Tomographic observation of shallow-water inhomogeneities in the case of probing by a focused high-frequency acoustic field. I. Structure of simulation model

We study the possibilities of acoustic tomography observation of small-size bodies in shallow-water layered oceanic waveguides within the framework of geometric acoustics. For increasing the spatial resolution and sensitivity in the considered inverse problem, we used the waveguide-matched focusing of the received and radiated fields into the region of expected location of the observed body. The algorithm of observation in this case consists of search for a global extremum of decision statistics, which is determined by the difference between the measured data and the hypothetic body location. Such hypotheses are formed on the basis of a priori information in the form of the waveguide model and the data on the structure of the observation system. For decreasing the influence of noise associated with the interference of fields in the waveguide, selection of separate tomographic ray projections with the subsequent incoherent accumulation of partial images is used. A tomographic shallow-water observation model based on such principles is analyzed. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 52, No. 2, pp. 134–150, February 2009.     

Similarity relations for physical modeling of the acoustic fields in a shallow sea

Using the mode formalism, we consider the similarity relations for scale modeling of the acoustic fields in a shallow sea. The corresponding conditions for physical modeling of sound propagation and diffraction in a waveguide with regular parameters are obtained. The similarity relations for spatio-temporal mode correlation functions are also found in the case of acoustic fluctuations caused by wind waves and random internal waves. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 52, No. 4, pp. 318–327, April 2009.     

Multistop analyzer for time-of-flight measurements at a resolution of ±5 ns

A multichannel multistop time analyzer that provides the measurement of the time intervals between start and stop pulses and the accumulation of their time distribution in the memory of its unit is described. The time of arrival of a stop signal is recorded at a resolution of ±5 ns and a dead time of 30 ns. The number of stops per start can achieve 6000. The number of channels is 131072 (2¹⁷). The time analyzer is based on a CAMAC unit and can be used to design measurement-information systems for solving problems in neutron spectrometry and mass spectrometry by time-of-flight methods and for studying the time characteristics of luminescence radiation.     

Formation,propagation, and focusing of acoustic beams in oceanic waveguides. The quasi-optics approximation

Using the WKB approximation and assuming that the spatial spectrum of modes excited by a vertical array is sufficiently narrow, a quasi-optical theory is developed to describe the fundamental regularities manifesting themselves in the formation, propagation, and focusing of multimode acoustic beams in oceanic waveguides. Functional dependences on the parameters of both the transmitting array and the oceanic waveguide are obtained for horizontal distances at which ordinary beams form refraction focusing zones. Conditions ensuring the formation of a beam with the minimum wave front divergence are formulated for the distribution of the source excitation factor over the array aperture.     

High-frequency acoustical observation of inhomogeneities in shallow water oceanic waveguides with an irregular bottom in the presence of strong reverberation

Possibilities of high-frequency acoustical underwater observations of small-size objects in marine shelf zones are experimentally investigated using vertical and horizontal arrays radiating and receiving complex structure pulses in the presence of strong reverberation. Reconstruction of parameters of the observed objects yielded 35- to 40-dB weakening of the reverberation interferences due to medium-matched spatial, temporal, and Doppler filtering.     

Setup for taking the radiation spectra of wideband semiconductors

A setup is developed for measuring the spectra of wideband semiconductors (III nitrides) and related heterostructures. The setup makes it possible to trace the time distribution of the luminescence intensity at a fixed wavelength with a resolution of ±5 ns and a sampling rate of up to 10 MHz in the time interval from several microseconds to several hundreds of microseconds. Also, it plots the integral intensity of luminescence versus the wavelength. Precision measurement conditions are provided.     

On the possibility of using two models of the viscosity superanomaly effect for analyzing the flow curves of structured disperse systems

Two known models of the viscosity superanomaly effect are analyzed: the microrheological model developed by Uriev and the kinetic model proposed by Stolin and coworkers. The possibility of using these models for analyzing the flow curves of real structured disperse systems with a yield point is evaluated. As is shown, within these approaches one can distinguish the conditions under which three types of flow in structured disperse systems are observed.     

Electrospun nanofibers of ZnO‐TiO2 hybrid: characterization and potential as an extracellular scaffold for supporting myoblasts

One‐dimensional nanofibers have attracted tremendous attention because of their potential applications. Electrospinning technology enables industrial production of these nanofibers. This study aims to fabricate one‐dimensional ZnO doped TiO₂ by electrospinning and to characterize these hybrid nanofibers. The nanocomposite was prepared using colloidal gel composed of zinc nitrate, titanium isopropoxide and polyvinyl acetate. X‐ray diffraction, energy dispersive x‐ray analysis and transmission electron microscopy analysis confirmed the purity and crystalline nature of this material, whereas the diameter of these nanofibres estimated from scanning electron microscope (SEM), field emission SEM and transmission electron microscopy are between 200 and 300 nm. Cell counting with Kit‐8 assay at regular time intervals and phase‐contrast microscopy data revealed that C2C12 cells proliferated well on ZnO/TiO₂ nanofibers between 1 and 10 µg/ml, and cellular attachments are visible by SEM. The nanostructured ZnO/TiO₂ hybrid nanofibers show higher cell adhesion, proliferation and spreading behavior compared with the titanium substrate and control. Our study suggests that ZnO/TiO₂ nanofibers could potentially be used in tissue engineering applications. The scalability, low cost, reproducibility and high‐throughput capability of this technology is potentially beneficial to examine and optimizing a wide array of cell‐nanofiber systems prior to in vivo experiments. Copyright © 2013 John Wiley & Sons, Ltd.     

Simultaneous determination of dimethoate and its metabolite omethoate in curry leaf using LC-MS/MS and risk assessment

This study presents the method development, validation, and simultaneous determination of dimethoate and its metabolite omethoate in curry leaf. Samples were extracted following modified quick, easy, cheap, effective, rugged, and safe extraction protocol and analyzed using liquid chromatography-tandem mass spectrometry. The limit of quantification in the matrix was 0.005 μg g⁻¹ for dimethoate and omethoate. Extraction using acetonitrile recorded the average recoveries in the range of 82.25 to 112.97% for dimethoate and 85.57 to 107.22% for omethoate at 0.005, 0.025 and 0.050 μg g⁻¹ fortification levels and relative standard deviation less than 5%. Similarly, the relative standard deviation values for intraday (Repeatability) and interday (Reproducibility) tests were less than 15%. Dissipation kinetics of dimethoate 30% emulsifiable concentrate at 200 and 400 g a.i h⁻¹ recorded initial deposits of 5.20 and 10.05 μg g⁻¹ and 0.33 and 0.48 μg g⁻¹ for dimethoate and omethoate, respectively, and half-life of 3.07 and 3.34 days. The estimated hazard index value found more than one at a day after dimethoate application. It is not safe for consumer health to use curry leaves in the initial days after application.