TO A QUESTION ABOUT QUASIBAND OF ACOUSTIC AXIS OF THE ANGLE BEAM PROBE

On the basis of modelling an acoustic path of the angle beam probe with a reflector as a side drilled hole influence of two factors resulting to quasiband of acoustic axis of the angle beam probe is shown, first of which is connected to change of amplitude echo signal owing to attenuation of a shear wave in the environment due to absorption and dispersion, and the second factor – with change of amplitude owing to a divergence of wave fronts radiated and received elastic waves. Influence of the first factor is increased with growth of attenuation and depth of reflector, and the second – on increase of distance up to a reflector practically does not depend. Quantitative estimations have revealed a ratio of influence of both factors on size of a angle quasiband of acoustic axis on value of factor of attenuation of shear waves. Reduction of an angle quasidand with increase of radius piezoplate of the angle beam probe is shown at constant operation frequency, that is at narrowing the directivity characteristic of the probe.

Broadband Time-Resolved Absorption and Dispersion Spectroscopy of Methane and Ethane in a Plasma Using a Mid-Infrared Dual-Comb Spectrometer

Conventional mechanical Fourier Transform Spectrometers (FTS) can simultaneously measure absorption and dispersion spectra of gas-phase samples. However, they usually need very long measurement times to achieve time-resolved spectra with a good spectral and temporal resolution. Here, we present a mid-infrared dual-comb-based FTS in an asymmetric configuration, providing broadband absorption and dispersion spectra with a spectral resolution of 5 GHz (0.18 nm at a wavelength of 3333 nm), a temporal resolution of 20 μs, a total wavelength coverage over 300 cm−1 and a total measurement time of ~70 s. We used the dual-comb spectrometer to monitor the reaction dynamics of methane and ethane in an electrical plasma discharge. We observed ethane/methane formation as a recombination reaction of hydrocarbon radicals in the discharge in various static and dynamic conditions. The results demonstrate a new analytical approach for measuring fast molecular absorption and dispersion changes and monitoring the fast dynamics of chemical reactions over a broad wavelength range, which can be interesting for chemical kinetic research, particularly for the combustion and plasma analysis community.

Broadband Time-Resolved Absorption and Dispersion Spectroscopy of Methane and Ethane in A Plasma Using a Mid-Infrared Dual-Comb Spectrometer

Conventional mechanical Fourier Transform Spectrometers (FTS) are able to simultaneously measure absorption and dispersion spectra of gas-phase samples. However, they usually need very long measurement times to achieve time-resolved spectra with a good spectral and temporal resolution. Here, we present a mid-infrared dual-comb-based FTS in an asymmetric configuration, providing broadband absorption and dispersion spectra with a spectral resolution of 5 GHz, a temporal resolution of 20 μs, and a total measurement time of a few minutes. We used the dual-comb spectrometer to monitor the reaction dynamics of methane and ethane in an electrical plasma discharge. We observed ethane/methane formation as a recombination reaction of hydrocarbon radicals in the discharge in various static and dynamic conditions. The results demonstrate a new analytical approach for measuring fast molecular absorption and dispersion changes and monitoring fast dynamics of chemical reactions, which can be interesting for chemical kinetic research and particularly for the combustion and plasma analysis community.

On a Fractional in Time Nonlinear Schrödinger Equation with Dispersion Parameter and Absorption Coefficient

This paper is concerned with the nonexistence of global solutions to fractional in time nonlinear Schrödinger equations of the form i α ∂ t α ω ( t , z ) + a 1 ( t ) Δ ω ( t , z ) + i α a 2 ( t ) ω ( t , z ) = ξ | ω ( t , z ) | p , ( t , z ) ∈ ( 0 , ∞ ) × R N , where N ≥ 1 , ξ ∈ C \ { 0 } and p > 1 , under suitable initial data. To establish our nonexistence theorem, we adopt the Pohozaev nonlinear capacity method, and consider the combined effects of absorption and dispersion terms. Further, we discuss in details some special cases of coefficient functions a 1 , a 2 ∈ L l o c 1 ( [ 0 , ∞ ) , R ) , and provide two illustrative examples.

DUICM Deep Underwater Image Classification Mobdel using Convolutional Neural Networks

Classification of underwater images is a challenging task due to wavelength-dependent light propagation, absorption, and dispersion distort the visibility of images, which produces low contrast and degraded images in difficult operating environments. Deep learning algorithms are suitable to classify the turbid images, for that softmax activation function used for classification and minimize cross-entropy loss. The proposed deep underwater image classification model (DUICM) uses a convolutional neural network (CNN), a machine learning algorithm, for automatic underwater image classification. It helps to train the image and apply the classification techniques to categorise the turbid images for the selected features from the Benchmark Turbid Image Dataset. The proposed system was trained with several underwater images based on CNN models, which are independent to each sort of underwater image formation. Experimental results show that DUICM provides better classification accuracy against turbid underwater images. The proposed neural network model is validated using turbid images with different characteristics to prove the generalization capabilities.

Controllable optical steady-state behavior at multi-frequency channels

We identify a scheme in which we can control the behavior of an atomic medium to switch between optical bistability (OB) and optical multistability (OM) at multiple frequencies. The scheme relies on the absorption and dispersion characteristics of the optical medium at different frequencies, which can be modulated significantly by changing the magnetic field [Formula: see text] for tuning the energy difference between Zeeman sublevels. The result shows that the transition from OB to OM or vice versa can be easily realized not only at single frequency channel but also between multiple frequency channels. Furthermore, the optical steady-state behavior also varies with the ratio of the applied two coupling fields at any frequency channel. Such controllable switching between multiple frequency channels could also be used as some applications in all-optical switching and quantum information processing.