scholarly journals THE STUDY OF THE INFLUENCE OF X-RAY IRRADIATION ON DISLOCATION CHARACTERISTICS IN LiF CRYSTALS

2021 ◽  
pp. 21-25
Author(s):  
О.M. Petchenko ◽  
G.О. Petchenko ◽  
S.M. Boiko ◽  
А.S. Litvinenko
Keyword(s):  
Irradiation Time ◽  
Acoustic Pulse ◽  
Residual Deformation ◽  
Ultrasound Velocity ◽  
Wide Frequency Range ◽  
Effective Length ◽  
Acoustic Characteristics ◽  
Frequency Branch ◽  
Attenuation Mechanism ◽  
Pulse Echo

The dependences of the absorption α and the ultrasound velocity in LiF single crystals with residual deformation ε = 0.65% at 300 K in the range of radiation doses 0...1057 R were studied using the acoustic pulse echo method at a frequency of 7.5 MHz. Based on the results of measurements of the acoustic characteristics, the absolute values of the parameters of the dislocation structure – the average effective length of the dislocation loop L and the dislocation density Λ and their dependences on the irradiation time are determined. The calculated characteristics are compared with the previously obtained results for the high-frequency branch of the damped dislocation resonance and using the selective etching method. The revealed noticeable discrepancy in the values of these parameters is explained by the impossibility of describing a single attenuation mechanism for acoustic measurements carried out in a wide frequency range.

Estimates of Q in central Asia as a function of frequency and depth using the coda of locally recorded earthquakes

1982 ◽  
Vol 72 (1) ◽  
pp. 129-149
Author(s):  
S. W. Roecker ◽  
B. Tucker ◽  
J. King ◽  
D. Hatzfeld
Keyword(s):  
Frequency Dependence ◽  
Central Asia ◽  
Wide Frequency Range ◽  
S Wave ◽  
Uppermost Mantle ◽  
Regional Heterogeneity ◽  
S Waves ◽  
Tectonic Processes ◽  
Hindu Kush ◽  
Attenuation Mechanism

abstract Digital recordings of microearthquake codas from shallow and intermediate depth earthquakes in the Hindu Kush region of Afghanistan were used to determine the attenuation factors of the S-wave coda (Qc) and primary S waves (Qβ). An anomalously rapid decay of the coda shortly after the S-wave arrival, observed also in a study of coda in central Asia by Rautian and Khalturin (1978), seems to be due primarily to depth-dependent variations in Qc. In particular, we deduce the average Qc in the crust and uppermost mantle (<100-km depth) is approximately four times lower than the deeper mantle (<400-km depth) over a wide frequency range (0.4 to 24 Hz). Further, while Qc generally increases with frequency at any depth, the degree of frequency dependence of Qc depends on depth. Except at the highest frequency studied here (∼48 Hz), the magnitude of Qc at a particular frequency increases with depth while its frequency dependence decreases. For similar depths, determinations of Qβ and Qc agree, suggesting a common wave composition and attenuation mechanism for S waves and codas. Comparison of these determinations of Qc in Afghanistan with those in other parts of the world shows that the degree of frequency dependence of Qc correlates with the expected regional heterogeneity. Such a correlation supports the prejudice that Qc is primarily influenced by scattering and suggests that tectonic processes such as folding and faulting are instrumental in creating scattering environments.

Ultrasound Velocity Imaging by a Pulse-Echo Technique

1992 ◽  
pp. 475-480 ◽  
Author(s):  
W. C. A. Pereira ◽  
S. Leeman ◽  
J. C. Machado
Keyword(s):  
Ultrasound Velocity ◽  
Velocity Imaging ◽  
Pulse Echo

Evaluation of diffraction errors in precise pulse-echo measurements of ultrasound velocity in chambers with waveguide

Ultrasonics ◽  
2002 ◽  
Vol 40 (1-8) ◽  
pp. 853-858 ◽  
Author(s):  
R. Kažys ◽  
L. Mažeika ◽  
R. Barauskas ◽  
E. Jasiūnien≐ ◽  
V. Daniulaitis
Keyword(s):  
Ultrasound Velocity ◽  
Pulse Echo

Acoustic pulse echo measurements at 200 MHz

1977 ◽  
Vol 30 (2) ◽  
pp. 78-80 ◽  
Author(s):  
B. T. Khuri‐Yakub ◽  
G. S. Kino
Keyword(s):  
Acoustic Pulse ◽  
Pulse Echo

Ultrasonic Reflectivity Imaging in Three Dimensions: Reconstruction with Spherical Transducer Arrays

1979 ◽  
Vol 1 (3) ◽  
pp. 210-231 ◽  
Author(s):  
Stephen J. Norton ◽  
Melvin Linzer
Keyword(s):  
Signal To Noise Ratio ◽  
Acoustic Pulse ◽  
Cutoff Frequency ◽  
Three Dimensional ◽  
Point Sources ◽  
Three Dimensions ◽  
Reconstruction Process ◽  
Dimensional Reconstruction ◽  
Reflectivity Data ◽  
Pulse Echo

Three-dimensional backprojection for reconstructing acoustic reflectivity within a volume is examined. The reflectivity data are acquired by means of a spherical array of point sources-receivers which encloses the object under study. Reconstruction of the image is obtained by back-projecting the recorded pulse-echo data over spherical surfaces in image space. An analytical expression for the point spread function (PSF) generated by the backprojection process has been derived. This expression was evaluated for several different choices of the acoustic pulse: a narrowband pulse, wideband pulse, and two analytically-derived optimum pulses which provide the best sidelobe response and a mainlobe width equal to approximately 0.4Λc, where Λc is the wavelength corresponding to the upper cutoff frequency of the pulse. Excellent agreement was obtained between the theoretical PSF's for the different pulses and those obtained by computer simulation. A number of potential advantages of direct three-dimensional reconstruction relative to two-dimensional tomographic techniques are discussed, including (1) high resolution in three dimensions (2) the possibility of incorporating refraction effects in the reconstruction process (3) reduced sensitivity to limited viewing anglesand (4) improved signal-to-noise ratio (thus minimizing requirements for data redundancy).

Optimization of the Aerodynamic and Aeroacoustic Characteristics of a Small Centrifugal Fan by Means of Inverse Design and Evolutionary Algorithms

2020 ◽  
Author(s):  
Chris Eisenmenger ◽  
Stefan Frank ◽  
Paul Uwe Thamsen
Keyword(s):  
High Efficiency ◽  
Wide Frequency Range ◽  
Low Noise ◽  
Inverse Design ◽  
Centrifugal Fan ◽  
Test Rig ◽  
Design Code ◽  
Acoustic Characteristics ◽  
Ongoing Research ◽  
Wide Operating

Abstract In this work, the inverse design code TURBOdesign 1 has been used in a direct approach to optimize both the aerodynamic and aeroacoustic properties of a small centrifugal fan with backward-curved blades. Two promising fan designs along with a reference fan have been investigated numerically using CFD and the results have been validated experimentally using a chamber test rig for the aerodynamics and the in-duct method for acoustics. A design aiming for good aerodynamic performance showed an increased efficiency in a wide operating range of about 5 to 10%. Another design aiming for low noise showed a numerically determined reduction in the overall sound radiation of 1 dB on average. This trend could not be reproduced in the experiments, instead the high efficiency design showed the best acoustic characteristics in a wide frequency range, which is why this is a subject of ongoing research.

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