Technical Reports Server (NTRS)
Jacobson, Mark D.; Snider, J. B.; Westwater, E. R.
1993-01-01
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.
NASA Astrophysics Data System (ADS)
Mao, Xia; Liu, Yun-Long; Chen, Li-Jiang; Xue, Yu-Li
2013-04-01
At millimeter wavelengths, normalized fog attenuation (NFA) in units of (dB/km)/ (g/m3) is generally calculated by the Rayleigh approximation when working wavelengths are much larger than the average diameter of fog droplets. The calculations of the Rayleigh approximation are much less than those of Mie scattering theory, but still complex and heavy. To solve the above problem and facilitate the engineering applications of the Rayleigh approximation, a new empirical formula is discussed to estimate NFA in the frequency range 30 ~ 100 GHz and the fog common temperature range -8 ~ 20 °C. The simulation results of the new formula are compared with those got by other three empirical formulae: the Altshuler empirical formula, the Liebe empirical formula and the Zhao empirical formula. Maximal absolute value of the relative errors (MAVRE) and Pearson correlation coefficient (PCC) indicate the largest deviation of estimated results and the fitting performance of an empirical formula, respectively. Comparisons show that the MAVRE of the new formula is only 4.482 %, which is much smaller than those of the other three formulae. The mean value of the Pearson correlation coefficients (PCCs) of the proposed formula is 0.999943, larger than those of other methods. Additionally, relative error (RE) curves of the four empirical formulae are given at four certain temperatures -8 °C, 0 °C, 10 °C and 20 °C.
Villalobos-Escobar, Gina P; Castro, Raúl R
2014-01-01
We used a new data set of relocated earthquakes recorded by the Seismic Network of Northeastern Sonora, Mexico (RESNES) to characterize the attenuation of S-waves in the fault zone of the 1887 Sonora earthquake (M w 7.5). We determined spectral attenuation functions for hypocentral distances (r) between 10 and 140 km using a nonparametric approach and found that in this fault zone the spectral amplitudes decay slower with distance at low frequencies (f?attenuation functions obtained for 23 frequencies (0.4???f???63.1 Hz) permit us estimating the average quality factor Q S ?=?(141 ± 1.1 )f ((0.74 ± 0.04)) and a geometrical spreading term G(r) =?1/r (0.21). The values of Q estimated for S-wave paths traveling along the fault system that rupture during the 1887 event, in the north-south direction, are considerably lower than the average Q estimated using source-station paths from multiple stations and directions. These results indicate that near the fault zone S waves attenuate considerably more than at regional scale, particularly at low frequencies. This may be the result of strong scattering near the faults due to the fractured upper crust and higher intrinsic attenuation due to stress concentration near the faults. PMID:25674476
NASA Astrophysics Data System (ADS)
Sun, Chengliang; Soon, Bo Woon; Zhu, Yao; Wang, Nan; Loke, Samuel Pei Hao; Mu, Xiaojing; Tao, Jifang; Gu, Alex Yuandong
2015-06-01
An AlN piezoelectric Lamb-wave resonator, which is excited by two dimensional electric field, is reported in this paper. Rhombus-shape electrodes are arranged on AlN thin film in a checkered formation. When out-of-phase alternating currents are applied to adjacent checkers, two dimensional acoustic Lamb waves are excited in the piezoelectric layer along orthogonal directions, achieving high electromechanical coupling coefficient, which is comparable to film bulk acoustic resonators. The electromechanical coupling coefficient of the 285.3 MHz resonator presented in this paper is 5.33%, which is the highest among AlN based Lamb-wave resonators reported in literature. Moreover, the spurious signal within a wide frequency range is significantly suppressed to be 90% lower than that of the resonance mode. By varying the electrode dimension and inter-electrode distance, resonators having different resonant frequencies can be fabricated on a single wafer, making single-chip broadband filters, duplexers, and multiplexers possible.
NASA Technical Reports Server (NTRS)
Hawkins, Richard; Penland, Jim A.
1997-01-01
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.
Wave-induced fluid flow in random porous media: Attenuation and ...
2005-04-20
small compared to the wavelength. Various laboratory ... in the light of existing theories for wave propagation in po- roelastic media ... of solid particles in a viscous fluid. ... tion term which accounts for the conversion scattering from fast into ...... 28 R. J. Urick, ''The absorption of sound in suspensions of irregular par- ticles,'' J.
Sergei A. Stanchits; David A. Lockner; Alexander V. Ponomarev
2003-01-01
4 Abstract. Fluid infiltration and pore fluid pressure changes are known to have a significant effect on the occurrence of earthquakes. Yet, for most damaging earthquakes, with nucleation zones below a few kilometers depth, direct measurements of fluid pressure variations are not available. Instead, pore fluid pressures are inferred primarily from seismic wave propagation characteristics such as V p\\/Vs ratio,
Manohar R. Kulkarni; John P. Barton
1989-01-01
The results of a theoretical investigation of the interaction between electromagnetic fields and acoustic and entropy waves in a partially ionized gas are presented. The simulation uses for the first time actual property curve fits for a coal-combustion plasma rather than the perfect gas relationships that were used in previous studies. The working fluid employed was a combustion plasma from
NASA Astrophysics Data System (ADS)
Lin, G.
2013-12-01
I present a frequency-independent three-dimensional (3D) compressional wave attenuation model (indicated by quality factor Qp) for the crust and uppermost mantle of northern and central California. The tomographic inversion used t* values measured from amplitude spectra of 80,988 P-wave arrivals of 3247 events recorded by 463 network stations through a 3D seismic velocity model. The model has a uniform horizontal grid spacing of 15 km and the vertical node intervals range between 2 and 10 km down to 45 km depth. The resulting Qp model provides an important complement to the existing regional-scale velocity models for interpreting structural heterogeneity and fluid saturation of rocks in the study area. In general, the Qp values increase with depth and agree with the surface geology at shallow depth layers. The most significant features observed in the Qp model are the high Qp values in the Sierra Nevada mountains and low Qp anomalies in the western fault zones. Low Qp values are also imaged in Owens Valley and Long Valley at shallow depths and the Mendocino fault zones in the lower crust. An overall contrast of Qp values across the fault is observed in the creeping, Parkfield and Cholame-Carrizo sections of the San Andreas Fault. Very high Qp anomalies are seen near and below the seismogenic zones at depths in several faults. A nice correlation between shallow Qp values and hear flow is also shown.
Lee, M.C.
1995-11-30
The AFOSR grant has been used to support research on EM wave propagation and interaction with the magnetized plasmas generated in the Versatile Toroidal Facility (VTF). The VTF has been used to investigate ionospheric plasma turbulence and cross-checking the plasma heating experiments at Arecibo, Puerto Rico. The authors have successfully reproduced their Arecibo experimental results with VTF and have developed a theory to explain the generation of frequency upshifted plasma modes.
VHF\\/UHF wave attenuation in a city with regularly spaced buildings
N. Blaunstein; M. Levin
1996-01-01
In this work a theoretical and experimental investigation analyzing VHF\\/UHF radio wave propagation in a suburban environment with a grid-type street plan is presented for the purpose of personal communication services prediction. A waveguide with randomly distributed gaps (slits) between the sides of buildings is considered as a model of straight streets with two- and three-story buildings. The average field
Pingenot, J; Rieben, R; White, D
2004-12-06
We present a computational study of signal propagation and attenuation of a 200 MHz dipole antenna in a cave environment. The cave is modeled as a straight and lossy random rough wall. To simulate a broad frequency band, the full wave Maxwell equations are solved directly in the time domain via a high order vector finite element discretization using the massively parallel CEM code EMSolve. The simulation is performed for a series of random meshes in order to generate statistical data for the propagation and attenuation properties of the cave environment. Results for the power spectral density and phase of the electric field vector components are presented and discussed.
Role of vegetation on the attenuation of forces on structures due to cnoidal waves
NASA Astrophysics Data System (ADS)
2009-04-01
The evaluation of forces on structures in the marine environment due to ocean waves is absolutely essential in the planning and development of mitigation measures against natural coastal hazards and dictates their design. Further, studies on the forces on coastal structures due to regular and random waves are well entrenched in literature, whereas, that due to shallow water waves are rather scanty. The recent tsunami has added a new dimension on the role of vegetation on the forces on structures. Due the propagation of tsunami, a number of signature studies have revealed that structures fronted by vegetation have suffered minimum damage compared to that in its absence and as also reported by Yanagisawa (2008). In the present paper, the results from an experimental study to investigate the effect of vegetation on a typical structure located onshore over a slope of 1:30 are reported. The tests were carried out in a wave flume of length 72m, width 2m and 2.7m depth. The water depth at the toe of the slope was 1m. Slender flexible cylindrical members that represent plantation along the coast have been adopted for the tests. Experiments were carried out for different G/B ratios of 0, 0.5,1 and 1.5. (Where G is the distance between front face of vegetation/ green belt and the rear face of the building and B is width of the building). Experiments were repeated for three widths of Green belts (BG) and for each of the green belt, two different diameters of the cylinders of 10mm and 3.0mm were used. The forces on structure were measured with load cells in the presence and absence of the green belt. The Cnoidal waves covering a range of Ursell parameter between 18 and 700 were employed for the experiments. The different vegetal and flow parameters in a non-dimensional form have been identified. The variation of non-dimensionalised force over the slope in the presence and absence of vegetation as a function of the Ursell parameter, Relative rigidity and Reduced velocity for different dimensionless SP/D of the green belt (where SP is the spacing between plantation/diameter of plantation) clearly indicates that there is a significant reduction in the force due to the presence of vegetation. Prior to the experiments with the green belt, for the purpose of validation tests were carried out on the force measurements of waves over a plane slope, the results of which compared with existing results exhibited a good agreement. The details of the experimental set-up, procedure and analysis and discussion of the results are reported in this paper. It has been found that, • The non-dimensional Forces on the structure increases by about 80 %, when the distance between the structure and the Green Belt is in the range of 0.5B to 1.5B. • The most favorable location for the Structure is adjacent to the Green Belt or away from the Green Belt by more than twice the width of the structure. For this configuration, the forces were found to reduce to an extent ranging between 50% and 90%. References Yanagisawa,H., Koshimsura,S., Got,K., Miyagi,T., Imamura, F., Ruangrassamee, A. and Tanavud, C. "The reduction effects of Mangrove forest on a tsunami based on field surveys at Pakarang Cape, Thailan and Numerical Analysis" Estuarine, Coastal and shelf Science, Oct 2008, pp 1-11.
Role of vegetation on the attenuation of forces on structures due to Cnoidal waves
NASA Astrophysics Data System (ADS)
Sundar, V.; Norayanan, L.; Murali, K.
2009-04-01
The evaluation of forces on structures in the marine environment due to ocean waves is absolutely essential in the planning and development of mitigation measures against natural coastal hazards and dictates their design. Further, studies on the forces on coastal structures due to regular and random waves are well entrenched in literature, whereas, that due to shallow water waves are rather scanty. The recent tsunami has added a new dimension on the role of vegetation on the forces on structures. Due the propagation of tsunami, a number of signature studies have revealed that structures fronted by vegetation have suffered minimum damage compared to that in its absence and as also reported by Yanagisawa (2008). In the present paper, the results from an experimental study to investigate the effect of vegetation on a typical structure located onshore over a slope of 1:30 are reported. The tests were carried out in a wave flume of length 72m, width 2m and 2.7m depth. The water depth at the toe of the slope was 1m. Slender flexible cylindrical members that represent plantation along the coast have been adopted for the tests. Experiments were carried out for different G/B ratios of 0, 0.5,1 and 1.5. (Where G is the distance between front face of vegetation/ green belt and the rear face of the building and B is width of the building). Experiments were repeated for three widths of Green belts (BG) and for each of the green belt, two different diameters of the cylinders of 10mm and 3.0mm were used. The forces on structure were measured with load cells in the presence and absence of the green belt. The Cnoidal waves covering a range of Ursell parameter between 18 and 700 were employed for the experiments. The different vegetal and flow parameters in a non-dimensional form have been identified. The variation of non-dimensionalised force over the slope in the presence and absence of vegetation as a function of the Ursell parameter, Relative rigidity and Reduced velocity for different dimensionless SP/D of the green belt (where SP is the spacing between plantation/diameter of plantation) clearly indicates that there is a significant reduction in the force due to the presence of vegetation. Prior to the experiments with the green belt, for the purpose of validation tests were carried out on the force measurements of waves over a plane slope, the results of which compared with existing results exhibited a good agreement. The details of the experimental set-up, procedure and analysis and discussion of the results are reported in this paper. It has been found that, The non-dimensional Forces on the structure increases by about 80 %, when the distance between the structure and the Green Belt is in the range of 0.5B to 1.5B. The most favorable location for the Structure is adjacent to the Green Belt or away from the Green Belt by more than twice the width of the structure. For this configuration, the forces were found to reduce to an extent ranging between 50% and 90%. References Yanagisawa,H., Koshimsura,S., Got,K., Miyagi,T., Imamura, F., Ruangrassamee, A. and Tanavud, C. "The reduction effects of Mangrove forest on a tsunami based on field surveys at Pakarang Cape, Thailan and Numerical Analysis" Estuarine, Coastal and shelf Science, Oct 2008, pp 1-11.
Sea ice floes dissipate the energy of steep ocean waves
Toffoli, Alessandro; Meylan, Michael H; Cavaliere, Claudio; Alberello, Alberto; Elsnab, John; Monty, Jason P
2015-01-01
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.
Delamination of southern Puna lithosphere revealed by body wave attenuation tomography
NASA Astrophysics Data System (ADS)
Liang, Xiaofeng; Sandvol, Eric; Kay, Suzanne; Heit, Benjamin; Yuan, Xiaohui; Mulcahy, Patrick; Chen, Chen; Brown, Larry; Comte, Diana; Alvarado, Patricia
2014-01-01
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.
Evans, Joshua D. Yu, Yaduo; Williamson, Jeffrey F.; Whiting, Bruce R.; O’Sullivan, Joseph A.; Politte, David G.; Klahr, Paul H.
2013-12-15
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.
Intensified and attenuated waves in a microbubble Taylor-Couette flow
NASA Astrophysics Data System (ADS)
Watamura, T.; Tasaka, Y.; Murai, Y.
2013-05-01
The effect of the presence of microbubbles on a flow state is experimentally investigated in a Taylor-Couette flow with azimuthal waves, in order to examine the interaction mechanism of bubbles and flows that result in drag reduction. The average diameter of the bubbles is 60 ?m, which is smaller than the Kolmogorov length scale, and the maximum void fraction is 1.2 × 10-4 at the maximum case. The modifications of the fluid properties, bulk density, effective viscosity, and the extra energy input caused by the addition of microbubbles are expected to have a small effect on modifying flow states. The power of the basic wave propagating in the azimuthal direction is enhanced; its modulation, however, is decreased by adding microbubbles in the flow regime corresponding to modulated Taylor vortex flow. Moreover, the gradient of the azimuthal velocity near the walls, source of the wall shear stress, decreases by 10%. The modified velocity distribution by adding microbubbles is comparable to that obtained with a 20% lower Reynolds number. Microbubbles in the coherent structure of the wavy Taylor vortices are visualized and exhibit a preferential distribution and motion at the crests and troughs of the waviness. The roles of the inhomogeneously distributed microbubbles in wavy vortical structures are discussed in view of our findings.
NASA Astrophysics Data System (ADS)
Draganov, Deyan; Ruigrok, Elmer; Ghose, Ranajit; Mikesell, Dylan; van Wijk, Kasper
2015-01-01
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.
Attenuation of high frequency P and S waves in the crust of the East-Central Iran
NASA Astrophysics Data System (ADS)
Ma'hood, M.; Hamzehloo, H.; Doloei, G. J.
2009-12-01
We simultaneously estimated Qp-1 and Qs-1 by applying the extended coda-normalization method at 39 stations of three local networks in the East-Central Iran. We measured frequency-dependent attenuation of both P and S waves for the frequency range of 1.5, 3.0, 6.0, 12 and 24 Hz. We have analysed 266 three-component seismograms of 53 local earthquakes, having focal depths less than 25 km, which occurred from 2003 December 28 to 2005 April 11. By fitting power-law frequency dependence to the estimated values over the whole stations, we obtained Qp-1 = (25 +/- 3) × 10-3 f (-0.99+/-0.04) and Qs-1 = (19 +/- 2) × 10-3 f(-1.02+/-0.06) in the upper crust of the East-Central Iran, where f is frequency in Hz. Our results are in the range of those estimated for Qp-1 and Qs-1 of the other seismically active regions.
NASA Astrophysics Data System (ADS)
Chen, C.; Weng, C.; Chang, W.
2007-12-01
The Morlet wavelet multiple-filter method is applied to measure relative group delays from first cycle P waves, from eight CWBSN stations located near the source of the 1999 Chi Chi, and Chia-Yi, Taiwan earthquakes. The data used in this study is from the year between 1998 and 2000. The epicentral distance is less than 30 km with depth less than 25 km and ML?3.0. Using continuous relaxation model, we can relates intrinsic dispersion to attenuation and by applying the genetic algorithm (GA), we are able to determine Qp, which allows us to investigate the temporal variations of Qp before and after the occurrence of a large earthquake. Our results indicate that the Qp is highly sensitive to crack density. Before the occurrence of a large earthquake, Qp increases significantly, which indicates that the pre-seismic stress accumulation may associate with fluid-filled higher density fractured rock in the source area and causes crack density to increase. One interesting phenomena that we find is that Qp decreases right before the occurrence of a large earthquake, not after the occurrence of an earthquake. This observation implies that t the temporal variation pattern of Qp can serve as an important indicator for stress level change before an earthquake occurs, which also provides another perspective to understand the siemogeneric process in the source area.
Long-Term Change of Sound Wave Propagation Attenuation Due to the Effects of Ocean Acidification
NASA Astrophysics Data System (ADS)
Gotoh, S.; Tsuchiya, T.; Hiyoshi, Y.
2014-12-01
In recent years, the concentration of carbon dioxide in the atmosphere is increasing due to global warming. And, the ocean acidification advances because this melts into seawater, pH decrease in seawater are concerned. The sound wave to propagate seawater, pH is known to affect absorption loss (?) by chemical buffer effects of the seawater. However, conventionally, ? has not been investigated much in the calculation of pH. Therefore, when calculating the propagation distance in the sonar equation, pH =8~8.1 (Weak alkaline) are used empirically. Therefore we used an actual value of pH of 30 years from 1984 in the sea near the Japan, and investigated change over the years of absorption loss (?) at some frequency. As a result, we found that ? value decreases gradually in the past 30 years, as high-latitude decreases. Further, the future, assuming that ocean acidification is more advanced, and to simulate a change of the absorption loss and propagation loss in end of this century using the pH value reported from the "Intergovernmental Panel on Climate Change" (IPCC). As a result, it was just suggested that ? decreased more in the end of this century and affected the submarine detection. In addition, in recent years, we examined the effects of noise that offshore wind power construction proceeds in each country emits gives to the underwater sound. As a result, in the end of this century, an underwater noise increases about 17%, and underwater sound environmental degradation of the sea is concerned.
R. A. Challinor
1967-01-01
Radio-atmospherics of known origin were recorded on magnetic tape from two broad-band receivers 285 km apart in the United Kingdom, and, from photographs of the waveforms, the Fourier phase and amplitude spectra of the pulses were computed. This enabled the phase velocity and attenuation of radio waves in the frequency range 40 c\\/s-10 kc\\/s to be calculated. Observations were made
Second coefficient of viscosity in air
NASA Technical Reports Server (NTRS)
Ash, Robert L.; Zuckerwar, Allan J.; Zheng, Zhonquan
1991-01-01
Acoustic attenuation measurements in air were analyzed in order to estimate the second coefficient of viscosity. Data over a temperature range of 11 C to 50 C and at relative humidities between 6 percent and 91 percent were used. This analysis showed that the second coefficient of viscosity varied between 1900 and 20,000 times larger than the dynamic or first coefficient of viscosity over the temperature and humidity range of the data. In addition, the data showed that the molecular relaxation effects, which are responsible for the magnitude of the second coefficient of viscosity, place severe limits on the use of time-independent, thermodynamic equations of state. Compressible flows containing large streamwise velocity gradients, like shock waves, which cause significant changes in particle properties to occur during time intervals shorter than hundredths of seconds, must be modeled using dynamic equations of state. The dynamic model approach is described briefly.
Wang, Wenbo; He, Xingli; Ye, Zhi, E-mail: yezhi@zju.edu.cn, E-mail: jl2@bolton.ac.uk; Wang, Xiaozhi [Department of Information Science and Electronic Engineering, Zhejiang University and Cyrus Tang Centre for Sensor Materials and Applications, 38 Zheda Road, Hangzhou 310027 (China); Mayrhofer, Patrick M.; Gillinger, Manuel; Bittner, Achim; Schmid, Ulrich [Institute of Sensor and Actuator Systems, Vienna University of Technology, Floragasse, 7/2/366-MST, A-1040 Vienna (Austria); Luo, J. K., E-mail: yezhi@zju.edu.cn, E-mail: jl2@bolton.ac.uk [Institute of Renewable Energy Environmental Technology, University of Bolton, Deane Road, Bolton BL3 5AB (United Kingdom); Department of Information Science and Electronic Engineering, Zhejiang University and Cyrus Tang Centre for Sensor Materials and Applications, 38 Zheda Road, Hangzhou 310027 (China)
2014-09-29
AlN and AlScN thin films with 27% scandium (Sc) were synthesized by DC magnetron sputtering deposition and used to fabricate surface acoustic wave (SAW) devices. Compared with AlN-based devices, the AlScN SAW devices exhibit much better transmission properties. Scandium doping results in electromechanical coupling coefficient, K{sup 2}, in the range of 2.0%???2.2% for a wide normalized thickness range, more than a 300% increase compared to that of AlN-based SAW devices, thus demonstrating the potential applications of AlScN in high frequency resonators, sensors, and high efficiency energy harvesting devices. The coupling coefficients of the present AlScN based SAW devices are much higher than that of the theoretical calculation based on some assumptions for AlScN piezoelectric material properties, implying there is a need for in-depth investigations on the material properties of AlScN.
On the apparent attenuation in the spatial coherence estimated from seismic arrays
NASA Astrophysics Data System (ADS)
Menon, Ravishankar; Gerstoft, Peter; Hodgkiss, William S.
2014-04-01
Several recent studies have used the coherence of seismic noise between stations to retrieve the phase slowness and attenuation. However, there is considerable debate on the feasibility of attenuation retrieval, its interpretation, and its dependence on the noise directionality and has been the subject of several analytical and numerical studies. In this article, we perform a detailed analysis of the various factors that play a role in the estimation of spatial coherence and attenuation from seismic arrays using data from the Southern California Seismic Network. For instance, certain common preprocessing steps such as averaging neighboring frequencies to improve the estimate are sufficient to introduce attenuation-like effects. The presence of first-mode surface Rayleigh wave and P waves in addition to the fundamental mode in Southern California (at frequencies 0.05-0.2 Hz) suggests that the underlying spatial coherence is better modeled as a linear combination of the above wave types. Although this describes the observed coherence better than a simple zeroth-order Bessel function, the resulting phase cancelations due to the multiple seismic waves can be misconstrued as attenuation if not taken into consideration. Using simulations, we show that due to the slowness inhomogeneity, azimuthally averaging the coherence is not equivalent to homogenizing the medium and instead introduces apparent attenuation in the coherence due to interference. Trying to fit an exponential decay model to this apparent attenuation results in an attenuation coefficient which is similar to previously published results.
Chen, Shi; Zhang, Yinhong; Lin, Shuyu; Fu, Zhiqiang
2014-02-01
The electromechanical coupling coefficient of Rayleigh-type surface acoustic waves in semi-infinite piezoelectrics/non-piezoelectrics superlattices is investigated by the transfer matrix method. Research results show the high electromechanical coupling coefficient can be obtained in these systems. The optimization design of it is also discussed fully. It is significantly influenced by electrical boundary conditions on interfaces, thickness ratios of piezoelectric and non-piezoelectric layers, and material parameters (such as velocities of pure longitudinal and transversal bulk waves in non-piezoelectric layers). In order to obtain higher electromechanical coupling coefficient, shorted interfaces, non-piezoelectric materials with large velocities of longitudinal and transversal bulk waves, and proper thickness ratios should be chosen. PMID:24035609
P. Peterková; L'. Lap?ík Jr
2000-01-01
The diffusion coefficient of water into thin polymer layers of glutar aldehyde cross-linked atelocollagen type I matrix (sample\\u000a 1, the typical layer thickness was about 0.065?×?10?3?m) at 23?°C was 1.142?×?10?10?m2?s?1. At twice the concentration of the cross-linking agent (sample 2) the diffusion coefficient was 2.795?×?10?10?m2 s?1. This increase was attributed to the more ordered morphology and the creation of ordered
Mohammed, Arshed Abdulhamed; Haris, Sallehuddin Mohamed; Nuawi, Mohd Zaki
2015-01-01
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
Midgley, Stewart; Schleich, Nanette
2015-05-01
A novel method for dual-energy X-ray analysis (DEXA) is tested using measurements of the X-ray linear attenuation coefficient ?. The key is a mathematical model that describes elemental cross sections using a polynomial in atomic number. The model is combined with the mixture rule to describe ? for materials, using the same polynomial coefficients. Materials are characterized by their electron density Ne and statistical moments Rk describing their distribution of elements, analogous to the concept of effective atomic number. In an experiment with materials of known density and composition, measurements of ? are written as a system of linear simultaneous equations, which is solved for the polynomial coefficients. DEXA itself involves computed tomography (CT) scans at two energies to provide a system of non-linear simultaneous equations that are solved for Ne and the fourth statistical moment R4. Results are presented for phantoms containing dilute salt solutions and for a biological specimen. The experiment identifies 1% systematic errors in the CT measurements, arising from third-harmonic radiation, and 20-30% noise, which is reduced to 3-5% by pre-processing with the median filter and careful choice of reconstruction parameters. DEXA accuracy is quantified for the phantom as the mean absolute differences for Ne and R4: 0.8% and 1.0% for soft tissue and 1.2% and 0.8% for bone-like samples, respectively. The DEXA results for the biological specimen are combined with model coefficients obtained from the tabulations to predict ? and the mass energy absorption coefficient at energies of 10?keV to 20?MeV. PMID:25931101
Pingenot, J; Rieben, R; White, D; Dudley, D
2005-10-31
We present a computational study of signal propagation and attenuation of a 200 MHz planar loop antenna in a cave environment. The cave is modeled as a straight and lossy random rough wall. To simulate a broad frequency band, the full wave Maxwell equations are solved directly in the time domain via a high order vector finite element discretization using the massively parallel CEM code EMSolve. The numerical technique is first verified against theoretical results for a planar loop antenna in a smooth lossy cave. The simulation is then performed for a series of random rough surface meshes in order to generate statistical data for the propagation and attenuation properties of the antenna in a cave environment. Results for the mean and variance of the power spectral density of the electric field are presented and discussed.
Feasibility of determining Q of near-surface materials from Love waves
NASA Astrophysics Data System (ADS)
Xia, Jianghai; Yin, Xiaofei; Xu, Yixian
2013-08-01
High-frequency (? 2 Hz) Multi-channel Analysis of Love Waves (MALW) provides a practical way to determine velocity of horizontally polarized shear (SH) waves for a layered earth model up to 30 m below the ground surface in many geological settings. The information used in the MALW method is phase of Love waves. Information on amplitude of Love waves is not utilized in the MALW method. In this paper we present a method that uses information on amplitude of high-frequency Love waves to estimate quality factors (Qs) of near-surface materials. Unlike Rayleigh waves, attenuation coefficients (amplitude) of Love waves are independent of quality factors for P waves and are function of quality factors of Love waves. In theory, a fewer parameters make the inversion of attenuation coefficients of Love waves more stable and reduce the degree of nonuniqueness. We discussed sensitivity of an inversion system based on a linear relationship between attenuation coefficients and dissipation factors (1/Qs). The sensitivity analysis suggested that damping and constraints to an inversion system are necessary to obtain a smooth and meaningful quality factor model when no other information is available. We used synthetic and real-world data to demonstrate feasibility of inversion of attenuation coefficients of high-frequency Love-wave data acquired with the MALW method for quality factors with a linear, damped and constrained system.
Modeling ultrasonic noise and attenuation in elongated duplex polycrystalline materials
NASA Astrophysics Data System (ADS)
Dorval, V.; Ganjehi, L.; Chatillon, S.; Jenson, F.
2013-01-01
The interaction between ultrasonic waves and the polycrystalline microstructure of metals leads to structural noise and attenuation, which can cause significant losses in detection performances. Taking these phenomena into account in UT simulation can help designing suitable inspection procedures. It is possible to model them based on the intrinsic scattering coefficients of a material. Expressions of this coefficient valid for duplex elongated materials and for any mode and scattering direction are given in this communication. Structural noise from a titanium alloy was computed based on these expressions and is compared to measurement.
Zhong, Wei-Ping; Beli?, Milivoj; Zhang, Yiqi
2015-02-01
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
Attenuation in the Upper Mantle Beneath "Normal" Old Seafloor in the Western Pacific
NASA Astrophysics Data System (ADS)
Forsyth, D. W.; Weeraratne, D. S.
2014-12-01
The Pacific Lithosphere Anisotropy and Thickness Experiment (PLATE) ocean bottom seismometer array south of the Shatsky Rise allows imaging the attenuation structure of the upper mantle beneath the oldest (~ 150 Ma) parts of the Pacific seafloor that have not been affected by subsequent volcanism. The array consisted of eight seismometers plus three stations with only differential pressure gauges covering a lateral extent of 200 km by 600 km in seafloor with an average depth of about 6000 m. Intermediate- and deep-focus earthquakes in the Mariana and Izu-Bonin subduction zones provide paths for P waves that probe different depths beneath the seafloor and globally distributed shallow earthquakes serve as Rayleigh wave sources. Q estimates from P waves are based on frequencies from 1 to 15 Hz, primarily 2 to 10 Hz, while Rayleigh wave attenuation is measured in the 0.007 to 0.045 Hz range. Qp is statistically required to be frequency dependent, with a best-fitting power law coefficient ? = 0.40. A different form of frequency dependence is required to reconcile Rayleigh wave and P wave attenuation. Not surprisingly, both P wave and Rayleigh wave data sets require a very low attenuation, high Q lithosphere. Two other aspects of the model are more surprising. First, Q in the asthenosphere in the depth range 100-250 km is quite low, with attenuation comparable to that in the highly attenuating wedges above subducting plates in back arc regions. This observation suggests the accumulation of a small melt fraction beneath the lithosphere. Second, attenuation in the transition zone deeper than 410 km is negligible, suggesting that the transition zone seaward of the subducting Pacific plate is dehydrated.
SEISMIC ATTENUATION FOR RESERVOIR CHARACTERIZATION
Joel Walls; M.T. Taner; Gary Mavko; Jack Dvorkin
2002-04-01
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.
NASA Astrophysics Data System (ADS)
Vikas, Kumar; K. Gupta, R.; Ram, Jiwari
2014-03-01
In this paper, the variable-coefficient diffusion—advection (DA) equation, which arises in modeling various physical phenomena, is studied by the Lie symmetry approach. The similarity reductions are derived by determining the complete sets of point symmetries of this equation, and then exact and numerical solutions are reported for the reduced second-order nonlinear ordinary differential equations. Further, an extended (G'/G)-expansion method is applied to the DA equation to construct some new non-traveling wave solutions.
NASA Astrophysics Data System (ADS)
Dobrynina, Anna; Sankov, Vladimir; Chechelnitsky, Vladimir
2014-05-01
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).
Ultrasonic Attenuation in Zircaloy-4
Gomez, M.P.; Banchik, A.D.; Lopez Pumarega, M.I.; Ruzzante, J.E.
2005-04-09
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.
Slack, P.D.; Davis, P.M.; Baldridge, W.S.; Olsen, K.H.; Glahn, A.; Achauer, U.; Spence, W.
1996-01-01
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.
NASA Astrophysics Data System (ADS)
Wang, Ming-Zhen; Gao, Yi-Tian; Zhang, Cheng; Meng, Xiang-Hua; Yu, Xin; Xu, Tao; Feng, Qian
A variable-coefficient variant Boussinesq (VCVB) model describes the propagation of long waves in shallow water, the nonlinear lattice waves, the ion sound waves in plasmas, and the vibrations in a nonlinear string. With the help of symbolic computation, a VCVB model is investigated for its integrability through the Painlevé analysis. Then, by truncating the Painlevé expansion at the constant level term with two singular manifolds, the dependent variable transformations are obtained through which the VCVB model is bilinearized. Furthermore, the corresponding N-solitonic solutions with graphic analysis are given by the Hirota method and Wronskian technique. Additionally, a bilinear Bäcklund transformation is constructed for the VCVB model, by which a sample one-solitonic solution is presented.
NASA Astrophysics Data System (ADS)
Fujita, Yoshitaka; Kobayashi, Hiroshi
2011-08-01
The Brillouin spectra of di(2-ethylhexyl) sebacate, which is a liquid lubricant known as DOS, were measured at up to 5 GPa at 25 °C and up to 2.5 GPa at 80 °C. At 25 °C, the Brillouin frequency linewidth (acoustic attenuation) has a large maximum at 0.1 MPa, and at 80 °C, it has a large broad maximum at 0.8 GPa. The Brillouin frequency shift (sound velocity) and linewidth obtained indicate that the large dispersion of the sound velocities of DOS occurs from 0.1 MPa at 25 °C and from 0.8 GPa at 80 °C. The origins of this attenuation and dispersion are discussed on the basis of the theory for a viscoelastic liquid. It is proposed that the large acoustic attenuation and dispersion of DOS are due to the production of higher-rank structures with nano-order domains in a polymeric liquid by pressurization. The results show that DOS is strongly viscoelastic above 0.8 GPa at 80 °C, but it is not viscous below 0.8 GPa at 80 °C, with the disappearance of the frequency dispersion. The result obtained is used to explain a limiting shear stress observed in a traction oil. Above a given sliding speed, the oil reaches the region of temperature and pressure in which its viscosity decreases with increasing shear rate and conveys a constant torque above some high shear rate. Then, the oil flows as a plastic solid at a limiting shear stress. These findings regarding the dynamical properties of DOS under high pressures are very useful for the production and analysis of lubricants and traction oils.
Tombes, R M; Brokaw, C J; Shapiro, B M
1987-01-01
The significance of a phosphocreatine (PCr) shuttle in the energy transport of motile spermatozoa (Tombes, R. M., and B. M. Shapiro, 1985, Cell, 41:325-334) has been tested by a quantitative analysis of motility. Computer-assisted analysis of stroboscopic photomicrographs of live sea urchin spermatozoa whose creatine kinase has been specifically inhibited by fluorodinitrobenzene reveals that motility is impaired due to a progressive damping of bending waves as they propagate along the flagellum. This lesion, which has been defined as attenuation and can be quantified, is repaired when these spermatozoa are demembranated and reactivated to swim with ATP. The implication that attenuation is due to the inhibition of energy transport via a PCr shuttle resulting in the decrease of ATP and accumulation of inhibitory levels of ADP distally has been supported by calculating sperm PCr and ATP levels resulting from diffusion along the flagellum. The specific alterations of motility seen with creatine kinase inhibition and their reversal with ATP are as expected from the model and provide strong support for the PCr shuttle in high energy phosphate transport. Images FIGURE 1 PMID:2955815
NASA Astrophysics Data System (ADS)
Al-Damegh, Khaled; Sandvol, Eric; Al-Lazki, Ali; Barazangi, Muawia
2004-05-01
Continuous recordings of 17 broadband and short-period digital seismic stations from a newly established seismological network in Saudi Arabia, along with digital recordings from the broadband stations of the GSN, MEDNET, GEOFON, a temporary array in Saudi Arabia, and temporary short period stations in Oman, were analysed to study the lithospheric structure of the Arabian Plate and surrounding regions. The Arabian Plate is surrounded by a variety of types of plate boundaries: continental collision (Zagros Belt and Bitlis Suture), continental transform (Dead Sea fault system), young seafloor spreading (Red Sea and the Gulf of Aden) and oceanic transform (Owen fracture zone). Also, there are many intraplate Cenozoic processes such as volcanic eruptions, faulting and folding that are taking place. We used this massive waveform database of more than 6200 regional seismograms to map zones of blockage, inefficient and efficient propagation of the Lg and Sn phases in the Middle East and East Africa. We observed Lg blockage across the Bitlis Suture and the Zagros fold and thrust belt, corresponding to the boundary between the Arabian and Eurasian plates. This is probably due to a major lateral change in the Lg crustal waveguide. We also observed inefficient Lg propagation along the Oman mountains. Blockage and inefficient Sn propagation is observed along and for a considerable distance to the east of the Dead Sea fault system and in the northern portion of the Arabian Plate (south of the Bitlis Suture). These mapped zones of high Sn attenuation, moreover, closely coincide with extensive Neogene and Quaternary volcanic activity. We have also carefully mapped the boundaries of the Sn blockage within the Turkish and Iranian plateaus. Furthermore, we observed Sn blockage across the Owen fracture zone and across some segments of the Red Sea. These regions of high Sn attenuation most probably have anomalously hot and possibly thin lithospheric mantle (i.e. mantle lid). A surprising result is the efficient propagation of Sn across a segment of the Red Sea, an indication that active seafloor spreading is not continuous along the axis of the Red Sea. We also investigated the attenuation of Pn phase (QPn) for 1-2 Hz along the Red Sea, the Dead Sea fault system, within the Arabian Shield and in the Arabian Platform. Consistent with the Sn attenuation, we observed low QPn values of 22 and 15 along the western coast of the Arabian Plate and along the Dead Sea fault system, respectively, for a frequency of 1.5 Hz. Higher QPn values of the order of 400 were observed within the Arabian Shield and Platform for the same frequency. Our results based on Sn and Pn observations along the western and northern portions of the Arabian Plate imply the presence of a major anomalously hot and thinned lithosphere in these regions that may be caused by the extensive upper mantle anomaly that appears to span most of East Africa and western Arabia.
NASA Astrophysics Data System (ADS)
Prieux, Vincent; Brossier, Romain; Operto, Stéphane; Virieux, Jean
2013-09-01
Multiparameter full waveform inversion (FWI) is a challenging quantitative seismic imaging method for lithological characterization and reservoir monitoring. The difficulties in multiparameter FWI arise from the variable influence of the different parameter classes on the phase and amplitude of the data, and the trade-off between these. In this framework, choosing a suitable parametrization of the subsurface and designing the suitable FWI workflow are two key methodological issues in non-linear waveform inversion. We assess frequency-domain visco-acoustic FWI to reconstruct the compressive velocity (VP), the density (?) or the impedance (IP) and the quality factor (QP), from the hydrophone component, using a synthetic data set that is representative of the Valhall oil field in the North Sea. We first assess which of the (VP, ?) and (VP, IP) parametrizations provides the most reliable FWI results when dealing with wide-aperture data. Contrary to widely accepted ideas, we show that the (VP, ?) parametrization allows a better reconstruction of both the VP, ? and IP parameters, first because it favours the broad-band reconstruction of the dominant VP parameter, and secondly because the trade-off effects between velocity and density at short-to-intermediate scattering angles can be removed by multiplication, to build an impedance model. This allows for the matching of the reflection amplitudes, while the broad-band velocity model accurately describes the kinematic attributes of both the diving waves and reflections. Then, we assess different inversion strategies to recover the quality factor QP, in addition to parameters VP and ?. A difficulty related to attenuation estimation arises because, on the one hand the values of QP are on average one order of magnitude smaller than those of VP and ?, and on the other hands model perturbations relative to the starting models can be much higher for QP than for VP and ? during FWI. In this framework, we show that an empirical tuning of the FWI regularization, which is adapted to each parameter class, is a key issue to correctly account for the attenuation in the inversion. We promote a hierarchical approach where the dominant parameter VP is reconstructed first from the full data set (i.e. without any data preconditioning) to build a velocity model as kinematically accurate as possible before performing the joint update of the three parameter classes during a second step. This hierarchical imaging of compressive wave speed, density and attenuation is applied to a real wide-aperture ocean-bottom-cable data set from the Valhall oil field. Several geological features, such as accumulation of gas below barriers of claystone and soft quaternary sediment are interpreted in the FWI models of density and attenuation. The models of VP, ? and QP that have been developed by visco-acoustic FWI of the hydrophone data can be used as initial models to perform visco-elastic FWI of the geophone data for the joint update of the compressive and shear wave speeds.
Cui, Z W; Wang, K X; Cui, Zhi-Wen.; Liu, Jin-Xia.; Wang, Ke-Xie.
2003-01-01
In this paper, the reservoir is modeled by homogeneous two-phase media based on BISQ model. We focus on the effects of the squirt flow on the fundamental guided waves propagation in borehole embedded in saturated porous media excited by monopole, dipole and quadrupole point sources. The full waveforms acoustic logging in a fluid-filled borehole are simulated. The curves of velocity dispersion, attenuation coefficients and excitation of the fundamental guided waves have shown that velocity dispersions are almost independent of the characteristic squirt flow length, attenuations of guided waves are enhanced due to the squirt flow, and excitations of guided waves are decreased due to the squirt flow. It is possible to estimate the characteristic squirt flow length by attenuation coefficients of the guided waves from acoustical logging data.
Qiu, Xiaotun; Wang, Ziyu; Zhu, Jie; Oiler, Jon; Tang, Rui; Yu, Cunjiang; Yu, Hongyu
2010-09-01
This study describes the influence of relative humidity (RH) and reducing gases on the temperature coefficient of resonant frequency (TCF) of ZnO-based film bulk acoustic wave resonator (FBAR). Upon exposure to moisture or reducing gases, the TCF of FBAR decreased. Water molecules can replace adsorbed oxygen on the ZnO surface. This process was less effective at high temperature, resulting in a lower TCF in high RH. Reducing gases, such as acetone, can reduce the density of ZnO through reaction with the adsorbed oxygen, leading to a lower TCF. PMID:20875979
NASA Astrophysics Data System (ADS)
Azzam, R. M. A.; Sudradjat, F. F.
2008-03-01
The complex-amplitude reflection coefficients of p- and s-polarized light by a transparent freestanding, embedded, or deposited quarter-wave layer (QWL) are derived as explicit functions of the angle of incidence and layer refractive index. This provides the basis for the design of 50%-50% beam splitters for incident s-polarized or unpolarized light that use a high-index (e.g., TiO2 or Ge) QWL embedded in a glass cube in the visible and near infrared spectral range. These simple devices have good angular and spectral response and are insensitive to small film thickness errors to the first order.
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).
On-chip temperature-compensated Love mode surface acoustic wave device for gravimetric sensing
Liu, Q.; Flewitt, A. J.
2014-11-26
energy attenuation through losses into the liquid environment.2 To generate high quality Love wave resonance, a piezoelectric substrate with a high electromechanical coupling coefficient needs to be used. However, high coupling coefficient materials... TUS (High Target Utilization Sputtering) system which offers high uniformity, low stress and highly oriented ZnO films.14 Finally shallow grooves in the ZnO guiding layer are etched by 0.11% hydrochloric acid to enhance the Love wave resonance, as shown...
NASA Astrophysics Data System (ADS)
Sarkar, Tanmay
2015-06-01
In this paper, we demonstrate that previously reported traveling wave solutions for the fifth order KdV type equations with time dependent coefficients (Triki and Wazwaz, 2014) are incorrect. We present the corrected traveling wave solutions for fifth order KdV type equations using sine-cosine method. In addition, we provide traveling wave solutions for the Kawahara equation and Kaup-Kupershmidt equation as an application.
Diffracted and head waves associated with waves on nonseparable surfaces
NASA Technical Reports Server (NTRS)
Barger, Raymond L.
1992-01-01
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.
J. K. K. Ip; George Burns
1969-01-01
The bromine atom recombination rate constants, kr,fl's, obtained in flash photolysis experiments between 300 and 1300°K (preceding paper) were compared with the dissociation rate constants of Br2, kd,sh's, obtained in shock-wave experiments between 1250 and 2300°K. It was found that the phenomenological equation kd,sh ? kr,fl = K, where K is the equilibrium constant, is not obeyed if the kd,sh
Controlling frontal photopolymerization with optical attenuation and mass diffusion.
Hennessy, Matthew G; Vitale, Alessandra; Matar, Omar K; Cabral, João T
2015-06-01
Frontal photopolymerization (FPP) is a versatile directional solidification process that can be used to rapidly fabricate polymer network materials by selectively exposing a photosensitive monomer bath to light. A characteristic feature of FPP is that the monomer-to-polymer conversion profiles take on the form of traveling waves that propagate into the unpolymerized bulk from the illuminated surface. Practical implementations of FPP require detailed knowledge about the conversion profile and speed of these traveling waves. The purpose of this theoretical study is to (i) determine the conditions under which FPP occurs and (ii) explore how optical attenuation and mass transport can be used to finely tune the conversion profile and propagation kinetics. Our findings quantify the strong optical attenuation and slow mass transport relative to the rate of polymerization required for FPP. The shape of the traveling wave is primarily controlled by the magnitude of the optical attenuation coefficients of the neat and polymerized material. Unexpectedly, we find that mass diffusion can increase the net extent of polymerization and accelerate the growth of the solid network. The theoretical predictions are found to be in excellent agreement with experimental data acquired for representative systems. PMID:26172720
Simeone, Timothy A.; Samson, Kaeli K.; Matthews, Stephanie A.; Simeone, Kristina A.
2014-01-01
Summary 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. Synaptic activity of hyperexcitable KO mossy fibers significantly decreased CA3 principal cell spike-timing reliability contributing to this network pathology. Also, we have demonstrated that the KD reduces seizures by 75% in KO mice. Here, we determined whether 10-14 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 EPSP-spike coupling 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
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
NASA Astrophysics Data System (ADS)
Sumy, D. F.; Cochran, E. S.; Keranen, K. M.; Neighbors, C.; Atkinson, G. M.
2014-12-01
During November 2011, three M?5.0 earthquakes and thousands of aftershocks occurred on and near the Wilzetta fault, a structurally complex ~200 km long, Pennsylvanian-aged fault near Prague, Oklahoma, in close proximity to several active wastewater injection wells. All three M?5.0 earthquakes had strike-slip mechanisms consistent with rupture on three independent focal planes, suggesting activation of three different strands of the Wilzetta fault. Wastewater injection can cause a buildup of pore ?uid pressure along the fault, which decreases the fault strength and may induce earthquakes. Based on the proximity of earthquakes to active ?uid injection wells, the unilateral progression of aftershocks away from the initial M5.0 event, and shallow earthquake depths, Keranen et al. [2013] concluded that fluid injection was responsible for inducing the first M5.0 event. Furthermore, Sumy et al. [2014] found that the initial M5.0 event increased the Coulomb stress in the region of the M5.7 mainshock, triggering a cascade of earthquakes along the Wilzetta fault. Thus, while nearby wastewater injection directly induced the initial M5.0 event, this earthquake triggered successive failure along the Wilzetta fault; however, it remains unclear if the additional ruptured fault strands are also influenced by fluid injection. In this study, we explore instrumental ground motions and shear-wave splitting of the November 2011 Prague, Oklahoma sequence, in order to construct ground motion prediction equations (GMPEs) and understand the local stress regime, respectively. We examine ~1,000 earthquakes recorded by a total of 47 seismometers, located within ~150 km of the Wilzetta fault. With respect to GMPEs, initial results suggest that the ground motions are smaller than similar magnitude earthquakes of natural/tectonic origins, and these lower intensities may be a result of lower stress drops [e.g. Hough, 2014]. With respect to shear-wave splitting, we examine quality graded fast polarization and delay time measurements and observe fast directions oriented roughly E-W across the study area, which is consistent with the maximum principal stress of N80E determined from the focal mechanism inversion of Sumy et al. [2014].
Yuen, Chun-Man; Chung, Sheng-Ying; Tsai, Tzu-Hsien; Sung, Pei-Hsun; Huang, Tien-Hung; Chen, Yi-Ling; Chen, Yung-Lung; Chai, Han-Tan; Zhen, Yen-Yi; Chang, Meng-Wei; Wang, Ching-Jen; Chang, Hsueh-Wen; Sun, Cheuk-Kwan; Yip, Hon-Kan
2015-01-01
Background: To investigate the effect of shock wave (SW) on brain-infarction volume (BIV) and neurological function in acute ischemic stroke (AIS) by left internal carotid artery occlusion in rats. Methods and results: SD rats (n=48) were divided into group 1 [sham-control (SC)], group 2 [SC-ECSW (energy dosage of 0.15 mJ/mm2/300 impulses)], group 3 (AIS), and group 4 (AIS-ECSW) and sacrificed by day 28 after IS induction. In normal rats, caspase-3, Bax and TNF-? biomarkers did not differ between animals with and without ECSW therapy, whereas Hsp70 was activated post-ECSW treatment. By day 21 after AIS, Sensorimotor-functional test identified a higher frequency of turning movement to left in group 3 than that in group 4 (P<0.05). By day 28, brain MRI demonstrated lager BIV in group 3 than that in group 4 (P<0.001). Angiogenesis biomarkers at cellular (CD31, ?-SMA+) and protein (eNOS) levels and number of neuN+ cells were higher in groups 1 and 2 than those in groups 3 and 4, and higher in group 4 than those in group 3, whereas VEGF and Hsp70 levels were progressively increased from groups 1 and 2 to group 4 (all P<0.001). Protein expressions of apoptosis (Bax, caspase 3, PARP), inflammation (MMP-9, TNF-?), oxidative stress (NOX-1, NOX-2, oxidized protein) and DNA-damage marker (?-H2AX), and expressions of ?-H2AX+, GFAP+, AQP-4+ cells showed an opposite pattern compared to that of angiogenesis among the four groups (all P<0.001). Conclusion: ECSW therapy was safe and effective in reducing BIV and improved neurological function.
Cao, Wenwu
.68Pb,,Mg1/3Nb2/3...O30.32PbTiO3 single crystals poled along 001 and 110 Rui Zhang, Wenhua Jiang PMN-32%PT single crystals poled along 001 and 110 , respectively. The measured dispersion of longitudinal wave velocity and attenuation in the multidomain PMN-32%PT crystals are smaller than that of PZT-4
Excitation and propagation of surface acoustic waves in monolithic structures GaAs-SiO2-ZnO-Al
NASA Astrophysics Data System (ADS)
Miškinis, R.; Rutkowski, P.; Sashchuk, A.; Urba, E.; Fedoretz, V.
1996-07-01
Experimental investigation of surface acoustic wave (SAW) velocity, attenuation and electromechanical coupling coefficient dependences on ZnO layers thickness for GaAs-SiO2-IDT-ZnO-Al structures has been performed. It has been established that the structures studied grown on (001) cut of GaAs have higher electromechanical coupling coefficient compared to that of GaAs crystal with the same orientation. The Al film deposition on the top of these layered structures proved to change the SAW velocity. The investigation of SAW attenuation has demonstrated less attenuation for thinner ZnO layer.
Lidar measurement of light attenuation in water
NASA Astrophysics Data System (ADS)
Bazzani, Marco; Cecchi, Giovanna; Pantani, Luca; Raimondi, Valentina
1998-12-01
The total attenuation coefficient is a significant parameter of the water column being strictly related to the light penetration depth and to the quantity of suspended and dissolved substances. This parameter is measured in situ by optical instruments while its remote measurement can be achieved by lidars. The lidar measurement of the total attenuation coefficient is based on the Raman scattering due to the OH stretching of water molecule. This paper discusses the analytical base of the measurement.
AVO correction for scalar waves in the case of a thinly layered reflector overburden
Martin T. Widmaier; S. A. Shapiro; P. Hubral
1996-01-01
The reflection response of a seismic target is significantly affected by a thinly layered overburden, which creates velocity anisotropy and a transmission loss by scattering attenuation. These effects must be taken into account when imaging a target reflector and when inverting reflection coefficients. Describing scalar wave (i.e., acoustic wave or SH-wave) propagation through a stack of thin layers by equivalent-medium
Prediction of spectral acceleration response ordinates based on PGA attenuation
Graizer, V.; Kalkan, E.
2009-01-01
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.
Propagation properties of guided wave in the anchorage structure of rock bolts
NASA Astrophysics Data System (ADS)
Wang, Cheng; He, Wen; Ning, Jianguo; Zhang, Changsuo
2009-12-01
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.
Attenuation of short strongly nonlinear stress pulses in dissipative granular chains
S. Y. Wang; V. F. Nesterenko
2015-04-16
Attenuation of short, strongly nonlinear stress pulses in chains of spheres and cylinders was investigated experimentally and numerically for two ratios of their masses keeping their contacts identical. The chain with mass ratio 0.98 supports solitary waves and another one (with mass ratio 0.55) supports nonstationary pulses which preserve their identity only on relatively short distances, but attenuate on longer distances because of radiation of small amplitude tails generated by oscillating small mass particles. Pulse attenuation in experiments in the chain with mass ratio 0.55 was faster at the same number of the particles from the entrance than in the chain with mass ratio 0.98. It is in quantitative agreement with results of numerical calculations with effective damping coefficient 6 kg/s. This level of damping was critical for eliminating the gap openings between particles in the system with mass ratio 0.55 present at lower or no damping. However with increase of dissipation numerical results show that the chain with mass ratio 0.98 provides faster attenuation than chain with mass ratio 0.55 due to the fact that the former system supports the narrower pulse with the larger difference between velocities of neighboring particles. The investigated chains demonstrated different wave structure at zero dissipation and at intermediate damping coefficients and the similar behavior at large damping.
One-Dimensional Plane Monochromatic Filtration Waves
NASA Astrophysics Data System (ADS)
Filippov, A. I.; Akhmetova, O. V.
2015-03-01
Equations and relations to describe one-dimensional plane monochromatic fi ltration waves in a homogeneous isotropic porous medium have been obtained. To this end, use was made of the equation of motion of a liquid phase with account of frictional forces, which in the case of steady-state fi ltration with parallel streamlines agrees with Darcy's fi ltration law for an anisotropic medium. The equations of motion and continuity reduced to an equation of telegraphy enabled us to construct relations for the wave number, the absorption and attenuation coefficients, and the velocity of filtration waves.
Seismic Attenuation Inversion with t* Using tstarTomog.
Preston, Leiph
2014-09-01
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.
Ploix, Marie-Aude; Guy, Philippe; Chassignole, Bertrand; Moysan, Joseph; Corneloup, Gilles; El Guerjouma, Rachid
2014-09-01
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
Site-Dependent Response Spectral Attenuation Modelling
HING-HO TSANG; NELSON T. K. LAM
2007-01-01
A site-dependent response spectral attenuation model is an important element in a site-dependent seismic hazard assessment. Seismic attenuation beha viour is controlled by a large number of wave modification mechanisms, some of which have characteristics specific to a local area or a particular s ite, whilst others can be generalised to the entire seismic reg ion. Factors representing these mechanisms
Ultrasonic attenuation in Voronoi polycrystals
Joseph A. Turner; Goutam Ghoshal
2001-01-01
Studies of elastic wave scattering in polycrystalline media are applicable to ultrasonic materials characterization and nondestructive evaluation. Ultrasonic attenuation is used to extract microstructural parameters such as grain size and grain texture. The relations between experimental data and microstructural information require ultrasonic scattering models that often oversimplify real microstructures. Here, these relations are examined in terms of numerical simulations of
NASA Astrophysics Data System (ADS)
Miyano, Shun; Tonokura, Kenichi
2011-01-01
Mid-infrared absorption spectroscopy was applied to the detection of the hydroperoxyl radical (HO 2) in pulsed laser photolysis combined with a laser absorption kinetics reactor. The transition of the ?3 vibrational band assigned to the O-O stretch mode around 1065 cm -1 was probed with a thermoelectrically cooled, continuous wave, mid-infrared, distributed feedback quantum cascade laser (QCL). The HO 2 was generated through 355 nm photolysis of Cl 2/1,4- c-C 6H 8/O 2 mixtures. The mid-infrared absorption spectrum of the HO 2 radical was recorded between 1064 and 1065.5 cm -1. The absorption line shapes were well represented by the Voigt profile. The nitrogen-broadening coefficients of the HO 2 radical at 295 K were determined for four absorption lines around 1065 cm -1. Mid-infrared absorption detection using a QCL as a spectroscopic light source is a powerful method in spectroscopic and kinetics studies of the HO 2 radical.
Attenuation of short strongly nonlinear stress pulses in dissipative granular chains
NASA Astrophysics Data System (ADS)
Wang, S. Y.; Nesterenko, V. F.
2015-06-01
Attenuation of short, strongly nonlinear stress pulses in chains of spheres and cylinders was investigated experimentally and numerically for two ratios of their masses keeping their contacts identical. The chain with mass ratio 0.98 supports solitary waves and another one (with mass ratio 0.55) supports nonstationary pulses, which preserve their identity only on relatively short distances, but attenuate on longer distances because of radiation of small amplitude tails generated by oscillating small mass particles. Pulse attenuation in experiments in the chain with mass ratio 0.55 was faster at the same number of the particles from the entrance than in the chain with mass ratio 0.98. It is in quantitative agreement with results of numerical calculations with effective damping coefficient 6 kg/s. This level of damping was critical for eliminating the gap openings between particles in the system with mass ratio 0.55 present at lower or no damping. With increase of dissipation numerical results show that the chain with mass ratio 0.98 provides faster attenuation than the chain with mass ratio 0.55 due to the fact that the former system supports the narrower pulse with the larger difference between velocities of neighboring particles. The investigated chains demonstrated similar behavior at large damping coefficient 100 kg/s.
ERIC Educational Resources Information Center
Greenslade, Thomas B., Jr.
1994-01-01
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)
Generalized O`Doherty-Anstey formula for P-SV waves in random multilayered elastic media
Shapiro, S.A.; Hubral, P. [Univ. of Karlsruhe (Germany)
1994-12-31
The authors study the influence of elastic vertically inhomogeneous, e.g., finely layered random media (of variable density and shear and sonic velocities) on the kinematics and dynamics of an obliquely propagating P-SV plane-wave transmissivity. They obtain explicit analytic solutions for the attenuation coefficients and phase velocities. These solutions are valid for all frequencies. They are fairly simple and can be directly used for practical applications. The theory has been numerically tested on practically relevant models of media. The results of simulations agree very well with the analytic solutions. The theory describes the effect of frequency-dependent anisotropy of velocities and attenuations of transmitted waves due to elastic multilayering. Its low- and high-frequency asymptotic results for the phase velocities agree with those of Backus averaging and ray approximation respectively. The results for the attenuation coefficients constitute a set of generalized O`Doherty-Anstey formulas.
Sound attenuation in magnetorheological fluids
NASA Astrophysics Data System (ADS)
Rodríguez-López, J.; Elvira, L.; Resa, P.; Montero de Espinosa, F.
2013-02-01
In this work, the attenuation of ultrasonic elastic waves propagating through magnetorheological (MR) fluids is analysed as a function of the particle volume fraction and the magnetic field intensity. Non-commercial MR fluids made with iron ferromagnetic particles and two different solvents (an olive oil based solution and an Araldite-epoxy) were used. Particle volume fractions of up to 0.25 were analysed. It is shown that the attenuation of sound depends strongly on the solvent used and the volume fraction. The influence of a magnetic field up to 212 mT was studied and it was found that the sound attenuation increases with the magnetic intensity until saturation is reached. A hysteretic effect is evident once the magnetic field is removed.
Full-wave description of the lower hybrid reflection of whistler waves
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
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.
Study on laser and infrared attenuation performance of carbon nanotubes
NASA Astrophysics Data System (ADS)
Liu, Xiang-cui; Liu, Qing-hai; Dai, Meng-yan; Cheng, Xiang; Fang, Guo-feng; Zhang, Tong; Liu, Haifeng
2014-11-01
In recent years, the weapon systems of laser and infrared (IR) imaging guidance have been widely used in modern warfare because of their high precision and strong anti-interference. However, military smoke, a rapid and effective passive jamming method, can effectively counteract the attack of precision-guided weapons by their scattering and absorbing effects. The traditional smoke has good visible light (0.4-0.76?m) obscurant performance, but hardly any effects to other electromagnetic wave bands while the weapon systems of laser and IR imaging guidance usually work in broad band, including the near-infrared (1-3?m), middle-infrared (3-5?m), far-infrared (8-14?m), and so on. Accordingly, exploiting new effective obscurant materials has attracted tremendous interest worldwide nowadays. As is known, the nano-structured materials have lots of unique properties comparing with the traditional materials suggesting that they might be the perfect alternatives to solve the problems above. Carbon nanotubes (CNTs) are well-ordered, all-carbon hollow graphitic nano-structured materials with a high aspect ratio, lengths from several hundred nanometers to several millimeters. CNTs possess many unique intrinsic physical-chemical properties and are investigated in many areas reported by the previous studies. However, no application research about CNTs in smoke technology field is reported yet. In this paper, the attenuation performances of CNTs smoke to laser and IR were assessed in 20m3 smoke chamber. The testing wavebands employed in experiments are 1.06?m and 10.6?m laser, 3-5?m and 8-14?m IR radiation. The main parameters were obtained included the attenuation rate, transmission rate, mass extinction coefficient, etc. The experimental results suggest that CNTs smoke exhibits excellent attenuation ability to the broadband IR radiation. Their mass extinction coefficients are all above 1m2·g-1. Nevertheless, the mass extinction coefficients vary with the sampling time and smoke particles concentrations, even in the same testing waveband. With the time going the mass extinction coefficients will increase gradually. Based on the above results, theoretical calculations are also carried out for further exploitations. In general, CNTs smoke behaves excellent attenuation ability toward laser and IR under the experimental conditions. Therefore, they have great potentials to develop new smoke obscurant materials which could effectively interfere with broadband IR radiation including 1.06?m, 10.6?m, 3-5?m and 8-12?m IR waveband.
Toward accurate attenuation correction in SPECT without transmission measurements.
Welch, A; Clack, R; Natterer, F; Gullberg, G T
1997-10-01
The current trend in attenuation correction for single photon emission computed tomography (SPECT) is to measure and reconstruct the attenuation coefficient map using a transmission scan, performed either sequentially or simultaneously with the emission scan. This approach requires dedicated hardware and increases the cost (and in some cases the scanning time) required to produce a clinical SPECT image. Furthermore, if short focal-length fan-beam collimators are used for transmission imaging, the projection data may be truncated, leading to errors in the attenuation coefficient map. Our goal is to obtain information about the attenuation distribution from only the measured emission data by exploiting the fact that only certain attenuation distributions are consistent with a given emission dataset. Ultimately this consistency information will either be used directly to compensate for attenuation or combined with the incomplete information from fan-beam transmission measurements to produce a more accurate attenuation coefficient map. In this manuscript the consistency conditions (which relate the measured SPECT data to the sinogram of the attenuation distribution) are used to find the uniform elliptical attenuation object which is most consistent with the measured emission data. This object is then used for attenuation correction during the reconstruction of the emission data. The method is tested using both simulated and experimentally acquired data from uniformly and nonuniformly attenuating objects. The results show that, for uniform elliptical attenuators, the consistency conditions of the SPECT data can be used to produce an accurate estimate of the attenuation map without performing any transmission measurements. The results also show that, in certain circumstances, the consistency conditions can prove useful for attenuation compensation with nonuniform attenuators. PMID:9368109
G. Varotto; E. M. Staderini
2008-01-01
This paper describes a simple 2D model for the propagation of electro-magnetic (EM) pulses in human tissues. To assess the reliability of using this model for fast attenuation evaluation of UWB radar pulses in the body, the model is compared with a well known 3D FDTD numeric simulator using a simple multilayer geometry. Results from the 2D model were found
Shear waves in vegetal tissues at ultrasonic frequencies
NASA Astrophysics Data System (ADS)
Fariñas, M. D.; Sancho-Knapik, D.; Peguero-Pina, J. J.; Gil-Pelegrín, E.; Gómez Álvarez-Arenas, T. E.
2013-03-01
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.
Acoustic waves in a Biot-type porous snow model: The fast slow wave in light snow
Sidler, Rolf
2015-01-01
Wave velocities, attenuation and reflection coefficients in snow can not be explained by the widely used elastic or viscoelastic models for wave propagation. Instead, Biot's model of wave propagation in porous materials should be used. However, the application of Biot's model is difficult due to the large property space of the underlying porous material. Here we use the properties of ice and air as well as empirical relationships to define the properties of snow as a function of porosity. This reduction allows to predict phase velocities and attenuation of the shear- and compressional-waves as functions of porosity or density. For light snow the peculiarity was found that the velocity of the compressional wave of the first kind is lower than the compressional wave of the second kind that is commonly referred to as the "slow" wave. The reversal of the velocities comes with an increase of attenuation for the first compressional wave. This is in line with the common observation that sound is strongly absorbed af...
Hargrove, Douglas L.
2004-09-14
A portable, hand-held meter used to measure direct current (DC) attenuation in low impedance electrical signal cables and signal attenuators. A DC voltage is applied to the signal input of the cable and feedback to the control circuit through the signal cable and attenuators. The control circuit adjusts the applied voltage to the cable until the feedback voltage equals the reference voltage. The "units" of applied voltage required at the cable input is the system attenuation value of the cable and attenuators, which makes this meter unique. The meter may be used to calibrate data signal cables, attenuators, and cable-attenuator assemblies.
Pinfield, Valerie J; Challis, Richard E
2011-04-01
Classical long wavelength approximate solutions to the scattering of acoustic waves by a spherical liquid particle suspended in a liquid (an emulsion) show small but significant differences from full solutions at very low k(c)a (typically k(c)a < 0.01) and above at k(c)a > 0.1, where k(c) is the compressional wavenumber and a the particle radius. These differences may be significant in the context of dispersed particle size estimates based on compression wave attenuation measurements. This paper gives an explanation of how these differences arise from approximations based on the significance of terms in the modulus of the complex zero-order partial wave coefficient, A(0). It is proposed that a more accurate approximation results from considering the terms in the real and imaginary parts of the coefficient, separately. PMID:21476641
Wear, Keith A
2013-04-01
The presence of two longitudinal waves in poroelastic media is predicted by Biot's theory and has been confirmed experimentally in through-transmission measurements in cancellous bone. Estimation of attenuation coefficients and velocities of the two waves is challenging when the two waves overlap in time. The modified least squares Prony's (MLSP) method in conjuction with curve-fitting (MLSP + CF) is tested using simulations based on published values for fast and slow wave attenuation coefficients and velocities in cancellous bone from several studies in bovine femur, human femur, and human calcaneus. The search algorithm is accelerated by exploiting correlations among search parameters. The performance of the algorithm is evaluated as a function of signal-to-noise ratio (SNR). For a typical experimental SNR (40 dB), the root-mean-square errors (RMSEs) for one example (human femur) with fast and slow waves separated by approximately half of a pulse duration were 1 m/s (slow wave velocity), 4 m/s (fast wave velocity), 0.4 dB/cm MHz (slow wave attenuation slope), and 1.7 dB/cm MHz (fast wave attenuation slope). The MLSP + CF method is fast (requiring less than 2 s at SNR = 40 dB on a consumer-grade notebook computer) and is flexible with respect to the functional form of the parametric model for the transmission coefficient. The MLSP + CF method provides sufficient accuracy and precision for many applications such that experimental error is a greater limiting factor than estimation error. PMID:23556613
Shock propagation and attenuation in Green River oil shale
NASA Astrophysics Data System (ADS)
Grady, D. E.
2014-05-01
Shock waves produced by planar impact of thin plates onto samples of oil shale are monitored with time-resolved velocity interferometer diagnostics. Peak shock stresses are below the Hugoniot elastic limit. Stress wave measurements at successive sample thickness are analysed to determine the experimental shock energy attenuation with propagation distance. Shock attenuation is attributed to stress wave scattering at planes of oil shale kerogen within the shale matrix. Wave scattering from planar defects are evaluated from a shock physics perspective and a scattering model is constructed that sensibly reproduces the experimental observation of shock energy attenuation.
The attenuation of microwave radiation by fog and rain
J. D. Pendleton; Stanley Niles
1994-01-01
In this report, the equations which describe the attenuation of long-wavelength electromagnetic radiation by water fogs and rain are briefly reviewed and explained under the assumption that the aerosol droplets are spherical and that the irradiance of the beam is in the 'linear' regime. Calculations of water fog attenuation coefficients are made using the Rayleigh approximation, and an approximate error
Attenuation Measurements in Solutions of Some Carbohydrates
Gagandeep [Guru Nanak Dev University (India); Singh, Kulwant [Guru Nanak Dev University (India); Lark, B.S. [Guru Nanak Dev University (India); Sahota, H.S. [Punjabi University (India)
2000-02-15
The linear attenuation coefficients in aqueous solutions of three carbohydrates, glucose (C{sub 6}H{sub 12}O{sub 6}), maltose monohydrate (C{sub 12}H{sub 22}O{sub 11}.H{sub 2}O), and sucrose (C{sub 12}H{sub 22}O{sub 11}), were determined at 81, 356, 511, 662, 1173, and 1332 keV by the gamma-ray transmission method in a good geometry setup. From the precisely measured densities of these solutions, mass attenuation coefficients were then obtained that varied systematically with the corresponding changes in the concentrations (g/cm{sup 3}) of these solutions. The experimental results were used in terms of effective atomic numbers and electron densities. A comparison between experimental and theoretical values of attenuation coefficients has proven that the study has a potential application for the determination of attenuation coefficients of solid solutes from their solutions without obtaining them in pure crystalline form.
Attenuation measurements in solutions of some carbohydrates
Gagandeep; Singh, K.; Lark, B.S.; Sahota, H.S.
2000-02-01
The linear attenuation coefficients in aqueous solutions of three carbohydrates, glucose (C{sub 6}H{sub 12} O{sub 6}), maltose monohydrate (C{sub 12}H{sub 22}O{sub 11}{center{underscore}dot}H{sub 2}O), and sucrose (C{sub 12}H{sub 22}O{sub 11}), were determined at 81, 356, 511, 662, 1,173, and 1,332 keV by the gamma-ray transmission method in a good geometry setup. From the precisely measured densities of these solutions, mass attenuation coefficients were then obtained that varied systematically with the corresponding changes in the concentrations (g/cm{sup 3}) of these solutions. The experimental results were used in terms of effective atomic numbers and electron densities. A comparison between experimental and theoretical values of attenuation coefficients has proven that the study has a potential application for the determination of attenuation coefficients of solid solutes from their solutions without obtaining them in pure crystalline form.
Franceschini Simultaneous estimation of attenuation and structure
Paris-Sud XI, Université de
in vivo scanning, three skin-mimicking phantoms with different attenuation coefficients were successively the Structure Factor Size Estimator (SFSE).1 The SFSE is a second-order data reduction model based by a modified SFSE model. This approach is similar to that presented by Bigelow et al.3 , who estimated
NASA Astrophysics Data System (ADS)
Pisa, D.; Nemec, F.; Parrot, M.; Santolik, O.
2013-05-01
Although there has been a significant progress in our understanding of seismo-ionospheric coupling in the past few decades, an exact description of mechanisms and effects that could be used as short-time precursors is still missing. We use the electromagnetic wave data measured by the DEMETER satellite at an altitude of about 700 km to check for the presence of statistically significant changes of VLF wave intensity related to the seismic activity. All relevant data acquired by DEMETER during almost 6.5 years of the mission have been analyzed. A robust two-step data processing has been used. It enables us to compare data from the vicinity of more than 9000 earthquakes with an unperturbed background distribution based on data collected during the whole DEMETER mission and to evaluate a statistical significance of the observed effects. We confirm the previously reported results of a statistically significant decrease of the wave intensity at the frequency of about 1.7 kHz using nearly twice larger data set. The effect is observed a few hours before the time of the main shock and it occurs exclusively during the night. Results can be explained by a variations of properties of the Earth-Ionospheric waveguide. This modification of the waveguide can change the propagation of electromagnetic waves generated by lightning discharges, which subsequently penetrate to the altitude of the satellite. The effect is very weak compared to common variation of wave intensity in the ionosphere. This decrease of the wave intensity is observable only on a large dataset and can not be considered as a possible short-time earthquake precursor.
LaCure, Mari Mae
2010-04-29
Waves is the supporting document to the Master of Fine Arts thesis exhibition of the same title. Exhibited March 7-12 2010 in the Art and Design Gallery at the University of Kansas, Waves was comprised of a series of mixed media drawings...
SEISMIC ATTENUATION FOR RESERVOIR CHARACTERIZATION
Joel Walls; M.T. Taner; Gary Mavko; Jack Dvorkin
2002-07-01
In fully-saturated rock and at ultrasonic frequencies, the microscopic squirt flow induced between the stiff and soft parts of the pore space by an elastic wave is responsible for velocity-frequency dispersion and attenuation. In the seismic frequency range, it is the macroscopic cross-flow between the stiffer and softer parts of the rock. We use the latter hypothesis to introduce simple approximate equations for velocity-frequency dispersion and attenuation in a fully water saturated reservoir. The equations are based on the assumption that in heterogeneous rock and at a very low frequency, the effective elastic modulus of the fully-saturated rock can be estimated by applying a fluid substitution procedure to the averaged (upscaled) dry frame whose effective porosity is the mean porosity and the effective elastic modulus is the Backus-average (geometric mean) of the individual dry-frame elastic moduli of parts of the rock. At a higher frequency, the effective elastic modulus of the saturated rock is the Backus-average of the individual fully-saturated-rock elastic moduli of parts of the rock. The difference between the effective elastic modulus calculated separately by these two methods determines the velocity-frequency dispersion. The corresponding attenuation is calculated from this dispersion by using (e.g.) the standard linear solid attenuation model.
Light attenuation on unicellular marine phytoplankton
NASA Astrophysics Data System (ADS)
Krol, Tadeusz; Lotocka, Maria
1994-10-01
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 and the blue-green alga Chroococcus minor. The cultures were subjected to chemical (NaOH and temperature) or physical (ultrasounds) factors which altered their internal cell structures. Distinct changes in the light attenuation spectrum were observed as a result of the modification of the internal cell structures. Light attenuation cross-sections of those phytoplankton cells were also determined.
Christie, Alan M. (Swissvale, PA); Snyder, Kurt I. (Murrysville, PA)
1985-01-01
A pressure surge attenuation system for pipes having a fluted region opposite crushable metal foam. As adapted for nuclear reactor vessels and heads, crushable metal foam is disposed to attenuate pressure surges.
Inferential Theory for Partially Disattenuated Correlation Coefficients.
ERIC Educational Resources Information Center
Hakstian, A. Ralph; And Others
1989-01-01
Four measurement designs are presented for use with correlation coefficients corrected, in one variable, for attenuation due to unreliability (partially disattenuated). Associated asymptotic variance/covariance expressions are presented. Empirical simulation results illustrate the satisfactory Type I error control and statistical power of the…
Brodsky
1990-01-01
Compressional wave ultrasonic data were used to qualitatively assess the extent of crack closure during hydrostatic compression of damaged specimens of WIPP salt. Cracks were introduced during constant strain-rate triaxial tests at low confining pressure (0.5 MPa) as specimens were taken to either 0.5, 1.0, or 1.5 percent axial strain. For three specimens taken to 1.0 percent axial strain, the
NASA Astrophysics Data System (ADS)
Scherbaum, Frank; Sato, Haruo
1991-02-01
The envelope shape around the arrival of the direct waves of seismic signals traveling in a randomly inhomogeneous medium has been predicted, based on the parabolic approximation, to be a measure of the long-wavelength components of the randomness as well as the attenuation properties of the medium. We use a nonlinear Marquardt-Levenberg inversion technique in order to model the SH wave envelopes of 119 earthquakes in the frequency band 2-6 Hz for lapse times less than 1.5 times the shear wave travel time. We attempted to obtain the ratio of the mean square fractional velocity fluctuation to the correlation length (?2V/a) estimates as well as estimates of attenuation Qs-1. For the majority of the events we found a good correlation between the envelope shape and the hypocentral distances. The resultant ?2V/a of 10-3.27±0.32 km-1 is independent of frequency. It agrees well with the choice of the Gaussian autocorrelation function for the long-wavelength components of the random velocity fluctuations. The resultant attenuation Qs-1 is roughly proportional to the reciprocal of frequency. We may interpret it as either the scattering loss due to short-wavelength components of randomness or intrinsic loss. We have performed numerical simulations of the inversion process to quantify the model parameter uncertainties and to obtain a better understanding of the model parameter resolution. By modeling the wave envelopes as a superposition of noise-free wave envelopes and band-pass-filtered Gaussian noise we were able to reproduce the visual appearance of the observed envelopes as well as the observed features in the model parameter dependency. We find that for long hypocentral distances the envelope shape is controlled by the attenuation coefficient, while for short hypocentral distances the velocity fluctuations contribute dominantly.
Attenuation of Seismic Energy in the Upper Mantle
Don L. Anderson; Ari Ben-Menahem; C. B. Archambeau
1965-01-01
The amplitude attenuation and phase dispersion for Love and Rayleigh waves in the period range 50 to 300 sec is determined from two earthquakes by digital techniques. A distribution of Q, or anelasticity, is determined for the upper mantle which satisfies the amplitude decay data for Love and Rayleigh waves and which is consistent with available body wave data. An
Yellowstone Attenuation Tomography from Ambient Seismic Noise
NASA Astrophysics Data System (ADS)
Doungkaew, N.; Seats, K.; Lawrence, J. F.
2013-12-01
The goal of this study is to create a tomographic attenuation image for the Yellowstone region by analyzing ambient seismic noise. An attenuation image generated from ambient noise should provide more information about the structure and properties beneath Yellowstone, especially the caldera, which is known to be active. I applied the method of Lawrence & Prieto [2011] to examine lateral variations in the attenuation structure of Yellowstone. Ambient noise data were collected from broadband seismic stations located around Yellowstone National Park from 1999-2013. Noise correlation functions derived from cross correlations of the ambient noise at two stations were used to calculate a distance dependent decay (an attenuation coefficient) at each period and distance. An inversion was then performed to isolate and localize the spatial attenuation coefficients within the study area. I observe high amplitude decay of the ambient noise at the Yellowstone caldera, most likely due to elevated temperature and crustal melts caused by volcanism, geothermal heat flow, and hydrothermal activity such as geysers.
On the reliability of attenuation measurements from ambient noise crosscorrelations
Johnson, Cari
On the reliability of attenuation measurements from ambient noise crosscorrelations FanChi Lin,1 variations in attenuation. Citation: Lin, F.C., M. H. Ritzwoller, and W. Shen (2011), On the reliability wave amplitudes obtained from ambient noise crosscorrelations produce reliable constraints on seismic
Foltyn, S.R.
1987-05-29
The disclosure relates to low loss, high power variable attenuators comprising one or more transmissive and/or reflective multilayer dielectric filters. The attenuator is particularly suitable to use with unpolarized lasers such as excimer lasers. Beam attenuation is a function of beam polarization and the angle of incidence between the beam and the filter and is controlled by adjusting the angle of incidence the beam makes to the filter or filters. Filters are selected in accordance with beam wavelength. 9 figs.
Measured attenuation correction methods
Hermann Ostertag; Wolfgang K. Kiibler; Josef Doll; Walter J. Lorenz
1989-01-01
Accurate attenuation correction is a prerequisite for the determination of exact local radioactivity concentrations in positron emission tomography. Attenuation correction factors range from 4–5 in brain studies to 50–100 in whole body measurements. This report gives an overview of the different methods of determining the attenuation correction factors by transmission measurements using an external positron emitting source. The long-lived generator
Foltyn, Stephen R. (Los Alamos, NM)
1988-01-01
The disclosure relates to low loss, high power variable attenuators comprng one or more transmissive and/or reflective multilayer dielectric filters. The attenuator is particularly suitable to use with unpolarized lasers such as excimer lasers. Beam attenuation is a function of beam polarization and the angle of incidence between the beam and the filter and is controlled by adjusting the angle of incidence the beam makes to the filter or filters. Filters are selected in accordance with beam wavelength.
A model for the diffuse attenuation coefficient of downwelling irradiance
Lee, Zhongping
studies. For the vast ocean the only feasible means to get fine-scale measurements of Kd is by ocean color different particle phase functions, and the modeled Kd are found matching Hydrolight Kd very well ($2, 1976], and Kd is a critical parameter for accurate estimation of the light inten- sity at depth
Global survey of frequency dependent attenuation
NASA Astrophysics Data System (ADS)
McNamara, D. E.; Benz, H.; Gee, L. S.; Frankel, A. D.
2011-12-01
We analyze frequency-dependent attenuation of Lg waves, 1/Q(f), for numerous tectonic environments. Tectonic environments studied include: south Pacific oceanic subduction zone near Samoa, the oblique subduction zone off Hispaniola, two continental-oceanic subduction zones in Chile and Alaska, the continental-continental collision zone of the Tibetan Plateau, stable continental interior regions of the central US and Colorado Plateau, the eastern US passive margin and the active margins of the western US. Lg propagates with a group velocity of about 3.5 km/s, the average crustal shear wave velocity. This wave is commonly observed as the dominant phase on high-frequency seismograms at regional distances and is generated by a superposition of higher-mode surface waves or multiply-reflected shear energy in a crustal waveguide. Consequently, Lg provides a good measure of path-averaged crustal properties, such as shear-wave velocity and attenuation. Lg is particularly useful since its amplitude is sensitive to lateral heterogeneity in the crust due to varying tectonic environment. In this global survey we observe that Lg attenuation is generally higher for tectonically active regions than for stable continental interiors. Q(f) is an important physical parameter and is required for a variety of USGS research projects such as the simulation of strong ground motion and seismic network magnitude detection threshold modeling.
Evans, J.R.; Zucca, J.J.
1988-01-01
Medicine Lake volcano is a basalt through rhyolite shield volcano of the Cascade Range, lying east of the range axis. The Pg wave from eight explosive sources which has traveled upward through the target volume to a dense array of 140 seismographs provides 1- to 2-km resolution in the upper 5 to 7 km of the crust beneath the volcano. The experiment tests the hypothesis that Cascade Range volcanoes of this type are underlain only by small silicic magma chambers. We image a low-velocity low-Q region not larger than a few tens of cubic kilometers in volume beneath the summit caldera, supporting the hypothesis. A shallower high-velocity high-density feature, previously known to be present, is imaged for the first time in full plan view; it is east-west elongate, paralleling a topographic lineament between Medicine Lake volcano and Mount Shasta. Differences between this high-velocity feature and the equivalent feature at Newberry volcano, a volcano in central regon resembling Medicine Lake volcano, may partly explain the scarcity of surface hydrothermal features at Medicine Lake volcano. A major low-velocity low-Q feature beneath the southeast flank of the volcano, in an area with no Holocene vents, is interpreted as tephra, flows, and sediments from the volcano deeply ponded on the downthrown side of the Gillem fault. A high-Q normal-velocity feature beneath the north rim of the summit caldera may be a small, possibly hot, subsolidus intrusion. A high-velocity low-Q region beneath the eastern caldera may be an area of boiling water between the magma chamber and the ponded east flank material. -from Authors
NASA Astrophysics Data System (ADS)
Jiménez Riobóo, Rafael J.; Prieto, Carlos; Cuscó, Ramón; Artús, Lluís; Boney, Chris; Bensaoula, Abdelhak; Yamaguchi, Tomohiro; Nanishi, Yasushi
2013-05-01
Temperature-dependent surface acoustic wave (SAW) propagation velocity and temperature coefficient of frequency (TCF) have been determined for the first time in InxGa1-xN alloys by means of high-resolution Brillouin spectroscopy (HRBS). HRBS offers an alternative way of determining TCF. The obtained TCF values present a non-linear behavior with the In concentration. TCF of pure InN (-13.75 ppm/K) is similar to those of AlN and GaN (-19 and -17.7 ppm/K, respectively). InxGa1-xN samples exhibit frequency values that are very stable against temperature changes, which makes InxGa1-xN a good candidate for current SAW-based technological applications.
Measurement of higher-order mode attenuation in single-mode fibers: effective cutoff wavelength.
van Leeuwen, K A; Nijnuis, H T
1984-06-01
A technique for the determination of the wavelength-dependent attenuation coefficient of the LP(11) mode in sing]emode fibers is presented. Knowledge of the magnitude of this coefficient is required, e.g., for the quantitative prediction of modal noise in an optical-fiber communication system. An effective cutoff wavelength of the LP(11) mode can be unambiguously defined as the wavelength at which the attenuation coefficient equals a specified value. PMID:19721561
Multiple resolution seismic attenuation imaging at Mt. Vesuvius
NASA Astrophysics Data System (ADS)
De Siena, Luca; Del Pezzo, Edoardo; Bianco, Francesca; Tramelli, Anna
2009-03-01
A three-dimensional S wave attenuation tomography of Mt. Vesuvius has been obtained with multiple measurements of coda-normalized S-wave spectra of local small magnitude earthquakes. We used 6609 waveforms, relative to 826 volcano-tectonic earthquakes, located close to the crater axis in a depth range between 1 and 4 km (below the sea level), recorded at seven 3-component digital seismic stations. We adopted a two-point ray-tracing; rays were traced in an high resolution 3-D velocity model. The spatial resolution achieved in the attenuation tomography is comparable with that of the velocity tomography (we resolve 300 m side cubic cells). We statistically tested that the results are almost independent from the radiation pattern. We also applied an improvement of the ordinary spectral-slope method to both P- and S-waves, assuming that the differences between the theoretical and the experimental high frequency spectral-slope are only due to the attenuation effects. Consequently we could check the coda-normalization method also comparing the S attenuation image with the P attenuation image. The images were obtained inverting the spectral data with a multiple resolution approach. Results have shown the general coincidence of low attenuation with high velocity zones. The joint interpretation of velocity and attenuation images allows us to interpret the low attenuation zone intruding toward the surface until a depth of 500 m below the sea level as related to the residual part of solidified magma from the last eruption. In the depth range between -700 and -2300 images are consistent with the presence of multiple acquifer layers. No evidence of magma patches greater than the minimum cell dimension (300 m) has been found. A shallow P wave attenuation anomaly (beneath the southern flank of the volcano) is consitent with the presence of gas saturated rocks. The zone characterized by the maximum seismic energy release cohincides with a high attenuation and low velocity volume, interpreted as a cracked medium.
Hart, A.; Hippel, G. M. von; Horgan, R. R.
2007-01-01
We construct the S-wave part of the electromagnetic vector annihilation current to O({alpha}{sub s}v{sup 2}) on the lattice for heavy quarks whose dynamics are described by the NRQCD action, and v is the nonrelativistic quark velocity inside the meson. The lattice vector current for QQ annihilation is expressed as a linear combination of lattice operators with quantum numbers L=0, J{sup P}=1{sup -}, and the coefficients are determined by matching this lattice current to the corresponding continuum current in QCD to O(v{sup 2}) at one-loop. The annihilation channel gives a complex amplitude and a proper choice for the contours of integration is needed; a simple Wick rotation is not possible. In this way, and with a careful choice of subtraction functions in the numerical integration, the Coulomb-exchange and infrared singularities appearing in the amplitudes are successfully treated. The matching coefficients are given as a function of the heavy quark mass Ma in lattice units. An automated vertex generation program written in Python is employed, allowing us to use a realistic NRQCD action and an improved gluon lattice action. A change in the definition of either action is easily accommodated in this procedure. The final result, when combined with lattice simulation results, describes the electromagnetic decays of heavy quarkonia, notably the {upsilon} meson.
Swell and the drag coefficient
NASA Astrophysics Data System (ADS)
Potter, Henry
2015-03-01
Simultaneous measurements of waves and turbulent fluxes were collected from a moored surface buoy in the Philippine Sea. Waves were partitioned into their wind sea and swell components, and the ratio of swell to wind sea energy was used to assign a swell index. The 10-m neutral drag coefficient was calculated using the eddy correlation method. Four hundred hours of data were processed in 30 minute runs for wind speeds 8.5 to 16.5 m s-1 when the peak wave direction was within 90° of the wind direction and included observations during mixed seas, swell dominant, and wind sea dominant conditions. The data were analyzed to explore the influence of swell on the drag coefficient. It was found that when compared to periods of equal wind speed, the drag coefficient was reduced up to 37 % when swell energy was twice that of the wind sea energy. It is believed that this reduction was due to a decrease in the turbulent flux around the swell frequency, suggesting that the swell diminishes the surface aerodynamic roughness.
Landing gear noise attenuation
NASA Technical Reports Server (NTRS)
Moe, Jeffrey W. (Inventor); Whitmire, Julia (Inventor); Kwan, Hwa-Wan (Inventor); Abeysinghe, Amal (Inventor)
2011-01-01
A landing gear noise attenuator mitigates noise generated by airframe deployable landing gear. The noise attenuator can have a first position when the landing gear is in its deployed or down position, and a second position when the landing gear is in its up or stowed position. The noise attenuator may be an inflatable fairing that does not compromise limited space constraints associated with landing gear retraction and stowage. A truck fairing mounted under a truck beam can have a compliant edge to allow for non-destructive impingement of a deflected fire during certain conditions.
Time domain attenuation estimation method from ultrasonic backscattered signals
Ghoshal, Goutam; Oelze, Michael L.
2012-01-01
Ultrasonic attenuation is important not only as a parameter for characterizing tissue but also for compensating other parameters that are used to classify tissues. Several techniques have been explored for estimating ultrasonic attenuation from backscattered signals. In the present study, a technique is developed to estimate the local ultrasonic attenuation coefficient by analyzing the time domain backscattered signal. The proposed method incorporates an objective function that combines the diffraction pattern of the source/receiver with the attenuation slope in an integral equation. The technique was assessed through simulations and validated through experiments with a tissue mimicking phantom and fresh rabbit liver samples. The attenuation values estimated using the proposed technique were compared with the attenuation estimated using insertion loss measurements. For a data block size of 15 pulse lengths axially and 15 beamwidths laterally, the mean attenuation estimates from the tissue mimicking phantoms were within 10% of the estimates using insertion loss measurements. With a data block size of 20 pulse lengths axially and 20 beamwidths laterally, the error in the attenuation values estimated from the liver samples were within 10% of the attenuation values estimated from the insertion loss measurements. PMID:22779499
Huntzicker, Steven; Nayak, Rohit; Doyley, Marvin M.
2014-01-01
Abstract. Quantitative sparse array vascular elastography visualizes the shear modulus distribution within vascular tissues, information that clinicans could use to reduce the number of strokes each year. However, the low transmit power sparse array (SA) imaging could hamper the clinical usefulness of the resulting elastograms. In this study, we evaluated the performance of modulus elastograms recovered from simulated and physical vessel phantoms with varying attenuation coefficients (0.6, 1.5, and 3.5??cm?1) and modulus contrasts (?12.04, ?6.02, and ?2.5??dB) using SA imaging relative to those obtained with conventional linear array (CLA) and plane-wave (PW) imaging techniques. Plaques were visible in all modulus elastograms, but those produced using SA and PW contained less artifacts. The modulus contrast-to-noise ratio decreased rapidly with increasing modulus contrast and attenuation coefficient, but more quickly when SA imaging was performed than for CLA or PW. The errors incurred varied from 10.9% to 24% (CLA), 1.8% to 12% (SA), and ?4% (PW). Modulus elastograms produced with SA and PW imagings were not significantly different (p>0.05). Despite the low transmit power, SA imaging can produce useful modulus elastograms in superficial organs, such as the carotid artery. PMID:26158040
Factor Scores, Structure Coefficients, and Communality Coefficients
ERIC Educational Resources Information Center
Goodwyn, Fara
2012-01-01
This paper presents heuristic explanations of factor scores, structure coefficients, and communality coefficients. Common misconceptions regarding these topics are clarified. In addition, (a) the regression (b) Bartlett, (c) Anderson-Rubin, and (d) Thompson methods for calculating factor scores are reviewed. Syntax necessary to execute all four…
Attenuation of millimeter wavelength radiation by gaseous water.
Hall, J T
1967-08-01
A theoretical computation and absorption by water vapor of radiation within the millimeter and submillimeter region of the electromagnetic spectrum permits the determination of attenuation coefficients for given vapor densities, pressures, and temperatures. The rigid asymmetrical top rotor approximation for all angular momentum quantum numbers J
The Physics Analysis of a Gas Attenuator with Argon as a Working Gas
Ryutov,, D.D.
2010-12-07
A gas attenuator is an important element of the LCLS facility. The attenuator must operate in a broad range of x-ray energies, provide attenuation coefficient between 1 and 10{sup 4} with the accuracy of 1% and, at the same time, be reliable and allow for many months of un-interrupted operation. S. Shen has recently carried out a detailed design study of the attenuator based on the use of nitrogen as a working gas. In this note we assess the features of the attenuator based on the use of argon. We concentrate on the physics issues, not the design features.
SEISMIC ATTENUATION FOR RESERVOIR CHARACTERIZATION
Joel Walls; M.T. Taner; Naum Derzhi; Gary Mavko; Jack Dvorkin
2003-12-01
We have developed and tested technology for a new type of direct hydrocarbon detection. The method uses inelastic rock properties to greatly enhance the sensitivity of surface seismic methods to the presence of oil and gas saturation. These methods include use of energy absorption, dispersion, and attenuation (Q) along with traditional seismic attributes like velocity, impedance, and AVO. Our approach is to combine three elements: (1) a synthesis of the latest rock physics understanding of how rock inelasticity is related to rock type, pore fluid types, and pore microstructure, (2) synthetic seismic modeling that will help identify the relative contributions of scattering and intrinsic inelasticity to apparent Q attributes, and (3) robust algorithms that extract relative wave attenuation attributes from seismic data. This project provides: (1) Additional petrophysical insight from acquired data; (2) Increased understanding of rock and fluid properties; (3) New techniques to measure reservoir properties that are not currently available; and (4) Provide tools to more accurately describe the reservoir and predict oil location and volumes. These methodologies will improve the industry's ability to predict and quantify oil and gas saturation distribution, and to apply this information through geologic models to enhance reservoir simulation. We have applied for two separate patents relating to work that was completed as part of this project.
Attenuation in Superconducting Rectangular Waveguides
NASA Astrophysics Data System (ADS)
Yeap, Kim Ho; Mei Teh, Joyce Shu; Nisar, Humaira; Yeong, Kee Choon; Hirasawa, Kazuhiro
2015-03-01
We present an accurate analysis on the attenuation of waves, propagating in rectangular waveguides with superconducting walls. The wavenumbers kx and ky in the x and y directions, respectively, are first obtained as roots of a set of transcendental equations developed by matching the tangential fields at the surface of the wall with the electrical properties of the wall material. The complex conductivity of the superconducting waveguide is obtained from the extended Mattis-Bardeen theory. The propagation constant kz is found by substituting the values of kx and ky into the dispersion relation. We have computed and compared the loss in the waveguides below and above the critical temperature. At frequencies above the cutoff frequency fc but below the gap frequency fg, the loss in the superconducting waveguide is significantly lower than that in a normal conducting waveguide. Above the gap frequency, however, the result indicates that the attenuation in the waveguide below the critical temperature is higher than that at room temperature. We attribute the higher loss as due to the higher surface resistance and field penetration for superconducting waveguides operating above the gap frequency.
Seismic viscoelastic attenuation Submitted to
Cormier, Vernon F.
Seismic viscoelastic attenuation Submitted to: Encyclopedia of Solid Earth Geophysics Harsh Gupta-3046 USA E-mail: vernon.cormier@uconn.edu Tel: 860-486-3547 Fax: 860-486-3346 #12;SEISMIC VISCOELASTIC ATTENUATION Synonyms Seismic intrinsic attenuation Definitions Linear viscoelastic attenuation. The loss
Orientation dependence of ultrasonic attenuation
NASA Astrophysics Data System (ADS)
Raju, K. M.; Kailash; Srivastava, R. K.
2010-01-01
An effort has been made for obtaining higher order elastic constants of MgO starting from basic parameters viz. nearest neighbor distance, hardness parameter and using Coulomb and Börn- Mayer potentials. These values are utilized to obtain Grüneisen parameters and non-linearity constants. Non-linearity constants ratio, ultrasonic velocity, ultrasonic attenuation due to phonon-phonon interaction (?/f2)p-p and thermo elastic loss (?/f2)th are calculated in a wide temperature range (100-1000 K) along < 100 > , < 110 > and < 111 > crystallographic directions of propagation for longitudinal and shear waves and compared with available theoretical and experimental results. It is concluded that the absorption is strongly dependent on the direction of polarization.
SEISMIC ATTENUATION FOR RESERVOIR CHARACTERIZATION
Joel Walls; M.T. Taner; Naum Derzhi; Gary Mavko; Jack Dvorkin
2002-10-01
RSI has access to two synthetic seismic programs: Osiris seismic modeling system provided by Odegaard (Osiris) and synthetic seismic program, developed by SRB, implementing the Kennett method for normal incidence. Achieving virtually identical synthetic seismic traces from these different programs serves as cross-validation for both. The subsequent experiments have been performed with the Kennett normal incidence code because: We have access to the source code, which allowed us to easily control computational parameters and integrate the synthetics computations with our graphical and I/O systems. This code allows to perform computations and displays on a PC in MatLab or Octave environment, which is faster and more convenient. The normal incidence model allows us to exclude from the synthetic traces some of the physical effects that take place in 3-D models (like inhomogeneous waves) but have no relevance to the topic of our investigation, which is attenuation effects on seismic reflection and transmission.
Attenuation of coda waves in northern Greece
P. M. Hatzidimitriou
1993-01-01
The single scattering model has been applied for the estimation of codaQ values for local earthquakes that occurred in northern Greece during the period 1983–1989 and recorded by the telemetered network of the Geophysical Laboratory of the University of Thessaloniki. CodaQ estimations were made for four frequency bands centered at 1.5 Hz, 3.0 Hz, 6.0 Hz and 12.0 Hz and
Attenuation of coda waves in northern Greece
P. M. Hatzidimitriou
1993-01-01
The single scattering model has been applied for the estimation of coda Q values for local earthquakes that occurred in northern Greece during the period 1983 1989 and recorded by the telemetered network of the Geophysical Laboratory of the University of Thessaloniki. Coda Q estimations were made for four frequency bands centered at 1.5 Hz, 3.0 Hz, 6.0 Hz and
Approximate reconstruction of attenuation map in SPECT imaging
Bronnikov, A.V. [Russian Academy of Sciences, Novosibirsk (Russian Federation). Inst. for Theoretical and Applied Mechanics] [Russian Academy of Sciences, Novosibirsk (Russian Federation). Inst. for Theoretical and Applied Mechanics
1995-10-01
The influence of linear attenuation presents certain difficulties for quantitative single-photon emission computed tomography (SPECT) in medical imaging. To apply an attenuation correction algorithm, one has first to estimate the attenuation map from some additional measurements or by the use of SPECT data. The determination of the attenuation map from SPECT-type data may also be considered as a special problem of nondestructive evaluation of materials. A new technique for obtaining the attenuation map from SPECT data is proposed. Unlike other methods, the approach suggested demands no a priori knowledge of the problem. The method has been derived on the basis of the approximate linear relation between SPECT data and the attenuation map. The approach permits local changes of the attenuation coefficient to be reconstructed rather than its actual value. In this way, such details of the attenuation map as spots, curves and edges can be localized. Limitations of application of the suggested technique to real data are considered. Results of numerical evaluation and real data processing are presented.
Ikenaga, Yuki; Nishi, Shohei; Komagata, Yuka; Saito, Masashi; Lagrée, Pierre-Yves; Asada, Takaaki; Matsukawa, Mami
2013-11-01
A pulse wave is the displacement wave which arises because of ejection of blood from the heart and reflection at vascular bed and distal point. The investigation of pressure waves leads to understanding the propagation characteristics of a pulse wave. To investigate the pulse wave behavior, an experimental study was performed using an artificial polymer tube and viscous liquid. A polyurethane tube and glycerin solution were used to simulate a blood vessel and blood, respectively. In the case of the 40 wt% glycerin solution, which corresponds to the viscosity of ordinary blood, the attenuation coefficient of a pressure wave in the tube decreased from 4.3 to 1.6 dB/m because of the tube stiffness (Young's modulus: 60 to 200 kPa). When the viscosity of liquid increased from approximately 4 to 10 mPa·s (the range of human blood viscosity) in the stiff tube, the attenuation coefficient of the pressure wave changed from 1.6 to 3.2 dB/m. The hardening of the blood vessel caused by aging and the increase of blood viscosity caused by illness possibly have opposite effects on the intravascular pressure wave. The effect of the viscosity of a liquid on the amplitude of a pressure wave was then considered using a phantom simulating human blood vessels. As a result, in the typical range of blood viscosity, the amplitude ratio of the waves obtained by the experiments with water and glycerin solution became 1:0.83. In comparison with clinical data, this value is much smaller than that seen from blood vessel hardening. Thus, it can be concluded that the blood viscosity seldom affects the attenuation of a pulse wave. PMID:24158293
Mean drift velocity in the Stokes interfacial edge wave
NASA Astrophysics Data System (ADS)
Weber, Jan Erik H.; StøYlen, Eivind
2011-04-01
The Stokes interfacial edge wave in a viscous rotating two-layer system is studied theoretically. The mean wave-induced Lagrangian drift velocity is obtained from the vertically integrated Eulerian equations of momentum and mass, correct to second order in wave steepness. The analysis is valid for shallow-water waves in the case when the upper layer is much thicker than the lower layer. In the lower layer the effect of viscosity is confined to a frictional boundary layer at the bottom. The waves are trapped by the bottom slope and can propagate in either direction along the bottom contours (in the y direction). Assuming that the waves attenuate in space as they propagate, this yields a Stokes drift velocity and a mean energy density E that decay exponentially in y. In this problem -?E/?y is the relevant radiation stress forcing in the wave propagation direction. It is explained why this differs from the radiation-stress forcing of -??E/?y for plane waves in an unbounded nonrotating shallow ocean. The bottom stress acting on the mean Eulerian wave-induced flow is modeled by a turbulent friction coefficient. The results show that the maximum mean Eulerian drift current is considerably larger than the maximum Stokes drift velocity. Since the Eulerian current becomes negative at larger seaward distances, the total mean Lagrangian drift current is confined to a rather narrow wedge in the lower layer.
Radiofrequency attenuator and method
Warner, Benjamin P. (Los Alamos, NM); McCleskey, T. Mark (Los Alamos, NM); Burrell, Anthony K. (Los Alamos, NM); Agrawal, Anoop (Tucson, AZ); Hall, Simon B. (Palmerston North, NZ)
2009-11-10
Radiofrequency attenuator and method. The attenuator includes a pair of transparent windows. A chamber between the windows is filled with molten salt. Preferred molten salts include quarternary ammonium cations and fluorine-containing anions such as tetrafluoroborate (BF.sub.4.sup.-), hexafluorophosphate (PF.sub.6.sup.-), hexafluoroarsenate (AsF.sub.6.sup.-), trifluoromethylsulfonate (CF.sub.3SO.sub.3.sup.-), bis(trifluoromethylsulfonyl)imide ((CF.sub.3SO.sub.2).sub.2N.sup.-), bis(perfluoroethylsulfonyl)imide ((CF.sub.3CF.sub.2SO.sub.2).sub.2N.sup.-) and tris(trifluoromethylsulfonyl)methide ((CF.sub.3SO.sub.2).sub.3 C.sup.-). Radicals or radical cations may be added to or electrochemically generated in the molten salt to enhance the RF attenuation.
Radiofrequency attenuator and method
Warner, Benjamin P. (Los Alamos, NM); McCleskey, T. Mark (Los Alamos, NM); Burrell, Anthony K. (Los Alamos, NM); Agrawal, Anoop (Tucson, AZ); Hall, Simon B. (Palmerston North, NZ)
2009-01-20
Radiofrequency attenuator and method. The attenuator includes a pair of transparent windows. A chamber between the windows is filled with molten salt. Preferred molten salts include quarternary ammonium cations and fluorine-containing anions such as tetrafluoroborate (BF.sub.4.sup.-), hexafluorophosphate (PF.sub.6.sup.-), hexafluoroarsenate (AsF.sub.6.sup.-), trifluoromethylsulfonate (CF.sub.3SO.sub.3.sup.-), bis(trifluoromethylsulfonyl)imide ((CF.sub.3SO.sub.2).sub.2N.sup.-), bis(perfluoroethylsulfonyl)imide ((CF.sub.3CF.sub.2SO.sub.2).sub.2N.sup.-) and tris(trifluoromethylsulfonyl)methide ((CF.sub.3SO.sub.2).sub.3C.sup.-). Radicals or radical cations may be added to or electrochemically generated in the molten salt to enhance the RF attenuation.
Local threshold for segmented attenuation correction of PET imaging of the thorax
M. Xu; W. K. Luk; P. D. Cutler; W. M. Digby
1994-01-01
A local threshold for segmented attenuation correction technique has been developed for positron emission tomography using short (2-3 minutes) post-injection transmission scans. The technique implements an optimal threshold method on localized histograms to get pseudo-anatomic segmentation on transmission images. Theoretical values of attenuation coefficients are assigned to corresponding anatomic regions. Emission images are reconstructed using attenuation correction factors computed by
The distribution of seismic velocities and attenuation in the earth. Ph.D. Thesis
NASA Technical Reports Server (NTRS)
Hart, R. S.
1977-01-01
Estimates of the radial distribution of seismic velocities and density and of seismic attenuation within the earth are obtained through inversion of body wave, surface wave, and normal mode data. The effect of attenuation related dispersion on gross earth structure, and on the reliability of eigenperiod identifications is discussed. The travel time baseline discrepancies between body waves and free oscillation models are examined and largely resolved.
Double peak attenuation method for estimating organ location.
Nosil, J; Sethi, V; Bland, J; Kloiber, R
1987-11-01
Radioactive sources of finite volume containing 133Xe, 67Ga, 99Tcm and 111In were used to measure the attenuation coefficient, mu, in water at six different energies in the range 80-296 keV using an Anger camera. The experimental accuracy was about 7% for the volume range from 40-225 ml when corrections were made for background. The same radioactive sources were used to measure zero attenuation count rates per unit of activity. The theoretical basis was also derived, which confirms our experimental findings, i.e. the measurement of the thickness of the attenuator using a dual energy method. The determination of the linear attenuation coefficient in the broad-beam geometry situation is possible by accounting for cross-talk, scatter and out-of-target activity. By correcting for the broad-beam geometry, agreement with the narrow-beam geometry linear attenuation coefficient was obtained. We also demonstrate the use of the technique to accurately determine the depth of the organ using two separate energies. This methodology is independent of the organ volume for determination of the depth. It is hoped that our findings will provide a better understanding of the photon interactions when extended sources are used. Such a knowledge can also be applied to organ volume measurements. PMID:3423113
A global tomographic model of shear attenuation in the upper mantle
NASA Astrophysics Data System (ADS)
Romanowicz, B.
1995-07-01
We present a global three-dimensional model of shear attenuation in the upper mantle, based on the measurement of amplitudes of low-frequency (100-300s) Rayleigh waves observed at stations of the Geoscope and Iris networks. Attenuation coefficients are measured on R1 and R2 paths using a method which minimizes the effects of focussing due to propagation in a three-dimensional elastic Earth. Through a series of tests which, in particular, involve the computation of synthetic models of attenuation and focussing, we demonstrate that long wavelength lateral variations in attenuation in the first 400-500 km of the mantle can indeed be resolved. The model is obtained in a two-step procedure. The first step consists in the computation of maps of Rayleigh wave attenuation at different periods, using an inversion method without a priori parametrisation, which involves the introduction of a correlation length, chosen here at 3000 km to optimize the trade-off between resolution and variance in the model. In the second step, after corrections for shallow structure, an inversion with depth is performed, assuming lateral heterogeneity is confined to depths between 80 and 650 km. The resulting model presents lateral variations in Q? that are correlated with tectonic features, in particular ridges and shields in the first 250 km of the upper mantle. Below that depth the pattern shifts and becomes correlated with the hotspot distribution, particularly so if the buoyancy strength of hotspots is taken into account. Two major low-velocity zones appear to be located in the central pacific and beneath northern Africa, in the depth range 300-500 km. This pattern seems to continue at greater depth, but resolution becomes insufficient below 500 km to draw definitive conclusions. The smooth lateral variations retrieved are on the order of ±50% down to 400 km. We propose an interpretation in terms of plume/lithosphere/ridge interaction in the upper mantle, arguing for deflection of the bulk of hot upwelling material from plumes towards ridges, which may be occurring between 200 and 300 km depth.
X-Ray Attenuation and Absorption for Materials of Dosimetric Interest
National Institute of Standards and Technology Data Gateway
SRD 126 X-Ray Attenuation and Absorption for Materials of Dosimetric Interest (Web, free access) Tables and graphs of the photon mass attenuation coefficient and the mass energy-absorption coefficient 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.
Numerical Modeling of Radiant Heat Attenuation Through Water Mist
E. P. KERAMIDA; A. N. KARAYANNIS; A. G. BOUDOUVIS; N. C. MARKATOS
2000-01-01
This paper describes the development of a two-phase radiation model for the prediction of radiant heat attenuation in fires by water mist. It has been especially developed for incorporation in comprehensive field models of fire extinguishment by a water mist. The model predicts the opacity of the mist by summing over the absorption and scattering coefficients for each particle size
Tritium Attenuation by Distillation
Wittman, N.E.
2001-07-31
The objective of this study was to determine how a 100 Area distillation system could be used to reduce to a satisfactory low value the tritium content of the dilute moderator produced in the 100 Area stills, and whether such a tritium attenuator would have sufficient capacity to process all this material before it is sent to the 400 Area for reprocessing.
Attenuation Measurements of Cell Pellets Using Through Transmission
NASA Astrophysics Data System (ADS)
Vadas, Justin; Greene, Claudia; Grygotis, Emma; Kuhn, Stephen; Mahlalela, Sanele; Newland, Tinisha; Ovutmen, Idil; Herd, Maria-Teresa
2011-10-01
A better understanding of differences in ultrasound tissue characteristics (such as speed of sound, attenuation, and backscatter coefficients) of benign compared to malignant cells could lead to improved cancer detection and diagnosis. A narrow band technique for measuring ultrasonic speed of sound and attenuation of small biological materials was developed and tested. Several mechanical improvements were made to the system to drastically improve alignment, allowing for accurate measurements of small cell pellets. Narrow band attenuation measurements were made first with tissue-mimicking phantoms and then with three different types of cell pellets: Chinese hamster ovary cells, healthy human prostate cells, and cancerous human prostate cells. Attenuation and speed of sound results for all three cell types, as well as the culture medium and tissue mimicking phantoms, are presented for a frequency range of 5 to 25 MHz.
Crustal attenuation characteristics in western Turkey
NASA Astrophysics Data System (ADS)
Kurtulmu?, Tevfik Özgür; Akyol, Nihal
2013-11-01
We analysed 1764 records produced by 322 micro- and moderate-size local earthquakes in western Turkey to estimate crustal attenuation characteristics in the frequency range of 1.0 ? f ? 10 Hz. In the first step, we obtained non-parametric attenuation functions and they show that seismic recordings of transverse and radial S waves exhibit different characteristics at short and long hypocentral distances. Applying a two-step inversion, we parametrized Q( f ) and geometrical spreading exponent b( f ) for the entire distance range between 10 and 200 km and then we estimated separately Q and b values for short (10-70 km) and large (120-200 km) distance ranges. We could not observe significant frequency dependencies of b for short distance range, whereas the significant frequency dependence of b was observed for large distances. Low Q0 values (˜60) with strong frequency dependence of Q (˜1.4) for short distances suggest that scattering might be an important factor contributing to the attenuation of body waves in the region, which could be associated to a high degree of fracturing, fluid filled cracks, young volcanism and geothermal activity in the crust. Weak Q frequency dependence and higher Q0 values for large distances manifest more homogenous medium because of increasing pressure and enhanced healing of cracks with increasing temperature and depth. Q anisotropy was also observed for large hypocentral distance ranges.
Observations of acoustic surface waves in outdoor sound propagation
NASA Astrophysics Data System (ADS)
Albert, Donald G.
2003-05-01
Acoustic surface waves have been detected propagating outdoors under natural conditions. Two critical experimental conditions were employed to ensure the conclusive detection of these waves. First, acoustic pulses rather than a continuous wave source allowed an examination of the waveform shape and avoided the masking of wave arrivals. Second, a snow cover provided favorable ground impedance conditions for surface waves to exist. The acoustic pulses were generated by blank pistol shots fired 1 m above the snow. The resultant waveforms were measured using a vertical array of six microphones located 60 m away from the source at heights between 0.1 and 4.75 m. A strong, low frequency ``tail'' following the initial arrival was recorded near the snow surface. This tail, and its exponential decay with height (z) above the surface (~e-?z), are diagnostic features of surface waves. The measured attenuation coefficient ? was 0.28 m-1. The identification of the surface wave is confirmed by comparing the measured waveforms with waveforms predicted by the theoretical evaluation of the explicit surface wave pole term using residue theory.
NASA Technical Reports Server (NTRS)
Atlas, David; Rosenfeld, Daniel; Wolff, David B.
1993-01-01
The probability matching method (PMM) is used as a basis for estimating attenuation in tropical rains near Darwin, Australia. PMM provides a climatological relationship between measured radar reflectivity and rain rate, which includes the effects of rain and cloud attenuation. When the radar sample is representative, PMM estimates the rainfall without bias. When the data are stratified for greater than average rates, the method no longer compensates for the higher attenuation and the radar rainfall estimates are biased low. The uncompensated attenuation is used to estimate the climatological attenuation coefficient. The two-way attenuation coefficient was found to be 0.0085 dB/km ( mm/h) exp -1.08 for the tropical rains and associated clouds in Darwin for the first two months of the year for horizontally polarized radiation at 5.63 GHz. This unusually large value is discussed. The risks of making real-time corrections for attenuation are also treated.
Chassignole, B; Duwig, V; Ploix, M-A; Guy, P; El Guerjouma, R
2009-12-01
Multipass welds made in austenitic stainless steel, in the primary circuit of nuclear power plants with pressurized water reactors, are characterized by an anisotropic and heterogeneous structure that disturbs the ultrasonic propagation and makes ultrasonic non-destructive testing difficult. The ATHENA 2D finite element simulation code was developed to help understand the various physical phenomena at play. In this paper, we shall describe the attenuation model implemented in this code to give an account of wave scattering phenomenon through polycrystalline materials. This model is in particular based on the optimization of two tensors that characterize this material on the basis of experimental values of ultrasonic velocities attenuation coefficients. Three experimental configurations, two of which are representative of the industrial welds assessment case, are studied in view of validating the model through comparison with the simulation results. We shall thus provide a quantitative proof that taking into account the attenuation in the ATHENA code dramatically improves the results in terms of the amplitude of the echoes. The association of the code and detailed characterization of a weld's structure constitutes a remarkable breakthrough in the interpretation of the ultrasonic testing on this type of component. PMID:19450861
Attenuation of multiple-scattered sound
NASA Astrophysics Data System (ADS)
Sigalas, M. M.; Economou, E. N.
1996-11-01
We study acoustic waves propagating in two-dimensional (2D) systems consisting of steel cylinders surrounded by air. We use the plane-wave method in order to get the band structure of waves propagating in an infinite periodic system. In addition, we employed, for the first time for acoustic waves, the transfer matrix method in order to find the transmission coefficient of waves propagating along a system with a finite thickness. Both methods are in good agreement with each other and their results agree with recent measurements in a similar system (R. Martinez-Sala et al., Nature, 378 (1995) 241). We also find the optimum conditions for the appearance of spectral gaps.
Leaky surface acoustic waves in Z-LiNbO{sub 3} substrates with epitaxial AIN overlays
Bu, G.; Ciplys, D.; Shur, M.S.; Namkoong, G.; Doolittle, W.A.; Hunt, W.D. [Department of Electrical, Computer, and Systems Engineering, Rensselaer Polytechnic Institute, 110 8th Street, Troy, New York 12180-3590 (United States); Georgia Institute of Technology, School of Electrical and Computer Engineering, Microelectronic Research Center, 791 Atlantic Drive, Atlanta, Georgia 30332-0269 (United States)
2004-10-11
The properties of leaky surface acoustic waves (LSAW) in MBE grown AIN layer on Z-cut LiNbO{sub 3} structures have been studied by numerical simulation and experimental measurements and compared with those of Rayleigh waves in the same structure. In the range of AIN layer thicknesses studied (0
SIMULTANEOUS BACKSCATTER AND ATTENUATION ESTIMATION USING A LEAST SQUARES METHOD WITH CONSTRAINTS
Nam, Kibo; Zagzebski, James A.; Hall, Timothy J.
2011-01-01
Backscatter and attenuation variations are essential contrast mechanisms in ultrasound B-mode imaging. Emerging Quantitative Ultrasound methods extract and display absolute values of these tissue properties. However, in clinical applications, backscatter and attenuation parameters sometimes are not easily measured because of tissues inhomogeneities above the region of interest. We describe a least squares method (LSM) that fits the echo signal power spectra from a region of interest (ROI) to a 3-parameter tissue model that simultaneously yields estimates of attenuation losses and backscatter coefficients. To test the method, tissue-mimicking phantoms with backscatter and attenuation contrast as well as uniform phantoms were scanned with linear array transducers on a Siemens S2000. Attenuation and backscatter coefficients estimated by the LSM were compared with those derived using a reference phantom method (Yao et al. 1990). Results show that the LSM yields effective attenuation coefficients for uniform phantoms comparable to values derived using the reference phantom method. For layered phantoms exhibiting non-uniform backscatter, the LSM resulted in smaller attenuation estimation errors than the reference phantom method. Backscatter coefficients derived using the LSM were in excellent agreement with values obtained from laboratory measurements on test samples and with theory. The LSM is more immune to depth-dependent backscatter changes than commonly used reference phantom methods. PMID:21963038
Nonlinear frequency-dependent attenuation in sandy sediments.
Holmes, J D; Carey, W M; Dediu, S M; Siegmann, W L
2007-05-01
This paper summarizes evidence of a nonlinear frequency dependence of attenuation for compressional waves in shallow-water waveguides with sandy sediment bottoms. Sediment attenuation is found consistent with alpha(f) = alpha(f(o)) x (f/f(o))n, n approximately 1.8 +/- 0.2 at frequencies less than 1 kHz in agreement with the theoretical expectation, (n = 2), of Biot [J. Acoust. Soc. Am. 28(2), 168-178, 1956]. For frequencies less than 10 kHz, the sediment layers, within meters of the water-sediment interface, appear to play a role in the attenuation that strongly depends on the power law. The accurate calculation of sound transmission in a shallow-water waveguide requires the depth-dependent sound speed, density, and frequency-dependent attenuation. PMID:17550206
Differences in attenuation among the stable continental regions
Bakun, W.H.; McGarr, A.
2002-01-01
There are systematic differences in the attenuation of damaging earthquake ground motions between different stable continental regions (SCRs). Seismic intensity and weak-motion data show that the attenuation in seismic waves for eastern North America (ENA) is less than for India, Africa, Australia, and northwest Europe. If ENA ground-motion attenuation relations are used in seismic hazard models for other SCRs, as is commonly done, then the estimated ground motions and resulting hazard may be too large. If an attenuation model that averages observations from ENA and the other SCRs is used to estimate the magnitudes of large historical earthquakes in ENA, as is the case for recent estimates of M for the 1811-1812 New Madrid, Missouri and the 1886 Charleston, South Carolina events, then the magnitude estimates for these events will be too large, as will be the resulting hazard.
AllamehZadeh, Mostafa, E-mail: dibaparima@yahoo.com [International Institute of Earthquake Engineering and Seismology (Iran, Islamic Republic of)
2011-12-15
A Quadratic Neural Networks (QNNs) model has been developed for identifying seismic source classification problem at regional distances using ARMA coefficients determination by Artificial Neural Networks (ANNs). We have devised a supervised neural system to discriminate between earthquakes and chemical explosions with filter coefficients obtained by windowed P-wave phase spectra (15 s). First, we preprocess the recording's signals to cancel out instrumental and attenuation site effects and obtain a compact representation of seismic records. Second, we use a QNNs system to obtain ARMA coefficients for feature extraction in the discrimination problem. The derived coefficients are then applied to the neural system to train and classification. In this study, we explore the possibility of using single station three-component (3C) covariance matrix traces from a priori-known explosion sites (learning) for automatically recognizing subsequent explosions from the same site. The results have shown that this feature extraction gives the best classifier for seismic signals and performs significantly better than other classification methods. The events have been tested, which include 36 chemical explosions at the Semipalatinsk test site in Kazakhstan and 61 earthquakes (mb = 5.0-6.5) recorded by the Iranian National Seismic Network (INSN). The 100% correct decisions were obtained between site explosions and some of non-site events. The above approach to event discrimination is very flexible as we can combine several 3C stations.
Intensity attenuation in the Pannonian Basin
NASA Astrophysics Data System (ADS)
Gy?ri, Erzsébet; Gráczer, Zoltán; Szanyi, Gyöngyvér
2015-04-01
Ground motion prediction equations play a key role in seismic hazard assessment. Earthquake hazard has to be expressed in macroseismic intensities in case of seismic risk estimations where a direct relation to the damage associated with ground shaking is needed. It can be also necessary for shake map generation where the map is used for prompt notification to the public, disaster management officers and insurance companies. Although only few instrumental strong motion data are recorded in the Pannonian Basin, there are numerous historical reports of past earthquakes since the 1763 Komárom earthquake. Knowing the intensity attenuation and comparing them with relations of other areas - where instrumental strong motion data also exist - can help us to choose from the existing instrumental ground motion prediction equations. The aim of this work is to determine an intensity attenuation formula for the inner part of the Pannonian Basin, which can be further used to find an adaptable ground motion prediction equation for the area. The crust below the Pannonian Basin is thin and warm and it is overlain by thick sediments. Thus the attenuation of seismic waves here is different from the attenuation in the Alp-Carpathian mountain belt. Therefore we have collected intensity data only from the inner part of the Pannonian Basin and defined the boundaries of the studied area by the crust thickness of 30 km (Windhoffer et al., 2005). 90 earthquakes from 1763 until 2014 have sufficient number of macroseismic data. Magnitude of the events varies from 3.0 to 6.6. We have used individual intensity points to eliminate the subjectivity of drawing isoseismals, the number of available intensity data is more than 3000. Careful quality control has been made on the dataset. The different types of magnitudes of the used earthquake catalogue have been converted to local and momentum magnitudes using relations determined for the Pannonian Basin. We applied the attenuation formula by Sorensen et al. (2009) using a least-squares regression method. This expression is comparable with the common type of strong-motion attenuation equations (e.g., Joyner and Boore, 1993). Joyner, W. B. and Boore, D. M. (1993). Methods for regression analysis of strong-motion data. BSSA, 83(2), 469-487. Sørensen, M. B., Stromeyer, D., Grünthal, G. (2009). Attenuation of macroseismic intensity: a new relation for the Marmara Sea region, northwest Turkey. BSSA, 99(2A), 538-553. Windhoffer, G., Dombrádi, E., Horváth, F., Székely, B., Bada, G., Szafián, P., Dövényi, P., Tóth, L., Grenerczy, Gy. and G. Timár (2005) Geodynamic Atlas of the Pannonian Basin and the Surrounding Orogens. 7th Workshop on Alpine Geological Studies, Abstract Book, p. 109.
Multiple resolution seismic attenuation imaging at Mt. Vesuvius
Luca De Siena; Edoardo Del Pezzo; Francesca Bianco; Anna Tramelli
2009-01-01
A three-dimensional S wave attenuation tomography of Mt. Vesuvius has been obtained with multiple measurements of coda-normalized S-wave spectra of local small magnitude earthquakes. We used 6609 waveforms, relative to 826 volcano-tectonic earthquakes, located close to the crater axis in a depth range between 1 and 4km (below the sea level), recorded at seven 3-component digital seismic stations. We adopted
Multiple resolution seismic attenuation imaging at Mt. Vesuvius
Luca de Siena; Edoardo Del Pezzo; Francesca Bianco; Anna Tramelli
2009-01-01
A three-dimensional S wave attenuation tomography of Mt. Vesuvius has been obtained with multiple measurements of coda-normalized S-wave spectra of local small magnitude earthquakes. We used 6609 waveforms, relative to 826 volcano-tectonic earthquakes, located close to the crater axis in a depth range between 1 and 4 km (below the sea level), recorded at seven 3-component digital seismic stations. We
Seismic-frequency attenuation and moduli estimates using a fiber-optic strainmeter Ludmila Adam 1
Seismic-frequency attenuation and moduli estimates using a fiber-optic strainmeter Ludmila Adam 1 Summary We have developed a fiber-optic strainmeter to estimate velocities and attenuation at seismic properties such as broadband compressional and shear wave velocities, elastic moduli and seismic anisotropy
Lihua Li; Stephen M. Sekelsky; Steven C. Reising; Calvin T. Swift; Stephen L. Durden; Gregory A. Sadowy; Steven J. Dinardo; Fuk K. Li; Arlie Huffman; Graeme Stephens; David M. Babb; Hans W. Rosenberger
2001-01-01
Cloud measurements at millimeter-wave frequencies are affected by attenuation due to atmospheric gases, clouds, and precipitation. Estimation of the true equivalent radar reflectivity, Ze, is complicated because extinction mechanisms are not well characterized at these short wavelengths. This paper discusses cloud radar calibration and intercomparison of airborne and ground-based radar measurements and presents a unique algorithm for attenuation retrieval. This
Creating materials with a desired refraction coefficient
A. G. Ramm
2009-09-02
A method is given for creating material with a desired refraction coefficient. The method consists of embedding into a material with known refraction coefficient many small particles of size $a$. The number of particles per unit volume around any point is prescribed, the distance between neighboring particles is $O(a^{\\frac{2-\\kappa}{3}})$ as $a\\to 0$, $0<\\kappa<1$ is a fixed parameter. The total number of the embedded particle is $O(a^{\\kappa-2})$. The physical properties of the particles are described by the boundary impedance $\\zeta_m$ of the $m-th$ particle, $\\zeta_m=O(a^{-\\kappa})$ as $a\\to 0$. The refraction coefficient is the coefficient $n^2(x)$ in the wave equation $[\
Gamma and neutron attenuation properties of barite-cement mixture
NASA Astrophysics Data System (ADS)
Picha, R.; Channuie, J.; Khaweerat, S.; Liamsuwan, T.; Promping, J.; Ratanatongchai, W.; Silva, K.; Wonglee, S.
2015-05-01
For the neutron radiography facility renovation plan at Thai Research Reactor, mixed barite-concrete blocks of different compositions were tested for their photon and neutron radiation attenuation properties. 60Co and 137Cs isotopes were used as the gamma sources; 241Am-Be was used as the neutron source. For detection, a scintillation counter and a BF3 tube were used. The intensities at various energies were measured and attenuation coefficients were calculated. Samples of barite mixture were analyzed with X-ray. The results involving the effects of barite are reported and discussed.
Anderson, Mary Elizabeth
2011-10-21
Wave attenuation by vegetation is a highly dynamic process and its quantification is important for accurately understanding and predicting coastal hydrodynamics. However, the influence of vegetation on wave dissipation is not yet fully established...
Scattering versus intrinsic attenuation in periodically layered media
Alexey Stovas; Yuriy Roganov
2010-01-01
The propagation of acoustic waves in a layered medium results in the energy loss due to scattering effect. The intrinsic attenuation is an additional effect which plays a very important role in seismic data inversion and reservoir characterization. In this paper we provide the theoretical and numerical study to compare both effects for a periodically layered medium. We also investigate
A ?nite element method to model attenuation and dispersion effects ...
Patricio
A fast P—wave travelling in an heterogeneous ?uid~saturated porous material induces ?uid-pressure gradients in the ... attenuation and velocity dispersion effects at seismic frequencies. ... papermill and a fertilizer plant. ... In {2.l)-(2.2) pi,- and ,0; are the mass densities of the solid grains and the saturating ?uid and p'" =
Influence of modal attenuation on shallow water propagation
NASA Astrophysics Data System (ADS)
Saintval, Wendy
2008-12-01
A recent simplification of Biot theory is used to illustrate relationships between the intrinsic sediment attenuation, the attenuation of individual modes (as expressed by the modal attenuation coefficients or MACs), and the energy loss of the total field. The simplest two-layer, isospeed waveguides yield MACs that decrease from f-2 to f-1 as frequency f becomes large. A heuristic modification of the environment suggests how a change in the magnitude and frequency behavior of the MACs may arise. We demonstrate how the MACs increase with the incorporation of a fluid-saturated porous layer in the waveguide by using a convenient parameterization and numerical results. The frequency power-law behavior observed increases from f0.7 to f1.7 as the thickness of this layer increases from 2% to 15% of the water depth. Numerical calculations for more realistic waveguides use sandy bottom sediments and isospeed, linear, and piecewise linear water depth profiles. These are environmental simplifications that preserve key features of waveguides from experiments near the New Jersey continental shelf. Principal characteristics of the calculated MACs at frequencies up to 2 kHz include: increased magnitude in the presence of near-interface gradients, reordering of least-attenuated modes for downward refracting water sound speed profiles, and variations of frequency behavior from f-1 to f1. We also demonstrate the sensitivity of the MACs to experimentally-determined upward, isospeed, and downward-refracting sound speed profiles in a shallow water environment with sandy, depositional layers located in the Gulf of Mexico. A comparison of these results with previous numerical studies shows good agreement with water sound speed profiles for nearly isospeed and weakly downward refracting cases. Water sound speed has a significant influence on modal attenuation and, consequently, on the effective attenuation coefficient, which estimates the average transmission decrease with range. The effective attenuation coefficients behave with frequency from f0.0 for isospeed to f0.9 for strongly downward refracting water. Analysis demonstrates how a band of least-attenuated modes contribute to this rate of decrease with range. For a strongly downward refracting linear water sound speed profile, very good approximations of effective attenuation coefficients are shown. At 500, 1000, 1500, and 2000 Hz, the least-attenuated modes, which contribute 90% or more of the effective attenuation coefficient, are modes 1--17, 1--26, 5--21, and 13--31. At large frequencies a parallel trend is apparent between the envelope of the family of MAC curves and EAC. These new results may help interpretation and prediction of data when seasonal changes occur and provide insights into the influence of depth structures and frequency-dependent characteristics of the upper sediment layer on field attenuation.
Computational Study of Thrust Generation from Laser-Driven Blast Wave
Ohnishi, Naofumi; Ogino, Yousuke
2008-04-28
We have performed axisymmetric simulations in order to investigate the thrust generation resulting from the interference between the projectile and the blast wave produced by a pulsed laser. The results obtained by our numerical code well agree for the pressure history and the momentum coupling coefficient with the experimental data. In such analysis, it is found that the approximate impulse estimated only by the pressure history at the projectile base is difficult to predict the actual one. Since the shock wave rapidly attenuates in low fill pressure, and the interaction with the projectile almost finishes in the shroud, a high momentum coupling coefficient can be achieved unlike the case of high fill pressure in which the projectile experiences the subsequent negative thrust.
Radius of B-8 halo from the asymptotic normalization coefficient
Carstoiu, F.; Trache, L.; Gagliardi, Carl A.; Tribble, Robert E.; Mukhamedzhanov, AM.
2001-01-01
The experimental asymptotic normalization coefficient determined from peripheral transfer reactions is used to obtain the root-mean-square radius of the wave function for the loosely bound proton in SB. It is shown that the asymptotic region...
Correlations of shock Mach number attenuation in small size diameter tubes
NASA Astrophysics Data System (ADS)
Zeitoun, David E.
2015-01-01
From previous works on the shock Mach number attenuation along small size diameter tubes, two different power-law correlations in laminar and turbulent flows in shock tube are proposed in this paper for describing this attenuation and the shock wave behavior. These correlations are based on a local scaling ratio built from driven gas conditions, hydraulic diameter tube, and shock wave propagation distance. A comparison to numerical and experimental existing data is presented and discussed.
SAS: low frequency Seismic Attenuation System
NASA Astrophysics Data System (ADS)
Takamori, Akiteru
2001-10-01
Currently there are various R&D programs available for the next generation of the interferometric gravitational wave detectors. To achieve the goal of a superior sensitivity desired for refined astronomical observations by these detectors, much sophisticated technologies and detail are required for the advanced laser interferometer components. One of the major obstacles for such a ground-based interferometer is the seismic disturbance. In order to obtain a wide observation band around low frequencies, the seismic noise at the level of optics needs to be attenuated. The SAS (Seismic Attenuation System) has been developed with an international collaboration between TAMA, LIGO and some European institutes, with the main objective of achieving sufficient low frequency seismic attenuation. The system, not only suppresses the seismic noise well below the other noise levels present at very low frequencies around few Hz, but it also in turn reduces the residual motion of the optics to well below one micron, which is necessary for a stable operation of the interferometer. The SAS, basically a passive mechanical filter, constitutes of ultra low frequency mechanical isolators, an inverted pendulum and GAS (Geometric Anti-Sprig) filters. Additionally, the SAS is implemented with an active damping on the mechanical filters. Here we discuss the basics of passive isolation and main features employed by the SAS.
Gullberg, Grant T.
1980-03-01
The properties of the attenuated Radon transform and its application to single-photon emission computed tomography (ECT) are analyzed in detail. In nuclear medicine and biological research, the objective of ECT is to describe quantitatively the position and strengths of internal sources of injected radiopharmaceuticals and radionuclides where the attenuation between the sources and detector is unknown. The problem is mathematically and practically quite different from well-known methods in transmission computed tomography (TCT) where only the attenuation is unknown. A mathematical structure using function theory and the theory of linear operators on Hilbert spaces is developed to better understand the spectral properties of the attenuated Radon transform. The continuous attenuated Radon transform is reduced to a matrix operator for discrete angular and lateral sampling, and the reconstruction problem reduces to a system of linear equations. For variable attenuation coefficients frequently found in imaging internal organs, the numerical methods developed in this paper involve iterative techniques of performing the generalized inverse. Its application to nuclear medicine is demonstrated by reconstructions of transverse sections of the brain, heart, and liver.
Electromagnetic waves in the atmosphere and space
A. V. Sokolov; A. A. Semenov
1986-01-01
The papers presented in this volume provide an overview of recent research related to the propagation of electromagnetic waves of various wavelengths at ground and space paths, in the troposphere, and in plasma media. Topics discussed include radio wave propagation in an anisotropic turbulent atmosphere, propagation and scattering of millimeter waves, attenuation of radio waves in rain and its prediction,
Acoustic wave propagation in one-dimensional random media: the wave localization approach
van der Baan, Mirko
attenuation is strongest in the domain of Mie scattering except for fractal-like media. In such media phases. Key words: attenuation, dispersion, inhomogeneous media, scattering, statistical methods, wave wave scattering in strongly heterogeneous media is a very complicated phenomenon. Although
Attenuation tomography of the western United States from ambient seismic noise
NASA Astrophysics Data System (ADS)
Lawrence, Jesse F.; Prieto, GermáN. A.
2011-06-01
We show that the spatial coherency of the ambient seismic field can be used for attenuation tomography in the western United States. We evaluate the real portion of the spatial coherency with an elastic geometric spreading term (a Bessel function) and a distance dependent decay (an attenuation coefficient). In order to invert the spatial coherency, a weight stack inversion technique is applied. We recover phase velocity and attenuation coefficient maps at periods of 8-32s, which correspond to the elastic and anelastic structure at crustal and upper mantle depths. The phase velocity maps obtained by this method are of similar resolution to more standard two-station methods. The attenuation results provide an important complement to the information extracted from earthquake-based tomography. Several geological features are easily identifiable in the attenuation coefficient maps, such as the highly attenuating sedimentary basins along the West Coast of the United States, and the highly attenuating Yellowstone region, and the boundaries of the Snake River Plains.
A hybrid attenuation correction technique to compensate for lung density in 3-D total body PET
Tai, Y.C.; Dahlbom, M.; Hoffman, E.J. [UCLA School of Medicine, Los Angeles, CA (United States)
1994-05-01
The purpose of this investigation was to develop a technique for correcting attenuation in noisy emission images without using standard measured attenuation techniques. Data sets in 3-D total body PET are very noisy. In order to have attenuation correction in this imaging modality, excessive times required for transmission scans, isotope uptake and imaging procedure must be reduced. The technique requires: (1) Short transmission scans (3-9 m total) are taken of thorax just before, or 1 or 2 days before or after emission scans. (2) The subject is injected with 18-FDG, allowed a 30 m uptake period, then placed in the PET system, and a total body data set is collected. (3) The emission and attenuation coefficient images are reconstructed with the same zoom factor. (4) The tissue-lung and tissue-air boundaries are determined in the attenuation coefficient image, forming a 3-D binary image of the thorax. (5) The binary image is used as an overlay on a side by side display of the transverse, coronal and sagittal slices from the uncorrected emission data. Using landmarks, such as the heart, apex and base of the lungs, position and thickness of anterior and posterior chest wall, etc., the user can translate and rotate the binary image to fit within the thorax. The outer edges of the body are estimated with edge finding techniques from the emission image. (6) Attenuation coefficients are assigned each region and the attenuation correction determined by forward projection of the synthetic attenuation coefficient image. The resulting images in volunteers are comparable to those that use the standard attenuation correction technique. The errors caused by subject motion were larger than the errors caused by the approximations introduced in this technique, at least in terms of visible artifacts.
Soliton Attenuation and Emergent Hydrodynamics in Fragile Matter
NASA Astrophysics Data System (ADS)
Upadhyaya, N.; Gómez, L. R.; Vitelli, V.
2014-01-01
Disordered packings of soft grains are fragile mechanical systems that lose rigidity upon lowering the external pressure toward zero. At zero pressure, we find that any infinitesimal strain impulse propagates initially as a nonlinear solitary wave progressively attenuated by disorder. We demonstrate that the particle fluctuations generated by the solitary-wave decay can be viewed as a granular analogue of temperature. Their presence is manifested by two emergent macroscopic properties absent in the unperturbed granular packing: a finite pressure that scales with the injected energy (akin to a granular temperature) and an anomalous viscosity that arises even when the microscopic mechanisms of energy dissipation are negligible. Consistent with the interpretation of this state as a fluidlike thermalized state, the shear modulus remains zero. Further, we follow in detail the attenuation of the initial solitary wave, identifying two distinct regimes—an initial exponential decay, followed by a longer power-law decay—and suggest simple models to explain these two regimes.
Signal to noise ratio comparisons for ultrasound attenuation slope estimation algorithms
Omari, Eenas A.; Varghese, Tomy
2014-01-01
Purpose: Attenuation imaging has a promising role in the detection of tissue abnormalities. The authors have previously compared three different frequency domain ultrasound attenuation estimation methods, for accuracy and bias. The mean estimated attenuation value in a region of interest has been the determining factor of how well a method performs; however, the noise level has not been quantified for attenuation estimated using different methods. Methods: The authors compare three different frequency domain ultrasound attenuation estimation methods [the reference phantom method (RPM), the centroid downshift method (CEN), and the hybrid method (HYB)] using the signal to noise ratio (SNR) metric. Both simulated and experimental tissue-mimicking phantoms are used in the performance comparison study, evaluating the impact of the variation in acoustical properties. Results: For attenuation estimation in a tissue-mimicking phantom with a known attenuation coefficient of 0.5 dB/cm/MHz, all the three methods estimated the attenuation coefficient to be ? 0.49 dB/cm/MHz for a transmit center frequency of 6 MHz, however, the signal to noise ratio obtained was found to be 8.5, 5.7, and 2.2 for the HYB, RPM, and CEN methods, respectively. These results demonstrate the need for the SNR metric in the comparison of different algorithms and to evaluate the impact of varying different ultrasound system and tissue parameters. Conclusions: In this paper, the authors demonstrate that although the estimated mean attenuation value with a region of interest may be closely estimated using different methods, the signal to noise ratio obtained of the estimates can vary significantly. The centroid downshift method presented with the lowest signal-to-noise ratio of the methods compared. The hybrid method was the least susceptible to changes in the acoustical properties and provided unbiased attenuation coefficient estimates with the highest signal-to-noise ratios. PMID:24593741
NASA Technical Reports Server (NTRS)
Buzzetti, Mike F. (Inventor)
1994-01-01
A fiber optic attenuator of the invention is a mandrel structure through which a bundle of optical fibers is wrapped around in a complete circle. The mandrel structure includes a flexible cylindrical sheath through which the bundle passes. A set screw on the mandrel structure impacts one side of the sheath against two posts on the opposite side of the sheath. By rotating the screw, the sheath is deformed to extend partially between the two posts, bending the fiber optic bundle to a small radius controlled by rotating the set screw. Bending the fiber optic bundle to a small radius causes light in each optical fiber to be lost in the cladding, the amount depending upon the radius about which the bundle is bent.
An attenuated philosophical gentleman.
Christie, John R R
2014-06-20
Dr. Joseph Black had at one time, a house near us to the west. He was a striking and beautiful person; tall, very thin, and cadaverously pale; his hair carefully powdered, though there was little of it except what was collected in a long thin queue; his eyes dark, clear and large, like deep pools of pure water. He wore black speckless clothes, silk stockings, silver buckles, and either a slim green umbrella, or a genteel brown cane. The general frame and air were feeble and slender. The wildest boy respected Black. No lad could be irreverent toward a man so pale, so gentle, so elegant and so illustrious. So he glided, like a spirit, through our rather mischievous sportiveness, unharmed. He died seated, with a bowl of milk upon his knee, of which his ceasing to be did not spill a drop; a departure which it seemed, after the event, might have been foretold of this attenuated philosophical gentleman. PMID:24921110
Live attenuated influenza vaccine.
Jin, Hong; Subbarao, Kanta
2015-01-01
Cold-adapted Ann Arbor based live attenuated influenza vaccine (LAIV) has been available in the USA since 2003. The vaccine is efficacious against influenza infection. Features of LAIV include: easy administration suitable for mass immunization, cross-reactivity to drifted strains for broader coverage, and establishment of herd immunity for control of influenza spread. Annual seasonal LAIV now contains four strains against influenza A H1N1, H3N2, influenza B-Victoria, and B-Yamagata lineages that are co-circulating in humans. LAIV played a significant role in protecting the public from the 2009 H1N1 pandemic and has been evaluated for pandemic preparedness. Pandemic vaccines including influenza H2, H5, H6, H7, and H9 subtypes have been produced and evaluated in preclinical and small-scale phase I clinical studies. This review summarizes the current status and perspectives of seasonal and pandemic LAIV. PMID:25059893
Surface acoustic wave determination of the superconducting fraction of a Nb/sub 3/Ge film
Salvo, H. Jr.; Fredricksen, H.P.; Levy, M.; Gavaler, J.
1982-08-01
Surface acoustic waves 1200 MHz were used to investigate the properties of a 0.5-..mu..m-thick film of Nb/sub 3/Ge. This film was rf-sputtered onto a substrate consisting of a piezoelectrically active 3.5-..mu..m AlN layer which was chemically vapor-deposited over a sapphire substrate. The attenuation coefficient ..cap alpha.. of the surface acoustic waves was measured from 0.8 to 30 K. The raw data are analyzed to eliminate interference effects due to splitting of the wave into two components. One of these is at the surface of the film and the other may be a ''surface skimming bulk mode'' which is at the film-substrate interface. The resultant curve of attenuation versus temperature in the superconducting region is then used to determine the distribution function of the superconducting transition temperature of the film. Although the film starts to become superconducting at 21 K and the majority of the film appears to become superconducting at 18 K, it is also found that a significant amount of the film does not become superconducting until 10 K. The difference between the attenuation measured in the normal state and the superconducting state is used to obtain the electron mean free path in the film. This is compared to values obtained from electrical measurements.
Coupled attenuation and multiscale damage model for composite structures
NASA Astrophysics Data System (ADS)
Moncada, Albert M.; Chattopadhyay, Aditi; Bednarcyk, Brett; Arnold, Steven M.
2011-04-01
Composite materials are widely used in many applications for their high strength, low weight, and tailorability for specific applications. However, the development of robust and reliable methodologies to detect micro level damage in composite structures has been challenging. For composite materials, attenuation of ultrasonic waves propagating through the media can be used to determine damage within the material. Currently available numerical solutions for attenuation induce arbitrary damage, such as fiber-matrix debonding or inclusions, to show variations between healthy and damaged states. This paper addresses this issue by integrating a micromechanics analysis to simulate damage in the form of a fiber-matrix crack and an analytical model for calculating the attenuation of the waves when they pass through the damaged region. The hybrid analysis is validated by comparison with experimental stress-strain curves and piezoelectric sensing results for attenuation measurement. The results showed good agreement between the experimental stress-strain curves and the results from the micromechanics analysis. Wave propagation analysis also showed good correlation between simulation and experiment for the tested frequency range.
Prediction of Attenuation by Rain
ROBERT K. CRANE
1980-01-01
A new model is presented for the prediction of attenuation by rain on either terrestrial or slant earth-to-space propagation paths. The model was developed using geophysical observations of the statistics of point rain rate, of the horizontal structure of rainfall, and of the vertical temperature structure of the atmosphere. The model was tested by comparison with attenuation distribution observations. The
Micromachined variable optical attenuator (VOA)
NASA Astrophysics Data System (ADS)
Li, J.; Zhang, Xu M.; Liu, Ai Q.; Zhang, Q. X.; Mei, Ting
2001-10-01
Variable optical attenuator (VOA) is undergoing to be a mainstream component of wavelength division multiplex (WDM) networks to monitor and control the optical power of wavelength channels. In this paper, a free-space VOA fabricated by micro electromechanical systems (MEMS) technology to operate in the 1.55 micrometers wavelength region is described. It employs a micromirror driven by an electrostatic comb drive to cut partially into the light beam between two single mode fibers (SMFs), enabling the attenuation. The micromirror has a size of 30 micrometers X 30 micrometers and is coated with aluminum to increase the reflectance. The moving fingers of comb drive and the micromirror are supported by folded suspension beams over the substrate. By applying different voltage to the comb drive, the micromirror translates to different position to achieve an attenuation ranging from 0.4dB to 50dB, and even higher. The nonlinear relationship between the position of the micromirror and attenuation is analyzed. The distributions of the light beams at the micromirror and the output fiber end are investigated respectively. And the influence of the separations between the micromirror, the input and output fiber ends is also discussed to obtain different attenuation resolutions. At low attenuation stages, fine tuning of attenuation is obtainable. The largest attenuation is driven by 21voltage. Deep reactive ion etching (DRIE) process is employed to fabricate the VOA and the micro loading effect is remedied by mask design.
A unifying fractional wave equation for compressional and shear waves.
Holm, Sverre; Sinkus, Ralph
2010-01-01
This study has been motivated by the observed difference in the range of the power-law attenuation exponent for compressional and shear waves. Usually compressional attenuation increases with frequency to a power between 1 and 2, while shear wave attenuation often is described with powers less than 1. Another motivation is the apparent lack of partial differential equations with desirable properties such as causality that describe such wave propagation. Starting with a constitutive equation which is a generalized Hooke's law with a loss term containing a fractional derivative, one can derive a causal fractional wave equation previously given by Caputo [Geophys J. R. Astron. Soc. 13, 529-539 (1967)] and Wismer [J. Acoust. Soc. Am. 120, 3493-3502 (2006)]. In the low omegatau (low-frequency) case, this equation has an attenuation with a power-law in the range from 1 to 2. This is consistent with, e.g., attenuation in tissue. In the often neglected high omegatau (high-frequency) case, it describes attenuation with a power-law between 0 and 1, consistent with what is observed in, e.g., dynamic elastography. Thus a unifying wave equation derived properly from constitutive equations can describe both cases. PMID:20058999
Wear, Keith A
2015-03-01
Through-transmission measurements were performed on 30 human calcaneus samples in vitro. Nonlinear attenuation and dispersion measurements were investigated by estimating 95% confidence intervals of coefficients of polynomial expansions of log magnitude and phase of transmission coefficients. Bone mineral density (BMD) was measured with dual x-ray absorptiometry. Microarchitecture was measured with microcomputed tomography. Statistically significant nonlinear attenuation and nonzero dispersion were confirmed for a clinical bandwidth of 300-750?kHz in 40%-43% of bone samples. The mean linear coefficient for attenuation was 10.3?dB/cm MHz [95% confidence interval (CI): 9.0-11.6?dB/cm MHz]. The mean quadratic coefficient for attenuation was 1.6?dB/cm MHz(2) (95% CI: 0.4-2.8?dB/cm MHz(2)). Nonlinear attenuation provided little information regarding BMD or microarchitecture. The quadratic coefficient for phase (which is related to dispersion) showed moderate correlations with BMD (r?=?-0.65; 95% CI: -0.82 to -0.36), bone surface-to-volume ratio (r?=?0.47; 95% CI: 0.12-0.72) and trabecular thickness (r?=?-0.40; 95% CI: -0.67 to -0.03). Dispersion was proportional to bone volume fraction raised to an exponent of 2.1?±?0.2, which is similar to the value for parallel nylon-wire phantoms (2.4?±?0.2) and supports a multiple-scattering model for dispersion. PMID:25786928
NASA Astrophysics Data System (ADS)
Mirzade, F.
2015-10-01
The present paper is aimed at studying the boundary value problem in elasticity theory concerning the propagation behavior of harmonic waves and vibrations on the surface of the transversely isotropic laser-excited crystalline solids with atomic defect generation. Coupled dynamical diffusion--deformation interaction model is employed to study this problem. The frequency equations of surface waves in closed form are derived and discussed. The three motions, namely, longitudinal, transverse, and diffusion of the medium are found to be dispersive and coupled with each other due to the defect concentration changes and anisotropic effects. The phase velocity and attenuation coefficient of the surface waves get modified due-to the defect-strain coupling and anisotropic effects, and are also influenced by the defect relaxation time. A softening of frequencies of surface acoustic waves (instability of frequencies) is obtained. Relevant results of previous investigations are deduced as special and limiting cases.
ATS-6 attenuation diversity measurements at 20 and 30 GHz
NASA Technical Reports Server (NTRS)
Vogel, W. J.; Straiton, A. W.; Fannin, B. M.; Wagner, N. K.
1975-01-01
The results of data obtained at The University of Texas at Austin in conjunction with the ATS-6 millimeter wave experiment are presented. Attenuation measurements at 30 GHz and sky noise data at 20 GHz were obtained simultaneously at each of two sites separated by 11 km. Space diversity reduces outage time for a system in Austin, Texas with a 10 dB fade margin at 30 GHz from 15 hours to 16 minutes per year. The maximum cloud height shows a good correlation to the maximum attenuations measured.
Low-energy gamma ray attenuation characteristics of aviation fuels
NASA Technical Reports Server (NTRS)
Singh, Jag J.; Shen, Chih-Ping; Sprinkle, Danny R.
1990-01-01
Am241 (59.5 keV) gamma ray attenuation characteristics were investigated in 270 aviation fuel (Jet A and Jet A-1) samples from 76 airports around the world as a part of world wide study to measure the variability of aviation fuel properties as a function of season and geographical origin. All measurements were made at room temperature which varied from 20 to 27 C. Fuel densities (rho) were measured concurrently with their linear attenuation coefficients (mu), thus providing a measure of mass attenuation coefficient (mu/rho) for the test samples. In 43 fuel samples, rho and mu values were measured at more than one room temperature, thus providing mu/rho values for them at several temperatures. The results were found to be independent of the temperature at which mu and rho values were measured. It is noted that whereas the individual mu and rho values vary considerably from airport to airport as well as season to season, the mu/rho values for all samples are constant at 0.1843 + or - 0.0013 cu cm/gm. This constancy of mu/rho value for aviation fuels is significant since a nuclear fuel quantity gauging system based on low energy gamma ray attenuation will be viable throughout the world.
Hor, Yew Li; Federici, John F; Wample, Robert L
2008-01-01
Natural cork enclosures, due to their cell structure, composition, and low moisture are fairly transparent to terahertz (THz) and millimeter waves enabling nondestructive evaluation of the cork's surface and interior. It is shown that the attenuation coefficient of the defect-free cork can be modeled with a Mie scattering model in the weakly scattering limit. Contrast in the THz images is a result of enhanced scattering of THz radiation by defects or voids as well as variations in the cork cell structure. The presence of voids, defects, and changes in grain structure can be determined with roughly 100-300 microm resolution. PMID:18157279
Surface acoustic wave on the (112) cut [11¯0] direction of gallium arsenide
NASA Astrophysics Data System (ADS)
Miškinis, Rimantas; Urba, Emilis
1995-12-01
The properties of an acoustoelectrically active surface acoustic wave (SAW) propagated on the (112) cut [11¯0] direction of gallium arsenide are studied theoretically. The leaky nature of this SAW (LSAW) which has three displacement components of comparable magnitude is demonstrated. The low attenuation (4.94×10-5 dB per wavelength) of the LSAW is obtained. The values of the velocity and the electromechanical coupling coefficient of the LSAW, equal to 3047.4 m/s and 9.3×10-4, respectively, are acquired and agree with the results of experiments carried out previously.
NASA Technical Reports Server (NTRS)
Snyder, G. Jeffrey (Inventor)
2015-01-01
A high temperature Seebeck coefficient measurement apparatus and method with various features to minimize typical sources of errors is described. Common sources of temperature and voltage measurement errors which may impact accurate measurement are identified and reduced. Applying the identified principles, a high temperature Seebeck measurement apparatus and method employing a uniaxial, four-point geometry is described to operate from room temperature up to 1300K. These techniques for non-destructive Seebeck coefficient measurements are simple to operate, and are suitable for bulk samples with a broad range of physical types and shapes.
Linear and nonlinear optical absorption coefficients of spherical dome shells
NASA Astrophysics Data System (ADS)
Guo, Kangxian; Liu, Guanghui; Huang, Lu; Zheng, Xianyi
2015-08-01
Linear and nonlinear optical absorption coefficients of spherical dome shells are theoretically investigated within analytical wave functions and numerical quantized energy levels. Our results show that the inner radius, the outer radius and the cut-off angle of spherical dome shells have great influences on linear and nonlinear optical absorption coefficients as well as the total optical absorption coefficients. It is found that with the increase of the inner radius and the outer radius, linear and nonlinear optical absorption coefficients exhibit a blueshift and a redshift, respectively. However, with the increase of the cut-off angle, linear and nonlinear optical absorption coefficients do not shift. Besides, the resonant peaks of linear and nonlinear optical absorption coefficients climb up and then decrease with increasing the cut-off angle. The influences of the incident optical intensity on the total optical absorption coefficients are studied. It is found that the bleaching effect occurs at higher incident optical intensity.
Weijgaert, Rien van de
;14/03/2014 3 Kayak Surfing on ocean gravity waves Oregon Coast Waves: sea & ocean waves #12;14/03/2014 4 Sound Waves Sound Waves: #12;14/03/2014 5 Sound Waves Linear Waves Sound Waves compression rarefaction #12 are inevitable if sound waves propagate over long distances; 4. Shocks always occur when a flow hits an obstacle
Wave propagation with different pressure signals: an experimental study on the latex tube.
Ursino, M; Artioli, E; Gallerani, M
1993-07-01
To have deeper insight into the main factors affecting wave propagation in real hydraulic lines, we measured the true propagation coefficient in two latex rubber tubes via the three-point pressure method. The measurements were performed using both sinusoidal pressure signals of different amplitudes and periodic square waves as well as aperiodic pressure impulses. The results obtained were then compared with those predicted by a classic linear model valuable for a purely elastic maximally tethered tube. Our measurements demonstrate that the three-point pressure method may introduce significant errors at low frequencies (below 1 Hz in the present experiments) when the distance between two consecutive transducers becomes much lower than the wavelength. The pattern of phase velocity in the range 2-20 Hz turns out to be about 10 per cent higher than the theoretical one computed using the static value of the Young modulus. This result supports the idea that the dynamic Young modulus of the material is slightly higher than that measured in static conditions. The experimental attenuation per wavelength is significantly higher than the theoretical one over most of the frequencies examined, and settles at a constant value as frequency increases. Introduction of wall viscoelasticity in the theoretical model can explain only a portion of the observed high frequency damping and wave attenuation. Finally, increasing the amplitude of pressure changes significantly affects the measured value of the propagation coefficient, especially at those frequencies for which direct and reflected waves sum together in a positive fashion. In these conditions we observed a moderate increase in phase velocity and a much more evident increase in attenuation per wavelength. PMID:8231298
Spectral attenuation and backscattering as indicators of average particle size.
Slade, Wayne Homer; Boss, Emmanuel
2015-08-20
Measurements of the particulate beam attenuation coefficient at multiple wavelengths in the ocean typically exhibit a power law dependence on wavelength, and the slope of that power law has been related to the slope of the particle size distribution (PSD), when assumed to be a power law function of particle size. Recently, spectral backscattering coefficient measurements have been made using sensors deployed at moored observatories, on autonomous underwater vehicles, and even retrieved from space-based measurements of remote sensing reflectance. It has been suggested that these backscattering measurements may also be used to obtain information about the shape of the PSD. In this work, we directly compared field-measured PSD with multispectral beam attenuation and backscattering coefficients in a coastal bottom boundary later. The results of this comparison demonstrated that (1) the beam attenuation spectral slope correlates with the average particle size as suggested by theory for idealized particles and PSD; and (2) measurements of spectral backscattering also contain information reflective of the average particle size in spite of large deviations of the PSD from a spectral power law shape. PMID:26368762
Clustering coefficients Winfried Just
Just, Winfried
Clustering coefficients Winfried Just Hannah Callender M. Drew LaMar§ January 30, 2015 Prevalence plot. c Winfried Just, Hannah Callender, M. Drew LaMar 2015 Department of Mathematics, Ohio@up.edu § The College of William and Mary E-mail: drew.lamar@gmail.com 1 See Exercise 4 of our module A quick tour
Continuously tunable fibre attenuator operating in the wavelength range near 1.5 {mu}m
Baum, Ol'ga I; Mishakov, Gennadii V; Sokolov, Viktor I [Institute of Laser and Information Technologies, Russian Academy of Sciences, Troitsk, Moscow Region (Russian Federation); Varlamova, Nina V; Zapadinskii, Boris I [N.N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, Moscow (Russian Federation)
2004-09-30
A fibre attenuator is fabricated for the telecommunication wavelength range near 1.5 {mu}m in which a single-mode silica fibre with side polishing is used. The fibre surface is covered by a layer of fluorine-containing polymer with a large thermooptic coefficient. The principle of attenuator operation is based on a change in the conditions of total internal reflection for a guided mode in the polished region due to thermally induced variation in the refractive index of the fluoropolymer layer. The attenuator is insensitive to light polarisation, it has a continuously variable attenuation coefficient in the range 0.2-27 dB, and can be easily incorporated into fibreoptic links. (fibre optics)
Wave Propagation in a Circular Waveguide with an Absorbing Wall
A. Mohsen; M. A. K. Hamid
1970-01-01
The attenuation of waves propagating in an electromagnetic waveguide or acoustic pipe with an absorbing wall has been of recent interest due to its importance in the transmission of power at high frequencies and in the design of fixed-length signal attenuators. Since little is known regarding the attenuation characteristics of these devices, the purpose of this communica tion is to
Attenuation tomography of the Southern Apennines (Italy)
NASA Astrophysics Data System (ADS)
Zolezzi, F.; Morasca, P.; Mayeda, K.; Phillips, W. S.; Eva, C.
2008-07-01
The aim of this study is to improve our knowledge of the attenuation structure in the Southern Apennines using a new amplitude ratio tomography method (Phillips et al., Geophys Res Lett 32(21):L21301, 2005) applied on both direct and coda envelope measurements derived from 150 events recorded by 47 stations of the Istituto Nazionale di Geofisica e Vulcanologia National Seismic Network (Rete Sismica Nazionale Centralizzata). The two-dimensional (2-D) analysis allows us to take into account lateral crustal variations and heterogeneities of this region. Using the same event and station distribution, we also applied a simple 1-D methodology, and the performance of the 1-D and 2-D path assumptions is tested by comparing the average interstation variance for the path-corrected amplitudes using coda and direct waves. In general, coda measurement results are more stable than using direct waves when the same methodology is applied. Using the 2-D approach, we observe more stable results for both waves. However, the improvement is quite small, probably because the crustal heterogeneity is weak. This means that, for this region, the 1-D path assumption is a good approximation of the attenuation characteristics of the region. A comparison between Q tomography images obtained using direct and coda amplitudes shows similar results, consistent with the geology of the region. In fact, we observe low Q along the Apennine chain toward the Tyrrhenian Sea and higher values to the east, in correspondence with the Gargano zone that is related to the Apulia Carbonate Platform. Finally, we compared our results with the coda Q values proposed by Bianco et al. (Geophys J Int 150:10 22, 2002) for the same region. The good agreement validates our results as the authors used a completely independent methodology.
Reflection Coefficients on Surfaces of Different Periodic Structure
NASA Technical Reports Server (NTRS)
Niu, Pengfei; Kogut, Al
1997-01-01
Diffraction properties of lossy periodic gratings with the metal base were investigated by solving Maxwell's equations numerically using the differential method. Two periodic surfaces were employed in the simulation: triangle structure and tilting triangle structure. Based on the numerical solution and in conjunction with the algorithm of Adams-Moulton, we computed reflection coefficients of plane waves with different wavelengths and different incident angles. The dielectric properties were also explored using various dielectric constants. The results show that the reflection coefficients of both TE and TM waves are quite sensitive to the incident angles of the plane waves when the metal sheet exists, which is in good agreement with the experimental data.
Rayleigh surface wave interaction with the 2D exciton Bose-Einstein condensate
NASA Astrophysics Data System (ADS)
Boev, M. V.; Kovalev, V. M.
2015-06-01
We describe the interaction of a Rayleigh surface acoustic wave (SAW) traveling on the semiconductor substrate with the excitonic gas in a double quantum well located on the substrate surface. We study the SAW attenuation and its velocity renormalization due to the coupling to excitons. Both the deformation potential and piezoelectric mechanisms of the SAW-exciton interaction are considered. We focus on the frequency and excitonic density dependences of the SAW absorption coefficient and velocity renormalization at temperatures both above and well below the critical temperature of Bose-Einstein condensation of the excitonic gas. We demonstrate that the SAW attenuation and velocity renormalization are strongly different below and above the critical temperature.
P. S. Hill; Emmanuel Boss; J. P. Newgard; B. A. Law; T. G. Milligan
2011-01-01
The goal of this study was to test the hypothesis that the aggregated state of natural marine particles constrains the sensitivity of optical beam attenuation to particle size. An instrumented bottom tripod was deployed at the 12-m node of the Martha's Vineyard Coastal Observatory to monitor particle size distributions, particle size-versus-settling-velocity relationships, and the beam attenuation coefficient (cp) in the
Role of Hydraulic Geometry in Flood Wave Propagation
NASA Astrophysics Data System (ADS)
Orlandini, S.
2010-12-01
The role of hydraulic geometry in flood wave propagation is investigated by using a diffusion wave model with inertial effects. Power function relationships W = a’Qb’ and kS = r’Qy’ are used to reproduce the at-a-station variations of water-surface width W and Gauckler-Strickler conductance coefficient kS (the inverse of Manning resistance coefficient) with flow discharge Q. Downstream variations of coefficients a’ and r’ are not considered in this study. The considered hydraulic geometry relationships are incorporated into a diffusion wave model in which the term (1 - Ve2), Ve being the Vedernikov number, multiplies the Hayami’s diffusivity Q/(2WS0), S0 being the channel bed slope. This mathematical model is solved numerically by using a matched artificial diffusivity method. Numerical experiments are carried out by evaluating peak attenuation and mean peak celerity of flood waves propagating along channel reaches characterized by coefficients a’ and r’ equal to the average values observed in natural rivers, by all the combinations of exponents b’ and y’ laying in the range 0-0.5, and by values of S0 laying in the range 0.000125-0.032. It is found that: (1) peak attenuation and mean peak celerity display the minimum values for b’ = 0.5 and y’ = 0, (2) for high values of y’, Ve displays values greater than 1 indicating physical instability of flood waves, and (3) around the condition b’ = 0 and y’ = 0, for high values of Q/W and low values of S0, the Peclet number Pe (evaluated over the channel reach length) displays values less than 2 indicating unrealistic hydraulic diffusion (more storage effects than those produced by a reservoir). The region of the plane b’y’ representing relevant flood waves lays therefore between the instability region Ve > 1, where unstable flood waves are physically possible but rarely observed in natural channels and not reproducible with the considered model, and the region of unrealistic diffusion Pe < 2, where numerical solutions are possible but physically questionable. In this region, peak attenuation and mean peak celerity are found to be more sensitive to variations in y’ than in b’. The developed diffusion wave model provides a reliable description of the advection and diffusion processes determining travel times and storage variations at the channel reach scale, with clear implications for reproducing surface flows and their interaction with the subsurface. The obtained results indicate that stream channel geometry plays a critical role in runoff propagation, and thus caution must be exercised in river engineering when altering shape and resistance to flow of channels. In addition, they suggest that the developed model can be usefully combined with field data to understand how kinematic wave celerity and hydraulic diffusivity scale when mountain streams and hillslope rivulets are considered, a challenge for the definition of a new generation of distributed models that are really based on physics at all the spatial and temporal scales characterizing the different processes that occur within the drainage basin.
Attenuation correction for small animal SPECT imaging using x-ray CT data
Hwang, Andrew B.; Hasegawa, Bruce H. [Bioengineering Graduate Group, University of California at Berkeley and University of California, San Francisco, Berkeley, California 94720 (United States); Bioengineering Graduate Group, University of California at Berkeley and University of California, San Francisco, Berkeley, California 94720 and Department of Radiology, University of California, 185 Berry Street, Suite 350, San Francisco, San Francisco, California 94143-0943 (United States)
2005-09-15
Photon attenuation in small animal nuclear medicine scans can be significant when using isotopes that emit lower energy photons such as iodine-125. We have developed a method to use microCT data to perform attenuation corrected small animal single-photon emission computed tomography (SPECT). A microCT calibration phantom was first imaged, and the resulting calibration curve was used to convert microCT image values to linear attenuation coefficient values that were then used in an iterative SPECT reconstruction algorithm. This method was applied to reconstruct a SPECT image of a uniform phantom filled with {sup 125}I-NaI. Without attenuation correction, the image suffered a 30% decrease in intensity in the center of the image, which was removed with the addition of attenuation correction. This reduced the relative standard deviation in the region of interest from 10% to 6%.
Generalized Reflection Coefficients
NASA Astrophysics Data System (ADS)
Remling, Christian
2015-07-01
I consider general reflection coefficients for arbitrary one-dimensional whole line differential or difference operators of order 2. These reflection coefficients are semicontinuous functions of the operator: their absolute value can only go down when limits are taken. This implies a corresponding semicontinuity result for the absolutely continuous spectrum, which applies to a very large class of maps. In particular, we can consider shift maps (thus recovering and generalizing a result of Last-Simon) and flows of the Toda and KdV hierarchies (this is new). Finally, I evaluate an attempt at finding a similar general setup that gives the much stronger conclusion of reflectionless limit operators in more specialized situations.
The Inhomogeneous Waves in a Rotating Piezoelectric Body
Chen, Si
2013-01-01
This paper presents the analysis and numerical results of rotation, propagation angle, and attenuation angle upon the waves propagating in the piezoelectric body. Via considering the centripetal and Coriolis accelerations in the piezoelectric equations with respect to a rotating frame of reference, wave velocities and attenuations are derived and plotted graphically. It is demonstrated that rotation speed vector can affect wave velocities and make the piezoelectric body behaves as if it was damping. Besides, the effects of propagation angle and attenuation angle are presented. Critical point is found when rotation speed is equal to wave frequency, around which wave characteristics change drastically. PMID:24298219
Dual energy CT for attenuation correction with PET/CT
Xia, Ting [Department of Bioengineering, University of Washington, Seattle, Washington 98105 (United States)] [Department of Bioengineering, University of Washington, Seattle, Washington 98105 (United States); Alessio, Adam M. [Department of Radiology, University of Washington, Seattle, Washington 98105 (United States)] [Department of Radiology, University of Washington, Seattle, Washington 98105 (United States); Kinahan, Paul E., E-mail: kinahan@uw.edu [Departments of Radiology and Bioengineering, University of Washington, Seattle, Washington 98105 (United States)
2014-01-15
Purpose: The authors evaluate the energy dependent noise and bias properties of monoenergetic images synthesized from dual-energy CT (DECT) acquisitions. These monoenergetic images can be used to estimate attenuation coefficients at energies suitable for positron emission tomography (PET) and single-photon emission computed tomography (SPECT) imaging. This is becoming more relevant with the increased use of quantitative imaging by PET/CT and SPECT/CT scanners. There are, however, potential variations in the noise and bias of synthesized monoenergetic images as a function of energy. Methods: The authors used analytic approximations and simulations to estimate the noise and bias of synthesized monoenergetic images of water-filled cylinders with different shapes and the NURBS-based cardiac-torso (NCAT) phantom from 40 to 520 keV, the range of SPECT and PET energies. The dual-kVp spectra were based on the GE Lightspeed VCT scanner at 80 and 140 kVp with added filtration of 0.5 mm Cu. The authors evaluated strategies of noise suppression with sinogram smoothing and dose minimization with reduction of tube currents at the two kVp settings. The authors compared the impact of DECT-based attenuation correction with single-kVp CT-based attenuation correction on PET quantitation for the NCAT phantom for soft tissue and high-Z materials of bone and iodine contrast enhancement. Results: Both analytic calculations and simulations displayed the expected minimum noise value for a synthesized monoenergetic image at an energy between the mean energies of the two spectra. In addition the authors found that the normalized coefficient of variation in the synthesized attenuation map increased with energy but reached a plateau near 160 keV, and then remained constant with increasing energy up to 511 keV and beyond. The bias was minimal, as the linear attenuation coefficients of the synthesized monoenergetic images were within 2.4% of the known true values across the entire energy range. Compared with no sinogram smoothing, sinogram smoothing can dramatically reduce noise in the DECT-derived attenuation map. Through appropriate selection of tube currents for high and low kVp scans, DECT can deliver roughly the same amount of radiation dose as that of a single kVp CT scan, but could be used for PET attenuation correction with reduced bias in contrast agent regions by a factor of ?2.6 and slightly reduced RMSE for the total image. Conclusions: When DECT is used for attenuation correction at higher energies, there is a noise amplification that is dependent on the energy of the synthesized monoenergetic image of linear attenuation coefficients. Sinogram smoothing reduces the noise amplification in DECT-derived attenuation maps without increasing bias. With an appropriate selection of CT techniques, a DECT scan with the same radiation dose as a single CT scan can result in a PET image with improved quantitative accuracy.
Dual energy CT for attenuation correction with PET/CT
Xia, Ting; Alessio, Adam M.; Kinahan, Paul E.
2014-01-01
Purpose: The authors evaluate the energy dependent noise and bias properties of monoenergetic images synthesized from dual-energy CT (DECT) acquisitions. These monoenergetic images can be used to estimate attenuation coefficients at energies suitable for positron emission tomography (PET) and single-photon emission computed tomography (SPECT) imaging. This is becoming more relevant with the increased use of quantitative imaging by PET/CT and SPECT/CT scanners. There are, however, potential variations in the noise and bias of synthesized monoenergetic images as a function of energy. Methods: The authors used analytic approximations and simulations to estimate the noise and bias of synthesized monoenergetic images of water-filled cylinders with different shapes and the NURBS-based cardiac-torso (NCAT) phantom from 40 to 520 keV, the range of SPECT and PET energies. The dual-kVp spectra were based on the GE Lightspeed VCT scanner at 80 and 140 kVp with added filtration of 0.5 mm Cu. The authors evaluated strategies of noise suppression with sinogram smoothing and dose minimization with reduction of tube currents at the two kVp settings. The authors compared the impact of DECT-based attenuation correction with single-kVp CT-based attenuation correction on PET quantitation for the NCAT phantom for soft tissue and high-Z materials of bone and iodine contrast enhancement. Results: Both analytic calculations and simulations displayed the expected minimum noise value for a synthesized monoenergetic image at an energy between the mean energies of the two spectra. In addition the authors found that the normalized coefficient of variation in the synthesized attenuation map increased with energy but reached a plateau near 160 keV, and then remained constant with increasing energy up to 511 keV and beyond. The bias was minimal, as the linear attenuation coefficients of the synthesized monoenergetic images were within 2.4% of the known true values across the entire energy range. Compared with no sinogram smoothing, sinogram smoothing can dramatically reduce noise in the DECT-derived attenuation map. Through appropriate selection of tube currents for high and low kVp scans, DECT can deliver roughly the same amount of radiation dose as that of a single kVp CT scan, but could be used for PET attenuation correction with reduced bias in contrast agent regions by a factor of ?2.6 and slightly reduced RMSE for the total image. Conclusions: When DECT is used for attenuation correction at higher energies, there is a noise amplification that is dependent on the energy of the synthesized monoenergetic image of linear attenuation coefficients. Sinogram smoothing reduces the noise amplification in DECT-derived attenuation maps without increasing bias. With an appropriate selection of CT techniques, a DECT scan with the same radiation dose as a single CT scan can result in a PET image with improved quantitative accuracy. PMID:24387525
NASA Astrophysics Data System (ADS)
Tisato, Nicola; Madonna, Claudio
2012-11-01
Wave attenuation at low seismic frequencies (0.1-100 Hz) in the earth crust has been explained by stress-induced fluid flow in partially saturated porous media. We present the pressure vessel called Broad Band Attenuation Vessel (BBAV) and two series of attenuation (QE- 1) measurements conducted on Berea sandstone. The BBAV employs the sub-resonance method to measure seismic wave attenuation in the frequency range from 0.01 to 100 Hz, under confining pressure up to 25 MPa and generating a bulk strain around 10- 6 in a cylindrical sample with maximum size of 76 mm in diameter and 250 mm in length. The BBAV has been successfully designed, built and tested. The calibrations obtained with aluminum (EN AW-6082) and Polymethyl-methacrylate (PMMA or Plexiglas) agree with literature values. Two 20% porosity and 1.97 × 10- 13 - 9.87 × 10- 13 m2 permeability Berea sandstone samples were tested. The stress conditions were: i) unconfined, ii) confined at 2 MPa and iii) confined at 15 MPa. Dry samples exhibited always attenuation around 0.01, while saturated samples exhibited attenuation between 0.01 and 0.04. Attenuation values in ? 60% water saturated samples were frequency-dependent only for confining pressures ? 2 MPa. One explanation to this observation, which requires more experiments to be established, is that for confining pressures > 10 MPa the microcracks in the sample would be closed, impeding attenuation related to squirt flow.
Attenuation of ground vibrations due to different technical sources
NASA Astrophysics Data System (ADS)
Auersch, L.; Said, S.
2010-09-01
The attenuation of technically induced surface waves is studied theoretically and experimentally. In this paper, nineteen measurements of ground vibrations induced by eight different technical sources including road and rail traffic, vibratory and impulsive construction work or pile driving, explosions, hammer impulses and mass drops are described, and it is shown that the technically induced ground vibrations exhibit a power-law attenuation v ˜ r - q where the exponents q are in the range of 0.5 to 2.0 and depend on the source types. Comparisons performed demonstrate that the measured exponents are considerably higher than theoretically expected. Some potential effects on ground vibration attenuation are theoretically analyzed. The most important effect is due to the material or scattering damping. Each frequency component is attenuated exponentially as exp(- kr), but for a broad-band excitation, the sum of the exponential laws also yields a power law but with a high exponent. Additional effects are discussed, for example the dispersion of the Rayleigh wave due to soil layering, which yields an additional exponent of 0.5 in cases of impulsive loading.
Radar attenuation and temperature within the Greenland Ice Sheet
MacGregor, Joseph A; Li, Jilu; Paden, John D; Catania, Ginny A; Clow, Gary D.; Fahnestock, Mark A; Gogineni, S. Prasad; Grimm, Robert E.; Morlighem, Mathieu; Nandi, Soumyaroop; Seroussi, Helene; Stillman, David E
2015-01-01
The flow of ice is temperature-dependent, but direct measurements of englacial temperature are sparse. The dielectric attenuation of radio waves through ice is also temperature-dependent, and radar sounding of ice sheets is sensitive to this attenuation. Here we estimate depth-averaged radar-attenuation rates within the Greenland Ice Sheet from airborne radar-sounding data and its associated radiostratigraphy. Using existing empirical relationships between temperature, chemistry, and radar attenuation, we then infer the depth-averaged englacial temperature. The dated radiostratigraphy permits a correction for the confounding effect of spatially varying ice chemistry. Where radar transects intersect boreholes, radar-inferred temperature is consistently higher than that measured directly. We attribute this discrepancy to the poorly recognized frequency dependence of the radar-attenuation rate and correct for this effect empirically, resulting in a robust relationship between radar-inferred and borehole-measured depth-averaged temperature. Radar-inferred englacial temperature is often lower than modern surface temperature and that of a steady state ice-sheet model, particularly in southern Greenland. This pattern suggests that past changes in surface boundary conditions (temperature and accumulation rate) affect the ice sheet's present temperature structure over a much larger area than previously recognized. This radar-inferred temperature structure provides a new constraint for thermomechanical models of the Greenland Ice Sheet.
Radar attenuation and temperature within the Greenland Ice Sheet
NASA Astrophysics Data System (ADS)
MacGregor, Joseph A.; Li, Jilu; Paden, John D.; Catania, Ginny A.; Clow, Gary D.; Fahnestock, Mark A.; Gogineni, S. Prasad; Grimm, Robert E.; Morlighem, Mathieu; Nandi, Soumyaroop; Seroussi, Hélène; Stillman, David E.
2015-06-01
The flow of ice is temperature-dependent, but direct measurements of englacial temperature are sparse. The dielectric attenuation of radio waves through ice is also temperature-dependent, and radar sounding of ice sheets is sensitive to this attenuation. Here we estimate depth-averaged radar-attenuation rates within the Greenland Ice Sheet from airborne radar-sounding data and its associated radiostratigraphy. Using existing empirical relationships between temperature, chemistry, and radar attenuation, we then infer the depth-averaged englacial temperature. The dated radiostratigraphy permits a correction for the confounding effect of spatially varying ice chemistry. Where radar transects intersect boreholes, radar-inferred temperature is consistently higher than that measured directly. We attribute this discrepancy to the poorly recognized frequency dependence of the radar-attenuation rate and correct for this effect empirically, resulting in a robust relationship between radar-inferred and borehole-measured depth-averaged temperature. Radar-inferred englacial temperature is often lower than modern surface temperature and that of a steady state ice-sheet model, particularly in southern Greenland. This pattern suggests that past changes in surface boundary conditions (temperature and accumulation rate) affect the ice sheet's present temperature structure over a much larger area than previously recognized. This radar-inferred temperature structure provides a new constraint for thermomechanical models of the Greenland Ice Sheet.
Molar extinction coefficients of some fatty acids
NASA Astrophysics Data System (ADS)
Sandhu, G. K.; Singh, Kulwant; Lark, B. S.; Gerward, L.
2002-10-01
The attenuation of gamma rays in some fatty acids, viz. formic acid (CH 2O 2), acetic acid (C 2H 4O 2), propionic acid (C 3H 6O 2), butyric acid (C 4H 8O 2), n-hexanoic acid (C 6H 12O 2), n-caprylic acid (C 8H 16O 2), lauric acid (C 12H 24O 2), myristic acid (C 14H 28O 2), palmitic acid (C 16H 32O 2), oleic acid (C 18H 34O 2) and stearic acid (C 18H 36O 2), has been measured at the photon energies 81, 356, 511, 662, 1173 and 1332 keV. Experimental values for the molar extinction coefficient, the effective atomic number and the electron density have been derived and compared with theoretical calculations. There is good agreement between experiment and theory.
Water Waves Over Non-Rigid Muddy Bottoms
NASA Astrophysics Data System (ADS)
Alam, M.; Liu, Y.; Yue, D.
2007-12-01
The phenomenon of the wave-attenuation over muddy sea beds is considered invoking a mass-spring-damper bottom model. Reports of observed strong dissipation for surface waves traveling over muddy bottoms in Gulf of Mexico and Indian ocean inflamed a great deal of attention in the late past century. Numerous models including two-layer models with Newtonian and/or non-Newtonian lower layer, porous ground models, and bottom friction models were developed. Considering the limitations of existing models due to the complicated nature of the mud, we develop a visco- elastic bottom model where the inertia, elasticity coefficient and the damping coefficient are dependent on the mud properties. The proposed system admits up to four eigen-mode solutions with oscillatory and exponentially decaying parts. Contrary to all existing models, and supportive to some recent observations (see for example Sheremet & Stone 2003; Sheremet 2005), the model explains the possibility of larger energy decay rate for higher incident wave frequencies. Amenable to numerical simulations, the model is converted to the classic flat bottom problem with a modified free surface boundary condition. An efficient numerical scheme based on the higher-order spectral method is adopted, and general cases including the evolution of broadband incident waves is studied. The effect of weak nonlinearity is considered numerically and theoretically. Sheremet, A. & Stone, G.~W. 2003 Observation of nearshore wave dissipation over muddy sea beds. Journal of Geophysical Research 108~(C11), 21(1--11). Sheremet, A., Mehta-A.J. Liu B. Stone~G.W. 2005 Wave-sediment interaction on a muddy inner shelf during hurricane claudette. ESTUARINE COASTAL AND SHELF SCIENCE 63~(1-2), 225--233.
Amplification, attenuation, and dispersion of sound in inhomogeneous flows
NASA Technical Reports Server (NTRS)
Kentzer, C. P.
1975-01-01
First order effects of gradients in nonuniform potential flows of a compressible gas are included in a dispersion relation for sound waves. Three nondimensional numbers, the ratio of the change in the kinetic energy in one wavelength to the thermal energy of the gas, the ratio of the change in the total energy in one wavelength to the thermal energy, and the ratio of the dillatation frequency (the rate of expansion per unit volume) to the acoustic frequency, play a role in the separation of the effects of flow gradients into isotropic and anisotropic effects. Dispersion and attenuation (or amplification) of sound are found to be proportional to the wavelength for small wavelength, and depend on the direction of wave propagation relative to flow gradients. Modification of ray acoustics for the effects of flow gradients is suggested, and conditions for amplification and attenuation of sound are discussed.
NASA Astrophysics Data System (ADS)
Pradhan, O.; Matsushima, J.; Suzuki, M.
2012-12-01
Methane hydrate bearing sediment possesses unique seismic wave propagation properties. Both high seismic wave velocity and high wave attenuation are observed in methane hydrate bearing sediment. We used brine with salinity 2% in analogous to methane hydrate for conducting laboratory waveform measurement and characterization by using nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) technique. When brine undergoes freezing, only pure water freezes into ice and salt remains in solution with successively increasing salinity and decreasing freezing point of the solution. Unfrozen brine is enclosed inside micro pores in ice, with exhibiting solid-liquid coexisting system. We used conventional pulse transmission technique to measure compressional wave velocity in partially frozen brine when brine is subjected cooling down to -12oC. Waveform measurement shows sudden increase in compressional wave velocity at temperature -3oC. Below -3oC, velocity increases slightly. Largest wave attenuation is observed at around -3oC. We conducted MRI experiment by using instrument Varian Unity Inova 4.7T. T1 weighted and diffusion weighted (DW) MR images were prepared by applying magnetic field gradient of 0.3 gauss/cm. We observe the spatial distribution of pores, microstructures and heterogeneity in partially frozen brine sample slices. Two dimensional apparent diffusion coefficient (ADC) maps are prepared from DW images with b-values 0 and 81 s/mm2 respectively. We estimate porosity quantitatively from each MR slices at temperature -3, -5, -7 and -12oC by using image analysis technique. Gassmann equation is applied to calculate compressional wave velocity from the porosity data and compared with the measured velocity obtained by waveform analysis technique. The NMR results show the existence of high and low mobility unfrozen brine in the pore space. MR imaging shows the heterogeneously distributed porosity values within a single slice with low porosity and high compressional wave velocity zone in the top part of the sample.
Lamb wave behavior in bridge girder geometries
I. J. Oppenheim; D. W. Greve; N. L. Tyson
2006-01-01
Lamb waves in plates and in cylindrical pipes have been the subject of extensive study, largely because they propagate great distances with little attenuation, and can therefore be used to detect flaws. In this paper we report finite element simulations and experimental studies of Lamb waves in steel bridge girder geometries. In our studies the Lamb waves are generated by
Attenuation and Dispersion in Earth's Materials
NASA Astrophysics Data System (ADS)
Gueguen, Y.
2012-04-01
One of the last challenges of Pr. Luigi Burlini has been to set up an experimental apparatus that would measure elastic wave attenuation under high pressure conditions. This project has since been developed by his colleagues and students at ETH. As a tribute to Luigi Burlini, this presentation aims at recalling why such measurements are important , how challenging such a project is, and what the main issues ahead are. Most of our knowledge about either crustal layers (seismic exploration) or deeper layers (seismology) results from data related to elastic wave propagation inside the Earth. The large amount of available data as well as the huge capability of computers are such that descriptions in terms of isotropic homogeneous layers appear to be very crude today. Anisotropic, heterogeneous models are reported at various scales. In addition, accounting for wave attenuation (the Q factor) is potentially of great interest. The Q factor is highly sensitive to processes that involve some departure from perfect elasticity. Its knowledge may provide information on possible fluid content, temperature, etc. This is because various processes may dissipate energy (and thus lower Q value) as a result of fluid flow, solid flow, etc., depending on the precise P-T conditions at depth. This points immediately to the theoretical challenge of Q investigations: there are many possible ways for a rock to not behave as a perfect elastic body. To model these various mechanisms and identify in which conditions they can take place is a first major challenge. The second challenge is on the experimental ground. What is looked for is to get low frequencies (f close to seismic frequencies) Q data on crustal (or mantle) rocks at high pressure P-high temperature T. Experiments in such highT-high P-low f conditions are extremely difficult to perform. Only in Canberra (I. Jackson) and now in Zurich such conditions have been achieved. Attenuation and dispersion (frequency dependence) of elastic waves are related through Kramers-Kronig equations. Using simple viscoelastic models such as the Zener model, one can show that Q-1 is maximum at a critical frequency fc, and, correlatively, that the wavespeed increases from low to high f by an amount ?V/V = (Q-1)max. This means that another (equivalent) way to look at attenuation is to look at dispersion. Experimentally, this implies to measure high and low frequency wavespeeds or elastic moduli. High frequency measurements have been performed for a long time (including high P-high T conditions) but low frequency measurements remain a challenge. Such data are however of major importance: seismic velocities data (1 H-1 kHz range) are obtained at much lower frequencies than laboratory data (MHz range). A difference by up to 6 orders of magnitudes in frequency exist between both set of data. Yet it has been mainly assumed that the frequency dependence can be neglected. Several set of experimental data show that it is not true. The implications for the crust and for the mantle will be discussed.
Attenuation in Southeastern Sicily (Italy) by applying different coda methods
E. Giampiccolo; G. Tusa; H. Langer; S. Gresta
2002-01-01
The attenuation in Southeastern Sicily has been investigated using 40aftershocks of the December 13 1990, earthquake. The quality factor ofcoda waves (Qc) was estimated in the frequency range 1.5–24 Hz,applying three different methods in time and frequency domains. On thewhole, a clear dependence of Qc on frequency was observed,according to the general law Q = Q0(f\\/f0)n . Thefrequency dependence relationships
Acoustic attenuation analysis program for ducts with mean flow
NASA Technical Reports Server (NTRS)
Kunze, R. K., Jr.
1972-01-01
A computerized acoustic attenuation prediction procedure has been developed to evaluate acoustically lined ducts for various geometric and environmental parameters. The analysis procedure is based on solutions to the acoustic wave equation, assuming uniform airflow on a duct cross section, combined with appropriate mathematical lining impedance models. The impedance models included in the analysis procedure are representative of either perforated sheet or porous polyimide impregnated fiberglass facing sheet coupled with a cellular backing space. Advantages and limitations of the analysis procedure are reviewed.
Frequency dependent Lg attenuation in Northeast China and Korean Peninsula
NASA Astrophysics Data System (ADS)
Ranasinghe, N. R.; Gallegos, A. C.; Trujillo, A. R.; Blanchette, A. R.; Hearn, T. M.; Sandvol, E. A.; Ni, J.; Grand, S. P.; Niu, F.; Chen, Y. J.; Ning, J.; Kawakatsu, H.; Tanaka, S.; Obayashi, M.
2014-12-01
Lg spectra are collected from 452 crustal events spanning from 1995 to 2014 in Northeast (NE) China and surrounding areas using 202 seismic stations from Northeast China extended seismic Array (NECESSArray), GSN stations in NE Asia, China national seismic network, IRIS PASSCAL experiments in NE China, Korean and Japanese permanent seismic networks to study Lg attenuation in NE Asia. Using reverse two-station and two-station methods we obtained frequency dependent Lg attenuation models for a frequency range between 0.5 Hz to 5 Hz with a resolution of about 2°. We solved for the geometric spreading term by fitting the amplitude to the two-station distance ratios and the absolute distances. The best fit yields a spreading coefficient of 0.36 instead of the traditional cylindrical spreading term of 0.50. Lg Q values in NE China and the Korean Peninsula vary from 50 to 1600. Q values increase rapidly in the Songliao Basin (SNB) for higher frequencies (? 2Hz), while they stay relatively constant in the Great Xing'an Range (GXR). Low attenuation regions are found in the Great Xing'an, Lesser Xing'an (LXR) and Songen-Zhangguangcai Ranges (SZR). Overall, attenuation is high in the Songliao, Sanjiang (SNB), Bohai (BHB), Erlian (EB) and Hailar (HB) basins. The highest attenuation is found in the vicinity of Wudalicanchi (WVF), Changbaishan (CBV), and Quaternary volcanic regions, the southern Songliao Basin, west of Erlian Basin, Bohai Basin and the Sanjiang Basin. In general regions with low attenuation (Q > 800) have a low heat flow value (<70 mW/m2) and very thin (< 1 km) or no sediments.