A modulation method is proposed for generating identical UWB chaotic radio pulses using an analog generator of chaotic oscillations. The problem is on the edge of two contradicting requirements: (1) ...theoretical ability to produce a huge number of various-shape signals, because of high sensitivity to the initial conditions of the generator; (2) the necessity to reproduce oscillations of the same shape both in the receiver and in the transmitter for the implementation of coherent methods of signal processing. The considered method allows us to resolve this contradiction. A single-transistor chaotic oscillator with single power supply and frequency range 100 to 500 MHz is proposed. A mathematical model of the generator (a system of ODEs) was derived. A method of generating chaotic radio pulses with a reproducible shape that could be varied in a manner that is controlled and natural for UWB radio by means of changing the supply voltage of the chaotic oscillator is shown. The mathematical model of the generator is simulated numerically and proves the proposed ideas. The shaping and the replicability of UWB pulses was experimentally proven in an analog domain on a testbed with four instances of the chaotic generator.
Analytical dependencies for calculating the economically optimal value of the conditional gas velocity in a cyclone are identified taking into account both technical and economic parameters that ...affect the gas cleaning cost. A method for determining the optimal cyclone diameter and the number of cyclones corresponding to the minimum cost of gas cleaning taking into account the required dust collection efficiency is proposed. Based on the dependencies identified, it has been established that the recommended fixed values of the conditional gas velocity used today when selecting a cyclone are overestimated in most cases.
The article considers the methods for choosing an economically optimal standard size of a cyclone-dust collector: choosing the optimal type, diameter and number of cyclones. The results of ...calculating the most profitable options (for given cleaning conditions), as well as economic and energy losses that may occur with an arbitrary choice of the cyclone type and the use of a simplified calculation method used today based on the recommended fixed values of the conventional gas velocity, are presented. Based on the technical and economic calculations, an analysis of the manufactured range of the most common NIIOGAZ cyclones has been performed; a number of missing options for cyclone standard sizes that would reduce the cost of cyclone gas cleaning have been detected.
The present work focuses on a comprehensive density functional theory (DFT) study of newly discovered base-catalyzed substrate-controlled dimerizations of aliphatic alkynones. In order to understand ...the origin of selectivity of the cascade assemblies of 6-methylene-5-oxaspiro2.4heptanones and 2-alkenylfurans, structural and electronic properties of neutral and deprotonated alkynone molecules, thermodynamic and kinetic characteristics of the deprotonation of alkynones having diverse C–H active substituents at the carbonyl function under the action of a base, and thermodynamic and kinetic characteristics of possible mechanisms of the discussed cascade reactions were theoretically assessed. The obtained computational results have confirmed and clarified an early qualitative assumption on the key role of the nature of the aliphatic substituent. Apart from fully rationalizing the experimental results, the theoretical DFT data give valuable details and data for predicting the outcome of related base-catalyzed reactions between various electrophilic substrates and nucleophilic species formed from C–H active aliphatic alkynones.
The possibility of processing the spent extractant of the PUREX-process by thermochemical decomposition of tributyl phosphate (TBP) to hydrocarbons and phosphoric acid was investigated. It was shown ...that the main condition for the intensive and complete decomposition of TBP is the presence of free phosphoric acid in the system, which ensures the course of the process in an autocatalytic mode. This is observed at a molar ratio of H3PO4: TBP > 2: 1 and can be achieved in the technological process using recycled phosphoric acid. Under these conditions, at a temperature of 190–200 °C, the decomposition of TBP proceeds quantitatively within 5–10 min. It was found that the process proceeds with the formation of butene and a large amount of alkanes and alkenes of various molecular weights, which is caused by secondary processes of polymerization and cyclization of decomposition products catalyzed by excess phosphoric acid. During the decomposition of TBP, radioactive impurities pass into the phosphoric acid phase, which creates the possibility of their neutralization and disposal in the form of phosphate glasses.
•Tributyl phosphate is decomposed by the reaction product, phosphoric acid.•Hydrocarbons are formed.•Radioactive impurities pass into phosphoric acid.
The precipitation of phosphoric acid as a hydroxyphosphate from nitric acid solutions in the presence of iron(III) oxides and hydroxyoxides under hydrothermal conditions was studied. It was shown ...that the dephosphorization process proceeds with the formation of iron(III) hydroxyphosphate (giniite) Fe5(PO4)4(OH)3∙2H2O. The most efficient and speedy process is implemented at temperatures of 180–200 °C and above. It was found that the concentration of phosphoric acid in the solution as a result can be reduced to 0.001 mol/L and below. Lanthanide, uranium, and thorium nitrates are stable under conditions of hydrothermal dephosphorization of solutions, in contrast to iron(III) nitrates decomposing to hematite and nitric acid. The features of the studied hydrothermal process were used to increase the efficiency of direct nitric acid leaching of monazite iron-bearing ores of the Chuktukon rare metal deposit.
•Phosphoric acid is precipitated from nitric solutions with the formation of giniite.•REM, uranium and thorium remain in solution during dephosphorization.•Features of the process can be used to improve the breaking down of monazite ores.
For RNA viruses, rapid viral evolution and the biological similarity of closely related host species have been proposed as key determinants of the occurrence and long-term outcome of cross-species ...transmission. Using a data set of hundreds of rabies viruses sampled from 23 North American bat species, we present a general framework to quantify per capita rates of cross-species transmission and reconstruct historical patterns of viral establishment in new host species using molecular sequence data. These estimates demonstrate diminishing frequencies of both cross-species transmission and host shifts with increasing phylogenetic distance between bat species. Evolutionary constraints on viral host range indicate that host species barriers may trump the intrinsic mutability of RNA viruses in determining the fate of emerging host-virus interactions.
The complex niobium–rare earth pyrochlore–monazite–crandallite ores of the Tomtor deposit, located in the Siberian Arctic, should be considered as a new type of rare metal materials. The major ...valuable components of the ore are niobium (1.63–16.4%), rare earth elements (2.2–27.8%), yttrium (0.18–2.9%), and scandium (0.015–0.15%); associated components are titanium, vanadium, aluminum, and phosphorus. Because of the irregular distribution of the rare earth metals and niobium according to grain size, the extremely finely dispersed nature of the minerals and their close interpenetration to each other, ore processing by gravitation and flotation is not successful. The processes studied for the treatment of the Tomtor ores use direct alkaline-acid leaching to open the ore. A problem in the first stage of alkaline leaching is the high aluminum content, which decreases the activity of sodium hydroxide and alkaline-earth metals, which are bound to phosphorus. Ore processing using alkaline-nitrate and alkaline-chloride leaching was proposed and investigated. The first variant was used to obtain rare earth and scandium materials and a niobium–titanium concentrate, which can be a stock material for processors who use chlorination for the processing of ores and concentrates. The second variant is a complex advanced ore processing scheme with electrochemical regeneration of the waste chloride solutions obtaining sodium hydroxide, hydrochloric acid, and chloridizing agents. Moreover trisodium phosphate is used for purification of the waste mother liquors from metal cations. The complex salt, NaAlCl
4
, is proposed as the chloridizing agent for the decomposition of the niobium–titanium concentrate. The recovery of rare earth metals in the second variant of processing is about 95%; while for niobium and titanium, this value is 92–94%.
A technique for determining the microstructural wettability of a carbonate rock using a scanning electron microscope (SEM) in the low-vacuum mode employing a special chamber and the results of ...respective experiments are described. To this end, the principle of the spontaneous formation of microscopic water droplets on the sample surface as a result of vapor condensation and measurement of the contact angle on SEM images is implemented. The possibility of determining the surface properties of dispersed particles with different mineral compositions is shown. Analysis of the surface properties of the pore space of oil-saturated rocks using a SEM makes it possible to specify the wetting properties in the pore space at the microscale level. These studies are of practical importance for petroleum geology. Detailed determination of the wettability makes it possible to predict the water cut of the produced products and provides additional possibilities for adopting special methods to decrease the amount of residual oil in the reservoir and increase the production of hydrocarbons.
The extraction of cadmium from sulfuric acid solutions and its separation from nickel with salts of bis(2,4,4-trimethylpentyl)dithiophosphinic acid (Cyanex 301) and amines was studied. The data ...obtained show that extractants based on Cyanex 301 and Quaternary ammonium bases are most suitable for this since it is possible to extract cadmium in the form of sulfates and bisulfates as well as stripping metal from the organic phase. For deep extraction of cadmium from sulfate solutions in this system, 1–2 stages of extraction are sufficient. At this stage, the separation coefficient of cadmium and nickel β
Cd/Ni
reaches values > 10
6
, and the distribution coefficient of cadmium reaches almost 10
4
. Cadmium stripping is achieved by treating the organic phase with an ammonia solution containing ammonia more than 4 mol/L. The process can be used in the processing of cadmium–nickel batteries.
