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Pre-orientation stretching of high-density polyethylene improves the charge stability of electrets produced in corona discharge. Electrets made of oriented polyethylene charged in the corona under uniaxial tensile mechanical stress have even greater stability. The increased stability of electrets is due to the capture of electrons in deep structural traps formed after the rupture of macromolecules during orientation and mechanical stress. By the method of thermally stimulated electron emission, it is shown that the charge of electrets is formed at the expense of electrons. New convenient formulas for calculation of electrical voltages in multilayer insulation with electrets were obtained. [ABSTRACT FROM AUTHOR]

This study examines the efficiency of a microprocessor's cooling system and maintaining the optimal temperature of electronic components. To do this, experiments are carried out on the existing cooling system of the microprocessor with control of all main parameters, primarily such as the temperature and coolant flow, as well as the performance and temperature of the processor. Based on the data obtained, a mathematical model is built that describes the change in the microprocessor's power and allows us to calculate the temperatures and speeds of coolants, as well as obtain the most effective modes for the operation of the cooling system. The obtained experimental data and mathematical model make it possible to predict the required power of the cooling system and the operating parameters of microelectronic components, which is especially important when new generations of microprocessors with the highest performance appear. The data obtained also makes it possible to calculate parameters for existing processors in order to maximize the efficiency and reliability of their operation, which is also relevant for other electronic devices, in particular microcontrollers. [ABSTRACT FROM AUTHOR]

This study investigated the formation of associated petroleum gas (APG) hydrate from frozen solutions of promoterфs (sodium dodecyl sulfate and trisulfonated castor oil) under static conditions. The experiment utilized differential scanning calorimetry to analyze phase changes, such as ice crystallization, hydrate formation, and joint ice melting and hydrate formation. The visualization of the hydrate formation process helped identify factors that influence APG hydrates' growth under the given conditions. The study concluded that the type and presence of promoters significantly affect the growth rate of hydrates, while the preparation protocol has a greater impact on the reproducibility of the process. [ABSTRACT FROM AUTHOR]

This paper introduces a laboratory setup designed to produce gas hydrate under static conditions and to compress hydrate pellets directly within the reactor. The setup is intended to facilitate development of effective methods for obtaining and storing gas hydrates. The paper discusses the design specifics of the setup, outlines the sequence of operations for producing methane hydrate and granules from it, and provides examples of experimental data related to accelerated production and compression of methane hydrate from a kinetic promoter solution. [ABSTRACT FROM AUTHOR]

This paper studied the process of methane hydrate formation from frozen solutions containing small amounts of promoters (sodium dodecyl sulfate and tri-sulfonated castor oil) under static conditions using differential scanning calorimetry (DSC). The research revealed regularities of phase transformations under the studied conditions (from ice and/or hydrate crystallization to joint ice melting and hydrate formation). Coupling the DSC tests with visualization of the forming hydrates allowed the factors affecting the growth rate of methane hydrate during ice melting to be established. These factors included the protocol for obtaining hydrates, which involved temperature and pressure control at different stages of the process, and the force of interaction of hydrate crystallites with each other and with cell walls. [ABSTRACT FROM AUTHOR]

The effect of mixtures of fish gelatin (protein) from Atlantic cod skin and sodium alginate (polysaccharide) from brown algae on the nucleation of methane-propane hydrate with cubic structure II was studied. The rocking cell method with cooling at a constant rate was used to determine the supercooling required for the formation of hydrates both from solutions of the individual polymers and from their mixtures. It was shown that sodium alginate has practically no effect on the formation of the gas hydrates in contrast to gelatin, the inhibiting activity of which had an intermediate value between polyvinylpyrrolidone and polyvinylcaprolactam (commercial kinetic hydrate inhibitors). In the case of blends of the polymers, an insignificant effectiveness reduction was observed with a decrease in the sodium alginate concentration at a fixed gelatin content. The results indicate antagonism in the kinetic inhibition of methane–propane hydrate by mixtures of polyelectrolytes of biological origin. Intermolecular interactions in the polysaccharide–gelatin complexes inevitably affect the ability of the polymers to retard the nucleation process. A more detailed investigation of the hydrate formation kinetics in relation to the ratio of the polymers in the solution will make it possible to reveal the mechanism of their effect and propose mixed reagents to control the hydrate formation process. [ABSTRACT FROM AUTHOR]

Novel derivatives based on 6-methyluracil and condensed uracil, 2,4-quinazoline-2,4-dione, were synthesized with terminal meta- and para-benzoate moieties in polymethylene chains at the N atoms of the pyrimidine ring. In the synthesized compounds, the polymethylene chains were varied from having tris- to hexamethylene chains and quaternary ammonium groups; varying substituents (ester, salt, acid) at benzene ring were introduced into the chains and benzoate moieties. In vivo biological experiments demonstrated the potency of these compounds in decreasing the number of β-amyloid plaques and their suitability for the treatment of memory impairment in a transgenic model of Alzheimer's disease. [ABSTRACT FROM AUTHOR]

The article considers a hysteretic model of consumer behaviour in mono-product markets. Demand generation with regard to an individual consumer is modeled using a non-ideal relay with inverted thresholds. Therefore, the sales rate is defined as an analogue of the Preisach converter. The article considers the problem of the optimal production, storage, and distribution of goods, taking into account the hysteretic nature of the demand curve. The problem is reduced to a non-classical optimal control problem with hysteretic non-linearities. The latter is solved using Pontryagin's maximum principle. The adopted economic model is based on the binary relationship of consumers to the product: the product is bought or the product is not bought. Transitions between these states are determined within the framework of our model only by the price of the goods; therefore, only the operator of a non-ideal relay can accurately describe such a dependence. The article presents the results of computational experiments illustrating the theoretical assumptions. [ABSTRACT FROM AUTHOR]

The paper investigates a modified van der Pol equation with hysteresis nonlinearity which is formalized within the Preisach approach. The system considered in the work is a mathematical model of an electrical system similar to the classical van der Pol system where characteristics of the nonlinear part are of hysteresis nature. The main method for studying this system is the classical small parameter approach. Within this method, an analytical solution to the equation describing the system under consideration was obtained. Numerical results are presented and a comparative analysis of the dynamics of the system under consideration with the dynamics of the classical van der Pol oscillator is carried out. Dynamic modes of the modified oscillator are investigated depending on the parameters of the system. Spectral characteristics are also compared to the corresponding characteristics of the classical van der Pol oscillator. [ABSTRACT FROM AUTHOR]

We compare the solution to the problem of scattering and absorption of a plane electromagnetic wave by a small spherical particle in the quasistatic dipole approximation with the general solution obtained by Gustav Mie for this problem. It is shown that in certain cases, the condition of smallness of the particle radius compared with the wavelength in the outer medium is insufficient for justification of the use of the quasistatic dipole approximation, and the quasistatic formulas for induced dipole moments, the absorbed power, and the scattered power become incorrect. Refined inequalities are found, which describe applicability of the quasistatic dipole approximation for a spherical particle both in free space and a homogeneous medium, and applicability of this approximation is tested in various cases. The results of solution of the problem are presented, which yield the absorbed and scattered powers at dipole resonances of various types for various parameters of the scattering object and the surrounding medium. Expressions for the parameters of the Lorentzian line near the magnetic dipole resonance of a small dielectric particle with a high refractive index and low losses are presented. [ABSTRACT FROM AUTHOR]

This study is focused on the investigation of stabilization problem for the system of coupled inverted pendula. The corresponding algorithm of control is based on the feedback principles and demonstrates some features in the physical implementation of the stabilization process. In the discrete case, the wave-like motion appears and leads to an observable interference pattern. In the continuous case, the provided feedback algorithm allows to simulate the stabilization process for the initially unstable solid medium. In these case conditions, ensuring the stabilization process is presented in the form of corresponding physical restrictions on the wave motion. Also, within the small parameter method, we investigate the nonlinear oscillatory motion of the material (the solid medium is modeled by the proposed system with nonlinear coupling). Results of numerical simulation for the system under consideration are presented and discussed. Particularly, numerical results show that the nonlinear material exhibits greater stability than the linear one. [ABSTRACT FROM AUTHOR]

"Double" derivatives of the drug Xymedon (1,2-dihydro-4,6-dimethyl-1-N-(hydroxyethyl)pyrimidone-2), hereafter referred to as pyrimidine (I), in which the pyrimidine (I) molecules are joined by an alkyl(xylylenyl)dionate bridge have been synthesized. Primary data on the hepatoprotective activity of five "double" pyrimidine (I) derivatives with different numbers of methylene groups and a meta-xylylene fragment in the ester bridge have been obtained on normal human hepatocytes of the Chang Liver cell line. The cytotoxicity and the cytoprotective properties of the new compounds against the background of exposure to d-galactosamine at a concentration of 150 mmol/L have been determined, their effect on the cell cycle compared with that of the initial pyrimidine (I) has been studied, and the dependence of the biological properties of the derivatives on their structure has been established. [ABSTRACT FROM AUTHOR]

This paper is dedicated to comparative analysis of nonlinear damping in the oscillating systems. More specifically, we present the particular results for linear and nonlinear viscous dampers, fractional damper, as well as for the hysteretic damper in linear and nonlinear (Duffing-like) oscillating systems. We consider a constructive mathematical model of the damper with hysteretic properties on the basis of the Ishlinskii-Prandtl model. Numerical results for the observable characteristics, such as the force transmission function and the "force-displacement" transmission function are obtained and analyzed for both cases of the periodic affection, as well as for the impulse affection (in the form of δ-function). A comparison of an efficiency (in terms of the corresponding transmission functions) of the nonlinear viscous damper and the hysteretic damper is also presented and discussed. [ABSTRACT FROM AUTHOR]

The results of investigations into the kinetics of formation and decomposition of natural gas hydrates obtained from shaped ice using the thermocycling method are reviewed. These data make it possible to find the weight distribution, specific gas content, and features of decomposition of different hydrate shapes synthesized in a reactor. [ABSTRACT FROM AUTHOR]

A spherical pore in the ionic crystalline material subjected to a linearly polarized microwave radiation is shown to flatten along the electric field vector. The deformation of the pore occurs due to rectification of high-frequency flows of charged vacancies in the course of their nonlinear interaction with the electric field near the pore surface. The estimates show that the effect is most pronounced in the materials with a significant contribution of mobile vacancies into microwave absorption. Preferred orientation of pores has been observed experimentally in a zirconia ceramic sample sintered under heating by a linearly polarized microwave radiation. [ABSTRACT FROM AUTHOR]

In recent years, a considerable interest has been drawn to microwave heating of powder metals and other electrically conductive materials. In this paper a consistent formulation describing the absorption of microwaves in electrically conductive materials under different microwave heating conditions is developed. A special case when conductive powder particles are surrounded by insulating oxide layers is investigated in detail using the effective-medium approximation. The conditions giving rise to skin effect governed, volumetric, and localized microwave heating are analyzed. Experimental observations of different microwave heating regimes in silicon, iron, and copper powder compacts are in general agreement with the theoretical model. [ABSTRACT FROM AUTHOR]

[Display omitted] Novel energetic azoxy- and azofurazans bearing nitro- NNO - azoxy and amino groups were synthesized using the ammonolysis of some known (nitro- NNO -azoxy)furazans. 3-Amino-4-{[4′-(nitro- NNO -azoxy)f urazan-3′-yl]- NNO - azoxy}furazan displays the highest melting point (114 °C, decomp.) among the known (nitro- NNO -azoxy)furazans, optimal density (1.80 g cm−3), high experimental enthalpy of formation (639 kcal kg−1) and mechanical sensitivity on the level of PETN. In terms of the specific impulse level, the model solid composite propellant formulations based on this compound outperform similar formulations based on RDX, HMX or CL-20 by 7–12 s. [ABSTRACT FROM AUTHOR]

The experimental study of polymer degradation processes in a solution is carried out. A mathematical description of the time dependences of the main polymer structural characteristics, i.e., the number average Mw and the weight average Mn molecular weight and the polydispersity coefficient Kp are obtained. For the model adequacy to be tested and the calculation error to be estimated, linear polymers—SKD-ND rubbers— are used as experimental samples. The change in the polymer molecular weight distribution (MWD) and its parameters are studied by gel permeation chromatography. The resulting dependences can be used for the process control systems. The developed mathematical description relates the controllable and control parameters in the structure (initial reagent concentrations, the reagent ratio, reaction temperature, etc.). However, the complete reconstruction of the mode of the MWD and its time dependence cannot be achieved. [ABSTRACT FROM AUTHOR]

A mathematical model of an unstable system in the form of inverted coupled pendulums is developed and simulated. Dynamics of such a system is investigated, and the stability zones are identified in the explicit form. The algorithm of stabilization of the pendulums near the vertical position is constructed and verified. [ABSTRACT FROM AUTHOR]

Antiradical activity and antioxidant properties of a conjugate of Xymedon with L-ascorbic acid were studied. In contrast to Xymedon, a conjugate of Xymedon with L-ascorbic acid was found to react with free radicals. Pro-oxidant activity of the conjugate of Xymedon with L-ascorbic acid in a chemiluminescence system is weaker as compared to individual L-ascorbic acid. This is the evidence of the increase in the stability of ascorbic acid upon conjugation with a molecule of Xymedon. Conjugate of Xymedon with L-ascorbic acid facilitates the decrease in the concentration of a lipid peroxidation product (malondialdehyde) and the activity of superoxide dismutase in liver and serum of laboratory animals exposed to intoxication with a known hepatotropic toxin CCl4. This observation shows the contribution of the antioxidant action to the hepatoprotective effect of the studied Xymedon derivative. [ABSTRACT FROM AUTHOR]

We propose a model for determination of the effective complex permeability of compacted metal-powder media. It is based on the equality of the magnetic moment in a given volume of the media with the desired effective permeability to the total magnetic moment of metal particles in the external high-frequency magnetic field, which arises due to excitation of electric eddy currents in the particles. Calculations within the framework of the proposed model allow us to refine the values of the real and imaginary components of the permeability of metal powder compacts in the microwave band. The conditions of applicability of the proposed model are formulated, and their fulfillment is verified for metal powder compacts in the microwave and millimeter wavelength bands. [ABSTRACT FROM AUTHOR]

Multipactor breakdown is studied inside the capacitive iris of a rectangular waveguide with a skewed slot along its longitudinal cross section. Both the iris length and height are assumed to be small compared to the electromagnetic wavelength. Therefore, the quasi-static approximation is applied so as to describe the RF field distribution inside the iris gap, whereas a 2-D model is used to analyze the electron motion. The peculiarities of RF field structure are studied using the conformal mapping approach, which shows that the electric field lines can be approximated by circular arcs when the iris length is much larger than its height. The electron motion inside the iris gap is analyzed using different analytical approaches as well as numerical simulations. The simplest analytical consideration is based on the general theory of multipactor between curved surfaces. Within the more sophisticated model, the fringing field effect on electron motion inside the iris is calculated assuming circular structure of electric field lines. It is demonstrated within all approaches that the electron losses within the iris gap increase considerably with the skew angle, deviating from the rectangular iris shape. As a result, the multipactor becomes impossible at a relatively small value of this angle. [ABSTRACT FROM AUTHOR]

The study examined the myocardial ultrastructural alterations in rats maintained on various atherogenic diets. It revealed the complex ultrastructural alterations of cardiomyocytes and endotheliocytes (including the lytic and destructive changes of the intracellular organelles, upregulation of the autophagocytosis in the cardiomyocytes, and necrobiosis with apoptosis of endotheliocytes) reflecting the cytopathic features of circulating cholesterol and lipoproteins, whose elevation determined the intensity of destructive processes. The revealed peculiarities in the changes of lipid inclusions (their osmiophilic transformation) in cardiomyocytes can be provoked by entry of cholesterol into the cells and its further metabolic modifications. During moderate dyslipidemia, the cardiomyocytes demonstrated the ultrastructural signs of induction of intracellular regeneration (marked with the clusters of polysomes in the intermyofibrillar and subsarcolemmal spaces with appearance of neogenic myofilaments) and upregulated pinocytotic activity. In all cases, up-regulated autophagocytosis in cardiomyocytes was accompanied by accumulation of myelin- and vacuole-like structures in the intercellular spaces and capillary lumens paralleled with appearance of activated forms of macrophages and fibroblasts in the myocardium. [ABSTRACT FROM AUTHOR]

We consider a gas-dynamic model of a one-dimensional flow of non-viscous perfect gas in the absence of heat conduction when a high-power localized heat source is switched on. Within the framework of this model, it is possible to thoroughly analyze the problem of the gas-flow regimes, which occur as a result of switch-on of such a source, in a wide range of values of the energy-deposition power and initial gas-dynamic characteristics of the flow. Eventually, we obtain a sufficiently general insight into the character of the resulting flows and the conditions of their realizations. [ABSTRACT FROM AUTHOR]

The results of simulating the rapid microwave heating of spherical clusters of metal particles to the melting point are reported. In the simulation, the cluster is subjected to a plane electromagnetic wave. The cluster size is comparable to the wavelength; the perturbations of the field inside the cluster are accounted for within an effective medium approximation. It is shown that the time of heating in vacuum to the melting point does not exceed 1 s when the electric field strength in the incident wave is about 2 kV/cm at a frequency of 24 GHz or 5 kV/cm at a frequency of 2.45 GHz. The obtained results demonstrate feasibility of using rapid microwave heating for the spheroidization of metal particles with an objective to produce high-quality powders for additive manufacturing technologies. [ABSTRACT FROM AUTHOR]

We present an analytical model of cold atmospheric plasma formed by a dielectric barrier discharge (DBD), which is based on the lumped and distributed elements of an equivalent electric circuit of this plasma. This model is applicable for a wide range of frequencies and amplitudes of the applied voltage pulses, no matter whether or not the generated plasma plume interacts with a target. The model allows quantitative estimation of the plasma plume length and the energy delivered to the plasma. Also, the results of this model can be used for the design of DBD guns which efficiently generate cold atmospheric plasma. A comparison of the results of the model with those obtained in experiments shows a fairly good agreement. [ABSTRACT FROM AUTHOR]

Knowledge of dielectric and magnetic properties is crucially important in the numerical modeling of high-temperature microwave processing of materials. To enhance the accuracy of modeling for metal powders and metal-containing composites, adequate description is required for the interaction of the electromagnetic field with the electrically conductive particles. A theoretical model for the calculation of effective complex dielectric permittivity of an ensemble of spherical metal particles surrounded by thin insulating layers is presented. The model is based on the effective medium approximation. It accounts for the nonuniform distribution of the electromagnetic field that exists inside individual particles when the electromagnetic wavelength or penetration depth is smaller than the particle size. The effective dielectric losses predicted by the model can be highly significant compared with the magnetic losses that arise due to the eddy currents induced in metal particles by microwaves. Reasonable agreement with the experiment has been demonstrated for the millimeter-wave absorption in metal–ceramic composites with significant volume fraction of metal particles. The model can be utilized for assessing the feasibility of microwave heating of powder metals and metal–ceramic composites. [ABSTRACT FROM AUTHOR]

The simplified model is proposed to simulate numerically air breakdown in a focused microwave beam. The model is 1D from the mathematical point of view, but it takes into account the spatial non-uniformity of microwave field amplitude along the beam axis. The simulations are completed for different frequencies and different focal lengths of microwave beams. The results demonstrate complicated regimes of the breakdown evolution which represents a series of repeated ionization waves. These waves start at the focal point and propagate towards incident microwave radiation. The ionization wave parameters vary during propagation. At relatively low frequencies, the propagation regime of subsequent waves can also change qualitatively. Each next ionization wave is less pronounced than the previous one, and the breakdown evolution approaches the steady state with relatively small plasma density. The ionization wave parameters are sensitive to the weak source of external ionization, but the steady state is independent on such a source. As the beam focal length decreases, the stationary plasma density increases and the onset of the steady state occurs faster. [ABSTRACT FROM AUTHOR]

An analytical study of the electron trajectories between two opposite electrodes having curved surfaces is undertaken for the case when the electron transit time exceeds the RF period. The analysis is based on a statistical approach, which makes it possible to calculate the width of an electron bunch after a number of electron transits taking into account the spread of electron emission velocity, and the spatial nonuniformity of the RF field using the concept of the ponderomotive force. The results are used to estimate the multipactor threshold in terms of a value of the secondary emission yield, which is necessary to balance electron losses. Based on the model, it is predicted that multipactor is impossible inside the realistic configuration of a helix antenna where four electrodes are placed on the same cylindrical surface. [ABSTRACT FROM AUTHOR]

A simplified analytical model is developed to predict the spectrum of electric current induced by the multipacting electrons between two parallel electrodes exposed to an rf voltage of fixed amplitude. The model is based on the resonant multipactor theory and makes it possible to calculate the relative spectral amplitudes of electric current at different harmonics and sub-harmonics of the applied rf frequency. The theoretical predictions are confirmed by numerical simulations of multipactor inside a rectangular waveguide. Specifically it is seen that the relative height of the spectral peaks decreases with increasing gap height. [ABSTRACT FROM AUTHOR]

Single-surface multipactor on metal surfaces is studied in the case when the microwave electric field is superimposed on a dc electric and a permanent magnetic field. Based on a simple analysis of the electron motion, it is predicted that considerable reduction in the multipactor threshold is possible when the electron cyclotron frequency is equal to the microwave field frequency and the permanent magnetic field has the proper orientation with respect to the metal surface. The prediction is confirmed by numerical simulations, and some experimental indications of the reduced multipactor threshold are also presented. [ABSTRACT FROM PUBLISHER]

Abstract: Replacement of terminal atoms of Br in 1,3-bis(bromopentyl)-5(6)-substituted uracils with 2-mercapto-5-methyl-1,3,4-thiadiazole, 2,5-dimercapto-1,3,4-thiadiazole, 2-mercaptoimidazole, and 2-mercaptobenzimidazoles resulted in a series of acyclic compounds and isomeric heterocyclophanes. Structures of macrocyclic regioisomers were unambiguously determined by NMR data. One of the regioisomers exhibits a hypochromic effect with respect to model compounds. The acyclic uracils obtained bridged with five-membered heterocycles are alkylated with methyliodide and methyl tosylate, and oxidated with m-CPBA, H2O2, and I2. [Copyright &y& Elsevier]

Abstract: Reactions of pyrimidinophanes with two 6-methylthiocytosine and one 5(6)-alkyluracil moieties bridged with each other by polymethylene spacers with methyl or nonyl p-toluenesulfonate, p-toluenesulfonic acid, methanesulfonate and trifluorosulfonate afforded amphiphilic macrocyclic bis-p-toluene-, methane- and trifluorosulfonates. Despite the presence of several reaction centers in the initial pyrimidinophane molecules, protonation and methylation occurred only at the N1 atom (with quaternization) of the 6-methylthiocytosine moieties. The bacteriostatic and fungistatic activity of the products was estimated. Macrocyclic tosylates exhibit a remarkable selectivity towards Staphylococcus aureus, with MIC values comparable with a reference drug. Bacteriostatic activity of the amphiphilic pyrimidinophanes depends on the size of the macrocycles, and the highest activity corresponds to definite lengths of polymethylene bridges. Besides, the antimicrobial activity of the screened pyrimidine derivatives depends on their topology. While macrocyclic tosylates are more active against bacteria than against fungi, acyclic tosylate with the same structural fragments shows a dramatical decrease of MIC towards mold and yeast with respect to the corresponding macrocycle. It is found that macrocyclic and acyclic tosylates in high dilutions decrease the extracellular lipase activity. [Copyright &y& Elsevier]

Simulations have been performed to determine the multipactor breakdown threshold in a microwave structure composed of two parallel cylinders, chosen to be an approximate model of an open helix microwave antenna system. The electromagnetic field between the cylinders is available in closed analytical form, and a Monte Carlo software has been developed to calculate the 2-D electron trajectories and to simulate the multipactor avalanche in this inhomogeneous electric field for different ratios of cylinder radius and distance of separation between the cylinders. The results are compared with those of a recently published analytical theory and show a qualitatively good agreement. In particular, it is confirmed that, for a given distance between cylinders, there exists a smallest cylinder radius below which no two-sided multipactor breakdown can occur. The basic physical explanation is a loss mechanism for secondary emitted electrons that is caused by the curvature of the cylinder surfaces together with the strong electric field at the surfaces. The results imply that the breakdown threshold in realistic open helix antennas is significantly higher than those predicted using extrapolations based on resonance theory and the classical two parallel plate model. [ABSTRACT FROM PUBLISHER]

Detailed numerical simulations have been done to investigate the properties of multipactor breakdown in circular waveguides operating in the propagating fundamental TE11 mode. Main attention has been given to a comparison between the two fundamental cases corresponding to linear and circular polarizations, respectively, of the propagating electromagnetic wave. It is found that circular polarization is considerably more susceptible to multipactor than linear polarization. The reason for this difference is clarified by a comprehensive study of the electron motion in the waveguide. [ABSTRACT FROM AUTHOR]

By condensation of thiourea with 6-methyluracyl derivatives containing ketone and ketoester fragmenst in the alkyl chains attached to the nitrogen atoms of the pyrimidine ring the products containing 6-methyl- or 3,6-dimethyluracyl fragment and one or two 6-methyl-4-oxo-2-thio-1,2,3,4-tetrahydropyrimidin-5-yl fragments were synthesized. These compounds can be alkylated with alkyl bromides. [ABSTRACT FROM AUTHOR]

Reaction of acetylacetone and ethyl acetoacetate with 1-(ω-bromoalkyl)-3,6-dimethyluracyls and 1,3-bis(ω-bromoalkyl)-6-methyluracyls lead to the formation of uracyl derivatives containing the ketone and ketoester fragments. Conditions leading to the highest yields of the compounds synthesized were found. [ABSTRACT FROM AUTHOR]

A detailed numerical simulation analysis is made of the saturation stage of multipactor discharges between two infinite parallel metal plates in vacuum exposed to a rf voltage. The main physical effect causing saturation of the multipactor discharge is increased space charge, as the electron density becomes large. It is found that the properties of the saturation stage depend crucially on the value of the secondary emission yield of the metal surfaces. Below a certain threshold value, the discharge has a two-sided character, but at this threshold the discharge makes an abrupt transition into two decoupled single-sided multipactor discharges containing significantly increased electron densities. The result of the numerical simulations gives a good picture of the saturation properties of the multipactor discharge and is also supplemented by an approximate analytical investigation that highlights and explains the characteristic properties of the observed saturation behavior. [ABSTRACT FROM AUTHOR]

The reaction of 1,3-bis(5-bromopentyl)alloxazine with ethylamine in propan-2-ol resulted in replacement of the terminal bromine atoms by ethylamino groups and was accompanied by contraction of the pyrimidine ring so that the products were 1,3-bis[5-(ethylamino)pentyl]alloxazine and 1,3-bis[5-(ethylamino)-pentyl]imidazo[4,5- b]quinoxalin-2-one. [ABSTRACT FROM AUTHOR]

A detailed analysis is made of the effect of reflection of low-energy secondary emitted electrons on the susceptibility diagrams for multipactor breakdown between two parallel metal plates. The problem is studied using both analytical and numerical methods. The left boundary of the first resonance zone for the multipactor is shown to be significantly modified when electrons with impact energy of the order of their initial energy are completely reflected. Specifically, in this case, the multipactor avalanche may grow even when the gap between the metal plates is very narrow if the applied RF voltage is high enough to provide electron acceleration up to energies exceeding the first crossover energy of the secondary emission curve. This effect is proposed as a means for experimentally investigating the reflection properties of low-energy electrons from the surface of different materials. [ABSTRACT FROM AUTHOR]

A series of pyrimidinophanes containing two uracil units and nitrogen atoms in bridging polymethylene chains –(CH2) nN(Et)(CH2) m– ( n, m = 5, 6) have been synthesized. The uracil moieties are represented by 6-methyl-, 5-decyl-6-methyl-, and 5-fluorouracils. Quaternization of the bridging N atom with ethylbromide or n-decylbromide yielded amphiphilic pyrimidinophanes, which were evaluated for their antibacterial and antifungal activity in terms of minimal inhibiting concentration (MIC) against Gram-positive and Gram-negative bacteria and fungi. It has been found that MICs of the amphiphilic pyrimidinophanes decrease with increasing lipophilicity of the alkyl substituents at the bridging N atoms and with increasing polymethylene N(pyr)–N chain length (in some cases MIC against Staphylococcus aureus is below 1 ìg/mL). The MICs increase dramatically upon introduction of lipophilic n-decyl substituents at C(5) atoms of the uracil moiety. The results can be used in the search for new highly effective antimicrobial agents. [ABSTRACT FROM AUTHOR]

When electrons travel through the sheath toward a plasma-facing surface, they lose a part of their kinetic energy due to the negative work of the electric field in the sheath. What happens to this energy? Does it need to be accounted for if one needs to calculate an energy flux to a wall? In this note, the above questions are answered for three different cases of the boundary conditions: (a) electrically isolated surface charged to a steady-state value corresponding to a floating potential; (b) an isolated wall not yet charged to the floating potential; and (c) biased electrode conducting a steady-state current. The answers are found to be different in each case, but the general conclusion is that to evaluate surface power deposition due to particle bombardment, electron and ion energy fluxes need to be calculated at the wall, and not in the quasineutral plasma. [ABSTRACT FROM AUTHOR]

Reactions of pyrimidinophanes containing two 6-methylthiocytosine and one 6-methyluracil fragments with methyl p-toluenesulfonate gave amphiphilic macrocyclic bis- p-toluenesulfonates. Despite the presence of several reaction centers in the initial pyrimidinophane molecules, methylation occurred only at the N1 atom (with quaternization) of the 6-methylthiocytosine fragments. Bacteriostatic and fungistatic activity of the products was estimated. [ABSTRACT FROM AUTHOR]

The charging of a metal sphere in a weakly ionized collisional plasma in a uniform external electric field is investigated with allowance for the effect of the space charge field and ionization-recombination processes. The sphere charge and the spatial distributions of charged plasma particles are calculated both numerically and analytically (for some particular cases) for the case of a strong external field. It is found that the size of the perturbed plasma region is determined by the external field and the intensity of recombination processes. It is shown that the total electric charge (the sphere charge plus the plasma space charge) is zero in accordance with predictions of the theory of static currents in a conducting medium. [ABSTRACT FROM AUTHOR]

Abstract: The conformational structure of macrocycles obtained from two thiopyrimidine and uracil nucleic acids linked by polymethylene spacers is determined by the length of the spacers, intramolecular NH bonding, pH and solvent. In CDCl3, NH–On bonding can impact the overall stabilization of the folded conformation, however spatial preorganization to such hydrogen bonding is a prerequisite. Protonation leads to disruption of intramolecular hydrogen bonds, destabilization of the folded conformation and to strong counterion assisted self-aggregation of macrocyles which can be destroyed in polar solvents. [Copyright &y& Elsevier]

Abstract: Cyclization of 1,3-bis(ω-bromoalkyl)-5-bromouracil with p-methoxybenzylamine or sodium sulfide led to a series of pyrimidinophanes containing heteroatoms in bridges. An unusual behaviour of the 5-bromouracil ring, namely its contraction into hydantoin units during the cyclization reactions with p-methoxybenzylamine was observed. Sodium sulfide does not affect the 5-bromouracil ring, and no transformation products were observed in the synthesis of pyrimidinophanes with sulfur bridges. A possible reaction mechanism is given. [Copyright &y& Elsevier]

The article presents a reprint of the article "The Value Orientations of Today's Young People," by V. E. Semenov, which appeared in the journal "Russian Education and Society," vol. 50. It discusses how the concept of upbringing disappeared from the field of education and policy of youth, after the transformation of Russia from being a Soviet country in 1990 and focuses on the relevance of upbringing to the young adults.