Acoustic cross sections and resonance frequencies of large fish schools

2011 ◽  
Vol 130 (4) ◽  
pp. 2337-2337
Author(s):  
Thomas R. Hahn ◽  
Orest Diachok
Keyword(s):  
Cross Sections ◽  
Large Fish ◽  
Fish Schools ◽  
Resonance Frequencies

Resonant Gas Oscillations in a Linear Area Variation Cavity: Rectangular Versus Circular Cross Section

2015 ◽  
Vol 138 (1) ◽  
Author(s):  
Sonu K. Thomas ◽  
T. M. Muruganandam
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Second Harmonic ◽  
Circular Cross Section ◽  
High Amplitude ◽  
Rectangular Section ◽  
Closed Cavity ◽  
Circular Section ◽  
Resonance Frequencies ◽  
Area Variation

Resonant gas oscillations in a linear area variation closed cavity are investigated, for two duct cross sections: rectangular and circular. The resonance frequencies were similar for both the ducts. Increased drive amplitude produced higher distortions in the waveform. It was found that both resonators exhibited commensurate behavior. This is opposed to noncommensurate behavior observed in nonuniform circular cross section resonators. The rectangular section duct had higher energy than circular section duct, in second harmonic for the same drive amplitude. The results reveal that in order to achieve shockless high amplitude pressure oscillations in a duct, both nonuniform area variation and circular cross section are required.

scholarly journals In Situ Measurement of Sound Attenuation by Fish Schools (Japanese Horse Mackerel, Trachurus japonicus) at Mid-Frequency Bands

2021 ◽  
Vol 11 (4) ◽  
pp. 1944
Author(s):  
Hansoo Kim ◽  
Dong-Guk Paeng
Keyword(s):  
Cross Sections ◽  
Acoustic Waves ◽  
Horse Mackerel ◽  
Attenuation Coefficients ◽  
Trachurus Japonicus ◽  
Frequency Bands ◽  
Fish Schools ◽  
Fish School ◽  
Net Cage

Acoustic waves are attenuated by fish schools as they propagate through the ocean. The attenuation by fish schools is not currently considered in fishery acoustics and sonar applications, especially at mid-frequency bands. In this study, fish school attenuation experiments were conducted with a number of individual fish in situ in a net cage at mid-frequency bands (3–7 kHz). The target fish species was the Japanese horse mackerel (Trachurus japonicus), which typically forms fish schools in the coastal ocean of northeastern Asia. The attenuated acoustic waves were measured for the cases of non-net, only net (0), 100, 200, 300, 400, and 500 individual horse mackerels in the net cage. Results showed that the acoustic signal attenuation increased with the number of horse mackerels. The mean and maximum attenuation coefficients were approximately 6.0–15.4 dB/m and 6.5–21.8 dB/m for all frequencies, respectively. The measured attenuation coefficients were compared with the ones from previous studies to propose new regression models with normalized extinction cross-sections of weight and length of fish. This study confirmed that the fish school attenuation could not be ignored and compensated at mid-frequencies in the ocean. These results would be useful for fishery acoustics, especially in the development of scientific echo-sounder, and naval applications of sonar operations and analysis.

scholarly journals Анизотропия оптических свойств металлических нанодисков

2021 ◽  
Vol 129 (11) ◽  
pp. 1435
Author(s):  
А.В. Коротун ◽  
Н.И. Павлище
Keyword(s):  
Surface Plasmon Resonance ◽  
Surface Plasmon ◽  
Cross Sections ◽  
Plasmon Resonance ◽  
Polarizability Tensor ◽  
Absorption Cross ◽  
Aspect Ratios ◽  
Resonance Frequencies ◽  
Frequency Dependences ◽  
Significant Factors

Expressions for the diagonal components of the polarizability tensor, absorption cross sections, and dimensional dependences of the surface plasmon resonance frequencies of metal nanodisks are obtained in the work in the classical approximation. Calculations of the frequency and size dependences of these characteristics for disks of different metals and with different aspect ratios are presented. The influence of the aspect ratio on the evolution of the frequency dependences of the components of the polarizability tensor and absorption cross sections is analyzed. The most significant factors influencing the splitting of the surface plasmon resonance in metal nanodisks with a small asect ratio have been determined.

Modeling the acoustic scattering from large fish schools using the Bloch-Floquet theorem

2013 ◽  
Vol 133 (5) ◽  
pp. 3538-3538
Author(s):  
Jason A. Kulpe ◽  
Michael J. Leamy ◽  
Karim G. Sabra
Keyword(s):  
Acoustic Scattering ◽  
Large Fish ◽  
Fish Schools ◽  
Floquet Theorem

Analysis of STEM micrographs of thick objects

1978 ◽  
Vol 36 (2) ◽  
pp. 106-107
Author(s):  
S. Golladay
Keyword(s):  
Inelastic Scattering ◽  
Multiple Scattering ◽  
Mass Distribution ◽  
Cross Sections ◽  
Phase Contrast ◽  
Image Point ◽  
Contrast Effects ◽  
Total Cross Sections ◽  
Elastic And Inelastic Scattering

The theory of multiple scattering has been worked out by Groves and comparisons have been made between predicted and observed signals for thick specimens observed in a STEM under conditions where phase contrast effects are unimportant. Independent measurements of the collection efficiencies of the two STEM detectors, calculations of the ratio σe/σi = R, where σe, σi are the total cross sections for elastic and inelastic scattering respectively, and a model of the unknown mass distribution are needed for these comparisons. In this paper an extension of this work will be described which allows the determination of the required efficiencies, R, and the unknown mass distribution from the data without additional measurements or models. Essential to the analysis is the fact that in a STEM two or more signal measurements can be made simultaneously at each image point.

Direct Observation of Heat Exchanger Deposits by Cross Sectioning

1967 ◽  
Vol 25 ◽  
pp. 364-365
Author(s):  
R. W. Anderson ◽  
D. L. Senecal
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Heat Exchanger ◽  
Direct Observation ◽  
Cross Sections ◽  
Preparation Method ◽  
Specimen Preparation ◽  
Flowing Water ◽  
Transmission Electron ◽  
Deposit Layer

A problem was presented to observe the packing densities of deposits of sub-micron corrosion product particles. The deposits were 5-100 mils thick and had formed on the inside surfaces of 3/8 inch diameter Zircaloy-2 heat exchanger tubes. The particles were iron oxides deposited from flowing water and consequently were only weakly bonded. Particular care was required during handling to preserve the original formations of the deposits. The specimen preparation method described below allowed direct observation of cross sections of the deposit layers by transmission electron microscopy.The specimens were short sections of the tubes (about 3 inches long) that were carefully cut from the systems. The insides of the tube sections were first coated with a thin layer of a fluid epoxy resin by dipping. This coating served to impregnate the deposit layer as well as to protect the layer if subsequent handling were required.

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