scholarly journals Acoustic transfer admittance of cylindrical cavities in infrasonic frequency range

Metrologia ◽  
2018 ◽  
Vol 56 (1) ◽  
pp. 015003 ◽  
Author(s):  
P Vincent ◽  
D Rodrigues ◽  
F Larsonnier ◽  
C Guianvarc’h ◽  
S Durand
Keyword(s):  
Frequency Range ◽  
Infrasonic Frequency ◽  
Cylindrical Cavities

scholarly journals IDENTIFICATION OF NORMAL WAVES FORMING A SOUND FIELD IN A SHALLOW SEA AT THE INFRASONIC FREQUENCY RANGE. Part II

2020 ◽  
Author(s):  
С.Б. Касаткин
Keyword(s):  
Experimental Studies ◽  
Sound Field ◽  
Noise Signal ◽  
Energy Structure ◽  
Frequency Range ◽  
Field Zone ◽  
Normal Waves ◽  
Infrasonic Frequency ◽  
Scholte Waves ◽  
Scholte Wave

Анализируются результаты экспериментальных исследований звукового поля, зарегистрированного комбинированными приемниками, образующими вертикально ориентированную двухэлементную антенну. Звуковое поле формировалось дискретными составляющими вально-лопастного звукоряда шумового сигнала НИС «Юрий Молоков» в инфразвуковом диапазоне частот 2–20 Гц, а также буксируемым низкочастотным излучателем полигармонического сигнала в диапазоне частот 30–60 Гц. Глубина моря и рабочий диапазон частот 2–20 Гц исключали возможность возбуждения нормальных волн дискретного спектра в модельном волноводе Пекериса в этом диапазоне частот. По результатам спектрального анализа шумового сигнала получена оценка потенциальной помехоустойчивости комбинированного приемника при использовании полного набора информативных параметров, характеризующих энергетическую структуру звукового поля. По результатам анализа вертикальной структуры звукового поля в инфразвуковом диапазоне частот был сделан вывод о том, что звуковое поле сформировано неоднородными нормальными волнами Шолте, регулярной и обобщенной (гибридной). В дальней зоне источника доминирует регулярная волна Шолте, локализованная на границы раздела вода – морское дно. В ближней зоне источника возрастает роль обобщенной волны Шолте, локализованной на горизонте источника, а звуковое поле формируется парой волн Шолте, регулярной и обобщенной. The results of experimental studies of the sound field recorded by combined receivers forming a vertically oriented two-element antenna are analyzed. The sound field was formed by discrete components of the vane-blade scale of the noise signal of the science ship «Yuri Molokov» in the infrasonic frequency range of 2–20 Hz, as well as by a towed low-frequency emitter of a polyharmonic signal in the frequency range 30–60 Hz. The depth of the sea and the operating frequency range of 2–20 Hz excluded the possibility of exciting normal waves of the discrete spectrum in the model Pekeris waveguide in this frequency range. Based on the results of spectral analysis of the noise signal, an estimate of the potential noise immunity of the combined receiver was obtained using a full set of informative parameters characterizing the energy structure of the sound field. Based on the results of the analysis of the vertical structure of the sound field in the infrasonic frequency range, it was concluded that the sound field is formed by inhomogeneous normal Scholte waves, regular and generalized (hybrid). In the far zone of the source, a regular Scholte wave dominates, localized at the water – seabed interface. In the near-field zone of the source, the role of the generalized Scholte wave localized at the source horizon increases, and the sound field is formed by a pair of Scholte waves, regular and generalized.

scholarly journals IDENTIFICATION OF NORMAL WAVES FORMING A SOUND FIELD IN A SHALLOW SEA AT THE INFRASONIC FREQUENCY RANGE. Part I

2020 ◽  
Author(s):  
С.Б. Касаткин
Keyword(s):  
Experimental Studies ◽  
Sound Field ◽  
Noise Signal ◽  
Operating Frequency ◽  
Energy Structure ◽  
Frequency Range ◽  
Normal Waves ◽  
Inhomogeneous Waves ◽  
Infrasonic Frequency ◽  
Operating Frequency Range

Анализируются результаты экспериментальных исследований звукового поля, зарегистрированного комбинированными приемниками, образующими вертикально ориентированную трехэлементную антенну. Звуковое поле формировалось шумами НИС «Юрий Молоков» в инфразвуковом диапазоне частот. Глубина моря и рабочий диапазон частот исключали возможность возбуждения нормальных волн дискретного спектра в модельном волноводе Пекериса. По результатам спектрального анализа шумового сигнала получена оценка потенциальной помехоустойчивости комбинированного приемника при использовании полного набора информативных параметров, характеризующих энергетическую структуру звукового поля. По результатам анализа вертикальной структуры звукового поля был сделан вывод о том, что звуковое поле сформировано неоднородными нормальными волнами, локализованными на горизонте источника, которые относятся к обобщенным (гибридным) волнам. По результатам анализа вертикального волнового числа, которое принимает чисто мнимые значения в поле неоднородных волн, были получены оценки групповой скорости переноса энергии в рабочем диапазоне частот и выполнена идентификация неоднородных нормальных волн, формирующих суммарное звуковое поле. The results of experimental studies of the sound field recorded by combined receivers forming a vertically oriented three-element antenna are analyzed. The sound field was formed by the noise of the science ship «Yuri Molokov» in the infrasonic frequency range. The depth of the sea and the operating frequency range excluded the possibility of excitation of normal waves of the discrete spectrum in the model Pekeris waveguide. Based on the results of the spectral analysis of the noise signal, an estimate of the potential noise immunity of the combined receiver was obtained using a full set of informative parameters characterizing the energy structure of the sound field. Based on the results of the analysis of the vertical structure of the sound field, it was concluded that the sound field is formed by inhomogeneous normal waves localized at the source horizon, which are referred to as generalized (hybrid) waves. Based on the results of the analysis of the vertical wavenumber, which takes on purely imaginary values in the field of inhomogeneous waves, estimates of the group velocity of energy transfer in the operating frequency range were obtained and identification of inhomogeneous normal waves that form the total sound field was performed.

Density-based discrimination of protein and RNA in the ribosome

1992 ◽  
Vol 50 (1) ◽  
pp. 464-465
Author(s):  
Joachim Frank
Keyword(s):  
Transfer Function ◽  
Spatial Frequency ◽  
Three Dimensional ◽  
Wiener Filter ◽  
Dark Field Image ◽  
Dark Field ◽  
Frequency Range ◽  
Bright Field ◽  
Contrast Transfer Function ◽  
Pass Filter

Cryo-electron microscopy combined with single-particle reconstruction techniques has allowed us to form a three-dimensional image of the Escherichia coli ribosome.In the interior, we observe strong density variations which may be attributed to the difference in scattering density between ribosomal RNA (rRNA) and protein. This identification can only be tentative, and lacks quantitation at this stage, because of the nature of image formation by bright field phase contrast. Apart from limiting the resolution, the contrast transfer function acts as a high-pass filter which produces edge enhancement effects that can explain at least part of the observed variations. As a step toward a more quantitative analysis, it is necessary to correct the transfer function in the low-spatial-frequency range. Unfortunately, it is in that range where Fourier components unrelated to elastic bright-field imaging are found, and a Wiener-filter type restoration would lead to incorrect results. Depending upon the thickness of the ice layer, a varying contribution to the Fourier components in the low-spatial-frequency range originates from an “inelastic dark field” image. The only prospect to obtain quantitatively interpretable images (i.e., which would allow discrimination between rRNA and protein by application of a density threshold set to the average RNA scattering density may therefore lie in the use of energy-filtering microscopes.

Evaluation of Special Hearing Aids for Deaf Children

1971 ◽  
Vol 36 (4) ◽  
pp. 527-537 ◽  
Author(s):  
Norman P. Erber
Keyword(s):  
Hearing Aids ◽  
High Frequency ◽  
Hearing Aid ◽  
Low Frequency ◽  
Acoustic Stimulation ◽  
Deaf Children ◽  
Frequency Range ◽  
Frequency Limit ◽  
Unpublished Studies ◽  
Published Research

Two types of special hearing aid have been developed recently to improve the reception of speech by profoundly deaf children. In a different way, each special system provides greater low-frequency acoustic stimulation to deaf ears than does a conventional hearing aid. One of the devices extends the low-frequency limit of amplification; the other shifts high-frequency energy to a lower frequency range. In general, previous evaluations of these special hearing aids have obtained inconsistent or inconclusive results. This paper reviews most of the published research on the use of special hearing aids by deaf children, summarizes several unpublished studies, and suggests a set of guidelines for future evaluations of special and conventional amplification systems.

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