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Sample records for wave attenuation measurements

  1. 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.

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

    NASA Astrophysics Data System (ADS)

    Ozeren, Y.; Wren, D. G.

    2010-12-01

    It is well accepted that wetlands have an important role in shoreline protection against wave damage. However, there is still a lack of knowledge on primary mechanisms of wave attenuation though wetland vegetation. The purpose of this study was to understand these mechanisms and quantify the impact of vegetation on the waves through a series of laboratory experiments. Experiments were conducted in a wave tank at the USDA-ARS-National Sedimentation Laboratory to measure the rate of wave attenuation through emergent and submerged rigid and flexible cylindrical stems, and live vegetation. Dormant and healthy Spartina alterniflora and healthy Juncus romerianus, two common plant species in coastal areas, were used during the tests. The time series water surface elevation at five locations was recorded by wave probes and the water surface profile through the vegetation field was recorded using a digital video camera. The recorded data were analyzed with imaging techniques to identify the wave attenuation characteristic of wetland vegetation and drag coefficients.

  3. 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

  4. Sound wave attenuation in foam

    NASA Astrophysics Data System (ADS)

    Faerman, V. T.

    2016-01-01

    Experimental measurements are presented for sound wave attenuation in foam without additives (standing wave method) and in foam with added particles (pulse method). A setup is developed that makes it possible to obtain a standing sound wave in stable foam and estimate the attenuation coefficient. A comparison is made of the coefficients of sound attenuation in foam in the sonic and ultrasonic frequency ranges, which have been published in a number of works. It is shown that the introduction of particles into foam leads to an increase in sound wave attenuation and may be the result of the viscous mechanism of sound wave energy loss.

  5. Characterization of guided wave velocity and attenuation in anisotropic materials from wavefield measurements

    NASA Astrophysics Data System (ADS)

    Williams, Westin B.; Michaels, Thomas E.; Michaels, Jennifer E.

    2016-02-01

    The behavior of guided waves propagating in anisotropic composite panels can be substantially more complicated than for isotropic, metallic plates. The angular dependency of wave propagation characteristics need to be understood and quantified before applying methods for damage detection and characterization. This study experimentally investigates the anisotropy of wave speed and attenuation for the fundamental A0-like guided wave mode propagating in a solid laminate composite panel. A piezoelectric transducer is the wave source and a laser Doppler vibrometer is used to measure the outward propagating waves along radial lines originating at the source transducer. Group velocity, phase velocity and attenuation are characterized as a function of angle for a single center frequency. The methods shown in this paper serve as a framework for future adaptation to damage imaging methods using guided waves for structural health monitoring.

  6. 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...

  7. 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.

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

    PubMed

    Seldis, Thomas

    2013-09-01

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

  9. Measurement of attenuation coefficients of the fundamental and second harmonic waves in water

    NASA Astrophysics Data System (ADS)

    Zhang, Shuzeng; Jeong, Hyunjo; Cho, Sungjong; Li, Xiongbing

    2016-02-01

    Attenuation corrections in nonlinear acoustics play an important role in the study of nonlinear fluids, biomedical imaging, or solid material characterization. The measurement of attenuation coefficients in a nonlinear regime is not easy because they depend on the source pressure and requires accurate diffraction corrections. In this work, the attenuation coefficients of the fundamental and second harmonic waves which come from the absorption of water are measured in nonlinear ultrasonic experiments. Based on the quasilinear theory of the KZK equation, the nonlinear sound field equations are derived and the diffraction correction terms are extracted. The measured sound pressure amplitudes are adjusted first for diffraction corrections in order to reduce the impact on the measurement of attenuation coefficients from diffractions. The attenuation coefficients of the fundamental and second harmonics are calculated precisely from a nonlinear least squares curve-fitting process of the experiment data. The results show that attenuation coefficients in a nonlinear condition depend on both frequency and source pressure, which are much different from a linear regime. In a relatively lower drive pressure, the attenuation coefficients increase linearly with frequency. However, they present the characteristic of nonlinear growth in a high drive pressure. As the diffraction corrections are obtained based on the quasilinear theory, it is important to use an appropriate source pressure for accurate attenuation measurements.

  10. Electromagnetic wave attenuation measurements in a ring-shaped inductively coupled air plasma

    SciTech Connect

    Xiaolong, Wei; Haojun, Xu; Min, Lin; Chen, Su; Jianhai, Li

    2015-05-28

    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{sub 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 cm{sup 3} 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{sub e} achieves nearly uniform within the electronegative core and sharply steepens in the edge. The N{sub 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.

  11. Attenuation of compressional waves in peridotite measured as a function of temperature at 200 MPa

    NASA Astrophysics Data System (ADS)

    Sato, Hiroki; Sacks, I. Selwyn; Murase, Tsutomu; Muncill, Gregory; Fukuyama, Hiroyuki

    1988-03-01

    A technique has been developed to determine attenuation in rocks at high temperature using a gas-media, high-pressure apparatus. A pulse transmission technique and a spectral ratio method are used to study compressional seismic properties of rocks. Seismic waves are transmitted to and from the sample through buffer rods of mullite. The effect of seismic wave reflections within the sample assembly are cancelled out by taking ratios of the spectra measured at different temperatures. In order to obtain good signal-to-noise ratio for resolving the attenuation at high pressure and temperature, special care is taken in the sample assembly and the ultrasonic coupling between the sample, buffer rods and transducers. A very tight connection of the sample-buffer rod-transducer is essential for obtaining high frequency signals (>300 kHz) at high temperature. A small mass is attached to each outside end of the transducer to drive low frequency signals (<250 kHz) into the sample. Before attenuation measurements, the sample and the buffer rods are tightly compacted in a platinum tube at high pressure and room temperature to ensure pressure seal of the sample assembly. The frequency range of measurement covers 50 to 450 kHz for the sample. Attenuation is very small in the buffer rod compared to the sample for the entire temperature range of the study. Because of the small attenuation, a wide frequency band of 50 kHz to 3.2 MHz can be covered for investigating the attenuation in the buffer rod. The technique has been used to measure attenuation at high confining pressure, and temperatures including sub- and hyper-solidus of upper mantle rocks. Therefore, effects of partial melting on attenuation can be studied. The method is applied to the attenuation measurement in a peridotite as a function of temperature to 1225°C at 200 MPa confining pressure. At high temperature, signal amplitude decays more rapidly at high frequency than at low frequency, from which attenuation (and Q) can be determined using a spectral ratio method. No frequency dependence of Q is resolved for both the sample and the buffer rod over the entire temperature and frequency ranges of the measurement. The results show that Q decreases rapidly with increasing temperature even in the temperature range below the solidus of peridotites. Such temperature sensitivity of Q is probably more useful to probe thermal structure in the upper mantle than that of conductivity at temperatures below the solidus. The results in this study are compared with available seismic velocity, electrical conductivity and solidus data for peridotites, suggesting that there is no discontinuous change in both mechanical and electrical properties of peridotites at the solidus temperature. Even at hypersolidus temperatures, it appears that velocity drops and conductivity increases continuously (not abruptly) with increasing melt fraction. This implies that mechanical and electrical properties of the upper mantle will gradually change at the boundary where the geotherm crosses the solidus.

  12. Laboratory measurement of elastic-wave velocity, associated dispersion, attenuation and particle resonance

    NASA Astrophysics Data System (ADS)

    Molyneux, Joseph Benedict

    Laboratory velocity measurements are an integral component of solid earth seismic investigations. Typically, ultrasonic measurements from centimeter scale plug samples are used to model large sections of the crust, core and mantle. By using the laboratory determined velocities, the seismic arrival time can more accurately calibrate spatial physical properties of the solid-earth. A semi-automated picking procedure is presented which determines the velocity measured from recorded ultrasonic pulses propagated through laboratory samples. This procedure is quicker and more consistent than the standard hand picking method, allowing larger data sets to be accurately investigated. Furthermore, a series of common velocity analyses are compared to the physical properties of phase and group velocity in an attenuating medium of glycerol saturated glass bead packs (Q ˜ 3). It is found that the velocity determined from the first break of the waveform (signal velocity) is up to 13% different from group and phase velocities. This illustrates that signal velocity is unsuitable to determine rock properties in highly attenuating media. Also, greater than 81% velocity dispersion is observed when the dominant propagating wavelength is comparable to the bead size. More surprisingly, on propagation of the broad band input signal a bimodal amplitude spectrum becomes apparent. The low frequency peak is consistent with standard attenuation, whereas the high frequency peak is related to resonance of either the constituent beads or the interbead fluid cavity. Such resonance partitions energy of the main incoming signal. This phenomenon represents a new and fundamental attenuation mechanism that should be considered in many wave-propagation experiments.

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

    PubMed

    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 β11 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 β11(7075)/β11(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

  14. 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.

  15. 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 (α, 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 α and ice thickness was demonstrated, using ice thickness from a novel dynamic/thermodynamic model. A simple expression for α in terms of wave period and ice thickness was derived, for application in research and operational models. The variation of α 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.

  16. FRACTIONAL WAVE EQUATIONS WITH ATTENUATION

    PubMed Central

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

    2013-01-01

    Fractional wave equations with attenuation have been proposed by Caputo [5], Szabo [27], Chen and Holm [7], and Kelly et al. [11]. These equations capture the power-law attenuation with frequency observed in many experimental settings when sound waves travel through inhomogeneous media. In particular, these models are useful for medical ultrasound. This paper develops stochastic solutions and weak solutions to the power law wave equation of Kelly et al. [11]. PMID:25045309

  17. Imaging Rayleigh wave attenuation with USArray

    NASA Astrophysics Data System (ADS)

    Bao, Xueyang; Dalton, Colleen A.; Jin, Ge; Gaherty, James B.; Shen, Yang

    2016-04-01

    The EarthScope USArray provides an opportunity to obtain detailed images of the continental upper mantle at an unprecedented scale. The majority of mantle models derived from USArray data to date contain spatial variations in seismic-wave speed; however, in many cases these data sets do not by themselves allow a non-unique interpretation. 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. The surface-wave amplitudes that constrain upper-mantle attenuation are sensitive to factors in addition to attenuation, including the earthquake source excitation, focusing and defocusing by elastic structure, and local site amplification. Because of the difficulty of isolating attenuation from these other factors, little is known about the attenuation structure of the North American upper mantle. In this study, Rayleigh wave travel time and amplitude in the period range 25-100 s are measured using an interstation cross-correlation technique, which takes advantage of waveform similarity at nearby stations. Several estimates of Rayleigh wave attenuation and site amplification are generated at each period, using different approaches to separate the effects of attenuation and local site amplification on amplitude. It is assumed that focusing and defocusing effects can be described by the Laplacian of the travel-time field. All approaches identify the same large-scale patterns in attenuation, including areas where the attenuation values are likely contaminated by unmodelled focusing and defocusing effects. Regionally averaged attenuation maps are constructed after removal of the contaminated attenuation values, and the variations in intrinsic shear attenuation that are suggested by these Rayleigh wave attenuation maps are explored.

  18. Compressional wave attenuation in oceanic basalts

    NASA Astrophysics Data System (ADS)

    Wepfer, William W.; Christensen, Nikolas I.

    1990-10-01

    To understand better the seismic attenuation in the upper volcanic regions of the oceanic crust, compressional wave attenuations of oceanic basalts have been measured as a function of confining pressure using an ultrasonic pulse-echo spectral ratio technique capable of measuring attenuations to pressures of 500 MPa. Seven basalts, five from Deep Sea Drilling Project cores and two from dredge samples, have wide ranges of densities, porosities, and alterations, making possible an analysis of the parameters influencing basalt attenuation. Attenuation increases with the volume of secondary minerals present and with increasing porosity. Thus vesicularity and compositional changes associated with basalt alteration will produce variations in attenuation. With the application of hydrostatic pressure, cracks close, thereby reducing attenuations. This pressure dependence should be manifested in oceanic layer 2 by decreasing attenuation with depth. An inverse relationship between velocity and attenuation is observed at high hydrostatic pressures. Water saturation increases attenuation at pressures below 200 MPa and enhances the sensitivity of attenuation to pressure, thus making the state of saturation important in the 40 to 100 MPa range generally found in layer 2. These results provide a framework for interpreting marine attenuation data.

  19. Diffraction effects on bulk-wave ultrasonic velocity and attenuation measurements

    PubMed

    Kushibiki; Arakawa

    2000-08-01

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

  20. Compressional head waves in attenuative formations

    SciTech Connect

    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.

  1. Spatial and seasonal variation in wave attenuation over Zostera noltii

    NASA Astrophysics Data System (ADS)

    Paul, M.; Amos, C. L.

    2011-08-01

    Wave attenuation is a recognized function of sea grass ecosystems which is believed to depend on plant characteristics. This paper presents field data on wave attenuance collected over a 13 month period in a Zostera noltii meadow. The meadow showed a strong seasonality with high shoot densities in summer (approximately 4,600 shoots/m2) and low densities in winter (approximately 600 shoots/m2). Wave heights and flow velocities were measured along a transect at regular intervals during which the site was exposed to wind waves and boat wakes that differ in wave period and steepness. This difference was used to investigate whether wave attenuation by sea grass changes with hydrodynamic conditions. A seasonal change in wave attenuation was observed from the data. Results suggest that a minimum shoot density is necessary to initiate wave attenuation by sea grass. Additionally, a dependence of wave attenuation on hydrodynamics was found. Results suggest that the threshold shoot density varies with wave period and a change in energy dissipation toward the shore was observed once this threshold was exceeded. An attempt was made to quantify the bed roughness of the meadow; the applicability of this roughness value in swaying vegetation is discussed. Finally, the drag coefficient for the meadow was computed: A relationship between wave attenuance and vegetation Reynolds number was found which allows comparing the wave attenuating effect of Zostera noltii to other plant species.

  2. Measurement of intrinsic and scattering attenuation of shear waves in two sedimentary basins and comparison to crystalline sites in Germany

    NASA Astrophysics Data System (ADS)

    Eulenfeld, Tom; Wegler, Ulrich

    2016-05-01

    We developed an improved method for the separation of intrinsic and scattering attenuation of seismic shear waves by envelope inversion called Qopen. The method optimizes the fit between Green's functions for the acoustic, isotropic radiative transfer theory and observed energy densities of earthquakes. The inversion allows the determination of scattering and intrinsic attenuation, site corrections and spectral source energies for the investigated frequency bands. Source displacement spectrum and the seismic moment of the analysed events can be estimated from the obtained spectral source energies. We report intrinsic and scattering attenuation coefficients of shear waves near three geothermal reservoirs in Germany for frequencies between 1 and 70 Hz. The geothermal reservoirs are located in Insheim, Landau (both Upper Rhine Graben) and Unterhaching (Molasse basin). We compare these three sedimentary sites to two sites located in crystalline rock with respect to scattering and intrinsic attenuation. The inverse quality factor for intrinsic attenuation is constant in sediments for frequencies smaller than 10 Hz and decreasing for higher frequencies. For crystalline rock, it is on a lower level and strictly monotonic decreasing with frequency. Intrinsic attenuation dominates scattering except for the Upper Rhine Graben, where scattering is dominant for frequencies below 10 Hz. Observed source displacement spectra show a high-frequency fall-off greater than or equal to 3.

  3. Effects of Wave Nonlinearity on Wave Attenuation by Vegetation

    NASA Astrophysics Data System (ADS)

    Wu, W. C.; Cox, D. T.

    2014-12-01

    The need to explore sustainable approaches to maintain coastal ecological systems has been widely recognized for decades and is increasingly important due to global climate change and patterns in coastal population growth. Submerged aquatic vegetation and emergent vegetation in estuaries and shorelines can provide ecosystem services, including wave-energy reduction and erosion control. Idealized models of wave-vegetation interaction often assume rigid, vertically uniform vegetation under the action of waves described by linear wave theory. A physical model experiment was conducted to investigate the effects of wave nonlinearity on the attenuation of random waves propagating through a stand of uniform, emergent vegetation in constant water depth. The experimental conditions spanned a relative water depth from near shallow to near deep water waves (0.45 < kh <1.49) and wave steepness from linear to nonlinear conditions (0.03 < ak < 0.18). The wave height to water depth ratios were in the range 0.12 < Hs/h < 0.34, and the Ursell parameter was in the range 2 < Ur < 68. Frictional losses from the side wall and friction were measured and removed from the wave attenuation in the vegetated cases to isolate the impact of vegetation. The normalized wave height attenuation decay for each case was fit to the decay equation of Dalrymple et al. (1984) to determine the damping factor, which was then used to calculate the bulk drag coefficients CD. This paper shows that the damping factor is dependent on the wave steepness ak across the range of relative water depths from shallow to deep water and that the damping factor can increase by a factor of two when the value of ak approximately doubles. In turn, this causes the drag coefficient CD to decrease on average by 23%. The drag coefficient can be modeled using the Keulegan-Carpenter number using the horizontal orbital wave velocity estimate from linear wave theory as the characteristic velocity scale. Alternatively, the Ursell parameter can be used to parameterize CD to account for the effect of wave nonlinearity, particularly in shallow water, for vegetation of single stem diameter.

  4. Graphene-Based Waveguide Terahertz Wave Attenuator

    NASA Astrophysics Data System (ADS)

    Jian-rong, Hu; Jiu-sheng, Li; Guo-hua, Qiu

    2016-02-01

    We design an electrically controllable terahertz wave attenuator by using graphene. We show that terahertz wave can be confined and propagate on S-shaped graphene waveguide with little radiation losses, and the confined terahertz wave is further manipulated and controlled via external applied voltage bias. The simulated results show that, when chemical potential changes from 0.03 into 0.05 eV, the extinction ratio of the terahertz wave attenuator can be tuned from 1.28 to 39.42 dB. Besides the simplicity, this novel terahertz wave attenuator has advantages of small size (24 × 30 μm2), a low insertion loss, and good controllability. It has a potential application for forthcoming planar terahertz wave integrated circuit fields.

  5. Wave attenuation in thick graphite/epoxy composites

    NASA Technical Reports Server (NTRS)

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

    1992-01-01

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

  6. 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.

  7. 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.

  8. Attenuation of seismic waves in Central Egypt

    NASA Astrophysics Data System (ADS)

    Morsy, Mamdouh Abbas; Abed, Azza M.

    2013-06-01

    Attenuation of seismic waves in central Egypt had never been studied before. The results of the research on the seismic attenuation are based upon the information collected by the seismological network from 1998 to 2011. 855 earthquakes were selected from the Egyptian seismological catalog, with their epicenter distances between 15 and 150 km, their magnitudes ranging from 2 and 4.1 and focal depths reaching up to 30 km. The first systematic study of attenuation derived from the P-, S- and coda wave in the frequency range 1-24 Hz is presented. In the interpretation of the results both single and multiple scattering in a half space are considered. The single scattering model proposed by Sato (1977) was used. Two methods, the coda (Qc) and the Multiple Lapse Time Window (MLTW) method are used. The aim of this study is to validate these interpretations in the region and to try to identify the effects of attenuation due to intrinsic (Qi) and scattering attenuation (Qsc). The mean Qc value calculated was Qc = (39 ± 1)f1.0±0.009. The average Qc at 1.5 Hz is (53 ± 6) and Qc = (900 ± 195) at 24 Hz with Qo ranging between 23 and 107, where η ranging between 0.9 and 1.3. The quality factor (Q) was estimated from spectra of P- and S-waves by applying a spectral ratio technique. The results show variations in Qp and QS as a function of frequency, according to the power law Q = 56η1.1. The seismic albedo is 0.7 at all stations and it mean that the earthquake activity is due to tectonic origin. The attenuation and frequency dependency for different paths and the correlation of the results with the geotectonic of the region are presented. The Qc values were calculated and correlated with the geology and tectonics of the area. The relatively low Qo and the high frequency dependency agree with the values of a region characterized by a low tectonic activity and vise versa.

  9. Sonic well logging tool longitudinal wave attenuator

    SciTech Connect

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

    1989-10-10

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

  10. Guided wave attenuation in coated pipes buried in sand

    NASA Astrophysics Data System (ADS)

    Leinov, Eli; Cawley, Peter; Lowe, Michael J. S.

    2016-02-01

    Long-range guided wave testing (GWT) is routinely used for the monitoring and detection of corrosion defects in above ground pipelines in various industries. The GWT test range in buried, coated pipelines is greatly reduced compared to aboveground pipelines due to energy leakage into the embedding soil. In this study, we aim to increase test ranges for buried pipelines. The effect of pipe coatings on the T(0,1) and L(0,2) guided wave attenuation is investigated using a full-scale experimental apparatus and model predictions. Tests are performed on a fusion-bonded epoxy (FBE)-coated 8" pipe, buried in loose and compacted sand over a frequency range of 10-35 kHz. The application of a low impedance coating is shown to effectively decouple the influence of the sand on the ultrasound leakage from the buried pipe. We demonstrate ultrasonic isolation of a buried pipe by coating the pipe with a Polyethylene (PE)-foam layer that has a smaller impedance than both pipe and sand and the ability to withstand the overburden load from the sand. The measured attenuation in the buried PE-foam-FBE-coated pipe is substantially reduced, in the range of 0.3-1.2 dBm-1 for loose and compacted sand conditions, compared to buried FBE-coated pipe without the PE-foam, where the measured attenuation is in the range of 1.7-4.7 dBm-1. The acoustic properties of the PE-foam are measured independently using ultrasonic interferometry technique and used in model predictions of guided wave propagation in a buried coated pipe. Good agreement is found between the attenuation measurements and model predictions. The attenuation exhibits periodic peaks in the frequency domain corresponding to the through-thickness resonance frequencies of the coating layer. The large reduction in guided wave attenuation for PE-coated pipes would lead to greatly increased GWT test ranges, so such coatings would be attractive for new pipeline installations.

  11. Seismic attenuation: Laboratory measurements in fluid saturated rocks

    NASA Astrophysics Data System (ADS)

    Subramaniyan, Shankar; Madonna, Claudio; Tisato, Nicola; Saenger, Erik; Quintal, Beatriz

    2014-05-01

    Seismic wave attenuation could be used as an indicator of reservoir fluids due to its dependence on rock and fluid properties. Over the past 30 years, many laboratory methodologies to study attenuation in rocks have been employed, such as ultrasonic (MHz), resonant bar (kHz) and forced oscillation methods in the low frequency range (0.01-100Hz) (Tisato & Madonna 2012; Madonna & Tisato 2013). Forced oscillation methods have gained prominence over time as the frequency range of measurements correspond to that of field seismic data acquired for oil/gas exploration. These experiments measure attenuation as the phase shift between the applied stress (sinusoidal) and measured strain. Since the magnitudes of measured phase shifts are quite low (Q-1 ~0.01-0.1) and the amplitudes of strain applied to the rock samples are of the order ~10-6 (i.e., similar orders of magnitude to seismic waves), it is challenging. A comparison of such forced oscillation setups will be presented to provide an overview of the various possibilities of design and implementation for future setups. In general, there is a lack of laboratory data and most of the published data are for sandstones. Currently, attenuation measurements are being carried out on carbonate and sandstone samples. We employ the Seismic Wave Attenuation Module (SWAM, Madonna & Tisato 2013) to measure seismic attenuation in these samples for different saturation degrees (90% and 100% water) and under three different confining pressures (5, 10 and 15MPa). Preliminary results from these investigations will be discussed. REFERENCES Madonna, C. & Tisato, N. 2013: A new seismic wave attenuation module to experimentally measure low-frequency attenuation in extensional mode. Geophysical Prospecting, doi: 10.1111/1365-2478.12015. Tisato, N. & Madonna, C. 2012: Attenuation at low seismic frequencies in partially saturated rocks: Measurements and description of a new apparatus. Journal of Applied Geophysics, 86, 44-53.

  12. A Heterogeneous Nonlinear Attenuating Full-Wave Model of Ultrasound

    PubMed Central

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

    2015-01-01

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

  13. Wave attenuation in the marginal ice zone during LIMEX

    NASA Technical Reports Server (NTRS)

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

    1992-01-01

    The effect of ice cover on ocean-wave attenuation is investigated for waves under flexure in the marginal ice zone (MIZ) with SAR image spectra and the results of models. Directional wavenumber spectra are taken from the SAR image data, and the wave-attenuation rate is evaluated with SAR image spectra and by means of the model by Liu and Mollo-Christensen (1988). Eddy viscosity is described by means of dimensional analysis as a function of ice roughness and wave-induced velocity, and comparisons are made with the remotely sensed data. The model corrects the open-water model by introducing the effects of a continuous ice sheet, and turbulent eddy viscosity is shown to depend on ice thickness, floe sizes, significant wave height, and wave period. SAR and wave-buoy data support the trends described in the model results, and a characteristic rollover is noted in the model and experimental wave-attenuation rates at high wavenumbers.

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

    NASA Astrophysics Data System (ADS)

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

    2006-05-01

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

  15. Wave Dispersion and Attenuation on Human Femur Tissue

    PubMed Central

    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

  16. Damping factor estimation using spin wave attenuation in permalloy film

    SciTech Connect

    Manago, Takashi; Yamanoi, Kazuto; Kasai, Shinya; Mitani, Seiji

    2015-05-07

    Damping factor of a Permalloy (Py) thin film is estimated by using the magnetostatic spin wave propagation. The attenuation lengths are obtained by the dependence of the transmission intensity on the antenna distance, and decrease with increasing magnetic fields. The relationship between the attenuation length, damping factor, and external magnetic field is derived theoretically, and the damping factor was determined to be 0.0063 by fitting the magnetic field dependence of the attenuation length, using the derived equation. The obtained value is in good agreement with the general value of Py. Thus, this estimation method of the damping factor using spin waves attenuation can be useful tool for ferromagnetic thin films.

  17. A poroelastic model for ultrasonic wave attenuation in partially frozen brines

    NASA Astrophysics Data System (ADS)

    Matsushima, Jun; Nibe, Takao; Suzuki, Makoto; Kato, Yoshibumi; Rokugawa, Shuichi

    2011-02-01

    Although there are many possible mechanisms for the intrinsic seismic attenuation in composite materials that include fluids, relative motion between solids and fluids during seismic wave propagation is one of the most important attenuation mechanisms. In our previous study, we conducted ultrasonic wave transmission measurements on an ice-brine coexisting system to examine the influence on ultrasonic waves of the unfrozen brine in the pore microstructure of ice. In order to elucidate the physical mechanism responsible for ultrasonic wave attenuation in the frequency range of 350-600kHz, measured at different temperatures in partially frozen brines, we employed a poroelastic model based on the Biot theory to describe the propagation of ultrasonic waves through partially frozen brines. By assuming that the solid phase is ice and the liquid phase is the unfrozen brine, fluid properties measured by a pulsed nuclear magnetic resonance technique were used to calculate porosities at different temperatures. The computed intrinsic attenuation at 500kHz cannot completely predict the measured attenuation results from the experimental study in an ice-brine coexisting system, which suggests that other attenuation mechanisms such as the squirt-flow mechanism and wave scattering effect should be taken into account.

  18. Scattering and attenuation of seismic waves, Part 3

    SciTech Connect

    Wu, R.S. ); Aki, K. )

    1989-01-01

    The topics covered in this book include: Propagation and attenuation characteristics of the crustal phase, Seismic scattering near the earth's surface, Stratigraphic filtering, The scattering of shear waves in the crust, Unified approach to amplitude attenuation and coda excitation in the randomly inhomogeneous lithosphere, Time-domain solution for multiple scattering and the coda envelopes, Inhomogeneities near the core-mantle boundary evidenced from scattering waves: a review, and Transmission fluctuations across an array and heterogeneities in the crust and upper mantle.

  19. Theoretical study of different attenuation measurement by acoustic microscopy

    NASA Astrophysics Data System (ADS)

    Hamdi, F.; Bouhedja, S.; Amrani, H.

    2013-10-01

    Many works are devoted to study the attenuation of surface waves in media, particularly, leaky surface acoustic waves (LSAW). In this work, a big part of the study is based on the intensity of the output signal, i.e., acoustic signature, V(z). The latter is obtained by the use of quantitative mode of acoustic microscopy in order to measure the velocity and the attenuation of those excited waves at the limit between the specimen and the coupling liquid. Our aim is to compare the attenuation values of the LSAW propagation in porous silicon obtained with three different methods. The first is obtained by resolving Viktorov equation. The second method is the spectral analysis acoustical signature V(z) curves. The third method uses the dark field. The obtained results are in a good agreement with those experiments.

  20. Attenuation of seismic waves by grain boundary relaxation.

    PubMed

    Jackson, D D

    1971-07-01

    Experimental observations of the attenuation of elastic waves in polycrystalline ceramics and rocks reveal an attenuation mechanism, called grain boundary relaxation, which is likely to be predominant cause of seismic attenuation in the earth's mantle. For this mechanism, the internal friction (the reciprocal of the "intrinsic Q" of the material) depends strongly upon frequency and is in good agreement with Walsh's theory of attenuation (J. Geophys. Res., 74, 4333, 1969) in partially melted rock. When Walsh's theory is extended to provide a model of the anelasticity of the earth, using the experimental values of physical parameters reported here, the results are in excellent agreement with seismic observations. PMID:16591937

  1. Field observations and modeling of wave attenuation over colonized beachrocks

    NASA Astrophysics Data System (ADS)

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

    2012-10-01

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

  2. Seismic attenuation due to wave-induced flow

    SciTech Connect

    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.

  3. Attenuation anisotropy and the relative frequency content of split shear waves

    NASA Astrophysics Data System (ADS)

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

    2006-06-01

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

  4. Oceanic wave measurement system

    NASA Technical Reports Server (NTRS)

    Holmes, J. F.; Miles, R. T. (Inventor)

    1980-01-01

    An oceanic wave measured system is disclosed wherein wave height is sensed by a barometer mounted on a buoy. The distance between the trough and crest of a wave is monitored by sequentially detecting positive and negative peaks of the output of the barometer and by combining (adding) each set of two successive half cycle peaks. The timing of this measurement is achieved by detecting the period of a half cycle of wave motion.

  5. Investigation of guided wave propagation and attenuation in pipe buried in sand

    NASA Astrophysics Data System (ADS)

    Leinov, Eli; Lowe, Michael J. S.; Cawley, Peter

    2015-07-01

    Long-range guided wave testing is a well-established method for detection of corrosion defects in pipelines. The method is currently used routinely for above ground pipelines in a variety of industries, e.g. petrochemical and energy. When the method is applied to pipes buried in soil, test ranges tend to be significantly compromised and unpredictable due to attenuation of the guided wave resulting from energy leakage into the embedding soil. The attenuation characteristics of guided wave propagation in an 8 in. pipe buried in sand are investigated using a laboratory full-scale experimental rig and model predictions. We report measurements of attenuation of the T(0,1) and L(0,2) guided wave modes over a range of sand conditions, including loose, compacted, mechanically compacted, water saturated and drained. Attenuation values are found to be in the range of 1.65-5.5 dB/m and 0.98-3.2 dB/m for the torsional and longitudinal modes, respectively, over the frequency of 11-34 kHz. The application of overburden pressure modifies the compaction of the sand and increases the attenuation. Mechanical compaction of the sand yields similar attenuation values to those obtained with applied overburden pressure. The attenuation decreases in the fully water-saturated sand, and increases in drained sand to values comparable with those obtained for compacted sand. Attenuation measurements are compared with Disperse software model predictions and confirm that the attenuation phenomenon in buried pipes is essentially governed by the bulk shear velocity in the sand. The attenuation behaviour 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.

  6. Stochastic solution to a time-fractional attenuated wave equation

    PubMed Central

    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

  7. 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.

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

    USGS Publications Warehouse

    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.

  9. Teleseismic Body-Wave Attenuation beneath the Western and Central United States

    NASA Astrophysics Data System (ADS)

    Yang, B.; Reed, C. A.; Liu, K. H.; Gao, S. S.

    2014-12-01

    Attenuation of seismic waves is the consequence of anelasticity of the Earth's layers along the path of propagation. Joint analyses of seismic velocity with attenuation anomalies can significantly reduce the non-uniqueness in the interpretation of velocity images and result in a better understanding of the Earth's interior structure, composition, and dynamics. Employing a Bayesian approach with a common spectrum simultaneous inversion for attenuation factors (Gao, 1997), we have processed over 14,000 teleseismic body-wave seismograms recorded by all publicly available broadband seismic stations in the western and central United States. Preliminary results show extensive low-attenuation areas beneath the central United States probably related to fragments of the ancient Farallon slab, while less pronounced regions of likely cold material underlie the Colorado Plateau. High-attenuation anomalies are discovered in association with the Snake River Plain and the Rio Grande Rift. We apply station-averaged parameters and P-S attenuation ratios and compare our findings with published shear-wave splitting results to examine the presence of partial melt and asthenospheric upwelling. Additionally, we examine the azimuthal variation of attenuation measurements to constrain the possible existence of attenuation anisotropy and attempt to constrain the source depth of anisotropy through tomographic methods.

  10. Gravitons to photons — Attenuation of gravitational waves

    NASA Astrophysics Data System (ADS)

    Jones, Preston; Singleton, Douglas

    2015-11-01

    In this essay, we examine the response of an Unruh-DeWitt (UD) detector (a quantum two-level system) to a gravitational wave background. The spectrum of the UD detector is of the same form as some scattering processes or three body decays such as muon-electron scattering or muon decay. Based on this similarity, we propose that the UD detector response implies a “decay” or attenuation of gravitons, G, into photons, γ, via G + G → γ + γ or G → γ + γ + G. Over large distances such a decay/attenuation may have consequences in regard to the detection of gravitational waves.

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

    SciTech Connect

    Brodsky, N.S. )

    1990-11-01

    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 pressure was increased to 5, 10 or 15 MPa. For the remaining specimens, pressure was raised to 15 MPa. Waveforms for compressional waves traveling both parallel and perpendicular to the direction of maximum principal stress were measured in the undamaged state, during constant strain-rate tests, and then monitored as functions of time while the specimens were held at pressure. Both wave velocities and amplitudes increased over time at pressure, indicating that cracks closed and perhaps healed. The recovery of ultrasonic wave characteristics depended upon both pressure and damage level. The higher the pressure, the greater the velocity recovery; however, amplitude recovery showed no clear correlation with pressure. For both amplitudes and velocities, recoveries were greatest in the specimens with the least damage. 13 refs., 15 figs., 1 tab.

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

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

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

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

    SciTech Connect

    Price, R.H.; Martin, R.J. III; Haupt, R.W.

    1994-07-01

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

  14. Estimates of millimeter wave attenuation for 18 United States cities

    NASA Astrophysics Data System (ADS)

    Allen, K. C.; Liebe, H. J.; Rush, C. M.

    1983-05-01

    Brief discussions of three mechanisms that attenuate millimeter waves in the atmosphere are presented: rain attenuation, clear air absorption, and atmospheric multipath. Propagation models were combined with meteorological statistics to obtain estimates of average year attenuation distributions for 18 cities in the United States. The estimates are presented in such a way to elucidate the restrictions on system parameters required for reliable operation, i.e. frequency, path length for terrestrial paths, and path elevation angle for earth-satellite paths. The variation imposed by the diverse climates within the United States is demonstrated. Generally, in regions that have humid climates, millimeter wave systems perform less favorably than in areas where arid or semi-arid conditions prevail.

  15. Resonant attenuation of surface acoustic waves by a disordered monolayer of microspheres

    NASA Astrophysics Data System (ADS)

    Eliason, J. K.; Vega-Flick, A.; Hiraiwa, M.; Khanolkar, A.; Gan, T.; Boechler, N.; Fang, N.; Nelson, K. A.; Maznev, A. A.

    2016-02-01

    Attenuation of surface acoustic waves (SAWs) by a disordered monolayer of polystyrene microspheres is investigated. Surface acoustic wave packets are generated by a pair of crossed laser pulses in a glass substrate coated with a thin aluminum film and detected via the diffraction of a probe laser beam. When a 170 μm-wide strip of micron-sized spheres is placed on the substrate between the excitation and detection spots, strong resonant attenuation of SAWs near 240 MHz is observed. The attenuation is caused by the interaction of SAWs with a contact resonance of the microspheres, as confirmed by acoustic dispersion measurements on the microsphere-coated area. Frequency-selective attenuation of SAWs by such a locally resonant metamaterial may lead to reconfigurable SAW devices and sensors, which can be easily manufactured via self-assembly techniques.

  16. Body Wave Crustal Attenuation Characteristics in the Garhwal Himalaya, India

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

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

  17. Attenuation of seismic waves obtained by coda waves analysis in the West Bohemia earthquake swarm region

    NASA Astrophysics Data System (ADS)

    Bachura, Martin; Fischer, Tomas

    2014-05-01

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

  18. 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.

  19. Frequency-dependent Lg-wave attenuation in northern Morocco

    NASA Astrophysics Data System (ADS)

    Noriega, Raquel; Ugalde, Arantza; Villaseñor, Antonio; Harnafi, Mimoun

    2015-11-01

    Frequency-dependent attenuation (Q- 1) in the crust of northern Morocco is estimated from Lg-wave spectral amplitude measurements every quarter octave in the frequency band 0.8 to 8 Hz. This study takes advantage of the improved broadband data coverage in the region provided by the deployment of the IberArray seismic network. Earthquake data consist of 71 crustal events with magnitudes 4 ≤ mb ≤ 5.5 recorded on 110 permanent and temporary seismic stations between January 2008 and December 2013 with hypocentral distances between 100 and 900 km. 1274 high-quality Lg waveforms provide dense path coverage of northern Morocco, crossing a region with a complex structure and heterogeneous tectonic setting as a result of continuous interactions between the African and Eurasian plates. We use two different methods: the coda normalization (CN) analysis, that allows removal of the source and site effects from the Lg spectra, and the spectral amplitude decay (SAD) method, that simultaneously inverts for source, site, and path attenuation terms. The CN and SAD methods return similar results, indicating that the Lg Q models are robust to differences in the methodologies. Larger errors and no significant frequency dependence are observed for frequencies lower than 1.5 Hz. For distances up to 400 km and the frequency band 1.5 ≤ ƒ (Hz) ≤ 4.5, the model functions Q(f) = (529- 22+ 23)(f/1.5)0.23 ± 0.06 and Q(f) = (457- 7+ 7)(f/1.5)0.44 ± 0.02 are obtained using the CN and SAD methods, respectively. A change in the frequency dependence is observed above 4.5 Hz for both methods which may be related to the influence of the Sn energy on the Lg window. The frequency-dependent Q- 1 estimates represent an average attenuation beneath a broad region including the Rif and Tell mountains, the Moroccan and Algerian mesetas, the Atlas Mountains and the Sahara Platform structural domains, and correlate well with areas of moderate seismicity where intermediate Q values have been obtained.

  20. GPR measurements of attenuation in concrete

    SciTech Connect

    Eisenmann, David Margetan, Frank J. Pavel, Brittney

    2015-03-31

    Ground-penetrating radar (GPR) signals from concrete structures are affected by several phenomenon, including: (1) transmission and reflection coefficients at interfaces; (2) the radiation patterns of the antenna(s) being used; and (3) the material properties of concrete and any embedded objects. In this paper we investigate different schemes for determining the electromagnetic (EM) attenuation of concrete from measured signals obtained using commercially-available GPR equipment. We adapt procedures commonly used in ultrasonic inspections where one compares the relative strengths of two or more signals having different travel paths through the material of interest. After correcting for beam spread (i.e., diffraction), interface phenomena, and equipment amplification settings, any remaining signal differences are assumed to be due to attenuation thus allowing the attenuation coefficient (say, in dB of loss per inch of travel) to be estimated. We begin with a brief overview of our approach, and then discuss how diffraction corrections were determined for our two 1.6 GHz GPR antennas. We then present results of attenuation measurements for two types of concrete using both pulse/echo and pitch/catch measurement setups.

  1. Spatial variation of coda wave attenuation in northwestern Colombia

    NASA Astrophysics Data System (ADS)

    Vargas, Carlos A.; Ugalde, Arantza; Pujades, Llus G.; Canas, Jos A.

    2004-08-01

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

  2. Investigating the Influence of Surface-Wave Focusing Effects on Global Attenuation models

    NASA Astrophysics Data System (ADS)

    Bao, X.; Dalton, C. A.

    2012-12-01

    Seismic velocity and attenuation have different and complementary sensitivities to temperature, composition, melt, and volatiles. Jointly interpreting these two data sets should help improve and reduce some of the ambiguity in traditional interpretations of wave speed. However, the development of attenuation models has lagged behind velocity models because seismic-wave amplitudes can be affected by several factors in addition to attenuation, including uncertainties in source excitation and the station response, and focusing and scattering by elastic heterogeneity. In this study, we investigate how the use of different theoretical treatments for the effect of focusing on surface-wave amplitudes influences the retrieved attenuation models. A large data set of multimode Rayleigh wave phase velocity and amplitude is analyzed to establish new global models of surface wave attenuation in the period range 38-376 s from 1461 seismic stations and 12121 earthquakes between 1991 and 2007. The amplitudes due to focusing and defocusing effects are predicted using the great-circle ray theory, exact ray theory (JWKB theory), and finite-frequency theory using relatively smooth phase-velocity maps (spherical-harmonic degree 20) as well as higher-degree maps that contain smaller-scale features. The amplitude data, corrected for focusing effects, are then inverted for global maps of attenuation as well as frequency-dependent source and receiver correction factors. In all cases, the attenuation maps contain robust features that correlate with surface tectonics, including high attenuation along western North America and the East Pacific Rise and other ridge systems and low attenuation associated with stable continental interiors. Differences between the global attenuation maps determined using different methods to predict focusing effects are most significant at longer periods. Approximating surface-wave propagation as a thin ray becomes less accurate at the large wavelengths associated with long periods. We also find that the magnitude of the source and receiver correction factors correlates with tectonic setting, likely because the amplitude measurements are made with respect to synthetic seismograms calculated using the one-dimensional PREM as the reference model instead of a three-dimension reference model.

  3. Asymptotic Law of Attenuation of Overcompressed Detonation Waves in Gases

    NASA Astrophysics Data System (ADS)

    Prokhorov, E. S.

    2013-07-01

    Basic propositions of an isothermal detonation model used for a simplified description of overcompressed detonation waves in gases have been formulated. Within the framework of the present model, the author has derived an asymptotic law of attenuation of plane overcompressed detonation up to the Chapman-Jouguet regime in accordance with which the detonation-front velocity decreases more slowly than was considered to be the case before.

  4. Attenuation of shock waves in copper and stainless steel

    SciTech Connect

    Harvey, W.B.

    1986-06-01

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

  5. Seismic interferometry of scattered surface waves in attenuative media

    NASA Astrophysics Data System (ADS)

    Halliday, David; Curtis, Andrew

    2009-07-01

    Seismic interferometry can be used to estimate interreceiver surface wave signals by cross-correlation of signals recorded at each receiver that are emitted from a surrounding boundary of impulsive or uncorrelated noise sources. We study seismic interferometry for scattered surface waves using a stationary-phase analysis and surface wave Green's functions for isotropic point scatterers embedded in laterally homogeneous media. Our analysis reveals key differences between the interferometric construction of reflected and point-scattered body or surface waves, since point scatterers radiate energy in all directions but a reflection from a finite flat reflector is specular. In the case of surface waves, we find that additional cancelling terms are introduced in the stationary-phase analysis for scattered waves related to the constraint imposed by the optical theorem for surface waves. The additional terms are of second order even for single-scattered waves, and we show that these can be highly significant in multiple-scattering cases. In attenuative media errors are introduced due to amplitude errors in these additional terms. Further, we find that as the distribution of scatterers in a medium becomes more complex the errors in correlation-type interferometry caused by attenuation in the background medium become larger. Convolution-type interferometry has been shown to be effective when considering electromagnetic wavefields in lossy media, and we show that this is also true for scattered surface waves in attenuating elastic media. By adapting our stationary-phase approach to this case, we reveal why convolution-type interferometry performs well in such media: the second-order cancelling terms that appear in the correlation-type approach do not appear in convolution-type interferometry. Finally, we find that when using both correlation- and convolution-type interferometry with realistic source geometries (illustrative of both industrial seismics and `passive noise' interferometry), we cannot necessarily expect to produce estimates with all dominant scattering events present. This is shown to be especially important if, as proposed previously for electromagnetic applications, the convolution and correlation approaches are compared to help identify errors in the interferometric estimates.

  6. P wave attenuation structure below the Tokyo Metropolitan area

    NASA Astrophysics Data System (ADS)

    Panayotopoulos, Y.; Sakai, S.; Nakagawa, S.; Kasahara, K.; Hirata, N.; Aketagawa, T.; Kimura, H.; Lee, C.

    2010-12-01

    The material properties of the complex subduction zone beneath the Tokyo Metropolitan can be estimated by the seismic attenuation Q-1 of seismic waves observed at local seismic stations. The attenuation of seismic waves is represented by the t* attenuation operator that can be estimated by fitting the observed P wave amplitude spectrum to a theoretical spectrum using an ω2 source model. The waveform data used in this study are recorded at the dense seismic array of the Metropolitan Seismic Observation network (MeSO-net). The station network is distributed on five lines with an average spacing of 3 km and in an area with a spacing of 5 km in the central part of Kanto plane. The MeSO-net stations are equipped with a three-component accelerometer at a bottom of a 20-m-deep borehole, signals from which are digitized at a sampling rate of 200 Hz with a dynamic range of 135 dB.The waveforms of 141 earthquakes observed at 226 stations were selected from the Japan Meteorological Agency (JMA) unified earthquake list from January 1st 2010 to August 4th 2010. Only high-quality amplitude spectra of earthquakes with M > 3 were used for the estimation of reliable attenuation parameters. The acceleration waveforms were integrated twice to yield the corresponding displacement vectors, applying a high pass filter to remove the effect of the low-frequency background noise. Taking into account that the majority of the events occurred at depth greater than 30 km a search window of 5 sec starting 1 sec before the P wave arrival was implemented for the creation of the dataset. The t* values were estimated from the amplitude spectra of approximately 33800 P wave waveforms conducting a fast Fourier transform analysis. The Q values for the Tokyo Metropolitan area estimate by this study range from 100 to 500 in the upper 30 km of the crust. A site effect on the attenuation near stations inside a densely populated area is also a possible reason for the large Q variations observed.

  7. Wave Height Attenuation in Heterogeneous Vegetation using Laboratory Observation and Numerical Simulations

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

  8. 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.

  9. Attenuation measurements in solutions of some carbohydrates

    SciTech Connect

    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.

  10. Attenuation Measurements in Solutions of Some Carbohydrates

    SciTech Connect

    Gagandeep; Singh, Kulwant; Lark, B.S.; Sahota, H.S.

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

  12. Numerical simulation of attenuation and group velocity of guided ultrasonic wave in grouted rock bolts

    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.

  13. Surface Wave Constraints on Q in the Upper Mantle: Isolating the Signal of Attenuation

    NASA Astrophysics Data System (ADS)

    Dalton, C.; Ekström, G.

    2003-12-01

    We use more than 60,000 surface wave amplitude measurements in the period range 150-300 seconds (Ekström et al., 1997) to construct maps of attenuation, or 1/Q, in the upper mantle. We initially calculate Q by constructing a datum that uses four consecutive wave trains to desensitize the amplitudes to effects from the source, instrument, and elastic structure. These Q measurements are inverted for maps of even-degree attenuation structure, and the results show variations of approximately 50% from PREM. When the Q measurements are averaged for nearly coincident great-circle paths, the resulting attenuation maps are nearly identical to the original ones, confirming that, despite extraneous effects, there is a robust signal in the amplitudes. Using the method of Selby and Woodhouse (2002), we invert minor- and major-arc Rayleigh and Love wave amplitudes for even- and odd-degree Q structure. When we assume that the amplitude anomaly is due entirely to intrinsic attenuation, the ability of the models obtained through this process to fit the data is poor. We next include terms in the inversion that allow the source moment and instrument gain to be corrected. These corrections greatly improve the fit of the data by the models. The path integral approximation to the amplitude anomaly (Woodhouse and Wong, 1986) is used both to predict the effect of focusing from existing phase velocity maps and to jointly invert for attenuation and phase velocity. We also perform a pure-path regionalized inversion using a six-tectonic-region model of the Earth, GTR1 (Jordan, 1981). On the most simplistic level, the results show that oceans are more strongly attenuating than continents at all periods, and that the surface wave attenuation values of PREM fall in between those of continents and oceans. The results using the great-circle Q measurements show many familiar patterns, in particular that young oceans are more highly attenuating than older oceans. Although the data set of minor- and major-arc amplitudes is somewhat noisy, its ability to match the results of the great-circle Q regionalization is a good measure of the usefulness of the amplitude corrections described above.

  14. Anelastic Attenuation and Elastic Scattering of Seismic Waves in the Los Angeles Region

    NASA Astrophysics Data System (ADS)

    Song, X.; Jordan, T. H.

    2013-12-01

    The accuracy of earthquake simulations needed for physics-based seismic hazard analysis depends on good information about crustal structure. For low-frequency (f < 0.3 Hz) simulations, the most important structural parameters are the seismic wave velocities, but as the frequencies increase, seismic wave attenuation becomes more important. We compare attenuation models that have been recently used in the CyberShake hazard model (Graves et al., 2011) and other simulation studies for the Los Angeles region (Olsen et al., 2009; Taborda & Bielak, 2013) with constraints from local earthquake data out to 10 Hz, which include those from Hauksson & Shearer's (2006) attenuation tomography as well as our own measurements. We show that the velocity-attenuation scaling relationship for shear waves employed by CyberShake (QS = 50VS, where VS is in km/s) provides a good approximation to the average crustal structure at f = 0.3 Hz, but it does not capture the lateral variations in QS at shallow depths. Moreover, this frequency-independent model is inconsistent with the high QS values observed throughout most of the crust at f > 1 Hz. The data indicate a frequency-dependent attenuation of the form QS ~ f γ, where 0.5 ≤ γ ≤ 0.8. Anomalously low QS factors are observed at very shallow depths, which can be explained by a combination of anelastic attenuation and elastic scattering. The scattering parameters are roughly consistent with small-scale, near-surface heterogeneities observed in well-logs and seismic reflection surveys in the Los Angeles basin. High-frequency scattering may also play a role in explaining Hauksson & Shearer's (2006) observation that the QP/QS ratio is anomalously low (~ unity). We summarize the observations in a new attenuation and scattering model for the CyberShake region that is laterally heterogeneous and frequency dependent.

  15. Amplitude-frequency dependencies of wave attenuation in single-crystal quartz: Experimental study

    NASA Astrophysics Data System (ADS)

    Mashinskii, E. I.

    2008-11-01

    The experiments have been conducted to investigate the effect of strain amplitude and frequency on the compressional and shear wave attenuation in quartz samples of three types: the intact quartz, fractured quartz, and smoky quartz. The measurements were performed using the reflection method on a pulse frequency of 1 MHz with changing strain in the range 0.3 ≤ ɛ ≤ 2.0 μstrain under a confining pressure of 10 MPa and at ambient temperature. The essential difference in amplitude-frequency characteristics of wave attenuation in three quartz types has been detected. The intact quartz shows the more "simple" behavior in comparison with the fractured and smoky quartz. The attenuation (the inverse quality factor Q) depends on strain amplitude as Q-1(ɛ) ˜ ɛ-n, where n ≅ 0.005-0.085, with the greatest decrease in the smoky and fractured quartz reaching of about 15%. Relaxation spectra of attenuation are presented in the frequency range from 0.4 to 1.4 MHz. The dependence Qp-1(f) ˜ f-1.2 characterizes the intact and fractured quartz, whereas the smoky quartz has the relaxation peak. The dependence Qs-1(f) ˜ f-0.84 presents S wave relaxation spectrum in the intact quartz; in the fractured and smoky quartz, the attenuation peaks take place. The strain amplitude variation exerts influence on the relaxation strength, the peak frequency, and the width of the relaxation peak. Such behavior of attenuation can be explained by a joint action of viscoelastic and microplastic mechanisms. These results can be considered as a contribution for providing the experimental background to the theory of attenuation in rocks. They can also be used in solving applied problems in material science, seismic prospecting, etc.

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

    NASA Technical Reports Server (NTRS)

    Jackson, D. D.

    1971-01-01

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

  17. Influence of reef geometry on wave attenuation on a Brazilian coral reef

    NASA Astrophysics Data System (ADS)

    Costa, Mirella B. S. F.; Araújo, Moacyr; Araújo, Tereza C. M.; Siegle, Eduardo

    2016-01-01

    This study presents data from field experiments that focus on the influence of coral reef geometry on wave transformation in the Metropolitan Area of Recife (MAR) on the northeast coast of Brazil. First, a detailed bathymetric survey was conducted, revealing a submerged reef bank, measuring 18 km long by 1 km wide, parallel to the coastline with a quasi-horizontal top that varies from 0.5 m to 4 m in depth at low tide. Cluster similarity between 180 reef profiles indicates that in 75% of the area, the reef geometry has a configuration similar to a platform reef, whereas in 25% of the area it resembles a fringing reef. Measurements of wave pressure fluctuations were made at two stations (experiments E1 and E2) across the reef profile. The results indicate that wave height was tidally modulated at both experimental sites. Up to 67% (E1) and 99.9% (E2) of the incident wave height is attenuated by the reef top at low tide. This tidal modulation is most apparent at E2 due to reef geometry. At this location, the reef top is only approximately 0.5 m deep during mean low spring water, and almost all incident waves break on the outer reef edge. At E1, the reef top depth is 4 m, and waves with height ratios smaller than the critical breaking limit are free to pass onto the reef and are primarily attenuated by bottom friction. These results highlight the importance of reef geometry in controlling wave characteristics of the MAR beaches and demonstrate its effect on the morphology of the adjacent coast. Implications of differences in wave attenuation and the level of protection provided by the reefs to the adjacent shoreline are discussed.

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

    NASA Astrophysics Data System (ADS)

    Marsooli, Reza; Wu, Weiming

    2014-12-01

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

  19. 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.

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

    SciTech Connect

    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

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

    NASA Astrophysics Data System (ADS)

    Ma, Z.; Masters, G.

    2011-12-01

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

  2. Seismic-wave attenuation associated with crustal faults in the New Madrid seismic zone

    USGS Publications Warehouse

    Hamilton, R.M.; Mooney, W.D.

    1990-01-01

    The attenuation of upper crustal seismic waves that are refracted with a velocity of about 6 kilometers per second varies greatly among profiles in the area of the New Madrid seismic zone in the central Mississippi Valley. The waves that have the strongest attenuation pass through the seismic trend along the axis of the Reelfoot rift in the area of the Blytheville arch. Defocusing of the waves in a low-velocity zone and/ or seismic scattering and absorption could cause the attenuation; these effects are most likely associated with the highly deformed rocks along the arch. Consequently, strong seismic-wave attenuation may be a useful criterion for identifying seismogenic fault zones.

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

    NASA Astrophysics Data System (ADS)

    Sleep, Norman H.; Erickson, Brittany A.

    2014-04-01

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

  4. Elimination of bandwidth effect in attenuation measurement with picosecond ultrasonics

    NASA Astrophysics Data System (ADS)

    Maehara, Atsushi; Nakamura, Nobutomo; Ogi, Hirotsugu; Hirao, Masahiko

    2014-08-01

    We study the broadening effect of probing pulse light on the apparent attenuation of the Brillouin oscillation measured with picosecond ultrasonics. We observe experimentally that the attenuation of the Brillouin oscillation is sensitive to the bandwidth, and the apparent attenuation coefficient increases as the bandwidth increases, being far from the intrinsic attenuation coefficient. Theoretical calculation is performed to reconstruct the observed oscillations, and it is confirmed that there are several factors affecting the apparent attenuation in addition to the bandwidth. We finally propose equations that deduce the contribution of the broadening to the apparent attenuation of the Brillouin oscillation.

  5. Wave Velocity Attenuation and Sediment Retention among Different Vegetation Types in a Pacific Northwest Estuary

    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.

  6. ATTENUATION OF REFLECTED WAVES IN MAN DURING RETROGRADE PROPAGATION FROM FEMORAL ARTERY TO PROXIMAL AORTA

    PubMed Central

    Baksi, A John; Davies, Justin E; Hadjiloizou, Nearchos; Baruah, Resham; Unsworth, Beth; Foale, Rodney A; Korolkova, Olga; Siggers, Jennifer H; Francis, Darrel P; Mayet, Jamil; Parker, Kim H; Hughes, Alun D

    2015-01-01

    Background Wave reflection may be an important influence on blood pressure, but the extent to which reflections undergo attenuation during retrograde propagation has not been studied. We quantified retrograde transmission of a reflected wave created by occlusion of the left femoral artery in man. Methods 20 subjects (age 31-83 y; 14 male) underwent invasive measurement of pressure and flow velocity with a sensor-tipped intra-arterial wire at multiple locations distal to the proximal aorta before, during and following occlusion of the left femoral artery by thigh cuff inflation. A numerical model of the circulation was also used to predict reflected wave transmission. Wave reflection was measured as the ratio of backward to forward wave energy (WRI) and the ratio of peak backward to forward pressure (Pb/Pf). Results Cuff inflation caused a marked reflection which was largest 5-10cm from the cuff (change (Δ) in WRI = 0.50 (95% CI 0.38, 0.62); p<0.001, ΔPb/Pf = 0.23 (0.18 - 0.29); p<0.001). The magnitude of the cuff-induced reflection decreased progressively at more proximal locations and was barely discernible at sites >40cm from the cuff including in the proximal aorta. Numerical modelling gave similar predictions to those observed experimentally. Conclusions Reflections due to femoral artery occlusion are markedly attenuated by the time they reach the proximal aorta. This is due to impedance mismatches of bifurcations traversed in the backward direction. This degree of attenuation is inconsistent with the idea of a large discrete reflected wave arising from the lower limb and propagating back into the aorta. PMID:26436672

  7. P-wave attenuation tomography of Mount St. Helens: preliminary results from coda-normalized spectra

    NASA Astrophysics Data System (ADS)

    de Siena, L.; Hicks, S.; Waite, G. P.; Moran, S. C.

    2010-12-01

    The P-wave velocity structure of Mount St. Helens has been recently imaged with local earthquake tomography, using the data recorded since its eruption in 1980. Part of this dataset has been processed to obtain a preliminary frequency dependent Qp image of the crust below the volcanic cone. We extended the so-called coda-normalization method, usually applied to S-waves, to the measurement of path-dependent P-wave attenuation. A scattering model has been developed in order to select the best time-window to measure the P-wave spectral amplitude on each trace. The objective is to average the effect of the source radiation pattern with the properties of early coda. The weighting matrix in the final inversion is dependent on the source radiation pattern and the spectral amplitude of noise. The Discrete Picard Condition and the Discrepancy Principle have been applied to investigate the maximum resolution available in each part of the medium. Truncated Singular Value Decomposition as well as Zeroth-, first- and second-order Tikhonov regularization techniques have been investigated by using the multi-resolution inversion code (MuReATA). The interpretation of the preliminary results is carried out by using cluster analysis on velocity and attenuation measurements.

  8. Seismic‐wave attenuation determined from tectonic tremor in multiple subduction zones

    USGS Publications Warehouse

    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.

  9. Propagation and attenuation of P-waves in patchy saturated porous media

    NASA Astrophysics Data System (ADS)

    Zhang, Hui-Xing; He, Bing-Shou

    2015-09-01

    We establish a patchy saturation model and derive the seismic wave equations for patchy saturated porous media on the basis of Biot's equations and Johnson's bulk modulus. We solve the equations, obtain the attenuation coefficients, and analyze the characteristics of wave attenuation in the seismic frequency range. The results suggest that seismic waves show attenuation and dispersion in partially saturated rocks in the low frequency range. With frequency increasing, attenuation increases. The attenuation of P-waves of the second kind is more pronounced in agreement with Biot's theory. We also study the effect of porosity, saturation, and inner sphere radius on the attenuation of the P-waves of the first kind and find that attenuation increases with increasing frequency and porosity, and decreases with increasing frequency and degree of saturation. As for the inner sphere radius, wave attenuation is initially increasing with increasing frequency and inner sphere radius less than half the outer radius. Subsequently, wave attenuation decreases with increasing frequency and inner sphere radius is higher than half the outer sphere radius.

  10. Surface wave tomography with USArray based on phase front tracking and amplitude mapping: isotropic, anisotropic, and intrinsic attenuation structures

    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.

  11. Imaging the attenuation structure beneath the northwestern margin of Colorado Plateau: Integrating seismic body-wave observations and forward modeling

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

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

    NASA Astrophysics Data System (ADS)

    Zhao, Liang; Xue, Mei

    2015-04-01

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

  13. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

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

  15. 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.

  16. 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 areasJamnagar 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(0.990.04) (lapse time : 20 s), Q c = (170 4.4)f(0.970.02) (lapse time : 30 s) and Q c = (229 6.6)f(0.940.03) (lapse time : 40 s) and for the Jamnagar area are: Q c = (178 3)f(0.950.05) (lapse time : 20 s), Q c = (224 6)f(0.980.06) (lapse time : 30 s) and Q c = (282 7)f(0.910.03) (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.

  17. Apparent Attenuation and Dispersion Arising in Seismic Body-Wave Velocity Retrieval

    NASA Astrophysics Data System (ADS)

    Wirgin, Armand

    2016-04-01

    The fact that seismologists often make measurements, using natural seismic solicitations, of properties of the Earth on rather large scales (laterally and in terms of depth) has led to interrogations as to whether attenuation of body waves is dispersive and even significant. The present study, whose aim is to clarify these complicated issues, via a controlled thought measurement, concerns the retrieval of a single, real body wave velocity of a simple geophysical configuration (involving two homogeneous, isotropic, non-dissipative media, one occupying the layer, the other the substratum), from its simulated response to pulsed plane wave probe radiation. This inverse problem is solved, at all frequencies within the bandwidth of the pulse. Due to discordance between the models associated with the assumed and trial responses, the imaginary part of the retrieved velocity turns out to be non-nil even when both the layer and substratum are non-lossy, and, in fact, to be all the greater, the larger is the discordance. The reason for this cannot be due to intrinsic attenuation, scattering, or geometrical spreading since these phenomena are absent in the chosen thought experiment, but rather to uncertainty in the measurement model.

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

    PubMed

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

    2012-11-01

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

  19. Subduction zone guided waves: 3D modelling and attenuation effects

    NASA Astrophysics Data System (ADS)

    Garth, T.; Rietbrock, A.

    2013-12-01

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

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

    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.

  1. Numerical and Experimental Investigation on the Attenuation of Electromagnetic Waves in Unmagnetized Plasmas Using Inductively Coupled Plasma Actuator

    NASA Astrophysics Data System (ADS)

    Lin, Min; Xu, Haojun; Wei, Xiaolong; Liang, Hua; Song, Huimin; Sun, Quan; Zhang, Yanhua

    2015-10-01

    The attenuation of electromagnetic (EM) waves in unmagnetized plasma generated by an inductively coupled plasma (ICP) actuator has been investigated both theoretically and experimentally. A numerical study is conducted to investigate the propagation of EM waves in multilayer plasma structures which cover a square flat plate. Experimentally, an ICP actuator with dimensions of 20 cm×20 cm×4 cm is designed to produce a steady plasma slab. The attenuation of EM waves in the plasma generated by the ICP actuator is measured by a reflectivity arch test method at incident waves of 2.3 GHz and 10.1 GHz, respectively. A contrastive analysis of calculated and measured results of these incident wave frequencies is presented, which suggests that the experiment accords well with our theory. As expected, the plasma slab generated by the ICP actuator can effectively attenuate the EM waves, which may have great potential application prospects in aircraft stealth. supported by National Natural Science Foundation of China (Nos. 51276197, 11472306 and 11402301)

  2. Time-reverse modelling of acoustic wave propagation in attenuating media

    NASA Astrophysics Data System (ADS)

    Zhu, Tieyuan

    2014-04-01

    Time-reverse modelling (TRM) of acoustic wave propagation has been widely implemented in seismic migration and time-reversal source imaging. The basic assumption of this modelling is that the wave equation is time-invariant in non-attenuating media. In the Earth, attenuation often invalidates this assumption of time-invariance. To overcome this problem, I propose a TRM approach that compensates for attenuation and dispersion effects during the wave propagation in attenuating media. This approach is based on a viscoacoustic wave equation which explicitly separates attenuation and dispersion following a constant-Q model. Compensating for attenuation and dispersion during TRM is achieved by reversing the sign of the attenuation operator coefficient while leaving the counterpart dispersion parameter unchanged in this viscoacoustic wave equation. A low-pass filter is included to avoid amplifying high-frequency noise during TRM. I demonstrate the effects of the filter on the attenuation and the phase velocity by comparing with theoretical solutions in a 1-D Pierre shale homogeneous medium. Three synthetic examples are used to demonstrate the feasibility of attenuation compensation during TRM. The first example uses a 1-D homogeneous model to demonstrate the accuracy of the numerical implementation of the methodology. The second example shows the applicability of source location using a 2-D layering model. The last example uses a 2-D cross-well synthetic experiment to show that the methodology can also be implemented in conjunction with reverse-time migration to image subsurface reflectors. When attenuation compensation is included, I find improved estimation of the source location, the excitation timing of the point source, the magnitude of the focused source wavelet and the reflectivity image of reflectors, particularly for deep structures underneath strongly attenuating zones.

  3. Seismic-wave attenuation associated with crustal faults in the new madrid seismic zone.

    PubMed

    Hamilton, R M; Mooney, W D

    1990-04-20

    The attenuation of upper crustal seismic waves that are refracted with a velocity of about 6 kilometers per second varies greatly among profiles in the area of the New Madrid seismic zone in the central Mississippi Valley. The waves that have the strongest attenuation pass through the seismic trend along the axis of the Reelfoot rift in the area of the Blytheville arch. Defocusing of the waves in a low-velocity zone and/or seismic scattering and absorption could cause the attenuation; these effects are most likely associated with the highly deformed rocks along the arch. Consequently, strong seismic-wave attenuation may be a useful criterion for identifying seismogenic fault zones. PMID:17784489

  4. Interlaboratory Comparison Of Multimode Optical Fiber Attenuation Measurement

    NASA Astrophysics Data System (ADS)

    Luo, Li; Tongcun, Jiang; Ling, Luo; Shao, Yang

    1985-11-01

    Experiments show that optical fiber attenuation measurement systems used by many laboratories in China meet the requirements of standard measurement methods recommended by the International Telegraph and Telephone Consultative Committee (CCITT) and the International Electrotechnical Commission (IEC). A simplified, practical criterion for checking equilibrium mode distribution (EMD) has been obtained. Round-robin results show good agreement of attenuation measurement for six Chinese laboratories using this criterion.

  5. 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 η. 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 η spatial variation map show that intermediate η values characterize most of the analyzed region.

  6. BROADBAND ATTENUATION MEASUREMENTS OF PHOSPHOLIPID-SHELLED ULTRASOUND CONTRAST AGENTS

    PubMed Central

    Raymond, Jason L.; Haworth, Kevin J.; Bader, Kenneth B.; Radhakrishnan, Kirthi; Griffin, Joseph K.; Huang, Shao-Ling; McPherson, David D.; Holland, Christy K.

    2014-01-01

    The aim of this study was to characterize the frequency-dependent acoustic attenuation of three phospholipid-shelled ultrasound contrast agents (UCAs): Definity, MicroMarker and echogenic liposomes. A broadband through-transmission technique allowed for measurement over 2 to 25 MHz with a single pair of transducers. Viscoelastic shell parameters of the UCAs were estimated using a linearized model developed by N. de Jong, L. Hoff, T. Skotland and N. Bom (Ultrasonics 1992; 30:95–103). The effect of diluent on the attenuation of these UCA suspensions was evaluated by performing attenuation measurements in 0.5% (w/v) bovine serum albumin and whole blood. Changes in attenuation and shell parameters of the UCAs were investigated at room temperature (25°C) and physiologic temperature (37°C). The attenuation of the UCAs diluted in 0.5% (w/v) bovine serum albumin was found to be identical to the attenuation of UCAs in whole blood. For each UCA, attenuation was higher at 37°C than at 25°C, underscoring the importance of conducting characterization studies at physiologic temperature. Echogenic liposomes exhibited a larger increase in attenuation at 37°C versus 25°C than either Definity or MicroMarker. PMID:24262056

  7. 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.

  8. Determination of particle size distributions from acoustic wave propagation measurements

    SciTech Connect

    Spelt, P.D.; Norato, M.A.; Sangani, A.S.; Tavlarides, L.L.

    1999-05-01

    The wave equations for the interior and exterior of the particles are ensemble averaged and combined with an analysis by Allegra and Hawley [J. Acoust. Soc. Am. {bold 51}, 1545 (1972)] for the interaction of a single particle with the incident wave to determine the phase speed and attenuation of sound waves propagating through dilute slurries. The theory is shown to compare very well with the measured attenuation. The inverse problem, i.e., the problem of determining the particle size distribution given the attenuation as a function of frequency, is examined using regularization techniques that have been successful for bubbly liquids. It is shown that, unlike the bubbly liquids, the success of solving the inverse problem is limited since it depends strongly on the nature of particles and the frequency range used in inverse calculations. {copyright} {ital 1999 American Institute of Physics.}

  9. A direct measurement of skull attenuation for quantitative SPECT

    SciTech Connect

    Turkington, T.G.; Gilland, D.R.; Jaszczak, R.J.; Greer, K.L.; Coleman, R.E. . Dept. of Radiology); Smith, M.F. . Dept. of Biomedical Engineering)

    1993-08-01

    The attenuation of 140 keV photons was measured in three empty skulls by placing a [sup 99m]Tc line source inside each one and acquiring projection data. These projections were compared to projections of the line source alone to determine the transmission through each point in the skull surrounding the line source. The effective skull thickness was calculated for each point using an assumed dense bone attenuation coefficient. The relative attenuation for this thickness of bone was compared to that of an equivalent amount of soft tissue to evaluate the increased attenuation of photons in brain SPECT relative to a uniform soft tissue approximation. For the skull regions surrounding most of the brain, the effective bone thickness varied considerably, but was generally less than 6 mm, resulting in a relative attenuation increases of less than 6%.

  10. 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.

  11. Differential shear wave attenuation and its lateral variation in the North Atlantic region

    NASA Technical Reports Server (NTRS)

    Sheehan, Anne F.; Solomon, Sean C.

    1992-01-01

    A digital data base of over 150 seismograms and a spectral radio technique are used to measure SS-S differential attenuation in the North Atlantic region. Differential attenuation is positively correlated with SS-S travel time residual, and both differential attentuation and travel time residual decrease with increasing seafloor age. Models are developed for seismic Q in which lateral variations include contributions from the asthenospheric low-Q zone as well as from lithospheric cooling. The Q models obtained under this assumption are in good agreement with those obtained from surface wave studies and are therefore preferred over those models with lateral variations confined to the upper 125 km. Systematic long-wavelength (1000-7000 km) variations in differential attenuation, corrected for seafloor age, are evident along the axis of the Mid-Atlantic Ridge. These variations can be qualitatively correlated with long-wavelength variations in SS-S differential travel time residuals and are attributed to along-axis differences in upper mantle temperature.

  12. Attenuation of high-frequency body waves in the crust of the Central External Dinarides

    NASA Astrophysics Data System (ADS)

    Dasović, Iva; Ruščić, 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), Morići (MORI), Kijevo (KIJV), Čačvina (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.

  13. ORNL system for measurement of telephone-line attenuation

    SciTech Connect

    Rochelle, R.W.; Williams, I.E.

    1988-06-01

    The purpose of modifying the TS-100 Automated Tempest Test System software was to use the equipment for making radio-frequency attenuation measurements between an input port and an output port of a telephone network. One set of tests was performed to simulate the electromagnetic radiation from a secure computer terminal and its coupling to telephone lines within a building. Another set of tests was conducted to determine the procedures for measuring attenuation on telephone lines between buildings that are all within the secure zone. The measurements indicate that attenuation between the terminal and the telephone is a function of many variables; however, attenuation in the cable between the buildings is proportional to the length of the cable between the buildings. 1 ref., 2 figs.

  14. 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.

  15. Effects of Pressure on Attenuation of Seismic Waves Through Sedimentary Rocks

    NASA Astrophysics Data System (ADS)

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

    2009-05-01

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

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

    USGS Publications Warehouse

    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

  17. Seismic tomography of compressional wave attenuation structure for Kı¯lauea Volcano, Hawai`i

    NASA Astrophysics Data System (ADS)

    Lin, Guoqing; Shearer, Peter M.; Amelung, Falk; Okubo, Paul G.

    2015-04-01

    We present a frequency-independent three-dimensional (3-D) compressional wave attenuation model (indicated by the reciprocal of quality factor Qp) for Kı¯lauea Volcano in Hawai`i. We apply the simul2000 tomographic algorithm to the attenuation operator t* values for the inversion of Qp perturbations through a recent 3-D seismic velocity model and earthquake location catalog. The t* values are measured from amplitude spectra of 26708 P wave arrivals of 1036 events recorded by 61 seismic stations at the Hawaiian Volcanology Observatory. The 3-D Qp model has a uniform horizontal grid spacing of 3 km, and the vertical node intervals range between 2 and 10 km down to 35 km depth. In general, the resolved Qp values increase with depth, and there is a correlation between seismic activity and low-Qp values. The area beneath the summit caldera is dominated by low-Qp anomalies throughout the entire resolved depth range. The Southwest Rift Zone and the East Rift Zone exhibit very high Qp values at about 9 km depth, whereas the shallow depths are characterized with low-Qp anomalies comparable with those in the summit area. The seismic zones and fault systems generally display relatively high Qp values relative to the summit. The newly developed Qp model provides an important complement to the existing velocity models for exploring the magmatic system and evaluating and interpreting intrinsic physical properties of the rocks in the study area.

  18. Reflective attenuator for high-energy laser measurements

    SciTech Connect

    Lehman, John H.; Livigni, David; Li Xiaoyu; Cromer, Christopher L.; Dowell, Marla L

    2008-06-20

    A high-energy laser attenuator in the range of 250 mJ (20 ns pulse width, 10 Hz repetition rate, 1064 nm wavelength) is described. The optical elements that constitute the attenuator are mirrors with relatively low reflectance, oriented at a 45 deg. angle of incidence. By combining three pairs of mirrors, the incoming radiation is collinear and has the same polarization orientation as the exit. We present damage testing and polarization-dependent reflectance measurements for 1064 nm laser light at 45 deg. angle of incidence for molybdenum, silicon carbide, and copper mirrors. A six element, 74 times (18 dB) attenuator is presented as an example.

  19. Ultrasonic attenuation measurements determine onset, degree, and completion of recrystallization

    NASA Technical Reports Server (NTRS)

    Generazio, E. R.

    1988-01-01

    Ultrasonic attenuation was measured for cold worked Nickel 200 samples annealed at increasing temperatures. Localized dislocation density variations, crystalline order and volume percent of recrystallized phase were determined over the anneal temperature range using transmission electron microscopy, X-ray diffraction, and metallurgy. The exponent of the frequency dependence of the attenuation was found to be a key variable relating ultrasonic attenuation to the thermal kinetics of the recrystallization process. Identification of this key variable allows for the ultrasonic determination of onset, degree, and completion of recrystallization.

  20. Mid frequency shallow water fine-grained sediment attenuation measurements.

    PubMed

    Holland, Charles W; Dosso, Stan E

    2013-07-01

    Attenuation is perhaps the most difficult sediment acoustic property to measure, but arguably one of the most important for predicting passive and active sonar performance. Measurement techniques can be separated into "direct" measurements (e.g., via sediment probes, sediment cores, and laboratory studies on "ideal" sediments) which are typically at high frequencies, O(10(4)-10(5)) Hz, and "indirect" measurements where attenuation is inferred from long-range propagation or reflection data, generally O(10(2)-10(3)) Hz. A frequency gap in measurements exists in the 600-4000 Hz band and also a general acknowledgement that much of the historical measurements on fine-grained sediments have been biased due to a non-negligible silt and sand component. A shallow water measurement technique using long range reverberation is critically explored. An approximate solution derived using energy flux theory shows that the reverberation is very sensitive to depth-integrated attenuation in a fine-grained sediment layer and separable from most other unknown geoacoustic parameters. Simulation using Bayesian methods confirms the theory. Reverberation measurements across a 10 m fine-grained sediment layer yield an attenuation of 0.009 dB/m/kHz with 95% confidence bounds of 0.006-0.013 dB/m/kHz. This is among the lowest values for sediment attenuation reported in shallow water. PMID:23862792

  1. 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.

  2. Spatial variation of coda-wave attenuation in north-western Colombia

    NASA Astrophysics Data System (ADS)

    Vargas, C. A.; Ugalde, A.; Pujades, L. G.; Canas, J. A.

    2003-04-01

    Seismic wave attenuation in Colombia has been studied using coda waves. Waveform data used were selected from 1200 regional earthquakes occurred between December, 1992 and June, 1999 which were recorded by 17 three-component short-period seismic stations of the Colombian National Seismological Network. Local magnitudes ranged from 2.9 to 6.0 and focal depths were less than 296 km. Two methods were used to estimate coda wave attenuation: 1/Qc was obtained using the single scattering theory and the contribution of intrinsic absorption (1/Qi) and scattering (1/Qs) to total attenuation (1/Qt) was estimated by means of a Multiple Lapse Time Window Analysis method based on the hypothesis of isotropic scattering with uniform distribution of scatterers. The frequencies of interest laid between 1 and 19 Hz. A regionalization of the estimated Q values was also performed by means of a generalized inversion technique. Results show significant spatial variations of attenuation which are related to different geological and tectonic characteristics. A contour map of seismic attenuation in Colombia is presented, where at least seven sub-regions with different attenuation properties are shown. A correlation of seismic attenuation with other geophysical parameters as geothermic gradient and gravimetric anomalies has also been observed.

  3. Two-dimensional global Rayleigh wave attenuation model by accounting for finite-frequency focusing and defocusing effect

    NASA Astrophysics Data System (ADS)

    Ma, Zhitu; Masters, Guy; Mancinelli, Nicholas

    2016-01-01

    In this study, we obtain a set of 2-D global phase velocity and attenuation maps for Rayleigh waves between 5 and 25 mHz. Correcting the effect of focusing-defocusing is crucial in order to obtain reliable attenuation structure. Great circle linearized ray theory, which has been used to date, can give useful predictions of this effect if careful attention is paid to how the phase velocity model is smoothed. In contrast, predictions based on the 2-D finite-frequency kernels are quite robust in this frequency range and suggest that they are better suited as a basis for inversion. We use a large data set of Rayleigh wave phase and amplitude measurements to invert for the phase velocity, attenuation, source and receiver terms simultaneously. Our models provide 60-70 per cent variance reduction to the raw data though the source terms are the biggest contribution to the fit of the data. The attenuation maps show structures that correlate well with surface tectonics and the age progression trend of the attenuation is clearly seen in the ocean basins. We have also identified problematic stations and earthquake sources as a by-product of our data selection process.

  4. 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...

  5. Rain attenuation measurements: Variability and data quality assessment

    NASA Technical Reports Server (NTRS)

    Crane, Robert K.

    1989-01-01

    Year to year variations in the cumulative distributions of rain rate or rain attenuation are evident in any of the published measurements for a single propagation path that span a period of several years of observation. These variations must be described by models for the prediction of rain attenuation statistics. Now that a large measurement data base has been assembled by the International Radio Consultative Committee, the information needed to assess variability is available. On the basis of 252 sample cumulative distribution functions for the occurrence of attenuation by rain, the expected year to year variation in attenuation at a fixed probability level in the 0.1 to 0.001 percent of a year range is estimated to be 27 percent. The expected deviation from an attenuation model prediction for a single year of observations is estimated to exceed 33 percent when any of the available global rain climate model are employed to estimate the rain rate statistics. The probability distribution for the variation in attenuation or rain rate at a fixed fraction of a year is lognormal. The lognormal behavior of the variate was used to compile the statistics for variability.

  6. The Influence of Water on Seismic Wave Attenuation in the Upper Mantle

    NASA Astrophysics Data System (ADS)

    David, E. C.; Jackson, I.; Faul, U.; Berry, A.

    2014-12-01

    Trace amounts of water, present as protons structurally bound in olivine crystal defects, are inferred to significantly enhance the low-strain solid-state viscoelastic relaxation responsible for attenuation and dispersion of seismic waves in the upper mantle. This inferrence is supported by recent observation of water weakening at moderate compressive strains in synthetic, water-undersaturated aggregates (Faul et al., in preparation). In these fine-grained olivine polycrystals of Fo90 composition, doped with 0.02wt% TiO2, "water" is incorporated in the remarkably stable Ti-clinohumite defect. Such synthetic olivine specimens reproduce the infrared spectra of natural mantle olivines (Berry et al., 2005), and present the advantage of being melt-free and of low dislocation density. The water contents in such synthetic polycrystalline olivine aggregates, which can be quantitatively measured by Fourier Transform Infrared Spectroscopy (FTIR), range up to 90 ppm, and are thus representative of water-undersaturated conditions in the upper mantle. We will report here the outcome of torsional-oscillation tests,in which attenuation and shear modulus were measured at seismic frequencies (mHz-Hz) and various temperatures up to 1300C on Pt-encapsulated, Ti-doped olivine specimens, enclosed within a mild-steel jacket.

  7. Upper mantle and crustal P-wave attenuation beneath the North Korea region

    NASA Astrophysics Data System (ADS)

    Cleveland, M.; Randall, G. E.; Patton, H. J.; Phillips, W. S.

    2014-12-01

    Accurate estimation of the magnitude of crustal seismic sources is dependent upon a strong understanding of the anelastic P-wave attenuation in the crust and upper mantle. In this study, we estimate the crustal/upper mantle average attenuation (t*) for the region around North Korea by expanding upon methods described by Ichinose et al. [2013]. We estimate t* by modeling the observed spectra and spectral ratio of regional and teleseismic P- and pP-phases of large, deep (> 500 km) earthquakes rupturing beneath the North Korea region. We use seismograms, acquired from the IRIS data archive, from operational stations at the time of each earthquake. Because of a trade-off between the variables, we use multi-variable optimization to estimate the best-fitting corner frequency (fc) and t* for each spectrum. In addition to using a more quantitative and global approach than earlier studies, we introduce new measurement approaches enabling a better understanding of the uncertainty in the measured t* value and its trade-off with fc.

  8. 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.

  9. P- and S-wave seismic attenuation for deep natural gas exploration and development

    SciTech Connect

    Walls, Joel; Uden, Richard; Singleton, Scott; Shu, Rone; Mavko, Gary

    2005-04-12

    Using current methods, oil and gas in the subsurface cannot be reliably predicted from seismic data. This causes domestic oil and gas fields to go undiscovered and unexploited, thereby increasing the need to import energy.The general objective of this study was to demonstrate a simple and effective methodology for estimating reservoir properties (gas saturation in particular, but also including lithology, net to gross ratios, and porosity) from seismic attenuation and other attributes using P- and S-waves. Phase I specific technical objectives: Develop Empirical or Theoretical Rock Physics Relations for Qp and Qs; Create P-wave and S-wave Synthetic Seismic Modeling Algorithms with Q; and, Compute P-wave and S-wave Q Attributes from Multi-component Seismic Data. All objectives defined in the Phase I proposal were accomplished. During the course of this project, a new class of seismic analysis was developed based on compressional and shear wave inelastic rock properties (attenuation). This method provides a better link between seismic data and the presence of hydrocarbons. The technique employs both P and S-wave data to better discriminate between attenuation due to hydrocarbons versus energy loss due to other factors such as scattering and geometric spreading. It was demonstrated that P and S attenuation can be computed from well log data and used to generate synthetic seismograms. Rock physics models for P and S attenuation were tested on a well from the Gulf of Mexico. The P- and S-wave Q attributes were computed on multi-component 2D seismic data intersecting this well. These methods generated reasonable results, and most importantly, the Q attributes indicated gas saturation.

  10. Propagation and attenuation of Lg waves in South America

    NASA Astrophysics Data System (ADS)

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

    1989-09-01

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

  11. Laboratory measurements of seismic attenuation in partially saturated rocks

    NASA Astrophysics Data System (ADS)

    Chapman, Samuel; Tisato, Nicola; Quintal, Beatriz; Holliger, Klaus

    2014-05-01

    Laboratory measurements of seismic attenuation and transient pore fluid pressure are performed on partially saturated Berea sandstone and synthetic borosilicate samples. Various degrees of water (liquid) and nitrogen (gas) saturation are considered. These measurements are carried out at room temperature and under confining pressures varying from ambient conditions up to 25 MPa. The cylindrical samples are 25 cm long and have a diameter of 7.6 cm. In the context of the experimental setup, the solid frames of both the Berea sandstone and the borosilicate samples can be considered homogenous, which in turn allows for isolating and exploring the effects of partial saturation on seismic attenuation. We employ the sub-resonance method, which is based on the application of a time-harmonic vertical stress to the top of the sample and the measurement of the thus resulting strain. For any given frequency, the attenuation is then inferred as the tangent of the phase shift between the applied stress and the observed strain. Using five equally spaced sensors along the central axis of the cylindrical sample, we measure the transient fluid pressure induced by the application of a step-function-type vertical stress to the top of the sample. Both the sensors and the sample are sealed off with the regard to the confining environment. Together with the numerical results from corresponding compressibility tests based on the quasi-static poroelastic equations, these transient fluid pressure measurements are then used to assist the interpretation of the seismic attenuation measurements.

  12. Surface Wave Attenuation and Blockages in the Area of the Great Caucasus Mountains and the Caspian Sea

    NASA Astrophysics Data System (ADS)

    Stroujkova, A. F.; Bonner, J.

    2010-12-01

    The ratio of body-wave to surface-wave magnitudes (mb:Ms) is one of the most robust and reliable discriminants between earthquakes and explosions. We have estimated the surface wave magnitudes for approximately 120 events located in the Middle East with reported body wave magnitudes (mb) between 3.8 and 5.6. The magnitudes were measured using the Matlab program EVALSURF (Bonner et al., 2006), which estimates variable-period (8 < T < 40 sec) surface wave magnitudes using Ms(VMAX) technique developed by Russell (2006). To improve event discrimination we estimated magnitudes using both Love and Rayleigh waves. We found that there is a significant surface wave magnitude bias between the stations situated to the NW and NE from the area of study, with NW stations consistently reporting lower magnitudes than the NE stations. This bias may lead to errors in the magnitude estimates, especially for smaller events for which only a limited number of magnitude measurements are available. Different factors can potentially contribute to the magnitude bias, including high attenuation along the boundary between the Arabian, African and the Eurasian plates. Our analysis, however, indicates that the scattering by the Caspian Sea and the Great Caucasus Mountains has the greatest impact on the surface wave amplitudes recorded by the European stations located to the NW of the area. We are currently developing methods to account for the magnitude variations due to a presence of large tectonic features.

  13. Seismic wave attenuation in Israel region estimated from the multiple lapse time window analysis and S-wave coda decay rate

    NASA Astrophysics Data System (ADS)

    Meirova, Tatiana; Pinsky, Vladimir

    2014-04-01

    For the first time, a regional seismic attenuation for the Israel region is quantitatively estimated as a combination of intrinsic and scattering attenuations. We use a multiple lapse time windows analysis (MLTWA) to determinate the relative contributions of intrinsic absorption and scattering processes to the total regional attenuation in the crust. A single isotropic scattering model assuming a uniform half-space lithosphere is used to fit MLTWA predicted and measured energies from the records of 232 regional earthquakes recorded at 17 short-period and 5 broad-band local seismic stations. Analysis is performed for a set of 10 frequencies between 0.5 and 10 Hz. The frequency-dependent quality factor Q obtained by MLTWA ranges between Q = 77f0.96 in the Northern Israel and Q = 132f0.96 in Southern Israel. Independent estimates of regional coda Q value based on S-wave coda decay rate obtained by averaging of five broad-band Israel Seismic Network stations are approximated by the relation Qc = 126f1.05. As a whole, our findings indicate that in the Israel region, intrinsic absorption prevails over scattering attenuation. Separate analysis for three tectonically different regions in Israel region-Galilee-Lebanon, Judea-Samaria and Eastern Sinai-shows a regional dependence of attenuation parameters. The variation of attenuation characteristics implies different physical mechanisms of seismic attenuation in the Israel region and is related to the differences of structure in the Earth's crust beneath Israel. Such variation in the attenuation patterns is in agreement with the assumption that Northern Israel is tectonically more active than Southern Israel and that in the northern and central parts of Israel the upper crust is more heterogeneous than in the southern part.

  14. Dynamic aspects of apparent attenuation and wave localization in layered media

    USGS Publications Warehouse

    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.

  15. Propagation and attenuation of Rayleigh waves in generalized thermoelastic media

    NASA Astrophysics Data System (ADS)

    Sharma, M. D.

    2014-01-01

    This study considers the propagation of Rayleigh waves in a generalized thermoelastic half-space with stress-free plane boundary. The boundary has the option of being either isothermal or thermally insulated. In either case, the dispersion equation is obtained in the form of a complex irrational expression due to the presence of radicals. This dispersion equation is rationalized into a polynomial equation, which is solvable, numerically, for exact complex roots. The roots of the dispersion equation are obtained after removing the extraneous zeros of this polynomial equation. Then, these roots are filtered out for the inhomogeneous propagation of waves decaying with depth. Numerical examples are solved to analyze the effects of thermal properties of elastic materials on the dispersion of existing surface waves. For these thermoelastic Rayleigh waves, the behavior of elliptical particle motion is studied inside and at the surface of the medium. Insulation of boundary does play a significant role in changing the speed, amplitude, and polarization of Rayleigh waves in thermoelastic media.

  16. Multiple attenuation to reflection seismic data using Radon filter and Wave Equation Multiple Rejection (WEMR) method

    SciTech Connect

    Erlangga, Mokhammad Puput

    2015-04-16

    Separation between signal and noise, incoherent or coherent, is important in seismic data processing. Although we have processed the seismic data, the coherent noise is still mixing with the primary signal. Multiple reflections are a kind of coherent noise. In this research, we processed seismic data to attenuate multiple reflections in the both synthetic and real seismic data of Mentawai. There are several methods to attenuate multiple reflection, one of them is Radon filter method that discriminates between primary reflection and multiple reflection in the τ-p domain based on move out difference between primary reflection and multiple reflection. However, in case where the move out difference is too small, the Radon filter method is not enough to attenuate the multiple reflections. The Radon filter also produces the artifacts on the gathers data. Except the Radon filter method, we also use the Wave Equation Multiple Elimination (WEMR) method to attenuate the long period multiple reflection. The WEMR method can attenuate the long period multiple reflection based on wave equation inversion. Refer to the inversion of wave equation and the magnitude of the seismic wave amplitude that observed on the free surface, we get the water bottom reflectivity which is used to eliminate the multiple reflections. The WEMR method does not depend on the move out difference to attenuate the long period multiple reflection. Therefore, the WEMR method can be applied to the seismic data which has small move out difference as the Mentawai seismic data. The small move out difference on the Mentawai seismic data is caused by the restrictiveness of far offset, which is only 705 meter. We compared the real free multiple stacking data after processing with Radon filter and WEMR process. The conclusion is the WEMR method can more attenuate the long period multiple reflection than the Radon filter method on the real (Mentawai) seismic data.

  17. Ultrasonic attenuation - Q measurements on 70215,29. [lunar rock

    NASA Technical Reports Server (NTRS)

    Warren, N.; Trice, R.; Stephens, J.

    1974-01-01

    Ultrasonic attenuation measurements have been made on an aluminum alloy, obsidian, and rock samples including lunar sample 70215,29. The measurement technique is based on a combination of the pulse transmission method and the forced resonance method. The technique is designed to explore the problem of defining experimentally, the Q of a medium or sample in which mode conversion may occur. If modes are coupled, the measured attenuation is strongly dependent on individual modes of vibration, and a range of Q-factors may be measured over various resonances or from various portions of a transient signal. On 70215,29, measurements were made over a period of a month while the sample outgassed in hard varuum. During this period, the highest measured Q of this sample increased from a few hundred into the range of 1000-1300.

  18. Q c and Q S wave attenuation of South African earthquakes

    NASA Astrophysics Data System (ADS)

    Brandt, Martin B. C.

    2016-04-01

    Quality factor Q, which describes the attenuation of seismic waves with distance, was determined for South Africa using data recorded by the South African National Seismograph Network. Because of an objective paucity of seismicity in South Africa and modernisation of the seismograph network only in 2007, I carried out a coda wave decay analysis on only 13 tectonic earthquakes and 7 mine-related events for the magnitude range 3.6 ≤ M L ≤ 4.4. Up to five seismograph stations were utilised to determine Q c for frequencies at 2, 4, 8 and 16 Hz resulting in 84 individual measurements. The constants Q 0 and α were determined for the attenuation relation Q c( f) = Q 0 f α . The result was Q 0 = 396 ± 29 and α = 0.72 ± 0.04 for a lapse time of 1.9*( t s - t 0) (time from origin time t 0 to the start of coda analysis window is 1.9 times the S-travel time, t s) and a coda window length of 80 s. This lapse time and coda window length were found to fit the most individual frequencies for a signal-to-noise ratio of at least 3 and a minimum absolute correlation coefficient for the envelope of 0.5. For a positive correlation coefficient, the envelope amplitude increases with time and Q c was not calculated. The derived Q c was verified using the spectral ratio method on a smaller data set consisting of nine earthquakes and one mine-related event recorded by up to four seismograph stations. Since the spectral ratio method requires absolute amplitudes in its calculations, site response tests were performed to select four appropriate stations without soil amplification and/or signal distortion. The result obtained for Q S was Q 0 = 391 ± 130 and α = 0.60 ± 0.16, which agrees well with the coda Q c result.

  19. Q c and Q S wave attenuation of South African earthquakes

    NASA Astrophysics Data System (ADS)

    Brandt, Martin B. C.

    2015-11-01

    Quality factor Q, which describes the attenuation of seismic waves with distance, was determined for South Africa using data recorded by the South African National Seismograph Network. Because of an objective paucity of seismicity in South Africa and modernisation of the seismograph network only in 2007, I carried out a coda wave decay analysis on only 13 tectonic earthquakes and 7 mine-related events for the magnitude range 3.6 ? M L ? 4.4. Up to five seismograph stations were utilised to determine Q c for frequencies at 2, 4, 8 and 16 Hz resulting in 84 individual measurements. The constants Q 0 and ? were determined for the attenuation relation Q c(f) = Q 0 f ? . The result was Q 0 = 396 29 and ? = 0.72 0.04 for a lapse time of 1.9*(t s - t 0) (time from origin time t 0 to the start of coda analysis window is 1.9 times the S-travel time, t s) and a coda window length of 80 s. This lapse time and coda window length were found to fit the most individual frequencies for a signal-to-noise ratio of at least 3 and a minimum absolute correlation coefficient for the envelope of 0.5. For a positive correlation coefficient, the envelope amplitude increases with time and Q c was not calculated. The derived Q c was verified using the spectral ratio method on a smaller data set consisting of nine earthquakes and one mine-related event recorded by up to four seismograph stations. Since the spectral ratio method requires absolute amplitudes in its calculations, site response tests were performed to select four appropriate stations without soil amplification and/or signal distortion. The result obtained for Q S was Q 0 = 391 130 and ? = 0.60 0.16, which agrees well with the coda Q c result.

  20. Measurements of seismic attenuation in ice: A potential proxy for englacial temperature?

    NASA Astrophysics Data System (ADS)

    Peters, L. E.; Anandakrishnan, S.

    2010-12-01

    Constraints on seismic attenuation in ice are key to determining conditions at the ice-bed interface and below. Variations in this value by as little as a factor of two can make the difference between identifying a soft, deformable sediment bed or hard bedrock stratum from seismic data (both of which have quite different effects on ice dynamics), making the need to understand this parameter imperative for accurate seismic analysis of the subglacial environment. While laboratory tests have demonstrated that seismic attenuation in ice is quite sensitive to englacial temperature, especially as the pressure-melting point is approached, little validation has been performed in the field to confirm this. The results presented here are from a series of wide-angle common midpoint (CMP) seismic datasets across Antarctica and Greenland, where both englacial and basal seismic reflections are observed, each having calculated englacial seismic attenuation values that exhibit a positive correlation with observed and predicted englacial temperatures. We investigate the effects of energy losses due to dissipation as a seismic wave propagates through the ice. Various seismic signals are analyzed in both the time and frequency domains to determine the frequency-dependency of seismic attenuation with respect to depth in the ice column, source-receiver offset, and the frequency spectra of both the source and observed seismic signal. Surface wave data from ten locations across Antarctica and Greenland are analyzed in the time domain to determine near-surface frequency-dependent seismic attenuation, focusing on the upper 100 - 500 m of the ice column where englacial temperatures are indicative of the mean annual surface temperature. These data yield lower attenuation values in the colder regions of Antarctica and higher attenuation values at the warmer locations. Spectral analysis of the basal reflection at each location produces similar results: regions where the bulk temperature of the ice column is predicted to be colder give lower attenuation values, and vice versa for the warmer ice columns. Spectral analysis of the observed englacial reflectors at a few locations across Antarctica and Greenland are also analyzed, highlighting an increase in seismic attenuation with depth through the ice column at each location. Comparison of these results to an in-situ englacial temperature profile near our Greenland site shows strong agreement between increasing englacial temperatures and seismic attenuation with depth. This proxy for englacial temperature via active seismic methods demonstrates a fast and potentially effective way to provide ice sheet modelers with better constraint on the thermal regime of an ice sheet or glacier, especially in fast-flow glaciated regions where the collection of in-situ measurements are unfeasible.

  1. Acoustic Measurement of Suspended Fine Particle Concentrations by Attenuation

    Technology Transfer Automated Retrieval System (TEKTRAN)

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

  2. Attenuation of sonic waves in water-saturated alluvial sediments due to wave-induced fluid flow at microscopic, mesoscopic and macroscopic scales

    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.

  3. In situ measurements of an energetic wave event in the Arctic marginal ice zone

    NASA Astrophysics Data System (ADS)

    Collins, Clarence O.; Rogers, W. Erick; Marchenko, Aleksey; Babanin, Alexander V.

    2015-03-01

    R/V Lance serendipitously encountered an energetic wave event around 77°N, 26°E on 2 May 2010. Onboard GPS records, interpreted as the surface wave signal, show the largest waves recorded in the Arctic region with ice cover. Comparing the measurements with a spectral wave model indicated three phases of interaction: (1) wave blocking by ice, (2) strong attenuation of wave energy and fracturing of ice by wave forcing, and (3) uninhibited propagation of the peak waves and an extension of allowed waves to higher frequencies (above the peak). Wave properties during fracturing of ice cover indicated increased groupiness. Wave-ice interaction presented binary behavior: there was zero transmission in unbroken ice and total transmission in fractured ice. The fractured ice front traveled at some fraction of the wave group speed. Findings do not motivate new dissipation schemes for wave models, though they do indicate the need for two-way, wave-ice coupling.

  4. Methods of measuring the attenuation of hearing protection devices.

    PubMed

    Berger, E H

    1986-06-01

    The published literature describing three real-ear-attenuation-at-threshold (REAT), nine above-threshold, and four objective methods of measuring hearing protector attenuation is reviewed and analyzed with regard to the accuracy, practicality, and applicability of the various techniques. The analysis indicates that the REAT method is one of the most accurate available techniques since it assesses all of the sound paths to the occluded ear and, depending upon the experimenter's intention, can reflect actual in-use attenuation as well. An artifact in the REAT paradigm is that masking in the occluded ear due to physiological noise can spuriously increase low-frequency (less than or equal to 500 Hz) attenuation, although the error never exceeds approximately 5 dB, regardless of the device, except below 125 Hz. Since the preponderance of available data indicates that attenuation is independent of sound level for intentionally linear protectors, the use of above-threshold procedures to evaluate attenuation is not a necessity. An exception exists in the case of impulsive noises, for which the existing data are not unequivocal with regard to hearing protector response characteristics. Two of the objective methods (acoustical test fixture and microphone in real ear) are considerable time savers. All objective procedures are lacking in their ability to accurately determine the importance of the flanking bone-conduction paths, although some authors have incorporated this feature as a post-measurement correction. The microphone in real-ear approach is suggested to be one of the most promising for future standardization efforts and research purposes, and the acoustical test fixture technique is recommended (with certain reservations) for quality control and buyer acceptance testing. PMID:3522700

  5. An evaluation of two millimeter wave propagation models for horizontal atmospheric attenuation at 70-115 GHZ

    NASA Astrophysics Data System (ADS)

    Vogel, Gerard N.

    1988-02-01

    An evaluation is performed for two millimeter wave propagation models: the LIEBE model, developed at the Institute for Telecommunications, Boulder, CO, under the guidance of Dr. H. Liebe; and the EOSAEL model, developed at the U. S. Army Atmospheric Laboratory at White Sands Missile Range, NM. This evaluation is conducted for horizontal attenuation due to both clear atmosphere and hydrometer effects under typical surface meteorological conditions, and within the frequency range 70-115 GHz. Intercomparisons of model theories and predictions show slight differences for molecular oxygen and fog attenuations, but significant differences for water vapor and rain attenuations. Results indicate that, while the qualitative agreement between either the EOSAEL or LIEBE model predictions, and measurements, for horizontal attenuation due to oxygen, water vapor, fog and rain is certainly satisfactory, there is a definite need for improvement. Overall, no clear preference for either the EOSAEL or LIEBE model for operational use is ascertained. Data comparisons suggest that, for several attenuation types, model preference is dependent on either the frequency or meteorological conditions.

  6. Millimeter wave reflectivity measurement system

    NASA Astrophysics Data System (ADS)

    Trott, Keith D.; Walker, John R., Jr.

    1993-09-01

    The RF Technology Section of WL/MNGS is developing an in-house capability for modeling and measurement of target scattering and material characteristics at millimeter wave (MMW) frequencies. The goal of the modeling effort is to understand the basic mechanisms that contribute to the target scattering (coated and uncoated) at MMW frequencies. The measurement effort is two-fold: verify theoretical models (target and materials); and assess the effectiveness of actualcountermeasures. The MMW Reflectivity Measurement System (MRMS) is capable of bistatic swept frequency measurements for copolarized (COPOL) transmit and receive signals, and it gives a quick-look capability useful in evaluating countermeasures. The primary goal is the understanding of the various mechanisms that contribute to the scattering in order to develop the algorithms and technology necessary to exploit these effects and improve seeker guidance techniques. This paper discusses the current hardware configuration and planned upgrades and outlines the modeling effort. Examples of the MRMS measurements are compared to theoretical predictions.

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

    NASA Technical Reports Server (NTRS)

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

    1970-01-01

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

  8. Laboratory Measurement of Guided Wave (Krauklis Wave) Propagation Within a Fluid-Saturated Fracture

    NASA Astrophysics Data System (ADS)

    Nakagawa, S.; Korneev, V. A.

    2013-12-01

    A fluid-saturated flat channel between two solid half-spaces (i.e. a fracture) is known to support a guided wave called the Krauklis wave. In the field, this wave can potentially be used to examine the size and connectivity of natural and hydraulically induced fractures from a borehole. Krauklis waves propagate primarily within the fluid part of a fracture, can have very low velocity and large attenuation, and are very dispersive at low frequencies. We conducted laboratory measurements of the velocity of Krauklis waves using analogue fracture models at frequencies below 1 kHz. The models consisted of (1) two concentric aluminum cylinders with a water-filled gap and (2) a pair of rectangular aluminum plates containing a thin water-filled gap (tri-layer mode). In the latter, the water was contained by an o-ring along the edge of the plates. The velocity of the waves propagating within the models was determined both from waveforms in the time domain measured along the wave path and from acoustic resonances in the system. The results indicated that the waves measured from the cylindrical model were not dispersive at frequencies below 400 Hz, with a phase velocity of ~250 m/s. In contrast, the tri-layer model exhibited strongly dispersive velocity at measured frequencies of 7.5 Hz-500 Hz, with the lowest phase velocity being ~14 m/s at 7.5 Hz. These measurements agree well with our theoretical model predictions.

  9. 2-D Coda and Direct Wave Attenuation Tomography in Northern Italy

    SciTech Connect

    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.

  10. Oceanic-wave-measurement system

    NASA Technical Reports Server (NTRS)

    Holmes, J. F.; Miles, R. T.

    1980-01-01

    Barometer mounted on bouy senses wave heights. As wave motion raises and lowers barometer, pressure differential is proportional to wave height. Monitoring circuit samples barometer output every half cycle of wave motion and adds magnitudes of adjacent positive and negative peaks. Resulting output signals, proportional to wave height, are transmitted to central monitoring station.

  11. Measurment and Interpretation of Seismic Attenuation for Hydrocarbon Exploration

    SciTech Connect

    Michael Batzle; Luca Duranti; James Rector; Steve Pride

    2007-12-31

    This research project is the combined effort of several leading research groups. Advanced theoretical work is being conducted at the Lawrence Berkeley National Laboratory. Here, the fundamental controls on loss mechanisms are being examined, primarily by use of numerical models of heterogeneous porous media. At the University of California, Berkeley, forward modeling is combined with direct measurement of attenuation. This forward modeling provides an estimate of the influence of 1/Q on the observed seismic signature. Direct measures of losses in Vertical Seismic Profiles (VSPs) indicate mechanisms to separate scattering versus intrinsic losses. At the Colorado School of Mines, low frequency attenuation measurements are combined with geologic models of deep water sands. ChevronTexaco is our corporate cosponsor and research partner. This corporation is providing field data over the Genesis Field, Gulf of Mexico. In addition, ChevronTexaco has rebuilt and improved their low frequency measurement system. Soft samples representative of the Genesis Field can now be measured for velocities and attenuations under reservoir conditions. Throughout this project we have: Assessed the contribution of mechanical compaction on time-lapse monitoring; Developed and tested finite difference code to model dispersion and attenuation; Heterogeneous porous materials were modeled and 1/Q calculated vs. frequency; 'Self-affine' heterogeneous materials with differing Hurst exponent modeled; Laboratory confirmation was made of meso-scale fluid motion influence on 1/Q; Confirmed theory and magnitude of layer-based scattering attenuation at Genesis and at a shallow site in California; Scattering Q's of between 40 and 80 were obtained; Measured very low intrinsic Q's (2-20) in a partially saturated vadose zone VSP; First field study to separate scattering and intrinsic attenuation in real data set; Revitalized low frequency device at ChevronTexaco's Richmond lab completed; First complete frequency dependent measurements on Berea sandstones from dry to various saturations (brine and decane); Frequency dependent forward modeling code is running, and tested on a couple of Cases--derives frequency dependent reflectivity from porosity based logs; Genesis seismic data obtained but is on hold until forward modeling is complete; Boundary and end effects modeled for soft material measurements at CSM; and Numerous papers published or submitted and presentations made.

  12. 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.

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

    PubMed

    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

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

    NASA Astrophysics Data System (ADS)

    Hinders, Mark Karl

    1990-01-01

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

  15. Effects of microstructure on the speed and attenuation of elastic waves

    SciTech Connect

    Gubernatis, J.E.; Domany, E.

    1982-01-01

    A unified theory pertaining to the sensitivity of the propagation of an elastic wave to changes in the microstructural details of a material is discussed. In contrast to nearly all previous treatments a first principles approach, using developments from other multiple scattering problems and adapting them to the elastic wave case, is followed. We then present several simple, standard approximations. In the process the validity of the commonly made assumption that ..cap alpha.. = n anti sigma is clarified, and the effective speed, illustrating its complementary character to the attenuation, is computed. The principal objective is to present the formal analysis necessary to treat systematically the dependency of the wave propagation on microstructural statistics.

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

    USGS Publications Warehouse

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

    2004-01-01

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

  17. ULTRASONIC MEASUREMENT MODELS FOR SURFACE WAVE AND PLATE WAVE INSPECTIONS

    SciTech Connect

    Schmerr, Lester W. Jr.; Sedov, Alexander

    2010-02-22

    A complete ultrasonic measurement model for surface and plate wave inspections is obtained, where all the electrical, electromechanical, and acoustic/elastic elements are explicitly described. Reciprocity principles are used to describe the acoustic/elastic elements specifically in terms of an integral of the incident and scattered wave fields over the surface of the flaw. As with the case of bulk waves, if one assumes the incident surface waves or plate waves are locally planar at the flaw surface, the overall measurement model reduces to a very modular form where the far-field scattering amplitude of the flaw appears explicitly.

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

    PubMed

    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

  19. 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.

  20. Attenuation of Slab determined from T-wave generation by deep earthquakes

    NASA Astrophysics Data System (ADS)

    Huang, J.; Ni, S.

    2006-05-01

    T-wave are seismically generated acoustic waves that propagate over great distance in the ocean sound channel (SOFAR). Because of the high attenuation in both the upper mantle and the ocean crust, T wave is rarely observed for earthquakes deeper than 80 km. However some deep earthquakes deeper than 80km indeed generate apparent T-waves if the subducted slab is continuous Okal et al. (1997) . We studied the deep earthquakes in the Fiji/Tonga region, where the subducted lithosphere is old and thus with small attenuation. After analyzing 33 earthquakes with the depth from 10 Km to 650 Km in Fiji/Tonga, we observed and modeled obvious T-phases from these earthquakes observed at station RAR. We used the T-wave generated by deep earthquakes to compute the quality factor of the Fiji/Tonga slab. The method used in this study is followed the equation (1) by [Groot-Hedlin et al,2001][1]. A=A0/(1+(Ω0/Ω)2)×exp(-LΩ/Qv)×Ωn where the A is the amplitude computed by the practicable data, amplitude depending on the earthquakes, and A0 is the inherent frequency related with the earthquake's half duration, L is the length of ray path that P wave or S travel in the slab, and the V is the velocity of P-wave. In this study, we fix the n=2, by assuming the T- wave scattering points in the Fiji/Tonga island arc having the same attribution as the continental shelf. After some computing and careful analysis, we determined the quality factor of the Fiji/Tonga to be around 1000, Such result is consistent with results from the traditional P,S-wave data[Roth & Wiens,1999][2] . Okal et al. (1997) pointed out that the slab in the part of central South America was also a continuous slab, by modeling apparent T-waves from the great 1994 Bolivian deep earthquake in relation to channeling of S wave energy propagating upward through the slab[3]. [1]Catherine D. de Groot-Hedlin, John A. Orcutt, excitation of T-phases by seafloor scattering, J. Acoust. Soc, 109,1944-1954,2001. [2]Erich G.Roth and Douglas A.Wiens, Leroy M.Dorman, Seismic attenuation tomography of the Tonga-Fiji region using phase pair methods, Geophys. Res.,104,4795-4809,1999. [3]Emile A.Okal and Jacques Talandier, T waves from the great 1994 Bolivian deep earthquake in relation to channeling of S wave energy up the slab, J.Geophys. Res.,102(12):27421-27437,1997.

  1. Strong Lg-wave attenuation in the Middle East continental collision orogenic belt

    NASA Astrophysics Data System (ADS)

    Zhao, Lian-Feng; Xie, Xiao-Bi

    2016-04-01

    Using Lg-wave Q tomography, we construct a broadband crustal attenuation model for the Middle East. The QLg images reveal a relationship between attenuation and geological structures. Strong attenuation is found in the continental collision orogenic belt that extends from the Turkish and Iranian plateau to the Pamir plateau. We investigate the frequency dependence of QLg in different geologic formations. The results illustrate that QLg values generally increase with increasing frequency but exhibit complex relationships both with frequency and between regions. An average QLg value between 0.2 and 2.0 Hz, QLg (0.2-2.0 Hz), may be a critical index for crustal attenuation and is used to infer the regional geology. Low-QLg anomalies are present in the eastern Turkish plateau and correlate well with low Pn-velocities and Cenozoic volcanic activity, thus indicating possible partial melting within the crust in this region. Very strong attenuation is also observed in central Iran, the Afghanistan block, and the southern Caspian Sea. This in line with the previously observed high crustal temperature, high-conductivity layers, and thick marine sediments in these areas, suggests the high Lg attenuation is caused by abnormally high tectonic and thermal activities.

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

    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 ω2 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.

  3. Complex Contact-Based Dynamics of Microsphere Monolayers Revealed by Resonant Attenuation of Surface Acoustic Waves.

    PubMed

    Hiraiwa, M; Abi Ghanem, M; Wallen, S P; Khanolkar, A; Maznev, A A; Boechler, N

    2016-05-13

    Contact-based vibrations play an essential role in the dynamics of granular materials. Significant insights into vibrational granular dynamics have previously been obtained with reduced-dimensional systems containing macroscale particles. We study contact-based vibrations of a two-dimensional monolayer of micron-sized spheres on a solid substrate that forms a microscale granular crystal. Measurements of the resonant attenuation of laser-generated surface acoustic waves reveal three collective vibrational modes that involve displacements and rotations of the microspheres, as well as interparticle and particle-substrate interactions. To identify the modes, we tune the interparticle stiffness, which shifts the frequency of the horizontal-rotational resonances while leaving the vertical resonance unaffected. From the measured contact resonance frequencies we determine both particle-substrate and interparticle contact stiffnesses and find that the former is an order of magnitude larger than the latter. This study paves the way for investigating complex contact-based dynamics of microscale granular crystals and yields a new approach to studying micro- to nanoscale contact mechanics in multiparticle networks. PMID:27232047

  4. Complex Contact-Based Dynamics of Microsphere Monolayers Revealed by Resonant Attenuation of Surface Acoustic Waves

    NASA Astrophysics Data System (ADS)

    Hiraiwa, M.; Abi Ghanem, M.; Wallen, S. P.; Khanolkar, A.; Maznev, A. A.; Boechler, N.

    2016-05-01

    Contact-based vibrations play an essential role in the dynamics of granular materials. Significant insights into vibrational granular dynamics have previously been obtained with reduced-dimensional systems containing macroscale particles. We study contact-based vibrations of a two-dimensional monolayer of micron-sized spheres on a solid substrate that forms a microscale granular crystal. Measurements of the resonant attenuation of laser-generated surface acoustic waves reveal three collective vibrational modes that involve displacements and rotations of the microspheres, as well as interparticle and particle-substrate interactions. To identify the modes, we tune the interparticle stiffness, which shifts the frequency of the horizontal-rotational resonances while leaving the vertical resonance unaffected. From the measured contact resonance frequencies we determine both particle-substrate and interparticle contact stiffnesses and find that the former is an order of magnitude larger than the latter. This study paves the way for investigating complex contact-based dynamics of microscale granular crystals and yields a new approach to studying micro- to nanoscale contact mechanics in multiparticle networks.

  5. Freak waves statistics measured off Brazil

    NASA Astrophysics Data System (ADS)

    Pinho, Uggo; Babanin, Alexander; Liu, Paul

    2015-04-01

    Freaque wave statistics is analysed based on the data of South East coast of the Brazil. It is shown that such waves can be both due to linear and nonlinear dynamics. The wave climate in this area is very often dominated by a few uncorrelated wave systems and then the superposition of waves from different directions become likely. The available wave data was measured by wave buoys deployed off Rio de Janeiro State coast, where swell coming from the south are usually concomitant with northeast windsea generated by the South Atlantic anticyclone.

  6. Radio Frequency (RF) Attenuation Measurements of the Space Shuttle Vehicle

    NASA Technical Reports Server (NTRS)

    Scully, R. C.; Kent, B. M.; Kempf, D. R.; Johnk, R. T.

    2006-01-01

    Following the loss of Columbia, the Columbia Accident Investigation Board (CAIB) provided recommendations to be addressed prior to Return To Flight (RTF). As a part of CAIB Recommendation 3.4.1 - Ground Based Imagery, new C-band and X-band radars were added to the array of ground-based radars and cameras already in-situ at Kennedy Space Center. Because of higher power density considerations and new operating frequencies, the team of Subject Matter Experts (SMEs) assembled to investigate the technical details of introducing the new radars recommended a series of radio frequency (RF) attenuation tests be performed on the Space Shuttle vehicle to establish the attenuation of the vehicle outer mold line structure with respect to its external RF environment. Because of time and complex logistical constraints, it was decided to split the test into two separate efforts. The first of these would be accomplished with the assistance of the Air Force Research Laboratory (AFRL), performing RF attenuation measurements on the aft section of OV-103 (Discovery) while in-situ in Orbiter Processing Facility (OPF) 3, located at Kennedy Space Center. The second would be accomplished with the assistance of the National Institute of Standards and Technology (NIST) and the electromagnetic interference (EMI) laboratory out of the Naval Air Warfare Center, Patuxent River, Maryland (PAX River), performing RF attenuation measurements on OV-105 (Endeavour) in-situ inside the Space Shuttle Landing Facility (SLF) hangar, also located at Kennedy Space Center. This paper provides a summary description of these efforts and their results.

  7. Attenuation of high-frequency P and S waves in Garhwal Himalaya, India

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    Tectonics of a region plays important role on the attenuation characteristics of the region. Attenuation characteristics have been estimated to understand the effect of the heterogeneity of the region in a tectonically active Garhwal region of Himalaya. Seismic body wave attenuation characteristics in the region is studied using 234 short-period, seismic observations from local events. The P-wave attenuation (QP- 1) and S-wave attenuation (QS- 1) were estimated by applying the state-of-the-art, extended coda normalization method for the frequency range from 1.5 to 24 Hz. Estimates of QP- 1 and QS- 1 decrease from (15.86 ± 0.90) × 10- 3 and (5.35 ± 0.51) × 10- 3 at 1.5 Hz to (0.54 ± 0.11) × 10- 3 and (0.34 ± 0.06) × 10- 3 at 24 Hz, respectively. The values of QP- 1 and QS- 1 show strong frequency dependence and fit the power-law relation QP- 1(f) = (27.43 ± 3.15) × 10- 3f(- 1.16 ± 0.06) and QS- 1(f) = (8.05 ± 0.74) × 10- 3f(- 0.93 ± 0.05), respectively. Obtained results are in the range of those reported for QP- 1 and QS- 1 of the other seismically active regions. The ratio of QP- 1/QS- 1 is larger than unity in the entire analyzed frequency range and may suggest high degree of heterogeneity in the region.

  8. Study of wind speed attenuation at Kavaratti Island using land-based, offshore, and satellite measurements

    NASA Astrophysics Data System (ADS)

    Joseph, Antony; Rivonkar, Pradhan; Balakrishnan Nair, T. M.

    2012-06-01

    The role of dense coconut palms in attenuating the wind speed at Kavaratti Island, which is located in the southeastern Arabian Sea, is examined based on land-based and offshore wind measurements (U10) using anchored-buoy-mounted and satellite-borne sensors (QuikSCAT scatterometer and TMI microwave imager) during an 8-year period (2000-2007). It is found that round the year monthly-mean wind speed measurements from the Port Control Tower (PCT) located within the coconut palm farm at the Kavaratti Island are weaker by 15-61% relative to those made from the nearby offshore region. Whereas wind speed attenuation at the island is ~15-40% in the mid-June to mid-October south-west monsoon period, it is ~41-61% during the rest of the year. Wind direction measurements from all the devices overlapped, except in March-April during which the buoy measurements deviated from the other measurements by ~20°. U10 wind speed measurements from PCT during the November 2009 tropical cyclone "Phyan" indicated approximately 50-80% attenuation relative to those from the seaward boundary of the island's lagoon (and therefore least influenced by the coconut palms). The observed wind speed attenuation can be understood through the theory of free turbulent flow jets embodied in the boundary-layer fluid dynamics, according to which both the axial and transverse components of the efflux of flows discharged through the inter-leaves porosity (orifice) undergo increasing attenuation in the downstream direction with increasing distance from the orifice. Thus, the observed wind speed attenuation at Kavaratti Island is attributable to the decline in wind energy transmission from the seaward boundary of the coconut palm farm with distance into the farm. Just like mangrove forests function as bio-shields against forces from oceanic waves and stormsurges through their large above-ground aerial root systems and standing crop, and thereby playing a distinctive role in ameliorating the effects of catastrophies such as hurricanes, tidal bores, cyclones, and tsunamis, the present study provides an indication that densely populated coconut palms and other tall tree vegetation would function as bio-shields against the damaging effects of storms through attenuation of wind speed.

  9. Dislocation damping and anisotropic seismic wave attenuation in Earth's upper mantle.

    PubMed

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

    2012-04-20

    Crystal defects form during tectonic deformation and are reactivated by the shear stress associated with passing seismic waves. Although these defects, known as dislocations, potentially contribute to the attenuation of seismic waves in Earth's upper mantle, evidence for dislocation damping from laboratory studies has been circumstantial. We experimentally determined the shear modulus and associated strain-energy dissipation in pre-deformed synthetic olivine aggregates under high pressures and temperatures. Enhanced high-temperature background dissipation occurred in specimens pre-deformed by dislocation creep in either compression or torsion, the enhancement being greater for prior deformation in torsion. These observations suggest the possibility of anisotropic attenuation in relatively coarse-grained rocks where olivine is or was deformed at relatively high stress by dislocation creep in Earth's upper mantle. PMID:22517856

  10. 40 CFR 211.206 - Methods for measurement of sound attenuation.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 40 Protection of Environment 26 2012-07-01 2011-07-01 true Methods for measurement of sound attenuation. 211.206 Section 211.206 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED... measurement of sound attenuation....

  11. 40 CFR 211.206 - Methods for measurement of sound attenuation.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 24 2010-07-01 2010-07-01 false Methods for measurement of sound attenuation. 211.206 Section 211.206 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED... measurement of sound attenuation....

  12. 40 CFR 211.206 - Methods for measurement of sound attenuation.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 25 2014-07-01 2014-07-01 false Methods for measurement of sound attenuation. 211.206 Section 211.206 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED... measurement of sound attenuation....

  13. 40 CFR 211.206 - Methods for measurement of sound attenuation.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 40 Protection of Environment 25 2011-07-01 2011-07-01 false Methods for measurement of sound attenuation. 211.206 Section 211.206 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED... measurement of sound attenuation....

  14. 40 CFR 211.206 - Methods for measurement of sound attenuation.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 26 2013-07-01 2013-07-01 false Methods for measurement of sound attenuation. 211.206 Section 211.206 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED... measurement of sound attenuation....

  15. Regional variations of seismic attenuation of Lg waves in southern Mexico

    NASA Astrophysics Data System (ADS)

    DomíNguez, Tonatiuh; Rebollar, Cecilio J.; Castro, Raúl R.

    1997-12-01

    Attenuation of Lg waves is estimated using 61 events located in the subduction zone of the Middle American trench and recorded by the seismic network of Laguna Verde, Veracruz, Mexico. We estimate the anelastic attenuation coefficient γ of Lg waves or, equivalently, QLg by calculating the rate of acceleration spectra decay with distance. We consider paths from two regions: Guerrero-Veracruz (NE-SW direction) and Oaxaca-Veracruz (North-South direction). Assuming a frequency dependence of γ of the form γ(ƒ) = γ0ƒη, we find that η=0.175±0.05 for both regions and that γ0 was lower for paths from Guerrero to Veracruz (γ0=0.0071±0.002) than for paths from Oaxaca to Veracruz (γ0=0.0161±0.003) in the frequency range from 2 to 7 Hz. In terms of the quality factor QLg, values of QLg= 134±30ƒ0.83±0.2 and QLg=59±10ƒ0.81±0.2 were found for the Guerrero-Veracruz and the Oaxaca-Veracruz paths, respectively. This difference in attenuation may be due to the state of stresses that prevails in both regions including the density and fluid content of fractures, which are attenuation mechanisms also suggested for other regions [Mitchell, 1995].

  16. Pore-Scale Modeling of Pore Structure Effects on P-Wave Scattering Attenuation in Dry Rocks

    PubMed Central

    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

  17. Pore-scale modeling of pore structure effects on P-wave scattering attenuation in dry rocks.

    PubMed

    Wang, Zizhen; Wang, Ruihe; 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

  18. Attenuation of Surface Acoustic Waves Interacting with Electrons in a Narrow Channel within a Piezoelectric Material

    NASA Astrophysics Data System (ADS)

    Gumbs, Godfrey; Aizin, G. R.; Pepper, Michael

    1998-03-01

    The velocity change and the attenuation coefficient of the transmitted surface acoustic wave (SAW) of wave number k interacting with a 2DEG in a piezoelectric semiconductor are well-known. Here, the energy change ? U/U is calculated for a narrow channel of width r_? (kr_? << 1) at distance d below the surface of a slab of piezoelectric material of finite thickness when an elastic wave is launched on the surface. We obtain ? U/U as a closed-form expression in terms of the velocity of the elastic wave, the elastic constants and the piezoelectric tensor. Numerical results are presented for ? U/U as a function of kd for several values of the thickness of a slab of GaAs/Al_xGa_1-xAs.

  19. S-wave attenuation characteristics in the Galeras volcanic complex (south western Colombia)

    NASA Astrophysics Data System (ADS)

    Ugalde, Arantza; Carcolé, Eduard; Vargas, Carlos A.

    2010-08-01

    Vertical-component, short period seismograms from 435 well located volcano-tectonic earthquakes are used to estimate S-wave attenuation in the Galeras volcanic complex (south western Colombia) using coda waves. The coda magnitudes ( Mc) of the events are less than 2. Event depths are less than 10 km and hypocentral distances up to 16 km. Intrinsic absorption ( Qi-1) and scattering attenuation ( Qs-1) are estimated by means of a fitting procedure between the observed and synthetic coda envelopes in four frequency bands (1-2, 2-4, 4-8, and 8-12 Hz). The observations are compared with the theoretical predictions by an accurate approximate analytical solution of the radiative transfer equation which is based on the assumptions of multiple isotropic scattering, impulsive isotropic point source, and a medium with homogeneous scattering and absorption properties. Results show that scattering is strong and it constitutes the predominant attenuation effect in this region. In the frequency range analyzed in this study the values of the mean free path for scattering of S waves range between 2.7 ≤ l ≤ 8.1 km, which are clearly higher than those obtained in other volcanic regions of the world, but about two orders of magnitude smaller than average estimates for the Earth's crust. The characteristic length scale of intrinsic absorption gives values of 2.5 ≤ la ≤ 77 km, which are on the same order as the usual values for the Earth's crust.

  20. Representative Elementary Length to Measure Soil Mass Attenuation Coefficient

    PubMed Central

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

    2014-01-01

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

  1. Fourier transform profilometry for water waves: how to achieve clean water attenuation with diffusive reflection at the water surface?

    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.

  2. Experimental study of the amplitude effect on wave velocity and attenuation in consolidated rocks under confining pressure

    NASA Astrophysics Data System (ADS)

    Mashinskii, E. I.

    2005-09-01

    A series of experiments were carried out to investigate the influence of strain amplitude on wave velocity and attenuation in dry sandstone and smoky quartz. Measurements were performed using the reflection method at a frequency of 1 MHz at strains ~(0.3-2.0) × 10-6 under a confining pressure of 20 MPa. The dependence of the compressional velocity on the strain amplitude in sandstone is ambiguous. On one hand, the velocity calculated by means of measurement of the propagation time of the first pulse minimum (Vminp) does not change with increasing amplitude. On the other hand, the velocity determined by the propagation time of the first pulse maximum (Vmaxp) slightly but surely increases with amplitude. In view of the small variation in velocity (~0.7%) this result is regarded only as a tendency. The Q-1p in sandstone decreases with increasing amplitude. The decrease is 16% in all the amplitude range. Vp and Vs in smoky quartz do not depend on the strain amplitude, but Q-1p and Q-1s decrease with amplitude. The decrease in attenuation is 10% and 6.5% respectively. This result contradicts the existing concept. The unusual behaviour of the attenuation is presumably explained by the inelasticity of the rock (at least by microplasticity). Amplitude dependence can be used as an additional criterion in the geological interpretation of seismic data.

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

    NASA Astrophysics Data System (ADS)

    Hwang, Yong Keun; Ritsema, Jeroen; Goes, Saskia

    2009-06-01

    We estimate the spatial variation of the seismic parameter t* using teleseismic (epicentral distance = 30°-85°) P wave spectra of about 200 deep (focal depths > 200 km) earthquakes recorded by 378 broadband seismometers in the United States and Canada. Relative P wave spectral ratios up to 1 Hz for about 63,000 station pairs with high signal-to-noise ratio and impulsive P waveforms are inverted for t*P by least squares inversion. The continental-scale t*P pattern correlates to the age of geological terrains and the seismic, heat flow, gravity, and magnetic variations across North America. Predominantly low values of t*P are obtained in stable central North America (SNA), and high t*P values are obtained for stations in the tectonically active western part of the continent (TNA). This variation is similar to that observed previously in short-period amplitude anomalies, spectral ratio variations, and ScS reverberations. On average, we resolve a contrast in t*P between SNA and TNA of about 0.2 s. We resolve regional variations in t*P, which correlate with tectonics. Relatively low t*P is associated with currently active subduction below Alaska. Relatively high t*P is found in SNA below the Appalachians and the Gulf Coast. The consistency between t*P and tectonics suggests that the observed variations in t*P are, on the scale of around 200-500 km, predominantly due to intrinsic attenuation. The similar patterns in t*P and predicted values for a recent global attenuation model confirm this further. The compatibility with the t*P computed for attenuation estimated via a thermal interpretation of shear wave velocity anomalies illustrates that variations in seismic velocity are predominantly due to physical effects with a strong attenuation signature, most likely temperature or a combination of temperature and water content.

  4. Scattering versus intrinsic attenuation in the near surface: Measurements from permanent down-hole geophones

    NASA Astrophysics Data System (ADS)

    Mangriotis, Maria-Daphne

    The study of attenuation, equivalently of the quality (Q) factor, in the near-surface has three main applications. Firstly, low Q values, which are fairly common in near-surface materials, aside from decreasing seismic energy, also distort the waveforms; treatment of this disturbance effect with inverse-Q filters requires reliable Q estimates. Secondly, attenuation is a seismic parameter which improves interpretation of seismograms, as it is correlated with lithological properties. Thirdly, establishing near-surface Q is important in assessing site effects on strong ground motion events in applications of earthquake modeling and seismic engineering design. In view of these applications, theoretical treatments of attenuation, as well as laboratory and field tests, aim at estimating Q as a function of frequency and strain level. To determine the applicability of using different types of Q measurements, laboratory vs. in-situ measurements, to predict Q behavior across the different frequency bands and strain-levels of interest, it is necessary to model and separate the attenuation mechanisms into scattering (heterogeneity of elastic properties causing energy to be redistributed in space) and intrinsic (energy absorption due to conversion to heat) components. The objective of the presented study was to separate scattering versus intrinsic attenuation in the near-surface from a shallow VSP experiment conducted in the Lawrence Livermore National Laboratory (LLNL) facility using permanent down-hole geophones and a vertical impact source. Given that the VSP array was above the watertable, the Q characterization lies within the vadose zone. The first arrival of the vertically-incident transmitted P-wave was used to estimate the P-wave attenuation in the field data. Scattering attenuation estimates were established for a selected range of elastic models, which addressed both the effect of the variance of the elastic properties (density and velocity), as well as the effect of the structure of the variation, i.e. 1D versus 3D heterogeneity, on scattering. The elastic profiles were constructed from a superposition of interval values determined from log information (for the density profile) and first-break arrivals (for the velocity profile) and a high-frequency random component with variance range typical of sedimentary basins. The results for the scattering Q estimates related to one-way transmission and multiple reflections are in the order of 20 to 100, as obtained from 1D analytical and elastic finite-difference models. Given the short propagation pathlengths in the experiment, the results show that attenuation due to lateral heterogeneity is non-significant. In addition, given the experimental geometry of shallow VSP studies, it is shown that the scattering estimates are affected from the presence of the near-field, local impedance, and interference effects, which are termed 'pseudo-Q' factors. The pseudo-Q factors result in a biased estimate for scattering Q derived from both time-domain and frequency-domain methods. Hence, to accurately model the scattering vs. intrinsic components of attenuation, the bias due to the pseudo-Q factors was accounted for. The intrinsic attenuation was deduced from comparison of the field data Q estimates, which contain scattering attenuation, intrinsic attenuation and effects from pseudo-Q factors with the elastic synthetic Q estimates. Results yield very low intrinsic Q values, in the order of 4 to 15, for the low and high scattering attenuation estimates respectively. The intrinsic attenuation is attributed to the interaction of the free gas present in the vadose zone with the compressional wave, which is the only known mechanism that can lead to absorption at seismic frequencies (White, 1975; Dutta and Seriff, 1979). Visco-elastic modeling shows that aside from amplitude decay, an intrinsic attenuation mechanism is required to produce the pulse broadening observed in the field data. For a typical set of conditions in the vadose zone, analytical modeling shows that it is possible for the effect of the free gas to account for the intrinsic Q values estimated for the LLNL profile. It is anticipated that attenuation will be very high in vadose environments similar to the LLNL profile, with intrinsic attenuation being the primary loss mechanism. Further research is required to establish the Q filter characteristics due to the free gas effect in the vadose zone and verify if an approximation with standard visco-elastic models, such as the SLS, is appropriate.

  5. The Use of Ultrasonic Seismic Wave Attenuation (Q) for Better Subsurface Imaging, Energy Exploration, and Tracking of Sequestrated Carbon Dioxide

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

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

    USGS Publications Warehouse

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  8. INDIRECT MEASUREMENT OF BIOLOGICAL ACTIVITY TO MONITOR NATURAL ATTENUATION

    EPA Science Inventory

    The remediation of ground water contamination by natural attenuation, specifically biodegradation, requires continual monitoring. This research is aimed at improving methods for evaluating the long-term performance of Monitored Natural Attenuation (MNA), specifically changes in ...

  9. Wave-speed dispersion associated with an attenuation obeying a frequency power law.

    PubMed

    Buckingham, Michael J

    2015-11-01

    An attenuation scaling as a power of frequency, |ω|(β), over an infinite bandwidth is neither analytic nor square-integrable, thus calling into question the application of the Kramers-Krönig dispersion relations for determining the frequency dependence of the associated phase speed. In this paper, three different approaches are developed, all of which return the dispersion formula for the wavenumber, K(ω). The first analysis relies on the properties of generalized functions and the causality requirement that the impulse response, k(t), the inverse Fourier transform of -iK(ω), must vanish for t < 0. Second, a wave equation is introduced that yields the phase-speed dispersion associated with a frequency-power-law attenuation. Finally, it is shown that, with minor modification, the Kramers-Krönig dispersion relations with no subtractions (the Plemelj formulas) do in fact hold for an attenuation scaling as |ω|(β), yielding the same dispersion formula as the other two derivations. From this dispersion formula, admissible values of the exponent β are established. Physically, the inadmissible values of β, which include all the integers, correspond to attenuation-dispersion pairs whose Fourier components cannot combine in such a way as to make the impulse response, k(t), vanish for t < 0. There is no upper or lower limit on the value that β may take. PMID:26627763

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

    USGS Publications Warehouse

    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.

  11. S-wave attenuation structure beneath the northern Izu-Bonin arc

    NASA Astrophysics Data System (ADS)

    Takahashi, Tsutomu; Obana, Koichiro; Kodaira, Shuichi

    2016-04-01

    To understand temperature structure or magma distribution in the crust and uppermost mantle, it is essential to know their attenuation structure. This study estimated the 3-D S-wave attenuation structure in the crust and uppermost mantle at the northern Izu-Bonin arc, taking into account the apparent attenuation due to multiple forward scattering. In the uppermost mantle, two areas of high seismic attenuation (high Q -1) imaged beneath the volcanic front were mostly colocated with low-velocity anomalies. This coincidence suggests that these high- Q -1 areas in low-velocity zones are the most likely candidates for high-temperature regions beneath volcanoes. The distribution of random inhomogeneities indicated the presence of three anomalies beneath the volcanic front: Two were in high- Q -1 areas but the third was in a moderate- Q -1 area, indicating a low correlation between random inhomogeneities and Q -1. All three anomalies of random inhomogeneities were rich in short-wavelength spectra. The most probable interpretation of such spectra is the presence of volcanic rock, which would be related to accumulated magma intrusion during episodes of volcanic activity. Therefore, the different distributions of Q -1 and random inhomogeneities imply that the positions of hot regions in the uppermost mantle beneath this arc have changed temporally; therefore, they may provide important constraints on the evolutionary processes of arc crust and volcanoes.

  12. An SVD-Polarization Filter for Surface Wave Attenuation on Multi-Component Data.

    NASA Astrophysics Data System (ADS)

    de Meersman, K.; Grion, S.; Ronen, S.

    2006-12-01

    We introduce a time-domain, complex SVD method to estimate and remove surface wave energy from multi- component exploration seismic data. Surface waves typically obscure the lower frequencies (5-20 Hz) of P- waves and S-waves that are reflected from potential exploration targets. They are therefore considered noise. Singular Value Decomposition, or SVD, is useful to extract surface wave energy from a set of seismic records that are `contaminated' with other modes and ambient noise. In ideal circumstances and with increasing number of traces N, the SVD provides a ground roll estimate in which leakage from P-wave and S-wave energy is reduced by √(N). The principal assumption is that for a fixed time-lag between traces, surface wave energy is correlated while other signals and noise are uncorrelated. When applied to multi-component data SVD not only has more data to work with, but it will also provide information on the polarization properties of the estimated waveform. This allows the design of so-called polarization filters that remove signals with specific polarization properties. The Hilbert transform is used to form the band limited analytic signal of a number of nearby multi-component records. We then run SVD over a sliding data-window to adaptively estimate the dominant signal, or first eigenimage, at the station of interest. Surface wave energy within this eigenimage can then be detected automatically using polarization and amplitude attributes that are provided by the SVD as well as velocity properties. A pure Rayleigh wave is elliptically polarized and of higher amplitude than linearly polarized reflections. Backscattered surface wave energy has random polarization, but is still typically of higher energy than reflections. Once the desired energy is removed from the first eigenimage we are left with a noise model that can be subtracted form the original shot record. We tested our adaptive polarization filter on synthetic and field data and we compare the output to that of other industry-standard surface wave attenuation techniques. Results indicate that our filter successfully removes surface wave energy. In contrast to FK-(dip)filters we find that our approach shows little sensitivity to spatial sampling and spatial aliasing. An additional advantage over FK-filters is that our approach provides better preservation of reflected signal within the surface wave frequency range.

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    On July 17, 2011 a ML 4.8 earthquake occurred in the PO valley at a 48 km epicentral distance from a seismic station located at Palazzo Te (Mantova). The station is situated on deep quaternary sediments: the uppermost layers are mainly composed of clay and silty clay with interbedded sands; the Robertson index is 1.4wave particle motion, that appears rather difficult to explain if we assume the homogeneity of the P waves (that means attenuation is scalar). Note that the degree of nonlinearity is very low given that the maximum strain can be roughly estimated as 10-5 on the basis of maximum ground velocity of the P wave train considered and the Vp. On the contrary we show that P wave particle motion can be fully (and easily) described by a Homogeneous Isotropic Linear Viscoelastic model (HILV). HILV, as in the 2009 Borcherdt formulation adopted here, allows two different directions of propagation and attenuation; in other words attenuation becomes a vector that is not necessarily parallel to the propagation vector. The results evidence that the incidence angle and the inhomogeneity angle (it is the angle between propagation and attenuation vectors and it is closely related to Q factor) are in good agreement with the geological conditions of the site. Finally, we observed that these results are very similar to the ones obtained when we analyzed two explosions recorded by a seismic station in Milano, also situated in the Po valley at some 140 km from Mantova (Marcellini & Tento, 2011). Borcherdt, R.D. (2009) 'Viscoelastic Waves in Layered Media', Cambridge University Press, Cambridge, United Kingdom, 305 pp. Marcellini, A. and A. Tento (2011) ' Explosive Sources Prove the Validity of Homogeneous Isotropic Linear Viscoelastic Models', BSSA, Vol. 101, No. 4, pp. 1576-1583.

  14. Measurement of ultrasonic scattering attenuation in austenitic stainless steel welds: realistic input data for NDT numerical modeling.

    PubMed

    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

  15. Tracking accelerated aging of composites with ultrasonic attenuation measurements

    SciTech Connect

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

    1996-10-01

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

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

    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.

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

    SciTech Connect

    Bull, Diana L; Ochs, Margaret Ellen

    2013-09-01

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

  18. Lapse time dependence of coda wave attenuation in Central West Turkey

    NASA Astrophysics Data System (ADS)

    Akyol, Nihal

    2015-09-01

    The attenuation of coda waves has been inferred for Central West Turkey, which is characterized by a very complex tectonic evolution. The selected dataset is composed of 440 waveforms from 228 local earthquakes with a magnitude range of 2.9-4.9. The coda quality factor (Qc) was estimated for five central frequencies (fc = 1.5, 3, 5, 7, 10 Hz) and eight lapse times (tL, ranging from 25 to 60 s), based on the assumption of single isotropic scattering model. Estimated Qc values were strongly dependent on frequency and lapse time. The frequency dependence of Qc values for each lapse time was inferred from Qc(f) = Q0fn relationships. Q0 values change between 32.7 and 82.1, while n values changes between 0.91 and 0.79 for the lapse times of 25 and 60 s, respectively. The obtained low Q0 values show that the Central West Turkey region is characterized by a high seismic attenuation, in general. The whole region was divided into four subregions to examine spatial differences of attenuation characteristics. Obtained 1/Q0 and n values versus the lapse time for each subregion implies the tectonic complexity of the region. Lapse time dependencies of attenuation and n values were also examined for subdatasets from two different ranges of event depth (h < 10 km and h ? 10 km) and distance (r < 40 km and r ? 40 km). High attenuation and its high frequency dependence for long distances manifest the elevation of isotherms and increasing heterogeneity with depth. This could be associated with the extensional intra-continental plate setting, forming regional tectonics in the back-arc area.

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

  20. Effect of soil texture and excitation frequency on the propagation and attenuation of acoustic waves at saturated conditions

    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.

  1. Measurements of seismic attenuation and transient fluid pressure in partially saturated Berea sandstone: evidence of fluid flow on the mesoscopic scale

    NASA Astrophysics Data System (ADS)

    Tisato, Nicola; Quintal, Beatriz

    2013-10-01

    A novel laboratory technique is proposed to investigate wave-induced fluid flow on the mesoscopic scale as a mechanism for seismic attenuation in partially saturated rocks. This technique combines measurements of seismic attenuation in the frequency range from 1 to 100 Hz with measurements of transient fluid pressure as a response of a step stress applied on top of the sample. We used a Berea sandstone sample partially saturated with water. The laboratory results suggest that wave-induced fluid flow on the mesoscopic scale is dominant in partially saturated samples. A 3-D numerical model representing the sample was used to verify the experimental results. Biot's equations of consolidation were solved with the finite-element method. Wave-induced fluid flow on the mesoscopic scale was the only attenuation mechanism accounted for in the numerical solution. The numerically calculated transient fluid pressure reproduced the laboratory data. Moreover, the numerically calculated attenuation, superposed to the frequency-independent matrix anelasticity, reproduced the attenuation measured in the laboratory in the partially saturated sample. This experimental-numerical fit demonstrates that wave-induced fluid flow on the mesoscopic scale and matrix anelasticity are the dominant mechanisms for seismic attenuation in partially saturated Berea sandstone.

  2. Quantum nondemolition measurements. [by gravitational wave antennas

    NASA Technical Reports Server (NTRS)

    Braginskii, V. B.; Vorontsov, Iu. I.; Thorne, K. S.

    1980-01-01

    The article describes new electronic techniques required for quantum nondemolition measurements and the theory underlying them. Consideration is given to resonant-bar gravitational-wave antennas. Position measurements are discussed along with energy measurements and back-action-evading measurements. Thermal noise in oscillators and amplifiers is outlined. Prospects for stroboscopic measurements are emphasized.

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

    PubMed

    Calvet, Marie; Margerin, Ludovic

    2012-03-01

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

  4. Magellan radio occultation measurements of atmospheric waves on Venus

    NASA Technical Reports Server (NTRS)

    Hinson, David P.; Jenkins, J. M.

    1995-01-01

    Radio occultation experiments were conducted at Venus on three consecutive orbits of the Magellan spacecraft in October 1991. Each occultation occurred over the same topography (67 deg N, 127 deg E) and at the same local time (22 hr 5 min), but the data are sensitive to zonal variations because the atmosphere rotates significantly during one orbit. Through comparisons between observations and predictions of standard wave theory, we have demonstrated that small-scale oscillations in retrieved temperature profiles as well as scintillations in received signal intensity are caused by a spectrum of vertically propagating internal gravity waves. There is a strong similarity between the intensity scintillations observed here and previous measurements, which pertain to a wide range of locations and experiment dates. This implies that the same basic phenomenon underlies all the observations and hence that gravity waves are a persistent, global feature of Venus' atmosphere. We obtained a fairly complete characterization of a gravity wave that appears above the middle cloud in temperature measurements on all three orbits. The amplitude and vertical wavelength are about 4 K and 2.5 km respectively, at 65 km. A model for radiative damping implies that the wave intrinsic frequency is approximately 2 x 10(exp 4) rad/sec, the corresponding ratio between horizontal and vertical wavelengths is approximately 100. The wave is nearly stationary relative to the surface or the Sun. Radiative attenuation limits the wave amplitude at altitudes above approximately 65 km, leading to wave drag on the mean zonal winds of about +0.4 m/sec per day (eastward). The sign, magnitude, and location of this forcing suggest a possible role in explaining the decrease with height in the zonal wind speed that is believed to occur above the cloud tops. Temperature oscillations with larger vertical wavelengths (5-10 km) were also observed on all three orbits, but we are able unable to interpret these unambiguously.

  5. Experimental and theoretical investigation of stress wave attenuation in fiber reinforced composites.

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-03-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2008-03-01

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

  9. Degree-2 pattern of attenuation structure in the upper mantle from apparent complex frequency measurements of fundamental spheroidal modes

    SciTech Connect

    Suda, Naoki; Shibata, Naoki; Fukao, Yoshio )

    1991-06-01

    The authors present preliminary results of an analysis of global lateral variations in elastic and anelastic structure of the upper mantle. Using the Sompi method, they have analyzed IDA records to measure apparent complex frequencies of fundamental spheroidal modes {sub 0}S{sub 21}-{sub 0}S{sub 34}, which are primarily sensitive to the structure of the transition zone. The apparent complex frequencies have then been inverted into local frequency and attenuation maps using the new inversion method. The authors have obtained consistent degree-2 patterns in the local attenuation maps as well as in the local frequency maps. The high-attenuation anomalies correlate with regions of slow P-wave velocity in the lower mantle and with regions of high hotspot density. This may represent a continuation of lower-mantle upwelling into the transition zone.

  10. Physical Models of Seismic-Attenuation Measurements on Lab Samples

    NASA Astrophysics Data System (ADS)

    Coulman, T. J.; Morozov, I. B.

    2012-12-01

    Seismic attenuation in Earth materials is often measured in the lab by using low-frequency forced oscillations or static creep experiments. The usual assumption in interpreting and even designing such experiments is the "viscoelastic" behavior of materials, i.e., their description by the notions of a Q-factor and material memory. However, this is not the only theoretical approach to internal friction, and it also involves several contradictions with conventional mechanics. From the viewpoint of mechanics, the frequency-dependent Q becomes a particularly enigmatic property attributed to the material. At the same time, the behavior of rock samples in seismic-attenuation experiments can be explained by a strictly mechanical approach. We use this approach to simulate such experiments analytically and numerically for a system of two cylinders consisting of a rock sample and elastic standard undergoing forced oscillations, and also for a single rock sample cylinder undergoing static creep. The system is subject to oscillatory compression or torsion, and the phase-lag between the sample and standard is measured. Unlike in the viscoelastic approach, a full Lagrangian formulation is considered, in which material anelasticity is described by parameters of "solid viscosity" and a dissipation function from which the constitutive equation is derived. Results show that this physical model of anelasticity predicts creep results very close to those obtained by using empirical Burger's bodies or Andrade laws. With nonlinear (non-Newtonian) solid viscosity, the system shows an almost instantaneous initial deformation followed by slow creep towards an equilibrium. For Aheim Dunite, the "rheologic" parameters of nonlinear viscosity are υ=0.79 and η=2.4 GPa-s. Phase-lag results for nonlinear viscosity show Q's slowly decreasing with frequency. To explain a Q increasing with frequency (which is often observed in the lab and in the field), one has to consider nonlinear viscosity with υ < 0.5 and/or include thermoelastic effects. The model also shows how the Q values measured on the samples depend on the shapes and dimensions of the elements of the experimental system.; Non-linear creep approximating the anelastic part of Burgers' model for Aheim dunite (Chopra, 1997). Non-linear model parameters are υ=0.79, η=2.4 GPa-s, and the Burger's model parameters are: μ=15.75 GPa and viscosity η=2040 GPa-s.

  11. Measurement of Elastic Properties of Tissue by Shear Wave Propagation Generated by Acoustic Radiation Force

    NASA Astrophysics Data System (ADS)

    Marie Tabaru,; Takashi Azuma,; Kunio Hashiba,

    2010-07-01

    Acoustic radiation force (ARF) imaging has been developed as a novel elastography technology to diagnose hepatic disease and breast cancer. The accuracy of shear wave speed estimation, which is one of the applications of ARF elastography, is studied. The Young’s moduli of pig liver and foie gras samples estimated from the shear wave speed were compared with those measured the static Young’s modulus measurement. The difference in the two methods was 8%. Distance attenuation characteristics of the shear wave were also studied using finite element method (FEM) analysis. We found that the differences in the axial and lateral beam widths in pressure and ARF are 16 and 9% at F-number=0.9. We studied the relationship between two branch points in distance attenuation characteristics and the shape of ARF. We found that the maximum measurable length to estimate shear wave speed for one ARF excitation was 8 mm.

  12. Measurement of Elastic Properties of Tissue by Shear Wave Propagation Generated by Acoustic Radiation Force

    NASA Astrophysics Data System (ADS)

    Tabaru, Marie; Azuma, Takashi; Hashiba, Kunio

    2010-07-01

    Acoustic radiation force (ARF) imaging has been developed as a novel elastography technology to diagnose hepatic disease and breast cancer. The accuracy of shear wave speed estimation, which is one of the applications of ARF elastography, is studied. The Young's moduli of pig liver and foie gras samples estimated from the shear wave speed were compared with those measured the static Young's modulus measurement. The difference in the two methods was 8%. Distance attenuation characteristics of the shear wave were also studied using finite element method (FEM) analysis. We found that the differences in the axial and lateral beam widths in pressure and ARF are 16 and 9% at F-number=0.9. We studied the relationship between two branch points in distance attenuation characteristics and the shape of ARF. We found that the maximum measurable length to estimate shear wave speed for one ARF excitation was 8 mm.

  13. Characteristics of the near-bottom suspended sediment field over the continental shelf off northern California based on optical attenuation measurements during STRESS and SMILE

    USGS Publications Warehouse

    Trowbridge, J.H.; Butman, B.; Limeburner, R.

    1994-01-01

    Time-series measurements of current velocity, optical attenuation and surface wave intensity obtained during the Sediment Transport Events on Shelves and Slopes (STRESS) experiments, combined with shipboard measurements of conductivity, temperature and optical attenuation obtained during the Shelf Mixed Layer Experiment (SMILE), provide a description of the sediment concentration field over the central and outer shelf off northern California. The questions addressed are: (1) existence and characteristics of bottom nepheloid layers and their relationship to bottom mixed layers; (2) characteristics of temporal fluctuations in sediment concentration and their relationship to waves and currents; (3) spatial scales over which suspended sediment concentrations vary horizontally; and (4) vertical distribution of suspended sediment. ?? 1994.

  14. High-resolution 3-D P wave attenuation structure of the New Madrid Seismic Zone using local earthquake tomography

    NASA Astrophysics Data System (ADS)

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

    2014-01-01

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

  15. Wave measurements using GPS velocity signals.

    PubMed

    Doong, Dong-Jiing; Lee, Beng-Chun; Kao, Chia Chuen

    2011-01-01

    This study presents the idea of using GPS-output velocity signals to obtain wave measurement data. The application of the transformation from a velocity spectrum to a displacement spectrum in conjunction with the directional wave spectral theory are the core concepts in this study. Laboratory experiments were conducted to verify the accuracy of the inversed displacement of the surface of the sea. A GPS device was installed on a moored accelerometer buoy to verify the GPS-derived wave parameters. It was determined that loss or drifting of the GPS signal, as well as energy spikes occurring in the low frequency band led to erroneous measurements. Through the application of moving average skill and a process of frequency cut-off to the GPS output velocity, correlations between GPS-derived, and accelerometer buoy-measured significant wave heights and periods were both improved to 0.95. The GPS-derived one-dimensional and directional wave spectra were in agreement with the measurements. Despite the direction verification showing a 10° bias, this exercise still provided useful information with sufficient accuracy for a number of specific purposes. The results presented in this study indicate that using GPS output velocity is a reasonable alternative for the measurement of ocean waves. PMID:22346618

  16. Comparison of OLYMPUS beacon and radiometric attenuation measurements at Blacksburg, Virginia

    NASA Technical Reports Server (NTRS)

    Snider, J. B.; Jacobson, M. D.; Beeler, R. H.; Hazen, D. A.

    1991-01-01

    Measurements of attenuation of the 20 and 30 GHz beacons onboard the OLYMPUS satellite are compared to simultaneous observations of atmospheric attenuation by a multichannel microwave radiometer along the same path. Departures from high correlation between the two measurements are believed to be related to differences in antenna beamwidths. Mean equivalent zenith attenuations derived from the slant path data are compared to zenith observations made at previous locations.

  17. Frequency dependent attenuation characteristics of coda waves in the Northwestern Himalayan (India) region

    NASA Astrophysics Data System (ADS)

    Kumar, Sushil; Singh, Priyamvada; Singh, Pitam; Biswal, Shubhasmita; Parija, Mahesh Prasad

    2016-03-01

    Digital seismogram data of 82 earthquakes from the Northwestern Himalayan (India) region recorded at different stations during 2004-2006 were analyzed to study the seismic coda wave attenuation characteristics in this region. We used 132 seismic observations from local earthquakes with a hypocentral distance <240 km and a magnitude range of 1.2-4.9 to study the coda QC using the single isotropic scattering model. These earthquakes were recorded at 20 temporary seismic stations installed in the Northwestern Himalayas (India) by the Wadia institute of Himalayan Geology, Dehradun. The QC values were estimated at 10 central frequencies: 1.5, 3, 5, 7, 9, 12, 16, 20, 24, and 28 Hz using starting lapse-times of 10, 20, 30, 40, 50, and 60 s and coda window-lengths of 10, 20, 30, 40, and 50 s. The QC fits the frequency dependent power-law, QC =Q0fn . For a 10 s lapse time with a 10-s coda window length QC = 47.42f1.012 and for a 50 s lapse time with a 50 s coda window length, QC = 204.1f0.934 . Q0 (QC at 1 Hz) varied from ∼47 for a 10 s lapse time and a 10 s window length, to ∼204 for a 50 s lapse time and a 50 s window length. An average frequency dependent power law fit for the study region may be given as QC = 116.716f0.9943 . The exponent of the frequency dependence law n ranged from 1.08 to 0.9, which correlates well with values obtained in other seismically and tectonically active and heterogeneous regions of the world. In our study region, QC increases both with respect to lapse time and frequency, i.e., the attenuation decreases as the quality factor is inversely proportional to attenuation. The low QC values or high attenuation at lower frequencies and high QC values or low attenuation at higher frequencies suggest that the heterogeneity decreases with increasing depth in our study region.

  18. Measurements for the JASPER Program radial shield attenuation experiment

    SciTech Connect

    Mukenthaler, F.J.

    1987-05-01

    The Radial Shield Attenuation Experiment was conducted at the Oak Ridge National Laboratory Tower Shielding Facility during FY 1986 to: provide data for calculating the shielding effectiveness of combinations of stainless steel, graphite, and boron carbide shield designs; verify the accuracy of related radiation transport methods and nuclear data; and substantiate the effectiveness of shield designs currently proposed by advanced Liquid Metal Reactor (LMR) designers in Japan and the United States. The Tower Shielding Reactor source was modified to represent neutron spectra at a specified location near the core and in the sodium pool of a typical liquid-metal-cooled reactor. The experimental configurations resulted from successive additions of the various layers of material as specified in the program plan. Integral neutron fluxes were measured behind each of the configurations at specified locations, and neutron spectra were obtained for selected mockups. The experimental data are presented in both tabular and graphical form. This experiment is the first in a series of six experiments to be performed as part of a cooperative effort between the United States Department of Energy and the Japan Power Reactor and Nuclear Fuel Development Corporation. The research program is intended to provide support for the development of advanced sodium-cooled reactors.

  19. Systematic scanner variability of patient CT attenuation measurements

    NASA Astrophysics Data System (ADS)

    Judy, Philip F.; Nawfel, Richard D.; Silverman, Stuart G.

    2009-02-01

    CT numbers of the spleen, liver, and trachea air were measured from non-contrast images obtained from 4-channel and 64-channel scanners from the same vendor. Image sections of 1 mm and 5 mm were reconstructed using smooth and sharp kernels. For spleen and liver, no significant differences associated with the variations in kernels or slice thickness could be demonstrated. The increase of the number of channels from 4 to 64 lowered the spleen CT numbers from 53 HU to 43 HU (p <0.00001). The 4-channel spleen CT numbers slightly increased as function of patient size, while the 64-channel CT numbers decreased as function of patient size. Linear regressions predicted for 40-cm patients the spleen 64-channel CT values were 23 HU lower than 4-channel CT numbers. The smooth kernel, 4-channel trachea air CT numbers had mean of -1004 +/-4.8 HU and the 64-channel trachea air CT numbers had a mean of -989+/-4.5 HU. The patient-size dependencies suggest that the CT attenuation variation is associated with increased scatter in 64-channel MSCT. Using CT number to distinguish solid lesions from cysts or quantitative evaluation of COPD disease using CT images may be complicated by inconsistencies between CT scanners.

  20. A Simulation Study to Explain the Variability of Ultrasonic Attenuation Measurement in RTM Composites

    NASA Astrophysics Data System (ADS)

    Lonné, Sébastien; Lhémery, Alain; Thévenot, Françoise

    2004-02-01

    Ultrasonic attenuation is strongly variable and possibly high in parts made of RTM (resin transfer molding) composite that often possess an irregular inner structure. To explain this, models of attenuation phenomena at different scales are used in an overall model of wave propagation: multiple scattering by fibers coupled with viscoelastic losses, viscoelastic losses in pure matrix layers, scattering by porosities and by irregular interface geometry. A statistical study with variable structural parameters successfully explains amplitude variability experimentally observed.

  1. Shear wave speed and dispersion measurements using crawling wave chirps.

    PubMed

    Hah, Zaegyoo; Partin, Alexander; Parker, Kevin J

    2014-10-01

    This article demonstrates the measurement of shear wave speed and shear speed dispersion of biomaterials using a chirp signal that launches waves over a range of frequencies. A biomaterial is vibrated by two vibration sources that generate shear waves inside the medium, which is scanned by an ultrasound imaging system. Doppler processing of the acquired signal produces an image of the square of vibration amplitude that shows repetitive constructive and destructive interference patterns called "crawling waves." With a chirp vibration signal, successive Doppler frames are generated from different source frequencies. Collected frames generate a distinctive pattern which is used to calculate the shear speed and shear speed dispersion. A special reciprocal chirp is designed such that the equi-phase lines of a motion slice image are straight lines. Detailed analysis is provided to generate a closed-form solution for calculating the shear wave speed and the dispersion. Also several phantoms and an ex vivo human liver sample are scanned and the estimation results are presented. PMID:24658144

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

    PubMed

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

    2013-12-01

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

  3. Closing the Gap on Measuring Heat Waves

    NASA Astrophysics Data System (ADS)

    Perkins, S. E.; Alexander, L.

    2012-12-01

    Since the 4th IPCC assessment report, the scientific literature has established that anthropogenic climate change encompasses adverse changes in both mean climate conditions and extreme events, such as heat waves. Indeed, the affects of heat waves are felt across many different sectors, and have high economic, human, and physical impacts over many global regions. The spatial and monetary scale of heat wave impacts emphasizes the necessity of measuring and studying such events in an informative manner, which gives justice to the geographical region affected, the communities impacted, and the climatic fields involved. However, due to such wide interest in heat waves, their definition remains broad in describing a period of consecutive days where conditions are excessively hotter than normal. This has allowed for the employment of a plethora of metrics, which are usually unique to a given sector, or do not appropriately describe some of the important features of heat wave events. As such, it is difficult to ascertain a clear message regarding changes in heat waves, both in the observed record and in projections of future climate. This study addresses this issue by developing a multi-index, multi-aspect framework in which to measure heat waves. The methodology was constructed by assessing a wide range of heat wave and heat wave-related indices, both proposed and employed in the scientific literature. The broad implications of the occurrences, frequency and duration of heat waves and respective changes were also highly considered. The resulting indices measure three or more consecutive days where 1) maximum temperature exceeds the 90th percentile (TX90pct); 2) minimum temperature exceeds the 90th percentile (TN90pct); and 3) daily average temperature has a positive excess heat factor (EHF). The 90th percentiles from which TX90pct and TN90pct are calculated are based on 15-day windows for each calendar day, whereas the EHF is based upon two pre-calculated indices that compare the temperature of a three-day window to the previous 30 days and the climatological 95th percentile (see Nairn and Fawcett, 2012, CAWCR Technical Report). Based on a previously defined methodology (Fischer and Shar, 2010, Nature Geoscience), each index is analysed with respect to five properties - heat wave number (HWN) and length (HWD), the number of participating days (HWF), the amplitude or peak of the hottest day (HWA), and mean heat wave magnitude (HWM), thereby assessing the occurrence, intensity and duration of heat waves for each index. The methodology is demonstrated for characterizing changes in observed heat waves at the global scale and regionally over Australia for the latter half of the 20th Century. Overall, general increases in heat wave intensity and duration occur, although the magnitude and significance of this trend shows variation both regionally and among the indices. Trend magnitudes also differ for "warm-spell" (year-round) and summer only events. This framework therefore allows for the broad examination of heat waves, such that the results presented are informative to multiple sectors affected by such events. Indeed, it "closes the gap" on heat wave measurement by reducing the number of indices employed, yet realizing that heat wave measurement cannot be a one size fits all approach, and that there is more than one feature of heat waves that causes adverse impacts.

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

    NASA Astrophysics Data System (ADS)

    Li, Xiaobo; Dong, Liangguo; Zhao, Qun

    2014-12-01

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

  5. Weak measurement and Bohmian conditional wave functions

    SciTech Connect

    Norsen, Travis; Struyve, Ward

    2014-11-15

    It was recently pointed out and demonstrated experimentally by Lundeen et al. that the wave function of a particle (more precisely, the wave function possessed by each member of an ensemble of identically-prepared particles) can be “directly measured” using weak measurement. Here it is shown that if this same technique is applied, with appropriate post-selection, to one particle from a perhaps entangled multi-particle system, the result is precisely the so-called “conditional wave function” of Bohmian mechanics. Thus, a plausibly operationalist method for defining the wave function of a quantum mechanical sub-system corresponds to the natural definition of a sub-system wave function which Bohmian mechanics uniquely makes possible. Similarly, a weak-measurement-based procedure for directly measuring a sub-system’s density matrix should yield, under appropriate circumstances, the Bohmian “conditional density matrix” as opposed to the standard reduced density matrix. Experimental arrangements to demonstrate this behavior–and also thereby reveal the non-local dependence of sub-system state functions on distant interventions–are suggested and discussed. - Highlights: • We study a “direct measurement” protocol for wave functions and density matrices. • Weakly measured states of entangled particles correspond to Bohmian conditional states. • Novel method of observing quantum non-locality is proposed.

  6. Using Kinect to Measure Wave Spectrum

    NASA Astrophysics Data System (ADS)

    Fong, J.; Loose, B.; Lovely, A.

    2012-12-01

    Gas exchange at the air-sea interface is enhanced by aqueous turbulence generated by capillary-gravity waves, affecting the absorption of atmospheric carbon dioxide by the ocean. The mean squared wave slope of these waves correlates strongly with the gas transfer velocity. To measure the energy in capillary-gravity waves, this project aims to use the Microsoft Xbox Kinect to measure the short period wave spectrum. Kinect is an input device for the Xbox 360 with an infrared laser and camera that can be used to map objects at high frequency and spatial resolution, similar to a LiDAR sensor. For air-sea gas exchange, we are interested in the short period gravity waves with a wavenumber of 40 to 100 radians per meter. We have successfully recorded data from Kinect at a sample rate of 30 Hz with 640x480 pixel resolution, consistent with the manufacturer specifications for its scanning capabilities. At 0.5 m distance from the surface, this yields a nominal resolution of approximately 0.7 mm with a theoretical vertical precision of 0.24 mm and a practical 1 σ noise level of 0.91 mm. We have found that Kinect has some limitations in its ability to detect the air-water interface. Clean water proved to be a weaker reflector for the Kinect IR source, whereas a relatively strong signal can be received for liquids with a high concentration of suspended solids. Colloids such as milk and Ca(OH)2 in water proved more suitable media from which height and wave spectra were detectable. Moreover, we will show results from monochromatic as well as wind-wave laboratory studies. With the wave field measurements from Kinect, gas transfer velocities at the air-sea interface can be determined.

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

    NASA Technical Reports Server (NTRS)

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

    2007-01-01

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

  8. Attenuation Characteristics of Body-Waves for the Bilaspur Region of Himachal Lesser Himalaya

    NASA Astrophysics Data System (ADS)

    Vandana; Kumar, Ashwani; Gupta, S. C.

    2016-02-01

    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 α ) and S-waves ( Q β ) in the frequency range from 1.5 to 24 Hz are: ( Q α ) = (43 ± 4) f 1.30±0.04 and Q β = (79 ± 6) f 1.25±0.02. The average estimates of ( Q α ) and ( Q β ) are found to vary from 71 and 125 at 1.5 Hz to 2901 and 4243 at 24 Hz, respectively. The ( Q α ) and ( Q β ) 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 α ) estimates at 1 Hz vary between 22 (for the Kumaon Himalaya) and 97 (for the northwest Himalaya), whereas ( Q β ) estimates range between 63 (for the Garhwal Himalaya) and 127 (for the northwest Himalaya). For the Bilaspur region, the ( Q β )/( Q α ) 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.

  9. Continuous measurement with traveling-wave probes

    SciTech Connect

    Silberfarb, Andrew; Deutsch, Ivan H.

    2003-07-01

    We consider the use of a traveling-wave probe to continuously measure the quantum state of an atom in free space. Unlike the more familiar cavity QED geometry, the traveling wave is intrinsically a multimode problem. Using an appropriate modal decomposition, we determine the effective measurement strength for different atom-field interactions and different initial states of the field. These include the interaction of a coherent-state pulse with an atom, the interaction of a Fock-state pulse with an atom, and the use of Faraday rotation of a polarized laser probe to perform a quantum nondemolition measurement on an atomic spin.

  10. Ultrasonic attenuation measurements at very high SNR: Correlation, information theory and performance

    NASA Astrophysics Data System (ADS)

    Challis, Richard; Ivchenko, Vladimir; Al-Lashi, Raied

    2013-08-01

    This paper describes a system for ultrasonic wave attenuation measurements which is based on pseudo-random binary codes as transmission signals combined with on-the-fly correlation for received signal detection. The apparatus can receive signals in the nanovolt range against a noise background in the order of hundreds of microvolts and an analogue to digital convertor (ADC) bit-step also in the order of hundreds of microvolts. Very high signal to noise ratios (SNRs) are achieved without recourse to coherent averaging with its associated requirement for high sampling times. The system works by a process of dithering - in which very low amplitude received signals enter the dynamic range of the ADC by 'riding' on electronic noise at the system input. The amplitude of this 'useful noise' has to be chosen with care for an optimised design. The process of optimisation is explained on the basis of classical information theory and is achieved through a simple noise model. The performance of the system is examined for different transmitted code lengths and gain settings in the receiver chain. Experimental results are shown to verify the expected operation when the system is applied to a very highly attenuating material - an aerated slurry.

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

    NASA Technical Reports Server (NTRS)

    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.

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

    SciTech Connect

    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.

  13. An improvement in the VIRGO Super Attenuator for interferometric detection of gravitational waves: The use of a magnetic antispring

    SciTech Connect

    Braccini, S.; Bradaschia, C.; Cobal, M.; Del Fabbro, R.; Di Virgilio, A.; Flaminio, R.; Giazotto, A.; Kautzky, H.; Morganti, M.; Passuello, D. ); Calloni, E.; Di Fiore, L. ); Holloway, L.E. ); Montelatici, V. )

    1993-02-01

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

  14. Flying helmet attenuation, and the measurement, with particular reference to the Mk 4 helmet

    NASA Astrophysics Data System (ADS)

    Rood, G. M.

    1981-06-01

    To predict the intelligibility of communication systems, it is necessary to be able to measure helmet attenuation accurately and repeatably, and it is this particular aspect which is highlighted. Some of the results from a comprehensive series of tests involving subjective and semiobjective measurement of the attenuation of noise by flying helmets are discussed. The analysis shows that the semiobjective method of ascertaining hearing protector or flying helmet attenuation, using miniature measuring microphones, is a viable alternative to the existing standard REAT methods, and has considerable advantages in providing more useful information in less time. Additionally, high correlations exist between laboratory and in-flight mesurements of attenuation, clearly indicating that laboratory measurements reproduce helmet attenuation actually found in the air.

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

    NASA Astrophysics Data System (ADS)

    Lin, Guoqing

    2014-04-01

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

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

    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.

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

    SciTech Connect

    Maurel, Agnes; Pagneux, Vincent; Barra, Felipe; Lund, Fernando

    2005-11-01

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

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

    ERIC Educational Resources Information Center

    Padilla, Miguel A.; Veprinsky, Anna

    2012-01-01

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

  19. Assessment of Reinforced Concrete Surface Breaking Crack Using Rayleigh Wave Measurement

    PubMed Central

    Lee, Foo Wei; Chai, Hwa Kian; Lim, Kok Sing

    2016-01-01

    An improved single sided Rayleigh wave (R-wave) measurement was suggested to characterize surface breaking crack in steel reinforced concrete structures. Numerical simulations were performed to clarify the behavior of R-waves interacting with surface breaking crack with different depths and degrees of inclinations. Through analysis of simulation results, correlations between R-wave parameters of interest and crack characteristics (depth and degree of inclination) were obtained, which were then validated by experimental measurement of concrete specimens instigated with vertical and inclined artificial cracks of different depths. Wave parameters including velocity and amplitude attenuation for each case were studied. The correlations allowed us to estimate the depth and inclination of cracks measured experimentally with acceptable discrepancies, particularly for cracks which are relatively shallow and when the crack depth is smaller than the wavelength. PMID:26959028

  20. Assessment of Reinforced Concrete Surface Breaking Crack Using Rayleigh Wave Measurement.

    PubMed

    Lee, Foo Wei; Chai, Hwa Kian; Lim, Kok Sing

    2016-01-01

    An improved single sided Rayleigh wave (R-wave) measurement was suggested to characterize surface breaking crack in steel reinforced concrete structures. Numerical simulations were performed to clarify the behavior of R-waves interacting with surface breaking crack with different depths and degrees of inclinations. Through analysis of simulation results, correlations between R-wave parameters of interest and crack characteristics (depth and degree of inclination) were obtained, which were then validated by experimental measurement of concrete specimens instigated with vertical and inclined artificial cracks of different depths. Wave parameters including velocity and amplitude attenuation for each case were studied. The correlations allowed us to estimate the depth and inclination of cracks measured experimentally with acceptable discrepancies, particularly for cracks which are relatively shallow and when the crack depth is smaller than the wavelength. PMID:26959028

  1. Teleseismic P wave spectra from USArray and implications for upper mantle attenuation and scattering

    NASA Astrophysics Data System (ADS)

    Cafferky, Samantha; Schmandt, Brandon

    2015-10-01

    Teleseismic P wave amplitude spectra from deep earthquakes recorded by USArray are inverted for maps of upper mantle ?t* for multiple frequency bands within 0.08-2 Hz. All frequency bands show high ?t* regions in the southwestern U.S., southern Rocky Mountains, and Appalachian margin. Low ?t* is more common across the cratonic interior. Inversions with narrower frequency bands yield similar patterns, but greater ?t* magnitudes. Even the two standard deviation ?t* magnitude for the widest band is 2-7 times greater than predicted by global QS tomography or an anelastic olivine thermal model, suggesting that much of the ?t* signal is nonthermal in origin. Nonthermal contributions are further indicated by only a moderate correlation between ?t* and P travel times. Some geographic variations, such as high ?t* in parts of the cratonic interior with high mantle velocities and low heat flow, demonstrate that the influence of temperature is regionally overwhelmed. Transverse spectra are used to investigate the importance of scattering because they would receive no P energy in the absence of 3-D heterogeneity or anisotropy. Transverse to vertical (T/Z) spectral ratios for stations with high ?t* are higher and exhibit steeper increases with frequency compared to T/Z spectra for low ?t* stations. The large magnitude of ?t* estimates and the T/Z spectra are consistent with major contributions to ?t* from scattering. A weak positive correlation between intrinsic attenuation and apparent attenuation due to scattering may contribute to ?t* magnitude and the moderate correlation of ?t* with travel times.

  2. Seismoelectric Wave Measurements in Borehole Models

    NASA Astrophysics Data System (ADS)

    Wang, J.; Hu, H.; Guan, W.

    2014-12-01

    An experimental system was built in the laboratory based on the electrokinetic theory, which contains a small scaled seismoelectric detector and a high resolution digitizer ( 1 MS/s, 22 bits ). The electrokinetic measurements are carried out with seismoelectric well logging technique in borehole models at high frequency (90 kHz), and the localized electrokinetic fields that accompany compressional wave, shear wave and Stoneley wave are clearly observed with monopole source in two sandstone models that are saturated by tap water. The magnitudes of these seismoelectric waves are in the range of 1-100 microvolt, which is useful for designing the seismoelectric logging instruments. The experimental results also show that the seismoelectric well logging signals are related to the permeability of borehole formations. Their amplitudes become larger in the high permeability model, which can be used to measure the permeability of rock formation although no such relationship has ever been provided in existing theories. We also made seismoelectric measurements in a lucite borehole model, but no observable seismoelectric signals were recorded by the electrode. This is not out of our expectation because the lucite formation is not porous and no electrokinetic conversion occurs in such material. However, the electric signal recorded in the Lucite borehole represents the background noise of our measurement system, which is less than 0.5 microvolt. This study verifies the feasibility of seismoelectric well logging, and also presents the range of seismoelectric signals in borehole saturated by tap water that is much closer to the condition of actual formation.

  3. Vibration and wave propagation attenuation for metamaterials by periodic piezoelectric arrays with high-order resonant circuit shunts

    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.

  4. Spectroscopic measurement of an atomic wave function

    SciTech Connect

    Kapale, Kishore T.; Qamar, Shahid; Zubairy, M. Suhail

    2003-02-01

    We present a simple spectroscopic method based on Autler-Townes spectroscopy to determine the center-of-mass atomic wave function. The detection of spontaneously emitted photons from a three-level atom, in which two upper levels are driven by a classical standing light, yields information about the position and momentum distribution of the atom [A. M. Herkommer, W. P. Schleich, and M. S. Zubairy, J. Mod. Opt. 44, 2507 (1997)]. In this paper, we show that both the amplitude and phase information of the center-of-mass atomic wave function can be obtained from these distributions after a series of conditional measurements on the atom and the emitted photon.

  5. Measuring the quantum mechanical wave function

    NASA Astrophysics Data System (ADS)

    Raymer, M. G.

    1997-05-01

    In the past few years experimenters have learned how to determine the complete quantum state of an ensemble of particles or fields which have been prepared according to some unknown procedure. Through these experiments they have answered a question posed by W. Pauli in the 1930s. The methods used involve measuring statistical distributions of a well chosen set of physical observables and using a tomographic inversion algorithm to reconstruct the Wigner function and its corresponding wave function or density matrix. Recontructions have been successfully carried out in atomic, molecular, and optical physics. The development of these procedures helps to firm up the interpretation of the Schrodinger wave function.

  6. Effect of Viscous Cross Coupling between two Immiscible Fluids on Elastic Wave Propagation and Attenuation in Unsaturated Porous Media

    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.

  7. Nonlinear attenuation from the interaction between different types of seismic waves and interaction of seismic waves with shallow ambient tectonic stress

    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.

  8. Improved estimation of P-wave velocity, S-wave velocity, and attenuation factor by iterative structural joint inversion of crosswell seismic data

    NASA Astrophysics Data System (ADS)

    Zhu, Tieyuan; Harris, Jerry M.

    2015-12-01

    We present an iterative joint inversion approach for improving the consistence of estimated P-wave velocity, S-wave velocity and attenuation factor models. This type of inversion scheme links two or more independent inversions using a joint constraint, which is constructed by the cross-gradient function in this paper. The primary advantages of this joint inversion strategy are: avoiding weighting for different datasets in conventional simultaneous joint inversion, flexible for incorporating prior information, and relatively easy to code. We demonstrate the algorithm with two synthetic examples and two field datasets. The inversions for P- and S-wave velocity are based on ray traveltime tomography. The results of the first synthetic example show that the iterative joint inversion take advantages of both P- and S-wave sensitivity to resolve their ambiguities as well as improve structural similarity between P- and S-wave velocity models. In the second synthetic and field examples, joint inversion of P- and S-wave traveltimes results in an improved Vs velocity model that shows better structural correlation with the Vp model. More importantly, the resultant VP/VS ratio map has fewer artifacts and is better correlated for use in geological interpretation than the independent inversions. The second field example illustrates that the flexible joint inversion algorithm using frequency-shift data gives a structurally improved attenuation factor map constrained by a prior VP tomogram.

  9. Attenuation of elastic waves in bentonite and monitoring of radioactive waste repositories

    NASA Astrophysics Data System (ADS)

    Biryukov, A.; Tisato, N.; Grasselli, G.

    2016-04-01

    Deep geological repositories, isolated from the geosphere by an engineered bentonite barrier, are currently considered the safest solution for high-level radioactive waste (HLRW) disposal. As the physical conditions and properties of the bentonite barrier are anticipated to change with time, seismic tomography was suggested as a viable technique to monitor the physical state and integrity of the barrier and to timely detect any unforeseen failure. To do so, the seismic monitoring system needs to be optimized, and this can be achieved by conducting numerical simulations of wave propagation in the repository geometry. Previous studies treated bentonite as an elastic medium, whereas recent experimental investigations indicate its pronounced viscoelastic behaviour. The aims of this contribution are (i) to numerically estimate the effective attenuation of bentonite as a function of temperature T and water content Wc, so that synthetic data can accurately reproduce experimental traces and (ii) assess the feasibility and limitation of the HLRW repository monitoring by simulating the propagation of sonic waves in a realistic repository geometry. A finite difference method was utilized to simulate the wave propagation in experimental and repository setups. First, the input of the viscoelastic model was varied to achieve a match between experimental and numerical traces. The routine was repeated for several values of Wc and T, so that quality factors Qp(Wc, T) and Qs(Wc, T) were obtained. Then, the full-scale monitoring procedure was simulated for six scenarios, representing the evolution of bentonite's physical state. The estimated Qp and Qs exhibited a minimum at Wc = 20 per cent and higher sensitivity to Wc, rather than T, suggesting that pronounced inelasticity of the clay has to be taken into account in geophysical modelling and analysis. The repository-model traces confirm that active seismic monitoring is, in principle, capable of depicting physical changes in the bentonite barrier. However, the locations of sources and receivers relative to the tunnel need to be optimized to achieve best sensitivity to the changes. It was also observed that first arrivals do not necessarily represent the most informative part of the signal; thus the time windows of the analysis need to be selected, accounting for the geometry of the acquisition system. This contribution should be considered as a next step towards the development of a numerical approach to aid in the design and optimization of a non-intrusive monitoring system in HLRW repositories.

  10. Computer signal processing for ultrasonic attenuation and velocity measurements for material property characterizations

    NASA Technical Reports Server (NTRS)

    Vary, A.

    1979-01-01

    Instrumentation and computer programming concepts that were developed for ultrasonic materials characterization are described. Methods that facilitate velocity and attenuation measurements are outlined. The apparatus described is based on a broadband, buffered contact probe using a pulse-echo approach for simultaneously measuring velocity and attenuation. Instrumentation, specimen condition, and signal acquisition and acceptance criteria are discussed. Typical results with some representative materials are presented.

  11. Setting Time Measurement Using Ultrasonic Wave Reflection

    SciTech Connect

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

    2012-01-09

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

  12. Preparation, Characterization, and Millimeter Wave Attenuation of Carbon Fibers Coated with Ni-Cu-P and Ni-Co-P Alloys

    NASA Astrophysics Data System (ADS)

    Ye, Mingquan; Li, Zhitao; Wang, Chen; Han, Aijun

    2015-12-01

    Composite carbon fibers (CFs) coated with Ni-X-P (X = Cu, Co, none) alloys were prepared by electroless plating. The morphology, crystal structure, elemental composition, and millimeter wave (MMW) attenuation performance of the alloy-coated CFs were characterized by scanning electron microscopy, x-ray diffractometry, energy-dispersive spectrometry, and microwave attenuation. CFs were coated with a layer of alloy particles. The P content in the Ni-Cu-P or Ni-Co-P-coated alloy was lower than that in the Ni-P alloy, and coating alloy Ni-P was amorphous. Coating alloys exhibited crystal characteristics after Cu or Co introduction. MMW-attenuation performance of alloy-coated CFs showed that the 3 and 8 mm wave-attenuation effects of CF/Ni-Cu-P and CF/Ni-Co-P were better than those of CF/Ni-P and CFs. The 8 mm wave-attenuation values and their increases were larger than those of the 3 mm wave. The MMW-attenuation performance is attributable to the alloy bulk resistivity and P content. The 3 mm wave-attenuation effects of wavelength-coated CF samples were slightly larger than those of the half wavelength samples. An optimal weight gain value existed for the MMW-attenuation performance of alloy-coated CFs.

  13. The Characteristics Of Intrinsic And Attenuative Dispersion Of Direct P-waves: Application In The Study Of Earthquake Precursory

    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.

  14. Measurement of breast-tissue x-ray attenuation by spectral mammography: solid lesions

    NASA Astrophysics Data System (ADS)

    Fredenberg, Erik; Kilburn-Toppin, Fleur; Willsher, Paula; Moa, Elin; Danielsson, Mats; Dance, David R.; Young, Kenneth C.; Wallis, Matthew G.

    2016-04-01

    Knowledge of x-ray attenuation is essential for developing and evaluating x-ray imaging technologies. For instance, techniques to distinguish between cysts and solid tumours at mammography screening would be highly desirable to reduce recalls, but the development requires knowledge of the x-ray attenuation for cysts and tumours. We have previously measured the attenuation of cyst fluid using photon-counting spectral mammography. Data on x-ray attenuation for solid breast lesions are available in the literature, but cover a relatively wide range, likely caused by natural spread between samples, random measurement errors, and different experimental conditions. In this study, we have adapted a previously developed spectral method to measure the linear attenuation of solid breast lesions. A total of 56 malignant and 5 benign lesions were included in the study. The samples were placed in a holder that allowed for thickness measurement. Spectral (energy-resolved) images of the samples were acquired and the image signal was mapped to equivalent thicknesses of two known reference materials, which can be used to derive the x-ray attenuation as a function of energy. The spread in equivalent material thicknesses was relatively large between samples, which is likely to be caused mainly by natural variation and only to a minor extent by random measurement errors and sample inhomogeneity. No significant difference in attenuation was found between benign and malignant solid lesions. The separation between cyst-fluid and tumour attenuation was, however, significant, which suggests it may be possible to distinguish cystic from solid breast lesions, and the results lay the groundwork for a clinical trial. In addition, the study adds a relatively large sample set to the published data and may contribute to a reduction in the overall uncertainty in the literature.

  15. Measurement of breast-tissue x-ray attenuation by spectral mammography: solid lesions.

    PubMed

    Fredenberg, Erik; Kilburn-Toppin, Fleur; Willsher, Paula; Moa, Elin; Danielsson, Mats; Dance, David R; Young, Kenneth C; Wallis, Matthew G

    2016-04-01

    Knowledge of x-ray attenuation is essential for developing and evaluating x-ray imaging technologies. For instance, techniques to distinguish between cysts and solid tumours at mammography screening would be highly desirable to reduce recalls, but the development requires knowledge of the x-ray attenuation for cysts and tumours. We have previously measured the attenuation of cyst fluid using photon-counting spectral mammography. Data on x-ray attenuation for solid breast lesions are available in the literature, but cover a relatively wide range, likely caused by natural spread between samples, random measurement errors, and different experimental conditions. In this study, we have adapted a previously developed spectral method to measure the linear attenuation of solid breast lesions. A total of 56 malignant and 5 benign lesions were included in the study. The samples were placed in a holder that allowed for thickness measurement. Spectral (energy-resolved) images of the samples were acquired and the image signal was mapped to equivalent thicknesses of two known reference materials, which can be used to derive the x-ray attenuation as a function of energy. The spread in equivalent material thicknesses was relatively large between samples, which is likely to be caused mainly by natural variation and only to a minor extent by random measurement errors and sample inhomogeneity. No significant difference in attenuation was found between benign and malignant solid lesions. The separation between cyst-fluid and tumour attenuation was, however, significant, which suggests it may be possible to distinguish cystic from solid breast lesions, and the results lay the groundwork for a clinical trial. In addition, the study adds a relatively large sample set to the published data and may contribute to a reduction in the overall uncertainty in the literature. PMID:26961507

  16. In situ acoustic and laboratory ultrasonic sound speed and attenuation measured in heterogeneous soft seabed sediments: Eel River shelf, California

    USGS Publications Warehouse

    Gorgas, T.J.; Wilkens, R.H.; Fu, S.S.; Neil, Frazer L.; Richardson, M.D.; Briggs, K.B.; Lee, H.

    2002-01-01

    We compared in situ and laboratory velocity and attenuation values measured in seafloor sediments from the shallow water delta of the Eel River, California. This region receives a substantial volume of fluvial sediment that is discharged annually onto the shelf. Additionally, a high input of fluvial sediments during storms generates flood deposits that are characterized by thin beds of variable grain-sizes between the 40- and 90-m isobaths. The main objectives of this study were (1) to investigate signatures of seafloor processes on geoacoustic and physical properties, and (2) to evaluate differences between geoacoustic parameters measured in situ at acoustic (7.5 kHz) and in the laboratory at ultrasonic (400 kHz) frequencies. The in situ acoustic measurements were conducted between 60 and 100 m of water depth. Wet-bulk density and porosity profiles were obtained to 1.15 m below seafloor (m bsf) using gravity cores of the mostly cohesive fine-grained sediments across- and along-shelf. Physical and geoacoustic properties from six selected sites obtained on the Eel margin revealed the following. (1) Sound speed and wet-bulk density strongly correlated in most cases. (2) Sediment compaction with depth generally led to increased sound speed and density, while porosity and in situ attenuation values decreased. (3) Sound speed was higher in coarser- than in finer-grained sediments, on a maximum average by 80 m s-1. (4) In coarse-grained sediments sound speed was higher in the laboratory (1560 m s-1) than in situ (1520 m s-1). In contrast, average ultrasonic and in situ sound speed in fine-grained sediments showed only little differences (both approximately 1480 m s-1). (5) Greater attenuation was commonly measured in the laboratory (0.4 and 0.8 dB m-1 kHz-1) than in situ (0.02 and 0.65 dB m-1 kHz-1), and remained almost constant below 0.4 m bsf. We attributed discrepancies between laboratory ultrasonic and in situ acoustic measurements to a frequency dependence of velocity and attenuation. In addition, laboratory attenuation was most likely enhanced due to scattering of sound waves at heterogeneities that were on the scale of ultrasonic wavelengths. In contrast, high in situ attenuation values were linked to stratigraphic scattering at thin-bed layers that form along with flood deposits. ?? 2002 Published by Elsevier Science B.V.

  17. Ultrasonic attenuation in pearlitic steel.

    PubMed

    Du, Hualong; Turner, Joseph A

    2014-03-01

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

  18. Thermoreflectance temperature measurement with millimeter wave

    SciTech Connect

    Pradere, C. Caumes, J.-P.; BenKhemis, S.; Palomo, E.; Batsale, J.-C.; Pernot, G.; Dilhaire, S.

    2014-06-15

    GigaHertz (GHz) thermoreflectance technique is developed to measure the transient temperature of metal and semiconductor materials located behind an opaque surface. The principle is based on the synchronous detection, using a commercial THz pyrometer, of a modulated millimeter wave (at 110 GHz) reflected by the sample hidden behind a shield layer. Measurements were performed on aluminum, copper, and silicon bulks hidden by a 5 cm thick Teflon plate. We report the first measurement of the thermoreflectance coefficient which exhibits a value 100 times higher at 2.8 mm radiation than those measured at visible wavelengths for both metallic and semiconductor materials. This giant thermoreflectance coefficient κ, close to 10{sup −3} K{sup −1} versus 10{sup −5} K{sup −1} for the visible domain, is very promising for future thermoreflectance applications.

  19. Microwave radar measurements of ocean wave propagation - Initial results

    SciTech Connect

    Poulter, E.M.; Smith, M.J.; McGregor, J.A.

    1990-11-01

    A microwave radar has been developed to measure the surface orbital velocities of ocean waves, and hence estimate the wave height spectra. The Doppler radar exploits the frequency modulated continuous wave (FMCW) technique to provide good spatial resolution (much less than the ocean wavelengths of interest) making it suitable for ocean wave propagation studies. The authors present initial data demonstrating the radar's capabilities to deduce near-shore ocean wave properties. The spatial and temporal variations of the orbital velocities reveal the wave propagation, and the deduced wave height spectra show wave growth as they approach the shore.

  20. Structure of the Cocos subduction zone in central and southern Mexico from three-dimensional body-wave attenuation and travel time tomography

    NASA Astrophysics Data System (ADS)

    Chen, T.; Clayton, R. W.

    2011-12-01

    The 3D P- and S-wave attenuation and velocity structure of the Cocos subduction zone in Mexico is imaged using seismic events recorded by the MASE (100 seismometers running across central Mexico, 2005-2007) and VEOX (47 seismometers running across southern Mexico, 2007-2009) arrays, supplemented by stations from the National Seismic Network in Mexico (SSN). Using a spectral-decay method, we obtain a path attenuation operator t* for each seismogram in the frequency band 1 to 30 Hz, depending on the signal quality. These measurements are then inverted for 3D spatial variations in attenuation. Direct body-wave arrivals from local events are used for 3D velocity inversion. Deeper velocity structures along MASE and VEOX arrays are obtained by including teleseismic events. Inversion results show low attenuation associated with the Cocos slab, and show the slab dip angle increases from central to southern Mexico. High attenuation is imaged in the mantle wedge and the crust above. The highest attenuation is found in the crust near the active Los Tuxtlas volcanic field, probably related to the dehydration and melting process. Low velocity is observed in the mantle wedge and the crust above from velocity inversion. The Cocos slab is traced as high-velocity structure. The Cocos slab dips down to about 500 km in central Mexico along MASE array as shown by previous study (Perez-Campos, GRL, 2008). In southern Mexico along VEOX line, no clear continuous Cocos slab is observed deeper than about 150 km, which is also found by receiver function studies (Kim et al., in press; Perez-Campos et al., in press). There are some indications that the Cocos slab in southern Mexico near the Isthmus of Tehuantepec is truncated by some high-velocity structure dipping south from the Gulf of Mexico. This anomalous south-dipping structure is also seen in receiver function images, and may be related to the collision between the Yucatan Block and Mexico in the Miocene (Kim et al., in press).

  1. Measurement and analysis of patient attenuation correction factor during radioiodine therapy.

    PubMed

    Soliman, K; Alenezi, A; Bakkari, M; Shirbini, H

    2015-07-01

    The calculated dose rate from the radioiodine therapy patient should normally include a factor accounting for the attenuation and scatter of patient body tissues. The attenuation factor is currently neglected, and not applied in operational radiation protection. Realistic estimation of radiation dose rate levels from radioiodine therapy patients when properly performed will reduce operational cost and optimise institutional radiation protection practice. In this work, the existence of a patient body tissue attenuation factor is verified by comparing the dose rates measured from the radioiodine capsules immediately before administration with those measured from the patient immediately after administration. The correlation between the factors suspected to influence the patient body tissue attenuation and the measured dose rates from the patient normalised per unit activity is statistically analysed. The calculated attenuation correction factor based on authors' measurements was (0.55 ± 0.17). The measured dose rate per unit of radioactivity from the patient showed a negative correlation with their body mass index. PMID:25862533

  2. Temperature Measurements of the Low-Attenuation Radiographic Ice Ball During CT-Guided Renal Cryoablation

    SciTech Connect

    Permpongkosol, Sompol; Link, Richard E.; Kavoussi, Louis R.; Solomon, Stephen B.

    2008-01-15

    During renal cryoablation a low-attenuation area on CT develops around the cryoprobe. Knowledge of the temperature of the growing low-attenuation area can guide therapy and ensure lethal temperatures. Herein, we report thermocouple results and correlating CT images during the development of the low-attenuation 'radiographic ice ball.' Five patients who underwent percutaneous CT-guided renal cryoablation were identified who had thermocouples inserted and serial intraprocedural CT images that included images with thermocouple measurements of 0{sup o} and sub-0{sup o}C. Thermocouples had been percutaneously placed just beyond the edge of the tumors either to ensure adequate cooling or to ensure safety to adjacent critical structures. Renal cryotherapy under CT guidance produced a growing low-attenuation area corresponding to the radiographic ice ball. When the thermocouple measured 0{sup o}C, CT images showed the thermocouple tip at the edge of the low-attenuation ice ball. At lower temperatures the tip was within the low-attenuation ice ball. We conclude that knowledge of the temperature at the ice ball edge during cryoablation can be used to predict the extent of tissue necrosis and thus provide an estimate of cryotherapy effectiveness during the procedure. Further work is necessary to establish a firm relationship between the thermal conditions and the zone of damage.

  3. First measurements of plasma waves near Mars

    NASA Technical Reports Server (NTRS)

    Grard, R.; Pedersen, A.; Klimov, S.; Savin, S.; Skalskii, A.

    1989-01-01

    Preliminary results from electric field measurements in the environment of Mars using the plasma-wave system on board Phobos 2 are reported. Electron-plasma oscillations observed upstream of the bow shock correspond to a solar-wind density of 2/cu cm. The shock-foot boundary was crossed up to three times on each orbit. The shock ramp was detected at altitudes between 0.45 and 0.75 Mars radii R(M) above the planetary surface. The density increased by about a factor of two at the ramp. The shock position, although variable, seems to be consistent with previous measurements. The downstream magnetosheath contained broadband electric-field noise below the plasma frequency. The boundary of th obstacle, or plasmapause, was crossed at altitudes of the order of 0.28 R(M); the cold plasma density was highly variable within the planetopause and reached the unexpected value of 700/cu cm on the third orbit, at 0.25 R(M) altitude. Bursts of waves with frequencies below the electron cyclotron frequency occur within the planetopause.

  4. Lidar measurement as support to the ocular hazard distance calculation using atmospheric attenuation

    NASA Astrophysics Data System (ADS)

    Gustafsson, K. Ove S.; Persson, Rolf; Gustafsson, Frank; Berglund, Folke; Malmquist, Jonas

    2015-10-01

    The reduction of the laser hazard distance range using atmospheric attenuation has been tested with series of lidar measurements accomplished at the Vidsel Test Range, Vidsel, Sweden. The objective was to find situations with low level of aerosol backscatter during this campaign, with the implications of low extinction coefficient, since the lowest atmospheric attenuation gives the highest ocular hazards. The work included building a ground based backscatter lidar, performing a series of measurements and analyzing the results. The measurements were performed during the period June to November, 2014. The results of lidar measurements showed at several occasions' very low atmospheric attenuation as a function of height to an altitude of at least 10 km. The lowest limit of aerosol backscatter coefficient possible to measure with this instrument is less than 0.3•10-7 m-1 sr-1. Assuming an aerosol lidar ratio between 30 - 100 sr this leads to an aerosol extinction coefficient of about 0.9 - 3•10-6 m-1. Using a designator laser as an example with wavelength 1064 nm, power 0.180 W, pulse length 15 ns, PRF 11.5 Hz, exposure time of 10 sec and beam divergence of 0.08 mrad, it will have a NOHD of 48 km. With the measured aerosol attenuation and by assuming a molecule extinction coefficient to be 5•10-6 m-1 (calculated using MODTRAN (Ontar Corp.) assuming no aerosol) the laser hazard distance will be reduced with 51 - 58 %, depending on the lidar ratio assumption. The conclusion from the work is; reducing of the laser hazard distance using atmospheric attenuation within the NOHD calculations is possible but should be combined with measurements of the attenuation.

  5. Torsional ultrasonic wave based level measurement system

    DOEpatents

    Holcomb, David E.; Kisner, Roger A.

    2012-07-10

    A level measurement system suitable for use in a high temperature and pressure environment to measure the level of coolant fluid within the environment, the system including a volume of coolant fluid located in a coolant region of the high temperature and pressure environment and having a level therein; an ultrasonic waveguide blade that is positioned within the desired coolant region of the high temperature and pressure environment; a magnetostrictive electrical assembly located within the high temperature and pressure environment and configured to operate in the environment and cooperate with the waveguide blade to launch and receive ultrasonic waves; and an external signal processing system located outside of the high temperature and pressure environment and configured for communicating with the electrical assembly located within the high temperature and pressure environment.

  6. 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.

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

    NASA Technical Reports Server (NTRS)

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

    1980-01-01

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

  8. Photogrammetric Measurements of CEV Airbag Landing Attenuation Systems

    NASA Technical Reports Server (NTRS)

    Barrows, Danny A.; Burner, Alpheus W.; Berry, Felecia C.; Dismond, Harriett R.; Cate, Kenneth H.

    2008-01-01

    High-speed photogrammetric measurements are being used to assess the impact dynamics of the Orion Crew Exploration Vehicle (CEV) for ground landing contingency upon return to earth. Test articles representative of the Orion capsule are dropped at the NASA Langley Landing and Impact Research (LandIR) Facility onto a sand/clay mixture representative of a dry lakebed from elevations as high as 62 feet (18.9 meters). Two different types of test articles have been evaluated: (1) half-scale metal shell models utilized to establish baseline impact dynamics and soil characterization, and (2) geometric full-scale drop models with shock-absorbing airbags which are being evaluated for their ability to cushion the impact of the Orion CEV with the earth s surface. This paper describes the application of the photogrammetric measurement technique and provides drop model trajectory and impact data that indicate the performance of the photogrammetric measurement system.

  9. Attenuation of treatment effect due to measurement variability in assessment of progression-free survival.

    PubMed

    Hong, S; Schmitt, N; Stone, A; Denne, J

    2012-01-01

    For normally distributed data analyzed with linear models, it is well known that measurement error on an independent variable leads to attenuation of the effect of the independent variable on the dependent variable. However, for time-to-event variables such as progression-free survival (PFS), the effect of the measurement variability in the underlying measurements defining the event is less well understood. We conducted a simulation study to evaluate the impact of measurement variability in tumor assessment on the treatment effect hazard ratio for PFS and on the median PFS time, for different tumor assessment frequencies. Our results show that scan measurement variability can cause attenuation of the treatment effect (i.e. the hazard ratio is closer to one) and that the extent of attenuation may be increased with more frequent scan assessments. This attenuation leads to inflation of the type II error. Therefore, scan measurement variability should be minimized as far as possible in order to reveal a treatment effect that is closest to the truth. In disease settings where the measurement variability is shown to be large, consideration may be given to inflating the sample size of the study to maintain statistical power. PMID:22740352

  10. Neutral atmospheric waves determined from Atmospheric Explorer measurements

    NASA Technical Reports Server (NTRS)

    Hoegy, W. R.; Wharton, L. E.; Spencer, N. W.; Dyson, P. L.

    1979-01-01

    A description is presented of the first observations of neutral gravity waves in which a sufficient number of wave parameters are detected to allow a specification of the neutral wave characteristics. In situ measurements of neutral wind, temperature, and composition from Atmospheric Explorer are used to obtain wave amplitudes and phases for N2 temperature and wind, and N2, O, and He densities. These amplitudes and phases along with the Doppler shifted wave frequency provide sufficient information to evaluate the wave frequency and the wave vector.

  11. Spatial changes of seismic attenuation and multiscale geological heterogeneity in the Baikal rift and surroundings from analysis of coda waves

    NASA Astrophysics Data System (ADS)

    Dobrynina, Anna A.; Sankov, Vladimir A.; Chechelnitsky, Vladimir V.; Déverchère, Jacques

    2016-04-01

    The Baikal rift system is undergoing an active tectonic deformation expressed by a high level of seismic activity. This deformation leads to physical and mechanical changes of crustal properties which can be investigated by the seismic quality factor and its frequency dependence. Using a single backscattering model, a seismic quality-factor (QC), a frequency parameter (n) and an attenuation coefficient (δ) have been estimated by analyzing coda waves of 274 local earthquakes of the Baikal rift system for nineteen lapse time windows (W) from 10 to 100 s every 5 s and for six central frequencies (0.3, 0.75, 1.5, 3, 6 and 12 Hz). The average QC value increases with the frequency and lapse time window from 46 ± 52 (at 0.75 Hz) to 502 ± 109 (at 12 Hz) for W = 10 s and from 114 ± 49 (at 0.3 Hz) to 1865 ± 679 (at 12 Hz) for W = 100 s. The values of QC(f) and δ were estimated for the whole Baikal rift system and for separate tectonic blocks: the stable Siberian Platform, main rift basins, spurs and uplifts. Along the rift system, the Q0-value (QC-factor at the frequency f = 1 Hz) varies within 72-109 and the frequency parameter n ranges from 0.87 to 1.22, whereas Q0 is 134 and n is 0.48 for the stable Siberian Platform. Vertical variations of attenuation reveal that sharp changes of δ and n are confined to the velocity discontinuities. The comparison of lateral variations of seismic wave attenuation and geological and geophysical characteristics of the Baikal rift system shows that attenuation is correlated with both seismic activity and heat flow and in a lesser degree with the surface fault density and the age of the crust. Seismic wave attenuation found across the main shear zones of the south-western Baikal rift (Main Sayan strike-slip fault zone and Tunka, Obruchev and Primorsky normal faults) is increased by more than 25-60% compared to the neighboring areas.

  12. Investigation of the tone-burst tube for duct lining attenuation measurement

    NASA Technical Reports Server (NTRS)

    Soffel, A. R.; Morrow, P. F.

    1972-01-01

    The tone burst technique makes practical the laboratory evaluation of potential inlet and discharge duct treatments. Tone burst apparatus requires only simple machined parts and standard components. Small, simply made, lining samples are quickly and easily installed in the system. Two small electromagnetric loudspeaker drivers produce peak sound pressure level of over 166 db in the 3-square-inch sample duct. Air pump available in most laboratories can produce air flows of over plus and minus Mach 0.3 in the sample duct. The technique uses short shaped pulses of sound propagated down a progressive wave tube containing the sample duct. The peak pressure level output of the treated duct is compared with the peak pressure level output of a substituted reference duct. The difference between the levels is the attenuation or insertion loss of the treated duct. Evaluations of resonant absorber linings by the tone burst technique check attenuation values predicted by empirical formulas based on full scale ducts.

  13. Attenuation and Shock Waves in Linear Hereditary Viscoelastic Media; Strick-Mainardi, Jeffreys-Lomnitz-Strick and Andrade Creep Compliances

    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.

  14. Deep-Ocean Measurements of Tsunami Waves

    NASA Astrophysics Data System (ADS)

    Rabinovich, Alexander B.; Eblé, Marie C.

    2015-12-01

    Deep-ocean tsunami measurements play a major role in understanding the physics of tsunami wave generation and propagation, and in improving the effectiveness of tsunami warning systems. This paper provides an overview of the history of tsunami recording in the open ocean from the earliest days, approximately 50 years ago, to the present day. Modern tsunami monitoring systems such as the self-contained Deep-ocean Assessment and Reporting of Tsunamis and innovative cabled sensing networks, including, but not limited to, the Japanese bottom cable projects and the NEPTUNE-Canada geophysical bottom observatory, are highlighted. The specific peculiarities of seafloor longwave observations in the deep ocean are discussed and compared with observations recorded in coastal regions. Tsunami detection in bottom pressure observations is exemplified through analysis of distant (22,000 km from the source) records of the 2004 Sumatra tsunami in the northeastern Pacific.

  15. Systematic Evaluation of the Relationship between Physical and Psychoacoustical Measurements of Hearing Protectors' Attenuation.

    PubMed

    Nlisse, Hugues; Le Cocq, Ccile; Boutin, Jrme; Laville, Frdric; Voix, Jrmie

    2015-01-01

    The most commonly used methods to measure hearing protectors attenuation can be divided into two categories: psychoacoustical (subjective) and physical (objective) methods. In order to better understand the relationship between these methods, this article presents various factors relating attenuation values obtained with these methods through a series of tests. Experiments on human subjects were carried out where the subjects were instrumented on both ears with miniature microphones outside and underneath the protector. The subjects were then asked to go through a series of hearing threshold measurements (psychoacoustical method) followed by microphone sound recordings using high-level diffuse field broadband noises (physical method). The proposed test protocol allowed obtaining various factors relating the test methods as well as attenuation values and ratings for different protection conditions (open ear, earmuffs, earplugs, and dual protection). Results are presented for three models of passive earmuffs, three models of earplugs and all their combinations as dual hearing protectors. The validity and the relative importance of various terms used to correct the physical attenuation values when comparing with psychoacoustical attenuation values are examined. PMID:26023884

  16. Synergistic measurements of ocean winds and waves from SAR

    NASA Astrophysics Data System (ADS)

    Zhang, Biao; Li, Xiaofeng; Perrie, William; He, Yijun

    2015-09-01

    In this study we present a synergistic method to retrieve both ocean surface wave and wind fields from spaceborne quad-polarization (QP) synthetic aperture radar (SAR) imaging mode data. This algorithm integrates QP-SAR wind vector retrieval model and the wave retrieval model, with consideration to the nonlinear mapping relationship between ocean wave spectra and SAR image spectra, in order to synergistically retrieve wind fields and wave directional spectra. The method does not require a priori information on the sea state. It combines the observed VV-polarized SAR image spectra with the retrieved wind vectors from the VH-polarized SAR image, to estimate the wind-generated wave directional spectra. The differences between the observed SAR spectra and optimal SAR image spectra associated with the wind waves are interpreted as the contributions from the swell waves. The retrieved ocean wave spectra are used to estimate the integrated spectral wave parameters such as significant wave heights, wavelengths, wave directions and wave periods. The wind and wave parameters retrieved by QP-SAR are validated against those measured by the National Data Buoy Center (NDBC) directional wave buoys under different sea states. The validation results show that the QP-SAR SAR has potential to simultaneously measure the ocean surface waves and wind fields from space.

  17. On the excess attenuation of sound in the atmosphere

    NASA Technical Reports Server (NTRS)

    Deloach, R.

    1975-01-01

    The attenuation suffered by an acoustic plane wave propagating from an elevated source to the ground, in excess of absorption losses, was studied. Reported discrepancies between attenuation measurements made in the field and theories which only account for absorption losses are discussed. It was concluded that the scattering of sound by turbulence results in a nonnegligible contribution to the total attenuation.

  18. Water wave measurement from stereo images of specular reflections

    NASA Astrophysics Data System (ADS)

    Kiefhaber, Daniel; Caulliez, Guillemette; Zappa, Christopher J.; Schaper, Julia; Jähne, Bernd

    2015-11-01

    A new optical instrument for the study of ocean waves, the Reflective Stereo Slope Gauge, has been developed. Its purpose is to measure ocean wave field parameters that are crucial to the air-sea exchange of momentum, heat and gases. The instrument combines a statistical wave slope measurement method similar to Cox and Munk’s sun glitter technique with a dedicated stereo camera and associated illumination setup for direct wave height measurements. The instrument output was validated under controlled conditions in a wind-wave facility.

  19. Centimeter and millimeter wave attenuation and brightness temperature due to atmospheric oxygen and water vapor

    NASA Technical Reports Server (NTRS)

    Smith, E. K.

    1982-01-01

    Calculations are presented for atmospheric absorption and radiation emission for several atmospheric conditions and elevation angles. The calculations are for frequencies in the 1 to 340 GHz frequency range. The calculations are compared to those from other models. Agreement is found to within 15% for absorption coefficient (7.5 g/m/cubed water vapor at 290 K) and approximately the same for total zenithal attenuation. The attenuation and gaseous emission noise curves defined by the International Radio Consultative Committee are found to have minor inconsistencies.

  20. Measurement of ultrasonic attenuation in diabetic neuropathic sciatic nerves for diagnostic and therapeutic applications.

    PubMed

    Chen, Gin-Shin; Lee, Yee-Fun; Cheng, Jung-Sung

    2014-08-01

    Measurements of ultrasonic attenuation in the sciatic nerves of rats were performed to verify the feasibility of ultrasound diagnosis of peripheral neuropathy and to avoid damage to the nerves caused by overheating in pain management applications. A rat model of diabetic peripheral neuropathy was established. The proximal-segment and middle-segment sciatic nerves of control and neuropathic rats were dissected for the attenuation measurement. Two commercial ultrasound transducers and a self-developed experimental platform were used in the measurements. Using H&E staining and transmission electron (TE) microscopy, morphological analysis of the control and neuropathic nerves was performed to determine the relationship between attenuation and the histology of the nerves. The experimental results showed that the attenuation coefficients of the control, second-week, fourth-week, and eighth-week neuropathic nerves were -6.68 0.50, -5.61 0.34, -6.27 0.40, and -7.10 0.35 dB/cm at 2.68 MHz, respectively. The respective values at 7.50 MHz were -14.96 0.79, -12.65 0.28, -13.98 1.07, and -16.00 0.54 dB/cm. The changes in the attenuation coefficients were significantly different among the second-week, fourth-week, and eighth-week DN nerves. Additionally, the ultrasonic attenuation coefficient of the rat sciatic nerve was fourfold that of the cat brain and cow liver and twofold that of human muscle. PMID:24566928

  1. The feasibility of ranking material fracture toughness by ultrasonic attenuation measurements

    NASA Technical Reports Server (NTRS)

    Vary, A.

    1975-01-01

    A preliminary study was conducted to assess the feasibility of ultrasonically ranking material fracture toughness. Specimens of two grades of maraging steel for which fracture toughness values were measured were subjected to ultrasonic probing. The slope of the attenuation coefficient versus frequency curve was empirically correlated with the plane strain fracture toughness value for each grade of steel.

  2. The feasibility of ranking material fracture toughness by ultrasonic attenuation measurements

    NASA Technical Reports Server (NTRS)

    Vary, A.

    1975-01-01

    A preliminary study was conducted to assess the feasibility of ultrasonically ranking material fracture toughness. Specimens of two grades of maraging steel for which fracture toughness values were measured were subjected to ultrasonic probing. The slope of the attenuation coefficient vs frequency curve was empirically correlated with the plane strain fracture toughness value for each grade of steel.

  3. The Correction for Attenuation Due to Measurement Error: Clarifying Concepts and Creating Confidence Sets

    ERIC Educational Resources Information Center

    Charles, Eric P.

    2005-01-01

    The correction for attenuation due to measurement error (CAME) has received many historical criticisms, most of which can be traced to the limited ability to use CAME inferentially. Past attempts to determine confidence intervals for CAME are summarized and their limitations discussed. The author suggests that inference requires confidence sets…

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

    SciTech Connect

    Apel, W. D.; Badea, F.; Bekk, K.; Bozdog, H.; Daumiller, K.; Doll, P.; Engel, R.; Engler, J.; Finger, M.; Gils, H. J.; Haungs, A.; Heck, D.; Huege, T.; Isar, P. G.; Klages, H. O.; Mathes, H. J.; Mayer, H. J.; Milke, J.; Nehls, S.; Oehlschlaeger, J.

    2009-07-15

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

  5. Accuracy of Satellite-Measured Wave Heights in the Australian Region for Wave Power Applications

    ERIC Educational Resources Information Center

    Meath, Sian E.; Aye, Lu; Haritos, Nicholas

    2008-01-01

    This article focuses on the accuracy of satellite data, which may then be used in wave power applications. The satellite data are compared to data from wave buoys, which are currently considered to be the most accurate of the devices available for measuring wave characteristics. This article presents an analysis of satellite- (Topex/Poseidon) and…

  6. Accuracy of Satellite-Measured Wave Heights in the Australian Region for Wave Power Applications

    ERIC Educational Resources Information Center

    Meath, Sian E.; Aye, Lu; Haritos, Nicholas

    2008-01-01

    This article focuses on the accuracy of satellite data, which may then be used in wave power applications. The satellite data are compared to data from wave buoys, which are currently considered to be the most accurate of the devices available for measuring wave characteristics. This article presents an analysis of satellite- (Topex/Poseidon) and

  7. Finite-difference numerical modelling of gravito-acoustic wave propagation in a windy and attenuating atmosphere

    NASA Astrophysics Data System (ADS)

    Brissaud, Quentin; Martin, Roland; Garcia, Raphaël F.; Komatitsch, Dimitri

    2016-04-01

    Acoustic and gravity waves propagating in planetary atmospheres have been studied intensively as markers of specific phenomena such as tectonic events or explosions or as contributors to atmosphere dynamics. To get a better understanding of the physics behind these dynamic processes, both acoustic and gravity waves propagation should be modelled in a 3D attenuating and windy atmosphere extending from the ground to the upper thermosphere. Thus, in order to provide an efficient numerical tool at the regional or global scale we introduce a finite difference in the time domain (FDTD) approach that relies on the linearized compressible Navier-Stokes equations with a background flow (wind). One significant benefit of such a method is its versatility because it handles both acoustic and gravity waves in the same simulation, which enables one to observe interactions between them. Simulations can be performed for 2D or 3D realistic cases such as tsunamis in a full MSISE-00 atmosphere or gravity-wave generation by atmospheric explosions. We validate the computations by comparing them to analytical solutions based on dispersion relations in specific benchmark cases: an atmospheric explosion, and a ground displacement forcing.

  8. Seismic velocities and attenuation from borehole measurements near the Parkfield prediction zone, Central California

    USGS Publications Warehouse

    Gibbs, James F.; Roth, Edward F.

    1989-01-01

    Shear (S)- and compressional (P)- wave velocities were measured to a depth of 195 m in a borehole near the San Andreas fault where a recurrence of a moderate Parkfield earthquake is predicted. S-wave velocities determined from orthogonal directions of the S-wave source show velocity differences of approximately 20 percent. An average shear-wave Q of 4 was determined in relatively unconsolidated sands and gravels of the Paso Robles Formation in the depth interval 57.5-102.5 m.

  9. Reference Phantom Method for Acoustic Backscatter Coefficient and Attenuation Coefficient Measurements.

    NASA Astrophysics Data System (ADS)

    Yao, Linxin

    1990-08-01

    In previous work in our laboratory accurate backscatter coefficient measurements were obtained with a data reduction method that explicitly accounts for experimental factors involved in recording echo data. An alternative, relative processing method for determining the backscatter coefficient and the attenuation coefficient is presented here. This method involves comparison of echo data from a sample with data recorded from a reference phantom whose backscatter and attenuation coefficients are known. The ratio of the signals cancels depth-dependent instrumentation factors. This saves the efforts of beam profile computation and various calibrations. The attenuation coefficient and backscatter coefficient of the sample are found from these ratios and the known acoustic properties of the reference phantom. This method is tested using tissue-mimicking phantoms with known scattering and attenuation properties. Various experiments have been done using clinical scanners with different transducers to compute attenuation coefficients and backscatter coefficients, and to make quantitative images. This method has been found to be accurate for media containing Rayleigh scatterers, as well as samples containing intermediate-size scatterers. Accuracy was maintained over different frequency bands and for a wide range of transducer-to-ROI distances. Measurements were done in vivo for human livers, kidneys and dog myocardium. The results have shown that the reference phantom method simplifies the measurement procedure as well as keeps the accuracy, and therefore is practical clinically. Statistical uncertainties propagated in the data reduction have been analyzed in detail. Formulae are deduced to predict statistical errors in the attenuation and backscatter coefficients measured with the reference phantom method. Spatial correlations of the echo signals are also considered. A 2-dimensional lateral correlation matrix is introduced to compute the number of effective independent lines from the acoustic lines acquired by a clinical scanner, and a 1-dimensional axial correlation array is used to estimate the number of effective independent samples along a line. Thus, for a given volume of tissue the uncertainty in the attenuation and backscatter coefficients measured from scattered echo data can be computed.

  10. Estimation of effective x-ray tissue attenuation differences for volumetric breast density measurement

    NASA Astrophysics Data System (ADS)

    Chen, Biao; Ruth, Chris; Jing, Zhenxue; Ren, Baorui; Smith, Andrew; Kshirsagar, Ashwini

    2014-03-01

    Breast density has been identified to be a risk factor of developing breast cancer and an indicator of lesion diagnostic obstruction due to masking effect. Volumetric density measurement evaluates fibro-glandular volume, breast volume, and breast volume density measures that have potential advantages over area density measurement in risk assessment. One class of volume density computing methods is based on the finding of the relative fibro-glandular tissue attenuation with regards to the reference fat tissue, and the estimation of the effective x-ray tissue attenuation differences between the fibro-glandular and fat tissue is key to volumetric breast density computing. We have modeled the effective attenuation difference as a function of actual x-ray skin entrance spectrum, breast thickness, fibro-glandular tissue thickness distribution, and detector efficiency. Compared to other approaches, our method has threefold advantages: (1) avoids the system calibration-based creation of effective attenuation differences which may introduce tedious calibrations for each imaging system and may not reflect the spectrum change and scatter induced overestimation or underestimation of breast density; (2) obtains the system specific separate and differential attenuation values of fibroglandular and fat for each mammographic image; and (3) further reduces the impact of breast thickness accuracy to volumetric breast density. A quantitative breast volume phantom with a set of equivalent fibro-glandular thicknesses has been used to evaluate the volume breast density measurement with the proposed method. The experimental results have shown that the method has significantly improved the accuracy of estimating breast density.

  11. Measurement and fitting techniques for the assessment of material nonlinearity using nonlinear Rayleigh waves

    SciTech Connect

    Torello, David; Kim, Jin-Yeon; Qu, Jianmin; Jacobs, Laurence J.

    2015-03-31

    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 β{sub 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 β{sub 11}{sup 7075}/β{sub 11}{sup 2024} measure of 1.363 agrees well with previous literature and earlier work.

  12. Correlation of effective atomic number and electron density with attenuation coefficients measured with polychromatic x rays.

    PubMed

    Phelps, M E; Gado, M H; Hoffman, E J

    1975-12-01

    Attenuation coefficients of nine different plastics and water were measured with EMI computed transaxial tomography (CT) and radioisotopic sources with photons of 14 to 136 keV. The EMI values were correlated with physical density, electron density, and atomic number cubed (Z3). The best correlation was obtained with electron density, the exception being the value for water. This descrepancy was explained on the basis of X-dependent photoelectric absorption with verification from monoenergetic measurements. PMID:1188103

  13. Quantitative measurement of permeabilization of living cells by terahertz attenuated total reflection

    NASA Astrophysics Data System (ADS)

    Grognot, Marianne; Gallot, Guilhem

    2015-09-01

    Using Attenuated Total Reflection imaging technique in the terahertz domain, we demonstrate non-invasive, non-staining real time measurements of cytoplasm leakage during permeabilization of epithelial cells by saponin. The terahertz signal is mostly sensitive to the intracellular protein concentration in the cells, in a very good agreement with standard bicinchoninic acid protein measurements. It opens the way to in situ real time dynamics of protein content and permeabilization in live cells.

  14. Pn wave geometrical spreading and attenuation in Northeast China and the Korean Peninsula constrained by observations from North Korean nuclear explosions

    NASA Astrophysics Data System (ADS)

    Zhao, Lian-Feng; Xie, Xiao-Bi; Tian, Bao-Feng; Chen, Qi-Fu; Hao, Tian-Yao; Yao, Zhen-Xing

    2015-11-01

    We investigate the geometric spreading and attenuation of seismic Pn waves in Northeast China and the Korean Peninsula. A high-quality broadband Pn wave data set generated by North Korean nuclear tests is used to constrain the parameters of a frequency-dependent log-quadratic geometric spreading function and a power law Pn Q model. The geometric spreading function and apparent Pn wave Q are obtained for Northeast China and the Korean Peninsula between 2.0 and 10.0 Hz. Using the two-station amplitude ratios of the Pn spectra and correcting them with the known spreading function, we remove the contributions of the source and crust from the apparent Pn Q and retrieve the P wave attenuation information along the pure upper mantle path. We then use both Pn amplitudes and amplitude ratios in a tomographic approach to obtain the upper mantle P wave attenuation in the studied area. The Pn wave spectra observed in China are compared with those recorded in Japan, and the result reveals that the high-frequency Pn signal across the oceanic path attenuated faster compared with those through the continental path.

  15. Roadside tree attenuation measurements at UHF for land mobile satellite systems

    NASA Technical Reports Server (NTRS)

    Goldhirsh, Julius; Vogel, Wolfhard J.

    1987-01-01

    Tree attenuation results at 870 MHz are described for experiments conducted in October 1985 and March 1986 in Central Maryland. These experiments employed a helicopter as a source platform and a van with receiver and data acquisition instrumentation. Tree attenuation results were obtained for the cases in which the van was stationary and in motion. The experiments were performed for the purpose of providing the designers of planned land mobile satellite systems with important elements in the determination of link parameter requirements; namely, the expected fading statistics due to roadside trees for both mobile and stationary vehicles. Single tree attenuation results gave worst case median fades as high as 15 dB although roadside tree values were noted to produce fades in excess of 20 dB for small percentages of time. The cumulative fade distributions and their relative contributions as a function of path elevation angle, right side versus left side driving, and different road types are derived from the field measurements. Upon comparing the attenuations from bare deciduous trees (March 1986) with those due to trees in full foliage (October 1985), the increase in dB attenuations were, in general, less than 25 percent for the dynamic cases, and less than 40 percent for the worst case static configuration. This result demonstrates that the dominant fading is caused by the wooded tree branches as opposed to the leaves on these branches. The tail end of the observed fade distributions was observed to follow lognormal distributions with respect to dB attenuation.

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

    NASA Technical Reports Server (NTRS)

    Campbell, Richard L.; Estus, Robert

    1988-01-01

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

  17. Effect of duct shape, Mach number, and lining construction on measured suppressor attenuation and comparison with theory

    NASA Technical Reports Server (NTRS)

    Olsen, W. A.; Krejsa, E. A.; Coats, J. W.

    1972-01-01

    Noise attenuation was measured for several types of cylindrical suppressors that use a duct lining composed of honeycomb cells covered with a perforated plate. The experimental technique used gave attenuation data that were repeatable and free of noise floors and other sources of error. The suppressor length, the effective acoustic diameter, suppressor shape and flow velocity were varied. The agreement among the attenuation data and two widely used analytical models was generally satisfactory. Changes were also made in the construction of the acoustic lining to measure their effect on attenuation. One of these produced a very broadband muffler.

  18. Snowpack snow water equivalent measurement using the attenuation of cosmic gamma radiation

    SciTech Connect

    Osterhuber, R.; Fehrke, F.; Condreva, K.

    1998-05-01

    Incoming, background cosmic radiation constantly fluxes through the earth`s atmosphere. The high energy gamma portion of this radiation penetrates many terrestrial objects, including the winter snowpack. The attenuation of this radiation is exponentially related to the mass of the medium through which it penetrates. For the past three winters, a device measuring cosmic gamma radiation--and its attenuation through snow--has been installed at the Central Sierra Snow Laboratory, near Donner Pass, California. This gamma sensor, measuring energy levels between 5 and 15 MeV, has proved to be an accurate, reliable, non-invasive, non-mechanical instrument with which to measure the total snow water equivalent of a snowpack. This paper analyzes three winters` worth of data and discusses the physics and practical application of the sensor for the collection of snow water equivalent data from a remote location.

  19. Determination of rain rate from a spaceborne radar using measurements of total attenuation

    NASA Technical Reports Server (NTRS)

    Meneghini, R.; Eckerman, J.; Atlas, D.

    1981-01-01

    Studies shows that path-integrated rain rates can be determined by means of a direct measurement of attenuation. For ground based radars this is done by measuring the backscattering cross section of a fixed target in the presence and absence of rain along the radar beam. A ratio of the two measurements yields a factor proportional to the attenuation from which the average rain rate is deduced. The technique is extended to spaceborne radars by choosing the ground as reference target. The technique is also generalized so that both the average and range-profiled rain rates are determined. The accuracies of the resulting estimates are evaluated for a narrow beam radar located on a low earth orbiting satellite.

  20. Laser-vibrometric measurement of oscillating piezoelectric actuators and of Lamb waves in CFRP plates for structural health monitoring

    NASA Astrophysics Data System (ADS)

    Pohl, Jürgen; Mook, Gerhard; Lammering, Rolf; von Ende, Sven

    2010-05-01

    The use of Lamb waves is attractive for structural health monitoring of plate and shell structures since their propagation in thin-walled structures is disturbed at damage locations especially at high frequencies. Lamb waves can easily be generated by thin piezoelectric plates which are attached to the surface of the structure. For the observation of the oscillating actuator as well as the propagating Lamb waves laser vibrometry is a powerful tool. Examples of vibrations of free and bonded piezoelectric actuators are given with special regard to the influences of contacts and other parameters, affecting the effectiveness of the wave generation. The determination of important features of Lamb wave propagation in carbon fibre reinforced plastics includes the measurement of dispersion curves and the estimation of attenuation and anisotropy. The interactions of Lamb waves with defects represented by reflections, transmissions and mode conversions are visualised and are easily to interpret.

  1. Correlation techniques and measurements of wave-height statistics

    NASA Technical Reports Server (NTRS)

    Guthart, H.; Taylor, W. C.; Graf, K. A.; Douglas, D. G.

    1972-01-01

    Statistical measurements of wave height fluctuations have been made in a wind wave tank. The power spectral density function of temporal wave height fluctuations evidenced second-harmonic components and an f to the minus 5th power law decay beyond the second harmonic. The observations of second harmonic effects agreed very well with a theoretical prediction. From the wave statistics, surface drift currents were inferred and compared to experimental measurements with satisfactory agreement. Measurements were made of the two dimensional correlation coefficient at 15 deg increments in angle with respect to the wind vector. An estimate of the two-dimensional spatial power spectral density function was also made.

  2. The relationship between shear wave velocity, temperature, attenuation and viscosity in the shallow part of the mantle

    NASA Astrophysics Data System (ADS)

    Priestley, Keith; McKenzie, Dan

    2013-11-01

    Surface wave tomography, using the fundamental Rayleigh wave velocities and those of higher modes between 1 and 4 and periods between 50 and 160 s, is used to image structures with a horizontal resolution of ˜250 km and a vertical resolution of ˜50 km to depths of ˜300 km in the mantle. A new model, PM_v2_2012, obtained from 3×106 seismograms, agrees well with earlier lower resolution models. It is combined with temperature estimates from oceanic plate models and with pressure and temperature estimates from the mineral compositions of garnet peridotite nodules to generate a number of estimates of SV(P,T) based on geophysical and petrological observations alone. These are then used to estimate the unrelaxed shear modulus and its derivatives with respect to pressure and temperature, which agree reasonably with values from laboratory experiments. At high temperatures relaxation occurs, causing the shear wave velocity to depend on frequency. This behaviour is parameterised using a viscosity to obtain a Maxwell relaxation time. The relaxation behaviour is described using a dimensionless frequency, which depends on an activation energy E and volume Va. The values of E and Va obtained from the geophysical models agree with those from laboratory experiments on high temperature creep. The resulting expressions are then used to determine the lithospheric thickness from the shear wave velocity variations. The resolution is improved by about a factor of two with respect to earlier models, and clearly resolves the thick lithosphere beneath active intracontinental belts that are now being shortened. The same expressions allow the three dimensional variations of the shear wave attenuation and viscosity to be estimated.

  3. Acoustic Measurement of Surface Wave Damping by a Meniscus

    NASA Astrophysics Data System (ADS)

    Michel, Guillaume; Pétrélis, François; Fauve, Stéphan

    2016-04-01

    We investigate the reflection of gravity-capillary surface waves by a plane vertical barrier. The size of the meniscus is found to strongly affect reflection: the energy of the reflected wave with a pinned contact line is around twice the one corresponding to a fully developed meniscus. To perform these measurements, a new experimental setup similar to an acousto-optic modulator is developed and offers a simple way to measure the amplitude, frequency and direction of propagation of surface waves.

  4. Dual shear wave induced laser speckle contrast signal and the improvement in shear wave speed measurement

    PubMed Central

    Li, Sinan; Cheng, Yi; Eckersley, Robert J; Elson, Daniel S; Tang, Meng-Xing

    2015-01-01

    Shear wave speed is quantitatively related to tissue viscoelasticity. Previously we reported shear wave tracking at centimetre depths in a turbid optical medium using laser speckle contrast detection. Shear wave progression modulates displacement of optical scatterers and therefore modulates photon phase and changes the laser speckle patterns. Time-resolved charge-coupled device (CCD)-based speckle contrast analysis was used to track shear waves and measure the time-of-flight of shear waves for speed measurement. In this manuscript, we report a new observation of the laser speckle contrast difference signal for dual shear waves. A modulation of CCD speckle contrast difference was observed and simulation reproduces the modulation pattern, suggesting its origin. Both experimental and simulation results show that the dual shear wave approach generates an improved definition of temporal features in the time-of-flight optical signal and an improved signal to noise ratio with a standard deviation less than 50% that of individual shear waves. Results also show that dual shear waves can correct the bias of shear wave speed measurement caused by shear wave reflections from elastic boundaries. PMID:26114021

  5. A tunable coherent CO2 lidar for measurements of atmospheric aerosol backscatter and attenuation

    NASA Technical Reports Server (NTRS)

    Menzies, R. T.

    1983-01-01

    A coherent laser radar system using a grating-tunable, injection-locked TEA-CO2 transmitter is being used to measure the altitude dependence of atmospheric aerosol backscatter and attenuation at a variety of CO2 laser wavelengths in the 9-11 micron region. Injection control of the TEA-CO2 laser allows one to obtain Single-Longitudinal-Mode (SLM) pulses which will follow the frequency of the injected radiation if the TEA laser cavity length is adjusted so that a cavity resonance is in proximity with the injected signal frequency, and if various additional conditions are satisfied. Requirements for generation of SLM pulses in this manner from a TEA CO2 laser with an unstable resonator cavity will be discussed. Procedures used for quantitative range-gated measurements of aerosol backscatter and attenuation will also be discussed.

  6. Source self-attenuation in ionization chamber measurements of (57)Co solutions.

    PubMed

    Cessna, Jeffrey T; Golas, Daniel B; Bergeron, Denis E

    2016-03-01

    Source self-attenuation for solutions of (57)Co of varying density and carrier concentration was measured in nine re-entrant ionization chambers maintained at NIST. The magnitude of the attenuation must be investigated to determine whether a correction is necessary in the determination of the activity of a source that differs in composition from the source used to calibrate the ionization chamber. At our institute, corrections are currently made in the measurement of (144)Ce, (109)Cd, (67)Ga, (195)Au, (166)Ho, (177)Lu, and (153)Sm. This work presents the methods used as recently applied to (57)Co. A range of corrections up to 1% were calculated for dilute to concentrated HCl at routinely used carrier concentrations. PMID:26717794

  7. Development of far infrared attenuation to measure electron densities in cw pin discharge lasers

    NASA Technical Reports Server (NTRS)

    Babcock, R. V.

    1977-01-01

    A two beam attenuation technique was devised to measure electron densities 10 to the 9th power to 10 to the 11th power cm/3 resolved to 1 cm, in a near atmospheric COFFEE laser discharge, using 496 micrometer and 1,220 micrometer radiations from CH3F, optically pumped by a CO2 laser. A far infrared generator was developed which was suitable except for a periodic intensity variation in FIR output deriving from frequency variation of the pump radiation.

  8. Self-attenuation correction factors for bioindicators measured by ? spectrometry for energies <100 keV

    NASA Astrophysics Data System (ADS)

    Manduci, L.; Tenailleau, L.; Trolet, J. L.; De Vismes, A.; Lopez, G.; Piccione, M.

    2010-01-01

    The mass attenuation coefficients for a number of marine and terrestrial bioindicators were measured using ? spectrometry for energies between 22 and 80 keV. These values were then used to find the correction factor k for the apparent radioactivity. The experimental results were compared with a Monte Carlo simulation performed using PENELOPE in order to evaluate the reliability of the simplified calculation and to determine the correction factors.

  9. CTS attenuation and cross-polarization measurements at 11.7 GHz

    NASA Technical Reports Server (NTRS)

    Vogel, W. J.; Straiton, A. W.

    1977-01-01

    The results of data obtained 80 days preceding the solar eclipse shutdown of the CTS 11.7 GHz righthand circularly polarized beacon transmitter are presented. Attenuation and cross polarization isolation were measured. It was determined that depolarization presents a serious limitation to satellite system reliability when frequency reuse by polarization diversity is employed. A 27 db isolation margin would reduce reliability below 99.95%. For the same percentage the required fade margin was below 3 db.

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

    NASA Astrophysics Data System (ADS)

    Lastovicka, J.; Boska, J.; Buresova, D.

    1993-10-01

    Low frequency (LF) radio wave absorption in the lower ionosphere has been measured at Pruhonice (approximately 50 deg N) since 1957. A new digital computer-controlled measuring-recording-processing system was introduced in 1988. The A3 method of radio wave absorption measurement, the measuring equipment used for the digital measurements at 270 kHz, is briefly described. The digital nighttime LF A3 measurements allow the use of absorption data for studying and monitoring the gravity wave activity in the upper middle atmosphere in the period range 10 min-3(2) hours. The resulting gravity wave spectra are as expected even though their shapes vary. Individual period bands sometimes exhibit a similar general pattern of variability in gravity wave activity (winter 1990), while in other intervals we observe a shift of gravity wave energy from one period band to another (winter 1991). No strong, pronounced and consistent response to strong geomagnetic storms and midwinter stratospheric warming is found. An apparent seasonal variation with winter minima observed in shorter-period gravity wave activity is an artefact of the changing length of the night. There is no significant seasonal variation of gravity wave activity in the analysed data. The method is very cheap -- the results are a by-product of measurements made for ionospheric purposes.

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

    NASA Astrophysics Data System (ADS)

    Li, Ting

    2005-07-01

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

  12. Measurement of light attenuation extends the application of suspended sediment monitoring in rivers

    NASA Astrophysics Data System (ADS)

    Hughes, A. O.; Davies-Colley, R. J.; Elliott, A. H.

    2015-03-01

    Turbidity is often monitored continuously as a proxy for suspended sediment in catchment sediment load studies, but is less often applied to measuring optical `loads' as they affect water quality in downstream waters. We added measurements of visual clarity, from which light (beam) attenuation can be estimated, to auto-sampler monitoring over storm events in tributary rivers of the Kaipara Harbour, a large barrier enclosed estuary complex in northern New Zealand. This paper presents, for the first time, evidence of the mutual relationships between turbidity, total suspended sediment (TSS), and visual clarity, from water samples collected under event flow conditions. The mutual relationships between turbidity, TSS and visual clarity for our monitoring sites were fairly close over about three orders of magnitude (TSS ranging from about 1-1000 mg L-1). Our results show that visual clarity (and hence light attenuation) can be predicted from turbidity, at least as precisely as more traditional predictions of TSS from turbidity. The estimation of light attenuation and corresponding load estimates from visual clarity measurements, for relatively little marginal extra effort, extends the environmental relevance and application of suspended sediment monitoring.

  13. Sparse signal reconstruction from polychromatic X-ray CT measurements via mass attenuation discretization

    SciTech Connect

    Gu, Renliang; Dogandžić, Aleksandar

    2014-02-18

    We propose a method for reconstructing sparse images from polychromatic x-ray computed tomography (ct) measurements via mass attenuation coefficient discretization. The material of the inspected object and the incident spectrum are assumed to be unknown. We rewrite the Lambert-Beer’s law in terms of integral expressions of mass attenuation and discretize the resulting integrals. We then present a penalized constrained least-squares optimization approach for reconstructing the underlying object from log-domain measurements, where an active set approach is employed to estimate incident energy density parameters and the nonnegativity and sparsity of the image density map are imposed using negative-energy and smooth ℓ{sub 1}-norm penalty terms. We propose a two-step scheme for refining the mass attenuation discretization grid by using higher sampling rate over the range with higher photon energy, and eliminating the discretization points that have little effect on accuracy of the forward projection model. This refinement allows us to successfully handle the characteristic lines (Dirac impulses) in the incident energy density spectrum. We compare the proposed method with the standard filtered backprojection, which ignores the polychromatic nature of the measurements and sparsity of the image density map. Numerical simulations using both realistic simulated and real x-ray ct data are presented.

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

    NASA Astrophysics Data System (ADS)

    Maruvada, Subha

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

  15. Sparse signal reconstruction from polychromatic X-ray CT measurements via mass attenuation discretization

    NASA Astrophysics Data System (ADS)

    Gu, Renliang; Dogandi?, Aleksandar

    2014-02-01

    We propose a method for reconstructing sparse images from polychromatic x-ray computed tomography (ct) measurements via mass attenuation coefficient discretization. The material of the inspected object and the incident spectrum are assumed to be unknown. We rewrite the Lambert-Beer's law in terms of integral expressions of mass attenuation and discretize the resulting integrals. We then present a penalized constrained least-squares optimization approach for reconstructing the underlying object from log-domain measurements, where an active set approach is employed to estimate incident energy density parameters and the nonnegativity and sparsity of the image density map are imposed using negative-energy and smooth ?1-norm penalty terms. We propose a two-step scheme for refining the mass attenuation discretization grid by using higher sampling rate over the range with higher photon energy, and eliminating the discretization points that have little effect on accuracy of the forward projection model. This refinement allows us to successfully handle the characteristic lines (Dirac impulses) in the incident energy density spectrum. We compare the proposed method with the standard filtered backprojection, which ignores the polychromatic nature of the measurements and sparsity of the image density map. Numerical simulations using both realistic simulated and real x-ray ct data are presented.

  16. Prediction of attenuation of the 28 GHz COMSTAR beacon signal using radar and measured rain drop spectra

    NASA Technical Reports Server (NTRS)

    Goldhirsh, J.

    1977-01-01

    Disdrometer measurements and radar reflectivity measurements were injected into a computer program to estimate the path attenuation of the signal. Predicted attenuations when compared with the directly measured ones showed generally good correlation on a case by case basis and very good agreement statistically. The utility of using radar in conjunction with disdrometer measurements for predicting fade events and long term fade distributions associated with earth-satellite telecommunications is demonstrated.

  17. Modelling of wave propagation and attenuation in the Osaka sedimentary basin, western Japan, during the 2013 Awaji Island earthquake

    NASA Astrophysics Data System (ADS)

    Asano, Kimiyuki; Sekiguchi, Haruko; Iwata, Tomotaka; Yoshimi, Masayuki; Hayashida, Takumi; Saomoto, Hidetaka; Horikawa, Haruo

    2016-03-01

    On 2013 April 13, an inland earthquake of Mw 5.8 occurred in Awaji Island, which forms the western boundary of the Osaka sedimentary basin in western Japan. The strong ground motion data were collected from more than 100 stations within the basin and it was found that in the Osaka Plain, the pseudo velocity response spectra at a period of around 6.5 s were significantly larger than at other stations of similar epicentral distance outside the basin. The ground motion lasted longer than 3 min in the Osaka Plain where its bedrock depth spatially varies from approximately 1 to 2 km. We modelled long-period (higher than 2 s) ground motions excited by this earthquake, using the finite difference method assuming a point source, to validate the present velocity structure model and to obtain better constraint of the attenuation factor of the sedimentary part of the basin. The effect of attenuation in the simulation was included in the form of Q(f) = Q0(f/f0), where Q0 at a reference frequency f0 was given by a function of the S-wave velocity, Q0 = αVS. We searched for appropriate Q0 values by changing α for a fixed value of f0 = 0.2 Hz. It was found that values of α from 0.2 to 0.5 fitted the observations reasonably well, but that the value of α = 0.3 performed best. Good agreement between the observed and simulated velocity waveforms was obtained for most stations within the Osaka Basin in terms of both amplitude and ground motion duration. However, underestimation of the pseudo velocity response spectra in the period range of 5-7 s was recognized in the central part of the Osaka Plain, which was caused by the inadequate modelling of later phases or wave packets in this period range observed approximately 2 min after the direct S-wave arrival. We analysed this observed later phase and concluded that it was a Love wave originating from the direction of the east coast of Awaji Island.

  18. Terahertz reflection response measurement using a phonon polariton wave

    NASA Astrophysics Data System (ADS)

    Inoue, Hayato; Katayama, Kenji; Shen, Qing; Toyoda, Taro; Nelson, Keith A.

    2009-03-01

    We developed a new technique for the measurement of terahertz reflection responses utilizing a propagating phonon polariton wave. Frequency tunable phonon polariton waves were generated by the recently developed continuously variable spatial frequency transient grating method [K. Katayama, H. Inoue, H. Sugiya, Q. Shen, T. Taro, and K. A. Nelson, Appl. Phys. Lett. 92, 031906 (2008)]. The phonon polariton wave traveled in a ferroelectric crystal in an in-plane direction with an inclined angle of 26°, and the wave reflected at the crystal edge where a sample was positioned. The reflected polariton wave was detected by the same method as that used for the generation of the polariton waves. By comparing the reflection intensities in the presence and absence of the sample, reflectivity of the polariton wave was calculated, and the refractive index and absorption in the terahertz region were obtained.

  19. Measurement and characterization of the wave-induced components of winds over waves

    NASA Astrophysics Data System (ADS)

    Grare, L.; Lenain, L.; Melville, W. K.

    2012-12-01

    Current wind-wave numerical models are largely based on a statistical description of the surface waves and the marine atmospheric boundary layer (MABL) and do not resolve the phase of the waves nor the modulation of the wind by the waves. However, the new generation of LES models provides wave-resolved dynamics, kinematics and the associated wave-coherent air-flow. Thus, it is important to provide experimental descriptions of the wave field and the structure of the MABL to test the validity of the numerical simulations. We present an analysis of coherent measurements of winds and waves from data collected during the ONR HiReS program from R/P FLIP off the coast of northern California in June 2010. A suite of wind and wave measuring systems were deployed allowing the resolution of the modulation of the MABL by the waves. Spectral analysis of the data gave the wave-induced components of the wind velocity for various wind and wave conditions over a large range of frequencies. The power spectral density, phase shift and transfer functions (relative to the waves) of these wave-induced components are computed and bin-averaged over normalized wave age c/U, or c/u*, and over the normalized height kz, where c and k are the phase speed and wavenumber, U is the mean wind speed, u* is the friction velocity in the air, and z is the height above the mean surface. Results are consistent with the critical layer theory of Miles (1957, 1959) for wave ages c/U up to 2 but show a different pattern for larger wave ages. Measurements of the phase shift between vertical and along-wave components of the wind with the waves show a jump at the critical height zc defined as U(zc)=c. The distribution of the coherent structures associated with the waves as function of the wave-age c/U shows a bi-modal distribution centered at c/U=1, or c/u*=20-30. This result is a consequence of the drop-off of the amplitude of the wave-induced velocity at the critical height. The normalized vertical profiles of the along wave and vertical wave-induced components of the wind do not follow an expected exponential trend. Indeed, for fast waves (c/U > 2), these wave-induced fluctuations reach a maximum around kz=1. Furthermore, these fast ("old") waves produce a positive vertical wave-induced momentum flux. These results are in agreement with the numerical study of Sullivan et al. (2008), for old waves or swell, that showed a coherent pattern of accelerated wind speed (with a maximum close to kz=1) over the troughs associated with decelerated wind speed over the crests.

  20. Heterogeneities of the field of short-period shear wave attenuation in the lithosphere of Central Asia and their relationship with seismicity

    NASA Astrophysics Data System (ADS)

    Kopnichev, Yu. F.; Sokolova, I. N.

    2011-03-01

    The characteristics of the short-period shear wave attenuation field in the lithosphere of the Turanian Plate, West Tien Shan, Pamir, and Hindu Kush have been studied. The method based on analysis of the logarithm of the ratio between maximal amplitudes of Sn and Pn waves ( Sn/ Pn parameter) has been applied. More than 400 records of earthquakes, obtained at distances of ˜400-1000 km from the AAK digital station, have been processed. It has been found that relatively weak attenuation is observed in the regions of the West Tien Shan and Pamir. The largest area of strong attenuation is located in the region of the Afghan-Tadjik Depression adjacent to Hindu Kush. A wide band of low Sn/ Pn parameter values, stretched northeastwards, has been distinguished. Along with the analogous band of strong attenuation, distinguished before in the regions of Central Tien Shan and Dzungaria, it is the continuation of the largest Chaman Fault, which stretches 850 km along the boundary of the Indian Plate. Source zones of strong earthquakes with M ≥ 7.0 that occurred in the first half of 20th century correspond to relatively weak attenuation. Areas of high attenuation, where strong seismic events have not occurred for the last 110 years, are outlined. Analogously to other seismoactive regions, it is supposed that these areas are related to preparation of strong earthquakes.

  1. IWA : an analysis program for isentropic wave measurements.

    SciTech Connect

    Ao, Tommy

    2009-02-01

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

  2. Spatiotemporal measurement of surfactant distribution on gravity-capillary waves

    NASA Astrophysics Data System (ADS)

    Strickland, Stephen; Shearer, Michael; Daniels, Karen

    2015-11-01

    Materials adsorbed to the surface of a fluid - for instance, crude oil, biogenic slicks, or industrial/medical surfactants - will move in response to surface waves. Due to the difficulty of non-invasive measurement of the spatial distribution of a molecular monolayer, little is known about the dynamics that couple the surface waves and the evolving density field. We report measurements of the spatiotemporal dynamics of the density field of an insoluble surfactant driven by gravity-capillary waves in a shallow cylindrical container. Standing Faraday waves and traveling waves generated by the meniscus are superimposed to create a non-trivial surfactant density field. We measure both the height field of the surface using moire-imaging and the density field of the surfactant via the fluorescence of NBD-tagged phosphatidylcholine. Through phase-averaging stroboscopically-acquired images of the density field, we determine that the surfactant accumulates on the leading edge of the traveling meniscus waves and in the troughs of the standing Faraday waves. We fit the spatiotemporal variations in the two fields and report measurements of the wavenumbers as well as a temporal phase shift between the two fields. These measurements suggest that longitudinal waves contribute to the dynamics. Funded by NSF grant DMS-0968258.

  3. 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.

  4. Spinal axis irradiation with electrons: Measurements of attenuation by the spinal processes

    SciTech Connect

    Muller-Runkel, R.; Vijayakumar, S.

    1986-07-01

    Electrons may be used beneficially for spinal axis irradiation in medulloblastoma children to avoid some of the long-term sequelae induced by megavoltage photons. However, the attenuation by the intervening bone ought to be considered. Three-dimensional computer treatment planning with inhomogeneity correction for electron beams is not yet generally available, and alternate methods are needed to evaluate the attenuation by the complex bony structure of the spine. Here, we present our experimental data showing the alteration in the electron isodoses due to the intervening spinous processes. Film dosimetric measurements were made in the vertebral columns obtained from autopsies of a goat, a dog, and a child. Our results show that electron beam therapy for the spinal axis is a viable option.

  5. Correlating index properties of rocks with P-wave measurements

    NASA Astrophysics Data System (ADS)

    Khandelwal, Manoj; Ranjith, P. G.

    2010-05-01

    The determination of index properties of rock, such as Cerchar Abrasivity Index, Shore Hardness, Protodyakonov Index and Vickers Hardness in laboratory or insitu conditions is time-consuming and requires special equipment and expertise. However, the use of P-wave technology to measure the P-wave velocity of rock is a relatively simple task because the portable equipment can be used in the laboratory or in the field without tedious preparation of rock cores and it is non-destructive. This paper presents an experimental study of the measurement of P-waves of several types of igneous, sedimentary and metamorphic rock. The index properties were also determined in the laboratory to obtain correlations between P-waves and various index properties. Good linear relationships were found between all the index properties determined and the P-wave measurements.

  6. New lifetime measurements in the stable semimagic Sn isotopes using the Doppler-shift attenuation technique

    NASA Astrophysics Data System (ADS)

    Jungclaus, A.; Walker, J.; Leske, J.; Speidel, K.-H.; Stuchbery, A. E.; East, M.; Boutachkov, P.; Cederkäll, J.; Doornenbal, P.; Egido, J. L.; Ekström, A.; Gerl, J.; Gernhäuser, R.; Goel, N.; Górska, M.; Kojouharov, I.; Maier-Komor, P.; Modamio, V.; Naqvi, F.; Pietralla, N.; Pietri, S.; Prokopowicz, W.; Schaffner, H.; Schwengner, R.; Wollersheim, H.-J.

    2011-09-01

    Precise measurements of lifetimes in the picosecond range of excited states in the stable even-A Sn isotopes 112,114,116,122Sn have been performed using the Doppler shift attenuation technique. For the first excited 2+ states in 112Sn, 114Sn and 116Sn the E2 transition strengths deduced from the measured lifetimes are in disagreement with the previously adopted values. They indicate a shallow minimum at N = 66 in contrast to the maximum at mid-shell predicted by modern shell model calculations.

  7. The moon and Q. [lunar basalt acoustic attenuation measurement by resonance method

    NASA Technical Reports Server (NTRS)

    Schreiber, E.

    1977-01-01

    The acoustic attenuation of a sample of lunar basalt 70215 was measured by the method of sphere resonance. A Q of 1185 was achieved under a vacuum of 7 millionths torr after heating the sample. He and CO2 gas caused a small decrease of Q. H2O vapor, however, resulted in a major decrease in Q. The Q of lunar material when measured on earth is low because of adsorbed gases. However, it is not clear that this effect explains completely the observed high lunar Q.

  8. Ultrasonic database development for the acoustic inspection device: the velocity-attenuation measurement system (VAMS)

    SciTech Connect

    Diaz, Aaron A.; Burghard, Brion J.; Valencia, Juan D.; Samuel, Todd J.; Doctor, S. R.

    2004-08-01

    The inspection of sealed containers is a critical task for personnel charged with enforcing government policies, maintaining public safety, and ensuring national security. The Pacific Northwest National Laboratory (PNNL) has developed a portable, handheld acoustic inspection device (AID) that provides non-invasive container interrogation and material identification capabilities. The AID technology has been deployed worldwide and user's are providing feedback and requesting additional capabilities and functionality. Recently, PNNL has developed a laboratory-based system for automated, ultrasonic characterization of fluids to support database development for the AID. Using pulse-echo ultrasound, ultrasonic pulses are launched into a container or bulk-solid commodity. The return echoes from these pulses are analyzed in terms of time-of-flight and frequency content (as a function of temperature) to extract physical property measurements (acoustic velocity and attenuation) of the material under test. These measured values are then compared to a tailored database of materials and fluids property data acquired using the Velocity-Attenuation Measurement System (VAMS). This bench-top platform acquires key ultrasonic property measurements as a function of temperature and frequency. This paper describes the technical basis for operation of the VAMS, recent enhancements to the measurement algorithms for both the VAMS and AID technologies, and new measurement data from laboratory testing and performance demonstration activities. Applications for homeland security and counter terrorism, law enforcement, drug-interdiction and fuel transportation compliance activities will be discussed.

  9. Ultrasonic database development for the acoustic inspection device: the velocity-attenuation measurement system (VAMS)

    NASA Astrophysics Data System (ADS)

    Diaz, Aaron A.; Burghard, Brion J.; Valencia, Juan D.; Samuel, Todd J.

    2004-07-01

    The inspection of sealed containers is a critical task for personnel charged with enforcing government policies, maintaining public safety, and ensuring national security. The Pacific Northwest National Laboratory (PNNL) has developed a portable, handheld acoustic inspection device (AID) that provides non-invasive container interrogation and material identification capabilities. The AID technology has been deployed worldwide and user"s are providing feedback and requesting additional capabilities and functionality. Recently, PNNL has developed a laboratory-based system for automated, ultrasonic characterization of fluids to support database development for the AID. Using pulse-echo ultrasound, ultrasonic pulses are launched into a container or bulk-solid commodity. The return echoes from these pulses are analyzed in terms of time-of-flight and frequency content (as a function of temperature) to extract physical property measurements (acoustic velocity and attenuation) of the material under test. These measured values are then compared to a tailored database of materials and fluids property data acquired using the Velocity-Attenuation Measurement System (VAMS). This bench-top platform acquires key ultrasonic property measurements as a function of temperature and frequency. This paper describes the technical basis for operation of the VAMS, recent enhancements to the measurement algorithms for both the VAMS and AID technologies, and new measurement data from laboratory testing and performance demonstration activities. Applications for homeland security and counterterrorism, law enforcement, drug-interdiction and fuel transportation compliance activities will be discussed.

  10. Method of determining ultrasonic attenuation of tissue using reflective tomographic reconstruction

    SciTech Connect

    Flax, S. W.; Glover, G. H.

    1984-10-09

    Ultrasonic wave attenuation is determined for a plurality of limited volumes of tissue comprising a body under examination by directing ultrasonic waves through each limited volume along a plurality of vectors, determining a measure of attenuation of the limited volume by detecting the frequency shift of reflections of the ultrasonic wave along each vector, and averaging the attenuation of each limited volume from each vector intersecting the limited volume.

  11. Measurement of Oblique Impact-generated Shear Waves

    NASA Technical Reports Server (NTRS)

    Dahl, J. M.; Schultz, P. H.

    2001-01-01

    Experimental strain measurements reveal that oblique impacts can generate shear waves with displacements as large as those in the P-wave. Large oblique impacts may thus be more efficient sources of surface disruption than vertical impacts. Additional information is contained in the original extended abstract.

  12. Rotary antenna attenuator

    NASA Technical Reports Server (NTRS)

    Dickinson, R. M.; Hardy, J. C.

    1969-01-01

    Radio frequency attenuator, having negligible insertion loss at minimum attenuation, can be used for making precise antenna gain measurements. It is small in size compared to a rotary-vane attenuator.

  13. Estimation of Complex-Valued Stiffness Using Acoustic Waves Measured with Magnetic Resonance

    NASA Astrophysics Data System (ADS)

    Oliphant, Travis E.; Ehman, Richard L.; Greenleaf, James F.

    Tissue stiffness can be a useful indicator of diseased tissue. Noninvasive quantitation of the mechanical properties of tissue could improve early detection of such pathology. A method for detecting displacement from propagating shear waves using a phase-contrast MRI technique has been developed previously. In this chapter the principles behind the measurement technique are reviewed, and the mechanical properties that can be determined from the displacement data are investigated for isotropic materials. An algebraic inversion approach useful for piece-wise homogeneous materials is described in detail for the general isotropic case, which is then specialized to incompressible materials as a model for tissue. Results of the inversion approach are presented for an experimental phantom and in-vivo breast tumor. These results show that the technique can be used to obtain shear-wave speed and attenuation in regions where there is sufficient signal-to-noise ratio in the displacement and its second spatial derivatives. The sensitivity to noise is higher in the attenuation estimates than in the shear-wave speed estimates.

  14. Spaced measurements and progress in understanding space plasma waves

    NASA Astrophysics Data System (ADS)

    Kintner, P. M.; Schuck, P. W.; Franz, J. R.

    2000-05-01

    Measuring plasma wave properties with spatially separated antennae observes wavelength, propagation speed, and direction as well as frequency. This approach has been pivotal to progress in understanding three phenomena in space plasmas. The first is lower hybrid solitary waves, which are waves with cylindrical symmetry propagating inside a density cavity. The second is electron phase-space holes, which are propagating vortices in phase space. The third is called broadband ELF (extra low frequency) electric fields and is an important but poorly understood wave process essential to transverse ion acceleration.

  15. Measurements of the Gravity Waves Velocity

    NASA Astrophysics Data System (ADS)

    Dubrovskiy, Vladimir A.

    We suppose the gravity waves excite microseismic background. Peaks of the background spectrum can be observed if the wave length l is comparable with distance L between Earth and some cosmic gravity object. Such resonance peaks where observed using laser interferometer and spectranalyser SK4-72 that enlarges periodical signal component relative chaotic one. They are around 2.3 1.0 0.9 0.6 0.4 0.2 Hz. And there exist massive gravity objects at 1.3 2.7 3.5 5.0 8.0 and 11.0 parsecs distances (nearest and brightest stars). This all distances correspond to all peaks in accordance with f=C/l (l/2~L due to resonance) only if the gravity velocity C should be nearly nine order more then light velocity. If this conclusion is not casual it is possible to observe resonance peaks corresponding to the gravity waves exchange of the Earth with Moon (~240MHz) Sun (~0.6MHz) Venus (0.3-2.2MHz) Jupiter (100-150kHz) Saturn (58-72kHz). Moreover peak corresponding to Venus Jupiter or Saturn should change its frequency position during orbital motion. Such correlation will support decisively the presented result elastic model of the physical vacuum and Laplace's result concerning to the lower limit of the gravity velocity.

  16. Direct Measurement of Wave Kernels in Time-Distance Helioseismology

    NASA Technical Reports Server (NTRS)

    Duvall, T. L., Jr.

    2006-01-01

    Solar f-mode waves are surface-gravity waves which propagate horizontally in a thin layer near the photosphere with a dispersion relation approximately that of deep water waves. At the power maximum near 3 mHz, the wavelength of 5 Mm is large enough for various wave scattering properties to be observable. Gizon and Birch (2002,ApJ,571,966)h ave calculated kernels, in the Born approximation, for the sensitivity of wave travel times to local changes in damping rate and source strength. In this work, using isolated small magnetic features as approximate point-sourc'e scatterers, such a kernel has been measured. The observed kernel contains similar features to a theoretical damping kernel but not for a source kernel. A full understanding of the effect of small magnetic features on the waves will require more detailed modeling.

  17. Influence of bubble size and thermal dissipation on compressive wave attenuation in liquid foams

    NASA Astrophysics Data System (ADS)

    Monloubou, M.; Saint-Jalmes, A.; Dollet, B.; Cantat, I.

    2015-11-01

    Acoustic or blast wave absorption by liquid foams is especially efficient and bubble size or liquid fraction optimization is an important challenge in this context. A resonant behavior of foams has recently been observed, but the main local dissipative process is still unknown. In this paper, we evidence the thermal origin of the dissipation, with an optimal bubble size close to the thermal boundary layer thickness. Using a shock tube, we produce typical pressure variation at time scales of the order of the millisecond, which propagates in the foam in linear and slightly nonlinear regimes.

  18. Ocean Wave Separation Using CEEMD-Wavelet in GPS Wave Measurement.

    PubMed

    Wang, Junjie; He, Xiufeng; Ferreira, Vagner G

    2015-01-01

    Monitoring ocean waves plays a crucial role in, for example, coastal environmental and protection studies. Traditional methods for measuring ocean waves are based on ultrasonic sensors and accelerometers. However, the Global Positioning System (GPS) has been introduced recently and has the advantage of being smaller, less expensive, and not requiring calibration in comparison with the traditional methods. Therefore, for accurately measuring ocean waves using GPS, further research on the separation of the wave signals from the vertical GPS-mounted carrier displacements is still necessary. In order to contribute to this topic, we present a novel method that combines complementary ensemble empirical mode decomposition (CEEMD) with a wavelet threshold denoising model (i.e., CEEMD-Wavelet). This method seeks to extract wave signals with less residual noise and without losing useful information. Compared with the wave parameters derived from the moving average skill, high pass filter and wave gauge, the results show that the accuracy of the wave parameters for the proposed method was improved with errors of about 2 cm and 0.2 s for mean wave height and mean period, respectively, verifying the validity of the proposed method. PMID:26262620

  19. Ocean Wave Separation Using CEEMD-Wavelet in GPS Wave Measurement

    PubMed Central

    Wang, Junjie; He, Xiufeng; Ferreira, Vagner G.

    2015-01-01

    Monitoring ocean waves plays a crucial role in, for example, coastal environmental and protection studies. Traditional methods for measuring ocean waves are based on ultrasonic sensors and accelerometers. However, the Global Positioning System (GPS) has been introduced recently and has the advantage of being smaller, less expensive, and not requiring calibration in comparison with the traditional methods. Therefore, for accurately measuring ocean waves using GPS, further research on the separation of the wave signals from the vertical GPS-mounted carrier displacements is still necessary. In order to contribute to this topic, we present a novel method that combines complementary ensemble empirical mode decomposition (CEEMD) with a wavelet threshold denoising model (i.e., CEEMD-Wavelet). This method seeks to extract wave signals with less residual noise and without losing useful information. Compared with the wave parameters derived from the moving average skill, high pass filter and wave gauge, the results show that the accuracy of the wave parameters for the proposed method was improved with errors of about 2 cm and 0.2 s for mean wave height and mean period, respectively, verifying the validity of the proposed method. PMID:26262620

  20. Volumetric measurements of a spatially growing dust acoustic wave

    SciTech Connect

    Williams, Jeremiah D.

    2012-11-15

    In this study, tomographic particle image velocimetry (tomo-PIV) techniques are used to make volumetric measurements of the dust acoustic wave (DAW) in a weakly coupled dusty plasma system in an argon, dc glow discharge plasma. These tomo-PIV measurements provide the first instantaneous volumetric measurement of a naturally occurring propagating DAW. These measurements reveal over the measured volume that the measured wave mode propagates in all three spatial dimensional and exhibits the same spatial growth rate and wavelength in each spatial direction.

  1. 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 μm, 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.

  2. Diver visibility measured with a compact scattering-attenuation meter (SAM) compatible with AUVs and other small deployment platforms

    NASA Astrophysics Data System (ADS)

    Twardowski, Michael S.; Zaneveld, J. Ronald V.; Moore, Casey M.; Mueller, James; Trees, Charles; Schofield, Oscar; Freeman, Scott; Helble, Tyler; Hong, Gerry

    2005-05-01

    An appropriate determination of water clarity is required by defense and security operations assessing subsurface threats compromising harbor and coastal security. For search and inspection operations involving divers, underwater imaging, and electro-optical identification (EOID) systems such as laser line-scanners, the key environmental parameter needed is the optical attenuation coefficient (directly related to diver visibility). To address this need, a scattering-attenuation meter (SAM) measuring attenuation and diver visibility was developed for integration on new compact surveying platforms such as ROVs and the REMUS and glider AUVs. The sensor is compact (18X8X6 cm3), low power, robust, and hydrodynamic with a flat sensing face. The SAM measures attenuation using a novel dual-scattering approach that solves the paradox of making high-resolution attenuation measurements over the long pathlengths required for natural waters with a compact sensor. Attenuation and visibility data is presented from San Diego harbor in coordination with video images of bottom topography collected with a REMUS vehicle, from around New York harbor with a SAM mounted in an autonomous Slocum glider, and from Narragansett Bay. Results show that 1) visibility and/or attenuation in harbor and coastal regions can change rapidly over small scales (meters), especially near the bottom, 2) turbid bottom nepheloid layers are common, 3) typical visibility and/or attenuation levels fall in a range where knowledge of visibility and/or attenuation can be essential in the decision making process for security operations, and 4) attenuation is a significantly more accurate proxy for diver visibility than backscattering.

  3. An inexpensive instrument for measuring wave exposure and water velocity

    USGS Publications Warehouse

    Figurski, J.D.; Malone, D.; Lacy, J.R.; Denny, M.

    2011-01-01

    Ocean waves drive a wide variety of nearshore physical processes, structuring entire ecosystems through their direct and indirect effects on the settlement, behavior, and survivorship of marine organisms. However, wave exposure remains difficult and expensive to measure. Here, we report on an inexpensive and easily constructed instrument for measuring wave-induced water velocities. The underwater relative swell kinetics instrument (URSKI) is a subsurface float tethered by a short (<1 m) line to the seafloor. Contained within the float is an accelerometer that records the tilt of the float in response to passing waves. During two field trials totaling 358 h, we confirmed the accuracy and precision of URSKI measurements through comparison to velocities measured by an in situ acoustic Doppler velocimeter and those predicted by a standard swell model, and we evaluated how the dimensions of the devices, its buoyancy, and sampling frequency can be modified for use in a variety of environments.

  4. Effect of decay on ultrasonic velocity and attenuation measurements in wood

    NASA Astrophysics Data System (ADS)

    McGovern, Megan; Senalik, Adam; Chen, George; Beall, Frank C.; Reis, Henrique

    2011-04-01

    Loblolly pine (Pinus taeda) wood cube specimens were exposed to Gloeophyllum fungus (Gloeophyllum trabeum) for increasing periods of time ranging from one week to twelve weeks. The corresponding mass of each of these specimens was recorded before and after they were subjected to the controlled decay. Using X-ray computed tomography (CT) the specimens' corresponding mass loss due to decay and corresponding densities were calculated. For each of the three principal material directions of these specimens with controlled decay, ultrasonic longitudinal and (polarized) shear velocity measurements along with the corresponding attenuation measurements are presented. The measurements were carried out using longitudinal and shear ultrasonic transducers with a center frequency of 100 kHz. A steel delay line was used because of the relative small size of the wooden specimens relative to the used wavelengths. Waveform averaging was used along with the phase-slope method to measure velocities. It was observed that the velocities increase with increasing frequency and decrease with increasing amount of decay, while the corresponding attenuations increase with increasing frequency and with amount of decay.

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

    NASA Astrophysics Data System (ADS)

    Boatwright, J.; Seekins, L. C.

    2009-12-01

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

  6. Millimeter-Wave Propagation Measurements At The Ballistic Research Laboratory

    NASA Astrophysics Data System (ADS)

    Wallace, H. Bruce

    1981-12-01

    Since the early 1960s, the Ballistic Research Laboratory (BRL) has been involved in the characterization of millimetre-wave propagation as it applies to military systems. Measurements have been made with radars and radiometers from 30 to 600 GHz of near earth propagation through both natural and cultural obscurants. Results of measurements made in rain, fog, snow, high humidity, dust and some smokes are presented for the major millimetre-wave windows. Some modeling performed by other agencies are presented for comparison.

  7. High frequency measurement of P- and S-wave velocities on crystalline rock massif surface - methodology of measurement

    NASA Astrophysics Data System (ADS)

    Vilhelm, Jan; Slavík, Lubomír

    2014-05-01

    For the purpose of non-destructive monitoring of rock properties in the underground excavation it is possible to perform repeated high-accuracy P- and S-wave velocity measurements. This contribution deals with preliminary results gained during the preparation of micro-seismic long-term monitoring system. The field velocity measurements were made by pulse-transmission technique directly on the rock outcrop (granite) in Bedrichov gallery (northern Bohemia). The gallery at the experimental site was excavated using TBM (Tunnel Boring Machine) and it is used for drinking water supply, which is conveyed in a pipe. The stable measuring system and its automatic operation lead to the use of piezoceramic transducers both as a seismic source and as a receiver. The length of measuring base at gallery wall was from 0.5 to 3 meters. Different transducer coupling possibilities were tested namely with regard of repeatability of velocity determination. The arrangement of measuring system on the surface of the rock massif causes better sensitivity of S-transducers for P-wave measurement compared with the P-transducers. Similarly P-transducers were found more suitable for S-wave velocity determination then P-transducers. The frequency dependent attenuation of fresh rock massif results in limited frequency content of registered seismic signals. It was found that at the distance between the seismic source and receiver from 0.5 m the frequency components above 40 kHz are significantly attenuated. Therefore for the excitation of seismic wave 100 kHz transducers are most suitable. The limited frequency range should be also taken into account for the shape of electric impulse used for exciting of piezoceramic transducer. The spike pulse generates broad-band seismic signal, short in the time domain. However its energy after low-pass filtration in the rock is significantly lower than the energy of seismic signal generated by square wave pulse. Acknowledgments: This work was partially supported by the Technology Agency of the Czech Republic, project No. TA 0302408

  8. Using Ultrasonic Lamb Waves To Measure Moduli Of Composites

    NASA Technical Reports Server (NTRS)

    Kautz, Harold E.

    1995-01-01

    Measurements of broad-band ultrasonic Lamb waves in plate specimens of ceramic-matrix/fiber and metal-matrix/fiber composite materials used to determine moduli of elasticity of materials. In one class of potential applications of concept, Lamb-wave responses of specimens measured and analyzed at various stages of thermal and/or mechanical processing to determine effects of processing, without having to dissect specimens. In another class, structural components having shapes supporting propagation of Lamb waves monitored ultrasonically to identify signs of deterioration and impending failure.

  9. Acoustic Measurement of Surface Wave Damping by a Meniscus.

    PubMed

    Michel, Guillaume; Pétrélis, François; Fauve, Stéphan

    2016-04-29

    We investigate the reflection of gravity-capillary surface waves by a plane vertical barrier. The size of the meniscus is found to strongly affect reflection: the energy of the reflected wave with a pinned contact line is around twice the one corresponding to a fully developed meniscus. To perform these measurements, a new experimental setup similar to an acousto-optic modulator is developed and offers a simple way to measure the amplitude, frequency and direction of propagation of surface waves. PMID:27176523

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

    SciTech Connect

    Friedman, W.

    1999-07-29

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

  11. In vitro measurement of attenuation and nonlinear scattering from Echogenic liposomes

    PubMed Central

    Paul, Shirshendu; Russakow, Daniel; Nahire, Rahul; Nandy, Tapas; Ambre, Avinash H.; Katti, Kalpana; Mallik, Sanku; Sarkar, Kausik

    2013-01-01

    Echogenic liposomes (ELIP) are an excellent candidate for concurrent imaging and drug delivery applications. They combine the advantages of liposomes—biocompatibility and ability to encapsulate both hydrophobic and hydrophilic drugs—with strong reflections of ultrasound. The objective of this study is to perform a detailed in vitro acoustic characterization—including nonlinear scattering that has not been studied before—along with an investigation of the primary mechanism of echogenicity. Both components are critical for developing viable clinical applications of ELIP. Mannitol, a cryoprotectant, added during the preparation of ELIP is commonly believed to be critical in making them echogenic. Accordingly, here ELIP prepared with varying amount of mannitol concentration are investigated for their pressure dependent linear and non-linear scattered responses. The average diameter of these liposomes is measured to be 125–185 nm. But they have a broad size distribution including liposomes with diameters over a micro-meter as observed by TEM and AEM. These larger liposomes are critical for the overall echogenicity. Attenuation through liposomal solution is measured with four different transducers (central frequencies 2.25, 3.5, 5, 10 MHz). Measured attenuation increases linearly with liposome concentration indicating absence of acoustic interactions between liposomes. Due to the broad size distribution, the attenuation shows a flat response without a distinct peak in the range of frequencies (1–12 MHz) investigated. A 15–20 dB enhancement is observed both for the scattered fundamental and the second harmonic responses at 3.5 MHz excitation frequency and 50–800 kPa amplitude. It demonstrates the efficacy of ELIP for fundamental as well as harmonic ultrasound imaging. The scattered response however does not show any distinct subharmonic peak for the acoustic excitation parameters studied. Small amount of mannitol proves critical for echogenicity. However, mannitol variation above 100 mM shows no effect. PMID:22652364

  12. Measurements of inertial limit Alfvén wave dispersion for finite perpendicular wave number.

    PubMed

    Kletzing, C A; Thuecks, D J; Skiff, F; Bounds, S R; Vincena, S

    2010-03-01

    Measurements of the dispersion relation for shear Alfvén waves as a function of perpendicular wave number are reported for the inertial regime for which V{A}>V{Te}. The parallel phase velocity and damping are determined as k{ perpendicular} varies and the measurements are compared to theoretical predictions. The comparison shows that the best agreement between theory and experiment is achieved for a fully complex plasma dispersion relation which includes the effects of electron collisions. PMID:20366989

  13. Measurements of Inertial Limit Alfven Wave Dispersion for Finite Perpendicular Wave Number

    SciTech Connect

    Kletzing, C. A.; Thuecks, D. J.; Skiff, F.; Bounds, S. R.; Vincena, S.

    2010-03-05

    Measurements of the dispersion relation for shear Alfven waves as a function of perpendicular wave number are reported for the inertial regime for which V{sub A}>V{sub Te}. The parallel phase velocity and damping are determined as k{sub perpendicular} varies and the measurements are compared to theoretical predictions. The comparison shows that the best agreement between theory and experiment is achieved for a fully complex plasma dispersion relation which includes the effects of electron collisions.

  14. Comparing shear-wave velocity profiles inverted from multichannel surface wave with borehole measurements

    USGS Publications Warehouse

    Xia, J.; Miller, R.D.; Park, C.B.; Hunter, J.A.; Harris, J.B.; Ivanov, J.

    2002-01-01

    Recent field tests illustrate the accuracy and consistency of calculating near-surface shear (S)-wave velocities using multichannel analysis of surface waves (MASW). S-wave velocity profiles (S-wave velocity vs. depth) derived from MASW compared favorably to direct borehole measurements at sites in Kansas, British Columbia, and Wyoming. Effects of changing the total number of recording channels, sampling interval, source offset, and receiver spacing on the inverted S-wave velocity were studied at a test site in Lawrence, Kansas. On the average, the difference between MASW calculated Vs and borehole measured Vs in eight wells along the Fraser River in Vancouver, Canada was less than 15%. One of the eight wells was a blind test well with the calculated overall difference between MASW and borehole measurements less than 9%. No systematic differences were observed in derived Vs values from any of the eight test sites. Surface wave analysis performed on surface data from Wyoming provided S-wave velocities in near-surface materials. Velocity profiles from MASW were confirmed by measurements based on suspension log analysis. ?? 2002 Elsevier Science Ltd. All rights reserved.

  15. A New Understanding for the Rain Rate retrieval of Attenuating Radars Measurement

    NASA Astrophysics Data System (ADS)

    Koner, P.; Battaglia, A.; Simmer, C.

    2009-04-01

    The retrieval of rain rate from the attenuated radar (e.g. Cloud Profiling Radar on board of CloudSAT in orbit since June 2006) is a challenging problem. ĹEcuyer and Stephens [1] underlined this difficulty (for rain rates larger than 1.5 mm/h) and suggested the need of additional information (like path-integrated attenuations (PIA) derived from surface reference techniques or precipitation water path estimated from co-located passive microwave radiometer) to constrain the retrieval. It is generally discussed based on the optimal estimation theory that there are no solutions without constraining the problem in a case of visible attenuation because there is no enough information content to solve the problem. However, when the problem is constrained by the additional measurement of PIA, there is a reasonable solution. This raises the spontaneous question: Is all information enclosed in this additional measurement? This also contradicts with the information theory because one measurement can introduce only one degree of freedom in the retrieval. Why is one degree of freedom so important in the above problem? This question cannot be explained using the estimation and information theories of OEM. On the other hand, Koner and Drummond [2] argued that the OEM is basically a regularization method, where a-priori covariance is used as a stabilizer and the regularization strength is determined by the choices of the a-priori and error covariance matrices. The regularization is required for the reduction of the condition number of Jacobian, which drives the noise injection from the measurement and inversion spaces to the state space in an ill-posed inversion. In this work, the above mentioned question will be discussed based on the regularization theory, error mitigation and eigenvalue mathematics. References 1. L'Ecuyer TS and Stephens G. An estimation based precipitation retrieval algorithm for attenuating radar. J. Appl. Met., 2002, 41, 272-85. 2. Koner PK, Drummond JR. A comparison of regularization techniques for atmospheric trace gases retrievals. JQSRT 2008; 109:514-26.

  16. Q-structure beneath the north and central Indian Ocean from the inversion of observed Love and Rayleigh wave attenuation data

    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 ( Qβ ≈ 125) for the Bay of Bengal Fan. Similarly, a high-attenuation zone ( Qβ ≈ 40-70) occurs at a depth of 60-160 km for the Arabian Fan at 100-160 km ( Qβ ≈ 115) for the Indian Ocean off Ninetyeast Ridge, and at 80-160 km ( Qβ ≈ 80) for the Indian Ocean across the Ninetyeast Ridge. The Qβ-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 Qβ-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.

  17. Study of EMIC wave excitation using direct ion measurements

    NASA Astrophysics Data System (ADS)

    Min, Kyungguk; Liu, Kaijun; Bonnell, John W.; Breneman, Aaron W.; Denton, Richard E.; Funsten, Herbert O.; Jahn, Jöerg-Micha; Kletzing, Craig A.; Kurth, William S.; Larsen, Brian A.; Reeves, Geoffrey D.; Spence, Harlan E.; Wygant, John R.

    2015-04-01

    With data from Van Allen Probes, we investigate electromagnetic ion cyclotron (EMIC) wave excitation using simultaneously observed ion distributions. Strong He band waves occurred while the spacecraft was moving through an enhanced density region. We extract from helium, oxygen, proton, and electron mass spectrometer measurement the velocity distributions of warm heavy ions as well as anisotropic energetic protons that drive wave growth through the ion cyclotron instability. Fitting the measured ion fluxes to multiple sinm-type distribution functions, we find that the observed ions make up about 15% of the total ions, but about 85% of them are still missing. By making legitimate estimates of the unseen cold (below ˜2 eV) ion composition from cutoff frequencies suggested by the observed wave spectrum, a series of linear instability analyses and hybrid simulations are carried out. The simulated waves generally vary as predicted by linear theory. They are more sensitive to the cold O+ concentration than the cold He+ concentration. Increasing the cold O+ concentration weakens the He band waves but enhances the O band waves. Finally, the exact cold ion composition is suggested to be in a range when the simulated wave spectrum best matches the observed one.

  18. An arbitrary high-order Discontinuous Galerkin method for elastic waves on unstructured meshes - III. Viscoelastic attenuation

    NASA Astrophysics Data System (ADS)

    Käser, Martin; Dumbser, Michael; de la Puente, Josep; Igel, Heiner

    2007-01-01

    We present a new numerical method to solve the heterogeneous anelastic, seismic wave equations with arbitrary high order accuracy in space and time on 3-D unstructured tetrahedral meshes. Using the velocity-stress formulation provides a linear hyperbolic system of equations with source terms that is completed by additional equations for the anelastic functions including the strain history of the material. These additional equations result from the rheological model of the generalized Maxwell body and permit the incorporation of realistic attenuation properties of viscoelastic material accounting for the behaviour of elastic solids and viscous fluids. The proposed method combines the Discontinuous Galerkin (DG) finite element (FE) method with the ADER approach using Arbitrary high order DERivatives for flux calculations. The DG approach, in contrast to classical FE methods, uses a piecewise polynomial approximation of the numerical solution which allows for discontinuities at element interfaces. Therefore, the well-established theory of numerical fluxes across element interfaces obtained by the solution of Riemann problems can be applied as in the finite volume framework. The main idea of the ADER time integration approach is a Taylor expansion in time in which all time derivatives are replaced by space derivatives using the so-called Cauchy-Kovalewski procedure which makes extensive use of the governing PDE. Due to the ADER time integration technique the same approximation order in space and time is achieved automatically and the method is a one-step scheme advancing the solution for one time step without intermediate stages. To this end, we introduce a new unrolled recursive algorithm for efficiently computing the Cauchy-Kovalewski procedure by making use of the sparsity of the system matrices. The numerical convergence analysis demonstrates that the new schemes provide very high order accuracy even on unstructured tetrahedral meshes while computational cost and storage space for a desired accuracy can be reduced when applying higher degree approximation polynomials. In addition, we investigate the increase in computing time, when the number of relaxation mechanisms due to the generalized Maxwell body are increased. An application to a well-acknowledged test case and comparisons with analytic and reference solutions, obtained by different well-established numerical methods, confirm the performance of the proposed method. Therefore, the development of the highly accurate ADER-DG approach for tetrahedral meshes including viscoelastic material provides a novel, flexible and efficient numerical technique to approach 3-D wave propagation problems including realistic attenuation and complex geometry.

  19. Full Wave Analysis of RF Signal Attenuation in a Lossy Cave using a High Order Time Domain Vector Finite Element Method

    SciTech Connect

    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.

  20. Development of a 3D finite element model evaluating air-coupled ultrasonic measurements of nonlinear Rayleigh waves

    NASA Astrophysics Data System (ADS)

    Uhrig, Matthias P.; Kim, Jin-Yeon; Jacobs, Laurence J.

    2016-02-01

    This research presents a 3D numerical finite element (FE) model which, previously developed, precisely simulates non-contact, air-coupled measurements of nonlinear Rayleigh wave propagation. The commercial FE-solver ABAQUS is used to perform the simulations. First, frequency dependent pressure wave attenuation is investigated numerically to reconstruct the sound pressure distribution along the active surface of the non-contact receiver. Second, constitutive law and excitation source properties are optimized to match nonlinear ultrasonic experimental data. Finally, the FE-model data are fit with analytical solutions showing a good agreement and thus, indicating the significance of the study performed.

  1. Mechanical Loss Measurements of Coated Substrates for Gravitational Wave Interferometry

    NASA Astrophysics Data System (ADS)

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

    2013-03-01

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

  2. Mechanical Loss Measurements of Coated Substrates for Gravitational Wave Interferometry

    NASA Astrophysics Data System (ADS)

    Baringer, Thaddeus; Harry, Gregory; Newport, Jonathan; Fair, Hannah; France, Alexandra; LIGO Collaboration

    2014-03-01

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

  3. Stiffness measurement using terahertz and acoustic waves for biological samples.

    PubMed

    Yoon, Jong-Hyun; Yang, Young-Joong; Park, Jinho; Son, Heyjin; Park, Hochong; Park, Gun-Sik; Ahn, Chang-Beom

    2015-12-14

    A method is proposed to measure sample stiffness using terahertz wave and acoustic stimulation. The stiffness-dependent vibration is measured using terahertz wave (T-ray) during an acoustic stimulation. To quantify the vibration, time of the peak amplitude of the reflected T-ray is measured. In our experiment, the T-ray is asynchronously applied during the period of the acoustic stimulation, and multiple measurements are taken to use the standard deviation and the maximum difference in the peak times to estimate the amplitude of the vibration. Some preliminary results are shown using biological samples. PMID:26699056

  4. Different methods of mass attenuation coefficient evaluation: Influences in the measurement of some soil physical properties.

    PubMed

    Pires, L F; Medhat, M E

    2016-05-01

    The mass attenuation coefficients of Brazilian soils (μs) and water (μw) were measured and calculated at 59.5keV ((241)Am) photon energy. The μs and μw experimental values were compared using XCOM and Monte Carlo computer codes (FLUKA, GEANT4 and MCNP). The influence of different methods of µ evaluation on the measurement of soil bulk density (ρs) and soil water content (θ) distributions and soil water retention (SWRC) was investigated. ρs and θ distributions were analyzed by using computed tomography (CT). Distinct ρs distributions were obtained even for similar µs values measured among methods. θ distributions were also greatly influenced by the different methods of μw evaluation. Regarding the SWRC, the results exhibited great differences in the region of structural pores, which directly affected the pore size distribution. PMID:26926378

  5. Multifrequency measurements of core-diffracted P waves (Pdiff) for global waveform tomography

    NASA Astrophysics Data System (ADS)

    Hosseini, Kasra; Sigloch, Karin

    2015-10-01

    The lower third of the mantle is sampled extensively by body waves that diffract around the earth's core (Pdiff and Sdiff phases), which could deliver highly resolved tomographic images of this poorly understood region. But core-diffracted waves-especially Pdiff waves-are not often used in tomography because they are difficult to model adequately. Our aim is to make core-diffracted body waves usable for global waveform tomography, across their entire frequency range. Here we present the data processing part of this effort. A method is demonstrated that routinely calculates finite-frequency traveltimes of Pdiff waves by cross-correlating large quantities of waveform data with synthetic seismograms, in frequency passbands ranging from 30.0 to 2.7 s dominant period. Green's functions for 1857 earthquakes, typically comprising thousands of seismograms, are calculated by theoretically exact wave propagation through a spherically symmetric earth model, up to 1 Hz dominant period. Out of 418 226 candidates, 165 651 (39.6 per cent) source-receiver pairs yielded at least one successful passband measurement of a Pdiff traveltime anomaly, for a total of 479 559 traveltimes in the eight passbands considered. Measurements of teleseismic P waves yielded 448 178 usable source-receiver paths from 613 057 candidates (73.1 per cent success rate), for a total of 2 306 755 usable teleseismic dT in eight passbands. Observed and predicted characteristics of Pdiff traveltimes are discussed and compared to teleseismic P for this very large data set. Pdiff measurements are noise-limited due to severe wave attenuation with epicentral distance and frequency. Measurement success drops from 40-60 per cent at 80° distance, to 5-10 per cent at 140°. Frequency has a 2-3 times stronger influence on measurement success for Pdiff than for P. The fewest usable dT measurements are obtained in the microseismic noise band, whereas the fewest usable teleseismic P measurements occur at the highest frequencies. dT anomalies are larger for Pdiff than for P, and frequency dependence of dT due to 3-D heterogeneity (rather than just diffraction) is larger for Pdiff as well. Projecting the Pdiff traveltime anomalies on their core-grazing segments, we retrieve well-known, large-scale structural heterogeneities of the lowermost mantle, such as the two Large Low Shear Velocity Provinces, an Ultra-Low Velocity Zone west of Hawaii, and subducted slab accumulations under East Asia and Central America.

  6. 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 (α) by chemical buffer effects of the seawater. However, conventionally, α 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 (α) at some frequency. As a result, we found that α 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 α 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.

  7. Comparison of Instantaneous Frequency Scaling from Rain Attenuation and Optical Disdrometer Measurements at K/Q bands

    NASA Technical Reports Server (NTRS)

    Nessel, James; Zemba, Michael; Luini, Lorenzo; Riva, Carlo

    2015-01-01

    Rain attenuation is strongly dependent on the rain rate, but also on the rain drop size distribution (DSD). Typically, models utilize an average drop size distribution, such as those developed by Laws and Parsons, or Marshall and Palmer. However, individual rain events may possess drop size distributions which could be significantly different from the average and will impact, for example, fade mitigation techniques which utilize channel performance estimates from a signal at a different frequency. Therefore, a good understanding of the characteristics and variability of the raindrop size distribution is extremely important in predicting rain attenuation and instantaneous frequency scaling parameters on an event-toevent basis. Since June 2014, NASA Glenn Research Center (GRC) and the Politecnico di Milano (POLIMI) have measured the attenuation due to rain in Milan, Italy, on the 20/40 GHz beacon signal broadcast from the Alphasat TDP#5 Aldo Paraboni Q/V-band Payload. Concomitant with these measurements are the measurements of drop size distribution and rain rate utilizing a Thies Clima laser precipitation monitor (disdrometer). In this paper, we discuss the comparison of the predicted rain attenuation at 20 and 40 GHz derived from the drop size distribution data with the measured rain attenuation. The results are compared on statistical and real-time bases. We will investigate the performance of the rain attenuation model, instantaneous frequency scaling, and the distribution of the scaling factor. Further, seasonal rain characteristics will be analysed.

  8. Interpretation of measurements of the polarization percentage for plasma waves

    NASA Astrophysics Data System (ADS)

    Pincon, J. L.; Marouan, Y.; Lefeuvre, F.

    1992-02-01

    The conditions of the application of the pure-state concept to the analysis of a plasma wave in a magnetoplasma are studied. Estimations of the Samson percentage of polarization are discussed. The best results are obtained with the minimum prediction error estimator. Simple physical interpretation is possible when the estimator is derived from the three magnetic-wave-field components only. There is an exception for electrostatic waves. Propagation modes and the region of the Clemmow-Mullaly-Allis diagram exist for which the percentage of polarization may be considered as a measure of the dispersion in k vectors.

  9. A Novel Distance Measurement System with a Planar Light Wave Circuit

    NASA Astrophysics Data System (ADS)

    Harada, Masaki; Doi, Masaaki; Iwasaki, Yutaka

    2002-07-01

    We have developed a novel distance measurement (DM) system with a silica-based planar light wave circuit (PLC) and fiber optics for construction and civil engineering. The PLC contains thermooptic switches (TOSWs) that utilize the index change caused by the thermooptic effect. These switches are used for changing the light path and attenuating the light signal. The performance of the DM system was evaluated by the outdoor DM and linearity measurement. The outdoor DM at the distance of 104 m was achieved with the commercial retroreflective sheet and the measurement at the distance of 1 km with a corner-cube prism is possible. The resolution of the system is about 1.7 mm (1σ). These results show our DM system fulfills the same required specifications as the conventional system that utilizes bulk optics. Moreover, the system has many advantages such as robustness, compactness, being noise-free, ease of alignment and stability.

  10. A Nonlinear Theory for Predicting the Effects of Unsteady Laminar, Turbulent, or Transitional Boundary Layers on the Attenuation of Shock Waves in a Shock Tube with Experimental Comparison

    NASA Technical Reports Server (NTRS)

    Trimpi, Robert L.; Cohen, Nathaniel B.

    1961-01-01

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

  11. DE-1 measurements of AKR wave directions. [auroral kilometric radiation

    NASA Technical Reports Server (NTRS)

    Calvert, W.

    1985-01-01

    In addition to its wave rotation sense, the direction of auroral kilometric radiation (AKR) can also be measured with the plasma wave instrument on Dynamics Explorer 1, from the relative phase of the signals received by its orthogonal electric dipole antennas. By this method, which differs in principle from the previous spin-null method for measuring wave directions, it has been found possible to pinpoint the AKR source by triangulation, using measurements from different points along the DE-1 orbit. The resulting apparent source, in one instance, seemed to occupy a well-defined auroral-zone invariant magnetic latitude and showed the expected increase of altitude with decreasing frequency. An analysis of the method also confirmed the validity of the previous rotation sense measurements.

  12. S-wave attenuation in northeastern Sonora, Mexico, near the faults that ruptured during the earthquake of 3 May 1887 Mw 7.5.

    PubMed

    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 < 4 Hz) compared to those reported in previous studies in the region using more distant recordings. The 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

  13. Millimeter Wave Propagation Measurements At The Ballistic Research Laboratory

    NASA Astrophysics Data System (ADS)

    Wallace, H. B.

    1983-02-01

    Measurements have been made with radars from 35 to 217 GHz of near-earth propagation through both natural and cultural obscurants. Results of measurements made in rain, fog, snow, high humidity, dust, and some smokes are presented for the major millimeter wave windows. Some modeling performed by other agencies is presented for comparison.

  14. Millimeter wave propagation measurements at the Ballistic Research Laboratory

    NASA Astrophysics Data System (ADS)

    Wallace, H. B.

    1983-02-01

    Measurements have been made with radars from 35 to 217 GHz of near-earth propagation through both natural and cultural obscurants. Results of measurements made in rain, fog, snow, high humidity, dust, and some smokes are presented for the major millimeter wave windows. Some modeling performed by other agencies is presented for comparison

  15. Slow-Wave Acoustic Isolation For Measurement Of Flow

    NASA Technical Reports Server (NTRS)

    Lynnworth, Lawrence C.; Aurilio, Marco

    1993-01-01

    Propagation of interfering signals delayed. Experiments demonstrated utility of slow-wave isolation between transmitting and receiving transducers in acoustic measurements of sound speed and/or flow velocity in ducts. Specifically, finding pertains to acoustic measurements of speeds of flow of low-molecular-weight gases at pressures low enough to be contained in thin-walled metal conduits.

  16. Measurements of mass attenuation coefficient, effective atomic number and electron density of some amino acids

    NASA Astrophysics Data System (ADS)

    Kore, Prashant S.; Pawar, Pravina P.

    2014-05-01

    The mass attenuation coefficients of some amino acids, such as DL-aspartic acid-LR(C4H7NO4), L-glutamine (C4H10N2O3), creatine monohydrate LR(C4H9N3O2H2O), creatinine hydrochloride (C4H7N3O·HCl) L-asparagine monohydrate(C4H9N3O2H2O), L-methionine LR(C5H11NO2S), were measured at 122, 356, 511, 662, 1170, 1275 and 1330 keV photon energies using a well-collimated narrow beam good geometry set-up. The gamma-rays were detected using NaI (Tl) scintillation detection system with a resolution of 0.101785 at 662 keV. The attenuation coefficient data were then used to obtain the effective atomic numbers (Zeff), and effective electron densities (Neff) of amino acids. It was observed that the effective atomic number (Zeff) and effective electron densities (Neff) initially decrease and tend to be almost constant as a function of gamma-ray energy. Zeff and Neff experimental values showed good agreement with the theoretical values with less than 1% error for amino acids.

  17. Comparison of Predicted and Measured Attenuation of Turbine Noise from a Static Engine Test

    NASA Technical Reports Server (NTRS)

    Chien, Eugene W.; Ruiz, Marta; Yu, Jia; Morin, Bruce L.; Cicon, Dennis; Schwieger, Paul S.; Nark, Douglas M.

    2007-01-01

    Aircraft noise has become an increasing concern for commercial airlines. Worldwide demand for quieter aircraft is increasing, making the prediction of engine noise suppression one of the most important fields of research. The Low-Pressure Turbine (LPT) can be an important noise source during the approach condition for commercial aircraft. The National Aeronautics and Space Administration (NASA), Pratt & Whitney (P&W), and Goodrich Aerostructures (Goodrich) conducted a joint program to validate a method for predicting turbine noise attenuation. The method includes noise-source estimation, acoustic treatment impedance prediction, and in-duct noise propagation analysis. Two noise propagation prediction codes, Eversman Finite Element Method (FEM) code [1] and the CDUCT-LaRC [2] code, were used in this study to compare the predicted and the measured turbine noise attenuation from a static engine test. In this paper, the test setup, test configurations and test results are detailed in Section II. A description of the input parameters, including estimated noise modal content (in terms of acoustic potential), and acoustic treatment impedance values are provided in Section III. The prediction-to-test correlation study results are illustrated and discussed in Section IV and V for the FEM and the CDUCT-LaRC codes, respectively, and a summary of the results is presented in Section VI.

  18. Electric field vector measurements in a surface ionization wave discharge

    NASA Astrophysics Data System (ADS)

    Goldberg, Benjamin M.; Böhm, Patrick S.; Czarnetzki, Uwe; Adamovich, Igor V.; Lempert, Walter R.

    2015-10-01

    This work presents the results of time-resolved electric field vector measurements in a short pulse duration (60 ns full width at half maximum), surface ionization wave discharge in hydrogen using a picosecond four-wave mixing technique. Electric field vector components are measured separately, using pump and Stokes beams linearly polarized in the horizontal and vertical planes, and a polarizer placed in front of the infrared detector. The time-resolved electric field vector is measured at three different locations across the discharge gap, and for three different heights above the alumina ceramic dielectric surface, ~100, 600, and 1100 μm (total of nine different locations). The results show that after breakdown, the discharge develops as an ionization wave propagating along the dielectric surface at an average speed of 1 mm ns-1. The surface ionization wave forms near the high voltage electrode, close to the dielectric surface (~100 μm). The wave front is characterized by significant overshoot of both vertical and horizontal electric field vector components. Behind the wave front, the vertical field component is rapidly reduced. As the wave propagates along the dielectric surface, it also extends further away from the dielectric surface, up to ~1 mm near the grounded electrode. The horizontal field component behind the wave front remains quite significant, to sustain the electron current toward the high voltage electrode. After the wave reaches the grounded electrode, the horizontal field component experiences a secondary rise in the quasi-dc discharge, where it sustains the current along the near-surface plasma sheet. The measurement results indicate presence of a cathode layer formed near the grounded electrode with significant cathode voltage fall, ≈3 kV, due to high current density in the discharge. The peak reduced electric field in the surface ionization wave is 85-95 Td, consistent with dc breakdown field estimated from the Paschen curve for hydrogen. The present set of data on electric field distribution in a surface ionization wave discharge provides an experimental reference for validation of kinetic models and assessing their predictive capability.

  19. Spatio-temporal variations in the structure of the attenuation field of the S-wave in the region of Nevada nuclear test site

    NASA Astrophysics Data System (ADS)

    Kopnichev, Yu. F.; Sokolova, I. N.; Sokolov, K. N.

    2013-11-01

    The characteristics of the attenuation field of short-period shear waves in the region of Nevada nuclear test site (NNTS) are studied. The seismograms of underground nuclear explosions (UNEs) and earthquakes recorded by three seismic stations in 1975-2012 at the epicentral distances of up to 1000 km are processed by the methods based on the analysis of the amplitude ratios of Sn to Pn and Lg to Pg waves, as well as the S-coda envelopes for close events. It is shown that the structure of the attenuation field in the Earth's crust and upper mantle in the NNTS region experienced significant temporal variations during the interval of nuclear operations. The strongest variations were associated with UNEs conducted in the Pahute Mesa area, which held about two-thirds of the most intense explosions. Our data indicate that temporal variations in the structure of the attenuation field are related to the migration of deep fluids. A comparison of the general characteristics of the attenuation field in the regions of the three large nuclear test sites is presented.

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

    PubMed Central

    Härdig, Bjarne Madsen; Carlson, Jonas; Roijer, Anders

    2008-01-01

    Background Ultrasound (US) has been used to enhance thrombolytic therapy in the treatment of stroke. Considerable attenuation of US intensity is however noted if US is applied over the temporal bone. The aim of this study was therefore to explore possible changes in the effect of thrombolytic drugs during low-intensity, high-frequency continuous-wave ultrasound (CW-US) exposure. Methods Clots were made from fresh venous blood drawn from healthy volunteers. Each clot was made from 1.4 ml blood and left to coagulate for 1 hour in a plastic test-tube. The thrombolytic drugs used were, 3600 IU streptokinase (SK) or 0.25 U reteplase (r-PA), which were mixed in 160 ml 0.9% NaCl solution. Continuous-wave US exposure was applied at a frequency of 1 MHz and intensities ranging from 0.0125 to 1.2 W/cm2. For each thrombolytic drug (n = 2, SK and r-PA) and each intensity (n = 9) interventional clots (US-exposed, n = 6) were submerged in thrombolytic solution and exposed to CW-US while control clots (also submerged in thrombolytic solution, n = 6) were left unexposed to US. To evaluate the effect on clot lysis, the haemoglobin (Hb) released from each clot was measured every 20 min for 1 hour (20, 40 and 60 min). The Hb content (mg) released was estimated by spectrophotometry at 540 nm. The difference in effect on clot lysis was expressed as the difference in the amount of Hb released between pairs of US-exposed clots and control clots. Statistical analysis was performed using Wilcoxon's signed rank test. Results Continuous-wave ultrasound significantly decreased the effects of SK at intensities of 0.9 and 1.2 W/cm2 at all times (P < 0.05). Continuous-wave ultrasound significantly increased the effects of r-PA on clot lysis following 20 min exposure at 0.9 W/cm2 and at 1.2 W/cm2, following 40 min exposure at 0.3, 0.6, 0.9 and at 1.2 W/cm2, and following 60 min of exposure at 0.05 0.3, 0.6, 0.9 and at 1.2 W/cm2 (all P < 0.05). Conclusion Increasing intensities of CW-US exposure resulted in increased clot lysis of r-PA-treated blood clots, but decreased clot lysis of SK-treated clots. PMID:18727834

  1. Measurements of radiated elastic wave energy from dynamic tensile cracks

    NASA Technical Reports Server (NTRS)

    Boler, Frances M.

    1990-01-01

    The role of fracture-velocity, microstructure, and fracture-energy barriers in elastic wave radiation during a dynamic fracture was investigated in experiments in which dynamic tensile cracks of two fracture cofigurations of double cantilever beam geometry were propagating in glass samples. The first, referred to as primary fracture, consisted of fractures of intact glass specimens; the second configuration, referred to as secondary fracture, consisted of a refracture of primary fracture specimens which were rebonded with an intermittent pattern of adhesive to produce variations in fracture surface energy along the crack path. For primary fracture cases, measurable elastic waves were generated in 31 percent of the 16 fracture events observed; the condition for radiation of measurable waves appears to be a local abrupt change in the fracture path direction, such as occurs when the fracture intersects a surface flaw. For secondary fractures, 100 percent of events showed measurable elastic waves; in these fractures, the ratio of radiated elastic wave energy in the measured component to fracture surface energy was 10 times greater than for primary fracture.

  2. Methods for the treatment of acoustic and absorptive/dispersive wave field measurements

    NASA Astrophysics Data System (ADS)

    Innanen, Kristopher Albert Holm

    Many recent methods of seismic wave field processing and inversion concern themselves with the fine detail of the amplitude and phase characteristics of measured events. Processes of absorption and dispersion have a strong impact on both; the impact is particularly deleterious to the effective resolution of images created from the data. There is a need to understand the dissipation of seismic wave energy as it affects such methods. I identify: algorithms based on the inverse scattering series, algorithms based on multiresolution analysis, and algorithms based on the estimation of the order of the singularities of seismic data, as requiring this kind of study. As it turns out, these approaches may be cast such that they deal directly with issues of attenuation, to the point where they can be seen as tools for viscoacoustic forward modelling, Q estimation; viscoacoustic inversion, and/or Q compensation. In this thesis I demonstrate these ideas in turn. The forward scattering series is formulated such that a viscoacoustic wave field is represented as an expansion about an acoustic reference; analysis of the convergence properties and scattering diagrams are carried out, and it is shown that (i) the attenuated wave field may be generated by the nonlinear interplay of acoustic reference fields, and (ii) the cumulative effect of certain scattering types is responsible for macroscopic wave field properties: also, the basic form of the absorptive/dispersive inversion problem is predicted. Following this, the impact of Q on measurements of the local regularity of a seismic trace, via Lipschitz exponents, is discussed, with the aim of using these exponents as a means to estimate local Q values. The problem of inverse scattering based imaging and inversion is treated next: I present a simple, computable form for the simultaneous imaging and wavespeed inversion of 1D acoustic wave field data. This method is applied to 1D, normal incidence synthetic data: its sensitivity with respect to contrast, complexity, noise and bandlimited data are concurrently surveyed. I next develop and test a Born inversion for simultaneous contrasts in wavespeed and Q, distinguishing between the results of a pure Born inversion and a further, bootstrap, approach that improves the quality of the linear results. The nonlinear inversion subseries of the inverse scattering series is then cast for simplified viscoacoustic media, to understand the behaviour and implied capabilities of the series/subseries to handle Q. (Abstract shortened by UMI.)

  3. Wave-induced pore pressure measurements near a coastal structure

    NASA Astrophysics Data System (ADS)

    Michallet, H.; Mory, M.; Piedra-Cueva, I.

    2009-06-01

    Wave-induced pore pressures were measured at various depths below the sandy bed in front of a coastal structure. The results of a weeklong field experiment carried out in September 2003 on the beach of Capbreton, in southwest France, are presented. The coastal structure was located in the intertidal zone of the beach. The transmission of pressure variations inside the soil, as compared to the pressure variations produced by the waves in the water layer, are analyzed in terms of both amplitude decay and phase shifts and compared to theoretical models. The gas content inside the soil was also measured. The results confirm that the gas content is a key parameter affecting the transmission of pressure inside the soil. It is shown that a significant upward pressure gradient is generated during a wave period, which can liquefy a 30 cm deep superficial layer of the soil. This is interpreted in terms of momentary liquefaction events. The manner in which the phenomena change during the different tidal periods investigated is described. The dependence of the results on wave height and bed level is discussed. Whereas the soil properties were not modified over a tidal period when the wave activity was sufficiently low, a significant change in the transmission of pressure variations inside the soil was observed when the structure was subjected to larger waves. This is interpreted in terms of a change in the gas content in the superficial layer.

  4. Feasibility of hydromagnetic wave measurements on space shuttle

    NASA Technical Reports Server (NTRS)

    Mcpherron, R. L.

    1974-01-01

    The feasibility of using a hydromagnetic wave sensor on the space shuttles was investigated. It was found that although existing sensors are inadequate in terms of resolution, dynamic range, and frequency range, they can be modified to make the necessary measurements. It is shown that since the sensor cannot be mounted on the shuttle itself because of high levels of magnetic noise, a free subsatellite that can be positioned and stabilized may be used for locating the hydromagnetic wave sensor. Other results show that studies of long period waves would require either an array of sensors in shuttle orbit or a long-term mapping of the crustal anomalies, and that effective wave studies would require at least two variably spaced sensors in shuttle orbit and one ground station.

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

    NASA Astrophysics Data System (ADS)

    Muggleton, J. M.; Yan, J.

    2013-03-01

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

  6. Properties of material in the submillimeter wave region (instrumentation and measurement of index of refraction)

    NASA Technical Reports Server (NTRS)

    Lally, J.; Meister, R.

    1983-01-01

    The Properties of Materials in the Submillimeter Wave Region study was initiated to instrument a system and to make measurements of the complex index of refraction in the wavelength region between 0.1 to 1.0 millimeters. While refractive index data is available for a number of solids and liquids there still exists a need for an additional systematic study of dielectric properties to add to the existing data, to consider the accuracy of the existing data, and to extend measurements in this wavelength region for other selected mateials. The materials chosen for consideration would be those with useful thermal, mechanical, and electrical characteristics. The data is necessary for development of optical components which, for example, include beamsplitters, attenuators, lenses, grids, all useful for development of instrumentation in this relatively unexploited portion of the spectrum.

  7. Ultrasonic metal sheet thickness measurement without prior wave speed calibration

    NASA Astrophysics Data System (ADS)

    Dixon, S.; Petcher, P. A.; Fan, Y.; Maisey, D.; Nickolds, P.

    2013-11-01

    Conventional ultrasonic mensuration of sample thickness from one side only requires the bulk wave reverberation time and a calibration speed. This speed changes with temperature, stress, and microstructure, limiting thickness measurement accuracy. Often, only one side of a sample is accessible, making in situ calibration impossible. Non-contact ultrasound can generate multiple shear horizontal guided wave modes on one side of a metal plate. Measuring propagation times of each mode at different transducer separations, allows sheet thickness to be calculated to better than 1% accuracy for sheets of at least 1.5 mm thickness, without any calibration.

  8. Evaluation of multilayered pavement structures from measurements of surface waves

    USGS Publications Warehouse

    Ryden, N.; Lowe, M.J.S.; Cawley, P.; Park, C.B.

    2006-01-01

    A method is presented for evaluating the thickness and stiffness of multilayered pavement structures from guided waves measured at the surface. Data is collected with a light hammer as the source and an accelerometer as receiver, generating a synthetic receiver array. The top layer properties are evaluated with a Lamb wave analysis. Multiple layers are evaluated by matching a theoretical phase velocity spectrum to the measured spectrum. So far the method has been applied to the testing of pavements, but it may also be applicable in other fields such as ultrasonic testing of coated materials. ?? 2006 American Institute of Physics.

  9. Broadband ultrasound attenuation imaging: influence of location of region of measurement.

    PubMed

    Damilakis, J; Papadakis, A; Perisinakis, K; Gourtsoyiannis, N

    2001-01-01

    The aim of the study was to investigate the effect of three different regions of interest (ROIs) varying in size and shape on broadband ultrasound attenuation (BUA) measurements of the calcaneus. Two hundred and sixty-five postmenopausal Caucasian women participated in this study. In 43 women osteoporotic fractures were documented on spinal radiographs. Bone mineral density (BMD) measurements of the lumbar spine and the femur were made using dual-energy X-ray absorptiometry. BUA measurements were obtained at a circular ROI automatically determined by the imaging system (ROIc), at a manually traced irregular ROI encompassing the posterior part of the calcaneus (ROIi), and at an anatomical square ROI located in the posterior part of the calcaneus (ROIs). Reproducibility was better in ROIc than in ROIi and ROIs. High correlations were found between BUA measurements with ROIc and ROIs (r = 0.981, P < 0.0001) as well as between those with ROIc and ROIi (r = 0.965, P < 0.0001). There were no significant differences between the correlations of BUA with axial BMD at ROIc compared with ROIi and ROIs. No significant difference was found between the areas under the ROC curve at ROIi, ROIc, and ROIs for women with fractures. The results show that superior reproducibility makes ROIc the most appropriate region of BUA measurement in a comparison with ROIi and ROIs. PMID:11471598

  10. Measurements of wave height statistics and radar, cross-section in a wind wave tank

    NASA Technical Reports Server (NTRS)

    Johnson, J. W.; Cross, A. E.

    1976-01-01

    There is currently wide interest among oceanographers and meteorologists in remote sensing of ocean surface characteristics. A wind wave tank developed at Langley Research Center is used to evaluate various remote sensing techniques based on electromagnetic scattering phenomena, and in the development and evaluation of theoretical scattering models. The wave tank is described, the statistics of the rough water surface are documented, and microwave radar cross-section measurement results are presented. The water surface statistics are similar in key respects to the open ocean, and the microwave scattering measurements show, qualitatively, theoretically predicted large and small scale scattering effects.

  11. A short-pulse Ka-band instrumentation radar for foliage attenuation measurements

    NASA Astrophysics Data System (ADS)

    Puranen, Mikko; Eskelinen, Pekka

    2008-10-01

    A portable Ka-band instrumentation radar for foliage attenuation measurements has been designed. It uses direct dielectric resonator oscillator multiplier pulse modulation giving a half power pulse width of 17 ns. The dual conversion scalar receiver utilizes either a digital storage oscilloscope in envelope detection format or a special gated comparator arrangement providing 1 m resolution and associated led seven segment display for data analysis. The calibrated dynamic range is better than 37 dB with an equivalent noise floor of 0.005 dBsm at 25 m test range distance. First experiments indicate an effective beamwidth close to 1. The total weight is below 5 kg and the unit can be mounted on a conventional photographic tripod. Power is supplied from a 12 V/6 A h sealed lead acid battery giving an operating time in excess of 10 h.

  12. In situ measurements of impact-induced pressure waves in sandstone targets

    NASA Astrophysics Data System (ADS)

    Hoerth, Tobias; Schäfer, Frank; Nau, Siegfried; Kuder, Jürgen; Poelchau, Michael H.; Thoma, Klaus; Kenkmann, Thomas

    2014-10-01

    In the present study we introduce an innovative method for the measurement of impact-induced pressure waves within geological materials. Impact experiments on dry and water-saturated sandstone targets were conducted at a velocity of 4600 m/s using 12 mm steel projectiles to investigate amplitudes, decay behavior, and speed of the waves propagating through the target material. For this purpose a special kind of piezoresistive sensor capable of recording transient stress pulses within solid brittle materials was developed and calibrated using a Split-Hopkinson pressure bar. Experimental impact parameters (projectile size and speed) were kept constant and yielded reproducible signal curves in terms of rise time and peak amplitudes. Pressure amplitudes decreased by 3 orders of magnitude within the first 250 mm (i.e., 42 projectile radii). The attenuation for water-saturated sandstone is higher compared to dry sandstone which is attributed to dissipation effects caused by relative motion between bulk material and interstitial water. The proportion of the impact energy radiated as seismic energy (seismic efficiency) is in the order of 10-3. The present study shows the feasibility of real-time measurements of waves caused by hypervelocity impacts on geological materials. Experiments of this kind lead to a better understanding of the processes in the crater subsurface during a hypervelocity impact.

  13. Measurements of parallel electron velocity distributions using whistler wave absorption

    SciTech Connect

    Thuecks, D. J.; Skiff, F.; Kletzing, C. A.

    2012-08-15

    We describe a diagnostic to measure the parallel electron velocity distribution in a magnetized plasma that is overdense ({omega}{sub pe} > {omega}{sub ce}). This technique utilizes resonant absorption of whistler waves by electrons with velocities parallel to a background magnetic field. The whistler waves were launched and received by a pair of dipole antennas immersed in a cylindrical discharge plasma at two positions along an axial background magnetic field. The whistler wave frequency was swept from somewhat below and up to the electron cyclotron frequency {omega}{sub ce}. As the frequency was swept, the wave was resonantly absorbed by the part of the electron phase space density which was Doppler shifted into resonance according to the relation {omega}-k{sub ||v||} = {omega}{sub ce}. The measured absorption is directly related to the reduced parallel electron distribution function integrated along the wave trajectory. The background theory and initial results from this diagnostic are presented here. Though this diagnostic is best suited to detect tail populations of the parallel electron distribution function, these first results show that this diagnostic is also rather successful in measuring the bulk plasma density and temperature both during the plasma discharge and into the afterglow.

  14. Measurements of parallel electron velocity distributions using whistler wave absorption.

    PubMed

    Thuecks, D J; Skiff, F; Kletzing, C A

    2012-08-01

    We describe a diagnostic to measure the parallel electron velocity distribution in a magnetized plasma that is overdense (ω(pe) > ω(ce)). This technique utilizes resonant absorption of whistler waves by electrons with velocities parallel to a background magnetic field. The whistler waves were launched and received by a pair of dipole antennas immersed in a cylindrical discharge plasma at two positions along an axial background magnetic field. The whistler wave frequency was swept from somewhat below and up to the electron cyclotron frequency ω(ce). As the frequency was swept, the wave was resonantly absorbed by the part of the electron phase space density which was Doppler shifted into resonance according to the relation ω - k([parallel])v([parallel]) = ω(ce). The measured absorption is directly related to the reduced parallel electron distribution function integrated along the wave trajectory. The background theory and initial results from this diagnostic are presented here. Though this diagnostic is best suited to detect tail populations of the parallel electron distribution function, these first results show that this diagnostic is also rather successful in measuring the bulk plasma density and temperature both during the plasma discharge and into the afterglow. PMID:22938290

  15. Measurement of Attenuation with Airborne and Ground-Based Radar in Convective Storms Over Land and Its Microphysical Implications

    NASA Technical Reports Server (NTRS)

    Tian, Lin; Heymsfield, G. M.; Srivastava, R. C.; Starr, D. OC. (Technical Monitor)

    2001-01-01

    Observations by the airborne X-band Doppler radar (EDOP) and the NCAR S-band polarimetric (S-POL) radar from two field experiments are used to evaluate the Surface ref'ercnce technique (SRT) for measuring the path integrated attenuation (PIA) and to study attenuation in deep convective storms. The EDOP, flying at an altitude of 20 km, uses a nadir beam and a forward pointing beam. It is found that over land, the surface scattering cross-section is highly variable at nadir incidence but relatively stable at forward incidence. It is concluded that measurement by the forward beam provides a viable technique for measuring PIA using the SRT. Vertical profiles of peak attenuation coefficient are derived in vxo deep convective storms by the dual-wavelength method. Using the measured Doppler velocity, the reflectivities at. the two wavelengths, the differential reflectivity and the estimated attenuation coefficients, it is shown that: supercooled drops and dry ice particles probably co-existed above the melting level in regions of updraft, that water-coated partially melted ice particles probably contributed to high attenuation below the melting level, and that the data are not readil explained in terms of a gamma function raindrop size distribution.

  16. Measurement of Attenuation with Airborne and Ground-Based Radar in Convective Storms Over Land Its Microphysical Implications

    NASA Technical Reports Server (NTRS)

    Tian, Lin; Heymsfield, G. M.; Srivastava, R. C.; O'C.Starr, D. (Technical Monitor)

    2001-01-01

    Observations by the airborne X-band Doppler radar (EDOP) and the NCAR S-band polarimetric (S-Pol) radar from two field experiments are used to evaluate the surface reference technique (SRT) for measuring the path integrated attenuation (PIA) and to study attenuation in deep convective storms. The EDOP, flying at an altitude of 20 km, uses a nadir beam and a forward pointing beam. It is found that over land, the surface scattering cross-section is highly variable at nadir incidence but relatively stable at forward incidence. It is concluded that measurement by the forward beam provides a viable technique for measuring PIA using the SRT. Vertical profiles of peak attenuation coefficient are derived in two deep convective storms by the dual-wavelength method. Using the measured Doppler velocity, the reflectivities at the two wavelengths, the differential reflectivity and the estimated attenuation coefficients, it is shown that: supercooled drops and (dry) ice particles probably co-existed above the melting level in regions of updraft, that water-coated partially melted ice particles probably contributed to high attenuation below the melting level.

  17. Field measurements and modeling of attenuation from near-surface bubbles for frequencies 1-20 kHz.

    PubMed

    Dahl, Peter H; Choi, Jee Woong; Williams, Neil J; Graber, Hans C

    2008-09-01

    Measurements of excess attenuation from near-surface bubbles from the Shallow Water '06 experiment are reported. These are transmission measurements made over the frequency range 1-20 kHz, and they demonstrate a frequency, grazing angle, and wind speed dependence in attenuation. Data modeling points to bubble void fractions of order 10(-6) in effect for wind speeds 10-13 m/s. Simultaneous measures of wind speed made within 1.5 and 11 km of the open water experimental location differed by 2 m/s in their respective 30 min average; this has cautionary implications for empirical models for bubble attenuation that are a strong function of wind speed. PMID:19045560

  18. Excimer laser drilling of bone: shock wave and profile measurements

    NASA Astrophysics Data System (ADS)

    Sviridov, Alexander P.; Dmitriev, A. K.; Karoutis, Athanase D.; Christodoulou, P. N.; Helidonis, Emmanuel S.

    1995-01-01

    The shock wave generation in stapes models during laser ear surgery is experimentally investigated. The intensity absolute measurements of shock waves generated by excimer laser in the treated bone are performed. It is shown that the roughness of the crater bottom profile depends on the laser beam fluence. It is revealed that in the pulse repetition regime of bone drilling there exists an optimal laser beam fluence, which provides as high a rate of drilling as the smooth bottom of the crater. For ArF and KrF excimer lasers the optimal fluence is equal to about 0.4 - 0.5 J/cm2 at the repetition rate 5 Hz. The amplitude of shock wave induced at these parameters of laser beam in the back side of the bone sample of 1.1 mm thickness was measured to be about 25 bar and the corresponding pressure gradient 0.35 bar/micrometers .

  19. Measurement of ocean wave heights using the Geos 3 altimeter

    NASA Technical Reports Server (NTRS)

    Rufenach, C. L.; Alpers, W. R.

    1978-01-01

    Radar altimeter signals transmitted from the low-orbiting satellite Geos 3 were analyzed for two selected orbits over high seas associated with hurricane 'Caroline' in the Gulf of Mexico and a North Atlantic storm. The measured values of significant wave height are in reasonable agreement with surface measurements, provided that the altimeter data are properly edited. The internal consistency of estimated wave heights for the North Atlantic storm, a standard deviation of 0.6 m or less, and the good agreement with surface truth lend credence to the method. A statistical analysis of the pulse slope variation gives estimated values of significant wave height within + or - 1 m of the true values 75% of the time for spatial averaging over 70 km.

  20. Measurement of the Expansion Rate of the Universe from ?-Ray Attenuation

    NASA Astrophysics Data System (ADS)

    Domnguez, Alberto; Prada, Francisco

    2013-07-01

    A measurement of the expansion rate of the universe (that is, the Hubble constant, H 0) is derived here using the ?-ray attenuation observed in the spectra of ?-ray sources produced by the interaction of extragalactic ?-ray photons with the photons of the extragalactic background light (EBL). The Hubble constant determined with our technique, for a ?CDM cosmology, is H_{0}=71.8_{-5.6}^{+4.6}(stat)_{-13.8}^{+7.2}(syst) km s-1 Mpc-1. This value is compatible with present-day measurements using well-established methods such as local distance ladders and cosmological probes. The recent detection of the cosmic ?-ray horizon (CGRH) from multiwavelength observations of blazars, together with the advances in the knowledge of the EBL, allow us to measure the expansion rate of the universe. This estimate of the Hubble constant shows that ?-ray astronomy has reached a mature enough state to provide cosmological measurements, which may become more competitive in the future with the construction of the Cherenkov Telescope Array. We find that the maximum dependence of the CGRH on the Hubble constant is approximately between redshifts 0.04 and 0.1, thus this is a smoking gun for planning future observational efforts. Other cosmological parameters, such as the total dark matter density ? m and the dark energy equation of state w, are explored as well.

  1. Survey of Temperature Measurement Techniques For Studying Underwater Shock Waves

    NASA Technical Reports Server (NTRS)

    Danehy, Paul M.; Alderfer, David W.

    2004-01-01

    Several optical methods for measuring temperature near underwater shock waves are reviewed and compared. The relative merits of the different techniques are compared, considering accuracy, precision, ease of use, applicable temperature range, maturity, spatial resolution, and whether or not special additives are required.

  2. A revision factor to the Cutshall self-attenuation correction in (210)Pb gamma-spectrometry measurements.

    PubMed

    Jod?owski, Pawe?

    2016-03-01

    The Cutshall transmission method of determination of self-attenuation correction in (210)Pb measurements by gamma-spectrometry gives the results burdened with errors of up to 10%. The author proposes introducing into the Cutshall correction Cs,Cuts an additional revision factor CCs,Cuts to eliminate errors. The proposed formula of the revision factor describes the CCs,Cuts value depending on the experimentally obtained Cs,Cuts correction. Formula holds true in wide ranges of the measurement geometries and linear attenuation coefficients of both the standard and the sample. PMID:26702546

  3. Measurement of sound speed vs. depth in South Pole ice: pressure waves and shear waves

    SciTech Connect

    IceCube Collaboration; Klein, Spencer

    2009-06-04

    We have measured the speed of both pressure waves and shear waves as a function of depth between 80 and 500 m depth in South Pole ice with better than 1% precision. The measurements were made using the South Pole Acoustic Test Setup (SPATS), an array of transmitters and sensors deployed in the ice at the South Pole in order to measure the acoustic properties relevant to acoustic detection of astrophysical neutrinos. The transmitters and sensors use piezoceramics operating at {approx}5-25 kHz. Between 200 m and 500 m depth, the measured profile is consistent with zero variation of the sound speed with depth, resulting in zero refraction, for both pressure and shear waves. We also performed a complementary study featuring an explosive signal propagating vertically from 50 to 2250 m depth, from which we determined a value for the pressure wave speed consistent with that determined for shallower depths, higher frequencies, and horizontal propagation with the SPATS sensors. The sound speed profile presented here can be used to achieve good acoustic source position and emission time reconstruction in general, and neutrino direction and energy reconstruction in particular. The reconstructed quantities could also help separate neutrino signals from background.

  4. Hydrometeor Size Distribution Measurements by Imaging the Attenuation of a Laser Spot

    NASA Technical Reports Server (NTRS)

    Lane, John

    2013-01-01

    The optical extinction of a laser due to scattering of particles is a well-known phenomenon. In a laboratory environment, this physical principle is known as the Beer-Lambert law, and is often used to measure the concentration of scattering particles in a fluid or gas. This method has been experimentally shown to be a usable means to measure the dust density from a rocket plume interaction with the lunar surface. Using the same principles and experimental arrangement, this technique can be applied to hydrometeor size distributions, and for launch-pad operations, specifically as a passive hail detection and measurement system. Calibration of a hail monitoring system is a difficult process. In the past, it has required comparison to another means of measuring hydrometeor size and density. Using a technique recently developed for estimating the density of surface dust dispersed during a rocket landing, measuring the extinction of a laser passing through hail (or dust in the rocket case) yields an estimate of the second moment of the particle cloud, and hydrometeor size distribution in the terrestrial meteorological case. With the exception of disdrometers, instruments that measure rain and hail fall make indirect measurements of the drop-size distribution. Instruments that scatter microwaves off of hydrometeors, such as the WSR-88D (Weather Surveillance Radar 88 Doppler), vertical wind profilers, and microwave disdrometers, measure the sixth moment of the drop size distribution (DSD). By projecting a laser onto a target, changes in brightness of the laser spot against the target background during rain and hail yield a measurement of the DSD's second moment by way of the Beer-Lambert law. In order to detect the laser attenuation within the 8-bit resolution of most camera image arrays, a minimum path length is required. Depending on the intensity of the hail fall rate for moderate to heavy rainfall, a laser path length of 100 m is sufficient to measure variations in optical extinction using a digital camera. For hail fall only, the laser path may be shorter because of greater scattering due to the properties of hailstones versus raindrops. A photodetector may replace the camera in automated installations. Laser-based rain and hail measurement systems are available, but they are based on measuring the interruption of a thin laser beam, thus counting individual hydrometeors. These systems are true disdrometers since they also measure size and velocity. The method reported here is a simple method, requiring far less processing, but it is not a disdrometer.

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

    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 αatt 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 αatt < 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 1.3μm to 28μm. This measurement system achieves the high accuracy of (triangle)αatt ~ 0.01cm-1. As a result, high-resistivity single-crystal CdZnTe, single-crystal Ge, single-crystal Si, CVD-ZnSe, and CVD-ZnS show αatt < 0.01cm-1 at the wavelength range of 5.5 - 19.0μm, 2.0 - 10.5μm, 1.3 - 5.4μm, 1.7 - 13.2μm, and 1.9 - 9.2μm, 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.

  6. Measurement of semi-rigid coaxial cables at cryogenic temperature -thermal conductance and attenuation-

    NASA Astrophysics Data System (ADS)

    Kasai, Soichi; Kushino, Akihiro

    2013-03-01

    We are developing semi-rigid coaxial cables for low temperature experiments which require fast readout with low noise. Coaxial cables used at low temperature are made of low thermal conductivity materials, such as stainless-steel, cupro-nickel and polytetrafluoroethylene to suppress heat penetration through cables. As the thermal conductivity of such alloys is affected by the thermal and mechanical treatment in forming process, we have to measure thermal property of coaxial cables after forming. The low thermal conductance of 5.5 cm specimen was measured by the steady-state heat-flow method with 1m long and thin niobium-titanium wiring for thermometers and heaters. Signal attenuation of coaxial cables was measured at 3K stage of an adiabatic demagnetization refrigerator. In order to cool center electrical conductor, the cables with 1m long length were coiled, and surrounded by copper blocks then attached to 3K stage. We successfully observed superconducting transition of center conductor of superconducting niobium-titanium coaxial cables with this method.

  7. Measurements on wave propagation characteristics of spiraling electron beams

    NASA Technical Reports Server (NTRS)

    Singh, A.; Getty, W. D.

    1976-01-01

    Dispersion characteristics of cyclotron-harmonic waves propagating on a neutralized spiraling electron beam immersed in a uniform axial magnetic field are studied experimentally. The experimental setup consisted of a vacuum system, an electron-gun corkscrew assembly which produces a 110-eV beam with the desired delta-function velocity distribution, a measurement region where a microwave signal is injected onto the beam to measure wavelengths, and a velocity analyzer for measuring the axial electron velocity. Results of wavelength measurements made at beam currents of 0.15, 1.0, and 2.0 mA are compared with calculated values, and undesirable effects produced by increasing the beam current are discussed. It is concluded that a suitable electron beam for studies of cyclotron-harmonic waves can be generated by the corkscrew device.

  8. Inter-laboratory comparison of wave velocity measures.

    USGS Publications Warehouse

    Waite, William F.; Santamarina, J.C.; Rydzy, M.; Chong, S.H.; Grozic, J.L.H.; Hester, K.; Howard, J.; Kneafsey, T.J.; Lee, J.Y.; Nakagawa, S.; Priest, J.; Reese, E.; Koh, H.; Sloan, E.D.; Sultaniya, A.

    2011-01-01

     This paper presents an eight-laboratory comparison of compressional and shear wave velocities measured in F110 Ottawa sand. The study was run to quantify the physical property variations one should expect in heterogeneous, multiphase porous materials by separately quantifying the variability inherent in the measurement techniques themselves. Comparative tests were run in which the sand was dry, water-saturated, partially water-saturated, partially ice-saturated and partially hydrate-saturated. Each test illustrates a collection of effects that can be classified as inducing either specimen-based or measurement-based variability. The most significant variability is due to void ratio variations between samples. Heterogeneous pore-fill distributions and differences in measurement techniques also contribute to the observed variability, underscoring the need to provide detailed sample preparation and system calibration information when reporting wave velocities in porous media. 

  9. Multipath Effects on Phase Measurements with Continuous Terahertz Waves

    NASA Astrophysics Data System (ADS)

    Cordes, A. H.; Albarracin, M. G.; Thomas, D. H.; von der Weid, J. P.

    2015-12-01

    We evaluate the effect of multipath waves on terahertz phase measurements due to multiple reflections between the transmitter antenna and the sample. We show that the phase shift introduced by the sample will be biased by a value which depends on the sample position in the terahertz path. We show how to remove the bias and use the technique in the measurement of the index of refraction of Mylar at 194.4 GHz.

  10. Multipath Effects on Phase Measurements with Continuous Terahertz Waves

    NASA Astrophysics Data System (ADS)

    Cordes, A. H.; Albarracin, M. G.; Thomas, D. H.; von der Weid, J. P.

    2016-05-01

    We evaluate the effect of multipath waves on terahertz phase measurements due to multiple reflections between the transmitter antenna and the sample. We show that the phase shift introduced by the sample will be biased by a value which depends on the sample position in the terahertz path. We show how to remove the bias and use the technique in the measurement of the index of refraction of Mylar at 194.4 GHz.

  11. AMPTE CCE plasma wave measurements during magnetospheric compressions

    NASA Technical Reports Server (NTRS)

    Strangeway, R. J.; Zanetti, L. J.; Klumpar, D. M.; Scarf, F. L.

    1988-01-01

    This paper summarizes plasma wave observations for the AMPTE Charge Composition Explorer bow-shock crossings of November 1, 1984, and February 8, 1986, and investigates the details of the 1984 interval during which multiple periodic shock crossings were observed. For this case, it is demonstrated that the characteristic features observed in the wave measurements provide unique signatures for the magnetosheath, bow shock, and foreshock. It was found that multiple quasi-periodic bow shock crossings detected near 0900 UT, November 1, 1984, were associated with wavelike motion of the shock surface, rather than with the structure of the shock itself.

  12. A self-zeroing capacitance probe for water wave measurements

    NASA Technical Reports Server (NTRS)

    Long, Steven R.

    1992-01-01

    The wave probe developed at the Air-Sea Interaction Research Facility was designed to measure the surface elevation fluctuations of water waves. Design criteria included being linear in response, self-zeroing to the mean water level, having multiple operating ranges so that the instrument's maximum output could be matched to the maximum surface elevation over varying conditions, and be as noise-free as possible. The purpose of this publication is to provide a detailed description of the design and construction of this probe.

  13. DC attenuation meter

    SciTech Connect

    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.

  14. Correcting Four Similar Correlational Measures for Attenuation Due to Errors of Measurement in the Dependent Variable: Eta, Epsilon, Omega, and Intraclass r.

    ERIC Educational Resources Information Center

    Stanley, Julian C.; Livingston, Samuel A.

    Besides the ubiquitous Pearson product-moment r, there are a number of other measures of relationship that are attenuated by errors of measurement and for which the relationship between true measures can be estimated. Among these are the correlation ratio (eta squared), Kelley's unbiased correlation ratio (epsilon squared), Hays' omega squared,…

  15. Imaging mantle plumes with instantaneous phase measurements of diffracted waves

    NASA Astrophysics Data System (ADS)

    Rickers, Florian; Fichtner, Andreas; Trampert, Jeannot

    2012-07-01

    In a synthetic tomographic experiment, we succeeded to recover an idealized narrow mantle plume reaching deep into the lower mantle by using a misfit based on the instantaneous phase difference. A misfit based on simple cross-correlation traveltime shifts leaves the lower mantle part of the plume largely unresolved, despite the use of finite-frequency sensitivity kernels. The time-continuous and amplitude-independent instantaneous phase misfit allows us to measure the interaction between direct and diffracted waves as a function of time, which is difficult to capture by simple cross-correlation traveltime measurements. The diffracted waves arriving later than the main phase are essential to improve the tomographic result. The measurement of diffracted waves yields the necessary information to recover the plume correctly even in the lower mantle. The instantaneous phase measurement is ideal to capture this interaction, but other time- or frequency-dependent measurements may give similar results. We also investigated the effect of wavefront healing on cross-correlation traveltime shifts for a range of differently sized idealized mantle plumes. We confirm that wavefront healing severely reduces traveltime shifts when the plume conduit is considerably thinner than the width of the first Fresnel zone. For plume conduits with a diameter on the order of 100 km, even traveltime shifts measured at periods as short as T= 1 s are affected.

  16. Attenuation of copper in runoff from copper roofing materials by two stormwater control measures.

    PubMed

    LaBarre, William J; Ownby, David R; Lev, Steven M; Rader, Kevin J; Casey, Ryan E

    2016-01-01

    Concerns have been raised over diffuse and non-point sources of metals including releases from copper (Cu) roofs during storm events. A picnic shelter with a partitioned Cu roof was constructed with two types of stormwater control measures (SCMs), bioretention planter boxes and biofiltration swales, to evaluate the ability of the SCMs to attenuate Cu in stormwater runoff from the roof. Cu was measured as it entered the SCMs from the roof as influent as well as after it left the SCMs as effluent. Samples from twenty-six storms were collected with flow-weighted composite sampling. Samples from seven storms were collected with discrete sampling. Total Cu in composite samples of the influent waters ranged from 306 to 2863 μg L(-1) and had a median concentration of 1087 μg L(-1). Total Cu in the effluent from the planter boxes ranged from 28 to 141 μg L(-1), with a median of 66 μg L(-1). Total Cu in effluent from the swales ranged from 7 to 51 μg L(-1) with a median of 28 μg L(-1). Attenuation in the planter boxes ranged from 85 to 99% with a median of 94% by concentration and in the swales ranged from 93 to 99% with a median of 99%. As the roof aged, discrete storm events showed a pronounced first-flush effect of Cu in SCM influent but this was less pronounced in the planter outlets. Stormwater retention time in the media varied with antecedent conditions, stormwater intensity and volume with median values from 6.6 to 73.5 min. Based on local conditions, a previously-published Cu weathering model gave a predicted Cu runoff rate of 2.02 g m(-2) yr(-1). The measured rate based on stormwater sampling was 2.16 g m(-2) yr(-1). Overall, both SCMs were highly successful at retaining and preventing offsite transport of Cu from Cu roof runoff. PMID:26497938

  17. Planetary waves in the equatorial mesosphere and ionosphere measurements

    NASA Astrophysics Data System (ADS)

    Lima, L. M.; Araujo, L. R.; Takahashi, H.; Batista, P. P.; Batista, I. S.; Silva, M. F.

    2013-05-01

    Mesosphere-ionosphere coupling through signature of planetary waves is investigated from equatorial meteor wind, obtained at São João do Cariri-PB (7.4°S, 36.5°W), from four magnetometer data and from evening F region vertical plasma drift measurements, obtained by digital ionospheric sounder (DPS-4) at Fortaleza (3.9°S, 38.4°W). To examine the temporal variations in meteor winds, magnetometer data and in vertical plasma drifts we used the S-transform method. The spectral analysis shows distinct power spectrum with peaks with low-frequency oscillations, which are associated with planetary waves, mainly those with period near 2 days and 6-7 days. The presence of these periodic variations, in these three different types of data, suggests that ionosphere has been modulated by mesospheric oscillations with period of planetary waves.

  18. Direct measurement of nonlinear dispersion relation for water surface waves

    NASA Astrophysics Data System (ADS)

    Magnus Arnesen Taklo, Tore; Trulsen, Karsten; Elias Krogstad, Harald; Gramstad, Odin; Nieto Borge, José Carlos; Jensen, Atle

    2013-04-01

    The linear dispersion relation for water surface waves is often taken for granted for the interpretation of wave measurements. High-resolution spatiotemporal measurements suitable for direct validation of the linear dispersion relation are on the other hand rarely available. While the imaging of the ocean surface with nautical radar does provide the desired spatiotemporal coverage, the interpretation of the radar images currently depends on the linear dispersion relation as a prerequisite, (Nieto Borge et al., 2004). Krogstad & Trulsen (2010) carried out numerical simulations with the nonlinear Schrödinger equation and its generalizations demonstrating that the nonlinear evolution of wave fields may render the linear dispersion relation inadequate for proper interpretation of observations, the reason being that the necessary domain of simultaneous coverage in space and time would allow significant nonlinear evolution. They found that components above the spectral peak can have larger phase and group velocities than anticipated by linear theory, and that the spectrum does not maintain a thin dispersion surface. We have run laboratory experiments and accurate numerical simulations designed to have sufficient resolution in space and time to deduce the dispersion relation directly. For a JONSWAP spectrum we find that the linear dispersion relation can be appropriate for the interpretation of spatiotemporal measurements. For a Gaussian spectrum with narrower bandwidth we find that the dynamic nonlinear evolution in space and time causes the directly measured dispersion relation to deviate from the linear dispersion surface in good agreement with our previous numerical predictions. This work has been supported by RCN grant 214556/F20. Krogstad, H. E. & Trulsen, K. (2010) Interpretations and observations of ocean wave spectra. Ocean Dynamics 60:973-991. Nieto Borge, J. C., Rodríguez, G., Hessner, K., Izquierdo, P. (2004) Inversion of marine radar images for surface wave analysis. J. Atmos. Ocean. Tech. 21:1291-1300.

  19. Measurement of viscosity of highly viscous non-Newtonian fluids by means of ultrasonic guided waves.

    PubMed

    Kazys, Rymantas; Mazeika, Liudas; Sliteris, Reimondas; Raisutis, Renaldas

    2014-04-01

    In order to perform monitoring of the polymerisation process, it is necessary to measure viscosity. However, in the case of non-Newtonian highly viscous fluids, viscosity starts to be dependent on the vibration or rotation frequency of the sensing element. Also, the sensing element must possess a sufficient mechanical strength. Some of these problems may be solved applying ultrasonic measurement methods, however until now most of the known investigations were devoted to measurements of relatively low viscosities (up to a few Pas) of Newtonian liquids. The objective of the presented work is to develop ultrasonic method for measurement of viscosity of high viscous substances during manufacturing process in extreme conditions. For this purpose the method based on application of guided Lamb waves possessing the predominant component of in-plane displacements (the S0 and the SH0 modes) and propagating in an aluminium planar waveguide immersed in a viscous liquid has been investigated. The simulations indicated that in the selected modes mainly in-plane displacements are dominating, therefore the attenuation of those modes propagating in a planar waveguide immersed in a viscous liquid is mainly caused by viscosity of the liquid. The simulation results were confirmed by experiments. All measurements were performed in the viscosity standard Cannon N2700000. Measurements with the S0 wave mode were performed at the frequency of 500kHz. The SH0 wave mode was exited and used for measurements at the frequency of 580kHz. It was demonstrated that by selecting the particular mode of guided waves (S0 or SH0), the operation frequency and dimensions of the aluminium waveguide it is possible to get the necessary viscosity measurement range and sensitivity. The experiments also revealed that the measured dynamic viscosity is strongly frequency dependent and as a characteristic feature of non-Newtonian liquids is much lower than indicated by the standards. Therefore, in order to get the absolute values of viscosity in this case an additional calibration procedure is required. Feasibility to measure variations of high dynamic viscosities in the range of (20-25,000) Pas was theoretically and experimentally proved. The proposed solution differently from the known methods in principle is more mechanically robust and better fitted for measurements in extreme conditions. PMID:24491274

  20. Diffuse-light two-dimensional line-of-sight attenuation for soot concentration measurements.

    PubMed

    Thomson, Kevin A; Johnson, Matthew R; Snelling, David R; Smallwood, Gregory J

    2008-02-10

    A technique of diffuse-light two-dimensional line-of-sight attenuation (diffuse 2D-LOSA) is described and demonstrated that achieves very high levels of sensitivity in transmissivity measurements (optical thicknesses down to 0.001) while effectively mitigating interferences due to beam steering. An optical system is described in which an arc lamp coupled with an integrating sphere is used as a source of diffuse light that is imaged to the center of the particulate laden medium. The center of the medium is then imaged onto a CCD detector with 1:1 magnification. Comparative measurements with collimated 2D-LOSA in nonpremixed flames demonstrate the accuracy and improved optical noise rejection of the technique. Tests in weakly sooting, nonpremixed methane-air flames, and in high pressure methane-air flames, reveal the excellent sensitivity of diffuse 2D-LOSA, which is primarily limited by the shot noise of the lamp and CCD detector. PMID:18268781

  1. Evaluating LNAPL contamination using GPR signal attenuation analysis and dielectric property measurements: Practical implications for hydrological studies

    NASA Astrophysics Data System (ADS)

    Cassidy, Nigel J.

    2007-10-01

    Groundwater and sub-surface contamination by Light Non-Aqueous Phase Liquids (LNAPLs) is one of the industrial world's most pressing environmental issues and a thorough understanding of the hydrological, physical and bio-chemical properties of the sub-surface is key to determining the spatial and temporal development of any particular contamination event. Non-invasive geophysical techniques (such as electrical resistivity, electromagnetic conductivity, Ground-Penetrating Radar, etc.) have proved to be successful sub-surface investigation and characterisation tools with Ground-Penetrating Radar (GPR) being particularly popular. Recent studies have shown that the spatial/temporal variation in GPR signal attenuation can provide important information on the electrical properties of the sub-surface materials that, in turn, can be used to assess the physical and hydrological nature of the pore fluids and associated contaminants. Unfortunately, a high percentage of current LNAPL-related GPR studies focus on contaminant mapping only, with little emphasis being placed on characterising the hydrological properties (e.g., determining contaminant saturation index, etc.). By comparing laboratory-based, dielectric measurements of LNAPL contaminated materials with the GPR signal attenuation observed in both contaminated and 'clean' areas of an LNAPL contaminated site, new insights have been gained into the nature of contaminant distribution/saturation and the likely signal attenuation mechanisms. The results show that, despite some practical limitations of the analysis technique, meaningful hydrological interpretations can be obtained on the contaminant properties, saturation index and bio-degradation processes. A generalised attenuation/saturation model has been developed that describes the physical and attenuation enhancement characteristics of the contaminated areas and reveals that the most significant attenuation is related to smeared zone surrounding the seasonally changing water table interface. It is envisaged that the model will provide a basis for the interpretation of GPR data from analogous LNAPL contaminated sites and provide investigators with an appreciation of the merits and limitations of GPR-based, attenuation analysis techniques for hydrological applications.

  2. A COMPARISON OF MEASURED AND CALCULATED GAMMA RAY ATTENUATION FOR A COMMON COUNTING GEOMETRY

    SciTech Connect

    Gaylord, R F

    2004-02-26

    In order to perform quantitative gamma spectroscopy, it is necessary to know the sample-specific detection efficiency for photons as a function of energy. The detection efficiency, along with the branching ratio for the isotope and gamma ray of interest, is used to convert observed counts/second to actual disintegrations/second, and, hence, has a large effect on the accuracy of the measurement. In cases where the geometry of the source is simple and reproducible, such as a point source, small vial of solid, or jar of liquid, geometry-specific standards may be counted to determine the detection efficiency. In cases where the samples are large, irregular, or unique, this method generally cannot be used. For example, it is impossible to obtain a NIST-traceable standard glovebox or 55-gallon drum. In these cases, a combination of measured absolute detector efficiency and calculated sample-specific correction factors is commonly used. The correction factors may be calculated via Monte Carlo simulation of the item (the method used by Canberra's ISOCS system), or via semi-empirical calculation of matrix and container attenuations based on the thickness and composition of the container and radioactive matrix (ISOTOPIC by EG&G Ortec uses this method). The accuracy of these correction factors for specific geometries is often of vital interest when assessing the quality of gamma spectroscopy data. During the Building 251 Risk-Reduction Project, over 100 samples of high activity actinides will be characterized via gamma spectroscopy, typically without removing the material from the current storage containers. Most of the radioactive materials in B-251 are stored in cylindrical stainless steel canisters (called USV containers, after the Underground Storage Vaults they are commonly stored in), 13 cm in diameter, by 28 cm high, with walls that are 1.8 mm thick. While the actual samples have a variety of configurations inside the USV container, a very common configuration is the material (usually as an oxide powder pellet of approximately 2 cm diameter by {approx}2 mm thick) in a squat glass jar, with the jar placed in a thin steel food-pack can, which is then placed in the bottom of the USV canister. During data acquisition, the USV containers are typically rotated at approximately 4 rpm on a turntable to eliminate errors due to the material not being centered in the can, or attenuation not being isotropic. An aluminum plate is placed over the container, secured by three vertical rods, to securely hold the container. Pictures of both the containers, and this typical counting configuration are shown below.

  3. MEASUREMENT OF THE EXPANSION RATE OF THE UNIVERSE FROM {gamma}-RAY ATTENUATION

    SciTech Connect

    Dominguez, Alberto; Prada, Francisco

    2013-07-10

    A measurement of the expansion rate of the universe (that is, the Hubble constant, H{sub 0}) is derived here using the {gamma}-ray attenuation observed in the spectra of {gamma}-ray sources produced by the interaction of extragalactic {gamma}-ray photons with the photons of the extragalactic background light (EBL). The Hubble constant determined with our technique, for a {Lambda}CDM cosmology, is H{sub 0}=71.8{sub -5.6}{sup +4.6}(stat){sub -13.8}{sup +7.2}(syst) km s{sup -1} Mpc{sup -1}. This value is compatible with present-day measurements using well-established methods such as local distance ladders and cosmological probes. The recent detection of the cosmic {gamma}-ray horizon (CGRH) from multiwavelength observations of blazars, together with the advances in the knowledge of the EBL, allow us to measure the expansion rate of the universe. This estimate of the Hubble constant shows that {gamma}-ray astronomy has reached a mature enough state to provide cosmological measurements, which may become more competitive in the future with the construction of the Cherenkov Telescope Array. We find that the maximum dependence of the CGRH on the Hubble constant is approximately between redshifts 0.04 and 0.1, thus this is a smoking gun for planning future observational efforts. Other cosmological parameters, such as the total dark matter density {Omega}{sub m} and the dark energy equation of state w, are explored as well.

  4. Full Wave Analysis of RF Signal Attenuation in a Lossy Rough Surface Cave using a High Order Time Domain Vector Finite Element Method

    SciTech Connect

    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.

  5. Laboratory measurements of compressional and shear wave speeds through methane hydrate

    USGS Publications Warehouse

    Waite, W.F.; Helgerud, M.B.; Nur, A.; Pinkston, J.C.; Stern, L.A.; Kirby, S.H.; Durham, W.B.

    2000-01-01

    Simultaneous measurements of compressional and shear wave speeds through polycrystalline methane hydrate have been made. Methane hydrate, grown directly in a wave speed measurement chamber, was uniaxially compacted to a final porosity below 2%. At 277 K, the compacted material had a compressional wave speed of 3650 ?? 50 m/s. The shear wave speed, measured simultaneously, was 1890 ?? 30 m/s. From these wave speed measurements, we derive V(p)/V(s), Poisson's ratio, bulk, shear, and Young's moduli.

  6. Human Pulse Wave Measurement by MEMS Electret Condenser Microphone

    NASA Astrophysics Data System (ADS)

    Nomura, Shusaku; Hanasaka, Yasushi; Ishiguro, Tadashi; Ogawa, Hiroshi

    A micro Electret Condenser Microphone (ECM) fabricated by Micro Electro Mechanical System (MEMS) technology was employed as a novel apparatus for human pulse wave measurement. Since ECM frequency response characteristic, i.e. sensitivity, logically maintains a constant level at lower than the resonance frequency (stiffness control), the slightest pressure difference at around 1.0Hz generated by human pulse wave is expected to detect by MEMS-ECM. As a result of the verification of frequency response of MEMS-ECM, it was found that -20dB/dec of reduction in the sensitivity around 1.0Hz was engendered by a high input-impedance amplifier, i.e. the field effect transistor (FET), mounted near MEMS chip for amplifying tiny ECM signal. Therefore, MEMS-ECM is assumed to be equivalent with a differentiation circuit at around human pulse frequency. Introducing compensation circuit, human pulse wave was successfully obtained. In addition, the radial and ulnar artery tracing, and pulse wave velocity measurement at forearm were demonstrated; as illustrating a possible application of this micro device.

  7. Acoustic measurements of a liquefied cohesive sediment bed under waves

    NASA Astrophysics Data System (ADS)

    Mosquera, R.; Groposo, V.; Pedocchi, F.

    2014-04-01

    In this article the response of a cohesive sediment deposit under the action of water waves is studied with the help of laboratory experiments and an analytical model. Under the same regular wave condition three different bed responses were observed depending on the degree of consolidation of the deposit: no bed motion, bed motion of the upper layer after the action of the first waves, and massive bed motion after several waves. The kinematic of the upper 3 cm of the deposit were measured with an ultrasound acoustic profiler, while the pore-water pressure inside the bed was simultaneously measured using several pore pressure sensors. A poro-elastic model was developed to interpret the experimental observations. The model showed that the amplitude of the shear stress increased down into the bed. Then it is possible that the lower layers of the deposit experience plastic deformations, while the upper layers present just elastic deformations. Since plastic deformations in the lower layers are necessary for pore pressure build-up, the analytical model was used to interpret the experimental results and to state that liquefaction of a self consolidated cohesive sediment bed would only occur if the bed yield stress falls within the range defined by the amplitude of the shear stress inside the bed.

  8. Rapid miniature fiber optic pressure sensors for blast wave measurements

    NASA Astrophysics Data System (ADS)

    Zou, Xiaotian; Wu, Nan; Tian, Ye; Niezrecki, Christopher; Chen, Julie; Wang, Xingwei

    2013-02-01

    Traumatic brain injury (TBI) is a serious potential threat to soldiers who are exposed to explosions. Since the pathophysiology of TBI associated with a blast wave is not clearly defined, it is crucial to have a sensing system to accurately quantify the blast wave dynamics. This paper presents an ultra-fast fiber optic pressure sensor based on Fabry-Perot (FP) interferometric principle that is capable of measuring the rapid pressure changes in a blast event. The blast event in the experiment was generated by a starter pistol blank firing at close range, which produced a more realistic wave profile compared to using compressed air driven shock tubes. To the authors' knowledge, it is also the first study to utilize fiber optic pressure sensors to measure the ballistics shock wave of a pistol firing. The results illustrated that the fiber optic pressure sensor has a rise time of 200 ns which demonstrated that the sensor has ability to capture the dynamic pressure transient during a blast event. Moreover, the resonant frequency of the sensor was determined to be 4.11 MHz, which agrees well with the specific designed value.

  9. Study of atmospheric parameters measurements using MM-wave radar in synergy with LITE-2

    NASA Astrophysics Data System (ADS)

    Andrawis, Madeleine Y.

    1994-12-01

    The Lidar In-Space Technology Experiment, (LITE), has been developed, designed, and built by NASA Langley Research Center, to be flown on the space shuttle 'Discovery' on September 9, 1994. Lidar, which stands for light detecting and ranging, is a radar system that uses short pulses of laser light instead of radio waves in the case of the common radar. This space-based lidar offers atmospheric measurements of stratospheric and tropospheric aerosols, the planetary boundary layer, cloud top heights, and atmospheric temperature and density in the 10-40 km altitude range. A study is being done on the use, advantages, and limitations of a millimeterwave radar to be utilized in synergy with the Lidar system, for the LITE-2 experiment to be flown on a future space shuttle mission. The lower atmospheric attenuation, compared to infrared and optical frequencies, permits the millimeter-wave signals to penetrate through the clouds and measure multi-layered clouds, cloud thickness, and cloud-base height. These measurements would provide a useful input to radiation computations used in the operational numerical weather prediction models, and for forecasting. High power levels, optimum modulation, data processing, and high antenna gain are used to increase the operating range, while space environment, radar tradeoffs, and power availability are considered. Preliminary, numerical calculations are made, using the specifications of an experimental system constructed at Georgia Tech. The noncoherent 94 GHz millimeter-wave radar system has a pulsed output with peak value of 1 kW. The backscatter cross section of the particles to be measured, that are present in the volume covered by the beam footprint, is also studied.

  10. Study of atmospheric parameters measurements using MM-wave radar in synergy with LITE-2

    NASA Technical Reports Server (NTRS)

    Andrawis, Madeleine Y.

    1994-01-01

    The Lidar In-Space Technology Experiment, (LITE), has been developed, designed, and built by NASA Langley Research Center, to be flown on the space shuttle 'Discovery' on September 9, 1994. Lidar, which stands for light detecting and ranging, is a radar system that uses short pulses of laser light instead of radio waves in the case of the common radar. This space-based lidar offers atmospheric measurements of stratospheric and tropospheric aerosols, the planetary boundary layer, cloud top heights, and atmospheric temperature and density in the 10-40 km altitude range. A study is being done on the use, advantages, and limitations of a millimeterwave radar to be utilized in synergy with the Lidar system, for the LITE-2 experiment to be flown on a future space shuttle mission. The lower atmospheric attenuation, compared to infrared and optical frequencies, permits the millimeter-wave signals to penetrate through the clouds and measure multi-layered clouds, cloud thickness, and cloud-base height. These measurements would provide a useful input to radiation computations used in the operational numerical weather prediction models, and for forecasting. High power levels, optimum modulation, data processing, and high antenna gain are used to increase the operating range, while space environment, radar tradeoffs, and power availability are considered. Preliminary, numerical calculations are made, using the specifications of an experimental system constructed at Georgia Tech. The noncoherent 94 GHz millimeter-wave radar system has a pulsed output with peak value of 1 kW. The backscatter cross section of the particles to be measured, that are present in the volume covered by the beam footprint, is also studied.

  11. An Analysis of Fundamental Mode Surface Wave Amplitude Measurements

    NASA Astrophysics Data System (ADS)

    Schardong, L.; Ferreira, A. M.; van Heijst, H. J.; Ritsema, J.

    2014-12-01

    Seismic tomography is a powerful tool to decipher the Earth's interior structure at various scales. Traveltimes of seismic waves are widely used to build velocity models, whereas amplitudes are still only seldomly accounted for. This mainly results from our limited ability to separate the various physical effects responsible for observed amplitude variations, such as focussing/defocussing, scattering and source effects. We present new measurements from 50 global earthquakes of fundamental-mode Rayleigh and Love wave amplitude anomalies measured in the period range 35-275 seconds using two different schemes: (i) a standard time-domain amplitude power ratio technique; and (ii) a mode-branch stripping scheme. For minor-arc data, we observe amplitude anomalies with respect to PREM in the range of 0-4, for which the two measurement techniques show a very good overall agreement. We present here a statistical analysis and comparison of these datasets, as well as comparisons with theoretical calculations for a variety of 3-D Earth models. We assess the geographical coherency of the measurements, and investigate the impact of source, path and receiver effects on surface wave amplitudes, as well as their variations with frequency in a wider range than previously studied.

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

    PubMed

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

    2015-05-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

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

  14. Rapid Response Measurements of Hurricane Waves and Storm Surge

    NASA Astrophysics Data System (ADS)

    Gravois, U.

    2010-12-01

    Andrew (1992), Katrina (2005), and Ike (2008) are recent examples of extensive damage that resulted from direct hurricane landfall. Some of the worst damages from these hurricanes are caused by wind driven waves and storm surge flooding. The potential for more hurricane disasters like these continues to increase as a result of population growth and real estate development in low elevation coastal regions. Observational measurements of hurricane waves and storm surge play an important role in future mitigation efforts, yet permanent wave buoy moorings and tide stations are more sparse than desired. This research has developed a rapid response method using helicopters to install temporary wave and surge gauges ahead of hurricane landfall. These temporary installations, with target depths from 10-15 m and 1-7 km offshore depending on the local shelf slope, increase the density of measurement points where the worst conditions are expected. The method has progressed to an operational state and has successfully responded to storms Ernesto (2006), Noel (2007), Fay (2008), Gustav (2008), Hanna (2008) and Ike (2008). The temporary gauges are pressure data loggers that measure at 1 Hz continuously for 12 days and are post-processed to extract surge and wave information. For the six storms studied, 45 out of 49 sensors were recovered by boat led scuba diver search teams, with 43 providing useful data for an 88 percent success rate. As part of the 20 sensor Hurricane Gustav response, sensors were also deployed in lakes and bays inLouisiana, east of the Mississippi river delta. Gustav was the largest deployment to date. Generally efforts were scaled back for storms that were not anticipated to be highly destructive. For example, the cumulative total of sensors deployed for Ernesto, Noel, Fay and Hanna was only 20. Measurement locations for Gustav spanned over 800 km of exposed coastline from Louisiana to Florida with sensors in close proximity to landfall near Cocodrie, Louisiana. Surge measurements between landfall and the Mississippi delta show 1.5 - 2 m of surge and values exceeding 2 m further from landfall north of the Mississippi delta. These observations demonstrate the importance of coastal geography on storm surge vulnerability. Waves measurements from Gustav show large waves of 5 m at all exposed locations from landfall to western Florida. Some smaller values were also recorded, likely to be due to depth limited breaking or sheltering from the Mississippi delta. Two weeks after Hurricane Gustav, major Hurricane Ike entered the Gulf of Mexico threatening Texas. Unfortunately the sensors already deployed for Gustav reached the 12 day memory limit and did not catch the most extreme conditions of Ike. However, 9 additional sensors were deployed for Ike spanning 360 km of the Texas coast. These measurements show surge east of the Galveston, Texas landfall exceeding 4.5 m and wave heights greater than 5 m. Hurricane Ike was by far the most destructive of the 6 storms measured and has spawned separate work relating the extent of building damage to these measurements.

  15. Wave intensity wall analysis: a novel noninvasive method to measure wave intensity.

    PubMed

    Larsson, Matilda; Bjällmark, Anna; Lind, Britta; Balzano, Rita; Peolsson, Michael; Winter, Reidar; Brodin, Lars-Ake

    2009-09-01

    Wave intensity analysis is a concept providing information about the interaction of the heart and the vascular system. Originally, the technique was invasive. Since then new noninvasive methods have been developed. A recently developed ultrasound technique to estimate tissue motion and deformation is speckle-tracking echocardiography. Speckle tracking-based techniques allow for accurate measurement of movement and deformation variables in the arterial wall in both the radial and the longitudinal direction. The aim of this study was to test if speckle tracking-derived deformation data could be used as input for wave intensity calculations. The new concept was to approximate changes of flow and pressure by deformation changes of the arterial wall in longitudinal and radial directions. Flow changes (dU/dt) were approximated by strain rate (sr, 1/s) of the arterial wall in the longitudinal direction, whereas pressure changes (dP/dt) were approximated by sign reversed strain rate (1/s) in the arterial wall in the radial direction. To validate the new concept, a comparison between the newly developed Wave Intensity Wall Analysis (WIWA) algorithm and a commonly used and validated wave intensity system (SSD-5500, Aloka, Tokyo, Japan) was performed. The studied population consisted of ten healthy individuals (three women, seven men) and ten patients (all men) with coronary artery disease. The present validation study indicates that the mechanical properties of the arterial wall, as measured by a speckle tracking-based technique are a possible input for wave intensity calculations. The study demonstrates good visual agreement between the two systems and the time interval between the two positive peaks (W1-W2) measured by the Aloka system and the WIWA system correlated for the total group (r = 0.595, P < 0.001). The correlation for the diseased subgroup was r = 0.797, P < 0.001 and for the healthy subgroup no significant correlation was found (P > 0.05). The results of the study indicate that the mechanical properties of the arterial wall could be used as input for wave intensity calculations. The WIWA concept is a promising new method that potentially provides several advantages over earlier wave intensity methods, but it still has limitations and needs further refinement and larger studies to find the optimal clinical use. PMID:19784819

  16. Maximum Wave Run-up Measured on a Natural Beach Owing to Extreme Waves

    NASA Astrophysics Data System (ADS)

    Thornton, E. B.; MacMahan, J. H.

    2014-12-01

    Unique field data indicative of maximum run-up owing to extreme wave conditions with a 50 year return period are obtained from the distribution of sea-glass on 10-18 m high dunes. The hypothesis that sea-glass is an indicator of maximum run-up is verified by the observations that new sea-glass on a beach is found at the rackline, the highest point of run-up. The source of the sea-glass is a garbage dump on the dune in southern Monterey Bay from 1937-1951. It is estimated that the dump, located on an erosive shoreline, was falling into the ocean by at least 1960, so that the maximum run-up values have a return period of at least 50 years. Various empirical run-up models based both on extensive laboratory and field measurements are assessed to include contributions from sea-swell and infragravity waves, setup and tidal elevation, which are parameterized on wave height and surf parameter, P, which is a function of wave height, period and beach slope. Deep water hindcast waves (1958-2011) refracted to 4m water depth are used as input to the models. Beach and dune slopes averaged over the run-up region from mean water level to the maximum run-up ranged 0.1 - 0.63 (angle of repose). Reasonable comparison with model predicted run-up with distribution of sea-glass on the dune were obtained for P <2 events, but were underpredicted for large P. Large P events are associated with long period swell waves characteristic of the Pacific Ocean that are outside the empirical parameter space from which the model equations were derived, suggesting a possible deficiency in the models.

  17. Association of somatic burden of disease with age and neuropsychological measures in attenuated mucopolysaccharidosis types I, II and VI

    PubMed Central

    Ahmed, Alia; Shapiro, Elsa; Rudser, Kyle; Kunin-Batson, Alicia; King, Kelly; Whitley, Chester B.

    2016-01-01

    Introduction The mucopolysaccharidoses (MPSs) are a group of rare genetic lysosomal disorders with progressive multisystem involvement. An MPS-specific physical symptom scale was developed and introduced a Physical Symptom Score (PSS) to quantify the somatic disease burden across MPS I, II and VI. Hypothesis Somatic burden of disease in patients with attenuated MPS I, II and VI as measured by the PSS will be positively associated with age and negatively associated with neuropsychological functions [i.e. full scale intelligence quotient (FSIQ) and attention]. Materials and methods Forty-eight patients with attenuated MPS I (n = 24), II (n = 14), and VI (n = 10) aged 6 to 32 years on enzyme replacement therapy who were enrolled in “Longitudinal Studies of Brain Structure and Functions in MPS Disorders” across seven centers. Somatic disease burden was measured by the PSS. Neuropsychological functions were measured by the Wechsler Abbreviated Scale of Intelligence (WASI) and Test of Variables of Attention (TOVA). Results PSS was positively associated with age in attenuated MPS I (P < 0.001), MPS II (P < 0.01) and MPS VI (P < 0.05). There was a negative association of PSS with FSIQ in attenuated MPS I (P < 0.001) and in MPS VI (P < 0.001) but not with MPS II. Although attention scores were below average in all groups, a significant negative association between PSS and one measures of sustained attention (TOVA d prime) was found only in MPS VI. Conclusions Physical Symptom Score increased with age in attenuated MPS I, II and VI, reflecting progressive somatic burden of disease despite treatment with enzyme replacement therapy. Furthermore, the association of increased somatic disease burden with decreased neurocognitive ability suggests that both measures reflect disease severity and are not independent. PMID:27114913

  18. Far- and Deep-UV Spectroscopy of Semiconductor Nanoparticles Measured Based on Attenuated Total Reflectance spectroscopy.

    PubMed

    Tanabe, Ichiro; Yamada, Yosuke; Ozaki, Yukihiro

    2016-02-01

    Far- and deep-ultraviolet spectra (150-300 nm) of semiconductor nanoparticles (zinc oxide and zinc sulfide) are successfully measured by using attenuated total reflectance (ATR) spectroscopy, and analyzed using finite-difference time-domain (FDTD) simulations. The obtained spectra show good consistency with earlier synchrotron-radiation spectra and with theoretical calculations. The FDTD simulation results show that the present system collected the correct spectra. In the present system, the obtained spectra are affected by the real part n of the complex refractive index more strongly than the imaginary part k. It is also revealed both experimentally and theoretically that spectral intensities of the semiconductor nanoparticles are approximately one tenth those of liquid samples. These results provide insights into the far- and deep-ultraviolet spectroscopy based on the ATR system, and show the general applicability of our original ATR spectroscopy to semiconductor nanoparticles. The system needs neither high vacuum nor much space, and enables rapid and systematic investigation of the electronic states of various materials. PMID:26691240

  19. 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.

  20. In vivo evidence of methamphetamine induced attenuation of brain tissue oxygenation as measured by EPR oximetry

    SciTech Connect

    Weaver, John; Yang, Yirong; Purvis, Rebecca; Weatherwax, Theodore; Rosen, Gerald M.; Liu, Ke Jian

    2014-03-01

    Abuse of methamphetamine (METH) is a major and significant societal problem in the US, as a number of studies have suggested that METH is associated with increased cerebrovascular events, hemorrhage or vasospasm. Although cellular and molecular mechanisms involved in METH-induced toxicity are not completely understood, changes in brain O{sub 2} may play an important role and contribute to METH-induced neurotoxicity including dopaminergic receptor degradation. Given that O{sub 2} is the terminal electron acceptor for many enzymes that are important in brain function, the impact of METH on brain tissue pO{sub 2}in vivo remains largely uncharacterized. This study investigated striatal tissue pO{sub 2} changes in male C57BL/6 mice (16–20 g) following METH administration using EPR oximetry, a highly sensitive modality to measure pO{sub 2}in vivo, in situ and in real time. We demonstrate that 20 min after a single injection of METH (8 mg/kg i.v.), the striatal pO{sub 2} was reduced to 81% of the pretreatment level and exposure to METH for 3 consecutive days further attenuated striatal pO{sub 2} to 64%. More importantly, pO{sub 2} did not recover fully to control levels even 24 h after administration of a single dose of METH and continual exposure to METH exacerbates the condition. We also show a reduction in cerebral blood flow associated with a decreased brain pO{sub 2} indicating an ischemic condition. Our findings suggests that administration of METH can attenuate brain tissue pO{sub 2}, which may lead to hypoxic insult, thus a risk factor for METH-induced brain injury and the development of stroke in young adults. - Highlights: • Explored striatal tissue pO{sub 2}in vivo after METH administration by EPR oximetry. • pO{sub 2} was reduced by 81% after a single dose and 64% after 3 consecutive daily doses. • pO{sub 2} did not recover fully to control levels even 24 h after a single dose. • Decrease in brain tissue pO{sub 2} may be associated with a decrease in CBF. • Administration of methamphetamine may lead to hypoxic insult.

  1. Measurements of Turbulence Attenuation by a Dilute Dispersion of Solid Particles in Homogeneous Isotropic Turbulence

    NASA Astrophysics Data System (ADS)

    Eaton, John; Hwang, Wontae; Cabral, Patrick

    2002-11-01

    This research addresses turbulent gas flows laden with fine solid particles at sufficiently large mass loading that strong two-way coupling occurs. By two-way coupling we mean that the particle motion is governed largely by the flow, while the particles affect the gas-phase mean flow and the turbulence properties. Our main interest is in understanding how the particles affect the turbulence. Computational techniques have been developed which can accurately predict flows carrying particles that are much smaller than the smallest scales of turbulence. Also, advanced computational techniques and burgeoning computer resources make it feasible to fully resolve very large particles moving through turbulent flows. However, flows with particle diameters of the same order as the Kolmogorov scale of the turbulence are notoriously difficult to predict. Some simple flows show strong turbulence attenuation with reductions in the turbulent kinetic energy by up to a factor of five. On the other hand, some seemingly similar flows show almost no modification. No model has been proposed that allows prediction of when the strong attenuation will occur. Unfortunately, many technological and natural two-phase flows fall into this regime, so there is a strong need for new physical understanding and modeling capability. Our objective is to study the simplest possible turbulent particle-laden flow, namely homogeneous, isotropic turbulence with a uniform dispersion of monodisperse particles. We chose such a simple flow for two reasons. First, the simplicity allows us to probe the interaction in more detail and offers analytical simplicity in interpreting the results. Secondly, this flow can be addressed by numerical simulation, and many research groups are already working on calculating the flow. Our detailed data can help guide some of these efforts. By using microgravity, we can further simplify the flow to the case of no mean velocity for either the turbulence or the particles. In fact the addition of gravity as a variable parameter may help us to better understand the physics of turbulence attenuation. The experiments are conducted in a turbulence chamber capable of producing stationary or decaying isotropic turbulence with nearly zero mean flow and Taylor microscale Reynolds numbers up to nearly 500. The chamber is a 410 mm cubic box with the corners cut off to make it approximately spherical. Synthetic jet turbulence generators are mounted in each of the eight corners of the box. Each generator consists of a loudspeaker forcing a plenum and producing a pulsed jet through a 20 mm diameter orifice. These synthetic jets are directed into ejector tubes pointing towards the chamber center. The ejector tubes increase the jet mass flow and decrease the velocity. The jets then pass through a turbulence grid. Each of the eight loudspeakers is forced with a random phase and frequency. The resulting turbulence is highly Isotropic and matches typical behavior of grid turbulence. Measurements of both phases are acquired using particle image velocimetry (PIV). The gas is seeded with approximately 1 micron diameter seeding particles while the solid phase is typically 150 micron diameter spherical glass particles. A double-pulsed YAG laser and a Kodak ES-1.0 10-bit PIV camera provide the PIV images. Custom software is used to separate the images into individual images containing either gas-phase tracers or large particles. Modern high-resolution PIV algorithms are then used to calculate the velocity field. A large set of image pairs are acquired for each case, then the results are averaged both spatially and over the ensemble of acquired images. The entire apparatus is mounted in two racks which are carried aboard NASA's KC-135 Flying Microgravity Laboratory. The rack containing the turbulence chamber, the laser head, and the camera floats freely in the airplane cabin (constrained by competent NASA personnel) to minimize g-jitter.

  2. Measurements of Turbulence Attenuation by a Dilute Dispersion of Solid Particles in Homogeneous Isotropic Turbulence

    NASA Technical Reports Server (NTRS)

    Eaton, John; Hwang, Wontae; Cabral, Patrick

    2002-01-01

    This research addresses turbulent gas flows laden with fine solid particles at sufficiently large mass loading that strong two-way coupling occurs. By two-way coupling we mean that the particle motion is governed largely by the flow, while the particles affect the gas-phase mean flow and the turbulence properties. Our main interest is in understanding how the particles affect the turbulence. Computational techniques have been developed which can accurately predict flows carrying particles that are much smaller than the smallest scales of turbulence. Also, advanced computational techniques and burgeoning computer resources make it feasible to fully resolve very large particles moving through turbulent flows. However, flows with particle diameters of the same order as the Kolmogorov scale of the turbulence are notoriously difficult to predict. Some simple flows show strong turbulence attenuation with reductions in the turbulent kinetic energy by up to a factor of five. On the other hand, some seemingly similar flows show almost no modification. No model has been proposed that allows prediction of when the strong attenuation will occur. Unfortunately, many technological and natural two-phase flows fall into this regime, so there is a strong need for new physical understanding and modeling capability. Our objective is to study the simplest possible turbulent particle-laden flow, namely homogeneous, isotropic turbulence with a uniform dispersion of monodisperse particles. We chose such a simple flow for two reasons. First, the simplicity allows us to probe the interaction in more detail and offers analytical simplicity in interpreting the results. Secondly, this flow can be addressed by numerical simulation, and many research groups are already working on calculating the flow. Our detailed data can help guide some of these efforts. By using microgravity, we can further simplify the flow to the case of no mean velocity for either the turbulence or the particles. In fact the addition of gravity as a variable parameter may help us to better understand the physics of turbulence attenuation. The experiments are conducted in a turbulence chamber capable of producing stationary or decaying isotropic turbulence with nearly zero mean flow and Taylor microscale Reynolds numbers up to nearly 500. The chamber is a 410 mm cubic box with the corners cut off to make it approximately spherical. Synthetic jet turbulence generators are mounted in each of the eight corners of the box. Each generator consists of a loudspeaker forcing a plenum and producing a pulsed jet through a 20 mm diameter orifice. These synthetic jets are directed into ejector tubes pointing towards the chamber center. The ejector tubes increase the jet mass flow and decrease the velocity. The jets then pass through a turbulence grid. Each of the eight loudspeakers is forced with a random phase and frequency. The resulting turbulence is highly Isotropic and matches typical behavior of grid turbulence. Measurements of both phases are acquired using particle image velocimetry (PIV). The gas is seeded with approximately 1 micron diameter seeding particles while the solid phase is typically 150 micron diameter spherical glass particles. A double-pulsed YAG laser and a Kodak ES-1.0 10-bit PIV camera provide the PIV images. Custom software is used to separate the images into individual images containing either gas-phase tracers or large particles. Modern high-resolution PIV algorithms are then used to calculate the velocity field. A large set of image pairs are acquired for each case, then the results are averaged both spatially and over the ensemble of acquired images. The entire apparatus is mounted in two racks which are carried aboard NASA's KC-135 Flying Microgravity Laboratory. The rack containing the turbulence chamber, the laser head, and the camera floats freely in the airplane cabin (constrained by competent NASA personnel) to minimize g-jitter.

  3. Measurement of skeletal muscle radiation attenuation and basis of its biological variation

    PubMed Central

    Aubrey, J; Esfandiari, N; Baracos, V E; Buteau, F A; Frenette, J; Putman, C T; Mazurak, V C

    2014-01-01

    Skeletal muscle contains intramyocellular lipid droplets within the cytoplasm of myocytes as well as intermuscular adipocytes. These depots exhibit physiological and pathological variation which has been revealed with the advent of diagnostic imaging approaches: magnetic resonance (MR) imaging, MR spectroscopy and computed tomography (CT). CT uses computer-processed X-rays and is now being applied in muscle physiology research. The purpose of this review is to present CT methodologies and summarize factors that influence muscle radiation attenuation, a parameter which is inversely related to muscle fat content. Pre-defined radiation attenuation ranges are used to demarcate intermuscular adipose tissue [from −190 to −30 Hounsfield units (HU)] and muscle (−29 HU to +150 HU). Within the latter range, the mean muscle radiation attenuation [muscle (radio) density] is reported. Inconsistent criteria for the upper and lower HU cut-offs used to characterize muscle attenuation limit comparisons between investigations. This area of research would benefit from standardized criteria for reporting muscle attenuation. Available evidence suggests that muscle attenuation is plastic with physiological variation induced by the process of ageing, as well as by aerobic training, which probably reflects accumulation of lipids to fuel aerobic work. Pathological variation in muscle attenuation reflects excess fat deposition in the tissue and is observed in people with obesity, diabetes type II, myositis, osteoarthritis, spinal stenosis and cancer. A poor prognosis and different types of morbidity are predicted by the presence of reduced mean muscle attenuation values in patients with these conditions; however, the biological features of muscle with these characteristics require further investigation. PMID:24393306

  4. Laser vibrometer measurement of guided wave modes in rail track.

    PubMed

    Loveday, Philip W; Long, Craig S

    2015-03-01

    The ability to measure the individual modes of propagation is very beneficial during the development of guided wave ultrasound based rail monitoring systems. Scanning laser vibrometers can measure the displacement at a number of measurement points on the surface of the rail track. A technique for estimating the amplitude of the individual modes of propagation from these measurements is presented and applied to laboratory and field measurements. The method uses modal data from a semi-analytical finite element model of the rail and has been applied at frequencies where more than twenty propagating modes exist. It was possible to measure individual modes of propagation at a distance of 400 m from an ultrasonic transducer excited at 30 kHz on operational rail track and to identify the modes that are capable of propagating large distances. PMID:25497003

  5. Electromagnetic field measurements on a mm-wave linear accelerator

    SciTech Connect

    Matthews, P.; Kang, Y.; Berenc, T.; Kustom, R.; Willke, T.; Feinerman, A.

    1994-07-01

    Field strength measurements for the determination of the R/Q of a mm-wave, 50-MeV electron linear accelerator using perturbational techniques are described. The perturbation is achieved using optical fibers coated with a thin metallic film to form a hollow cylinder. The perturbational form factors for such a geometry are approximated using several simple analytical expressions which are compared to a finite difference calculation as well as experimental results on a known cavity.

  6. Measurement of cylindrical Rayleigh surface waves using line-focused PVDF transducers and defocusing measurement method.

    PubMed

    Lin, Chun-I; Lee, Yung-Chun

    2014-08-01

    Line-focused PVDF transducers and defocusing measurement method are applied in this work to determine the dispersion curve of the Rayleigh-like surface waves propagating along the circumferential direction of a solid cylinder. Conventional waveform processing method has been modified to cope with the non-linear relationship between phase angle of wave interference and defocusing distance induced by a cylindrically curved surface. A cross correlation method is proposed to accurately extract the cylindrical Rayleigh wave velocity from measured data. Experiments have been carried out on one stainless steel and one glass cylinders. The experimentally obtained dispersion curves are in very good agreement with their theoretical counterparts. Variation of cylindrical Rayleigh wave velocity due to the cylindrical curvature is quantitatively verified using this new method. Other potential applications of this measurement method for cylindrical samples will be addressed. PMID:24796246

  7. Frequency-dependent squeeze-amplitude attenuation and squeeze-angle rotation by electromagnetically induced transparency for gravitational-wave interferometers

    SciTech Connect

    Mikhailov, Eugeniy E.; Goda, Keisuke; Corbitt, Thomas; Mavalvala, Nergis

    2006-05-15

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

  8. Ultrasonic wave based pressure measurement in small diameter pipeline.

    PubMed

    Wang, Dan; Song, Zhengxiang; Wu, Yuan; Jiang, Yuan

    2015-12-01

    An effective non-intrusive method of ultrasound-based technique that allows monitoring liquid pressure in small diameter pipeline (less than 10mm) is presented in this paper. Ultrasonic wave could penetrate medium, through the acquisition of representative information from the echoes, properties of medium can be reflected. This pressure measurement is difficult due to that echoes' information is not easy to obtain in small diameter pipeline. The proposed method is a study on pipeline with Kneser liquid and is based on the principle that the transmission speed of ultrasonic wave in pipeline liquid correlates with liquid pressure and transmission speed of ultrasonic wave in pipeline liquid is reflected through ultrasonic propagation time providing that acoustic distance is fixed. Therefore, variation of ultrasonic propagation time can reflect variation of pressure in pipeline. Ultrasonic propagation time is obtained by electric processing approach and is accurately measured to nanosecond through high resolution time measurement module. We used ultrasonic propagation time difference to reflect actual pressure in this paper to reduce the environmental influences. The corresponding pressure values are finally obtained by acquiring the relationship between variation of ultrasonic propagation time difference and pressure with the use of neural network analysis method, the results show that this method is accurate and can be used in practice. PMID:26206527

  9. Quantum Measurement Theory in Gravitational-Wave Detectors

    NASA Astrophysics Data System (ADS)

    Danilishin, Stefan L.; Khalili, Farid Ya.

    2012-04-01

    The fast progress in improving the sensitivity of the gravitational-wave detectors, we all have witnessed in the recent years, has propelled the scientific community to the point at which quantum behavior of such immense measurement devices as kilometer-long interferometers starts to matter. The time when their sensitivity will be mainly limited by the quantum noise of light is around the corner, and finding ways to reduce it will become a necessity. Therefore, the primary goal we pursued in this review was to familiarize a broad spectrum of readers with the theory of quantum measurements in the very form it finds application in the area of gravitational-wave detection. We focus on how quantum noise arises in gravitational-wave interferometers and what limitations it imposes on the achievable sensitivity. We start from the very basic concepts and gradually advance to the general linear quantum measurement theory and its application to the calculation of quantum noise in the contemporary and planned interferometric detectors of gravitational radiation of the first and second generation. Special attention is paid to the concept of the Standard Quantum Limit and the methods of its surmounting.

  10. Attenuation length measurements of a liquid scintillator with LabVIEW and reliability evaluation of the device

    NASA Astrophysics Data System (ADS)

    Gao, Long; Yu, Bo-Xiang; Ding, Ya-Yun; Zhou, Li; Wen, Liang-Jian; Xie, Yu-Guang; Wang, Zhi-Gang; Cai, Xiao; Sun, Xi-Lei; Fang, Jian; Xue, Zhen; Zhang, Ai-Wu; L, Qi-Wen; Sun, Li-Jun; Ge, Yong-Shuai; Liu, Ying-Biao; Niu, Shun-Li; Hu, Tao; Cao, Jun; L, Jun-Guang

    2013-07-01

    An attenuation length measurement device was constructed using an oscilloscope and LabVIEW for signal acquisition and processing. The performance of the device has been tested in a variety of ways. The test results show that the set-up has a good stability and high precision (sigma/mean reached 0.4 percent). Besides, the accuracy of the measurement system will decrease by about 17 percent if a filter is used. The attenuation length of a gadolinium-loaded liquid scintillator (Gd-LS) was measured as 15.100.35 m where Gd-LS was heavily used in the Daya Bay Neutrino Experiment. In addition, one method based on the Beer-Lambert law was proposed to investigate the reliability of the measurement device, the R-square reached 0.9995. Moreover, three purification methods for Linear Alkyl Benzene (LAB) production were compared in the experiment.

  11. Dust attenuation in z ~ 1 galaxies from Herschel and 3D-HST Hα measurements

    NASA Astrophysics Data System (ADS)

    Puglisi, A.; Rodighiero, G.; Franceschini, A.; Talia, M.; Cimatti, A.; Baronchelli, I.; Daddi, E.; Renzini, A.; Schawinski, K.; Mancini, C.; Silverman, J.; Gruppioni, C.; Lutz, D.; Berta, S.; Oliver, S. J.

    2016-02-01

    We combined the spectroscopic information from the 3D-HST survey with Herschel data to characterize the Hα dust attenuation properties of a sample of 79 main sequence star-forming galaxies at z ~ 1 in the GOODS-S field. The sample was selected in the far-IR at λ = 100 and/or 160 μm and only includes galaxies with a secure Hα detection (S/N > 3). From the low resolution 3D-HST spectra we measured the redshifts and the Hα fluxes for the whole sample. (A factor of 1/1.2 was applied to the observed fluxes to remove the [NII] contamination.) The stellar masses (M⋆), infrared (LIR), and UV luminosities (LUV) were derived from the spectral energy distributions by fitting multiband data from GALEX near-UV to SPIRE 500 μm. We estimated the continuum extinction Estar(B-V) from both the IRX = LIR/LUV ratio and the UV-slope, β, and found excellent agreement between the two. The nebular extinction was estimated from comparison of the observed SFRHα and SFRUV. We obtained f = Estar(B-V) /Eneb(B-V) = 0.93 ± 0.06, which is higher than the canonical value of f = 0.44 measured in the local Universe. Our derived dust correction produces good agreement between the Hα and IR+UV SFRs for galaxies with SFR ≳ 20M⊙/yr and M⋆ ≳ 5 × 1010M⊙, while objects with lower SFR and M⋆ seem to require a smaller f-factor (i.e. higher Hα extinction correction). Our results then imply that the nebular extinction for our sample is comparable to extinction in the optical-UV continuum and suggest that the f-factor is a function of both M⋆ and SFR, in agreement with previous studies.

  12. Reflective measurement of water concentration using millimeter wave illumination

    NASA Astrophysics Data System (ADS)

    Sung, Shijun; Bennett, David; Taylor, Zachary; Bajwa, Neha; Tewari, Priyamvada; Maccabi, Ashkan; Culjat, Martin; Singh, Rahul; Grundfest, Warren

    2011-04-01

    THz and millimeter wave technology have shown the potential to become a valuable medical imaging tool because of its sensitivity to water and safe, non-ionizing photon energy. Using the high dielectric constant of water in these frequency bands, reflectionmode THz sensing systems can be employed to measure water content in a target with high sensitivity. This phenomenology may lead to the development of clinical systems to measure the hydration state of biological targets. Such measurements may be useful in fast and convenient diagnosis of conditions whose symptoms can be characterized by changes in water concentration such as skin burns, dehydration, or chemical exposure. To explore millimeter wave sensitivity to hydration, a reflectometry system is constructed to make water concentration measurements at 100 GHz, and the minimum detectable water concentration difference is measured. This system employs a 100 GHz Gunn diode source and Golay cell detector to perform point reflectivity measurements of a wetted polypropylene towel as it dries on a mass balance. A noise limited, minimum detectable concentration difference of less than 0.5% by mass can be detected in water concentrations ranging from 70% to 80%. This sensitivity is sufficient to detect hydration changes caused by many diseases and pathologies and may be useful in the future as a diagnostic tool for the assessment of burns and other surface pathologies.

  13. Advanced Sine Wave Modulation of Continuous Wave Laser System for Atmospheric CO2 Differential Absorption Measurements

    NASA Technical Reports Server (NTRS)

    Campbell, Joel F.; Lin, Bing; Nehrir, Amin R.

    2014-01-01

    NASA Langley Research Center in collaboration with ITT Exelis have been experimenting with Continuous Wave (CW) laser absorption spectrometer (LAS) as a means of performing atmospheric CO2 column measurements from space to support the Active Sensing of CO2 Emissions over Nights, Days, and Seasons (ASCENDS) mission.Because range resolving Intensity Modulated (IM) CW lidar techniques presented here rely on matched filter correlations, autocorrelation properties without side lobes or other artifacts are highly desirable since the autocorrelation function is critical for the measurements of lidar return powers, laser path lengths, and CO2 column amounts. In this paper modulation techniques are investigated that improve autocorrelation properties. The modulation techniques investigated in this paper include sine waves modulated by maximum length (ML) sequences in various hardware configurations. A CW lidar system using sine waves modulated by ML pseudo random noise codes is described, which uses a time shifting approach to separate channels and make multiple, simultaneous online/offline differential absorption measurements. Unlike the pure ML sequence, this technique is useful in hardware that is band pass filtered as the IM sine wave carrier shifts the main power band. Both amplitude and Phase Shift Keying (PSK) modulated IM carriers are investigated that exibit perfect autocorrelation properties down to one cycle per code bit. In addition, a method is presented to bandwidth limit the ML sequence based on a Gaussian filter implemented in terms of Jacobi theta functions that does not seriously degrade the resolution or introduce side lobes as a means of reducing aliasing and IM carrier bandwidth.

  14. Propagation through a stratified ocean wave guide with random volume and surface inhomogeneities, Part I. Theory: Attenuation, dispersion, and acoustic mirages

    NASA Astrophysics Data System (ADS)

    Ratilal, Purnima; Makris, Nicholas C.

    2002-11-01

    Analytic expressions for the mean field propagated through a stratified ocean with random volume or sufrace inhomogeneities of arbitrary size compared to the wavelength are derived from a wave guide scattering model stemming from Green's theorem. It is found that multiple scattering through inhomogeneities in the forward direction can be succinctly expressed in terms of modal attenuation and dispersion coefficients under widely satisfied conditions. The inhomogeneities can have an arbitrary distribution in depth so that the model can realistically apply to scattering from internal waves, bubbles, fish, seafloor and seasurface roughness as well as sub-bottom anomalies. An understanding of the coherence of the forward scattered field can be gained by analogy with the formation of optical mirages in low-grazing angle forward scatter from random surfaces.

  15. Study of Dual-Wavelength PIA Estimates: Ratio of Ka- and Ku-band Attenuations Obtained from Measured DSD Data

    NASA Astrophysics Data System (ADS)

    Liao, L.; Meneghini, R.; Tokay, A.

    2014-12-01

    Accurate attenuation corrections to the measurements of the Ku- and Ka-band dual-wavelength precipitation radar (DPR) aboard the Global Precipitation Measurement (GPM) satellite is crucial for estimates of precipitation rate and microphysical properties of hydrometeors. Surface reference technique (SRT) provides a means to infer path-integrated attenuation (PIA) by comparing differences of normalized surface cross sections (σ0) between rain and rain-free areas. Although single-wavelength SRT has been widely used in attenuation correction for airborne/spaceborne radar applications, its accuracy relies on the variance of σ0 in rain-free region. Dual-wavelength surface reference technique (DSRT) has shown promising ways to improve accuracy in PIA estimates over single-wavelength as a result of that the variance of the difference of PIA between two wavelengths (δPIA) is much smaller than the variance of σ0 at single wavelength arising from high correlation of σ0 between Ku- and Ka-bands. However, derivation of PIA at either wavelength from DSRT requires an assumption of the ratio of Ka- and Ku-band PIAs (p). Inappropriate assumption of this ratio will lead to the bias of PIA estimates. In this study the ratio p will be investigated through measured DSD data. The attenuation coefficients at Ku and Ka bands are first computed directly from measured DSD spectra, and then regression analysis is performed to the data points (Ku- and Ka-band attenuation coefficients) in obtaining p values for rain. Taking an advantage of large collection of the DSD measurements from various GPM Ground Validation (GPM GV) programs, the results of the ratio p will be examined from different climatological regimes. Because PIA is affected by all types of hydrometeors contained in the columns of radar measurements, the synthetic profiles composed of different types of hydrometeors are constructed using measured DSD to look into impacts of different phase hydrometeors on the p values. To generate these profiles fully-, partially- and un-correlated DSD data are employed in an attempt to describe wide dynamic range of microphysical structures of hydrometeors. Bright-band model is employed to take into account of mixed-phase region, and additional attenuations due to cloud water are also included in the profiles.

  16. Modified cavity attenuated phase shift (CAPS) method for airborne aerosol light extinction measurement

    NASA Astrophysics Data System (ADS)

    Perim de Faria, Julia; Bundke, Ulrich; Freedman, Andrew; Petzold, Andreas

    2015-04-01

    Monitoring the direct impact of aerosol particles on climate requires the consideration of at least two major factors: the aerosol single-scattering albedo, defined as the relation between the amount of energy scattered and extinguished by an ensemble of aerosol particles; and the aerosol optical depth, calculated from the integral of the particle extinction coefficient over the thickness of the measured aerosol layer. Remote sensing networks for measuring these aerosol parameters on a regular basis are well in place (e.g., AERONET, ACTRIS), whereas the regular in situ measurement of vertical profiles of atmospheric aerosol optical properties remains still an important challenge in quantifying climate change. The European Research Infrastructure IAGOS (In-service Aircraft for a Global Observing System; www.iagos.org) responds to the increasing requests for long-term, routine in situ observational data by using commercial passenger aircraft as measurement platform. However, scientific instrumentation for the measurement of atmospheric constituents requires major modifications before being deployable aboard in-service passenger aircraft. Recently, a compact and robust family of optical instruments based on the cavity attenuated phase shift (CAPS) technique has become available for measuring aerosol light extinction. In particular, the CAPS PMex particle optical extinction monitor has demonstrated sensitivity of less than 2 Mm-1 in 1 second sampling period; with a 60 s averaging time, a detection limit of less than 0.3 Mm-1 can be achieved. While this technique was successfully deployed for ground-based atmospheric measurements under various conditions, its suitability for operation aboard aircraft in the free and upper free troposphere still has to be demonstrated. Here, we report on the modifications of a CAPS PMex instrument for measuring aerosol light extinction on aircraft, and subsequent laboratory tests for evaluating the modified instrument prototype: (1) In a first set of tests, the robustness of the method was demonstrated down to pressure levels below 200 hPa, using air and CO2 as test gases. Rayleigh scattering cross-section values for both gases deviated by less than 5 % from literature data for all investigated pressure levels.(2) The measurement of aerosol particles at lower pressure levels required the modification of the air flow handling. A new flow scheme using mass flow controllers and a revised vacuum pump set-up was developed and successfully tested. The overall reduction of the instrument noise level to values less than 0.15 Mm-1 was achieved. (3) Polydisperse laboratory-generated ammonium sulphate particles and monodisperse polystyrene latex spheres where used to evaluate the instrument operation for the pressure range from 1000 hPa to less than 200 hPa against an optical particle counter. Reference aerosol extinction coefficients were calculated from measured size distributions, using Mie theory. We found less than 10 % deviation between the CAPS PMex instrument response and calcuated extinction coefficients over the investigated pressure range.

  17. Extracting Earth's Elastic Wave Response from Noise Measurements

    NASA Astrophysics Data System (ADS)

    Snieder, Roel; Larose, Eric

    2013-05-01

    Recent research has shown that noise can be turned from a nuisance into a useful seismic source. In seismology and other fields in science and engineering, the estimation of the system response from noise measurements has proven to be a powerful technique. To convey the essence of the method, we first treat the simplest case of a homogeneous medium to show how noise measurements can be used to estimate waves that propagate between sensors. We provide an overview of physics research—dating back more than 100 years—showing that random field fluctuations contain information about the system response. This principle has found extensive use in surface-wave seismology but can also be applied to the estimation of body waves. Because noise provides continuous illumination of the subsurface, the extracted response is ideally suited for time-lapse monitoring. We present examples of time-lapse monitoring as applied to the softening of soil after the 2011 Tohoku-oki earthquake, the detection of a precursor to a landslide, and temporal changes in the lunar soil.

  18. Measurements of beat wave accelerated electrons in a toroidal plasma

    SciTech Connect

    Rogers, J.H.; Hwang, D.W. |

    1992-06-01

    Electrons are accelerated by large amplitude electron plasma waves driven by counter-propagating microwaves with a difference frequency approximately equal to the electron plasma frequency. Energetic electrons are observed only when the phase velocity of the wave is in the range 3v{sub e} < v{sub ph} < 7v{sub e} (v{sub ph} was varied 2v{sub e} < v{sub ph} < 10v{sub e}), where v{sub e} is the electron thermal velocity, (kT{sub e}/m{sub e}){sup {1/2}}. As the phase velocity increases, fewer electrons are accelerated to higher velocities. The measured current contained in these accelerated electrons has the power dependence predicted by theory, but the magnitude is lower than predicted.

  19. Measurements of attenuation coefficient for evaluating the hardness of a cataract lens by a high-frequency ultrasonic needle transducer

    NASA Astrophysics Data System (ADS)

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

    2009-10-01

    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.

  20. Comparison of speech intelligibility measures for an electronic amplifying earmuff and an identical passive attenuation device

    PubMed Central

    Byrne, David C.; Palmer, Catherine V.

    2012-01-01

    The purpose of this study was to identify any differences between speech intelligibility measures obtained with MineEars electronic earmuffs (ProEars, Westcliffe, CO, USA) and the Bilsom model 847 (Sperian Hearing Protection, San Diego, CA, USA), which is a conventional passive-attenuation earmuff. These two devices are closely related, since the MineEars device consisted of a Bilsom 847 earmuff with the addition of electronic amplification circuits. Intelligibility scores were obtained by conducting listening tests with 15 normal-hearing human subject volunteers wearing the earmuffs. The primary research objective was to determine whether speech understanding differs between the passive earmuffs and the electronic earmuffs (with the volume control set at three different positions) in a background of 90 dB(A) continuous noise. As expected, results showed that speech intelligibility increased with higher speech-to-noise ratios; however, the electronic earmuff with the volume control set at full-on performed worse than when it was set to off or the lowest on setting. This finding suggests that the maximum volume control setting for these electronic earmuffs may not provide any benefits in terms of increased speech intelligibility in the background noise condition that was tested. Other volume control settings would need to be evaluated for their ability to produce higher speech intelligibility scores. Additionally, since an extensive electro-acoustic evaluation of the electronic earmuff was not performed as a part of this study, the exact cause of the reduced intelligibility scores at full volume remains unknown. PMID:26557334

  1. Measurement of chest wall displacement based on terahertz wave

    NASA Astrophysics Data System (ADS)

    Li, Hui; Lv, Hao; Jiao, Teng; Lu, Guohua; Li, Sheng; Li, Zhao; Liu, Miao; Jing, Xijing; Wang, Jianqi

    2015-02-01

    Measurement of chest wall displacement is an important approach for measuring mechanics of chest wall, which has considerable significance for assessing respiratory system and diagnosing pulmonary diseases. However, existing optical methods for measuring chest wall displacement are inconvenient for some specific patients such as the female patients and the patients with bandaged chest. In this letter, we proposed a method for measuring chest wall displacement based on terahertz wave and established corresponding mathematic model and set up a terahertz measurement system. The main advantages of this method are that it can measure the chest wall displacement of the subjects without taking off clothes or arranging any markers. To validate this method and assess the performance of the terahertz system, in vitro, the displacement of a water module driven by a linear guide rail was measured by the terahertz system and compared with the actual displacement of the water module. The results showed that the waveforms measured with two methods have a good agreement, and the relative error is less than 5% and sufficiently good for measurement demands. In vivo, the synchronous experiment was performed on five human volunteers with the terahertz system and a respiratory belt transducer. The results demonstrate that this method has good performance and promising prospects for measuring chest wall displacement.

  2. Measurement of atomic number and mass attenuation coefficient in magnesium ferrite

    NASA Astrophysics Data System (ADS)

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

    2007-05-01

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

  3. Evanescent wave absorption measurements of corroded materials using ATR and optical fibers

    NASA Astrophysics Data System (ADS)

    Namkung, Juock; Hoke, Mike; Schwartz, Andy

    2011-06-01

    The purpose of this research effort is to develop an in-situ corrosion sensing capability. The technique will permit detection of corrosion on and within aircraft structures. This includes component junctions that are susceptible to corrosion but which are not accessible for visual inspection. The prototype experimental configuration we are developing includes long wave infrared transmitting optical fiber probes interfaced with a Fourier Transform Infrared (FTIR) interferometer for evanescent wave absorption spectroscopic measurements. The mature and fielded technique will allow periodic remote sensing for detection of corrosion and for general onboard aircraft structural health monitoring. An experimental setup using an Attenuated Total Reflection (ATR) crystal integrated with an FTIR spectrometer has been assembled. Naturally occurring corrosion including Aluminum Hydroxide [Al(OH)3] is one of the main corrosion products of aluminum the principle structural metal of aircraft. Absorption spectra of our model corrosion product, pure Al(OH)3, have been collected with this ATR/FTIR experimental setup. The Al(OH)3spectra serve as reference spectral signatures. The spectra of corrosion samples from a simulated corrosion process have been collected and compared with the reference Al(OH)3 spectra. Also absorption spectra of naturally occurring corrosion collected from a fielded corroded aircraft part have been obtained and compared with the spectra from the simulated corrosion.

  4. Precipitation-attenuation studies based on measurements of ATS-6 20/30-GHz beacon signals at Clarksburg, Maryland

    NASA Technical Reports Server (NTRS)

    Fang, D. J.; Harris, J. M.

    1976-01-01

    Radiometric sky temperature and minute precipitation measurements were intended to broaden the data base required to advance the understanding of the propagation characteristics of the earth-satellite path at frequencies over 10 GHz. Analyses of the data collected from the measurement program have established a detailed correlation between the satellite signal and the signals from auxiliary ground-based measurements. The indirectly derived statistics agreed reasonably well (or can be reconciled) with the earlier published results. The correlations may therefore be used for indirectly estimating long term cumulative attenuation statistics in the absence of direct satellite signal measurements.

  5. CT-measured bone attenuation in patients with chronic obstructive pulmonary disease: relation to clinical features and outcomes.

    PubMed

    Romme, Elisabeth A P M; Murchison, John T; Edwards, Lisa D; van Beek, Edwin; Murchison, David M; Rutten, Erica P A; Smeenk, Frank W J M; Williams, Michelle C; Wouters, Emiel F M; MacNee, William

    2013-06-01

    Osteoporosis is highly prevalent in chronic obstructive pulmonary disease (COPD) patients and has been related to several clinical features. However, most studies have been in relatively small COPD cohorts. Therefore, the objectives of this study were to compare bone attenuation measured on low-dose chest computed tomography (CT) between COPD subjects and smoker and nonsmoker controls, and to relate bone attenuation to clinical parameters, inflammatory biomarkers, and outcomes in a large, well-characterized COPD cohort. We studied 1634 COPD subjects, 259 smoker controls, and 186 nonsmoker controls who participated in a large longitudinal study (ECLIPSE). We measured bone attenuation, extent of emphysema, and coronary artery calcification (Agatston score) on baseline CT scans, and clinical parameters, inflammatory biomarkers, and outcomes. Bone attenuation was lower in COPD subjects compared with smoker and nonsmoker controls (164.9 ± 49.5 Hounsfield units [HU] versus 183.8 ± 46.1 HU versus 212.1 ± 54.4 HU, p < 0.001). Bone attenuation was not significantly different between COPD subjects and smoker controls after adjustment for age, sex, and pack-years of smoking. In the COPD subjects, bone attenuation correlated positively with forced expiratory volume in 1 second (FEV₁, r = 0.062, p = 0.014), FEV₁/forced vital capacity (FVC) ratio (r = 0.102, p < 0.001), body mass index (r = 0.243, p < 0.001), fat-free mass index (FFMI, r = 0.265, p < 0.001), and C-reactive protein (r = 0.104, p < 0.001), and correlated negatively with extent of emphysema (r = -0.090, p < 0.001), Agatston score (r = -0.177, p < 0.001), and interleukin-8 (r = -0.054, p = 0.035). In a multiple regression model, older age, lower FFMI and higher Agatston score were associated with lower bone attenuation. Lower bone attenuation was associated with higher exacerbation (r = -0.057, p = 0.022) and hospitalization (r = -0.078, p = 0.002) rates but was not associated with all-cause mortality. In conclusion, CT-measured bone attenuation was lower in COPD subjects compared with nonsmoker controls but not compared with smoker controls, after adjustment for age, sex, and pack-years of smoking. In the COPD subjects, bone attenuation was associated with age, body composition, and coronary artery calcification but was not associated with all-cause mortality. PMID:23361992

  6. Measurements of wind velocity and pressure with a wave follower during Marsen

    NASA Technical Reports Server (NTRS)

    Hsiao, S. V.; Shemdim, O. H.

    1983-01-01

    Air pressure data are used in determining the rate of momentum transfer from wind to waves. On the basis of the wind velocity measurements, the wave-induced airflow and its coherence with waves are obtained for various wind velocities and phase speeds of the ocean waves. The pressure results suggest that momentum transfer to waves can be specified by a certain relation, which is given. The wind-velocity results suggest that the wave-induced airflow is much smaller than the mean wind speed. An empirical equation is proposed for the modulation of atmospheric transfer to short waves caused by the orbital velocity of long waves.

  7. 1D model of seismic wave attenuation in the crust and upper mantle in the north-eastern flanc of the Baikal rift system

    NASA Astrophysics Data System (ADS)

    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).

  8. Ground Motion Attenuation and Shear-Wave Splitting Analyses for the November 2011 M5.7 Prague, Oklahoma Earthquake

    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 fluid pressure along the fault, which decreases the fault strength and may induce earthquakes. Based on the proximity of earthquakes to active fluid 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].

  9. Biochemical measurement of bilirubin with an evanescent wave optical sensor

    NASA Astrophysics Data System (ADS)

    Poscio, Patrick; Depeursinge, Christian D.; Emery, Y.; Parriaux, Olivier M.; Voirin, Guy

    1991-09-01

    Optical sensing techniques can be considered as powerful information sources on the biochemistry of tissue, blood, and physiological fluids. Various sensing modalities can be considered: spectroscopic determination of the fluorescence or optical absorption of the biological medium itself, or more generally, of a reagent in contact with the biological medium. The principle and realization of the optical sensor developed are based on the use of polished fibers: the cladding of a monomode fiber is removed on a longitudinal section. The device can then be inserted into an hypodermic needle for in-vivo measurements. Using this minute probe, local measurements of the tissue biochemistry or metabolic processes can be obtained. The sensing mechanism is based on the propagation of the evanescent wave in the tissues or reagent: the proximity of the fiber core allows the penetration of the model field tail into the sensed medium, with a uniquely defined field distribution. Single or multi-wavelength analysis of the light collected into the fiber yields the biochemical information. Here an example of this sensing technology is discussed. In-vitro measurement of bilirubin in gastric juice demonstrates that the evanescent wave optical sensor provides a sensitivity which matches the physiological concentrations. A device is proposed for in-vivo monitoring of bilirubin concentration in the gastro-oesophageal tract.

  10. Blood pulse wave velocity measured by photoacoustic microscopy

    NASA Astrophysics Data System (ADS)

    Yeh, Chenghung; Hu, Song; Maslov, Konstantin; Wang, Lihong V.

    2013-03-01

    Blood pulse wave velocity (PWV) is an important indicator for vascular stiffness. In this letter, we present electrocardiogram-synchronized photoacoustic microscopy for in vivo noninvasive quantification of the PWV in the peripheral vessels of mice. Interestingly, strong correlation between blood flow speed and ECG were clearly observed in arteries but not in veins. PWV is measured by the pulse travel time and the distance between two spot of a chose vessel, where simultaneously recorded electrocardiograms served as references. Statistical analysis shows a linear correlation between the PWV and the vessel diameter, which agrees with known physiology. Keywords: photoacoustic microscopy, photoacoustic spectroscopy, bilirubin, scattering medium.