Bulk density of the energy of deformation in an anodic aluminum oxide with pores filled by threadlike metal nanocrystals

The problem of determining the bulk density of the energy of deformation in composites with threadlike metal nanocrystals in a matrix of anodic aluminum oxide is solved with allowance for the difference between the thermal coefficients of the linear extension of elements of heterogeneity. Model calculations are performed for nanocomposites with tin, zinc, and indium nanocrystals.     

A study of propylene polymerization over bimetallic titanium–vanadium catalysts

New bimetallic catalysts based on microspherical TiCl₃ modified with vanadium trichloride to obtain its different concentrations on the TiCl₃ surface were synthesized. The presence of a VCl₃ crystalline phase in the catalyst was confirmed by X-ray analysis. The synthesized catalysts were applied to studying propylene polymerization in a liquid monomer medium. The kinetics of the polymerization process was determined, and the structure and properties of the synthesized isotactic polypropylene (IPP) were established. It was demonstrated that the PPI samples synthesized over the developed titanium–vanadium catalysts has enhanced freeze resistance as compared to IPP sample obtained over conventional titanium catalysts.     

Analytical method for evaluating the quality of acoustic fields radiated by a multielement therapeutic array with electronic focus steering

The paper presents an analytical method for calculating and analyzing the quality of 3-D acoustic fields of multielement phased arrays used in noninvasive ultrasound surgical devices. An analytical solution for the far field of each of its elements is used when calculating the array field. This method significantly accelerates calculations while preserving the high accuracy of results as compared to conventional direct numerical integration. Radiation from typical phased arrays is calculated using this approach, and the quality of their dynamic focusing is analyzed. Undesired diffraction effects caused by electronic focus steering are considered: an amplitude decrease in the main maximum and the appearance of grating lobes. The quality of dynamic focusing of the acoustic fields of two practically interesting arrays with a quasi-random element distribution (256 and 1024 elements, respectively), as well as of the regular array consisting of 256 elements is compared. In addition as well, a study is made of how the dimensions of the array elements and their spatial distributions affect the dimensions of the areas in which dynamic focusing is possible without occurrence of strong grating lobes and significant decrease in pressure amplitude at the main focus.

     

Simulation of characteristics of optical gas sensors based on diode optopairs operating in the mid-IR spectral range

An analytic model is proposed for an optical gas sensor based on diode optopairs, which takes into account the line spectral structure of gases being analyzed, as well as peculiarities of spectral characteristics of immersion-type light-emitting diodes and photodiodes operating in the mid-IR spectral range. The model makes it possible to calculate the transfer characteristic of the sensor and to estimate the measurement error for gas analyzers operating on the basis of these sensors. The experiments demonstrate bright prospects of application of sensors based on immersion-type diode optopairs in small-size gas analyzers; the expected values of the threshold sensitivity of a CO₂ sensor at a level of 10 ppm and the absolute error of measurements below 0.1% (reduced error is 1%) in a range of up to 10 vol % at a speed of up to 10 counts per second exceed the parameters of available portable CO₂ gas analyzers. The validity of the model is confirmed by conformity between the calculated data and the experimental results obtained on a prototype of a CO₂ diode sensor.     

Use of focused ultrasound for stimulation of nerve structures

Pulsed focused ultrasound can stimulate the receptor and conductive nerve structures of humans and animals as well as the neurons of the central nervous system of invertebrates. The possibility of a wide practical use of this method in medicine and physiology is considered. For example, the stimulating ability of focused ultrasound is applied to the diagnosis of neurological diseases, to the study of skin and tissue sensitivity in man, to the diagnosis of hearing disorders, and to the introduction of auditory information to the deaf with certain forms of hearing pathology. The factors that affect focused ultrasound as a stimulus for the irritation of nerve structures are discussed.