On electrical characteristics of comb-shaped microstrip antennas

© 2017 IEEE.The microstrip antennas with symmetrical comb-shaped radiator are considered. The influence of depth of the cuts on main electrical characteristics of four- and eight-comb antennas is researched. The resonance frequency, the bandwidth and reflection coefficient are chosen as characteristics. The graphs of unknown dependencies are constructed for the two basic frequencies

The Effect of Surfactants on Equilibrium Wetting

Contact angles B0 of aqueous solutions contacting with hydrophilic and hydrophobic surfaces were studied as affected by various surfactants (alcohols, fatty acids, soaps) under conditions close to thermodynamic equilibrium (in the atmosphere saturated with the solution vapour). The conditions of transitions from limited wetting (Bo > 0) to complete wetting, i.e. spontaneous spreading were also studied. The effect of surfactants adsorption at the solid gas interface was estimated from the isotherms of wetting tension W = cr1g Cos B0 (cr1g is the surface tension of the solution) on the basis of equation describing W as a function of concentration. It is shown that adsorption of surfactants at the solid-gas interface markedly affects wetting of hydrophilic materials. For hydrophobic materials the effect is primarily due to adsorption of surfactants at the solid- solution and solution-gas interfaces. It was found that equilibrium wetting is affected by the type of adsorption at the solid surface (physical or chemical adsorption). The influence of hydrocarbon chain length in homological series of alcohols and fatty acids on equilibrium contact angles and on transition to spontaneous spreading was studied as well

Spontaneous synchronization of two bistable pyridine-furan nanosprings connected by an oligomeric bridge

The intensive development of nanodevices acting as two-state systems has motivated the search for nanoscale molecular structures whose long-term conformational dynamics are similar to the dynamics of bistable mechanical systems such as Euler arches and Duffing oscillators. Collective synchrony in bistable dynamics of molecular-sized systems has attracted immense attention as a potential pathway to amplify the output signals of molecular nanodevices. Recently, pyridin-furan oligomers of helical shape that are a few nanometers in size and exhibit bistable dynamics similar to a Duffing oscillator have been identified through molecular dynamics simulations. In this article, we present the case of dynamical synchronization of these bistable systems. We show that two pyridine-furan springs connected by a rigid oligomeric bridge spontaneously synchronize vibrations and stochastic resonance enhances the synchronization effect

Local taxonomic spectra in plants, animals, fungi and terrestrial protists show common mathematical patterns

Taxonomic spectra, i.e. relations between supraspecific taxa by the number of included species, remain poorly understood in aspect of the mathematical properties. We studied taxonomic spectra of plants (Magnoliophyta, Bryophyta), animals (Coleoptera, Aves), fungi (Agaricomycetes) and terrestrial protists (Myxomycetes), found in the Homilsha Forests National Nature Park (North-East of Ukraine), and concluded that they correspond to the hollow-curve distribution at the level of genera, families and orders. The spectra of most taxa, as shown by the Akaike information criterion, are closely approximated by the log-series distribution model at all taxonomic levels. This type of distribution is typical for the species abundance curves, based on collections made from small areas. At the same time, in the genera–families–orders row the similarity to the lognormal distribution increases. The central values and variability vary considerably between different taxonomic groups and ranks, however, without affecting the type of distribution. The number of orders in all taxa except Bryophyta has reached the saturation and coincides with the curve of the estimated number of orders according to the Chao1 coefficient. For families and especially genera the correspondence with estimated number of species is much lower. Our results do not confirm the assumption that hollow-curve distributions of taxonomic spectra result from the artificial fragmentation of taxa. These distributions neither depend on the insufficient knowledge about the species composition at the locality, nor reflect the size of the studied area. The presence of such distributions in both local and global biota of different groups may be explained by the common features of their evolution, especially by the existence of relict orphan groups. The fact that in Homilsha Forests the kurtosis and skewness of distributions decreases in the genera–families–orders row can therefore be explained by the relatively low percentage of the high-rank orphan taxa in the local biota. This may be a common feature of communities studied at small geographical scale, since orphan taxa often demonstrate a high level of endemism. Comparative studies of local communities from different climate zones may help to understand how universal are the patterns, described herein

Spontaneous Vibrations and Stochastic Resonance of Short Oligomeric Springs

There is growing interest in molecular structures that exhibit dynamics similar to bistable mechanical systems. These structures have the potential to be used as nanodevices with two distinct states. Particularly intriguing are structures that display spontaneous vibrations and stochastic resonance. Previously, through molecular dynamics simulations, it was discovered that short pyridine-furan springs, when subjected to force loading, exhibit the bistable dynamics of a Duffing oscillator. In this study, we extend these simulations to include short pyridine-pyrrole and pyridine-furan springs in a hydrophobic solvent. Our findings demonstrate that these systems also display the bistable dynamics of a Duffing oscillator, accompanied by spontaneous vibrations and stochastic resonance activated by thermal noise.Comment: arXiv admin note: substantial text overlap with arXiv:2110.0409

Improving aerodynamic characteristics for drag reduction of heavy truck

Significant increasing vehicle performance can be achieved by reducing aerodynamic drag because of rising average speeds and reducing fuel consumption. Russian truck manufacturers do not prioritize the truck aerodynamic issues, therefore majority of existed models has a very high value of drag coefficient, and moreover, vehicles older than 10 years predominate in operation. In this regard, against the background of rising prices for liquid fuel, the reduction in aerodynamic drag allows to solve the problems posed. The article presents the results of a study of the aerodynamic drag coefficient for KAMAZ heavy truck when using a set of cab fairings of different shapes. Using the software, the analysis of the influence of the shape of the fairing on the coefficient of air resistance of the car is made. As a result, fuel economy is calculated taking into account the selected optimal cab fairing and cab-side extenders from the aerodynamic drag coefficient. © 2020 IOP Publishing Ltd. All rights reserved