Search

In chemical technology, an important place is occupied by studies of the processes of mass and heat transfer in moving media. Obviously, in order to study these processes, it is necessary to know how the media move. Determining the velocity field of liquids and gases is a purely kinematic task. Can it be solved without resorting to the equations of motion, limited only by the continuity equation? [ABSTRACT FROM AUTHOR]

At present, the cross-section profile of the rolled strip is characterized by geometrical parameters such as wedging, convexity, difference of thickness, displacement of convexity, and edge wedging. Some of these parameters are redundant. The values of these parameters are calculated by known and generally accepted methods. However, some of the features of the cross-section profile of rolled strips, such as local thickenings/thinnings are calculated by unconventional methods. Practically every scientific school of rolling mill operators or rolling production specialists uses their own techniques, which often provide different results for the same cross-section profiles. The identification and calculation of the local thickenings/thinnings parameters of the cross-section profile of rolled strips consists in defining a so-called zero level, the excess/understatement of which is a sign of local thickening/thinning. The paper continues analyzing for the calculation of the parameters of the cross-section profile of rolled strips regarding local thickenings/thinnings for accuracy and adequacy. A new method based on statistical methods is proposed. The target function, the thickness distribution across the width of the rolled strip, is a symmetrical quadratic parabola. However, the actual distribution is always different from the target one for several reasons, such as ring wear of work rolls. In the first step of the proposed technique, strip thickness values dramatically different from the target distribution are eliminated as emissions by the Walter-Shewhart procedure (control charts). However, this procedure cannot be applied without excluding the nonlinear (parabolic) component of the measured cross-section profile and, therefore, applies to the first derivative of the function of the cross-section profile thickness distribution. To determine zero level, all of the thicknesses associated with these emissions are eliminated after calculating the upper and lower limits of the allowed values of the first derivative. The result of the repetitive process is zero level according to which the local thickening/thinning parameters are calculated. [ABSTRACT FROM AUTHOR]

As moist gas enters a reciprocating compressor in the course of the operation of the compressor, heating of the gas depends on the degree of dryness of the gas and the rate of evaporation of the liquid droplets in the gas as well as on the coefficient of thermal conductivity of the moist gas and on the coefficient of heat transfer from the walls of the compressor cylinder to the gas. However, once the rotational speed of the compressor shaft reaches 300 min–1, the length of the gas intake process falls to one-tenth the length of the period of total evaporation of the droplets, hence the process of evaporation begins to exert a practical influence on the temperature of the gas. The gas temperature increases substantially due to the increase in the thermal conductivity coefficient of the moist gas and in the coefficient of heat transfer from the walls of the compressor cylinder to the gas. With a decrease in the degree of dryness of the gas from 1.0 to 0.6, preheating of the gas grows 7–8-fold, which leads to a reduction in the density of the gas in the filled work space of the cylinder and, as a consequence, to a decrease in the adiabatic efficiency of the compressor ηi by 14–16%, and this must be taken into account in the management of the production process. [ABSTRACT FROM AUTHOR]

In view of the increasing competition in the market of rolled products, the problem of evaluation of the quality of strips in various stages of the process of rolling seems to be quite urgent. As the main geometric criteria of the quality of rolled strips, we can mention the cross-sectional profile of hot-rolled semifinished products and the plot of specific tension in the strips after cold rolling. We discuss the problems of formalization of measurements of the cross-sectional profiles, classification of hot-rolled profiles into characteristic types, and the influence of these criteria on the formation of the plots of specific tension in cold-rolled strips. [ABSTRACT FROM AUTHOR]

Silicon-vacancy (SiV) color centers in diamond offer a promising system for quantum information applications owing to their intense narrowband emission and optically detectable spin states. Here, the fluorescent properties of ensembles and single SiV centers in diamonds obtained by high-pressure high-temperature synthesis from adamantane (below referred to as adamantane diamonds) are investigated at liquid-helium temperatures. Ensembles of SiV centers (~103) are studied in large diamond crystals (1–2 µm in size). Despite the large number of excited centers, the fine structure of the zero-phonon line, corresponding to four allowed optical transitions between the ground- and excited-state doublets of the SiV center, can be observed in the fluorescence spectra of these crystals. The width of individual lines is in the range of 60–80 GHz, which is explained by their inhomogeneous broadening. Single SiV centers are studied in diamond crystallites with sizes of about 200 nm. The width of the narrowest transition lines observed in the fluorescence spectra of single SiV centers under resonant excitation is almost three orders of magnitude smaller than linewidths in the spectra of SiV ensembles and is as small as 94 MHz; i.e., these lines are so narrow that their width is determined by the lifetime of the upper state of the transition. Therefore, adamantane nanodiamond features the narrowest emission line width of a single SiV center at cryogenic temperatures among other types of SiV-con-taining nanodiamonds of similar sizes obtained by the high-pressure high-temperature and chemical vapor deposition techniques. [ABSTRACT FROM AUTHOR]

Calculation formulas for estimating the influence of the state parameters of temperature, pressure, and moisture content on the operation of a piston compressor are obtained. It is shown that at the start of compression in a compressor temperature depends mainly on heating of the gas produced by the walls and its moisture content. The pressure at the start of compression depends on the speed of the piston and the moisture content of the gas. The principal factors responsible for a reduction of the feed rate and efficiency of the compressor are the increase in temperature and the decrease in pressure at the start of compression. [ABSTRACT FROM AUTHOR]

We have implemented a trilayer technological approach to fabricate $$\mathrm {Nb}{-}\mathrm {Cu}_{0.47}\mathrm {Ni}_{0.53}{-} \mathrm {Nb}$$ superconducting phase inverters ( $$\pi $$ -junctions) with enhanced critical current. Within this technique, all three layers of the superconductor-ferromagnet-superconductor junction deposited in a single vacuum cycle that have allowed us to obtain $$\pi $$ -junctions with critical current density up to 20 kA/cm $$^2$$ . The value achieved is a factor of 10 higher than for the step-by-step method used in earlier works. Our additional experiments have shown that this difference is related to a bilayered CuNi/Cu barrier used in the case of the step-by-step technique and interlayer diffusion at the CuNi/Cu interface. We show that the interlayer diffusion can be utilized for fine tuning of the $$0{-}\pi $$ transition temperature of already fabricated junctions. The results obtained open new opportunities for the CuNi-based phase inverters in digital and quantum Josephson electronics. [ABSTRACT FROM AUTHOR]

This examines the issue of operability of PLC channels organized on 110 - 750 kV OHLs on which protective devices (PD) against lightning strikes are used in the form of overvoltage limiters and/or discharge devices. It is shown that the operation of PDs can under certain circumstances cause excessive disconnect of the line by phase-differential protection or directed protection during a short circuit on adjacent overhead lines (OHL), or passing an RP and/or EA command transferred on the PLC channel's DTESC. A conclusion is drawn regarding the necessity of setting up special work for more detailed consideration of the specified issue. [ABSTRACT FROM AUTHOR]

It follows from the Golod-Shafarevich theorem that if k ∈ N and R is an associative algebra given by n generators and quadratic relations, then R is not k-step nilpotent. We show that the above estimate is asymptotically optimal. Namely, for every k ∈ N, there is a sequence of algebras Rn given by n generators and dn quadratic relations such that R is k-step nilpotent and . [ABSTRACT FROM AUTHOR]

A quadratic semigroup algebra is an algebra over a field given by the generators x, . . . , x and a finite set of quadratic relations each of which either has the shape x x = 0 or the shape x x = x x. We prove that a quadratic semigroup algebra given by n generators and $${d\leq \frac{n^2+n}{4}}$$ relations is always infinite dimensional. This strengthens the Golod-Shafarevich estimate for the above class of algebras. Our main result however is that for every n, there is a finite dimensional quadratic semigroup algebra with n generators and δ relations, where δ is the first integer greater than $${\frac{n^2+n}{4}}$$ . That is, the above Golod-Shafarevich-type estimate for semigroup algebras is sharp. [ABSTRACT FROM AUTHOR]

The unusual phenomenon observed by D.I. Taylor and other researchers was explained. During the vortex motion of the liquid, the distributed component of the diffusing substance is concentrated only in the vortex core. The effect was explained in terms of our hypothesis that takes into account the dependence of the diffusing substance flow not only on the concentration gradients, but also on the vorticity of the liquid. The concept offers a new glimpse on natural and technical effects such as the tornado and the Ranque effect. [ABSTRACT FROM AUTHOR]

Experimental and theoretical studies of ferromagnet-superconductor hybrid systems consisting of a Josephson junction placed in the nonuniform field of submicron ferromagnetic particles are reviewed. [ABSTRACT FROM AUTHOR]

Let D be the differentiation operator Df = f′ acting on the Fréchet space H of all entire functions in one variable with the standard (compact-open) topology. It is known since the 1950's that the set H( D) of hypercyclic vectors for the operator D is non-empty. We treat two questions raised by Aron, Conejero, Peris and Seoane-Sepúlveda whether the set H( D) contains (up to the zero function) a non-trivial subalgebra of H or an infinite-dimensional closed linear subspace of H. In the present article both questions are answered affirmatively. [ABSTRACT FROM AUTHOR]

We prove that any bounded linear operator on L[0, 1] for 1 ≤ p < ∞, commuting with the Volterra operator V, is not weakly supercyclic, which answers affirmatively a question raised by Léon-Saavedra and Piqueras-Lerena. It is achieved by providing an algebraic type condition on an operator which prevents it from being weakly supercyclic and is satisfied for any operator commuting with V. [ABSTRACT FROM AUTHOR]

A unitary operator V and a rank 2 operator R acting on a Hilbert space $${\mathcal{H}}$$ are constructed such that V + R is hypercyclic. This answers affirmatively a question of Salas whether a finite rank perturbation of a hyponormal operator can be supercyclic. [ABSTRACT FROM AUTHOR]

Abstract  We construct a bounded linear operator on a separable, reflexive and strictly convex Banach space with the resolvent norm that is constant in a neighbourhood of zero. [ABSTRACT FROM AUTHOR]

It is shown that if 1 < p < ∞ and X is a subspace or a quotient of an ℓ p-direct sum of finite dimensional Banach spaces, then for any compact operator T on X such that ∥ I + T∥ > 1, the operator I + T attains its norm. A reflexive Banach space X and a bounded rank one operator T on X are constructed such that ∥ I + T∥ > 1 and I + T does not attain its norm. [ABSTRACT FROM AUTHOR]

Abstract  Given a Lebesgue measurable self-map $${\varphi}$$ of the interval [0, 1], the Volterra- composition operator is defined as $${(V_\varphi)(x)=\int\limits_0^{\varphi(x)}f(t)\,dt, \quad f \in L^p[0,1],\,\, 1\leq p \leq \infty.}$$ We develop the spectral theory of these operators. In particular, for a class of natural symbols $${\varphi}$$ , finiteness of the spectrum is characterized and formulae for the trace and the convergence exponent of eigenvalues are provided. The positivity of the spectrum as well as the analyticity of the eigenfunctions are also treated. The theory of entire functions as well as solving some Cauchy Problems will play a fundamental role in this theory. We also supply some examples of symbols $${\varphi}$$ to which the theory can be applied and, in particular, eigenvalues and eigenfunctions are computed explicitly. [ABSTRACT FROM AUTHOR]

The current problem of conveyor and cabinet drying of various materials is considered. Radiation infrared drying using nonlinear infrared radiation (IR) transducers based on a functional ceramic is studied. Use of IR of a special spectral composition and structure makes it possible to shorten processing duration considerably, to improve product quality, to simplify the design layout, and also to create conditions for mechanizing and automating production. [ABSTRACT FROM AUTHOR]

The multiplicative spectrum of a complex Banach space X is the class $$\mathcal{K}$$ ( X) of all (automatically compact and Hausdorff) topological spaces appearing as spectra of Banach algebras ( X, *) for all possible continuous multiplications on X turning X into a commutative associative complex algebra with unity. Properties of multiplicative spectra are studied. In particular, we show that $$\mathcal{K}$$ ( X n ) consists of countable compact spaces with at most n nonisolated points for any separable, hereditarily indecomposable Banach space X. We prove that $$\mathcal{K}$$ ( C[0, 1]) coincides with the class of all metrizable compact spaces. [ABSTRACT FROM AUTHOR]

We provide a sufficient condition of analyticity of infinitely differentiable eigenfunctions of operators of the form Uf(x)=∫a(x,y)f(b(x,y))μ(dy) acting on functions $f:\; [u,\; v]\backslash rightarrow\; \{\backslash Bbb\; C\}$ (evolution operators of one-dimensional dynamical systems and Markov processes have this form). We estimate from below the region of analyticity of the eigenfunctions and apply these results for studying the spectral properties of the Frobenius–Perron operator of the continuous fraction Gauss map. We prove that any infinitely differentiable eigenfunction f of this Frobenius–Perron operator, corresponding to a non-zero eigenvalue admits a (unique) analytic extension to the set $\{\backslash Bbb\; C\}\backslash setminus\; (-\backslash infty\; ,\; -1]$. Analyzing the spectrum of the Frobenius–Perron operator in spaces of smooth functions, we extend significantly the domain of validity of the Mayer and Röpstorff asymptotic formula for the decay of correlations of the Gauss map. [ABSTRACT FROM AUTHOR]

For the PPM algorithm, we suggest new definitions of generalized frequencies of characters and “escapes.” This considerably increases the efficiency of lossless coding (compression) for various types of real-world discrete data. [ABSTRACT FROM AUTHOR]

A scheme is proposed for concentration of zeolite-bearing basaltoids of the Margintuisk volcanic field of Transbaikalia, and a comparative investigation into physico-chemical and adsorption properties of synthetic and natural chabasite recovered from the basalts is conducted. It is shown that the chabasite concentrate extraction is possible with the use of sufficiently simple scheme of electromagnetic concentration. It is established that despite some differences in physico-chemical characteristics, the adsorption properties of natural chabasite are not inferior to the properties of synthetic analog. [ABSTRACT FROM AUTHOR]

Both the existence and the nonexistence of a linearly ordered (by certain natural order relations) effective set of comparison functions (=dense comparison class) are compatible with the ZFC axioms of set theory. [ABSTRACT FROM AUTHOR]

Let E be a nonnormable Fréchet space, and let E′ be the space of all continuous linear functionals on E in the strong topology. A continuous mapping f: E′→ E′ such that for any t0∈ℝ, x0∈ E′, the Cauchy problem x=f(x), x(t0 )=x0 has no solutions is constructed. [ABSTRACT FROM AUTHOR]

Results are reported for FeCO·2HO and Fe(CO)·5HO; various stages in the decomposition are demonstrated. The second compound on decomposition in nitrogen gives rise to finely divided FeO containing a little free metal. The conditions for this are established. [ABSTRACT FROM AUTHOR]