No abstract

An imidazoline‐based dissymmetric bis‐quaternary ammonium gemini surfactant has been synthesized. Its surface active properties at equilibrium in water at 25 °C were determined. The inhibitive effect of the compound on Q235 steel in 1 M hydrochloric solution was investigated by the weight‐loss method, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) analysis, and quantum chemical calculations. The results indicate that the compound has high surface properties and the inhibition efficiency (IE) increases with the increase in inhibitor concentration, which attain the maximum value around the CMC value. The imidazoline‐based dissymmetric bis‐quaternary ammonium acts as a mixed type inhibitor mainly inhibiting the cathodic processes and does not change the mechanism of either hydrogen evolution reaction or mild steel dissolution. The best IE is obtained at the immersion time of 144 h. The adsorption of the studied inhibitor on Q235 steel can be fitted to a Langmuir isotherm and the adsorption process is a spontaneous chemical adsorption. Quantum chemistry calculation results show that the imidazoline ring and heteroatoms of N, O, are the active sites of the inhibitors.

Improving the stability of underwater LIBS is a key point for its practical use in oceanic applications. The traditional normalization method by using the internal standard element is often limited...

The waveguide invariant β is typically discussed in terms of either a range-independent environment or a range-dependent environment under the adiabatic approximation, with few studies considering the effects of mode coupling. In this work, how internal solitary waves (ISWs) affect the waveguide invariant is investigated, and it is shown that mode-coupling effects introduce many additional components in the acoustic interference intensity. It is found that the striation slope and value of β for these additional components are determined not only by the acoustic modal dispersion, but are also dependent on the position where the mode coupling occurs. This can lead to a very complicated acoustic interference pattern and result in multiple peaks in the distribution of β. The sensitivity of β to the parameters of ISWs, such as amplitude, horizontal scale, and position, is analyzed. It is found that although all parameters can affect the energy of the peaks, only the position of the internal wave has an obvious impact on the peak values. This indicates that the peak values of β can be utilized for monitoring the position of the internal wave.

When there appears the relative motion between the sound source and the receiver, the received tonal signal will produce Doppler shift, and the Doppler information is relevant to the motion parameters of the target. According to the acoustic Doppler shift frequency, we propose the Doppler-warping transformation. The phase linearization of the Doppler signal can be realized by using the transformation. Then, we deduce the warping operator and propose an algorithm for estimating the target motion parameters by using the proposed transformation. Firstly, the Doppler-warping operator under different motion parameters is constructed. Secondly, the time resampling of the received time-domain signal is performed by using the operator. Then, the spectral function of the transformed signal is calculated. Finally, the spectral function entropy is minimized to estimate the objective parameter. The simulation results show the effectiveness of the proposed method. For a low signal-to-noise ratio of sea trial data, where the real speed of a fishing boat is 4.5 m/s, the result from the traditional minimum mean square error (MMSE) velocity estimation method is 5.2 m/s, and the estimation error is 15.56%. The proposed Doppler-warping transform method can estimate the target velocity more accurately, specifically, it is 4.7 m/s and its corresponding estimation error is 4.44%.