Science.gov

Sample records for wave attenuation measurements

  1. 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.

  2. 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...

  3. 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.

  4. 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.

  5. 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.

  6. Array-based measurements of surface wave dispersion and attenuation using frequency-wavenumber analysis

    NASA Astrophysics Data System (ADS)

    Yoon, Sungsoo

    2005-07-01

    Surface wave methods have been used to determine dynamic properties of near-surface soils in geotechnical engineering for the past 50 years. Although the capabilities of engineering surface wave methods have improved in recent years due to several advances, several issues including (1) near-field effects, (2) combined active and passive measurements, and (3) accurate measurements of surface wave attenuation still require study to further improve the capabilities of modern surface wave methods. Near-field effects have been studied for traditional surface wave methods with two receivers and several filtering criteria to mitigate the effects have been recommended. However, these filtering criteria are not applicable to surface wave methods with multiple receivers. Moreover, the criteria are not quantitatively based and do not account for different types of soil profiles, which strongly influence near-field effects. A new study of near-field effects on surface wave methods with multiple receivers was conducted with numerical and experimental methods. Two normalized parameters were developed to capture near-field effects. Quantitatively based near-field effect criteria for an ideal homogeneous half-space and three typical soil profiles are presented. Combining active and passive surface wave measurements allows developing a shear wave velocity profile to greater depth without sacrificing the near-surface resolution offered by active measurements. Generally, active and passive measurements overlap in the frequency range from approximately 4 to 10 Hz, and there are often systematic differences between the two measurements. The systematic errors in active and passive surface wave methods were explored to explain and resolve the differences, allowing for a more accurate composite dispersion curve. The accuracy of measured surface wave attenuation is improved by properly accounting for (1) geometric spreading, (2) near-field effects, and (3) ambient noise. In this study, a

  7. A novel protocol to measure the attenuation of electromagnetic waves through smoke

    NASA Astrophysics Data System (ADS)

    Yan-wu, Li; Hong-yong, Yuan; Yang, Lu; Xiaoxiang, Zhang; Ru-feng, Xu; Ming, Fu

    2016-06-01

    The electromagnetic properties of smoke from a structure fire are important in terms of their relation to the stability of wireless communication systems used in fire rescue. As it is hard to make a measurable electromagnetic environment for particles in the air, compressed and bulk samples are used instead to measure sand storms and smoke plumes. In this paper, an experiment system was designed to measure smoke particles in the air, in consideration of both smoke control and electromagnetic measurement. Several measures had been taken to create a fulfilled smoke environment. The simulated and measured transmission parameters of the electromagnetic testing area were approximate and the electromagnetic wave frequencies were set from 350 to 400 MHz. Repeated experiments have been conducted to test the stability of the results and they showed that there was no obvious attenuation until the smoke concentration was more than 10 dB m-1. It was found that the frequency around 355 and 360 MHz had a larger attenuation coefficient. The relationship between the attenuation coefficient and the smoke concentration was concluded to be linear. The results may help us understand the attenuation of electromagnetic waves within a smoke column.

  8. Seismic Attenuation of Teleseismic Body Waves in Cascadia, Measured on the Amphibious Array

    NASA Astrophysics Data System (ADS)

    Eilon, Z.; Abers, G. A.

    2015-12-01

    Fundamental questions remain about the nature of the asthenosphere, including its dynamical relationship to overlying lithosphere, melt content, and entrainment in subduction zones. We examine the evolution of this low-velocity, highly attenuating layer using data from the Cascadia Initiative's Amphibious Array, which provides unprecedented coverage of an oceanic plate from ridge crest to trench to sub-arc. Our study extends the suite of measurements achievable with OBS data, augmenting traditional travel time analysis with integrated attenuation data that are a powerful tool for imaging melt/fluids and the variation of asthenospheric character with age. Cooling models, coupled with experimentally-derived anelastic scaling relationships, indicate that thermal gradients should cause appreciable decrease in attenuation of teleseismic body waves with increasing age. This long-wavelength cooling trend may be perturbed by highly attenuating melt or volatiles concentrated at the ridge axis or beneath the Cascades arc, depending on melt fraction and pore geometry. Attenuation beyond the trench should be a strong function of the fate of asthenospheric entrainment beneath subducted plates, with implications for mass transfer to the deep mantle as well as recent models of sub-slab anisotropy. The Amphibious Array, with <70 km spacing of OBS and on-land broadband seismometers deployed between 2011 and 2015, provides a dataset of ~1 x 105 arrivals from ~700 Mw>6.0 teleseismic earthquakes. We use a spectral ratio method to compute differential attenuation (Δt*) from body wave teleseisms recorded at OBS and land stations, allowing us to estimate path-integrated quality factor in the upper mantle. Preliminary results reveal variations of ~3 s in differential travel time and >0.5 s in ΔtS* across the 0-10 Ma oceanic plate, demonstrating the strong thermal control on anelasticity. Large values of Δt* observed east of the trench may indicate entrainment of highly attenuating

  9. Measurements of frequency dependent shear wave attenuation in sedimentary basins using induced earthquakes

    NASA Astrophysics Data System (ADS)

    Richter, Tom; Wegler, Ulrich

    2015-04-01

    Modeling of peak ground velocity caused by induced earthquakes requires detailed knowledge about seismic attenuation properties of the subsurface. Especially shear wave attenuation is important, because shear waves usually show the largest amplitude in high frequency seismograms. We report intrinsic and scattering attenuation coefficients of shear waves near three geothermal reservoirs in Germany for frequencies between 2 Hz and 50 Hz. The geothermal plants are located in the sedimentary basins of the upper Rhine graben (Insheim and Landau) and the Molasse basin (Unterhaching). The method optimizes the fit between Green's functions for the acoustic, isotropic radiative transfer theory and observed energy densities of induced earthquakes. The inversion allows the determination of scattering and intrinsic attenuation, site corrections, and spectral source energies for the investigated frequency bands. We performed the inversion at the three sites for events with a magnitude between 0.7 and 2. We determined a transport mean free path of 70 km for Unterhaching. For Landau and Insheim the transport mean free path depends on frequency. It ranges from 2 km (at 2 Hz) to 30 km (at 40 Hz) for Landau and from 9 km to 50 km for Insheim. The quality factor for intrinsic attenuation is constant for frequencies smaller than 10 Hz at all three sites. It is around 100 for Unterhaching and 200 for Landau and Insheim with higher values above 10 Hz.

  10. Measurements of seismic wave attenuation for frequencies between 0.1 and 100 Hz in a Paterson Rig

    NASA Astrophysics Data System (ADS)

    Madonna, C.; Tisato, N.; Delle Piane, C.; Saenger, E. H.

    2012-04-01

    The study of wave attenuation in partially saturated porous rocks over a broad frequency range provides valuable information about reservoir fluid systems, which are inherently composed of multiple phase fluid. Following an original idea initiated by Luigi, we designed and set up a specific instrument, the Seismic Wave Attenuation Module (SWAM), to experimentally measure the bulk attenuation on partially saturated rocks at frequencies between 0.01 and 100 Hz, using natural rock samples under in situ conditions. We present its bench-top calibration, a series of data collected from different kind of rocks at different confing pressure and the numerical simulations, supporting the obtained results. We employ the sub-resonance test. Assuming that the rock behaves as a linear time invariant (LTI) system, the attenuation factor 1/Q (Q is the quality factor) is equal to the tangent of the phase shift between the stress and the strain signal. The new attenuation measurement equipment is calibrated in a gas apparatus (Paterson rig) using aluminum as elastic standard and Plexiglas as a viscoelastic standard. Measurements were performed on 25.4 mm diameter, 60 mm long samples. Berea sandstone samples with 20% porosity, and ~500 mD permeability have been measured at different saturation conditions. Attenuation measurements show dependence upon saturation. Moreover, measurements on two well-characterized shale samples have been performed. The two shales have significantly different quality factors; which result to be dependent on both the saturation state of the samples and the propagation direction of the oscillatory signal with respect to the sedimentary bedding. The attenuation coefficient parallel to bedding is less than that vertical to bedding. Thanks to Luigi's initiative and inspiration two generations of his Ph.D. students are now able to jointly present these new challenging experimental results.

  11. Imaging Rayleigh wave attenuation with USArray

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

    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 traveltime 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 traveltime 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.

  12. 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.

  13. Measurement and parameterization of wave attenuation and scattering in the Marginal Ice Zone using Sentinel-1 SAR data

    NASA Astrophysics Data System (ADS)

    Collard, F.; Ardhuin, F.; Guitton, G.; Dumont, D.; Nicot, P.; Accenti, M.; Girard-Ardhuin, F.

    2014-12-01

    Sentinel-1A launched by the European Space Agency in April 2014 will complete its full calibration and validation phase including Level2 products early in 2015 but image quality is already good enought for scientific exploitation of observed wave modulations. The larger frequency bandwidth and new acquisition modes are providing a much improved capability for imaging ocean waves in the open water and in the ice compared to Envisat. Here we estimate wave spectra in the Arctic assuming a spatially uniform modulation transfer function where the backscatter over ice is homogeneous, matching the wave heights in open ocean and ice at the ice edge. These wave properties are used to estimate attenuation scales for wavelength longer than twice the radar image resolution. These estimated attenuations are compared to model results based on WAVEWATCH III, where attenuation and scattering uses a combination of friction below the ice and scattering adapted from Dumont et al. (2011) and Williams et al. (2013).

  14. Wave Attenuation in Partially Saturated Porous Solids.

    NASA Astrophysics Data System (ADS)

    Yin, Chuan-Sheng

    1992-01-01

    This thesis consists of three independent papers. Paper 1 studies effects of pulsating gas pockets on wave propagation in partially saturated porous solids containing both liquid and gas phases. On the basis of Biot theory, an analytic solution for the White model for study of the effects of saturation history on wave attenuation is derived. One of the most significant findings of this work is that when the average spacing among the neighboring gas pockets is of the order of the boundary-layer thickness associated with the slow compressional (or P2) wave, the attenuation of the compressional (or P) wave due to local fluid flow reaches its maximum. Results of Paper 1 bear direct applications to seismic and logging responses of partially saturated rocks in prospecting for petroleum, and monitoring of oil and natural gas reservoirs. Paper 2 presents the results of the experimental studies of the effects of partial liquid/gas saturation on extensional wave attenuation in Berea sandstones. Two experimental methods are used; one is the resonant-bar method and the other the forced-deformation method. It is found that the wave attenuation depends on sample-saturation history (drainage or imbibition), as well as boundary-flow conditions, and the degree of saturation. The attenuation caused by "flowable" liquid is sensitive only in the region of low degree of gas saturation. An open-pore boundary tends to induce higher attenuation. The results obtained by the forced-deformation method show that the magnitude of the attenuation decreases substantially with decreasing frequency to the extent that no attenuation peak was apparent at frequencies below 100 Hz. Paper 3 analyzes extensional wave propagation in a porous fluid-saturated hollow-cylinder of infinite extent. Analytic solutions of complex Young's modulus for the long wavelength limit was obtained for a hollow -cylinder with open-pore inner surface. A simplified formula for estimating the frequency at which the

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

    NASA Astrophysics Data System (ADS)

    Hudier, E. J.; Bahoura, M.

    2012-12-01

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

  16. Attenuation of sound waves in drill strings

    SciTech Connect

    Drumheller, D.S. )

    1993-10-01

    During drilling of deep wells, digital data are often transmitted from sensors located near the drill bit to the surface. Development of a new communication system with increased data capacity is of paramount importance to the drilling industry. Since steel drill strings are used, transmission of these data by elastic carrier waves traveling within the drill pipe is possible, but the potential communication range is uncertain. The problem is complicated by the presence of heavy-threaded tool joints every 10 m, which form a periodic structure and produce classical patterns of passbands and stop bands in the wave spectra. In this article, field measurements of the attenuation characteristics of a drill string in the Long Valley Scientific Well in Mammoth Lakes, California are presented. Wave propagation distances approach 2 km. A theoretical model is discussed which predicts the location, width, and attenuation of the passbands. Mode conversion between extensional and bending waves, and spurious reflections due to deviations in the periodic spacings of the tool joints are believed to be the sources of this attenuation. It is estimated that attenuation levels can be dramatically reduced by rearranging the individual pipes in the drill string according to length. 7 refs., 20 figs., 4 tabs.

  17. Bubbles attenuate elastic waves at seismic frequencies

    NASA Astrophysics Data System (ADS)

    Tisato, Nicola; Quintal, Beatriz; Chapman, Samuel; Podladchikov, Yury; Burg, Jean-Pierre

    2016-04-01

    The vertical migration of multiphase fluids in the crust can cause hazardous events such as eruptions, explosions, pollution and earthquakes. Although seismic tomography could potentially provide a detailed image of such fluid-saturated regions, the interpretation of the tomographic signals is often controversial and fails in providing a conclusive map of the subsurface saturation. Seismic tomography should be improved considering seismic wave attenuation (1/Q) and the dispersive elastic moduli which allow accounting for the energy lost by the propagating elastic wave. In particular, in saturated media a significant portion of the energy carried by the propagating wave is dissipated by the wave-induced-fluid-flow and the wave-induced-gas-exsolution-dissolution (WIGED) mechanisms. The WIGED mechanism describes how a propagating wave modifies the thermodynamic equillibrium between different fluid phases causing the exsolution and the dissolution of the gas in the liquid, which in turn causes a significant frequency dependent 1/Q and moduli dispersion. The WIGED theory was initially postulated for bubbly magmas but only recently was extended to bubbly water and experimentally demonstrated. Here we report these theory and laboratory experiments. Specifically, we present i) attenuation measurements performed by means of the Broad Band Attenuation Vessel on porous media saturated with water and different gases, and ii) numerical experiments validating the laboratory observations. Finally, we will extend the theory to fluids and to pressure-temperature conditions which are typical of phreatomagmatic and hydrocarbon domains and we will compare the propagation of seismic waves in bubble-free and bubble-bearing subsurface domains. With the present contribution we extend the knowledge about attenuation in rocks which are saturated with multiphase fluid demonstrating that the WIGED mechanism could be extremely important to image subsurface gas plumes.

  18. 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.

  19. Graphene-Based Waveguide Terahertz Wave Attenuator

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

    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.

  20. UHF Radio Wave Attenuation Factor Database

    NASA Astrophysics Data System (ADS)

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

    2007-07-01

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

  1. Imaging Rayleigh Wave Attenuation Beneath North America with USArray

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

    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. Surface-wave amplitudes are sensitive to factors in addition to attenuation, including source excitation, focusing 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. We consider three different approaches for separating the effects of local site amplification and attenuation on the amplitude measurements. The attenuation values determined with these three approaches contain the same first-order features, which gives us confidence that these features are robust: high attenuation in the western U.S. and low attenuation in the central and eastern U.S., with slightly higher attenuation along the eastern seaboard. However, we also identify several areas where we suspect the imaged attenuation values reflect unmodelled focusing effects rather than anelastic attenuation. We therefore identify attenuation values that are likely contaminated by unmodelled focusing effects using the Laplacian of the phase-velocity map, eliminate those values, and generate 2-D attenuation maps through a regional average of the remaining values. We also investigate the range of intrinsic shear-attenuation values that are suggested by the Rayleigh wave attenuation maps at periods between 40 and 80 s. This preliminary model is the

  2. Waves in fragmented geomaterials with impact attenuation

    NASA Astrophysics Data System (ADS)

    Dyskin, Arcady; Pasternak, Elena

    2016-04-01

    Attenuation of waves in geomaterials, such as seismic waves is usually attributed to energy dissipation due to the presence of viscous fluid and/or viscous cement between the constituents. In fragmented geomaterials such as blocky rock mass there is another possible source of energy dissipation - impacting between the fragments. This can be characterised by the coefficient of restitution, which is the ratio between the rotational velocities after and before the impact. In particular, this manifests itself in the process of mutual rotations of the fragments/blocks, whereby in the process of oscillation different ends of the contacting faces of the fragments are impacting. During the rotational oscillations the energy dissipation is concentrated in the neutral position that is the one in which the relative rotation between two fragments is zero. We show that in a simple system of two fragments this dissipation is equivalent, in a long run, to the presence of viscous damper between the fragments (the Voigt model of visco-elasticity). Generalisation of this concept to the material consisting of many fragments leads to a Voigt model of wave propagation where the attenuation coefficient is proportional to the logarithm of restitution coefficient. The waves in such a medium show slight dispersion caused by damping and strong dependence of the attenuation on the wave frequency.

  3. 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.

  4. Attenuation of ultrasonic waves in rolled metals

    NASA Astrophysics Data System (ADS)

    Yang, Liyong; Turner, Joseph A.

    2004-12-01

    Scattering of ultrasonic waves in polycrystals with texture is studied in this article. The attenuations of the three wave modes are determined as a function of dimensionless frequency and propagation direction, respectively, for given orientation distribution coefficients (ODCs). The calculation is done in the case of a statistically orthorhombic sample made up of cubic crystallites. The wave propagation and scattering model is formulated by the Dyson equation using an anisotropic Green's function approach. Within the limits of the first-order smoothing approximation, the Dyson equation is solved in the spatial Fourier transform domain. The results presented are shown to be directional dependent, frequency dependent, and especially dependent on the texture coefficients (ODCs) for the quasilongitudinal and two quasishear waves. The theoretical results presented may be used to improve the understanding of the microstructure during recrystallization processes. .

  5. Attenuation of ultrasonic waves in rolled metals.

    PubMed

    Yang, Liyong; Turner, Joseph A

    2004-12-01

    Scattering of ultrasonic waves in polycrystals with texture is studied in this article. The attenuations of the three wave modes are determined as a function of dimensionless frequency and propagation direction, respectively, for given orientation distribution coefficients (ODCs). The calculation is done in the case of a statistically orthorhombic sample made up of cubic crystallites. The wave propagation and scattering model is formulated by the Dyson equation using an anisotropic Green's function approach. Within the limits of the first-order smoothing approximation, the Dyson equation is solved in the spatial Fourier transform domain. The results presented are shown to be directional dependent, frequency dependent, and especially dependent on the texture coefficients (ODCs) for the quasilongitudinal and two quasishear waves. The theoretical results presented may be used to improve the understanding of the microstructure during recrystallization processes.

  6. Review of methods to attenuate shock/blast waves

    NASA Astrophysics Data System (ADS)

    Igra, O.; Falcovitz, J.; Houas, L.; Jourdan, G.

    2013-04-01

    Quick and reliable shock wave attenuation is the goal of every protection facility and therefore it is not surprising that achieving this has drawn much attention during the past hundred years. Different options have been suggested; their usefulness varying from a reasonable protection to the opposite, a shock enhancement. An example for a suggestion for shock mitigation that turned out to be an enhancement of the impinging shock wave was the idea to cover a protected object with a foam layer. While the pressure behind the reflected shock wave from the foam frontal surface was smaller than that recorded in a similar reflection from a rigid wall [25], the pressure on the “protected” surface, attached to the foam's rear-surface, was significantly higher than that recorded in a similar reflection from a bare, rigid wall [11]. In protecting humans and installations from destructive shock and/or blast waves the prime goal is to reduce the wave amplitude and the rate of pressure increase across the wave front. Both measures result in reducing the wave harmful effects. During the past six decades several approaches for achieving the desired protection have been offered in the open literature. We point out in this review that while some of the suggestions offered are practical, others are impractical. In our discussion we focus on recent schemes for shock/blast wave attenuation, characterized by the availability of reliable measurements (notably pressure and optical diagnostics) as well as high-resolution numerical simulations.

  7. Attenuation of 7 GHz surface acoustic waves on silicon

    NASA Astrophysics Data System (ADS)

    Li, Dongyao; Cahill, David G.

    2016-09-01

    We measured the attenuation of GHz frequency surface acoustic waves (SAWs) on the Si (001) surface using an optical pump-probe technique at temperatures between 300 and 600 K. SAWs are generated and detected by a 700 nm Al grating fabricated by nanoimprint lithography. The grating for SAW generation is separated from the grating for SAW detection by ≈150 μ m . The amplitude of SAWs is attenuated by coupling to bulk waves created by the Al grating, diffraction due to the finite size of the source, and the intrinsic relaxational Akhiezer damping of elastic waves in Si. Thermal phonon relaxation time and Grüneisen parameters are fitted using temperature-dependent measurement. The f Q product of a hypothetical micromechanical oscillator limited by Akhiezer damping at this frequency is ˜3 ×1013 Hz.

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

    NASA Astrophysics Data System (ADS)

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

    2007-05-01

    Communities of benthic organisms can form very rough surfaces (canopies) on the seafloor. Previous studies have shown that an oscillatory flow induced by monochromatic surface waves will drive more flow inside a canopy than a comparable unidirectional current. This paper builds on these previous studies by investigating how wave energy is attenuated within canopies under spectral wave conditions, or random wave fields defined by many frequencies. A theoretical model is first developed to predict how flow attenuation within a canopy varies among the different wave components and predicts that shorter-period components will generally be more effective at driving flow within a canopy than longer-period components. To investigate the model performance, a field experiment was conducted on a shallow reef flat in which flow was measured both inside and above a model canopy array. Results confirm that longer-period components in the spectrum are significantly more attenuated than shorter-period components, in good agreement with the model prediction. This paper concludes by showing that the rate at which wave energy is dissipated by a canopy is closely linked to the flow structure within the canopy. Under spectral wave conditions, wave energy within a model canopy array is dissipated at a greater rate among the shorter-period wave components. These observations are consistent with previous observations of how wave energy is dissipated by the bottom roughness of a coral reef.

  9. Phase Aberration and Attenuation Effects on Acoustic Radiation Force-Based Shear Wave Generation.

    PubMed

    Carrascal, Carolina Amador; Aristizabal, Sara; Greenleaf, James F; Urban, Matthew W

    2016-02-01

    Elasticity is measured by shear wave elasticity imaging (SWEI) methods using acoustic radiation force to create the shear waves. Phase aberration and tissue attenuation can hamper the generation of shear waves for in vivo applications. In this study, the effects of phase aberration and attenuation in ultrasound focusing for creating shear waves were explored. This includes the effects of phase shifts and amplitude attenuation on shear wave characteristics such as shear wave amplitude, shear wave speed, shear wave center frequency, and bandwidth. Two samples of swine belly tissue were used to create phase aberration and attenuation experimentally. To explore the phase aberration and attenuation effects individually, tissue experiments were complemented with ultrasound beam simulations using fast object-oriented C++ ultrasound simulator (FOCUS) and shear wave simulations using finite-element-model (FEM) analysis. The ultrasound frequency used to generate shear waves was varied from 3.0 to 4.5 MHz. Results: The measured acoustic pressure and resulting shear wave amplitude decreased approximately 40%-90% with the introduction of the tissue samples. Acoustic intensity and shear wave displacement were correlated for both tissue samples, and the resulting Pearson's correlation coefficients were 0.99 and 0.97. Analysis of shear wave generation with tissue samples (phase aberration and attenuation case), measured phase screen, (only phase aberration case), and FOCUS/FEM model (only attenuation case) showed that tissue attenuation affected the shear wave generation more than tissue aberration. Decreasing the ultrasound frequency helped maintain a focused beam for creation of shear waves in the presence of both phase aberration and attenuation.

  10. Wave attenuation in the shallows of San Francisco Bay

    USGS Publications Warehouse

    Lacy, Jessica R.; MacVean, Lissa J.

    2016-01-01

    Waves propagating over broad, gently-sloped shallows decrease in height due to frictional dissipation at the bed. We quantified wave-height evolution across 7 km of mudflat in San Pablo Bay (northern San Francisco Bay), an environment where tidal mixing prevents the formation of fluid mud. Wave height was measured along a cross shore transect (elevation range−2mto+0.45mMLLW) in winter 2011 and summer 2012. Wave height decreased more than 50% across the transect. The exponential decay coefficient λ was inversely related to depth squared (λ=6×10−4h−2). The physical roughness length scale kb, estimated from near-bed turbulence measurements, was 3.5×10−3 m in winter and 1.1×10−2 m in summer. Estimated wave friction factor fw determined from wave-height data suggests that bottom friction dominates dissipation at high Rew but not at low Rew. Predictions of near-shore wave height based on offshore wave height and a rough formulation for fw were quite accurate, with errors about half as great as those based on the smooth formulation for fw. Researchers often assume that the wave boundary layer is smooth for settings with fine-grained sediments. At this site, use of a smooth fw results in an underestimate of wave shear stress by a factor of 2 for typical waves and as much as 5 for more energetic waves. It also inadequately captures the effectiveness of the mudflats in protecting the shoreline through wave attenuation.

  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. 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.

  13. Wave dispersion and attenuation on human femur tissue.

    PubMed

    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

  14. 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.

  15. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2013-11-01

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

  17. Attenuation of electromagnetic wave propagation in sandstorms incorporating charged sand particles

    NASA Astrophysics Data System (ADS)

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

    2005-06-01

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

  18. 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.

  19. Attenuation of Seismic Waves by Grain Boundary Relaxation

    PubMed Central

    Jackson, David D.

    1971-01-01

    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

  20. 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.

  1. Wave velocity dispersion and attenuation in media exhibiting internal oscillations

    NASA Astrophysics Data System (ADS)

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

    2010-05-01

    an arbitrary number of oscillators with different resonance frequencies. Exemplarily, we show a log-normal distribution of resonance frequencies. Such a distribution changes the acoustic properties significantly compared to the case with only one resonance frequency. The dispersion and attenuation resulting from our model agree well with the dispersion and attenuation (1) derived with a more exact mathematical treatment and (2) measured in laboratory experiments. (2) Three-phase model for residually saturated porous media We present a three-phase model describing wave propagation phenomena in residually saturated porous media. The model consists of a continuous non-wetting phase and a discontinuous wetting phase and is an extension of classical biphasic (Biot-type) models. The model includes resonance effects of single liquid bridges or liquid clusters with miscellaneous eigenfrequencies taking into account a visco-elastic restoring force (pinned oscillations and/or sliding motion of the contact line). In the present investigation, our aim is to study attenuation due to fluid oscillations and due to wave-induced flow with a macroscopic three-phase continuum model, i.e. a mixture consisting of one solid constituent building the elastic skeleton and two immiscible fluid constituents. Furthermore, we study monochromatic waves in transversal and longitudinal direction and discuss the resulting dispersion relations for a typical reservoir sandstone equivalent (Berea sandstone).

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

    PubMed Central

    Nelson, Amber M.; Hoffman, Joseph J.; Anderson, Christian C.; Holland, Mark R.; Nagatani, Yoshiki; Mizuno, Katsunori; Matsukawa, Mami; Miller, James G.

    2011-01-01

    Previous studies have shown that interference between fast waves and slow waves can lead to observed negative dispersion in cancellous bone. In this study, the effects of overlapping fast and slow waves on measurements of the apparent attenuation as a function of propagation distance are investigated along with methods of analysis used to determine the attenuation properties. Two methods are applied to simulated data that were generated based on experimentally acquired signals taken from a bovine specimen. The first method uses a time-domain approach that was dictated by constraints imposed by the partial overlap of fast and slow waves. The second method uses a frequency-domain log-spectral subtraction technique on the separated fast and slow waves. Applying the time-domain analysis to the broadband data yields apparent attenuation behavior that is larger in the early stages of propagation and decreases as the wave travels deeper. In contrast, performing frequency-domain analysis on the separated fast waves and slow waves results in attenuation coefficients that are independent of propagation distance. Results suggest that features arising from the analysis of overlapping two-mode data may represent an alternate explanation for the previously reported apparent dependence on propagation distance of the attenuation coefficient of cancellous bone. PMID:21973378

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

    PubMed

    Nelson, Amber M; Hoffman, Joseph J; Anderson, Christian C; Holland, Mark R; Nagatani, Yoshiki; Mizuno, Katsunori; Matsukawa, Mami; Miller, James G

    2011-10-01

    Previous studies have shown that interference between fast waves and slow waves can lead to observed negative dispersion in cancellous bone. In this study, the effects of overlapping fast and slow waves on measurements of the apparent attenuation as a function of propagation distance are investigated along with methods of analysis used to determine the attenuation properties. Two methods are applied to simulated data that were generated based on experimentally acquired signals taken from a bovine specimen. The first method uses a time-domain approach that was dictated by constraints imposed by the partial overlap of fast and slow waves. The second method uses a frequency-domain log-spectral subtraction technique on the separated fast and slow waves. Applying the time-domain analysis to the broadband data yields apparent attenuation behavior that is larger in the early stages of propagation and decreases as the wave travels deeper. In contrast, performing frequency-domain analysis on the separated fast waves and slow waves results in attenuation coefficients that are independent of propagation distance. Results suggest that features arising from the analysis of overlapping two-mode data may represent an alternate explanation for the previously reported apparent dependence on propagation distance of the attenuation coefficient of cancellous bone.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. [Attenuation of photosynthetically available radiation (PAR) in Meiliang Bay under different winds and waves].

    PubMed

    Zhang, Yunlin; Qin, Boqiang; Chen, Weimin; Hu, Weiping; Gao, Guang; Zhu, Guangwei; Luo, Liancong

    2005-06-01

    Based on the successive underwater irradiance measurement in situ from Jul. 12 to 17 in 2003, the attenuation of photosynthetically available radiation (PAR) and euphotic depth in Meiliang Bay were analyzed under different winds and waves. The results showed that the downward PAR attenuation coefficients ranged from 2.63 to 4.7 m(-1), with an average of 3.63 +/- 0.47 x m(-1), and the corresponding euphotic depth ranged from 0.98 to 1.75 m, with an average of 1.29 +/- 0.18 m, which demonstrated that phytoplankton and macrophyte could not grow below 1.5 m due to the lack of adequate solar radiation. The total suspended solids resulted from wind and wave increased the attenuation of light, with the downward attenuation coefficients of PAR being 2.63, 3.72 and 4.37 x m(-1) under small, medium and large wind and wave, respectively. Significant linear correlations were found between transparence, PAR attenuation coefficient, euphotic depth and total suspended solid, especially inorganic suspended solid, while chlorophyll a was the most nonsignificant light attenuator. Multiple stepwise linear regressions showed that inorganic suspended solid was the most important light attenuator dominating the light attenuation in wind-exposed Meiliang Bay.

  10. [Attenuation of photosynthetically available radiation (PAR) in Meiliang Bay under different winds and waves].

    PubMed

    Zhang, Yunlin; Qin, Boqiang; Chen, Weimin; Hu, Weiping; Gao, Guang; Zhu, Guangwei; Luo, Liancong

    2005-06-01

    Based on the successive underwater irradiance measurement in situ from Jul. 12 to 17 in 2003, the attenuation of photosynthetically available radiation (PAR) and euphotic depth in Meiliang Bay were analyzed under different winds and waves. The results showed that the downward PAR attenuation coefficients ranged from 2.63 to 4.7 m(-1), with an average of 3.63 +/- 0.47 x m(-1), and the corresponding euphotic depth ranged from 0.98 to 1.75 m, with an average of 1.29 +/- 0.18 m, which demonstrated that phytoplankton and macrophyte could not grow below 1.5 m due to the lack of adequate solar radiation. The total suspended solids resulted from wind and wave increased the attenuation of light, with the downward attenuation coefficients of PAR being 2.63, 3.72 and 4.37 x m(-1) under small, medium and large wind and wave, respectively. Significant linear correlations were found between transparence, PAR attenuation coefficient, euphotic depth and total suspended solid, especially inorganic suspended solid, while chlorophyll a was the most nonsignificant light attenuator. Multiple stepwise linear regressions showed that inorganic suspended solid was the most important light attenuator dominating the light attenuation in wind-exposed Meiliang Bay. PMID:16180769

  11. On wave radar measurement

    NASA Astrophysics Data System (ADS)

    Ewans, Kevin; Feld, Graham; Jonathan, Philip

    2014-09-01

    The SAAB REX WaveRadar sensor is widely used for platform-based wave measurement systems by the offshore oil and gas industry. It offers in situ surface elevation wave measurements at relatively low operational costs. Furthermore, there is adequate flexibility in sampling rates, allowing in principle sampling frequencies from 1 to 10 Hz, but with an angular microwave beam width of 10° and an implied ocean surface footprint in the order of metres, significant limitations on the spatial and temporal resolution might be expected. Indeed there are reports that the accuracy of the measurements from wave radars may not be as good as expected. We review the functionality of a WaveRadar using numerical simulations to better understand how WaveRadar estimates compare with known surface elevations. In addition, we review recent field measurements made with a WaveRadar set at the maximum sampling frequency, in the light of the expected functionality and the numerical simulations, and we include inter-comparisons between SAAB radars and buoy measurements for locations in the North Sea.

  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. Pressure wave attenuation and dispersion in two-phase flow

    SciTech Connect

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

    1987-01-01

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

  14. Measuring Acoustic Nonlinearity by Collinear Mixing Waves

    NASA Astrophysics Data System (ADS)

    Liu, M.; Tang, G.; Jacobs, L. J.; Qu, J.

    2011-06-01

    It is well known that the acoustic nonlinearity parameter β is correlated to fatigue damage in metallic materials. Various methods have been developed to measure β. One of the most often used methods is the harmonic generation technique, in which β is obtained by measuring the magnitude of the second order harmonic waves. An inherent weakness of this method is the difficulty in distinguishing material nonlinearity from the nonlinearity of the measurement system. In this paper, we demonstrate the possibility of using collinear mixing waves to measure β. The wave mixing method is based on the interaction between two incident waves in a nonlinear medium. Under certain conditions, such interactions generate a third wave of different frequency. This generated third wave is also called resonant wave, because its amplitude is unbounded if the medium has no attenuation. Such resonant waves are less sensitive to the nonlinearity of the measurement system, and have the potential to identify the source location of the nonlinearity. In this work, we used a longitudinal wave and a shear wave as the incident waves. The resonant shear wave is measured experimentally on samples made of aluminum and steel, respectively. Numerical simulations of the tests were also performed using a finite difference method.

  15. Modeling of aqueous foam blast wave attenuation

    NASA Astrophysics Data System (ADS)

    Del Prete, E.; Chinnayya, A.; Hadjadj, A.; Domergue, L.; Haas, J.-F.; Imbert, B.

    The use of aqueous foams enables the mitigation of blast waves induced by the explosion of energetic materials. The two-phase confinement gives rise to interphase interactions between the gaseous and liquid phases, which role have been emphasized in shock-tube studies with solid foams [1, 2]. Multifluid formalism enables the thermo-mechanical disequilibria between phases to be taken into account. The flow model ensures the correct estimation of the acoustic impedance of the two-phase media. As for the numerical scheme, Riemann solvers are used to describe the microscopic fluid interactions, the summation of which provides the multiphase flux. The role of the different transfer mechanisms is evaluated in the case where the liquid ligaments of the foam matrix have been shattered into droplets by the shock impingement. Characteristics of blast waves in heterogeneous media leads to a decrease of overpressure. The numerical results have been compared favorably to experimental data [3, 4].

  16. Generating attenuation-resistant frozen waves in absorbing fluid.

    PubMed

    Dorrah, Ahmed H; Zamboni-Rached, Michel; Mojahedi, Mo

    2016-08-15

    We demonstrate a class of nondiffracting beams, called frozen waves, with a central spot that can be made to maintain a predefined intensity profile while propagating in an absorbing fluid. Frozen waves are composed of Bessel beams with different transverse and longitudinal wavenumbers, and are generated using a programmable spatial light modulator. The attenuation-resistant frozen waves demonstrated here address the problem of propagation losses in absorbing media. This development can be beneficial for many applications in particle micro-manipulation, data communications, remote sensing, and imaging. PMID:27519067

  17. Generating attenuation-resistant frozen waves in absorbing fluid.

    PubMed

    Dorrah, Ahmed H; Zamboni-Rached, Michel; Mojahedi, Mo

    2016-08-15

    We demonstrate a class of nondiffracting beams, called frozen waves, with a central spot that can be made to maintain a predefined intensity profile while propagating in an absorbing fluid. Frozen waves are composed of Bessel beams with different transverse and longitudinal wavenumbers, and are generated using a programmable spatial light modulator. The attenuation-resistant frozen waves demonstrated here address the problem of propagation losses in absorbing media. This development can be beneficial for many applications in particle micro-manipulation, data communications, remote sensing, and imaging.

  18. 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.

  19. 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

  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. Attenuation Tomography of Body Waves in Thickness-varying Layered Media

    NASA Astrophysics Data System (ADS)

    Cao, H.; Zhou, H.

    2006-12-01

    The intrinsic attenuation of seismic waves, which is quantified as inverse to the quality factor (Q) of a medium, is a well-publicized and yet poorly studied subject. While it is common to deduce Q values from measured dispersion data for surface waves, previous studies on the intrinsic attenuation of body waves have relied on measurements of the waveform of first arrivals or reflections. Better understanding is needed for both solid Earth geophysics and applied seismology to quantify the contributing factors to seismic attenuation and decompose Q from other factors because Q is closely related to rock property and fluid saturation. This study focuses on forward modeling and tomographic inversion for the Q values in thickness-varying layered media. Many of the existing theoretical Q models work in such media. Our work is an extension of the deformable- layer tomography (Zhou, 2004) to dissipative media. In the first phase of this study, we evaluated, through numerical modeling the various factors contributing to the attenuation of body waves. Theoretically, there are intrinsic attenuation, which is related to rock and pore fluid properties, and attenuation due to wave propagation effects, such as geometrical spreading and energy partition across interfaces (transmission and reflection). We made several representative numerical models, and conducted forward modeling using both wave theory and ray theory to quantify the amount of the attenuation of body waves due to different factors. In the second phase, we are integrating the forward modeling with the deformable-layer tomography algorithm to develop means to invert for Q distribution in thickness-varying layer media. While the deformable-layer tomography determines layer velocities and geometry, the current work intends to invert for Q values of the thickness-varying model layers as well as parameters associated with interface energy partition and geometric spreading. In the third phase, we plan to apply the

  2. Experimental and Numerical Investigation of Pressure Wave Attenuation due to Bubbly Layers

    NASA Astrophysics Data System (ADS)

    Jayaprakash, Arvind; Fourmeau, Tiffany; Hsiao, Chao-Tsung; Chahine, Georges; Dynaflow Inc. Team

    2013-03-01

    In this work, the effects of dispersed microbubbles on a steep pressure wave and its attenuation are investigated both numerically and experimentally. Numerical simulations were carried out using a compressible Euler equation solver, where the liquid-gas mixture was modeled using direct numerical simulations involving discrete deforming bubbles. To reduce computational costs a 1D configuration is used and the bubbles are assumed distributed in layers and the initial pressure profile is selected similar to that of a one-dimensional shock tube problem. Experimentally, the pressure pulse was generated using a submerged spark electric discharge, which generates a large vapor bubble, while the microbubbles in the bubbly layer are generated using electrolysis. High speed movies were recorded in tandem with high fidelity pressure measurements. The dependence of pressure wave attenuation on the bubble radii, the void fraction, and the bubbly layer thickness were parametrically studied. It has been found that the pressure wave attenuation can be seen as due to waves reflecting and dispersing in the inter-bubble regions, with the energy absorbed by bubble volume oscillations and re-radiation. Layer thickness and small bubble sizes were also seen as having a strong effect on the attenuation with enhanced attenuation as the bubble size is reduced for the same void fraction. This study was supported by the Department of Energy, under SBIR Phase II Contract DE-FG02-07ER84839.

  3. 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.

  4. Spatial variation of coda wave attenuation in northwestern Colombia

    NASA Astrophysics Data System (ADS)

    Vargas, Carlos A.; Ugalde, Arantza; Pujades, Lluís G.; Canas, José 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)-η. The exponents of the frequency dependence law ranged from η= 0.65 to 1.01 for Q-1c, η= 0.62 to 1.78 for Q-1i, η= 0.28 to 1.49 for Q-1s, and η= 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

  5. Ocean waves across the Arctic: Attenuation due to dissipation dominates over scattering for periods longer than 19 s

    NASA Astrophysics Data System (ADS)

    Ardhuin, Fabrice; Sutherland, Peter; Doble, Martin; Wadhams, Peter

    2016-06-01

    The poorly understood attenuation of surface waves in sea ice is generally attributed to the combination of scattering and dissipation. Scattering and dissipation have very different effects on the directional and temporal distribution of wave energy, making it possible to better understand their relative importance by analysis of swell directional spreading and arrival times. Here we compare results of a spectral wave model—using adjustable scattering and dissipation attenuation formulations—with wave measurements far inside the ice pack. In this case, scattering plays a negligible role in the attenuation of long swells. Specifically, scattering-dominated attenuation would produce directional wave spectra much broader than the ones recorded, and swell events arriving later and lasting much longer than observed. Details of the dissipation process remain uncertain. Average dissipation rates are consistent with creep effects but are 12 times those expected for a laminar boundary layer under a smooth solid ice plate.

  6. 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.

  7. 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

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

    SciTech Connect

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

    2013-10-15

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

  9. Seismic Attenuation Technology for the Advanced Virgo Gravitational Wave Detector

    NASA Astrophysics Data System (ADS)

    Beker, M. G.; Blom, M.; van den Brand, J. F. J.; Bulten, H. J.; Hennes, E.; Rabeling, D. S.

    The current interferometric gravitational wave detectors are being upgraded to what are termed 'second generation' devices. Sensitivities will be increased by an order of magnitude and these new instruments are expected to uncover the field of gravitational astronomy. A main challenge in this endeavor is the mitigation of noise induced by seismic motion. Detailed studies with Virgo show that seismic noise can be reinjected into the dark fringe signal. For example, laser beam jitter and backscattered light limit the sensitivity of the interferometer. Here, we focus on seismic attenuators based on compact inverted pendulums in combination with geometric anti-prings to obtain 40 dB of attenuation above 4 Hz in six degrees of freedom. Low frequency resonances (< 0.5 Hz) are damped by using a control system based on input from LVDTs and geophones. Such systems are under development for the seismic attenuation of optical benches operated both in air and vacuum. The design and realization of the seismic attenuation system for the Virgo external injection bench, including its control scheme, will be discussed and stand-alone performance presented.

  10. Ultrasound attenuation as a quantitative measure of fracture healing

    NASA Astrophysics Data System (ADS)

    Gheduzzi, Sabina; Humphrey, Victor F.; Dodd, Simon P.; Cunningham, James L.; Miles, Anthony W.

    2004-10-01

    The monitoring of fracture healing still relies upon the judgment of callus formation and on the manual assessment of the stiffness of the fracture. A diagnostic tool capable of quantitatively measuring healing progression of a fracture would allow the fine-tuning of the treatment regime. Ultrasound attenuation measurements were adopted as a possible method of assessing the healing process in human long bones. The method involves exciting ultrasonic waves at 200 kHz in the bone and measuring the reradiation along the bone and across the fracture zone. Seven cadaveric femora were tested in vitro in intact form and after creating a transverse fracture by sawing through the cortex. The effects of five different fracture types were investigated. A partial fracture, corresponding to a 50% cut through the cortex, a closed fracture, and fractures of widths varying between 1, 2, and 4 mm were investigated. The introduction of a fracture was found to produce a dramatic effect on the amplitude of the signal. Ultrasound attenuation was found to be sensitive to the presence of a fracture, even when the fracture was well reduced. It would therefore appear feasible to adopt attenuation across a fracture as a quantitative measurement of fracture healing.

  11. Seismic Wave Attenuation Estimated from Tectonic Tremor and Radiated Energy in Tremor for Various Subduction Zones

    NASA Astrophysics Data System (ADS)

    Yabe, S.; Baltay, A.; Ide, S.; Beroza, G. C.

    2013-12-01

    Ground motion prediction is an essential component of earthquake hazard assessment. Seismic wave attenuation with distance is an important, yet difficult to constrain, factor for such estimation. Using the empirical method of ground motion prediction equations (GMPEs), seismic wave attenuation with distance, which includes both the effect of anelastic attenuation and scattering, can be estimated from the distance decay of peak ground velocity (PGV) or peak ground acceleration (PGA) of ordinary earthquakes; however, in some regions where plate-boundary earthquakes are infrequent, such as Cascadia and Nankai, there are fewer data with which to constrain the empirical parameters. In both of those subduction zones, tectonic tremor occurs often. In this study, we use tectonic tremor to estimate the seismic wave attenuation with distance, and in turn use the attenuation results to estimate the radiated seismic energy of tremor. Our primary interest is in the variations among subduction zones. Ground motion attenuation and the distribution of released seismic energy from tremors are two important subduction zone characteristics. Therefore, it is very interesting to see whether there are variations of these parameters in different subduction zones, or regionally within the same subduction zone. It is also useful to estimate how much energy is released by tectonic tremor from accumulated energy to help understand subduction dynamics and the difference between ordinary earthquakes and tremor. We use the tectonic tremor catalog of Ide (2012) in Nankai, Cascadia, Mexico and southern Chile. We measured PGV and PGA of individual tremor bursts at each station. We assume a simple GMPE relationship and estimate seismic attenuation and relative site amplification factors from the data. In the Nankai subduction zone, there are almost no earthquakes on the plate interface, but intra-slab earthquakes occur frequently. Both the seismic wave attenuation with distance and the site

  12. Impact of attenuator models on computed traveling wave tube performances

    NASA Astrophysics Data System (ADS)

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

    2007-09-01

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

  13. 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.

  14. 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.

  15. 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.

  16. Attenuation of high-frequency seismic waves in northeast India

    NASA Astrophysics Data System (ADS)

    Padhy, Simanchal; Subhadra, N.

    2010-04-01

    We studied attenuation of S and coda waves, their frequency and lapse time dependencies in northeast India in the frequency range of 1-24 Hz. We adopted theories of both single and multiple scattering to bandpass-filtered seismograms to fit coda envelopes to estimate Q for coda waves (QC) and Q for S-waves (QS) at five central frequencies of 1.5, 3, 6, 12 and 24 Hz. The selected data set consists of 182 seismograms recorded at ten seismic stations within epicentral distance of 22-300 km in the local magnitude range of 2.5-5.2. We found that with the increase in lapse time window from 40 to 60 s, Q0 (QC at 1 Hz) increases from 213 to 278, while the frequency dependent coefficient n decreases from 0.89 to 0.79. Both QC and QS increase with frequency. The average value of QS obtained by using coda normalization method for NE India has the power law form of (96.8 +/- 21.5)f(1.03+/-0.04) in 1-24 Hz. We adopted energy flux model (EFM) and diffusion model for the multiple scattered wave energy in three-dimensions. The results show that the contribution of multiple scattering dominates for longer lapse time close to or larger than mean free time of about 60 s. The estimates of QC are overestimated at longer lapse time by neglecting the effects of multiple scattering. Some discrepancies have been observed between the theoretical predictions and the observations, the difference could be due to the approximation of the uniform medium especially at large hypocentral distances. Increase in QC with lapse time can be explained as the result of the depth dependent attenuation properties and multiple scattering effect.

  17. Development of attenuation and diffraction corrections for linear and nonlinear Rayleigh surface waves radiating from a uniform line source

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

    In recent studies with nonlinear Rayleigh surface waves, harmonic generation measurements have been successfully employed to characterize material damage and microstructural changes, and found to be sensitive to early stages of damage process. A nonlinearity parameter of Rayleigh surface waves was derived and frequently measured to quantify the level of damage. The accurate measurement of the nonlinearity parameter generally requires making corrections for beam diffraction and medium attenuation. These effects are not generally known for nonlinear Rayleigh waves, and therefore not properly considered in most of previous studies. In this paper, the nonlinearity parameter for a Rayleigh surface wave is defined from the plane wave displacement solutions. We explicitly define the attenuation and diffraction corrections for fundamental and second harmonic Rayleigh wave beams radiated from a uniform line source. Attenuation corrections are obtained from the quasilinear theory of plane Rayleigh wave equations. To obtain closed-form expressions for diffraction corrections, multi-Gaussian beam (MGB) models are employed to represent the integral solutions derived from the quasilinear theory of the full two-dimensional wave equation without parabolic approximation. Diffraction corrections are presented for a couple of transmitter-receiver geometries, and the effects of making attenuation and diffraction corrections are examined through the simulation of nonlinearity parameter determination in a solid sample.

  18. Phase velocities and attenuations of shear, Lamb, and Rayleigh waves in plate-like tissues submerged in a fluid (L).

    PubMed

    Nenadic, Ivan Z; Urban, Matthew W; Bernal, Miguel; Greenleaf, James F

    2011-12-01

    In the past several decades, the fields of ultrasound and magnetic resonance elastography have shown promising results in noninvasive estimates of mechanical properties of soft tissues. These techniques often rely on measuring shear wave velocity due to an external or internal source of force and relating the velocity to viscoelasticity of the tissue. The mathematical relationship between the measured velocity and material properties of the myocardial wall, arteries, and other organs with non-negligible boundary conditions is often complicated and computationally expensive. A simple relationship between the Lamb-Rayleigh dispersion and the shear wave dispersion is derived for both the velocity and attenuation. The relationship shows that the shear wave velocity is around 20% higher than the Lamb-Rayleigh velocity and that the shear wave attenuation is about 20% lower than the Lamb-Rayleigh attenuation. Results of numerical simulations in the frequency range 0-500 Hz are presented. PMID:22225009

  19. Attenuation of the LG wave across the contiguous United States

    NASA Astrophysics Data System (ADS)

    Gallegos, Andrea Christina

    Lg waveforms recorded by EarthScope's Transportable Array (TA) are used to estimate Lg Q in the contiguous United States. Shear-wave crustal attenuation is calculated based on Lg spectral amplitudes filtered at several narrow bandwidths with central frequencies of 0.5, 1, 2, and 3 Hz. The two-station and reverse two-station techniques were used to calculate these Q values. 349 crustal earthquakes occurring from 2004 to 2015 and ranging from magnitude 3 to magnitude 6 were used in this study. The results show that the western U.S., an area ranging from 25°N to 50°N and from 125°W to 105°W is a primarily low Q (high attenuation) area, with isolated high Q (low attenuation) regions corresponding to the Colorado Plateau, the Rocky Mountains, the Columbia Plateau, and the Sierra Nevada Mountains. The central and eastern U.S., an area ranging from 105°W to 60°W, is found to be high Q overall, with isolated low Q areas along ft... Coastal Plain, the Reelfoot Rift, and the Wisconsin-Minnesota border region. A positive correlation between high heat flow, the presence of thick sediments, recent tectonic activity, and low Q is observed. Areas with low heat flow, thin sediment cover, and no recent tectonic activity were observed to have consistently high Q. Lg Q was found to have a power law type frequency dependence throughout the U.S., with an increase in central frequency resulting in an increase in Q. At higher frequencies, crustal attenuation is dominated by scattering. These new Lg tomography models are based on an unprecedented amount and coverage of data, providing improved accuracy and detail. This increase in detail can improve high frequency ground motion predictions of future large earthquakes for more accurate hazard assessment and improve overall understanding of the structure and assemblage of the contiguous United States.

  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. 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.

  2. 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

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

    NASA Technical Reports Server (NTRS)

    Reethof, G.

    1976-01-01

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

  4. Laboratory Measurements of Velocity and Attenuation in Sediments

    SciTech Connect

    Zimmer, M A; Berge, P A; Bonner, B P; Prasad, M

    2004-06-08

    Laboratory measurements are required to establish relationships between the physical properties of unconsolidated sediments and P- and S-wave propagation through them. Previous work has either focused on measurements of compressional wave properties at depths greater than 500 m for oil industry applications or on measurements of dynamic shear properties at pressures corresponding to depths of less than 50 m for geotechnical applications. Therefore, the effects of lithology, fluid saturation, and compaction on impedance and P- and S-wave velocities of shallow soils are largely unknown. We describe two state-of-the-art laboratory experiments. One setup allows us to measure ultrasonic P-wave velocities at very low pressures in unconsolidated sediments (up to 0.1 MPa). The other experiment allows P- and S-wave velocity measurements at low to medium pressures (up to 20 MPa). We summarize the main velocity and attenuation results on sands and sand - clay mixtures under partially saturated and fully saturated conditions in two ranges of pressures (0 - 0.1 MPa and 0.1 - 20 MPa) representative of the top few meters and the top 1 km, respectively. Under hydrostatic pressures of 0.1 to 20 MPa, our measurements demonstrate a P- and S-wave velocity-dependence in dry sands around a fourth root (0.23 -0.26) with the pressure dependence for S-waves being slightly lower. The P- velocity-dependence in wet sands lies around 0.4. The Vp-Vs and the Qp-Qs ratios together can be useful tools to distinguish between different lithologies and between pressure and saturation effects. These experimental velocities at the frequency of measurement (200 kHz) are slightly higher that Gassmann's static result. For low pressures under uniaxial stress, Vp and Vs were a few hundred meters per second with velocities showing a strong dependence on packing, clay content, and microstructure. We provide a typical shallow soil scenario in a clean sand environment and reconstruct the velocity profile of

  5. 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.

  6. Ultrasonic Attenuation Measurements in Thermally Degraded 2205 Duplex Stainless Steel

    NASA Astrophysics Data System (ADS)

    Ruiz, A.; Ortiz, N.; Carreón, H.; Sánchez, A.

    2009-03-01

    Ultrasonic attenuation plays an important role in materials characterization of metal components. This paper present data and discuss ultrasonic attenuation variations in a 2205 duplex stainless steel aged isothermally at 700° C and 900° C for different time intervals. Attenuation measurements as function of frequency where performed using pulse-echo immersion method and broad band planar transducers. Evidence is found of changes in the attenuation coefficient as aging time increases. The corresponding microstructure of aged specimens was observed and impact toughness was measured. Comparison is made with measurements of ferrite content for the two temperatures and different aging times.

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

    NASA Astrophysics Data System (ADS)

    Wirgin, Armand

    2016-07-01

    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.

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

    PubMed Central

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

    2012-01-01

    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

  9. 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

  10. 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.

  11. Flame attenuation effects on surface temperature measurements using IR thermography

    NASA Astrophysics Data System (ADS)

    de Vries, Jaap; Tabinowski, Robert

    2016-05-01

    Long-wave infrared (LWIR) cameras provide the unique ability to see through smoke and condensed water vapor. However, soot generated inside the flame does attenuate the LWIR signal. This work focuses on gas flame attenuation effects of LWIR signals originating from a blackbody. The experimental setup consists of time averaged, laboratory-scale turbulent diffusion flames with heat release rates set at 5 kW, 10 kW, and 15 kW. Propylene and ethylene were used as fuel, providing two different soot yields. A 30 cm by 30 cm blackbody was used with maximum surface temperatures set to 600°C. Both instantaneous and time-averaged blackbody temperature profiles through the flame were measured using a LWIR microbolometer camera (7.5-14 μm). Flame intermittency was quantified by color segmenting visible images. The experiments showed that low blackbody temperatures were significantly affected by the presence of the flame. At 600°C, the effect of flame absorption matches the emitted radiation from the flame itself. Using data obtained at various blackbody temperatures, the flame transmittance was obtained using a Generalized Reduced Gradient optimization method. The transmittance was lower for propylene flames compared to ethylene flames. Ethylene flames were shown to have higher temperatures. Using the values for flame radiance and transmissivity, the total averaged radiance of the flame plus the blackbody could be reproduced with 1% accuracy.

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

    NASA Technical Reports Server (NTRS)

    Kuntz, Herbert L.; Blackstock, David T.

    1987-01-01

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

  13. Compressional wave velocity and attenuation at ultrasonic and sonic frequencies in near-surface sedimentary rocks

    SciTech Connect

    Best, A.I.; Sams, M.S.

    1997-03-01

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

  14. 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

  15. Aircraft measurements of wave clouds

    NASA Astrophysics Data System (ADS)

    Cui, Z.; Blyth, A. M.; Bower, K. N.; Crosier, J.; Choularton, T.

    2012-10-01

    In this paper, aircraft measurements are presented of liquid phase (ice-free) wave clouds made at temperatures greater than -5°C that formed over Scotland, UK. The horizontal variations of the vertical velocity across wave clouds display a distinct pattern. The maximum updraughts occur at the upshear flanks of the clouds and the strong downdraughts at the downshear flanks. The cloud droplet concentrations were a couple of hundreds per cubic centimetres, and the drops generally had a mean diameter between 15-45 μm. A small proportion of the drops were drizzle. The measurements presented here and in previous recent studies suggest a different interaction of dynamics and microphysics in wave clouds from the accepted model. The results in this paper provide a case for future numerical simulation of wave cloud and the interaction between wave and cloud.

  16. Aircraft measurements of wave cloud

    NASA Astrophysics Data System (ADS)

    Cui, Z.; Blyth, A. M.; Bower, K. N.; Crosier, J.; Choularton, T.

    2012-05-01

    In this paper, aircraft measurements are presented of liquid phase (ice-free) wave clouds made at temperatures greater than -5 °C that formed over Scotland, UK. The horizontal variations of the vertical velocity across wave clouds display a distinct pattern. The maximum updraughts occur at the upshear flanks of the clouds and the strong downdraughts at the downshear flanks. The cloud droplet concentrations were a couple of hundreds per cubic centimetres, and the drops generally had a mean diameter between 15-45 μm. A small proportion of the drops were drizzle. A new definition of a mountain-wave cloud is given, based on the measurements presented here and previous studies. The results in this paper provide a case for future numerical simulation of wave cloud and the interaction between wave and clouds.

  17. Laboratory and field investigations of wave attenuation by live marsh vegetation

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Wave attenuation by live marsh vegetation was investigated experimentally in this study. Laboratory experiments were conducted in a 20.6 m long, 0.69 m wide and 1.22 m deep wave flume under regular and random waves. The vegetation species used are Spartina alterniflora and Juncus roemerianus, which ...

  18. A New Approach for Quantitative Evaluation of Ultrasonic Wave Attenuation in Composites

    NASA Astrophysics Data System (ADS)

    Ni, Qing-Qing; Li, Ran; Xia, Hong

    2016-06-01

    When ultrasonic waves propagate in composite materials, the propagation behaviors result from the combination effects of various factors, such as material anisotropy and viscoelastic property, internal microstructure and defects, incident wave characteristics and interface condition between composite components. It is essential to make it clear how these factors affect the ultrasonic wave propagation and attenuation characteristics, and how they mutually interact on each other. In the present paper, based on a newly developed time-domain finite element analysis code, PZflex, a unique approach for clarifying the detailed influence mechanism of aforementioned factors is proposed, in which each attenuation component can be extracted from the overall attenuation and analyzed respectively. By taking into consideration the interrelation between each individual attenuation component, the variation behaviors of each component and internal dynamic stress distribution against material anisotropy and matrix viscosity are separately and quantitatively evaluated. From the detailed analysis results of each attenuation component, the energy dissipation at interface is a major component in ultrasonic wave attenuation characteristics, which can provide a maximum contribution rate of 68.2 % to the overall attenuation, and each attenuation component is closely related to the material anisotropy and viscoelasticity. The results clarify the correlation between ultrasonic wave propagation characteristics and material viscoelastic properties, which will be useful in the further development of ultrasonic technology in defect detection.

  19. Measurements of spectral attenuation coefficients in the lower Chesapeake Bay

    NASA Technical Reports Server (NTRS)

    Houghton, W. M.

    1983-01-01

    The spectral transmission was measured for water samples taken in the lower Chesapeake Bay to allow characterization of several optical properties. The coefficients of total attenuation, particle attenuation, and absorption by dissolved organic matter were determined over a wavelength range from 3500 A to 8000 A. The data were taken over a 3 year period and at a number of sites so that an indication of spatial and temporal variations could be obtained. The attenuations determined in this work are, on the average, 10 times greater than those obtained by Hulburt in 1944, which are commonly accepted in the literature for Chesapeake Bay attenuation.

  20. Studies on Shock Attenuation in Plastic Materials and Applications in Detonation Wave Shaping

    NASA Astrophysics Data System (ADS)

    Khurana, Ritu; Gautam, P. C.; Rai, Rajwant; Kumar, Anil; Sharma, A. C.; Singh, Manjit, Dr

    2012-07-01

    Pressure in plastic materials attenuates due to change of impedance, phase change in the medium and plastic deformation. A lot of theoretical and experimental efforts have been devoted to the attenuation of shock wave produced by the impact of explosive driven flyer plate. However comparatively less work has been done on the attenuation of shock waves due to contact explosive detonation. Present studies deal with the attenuation of explosive driven shock waves in various plastic materials and its applications in design of Hybrid Detonation Wave Generator In present work shock attenuating properties of different polymers such as Perspex, Teflon, nylon, polypropylene and viton has been studied experimentally using rotating mirror streak camera and electrical position pins. High explosive RDX/TNT and OCTOL of diameter 75-100mm and thickness 20 to 50mm were detonated to induce shock wave in the test specimens. From experimental determined shock velocity at different locations the attenuation in shock pressure was calculated. The attenuation of shock velocity with thickness in the material indicates exponential decay according to relation US = UOexp(-ax). In few of the experiments manganin gauge of resistance 50 ohms was used to record stress time profile across shock wave. The shock attenuation data of Viton has successfully been used in the design of hybrid detonation wave generator using Octol as high explosive. While selecting a material it was ensured that the attenuated shock remains strong enough to initiate an acceptor explosive. Theoretical calculation were supported by Autodyne 2D hydro-code simulation which were validated with the experiments conducted using high speed streak photography and electrical shock arrival pins. Shock attenuation data of Perspex was used to establishing card gap test and wedge test in which test items is subjected to known pressure pulse by selecting the thickness of the plastic material.

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

    NASA Technical Reports Server (NTRS)

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

    1953-01-01

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

  3. Effects of elastic focusing on global models of Rayleigh wave attenuation

    NASA Astrophysics Data System (ADS)

    Bao, Xueyang; Dalton, Colleen A.; Ritsema, Jeroen

    2016-11-01

    Rayleigh wave amplitudes are the primary data set used for imaging shear attenuation in the upper mantle on a global scale. In addition to attenuation, surface-wave amplitudes are influenced by excitation at the earthquake source, focusing and scattering by elastic heterogeneity, and local structure at the receiver and the instrument response. The challenge of isolating the signal of attenuation from these other effects limits both the resolution of global attenuation models and the level of consistency between different global attenuation studies. While the source and receiver terms can be estimated using relatively simple approaches, focusing effects on amplitude are a large component of the amplitude signal and are sensitive to multiscale velocity anomalies. In this study we investigate how different theoretical treatments for focusing effects on Rayleigh wave amplitude influence the retrieved attenuation models. A new data set of fundamental-mode Rayleigh wave phase and amplitude at periods of 50 and 100 sis analysed. The amplitudes due to focusing effects are predicted using the great-circle ray approximation (GCRA), exact ray theory (ERT), and finite-frequency theory (FFT). Phase-velocity maps expanded to spherical-harmonic degree 20 and degree 40 are used for the predictions. After correction for focusing effects, the amplitude data are inverted for global attenuation maps and frequency-dependent source and receiver correction factors. The degree-12 attenuation maps, based on different corrections for focusing effects, all contain the same large-scale features, though the magnitude of the attenuation variations depends on the focusing correction. The variance reduction of the amplitudes strongly depends on the predicted focusing amplitudes, with the highest variance reduction for the ray-based approaches at 50 s and for FFT at 100 s. Although failure to account for focusing effects introduces artefacts into the attenuation models at higher spherical

  4. 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.}

  5. Tracing Shock Wave Attenuation in Porous, Particulate Targets: Insights from Impact Experiments and Numerical Modeling

    NASA Astrophysics Data System (ADS)

    Hamann, C.; Zhu, M.-H.; Wünnemann, K.; Hecht, L.; Stöffler, D.

    2016-08-01

    We directly compare shock zoning (representing shock pressures from ~59 to ~5 GPa) preserved in layered melt particles recovered from impact experiments with quartz sand targets with numerical models of crater formation and shock wave attenuation.

  6. 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.

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

    PubMed

    Xie, Li; Li, Xingcai; Zheng, Xiaojing

    2010-12-10

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

  8. Ionospheric wave spectrum measurements

    NASA Technical Reports Server (NTRS)

    Harker, K. J.; Ilic, D. B.; Crawford, F. W.

    1979-01-01

    The local spectrum S(k, omega) of either potential or electron-density fluctuations can be used to determine macroscopic-plasma characteristics such as the local density and temperature, transport coefficients, and drift current. This local spectrum can be determined by measuring the cross-power spectrum. The paper examines the practicality of using the cross-power spectrum analyzer on the Space Shuttle to measure ionospheric parameters. Particular attention is given to investigating the integration time required to measure the cross-power spectral density to a desired accuracy.

  9. 2D Global Rayleigh Wave Attenuation Model Using Finite Frequency Focusing and Defocusing Theory

    NASA Astrophysics Data System (ADS)

    Ma, Z.; Masters, G.; Dalton, C. A.

    2015-12-01

    We have developed an efficient technique to process and measure surface-wave amplitude and phase from a large collection of seismic waveforms. These amplitude and phase data sets are used to jointly invert for 2D phase velocity and attenuation maps. As demonstrated by Dalton and Ekstrom (2006), correcting for the effects of focusing and defocusing by elastic structure is crucial in order to obtain reliable attenuation structures. A robust theory that can reliably predict focusing-defocusing effects and is insensitive to the details of making the phase velocity maps is preferred. Great circle ray theory can give useful predictions for the focusing-defocusing effects if careful attention is paid to how the phase velocity model is smoothed. However, the predictions of the finite frequency kernels are more robust at the low-intermediate frequency range (below 25mHz) and suggest that they are better suited as a basis for inversion.We invert for the phase velocity, attenuation, source, and receiver terms simultaneously. Our models provide 60-70% 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-dependent trend of 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. Although our approach was developed for a global study, it can be extended to regional studies. Our first regional-scale application of this approach is to the Atlantic upper mantle.

  10. 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

  11. 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%.

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

    NASA Astrophysics Data System (ADS)

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

    2014-07-01

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

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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

  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.

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

    NASA Astrophysics Data System (ADS)

    Ootsuta, Katsuhisa; Matsuoka, Kei; Sasoh, Akihiro; Takayama, Kazuyoshi

    1998-04-01

    A device for attenuating weak shock waves propagating in a duct has been developed utilizing sound-absorbent plastic which is usually used for attenuating sound waves. The device has a tube made of the sound-absorbent plastic installed coaxially to a surrounding metal tube with a clearance between them. The clearance acts as an air layer to enhance the performance of the shock wave attenuation. When a weak shock wave propagates through this device, the pressure gradient of the shock wave is gradually smeared and hence its overpressure is decreased. The performance of the device was examined using a 1/250-scaled train tunnel simulator which simulated the discharge of weak shock waves created by high-speed entry of trains to tunnels. The overpressure of the shock waves ranged up to 5 kPa. The shock wave overpressure was decreased by 90% with the present attenuator attached. This device can be applied to various industrial noise suppressions which are associated with unsteady compressible flows.

  2. Underdetermined system theory applied to qualitative analysis of response caused by attenuating plane waves

    NASA Astrophysics Data System (ADS)

    Sano, Yukio

    1989-05-01

    A qualitative analysis of the mechanical response of rate-dependent media caused by a one-dimensional plane smooth wave front and by a continuous wave front attenuating in the media is performed by an underdetermined system of nonlinear partial differential equations. The analysis reveals that smooth strain, particle velocity, and stress profiles, which the smooth wave front has, are not similar and that the wave front is composed of some partial waves having different properties. The property is represented by a set of strain rate, acceleration, and stress rate. The wave front derived here from the analysis is composed of four different partial waves. The front of the wave front is necessarily a contraction wave in which strain, particle velocity, and stress increase with time, while the rear is a rarefaction wave where they all decrease with time. Between these two wave fronts there are two remaining wave fronts. We call these wave fronts mesocontraction waves I and II. Wave front I is a wave in which stress decreases notwithstanding the increase in strain and particle velocity with time, which is followed by the other, i.e., wave front II, where with time, particle velocity, and stress decrease in spite of the increase in strain. The continuous wave front having continuous and nonsmooth profiles of strain, particle velocity, and stress can also be composed of four waves. These waves possess the same property as the corresponding waves in the smooth wave front mentioned above. The velocities at three boundaries that the waves have are discontinuous. Therefore, these four wave fronts are independent waves, just as a shock wave and a rarefraction wave. Specifically, the front wave, i.e., a contraction wave front is being outrun by a second wave front, the second one is being outrun by a third wave front, and the third is being outrun by a fourth wave front, i.e., a rarefaction wave. We call the second wave front degenerate contraction wave I. We also call the third

  3. 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.

  4. Frequency-Dependent Attenuation of Blasting Vibration Waves

    NASA Astrophysics Data System (ADS)

    Zhou, Junru; Lu, Wenbo; Yan, Peng; Chen, Ming; Wang, Gaohui

    2016-10-01

    The dominant frequency, in addition to the peak particle velocity, is a critical factor for assessing adverse effects of the blasting vibration on surrounding structures; however, it has not been fully considered in blasting design. Therefore, the dominant frequency-dependent attenuation mechanism of blast-induced vibration is investigated in the present research. Starting with blasting vibration induced by a spherical charge propagating in an infinite viscoelastic medium, a modified expression of the vibration amplitude spectrum was derived to reveal the frequency dependency of attenuation. Then, ground vibration induced by more complex and more commonly used cylindrical charge that propagates in a semi-infinite viscoelastic medium was analyzed by numerical simulation. Results demonstrate that the absorptive property of the medium results in the frequency attenuation versus distance, whereas a rapid drop or fluctuation occurs during the attenuation of ground vibration. Fluctuation usually appears at moderate to far field, and the dominant frequency generally decreases to half the original value when rapid drop occurs. The decay rate discrepancy between different frequency components and the multimodal structure of vibration spectrum lead to the unsmooth frequency-dependent attenuation. The above research is verified by two field experiments. Furthermore, according to frequency-based vibration standards, frequency drop and fluctuation should be considered when evaluating blast safety. An optimized piecewise assessment is proposed for more accurate evaluation: With the frequency drop point as the breakpoint, the assessment is divided into two independent sections along the propagating path.

  5. Crosswell seismic studies in gas hydrate-bearing sediments: P wave velocity and attenuation tomography

    NASA Astrophysics Data System (ADS)

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

    2003-04-01

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

  6. Comparison of viscoelastic-type models for ocean wave attenuation in ice-covered seas

    NASA Astrophysics Data System (ADS)

    Mosig, Johannes E. M.; Montiel, Fabien; Squire, Vernon A.

    2015-09-01

    Continuum-based models that describe the propagation of ocean waves in ice-infested seas are considered, where the surface ocean layer (including ice floes, brash ice, etc.) is modeled by a homogeneous viscoelastic material which causes waves to attenuate as they travel through the medium. Three ice layer models are compared, namely a viscoelastic fluid layer model currently being trialed in the spectral wave model WAVEWATCH III® and two simpler viscoelastic thin beam models. All three models are two dimensional. A comparative analysis shows that one of the beam models provides similar predictions for wave attenuation and wavelength to the viscoelastic fluid model. The three models are calibrated using wave attenuation data recently collected in the Antarctic marginal ice zone as an example. Although agreement with the data is obtained with all three models, several important issues related to the viscoelastic fluid model are identified that raise questions about its suitability to characterize wave attenuation in ice-covered seas. Viscoelastic beam models appear to provide a more robust parameterization of the phenomenon being modeled, but still remain questionable as a valid characterization of wave-ice interactions generally.

  7. 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...

  8. Optimized ultrasonic attenuation measures for non-homogeneous materials.

    PubMed

    Genovés, V; Gosálbez, J; Carrión, A; Miralles, R; Payá, J

    2016-02-01

    In this paper the study of frequency-dependent ultrasonic attenuation in strongly heterogeneous materials is addressed. To determine the attenuation accurately over a wide frequency range, it is necessary to have suitable excitation techniques. Three kinds of transmitted signals have been analysed, grouped according to their bandwidth: narrowband and broadband signals. The mathematical formulation has revealed the relation between the distribution of energy in their spectra and their immunity to noise. Sinusoidal and burst signals have higher signal-to-noise ratios (SNRs) but need many measurements to cover their frequency range. However, linear swept-frequency signals (chirp) improve the effective bandwidth covering a wide frequency range with a single measurement and equivalent accuracy, at the expense of a lower SNR. In the case of highly attenuating materials, it is proposed to use different configurations of chirp signals, enabling injecting more energy, and therefore, improving the sensitivity of the technique without a high time cost. Thus, if the attenuation of the material and the sensitivity of the measuring equipment allows the use of broadband signals, the combination of this kind of signal and suitable signal processing results in an optimal estimate of frequency-dependent attenuation with a minimum measurement time. PMID:26432190

  9. Amplitude measurements in ambient noise correlations -- application to attenuation and site response measurements

    NASA Astrophysics Data System (ADS)

    Bowden, D. C.; Tsai, V. C.; Lin, F.

    2013-12-01

    Traditional ambient noise cross correlations between seismic stations have proven to be an effective means of extracting travel time information of surface waves. However, while the raw noise data is usually processed in a way which suppresses large amplitude earthquake events, it also distorts all relative amplitude information. Such information is the key to accurately retrieving attenuation and local site response measurements. Previous work using earthquake sources to track wave front propagation across the U.S. Array has been used to distinguish between effects on amplitude variation. Applying a similar approach to ambient noise studies offers potentially increased flexibility in such studies. We attempt a varied application of the methods which should preserve relative amplitudes in the Noise Correlation Function (NCF) across a given day or hour. Considering each station as a virtual source, a large number of travel time and relative amplitude maps can be constructed. By applying spatial differential operators to these maps, we track the effect of phase-front focusing and defocusing. By comparing amplitude variation for waves propagating in opposite directions, we attempt to independently infer the effects of seismic intrinsic attenuation and local site response. We have applied the approach on two datasets of vastly different scale. A dense array of single-component, broadband seismometers in Long Beach, CA (>4000 in an area around 100 sq-km) allows us to explore the higher frequency end of these measurements, up to 4Hz. In contrast, data collected over 4 years from the U.S. Array provide continental scale application, with useful periods of 8-30 seconds and depth sensitivities down to the uppermost mantle. We compare our results with previous studies based on earthquakes.

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

    PubMed

    Holm, Sverre; Näsholm, Sven Peter

    2014-04-01

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

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

    PubMed

    Näsholm, Sven Peter; Holm, Sverre

    2011-11-01

    The acoustic wave attenuation is described by an experimentally established frequency power law in a variety of complex media, e.g., biological tissue, polymers, rocks, and rubber. Recent papers present a variety of acoustical fractional derivative wave equations that have the ability to model power-law attenuation. On the other hand, a multiple relaxation model is widely recognized as a physically based description of the acoustic loss mechanisms as developed by Nachman et al. [J. Acoust. Soc. Am. 88, 1584-1595 (1990)]. Through assumption of a continuum of relaxation mechanisms, each with an effective compressibility described by a distribution related to the Mittag-Leffler function, this paper shows that the wave equation corresponding to the multiple relaxation approach is identical to a given fractional derivative wave equation. This work therefore provides a physically based motivation for use of fractional wave equations in acoustic modeling.

  12. Regional Body-Wave Attenuation Using a Coda Source Normalization Method: Application to MEDNET Records of Earthquakes in Italy

    SciTech Connect

    Walter, W R; Mayeda, K; Malagnini, L; Scognamiglio, L

    2007-02-01

    We develop a new methodology to determine apparent attenuation for the regional seismic phases Pn, Pg, Sn, and Lg using coda-derived source spectra. The local-to-regional coda methodology (Mayeda, 1993; Mayeda and Walter, 1996; Mayeda et al., 2003) is a very stable way to obtain source spectra from sparse networks using as few as one station, even if direct waves are clipped. We develop a two-step process to isolate the frequency-dependent Q. First, we correct the observed direct wave amplitudes for an assumed geometrical spreading. Next, an apparent Q, combining path and site attenuation, is determined from the difference between the spreading-corrected amplitude and the independently determined source spectra derived from the coda methodology. We apply the technique to 50 earthquakes with magnitudes greater than 4.0 in central Italy as recorded by MEDNET broadband stations around the Mediterranean at local-to-regional distances. This is an ideal test region due to its high attenuation, complex propagation, and availability of many moderate sized earthquakes. We find that a power law attenuation of the form Q(f) = Q{sub 0}f{sup Y} fit all the phases quite well over the 0.5 to 8 Hz band. At most stations, the measured apparent Q values are quite repeatable from event to event. Finding the attenuation function in this manner guarantees a close match between inferred source spectra from direct waves and coda techniques. This is important if coda and direct wave amplitudes are to produce consistent seismic results.

  13. Detailed Study of Seismic Wave Attenuation in Carbonate Rocks: Application on Abu Dhabi Oil Fields

    NASA Astrophysics Data System (ADS)

    Bouchaala, F.; Ali, M. Y.; Matsushima, J.

    2015-12-01

    Seismic wave attenuation is a promising attribute for the petroleum exploration, thanks to its high sensitivity to physical properties of subsurface. It can be used to enhance the seismic imaging and improve the geophysical interpretation which is crucial for reservoir characterization. However getting an accurate attenuation profile is not an easy task, this is due to complex mechanism of this parameter, although that many studies were carried out to understand it. The degree of difficulty increases for the media composed of carbonate rocks, known to be highly heterogeneous and with complex lithology. That is why few attenuation studies were done successfully in carbonate rocks. The main objectives of this study are, Getting an accurate and high resolution attenuation profiles from several oil fields. The resolution is very important target for us, because many reservoirs in Abu Dhabi oil fields are tight.Separation between different modes of wave attenuation (scattering and intrinsic attenuations).Correlation between the attenuation profiles and other logs (Porosity, resistivity, oil saturation…), in order to establish a relationship which can be used to detect the reservoir properties from the attenuation profiles.Comparison of attenuation estimated from VSP and sonic waveforms. Provide spatial distribution of attenuation in Abu Dhabi oil fields.To reach these objectives we implemented a robust processing flow and new methodology to estimate the attenuation from the downgoing waves of the compressional VSP data and waveforms acquired from several wells drilled in Abu Dhabi. The subsurface geology of this area is primarily composed of carbonate rocks and it is known to be highly fractured which complicates more the situation, then we separated successfully the intrinsic attenuation from the scattering. The results show that the scattering is significant and cannot be ignored. We found also a very interesting correlation between the attenuation profiles and the

  14. Experimental study of the stress effect on attenuation of normally incident P-wave through coal

    NASA Astrophysics Data System (ADS)

    Feng, Junjun; Wang, Enyuan; Chen, Liang; Li, Xuelong; Xu, Zhaoyong; Li, Guoai

    2016-09-01

    The purpose of this study is to experimentally investigate the stress effect on normally incident P-wave attenuation through coal specimens. Laboratory tests were carried out using a Split Hopkinson pressure bar (SHPB) system, and a modified method was proposed to determine the quality factor (Q) of P-waves through coal specimens. Larger quality factor denotes less energy attenuated during P-wave propagating through coal. Experimental results indicate that the quality factor and stress (σ) within coal specimens are positively correlated. The P-wave propagation through coal specimens causes crack closure at the beginning of the coal fracture process in SHPB tests, an innovative model was thus proposed to describe the relationship between the crack closure length and the dynamic stress induced by P-wave. Finally, the stress effect on P-wave attenuation through coal was quantitatively represented by a power function Q = a(c-bσ)- 6, and the material constants a, b, and c were determined as 1.227, 1.314, and 0.005, respectively. The results obtained in this study would be helpful for engineers to estimate seismic energy attenuation and coal mass instability in coal mines.

  15. 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.

  16. 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

  17. A web-based tutorial for ultrasonic attenuation measurement

    NASA Astrophysics Data System (ADS)

    Margetan, Frank J.; Barnard, Dan; Orman, David; Feygin, Alex; Pavel, Brittney

    2014-02-01

    An ultrasonic attenuation-versus-frequency curve can serve as an "ultrasonic signature" which may be correlated with microstructural properties of interest such as grain size in metals or porosity level in composites. Attenuation also plays a role in ultrasonic inspections and is consequently a key input into many inspection simulation models. A web-based self-tutorial on practical attenuation measurements is under development. The focus is on pulse/echo immersion measurements made using a broadband transducer to deduce attenuation within the transducer's useable bandwidth. Two approaches are considered: one using a calibration specimen having a known attenuation curve, and one without. In the first approach a back-wall (BW) echo in the calibration specimen is compared with a BW echo in the test specimen. In the second approach various BW reverberation echoes in the test specimen are compared with one another or with a front-wall echo. The web-based tutorial incorporates three classes of materials. The first includes written documentation and videos describing the measurement setups, the data-acquisition and analysis procedures, and the underlying models use to analyze the raw UT data. Secondly, general purpose "stand-alone" data-analysis software is supplied that is designed to be used with any ultrasonic inspection system that can output A-scan data as a text file. This includes both FORTRAN software and Excel spreadsheet calculators that accept A-scan text data as inputs. Thirdly, we supply demonstration software where the data acquisition and analysis procedures are integrated with a specific class of commercial ultrasonic test instruments, namely those running UTEX Winpect control software. This paper provides an overview of the measurement methods and tutorial materials. We also present early results from round-robin trials in which selected metal and composite specimens are being sent to participating partners for attenuation measurement.

  18. 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.

  19. 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.

  20. 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.

  1. Millimeter-wave propagation measurements at the Ballistic Research Laboratory

    NASA Astrophysics Data System (ADS)

    Wallace, H. Bruce

    1988-05-01

    Results of measurements made with radars from 35 to 217 GHz of near-earth propagation in rain, fog, snow, and humidity are presented. The effects of water vapor are characterized by an attenuation coefficient that is a function of vapor pressure or absolute humidity. Backscatter contributes significantly to the adverse effect of rain on mm-wave radars because the droplet sizes become comparable to signal wavelengths. Path losses from fogs, haze, or clouds, are caused by both absorption and scattering by water droplets. Attenuation due to falling snow is difficult to link to and single characteristics.

  2. 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.

  3. 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.

  4. 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.

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

    PubMed

    Chotiros, Nicholas P; Isakson, Marcia J

    2014-06-01

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

  6. Shear wave transmissivity measurement by color Doppler shear wave imaging

    NASA Astrophysics Data System (ADS)

    Yamakoshi, Yoshiki; Yamazaki, Mayuko; Kasahara, Toshihiro; Sunaguchi, Naoki; Yuminaka, Yasushi

    2016-07-01

    Shear wave elastography is a useful method for evaluating tissue stiffness. We have proposed a novel shear wave imaging method (color Doppler shear wave imaging: CD SWI), which utilizes a signal processing unit in ultrasound color flow imaging in order to detect the shear wave wavefront in real time. Shear wave velocity is adopted to characterize tissue stiffness; however, it is difficult to measure tissue stiffness with high spatial resolution because of the artifact produced by shear wave diffraction. Spatial average processing in the image reconstruction method also degrades the spatial resolution. In this paper, we propose a novel measurement method for the shear wave transmissivity of a tissue boundary. Shear wave wavefront maps are acquired by changing the displacement amplitude of the shear wave and the transmissivity of the shear wave, which gives the difference in shear wave velocity between two mediums separated by the boundary, is measured from the ratio of two threshold voltages required to form the shear wave wavefronts in the two mediums. From this method, a high-resolution shear wave amplitude imaging method that reconstructs a tissue boundary is proposed.

  7. Guided Waves Attenuation in Water Immersed Corrugated Plates

    NASA Astrophysics Data System (ADS)

    Meier, Dominique; Franklin, Hervé; Izbicki, Jean Louis; Predoi, Mihai; Rousseau, Martine

    Influences of surface corrugations on the propagation of guided waves along an immersed elastic plate are investigated. The Finite Elements Method is used to compute the reflected and transmitted pressure fields for oblique incident plane harmonic waves in a selected frequency range. The effects of corrugations can also be accounted by means of a rheological model. The corrugated surface is then modeled by using modified boundary conditions at the liquid - corrugated plate interface. In this condition a parameter is introduced that can be evaluated by a fit procedure between the analytical solutions of modal resonance peaks and the FEM results for the corrugated plate.

  8. 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.

  9. 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.

  10. 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.

  11. 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

  12. 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.

  13. 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

  14. Stacking coda waves to resolve the scattering and attenuation structure of Southern California

    NASA Astrophysics Data System (ADS)

    Wang, W.; Shearer, P. M.

    2015-12-01

    Seismic attenuation is caused by two factors, scattering and intrinsic absorption. Charactering the scattering and attenuation properties and the power spectrum of crustal heterogeneity is a fundamental problem for informing strong ground motion estimates at high frequencies, where scattering and attenuation effects are critical. Determining the relative amount of attenuation caused by scattering and intrinsic absorption has been a long-standing interest of seismologists. The wavetrain following the direct body-wave phases is called the coda and is caused by scattered energy. Many studies have analyzed local-event coda to infer crustal and upper-mantle scattering strength and intrinsic attenuation. Here we describe a comprehensive study of coda behavior in Southern California to resolve scattering and intrinsic attenuation structure. First, we apply an envelope-function stacking method to 287,410 seismograms from 6928 geographically dispersed events of M ≥ 1.8 from 1981-2005. The results are presented as spatial averages as a function of distance, source depth, and frequency. Second, we use a Monte Carlo seismic phonon algorithm to simulate the effects of depth-dependent scattering and intrinsic attenuation, which computes scattering probabilities and scattering angles based on theoretical results for random heterogeneity models. This method has the advantage of including both P- and S-wave scattering and is energy conserving even for multiple scattering models. The input 1-D velocity model can be layered to incorporate reflected phases, such as PmP and SmS, to better fit the observations. We will summarize our results for the average scattering and attenuation properties of the southern California crust and the implications for strong ground motion predictions.

  15. 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.

  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

  17. 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.

  18. Plasma-parameter measurements using neutral-particle-beam attenuation

    SciTech Connect

    Foote, J H; Molvik, A W; Turner, W C

    1982-07-07

    Intense and energetic neutral-particle-beam injection used for fueling or heating magnetically confined, controlled-fusion experimental plasmas can also provide diagnostic measurements of the plasmas. The attenuation of an atomic beam (mainly from charge-exchange and ionization interactions) when passing through a plasma gives the plasma line density. Orthogonal arrays of highly collimated detectors of the secondary-electron-emission type have been used in magnetic-mirror experiments to measure neutral-beam attenuation along chords through the plasma volume at different radial and axial positions. The radial array is used to infer the radial plasma-density profile; the axial array, to infer the axial plasma-density profile and the ion angular distribution at the plasma midplane.

  19. 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

  20. 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.

  1. Attenuation of shock waves propagating through nano-structured porous materials

    NASA Astrophysics Data System (ADS)

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

    2013-07-01

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

  2. Sensitivity of seismic measurements to frequency-dependent attenuation and upper mantle structure: An initial approach

    NASA Astrophysics Data System (ADS)

    Bellis, C.; Holtzman, B.

    2014-07-01

    This study addresses the sensitivity of seismic attenuation measurements to dissipative mechanisms and structure in the Earth's upper mantle. The Andrade anelastic model fits experimental attenuation data with a mild power law frequency dependence and can be scaled from laboratory to Earth conditions. We incorporate this anelastic model into 400km 1-D thermal profiles of the upper mantle. These continuous-spectrum models are approximated by multiple relaxation mechanisms that are implemented within a finite-difference scheme to perform wave propagation simulations in 1-D domains. In two sets of numerical experiments, we evaluate the measurable signature of the intrinsic attenuation structure. The two sets are defined by thermal profiles with added step functions of temperature, varying in (i) amplitude and depth or (ii) amplitude and sharpness. The corresponding synthetic data are processed using both the conventional t* approach, i.e., a linear regression of the displacement frequency spectrum, and an alternative nonlinear fit to identify the integrated value of attenuation and its frequency dependence. The measured sensitivity patterns are analyzed to assess the effects of the anelastic model and its spatial distribution on seismic data (in the absence of scattering effects). We have two straightforward results: (1) the frequency dependence power law is recoverable from the measurements; (2) t* is sensitive to both the depth and the amplitude of the step, and it is insensitive to the sharpness of the step, in the 0.25 to 2 Hz band. There is much potential for gaining information about the upper mantle thermodynamic state from careful interpretation of attenuation.

  3. 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.

  4. An energy-based approach to estimate seismic attenuation due to wave-induced fluid flow in heterogeneous poroelastic media

    NASA Astrophysics Data System (ADS)

    Solazzi, Santiago G.; Rubino, J. Germán; Müller, Tobias M.; Milani, Marco; Guarracino, Luis; Holliger, Klaus

    2016-11-01

    Wave-induced fluid flow (WIFF) due to the presence of mesoscopic heterogeneities is considered as one of the main seismic attenuation mechanisms in the shallower parts of the Earth's crust. For this reason, several models have been developed to quantify seismic attenuation in the presence of heterogeneities of varying complexity, ranging from periodically layered media to rocks containing fractures and highly irregular distributions of fluid patches. Most of these models are based on Biot's theory of poroelasticity and make use of the assumption that the upscaled counterpart of a heterogeneous poroelastic medium can be represented by a homogeneous viscoelastic solid. Under this dynamic-equivalent viscoelastic medium (DEVM) assumption, attenuation is quantified in terms of the ratio of the imaginary and real parts of a frequency-dependent, complex-valued viscoelastic modulus. Laboratory measurements on fluid-saturated rock samples also rely on this DEVM assumption when inferring attenuation from the phase shift between the applied stress and the resulting strain. However, whether it is correct to use an effective viscoelastic medium to represent the attenuation arising from WIFF at mesoscopic scales in heterogeneous poroelastic media remains largely unexplored. In this work, we present an alternative approach to estimate seismic attenuation due to WIFF. It is fully rooted in the framework of poroelasticity and is based on the quantification of the dissipated power and stored strain energy resulting from numerical oscillatory relaxation tests. We employ this methodology to compare different definitions of the inverse quality factor for a set of pertinent scenarios, including patchy saturation and fractured rocks. This numerical analysis allows us to verify the correctness of the DEVM assumption in the presence of different kinds of heterogeneities. The proposed methodology has the key advantage of providing the local contributions of energy dissipation to the overall

  5. An energy-based approach to estimate seismic attenuation due to wave-induced fluid flow in heterogeneous poroelastic media

    NASA Astrophysics Data System (ADS)

    Solazzi, Santiago G.; Rubino, J. Germán; Müller, Tobias M.; Milani, Marco; Guarracino, Luis; Holliger, Klaus

    2016-08-01

    Wave-induced fluid flow (WIFF) due to the presence of mesoscopic heterogeneities is considered as one of the main seismic attenuation mechanisms in the shallower parts of the Earth's crust. For this reason, several models have been developed to quantify seismic attenuation in the presence of heterogeneities of varying complexity, ranging from periodically-layered media to rocks containing fractures and highly-irregular distributions of fluid patches. Most of these models are based on Biot's theory of poroelasticity and make use of the assumption that the upscaled counterpart of a heterogeneous poroelastic medium can be represented by a homogeneous viscoelastic solid. Under this dynamic-equivalent viscoelastic medium (DEVM) assumption, attenuation is quantified in terms of the ratio of the imaginary and real parts of a frequency-dependent, complex-valued viscoelastic modulus. Laboratory measurements on fluid-saturated rock samples also rely on this DEVM assumption when inferring attenuation from the phase shift between the applied stress and the resulting strain. However, whether it is correct to use an effective viscoelastic medium to represent the attenuation arising from WIFF at mesoscopic scales in heterogeneous poroelastic media remains largely unexplored. In this work, we present an alternative approach to estimate seismic attenuation due to WIFF. It is fully rooted in the framework of poroelasticity and is based on the quantification of the dissipated power and stored strain energy resulting from numerical oscillatory relaxation tests. We employ this methodology to compare different definitions of the inverse quality factor for a set of pertinent scenarios, including patchy saturation and fractured rocks. This numerical analysis allows us to verify the correctness of the DEVM assumption in the presence of different kinds of heterogeneities. The proposed methodology has the key advantage of providing the local contributions of energy dissipation to the overall

  6. Flow velocity measurement with the nonlinear acoustic wave scattering

    NASA Astrophysics Data System (ADS)

    Didenkulov, Igor; Pronchatov-Rubtsov, Nikolay

    2015-10-01

    A problem of noninvasive measurement of liquid flow velocity arises in many practical applications. To this end the most often approach is the use of the linear Doppler technique. The Doppler frequency shift of signal scattered from the inhomogeneities distributed in a liquid relatively to the emitted frequency is proportional to the sound frequency and velocities of inhomogeneities. In the case of very slow flow one needs to use very high frequency sound. This approach fails in media with strong sound attenuation because acoustic wave attenuation increases with frequency and there is limit in increasing sound intensity, i.e. the cavitation threshold. Another approach which is considered in this paper is based on the method using the difference frequency Doppler Effect for flows with bubbles. This method is based on simultaneous action of two high-frequency primary acoustic waves with closed frequencies on bubbles and registration of the scattered by bubbles acoustic field at the difference frequency. The use of this method is interesting since the scattered difference frequency wave has much lower attenuation in a liquid. The theoretical consideration of the method is given in the paper. The experimental examples confirming the theoretical equations, as well as the ability of the method to be applied in medical diagnostics and in technical applications on measurement of flow velocities in liquids with strong sound attenuation is described. It is shown that the Doppler spectrum form depends on bubble concentration velocity distribution in the primary acoustic beams crossing zone that allows one to measure the flow velocity distribution.

  7. Flow velocity measurement with the nonlinear acoustic wave scattering

    SciTech Connect

    Didenkulov, Igor; Pronchatov-Rubtsov, Nikolay

    2015-10-28

    A problem of noninvasive measurement of liquid flow velocity arises in many practical applications. To this end the most often approach is the use of the linear Doppler technique. The Doppler frequency shift of signal scattered from the inhomogeneities distributed in a liquid relatively to the emitted frequency is proportional to the sound frequency and velocities of inhomogeneities. In the case of very slow flow one needs to use very high frequency sound. This approach fails in media with strong sound attenuation because acoustic wave attenuation increases with frequency and there is limit in increasing sound intensity, i.e. the cavitation threshold. Another approach which is considered in this paper is based on the method using the difference frequency Doppler Effect for flows with bubbles. This method is based on simultaneous action of two high-frequency primary acoustic waves with closed frequencies on bubbles and registration of the scattered by bubbles acoustic field at the difference frequency. The use of this method is interesting since the scattered difference frequency wave has much lower attenuation in a liquid. The theoretical consideration of the method is given in the paper. The experimental examples confirming the theoretical equations, as well as the ability of the method to be applied in medical diagnostics and in technical applications on measurement of flow velocities in liquids with strong sound attenuation is described. It is shown that the Doppler spectrum form depends on bubble concentration velocity distribution in the primary acoustic beams crossing zone that allows one to measure the flow velocity distribution.

  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

  9. Phase velocity and attenuation predictions of waves in cancellous bone using an iterative effective medium approximation.

    PubMed

    Potsika, Vassiliki T; Protopappas, Vasilios C; Vavva, Maria G; Polyzos, Demosthenes; Fotiadis, Dimitrios I

    2013-01-01

    The quantitative determination of wave dispersion and attenuation in bone is an open research area as the factors responsible for ultrasound absorption and scattering in composite biological tissues have not been completely explained. In this study, we use the iterative effective medium approximation (IEMA) proposed in [1] so as to calculate phase velocity and attenuation in media with properties similar to those of cancellous bones. Calculations are performed for a frequency range of 0.4-0.8 MHz and for different inclusions' volume concentrations and sizes. Our numerical results are compared with previous experimental findings so as to assess the effectiveness of IEMA. It was made clear that attenuation and phase velocity estimations could provide supplementary information for cancellous bone characterization. PMID:24111396

  10. 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....

  11. 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....

  12. 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....

  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, 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....

  15. 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

  16. 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.

  17. 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

  18. 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.

  19. 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].

  20. Determination of aerosol size distributions from spectral attenuation measurements.

    PubMed

    Grassl, H

    1971-11-01

    An iteration method for the determination of size distributions of aerosols from spectral attenuation data, similar to the one previously published for clouds, is presented. The basis for this iteration is to consider the extinction efficiency factor of particles as a set of weighting functions covering the entire radius region of a distribution. The weighting functions were calculated exactly from the Mie theory. Aerosol distributions are shown derived from tests with analytical size distributions and also generated from measured aerosol extinction data in seven spectral channels from 0.4-microto 10-micro wavelength in continental aerosols. The influence of relative humidity on the complex index of refraction is also discussed.

  1. Estimates of ocean wave heights and attenuation in sea ice using the SAR wave mode on Sentinel-1A

    NASA Astrophysics Data System (ADS)

    Ardhuin, Fabrice; Collard, Fabrice; Chapron, Bertrand; Girard-Ardhuin, Fanny; Guitton, Gilles; Mouche, Alexis; Stopa, Justin E.

    2015-04-01

    Swell evolution from the open ocean into sea ice is poorly understood, in particular the amplitude attenuation expected from scattering and dissipation. New synthetic aperture radar (SAR) data from Sentinel-1A wave mode reveal intriguing patterns of bright oscillating lines shaped like instant noodles. We investigate cases in which the oscillations are in the azimuth direction, around a straight line in the range direction. This observation is interpreted as the distortion by the SAR processing of crests from a first swell, due to the presence of a second swell. Since deviations from a straight line should be proportional to the orbital velocity toward the satellite, swell height can be estimated, from 1.5 to 5 m in the present case. The evolution of this 13 s period swell across the ice pack is consistent with an exponential attenuation on a length scale of 200 km.

  2. Estimates of ocean wave heights and attenuation in sea ice using the SAR wave mode on Sentinel-1A

    NASA Astrophysics Data System (ADS)

    Ardhuin, Fabrice; Collard, Fabrice; Chapron, Bertrand; Girard-Ardhuin, Fanny; Guitton, Gilles; Mouche, Alexis; Stopa, Justin

    2015-04-01

    Swell evolution from the open ocean into sea ice is poorly understood, in particular the amplitude attenuation expected from scattering and dissipation. New synthetic aperture radar (SAR) data from Sentinel-1 wave mode reveal intriguing patterns of bright oscillating lines shaped like instant noodles. We investigate cases in which the oscillations are in the azimuth direction, around a straight line in the range direction. This observation is interpreted as the distortion by the SAR processing of crests from a first swell, due to the presence of a second swell. As deviations from a straight line should be proportional to the orbital velocity towards the satellite, swell height can be estimated, from 1.5 to 5 m in the present case. This evolution of this 13 s period swell across the ice pack is consistent with an exponential attenuation on a length scale of 200 km.

  3. 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

  4. 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.

  5. 2D Global Attenuation Model of the Upper Mantle from Combined Analysis of Surface Wave Phase and Amplitude Data

    NASA Astrophysics Data System (ADS)

    Ma, Z.; Masters, G.

    2014-12-01

    We have developed a technique that uses a cluster analysis method to measure Rayleigh wave phase and amplitude anomalies. The measurements are 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 2007. Joint inversions for 2D phase velocity and attenuation maps are performed, allowing the coupling through physical dispersion (e.g. Zhou 2009). As demonstrated in Dalton and Ekstrom (2006), correcting the effect of focusing-defocusing is crucial in order to obtain reliable attenuation structures. Ray theory, which has been used to date, may not give reliable predictions of such effects, because it depends strongly on short wavelength velocity structures and so is very sensitive to how the phase velocity maps are smoothed. Instead, we use the 2D finite frequency amplitude kernel (Zhou et al, 2004) to model the focusing-defocusing effect. Attenuation models and evaluations of model error and resolution will be presented.

  6. Sensitivity of modeled ocean heat content to errors in short wave radiation and its attenuation with depth

    NASA Astrophysics Data System (ADS)

    Shulman, Igor; Gould, Richard W.; Anderson, Stephanie; Sakalaukus, Peter

    2016-05-01

    Short wave radiation (SWR) and its attenuation with depth have a major impact on the vertical distribution of the oceanic water temperature, dynamical processes, and ocean-atmosphere interactions. In numerical modeling of oceanic processes, the SWR usually comes from the atmospheric model predictions, while the short wave attenuation schemes are internally prescribed (estimated) inside the oceanic dynamical model. It has been reported that atmospheric models show a tendency to overestimate the shortwave radiation due to underestimation of predicted low-level clouds. Most existing schemes to specify the attenuation of SWR with depth in numerical models are based on: the Jerlov (1976) water-types classification; climatological estimates of attenuation coefficients or from the biological model predictions of light-absorbing and scattering water constituents. All of the above attenuation schemes are prone to introducing errors in the attenuation of short wave radiation with depth. As a result, we have to deal with two types of errors in the oceanic modeling: those due to the incorrect specification of the magnitude of SWR at the surface (from the atmospheric model), and those due to inaccurate vertical attenuation of SWR (prescribed in the oceanic model). We have developed an approach for estimating errors in the oceanic model heat budget due to errors in surface values of SWR and in its attenuation with depth. Based on this approach, we present examples illustrating sensitivities of the heat budget of the water column to the changes in specification of surface SWR and its attenuation.

  7. 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

  8. Measurement of elastic wave dispersion on human femur tissue

    NASA Astrophysics Data System (ADS)

    Strantza, M.; Louis, O.; Polyzos, D.; Boulpaep, F.; Van Hemelrijck, D.; Aggelis, D. G.

    2014-03-01

    Cortical bone is one of the most complex heterogeneous media exhibiting strong wave dispersion. In such media when a burst of energy goes into the formation of elastic waves the different modes tend to separate according to the velocities of the frequency components as usually occurs in waveguides. In this study human femur specimens were subjected to elastic wave measurements. The main objective of the study is using broadband acoustic emission sensors to measure parameters like wave velocity dispersion and attenuation. Additionally, waveform parameters like the duration, rise time and average frequency, are also examined relatively to the propagation distance as a preparation for acoustic emission monitoring during fracture. To do so, four sensors were placed at adjacent positions on the surface of the cortical bone in order to record the transient response after pencil lead break excitation. The results are compared to similar measurements on a bulk metal piece which does not exhibit heterogeneity at the scale of the propagating wave lengths. It is shown 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.

  9. 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.

  10. 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 ...

  11. 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.

  12. Ultrasonic wave propagation in thermoviscous moving fluid confined by heating pipeline and flow measurement performance.

    PubMed

    Chen, Yong; Huang, Yiyong; Chen, Xiaoqian

    2013-09-01

    Ultrasonic wave propagation in thermoviscous fluid with pipeline shear mean flow in the presence of a temperature gradient is investigated. On the assumption of irrotational and axisymmetric wave propagation, a mathematical formulation of the convected wave equation is proposed without simplification in the manner of Zwikker and Kosten. A method based on the Fourier-Bessel theory, which is complete and orthogonal in Lebesgue space, is introduced to convert the wave equations into homogeneous algebraic equations. Then numerical calculation of the axial wavenumber is presented. In the end, wave attenuation in laminar and turbulent flow is numerically studied. Meanwhile measurement performance of an ultrasonic flow meter is parametrically analyzed.

  13. Ultrasonic wave propagation in thermoviscous moving fluid confined by heating pipeline and flow measurement performance.

    PubMed

    Chen, Yong; Huang, Yiyong; Chen, Xiaoqian

    2013-09-01

    Ultrasonic wave propagation in thermoviscous fluid with pipeline shear mean flow in the presence of a temperature gradient is investigated. On the assumption of irrotational and axisymmetric wave propagation, a mathematical formulation of the convected wave equation is proposed without simplification in the manner of Zwikker and Kosten. A method based on the Fourier-Bessel theory, which is complete and orthogonal in Lebesgue space, is introduced to convert the wave equations into homogeneous algebraic equations. Then numerical calculation of the axial wavenumber is presented. In the end, wave attenuation in laminar and turbulent flow is numerically studied. Meanwhile measurement performance of an ultrasonic flow meter is parametrically analyzed. PMID:23967920

  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.

  15. Error in total ozone measurements arising from aerosol attenuation

    NASA Technical Reports Server (NTRS)

    Thomas, R. W. L.; Basher, R. E.

    1979-01-01

    A generalized least squares method for deducing both total ozone and aerosol extinction spectrum parameters from Dobson spectrophotometer measurements was developed. An error analysis applied to this system indicates that there is little advantage to additional measurements once a sufficient number of line pairs have been employed to solve for the selected detail in the attenuation model. It is shown that when there is a predominance of small particles (less than about 0.35 microns in diameter) the total ozone from the standard AD system is too high by about one percent. When larger particles are present the derived total ozone may be an overestimate or an underestimate but serious errors occur only for narrow polydispersions.

  16. 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.

  17. Attenuation of laser generated ultrasound in steel at high temperatures; comparison of theory and experimental measurements.

    PubMed

    Kube, Christopher M

    2016-08-01

    This article reexamines some recently published laser ultrasound measurements of the longitudinal attenuation coefficient obtained during annealing of two steel samples (DP600 and S550). Theoretical attenuation models based on perturbation theory are compared to these experimental measurements. It is observed that the Rayleigh attenuation formulas provide the correct qualitative agreement, but overestimate the experimental values. The more general theoretical attenuation model considered here demonstrates strong quantitative agreement, which highlights the applicability of the model during real-time metal processing.

  18. 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.

  19. 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.

  20. 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.

  1. A high-impedance attenuator for measurement of high-voltage nanosecond-range pulses.

    PubMed

    Yu, Binxiong; Liu, Jinliang; Zhang, Tianyang; Hong, Zhiqiang

    2013-05-01

    A novel kind of high-impedance cable attenuator for measurement of high-voltage ns-range pulses is investigated in this paper. The input and output ports of the proposed attenuator were both high-impedance ports, and good pulse response characteristics of the proposed attenuator were obtained with pulse response time less than 1 ns. According to the requirement of measurement, two attenuators with lengths at 14 m and 0.7 m were developed with response time of 1 ns and 20 ns, and the attenuation coefficient of 96 and 33.5, respectively. The attenuator with the length of 14 m was used as a secondary-stage attenuator of a capacitive divider to measure the high-voltage pulses at several hundred ns range. The waveform was improved by the proposed attenuator in contrast to the result only measured by the same capacitive divider and a long cable line directly. The 0.7 m attenuator was also used as a secondary-stage attenuator of a standard resistant divider for an accurate measurement of high-voltage pulses at 100 ns range. The proposed cable attenuator can be used to substitute the traditional secondary-stage attenuators for the measurement of high-voltage pulses.

  2. Wave measurement and modeling in Chesapeake Bay

    NASA Astrophysics Data System (ADS)

    Lin, Weiqi; Sanford, Lawrence P.; Suttles, Steven E.

    2002-12-01

    Three recently measured wind and wave data sets in the northern part of Chesapeake Bay (CB) are presented. Two of the three data sets were collected in late 1995. The third one was collected in July of 1998. The analyzed wind and wave data show that waves were dominated by locally generated, fetch limited young wind seas. Significant wave heights were highly correlated to the local driving wind speeds and the response time of the waves to the winds was about 1 h. We also tested two very different numerical wave models, Simulation of WAves Nearshore (SWAN) and Great Lakes Environmental Research Laboratory (GLERL), to hind-cast the wave conditions against the data sets. Time series model-data comparisons made using SWAN and GLERL showed that both models behaved well in response to a suddenly changing wind. In general, both SWAN and GLERL over-predicted significant wave height; SWAN over-predicted more than GLERL did. SWAN had a larger scatter index and a smaller correlation coefficient for wave height than GLERL had. In addition, both models slightly under-predicted the peak period with a fairly large scatter and low correlation coefficient. SWAN predicted mean wave direction better than GLERL did. Directional wave spectral comparisons between SWAN predictions and the data support these statistical comparisons. The GLERL model was much more computationally efficient for wind wave forecasts in CB. SWAN and GLERL predicted different wave height field distributions for the same winds in deeper water areas of the Bay where data were not available, however. These differences are as yet unresolved.

  3. 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.

  4. Producing acoustic 'Frozen Waves': simulated experiments with diffraction/attenuation resistant beams in lossy media.

    PubMed

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

    2014-08-01

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

  5. The depolarization - attenuated backscatter relation: CALIPSO lidar measurements vs. theory.

    PubMed

    Hu, Yongxiang; Vaughan, Mark; Liu, Zhaoyan; Lin, Bing; Yang, Ping; Flittner, David; Hunt, Bill; Kuehn, Ralph; Huang, Jiangping; Wu, Dong; Rodier, Sharon; Powell, Kathy; Trepte, Charles; Winker, David

    2007-04-30

    Using measurements obtained by the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite, relationships between layer-integrated depolarization ratio (delta) and layer-integrated attenuated backscatter (gamma) are established for moderately thick clouds of both ice and water. A new and simple form of the delta-gamma relation for spherical particles, developed from Monte Carlo simulations and suitable for both water clouds and spherical aerosol particles, is found to agree well with the observations. A high-backscatter, low-depolarization delta-gamma relationship observed for some ice clouds is shown to result primarily from horizontally oriented plates and implies a preferential lidar ratio - depolarization ratio relation in nature for ice cloud particles containing plates.

  6. Mucosal Wave Measurement and Visualization Techniques

    PubMed Central

    Krausert, Christopher R.; Olszewski, Aleksandra E.; Taylor, Lindsay N.; McMurray, James S.; Dailey, Seth H.; Jiang, Jack J.

    2010-01-01

    Organized vibration of the vocal folds is critical to high quality voice production. When the vocal folds oscillate, the superficial tissue of the vocal fold is displaced in a wave-like fashion, creating the so called “mucosal wave”. Because the mucosal wave is dependent on vocal fold structure, physical alterations of that structure cause mucosal wave abnormalities. Visualization and quantification of mucosal wave properties have become useful parameters in diagnosing and managing vocal fold pathology. Mucosal wave measurement provides information about vocal fold characteristics that cannot be determined with other assessment techniques. Here, we discuss the benefits, disadvantages, and clinical applicability of the different mucosal wave measurement techniques, such as electroglottography (EGG), photoglottography (PGG), and ultrasound and visualization techniques that include videokymography (VKG), stroboscopy, and high-speed digital imaging (HSDI). The various techniques and their specific uses are reviewed with the intention of helping researchers and clinicians choose a method for a given situation and understand its limitations as well as its potential applications. Recent applications of these techniques for quantitative assessment demonstrate that additional research must be conducted to realize the full potential of these tools. Evaluations of existing research and recommendations for future research are given to promote both the quantitative study of the mucosal wave through accurate and standardized measurement of mucosal wave parameters and the development of reliable methods with which physicians can diagnose vocal disorders. PMID:20471798

  7. Direct measurement of light waves.

    PubMed

    Goulielmakis, E; Uiberacker, M; Kienberger, R; Baltuska, A; Yakovlev, V; Scrinzi, A; Westerwalbesloh, Th; Kleineberg, U; Heinzmann, U; Drescher, M; Krausz, F

    2004-08-27

    The electromagnetic field of visible light performs approximately 10(15) oscillations per second. Although many instruments are sensitive to the amplitude and frequency (or wavelength) of these oscillations, they cannot access the light field itself. We directly observed how the field built up and disappeared in a short, few-cycle pulse of visible laser light by probing the variation of the field strength with a 250-attosecond electron burst. Our apparatus allows complete characterization of few-cycle waves of visible, ultraviolet, and/or infrared light, thereby providing the possibility for controlled and reproducible synthesis of ultrabroadband light waveforms.

  8. Directional wave measurements using an autonomous vessel

    NASA Astrophysics Data System (ADS)

    Hole, Lars R.; Fer, Ilker; Peddie, David

    2016-08-01

    An autonomous vessel, the Offshore Sensing Sailbuoy, was used for wave measurements near the Ekofisk oil platform complex in the North Sea (56.5º N, 3.2º E, operated by ConocoPhillips) from 6 to 20 November 2015. Being 100 % wind propelled, the Sailbuoy has two-way communication via the Iridium network and has the capability for missions of 6 months or more. It has previously been deployed in the Arctic, Norwegian Sea and the Gulf of Mexico, but the present study was the first test for wave measurements. During the campaign the Sailbuoy held position about 20 km northeast of Ekofisk (on the lee side) during rough conditions. Mean wind speed measured at Ekofisk during the campaign was 9.8 m/s, with a maximum of 20.4 m/s, with wind mostly from south and southwest. A Datawell MOSE G1000 GPS-based 2 Hz wave sensor was mounted on the Sailbuoy. Mean significant wave height (H s 1 min) measured was 3 m, whereas maximum H s was 6 m. Mean wave period was 7.7 s, while maximum wave height, H max, was 12.6 m. These measurements have been compared with non-directional Waverider observations at the Ekofisk complex. The agreement between the two data sets was very good, with a mean percent absolute error of 7 % and a linear correlation coefficient of 0.97. The wave frequency spectra measured by the two instruments compared very well, except for low H s (˜1 m), where the motion of the vessel seemed to influence the measurements. Nevertheless, the Sailbuoy performed well during this campaign, and results suggest that it is a suitable platform for wave measurements in a broad range of sea conditions.

  9. Directional wave measurements using an autonomous vessel

    NASA Astrophysics Data System (ADS)

    Hole, Lars R.; Fer, Ilker; Peddie, David

    2016-09-01

    An autonomous vessel, the Offshore Sensing Sailbuoy, was used for wave measurements near the Ekofisk oil platform complex in the North Sea (56.5º N, 3.2º E, operated by ConocoPhillips) from 6 to 20 November 2015. Being 100 % wind propelled, the Sailbuoy has two-way communication via the Iridium network and has the capability for missions of 6 months or more. It has previously been deployed in the Arctic, Norwegian Sea and the Gulf of Mexico, but the present study was the first test for wave measurements. During the campaign the Sailbuoy held position about 20 km northeast of Ekofisk (on the lee side) during rough conditions. Mean wind speed measured at Ekofisk during the campaign was 9.8 m/s, with a maximum of 20.4 m/s, with wind mostly from south and southwest. A Datawell MOSE G1000 GPS-based 2 Hz wave sensor was mounted on the Sailbuoy. Mean significant wave height ( H s 1 min) measured was 3 m, whereas maximum H s was 6 m. Mean wave period was 7.7 s, while maximum wave height, H max, was 12.6 m. These measurements have been compared with non-directional Waverider observations at the Ekofisk complex. The agreement between the two data sets was very good, with a mean percent absolute error of 7 % and a linear correlation coefficient of 0.97. The wave frequency spectra measured by the two instruments compared very well, except for low H s (˜1 m), where the motion of the vessel seemed to influence the measurements. Nevertheless, the Sailbuoy performed well during this campaign, and results suggest that it is a suitable platform for wave measurements in a broad range of sea conditions.

  10. 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

  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. Wave Measurements Using GPS Velocity Signals

    PubMed Central

    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

  14. Measurements of ultrasound velocity and attenuation in numerical anisotropic porous media compared to Biot's and multiple scattering models.

    PubMed

    Mézière, Fabien; Muller, Marie; Bossy, Emmanuel; Derode, Arnaud

    2014-07-01

    This article quantitatively investigates ultrasound propagation in numerical anisotropic porous media with finite-difference simulations in 3D. The propagation media consist of clusters of ellipsoidal scatterers randomly distributed in water, mimicking the anisotropic structure of cancellous bone. Velocities and attenuation coefficients of the ensemble-averaged transmitted wave (also known as the coherent wave) are measured in various configurations. As in real cancellous bone, one or two longitudinal modes emerge, depending on the micro-structure. The results are confronted with two standard theoretical approaches: Biot's theory, usually invoked in porous media, and the Independent Scattering Approximation (ISA), a classical first-order approach of multiple scattering theory. On the one hand, when only one longitudinal wave is observed, it is found that at porosities higher than 90% the ISA successfully predicts the attenuation coefficient (unlike Biot's theory), as well as the existence of negative dispersion. On the other hand, the ISA is not well suited to study two-wave propagation, unlike Biot's model, at least as far as wave speeds are concerned. No free fitting parameters were used for the application of Biot's theory. Finally we investigate the phase-shift between waves in the fluid and the solid structure, and compare them to Biot's predictions of in-phase and out-of-phase motions.

  15. Variation of Seismic Coda Wave Attenuation in the Garhwal Region, Northwestern Himalaya

    NASA Astrophysics Data System (ADS)

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

    2012-01-01

    Seismic coda wave attenuation ( Q_{text{c}}^{ - 1} ) characteristics in the Garhwal region, northwestern Himalaya is studied using 113 short-period, vertical component seismic observations from local events with hypocentral distance less than 250 km and magnitude range between 1.0 to 4.0. They are located mainly in the vicinity of the Main Boundary Thrust (MBT) and the Main Central Thrust (MCT), which are well-defined tectonic discontinuities in the Himalayas. Coda wave attenuation ( Q_{text{c}}^{ - 1} ) is estimated using the single isotropic scattering method at central frequencies 1.5, 3, 5, 7, 9, 12, 16, 20, 24 and 28 Hz using several starting lapse times and coda window lengths for the analysis. Results show that the ( Q_{text{c}}^{ - 1} ) values are frequency dependent in the considered frequency range, and they fit the frequency power law ( Q_{text{c}}^{ - 1} left( f right) = Q0^{ - 1} f^{ - n} ). The Q 0 ( Q c at 1 Hz) estimates vary from about 50 for a 10 s lapse time and 10 s window length, to about 350 for a 60 s lapse time and 60 s window length combination. The exponent of the frequency dependence law, n ranges from 1.2 to 0.7; however, it is greater than 0.8, in general, which correlates well with the values obtained in other seismically and tectonically active and highly heterogeneous regions. The attenuation in the Garhwal region is found to be lower than the Q {c/-1} values obtained for other seismically active regions of the world; however, it is comparable to other regions of India. The spatial variation of coda attenuation indicates that the level of heterogeneity decreases with increasing depth. The variation of coda attenuation has been estimated for different lapse time and window length combinations to observe the effect with depth and it indicates that the upper lithosphere is more active seismically as compared to the lower lithosphere and the heterogeneity decreases with increasing depth.

  16. Laser-generated shock wave attenuation aimed at microscale pyrotechnic device design

    NASA Astrophysics Data System (ADS)

    Yu, Hyeonju; Yoh, Jack J.

    2016-05-01

    To meet the rising demand for miniaturizing the pyrotechnic device that consists of donor/acceptor pair separated by a bulkhead or a thin gap, the shock initiation sensitivity in the microscale gap test configuration is investigated. For understanding the shock attenuation within a gap sample (304 stainless steel) thickness of 10˜800 μm, the laser-generated shock wave in water confinement is adopted. The shock properties are obtained from the free surface velocity by making use of a velocity interferometer system for any reflector (VISAR). Analytical models for plasma generation in a confined geometry and for evolution and decay of shock waves during the propagation are considered. The shape and amplitude of the laser-driven initial pressure load and its attenuation pattern in the gap are effectively controlled for targeting the microscale propagation distance and subsequent triggering pressure for the acceptor charge. The reported results are important in the precise controlling of the shock strength during the laser initiation of microscale pyrotechnic devices.

  17. 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.

  18. 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

  19. Finite Difference Numerical Modeling of Gravito-Acoustic Wave Propagation in a Windy and Attenuating Atmosphere

    NASA Astrophysics Data System (ADS)

    Brissaud, Q.; Garcia, R.; Martin, R.; Komatitsch, D.

    2015-12-01

    The acoustic and gravity waves propagating in the planetary atmospheres have been studied intensively as markers of specific phenomena (tectonic events, explosions) or as contributors to the atmosphere dynamics. To get a better understanding of the physic behind these dynamic processes, both acoustic and gravity waves propagation should be modeled in an attenuating and windy 3D atmosphere from the ground to the upper thermosphere. Thus, In order to provide an efficient numerical tool at the regional or the global scale a high order finite difference time domain (FDTD) approach is proposed that relies on the linearized compressible Navier-Stokes equations (Landau 1959) with non constant physical parameters (density, viscosities and speed of sound) and background velocities (wind). One significant benefit from this code is its versatility. Indeed, it handles both acoustic and gravity waves in the same simulation that enables one to observe correlations between the two. Simulations will also be performed on 2D/3D realistic cases such as tsunamis in a full MSISE-00 atmosphere and gravity-wave generation through atmospheric explosions. Computations are validated by comparison to well-known analytical solutions based on dispersion relations in specific benchmark cases (atmospheric explosion and bottom displacement forcing).

  20. Anisotropy and attenuation of crosshole channel waves from the Antrim Shale gas play, Michigan Basin

    NASA Astrophysics Data System (ADS)

    Liu, Enru; Queen, John H.; Cox, V. Dale

    2000-04-01

    We analyze the crosshole data from the Antrim Shale gas play at the MIT test site in the Michigan Basin. A crosshole seismic logging analysis has revealed the presence of strong transverse isotropy possibly due to the alignment of clay platelets along the bedding plane or sedimentary bedding, and strong continuity in the depth interval covered in this study. We find that the data are dominated by channel waves associated with low velocity zones (waveguides) identified in the sonic logs. Channel waves are characterized by their unique characteristics, such as dispersion and amplitude variation with depth. The channel-wave analysis has revealed the possible presence of azimuthal anisotropy at the top of the depth covered in this survey, which may be related to fracturing in the Antrim Shale formation. The data also show strong attenuation of S-waves characterized by very low frequency contents which may be due to viscoelastic properties of shaly sands or scattering by fractures. However, direct estimates of fracture parameters are not possible due to the limited data available. Finally, we have modeled the data with synthetic seismograms using a model with a 30% anisotropy.

  1. Finite-difference numerical modelling of gravitoacoustic wave propagation in a windy and attenuating atmosphere

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

    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 3-D 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 2-D or 3-D 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.

  2. 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

  3. Structure-preserving spectral element method in attenuating seismic wave modeling

    NASA Astrophysics Data System (ADS)

    Cai, Wenjun; Zhang, Huai

    2016-04-01

    This work describes the extension of the conformal symplectic method to solve the damped acoustic wave equation and the elastic wave equations in the framework of the spectral element method. The conformal symplectic method is a variation of conventional symplectic methods to treat non-conservative time evolution problems which has superior behaviors in long-time stability and dissipation preservation. To construct the conformal symplectic method, we first reformulate the damped acoustic wave equation and the elastic wave equations in their equivalent conformal multi-symplectic structures, which naturally reveal the intrinsic properties of the original systems, especially, the dissipation laws. We thereafter separate each structures into a conservative Hamiltonian system and a purely dissipative ordinary differential equation system. Based on the splitting methodology, we solve the two subsystems respectively. The dissipative one is cheaply solved by its analytic solution. While for the conservative system, we combine a fourth-order symplectic Nyström method in time and the spectral element method in space to cover the circumstances in realistic geological structures involving complex free-surface topography. The Strang composition method is adopted thereby to concatenate the corresponding two parts of solutions and generate the completed numerical scheme, which is conformal symplectic and can therefore guarantee the numerical stability and dissipation preservation after a large time modeling. Additionally, a relative larger Courant number than that of the traditional Newmark scheme is found in the numerical experiments in conjunction with a spatial sampling of approximately 5 points per wavelength. A benchmark test for the damped acoustic wave equation validates the effectiveness of our proposed method in precisely capturing dissipation rate. The classical Lamb problem is used to demonstrate the ability of modeling Rayleigh-wave propagation. More comprehensive

  4. 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.

  5. 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.

  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. 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.

  8. Effects of heterogeneities on the propagation, scattering and attenuation of seismic waves and the characterization of seismic source. Final report, 1 December 1982-30 November 1985

    SciTech Connect

    Aki, K.; Cormier, V.F.; Toksoz, M.N.

    1985-01-01

    During this reporting period, work was completed on testing alternative measures of body-wave magnitude. It was found that alternative measures of body waves magnitude often exhibit as much scatter as classical measures of magnitude, although coda magnitudes usually have slightly less scatter than spectral and classical magnitudes. In the cases investigated, these differences were usually not statistically significant. Another completed task was an investigation of the intrinsic attenuation of the Earth's mantle selected paths from the Sea of Okhotsk to Regional Seismic Test Network (RSTN) and Global Digital Seismic Network (GDSN) Stations in North America. It was concluded that the intrinsic attenuation in the mantle beneath eastern North America is both depth and frequency dependent and that spectral and time domain studies of attenuation can be reconciled in the frequency band up to 2 Hz. The focus of the project was then divided between source problems related to scattering and seismic wave propagation in three-dimensional, heterogeneous media. A significant result was that short period and broadband waveforms can improve the depth-resolution-determined earthquakes and underground nuclear explosions, forming a powerful discriminant. Scattering was studied theoretically and observationally. The significant result of that work is that the Earth's lithosphere must possess multiple scales of heterogeneity in order to explain both the amplitude and phase fluctuations at large arrays as well as the shapes of local S coda.

  9. Experimental measurements of seismic attenuation in microfracture sedimentary rock

    SciTech Connect

    Peacock, S.; McCann, C.; Sothcott, J.; Astin, T.R. . Research Inst. for Sedimentology)

    1994-09-01

    In a previous paper (Peacock et al., 1994), the authors related ultrasonic velocities in water-saturated Carrara Marble to crack densities in polished sections to verify Hudson's (1980, 1981, 1986) theory for velocities in cracked rock. They describe the empirical relationships between attenuation and crack density that they established during these experiments in the hope of clarifying the mechanism of attenuation in rocks with fluid-filled cracks. Relating seismic velocity and attenuation to crack density is important in predicting the productivity of fractured petroleum reservoirs such as the North Sea Brent Field. It also allows cracks to be used as stress indicators throughout the shallow crust (Crampin and Lovell, 1991).

  10. 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.

  11. New procedures for analyzing Doppler-shift attenuation lifetime measurements

    NASA Astrophysics Data System (ADS)

    Petkov, P.; Dewald, A.; Tonev, D.; Goutev, N.; Asova, G.; Dimitrov, B.; Gavrilov, G.; Mineva, M. N.; Yavahchova, M. S.

    2015-05-01

    A generalization of an earlier proposed version of the Differential decay curve method is presented for the analysis of Doppler-shift attenuation lifetime measurements. The lifetime is derived directly from the line shapes of the depopulating and feeding transitions without any assumptions about or fitting of the time dependence of the population of the corresponding levels except for unobserved feeding when relevant. Fitting of the line shapes is also not necessary. The only approximation involved is related to the continuous treatment of the nuclear scattering events in the Monte Carlo simulation needed. Tests with simulated and real data reveal good reliability of this method. We propose also a new precise procedure where the lifetime is derived by fitting the time dependence of the population of the level of interest using the line shape of the depopulating transition and the difference of the spectra of the depopulating and feeding transitions. Practical application to simulated and real data proves the applicability of the new procedure.

  12. Body-wave Attenuation in the South-Central Region of the Gulf of California, México

    NASA Astrophysics Data System (ADS)

    Castro, R. R.; Vidales-Basurto, C. A.; Huerta, C. I.; Sumy, D. F.; Gaherty, J. B.; Collins, J. A.

    2014-12-01

    We present results from a recent study of seismic attenuation of body waves in the south-central region of the Gulf of California (GoC) obtained using records from the Network of Autonomously Recording Seismographs of Baja California (NARS-Baja), from the CICESE's Broadband Seismological Network of the GoC (RESBAN), and from the Ocean Bottom Seismographs (OBS) deployed as part of the Sea of Cortez Ocean Bottom Array experiment (SCOOBA). We examine 27 well-located earthquakes that occurred from October 2005 to October 2006 with magnitudes (Mw) between 3.5 and 4.8. We estimated S-wave site effects by calculating horizontal to vertical spectral ratios and determined attenuation functions with a nonparametric model by inverting the observed spectral amplitudes of 21 frequencies between 0.13 and 12.59 Hz for the SCOOBA (OBS) stations and 19 frequencies between 0.16 and 7.94 Hz for NARS-Baja and RESBAN stations. We calculated the geometrical spreading and the attenuation (1/Q) factors for two distance intervals (10-120 km and 120-220 km, respectively) for each frequency considered. The estimates of Q obtained with the SCOOBA (OBS) records for the interval 10-120 km indicate that the P waves attenuate more than S waves (QP=34 f 0.82, QS=59 f 0.90) for frequencies between 0.6 and 12.6 Hz; while for the 120-220 km interval, where ray-paths travel deeper, S waves attenuate more than P waves (QP=117 f 0.44, QS=51 f 1.12). The estimates of Q obtained using NARS-Baja and RESBAN records, within 10-120 km, indicate that P waves attenuate more than S waves (QP=69 f 0.87, QS=176 f 0.61) at frequencies between 0.3 and 6.3 Hz; while at the 120-220 km distance interval S waves attenuate slightly more than P waves (QP=39 f 0.64, QS=48 f 0.37) at high frequencies (f > 3 Hz). These results, based on a unique OBS dataset, provide an indirect mean to constrain future models of the thermal structure beneth the GoC.

  13. 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.

  14. 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

  15. 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.

  16. Attenuation, source parameters and site effects of SH waves in Taiwan

    NASA Astrophysics Data System (ADS)

    Chang, Shun-Chiang; Wen, Kuo-Liang

    2016-04-01

    Generalized inversion technique (GIT) (Castro et al., 1990) was used to derive SH-wave in the frequency range 0.2-25 Hz (interval 0.1 Hz). The inversion results can find attenuation characteristics, earthquake source parameters and site amplification functions. The characteristics of the site amplification are referred to horizontal-to-vertical (H/V) Fourier spectral ratios of microtremor for a referent rock site. The SH-wave from 28 earthquakes with magnitude ranging from ML 5 to 7, of 1319 earthquake records at 146 TSMIP strong motion stations in Jianan Plain, southwestern Taiwan are used in this analysis. The SH-wave quality factor Q(f) is estimated as 52.83f0.77 for 0.2<= f < =25 Hz. The stress drops can be found from source spectra by using the omega-square model. The results of site amplification are similar to horizontal-to-vertical spectral ratio of the microtremor which have clearly and similar predominant peaks.

  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 of two types of dilatational waves in an air-filled unconsolidated sand

    SciTech Connect

    Hickey, C.J.; Sabatier, J.M.

    1997-07-01

    This study consists of laboratory measurements of dilatational waves propagating through an air-filled unconsolidated sand. One excitation technique consists of a loudspeaker suspended in the air above the packing of sand. A second excitation technique uses a mechanical shaker in contact with the sand. The transmitted signals are received using microphones and geophones located at various depths within the sand. An interpretation based on measured phase speeds indicates that the transmitted energy from the suspended loudspeaker source is partitioned primarily but not exclusively into the type-II dilatational wave. This wave attenuates rapidly and is only detected at depths of less than about 15 cm for this particular sample. At the deeper depths the detected signal is associated with the type-I dilatational wave. The mechanical shaker produces only a type-I dilatational wave. Both the geophone and microphone sensors can detect both types of dilatational waves. {copyright} {ital 1997 Acoustical Society of America.}

  19. Attenuation of laser generated ultrasound in steel at high temperatures; comparison of theory and experimental measurements.

    PubMed

    Kube, Christopher M

    2016-08-01

    This article reexamines some recently published laser ultrasound measurements of the longitudinal attenuation coefficient obtained during annealing of two steel samples (DP600 and S550). Theoretical attenuation models based on perturbation theory are compared to these experimental measurements. It is observed that the Rayleigh attenuation formulas provide the correct qualitative agreement, but overestimate the experimental values. The more general theoretical attenuation model considered here demonstrates strong quantitative agreement, which highlights the applicability of the model during real-time metal processing. PMID:27235777

  20. 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.

  1. 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.

  2. Anisotropic physical properties of myocardium characterized by ultrasonic measurements of backscatter, attenuation, and velocity

    NASA Astrophysics Data System (ADS)

    Baldwin, Steven L.

    The goal of elucidating the physical mechanisms underlying the propagation of ultrasonic waves in anisotropic soft tissue such as myocardium has posed an interesting and largely unsolved problem in the field of physics for the past 30 years. In part because of the vast complexity of the system being studied, progress towards understanding and modeling the mechanisms that underlie observed acoustic parameters may first require the guidance of careful experiment. Knowledge of the causes of observed ultrasonic properties in soft tissue including attenuation, speed of sound, and backscatter, and how those properties are altered with specific pathophysiologies, may lead to new noninvasive approaches to the diagnosis of disease. The primary aim of this Dissertation is to contribute to an understanding of the physics that underlies the mechanisms responsible for the observed interaction of ultrasound with myocardium. To this end, through-transmission and backscatter measurements were performed by varying acoustic properties as a function of angle of insonification relative to the predominant myofiber direction and by altering the material properties of myocardium by increased protein cross-linking induced by chemical fixation as an extreme form of changes that may occur in certain pathologies such as diabetes. Techniques to estimate acoustic parameters from backscatter were broadened and challenges to implementing these techniques in vivo were addressed. Provided that specific challenges identified in this Dissertation can be overcome, techniques to estimate attenuation from ultrasonic backscatter show promise as a means to investigate the physical interaction of ultrasound with anisotropic biological media in vivo. This Dissertation represents a step towards understanding the physics of the interaction of ultrasonic waves with anisotropic biological media.

  3. 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.

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

    PubMed

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

    2016-03-05

    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.

  5. 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

  6. Estimating Attenuation Coefficients and P-Wave Velocities of the Shallow San Jacinto Fault Zone from Betsy Gunshots Data Recorded by a Spatially Dense Array with 1108 Sensors

    NASA Astrophysics Data System (ADS)

    Ozakin, Yaman; Ben-Zion, Yehuda

    2016-04-01

    We estimate values of P wave velocity and P attenuation coefficients (QP) for the subsurface material at the Sage Brush Flat site along the Clark branch of the San Jacinto Fault Zone. The data are generated by 33 Betsy gunshots and recorded by a spatially dense array of 1108 vertical component geophones deployed in a rectangular grid that is approximately 600 m x 600 m. We automatically pick the arrival times of the seismic body waves from each explosion arriving at stations within 200 m. These measurements are used to derive an average velocity map with velocity values ranging from 500 m/s to 1250 m/s. We estimate the energy of the early P waves by squaring the amplitudes in a short window relative to the automatic picks. These energies are fitted to a decay function representing the geometrical spreading and intrinsic attenuation. By separating the stations into spatial bins and calculating attenuation values for each by linear regression, we construct a QP values map. Most of the QP values are in 5-20 range, which is consistent with other studies of shallow fault zone regions.

  7. 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.

  8. 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…

  9. Measurement of photon attenuation from different cardiac chambers

    SciTech Connect

    Keller, A.M.; Simon, T.R.; Malloy, C.R.; Dehmer, G.J.; Smitherman, T.C.

    1985-05-01

    Accounting for the attenuation (AT) of photons within cardiac chambers is crucial to accurate non-geometric volume determinations from gated blood pool scintigraphy. Previous techniques to determine AT for each patient have assumed an attenuation factor of 0.15/cm for Tc-99m, the value of water. To verify this, the authors determined the AT at various tissue distances (TD) in vivo. As a point source they used the balloon of a 5 French Swan-Ganz catheter which could reproducibly be filled with a constant amount of Tc-99m and could be placed within the left or right cardiac chambers. The exact location of the balloon, once inflated, and the TD from the balloon to the collimator of a small field-of-view Anger camera was determined using biplane orthogonal fluoroscopy. AT was determined by counting the inflated Tc-99m filled balloon in air and dividing that value by the counts of the same balloon within the heart. The authors positioned the balloon in the apex of the right and left ventricle, the ascending aorta and at the junction of the right atrium and inferior vena cava to give a total of 36 simultaneous observations of AT and TD. For our data the slope of the regression of the natural log of AT versus TD, when forced through zero, was 0.102, the calculated attenuation factor. The authors conclude that the attenuation factor that should be used for determining cardiac volumes with gated blood pool scans is 0.102/cm, not the value for water.

  10. 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 Δt* for multiple frequency bands within 0.08-2 Hz. All frequency bands show high Δt* regions in the southwestern U.S., southern Rocky Mountains, and Appalachian margin. Low Δt* is more common across the cratonic interior. Inversions with narrower frequency bands yield similar patterns, but greater Δt* magnitudes. Even the two standard deviation Δt* 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 Δt* signal is nonthermal in origin. Nonthermal contributions are further indicated by only a moderate correlation between Δt* and P travel times. Some geographic variations, such as high Δt* 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 Δt* are higher and exhibit steeper increases with frequency compared to T/Z spectra for low Δt* stations. The large magnitude of Δt* estimates and the T/Z spectra are consistent with major contributions to Δt* from scattering. A weak positive correlation between intrinsic attenuation and apparent attenuation due to scattering may contribute to Δt* magnitude and the moderate correlation of Δt* with travel times.

  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. Influence of forward and multiple light scatter on the measurement of beam attenuation in highly scattering marine environments.

    PubMed

    Piskozub, Jacek; Stramski, Dariusz; Terrill, Eric; Melville, W Kendall

    2004-08-20

    Using three-dimensional Monte Carlo radiative transfer simulations, we examine the effect of beam transmissometer geometry on the relative error in the measurement of the beam-attenuation coefficient in an aquatic environment characterized by intense light scattering, especially within submerged bubble clouds entrained by surface-wave breaking. We discuss the forward-scattering error associated with the detection of photons scattered at small angles (< 1 degrees) and the multiple-scattering error associated with the detection of photons scattered more than once along the path length of the instrument. Several scattering phase functions describing bubble clouds at different bubble void fractions in the water are considered. Owing to forward-scattering error, a beam-attenuation meter (beam transmissometer) with a half-angle of receiver acceptance of 1.0 degrees and a path length of 0.1 m can underestimate the true beam attenuation within the bubble cloud by more than 50%. For bubble clouds with a beam attenuation of as much as 100 m(-1), the multiple-scattering error is no more than a few percent. These results are compared with simulations for some example phase functions that are representative of other scattering regimes found in natural waters. The forward-scattering error for the Petzold phase function of turbid waters is 16% for a typical instrument geometry, whereas for the Henyey-Greenstein phase function with the asymmetry parameter of 0.7 and 0.9 the error range is 8-28%.

  13. 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

  14. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2007-02-01

    Attenuation of Stoneley waves and higher Lamb modes propagating along an irregular surface of a fluid-filled borehole is investigated. This problem generalizes the problem on the attenuation of Rayleigh waves by an irregular surface of an empty borehole [10]. The technique used to evaluate the attenuation coefficient is based on the perturbation method (surface irregularity heights are considered to be small in comparison with the wavelength) and the mean field method. As a result, an expression is obtained for the partial coefficients of the eigenmode attenuation due to the scattering of eigenmodes by the irregularities of the borehole walls into the same or other eigenmodes, as well as into the bulk longitudinal and transverse waves. The frequency-dependent behavior of the partial attenuation coefficients of both Stoneley waves and higher modes is analyzed against the ratio between the irregularity correlation length and the borehole radius for different correlation functions of irregularities.

  16. 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.

  17. Effective x-ray attenuation measurements with full field digital mammography

    SciTech Connect

    Heine, John J.; Behera, Madhusmita

    2006-11-15

    This work shows that effective x-ray attenuation coefficients may be estimated by applying Beer's Law to phantom image data acquired with the General Electric Senographe 2000D full field digital mammography system. Theoretical developments are provided indicating that an approximate form of the Beer's relation holds for polychromatic x-ray beams. The theoretical values were compared with experimentally determined measured values, which were estimated at various detector locations. The measured effective attenuation coefficients are in agreement with those estimated with theoretical developments and numerical integration. The work shows that the measured quantities show little spatial variation. The main ideas are demonstrated with polymethylmethacrylate and breast tissue equivalent phantom imaging experiments. The work suggests that the effective attenuation coefficients may be used as known values for radiometric standardization applications that compensate for the image acquisition influences. The work indicates that it is possible to make quantitative attenuation coefficient measurements from a system designed for clinical purposes.

  18. Summary of oceanographic measurements for characterizing light attenuation and sediment resuspension in the Barnegat Bay-Little Egg Harbor Estuary, New Jersey, 2013

    USGS Publications Warehouse

    Dickhudt, Patrick J.; Ganju, Neil K.; Montgomery, Ellyn T.

    2015-08-28

    The U.S. Geological Survey, in cooperation with the New Jersey Department of Environmental Protection, measured suspended-sediment concentrations, currents, waves, light attenuation, and a variety of other water-quality parameters in the summer of 2013 in Barnegat Bay-Little Egg Harbor, New Jersey. These measurements quantified light attenuation and sediment resuspension in three seagrass meadows. Data were acquired sequentially at three paired channel-shoal sites, as the equipment was moved from south to north in the estuary. Data were collected for approximately 3 weeks at each site.

  19. Ocean Lidar Measurements of Beam Attenuation and a Roadmap to Accurate Phytoplankton Biomass Estimates

    NASA Astrophysics Data System (ADS)

    Hu, Yongxiang; Behrenfeld, Mike; Hostetler, Chris; Pelon, Jacques; Trepte, Charles; Hair, John; Slade, Wayne; Cetinic, Ivona; Vaughan, Mark; Lu, Xiaomei; Zhai, Pengwang; Weimer, Carl; Winker, David; Verhappen, Carolus C.; Butler, Carolyn; Liu, Zhaoyan; Hunt, Bill; Omar, Ali; Rodier, Sharon; Lifermann, Anne; Josset, Damien; Hou, Weilin; MacDonnell, David; Rhew, Ray

    2016-06-01

    Beam attenuation coefficient, c, provides an important optical index of plankton standing stocks, such as phytoplankton biomass and total particulate carbon concentration. Unfortunately, c has proven difficult to quantify through remote sensing. Here, we introduce an innovative approach for estimating c using lidar depolarization measurements and diffuse attenuation coefficients from ocean color products or lidar measurements of Brillouin scattering. The new approach is based on a theoretical formula established from Monte Carlo simulations that links the depolarization ratio of sea water to the ratio of diffuse attenuation Kd and beam attenuation C (i.e., a multiple scattering factor). On July 17, 2014, the CALIPSO satellite was tilted 30° off-nadir for one nighttime orbit in order to minimize ocean surface backscatter and demonstrate the lidar ocean subsurface measurement concept from space. Depolarization ratios of ocean subsurface backscatter are measured accurately. Beam attenuation coefficients computed from the depolarization ratio measurements compare well with empirical estimates from ocean color measurements. We further verify the beam attenuation coefficient retrievals using aircraft-based high spectral resolution lidar (HSRL) data that are collocated with in-water optical measurements.

  20. 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.

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

    NASA Technical Reports Server (NTRS)

    Vary, A.

    1979-01-01

    This report deals with instrumentation and computer programming concepts that have been developed for ultrasonic materials characterization. Methods that facilitate velocity and attenuation measurements are described. 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.

  2. 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, Wei-Cheng; Yeh, Chao-Lung; Lee, Jhe-Wei

    2015-09-01

    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 elusive. In the present study, the theoretical model developed for describing immiscible two-phase fluid flows in a deformable porous medium related to harmonic wave perturbation is generalized to account for viscous cross coupling due to relative velocity between two adjacent fluids. The corresponding dispersion relations whose coefficients feature all elasticity, inertial-drag, and viscous-drag parameters are then precisely formulated, in a physical context characterizing three compressional waves and one shear wave. To evaluate quantitatively this as-yet unknown effect, numerical calculations are conducted to solve the dispersion relations for Columbia fine sandy loam bearing an oil-water mixture as a function of water saturation and excitation frequency. Our results show that the phase speed and attenuation coefficient of the P3 wave which has the smallest speed is strongly sensitive to the presence of viscous cross coupling, as expected since this wave is 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 P1 wave whose speed is greatest, which exhibits two opposite trends at different ranges of low and high water contents. Relative differences in these wave attributes are principally independent of excitation frequency. A sensitivity analysis is carried out to assess how changes in viscous cross coupling affect these differences, revealing that some of them become more significant as viscous cross

  3. Thermoreflectance temperature measurement with millimeter wave.

    PubMed

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

    2014-06-01

    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(-3) K(-1) versus 10(-5) K(-1) for the visible domain, is very promising for future thermoreflectance applications.

  4. 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.

  5. Thermoreflectance temperature measurement with millimeter wave

    NASA Astrophysics Data System (ADS)

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

    2014-06-01

    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 10-3 K-1 versus 10-5 K-1 for the visible domain, is very promising for future thermoreflectance applications.

  6. Thermoreflectance temperature measurement with millimeter wave.

    PubMed

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

    2014-06-01

    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(-3) K(-1) versus 10(-5) K(-1) for the visible domain, is very promising for future thermoreflectance applications. PMID:24985839

  7. 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

  8. Lidar Measurements Supporting the Ocular Hazard Distance Calculation Using Atmospheric Attenuation

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

    A series of lidar measurements has been performed at the Vidsel Test Range, Vidsel, situated in the inland of the very northern part of Sweden, as a part of an assessment of reducing the laser hazard distance using atmospheric attenuation within the calculations of nominal ocular hazard distance (NOHD). The question was "How low is the atmospheric attenuation as function of height in this area, using a wavelength of 1064 nm?" The work included building a ground based backscatter lidar, performing a series of measurements and analyzing the results. The measurements were performed during June to November, 2014, with the objective to measure at clear air and good weather situations. The lidar measurements at 1064 nm showed a very low atmospheric attenuation as a function of height to altitudes of at least 10 km at several occasions. The lowest limit of backscatter coefficient possible to measure with this instrument is 0.3·10-7 m-1 sr-1. Assuming a lidar ratio varying between 30 - 100 sr, this was leading to an extinction coefficient of about 0.9 - 3·10-6 m-1. The atmospheric attenuation reduces the laser hazard distance with about 50 - 56 % depending on the lidar ratio. A recommendation is to monitor the atmospheric attenuation at the occasions when the method to the reduced laser hazard distance using atmospheric attenuation is used.

  9. Polarimetric X-band weather radar measurements in the tropics: radome and rain attenuation correction

    NASA Astrophysics Data System (ADS)

    Schneebeli, M.; Sakuragi, J.; Biscaro, T.; Angelis, C. F.; Carvalho da Costa, I.; Morales, C.; Baldini, L.; Machado, L. A. T.

    2012-09-01

    A polarimetric X-band radar has been deployed during one month (April 2011) for a field campaign in Fortaleza, Brazil, together with three additional laser disdrometers. The disdrometers are capable of measuring the raindrop size distributions (DSDs), hence making it possible to forward-model theoretical polarimetric X-band radar observables at the point where the instruments are located. This set-up allows to thoroughly test the accuracy of the X-band radar measurements as well as the algorithms that are used to correct the radar data for radome and rain attenuation. For the campaign in Fortaleza it was found that radome attenuation dominantly affects the measurements. With an algorithm that is based on the self-consistency of the polarimetric observables, the radome induced reflectivity offset was estimated. Offset corrected measurements were then further corrected for rain attenuation with two different schemes. The performance of the post-processing steps was analyzed by comparing the data with disdrometer-inferred polarimetric variables that were measured at a distance of 20 km from the radar. Radome attenuation reached values up to 14 dB which was found to be consistent with an empirical radome attenuation vs. rain intensity relation that was previously developed for the same radar type. In contrast to previous work, our results suggest that radome attenuation should be estimated individually for every view direction of the radar in order to obtain homogenous reflectivity fields.

  10. 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.

  11. 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.

  12. 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

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

    NASA Astrophysics Data System (ADS)

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

    2005-08-01

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

  14. Accurate and efficient modeling of global seismic wave propagation for an attenuative Earth model including the center

    NASA Astrophysics Data System (ADS)

    Toyokuni, Genti; Takenaka, Hiroshi

    2012-06-01

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

  15. Torsional ultrasonic wave based level measurement system

    SciTech Connect

    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.

  16. 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.

  17. 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.

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

    SciTech Connect

    Berryman, J.G.; Wang, H.F.

    1998-10-12

    To account for large-volume low-permeability storage porosity and low-volume high-permeability fracture/crack porosity in oil and gas reservoirs, phenomenological equations for the poroelastic behavior of a double porosity medium have been formulated and the coefficients in these linear equations identified. The generalization from a single porosity model increases the number of independent inertial coefficients from three to six, the number of independent drag coefficients from three to six, and the number of independent stress-strain coefficients from three to six for an isotropic applied stress and assumed isotropy of the medium. The analysis leading to physical interpretations of the inertial and drag coefficients is relatively straightforward, whereas that for the stress-strain coefficients is more tedious. In a quasistatic analysis, the physical interpretations are based upon considerations of extremes in both spatial and temporal scales. The limit of very short times is the one most relevant for wave propagation, and in this case both matrix porosity and fractures are expected to behave in an undrained fashion, although our analysis makes no assumptions in this regard. For the very long times more relevant for reservoir drawdown, the double porosity medium behaves as an equivalent single porosity medium. At the macroscopic spatial level, the pertinent parameters (such as the total compressibility) may be determined by appropriate field tests. At the mesoscopic scale pertinent parameters of the rock matrix can be determined directly through laboratory measurements on core, and the compressibility can be measured for a single fracture. We show explicitly how to generalize the quasistatic results to incorporate wave propagation effects and how effects that are usually attributed to squirt flow under partially saturated conditions can be explained alternatively in terms of the double-porosity model. The result is therefore a theory that generalizes, but is

  19. Wave reflection in a reaction-diffusion system: breathing patterns and attenuation of the echo.

    PubMed

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

    2014-05-01

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

  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. Change in Seismic Attenuation of the Nojima Fault Zone Measured Using Spectral Ratios from Borehole Seismometers

    NASA Astrophysics Data System (ADS)

    Kano, Y.; Tadokoro, K.; Nishigami, K.; Mori, J.

    2006-12-01

    We measured the seismic attenuation of the rock mass surrounding the Nojima fault, Japan, by estimating the P-wave quality factor, Qp, using spectral ratios derived from a multi-depth (800 m and 1800 m) seismometer array. We detected an increase of Qp in 2003-2006 compared to 1999-2000. Following the 1995 Kobe earthquake, the project "Fault Zone Probe" drilled three boreholes to depths of 500 m, 800 m, 1800 m, in Toshima, along the southern part of the Nojima fault. The 1800-m borehole was reported to reach the fault surface. One seismometer (TOS1) was installed at the bottom of the 800-m borehole in 1996 and another (TOS2) at the bottom of 1800-m borehole in 1997. The sampling rate of the seismometers is 100 Hz. The slope of the spectral ratios for the two stations plotted on a linear-log plot is -π t^{*}, where t^{*} is the travel time divided by the Qp for the path difference between the stations. For the estimation of Qp, we used events recorded by both TOS1 and TOS2 for periods of 1999-2000 and 2003-2006. To improve the signal-to-noise ratio of the spectral ratios, we first calculated spectra ratios between TOS1 and TOS2 for each event and averaged the values over the earthquakes for each period. We used the events that occurred within 10 km from TOS2, and the numbers of events are 74 for 1999-2000 and 105 for 2003-2006. Magnitudes of the events range from M0.5 to M3.1. The average value of Qp for 1999-2000 increased significantly compared to 2003-2006. The attenuation of rock mass surrounding the fault in 2003-2006 is smaller than that in 1999-2000, which suggests that the fault zone became stiffer after the earthquake. At the Nojima fault, permeability measured by repeated pumping tests decreased with time from the Kobe earthquake, infering the closure of cracks and a fault healing process occurred The increase of Qp is another piece of evidence for the healing process of the Nojima fault zone. u.ac.jp/~kano/

  2. 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.

  3. 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.

  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. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2010-09-01

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

  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. Modeling and experiment of the suspended seismometer concept for attenuating the contribution of tilt motion in horizontal measurements

    NASA Astrophysics Data System (ADS)

    Matichard, F.; Evans, M.; Mittleman, R.; MacInnis, M.; Biscans, S.; Dooley, K. L.; Sohier, H.; Lauriero, A.; Paris, H.; Koch, J.; Knothe, P.; Carbajo, A.; Dufort, C.

    2016-06-01

    Tilt-horizontal coupling in inertial sensors limits the performance of active isolation systems such as those used in gravitational wave detectors. Inertial rotation sensors can be used to subtract the tilt component from the signal produced by horizontal inertial sensors, but such techniques are often limited by the sensor noise of the tilt measurement. A different approach is to mechanically filter the tilt transmitted to the horizontal inertial sensor, as discussed in this article. This technique does not require an auxiliary rotation sensor and can produce a lower noise measurement. The concept investigated uses a mechanical suspension to isolate the inertial sensor from input tilt. Modeling and simulations show that such a configuration can be used to adequately attenuate the tilt transmitted to the instrument, while maintaining translation sensitivity in the frequency band of interest. The analysis is supported by experimental results showing that this approach is a viable solution to overcome the tilt problem in the field of active inertial isolation.

  9. Influence of Forward and Multiple Light Scatter on the Measurement of Beam Attenuation in Highly Scattering Marine Environments

    NASA Astrophysics Data System (ADS)

    Piskozub, Jacek; Stramski, Dariusz; Terrill, Eric; Melville, W. Kendall

    2004-08-01

    Using three-dimensional Monte Carlo radiative transfer simulations, we examine the effect of beam transmissometer geometry on the relative error in the measurement of the beam-attenuation coefficient in an aquatic environment characterized by intense light scattering, especially within submerged bubble clouds entrained by surface-wave breaking. We discuss the forward-scattering error associated with the detection of photons scattered at small angles (< 1°) and the multiple-scattering error associated with the detection of photons scattered more than once along the path length of the instrument. Several scattering phase functions describing bubble clouds at different bubble void fractions in the water are considered. Owing to forward-scattering error, a beam-attenuation meter (beam transmissometer) with a half-angle of receiver acceptance of 1.0° and a path length of 0.1 m can underestimate the true beam attenuation within the bubble cloud by more than 50%. For bubble clouds with a beam attenuation of as much as 100 m^-1, the multiple-scattering error is no more than a few percent. These results are compared with simulations for some example phase functions that are representative of other scattering regimes found in natural waters. The forward-scattering error for the Petzold phase function of turbid waters is 16% for a typical instrument geometry, whereas for the Henyey-Greenstein phase function with the asymmetry parameter of 0.7 and 0.9 the error range is 8-28%.

  10. Measuring the speed of cosmological gravitational waves

    NASA Astrophysics Data System (ADS)

    Raveri, Marco; Baccigalupi, Carlo; Silvestri, Alessandra; Zhou, Shuang-Yong

    2015-03-01

    In general relativity gravitational waves propagate at the speed of light; however, in alternative theories of gravity that might not be the case. We investigate the effects of a modified speed of gravity, cT2, on the B modes of the cosmic microwave background (CMB) anisotropy in polarization. We find that a departure from the light speed value would leave a characteristic imprint on the BB spectrum part induced by tensors, manifesting as a shift in the angular scale of its peaks which allows us to constrain cT without any significant degeneracy with other cosmological parameters. We derive constraints from current data and forecast the accuracy with which cT will be measured by the next generation CMB satellites. In the former case, using the available Planck and BICEP2 data sets, we obtain cT2=1.30 ±0.79 and cT2<2.85 at 95% C.L. by assuming a power law primordial tensor power spectrum and cT2<2.33 at 95% C.L. if the running of the spectral index is allowed. More interestingly, in the latter case we find future CMB satellites capable of constraining cT2 at percent level, comparable with bounds from binary pulsar measurements, largely due to the absence of degeneracy with other cosmological parameters.

  11. 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.

  12. Interpretation of laser attenuation measurements in sooty fires

    SciTech Connect

    Grosshandler, W.L. . Dept. of Mechanical Engineering)

    1989-12-01

    This paper presents a sensitivity analysis to determine the impact of particle size, and thus scattering, on the interpretation of the measurements from fiber optic soot probes of two different designs. The single-pass fiber optic probe is found to accurately estimate the monochromatic absorption coefficient in flames with soot size parameters up to 0.5. For larger-diameter soot particles, Beer's law yields values between the true absorption and extinction coefficients. If the probe is properly designed it can give reliable extinction coefficients for size parameters in excess of 10 for both lightly and heavily sooting flames.

  13. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2009-12-01

    Several attenuation relationships have been developed for Mexico, mostly after the earthquake of September 19, 1985, an event that gave great impetus to the development of engineering seismology in Mexico. Since 1985, the number of seismic stations in the country has increased significantly, especially between the Coast of Guerrero and Mexico City. This is due to the infamous large amplifications observed in the lake area of Mexico City with respect to hard ground sites. Some studies have analyzed how seismic waves are attenuated or amplified from the Pacific Coast toward the inland. The attenuation relationship used for seismic hazard assessment in Mexico is that of Ordaz (1989), which uses data from the Guerrero acceleration network. Another recent study is that of García et al. (2005), which uses more recent data from intraplate earthquakes recorded at the Guerrero acceleration network. It is important to note that, since these relations were derived for only part of the Mexican subduction zone and for certain types of seismic sources, caution should be exercised when using them for earthquake risk studies in other regions of Mexico. In the present work, we study the state of Michoacán, one of the most important seimogenic zones in Mexico. Three kinds of sources exist in the state, producing tectonic earthquakes, volcanic earthquakes, and events due to local faults in the region. For this reason, it is of vital importance to study the propagation of seismic waves within Michoacán state, and in this paper in particular we study their attenuation. We installed a temporary network consisting of 7 accelerograph stations across the state, at the following locations: Faro de Brucerías, Aguililla, Apatzingán, Taretán, Pátzcuaro, Morelia, and Maravatío. The stations form a line that is perpendicular to the coastline and has a total length of 366 km, while the distance between neighboring stations varies from 60 to 80 km. Among all the seismic events recorded at

  15. 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…

  16. 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.

  17. Symphony orchestra musicians' use of hearing protection and attenuation of custom-made hearing protectors as measured with two different real-ear attenuation at threshold methods.

    PubMed

    Huttunen, K H; Sivonen, V P; Poykko, V T

    2011-01-01

    Despite a high level of sound exposure and a fairly large selection of earplugs available, musicians have often been reported to use personal hearing protectors only seldom. For better hearing conservation, it is important to identify and eliminate the causes for the low motivation to use hearing protection. We explored the usage rate of custom-molded musician's earplugs (ER-15) among 15 symphony orchestra musicians with a questionnaire, and measured the attenuation properties of their earplugs with a Real-Ear Attenuation at Threshold (REAT) procedure in a sound field. Earplug use was found to be low, and the musicians reported that earplugs hampered listening to their own and their colleagues' playing; earplugs affected either timbre or dynamics, or both. Additionally, several reasons related to discomfort of use were itemized, but the musicians who consistently used their earplugs did so in spite of problems with use. The REAT values obtained in sound field were relatively close to the manufacturer's nominal specifications, being 13.7 dB, on average. In the frequency range studied (0.125-8 kHz), individual variation in REAT was, however, up to 15 dB across the measured frequencies. Fluctuation in attenuation might be related to low use of hearing protectors, and REAT measured at fixed center frequencies may be too robust a method to uncover it. We therefore tested 10 additional subjects to find out whether a sweeping signal used in Bιkιsy audiometry would bring more detailed information on earplug attenuation. Mean attenuation was found to be somewhat closer to the nominal attenuation of the ER-9 and ER-15 earplugs up to about 1 kHz, whereas REAT measurements in sound field revealed more even attenuation at frequencies between 1 and 6 kHz. No significant association was found between earplug attenuation properties and earplug use. It was concluded that support and determination to get accustomed to hearing protector use are important factors in hearing

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

    NASA Technical Reports Server (NTRS)

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

    1995-01-01

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

  19. 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.

  20. Rainfall rate measurement with a polarimetric radar at an attenuated wavelength

    NASA Astrophysics Data System (ADS)

    Sauvageot, Henri; Mesnard, Frédéric; Illingworth, Anthony J.; Goddard, John W. F.

    Among the many ways investigated for radar estimation of rainfall, polarimetric methods are the most promising. However most polarimetric algorithms are degraded by attenuation by precipitation and clouds and by calibration error. A new method was recently proposed in which the differential polarimetric attenuation is used to perform an accurate rain rate measurement. The method is independent of the radar calibration and of the attenuation by undetected clouds. This algorithm is also usable as a qualitative hail detector, as well as a detector of anomalous propagation. The goal of the paper is to describe the results of the first experimental implementation of this method using the 35 GHz RABELAIS radar, as attenuated radar, and the 3 GHz CAMRa radar as a reference. We show that the proposed algorithm is stable and enables us to retrieve the actual rain rate even from an observed signal attenuated by more than 30 dB. The results are insensitive to the value used for the power coefficient of the Z(R) relation.

  1. Attenuation of transverse waves by using a metamaterial beam with lateral local resonators

    NASA Astrophysics Data System (ADS)

    Huang, Hsin-Haou; Lin, Chi-Kuang; Tan, Kwek-Tze

    2016-08-01

    This study numerically and experimentally investigated the wave propagation and vibrational behavior of a metamaterial beam with lateral local resonators. A two-dimensional simplified analytical model was proposed for feasibly and accurately capturing the in-plane dispersion behavior, which can be used for the initial design. The out-of-plane wave motions, however, required advanced three-dimensional (3D) modeling. Through experimental validations, 3D finite element simulations were demonstrated to be suitable for advanced design and analysis. This study provided a basis for designing metabeams for transverse wave mitigation. The proposed concept can be further extended to 3D metamaterial plates for wave and vibrational mitigation applications.

  2. 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.

  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. 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

  6. 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.

  7. 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.

  8. 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.

  9. Calculation of UV attenuation and colored dissolved organic matter absorption spectra from measurements of ocean color

    NASA Astrophysics Data System (ADS)

    Johannessen, S. C.; Miller, W. L.; Cullen, J. J.

    2003-09-01

    The absorption of ultraviolet and visible radiation by colored or chromophoric dissolved organic matter (CDOM) drives much of marine photochemistry. It also affects the penetration of ultraviolet radiation (UV) into the water column and can confound remote estimates of chlorophyll concentration. Measurements of ocean color from satellites can be used to predict UV attenuation and CDOM absorption spectra from relationships between visible reflectance, UV attenuation, and absorption by CDOM. Samples were taken from the Bering Sea and from the Mid-Atlantic Bight, and water types ranged from turbid, inshore waters to the Gulf Stream. We determined the following relationships between in situ visible radiance reflectance, Lu/Ed (λ) (sr-1), and diffuse attenuation of UV, Kd(λ) (m-1): Kd(323nm) = 0.781[Lu/Ed(412)/Lu/Ed(555)]-1.07; Kd(338nm) = 0.604[Lu/Ed(412)/Lu/Ed(555)]-1.12; Kd(380 nm) = 0.302[Lu/Ed(412)/Lu/Ed(555)]-1.24. Consistent with published observations, these empirical relationships predict that the spectral slope coefficient of CDOM absorption increases as diffuse attenuation of UV decreases. Excluding samples from turbid bays, the ratio of the CDOM absorption coefficient to Kd is 0.90 at 323 nm, 0.86 at 338 nm, and 0.97 at 380 nm. We applied these relationships to SeaWiFS images of normalized water-leaving radiance to calculate the CDOM absorption and UV attenuation in the Mid-Atlantic Bight in May, July, and August 1998. The images showed a decrease in UV attenuation from May to August of approximately 50%. We also produced images of the areal distribution of the spectral slope coefficient of CDOM absorption in the Georgia Bight. The spectral slope coefficient increased offshore and changed with season.

  10. Laboratory Measurements of Droplets Generated by Breaking Water Waves

    NASA Astrophysics Data System (ADS)

    Liu, X.; Duncan, J. H.

    2008-11-01

    The sizes and motions of droplets that are generated by single breaking water waves are explored in a wave tank that is 11.8 m long, 1.1 m wide and 2.2 m high (0.91 m water depth). A programmable wave maker is used to generate wave packets (central frequency 1.15 Hz) that create breakers by dispersive focusing. Different amplitudes of the wave maker motion are used to generate various breaking waves ranging from weakly spilling breakers to plunging breakers. The profile histories of the breaking wave crests along the center plane of the tank are measured with a cinematic LIF technique. The droplets at various heights and positions above the crests of the breaking waves are measured with a shadowgraph technique that uses a double-pulsed laser, a long-distance microscope lens and a CCD camera. These two measurement systems are mounted on an instrument carriage that moves along the tank with the speed of the breaking crests. The results include the size distributions of the droplets, the variations of the droplet number with height above the wave crest and the velocities of the droplets. The effects of the intensity of the breaking waves on the dynamics of the droplets are discussed.

  11. 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.

  12. 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.

  13. Attenuation measurements from sonic waveform logs in methane hydrate-bearing sediments at the Nankai Trough exploratory well off Tokai, central Japan

    NASA Astrophysics Data System (ADS)

    Matsushima, Jun

    2005-02-01

    I have used full waveform logs from the Nankai Trough exploratory well off central Japan to estimate both compressional and shear attenuation in sediments containing methane hydrate (MH). The attenuation estimates are based on a median frequency shift to the amplitude spectrum of the recorded waveforms. This paper is concerned with attenuation at sonic frequencies of 10-20 kHz for compressional waves and 500-1000 Hz for shear waves. I observed that the presence of MH increases the host sediments' seismic attenuation, and shear attenuation may be more helpful than compressional attenuation in detecting or characterizing MH-bearing sediments as compressional attenuation is affected by the presence of gas. Moreover, the ratio of compressional to shear attenuation is found to be a more sensitive indicator of the presence of low-saturation gas than the corresponding velocity ratio.

  14. Retardation Measurements of Infrared PVA Wave plate

    NASA Astrophysics Data System (ADS)

    Sun, Y.; Z, H.; W, D.; D, Y.; Z, Z.; S, J.

    The wave plate made of Polyvinyl Alcohol PVA plastic film has several advantages such as its lower cost and insensitivity to temperature and incidence angle so it has been used in the Solar Multi-Channel Telescope SMCT in China But the important parameter retardations of PVA wave plates in the near infrared wavelength have never been provided In this paper a convenient and high precise instrument to get the retardations of discrete wavelengths or a continuous function of wavelength in near infrared is developed In this method the retardations of wave plates have been determined through calculating the maximum and minimum of light intensity The instrument error has been shown Additionally we can get the continuous direction of wavelength retardations in the ultraviolet visible or infrared spectral in another way

  15. Compressional Wave Q in the Uppermost Mantle Beneath the Tibetan Plateau Measured Using Pn Wave Spectra

    NASA Astrophysics Data System (ADS)

    Xie, J.

    2003-12-01

    Pn waves from three near-colocated seismic events in the eastern Tarim Basin are well-recorded by the INDEPTH III and II arrays, which are deployed from northern to southern Tibet with a small east-west spread (between ˜88 and 91° E). The paths run southward and sample the Tibetan mantle with epicentral distances increasing from 870 to 1540 km. These waves have spectral contents that are distinctly different from those collected from the Kyrghistan network (KNET), to which the paths traverse westward through the eastern Tienshan. Pn Q beneath Tibet and Tienshan must therefore be different. Xie and Patton (1999,JGR, 104, 941-954) have simultaneously estimated source spectra of the co-located events, and path-averaged Pn Q to the KNET stations. Under a simplified geometrical spreading of Δ -1.3, they have estimated Q0 and η (Pn Q at 1 Hz and its frequency dependence) to KNET to be about 360 and 0.5, respectively. Using those estimates as a priori knowledge, we estimate that Q0 and η are ~180 and 0.3 along paths to northern Tibet, and ˜260 and 0.0 along paths to southern Tibet. The southward increase of Q0 correlates well with a similar increase in Pn velocity contained in previous tomographic images. Additionally, we measured Pn Q using a two-station method along two profiles (from station SANG to TUNL, and GANZ to MAQI) deployed during the 1991-1992 Sino-US Tibetan Plateau experiment. Both profiles are located to the east of 92° E. Along profile SANG-TUNL, we estimate Q0 and η to be ˜270 and 0.0, respectively. The Q0 value is rather high, but correlates well with the high Pn velocities of > 8.1 km/s re-measured in this study. Our results suggest that the zone of low Pn Q0 and velocity in northern Tibet, which is likely caused by high mantle temperature and partial melting, is confined to the west of 92° E. This is so despite that the zone of high Sn attenuation extends to further east.

  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. Filter Paper: Solution to High Self-Attenuation Corrections in HEPA Filter Measurements

    SciTech Connect

    Oberer, R.B.; Harold, N.B.; Gunn, C.A.; Brummett, M.; Chaing, L.G.

    2005-10-01

    An 8 by 8 by 6 inch High Efficiency Particulate Air (HEPA) filter was measured as part of a uranium holdup survey in June of 2005 as it has been routinely measured every two months since 1998. Although the survey relies on gross gamma count measurements, this was one of a few measurements that had been converted to a quantitative measurement in 1998. The measurement was analyzed using the traditional Generalized Geometry Holdup (GGH) approach, using HMS3 software, with an area calibration and self-attenuation corrected with an empirical correction factor of 1.06. A result of 172 grams of {sup 235}U was reported. The actual quantity of {sup 235}U in the filter was approximately 1700g. Because of this unusually large discrepancy, the measurement of HEPA filters will be discussed. Various techniques for measuring HEPA filters will be described using the measurement of a 24 by 24 by 12 inch HEPA filter as an example. A new method to correct for self attenuation will be proposed for this measurement Following the discussion of the 24 by 24 by 12 inch HEPA filter, the measurement of the 8 by 8 by 6 inch will be discussed in detail.

  18. Analysis of Measured and Simulated Supraglottal Acoustic Waves.

    PubMed

    Fraile, Rubén; Evdokimova, Vera V; Evgrafova, Karina V; Godino-Llorente, Juan I; Skrelin, Pavel A

    2016-09-01

    To date, although much attention has been paid to the estimation and modeling of the voice source (ie, the glottal airflow volume velocity), the measurement and characterization of the supraglottal pressure wave have been much less studied. Some previous results have unveiled that the supraglottal pressure wave has some spectral resonances similar to those of the voice pressure wave. This makes the supraglottal wave partially intelligible. Although the explanation for such effect seems to be clearly related to the reflected pressure wave traveling upstream along the vocal tract, the influence that nonlinear source-filter interaction has on it is not as clear. This article provides an insight into this issue by comparing the acoustic analyses of measured and simulated supraglottal and voice waves. Simulations have been performed using a high-dimensional discrete vocal fold model. Results of such comparative analysis indicate that spectral resonances in the supraglottal wave are mainly caused by the regressive pressure wave that travels upstream along the vocal tract and not by source-tract interaction. On the contrary and according to simulation results, source-tract interaction has a role in the loss of intelligibility that happens in the supraglottal wave with respect to the voice wave. This loss of intelligibility mainly corresponds to spectral differences for frequencies above 1500 Hz. PMID:26377510

  19. 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.

  20. Time-domain comparisons of power law attenuation in causal and noncausal time-fractional wave equations.

    PubMed

    Zhao, Xiaofeng; McGough, Robert J

    2016-05-01

    The attenuation of ultrasound propagating in human tissue follows a power law with respect to frequency that is modeled by several different causal and noncausal fractional partial differential equations. To demonstrate some of the similarities and differences that are observed in three related time-fractional partial differential equations, time-domain Green's functions are calculated numerically for the power law wave equation, the Szabo wave equation, and for the Caputo wave equation. These Green's functions are evaluated for water with a power law exponent of y = 2, breast with a power law exponent of y = 1.5, and liver with a power law exponent of y = 1.139. Simulation results show that the noncausal features of the numerically calculated time-domain response are only evident very close to the source and that these causal and noncausal time-domain Green's functions converge to the same result away from the source. When noncausal time-domain Green's functions are convolved with a short pulse, no evidence of noncausal behavior remains in the time-domain, which suggests that these causal and noncausal time-fractional models are equally effective for these numerical calculations. PMID:27250193

  1. Time-domain comparisons of power law attenuation in causal and noncausal time-fractional wave equations.

    PubMed

    Zhao, Xiaofeng; McGough, Robert J

    2016-05-01

    The attenuation of ultrasound propagating in human tissue follows a power law with respect to frequency that is modeled by several different causal and noncausal fractional partial differential equations. To demonstrate some of the similarities and differences that are observed in three related time-fractional partial differential equations, time-domain Green's functions are calculated numerically for the power law wave equation, the Szabo wave equation, and for the Caputo wave equation. These Green's functions are evaluated for water with a power law exponent of y = 2, breast with a power law exponent of y = 1.5, and liver with a power law exponent of y = 1.139. Simulation results show that the noncausal features of the numerically calculated time-domain response are only evident very close to the source and that these causal and noncausal time-domain Green's functions converge to the same result away from the source. When noncausal time-domain Green's functions are convolved with a short pulse, no evidence of noncausal behavior remains in the time-domain, which suggests that these causal and noncausal time-fractional models are equally effective for these numerical calculations.

  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. Fiber optic techniques for measuring various properties of shock waves

    NASA Astrophysics Data System (ADS)

    Prinse, Wim C.; van Esveld, Rene; Oostdam, Rene; van Rooijen, Murk; Bouma, Richard

    1999-06-01

    For the past years we have developed several optical techniques to measure properties of shock waves. The fiber optic probe (FOP) is developed to measure the shock-wave velocity and/or the detonation velocity inside an explosive. The space resolution can be as small as 0.5 mm. Single fibers are used as velocity pins, and as devices to measure the flatness of flyers. Arrays of fibers are used to measure the curvature of a shock or detonation front. Also a Fabry-Perot velocity Interferometer System is constructed to measure the velocity of the flyer of an electric gun and the particle velocity in a shock wave. It is possible to combine these two measurements to determine simultaneously the flyer velocity that induces a shock wave in sample and the particle velocity in a window material at the back in a single streak record.

  4. 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.

  5. Microstrip ring resonator technique for measuring microwave attenuation in high-Tc superconducting thin films

    NASA Astrophysics Data System (ADS)

    Takemoto, June H.; Oshita, Floyd K.; Fetterman, Harold R.; Kobrin, Paul; Sovero, Emilio

    1989-10-01

    Microwave attenuation of high-Tc superconducting (HTS) films sputtered on MgO and ZrO2 were measured using a microstrip ring resonator circuit. The results for Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O resonators were compared to those for gold-plated resonators of identical design. The losses of superconducting and gold-plated films were determined from unloaded Q-factor measurements. The attenuation of Y-Ba-Cu-O film on an MgO substrate is approximately 31 percent lower than that of gold films at 6.6 GHz and 33 percent lower at 19.2 GHz for temperatures below 50 K. The approach of using microstrips to characterize microwave losses shows the usefulness of HTS films in integrated circuit technology.

  6. 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.

  7. Local temperature variation measurement by anti-Stokes luminescence in attenuated total reflection geometry.

    PubMed

    Yamamoto, Ken; Togawa, Ryotaro; Fujimura, Ryushi; Kajikawa, Kotaro

    2016-08-22

    Strong temperature dependence of anti-Stokes luminescence intensity from Rhodamine 101 is used to probe local temperature variation at a surface region in the attenuated total reflection geometry (ATR), when heating with laser light. In this method, the measured region can be limited by observing evanescent luminescence. The near-field depth (penetration depth) was changed by the observation angle θout of the evanescent luminescence and the spatial temperature variation was observed. PMID:27557182

  8. 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.

  9. Testing THEMIS wave measurements against the cold plasma theory

    NASA Astrophysics Data System (ADS)

    Taubenschuss, Ulrich; Santolik, Ondrej; Le Contel, Olivier; Bonnell, John

    2016-04-01

    The THEMIS (Time History of Events and Macroscale Interactions during Substorms) mission records a multitude of electromagnetic waves inside Earth's magnetosphere and provides data in the form of high-resolution electric and magnetic waveforms. We use multi-component measurements of whistler mode waves and test them against the theory of wave propagation in a cold plasma. The measured ratio cB/E (c is speed of light in vacuum, B is magnetic wave amplitude, E is electric wave amplitude) is compared to the same quantity calculated from cold plasma theory over linearized Faraday's law. The aim of this study is to get estimates for measurement uncertainties, especially with regard to the electric field and the cold plasma density, as well as evaluating the validity of cold plasma theory inside Earth's radiation belts.

  10. 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.

  11. 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.

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

    NASA Astrophysics Data System (ADS)

    Gu, Renliang; Dogandžić, 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 ℓ1-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.

  13. Broadband high-frequency measurement of ultrasonic attenuation of tissues and liquids.

    PubMed

    Bauer-Marschallinger, Johannes; Berer, Thomas; Grun, Hubert; Roitner, Heinz; Reitinger, Bernhard; Burgholzer, Peter

    2012-12-01

    The ongoing expansion of the frequency range used for ultrasonic imaging requires increasing attention to the acoustic attenuation of biomaterials. This work presents a novel method for measuring the attenuation of tissue and liquids in vitro on the basis of single transmission measurements. Ultrasound was generated by short laser pulses directed onto a silicon wafer. In addition, unfocused piezoelectric transducers with a center frequency of 50 MHz were used to detect and emit ultrasound. The laser ultrasound method produces signals with a peak frequency of 30 MHz. In comparison to piezoelectric generation, pulse laser excitation provides approximately 4 times higher amplitudes and 20% larger bandwidth. By using two excitation methods in succession, the attenuation parameters of porcine fat samples with thicknesses in the range of 1.5 to 20 mm could be determined quantitatively within a total frequency range of 5 to 45 MHz. The setup for liquid measurements was tested on samples of human blood and olive oil. Our results are in good agreement with reports in literature. PMID:23221212

  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. Measurement of the density of liquid aluminum-319 alloy by an x-ray attenuation technique

    SciTech Connect

    Smith, P.M.; Gallegos, G.F.

    1994-11-01

    This study was made for assisting in casting simulations. A relatively simple apparatus was constructed for measuring the density of Al-based alloys in the solid and liquid states up to 900 C. One of the more important physical properties of a casting alloy, solidification shrinkage, was measured for a commercial Al alloy (Al-319). It was found that while the thermal expansion of Al-319 in both solid and liquid phases is similar to that of pure Al, the density of the liquid alloy is lower than estimated by averaging the atomic volumes of the pure liquid components. The densities were measured by x-ray attenuation.

  16. Unsteady Heat-Flux Measurements of Second-Mode Instability Waves in a Hypersonic Boundary Layer

    NASA Technical Reports Server (NTRS)

    Kergerise, Michael A.; Rufer, Shann J.

    2016-01-01

    In this paper we report on the application of the atomic layer thermopile (ALTP) heat- flux sensor to the measurement of laminar-to-turbulent transition in a hypersonic flat plate boundary layer. The centerline of the flat-plate model was instrumented with a streamwise array of ALTP sensors and the flat-plate model was exposed to a Mach 6 freestream over a range of unit Reynolds numbers. Here, we observed an unstable band of frequencies that are associated with second-mode instability waves in the laminar boundary layer that forms on the flat-plate surface. The measured frequencies, group velocities, phase speeds, and wavelengths of these instability waves are in agreement with data previously reported in the literature. Heat flux time series, and the Morlet-wavelet transforms of them, revealed the wave-packet nature of the second-mode instability waves. In addition, a laser-based radiative heating system was developed to measure the frequency response functions (FRF) of the ALTP sensors used in the wind tunnel test. These measurements were used to assess the stability of the sensor FRFs over time and to correct spectral estimates for any attenuation caused by the finite sensor bandwidth.

  17. Stiffness matrix determination of composite materials using lamb wave group velocity measurements

    NASA Astrophysics Data System (ADS)

    Putkis, O.; Croxford, A. J.

    2013-04-01

    The use of Lamb waves in Non-Destructive Evaluation (NDE) and Structural Health Monitoring (SHM) is gaining popularity due to their ability to travel long distances without significant attenuation, therefore offering large area inspections with a small number of sensors. The design of a Lamb-wave-based NDE/SHM system for composite materials is more complicated than for metallic materials due to the directional dependence of Lamb wave propagation characteristics such as dispersion and group velocity. Propagation parameters can be theoretically predicted from known material properties, specifically the stiffness matrix and density. However, in practice it is difficult to obtain the stiffness matrix of a particular material or structure with high accuracy, hence introducing errors in theoretical predictions and inaccuracies in the resulting propagation parameters. Measured Lamb wave phase velocities can be used to infer the stiffness matrix, but the measurements are limited to the principal directions due to the steering effect (different propagation directions of phase and corresponding group velocities). This paper proposes determination of the stiffness matrix from the measured group velocities, which can be unambiguously measured in any direction. A highly anisotropic carbon-fibre-reinforced polymer plate is chosen for the study. The influence of different stiffness matrix elements on the directional group velocity profile is investigated. Thermodynamic Simulated Annealing (TSA) is used as a tool for inverse, multi variable inference of the stiffness matrix. A good estimation is achieved for particular matrix elements.

  18. Extraordinary views of ordinary galaxies: Multiwavelength measures of star formation and attenuation

    NASA Astrophysics Data System (ADS)

    Johnson, Benjamin D.

    2008-01-01

    The meaningful comparison of models of galaxy evolution to observations is critically dependent on the accurate treatment of dust attenuation. To investigate dust absorption and emission in galaxies we have assembled a sample of ~1000 galaxies from the ultrviolet (UV) through the Infrared (IR) by the GALEX, SDSS, and Spitzer observatories. The ratio of IR to UV emission (IRX) is used to constrain the dust attenuation in galaxies. We consider this measure in optically red galaxies making several simplfying assumptions we estimate the fraction of IR emission due to the heating of by old stars to be as much as 99%. We use the 4000Å break as a robust and useful, though coarse, indicator of star formation history (SFH). Dust attenuation and star formation history (SFH) are the dominant factors affecting the color of galaxies. We explore the empirical relation between SFH, attenuation, and color (especially the UV color) for a wide range of galaxies, including early types. This relation is compared to models that separately predict the effects of dust and SFH on color. We perform fits to the relation between SFH, attenuation, and color, which links the production of starlight and its absorption by dust to the subsequent reemmision of the absorbed light in the IR. Galaxy models that self-consistently treat dust absorption and emission as well as stellar populations will need to reproduce these fitted relations in the low-redshift universe. We construct estimates of dust attenuation and star formation rate (SFR) from the UV and IR photmetry and compare them to optical indicators, including the SFR b of Brinchmann et al. (2004). We find that there is a significant trend of the ratio of SFR b to the IR+UV luminosity with D n (4000) that cannot be explained as due to the additional IR emission from dust heatred by old stars. We find that the dust attenuation inferred from the ratio of optical emission lines is ~ 2-3 times higher than that inferred from IRX for a wide range

  19. Spectroscopic Measurements of the Far-Ultraviolet Dust Attenuation Curve at z ˜ 3

    NASA Astrophysics Data System (ADS)

    Reddy, Naveen A.; Steidel, Charles C.; Pettini, Max; Bogosavljević, Milan

    2016-09-01

    We present the first spectroscopic measurements of the shape of the far-ultraviolet (far-UV; λ =950{--}1500 Å) dust attenuation curve at high redshift (z˜ 3). Our analysis employs rest-frame UV spectra of 933 galaxies at z˜ 3, 121 of which have very deep spectroscopic observations (≳ 7 hr) at λ =850{--}1300 \\mathring{{A}} , with the Low Resolution Imaging Spectrograph on the Keck Telescope. By using an iterative approach in which we calculate the ratios of composite spectra in different bins of continuum color excess, E(B-V), we derive a dust curve that implies a lower attenuation in the far-UV for a given E(B-V) than those obtained with standard attenuation curves. We demonstrate that the UV composite spectra of z˜ 3 galaxies can be modeled well by assuming our new attenuation curve, a high covering fraction of H i, and absorption from the Lyman-Werner bands of {{{H}}}2 with a small (≲ 20 % ) covering fraction. The low covering fraction of {{{H}}}2 relative to that of the {{H}} {{I}} and dust suggests that most of the dust in the ISM of typical galaxies at z˜ 3 is unrelated to the catalysis of {{{H}}}2, and is associated with other phases of the ISM (i.e., the ionized and neutral gas). The far-UV dust curve implies a factor of ≈ 2 lower dust attenuation of Lyman continuum (ionizing) photons relative to those inferred from the most commonly assumed attenuation curves for L* galaxies at z˜ 3. Our results may be utilized to assess the degree to which ionizing photons are attenuated in H ii regions or, more generally, in the ionized or low column density (N({{H}} {{I}})≲ {10}17.2 cm-2) neutral ISM of high-redshift galaxies. Based on data obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA, and was made possible by the generous financial support of the W.M. Keck Foundation.

  20. 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.

  1. 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.

  2. Dispersion and Attenuation of Surface Acoustic Waves of Various Polarizations on a Stress-Free Randomly Rough Surface of Solid

    NASA Astrophysics Data System (ADS)

    Kosachev, V. V.; Shchegrov, A. V.

    1995-06-01

    An approach to obtaining the dispersion equation of surface acoustic waves (SAWs) on a stress-free, randomly rough surface of an anisotropic elastic medium is suggested. The problem is solved in the approximation of a weakly rough surface using Green's function technique. The dispersion and attenuation of sagittally and shear horizontally (SH) polarized SAWs are investigated both analytically and numerically for a three-dimensionally (3D) and a two-dimensionally (2D) rough surface of an isotropic medium. The results for 2D roughness are shown to be contained in the more general expressions for the 3D case, and the connection between the results for the 3D and the 2D cases is pointed out. Dispersion relations are derived for SAWs of both polarizations propagating in an arbitrary direction along a 2D rough surface. The SAW attenuation mechanisms are investigated at various incidence angles. It is concluded that all three mechanisms (viz. scattering into bulk transverse, longitudinal, and Rayleigh surface acoustic waves) are involved for the Rayleigh and SH polarized SAWs at certain incidence angles, whereas at the other angles only some of the mechanisms are. The criterion for the existence of SH polarized SAWs on a rough surface is considered. A possible increase of the SAW phase velocity on a rough surface compared with that for a flat boundary is discussed. In the limit λ ≫ a (where a is the roughness correlation length) simple explicit expressions for the phase velocities of Rayleigh and SH polarized SAWs are derived. A comparison of the results obtained herein with those of other workers is presented.

  3. Volumetric measurements of a spatially growing dust acoustic wave

    NASA Astrophysics Data System (ADS)

    Williams, Jeremiah D.

    2012-11-01

    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.

  4. Attenuation on an Earth-space path measured in the wavelength range of 8 to 14 micrometers.

    PubMed

    Wilson, R W

    1970-06-19

    A telescope operating over the wavelength range of 8 to 14 micrometers has been added to the Crawford Hill sun tracker for the purpose of measuring attenuation in that atmospheric window. Over a 9-month period the attenuation (typically from clouds) exceeded 10, 20, and 30 decibels for 48, 43, and 34 percent of the time.

  5. Measurement of breast-tissue x-ray attenuation by spectral mammography: first results on cyst fluid

    NASA Astrophysics Data System (ADS)

    Fredenberg, Erik; Dance, David R.; Willsher, Paula; Moa, Elin; von Tiedemann, Miriam; Young, Kenneth C.; Wallis, Matthew G.

    2013-12-01

    Knowledge of x-ray attenuation is essential for developing and evaluating x-ray imaging technologies. For instance, techniques to better characterize cysts at mammography screening would be highly desirable to reduce recalls, but the development is hampered by the lack of attenuation data for cysts. We have developed a method to measure x-ray attenuation of tissue samples using a prototype photon-counting spectral mammography unit. The method was applied to measure the attenuation of 50 samples of breast cyst fluid and 50 samples of water. 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 attenuation of cyst fluid was found to be significantly different from water. There was a relatively large natural spread between different samples of cyst fluid, whereas the homogeneity of each individual sample was found to be good; the variation within samples did not reach above the quantum noise floor. The spectral method proved stable between several measurements on the same sample. Further, chemical analysis and elemental attenuation calculation were used to validate the spectral measurement on a subset of the samples. The two methods agreed within the precision of the elemental attenuation calculation over the mammographic energy range.

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

    PubMed

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

    2015-08-07

    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.

  7. 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

  8. Laboratory Measurements of Droplets Generated by Breaking Water Waves

    NASA Astrophysics Data System (ADS)

    Wang, D.; Liu, X.; Duncan, J. H.

    2010-11-01

    The production of droplets generated by breaking water waves greatly affects the heat, mass and momentum transfer between the atmosphere and the sea surface. In this study, the generation of droplets by single breaking water waves, was explored in a wave tank. Plunging breakers were generated from dispersively focused wave packets (average frequency 1.15 Hz) using a programmable wave maker. The profile histories of the breaking wave crests along the center plane of the tank were measured with a cinematic laser-induced fluorescence technique, while the droplet diameters and motions were measured with a double-pulsed cinematic shadowgraph technique. The two measurement systems were mounted on an instrument carriage that was set to move along the tank following the breaking crests. It was found that droplets are primarily generated when the wave's plunging jet generates strong turbulence during impact with the wave's front face and when large air bubbles, entrapped during the plunging process, rise to the free surface and pop.

  9. Results of attenuation measurements for optical wireless channels under dense fog conditions regarding different wavelengths

    NASA Astrophysics Data System (ADS)

    Flecker, B.; Gebhart, M.; Leitgeb, E.; Sheikh Muhammad, S.; Chlestil, C.

    2006-08-01

    Free Space Optics (FSO) has gained considerable importance in this decade of demand for high bandwidth transmission capabilities. FSO can provide the last mile solution, but the availability and reliability issues concerned with it can not be ignored, and requires thorough investigations. In this work, we present our results about light attenuation at 950 and 850 nm wavelengths in continental city fog conditions with peak values up to 130 dB/km and compare them with attenuation under dense maritime conditions with peak values up to 480 dB/km. Dense fog is the most severe limiting factor in terrestrial optical wireless applications and light propagation in fog has properties in the spatial, spectral and the time domain, which are of importance to free-space optic data communication. In 2004 (within a short term scientific mission of COST 270) measurements of very dense maritime fog and low clouds were made in the mountains of La Turbie, close to the coast of southern France. Using the same equipment, the measurements were continued for the conditions of the continental city of Graz, Austria. This campaign was done in the winter months from 2004 to 2005 and 2005 to 2006 and allows us to compare fog properties for different environments, and the impact of snow fall. We provide detail analysis of a fog and a snow event for better understanding of their attenuation behavior.

  10. Measurements of atmospheric attenuation at ultrasonic frequencies and the significance for echolocation by bats.

    PubMed

    Lawrence, B D; Simmons, J A

    1982-03-01

    The absorption of sound propagating through the atmosphere under laboratory conditions of 25 degrees C and 50% relative humidity was measured at frequencies from 30 to 200 kHz. The attenuating effect on the passage of ultrasonic sounds through air ranged from 0.7 dB/m at 30 kHz. These measurements confirm theoretical expectations and earlier observations that atmospheric attenuation is progressively more severe at higher frequencies and that the atmosphere acts as a low-pass filter for conducting sounds in the frequency range used for echolocation by bats. Different species of bats use different portions of this range of frequencies, and bats emitting sonar signals predominantly above 100 kHz encounter especially severe attenuation of over 3 dB/m. With the greatly restricted operating distances for echolocation at such high frequencies, bats using these higher frequencies must be under compelling ecological pressures of a higher priority than long-range detection of targets.

  11. 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.

  12. Measurement of mass attenuation coefficients in air by application of detector linearity tests

    NASA Astrophysics Data System (ADS)

    Peele, A. G.; Chantler, C. T.; Paterson, D.; McMahon, P. J.; Irving, T. H.; Lin, J. J.; Nugent, K. A.; Brunton, A. N.; McNulty, I.

    2002-10-01

    Accurate knowledge of x-ray mass attenuation coefficients is essential for studies as diverse as atomic physics, materials science, and radiation safety. However, a significant discrepancy exists between theoretical tabulated results for air at soft x-ray energies. We outline a precision measurement of the mass attenuation coefficients for air at various energies using two types of detectors and a simple test of detector response. We discuss whether sufficient accuracy can be obtained using this data to distinguish between competing theoretical estimates. In the process, we investigate the intensity response of two common synchrotron x-ray detectors: an x ray to optical charge-coupled device camera using a crystal scintillator and an x-ray sensitive photodiode.

  13. 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.

  14. X-ray attenuation of adipose breast tissue: in-vitro and in-vivo measurements using spectral imaging

    NASA Astrophysics Data System (ADS)

    Fredenberg, Erik; Erhard, Klaus; Berggren, Karl; Dance, David R.; Young, Kenneth C.; Cederström, Björn; Johansson, Henrik; Lundqvist, Mats; Moa, Elin; Homan, Hanno; Willsher, Paula; Kilburn-Toppin, Fleur; Wallis, Matthew

    2015-03-01

    The development of new x-ray imaging techniques often requires prior knowledge of tissue attenuation, but the sources of such information are sparse. We have measured the attenuation of adipose breast tissue using spectral imaging, in vitro and in vivo. For the in-vitro measurement, fixed samples of adipose breast tissue were imaged on a spectral mammography system, and the energy-dependent x-ray attenuation was measured in terms of equivalent thicknesses of aluminum and poly-methyl methacrylate (PMMA). For the in-vivo measurement, a similar procedure was applied on a number of spectral screening mammograms. The results of the two measurements agreed well and were consistent with published attenuation data and with measurements on tissue-equivalent material.

  15. Surface wave attenuation in the shallow subsurface from multichannel-multishot seismic data: a new approach for detecting fractures and lithological discontinuities

    NASA Astrophysics Data System (ADS)

    Ikeda, Tatsunori; Tsuji, Takeshi

    2016-07-01

    Surface wave analysis generally neglects amplitude information, instead using phase information to delineate near-surface S-wave velocity structures. To effectively characterize subsurface heterogeneities from amplitude information, we propose a method of estimating lateral variation of attenuation coefficients of surface waves from multichannel-multishot (multifold) seismic data. We extend the concept of the common midpoint cross-correlation method, used for phase velocity estimation, to the analysis of attenuation coefficients. Our numerical experiments demonstrated that when used together, attenuation coefficients and phase velocities could characterize a lithological boundary as well as fracture zone. We applied the proposed method to multifold seismic reflection data acquired in Shikoku Island, Japan. We clearly observed abrupt changes in lateral variation of estimated attenuation coefficients around fault locations associated with a lithological boundary and with well-developed fractures, whereas phase velocity results could detect only the lithological boundary. Our study demonstrated that simultaneous interpretation of attenuation coefficients and phase velocities has the potential to distinguish localized fractures from lithological boundaries.

  16. Shear wave attenuation estimated from the spectral decay rate in the vicinity of the Petropavlovsk station, Kamchatka

    NASA Astrophysics Data System (ADS)

    Gusev, A. A.; Guseva, E. M.

    2016-07-01

    The parameters of S-wave attenuation (the total effect of absorption and scattering) near the Petropavlovsk (PET) station in Kamchatka were estimated by means of the spectral method through an original procedure. The spectral method typically analyzes the changes with distance of the shape of spectra of the acceleration records assuming that the acceleration spectrum at the earthquake source is flat. In reality, this assumption is violated: the source acceleration spectra often have a high-frequency cutoff (the source-controlled f max) which limits the spectral working bandwidth. Ignoring this phenomenon not only leads to a broad scatter of the individual estimates but also causes systematic errors in the form of overestimation of losses. In the approach applied in the present study, we primarily estimated the frequency of the mentioned high-frequency cutoff and then constructed the loss estimates only within the frequency range where the source spectrum is approximately flat. The shape of the source spectrum was preliminarily assessed by the approximate loss compensation technique. For this purpose, we used the tentative attenuation estimates which are close to the final ones. The difference in the logarithms of the spectral amplitudes at the edges of the working bandwidth is the input for calculating the attenuation. We used the digital accelerograms from the PET station, with 80 samples per second digitization rate, and based on them, we calculated the averaged spectrum of the S-waves as the root mean square along two horizontal components. Our analysis incorporates 384 spectra from the local earthquakes with M = 4-6.5 at the hypocentral distances ranging from 80 to 220 km. By applying the nonlinear least-square method, we found the following parameters of the loss model: the Q-factor Q 0 = 156 ± 33 at frequency f = 1 Hz for the distance interval r = 0-100 km; the exponent in the power-law relationship describing the growth of the Q-factor with frequency,

  17. Laser probe for measuring 2-D wave slope spectra of ocean capillary waves

    NASA Technical Reports Server (NTRS)

    Palm, C. S.; Anderson, R. C.; Reece, A. M.

    1977-01-01

    A laser-optical instrument for use in determining the two-dimensional wave-slope spectrum of ocean capillary waves is described. The instrument measures up to a 35-deg tip angle of the surface normal by measuring the position of a refracted laser beam directed vertically upward through a water surface. A telescope, a continuous two-dimensional Schottky barrier photodiode, and a pair of analog dividers render the signals independent of water height and insensitive to laser-beam intensity fluctuations. Calibration is performed entirely in the laboratory before field use. Sample records and wave-slope spectra are shown for one-dimensional wave-tank tests and for two-dimensional ocean tests. These are presented along with comparison spectra for calm and choppy water conditions. A mechanical wave follower was used to adjust the instrument position in the presence of large ocean swell and tides.

  18. Laser probe for measuring 2-D wave slope spectra of ocean capillary waves.

    PubMed

    Palm, C S; Anderson, R C; Reece, A M

    1977-04-01

    A laser-optical instrument for use in determining the 2-D wave slope spectrum of ocean capillary waves is described. The instrument measures up to a 35 degrees tip angle of the surface normal by measuring the position of a refracted laser beam directed vertically upward through a water surface. A telescope, a continuous 2-D Schottky barrier photodiode, and a pair of analog dividers render the signals independent of water height and insensitive to laser beam intensity fluctuations. Calibration is performed entirely in the laboratory before field use. Sample records and wave slope spectra are shown for 1-D wave tank tests and for 2-D ocean tests. These are presented along with comparison spectra for calm and choppy water conditions. A mechanical wave follower was used to adjust the instrument position in the presence of large ocean swell and tides. PMID:20168638

  19. 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.

  20. 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

  1. 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.

  2. 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.

  3. 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

  4. 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.

  5. Broadband ultrasound attenuation at the calcaneus measured using a new contact ultrasound unit.

    PubMed

    Fauchet, M; Andrieux, P; Roux, C; Sebert, J L

    1998-04-01

    We evaluated a new contact ultrasound device, developed and manufactured in France, for measuring broadband ultrasound attenuation at the calcaneus. We first studied the influence on measurement results of a number of parameters including the nature of the coupling agent, heel position, transducer temperature, and foot vasodilation. We then determined the reproducibility of the measurements (2.14 +/- 1.07% in the medium-term) and established reference values in women (n = 612) and men (n = 106). Broadband ultrasound attenuation decreased between 25 and 85 years of age by 34% in women and 17% in men. Sensitivity and specificity for detection of decreased bone mass at the calcaneus were 85.5% and 81.5%, respectively. Sensitivity and specificity of the measurement at the calcaneus as compared to the lumbar spine were 90.7% and 89.1%, respectively. This unit intended for screening purposes is very easy to use, and the measurements it provides are immediately available. It can be expected to help determine the optimal strategy for use of ultrasound in the management of osteoporosis.

  6. High-frequency attenuation and backscatter measurements of rat blood between 30 and 60 MHz

    NASA Astrophysics Data System (ADS)

    Huang, Chih-Chung

    2010-10-01

    There has recently been a great deal of interest in noninvasive high-frequency ultrasound imaging of small animals such as rats due to their being the preferred animal model for gene therapy and cancer research. Improving the interpretation of the obtained images and furthering the development of the imaging devices require a detailed knowledge of the ultrasound attenuation and backscattering of biological tissue (e.g. blood) at high frequencies. In the present study, the attenuation and backscattering coefficients of the rat red blood cell (RBC) suspensions and whole blood with hematocrits ranging from 6% to 40% were measured between 30 and 60 MHz using a modified substitution approach. The acoustic parameters of porcine blood under the same conditions were also measured in order to compare differences in the blood properties between these two animals. For porcine blood, both whole blood and RBC suspension were stirred at a rotation speed of 200 rpm. Three different rotation speeds of 100, 200 and 300 rpm were carried out for rat blood experiments. The attenuation coefficients of both rat and porcine blood were found to increase linearly with frequency and hematocrit (the values of coefficients of determination (r2) are around 0.82-0.97 for all cases). The average attenuation coefficient of rat whole blood with a hematocrit of 40% increased from 0.26 Nepers mm-1 at 30 MHz to 0.47 Nepers mm-1 at 60 MHz. The maximum backscattering coefficients of both rat and porcine RBC suspensions were between 10% and 15% hematocrits at all frequencies. The fourth-power dependence of backscatter on frequency was approximately valid for rat RBC suspensions with hematocrits between 6% and 40%. However, the frequency dependence of the backscatter estimate deviates from a fourth-power law for porcine RBC suspension with hematocrit higher than 20%. The backscattering coefficient plateaued for hematocrits higher than 15% in porcine blood, but for rat blood it was maximal around a

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

    PubMed

    Carcione; Poletto

    2000-07-01

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

  8. 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

  9. Airborne microwave Doppler measurements of ocean wave directional spectra

    NASA Technical Reports Server (NTRS)

    Plant, W. J.; Keller, W. C.; Reeves, A. B.; Uliana, E. A.; Johnson, J. W.

    1987-01-01

    A technique is presented for measuring ocean wave directional spectra from aircraft using microwave Doppler radar. The technique involves backscattering coherent microwave radiation from a patch of sea surface which is small compared to dominant ocean wavelengths in the antenna look direction, and large compared to these lengths in the perpendicular (azimuthal) direction. The mean Doppler shift of the return signal measured over short time intervals is proportional to the mean sea surface velocity of the illuminated patch. Variable sea surface velocities induced by wave motion therefore produce time-varying Doppler shifts in the received signal. The large azimuthal dimension of the patch implies that these variations must be produced by surface waves traveling near the horizontal antenna look direction thus allowing determination of the direction of wave travel. Linear wave theory is used to convert the measured velocities into ocean wave spectral densities. Spectra measured simultaneously with this technique and two laser profilometers, and nearly simultaneous with this technique and two laser profilometers, and nearly simultaneous with a surface buoy, are presented. Applications and limitations of this airborne Doppler technique are discussed.

  10. Measurement of Strength at High Pressures Using Oblique Shock Waves

    NASA Astrophysics Data System (ADS)

    Stolyar, Victoria; Ravichandran, Guruswami; Alexander, Scott

    2013-06-01

    At high pressures and high strain rates, the measurement of strength is important to many implications including planetary impact and inertial confinement fusion. Understanding how strength depends on pressure allows for the characterization of materials and validation of constitutive models. Slotted barrel guns have traditionally been used in experiments, such as the pressure-shear plate impact technique, to generate longitudinal and shear waves through an oblique impact. A new methodology for measuring material strength using normal impact (1-2 km/s) is described. In this configuration, a composite target is designed with an angled material of interest embedded into a driver material. This driver material is used to generate an oblique shock wave that is followed by a shear wave, due to the angled nature of the target material. Using shock polar analysis, the rear surface of the target is designed to be parallel to the transmitted shock wave in order to mitigate wave interactions at the rear surface. A window is used on the rear surface of the target to measure the in-situ particle velocities at the target-window interface. Using three VISAR measurements, the tangential and longitudinal particle velocities at the rear surface of the target are found from which the shear stress (strength) is inferred as a function of pressure. Results are presented for 6061-T6 Aluminum as well as Tantalum. Hydrocode simulations are used to predict the experimental results as well as characterize the wave interactions in the oblique wedge experiments.

  11. 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.

  12. 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%.

  13. 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

  14. Optical measuring technique for small scale water surface waves

    NASA Astrophysics Data System (ADS)

    Jahne, Bernd; Waas, Stefan

    1989-10-01

    This paper describes two optical measuring techniques for determining the spatial and temporal structure of small-scale surface waves: (1) the imaging slope gage (ISG) and (2) the reflective stereo slope gage (RSSG). The ISG is based on light refraction at the water surface; it records image sequences of the wave slope at a maximum area of 1 sq m. The RSSG technique involves illumination of the water surface from above by a monochromatic light source; its two CCD camera take stereo images of sequences of the specular reflexes returned by the water surface. Both instruments were successfully used in wind/wave facility investigations. The results show that they permit a much more detailed investigation of the physics of small scale waves than those made using conventional equipment, such as point measuring devices or laser slope gages.

  15. 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.

  16. 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.

  17. Modeling and experiment of the suspended seismometer concept for attenuating the contribution of tilt motion in horizontal measurements.

    PubMed

    Matichard, F; Evans, M; Mittleman, R; MacInnis, M; Biscans, S; Dooley, K L; Sohier, H; Lauriero, A; Paris, H; Koch, J; Knothe, P; Carbajo, A; Dufort, C

    2016-06-01

    Tilt-horizontal coupling in inertial sensors limits the performance of active isolation systems such as those used in gravitational wave detectors. Inertial rotation sensors can be used to subtract the tilt component from the signal produced by horizontal inertial sensors, but such techniques are often limited by the sensor noise of the tilt measurement. A different approach is to mechanically filter the tilt transmitted to the horizontal inertial sensor, as discussed in this article. This technique does not require an auxiliary rotation sensor and can produce a lower noise measurement. The concept investigated uses a mechanical suspension to isolate the inertial sensor from input tilt. Modeling and simulations show that such a configuration can be used to adequately attenuate the tilt transmitted to the instrument, while maintaining translation sensitivity in the frequency band of interest. The analysis is supported by experimental results showing that this approach is a viable solution to overcome the tilt problem in the field of active inertial isolation. PMID:27370484

  18. Modelling ultrasound guided wave propagation for plate thickness measurement

    NASA Astrophysics Data System (ADS)

    Malladi, Rakesh; Dabak, Anand; Murthy, Nitish Krishna

    2014-03-01

    Structural Health monitoring refers to monitoring the health of plate-like walls of large reactors, pipelines and other structures in terms of corrosion detection and thickness estimation. The objective of this work is modeling the ultrasonic guided waves generated in a plate. The piezoelectric is excited by an input pulse to generate ultrasonic guided lamb waves in the plate that are received by another piezoelectric transducer. In contrast with existing methods, we develop a mathematical model of the direct component of the signal (DCS) recorded at the terminals of the piezoelectric transducer. The DCS model uses maximum likelihood technique to estimate the different parameters, namely the time delay of the signal due to the transducer delay and amplitude scaling of all the lamb wave modes due to attenuation, while taking into account the received signal spreading in time due to dispersion. The maximum likelihood estimate minimizes the energy difference between the experimental and the DCS model-generated signal. We demonstrate that the DCS model matches closely with experimentally recorded signals and show it can be used to estimate thickness of the plate. The main idea of the thickness estimation algorithm is to generate a bank of DCS model-generated signals, each corresponding to a different thickness of the plate and then find the closest match among these signals to the received signal, resulting in an estimate of the thickness of the plate. Therefore our approach provides a complementary suite of analytics to the existing thickness monitoring approaches.

  19. Wave electric field measurements of Trivelpiece-Gould waves in a helicon discharge.

    NASA Astrophysics Data System (ADS)

    Franck, Christian; Scime, Earl; Kline, John; Klinger, Thomas

    2000-10-01

    A new type of measurement for the detection of Trivelpiece-Gould (TG) modes in a helicon discharge is proposed and tested. TG modes are one of the many candidates for explaining the surprisingly efficient transfer of helicon wave energy into the plasma. Recent research efforts have been made to detect TG-modes in helicon discharges, but wavefield structure measurements have been equivocal. Skiff(F. Skiff and F. Anderegg, PRL 59, 896 (1987).) proposed a method for determining the wavenumber of an electrostatic wave in a collisionless plasma by measuring the perturbed ion distribution function (f_1) with laser induced fluorenscence (LIF). This method has already been succesfully applied in studies of ion cyclotron waves in helicon sources(J. Kline, E. Scime, et.al., Phys. Plasmas 6, 4767 (1999).). We have non-invasively measured the wavelength of electrostatic oscillations in a helicon discharge directly with LIF. The perturbed part f_1, due to the wave electric fields, is obtained if the LIF measurements are phase-correlated with the driving antenna signal. Theoretical calculations show that clearly identifiable perturbation f1 is expected for TG-waves in the plasma. We will present the theoretical calculations with our initial measurements.

  20. 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

  1. Energy and phase velocity considerations required for attenuation and velocity measurements of anisotropic composites.

    PubMed

    Carroll, N L; Humphrey, V F; Smith, J D

    2002-05-01

    Viscoelastic fibre-reinforced composite materials have a number of possible advantages for use in underwater acoustic applications. In order to exploit these materials it is important to be able to measure their complex stiffness matrix in order to determine their acoustic response. Ultrasonic transmission measurements on parallel-sided samples, employing broadband pulsed transducers at 2.25 MHz and an immersion method, have been used to determine the viscoelastic properties of a glass-reinforced composite with uniaxially aligned fibres. The composite measured was constructed from Cytecfiberite's CYCOM 919 E-glass. The theory of acoustic propagation in anisotropic materials shows that the direction of energy propagation is, in general, different from that given by Snell's Law. At 15 degrees incidence, Snell's Law implies a refracted angle of 40 +/- 2 degrees, whereas the energy direction is observed to be 70 +/- 2 degrees. Despite this, the experimental data indicates that the position of the receiving transducer has relatively little effect on the apparent phase velocity measured. The phase velocities measured at positions determined from the refracted angle and energy direction are 3647 and 3652 +/- 50 m s(-1), respectively. However, the amplitude of the received signal, and hence estimate of attenuation, is highly sensitive to the receiver position. This indicates that the acoustic Poynting vector must be considered in order to precisely determine the correct position of the receiving transducer for attenuation measurements. The beam displacement for a 17.6 mm sample at 15 degrees incidence is 9.5 and 40 mm by Snell's Law and Poynting's Theorem, respectively. Measured beam displacements have been compared with predictions derived from material stiffness coefficients. These considerations are important in recovering the complex stiffness matrix. PMID:12159995

  2. Surprisingly low frequency attenuation effects in long tubes when measuring turbulent fluxes at tall towers

    NASA Astrophysics Data System (ADS)

    Ibrom, Andreas; Brændholt, Andreas; Pilegaard, Kim

    2016-04-01

    The eddy covariance technique relies on the fast and accurate measurement of gas concentration fluctuations. While for some gasses robust and compact sensors are available, measurement of, e.g., non CO2 greenhouse gas fluxes is often performed with sensitive equipment that cannot be run on a tower without massively disturbing the wind field. To measure CO and N2O fluxes, we installed an eddy covariance system at a 125 m mast, where the gas analyser was kept in a laboratory close to the tower and the sampling was performed using a 150 m long tube with a gas intake at 96 m height. We investigated the frequency attenuation and the time lag of the N2O and CO concentration measurements with a concentration step experiment. The results showed surprisingly high cut-off frequencies (close to 2 Hz) and small low-pass filter induced time lags (< 0.3 s), which were similar for CO and N2O. The results indicate that the concentration signal was hardly biased during the ca 10 s travel through the tube. Due to the larger turbulence time scales at large measurement heights the low-pass correction was for the majority of the measurements < 5%. For water vapour the tube attenuation was massive, which had, however, a positive effect by reducing both the water vapour dilution correction and the cross sensitivity effects on the N2O and CO flux measurements. Here we present the set-up of the concentration step change experiment and its results and compare them with recently developed theories for the behaviour of gases in turbulent tube flows.

  3. 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.

  4. Range Measurement Using Ultrasound FMCW Wave

    NASA Astrophysics Data System (ADS)

    Kunita, M.; Miki, T.; Arai, I.

    The authors have proposed an ultrasound FMCW range-measuring system for diagnosis. In the proposed system, a transmitter and receiver operate at very low voltage. It is desirable to compose a simple transmitter and receiver and to protect the human body against damage caused by ultrasound power. The system results analyzed using saw-tooth and isosceles modulation waveform agreed with experiment results derived using delay lines.

  5. Continuous wave lidar measurement of atmospheric visibility

    NASA Technical Reports Server (NTRS)

    Bufton, J. L.; Iyer, R. S.

    1978-01-01

    The technique of measurement of phase shift with a modulated CW lidar system for the purpose of atmospheric visibility assessment was evaluated both theoretically and experimentally. A closed form solution for prediction of phase shift as a function of visibility and modulation frequency was developed. Data obtained with a bistatic CW lidar configuration were compared with predictions. Results indicate the expected trends with equipment parameters and call for more extensive experiments.

  6. IR surface electromagnetic-wave measurement of hydrogen adsorption and surface reconstruction on W(100)

    SciTech Connect

    Hanssen, L.M.

    1985-01-01

    Both the clean and hydrogen covered W(100) surfaces are probed with an inhomogenous electromagnetic mode which is bound to the metal surface. This Surface Electromagnetic Wave (SEW) is generated from a plane-wave spectrum by means of a grating directly etched into the metal surface. A second grating, spaced about 5 cm from the first, transforms the SEW back into a plane wave infrared beam. Near room temperature, the temperature dependence of the magnitude of the SEW signal agrees with the Drude model prediction using the d.c. resistivity. At high temperatures (>1000K) however, SEW signal is attenuated to such a large extent that plane wave radiation generated at the first grating can be detected as well. The first SEW spectrum of surface reconstruction was observed upon hydrogen adsorption on a W(100) sample maintained near room temperature. The reconstruction of the W(100)-H surface is checked and calibrated through LEED observations and thermal desorption measurements. The SEW signal is found to follow a sigmoid curve as a function of coverage. Intensity changes as large as 30% of the clean surface value occur as the state of the W(100)-H surface changes. This extreme sensitivity of the SEW attentuation length to surface reconstruction is shown to be consistent with changes in the diffuse surface scattering component of the conduction electron scattering time.

  7. An instrument for in situ comet nucleus surface density profile measurement by gamma ray attenuation

    NASA Astrophysics Data System (ADS)

    Ball, Andrew J.; Gadomski, Stanislaw; Banaszkiewicz, Marek; Spohn, Tilman; Ahrens, Thomas J.; Whyndham, Matthew; Zarnecki, John C.

    2001-08-01

    The MUPUS experiment on the Rosetta Lander will measure thermal and mechanical properties as well as the bulk density of the cometary material at and just below the surface of the nucleus of comet 46P/Wirtanen. A profile of bulk density vs. depth will be obtained by measuring the attenuation of 662 keV gamma rays emitted by a 137Cs source. Compton scattering is the dominant interaction process at this energy, the attenuation depending directly on the total number of electrons along the source-detector path. This in turn is approximately proportional to the column density. We report here on the design of the bulk density instrument and the results of related Monte Carlo simulations, laboratory tests and calculations of the instrument's performance. The 137Cs radioisotope source is mounted in the tip of the MUPUS thermal probe - a 10 mm diameter rod, to be hammered into the surface of the nucleus to a depth of ˜370 mm. Two cadmium zinc telluride (CZT) detectors mounted at the top of the probe will monitor the count rate of 662 keV photons. Due to the statistics of photon counting, the integration time required to measure column density to a particular accuracy varies with depth as well as with bulk density. The required integration time is minimised for a material thickness equal to twice the exponential attenuation length. At shallower depths the required time rises due to the smaller fractional change in count rate with varying depth, while at greater depths the reduced count rate demands longer integration times. The former effect and the fact that the first 45 mm of the source-detector path passes not through the comet but through the material of the probe, mean that the first density measurement cannot be made until the source has reached a depth of perhaps 100 mm. The laboratory experiments indicate that at this depth an integration time no less than 348 s (falling to 93.9 s at full penetration) would be required to measure a bulk density of 1000 kg m -3 to 5

  8. 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.

  9. 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.

  10. 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.

  11. Precision Measurements with Matter-wave Interferometry

    NASA Astrophysics Data System (ADS)

    Erickson, Christopher; Christensen, Dan; Washburn, Matthew; Archibald, James; van Zjill, Marshall; Birrell, Jeremiah; Burdett, Adam; Durfee, Dallin

    2007-06-01

    We will discuss progress on a neutral-calcium beam interferometer which is nearing completion. We will also present a proposal to measure electric and magnetic fields with extreme precision using a slow ion interferometer. The calcium interferometer utilizes a thermal beam for simplicity and high atom flux. Doppler shifts will be reduced using a novel alignment scheme for the Ramsey beams using precision prisms. The ion interferometer will utilize a slow beam of strontium-87 ions created by photon-ionizing a slow atomic beam. The ions will interact with three sets of laser beams which will drive stimulated Raman transitions. The proposed device will be used to search for variations from Coulomb's inverse-square law and a possible photon rest mass with a precision which is several orders of magnitude better than previous laboratory experiments.

  12. 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.

  13. Spatio-Temporal Measurements of Short Wind Water Waves

    NASA Astrophysics Data System (ADS)

    Rocholz, Roland; Jähne, Bernd

    2010-05-01

    Spatio-temporal measurements of wind-driven short-gravity capillary waves are reported for a wide range of experimental conditions, including wind, rain and surface slicks. The experiments were conducted in the Hamburg linear wind/wave flume in cooperation with the Institute of Oceanography at the University of Hamburg, Germany. Both components of the slope field were measured optically at a fetch of 14.4 m using a color imaging slope gauge (CISG) with a footprint of 223 x 104 mm and a resolution of 0.7 mm. The instrument was improved versus earlier versions (Jähne and Riemer (1990), Klinke (1992)) to achieve a sampling rate of 312.5 Hz, which now allows for the computation of 3D wavenumber-frequency spectra (see Rocholz (2008)). This made it possible to distinguish waves traveling in and against wind direction, which proved useful to distinguish wind waves from ring waves caused by rain drop impacts. Using a new calibration method it was possible to correct for the intrinsic nonlinearities of the instrument in the slope range up to ±1. In addition, the Modulation Transfer Function (MTF) was measured and employed for the restoration of the spectral amplitudes for wavenumbers in the range from 60 to 2300 rad/m. The spectra for pure wind conditions are generally consistent with previous measurements. But, the shape of the saturation spectra in the vicinity of k~1000 rad/m (i.e. pure capillary waves) stands in contradiction to former investigations where a sharp spectral cutoff (k^(-2) or k^(-3)) is commonly reported (e.g. Jähne and Riemer (1990)). This cutoff is reproduced by almost all semi-empirical models of the energy flux in the capillary range (e.g. Kudryavtsev et al. (1999), Apel (1994)). However, the new MTF corrected spectra show only a gentle decrease (between k^(-0.5) and k^(-1)) for k > 1000 rad/m. Therefore the question for the relative importance of different dissipation mechanisms might need a new assessment. References: J. R. Apel. An improved

  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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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

  1. Measuring and Modeling of the Dielectric Properties and Attenuation of Vegetation

    NASA Technical Reports Server (NTRS)

    Ulaby, F. T.

    1984-01-01

    The dielectric properties of vegetation material--primarily agricultural plants--as a function of moisture content and microwave frequency was measured and used to develop dielectric mixing models for the vegetation-water mixture. A model for the loss factor of a vegetation canopy was also developed. During the first phase of this investigation, three waveguide transmission systems covering from 1 to 2-GHz, from 3.5 to 6.5-GHz, and from 7.5 to 8.5-GHz bands were constructed and calibrated. By measuring the magnitude and phase of the field transmission coefficient of a given sample, it was possible to calculate the real and imaginary parts of the complex dielectric constant of the sample. Measurements were made for numerous samples of leaves and stalks of wheat and corn, and for wheat heads. Also, dielectric measurements were made of the liquid included in the vegetation material after extraction by mechanical means. The propagation loss is more than an order of magnitude greater than had previously been assumed. Various types of dielectric mixing models were investigated in terms of the available data, and a propagation model was developed and evaluated against direct canopy attenuation measurements. The canopy measurements were made by transmitting a signal from a radar antenna mounted atop a truck-mounted boom, and using a small antenna mounted on a rail beneath the canopy to receive it.

  2. New data on seismic wave attenuation in the lithosphere and upper mantle of the northeastern flank of the Baikal rift system

    NASA Astrophysics Data System (ADS)

    Dobrynina, A. A.; Sankov, V. A.; Chechelnitsky, V. V.

    2016-05-01

    The investigation data on seismic wave attenuation in the lithosphere and upper mantle of the northeastern flank of the Baikal rift system obtained with a seismic coda envelope and sliding window are considered. Eleven local districts were described by one-dimensional attenuation models characterized by alternation of high and low attenuation layers, which are consistent with the results obtained previously by Yu.F. Kopnichev for the southwestern flank of the Baikal rift system [9]. The subcrust of the lithosphere contains a thin layer with high attenuation of seismic waves likely related to higher heterogeneity (fragmentation) and occurrence of fluids. The lithosphere basement depth varies from 100-120 km in the west within the Baikal folded area to 120-140 km in the east within the Siberian Platform. It is concluded that there are two asthenosphere layers. Based on specific features of the lithosphere and upper mantle structure, it can be assumed that they were subject to gradual modification involving fluidization processes and partial melting in the Late Cenozoic extension under the influence of distant tectogenesis sources.

  3. Directional ocean wave spectrum estimation based on the joint measurement from synthetic aperture radar and wave spectrometer

    NASA Astrophysics Data System (ADS)

    Ren, Lin; Pan, Delu; Hao, Zengzhou; Mao, Zhihua; He, Xianqiang

    2011-11-01

    Synthetic aperture radar (SAR) can measure directional wave spectrum based on the closed nonlinear SAR-ocean mapping mechanism. The according wave spectrum retrieval algorithm has been developing for decades, but some limitations remain, like high wave number cut off in azimuthal direction and the need for the first guess spectrum. Wave spectrometer is a kind of new satellite-based real aperture radar (RAR) operating at low incidence, which has a narrow beam and scans complete 360° by antenna rotation. It derives wave spectrum by the simple linear relation between the wave spectrum and the modulation spectrum from the wave spectrometer. The linear coefficient can be estimated by the nadir beam or external wind speed information. This paper proposes a method on the wave spectrum estimation based on the joint measurement from synchronous SAR and wave spectrometer. Firstly, the modulation spectrum is derived from the signal spectrum of the wave spectrometer, from which the relative wave spectrum can be constructed. Then the relative wave spectrum is seen as the first guess spectrum for the wave spectrum retrieval of SAR image. Because the relative wave spectrum has the same pattern with the real wave spectrum but has different absolute energy, we can retrieve the directional wave spectrum by the iteration way based on the relative wave spectrum from the SAR image. This paper makes use of simulation technology to validate the joint measurement. The simulation compares the input spectrum and the retrieved one in terms of peak direction, peak wavelength and significant wave height, which has a deviation of 6°, 4m and 0.3m, respectively. Simulation results show the joint measurement has the feasibility for the retrieval of directional ocean wave spectrum.

  4. 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.

  5. Global Attenuation Model of the Upper Mantle

    NASA Astrophysics Data System (ADS)

    Adenis, A.; Debayle, E.; Ricard, Y. R.

    2015-12-01

    We present a three-dimensional shear attenuation model based on a massive surface wave data-set (372,629 Rayleigh waveforms analysed in the period range 50-300s by Debayle and Ricard, 2012). For each seismogram, this approach yields depth-dependent path average models of shear velocity and quality factor, and a set of fundamental and higher-mode dispersion and attenuation curves. We combine these attenuation measurements in a tomographic inversion after a careful rejection of the noisy data. We first remove data likely to be biased by a poor knowledge of the source. Then we assume that waves corresponding to events having close epicenters and recorded at the same station sample the same elastic and anelastic structure, we cluster the corresponding rays and average the attenuation measurements. Logarithms of the attenuations are regionalized using the non-linear east square formalism of Tarantola and Valette (1982), resulting in attenuation tomographic maps between 50s and 300s. After a first inversion, outlyers are rejected and a second inversion yields a moderate variance reduction of about 20%. We correct the attenuation curves for focusing effect using the linearized ray theory of Woodhouse and Wong (1986). Accounting for focussing effects allows building tomographic maps with variance reductions reaching 40%. In the period range 120-200s, the root mean square of the model perturbations increases from about 5% to 20%. Our 3-D attenuation models present strong agreement with surface tectonics at period lower than 200s. Areas of low attenuation are located under continents and areas of high attenuation are associated with oceans. Surprisingly, although mid oceanic ridges are located in attenuating regions, their signature, even if enhanced by focusing corrections, remains weaker than in the shear velocity models. Synthetic tests suggests that regularisation contributes to damp the attenuation signature of ridges, which could therefore be underestimated.

  6. 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.

  7. 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. 

  8. 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.

  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.

    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.

  10. Dual differential interferometer for measurements of broadband surface acoustic waves

    NASA Technical Reports Server (NTRS)

    Turner, T. M.; Claus, R. O.

    1981-01-01

    A simple duel interferometer which uses two pairs of orthogonally polarized optical beams to measure both the amplitude and direction of propagation of broadband ultrasonic surface waves is described. Each pair of focused laser probe beams is used in a separate wideband differential interferometer to independently detect the component of surface wave motion along one direction on the surface. By combining the two output signals corresponding to both components, the two dimensional surface profile and its variation as a function of time is determined.

  11. Phase Velocity Method for Guided Wave Measurements in Composite Plates

    NASA Astrophysics Data System (ADS)

    Moreno, E.; Galarza, N.; Rubio, B.; Otero, J. A.

    Carbon Fiber Reinforced Polymer is a well-recognized material for aeronautic applications. Its plane structure has been widely used where anisotropic characteristics should be evaluated with flaw detection. A phase velocity method of ultrasonic guided waves based on a pitch-catch configuration is presented for this purpose. Both shear vertical (SV) and shear horizontal (SH) have been studied. For SV (Lamb waves) the measurements were done at different frequencies in order to evaluate the geometrical dispersion and elastic constants. The results for SV are discussed with an orthotropic elastic model. Finally experiments with lamination flaws are presented.

  12. Phase speed and attenuation in bubbly liquids inferred from impedance measurements near the individual bubble resonance frequency.

    PubMed

    Wilson, Preston S; Roy, Ronald A; Carey, William M

    2005-04-01

    In the ocean, natural and artificial processes generate clouds of bubbles that scatter and attenuate sound. Measurements have shown that at the individual bubble resonance frequency, sound propagation in this medium is highly attenuated and dispersive. The existing theory to explain this behavior is deemed adequate away from resonance. However, due to excessive attenuation near resonance, little experimental data exists for a comparison with model predictions. An impedance tube was developed specifically for exploring this regime. The effective medium phase speed and attenuation were inferred from measurements of the surface impedance of a layer of bubbly liquid composed of air bubbles and distilled water, for void fractions from 6.2 x 10(-5) to 5.4 x 10(-4) and bubble sizes centered around 0.62 mm in radius. Improved measurement speed, accuracy, and precision is possible with the new instrument, and both instantaneous and time-averaged measurements were obtained. The phase speed and attenuation at resonance was observed to be sensitive to the bubble population statistics and agreed with an existing model [J. Acoust. Soc. Am. 85, 732-746 (1989)], within the uncertainty of the bubble population parameters. Agreement between the model and the data reported here is better than for the data that was available when the model was originally published.

  13. 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.

  14. 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.

  15. The Influence of Water on Seismic Wave Speeds and Attenuation in the Upper Mantle: an update from the Laboratory

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

    A fine-grained synthetic olivine (Fo90) polycrystal, doped with ~0.04 wt. % TiO2, has been prepared with ~70 wt. ppm H2O accommodated in the remarkably stable Ti-clinohumite defect typical of natural olivines from the Earth's generally water-undersaturated upper mantle (Berry et al., 2005). A precision-ground specimen of this material, sleeved in Pt tubing within a mild-steel jacket, was tested in torsional forced oscillation at seismic frequencies (mHz-Hz) and temperatures to 1200 °C, under 200 MPa confining pressure. The shear modulus was observed to decrease systematically with increasing oscillation period and temperature, accompanied by monotonically increasing dissipation, which are characteristic of absorption band or high-temperature-background behaviour. In a previous preliminary report, the new data were compared with the model of Jackson and Faul (Phys. Earth Planet. Interiors, 2010) for a suite of essentially anhydrous Ti-free olivine polycrystals, evaluated at the 25 μm grain size of the hydrous titaniferous olivine specimen, showing that the latter is vastly more dissipative than its anhydrous equivalent (by an order of magnitude at 1200 °C) and correspondingly lower in shear modulus. The results of additional experiments now better constrain the mechanical behaviour of the enclosing Pt sleeve and allow direct comparison with data for an anhydrous titaniferous olivine of comparable grain size. The latest results confirm a very strong influence of water on seismic wave attenuation, even under the water-undersaturated conditions expected to prevail in the Earth's upper mantle.

  16. Velocity and attenuation of shear waves in the phantom of a muscle-soft tissue matrix with embedded stretched fibers

    NASA Astrophysics Data System (ADS)

    Rudenko, O. V.; Tsyuryupa, S. N.; Sarvazyan, A. P.

    2016-09-01

    We develop a theory of the elasticity moduli and dissipative properties of a composite material: a phantom simulating muscle tissue anisotropy. The model used in the experiments was made of a waterlike polymer with embedded elastic filaments imitating muscle fiber. In contrast to the earlier developed phenomenological theory of the anisotropic properties of muscle tissue, here we obtain the relationship of the moduli with characteristic sizes and moduli making up the composite. We introduce the effective elasticity moduli and viscosity tensor components, which depend on stretching of the fibers. We measure the propagation velocity of shear waves and the shear viscosity of the model for regulated tension. Waves were excited by pulsed radiation pressure generated by modulated focused ultrasound. We show that with increased stretching of fibers imitating muscle contraction, an increase in both elasticity and viscosity takes place, and this effect depends on the wave propagation direction. The results of theoretical and experimental studies support our hypothesis on the protective function of stretched skeletal muscle, which protects bones and joints from trauma.

  17. A standing-wave flow measurement system for small diameter pipes using long acoustic waves

    NASA Astrophysics Data System (ADS)

    Ikpe, E. S.; Scarrott, G.; Weight, J. P.; Grattan, K. T. V.

    1993-09-01

    An exploratory investigation, using laboratory fabricated acoustic components, of standing-wave flow measurement techniques for liquids and gases in pipes of diameter up to about 25 mm was undertaken, using long acoustic waves. The results show a linear sensitivity based on the ``sing-around'' technique, often associated with contrapropagating time-of-flight flowmeters. A repeatability test at a volume flow rate of 1.5 l per minute indicates that, within the 95% confidence limit, only 5% of the readings will lie outside the range of 1.1-1.9 l per minute. The transducer used in the above investigation comprises a section of the pipe wall which acts as part of a resonating transmitter or detector of long waves in a fluid. The measurement cell is closed and generates a known standing-wave pattern. The results obtained suggest that, in the future, the initial accuracy obtained in this study can be significantly enhanced with further improvements to the transducers, the measurement cell, the electronics, and test procedures, on which work is continuing, to produce a device competitive with those using other technologies.

  18. Pressure measurements of a three wave journal air bearing

    NASA Technical Reports Server (NTRS)

    Dimofte, Florin; Addy, Harold E., Jr.

    1994-01-01

    In order to validate theoretical predictions of a wave journal bearing concept, a bench test rig was assembled at NASA Lewis Research Center to measure the steady-state performance of a journal air bearing. The tester can run up to 30,000 RPM and the spindle has a run out of less than 1 micron. A three wave journal bearing (50 mm diameter and 58 mm length) has been machined at NASA Lewis. The pressures at 16 ports along the bearing circumference at the middle of the bearing length were measured and compared to the theoretical prediction. The bearing ran at speeds up to 15,000 RPM and certain loads. Good agreement was found between the measured and calculated pressures.

  19. Detection of cerebral ischemia using the power spectrum of the pulse wave measured by near-infrared spectroscopy.

    PubMed

    Ebihara, Akira; Tanaka, Yuichi; Konno, Takehiko; Kawasaki, Shingo; Fujiwara, Michiyuki; Watanabe, Eiju

    2013-10-01

    The diagnosis and medical treatment of cerebral ischemia are becoming more important due to the increase in the prevalence of cerebrovascular disease. However, conventional methods of evaluating cerebral perfusion have several drawbacks: they are invasive, require physical restraint, and the equipment is not portable, which makes repeated measurements at the bedside difficult. An alternative method is developed using near-infrared spectroscopy (NIRS). NIRS signals are measured at 44 positions (22 on each side) on the fronto-temporal areas in 20 patients with cerebral ischemia. In order to extract the pulse-wave component, the raw total hemoglobin data recorded from each position are band-pass filtered (0.8 to 2.0 Hz) and subjected to a fast Fourier transform to obtain the power spectrum of the pulse wave. The ischemic region is determined by single-photon emission computed tomography. The pulse-wave power in the ischemic region is compared with that in the symmetrical region on the contralateral side. In 17 cases (85%), the pulse-wave power on the ischemic side is significantly lower than that on the contralateral side, which indicates that the transmission of the pulse wave is attenuated in the region with reduced blood flow. Pulse-wave power might be useful as a noninvasive marker of cerebral ischemia.

  20. Multipoint Plasma Density Measurements from Cluster Wave and Particle Instruments

    NASA Astrophysics Data System (ADS)

    Persoon, A.; Gurnett, D.; Pickett, J.; Canu, P.; Décréau, P.; Laakso, H.; Pedersen, A.; Andre, M.; Parks, G.; Wilber, M.; Reme, H.; Goldstein, M.; Fazakerly, A.

    2001-12-01

    Measurements from instruments onboard the Cluster spacecraft are used to study regions of diminished plasma density inside and poleward of the nightside auroral zone. The plasma density is derived from the digitization of the electron plasma frequency cutoff of the whistler mode auroral hiss, using the electric field spectrum measurements from the Wideband Plasma Wave Instrument (WBD). Two nightside auroral zone crossings, on May 8 and July 21, 2001, each with simultaneous measurements from two Cluster spacecraft, have been selected for this study. Both of these intervals contain multiple low density structures and provide an opportunity to make multi-instrument comparisons of the WBD electric spectrum measurements with the electron plasma frequency measurements of the WHISPER experiment and the spacecraft potential measurements of the Electric Fields and Waves (EFW) experiment. Since the satellite potential measurements are very sensitive to variations in the electron density, EFW spacecraft potential and density measurements will complement the WBD density measurements in the low density regions. Density variations will also be compared to the observed ion fluxes, using the ion distribution functions of the Cluster Ion Spectrometry (CIS) instruments and the low energy electron fluxes, using the electron velocity and energy distributions of the Electron and Current Experiment (PEACE).

  1. 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

  2. Measurement of Rain Induced Attenuation over a Line of Sight Link Operating at 28.75 GHz at Amritsar (INDIA)

    NASA Astrophysics Data System (ADS)

    Sharma, Parshotam; Hudiara, I. S.; Singh, M. L.

    2009-08-01

    The need of higher bandwidth systems has led the system designer to shift into higher frequency region. But working at these high frequency regions is not that easy. The paper presents results of the measurements of rain induced attenuation of a LOS link operating at 28.75 GHz at Amritsar (31°36' N 74° 52' E) for a single event that occurred on the 15th Nov., 2004. The results have been compared with those of ITU-R Model. It is observed that there is a significant difference between the attenuation levels measured and those predicted by using ITU-R model.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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

  8. 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.

  9. 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

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. Evaluating LNAPL contamination using GPR signal attenuation analysis and dielectric property measurements: practical implications for hydrological studies.

    PubMed

    Cassidy, Nigel J

    2007-10-30

    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

  15. 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.

  16. DC attenuation meter

    DOEpatents

    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.

  17. Low-frequency sound speed and attenuation in sandy seabottom from long-range broadband acoustic measurements.

    PubMed

    Wan, Lin; Zhou, Ji-Xun; Rogers, Peter H

    2010-08-01

    A joint China-U.S. underwater acoustics experiment was conducted in the Yellow Sea with a very flat bottom and a strong and sharp thermocline. Broadband explosive sources were deployed both above and below the thermocline along two radial lines up to 57.2 km and a quarter circle with a radius of 34 km. Two inversion schemes are used to obtain the seabottom sound speed. One is based on extracting normal mode depth functions from the cross-spectral density matrix. The other is based on the best match between the calculated and measured modal arrival times for different frequencies. The inverted seabottom sound speed is used as a constraint condition to extract the seabottom sound attenuation by three methods. The first method involves measuring the attenuation coefficients of normal modes. In the second method, the seabottom sound attenuation is estimated by minimizing the difference between the theoretical and measured modal amplitude ratios. The third method is based on finding the best match between the measured and modeled transmission losses (TLs). The resultant seabottom attenuation, averaged over three independent methods, can be expressed as alpha=(0.33+/-0.02)f(1.86+/-0.04)(dB/m kHz) over a frequency range of 80-1000 Hz.

  18. Proposed Atom Interferometry Gravitational Wave Measurements Over a Single Baseline

    NASA Astrophysics Data System (ADS)

    Bender, Peter L.

    2013-04-01

    A recent paper by Graham et al. [1] proposed gravitational wave measurements using an atom interferometer at each end of a single baseline between two spacecraft. The suggested approach makes use of extremely narrow linewidth single photon transitions, such as the 698 nm clock transition in Sr-87. A case discussed has a L = 500 km baseline length between spacecraft, N = 300 large momentum transfer beamsplitters, and a total measurement time of 100 s. The authors point out that many sources of errors in measuring GW signals cancel because they are nearly the same for both parts of the split atom wave functions and/or for both interferometers. Thus a much reduced sensitivity to laser frequency noise is reported. However, it seems that the requirements on this kind of mission are still very demanding. For example, large differences in phase between the 2 parts of the wave function for each interferometer are expected due to jitter in the timing of the laser pulses. This makes it more difficult to determine the sign of the desired GW signals. And, if the atom cloud temperature of 100 pK and the Rabi frequency of 500 Hz considered in previous papers are assumed, the fraction of the atoms contributing to the final signal would be small. This is because of the total of 2,400 successful state transitions required for each half of the wave function if N = 300 LMT beamsplitters are used. [1] P. W. Graham, J. M. Hogan, M. A. Kasevich, and S. Rajendran, arXiv:1206.0818v1 [gr-qc] 5 Jun 2012.

  19. Measurements of plasma wave spectra in Jupiter's magnetosphere

    NASA Technical Reports Server (NTRS)

    Scarf, F. L.; Gurnett, D. A.; Kurth, W. S.

    1981-01-01

    Compressed plots of E field averages for all of the 16-channel spectrum analyzer data from the Voyager 1 and 2 magnetosphere traversals are presented to provide an overall framework for the discussion. The importance of considering peaks as well as averages is illustrated by using 16-channel measurements from the first inbound and last outbound bow shock for Voyager 2. Selected wideband measurements from the waveform receivers are presented to demonstrate how many important wave bursts are variable in times less than or comparable to the 4-s scan period of the 16-channel analyzer.

  20. Gravitational waves from pulsars with measured braking index

    NASA Astrophysics Data System (ADS)

    de Araujo, José C. N.; Coelho, Jaziel G.; Costa, Cesar A.

    2016-09-01

    We study the putative emission of gravitational waves (GWs) in particular for pulsars with measured braking index. We show that the appropriate combination of both GW emission and magnetic dipole brakes can naturally explain the measured braking index, when the surface magnetic field and the angle between the magnetic dipole and rotation axes are time dependent. Then we discuss the detectability of these very pulsars by aLIGO and the Einstein Telescope. We call attention to the realistic possibility that aLIGO can detect the GWs generated by at least some of these pulsars, such as Vela, for example.

  1. Tree attenuation at 869 MHz derived from remotely piloted aircraft measurements

    NASA Technical Reports Server (NTRS)

    Vogel, Wolfhard J.; Goldhirsh, Julius

    1986-01-01

    Attenuation due to single trees is experimentally investigated using UHF transmissions at 869 MHz between a remotely piloted aircraft and a ground receiver system located in a stationary vehicle. Single trees of each tree type in full foliage were found to attenuate from 10-20 dB, with an average median value of about 12 dB. Attenuation coefficients associated with path lengths through the foliage may on average be about 1 dB/m, with maximum values closer to 2 dB/m.

  2. Source Parameters and Crustal Attenuation in Interior Alaska: Estimates Using Broadband Lg-Wave Spectra Derived from the BEAAR Experiment Data.

    NASA Astrophysics Data System (ADS)

    Marriott, D. A.; Hansen, R. A.

    2002-12-01

    Source parameters, site effects, and regional crustal attenuation in interior Alaska were estimated using displacement amplitude spectra of Lg phase arrivals derived from the Broadband Experiment Across the Alaska Range (BEAAR) seismic data. The BEAAR project consisted of 36 three component broadband seismometers temporarily installed across the Alaska Range. This array stretched across a large portion of interior Alaska, providing excellent recordings of regional events. The model parameters were estimated using a simultaneous nonlinear least squares inversion including all the spectral data. The source parameters estimated were the seismic moment, Mo, and the corner frequency, fo, for each event. The values of Mo were well constrained and yielded an empirical relationship between ML and Mo for interior Alaska. Estimates of the corner frequency for each event, along with the Mo values, yielded an estimate of stress drop for each event. For events larger then ML = 3 in Alaska, stress drop showed no significant dependence on magnitude. A frequency dependent local site amplification term was estimated for each station in the inversion as an average of the residuals for each station over many events. The inclusion of this site term reduced the total residuals of the regional attenuation model calculations. A preliminary model for regional attenuation of the Lg seismic phase averaged over all tectonic regions across continental Alaska from BEAAR data was derived to be: QLg(f) = 166f0.58. This model was estimated from 123 shallow earthquakes larger than M =3 located in continental Alaska, and more than 1,000 spectra. Because the Lg phase was trapped in the crustal wave-guide, QLg gave a good representation of attenuation in the crust, and appears to correlate with crustal structure. Estimates of attenuation for each ray path show local variation in QLg. This variation may be caused by changes in crustal structure such as faulting, deformation, or differences in

  3. 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.

  4. 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.

  5. 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.

  6. Multi-stage temperature compensation method for Lamb wave measurements

    NASA Astrophysics Data System (ADS)

    Dworakowski, Ziemowit; Ambrozinski, Lukasz; Stepinski, Tadeusz

    2016-11-01

    One of the important issues related to the applications of Lamb waves for structural health monitoring is their undesired sensitivity to variation of environmental conditions. Temperature is the main factor that can affect wave propagation and hence significantly reduce performance of a SHM system. Therefore, there is a need for development of robust monitoring methods with low sensitivity to temperature variations. This paper is aimed at verification of efficiency of four methods designed for damage detection using Lamb wave measurements performed in variable environmental conditions. The methods investigated in the comparison are the following: optimal baseline selection approach, the damage index based on a signal alignment with respect to instantaneous phase, and a group measurement approach capable of distinguishing local damage-related changes from temperature-induced global ones. The fourth method relies on fusion all these solutions simultaneously. The methods' ability to damage detection is compared using a specimen that is subjected to large temperature changes. It is found that although all the methods have their strengths and weaknesses, a cooperation of all solutions allows for significant increase of the damage detection efficiency.

  7. Caffeine attenuates practice effects in word stem completion as measured by fMRI BOLD signal.

    PubMed

    Bendlin, Barbara B; Trouard, Theodore P; Ryan, Lee

    2007-07-01

    Caffeine ingestion results in increased brain cell metabolism (Nehlig et al. [1992] Brain Res Brain Res Rev 17:139-170) and decreased cerebral blood flow (Field et al. [2003] Radiology 227:129-135; Mulderink et al. [2002] Neuroimage 15:37-44). The current study investigated the effect of caffeine in a word stem completion task using only novel word stems (no repeated stimuli). Resting perfusion was measured with arterial spin labeled perfusion MRI, along with blood oxygenation level-dependent (BOLD) signal before and after ingestion of regular coffee, decaffeinated coffee, and water. Based on previous research (Laurienti et al. [2002] Neuroimage 17:751-757; Mulderink et al. [2002] Neuroimage 15:37-44), we hypothesized that caffeine would result in increased BOLD signal intensity and extent of BOLD activation. As expected, caffeine resulted in a significant decrease in cerebral perfusion. However, both the control and caffeine groups showed an increase in BOLD signal amplitude across two sets of novel word stems. Additionally, the control group showed a 50% reduction in the extent of BOLD activation, while the caffeine group showed no change in activation extent. Neither group showed changes in BOLD baseline signal over time, which had been suggested to mediate caffeine-related BOLD signal changes. The results suggest that caffeine may attenuate general task practice effects that have been described in recent functional MRI studies of word stem completion (Buckner et al. [2000] Brain 123:620-640).

  8. Quantitative orientation measurements in thin lipid films by attenuated total reflection infrared spectroscopy.

    PubMed Central

    Picard, F; Buffeteau, T; Desbat, B; Auger, M; Pézolet, M

    1999-01-01

    Quantitative orientation measurements by attenuated total reflectance (ATR) infrared spectroscopy require the accurate knowledge of the dichroic ratio and of the mean-square electric fields along the three axes of the ATR crystal. In this paper, polarized ATR spectra of single supported bilayers of the phospholipid dimyristoylphosphatidic acid covered by either air or water have been recorded and the dichroic ratio of the bands due to the methylene stretching vibrations has been calculated. The mean-square electric field amplitudes were calculated using three formalisms, namely the Harrick thin film approximation, the two-phase approximation, and the thickness- and absorption-dependent one. The results show that for dry bilayers, the acyl chain tilt angle varies with the formalism used, while no significant variations are observed for the hydrated bilayers. To test the validity of the different formalisms, s- and p-polarized ATR spectra of a 40-A lipid layer were simulated for different acyl chain tilt angles. The results show that the thickness- and absorption-dependent formalism using the mean values of the electric fields over the film thickness gives the most accurate values of acyl chain tilt angle in dry lipid films. However, for lipid monolayers or bilayers, the tilt angle can be determined with an acceptable accuracy using the Harrick thin film approximation. Finally, this study shows clearly that the uncertainty on the determination of the tilt angle comes mostly from the experimental error on the dichroic ratio and from the knowledge of the refractive index. PMID:9876167

  9. Chemical amplification--cavity attenuated phase shift spectroscopy measurements of atmospheric peroxy radicals.

    PubMed

    Wood, Ezra C; Charest, John R

    2014-10-21

    We describe a new instrument for the quantification of atmospheric peroxy radicals (HO2, CH3O2, C2H5O2, etc.) using the chemical amplification method. Peroxy radicals are mixed with high concentrations of NO and CO, causing a chain reaction that produces a measurable increase in NO2 which is quantified by cavity attenuated phase shift (CAPS) spectroscopy, a highly sensitive spectroscopic detection technique. The instrument utilizes two identical reaction chambers, each with a dedicated CAPS NO2 sensor. Similar to all dual-channel chemical amplifiers, one reaction chamber operates in amplification or "ROx" mode and the other in background or "Ox" mode. The peroxy radical mixing ratio is determined by the difference between the two channels' NO2 readings divided by a laboratory-determined chain length. Each reaction chamber alternates between ROx and Ox mode on an anti-synchronized schedule, eliminating the effect of CAPS baseline offsets on the calculated peroxy radical concentrations. The chain length is determined by a new calibration method: peroxyacetyl and methyl peroxy radicals are produced by the photolysis of acetone and quantified as NO2 following reaction with excess NO. We demonstrate the performance of the instrument with results from ambient sampling in Amherst and several diagnostics of its precision. The detection limit while sampling ambient air at a relative humidity (RH) of 40% is 0.6 ppt (1 min average, signal-to-noise ratio =2), with an estimated accuracy of 25% (2σ).

  10. Attenuation of Bragg backscattering of electromagnetic waves from density fluctuations near the region of polarization degeneracy in magnetoactive plasma

    NASA Astrophysics Data System (ADS)

    Gospodchikov, E. D.; Khusainov, T. A.; Shalashov, A. G.

    2016-08-01

    Specific features of Bragg backscattering under conditions of strong polarization degeneracy near the cutoff surface in an anisotropic medium are studied analytically and numerically. It is shown that the linear interaction of normal waves can substantially affect wave scattering by suppressing the amplification of Bragg backscattering near the cutoff region in the case of weak coupling between normal waves.

  11. 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

  12. Surface Acoustic Wave Vibration Sensors for Measuring Aircraft Flutter

    NASA Technical Reports Server (NTRS)

    Wilson, William C.; Moore, Jason P.; Juarez, Peter D.

    2016-01-01

    Under NASA's Advanced Air Vehicles Program the Advanced Air Transport Technology (AATT) Project is investigating flutter effects on aeroelastic wings. To support that work a new method for measuring vibrations due to flutter has been developed. The method employs low power Surface Acoustic Wave (SAW) sensors. To demonstrate the ability of the SAW sensor to detect flutter vibrations the sensors were attached to a Carbon fiber-reinforced polymer (CFRP) composite panel which was vibrated at six frequencies from 1Hz to 50Hz. The SAW data was compared to accelerometer data and was found to resemble sine waves and match each other closely. The SAW module design and results from the tests are presented here.

  13. Measurements of beat wave accelerated electrons in a toroidal plasma

    SciTech Connect

    Rogers, J.H. . Plasma Physics Lab.); Hwang, D.W. . Dept. of Applied Science Lawrence Livermore National Lab., CA )

    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.

  14. Unsteady heat-flux measurements of second-mode instability waves in a hypersonic flat-plate boundary layer

    NASA Astrophysics Data System (ADS)

    Kegerise, Michael A.; Rufer, Shann J.

    2016-08-01

    In this paper, we report on the application of the atomic layer thermopile (ALTP) heat-flux sensor to the measurement of laminar-to-turbulent transition in a hypersonic flat-plate boundary layer. The centerline of the flat-plate model was instrumented with a streamwise array of ALTP sensors, and the flat-plate model was exposed to a Mach 6 freestream over a range of unit Reynolds numbers. Here, we observed an unstable band of frequencies that are associated with second-mode instability waves in the laminar boundary layer that forms on the flat-plate surface. The measured frequencies, group velocities, phase speeds, and wavelengths of these instability waves are consistent with data previously reported in the literature. Heat flux time series, and the Morlet wavelet transforms of them, revealed the wave-packet nature of the second-mode instability waves. In addition, a laser-based radiative heating system was used to measure the frequency response functions (FRF) of the ALTP sensors used in the wind tunnel test. These measurements were used to assess the stability of the sensor FRFs over time and to correct spectral estimates for any attenuation caused by the finite sensor bandwidth.

  15. 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

    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.

  16. Remote wave measurements using autonomous mobile robotic systems

    NASA Astrophysics Data System (ADS)

    Kurkin, Andrey; Zeziulin, Denis; Makarov, Vladimir; Belyakov, Vladimir; Tyugin, Dmitry; Pelinovsky, Efim

    2016-04-01

    The project covers the development of a technology for monitoring and forecasting the state of the coastal zone environment using radar equipment transported by autonomous mobile robotic systems (AMRS). Sought-after areas of application are the eastern and northern coasts of Russia, where continuous collection of information on topographic changes of the coastal zone and carrying out hydrodynamic measurements in inaccessible to human environment are needed. The intensity of the reflection of waves, received by radar surveillance, is directly related to the height of the waves. Mathematical models and algorithms for processing experimental data (signal selection, spectral analysis, wavelet analysis), recalculation of landwash from data on heights of waves far from the shore, determination of the threshold values of heights of waves far from the shore have been developed. There has been developed the program complex for functioning of the experimental prototype of AMRS, comprising the following modules: data loading module, reporting module, module of georeferencing, data analysis module, monitoring module, hardware control module, graphical user interface. Further work will be connected with carrying out tests of manufactured experimental prototype in conditions of selected routes coastline of Sakhalin Island. Conducting field tests will allow to reveal the shortcomings of development and to identify ways of optimization of the structure and functioning algorithms of AMRS, as well as functioning the measuring equipment. The presented results have been obtained in Nizhny Novgorod State Technical University n.a. R. Alekseev in the framework of the Federal Target Program «Research and development on priority directions of scientific-technological complex of Russia for 2014 - 2020 years» (agreement № 14.574.21.0089 (unique identifier of agreement - RFMEFI57414X0089)).

  17. 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.

  18. l-Citrulline supplementation attenuates blood pressure, wave reflection and arterial stiffness responses to metaboreflex and cold stress in overweight men.

    PubMed

    Figueroa, Arturo; Alvarez-Alvarado, Stacey; Jaime, Salvador J; Kalfon, Roy

    2016-07-01

    Combined isometric exercise or metaboreflex activation (post-exercise muscle ischaemia (PEMI)) and cold pressor test (CPT) increase cardiac afterload, which may lead to adverse cardiovascular events. l-Citrulline supplementation (l-CIT) reduces systemic arterial stiffness (brachial-ankle pulse wave velocity (baPWV)) at rest and aortic haemodynamic responses to CPT. The aim of this study was to determine the effect of l-CIT on aortic haemodynamic and baPWV responses to PEMI+CPT. In all, sixteen healthy, overweight/obese males (age 24 (sem 6) years; BMI 29·3 (sem 4·0) kg/m2) were randomly assigned to placebo or l-CIT (6 g/d) for 14 d in a cross-over design. Brachial and aortic systolic blood pressure (SBP), diastolic blood pressure (DBP) and mean arterial pressure (MAP), aortic augmented pressure (AP), augmentation index (AIx), baPWV, reflection timing (Tr) and heart rate (HR) were evaluated at rest and during isometric handgrip exercise (IHG), PEMI and PEMI+CPT at baseline and after 14 d. No significant effects were evident after l-CIT at rest. l-CIT attenuated the increases in aortic SBP and wave reflection (AP and AIx) during IHG, aortic DBP, MAP and AIx during PEMI, and aortic SBP, DBP, MAP, AP, AIx and baPWV during PEMI+CPT compared with placebo. HR and Tr were unaffected by l-CIT in all conditions. Our findings demonstrate that l-CIT attenuates aortic blood pressure and wave reflection responses to exercise-related metabolites. Moreover, l-CIT attenuates the exaggerated arterial stiffness response to combined metaboreflex activation and cold exposure, suggesting a protective effect against increased cardiac afterload during physical stress.

  19. l-Citrulline supplementation attenuates blood pressure, wave reflection and arterial stiffness responses to metaboreflex and cold stress in overweight men.

    PubMed

    Figueroa, Arturo; Alvarez-Alvarado, Stacey; Jaime, Salvador J; Kalfon, Roy

    2016-07-01

    Combined isometric exercise or metaboreflex activation (post-exercise muscle ischaemia (PEMI)) and cold pressor test (CPT) increase cardiac afterload, which may lead to adverse cardiovascular events. l-Citrulline supplementation (l-CIT) reduces systemic arterial stiffness (brachial-ankle pulse wave velocity (baPWV)) at rest and aortic haemodynamic responses to CPT. The aim of this study was to determine the effect of l-CIT on aortic haemodynamic and baPWV responses to PEMI+CPT. In all, sixteen healthy, overweight/obese males (age 24 (sem 6) years; BMI 29·3 (sem 4·0) kg/m2) were randomly assigned to placebo or l-CIT (6 g/d) for 14 d in a cross-over design. Brachial and aortic systolic blood pressure (SBP), diastolic blood pressure (DBP) and mean arterial pressure (MAP), aortic augmented pressure (AP), augmentation index (AIx), baPWV, reflection timing (Tr) and heart rate (HR) were evaluated at rest and during isometric handgrip exercise (IHG), PEMI and PEMI+CPT at baseline and after 14 d. No significant effects were evident after l-CIT at rest. l-CIT attenuated the increases in aortic SBP and wave reflection (AP and AIx) during IHG, aortic DBP, MAP and AIx during PEMI, and aortic SBP, DBP, MAP, AP, AIx and baPWV during PEMI+CPT compared with placebo. HR and Tr were unaffected by l-CIT in all conditions. Our findings demonstrate that l-CIT attenuates aortic blood pressure and wave reflection responses to exercise-related metabolites. Moreover, l-CIT attenuates the exaggerated arterial stiffness response to combined metaboreflex activation and cold exposure, suggesting a protective effect against increased cardiac afterload during physical stress. PMID:27160957

  20. 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; Lü, Qi-Wen; Sun, Li-Jun; Ge, Yong-Shuai; Liu, Ying-Biao; Niu, Shun-Li; Hu, Tao; Cao, Jun; Lü, 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 15.10±0.35 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.

  1. 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

  2. New Laboratory-Based Attenuation Measurements on Ice to Support Tidal Heating Models

    NASA Astrophysics Data System (ADS)

    Castillo-Rogez, J.; Choukroun, M.; Young, J.; Zhong, F.; Engelhardt, H.; Barmatz, M.

    2008-12-01

    The response of icy satellite materials to tidal stress has important consequences on their geophysical, geological, and dynamical evolution. The major issue with modeling the tidal response of these objects is that the viscoelastic properties of planetary material are not constrained by laboratory measurements for the relevant frequency range 10e-7 to 10e-5 Hz. While the Maxwell model is usually applied in icy satellite tidal modeling, laboratory measurements for the Earth's mantle have shown that this model is not applicable at forcing frequencies away from the Maxwell frequency. Alternative models (e.g., Andrade, Cole) based on measurements on silicates or terrestrial ice sheets may be better suited to describe ice attenuation, but they have not been introduced in planetary science studies, in part because laboratory measurements are necessary in order to warrant their extrapolation to conditions applicable to icy satellites. The reason why the laboratory data needed for modeling tidal processes at icy satellites are missing is that it is a challenge to achieve measurements at the low stress, low frequencies, and cryogenic conditions relevant to these objects. In the JPL Ice Physical Properties Laboratory an Instron compression system has been implemented with the capability to measure the phase lag between strain and stress, i.e., the internal friction, of an icy sample at frequencies as low as Enceladus' tidal forcing frequency, temperatures as low as 90 K, and cyclic peak stress lower than 0.1 MPa, characteristic of tidal stress at Enceladus or Europa. We will present the first measurements obtained with this system on monocrystalline ice in the frequency range 6x10e-6 to 10e-2 Hz and temperature range 233 - 253 K. We observed a change in frequency-dependence of the friction coefficient at a frequency about the inverse of the Maxwell time. While the Andrade model can fit the phase lags measured over the entire frequency range, it fails to reproduce the

  3. Reliability assessment for pulse wave measurement using artificial pulse generator.

    PubMed

    Chang, Chi-Wei; Wang, Wei-Kung

    2015-04-01

    This study aimed to assess intrinsic reliabilities of devices for pulse wave measurement (PWM). An artificial pulse generator system was constructed to create a periodic pulse wave. The stability of the periodic output was tested by the DP103 pressure transducer. The pulse generator system was then used to evaluate the TD01C system. Test-re-test and inter-device reliability assessments were conducted on the TD01C system. First, 11 harmonic components of the pulse wave were calculated using Fourier series analysis. For each harmonic component, coefficient of variation (CV), intra-class correlation coefficient (ICC) and Bland-Altman plot were used to determine the degree of reliability of the TD01C system. In addition, device exclusion criteria were pre-specified to improve consistency of devices. The artificial pulse generator system was stable to evaluate intrinsic reliabilities of devices for PWM (ICCs > 0.95, p < 0.001). TD01C was reliable for repeated measurements (ICCs of test-re-test reliability > 0.95, p < 0.001; CVs all < 3%). Device exclusion criteria successfully excluded the device with defect; therefore, the criteria reduced inter-device CVs of harmonics and improved consistency of the selected devices for all harmonic components. This study confirmed the feasibility of intrinsic reliability assessment of devices for PWM using an artificial pulse generator system. Moreover, potential novel findings on the assessment combined with device exclusion criteria could be a useful method to select the measuring devices and to evaluate the qualities of them in PWM.

  4. 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

  5. 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.

  6. On correlation measurements of electron Bernstein wave emission

    NASA Astrophysics Data System (ADS)

    Popov, A.; Irzak, M.

    2014-02-01

    A systematic study of the electron Bernstein wave (EBW) emission from either overdense plasmas or plasmas with moderate electron temperatures is presented. Starting from description of the bare electrons microscopic thermal radiation we finally arrive at the macroscopic expression for the radiation temperature. The latter is shown to be a sum of the electron temperature and a fluctuating piece caused by the fluctuations of both the EBW emission source and the EBW damping rate within the ECR layer. It is shown that the correlation measurements of the EBW emission at two separate frequencies reveal information on the correlation length of the low frequency turbulence.

  7. Development, Test, and Evaluation of Microwave Radar Water Level (MWWL) Sensors' Wave Measurement Capability

    NASA Astrophysics Data System (ADS)

    Iyer, S. K.; Heitsenrether, R.

    2015-12-01

    Waves can have a significant impact on many coastal operations including navigational safety, recreation, and even the economy. Despite this, as of 2009, there were only 181 in situ real-time wave observation networks nationwide (IOOS 2009). There has recently been interest in adding real-time wave measurement systems to already existing NOAA Center for Operational Oceanographic Products and Services (CO-OPS) stations. Several steps have already been taken in order to achieve this, such as integrating information from existing wave measurement buoys and initial testing of multiple different wave measurement systems (Heitsenrether et al. 2012). Since wave observations can be derived from high frequency water level changes, we will investigate water level sensors' capability to measure waves. Recently, CO-OPS has been transitioning to new microwave radar water level (MWWL) sensors which have higher resolution and theoretically a greater potential wave measurement capability than the acoustic sensors in stilling wells. In this study, we analyze the wave measurement capability of MWWL sensors at two high energy wave environments, Duck, NC and La Jolla, CA, and compare results to two "reference" sensors (A Nortek acoustic waves and currents profiler (AWAC) at Duck and a single point pressure sensor at La Jolla). A summary of results from the two field test sites will be presented, including comparisons of wave energy spectra, significant wave height, and peak period measured by the test MWWL sensors and both reference AWAC and pressure sensors. In addition, relationships between MWWL versus reference wave sensor differences and specific wave conditions will be discussed. Initial results from spectral analysis and the calculation of bulk wave parameters indicate that MWWL sensors set to the "NoFilter" processing setting can produce wave measurements capability that compare well to the two reference sensors. These results support continued development to enable the

  8. 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.

  9. Speech articulator measurements using low power EM-wave sensors

    SciTech Connect

    Holzrichter, J.F.; Burnett, G.C.; Ng, L.C.; Lea, W.A.

    1998-01-01

    Very low power electromagnetic (EM) wave sensors are being used to measure speech articulator motions as speech is produced. Glottal tissue oscillations, jaw, tongue, soft palate, and other organs have been measured. Previously, microwave imaging (e.g., using radar sensors) appears not to have been considered for such monitoring. Glottal tissue movements detected by radar sensors correlate well with those obtained by established laboratory techniques, and have been used to estimate a voiced excitation function for speech processing applications. The noninvasive access, coupled with the small size, low power, and high resolution of these new sensors, permit promising research and development applications in speech production, communication disorders, speech recognition and related topics. {copyright} {ital 1998 Acoustical Society of America.}

  10. Quantum analysis of the direct measurement of light waves

    NASA Astrophysics Data System (ADS)

    Saldanha, Pablo L.

    2014-01-01

    In a beautiful experiment performed about a decade ago, Goulielmakis et al (2004 Science 305 1267-69) made a direct measurement of the electric field of light waves. However, they used a laser source to produce the light field, whose quantum state has a null expectation value for the electric field operator, so how was it possible to measure this electric field? Here we present a quantum treatment for the f:2f interferometer used to calibrate the carrier-envelope phase of the light pulses in the experiment. We show how the special nonlinear features of the f:2f interferometer can change the quantum state of the electromagnetic field inside the laser cavity to a state with a definite oscillating electric field, explaining how the ‘classical’ electromagnetic field emerges in the experiment. We discuss that this experiment was, to our knowledge, the first demonstration of an absolute coherent superposition of different photon number states in the optical regime.

  11. Velocity and Attenuation Structure of the Tibetan Lithosphere using Seismic Attributes of P-waves from Regional Earthquakes Recorded by the Hi-CLIMB Array

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

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

  12. The southern stratospheric gravity wave hot spot: individual waves and their momentum fluxes measured by COSMIC GPS-RO

    NASA Astrophysics Data System (ADS)

    Hindley, N. P.; Wright, C. J.; Smith, N. D.; Mitchell, N. J.

    2015-07-01

    Nearly all general circulation models significantly fail to reproduce the observed behaviour of the southern wintertime polar vortex. It has been suggested that these biases result from an underestimation of gravity wave drag on the atmosphere at latitudes near 60° S, especially around the "hot spot" of intense gravity wave fluxes above the mountainous Southern Andes and Antarctic peninsula. Here, we use Global Positioning System radio occultation (GPS-RO) data from the COSMIC satellite constellation to determine the properties of gravity waves in the hot spot and beyond. We show considerable southward propagation to latitudes near 60° S of waves apparently generated over the southern Andes. We propose that this propagation may account for much of the wave drag missing from the models. Furthermore, there is a long leeward region of increased gravity wave energy that sweeps eastwards from the mountains over the Southern Ocean. Despite its striking nature, the source of this region has historically proved difficult to determine. Our observations suggest that this region includes both waves generated locally and orographic waves advected downwind from the hot spot. We describe and use a new wavelet-based analysis technique for the quantitative identification of individual waves from COSMIC temperature profiles. This analysis reveals different geographical regimes of wave amplitude and short-timescale variability in the wave field over the Southern Ocean. Finally, we use the increased numbers of closely spaced pairs of profiles from the deployment phase of the COSMIC constellation in 2006 to make estimates of gravity wave horizontal wavelengths. We show that, given sufficient observations, GPS-RO can produce physically reasonable estimates of stratospheric gravity wave momentum flux in the hot spot that are consistent with measurements made by other techniques. We discuss our results in the context of previous satellite and modelling studies and explain how they

  13. Estimation of diffuse attenuation of ultraviolet light in optically shallow Florida Keys waters from MODIS measurements

    EPA Science Inventory

    Diffuse attenuation of solar light (Kd, m−1) determines the percentage of light penetrating the water column and available for benthic organisms. Therefore, Kd can be used as an index of water quality for coastal ecosystems that are dependent on photosynthesis, such as the coral ...

  14. Spectroscopic Measurements of the Far-Ultraviolet Dust Attenuation Curve at z ∼ 3

    NASA Astrophysics Data System (ADS)

    Reddy, Naveen A.; Steidel, Charles C.; Pettini, Max; Bogosavljević, Milan

    2016-09-01

    We present the first spectroscopic measurements of the shape of the far-ultraviolet (far-UV; λ =950{--}1500 Å) dust attenuation curve at high redshift (z∼ 3). Our analysis employs rest-frame UV spectra of 933 galaxies at z∼ 3, 121 of which have very deep spectroscopic observations (≳ 7 hr) at λ =850{--}1300 \\mathring{{A}} , with the Low Resolution Imaging Spectrograph on the Keck Telescope. By using an iterative approach in which we calculate the ratios of composite spectra in different bins of continuum color excess, E(B-V), we derive a dust curve that implies a lower attenuation in the far-UV for a given E(B-V) than those obtained with standard attenuation curves. We demonstrate that the UV composite spectra of z∼ 3 galaxies can be modeled well by assuming our new attenuation curve, a high covering fraction of H i, and absorption from the Lyman–Werner bands of {{{H}}}2 with a small (≲ 20 % ) covering fraction. The low covering fraction of {{{H}}}2 relative to that of the {{H}} {{I}} and dust suggests that most of the dust in the ISM of typical galaxies at z∼ 3 is unrelated to the catalysis of {{{H}}}2, and is associated with other phases of the ISM (i.e., the ionized and neutral gas). The far-UV dust curve implies a factor of ≈ 2 lower dust attenuation of Lyman continuum (ionizing) photons relative to those inferred from the most commonly assumed attenuation curves for L* galaxies at z∼ 3. Our results may be utilized to assess the degree to which ionizing photons are attenuated in H ii regions or, more generally, in the ionized or low column density (N({{H}} {{I}})≲ {10}17.2 cm‑2) neutral ISM of high-redshift galaxies. Based on data obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA, and was made possible by the generous financial support of the W.M. Keck Foundation.

  15. Ionospheric response to tidal waves measured by dynasonde techniques

    NASA Astrophysics Data System (ADS)

    Negrea, Cǎtǎlin; Zabotin, Nikolay; Bullett, Terence; Codrescu, Mihail; Fuller-Rowell, Tim

    2016-01-01

    Atmospheric tides are known to have a dramatic influence on thermospheric and ionospheric structure and variability. Considerable effort goes into understanding characteristics of tidal modes, their interactions with planetary and gravity waves and other tidal modes, as well as their influence on the background state of the thermosphere-ionosphere system. For the altitude interval between roughly 120 and 400 km, this effort is somewhat hindered by the lack of global observations. We propose a new method of determining tidal variability by making use of dynasonde measurements. The NeXtYZ inversion procedure produces altitude profiles of the ionospheric parameters with a vertical resolution typically better than 1 km. This, together with the typical 2 min cadence of the instrument, results in extensive data sets with wide temporal and altitude coverage. At any given altitude we have nonuniform sampling due to the natural ionospheric variability. A Lomb-Scargle implementation is used to obtain equivalent results at all altitudes and locations. We report height profiles of the first three tidal harmonics derived from dynasonde measurements. The data analyzed include the vertical electron density profiles, the ionospheric X (east-west) "tilt" measurement, and the derived zonal plasma density gradient. Both the tilt and the gradient are shown to be sensitive tracers of atmospheric waves. We use data from Wallops Island and San Juan, for two time intervals: 6 May- 6 June and 9 October- 8 November 2013, thus capturing seasonal, latitudinal, and altitude variations of tidal amplitude and phase. This proves the potential of using dynasonde-capable instruments as a data source for tidal studies in the thermosphere.

  16. Controllable attenuators

    NASA Astrophysics Data System (ADS)

    Krylov, G. M.; Khoniak, E. I.; Tynynyka, A. N.; Iliushenko, V. N.; Sikolenko, S. F.

    Methods for the synthesis of controllable attenuators and their implementations are examined. In particular, attention is given to the general properties of controllable attenuators, control elements, types of controllable attenuators and methods of their analysis, and synthesis of the control characteristic of attenuators. The discussion also covers the efficiency of attenuator control, the use of transmission line segments in wide-band controllable attenuators, and attenuators with a discretely controlled transmission coefficient.

  17. Measurement of thermal transport using time-resolved thermal wave microscopy

    SciTech Connect

    Marat Khafizov; David H. Hurley

    2011-10-01

    A theoretical and experimental analysis of time-resolved thermal wave microscopy (TRTWM) technique used for thermal wave imaging is presented. TRTWM combines the elements of both frequency and time domain laser based thermoreflectance approaches widely used for thermal wave imaging and measurement of thermal transport. An analytical thermal wave model used for analysis is described and compared to experimental results. Implementation of TRTWM to measure thermal conductivities of materials of interest is demonstrated.

  18. Optical technique for measurement of random water wave surfaces

    NASA Technical Reports Server (NTRS)

    Sorrell, F. Y.; Withers, A. L.

    1976-01-01

    An optical system using the refraction of a vertical light ray has been developed for measuring the slope of random wind-generated water waves. The basic elements of the system are photovoltaic cells which are connected to individual amplifiers so that when the refracted light beam is incident on a cell, the output of the cell is amplified and then supplied as input to a comparator. The comparator then provides a specified voltage output, independent of the incident light intensity, as long as it is above a designated background value. The comparators are designed to give output voltages comparable with standard TTL. This arrangement provides a high signal from the cell when it experiences incident light, and a low signal when there is only background light, with the high and low signals at TTL voltage levels.

  19. A comparison of the measured North Sea Andrea rogue wave with numerical simulations

    NASA Astrophysics Data System (ADS)

    Bitner-Gregersen, E. M.; Fernandez, L.; Lefèvre, J. M.; Monbaliu, J.; Toffoli, A.

    2013-09-01

    A coupling of a spectral wave model with a nonlinear phase resolving model is used to reconstruct the evolution of wave statistics during a storm crossing the North Sea on 8-9 November 2007. During this storm a rogue wave (named the Andrea wave) was recorded at the Ekofisk field. The wave has characteristics comparable to the well-known New Year wave measured by Statoil at the Draupner platform the 1 January 1995. Hindcast data of the storm are here applied as input to calculate random realizations of sea surface and evolution of its statistical properties associated with this specific wave event by solving the Euler equations with a Higher Order Spectral Method (HOSM). The numerical results are compared with the Andrea wave profile as well as characteristics of the Andrea wave record measured by the down-looking lasers at the Ekofisk field.

  20. Radar estimation of slant path rain attenuation at frequencies above 10 GHz and comparisons with measured multi-season results

    NASA Technical Reports Server (NTRS)

    Goldhirsh, J.

    1980-01-01

    Techniques and results pertaining to estimating Earth satellite path rain attenuation events and statistics using radar at nonattenuating wavelengths are presented. The radar formulation and beam scanning methods are described and the procedure for relating the radar measured Rayleigh reflectivity to the high frequency Mie attenuation coefficient are given. Examples of radar derived single terminal statistics and estimation criteria as they relate to path angle and frequency are reviewed. Radar derived space diversity statistics and their dependence on terminal spacing and frequency are described. Site diversity