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1

Pulse-echo method can't measure wave attenuation accurately  

E-print Network

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

Pal, Barnana

2014-01-01

2

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

Microsoft Academic Search

It is well accepted that wetlands have an important role in shoreline protection against wave damage. However, there is still a lack of knowledge on primary mechanisms of wave attenuation though wetland vegetation. The purpose of this study was to understand these mechanisms and quantify the impact of vegetation on the waves through a series of laboratory experiments. Experiments were

Y. Ozeren; D. G. Wren

2010-01-01

3

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

PubMed

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

Seldis, Thomas

2013-09-01

4

Simultaneous measurement and inversion of surface wave dispersion and attenuation curves  

Microsoft Academic Search

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

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

2002-01-01

5

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...

6

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

PubMed

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

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

2015-02-01

7

Measurement of alkali-silica reaction progression by ultrasonic waves attenuation  

SciTech Connect

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

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

2007-06-15

8

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

Microsoft Academic Search

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

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

1970-01-01

9

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

NASA Astrophysics Data System (ADS)

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

Hudier, E. J.; Bahoura, M.

2012-12-01

10

Midperiod Rayleigh wave attenuation model for Asia  

Microsoft Academic Search

We present an attenuation model for midperiod Rayleigh waves in Central Asia and surrounding regions. This model is defined by maps of attenuation coefficient across the region of study in the period band 14–24 s. The model is constructed to characterize the regional variations in attenuation of seismic waves in the crust, which are related to the tectonic history of

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

2010-01-01

11

Attenuation coefficients of Rayleigh and Lg waves  

Microsoft Academic Search

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

Igor B. Morozov

2010-01-01

12

Wave attenuation in thick graphite\\/epoxy composites  

Microsoft Academic Search

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

A. K. Mal; Y. Bar-Cohen

1992-01-01

13

Wave attenuation in thick graphite/epoxy composites  

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

14

Wave attenuation due to Posidonia oceanica meadows  

Microsoft Academic Search

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

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

2011-01-01

15

SEISMIC WAVE ATTENUATION IN FLUIDSATURATED POROUS MEDIA  

E-print Network

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

16

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

E-print Network

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

Langendoen, Koen

17

Attenuation of electromagnetic waves in onion-like carbon composites  

Microsoft Academic Search

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

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

2007-01-01

18

The attenuation of strong shock waves  

E-print Network

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

Kirkpatrick, Ronald Crecelius

1963-01-01

19

Seismic attenuation: Laboratory measurements in fluid saturated rocks  

NASA Astrophysics Data System (ADS)

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.

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

2014-05-01

20

Lateral variations of coda wave attenuation in the Alps  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

21

Millimeter wave attenuation prediction using a piecewise uniform rain rate model  

NASA Technical Reports Server (NTRS)

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

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

1980-01-01

22

Pressure wave attenuating main steam line apparatus  

SciTech Connect

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

Arinobu, M.; Suzuki, I.

1984-05-15

23

Influences of obstacle geometries on shock wave attenuation  

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

24

Measurements of Gamma-Ray Attenuation Coefficients  

Microsoft Academic Search

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

B. Goswami; N. Chaudhuri

1973-01-01

25

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

E-print Network

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

Al-Zahrani, Said Awdhah

1992-01-01

26

Millimeter wave attenuation prediction using a piecewise uniform rain rate model  

Microsoft Academic Search

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

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

1980-01-01

27

Wave dispersion and attenuation on human femur tissue.  

PubMed

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

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

2014-01-01

28

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

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

29

Wave attenuation characteristics of a tethered float system  

Microsoft Academic Search

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

P. Vethamony

1995-01-01

30

ATS-6 attenuation diversity measurements at 20 and 30 GHz  

NASA Technical Reports Server (NTRS)

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.

Vogel, W. J.; Straiton, A. W.; Fannin, B. M.; Wagner, N. K.

1975-01-01

31

Research on the Submillimeter Wave Hydrometeors Attenuation Characteristic  

Microsoft Academic Search

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

Bing Gong; Guowei Lou; Xingguo Li

2009-01-01

32

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

NASA Astrophysics Data System (ADS)

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

Wei, W.; Fu, L.

2012-12-01

33

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

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

34

Gamma-Ray Attenuation Coefficient Measurements  

Microsoft Academic Search

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

S. Gopal; B. Sanjeevaiah

1973-01-01

35

Seismic attenuation due to wave-induced flow  

SciTech Connect

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

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

2003-10-09

36

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

USGS Publications Warehouse

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

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

2003-01-01

37

Dispersion and attenuation of acoustic waves in randomly heterogeneous media  

NASA Astrophysics Data System (ADS)

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

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

1999-10-01

38

ELASTIC WAVE ATTENUATION IN ROCKS CONTAINING FLUIDS  

E-print Network

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

39

Broadband ultrasonic attenuation: are current measurement techniques inherently inaccurate?  

PubMed

Measurements of broadband ultrasonic attenuation (BUA) are currently made using large aperture, piezoelectric transducers. The use of such a receiver is known to lead to the possibility of an overestimate of ultrasonic attenuation due to phase cancellation and it is shown theoretically that this same effect can also lead to an overestimate of BUA. Using a new scanning approach, BUA was measured using two methods, one sensitive to the phase of the acoustic wave, the other not. The phase sensitive BUA measurements were found to be of significantly higher value (p < 0.0001) than the phase insensitive measurements with a mean difference of 31.2 dB MHz-1. These findings are compatible with the hypothesis that BUA measurement systems with large aperture, piezo-electric receivers are inherently inaccurate. PMID:8542228

Petley, G W; Robins, P A; Aindow, J D

1995-11-01

40

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

SciTech Connect

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

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

1994-07-01

41

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

42

Ultrasound attenuation measurement the presence scatterer variation  

E-print Network

Ultrasound attenuation measurement the presence scatterer variation for reduction shadowing.cam.ac.uk #12; #12; Abstract Pulse­echo ultrasound display relies many assumptions which known incorrect. De­ parture these makes interpretation conventional ultrasound images di#cult, and visu­ alisations harder

Drummond, Tom

43

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

NASA Astrophysics Data System (ADS)

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

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

2010-07-01

44

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

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.

Brodsky, N.S. (RE/SPEC, Inc., Rapid City, SD (USA))

1990-11-01

45

Plane-wave attenuation anisotropy in orthorhombic media  

Microsoft Academic Search

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

Yaping Zhu; Ilya Tsvankin

2007-01-01

46

Attenuation of sound waves in drill strings  

Microsoft Academic Search

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

Douglas S. Drumheller

1993-01-01

47

Attenuation of coda waves in Western Anatolia  

Microsoft Academic Search

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

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

1994-01-01

48

Simultaneous measurement of local longitudinal and transverse wave velocities, attenuation, density, and thickness of films by using point-focus ultrasonic spectroscopy  

NASA Astrophysics Data System (ADS)

This paper presents an ultrasonic technique for simultaneous determination of the complete set of acoustical and geometrical properties of a film or a thin layer in a stratified material embedded between two known materials using point-focus ultrasonic spectroscopy, which provides a high lateral resolution. The theoretical model of the two-dimensional spectrum Rt(?,?) of the stratified material is calculated as a function of six parameters of the unknown layer: longitudinal and transverse velocities cl, ct, attenuation ?l, ?t, density ?, and thickness h, which fully determined the properties of the film. The experimental spectrum Re(?,?) can be measured by V(z,t) technique. A two-step algorithm is presented to decompose the searching process of parameters from one six-dimensional to two three-dimensional spaces. The sensitivity of the two-dimensional spectrum to individual properties and its stability against experimental noise are studied. The full set properties of a 250 ?m thick stainless steel film and a 930 ?m thick SiO2 thin layer of a three layered stratified material immersed in water are determined. The proposed technique used a point-focus transducer, which makes the setup simple and reliable. It allows measurement of the local properties of the film and enables precision material characterization.

Ju, Bing-Feng; Bai, Xiaolong; Chen, Jian

2012-10-01

49

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

Microsoft Academic Search

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

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

2007-01-01

50

Oceanic wave measurement system  

NASA Technical Reports Server (NTRS)

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.

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

1980-01-01

51

Gamma-Ray Attenuation-Coefficient Measurements  

Microsoft Academic Search

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

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

1970-01-01

52

Body Wave Crustal Attenuation Characteristics in the Garhwal Himalaya, India  

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

53

Attenuation of acoustic waves in glacial ice and salt domes  

E-print Network

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

P. B. Price

2005-06-27

54

Ultrasound attenuation as a quantitative measure of fracture healing  

NASA Astrophysics Data System (ADS)

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.

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

2004-10-01

55

Spatial variation of coda wave attenuation in northwestern Colombia  

NASA Astrophysics Data System (ADS)

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

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

2004-08-01

56

Developing a Short-Period, Fundamental-Mode Rayleigh-Wave Attenuation Model for Asia  

NASA Astrophysics Data System (ADS)

We are developing a 2D, short-period (12 - 22 s), fundamental-mode Rayleigh-wave attenuation model for Asia. This model can be used to invert for a 3D attenuation model of the Earth's crust and upper mantle as well as to implement more accurate path corrections in regional surface-wave magnitude calculations. The prerequisite for developing a reliable Rayleigh-wave attenuation model is the availability of accurate fundamental-mode Rayleigh-wave amplitude measurements. Fundamental-mode Rayleigh-wave amplitudes could be contaminated by a variety of sources such as multipathing, focusing and defocusing, body wave, higher-mode surface wave, and other noise sources. These contaminations must be reduced to the largest extent possible. To achieve this, we designed a procedure by taking advantage of certain Rayleigh-wave characteristics, such as dispersion and elliptical particle motion, for accurate amplitude measurements. We first analyze the dispersion of the surface-wave data using a spectrogram. Based on the characteristics of the data dispersion, we design a phase-matched filter by using either a manually picked dispersion curve, or a group-velocity-model predicted dispersion curve, or the dispersion of the data, and apply the filter to the seismogram. Intelligent filtering of the seismogram and windowing of the resulting cross-correlation based on the spectrogram analysis and the comparison between the phase-match filtered data spectrum, the raw-data spectrum and the theoretical source spectrum effectively reduces amplitude contaminations and results in reliable amplitude measurements in many cases. We implemented these measuring techniques in a graphic-user-interface tool called Surface Wave Amplitude Measurement Tool (SWAMTOOL). Using the tool, we collected and processed waveform data for 200 earthquakes occurring throughout 2003-2006 inside and around Eurasia. The records from 135 broadband stations were used. After obtaining the Rayleigh-wave amplitude measurements, we analyzed the attenuation behavior of the amplitudes using source- and receiver-specific terms calculated from a 3D velocity model of the region. Based on the results, we removed amplitudes that yielded negative average attenuation coefficients, and included an additional parameter in the inversion to account for the possible bias of the CMT moments. Using the high-quality amplitude measurements in a tomographic inversion, we obtained a fundamental-mode Rayleigh-wave attenuation- coefficient model for periods between 12 and 22 s for Asia and surrounding regions. The inverted attenuation model is consistent with the geological features of Asia. We observe low attenuation in stable regions such as eastern Europe, the Siberian platforms, the Indian shield, the Arabian platform, the Yangtze craton, and others. High attenuation is observed in tectonically active regions such as the Himalayas, the Tian Shan, Pamir and Zagros mountains.

Yang, X.; Levshin, A. L.; Barmin, M. P.; Ritzwoller, M. H.

2008-12-01

57

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

NASA Astrophysics Data System (ADS)

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

Kinzie, Aaron Wagner

58

Wave attenuation over coastal salt marshes under storm surge conditions  

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

59

Seismic wave attenuation and dispersion in thin layer sequences  

E-print Network

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

Edwards, Clifford Murray

1975-01-01

60

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

PubMed

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

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

2013-10-01

61

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

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

62

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

SciTech Connect

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

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

2013-10-15

63

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

64

A COMPARISON OF MEASURED RAIN ATTENUATION, RAIN RATES AND DROP SIZE DISTRIBUTIONS  

Microsoft Academic Search

This paper summarises a study of millimetre wave propagation models of precipitation in the atmosphere. Measurements of drop size distributions (DSDs), rain rates and millimetre wave attenuation have formed the key input to the analyses. In addition 20-30 years of rainfall from 3 sites in Norway have been investigated. The work includes physical and empirical modelling, and development of a

Walther Åsen; Chris Gibbins; Terje Tjelta

65

Attenuation of shock waves in copper and stainless steel  

SciTech Connect

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

Harvey, W.B.

1986-06-01

66

Dispersion and attenuation for an acoustic wave equation consistent with viscoelasticity  

E-print Network

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

Andrzej Hanyga

2014-01-30

67

An experimental model of ice floe induced attenuation of ocean waves  

E-print Network

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

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

2014-01-01

68

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

69

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

PubMed

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

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

2009-12-01

70

On wave radar measurement  

NASA Astrophysics Data System (ADS)

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.

Ewans, Kevin; Feld, Graham; Jonathan, Philip

2014-08-01

71

On wave radar measurement  

NASA Astrophysics Data System (ADS)

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.

Ewans, Kevin; Feld, Graham; Jonathan, Philip

2014-09-01

72

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

SciTech Connect

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

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

1992-03-01

73

Impact of attenuator models on computed traveling wave tube performances  

NASA Astrophysics Data System (ADS)

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

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

2007-09-01

74

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

NASA Astrophysics Data System (ADS)

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

Zucca, John J.; Evans, John R.

1992-07-01

75

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

SciTech Connect

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

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

1988-05-10

76

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

Microsoft Academic Search

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

Kevin Bradley; Chris Houser

2009-01-01

77

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

NASA Astrophysics Data System (ADS)

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

Marsooli, Reza; Wu, Weiming

2014-12-01

78

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

Microsoft Academic Search

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

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

2012-01-01

79

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

NASA Technical Reports Server (NTRS)

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

Reethof, G.

1976-01-01

80

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

NASA Astrophysics Data System (ADS)

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

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

2014-02-01

81

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

USGS Publications Warehouse

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

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

2014-01-01

82

Measurement by reflection analysis of optical attenuation through windows  

Microsoft Academic Search

Free space optical communication systems deployed in office buildings are subject to transmission loss through windows. Window attenuation varies between 0.4 and more than 15 dB. Window attenuation values are required to calculate communications link power budget and availability. But direct measurement of window attenuation in high-rise buildings is difficult since it requires access to both sides of the window.

Eric C. Eisenberg; Jeff C. Adams; Carrie S. Cornish

2001-01-01

83

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

Microsoft Academic Search

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

P. K. Jain; B. N. Basu

1988-01-01

84

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

NASA Astrophysics Data System (ADS)

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

Sleep, Norman H.; Erickson, Brittany A.

2014-04-01

85

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

NASA Astrophysics Data System (ADS)

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

Zhao, Liang; Xue, Mei

2015-04-01

86

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

NASA Astrophysics Data System (ADS)

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

Gibson, Alex; Gallo, Gonzalo E.

2004-02-01

87

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

NASA Astrophysics Data System (ADS)

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

Tutuncu, Azra Nur

88

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

Microsoft Academic Search

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

Katsuhisa Ootsuta; Kei Matsuoka; Akihiro Sasoh; Kazuyoshi Takayama

1998-01-01

89

Parameters Affecting Water Hammer Wave Attenuation, Shape by Anton Bergant1  

E-print Network

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

Eindhoven, Technische Universiteit

90

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

E-print Network

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

Paris-Sud XI, Université de

91

Precision microwave attenuation measurement by time interval ratio  

Microsoft Academic Search

A method of measuring microwave attenuation by substitution is described. As attenuation is inserted into the device under test, the pulse repetition frequency of a pulse modulated PIN diode switch in series with the device is changed to maintain a constant mean power output from the circuit. The ratio of the pulse repetition frequencies before and after insertion is shown

P. Cummings; R. H. Johnson

1985-01-01

92

Dynamic Measurements of Laser Light Attenuation by Cryogen Film and Frost Formation  

Microsoft Academic Search

The purpose of this study was to investigate the dynamics of laser light attenuation during cryogen spray cooling (CSC). Two detection schemes were used to approximate collimated and diffuse light transmittance measurements of continuous-wave (? = 594 nm) and pulsed (? = 585 nm) laser light during application of short (20-100 ms duration) cryogen spurts on a glass substrate. High-speed

Bernard Choi; Guillermo Aguilar; Gracie Vargas; A. J. Welch; J. Stuart Nelson

93

Measurement of $gamma$-ray attenuation coefficients  

Microsoft Academic Search

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

Christmas

1974-01-01

94

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

Microsoft Academic Search

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

Guido Kneib; S. A. Shapiro

1995-01-01

95

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

NASA Astrophysics Data System (ADS)

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

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

2015-03-01

96

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

NASA Astrophysics Data System (ADS)

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

Kulikovskii, V. A.

1983-06-01

97

BROADBAND ATTENUATION MEASUREMENTS OF PHOSPHOLIPID-SHELLED ULTRASOUND CONTRAST AGENTS  

PubMed Central

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

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

2014-01-01

98

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

99

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

NASA Astrophysics Data System (ADS)

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

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

100

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

PubMed

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

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

2012-11-01

101

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

PubMed Central

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

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

2012-01-01

102

TOWARD A RAYLEIGH WAVE ATTENUATION MODEL FOR ASIA AND SURROUNDING REGIONS  

Microsoft Academic Search

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

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

103

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

NASA Technical Reports Server (NTRS)

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

Kuntz, Herbert L.; Blackstock, David T.

1987-01-01

104

A direct measurement of skull attenuation for quantitative SPECT  

SciTech Connect

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%.

Turkington, T.G.; Gilland, D.R.; Jaszczak, R.J.; Greer, K.L.; Coleman, R.E. (Duke Univ. Medical Center, Durham, NC (United States). Dept. of Radiology); Smith, M.F. (Duke Univ., Durham, NC (United States). Dept. of Biomedical Engineering)

1993-08-01

105

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

NASA Astrophysics Data System (ADS)

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

Quintal, B.; Frehner, M.

2012-04-01

106

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

NASA Astrophysics Data System (ADS)

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

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

1987-06-01

107

Mid frequency shallow water fine-grained sediment attenuation measurements.  

PubMed

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

Holland, Charles W; Dosso, Stan E

2013-07-01

108

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

NASA Astrophysics Data System (ADS)

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

Houser, C.; Hill, P. R.

2010-12-01

109

Subduction zone guided waves: 3D modelling and attenuation effects  

NASA Astrophysics Data System (ADS)

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

Garth, T.; Rietbrock, A.

2013-12-01

110

Reconciling mantle attenuation-temperature relationships from seismology, petrology, and laboratory measurements  

NASA Astrophysics Data System (ADS)

attenuation measurements provide a powerful tool for sampling mantle properties. Laboratory experiments provide calibrations at seismic frequencies and mantle temperatures for dry melt-free rocks, but require ˜102-103 extrapolations in grain size to mantle conditions; also, the effects of water and melt are not well understood. At the same time, body wave attenuation measured from dense broadband arrays provides reliable estimates of shear wave attenuation (QS-1), affording an opportunity for calibration. We reanalyze seismic data sets that sample arc and back-arc mantle in Central America, the Marianas, and the Lau Basin, confirming very high attenuation (QS ˜ 25-80) at 1 Hz and depths of 50-100 km. At each of these sites, independent petrological studies constrain the temperature and water content where basaltic magmas last equilibrated with the mantle, 1300-1450°C. The QS measurements correlate inversely with the petrologically inferred temperatures, as expected. However, dry attenuation models predict QS too high by a factor of 1.5-5. Modifying models to include effects of H2O and rheology-dependent grain size shows that the effects of water-enhanced dissipation and water-enhanced grain growth nearly cancel, so H2O effects are modest. Therefore, high H2O in the arc source region cannot explain the low QS, nor in the back arc where lavas show modest water content. Most likely, the high attenuation reflects the presence of melt, and some models of melt effects come close to reproducing observations. Overall, body wave QS can be reconciled with petrologic and laboratory inferences of mantle conditions if melt has a strong influence beneath arcs and back arcs.

Abers, G. A.; Fischer, K. M.; Hirth, G.; Wiens, D. A.; Plank, T.; Holtzman, B. K.; McCarthy, C.; Gazel, E.

2014-09-01

111

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

E-print Network

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

Podladchikov, Yuri

112

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

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

113

Measuring Distance with Sound Waves  

NSDL National Science Digital Library

Students learn about sound waves and use them to measure distances between objects. They explore how engineers incorporate ultrasound waves into medical sonogram devices and ocean sonar equipment. Students learn about properties, sources and applications of three types of sound waves, known as the infra-, audible- and ultra-sound frequency ranges. They use ultrasound waves to measure distances and understand how ultrasonic sensors are engineered.

2014-09-18

114

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

NASA Technical Reports Server (NTRS)

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

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

1953-01-01

115

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

NASA Technical Reports Server (NTRS)

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

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

2002-01-01

116

Rain attenuation measurements: Variability and data quality assessment  

NASA Technical Reports Server (NTRS)

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

Crane, Robert K.

1989-01-01

117

Measurement and Modeling of Ultrasonic Attenuation in Aluminum Rolled Plate  

NASA Astrophysics Data System (ADS)

When fabricating a new set of calibration blocks for Aluminum 7075 plate inspections, it is advantageous that the new blocks have similar ultrasonic attenuation to existing block sets. This allows the new set to qualify under the same ASTM procedures used for older sets. In the course of surveying candidate materials for possible use as calibration blocks, some interesting attenuation results were observed. When a candidate block was cut from a thick section of rolled plate, measured back-wall attenuation values in the rolling or transverse direction were quite sensitive to position in the plate-normal direction. Such variations are presumably tied to microstructural variations within the plate, as revealed by metallography. Some measured attenuation values were found to be in good agreement with predictions of the Stanke-Kino model, while others were not. The measurements and modeling work are reviewed, and additional experiments conducted to clarify certain issues are discussed. Those additional experiments suggest that beam distortion effects, due to microstructure variations within the beam cross-section, are primarily responsible for differences between measured and predicted attenuation values.

Li, Anxiang; Kim, Hak-Joon; Margetan, Frank; Thompson, R. B.

2006-03-01

118

The Measurement of Broadband Ultrasonic Attenuation in Cancellous Bone  

Microsoft Academic Search

We have carried out measurements of the frequency dependence of ultrasonic attenuation in the range 0.2–1 MHz in in vitro samples of bovine cancellous bone and in vivo os calcis heel bones. A comparison of the results allows us to infer that the in vivo measurements are dependent on the bone mineral content of the os calcis. The bone mineral

C M Langton; S B Palmer; R W Porter

1984-01-01

119

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

NASA Technical Reports Server (NTRS)

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

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

1984-01-01

120

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

Microsoft Academic Search

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

Aybige Akinci; Haluk Eyido?an

1996-01-01

121

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

NASA Astrophysics Data System (ADS)

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

Mangriotis, Maria-Daphne

122

Broadband time-domain reflectometry measurement of attenuation and phase velocity in highly attenuating suspensions with application to the ultrasound contrast medium Albunex.  

PubMed

We describe a technique for broadband measurements of the attenuation coefficient and phase velocity of highly attenuating liquid suspensions. To validate the technique we apply it to the ultrasound contrast agent Albunex at concentrations ranging from 0.69 x 10(6) particles/mL to 364 x 10(6) particles/mL. These longitudinal wave measurements were performed on Albunex suspensions maintained at 37 degrees C in a special time-domain reflectometer designed and constructed in our laboratory. The frequency-dependent attenuation coefficients and phase velocities obtained in the reflectometer are compared to broadband through-transmission measurements of these same quantities, which were also performed in our laboratory. Although comparison data between the two techniques are only available at lower concentrations, the agreement is quite good and serves to validate the methods described in this paper. PMID:10955648

Hughes, M S; Klibanov, A L; Marsh, J N; Miller, J G; Brandenburger, G H

2000-08-01

123

Laboratory measurements of seismic attenuation in partially saturated rocks  

NASA Astrophysics Data System (ADS)

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.

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

2014-05-01

124

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

USGS Publications Warehouse

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

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

1988-01-01

125

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

Microsoft Academic Search

Summary A central issue in the successful application of acoustic wave method to detect subsurface hydrological properties is a better understanding of the influence of soil tex- ture on the propagation and attenuation of acoustic wave as moisture content is varied, which was numerically investigated in the present study. Our earlier studies have demon- strated the existence of three different

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

2007-01-01

126

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

E-print Network

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

Torres-Verdín, Carlos

127

REVIEW ARTICLE: Ultrasonic attenuation measurements in metals at low temperatures  

Microsoft Academic Search

The experimental techniques are reviewed for making ultrasonic measurements at frequencies from 10 MHz to 10 GHz in metals at temperatures down to 25 mK. The principles of attenuation measurements by the pulse-echo method and the electronic equipment for low temperature measurements are described. The theory and design of sample holders using nonresonant, re-entrant and helical cavities at ultralow temperatures

E. R. Dobbs; E. Hughes; N. S. Lawson; M. J. Lea; D. J. Meredith; W. E. Timms

1973-01-01

128

Measurement of Acoustic Attenuation and Absorption Coefficients using Thermometry  

Microsoft Academic Search

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

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

2007-01-01

129

Acoustic Measurement of Suspended Fine Particle Concentrations by Attenuation  

Technology Transfer Automated Retrieval System (TEKTRAN)

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

130

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

NASA Astrophysics Data System (ADS)

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

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

1988-10-01

131

Determination of particle size distributions from acoustic wave propagation measurements  

SciTech Connect

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.}

Spelt, P.D.; Norato, M.A.; Sangani, A.S.; Tavlarides, L.L. [Department of Chemical Engineering and Materials Science, Syracuse University, Syracuse, New York 13244 (United States)] [Department of Chemical Engineering and Materials Science, Syracuse University, Syracuse, New York 13244 (United States)

1999-05-01

132

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

133

The measurement of attenuation from vertical seismic profiles  

E-print Network

seismograms made from a sonic log recorded in a nearby well, 30 to 50 percent of the measured field 'attenuation' was found to be intrabed multiple induced effects. The authors stated that the effect measured on the synthetic data may be too large due...), amplitude ratios were determined from downhole and monitor spectra. A synthetic vertical seismic profile (VSP) was made using the sonic log from the well. Amplitude ratios calculated from this synthetic were used to remove interference and intrabed...

Davis, Francis Erwin

1983-01-01

134

Measurment and Interpretation of Seismic Attenuation for Hydrocarbon Exploration  

SciTech Connect

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

Michael Batzle; Luca Duranti; James Rector; Steve Pride

2007-12-31

135

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

Microsoft Academic Search

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

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

2004-01-01

136

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

137

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

PubMed

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

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

2006-12-22

138

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...

139

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

Microsoft Academic Search

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

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

1987-01-01

140

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

PubMed

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

Holm, Sverre; Näsholm, Sven Peter

2014-04-01

141

Plasma-parameter measurements using neutral-particle-beam attenuation  

SciTech Connect

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.

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

1982-07-07

142

Dynamic aspects of apparent attenuation and wave localization in layered media  

USGS Publications Warehouse

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

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

2008-01-01

143

Wave attenuation over coastal salt marshes under storm surge conditions  

E-print Network

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

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

2014-09-29

144

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

NASA Astrophysics Data System (ADS)

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

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

2012-06-01

145

Signal Processing of Broadband Pulsed Ultrasound: Measurement of Attenuation of Soft Biological Tissues  

Microsoft Academic Search

In this paper we will discuss the measurement of attenuation of soft tissues using broadband pulsed ultrasound. While all the methods presented here may be used for measuring the attenuation coefficient of single layers, some of the methods can also be used for measuring integrated attenuation of composite layers of soft tissue. These latter methods do not require knowledge of

Avinash C. Kak; Kris A. Dines

1978-01-01

146

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

Microsoft Academic Search

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

O. F. Tyrnov

1974-01-01

147

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

Microsoft Academic Search

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

A. L. Kohout; M. H. Meylan

2008-01-01

148

Shear wave attenuation and dispersion in melt-bearing olivine polycrystals  

E-print Network

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

149

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

Microsoft Academic Search

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

L. Margerin

2006-01-01

150

Shear wave attenuation and dispersion in melt-bearing olivine polycrystals  

E-print Network

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

151

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

NASA Technical Reports Server (NTRS)

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

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

1970-01-01

152

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

E-print Network

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

Boyer, Edmond

153

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

Microsoft Academic Search

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

Michael Fehler; Peter Roberts; Tom Fairbanks

1988-01-01

154

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

SciTech Connect

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

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

2007-10-17

155

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

NASA Astrophysics Data System (ADS)

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

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

2007-03-01

156

Wave energy attenuation and shoreline alteration characteristics of submerged breakwaters  

E-print Network

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

Krafft, Katherine Margaret

1993-01-01

157

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

NASA Astrophysics Data System (ADS)

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

?ahin, ?akir; Çinar, Mutlu

2014-07-01

158

Representative Elementary Length to Measure Soil Mass Attenuation Coefficient  

PubMed Central

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

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

2014-01-01

159

Measurement of Acoustic Attenuation and Absorption Coefficients using Thermometry  

NASA Astrophysics Data System (ADS)

Accurate knowledge of both the attenuation and the absorption coefficient of tissue are required when planning an optimal high intensity focused ultrasound treatment. A novel technique for simple measurement of this parameters has been developed in which a thin-film thermocouple (TFT) is placed between two layers of tissue of different thicknesses. The sample can be rotated about an axis through the junction of the TFT so that it can be insonated from either side leaving the tissue adjacent to the junction unchanged, but changing the overlying thickness. The attenuation and absorption coefficients can be calculated from the heating curves measured in the two orientations. Experiments have been carried out in both tissue mimicking material (TMM) and in ex vivo liver tissue. Weakly focused transducers, resonant at 1.05 MHz, 2.4 MHz and 3.55 MHz were used at free-field spatial peak intensities of 9-14 W/cm2. The temperature rise was measured as a function of time using a TFT. These thermocouples are not subject to the viscous heating artefact that is common to other thermocouple devices and so are advantageous for this purpose. Alignment was achieved with a 3D automated gantry system, which was controlled with specialised software. Timing and data acquisition were also controlled with this software. All experiments were carried out in degassed water. Results for TMM and degassed excised bovine liver are presented.

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

2007-05-01

160

Representative elementary length to measure soil mass attenuation coefficient.  

PubMed

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

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

2014-01-01

161

Evaluation of ultrasonic wave propagation to measure chilling injury in tomatoes  

Microsoft Academic Search

Chilling injury was induced by storing tomatoes at 3°C. Texture changes related to chilling injury were evaluated by acoustic firmness measurements and ultrasonic wave propagation. Because of the very high attenuation of the ultrasonic waves it was not possible to measure through a whole tomato. The ultrasonic transducers were fitted with beam focussing probes that were driven into the tomato

Bert E. Verlinden; Veerle De Smedt

2004-01-01

162

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

PubMed

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

Morin, Claire; Hellmich, Christian

2014-07-01

163

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

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

164

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 ...

165

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

Microsoft Academic Search

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

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

2010-01-01

166

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

PubMed

Multipass welds made of 316L stainless steel are specific welds of the primary circuit of pressurized water reactors in nuclear power plants. Because of their strong heterogeneous and anisotropic nature due to grain growth during solidification, ultrasonic waves may be greatly deviated, split and attenuated. Thus, ultrasonic assessment of the structural integrity of such welds is quite complicated. Numerical codes exist that simulate ultrasonic propagation through such structures, but they require precise and realistic input data, as attenuation coefficients. This paper presents rigorous measurements of attenuation in austenitic weld as a function of grain orientation. In fact attenuation is here mainly caused by grain scattering. Measurements are based on the decomposition of experimental beams into plane-wave angular spectra and on the modeling of the ultrasonic propagation through the material. For this, the transmission coefficients are calculated for any incident plane wave on an anisotropic plate. Two different hypotheses on the welded material are tested: first it is considered as monoclinic, and then as triclinic. Results are analyzed, and validated through comparison to theoretical predictions of related literature. They underline the great importance of well-describing the anisotropic structure of austenitic welds for UT modeling issues. PMID:24759567

Ploix, Marie-Aude; Guy, Philippe; Chassignole, Bertrand; Moysan, Joseph; Corneloup, Gilles; El Guerjouma, Rachid

2014-09-01

167

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

NASA Astrophysics Data System (ADS)

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

Wismer, Margaret Gertrude

168

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

NASA Astrophysics Data System (ADS)

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.

Nakagawa, S.; Korneev, V. A.

2013-12-01

169

Attenuation of coda waves in the Garhwal Lesser Himalaya, India  

NASA Astrophysics Data System (ADS)

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

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

2015-04-01

170

Radiometric rain attenuation measurements at 11.6 GHz in Peru  

Microsoft Academic Search

Rain attenuation is one of the key design parameters for satellite communication systems at frequencies above 10 GHz. Here, the results of one year of rain attenuation measurements in a heavy rainfall region of Peru are presented. Rainfall in this region is dominated by thunderstorm activity. Poor agreement is found with the 1986 CCIR attenuation prediction model; the modified CCIR

A. W. Dissanayake; J. E. Allnutt; D. K. McCarthy

1990-01-01

171

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

NASA Astrophysics Data System (ADS)

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

Birger, B. I.

2006-11-01

172

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

Microsoft Academic Search

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

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

2006-01-01

173

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

NASA Astrophysics Data System (ADS)

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

Hamada, K.; Yoshizawa, K.

2013-12-01

174

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

NASA Astrophysics Data System (ADS)

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

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

2012-11-01

175

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

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

176

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

Microsoft Academic Search

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

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

2007-01-01

177

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

USGS Publications Warehouse

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

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

1998-01-01

178

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

USGS Publications Warehouse

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

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

2011-01-01

179

Oceanic-wave-measurement system  

NASA Technical Reports Server (NTRS)

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.

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

1980-01-01

180

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

181

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

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.

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

1994-01-01

182

Measurements and Linear Wave Theory Based Simulations of Vegetated Wave Hydrodynamics for Practical Applications  

E-print Network

Wave attenuation by vegetation is a highly dynamic process and its quantification is important for accurately understanding and predicting coastal hydrodynamics. However, the influence of vegetation on wave dissipation is not yet fully established...

Anderson, Mary Elizabeth

2011-10-21

183

ULTRASONIC MEASUREMENT MODELS FOR SURFACE WAVE AND PLATE WAVE INSPECTIONS  

SciTech Connect

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.

Schmerr, Lester W. Jr. [Center for NDE, Iowa State University, Ames, IA, 50011 (United States); Dept. of Aerospace Eng., Iowa State University, Ames, IA, 50011 (United States); Sedov, Alexander [Dept of Mech. Eng., Lakehead University, Thunder Bay, ON, P7B 5E1 (Canada)

2010-02-22

184

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

SciTech Connect

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

Bull, Diana L; Ochs, Margaret Ellen

2013-09-01

185

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

186

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

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

187

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

NASA Astrophysics Data System (ADS)

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

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

1996-10-01

188

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

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

189

Ground-based radiometric measurements of slant-path attenuation in the V/W bands  

NASA Astrophysics Data System (ADS)

Ground-based radiometric techniques were applied to measure the slant-path attenuation cumulative distribution function to over 20 dB of attenuation and to less than 1% exceedance probability at the V and W band frequencies of 72.5 and 82.5 GHz. These are the first such measurements in these frequency bands. Brightness temperature measurements were collected at an elevation angle of 36° in Rome, NY, using a four-channel radiometer that included 23.8 and 31.4 GHz receivers. A model-based approach was used to invert brightness temperature to attenuation. An atmospheric model relevant to the geographic location and statistically representative of the attenuating conditions was developed for this purpose. The main assumption of the atmospheric model was that the sources of attenuation for exceedance probabilities of concern were dominated by stratiform rain. Monte Carlo solutions to the radiative transfer equation for the precipitating atmosphere were used to generate the attenuation retrieval algorithm. Sensitivity analysis showed that the attenuation retrieval algorithm was robust to uncertainties in the model parameters. Slant-path attenuation was also measured with the radiometer using the Sun as a source of radiation. Over 30 dB of attenuation dynamic range was possible with this technique. Sun-beacon measurements were used to test model predictions.

Brost, George; Magde, Kevin

2014-12-01

190

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

NASA Astrophysics Data System (ADS)

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

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

2015-03-01

191

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

192

Attenuation of lateral propagating light in sea ice measured with an artificial lamp in winter Arctic  

Microsoft Academic Search

The attenuation property of a lateral propagating light (LPL) in sea ice was measured using an artificial lamp in the Canadian Arctic during the 2007\\/2008 winter. A measurement method is proposed and applied whereby a recording instrument is buried in the sea ice and an artificial lamp is moved across the instrument. The apparent attenuation coefficient ?(?) for the lateral

J.-P. Zhao; T. Li; D. Barber; J.-P. Ren; M. Pucko; S.-J. Li; X. Li

2010-01-01

193

Effect of finite absorber dimensions on gamma-ray attenuation measurements  

Microsoft Academic Search

Using 137Cs gamma rays, the effect of finite absorber dimensions on attenuation measurements has been studied. Copper and mercury targets were used. Absorber dimensions up to five mean free paths were used. A correlated effect was observed in the measurements due to absorber thickness and its dimensions in the transverse directions. The values of the attenuation coefficients for copper and

K. M. Varier; S. Nasiruddeen Kunju; K. Madhusudanan

1986-01-01

194

Measurements for the JASPER Program radial shield attenuation experiment  

SciTech Connect

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

Mukenthaler, F.J.

1987-05-01

195

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

NASA Astrophysics Data System (ADS)

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

Dobrynina, Anna

2013-04-01

196

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

NASA Astrophysics Data System (ADS)

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

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

2008-03-01

197

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

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

198

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

199

Application of gamma-ray attenuation technology in density measurement of a slurry reactor  

Microsoft Academic Search

Axial density profile of the gas-liquid-solid mixture in a slurry bubble column was measured by gamma-ray attenuation technology.\\u000a Several measures for improving measurement precision were presented based on the discussion on attenuation law. It was found\\u000a that the response frequency and the ray intensity should be as high as possible to improve the measurement precision. The\\u000a mass absorption coefficient depended

Jian Xu; Weisheng Wei; Kai Zhang

2010-01-01

200

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

NASA Astrophysics Data System (ADS)

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

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

2008-02-01

201

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

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

202

Effect of collimator size and absorber thickness on gamma ray attenuation measurements for bakelite and perspex  

Microsoft Academic Search

The mass attenuation coefficient (m m ) of 662 keV gamma rays have been measured in the extended media of bakelite and perspex under different collimation conditions. The increase in attenuation coefficient is seen with increase in sample thickness as well as with collimator size due to the contribution of multiple scattered photons in the uncollided beam of 662 keV

Gurdeep S. Sidhu; Karamjit Singh; Parjit S. Singh; Gurmel S. Mudahar

1999-01-01

203

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

PubMed

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

Chen, Yong; Huang, Yiyong; Chen, Xiaoqian

2013-09-01

204

Gamma ray attenuation coefficient measurement for neutron-absorbent materials  

Microsoft Academic Search

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

Majid Jalali; Ali Mohammadi

2008-01-01

205

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

206

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

E-print Network

The so-called Localized Waves (LW), and the "Frozen Waves" (FW), have arisen significant attention in the areas of Optics and Ultrasound, because of their surprising energy localization properties. The LWs resist the effects of diffraction for large distances, and possess an interesting self-reconstruction (self-healing) property, after obstacles with size smaller than the antenna's; while the FWs, a sub-class of theirs, offer the possibility of arbitrarily modeling the field longitudinal intensity pattern inside a prefixed interval, for instance 0 < z < L, of the wave propagation axis. More specifically, the FWs are localized fields "at rest", that is, with a static envelope (within which only the carrier wave propagates), and can be endowed moreover with a high transverse localization. In this paper we investigate by simulated experiments, various cases of generation of ultrasonic FW fields, with frequency f_o = 1 MHz in a water-like medium, taking account of the effects of attenuation. We present res...

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

2013-01-01

207

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

NASA Astrophysics Data System (ADS)

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

Li, Chuanhui; Feng, Kai; Liu, Xuewei

2014-11-01

208

Measurement of elastic wave dispersion on human femur tissue  

NASA Astrophysics Data System (ADS)

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.

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

2014-03-01

209

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

210

Macro-Bending Influence on Radiation Induced Attenuation Measurement in Optical Fibres  

E-print Network

Influence of the bending radius on the measurement of radiation induced attenuation in glass optical fibres is discussed in this paper. Radiation induced attenuation measured in two single-mode fibre types shows discrepancies when coiled around a low bending radius spool: the observed attenuation is lower than expected. A series of dedicated tests reveals that this invalid measurement is related to the displacement of the mode field towards the cladding when the fibre is bent with a low radius, and to the different radiation resistances of the core and cladding glasses. For irradiation tests of optical fibres, the spool radius should therefore be carefully chosen.

Guillermain, E; Ricci, D; Weinand, U

2014-01-01

211

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

NASA Astrophysics Data System (ADS)

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

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

2011-04-01

212

An in situ measurement of the radio-frequency attenuation in ice at Summit Station, Greenland  

E-print Network

We report an in situ measurement of the electric field attenuation length at radio frequencies for the bulk ice at Summit Station, Greenland, made by broadcasting radio-frequency signals vertically through the ice and measuring the relative power in the return ground bounce signal. We find the depth-averaged field attenuation length to be 947 +92/-85 meters at 75 MHz. While this measurement has clear radioglaciological applications, the radio clarity of the ice also has implications for the detection of ultra-high energy (UHE) astrophysical particles via their radio emission in dielectric media such as ice. The measured attenuation length at Summit Station is comparable to previously measured radio-frequency attenuation lengths at candidate particle detector sites around the world, and strengthens the case for Summit Station as the most promising northern site for UHE neutrino detection.

J. Avva; J. M. Kovac; C. Miki; D. Saltzberg; A. G. Vieregg

2014-09-30

213

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

Microsoft Academic Search

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

C. D. Field; F. R. Fricke

1998-01-01

214

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

NASA Astrophysics Data System (ADS)

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

Li, Xiaobo; Dong, Liangguo; Zhao, Qun

2014-12-01

215

Experimental Studies on Role of Scattering Centers on Wave Energy Attenuation  

SciTech Connect

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

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

2000-06-18

216

Effect of collimator size and absorber thickness on gamma ray attenuation measurements  

Microsoft Academic Search

Mass attenuation coefficients have been measured in extended media of soil and water for 662 keV gamma rays under different collimation conditions. A correlation effect due to absorber thickness and collimator size has been observed.

G. S. Sidhu; K. Singh; P. S. Singh; G. S. Mudahar

1999-01-01

217

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

NASA Technical Reports Server (NTRS)

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

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

2007-01-01

218

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

NASA Technical Reports Server (NTRS)

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.

Vary, A.

1979-01-01

219

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

E-print Network

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

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

2009-01-01

220

Quantum nondemolition measurements. [by gravitational wave antennas  

NASA Technical Reports Server (NTRS)

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.

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

1980-01-01

221

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

Microsoft Academic Search

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

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

2007-01-01

222

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

PubMed

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

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

2013-12-01

223

Ultrasonic attenuation in pearlitic steel.  

PubMed

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

Du, Hualong; Turner, Joseph A

2014-03-01

224

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

SciTech Connect

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

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

2009-02-26

225

P-wave seismic attenuation by slow-wave diffusion. Effects of ...  

E-print Network

tradiction with experimental data (e.g., Jones, 1986). Another ... capable of describing the measured levels of dissipation at seismic frequencies (Diallo .... permeability regions, sealing faults and hydrocarbons caps, which prevent pressure.

2005-09-20

226

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

NASA Astrophysics Data System (ADS)

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

Lin, Guoqing

2014-04-01

227

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

NASA Technical Reports Server (NTRS)

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

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

1972-01-01

228

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

PubMed

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

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

2014-04-01

229

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

Microsoft Academic Search

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

A-M Roux

1976-01-01

230

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

Microsoft Academic Search

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

A.-M. Roux

1976-01-01

231

Effect of collimator size and absorber thickness on gamma ray attenuation measurements for bakelite and perspex  

Microsoft Academic Search

The mass attenuation coefficient (?\\u000a m) of 662 keV gamma rays have been measured in the extended media of bakelite and perspex under different collimation conditions.\\u000a The increase in attenuation coefficient is seen with increase in sample thickness as well as with collimator size due to the\\u000a contribution of multiple scattered photons in the uncollided beam of 662 keV gamma

Gurdeep S Sidhu; Karamjit Singh; Parjit S Singh; Gurmel S Mudahar

1999-01-01

232

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

SciTech Connect

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

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

2005-11-01

233

Determination of Rain Rate from a Spaceborne Radar Using Measurements of Total Attenuation  

Microsoft Academic Search

Several experimental and theoretical studies have shown that path-integrated rain rates can be determined by means of a direct measurement of attenuation. For ground-based radars, this is done by measuring the backscattering cross section of a fixed target in the presence and absence of rain along the radar beam. A ratio of the two measurements yields a factor proportional to

Robert Meneghini; Jerome Eckerman; David Atlas

1983-01-01

234

Beamwidth measurement of individual lithotripter shock waves  

PubMed Central

New lithotripters with narrower foci and higher peak pressures than the original Dornier HM3 electrohydraulic lithotripter have proven to be less effective and less safe. Hence, accurate measurements of the focal characteristics of lithotripter shock waves are important. The current technique for measuring beamwidth requires a collection of single-point measurements over multiple shock waves, thereby introducing error as a result of any shock-to-shock variability. This work reports on the construction of a hydrophone array sensor and on array measurements of individual lithotripter shock waves. Beamwidths for an electrohydraulic lithotripter with a broad-focus HM3-style reflector and a narrow-focus modified reflector were measured using both new and worn electrodes as well as two different electrical charging potentials. The array measured the waveform, beamwidth, and focal location of individual shock waves. The HM3-style reflector produced repeatable focal waveforms and beam profiles at an 18 kV charging potential with new and worn electrodes. Corresponding measurements suggest a narrower beamwidth than reported previously from averaged point measurements acquired under the same conditions. In addition, a lack of consistency in the measured beam profiles at 23 kV underscores the value of measuring individual shock waves. PMID:19206897

Kreider, Wayne; Bailey, Michael R.; Ketterling, Jeffrey A.

2009-01-01

235

Measurement of the seismic attenuation performance of the VIRGO Superattenuator  

Microsoft Academic Search

The gravitational wave detector VIRGO aims at extending the detection band down to a few Hertz by isolating the mirrors of the interferometer from seismic noise. This result is achieved by hanging each mirror through an elastic suspension (Superattenuator), designed to filter mechanical vibrations in all the degrees of freedom. An experimental upper limit of the mirror residual seismic noise

S. Braccini; L. Barsotti; C. Bradaschia; G. Cella; A. Di Virgilio; I. Ferrante; F. Fidecaro; I. Fiori; F. Frasconi; A. Gennai; A. Giazotto; F. Paoletti; R. Passaquieti; D. Passuello; R. Poggiani; E. Campagna; G. Guidi; G. Losurdo; F. Martelli; M. Mazzoni; B. Perniola; F. Piergiovanni; R. Stanga; F. Vetrano; A. Viceré; L. Brocco; S. Frasca; E. Majorana; A. Pai; C. Palomba; P. Puppo; P. Rapagnani; F. Ricci; G. Ballardin; R. Barillé; R. Cavalieri; E. Cuoco; V. Dattilo; D. Enard; R. Flaminio; A. Freise; S. Hebri; L. Holloway; P. La Penna; M. Loupias; J. Marque; C. Moins; A. Pasqualetti; P. Ruggi; R. Taddei; Z. Zhang; F. Acernese; S. Avino; F. Barone; E. Calloni; R. De Rosa; L. Di Fiore; A. Eleuteri; L. Giordano; L. Milano; S. Pardi; K. Qipiani; I. Ricciardi; G. Russo; S. Solimeno; D. Babusci; G. Giordano; P. Amico; L. Bosi; L. Gammaitoni; F. Marchesoni; M. Punturo; F. Travasso; H. Vocca; C. Boccara; J. Moreau; V. Loriette; V. Reita; J. M. Mackowski; N. Morgado; L. Pinard; A. Remillieux; M. Barsuglia; M. A. Bizouard; V. Brisson; F. Cavalier; A. C. Clapson; M. Davier; P. Hello; S. Krecklbergh; F. Beauville; D. Buskulic; R. Gouaty; D. Grosjean; F. Marion; A. Masserot; B. Mours; E. Tournefier; D. Tombolato; D. Verkindt; M. Yvert; S. Aoudia; F. Bondu; A. Brillet; E. Chassande-Mottin; F. Cleva; J. P. Coulon; B. Dujardin; J. D. Fournier; H. Heitmann; C. N. Man; A. Spallicci; J. Y. Vinet

2005-01-01

236

Modelling of Drop Size Distribution of Rain from Rain Rate and Attenuation Measurements at Millimeter and Optical Wavelengths  

Microsoft Academic Search

This paper describes a technique for modelling of rain drop size distributions at Calcutta in terms of negative exponential function, from the measurements of rain rate and attenuation over a dual wavelength LOS link at millimeter and optical frequencies. The DSD model obtained is then used to determine the attenuation at 94 GHz, for comparison with experimentally obtained attenuation at

S. Bhattacharyya; Marina Dan; A. K. Sen

2000-01-01

237

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

Microsoft Academic Search

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

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

1992-01-01

238

Relative attenuation measurements of ultrasound in the liver using the zerocrossing method.  

PubMed

The zerocrossing method for measurement of the frequency dependence of ultrasound attenuation was used to study the livers of 10 healthy subjects and 9 patients. Increased attenuation in vivo was observed in 5 patients who were seen to have a 'bright liver' during B-scanning. Normal attenuation was seen in 3 patients who had pathologic liver biopsies, but normal B-scan images. Increased attenuation was seen in one patient who had a nodular appearance of the liver during B-scanning; biopsy showed steatosis. These results indicate that the zerocrossing method makes it possible to quantify some of the changes seen in the B-scan image. A detailed description, including block diagrams, is given of a zerocrossing detector which can be connected to a commercially available scanner (Brüel & Kjaer Ultrasound Scanner Type 1846). PMID:2660889

Fredfeldt, K E

1989-01-01

239

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

SciTech Connect

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

Permpongkosol, Sompol [Johns Hopkins University School of Medicine, Johns Hopkins Hospital, James Buchanan Brady Urological Institute (United States); Link, Richard E. [Baylor College of Medicine, Scott Department of Urology (United States); Kavoussi, Louis R. [North Shore LIJ Health System, Institute for Urology (United States); Solomon, Stephen B. [Memorial Sloan-Kettering Cancer Center, Department of Radiology (United States)], E-mail: Solomons@mskcc.org

2008-01-15

240

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

SciTech Connect

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.}

Hickey, C.J.; Sabatier, J.M. [National Center for Physical Acoustics and Department of Physics and Astronomy, University of Mississippi, University, Mississippi 38677 (United States)] [National Center for Physical Acoustics and Department of Physics and Astronomy, University of Mississippi, University, Mississippi 38677 (United States)

1997-07-01

241

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

NASA Astrophysics Data System (ADS)

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

Takahashi, Tsutomu

2012-06-01

242

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

NASA Astrophysics Data System (ADS)

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

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

2007-10-01

243

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

Microsoft Academic Search

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

S. Gopal; B. Sanjeevaiah

1977-01-01

244

Measured surface magnetic field attenuation of shielded windows and wire mesh over an electrically small enclosure  

Microsoft Academic Search

The surface magnetic field attenuation of five types of shielded transparency (window) material was measured over the frequency range 10 kHz to 100 MHz by installing them on a .61 m x .61 m x .2 m enclosure, placing the enclosure on the wall of a TEM cell and measuring the surface and interior magnetic fields using a computer-controlled network

L. O. Hoeft; R. J. Karaskiewicz; J. S. Hofstra; G. Wiser

1984-01-01

245

Measured surface magnetic field attenuation of shielded windows and wire mesh over an electrically small enclosure  

Microsoft Academic Search

The surface magnetic field attenuation of five types of shielded transparency (window) material was measured over the frequency range 10 kHz to 100 MHz by installing them on an .61 m x .61 m x .2 m enclosure, placing the enclosure on the wall of a TEM cell and measuring the surface and interior magnetic fields using a computer-controlled network

L. O. Hoeft; J. S. Hofstra; R. J. Karaskiewicz; George Wiser

1984-01-01

246

Closing the Gap on Measuring Heat Waves  

NASA Astrophysics Data System (ADS)

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

Perkins, S. E.; Alexander, L.

2012-12-01

247

On the excess attenuation of sound in the atmosphere  

NASA Technical Reports Server (NTRS)

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

Deloach, R.

1975-01-01

248

Continuous measurement with traveling-wave probes  

SciTech Connect

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

Silberfarb, Andrew; Deutsch, Ivan H. [Department of Physics and Astronomy, University of New Mexico, Albuquerque, New Mexico 87131, USA (United States)

2003-07-01

249

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

NASA Astrophysics Data System (ADS)

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

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

2010-09-01

250

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

Microsoft Academic Search

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

Fidèle Moupfouma

2009-01-01

251

Attenuation statistics derived from emission measurements by a network of ground-based microwave radiometers  

NASA Technical Reports Server (NTRS)

Two seasons of thermal emission measurements, running from December 1987 through February 1988 and from June through August 1988 of thermal emission measurements, taken by a multi-channel, ground-based microwave radiometer, are used to derive single-station zenith attenuation statistics at 20.6 and 31.65 GHz. For the summer period, statistics are also derived for 52.85 GHz. In addition, data from two dual-channel radiometers, separated from Denver by baseline distances of 49 and 168 km, are used to derive two-station attenuation diversity statistics at 20.6 and 31.65 GHz. The multi-channel radiometer is operated at Denver, Colorado; the dual-channel devices are operated at Platteville and Flagler, Colorado. The diversity statistics are presented by cumulative distributions of maximum and minimum attenuation.

Westwater, E. R.; Snider, J. B.; Falls, M. J.; Fionda, E.

1990-01-01

252

Wideband measurements of ice sheet attenuation and basal scattering  

E-print Network

We are developing a multifirequency multistatic synthetic aperture radar (SAR) for determining polar ice sheet basal conditions. To obtain data for designing and optimizing radar performance, we performed field measurements with a network-analyzer...

Allen, Christopher Thomas; Gogineni, Sivaprasad; Paden, J. D.; Jezek, K. C.; Dahl-Jensen, D.; Larsen, L. B.

2005-04-01

253

Photogrammetric Measurements of CEV Airbag Landing Attenuation Systems  

NASA Technical Reports Server (NTRS)

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.

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

2008-01-01

254

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

Microsoft Academic Search

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

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

2011-01-01

255

Blood glucose measurement by using hollow optical fiber-based attenuated total reflection probe  

NASA Astrophysics Data System (ADS)

A noninvasive glucose monitoring system based on mid-infrared, attenuated total reflection spectroscopy using a hollow optical fiber probe is developed. Owing to the flexible fiber probe, measurement of oral mucosa, where blood capillaries are near the skin surface, is possible. Blood glucose levels are measured by detecting the peak intensity of glucose absorption bands, and the experimental results showed that the reproducibility of the measurement is high enough for monitoring blood glucose.

Kino, Saiko; Tanaka, Yuki; Matsuura, Yuji

2014-05-01

256

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

NASA Technical Reports Server (NTRS)

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.

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

1972-01-01

257

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

Microsoft Academic Search

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

Elimoel A. Elias

2003-01-01

258

WATER CONTENT MEASUREMENT WITH 60 keV GAMMA RAY ATTENUATION  

Microsoft Academic Search

The purpose of this paper is to discuss the specific problems dealing with the use of Americium 241 for measuring the water content of soil sample by attenuation of low energy gamma rays. One of the advantages is that the optimum thickness of the soil sample is about 4 to 5 cm. However, one of the difficulties encountered is related

P. H. GROENEVELT; J. G. de SWART; J. CISLER

1969-01-01

259

The feasibility of ranking material fracture toughness by ultrasonic attenuation measurements  

NASA Technical Reports Server (NTRS)

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

Vary, A.

1975-01-01

260

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

ERIC Educational Resources Information Center

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

Charles, Eric P.

2005-01-01

261

The feasibility of ranking material fracture toughness by ultrasonic attenuation measurements  

NASA Technical Reports Server (NTRS)

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

Vary, A.

1975-01-01

262

A technique for measuring velocity and attenuation of ultrasound in liquid foams , F. Elias2  

E-print Network

an experimental setup specifically designed for measuring the ultrasonic transmission through liquid foams, over a broad range of frequencies (60-600 kHz). The question of determining the ultrasonic properties during the coarsening. The ultrasonic velocity and attenuation are found to be very sensitive to the foam

Boyer, Edmond

263

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

E-print Network

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

2005-04-20

264

Review of underground salt attenuation measurements for SalSA  

NASA Astrophysics Data System (ADS)

We report on the status of the Salt Sensor Array (SalSA), a proposed experiment for detecting ultra-high energy neutrinos through the radio Cherenkov technique with an array of radio-microwave antennas embedded in a large, naturally occurring salt formation. We review the measurements to date aimed at assessing SalSA's feasibility, including a return visit of the Hockley Salt Mine in Hockley, Texas, and discuss the current status of the project.

Connolly, Amy; SalSA Collaboration

2012-01-01

265

Can We Measure the Wave Function of a SingleWave Packet of Light?  

E-print Network

Can We Measure the Wave Function of a SingleWave Packet of Light? Brownian Motion and Continuous packet of light.- A signal wave packet of light, 1I)&, is correlated to a probe wave packet, 1a Wave Packet Collapse in RepeatedWeak Quantum Nondemolition Measurements ORLY ALTER AND YOSHIHISA

Utah, University of

266

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

E-print Network

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

Cao, Wenwu

267

Spectroscopic measurement of an atomic wave function  

E-print Network

either tomographic or interferometric @11#. Ex- perimentally, tomographic method has been applied to the vibrational state of a diatomic molecule @12# and interfero- metric method for the holographic reconstruction of molecu- lar wave packets @13... on the measurement of Wigner function that bears a close connec- tion with the density operator of the system @3#, thus charac- terizing the quantum state completely. There are also several other techniques outside this tomographic @4,5# arena for measurement...

Kapale, KT; Qamar, S.; Zubairy, M. Suhail.

2003-01-01

268

Normal mode splitting function measurements of anelasticity and attenuation in the Earth's inner core  

NASA Astrophysics Data System (ADS)

We have used the iterative spectral fitting method to measure both the elastic and anelastic splitting functions of 20 inner core sensitive normal modes. These modes show significant improvement in spectral fit when anelastic splitting function coefficients dst are introduced in addition to the elastic splitting function coefficients cst. We employ two separate anelastic treatments: (i) fully anelastic measurement, in which a complete set of anelastic splitting function coefficients is measured in addition to the elastic coefficients, and (ii) zonal anelastic measurement, in which anelasticity is only allowed in zonal splitting function coefficients. Together, these two approaches confirm that normal modes sensitive to the Earth's inner core resolve zonally dominant elastic and anelastic structures. The zonal dominance of anelasticity suggests that the inner core exhibit cylindrical attenuation anisotropy in addition to cylindrical velocity anisotropy. In particular, the zonally dominant anelasticity correlates with zonal elastic structure, that is, directions of higher velocity in the inner core also appear more attenuating.

Mäkinen, Anna M.; Deuss, Arwen

2013-07-01

269

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

NASA Technical Reports Server (NTRS)

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.

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

1972-01-01

270

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

NASA Astrophysics Data System (ADS)

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.

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

2014-03-01

271

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

E-print Network

The bubbles involved in sonochemistry and other applications of cavitation oscillate inertially. A correct estimation of the wave attenuation in such bubbly media requires a realistic estimation of the power dissipated by the oscillation of each bubble, by thermal diffusion in the gas and viscous friction in the liquid. Both quantities and calculated numerically for a single inertial bubble driven at 20 kHz, and are found to be several orders of magnitude larger than the linear prediction. Viscous dissipation is found to be the predominant cause of energy loss for bubbles small enough. Then, the classical nonlinear Caflish equations describing the propagation of acoustic waves in a bubbly liquid are recast and simplified conveniently. The main harmonic part of the sound field is found to fulfill a nonlinear Helmholtz equation, where the imaginary part of the squared wave number is directly correlated with the energy lost by a single bubble. For low acoustic driving, linear theory is recovered, but for larger ...

Louisnard, Olivier

2013-01-01

272

Spectroscopic measurement of an atomic wave function  

NASA Astrophysics Data System (ADS)

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

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

2003-02-01

273

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

NASA Astrophysics Data System (ADS)

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

Sertçelik, Fadime

2012-07-01

274

Roadside tree attenuation measurements at UHF for land mobile satellite systems  

NASA Technical Reports Server (NTRS)

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.

Goldhirsh, Julius; Vogel, Wolfhard J.

1987-01-01

275

Laboratory Measurements of Turbulence Under Shoaling Waves  

NASA Astrophysics Data System (ADS)

Understanding the sediment transport in surf and swash zone is essential for numerous coastal projects and applications. Many time-dependent models parameterize the sediment transport. While some can be quite successful in predicting the evolution of the bed shape, our understanding of the sediment suspension mechanisms is still rather poor. When the waves approach the shore and break, the energy of the waves is lost to the generation of turbulence and currents, the entrainment of bubbles, and a fraction of the energy from breaking waves is transferred to suspend the sediment particles. A further investigation of the turbulence caused by breaking waves, resulting in the suspension of the sediment particles from the beach bed, is therefore necessary to improve our understanding of the suspension processes. We have used a Particle Image Velocimetry (PIV) technique to study the temporal and spatial structure of the turbulence in the bottom boundary layer. The experiments were performed in the large linear wave flume at the Air-Sea Interaction Laboratory at the University of Delaware. Continuous linear monochromatic deepwater waves were mechanically generated and sent to break naturally on an adjustable planner Plexiglas beach. The beach angle was adjusted to 1:2.6, 1:3.2, or 1:4.6 and a number of wave amplitudes were utilized for each of the beach angle. The PIV field of view was also arranged parallel to the beach bottom and in the vertical plane. The measurements were taken after reaching a quasi-steady state. Ensemble phase averages are used to obtain mean and turbulent fields. Time evolution is studied to investigate the formation and evolution of the turbulent structures and hairpin vortices within the bottom boundary layer. The results are discussed in the context of sediment transport.

Kikuchi, M.; Veron, F.

2003-12-01

276

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

Microsoft Academic Search

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

Sean C. Solomon

1972-01-01

277

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

SciTech Connect

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

Osterhuber, R. [Univ. of California, Soda Springs, CA (United States). Central Sierra Snow Lab.; Fehrke, F. [California Dept. of Water Resources, Sacramento, CA (United States); Condreva, K. [Sandia National Labs., Livermore, CA (United States)

1998-05-01

278

Ultrafast optical measurements of ultrasound attenuation in amorphous silicon at 50 and 100 GHz  

NASA Astrophysics Data System (ADS)

We present ultrafast optical measurements of the attenuation of 50 -- 100 GHz ultrasound in hydrogenated amorphous silicon (a-Si:H) thin films. The films were grown using a modified very high frequency glow discharge method on steel substrates. The deposition conditions were similar to those used for high efficiency solar cells. The measurements were performed at 300 K using the picosecond ultrasonics technique. Films of varying thickness were measured so that the effect of intrinsic acoustic loss within the a-Si:H could be determined. We find that the ultrasonic attenuation in a-Si:H at 100 GHz is more than an order of magnitude lower than is found in other amorphous materials. Our results may impact theoretical models of thermal transport in amorphous materials, and could provide a new avenue for studying voids in a-Si:H and nanocrystalline Si films.

Daly, Brian; Hondongwa, Donald; Norris, Theodore; Yan, Baojie; Yang, Jeff; Guha, Subhendu

2011-03-01

279

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

280

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

E-print Network

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

Santolik, Ondrej

281

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

E-print Network

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

Santolik, Ondrej

282

Estimation of seabed sound speed and attenuation using broadband acoustic measurements from L-shaped arrays  

NASA Astrophysics Data System (ADS)

One-step inversion algorithms using a cost function defined only by energy loss may not result in a unique solution of geo-acoustic inversion problem because of the coupling between seabed sound speed and attenuation [Zhou, Zhang, and Knobles, J. Acoust. Soc. Am., 125, 2009]. The present paper utilizes different characteristics of normal modes, including modal dispersion and modal based spatial coherence, to define appropriate cost functions in a two-step inversion scheme for geo-acoustic parameter estimation. This inversion scheme is applied to the long rang broadband acoustic data obtained from L-shaped arrays in the Shallow Water 2006 experiment. The sound speed in the half-space basement over a frequency range of 18-160 Hz and the seabed attenuations over a frequency range of 50-500 Hz are estimated by minimizing the cost function at each step. The results show a nonlinear frequency dependence of attenuation, which is similar to the seabed attenuation derived from measured time series and Transmission Loss data at the same experimental site [Knobles, Wilson, Goff, and Cho, J. Acoust. Soc. Am., 124, 2008].

Wan, Lin; Badiey, Mohsen

2012-11-01

283

Setting Time Measurement Using Ultrasonic Wave Reflection  

SciTech Connect

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.

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

2012-01-09

284

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

USGS Publications Warehouse

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

Gibbs, James F.; Roth, Edward F.

1989-01-01

285

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

NASA Technical Reports Server (NTRS)

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.

Babcock, R. V.

1977-01-01

286

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

Microsoft Academic Search

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

M. Rettschlag; R. Berndt; P. Mortreau

2007-01-01

287

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

Microsoft Academic Search

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

N. Ekinci; N. Astam

2007-01-01

288

An instrument for measuring high-power laser beam profiles and beam attenuation  

SciTech Connect

An instrument has been developed for measuring high-power laser beam profiles and the amount of beam attenuation during radiative ignition of solid propellants. The detector houses a 1.0 mm square PZT (lead-zirconate-titanate) sensing element that responds to changes in incident laser beam intensity. A chopper wheel with three slots was employed to produce the changes in beam intensity required by the element. The resultant output signal is a series of spikes'' whose height corresponds to the level of beam intensity. Profiles of a high-power CO{sub 2} laser beam were obtained by using the detector to acquire a series of radial data points which were then graphed to yield the beam profile. Experiments were also conducted to measure the amount of attenuation of the laser beam during the ignition of solid propellants. This was done by mounting a small sample of propellant on a thin plate above the detector, cutting a 1.5 mm hole through the propellant and the plate, and aligning the hole with the sensing element. The gases and particles evolved during ignition and subsequent combustion of the propellant attenuated the laser beam as it passed through the gaseous plume and the small hole in the sample before being measured by the sensor. The intensity measured by the sensor was then used to quantify the level of transmittance of the beam through the gaseous plume to the propellant sample surface. Results are presented and discussed for a beam profile test and two attenuation tests performed on different energetic materials.

Fetherolf, B.L.; Litzinger, T.A.; Kuo, K.K. (The Pennsylvania State University, Department of Mechanical Engineering, University Park, Pennsylvania 16802 (US))

1990-01-01

289

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

NASA Astrophysics Data System (ADS)

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

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

2010-01-01

290

Attenuation predictions at extremely low frequencies for measurement-while-drilling electromagnetic telemetry system  

Microsoft Academic Search

Extremely low frequencies (ELFs) are employed to transmit data from underground to the ground surface in the measurement-while-drilling electromagnetic (MWD-EM) telemetry system. Based on electromagnetic field theory, the present work is aimed at predicting the receivability of the signals at the surface. A unified analytic method that is suitable for vertical, directional, or horizontal wells is presented. Attenuation properties are

M. Y. Xia; Z. Y. Chen

1993-01-01

291

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

SciTech Connect

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

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

1984-11-27

292

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

293

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

E-print Network

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

Toksoz, M. Nafi

1984-01-01

294

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

PubMed

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

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

2012-12-01

295

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

NASA Astrophysics Data System (ADS)

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.

Maruvada, Subha

296

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

NASA Astrophysics Data System (ADS)

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

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

2015-03-01

297

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

NASA Astrophysics Data System (ADS)

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

Gu, Renliang; Dogandži?, Aleksandar

2014-02-01

298

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

NASA Technical Reports Server (NTRS)

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

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

1995-01-01

299

Thermoreflectance temperature measurement with millimeter wave  

SciTech Connect

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 ?, 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.

Pradere, C., E-mail: christophe.pradere@ensam.eu; Caumes, J.-P.; BenKhemis, S.; Palomo, E.; Batsale, J.-C. [I2M (Institut de Mécanique et d’Ingénierie de Bordeaux) UMR CNRS 5295, TREFLE Department, Esplanade des Arts et Métiers, F-33405 Talence Cedex (France); Pernot, G.; Dilhaire, S. [LOMA UMR 5798: CNRS-UB1, 351 Cours de la Libération, 33405 Talence Cedex (France)

2014-06-15

300

Shock propagation and attenuation in Green River oil shale  

NASA Astrophysics Data System (ADS)

Shock waves produced by planar impact of thin plates onto samples of oil shale are monitored with time-resolved velocity interferometer diagnostics. Peak shock stresses are below the Hugoniot elastic limit. Stress wave measurements at successive sample thickness are analysed to determine the experimental shock energy attenuation with propagation distance. Shock attenuation is attributed to stress wave scattering at planes of oil shale kerogen within the shale matrix. Wave scattering from planar defects are evaluated from a shock physics perspective and a scattering model is constructed that sensibly reproduces the experimental observation of shock energy attenuation.

Grady, D. E.

2014-05-01

301

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

SciTech Connect

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.

Muller-Runkel, R.; Vijayakumar, S.

1986-07-01

302

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

NASA Technical Reports Server (NTRS)

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

Campbell, Richard L.; Estus, Robert

1988-01-01

303

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

NASA Astrophysics Data System (ADS)

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

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

2004-11-01

304

Wave buoy measurements at the Antarctic sea ice edge compared with an enhanced ECMWF WAM: Progress towards global waves-in-ice modelling  

NASA Astrophysics Data System (ADS)

The breakup of pack ice in the Weddell Sea is examined with respect to a single wave buoy, frozen into the pack ice six months earlier, and the ECMWF WAM model. The pack ice broke up around the buoy on 14th September 2000 as large amplitude storm waves approached the ice edge at the buoy's location. The WAM model is modified to allow waves to propagate into the ice cover, in contrast to the operational scheme which sets wave energy to zero at ice concentrations over 30%. A simple, lookup-table-based, wave scattering attenuation scheme is then added and is combined with a sea ice drag attenuation parameterisation. WAM results at the location of the buoy are compared to the observations over a two-month period straddling the breakup. The modified WAM scheme generally reproduces the significant wave height, wave period and spectral characteristics measured by the buoy, though the model does not yet have any concept of floe breaking and re-freezing, assuming only that the ice cover is broken if the concentration is less than 80%. The simplistic nature of these modifications is designed to allow operational implementation, to eventually provide a global assessment of the wave-influenced ice zone.

Doble, Martin J.; Bidlot, Jean-Raymond

2013-10-01

305

Method of determining ultrasonic attenuation of tissue using reflective tomographic reconstruction  

SciTech Connect

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.

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

1984-10-09

306

An Empirical Assessment of Exposure Measurement Error and Effect Attenuation in Bipollutant Epidemiologic Models  

PubMed Central

Background: Using multipollutant models to understand combined health effects of exposure to multiple pollutants is becoming more common. However, complex relationships between pollutants and differing degrees of exposure error across pollutants can make health effect estimates from multipollutant models difficult to interpret. Objectives: We aimed to quantify relationships between multiple pollutants and their associated exposure errors across metrics of exposure and to use empirical values to evaluate potential attenuation of coefficients in epidemiologic models. Methods: We used three daily exposure metrics (central-site measurements, air quality model estimates, and population exposure model estimates) for 193 ZIP codes in the Atlanta, Georgia, metropolitan area from 1999 through 2002 for PM2.5 and its components (EC and SO4), as well as O3, CO, and NOx, to construct three types of exposure error: ?spatial (comparing air quality model estimates to central-site measurements), ?population (comparing population exposure model estimates to air quality model estimates), and ?total (comparing population exposure model estimates to central-site measurements). We compared exposure metrics and exposure errors within and across pollutants and derived attenuation factors (ratio of observed to true coefficient for pollutant of interest) for single- and bipollutant model coefficients. Results: Pollutant concentrations and their exposure errors were moderately to highly correlated (typically, > 0.5), especially for CO, NOx, and EC (i.e., “local” pollutants); correlations differed across exposure metrics and types of exposure error. Spatial variability was evident, with variance of exposure error for local pollutants ranging from 0.25 to 0.83 for ?spatial and ?total. The attenuation of model coefficients in single- and bipollutant epidemiologic models relative to the true value differed across types of exposure error, pollutants, and space. Conclusions: Under a classical exposure-error framework, attenuation may be substantial for local pollutants as a result of ?spatial and ?total with true coefficients reduced by a factor typically < 0.6 (results varied for ?population and regional pollutants). Citation: Dionisio KL, Baxter LK, Chang HH. 2014. An empirical assessment of exposure measurement error and effect attenuation in bipollutant epidemiologic models. Environ Health Perspect 122:1216–1224;?http://dx.doi.org/10.1289/ehp.1307772 PMID:25003573

Baxter, Lisa K.; Chang, Howard H.

2014-01-01

307

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

SciTech Connect

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

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

1989-05-25

308

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

Microsoft Academic Search

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

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

2012-01-01

309

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

NASA Astrophysics Data System (ADS)

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 hematocrit of 20% at the same rotation speed, and shifted to a hematocrit of 10% at a higher speed. The backscattering properties of rat RBCs in plasma are similar to those of RBCs in saline at a higher rotation speed. The differences in attenuation and backscattering between rat and porcine blood may be attributed to RBCs' being smaller and the RBC aggregation level being lower for rat blood than for porcine blood.

Huang, Chih-Chung

2010-10-01

310

Torsional ultrasonic wave based level measurement system  

DOEpatents

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.

Holcomb, David E. (Oak Ridge, TN); Kisner, Roger A. (Knoxville, TN)

2012-07-10

311

Airborne measurements of gravity wave breaking at the tropopause  

Microsoft Academic Search

A breaking atmospheric gravity wave was investigated with a combination of airborne in-situ dynamical measurements and ground-based VHF radar observations. The wave was generated by flow over mountains and it was observed to break near the tropopause. The measurements reveal that the wave was overturning at the tropopause and that the initial breakdown into turbulence involved the generation of smaller

James A. Whiteway; Edward G. Pavelin; Reinhold Busen; Jorg Hacker; Simon Vosper

2003-01-01

312

Blood glucose measurement by multiple attenuated total reflection and infrared absorption spectroscopy.  

PubMed

The difficulty of measuring physiological concentrations of glucose in blood by conventional infrared absorption spectroscopy is due to the intrinsic high background absorption of water. This limitation can be largely overcome by the use of a CO2 laser as an infrared source in combination with a multiple attenuated total reflection (ATR) technique. To demonstrate the applicability of this technique, we compared in vitro measurements of glucose in blood obtained from an experimental infrared laser spectrometer with independent measurements made by a standard YSI 23A laboratory glucose analyzer. The capability of continuous measurement of blood glucose concentration is of primary importance in the future development of a glucose sensor for diabetic patients. PMID:2345001

Mendelson, Y; Clermont, A C; Peura, R A; Lin, B C

1990-05-01

313

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

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

314

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

Microsoft Academic Search

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

Yong Keun Hwang; Jeroen Ritsema; Saskia Goes

2009-01-01

315

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

316

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

NASA Astrophysics Data System (ADS)

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

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

2001-03-01

317

Ultrasonic interferometry for the measurement of shear velocity and attenuation in viscoelastic solids.  

PubMed

A method for the measurement of the shear properties of solid viscoelastic materials is presented. The viscoelastic material is cut into a cylindrical sample which is clamped between two rods. The transmission and reflection coefficient spectra of the fundamental torsional mode through the sample are measured by means of two pairs of piezoelectric transducers placed at the free ends of the rod-sample-rod system. Such spectra exhibit maxima and minima which occur approximately at the resonance frequencies of the free viscoelastic cylinder. Therefore, the shear velocity can be obtained by measuring the frequency interval between two consecutive maxima or minima. The shear attenuation is derived by best fitting the analytical expression of the reflection and transmission coefficients to the experimental spectra. The test is very quick to set up as the sample is simply clamped between the two rods. PMID:14759006

Simonetti, F; Cawley, P

2004-01-01

318

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

NASA Astrophysics Data System (ADS)

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

Li, Ting

2005-07-01

319

Deep-Ocean Measurements of Tsunami Waves  

NASA Astrophysics Data System (ADS)

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.

Rabinovich, Alexander B.; Eblé, Marie C.

2015-03-01

320

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

Microsoft Academic Search

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

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

2007-01-01

321

Broadband optoacoustic measurements of ultrasound attenuation in severely plastically deformed nickel  

NASA Astrophysics Data System (ADS)

Laser optoacoustics and immersion techniques allowed a broadband ultrasound spectroscopy which was used for measuring the attenuation of severely plastically deformed nickel. A disk shaped specimen of nickel of about 33 mm diameter and 2.5 mm thickness was prepared by the high pressure torsion method. The produced equivalent shear strain linearly increased from a minimum at the center up to 1000% at the edge, gradually refining the grain size distribution down to 200 nm. The metal water interface was illuminated by 5 ns laser pulses, generating longitudinal ultrasound pulses with a pronounced compression phase and a smooth spectrum covering the range from 0.1 up to 150 MHz. The laser beam spot diameter was 6 mm, yielding a maximum power density below 15 MW/cm2. The ultrasound passed through the sample thickness and a 2 mm layer of coupling water. The pulse was detected by a 25 ?m thick piezoelectric foil transducer with a diameter of the sensitive area of 2 mm. The transient signals were locally measured at different radii of the specimen. The attenuation almost linearly increases with frequency while its absolute value decreases from the center to the edge of the specimen.

Kozhushko, Victor V.; Paltauf, Günther; Krenn, Heinz; Scheriau, Stephan; Pippan, Reinhard

2010-05-01

322

Ultrasonic characterization of materials by means of under water Laser Doppler Vibrometer measurements of continuous waves  

NASA Astrophysics Data System (ADS)

Pulse signals are widely use for several ultrasonic testing. They indeed allow an easy estimation of the delays occurring in echo and transmission measurements and give the possibility to filter the noise (i.e undesired reflections occurring in the surface of the transducers) applying a window in the time domain. However their high crest factor makes these signals unsuitable to test attenuating materials. For this reason this paper proposes a new method, based on continuous waves, for ultrasonic characterization of materials. A a wave propagation model in the frequency domain is presented, to determine simultaneously acoustic velocity, mass density, and thickness of two Plexiglas plates, during transmission experiments. The Ultrasonic waves are captured by a Scanning Laser Doppler Vibrometer (SLDV) in order to guarantee a large number of spatial points, acquired with a high resolution.

Longo, Roberto; Steenackers, Gunther; Vanlanduit, Steve; Guillaume, Patrick

2010-05-01

323

Cluster multispacecraft measurement of spatial scales of foreshock Langmuir waves  

E-print Network

Cluster multispacecraft measurement of spatial scales of foreshock Langmuir waves J. Soucek,1 O multispacecraft study of spatial scales of Langmuir wave packets in the terrestrial foreshock. We used data from. Our analysis shows that the typical scale of Langmuir wave packets in the direction transverse

Santolik, Ondrej

324

Diffraction correction for precision surface acoustic wave velocity measurements  

E-print Network

Diffraction correction for precision surface acoustic wave velocity measurements Alberto Ruiz M is the diffraction of the surface acoustic wave SAW as it travels over the surface of the specimen. The results suggest that a diffraction correction may be introduced to increase the accuracy of surface wave

Nagy, Peter B.

325

Measurements of shoaling internal waves and turbulence in an estuary  

E-print Network

. In the deeper part of the study domain, the waves propagated according to the predictions of linear theory losses during propagation [Shroyer et al., 2010a]. Vertical heat flux associated with the wavesMeasurements of shoaling internal waves and turbulence in an estuary Clark Richards,1 Daniel

Kelley, Dan

326

Measurements of shoaling internal waves and turbulence in an estuary  

E-print Network

of the study domain, the waves propagated according to the predictions of linear theory. In intermediate losses during propagation [Shroyer et al., 2010a]. Vertical heat flux associated with the wavesMeasurements of shoaling internal waves and turbulence in an estuary Clark Richards,1 Daniel

327

Measuring the speed of cosmological gravitational waves  

NASA Astrophysics Data System (ADS)

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.

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

2015-03-01

328

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

ERIC Educational Resources Information Center

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…

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

2008-01-01

329

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

Microsoft Academic Search

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

B. P. Cohee

1991-01-01

330

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

PubMed Central

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

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

2010-01-01

331

DC attenuation meter  

DOEpatents

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.

Hargrove, Douglas L.

2004-09-14

332

Measurement of Attenuation with Airborne and Ground-Based Radar in Convective Storms Over Land and Its Microphysical Implications  

NASA Technical Reports Server (NTRS)

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.

Tian, Lin; Heymsfield, G. M.; Srivastava, R. C.; Starr, D. OC. (Technical Monitor)

2001-01-01

333

Measurement of Attenuation with Airborne and Ground-Based Radar in Convective Storms Over Land Its Microphysical Implications  

NASA Technical Reports Server (NTRS)

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.

Tian, Lin; Heymsfield, G. M.; Srivastava, R. C.; O'C.Starr, D. (Technical Monitor)

2001-01-01

334

ON THE DETERMINATION OF GAMMA-RAY ATTENUATION FACTORS OF SHIELDING MATERIALS BY MEANS OF DIFFERENTIAL BUILD-UP-MEASURING  

Microsoft Academic Search

A method for measuring gamma-ray attenuation factors of shielding ; materials is described in which only small samples of material are needed. This ; method makes use of a narrow beam. The scattered radiation is measured by means ; of a scintiliation crystal in dependence of the distance aside from the primary ; beam immediately behind the shield. The first

W. Futtermenger; H. Glubrecht; E. G. Niemann; H. Schultz

1962-01-01

335

Correlation techniques and measurements of wave-height statistics  

NASA Technical Reports Server (NTRS)

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.

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

1972-01-01

336

Independent measurements of the frequency and wavelength of electromagnetic waves  

NASA Astrophysics Data System (ADS)

Very few measurements that directly investigate the frequency of electromagnetic waves are accessible to undergraduate or high school laboratories because of the expense of most spectrum analyzers as well as the extremely high frequencies of many electromagnetic waves. However, an affordable setup for measuring electromagnetic wave properties, including frequency and wavelength, can be made using a wireless network spectrum analyzer. Capabilities of an inexpensive spectrum analyzer are examined and illustrative samples of wave property measurements are presented. These allow determination of the speed of propagation so that comparison with the speed of visible light can help integrate student understanding of the electromagnetic spectrum.

Howald, Craig

2009-10-01

337

Elastic property measurement using Rayleigh-Lamb waves  

Microsoft Academic Search

A nondestructive technique is described for the measurement of elastic constants of isotropic plates using ultrasonic Rayleigh-Lamb waves. The experimental method employs continuous harmonic waves and a pair of variable-angle contact transducers in pitch-catch mode. The phase velocity of the R-L waves at a particular frequency is determined from the phase shift over a measured path length. This simple experimental

W. P. Rogers

1995-01-01

338

Offshore wave power measurements—A review  

Microsoft Academic Search

The first wave power patent was filed in 1799. Since then, hundreds of ideas for extraction of energy from ocean waves have surfaced. In the process of developing a concept, it is important to learn from previous successes and failures, and this is not least important when moving into the ocean. In this paper, a review has been made with

Simon Lindroth; Mats Leijon

2011-01-01

339

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

340

Delamination of southern Puna lithosphere revealed by body wave attenuation tomography  

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

341

Analysis of Gravity Waves from Radio Occultation Measurements  

E-print Network

Analysis of Gravity Waves from Radio Occultation Measurements Martin Lange and Christoph Jacobi occultation mea- surements. Due to the spherical symmetry assumption in the retrieval algorithm and the low that with radio occultation measurements more than 90% of the simulated wave spectrum can be resolved

342

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

PubMed

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

Carcione; Poletto

2000-07-01

343

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

NASA Astrophysics Data System (ADS)

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.

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

2009-08-01

344

Measuring rms Wave Height and the Scalar Ocean Wave Spectrum With HF Skywave Radar  

Microsoft Academic Search

Estimates of rms wave height and the scalar ocean wave frequency spectrum were made by inverting high-frequency (HF) skywave radar-measured sea-echo Doppler spectra. Whereas low-power surface- wave radars can make these measurements out to approximately 100 km from the radar, coverage out to 3000 km can be obtained with skywave radars that illuminate the sea via a single ionospheric reflection.

Joseph W. Maresca; T. M. Georges

1980-01-01

345

Nanosecond freezing of water under multiple shock wave compression: Continuum modeling and wave profile measurements  

Microsoft Academic Search

Using real time optical transmission and imaging measurements in multiple shock wave compression experiments, water was shown to solidify on nanosecond time scales [D. H. Dolan and Y. M. Gupta, J. Chem. Phys. 121, 9050 (2004)]. Continuum modeling and wave profile measurements, presented here, provide a complementary approach to examine the freezing of shocked water. The water model consisted of

D. H. Dolan; J. N. Johnson; Y. M. Gupta

2005-01-01

346

Correcting Four Similar Correlational Measures for Attenuation Due to Errors of Measurement in the Dependent Variable: Eta, Epsilon, Omega, and Intraclass r.  

ERIC Educational Resources Information Center

Besides the ubiquitous Pearson product-moment r, there are a number of other measures of relationship that are attenuated by errors of measurement and for which the relationship between true measures can be estimated. Among these are the correlation ratio (eta squared), Kelley's unbiased correlation ratio (epsilon squared), Hays' omega squared,…

Stanley, Julian C.; Livingston, Samuel A.

347

Hydrometeor Size Distribution Measurements by Imaging the Attenuation of a Laser Spot  

NASA Technical Reports Server (NTRS)

The optical extinction of a laser due to scattering of particles is a well-known phenomenon. In a laboratory environment, this physical principle is known as the Beer-Lambert law, and is often used to measure the concentration of scattering particles in a fluid or gas. This method has been experimentally shown to be a usable means to measure the dust density from a rocket plume interaction with the lunar surface. Using the same principles and experimental arrangement, this technique can be applied to hydrometeor size distributions, and for launch-pad operations, specifically as a passive hail detection and measurement system. Calibration of a hail monitoring system is a difficult process. In the past, it has required comparison to another means of measuring hydrometeor size and density. Using a technique recently developed for estimating the density of surface dust dispersed during a rocket landing, measuring the extinction of a laser passing through hail (or dust in the rocket case) yields an estimate of the second moment of the particle cloud, and hydrometeor size distribution in the terrestrial meteorological case. With the exception of disdrometers, instruments that measure rain and hail fall make indirect measurements of the drop-size distribution. Instruments that scatter microwaves off of hydrometeors, such as the WSR-88D (Weather Surveillance Radar 88 Doppler), vertical wind profilers, and microwave disdrometers, measure the sixth moment of the drop size distribution (DSD). By projecting a laser onto a target, changes in brightness of the laser spot against the target background during rain and hail yield a measurement of the DSD's second moment by way of the Beer-Lambert law. In order to detect the laser attenuation within the 8-bit resolution of most camera image arrays, a minimum path length is required. Depending on the intensity of the hail fall rate for moderate to heavy rainfall, a laser path length of 100 m is sufficient to measure variations in optical extinction using a digital camera. For hail fall only, the laser path may be shorter because of greater scattering due to the properties of hailstones versus raindrops. A photodetector may replace the camera in automated installations. Laser-based rain and hail measurement systems are available, but they are based on measuring the interruption of a thin laser beam, thus counting individual hydrometeors. These systems are true disdrometers since they also measure size and velocity. The method reported here is a simple method, requiring far less processing, but it is not a disdrometer.

Lane, John

2013-01-01

348

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

Microsoft Academic Search

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

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

2000-01-01

349

Attenuation predictions at extremely low frequencies for measurement-while-drilling electromagnetic telemetry system  

SciTech Connect

Extremely low frequencies (ELF) are employed to transmit data from underground to the ground surface for Measurement-While-Drilling Electromagnetic (MWD-EM) telemetry system. Based on electromagnetic field theory, the work is aimed at predicting the receivability of the signals on the ground surface. A unified analytic method that is suitable for vertical well, directional well, and horizontal well is presented. Attenuation properties are examined for various parameters, including the earth`s conductivity, operating frequency and the length of the drill string. Frequency dependence of the receivability in reference to a noise level is illustrated for different depths of well and different earth cases. It is also demonstrated that the electric field distributions on the ground surface have the same features for the three types of well, and the measurements should be carried out near the well heads for any type of well. A scale model experiment is made to test the authors` theoretical results. The measured data and the computed results are comparable.

Xia, M.Y.; Chen, Z.Y. [Academia Sinica, Beijing (China). Inst. of Electronics] [Academia Sinica, Beijing (China). Inst. of Electronics

1993-11-01

350

Measurement of the transfer function of the steering filter of the Virgo super attenuator suspension  

NASA Astrophysics Data System (ADS)

The optical elements of the Virgo antenna are supported and isolated from seismic noise disturbances by super attenuator (SA) suspensions. The steering filter (SF) is a component of the SA, designed for the mirror control. The dynamical properties of the SF are described by transfer functions, which have been measured in order to define the control strategy; the results have made it possible to set and tune the parameters of a simulation of the SA. The measuring devices were linear voltage differential transducers: they were found to be quite effective and flexible in usage. An auto-regressive model was used to fit the experimental data, implementing the linear relation between the input forces and the resulting motion. The ability of the model to reproduce the experimental behavior was a clear indication of the good data quality, showing that the contaminating noise was under control. The simulation was able to reproduce the qualitative behavior, and the simulation parameters were estimated, with 10% and 20% accuracy. The estimations were later found to be consistent with the measurements taken on a full SA equipped with the same steering filter. Unknown spectral structures were found only above 20 Hz.

Ballardin, G.; Braccini, S.; Bradaschia, C.; Casciano, C.; Cavalieri, R.; Cecchi, R.; Chickarmane, V.; Dattilo, V.; Di Virgilio, A.; Ferrante, I.; Fidecaro, F.; Frasconi, F.; Gaddi, A.; Gennai, A.; Giazotto, A.; Holloway, L.; Lomtazde, T.; Paoletti, F.; Pasqualetti, A.; Passaquieti, R.; Passuello, D.; Poggiani, R.; Taddei, R.; Viceré, A.; Zhang, Z.; Cuoco, E.; Losurdo, G.; Ni, Wei-Tou; Wu, Jeah-Sheng; Chang, Chun-Hsiung

2001-09-01

351

Measurement of semi-rigid coaxial cables at cryogenic temperature -thermal conductance and attenuation-  

NASA Astrophysics Data System (ADS)

We are developing semi-rigid coaxial cables for low temperature experiments which require fast readout with low noise. Coaxial cables used at low temperature are made of low thermal conductivity materials, such as stainless-steel, cupro-nickel and polytetrafluoroethylene to suppress heat penetration through cables. As the thermal conductivity of such alloys is affected by the thermal and mechanical treatment in forming process, we have to measure thermal property of coaxial cables after forming. The low thermal conductance of 5.5 cm specimen was measured by the steady-state heat-flow method with 1m long and thin niobium-titanium wiring for thermometers and heaters. Signal attenuation of coaxial cables was measured at 3K stage of an adiabatic demagnetization refrigerator. In order to cool center electrical conductor, the cables with 1m long length were coiled, and surrounded by copper blocks then attached to 3K stage. We successfully observed superconducting transition of center conductor of superconducting niobium-titanium coaxial cables with this method.

Kasai, Soichi; Kushino, Akihiro

2013-03-01

352

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

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

353

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

NASA Astrophysics Data System (ADS)

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

Vilhelm, Jan; Slavík, Lubomír

2014-05-01

354

Compressive Direct Measurement of the Quantum Wave Function  

NASA Astrophysics Data System (ADS)

The direct measurement of a complex wave function has been recently realized by using weak values. In this Letter, we introduce a method that exploits sparsity for the compressive measurement of the transverse spatial wave function of photons. The procedure involves weak measurements of random projection operators in the spatial domain followed by postselection in the momentum basis. Using this method, we experimentally measure a 192-dimensional state with a fidelity of 90% using only 25 percent of the total required measurements. Furthermore, we demonstrate the measurement of a 19 200-dimensional state, a task that would require an unfeasibly large acquiring time with the standard direct measurement technique.

Mirhosseini, Mohammad; Magaña-Loaiza, Omar S.; Hashemi Rafsanjani, Seyed Mohammad; Boyd, Robert W.

2014-08-01

355

Transmission measurement correction for self-attenuation in gamma-ray assays of special nuclear materials  

Microsoft Academic Search

The central and most difficult problem in the NDA of bulk samples by passive gamma-ray spectroscopy is the correction of the sample self-attenuation. Because of the severity of the problems in many plutonium and uranium samples, the usual calibration and attenuation correction methods involving direct comparison to standards or exploitation of prior knowledge of chemical composition are often not applicable.

J. L. Parker; T. D. Reilly

2009-01-01

356

A theoretical comparison of attenuation measurement techniques from backscattered ultrasound echoes  

E-print Network

characterization of tissue pathologies using ultrasonic attenuation is strongly dependent on the accuracy, 43.20.Hq, 43.20.Fn, 43.20.Ei [CCC] Pages: 2316­2324 I. INTRODUCTION The ultrasonic attenuation coefficient is an important pa- rameter in the characterization of tissue pathologies. In liver disease

Illinois at Urbana-Champaign, University of

357

Preliminary Measurements of the Attenuation Properties of Polycrystalline Water Ice and CO2 Clathrate Hydrates at the Tidal Frequencies of Europa and Enceladus  

Microsoft Academic Search

We will report measurements of the attenuation properties of polycrystalline water ice and CO2 clathrate hydrates samples obtained in the frequency range 3x10-6 to 10-2 Hz, which encompasses the tidal frequencies of Europa and Enceladus. Previous attenuation measurements obtained on a variety of planetary materials have demonstrated that the mechanisms driving attenuation in the frequency range 10-4 to 1 Hz

M. Choukroun; J. C. Castillo; J. B. Young; R. Mielke

2009-01-01

358

Rain attenuation measurements at 28.8, 57.6, and 96.1 GHz on a 1-km path  

NASA Astrophysics Data System (ADS)

An experimental millimeter-wave propagation link was installed on a 1-km path in the northern California area (Gasquet) to compare rain rate and attenuation at 28.8,57.6, and 96.1 GHz. During the monitoring period (January 26 through April 14), rain occurred on 27 days with an accumulation of 514 mm (20.25 in). For periods when the rain rate exceeded 5 mm/h, both VV (vertical polarization at the transmitter and vertical polarization at the receiver) and VH (vertical polarization at the transmitter and horizontal polarization at the receiver) signals were recorded. Maximum rain rates exceeded 50mm/h and maximum attenuations of 4, 10, and 17 dB were observed on the 28.8, 57.6, and 96.1 GHz channels, respectively.

Espeland, R. H.; Violette, E. J.; Allen, K. C.

1986-02-01

359

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

Microsoft Academic Search

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

R. Moreh; D. Salzmann; Y. Wand

1969-01-01

360

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

Microsoft Academic Search

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

Thomas J. Gorgas; Roy H. Wilkens; Shung S. Fu; L. Neil Frazer; Mike D. Richardson; Kevin B. Briggs; Homa Lee

2002-01-01

361

The Measurement of Broadband Ultrasonic Attenuation in Cancellous Bone-A Review of the Science and Technology  

Microsoft Academic Search

The measurement of broadband ultrasonic attenuation (BUA) in cancellous bone at the calcaneus was first described in 1984. The assessment of osteoporosis by BUA has recently been recognized by Universities UK, within its EurekaUK book, as being one of the \\

Christian M. Langton; Christopher F. Njeh

2008-01-01

362

Test of the probability formulation of the Synthetic Storm Technique against reliable measurements of rain rate and rain attenuation  

Microsoft Academic Search

Even long term measurements of substantially concurrent rain rate and rain attenuation pdfs, as much reliable as is experimentally possible, need to be inspected by a specialist to avoid intervals of dubious data (see also [2]). This hard, difficult and time-consuming work is the inevitable price to pay for obtaining, at last, a useful data bank of concurrent rain rate

E. Matricciani; C. Riva

2008-01-01

363

Frequency dependent elastic properties and attenuation in heavy-oil sands: comparison between mea-sured and modeled data  

E-print Network

Frequency dependent elastic properties and attenuation in heavy-oil sands: comparison between mea) properties of heavy-oil sands over a range of frequencies (2 - 2000Hz) covering the seismic bandwidth and at ultrasonic frequencies (0.8MHz). The measurements were carried on heavy-oil sand sample from Asphalt Ridge

364

IWA : an analysis program for isentropic wave measurements.  

SciTech Connect

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.

Ao, Tommy

2009-02-01

365

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

Microsoft Academic Search

Creep damage in SUS304 steel samples fabricated by a hot isostatic press (HIP) at 1050°C was evaluated using the electromagnetic acoustic resonance (EMAR), noise energy and ultrasonic spectroscopy (first moment) methods. The coefficients of attenuation of 1.1 to 5.4 MHz electromagnetically excited acoustic waves in the samples were investigated. By reducing diffraction loss and the loss to the electromagnetic acoustic

Hidetaka Nishida; Hiroshi Yamaguchi; Masashi Yoshida

2001-01-01

366

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

Microsoft Academic Search

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

Bjarne Madsen Härdig; Jonas Carlson; Anders Roijer

2008-01-01

367

Retardation Measurements of Infrared PVA Wave plate  

NASA Astrophysics Data System (ADS)

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

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

368

The MOSDEF Survey: Measurements of Balmer Decrements and the Dust Attenuation Curve at Redshifts z~1.4-2.6  

E-print Network

We present results on the dust attenuation curve of z~2 galaxies using early observations from the MOSFIRE Deep Evolution Field (MOSDEF) survey. Our sample consists of 224 star-forming galaxies with nebular spectroscopic redshifts in the range z= 1.36-2.59 and high S/N measurements of, or upper limits on, the H-alpha and H-beta emission lines obtained with Keck/MOSFIRE. We construct composite SEDs of galaxies in bins of specific SFR and Balmer optical depth in order to directly constrain the dust attenuation curve from the UV through near-IR for typical star-forming galaxies at high redshift. Our results imply an attenuation curve that is very similar to the SMC extinction curve at wavelengths redward of 2500 Angstroms. At shorter wavelengths, the shape of the curve is identical to that of the Calzetti relation, but with a lower normalization (R_V). Hence, the new attenuation curve results in SFRs that are ~20% lower, and log stellar masses that are 0.16 dex lower, than those obtained with the Calzetti attenu...

Reddy, Naveen A; Shapley, Alice E; Freeman, William R; Siana, Brian; Coil, Alison L; Mobasher, Bahram; Price, Sedona H; Sanders, Ryan L; Shivaei, Irene

2015-01-01

369

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

PubMed

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

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

2015-05-01

370

Three-wave electron vortex lattices for measuring nanofields.  

PubMed

It is demonstrated how an electron-optical arrangement consisting of two electron biprisms can be used to generate three-wave vortex lattices with effective lattice spacings between 0.1 and 1 nm. The presence of vortices in these lattices was verified by using a third biprism to perform direct phase measurements via off-axis electron holography. The use of three-wave lattices for nanoscale electromagnetic field measurements via vortex interferometry is discussed, including the accuracy of vortex position measurements and the interpretation of three-wave vortex lattices in the presence of partial spatial coherence. PMID:25222141

Dwyer, C; Boothroyd, C B; Chang, S L Y; Dunin-Borkowski, R E

2015-01-01

371

Volumetric measurements of a spatially growing dust acoustic wave  

SciTech Connect

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.

Williams, Jeremiah D. [Physics Department, Wittenberg University, Springfield, Ohio 45504 (United States)

2012-11-15

372

MEASUREMENT OF THE EXPANSION RATE OF THE UNIVERSE FROM {gamma}-RAY ATTENUATION  

SciTech Connect

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.

Dominguez, Alberto [Department of Physics and Astronomy, University of California, Riverside, CA 92521 (United States); Prada, Francisco, E-mail: albertod@ucr.edu [Campus of International Excellence UAM-CSIC, Cantoblanco, E-28049 Madrid (Spain)

2013-07-10

373

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

374

Visualisation and Measurement of Internal Waves by Synthetic Schlieren\\  

Microsoft Academic Search

We present measurements of the density and velocity fields produced when an oscillating circular cylinder... In this paper we examine the structure and amplitude of internal gravity waves generated by a cylinder oscillating vertically at different frequencies and amplitudes, paying particular attention to the role of viscosity in determining the evolution of the waves. In qualitative agreement with theory, it

Bruce R. Sutherland; Stuart B. Dalziel; Graham O. Hughes; P. F. Linden

1999-01-01

375

Measurement of ocean wave spectra using polarimetric AIRSAR data  

NASA Technical Reports Server (NTRS)

A polarimetric technique for improving the visibility of waves, whose propagation direction has an azimuthal component, in RAR (real aperture radar) or SAR (synthetic aperture radar) images has been investigated. The technique shows promise as a means of producing more accurate 2-D polarimetric RAR ocean wave spectra. For SAR applications domination by velocity-bunching effects may limit its usefulness to long ocean swell. A modification of this technique involving measurement of polarization signature modulations in the image is useful for detecting waves in SAR images and, potentially, estimating RMS wave slopes.

Schuler, D. L.

1993-01-01

376

Tree attenuation at 869 MHz derived from remotely piloted aircraft measurements  

NASA Technical Reports Server (NTRS)

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.

Vogel, Wolfhard J.; Goldhirsh, Julius

1986-01-01

377

Attenuation length measurements of a liquid scintillator with LabVIEW and reliability evaluation of the device  

NASA Astrophysics Data System (ADS)

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.

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

378

Direct Measurement of Wave Kernels in Time-Distance Helioseismology  

NASA Technical Reports Server (NTRS)

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.

Duvall, T. L., Jr.

2006-01-01

379

The effect of fracture and fracture fixation on ultrasonic velocity and attenuation  

Microsoft Academic Search

Measurement of the velocity of propagation and attenuation of ultrasound (200 kHz) is believed to be a useful non-invasive technique for assessing the mechanical properties of bone. A new method for the determination of ultrasound velocity and attenuation of longitudinal waves in cortical bone was used in vivo and in situ on intact and fractured human tibiae. The measured ultrasound

J Saulgozis; I Pontaga; G Lowet; G Van der Perre

1996-01-01

380

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

Microsoft Academic Search

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

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

2007-01-01

381

An inexpensive instrument for measuring wave exposure and water velocity  

USGS Publications Warehouse

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.

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

2011-01-01

382

Measurements of Turbulence Attenuation by a Dilute Dispersion of Solid Particles in Homogeneous Isotropic Turbulence  

NASA Technical Reports Server (NTRS)

This research addresses turbulent gas flows laden with fine solid particles at sufficiently large mass loading that strong two-way coupling occurs. By two-way coupling we mean that the particle motion is governed largely by the flow, while the particles affect the gas-phase mean flow and the turbulence properties. Our main interest is in understanding how the particles affect the turbulence. Computational techniques have been developed which can accurately predict flows carrying particles that are much smaller than the smallest scales of turbulence. Also, advanced computational techniques and burgeoning computer resources make it feasible to fully resolve very large particles moving through turbulent flows. However, flows with particle diameters of the same order as the Kolmogorov scale of the turbulence are notoriously difficult to predict. Some simple flows show strong turbulence attenuation with reductions in the turbulent kinetic energy by up to a factor of five. On the other hand, some seemingly similar flows show almost no modification. No model has been proposed that allows prediction of when the strong attenuation will occur. Unfortunately, many technological and natural two-phase flows fall into this regime, so there is a strong need for new physical understanding and modeling capability. Our objective is to study the simplest possible turbulent particle-laden flow, namely homogeneous, isotropic turbulence with a uniform dispersion of monodisperse particles. We chose such a simple flow for two reasons. First, the simplicity allows us to probe the interaction in more detail and offers analytical simplicity in interpreting the results. Secondly, this flow can be addressed by numerical simulation, and many research groups are already working on calculating the flow. Our detailed data can help guide some of these efforts. By using microgravity, we can further simplify the flow to the case of no mean velocity for either the turbulence or the particles. In fact the addition of gravity as a variable parameter may help us to better understand the physics of turbulence attenuation. The experiments are conducted in a turbulence chamber capable of producing stationary or decaying isotropic turbulence with nearly zero mean flow and Taylor microscale Reynolds numbers up to nearly 500. The chamber is a 410 mm cubic box with the corners cut off to make it approximately spherical. Synthetic jet turbulence generators are mounted in each of the eight corners of the box. Each generator consists of a loudspeaker forcing a plenum and producing a pulsed jet through a 20 mm diameter orifice. These synthetic jets are directed into ejector tubes pointing towards the chamber center. The ejector tubes increase the jet mass flow and decrease the velocity. The jets then pass through a turbulence grid. Each of the eight loudspeakers is forced with a random phase and frequency. The resulting turbulence is highly Isotropic and matches typical behavior of grid turbulence. Measurements of both phases are acquired using particle image velocimetry (PIV). The gas is seeded with approximately 1 micron diameter seeding particles while the solid phase is typically 150 micron diameter spherical glass particles. A double-pulsed YAG laser and a Kodak ES-1.0 10-bit PIV camera provide the PIV images. Custom software is used to separate the images into individual images containing either gas-phase tracers or large particles. Modern high-resolution PIV algorithms are then used to calculate the velocity field. A large set of image pairs are acquired for each case, then the results are averaged both spatially and over the ensemble of acquired images. The entire apparatus is mounted in two racks which are carried aboard NASA's KC-135 Flying Microgravity Laboratory. The rack containing the turbulence chamber, the laser head, and the camera floats freely in the airplane cabin (constrained by competent NASA personnel) to minimize g-jitter.

Eaton, John; Hwang, Wontae; Cabral, Patrick

2002-01-01

383

Measurements of Turbulence Attenuation by a Dilute Dispersion of Solid Particles in Homogeneous Isotropic Turbulence  

NASA Astrophysics Data System (ADS)

This research addresses turbulent gas flows laden with fine solid particles at sufficiently large mass loading that strong two-way coupling occurs. By two-way coupling we mean that the particle motion is governed largely by the flow, while the particles affect the gas-phase mean flow and the turbulence properties. Our main interest is in understanding how the particles affect the turbulence. Computational techniques have been developed which can accurately predict flows carrying particles that are much smaller than the smallest scales of turbulence. Also, advanced computational techniques and burgeoning computer resources make it feasible to fully resolve very large particles moving through turbulent flows. However, flows with particle diameters of the same order as the Kolmogorov scale of the turbulence are notoriously difficult to predict. Some simple flows show strong turbulence attenuation with reductions in the turbulent kinetic energy by up to a factor of five. On the other hand, some seemingly similar flows show almost no modification. No model has been proposed that allows prediction of when the strong attenuation will occur. Unfortunately, many technological and natural two-phase flows fall into this regime, so there is a strong need for new physical understanding and modeling capability. Our objective is to study the simplest possible turbulent particle-laden flow, namely homogeneous, isotropic turbulence with a uniform dispersion of monodisperse particles. We chose such a simple flow for two reasons. First, the simplicity allows us to probe the interaction in more detail and offers analytical simplicity in interpreting the results. Secondly, this flow can be addressed by numerical simulation, and many research groups are already working on calculating the flow. Our detailed data can help guide some of these efforts. By using microgravity, we can further simplify the flow to the case of no mean velocity for either the turbulence or the particles. In fact the addition of gravity as a variable parameter may help us to better understand the physics of turbulence attenuation. The experiments are conducted in a turbulence chamber capable of producing stationary or decaying isotropic turbulence with nearly zero mean flow and Taylor microscale Reynolds numbers up to nearly 500. The chamber is a 410 mm cubic box with the corners cut off to make it approximately spherical. Synthetic jet turbulence generators are mounted in each of the eight corners of the box. Each generator consists of a loudspeaker forcing a plenum and producing a pulsed jet through a 20 mm diameter orifice. These synthetic jets are directed into ejector tubes pointing towards the chamber center. The ejector tubes increase the jet mass flow and decrease the velocity. The jets then pass through a turbulence grid. Each of the eight loudspeakers is forced with a random phase and frequency. The resulting turbulence is highly Isotropic and matches typical behavior of grid turbulence. Measurements of both phases are acquired using particle image velocimetry (PIV). The gas is seeded with approximately 1 micron diameter seeding particles while the solid phase is typically 150 micron diameter spherical glass particles. A double-pulsed YAG laser and a Kodak ES-1.0 10-bit PIV camera provide the PIV images. Custom software is used to separate the images into individual images containing either gas-phase tracers or large particles. Modern high-resolution PIV algorithms are then used to calculate the velocity field. A large set of image pairs are acquired for each case, then the results are averaged both spatially and over the ensemble of acquired images. The entire apparatus is mounted in two racks which are carried aboard NASA's KC-135 Flying Microgravity Laboratory. The rack containing the turbulence chamber, the laser head, and the camera floats freely in the airplane cabin (constrained by competent NASA personnel) to minimize g-jitter.

Eaton, John; Hwang, Wontae; Cabral, Patrick

2002-11-01

384

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

Microsoft Academic Search

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

David C. Adams; Eugene D. Humphreys

2010-01-01

385

Electron Bernstein Wave Coupling and Emission Measurements on NSTX  

Microsoft Academic Search

Electron Bernstein waves (EBWs) offer the potential for Te(R,t) measurements and local current drive in overdense NSTX plasmas. However, these applications require resilient and efficient coupling between EBWs and electromagnetic waves outside the plasma. Two new remotely steered, obliquely viewing, quad-ridged horn antennas connected to absolutely calibrated dual-channel radiometers have simultaneously measured 8-18 GHz (fundamental) and 18-40 GHz (second and

G. Taylor; S. J. Diem; J. B. Caughman; P. C. Efthimion; R. W. Harvey; B. P. Leblanc; C. K. Phillips; J. Preinhaelter; J. Urban; J. B. Wilgen

2006-01-01

386

Measurement of atomic number and mass attenuation coefficient in magnesium ferrite  

Microsoft Academic Search

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

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

2007-01-01

387

Measurement of skeletal muscle radiation attenuation and basis of its biological variation  

PubMed Central

Skeletal muscle contains intramyocellular lipid droplets within the cytoplasm of myocytes as well as intermuscular adipocytes. These depots exhibit physiological and pathological variation which has been revealed with the advent of diagnostic imaging approaches: magnetic resonance (MR) imaging, MR spectroscopy and computed tomography (CT). CT uses computer-processed X-rays and is now being applied in muscle physiology research. The purpose of this review is to present CT methodologies and summarize factors that influence muscle radiation attenuation, a parameter which is inversely related to muscle fat content. Pre-defined radiation attenuation ranges are used to demarcate intermuscular adipose tissue [from ?190 to ?30 Hounsfield units (HU)] and muscle (?29 HU to +150 HU). Within the latter range, the mean muscle radiation attenuation [muscle (radio) density] is reported. Inconsistent criteria for the upper and lower HU cut-offs used to characterize muscle attenuation limit comparisons between investigations. This area of research would benefit from standardized criteria for reporting muscle attenuation. Available evidence suggests that muscle attenuation is plastic with physiological variation induced by the process of ageing, as well as by aerobic training, which probably reflects accumulation of lipids to fuel aerobic work. Pathological variation in muscle attenuation reflects excess fat deposition in the tissue and is observed in people with obesity, diabetes type II, myositis, osteoarthritis, spinal stenosis and cancer. A poor prognosis and different types of morbidity are predicted by the presence of reduced mean muscle attenuation values in patients with these conditions; however, the biological features of muscle with these characteristics require further investigation. PMID:24393306

Aubrey, J; Esfandiari, N; Baracos, V E; Buteau, F A; Frenette, J; Putman, C T; Mazurak, V C

2014-01-01

388

Simultaneous synthetic schlieren and PIV measurements for internal solitary waves  

Microsoft Academic Search

Large-amplitude internal solitary waves in a stratification comprising a thick, lower, homogeneous layer separated from a thin, upper, homogeneous layer by a broad gradient region are studied using simultaneous measurements of the density and velocity fields. Density field measurements are achieved through synthetic schlieren, operating in an absolute mode to allow efficient and accurate measurements of density in systems with

Stuart B Dalziel; Magda Carr; J Kristian Sveen; Peter A Davies

2007-01-01

389

Atmospheric Peroxy Radical Measurements by Chemical Amplification - Cavity Attenuated Phase Shift Spectroscopy  

NASA Astrophysics Data System (ADS)

We present a new chemical amplifier for the detection of peroxy radicals using Cavity Attenuated Phase Shift spectroscopy (CAPS) detection of NO2. The amplification scheme is similar to other chemical amplifiers and involves addition of CO (8%) and NO (3 ppm) to air sampled in a PFA tube. The chain length is quantified by amplification of a known concentration of methyl peroxy radicals (CH3O2) and peroxyacetyl radicals (CH3COO2) sampled by the instrument's reactor. The CH3O2 and CH3COO2 radicals are produced by photolysis of acetone at 254 nm and quantified by conversion to NO2 by reaction with excess NO. The chain length (CL) in dry air is over 200 and constant at RO2 concentrations under 500 ppt. The CL decreases by 55% at a relative humidity of 50%. A 0.95 cm (3/8') ID PFA tube, a 0.32 cm (1/8' ID) PFA tube, and a 0.48 cm ID quartz reactor give near-identical chain lengths and RH dependence, demonstrating the small importance of wall reactions (for clean tubing) as radical termination steps. The instrument comprises two independent inlets and CAPS detectors, allowing for simultaneous measurements in ROx mode (= NO2 + O3 + RO2 + HO2) and Ox mode (= NO2 + O3) thereby greatly reducing the effect of variations in background [Ox]. The 1? precision of the instrument at constant background [Ox] and 0% relative humidity is 0.2 ppt ROx with 100 second averaging and increases to 0.3 ppt at an RH of 50%. The absolute uncertainty of the measurements is estimated as 20% and is affected by the accuracy of the NO2 calibration, the precision of the CAPS when calibrating at low RO2 concentrations, and the uncertainty in the photolysis quantum yield for the CH3CO + CH3 channel of acetone photolysis.

Wood, E. C.; Charest, J. R.

2013-12-01

390

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

NASA Astrophysics Data System (ADS)

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

Muggleton, J. M.; Yan, J.

2013-03-01

391

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

USGS Publications Warehouse

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.

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

2002-01-01

392

Precipitation-attenuation studies based on measurements of ATS-6 20/30-GHz beacon signals at Clarksburg, Maryland  

NASA Technical Reports Server (NTRS)

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.

Fang, D. J.; Harris, J. M.

1976-01-01

393

Modelling ultrasound guided wave propagation for plate thickness measurement  

NASA Astrophysics Data System (ADS)

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.

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

2014-03-01

394

Dielectric measurements and radar attenuation estimation of ice/basalt sand mixtures as martian Polar Caps analogues  

NASA Astrophysics Data System (ADS)

The nature of the materials underlying the superficial deposits of Mars can be inferred, applying an inversion algorithm, from the data acquired by the orbiting HF radars MARSIS and SHARAD. This approach requires the knowledge of the electromagnetic properties of the shallow deposits and an accurate evaluation of the signal attenuation. The present work is focused on the determination of the dielectric parameters of several geo-materials. We performed the measurements of the complex permittivity, in a wide range of temperature (150-250 K) and frequency (20 Hz-1 MHz), on pure water ice, dry basalt sand and ice/basalt mixtures with different sand volume fractions. The data are presented in terms of attenuation as a function of basalt volume fraction, frequency and temperature, and discussed in terms of extrapolation to MARSIS and SHARAD frequency bands. The results show that, besides the expected dependence of the attenuation from temperature, the presence of the solid inclusions in the ice strongly affects the behaviour of the attenuation versus frequency.

Mattei, E.; Lauro, S. E.; Vannaroni, G.; Cosciotti, B.; Bella, F.; Pettinelli, E.

2014-02-01

395

Mechanical Loss Measurements of Coated Substrates for Gravitational Wave Interferometry  

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

396

Physical measurements of breaking wave impact on a floating wave energy converter  

NASA Astrophysics Data System (ADS)

Marine energy converter must both efficiently extract energy in small to moderate seas and also successfully survive storms and potential collisions. Extreme loads on devices are therefore an important consideration in their design process. X-MED is a SuperGen UKCMER project and is a collaboration between the Universities of Manchester, Edinburgh and Plymouth and the Scottish Association for Marine Sciences. Its objective is to extend the knowledge of extreme loads due to waves, currents, flotsam and mammal impacts. Plymouth Universities contribution to the X-MED project involves measuring the loading and response of a taut moored floating body due to steep and breaking wave impacts, in both long crested and directional sea states. These measurements are then to be reproduced in STAR-CCM+, a commercial volume of fluid CFD solver, so as to develop techniques to predict the wave loading on wave energy converters. The measurements presented here were conducted in Plymouth Universities newly opened COAST laboratories 35m long, 15.5m wide and 3m deep ocean basin. A 0.5m diameter taut moored hemispherical buoy was used to represent a floating wave energy device or support structure. The changes in the buoys 6 degree of freedom motion and mooring loads are presented due to focused breaking wave impacts, with the breaking point of the wave changed relative to the buoy.

Hann, Martyn R.; Greaves, Deborah M.; Raby, Alison

2013-04-01

397

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

NASA Astrophysics Data System (ADS)

In the present study we introduce an innovative method for the measurement of impact-induced pressure waves within geological materials. Impact experiments on dry and water-saturated sandstone targets were conducted at a velocity of 4600 m/s using 12 mm steel projectiles to investigate amplitudes, decay behavior, and speed of the waves propagating through the target material. For this purpose a special kind of piezoresistive sensor capable of recording transient stress pulses within solid brittle materials was developed and calibrated using a Split-Hopkinson pressure bar. Experimental impact parameters (projectile size and speed) were kept constant and yielded reproducible signal curves in terms of rise time and peak amplitudes. Pressure amplitudes decreased by 3 orders of magnitude within the first 250 mm (i.e., 42 projectile radii). The attenuation for water-saturated sandstone is higher compared to dry sandstone which is attributed to dissipation effects caused by relative motion between bulk material and interstitial water. The proportion of the impact energy radiated as seismic energy (seismic efficiency) is in the order of 10-3. The present study shows the feasibility of real-time measurements of waves caused by hypervelocity impacts on geological materials. Experiments of this kind lead to a better understanding of the processes in the crater subsurface during a hypervelocity impact.

Hoerth, Tobias; Schäfer, Frank; Nau, Siegfried; Kuder, Jürgen; Poelchau, Michael H.; Thoma, Klaus; Kenkmann, Thomas

2014-10-01

398

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

Microsoft Academic Search

For the simulation of therapeutic ultrasound applications, a method including frequency-dependent attenuation effects directly in the time domain is highly desirable. This paper describes an efficient numerical time-domain implementation of the power-law attenuation model presented by Szabo [Szabo, J. Acoust. Soc. Am. 96, 491-500 (1994)]. Simulations of therapeutic ultrasound applications are feasible in conjunction with a previously presented finite differences

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

2004-01-01

399

Measurement of atomic number and mass attenuation coefficient in magnesium ferrite  

Microsoft Academic Search

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

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

2007-01-01

400

Monitoring the wave function by time continuous position measurement  

E-print Network

We consider a single copy of a quantum particle moving in a potential and show that it is possible to monitor its complete wave function by only continuously measuring its position. While we assume that the potential is known, no information is available about its state initially. In order to monitor the wave function, an estimate of the wave function is propagated due to the influence of the potential and continuously updated according to the results of the position measurement. We demonstrate by numerical simulations that the estimation reaches arbitrary values of accuracy below 100 percent within a finite time period for the potentials we study. In this way our method grants, a certain time after the beginning of the measurement, an accurate real-time record of the state evolution including the influence of the continuous measurement. Moreover, it is robust against sudden perturbations of the system as for example random momentum kicks from environmental particles, provided they occur not too frequently.

Konrad, Thomas; Petruccione, Francesco; Diósi, Lajos

2009-01-01

401

Monitoring the wave function by time continuous position measurement  

E-print Network

We consider a single copy of a quantum particle moving in a potential and show that it is possible to monitor its complete wave function by only continuously measuring its position. While we assume that the potential is known, no information is available about its state initially. In order to monitor the wave function, an estimate of the wave function is propagated due to the influence of the potential and continuously updated according to the results of the position measurement. We demonstrate by numerical simulations that the estimation reaches arbitrary values of accuracy below 100 percent within a finite time period for the potentials we study. In this way our method grants, a certain time after the beginning of the measurement, an accurate real-time record of the state evolution including the influence of the continuous measurement. Moreover, it is robust against sudden perturbations of the system as for example random momentum kicks from environmental particles, provided they occur not too frequently.

Thomas Konrad; Andreas Rothe; Francesco Petruccione; Lajos Diósi

2009-02-13

402

Measurement of Light-Cone Wave Functions by Diffractive Dissociation  

E-print Network

Diffractive dissociation of particles can be used to study their light-cone wave function. Results from Fermilab experiment E791 for diffractive dissociation of 500 GeV/c $\\pi^-$ mesons into di-jets are presented. The results show that the $|q\\bar {q}>$ light-cone asymptotic wave function describes the data well for $Q^2 \\sim 10 ~{\\rm (GeV/c)^2}$ or more. Evidence for color transparency comes from a measurement of the $A$-dependence of the yield of the diffractive di-jets. It is proposed to carry out similar studies for the light-cone wave function of the photon.

Daniel Ashery

2000-08-22

403

Measurements and global models of surface wave propagation  

Microsoft Academic Search

A new technique for making single-station phase velocity measurements is developed and applied to a large number of globally recorded Rayleigh and Love waves in the period range 35-150 s. The method is based on phase-matched filter theory and iteratively suppresses the effect of interfering overtones by minimizing residual dispersion. The model surface wave signal is described by its amplitude

Göran Ekström; Jeroen Tromp; Erik W. F. Larson

1997-01-01

404

Measurements of Nonlinearities in a Travelling-wave Tube  

Microsoft Academic Search

Measurements of the non-linear amplitude distortion and phase shift in a travelling-wave tube (TWT) are reported. The test object is a commercial 2 w, S-band, O-type TWT with a helical slow-wave structure.An extensive set of output amplitude and phase data was recorded for a wide range of input powers and helix voltages. The results are in good qualitative agreement with

J. I. LINDSTRÖM

1966-01-01

405

Measurements of a saturated range in ocean wave spectra  

Microsoft Academic Search

Wavestaff measurements made in the Gulf of Mexico and Waverider measurements from the Baltimore Canyon area have been used to study the form of ocean wave spectra at high frequencies. The observations are statistically consistent with the idea that the tail of the spectrum is in equilibrium with the local wind. Analysis showed that the spectral range between the mean

George Z. Forristall

1981-01-01

406

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

PubMed

Groundwater and sub-surface contamination by Light Non-Aqueous Phase Liquids (LNAPLs) is one of the industrial world's most pressing environmental issues and a thorough understanding of the hydrological, physical and bio-chemical properties of the sub-surface is key to determining the spatial and temporal development of any particular contamination event. Non-invasive geophysical techniques (such as electrical resistivity, electromagnetic conductivity, Ground-Penetrating Radar, etc.) have proved to be successful sub-surface investigation and characterisation tools with Ground-Penetrating Radar (GPR) being particularly popular. Recent studies have shown that the spatial/temporal variation in GPR signal attenuation can provide important information on the electrical properties of the sub-surface materials that, in turn, can be used to assess the physical and hydrological nature of the pore fluids and associated contaminants. Unfortunately, a high percentage of current LNAPL-related GPR studies focus on contaminant mapping only, with little emphasis being placed on characterising the hydrological properties (e.g., determining contaminant saturation index, etc.). By comparing laboratory-based, dielectric measurements of LNAPL contaminated materials with the GPR signal attenuation observed in both contaminated and 'clean' areas of an LNAPL contaminated site, new insights have been gained into the nature of contaminant distribution/saturation and the likely signal attenuation mechanisms. The results show that, despite some practical limitations of the analysis technique, meaningful hydrological interpretations can be obtained on the contaminant properties, saturation index and bio-degradation processes. A generalised attenuation/saturation model has been developed that describes the physical and attenuation enhancement characteristics of the contaminated areas and reveals that the most significant attenuation is related to smeared zone surrounding the seasonally changing water table interface. It is envisaged that the model will provide a basis for the interpretation of GPR data from analogous LNAPL contaminated sites and provide investigators with an appreciation of the merits and limitations of GPR-based, attenuation analysis techniques for hydrological applications. PMID:17601633

Cassidy, Nigel J

2007-10-30

407

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

Microsoft Academic Search

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.

Subha Maruvada

2000-01-01

408

Imaging subtle microstructural variations in ceramics with precision ultrasonic velocity and attenuation measurements  

NASA Technical Reports Server (NTRS)

Acoustic images of a silicon carbide ceramic disk were obtained using a precision scanning contact pulse echo technique. Phase and cross-correlation velocity, and attenuation maps were used to form color images of microstructural variations. These acoustic images reveal microstructural variations not observable with X-ray radiography.

Generazio, Edward R.; Roth, Don J.; Baaklini, George Y.

1987-01-01

409

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

Microsoft Academic Search

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

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

2000-01-01

410

Measurement of pulmonary edema in intact dogs by transthoracic gamma-ray attenuation  

Microsoft Academic Search

Attenuation of the 122 keV gamma rays of cobalt-57 across the thorax of anesthetized dogs was evaluated as a method for following the time course of lung water changes in acute pulmonary edema induced by either increased microvascular permeability or increased microvascular hydrostatic pressure. The gamma rays traversed the thorax centered on the seventh rib laterally where the lung mass

D. S. Simon; J. F. Murray; N. C. Staub

1979-01-01

411

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

NASA Astrophysics Data System (ADS)

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

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

2011-01-01

412

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

NASA Technical Reports Server (NTRS)

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 performance curves obtained by radar and radiometry are compared with each other demonstrating the utility of radar methods. Results of a multi-year experiment to test, refine, and establish accuracies of radar methods for arriving at estimates of rain attenuation along an Earth-satellite path are discussed. Comparisons of measured and radar estimated fade events are presented and found to be good. Comparisons of cumulative fade distributions show agreement to be excellent giving an rms deviation of 1 dB.

Goldhirsh, J.

1980-01-01

413

Measured and calculated acoustic attenuation rates of tuned resonator arrays for two surface impedance distribution models with flow  

NASA Technical Reports Server (NTRS)

An experiment was performed to validate two analytical models for predicting low frequency attenuation of duct liner configurations built from an array of seven resonators that could be individually tuned via adjustable cavity depths. These analytical models had previously been developed for high frequency aero-engine inlet duct liner design. In the low frequency application, the liner surface impedance distribution is unavoidably spatially varying by virtue of available fabrication techniques. The characteristic length of this spatial variation may be a significant fraction of the acoustic wavelength. Comparison of measured and predicted attenuation rates and transmission losses for both modal decomposition and finite element propagation models were in good to excellent agreement for a test frequency range that included the first and second cavity resonance frequencies. This was true for either of two surface impedance distribution modeling procedures used to simplify the impedance boundary conditions. In the presence of mean flow, measurements revealed a fine scale structure of acoustic hot spots in the attenuation and phase profiles. These details were accurately predicted by the finite element model. Since no impedance changes due to mean flow were assumed, it is concluded that this fine scale structure was due to convective effects of the mean flow interacting with the surface impedance nonuniformities.

Parrott, Tony L.; Abrahamson, A. Louis; Jones, Michael G.

1988-01-01

414

Simultaneous measurement of unfrozen water content and ice content in frozen soil using gamma ray attenuation and TDR  

NASA Astrophysics Data System (ADS)

The freezing temperature of water in soil is not constant but varies over a range determined by soil texture. Consequently, the amounts of unfrozen water and ice change with temperature in frozen soil, which in turn affects hydraulic, thermal, and mechanical properties of frozen soil. In this paper, an Am-241 gamma ray source and time-domain reflectometry (TDR) were combined to measure unfrozen water content and ice content in frozen soil simultaneously. The gamma ray attenuation was used to determine total water content. The TDR was used to determine the dielectric constant of the frozen soil. Based on a four-phase mixing model, the amount of unfrozen water content in the frozen soil could be determined. The ice content was inferred by the difference between total water content and unfrozen water content. The gamma ray attenuation and the TDR were both calibrated by a gravimetric method. Water contents measured by gamma ray attenuation and TDR in an unfrozen silt column under infiltration were compared and showed that the two methods have the same accuracy and response to changes of water content. Unidirectional column freezing experiments were performed to apply the combined method of gamma ray attenuation and TDR for measuring unfrozen water content and ice content. The measurement error of the gamma ray attenuation and TDR was around 0.02 and 0.01 m3/m3, respectively. The overestimation of unfrozen water in frozen soil by TDR alone was quantified and found to depend on the amount of ice content. The higher the ice content, the larger the overestimation. The study confirmed that the combined method could accurately determine unfrozen water content and ice content in frozen soil. The results of soil column freezing experiments indicate that total water content distribution is affected by available pore space and the freezing front advance rate. It was found that there is similarity between the soil water characteristic and the soil freezing characteristic of variably saturated soil. Unfrozen water content is independent of total water content and affected only by temperature when the freezing point is reached.

Zhou, Xiaohai; Zhou, Jian; Kinzelbach, Wolfgang; Stauffer, Fritz

2014-12-01

415

Feasibility of hydromagnetic wave measurements on space shuttle  

NASA Technical Reports Server (NTRS)

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.

Mcpherron, R. L.

1974-01-01

416

Measurement of Moving Speed Using a Leaky Lamb Wave Device  

NASA Astrophysics Data System (ADS)

A technique for measuring the moving speed of a tested object is described using a leaky Lamb wave device composed of two interdigital transducers (IDTs). The IDT on a thin piezoelectric ceramic plate radiates as an ultrasound beam into a liquid and also operates as a detector of the ultrasound signal reflected from a moving medium, at a liquid-solid interface. The delayed output has a frequency shift via a Doppler effect, corresponding to the moving speed of the reflection object. Basic performances of the leaky Lamb wave device and the measured results of the moving speed of a metal disk are presented.

Fujita, Takeshi; Toda, Kohji

2001-09-01

417

Evaluation of Multilayered Pavement Structures from Measurements of Surface Waves  

NASA Astrophysics Data System (ADS)

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.

Ryden, Nils; Lowe, Michael J. S.; Cawley, Peter; Park, Choon B.

2006-03-01

418

Ultrasonic metal sheet thickness measurement without prior wave speed calibration  

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

419

Subwavelength position measurements with running-wave driving fields  

SciTech Connect

Subwavelength position measurement of quantum particles is discussed. Our setup is based on a closed-loop driving-field configuration, which enforces a sensitivity of the particle dynamics to the phases of the applied fields. Thus, running wave fields are sufficient, avoiding limitations associated with standing-wave-based localization schemes. Reversing the directions of the driving laser fields switches between different magnification levels for the position determination. This allows us to optimize the localization, and at the same time eliminates the need for additional classical measurements common to all previous localization schemes based on spatial periodicity.

Evers, Joerg [Max-Planck-Institut fuer Kernphysik, Saupfercheckweg 1, D-69117 Heidelberg (Germany); Qamar, Sajid [Max-Planck-Institut fuer Kernphysik, Saupfercheckweg 1, D-69117 Heidelberg (Germany); Centre for Quantum Physics, COMSATS Institute of Information Technology, Islamabad (Pakistan)

2011-08-15

420

Measurement of viscosity of highly viscous non-Newtonian fluids by means of ultrasonic guided waves.  

PubMed

In order to perform monitoring of the polymerisation process, it is necessary to measure viscosity. However, in the case of non-Newtonian highly viscous fluids, viscosity starts to be dependent on the vibration or rotation frequency of the sensing element. Also, the sensing element must possess a sufficient mechanical strength. Some of these problems may be solved applying ultrasonic measurement methods, however until now most of the known investigations were devoted to measurements of relatively low viscosities (up to a few Pas) of Newtonian liquids. The objective of the presented work is to develop ultrasonic method for measurement of viscosity of high viscous substances during manufacturing process in extreme conditions. For this purpose the method based on application of guided Lamb waves possessing the predominant component of in-plane displacements (the S0 and the SH0 modes) and propagating in an aluminium planar waveguide immersed in a viscous liquid has been investigated. The simulations indicated that in the selected modes mainly in-plane displacements are dominating, therefore the attenuation of those modes propagating in a planar waveguide immersed in a viscous liquid is mainly caused by viscosity of the liquid. The simulation results were confirmed by experiments. All measurements were performed in the viscosity standard Cannon N2700000. Measurements with the S0 wave mode were performed at the frequency of 500kHz. The SH0 wave mode was exited and used for measurements at the frequency of 580kHz. It was demonstrated that by selecting the particular mode of guided waves (S0 or SH0), the operation frequency and dimensions of the aluminium waveguide it is possible to get the necessary viscosity measurement range and sensitivity. The experiments also revealed that the measured dynamic viscosity is strongly frequency dependent and as a characteristic feature of non-Newtonian liquids is much lower than indicated by the standards. Therefore, in order to get the absolute values of viscosity in this case an additional calibration procedure is required. Feasibility to measure variations of high dynamic viscosities in the range of (20-25,000) Pas was theoretically and experimentally proved. The proposed solution differently from the known methods in principle is more mechanically robust and better fitted for measurements in extreme conditions. PMID:24491274

Kazys, Rymantas; Mazeika, Liudas; Sliteris, Reimondas; Raisutis, Renaldas

2014-04-01

421

Spatiotemporal measurement of surfactant distribution on gravity-capillary waves  

E-print Network

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. Here, 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 moir\\'e-imaging, and the density field of the surfactant via the fluorescence of NBD-tagged phosphatidylcholine, a lipid. Through phase-averaging stroboscopically-acquired images of the density field, we determine that the surfactant accumulates on the leading edge of the traveling menis...

Strickland, Stephen L; Daniels, Karen E

2015-01-01

422

Measurements of parallel electron velocity distributions using whistler wave absorption  

SciTech Connect

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.

Thuecks, D. J.; Skiff, F.; Kletzing, C. A. [Department of Physics and Astronomy, University of Iowa, 203 Van Allen Hall, Iowa City, Iowa 52242 (United States)

2012-08-15

423

Diffraction correction for precision surface acoustic wave velocity measurements  

NASA Astrophysics Data System (ADS)

Surface wave dispersion measurements can be used to nondestructively characterize shot-peened, laser shock-peened, burnished, and otherwise surface-treated specimens. In recent years, there have been numerous efforts to separate the contribution of surface roughness from those of near-surface material variations, such as residual stress, texture, and increased dislocation density. As the accuracy of the dispersion measurements was gradually increased using state-of-the-art laser-ultrasonic scanning and sophisticated digital signal processing methods, it was recognized that a perceivable dispersive effect, similar to the one found on rough shot-peened specimens, is exhibited by untreated smooth surfaces as well. This dispersion effect is on the order of 0.1%, that is significantly higher than the experimental error associated with the measurements and comparable to the expected velocity change produced by near-surface compressive residual stresses in metals below their yield point. This paper demonstrates that the cause of this apparent dispersion is the diffraction of the surface acoustic wave (SAW) as it travels over the surface of the specimen. The results suggest that a diffraction correction may be introduced to increase the accuracy of surface wave dispersion measurements. A simple diffraction correction model was developed for surface waves and this correction was subsequently validated by laser-interferometric velocity measurements on aluminum specimens. copyright 2002 Acoustical Society of America.

Ruiz M., Alberto; Nagy, Peter B.

2002-09-01

424

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

PubMed

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

Trunova, Valentina; Sidorina, Anna; Kriventsov, Vladimir

2014-10-17

425

Quantitative RNFL attenuation coefficient measurements by RPE-normalized OCT data  

NASA Astrophysics Data System (ADS)

We demonstrate significantly different scattering coefficients of the retinal nerve fiber layer (RNFL) between normal and glaucoma subjects. In clinical care, SD-OCT is routinely used to assess the RNFL thickness for glaucoma management. In this way, the full OCT data set is conveniently reduced to an easy to interpret output, matching results from older (non- OCT) instruments. However, OCT provides more data, such as the signal strength itself, which is due to backscattering in the retinal layers. For quantitative analysis, this signal should be normalized to adjust for local differences in the intensity of the beam that reaches the retina. In this paper, we introduce a model that relates the OCT signal to the attenuation coefficient of the tissue. The average RNFL signal (within an A-line) was then normalized based on the observed RPE signal, resulting in normalized RNFL attenuation coefficient maps. These maps showed local defects matching those found in thickness data. The average (normalized) RNFL attenuation coefficient of a fixed band around the optic nerve head was significantly lower in glaucomatous eyes than in normal eyes (3.0mm-1 vs. 4.9mm-1, P<0.01, Mann-Whitney test).

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

2012-03-01

426

Simultaneous Measurements of Fluorescence and Beam Attenuation: Instrument Characterization and Interpretation of Signals from Stratified Coastal Waters  

NASA Astrophysics Data System (ADS)

Hydrographic (conductivity, temperature, depth), optical (fluorescence and beam attenuation) and chemical (suspended particulate material, chlorophyll, gelbstoff) observations were made in sea lochs off the west coast of Scotland. A strong link was observed between hydrographic and optical layering in these waters. In order to assist the interpretation of the optical data, relationships between fluorescence and extracted chlorophyll and dry weight and beam attenuation were determined in the laboratory for five species of cultured phytoplankton and three types of inorganic particles. The inherent variation in these relationships from one class of material to another precluded the development of generally applicable algorithms for retrieving mass concentrations from 2-parameter optical data. However the instrument calibrations were used to partition a bivariate plot of fluorescence against attenuation on which the in situdata formed well defined clusters. This made it possible to deduce distribution profiles of phytoplankton and suspended sediment in the water column. The results indicate that even in the absence of absolute calibrations, multiparameter optical measurements can provide valuable information on fine-scale variations in seawater composition, and enhance the identification and discrimination of water masses in fjords and other highly structured water bodies.

McKee, D.; Cunningham, A.; Jones, K.

1999-01-01

427

Measurement of the normalized broadband ultrasound attenuation in trabecular bone by using a bidirectional transverse transmission technique  

NASA Astrophysics Data System (ADS)

A new method for measuring the normalized broadband ultrasound attenuation (nBUA) in trabecular bone by using a bidirectional transverse transmission technique was proposed and validated with measurements obtained by using the conventional transverse transmission technique. There was no significant difference between the nBUA measurements obtained for 14 bovine femoral trabecular bone samples by using the bidirectional and the conventional transverse transmission techniques. The nBUA measured by using the two transverse transmission techniques showed strong positive correlations of r = 0.87 to 0.88 with the apparent bone density, consistent with the behavior in human trabecular bone invitro. We expect that the new method can be usefully applied for improved accuracy and precision in clinical measurements.

Lee, Kang Il

2015-01-01

428

Study of atmospheric parameters measurements using MM-wave radar in synergy with LITE-2  

NASA Technical Reports Server (NTRS)

The Lidar In-Space Technology Experiment, (LITE), has been developed, designed, and built by NASA Langley Research Center, to be flown on the space shuttle 'Discovery' on September 9, 1994. Lidar, which stands for light detecting and ranging, is a radar system that uses short pulses of laser light instead of radio waves in the case of the common radar. This space-based lidar offers atmospheric measurements of stratospheric and tropospheric aerosols, the planetary boundary layer, cloud top heights, and atmospheric temperature and density in the 10-40 km altitude range. A study is being done on the use, advantages, and limitations of a millimeterwave radar to be utilized in synergy with the Lidar system, for the LITE-2 experiment to be flown on a future space shuttle mission. The lower atmospheric attenuation, compared to infrared and optical frequencies, permits the millimeter-wave signals to penetrate through the clouds and measure multi-layered clouds, cloud thickness, and cloud-base height. These measurements would provide a useful input to radiation computations used in the operational numerical weather prediction models, and for forecasting. High power levels, optimum modulation, data processing, and high antenna gain are used to increase the operating range, while space environment, radar tradeoffs, and power availability are considered. Preliminary, numerical calculations are made, using the specifications of an experimental system constructed at Georgia Tech. The noncoherent 94 GHz millimeter-wave radar system has a pulsed output with peak value of 1 kW. The backscatter cross section of the particles to be measured, that are present in the volume covered by the beam footprint, is also studied.

Andrawis, Madeleine Y.

1994-01-01