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1

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

NASA Astrophysics Data System (ADS)

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

Ozeren, Y.; Wren, D. G.

2010-12-01

2

Millimeter wave attenuation in moist air: Laboratory measurements and analysis  

NASA Astrophysics Data System (ADS)

Experiments were performed with a millimeter wave resonance-spectrometer capable of measuring absolute attenuation rates alpha (dB/km) by water vapor up to saturation pressures. Vapor (e) and air (p) pressures were varied at constant temperature and set frequency. Anomalous absorption behavior (i.e., high rates alpha, extreme temperature dependences, hystereses in pressure and temperature cycles) could be identified as being caused largely by instrumental condensation effects. Uncorrupted data at 138 GHz display, in addition to air-broadening, a strong self-broadening component. Based upon these results, a practical atmospheric millimeter wave propagation model was formulated that predicts attenuation, delay and noise properties of moist air over the frequency range of 1 to 1000 GHz and a height range of 0 to 100 km. The main spectroscopic data base consists of 48 O2 and 30 H2O local absorption lines complemented by continuum spectra for dry air and water vapor. Model input relies upon distributions of meteorological variables along an anticipated radio path. These variables are pressure, temperature, and relative humidity for moist air; suspended droplet concentration for haze, fog, cloud conditions; and a rain rate. In special cases, trace gas concentrations for ozone and carbon monoxide and the geomagnetic field strength can be added.

Liebe, H. J.

1984-03-01

3

Laboratory Measurements of Seismic Wave Attenuation in Natural Dunite  

NASA Astrophysics Data System (ADS)

In order to examine the processes responsible for the attenuation of seismic shear waves in the Earth's upper mantle, torsional forced-oscillation and microcreep experiements have been conducted on a natural dunite specimen at high temperatures to 1300° C and seismic frequencies from 0.001 to 1Hz. The dunite specimen (from Anita Bay, NZ) consists mainly of olivine (olivine 94%, orthopyroxene 5%, chromite 1%) of about 100 micron average grain size, but some olivine crystals of size up to several millimeters occur randomly. It also contains trace amounts of hydrous phases (loss on ignition is 0.2 wt.%). We measured both untreated and prefired (1200° C, 15hrs) specimens to assess the possible role of water on viscoelasticity. Water weakening of olivine aggregates in creep is currently interpreted in terms of increased concentrations of point defects, resulting in enhanced rates of ionic diffusion and dislocation climb. By analogy, it has been speculated that water significantly affects low-strain viscoelastic behavior as well. Our measurements suggest that shear modulus (G) and dissipation (Q-1) of the prefired specimen are generally larger than those of untreated one. In addition, frequency-dependence of G and Q-1 for the prefired specimen is substantially larger than those of the untreated one. Compared to calculations based on melt-free olivine polycrystals with an average grain size of 100 microns, the measured G and Q-1 are smaller than those calculated. On the other hand, the frequency-dependence of G and Q-1 for the untreated specimen is consistent with those of calculations, although frequency-dependence for the prefired specimen is generally larger relative to the calculations. No distinct dissipation peaks are observed related to the presence of melt, even though the untreated specimen has on the order of 1% melt, and the prefired one also contains a trace amount of melt. Because the measurements were mostly performed at temperatures higher than solidus temperatures, physical properties and distributions of melt may play major roles on interpreting the present experimental results. In the untreated specimen, melt is localized and the dimension of melt pockets is highly heterogeneous. Microstructures and water contents for both specimens will be discussed in detail.

Aizawa, Y.; Barnhoorn, A.; Fitzgerald, J. D.; Faul, U. H.; Jackson, I.

2005-12-01

4

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...

5

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

6

FRACTIONAL WAVE EQUATIONS WITH ATTENUATION  

PubMed Central

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

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

2013-01-01

7

Teleseismic Body Wave Attenuation and Diffraction  

NASA Astrophysics Data System (ADS)

Using available digital seismic stations deployed since the 1980's, the largest data set based on broadband waveforms among studies on body-wave attenuation (t*) and quality factor (Q) are used in this thesis. The use of nearly 300,000 measurements of body-wave spectral ratio from globally distributed stations renders better constraints of t* and Q variations with higher spatial and depth resolutions in the mantle than have been previously available. The maps of body-wave t* correlate well with the variations of t* computed from the most recent surface-wave Q model QRFSI12 indicating that body-wave and surface-wave t* reflect the same intrinsic attenuation even though these waves sample the upper mantle entirely differently. The high correlation between body-wave t* maps and the t* inferred from a thermal interpretation of shear-wave velocity tomography S20RTS suggests that temperature controls both variations in attenuation and velocity in the upper mantle. The distance variations of P- and S-wave t* (t*P and t*S) are inverted for a radial profile of the quality factor Qmu in the lower mantle. On average, t* P and t*S increase by about 0.2 s and 0.7 s, respectively, between epicentral distances of 30° and 97°. The body-wave spectra are explained best if Qmu, increases in the lower mantle with the rate of 0.1/km. The relatively strong increase of t*S compare to t*P (t*S ? 4 t*P) suggests that intrinsic attenuation is the cause of the overall trend in our data. The ratio of P- and S-wave quality factor determined in this thesis (QP/Qmu = 2.27) confirms that intrinsic attenuation occurs mostly in shear and that bulk attenuation is negligible in the mantle. Finally, the delay of seismic waves which traversed numerical mantle plumes are calculated in this thesis for the first time. High-resolution numerical simulations of mantle plume are used to investigate the effects of numerical plumes on waveforms. The measurements of wave front delay demonstrate that the delay of shear-waves by plume tails at depths larger than 1000 km are immeasurably small (< 0.2 s) at seismic periods commonly used in waveform analysis.

Hwang, Yong Keun

8

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

9

Measurement of the speed and attenuation of the Biot slow wave using a large ultrasonic transmitter  

Microsoft Academic Search

Two compressional wave modes, a fast P1 and a slow P2, propagate through fluid-saturated porous and permeable media. This contribution focuses on new experimental tests of existing theories describing wave propagation in such media. Updated observations of this P2 mode are obtained through a water-loaded, porous sintered glass bead plate with a novel pair of ultrasonic transducers consisting of a

Youcef Bouzidi; Douglas R. Schmitt

2009-01-01

10

Shear wave speed dispersion and attenuation in granular marine sediments.  

PubMed

The reported compressional wave speed dispersion and attenuation could be explained by a modified gap stiffness model incorporated into the Biot model (the BIMGS model). In contrast, shear wave speed dispersion and attenuation have not been investigated in detail. No measurements of shear wave speed dispersion have been reported, and only Brunson's data provide the frequency characteristics of shear wave attenuation. In this study, Brunson's attenuation measurements are compared to predictions using the Biot-Stoll model and the BIMGS model. It is shown that the BIMGS model accurately predicts the frequency dependence of shear wave attenuation. Then, the shear wave speed dispersion and attenuation in water-saturated silica sand are measured in the frequency range of 4-20?kHz. The vertical stress applied to the sample is 17.6?kPa. The temperature of the sample is set to be 5?°C, 20?°C, and 35?°C in order to change the relaxation frequency in the BIMGS model. The measured results are compared with those calculated using the Biot-Stoll model and the BIMGS model. It is shown that the shear wave speed dispersion and attenuation are predicted accurately by using the BIMGS model. PMID:23862793

Kimura, Masao

2013-07-01

11

Constraints on melt retention in the upper mantle from laboratory measurements of shear wave speed and attenuation  

NASA Astrophysics Data System (ADS)

The influence of a small basaltic melt fraction (0.004--0.037) on the seismic properties of fine-grained synthetic polycrystals of Fo90 olivine has been explored at seismic frequencies with torsional forced oscillation/microcreep methods. The presence of a broad dissipation peak superimposed on the monotonically frequency and temperature dependent background clearly distinguishes melt-bearing from melt-free materials containing as little as ˜0.5% melt. In both types of material the observed dissipation is attributed to grain-boundary sliding involving a mixture of elastic and diffusional accommodation. The difference in mechanical behaviour is ascribed to the rounding of olivine grain edges at melt-bearing grain-edge tubules -- allowing sufficient localisation of dissipation in frequency-temperature space to produce a resolvable peak representing mainly elastically accommodated sliding. The grain-boundary triple junction geometry imposed at high temperature is retained during staged cooling and crystallisation to form an intergrowth of crystallites of plagioclase and residual glass. An empirical model has been developed that adequately describes the dependence of 1/Q upon period, temperature, grain size and maximum melt fraction. This model has been extrapolated to the larger grainsizes and P-T conditions (2 GPa, 1300^oC) representative of decompression melting in the mantle. The inferred levels of attenuation are generally somewhat higher than those measured seismologically, but the low spatial resolution of seismological studies means that the latter may average the properties of melt-free and partially molten parts of the upper mantle. The superposition of the melt-related dissipation peak upon the monotonic background is such that, for appropriate combinations of grain size, melt fraction and temperature, nearly frequency-independent attenuation is to be expected. Progress will be reported in the development of a procedure for the simultaneous inversion of dissipation and associated shear modulus dispersion data for the creep function that provides a complete description of the viscoelastic behaviour. Knowledge of the creep function will allow an internally consistent treatment of the impact of partial melting on wave speeds and attenuation in the interpretation of seismological models.

Faul, U. H.; Fitz Gerald, J. D.; Jackson, I.

2003-04-01

12

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

13

The attenuation of strong shock waves  

E-print Network

THE ATTENUATION OF STRONG SHOCK WAVES A Thesis By Ronald Crecelius Kirkpatrick Submitted to the Graduate School of the Agricultural and Mechanical College of Texas in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE... May 1963 Major Subject: Physics. THE ATTENUATION OF STRONG SHOCK WAVES A Thesis By Ronald Crecelius Kirkpatrick Approved as to style and content by: (Chairman of Committee (He of Departme ) May 1963 TABLE OF CONTENTS INT R ODU C TI ON ~Pe e...

Kirkpatrick, Ronald Crecelius

2012-06-07

14

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

15

Polymer gel as thermally responsive attenuator for ultrasonic waves  

NASA Astrophysics Data System (ADS)

The ultrasonic attenuation in N-isopropylacrylamide (NIPA) gel has been measured as a function of temperature at various frequencies. It is found that at room temperature, the attenuation of a longitudinal ultrasonic wave in the gel is small and close to that of pure water. However, as the temperature increases above the spinodal phase transition point of the gel, the attenuation increases drastically. This change of the attenuation is completely reversible and due to the microdomains formed in the NIPA gel above its phase transition temperature. The increase of attenuation at 15 MHz from 26 to 45 °C is about 26 dB/cm. The attenuation varies within 5 min after the temperature change is made for a sample with diameter 1 cm and height 0.8 cm. The results reported here may have potential applications from ultrasonic assisted drug release to a switch for ultrasonic signals.

Yuan, Kaihua; Hu, Zhibing; Li, Yong

1999-04-01

16

Precise measurements of bulk-wave ultrasonic velocity dispersion and attenuation in solid materials in the VHF range  

NASA Astrophysics Data System (ADS)

A general method was established for precisely measuring velocity dispersion and attenuation in solid specimens with acoustic losses in the very high frequency (VHF) range, using the complex-mode measurement method and the diffraction correction method. Experimental procedures were presented for implementing such a method and demonstrated this measurement method in the frequency range of 50-230 MHz, using borosilicate glass (C-7740) as a dispersive specimen and synthetic silica glass (C-7980) as a nondispersive standard specimen. C-7980 exhibited no velocity dispersion; velocity was constant at 5929.14+/-0.03 m/s. C-7740 exhibited velocity dispersion, from 5542.27 m/s at 50 MHz to 5544.47 m/s at 230 MHz with an increase of about 2 m/s in the measured frequency range. When frequency dependence of attenuation was expressed as ?=?0f?, the results were as follows: ?0=1.07×10-16 s2/m and ?=2 for C-7980 and ?0=5.16×10-9 s1.25/m and ?=1.25 for C-7740.

Kushibiki, Jun-Ichi; Okabe, Ryoichi; Arakawa, Mototaka

2003-06-01

17

UHF Radio Wave Attenuation Factor Database  

Microsoft Academic Search

As is known each sea-going vessel is equipped with navigation, communication and other radio engineering facilities that serve to secure the safety of navigation and are chiefly operated at UHF-wave band. In developing these systems and calculating the energy potential for a necessary coverage range one should be well aware of the radio signal attenuation processes on a propagation path.

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

2007-01-01

18

Experimental study of wave dispersion and attenuation in concrete.  

PubMed

Results from an experimental study concerning wave propagation in cementitious materials are presented in this paper. Narrow band pulses at several frequencies were introduced into specimens of cement paste, mortar and concrete allowing direct measurement of longitudinal wave velocities and amplitude for each frequency. It is shown that aggregate content play an important role in wave propagation increasing considerably the wave velocity, while the aggregate size seems to control the attenuation observed. Slight velocity variations observed with frequency are discussed in relation to the degree of inhomogeneity of the materials. PMID:15950034

Philippidis, T P; Aggelis, D G

2005-06-01

19

Attenuation of seismic waves in the Jan Mayen island area  

Microsoft Academic Search

An analysis of the attenuation of seismic waves as measured by the quality factorQc (for coda waves) has been performed for the volcanic Jan Mayen island in the Norwegian Sea, using earthquakes near the Jan\\u000a Mayen Fracture Zone and local seismic stations on the Jan Mayen island.Qc values of the order of 100 at a frequency of 1 Hz are

J. Havskov; L. B. Kvamme; H. Bungum

1986-01-01

20

Attenuation of seismic waves in Central Egypt  

NASA Astrophysics Data System (ADS)

Attenuation of seismic waves in central Egypt had never been studied before. The results of the research on the seismic attenuation are based upon the information collected by the seismological network from 1998 to 2011. 855 earthquakes were selected from the Egyptian seismological catalog, with their epicenter distances between 15 and 150 km, their magnitudes ranging from 2 and 4.1 and focal depths reaching up to 30 km. The first systematic study of attenuation derived from the P-, S- and coda wave in the frequency range 1-24 Hz is presented. In the interpretation of the results both single and multiple scattering in a half space are considered. The single scattering model proposed by Sato (1977) was used. Two methods, the coda (Qc) and the Multiple Lapse Time Window (MLTW) method are used. The aim of this study is to validate these interpretations in the region and to try to identify the effects of attenuation due to intrinsic (Qi) and scattering attenuation (Qsc). The mean Qc value calculated was Qc = (39 ± 1)f1.0±0.009. The average Qc at 1.5 Hz is (53 ± 6) and Qc = (900 ± 195) at 24 Hz with Qo ranging between 23 and 107, where ? ranging between 0.9 and 1.3. The quality factor (Q) was estimated from spectra of P- and S-waves by applying a spectral ratio technique. The results show variations in Qp and QS as a function of frequency, according to the power law Q = 56?1.1. The seismic albedo is 0.7 at all stations and it mean that the earthquake activity is due to tectonic origin. The attenuation and frequency dependency for different paths and the correlation of the results with the geotectonic of the region are presented. The Qc values were calculated and correlated with the geology and tectonics of the area. The relatively low Qo and the high frequency dependency agree with the values of a region characterized by a low tectonic activity and vise versa.

Morsy, Mamdouh Abbas; Abed, Azza M.

2013-06-01

21

Attenuation of transverse magnetoelastic waves in a ferromagnetic plate  

NASA Astrophysics Data System (ADS)

The attenuation of backward transverse acoustic waves in a ferromagnetic plate is investigated. It is shown that magnetostriction in yttrium-iron-garnet plates can produce appreciable oscillations of the attenuation of magnetostatic waves, even if the acoustic waves are practically nonpropagating at the synchronism frequencies.

Nechiporenko, V. N.; Rapoport, Iu. G.

1985-06-01

22

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

23

5. SOUND ATTENUATION 5.1 NATURE OF SOUND WAVE  

E-print Network

5. SOUND ATTENUATION 5.1 NATURE OF SOUND WAVE Historically, acoustic is the scientific study of sound. Sound can be considered as a wave phenomenon. A sound wave is a longitudinal wave where particles the sound wave, the particles of the medium through which the sound moves is vibrating in a back and forth

Cambridge, University of

24

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

25

Wave Dispersion and Attenuation on Human Femur Tissue  

PubMed Central

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

26

Wave energy attenuation and shoreline alteration characteristics of submerged breakwaters  

E-print Network

WAVE ENERGY ATTENUATION AND SHORELINE ALTERATION CHARACTERISTICS OF SUBMERGED BREAKWATERS A Thesis by KATHERINE MARGARET KRAFFT Submitted to the Office of Graduate Studies of Texas AIM University in partial fulfillment of the requirements... for the degree of MASTER OF SCIENCE August 1993 Major Subject: Ocean Engineering WAVE ENERGY ATTENUATION AND SHORELINE ALTERATION CHARACTERISTICS OF SUBMERGED BREAKWATERS A Thesis by KATHERINE MARGARET KRAFFT Approved as to style and content by: John...

Krafft, Katherine Margaret

2012-06-07

27

Tide Effects on Wave Attenuation and Wave Set-up on a Caribbean Coral Reef  

NASA Astrophysics Data System (ADS)

The effects of tides on wave attenuation and wave set-up were investigated at Great Pond Bay, a Caribbean reef located in St Croix, U.S. Virgin Islands. Measurements of wave pressure fluctuations were made at three stations across the reef profile. Total wave set-up was measured between the forereef and the reef crest or backreef lagoon. Wave spectra indicate significant filtering of energy at the peak frequencies as waves traveled across the reef. The energy dissipation calculations imply an average energy reduction of 62% between the forereef and reef crest. Mean energy reduction between the forereef and lagoon was 90%. Energy dissipation between the forereef and reef crest increased 15% between high and low tide and 6% between forereef and lagoon. Tidal reduction of water depth at the reef crest intensified wave breaking and this condition increased energy dissipation. Measurements of wave set-up ranged from 0·8 to 1·5 cm. Calculations of wave set-up using Tait's 1972 model showed good agreement with observations.

Lugo-Fernández, A.; Roberts, H. H.; Wiseman, W. J., Jr.

1998-10-01

28

Attenuation anisotropy and the relative frequency content of split shear waves  

NASA Astrophysics Data System (ADS)

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

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

2006-06-01

29

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

30

Stochastic solution to a time-fractional attenuated wave equation  

PubMed Central

The power law wave equation uses two different fractional derivative terms to model wave propagation with power law attenuation. This equation averages complex nonlinear dynamics into a convenient, tractable form with an explicit analytical solution. This paper develops a random walk model to explain the appearance and meaning of the fractional derivative terms in that equation, and discusses an application to medical ultrasound. In the process, a new strictly causal solution to this fractional wave equation is developed. PMID:23258950

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

2012-01-01

31

Attenuation character of seismic waves in Sikkim Himalaya  

NASA Astrophysics Data System (ADS)

In this study, we investigate the seismic wave attenuation beneath Sikkim Himalaya using P, S and coda waves from 68 local earthquakes registered by eight broad-band stations of the SIKKIM network. The attenuation quality factor (Q) depends on frequency as well as lapse time and depth. The value of Q varies from (i) 141 to 639 for P waves, (ii) 143 to 1108 for S waves and (iii) 274 to 1678 for coda waves, at central frequencies of 1.5 Hz and 9 Hz, respectively. The relations that govern the attenuation versus frequency dependence are Q? = (96 ± 0.9) f (0.94 ± 0.01), Q? = (100 ± 1.4) f (1.16 ± 0.01) and Qc = (189 ± 1.5) f (1.2 ± 0.01) for P, S and coda waves, respectively. The ratio between Q? and Q? is larger than unity, implying larger attenuation of P compared to S waves. Also, the values of Qc are higher than Q?. Estimation of the relative contribution of intrinsic (Qi) and scattering (Qs) attenuation reveals that the former mechanism is dominant in Sikkim Himalaya. We note that the estimates of Qc lie in between Qi and Qs and are very close to Qi at lower frequencies. This is in agreement with the theoretical and laboratory experiments. The strong frequency and depth dependence of the attenuation quality factor suggests a highly heterogeneous crust in the Sikkim Himalaya. Also, the high Q values estimated for this region compared to the other segments of Himalaya can be reconciled in terms of moderate seismic activity, unlike rest of the Himalaya, which is seismically more active.

Hazarika, Pinki; Kumar, M. Ravi; Kumar, Dinesh

2013-10-01

32

Attenuation of coda waves in the Northeastern Region of India  

Microsoft Academic Search

Coda wave attenuation quality factor Qc is estimated in the northeastern region of India using 45 local earthquakes recorded\\u000a by regional seismic network. The quality factor Qc was estimated using the single backscattering model modified by Sato (J\\u000a Phys Earth 25:27–41, 1977), in the frequency range 1–18 Hz. The attenuation and frequency dependence for different paths and the correlation of the

Devajit Hazarika; Saurabh Baruah; Naba Kumar Gogoi

2009-01-01

33

Estimation of frequency dependent coda wave attenuation structure at the vicinity of Cairo Metropolitan Area  

NASA Astrophysics Data System (ADS)

Estimation of seismic wave attenuation in the shallow crust in terms of coda wave Q structure previously investigated in the vicinity of Cairo Metropolitan Area was improved using seismograms of local earthquakes recorded by the Egyptian National Seismic Network. The seismic wave attenuation was measured from the time decay of coda wave amplitudes on narrow bandpass filtered seismograms based on the single scattering theory. The frequency bands of interest are from 1.5 to 18 Hz. In general, the values obtained for various events recorded at El-Fayoum and Wadi Hagul stations are very similar for all frequency bands. A regional attenuation law Q c = 85.66 f 0.79 was obtained.

El-Hadidy, Salah; Adel, M. E. Mohamed; Deif, Ahmed; Abu El-Ata, Ahmed Sayed; Sayed, S. R. Moustafa

2006-06-01

34

Time-domain apparent-attenuation operators for compressional and shear waves: Experiment versus single-scattering theory  

NASA Astrophysics Data System (ADS)

We derive time-domain apparent-attenuation operators from both laboratory data and a single-scattering theory. The scattering medium consists of a homogeneous elastic block containing parallel cylindrical voids, with volume fractions in the range from 0.66% to 3.75%. The attenuation operators were computed by first measuring (or theoretically predicting) the attenuation of spectral amplitude and then constructing a causal seismogram using the Kramers-Kronig (KK) relation. Theory and experiment broadly agree, with the following exceptions: theory underestimated the overall level of attenuation, compressional wave attenuation is more poorly predicted than shear wave attenuation, and the theoretical attenuation operators tend to be larger in amplitude and less oscillatory than is observed. The KK attenuation operators are compared with attenuation operators derived from a least squares deconvolution (LSD) of the attenuated and unattenuated time series. The KK and LSD attenuation operators are superficially very different, reflecting different limitations in the methods. The LSD attenuation operators tend to be narrower than the KK attenuation operators and should not be used to measure pulse width.

Dubendorff, Bruce; Menke, William

1986-12-01

35

Grain-size dependence of shear wave speed dispersion and attenuation in granular marine sediments.  

PubMed

The author has shown that measured shear wave speed dispersion and attenuation in water-saturated silica sand can be predicted by using a gap stiffness model incorporated into the Biot model (the BIMGS model) [Kimura, J. Acoust. Soc. Am. 134, 144-155 (2013)]. In this study, the grain-size dependence of shear wave speed dispersion and attenuation in four kinds of water-saturated silica sands with different grain sizes is measured and calculated. As a result, the grain-size dependence of the aspect ratio in the BIMGS model can be validated and the effects of multiple scattering for larger grain sizes are demonstrated. PMID:24993238

Kimura, Masao

2014-07-01

36

Estimates of millimeter wave attenuation for 18 United States cities  

NASA Astrophysics Data System (ADS)

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

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

1983-05-01

37

Knife Edge Diffraction Signal attenuation caused by diffraction of waves  

E-print Network

Knife Edge Diffraction · Signal attenuation caused by diffraction of waves ­ Huygen's principle E E d i i d : Diffraction loss due to the presence of knife-edge wrt free space LOS E-field #12 The diffraction loss due to the presence of a knife edge, as compared to the free space E-field can be given

Cetiner, Bedri A.

38

Attenuation Measurements in Cement-Based Materials Using Laser Ultrasonics  

Microsoft Academic Search

This research uses laser ultrasonic techniques to quantify the frequency-dependent attenuation losses of Rayleigh waves in cement-based materials; these materials are heterogeneous in nature, and this heterogeneity is seen at multiple length scales. As a result, ultrasonic waves that propagate in cement-based materials exhibit a high degree of (material) attenuation losses. Physically, these attenuation losses are a com- bination of

Joseph O. Owino; Laurence J. Jacobs

1999-01-01

39

Modeling of aqueous foam blast wave attenuation  

NASA Astrophysics Data System (ADS)

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

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

40

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

41

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

42

Radio-wave attenuation and sulfuric-acid vapor content in the Venus atmosphere  

NASA Astrophysics Data System (ADS)

Radio-wave absorption in the Venus atmosphere is investigated using radio probing data on variations of the field strengths of 5-cm and 32-cm signals. It is shown that the most probable cause of cm-wave attenuation at altitudes below 50 km is absorption by sulfuric-acid vapor. Sulfuric-acid vapor contents equal to 15 ppm at 48 km and 19 ppm at 47 km were determined, which agree well with Pioneer-Venus measurements at 13 cm.

Gubenko, V. N.; Iakovlev, O. I.; Matiugov, S. S.; Kucheriavenkov, A. I.; Vaganov, I. R.

1989-11-01

43

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

NASA Astrophysics Data System (ADS)

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

Jayaprakash, Arvind; Fourmeau, Tiffany; Hsiao, Chao-Tsung; Chahine, Georges

2013-03-01

44

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

NASA Astrophysics Data System (ADS)

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 depend primarily on thickness) of the ice floes. The model neglects all nonlinear effects as well as floe collisions or ice creep and is therefore most applicable to floes which are large compared to the thickness and to wave conditions which are not extreme. The solution for a given arrangement of floes is fully coherent, and the results are therefore dependent on the exact geometry. We firstly show that this dependence can be removed by averaging over a distribution of floe lengths (we choose the Rayleigh distribution). We then show that after this averaging, the attenuation coefficient is a function of floe number and independent of floe length, provided the floe lengths are sufficiently large. The model predicts an exponential decay of energy, just as is shown experimentally. This enables us to provide explicit values for the attenuation coefficient, as a function of the average floe thickness and wave period. We compare our theoretical predictions of the wave attenuation with measured data and other scattering models. The limited data allows us to conclude that our model is applicable to large floes for short to medium wave periods (6 to 15 seconds). We also derive a floe breaking model, based on our wave attenuation model, which indicates that we are under-predicting the attenuation coefficients at long periods.

Kohout, A. L.; Meylan, M. H.

2008-09-01

45

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

46

Seismic Wave Attenuation in the Greater Cairo Region, Egypt  

NASA Astrophysics Data System (ADS)

In the present study, a digital waveform dataset of 216 local earthquakes recorded by the Egyptian National Seismic Network (ENSN) was used to estimate the attenuation of seismic wave energy in the greater Cairo region. The quality factor and the frequency dependence for Coda waves and S-waves were estimated and clarified. The Coda waves ( Q c) and S-waves ( Q d) quality factor were estimated by applying the single scattering model and Coda Normalization method, respectively, to bandpass-filtered seismograms of frequency bands centering at 1.5, 3, 6, 12, 18 and 24 Hz. Lapse time dependence was also studied for the area, with the Coda waves analyzed through four lapse time windows (10, 20, 30 and 40 s). The average quality factor as function of frequency is found to be Q c = 35 ± 9 f 0.9±0.02 and Q d = 10 ± 2 f 0.9±0.02 for Coda and S-waves, respectively. This behavior is usually correlated with the degree of tectonic complexity and the presence of heterogeneities at several scales. The variation of Q c with frequency and lapse time shows that the lithosphere becomes more homogeneous with depth. In fact, by using the Coda Normalization method we obtained low Q d values as expected for a heterogeneous and active zone. The intrinsic quality factor ( Q {i/-1}) was separated from the scattering quality factor ( Q {s/-1}) by applying the Multiple Lapse Time Domain Window Analysis (MLTWA) method under the assumption of multiple isotropic scattering with uniform distribution of scatters. The obtained results suggest that the contribution of the intrinsic attenuation ( Q {i/-1}) prevails on the scattering attenuation ( Q {s/-1}) at frequencies higher than 3 Hz.

Badawy, Ahmed; Morsy, Mamdouh A.

2012-09-01

47

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

NASA Astrophysics Data System (ADS)

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

Bachura, Martin; Fischer, Tomas

2014-05-01

48

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

49

Seismic wave attenuation and dispersion in thin layer sequences  

E-print Network

The propagation of plane waves in thin layer sequences in which the velocity variation is approxmiately cyclic is characterized by both absorption and attenuation. Both factors contain important sub- surface information. Absorption is related to the nature... with velocity layering. In cyclic sequences the transmission losses caused by propaga tion through large numbers of interfaces may be considerable. How- ever, short path multiples which are reflected from the top and bottom of the same layer combine...

Edwards, Clifford Murray

1975-01-01

50

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

51

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

52

Frequency-dependent attenuation of S-waves in the Kanto region, Japan  

NASA Astrophysics Data System (ADS)

Apparent, scattering, and intrinsic S-wave attenuations (QS-1, Qscat-1 and Qint-1) of the upper lithosphere in the Kanto region of Japan were measured in the 1- to 32-Hz frequency range using Multiple Lapse Time Window Analysis (MLTWA) for 115 borehole seismograms of local earthquakes. A new set of time windows for MLTWA, in which multiple isotropic scattering is assumed, was proposed and employed to estimate the frequency dependence of S-wave attenuation parameters. Scattering attenuation was found to dominate intrinsic attenuation in the S-wave attenuation mechanism at low frequencies (<2 Hz), whereas the opposite relation was observed at high frequencies. The transition is caused by the different frequency dependences of Qscat-1(? f -1.5) and Qint-1(? f -0.7) at this frequency. Interestingly, Qscat-1 is almost frequency independent at frequencies >8 Hz, which implies the self-similar nature of short-wavelength heterogeneities in the upper lithosphere. In terms of the upper lithosphere of the Kanto region, these results may indicate that the random heterogeneities characterized by the Gaussian autocorrelation function with a fractional fluctuation ? ? 10% and a correlation length a ? 2 km are superimposed on the weak background self-similar heterogeneity.

Yoshimoto, K.; Okada, M.

2009-09-01

53

Measured and Calculated Magnetic Field Dependence of Ultrasonic Attenuation and Velocity in Copper  

Microsoft Academic Search

A new method for measuring the attenuation and relative velocity of ultrasonic waves using continuous wave signals and the Fast Fourier Transform is presented. A detailed explanation of the technique is given along with an analysis of the equipment used (a vector network analyzer) and the quality of the data produced. The technique was applied to very pure copper crystals

Michael David Foegelle

1996-01-01

54

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

NASA Astrophysics Data System (ADS)

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

Song, X.; Jordan, T. H.

2013-12-01

55

Measuring Acoustic Nonlinearity by Collinear Mixing Waves  

NASA Astrophysics Data System (ADS)

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

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

2011-06-01

56

Seismic Attenuation Technology for the Advanced Virgo Gravitational Wave Detector  

NASA Astrophysics Data System (ADS)

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

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

57

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

58

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

NASA Technical Reports Server (NTRS)

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

Jackson, D. D.

1971-01-01

59

Electromagnetic Shock Tube capable of producing a Well-formed shock Wave of Low Attenuation  

Microsoft Academic Search

WHILE present electromagnetic shock tubes1,2 will generate very strong shock waves frequently and in a simple manner, many designs suffer from pronounced attenuation of the shock wave together with the formation of secondary shock waves.

P. R. Smy

1962-01-01

60

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

61

Estimation of coda wave attenuation in East Central Iran  

Microsoft Academic Search

The attenuation of coda waves, Q\\u000a \\u000a c\\u000a , has been estimated in Zarand, Jiroft, and Bam regions of east central Iran using a single back-scattering model of S-coda\\u000a envelopes. For this purpose, the recordings of 97 earthquakes by three seismic networks and a local strong ground motion network\\u000a have been used. In this research, the frequency-dependent Q\\u000a \\u000a c\\u000a values are

M. Ma’hood; H. Hamzehloo

2009-01-01

62

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

PubMed

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

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

2011-12-01

63

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

64

Lg waves attenuation studies over the Iranian Plateau and Zagros  

NASA Astrophysics Data System (ADS)

Waveforms from regional events collected over the last 15 years by the permanent seismological networks and temporary deployments deployed within the Iranian plateau provide a unique and unprecedented opportunity to investigate the crustal and mantle attenuation characteristics by analysis of the regional phases including Lg and Pg waves. We have investigated the crustal attenuation using Lg waveforms available from 305 stations consisting of 101 permanent and 204 temporary stations. This study is performed within the framework of a larger project aimed at developing high-resolution seismic attenuation models for the Iranian plateau and the Zagros mountains using different data and approaches. We have combined the Iranian data set with data from numerous networks across Turkey, Georgia, Azerbaijan, Syria, Jordan, and Saudi Arabia. This combination provides us with waveforms from over 550 stations spanning most of the Northern Middle East. Simultaneous inversion of the Lg Q values calculated using two-station paths gives us a model of Lg Q that extends from the western Anatolian plate to the eastern edge of the Iranian plateau. Prior studies have suggested strong complexity in the crustal and uppermost mantle attenuation structure beneath much of the Iranian plateau and the surrounding regions. Lg waves propagating over different paths in this region show strong variations in amplitude and frequency content due to this very complex structure. We have created a frequency dependent Lg Q model that covers most of the Iranian plateau using instrument corrected two station method that eliminates the contributions from the source. Our model maps Lg Q around 200 for most part of the central Iranian plateau and Alborz mountains whereas it is lower than 150 for the western Anatolian plateau. Relatively high Q values (>300) are observed in the Zagros belt that abruptly changes across the Zagros suture. We have also found unexpected results, including a high Q zone that surrounds the Caspian Sea. We argue that it originates from energy that is bending around the south Caspian Sea oceanic crust as well as efficient Lg propagation through the Alborz mountain crust.

Kaviani, A.; Sandvol, E. A.; Rumpker, G.; Ku, W.; Gok, R.

2012-12-01

65

Extraction of surface wave attenuation from ambient noise: approaches to simulated and real data  

NASA Astrophysics Data System (ADS)

Attenuation, or its inverse, quality factor (Q), is one of the most fundamental parameters of the Earth's media. Measurement of attenuation at regional distances traditionally uses seismic waves generated by earthquakes, which generally requires either a good knowledge of the source or a special choice of geometries to cancel out source effects. Seismic ambient noise correlation methodology has been demonstrated to be highly effective at extracting seismic velocities. Extracting amplitude information is more challenging. The greatest challenge is that the Earth's ambient noise field is highly anisotropic, non-uniform, and variable with time. Here, we explore the methodologies and procedures for extracting surface wave attenuation from empirical Green functions (EGFs) constructed from seismic ambient noise. Our approaches are to combine sound theoretical understanding and practical considerations with real data. Recent theoretical derivations and numerical simulations show that even in the case of incompletely diffuse noise fields, we can robustly recover not only travel times, but also ray arrival amplitudes, the ambient field's specific intensity, the strength and density of its scatterers if any, site amplification factors, and most importantly attenuation. In applications to the Earth, we propose two approaches with detailed formulations: linear array methods and more general methods for 2D station networks, each to be developed through applications to numerically simulated data, and to real data. In the preprocessing of real data, we explore a temporal "flattening" procedure, which speeds up EGF convergence and, in the mean time, preserves amplitudes.

Song, X.; Zhou, L.; Weaver, R. L.

2012-12-01

66

Simultaneous estimation of SPECT activity and attenuation distributions from measured phantom data using a differential attenuation method  

Microsoft Academic Search

The Differential Attenuation Method (DAM) simultaneously estimates SPECT activity and attenuation distributions from emission data. In this work, we extend the investigation of DAM to measured data and compare the results obtained with FBP without compensating for attenuation, and Penalized Weighted Least Squares (PWLS) with uniform and no attenuation. An anthropomorphic torso phantom with a heart insert containing a myocardial

H. Vija; M. S. Kaplan; D. R. Haynor

1999-01-01

67

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

68

Attenuation of coda waves in the Garhwal Himalaya, India  

NASA Astrophysics Data System (ADS)

Qc estimates have been obtained by analysing coda waves of seven local earthquakes recorded in the Garhwal Himalaya. The earthquakes have their epicentral distances within 100 km, focal depths up to 20 km with 2.4 ? ML ? 4.9. Qc values have been computed at central frequencies of 1.5, 3.0, 6.0, 12.0 and 18.0 Hz for different earthquake stations falling in the lapse time window of 30-60 s using a single backscattering model. The mean value of Qc shows a dependence on frequency, varying from 206 at 1.5 Hz to 2090 at 18 Hz. The frequency-dependence average Qc relationship ( Qc = Q0fn) has been obtained for the region as Qc = 126 f0.95 which indicates that attenuation at higher frequencies is less pronounced. Qc values estimated for the region represent the average attenuation properties for a surface area of about 20 000 km 2 in a circular shape with a radius of about 80 km assuming single backscattering.

Gupta, S. C.; Singh, V. N.; Kumar, Ashwani

1995-01-01

69

Measurements of spectral attenuation coefficients in the lower Chesapeake Bay  

NASA Technical Reports Server (NTRS)

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

Houghton, W. M.

1983-01-01

70

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

71

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

72

Assessment of broadband ultrasonic attenuation measurements in inhomogeneous media.  

PubMed

In this paper, we address the problem of evaluating the acoustic attenuation of "difficult" media, i.e. highly attenuating and scattering media. In a broadband, through transmission setup, the signals acquired from such media are characterized by a poor signal-to-noise ratio. Therefore, an accurate estimate of attenuation cannot be obtained from a single measurement, but multiple measurements must be combined. Two methods are considered to yield a single estimate of attenuation from multiple measurements. The first one, the "average attenuation" (AA) method, consists in a simple average of individual attenuation estimates. The second one, the "cross spectrum" (CS) method, is based on a system identification approach. In order to evaluate the estimation errors for these methods, ultrasonic signals transmitted through a material of known attenuation were simulated and mixed with both coherent and incoherent noise. In all tests performed, the "CS" method was found to yield the most accurate estimate. This method, combined time delay compensation, is then applied to real signals measured from a concrete slab. A valid frequency band for the attenuation estimate can be defined based on the coherence function. Results from this research are being applied to characterize the degradation of concrete structures using high-frequency ultrasound. PMID:12160042

Goueygou, M; Piwakowski, B; Ould Naffa, S; Buyle-Bodin, F

2002-05-01

73

Interlaboratory Comparison Of Multimode Optical Fiber Attenuation Measurement  

NASA Astrophysics Data System (ADS)

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

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

1985-11-01

74

Optimization of Power Consumption for Centrifugation Process Based on Attenuation Measurements  

NASA Astrophysics Data System (ADS)

The main objective of this research is to produce a mathematical model that allows decreasing the electrical power consumption of centrifugation process based on attenuation measurements. The centrifugation time for desired separation efficiency may be measured to determine the power consumed of laboratory centrifuge device. The power consumption is one of several parameters that affect the system reliability and productivity. Attenuation measurements of wave propagated through blood sample during centrifugation process were used indirectly to measure the power consumption of device. A mathematical model for power consumption was derived and used to modify the speed profile of centrifuge controller. The power consumption model derived based on attenuation measurements has successfully save the power consumption of centrifugation process keeping high separation efficiency. 18kW.h monthly for 100 daily time device operation had been saved using the proposed model.

Salim, M. S.; Abd Malek, M. F.; Sabri, Naseer; Omar, M. Iqbal bin; Mohamed, Latifah; Juni, K. M.

2013-04-01

75

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

76

Broadband attenuation measurements of phospholipid-shelled ultrasound contrast agents.  

PubMed

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

2014-02-01

77

Numerical simulation of ultrasonic wave propagation in anisotropic and attenuative solid materials  

NASA Astrophysics Data System (ADS)

The axisymmetric elastodynamic finite element code developed is capable of predicting quantitatively accurate displacement fields for elastic wave propagation in isotropic and transversely isotropic materials. The numerical algorithm incorporates viscous damping by adding a time-dependent tensor to Hooke's law. Amplitude comparisons are made between the geometric attenuation in the far field and the corresponding finite element predictions to investigate the quality and validity of the code. Through-transmission experimental measurements made with a 1-MHz L-wave transducer attached to an aluminum sample support the code predictions. The algorithm successfully models geometric beam spreading dispersion and energy absorption due to viscous damping. Extension of the model to include anisotropy, inhomogeneities and the awkward boundaries associated with finite aperture transducers, and realistic defect shapes makes this numerical model a viable tool for the study of elastic wave propagation in nondestructive testing applications.

You, Zhongqing; Lusk, M.; Ludwig, Reinhold; Lord, William

1991-09-01

78

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

79

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

80

Effect of finite absorber dimensions on ?-ray attenuation measurements  

NASA Astrophysics Data System (ADS)

Using 137Cs ? 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 mercury have also been determined.

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

1986-04-01

81

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

82

Material hardness and ageing measurement using guided ultrasonic waves.  

PubMed

Elastic properties of materials can be easily determined from the ultrasonic wave velocity measurement. However, material hardness cannot be obtained from the ultrasonic wave speed. Heat treatment and ageing affect the microstructure of many materials changing their hardness and strength. It has been already established that ultrasonic attenuation and dispersion are also affected by the material microstructure. It is investigated in this paper if the attenuation of ultrasonic guided waves can be correlated with the material ageing or duration of heat treatment and material hardness. To this aim six identical aluminum 2024 alloy plate specimens were subjected to different durations of heat treatment at 150°C and were inspected nondestructively propagating Lamb waves through the specimens. Attenuation of the Lamb wave was found to be inversely related to the hardness. Rockwell hardness test was performed to corroborate the ultrasonic observations. In comparison to the Rockwell hardness test the ultrasonic inspection was found to be more sensitive to the heat treatment duration and material ageing. From these results it is concluded that guided wave inspection method is a reliable and probably more desirable alternative for characterizing the hardness and microstructure of heat treated materials. Earlier investigations correlated the bulk wave attenuation with the material ageing while this work is the first attempt to correlate the guided wave attenuation to the material hardness and ageing. PMID:23047018

Korde, Nilesh; Kundu, Tribikram

2013-02-01

83

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

SciTech Connect

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

Best, A.I. [Univ. of Reading (United Kingdom). Postgraduate Research Inst. for Sedimentology] [Univ. of Reading (United Kingdom). Postgraduate Research Inst. for Sedimentology; Sams, M.S. [Imperial College of Science, Technology and Medicine, London (United Kingdom). Dept. of Geology] [Imperial College of Science, Technology and Medicine, London (United Kingdom). Dept. of Geology

1997-03-01

84

Attenuation Measurements of Cell Pellets Using Through Transmission  

NASA Astrophysics Data System (ADS)

A better understanding of differences in ultrasound tissue characteristics (such as speed of sound, attenuation, and backscatter coefficients) of benign compared to malignant cells could lead to improved cancer detection and diagnosis. A narrow band technique for measuring ultrasonic speed of sound and attenuation of small biological materials was developed and tested. Several mechanical improvements were made to the system to drastically improve alignment, allowing for accurate measurements of small cell pellets. Narrow band attenuation measurements were made first with tissue-mimicking phantoms and then with three different types of cell pellets: Chinese hamster ovary cells, healthy human prostate cells, and cancerous human prostate cells. Attenuation and speed of sound results for all three cell types, as well as the culture medium and tissue mimicking phantoms, are presented for a frequency range of 5 to 25 MHz.

Vadas, Justin; Greene, Claudia; Grygotis, Emma; Kuhn, Stephen; Mahlalela, Sanele; Newland, Tinisha; Ovutmen, Idil; Herd, Maria-Teresa

2011-10-01

85

The measurement of attenuation from vertical seismic profiles  

E-print Network

log and attenuation zones. VSP1 Figure 23. AGC section. VSP2 52 Figure 24. Nonitor and downhole direct arrivals, VSP2 53 Figure 25. Cumulative attenuation. (A) Downhole. (8) Monitor. (C) Downhole corrected by monitor. VSP2 55 Figure 26. Downhole..., stacked, 3-fold averaged downhole corrected by monitor. (B) 3-fold average frequency domain synthetic. (C) A ? B. VSP2 73 Figure 37. SP, sonic, deep induction logs and Q zones. VSP2 77 Figure 38. AGC section. VSP3 80 Figure 39. P-wave direct arrival...

Davis, Francis Erwin

1983-01-01

86

Analytical Method for Guided Waves Propagating in a Fluid-Filled Pipe with Attenuation  

NASA Astrophysics Data System (ADS)

To ensure the safety of nuclear power plants, a relatively rapid nondestructive evaluation (NDE) of cylindrical pipes that carry water is needed. NDE methods that use guided waves are a possible solution because a guided wave has a long propagation range. In this study, we developed an analytical method of modeling guided waves that propagate in a fluid-filled cylindrical pipe with attenuation. The analytical method was used to determine the dispersion curves affected by the attenuation of the pipe or fluid itself. We calculated the dispersion curves and amplitudes of displacements, and discussed the effect of attenuation.

Sato, Harumichi; Ogiso, Hisato

2013-07-01

87

Measurements of earth-space attenuation at 230 GHz  

NASA Technical Reports Server (NTRS)

Measurements of attenuation at 230 GHz through the total atmosphere due to the presence of oxygen and water vapor molecules, clouds, and rain are presented. The measurements were carried out using a specially designed superheterodyne receiver mounted on a sun tracker. Simultaneous measurements were also carried out at 13 GHz. For a measuring site close to sea level at Holmdel, NJ, the 'clear-sky' zenith attenuation was found as a function of the measured ground water vapor density. When the ground temperature was below about 7 C, most cloud and overcast gave less than 0.5-dB attenuation, whereas with a ground temperature greater than 13 C, cloud attenuation was 8-10 times greater. Calculations of zenith attenuation in the 230-GHz atmospheric window were also made using the Gross analytic line shape, Schulze-Tolbert empirical line shape, and an empirically modified Gross line shape. These calculations were based on determinations of water vapor density and temperature made at the measurement site, and on radiosonde measurements made at a distance of 80 km away.

Wrixon, G. T.; Mcmillan, R. W.

1978-01-01

88

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

E-print Network

. Acoustical properties like attenuation of propagating ultrasonic waves through polymers vary in a broad of acrylic (PMMA, polymethyl methacrylate), thermoplastic, using guided Lamb wave. Lamb waves are generated. In industrial applications, ultrasonic testing is commonly used on metals, plastics, composites, and ceramics

Boyer, Edmond

89

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

90

Giant Quantum Oscillations in the Attenuation of Rayleigh Waves in Gallium  

Microsoft Academic Search

Giant quantum oscillations in the attenuation of Rayleigh waves with the magnetic field normal to the metal surface are reported. These oscillations have a spikelike character. The experiments are made at frequencies up to 120 MHz and temperatures down to 0.4 K. The line shape is studied and compared with that of the giant quantum oscillations in the attenuation of

G. Bellessa

1975-01-01

91

The Attenuation of Electromagnetic Waves By Multiple Knife-Edge Diffraction  

Microsoft Academic Search

ABSTRACT TABLE OF CONTENTS Page 1 l. INTRODUCTION 2. , NUMERICAL EVALUATION,9 4. EXAMPLE CALCULATIONS,13 5. SUMt1ARY,18 6. ACKNmILEDG~1ENTS,19 7. REFERENCES,19 iii THE ATTENUATION OF ELECTROMAGNETIC WAVES BY

L. E. Vogler

1981-01-01

92

Shear wave attenuation and dispersion in melt-bearing olivine polycrystals  

E-print Network

: Plasticity, diffusion, and creep; 5144 Physical Properties of Rocks: Wave attenuation; KEYWORDS: anelasticity imposed stress field. As a consequence of the distortion of the matrix, each fluid inclusion is exposed

93

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

94

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

95

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

96

Measurement and Modeling of Ultrasonic Attenuation in Aluminum Rolled Plate  

SciTech Connect

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. [Center for Nondestructive Evaluation, Iowa State University, Ames, IA 50011 (United States)

2006-03-06

97

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

NASA Technical Reports Server (NTRS)

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

Sheehan, Anne F.; Solomon, Sean C.

1992-01-01

98

Attenuation of Lamb waves in the vicinity of a forbidden band in a phononic crystal  

NASA Astrophysics Data System (ADS)

When a Lamb wave propagates on a plate engraved by a periodic grating, it may exhibit attenuation. This attenuation is related to a coupling of this incident mode with other propagating modes. As the propagation takes place in a periodic medium, the dispersion curves of the modes are of interest because they exhibit pass bands and stop bands related to the geometry of the waveguide. The goal of this work is to quantitatively establish the relation between the value of the attenuation of the propagating waves and the width of the forbidden bands appearing inside the Brillouin zone. This study is performed by using a finite element method (ATILA® code).

Bavencoffe, M.; Hladky-Hennion, A.-C.; Morvan, B.; Izbickil, J.-L.

99

Attenuation and distortion of compression waves propagating in very long tube  

NASA Astrophysics Data System (ADS)

A lot of phenomena related to propagating various waves are seen when the high-speed train goes through the tunnel, the gas pipeline is broken due to an accident or the air brake of the wagon operates. For instance, a compression wave generated ahead of a high-speed train entering a tunnel propagates to the tunnel exit and spouts as a micro pressure wave, which causes an exploding sound. In order to estimate the magnitude correctly, the mechanism of the attenuation and distortion of a compression wave propagating along a very long tunnel must be understood and the experimental information on these phenomena is required. An experimental investigation is carried out to clarify the attenuation and distortion of the propagating compression wave in a very long tube. Experimental results show that the strength of a compression wave decreases with distance. The attenuation and distortion of compression waves are affected by the initial waveform of the compression wave and by the unsteady boundary layer induced by the propagating wave. The shape of a compression wave becomes different with the propagating distance; that is, a shock wave appears just head of a wavefront and an overshoot on pressure distribution is observed behind a shock wave due to the transition of the unsteady boundary layer.

Nakamura, Shinya; Sasa, Daisuke; Aoki, Toshiyuki

2011-03-01

100

JOURNAL OF GEOPHYSICAL RESEARCH: SPACE PHYSICS, VOL. 118, 52865295, doi:10.1002/jgra.50469, 2013 Additional attenuation of natural VLF electromagnetic waves  

E-print Network

Additional attenuation of natural VLF electromagnetic waves observed by the DEMETER spacecraft resulting from VLF electromagnetic wave data measured by the DEMETER (Detection of Electro-Magnetic Emissions has been made in the field of seismo-electromagnetic effects. The main aim of this study is to look

Santolik, Ondrej

101

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

NASA Technical Reports Server (NTRS)

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

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

1974-01-01

102

Measurement of acoustic attenuation in South Pole ice  

Microsoft Academic Search

Using the South Pole Acoustic Test Setup (SPATS) and a retrievable transmitter deployed in holes drilled for the IceCube experiment, we have measured the attenuation of acoustic signals by South Pole ice at depths between 190m and 500m. Three data sets, using different acoustic sources, have been analyzed and give consistent results. The method with the smallest systematic uncertainties yields

R. Abbasi; Y. Abdou; T. Abu-Zayyad; J. Adams; J. A. Aguilar; M. Ahlers; K. Andeen; J. Auffenberg; X. Bai; M. Baker; S. W. Barwick; R. Bay; J. L. Bazo Alba; K. Beattie; J. J. Beatty; S. Bechet; J. K. Becker; M. L. Benabderrahmane; J. Berdermann; P. Berghaus; D. Berley; E. Bernardini; D. Bertrand; M. Bissok; E. Blaufuss; D. J. Boersma; C. Bohm; S. Böser; O. Botner; L. Bradley; J. Braun; S. Buitink; M. Carson; D. Chirkin; B. Christy; J. Clem; F. Clevermann; S. Cohen; C. Colnard; D. F. Cowen; M. V. D’Agostino; C. De Clercq; L. Demirörs; O. Depaepe; F. Descamps; P. Desiati; G. de Vries-Uiterweerd; T. DeYoung; J. C. Díaz-Vélez; J. Dreyer; M. R. Duvoort; R. Ehrlich; J. Eisch; R. W. Ellsworth; O. Engdegård; S. Euler; P. A. Evenson; O. Fadiran; A. R. Fazely; T. Feusels; K. Filimonov; C. Finley; M. M. Foerster; B. D. Fox; A. Franckowiak; R. Franke; T. K. Gaisser; J. Gallagher; R. Ganugapati; M. Geisler; L. Gerhardt; L. Gladstone; T. Glüsenkamp; A. Goldschmidt; J. A. Goodman; D. Grant; T. Griesel; A. Gross; S. Grullon; R. M. Gunasingha; L. Gustafsson; C. Ha; A. Hallgren; F. Halzen; K. Han; K. Hanson; K. Helbing; P. Herquet; S. Hickford; G. C. Hill; K. D. Hoffman; A. Homeier; K. Hoshina; D. Hubert; W. Huelsnitz; J.-P. Hülß; K. Hultqvist; S. Hussain; R. L. Imlay; A. Ishihara; J. Jacobsen; G. S. Japaridze; H. Johansson; J. M. Joseph; K.-H. Kampert; A. Kappes; T. Karg; A. Karle; J. L. Kelley; N. Kemming; P. Kenny; J. Kiryluk; F. Kislat; S. R. Klein; S. Knops; J.-H. Köhne; G. Kohnen; H. Kolanoski; L. Köpke; D. J. Koskinen; M. Kowalski; T. Kowarik; M. Krasberg; T. Krings; G. Kroll; K. Kuehn; T. Kuwabara; M. Labare; S. Lafebre; K. Laihem; H. Landsman; R. Lauer; R. Lehmann; D. Lennarz; J. Lünemann; J. Madsen; P. Majumdar; R. Maruyama; K. Mase; H. S. Matis; M. Matusik; K. Meagher; M. Merck; P. Mészáros; T. Meures; E. Middell; N. Milke; T. Montaruli; R. Morse; S. M. Movit; R. Nahnhauer; J. W. Nam; U. Naumann; P. Nießen; D. R. Nygren; S. Odrowski; A. Olivas; M. Olivo; S. Panknin; L. Paul; C. Pérez de los Heros; J. Petrovic; A. Piegsa; D. Pieloth; R. Porrata; J. Posselt; P. B. Price; M. Prikockis; G. T. Przybylski; K. Rawlins; P. Redl; E. Resconi; W. Rhode; M. Ribordy; A. Rizzo; J. P. Rodrigues; F. Rothmaier; C. Rott; C. Roucelle; T. Ruhe; D. Rutledge; B. Ruzybayev; D. Ryckbosch; H.-G. Sander; S. Sarkar; K. Schatto; S. Schlenstedt; T. Schmidt; D. Schneider; A. Schukraft; O. Schulz; M. Schunck; D. Seckel; B. Semburg; S. H. Seo; Y. Sestayo; S. Seunarine; A. Silvestri; G. M. Spiczak; C. Spiering; M. Stamatikos; T. Stanev; G. Stephens; T. Stezelberger; R. G. Stokstad; S. Stoyanov; E. A. Strahler; T. Straszheim; G. W. Sullivan; Q. Swillens; I. Taboada; A. Tamburro; O. Tarasova; A. Tepe; S. Ter-Antonyan; P. A. Toale; D. Tosi; D. Tur?an; N. van Eijndhoven; J. Vandenbroucke; A. Van Overloop; J. van Santen; B. Voigt; C. Walck; T. Waldenmaier; M. Wallraff; C. Wendt; S. Westerhoff; N. Whitehorn; K. Wiebe; C. H. Wiebusch; G. Wikström; D. R. Williams; R. Wischnewski; H. Wissing; K. Woschnagg; C. Xu; X. W. Xu; J. P. Yanez; G. Yodh; S. Yoshida; P. Zarzhitsky

2011-01-01

103

Ultrasound attenuation measurement in the presence of scatterer variation  

E-print Network

1 Introduction It is well known that medical ultrasound images contain many artefacts dueUltrasound attenuation measurement in the presence of scatterer variation for reduction@eng.cam.ac.uk #12;Abstract Pulse-echo ultrasound display relies on many assumptions which are known

Drummond, Tom

104

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...

105

P-wave scattering attenuation images of Tenerife island using Autocorrelation Functions from velocity seismic tomography fluctuations  

NASA Astrophysics Data System (ADS)

We use the new quantitative approach developed by De Siena et al., 2011, to calculate the scattering attenuation coefficient at Tenerife (Canary Island, Spain) from the space distribution of the P-wave seismic velocity. We calculate the space autocorrelation function (ACF) of the vertical velocity fluctuations, as a function of depth and for any couple of surface coordinates from the velocity tomography obtained by Garcia-Yeguas et al. (2012). We then fit the measured velocity random fluctuations with the theoretical exponential ACF, and estimate from the fit both spatially averaged the mean square (MS) fractional fluctuations and correlation distance, in turn associated with the inverse scattering quality factor, assuming a Born scattering fluctuations. In this way for any couple of space surface coordinates we associate an average (over depth) inverse quality factor, Q-1PSc. The Q-1PSc map shows that the largest scattering attenuation is located in the middle of the island, in a zone almost coincident with the caldera structure. The S-wave scattering attenuation shows an opposite pattern (Prudencio et al., 2013) with the minimum scattering attenuation coinciding with the caldera structure. This (preliminary) result may appear as contradictory, but in reality shows that most the of scattering phenomena at high frequency are associated with the shear waves.

Garcia-Yeguas, Araceli; Del Pezzo, Edoardo; Prudencio, Ianire; Ibañez, Jesús M.; De Siena, Luca; Diaz, Alejandro

2014-05-01

106

The attenuation mechanism of S-waves in the source zone of the 1999 Chamoli earthquake  

NASA Astrophysics Data System (ADS)

In the present study the attenuation mechanism of seismic wave energy in and around the source area of the Chamoli earthquake of 29th March 1999 is estimated using the aftershock data. Most of the analyzed events are from the vicinity of the Main Central Thrust (MCT), which is a well-defined tectonic discontinuity in the Himalayas. Separation of intrinsic (Qi-1) and scattering (Qs-1) attenuation coefficient is done over the frequencies 1, 2, 4, 8 and 16 Hz using Multiple Lapse Time Window Analysis (MLTWA) method. It is observed that S-waves and their coda are primarily attenuated due to scattering attenuation and seismic albedo is very high at all the frequencies. A comparison of attenuation characteristics obtained using these aftershock data with those obtained using data of general seismicity of this region reveal that at lower frequencies both intrinsic and scattering attenuation for Chamoli was much higher compared to those for Garwhal-Kumaun region using general seismicity data. At higher frequencies intrinsic attenuation for Chamoli is lower than and scattering attenuation is comparable to those obtained using general seismicity data of Garwhal-Kumaun region.

Mukhopadhyay, S.; Kumar, A.; Garg, A.; Del-Pezzo, E.; Kayal, J. R.

2014-01-01

107

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

Microsoft Academic Search

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

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

2010-01-01

108

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

109

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

110

Attenuation zones of periodic pile barriers and its application in vibration reduction for plane waves  

NASA Astrophysics Data System (ADS)

The periodic theory of solid-state physics is introduced to study the reduction characteristics of periodic pile barriers. The attenuation zones of a two-dimensional infinite periodic pile barrier subjected to plane waves are analyzed by plane wave expansion method. Influences of soil parameters and pile configurations on the first no-directional attenuation zone are discussed. The screening effectiveness of finite periodic pile barriers is simulated by the finite element method. The present theoretical results are in well agreement with experimental data, which validates the existence of attenuation zones in the periodic structures. The results show that vibrations with frequencies in the attenuation zones can be reduced significantly. The present investigation provides a new concept for designing pile barriers to block mid-frequency vibration.

Huang, Jiankun; Shi, Zhifei

2013-09-01

111

DTS Measurements Waves Model Toroidal field discussion Experimental magnetostrophic waves  

E-print Network

DTS Measurements Waves Model Toroidal field discussion Experimental magnetostrophic waves T #12;DTS Measurements Waves Model Toroidal field discussion The Earth Magnetostrophic waves Hartmann meeting, Coventry 15-16 February 2007 #12;DTS Measurements Waves Model Toroidal field discussion The Earth

Low, Robert

112

The Effect of Methane Hydrate Formation on Seismic Wave Attenuation in Sand  

NASA Astrophysics Data System (ADS)

Knowledge of seismic wave attenuation in hydrate-bearing sediments can potentially improve the geophysical quantification of seafloor methane hydrates with applications to climate change, geohazards and economic resource studies. With this aim, we conducted a series of small strain (< 10-6), seismic frequency (50 - 550 Hz), laboratory resonant column experiments on synthetic methane hydrate-bearing sands, created under excess-gas and excess-water conditions, at an effective pressure of 500 kPa, for controlled hydrate saturations Sh between 0 - 0.43. The excess-gas method resulted in predominantly methane saturated, hydrate-bearing sand (water saturation Sw = 0.01), while the excess-water method produced a water saturated (Sw = 1.0), hydrate-bearing sand. Previously reported velocity results for P- and S-waves can be explained by grain coating hydrate for excess-gas formation, and by pore-filling hydrate for excess-water formation, based on theoretical velocity models. Both hydrate formation methods gave elevated P- and S-wave attenuations (here denoted as inverse quality factor Qp-1 and Qs-1 respectively) up to, for excess-gas 0.036 (Qp-1) and 0.025 (Qs-1), and for excess-water 0.1 (Qp-1) and 0.03 (Qs-1.). These values are always greater than those for sand without any hydrate, either water or partially water saturated; excess-water attenuation is always higher than excess-gas attenuation values above Sh = 0.1 (note that data were collected at discrete hydrate saturations between Sh = 0 - 0.43 only). Despite experimental errors of ± 10%, the attenuations show significant variations with hydrate saturation, and evidence for attenuation peaks at Sh = 0.05 for excess-gas, and at Sh = 0.13, 0.32 for excess-water, formation. Theoretical attenuation modelling with grain coating hydrate cement or load-bearing hydrate or pore-filling hydrate, based on extant velocity models, suggests that load-bearing hydrate is an important cause of heightened attenuation for both P- and S-waves in gas and water saturated sand, while pore-filling hydrate also contributes significantly to P-wave attenuation in water saturated sand. A poro-viscoelastic attenuation mechanism related to microporous hydrate and the formation of low aspect ratio pores adjacent to sand grains is thought to be responsible for the heightened levels of attenuation, whether in gas or water saturated sand. The model can be extended to clay-rich sediments.

Best, A. I.; Priest, J.; Clayton, C. R.; Rees, E. V.

2012-12-01

113

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

NASA Astrophysics Data System (ADS)

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

Meirova, Tatiana; Pinsky, Vladimir

2014-04-01

114

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...

115

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

116

Centimeter and millimeter wave attenuation by atmospheric gases and rainfall at a tropical station  

NASA Astrophysics Data System (ADS)

The mean surface air pressure, temperature, and water temperature for a site in southern Nigeria are used to compute the radio wavelength attenuation due to oxygen and water vapor over the 3-350 GHz range. Attenuation is found to be generally higher at this tropical location than at temperate climates. A similar analysis was performed for rainfall attenuation using rainfall intensity measurements, and results obtained with three different expressions for rain height led to a 3-km value for the estimation of earth-space rainfall attenuation at this location. Results indicate that while the contributions of oxygen and water vapor to the total atmospheric attenuation could be neglected when compared with rainfall attenuation, up to about 150 GHz, the contribution becomes significant above 190 GHz.

Ajayi, G. O.; Kolawole, L. B.

1984-07-01

117

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

NASA Astrophysics Data System (ADS)

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

Vogel, Gerard N.

1988-02-01

118

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

119

Upper mantle attenuation structure beneath East Africa from relative t* measurements  

NASA Astrophysics Data System (ADS)

We are studying the attenuation structure of the upper mantle beneath east Africa using body waves recorded by a PASSCAL array that was deployed in Tanzania between 1994-1995. The array runs along two profiles (EW and NE-SW) that traverse the Tanzania craton and the surrounding rifted mobile belts. Studying this region may provide important clues on the initiation of Cenozoic rifting in east Africa and hence, give us insights into the tectonic and geodynamic processes that occur during the initial stages of rift development. The same dataset has been used to obtain tomographic velocity models, so we can compare the velocity structure to the attenuation structure. We determined the P wave spectral amplitude ratios of data from the same earthquake recorded at different stations (thereby eliminating the source effect), and computed relative t* (path integrated attenuation) from the slopes of these ratios. We then used a least-squares inversion to determine the t* at each station relative to the average t* of the array. We applied the same procedure to determine relative t* for S waves from the transverse components of the data (i.e., SH only). To simplify the problem, we selected events that have azimuths along the two profiles, and we have initially focused on events along the EW profile. On comparing the estimates of t* to the residual travel times estimated by Ritsema et. al., (1998), we observe that the t* values and residual travel times are not always correlated. Also, the observed t* values from P wave data are anti-correlated to the observed S wave data for stations within the craton. We are planning to compute forward models in order to isolate elastic from anelastic effects on our t* measurements, and to place constraints on upper mantle Q values.

Nyblade, A. A.; Venkataraman, A.; Ritsema, J.

2003-12-01

120

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

121

Physics of the Earth and Planetary Interiors 151 (2005) 243258 Estimation of coda wave attenuation for NW Himalayan  

E-print Network

Physics of the Earth and Planetary Interiors 151 (2005) 243­258 Estimation of coda wave attenuation, India b H. No. 360, Sector 71, SAS Nagar (Mohali), Ropar, Punjab 160071, India Received 6 October 2004; received in revised form 2 January 2005; accepted 20 March 2005 Abstract The attenuation of seismic wave

Parvez, Imtiyaz Ahmed

122

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

NASA Technical Reports Server (NTRS)

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

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

2006-01-01

123

Attenuation of P, S, and coda waves in Koyna region, India  

Microsoft Academic Search

The attenuation properties of the crust in the Koyna region of the Indian shield have been investigated using 164 seismograms\\u000a from 37 local earthquakes that occurred in the region. The extended coda normalization method has been used to estimate the\\u000a quality factors for P waves $$ {\\\\left( {Q_{\\\\alpha } } \\\\right)} $$ and S waves $$ {\\\\left( {Q_{\\\\beta } }

Babita Sharma; S. S. Teotia; Dinesh Kumar

2007-01-01

124

The influence of pressure waves on measurements of high speed train noise  

Microsoft Academic Search

Pressure waves are studied experimentally and theoretically; their attenuation by high pass filters is calculated. Relative to an observer at rest, strong pressure fluctuations (pressure waves) are generated by high speed trains. Intensities are typically two orders of magnitude higher than those of radiated noise. Although this can cause problems when measuring noise close to the track, pressure waves can

D. Bechert

1980-01-01

125

Parameters affecting water-hammer wave attenuation, shape and timing—Part 1: Mathematical tools  

Microsoft Academic Search

This two-part paper investigates key parameters that may affect the pressurewaveform predicted by the classical theory ofwater-hammer. Shortcomings in the prediction of pressure wave attenuation, shape and timing originate from violation of assumptions made in the derivation of the classical waterhammer equations. Possible mechanisms that may significantly affect pressure waveforms include unsteady friction, cavitation (including column separation and trapped air

Anton Bergant; Arris S. Tijsseling; John P. Vítkovský; Dídia I. C. Covas; Angus R. Simpson; Martin F. Lambert

2008-01-01

126

Attenuation of acoustic waves in glacial ice and salt domes P. B. Price  

E-print Network

Cl (rock salt) with grain size 0.75 cm, scattering lengths are calculated to be 120 and 1.4 km at 10 and 30Attenuation of acoustic waves in glacial ice and salt domes P. B. Price Physics Department and salt domes, are under consideration as media in which to deploy instruments for detection of neutrinos

Price, P. Buford

127

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

128

Global Love wave overtone measurements  

NASA Astrophysics Data System (ADS)

Love wave phase velocities for fundamental and higher modes are difficult to measure because the different modes cannot easily be separated. Following Yoshizawa and Kennett (2002), we generate suites of path specific one-dimensional shear wave velocity profiles using the Neighbourhood Algorithm of Sambridge (1999a). From this family of O(104) models both fundamental and higher mode phase velocities with mutually consistent uncertainties are calculated. We have fully automated the method and analysed over forty thousand Love wave seismograms from the GDSN and GEOSCOPE global networks from 1994-2004. Our phase velocity measurements agree remarkably well with previous studies, but we have been able to enlarge the available dataset dramatically. We present global Love wave phase velocity maps (up to the fifth overtone) with unprecedented resolution due to the improved path coverage. Comparing these maps to existing tomographic models, we discern evidence of significant anisotropy in the lower mantle around a depth of 1000 km in the Pacific.

Visser, K.; Lebedev, S.; Trampert, J.; Kennett, B. L. N.

2007-02-01

129

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

130

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

131

Attenuation of coda waves in the Garhwal Himalaya, India  

Microsoft Academic Search

Qc estimates have been obtained by analysing coda waves of seven local earthquakes recorded in the Garhwal Himalaya. The earthquakes have their epicentral distances within 100 km, focal depths up to 20 km with 2.4 ? ML ? 4.9. Qc values have been computed at central frequencies of 1.5, 3.0, 6.0, 12.0 and 18.0 Hz for different earthquake stations falling

S. C. Gupta; V. N. Singh; Ashwani Kumar

1995-01-01

132

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

133

Radiometric measurements of cloud attenuation at a tropical location in India  

NASA Astrophysics Data System (ADS)

The effect of the earth's atmosphere on radio waves propagating over an earth-space path is a major concern in the design and performance of satellite communications systems. Some characteristics of cloud and its effect on signal propagation has been studied using multi-wavelength radiometer at a tropical location of Kolkata, India. The liquid water content profile shows high values at higher altitude during pre-monsoon season indicating the presence of cloud above zero degree isotherm. Significant change in attenuation value is observed for same liquid water content due to change in temperature and accordingly a suitable relationship is obtained for the present location. The measurements indicate that ~4 dB and ~12 dB attenuation is caused due to cloud at 0.01% outage probability at the Ka and V band, respectively. ITU-R model is found to be overestimating the cloud attenuation over this location and indicate the need for more experimental measurement from tropical region.

Das, Saurabh; Chakraborty, Swastika; Maitra, Animesh

2013-12-01

134

Point-to-point measurement of radio frequency attenuation in South Polar ice  

NASA Astrophysics Data System (ADS)

For ultra high energy (UHE) electromagnetic showers in a dense medium, radio frequency Cherenkov emission is enhanced due to the Askaryan effect. Present and future detectors such as RICE, ANITA, ARIANNA and the Askaryan Radio Array (ARA) exploit this effect to detect UHE neutrinos interacting with Antarctic ice. The radio frequency electromagnetic wave attenuation length (the distance over which signal amplitude diminishes by a factor of 1/e due to absorption or scattering) is of tantamount importance as it determines the size scale and effective volume of these detectors. Previous attenuation measurements rely on reflections off the bedrock of signals from a surface-mounted transmitter. Using RICE in-ice transmitters and IceCube Radio Extension in-ice receivers, we are conducting a point-to-point attenuation measurement in the upper 1500 meters of South Polar ice, the region of interest for planned near-surface detectors such as ARA. We will present the analysis method as well as preliminary results.

Richman, Michael; Hoffman, Kara

2011-04-01

135

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 ...

136

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

137

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

138

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

139

Attenuation and localization of bending waves in a periodic/disordered fourfold composite beam  

NASA Astrophysics Data System (ADS)

By using the transfer matrix method this paper presents a study of the complex band structure, attenuation spectra and localization of bending waves in a periodic/disordered fourfold composite beam constructed by inserting thin piezoelectric or soft rubber layer at each interface of original elastic composite structures. Numerical examples are presented and the accuracy is validated by the wavelet method. The results show that the piezoelectricity can adjust the band gaps and the soft rubber can enlarge the degree of the localization and the frequency ranges of the complex band gaps. The localization factor resembles the shape of the attenuation curve in the complex band gaps. Subtle differences between the random disorder and the deterministic disorder are observed, except at lower frequencies. The behavior of the wave propagation and localization in random disordered beams can be altered by tuning different inserting position. The existence of piezoelectricity and/or soft rubber layers lends new insight into the vibration control of composite beams.

Yan, Zhi-Zhong; Zhang, Chuanzeng; Wang, Yue-Sheng

2009-10-01

140

Parameters affecting water-hammer wave attenuation, shape and timing—Part 2: Case studies  

Microsoft Academic Search

This two-part paper investigates parameters that may significantly affect water-hammer wave attenuation, shape and timing. Possible sources that may affect the waveform predicted by classical water-hammer theory include unsteady friction, cavitation (including column separation and trapped air pockets), a number of fluid–structure interaction effects, viscoelastic behaviour of the pipe-wall material, leakages and blockages. Part 1 of this two-part paper presents

Anton Bergant; Arris S. Tijsseling; John P. Vítkovský; Dídia I. C. Covas; Angus R. Simpson; Martin F. Lambert

2008-01-01

141

Seismic attenuation in the eastern Australian and Antarctic plates, from multiple ScS waves  

NASA Astrophysics Data System (ADS)

The attenuation of seismic shear waves in the mantle beneath the eastern Australian and Antarctic plates is analysed using a large data set of multiple ScSn waves, reflected n times at the core-mantle boundary and (n-1) times at the surface. The data are the transverse components of deep earthquakes from the subduction zones north and east of Australia, recorded at stations in Antarctica, Australia, Indonesia, New Caledonia and New Zealand. The data are filtered with narrow bandpass filters at five frequencies in the range 0.013-0.040 Hz. The ScSn+1/ScSn amplitude ratios of successive ScS phases are compared to the ratios computed for synthetic seismograms for the same paths and same focal mechanisms, to eliminate the effects of source radiation and geometric attenuation. The synthetic seismograms are computed from a summation of toroidal modes for the 1-D reference model PREM. The observed to computed spectral ratios appear consistent for similar paths. They reveal that the attenuation is not frequency dependent, that the contribution of scattering to attenuation is low, and that the PREM model is a valuable reference model for the study region at the considered frequencies. An inversion of the data at 0.026 Hz is performed to retrieve the quality factor Q in the upper mantle, in regions defined using a priori constraints inferred from seismic shear velocities. Q-values close to those of PREM are found beneath the Australian and Antarctic cratons, lower values beneath the Eastern Australian Phanerozoic margin, and very low values beneath the oceanic region between Australia and Antarctica, where ridges and a triple junction are present. The Australian-Antarctic Discordance along the South-Indian ridge appears as an exception with a Q-value close to those of stable continents. The highest Q-values are found beneath the subduction zones, a feature which is not apparent in global attenuation models possibly because of its narrow lateral extension, and because it extends at depths larger than those sampled by surface waves. Despite limitations due to the uneven distribution of the ScSn bounce points at the surface and to the difficulty of collecting a large number of high quality data, our approach appears very promising. It is complementary to the more widely used determination of seismic attenuation using surface waves because it provides increased depth coverage, and a broader spectral coverage. It therefore has a considerable potential in future investigations of mantle structure and dynamics.

Souriau, Annie; Rivera, Luis; Maggi, Alessia; Lévêque, Jean-Jacques

2012-07-01

142

Q-structure beneath the Tibetan Plateau from the inversion of Love- and Rayleigh-wave attenuation data  

NASA Astrophysics Data System (ADS)

The fundamental mode Love and Rayleigh waves generated by ten earthquakes and recorded across the Tibet Plateau, at QUE, LAH, NDI, NIL, KBL, SHL, CHG, SNG and HKG are analysed. Love- and Rayleigh-wave attenuation coefficients are obtained at time periods of 5-120 s using the spectral amplitudes of these waves for 23 different paths. Love wave attenuation coefficient varies from 0.0021 km -1, at a period of 10 s, to 0.0002 km -1 at a period of 90 s, attaining two maxima at time periods of 10 and 115 s, and two minima at time periods of 25 and 90 s. The Rayleigh-wave attenuation coefficient also shows a similar trend. The very low value for the dissipation factor, Q?, obtained in this study suggests high dissipation across the Tibetan paths. Backus-Gilbert inversion theory is applied to these surface wave attenuation data to obtain average Q?-1 models for the crust and uppermost mantle beneath the Tibetan Plateau. Independent inversion of Love- and Rayleigh-wave attenuation data shows very high attenuation at a depth of ˜50-120 km ( Q ? ? 10 ). The simultaneous inversion of the Love and Rayleigh wave data yields a model which includes alternating regions of high and low Q?-1 values. This model also shows a zone of high attenuating material at a depth of ˜40-120 km. The very high inferred attenuation at a depth of ˜40-120 km supports the hypothesis that the Tibetan Plateau was formed by horizontal compression, and that thickening occurred after the collision of the Indian and Eurasian plates.

Singh, D. D.; Gupta, Harsh K.

1982-08-01

143

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

144

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

145

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

146

Reflective attenuator for high-energy laser measurements  

Microsoft Academic Search

A high-energy laser attenuator in the range of 250 mJ (20 ns pulse width, 10 Hz repetition rate, 1064 nm wavelength) is described. The optical elements that constitute the attenuator are mirrors with relatively low reflectance, oriented at a 45 deg. angle of incidence. By combining three pairs of mirrors, the incoming radiation is collinear and has the same polarization

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

2008-01-01

147

Experimental measurements of seismic attenuation In microfractured sedimentary rock  

Microsoft Academic Search

In a previous paper (Peacock et al., 1994), the authors related ultrasonic velocities in water-saturated Carrara Marble to crack densities in polished sections to verify Hudson's (1980, 1981, 1986) theory for velocities in cracked rock. They describe the empirical relationships between attenuation and crack density that they established during these experiments in the hope of clarifying the mechanism of attenuation

Sheila Peacock; C. McCann; J. Sothcott; T. R. Astin

1994-01-01

148

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

149

Physical Models of Seismic-Attenuation Measurements on Lab Samples  

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

150

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

151

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

152

Millimeter-wave attenuation and delay rates due to fog/cloud conditions  

NASA Astrophysics Data System (ADS)

Propagation properties of suspended water and ice particles which make up atmospheric haze, fog, and clouds were examined for microwave and millimeter-wave frequencies. Rates of attenuation alpha (dB/km) and delay tau (ps/km) are derived from a complex refractivity based on the Rayleigh absorption approximation of Mie's scattering theory. Key variables are particle mass content and permittivity, which depends on frequency and temperature both for liquid and ice states. Water droplet attenuation can be estimated within a restricted (10 + or - 10 C) temperature range using a simple two-coefficient approximation. Experimental data on signal loss and phase delay caused by fog at four frequencies (50, 82, 141, and 246 GHz) over a 0.81-km line-of-sight path were found to be consistent with the model.

Liebe, Hans J.; Hufford, George A.; Manabe, Takeshi

1989-12-01

153

Attenuation and localization of an electromagnetic wave on the surface of a cylindrical conductor  

NASA Astrophysics Data System (ADS)

An analytical study of the linear attenuation and the rate of localization of the energy of an electromagnetic wave propagating on the surface of a cylinder coated with a dielectric and imbedded in another dielectric is presented. The system is described in cylindrical coordinates, and the second dielectric is regarded as being possibly air, as would happen in an antenna configuration. The attenuation of the signal is calculated for all values of the ratio of the radius of the external layer to the first, conductive cylinder radius, and the phase shift is shown to vary with the ratio. The losses of energy through the dielectric layer are shown to have a negligible impact on the distribution of energy on the cylinder surface.

Zepp, G.; Wick, A.; Fabre, G.; Ritoux, G.

1982-10-01

154

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

155

Attenuation characteristics of the guided THz wave in parallel-plate ferroelectric-graphene waveguides  

NASA Astrophysics Data System (ADS)

Guided THz wave characteristics in a parallel-plate waveguide (PPWG) consisting of ferroelectric film (LiNbO3 and LiTaO3) and multilayer graphene (MLG) is studied in this paper, with their low and tunable attenuation valley predicted. The electrical conductivity of MLG is calculated by a set of closed-form equations with the coupling effect between the bottom graphene layer (BGL) and its substrate taken into account carefully, while the dispersive behavior of ferroelectric film itself is described by the Lorentz model over an ultra-wide THz band. It is shown that the guided TM-mode propagation can be adjusted effectively by changing temperature, frequency, optical pumping intensity, MLG layer number, film thickness and its transverse optical-phonon frequency. Moreover, one low attenuation valley of TM-mode in such ferroelectric-graphene waveguide is captured, which can be exploited for developing some THz planar tunable waveguides with ultra-low loss.

Gu, Xiao-Qiang; Yin, Wen-Yan; Zheng, Ting

2014-11-01

156

Cloud Attenuation in Millimeter Wave and Microwave Frequencies for Satellite Applications over Equatorial Climate  

NASA Astrophysics Data System (ADS)

A propagation experiment has been carried out at Penang using the SUPERBIRD-C satellite beacon. Cloud occurrences were observed during different months and it is seen that the low cloud occurrences over Penang is very significant from October to January. The cloud attenuation results that are presented, which include the testing of models, have been obtained from the data gathered over five years. The specific attenuation of radio wave due to clouds at various frequencies 12 GHz, 20 GHz, 75 GHz, 50 GHz and 100 GHz has been estimated whereby the values varies from 0.14 dB/km at 12 GHz to 10.1 dB/km at 100 GHz.

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

2008-02-01

157

Attenuation Of Current Wave Propagating Along A Perfectly Conducting Wire: Application To Lightning  

NASA Astrophysics Data System (ADS)

In this study, using the finite-difference time-domain (FDTD) method for solving Maxwell_fs equations, we demonstrate that a vertical phased array of current sources above perfectly conducting ground, activated as prescribed by the transmission line (TL) model with return-stroke speed equal to the speed of light (v = c), produces a spherical TEM wave, identical to that analytically derived for the TL model with v = c by Thottappillil et al. [2001]. (This can be viewed as a proof of validity of the FDTD method used here.) Then, we apply the same approach to the case of a lumped current source at the bottom of a vertical perfectly conducting wire above perfectly conducting ground and show that the current wave launched by the current source propagates upward with attenuation and that the resultant field structure is non-TEM, as also follows from other lightning return stroke models based on solving Maxwell_fs equations. The attenuation is stronger for shorter current pulses and for current sources of smaller length. Thus, it appears that the basic assumption of the TL model (no current attenuation with height) is inconsistent with Maxwell_fs equations, unless the lightning channel is viewed as a phased array of current sources. It is inconsistent with the transmission line theory either, since a vertical wire above ground constitutes a non-uniform transmission line, whose characteristic impedance varies with height. We will try to explain the mechanism of current attenuation on a vertical perfectly conducting wire above perfectly conducting ground, usually attributed to radiation losses, on the basis of the electromagnetic field theory. In particular, we will discuss the interaction of the electromagnetic field produced by the source with the vertical conductor and ground and the direction of resultant Poynting vector. Thottappillil, R., J. Schoene, and M. A. Uman, Return stroke transmission line model for stroke speed near and equal that of light, Geophys. Res. Lett, 28(18), 3593-3596, 2001.

Baba, Y.; Rakov, V. A.

2003-12-01

158

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

159

Experimental measurements of seismic attenuation in microfracture sedimentary rock  

SciTech Connect

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

Peacock, S.; McCann, C.; Sothcott, J.; Astin, T.R. (Univ. of Reading (United Kingdom). Research Inst. for Sedimentology)

1994-09-01

160

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

161

Systematic scanner variability of patient CT attenuation measurements  

NASA Astrophysics Data System (ADS)

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

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

2009-02-01

162

Effects of finite electron mean free path on the attenuation, electromagnetic generation, and detection of ultrasonic shear waves in superconductors  

Microsoft Academic Search

Use of the general many-body formalism allows us to derive a system of equations describing the propagation of electromagnetic shear waves coupled to ultrasonic shear waves in normal and superconducting metals with arbitrary electron mean free paths. From this system of equations we derive general expressions in terms of correlation functions for the attenuation coefficient as well as for the

Kurt Scharnberg

1978-01-01

163

Ultrasonic velocity and attenuation during CO 2 injection into water-saturated porous sandstone: Measurements using difference seismic tomography  

NASA Astrophysics Data System (ADS)

We undertook laboratory-based seismic measurements with dense sensor array at ultrasonic frequencies during the injection of CO 2 into a water-saturated sandstone specimen. The resulting high-quality seismic data enabled detailed determination of the relative velocity and attenuation coefficient of the compressional wave using difference seismic tomography, which directly inverses time-lapse changes in rock properties from time-lapse changes in observed data. CO 2 migration and water displacement were clearly mapped using tomographic images of relative velocity and the attenuation coefficient. The final and largely stabilised volume fraction of CO 2 in the pore space of the sample is about 30-40%. On average, the P-velocity fell by 7.5, 12, and 14.5% and the attenuation coefficient Q-1 increased by factors of 3.3, 2.7, and 3.7 as a result of the replacement of water with CO 2 during the injection of gaseous, liquid, and supercritical CO 2, respectively. As a function of gas saturation, both the velocity and attenuation data are in good agreement with results obtained using the White and Dutta-Odé model for partial saturation, indicating that viscous losses due to fluid diffusion are of significant importance for compressional waves travelling at ultrasonic frequencies in porous rocks.

Lei, Xinglin; Xue, Ziqiu

2009-10-01

164

Gamma ray attenuation coefficient measurement for neutron-absorbent materials  

NASA Astrophysics Data System (ADS)

The compounds Na 2B 4O 7, H 3BO 3, CdCl 2 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 1408 keV, have been determined by the ? rays transmission method in a good geometry setup; also, these coefficients were calculated by MCNP code. A comparison between experiments, simulations and Xcom code has shown that the study has potential application for determining the attenuation coefficient of various compound materials. Experiment and computation show that H 3BO 3 with the lowest average Z has the highest gamma ray attenuation coefficient among the aforementioned compounds.

Jalali, Majid; Mohammadi, Ali

2008-05-01

165

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

PubMed

The so-called Localized Waves (LW), and the "Frozen Waves" (FW), have raised significant attention in the areas of Optics and Ultrasound, because of their surprising energy localization properties. The LWs resist the effects of diffraction for large distances, and possess an interesting self-reconstruction -self-healing- property (after obstacles with size smaller than the antenna's); while the FWs, a sub-class of LWs, offer the possibility of arbitrarily modeling the longitudinal field intensity pattern inside a prefixed interval, for instance 0?z?L, of the wave propagation axis. More specifically, the FWs are localized fields "at rest", that is, with a static envelope (within which only the carrier wave propagates), and can be endowed moreover with a high transverse localization. In this paper we investigate, by simulated experiments, various cases of generation of ultrasonic FW fields, with the frequency of f0=1 MHz in a water-like medium, taking account of the effects of attenuation. We present results of FWs for distances up to L=80 mm, in attenuating media with absorption coefficient ? in the range 70???170 dB/m. Such simulated FW fields are constructed by using a procedure developed by us, via appropriate finite superpositions of monochromatic ultrasonic Bessel beams. We pay due attention to the selection of the FW parameters, constrained by the rather tight restrictions imposed by experimental Acoustics, as well as to some practical implications of the transducer design. The energy localization properties of the Frozen Waves can find application even in many medical apparatus, such as bistouries or acoustic tweezers, as well as for treatment of diseased tissues (in particular, for the destruction of tumor cells, without affecting the surrounding tissues; also for kidney stone shuttering, etc.). PMID:24709072

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

2014-08-01

166

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

167

High frequency attenuation measurements of lipid encapsulated contrast agents.  

PubMed

A number of recent studies have indicated the potential of ultrasound contrast agent imaging at high ultrasound frequencies. However, the acoustic properties of microbubbles at frequencies above 10 MHz remain poorly understood at present. In this study we characterize the high frequency attenuation properties of (1) BR14, (2) BR14 that has been mechanically filtered (1 and 2 microm pore sizes) to exclude larger bubbles, and (3) the micron to submicron agent BG2423. A narrowband pulse-echo substitution method is employed with a series of four transducers covering the frequency range from 2 to 50 MHz. For BR14, attenuation decreases rapidly from 2 to 10 MHz and then more gradually from 10 to 50 MHz. For 2 microm filtration, the attenuation peaks between 10 and 15 MHz. For 1 microm filtration, attenuation continues to rise until 50 MHz. The agent BG2423 exhibits a diffuse attenuation peak in the range of 15-25 MHz and remains high until 50 MHz. These results demonstrate a strong influence of bubble size on high frequency attenuation curves, with bubble diameters of 1-2 microm and below having more pronounced acoustic activity at frequencies above 10 MHz. PMID:16843511

Goertz, D E; Frijlink, M E; Voormolen, M M; de Jong, N; van der Steen, A F W

2006-12-22

168

Acoustic measurements of air entrainment by breaking waves  

NASA Astrophysics Data System (ADS)

Wave breaking at the surface of the ocean plays an important role in air-sea interaction processes. Bubbles entrained by breaking waves not only enhance the transfer of atmospheric gases to the ocean, but also modify the phase speed and attenuation of acoustic waves propagating through the bubbly medium. The development of acoustic instruments to measure bubbles and the results obtained from a number of field and laboratory experiments are presented. The first part of this dissertation addresses sound speed measurements made in the North Atlantic as part of the Acoustic Surface Reverberation Experiment (ASREX). An autonomous buoy system that directly measures the sound speed in the surface wave layer was developed. Data obtained with the instrument spanned several storm cycles with wind speeds and significant wave heights reaching 20 m/s and 8 m, respectively. The use of Wood's relation (1946) allows the calculation of the void fraction of air based on the low-frequency sound speed measurements. The highly variable near-surface sound speed/void fraction field is analyzed with respect to wind and surface wave- breaking parameters. The second part of this dissertation presents the development of a broadband acoustic technique which simultaneously measures the phase speed and attenuation at acoustic frequencies ranging from 4-100 kHz. The acoustic data is inverted for the size distribution of bubbles using algorithms that are based upon the physics of sound propagation through a bubbly mixture. This acoustic technique was evaluated in the large wave channel at the Hydraulics Laboratory, Scripps Institution of Oceanography, using mechanically generated breaking waves in seawater. Field measurements of bubble concentrations that result from wave breaking were made in both shallow water off Scripps Pier, California and in deep water near Point Conception, California using the broadband technique. Significant variability is observed in the bubble field, characterized by number densities of bubbles changing several orders of magnitude over short time periods. Analysis of the data with supporting environmental measurements reveal that features in the observed bubble size distributions correlate with mixing and transport processes.

Terrill, Eric James

1998-11-01

169

On the validity and improvement of the ultrasonic pulse-echo immersion technique to measure real attenuation.  

PubMed

A fundamental assumption embraced in conventional use of the ultrasonic pulse-echo immersion technique to measure attenuation in solid materials is revisited. The cited assumption relies on perfect and immutable adhesion at the water to sample interface, a necessary condition that allows calculating the reflection coefficient at any interface from elastic wave propagation theory. This parameter is then used to correct the measured signal and obtain the real attenuation coefficient of the sample under scrutiny. In this paper, cases in which the perfectly cohesive interfacial condition is not satisfied are presented. It is shown also that in those cases, the repeatability of the conditions at the interface is always uncertain. This implies that the reflection coefficients are unknown, even when density is known. A new method of simultaneously measuring the reflection coefficients for both exposed interfaces that are normal to the transducer, and the attenuation coefficient of the specimen is developed and is presented here. The robustness of the new method is proven, as we demonstrate that the proper value of attenuation is achieved independently of the continuously varying interfacial conditions of these non-ideal cases. PMID:23998204

Goñi, Miguel A; Rousseau, Carl-Ernst

2014-02-01

170

Calculation of the probability distributions of cm-wave and mm-wave attenuation on communications links, taking various atmospheric phenomena into account  

NASA Astrophysics Data System (ADS)

The paper presents a review of the literature on the current status of the problem of calculating radio-wave attenuation on communications links. The calculation of the mean values of probability distributions of radio-wave attenuation due to different factors is considered together with the ranges of possible variations of these distributions with respect to the calculated mean. Particular attention is given to the fading statistics of radio waves on surface links associated with anomalies of the air refractive index in the atmospheric surface layer.

Pozhidaev, V. N.

1992-10-01

171

Measuring the frequency-dependent attenuation in lossy material using large time-bandwidth product ultrasound signals  

NASA Astrophysics Data System (ADS)

Broadband signals are commonly used in ultrasonic spectroscopy to measure the frequency dependent attenuation characteristics of lossy solid media. Compared to narrowband signals, broadband signals are preferred since they do not require tedious frequency scanning and extensive data reduction efforts. Typically these broadband signals take the form of a pulse. Although the spectral range of a pulse is wide, the spectral resolution is limited by the duration of the signal. By employing signals with large time- bandwidth-products, the overall accuracy and resolution of ultrasonic spectroscopy can be improved. Expressions for the interaction of longitudinal waves, with large time- bandwidth-product, and isotropic materials are developed. The approach is effective for evaluating material with signals optimized for a frequency resolution and range of interest, but can also be used when thin materials (wave-speed and attenuation can be determined when density and thickness are measured. Explicit account is made for diffraction corrections, multiple echo contributions, and interface scattering losses. The formalism is compared with the traditional analysis approach to illustrate the improved accuracy of the new technique, detailing where diffraction correction and multiple echo effects can become significant. Measured attenuation spectra are presented for common plastic materials as well as for a castable polyurethane commonly used in ultrasonic transducer fabrication.

Gordon, Grant A.

1999-06-01

172

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

173

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

ERIC Educational Resources Information Center

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

Padilla, Miguel A.; Veprinsky, Anna

2012-01-01

174

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

E-print Network

Dynamic Measurements of Laser Light Attenuation by Cryogen Film and Frost Formation Bernard Choi1 surface. The cryogen pool eventually evaporates as frost forms on the skin surface due to condensation. The purpose of this study was to investigate laser light attenuation by the cryogen film/frost layer. Medical

Aguilar, Guillermo

175

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

NASA Astrophysics Data System (ADS)

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

Baldwin, Steven L.

176

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

177

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

178

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

179

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

180

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

NASA Astrophysics Data System (ADS)

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.

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

1999-11-01

181

Attenuation in the Australian-Antarctic region from multiple ScS waves  

NASA Astrophysics Data System (ADS)

The shear attenuation in the mantle beneath the Australian-Antarctic region is analyzed using a large data set of multiple ScSn waves. The data are the transverse components of deep earthquakes from the subduction zones North and East of Australia, recorded at stations in Antarctica, Australia, Indonesia, New Caledonia and New Zealand. The ScS(n+1)/ScSn amplitude ratios of successive ScS phases are compared to the ratios computed for PREM synthetic seismograms for the same paths and same focal mechanisms, in order to eliminate the effects of source radiation and geometric attenuation. A possible Q frequency dependence is investigated using narrow band-pass filters at several frequencies in the range 0.013-0.040 Hz. Assuming that Q heterogeneities are concentrated in the upper mantle, close to the upper bounce points, an inversion of the data at 0.026 Hz is performed to retrieve the quality factor in 5 regions defined using a priori constraints inferred from seismic shear velocities. Most stable results are obtained when restricting the analysis to ScS3/ScS2 and ScS4/ScS3 ratios, for which seismic phases can be properly isolated and whose bounce points sample sufficiently 4 of the 5 regions. Q values close to PREM's one are found beneath the Australian and Antarctic cratons, lower values beneath the Eastern Australian Phanerozoic margin, and very low values beneath the oceanic region between Australia and Antarctica, where ridges and a triple junction are present. The highest Q values are found beneath the subduction zones, a feature which is not apparent in global attenuation models. In the frequency range considered (0.013-0.040 Hz), our data do not require a frequency dependent quality factor. This result is robust and is consistent with previous results based on the decay of ScSn spectral ratios, obtained for various regions of the world.

Souriau, A.; Rivera, L.; Maggi, A.; Lévêque, J.-J.

2012-04-01

182

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

NASA Technical Reports Server (NTRS)

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

Vary, A.

1979-01-01

183

Acoustic attenuation measurements in transparent materials in the hypersonic range by picosecond ultrasonics  

NASA Astrophysics Data System (ADS)

The authors report on acoustic attenuation measurements in transparent thin films by picosecond ultrasonics. This ultrafast technique has already been proposed for such measurements but usually attenuation is overestimated and a specific sample configuration is needed. Here they present another way of using this technique which overcomes both difficulties. Experimental results obtained for silica show a very good agreement with literature. This validates the protocol which is then applied to various other materials used in microelectronics.

Emery, P.; Devos, A.

2006-11-01

184

Measurements of linear attenuation coefficients of irregular shaped samples by two media method  

NASA Astrophysics Data System (ADS)

The linear attenuation coefficient values of regular and irregular shaped flyash materials have been measured without knowing the thickness of a sample using a new technique namely "two media method". These values have also been measured with a standard gamma ray transmission method and obtained theoretically with winXCOM computer code. From the comparison it is reported that the two media method has given accurate results of attenuation coefficients of flyash materials.

Singh, Sukhpal; Kumar, Ashok; Thind, Kulwant Singh; Mudahar, Gurmel S.

2008-04-01

185

Atmospheric Gravity Wave Processes from Aqua Measurements  

NASA Astrophysics Data System (ADS)

Although not originally designed for this purpose, the high spatial resolution of AIRS and AMSU measurements have revealed new details of small-scale atmospheric gravity waves and their many effects on climate processes during the last decade. Gravity waves themselves drive localized temperature fluctuations with important impacts on clouds, precipitation, and atmospheric chemistry. Drag forces associated with gravity wave breaking drive circulation changes in climate models with additional wide-ranging effects. Models used for global weather forecasting now resolve some gravity wave features with scales of several hundred km, but many other gravity waves remain unresolved, while climate models resolve only some of the largest scale gravity waves. Understanding these waves, how they are generated, and how their climate effects can be best parameterized have become important issues both for testing current models and improving next generation climate predictions. Our research focuses both on waves from convection and mountain waves. AIRS radiance measurements provide the highest resolution, and we use these data to quantify wave generation by small mountainous islands and the effects of these waves on the general circulation. We also estimate the relative importance of the smallest-resolvable versus larger-scale mountain waves to the circulation directly from AIRS measurements. Details of wave generation within convective clouds are also examined, where AIRS measurements provide the constraints for simulations of their generation and propagation. These studies allow us to test assumptions employed in current parameterization methods. We will also show how the local-time sampling of Aqua is an important limitation for studies of gravity waves generated by convection.

Alexander, M.; Eckermann, S. D.; Grimsdell, A.; Hoffmann, L.; Teitelbaum, H.

2011-12-01

186

Attenuation of seismic waves and the universal rheological model of the Earth's mantle  

NASA Astrophysics Data System (ADS)

Analysis of results of laboratory studies on creep of mantle rocks, data on seismic wave attenuation in the mantle, and rheological micromechanisms shows that the universal, i.e., relevant to all time scales, rheological model of the mantle can be represented as four rheological elements connected in series. These elements account for elasticity, diffusion rheology, high temperature dislocation rheology, and low temperature dislocation rheology. The diffusion rheology element is described in terms of a Newtonian viscous fluid. The high temperature dislocation rheology element is described by the rheological model previously proposed by the author. This model is a combination of a power-law non-Newtonian fluid model for stationary flows and the linear hereditary Andrade model for flows associated with small strains. The low temperature dislocation rheology element is described by the linear hereditary Lomnitz model.

Birger, B. I.

2007-08-01

187

Pressure measurements of nonplanar stress waves  

SciTech Connect

A useful gage has been developed for measuring pressure of nonplanar or obliquely incident stress waves. The measurements made with these gages are not as precise as direct strain gage measurements, but are very good considering the conditions under which these gages are used. We feel a need to further develop our ability to measure nonplanar stress waves in the 0 to 10 kbar range. Carbon or ytterbium will probably be chosen for the sensing element.

Carlson, G.H.; Charest, J.A.

1981-02-27

188

Quasi-cylindrical 2.5-D wave modeling with a moment-tensor point source and the anelastic attenuation  

NASA Astrophysics Data System (ADS)

An accurate and efficient modeling of regional seismic wave propagation can be achieved by the axisymmetric modeling using the cylindrical coordinates (r, ? , z). It assumes the structural model as rotationally symmetric along the vertical axis (z) including a seismic source, and then solves the 3-D wave equation in cylindrical coordinates only on a 2-D structural cross section. Therefore, this method, a kind of the 2.5-D modeling, can correctly model 3-D geometrical spreading effects and the pulse shape, with computation time and memory comparable to 2-D modeling. On the other hand, application of the conventional purely axisymmetric approximation is difficult in practice because the structure along the measurement line of the seismic survey is rarely symmetric with respect to the source location. To overcome this difficulty, Takenaka et al. (2003, GRL) proposed a 'quasi-cylindrical approach'. It solves the wave equation not in the usual cylindrical domain (0 ? r < ? , -? ? ? ? ? , 0 ? z < ? ), but instead in a newly defined ``quasi-cylindrical domain'' (-? < r < ? , -? /2 ? ? ? ? /2, 0 ? z < ? ). They developed a numerical scheme with the finite-difference method (FDM). The quasi-cylindrical FDM enables modeling of regional seismic wave propagation in a 2-D slice of a structural model of arbitrary lateral heterogeneity, with full consideration of the 3-D geometrical spreading effects. Since the quasi-cylindrical approach was developed for seismic exploration, the FDM code has only treated axisymmetric source mechanisms. In this work we have improved this scheme to include an arbitrary moment-tensor point source and the anelastic attenuation for further realistic modeling. The moment-tensor source can be treated by the Fourier expansion of all wavefield variables in ? direction considering source radiation patterns. This process corresponds to decomposing an arbitrary source mechanism into five moment-tensor elements. Synthesizing all contributions enables us to model wavefields by the asymetric excitation. The anelastic attenuation is also adopted by the so-called memory variables (e.g., Emmerich & Korn, 1987, Geophysics). In the presentation, we will show realistic numerical examples using tomography models of plate subduction zone and shear dislocation sources.

Toyokuni, G.; Takenaka, H.; Okamoto, T.; Zhao, D.

2013-12-01

189

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

190

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

191

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

192

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

193

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

194

Mucosal Wave Measurement and Visualization Techniques  

PubMed Central

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

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

2010-01-01

195

Automatic millimeter wave mixer noise figure measurements  

NASA Technical Reports Server (NTRS)

Systems for making automatic noise figure measurements of millimeter wave mixers have been developed using both analog and digital techniques. The effect of IF mismatch on the measured noise figures is also determined with these methods (Forsythe, 1982). The measurement systems are versatile enough to be used to measure the noise figure of receivers anywhere from 30 to 300 GHz.

Forsythe, R. E.; Mcsheehy, J. J.

1982-01-01

196

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

NASA Astrophysics Data System (ADS)

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 gamma rays.

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

1999-11-01

197

Internal Wave Measurements From a Midwater Float  

Microsoft Academic Search

An instrument package has been developed that drifts along freely with the water while it repeatedly profiles ocean temperature. Profiling during drifting reduces the Doppler and line structure effects that usually contaminate internal wave measurements. Six days o1' exceptionally clean internal wave records were acquired 470 km offshore of San Diego, Calitbrnia, in June 1973 at a nominal depth of

James Lowell Cairns

1975-01-01

198

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

199

Anisotropic Changes in P-Wave Velocity and Attenuation during Deformation and Fluid Infiltration of Granite  

Microsoft Academic Search

4 Abstract. Fluid infiltration and pore fluid pressure changes are known to have a significant effect on the occurrence of earthquakes. Yet, for most damaging earthquakes, with nucleation zones below a few kilometers depth, direct measurements of fluid pressure variations are not available. Instead, pore fluid pressures are inferred primarily from seismic wave propagation characteristics such as V p\\/Vs ratio,

Sergei A. Stanchits; David A. Lockner; Alexander V. Ponomarev

2003-01-01

200

The attenuation coefficient of ammonium chloride for 662 keV gamma radiation, measured for dilute solutions  

NASA Astrophysics Data System (ADS)

The technique developed for the direct measurement of linear attenuation and mass attenuation (or absorption) coefficients of dilute solutions of salts has been applied to the attenuation of 662 keV gamma rays from 137Cs in dilute NH 4Cl solution.

Teli, M. T.; Chaudhari, L. M.

1996-04-01

201

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

202

Retrieval of atmospheric attenuation using combined ground-based and airborne 95-GHz cloud radar measurements  

NASA Technical Reports Server (NTRS)

This paper discusses cloud radar calibration and intercomparison of airborne and ground-based radar measurements and presents a unique algorithm for attenuation retrieval. This algorithm is based on dual 95-GHz radar measurements of the same cloud and precipitation volumes collected from opposing viewing angles.

Li, L.; Sekelsky, S.; Reising, S.; Swift, C.; Durden, S.; Sadowy, G.; Dinardo, S.; Li, F.; Huffman, A.; Stephens, G.; Babb, D.; Rosenberger, H.

2001-01-01

203

The role of the reflection coefficient in precision measurement of ultrasonic attenuation  

NASA Technical Reports Server (NTRS)

Ultrasonic attenuation measurements using contact, pulse-echo techniques are sensitive to surface roughness and couplant thickness variations. This can reduce considerable inaccuracies in the measurement of the attenuation coefficient for broadband pulses. Inaccuracies arise from variations in the reflection coefficient at the buffer-couplant-sample interface. The reflection coefficient is examined as a function of the surface roughness and corresponding couplant thickness variations. Interrelations with ultrasonic frequency are illustrated. Reliable attenuation measurements are obtained only when the frequency dependence of the reflection coefficient is incorporated in signal analysis. Data are given for nickel 200 samples and a silicon nitride ceramic bar having surface roughness variations in the 0.3 to 3.0 microns range for signal bandwidths in the 50 to 100 MHz range.

Generazio, E. R.

1984-01-01

204

Measurement of neutron attenuation through thick shields and comparison with calculation  

SciTech Connect

The large neutrino experiments conducted over the last several years at the Los Alamos Neutron Science Center (LANSCE) have provided the opportunity to measure the effects of neutron attenuation in very thick shields. These experiments have featured detectors with active masses of 6 to 150 tons and shield thicknesses ranging from 3000 to 5280 g/cm{sup 2}. An absolute measurement of the high-energy neutron flux was made from the beam stop in a neutrino cave at ninety degrees and nine meters from the beam stop. Differential neutron shielding measurements in iron were also performed, resulting in an attenuation length of 148 g/cm{sup 2}. These measurements allow for the testing of radiation shielding codes for deep penetration problems. The measured flux and attenuation length is compared to calculations using the LAHET Code System (LCS). These codes incorporate biasing techniques, allowing for direct calculation of deep penetration shielding problems. Calculations of the neutron current and attenuation length are presented and compared with measured values. Results from the shielding codes show good agreement with the measured values.

Bull, J.S.; Donahue, J.B.; Burman, R.L.

1998-12-31

205

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

206

S-waves attenuation and separation of scattering and intrinsic absorption of seismic energy in southeastern Sicily (Italy)  

NASA Astrophysics Data System (ADS)

Seismic wave attenuation in southeastern Sicily was investigated by using a data set of about 180 local earthquakes (1.5 <=ML<= 4.6) recorded in the period 1994-2003. We first estimated the quality factor of S waves (QS) and clarified its frequency dependence by means of the coda-normalization method, applied in the frequency range 1.5-15 Hz. The average QS as function of frequency is given by QS= 49f0.88. A detailed separation of scattering attenuation (Q-1s) from intrinsic absorption (Q-1i) was also attempted by applying the multiple lapse time window analysis (MLTWA), under the hypothesis of multiple isotropic scattering with uniform distribution of scatterers. Intrinsic absorption dominates over scattering in the attenuation process at high frequencies (above 3 Hz). Below 3 Hz scattering is the predominant attenuation effect in the region, at the scale length of these frequencies. However, some discrepancies have been observed between the theoretical model and the observations. This indicates that models with depth-dependent velocity structure and/or non isotropic scattering should be taken into account in order to remove ambiguities in the interpretation of the results.

Giampiccolo, E.; Tuvè, T.; Gresta, S.; Patanè, D.

2006-04-01

207

Shear wave speed and dispersion measurements using crawling wave chirps.  

PubMed

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

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

2014-10-01

208

Pressure measurements of nonplanar stress waves  

Microsoft Academic Search

Measuring the pressure of non-planar stress waves using thin piezo-resistive gages requires correcting for induced strain parallel to the sensing elements. A technique has been developed that permits such measurements, making use of a dual element gage. One element, Manganin, is sensitive to stress both parallel and perpendicular to the sensing element; the other element, Constantan, is primarily sensitive to

G. H. Carlson; J. A. Charest

1981-01-01

209

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

210

Methods for calculating probability distributions of radio-wave attenuation on ground paths due to anomalies of the air refractive index  

NASA Astrophysics Data System (ADS)

The paper analyzes and compares existing methods for calculating radio-wave attenuation statistics at frequencies above 10 GHz associated with anomalies of the air refractive index. An algorithm is proposed for calculating the sum distributions.

Pozhidaev, V. N.; Sviatogor, V. V.

1992-07-01

211

The effect of methane hydrate morphology and water saturation on seismic wave attenuation in sand under shallow sub-seafloor conditions  

NASA Astrophysics Data System (ADS)

A better understanding of seismic wave attenuation in hydrate-bearing sediments is needed for the improved geophysical quantification of seafloor methane hydrates, important for climate change, geohazard and economic resource assessment. Hence, we conducted a series of small strain (<10-6), seismic frequency (50-550 Hz), laboratory resonant column experiments on synthetic methane hydrate-bearing sands under excess-water seafloor conditions. The results show a complex dependence of P- and S-wave attenuation on hydrate saturation and morphology. P- and S-wave attenuation in excess-water hydrate-bearing sand is much higher than in excess-gas hydrate-bearing sand and increases with hydrate saturation between 0 and 0.44 (the experimental range). Theoretical modelling suggests that load-bearing hydrate is an important cause of heightened attenuation for both P- and S-waves in gas and water saturated sands, while pore-filling hydrate also contributes significantly to P-wave attenuation in water saturated sands. A squirt flow attenuation mechanism, related to microporous hydrate and low aspect ratio pores at the interface between sand grains and hydrate, is thought to be responsible for the heightened levels of attenuation in hydrate-bearing sands at low hydrate saturations (<0.44).

Best, Angus I.; Priest, Jeffrey A.; Clayton, Christopher R. I.; Rees, Emily V. L.

2013-04-01

212

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

213

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

NASA Astrophysics Data System (ADS)

We propose a method for modeling global seismic wave propagation through an attenuative Earth model including the center. This method enables accurate and efficient computations since it is based on the 2.5-D approach, which solves wave equations only on a 2-D cross section of the whole Earth and can correctly model 3-D geometrical spreading. We extend a numerical scheme for the elastic waves in spherical coordinates using the finite-difference method (FDM), to solve the viscoelastodynamic equation. For computation of realistic seismic wave propagation, incorporation of anelastic attenuation is crucial. Since the nature of Earth material is both elastic solid and viscous fluid, we should solve stress-strain relations of viscoelastic material, including attenuative structures. These relations represent the stress as a convolution integral in time, which has had difficulty treating viscoelasticity in time-domain computation such as the FDM. However, we now have a method using so-called memory variables, invented in the 1980s, followed by improvements in Cartesian coordinates. Arbitrary values of the quality factor (Q) can be incorporated into the wave equation via an array of Zener bodies. We also introduce the multi-domain, an FD grid of several layers with different grid spacings, into our FDM scheme. This allows wider lateral grid spacings with depth, so as not to perturb the FD stability criterion around the Earth center. In addition, we propose a technique to avoid the singularity problem of the wave equation in spherical coordinates at the Earth center. We develop a scheme to calculate wavefield variables on this point, based on linear interpolation for the velocity-stress, staggered-grid FDM. This scheme is validated through a comparison of synthetic seismograms with those obtained by the Direct Solution Method for a spherically symmetric Earth model, showing excellent accuracy for our FDM scheme. As a numerical example, we apply the method to simulate seismic waves affected by hemispherical variations of P-wavespeed and attenuation in the top 300 km of the inner core.

Toyokuni, Genti; Takenaka, Hiroshi

2012-06-01

214

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

215

Geodynamic Environment by Satellite Geodesy, Seismic Attenuation and S-wave Splitting. Example from Vrancea Seismogenic Zone, SE Carpathians  

NASA Astrophysics Data System (ADS)

In the Vrancea seismogenic zone (SE Carpathians), where very strong earthquakes (Mw > 7) are reported several times a century, the seismotectonics is very complex. It develops beneath the contact between the Moldavian East European Platform, the Scythian Platform, and the Moesian Platform, to the east and southeast, and terranes of the Transylvania Basin lying within the Carpathian arc. Several hypothesis have been considered by scientists in order to explain the clustered foci of crustal and intermediate events (as deep as 200 km). However, until now, there is no tectonic scenario which could explain all geological and geophysical observations. We try to integrate long-term permanent and campaign GPS outcomes with contributions from seismic attenuation and S-wave splitting results. GPS contributions mainly refer to determination of velocity vectors. 15 campaigns and seven permanent stations are being used in order to determine the detailed kinematics of an area characterized by very small velocities (1-2 mm/y), bringing the satellite technique to almost its limit. The results suggest a counterclockwise mantle flow around the Vrancea seismogenic zone, which is a high velocity body developed in an almost vertical position, developing deeper than 200 km. This results is also supported by seismic attenuation studies. We found that models like delamination and subduction could be supported by seismic attenuation studies in this zone. The delamination model implies strong upwelling and horizontal inflow of asthenosphere into the gap between the delaminating and remnant lithosphere. The other model implies downwelling and perhaps lateral-horizontal inflow along the slab detachment or tear. The models imply different distributions of density and rheological properties associated with the different lithosphere - asthenosphere structures. We use the ratio of spectral amplitudes of P and S waves from vertical and transverse seismograms to estimate the S to P ratio in the frequency domain, and then we calculate Qs, the relative shear wave attenuation via two complementary techniques: We find that stations located near and above the Vrancea zone and in the Transylvanian Basin, attenuation is high (low Q). Stations situated on the East European, Moesian, and Scythian Platforms are characterized by higher Qs (low attenuation). We interpret the high attenuation in the Vrancea and Transylvanian Basin is the result of shallow hot asthenosphere present in this area. Observations of source-side shear wave splitting clearly show that upper mantle anisotropy is strongly variable in the region of the tightly curved Carpathian Arc: shear waves taking off from Vrancea along paths that sample the East and Southern Carpathians have fast anisotropy axes parallel to these ranges, whereas those leaving the source region to traverse the upper mantle beneath the Transylvanian Basin (i.e., mantle wedge side) trend NE-SW. Shear waves sampling the East European and Scythian Platforms are separable into two groups, one characterized by fast shear trends to the NE-SW, and a second, deeper group, with trends to NW-SE; also, the majority of null splits occur along paths leaving Vrancea in these NE-E azimuths. Deeper fabric with E-W trend marking asthenospheric flow beneath the craton's base. This more complex anisotropy beneath the western edge of the East European Platform would account for both the variability of observed splitting of waves that sample this volume.

Mocanu, Victor; Russo, Raymond; Ambrosius, Boudewijn

2010-05-01

216

Internal reflection beneath capillary water waves: a method for measuring wave slope  

E-print Network

Internal reflection beneath capillary water waves: a method for measuring wave slope J. R. Saylor of America Key words: Wave slope measurement, internal reflection, capillary waves. 1. Introduction The waves Ray-tracing simulations were performed to explore total internal reflection of light rays beneath

Saylor, John R.

217

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

E-print Network

The attenuation length measuring device was constructed by using oscilloscope and LabVIEW for signal acquisition and processing. The performance of the device has been tested with 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 gadolinium-loaded liquid scintillator (Gd-LS) was measured as 15.10 plus or minus 0.35 m where Gd-LS was heavily used in 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.

L. Gao; BX. Yu; YY. Ding; L. Zhou; LJ. Wen; YG. Xie; ZG. Wang; X. Cai; XL. Sun; J. Fang; Z. Xue; AW. Zhang; QW. LÜ; LJ. Sun; YS. Ge; YB. Liu; SL. Niu; T. Hu; J. Cao; JG. LÜ

2013-05-07

218

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

E-print Network

The attenuation length measuring device was constructed by using oscilloscope and LabVIEW for signal acquisition and processing. The performance of the device has been tested with 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 gadolinium-loaded liquid scintillator (Gd-LS) was measured as 15.10 plus or minus 0.35 m where Gd-LS was heavily used in 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, L; Ding, YY; Zhou, L; Wen, LJ; Xie, YG; Wang, ZG; Cai, X; Sun, XL; Fang, J; Xue, Z; Zhang, AW; LÜ, QW; Sun, LJ; Ge, YS; Liu, YB; Niu, SL; Hu, T; Cao, J; LÜ, JG

2013-01-01

219

Measurement of Particle Size Distribution and Volume Concentration based on Ultrasonic Attenuation Spectrum in Fat Emulsion  

NASA Astrophysics Data System (ADS)

The determination of particle size distribution in concentrated polydisperse fat emulsions measured by ultrasonic attenuation spectrum is studied in this paper. Based on theoretical analysis, ultrasonic attenuation spectrum of fat emulsion samples containing different droplet concentrations (1˜20%) is measured over the range of 2˜13MHz. Then the droplet size and distribution are determined by processing the experiment data with inversion arithmetic. The particle size distribution of original sample determined by ultrasonic spectrum gives excellent agreement with that of diluted sample measured by an optical instrument TSM(Totally Scattering Measurement). This indicates that ultrasonic spectrum is capable of determining the particle size distribution and dispersed-phase volume fraction of concentrated fat emulsions in a non-destructive approach.

Dong, Lili; Su, Mingxu; Xue, Minghua; Cai, Xiaoshu; Shang, Zhitao

2007-06-01

220

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

221

Seismic wave attenuation in methane hydrate-bearing sediments: Vertical seismic profiling data from the Nankai Trough exploratory well, offshore Tokai, central Japan  

NASA Astrophysics Data System (ADS)

Data from two vertical seismic profiles (VSPs) from the Nankai Trough exploratory well, offshore Tokai, central Japan, are used to estimate compressional attenuation in methane hydrate (MH)-bearing sediments at seismic frequencies of 30-110 Hz. We compare spectral ratio and centroid frequency shift methods for measuring attenuation. To isolate intrinsic attenuation from total attenuation, attenuation is computed from multiples using one-dimensional synthetic VSP data from sonic and density logs. The use of two different measurement methods and two VSPs recorded at just 100 m separation provides an opportunity to validate the attenuation measurements. No significant compressional attenuation was observed in MH-bearing sediments at seismic frequencies. Macroscopically, the peaks of highest attenuation in the seismic frequency range correspond to low-saturation gas zones. In contrast, high compressional attenuation zones in the sonic frequency range (10-20 kHz) are affected by the presence of methane hydrates in the same well locations. Thus this study demonstrated the frequency dependence of attenuation in MH-bearing sediments; MH-bearing sediments cause attenuation in the sonic frequency range rather than the seismic frequency range.

Matsushima, Jun

2006-10-01

222

10 GHz-Range Surface Acoustic Wave Low Loss Filter Measured at Low Temperature  

Microsoft Academic Search

The 10 GHz-range surface acoustic wave (SAW) is of great importance in the field of physical acoustics and application of SAW devices, for example, in mobile and wireless communications. The temperature dependency of the propagation attenuation at 10 GHz-range is measured using the three-transducer system with an electrode width of less than 0.1 µm, which is fabricated using an electron

Kazuhiko Yamanouchi; Hideyuki Nakagawa; Jamil Ahmad Qureshi; Hiroyuki Odagawa

1999-01-01

223

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

SciTech Connect

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

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

2005-10-01

224

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

Santolik, Ondrej

225

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 is the first satellite specially dedicated to observe the electromagnetic10 phenomena connected of VLF electromagnetic waves observed in the upper ionosphere. A robust two-step data processing has been

Santolik, Ondrej

226

Space-time variations of the shear wave attenuation field in the upper mantle of seismic and low seismicity areas  

Microsoft Academic Search

This paper deals with characteristics of the short period S-wave attenuation field in the rupture zones of 37 large and great earthquakes with M\\u000a s\\u000a = 7.0–8.6, as well as in low seismicity areas. We estimate the effective quality factor from Sn and Lg coda envelopes in two time intervals (Q\\u000a 1 and Q\\u000a 2). The quantity Q\\u000a 1 is

Yu. F. Kopnichev; D. D. Gordienko; I. N. Sokolova

2009-01-01

227

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

NASA Astrophysics Data System (ADS)

Dispersion, attenuation and wavefronts in a class of linear viscoelastic media proposed by Strick and Mainardi (Geophys J R Astr Soc 69:415-429, 1982) and a related class of models due to Lomnitz, Jeffreys and Strick are studied by a new method due to the author. Unlike the previously studied explicit models of relaxation modulus or creep compliance, these two classes support propagation of discontinuities. Due to an extension made by Strick, either of these two classes of models comprise both viscoelastic solids and fluids. We also discuss the Andrade viscoelastic media. The Andrade media do not support discontinuity waves and exhibit the pedestal effect.

Hanyga, Andrzej

2014-09-01

228

On the measurement of frequency-dependent ultrasonic attenuation in strongly heterogeneous materials.  

PubMed

This paper deals with the measurement of frequency-dependent ultrasonic attenuation in strongly heterogeneous materials, such as cementitious materials. To improve the measurement of this parameter on this kind of materials, a linear swept-frequency signal is used to drive an emitter transducer to conduct a through-transmission inspection in immersion. To filter out undesirable frequency content, time-frequency filtering and detection process are performed. The use of this method has been compared with two excitation techniques, the broadband and the narrowband pulses. The results obtained using the swept-frequency excitation together with the time-frequency filtering, allows the determination of the attenuation curves with high accuracy over a wide frequency range without the need for complicated equipment, and improves the effective bandwidth by using a unique pair of transducers. PMID:20537363

Molero, M; Segura, I; Aparicio, S; Hernández, M G; Izquierdo, M A G

2010-08-01

229

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

NASA Astrophysics Data System (ADS)

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 2615 keV. These experimental results were compared with previous experimental and theoretical data. Good agreements are observed in the 240-800 keV energy range, whereas differences up to maximum 10% are observed out of these limits.

Rettschlag, M.; Berndt, R.; Mortreau, P.

2007-11-01

230

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

231

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

SciTech Connect

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 ?{sub 1}-norm penalty terms. We propose a two-step scheme for refining the mass attenuation discretization grid by using higher sampling rate over the range with higher photon energy, and eliminating the discretization points that have little effect on accuracy of the forward projection model. This refinement allows us to successfully handle the characteristic lines (Dirac impulses) in the incident energy density spectrum. We compare the proposed method with the standard filtered backprojection, which ignores the polychromatic nature of the measurements and sparsity of the image density map. Numerical simulations using both realistic simulated and real x-ray ct data are presented.

Gu, Renliang; Dogandži?, Aleksandar [Iowa State University, Center for Nondestructive Evaluation, 1915 Scholl Road, Ames, IA 50011 (United States)

2014-02-18

232

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

233

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

NASA Astrophysics Data System (ADS)

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

234

Laboratory experiments and numerical modeling of wave attenuation through artificial vegetation  

E-print Network

It is commonly known that coastal vegetation dissipates energy and aids in shoreline protection by damping incoming waves and depositing sediment in vegetated regions. However, this critical role of vegetation to dampen wave forces is not fully...

Augustin, Lauren Nicole

2009-05-15

235

Nondestructive Pressure Measurement in Vessels Using Rayleigh Waves and LCR Waves  

Microsoft Academic Search

In order to avoid the potential safety problems caused by applying traditional pressure measurement methods in vessels, a nondestructive pressure measurement method is presented. This method utilizes ultrasonic Rayleigh waves and critically refracted longitudinal waves (LCr waves). Considering the effect of pressure and temperature of the vessel on both the wave speed and the propagation distance of ultrasonic, a modified

Zhangwei Ling; Hongjian ZhangandHongliang Zhou; Hongliang Zhou

2008-01-01

236

Seismic wave attenuation in methane hydrate-bearing sediments: vertical seismic profiling data from the Nankai Trough exploratory well, offshore Tokai, central Japan  

NASA Astrophysics Data System (ADS)

Data from two vertical seismic profiles (VSPs) from the Nankai Trough exploratory well, offshore Tokai, central Japan, are used to estimate compressional attenuation in methane hydrate (MH)-bearing sediments at seismic frequencies of 30-110 Hz. We compare spectral ratio and centroid frequency shift methods for measuring attenuation. To isolate intrinsic attenuation from total attenuation, attenuation is computed from multiples using one-dimensional synthetic VSP data from sonic and density logs. The use of two different measurement methods and two VSPs recorded at just 100 m separation provides an opportunity to validate the attenuation measurements. Macroscopically, the peaks of highest attenuation in the seismic frequency range correspond to low-saturation gas zones. This interpretation is supported by raw-level data such as the centroid frequency. No significant compressional attenuation was observed in MH-bearing sediments at seismic frequencies. In contrast, high compressional attenuation zones in the sonic frequency range (10-20 kHz) are affected by the presence of methane hydrates in the same well locations. Thus, this study demonstrated the frequency-dependence of attenuation in MH-bearing sediments.

Matsushima, J.

2005-12-01

237

Altimeter height measurement errors introduced by the presence of variable cloud and rain attenuation  

NASA Technical Reports Server (NTRS)

It has recently been recognized that spatially inhomogeneous clouds and rain can substantially affect the height precision obtainable from a spaceborne radar altimeter system. Through computer simulation, it has been found that typical levels of cloud and rain intensities and associated spatial variabilities may degrade altimeter precision at 13.5 GHz and, in particular, cause severe degradation at 35 GHz. This degradation in precision is a result of radar signature distortion caused by variable attenuation over the beam limited altimeter footprint. Because attenuation effects increase with frequency, imprecision caused by them will significantly impact on the frequency selection of future altimeters. In this paper the degradation of altimeter precision introduced by idealized cloud and rain configurations as well as for a realistic rain configuration as measured with a ground based radar is examined.

Monaldo, F. M.; Goldhirsh, J.; Walsh, E. J.

1984-01-01

238

Altimeter height measurement error introduced by the presence of variable cloud and rain attenuation  

NASA Technical Reports Server (NTRS)

It has recently been recognized that spatially inhomogeneous clouds and rain can substantially affect the height precision obtainable from a spaceborne radar altimeter system. Through computer simulation, it has been found that typical levels of cloud and rain intensities and associated spatial variabilities may degrade altimeter precision at 13.5 GHz and, in particular, cause severe degradation at 35 GHz. This degradation in precision is a result of radar signature distortion caused by variable attenuation over the beam limited altimeter footprint. Because attenuation effects increase with frequency, imprecision caused by them will significantly impact on the frequency selection of future altimeters. In this paper the degradation of altimeter precision introduced by idealized cloud and rain configurations as well as for a realistic rain configuration as measured with a ground based radar is examined.

Monaldo, F. M.; Goldhirsh, J.; Walsh, E. J.

1986-01-01

239

Thermoreflectance temperature measurement with millimeter wave  

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

240

Thermoreflectance temperature measurement with millimeter wave.  

PubMed

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

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

2014-06-01

241

Effect of phase change on shock wave attenuation in GeO2 and T. J. Ahrens  

E-print Network

February 2002 Stress-wave profiles in vitreous GeO2 induced by planar and spherical projectile impact were wave achieving the final shock state forms when peak pressure is 6 GPa specified by linear shock- teraction with rock of nuclear explosions in the Earth, a de- tailed series of shock measurements on SiO2

Stewart, Sarah T.

242

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

NASA Astrophysics Data System (ADS)

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

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

2004-07-01

243

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

244

Radar reflectivity and attenuation of radio waves in the melting layer of precipitation  

NASA Astrophysics Data System (ADS)

The melting layer in precipitation is physically modeled and compared with high resolution Doppler radar data. The model includes a new formulation of the dielectric properties and can handle all ice particles with densities ranging between pure snow and hail. The air temperature is calculated from the vertical air velocity. The model can handle aggregation, breakup, and collapse of the melting particles. The results of the model are in good agreement with the Doppler radar observations. The model shows that the reflectivity and attenuation are very sensitive to the dielectric properties and density of the melting particles, and that the influence of aggregation and the collapse is restricted. Simple relations between the attenuation and the rain intensity and maximum reflectivity are derived from a statistical analysis.

Klaassen, W.

1987-05-01

245

Attenuation of High-Frequency Lg Waves in the Crust of the Southeastern S. Korea  

Microsoft Academic Search

The attenuation study of Lg is very important in the southeastern South Korea because the Yangsan fault, an active fault lies in the industrial region where nuclear power plants are located. It is generally observed that QLg-1 is higher for seismically active areas than stable ones. In this study, using vertical-component recordings of the short-period velocity network data, we analyze

T. Chung; K. Lee

2002-01-01

246

Attenuation of High-Frequency Lg Waves in the Crust of the Southeastern S. Korea  

NASA Astrophysics Data System (ADS)

The attenuation study of Lg is very important in the southeastern South Korea because the Yangsan fault, an active fault lies in the industrial region where nuclear power plants are located. It is generally observed that QLg-1 is higher for seismically active areas than stable ones. In this study, using vertical-component recordings of the short-period velocity network data, we analyze the attenuation of Lg by means of a reversed two-station method (RSTM) devised by Chun et al. (1987). 32 combinations of 6 interstation paths are possible for RSTM from 18 earthquakes with the epicentral distances from 87 to 359 km, and the interstation path length from 58 to 84 km. The attenuation coefficient ? (f) of Lg are fitted to be of the form ? = (0.009 \\pm 0.0004) f {0.62 +/- 0.03} between 0.6 and 10 Hz. This value is comparable to seismically active region such as South California (Frankel et al., 1990). However, very low QP-1 and QS-1 was reported recently for this area, derived from the coda-normalization method for the same seismic network data (Chung and Sato, 2001). This contradiction may be due to the block of Lg propagation near the East Sea (Japan Sea), which has a typical oceanic crust. Furumura and Kennett (2001) show blockage of Lg for the oceanic crustal region deeper than the 1000-m contour.

Chung, T.; Lee, K.

2002-05-01

247

Estimation of patient attenuation factor for iodine-131 based on direct dose rate measurements from radioiodine therapy patients.  

PubMed

The aim of the study was to measure the actual dose at 1?m from the patients per unit activity with the aim of providing a more accurate prediction of the dose levels around radioiodine patients in the hospital, as well as to compare our results with the literature. In this work the demonstration of a patient body tissue attenuation factor is verified by comparing the dose rates measured from the patients with those measured from the unshielded radioiodine capsules immediately after administration of the radioactivity. The normalized dose rate per unit activity is therefore proposed as an operational quantity that can be used to predict exposure rates to staff and patients' relatives. The average dose rate measured from our patient per unit activity was 38.4±11.8??Sv/h/GBq. The calculated attenuation correction factor based on our measurements was 0.55±0.17. The calculated dose rate from a radioiodine therapy patient should normally include a factor accounting for patient body tissue attenuation and scatter. The attenuation factor is currently neglected and not applied in operational radiation protection. Realistic estimation of radiation dose levels from radioiodine therapy patients when properly performed will reduce the operational cost and optimize institutional radiation protection practice. It is recommended to include patient attenuation factors in risk assessment exercises - in particular, when accurate estimates of total effective doses to exposed individuals are required when direct measurements are not possible. The information provided about patient attenuation might benefit radiation protection specialists and regulators. PMID:25279710

Soliman, Khaled; Alenezi, Ahmed

2015-02-01

248

Effect of decay on ultrasonic velocity and attenuation measurements in wood  

NASA Astrophysics Data System (ADS)

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

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

2011-04-01

249

High pressure hugoniot measurements using mach waves  

NASA Astrophysics Data System (ADS)

Traditionally, most dynamic shock compression experiments are conducted using a plane one-dimensional wave of uniaxial strain. In this case, the evaluation of the equation of state is simplified due to the geometry, but the amplitude of the induced shock wave is limited by the magnitude of the input load. In an effort to dramatically increase the range of pressures that can be accessed by traditional loading methods, a composite target assembly is examined. The target consists of two concentric cylinders aligned with the axial direction parallel to the loading. The target is designed such that on initial loading, the outer cylinder will have a higher shock velocity than the inner material of interest. Conically converging shocks will be generated at the interface between the two materials due to the impedance mismatch. Upon convergence, an irregular reflection occurs and the conical analog of a Mach reflection develops. The Mach reflection will grow until it reaches a steady state, at which point the wave configuration becomes self similar. The resulting high pressure Hugoniot state can then be measured using velocity interferometry and impedance matching. The technique is demonstrated using a planar mechanical impact generated by a powder gun to study the shock response of copper. Two systems are examined which utilize either a low impedance (6061-T6 aluminum) or a high impedance (molybdenum) outer cylinder. A multipoint VISAR experiment will be presented to validate the technique, and will be compared to numerical simulations. The feasibility of measuring an entire Hugoniot curve using full field velocity interferometry (ORVIS) will also be discussed.

Brown, Justin; Ravichandran, Guruswami

2012-03-01

250

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

SciTech Connect

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

Friedman, W.

1999-07-29

251

Polymer Gels as Temperature-responsive Attenuator  

NASA Astrophysics Data System (ADS)

The ultrasonic attenuation in N-isopropylacrylamide (NIPA) gel has been measured as a function of temperature at various frequencies. It is found that at room temperature, the attenuation of a longitudinal ultrasonic wave in the gel is small and close to that of pure water. However, as the temperature increases above the spinodal phase transition point of the gel, the attenuation increases drastically. This change of the attenuation is completely reversible and due to the micro-domains formed in the NIPA gel above its phase transition temperature. The change of attenuation at 15 MHz in the temperature range between 26 and 45 ^0C is about 26 dB/cm. The rate of attenuation change is within 5 minutes for a sample with diameter 1 cm and height 0.8 cm. The results reported here may have potential applications from ultrasonic assistant drug-release to a switch for ultrasonic signals.

Yuan, Kaihua; Hu, Zhibing; Li, Yong

1998-10-01

252

Pressure measurements of nonplanar stress waves  

SciTech Connect

Measuring the pressure of non-planar stress waves using thin piezo-resistive gages requires correcting for induced strain parallel to the sensing elements. A technique has been developed that permits such measurements, making use of a dual element gage. One element, Manganin, is sensitive to stress both parallel and perpendicular to the sensing element; the other element, Constantan, is primarily sensitive to stress parallel to the sensing element. The change in resistance in the Constantan element is thereby used to correct for the strain effect parallel to the Manganin element axis. Individual and combined Manganin and Constantan elements were subjected to controlled gas gun impact tests in the pressure and strain ranges of 0 to 50 kbar and 0 to 7%, respectively. From planar wave tests, the piezoresistivity of Constantan was found to be positive but negligible in comparison with Manganin. From combined stress and strain environments, the compression and tension strain factors of Constantan were found to be constant and equal to 2.06. The strain factors of Manganin were found to increase from 1.2 to 2.0 asymptotically in the range of 0 to 3% strain. It was experimentally demonstrated that, because of the closeness of their strain factors, the Manganin-Constantan dual element gage could be used in the differential recording mode to yield pressure directly. In this mode the gage is a strain compensating gage. Analytical techniques have also been developed for more accurate strain compensation.

Carlson, G.H.; Charest, J.A.

1981-01-01

253

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

NASA Astrophysics Data System (ADS)

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

Priestley, Keith; McKenzie, Dan

2013-11-01

254

Density and atomic number measurements with spectral x-ray attenuation method  

NASA Astrophysics Data System (ADS)

X-ray attenuation measurements are widely used in medical and industrial applications. The usual results are one- to three-dimensional representations of the attenuation coefficient ?(r). In this paper, we present the ?Z projection algorithm for obtaining the density ?(r) and atomic number Z(r) with an energy-resolving x-ray method. As input data the algorithm uses at least two measurements ?1,?2,… with different spectral weightings of the source spectrum S(E) and/or detector sensitivity D(E). Analytically, ? is a function of ?1-c?2, c=const, and Z is a function of ?1/?2. The full numerical treatment yields ?(?1,?2) and Z(?1,?2) with S(E) and D(E) as commutative parametric functions. We tested the method with dual-energy computed tomography measurements of an organic sample and a set of chemical solutions with predefined ? and Z. The resulting images show ? and Z as complementary information: The density ? reflects the morphology of the objects, whereas the atomic number Z=number of electrons/atom describes the material distribution. For our experimental setup we obtain an absolute precision of 0.1 for Z and 20 mg/cm3 for ?. The ?Z projection can potentially lead to these classes of quantitative information for various scientific, industrial, and medical applications.

Heismann, B. J.; Leppert, J.; Stierstorfer, K.

2003-08-01

255

Modeling attenuation and phase of radio waves in air at frequencies below 1000 GHz  

NASA Astrophysics Data System (ADS)

Moist air is characterized for the frequency range 1-1000 GHz as a nonturbulent propagation medium described by meteorological parameters. An adequate spectroscopic data base for air consists of three terms: (1) resonance information for 29 H2O lines up to 1097 GHz and 44 O2 lines up to 834 GHz in the form of intensity coefficients and center frequency for each line; (2) an empirical water vapor continuum spectrum; and (3) a liquid water attenuation term for haze and cloud conditions. This data base is the heart of two computer programs which calculate and plot attenuation rates (in decibels per kilometer), refractivity (in parts per million), and refractive dispersion (in parts per million). The first covers the troposphere and requires pressure, temperature, and relative humidity as input data. The second addresses isolated line behavior in the mesosphere wherein the geomagnetic field strength H is an additional input parameter due to the Zeeman effect of the O2 molecules. Each oxygen line splits proportionally with H into numerous sublines, which are juxtaposed to form Zeeman patterns spread over a megahertz scale. Patterns of three main polarization cases are considered. Various typical examples for a model atmosphere demonstrate the utility of the approach, provide new information, and underline the serious role that water vapor plays above 120 GHz.

Liebe, Hans J.

1981-11-01

256

An Study of S-wave Attenuation using records from the 20 May, 2012 Emilia Earthquake, Italy and the Main Aftershocks  

NASA Astrophysics Data System (ADS)

We analyze the S-wave spectral amplitude decay with distance using strong-motion records from the 20 May 2012 Emilia-Romagna earthquake (Mw6.1) and five aftershocks with magnitudes ranging between 4.9 and 5.9. The data set consist of 6 earthquakes, 44 stations and 248 records with hypocentral distances in the range 10 < r < 100 km. We rotated the accelerograms to calculate transversal and radial components of the acceleration spectrum. We found nonparametric attenuation functions that describe the spectral amplitude decay of SH and SV waves with distance at 60 different frequencies between 0.1 and 40 Hz. These attenuation functions provide an estimate of the quality factor Q at each frequency analyzed. Assuming that geometrical spreading is 1-r for r ˜ rx and 1/(rxr)0.5 for r>rx with rx= 60 km and normalizing at 15 km (the recording distance where the attenuation functions start to decay), we find that the average Q for SH waves can be approximated by QSH = 82f1.2 and by QSV = 79f1.2 for SV waves in the frequency range 0.10 ˜ f ˜ 10.7 Hz. At higher frequencies, 11.8 ˜ f ˜ 40 Hz, the frequency dependence of Q weakens and is approximated by QSH = 301f0.36 and QSV = 384f0.28. These results indicate that the S-wave attenuation is isotropic at local distances in the epicenter area. The estimates of total Q obtained (intrinsic and scattering attenuation) coincide with the estimates of total Q determined by Del Pezzo et al. (2011) in north central Italy using coda waves and Multiple Lapse Time Window Analysis (MLTWA).

Castro, Raul; Pacor, Francesca; Puglia, Rodolfo; Ameri, Gabriele; Letort, Jean; Massa, Marco; Luzi, Lucia; Augliera, Paolo

2013-04-01

257

Broadband attenuation and nonlinear propagation in biological fluids: an experimental facility and measurements.  

PubMed

The design and construction of a versatile experimental facility for making measurements of the frequency-dependence of attenuation coefficient (over the range 1 MHz to 25 MHz) and nonlinear propagation in samples of biological fluids is described. The main feature of the facility is the ability to perform all of the measurements on the same sample of fluid within a short period of time and under temperature control. In particular, the facility allows the axial development of nonlinear waveform distortion to be measured with a wideband bilaminar polyvinylidene difluoride membrane hydrophone to study nonlinear propagation in biological fluids. The system uses a variable length bellows to contain the fluid, with transparent Mylar end-windows to couple the acoustic field into the fluid. Example results for the frequency-dependence of attenuation of Dow Corning 200/350 silicone fluid, used as a standard fluid, are presented and shown to be in good agreement with alternative measurements. Measurements of finite amplitude propagation in amniotic fluid, urine and 4.5% human albumin solutions at physiological temperature (37 degrees C) are presented and compared with theoretical predictions using existing models. The measurements were made using a 2.25-MHz single-element transducer coupled to a polymethyl methacrylate lens with a focal amplitude gain of 12 in water. The transducer was driven with an eight-cycle tone burst at source pressures up to 0.137 MPa. In general, given an accurate knowledge of the medium parameters and source conditions, the agreement with theoretical prediction is good for the first five harmonics. PMID:16344135

Verma, Prashant K; Humphrey, Victor F; Duck, Francis A

2005-12-01

258

A new method to measure frequency dependent phase velocity and attenuation in ultrasonic frequency range  

NASA Astrophysics Data System (ADS)

A new method is established to derive frequency dependent acoustic properties of laboratory samples from the waveform data obtained in the ultrasonic frequency range. Unlike the previous methods, this method needs a waveform propagating only one path and does not need a reference waveform propagating the other path. Hence, we can apply this method to the wave directly transmitted from source to receiver. The essential part of this method is correction of the waveform data for the transducer effect and the source size effect, which are obtained theoretically. Validity of the method was demonstrated experimentally. We consider a broadband transducer consisting of piezoelectric disk and backing. Transducer effect is calculated for source and receiver by solving dynamic response of the disk to electrical input signal and incident wave, respectively. Source size effect is calculated by considering radiation from the source attached to semi-infinite medium. Also, we establish a method to estimate the material parameters of the disk and the backing by solving the dynamic response of two directly contacted transducers. Both transducer and source size effects cause ? /2 phase shift at low frequencies, indicating significant effects on traveltime at those frequencies. Experiments were conducted for stainless steel (Q ? 1000) and acrylic plastic (Q ~ 100) using broadband transducers (V103, Panametrics, Inc.). Using sinusoidal waves (100 kHz - 1 MHz), waveform data were obtained as a transfer function between source and receiver signals. Frequency dependent phase velocity and attenuation were obtained from the transfer function corrected for the transducer effect and source size effect. The obtained phase velocity satisfied the dispersion predicted from the value of Q, indicating the validity of this method.

Fujisawa, K.; Takei, Y.

2006-12-01

259

Direct Measurement of Wave-Induced Bottom Shear Stress Under Irregular Waves  

Microsoft Academic Search

\\u000a Wave-induced bottom shear stress is one of most important parameters in modelling of wave hydrodynamics and coastal sediment\\u000a transport, but has not been accurately estimated so far. A new type of shear plate is developed to measure instantaneous wave\\u000a bottom shear stress under both regular and irregular waves. The shear plate directly measures instantaneous horizontal force\\u000a by applying the Wheatstone

Zaijin You; Baoshu Yin; Guang Huo

260

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

261

Measuring the speed of cosmological gravitational waves  

E-print Network

In general relativity gravitational waves propagate at the speed of light, however in alternative theories of gravity that might not be the case. We study the effects of a modified speed of gravity, $c_T^2$, on the B-modes of the Cosmic Microwave Background (CMB) anisotropy in polarisation. 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. We derive constraints by using the available {\\it Planck} and BICEP2 datasets showing how $c_T^2$ can be measured, albeit obtaining weak constraints due to the overall poor accuracy of the current BB power spectrum measurements. The present constraint corresponds to $c_T^2 = 1.30 \\pm 0.79$ and $c_T^2< 2.85$ at $95%$ C.L. by assuming a power law primordial tensor power spectrum and $c_T^2<2.33$ at $95%$ C.L. if the running of the spectral index is allowed. We derive forecasts for the next generation CMB satellites, which we find capable of tightly constraining $c_T^2$ at percent level, comparable with bounds from binary pulsar measurements, largely due to the absence of degeneracy with other cosmological parameters.

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

2014-06-11

262

Intrinsic absorption and scattering attenuation of seismic waves in the southern part of the Netherlands  

NASA Astrophysics Data System (ADS)

The Q structure in the southern part of the Netherlands is determined using the coda Q model. Two models are tested, the single scattering and the multiple scattering model. In the coda Q method as originally proposed by Aki and Chouet (1975), the problem is the ambiguity in interpreting Qc (coda Q) in terms of Qt (total attenuation), Qs (scattering) and Qi (intrinsic absorption). The Multiple Lapse Time Window Analysis (MLTWA), assumes multiple scattering and suggest a possibility to separate the intrinsic attenuation from the scattering effect. However it assumes a simplified model of the crust and upper mantle. We have used both methods for data in the southern part of The Netherlands, as it provides reasonable first order approximations for Q. The single scattering interpretation shows a significant difference between small (< 25 km) epicentral distances and larger ones, while the assumption is that Qc is independent of epicentral distance. The Qc for the larger distances is significantly higher than Qc for the small distances. The multiple scattering interpretation suggests that intrinsic absorption dominates over scattering. A combined interpretation of both analysis methods shows that for small epicentral distances Qc approaches Qt and the single scattering interpretation seems valid. For larger epicentral distances (>25 km) Qc aproaches neither Qt nor Qi and consequently neither the single nor the multiple scattering model. Further, we observe that Qc is higher for larger distances than for small distances and the MLTWA method provides Qi > Qs. Together, these observations suggest that the lower crust and the upper mantle have a significant effect on the seismic coda and require better modelling.

Goutbeek, F. H.; Dost, B.; van Eck, T.

2003-04-01

263

Radiographic least-squares fitting technique accurately measures dimensions and x-ray attenuation  

SciTech Connect

In support of stockpile stewardship and other important nondestructive test (NDT) applications, the authors seek improved methods for rapid evaluation of materials to detect degradation, warping, and shrinkage. Typically, such tests involve manual measurements of dimensions on radiographs. The authors seek to speed the process and reduce the costs of performing NDT by analyzing radiographic data using a least-squares fitting technique for rapid evaluation of industrial parts. In 1985, Whitman, Hanson, and Mueller demonstrated a least-squares fitting technique that very accurately locates the edges of cylindrically symmetrical objects in radiographs. To test the feasibility of applying this technique to a large number of parts, the authors examine whether an automated least squares algorithm can be routinely used for measuring the dimensions and attenuations of materials in two nested cylinders. The proposed technique involves making digital radiographs of the cylinders and analyzing the images. In the authors` preliminary study, however, they use computer simulations of radiographs.

Kelley, T.A.; Stupin, D.M.

1997-10-01

264

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

NASA Astrophysics Data System (ADS)

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

Kore, Prashant S.; Pawar, Pravina P.

2014-05-01

265

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

NASA Technical Reports Server (NTRS)

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

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

2007-01-01

266

Phase velocity dispersion and attenuation of seismic waves due to trapped fluids in residual-saturated porous media  

NASA Astrophysics Data System (ADS)

Propagation of seismic waves in partially saturated porous media depends on various material properties, e.g. saturation, porosity, elastic properties of the skeleton, viscous properties of the pore fluids and, additionally, capillary pressure and effective permeability. If the wetting fluid is in a discontinuous state, i.e. residual-saturated configuration, phase velocities and frequency-dependent attenuation additionally depend on microscopical (pore-scale) properties such as droplet and/or ganglia size. To model wave propagation in residual-saturated porous media, we developed a three-phase model based on an enriched continuum mixture theory capturing the strong coupling between the micro- and the macroscale. The three-phase model comprises the porous solid skeleton, a continuous fluid part and a discontinuous fluid part. The discontinuous part describes the movement of blobs/clusters of the wetting fluid and is based on an oscillator rheology. On the microscale, the oscillators are determined by their mass, damping and eigenfrequency. Amongst others, these properties depend on the microscopic geometry and surface tension. To embed the microscopic oscillators into a macroscopic poroelastic description of the non-wetting fluid and the skeleton, a scale bridging between both spatial scales is applied conserving density, eigenfrequency and damping. This homogenization approach accounts for the discontinuous character of the wetting fluid. Furthermore, probability density functions are used to describe the size distribution of different kinds of fluid clusters. The discontinuous fluid part is linked to the continuous solid phase by momentum exchange in the form of pinned or sliding oscillators. The non-wetting continuous fluid phase exhibits similar behavior as the poroelastic model introduced by Biot. The final model delivers insight into the behavior of propagating waves on the macroscale, influenced by different properties of the microscopic oscillating fluid clusters. Furthermore, the dispersion relations allow for a comparison with continuous models, such as the Biot model, and for the calculation of characteristic values, which might be helpful for the comparison with experimental studies. We define a dimensionless parameter that determines if the overall motion of the residual fluid is dominated by oscillations (underdamped, resonance) or not (overdamped). Our results show that the residual fluid has a significant impact on the velocity dispersion and attenuation, no matter if it oscillates or not. For long wavelengths, our model coincides with the Biot-Gassmann equations. We show under which conditions and how the classical biphasic models can be used to approximate the dynamic behavior of residual-saturated porous media.

Steeb, H.; Kurzeja, P.; Frehner, M.; Schmalholz, S. M.

2012-04-01

267

Measurements of shoaling internal waves and turbulence in an estuary  

E-print Network

Measurements of shoaling internal waves and turbulence in an estuary Clark Richards,1 Daniel internal waves may represent an important source of mixing and transport in estuaries and coastal seas of the turbulent energetics, and two main features were studied. First, during a period of shoaling internal waves

Kelley, Dan

268

Measurements of shoaling internal waves and turbulence in an estuary  

E-print Network

Measurements of shoaling internal waves and turbulence in an estuary Clark Richards,1 Daniel 2012; accepted 30 October 2012. [1] The shoaling of horizontally propagating internal waves may energetics, and two main features were studied. First, during a period of shoaling internal waves, turbulence

269

Analysis of Gravity Waves from Radio Occultation Measurements  

E-print Network

Analysis of Gravity Waves from Radio Occultation Measurements Martin Lange and Christoph Jacobi. In the height range 10-30 km atmospheric gravity waves lead to pe- riodic perturbations of the background gravity waves in the range 100-1000 km horizontal and 1-10 km vertical wavelength is investi- gated

270

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.

271

High pressure Hugoniot measurements using Mach waves  

NASA Astrophysics Data System (ADS)

In an effort to dramatically increase the range of pressures which can be accessed by traditional shock loading methods, a composite target assembly is examined. The target consists of two concentric cylinders aligned with the axial direction parallel to the loading, and is designed such that the outer cylinder will initially have a higher shock velocity than the inner material of interest. Conically converging shocks will be generated at the interface between the two materials due to the impedance mismatch. Upon convergence, an irregular reflection occurs and the conical analog of a Mach reflection develops. The Mach reflection will grow until it reaches a steady state, at which point the wave configuration becomes self similar. The resulting high pressure Hugoniot state can then be measured using velocity interferometry and impedance matching. The technique is demonstrated using a planar mechanical impact generated by a powder gun to study the shock response of copper. Two systems are examined which utilize either a low impedance (6061-T6 aluminum) or a high impedance (molybdenum) outer cylinder. A dual-delay multipoint VISAR experiment will be presented to validate the technique, and will be compared to both numerical simulations and a simple hydrodynamic model. The feasibility of measuring an entire Hugoniot curve using full field velocity interferometry (ORVIS) will also be discussed, and initial experiments will be presented.

Brown, Justin; Ravichandran, Guruswami

2011-06-01

272

Equipment for continuous measurements of pulse wave velocities  

Microsoft Academic Search

Equipment that measures continously ‘foot to foot’ time intervals between two peripheral arterial pulse waves is described.\\u000a To calculate the pulse wave velocity one has to know, besides this time interval, the distance between the sites of the proximal\\u000a and distal pulse wave transducers. The foot of the proximal and the distal pulse waves is detected by differantiation and\\u000a by

J. Weinman; D. Sapoznikov

1971-01-01

273

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

274

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

275

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

NASA Astrophysics Data System (ADS)

The fundamental-mode Love and Rayleigh waves generated by 57 earthquakes which occurred in the north and central Indian Ocean (extending to 40°S) and recorded at Indian seismograph and other WWSSN stations such as HOW, SHL, VIS, MDR, HYB, KOD, CHG, TRD, POO, BOM, GOA, NDI, NIL and QUE are analysed. Love and Rayleigh wave attenuation coefficients are estimated at periods of 15-100 s using the spectral amplitude of these waves for 98 different paths across the Bay of Bengal Fan, the Arabian Fan, and the north and central Indian Ocean. The large standard deviations observed in the surface wave attenuation coefficients may be a result of regional variation of the attenuative properties of the crust and upper mantle beneath these regions. Love wave attenuation coefficients are found to vary from 0.000 03 to 0.000 45 km -1 for the Bay of Bengal Fan; from 0.000 03 to 0.000 85 km -1 for the Arabian Fan; and from 0.000 03 to 0.000 35 km -1 for the north and central Indian Ocean. Similarly, Rayleigh wave attenuation coefficients vary from 0.000 03 to 0.0004 km -1 for the Bay of Bengal Fan; from 0.000 06 to 0.0007 km -1 for the Arabian Fan; and from 0.000 03 to 0.0007 km -1 for the north and central Indian Ocean. Backus and Gilbert inversion theory is applied to these surface wave attenuation data to obtain average Q-1 models for the crust and upper mantle beneath the Bay of Bengal, the Arabian Fan, and the north and central Indian Ocean. Inversion of Love and Rayleigh wave attenuation data shows a high-attenuation zone centred at a depth of > 120 km ( Q? ? 125) for the Bay of Bengal Fan. Similarly, a high-attenuation zone ( Q? ? 40-70) occurs at a depth of 60-160 km for the Arabian Fan at 100-160 km ( Q? ? 115) for the Indian Ocean off Ninetyeast Ridge, and at 80-160 km ( Q? ? 80) for the Indian Ocean across the Ninetyeast Ridge. The Q?-1 models show a lithosphere thickness of 120 km beneath the Bay of Bengal Fan. Similarly, lithosphere thickness of 70, 100 and 80 km is estimated beneath the Arabian Fan, and the Indian Ocean off Ninetyeast Ridge and across Ninetyeast Ridge, respectively. The base of the lithosphere is identified as the depth at which there is a significant increase in the Q?-1 value, which attains its maximum value in the asthenosphere. The thinning of Indian lithosphere beneath the Arabian Fan suggests high temperature below Moho depth (60 km from surface) which has caused a high-attenuation zone at this shallow depth.

Singh, D. D.

276

Non-contact ultrasonic spectroscopy measurement of elastic constants and ultrasonic attenuation  

SciTech Connect

We have developed an ultrasonic spectroscopy method for measuring the elastic constants of solids in hostile environments and over a broad temperature regime. The sample is cut as a rectangular parallelepiped, approximately 1 mm{sup 3} in volume. One or two of the sample surfaces are coated with a thin film of a magnetostrictive material such as nickel. The sample is placed coaxially with two solenoids. One solenoid is used to generate an AC magnetic field of small amplitude which stretches the films. By sweeping the frequency of this field, the sample is excited successively into its various mechanical resonance modes. The second solenoid detects the mechanical resonances. The elastic constants are then deduced from the spectrum of mechanical resonances measured at constant temperature. The internal friction is deduced from the width of the resonance peaks. Because the technique is strictly non-contact (the sample may be encapsulated in a fused silica tube), it is deal for measuring elastic constants in hostile environments or under controlled atmospheres. In its present version the system allows us to measure the elastic constants and ultrasonic attenuation of a given sample between 80 and 100 K. The operation of the system is exemplified by measurements on amorphous Ni{sub 80}P{sub 20} and crystalline Ti{sub 60}Cr{sub 40}. 17 refs., 6 figs.

Schwarz, R.B.; Kuokkala, V.T.; Srinivasan, S.; Visscher, W.M.

1991-01-01

277

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

NASA Astrophysics Data System (ADS)

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

Puranen, Mikko; Eskelinen, Pekka

2008-10-01

278

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

279

Thermal Conductivity and Noise Attenuation in  

E-print Network

OF SOUND 5.1 NATURE OF SOUND WAVE 29 5.2 MEASURING SOUND WAVES 29 5.3 MECHANISM OF SOUND 30 5.3.1 Sound 32 5.3.3 Isolation 32 5.4 SOUND ABSORPTION MEASUREMENTS 32 5.6 SOUND ABSORPTION IN METAL FOAMS 33 6. MODEL DEVELOPED FOR SOUND ATTENUATION 37 7. RESULTS AND DISCUSSION 39 8. SUMMARY AND FUTURE WORK 41 9

Cambridge, University of

280

Delamination of southern Puna lithosphere revealed by body wave attenuation tomography  

NASA Astrophysics Data System (ADS)

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

281

Electromagnetic generation and attenuation of ultrasound in ferromagnetic metals. II  

Microsoft Academic Search

For pt.I see ibid., vol.10, p.2041 (1980). The generation and attenuation of ultrasonic waves due to incident radio frequency magnetic fields at the surface of a ferromagnetic metal are studied. Measurements are made of the attenuation and generation of longitudinal and shear waves as a function of the applied magnetic fields, frequencies and temperature (below 300K) for propagation along the

M. J. W. Povey; E. R. Dobbs; D. J. Meredith

1980-01-01

282

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

283

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

284

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

285

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

NASA Astrophysics Data System (ADS)

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

Putkis, O.; Croxford, A. J.

2013-04-01

286

Using a phonocardiography in a pulse wave velocity measurement  

Microsoft Academic Search

A data acquisition is realised using purely non-invasive measuring mode, i.e. phonocardiography, in this project. A blood pulse wave velocity (PWV) in human arterial tree is determined by analysing phonocardiographic (PCG) records. Two signals are needed at minimum for an estimation of the pulse wave velocity. All of these signals have to be measured simultaneously from different points on a

Martin Jelinek; J. Dobes; Lubomir PouSek; K. Hana

2003-01-01

287

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

NASA Astrophysics Data System (ADS)

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

Xie, J.

2003-12-01

288

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

289

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

NASA Technical Reports Server (NTRS)

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

Trimpi, Robert L.; Cohen, Nathaniel B.

1961-01-01

290

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

291

Interferometric Measurement of the Biphoton Wave Function  

NASA Astrophysics Data System (ADS)

Interference between an unknown two-photon state (a "biphoton") and the two-photon component of a reference state gives a phase-sensitive arrival-time distribution containing full information about the biphoton temporal wave function. Using a coherent state as a reference, we observe this interference and reconstruct the wave function of single-mode biphotons from a low-intensity narrow band squeezed vacuum state.

Beduini, Federica A.; Zieli?ska, Joanna A.; Lucivero, Vito G.; de Icaza Astiz, Yannick A.; Mitchell, Morgan W.

2014-10-01

292

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

293

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

294

Broadband superheterodyne tracking circuits for millimeter-wave measurements.  

PubMed

Superheterodyne stimulus-response measurements can be made with high dynamic range, but are often sensitive to oscillator frequency drift and noise. The usual techniques for reducing this sensitivity often become impractical at millimeter-wave frequencies and above. This paper describes a feedforward tracking technique and its application to single frequency millimeter-wave interferometry and Doppler-shift scattering measurements on tokamak plasmas. Swept frequency transmission measurements can also be made with high dynamic range using this technique. PMID:18647058

Doane, J L

1980-03-01

295

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

296

Lateral variations of coda Q and attenuation of seismic waves in the Gulf of Suez, Egypt  

Microsoft Academic Search

Gulf of Suez consists mainly of three tectonic provinces that are separated by two accommodation zones. The southern edge\\u000a of the gulf is bordered by N–S faults which mark the transition between the shallow water, Suez Basin and the deep northern\\u000a Red Sea Basin. The sensitivity of coda Q measurements with respect to geological differences in the crust is demonstrated

Mamdouh A. Morsy; Sherif El Hady; Salah M. Mahmoud; Enayat Abdel Moneim Awad

297

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.

298

An investigation of the use of transmission ultrasound to measure acoustic attenuation changes in thermal therapy.  

PubMed

The potential of using a commercial ultrasound transmission imaging system to quantitatively monitor tissue attenuation changes after thermal therapy was investigated. The ultrasound transmission imaging system used, the AcoustoCam (Imperium Inc., MD) allows ultrasonic images to be captured using principles similar to that of a CCD-type camera that collects light. Ultrasound energy is focused onto a piezoelectric array by an acoustic lens system, creating a gray scale acoustic image. In this work, the pixel values from the acoustic images were assigned acoustic attenuation values by imaging polyacrylamide phantoms of varying known attenuation. After the calibration procedure, data from heated polyacrylamide/bovine serum albumin (BSA) based tissue-mimicking (TM) phantoms and porcine livers were acquired. Samples were heated in water at temperatures of 35, 45, 55, 65, and 75 degrees C for 1 h. Regions of interest were chosen in the images and acoustic attenuation values before and after heating were compared. An increase in ultrasound attenuation was found in phantoms containing BSA and in porcine liver. In the presence of BSA, attenuation in the TM phantom increased by a factor of 1.5, while without BSA no significant changes were observed. The attenuation of the porcine liver increased by up to a factor of 2.4, consistent with previously reported studies. The study demonstrates the feasibility of using a quantitative ultrasound transmission imaging system for monitoring thermal therapy. PMID:16937194

Parmar, Neeta; Kolios, Michael C

2006-07-01

299

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

300

Pulsar timing measurements and the search for gravitational waves  

Microsoft Academic Search

Pulse arrival time measurements of pulsars may be used to search for gravitational waves with periods on the order of 1 to 10 years and dimensionless amplitudes of approximately 10 to the -11th power. The analysis of published data on pulsar regularity sets an upper limit to the energy density of a stochastic background of gravitational waves, with periods of

S. Detweiler

1979-01-01

301

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

PubMed

We describe a new instrument for the quantification of atmospheric peroxy radicals (HO2, CH3O2, C2H5O2, etc.) using the chemical amplification method. Peroxy radicals are mixed with high concentrations of NO and CO, causing a chain reaction that produces a measurable increase in NO2 which is quantified by cavity attenuated phase shift (CAPS) spectroscopy, a highly sensitive spectroscopic detection technique. The instrument utilizes two identical reaction chambers, each with a dedicated CAPS NO2 sensor. Similar to all dual-channel chemical amplifiers, one reaction chamber operates in amplification or "ROx" mode and the other in background or "Ox" mode. The peroxy radical mixing ratio is determined by the difference between the two channels' NO2 readings divided by a laboratory-determined chain length. Each reaction chamber alternates between ROx and Ox mode on an anti-synchronized schedule, eliminating the effect of CAPS baseline offsets on the calculated peroxy radical concentrations. The chain length is determined by a new calibration method: peroxyacetyl and methyl peroxy radicals are produced by the photolysis of acetone and quantified as NO2 following reaction with excess NO. We demonstrate the performance of the instrument with results from ambient sampling in Amherst and several diagnostics of its precision. The detection limit while sampling ambient air at a relative humidity (RH) of 40% is 0.6 ppt (1 min average, signal-to-noise ratio =2), with an estimated accuracy of 25% (2?). PMID:25260158

Wood, Ezra C; Charest, John R

2014-10-21

302

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

PubMed Central

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

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

1999-01-01

303

Measurement of mass attenuation coefficients for YBaCuO superconductor at different energies  

NASA Astrophysics Data System (ADS)

The mass attenuation coefficients for Y2O3, BaCO3, CuO compounds, and solid-state forms of YBa2Cu3O7 superconductor were determined at energies of 57.5, 59.5, 65.2, 74.8, 77.1, 87.3, 94.6, 98.4, 122, and 136 keV. The samples were irradiated using a 241Am point source emitting 59.5 keV photon energies and a 57Co point source emitting 122 and 136 keV photon energies. The other energies were obtained using secondary targets such as Ta, Bi2O3, and (CH3COO)2UO22H2O. The gamma- and x-rays were counted by a Si(Li) detector with a resolution of 160 eV at 5.9 keV. Samples were selected on the basis of known composition and mass densities were measured using a densitometer. The experimental results obtained in this study are compared with theoretical values.

Çevik, U.; Baltas, H.; Çelik, S.; Karaca, I.; Kopya, I.

2005-01-01

304

Short distance attenuation measurements at 900 MHz and 1.8 GHz using low antenna heights for microcells  

Microsoft Academic Search

Short-distance, low-antenna-height signal attenuation measurements are presented in connection with their use in the design of future microcell cellular radio networks. Measurements presented are based on the propagation along busy city streets in a direction radial to a fixed antenna site. Antenna heights between 5 m and 20 m were chosen for the fixed site, while 1.5 m was chosen

PHILIP HARLEY

1989-01-01

305

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

306

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

307

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

PubMed

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

2014-03-01

308

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

309

Selective continuous quantum measurements: Restricted path integrals and wave equations  

Microsoft Academic Search

We discuss both the restricted path integral (RPI) and the wave equation (WE) techniques in the theory of continuous quantum measurements. We intend to make Mensky's fresh review complete by transforming his \\

Lajos Diosi

1995-01-01

310

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

311

The measurement of shear and compression waves in curing epoxy adhesives using ultrasonic reflection and transmission techniques simultaneously  

NASA Astrophysics Data System (ADS)

Thin epoxy resin adhesive samples were ultrasonically measured during cure using normal incidence radially polarized shear wave electromagnetic acoustic transducers (EMATs). The EMATs used generated predominantly SH shear waves but they also generated/detected compression waves allowing the simultaneous measurement of shear and compression wave propagation through a curing epoxy in a non-contact regime. The source of the compression wave generation has been determined to be the in-plane shear Lorentz force. The adhesive thickness examined in the experiments was approximately 1 mm, which was optimal for experimental measurement using our apparatus: it temporally separated the ultrasonic waves of interest from others present in the pulse whilst remaining thin enough to be representative of a realistic adhesive layer. The rapid cure and standard or 'longer' cure epoxy adhesives described in this paper were supplied in a two-part cartridge form. The experiments show that there is a fundamental difference between the way that the elastic moduli develop in the rapid cure and the longer cure time epoxies. The rapid cure epoxy initially developed a shear elastic modulus at a fast rate, which suddenly decreased at approximately the same time that the temperature of the adhesive reached its maximum value during the exothermic reaction. The reflection measurements show that there was significant coupling of the shear wave into the adhesive even in its initial liquid-like state. The ultrasonic shear and compression wave velocities of the epoxy were calculated from the very outset of the cross-linking reaction using the reflection technique. A transmitted compression wave was visible from the outset of cure, and once a transmitted shear wave was detectable it was possible to measure attenuation for both; however, these data are not presented here as they are not key to the paper and they can be found in our previous publications that are referenced in this one.

Dixon, S.; Jaques, D.; Palmer, S. B.; Rowlands, G.

2004-05-01

312

Noncontact thickness measurement of dielectric coatings using millimeter waves  

NASA Astrophysics Data System (ADS)

Millimeter wave reflectometry offers a noncontact means of measuring the thicknesses of individual layers within multi-layer dielectric coatings on metallic substrates. Complex reflection coefficients of both TM and TE/TM waves incident on coated materials are measured over a range of frequencies and grazing angles of incidence. The sensitivity of the apparatus is such that single-layer coatings differing by 0.2 microns can be distinguished.

Lusk, Mark T.; Radhakrishnan, Kaladhar; Han, Hsiu C.; Mansueto, Edward S.

1994-09-01

313

The continuous measurement of arterial pulse wave velocity  

Microsoft Academic Search

It has long been known that arterial pulse wave velocity (PWV) depends on arterial extensibility. Since extensibility is a\\u000a function of arterial pressure, as well as of various pathological states, the measurement of PWV provides a promising approach\\u000a to the indirect monitoring of the cardiovascular system. The present paper describes a Pulse Wave Velocity Computer designed\\u000a to measure and record

Gershon Weltman; George Sullivan; Dale Bredon

1964-01-01

314

Noncontact thickness measurement of dielectric coatings using millimeter waves  

Microsoft Academic Search

Millimeter wave reflectometry offers a noncontact means of measuring the thicknesses of individual layers within multi-layer dielectric coatings on metallic substrates. Complex reflection coefficients of both TM and TE\\/TM waves incident on coated materials are measured over a range of frequencies and grazing angles of incidence. The sensitivity of the apparatus is such that single-layer coatings differing by 0.2 microns

Mark T. Lusk; Kaladhar Radhakrishnan; Hsiu C. Han; Edward S. Mansueto

1994-01-01

315

Using Ultrasonic Lamb Waves To Measure Moduli Of Composites  

NASA Technical Reports Server (NTRS)

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

Kautz, Harold E.

1995-01-01

316

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

317

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

NASA Astrophysics Data System (ADS)

The response of icy satellite materials to tidal stress has important consequences on their geophysical, geological, and dynamical evolution. The major issue with modeling the tidal response of these objects is that the viscoelastic properties of planetary material are not constrained by laboratory measurements for the relevant frequency range 10e-7 to 10e-5 Hz. While the Maxwell model is usually applied in icy satellite tidal modeling, laboratory measurements for the Earth's mantle have shown that this model is not applicable at forcing frequencies away from the Maxwell frequency. Alternative models (e.g., Andrade, Cole) based on measurements on silicates or terrestrial ice sheets may be better suited to describe ice attenuation, but they have not been introduced in planetary science studies, in part because laboratory measurements are necessary in order to warrant their extrapolation to conditions applicable to icy satellites. The reason why the laboratory data needed for modeling tidal processes at icy satellites are missing is that it is a challenge to achieve measurements at the low stress, low frequencies, and cryogenic conditions relevant to these objects. In the JPL Ice Physical Properties Laboratory an Instron compression system has been implemented with the capability to measure the phase lag between strain and stress, i.e., the internal friction, of an icy sample at frequencies as low as Enceladus' tidal forcing frequency, temperatures as low as 90 K, and cyclic peak stress lower than 0.1 MPa, characteristic of tidal stress at Enceladus or Europa. We will present the first measurements obtained with this system on monocrystalline ice in the frequency range 6x10e-6 to 10e-2 Hz and temperature range 233 - 253 K. We observed a change in frequency-dependence of the friction coefficient at a frequency about the inverse of the Maxwell time. While the Andrade model can fit the phase lags measured over the entire frequency range, it fails to reproduce the effective moduli measured at frequencies higher than 10e-5 Hz. On the other hand, the model developed by Cole (Philos. Mag. A, 72, 231-248, 1995) can account for both the phase lag and effective moduli data, but we had to determine two different sets of parameters in order to characterize the ice viscoelasticity at frequencies higher than the inverse of the Maxwell time, and lower than this reference. We will also present preliminary measurements on polycrystalline ice. Acknowledgements: This work has been conducted at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. Copyright 2008 California Institute of Technology. Government sponsorship acknowledged. Part of this work was also carried out in the Mars and Ice Simulation Laboratory at Caltech.

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

2008-12-01

318

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

NASA Technical Reports Server (NTRS)

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

Lally, J.; Meister, R.

1983-01-01

319

Development and validation of a field microphone-in-real-ear approach for measuring hearing protector attenuation.  

PubMed

Numerous studies have shown that the reliability of using laboratory measurements to predict individual or even group hearing protector attenuation for occupationally exposed workers is quite poor. This makes it difficult to properly assign hearing protectors when one wishes to closely match attenuation to actual exposure. An alternative is the use of field-measurement methods, a number of which have been proposed and are beginning to be implemented. We examine one of those methods, namely the field microphone-in-real-ear (F-MIRE) approach in which a dual-element microphone probe is used to measure noise reduction by quickly sampling the difference in noise levels outside and under an earplug, with appropriate adjustments to predict real-ear attenuation at threshold (REAT). We report on experiments that validate the ability of one commercially available F-MIRE device to predict the REAT of an earplug fitted identically for two tests. Results are reported on a representative roll-down foam earplug, stemmed-style pod plug, and pre-molded earplug, demonstrating that the 95% confidence level of the Personal Attenuation Rating (PAR) as a function of the number of fits varies from ± 4.4 dB to ± 6.3 dB, depending on the plug type, which can be reduced to ± 3.1 dB to ± 4.5 dB with a single repeat measurement. The added measurement improves precision substantially. However, the largest portion of the error is due to the user's fitting variability and not the uncertainty of the measurement system. Further we evaluated the inherent uncertainty of F-MIRE vs. the putative "gold standard" REAT procedures finding, that F-MIRE measurement uncertainty is less than one-half that of REAT at most test frequencies. An American National Standards Institute (ANSI) working group (S12/WG11) is currently involved in developing methods similar to those in this paper so that procedures for evaluating and reporting uncertainty on all types of field attenuation measurement systems can be standardized. We conclude that the hearing conservationist now has available a portable, convenient, quick, and easy-to-use system that can improve training and motivation of employees, assign hearing protection devices based on noise exposures, and address other management and compliance issues. PMID:21368442

Berger, E H; Voix, J; Kieper, R W; Le Cocq, C

2011-01-01

320

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

321

Measurement of atomic number and mass attenuation coefficient in magnesium ferrite  

NASA Astrophysics Data System (ADS)

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 (?), mass attenuation coefficient (?/?), total atomic cross-section (?_{tot}), total electronic cross-section (?_{ele}) and the effective atomic number (Z_{eff}) were calculated for pure magnesium ferrite (MgFe_{2}O_{4}). The values of ?-ray mass attenuation coefficient were obtained using a NaI energy selective scintillation counter with radioactive ?-ray sources having energy 0.36, 0.511, 0.662, 1.17 and 1.28 MeV. The experimentally obtained values of ?/? and Z_{eff} agreed fairly well with those obtained theoretically.

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

2007-05-01

322

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

323

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

NASA Astrophysics Data System (ADS)

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

324

Millimeter-Wave Substrate Mounted Antenna Measurements  

Microsoft Academic Search

A substrate mounted antenna is a type of integrated circuit antenna that, unlike the microstrip antenna, does not have a ground plane on the bottom surface of the substrate. The measurement apparatus is described, and the rerults of field pattern and absolute gain measurements at 230 GHz w+&-+e presented I. INTRODUCTION The long range goals of the substrate mounted antenna

M. Couker; J. J. Gallagher

1990-01-01

325

Measurements of colliding shock wave and supersonic gas flow  

NASA Astrophysics Data System (ADS)

The collision between a laser generated shock wave and a supersonic flow from a gas jet was studied using pump-probe Schlieren shadowgraphy. The velocity of a gas escaping into vacuum from a high pressure gas jet nozzle was measured and verified in simulation. Time resolved tracking of the shock wave provided critical information about the gas jet vertical velocity and horizontal gas density profile. The measured velocity of the diatomic gas jet was found to be close to the theoretical maximum escape velocity of the gas released into vacuum. Modification of the hemispherical shock wave structure by the supersonic flow was minimal. However, the propagation of the shock wave was observed to be substantially effected by the gas flow.

Kaganovich, D.; Helle, M. H.; Gordon, D. F.; Ting, A.

2010-11-01

326

Laser measurements of bacterial endospore destruction from shock waves  

NASA Astrophysics Data System (ADS)

The effects of shock waves on bioaerosols containing endospores were measured by combined laser absorption and scattering. Experiments were conducted in the Stanford aerosol shock tube for post-shock temperatures ranging from 400 K to 1100 K. Laser intensity measurements through the test section of the shock tube at wavelengths of 266 and 665 nm provided real-time monitoring of the morphological changes (includes changes in shape, structure and optical properties) in the endospores. Scatter of the visible light measured the integrity of endospore structure, while absorption of the UV light provided a measure of biochemicals released when endospores ruptured. For post-shock temperatures above 750 K the structural breakdown of Bacillus atrophaeus (BA) endospores was observed. A simple theoretical model using laser extinction is presented for determining the fraction of endospores that are ruptured by the shock waves. In addition, mechanisms of endospore mortality preceding their disintegration due to shock waves are discussed.

Lappas, Petros P.; McCartt, A. Daniel; Gates, Sean D.; Jeffries, Jay B.; Hanson, Ronald K.

2013-12-01

327

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

328

Create a millimeter-wave vector-measurement system  

Microsoft Academic Search

A new tool for millimeter-wave design engineers is a test system which is capable fo performing complex impedance measurements in real time. The millimeter-wave scattering-parameter test set utilizes the stabilities of the 47850H synthesized source and a phase-locked Gunn oscillator to provide accurate phase and magnitude readings. The approaches used for building a bridge are discussed along with the conduction

P. A. Gianfortune

1984-01-01

329

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

330

Measurement of x-ray attenuation coefficients of aqueous solutions of indocyanine green and glycated chitosan  

E-print Network

and glycated chitosan Fang Xu and Hong Liua) Department of Radiology and Biomedical Engineering, University of a light absorbing dye, indocyanine green, and an immunoadjuvant, glycated chitosan. In the treatment results show that glycated chitosan has a higher attenuation coefficient compared to indocyanine green

Jiang, Hangyi

331

BOTDA-nondestructive measurement of single-mode optical fiber attenuation characteristics using Brillouin interaction: theory  

Microsoft Academic Search

A theoretical investigation of Brillouin optical-fiber time-domain analysis (BOTDA) is described. BOTDA uses Brillouin interaction in optical fibers to analyze the attenuation characteristics of the optical fibers nondestructively. The dynamic range performance of BOTDA is approximately 10-dB greater than that of conventional optical time-domain reflectometry

Tsuneo Horiguchi; Mitsuhiro Tateda

1989-01-01

332

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

333

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

334

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

335

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

NASA Astrophysics Data System (ADS)

The half-value thicknesses, linear and mass attenuation coefficients of biological samples such as bone, muscle, fat and water have been measured at 140, 364 and 662 keV ?-ray energies by using the ATOMLABTM-930 medical spectrometer. The ?-rays were obtained from 99mTc, 131I and 137Cs ?-ray point sources. Also theoretical calculations have been performed in order to obtain the half-value thicknesses and, mass and linear attenuation coefficients at photon energies 0.001 keV 20 MeV for bone, muscle and water samples. The calculated value and the experimental results of this work and the other results in literature are found to be in good agreement.

Akar, A.; Balta?, H.; Çevik, U.; Korkmaz, F.; Okumu?o?lu, N. T.

2006-11-01

336

Simultaneous measurement of unfrozen water content and ice content in frozen soil using gamma ray attenuation and TDR  

NASA Astrophysics Data System (ADS)

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

337

Range Measurement Using Ultrasound FMCW Wave  

NASA Astrophysics Data System (ADS)

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

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

338

Evaluation of multilayered pavement structures from measurements of surface waves  

USGS Publications Warehouse

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

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

2006-01-01

339

Measurement of Ionization Energies of Nitrogen in 4H-SiC by Traveling-Wave Method  

NASA Astrophysics Data System (ADS)

The impurity bands and corresponding ionization energies of nitrogen atoms in a 4H-SiC crystal with a concentration of 1×1019 cm-3 are measured by a nondestructive and noncontact traveling-wave method. When a SiC sample was placed near the surface of a surface acoustic wave device, its conductivity can be obtained by measuring the attenuation of the piezo-potential traveling-wave grazing along the surface of the sample. Temperature-dependent conductivities corresponding to a freeze-out process of free carriers excited from nitrogen atoms were observed, and the corresponding ionization energies of the nitrogen atoms were estimated by the Arrhenius plot method. The ionization energies in the impurity bands originating from splits of the doping atoms at cubic and hexagonal sites in the carbon sublattice are 72.89 and 47.89 meV, respectively, at room temperature. The ionization energies are in good agreement with the results reported in other theoretical and experimental studies. We also found that the skin depth of the traveling wave in the sample is below 1 mm and that the mobility of the carriers is strongly affected by both ionized dopants and charged surface defects in the depletion region near the surface of the sample. The effects of the sample and traveling wave such as the polarization effects of the crystal and the frequency effects of the traveling wave are discussed.

Takase, Tsuyoshi; Sakaino, Masamichi; Sun, Yong; Miyasato, Tatsuro

2013-09-01

340

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

341

Apoptosis and necrosis-induced changes in light attenuation measured by optical coherence tomography  

Microsoft Academic Search

Optical coherence tomography (OCT) was used to determine optical properties of pelleted human fibroblasts in which necrosis\\u000a or apoptosis had been induced. We analysed the OCT data, including both the scattering properties of the medium and the axial\\u000a point spread function of the OCT system. The optical attenuation coefficient in necrotic cells decreased from 2.2?±?0.3 mm?1 to 1.3?±?0.6 mm?1, whereas, in the

Freek J. van der Meer; Dirk J. Faber; Maurice C. G. Aalders; Andre A. Poot; Istvan Vermes; Ton G. van Leeuwen

2010-01-01

342

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

343

Propagation through a stratified ocean wave guide with random volume and surface inhomogeneities, Part I. Theory: Attenuation, dispersion, and acoustic mirages  

NASA Astrophysics Data System (ADS)

Analytic expressions for the mean field propagated through a stratified ocean with random volume or sufrace inhomogeneities of arbitrary size compared to the wavelength are derived from a wave guide scattering model stemming from Green's theorem. It is found that multiple scattering through inhomogeneities in the forward direction can be succinctly expressed in terms of modal attenuation and dispersion coefficients under widely satisfied conditions. The inhomogeneities can have an arbitrary distribution in depth so that the model can realistically apply to scattering from internal waves, bubbles, fish, seafloor and seasurface roughness as well as sub-bottom anomalies. An understanding of the coherence of the forward scattered field can be gained by analogy with the formation of optical mirages in low-grazing angle forward scatter from random surfaces.

Ratilal, Purnima; Makris, Nicholas C.

2002-11-01

344

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

345

10 GHz-Range Surface Acoustic Wave Low Loss Filter Measured at Low Temperature  

NASA Astrophysics Data System (ADS)

The 10 GHz-range surface acoustic wave (SAW) is of great importance in the field of physical acoustics and application of SAW devices, for example, in mobile and wireless communications. The temperature dependency of the propagation attenuation at 10 GHz-range is measured using the three-transducer system with an electrode width of less than 0.1 µm, which is fabricated using an electron beam exposure and lift-off technique. The results show that the attenuation at room temperature is about 1.5 dB/(100 ?) at 10 GHz. Next, the temperature dependency of the insertion loss of a floating electrode reflection type unidirectional transducer (FEUDT) whose electrodes are respectively fabricated from Al and the superconductor Nb, is investigated experimentally. In the case of Al-FEUDT at 8 GHz, the insertion loss at a low temperature is about 8.5 dB, which is 3.4 dB lower than the insertion loss at room temperature. The main cause of decrease in the insertion loss is the decrease in the resistivity of the very thin and narrow metal electrodes. The results of Nb-FEUDT show a marked decrease in the insertion loss around the critical temperature Tc=9.23 K.

Yamanouchi, Kazuhiko; Nakagawa, Hideyuki; Qureshi, Jamil; Odagawa, Hiroyuki

1999-05-01

346

Measurement of ocean wave heights using the Geos 3 altimeter  

NASA Technical Reports Server (NTRS)

Radar altimeter signals transmitted from the low-orbiting satellite Geos 3 were analyzed for two selected orbits over high seas associated with hurricane 'Caroline' in the Gulf of Mexico and a North Atlantic storm. The measured values of significant wave height are in reasonable agreement with surface measurements, provided that the altimeter data are properly edited. The internal consistency of estimated wave heights for the North Atlantic storm, a standard deviation of 0.6 m or less, and the good agreement with surface truth lend credence to the method. A statistical analysis of the pulse slope variation gives estimated values of significant wave height within + or - 1 m of the true values 75% of the time for spatial averaging over 70 km.

Rufenach, C. L.; Alpers, W. R.

1978-01-01

347

Measurements of neutron effective doses and attenuation lengths for shielding materials at the heavy-ion medical accelerator in Chiba.  

PubMed

The effective doses and attenuation lengths for concrete and iron were measured for the design of heavy ion facilities. Neutrons were produced through the reaction of copper, carbon, and lead bombarded by carbon ions at 230 and 400 MeV.A, neon ions at 400 and 600 MeV.A, and silicon ions at 600 and 800 MeV.A. The detectors used were a Linus and a Andersson-Braun-type rem counter and a detector based on the activation of a plastic scintillator. Representative effective dose rates (in units of 10(-8) microSv h(-1) pps(-1) at 1 m from the incident target surface, where pps means particles per second) and the attenuation lengths (in units of m) were 9.4 x 10(4), 0.46 for carbon ions at 230 MeV.A; 8.9 x 10(5), 0.48 for carbon ions at 400 MeV.A; 9.3 x 10(5), 0.48 for neon ions at 400 MeV.A; 3.8 x 10(6), 0.50 for neon ions at 600 MeV.A; 3.9 x 10(6), 0.50 for silicon ions at 600 MeV.A; and 1.1 x 10(7), 0.51 for silicon ions at 800 MeV.A. The attenuation provided by an iron plate approximately 20 cm thick (nearly equal to the attenuation length) corresponded to that of a 50-cm block of concrete in the present energy range. Miscellaneous results, such as the angular distributions of the neutron effective dose, narrow beam attenuation experiments, decay of gamma-ray doses after the bombardment of targets, doses around an irradiation room, order effects in the multi-layer (concrete and iron) shielding, the doses from different targets, the doses measured with a scintillator activation detector, the gamma-ray doses out of walls and the ratio of the response between the Andersson-Braun-type and the Linus rem counters are also reported. PMID:15824595

Kumamoto, Yoshikazu; Noda, Yutaka; Sato, Yukio; Kanai, Tatsuaki; Murakami, Takeshi

2005-05-01

348

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

349

Analysis of elastic waves from two-point strain measurement  

Microsoft Academic Search

Provided that the one-dimensional wave equation applies, strain measurement at two sections of a linearly elastic cylindrical rod makes it possible to determine a number of important quantities at an arbitrary section of the rod; for example, strain, particle velocity and power transmission. The equations needed are derived, and the design of an analogue real-time analyzer is presented. The influence

B. Lundberg; A. Henchoz

1977-01-01

350

Survey of Temperature Measurement Techniques For Studying Underwater Shock Waves  

NASA Technical Reports Server (NTRS)

Several optical methods for measuring temperature near underwater shock waves are reviewed and compared. The relative merits of the different techniques are compared, considering accuracy, precision, ease of use, applicable temperature range, maturity, spatial resolution, and whether or not special additives are required.

Danehy, Paul M.; Alderfer, David W.

2004-01-01

351

Selective continuous quantum measurements: Restricted path integrals and wave equations  

E-print Network

We discuss both the restricted path integral (RPI) and the wave equation (WE) techniques in the theory of continuous quantum measurements. We intend to make Mensky's fresh review complete by transforming his "effective" WE with complex Hamiltonian into Ito-differential equations.

Lajos Diosi

1995-01-10

352

High resolution measurements in liquid metal by focused ultrasonic wave  

Microsoft Academic Search

High spatial resolution measurements in molten zinc at temperatures more than 600 °C are performed using a focused ultrasonic pulse-echo technique with clad metallic buffer rods. The focused ultrasonic waves are generated by a spherical acoustic lens which is fabricated at the end of the buffer rod. In order to evaluate its focussing ability, several experiments are carried out in

I. Ihara; C.-K. Jen; D. Ramos França

2000-01-01

353

Measuring and analysing the directional spectra of ocean waves  

E-print Network

Measuring and analysing the directional spectra of ocean waves 1415QS-NA-21367-EN-C COST Action 714 EUR 21367 Meteorology European cooperation in the field of scientific and technical research for European cooperation in the field of scientific and technical research -- is the oldest and widest European

Boyer, Edmond

354

Model-based tomographic optoacoustic reconstructions in acoustically attenuating media  

NASA Astrophysics Data System (ADS)

Acoustic attenuation influences the transmission of the ultrasonic waves excited optoacoustically in biological samples, in a way that the amplitude of the waves is reduced as they propagate through acoustically attenuating tissues. Furthermore, being dependent on frequency, acoustic attenuation also causes broadening of the time-resolved optoacoustic signals, which in turn leads to blurring of features and overall deterioration of image quality. The effects of acoustic attenuation are more prominent for the high frequency components of the optoacoustic waves and they must be taken into account for high resolution imaging. In this work, we modify a model-based reconstruction algorithm to incorporate the effects of acoustic attenuation in tomographic optoacoustic imaging set-ups. As the waves propagate from the excitation until the measurement points, they undergo space and frequency dependent attenuation, which can be effectively accounted for using the suggested model-based approach. The simulation results obtained showcase a good performance of the introduced method in terms of resolution improvement.

Deán-Ben, X. Luís.; Razansky, Daniel

2014-03-01

355

Broadband Lamb-wave measurements for materials characterization  

NASA Astrophysics Data System (ADS)

Conventional ultrasonic Lamb wave testing of materials often relies on the efficient generation and detection of a single Lamb wave mode that propagates in a relatively non- dispersive region of its characteristic. Such an approach allows identification of defect sites within the material by looking for distinct pulse reflections in the time domain. The fundamental symmetric mode is often utilized due to its low dispersion and relatively high velocity. However, this mode is restricted to a low frequency-plate thickness product where its wavelength may be several tens of millimeters with obvious implications for defect sensitivity. An alternative approach to single mode excitation is to utilize broadband Lamb wave measurements. Since a wider portion of the Lamb wave spectrum is now excited it is anticipated that defect resolution could be enhanced. We have investigated the propagation characteristics of ultrasonic Lamb waves in thin plates of metal and composite structure. Ultrasonic generation and detection was accomplished using a combination of non- contacting optical techniques, material integrated optical fiber sensor and conventional piezoelectric sources. Utilizing the broad optical techniques, material integrated optical fiber sensor and conventional piezoelectric sources. Utilizing the broad temporal and spatial bandwidth of a pulsed laser source combined with a point detector, it was possible to simultaneously measure the dispersion characteristics of several propagating Lamb wave modes in both aluminium and carbon fiber composite plates. An alternative approach to signal interpretation was undertaken by developing a NARMAX model of composite plates. An alternative approach to signal interpretation was undertaken by developing a NARMAX model of Lamb wave propagation in a sample plate and correlating properties of the model to damage in the samples. A possible extension to this techniques using a modulated laser diode for acoustic generation is also described. It is anticipated that these related techniques could be used to identify the presence of defects in addition to material ageing effects in composites.

Pierce, S. Gareth; Shan, Q.; Culshaw, Brian; Wolters, C.; Worden, Keith

1998-07-01

356

Motion artifact elimination using adaptive filter based on wavelet transform in pulse wave measurement  

Microsoft Academic Search

Measuring accuracy is very easily influenced by motion artifact in the measurement of pulse wave. Original pulse wave signal is processed by adaptive filter based on the wavelet transform to obtain higher amplitude detection precision and stronger motion artifact inhibition in photoplethysmography pulse wave measurement. Firstly, pulse wave is decomposed and motion artifact is reconstructed by Mallat algorithm based on

Qiao Xiaoyan; Yao feng; Dong Youer

2009-01-01

357

Measurement of sound speed vs. depth in South Pole ice: pressure waves and shear waves  

SciTech Connect

We have measured the speed of both pressure waves and shear waves as a function of depth between 80 and 500 m depth in South Pole ice with better than 1% precision. The measurements were made using the South Pole Acoustic Test Setup (SPATS), an array of transmitters and sensors deployed in the ice at the South Pole in order to measure the acoustic properties relevant to acoustic detection of astrophysical neutrinos. The transmitters and sensors use piezoceramics operating at {approx}5-25 kHz. Between 200 m and 500 m depth, the measured profile is consistent with zero variation of the sound speed with depth, resulting in zero refraction, for both pressure and shear waves. We also performed a complementary study featuring an explosive signal propagating vertically from 50 to 2250 m depth, from which we determined a value for the pressure wave speed consistent with that determined for shallower depths, higher frequencies, and horizontal propagation with the SPATS sensors. The sound speed profile presented here can be used to achieve good acoustic source position and emission time reconstruction in general, and neutrino direction and energy reconstruction in particular. The reconstructed quantities could also help separate neutrino signals from background.

IceCube Collaboration; Klein, Spencer

2009-06-04

358

Time resolved measurements of the energy distribution in unstable plasma II. Measurement in the ionization waves  

Microsoft Academic Search

A sampling technique described in Part I has been used, for measurement of the electron distribution function. Two groups of electrons and changes of the distribution function along the ionization waves of small amplitude have been found.

M. Šícha; V. ?ezá?ová; M. Tichý; V. Veselý; M. Drouet; Z. Zakrzewski

1971-01-01

359

Frequency Dependent Attenuation Revisited  

E-print Network

The work is inspired by thermo-and photoacoustic imaging, where recent efforts are devoted to take into account attenuation and varying wave speed parameters. In this paper we study causal equations describing propagation of attenuated pressure waves. We review standard models like frequency power laws and and the thermo-viscous equation. The lack of causality of standard models in the parameter range relevant for photoacoustic imaging requires to derive novel equations. The main ingredients for deriving causal equations are the Kramers-Kronig relation and the mathematical concept of linear system theory. The theoretical results of this work are underpined by numerical experiments.

Richard, Kowar; Xavier, Bonnefond

2009-01-01

360

Capillary wave measurements on helically-supported capillary channels  

NASA Astrophysics Data System (ADS)

NASA is considering power generation by the Rankine cycle to save weight on long-duration manned missions to the moon or Mars. Phase separation technology is critical to this process in microgravity. Arrays of capillary channels might be useful for filtering liquid drops from a flowing vapor. The efficiency of droplet capture by a helically-supported capillary channel is being studied. A droplet impinging on the channel launches capillary waves that propagate down the channel helping to dissipate some of the drop's kinetic energy. High-speed video of the channel combined with image processing allows for measurement of the amplitude and speed of the wave packets. Increasing the pitch of the support structure decreases the wave speed. An understanding of the dynamic response of the channel to drop impact is a first step in predicting drop-capture efficiency.

Chandurwala, Fahim; Thiessen, David

2010-10-01

361

Millimeter wave backscatter measurements in support of collision avoidance applications  

NASA Astrophysics Data System (ADS)

Millimeter-wave short range radar systems have unique advantages in surface navigation applications, such as military vehicle mobility, aircraft landing assistance, and automotive collision avoidance. In collision avoidance applications, characterization of clutter due to terrain and roadside objects is necessary in order to maximize the signal-to-clutter ratio (SCR) and to minimize false alarms. The results of two types of radar cross section (RCS) measurements at 95 GHz are reported in this paper. The first set of measurements presents data on the normalized RCS (NRCS) as well as clutter distributions of various terrain types at low grazing angles of 5° and 7.5°. The second set of measurements presents RCS data and statistics on various types of roadside objects, such as metallic and wooden sign posts. These results are expected to be useful for designers of short-range millimeter-wave collision avoidance radar systems.

Narayanan, Ram M.; Snuttjer, Brett R. J.

1997-11-01

362

SEISMIC ATTENUATION FOR RESERVOIR CHARACTERIZATION  

SciTech Connect

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

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

2002-04-01

363

Theoretical analysis and meteorological interpretation of the role of raindrop shape on microwave attenuation and propagation phase shifts - Implications for the radar measurement of rain  

NASA Technical Reports Server (NTRS)

The effects of raindrop shape on the attenuation and propagation phase shift at vertical and horizontal linear polarizations is examined, focusing on the implications of these effects on rain measurements by radars. Analytic expressions for the imaginary and real components of the forward scattering amplitude function are dervied for a wavelength of 2.2 cm. It is shown that the summation attenuation rate and the rate of summation propagation phase shift are both insensitive to the shapes of raindrops.

Jameson, A. R.

1989-01-01

364

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

USGS Publications Warehouse

The lithosphere beneath a continental rift should be significantly modified due to extension. To image the lithosphere beneath the Rio Grande rift (RGR), we analyzed teleseismic travel time delays of both P and S wave arrivals and solved for the attenuation of P and S waves for four seismic experiments spanning the Rio Grande rift. Two tomographic inversions of the P wave travel time data are given: an Aki-Christofferson-Husebye (ACH) block model inversion and a downward projection inversion. The tomographic inversions reveal a NE-SW to NNE-SSW trending feature at depths of 35 to 145 km with a velocity reduction of 7 to 8% relative to mantle velocities beneath the Great Plains. This region correlates with the transition zone between the Colorado Plateau and the Rio Grande rift and is bounded on the NW by the Jemez lineament, a N52??E trending zone of late Miocene to Holocene volcanism. S wave delays plotted against P wave delays are fit with a straight line giving a slope of 3.0??0.4. This correlation and the absolute velocity reduction imply that temperatures in the lithosphere are close to the solidus, consistent with, but not requiring, the presence of partial melt in the mantle beneath the Rio Grande rift. The attenuation data could imply the presence of partial melt. We compare our results with other geophysical and geologic data. We propose that any north-south trending thermal (velocity) anomaly that may have existed in the upper mantle during earlier (Oligocene to late Miocene) phases of rifting and that may have correlated with the axis of the rift has diminished with time and has been overprinted with more recent structure. The anomalously low-velocity body presently underlying the transition zone between the core of the Colorado Plateau and the rift may reflect processes resulting from the modern (Pliocene to present) regional stress field (oriented WNW-ESE), possibly heralding future extension across the Jemez lineament and transition zone.

Slack, P.D.; Davis, P.M.; Baldridge, W.S.; Olsen, K.H.; Glahn, A.; Achauer, U.; Spence, W.

1996-01-01

365

Laser vibrometer measurement of guided wave modes in rail track.  

PubMed

The ability to measure the individual modes of propagation is very beneficial during the development of guided wave ultrasound based rail monitoring systems. Scanning laser vibrometers can measure the displacement at a number of measurement points on the surface of the rail track. A technique for estimating the amplitude of the individual modes of propagation from these measurements is presented and applied to laboratory and field measurements. The method uses modal data from a semi-analytical finite element model of the rail and has been applied at frequencies where more than twenty propagating modes exist. It was possible to measure individual modes of propagation at a distance of 400m from an ultrasonic transducer excited at 30kHz on operational rail track and to identify the modes that are capable of propagating large distances. PMID:25497003

Loveday, Philip W; Long, Craig S

2015-03-01

366

Ocean Waves Measurement and Analysis, Fifth International Symposium WAVES 2005, 3rd-7th, July, 2005. Madrid, Spain Paper number: 197  

E-print Network

Ocean Waves Measurement and Analysis, Fifth International Symposium WAVES 2005, 3rd-7th, July, 2005. Madrid, Spain Paper number: 197 #12;Ocean Waves Measurement and Analysis, Fifth International Symposium WAVES 2005, 3rd-7th, July, 2005. Madrid, Spain #12;Ocean Waves Measurement and Analysis, Fifth

Grilli, Stéphan T.

367

Evanescent wave absorption measurements of corroded materials using ATR and optical fibers  

NASA Astrophysics Data System (ADS)

The purpose of this research effort is to develop an in-situ corrosion sensing capability. The technique will permit detection of corrosion on and within aircraft structures. This includes component junctions that are susceptible to corrosion but which are not accessible for visual inspection. The prototype experimental configuration we are developing includes long wave infrared transmitting optical fiber probes interfaced with a Fourier Transform Infrared (FTIR) interferometer for evanescent wave absorption spectroscopic measurements. The mature and fielded technique will allow periodic remote sensing for detection of corrosion and for general onboard aircraft structural health monitoring. An experimental setup using an Attenuated Total Reflection (ATR) crystal integrated with an FTIR spectrometer has been assembled. Naturally occurring corrosion including Aluminum Hydroxide [Al(OH)3] is one of the main corrosion products of aluminum the principle structural metal of aircraft. Absorption spectra of our model corrosion product, pure Al(OH)3, have been collected with this ATR/FTIR experimental setup. The Al(OH)3spectra serve as reference spectral signatures. The spectra of corrosion samples from a simulated corrosion process have been collected and compared with the reference Al(OH)3 spectra. Also absorption spectra of naturally occurring corrosion collected from a fielded corroded aircraft part have been obtained and compared with the spectra from the simulated corrosion.

Namkung, Juock; Hoke, Mike; Schwartz, Andy

2011-06-01

368

FROM SINGLE POINT GAUGE TO SPATIO-TEMPORAL MEASUREMENT OF OCEAN WAVES PROSPECTS AND PERSPECTIVES  

E-print Network

FROM SINGLE POINT GAUGE TO SPATIO-TEMPORAL MEASUREMENT OF OCEAN WAVES ­ PROSPECTS AND PERSPECTIVES With the recent advancement of spatial measurements of ocean waves, we are clearly facing new challenges regarding world of truly spatial ocean waves. INTRODUCTION Since the first successful development of a wave gauge

369

Measurement of plane wave acoustic fields in flow ducts  

NASA Astrophysics Data System (ADS)

Standing wave acoustic parameters describing the acoustic field within flow ducts can be conveniently derived by considering a sufficiently long section of duct as an impedance tube. This paper describes a measurement approach in which information is acquired by analysis of wall pressure records obtained simultaneously from a pair or an array of fixed points. This procedure minimizes most of the disadvantages associated with conventional methods, but requires facilities for fast digital data acquisition and processing.

Davies, P. O. A. L.; Bhattacharya, M.; Coelho, J. L. B.

1980-10-01

370

Measuring the gravitational wave background using precision pulsar timing  

NASA Astrophysics Data System (ADS)

We investigate the possibility of using high precision timing measurements of radio pulsars to constrain or detect the stochastic gravitational wave background (GWB). Improved algorithms are presented for more accurately determining the pulse times of arrival at Earth and characterizing pulse profile shape variation. Next, we describe the design and construction of a new set of pulsar backends based on clusters of standard personal computers. These machines, the Astronomy Signal Processors (ASPS), coherently correct the pulse broadening caused by interstellar plasma dispersion. Since they are based in software, they are inherently more flexible than previous generations of pulsar data recorders. In addition, they provide increased bandwidth and quantization accuracy. We apply these methods to 2.5 years worth of millisecond pulsar data recorded with the ASP systems at the Arecibo and Green Bank Telescopes, and present pulse profiles, dispersion measure variation, and timing model parameters derived from this data. We then develop the theory of gravitational wave detection using pulsar timing, and show how data from several pulsars can be combined into a pulsar timing array for this purpose. In particular, a new method of accounting for the effect of the timing model fit on the gravitational wave signal is presented. This method incorporates the exact timing model basis functions without relying on Monte Carlo simulation. We apply this method to the 2.5 year dataset previously mentioned and derive a gravitational wave limit of h c (1 yr -1 ) < 2.46 × 10 -14 . Finally, we study the 20-year timing record of PSR B1937+21 and obtain information on how severely interstellar medium effects will compromise future GWB detection. We predict that these developments, in conjunction with historical data, could provide the first successful direct gravitational wave detection on a 5-10 year timescale.

Demorest, Paul B.

2007-08-01

371

Measurement of Shock Wave Rise Times in Metal Thin Films  

NASA Astrophysics Data System (ADS)

We have measured the rise time of laser-generated shock waves in vapor plated metal thin films using frequency-domain interferometry with subpicosecond time resolution. 10%- 90% rise times of <6.25 ps were found in targets ranging from 0.25 to 2.0 ?m in thickness. Particle and average shock velocities were simultaneously determined. Shock velocities of ~5 nm/ps were inferred from the measured free surface velocity, corresponding to pressures of 30-50 kbar. Thus, the shock front extends only a few tens of lattice spacings.

Gahagan, K. T.; Moore, D. S.; Funk, David J.; Rabie, R. L.; Buelow, S. J.; Nicholson, J. W.

2000-10-01

372

Towards a quantitative, measurement-based estimate of the uncertainty in photon mass attenuation coefficients at radiation therapy energies.  

PubMed

In this study, a quantitative estimate is derived for the uncertainty in the XCOM photon mass attenuation coefficients in the energy range of interest to external beam radiation therapy-i.e. 100 keV (orthovoltage) to 25 MeV-using direct comparisons of experimental data against Monte Carlo models and theoretical XCOM data. Two independent datasets are used. The first dataset is from our recent transmission measurements and the corresponding EGSnrc calculations (Ali et al 2012 Med. Phys. 39 5990-6003) for 10-30 MV photon beams from the research linac at the National Research Council Canada. The attenuators are graphite and lead, with a total of 140 data points and an experimental uncertainty of ?0.5% (k = 1). An optimum energy-independent cross section scaling factor that minimizes the discrepancies between measurements and calculations is used to deduce cross section uncertainty. The second dataset is from the aggregate of cross section measurements in the literature for graphite and lead (49 experiments, 288 data points). The dataset is compared to the sum of the XCOM data plus the IAEA photonuclear data. Again, an optimum energy-independent cross section scaling factor is used to deduce the cross section uncertainty. Using the average result from the two datasets, the energy-independent cross section uncertainty estimate is 0.5% (68% confidence) and 0.7% (95% confidence). The potential for energy-dependent errors is discussed. Photon cross section uncertainty is shown to be smaller than the current qualitative 'envelope of uncertainty' of the order of 1-2%, as given by Hubbell (1999 Phys. Med. Biol 44 R1-22). PMID:25622289

Ali, E S M; Spencer, B; McEwen, M R; Rogers, D W O

2015-02-21

373

Towards a quantitative, measurement-based estimate of the uncertainty in photon mass attenuation coefficients at radiation therapy energies  

NASA Astrophysics Data System (ADS)

In this study, a quantitative estimate is derived for the uncertainty in the XCOM photon mass attenuation coefficients in the energy range of interest to external beam radiation therapy—i.e. 100 keV (orthovoltage) to 25 MeV—using direct comparisons of experimental data against Monte Carlo models and theoretical XCOM data. Two independent datasets are used. The first dataset is from our recent transmission measurements and the corresponding EGSnrc calculations (Ali et al 2012 Med. Phys. 39 5990–6003) for 10–30 MV photon beams from the research linac at the National Research Council Canada. The attenuators are graphite and lead, with a total of 140 data points and an experimental uncertainty of ?0.5% (k = 1). An optimum energy-independent cross section scaling factor that minimizes the discrepancies between measurements and calculations is used to deduce cross section uncertainty. The second dataset is from the aggregate of cross section measurements in the literature for graphite and lead (49 experiments, 288 data points). The dataset is compared to the sum of the XCOM data plus the IAEA photonuclear data. Again, an optimum energy-independent cross section scaling factor is used to deduce the cross section uncertainty. Using the average result from the two datasets, the energy-independent cross section uncertainty estimate is 0.5% (68% confidence) and 0.7% (95% confidence). The potential for energy-dependent errors is discussed. Photon cross section uncertainty is shown to be smaller than the current qualitative ‘envelope of uncertainty’ of the order of 1–2%, as given by Hubbell (1999 Phys. Med. Biol 44 R1–22).

Ali, E. S. M.; Spencer, B.; McEwen, M. R.; Rogers, D. W. O.

2015-02-01

374

Differential t* measurements via instantaneous frequency matching: observations of lower mantle shear attenuation heterogeneity beneath western Central America  

NASA Astrophysics Data System (ADS)

We infer shear attenuation in the lower mantle by using the method of instantaneous frequency matching to calculate differential t* between core-reflected ScS and direct S (?t*ScS-S). The instantaneous frequency at the envelope peak of a seismic phase is related to the average Fourier spectral frequency of that phase. To estimate ?t*ScS-S for a given trace, we first calculate the instantaneous frequency at the envelope peak of S and ScS. The trace is then attenuated through convolution with a suite of t* operators until the instantaneous frequency at the envelope peak of the seismic phase with the initially larger instantaneous frequency matches the value of the smaller instantaneous frequency from the initial calculation. The differential t* operator required to accomplish the match is then ?t*ScS-S. We also calculate ?t*ScS-S from the slope of the spectral ratio of windowed ScS and S. Both the spectral ratio and instantaneous frequency methods produce consistent results for high signal-to-noise ratio synthetic waveforms with S and ScS well separated in time, and where there are no other interfering phases. The instantaneous frequency method gives more stable results for low signal-to-noise ratio waveforms, and where S and/or ScS are affected by other interfering seismic phases. The instantaneous frequency matching method is applied to broadband data from South American earthquakes recorded in California that sample the lower mantle beneath Central America and the Cocos plate. ?t*ScS-S ranges from approximately -4 to 2 s, but are predominately negative, suggesting S is more attenuated than ScS for these data. We estimate the possibly contaminating effects of 3-D velocity heterogeneity on ?t*ScS-S through analysis of synthetic seismograms computed for a cross-section through a tomographically derived model of global shear wave heterogeneity, using an axisymmetric finite difference algorithm. Synthetics for path geometries of our data predict a ?t*ScS-S of ˜0.2 s. We investigate the effect of seismic anisotropy by comparing ?t*ScS-S before and after a subset of the data were corrected using splitting parameters obtained by linearizing the particle motion of the S and ScS phases. The rms error of the residuals between the corrected and uncorrected ?t*ScS-S is ˜0.2 s. Neither of these efforts, however, match the large negative observed ?t*ScS-S values, suggesting the mid-mantle beneath western Central America is in fact much more attenuating than the lowermost mantle below it, or S may be broadened by out-of-plane propagation effects, involving the remains of the Farallon plate containing stronger velocity heterogeneity than is imaged by seismic tomography.

Ford, Sean R.; Garnero, Edward J.; Thorne, Michael S.

2012-04-01

375

Extracting Earth's Elastic Wave Response from Noise Measurements  

NASA Astrophysics Data System (ADS)

Recent research has shown that noise can be turned from a nuisance into a useful seismic source. In seismology and other fields in science and engineering, the estimation of the system response from noise measurements has proven to be a powerful technique. To convey the essence of the method, we first treat the simplest case of a homogeneous medium to show how noise measurements can be used to estimate waves that propagate between sensors. We provide an overview of physics research—dating back more than 100 years—showing that random field fluctuations contain information about the system response. This principle has found extensive use in surface-wave seismology but can also be applied to the estimation of body waves. Because noise provides continuous illumination of the subsurface, the extracted response is ideally suited for time-lapse monitoring. We present examples of time-lapse monitoring as applied to the softening of soil after the 2011 Tohoku-oki earthquake, the detection of a precursor to a landslide, and temporal changes in the lunar soil.

Snieder, Roel; Larose, Eric

2013-05-01

376

Reduction of the Buildup Contribution in Gamma Ray Attenuation Measurements and a New Way to Study This Experiment in a Student Laboratory  

ERIC Educational Resources Information Center

In continuation of our investigation into the buildup phenomenon appearing in gamma ray attenuation measurements in laboratory experiments we study the dependence of the buildup factor on the area of the absorber in an effort to reduce the buildup of photons. Detailed measurements are performed for up to two mean free paths of [superscript 60]Co…

Adamides, E.; Kavadjiklis, A.; Koutroubas, S.K.; Moshonas, N.; Tzedakis, A.; Yiasemides, K.

2014-01-01

377

Multiparameter full waveform inversion of multicomponent ocean-bottom-cable data from the Valhall field. Part 1: imaging compressional wave speed, density and attenuation  

NASA Astrophysics Data System (ADS)

Multiparameter full waveform inversion (FWI) is a challenging quantitative seismic imaging method for lithological characterization and reservoir monitoring. The difficulties in multiparameter FWI arise from the variable influence of the different parameter classes on the phase and amplitude of the data, and the trade-off between these. In this framework, choosing a suitable parametrization of the subsurface and designing the suitable FWI workflow are two key methodological issues in non-linear waveform inversion. We assess frequency-domain visco-acoustic FWI to reconstruct the compressive velocity (VP), the density (?) or the impedance (IP) and the quality factor (QP), from the hydrophone component, using a synthetic data set that is representative of the Valhall oil field in the North Sea. We first assess which of the (VP, ?) and (VP, IP) parametrizations provides the most reliable FWI results when dealing with wide-aperture data. Contrary to widely accepted ideas, we show that the (VP, ?) parametrization allows a better reconstruction of both the VP, ? and IP parameters, first because it favours the broad-band reconstruction of the dominant VP parameter, and secondly because the trade-off effects between velocity and density at short-to-intermediate scattering angles can be removed by multiplication, to build an impedance model. This allows for the matching of the reflection amplitudes, while the broad-band velocity model accurately describes the kinematic attributes of both the diving waves and reflections. Then, we assess different inversion strategies to recover the quality factor QP, in addition to parameters VP and ?. A difficulty related to attenuation estimation arises because, on the one hand the values of QP are on average one order of magnitude smaller than those of VP and ?, and on the other hands model perturbations relative to the starting models can be much higher for QP than for VP and ? during FWI. In this framework, we show that an empirical tuning of the FWI regularization, which is adapted to each parameter class, is a key issue to correctly account for the attenuation in the inversion. We promote a hierarchical approach where the dominant parameter VP is reconstructed first from the full data set (i.e. without any data preconditioning) to build a velocity model as kinematically accurate as possible before performing the joint update of the three parameter classes during a second step. This hierarchical imaging of compressive wave speed, density and attenuation is applied to a real wide-aperture ocean-bottom-cable data set from the Valhall oil field. Several geological features, such as accumulation of gas below barriers of claystone and soft quaternary sediment are interpreted in the FWI models of density and attenuation. The models of VP, ? and QP that have been developed by visco-acoustic FWI of the hydrophone data can be used as initial models to perform visco-elastic FWI of the geophone data for the joint update of the compressive and shear wave speeds.

Prieux, Vincent; Brossier, Romain; Operto, Stéphane; Virieux, Jean

2013-09-01

378

Advanced Sine Wave Modulation of Continuous Wave Laser System for Atmospheric CO2 Differential Absorption Measurements  

NASA Technical Reports Server (NTRS)

NASA Langley Research Center in collaboration with ITT Exelis have been experimenting with Continuous Wave (CW) laser absorption spectrometer (LAS) as a means of performing atmospheric CO2 column measurements from space to support the Active Sensing of CO2 Emissions over Nights, Days, and Seasons (ASCENDS) mission.Because range resolving Intensity Modulated (IM) CW lidar techniques presented here rely on matched filter correlations, autocorrelation properties without side lobes or other artifacts are highly desirable since the autocorrelation function is critical for the measurements of lidar return powers, laser path lengths, and CO2 column amounts. In this paper modulation techniques are investigated that improve autocorrelation properties. The modulation techniques investigated in this paper include sine waves modulated by maximum length (ML) sequences in various hardware configurations. A CW lidar system using sine waves modulated by ML pseudo random noise codes is described, which uses a time shifting approach to separate channels and make multiple, simultaneous online/offline differential absorption measurements. Unlike the pure ML sequence, this technique is useful in hardware that is band pass filtered as the IM sine wave carrier shifts the main power band. Both amplitude and Phase Shift Keying (PSK) modulated IM carriers are investigated that exibit perfect autocorrelation properties down to one cycle per code bit. In addition, a method is presented to bandwidth limit the ML sequence based on a Gaussian filter implemented in terms of Jacobi theta functions that does not seriously degrade the resolution or introduce side lobes as a means of reducing aliasing and IM carrier bandwidth.

Campbell, Joel F.; Lin, Bing; Nehrir, Amin R.

2014-01-01

379

Shear wave propagation in unconsolidated fluid saturated porous media  

Microsoft Academic Search

Experimental shear wave speed and attenuation measurements are reported for four sizes of well sorted glass beads and three natural sands. Measurements were obtained for both air and water saturation without application of external pressure. The speed and attenuation for each sample was determined from the charge with transducer separation of the transit time and amplitude of an acoustic pulse.

D. W. Bell

1979-01-01

380

Effects of atmospheric turbulence on microwave and millimeter wave satellite communications systems. [attenuation statistics and antenna design  

NASA Technical Reports Server (NTRS)

A model of the microwave and millimeter wave link in the presence of atmospheric turbulence is presented with emphasis on satellite communications systems. The analysis is based on standard methods of statistical theory. The results are directly usable by the design engineer.

Devasirvatham, D. M. J.; Hodge, D. B.

1981-01-01

381

On the anomalously low attenuation of the leaky Rayleigh wave in a fluid-filled cylindrical cavity  

E-print Network

for ultrasonic nondestructive testing of inaccessible airframe structures for fatigue cracking. One particular such application of great in- terest in the aerospace industry is the inspection of weep holes drilled through. The conventional ultrasonic creeping wave tech- nique shown in Fig. 1 a experiences a strong specular re- flection

Nagy, Peter B.

382

An Electrophysiological Cardiac Model Approach to Measuring T-Wave Alternans  

E-print Network

An Electrophysiological Cardiac Model Approach to Measuring T-Wave Alternans MA Mneimneh, RJ is to automatically identify and measure T-wave alternans. The study presented here applies an electrophysiological is that the existence and magnitude of T-wave alternans can be identified and measured using a cardiac inverse problem

Povinelli, Richard J.

383

Effects of optimized and sub-optimum two degree of freedom lining tolerances on modeled inlet acoustic attenuation and Normal incidence impedance measurement at elevated temperatures  

NASA Astrophysics Data System (ADS)

This work first investigates the effect of manufacturing tolerances on realized attenuation for two degree-of-freedom linings with the use of lining models and finite element duct propagation codes. Acoustic linings were created for two turbofan engines that optimize attenuation at takeoff/sideline and approach conditions. Lining physical and geometric parameters were set, which best meet the optimum impedance requirements at two target frequencies. Similar linings were created to investigate sub-optimum designs. Variations of these parameters representing realistic manufacturing tolerances were used to systematically examine the effect on installed impedance and predicted attenuation. Attenuation at sideline and approach conditions was found to be sensitive to manufacturing tolerances around optimum conditions. The results of the study are case dependent; however the analysis scheme presented provides a method for cost-benefit analysis of manufacturing processes. In a second study, an impedance tube, with an associated data analysis method, was developed and analyzed for temperature uncertainties that allowed the measurement of impedance of acoustic samples at elevated temperatures. This impedance measurement method was validated at room temperature by comparing the results with predicted impedance from empirically based impedance models and with impedance measurements in a standard traversing microphone impedance tube. Impedance for four samples was measured at elevated temperatures, and the results were compared to room temperature measurements. For two of the samples, the impedances measured at elevated temperatures were compared to the results of extensions of room temperature empirical models, confirming the trend of the results of the elevated temperature measurements.

Burd, David R.

384

Acoustic measurement of suspensions of clay and silt particles using single frequency attenuation and backscatter  

Technology Transfer Automated Retrieval System (TEKTRAN)

The use of ultrasonic acoustic technology to measure the concentration of fine suspended sediments has the potential to greatly increase the temporal and spatial resolution of sediment measurements while reducing the need for personnel to be present at gauging stations during storm events. The conv...

385

Digital Foucault tester for the measurement of parabolic wave form  

NASA Astrophysics Data System (ADS)

Digital Foucault tester for quantitative estimate the wave form of aspheric surfaces is based on the high precision knife position determination and the image data processing methods. In this paper, we report a set of digital Foucault tester for the measurement of parabolic surface. The movement of the knife-edge is controlled by PC, and the shadow patterns are captured by a CCD in real time and then are fed back to the computer. A new kind of data processing method, which has the advantage of simple arithmetic and high precision, is given in the paper. The method offers a reliable base for Digital Foucault tester.

Wang, Xiao-peng; Zhu, Ri-hong; Wang, Lei

2009-07-01

386

THE EXTRAGALACTIC BACKGROUND LIGHT FROM THE MEASUREMENTS OF THE ATTENUATION OF HIGH-ENERGY GAMMA-RAY SPECTRUM  

SciTech Connect

The attenuation of high-energy gamma-ray spectrum due to the electron-positron pair production against the extragalactic background light (EBL) provides an indirect method to measure the EBL of the universe. We use the measurements of the absorption features of the gamma-rays from blazars as seen by the Fermi Gamma-ray Space Telescope to explore the EBL flux density and constrain the EBL spectrum, star formation rate density (SFRD), and photon escape fraction from galaxies out to z = 6. Our results are basically consistent with the existing determinations of the quantities. We find a larger photon escape fraction at high redshifts, especially at z = 3, compared to the result from recent Ly{alpha} measurements. Our SFRD result is consistent with the data from both gamma-ray burst and ultraviolet (UV) observations in the 1{sigma} level. However, the average SFRD we obtain at z {approx}> 3 matches the gamma-ray data better than the UV data. Thus our SFRD result at z {approx}> 6 favors the fact that star formation alone is sufficiently high enough to reionize the universe.

Gong Yan; Cooray, Asantha [Department of Physics and Astronomy, University of California, Irvine, CA 92697 (United States)

2013-07-20

387

Numerical support of laboratory experiments: Attenuation and velocity estimations  

NASA Astrophysics Data System (ADS)

We show that numerical support of laboratory experiments can significantly increase the understanding and simplify the interpretation of the obtained laboratory results. First we perform simulations of the Seismic Wave Attenuation Module to measure seismic attenuation of reservoir rocks. Our findings confirm the accuracy of this system. However, precision can be further improved by optimizing the sensor positions. Second, we model wave propagation for an ultrasonic pulse transmission experiment used to determine pressure- and temperature-dependent seismic velocities in the rock. Multiple waves are identified in our computer experiment, including bar waves. The metal jacket that houses the sample assembly needs to be taken into account for a proper estimation of the ultrasonic velocities. This influence is frequency-dependent.

Saenger, Erik H.; Madonna, Claudio; Frehner, Marcel; Almqvist, Bjarne S. G.

2014-02-01

388

Depth dependent seismic scattering attenuation in the Nuevo Cuyo region (southern central Andes)  

NASA Astrophysics Data System (ADS)

In the present work we separated intrinsic from scattering attenuation coefficients both for the crust and the upper mantle in the tectonically highly active areas of the Southern-Central Andes - Nuevo Cuyo region, analyzing two groups of earthquakes, well separated in depth. This region is characterized by the presence of flat subduction. We apply MLTWA (Multiple Lapse Time Window Analysis), coda normalization and Q-coda techniques to measure the scattering and intrinsic attenuation coefficient and the total Q for S waves. We find that intrinsic attenuation does not decrease with depth whereas scattering attenuation is higher in the crust than in the upper mantle, and that intrinsic attenuation predominates over scattering attenuation. We interpret this observation in terms of the release of water and other fluids into the overlying lithosphere due to the dynamics of the subduction process, in agreement with most of the prevalent geodynamic models.

Badi, G.; Del Pezzo, E.; Ibanez, J. M.; Bianco, F.; Sabbione, N.; Araujo, M.

2009-12-01

389

Waves  

NSDL National Science Digital Library

We will review some basic properties of waves and then further explore sound and light. For a quick overview of some properties of all waves, click on this first site. Make sure you fill out your hand out as you work! Waves and Wave Motion : Describing Waves Practice what you've already learned about waves with this site: Waves This site will let you play around some more with transverse waves: Wave on a String Sound waves are mechanical waves, ...

Petersen, Mrs.

2014-05-27

390

Gamma-Ray Attenuation Measurements as a Laboratory Experiment: Some Remarks  

ERIC Educational Resources Information Center

In this article we make some significant remarks on the experimental study of the absorption of gamma radiation passing through matter. These remarks have to do with the seemingly unexpected trend of the measured intensity of radiation versus the thickness of the absorber, which puzzles students and its explanation eludes many laboratory…

Adamides, E.; Koutroubas, S. K.; Moshonas, N.; Yiasemides, K.

2011-01-01

391

Probe impedance measurements for millimeter-wave integrated horn antennas  

NASA Technical Reports Server (NTRS)

In order to achieve an impedance-matched millimeter-wave integrated horn antenna mixer array, the characteristics of the antenna probes inside the horn must be known. This paper describes impedance measurements for various probes in low-frequency model horns of two different types: (1) a 3 x 3 array made of aluminum by electric discharge machining and (2) a half horn made of copper sheet placed on a big copper-clad circuit board that was used as an image plane. The results of measurements indicate that the presence of the horn increases the effective length of the probe element, in agreement with reports of Guo et al. (1991) and theoretical analysis of Eleftheriades et al. (1991). It was also found that the resonant frequencies can be controlled by changing the length of the probes or by loading the probes.

Guo, Yong; Chiao, Jung-Chih; Potter, Kent A.; Rutledge, David B.

1993-01-01

392

Prediction of wave-front sensor slope measurements with artificial neural networks  

Microsoft Academic Search

For adaptive optical systems to compensate for atmospheric turbulence effects, the wave-front perturbation must be measured with a wave-front sensor (WFS) and corrected with a deformable mirror. One limitation in this process is the time delay between the measurement of the aberrated wave front and implementation of the proper correction. Statistical techniques exist for predicting the atmospheric aberrations at the

Dennis A. Montera; Byron M. Welsh; Michael C. Roggemann; Dennis W. Ruck

1997-01-01

393

A LabVIEW based measure system for pulse wave transit time  

Microsoft Academic Search

Pulse wave transit time (PWTT) is used as a non-invasive and cuffless method for blood pressure estimation. In this paper, we design a system that can measure PWTT by monitoring ECG and pulse wave continuously. The system includes analog signal sampling in PCB, signal display and data processing in computer. We measure pulse wave by the photo-plethysmograph (PPG) device in

J. M. Zhang; P. F. Wei; Y. Li

2008-01-01

394

Ion species mix and ion density measurements using radio frequency waves  

Microsoft Academic Search

Radio frequency wave applications have demonstrated great versatility in tokamak plasmas. Two applications, using the same diagnostic design, can make use of a fast Alfven wave to make ion species mix and ion density measurements. A discussion and derivation, using the cold plasma approximation, is given for a fast Alfven radio wave used for making an interferometry density measurement, a

George Wilder Watson III

2003-01-01

395

Using airglow measurements to observe gravity waves in the Martian atmosphere  

E-print Network

Using airglow measurements to observe gravity waves in the Martian atmosphere Stella M.L. Melo a present the first results of model simulations of the airglow response to gravity waves propagating to monitor gravity wave activity in the Martian atmosphere through the measurement of contrast in the images

Strong, Kimberly

396

Flexible graphene based microwave attenuators.  

PubMed

We demonstrate flexible 3 dB and 6 dB microwave attenuators using multilayer graphene grown by the chemical vapor deposition method. On the basis of the characterized results of multilayer graphene and graphene-Au ohmic contacts, the graphene attenuators are designed and measured. The flexible graphene-based attenuators have 3 dB and 6 dB attenuation with a return loss of less than -15 dB at higher than 5 GHz. The devices have shown durability in a bending cycling test of 100 times. The circuit model of the attenuator based on the characterized results matches the experimental results well. PMID:25590144

Byun, Kisik; Ju Park, Yong; Ahn, Jong-Hyun; Min, Byung-Wook

2015-02-01

397

Flexible graphene based microwave attenuators  

NASA Astrophysics Data System (ADS)

We demonstrate flexible 3 dB and 6 dB microwave attenuators using multilayer graphene grown by the chemical vapor deposition method. On the basis of the characterized results of multilayer graphene and graphene–Au ohmic contacts, the graphene attenuators are designed and measured. The flexible graphene-based attenuators have 3 dB and 6 dB attenuation with a return loss of less than ?15 dB at higher than 5 GHz. The devices have shown durability in a bending cycling test of 100 times. The circuit model of the attenuator based on the characterized results matches the experimental results well.

Byun, Kisik; Park, Yong Ju; Ahn, Jong-Hyun; Min, Byung-Wook

2015-02-01

398

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

NASA Astrophysics Data System (ADS)

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

Blanc, Emilie; Chiavassa, Guillaume; Lombard, Bruno

2014-10-01

399

In situ thin film thickness measurement with acoustic Lamb waves  

NASA Astrophysics Data System (ADS)

In situ thin film thickness measurement is an important problem in semiconductor processing, which is currently limited by the lack of adequate sensors. Most of today's available techniques are restricted to certain type of films and many have difficulties in performing the measurement in situ. The fact that the velocity of an ultrasonic Lamb wave traveling in a silicon wafer is changed by the thin film coating on the wafer surface can be used as a monitoring method for basically any type of film—opaque, transparent, metal, or insulator. The acoustic sensors are easily implemented into plasma or CVD environments. We have demonstrated the technique in an aluminum sputtering system in which we measure Al film thickness with a resolution of ±100 Å. Even better resolution can be achieved for SiO2, copper, and tungsten films. This system has a variety of potential applications, not only in film thickness measurement, but also in characterization of film properties and multilayer deposition process control.

Pei, Jun; Degertekin, F. Levent; Khuri-Yakub, Butrus T.; Saraswat, Krishna C.

1995-04-01

400

Interplanetary dust fluxes measurements using the Waves instrument on STEREO  

NASA Astrophysics Data System (ADS)

Dust particles provide an important fraction of the matter composing the interplanetary medium, their mass density at 1 A.U. being comparable to the one of the solar wind. The impact of a dust particle on a spacecraft produces a plasma cloud whose associated electric field is detected by the on-board electric antennas. The signal measured by the wave instruments thus reveals the dust properties. We analyse the dust particle impacts on the STEREO spacecraft during the 2007-2010 period. We use the TDS waveform sampler of the STEREO/WAVES instrument, which enables us to deduce considerably more informations than in a previous study based on the LFR spectral analyzer [Meyer-Vernet et al., 2009]. We observe two distinct populations of dust that we infer to be nano and micron sized dust particles and we derive their fluxes at 1 AU and the evolution of these fluxes with time (and solar longitude). The observations are also in accord with the dynamics of nanometer-sized and micrometer-sized dust particles in the interplanetary medium.

Zaslavsky, A.; Meyer-Vernet, N.; Mann, I.; Czechowski, A.; Issautier, K.; Le Chat, G.; Maksimovic, M.; Kasper, J. C.

2010-12-01

401

Shear wave attenuation and dispersion in melt-bearing olivine polycrystals: 1. Specimen fabrication and mechanical testing  

NASA Astrophysics Data System (ADS)

Five melt-bearing polycrystalline olivine aggregates have been newly prepared by hot isostatic pressing and tested at high temperature and pressure with torsional forced-oscillation and microcreep methods. Cylindrical specimens, varying in average grain size from 7 to 52 ?m, were annealed and then tested during slow staged cooling under 200 MPa pressure from maximum temperatures of 1240-1300°C where they contained basaltic melt fractions ranging from ˜0.0001 to 0.037. For temperatures ?1000°C, pronounced departures from elastic behavior are evident in strain energy dissipation Q-1 and associated dispersion of the shear modulus G. In marked contrast with the high-temperature viscoelastic behavior of melt-free materials, a broad dissipation peak is observed for each of the melt-bearing specimens - superimposed upon a melt-enhanced level of monotonically frequency- and temperature-dependent "background" dissipation. The oscillation period at which the peak is centered decreases systematically with increasing temperature. A "global" model comprising an Andrade-pseudoperiod background plus Gaussian peak accounts adequately for the variation of Q-1 with frequency, temperature, average grain size and melt fraction. In the following paper (Part II) a microstructural explanation for the observed viscoelastic behavior is sought and the global model is used to extrapolate the experimental data to the conditions of teleseismic wave propagation in the Earth's upper mantle.

Jackson, Ian; Faul, Ulrich H.; Fitz Gerald, John D.; Tan, Ben H.

2004-06-01

402

Millimeter-wave spectrum of Ne CO: new measurements  

NASA Astrophysics Data System (ADS)

The b-type rotational transitions of the van der Waals complex, Ne-CO have been measured using the intracavity OROTRON jet spectrometer in the frequency range of 80-115 GHz. The high sensitivity of this technique enabled us to detect all three Ne isotopic modifications of the complex, 20Ne-CO, 22Ne-CO, and 21Ne-CO in natural abundance. The observed and assigned transitions belong to the Q-branch of the K = 1-0 subband and include also R (0) and P (2) lines. The newly obtained data were analysed together with previously observed millimeter-wave b-type and microwave a-type rotational transitions.

Surin, L. A.; Potapov, A. V.; Panfilov, V. A.; Dumesh, B. S.; Winnewisser, G.

2005-04-01

403

Measurements of Wavefunctions of Solar Acoustic Waves Scattered by Sunspots and Absorption/Scattering Cross Sections  

NASA Astrophysics Data System (ADS)

The solar acoustic wave around a sunspot is modified due to interaction with the sunspot. The modification in the wave could be viewed as that the sunspot excited by the incident wave generates a scattered wave, and the scattered wave is added to the incident wave to form the total wave around the sunspot. The incident wave could be converted into different modes. We device a scheme to measure the wavefunction of an incident plane wavepacket scattered by the sunspot on the solar surface as a function of time. The incident plane wavepacket is formed by the modes with a fixed radial order. We measure the scattered wavefunction between different radial orders for n=0-5, for NOAAs 11084 and 11092. It allows to study the mode conversion between different modes due to interaction. The absorption and scattering cross sections associated with each mode conversion are also measured. This provides information on the subsurface structure of sunspots.

Zhao, Hui; Chou, Dean-Yi

404

Measurement of a phase of a radio wave reflected from rock salt and ice irradiated by an electron beam for detection of ultra-high-energy neutrinos  

NASA Astrophysics Data System (ADS)

We have found a radio-wave-reflection effect in rock salt for the detection of ultra-high energy neutrinos (UHE?'s) which are expected to be generated in Greisen, Zatsepin, and Kuzmin (GZK) processes in the universe. When an UHE? interacts with rock salt or ice as a detection medium, a shower is generated. That shower is formed by hadronic and electromagnetic avalanche processes. The energy of the UHE? shower converts to thermal energy through ionization processes. Consequently, the temperature rises along the shower produced by the UHE?. The refractive index of the medium rises with temperature. The irregularity of the refractive index in the medium leads to a reflection of radio waves. This reflection effect combined with the long attenuation length of radio waves in rock salt and ice would yield a new method to detect UHE?'s. We measured the phase of the reflected radio wave under irradiation with an electron beam on ice and rock salt powder. The measured phase showed excellent consistence with the power reflection fraction which was measured directly. A model taking into account the temperature change explained the phase and the amplitude of the reflected wave. Therefore the reflection mechanism was confirmed. The power reflection fraction was compared with that calculated with the Fresnel equations, the ratio between the measured result and that obtained with the Fresnel equations in ice was larger than that of rock salt.

Chiba, Masami; Kamijo, Toshio; Tanikawa, Takahiro; Yano, Hiroyuki; Yabuki, Fumiaki; Yasuda, Osamu; Chikashige, Yuichi; Kon, Tadashi; Shimizu, Yutaka; Watanabe, Souichirou; Utsumi, Michiaki; Fujii, Masatoshi

2013-05-01

405

Effects of the NOP agonist SCH221510 on producing and attenuating reinforcing effects as measured by drug self-administration in rats.  

PubMed

Nociceptin/orphanin FQ peptide (NOP) receptor agonists attenuate morphine-induced conditioned place preference in rodents. However, it is not known whether NOP agonists have reinforcing properties or can inhibit mu opioid receptor (MOP)-mediated reinforcement as measured by drug self-administration in rodents. Further understanding the behavioral effects of NOP agonists could suggest them as having potential in attenuating reinforcing effects of opioids. In the first part of the study, reinforcing properties of selective NOP agonist SCH221510 were determined and compared with the full MOP agonist remifentanil under fixed-ratio 5 (FR5) and progressive-ratio (PR) schedules of drug self-administration. In the second part, effects of systemic and intracisternal pretreatment of SCH221510 were determined and compared with MOP antagonist naltrexone in attenuating reinforcing effects of remifentanil and a non-drug reinforcer (sucrose pellets). Remifentanil self-administration (0.3-10µg/kg/infusion) generated a biphasic dose-response curve, characteristic of drugs with reinforcing properties. SCH221510 (3-300µg/kg/infusion) self-administration resulted in flat dose-response curves and early break-points under the PR, indicative of drugs lacking reinforcing value. Intracisternally, but not systemically, administered SCH221510 (0.3-3µg) attenuated remifentanil self-administration, comparable with systemic naltrexone (0.03-0.3mg/kg). SCH221510 (1-3µg), unlike naltrexone (0.03-1mg/kg), attenuated responding for sucrose pellets. Both effects of SCH221510 were reversed by the NOP antagonist J-113397 (0.3-3µg). These results suggest that SCH221510 does not function as a reinforcer in rats, and that it can attenuate the reinforcing value of MOP agonists; therefore, the potential utility of NOP agonists for the treatment of drug addiction warrants further evaluation. PMID:25446568

Sukhtankar, Devki D; Lagorio, Carla H; Ko, Mei-Chuan

2014-12-15

406

Effects of sand aggregate on ultrasonic attenuation in cement-based materials  

Microsoft Academic Search

Ultrasonic wave attenuation measurements have been successfully used to characterize the microstructure and mechanical properties\\u000a of inhomogeneous materials; these ultrasonic techniques have the potential to provide for the in-situ characterization of\\u000a microstructure changes in cement-based materials due to damage. Recent research has applied acoustic scattering models to\\u000a quantitatively predict ultrasonic attenuation for evaluating the air void content in hardened cement

Martin Treiber; Jin-Yeon Kim; Jianmin Qu; Laurence J. Jacobs

2010-01-01

407

Attenuated Vector Tomography -- An Approach to Image Flow Vector Fields with Doppler Ultrasonic Imaging  

SciTech Connect

The measurement of flow obtained using continuous wave Doppler ultrasound is formulated as a directional projection of a flow vector field. When a continuous ultrasound wave bounces against a flowing particle, a signal is backscattered. This signal obtains a Doppler frequency shift proportional to the speed of the particle along the ultrasound beam. This occurs for each particle along the beam, giving rise to a Doppler velocity spectrum. The first moment of the spectrum provides the directional projection of the flow along theultrasound beam. Signals reflected from points further away from the detector will have lower amplitude than signals reflected from points closer to the detector. The effect is very much akin to that modeled by the attenuated Radon transform in emission computed tomography.A least-squares method was adopted to reconstruct a 2D vector field from directional projection measurements. Attenuated projections of only the longitudinal projections of the vector field were simulated. The components of the vector field were reconstructed using the gradient algorithm to minimize a least-squares criterion. This result was compared with the reconstruction of longitudinal projections of the vector field without attenuation. Ifattenuation is known, the algorithm was able to accurately reconstruct both components of the full vector field from only one set of directional projection measurements. A better reconstruction was obtained with attenuation than without attenuation implying that attenuation provides important information for the reconstruction of flow vector fields.This confirms previous work where we showed that knowledge of the attenuation distribution helps in the reconstruction of MRI diffusion tensor fields from fewer than the required measurements. In the application of ultrasound the attenuation distribution is obtained with pulse wave transmission computed tomography and flow information is obtained with continuous wave Doppler.

Huang, Qiu; Peng, Qiyu; Huang, Bin; Cheryauka, Arvi; Gullberg, Grant T.

2008-05-15

408

A review of techniques for measuring shear-wave splitting above small earthquakes  

Microsoft Academic Search

Seismic shear-wave splitting is difficult to measure accurately because of the complexity of the shear-wave signal. A variety of techniques have been developed for measuring time-delays and polarisations of shear-wave splitting above small earthquakes. These range from ‘display’ techniques, where measurements depend on visual examination of rotated seismograms and polarisation diagrams, through a range of increasingly automatic techniques, to what

Stuart Crampin; Yuan Gao

2006-01-01

409

MEASUREMENT OF OCEAN WAVES VELOCITY FIELDS FROM A SINGLE SPOT-5 DATASET USING CORRELATION BETWEEN  

E-print Network

MEASUREMENT OF OCEAN WAVES VELOCITY FIELDS FROM A SINGLE SPOT-5 DATASET USING CORRELATION BETWEEN Energies Alternatives, Siège-Saclay, 75000, Paris, France 1. ABSTRACT Ocean waves represent an important of the local ocean waves' velocity field and its temporal variation can provide invaluable information about

Paris-Sud XI, Université de

410

Measurements of Short Ocean Waves during the MBL ARI West Coast Experiment  

E-print Network

165 Measurements of Short Ocean Waves during the MBL ARI West Coast Experiment Jochen Klinke 1 of the oceanic capillary waves. Estimates of the equilibrium spectra oceanic capillary-gravity and capillary. In order to gain deeper insight into the dynamics and the energy balance of ocean wind waves, i

Jaehne, Bernd

411

Aircraft Measurements and Numerical Simulations of Gravity Waves in the Extratropical  

E-print Network

Aircraft Measurements and Numerical Simulations of Gravity Waves in the Extratropical UTLS Region: · Importance of Mesoscale Gravity Waves in A JetFront System · Flight Track Design in Research Flight 02 (RF02) of START08 field experiment for jetfront gravity waves · Spectral Analysis and Wavelet Analysis

Thompson, Anne

412

SNR measurements of silicon photomultipliers in the continuous wave regime  

NASA Astrophysics Data System (ADS)

We report on our Signal-to-Noise Ratio (SNR) measurements carried out, in the continuous wave regime, at different frequencies and at various temperatures, on a novel class of silicon photomultipliers (SiPMs) fabricated in planar technology on silicon p-type substrate. SNR of SiPMs is given by the ratio of the photogenerated current, filtered and averaged by a lock-in amplifier, and the Root Mean Square (RMS) deviation of the same current. In our measurements, we have employed a 10 Hz equivalent noise bandwidth, around the lock-in amplifier reference frequency. The measured noise takes into account the shot noise, resulting from the photocurrent and the dark current, while background light is not present in our setup. We have found that the SNR is independent from frequency in the evaluated range 1 - 100 kHz. Our measurements highlight a quasi-flat trend of the SiPM SNR up to an overvoltage of about 5 V (with respect to the breakdown voltage of 28.0 V). At higher overvoltages (OV), we have observed a SNR decrease, mainly because of the strong increase of the shot noise. We have also performed a comparison between the SiPM and the PhotoMultiplier Tube (PMT) SNR as a function of the temperature of the SiPM package and at different bias voltages. Our results show the outstanding performance of this novel class of SiPMs even without the need of any cooling system. Indeed, their SNR is only a few dBs below the PMT SNR at room temperature. Furthermore, cooling the SiPM at a package cell temperature of 3 °C, it reaches the PMT SNR values at room temperature despite the SiPM is biased in the range 28.7 - 33.5 V, while the PMT has a bias value up to 950 V.

Adamo, G.; Agrò, D.; Stivala, S.; Parisi, A.; Giaconia, C.; Busacca, A. C.; Fallica, G.

2014-03-01

413

Quantum analysis of the direct measurement of light waves  

E-print Network

In a beautiful experiment performed about a decade ago, Goulielmakis et al. made a direct measurement of the electric field of light waves [E. Goulielmakis et al., Science 305, 1267-1269 (2004)]. However, they used a laser source to produce the light field, whose quantum state has a null expectation value for the electric field operator, so how was it possible to measure this electric field? Here we present a quantum treatment for the f:2f interferometer used to calibrate the carrier-envelope phase of the light pulses in the experiment. We show how the special nonlinear features of the f:2f interferometer can change the quantum state of the electromagnetic field inside the laser cavity to a state with a definite oscillating electric field, explaining how the "classical" electromagnetic field emerges in the experiment. We discuss that this experiment was, to our knowledge, the first demonstration of an absolute coherent superposition of different photon number states in the optical regime.

Saldanha, Pablo L

2014-01-01

414

Ionospheric gravity wave measurements with the USU dynasonde  

NASA Technical Reports Server (NTRS)

A method for the measurement of ionospheric Gravity Wave (GW) using the USU Dynasonde is outlined. This method consists of a series of individual procedures, which includes functions for data acquisition, adaptive scaling, polarization discrimination, interpolation and extrapolation, digital filtering, windowing, spectrum analysis, GW dete